Photochemistry and Photobiology

Light-induced injury to the retina resembles many features of several retinal degenerative diseases, particularly age-related macular degeneration. This Symposium-in-Print on Retinal Photodamage discusses the mechanisms involved and protective strategies to increase the retinal resistance to damage and/or to counteract its deleterious effects. Recent results help explaining the wavelength dependence of susceptibility of the retina to photodamage and different sites of the initial injury for shorter- and longer-wavelength light. Still, there are many unanswered questions pointing toward next directions in research so as to increase the understanding of the responses of the retina to photodamage and help to develop effective therapeutic approaches for retinal degenerations.

Accumulation of all-trans-retinal (all-trans-RAL), reactive vitamin A aldehyde, is a key factor in initiating retinal photodamage, by light exposure in both acute and chronic fashion. Efficient transport and reduction of all-trans-RAL by key enzymes, ATP-binding cassette transporter 4 and all-trans-retinol dehydrogenase (RDH8) in the photoreceptor is essential for prevention of all-trans-RAL and its condensation products accumulation. This emphasizes the importance of this initial step in the visual cycle in maintaining the health of the retina. Recent understanding of all-trans-RAL toxicity and advanced in vivo imaging technologies have led to the development of new solutions to fight retinal degenerative diseases.

The human eye is constantly exposed to sunlight and artificial lighting and this is fundamental to its unique biological functions of directing vision and circadian rhythm. However, after the age of 40, exposure to ambient radiation can pose an ocular hazard. There are age-related changes in the natural chromophores (lipofuscin, A2E and all-trans-retinal derivatives) in the human retina that makes it more susceptible to visible light damage. Drugs have the potential to induce photodamage to the retina. This article reviews the underlying reasons why short blue visible light dramatically raises the risk of photodamage to the human retina.

Light initially impinges on the abundance of mitochondria in retinal ganglion cells before being transformed into visual information. Mitochondria can absorb light, and the blue light component in particular can generate reactive oxygen species to kill cells in culture. Experimental studies suggest that when retinal ganglion cells are already affected in diseases such as glaucoma or diabetes, the blue component of visual light might exacerbate the process.

All-trans retinal is a potent photosensitizer that is generated in vertebrate photoreceptor outer segments as a consequence of light detection. Reduction of all-trans retinal to retinol protects the photoreceptors from light-induced damage.

Toxic all-trans-retinal (AtRal) accumulates in the retina as a result of absorption of light by visual pigments. Here we show that AtRal is susceptible to degradation by visible light which reaches the adult human retina. Degraded AtRal (dAtRal) exhibits similar quantum yields of singlet oxygen generation but its absorption is shifted towards shorter wavelengths in comparison with AtRal. This may explain the UV maximum in the action spectra of retinal photodamage observed in animals. Interestingly, degraded AtRal is more cytotoxic to cultured ARPE-19 cells than AtRal also in dark, pointing to the need to further investigate its properties.

Lipofuscin and N-retinylidene-N-retinylethanolamine (A2E) accumulate with age in the retinal pigment epithelium of a retina that contains only cone photoreceptors.

The approach for collecting absorption spectra of intact melanosomes using photoemission electron microscopy is shown. Light enters the microscope at an angle of 77^o from the surface. Similar to an absorption spectrometer, regions of the substrate correspond to I₀ when the incident light arrives unobstructed by melanosomes, while the intensity of the photoemission in the shadow regions created by transmission through the melanosomes correspond to I. Analysis of the image then generates the absorption coefficient for the melanosomes at the incident wavelength.

There is heightened interest in naturally occurring compounds as potential therapeutic agents. One such compound is ursolic acid (UA), a triterpenoid found in common foods such as cranberries, apples, as well as rosemary and other herbs. When skin melanoma (SM) cells are treated with UA, they become more susceptible to UV and visible light exposure, in contrast to normal phenotype retinal pigment epithelial (RPE) cells, whose sensitivity to light damage is unchanged by UA treatment. The figure shows the appearance of SM and RPE cells 24 h following light exposure with or without UA pretreatment.

Rats were treated with various doses of zinc oxide and then exposed to intense visible light in a series of chambers like the one shown. Zinc treatment was effective in preventing retinal photoreceptor cell damage as determined by rhodopsin, retinal DNA recovery and retinal histology. Zinc was most effective when given before the onset of light and at doses slightly higher than found in the AREDS formulation. Zinc also altered the retinal gene expression profile, suggesting that it enhances antioxidative capacity in retina and that it reduces light-induced oxidative damage.

The retina is under constant threat of phototoxicity. Herein, we demonstrate that ascorbate (AscH) does not affect rose bengal-induced phototoxicity to ARPE-19 cells cultured in medium without iron supplement. In case of cells cultured in iron-supplemented medium, ascorbate exhibited protective effects at concentrations 0.35–0.70 mm during irradiation time of 20 min, but at longer irradiation time these concentrations of ascorbate exacerbated phototoxicity. Ascorbate at concentration of 1.4 mm exacerbated phototoxicity already for 20 min exposure. α-Tocopherol (TOH), particularly in combination with zeaxanthin (Zea), increased protective effects of ascorbate, but did not ameliorate the ascorbate-mediated increase in phototoxicity.

Pre-treatment with 670 nm light prevents photoreceptor cell death and maintains the integrity of the supporting glia in the retina, the Müller cells, following exposure to photic injury. Müller cells are the principal macroglial elements providing structural and metabolic support to the neighboring neurons. Protecting these cells is essential to the maintenance of retinal homeostasis. In this study, we show that photobiomodulation using 670 nm light provides protection to the Müller cells in the bright white light-stressed retina. By preserving Müller cell functions, 670 nm light treatment may enhance tissue recovery following injury or prevent progression of an existing damage.

Depletion of the ozone layer leads to increasing UV-B radiation on the earth's surface that has potential influence on the herbicide efficiency. In this study, we compared glyphosate efficacy on velvetleaf that was grown under with and without increased UV-B radiation. Glyphosate efficacy on velvetleaf, evaluated by shoot dry weight, was significantly decreased by increased UV-B radiation. The potential ways of decreased glyphosate efficiency by increased UV-B radiation was clarified. The results suggest that the influence of increased UV-B radiation on herbicide using cannot be ignored.

A novel and facile method for preparation of CdS/SiO₂ composite microspheres was developed. The as-prepared composite microspheres demonstrated excellent photocatalytic activity in the degradation of methylene blue, rhodamine 6G, methyl orange and rhodamine B. Moreover, this photocatalyst could be easily recycled and reused without notable loss of the photocatalytic activities.

The reactions of sterically hindered amines (SHA) were investigated in acetonitrile solutions and TiO₂ suspensions upon exposure to monochromatic radiation (λ = 365 nm) by in situ EPR spectroscopy. Experiments in homogeneous media using KO₂ and H₂O₂ evidenced alternative pathways for the SHA oxidation with a variety reactive oxygen species (ROS) involved. The influence of competitive reactions of SHA with ROS formed upon TiO₂ photoexcitation was investigated in a series of experiments using different additives (e.g. KO₂, H₂O₂, NaN₃, dimethylsulfoxide and methanol) under air or argon. The detailed analysis of paramagnetic intermediates formed upon the irradiation of the studied systems was accomplished using an EPR spin trapping technique.

Measurements were conducted with a pulse amplitude modulated fluorometer (Diving PAM) to investigate if the intertidal alga Fucus vesiculosus from the Norwegian Sea showed different photosynthetic characteristics compared to the sublittoral brown algae F. vesiculosus and F. radicans from the Bothnian Sea. The image shows the distal parts of F. vesiculosus from the Norwegian Sea (34–35 practical salinity units, psu) (a) and both distal and proximal parts of F. vesiculosus (b) and F. radicans (c) from the Bothnian Sea (4–5 psu).

The selective binding of the protonated merocyanine form of a photochromic dye in cucurbit[7]uril cavity leads to dual fluorescence, acceleration of the transformation to spiro isomer and decrease of acidity.

Owing to the current interest in natural photosynthesis as a blueprint for solar energy conversion, we have incorporated robust bacterial photosynthetic membrane vesicles into a dye-sensitized solar cell in place of the dye sensitizer, together with the biological electrolytes quinone and cytochrome c as redox mediators. This represents the fabrication of a self-contained biohybrid solar cell for the first time from a natural anoxygenic phototrophic system, capable of converting abundant near-IR solar radiation into a unidirectional flow of electrical current.

In the atmosphere OH radical is mainly produced by a reaction initiated by UV photolysis of ozone. Once produced in the atmosphere, a fraction is transferred to the surface layer of the ocean. In this study we demonstrated that the air-water transference of OH radical induces strong cell death on marine phytoplakton being picophytoplankton organisms the most vulnerable to its effects.

Ultraviolet germicidal irradiation (UVGI) lamps can be used to disinfect the air against viruses and bacteria. UV reflections from wall paints and ceiling tiles may be a concern for people in lower rooms. The reflective properties of wall paints have been studied, but not ceiling tiles. In our study, we measured the reflectance properties of ceiling tiles. We then estimated the lower-room irradiances that would be incident upon the occupants in various locations of a sample room, using our measurements and data obtained from other sources.

Measurements of broadband UVB irradiance at 14 locations in Spain for the period 2000–2009 have been used to generate instantaneous, hourly and daily values of irradiance and radiant exposure. For the UVB irradiance, the values corresponding to July (maximum) and December (minimum) have been analyzed as representative of the year during the whole period for all locations. For the UVB radiant exposure, the temporal evolution of daily values has been evaluated for all locations to estimate an average yearly behavior.

Compact fluorescent light (CFL) bulbs can provide the same amount of lumens as incandescent light bulbs, using one quarter of the energy. Measurements of UV emissions from these bulbs found significant levels of UVC and UVA, which appeared to originate from cracks in the phosphor coatings, present in all bulbs studied. Cells exposed to CFLs exhibited a decrease in the proliferation rate, migration, collagen contraction and increase in reactive oxygen species production. The response of the cells to the CFLs was consistent with damage from UV radiation, which was further enhanced by low dosages of TiO₂ nanoparticles, normally used for UV absorption.

25-OH-D3 serum levels were measured in two successive winters, 8 (interim) and 20 months after initiation of the study, in three groups of male outdoor workers, enrolled in either a complete, partial, or minimal sun protection program. No intragroup or intergroup differences were observed between interim- and postintervention mean 25-OH-D3 levels, which were close to 30 ng mL⁻¹. Significant risk factors for postintervention 25-OH-D3 levels >33.8 ng mL⁻¹ (a surrogate for reduced sun protection) were previous sunburn episodes and younger age. Borderline significant effects were seen for persons of Western, compared with Eastern paternal origin and for minimal intervention.

As suggested by the SCCS, dermal absorption of nanosized inorganic UV filters such as titanium dioxide (TiO₂) was to be reconsidered by taking into account the possible impact of abnormal skin barrier function and UV radiation on skin penetration. Using intact, damaged, irradiated and damaged/irradiated pigskin explants reproducing the worse real-life conditions of sunscreen application, we demonstrated that nanosized TiO₂ included in a sunscreen formed aggregates that remained in the uppermost layers of stratum corneum (SC), as shown by transmission electronic microscopy coupled with X-ray elemental analysis. Its bioavailability was not enhanced when skin barrier is first compromised, then submitted to solar radiation.

Solar UV stimulates metabolic (Cyp1A1) and inflammatory (IL-8) responses of human epidermal keratinocytes through AhR and NFκB signal transduction pathways. FICZ, a product of tryptophan photo-oxidation, activates AhR-Cyp axis. Resveratrol (RV) stimulates both Cyp1A1 and IL-8 via AhR and RV-specific transcription factor (TF). Cooperative action of the transcription factors underlies synergic cellular responses to UV-RV or FICZ-RV combinations.

Chemical structure of the conjugated porphyrin dimer (Oxdime).

Inhibition of the endogenous antioxidants SOD-1 (A) or glutathione synthase (B) makes neurons susceptible to mTHPC-mediated PDT. Using a 3D co-culture model containing dorsal root ganglion neurons and glial cells, use of DDC or l-BSO to inhibit antioxidant activity resulted in decreased neuronal viability compared with controls that were not treated with the inhibitors (^#P< 0.05, ^##P < 0.01, ^###P < 0.001) in which neurons survived mTHPC-mediated PDT.

The aim of the present study was to investigate the effects of low-level laser on the acute inflammatory phase following Achilles tendon injury with regard to the expression of pro-inflammatory and anti-inflammatory proteins. We conclude that the LLLT InGaAlP (660 nm) 100 mW power and energy of 6 J is an important modulator of inflammatory mediators during the process of tissue repair after injury to the Achilles tendon cutting common Wistar rats.