Effects Of UVA Research Articles

Hypericin phototoxicity induces different modes of cell death in melanoma and human skin cells

Hypericin, the major component of St. John’s Wort, absorbs light in the UV and visible ranges whereupon it becomes phototoxic through the production of reactive oxygen species. Although photodynamic mechanisms (i.e. through endogenous photosensitizers) play a role in UVA phototherapy for the treatment of skin disorders such as eczema and psoriasis, photodynamic therapy employing exogenous photosensitizers are currently being used only for the treatment of certain forms of non-melanoma skin cancers and actinic keratoses. There are few reports however on its use in treating melanomas. This in vitro study analyses the phototoxic effect of UVA (400–315 nm) – activated hypericin in human pigmented and unpigmented melanomas and immortalised keratinocytes and melanocytes. We show that neither hypericin exposure nor UV irradiation alone reduces cell viability. We show that an exposure to 1 μM UVA-activated hypericin does not bring about cell death, while 3 μM activated hypericin induces a necrotic mode of cell death in pigmented melanoma cells and melanocytes and an apoptotic mode of cell death in non-pigmented melanoma cells and keratinocytes. We hypothesis that the necrotic mode of cell death in the pigmented cells is possibly related to the presence of melanin-containing melanosomes in these cells and that the hypericin-induced increase in reactive oxygen species leads to an increase in permeability of melanosomes. This would result in toxic melanin precursors (of an indolic and phenolic nature) leaking into the cytoplasm which in turn leads to cell death. Hypericin localisation in the endoplasmic reticulum in these cells shown by fluorescent microscopy, further support a disruption in cellular processing and induction of cell death. In contrast, this study shows that cells that do not contain melanosomes (non-pigmented melanoma cells and keratinocytes) die by apoptosis. Further, using a mitochondrial-specific fluorescent dye, we show that intracellular accumulation of hypericin induces a mitochondrial-associated caspase-dependent apoptotic mode of cell death. This work suggests that UVA is effective in activating hypericin and that this phototoxicity may be considered as treatment option in some cases of lentigo maligna or lentigo maligna melanoma that are too large for surgical resection.

Waveband and Dose Dependency of Sunlight‐induced Immunomodulation and Cellular Changes†

Both the UVB and UVA wavebands within sunlight are immunosuppressive. This article reviews the relationship between wavebands and dose in UV-induced immunosuppression mainly concentrating on responses in humans. It also contrasts the effects of UVB and UVA on cellular changes involved in immunosuppression. Over physiological sunlight doses to which humans can be exposed during routine daily living or recreational pursuits, both UVA and UVB suppress immunity. While there is a linear dose relationship with UVB commencing at doses less than half of what is required to cause sunburn, UVA has a bell-shaped dose response over the range to which humans can be realistically exposed. At doses too low for either waveband to be suppressive, interactions between UVA and UVB augment each other, enabling immunosuppression to occur. At doses beyond where UVA is immunosuppressive, it still contributes to sunlight-induced immunosuppression via this interaction with UVB. While there is little research comparing the mechanisms by which UVB, UVA and their interactions can cause immunosuppression, it is likely that different chromophores and early molecular events are involved. There is evidence that both wavebands disrupt antigen presentation and effect T cell responses. Different individuals are likely to have different immunomodulatory responses to sunlight.

How Different Wavelengths of the Ultraviolet Spectrum Contribute to Skin Carcinogenesis: The Role of Cellular Damage Responses

The carcinogenic properties of ultraviolet (UV) light are mediated by its ability to generate DNA damage. Cellular responses to UV-induced DNA damage profoundly modulate the carcinogenic effects of UV exposures, and these responses are wavelength dependent. However, the exact contributions of different wavelengths of UV light to DNA damage, cellular damage responses, mutation, and skin carcinogenesis are incompletely understood. Given that UV-induced apoptosis is a protective cellular response to UV that prevents survival of damaged cells, inhibition of UVB-induced apoptosis by adding UVA, as reported by Ibuki et al. in this issue, may be a mechanism by which UVA augments UVB-mediated mutation and skin cancer formation.

Low Concentrations of Curcumin Induce Growth Arrest and Apoptosis in Skin Keratinocytes Only in Combination with UVA or Visible Light

It is well known that curcumin, a dietary pigment from the plant Curcuma longa, inhibits cell proliferation and induces apoptosis in different cell lines at concentrations ranging from 10 to 150 microM (3.7-55 microg/ml). In this study, we show that curcumin at low concentrations (0.2-1 microg/ml) also has an antiproliferative effect when applied in combination with UVA or visible light. We demonstrate that such a treatment induces apoptosis in human skin keratinocytes represented by the increase of fragmented cell nuclei, release of cytochrome c from mitochondria, activation of caspases-9 and -8, and inhibition of NF-kappaB activity. Furthermore, inhibition of extracellular regulated kinases 1/2 and protein kinase B was found to ensure the proapoptotic effect. Additionally, the EGFR, an upstream regulator of both kinases, was inhibited indicating that apoptosis is induced by blocking survival- and proliferation-associated signal cascades at the receptor level. In summary, these findings suggest a new therapeutic concept for the treatment of hyperproliferative diseases by combining topical curcumin with UVA or visible light. In particular, the latter avoids the use of carcinogenic irradiation that is part of regular phototherapy.

Photobiological effects of UVA and UVB light in zebrafish embryos: Evidence for a competent photorepair system

The consequences of UVB and UVA irradiation on hatch rate, mortality, and malformation were studied in embryonic zebrafish ( Danio rerio). The use of zebrafish embryos has expanded from traditional developmental models to diverse studies, including many techniques utilizing light exposure. To characterize useful indicators of photodamage, the responses and threshold limits of UV radiation as a function of embryonic stage and fish source were evaluated. Significant differences in UVB susceptibility were observed in embryos at 3, 6–7, 12, and 24 h post-fertilization (hpf), with the 1000-cell stage (3 hpf) having greatest tolerance to UVB. Embryos derived from zebrafish raised in outdoor ponds were more tolerant to UVB than were embryos from laboratory-raised fish. Combinations of UVB and UVA exposure were used to confirm the presence of a competent photorepair system in zebrafish that could return otherwise malformed embryos to a normal phenotype. Overall, embryonic zebrafish had large tolerances (LD 50 of 850 J/cm 2) to UVA, confirming their suitability for photoactivation and photorepair studies.

Production and biomass of picophytoplankton and larger autotrophs in Andean ultraoligotrophic lakes: differences in light harvesting efficiency in deep layers

We measured biomass and primary production of picophytoplankton (PicoPhy: 0.2–2 μm) and of autotrophic size fraction >2 μm in six deep ultraoligotrophic lakes in the Andean-Patagonian region (around 41°S) during summer stratification. Surface Photosynthetically Active Radiation (PAR) ranged from 1277 to 1849 μmol photons m−2 s−1, and the euphotic zone, generally deeper than the mixed layer, varied between 28 m and 49 m. We found a strong photoinhibiting effect of high PAR and UV-A at surface levels, whereas UV-B radiation (<320 nm) had low extra contribution in the photosynthesis inhibition. As a consequence, cell numbers, Chl a and primary production rates of both fractions increased towards deep layers in all lakes. The photosynthetic efficiency (Chl-specific production per photon unit) of both fractions increased with depth, although this increase was higher in PicoPhy, indicating a higher fitness to low-light. The per cent contribution of PicoPhy production to total production, showed an inverse significant relation with total dissolved phosphorus (TDP). Moreover our data fitted the existing database showing a significant trend towards a decrease of PicoPhy biomass and an increase of its relative contribution to total biomass with decreasing trophic state. At very low-phosphorus concentration, typical of north Patagonian lakes, we found good evidence of the competitive advantage of PicoPhy. Low-light and low TDP may interact to create the most favourable conditions for the smaller photosynthetic organisms. In conclusion, we found that at low-light and very low nutrient regime PicoPhy achieves higher photosynthetic efficiency than the larger autotrophic organisms.

The impact of nitrite and antioxidants on ultraviolet-A-induced cell death of human skin fibroblasts

Nitrite (NO 2 −) occurs ubiquitously in biological fluids such as blood and sweat. Ultraviolet A-induced nitric oxide formation via decomposition of cutaneous nitrite, accompanied by the production of reactive oxygen (ROS) or nitrogen species (RNS), represents an important source for NO in human skin physiology. Examining the impact of nitrite and the antioxidants glutathione (GSH), Trolox (TRL), and ascorbic acid (ASC) on UVA-induced toxicity of human skin fibroblasts (FB) we found that NO 2 − concentration-dependently enhances the susceptibility of FB to the toxic effects of UVA by a mechanism comprising enhanced induction of lipid peroxidation. While ASC completely protects FB cultures from UVA/NO 2 −-induced cell damage, GSH or TRL excessively enhances UVA/NO 2 −-induced cell death by a mechanism comprising nitrite concentration-dependent TRL radical formation or GSH-derived oxidative stress. Simultaneously, in the presence of GSH or TRL the mode of UVA/NO 2 −-induced cell death changes from apoptosis to necrosis. In summary, during photodecomposition of nitrite, ROS or RNS formation may act as strong toxic insults. Although inhibition of oxidative stress by NO and other antioxidants represents a successful strategy for protection from UVA/NO 2 −-induced injuries, GSH and TRL may nitrite-dependently aggravate the injurious impact by TRL or GSH radical formation, respectively.

Somatic-cell mutation induced by UVA and monochromatic UV radiation in repair-proficient and -deficient Drosophila melanogaster¶

Near-ultraviolet light (UVA: 320–400 nm) constitutes a major part of sunlight UV. It is important to know the effect of UVA on the biological activities of organisms on the earth. We have previously reported that black light induces somatic-cell mutation in Drosophila larvae. To investigate which wavelength of the UVA is responsible for the mutation we have now carried out a series of monochromatic irradiations (310, 320, 330, 340, 360, 380 and 400 nm) on Drosophila larvae, using the large spectrograph of the National Institute for Basic Biology (Okazaki National Research Institutes, Okazaki, Japan). Mutagenic activity was examined by the Drosophila wing-spot test in which we observe mutant wing hair colonies (spots) on the wings of adult flies obtained from the treated larvae. The induction of mutation was highest by irradiation at 310 nm and decreased as the wavelength became longer. Neither the 380 nor the 400 nm light was mutagenic. Excision repair is known to protect cells from UV damage. In the excision-repair–deficient Drosophila, the mutagenic response induced by 310 nm irradiation was 24-fold higher than that of the wild-type (7.2 ± 1.5 spots/wing/kJ vs 0.3 ± 0.08 spots/wing/kJ), and at 320 nm the difference of the response was 14-fold (0.21 vs 0.015 ± 0.005). In the case of irradiation at 330 and 340 nm the difference of the response was only two-fold (at 330 nm, 6.9 ± 2.9 × 10−3vs 3.1 ± 1.1 × 10−3 spots/wing/kJ; at 340 nm, 3.5 ± 0.9 × 10−3vs 2.0 ± 0.7 × 10−3). These results suggest that the lesion caused in the larvae by 320 nm irradiation may be similar to the damage induced by 310 nm and that the lights of 330 and 340 nm may induce damage different from the lesions induced by shorter-wavelength lights.

Inhibition of Photosynthetic Electron Transport by UV-A Radiation Targets the Photosystem II Complex¶

We have studied the inhibition of photosynthetic electron transport by UV-A (320–400 nm) radiation in isolated spinach thylakoids. Measurements of Photosystem II (PSII) and Photosystem I activity by Clark-type oxygen electrode demonstrated that electron flow is impaired primarily in PSII. The site and mechanism of UV-A induced damage within PSII was assessed by flash-induced oxygen and thermoluminescence (TL) measurements. The flash pattern of oxygen evolution showed an increased amount of the S0 state in the dark, which indicate a direct effect of UV-A in the water-oxidizing complex. TL measurements revealed the UV-A induced loss of PSII centers in which charge recombination between the S2 state of the water oxidizing complex and the semireduced QA− and QB− quinone electron acceptors occur. Flash-induced oscillation of the B TL band, originating from the S2QB− recombination, showed a decreased amplitude after the second flash relative to that after the first one, which is consistent with a decrease in the amount of QB− relative to QB in dark adapted samples. The efficiency of UV-A light in inhibiting PSII electron transport exceeds that of visible light 45-fold on the basis of equal energy and 60-fold on the basis of equal photon number, respectively. In conclusion, our data show that UV-A radiation is highly damaging for PSII, whose electron transport is affected both at the water oxidizing complex, and the binding site of the QB quinone electron acceptor in a similar way to that caused by UV-B radiation.

Effects of polyphenols on skin damage due to ultraviolet A rays: an experimental study on rats

Ultraviolet (UV) radiation causes many acute and chronic conditions such as oedema of the skin, sunburn, immunosuppression, photo-ageing and skin cancer. The use of antioxidants has become of paramount importance in prevention of the damage caused by ultraviolet radiation. Epigallocatechin-3-gallate (EGCG), one of the main components of green tea, has been reported to have anti-inflammatory, antioxidant and anticarcinogenic properties. The aim of this experimental study was to investigate to what extent EGCG prevented acute skin damage caused by UVA. The sample contained 2% EGCG, which was prepared in hydrophilic ointment (USP XXIV) as the vehicle. Twenty-four 12-week-old Wistar albino rats are included in the study and divided into four groups, each containing six rats. Group I was formed to be the control group, which was not applied any topical medication or exposed to UV radiation. Group II was formed to observe acute effects of UVA on the skin, Group III was formed to observe effectiveness of topical EGCG on the skin applied 30 min after exposure to UVA, and Group IV was formed to observe topical EGCG applied 30 min before exposure to UVA. All groups were examined for sunburn cells, leucocyte infiltration, dermo-epidermal activity, collagen changes and elastic fibre pathologies on 24 and 72 h. Statistical analysis was performed using spss 11.5, and chi-squared test was used for the evaluation of parameters. Group IV showed a statistically significant decrease in sunburn cells and dermo-epidermal activation compared with Group II. Group II showed significant increase in all parameters compared with Group I, showing the effects of UV exposure alone, and no difference was detected in Group II and III. These results show a protective effect of EGCG when applied topically before UVA exposure. No benefit was detected when EGCG was applied after UV exposure.

Effect of ultraviolet (UV) A, UVB or ionizing radiation on the cell cycle of human melanoma cells

One important component of the cellular response to irradiation is the activation of cell cycle checkpoints. It is known that both ultraviolet (UV) radiation and ionizing radiation (IR) can activate checkpoints at transitions from G(1) to S phase, from G(2) phase to mitosis and during DNA replication. To evaluate the effects of irradiation with different wavelengths on cell cycle alterations. p53-deficient IPC-298 melanoma cells were irradiated with 10 J cm(-2) UVA, 40 mJ cm(-2) UVB, or with 7.5 Gy IR. Cell cycle effects were then determined by DNA/5-bromodeoxyuridine dual-parameter flow cytometry. IPC-298 cells irradiated in G(1) with UVA were not arrested at the G(1)/S transition, but at the G(2)/M transition. Despite p53 deficiency, the cells showed a G(1) arrest after UVB exposure. Furthermore, IR did not affect G(1) or S phase, but induced G(2) phase arrest. Hence, the effects of UVA, but not of UVB, on the cell cycle in p53-deficient melanoma cells are comparable with those of IR. UVA and IR induce radical-mediated strand breaks and DNA lesions, and UVB essentially induces thymine dimers that lead to excision repair-related strand breaks. Different cell cycle effects may be a consequence of different types of DNA damage. The results showed that UVB-irradiated p53-deficient cells are arrested in G(1). Irradiation with the solar radiation component UVB can therefore result in a beneficial retardation of tumour promotion in human skin carrying p53-mutated cell clones.

In vivo release of non-neuronal acetylcholine from human skin by dermal microdialysis: Effects of sunlight, UV-A and tactile stimulus

Non-neuronal acetylcholine (ACh) is expressed in epithelial, endothelial and immune cells. For example, the in vivo release of ACh from the human skin pretreated with botulinum toxin has recently been demonstrated. In the present experiments the effects of light (sunlight and solar radiation by a commercial UV-A applier) and of a tactile stimulus on the release of non-neuronal ACh were investigated. Release of ACh from the proximal and distal shin, i.e. anterior tibial region, was measured by dermal microdialysis in 20 min samples over a time period of at least 140 min. Control experiments were performed in a dark room throughout. In some experiments volunteers were exposed to sunshine (80–140 min) or the shin region was illuminated (80–95 min) by a commercial UV-A lamp (400 W at a distance of 50 cm). In control experiments ACh release between 20 and 80 min (B1) amounted to 118±32 pmol (n=17) and gradually declined between 80 and 140 min (B2) to 112±34 pmol, resulting in a B2/B1 ratio of 0.95. When the skin was exposed to sunlight ACh release increased from 205±58 pmol (B1) to 349±122 pmol resulting in a B2/B1 ratio of 1.70. UV-A radiation, however, had no significant effect on the B2/B1 ratio. When very smooth tactile stimuli were applied by a cotton wool tip for 20 min to the skin close to the microdialysis membranes in a dark room, ACh release was increased from 9±2 pmol/20 min to 52±36 (n=7). In conclusion, the in vivo release of ACh from the human skin appears to be regulated by external stimuli like sunlight and tactile stimuli.

Reconstructed human skin: From photodamage to sunscreen photoprotection and anti-aging molecules

Acute or repetitive sun exposure has been shown to be responsible for various deletorious consequences such as sunburn reaction, photoaging and photocancers. Determination of early biological events occurring after UV exposure is essential for photoprotection. Using a human reconstructed skin in vitro, comprising both a fully differentiated epidermis and a living dermal equivalent, the effects of UVB and UVA were analysed in keratinocytes and fibroblasts. The efficiency of sunscreen protection was afforded after topical application. The effect of Vitamin C was analyzed. Reconstructed skin was exposed to UVB, UVA or SSR. Morphological aspect, DNA lesions, sunburn cells, MMP-1 were evaluated. Sunscreen photoprotection was assessed with formulations having different profile of absorption or photostability. Vitamin C was added to the culture medium during reconstruction of the skin. While UVB essentially induced direct epidermal damage such as DNA lesions or sunburn cells, UVA reached the dermis and led to alterations in fibroblasts and dermal extracellular matrix. Both UVB and UVA, alone or combined using solar simulated radiation (SSR), induced MMP-1 production, directly in dermal fibroblasts after UVA exposure, or through release of soluble epidermal factors after UVB. Based on the identification of these biological end-points, evaluation of sunscreeen photoprotection was performed after topical application of formulations. The data showed that broad UVB + UVA spectrum profile together with photostability are required for a real efficient protection. Finally, we found that Vitamin C could improve the morphogenesis of dermal epidermal junction, through its ability to promote synthesis of extracellular matrix and basement membrane proteins. These results may help in understanding the beneficial effects of such molecule in the treatment of photoaged skin. Altogether, these data emphazied the fact that human skin reconstructed in vitro is a valuable tool for research studies as well as for evaluation of compounds designed to prevent or correct photodamage.

Ultraviolet A in vitiligo

Both types of Ultraviolet (UV), UVB (290-320 nm) and UVA (320-400 nm), produce increased pigmentation or tanning. However, no evaluation of UVA alone in the treatment of vitiligo has been reported. Therefore, it was the purpose of this work to study the pigmentogenic effect of UVA (5 and 15 J/cm(2)) in vitiligo. The study included 20 randomly selected patients with vitiligo involving more than 30% of the body surface area with a bilateral/symmetrical distribution. They were equally divided into two groups each of 10 patients. All patients received three weekly sessions of UVA, 15 J/cm(2) in group I and 5 J/cm(2) in group II, a total of 48 sessions over 16 weeks. Overall pigmentation of 60% and above was recorded in 50% and 10% of patients in groups I and II, respectively. We conclude that broadband UVA alone, without psoralens, and in appropriate doses may be of important therapeutic value in vitiligo.

Exposure to ultraviolet radiation delays photosynthetic recovery in Arctic kelp zoospores.

Seasonal reproduction in some Arctic Laminariales coincides with increased UV-B radiation due to stratospheric ozone depletion and relatively high water temperatures during polar spring. To find out the capacity to cope with different spectral irradiance, the kinetics of photosynthetic recovery was investigated in zoospores of four Arctic species of the order Laminariales, the kelps Saccorhiza dermatodea, Alaria esculenta, Laminaria digitata, and Laminaria saccharina. The physiology of light harvesting, changes in photosynthetic efficiency and kinetics of photosynthetic recovery were measured by in vivo fluorescence changes of Photosystem II (PSII). Saturation irradiance of freshly released spores showed minimal I ( k ) values (photon fluence rate where initial slope intersects horizontal asymptote of the curve) values ranging from 13 to 18 micromol photons m(-2) s(-1) among species collected at different depths, confirming that spores are low-light adapted. Exposure to different radiation spectra consisting of photosynthetically active radiation (PAR; 400-700 nm), PAR+UV-A radiation (UV-A; 320-400 nm), and PAR+ UV-A+UV-B radiation (UV-B; 280-320 nm) showed that the cumulative effects of increasing PAR fluence and the additional effect of UV-A and UV-B radiations on photoinhibition of photosynthesis are species specific. After long exposures, Laminaria saccharina was more sensitive to the different light treatments than the other three species investigated. Kinetics of recovery in zoospores showed a fast phase in S. dermatodea, which indicates a reduction of the photoprotective process while a slow phase in L. saccharina indicates recovery from severe photodamage. This first attempt to study photoinhibition and kinetics of recovery in zoospores showed that zoospores are the stage in the life history of seaweeds most susceptible to light stress and that ultraviolet radiation (UVR) effectively delays photosynthetic recovery. The viability of spores is important on the recruitment of the gametophytic and sporophytic life stages. The impact of UVR on the zoospores is related to the vertical depth distribution of the large sporophytes in the field.

UVA-mediated down-regulation of MMP-2 and MT1-MMP coincides with impaired angiogenic phenotype of human dermal endothelial cells

UVA irradiation, dose-dependently (5–20 J/cm 2), was shown to impair the morphogenic differentiation of human microvascular endothelial cells (HMECs) on Matrigel. Parallely, UVA down-regulated the expression of MMP-2 and MT1-MMP, both at the protein and the mRNA levels. On the contrary, the production of MMP-1 and TIMP-1 by HMECs increased following UVA treatment. The inhibitory effect of UVA on MMP expression and pseudotubes formation was mediated by UVA-generated singlet oxygen ( 1O 2). The contribution of MT1-MMP, but not TIMP-1, to the regulation of HMECs’ angiogenic phenotype following UVA irradiation was suggested using elastin-derived peptides and TIMP-1 blocking antibody, respectively.

Ultraviolet a Radiation and The Need for Protection

Erythema is a readily visible, often painful, natural phenomenon indicative of prolonged cutaneous exposure to ultraviolet (UV) radiation in the UVB range. As a result, early sunscreens were designed to provide adequate protection from UVB radiation. However, the continuous rise in the melanoma incidence rate alludes to the existence of an established photocarcinogen from which we are not well protected. Recently, scientists have been evaluating the photodamaging effects caused by wavelengths other than UVB. They have presented evidence that suggests that UVA exposure poses a greater hazard than previously acknowledged. For this reason, more emphasis must be placed on the development of broad-spectrum sunscreens providing adequate UVA and UVB protection. Additionally, regular sunscreen application must be advocated, proactive sun-protective practices must be implemented, and greater public awareness of the harmful effects of UVA and UVB radiation must be improved on, with the hope of decreasing the rate of cutaneous malignant melanoma.

The induction of immunity to a protein antigen using an adjuvant is significantly compromised by ultraviolet A radiation

Ultraviolet (UV) radiation from sunlight causes skin cancer and inhibits priming of the immune system during vaccination. However the dose related effects of the different components of sunlight (UVA and UVB) are complex and require further investigation. Using ovalbumin as a model protein vaccine with saponin as adjuvant we show that both UVA and UVB can suppress the DTH response to a poorly immunogenic protein. Increasing doses of UVB induced increased levels of immunosuppression and tolerance. UVA however, caused a bi-phasic dose response with intermediate but not low or high doses causing primary immunosuppression. No dose of UVA caused significant tolerance. Similar results were observed in both C57BL/6 and Balb/c mice. Our data confirms the complex immunomodulatory dose effects of UVA and UVB for a protein antigen, and shows that both UVB and UVA can suppress immunity induced by a protein with adjuvant. This highlights the importance of considering sun exposure patterns in the future success of both preventing skin cancer development and enhancing vaccination regimes.

Radiation Sources Providing Increased UVNUVB Ratios Induce Photoprotection Dependent on the UVA Dose in Hairless Mice

In studies involving mice in which doses of UVA (320-400 nm) and UVB (290-320 nm) radiation were administered alone or combined sequentially, we observed a protective effect of UVA against UVB-induced erythema/edema and systemic suppression of contact hypersensitivity. The UVA immunoprotection was mediated by the induction of the stress enzyme heme oxygenase-1 (HO-1) in the skin, protection of the cutaneous Th1 cytokines interferon-gamma (IFN-gamma) and IL-12 and inhibition of the UVB-induced expression of the Th2 cytokine IL-10. In this study, we seek evidence for an immunological waveband interaction when UVA and UVB are administered concurrently to hairless mice as occurs during sunlight exposure in humans. A series of spectra providing varying ratios of UVA/UVB were developed, with the UVA ratio increased to approximately 3.5 times the UVA component in solar simulated UV (SSUV). We report that progressively increasing the UVA component of the radiation while maintaining a constant UVB dose resulted in a reduction of both the erythema/edema reaction and the degree of systemic immunosuppression, as measured as contact hypersensitivity. The UVA-enhanced immunoprotection was abrogated in mice treated with a specific HO enzyme inhibitor. UVA-enhanced radiation also upregulated the expression of cutaneous IFN-gamma and IL-12 and inhibited expression of both IL-6 and IL-10, compared with the activity of SSUV. The results were consistent with the previously characterized mechanisms of photoprotection by the UVA waveband alone and suggest that the UVA component of solar UV may have beneficial properties for humans.

Broad-spectrum sunscreens prevent the secretion of proinflammatory cytokines in human keratinocytes exposed to ultraviolet A and phototoxic lomefloxacin

The combination of phototoxic drugs and ultraviolet (UV) radiation can trigger the release of proinflammatory cytokines. The present study measured the ability of sunscreens to prevent cytokine secretion in human keratinocytes following cotreatment of these cells with a known photoreactive drug and UVA. Keratinocytes were treated for 1 h with increasing concentrations of lomefloxacin (LOM) or norfloxacin (NOR), exposed to 15 J/cm2 UVA, and incubated for 24 h. NOR, owing to the absence of a fluorine atom in position 8, was non-phototoxic and used as a negative control. Cell viability and the release of 3 cytokines were assessed, namely interleukin-1alpha (IL-1alpha), interleukin-6 (IL-6), and tumour necrosis factor-alpha (TNF-alpha). The measurement of these cytokines may be a useful tool for detecting photoreactive compounds. To measure their ability to prevent cytokine secretion, various sunscreens were inserted between the UVA source and the cells. Treatment with NOR, NOR plus UVA, or LOM had no effect on the cells. LOM plus UVA, however, had an effect on cell viability and on cytokine secretion. IL-1alpha levels increased with LOM concentration. The release of TNF-alpha and IL-6 followed the same pattern at lower concentrations of LOM but peaked at 15 micromol/L and decreased at higher concentrations. Sunscreens protected the cells from the effects of LOM plus UVA, as cell viability and levels of cytokines remained the same as in the control cells. In conclusion, the application of broad-spectrum sunscreen by individuals exposed to UVA radiation may prevent phototoxic reactions initiated by drugs such as LOM.