Protection against ultraviolet-B radiation-induced local and systemic suppression of contact hypersensitivity and edema responses in C3H/HeN mice by green tea polyphenols

Photoprotective effects of green tea polyphenols

Non-melanoma skin cancer is the most common malignancy in humans and is equivalent to the incidence of malignancies in all other organs combined in the United States. Current methods of prevention depend on sunscreens in humans, efficacy of which is largely undetermined for non-melanoma skin cancers. Green tea polyphenols have the greatest effect with respect to chemoprevention and have been found to be most potent at suppressing the carcinogenic activity of UV radiation. They protect against many of the other damaging effects of UV radiation such as UV-induced sunburn response, UV-induced immunosuppression and photoaging of the skin. They exert their photoprotective effects by various cellular, molecular and biochemical mechanisms in in vitro and in vivo systems. Green tea polyphenols thus have the potential, when used in conjunction with traditional sunscreens, to further protect the skin against the adverse effects of ultraviolet radiation.

Characterization of antioxidants using a fluidic chip in aqueous/organic media

Application of antioxidants in the cosmetic industry demands control of the efficiency of ROS-scavenging within the cream matrix. Our goal was to construct a system for the simultaneous detection of superoxide and hydrogen peroxide and their possible scavengers. DMSO is a good solvent for many cosmetic products, and thus the system should work in mixed aqueous-organic media. The fluidic chip developed consists of an ROS-generation chamber, a mixing section and a compartment for the biosensor chip. This electrode chip had two sensors: one sensor for each species. Cytochrome c was used as the sensing protein. Both the superoxide and the hydrogen peroxide sensors demonstrated sufficient sensitivity in DMSO-buffer mixtures within the concentration range 0.4 nM-1.2 nM (superoxide) and 50 microM-1000 microM (hydrogen peroxide). The influence of the flow conditions on the generation of ROS was investigated and the optimal parameters for the antioxidant detection were evaluated. The efficiency of ROS-scavenging was tested with typical antioxidants of enzymatic and non-enzymatic origin, as well as complex cosmetic creams.

The topical isoflavonoid NV-07alpha reduces solar-simulated UV-induced suppression of Mantoux reactions in humans

UV radiation suppresses delayed-type hypersensitivity responses to intradermally injected tuberculin purified protein derivative in Mantoux-positive individuals. The effect of the topically administered isoflavonoid NV-07alpha, a synthetic derivative of the isoflavonoid equol, on UV-induced suppression of Mantoux reactions was assessed in 18 healthy Mantoux-positive volunteers. A single, fixed dose of solar-simulated UV radiation was delivered to the volunteers' lower backs. Different concentrations of NV-07alpha or its vehicle were applied to different sites within the irradiated field immediately after UV exposure and again 24 h later. Forty-eight hours after irradiation, Mantoux testing was performed at both the irradiated sites and adjacent, unirradiated sites. The intensity of Mantoux reactions was measured 72 h later with a reflectance erythema meter and by measuring the diameter of each reaction. Although lower concentrations of NV-07alpha (0.5 and 2 mM) did not prevent UV immunosuppression, 4 mM NV-07alpha partially but significantly attenuated UV-induced suppression of Mantoux-induced erythema. Minimal erythema doses were also determined for sites treated with NV-07alpha or its vehicle immediately after UV exposure. NV-07alpha had no significant effects on UV erythema. We conclude that 4 mM NV-07alpha prevented the suppressive effects of UV radiation on Mantoux responses in humans but did not affect UV-induced erythema at the concentrations used.

Silymarin inhibits UV radiation-induced immunosuppression through augmentation of interleukin-12 in mice

We have shown previously that silymarin, a plant flavonoid, inhibits UVB-induced photocarcinogenesis in mice. As UVB-induced immunosuppression has been implicated in the development of skin cancer, we investigated whether silymarin can modulate the effects of UVB radiation on the immune system. Treatment of C3H/HeN mice with topically applied silymarin (0.5 or 1.0 mg/cm(2)) or silibinin, a major component of silymarin, markedly inhibited UVB (180 mJ/cm(2))-induced suppression of contact hypersensitivity response in a local model of immunosuppression and had a moderate inhibitory effect in a systemic model of contact hypersensitivity. Silymarin reduced the UVB-induced enhancement of the levels of the immunosuppressive cytokine, interleukin (IL)-10, in the skin and draining lymph nodes and enhanced the levels of the immunostimulatory cytokine, IL-12. Intraperitoneal injection of mice treated with silymarin with an endotoxin-free neutralizing anti-IL-12 antibody abrogated the protective effects of the silymarin against UVB-induced suppression of the contact hypersensitivity response. Furthermore, the treatment of silymarin did not prevent UVB-induced suppression of the contact hypersensitivity response in IL-12 knockout mice but prevented it in their wild-type mice. Moreover, i.p. injection of IL-12 to silymarin-treated or non-silymarin-treated IL-12 knockout mice resulted in an enhanced response to contact hypersensitivity compared with the response in mice that were exposed to either UVB alone or silymarin plus UVB. These data indicate for the first time that silymarin has the ability to protect mice from UVB-induced immunosuppression and that this protective effect is mediated, at least in part, through IL-12.

Interleukin-12-deficient mice are at greater risk of UV radiation-induced skin tumors and malignant transformation of papillomas to carcinomas

Solar UV radiation-induced immunosuppression is a risk factor for nonmelanoma skin cancer. Interleukin (IL)-12 has been shown to possess antitumor activity and inhibit the immunosuppressive effects of UV radiation in mice. In this study, we generated IL-12 knockout (KO) mice on a C3H/HeN background to characterize the role of IL-12 in photocarcinogenesis. After exposure of the mice to UVB (180 mJ/cm2) radiation thrice a week for 35 weeks, the development of UV-induced tumors was more rapid and the tumor multiplicity and tumor size were significantly higher in IL-12 KO mice than their wild-type (WT) counterparts (P < 0.05-0.001). Moreover, the malignant transformation of UVB-induced papillomas to carcinomas was higher in IL-12 KO mice in terms of carcinoma incidence (55%, P < 0.001), carcinoma multiplicity (77%, P < 0.001), and carcinoma size (81%, P < 0.001). As IL-12 has the ability to repair UV-induced DNA damage, we determined this effect in our in vivo IL-12 KO mouse model. We found that UVB-induced DNA damage in the form of cyclobutane pyrimidine dimers was removed or repaired more rapidly in WT mice than IL-12 KO mice. Similarly, the UVB-induced sunburn cell formation is primarily a consequence of DNA damage. It was observed that UVB-induced sunburn cells were repaired rapidly in WT mice compared with IL-12 KO mice. The rapid removal or repair of UV-induced cyclobutane pyrimidine dimers or sunburn cells will result in reduced risk of photocarcinogenesis. Taken together, our data show that IL-12 deficiency is associated with the greater risk of photocarcinogenesis in mice, and this may be due to reduction in damaged DNA repair ability.

Epigallocatechin-3-gallate (EGCG): chemical and biomedical perspectives

The compound (-)-epigallocatechin-3-gallate (EGCG) is the major catechin found in green tea [Camellia sinensis L. Ktze. (Theaceae)]. This polyphenolic compound and several related catechins are believed to be responsible for the health benefits associated with the consumption of green tea. The potential health benefits ascribed to green tea and EGCG include antioxidant effects, cancer chemoprevention, improving cardiovascular health, enhancing weight loss, protecting the skin from the damage caused by ionizing radiation, and others. The compound EGCG has been shown to regulate dozens of disease-specific molecular targets. Many of these molecular targets are only affected by concentrations of EGCG that are far above the levels achieved by either drinking green tea or consuming moderate doses of green tea extract-based dietary supplements. In spite of this, well-designed double-blinded controlled clinical studies have recently demonstrated the efficacy of green tea extracts and purified EGCG products in patients. Therefore, this review highlights results from what the authors believe to be some of the most clinically significant recent studies and describes current developments in the stereoselective total synthesis of EGCG.

(-)-Epigallocatechin-3-gallate prevents photocarcinogenesis in mice through interleukin-12-dependent DNA repair

We have shown previously that topical application of (-)-epigallocatechin-3-gallate (EGCG), the major polyphenol of green tea, prevents photocarcinogenesis in mice. EGCG prevents UVB-induced immunosuppression by inducing interleukin-12 (IL-12). As immunosuppression is a risk factor for photocarcinogenesis, we investigated the possibility that EGCG also prevents UVB-induced photocarcinogenesis through an IL-12-dependent DNA repair mechanism. To investigate this possibility, we determined the effects of EGCG on photocarcinogenesis in IL-12 knockout (KO) mice using the formation of cyclobutane pyrimidine dimers (CPD) as an indicator of the extent of UVB-induced DNA damage. Topical application of EGCG (1 mg/cm(2) skin) prevented photocarcinogenesis in wild-type (C3H/HeN) mice in terms of tumor incidence and tumor multiplicity but did not prevent photocarcinogenesis in IL-12 KO mice. UVB-induced DNA damage, as determined by the formation of CPDs and the number of sunburn cells, was resolved more rapidly in the skin of wild-type mice treated with EGCG than untreated control mice. In contrast, the extent of UVB-induced DNA damage and the numbers of sunburn cells were not significantly different in the EGCG-treated IL-12 KO mice and untreated control mice. In addition, treatment of XPA-proficient human fibroblast cells with EGCG promoted repair of UVB-induced CPDs in a dose-dependent manner but not in an XPA-deficient cells, indicating that the nucleotide excision repair mechanism is involved in EGCG-mediated DNA repair. Taken together, these results indicate for the first time that EGCG can prevent photocarcinogenesis through an EGCG-induced IL-12-dependent DNA repair mechanism.

Prevention of ultraviolet radiation-induced immunosuppression by (-)-epigallocatechin-3-gallate in mice is mediated through interleukin 12-dependent DNA repair

PURPOSE

Solar UV radiation-induced immunosuppression is considered to be a risk factor for melanoma and nonmelanoma skin cancers. We previously have shown that topical application of (-)-epigallocatechin-3-gallate (EGCG) prevents UV-induced immunosuppression in mice. We studied whether prevention of UV-induced immunosuppression by EGCG is mediated through interleukin 12 (IL-12)-dependent DNA repair.

EXPERIMENTAL DESIGN

IL-12 knockout (KO) mice on C3H/HeN background and DNA repair-deficient cells from xeroderma pigmentosum complementation group A (XPA) patients were used in this study. The effect of EGCG was determined on UV-induced suppression of contact hypersensitivity and UV-induced DNA damage in the form of cyclobutane pyrimidine dimers (CPD) in mice and XPA-deficient cells using immunohistochemistry and dot-blot analysis.

RESULTS

Topical treatment with EGCG prevented UV-induced suppression of the contact hypersensitivity in wild-type (WT) mice but did not prevent it in IL-12 KO mice. Injection of anti-IL-12 monoclonal antibody to WT mice blocked the preventive effect of EGCG on UV-induced immunosuppression. EGCG reduced or repaired UV-induced DNA damage in skin faster in WT mice as shown by reduced number of CPDs(+) cells and reduced the migration of CPD(+) antigen-presenting cells from the skin to draining lymph nodes. In contrast, this effect of EGCG was not seen in IL-12 KO mice. Further, EGCG was able to repair UV-induced CPDs in XPA-proficient cells obtained from healthy person but did not repair in XPA-deficient cells, indicating that nucleotide excision repair mechanism is involved in DNA repair.

CONCLUSIONS

These data identify a new mechanism by which EGCG prevents UV-induced immunosuppression, and this may contribute to the chemopreventive activity of EGCG in prevention of photocarcinogenesis.

(+)-Catechin prevents ultraviolet B-induced human keratinocyte death via inhibition of JNK phosphorylation

High levels of (+)-catechin are found in the skin and seed of many fruits such as apples and grapes. Dietary supplementation with (+)-catechin has been demonstrated to protect epidermal cells against damage induced by ultraviolet B (UVB) radiation. However, the underlying mechanisms are not well understood yet. To determine whether (+)-catechin protects keratinocytes from UVB-induced damage, the viability of UVB- and H2O2-treated cells was determined by cell viability assay. Intracellular H2O2 level was measured by flow cytometry. UVB- or H2O2-induced signaling pathways were detected by Western blotting. The results indicated that (+)-catechin inhibited UVB- and H2O2-induced keratinocyte death. In parallel, intracellular H2O2 generation in keratinocytes irradiated by UVB was inhibited by (+)-catechin in a concentration-dependent manner. (+)-Catechin also inhibited UVB- and H2O2-induced JNK activation in keratinocytes. However, it had little inhibitory effect on UVB- and H2O2-induced ERK and p38 activation even at a higher concentration, suggesting indirectly that JNK activation is required for the induction of apoptosis in keratinocytes exposed to UVB. Finally, we compared the cytotoxicity of (+)-catechin and (-)-epigallocatechin-3-gallate (EGCG) on keratinocytes. Cell viability assay showed that (+)-catechin was relatively nontoxic at higher doses. Taken together, our results demonstrate that (+)-catechin inhibits UVB- and oxidative stress-induced H2O2 production and JNK activation and enhances human keratinocyte survival. However, although it seems that (+)-catechin and EGCG are equally effective in preventing keratinocyte death, (+)-catechin is relatively nontoxic and thus is suitable for developing as an anti-ageing agent for skin care.

Epigallocatechin-3-gallate inhibits photocarcinogenesis through inhibition of angiogenic factors and activation of CD8+ T cells in tumors

There has been considerable interest in the use of botanical supplements to protect skin from the adverse effects of solar UV radiation, including photocarcinogenesis. We and others have shown that topical application of (-)-epigallocatechin-3-gallate (EGCG) from green tea prevents photocarcinogenesis in mice; however, the chemopreventive mechanism of EGCG in an in vivo tumor model is not clearly understood. In this study, UV-B-induced skin tumors with and without treatment of EGCG ( approximately 1 mg/cm(2)) and age-matched skin biopsies from SKH-1 hairless mice were used to identify potential molecular targets of skin cancer prevention by EGCG. These biopsies were analyzed for various biomarkers of angiogenesis and antitumor immune response using immunostaining, Western blotting and gelatinolytic zymography. We report that compared to non-EGCG-treated tumors, topical application of EGCG in UV-induced tumors resulted in inhibition of protein expression and activity of matrix metalloproteinase (MMP)-2 and MMP-9, which play crucial roles in tumor growth and metastasis. In contrast, tissue inhibitor of MMP-1 (TIMP-1), which inhibits MMP activity, was increased in tumors. With respect to the tumor vasculature, EGCG decreased the expression of CD31, a cell surface marker of vascular endothelial cells, and inhibited the expression of vascular endothelial growth factor in tumors, which are essential for angiogenesis. EGCG inhibited proliferating cell nuclear antigen in UV-B-induced tumors as well. Additionally, higher numbers of cytotoxic T lymphocytes (CD8(+) T cells) were detected in EGCG-treated tumors compared with non-EGCG-treated tumors. Together, these in vivo tumor data suggested that inhibition of photocarcinogenesis in mice by EGCG is associated with inhibition of angiogenic factors and induction of antitumor immune reactivity.

Chemoprevention of photocarcinogenesis by selected dietary botanicals

Epidemiological, clinical and laboratory studies have implicated solar ultraviolet (UV) radiation as a tumor initiator, tumor promoter and complete carcinogen, and their excessive exposure can lead to the development of various skin disorders including melanoma and nonmelanoma skin cancers. Sunscreens are useful, but their protection is not adequate to prevent the risk of UV-induced skin cancer. It may be because of inadequate use, incomplete spectral protection and toxicity. Therefore new chemopreventive methods are necessary to protect the skin from photodamaging effects of solar UV radiation. Chemoprevention refers to the use of agents that can inhibit, reverse or retard the process of skin carcinogenesis. In recent years, considerable interest has been focused on identifying naturally occurring botanicals, specifically dietary, for the prevention of photocarcinogenesis. A wide variety of botanicals, mostly dietary flavonoids or phenolic substances, have been reported to possess substantial anticarcinogenic and antimutagenic activities because of their antioxidant and antiinflammatory properties. This review summarizes chemopreventive effects of some selected botanicals, such as apigenin, curcumin, grape seed proanthocyanidins, resveratrol, silymarin, and green tea polyphenols, against photocarcinogenesis in in vitro and in vivo systems. Attention has also been focused on highlighting the mechanism of chemopreventive action of these dietary botanicals. We suggest that in addition to the use of these botanicals as dietary supplements for the protection of photocarcinogenesis, these botanicals may favorably supplement sunscreens protection and may provide additional antiphotocarcinogenic protection including the protection against other skin disorders caused by solar UV radiation.

Dietary grape-seed proanthocyanidin inhibition of ultraviolet B-induced immune suppression is associated with induction of IL-12

We have shown previously that dietary grape seed proanthocyanidins (GSPs) inhibit UVB-induced photocarcinogenesis in mice. As UVB-induced immune suppression has been implicated in the development of skin cancer risk, we investigated whether dietary GSPs can modulate the effects of UVB on the immune system. We found that the UVB-induced (180 mJ/cm2) ear swelling response (inflammatory reaction) was significantly lower in mice fed with a GSP-supplemented (0.5 and 1.0%, w/w) diet than mice fed with the standard AIN76A diet. Dietary GSPs markedly inhibited UVB-induced (180 mJ/cm2) suppression of contact hypersensitivity responses in a local model of immunosuppression but had only moderate inhibitory effect in a systemic model of immunosuppression. Dietary GSPs reduced the UVB-induced increase in immunosuppressive cytokine interleukin (IL)-10 in skin and draining lymph nodes compared with mice that did not receive GSPs. In contrast, GSPs enhanced the production of immunostimulatory cytokine IL-12 in the draining lymph nodes. Intraperitoneal injection of GSPs-fed mice with a neutralizing anti-IL-12 antibody abrogated the protective effects of the GSPs against UVB-induced suppression of the contact hypersensitivity response. These data indicate for the first time that GSPs modulate UVB-induced immunosuppression and suggest that this may be one of the possible mechanisms by which they prevent photocarcinogenesis in mice.

Ultraviolet B radiation-induced immunosuppression: molecular mechanisms and cellular alterations

About 30 years ago, the discovery of the connection between UV radiation and the immune system triggered the field of photoimmunology. In that time, many aspects were studied, and a complex picture emerged. UV absorption results in multi-tiered molecular and cellular UV radiation-induced events, eventually affecting the immune system. The shorter wavelengths of the UV spectrum, i.e. UVB appear to be the most critical players for impairing immune reactions. This review summarizes and discusses UVB radiation-induced effects on the skin, considering the primary efferent molecular events following energy absorption of UVB radiation, ending with the various afferent cellular changes, such as induction of regulatory T cells.

Protective effects of (-)-epicatechin-3-gallate on UVA-induced damage in HaCaT keratinocytes

(-)-Epigallocatechin-3-gallate (EGCG), a constituent of green tea, has been extensively studied and shown to be a powerful antioxidant protecting skin cells against photodamage. In this study, however, we demonstrated that another gallated catechin, (-)-epicatechin-3-gallate (ECG), was also able to protect human keratinocytes against damage induced by ultraviolet A (UVA) light. We found that ECG dose-dependently inhibited UVA-induced keratinocyte death as determined by cell viability assay. Moreover, ECG had similar potency to EGCG in inhibiting UVA-induced cell death. Therefore, the mechanism of action of ECG was further investigated. As assayed by flow cytometry, UVA-induced hydrogen peroxide (H2O2) production in keratinocytes was inhibited by ECG in a concentration-dependent manner, suggesting that ECG can act as a free radical scavenger while keratinocytes were photodamaged. The scavenging effect of ECG was confirmed by the fact that ECG treatment attenuated cell damage induced by H2O2 and hypoxanthine-xanthine oxidase. In a parallel experiment, UVA-induced activation of extracellular signal-regulated kinase in keratinocytes was blocked by ECG. We provided here the first evidence that ECG is a potent protectant that protects keratinocytes from photodamage. Because ECG is abundant in green tea, we believe that this compound is beneficial for skin care.

Green Tea Polyphenols Prevent Ultraviolet Light-Induced Oxidative Damage and Matrix Metalloproteinases Expression in Mouse Skin

Chronic exposure of solar ultraviolet (UV) light to human skin results in photoaging. UV-induced oxidative damage and induction of matrix metalloproteinases (MMP) have been implicated in this process. Because polyphenols from green tea (GTP) prevent other cutaneous adverse effects of UV radiation we hypothesized that UV irradiation-induced oxidative damage and induction of MMP might be prevented in vivo in mouse skin by oral administration of GTP. GTP was administered in drinking water (0.2%, wt/vol) to SKH-1 hairless mice, which were then exposed to multiple doses of UVB (90 mJ per cm2, for 2 mo on alternate days) following in vivo photoaging animal protocol. Treatment of GTP resulted in inhibition of UVB-induced protein oxidation in vivo in mouse skin, a hallmark of photoaging, when analyzed biochemically, by immunoblotting, and immunohistochemistry. GTP treatment also inhibited UVB-induced protein oxidation in vitro in human skin fibroblast HS68 cells, which supports in vivo observations. Moreover, oral administration of GTP also resulted in inhibition of UVB-induced expression of matrix degrading MMP, such as MMP-2 (67%), MMP-3 (63%), MMP-7 (62%), and MMP-9 (60%) in hairless mouse skin. These data suggest that GTP as a dietary supplement could be useful to attenuate solar UVB light-induced premature skin aging.

Polyphenol (−)-epigallocatechin gallate inhibits apoptosis induced by irradiation in human HaCaT keratinocytes

Green tea is a rich source of polyphenols, and (-)-epigallocatechin-3-gallate (EGCG) is a major constituent of green tea polyphenols. In the present study, we investigated the effect of EGCG on apoptosis induced by irradiation in the human keratinocytic cell line HaCaT. Irradiation by gamma-ray induced apoptosis with concomitant cleavage of caspase-3 and its in vivo substrate poly(ADP-ribose) polymerase. Treatment of cells with EGCG inhibited irradiation-induced apoptosis as detected by Hoechst staining and internucleosomal cleavage of DNA, and prevented the cleavage of these proteins by irradiation. We also found that the treatment of cells with EGCG alone suppressed cell growth and induced apoptosis in these cells. Our results suggest that EGCG inhibits irradiation-induced apoptosis by inactivating the caspase pathway in HaCaT cells. Our study also indicates that EGCG has a dual effect on the survival of these keratinocytes.

Suppression of UVB-induced phosphorylation of mitogen-activated protein kinases and nuclear factor kappa B by green tea polyphenol in SKH-1 hairless mice

Studies from our laboratory have shown that epigallocatechin-3-gallate, the major polyphenol present in green tea, inhibits ultraviolet (UV)B-exposure-mediated phosphorylation of mitogen-activated protein kinases (MAPKs) (Toxicol. Appl. Pharmacol. 176: 110-117, 2001) and activation of nuclear factor kappa B (NF-kappaB) (Oncogene 22: 1035-1044, 2003) pathways in normal human epidermal keratinocytes. This study was designed to investigate the relevance of these findings to the in vivo situations in SKH-1 hairless mouse model, which is regarded to have relevance to human situations. SKH-1 hairless mice were topically treated with GTP (5 mg/0.2 ml acetone/mouse) and were exposed to UVB 30 min later (180 mJ/cm2). These treatments were repeated every alternate day for 2 weeks, for a total of seven treatments. The animals were killed 24 h after the last UVB exposure. Topical application of GTP resulted in significant decrease in UVB-induced bifold-skin thickness, skin edema and infiltration of leukocytes. Employing Western blot analysis and immunohistochemical studies, we found that GTP resulted in inhibition of UVB-induced: (i) phosphorylation of extracellular-signal-regulated kinases (ERK1/2), (ii) c-Jun N-terminal kinases, and (iii) p38 protein expression. Since NF-kappaB plays a major role in inflammation and cell proliferation, we assessed the effect of GTP on UVB-mediated modulations in the NF-kappaB pathway. Our data demonstrated that GTP inhibited UVB-induced: (i) activation of NF-kappaB, (ii) activation of IKKalpha, and (iii) phosphorylation and degradation of IkappaBalpha. Our data suggest that GTP protects against the adverse effects of UV radiation via modulations in MAPK and NF-kappaB signaling pathways, and provides molecular basis for the photochemopreventive effect of GTP in an in vivo animal model system.

Topical vitamins, minerals and botanical ingredients as modulators of environmental and chronological skin damage

Ageing skin is characterized by fine lines, wrinkles, lentigines, dyspigmentation and increased coarseness. Topical preparations alleged to combat these changes abound in the over-the-counter market. Some of the most popular ingredients used in these products are vitamins, minerals and botanical extracts. Proposed mechanisms for antiageing effects on skin range from antioxidant properties to improved collagen synthesis or protection from collagen breakdown. Despite the media attention and consumer popularity that these ingredients have generated, there have been few scientific studies to support these claims. In this report, we review recent published studies on the most common of these ingredients for the topical photoprotection and the treatment of ageing skin.

Dual mechanisms of green tea extract (EGCG)-induced cell survival in human epidermal keratinocytes

Beneficial effects attributed to green tea, such as its anticancer and antioxidant properties, may be mediated by (-)-epigallocatechin-3-gallate (EGCG). In this study, the effects of EGCG on cell proliferation and UV-induced apoptosis were investigated in normal epidermal keratinocytes. When topically applied to aged human skin, EGCG stimulated the proliferation of epidermal keratinocytes, which increased the epidermal thickness. In addition, this topical application also inhibited the UV-induced apoptosis of epidermal keratinocytes. EGCG was found to increase the phosphorylation of Bad protein at the Ser112 and Ser136. Moreover, EGCG-induced Erk phosphorylation was found to be critical for the phosphorylation of Ser112 in Bad protein, and the EGCG-induced activation of the Akt pathway was found to be involved in the phosphorylation of Ser136. Furthermore, EGCG increased Bcl-2 expression but decreased Bax expression, causing an increase in the Bcl-2-to-Bax ratio. In addition, we demonstrate the differential growth inhibitory effects of EGCG on cancer cells. In conclusion, this study demonstrates that EGCG promotes keratinocyte survival and inhibits the UV-induced apoptosis via two mechanisms: by phosphorylating Ser112 and Ser136 of Bad protein through Erk and Akt pathways, respectively, and by increasing the Bcl-2-to-Bax ratio. Moreover, these two proposed mechanisms of EGCG-induced cell proliferation may differ kinetically to promote keratinocyte survival.

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

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

Refractoriness of UVA-induced protection from photoimmunosuppression correlates with heme oxygenase response to repeated UVA exposure

Single suberythemal exposures of UVA radiation have been shown to block the immunosuppressive effects of UVB radiation in the mouse. The immunoprotection is dependent both on the presence of the cytokine, IFN-gamma, and on the induction of the antioxidant stress enzyme, heme oxygenase (HO), in the skin. Recently, the transcriptional response of the HO-1 gene to UVA radiation in cultured human skin fibroblasts was reported to be refractory to a second UVA irradiation. In this study on the hairless mouse, we demonstrate that the inducibility of HO enzyme activity in the skin similarly became refractory to a second UVA irradiation at 24 h but, like the fibroblast response, was restored when the interval between the UVA exposures was increased to 96 h. Under the conditions of refractory HO enzyme induction, the protective effect of UVA radiation against the suppression of contact hypersensitivity induced by UVB radiation or cis-urocanic acid was strongly attenuated but was restored when the interval between UVA exposures was increased to 96 h. The results thus confirm the strong relationship between HO induction and photoimmunoprotection by UVA radiation, and describe a new phenomenon of immunological refractoriness that develops with rapidly repeated UVA exposures.

Ultraviolet radiation and the contact hypersensitivity reaction in mice

The article reviews the application of the contact hypersensitivity assay in mice to the science of photoimmunology. The contact hypersensitivity (CHS) reaction, which is suppressed by UV irradiation in mice similarly to their ability to respond immunologically to skin tumors, has been used very profitably to reveal many of the regulating factors that control photoimmunosuppression, such as the identity of the photoreceptors that initiate immunosuppression, the defects induced in the cutaneous antigen presenting pathway, the local cytokine imbalance, and the protective intervention by various molecules, drugs, or interacting UV wavebands. Technical hints to optimize the measurement of the CHS response are suggested, including information on UV radiation wavebands and dosages and sensitivities of different mouse strains.

Oxidative stress and its role in skin disease

Skin is a major target of oxidative stress due to reactive oxygen species (ROS) that originate in the environment and in the skin itself. ROS are generated during normal metabolism, are an integral part of normal cellular function, and are usually of little harm because of intracellular mechanisms that reduce their damaging effects. Antioxidants attenuate the damaging effects of ROS and can impair and/or reverse many of the events that contribute to epidermal toxicity and disease. However, increased or prolonged free radical action can overwhelm ROS defense mechanisms, contributing to the development of cutaneous diseases and disorders. Although ROS play a role in diseases such as skin cancer, their biological targets and pathogenic mode of action are still not fully understood. In addition, strategies useful in the therapeutic management of ROS action in human skin are still lacking. This review is intended to give investigators an introduction to ROS, antioxidants, two skin disorders influenced by ROS action (skin cancer and psoriasis), and relevant model systems used to study ROS action.

Green tea polyphenols: DNA photodamage and photoimmunology

Green tea is a popular beverage consumed worldwide. The epicatechin derivatives, which are commonly called 'polyphenols', are the active ingredients in green tea and possess antioxidant, anti-inflammatory and anti-carcinogenic properties. Studies conducted by our group on human skin have demonstrated that green tea polyphenols (GTP) prevent ultraviolet (UV)-B-induced cyclobutane pyrimidine dimers (CPD), which are considered to be mediators of UVB-induced immune suppression and skin cancer induction. GTP treated human skin prevented penetration of UV radiation, which was demonstrated by the absence of immunostaining for CPD in the reticular dermis. The topical application of GTP or its most potent chemopreventive constituent (-)-epigallocatechin-3-gallate (EGCG) prior to exposure to UVB protects against UVB-induced local as well as systemic immune suppression in laboratory animals. Additionally, studies have shown that EGCG treatment of mouse skin inhibits UVB-induced infiltration of CD11b+ cells. CD11b is a cell surface marker for activated macrophages and neutrophils, which are associated with induction of UVB-induced suppression of contact hypersensitivity responses. EGCG treatment also results in reduction of the UVB-induced immunoregulatory cytokine interleukin (IL)-10 in skin as well as in draining lymph nodes, and an elevated amount of IL-12 in draining lymph nodes. These in vivo observations suggest that GTPs are photoprotective, and can be used as pharmacological agents for the prevention of solar UVB light-induced skin disorders associated with immune suppression and DNA damage.

Isoflavonoid compounds from red clover (Trifolium pratense) protect from inflammation and immune suppression induced by UV radiation

Isoflavones derived from many edible plants have been reported to possess significant antioxidant, estrogenic and tyrosine kinase inhibitory activity. Genistein has been found previously to provide protection from oxidative damage induced by UV radiation both in vitro and following dietary administration. We have therefore examined the potential of a number of isoflavones from red clover (Trifolium pratense) and some metabolically related compounds to offer protection from UV irradiation in hairless mice by topical application after UV exposure. We show that whereas the primary isoflavones, daidzein, biochanin A and formononetin, were inactive, 20 microM lotions of genistein and the metabolites equol, isoequol and the related derivative dehydroequol had powerful potential to reduce the inflammatory edema reaction and the suppression of contact hypersensitivity induced by moderate doses of solar-simulated UV radiation. For equol the protection was concentration dependent and 5 microM equol markedly reduced the UV-induced inflammation but abrogated the UV-induced immunosuppression. Equol protected similarly from immunosuppression induced by the putative epidermal mediator, cis-urocanic acid (UCA), indicating a potential mechanism of action involving inactivation of this UV-photoproduct. Since immunosuppression induced by both UV radiation and by cis-UCA appears to be an oxidant-dependent response our observations support the actions of these topically applied isoflavones and their metabolites as antioxidants. They also indicate that lotions containing equol, unlike topical UV sunscreens, more readily protect the immune system from photosuppression than from the inflammation of the sunburn reaction, even when applied after exposure, and thus such compounds may have a future role as sun-protective cosmetic ingredients.

Cutaneous photoprotection from ultraviolet injury by green tea polyphenols

BACKGROUND

In animal models, extracts from green tea have been shown to be remarkably effective at reducing the severity of adverse human health effects of overexposure to ultraviolet (UV) radiation. Although sunscreens and other photoprotective measures have traditionally been used for this purpose, there is a need for additional measures and natural products are increasingly being explored for that purpose.

OBJECTIVE

Our purpose was to evaluate the effect of polyphenols from green tea on parameters associated with acute UV injury.

METHODS

Areas of skin of normal volunteers were treated with an extract of green tea or one of its constituents. Thirty minutes later, the treated sites were exposed to a 2 minimal erythema dose solar simulated radiation. UV-treated skin was examined clinically for UV-induced erythema, histologically for the presence of sunburn cells or Langerhans cell distributions, or biochemically for UV-induced DNA damage.

RESULTS

Application of green tea extracts resulted in a dose-dependent inhibition of the erythema response evoked by UV radiation. The (-)-epigallocatechin-3-gallate (EGCG) and (-)-epicatechin-3-gallate (ECG) polyphenolic fractions were most efficient at inhibiting erythema, whereas (-)-epigallocatechin (EGC) and (-)-epicatechin (EC) had little effect. On histologic examination, skin treated with green tea extracts reduced the number of sunburn cells and protected epidermal Langerhans cells from UV damage. Green tea extracts also reduced the DNA damage that formed after UV radiation.

CONCLUSION

Polyphenolic extracts of green tea are effective chemopreventive agents for many of the adverse effects of sunlight on human health and may thus serve as natural alternatives for photoprotection.

Lack of metallothionein-I and -II exacerbates the immunosuppressive effect of ultraviolet B radiation and cis-urocanic acid in mice

The effect of a null mutation for the metallothionein (MT)-I and -II isoforms in mice on the immunosuppressive action of ultraviolet B (UVB; 280-320 nm) radiation has been examined. Mice were exposed to a series of increasing daily UVB doses, each dose administered to the dorsum on 3 consecutive days. Erythema was assessed, and measured as its oedema component by the post-irradiation dorsal skinfold thickness, but there was no effect of the null mutation (MT-/-) observed after 3 x 3.4 kJ/m2 of UVB radiation. Immune function was assessed by the contact hypersensitivity (CHS) response, which was initiated by sensitization on unirradiated abdominal skin, and thus demonstrated the systemic effects of dorsal treatments. In comparison with the wild-type MT+/+ mouse, the MT-/- mouse was significantly more immunosuppressed by moderate daily UVB doses (1. 75-5.9 kJ/m2). When topically applied cis-urocanic acid (cis-UCA) replaced UVB radiation as the immunosuppressive agent, contact hypersensitivity in MT-/- mice was again markedly more suppressed than in MT+/+ mice, in a dose-responsive manner. The results infer that MT, which was shown immunohistochemically to be strongly induced in the epidermis of MT+/+ mice, but to be absent in MT-/- epidermis, has the potential to protect from photoimmunosuppression, and that the mechanism of action may be via the inactivation of the epidermal UVB-photoproduct, cis-UCA.

Tea polyphenols: prevention of cancer and optimizing health

The tea plant Camellia sinesis is cultivated in >30 countries. Epidemiologic observations and laboratory studies have indicated that polyphenolic compounds present in tea may reduce the risk of a variety of illnesses, including cancer and coronary heart disease. Most studies involved green tea, however; only a few evaluated black tea. Results from studies in rats, mice, and hamsters showed that tea consumption protects against lung, forestomach, esophagus, duodenum, pancreas, liver, breast, colon, and skin cancers induced by chemical carcinogens. Other studies showed the preventive effect of green tea consumption against atherosclerosis and coronary heart disease, high blood cholesterol concentrations, and high blood pressure. Because the epidemiologic studies and research findings in laboratory animals have shown the chemopreventive potential of tea polyphenols in cancer, the usefulness of tea polyphenols for humans should be evaluated in clinical trials. One such phase 1 clinical trial is currently under way at the MD Anderson Cancer Center in collaboration with Memorial Sloan-Kettering Cancer Center. This study will examine the safety and possible efficacy of consuming the equivalent of > or =10 cups (> or =2.4 L) of green tea per day. The usefulness of tea polyphenols may be extended by combining them with other consumer products such as food items and vitamin supplements. This "designer-item" approach may be useful for human populations, but it requires further study.

Green tea protects against psoralen plus ultraviolet A-induced photochemical damage to skin

The use of psoralens combined with exposure to ultraviolet A radiation is a major form of treatment for psoriasis and a number of other common skin diseases. Although psoralen plus ultraviolet A treatment is highly effective, careful follow-up cohort studies have shown that it greatly increases risk for the development of cutaneous squamous cell carcinoma and melanoma. Strategies to reduce the risk of cancer development in psoralen plus ultraviolet A-treated populations are highly desirable. In prior studies, we demonstrated that green tea and constituent polyphenols protect against ultraviolet B-induced carcinogenesis and reduce the growth rate of established tumors in skin. In this study, we show that pre- and post-treatment with standardized green tea extract in psoralen plus ultraviolet A treatment populations abrogates the psoralen plus ultraviolet A-induced photochemical damage to skin. Intact mouse and human skin and reconstituted human skin were employed to assess the effect of both topical and oral administration of standardized green tea extract against psoralen plus ultraviolet A-induced photodamage. Oral administration of standardized green tea extract prior to and during multiple psoralen plus ultraviolet A treatments reduced hyperplasia and hyperkeratosis in murine skin. Standardized green tea extract treatment also inhibited accumulation of c-fos and p53 protein induction following a single exposure to psoralen plus ultraviolet A. c-fos and p53 positive cells in psoralen plus ultraviolet A-treated skin were found to be increased by 55.4 +/- 13. 6% and 62.3 +/- 10.5%, respectively, compared with saline-treated unexposed control skin. Oral administration of 0.4 or 0.8% standardized green tea extract inhibited c-fos protein accumulation by 18.5% and 46.2% (p < 0.05), respectively, and p53 protein accumulation by 26.1% and 54.3% (p < 0.05), respectively. Similarly proliferating cell nuclear antigen staining, a marker of cell proliferation was induced (73.7%) in psoralen plus ultraviolet A-treated skin. Oral administration of 0.4% or 0.8% standardized green tea extract 1 d after psoralen plus ultraviolet A treatment was effective in reducing psoralen plus ultraviolet A-induced inflammatory responses including erythema and edema formation. When standardized green tea extract was applied to EpiDerm, a reconstituted human skin equivalent, psoralen plus ultraviolet A-induced 8-methoxypsoralen-DNA adduct formation and p53 protein accumulation were inhibited. Topical application of 0.2 mg 8-methoxypsoralen per cm2 followed by exposure to ultraviolet A (2.5 J per cm2) resulted in delayed erythema formation in human subjects. Pretreatment of human skin with topical application of 0.2 mg standardized green tea extract per cm2 30 min prior to psoralen plus ultraviolet A treatment resulted in an almost complete abrogation of psoralen plus ultraviolet A-induced erythema. In summary, these data demonstrate that standardized green tea extract protects against psoralen plus ultraviolet A-induced phototoxicity by inhibiting DNA damage and diminishing the inflammatory effects of this modality.

Prevention of UVB-induced immunosuppression in mice by the green tea polyphenol (-)-epigallocatechin-3-gallate may be associated with alterations in IL-10 and IL-12 production

UV exposure of the skin, particularly UVB (290-320 nm), causes adverse biological effects, including alterations in cutaneous immune cells, photoaging and photocarcinogenesis. Several studies have shown that polyphenolic compounds isolated from green tea afford protection against UVB-induced inflammatory responses and photocarcinogenesis in murine models. In this study we show that topical application of (-)-epigallocatechin-3-gallate (EGCG) (3 mg/mouse), a major polyphenolic component of green tea, before a single low dose UVB exposure (72 mJ/cm(2)) to C3H/HeN mice prevented UVB-induced inhibition of the contact hypersensitivity response and tolerance induction to the contact sensitizer 2, 4-dinitrofluorobenzene. Topical application of EGCG before UVB exposure reduced the number of CD11b+ monocytes/macrophages and neutrophils infiltrating into skin inflammatory lesions, which are considered to be responsible for creating the UV-induced immunosuppressive state. In addition, application of EGCG before UVB exposure decreased UVB-induced production of the immunomodulatory cytokine interleukin (IL)-10 in skin as well as in draining lymph nodes (DLN), whereas production of IL-12, which is considered to be a mediator and adjuvant for induction of contact sensitivity, was found to be markedly increased in DLN when compared with UVB alone-exposed mice. Taken together, our data demonstrate that EGCG protects against UVB-induced immunosuppression and tolerance induction by: (i) blocking UVB-induced infiltration of CD11b+ cells into the skin; (ii) reducing IL-10 production in skin as well as in DLN; (iii) markedly increasing IL-12 production in DLN. Protection against UVB-induced immunosuppression by EGCG may be associated with protection against UVB-induced photocarcinogenesis.

Heme oxygenase induction mediates the photoimmunoprotective activity of UVA radiation in the mouse

In contrast to the immunosuppressive potential of UVB (280-320 nm) radiation in experimental animals and humans, UVA (320-400 nm) radiation at environmentally relevant doses appears to be immunologically inert. However, such exposure to UVA radiation has been observed unexpectedly to induce resistance to UVB-induced immunosuppression in mice, by a mechanism resulting in the inactivation of cis-urocanic acid (UCA), an epidermal immunosuppressive UV photoproduct. In this study in mice, we show that the immunoprotective activity of UVA radiation, against the effects of both UVB radiation and cis-UCA, can be attributed to the induction of cutaneous heme oxygenase (HO; EC 1.14.99.3). Cell-mediated immune function was assessed in vivo by the contact hypersensitivity response induced to oxazolone at an unirradiated skin site, and HO enzyme activity was measured in cutaneous microsomal preparations from treated mice. There was a progressive increase in HO enzyme activity for at least 3 days after UVA irradiation. However HO activity, both constitutive and UVA radiation-induced, was sensitive to the effects of injecting mice with the specific HO inhibitor, tin protoporphyrin (Sn [IV] protoporphyrin IX; SnPP). We observed, in addition, that in SnPP-injected mice, the immunoprotective effect of UVA radiation against either UVB radiation or cis-UCA was abrogated. Because SnPP injection did not affect normal contact hypersensitivity responsiveness but did inhibit the constitutive HO enzyme activity, it appeared that only the inducible HO was active in modulating immune function. This finding indicates that UVA-induced HO activity is a major player in the skin defenses against UVB immunosuppression.

The effects of ultraviolet radiation on the human immune system

The adverse outcome of increased ultraviolet (UV) irradiation on human health is currently of concern. While many experiments have been carried out in rodent models, fewer have been designed to test the effects of UV exposure in human subjects. This review concentrates on the modulations induced in the human immune system by UV, and outlines changes in antigen presentation by Langerhans cells and macrophages, in the activities of natural killer cells and T cells, and in cytokine regulation. Precautionary measures which might be taken to help protect people against the immunosuppressive action of UV irradiation are considered.

Prevention of collagen-induced arthritis in mice by a polyphenolic fraction from green tea

Identification of common dietary substances capable of affording protection or modulating the onset and severity of arthritis may have important human health implications. An antioxidant-rich polyphenolic fraction isolated from green tea (green tea polyphenols, GTPs) has been shown to possess anti-inflammatory and anticarcinogenic properties in experimental animals. In this study we determined the effect of oral consumption of GTP on collagen-induced arthritis in mice. In three independent experiments mice given GTP in water exhibited significantly reduced incidence of arthritis (33% to 50%) as compared with mice not given GTP in water (84% to 100%). The arthritis index also was significantly lower in GTP-fed animals. Western blot analysis showed a marked reduction in the expression of inflammatory mediators such as cyclooxygenase 2, IFN-gamma, and tumor necrosis factor alpha in arthritic joints of GTP-fed mice. Histologic and immunohistochemical analysis of the arthritic joints in GTP-fed mice demonstrated only marginal joint infiltration by IFN-gamma and tumor necrosis factor alpha-producing cells as opposed to massive cellular infiltration and fully developed pannus in arthritic joints of non-GTP-fed mice. The neutral endopeptidase activity was approximately 7-fold higher in arthritic joints of non-GTP-fed mice in comparison to nonarthritic joints of unimmunized mice whereas it was only 2-fold higher in the arthritic joints of GTP-fed mice. Additionally, total IgG and type II collagen-specific IgG levels were lower in serum and arthritic joints of GTP-fed mice. Taken together our studies suggest that a polyphenolic fraction from green tea that is rich in antioxidants may be useful in the prevention of onset and severity of arthritis.

Modulation of the UVA activation of haem oxygenase, collagenase and cyclooxygenase gene expression by epigallocatechin in human skin cells

We have investigated the modifying effects of epigallocatechin, a major polyphenolic constituent of green tea, on ultraviolet-A-activated gene expression in human fibroblasts and keratinocytes using the stress responsive enzymes: haem oxygenase-1, interstitial collagenase and cyclooxygenase-2. Although epigallocatechin strongly reduced ultraviolet-A-induced haem oxygenase-1 activation in skin-derived 'fibroblasts, the same compound activated collagenase and cyclooxygenase expression. In a keratinocyte cell line, ultraviolet-A-mediated haem oxygenase-1 over-expression was low and epigallocatechin failed to modulate it further. In contrast to the results with fibroblasts, ultraviolet-A activation of cyclooxygenase in keratinocytes was reduced by epigallocatechin. The results indicate that the effect of this green tea polyphenol on cellular stress responses is complex and may involve direct effects on signal transduction as well as changes that may be associated with its antioxidant activity.

Protection by black tea and green tea against UVB and UVA + B induced skin cancer in hairless mice

The effects of green and black tea consumption on the early indices of UVB and UVA + B skin damage in hairless mice have been studied in the absence of any chemical tumour initiators or promoters. Black tea consumption was associated with a reduction in the number of sunburn cells in the epidermis of mice 24 h after UVA + B irradiation, although there was no effect of green tea. Other indices of early damage such as necrotic cells or mitotic figures were not affected. Neutrophil infiltration as a measure of skin redness was slightly lowered by tea consumption in the UVB group. Consumption of either green or black tea resulted in significantly fewer skin papillomas and tumours induced by UVA + B light, however black tea provided better protection against UVB-induced tumours than green tea. This study confirms earlier reports that tea consumption can reduce the incidence of skin cancer in hairless mice, and indicates that black tea may afford more protection against simulated solar irradiation than green tea.

Sunscreens and vitamin E provide some protection to the skin immune system from solar-simulated UV radiation

Previous studies have indicated that sunscreens designed to protect from erythema do not adequately prevent immunosuppression. Mice were irradiated with suberythemal doses of solar-simulated ultraviolet radiation (ssUVR) to assess the immunoprotective ability of sunscreens. Whereas C3H/HeJ and BALB/c mice had similar sensitivities to ssUVR-induced inflammation, C3H/HeJ mice were more sensitive to ssUVR-induced immunosuppression. Octyl dimethyl-p-aminobenzoic acid did not protect from immunosuppression and, thus, had an immune protection factor (IPF) of 1. 2-Ethylhexyl-p-methoxycinnamate and microfine titanium dioxide provided limited protection, both having IPF values of 1.127. Immune protection by the sunscreens appeared to be dependent upon absorption of UVA as well as UVB, and was much less than predicted from the sun protection factor. Vitamin E, an inhibitor of lipid peroxidation, also protected the immune system, with an IPF of 1.2, indicating that oxidation of lipids is involved in UVR-induced immunosuppression, and that it should be possible to develop sunscreens which protect the immune system.

Quercetin prevents UV-induced local immunosuppression, but does not affect UV-induced tumor growth in SKH-1 hairless mice

Ultraviolet is thought to induce skin tumors by its dual activity as a mutagenic agent and a suppressor of cell-mediated immunity. In the present study the effects of quercetin, a flavonoid-containing compound, on carcinogenesis and immunosuppression were studied in SKH hairless mice exposed to suberythemal doses of UV for up to 17 weeks. It was found that quercetin did not affect the onset or growth of non-melanoma skin tumors resulting from UV exposure. In contrast, it prevented the suppression in contact hypersensitivity (CHS) to picryl chloride induced by UV. The mechanism of this prevention might be explained by the observation that the decreased number of epidermal Langerhans' cells is partly prevented by the quercetin. Quercetin did not alter the effects of UV in increasing numbers of spleen and lymph node cells, only partly in decreasing the CD8-positive cells in spleen cell populations and decreasing the lymphoproliferative response of spleen cells to the mitogens concanavalin A and phytohemagglutinin. Thus oral quercetin did not prevent UV-induced carcinogenesis although it restored the skin-associated CHS response probably by protecting the antigen-presenting cells in the skin.

The effect of oral quercetin on UVB-induced tumor growth and local immunosuppression in SKH-1

The effects of quercetin (4%) on UVB-induced carcinogenesis and immunosuppression were studied in hairless SKH-1 mice exposed daily to suberythemal UVB for 12/13 and 16/17 weeks. Macroscopic and microscopic examinations showed that quercetin did not affect the onset and growth of UVB-induced non-melanoma skin tumors. Quercetin prevented the UV-induced suppression of the contact hypersensitivity (CHS) and the reduction of the percentage of CD8-positive cells in spleen and lymph nodes. Other immunological parameters were not affected. Thus, the results indicate that oral intake of a high dose of quercetin does not prevent UVB-induced carcinogenesis, although it restores the skin-associated CHS response.