Long wave ultraviolet radiation stimulates arachidonic acid release and cyclooxygenase activity in mammalian cells in culture

Gamma-Linolenic Acid (GLA) Protects against Ionizing Radiation-Induced Damage: An In Vitro and In Vivo Study

Radiation is pro-inflammatory in nature in view of its ability to induce the generation of reactive oxygen species (ROS), cytokines, chemokines, and growth factors with associated inflammatory cells. Cells are efficient in repairing radiation-induced DNA damage; however, exactly how this happens is not clear. In the present study, GLA reduced DNA damage (as evidenced by micronuclei formation) and enhanced metabolic viability, which led to an increase in the number of surviving RAW 264.7 cells in vitro by reducing ROS generation, and restoring the activities of desaturases, COX-1, COX-2, and 5-LOX enzymes, TNF-α/TGF-β, NF-kB/IkB, and Bcl-2/Bax ratios, and iNOS, AIM-2, and caspases 1 and 3, to near normal. These in vitro beneficial actions were confirmed by in vivo studies, which revealed that the survival of female C57BL/6J mice exposed to lethal radiation (survival~20%) is significantly enhanced (to ~80%) by GLA treatment by restoring altered levels of duodenal HMGB1, IL-6, TNF-α, and IL-10 concentrations, as well as the expression of NF-kB, IkB, Bcl-2, Bax, delta-6-desaturase, COX-2, and 5-LOX genes, and pro- and anti-oxidant enzymes (SOD, catalase, glutathione), to near normal. These in vitro and in vivo studies suggest that GLA protects cells/tissues from lethal doses of radiation by producing appropriate changes in inflammation and its resolution in a timely fashion.

The protective roles of TiO2 nanoparticles against UV-B toxicity in Daphnia magna

Aquatic environments are increasingly under environmental stress due to ultraviolet (UV) radiation and potential inputs of nanoparticles with intense application of nanotechnology. In this study, we investigated the interaction between UV-B radiation and titanium nanoparticles (TiO₂-NPs) in a model freshwater cladoceran Daphnia magna. UV-B toxicity to Daphnia magna was examined when the daphnids were exposed to a range of TiO₂-NPs concentrations with an initial 5 or 10min of 200μW/cm² UV-B radiation. In addition, UV-B toxicity was also examined in the presence of TiO₂-NPs in the body of daphnids. Our results demonstrated that the daphnid mortality under UV-B radiation decreased significantly in the presence of TiO₂-NPs both in the water and in the body, indicating that TiO₂-NPs had some protective effects on D. magna against UV-B. Such protective effect was mainly caused by the blockage of UV-B by TiO₂-NPs adsorption. UV-B produced reactive oxygen species (ROS) in the water and in the daphnids, which was not sufficient to cause mortality of daphnids over short periods of radiation. Previous studies focused on the effects of TiO₂-NPs on the toxicity of total UV radiation, and did not attempt to differentiate the potential diverse roles of UV-A and UV-B. Our study indicated that TiO₂-NPs may conversely protect the UV-B toxicity to daphnids.

UVA irradiation induced heme oxygenase-1: a novel phototherapy for morphea

Long wave UVA radiation (340-400 nm) causes detrimental as well as beneficial effects on human skin. Studies of human skin fibroblasts irradiated with UVA demonstrate increased expression of both antifibrotic heme oxygenase-1 (HO-1) and matrix metalloproteinase 1 (MMP-1). The use of UVA-induced MMP-1 is well-studied in treating skin fibrotic conditions such as localized scleroderma, now called morphea. However, the role that UVA-induced HO-1 plays in phototherapy of morphea has not been characterized. In the present manuscript, we have illustrated and reviewed the biological function of HO-1 and the use of UVA1 wavebands (340-400 nm) for phototherapy; the potential use of HO-1 induction in UVA therapy of morphea is also discussed.

Incorporation of phytosterols in human keratinocytes

We have designed experimental conditions allowing the replacement of 50% of cholesterol of human keratinocytes (SVK14 line) with sitosterol or stigmasterol without affecting cellular viability. We have investigated the influence of incorporating phytosterol on the ultraviolet-A-induced formation of lipid-peroxidation products (thiobarbituric reactive substances (TBARS)) in these cells. Our results show that ultraviolet-A-induced lipid peroxidation depends on the nature of the phytosterol. Sitosterol induces a significant decrease (-30%) of TBARS relative to the control whereas stigmasterol markedly increases lipid peroxidation (+70%). We have also studied the effect of plant sterols on prostaglandin release by using the Ca(2+) ionophore A23187 as an in vitro model of the inflammation induced by UVA radiation. We show that in the presence of 50% of phytosterol (particularly stigmasterol), the release of prostaglandin (6-ketoPG(1alpha), PGE(2)) is increased compared to untreated cells. This pro-inflammatory effect of phytosterols is correlated with a loss of the regulation of the intracellular Ca(2+) concentration.

Ultraviolet A exposure might increase metastasis of mouse melanoma: a pilot study

BACKGROUND

The major sources of long-wave ultraviolet A radiation (UVA; 320-400 nm) exposure are extensive sunbathing and tanning in solaria. While the carcinogenic effects of mid-wave ultraviolet B radiation (UVB; 280-320 nm) are well recognized, the potentially hazardous effects of UVA are less understood. Several studies have shown that a variety of physiological processes in the cell are modified by UVA exposure, some of which might be involved in the regulation of tumor metastasis. In this study we suggest that UVA radiation could lead to the increase of metastatic capability of melanoma cells in mice.

METHOD/RESULT

A pilot in vivo study was executed using C57BL/6 mice and syngeneic B16 melanoma cell lines. Mice were intravenously (i.v.) injected with either B16-F1 or B16-F10 melanoma cells into the tail vein and then immediately exposed to UVA. Fourteen days after melanoma injection, lungs were collected and the quantity and quality of metastases were determined under a dissecting microscope. As an outcome of the pilot study we observed that i.v. injected melanoma cells formed more lung metastases in the UVA-exposed mice in comparison with the control mice.

CONCLUSION

This result suggests that the UVA exposure of mice, with melanoma cells present in blood circulation, increases the formation of melanoma metastases in lungs. Further studies should determine whether a similar pro-metastatic effect, as observed in mice, could occur in humans and whether other than melanoma tumors might be susceptible.

Contribution of UVB and UVA to UV-dependent stimulation of cyclooxygenase-2 expression in artificial epidermis

Both UVB (280-320 nm) and UVA (320-400 nm) radiation lead to an enhanced expression of cyclooxygenase-2 (COX-2) in epidermal cells in various in-vitro and in-vivo models. It is demonstrated here that the expression of COX-2 is induced in artificial human epidermis exposed to simulated solar light (>290 nm). Employing filters eliminating specified regions from the simulated solar spectrum, the UVB and UVA-2 (320-350 nm) regions are shown to fully account for induction of COX-2 mRNA and protein as well as the enhanced production of prostaglandin E(2) after irradiation. At the protein level, approximately 70% of the total induction by solar light is due to light in the UVA-2 region. UVA-1 (350-400 nm), visible light and IR radiation are practically ineffective. COX-2 induction by simulated solar light is attenuated in the presence of inhibitors of p38(MAPK) or of c-Jun-N-terminal kinases (JNK), whereas COX-2 induction by UVA is blocked only by inhibition of JNK. UV-induced COX-2 expression is not affected by inhibition of the MEK 1,2/ERK 1,2 pathways.

The green tea polyphenol, epigallocatechin-3-gallate, protects against the oxidative cellular and genotoxic damage of UVA radiation

A number of biological activities have been ascribed to the major green tea polyphenol epigallocatechin-3-gallate (EGCG) to explain its chemopreventive properties. Its antioxidant properties emerge as a potentially important mode of action. We have examined the effect of EGCG treatment on the damaging oxidative effects of UVA radiation in a human keratinocyte line (HaCaT). Using the ROS-sensitive probes dihydrorhodamine 123 (DHR) and 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), we detected a reduction in fluorescence in UVA-irradiated (100 kJ/m(2)) cells in the case of the former but not the latter probe after a 24-hr treatment with EGCG (e.g., 14%, [p < 0.05] after 10 microM EGCG). In the absence of UVA, however, both DHR and DCFH detected a pro-oxidant effect of EGCG at the highest concentration used of 50 microM. Measurements of DNA damage in UVA-exposed cells using the single cell gel electrophoresis assay (comet assay) also showed the protective effects of EGCG. A concentration of 10 microM EGCG decreased the level of DNA single strand breaks and alkali-labile sites to 62% of the level observed in non-EGCG, irradiated cells (p < 0.001) with a 5-fold higher concentration producing little further effect. Correspondingly, EGCG ablated the mutagenic effects of UVA (500 kJ/m(2)) reducing an induced hypoxanthine-guanine phosphoribosyl transferase (HPRT) mutant frequency of (3.39 +/- 0.73) x 10(-6) to spontaneous levels (1.09 +/- 0.19) x 10(-6). Despite having an antiproliferative effect in the absence of UVA, EGCG also served to protect against the cytotoxic effects of UVA radiation. Our data demonstrate the ability of EGCG to modify endpoints directly relevant to the carcinogenic process in skin.

The role of p38 in UVA-induced cyclooxygenase-2 expression in the human keratinocyte cell line, HaCaT

We examined the expression of cycloxygenase-2, the rate-limiting enzyme in the production of prostaglandins, in the UVA-irradiated human keratinocyte cell line, HaCaT. UVA induced a dose-dependent increase in COX-2 at the protein level at 2 and 4 h post-irradiation and at the mRNA level at 1 and 2 h post-irradiation. Experiments using semi-quantitative RT-PCR demonstrate that UVA increased the half-life of the COX-2 message by more than fourfold in the presence of Actinomycin D (with a half life between 4 and 8 h post-irradiation), suggesting that UVA induction of COX-2 is post-transcriptionally regulated. Through the use of the specific p38 inhibitor, SB202190, increases in COX-2 message and protein levels were abrogated in UVA-irradiated cells. In UVA-irradiated cells treated with SB202190, the half-life of the COX-2 message was decreased to basal levels (between 1 and 2 h post-irradiation), indicating that p38 was responsible for the stabilization of the message. Luciferase activity was increased in UVA-irradiated cells transfected with reporter constructs containing the 3' UTR of COX-2, a region containing AU-rich elements (AREs). These regulatory sequences of AUUUA have been proposed as one mechanism of post-transcriptional regulation. Increases observed in luciferase activity could be decreased using a p38 dominant-negative construct. We report for the first that UVA can induce COX-2 expression in the human keratinocyte cell line, HaCaT. Additionally, p38 appears to play a critical role in the UVA-induced expression of COX-2 in these keratinocytes and may serve as a potential drug target in the chemoprevention of skin cancer.

Exposure of human breast cancer cells to the anti-inflammatory agent indomethacin alters choline phospholipid metabolites and Nm23 expression

We previously observed that changes in choline phospholipids of two malignant human mammary epithelial cells (HMECs) following treatment with a high dose of the cyclooxygenase (COX) inhibitor, indomethacin, mimicked changes following transfection with a metastasis suppressor gene, nm23. The similarity between response to indomethacin and nm23 transfection led us to 1) expand our (1)H NMR spectroscopy study of indomethacin treatment by determining the response at two doses for two nonmalignant and three malignant HMECs, 2) investigate COX-1 and COX-2 levels in HMECs and their relationship with choline phosholipid metabolites, and 3) determine changes in Nm23 expression following treatment with indomethacin. All HMECs exhibited a significant change in choline phospholipids following treatment with 300 microM indomethacin. At the lower dose of 50 microM, only nonmalignant HMECs and the estrogen-dependent malignant cell line, MCF-7, responded. COX-1 levels were significantly higher in malignant HMECs than in nonmalignant HMECs. A significant increase in Nm23 expression following 300 microM indomethacin was detected in MCF-12A and MCF-7 cells but not in MDA-MB-231 and MDA-MB-435 cells. These results suggest that COX-1 expression and its inhibition play a role in the choline phospholipid metabolism of HMECs, and the effect of indomethacin on HMECs may be mediated, in part, through upregulation of nm23.

Cell attachment to extracellular matrices is modulated by pulsed radiation at 820 nm and chemicals that modify the activity of enzymes in the plasma membrane

BACKGROUND AND OBJECTIVES

Adhesive interactions between cells and extracellular matrices play a regulative role in wound repair processes. The objective of this investigation is to study action mechanisms of pulsed radiation at 820 nm on cellular adhesion in vitro. Light emitting diodes (LED) at 820 nm are widely used for treatment of wounds of various etiology.

STUDY DESIGN/MATERIALS AND METHODS

The LED (820 +/- 10 nm, 10 Hz, 16-120 J/m(2)) is used for the irradiation of HeLa cell suspension. In parallel experiments, amiloride (5 x 10(-4) M), ouabain (7 x 10(-5) M, 7 x 10(-4) M), quinacrine (6 x 10(-4) M), arachidonic acid (1 x 10(-5) M), glucose (2 x 10(-4) M), and ATP (5 x 10(-5) M) are added to the cell suspension before or after the irradiation procedure. The cell-glass adhesion is studied using the adhesion assay technique described in Lasers Surg Med 1996; 18:171.

RESULTS

Cell-glass adhesion increases in a dose-dependent manner following the irradiation. Preirradiation eliminates the inhibition of cell attachment caused by ouabain, arachidonic acid, and ATP. The inhibitive effect of quinacrine on the cell attachment is eliminated by the irradiation performed after the treatment with the chemical. Irradiation and amiloride have a synergetic stimulative effect on the cell attachment. The threshold dose for the cell attachment stimulation by the irradiation is decreased by the treatment of the cell suspension with amiloride or ouabain.

CONCLUSIONS

The results obtained indicate that pulsed IR radiation at 820 nm increases the cell-matrix attachment. It is the modulation of the monovalent ion fluxes through the plasma membrane and not the release of arachidonic acid that is involved in the cellular signaling pathways activated by irradiation at 820 nm. Preirradiation has a protective effect against the inhibitive action of ouabain, arachidonic acid, ATP, and quinacrine on cell attachment process. It is supposed that irradiation activates those signaling pathways in cells which attenuate the inhibitive action of these chemicals.

UV-A irradiation induces a decrease in the mitochondrial respiratory activity of human NCTC 2544 keratinocytes

UV-A irradiation caused a dose-dependent decrease in cellular oxygen consumption (56%) and ATP content (65%) in human NCTC 2544 keratinocytes, one hour after treatment. This effect was partially reversed by maintaining the irradiated cells in normal culture conditions for 24 h. Using malate/glutamate or succinate as substrates for mitochondrial electron transport, the oxygen uptake of digitonin-permeabilised cells was greatly inhibited following UV-A exposure. These results strongly suggest that UV-A irradiation affects the state 3 respiration of the mitochondria. However, under identical conditions, UV-A exposure did not reduce the mitochondrial transmembrane potential. The antioxidant, vitamin E inhibited UV-A-induced lipid peroxidation, but did not significantly prevent the UV-A-mediated changes in cellular respiration nor the decrease in ATP content, suggesting that these effects were not the result of UV-A dependent lipid peroxidation. UV-A irradiation also led to an increase in MnSOD gene expression 24 hours after treatment, indicating that the mitochondrial protection system was enhanced in response to UV-A treatment. These findings provide evidence that impairment of mitochondrial respiratory activity is one of the early results of UV-A irradiation for light doses much lower than the minimal erythemal dose.

Photocarcinogenesis: UVA vs UVB

Ultraviolet B and A radiations (respective wavelength ranges 280-315 and 315-400 nm) are present in sunlight at ground level. The ultraviolet radiation does not penetrate any deeper than the skin and has been associated with various types of human skin cancers. The carcinogenicity of UVB radiation is well established experimentally and, to a large extent, understood as a process of direct photochemical damage to DNA from which gene mutations arise. Although UVA is generally far less carcinogenic than UVB radiation, it is present more abundantly in sunlight than UVB radiation (> 20 times radiant energy) and can, therefore, contribute appreciably to the carcinogenicity of sunlight. In contrast to UVB, UVA radiation is hardly absorbed by DNA. Hence, the absorption by other molecules (endogenous photosensitizers) becomes more important, thus radicals and, more specifically, reactive oxygen species can be generated that can damage DNA, membranes, and other cellular constituents. These photochemical differences between UVA and UVB radiations are reflected in differences in cellular responses and carcinogenesis.

Biphasic effect of UVA radiation on STAT1 activity and tyrosine phosphorylation in cultured human keratinocytes

The effect of ultraviolet A (UVA) radiation on the DNA-binding activity of the transcription factor STAT1 was studied by electromobility shift assay in the human keratinocyte cell line NCTC 2544. The STAT1-binding activity exhibited a biphasic pattern as a function of UVA doses. For UVA doses lower than 0.6 J/cm(2), a dose-dependent increase in STAT1 activity was observed. In a second phase, with higher UVA doses (1.5 to 9 J/cm(2)), the activity decreased and reached control value at 6 J/cm2. The enhancement of STAT1 activity was transient, peaked at 1 h after UV irradiation, and regularly decreased to control value 24 h after UV. Genistein, a tyrosine kinase inhibitor, H7, a serine/threonine kinase inhibitor, and PD 98059, a MEK inhibitor, prevented the UVA-induced enhancement of STAT1-binding activity, suggesting the involvement of Tyr, Ser/Thr kinases, and MEK in the observed effect. Immunoblot analysis directly demonstrated that the amount of Tyr-phosphorylated STAT1 was parallel to its DNA-binding activity. Immunoblot analysis also demonstrated the nuclear transport of STAT1 after UVA irradiation at low doses. At high doses, a decrease in the STAT1 level was observed both in the cytoplasmic and the nuclear compartments, suggesting that the inactivation was due to a degradation process. UVA irradiation initiated a dose-dependent increase in lipid peroxidation products and reactive oxygen species. Furthermore, the involvement of the oxidative stress in the UVA-induced effect on STAT1 activity is suggested by the protective action of the antioxidants alpha-tocopherol and N-acetylcysteine on both the activation phase (UVA doses lower than 1.5 J/cm(2)) and the inhibitory phase. By contrast, the pro-oxidant drug buthionine sulfoximine enhanced the effect of UVA on STAT1-binding activity. Since STATs are known as transducers of cytokine action, the enhancement of STAT1 activity by low doses of UVA might be related to the proinflammatory effect of solar radiations at the skin level.

In-vivo and in-vitro assessment of the free-radical-scavenger activity of Ginkgo flavone glycosides at high concentration

Free radicals are involved in numerous skin diseases, especially inflammatory reactions and photosenescence. To identify possible free-radical scavenging by an original terpene-free Ginkgo biloba extract containing 33% Ginkgo flavone glycosides, mostly quercetin and kaempferol derivatives, we studied its activity by means of in-vitro and in-vivo experiments, using superoxide dismutase (SOD) as a positive control. By means of an in-vitro electron-spin resonance (ESR) assay we compared the activity of the Ginkgo extract with that of its two aglycones, quercetin and kaempferol. Quercetin and Ginkgo extract had significant antioxidant properties without pro-oxidant effect. In contrast, kaempferol, above an optimum antioxidant concentration, behaved as a pro-oxidant. The in-vivo experiments were conducted on an anti-inflammatory model. The cutaneous blood flux which reflects the skin inflammatory level was recorded by means of a laser Doppler perfusion imager. The data confirmed the free-radical-scavenging property of both Ginkgo extract and SOD. The Ginkgo extract significantly inhibited (37%) cutaneous blood flux to the same extent as SOD. These data confirmed the antioxidant property of Ginkgo extract. A complementary spin-trapping technique would enable identification of the free radicals involved. This Ginkgo extract should be useful for protection of the skin against free radicals.

Cyclooxygenase dependent release of heme from microsomal hemeproteins correlates with induction of heme oxygenase 1 transcription in human fibroblasts

Induction of heme oxygenase 1 transcription and enzymatic activity is a common response after exposure of cells to various forms of oxidative stress including ultraviolet A radiation (UVA) and hydrogen peroxide. We now show that UVA irradiation or hydrogen peroxide treatment of human skin fibroblasts leads to an immediate release of the heme oxygenase substrate, heme, from microsomal hemeproteins. The release of heme by UVA apparently involves cyclooxygenase activity because it is inhibited by the cyclooxygenase inhibitor indomethacin. We also demonstrate a high degree of correlation between the amount of heme released and the degree of subsequent induction of heme oxygenase 1 transcription following UVA and hydrogen peroxide treatment. We propose that release of heme from microsomal hemeproteins determines the degree of induction of heme oxygenase 1 transcription in human fibroblasts after oxidative stress.

Potentials and limitations of the natural antioxidants RRR-alpha-tocopherol, L-ascorbic acid and beta-carotene in cutaneous photoprotection

Sun exposure has been linked to several types of skin damage including sun burn, photoimmunosuppression, photoaging and photocarcinogenesis. In view of the increasing awareness of the potentially detrimental long term side effects of chronic solar irradiation there is a general need for safe and effective photoprotectants. One likely hypothesis for the genesis of skin pathologies due to solar radiation is the increased formation of reactive oxidants and impairment of the cutaneous antioxidant system. Consequently, oral antioxidants that scavenge reactive oxidants and modulate the cellular redox status may be useful; systemic photoprotection overcomes some of the problems associated with the topical use of sunscreens. Preclinical studies amply illustrate the photoprotective properties of supplemented antioxidants, particularly RRR-alpha-tocopherol, L-ascorbate and beta-carotene. However, clinical evidence that these antioxidants prevent, retard or slow down solar skin damage is not yet convincing. The purpose of this review is to provide the reader with current information on cutaneous pathophysiology of photoxidative stress, to review the literature on antioxidant photoprotection and to discuss the caveats of the photo-oxidative stress hypothesis.

Singlet molecular oxygen ((1)O2): a possible effector of eukaryotic gene expression

Biological processes involving light may have both beneficial (photosynthesis) and destructive (photosensitization) consequences. Singlet molecular oxygen, (1)O2, and other reactive oxygen species such as hydrogen peroxide and hydroxyl radical, arise during the interaction of light with photosensitizing chemicals in the presence of molecular oxygen. (1)O2 oxidizes macromolecules such as lipids, nucleic acids, and protein, depending on its intracellular site of formation; and promotes detrimental processes such as lipid peroxidation, membrane damage, and cell death. Photochemical reactive oxygen species (ROS) generating systems induce the expression of several eukaryotic genes, which include stress proteins, early response genes, matrix metalloproteinases, immunomodulatory cytokines, and adhesion molecules. These gene expression phenomena may belong to cellular defensive mechanisms, or may promote further injury. Whereas the signal transduction pathways that link site-specific oxidative damage and gene expression are poorly understood, ROS may affect signalling components in the membrane, cytosol, or nucleus, leading to changes in phospholipase, cyclooxygenase, protein kinase, protein phosphatase, and transcription factor activities. Limited evidence for (1)O2 involvement in gene activation phenomena consists of deuterium oxide solvent effects, inhibition by (1)O2-quenchers, sensitization by porphyrins, chemical trapping methods, and comparative effects of photosensitizing dyes and thermolabile endoperoxides. The studies outlined in this review support an hypothesis that (1)O2 and other ROS generated during photochemical processes such as ultraviolet-A (320-380 nm) radiation exposure, or photosensitizer mediated oxidation may have dramatic effects on eukaryotic gene expression.

Molecular and cellular effects of ultraviolet light-induced genotoxicity

Exposure to the solar ultraviolet spectrum that penetrates the Earth's stratosphere (UVA and UVB) causes cellular DNA damage within skin cells. This damage is elicited directly through absorption of energy (UVB), and indirectly through intermediates such as sensitizer radicals and reactive oxygen species (UVA). DNA damage is detected as strand breaks or as base lesions, the most common lesions being 8-hydroxydeoxyguanosine (8OHdG) from UVA exposure and cyclobutane pyrimidine dimers from UVB exposure. The presence of these products in the genome may cause misreading and misreplication. Cells are protected by free radical scavengers that remove potentially mutagenic radical intermediates. In addition, the glutathione-S-transferase family can catalyze the removal of epoxides and peroxides. An extensive repair capacity exists for removing (1) strand breaks, (2) small base modifications (8OHdG), and (3) bulky lesions (cyclobutane pyrimidine dimers). UV also stimulates the cell to produce early response genes that activate a cascade of signaling molecules (e.g., protein kinases) and protective enzymes (e.g., haem oxygenase). The cell cycle is restricted via p53-dependent and -independent pathways to facilitate repair processes prior to replication and division. Failure to rescue the cell from replication block will ultimately lead to cell death, and apoptosis may be induced. The implications for UV-induced genotoxicity in disease are considered.

Ultraviolet-A induces activation of AP-1 in cultured human keratinocytes

UV-A irradiation induces a time-dependent activation of AP-1 in NCTC 2544 human keratinocytes. 4 h after irradiation, a 2-3-fold increase in AP-1 activity is observed in human keratinocytes and fibroblasts. Activation is still detectable 24 h later. The UV-A induced AP-1 binding complex is shown to contain c-Fos and c-Jun proteins. Lipophilic vitamin E impedes UV-A induced lipid peroxidation but does not prevent AP-1 activation which is inhibited by N-acetylcysteine, a hydrophilic antioxidant. This finding suggests that UV-A-dependent AP-1 activation is sensitive to the cellular redox state but is not related to membrane lipid peroxidation.

Lipid metabolite involvement in the activation of the human heme oxygenase-1 gene

Cellular effects of ultraviolet A (UVA) radiation include peroxidation of membrane lipids as well as a decrease in intracellular glutathione. We have investigated whether damage to membrane lipids is involved in the activation of the human heme oxygenase-1 gene by UVA. Irradiation of human skin fibroblasts in the presence of the lipophilic antioxidants, butylated hydroxytoluene and alpha-tocopherol, enhances the UVA-induced HO-1 mRNA accumulation, suggesting that peroxidation of plasma membrane lipids is not involved. Furthermore, sodium ascorbate, which induces lipid peroxidation mainly in the plasma membrane, induces HO-1 mRNA to low levels only. The decrease in GSH by UVA radiation is not affected by the presence of the lipophilic antioxidants while ascorbate treatment increases the intracellular GSH by twofold above controls. These results indicate that peroxidation of internal membrane lipids, a decrease in the intracellular GSH levels and the integrity of the plasma membrane are all important for the UVA-induction of heme oxygenase-1. Both nonenzymatic as well as enzymatic lipid peroxidation metabolites are inducers of heme oxygenase-1. The nonenzymatic lipid peroxidation product 4-hydroxynonenal induces heme oxygenase-1 mRNA up to 40-fold and the phospholipase metabolites diacylglycerol and arachidonic acid induce this mRNA by three-to sixfold above basal levels. We also demonstrate that the cyclooxygenase metabolites of arachidonic acid are important for the UVA-activation of the heme oxygenase-1 gene.

Ultraviolet action spectra for photobiological effects in cultured human lens epithelial cells

The action spectrum for cell killing by UV radiation in human lens epithelial (HLE) cells is not known. Here we report the action spectrum in the 297-365 nm region in cultured HLE cells with an extended lifespan (HLE B-3 cells) and define their usefulness as a model system for photobiological studies. Cells were irradiated with monochromatic radiation at 297, 302, 313, 325, 334 and 365 nm. Cell survival was determined using a clonogenic assay. Analysis of survival curves showed that radiation at 297 nm was six times more effective in cell killing than 302 nm radiation; 297 nm radiation was more than 260, 590, 1400 and 3000 times as effective in cell killing as 313, 325, 334 and 365 nm radiation, respectively. The action spectrum was similar in shape to that for other human epithelial cell lines and rabbit lens epithelial cells. The effect of UV radiation on crystallin synthesis was also determined at different wavelengths. To determine whether exposure to UV radiation affects the synthesis of beta-crystallin, cells were exposed to sublethal fluences of UV radiation at 302 and 313 nm, labeled with [35S]methionine and the newly synthesized beta-crystallin was analyzed by immunoprecipitation and western blotting using an antibody to beta-crystallin. The results show a decrease in crystallin synthesis in HLE cells irradiated at 302 and 313 nm at fluences causing low cytotoxicity. The effect of radiation on membrane perturbation was determined by measuring enhancement of synthesis of prostaglandin E2 (PGE2). Synthesis of PGE2 occurs at all UV wavelengths tested in the 297-365 nm region.(ABSTRACT TRUNCATED AT 250 WORDS)

Excimer laser photorefractive keratectomy

Excimer laser photorefractive keratectomy has been used for the correction of myopia, hyperopia and astigmatism. This laser removes tissue through a process termed photoablative decomposition, in which incident photon energy is sufficient to break molecular bonds. Selective removal of tissue across the anterior corneal surface results in a change in anterior corneal curvature. The surgical outcome may be influenced also by interindividual variability in wound healing and pharmacologic interventions. The nature of the excimer laser-tissue interaction, and clinical outcomes of predictability, stability and complications of surgery for myopia are discussed in detail.

Polyunsaturated fatty acid enrichment increases ultraviolet A-induced lipid peroxidation in NCTC 2544 human keratinocytes

The influence of cell enrichment with fatty acids with increasing degree of unsaturation on the ultraviolet A-induced formation of lipid-peroxidation products (thiobarbituric acid reactive substances [TBARS]) has been investigated in NCTC 2544 human keratinocytes. A 48-h preculture of cells in controlled medium supplemented with unsaturated fatty acids resulted in a marked increase in TBARS appearance under ultraviolet A exposure. This effect was dependent upon the degree of unsaturation of the fatty acids, with the following order of efficiency: arachidonic > linolenic > linoleic > oleic acid. For arachidonic acid (AA), the potentiating effect on ultraviolet A-induced lipid peroxidation was dependent upon the fatty acid concentration, with about a 2.5-fold increase in TBARS formation in cells pre-cultured with 5 x 10(-5) M AA, then exposed to a UVA dose of 13 J/cm2. The increase in TBARS formation by AA was almost totally prevented by supplementation of cells with 5 x 10(-5) M vitamin E, whereas buthionine sulfoximine, a chemical which depletes cell glutathione, potentiated lipid peroxidation. These results suggest that the nature of the fatty acids of cellular lipids could influence the response of keratinocytes to ultraviolet A, and especially the ultraviolet A-induced lipid peroxidation.

Keratinocytes and fibroblasts in a human skin equivalent model enhance melanocyte survival and melanin synthesis after ultraviolet irradiation

To investigate paracrine effects of fibroblasts and keratinocytes on melanocyte behavior after ultraviolet (UV) irradiation, we compared an in vitro skin equivalent model with melanocyte cultures. Human melanocytes were maintained alone in monolayer cultures or on dermal equivalents with or without keratinocytes and were irradiated daily with solar-simulated light. After seven daily UV irradiations, monolayer melanocytes displayed dose-dependent increases in cellular damage. In contrast, melanocytes on dermal equivalents survived strikingly better. Moreover, UV-irradiated skin equivalent melanocytes became highly dendritic as compared with sham-irradiated cells, closely mimicking their morphology in UV-irradiated skin. In addition, in skin equivalents melanocytes migrated from the center to the periphery of the keratinocyte layer after UV irradiation. Melanin production per culture, as measured by 14C-dihydroxyphenylalanine incorporation, was consistently higher in skin equivalent melanocytes than in monolayer melanocytes from the same donor, and it was highest in melanocytes from skin equivalents containing both keratinocytes and fibroblasts. Our data strongly suggest that fibroblasts and keratinocytes modulate melanocyte function in skin. The skin equivalent is a valuable model for investigating paracrine effects on melanocytes after UV irradiation.

Photodynamic action of ultraviolet A: induction of cellular hydroperoxides

Long-wavelength ultraviolet radiation (UVA) can cause cancer. A carcinogenic mechanism involved may be the induction of harmful reactive oxygen species resulting from photodynamic effects. UVA is generally assumed to induce photodynamic effects, but evidence from experiments with viable biological materials has been indirect until present. Here we measured the induction of (lipid) hydroperoxides as direct indicators of photodynamic reactions. Cultured human fibroblasts were irradiated with 10J UVA/cm2. The induced hydroperoxides were measured by an enzymatic method using glutathione peroxidase and glutathione reductase (GR). Additionally, reduced glutathione (GSH) was determined as parameter for the constitutive antioxidant defense. UVA was found to increase lipid hydroperoxides in fibroblasts by 116% (p < 0.001), when compared to nonirradiated controls. Conversely GSH was decreased in the irradiated cells by 51% (p < 0.001). Because of the induced hydroperoxides, it is concluded that the UVA effects were mediated by a photodynamic mechanism. The photodynamic mechanism resulted in the formation of reactive oxygen species and the consumption of constitutive antioxidants. This suggests a role for antioxidants during the photodynamic mechanism. Photodynamic mechanisms may play a crucial role in carcinogenic events, especially after UVA.

Cell membrane, a target for PUVA therapy

The photochemical reactions occurring in the cell membranes, sensitized photo-oxidation and psoralen photoaddition to lipids, are briefly reviewed. Phospholipid dynamics in the membrane structure, based on erythrocyte lipid organization, are described. Evidence for alterations of cell membrane functions under psoralen plus UVA radiation (PUVA) treatment in a variety of mammalian cells is presented. Cell receptor dysfunctions under PUVA treatment are demonstrated in a number of biological investigations. The purpose of this survey is to illustrate the feasibility of studying psoralen photobiology with phospholipids. The reaction of psoralens with phospholipids is considered to be one of the triggering mechanisms of the subsequent physiological responses, which may be relevant to PUVA photochemotherapy.

Inhibition of diphosphatidylglycerol synthesis by u.v. A radiations in N.C.T.C. 2544 human keratinocytes

The effects of u.v. A radiations on phospholipid synthesis were studied in the N.C.T.C. 2544 human keratinocyte cell line, by using [14C]arachidonic acid, [14C]oleic acid or sodium [32P]orthophosphate as precursors. Cells were irradiated in Hanks' medium with 365 nm light at doses up to 19 J/cm2, and then phospholipid synthesis from the three precursors was studied. Under these conditions, only small alterations in the incorporation pattern of [14C]arachidonic into phospholipids [phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI)] were observed, for u.v. A irradiation doses up to 19 J/cm2. In contrast, with [14C]oleic acid as precursor, two additional spots were observed, which co-migrate with pure phosphatidylglycerol (PG) and diphosphatidylglycerol (DPG) standards. The incorporation of [14C]oleic acid into PG and DPG was decreased in a dose-dependent manner after u.v. A exposure, with about 50% and 75% decreases at 9.5 J/cm2 and 19 J/cm2 respectively. As for arachidonic acid incorporation, no significant differences in the synthesis of the major phospholipids (PC, PE, PI) were noted upon u.v. A exposure. The dramatic and selective decrease in PG and DPG syntheses was confirmed with [32P]orthophosphate as precursor. As DPG is a specific component of the mitochondrial inner membrane, it appears that one of the early kinds of damage induced by u.v. A irradiation could be the impairment of mitochondrial functions.

Ultraviolet A decreases epidermal growth factor (EGF) processing in cultured human fibroblasts and keratinocytes: inhibition of EGF-induced diacylglycerol formation

The binding, uptake, and degradation of epidermal growth factor (EGF) has been studied in MRC5 human fibroblasts and NCTC 2544 human keratinocytes following ultraviolet A (UVA) irradiation at doses up to 18.9 J/cm2, which are not lethal to cells under our experimental conditions. A dose-dependent reduction in EGF binding was observed, with an approximately 75% decrease at the maximal studied UVA dose. At lower doses (6 to 12 J/cm2), EGF binding was more affected by ultraviolet A in fibroblasts than in keratinocytes. In both cell types, this effect of UVA appeared to be related to a reduction of the affinity of the EGF receptor for EGF. Kinetic studies by pulse-chase experiments indicated that EGF is more rapidly internalized by keratinocytes than by fibroblasts, and that UVA exposure resulted in a slower decay of EGF intracellular content. A 24-h pretreatment of cells with 5 x 10(-5) M vitamin E strongly reduced the appearance of light-induced lipid peroxidation products, measured via assay of thiobarbituric acid reactive substances formation, but only partially prevented the UVA-induced alterations of EGF processing by cells. Finally, UVA exposure almost completely abolished the EGF-induced increase in diacylglycerol production from 14C-arachidonic acid-labeled lipids in both cell types. These results demonstrate that UVA radiation induces important changes in EGF processing and could participate in the light-induced degenerative processes of the skin.

Protection against ultraviolet B radiation-induced effects in the skin of SKH-1 hairless mice by a polyphenolic fraction isolated from green tea

In prior studies we and others have shown that oral feeding of a polyphenolic fraction isolated from green tea (GTP) or water extract of green tea affords protection against ultraviolet B (UVB) radiation-induced carcinogenesis in SKH-1 hairless mice (Wang et al., Carcinogenesis 12, 1527-1530, 1991). It is known that exposure of murine skin to UVB radiation results in cutaneous edema, depletion of the antioxidant-defense system and induction of ornithine decarboxylase (ODC) and cyclooxygenase activities. In this study we assessed the protective effect of GTP on these UVB radiation-caused changes in murine skin. Oral feeding of 0.2% GTP (wt/vol) as the sole source of drinking water for 30 days to SKH-1 hairless mice followed by irradiation with UVB (900 mJ/cm2) resulted in significant protection against UVB radiation-caused cutaneous edema (P < 0.0005) and depletion of the antioxidant-defense system in epidermis (P < 0.01-0.02). The oral feeding of GTP also resulted in significant protection against UVB radiation-caused induction of epidermal ODC (P < 0.005-0.01) and cyclooxygenase activities (P < 0.0001) in a time-dependent manner. Our data indicate that the inhibition of UVB radiation-caused changes in these markers of tumor promotion in murine skin by GTP may be one of the possible mechanisms of chemopreventive effects associated with green tea against UVB-induced tumorigenesis. The results of this study suggest that green tea, specifically polyphenols present therein, may be useful against inflammatory responses associated with the exposure of skin to solar radiation.

Ultraviolet radiation-induced phospholipase A2 activation occurs in mammalian cell membrane preparations

Ultraviolet erythema in human skin is mediated in part by membrane derivatives of arachidonic acid (AA). UVA (320-400 nm) and UVB (290-320 nm) have been shown to induce release of AA from intact mammalian cells in culture. In order to investigate the mechanism of this release we examined the effect of UVA and UVB on release of [3H] AA from membrane preparations of murine fibroblasts. C3H 10T1/2 cells were prelabelled for 24 h with [3H] AA. The membrane fractions of the cells were separated after lysis by differential centrifugation. The membranes were irradiated in suspension and the [3H] AA released from the membranes was determined by scintillation spectroscopy of supernatants 3-4 h after irradiation. Both UVA and UVB induced release of AA from the membrane preparations. The response to UVB was small but significant, reaching levels approximately 150% of control release at doses of 1,200-4,000 J/m2. The response to UVA was larger; doses of 2.5-5.0 J/cm2 induced release equal to twice control (200%) levels, while doses of 10-20 J/cm2 induced maximal release at levels approximately 400% of control. Time course studies with UVB and UVA showed maximal release at 4 h after irradiation. When the membrane preparations were incubated with a polyclonal anti-phospholipase A2 antibody the UV induced release of [3H] AA was completely inhibited in both UVB (1200 J/m2) and UVA (10 J/cm2) treated cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of UV-induced inflammation

The inflammation produced by exposure to ultraviolet (UV) light has been well documented clinically and histologically. However, the mechanisms by which mediators induce this clinical response remain poorly defined. It is clear that photochemistry occurring after UV absorption must be responsible for initiating these events. Some of these underlying mechanisms have been defined. After exposure to UV light, the formation of prostaglandins and the release of histamine are increased. In addition to an increase in the quantity of these mediators, an increase in sensitivity of irradiated tissue to agonist stimulation also occurs. This increased sensitivity may cause tissue to respond to agonist levels previously present. Phospholipase activity also increases, making more substrate available for prostaglandin formation. Oxygen radical-induced peroxidation of membrane lipids caused by irradiation may contribute to increased phospholipase activity. Oxygen-free radicals also participate in sunburn cell formation and in UV-induced decreases in Langerhans cell numbers. Several enzymatic and non-enzymatic mechanisms are present in skin for reducing these highly reactive oxygen species.

Ultraviolet light irradiation increases cellular diacylglycerol and induces translocation of diacylglycerol kinase in murine keratinocytes

Cellular lipid metabolism can provide a variety of mediators of signal transduction, including diacylglycerols and inositol phosphates. These factors may be involved in the control of epidermal differentiation and proliferation because they are modulated by extracellular calcium, which also regulates the maturation phenotype of cultured keratinocytes. The effect of non-cytotoxic exposures to ultraviolet light on lipid metabolism was studied in cultured murine keratinocytes. Ultraviolet treatment of cultured murine keratinocytes growing in 0.05 mM Ca++ did not significantly change the total amount of [3H]inositol phosphates at 0.5, 8 or 24 h post-irradiation. Irradiated cells responded to an increase from 0.05 mM Ca++ to 1.4 mM Ca++ medium with increased formation of inositol phosphates suggesting irradiation did not alter the normal inositol lipid turnover in response to the Ca++ signal for terminal differentiation. Irradiation (20-120 J/m2 of UVB) induced a dose-dependent increase in the cellular level of diacylglycerols as measured at 24 h post-irradiation, without changing the turnover of other phospholipids including phosphatidylcholine and phosphatidylethanolamine. The increased cellular levels of diacylglycerols following ultraviolet exposure were accompanied by changes in the activity of diacylglycerol kinase (DAG-kinase). The cytosolic DAG-kinase activity was decreased whereas the DAG-kinase activity in the membrane fraction was increased. These results suggest that ultraviolet irradiation increases the level of diacylglycerols via changes in de novo metabolism through a DAG-kinase pathway. Elevated diacylglycerol may influence signal-transduction pathways mediated by cellular lipids and contribute to some keratinocyte responses to ultraviolet light.

Turnover of phospholipids in HUT 102 lymphoblasts and chromatographic characterization of purified lecithins after their exposure to long-wave UV light, psoralen, and UV light and psoralen

The turnover of 32P-labeled phospholipids in HUT 102 lymphoblasts was determined after a 2 h interaction of lymphoblasts with 8-methoxypsoralen (8-MOP) (15 micrograms ml-1), longwave UV light (UVA) irradiation and PUVA (8-MOP and UVA). In parallel experiments, micellar suspensions of lyso-phosphatidylcholine (PtdC), dipalmitoyl-PtdC and dilinoleoyl-PtdC, treated in a similar manner, served for the correlative assessments of cellular lipid changes. The dark reaction, UVA irradiation and PUVA all depressed total phospholipid levels in HUT 102 cells, although only PUVA induced a statistically significant decline. Thin layer chromatography (TLC) analysis revealed that neither UVA nor 8-MOP alone triggered any significant changes in the cellular content of phosphatidylinositol (PtdI), phosphatidylinositol 4-monophosphate (PtdIP) and phosphatidylinositol 4,5-bisphosphate (PtdIP2), whereas the lyso-PtdC and PtdI content of lymphoblasts showed a two-fold increase after PUVA. The TLC analysis of lyso-PtdC and micelles of dipalmitoyl-PtdC did not reveal any detectable changes after the dark reaction with 8-MOP, UVA irradiation and PUVA. In contrast, the derivatives of dark and UVA mediated reactions of 8-MOP with dilinoleoyl-PtdC were detected by TLC. These results suggest that the formation of 8-MOP derivatives of cellular phospholipids effected by PUVA, modulates the turnover of phosphoinositides and the rate of cellular proliferation.

Photoreactivation of ultraviolet radiation-induced release of arachidonic acid from marsupial cells

Exposure of an established marsupial cell line, PtK2 (Potorous tridactylus), to ultraviolet radiation (UVR) from an FS-40 sunlamp (280-400 nm) resulted in a fluence-dependent release of radiolabeled arachidonic acid (AA) from cell membranes. Post-UVR, but not pre-UVR, exposure to photoreactivating light reversed UVR-induced pyrimidine dimers in DNA and suppressed the UVR-induced release of AA. These data indicate that DNA damage contributes to the release of AA from membrane phospholipids.

Ferrous ion release from ferritin by ultraviolet-A radiations

Ferritin is the principal protein of iron storage (in the Fe(III) state). The UV-A irradiation of 0.25 microM ferritin solutions (from horse spleen) loaded with 530 microM Fe(III) induces Fe2+ release in the medium. The initial quantum yield is wavelength dependent (phi(365 nm) approximately 2 x 10(-3) but pH and oxygen independent. The Fe2+ release reaches a plateau which strongly depends on pH and oxygen. The amino acid composition of the apoprotein is not altered by the UV irradiation. Addition of formate ions enhances the Fe2+ production, suggesting that the ferritin photoreduction involves an electron transfer from an OH- ligand. The possible importance of this phenomenon in skin photobiology is discussed.

UVA-induced lipid peroxidation in cultured human fibroblasts

The UVA irradiation of cultured human fibroblasts leads to the formation and to the release of thiobarbituric acid-reactive substances in the supernatant. The major thiobarbituric acid-reactive substance is identified by fluorescence spectroscopy and HPLC, as malondialdehyde or malondialdehyde-forming substances under the thiobarbituric acid assay conditions. Malondialdehyde formation strongly suggests a UVA-induced lipid peroxidation. Lipid peroxidation is also supported by the inhibitory effect of D,L-alpha-tocopherol, the well-known chain breaking antioxidant, by the additional malondialdehyde formation in the dark after the photooxidative stress and by membrane damage revealed by lactate dehydrogenase leakage.

Photomodulation of enzymes

The photomodulation of enzymes involves the activation and inactivation of enzyme reactions by UV and visible light. Enzymes or their reactions may be affected directly or indirectly. Direct effects involve photoproduction of a substrate, photodissociation of an inhibitor, photochemistry of protein amino acids, irradiation of a chromophore and irradiation of an enzyme substrate. Indirect effects involve gene expression, phytochrome and other photoreceptors which are not part of the enzyme, protein synthesis, membranes and photosynthesis. Photoactivation of enzymes is related to photocarcinogenesis, photomorphogenesis of plants, primary effects or side effects of phototherapy, deoxyribose nucleic acid (DNA) repair and many other aspects of biology and medicine. Model systems may contribute to the knowledge of protein chemistry and medicinal chemistry.

Effects of in vitro UVA irradiation and PUVA treatment on membrane fatty acids and activities of antioxidant enzymes in human keratinocytes

Human Keratinocytes (NCTC 2544) in culture were exposed to either plain ultraviolet A (UVA) irradiation or to 8-methoxypsoralen plus UVA (PUVA) treatment. Lipid peroxidation, activities of antioxidant enzymes, and percentage amounts of 14C-arachidonic acid in various cellular lipid subclasses and in the culture medium were measured. Both UVA irradiation and PUVA treatment induced significant changes in the distribution of arachidonic acid and increased the liberation of arachidonic acid from membrane phospholipids. At 24 h after either UVA irradiation or PUVA treatment the formation of thiobarbituric acid reactive material was significantly increased, whereas the amount of conjugated dienes was unaffected. The activities of the antioxidant enzymes, catalase and superoxide dismutase, were already significantly decreased at 0.5 h after UVA irradiation or PUVA treatment. The enzyme activities were partially restored during the following 24 h incubation. From the present study, we suggest that in keratinocytes both plain UVA irradiation and PUVA treatment induce changes in the distribution of membrane fatty acids and cause an impairment in the enzymic defense system against oxidative stress.

Production of hydrogen peroxide by cutaneous T-cell lymphoma following photopheresis with psoralens and ultraviolet light

Treatment of peripheral blood mononuclear cells with 8-methoxypsoralen (8-MOP) and ultraviolet light, a procedure known as PUVA, has been found to be useful in the management of systemically disseminated cutaneous T-cell lymphoma (CTCL). In the present study we used a highly sensitive flow cytometric assay in conjunction with the hydroperoxide-sensitive dye 2',7'-dichlorofluorescein diacetate to measure intracellular hydrogen peroxide in normal lymphocytes and CTCL following PUVA treatment. Based on their laser light-scattering properties, lymphocytes were separated into three major subpopulations. We found that ultraviolet light alone caused an increase in the hydrogen peroxide content of each of the subpopulations, a response that was augmented when the cells were pretreated with 8-MOP (50 ng/ml). Cells from CTCL patients were more sensitive to the effects of 8-MOP than were normal lymphocytes. In both cell types, the production of hydrogen peroxide was found to be inhibitable by catalase. We noted an increase in hydrogen peroxide production following photopheresis; however, this was observed only 24 h after treatment. In addition, a further increase in hydrogen peroxide production was observed in lymphocytes isolated from peripheral blood that had been obtained from patients at 15 min after a second photopheresis treatment. Hydrogen peroxide is known to modulate the action of cytokines as well as the immunological responses of leukocytes. Our data suggest that the production of hydrogen peroxide by lymphocytes may be important in the action of PUVA in CTCL.

Long-wave ultraviolet light induces phospholipase activation in cultured human epidermal keratinocytes

Long wave ultraviolet radiation (UVA) has been shown to play an important role in the overall response of skin to solar radiation, including sunburn, tanning, premature aging, and non-melanoma skin cancer. UVA induction of inflammation in human skin is thought to be mediated by membrane lipid derived products. In order to investigate the mechanism of this response we examined the effect of UVA on phospholipid metabolism of human epidermal keratinocytes in culture. Keratinocytes were grown in serum free low calcium medium. The cells were prelabeled with [3H] arachidonic acid or [3H] choline and irradiated with UVA (Honle 2002-Hg vapor lamp). Identification and quantitation of specific membrane phospholipid-derived components was achieved using high-performance liquid chromatography, paper chromatography, and radioimmunoassay. UVA resulted in a linear dose dependent release of [3H] arachidonic acid into medium between 1 and 20 joule/cm2. This response was inhibited in an oxygen-reduced environment. The radiolabel released was predominantly free arachidonate and cyclooxygenase metabolites. Cyclooxygenase metabolites prostaglandin E2 and prostacyclin derivative, 6-keto-prostaglandin F1a, were stimulated following UVA irradiation, but the lipoxygenase metabolite, leukotriene B was not detected. Maximal release was measured immediately after irradiation and changed little over 24 h post-irradiation. UVA stimulated an increase of [3H] choline metabolites glycerophosphorylcholine and phosphorylcholine in media extracts suggesting UVA activation of phospholipase C and phospholipase A2 or diacylglyceride lipase.