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Skin protection against UV light by dietary antioxidants Cite this: DOI: 10.1039/c4fo00280f
Elisabet Ferna´ndez-Garc´ıa* There is considerable interest in the concept of additional endogenous photoprotection by dietary antioxidants. A number of efficient micronutrients are capable of contributing to the prevention of UV damage in humans. These compounds protect molecular targets by scavenging reactive oxygen species, including excited singlet oxygen and triplet state molecules, and also modulate stress-dependent signaling and/or suppress cellular and tissue responses like inflammation. Micronutrients present in the diet such as carotenoids, vitamins E and C, and polyphenols contribute to antioxidant defense and may also contribute to endogenous photoprotection. This review summarizes the literature concerning the use of dietary antioxidants as systemic photoprotective agents towards skin damage induced by UVA and UVB. Intervention studies in humans with carotenoid-rich diets have shown photoprotection. Interestingly, rather long treatment periods (a minimum of 10 weeks) were required to achieve this effect. Likewise, dietary Received 1st April 2014 Accepted 17th May 2014
carotenoids exert their protective antioxidant function in several in vitro and in vivo studies when present at sufficiently high concentration. A combination of vitamins E and C protects the skin against UV damage. It is suggested that daily consumption of dietary polyphenols may provide efficient protection against the
DOI: 10.1039/c4fo00280f
harmful effects of solar UV radiation in humans. Furthermore, the use of these micronutrients in
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combination may provide an effective strategy for protecting human skin from damage by UV exposure.
1. Introduction Human skin acts as a barrier between the internal and external environments, protecting the body from mechanical damage, Institute of Biochemistry and Molecular Biology I, Faculty of Medicine, Heinrich-Heine-University D¨ usseldorf, PO Box 101007, D-40001 D¨ usseldorf, Germany. E-mail: [email protected]; Fax: +49 211 13029; Tel: +49 211 8110526
Dr Fern´ andez-Garc´ıa is a Postdoctoral Researcher at Andalusian Center for Molecular Biology and Regenerative Medicine, in Seville, Spain. She studied chemistry at the University of Seville. From 2004 to 2011 she worked in Food Biotechnology Department, Instituto de la Grasa (CSIC), Seville, Spain and received her PhD. In 2012 she joined the Institute of Biochemistry and Molecular Biology I in Heinrich Heine-University D¨ usseldorf (Germany) supported by a fellowship from the Postdoctoral Fellowship Program (Alfonso Martin Escudero Foundation, Spain). Dr Fern´ andez-Garc´ıa has over 10 years of experience in the eld of dietary antioxidants. This journal is © The Royal Society of Chemistry 2014
noxious substances, invasion by microorganisms, and radiation. The skin plays an important role in regulating body homeostasis by keeping water loss to a minimum and by regulating body temperature. In recent years it has become clear that the skin is an essential part of the immune system. The skin condition and functioning are affected by environmental factors, such as ultraviolet (UV) radiation, free radicals, toxic and allergic compounds, and mechanical damage, and by endogenous factors, such as genetic predisposition, immune and hormone status, and stress. Consequently, the skin undergoes alterations resulting in photoaging, inammation, reduced immune function, imbalanced epidermal homeostasis and other skin disorders.1 Upon exposure to UV radiation from sunlight, photo-oxidative reactions are initiated which cause damage to biomolecules and affect the integrity of skin cells and damage skin. Such photo-oxidative damage plays a role in pathological processes and is involved in the development of many disorders affecting the skin.2 Based on wavelength, the UV radiation spectrum is divided into three regions: UVA (400–320 nm), UVB (320–290 nm), and UVC (290–200 nm). UVA (400–320 nm) radiation, which contributes to up to 95% of the total UV exposure, is not absorbed by DNA but it is a strong oxidant and considered the most important source of oxidative stress in human skin.3 UVA plays a major role in photoaging. This radiation can penetrate into the deeper dermis and induces the generation of reactive oxygen species
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(ROS), which can induce mutations in the mitochondrial DNA, thus leading to the loss of enzymes involved in oxidative phosphorylation and deciencies in energy metabolism.4 UVB (320–290 nm) is mainly absorbed by keratinocytes in the epidermis. By direct interaction with the DNA, it causes mutations and skin cancer. UVB also leads to sunburn, which is an erythema resulting from an inammatory response to the photodamage to the skin.4 A frequently used measure of UV irradiation-induced erythema is determination of the minimal erythema dose (MED), which is dened as the minimal amount of energy required to induce a uniform, clearly demarcated redness 16–24 h aer exposure to UV radiation. Although nature anticipates these conditions by increasing epidermal thickness, stimulating melanogenesis, and providing natural antioxidants in the supercial skin layers, supplementation with nutrients may support these processes and thereby serve as an additional protective measure against the harmful effects of UV light.1
2. Endogenous photoprotection by dietary antioxidants The concept of additional endogenous protection was proposed about 30 years ago.5,6 In order to increase the barrier for UV light, the compound should absorb UV light over a broad range of wavelengths with high efficacy. Antioxidants protect molecular targets by scavenging ROS, including excited singlet oxygen and triplet state molecules. Compounds that modulate stressdependent signaling and/or suppress cellular and tissue responses like inammation are suitable for this purpose. A number of efficient micronutrients are capable of directly scavenging lipophilic and hydrophilic prooxidants or serving as constituents of antioxidant enzymes. Carotenoids, polyphenols, vitamin E as well as vitamin C contribute to antioxidant defense and may also contribute to endogenous photoprotection.7,8 The concept of endogenous photoprotection implies that the active compound is available in sufficient amounts at the target site.9 Thus, structural features are important, and inuence pharmacokinetic parameters like absorption, distribution, and metabolism that may affect the level of the compound in skin.10,11 In this paper, photoprotective effects of dietary carotenoids, vitamins E and C, and polyphenols towards skin damage induced by UV light are reviewed in the available literature, underlying human intervention studies are discussed, and in vitro or in vivo assays are summarized.
3.
Carotenoids
Carotenoids are a family of compounds of over 600 fat-soluble plant pigments. Fruits and vegetables are major sources of carotenoids.12 Carotenoids exhibit a variety of biological properties. These include their role in light harvesting and photoprotection or provitamin and antioxidant functions in humans and animals. Carotenoids present a long central chain of conjugated double bonds carrying acyclic or cyclic substituents.
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Xanthophylls, also called oxocarotenoids, contain functional oxygen groups7 (see Fig. 1). Because of their structure and physicochemical properties, carotenoids could be involved in several ways to protect skin from sunlight damage, namely by increasing the optical density, quenching the singlet oxygen (1O2) or, for provitamin A carotenoids, via formation of retinoic acid. The role of 1O2 in UVA-induced oxidative stress is well established and has been reviewed extensively.13 Carotenoids can also scavenge other reactive oxygen species, such as superoxide anions, hydroxyl radicals or hydrogen peroxide. Under certain conditions, however, i.e. higher oxygen partial pressure, carotenoids may act as pro-oxidants.4 The most abundant carotenoids in the human organism are b-carotene, a-carotene, and lycopene, as well as the xanthophylls lutein, zeaxanthin, and a- and b-cryptoxanthin.14,15 Carotenoids are transported to the skin and accumulate mainly in the epidermal layers. The amount of these pigments deposited in skin correlates with dietary intake and bioavailability from the food source. Aer absorption, carotenoids are transported in the bloodstream via lipoproteins to various target tissues.16,17 Recently, cholesterol transporters such as scavenger receptor class B member 1 (SR-B1) and cluster of differentiation 36 (CD 36) were shown to mediate a facilitated absorption of carotenoids in the gut.18,19 It is likely that carotenoids are taken up by these transporters also in epidermis, which is an active site of cholesterol accumulation for the maintenance of permeability barrier function. SR-B1 is expressed in human epidermis,20 predominantly in the basal layers.3 The levels of these compounds in skin vary with respect to the skin area and skin layer. High levels of carotenoids are found in the skin of the forehead, the palm of the hand, and in dorsal skin; low levels are found in skin of the arm and the back of the hand (see Table 1 with data from ref. 8).
3.1. Human intervention studies Intervention studies in humans with carotenoid-rich diets have shown photoprotection of the skin as measured by decreased sensitivity to UV radiation-induced erythema (see Table 2).27–34 Stahl et al., 2001 (ref. 31) found that ingestion of tomato paste (40 g per day, equivalent to 16 mg lycopene per day) over a period of 10 weeks led to a 40% reduction in skin erythema development induced by exposure to solar-simulating UV radiation. Erythema was induced by a solar light simulator at 1.25 MED, and reddening of the skin was evaluated before and 24 hours aer irradiation by chromametry. Erythema intensity was lower aer the treatment. No signicant protection was found at week 4, but aer 10 weeks, erythema formation was signicantly lower in the group consuming the tomato paste than in the controls. In another study, protection against UV-induced erythema can be achieved aer ingestion of 24 mg of b-carotene (from the alga Dunaliella salina) for a period of 12 weeks. Erythema intensity was signicantly diminished from 8 weeks. However erythema suppression was more pronounced when a combination of carotenoids and vitamin E was supplied.29 Similar results have been found in other studies shown in
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Fig. 1
Examples of dietary antioxidants that protect against damage by UV radiation.
Table 2. Also listed are several intervention studies where no protection was observed. It is interesting to note that protection was only determined in studies where the intervention was for more than 10 weeks. Apparently a sufficiently long interval of treatment is needed to provide optimal protection of the skin against UV-induced erythema.
3.2. Photoprotection in vitro and in vivo Several studies have used cultured human or other skin broblasts to examine the protective effects of carotenoids on UVinduced lipid peroxidation.3 A variety of experimental studies investigated the antioxidant function of beta-carotene in the skin in vivo and in vitro. In rodents, beta-carotene was found to reduce lipid peroxidation.35 It has also been demonstrated that this compound quenches singlet oxygen-mediated photochemical reactions in rodent skin.36
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In cultured skin cells, a few in vitro studies have investigated the antioxidant potential of b-carotene. This compound decreased the photoinactivation of the enzymes catalase and superoxide dismutase as well as protein cross-linking.37 In rat kidney broblasts, b-carotene diminished UVA-induced catalase deactivation and lipid peroxidation.38 Lycopene, b-carotene and lutein, applied in liposomes as vehicles, decreased the UVB-induced formation of thiobarbituric acid-reactive substances (TBARS) at 1 hour to levels 40–50% of those of controls free of carotenoids.14 The amounts of carotenoid needed for optimal protection were 0.05, 0.40 and 0.30 nmol mg 1 protein for lycopene, b-carotene and lutein, respectively. A further increase of carotenoid content in cells beyond the optimum levels led to pro-oxidant effects. In another study, the depletion of catalase and superoxide dismutase by UVA was restored, and TBARS was reduced by culturing rat kidney broblasts with b-carotene or lutein (1 mM each), or with
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Carotenoids, a-tocopherol and ascorbic acid levels in human skin. Adapted from ref. 8
Table 1
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Micronutrient (skin layer)
Skin level (pmol mg
1
wet wt)
Reference
Carotenoids (epidermis and dermis) b-Carotene a-Carotene Lycopene Phytoene Phytouene b-Carotene a-Carotene Lycopene Lutein
0.05 0.04 0.02 0.01 0.13 0.10 0.12 0.04 0.03 0.02 0.11 0.01 0.01 0.01 0.22 0.01 0.03 0.01
21
a-Tocopherol Epidermis Dermis Stratum corneum
24.8 9.6 16.2 1.1 33.0 4.0
23 24 25
363.7 24.8 162.4 18.6 354.7 23.5 152.0 19.0
26
Ascorbic acid Epidermis from forearm Dermis from forearm Epidermis from upper-inner arm Dermis from upper-inner arm
22
astaxanthin, which was reported to give superior protective activity at concentrations as low as 10 nM.38 Lyons et al.39 examined the ability of an algal extract to protect against UVAinduced DNA alterations in human skin broblasts (1BR-3), human melanocytes (HEMAc) and human intestinal CaCo-2 cells. DNA damage was assessed using single cell gel electrophoresis or comet assay. The algal extract displayed protection against UVA-induced DNA damage when 10 mM astaxanthin was added to all three cell types. However, at lower concentrations (10 and 100 nM) no signicant protection was evident. In 1BR-3 cells, preincubation (18 h) with 10 mM of either the synthetic astaxanthin or the algal extract prevented UVA-induced alterations in cellular superoxide dismutase activity and cellular glutathione content. Studies in mouse models also conrm the prevention of oxidative stress induction in skin, caused by UV irradiation, by carotenoids.40 Heme-oxygenase 1 (HO-1) gene is strongly activated within the rst few hours that follow UVA irradiation of normal human dermal broblasts and this response is being used as a marker
Table 2
of oxidative stress in cells.3 Carotenoids could be expected to suppress the UVA induced HO-1 gene activation in human cells. Unexpectedly, two studies with skin broblasts in vitro found an opposite effect. The rst study applied b-carotene in cyclodextrins at levels of 0.5 and 5 mM.41 A signicant pro-oxidative effect and enhancement of UVA-induced HO-1 expression were observed. In the second study, b-carotene or lycopene (0.5– 1.0 mM) were prepared in nanoparticle formulations. As in the study above, either b-carotene or lycopene led to a further 1.5fold rise in the UVA-induced HO-1 mRNA levels.42 It should be pointed out that the protective properties of carotenoids are probably at least two-fold, consisting of (1) their potent antioxidant activity and (2) their ability to induce cellular protective response. Thus, dietary carotenoids and their metabolites induce phase 2 cytoprotective enzymes and share with all other classes of phase 2 inducers a common chemical property, the ability to react with sulydryl groups.43 Overall, these in vitro and in vivo studies show that carotenoids can exert their protective antioxidant function when present at sufficiently high concentration in the skin cells.
4. Vitamins E and C Vitamin E refers to a family of eight nutrients of which a-tocopherol is the most abundant and biologically active form in the human body (Fig. 1). This essential lipophilic nutrient is well known for its role as a chain-breaking antioxidant during lipid peroxidation and it protects polyunsaturated fatty acids in cell membranes from oxidation.14 Food sources include vegetables, vegetable oils, cereals and nuts.44 a-Tocopherol concentrations in skin can be increased with oral or topical delivery and are decreased with UV exposure. Vitamin E is the most abundant lipophilic antioxidant found in human skin (see Table 1). In humans, levels of vitamin E in the epidermis are higher than the dermis. Vitamin E and carotenoids are absorbed by the same pathway.14 Vitamin C is an effective antioxidant and an essential cofactor in numerous enzymatic reactions. The major source for vitamin C in the diet are fruits, especially citrus fruits, kiwifruit, cherries and melons, and vegetables such as tomatoes, leafy greens, broccoli, cauliower, Brussels sprouts, and cabbage.45 Vitamin C comprises two major forms: L-ascorbic acid, the reduced form, and L-dehydroascorbic acid, the oxidized form (Fig.1). Vitamin C uptake and distribution into tissues are mediated by an active transport mechanism. Levels of vitamin C
Antioxidant mixtures with photoprotective effects. Adapted from ref. 34
Carotenoid supplement and dose
Duration (week)
Result
Reference
b-Carotene 180 mg per day b-Carotene 30 mg per day b-Carotene 24 mg per day Mixed carotenoids (24 mg per day) (b-carotene, lycopene, lutein, 8 mg each) Lycopene 16 mg per day b-Carotene 60 mg per day + canthaxanthin 90 mg per day b-Carotene 90 mg per day
10 12 12 12 10 4 3
MED increased Erythema less pronounced Erythema less pronounced Erythema less pronounced Erythema less pronounced No effect No effect
27 28 29 30 31 32 33
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in the epidermis are higher than the dermis (see Table 1). Vitamin C distribution within the skin has also been determined.26
These studies suggest that vitamin C regenerates tocopherol from the tocopheroxyl radical and transfers the radical load to the aqueous compartment where it is nally eliminated by antioxidant enzymes.
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4.1. Human intervention studies One study showed that subjects treated with 400 IU per day atocopherol for 8 weeks had reduced skin malondialdehyde aer UV exposure but this intervention provided no protection from erythema.46 Werninghaus et al.47 showed no photoprotective effect aer 6 months of daily dietary supplementation of atocopherol acetate (400 IU) in 12 subjects with skin types II–IV. In both studies, a clinical measure of the minimum dose of UV necessary to induce erythema in a subject and a histologic measure of sunburn cells were compared. No difference was seen in skin a-tocopherol concentrations between treatment and placebo groups. Plasma a-tocopherol concentrations increased by 65% in the treatment group and by 18% in the placebo group, so there was no question of bioavailability. Other dietary studies have shown vitamin E as a photoprotectant when combined with other antioxidants (Table 3).48 Fuchs et al.55 reported no protection when vitamin C (3 g) and atocopherol (2 g or 3000 IU) were supplemented individually, but in combination these nutrients provided protection as assessed by increased MED aer 50 days of daily supplementation. Eberlein-K¨ onig et al.51 also observed increased MED in subjects supplemented daily with a combination of vitamin C (2 g) and a-tocopherol (1000 IU) aer only 8 days. Placzek et al.56 demonstrated a photoprotective effect aer 3 months of daily dietary supplementation with vitamin C (1 g) and a-tocopherol (500 IU). Participants showed increased resistance to UVBinduced sunburn and protection from UVA damage. This study provides evidence of long-term photoprotection of lower doses than had been previously tested.
Table 3
4.2. Photoprotection in vitro and in vivo Kondo et al.57 suggested that DL-alpha-tocopherol protects human skin broblasts against the cytotoxic effect of UVB, and its mechanism seems to be related to the inhibition of UVinduced lipid peroxidation or to the antioxidation effect of DLalpha-tocopherol. The lipid hydroperoxide concentration (determined by HPLC) in the ultraviolet radiation irradiated skin of a-tocopherol supplemented mice (diet containing 10.000 IU kg 1, fed over 30 days) was about one third of that seen in unsupplemented mice.58 Several mechanisms of action for a-tocopherol reducing the detrimental effects of ultraviolet radiation are possible. Besides scavenging reactive oxidants atocopherol may act as a cellular response modier or as a sunscreen. a-Tocopherol modulates the arachidonic acid cascade59 and modies the membrane uidity.60 Preincubation of mouse keratinocytes with vitamin C resulted in a signicant reduction in UVB-induced oxidative damage.61 Tebbe et al.62 investigated the antioxidative effect of Lascorbic acid on lipid peroxidation and on secretion and mRNA expression of interleukin (IL)-1 alpha and IL-6 aer UVA irradiation (20 J cm 2) in cultured human keratinocytes. L-Ascorbic acid was able to downregulate the IL-1 alpha mRNA expression in both UVA-irradiated and nonirradiated cells; however, IL-6 mRNA expression remained unaffected. These ndings indicate a major cell-protective effect of L-ascorbic acid on UVA-induced lipid peroxidation and the secretion of pro-inammatory cytokines by UVA-irradiated human keratinocytes.
Antioxidant mixtures with photoprotective effects. Adapted from ref. 48
Antioxidant mixtures
Outcome of the study
Reference
Vitamin C and E, lycopene, b-carotene, the rosemary polyphenol and carnosic acid
Vitamin C, vitamin E, and carnosic acid showed photoprotective potential human dermal broblasts exposed to UVA MED increased markedly aer intake of the combination of these micronutrients UV radiation-induced oxidative stress in human skin Scavenging ROS generated during photooxidative stress Protective agents in certain skin diseases caused, initiated, or exacerbated by sunlight irradiation Mean MED increased in the group received vitamins compared with baseline Many parameters of the epidermal defense against UV-induced damage were signicantly improved Signicant increase of melanin concentrations in skin was detected A selective protection of the skin against irradiation was conrmed
42
a-Tocopherol and ascorbate Oral vitamin E and b-carotene supplementation Carotenoids and tocopherols Quercetin, hesperetin and naringenin
Combination of vitamins E and C Lycopene, b-carotene, a-tocopherol and selenium b-Carotene, lycopene, a-tocopherol and ascorbic acid Carotenoids (b-carotene and lycopene), vitamins C and E, selenium, and proanthocyanidins
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48 49 29 50
51 52
53 54
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5.
Polyphenols
Polyphenols are a large family of naturally occurring plant products that are widely distributed in plant foods, including fruits, vegetables, nuts and seeds. Important dietary sources of polyphenols are onions (avonols); cacao, grape seeds (proanthocyanidins); tea, apples, and red wine (avonols and catechins); citrus fruits (avanones); berries and cherries (anthocyanidins); and soy (isoavones)63 (Fig. 1). These polyphenols contribute to the benecial health effects of vegetables and fruits. Most of the natural polyphenols are pigments, typically yellow, red or purple, and can absorb UV radiation. The radiation that polyphenols can absorb includes the entire UVB spectrum of wavelengths and part of the UVA spectra. The bioavailability and metabolism of polyphenols may inuence their effectiveness. The considerable structural diversity among the polyphenols can inuence the bioavailability of the individual components. Small molecules, like catechin monomers, can be easily absorbed through the gut barrier, whereas the large molecular weight polyphenols, such as proanthocyanidins and even ( )-epigallocatechin-3-gallate (EGCG), are poorly absorbed. Once absorbed, polyphenols are conjugated to glucuronide, sulphate and methyl groups in the gut mucosa and inner tissues. Non-conjugated polyphenols are virtually absent in plasma. During digestion in the gut, the large polyphenolic molecules break into multiple small molecules or metabolites and these may systemically induce benecial effects in the body.64
5.1. Human intervention studies EGCG from green tea (Camellia sinensis) is the most extensively studied polyphenol in terms of protection against UV radiationinduced photodamage. In a pharmacokinetic and safety study of green tea polyphenols, groups of eight healthy human subjects received one of the ve following treatments for a period of four weeks: 800 mg EGCG once a day, 400 mg EGCG twice a day, 800 mg EGCG within a dened decaffeinated green tea polyphenol mixture (polyphenol E) once a day, 400 mg EGCG as polyphenol E twice a day, or a placebo once a day.65 Skin erythema was evaluated, and the dose of UV radiation causing just perceptible erythema was determined at baseline and aer four weeks of green tea polyphenol intake. No change in MED in response to solar-simulating UV radiation was observed, but, interestingly, subjects reported that they experienced lessintensive sunburn reactions aer receiving the green tea polyphenol treatment. It is thus possible that there were subtle changes in skin photosensitivity without an impact on the MED. Other reasons for the apparent lack of change in MED could be that the local concentration of EGCG in skin aer oral intake was insufficient to provide protection or that protection could have been achieved by a longer duration of treatment.12 The effects of consumption of a avanol-rich cocoa beverage were studied54 observing a decreased UV-induced erythema by 15% aer only six weeks. In another study, two groups of women consumed either a high dose of avanol (326 mg per day, containing 61 mg epicatechin and 20 mg catechin) or a low
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dose of avanol (27 mg per day, containing 6.6 mg epicatechin and 1.2 mg catechin) cocoa powder dissolved in 100 mL water for 12 weeks.66 There was no change in erythema development in the group that consumed a low dose of avanol compared with baseline, there was an improvement in the skin condition and a signicant reduction in erythema in the group that consumed a high dose of avanol, by 15% at 6 weeks and by 25% at 12 weeks of treatment.12 5.2. Photoprotection in vitro and in vivo Mechanistic studies of photocarcinogenesis have revealed that the oral administration of green tea polyphenols (through addition to the drinking water) in SKH-1 hairless mice resulted in signicant inhibition of erythema.67 In this study, it was found that although administration of green tea polyphenols in drinking water signicantly reduced the UVB-induced tumor development in wild-type mice, this treatment had a nonsignicant effect in IL-12-knockout mice. Green tea polyphenols resulted in reduction in the levels of markers of inammation (cyclooxygenase-2, prostaglandin E2, proliferating cell nuclear antigen, and cyclin D1) and proinammatory cytokines (tumor necrosis factor-a, IL-6 and IL-1b) in chronically UVB-exposed skin and skin tumors of wild-type mice but less effective in IL12p40-KO mice. Prevention of photocarcinogenesis by green tea polyphenols is mediated through IL-12-dependent DNA repair and a subsequent reduction in skin inammation. Also dietary intake of grape seed proanthocyanidins and/or silymarin inhibited UVB radiation-induced erythema.64 Very recently it has been shown that exposure to green tea polyphenols protected against UV radiation-mediated DNA damage and apoptosis in human keratinocytes and human skin equivalents.68 This protection correlated with induction of IL-12 secretion and was almost completely reversed by the addition of an anti-IL-12 antibody, strongly implicating IL-12 as an important mediator of the protective effects of green tea polyphenols. Adult human skin broblasts and normal epidermal keratinocytes, cultured separately, had signicantly less DNA damage from UVA irradiation when treated with EGCG.69 EGCG treatment of human broblasts in culture blocked the UV-induced increase in collagen secretion and collagenase mRNA levels, and also inhibited the binding activities of the UV-induced nuclear transcription factors nuclear factor-kappaB (NF-kB) and activated protein AP-1.70 When HaCaT cells were treated with ( )-epicatechin-3-gallate (ECG) and exposed to UVB radiation, it was observed that avonoid could act as a free-radical scavenger when keratinocytes were photodamaged.71 The treatment of HaCaT cells with ECG also demonstrated its free-radical scavenging effects, when cells were irradiated with UVA radiation. These observations indicate that EGCG could play an important role in the attenuation of oxidative stress-mediated cellular signaling responses, which are essential factors in various skin diseases in humans.64 Resveratrol, a stilbene found in grapes, red wine, and nuts, is also a potential polyphenolic antioxidant. Pretreatment of human epidermal keratinocytes with resveratrol inhibited the UVB-mediated activation of the NF-kB pathway.72 The treatment
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of HaCaT cells with resveratrol before UVB irradiation resulted in an increase in cell survival of UVB-irradiated cells which was associated with the reduction in ROS production.73 Soybeans are a rich source of the isoavones, genistein and daidzein, and are photoprotective.74 Genistein has been shown to reduce UV radiation-induced oxidative and photodynamic DNA damage.75 Treatment of the human keratinocyte cell line NCTC 2544 with genistein prevented the UV-induced enhancement of the DNAbinding activity of the signal transducer and activator of transcription-1 by acting as a tyrosine kinase inhibitor, thus, limiting lipid peroxidation and increases in ROS generation.76 Based on the epidemiological evidence and laboratory studies conducted using in vitro and in vivo systems, it is suggested that routine consumption of these polyphenols may provide efficient protection against the harmful effects of solar UV radiation in humans.64
6. Endogenous photoprotection by dietary antioxidant combinations As mentioned before in this review, combinations of different antioxidants applied simultaneously can provide a synergistic effect. Several studies observed that dietary antioxidants are most effective when used in combination (Table 3).48 Offord et al.42 observed that b-carotene and lycopene must be delivered together with vitamin E to prevent the formation of oxidative derivatives, which may inuence the cellular and molecular responses. According to Offord et al.,42 interactions between structurally different compounds with variable antioxidant activity may provide additional protection against increased oxidative stress. Fern´ andez-Garc´ıa77 observed similar effects. This study strengthens the hypothesis that the combination of dietary antioxidants present in tomato (naringenin and lycopene) other than lycopene alone could play a role in the health effects of tomato as evidenced by epidemiological studies. Longterm radical-initiated UV damage may be mitigated by a balanced diet.78 Therefore, combinations of micronutrients may be envisaged for effective photoprotection.
7. Conclusions Upon exposure to UV radiation from sunlight, photo-oxidative reactions are initiated which cause damage to skin. A diet rich in antioxidants such as carotenoids, vitamins E and C, and polyphenols can provide photoprotection against the harmful effects of solar UV radiation in humans. The literature is replete with intervention studies which nd that supplementation with carotenoids, vitamins E and C, and polyphenols may protect from several markers of UV damage including lipid peroxidation, erythema, DNA damage, and apoptosis. Nevertheless, photoprotection can only be achieved if these micronutrients are available in sufficient amounts at the target site. More investigation of optimal doses and mechanisms of protection is needed to better target and prevent photodamage with diet. However, endogenous protection associated with the diet must
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be considered complementary to the topical use of a sunscreen with a high-sun protection factor. The use of dietary antioxidants in combination may provide an effective strategy for mitigating the effects of UV radiation that will lead to the protection of the skin from various skin diseases caused by excessive sun exposure.
Abbreviations ECG EGCG HO-1 IL MED NF-kB ROS 1 O2 TBARS UV
( )-Epicatechin-3-gallate ( )-Epigallocatechin-3-gallate Heme-oxygenase 1 Interleukin Minimal erythema dose Nuclear factor-kappaB Reactive oxygen species Singlet oxygen Thiobarbituric acid-reactive substances Ultraviolet
Acknowledgements E.F.G. is supported by fellowships from the Postdoctoral Fellowship Program (Alfonso Mart´ın Escudero Foundation, Spain), and the Junta de Andalucia (PII-CTS-7962 MO)/European Union (FEDER).
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F. J. Kelly, M. C. Polidori, C. Rice-Evans, S. Southon, T. van Vliet, J. Vi˜ na-Ribes, G. Williamson and S. B. Astley, Bioavailability and metabolism, Mol. Aspects Med., 2002, 23, 39–100. M. G. Traber and H. Sies, Vitamin E in humans: demand and delivery, Annu. Rev. Nutr., 1996, 16, 321–347. K. J. Yeum and R. M. Russell, Carotenoid bioavailability and bioconversion, Annu. Rev. Nutr., 2002, 22, 483–504. J. A. Evans and E. J. Johnson, The role of phytonutrients in skin health, Nutrients, 2010, 2, 903–928. R. M. Tyrrell, Role for singlet oxygen in biological effects of ultraviolet A radiation, Methods Enzymol., 2000, 319, 290– 296. F. Khachik, C. J. Spangler, J. C. Smith, L. M. Caneld, A. Steck and H. Pfander, Identication, quantication, and relative concentrations of carotenoids and their metabolites in human milk and serum, Anal. Chem., 1997, 69, 1873–1881. W. Stahl, A. R. Sundquist, M. Hanusch, W. Schwarz and H. Sies, Separation of b-carotene and lycopene geometrical isomers in biological samples, Clin. Chem., 1993, 39, 810– 814. G. M. Lowe, R. F. Bilton, I. G. Davies, T. C. Ford, D. Billington and A. Young, Carotenoid composition potential in subfractions of human low-density lipoprotein, Ann. Clin. Biochem., 1999, 36, 323–332. K. H. van het Hof, B. C. de Boer, L. B. Tijburg, B. R. Lucius, I. Zijp, C. E. West, J. G. Hautvast and J. A. Weststrate, Carotenoid bioavailability in humans from tomatoes processed in different ways determined from the carotenoid response in the triglyceride-rich lipoprotein fraction of plasma aer a single consumption and in plasma aer four days of consumption, J. Nutr., 2000, 130, 1189–1196. A. van Bennekum, M. Werder, S. T. Thuahnai, C. H. Han, P. Duong, D. L. Williams, P. Wetstein, G. Schulthess, M. C. Phillips and H. Hauser, Class B scavenger receptormediated intestinal absorption of dietary beta-carotene and cholesterol, Biochemistry, 2005, 44, 4517–4525. A. During, H. D. Dawson and E. H. Harrison, Carotenoid transport is decreased and expression of the lipid transporters SR-BI, NPC1L1, and ABCA1 is down regulated in Caco-2 cells treated with ezetimibe, J. Nutr., 2005, 135, 2305–2312. H. Tsuruoka, W. Khovidhunkit, B. E. Brown, J. W. Fluhr, P. M. Elias and K. R. Feingold, Scavenger receptor class B type I is expressed in cultured keratinocytes and epidermis. Regulation in response to change in cholesterol homeostasis and barrier requirements, J. Biol. Chem., 2002, 277, 2916–2922. T. R. Hata, T. A. Scholz, I. V. Ermakov, R. W. McClane, F. Khachik, W. Gellermann and L. K. Pershing, Noninvasive raman spectroscopic detection of carotenoids in human skin, J. Invest. Dermatol., 2000, 115, 441–448. Y. M. Peng, Y. S. Peng, Y. Lin, T. Moon and M. Baier, Micronutrient concentrations in paired skin and plasma of patients with actinic keratosis. Effect of prolonged retinol
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supplementation, Cancer Epidemiol., Biomarkers Prev., 1993, 2, 145–150. J. Fuchs, S. Weber, M. Podda, N. Groth, T. Herrling, L. Packer and R. Kaufmann, HPLC analysis of vitamin E isoforms in human epidermis: correlation with minimal erythema dose and free radical scavenging activity, Free Radical Biol. Med., 2003, 34, 330–336. Y. Shindo, E. Witt, D. Han, W. Epstein and L. Packer, Enzymic and non-enzymic antioxidants in epidermis and dermis of human skin, J. Invest. Dermatol., 1994, 102, 122– 124. J. J. Thiele, M. G. Traber and L. Packer, Depletion of human stratum corneum vitamin E: an early and sensitive in vivo marker of UV induced photo-oxidation, J. Invest. Dermatol., 1998, 110, 756–761. G. Rhie, M. H. Shin, J. Y. Seo, W. W. Choi, K. H. Cho, K. H. Kim, K. C. Park, H. C. Eun and J. H. Chung, Agingand photoaging-dependent changes of enzymic and nonenzymic antioxidants in the epidermis and dermis of human skin in vivo, J. Invest. Dermatol., 2001, 117, 1212– 1217. M. M. Mathews-Roth, M. A. Pathak, J. A. Parrish, T. B. Fitzpatrick, E. H. Kass, K. Toda and W. Clemens, A clinical trial of the effects of oral beta-carotene on the responses of human skin to solar radiation, J. Invest. Dermatol., 1972, 59, 349–353. H. P. M. Gollnick, W. Hopfenm¨ uller, C. Hemmes, S. C. Chun, C. Schmid, et al. Systemic beta carotene plus topical UVsunscreen are an optimal protection against harmful effects of natural UV-sunlight: results of the Berlin-Eilath study, Eur. J. Dermatol., 1996, 6, 200–205. W. Stahl, U. Heinrich, H. Jungmann, H. Sies and H. Tronnier, Carotenoids and carotenoids plus vitamin E protect against ultraviolet light-induced erythema in humans, Am. J. Clin. Nutr., 2000, 71, 795–798. U. Heinrich, C. Gartner, M. Wiebusch, O. Eichler, H. Sies, et al. Supplementation with beta-carotene or a similar amount of mixed carotenoids protects humans from UVinduced erythema, J. Nutr., 2003, 133, 98–101. W. Stahl, U. Heinrich, S. Wiseman, O. Eichler, H. Sies and H. Tronnier, Dietary tomato paste protects against ultraviolet light-induced erythema in humans, J. Nutr., 2001, 131, 1449–1451. C. Wolf, A. Steiner and H. H¨ onigsmann, Do oral carotenoids protect human skin against ultraviolet erythema, psoralen phototoxicity, and ultraviolet-induced DNA damage?, J. Invest. Dermatol., 1988, 90, 55–57. M. Garmyn, J. D. Ribaya-Mercado, R. M. Russell, J. Bhawan and B. A. Gilchrest, Effect of beta-carotene supplementation on the human sunburnreaction, Exp. Dermatol., 1995, 4, 104–111. H. Sies and W. Stahl, Carotenoids and UV protection, Photochem. Photobiol. Sci., 2004, 3, 749–752. L. Lomnitski, S. Grossman, M. Bergman, Y. Sofer and D. Sklan, In vitro and in vivo effects of beta-carotene on rat epidermal lipoxygenases, Int. J. Vitam. Nutr. Res., 1997, 67, 407–414.
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36 N. S. Ranadive, I. A. Menon, S. Shirwadkar and S. D. Persad, Quantitation of cutaneous inammation induced by reactive species generated by UV-visible irradiation of rose Bengal, Inammation, 1989, 13, 483–494. 37 M. Dalle Carbonare and M. A. Pathak, Skin photosensitizing agents and the role of reactive oxygen species in photoaging, J. Photochem. Photobiol., B, 1992, 14, 105–124. 38 I. O'Connor and N. O'Brien, Modulation of UVA lightinduced oxidative stress by beta-carotene, lutein and astaxanthin in cultured broblasts, J. Dermatol. Sci., 1998, 16, 226–230. 39 N. M. Lyons and N. M. O'Brien, Modulatory of an algal extract containing astaxanthin on UVA-irradiated cells in culture, J. Dermatol. Sci., 2002, 30, 73–84. 40 K. Someya, Y. Totsuka, M. Murakoshi, H. Kitano and T. J. Miyazawa, The antioxidant effect of palm fruit carotene on skin lipid peroxidation in guinea pigs as estimated by chemiluminescence-HPLC method, J. Nutr. Sci. Vitaminol., 1994, 40, 24–31. 41 U. C. Oberm¨ uller-Jevic, P. I. Francz, J. Frank, A. Flaccus and H. K. Biesalski, Enhancement of the UVA induction of haem oxygenase-1 expression by beta-carotene in human skin broblasts, FEBS Lett., 1999, 460, 212–216. 42 E. A. Offord, J. C. Gautier, O. Avanti, C. Scaletta, F. Runge, K. Kr¨ amer and L. A. Applegate, Photoprotective potential of lycopene, beta-carotene, vitamin E, vitamin C and carnosic acid in UVA-irradiated human skin broblasts, Free Radical Biol. Med., 2002, 32, 1293–1303. 43 A. T. Dinkova-Kostova, Phytochemicals as protectors against ultraviolet radiation: versatility of effects and mechanisms, Planta Med., 2008, 74, 1548–1559. 44 J. J. Thiele and S. Ekanayake-Mudiyanselage, Vitamin E in human skin: organ-specic physiology and considerations for its use in dermatology, Mol. Aspects Med., 2007, 28, 646–667. 45 W. Stahl and H. Sies, Antioxidant defense: vitamins E and C and carotenoids, Diabetes, 1997, 46, S14–S18. 46 D. C. McMillan, D. Talwar, N. Sattar, M. Underwood, D. O'Reilly and C. McArdle, The relationship between reduced vitamin antioxidant concentrations and the systemic inammatory response in patients with common solid tumors, Clin. Nutr., 2002, 21, 161–164. 47 K. Werninghaus, M. Meydani, J. Bhawan, R. Margolis, J. B. Blumberg and B. A. Gilchrest, Evaluation of the photoprotective effect of oral vitamin E supplementation, Arch. Dermatol., 1994, 130, 1257–1261. 48 R. Pandel, B. Poljsak, A. Godic and R. Dahmane, Skin photoaging and the role of antioxidants in its prevention, ISRN Dermatol., 2013, 2013, 1–11. 49 F. McArdle, L. E. Rhodes, R. A. G. Parslew, G. L. Close, C. I. A. Jack, P. S. Friedmann and M. J. Jackson, Effects of oral vitamin E and b-carotene supplementation on ultraviolet radiation-induced oxidative stress in human skin, Am. J. Clin. Nutr., 2004, 80, 1270–1275. 50 F. Bonina, M. Lanza, L. Montenegro, C. Puglisi, A. Tomaino, D. Trombetta, F. Castelli and A. Saija, Flavonoids as potential protective agents against photo-oxidative skin damage, Int. J. Pharm., 1996, 145, 87–94. This journal is © The Royal Society of Chemistry 2014
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51 B. Eberlein-K¨ onig, M. Placzek and B. Przybilla, Protective effect against sunburn of combined systemic ascorbic acid (vitamin C) and D-alpha-tocopherol(vitamin E), J. Am. Acad. Dermatol., 1998, 38, 45–48. 52 J. P. C´ esarini, L. Michel, J. M. Maurette, H. Adhoute and M. B´ ejot, Immediate effects of UV radiation on the skin:modication by an antioxidant complex containing carotenoids, Photodermatol., Photoimmunol. Photomed., 2003, 19, 182–189. 53 E. Postaire, H. Jungmann, M. Bejot, U. Heinrich and H. Tronnier, Evidence for antioxidant nutrients-induced pigmentation in skin: results of a clinical trial, Biochem. Mol. Biol. Int., 1997, 42, 1023–1033. 54 A. K. Greul, J. U. Grundmann, F. Heinrich, I. Ptzner, J. Bernhardt, A. Ambach, H. K. Bielsalski and H. Gollnick, Photoprotection of UV-irradiated human skin: an antioxidative combination of vitamins E and C, carotenoids, selenium and proanthocyanidins, Skin Pharmacol. Appl. Skin Physiol., 2002, 15, 307–315. 55 J. Fuchs and H. Kern, Modulation of UV-light-induced skin inammation by D-alpha-tocopherol and L-ascorbic acid: a clinical study using solar simulated radiation, Free Radical Biol. Med., 1998, 25, 1006–1012. 56 M. Placzek, S. Gaube, U. Kerkmann, K. P. Gilbertz, T. Herzinger, E. Haen and B. Przybilla, Ultraviolet Binduced DNA damage in human epidermis is modied by the antioxidants ascorbic acid and D-alpha-tocopherol, J. Invest. Dermatol., 2005, 124, 304–307. 57 S. Kondo, A. Mamada, J. Yamaguchi and S. Fukuro, Protective effect of racemic alpha-tocopherol on the cytotoxicity of ultraviolet B against human skin broblasts in vitro, Photodermatol., Photoimmunol. Photomed., 1990, 7, 173–177. 58 L. Packer, Ultraviolet radiation (UVA, UVB) and skin antioxidants, in Free radical damage and its control, ed. C. A. Rice Evans and R. H. Burdon, Elsevier Press, New York, 1994, pp. 234–255. 59 D. G. Cornwell and R. V. Panganamala, Vitamin E action in modulating the arachidonic acid cascade, in Vitamin E in health and disease, ed. L. Packer and J. Fuchs, Marcel Dekker, New York, 1993, pp. 385–410. 60 G. Zimmer, T. Th¨ urich and B. Scheer, Membrane uidity and vitamin E, in Vitamin E in health and disease, ed. L. Packer and J. Fuchs, Marcel Dekker, New York, 1993, pp. 207– 222. 61 M. S. Stewart, G. S. Cameron and B. C. Pence, Antioxidant nutrients protect against UVB-induced oxidative damage to DNA of mouse keratinocytes in culture, J. Invest. Dermatol., 1996, 106, 1976–1989. 62 B. Tebbe, S. Wu, C. C. Geilen, J. Eberle, V. Kodelija and C. E. Orfanos, L-Ascorbic acid inhibits UVA-induced lipid peroxidation and secretion of IL-1a and IL-6 in cultured human keratinocytes in vitro, J. Invest. Dermatol., 1997, 108, 302–306. 63 C. Manach, A. Scalbert, C. Morand, C. R´ em´ esy and L. Jim´ enez, Polyphenols: food sources and bioavailability, Am. J. Clin. Nutr., 2004, 79, 727–747.
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64 J. A. Nichols and S. K. Katiyar, Skin photoprotection by natural polyphenols: anti-inammatory, anti-oxidant and DNA repair mechanisms, Arch. Dermatol. Res., 2010, 302, 1–19. 65 H. H. Chow, Y. Cai, I. A. Hakim, J. A. Crowell, F. Shahi, C. A. Brooks, R. T. Dorr, Y. Hara and D. S. Alberts, Pharmacokinetics and safety of green tea polyphenols aer multiple-dose administration of epigallocatechingallate and polyphenol E in healthy individuals, Clin. Cancer Res., 2003, 9, 3312–3319. 66 U. Heinrich, K. Neukam, H. Tronnier, H. Sies and W. Stahl, Long-term ingestion of high avanol cocoa provides photoprotection against UV-induced erythema and improves skin condition in women, J. Nutr., 2006, 136, 1565–1569. 67 S. M. Meeran, S. Akhtar and S. K. Katiyar, Inhibition of UVBinduced skin tumor development by drinking green tea polyphenols is mediated through DNA repair and subsequent inhibition of inammation, J. Invest. Dermatol., 2009, 129, 1258–1270. 68 A. Schwarz, A. Maeda, D. Gan, T. Mammone, M. S. Matsui and T. Schwarz, Green tea phenol extracts reduce UVBinduced DNA damage in human cells via interleukin-12, Photochem. Photobiol., 2008, 84, 350–355. 69 N. Morley, T. Clifford, L. Salter, S. Campbell, D. Gould and A. Curnow, The green tea polyphenol ( )-epigallocatechin gallate and green tea can protect human cellular DNA from ultraviolet and visible radiation-induced damage, Photodermatol., Photoimmunol. Photomed., 2005, 21, 15–22. 70 J. Kim, J. S. Hwang, Y. K. Cho, Y. Han, Y. J. Jeon and K. H. Yang, Protective effects of ( )-epigallocatechin-3gallate on UVA-and UVB-induced skin damage, Skin Pharmacol. Appl. Skin Physiol., 2001, 14, 11–19.
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71 C. C. Huang, J. Y. Fang, W. B. Wu, H. S. Chiang, Y. J. Wei and C. F. Hung, Protective effects of ( )-epicatechin-3-gallate on UVA-induced damage in HaCaT keratinocytes, Arch. Dermatol. Res., 2005, 296, 473–481. 72 V. M. Adhami, F. Afaq and N. Ahmad, Suppression of ultraviolet B exposure-mediated activation of NF-kappaB in normal human keratinocytes by resveratrol, Neoplasia, 2003, 5, 74–82. 73 K. Park and J. H. Lee, Protective effects of resveratrol on UVBirradiated HaCaT cells through attenuation of the caspase pathway, Oncol. Rep., 2008, 19, 413–417. 74 H. Wei, R. Saladi, Y. Lu, Y. Wang, S. R. Palep, J. Moore, R. Phelps, E. Shyong and M. G. Lebwohl, Isoavonegenistein: photoprotection and clinical implications in dermatology, J. Nutr., 2003, 133, 3811S– 3819S. 75 J. O. Moore, Y. Wang, W. G. Stebbins, D. Gao, X. Zhou, R. Phelps, M. Lebwohl and H. Wei, Photoprotective effect of isoavone genistein on ultraviolet B induced pyrimidine dimer formation and PCNA expression in human reconstituted skin and its implications in dermatology and prevention of cutaneous carcinogenesis, Carcinogenesis, 2006, 27, 1627–1635. 76 C. Maziere, F. Dantin, F. Dubois, R. Santus and J. Mazi´ ere, Biphasic effect of UVA radiation on STAT1 activity and tyrosine phosphorylation in cultured human keratinocytes, Free Radical Biol. Med., 2000, 28, 1430–1437. 77 E. Fern´ andez-Garc´ıa, Photoprotection of human dermal broblasts against ultraviolet light by antioxidant combinations present in tomato, Food Funct., 2014, 5, 285–290. 78 F. B¨ ohm, R. Edge, L. Lange and T. G. Truscott, Enhanced protection of human cells against ultraviolet light by antioxidant combinations involving dietary carotenoids, J. Photochem. Photobiol., B, 1998, 44, 211–215.
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REVIEW
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Skin protection against UV light by dietary antioxidants Cite this: DOI: 10.1039/c4fo00280f
Elisabet Ferna´ndez-Garc´ıa* There is considerable interest in the concept of additional endogenous photoprotection by dietary antioxidants. A number of efficient micronutrients are capable of contributing to the prevention of UV damage in humans. These compounds protect molecular targets by scavenging reactive oxygen species, including excited singlet oxygen and triplet state molecules, and also modulate stress-dependent signaling and/or suppress cellular and tissue responses like inflammation. Micronutrients present in the diet such as carotenoids, vitamins E and C, and polyphenols contribute to antioxidant defense and may also contribute to endogenous photoprotection. This review summarizes the literature concerning the use of dietary antioxidants as systemic photoprotective agents towards skin damage induced by UVA and UVB. Intervention studies in humans with carotenoid-rich diets have shown photoprotection. Interestingly, rather long treatment periods (a minimum of 10 weeks) were required to achieve this effect. Likewise, dietary Received 1st April 2014 Accepted 17th May 2014
carotenoids exert their protective antioxidant function in several in vitro and in vivo studies when present at sufficiently high concentration. A combination of vitamins E and C protects the skin against UV damage. It is suggested that daily consumption of dietary polyphenols may provide efficient protection against the
DOI: 10.1039/c4fo00280f
harmful effects of solar UV radiation in humans. Furthermore, the use of these micronutrients in
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combination may provide an effective strategy for protecting human skin from damage by UV exposure.
1. Introduction Human skin acts as a barrier between the internal and external environments, protecting the body from mechanical damage, Institute of Biochemistry and Molecular Biology I, Faculty of Medicine, Heinrich-Heine-University D¨ usseldorf, PO Box 101007, D-40001 D¨ usseldorf, Germany. E-mail: [email protected]; Fax: +49 211 13029; Tel: +49 211 8110526
Dr Fern´ andez-Garc´ıa is a Postdoctoral Researcher at Andalusian Center for Molecular Biology and Regenerative Medicine, in Seville, Spain. She studied chemistry at the University of Seville. From 2004 to 2011 she worked in Food Biotechnology Department, Instituto de la Grasa (CSIC), Seville, Spain and received her PhD. In 2012 she joined the Institute of Biochemistry and Molecular Biology I in Heinrich Heine-University D¨ usseldorf (Germany) supported by a fellowship from the Postdoctoral Fellowship Program (Alfonso Martin Escudero Foundation, Spain). Dr Fern´ andez-Garc´ıa has over 10 years of experience in the eld of dietary antioxidants. This journal is © The Royal Society of Chemistry 2014
noxious substances, invasion by microorganisms, and radiation. The skin plays an important role in regulating body homeostasis by keeping water loss to a minimum and by regulating body temperature. In recent years it has become clear that the skin is an essential part of the immune system. The skin condition and functioning are affected by environmental factors, such as ultraviolet (UV) radiation, free radicals, toxic and allergic compounds, and mechanical damage, and by endogenous factors, such as genetic predisposition, immune and hormone status, and stress. Consequently, the skin undergoes alterations resulting in photoaging, inammation, reduced immune function, imbalanced epidermal homeostasis and other skin disorders.1 Upon exposure to UV radiation from sunlight, photo-oxidative reactions are initiated which cause damage to biomolecules and affect the integrity of skin cells and damage skin. Such photo-oxidative damage plays a role in pathological processes and is involved in the development of many disorders affecting the skin.2 Based on wavelength, the UV radiation spectrum is divided into three regions: UVA (400–320 nm), UVB (320–290 nm), and UVC (290–200 nm). UVA (400–320 nm) radiation, which contributes to up to 95% of the total UV exposure, is not absorbed by DNA but it is a strong oxidant and considered the most important source of oxidative stress in human skin.3 UVA plays a major role in photoaging. This radiation can penetrate into the deeper dermis and induces the generation of reactive oxygen species
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(ROS), which can induce mutations in the mitochondrial DNA, thus leading to the loss of enzymes involved in oxidative phosphorylation and deciencies in energy metabolism.4 UVB (320–290 nm) is mainly absorbed by keratinocytes in the epidermis. By direct interaction with the DNA, it causes mutations and skin cancer. UVB also leads to sunburn, which is an erythema resulting from an inammatory response to the photodamage to the skin.4 A frequently used measure of UV irradiation-induced erythema is determination of the minimal erythema dose (MED), which is dened as the minimal amount of energy required to induce a uniform, clearly demarcated redness 16–24 h aer exposure to UV radiation. Although nature anticipates these conditions by increasing epidermal thickness, stimulating melanogenesis, and providing natural antioxidants in the supercial skin layers, supplementation with nutrients may support these processes and thereby serve as an additional protective measure against the harmful effects of UV light.1
2. Endogenous photoprotection by dietary antioxidants The concept of additional endogenous protection was proposed about 30 years ago.5,6 In order to increase the barrier for UV light, the compound should absorb UV light over a broad range of wavelengths with high efficacy. Antioxidants protect molecular targets by scavenging ROS, including excited singlet oxygen and triplet state molecules. Compounds that modulate stressdependent signaling and/or suppress cellular and tissue responses like inammation are suitable for this purpose. A number of efficient micronutrients are capable of directly scavenging lipophilic and hydrophilic prooxidants or serving as constituents of antioxidant enzymes. Carotenoids, polyphenols, vitamin E as well as vitamin C contribute to antioxidant defense and may also contribute to endogenous photoprotection.7,8 The concept of endogenous photoprotection implies that the active compound is available in sufficient amounts at the target site.9 Thus, structural features are important, and inuence pharmacokinetic parameters like absorption, distribution, and metabolism that may affect the level of the compound in skin.10,11 In this paper, photoprotective effects of dietary carotenoids, vitamins E and C, and polyphenols towards skin damage induced by UV light are reviewed in the available literature, underlying human intervention studies are discussed, and in vitro or in vivo assays are summarized.
3.
Carotenoids
Carotenoids are a family of compounds of over 600 fat-soluble plant pigments. Fruits and vegetables are major sources of carotenoids.12 Carotenoids exhibit a variety of biological properties. These include their role in light harvesting and photoprotection or provitamin and antioxidant functions in humans and animals. Carotenoids present a long central chain of conjugated double bonds carrying acyclic or cyclic substituents.
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Xanthophylls, also called oxocarotenoids, contain functional oxygen groups7 (see Fig. 1). Because of their structure and physicochemical properties, carotenoids could be involved in several ways to protect skin from sunlight damage, namely by increasing the optical density, quenching the singlet oxygen (1O2) or, for provitamin A carotenoids, via formation of retinoic acid. The role of 1O2 in UVA-induced oxidative stress is well established and has been reviewed extensively.13 Carotenoids can also scavenge other reactive oxygen species, such as superoxide anions, hydroxyl radicals or hydrogen peroxide. Under certain conditions, however, i.e. higher oxygen partial pressure, carotenoids may act as pro-oxidants.4 The most abundant carotenoids in the human organism are b-carotene, a-carotene, and lycopene, as well as the xanthophylls lutein, zeaxanthin, and a- and b-cryptoxanthin.14,15 Carotenoids are transported to the skin and accumulate mainly in the epidermal layers. The amount of these pigments deposited in skin correlates with dietary intake and bioavailability from the food source. Aer absorption, carotenoids are transported in the bloodstream via lipoproteins to various target tissues.16,17 Recently, cholesterol transporters such as scavenger receptor class B member 1 (SR-B1) and cluster of differentiation 36 (CD 36) were shown to mediate a facilitated absorption of carotenoids in the gut.18,19 It is likely that carotenoids are taken up by these transporters also in epidermis, which is an active site of cholesterol accumulation for the maintenance of permeability barrier function. SR-B1 is expressed in human epidermis,20 predominantly in the basal layers.3 The levels of these compounds in skin vary with respect to the skin area and skin layer. High levels of carotenoids are found in the skin of the forehead, the palm of the hand, and in dorsal skin; low levels are found in skin of the arm and the back of the hand (see Table 1 with data from ref. 8).
3.1. Human intervention studies Intervention studies in humans with carotenoid-rich diets have shown photoprotection of the skin as measured by decreased sensitivity to UV radiation-induced erythema (see Table 2).27–34 Stahl et al., 2001 (ref. 31) found that ingestion of tomato paste (40 g per day, equivalent to 16 mg lycopene per day) over a period of 10 weeks led to a 40% reduction in skin erythema development induced by exposure to solar-simulating UV radiation. Erythema was induced by a solar light simulator at 1.25 MED, and reddening of the skin was evaluated before and 24 hours aer irradiation by chromametry. Erythema intensity was lower aer the treatment. No signicant protection was found at week 4, but aer 10 weeks, erythema formation was signicantly lower in the group consuming the tomato paste than in the controls. In another study, protection against UV-induced erythema can be achieved aer ingestion of 24 mg of b-carotene (from the alga Dunaliella salina) for a period of 12 weeks. Erythema intensity was signicantly diminished from 8 weeks. However erythema suppression was more pronounced when a combination of carotenoids and vitamin E was supplied.29 Similar results have been found in other studies shown in
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Fig. 1
Examples of dietary antioxidants that protect against damage by UV radiation.
Table 2. Also listed are several intervention studies where no protection was observed. It is interesting to note that protection was only determined in studies where the intervention was for more than 10 weeks. Apparently a sufficiently long interval of treatment is needed to provide optimal protection of the skin against UV-induced erythema.
3.2. Photoprotection in vitro and in vivo Several studies have used cultured human or other skin broblasts to examine the protective effects of carotenoids on UVinduced lipid peroxidation.3 A variety of experimental studies investigated the antioxidant function of beta-carotene in the skin in vivo and in vitro. In rodents, beta-carotene was found to reduce lipid peroxidation.35 It has also been demonstrated that this compound quenches singlet oxygen-mediated photochemical reactions in rodent skin.36
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In cultured skin cells, a few in vitro studies have investigated the antioxidant potential of b-carotene. This compound decreased the photoinactivation of the enzymes catalase and superoxide dismutase as well as protein cross-linking.37 In rat kidney broblasts, b-carotene diminished UVA-induced catalase deactivation and lipid peroxidation.38 Lycopene, b-carotene and lutein, applied in liposomes as vehicles, decreased the UVB-induced formation of thiobarbituric acid-reactive substances (TBARS) at 1 hour to levels 40–50% of those of controls free of carotenoids.14 The amounts of carotenoid needed for optimal protection were 0.05, 0.40 and 0.30 nmol mg 1 protein for lycopene, b-carotene and lutein, respectively. A further increase of carotenoid content in cells beyond the optimum levels led to pro-oxidant effects. In another study, the depletion of catalase and superoxide dismutase by UVA was restored, and TBARS was reduced by culturing rat kidney broblasts with b-carotene or lutein (1 mM each), or with
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Carotenoids, a-tocopherol and ascorbic acid levels in human skin. Adapted from ref. 8
Table 1
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Micronutrient (skin layer)
Skin level (pmol mg
1
wet wt)
Reference
Carotenoids (epidermis and dermis) b-Carotene a-Carotene Lycopene Phytoene Phytouene b-Carotene a-Carotene Lycopene Lutein
0.05 0.04 0.02 0.01 0.13 0.10 0.12 0.04 0.03 0.02 0.11 0.01 0.01 0.01 0.22 0.01 0.03 0.01
21
a-Tocopherol Epidermis Dermis Stratum corneum
24.8 9.6 16.2 1.1 33.0 4.0
23 24 25
363.7 24.8 162.4 18.6 354.7 23.5 152.0 19.0
26
Ascorbic acid Epidermis from forearm Dermis from forearm Epidermis from upper-inner arm Dermis from upper-inner arm
22
astaxanthin, which was reported to give superior protective activity at concentrations as low as 10 nM.38 Lyons et al.39 examined the ability of an algal extract to protect against UVAinduced DNA alterations in human skin broblasts (1BR-3), human melanocytes (HEMAc) and human intestinal CaCo-2 cells. DNA damage was assessed using single cell gel electrophoresis or comet assay. The algal extract displayed protection against UVA-induced DNA damage when 10 mM astaxanthin was added to all three cell types. However, at lower concentrations (10 and 100 nM) no signicant protection was evident. In 1BR-3 cells, preincubation (18 h) with 10 mM of either the synthetic astaxanthin or the algal extract prevented UVA-induced alterations in cellular superoxide dismutase activity and cellular glutathione content. Studies in mouse models also conrm the prevention of oxidative stress induction in skin, caused by UV irradiation, by carotenoids.40 Heme-oxygenase 1 (HO-1) gene is strongly activated within the rst few hours that follow UVA irradiation of normal human dermal broblasts and this response is being used as a marker
Table 2
of oxidative stress in cells.3 Carotenoids could be expected to suppress the UVA induced HO-1 gene activation in human cells. Unexpectedly, two studies with skin broblasts in vitro found an opposite effect. The rst study applied b-carotene in cyclodextrins at levels of 0.5 and 5 mM.41 A signicant pro-oxidative effect and enhancement of UVA-induced HO-1 expression were observed. In the second study, b-carotene or lycopene (0.5– 1.0 mM) were prepared in nanoparticle formulations. As in the study above, either b-carotene or lycopene led to a further 1.5fold rise in the UVA-induced HO-1 mRNA levels.42 It should be pointed out that the protective properties of carotenoids are probably at least two-fold, consisting of (1) their potent antioxidant activity and (2) their ability to induce cellular protective response. Thus, dietary carotenoids and their metabolites induce phase 2 cytoprotective enzymes and share with all other classes of phase 2 inducers a common chemical property, the ability to react with sulydryl groups.43 Overall, these in vitro and in vivo studies show that carotenoids can exert their protective antioxidant function when present at sufficiently high concentration in the skin cells.
4. Vitamins E and C Vitamin E refers to a family of eight nutrients of which a-tocopherol is the most abundant and biologically active form in the human body (Fig. 1). This essential lipophilic nutrient is well known for its role as a chain-breaking antioxidant during lipid peroxidation and it protects polyunsaturated fatty acids in cell membranes from oxidation.14 Food sources include vegetables, vegetable oils, cereals and nuts.44 a-Tocopherol concentrations in skin can be increased with oral or topical delivery and are decreased with UV exposure. Vitamin E is the most abundant lipophilic antioxidant found in human skin (see Table 1). In humans, levels of vitamin E in the epidermis are higher than the dermis. Vitamin E and carotenoids are absorbed by the same pathway.14 Vitamin C is an effective antioxidant and an essential cofactor in numerous enzymatic reactions. The major source for vitamin C in the diet are fruits, especially citrus fruits, kiwifruit, cherries and melons, and vegetables such as tomatoes, leafy greens, broccoli, cauliower, Brussels sprouts, and cabbage.45 Vitamin C comprises two major forms: L-ascorbic acid, the reduced form, and L-dehydroascorbic acid, the oxidized form (Fig.1). Vitamin C uptake and distribution into tissues are mediated by an active transport mechanism. Levels of vitamin C
Antioxidant mixtures with photoprotective effects. Adapted from ref. 34
Carotenoid supplement and dose
Duration (week)
Result
Reference
b-Carotene 180 mg per day b-Carotene 30 mg per day b-Carotene 24 mg per day Mixed carotenoids (24 mg per day) (b-carotene, lycopene, lutein, 8 mg each) Lycopene 16 mg per day b-Carotene 60 mg per day + canthaxanthin 90 mg per day b-Carotene 90 mg per day
10 12 12 12 10 4 3
MED increased Erythema less pronounced Erythema less pronounced Erythema less pronounced Erythema less pronounced No effect No effect
27 28 29 30 31 32 33
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in the epidermis are higher than the dermis (see Table 1). Vitamin C distribution within the skin has also been determined.26
These studies suggest that vitamin C regenerates tocopherol from the tocopheroxyl radical and transfers the radical load to the aqueous compartment where it is nally eliminated by antioxidant enzymes.
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4.1. Human intervention studies One study showed that subjects treated with 400 IU per day atocopherol for 8 weeks had reduced skin malondialdehyde aer UV exposure but this intervention provided no protection from erythema.46 Werninghaus et al.47 showed no photoprotective effect aer 6 months of daily dietary supplementation of atocopherol acetate (400 IU) in 12 subjects with skin types II–IV. In both studies, a clinical measure of the minimum dose of UV necessary to induce erythema in a subject and a histologic measure of sunburn cells were compared. No difference was seen in skin a-tocopherol concentrations between treatment and placebo groups. Plasma a-tocopherol concentrations increased by 65% in the treatment group and by 18% in the placebo group, so there was no question of bioavailability. Other dietary studies have shown vitamin E as a photoprotectant when combined with other antioxidants (Table 3).48 Fuchs et al.55 reported no protection when vitamin C (3 g) and atocopherol (2 g or 3000 IU) were supplemented individually, but in combination these nutrients provided protection as assessed by increased MED aer 50 days of daily supplementation. Eberlein-K¨ onig et al.51 also observed increased MED in subjects supplemented daily with a combination of vitamin C (2 g) and a-tocopherol (1000 IU) aer only 8 days. Placzek et al.56 demonstrated a photoprotective effect aer 3 months of daily dietary supplementation with vitamin C (1 g) and a-tocopherol (500 IU). Participants showed increased resistance to UVBinduced sunburn and protection from UVA damage. This study provides evidence of long-term photoprotection of lower doses than had been previously tested.
Table 3
4.2. Photoprotection in vitro and in vivo Kondo et al.57 suggested that DL-alpha-tocopherol protects human skin broblasts against the cytotoxic effect of UVB, and its mechanism seems to be related to the inhibition of UVinduced lipid peroxidation or to the antioxidation effect of DLalpha-tocopherol. The lipid hydroperoxide concentration (determined by HPLC) in the ultraviolet radiation irradiated skin of a-tocopherol supplemented mice (diet containing 10.000 IU kg 1, fed over 30 days) was about one third of that seen in unsupplemented mice.58 Several mechanisms of action for a-tocopherol reducing the detrimental effects of ultraviolet radiation are possible. Besides scavenging reactive oxidants atocopherol may act as a cellular response modier or as a sunscreen. a-Tocopherol modulates the arachidonic acid cascade59 and modies the membrane uidity.60 Preincubation of mouse keratinocytes with vitamin C resulted in a signicant reduction in UVB-induced oxidative damage.61 Tebbe et al.62 investigated the antioxidative effect of Lascorbic acid on lipid peroxidation and on secretion and mRNA expression of interleukin (IL)-1 alpha and IL-6 aer UVA irradiation (20 J cm 2) in cultured human keratinocytes. L-Ascorbic acid was able to downregulate the IL-1 alpha mRNA expression in both UVA-irradiated and nonirradiated cells; however, IL-6 mRNA expression remained unaffected. These ndings indicate a major cell-protective effect of L-ascorbic acid on UVA-induced lipid peroxidation and the secretion of pro-inammatory cytokines by UVA-irradiated human keratinocytes.
Antioxidant mixtures with photoprotective effects. Adapted from ref. 48
Antioxidant mixtures
Outcome of the study
Reference
Vitamin C and E, lycopene, b-carotene, the rosemary polyphenol and carnosic acid
Vitamin C, vitamin E, and carnosic acid showed photoprotective potential human dermal broblasts exposed to UVA MED increased markedly aer intake of the combination of these micronutrients UV radiation-induced oxidative stress in human skin Scavenging ROS generated during photooxidative stress Protective agents in certain skin diseases caused, initiated, or exacerbated by sunlight irradiation Mean MED increased in the group received vitamins compared with baseline Many parameters of the epidermal defense against UV-induced damage were signicantly improved Signicant increase of melanin concentrations in skin was detected A selective protection of the skin against irradiation was conrmed
42
a-Tocopherol and ascorbate Oral vitamin E and b-carotene supplementation Carotenoids and tocopherols Quercetin, hesperetin and naringenin
Combination of vitamins E and C Lycopene, b-carotene, a-tocopherol and selenium b-Carotene, lycopene, a-tocopherol and ascorbic acid Carotenoids (b-carotene and lycopene), vitamins C and E, selenium, and proanthocyanidins
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48 49 29 50
51 52
53 54
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5.
Polyphenols
Polyphenols are a large family of naturally occurring plant products that are widely distributed in plant foods, including fruits, vegetables, nuts and seeds. Important dietary sources of polyphenols are onions (avonols); cacao, grape seeds (proanthocyanidins); tea, apples, and red wine (avonols and catechins); citrus fruits (avanones); berries and cherries (anthocyanidins); and soy (isoavones)63 (Fig. 1). These polyphenols contribute to the benecial health effects of vegetables and fruits. Most of the natural polyphenols are pigments, typically yellow, red or purple, and can absorb UV radiation. The radiation that polyphenols can absorb includes the entire UVB spectrum of wavelengths and part of the UVA spectra. The bioavailability and metabolism of polyphenols may inuence their effectiveness. The considerable structural diversity among the polyphenols can inuence the bioavailability of the individual components. Small molecules, like catechin monomers, can be easily absorbed through the gut barrier, whereas the large molecular weight polyphenols, such as proanthocyanidins and even ( )-epigallocatechin-3-gallate (EGCG), are poorly absorbed. Once absorbed, polyphenols are conjugated to glucuronide, sulphate and methyl groups in the gut mucosa and inner tissues. Non-conjugated polyphenols are virtually absent in plasma. During digestion in the gut, the large polyphenolic molecules break into multiple small molecules or metabolites and these may systemically induce benecial effects in the body.64
5.1. Human intervention studies EGCG from green tea (Camellia sinensis) is the most extensively studied polyphenol in terms of protection against UV radiationinduced photodamage. In a pharmacokinetic and safety study of green tea polyphenols, groups of eight healthy human subjects received one of the ve following treatments for a period of four weeks: 800 mg EGCG once a day, 400 mg EGCG twice a day, 800 mg EGCG within a dened decaffeinated green tea polyphenol mixture (polyphenol E) once a day, 400 mg EGCG as polyphenol E twice a day, or a placebo once a day.65 Skin erythema was evaluated, and the dose of UV radiation causing just perceptible erythema was determined at baseline and aer four weeks of green tea polyphenol intake. No change in MED in response to solar-simulating UV radiation was observed, but, interestingly, subjects reported that they experienced lessintensive sunburn reactions aer receiving the green tea polyphenol treatment. It is thus possible that there were subtle changes in skin photosensitivity without an impact on the MED. Other reasons for the apparent lack of change in MED could be that the local concentration of EGCG in skin aer oral intake was insufficient to provide protection or that protection could have been achieved by a longer duration of treatment.12 The effects of consumption of a avanol-rich cocoa beverage were studied54 observing a decreased UV-induced erythema by 15% aer only six weeks. In another study, two groups of women consumed either a high dose of avanol (326 mg per day, containing 61 mg epicatechin and 20 mg catechin) or a low
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dose of avanol (27 mg per day, containing 6.6 mg epicatechin and 1.2 mg catechin) cocoa powder dissolved in 100 mL water for 12 weeks.66 There was no change in erythema development in the group that consumed a low dose of avanol compared with baseline, there was an improvement in the skin condition and a signicant reduction in erythema in the group that consumed a high dose of avanol, by 15% at 6 weeks and by 25% at 12 weeks of treatment.12 5.2. Photoprotection in vitro and in vivo Mechanistic studies of photocarcinogenesis have revealed that the oral administration of green tea polyphenols (through addition to the drinking water) in SKH-1 hairless mice resulted in signicant inhibition of erythema.67 In this study, it was found that although administration of green tea polyphenols in drinking water signicantly reduced the UVB-induced tumor development in wild-type mice, this treatment had a nonsignicant effect in IL-12-knockout mice. Green tea polyphenols resulted in reduction in the levels of markers of inammation (cyclooxygenase-2, prostaglandin E2, proliferating cell nuclear antigen, and cyclin D1) and proinammatory cytokines (tumor necrosis factor-a, IL-6 and IL-1b) in chronically UVB-exposed skin and skin tumors of wild-type mice but less effective in IL12p40-KO mice. Prevention of photocarcinogenesis by green tea polyphenols is mediated through IL-12-dependent DNA repair and a subsequent reduction in skin inammation. Also dietary intake of grape seed proanthocyanidins and/or silymarin inhibited UVB radiation-induced erythema.64 Very recently it has been shown that exposure to green tea polyphenols protected against UV radiation-mediated DNA damage and apoptosis in human keratinocytes and human skin equivalents.68 This protection correlated with induction of IL-12 secretion and was almost completely reversed by the addition of an anti-IL-12 antibody, strongly implicating IL-12 as an important mediator of the protective effects of green tea polyphenols. Adult human skin broblasts and normal epidermal keratinocytes, cultured separately, had signicantly less DNA damage from UVA irradiation when treated with EGCG.69 EGCG treatment of human broblasts in culture blocked the UV-induced increase in collagen secretion and collagenase mRNA levels, and also inhibited the binding activities of the UV-induced nuclear transcription factors nuclear factor-kappaB (NF-kB) and activated protein AP-1.70 When HaCaT cells were treated with ( )-epicatechin-3-gallate (ECG) and exposed to UVB radiation, it was observed that avonoid could act as a free-radical scavenger when keratinocytes were photodamaged.71 The treatment of HaCaT cells with ECG also demonstrated its free-radical scavenging effects, when cells were irradiated with UVA radiation. These observations indicate that EGCG could play an important role in the attenuation of oxidative stress-mediated cellular signaling responses, which are essential factors in various skin diseases in humans.64 Resveratrol, a stilbene found in grapes, red wine, and nuts, is also a potential polyphenolic antioxidant. Pretreatment of human epidermal keratinocytes with resveratrol inhibited the UVB-mediated activation of the NF-kB pathway.72 The treatment
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of HaCaT cells with resveratrol before UVB irradiation resulted in an increase in cell survival of UVB-irradiated cells which was associated with the reduction in ROS production.73 Soybeans are a rich source of the isoavones, genistein and daidzein, and are photoprotective.74 Genistein has been shown to reduce UV radiation-induced oxidative and photodynamic DNA damage.75 Treatment of the human keratinocyte cell line NCTC 2544 with genistein prevented the UV-induced enhancement of the DNAbinding activity of the signal transducer and activator of transcription-1 by acting as a tyrosine kinase inhibitor, thus, limiting lipid peroxidation and increases in ROS generation.76 Based on the epidemiological evidence and laboratory studies conducted using in vitro and in vivo systems, it is suggested that routine consumption of these polyphenols may provide efficient protection against the harmful effects of solar UV radiation in humans.64
6. Endogenous photoprotection by dietary antioxidant combinations As mentioned before in this review, combinations of different antioxidants applied simultaneously can provide a synergistic effect. Several studies observed that dietary antioxidants are most effective when used in combination (Table 3).48 Offord et al.42 observed that b-carotene and lycopene must be delivered together with vitamin E to prevent the formation of oxidative derivatives, which may inuence the cellular and molecular responses. According to Offord et al.,42 interactions between structurally different compounds with variable antioxidant activity may provide additional protection against increased oxidative stress. Fern´ andez-Garc´ıa77 observed similar effects. This study strengthens the hypothesis that the combination of dietary antioxidants present in tomato (naringenin and lycopene) other than lycopene alone could play a role in the health effects of tomato as evidenced by epidemiological studies. Longterm radical-initiated UV damage may be mitigated by a balanced diet.78 Therefore, combinations of micronutrients may be envisaged for effective photoprotection.
7. Conclusions Upon exposure to UV radiation from sunlight, photo-oxidative reactions are initiated which cause damage to skin. A diet rich in antioxidants such as carotenoids, vitamins E and C, and polyphenols can provide photoprotection against the harmful effects of solar UV radiation in humans. The literature is replete with intervention studies which nd that supplementation with carotenoids, vitamins E and C, and polyphenols may protect from several markers of UV damage including lipid peroxidation, erythema, DNA damage, and apoptosis. Nevertheless, photoprotection can only be achieved if these micronutrients are available in sufficient amounts at the target site. More investigation of optimal doses and mechanisms of protection is needed to better target and prevent photodamage with diet. However, endogenous protection associated with the diet must
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be considered complementary to the topical use of a sunscreen with a high-sun protection factor. The use of dietary antioxidants in combination may provide an effective strategy for mitigating the effects of UV radiation that will lead to the protection of the skin from various skin diseases caused by excessive sun exposure.
Abbreviations ECG EGCG HO-1 IL MED NF-kB ROS 1 O2 TBARS UV
( )-Epicatechin-3-gallate ( )-Epigallocatechin-3-gallate Heme-oxygenase 1 Interleukin Minimal erythema dose Nuclear factor-kappaB Reactive oxygen species Singlet oxygen Thiobarbituric acid-reactive substances Ultraviolet
Acknowledgements E.F.G. is supported by fellowships from the Postdoctoral Fellowship Program (Alfonso Mart´ın Escudero Foundation, Spain), and the Junta de Andalucia (PII-CTS-7962 MO)/European Union (FEDER).
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