Depletion of cutaneous glutathione and the induction of inflammation by 8-methoxypsoralen plus UVA radiation

The Roles of Vitamin C in Skin Health

The primary function of the skin is to act as a barrier against insults from the environment, and its unique structure reflects this. The skin is composed of two layers: the epidermal outer layer is highly cellular and provides the barrier function, and the inner dermal layer ensures strength and elasticity and gives nutritional support to the epidermis. Normal skin contains high concentrations of vitamin C, which supports important and well-known functions, stimulating collagen synthesis and assisting in antioxidant protection against UV-induced photodamage. This knowledge is often used as a rationale for the addition of vitamin C to topical applications, but the efficacy of such treatment, as opposed to optimising dietary vitamin C intake, is poorly understood. This review discusses the potential roles for vitamin C in skin health and summarises the in vitro and in vivo research to date. We compare the efficacy of nutritional intake of vitamin C versus topical application, identify the areas where lack of evidence limits our understanding of the potential benefits of vitamin C on skin health, and suggest which skin properties are most likely to benefit from improved nutritional vitamin C intake.

Action of bis(betachloroethyl)sulphide (BCES) on human epidermis reconstituted in culture: Morphological alterations and biochemical depletion of glutathione

Human keratinocyte cultures were treated with bis(betachloroethyl)sulphide (BCES), an alkylating and vesicant agent. At concentrations of 5 x 10(-4) to 5 x 10(-3)m, spontaneous detachment of the epithelium from the culture plate was observed, reproducing in vitro the cutaneous vesication observed in vivo. Progressive cellular alterations were shown with increasing concentrations of BCES (5 x 10(-5) to 5 x 10(-3)m). At low concentrations (5 x 10(-5)m), lesions of the nucleus, a significant target for BCES, were observed, along with lesions in the cytoplasmic organelles. An acute, dose-dependent depletion of cellular glutathione was observed, which occurred within 1 hr of treatment. Mechlorethamine, an analogue of BCES, induced at equivalent doses the same glutathione depletion and similar spontaneous detachment in vitro. We suggest that BCES, in addition to its genetic effects, acts by direct metabolic toxicity and induces glutathione depletion by direct conjugation. The lesions obtained in vitro reproduced those observed in vivo. Human keratinocyte cultures can be proposed as a good model for the study of the mechanisms of action of BCES.

Development of a quercetin-loaded nanostructured lipid carrier formulation for topical delivery

The main objective of this study was to evaluate the potential of quercetin-loaded nanostructured lipid carriers (QT-NLCs) as a topical delivery system. QT-NLCs were prepared by the method of emulsion evaporation-solidification at low temperature. The average entrapment efficiency and drug loading of the optimized QT-NLCs were 89.95 ± 0.16% and 3.05 ± 0.01%, respectively. Under the transmission electron microscope, the nanoparticles were spherically shaped. The average particle size was 215.2 nm, the zeta potential was -20.10 ± 1.22 mV and pH value of QT-NLCs system was 4.65. Topical delivery of QT in the form of NLCs was investigated in vitro and in vivo. The results showed that QT-NLCs could promote the permeation of QT, increase the amount of QT retention in epidermis and dermis, and enhance the effect of anti-oxidation and anti-inflammation exerted by QT. Then the mechanism of NLCs for facilitating drug penetration was further investigated through histological sections. In conclusion, NLCs could be a promising vehicle for topical delivery of QT.

Vitiligo treatment with vitamins, minerals and polyphenol supplementation

BACKGROUND

Mammalian pigmentation results from the synthesis and accumulation of photo protective epidermal melanin. Melanin was formed from the amino acid precursor L-tyrosine within specialized cells, the melanocytes. Oxidative stress has been suggested to be the initial pathogenetic event in melanocyte degeneration with H(2)O(2) accumulation in the epidermis of patients with active disease. Auto immunity has been also suggested as another hypothesis in the pathogenesis of depigmentation disorders. Topical corticosteroids and phototherapy as common treatment modalities have been prescribed in patients with vitiligo. However, they are often not effective and safe (epidermal atrophy). Therefore, research for alternative therapies continues.

AIMS

To evaluate the beneficial effects of a supplementation with antioxidant vitamins (A, C, E) and minerals (zinc, selenium) for vitiligo treatment.

METHODS

Forty experimental autoimmune vitiligo mice C57BL6, aged from 5 to 12 months showing visible signs of induced vitiligo, were sequentially randomized into five parallel groups (8 mice per group). Each group mice was allocated an identical pre coded cage. the first group (SZV) received the ED + 1,4 g zinc (Zn) + 0.04 g selenium (Se) + vitamins (A 118 UI, C 8,5 mg, E 5,4 UI) /kg diet, the second group (PSZV) received the ED + 1,4 g zinc (Zn) + 0.04 g selenium (Se) + vitamins (A 118 UI, C 8.5 mg, E 5,4 UI)/kg diet + Polyphenol orally, the group 3 (PSZ) received the ED + green tea decoction prepared from 100 g/l (polyphenol orally) + 1,4 g Zn + 0.04 g Se, the 4 (P) received the ED + green tea decoction prepared green tea decoction prepared from 100 g/l, the control group 5(C) received the ED + distilled water. Cure was defined as repigmentation of treated sites. Photographic and optical techniques were used both at the baseline and on weekly basis.

RESULTS

By the end of the study, mice showed visible repigmentation. Using the investigator's global assessment, therapeutic success in terms of a clear repigmentation documented in 70% of treated mice.

CONCLUSION

Our findings suggest that an antioxidant supplementation is significantly beneficial in contributing superior clinical efficacy to cure vitiligo.

In vitro evaluation of quercetin cutaneous absorption from topical formulations and its functional stability by antioxidant activity

Recently, it was demonstrated that two different formulations containing quercetin inhibit the UVB-induced cutaneous oxidative stress and inflammation. Therefore, in the present study it was evaluated the functional stability of those formulations by the antioxidant activity, the release of quercetin from the formulations, and its skin retention using modified Franz diffusion cells. Both formulations tested ((1) non-ionic emulsion with high lipid content and (2) anionic emulsion with low lipid content) remained functionally (hydrogen-donating ability) stable during 180 days. Furthermore, quercetin was released from both formulations as determined using nitrocellulose membrane. In vitro antioxidant activity of retained quercetin into the skin was observed for both formulations as detected by the inhibition of malondialdehyde formation. The effect of quercetin retention was time-dependent for formulation 1. Concluding, this study demonstrates that quercetin remains functionally stable in formulations, and measuring the antioxidant activity is an efficient approach to evaluate quercetin skin retention with minimal interference of the tissue products. Furthermore, the present results on skin retention explain the previous study on quercetin in vivo activities, and together, these data suggest that formulations containing quercetin may be used as topical active products to control UVB-mediated oxidative damage of the skin.

In vivo generation of free radicals in the skin of live mice under ultraviolet light, measured by L-band EPR spectroscopy

Although free radicals may be involved in various types of UV-induced injuries, only a few in vivo studies of the generation of free radicals, including oxygen radicals, during exposure to ultraviolet light (UV) have been reported. In this study, the nitroxyl probe 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl was intravenously injected into hairless mice, and its decay was monitored in the skin with an in vivo EPR spectrometer equipped with a surface-coil-type resonator. The rate of decay of the EPR signal increased during UV (UVA+B) irradiation. This increase in signal decay was suppressed by preadministration of a spin trap, N-tert-butyl-alpha-phenylnitrone (PBN). PBN did not change the rate of signal decay in nonirradiated mice. The correlation between signal decay rate and physiological parameters such as blood velocity, blood mass, or skin temperature was low. The decay rate responded rapidly and reversibly to starting and stopping the UV illumination. Hydroxyl and peroxyl radicals caused reduction of the probe signal in vitro, and PBN inhibited only the peroxyl radical-induced signal reduction. These observations suggest that peroxyl radicals are generated in the skin of live mice during UVA+B irradiation.

Protective effect of topical formulations containing quercetin against UVB-induced oxidative stress in hairless mice

UV radiation-induced skin damages may result in pre-cancerous and cancerous skin lesions, and acceleration of skin aging. It involves an imbalance of the endogenous antioxidant system that leads to the increase of free radical levels and inflammation. Therefore, antioxidant supplementation might inhibit such imbalance. In this regard, quercetin is a promising drug, this plant derived lipophilic flavonoid presents the higher antioxidant activity among flavonoids and multiple antioxidant mechanisms. Thus, the present study investigated the possible beneficial effects of topical formulations containing quercetin to inhibit UVB irradiation-induced oxidative damages. Quercetin was administered on the dorsal skin of hairless mice using two formulations, formulation 1 (non-ionic emulsion with high lipid content) and formulation 2 (anionic emulsion with low lipid content). The UVB irradiation (0.31-3.69 J/cm(2)) induced a dose-dependent increase in the myeloperoxidase (MPO) activity (4-2708%) and depletion of reduced glutathione (GSH) (22-68%) in the skin of hairless mice after 6h. These results demonstrated that the UVB doses are not excessive, and additionally, they are lower than the doses used in other similar studies. Proteinases secretion/activity, detected by the qualitative sodium dodecyl sulphate polyacrylamide gel electrophoresis substrate-embedded enzymography (zymography), was also enhanced in the same manner as MPO activity using the UVB dose of 1.23J /cm(2). Formulations 1 and 2 inhibited the MPO activity increase (62% and 59%, respectively), GSH depletion (119% and 53%, respectively) and proteinases secretion/activity. To our knowledge, this is the first study to demonstrate the effectiveness of topical formulations containing quercetin to inhibit the UVB irradiation-induced skin damages. Thus, these data suggest the possible usefulness of topical formulations containing quercetin to prevent UVB radiation skin damages.

Phospholipase A2 inhibitors in development

To date, three isoforms of phospholipase A2 (PLA2) have been identified. Of these, the two Ca2+-dependent isoforms, secretory (sPLA2) and cytosolic phospholipase A2 (cPLA2), are targets for new anti-inflammatory drugs. The catalytic mechanisms and functions of the third isoform, Ca2+-independent cytosolic phospholipase A2 (iPLA2), are unknown at present. sPLA2 and cPLA2 are both implicated in the release of arachidonic acid and prophlogistic lipid mediators. However, recent findings provide evidence that cPLA2 is the dominant isoform in various kinds of inflammation, such as T-cell-mediated experimental arthritis. A triple function of PLA2-derived lipid mediators has been suggested: causing immediate inflammatory signs, involvement in secondary processes, e.g., superoxide free radical (O2) generation, apoptosis, or tumour necrosis factor-alpha (TNF-alpha)-cytotoxicity, and controlling the expression and activation of pivotal proteins implicated in inflammation and cell development, e.g., cytokines, adhesion proteins, proteinases, NF-kappaB, fos/jun/AP-1, c-Myc, or p21ras. In the past, research predominantly focused on the development of sPLA2 inhibitors; however, present techniques enable discrimination of cPLA2, sPLA2, and iPLA2, and specific inhibitors of each of the three isoforms are likely to appear soon. Over the last decade, between 40 and 50 sPLA2 inhibitors have been described; and the list is growing. However, of these, few have the potential for clinical success, and those that do are predominantly active site-directed inhibitors, e.g., BMS-181162, LY311727, ARL-67974, FPL67047, SB-203347, Ro-23-9358, YM-26734, and IS-741. At present, there are no likely clinical candidates emerging from the ranks of cPLA2 and iPLA2 inhibitors in development. Indications for which PLA2 inhibitors are being pursued include, sepsis, acute pancreatitis, inflammatory skin and bowel diseases, asthma, and rheumatoid arthritis. The three main obstacles to the successful development of PLA2 inhibitors include, insufficient oral bioavailability, low affinity for the enzyme corresponding to low in vivo efficacy and insufficient selectivity.

In Vivo Oxygen Radical Generation in the Skin of the Protoporphyria Model Mouse with Visible Light Exposure: An L-Band ESR Study

Although oxygen radicals are thought to play a key role in the skin injury that is caused by protoporphyria, there is no direct evidence of generation of these radicals in vivo. This study measured the generation of oxygen radicals caused by visible light non-invasively in the skin of griseofulvin-induced protoporphyria model mice, using an in vivo electron spin resonance spectrometer equipped with a surface-coil-type resonator that could detect radicals within about 0.5 mm of the skin surface. A durable nitroxyl radical was administered intravenously as a probe. Light irradiation enhanced the decay of the nitroxyl signal in griseofulvin-treated mice, whereas light irradiation did not enhance the signal decay in control mice. The enhanced signal decay was completely suppressed by intravenous administration of hydroxyl radical scavengers, superoxide dismutase or catalase, or the intraperitoneal administration of desferrioxamine. The enhanced signal decay with illumination was reversible, and quickly responded to turning the light on and off. These observations suggest that the hydroxyl radical is generated via an iron-catalyzed reaction in the skin. This paper demonstrates, for the first time, the specific generation of oxygen radicals in response to light irradiation of the skin of protoporphyria model mice.

Evaluation of the effect of ascorbic acid treatment on wound healing in mice exposed to different doses of fractionated gamma radiation

Alteration of the radiation-induced changes in wound contraction, collagen synthesis and wound histology by ascorbic acid was studied in mice exposed to 10, 16 and 20 Gy of fractionated (2 Gy/fraction) gamma radiation. The animals were given double-distilled water or ascorbic acid daily before exposure to 2 Gy/day of fractionated irradiation. A full-thickness skin wound was created on the dorsum of the irradiated mice, and the progression of wound contraction and collagen synthesis were examined and histological evaluations were carried out at various times after wounding. Irradiation caused a dose-dependent delay in wound contraction, and pretreatment with ascorbic acid resulted in a significant increase in wound contraction. The greatest increase in wound contraction was observed 6 and 9 days after wounding in both groups. Pretreatment with ascorbic acid augmented the synthesis of collagen significantly as revealed by an increase in hydroxyproline content. The collagen deposition and fibroblast and vasculature densities declined in a dose-dependent manner in groups receiving radiation alone as indicated by histological evaluation. Pretreatment with ascorbic acid ameliorated the observed effect significantly. These studies demonstrate that pretreatment with ascorbic acid resulted in a significant reduction of radiation-induced delay in wound healing as shown by earlier wound closure and increased collagen content and fibroblast and vascular densities.

Modulatory effects of an algal extract containing astaxanthin on UVA-irradiated cells in culture

UV radiation from sunlight is the most potent environmental risk factor in skin cancer pathogenesis. In the present study the ability of an algal extract to protect against UVA-induced DNA alterations was examined in human skin fibroblasts (1BR-3), human melanocytes (HEMAc) and human intestinal CaCo-2 cells. The protective effects of the proprietary algal extract, which contained a high level of the carotenoid astaxanthin, were compared with synthetic astaxanthin. DNA damage was assessed using the single cell gel electrophoresis or comet assay. In 1BR-3 cells, synthetic astaxanthin prevented UVA-induced DNA damage at all concentrations (10 nM, 100 nM, 10 microM) tested. In addition, the synthetic carotenoid also prevented DNA damage in both the HEMAc and CaCo-2 cells. The algal extract displayed protection against UVA-induced DNA damage when the equivalent of 10 microM astaxanthin was added to all three-cell types, however, at the lower concentrations (10 and 100 nM) no significant protection was evident. There was a 4.6-fold increase in astaxanthin content of CaCo-2 cells exposed to the synthetic compound and a 2.5-fold increase in cells exposed to algal extract. In 1BR-3 cells, exposure to UVA for 2 h resulted in a significant induction of cellular superoxide dismutase (SOD) activity, coupled with a marked decrease in cellular glutathione (GSH) content. However pre-incubation (18 h) with 10 microM of the either the synthetic astaxanthin or the algal extract prevented UVA-induced alterations in SOD activity and GSH content. Similarly, in CaCo-2 cells a significant depletion of GSH was observed following UVA-irradiation which was prevented by simultaneously incubating with 10 microM of either synthetic astaxanthin or the algal extract. SOD activity was unchanged following UVA exposure in the intestinal cell line. This work suggests a role for the algal extract as a potentially beneficial antioxidant.

Changes in the levels of glutathione after cellular and cutaneous damage induced by squalene monohydroperoxide

Squalene monohydroperoxide (Sq-OOH), the initial product of ultraviolet-peroxidated squalene, was used to investigate the effect of peroxidative challenge upon the glutathione contents in rabbit ear skin and primary-cultured fibroblasts derived from rabbit ear skin. The cellular reduced glutathione (GSH) contents decreased during 30-minute incubations in vitro with Sq-OOH, and oxidized glutathione (GSSG) was formed concomitantly, indicating that Sq-OOH had a potential for GSH-depleting activity in vitro. When Sq-OOH was applied topically to the skin in vivo, only GSSG contents increased significantly within 30 minutes. Moreover, pretreatment with the GSH depletors, DL-buthionine sulfoximine (BSO) and diethyl maleate (DEM), could potentiate the cytotoxicity and comedogenicity induced by Sq-OOH. These findings suggest that the endogenous antioxidant, glutathione, is quite sensitive to Sq-OOH and may be an important material for protecting cells and/or tissues against the oxidative stress induced by Sq-OOH treatment.

UVA-induced immune suppression through an oxidative pathway

Although ultraviolet B (UVB) irradiation induces local immune or systemic immune suppression, depending on the dose, the immune suppression by ultraviolet A (UVA) has not been fully investigated. In this study, we investigated the effect of UVA on the immune response in vitro and in vivo. The effect of UVA on the antigen-presenting function of epidermal cells was measured in terms of antigen-specific T cell proliferation. A murine epidermal cell suspension was exposed to UVA in vitro, pulsed with trinitrobenzenesulfonic acid, and cultured with T cells prepared from syngeneic mice previously sensitized with trinitrochlorobenzene. UVA (5-20 J per cm2) suppressed the antigen-presenting function of epidermal cells in a dose-dependent manner, accompanied with suppression of the expression of costimulatory molecules on Langerhans cells. In order to investigate the effect of an antioxidant on the immune suppression, an epidermal cell suspension was irradiated with UVA in the presence or absence of glutathione. The suppressions of antigen-presenting function and ICAM-1 expression were significantly prevented by glutathione in a dose-dependent manner. Further, the effect of UVA on the immune response at the induction phase of contact hypersensitivity was evaluated in terms of lymph node cell proliferation ex vivo. UVA irradiation suppressed the endogenous proliferation of lymph node cells in trinitrochlorobenzene-painted mice, and this suppression was significantly reversed by the application of glutathione to the skin during irradiation. These results suggest that UVA-induced immune suppression may be mediated by reactive oxygen species, at least in part.

Quercetin protects cutaneous tissue-associated cell types including sensory neurons from oxidative stress induced by glutathione depletion: cooperative effects of ascorbic acid

Oxidation reactions are essential biological reactions necessary for the formation of high-energy compounds used to fuel metabolic processes, but can be injurious to cells when produced in excess. Cutaneous tissue is especially susceptible to damage mediated by reactive oxygen species and low-density lipoprotein oxidation, triggered by dysmetabolic diseases, inflammation, environmental factors, or aging. Here we have examined the ability of the flavonoid quercetin to protect cutaneous tissue-associated cell types from injury induced by oxidative stress, and possible cooperative effects of ascorbic acid. Human skin fibroblasts, keratinocytes, and endothelial cells were cultured in the presence of buthionine sulfoximine (BSO), an irreversible inhibitor of glutathione (GSH) synthesis. Depletion of intracellular levels of GSH leads to an accumulation of cellular peroxides and eventual cell death. Quercetin concentration-dependently (EC50: 30-40 microM) reduced oxidative injury of BSO to all cell types, and was also effective when first added after BSO washout. BSO caused marked decreases in the intracellular level of GSH, which remained depressed in quercetin-protected cells. Ascorbic acid, while by itself not cytoprotective synergized with quercetin, lowered the quercetin EC50 and prolonged the window for cytoprotection. The related flavonoids rutin and dihydroquercetin also decreased BSO-induced injury to dermal fibroblasts, albeit less efficaciously so than quercetin. The cytoprotective effect of rutin, but not that of dihydroquercetin, was enhanced in the presence of ascorbic acid. Further, quercetin rescued sensory ganglion neurons from death provoked by GSH depletion. Direct oxidative injury to this last cell type has not been previously demonstrated. The results show that flavonoids are broadly protective for cutaneous tissue-type cell populations subjected to a chronic intracellular form of oxidative stress. Quercetin in particular, paired with ascorbic acid, may be of therapeutic benefit in protecting neurovasculature structures in skin from oxidative damage.

Change of glutathione S-transferases in the skin by ultraviolet B irradiation

Glutathione S-transferases (GSTs) may play an important role in protecting skin from ultraviolet radiation (UVR). However, the study on the response of GST to UVR is limited at present. We have examined the effects of a single exposure to ultraviolet B (UVB) radiation on GST in cultured human keratinocytes and the epidermis of SKH/hr-1 hairless mice. We have also investigated the changes of skin GST by chronic irradiation of UVB on the hairless mice. Significant decreases in GST activities in vitro and in vivo were observed at 24 h after 30 and 50 mJ/cm2 UVB irradiation. Chronic UVB exposure also caused decrease in GST activities of the skin tissue. However, any changes in mRNA expression or protein amount of GST have not been observed by Northern blot analysis and Western blot analysis after 30 mJ/cm2 UVB irradiation in cultured human keratinocytes, which suggests that mRNA expression and protein amount of GST are not affected by UVB. These results suggest that UVB irradiation results in inhibitory effect on GST activity in the skin.

Inactivation of enzymes of the glutathione antioxidant system by treatment of cultured human keratinocytes with peroxides

Either metal ions, H2O2, t-butyl hydroperoxide (tBHP), or cumene hydroperoxide (CHP) was added to the medium of cultured human keratinocytes, and the activities of key peroxide-metabolizing enzymes were examined in a sonicated cell supernatant from the treated cells. 200 microM Fe++ +200 microM Fe was without effect on any enzyme activity. 700 microM CHP or tBHP decreased glutathione (GSH) peroxidase activity by 90% after 5 h and by 100% at 20 h, even if the CHP or tBHP was removed from the media after 90 min. H2O2 at 700 microM caused a brief 17% decrease in activity, which was followed by complete recovery. GSH peroxidase was found to be rapidly inactivated in vitro by CHP, but the enzyme was also inactivated at 37 degrees C even in the absence of CHP. GSH prevented both types of inactivation. Consistent with this in vitro data, in vivo depletion of the GSH pool with buthionine sulfoximine led to lower levels of GSH peroxidase and increased sensitivity to peroxide-induced inactivation. Neither GSH reductase nor GSH S-transferase were inactivated by any treatment although CHP did cause a small increase in the activity of the latter, which was not due to induction. The activity of glucose-6-phosphate dehydrogenase was decreased 50% following treatment for 5 h with 700 microM CHP or tBHP, whereas H2O2 treatment caused a brief 15% decline, followed by recovery. The effects of peroxides were not altered by changing the concentration of Ca++ in the media. Catalase was unaffected by concentrations of peroxide up to 700 microM. Inhibition of catalase with aminotriazole slightly enhanced the toxicity of 700 microns H2O2. In summary, organic hydroperoxides at relatively low concentrations inactive key enzymes of the glutathione pathway, but hydrogen peroxide does not.

Ultraviolet A-induced lipid peroxidation and antioxidant defense systems in cultured human skin fibroblasts

Cultured human skin fibroblasts from healthy donors were irradiated with 180 kJ.m-2 ultraviolet (UV) A (320-400 nm) and assayed for thiobarbituric acid-reactive substances (TBARS), taken as an indicator of lipid peroxidation. Antioxidant defenses, including total glutathione (GSH) levels, superoxide dismutase (SOD), glutathione peroxidase (GSHPx), and catalase (Cat) activities were simultaneously assayed before and after irradiation. For the various donors, with different activities of these antioxidant systems before irradiation, TBARS correlated positively with SOD activity and negatively with Cat activity, whereas no correlation with GSH level or GSHPx activity was found. These data support the view that O2- is generated by UVA irradiation. They also suggest that H2O2, arising from O2- dismutation by SOD is not completely removed by Cat. Thus, the sensitivity of human fibroblasts to UVA-induced lipid peroxidation depends on a balance between SOD and Cat activities. After UVA irradiation, Cat activity was strongly inhibited, whereas GSH level was slightly decreased. By contrast, GSHPx and SOD activity remained unchanged after UVA irradiation.

Antioxidant defense mechanisms in murine epidermis and dermis and their responses to ultraviolet light

A comprehensive comparison of antioxidant defenses in the dermis and epidermis and their response to exposure to ultraviolet (UV) irradiation has not previously been attempted. In this study, enzymic and non-enzymic antioxidants in epidermis and dermis of hairless mice were compared. Enzyme activities are presented both as units/gram of skin and units/milligram of protein; arguments are presented for the superiority of skin wet weight as a reference base. Catalase, glutathione peroxidase, and glutathione reductase (units/gram of skin) were higher in epidermis than dermis by 49%, 86%, and 74%, respectively. Superoxide dismutase did not follow this pattern. Lipophilic antioxidants (alpha-tocopherol, ubiquinol 9, and ubiquinone 9) and hydrophilic antioxidants (ascorbic acid, dehydroascorbic acid, and glutathione) were 24-95% higher in epidermis than in dermis. In contrast, oxidized glutathione was 60% lower in epidermis than in dermis. Mice were irradiated with solar light to examine the response of these cutaneous layers to UV irradiation. After irradiation with 25 J/cm2 (UVA + UVB, from a solar simulator), 10 times the minimum erythemal dose, epidermal and dermal catalase and superoxide dismutase activities were greatly decreased. alpha-Tocopherol, ubiquinol 9, ubiquinone 9, ascorbic acid, dehydroascorbic acid, and reduced glutathione decreased in both epidermis and dermis by 26-93%. Oxidized glutathione showed a slight, non-significant increase. Because the reduction in total ascorbate and catalase was much more severe in epidermis than dermis, it can be concluded that UV light is more damaging to the antioxidant defenses in the epidermis than in the dermis.

Characterization of the oxidative stress initiated in cultured human keratinocytes by treatment with peroxides

Cultured human keratinocytes were treated with H2O2, Fe++/Fe , H2O2 + Fe++/Fe , t-butylhydroperoxide (tBHP), or cumene hydroperoxide (CHP). Fe++ +/- Fe was without effect on cell viability. Neither CHP, tBHP, nor H2O2 at 200 microM led to alteration of trypan blue exclusion, but with 700 microM CHP or tBHP there was uptake of trypan blue after 20 min and lysis of cells beginning at 4 h of treatment. Lysis occurred even if the organic hydroperoxide was removed from the media after 1 h. Treatment with 700 microM H2O2 resulted in half of the cells becoming permeable to trypan blue by 60 min, but > 80% of the cells remained intact and functional, and eventually recovered their impermeability to trypan blue. No concentration of H2O2, tBHP, or CHP produced significant thiobarbituric acid (TBA)-reactive material, and Fe++/Fe , H2O2 + Fe++/Fe , and CHP + Fe++/Fe led to the formation of only small amounts of TBA-reactive material. This was attributed to a lack of polyunsaturated lipid in cells cultured in synthetic media. The activity of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is sensitive to oxidative damage and thus was used as an indicator of oxidative stress along with the ratio of reduced/oxidized glutathione (GSH/GSSG). Using these two criteria, we found that CHP or tBHP treatment led to an oxidative stress that was more protracted as compared with the effect of H2O2. The organic peroxides also led to depletion of total glutathione, an effect not found with H2O2. It was also found that H2O2 was more rapidly metabolized than the organic peroxides. In summary, cultured human keratinocytes treated with peroxides underwent a number of changes, which included inactivation of GAPDH, a decrease in the ratio GSH/GSSG, and a loss of trypan blue exclusion. However, as long as the duration of this oxidative stress was short, these changes were reversible and the cells survived. Prolonged oxidative stress led to irreversible damage and cell death. H2O2 was rapidly metabolized and relatively well tolerated by keratinocytes. On the other hand, organic hydroperoxides were metabolized more slowly and were lethal at sub-millimolar concentrations. The relative toxicity of organic hydroperoxides is hypothesized to be related to their non-polar nature.

Effect of glutathione depletion on sunburn cell formation in the hairless mouse

Cutaneous protection against ultraviolet B (UVB) radiation damage by endogenous glutathione (GSH) was evaluated in the epidermis of the hairless mouse by measuring the influence of GSH depletion on sunburn cell (SBC) formation. Cellular GSH exerts antioxidant effects and recent studies have suggested a role for oxygen radicals in the production of SBC. Hairless mice (Skh/h 1) received oral treatment with buthionine S,R-sulfoximine (BSO), an irreversible inhibitor of gamma-glutamylcysteine synthetase, to deplete cutaneous GSH; 4 d later their ears were exposed to UVB radiation. BSO treatment significantly reduced GSH levels in the epidermis to 10-15% of control levels. Twenty-four hours after UVB exposure, SBC counts in the ears of animals with and without BSO treatment were measured, and those exposed to UVB were found to have increased. Greater numbers of SBC were found in the ears of BSO-treated mice exposed to 15 or 20 mJ/cm2 UVB, than in non-BSO-treated mice exposed to the same UVB doses. At higher UVB doses, there were no statistically significant differences between the groups. The results show that endogenous GSH provides the epidermis with measurable protection against injury by low or moderate UVB doses.

New trends in photobiology. The interaction of UVA radiation with cultured cells

Recent work concerning the interaction of UVA radiation (320-380 nm) with cultured cells is reviewed with particular emphasis on the involvement of cellular oxidative stress in the biological effects of this radiation on eucaryotic cells. Possible chromophores are considered and their role in generation of various oxidant species including hydrogen peroxide, superoxide anion, singlet oxygen and hydroxyl radical. DNA and membranes are discussed as possible targets for the lethal action of long wavelength radiation. Four mechanisms of cellular defence are proposed: (1) DNA repair; (2) antioxidant enzymes; (3) endogenous free radical quenchers; (4) inducible protection.

Acute effects of near ultraviolet and visible light on the cutaneous antioxidant defense system

Reactive oxygen species are considered to play an important role in cutaneous pathology. Enzymic and non-enzymic antioxidants can prevent oxidative damage but may be overcome by strong pro-oxidative stimuli. The acute effect of a single exposure to near ultraviolet (UVA)/visible radiation (greater than 320 nm) on various skin antioxidants was examined in hairless mice immediately after irradiation. Impairment of cutaneous catalase and glutathione reductase activity was observed. Superoxide dismutase and glutathione peroxidase were not significantly influenced. Inhibition of catalase may render skin more susceptible to the damaging effects of hydrogen peroxide and its reaction products such as the hydroxyl radical. Partially diminished glutathione reductase activity is not accompanied by a change in reduced/oxidized glutathione level immediately after irradiation. There was a tendential (not statistically significant) decrease in cutaneous tocopherol, ubiquinol + ubiquinone 9 and ascorbic acid levels, either indicating direct photodestruction or consumption by reaction products of photooxidative stress. This partial impairment of the cutaneous antioxidant defense system by near ultraviolet/visible light, showing that the most susceptible component in skin is catalase, suggests possible pharmacological interventions.