Depletion of human stratum corneum vitamin E: an early and sensitive in vivo marker of UV induced photo-oxidation

The combined use of oral and topical lipophilic antioxidants increases their levels both in sebum and stratum corneum

The concentration of Vitamin E (vit E) and ubiquinone (CoQ10), which together with squalene (SQ), play a key role against external oxidative insult, has been shown to decrease significantly during ageing. The aim of the present study is to inquire the effect of the combined use of topical bio-cosmetics containing natural active principles (including sebum-like lipid fractions, sebum and epidermal lipophilic and hydrophilic antioxidants), and oral antioxidant supplements on the antioxidant content of sebum and stratum corneum. We therefore treated the face and the back of 50 female volunteers aged 21-40, daily for two months, with a base cream containing 0.05% ubiquinone, 0.1% vit E, and 1% squalene. In addition 50 mg of CoQ10 + 50 mg of d-RRR-alpha-tocopheryl acetate + 50 microg of selenium were administered orally to half of the volunteers (Group A). Group B was represented by 25 volunteers who were treated only topically. Every 15 days during treatment the levels of CoQ10, vit E and SQ were verified in sebum, stratum corneum, and plasma. The daily topical application of the cream led to a significant increase, that peaked after 60 days, of the levels of CoQ10, d-RRR-alpha-tocopherol and SQ in the sebum (Group B), without significantly affecting the stratum corneum or plasma concentrations of the redox couple CoQ10H2/CoQ10 and vit E. The concomitant oral admistration of antioxidants produced in Group A a significant increase of the levels of CoQ10H2/CoQ10 and vit E both in plasma and stratum corneum after 15 and 30 days treatment respectively, compared to Group B. However the sebum levels of lipophilic antioxidants and SQ did not show a significant increase. After the treatments, the levels of CoQ10H2/CoQ10, vit E and SQ went back to basal levels within 6-8 days in sebum, 12-16 days in the stratum corneum, and 3-6 days in plasma. Therefore topical application of the antioxidants was able to increase their level in sebum, while the concomitant oral administration also affected the levels of vit E and CoQ10 in the stratum corneum.

Pothomorphe umbellata Extract Prevents α-Tocopherol Depletion After UV-irradiation

In this work we evaluated the influence of topical application of P. umbellata root extract gel, containing 0.1% of 4-nerolidylcathecol, on the antioxidant network in UV-induced oxidative damage in hairless mouse skin. The UV-irradiation had no influence on ascorbic acid levels or on the antioxidant enzyme (superoxide dismutase, catalase, glutathione reductase and glutathione peroxidase) activities, but topical P. umbellata treatment protected alpha-tocopherol from being depleted after UV-irradiation. alpha-Tocopherol concentration decreased significantly (approximately 40%, P < 0.01) in the irradiated control groups, whereas in the P. umbellata-treated group, alpha-tocopherol was totally preserved (approximately 100%, P > 0.05). These data demonstrate that P. umbellata may be successfully used as a topical photoprotective agent.

Ozone exposure activates oxidative stress responses in murine skin

Ozone (O(3)) is among the most reactive environmental oxidant to which skin is exposed. O(3) exposure has previously been shown to induce antioxidant depletion as well as lipid and protein oxidation in the outermost skin layer, the stratum corneum (SC), but little is known regarding the potential effects of O(3) on the skin epidermis and dermis. To evaluate such skin responses to O(3), SKH-1 hairless mice were exposed for 2 h to 8.0 ppm O(3) or to ambient air. O(3) exposure caused a significant increase in skin carbonyls (28%) compared to the skin of air exposed control animals. An evident increase in 4-hydroxynonenal-protein adducts was detected after O(3) exposure. O(3) exposure caused a rapid up-regulation of HSP27 (20-fold), and more delayed induction of HSP70 (2.8-fold) and heme oxygenase-1 (5-fold). O(3) exposure also led to the induction of nitric oxide synthase (iNOS) 6-12 h following O(3) exposure. We conclude that skin exposure to high levels of O(3) not only affects antioxidant levels and oxidation markers in the SC, but also induces stress responses in the active layers of the skin, most likely by indirect mechanisms, since it is unlikely that O(3) itself penetrates the protective SC layers.

Antioxidants and the response of skin to oxidative stress: vitamin E as a key indicator

As the outermost barrier of the body, the skin is directly and frequently exposed to a prooxidative environment, including solar UVA and UVB radiation, and air pollution. The skin is equipped with an elaborate system of antioxidant substances and enzymes that includes a network of redox active antioxidants. Among these, vitamin E has been identified as the predominant antioxidant both in murine and human skin and shows a characteristic gradient with lower levels towards the outer stratum corneum layers. Skin exposure to UV and ozone alone and in combination resulted in a significant potentiation of the UV-induced vitamin E depletion. Oxidants and antioxidants play an important role in maintaining a balance between free radicals produced by metabolism or derived from environmental sources. Cellular antioxidants may change their redox state, be targeted for destruction, regulate oxidative process involved in signal transduction, affect gene expression and pathways of cell proliferation and death. Here we provide an overview of the antioxidant system with a special relevance to skin.

Role of ascorbic acid in stratum corneum lipid models exposed to UV irradiation

PURPOSE

The effects of ascorbic acid on Stratum corneum lipid models following ultraviolet irradiation were studied adding iron ions as transition metal catalysts.

METHODS

Lipid peroxidation was quantified by the thiobarbituric acid assay. The qualitative changes were studied on a molecular level by mass spectrometry. To elucidate the nature of free radical involvement we carried out electron paramagnetic resonance studies. The influence of ascorbic acid on the concentration of hydroxyl radicals was examined using the spin trapping technique. Moreover, we checked the vitamin's ability to react with stable radicals.

RESULTS

Ascorbic acid was found to have prooxidative effects in all lipid systems in a concentration dependent manner. The degradation products of ascorbic acid after its prooxidative action were detected. The concentration of the hydroxyl radicals in the Fenton assay was decreased by ascorbic acid. The quantification assay of 2,2-diphenyl-1-picrylhydrazyl hydrate showed reduced concentration levels of the stable radical caused by ascorbic acid.

CONCLUSIONS

Considering human skin and its constant exposure to UV light and oxygen, an increased pool of iron ions in irradiated skin and the depletion of co-antioxidants, the administration of ascorbic acid in cosmetic formulations or in sunscreens could unfold adverse effects among the Stratum corneum lipids.

Photoaging is associated with protein oxidation in human skin in vivo

There is increasing evidence for the generation of reactive oxygen species in skin upon ultraviolet exposure, but little is known about their pathophysiologic relevance in human skin in vivo. We hypothesized that chronic and acute photodamage is mediated by depleted antioxidant enzyme expression and increased oxidative protein modifications. Biopsies from patients with histologically confirmed solar elastosis, from non-ultraviolet-exposed sites of age-matched controls, and from young subjects were analyzed. To evaluate the influence of acute ultraviolet exposures, buttock skin of 12 healthy subjects was irradiated repetitively on 10 d with a solar simulator and compared intraindividually to non-ultraviolet-treated contralateral sites. The antioxidant enzymes catalase, copper-zinc superoxide dismutase, and manganese superoxide dismutase were investigated by immunohistochemistry. Protein carbonyls were analyzed by immunohistochemical and immunoblotting techniques in human skin and in cell models. Whereas overall expression of antioxidant enzymes was very high in the epidermis, low baseline levels were found in the dermis. In photoaged skin, a significant depletion of antioxidant enzyme expression was observed within the stratum corneum and in the epidermis. Importantly, an accumulation of oxidatively modified proteins was found specifically within the upper dermis of photoaged skin. Upon acute ultraviolet exposure of healthy subjects, depleted catalase expression and increased protein oxidation were detected. Exposures of keratinocytes and fibroblasts to ultraviolet B, ultraviolet A, and H2O2 led to dose-dependent protein oxidation and thus confirmed in vivo results. In conclusion, the correlation between photodamage and protein oxidation was demonstrated for the first time, which hence may be a relevant pathophysiologic factor in photoaging.

Decreased oxidative state in non-lesional skin of atopic dermatitis

BACKGROUND

The stratum corneum (SC), as the skin layer most exposed to various environmental factors, is particularly susceptible to oxidative stress. Due to the high lipid content of the SC, lipophilic antioxidants such as alpha-tocopherol are expected to play a major role in scavenging reactive oxidant intermediates produced during oxidative stress.

OBJECTIVES

Since the skin of atopic dermatitis patients has an impaired barrier function, we wondered if they were more susceptible to environmental oxidative stress than healthy subjects.

METHODS

SC was collected by scraping the forearm of 14 healthy volunteers and 14 patients with atopic dermatitis; then, alpha-tocopherol and lipid peroxide concentrations were assessed by high-performance liquid chromatography and ferrous oxidation, respectively.

RESULTS

The SC from atopic patients showed a higher concentration of alpha-tocopherol (16.1 +/- 2.2 nmol/g) as compared to healthy controls (7.7 +/- 0.9 nmol/g; p < 0.01), as well as a slightly but significantly lower concentration of lipid peroxides (1,353 +/- 128 and 1,818 +/- 154 nmol/g for atopic dermatitis patients and healthy controls, respectively; p < 0.05).

CONCLUSIONS

These results show that the SC of atopic dermatitis patients exhibits a significantly less pronounced oxidative state. This may be the consequence of an increase in cutaneous antioxidant defences due to chronic inflammation.

Antioxidant and photoprotective activity of a crude extract of Culcitium reflexum H.B.K. leaves and their major flavonoids

The aim of the present study was to evaluate the in vitro antioxidant and in vivo photoprotective activities of an ethanolic extract of Culcitium reflexum H.B.K. leaves (ECR extract). The antioxidant activity of the extract was assessed by means of three different in vitro tests: (1) bleaching of the stable 1,1-diphenyl-2-picrylhydrazyl radical; (2) peroxidation, induced by the water-soluble radical initiator 2,2'-azobis(2-amidinopropane)hydrochloride, on mixed dipalmitoylphosphatidylcholine/linoleic acid unilamellar vesicles; (3) UV radiation-induced peroxidation in phosphatidylcholine multilamellar vesicles. In all in vitro tests used the ECR extract showed a significant antioxidant effect. Furthermore, a gel formulation containing this extract proved, when topically applied, to afford a significant in vivo protection against UV-B-induced skin erythema in healthy human volunteers. Then, by chromatographic fractionation and spectroscopic methods, we identified some cinnamic acid derivatives and the major flavonoid constituents of the ECR extract, viz. the flavonols rutin, quercetin-3-O-beta-D-galactopyranoside-4'-O-beta-D-glucopyranoside, quercetin-3-O-beta-D-glucopyranoside, isorhamnetin-3-O-beta-D-galactopyranoside, quercetin and kaempferol.

Cutaneous vitamins A and E in the context of ultraviolet- or chemically-induced oxidative stress

Vitamins A and E are present in mammalian skin. Although the main circulating form of vitamin A in the blood is retinol, the epidermis stores it as retinyl esters. The epidermis can be easily loaded with high amounts of vitamin A by topical application of either retinol or retinaldehyde, two well-tolerated precursors of the biologically active retinoic acid, while topical alpha-tocopherol loads the epidermis with vitamin E. The probable physiological function of epidermal vitamin E is to contribute to the antioxidant defense of the skin, whereas that of epidermal vitamin A (retinol and retinyl esters) is not yet well understood. Besides being a precursor for retinoic acid, vitamin A also has a free radical scavenging potential. Due to their physical properties, vitamins A and E absorb ultraviolet (UV) light in the region of solar spectrum that is responsible for most of the deleterious biological effects of the sun. In the mouse, topical vitamin A has been shown to prevent the UV-induced epidermal hypovitaminosis A, while topical vitamin E prevents oxidative stress and cutaneous and systemic immunosuppression elicited by UV. Thus constitutive epidermal vitamins A and E appear complementary in preventing UV-induced deleterious cutaneous and systemic effects, and these properties can be reinforced by topical application of retinol or retinaldehyde and topical alpha-tocopherol.

Oxidative targets in the stratum corneum. A new basis for antioxidative strategies

As the outermost layer of skin, the stratum corneum (SC) is continuously exposed to an oxidative environment, including air pollutants, ultraviolet radiation, chemical oxidants, and aerobic microorganisms. Human SC reveals characteristic antioxidant and protein oxidation gradients with increasing antioxidant depletion and protein oxidation towards the outer layers. SC antioxidants, lipids, and proteins are oxidatively modified upon treatments with ultraviolet A/ultraviolet B, ozone, and benzoyl peroxide. alpha-Tocopherol represents the predominating SC antioxidant with respect to its concentration and its unique susceptibility to the various oxidative challenges tested. In sites rich in sebaceous glands, alpha-tocopherol is physiologically delivered to the surface via secretion of sebum. Oxidative damage in the human SC represents an early pathophysiological event preceding barrier disruption and inflammation in environmentally challenged skin. Furthermore, oxidative gradients in SC proteins may have implications for the process of desquamation in human skin.

Role of vitamins in skin care

Therapeutic (vitamins A and D, and their analogs) and antioxidant (vitamins C, E, and coenzyme Q) vitamins play an increasing role in skin care. Their benefits range from skin conditions such as acne and psoriasis to the protection against environmental insults.

Generation of oxidative stress in human cutaneous models following in vitro ozone exposure

Ozone, one of the main components of photochemical smog, represents an important source of environmental oxidative stress. The skin, being the outermost barrier of the body, is directly exposed to environmental oxidant toxicants. Skin sebum and cellular plasma membrane lipids contain polyunsaturated fatty acids which are primary targets for ozone and free radical attack induced lipid peroxides. These ozonation processes in skin can also generate aldehydes, hydroxyhydroperoxides and specific Criegee's ozonides. In order to evaluate in vitro human skin susceptibility to ozone, we have exposed cultured immortalized human keratinocytes (DK7-NR) and the reconstructed human epidermis Episkin to 10 ppm of ozone in a specific incubator. We measured the formation of protein carbonyls by an ELISA method and monitored the oxidative stress using the fluorogenic probe 2',7'-dichlorofluorescin-diacetate (DCFH-DA). Results showed a time-dependent increase of fluorescence levels (linked to oxidative stress) in both models exposed to ozone. Using this protocol, we investigated the protective potential of different products including vitamin C, a thiol derivative and a plant extract. All products dramatically reduced oxidative responses during ozone exposure. Decreases observed in fluorescence levels were between 60 and 90% as compared to non-protected controls. These results demonstrate: (a) cutaneous in vitro models are remarkably susceptible to oxidative stress generated by an environmental air pollutant as ozone, and (b) raw antioxidants, thiols and vitamin C were efficient products to prevent ozone induced cellular oxidative damage.

Photoprotective actions of topically applied vitamin E

Topical application of vitamin E has been shown to decrease the incidence of ultraviolet (UV)-induced skin cancer in mice. Vitamin E provides protection against UV-induced skin photodamage through a combination of antioxidant and UV absorptive properties. Topical application of alpha-tocopherol on mouse skin inhibits the formation of cyclobutane pyrimidine photoproducts. However, topically applied alpha-tocopherol is rapidly depleted by UVB radiation in a dose-dependent manner. The photooxidative fate of the alpha-tocopherol depends on the local environment of the vitamin E. alpha-Tocopherol quinone and alpha-tocopherol quinone epoxides are principal photoproducts of vitamin E that has penetrated into the epidermal layer of the skin, whereas tocopherol dimers and trimers are formed from alpha-tocopherol in a bulk phase at the skin surface. Dimer and trimer products may participate in prevention of UV-induced photodamage.

Protection of the flowers of Prunus persica extract from ultraviolet B-induced damage of normal human keratinocytes

For an attempt to develop safe materials protecting solar ultraviolet (UV)-induced skin damage, plant extracts were evaluated for their inhibitory activities of free radical generation and arachidonic acid/metabolites release from UVB-irradiated normal human keratinocytes. From the results of these screening procedures, the ethanol extract of the flowers of Prunus persica (Ku-35) was selected for further study. It was found that Ku-35 (100-1,000 microg/ml) inhibited the amount of 14C-arachidonic acid/metabolites release from UVB-irradiated keratinocytes. It was also demonstrated that Ku-35 possessed the protective activity against UV-induced cytotoxicity of keratinocytes and fibroblasts. In addition, Ku-35 was revealed to protect UVB-induced erythema formation using guinea pigs in preliminary in vivo study. All these results indicate that the flowers of P. persica extract may be beneficial for protecting UV-induced skin damage when topically applied.

Ozone potentiates vitamin E depletion by ultraviolet radiation in the murine stratum corneum

As the outermost layer of the skin, the stratum corneum is exposed to environmental oxidants. To investigate putative synergisms of environmental oxidative stressors in stratum corneum, hairless mice were exposed to ultraviolet radiation (UV) and ozone (O(3)) alone and in combination. Whereas a significant depletion of alpha-tocopherol was observed after individual exposure to either a 0.5 minimal erythemal dose of UV or 1 ppm O(3) for 2 h, the combination did not increase the effect of UV alone. However, a dose of 0.5 ppm O(3) x 2 h, which had no effect when used alone, significantly enhanced the UV-induced depletion of vitamin E. We conclude that concomitant exposure to low doses of UV and O(3) at levels near those that humans can be exposed to causes additive oxidative stress in the stratum corneum.

Vitamin C, uric acid, and glutathione gradients in murine stratum corneum and their susceptibility to ozone exposure

The stratum corneum has been recognized as the main cutaneous oxidation target of atmospheric ozone (O3), a major part of photochemical smog. This study reports the presence and distribution of vitamin C, glutathione, and uric acid in murine stratum corneum, and evaluates their susceptibility to acute environmental exposure to O3. Based on tape stripping and a modified extraction method with high performance liquid chromatography electrochemical analysis, we detected vitamin C (208.0 +/- 82.5 pmol per 10 consecutive pooled tapes), glutathione (283.7 +/-96.3), and uric acid (286.4 +/-47.1) in murine stratum corneum as compared with only 16.5 +/- 1.4 pmol alpha-tocopherol. Vitamin C, glutathione (both p < 00.001), and urate (p < 0.01) were found to exhibit a gradient with the lowest concentrations in the outer layers and a steep increase in the deeper layers. To investigate the effect of O3 exposure on hydrophilic antioxidants, we exposed SKH-1 hairless mice to O3 concentrations of 0, 0.8, 1, and 10 p.p.m., and stratum corneum was analyzed before and after exposure. Whereas mock exposure with 0 p.p. m. for 2 h had no significant effect, O3 doses of 1 p.p.m. for 2 h and above showed depletion of all three antioxidants. Vitamin C was decreased to 80% +/- 15% of its pretreatment content (p < 0.05), GSH to 41% +/- 24% (p < 0.01), and uric acid to 44% +/- 28% (p < 0.01). This report demonstrates the previously unrecognized role of hydrophilic antioxidants in the stratum corneum and provides further evidence that O3 induces oxidative stress in this outer skin layer.

Sebaceous gland secretion is a major physiologic route of vitamin E delivery to skin

Skin plays an important part in the protection against oxidative stressors, such as ultraviolet radiation, ozone, and chemicals. This study was based on the observation that upper facial stratum corneum contained significantly higher levels of the antioxidant alpha-tocopherol than corresponding layers of arm stratum corneum. We hypothesized that the underlying mechanism involves sebaceous gland secretion of vitamin E. To test this, we examined in eight human volunteers: (i) stratum corneum levels and distribution profiles of vitamin E in sites with a different sebaceous gland density (arm versus cheek); (ii) whether vitamin E is a significant constituent of human sebum; and (iii) if there is a correlation between levels of vitamin E and squalene, a marker of sebum secretion, in skin surface lipids. Using standardized techniques for stratum corneum tape stripping and sebum collection, followed by high-performance liquid chromatography analysis of tocopherols and squalene, we found that: (i) the ratio of cheek versus upper arm alpha-tocopherol levels was 20 : 1 for the upper stratum corneum and decreased gradually with stratum corneum depth; (ii) vitamin E (alpha- and gamma-tocopherol forms) is a significant constituent of human sebum and is continuously secreted at cheek and forehead sites during a test period of 135 min; and (iii) vitamin E correlates well with levels of cosecreted squalene (r2 = 0.86, p < 0.001). In conclusion, sebaceous gland secretion is a relevant physiologic pathway for the delivery of vitamin E to upper layers of facial skin. This mechanism may serve to protect skin surface lipids and the upper stratum corneum from harmful oxidation.

Protein oxidation in human stratum corneum: susceptibility of keratins to oxidation in vitro and presence of a keratin oxidation gradient in vivo

The stratum corneum is located at the interface between body and environment and thus is constantly exposed to a pro-oxidative environment. Previously, we have demonstrated that stratum corneum lipids are targets of oxidative stress induced by ozone and by ultraviolet A and B exposure. Here, we employed an immunoblotting technique to detect protein oxidation in human stratum corneum obtained by tape stripping. After lysis, protein carbonyl groups were measured by derivatization with dinitrophenylhydrazine, separation by sodium dodecylsulfate-polyacrylamide gel electrophoresis, and immunoblotting using antibodies against dinitrophenyl groups. Keratin 10, identified by use of specific antibodies and by microsequencing, was demonstrated in vitro to be oxidizable by ultraviolet A irradiation, hypochlorite, and benzoyl peroxide. In vivo, a keratin 10 oxidation gradient with low levels in the lower stratum corneum layers, and about 3-fold higher contents of carbonyl groups towards the outer layers was demonstrated in forehead stratum corneum of healthy volunteers (n = 6). As protein oxidation can be associated with an increased susceptibility to proteases, this finding may be important for better understanding the process of desquamation.

Differentiation of normal human keratinocytes influences hexavalent chromium uptake and distribution and the ability of cells to withstand Cr(VI) cytotoxicity

The degree of differentiation of normal human keratinocytes determines the biology of the cells to a large extent. We have previously documented that keratinocytes from different donors differ significantly in their ability to withstand hexavalent chromium [Cr(VI)]-induced cytotoxicity. Several factors may contribute to this differing donor sensitivity to Cr(VI). The aims of this study were to investigate to what extent keratinocyte differentiation might influence Cr(VI) uptake and the ability of cells to withstand Cr(VI)-induced cytotoxicity. Keratinocytes from different donors were cultured under identical conditions and exposed to Cr(VI) (as potassium dichromate) at different points during their maturation process. The degree of differentiation of the cells was assessed using a quantitative assay for involucrin and related to the Cr(VI) cytotoxicity experienced by the cells. Chromium content was measured in whole cell, cytosolic and particulate fractions. While proliferative keratinocytes exposed to Cr(VI) showed a high degree of cytotoxicity to dichromate exposure, the more differentiated cells showed significantly less cytotoxicity but a higher uptake of the metal ion into the cells. The relative percentage of cytosolic chromium was high in the proliferative cells and decreased as the cells matured, suggesting that differentiated cultures were binding most of the chromium to the particulate fraction. Total chromium also increased during differentiation. The use of the channel-blocking agent 4, 4'-diisothiocyanate-2-2'-stilbenedisulphonic acid confirmed the spatial differences of chromium accumulation in the phenotypically different cultures, in that it prevented Cr(VI) entry into the proliferative cells and attenuated dichromate cytotoxicity in these cultures, but had no effect on the Cr(VI) uptake in differentiated cells, nor did it reduce its cytotoxicity. These data support the hypothesis that the upper differentiated layers of the epidermis are able to offer considerable physical protection to the lower proliferative layers from chemical pro-oxidants.

UV-B-Induced photooxidation of vitamin E in mouse skin

Topically applied alpha-tocopherol (alpha-TH, vitamin E) inhibits UV-B (290-320 nm) photocarcinogenesis, yet alpha-TH undergoes rapid photooxidation by UV-B in vitro. To examine the effect of UV-B on alpha-TH in vivo, we studied the fate of alpha-TH in UV-B-irradiated mouse skin. [14C]-alpha-TH was applied to mouse skin at various times prior to UV-B irradiation. UV-B irradiation for 1 h at a dose rate of 2.6-2.9 J m-2 s-1 resulted in consumption of 40-60% of the applied dose and formation of oxidation products. The major product fraction formed in UV-B-irradiated mice treated topically with alpha-TH contained an alpha-TH dihydroxy dimer and its two-electron oxidation product, a spirodimer. Products previously identified as being derived from photochemical or peroxyl radical scavenging reactions of alpha-TH were also observed, including alpha-tocopherolquinone (alpha-TQ), alpha-tocopherolquinone 2, 3-epoxide (alpha-TQE 1), alpha-tocopherolquinone 5,6-epoxide (alpha-TQE 2), and 8a-(hydroperoxy)epoxytocopherones. These results indicate that topically applied alpha-TH is extensively oxidized in skin and suggest that alpha-TH photoproducts may be involved in the observed effects of topically applied vitamin E in UV-B-irradiated skin.

Topical melatonin in combination with vitamins E and C protects skin from ultraviolet-induced erythema: a human study in vivo

In this randomized, double-blind human study, the short-term photoprotective effects of different antioxidants and their combinations were evaluated in vivo. Vitamin C (ascorbic acid), vitamin E (alpha-tocopherol) and melatonin (N-acetyl-5-methoxytryptamine) were topically applied, alone or in combination, 30 min before ultraviolet-irradiation of the skin. The erythemal reaction was evaluated visually and non-invasively using different bioengineering methods (skin colour and skin blood flow). The results showed a modest protective effect of the vitamins when applied alone and a dose-dependent photoprotective effect of melatonin. Topical application of combinations of both vitamins, or of melatonin with vitamins, enhanced the photoprotective response. Better protection was obtained by using the combination of melatonin with both vitamins. The role of reactive oxygen species and oxygen-derived free radicals, as well as potential sunscreening properties of the employed antioxidants, are discussed in view of possible mechanisms to explain this elevated photoprotective effect.