Photochemistry and Photobiology

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.

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.

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.

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.

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 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.

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.

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.

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)

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.

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 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.

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.

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 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.

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. 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) 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.

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.

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 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.

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.

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.

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.

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

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.

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.

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

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).

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.

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.

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 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 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.

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.

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 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 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

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.

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.

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).

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.

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.

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®.

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. 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 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 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.

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.

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.

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.