Ultraviolet (UV) radiation, from the solar spectrum is a major etiological factor for many cutaneous pathologies including cancer. By understanding changes in cell signaling pathways induced by UVA and UVB, novel strategies for prevention and treatment of UV related pathologies could be developed. However, much of the information in the literature from various laboratories cannot cross talk because of difficulties associated with the use of ill-defined light sources and physiologically irrelevant light dosimetry. Here, we have assessed the effect of exposure of normal human epidermal keratinocytes (NHEK) to UVA (2 and 4 J/cm²) or UVB (20 and 40 mJ/cm²) radiation. Employing western blot analysis we found that exposure of NHEK to UVB, but not UVA, phosphorylates JNK1/2 at Th¹⁸³/Tyr¹⁸⁵, STAT3 at Ser⁷²⁷, AKT at Ser⁴⁷³ and increases c-Fos expression, whereas exposure to UVA, but not UVB, phosphorylates AKT at Thr³⁰⁸. UVB as well as UVA exposure leads to increased phosphorylation of (i) ERK1/2 at Th²⁰²/Tyr²⁰⁴, (ii) p38 at Th¹⁸⁰/Tyr²⁰⁴, (iii) STAT3 at Tyr⁷⁰⁵, (iv) mTOR at Thr²⁴⁴⁸ and (v) p70S6k at Thr⁴²¹/Ser⁴²⁴; enhanced expression of PI3K(p85) and c-jun; and nuclear translocation of NFκB proteins. These findings could be considered as a beginning for understanding the differential effects of UVA and UVB in the human skin and may have implications both with respect to risk assessment from exposure to solar UV radiation, and to target interventions against signaling events mediated by UVA and UVB.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

This work describes the synthesis of three new tetra- and octa-thio-pyridinium phthalocyanine derivatives. Photosensitizers 3a and 4a were prepared from the tetramerization of phthalonitriles 1 and 2, respectively, while photosensitizer 5 was prepared from the nucleophilic substitution of the 8 beta fluor atoms of hexadecafluorophthalocyaninatozinc(II) by mercaptopyridine, followed by cationization. The recombinant bioluminescent Escherichia coli strain was used to assess, in real time, the photoinactivation efficiency of these cationic phthalocyanines, under white and red light. The cellular localization and uptake were also determined to assess the potential of the new phthalocyanines as antibacterial agents. Derivative 3a was the most effective photosensitizer (PS), causing a 5 logs reduction in bioluminescence after 30 minutes of irradiation under white or red lights. The photoinactivation efficiency of the phthalocyanine 4a was similar (5 logs reduction in bioluminescence) to that of 3a when irradiated with white light, but the efficiency of inactivation was reduced (2.1 logs reduction in bioluminescence) under red light. The tetra-substituted phthalocyanine 3a also generates high amounts of singlet oxygen, does not aggregate in PBS and is highly fluorescent, which makes it an effective photosensitizer and a promising fluorescent labeling.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

Many studies have been conducted showing that ALA PDT can be an alternative treatment for recalcitrant warts. We recently, performed a study evaluating MAL PDT for the treatment of hand warts in a population of renal transplant patients. Two symmetrical targets were selected on each hand and randomly assigned to chemical keratolytic treatment followed by 3 cycles of ALA PDT (75 J/cm² red light). Patients were evaluated after 3 months and a second run of PDT was performed, if the total area and number of warts decrease was less than 50% with evaluation every three months for one year. Twenty patients have been included and 16 were evaluable (9 M, 7 F). After 6 months the reduction of warts area was 48,4% on the treated side versus 18,4% in the control area (p=0,021). The decrease in the total number of warts was 41% versus 19,4% (p=NS). The global tolerance of the treatment was good with acceptable pain during irradiation. These results suggest that ALA PDT is a safe and efficient treatment for transplanted patient warts. The improvement between treated and control zone is 20% due to the decrease in untreated wart’s area and number.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

Paracoccidioidomycosis (PCM) is a systemic mycosis caused by Paracoccidioides brasiliensis. Currently, the treatment approach involves the use of antifungal drugs and requires years of medical therapy, which can induce nephrotoxicity and lead to resistance in yeast strains. Photodynamic inactivation (PDI) is a new therapy capable of killing microorganisms via the combination of a nontoxic dye with visible light to generate toxic reactive oxygen species (ROS). We investigated the phototoxic effect of 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin (TMPyP), a cationic porphyrin, on the survival of P. brasiliensis following exposure to light. Phototoxicity was found to depend on both the fluence and concentration of the photosensitizer (PS). Although the biological effects of PDI are known, the molecular mechanisms underlying the resultant damage to cells are poorly defined. Therefore, we evaluated the molecular response to PDI-induced oxidative stress by using gene transcription analysis. We selected genes associated with the high-osmolarity glycerol (HOG)-mitogen-activated protein kinase (MAPK) pathway and antioxidant enzymes. The genes analyzed were all overexpressed after PDI treatment, suggesting that the oxidative stress generated in our experimental conditions induces antioxidant activity. In addition to PDI-induced gene expression, there was high cell mortality, suggesting that the antioxidant response was not sufficient to avoid fungal mortality.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

A measurement system is described that allows an objective review and evaluation of the amount of use by different population groups of provided shade structures. It employs the comparison of the erythemal UV exposure measured with dosimeters to either the vertex or the forehead to that in full sun. The technique has been developed using three shade structures and found to provide a linear relationship with an R² of 0.99 between the exposure ratio and the time spent in the shade for the solar zenith angle range of 19 to 53^o and for both low and high cloud levels. It provides an objective determination of the amount of shade use by population groups that have set periods of time outdoors.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

Hairless (HR) is a nuclear protein with co-repressor activity whose exact function in the skin remains to be determined. Mutations in both human and mouse Hairless lead to hair loss accompanied by the appearance of papules, a disorder called atrichia with papular lesions. Furthermore, mice with mutations in HR are known to have a higher susceptibility to ultraviolet radiation induced tumorigenesis, suggesting that HR plays a crucial role in the epidermal UVB response. Using normal human keratinocytes (NHKs) and keratinocytes containing a mutation in HR, we found that HR is an early UVB response gene that negatively regulates NFκB mRNA expression. HR mutant keratinocytes have a dysregulated UVB response that includes increased proliferation and the aberrant activation of NFκB effector genes. Additionally, we show that another UVB response gene, TNFα, negatively regulates HR mRNA expression. TNFα-induced negative regulation of HR occurs through a direct interaction of the p65 subunit with a single NFκB binding domain located in the HR promoter region. Therefore, we show for the first time that HR and NFκB participate in a positive feedback loop that can be initiated either by UVB or TNFα.

Ultraviolet A (UVA)-irradiated 4′-hydroxymethyl-4,5′,8-trimethyl psoralen (HMT) in the presence of a poly-dT₁₇ and A₇TTA₈ oligonucleotides produces HMT-dT₁₇ and HMT-A₇TTA₈ adducts in aqueous solution. In this article, we determine whether these HMT-dT₁₇ and HMT-A₇TTA₈ adducts can be detected with a molecular beacon (MB) probe. We measure the degree of damage in dT₁₇ and A₇TTA₈ solutions containing UVA-activated HMT via monitoring the decrease in MB fluorescence. Photoproduct formation is confirmed by matrix-assisted laser desorption / ionization time-of-fight mass spectrometry measurements (MALDI-TOF MS) and absorption spectroscopy. The MB fluorescence decreases upon UVA irradiation in the presence of HMT with a single-exponential time constants of 114.2 ± 6.5 min for HMT-dT₁₇ adducts and 677.8 ± 181.8 min for HMT-A₇TTA₈ adducts. Our results show that fluorescent molecular beacon probes are a selective, robust and accurate tool for detecting UVA-activated HMT-induced DNA damage.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

Chronic skin exposure to ultraviolet light stimulates production of cytokines known to be involved in the initiation of skin cancer. Recent studies in mouse models suggested a role for macrophage migration inhibitory factor (MIF) in the UVB-induced pathogenesis of non-melanoma skin cancer (NMSC). Our studies aimed at defining the pathophysiological function of MIF in cutaneous inflammatory reactions and in the development and progression of NMSC. Immunohistochemical analysis revealed a moderate expression of MIF in normal human skin samples but an enhanced expression of this cytokine in lesional skin of patients with actinic keratosis or cutaneous SCC. ELISA studies showed a time-dependent increase in MIF secretion after a moderate single dose UVB irradiation in NHEKs and SCC tumor cells. MIF is known to interact with CXCR2, CXCR4 and CD74. These receptors are not constitutively expressed in keratinocytes and HaCaT cells and their expression is not induced by UVB irradiation either. However stimulation with IFNγ upregulated CD74 surface expression in these cells. Affymetrix^® gene chip analysis revealed that only keratinocytes prestimulated with IFNγ are responsive to MIF. These findings indicate that MIF may be an important factor in the pathogenesis of NMSC tumorigenesis and progression in an inflammatory environment.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

Laser flash photolysis studies have been carried out to investigate the reactions of ciprofloxacin (CPX) with 2’-deoxyguanosine-5’-monophosphate (dGMP), N, N, N’, N’- tetramethyl–p–phenylenediamine (TMPD), and ferulic acid (FCA) in neutral aqueous solutions, respectively. CPX triplet-state (³CPX^*) can be quenched by TMPD, FCA, and dGMP, with rate constants of 1.8 × 10⁹, 1.5 × 10⁹, and 5.8 × 10⁷ dm³ mol⁻¹ s⁻¹, respectively. TMPD radical cation (TMPD^·+) and FCA radical cation (FCA^·+) were observed directly. The formation rates of CPX radical anion (CPX^·-) was determined to be 1.5 × 10⁹ dm³ mol⁻¹ s⁻¹. Redox reaction of dGMP was investigated through competing reactions by using TMPD and FCA as probe. The triplet energy of CPX was determined to be 262 KJ/mol. Electron transfer from TMPD, FCA, and dGMP to ³CPX^* was proposed.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

The growing resistance against antifungal drugs has renewed the search for alternative treatment modalities, and antimicrobial photodynamic therapy (PDT) seems to be a potential candidate.

Preliminary findings have demonstrated that dermatophytes and yeasts can be effectively sensitized in vitro and in vivo by administering photosensitizers (PSs) belonging to four chemical groups: phenothiazine dyes, porphyrins and phthalocyanines, as well as aminolevulinic acid, which, while not a PS in itself, is effectively metabolized into protoporphyrin IX. Besides efficacy, PDT has shown other benefits. First, the sensitizers used are highly selective, i.e., fungi can be killed at combinations of drug and light doses much lower than that needed for a similar effect on keratinocytes. Second, all investigated PSs lack genotoxic and mutagenic activity. Finally, the hazard of selection of drug resistant fungal strains has been rarely reported. We reviews the studies published to date on antifungal applications of PDT, with special focus on yeast, and aims to raise awareness of this area of research, which has the potential to make a significant impact in future treatment of fungal infections.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

The cell-permeable anthracene analog diethyl-3-3’-(9,10-anthracenediyl)bis acrylate (DADB) was recently identified as a highly-selective probe for singlet oxygen (¹O₂). We now show that DADB can be used to monitor ¹O₂ formation in cell culture during photodynamic therapy. An atypical property of DADB is that fluorescence emission is decreased upon oxidation. Using photosensitizers that target specific organelles, we determined that DADB could detect ¹O₂ whether formed in ER, mitochondria or lysosomes. DADB fluorescence was not, however, significantly altered when the photosensitizing agent was the palladium bacteriopheophorbide termed WST11, an agent reported to produce mainly oxygen radicals upon irradiation in an aqueous environment, while singlet oxygen was formed in organic solvents.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

UV light leads to release of different secretory factors from irradiated cells of which, some of them have been characterized. We have reported earlier that cells exposed to the supernatant medium from irradiated cells were resistant to killing by some genotoxic agents. In this report we present our finding that demonstrate DNA damage induced by UV or H₂O₂ is lowered on prior exposure to the UV released factors (UVRF). Production of ROS in cells and lipid peroxidation was also lowered. It was found that treatment of unexposed cells with UVRF present in the supernatant medium altered the antioxidant defense activity in cells. Significant was the increase in catalase (CAT) and Cu - Zn superoxide dismutase (SOD) activity while glutathione peroxidase (GPx) and reduced glutathione (GSH) levels remained unaffected. Cells exposed to UVRF prior to UV or H₂O₂ treatment also experienced such upregulation, however, the remarkable increase in the GPx activity exhibited by these cells was not observed in cells exposed to H₂O₂ or UV alone. It appears that exposure to UVRF tinkered with antioxidant defense in cells to facilitate its proliferation upon assault by agent that can produce oxidative damage.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

Photochemistry is a powerful tool for controlled synthesis of metal nanoparticles, their modification, and in many of the applications that these materials have. Plasmon transitions offer a unique way of delivering energy with exquisite spatial and temporal control and can be used to advantage where visible wavelength control is required. This account of research at the University of Ottawa summarizes details of the synthesis, modification and applications of silver nanostructures.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

A series of meso-substituted tetra-cationic porphyrins, which have methyl and octyl substituents, was studied in order to understand the effect of zinc chelation and photosensitizer subcellular localization in the mechanism of cell death. Zinc chelation does not change the photophysical properties of the photosensitizers (all molecules studied are type II photosensitizers) but affects considerably the interaction of the porphyrins with membranes, reducing considerable mitochondrial accumulation. The total amount of intracellular reactive species induced by treating cells with photosensitizer and light is similar for zinc-chelated and free-base porphyrins that have the same alkyl substituent. Zinc-chelated porphyrins, which are poorly accumulated in mitochondria, show higher efficiency of cell death with features of apoptosis (higher MTT response compared with trypan blue staining, specific Acridine Orange/Ethidium Bromide staining, loss of mitochondrial transmembrane potential, stronger cytochrome c release and larger sub-G1 cell population,) while non-chelated porphyrins, which are considerably more concentrated in mitochondria, triggered mainly necrotic cell death. We hypothesized that zinc-chelation protects the photoinduced properties of the porphyrins in the mitochondrial environment.

NO-releasing nonsteroidal anti-inflammatory drugs (NO-NSAIDs) have been shown to have anti-inflammatory, anti-proliferative and apoptosis-inducing effects in tumor cells. Here we have investigated the effects of NO-exisulind on the growth of UVB-induced skin tumor development in a murine model. We found that the topical treatment with NO-exisulind significantly reduced UVB-induced tumors in SKH-1 hairless mice. The tumors/tumor bearing mouse, the number of tumors/mouse and tumor volume/mouse decreased significantly (p<0.05) as compared to vehicle-treated and UVB-irradiated positive controls. Consistently, NO-exisulind-treated animals showed reduced expression of proliferation markers such as PCNA and cyclin D1. These mice also manifested increased expression of pro-apoptotic Bax and decreased expression of anti-apoptotic Bcl2 with an increase in the number of TUNEL-positive cells in tumors. We also investigated whether NO-exisulind-treated tumors are less invasive and progress less efficiently from benign to malignant carcinomas. For this, tumors were stained for various epithelial-mesenchymal transition (EMT) markers. NO-exisulind decreased the expression of mesenchymal markers such as Fibronectin, N-cadherin, SNAI, Slug and Twist and enhanced the epithelial marker E-cadherin. Similarly, UVB-induced phosphorylation of Erk1/2 and p38 was decreased in NO-exisulind-treated animals. These data suggest that NO-exisulind reduces tumor growth and inhibits tumor progression by blocking proliferation, inducing apoptosis and reducing EMT.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology

Lipids produced by microalgae can be grouped into two categories, storage lipids and structural lipids. Storage lipids are mainly triglycerides (TGs) made of saturated fatty acids; TGs can be transesterified to produce biodiesel. Structural lipids are made of polyunsaturated fatty acids (PUFAs), which are essential nutrients for aquatic animals and humans. The objectives of this study were (1) to determine the effect of UV-A at different levels of exposure on total lipid accumulation in Nannochloropsis oculata and check for reciprocity, and (2) to study the interactive effect of UV-A and nutrient concentration on lipid accumulation in N. oculata. Objective 1 was accomplished by testing the effects of a range of UV-A irradiance (I), duration of exposure (T), and UV-A doses (I x T) on lipid production by N. oculata. If the same doses have a similar effect, irrespective of I and T, reciprocity holds. UV-A treatments significantly increased the chlorophyll-specific lipid concentration of N. oculata cells, and we were unable to falsify that reciprocity holds. Objective 2 was addressed by a factorial bioassay experiment with manipulated nutrient and UV-A levels. UV-A and decreased nutrients had a synergistic effect on chlorophyll-specific lipid concentration of N. oculata, resulting in higher lipid:chl ratios.

© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiolog

Photodynamic therapy (PDT) is a minimally invasive therapeutic modality approved for palliative and curative treatment of some forms of local cancers, precancerous lesions and nononcological disorders. As a prerequisite for future studies in animal models aiming at an intraoperative application of PDT in osteosarcoma (OS), in the present study, we investigated the uptake and the dark- and photo-toxicity of the photosensitizer mTHPC in the metastatic human OS cell line 143B, which, intratibially injected into SCID mice, reproduces spontaneous, aggressive lung metastasis, the main cause of death in OS patients. The uptake of mTHPC by 143B cells was time- and dose-dependent. mTHPC accumulated to higher levels in the 143B than in the parental low-metastatic HOS cell line. A significant decrease in viability of 143B cells, reflecting mTHPC dark-toxicity, occurred upon incubation in the dark at mTHPC concentrations ≥2.5 μg mL⁻¹. In phototoxicity experiments with illumination by 652 nm laser light (2.5–10 J cm⁻²), the half-maximal lethal doses of mTHPC ranged from 0.012 to 0.047 μg mL⁻¹. This treatment activated caspase-3, -7 and -9 and Z-VAD-FMK-inhibitable PARP cleavage, indicating caspase-dependent apoptosis. In conclusion, PDT with mTHPC is effective in the metastatic 143B human osteosarcoma cell line in vitro.

In this study, we evaluated the effect of photodynamic therapy in a highly metastatic human osteosarcoma cell line after application of Foslipos^®, a liposomal formulation of 5,1,15,20-tetrakis(meta-hydroxyphenyl)chlorine (mTHPC). Confocal Microscopy displaying Foslipos uptake of 143B cells after 5 h incubation with 2.5 μg mL⁻¹ of the photosensitizer is visible in the figure: images in the three panels represent DAPI (left panel), Foslipos (middle panel) and the overlay image of the previous two (right panel). Nuclear localization is not observable.

The photocatalytic disinfection of Enterobacter cloacae and Enterobacter coli using microwave (MW), convection hydrothermal (HT) and Degussa P25 titania was investigated in suspension and immobilized reactors. In suspension reactors, MW-treated TiO₂ was the most efficient catalyst (per unit weight of catalyst) for the disinfection of E. cloacae. However, HT-treated TiO₂ was approximately 10 times more efficient than MW or P25 titania for the disinfection of E. coli suspensions in surface water using the immobilized reactor. In immobilized experiments, using surface water a significant amount of photolysis was observed using the MW- and HT-treated films; however, disinfection on P25 films was primarily attributed to photocatalysis. Competitive action of inorganic ions and humic substances for hydroxyl radicals during photocatalytic experiments, as well as humic substances physically screening the cells from UV and hydroxyl radical attack resulted in low rates of disinfection. A decrease in colony size (from 1.5 to 0.3 mm) was noted during photocatalytic experiments. The smaller than average colonies were thought to occur during sublethal ^•OH and O₂^•− attack. Catalyst fouling was observed following experiments in surface water and the ability to regenerate the surface was demonstrated using photocatalytic degradation of oxalic acid as a model test system.

Photographs of Enterobacter coli colonies on LB agar incubated for 18 h at 37°C. Plates represent E. coli cells within a 100 μL distilled water suspension after photocatalytic treatment with Degussa P25 and UVA irradiation for (A) 0 min; (B) 120 min; (C) 240 min; and (D) 360 min. As treatment progresses the diameter of a typical colony is significantly reduced from 15 mm, until at 360 min, colonies are so small (3 mm) that it is difficult to distinguish them with the naked eye. Small colony variants are thought to occur due to sublethal ^•OH attack.

The growing resistance to antibiotics has rendered antimicrobial photodynamic inactivation (PDI) an attractive alternative treatment modality for infectious diseases. Chitosan (CS) was shown to further potentiate the PDI effect of photosensitizers and was therefore used in this study to investigate its ability to potentiate the activity of erythrosine (ER) against bacteria and yeast. CS nanoparticles loaded with ER were prepared by ionic gelation method and tested for their PDI efficacy on planktonic cells and biofilms of Streptococcus mutans, Pseudomonas aeruginosa and Candida albicans. The nanoparticles were characterized for their size, polydispersity index and zeta potential. No toxicity was observed when planktonic cells and biofilms were treated with the nanoparticles in the dark. However, when the cells were exposed to light irradiation after treatment with free ER or ER/CS nanoparticles, a significant phototoxicity was observed. The antimicrobial activity of ER/CS nanoparticles was significantly higher than ER in free form. The particle size and incubation time of the nanoparticles also appeared to be important factors affecting their PDI activity against S. mutans and C. albicans.

Erythrosine (ER)-mediated photodynamic inactivation (PDI) was able to kill microorganisms. Chitosan nanoparticles loaded with ER exhibited better PDI efficacy than ER alone on microbial cultures and biofilms.

Malaysian tualang honey possesses strong antioxidant and anti-inflammatory properties. Here, we evaluated the effect of tualang honey on early biomarkers of photocarcinogenesis employing PAM212 mouse keratinocyte cell line. Keratinocytes were treated with tualang honey (1.0%, v/v) before a single UVB (150 mJ cm⁻²) irradiation. We found that the treatment of tualang honey inhibited UVB-induced DNA damage, and enhanced repair of UVB-mediated formation of cyclobutane pyrimidine dimers and 8-oxo-7,8-dihydro-2′-deoxyguanosine. Treatment of tualang honey inhibited UVB-induced nuclear translocation of NF-κB and degradation of IκBα in murine keratinocyte cell line. The treatment of tualang honey also inhibited UVB-induced inflammatory cytokines and inducible nitric oxide synthase protein expression. Furthermore, the treatment of tualang honey inhibited UVB-induced COX-2 expression and PGE2 production. Taken together, we provide evidence that the treatment of tualang honey to keratinocytes affords substantial protection from the adverse effects of UVB radiation via modulation in early biomarkers of photocarcinogenesis and provide suggestion for its photochemopreventive potential.

Malaysian tualang honey possesses strong antioxidant and anti-inflammatory properties. We found that treatment of tualang honey inhibited ultraviolet (UV) B-induced DNA damage, and enhanced repair of UVB-mediated formation of cyclobutane pyrimidine dimers and 8-oxo-7,8-dihydro-2′-deoxyguanosine in murine keratinocyte cell line PAM212. Treatment of tualang honey inhibited UVB-induced activation of NF-κB, inflammatory cytokines and inducible nitric oxide synthase. Furthermore, the treatment of tualang honey inhibited UVB-induced COX-2 expression and PGE2 production. Taken together, we provide evidence that the treatment of tualang honey to keratinocytes affords substantial protection from the adverse effects of UVB radiation via modulation in early biomarkers of photocarcinogenesis.

Biologically, light including ultraviolet (UV) radiation is vital for life. However, UV exposure does not come without risk, as it is a major factor in the development of skin cancer. Natural protections against UV damage may have been affected by lifestyle changes over the past century, including changes in our sun exposure due to working environments, and the use of sunscreens. In addition, extended “day time” through the use of artificial light may contribute to the disruption of our circadian rhythms; the daily cycles of changes in critical bio-factors including gene expression. Circadian disruption has been implicated in many health conditions, including cardiovascular, metabolic and psychiatric diseases, as well as many cancers. Interestingly, the pineal hormone melatonin plays a role in both circadian regulation as well as protection from UV skin damage, and is therefore an important factor to consider when studying the impact of UV light. This review discusses the beneficial and deleterious effects of solar exposure, including UV skin damage, Vitamin D production, circadian rhythm disruption and the impact of melatonin. Understanding these benefits and risks is critical for the development of protective strategies against solar radiation.

Biologically, light including ultraviolet (UV) radiations is vital for life. However, UV exposure does not come without risk, as it is a major factor in the development of skin cancer. This review discusses the beneficial and deleterious effects of solar exposure, including UV skin damage, Vitamin D production, circadian rhythm disruption and the impact of melatonin. Understanding of these benefits and risks is critical for the development of protective strategies against solar radiation.

1,2-Diaryloxyethene has recently been proposed as a linker in singlet oxygen-mediated drug release. Even though 1,2-diaryloxyethenes look very simple, their synthesis was not an easy task. Previous methods are limited to symmetric molecules, lengthy step and low yield. We report on a facile synthetic method not only for 1,2-diaryloxyethenes but also their sulfur and nitrogen analogs in yields ranging from 40 to 90% with more than 90% purity at the vinylation reaction.

Most recently, light-controlled drug release systems were proposed, where singlet oxygen generated from low energy light and a photosensitizer cleaves electron-rich alkenes, e.g. 1,2-diaryloxyethene. However, the synthesis of 1,2-diaryloxyethene was not well established. Herein, we report a facile synthesis of 1,2-diaryloxyethenes and its sulfur and nitrogen analogs. Model compounds were prepared in four steps from 4-phenylphenol via Ullman-type coupling reaction.

Measurements were conducted at San Ya, China (18.4°N, 109.7°E, altitude 18 m) to investigate the diurnal variation of ocular exposure to ultraviolet (UV) radiation. The experimental apparatus was composed of a manikin and a dual-detector spectrometer to simultaneously measure ocular and ambient UV data. The experimental apparatus was rotated clockwise to simulate three different types of exposure. When the manikin was facing into the sun, the ocular exposure to UV radiation on a summer day was bimodally distributed. The maximum ocular UV irradiance occurred at solar elevations of around 40° and 50° for UVA and UVB respectively. The spectral irradiances were measured at specific wavelength to obtain the ocular biologically effective UV (UV_BE) irradiances for photokeratitis, photoconjunctivitis and cataract, and the UV index (UVI) was calculated at the same time point for comparison. When the manikin faced the sun, the maximal ocular UV_BE irradiance values were obtained at the solar elevation where the UVI value was 8. The results of this study showed that protection against ocular overexposure during outdoor activities should be taken not only at noon but also at other times.

Measurements were conducted at San Ya, China (18.4°N, 109.7°E, altitude 18 m) to investigate the diurnal variation of ocular exposure to ultraviolet radiation, which could simulate three different types of exposure (maximum, average and minimum) by rotating the manikin. The diurnal variations of the ocular absolute irradiance and biologically effective UV irradiances in the maximum exposure were both different from the results of the ambient UV measurements. The results showed that protection against ocular overexposure during outdoor activities should be taken not only at noon but also at other times.

Assessing the effects of substituents on the spectra of chlorophylls is essential for gaining a deep understanding of photosynthetic processes. Chlorophyll a and b differ solely in the nature of the 7-substituent (methyl versus formyl), whereas chlorophyll a and d differ solely in the 3-substituent (vinyl versus formyl), yet have distinct long-wavelength absorption maxima: 665 (a) 646 (b) and 692 nm (d). Herein, the spectra, singlet excited-state decay characteristics, and results from DFT calculations are examined for synthetic chlorins and 13¹-oxophorbines that contain ethynyl, acetyl, formyl and other groups at the 3-, 7- and/or 13-positions. Substituent effects on the absorption spectra are well accounted for using Gouterman’s four-orbital model. Key findings are that (1) the dramatic difference in auxochromic effects of a given substituent at the 7- versus3- or 13-positions primarily derives from relative effects on the LUMO+1 and LUMO; (2) formyl at the 7- or 8-position effectively “porphyrinizes” the chlorin and (3) the substituent effect increases in the order of vinyl < ethynyl < acetyl < formyl. Thus, the spectral properties are governed by an intricate interplay of electronic effects of substituents at particular sites on the four frontier MOs of the chlorin macrocycle.

Chlorophyll a and b differ solely in the nature of the 7-substituent, whereas chlorophyll a and d differ solely in the 3-substituent, yet have distinct long-wavelength absorption maxima: 665 (a) 646 (b) and 692 nm (d). Herein, the spectra, singlet excited-state decay characteristics, and results from DFT calculations are examined for synthetic chlorins and 13¹-oxophorbines that contain a variety of substituents at the 3-, 7- and/or 13-positions. An intricate interplay of site-specific electronic effects of substituents on the four frontier MOs of the chlorin macrocycle is found to govern the spectral properties.

Excitation energy transfer in chlorosomes from photosynthetic green sulfur bacteria, Chlorobaculum (Cba.) tepidum and Prosthecochloris (Pst.) aestuarii, have been studied at room temperature by time-resolved femtosecond transient absorption spectroscopy. Bleach rise times from 117 to 270 fs resolved for both chlorosomes reflect extremely efficient intrachlorosomal energy transfer. Bleach relaxation times, from 1 to 3 ps and 25 to 35 ps, probed at 758 nm were tentatively assigned to intrachlorosomal energy transfer based on amplitude changes of the global fits and model calculations. The anisotropy decay constant of about 1 ps resolved at 807 nm probe wavelength for the chlorosomes from Chloroflexus aurantiacus, Pst. aestuarii and Cba. tepidum was related to energy transfer between bacteriochlorophyll a molecules of the baseplate and partly to intrachlorosomal energy transfer. The longer anisotropy components 6.6, 8.8 and 12.1 ps resolved for the three chlorosomes, respectively, were assigned to chlorosome to baseplate energy transfer. Global fits of magic-angle data also revealed longer chlorosome to baseplate energy transfer components from 95 to 135 ps, in accord with results from simulations.

Exceedingly efficient intrachlorosomal excitation energy transfer channel (sub 300 fs) in chlorosomes from photosynthetic green sulfur bacteria Chlorobaculum (Cba.) tepidum and Prosthecochloris (Pst.) aestuarii was identified by time-resolved femtosecond transient absorption spectroscopy. Anisotropy decay results suggested characteristic excitation transfer times from the red-most chlorosome antenna elements to the baseplate of 6.6, 8.8 ps and 12.1 ps for chlorosomes from Chloroflexus aurantiacus, Pst. aestuarii and Cba. tepidum, respectively. One picosecond anisotropy component, common to all three species, was assigned to energy transfer between bacteriochlorophyll a molecules of the baseplate.

Macroautophagy is a cellular response to various environmental stresses that ensures lysosomal degradation of long-lived and damaged proteins and cellular organelles. It occurs through the formation of an autophagosome, which then fuses with a lysosome to form an autolysosome. Depending on the cellular context, autophagy may promote cancer cell survival or it may serve as a mechanism of tumor suppression. Herein, we show that resveratrol, a natural phytoalexin, induces premature senescence in human A431 SCC cells, and that resveratrol-induced premature senescence is associated with a blockade of autolysosome formation, as assessed by the absence of colocalization of LC3 and Lamp-2, markers for autophagosomes and lysosomes, respectively. Further, we show that resveratrol downregulates the level of Rictor, a component of mTORC2, leading to decreased RhoA-GTPase and altered actin cytoskeleton organization. Exogenous overexpression of Rictor restores RhoA-GTPase activity and actin cytoskeleton network, and decreases resveratrol-induced senescence-associated β-gal activity, indicating a direct role of Rictor in senescence induction. Rictor is overexpressed in UV-induced murine SCCs, whereas its expression is diminished by oral administration of resveratrol. These data indicate that resveratrol attenuates autophagic process via Rictor, and suggest that downregulation of Rictor may be a mechanism of tumor suppression associated with premature senescence.

Resveratrol-induced premature senescence is associated with aberrant autophagic process in A431 cells in which resveratrol blocks autolysosome formation via the downregulation of Rictor-mediated RhoA-GTPase activity, leading to actin cytoskeleton reorganization. Rictor is overexpressed in UV-induced murine SCCs, whereas resveratrol decreases the level of Rictor and induces senescence in SCCs. This suggests that the downregulation of Rictor might serve as a mechanism of tumor suppression associated with premature senescence.

Conventional antimicrobial strategies have become increasingly ineffective due to the emergence of multidrug resistance among pathogenic microorganisms. The need to overcome these deficiencies has triggered the exploration of alternative treatments and unconventional approaches towards controlling microbial infections. Photodynamic therapy (PDT) was originally established as an anticancer modality and is currently used in the treatment of age-related macular degeneration. The concept of photodynamic inactivation requires cell exposure to light energy, typically wavelengths in the visible region that causes the excitation of photosensitizer molecules either exogenous or endogenous, which results in the production of reactive oxygen species (ROS). ROS produce cell inactivation and death through modification of intracellular components. The versatile characteristics of PDT prompted its investigation as an anti-infective discovery platform. Advances in understanding of microbial physiology have shed light on a series of pathways, and phenotypes that serve as putative targets for antimicrobial drug discovery. Investigations of these phenotypic elements in concert with PDT have been reported focused on multidrug efflux systems, biofilms, virulence and pathogenesis determinants. In many instances the results are promising but only preliminary and require further investigation. This review discusses the different antimicrobial PDT strategies and highlights the need for highly informative and comprehensive discovery approaches.

In just 20 years antimicrobial photodynamic therapy (PDT) has emerged as a discovery and development platform inspiring a proliferation of light-based antimicrobial explorations worldwide. However, the potential for microbial resistance development using PDT remains under-investigated. Studies of resistance have been sporadic but they are rapidly increasing, with recent reports examining key elements of the microbial phenotype. These include multidrug efflux systems, biofilm, spore formation, virulence and pathogenicity determinants. The emerging consensus is that the effectiveness of PDT may be profoundly impacted by all these systems, but the exact mechanisms of these effects remain elusive. For example, an array of studies suggests that antimicrobial photosensitizers are substrates of multidrug efflux systems. An evolving antimicrobial discovery concept is based on the exploration of synergies between photosensitizers and small molecules efflux pump inhibitors. PS photosensitizer (red), EPI efflux pump inhibitor (green).

The emission properties of a series of substituted 1,3-diarylisobenzofurans have been studied. Most compounds exhibit very intense emission in the nanosecond timescale at room temperature as well as at 77 K. The room temperature emission is attributed to the deactivation of a twisted intramolecular charge transfer excited state, based on its energy, shape and solvent dependence. The experimental results are strongly supported by a theoretical study on one representative compound. The DFT/TD-DFT calculations demonstrate that the initial excited state relaxes toward a twisted structure.

Upon light irradiation, the 1,3-diarylisobenzofurans undergo a charge transfer on the initially planar structure, followed by relaxation to an intramolecular twisted excited state responsible for the intense emission of such compounds. Experimental and theoretical results evidence this process.

We have isolated and characterized the light-driven proton pump Bop I from the ultrathin square archaeon Haloquadratum walsbyi, the most abundant component of the dense microbial community inhabiting hypersaline environments. The disruption of cells by hypo-osmotic shock yielded Bop I retinal protein highly enriched membranes, which contain one main 27 kDa protein band together with a high content of the carotenoid bacterioruberin. Light-induced pH changes were observed in suspensions of Bop I retinal protein-enriched membranes under sustained illumination. Solubilization of H. walsbyi cells with Triton X-100, followed by phenyl-Sepharose chromatography, resulted in isolation of two purified Bop I retinal protein bands; mass spectrometry analysis revealed that the Bop I was present as only protein in both the bands. The study of light/dark adaptations, M-decay kinetics, responses to titration with alkali in the dark and endogenous lipid compositions of the two Bop I retinal protein bands showed functional differences that could be attributed to different protein aggregation states. Proton-pumping activity of Bop I during the photocycle was observed in liposomes constituted of archaeal lipids. Similarities and differences of Bop I with other archaeal proton-pumping retinal proteins will be discussed.

Haloquadratum walsbyi is a peculiar organism which often dominates the microbial communities of the hypersaline ecosystems, such as salt lakes and solar saltern crystallizer ponds. It is extremely thin and possesses a unique square-like shape, with sharp edges and acute straight corners. The flat cells form large sheets similar to solar panels, able to efficiently collect light as an energy source for metabolism. Like other archaeal extremely halophilic microorganisms, square cells encode light-activated retinal-proteins to survive in hypersaline environments. In this study we describe the biochemical properties and the photochemistry of the light-activated proton pump Bop I of H. walsbyi, grown in laboratory.

UVR exposure is known to cause developmental defects in a variety of organisms including aquatic species but little is known about the underlying molecular mechanisms. In this work we used zebrafish (Danio rerio) embryos as a model system to characterize the UVR effects on fish species. Larval viability was measured for embryos exposed to several UVR spectral treatments by using a solar simulator lamp and an array of UV cutoff filters under controlled conditions in the laboratory. Survival rate and occurrence of development abnormalities, mainly caudal (posterior) notochord bending/torsion, were seriously affected in UV-exposed larvae reaching values of 53% and 72%, respectively, compared with non–UV-exposed larvae after 6 days postfertilization (dpf). In order to elucidate the molecular mechanisms involved, a matricellular glycoprotein named osteonectin and the expression of a DNA-repair related gene, p53, were studied in relation to UVR exposure. The results indicate that osteonectin and p53 expression were increased under UVR exposure due to wavelengths shorter than 335 nm (i.e. mainly UVB) and 350 nm (i.e. short UVA and UVB), respectively. Furthermore, parallel experiments with microinjections of osteonectin-capped RNA showed that malformations induced by osteonectin overexpression were similar to those observed after a UVR exposure. Consequently this study shows a potential role of osteonectin in morphological deformities induced by solar UV radiation in zebrafish embryos.

UV exposure is known to cause morphological deformities in fish embryos but the molecular mechanisms are unclear. Gene expression of osteonectin and p53 increases during UV exposure of zebrafish embryos. Expression is mainly a function of UVB exposure. Microinjection of osteonectin mRNA causes similar morphological deformities as UV exposure. This advances our understanding of the molecular basis of UV effects and importance of osteonectin in embryonic development.

The present study aimed to evaluate the photoprotective effects of cosmetic formulations containing a dispersion of liposome with magnesium ascorbyl phosphate (MAP), alpha-lipoic acid (ALA) and kinetin, as well as their effects on the hydration and viscoelastic skin properties. The photoprotection was determined in vitro (antioxidant activity) and in vivo on UV-irradiated hairless mouse skin. The hydration effects were performed with the application of the formulations under study on the forearm of human volunteers and skin conditions were analyzed before and after a single application and daily applications during 4 weeks in terms of transepidermal water loss (TEWL), skin moisture and viscoelastic properties. The raw material under study possessed free-radical scavenging activity and the formulation with it protected hairless mouse skin barrier function against UV damage. After 4 weeks of application on human skin, the formulation under study enhanced stratum corneum skin moisture and also showed hydration effects in deeper layers of the skin. Thus, it can be concluded that the cosmetic formulation containing a dispersion of liposome with MAP, ALA and kinetin under study showed photoprotective effects in skin barrier function as well as pronounced hydration effects on human skin, which suggests that this dispersion has potential antiaging effects.

Formulations containing, or not, 10% of a dispersion of liposome with magnesium ascorbyl phosphate (MAP), alpha-lipoic acid (ALA) and kinetin were evaluated. The in vitro studies showed that this association in liposomes possesses free-radical scavenging properties. The in vivo studies on animal model showed that this association protected skin barrier function against UV damage, seen by transepidermal water loss reduction. Clinical studies performed on human volunteers, forearms showed that the formulation with the active substances enhanced skin moisture and altered skin viscoelastic properties when compared with the vehicle, which suggests that kinetin, MAP and ALA in liposomes had sustained hydration effect and acted in the deeper layers of the skin provoking alterations in the viscoelastic-to-elastic ratio.

The aim of this study was to determine the photodynamic antimicrobial effect of hypericin on clinically isolated Staphylococcus aureus and Escherichia coli cells. Bacterial cells (10⁸ cells per mL) were incubated with hypericin (0–40 μm) for 30 min and followed by light irradiation of 600–800 nm at 5–30 J cm⁻². Cell survival was determined by colony counting, cellular hypericin uptake examined by flow cytometer, and cell membrane damage examined by scanning electron microscopy and leakage assay. The effectiveness of hypericin-mediated photodynamic killing was strongly affected by cellular structure and photosensitizer uptake. The combination of hypericin and light irradiation could induce significant killing of Gram positive methicillin-sensitive and -resistant S. aureus cells (>6 log reduction), but was not effective on Gram negative E. coli cells (<0.2 log reduction). The difference was caused by different cell wall/membrane structures that directly affected cellular uptake of hypericin.

Increasing prevalence of antibiotic-resistant bacteria is one of the most pressing global health issues. It is imperative to develop nonantibiotic approaches for combating antibiotic-resistant bacterial infections. Photodynamic antimicrobial chemotherapy (PACT) is a promising alternative. This study examined the effect of hypericin-mediated PACT on clinically isolated S. aureus and E. coli. Hypericin-mediated PACT could induce significant killing of Gram positive methicillin-sensitive and methicillin-resistant S. aureus cells (illustrated), but was ineffective on Gram negative E. coli cells. This phenomenon is due to the differences in bacterial wall/membrane structures that directly affect cellular uptake of hypericin.

The mammalian skin is a complex dynamic organ composed of thin multilayered epidermis and a thick underlying connective tissue layer dermis. The epidermis undergoes continuous renewal throughout life. The stems cells uniquely express particular surface markers utilized for their identification, isolation and localization in specific niches in epidermis as well as hair follicles (HFs). The two stage skin carcinogenesis model involves stepwise accumulation of genetic alterations and ultimately leading to malignancy. Whereas early research on skin carcinogenesis focused on the molecular nature of carcinogens and tumor promoters, more recent studies have focused on the identification of the target cells and tumor promoting cells for both chemical and physical carcinogens and promoters. Recent studies support the hypothesis that keratinocyte stem cells are the targets in skin carcinogenesis. In this review, we discuss briefly the localization of stem cells in the epidermis and HFs, and review the possibility that skin papillomas and carcinomas are derived from stem cells, as well as from other cells in the cutaneous epithelium whose stem cell properties are not well known.

The cutaneous epithelium of mammals is a complex dynamic tissue and undergoes continuous renewal throughout life. To date, several stem cell populations have been discovered and characterized in various skin lineages including interfollicular epidermis, and components of the hair follicle. However, key issues remain unresolved such as the identity of the target cells during nonmelanoma skin cancer. In this regard, the two stage skin chemical and UV radiation models have been useful for studying molecular carcinogenesis in detail. Significantly, transgenic mice have played an important role towards understanding the contribution of stem cells and their lineages during carcinogenesis such that there are now several reports confirming at least one population of stem cells as target cells in nonmelanoma skin cancer. Nevertheless, the role of other cell types and non-stem cells during cancer initiation, promotion, and progression cannot be ignored.

Sunscreens were originally designed to prevent sunburn and incorporated active ingredients that absorbed principally in the UVB region. However, over the past 20 years or so new ingredients have been developed that extend absorption across a much wider range of the solar ultraviolet spectrum in the belief that sunscreens should provide balanced spectral absorption. This article develops the rationale for spectral uniformity by showing that this requirement is aligned to more natural forms of photoprotection. It is shown that a modern sunscreen can provide a spectrally balanced absorption profile in line with shade and many types of clothing fabric. Finally, a new metric is introduced that measures how well the spectral absorption profile of topical sunscreens performs against this ideal.

For two decades manufacturers have sought to develop sunscreens with spectral profiles that approach uniform absorption across the solar ultraviolet spectrum. There has been considerable success in this regard and today we have available products that virtually meet this criterion of spectral uniformity. Yet to ensure optimal compliance by consumers, sunscreens need to be colorless when applied to the skin and hence their absorbance needs to fall to zero as the nonvisible UV wavelengths merge into the visible region. This figure compares our proposed ideal spectral profile of a topical sunscreen with the spectral sensitivity of the eye.

The objective of this study was to determine if and how photoproducts contribute to the antitumor effect of merocyanine-mediated PDT. A panel of barbituric, thiobarbituric and selenobarbituric acid analogues of Merocyanine 540 was photobleached, and the resulting photoproducts were characterized by absorption, fluorescence emission, mass, energy dispersive X-ray, and X-ray photoelectron spectroscopy and tested for cytotoxic activity against tumor cell lines and freshly explanted bone marrow cells. While all dyes were readily photobleached, only photoproducts of selone dyes showed cytotoxic activity. One-hour incubations with micromolar concentrations of selone-derived photoproducts were sufficient to reduce leukemia/lymphoma cells ≥10 000 fold, whereas preserving virtually all normal CD34-positive bone marrow cells. Of six multidrug-resistant tumor cell lines tested, five were as sensitive or more sensitive to photoproducts than the corresponding wild-type lines. Physicochemical characterizations of the cytotoxic activity indicated that it consisted of conjugates of subnano particles of elemental selenium and (lipo)proteins. The discovery of cytotoxic Se-protein conjugates provides a rare example of photoproducts contributing substantially to the antitumor effect of PDT and challenges the long-held view that Se in oxidation state zero is biologically inert. Agents modeled after our Se-protein conjugates may prove useful for the treatment of leukemia.

One-hour incubations with micromolar concentrations of selenomerocyanine-derived photoproducts reduce in vitro clonogenic wild-type leukemia cells (L1210) and melphalan-resistant leukemia cells (L1210/L-PAM1 and L1210/L-PAM2) by several orders of magnitude, but preserve virtually all normal CD34-positive normal bone marrow cells.

Residence in high ultraviolet (UV) locations is associated with increased risk for incident nonmelanoma skin cancer (NMSC). However, the effect of geographic location on multiple NMSC development has not been well studied. We evaluated the association between state of residence at birth, age 15 and 30 and risk of multiple NMSCs among 80 275 women and men. After adjusting for age, gender, hair color, number of sunburns, tanning ability, family history of melanoma and nevus count, the cumulative relative risks (RRs) of developing ≥1 NMSC for those consistently residing in medium- and high-UV index states were 1.20 (95% CI 1.14–1.27) and 1.42 (95% CI 1.32–1.53) respectively. We found that compared to individuals with one lifetime NMSC, the multivariate cumulative RRs of developing ≥2 NMSCs for those who stayed in medium- and high-UV index states at all three timepoints were 1.09 (95% CI 1.00–1.19) and 1.15 (95% CI 1.02–1.30) respectively. These results cannot account for migration during the interval period and seasonal changes in residence; further, as BCC is the predominant NMSC, the results may be BCC-driven. In conclusion, we found that consistent residence in medium- or high-UVR locations was significantly associated an incremental risk of ≥2 NMSCs later in life.

Ultraviolet (UV) index was developed to quantify the amount of ultraviolet radiation reaching the earth’s surface. The algorithm accounts for latitude, altitude, cloud cover, haze, time of day and ozone concentration. On the basis of mean UV index for the month of August each state in the United States was categorized into low-, medium- and high-UV index states. Residence in high-UV locations is associated with increased risk for incident nonmelanoma skin cancer (NMSC). This study focused on the association between geographic location based on UV index of residence and risk of multiple NMSCs. (Map was generated using http://monarch.tamu.edu/~maps2/us.htm)

In this contribution, we report studies on the interaction of an antituberculosis drug rifampicin (RF) in a macromolecular assembly of CTAB with an extrinsic fluorescent probe, dansyl chloride (DC). The absorption spectrum of the drug RF has been employed to study Förster resonance energy transfer (FRET) from DC, bound to the CTAB micelle using picosecond resolved fluorescence spectroscopy. We have applied a kinetic model developed by Tachiya to understand the kinetics of energy transfer and the distribution of acceptor (RF) molecules around the donor (DC) molecules in the micellar surface with increasing quencher concentration. The mean number of RF molecules associated with the micelle increases from 0.24 at 20 μm RF concentration to 1.5 at 190 μm RF concentration and consequently the quenching rate constant (k_q) due to the acceptor (RF) molecules increases from 0.23 to 0.75 ns⁻¹ at 20 and 190 μm RF concentration, respectively. However, the mean number of the quencher molecule and the quenching rate constant does not change significantly beyond a certain RF concentration (150 μm), which is consistent with the results obtained from time resolved FRET analysis. Moreover, we have explored the diffusion controlled FRET between DC and RF, using microfluidics setup, which reveals that the reaction pathway follows one-step process.

Interaction of an antituberculosis drug rifampicin (RF) in a nanoscopic macromolecular assembly of CTAB with an extrinsic fluorescent probe, dansyl chloride (DC) has been studied using picosecond resolved Förster resonance energy transfer (FRET). The well-known Tachiya model has been employed to understand the kinetics of energy transfer and the distribution of acceptor (RF) molecules around the donor (DC) molecules at the micellar surface with increasing RF concentration. The diffusion controlled FRET between DC and RF at the nanoscopic micellar surface has been studied using indigenously developed microfluidics setup.

The lipid mediator Platelet-activating factor (PAF) and oxidized glycerophosphocholine PAF agonists produced by UVB have been demonstrated to play a pivotal role in UVB-mediated systemic immunosuppression. Importantly, employing the ability of distant UVB irradiation to inhibit contact hypersensitivity (CHS) responses to the chemical antigen dinitrofluorobenzene (DNFB) to an area of unirradiated murine skin, we and others have demonstrated that UVB-mediated systemic immunosuppression was only observed in PAF-R expressing wild type (WT) mice and not in PAF-R-knockout (Pafr−/−) mice. As it is not known if PAF is involved in UVB-mediated local immunosuppression, these studies compared local UVB on CHS responses in WT versus Pafr−/− mice. We demonstrate that the application of DNFB onto UVB-exposed (locally) area of mouse skin resulted in a similar significant inhibition of subsequent CHS responses in both WT and Pafr−/− mice compared to sham-irradiated control mice. Furthermore, the expression of langerin, a marker for the presence of Langerhans cells was substantially reduced equally in the epidermal ears of UVB-irradiated WT and Pafr−/− mice compared to their respective sham control groups. These findings indicate that the PAF-R is not involved UVB-induced local immunosuppression.

Several studies including from our group have characterized the importance of oxidized proinflammatory lipid mediators with platelet-activating factor (PAF) activity in UVB-induced systemic immunosuppression. However, the role of PAF in local immunosuppression is unknown. These studies indicate that UVB irradiation results in an inhibition of contact hypersensitivity (CHS) to the chemical DNFB in both wild-type and PAF receptor-deficient mice. Thus, PAF-receptor signaling is not involved in local immunosuppression, unlike its critical role in systemic immunosuppression.

The mechanism of photoinactivation of Candida albicans by 3.5 μm uncharged, cationic or anionic porphyrins under blue light (407–420 nm) was found to be dependent on the uptake of porphyrins into yeast cells, and was also dependent on the presence or absence of proteins in the photosensitization medium. In a very protein-rich medium, a decrease in viability was observed only with the uncharged porphyrin. Photoinactivation by uncharged or cationic porphyrins in a protein-poorer medium resulted in total eradication, whereas no significant decrease was observed with the anionic porphyrin. Phototreatment in PBS resulted in eradication with all three porphyrins. X-ray microanalysis after phototreatment by the uncharged or cationic porphyrins in the protein-poor medium exhibited ion loss, indicating cell-membrane damage. Transmission electron microscopy indicated cellular and chromosomal damage. No ion loss or cell damage was observed in this medium with the anionic porphyrin. The efficiency of photoeradication of C. albicans is dependent on porphyrin uptake, which might lead (upon illumination) to processes that facilitate the formation of reactive oxygen species that damage the cells. Uptake of charged porphyrins is dependent on protein quantity and quality in the photosensitization microenvironment. This fact must be taken into account when using charged photosensitizers.

The mechanism of photoinactivation of Candida albicans by uncharged, cationic or anionic porphyrins under blue light, was found to be dependent on the uptake of the porphyrins into yeast cells, and was also dependent on the protein’s quantity and quality in the photosensitization medium. Only phototreatment in phosphate buffered saline resulted in eradication with all three porphyrins. X-ray microanalysis demonstrated that only with the uncharged or cationic porphyrins in a protein-poor medium exhibited ion loss, indicating cell-membrane damage. Transmission electron microscopy indicated cellular and chromosomal damage. Only taken up porphyrins might lead (upon illumination) to processes that facilitate the formation of reactive oxygen species that will damage and inactivate the yeast cells.

In photodynamic therapy (PDT), light activates a photosensitizer added to a tissue, resulting in singlet oxygen formation and cell death. The photosensitizer phthalocyanine 4 (Pc 4) localizes primarily to mitochondrial membranes in cancer cells, resulting in mitochondria-mediated cell death. The aim of this study was to determine how lysosomes contribute to PDT-induced cell killing by mitochondria-targeted photosensitizers such as Pc 4. We monitored cell killing of A431 cells after Pc 4-PDT in the presence and absence of bafilomycin, an inhibitor of the vacuolar proton pump of lysosomes and endosomes. Bafilomycin was not toxic by itself, but greatly enhanced Pc 4-PDT-induced cell killing. To investigate whether iron loading of lysosomes affects bafilomycin-induced killing, cells were incubated with ammonium ferric citrate (30 μm) for 30 h prior to PDT. Ammonium ferric citrate enhanced Pc 4 plus bafilomycin-induced cell killing without having toxicity by itself. Iron chelators (desferrioxamine and starch-desferrioxamine) and the inhibitor of the mitochondrial calcium (and ferrous iron) uniporter, Ru360, protected against Pc 4 plus bafilomycin toxicity. These results support the conclusion that chelatable iron stored in the lysosomes enhances the efficacy of bafilomycin-mediated PDT and that lysosomal disruption augments PDT with Pc 4.

Photodynamic therapy (PDT) is an attractive treatment for cancer. In PDT, light activates a photosensitizer added to a tissue, resulting in singlet oxygen formation and cell death. The aim of this study was to determine how lysosomes contribute to PDT-induced cell killing by mitochondria-targeted photosensitizers such as Pc 4. Our results demonstrate that strategies to collapse the lysosomal pH gradient without lysosomal membrane breakdown is sufficient to induce iron-dependent mitochondrial depolarization and subsequent cell killing during Pc 4-PDT. Thus, agents that disturb lysosomal function could potentially be used clinically as an adjuvant treatment with mitochondria-targeted photosensitizers.

We analyzed the photoinactivation of the membrane functions of bacteria and erythrocytes induced by xanthene dyes. The dyes tested were rose bengal, phloxine B, erythrosine B and eosin B. These dyes induced the leakage of K⁺ from Staphylococcus aureus cells within minutes of photoirradiation, in the order of rose bengal > phloxine B > erythrosine B > eosin B. The ability of dyes to inhibit respiration was weak, except for rose bengal, and the dyes dissipated the membrane potential in similar time traces with changes in K⁺ permeability. The xanthene dyes also induced the leakage of K⁺ from bovine erythrocytes upon photoirradiation in the same order as that observed with bacteria. Furthermore, we found that the ability to cause the leakage of K⁺ from erythrocytes was associated with dye-induced morphological changes, forming a crenated form from the normal discoid. These results are discussed in connection with the ability of xanthene dyes to generate singlet oxygen and bind to bacterial cells, and further compared with the actions of cationic porphyrins, which induced photoinactivation of bacteria through respiratory inhibition.

Singlet oxygen generated by the photoirradiation of xanthene dyes, such as rose bengal, phloxine B and erythrosine B, induced the leakage of K⁺ from Staphylococcus aureus cells and bovine erythrocytes, while the inhibition of respiration was weak except for rose bengal. The leakage of K⁺ was closely associated with the dissipation of bacterial membrane potential and the dye-induced morphological changes in erythrocytes.

Leishmania were previously shown to undergo photolysis when their transgenic mutants were induced endogenously to accumulate cytoplasmic uroporphyrin or when loaded exogenously with aluminum phthalocyanine chloride. A combinational use of both is reported here, which renders Leishmania far more susceptible to photolysis. Fluorescence microscopy of cells loaded with the two photosensitizers localized them to different subcellular sites. Pre-exposure of Leishmania to both synergistically sensitized them for photolysis as extracellular promastigotes and intracellular amastigotes in infected macrophages in vitro when illuminated at specific wavelengths to excite the respective photosensitizers for production of reactive oxygen species. Both Leishmania stages lost their viability completely when doubly photosensitized optimally and illuminated at low intensity, the host cells being left unscathed. Inoculation of mice with photoinactivated Leishmania produced no lesions, which invariably developed in the control groups during a period of observations for 8 weeks. Pretreatment of Leishmania with both photosensitizers rendered these cells susceptible to clearance from the ear dermis by white light illumination. The results suggest that double photosensitization for synergistic activity enhances the efficacy and safety of photodynamic therapy in general and for Leishmania in particular.

Leishmania parasitize the phagolysosomes of antigen-presenting cells and are thus uniquely suitable for targeted delivery of vaccines. When preloaded exogenously with photosensitizers, e.g. aluminum phthalocyanine chloride (AlPhCl; A) or when exposed to aminolevulinate as transgenic mutants to accumulate uroporphyrin endogenously (B), Leishmania are photolyzed in these cells selectively, but incompletely. Double photosensitization of Leishmania with both (C) increases their photolysis significantly so that no survivors are detectable in both in vitro and in vivo systems. The potential utility of Leishmania as a photodynamic vaccine carrier is thus enhanced by the double photosensitization to provide a favorable profile of their safety.

Excessive amounts of reactive oxygen species (ROS) induced by ultraviolet (UV) radiation cause skin aging via basement membrane/extracellular matrix degradation resulting from the action of matrix metalloproteinases (MMPs). Recently, phloroglucinol (1,3,5-trihydroxybenzene) was demonstrated to attenuate the cell damage induced by oxidative stress by quenching ROS and stimulating antioxidant systems. In the current study, the effect of phloroglucinol on UVB-induced photoaging was investigated in human HaCaT keratinocytes. Phloroglucinol significantly inhibited the UVB-induced (1) upregulation of MMP-1 mRNA, protein and activity; (2) augmentation of intracellular Ca²⁺ levels; (3) phosphorylation of mitogen-activated protein kinases (MAPKs); (4) expression of c-Fos and phospho c-Jun; and (5) enhancement of activator protein-1 (AP-1) binding to the MMP-1 promoter. In addition, the knockdown of MAPKs significantly inhibited UVB-induced MMP-1 expression. The results of this study suggest that phloroglucinol may be useful as a photoprotective compound for the skin.

UVB significantly induced the upregulation of MMP-1 mRNA, protein and activity in human HaCaT keratinocytes via induction of reactive oxygen species generation and augmentation of intracellular Ca²⁺ levels which are responsible for MAPKs activation. The activation of MAPKs stimulated c-Fos forming a heterodimer with phospho c-Jun, thus increasing the stability of the AP-1 complex, and further amplifying the capacity of AP-1 binding to the MMP-1 promoter, thereby inducing MMP-1 expression. Phloroglucinol dramatically suppressed UVB-inducing MMP-1 production via inhibition of this signaling pathway.

DNA photolesions induced by UV, cyclobutane pyrimidine dimer (CPD) and (6-4) photoproduct (6-4PP), are repaired by nucleotide excision repair (NER) in human cells. Various immunoassays using monoclonal antibodies specific for the photolesions have been developed and widely used for the analysis of cellular NER activity. In this study, we have newly developed a microplate-formatted cell-based immunoassay, based on indirect immunofluorescence staining with lesion-specific antibodies combined with an infrared imaging system. Using this assay, we show the repair kinetics of CPD and 6-4PP in various fibroblasts from newborn and adult donors with no age-related difference. Furthermore, epidermal keratinocytes and melanocytes exhibit comparable NER activity, and calcium ion-induced differentiation of keratinocytes has no significant impacts on their NER activity. We also evaluated the effects of a proteasome inhibitor, MG132, and a histone deacetylase inhibitor, sodium butyrate, on NER efficiency using this assay. All these results suggest that the new assay is highly useful for the rapid and quantitative analysis of NER activity in various primary cells with limited growth activity and is applicable to a screening system for drugs affecting NER efficiency.

DNA photolesions induced by UV, cyclobutane pyrimidine dimer (CPD) and (6-4) photoproduct (6-4PP), are repaired by nucleotide excision repair (NER) in human cells. In this study, we have developed a microplate-formatted cell-based immunoassay for NER of UV photoproducts (M-CINUP), based on indirect immunofluorescence staining with lesion-specific monoclonal antibodies combined with an infrared imaging system. Our results suggest that the new assay is highly useful for the rapid and quantitative analysis of NER activity in various primary cells with limited growth activity and is applicable to a screening system for drugs affecting NER efficiency.

Levofloxacin (LVFX) is a broad spectrum third generation fluoroquinolone antibiotic, used in the treatment of severe or life-threatening bacterial infections. Photosensitizing mechanism of LVFX was investigated under the ambient environmental intensities of UV-A, UV-B and sunlight exposure. Phototoxic effects of LVFX were assessed on NIH-3T3 and HaCaT cell lines. Results identified first time three photoproducts of LVFX at ambient levels of UV-R by LC-MS/MS. The generation of reactive oxygen species (ROS) was investigated photochemically as well as intracellularly in HaCaT cell line. ROS were significantly quenched by specific quenchers like DABCO, NaN₃, d-mannitol and NAC. Photosensitized LVFX caused lipid peroxidation at different concentrations. Quenching study with superoxide dismutase confirms the LVFX-induced lipid photoperoxidation. Further, photocytotoxicity of LVFX showed significant reduction in cell viability by MTT and neutral red uptake assays. LVFX caused cell arrest in G2/M phases as well as induced apoptosis through ROS-dependent pathway. In addition, photosensitized LVFX also induced upregulation of p21 and Bax/Bcl-2 genes ratio. India is a tropical country and most of the human activities such as agriculture, commerce, sports, etc. take place in bright sunlight; therefore, photosensitive LVFX may lead to skin/ocular disorders and immune suppression. Information is needed regarding the phototoxicity of LVFX for human safety.

Levofloxacin (LVFX) generates three photoproducts (identified by LC-MS/MS) after irradiation at ambient environmental intensities of UV-A, UV-B and sunlight that generate ¹O₂, O₂˙⁻ and ˙OH radical. Photocytotoxicity of LVFX showed significant reduction in cell viability by MTT and NRU. Photosensitized LVFX caused lipid peroxidation at different concentrations. Quenching with superoxide dismutase confirms LVFX-induced lipid photoperoxidation. Reactive oxygen species (ROS) mediated damage in cells, upregulation of p21 and Bax/Bcl-2 genes ratio. LVFX caused cell arrest in G2/M phases as well as induces apoptosis through ROS-dependent pathway.

In many recent publications, supposed athermal effects of water-filtered infrared A (wIRA) irradiation are discussed. Those effects are mainly attributed to wavelengths in the range from 780 to 1440 nm, and should not result from warming of cellular water or any aqueous medium surrounding the irradiated sample caused by wIRA absorption. Athermal effects are considered to be induced directly by absorption of different wavelengths of the wIRA spectrum by cellular molecules or structures except water. To distinguish between thermal and athermal effects, irradiated samples have to be subjected to a very effective and precise temperature homeostasis. Any experimental effects can only be attributed to pure athermal effects, if the temperature of the irradiated samples is verifiably constant and does not result in hyperthermia. Here, data of temperature distribution in Petri dishes of different types filled with aqueous medium are presented which were estimated by model calculation for different setups of cooling. Additionally, the real temperature development was directly measured. Such a cooling unit enables long-term application of high wIRA irradiances and large doses without any detectable warming of the irradiated samples, in single cell layers. Using such a setup, thermal and athermal effects can be compared and in addition to that quantified.

The investigation of athermal wIRA effects on single cells requires strict temperature homeostasis during wIRA exposure. This paper compares the often used air-cooling (left) with a suggested very effective water-cooling (right) setup. The graph indicates the major factors influencing sample temperature.

The pyrimidine nucleobases contained in DNA undergo a variety of photoinduced reactions in which two moieties become joined to form a product (e.g. formation of cyclobutane dimers and [6-4] adducts). Herein, we describe a new type of photoconjugation reaction that has been shown to occur for 5-methylcytosine (5-MeC), 1,5-dimethylcytosine (1,5-diMeC), 1-methylthymine and thymidine; in this reaction the 5-methyl group of one nucleobase (or nucleoside) becomes attached to the 4-position of the second moiety. For example, 5-MeC forms α-4′-(5′-methylpyrimidin-2′-one)-5-methylcytosine. The various (α-4) conjugates are produced upon irradiation of the parent compound in frozen aqueous solution at −78.5°C. The UV spectra of these compounds display a characteristic “double humped” profile, similar to that expected from overlaying the spectrum of parent nucleobase with that of a 2′-pyrimidone moiety. Preliminary results suggest that thymine and 5-methyl-2′-deoxycytidine (5-MedCyd) form analogous photoproducts. A variety of other previously unreported photoproducts are described as well for the 5-MeC, 1,5-diMeC and 5-MedCyd systems.

Irradiation of 5-methylcytosine, 1,5-dimethylcytosine, 1-methylthymine and thymidine in frozen aqueous solution induces photoreactions that form novel products termed as (α-4) conjugates. In this reaction, the 5-methyl group of nucleobase component of one reactant becomes attached to the 4-position of the nucleobase in the second reactant. The (α-4) photoconjugates display characteristic “double humped” UV absorption spectra. An example of this type of reaction is displayed schematically for thymidine in the accompanying scheme. There is evidence that thymine and 5-methyl-2′-deoxycytidine undergo similar photoconjugation reactions.

The selection of fungi resistant to currently used fungicides and the emergence of new pathogenic species make the development of alternative fungus-control techniques highly desirable. Photodynamic antimicrobial chemotherapy (PACT) is a promising method which combines a nontoxic photosensitizer (PS) with visible light to cause selective killing of microbial cells. The development of PACT to treat mycoses or kill fungi in the environment depends on identifying effective PS for the different pathogenic species and delivery systems able to expand and optimize their use. In the present study, the in vitro susceptibility of Cryptococcus neoformans melanized cells to the photodynamic effects of the PS agent ClAlPc in nanoemulsion (ClAlPc/NE) was examined. Cells were killed in a PS concentration- and light dose-dependent manner. Treatment with ClAlPc/NE, using PS concentrations (e.g. 4.5 μm) and light doses (e.g. 10 J cm⁻²) compatible with PACT, resulted in a reduction of up to 6 logs in survival. Washing the cells to remove unbound PS before light exposure did not inhibit fungal photodynamic inactivation. Internalization of ClAlPc by C. neoformans was confirmed by confocal fluorescence microscopy, and the degree of uptake was dependent on PS concentration.

The in vitro susceptibility of Cryptococcus neoformans melanized and nonmelanized cells to the photodynamic effects of the photosensitizer (PS) agent ClAlPc in nanoemulsion was examined. Cells were killed in a PS concentration- and light dose-dependent manner. Treatments with ClAlPc/NE, using PS concentrations and light doses compatible with photodynamic antimicrobial chemotherapy, resulted in a reduction of up to 6 logs in survival. Washing the cells to remove unbound PS before light exposure did not inhibit fungal photodynamic inactivation. Internalization of ClAlPc by C. neoformans was confirmed by confocal fluorescence microscopy, and the degree of uptake was dependent on PS concentration.

Recent increase and wider use of ionic liquids (ILs) for various applications has drawn attention to their toxicological consequence on human health. The present study explores effects of three different kinds of widely used ILs, such as 1-methyl-3-octylimidazolium chloride, 1-buytl-3-methyl imadazolium tetrafluoroborate and 1-benzyl-3-methyl imidazolium tetrafluoroborate, on liposome properties of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) by applying curcumin as molecular probe. Fluorescence intensity of curcumin is reported as a novel rotor which is sensitive to viscosity and thus the fluidity of the solvent. It follows a linear relationship of log fluorescence vs viscosity as proposed by Förster–Hoffmann equation. Curcumin binds strongly to liposome. At low concentration, the lipophilic drug curcumin does not appreciably influence the phase transition temperature of DPPC but as concentration reaches high levels significantly depresses the phase transition temperature. ILs diminish membrane fluidity. 1-methyl-3-octylimidazolium chloride disorders membrane properties by lowering the phase transition as is observed for higher concentration of curcumin, but 1-buytl-3-methyl imidazolium tetrafluoroborate and 1-benzyl-3-methyl imidazolium tetrafluoroborate do not modify phase transition temperature perceptibly; rather they broaden the phase transition at low molar concentration ratio. The three different kinds of ILs under study behave similarly at a high IL:DPPC ratio (1:2), while they behave differently at lower ratios (1:10–1:5).

Curcumin, a medicinal molecule, is a novel rotor sensitive to viscosity and membrane fluidity. At low molar ratio curcumin does not alter remarkably but at high molar ratio appreciably depresses the phase transition temperature of liposome. Ionic liquids decrease membrane fluidity and long chain ionic liquid lowers the phase transition temperature of liposomes. Short chains ionic liquid does not modify phase transition temperature perceptibly; rather it broadens the phase transition temperature of liposomes.

In this study, we report permeability coefficients of 30% glucose diffusion by the optical coherence tomography signal slope (OCTSS) method in four kinds of human lung tissue in vitro: normal lung tissue, benign granulomatosis lung tissue, squamous cell carcinoma and adenocarcinoma tumor. To quantify the permeability coefficient of the agent, the monitored region was 80 μm thickness at a tissue depth of ca 230 μm from the surface. The permeability coefficients of 30% glucose from 10 independent experiments were averaged and found to be (1.35 ± 0.13) × 10⁻⁵ cm s⁻¹ from the normal lung tissue, (1.78 ± 0.21) × 10⁻⁵ cm s⁻¹ from the benign granulomatosis lung tissue, (2.88 ± 0.19) × 10⁻⁵ cm s⁻¹ from the adenocarcinoma tumor and (3.53 ± 0.25) × 10⁻⁵ cm s⁻¹ from the squamous cell carcinoma, respectively. It could be clearly seen that the permeability coefficients of 30% glucose increase ca 32%, 113% and 162% in the benign granulomatosis, adenocarcinoma tumor and squamous cell carcinoma of human lung tissue compared with that from the normal lung tissue, respectively. Therefore, we inferred from this pilot study that the OCT imaging is a feasible method to distinguish normal and cancer lung tissue.

This figure represents the comparison of permeability coefficients (PCs) of 30% glucose diffusion in normal, benign granulomatosis, adenocarcinoma tumor and squamous cell carcinoma of human lung tissue in vitro. A fourier domain optical coherence tomography (FD OCT) system was used for experimentation. PCs were computed by analyzing the OCT signal slope changes induced by the agent diffusion in a specific depth region. Our results show that PCs of the same hyperosmotic agent in normal, benign and malignant lung tissues are apparently different. Therefore, FD OCT might provide a truly noninvasive way to evaluate of normal and abnormal tissues.

The mechanism of biocidal action of nano titania on Escherichia coli and Staphylococcus aureus has been evaluated by various biochemical techniques like lipid peroxidation, hydrolysis of orthonitrophenol β-d-galactopyranoside, estimation of protein–amino acid and bacterial nucleic acids leakage into solution, in addition to morphology studies by electron microscopy (TEM and SEM) and K⁺ ion leakage by inductively coupled plasma optical emission spectrometry. The active anatase phase of nano titania has been synthesized by sol-gel and pulverization techniques to obtain particle sizes averaging around 11 nm. The nano semiconductor with a bandgap of 3.2 eV responds well to the UV source to liberate reactive oxygen species (ROS). Gram negative bacteria easily succumb to the ROS at a faster rate than gram-positive bacteria with an observable difference in the mode of attack. The use of analytical techniques revealed the release of peroxidized lipid (26 nmol mL⁻¹) and protein content (370 μg mL⁻¹) with a K⁺ ion concentration of 22 000 ppb on complete destruction of E. coli.

Various analytical, bio and physical techniques of evaluation, experimented to study the disinfection capacity of pulverized nano-TiO₂, aids in better elucidation of the cell killing mechanism.

Absorption and emission yields for estrone and 17β-estradiol were measured in a variety of room temperature solvents. Molar extinction coefficients were found to not vary as a function of solvent, while fluorescence yields were found to be significantly affected by the polarity and hydrogen-bond accepting ability of the solvent, with the yield for 17β-estradiol being highest in nonpolar, hydrogen-bond donating solvents, and lowest in the nonpolar, hydrogen-bond accepting solvent ethyl acetate. Estrone’s emission yield was found to be a factor of ten smaller than 17β-estradiol’s. Strong solvent and excitation wavelength dependences were found for the relative amounts of emission between estrone’s two emission bands, with increased relative emission occurring in nonpolar aprotic solvents, and under higher excitation energies. These results are interpreted with the aid of vertical excitation energies from time-dependent density functional calculations using both explicit and implicit solvation models.

Pronounced solvent and excitation wavelength dependences on the emission yields and spectra of the endocrine disruptors estrogen and 17β-estradiol have been found.

Cerium-doped Titanium dioxide (TiO₂) nanoparticles are prepared by sol-gel method. Doping shifts the UV absorption edge of TiO₂ to the visible region, making it efficient for visible light photocatalysis. Incorporation of cerium decreases the effective band gap of TiO₂ and increases the Urbach energy levels. At the dopant concentrations of 0.015 and 0.025 mol the luminescence intensity increases compared to undoped TiO₂; however, the luminescence is quenched at 0.035 mol. Quenching of luminescence indicates efficient separation of charge carriers. Undoped TiO₂ is showing poor performance in the photocatalytic degradation of methyl orange under visible light. However, on cerium doping its photoactivity is increased, and is drastically enhanced at 0.035 mol of cerium. Further increase in Ce³⁺ doping level to 0.045 mol results in the reduction of the photodegradation of the dye. On UV irradiation, entire samples show good photocatalytic activity up to 30 min, but their efficiency decreases when irradiation time is increased to 45 min. Irradiation for longer time results in negative charging of the TiO₂ surface with migrating electrons. The negatively charged surface repels the OH⁻ ion and O₂ molecule from adsorbing on its surface thus decreasing the availability of hydroxyl and superoxide radical for dye degradation.

Photoluminescence intensity of TiO₂ nanoparticles is quenched at 0.035 mol of Ce³⁺ concentration. At higher doping level, the number of nonradiative recombination centers increases. This ultimately results in the reduction of emission intensity and increase in the number of free electrons and holes for taking part in photocatalytic activity. Cerium concentration of 0.035 is the optimum dopant concentration for use in photocatalysis, because the photocatalysis decreases at 0.045 mol of Ce³⁺. Although a similar trend is shown by all samples under UV light, the degradation efficiency decreases at maximum irradiation time due to negative charging of semiconductor surface.

There is considerable interest in the identification of natural agents capable of affording protection to skin from the adverse effects of solar ultraviolet B (UVB) radiation. Pomegranate (Punica granatum L.) fruit possesses as strong antioxidant, anti-inflammatory and antiproliferative properties. Recently, we have shown that oral feeding of pomegranate fruit extract (PFE) to mice afforded substantial protection from the adverse effects of single UVB radiation via modulation in early biomarkers of photocarcinogenesis. This study was designed to investigate the photochemopreventive effects of PFE (0.2%, wt/vol) after multiple UVB irradiations (180 mJ cm⁻², on alternative day, for a total of seven treatments) to the skin of SKH-1 hairless mice. Oral feeding of PFE to SKH-1 mice inhibited UVB-induced epidermal hyperplasia, infiltration of leukocytes, protein oxidation and lipid peroxidation. Immunoblot analysis demonstrated that oral feeding of PFE to mice inhibited UVB-induced (1) nuclear translocation and phosphorylation of nuclear factor kappa B/p65, (2) phosphorylation and degradation of IκBα, (3) activation of IKKα/ΙΚΚβ and (4) phosphorylation of mitogen-activated protein kinase proteins and c-Jun. PFE consumption also inhibited UVB-induced protein expression of (1) COX-2 and iNOS, (2) PCNA and cyclin D1 and (3) matrix metalloproteinases-2,-3 and -9 in mouse skin. Taken together, these data show that PFE consumption afforded protection to mouse skin against the adverse effects of UVB radiation by modulating UVB-induced signaling pathways.

Solar UV radiation, particularly its UVB component (280–320 nm), causes adverse cellular and molecular events leading to skin cancer. Therefore, additional approaches are needed to define novel agents to prevent skin cancer which results as a consequence of UVB exposure. In this study, we investigated the photochemopreventive effects of pomegranate fruit extract (PFE) after multiple UVB irradiations to the skin of SKH-1 hairless mice. Our data show that PFE consumption afforded protection to mouse skin by inhibiting UVB-induced inflammation and proliferation via modulation of nuclear factor kappa B and mitogen-activated protein kinases pathways. This study suggests the potential efficacy of PFE as a photochemopreventive agent for skin cancer.

Photodynamic therapy (PDT) of cancer induces oxidative stress, which intervenes in the expression of cytokines by tumor cells. The cytokines might have either a positive or a negative impact on tumor eradication. Here, we studied the expression of cytokines vascular endothelial growth factor (VEGF) and interleukin-1alpha (IL-1alpha) in the human epidermoid carcinoma A-431 cells following m-tetra(3-hydroxyphenyl)-chlorin (mTHPC)-mediated PDT in vitro and assessed the IL-1alpha effect on VEGF expression. Quantitative polymerase chain reaction and enzyme-linked immunosorbent assay revealed the enhanced production of VEGF and IL-1alpha both on mRNA and protein levels by mTHPC-loaded cells after light exposure. The silencing of IL1A by small interfering RNA resulted in decreased production of IL-1alpha and a reduced amount of VEGF. Furthermore, exogenous recombinant IL-1alpha stimulated the VEGF expression after PDT. Thus, in addition to the cytotoxic action on the A-431 cells, mTHPC-mediated PDT stimulated the production of VEGF and IL-1alpha, and IL-1alpha contributed to the VEGF overexpression. These data establish IL-1alpha as a possible target of combined cancer treatment.

In A-431 cells, mTHPC-mediated photodynamic treatment stimulated the production of VEGF and IL-1alpha, and IL-1alpha contributed to the VEGF overexpression.

The aim of this study was to investigate the efficacy of 5-aminolaevulinic acid (ALA)-mediated photodynamic therapy (PDT) in treatment of human papillomavirus (HPV)-associated cervical condylomata. A total of 56 patients with cervical and external condylomata lesions were recruited for this open-label study. HPV genotyping of exfoliated cells collected from the cervix and external lesions was performed. Cervical lesions were treated with PDT by applying ALA gel (10%) to the surface of the cervix for 4 h followed by irradiating with a 635 nm laser at 100 J cm⁻². PDT was repeated at 2-week intervals if lesion and HPV infection remained. Patients were followed up for 6–24 months. Genotyping analysis revealed four HPV subtypes (HPV6, 11, 16 and 18). The overall complete remission rate of 1–4 sessions of treatments was 98.2% and the corresponding HPV clearance rate was 83.9%. Ten cases showed complete removal of cervical lesions and HPV infection after a single treatment. Recurrence rate was 3.6%. Adverse effects were minimal and no structural complications were reported. In conclusion, topical ALA PDT is safe and effective for eradicating cervical HPV infection and eliminating condylomata lesion. Its definitive role in treating cervical condylomata deserves further investigation.

Condylomata acuminata (CA) are the most prevalent sexually transmitted disease and closely associated with human papillomavirus (HPV) infections. Although CA mainly occur in the external genital and perianal area, HPV infection in these areas in women can lead to further infections in the vaginal and cervical mucosal epithelia. This clinical study investigated the efficacy of ALA PDT in treatment of HPV-associated cervical condylomata. We demonstrated that topical ALA PDT could effectively eradicate cervical HPV infection and ablate warty lesion (illustrated).

In this study we developed a rat model of incipient caries to investigate the short-term effects of antimicrobial photodynamic therapy (aPDT) on oral microbiota regulation and demineralization arrestment. Twenty-nine male rats were submitted to caries induction. Early carious lesion was confirmed by optical coherence tomography (OCT) 5 days after experiment beginning in five animals. The remaining animals (n = 24) were randomly divided into two groups: control (n = 12), animals were untreated; and aPDT (n = 12), animals were treated with 100 μM of methylene blue for 5 min and irradiated by a light emitting diode at λ = 645 ± 30 nm, fluence rate of 480 mW cm⁻² and exposure time of 3 min. Bacterial burden was evaluated before, immediately after, 3, 7 and 10 days following treatment, and total number of microaerophilic bacteria was counted. OCT was also used to quantify teeth demineralization. A significant bacterial decrease of about 1.6 log was observed immediately after aPDT. Besides, bacterial load in aPDT group remained lower than control until 10 days post-treatment (P < 0.05) and variation of optical attenuation coefficient before and after aPDT was 15%, corroborating to caries arrestment. Put together, these findings suggest that aPDT was competent to reduce cariogenic bacteria and to avoid further mineral loss.

This study reports a potential use of antimicrobial photodynamic therapy (aPDT) to arrest caries progression. We developed a rat model of incipient caries to investigate the short-term effects of aPDT on oral microbiota regulation and enamel demineralization. Induced caries in rats’ molars was confirmed by optical coherence tomography (OCT) before aPDT. Bacterial load following aPDT remained significantly lower than untreated group until 10 days post-treatment. Data obtained from OCT signal showed that aPDT group presented lesser mineral loss corroborating caries arrestment. Put together, these findings suggest that aPDT could be a new approach for public health.

The ongoing anthropogenically caused ozone depletion and climate change has increased the amount of biologically harmful UV-B radiation, which is detrimental to fish in embryonal stages. The effects of UV-B radiation on the levels and locations of DNA damage manifested as cyclobutane pyrimidine dimers (CPDs), heat shock protein 70 (HSP70) and p53 protein in newly hatched embryos of pike were examined. Pike larvae were exposed in the laboratory to current and enhanced doses of UV-B radiation. UV-B exposure caused the formation of CPDs in a fluence rate-dependent manner, and the CPDs were found deeper in the tissues with increasing fluence rates. UV-B radiation induced HSP70 in epidermis, and caused plausible p53 activation in the brain and epidermis of some individuals. Also at a fluence rate occurring in nature, the DNA damage in the brain and eyes of pike and changes in protein expression were followed by severe behavioral disorders, suggesting that neural molecular changes were associated with functional consequences.

Posthatched embryos of northern pike were exposed in the laboratory to current and enhanced doses of UV-B radiation. UV-B exposure caused the formation of cyclobutane pyrimidine dimers (CPDs) in a fluence rate-dependent manner, and the CPDs were found deeper in the tissues with increasing fluence rates. UV-B radiation induced HSP70 in the epidermis, and caused plausible p53 activation in the brain and epidermis of some individuals. The DNA damage in the brain and eyes of pike and changes in protein expression were followed by severe behavioral disorders, suggesting that neural molecular changes were associated with functional consequences.

This paper reports a comprehensive photophysical study of the aggregation process of 1-azacarbazole, or α-carboline (9H-pyrido[2,3-b]indole), AC, in low polar aprotic solvents by using absorption, steady state and time-resolved fluorescence spectroscopic techniques. To ascertain the characteristics of the aggregation process we have studied the changes produced by the increase of the AC concentration and the decrease of the temperature on the absorption and fluorescence spectra of the AC monomer. Previously, to aid the interpretation of these results, the hydrogen bonding interactions of the AC monomer with pyridine, PY, and indole, IND, have been also analyzed. The results obtained from these studies reveal that, under our experimental conditions, AC does not form doubly hydrogen bonded cyclic dimers, (AC)₂, but singly hydrogen bonded open dimers, AC–AC, and open higher aggregates, (–AC–)_n. The formation of these species shifts to the red the absorption spectrum of the AC monomer and quenches its fluorescence.

In low polar aprotic solvents α-Carboline (1-Azacarbazole), AC, forms hydrogen bonded open dimers, AC–AC, and higher open aggregates (–AC–)_n, that quench the fluorescence.

A novel In³⁺-doped TiO₂ and TiO₂/In₂S₃ nanocomposites for photocatalytic degradation of environmental pollutants and stoichiometric degradation of warfare agents were prepared by a homogeneous hydrolysis with urea and thioacetamide, respectively. The prepared samples series TiInTAA were annealed at 600°C. The prepared samples were characterized by X-ray powder diffraction, IR spectroscopy, Raman spectroscopy, specific surface area (BET) and porosity determination. The method of UV–Vis diffuse reflectance spectroscopy was employed to estimate band-gap energies. The photocatalytic activity (PCA) was tested by degradation of Orange dye, whereas stoichiometric activity was studied by degradation of sulfur mustard. Incorporation of In³⁺ into titania lattice increases PCA of TiO₂ in the visible light and increases stoichiometric decomposition of sulfur mustard against nondoped TiO₂ as well. PCA of TiO₂/In₂S₃ composite depends on the optimal ratio of TiO₂:In₂S₃ in composite, while the activity for stoichiometric decomposition of sulfur mustards depends on the content of In₂S₃ in nanocomposite.

A new In³⁺-doped TiO₂ and TiO₂/In₂S₃ nanocomposites for photocatalytic degradation of environmental pollutants and stoichiometric degradation of warfare agents were prepared by a homogeneous hydrolysis with urea and thioacetamide, respectively. The photocatalytic activity (PCA) was tested by degradation of Orange dye, whereas stoichiometric activity was studied by degradation of sulfur mustard. PCA of TiO₂/In₂S₃ composite depends on the optimal ratio of TiO₂:In₂S₃ in composite, while the activity for stoichiometric decomposition of sulphur mustards depends on the content of In₂S₃ in nanocomposite.

UVA radiation (315–400 nm), which constitutes ca 95% of the UV irradiation in natural sunlight reaching earth surface, is a major environmental risk factor associated with human skin cancer pathogenesis. UVA is an oxidizing agent that causes significant damage to cellular components through the release of reactive oxygen species (ROS) and leads to photoaging and photocarcinogenesis. Here we investigate the effect of silibinin, the flavonolignan from Silybum marianum, on UVA-induced ROS and cell death in human keratinocyte cell line HaCaT. In addition, the effect of silibinin on UVA-induced intracellular ROS-mediated endoplasmic reticulum (ER) stress was also analyzed. UVA irradiation resulted in ROS production and apoptosis in HaCaT cells in a dose-dependent manner, and the ROS levels and apoptotic index were found to be elevated significantly when the cells were treated with 75 μmsilibinin for 2 h before UVA exposure. When the cells were pretreated with 10 mmN-acetyl cysteine, the enhancement of UVA-induced apoptosis by silibinin was compromised. Furthermore, we found that silibinin enhances ER stress-mediated apoptosis in HaCaT cells by increasing the expression of CHOP protein. These results suggest that silibinin may be beneficial in the removal of UVA-damaged cells and the prevention of skin cancer.

UVA radiation causes significant damage to cellular components through the release of reactive oxygen species (ROS). We report that silibinin enhances UVA-induced ROS generation and apoptosis in human keratinocyte HaCaT cells. Furthermore, we found that silibinin enhances ER stress-mediated apoptosis in HaCaT cells by increasing the expression of CHOP protein. These results suggest that silibinin may be beneficial in the removal of UVA-damaged cells and the prevention of skin cancer.

Hypericin is a natural photosensitizer considered for the new generation of photodynamic therapy (PDT) drugs. The aim of this study was to evaluate the in vitro fungicidal effect of hypericin PDT on various Candida spp., assessing its photocytotoxicity to keratinocytes (HaCaT) and dermal fibroblasts (hNDF) to determine possible side effects. A 3 log fungicidal effect was observed at 0.5 McFarland for two Candida albicans strains, Candida parapsilosis and Candida krusei with hypericin concentrations of 0.625, 1.25, 2.5 and 40 μm, respectively, at a fluence of 18 J cm⁻² (LED lamp emitting at 602 ± 10 nm). To obtain a 6 log reduction, significantly higher hypericin concentrations and light doses were needed (C. albicans 5 μm, C. parapsilosis 320 μM and C. krusei 320 μM; light dose 37 J cm⁻²). Keratinocytes and fibroblasts can be preserved by keeping the hypericin concentration below 1 μm and the light dose below 37 J cm⁻². C. albicans appears to be suitable for treatment with hypericin PDT without significant damage to cutaneous cells.

Photodynamic treatments using hypericin show a fungicidal effect on Candida spp., the most sensitive strain being Candida albicans and the most resistant Candida krusei. C. albicans infections could be suitable for treatment with hypericin PDT without significant damage to cutaneous cells.

The Stokes shift of tryptophan (Trp) fluorescence from layers of the lipid-containing bacteriophage φ6 is compared to determine the relative effect of the layers on virus hydrophobicity. In the inner most layer, the empty procapsid (PC) which contains 80–90% of the virion Trp residues, λ_max = 339.8 nm. The PC emission is substantially more redshifted than the other φ6 layers and nearer to that of the Pseudomonad host cell than the other φ6 layers. The Trp emission from the nucleocapsid (NC) with λ_max = 337.4 nm, is blueshifted by 2.4 nm relative to the PC although the number of Trp in the NC is identical to the PC. This shift represents an increase in Trp hydrophobicity, likely a requirement for the maintenance of A-form doubled-stranded RNA. Fluorescence from the completely assembled virion indicates it is in a considerably more hydrophobic environment with λ_max = 330.9 nm. Density measurements show that the water content in the NC does not change during envelope assembly, therefore the blueshifted φ6 emission suggests that the envelope changes the PC environment, probably via the P8 layer. This change in hydrophobicity likely arises from charge redistribution or envelope-induced structural changes in the PC proteins.

Tryptophan emission from the different layers of the bacteriophage ϕ6. Differences in Stokes shift correspond to differences in hydrophobicity of the layers. The hydrophobicity of the procapsid (PC) is similar to that of the pseudomonad host cell. Genome packaging of the PC increases accommodate A-form dsRNA and hydrophobicity. Assembly of the envelope greatly increases the hydrophobicity of the PC proteins, indicating a strong interaction between the envelope and the inner proteins.

Coral bleaching is the manifestation of the dysfunction of the symbiosis between scleractinian corals and dinoflagellates of the diverse genus Symbiodinium and is induced by elevated temperatures and high irradiance. We investigated the photophysiological response of two genetically distinct Symbiodinium subtypes within clade A upon exposure to elevated temperatures at two light intensities for 3 weeks. While both subtypes displayed a characteristic photoacclimation to high light (HL) (decrease in light-harvesting pigments, lower photochemical efficiency of photosystem II, increased xanthophyll pool sizes), the tolerance toward thermal stress clearly differed between the two subtypes. Symbiodinium Ax was highly susceptible to chronic photoinhibition at temperatures ≥30°C, which was exacerbated under HL conditions. A1 showed a capacity for photoacclimation and high thermal tolerance, which might be related to higher cellular concentrations of photoprotective xanthophylls and the low-molecular antioxidant glutathione (GSx) along with the dynamic regulation of these photoprotective pathways. Whereas HL conditions induced both accumulation of diatoxanthin and GSx, thermal stress further stimulated xanthophyll cycling, which might compensate for diminished amounts of GSx at elevated temperatures. Our results show that the two clade A subtypes clearly differ in their strategies to cope with thermal stress in combination with high irradiance.

Coral bleaching is the manifestation of the dysfunction of the symbiosis between scleractinian corals and dinoflagellates of the genus Symbiodinium and increasingly induced by elevated temperatures and high irradiance. In this study, we compared the capacity of two different Symbiodinium clade A phylotypes to employ photoprotective pathways under bleaching conditions (thermal and light stress). Both phylotypes clearly differed in thermal tolerance and cellular xanthophyll concentrations as well as xanthophyll cycling activity. For the first time measurements of glutathione pool size were applied to test for the stress tolerance of Symbiodinium phylotypes.

The production of vitamin D3 is a pharmaceutically relevant process, producing high added-value products. Precursors are extracts from vegetal origin but bearing mainly an E geometry in the 5,6 double bond. The synthesis of vitamin D3 (5-E-α-calcidol) with the correct Z stereochemistry in the 5,6 double bond from the E isomer using anthracene and triethylamine (TEA) as the sensitizer system was studied from the kinetic and mechanistic point of view. The sensitized isomerization of E-calcidol by irradiation of anthracene takes place only in deoxygenated solution and yields the Z isomer in ca 5% yield in the photostationary state. When TEA is added to the system, the E–Z reaction is not inhibited by oxygen any more, the quantum yield of photoisomerization to the Z isomer grows linearly with the concentration of E-calcidol, while conversions higher than 95% to the Z isomer are reached in the photostationary state and E–Z quantum yields as high as 45 at [E-calcidol] = 25 mm are reached. If TEA is replaced by 1,4-diazabicyclo[2.2.2]octane, the reaction rate drops to one-third at the same amine concentration. The observations can be explained by a quantum chain reaction mechanism. The high conversion achieved eliminates the need of isomer separation.

The photoisomerization of 5E-α-calcidol sensitized by anthracene and triethylamine takes place by a one-way quantum chain mechanism, which renders the biologically active Z isomer in >95% fraction in the photostationary state, with a quantum yield exceeding 40

This paper reports a morphological transition of the spherical colloidal structures of the sodium dodecyl sulfate-polyethylene-b-polyethylene glycol (SDS-PE-b-PEG) complex and anionic micelle (SDS) to “rod-shaped” colloidal structures induced by a charge transfer dye, 1,8-naphthalimide (NAPMD) (forms anions in aqueous solution by intermolecular charge transfer). The distinct steady-state results of NAPMD in the above two media point toward the formation of a new microenvironment. SDS and SDS-PE-b-PEG form unilamellar (ULV) and multilamellar vesicles (MLV), respectively, along with the rod-shaped colloidal structures as observed from transmission electron microscopy (TEM) images. This dye causes a variation in the hydrophilic/hydrophobic ratio and forms a hydrogen bond with the copolymer in the SDS-PE-b-PEG complex and subjected to electrostatic interaction with the SDS micelle in aqueous solution, which causes this morphological transformation. These vesicles show complete encapsulation of a hydrophobic dye in its interior as evident from the TEM images. ULV get ruptured at low pH, pointing toward their lower stability over MLV at low pH value. The formation of these vesicles with complete idea of its mechanism, encapsulation of bioactive molecules and its rupture at lower pH raise hope as a potential nanoscale vehicle for biologically relevant compounds and their release at low pH medium.

1,8 naphthalimide (NAPMD) undergoes intermolecular charge transfer in aqueous medium to form anionic NAPMD. This anionic NAPMD interacts with spherical aggregates of anionic micelle and micelle-diblock-copolymer complex and results in a morphological transition to rod-shaped structures and also forms unilamellar (ULV) and multilamellar vesicular (MLV) structures respectively. The ULVs get ruptured in response to low pH medium indicating its potential use in drug delivery systems whereas MLVs are found to be stable at low pH.

Widely used polymethylmethacrylate substrates for in vitro sun protection factor (SPF) testing of sunscreens do not mimic the rough surface structure of skin, and in addition, sample loading is less than that used in in vivo SPF testing (2.00 mg cm⁻²). We have developed a skin-mimicking substrate (SMS), which has furrows and ridges on its surface, like human skin. A comparison of the photodegradation profiles of sunscreens on commercially available substrates (including SMS) at the recommended application amounts, and on SMS at various application amounts showed that the photodegradation rate of photounstable sunscreen was dependent on the application amount being higher at lower application amounts. SMS at the recommended application amount of 2.00 mg cm⁻² provided in vitro SPF values that were comparable with in vivo SPF values. Our results confirm that, in order to develop a reliable in vitro SPF method, which is consistent with in vivo SPF determination, it is important to use the same application amount of sample as in the in vivo method, in order to take proper account of sunscreen photostability.

We have developed a polymethylmethacrylate skin-mimicking substrate (SMS), which has furrows and ridges on its surface, like human skin. A comparison of the photodegradation profiles of sunscreens on commercially available substrates (including SMS) at the recommended application amounts, and on SMS at various application amounts showed that the photodegradation rate of photounstable sunscreen was dependent on the application amount, being higher at lower application amounts. The recommended application amount for SMS is as high as that for in vivo measurement (2.00 mg cm⁻²), and SMS provided in vitro sun protection factor (SPF) values that were comparable with in vivo SPF values.

In the present work, two new chemical linkages (BPDA-PAM, BPDA-DG) are synthesized through the reaction between 4,4′-biphthalic anhydride (BPDA) and acrylamide (AM), diethylene glycol (DG), respectively. Then two novel series of multicomponent rare earth (Eu³⁺, Tb³⁺, Sm³⁺) polymeric hybrids have been assembled through the coordination bonding: one is from the linkage BPDA-PAM to form the hybrids BPDA-PAM-RE-phen(bipy) (2,2′-bipyridine (bipy) and 1,10-penanthroline (phen)), the other is from the linkage BPDA-DG to compose the hybrids BPDA-DG-RE-PVP and PVP (PVP = poly vinylpyridine). These hybrids are characterized and especially the photophysical properties (luminescence spectra, lifetimes and quantum efficiencies) are discussed in detail.

Two new chemical linkages (BPDA-PAM, BPDA-DG) are synthesized through the reaction between 4,4′-biphthalic anhydride (BPDA) and acrylamide (AM), diethylene glycol (DG), respectively. Then two novel series of multicomponent rare earth (Eu³⁺, Tb³⁺, Sm³⁺) polymeric hybrids have been assembled through the coordination bonding: one is from the linkage BPDA-PAM to form the hybrids BPDA-PAM-RE-phen(bipy) (2,2′-bipyridine (bipy) and 1,10-penanthroline (phen)), the other is from the linkage BPDA-DG to compose the hybrids BPDA-DG-RE-PVP and PVP (PVP = poly vinylpyridine).

Cutaneous and mucocutaneous Candida infections are considered to be important targets for antimicrobial photodynamic therapy (PDT). Clinical application of antimicrobial PDT will require strategies that enhance microbial killing while minimizing damage to host tissue. Increasing the sensitivity of infectious agents to PDT will help achieve this goal. Our previous studies demonstrated that raising the level of oxidative stress in Candida by interfering with fungal respiration increased the efficiency of PDT. Therefore, we sought to identify compounds in clinical use that would augment the oxidative stress caused by PDT by contributing to reactive oxygen species (ROS) formation themselves. Based on the ability of the antifungal miconazole to induce ROS in Candida, we tested several azole antifungals for their ability to augment PDT in vitro. Although miconazole and ketoconazole both stimulated ROS production in Candida albicans, only miconazole enhanced the killing of C. albicans and induced prolonged fungistasis in organisms that survived PDT using the porphyrin TMP-1363 and the phenothiazine methylene blue as photosensitizers. The data suggest that miconazole could be used to increase the efficacy of PDT against C. albicans, and its mechanism of action is likely to be multifactorial.

The confocal image shows yeast cells of the fungus Candida albicans stained with MitoTracker Red (Molecular Probes, Eugene, OR), visualizing ribbon-like mitochondria. Inhibition of mitochondrial respiration in Candida increases the efficacy of photodynamic therapy (PDT). In addition, the antifungal drug miconazole has adverse effects on C. albicans mitochondrial function. Our recent work demonstrates that efficacy of PDT against C. albicans is enhanced in combination with miconazole. Combined PDT-miconazole treatment may lower the effective dose of PDT against Candida, as well as reducing the frequency of application for an antifungal agent widely used for treatment of cutaneous and mucosal candidiasis.

We successfully identified the bystander effect in B16 murine melanoma cells exposed to UVA irradiation. The effect was identified based on melanogenesis following the medium transfer of the B16 cells, which had been cultured for 24 h after being exposed to UVA irradiation, to nonirradiated cells (bystander cells). Our confirmation study of the functional mechanism of bystander cells confirmed the reduced levels of mitochondrial membrane potential 1–4 h after the medium transfer. In addition, we observed increased levels of intracellular oxidation after 9–12 h, and the generation of melanin radicals, including long-lived radicals, 24 h after medium transfer. Further analysis of bystander factors revealed that the administration of EGTA treatment at the time of medium transfer led to an inhibition of melanogenesis and to neutralization of the mitochondrial membrane potential level, as well as to the restoration of intracellular oxidation levels to those of controls. The results demonstrated that the UVA irradiation bystander effect in B16 cells, as indicated by melanogenesis, was induced by the increase in intracellular oxidation due to the mitochondrial activity of calcium ions, which were among the bystander factors involved in the increase.

The melanogenesis in UVA-irradiated cell is promoted by bystander effect acting between melanocytes without contribution of the keratinocyte. The bystander factor such as Ca²⁺ decreases mitochondria membrane potential in a nonradiation cell and desorbs a large quantity of oxidation radicals to cytoplasm. As a result, intracellular level of oxidation increases, and the activation of melanogenesis genes occurs in nuclei. Melanogenesis by bystander effects is efficiently inhibited by treatment of EGTA.

Lasers are used in the minimalistic or noninvasive diagnosis and treatment of skin disorders. Less laser light reaches the deeper skin layers in dark skin types, due to its higher epidermal melanin concentration compared with lighter skin. Laser–tissue interaction modeling software can correct for this by adapting the dose applied to the skin. This necessitates an easy and reliable method to determine the skin’s type. Noninvasive measurement of the skin’s melanin content is the best method. However, access to samples of all skin types is often limited and skin-like phantoms are used instead. This study’s objective is to compare experimentally measured absorption features of liquid skin-like phantoms representing Skin Types I–VI with a realistic skin computational model component of ASAP^®. Sample UV–VIS transmittance spectra were measured from 370 to 900 nm and compared with simulated results from ASAP^® using the same optical parameters. Results indicated nonmonotonic absorption features towards shorter wavelengths, which may allow for more accurate ways of determining melanin concentration and expected absorption through the epidermal layer. This suggests possible use in representing optical characteristics of real skin. However, a more comprehensive model and phantoms are necessary to account for the effects of sun exposure.

In the past 50 years lasers have found numerous applications in medicine for minimalistic or noninvasive diagnosis and treatment. Often that means that the light must penetrate through the skin and the correct dose required relies on accurate information regarding the skin’s optical properties. Human skin consists of different layers, with the epidermal layer containing the melanin that is responsible for skin type. This study’s objective is to compare experimentally measured absorption features of melanin and lipid containing skin-like phantoms representing Skin Types I–VI with a realistic skin computational model component of ASAP®.

Modification of major lipid raft components, such as cholesterol and ceramide, plays a role in regulation of programmed cell death under various stimuli. However, the relationship between cholesterol level modification and the activation of apoptotic signaling cascades upon UVB light has not been established. In this report, we demonstrate that upon UVB irradiation cholesterol levels in membrane rafts of skin cells increase, which leads to Fas-receptor (Fas) aggregation in the rafts. Utilizing a continuous velocity floatation technique, we show that Fas accumulated in the lipid rafts of human melanoma M624 cells after UVB irradiation. The subsequent events of death-inducing signaling complex formation were also detected in the lipid raft fractions. Depletion of cholesterol by methyl-β-cyclodextrin reduces Fas aggregation, while overloading increases. Disruption of lipid rafts also prevents Fas death domain-associated protein (Daxx) from dissociating from Fas in the lipid rafts, which is accompanied with a reduced apoptotic, but increased nonapoptotic death of UVB-irradiated human keratinocytes, HaCaT cells. Results indicate that cholesterol located in the plasma membrane of skin cells is required for lipid raft domain formation and activation of UVB-induced apoptosis.

Alterations in lipid content, especially the elevation of cholesterol caused by UVB irradiation leads to activation of the Fas-FADD cascade and cell apoptosis. Depending on the cell type, a disruption of lipid rafts by MβCD could protect cells from UVB-induced apoptosis, but might also promote nonapoptotic death of the treated cells.

TiO₂ and Fe-titanate (different wt%) supported on zeolite were prepared by sol-gel and solid-state dispersion methods. The photocatalysts prepared were characterized by X-ray diffraction, scanning electron microscopy and ultraviolet (UV)–visible diffuse reflectance spectroscopy techniques. Photocatalytic reduction of nitrate in water and isopropanol/oxalic acid as hole scavengers are investigated in a batch reactor under UV illumination. The yield of urea increased notably when the catalysts were supported on zeolite. The Fe-titanate supported catalyst promotes the charge separation that contributes to an increase in selective formation of urea. The product formation is because of the high adsorption of in situ generated CO₂ and NH₃ over shape-selective property of the zeolite in the composite photocatalyst. The maximum yield of urea is found to be 18 ppm while 1% isopropanol containing solution over 10 wt% Fe-titanate/HZSM-5 photocatalyst was used.

TiO₂ and Fe-titanate (different wt%) supported on zeolite were prepared by sol-gel and solid-state dispersion methods. Photocatalytic reduction of nitrate in water and isopropanol/oxalic acid as hole scavengers were investigated in a batch reactor under ultraviolet illumination. The yield of urea increased notably when the catalysts were supported on zeolite. The product formation is because of the high adsorption of in situ generated CO₂ and NH₃ over shape-selective property of the zeolite in the composite photocatalyst.

We have explored the utility of pyrophthalones as violet-blue light filtering dyes in polymer matrices for wavelengths below 450 nm. Further, we have investigated the photodegradation of these molecules in thermoplastic media and the mechanisms behind their degradation. Finally, a range of additives have been explored to improve the photostability of these molecules to achieve the desired performance.

We have shown the utility of pyrophthalones as violet-blue light filtering dyes in polymer matrices for wavelengths below 450 nm. Further, we have investigated the photodegradation of these molecules in thermoplastic media, mechanisms behind their degradation and use of additives to arrest the photodegradation.

The complex nature of bacterial cell membrane and structure of biofilm has challenged the efficacy of antimicrobial photodynamic therapy. This study was aimed to synthesize a polycationic chitosan-conjugated rose bengal (CSRB) photosensitizer and test its antibiofilm efficacy on Enterococcus faecalis (gram positive) and Pseudomonas aeruginosa (gram negative) using photodynamic therapy. During experiments, CSRB was tested along with an anionic photosensitizer rose bengal (RB) and a cationic photosensitizer methylene blue (MB) for uptake and killing efficacy on 7-day-old E. faecalis and P. aeruginosa biofilms. Microbiological culture based analysis was used to analyze the cell viability, while laser scanning confocal microscopy (LSCM) was used to examine the structure of biofilm. The synthesized CSRB showed absorbance spectrum similar to the RB. The concentration of CSRB uptaken by both the bacterial biofilms was significantly higher than that of RB and MB (P < 0.05). Photoactivation resulted in significantly higher elimination of both bacterial biofilms sensitized with CSRB than RB and MB. The structure of biofilm under LSCM was found to be disrupted following CSRB treatment. The present study highlighted the importance of inherent cell membrane permeabilizing effect of chitosan and increased cell/biofilm uptake of conjugated photosensitizer to produce significant antibiofilm efficacy during photodynamic therapy.

The present study highlighted the importance of the inherent cell membrane permeabilizing effect of chitosan and increased cell/biofilm uptake of conjugated photosensitizer (CSRB) to produce significant antibiofilm efficacy during photodynamic therapy. CSRB was found to be significantly better in eliminating both gram-positive and gram-negative bacterial biofilms as compared to rose bengal and methylene blue.

The screening of recently patented derivatives of the standard phenothiazinium agents methylene blue and toluidine blue was carried out against Propionibacterium acnes, the main bacterium associated with acne vulgaris. Comparative tests were made using the topical agent benzoyl peroxide (BPO) and standard tetracyclines. Each of the photosensitizers employed, including the lead compounds, was photobactericidal at lower concentrations than BPO, and produced a much more rapid kill than the tetracyclines. In addition, the tetracyclic and pentacyclic phenothiazinium derivatives exhibited high light:dark kill ratios, suggesting that these examples might be particularly useful in practice.

New derivatives of the standard phenothiazinium photosensitizers methylene blue and toluidine blue exhibited much improved activity, compared with the lead compounds, against Propionibacterium acnes, the main bacterium associated with acne vulgaris. The new derivatives were also photobactericidal at much lower concentrations than the topical agent benzoyl peroxide and standard tetracyclines. Bactericidal activity was also significantly more rapid than the tetracyclines.

The importance of epigenetic alterations in the development of various diseases including the cancers has been realized. As epigenetic changes are reversible heritable changes, these can be utilized as an effective strategy for the prevention of cancers. DNA methylation is the most characterized epigenetic mechanism that can be inherited without changing the DNA sequence. Although limited available data suggest that silencing of tumor suppressor genes in ultraviolet (UV) radiation-exposed epidermis leads to photocarcinogenesis and is associated with a network of epigenetic modifications including alterations in DNA methylation, DNA methyltransferases and histone acetylations. Various bioactive dietary components have been shown to protect skin from UV radiation-induced skin tumors in animal models. The role of bioactive dietary components, such as, (−)-epicatechins from green tea and proanthocyanidins from grape seeds has been assessed in chemoprevention of UV-induced skin carcinogenesis and underlying epigenetic mechanism in vitro and in vivo animal models. These bioactive components have the ability to block UV-induced DNA hypermethylation and histone modifications in the skin required for the silencing of tumor suppressor genes (e.g. Cip1/p21, p16^INK4a). This information is of importance for understanding the role of epigenetic modulation in UV-induced skin tumor and the chemopreventive mechanism of bioactive dietary components.

Chronic skin exposure to ultraviolet (UV) radiation induces epigenetic modifications such that epigenetic mosaicism develops in patches of epidermal cells, which alters the levels of DNA methylation and histone acetylations. These epigenetic modifications in cells if not reversed or corrected may result in silencing of tumor suppressor genes and that will lead to the development of skin diseases including the development of melanoma and non-melanoma skin cancers. Topical application or consumption of dietary bioactive components may block, inhibit or slow down the progressing epigenetic alterations in cells exposed to UV radiation, and thus may result in prevention of the risk of skin cancers.

Photodynamic inactivation (PDI) of bacteria is a promising approach for combating the increasing emergence of antibiotic resistance in pathogenic bacteria. To further improve the PDI efficiency on bacteria, a bacteria-targeting liposomal formulation was investigated. A generation II photosensitizer (temoporfin) was incorporated into liposomes, followed by conjugation with a specific lectin (wheat germ agglutinin, WGA) on the liposomal surface. WGA was successfully coupled to temoporfin-loaded liposomes using an activated phospholipid containing N-hydroxylsuccinimide residue. Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa were selected to evaluate the WGA modified liposomes in terms of bacteria targeted delivery and in vitro PDI test. Fluorescence microscopy revealed that temoporfin was delivered to both kinds of bacteria, while flow cytometry demonstrated that WGA- modified liposomes delivered more temoporfin to bacteria compared to nonmodified liposomes. Consequently, the WGA- modified liposomes eradicated all MRSA and significantly enhanced the PDI of P. aeruginosa. In conclusion, the WGA- modified liposomes are a promising formulation for bacteria targeted delivery of temoporfin and for improving the PDI efficiency of temoporfin on both Gram-positive and Gram-negative bacterial cells.

The surface of temoporfin-loaded liposomes was modified with a bacteria-targeting ligand, wheat germ agglutinin, to prepare bacteria-targeting liposomes, which bind to bacteria and consequently increase the delivery of temoporfin to bacteria. After light illumination, the photosensitizers (temoporfin) generate reactive oxygen species, resulting in photodynamic inactivation of bacteria.

This article is a highlight of the paper by Anquez et al. in this issue of Photochemistry and Photobiology and describes the potential benefits of direct excitation of molecular oxygen to produce singlet oxygen (¹O₂) rather than using a photosensitizer. Due to its simplicity, the direct excitation of molecular oxygen can potentially overcome problems associated with systemic administration of dyes, such as skin photosensitivity and the clearance of free sensitizer from the body. However, concerns associated with the technique include indiscriminate generation of extracellular and intracellular ¹O₂, the difficulty of controlling necrotic vs apoptotic cell death and the possible consequences of thermal effects.

Direct excitation of O₂ provides an alternative to the generation of singlet oxygen (¹O₂) using a photosensitizer (PS) in the biological environment. Direct excitation of O₂ can potentially overcome problems associated with systemic administration of the PS, including skin photosensitivity and clearance of PS from the body. However, concerns associated with the technique include indiscriminate generation of extracellular and intracellular ¹O₂, the difficulty of controlling necrotic vs apoptotic cell death and the possible consequences of thermal effects. This Highlight Article contrasts direct excitation of O₂ as described by Anquez et al. in this issue with traditional photosensitized generation of ¹O₂.

Thiopurines are prescribed frequently as medication for cancer and for inflammatory disorders. One of them, azathioprine, has been the immunosuppressant of choice for organ transplant recipients for many years. Thiopurine use is associated with elevated sun sensitivity and skin cancer risk. Skin sensitization is selective for UVA. 6-TG integrates into DNA and unlike the canonical DNA bases, it is a strong UVA chromophore with an absorbance maximum at 342 nm. DNA 6-TG is a photosensitizer and a source of reactive oxygen species. Reactive oxygen that is generated from the photochemical activation of DNA 6-TG causes extensive damage to DNA and proteins. This damage is mutagenic and extremely toxic to cultured human cells. Here we describe some of the lesions that are known to be generated from UVA irradiation of DNA 6-TG. We discuss how this photochemical damage might contribute to the toxic effect of thiopurine/UVA treatment on cultured cells and to the high risk of skin cancer in thiopurine-treated patients.

Patients undergoing thiopurine immunosuppression or cancer treatment have 6-thioguanine in their DNA. This thio analog of guanine is a chromophore for ultraviolet A and when present in DNA it generates reactive oxygen species that damage DNA and protein. This photochemical damage includes the formation of inter- and intrastrand DNA crosslinks (1 & 2), DNA breakage (3), oxidation of DNA guanine (4) and 6-thioguanine (5) and the covalent attachment of protein to DNA (6). Some of the possible biological consequences of this damage, including a possible increased risk of skin cancer, are discussed.

Photoexcited TiO₂ has been found to generate reactive oxygen species, yet the precise mechanism and chemical nature of the generated oxy species especially regarding the different crystal phases remain to be elucidated. Visible light-induced reactions of a suspension of titanium dioxide (TiO₂) in water were investigated using electron paramagnetic resonance (EPR) coupled with the spin-trapping technique. Increased levels of both hydroxyl (˙OH) and superoxide anion (˙O₂⁻) radicals were detected in TiO₂ rutile and anatase nanoparticles (50 nm). The intensity of signals assigned to the ˙OH and ˙O₂⁻ radicals was larger for the anatase phase than that originating from rutile. Moreover, illumination with visible (nonUV) light enhanced ˙O₂⁻ formation in the rutile phase. Singlet oxygen was not detected in water suspension of TiO₂ neither in rutile nor in anatase nanoparticles, but irradiation of the rutile phase with visible light revealed a signal, which could be attributed to singlet oxygen formation. The blue part of visible spectrum (400–500 nm) was found to be responsible for the light-induced ROS in TiO₂ nanoparticles. The characterization of the mechanism of visible light-induced oxy radicals formation by TiO₂ nanoparticles could contribute to its use as a sterilization agent.

In view of the wide use of TiO₂ for biologic applications, it is important to study the reactivity of TiO₂ nanoparticles in water suspensions and under visible light illumination. The rutile and anatase TiO₂ nanoparticles phases were found to generate reactive oxygen species in aqueous suspensions. Both superoxide anions and hydroxyl radicals were detected in NP suspensions. TiO₂-rutile also responded to visible light irradiation, and elevated levels of superoxide and singlet oxygen were observed.

A series of novel organic/inorganic rare earth (europium, terbium) hybrid materials through the coordination bond and covalent bond are synthesized and form an inorganic Si–O–Si by the sol-gel process. Mercapto-functionalized 4-mercaptobenzoic acid (MBA-Si) is obtained by using MBA and 3-(triethoxysilyl)-propyl isocyanate (TESPIC) as an organic bridge molecule, and then the carboxyl group of the precursor MBA-Si is used to modify the titanium dioxide, so as to sensitize the luminescence of rare earth ions. CdS-TiO₂ is added to observe the influence of photoluminescence. 3-mercaptopropyltrimethoxysilane (MPS) is also used to modify the CdS quantum dot and obtain MPS functionalized MPS-CdS nanocomposite. These multicomponent hybrids with double cross-linking siloxane (MBA-Si) covalently bonding MPS-CdS are characterized. Subsequently, 1,10-phenanthroline (Phen) and 2,2,-bipyridyl (Bipy) as the assistant ligands together with water molecules are introduced into the rare earth hybrid system. The FT-IR, X-ray diffraction, UV–Vis, thermogravimetry and especially the photoluminescence properties of them are studied in detail.

Mercapto-functionalized MBA-Si is used to modify the titanium dioxide through its carboxylate group and 3-mercaptopropyltrimethoxysilane (MPS) is also used to modify the CdS quantum dot and obtain MPS functionalized MPS-CdS nanocomposite. These multicomponent rare earth hybrids with double cross-linking siloxane (MBA-Si) covalently bonding MPS-CdS are studied by physical characterization, especially the photophysical properties.

In the present study, we investigated the correlation between the hydroxyl radical formation rate (R_˙OH) and the degradation of a pesticide (mesotrione) in synthetic cloud water solutions and in two real atmospheric cloud waters collected at the top of puy de Dôme station (France). Using terephthalic acid as the hydroxyl radical chemical probe, we established the linear correlation between the photogenerated hydroxyl radical under polychromatic wavelengths and the pesticide degradation rate: (m s⁻¹) = (1.61 ± 0.15) × 10⁻¹(m s⁻¹). Moreover, the formation rate of hydroxyl radical in two natural cloud waters was estimated considering H₂O₂ and NO₃⁻ and the difference between the predicted values and those experimentally obtained could be attributed to the presence of other photochemical sources: iron-complexes and total organic matter. The organic constituents could play a dual role of sources and scavengers of photoformed hydroxyl radicals in the aqueous phase.

Hydrogen peroxide (H2O2) and nitrates (NO3-), naturally present in the atmospheric aqueous phase, are able to produce hydroxyl radicals (?OH) via light absorption. In the present work we correlated the photochemical production of hydroxyl radical in synthetic and real cloud waters with the degradation rate of a pesticide (mesotrione). Moreover we founded that hydrogen peroxide and nitrates are the most important photochemical sources of ?OH in atmospheric aqueous phases.

Exploration of environmental dynamics using intrinsic biological probe tryptophan is very important; however, it suffers from various difficulties. An alternative probe, kynurenine (KN), has been found to be an efficient probe for the ultrafast dynamics in the biological environment (Goswami et al., [2010] J. Phys. Chem. B., 114, 15236–15243). In the present study, we have investigated the efficacy of KN for the exploration of relatively slower dynamics of biologically relevant environments. A detailed investigation involving UV–Vis, steady-state/time-resolved fluorescence spectroscopy and Förster resonance energy transfer (FRET) studies on KN compared to a well-known solvation probe, H33258, a DNA-minor groove binder in a model nonionic reverse micelle reveals that ultrafast internal conversion associated with the hydrogen-bonding dynamics masks KN to become a dynamical reporter of the immediate environments of the probe.

Our work explores the efficacy of kynurenine (KN), one of the tryptophan metabolites as a potential probe for the slow solvent relaxation dynamics in a restricted medium of neutral reverse micelles (RM). While picosecond-resolved Förster resonance energy transfer study confirms the inclusion of the probe in the RM, details of the optical spectroscopic investigations reveal that ultrafast internal conversion associated with the hydrogen-bonding dynamics masks KN to become a dynamical reporter of the immediate environments of the probe.

Radiation damage can inter alia result in lipid peroxidation of macroalgal cell membranes. To prevent photo-oxidation within the cells, photoprotective substances such as phlorotannins are synthesized. In the present study, changes in total fatty acids (FA), FA composition and intra/extracellular phlorotannin contents were determined by gas chromatography and the Folin-Ciocalteu method to investigate the photoprotective potential of phlorotannins to prevent lipid peroxidation. Alaria esculenta juveniles (Phaeophyceae) were exposed over 20 days to high/low photosynthetically active radiation (PAR) in combination with UV radiation (UVR) in the treatments: PAB (low/high PAR + UV-B + UV-A), PA (low/high PAR + UV-A) or low/high PAR only. While extracellular phlorotannins increased after 10 days, intracellular phlorotannins increased with exposure time and PA and decreased under PAB. Interactive effects of time:radiation wavebands, time:PAR dose as well as radiation wavebands:PAR dose were observed. Low FA contents were detected in the PA and PAB treatments; interactive effects were observed between time:high PAR and PAB:high PAR. Total FA contents were correlated to extra/intracellular phlorotannin contents. Our results suggest that phlorotannins might play a role in intra/extracellular protection by absorption and oxidation processes. Changes in FA content/composition upon UVR and high PAR might be considered as an adaptive mechanism of the A. esculenta juveniles subjected to variations in solar irradiance.

Radiation damage can inter alia result in lipid peroxidation of macroalgal cell membranes. To prevent photo-oxidation within the cells, substances such as phlorotannins are synthesized. In the present study, changes in total fatty acids (FA), FA composition and intra/extracellular phlorotannin contents were determined in Alaria esculenta juveniles (Phaeophyceae) to investigate the photoprotective potential of phlorotannins to prevent lipid peroxidation. Our results suggest that phlorotannins might play a role in intra/extracellular protection by absorption and oxidation processes. Changes in FA content/composition upon exposure might be considered as an adaptive mechanism of the A. esculenta juveniles subjected to variations in solar irradiance.

Rapid adjustments of the photosynthetic machinery and efficient antioxidant mechanisms to scavenge harmful ROS are physiologic adaptions exhibited by intertidal seaweeds to persist in temperate regions. This study examines short-term (3 h) responses of three large kelps from the cold-temperate coast of Chile, normally adapted to water temperatures <16°C, but exposed abruptly to simultaneous high temperatures and UV radiation during low tide in summer. The kelps were exposed in the laboratory to three temperatures (10, 20 and 28°C) with and without UV radiation, and photochemical reactions, concentration of phlorotannins and antioxidant activity were examined. The exposure to elevated temperature (slightly exacerbated by the presence of UV radiation) decreased photochemical processes (measured as fluorescence kinetics) in the three studied species and increased lipid peroxidation in two of them. The concentration of total soluble phlorotannins was variable and correlated with the antioxidant activity in the presence of UV radiation. Insoluble phlorotannins did not change during the exposure. In all, the downregulation of the photochemical machinery, which was expressed as dynamic photoinhibition, and the rapid induction of soluble phlorotannins triggered by UV radiation minimized the effects of oxidative stress and maintained the operation of photochemical processes during short-term thermal stress.

Intertidal seaweeds from cold-temperate regions can be exposed to high solar radiation and temperature in their habitats, which can induce the formation of harmful reactive oxygen species (ROS). In brown algae, intracellular phenolic compounds known as phlorotannins (polymers of phloroglucinol) are rapidly synthesized to scavenge ROS (e.g. peroxides from photosynthetic membranes). The antioxidant activity mediated by phlorotannins in brown algae apparently permits them to tolerate the combined action of different stressors during low tide, especially the acute exposure to UV radiation and high temperature.