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Tea Extracts and Skin Health
Melanoma
Ultraviolet solar radiation may induce a variety of adverse effects in humans, including melanoma,25 photoaging of the skin,26-27 sunburn,28 and immunosuppression.29-30 Protection against UV-induced skin damage includes avoidance of sun exposure, application of sunscreens, low-fat diets,31-32 and pharmacologic intervention with retinoids.33 More recently, green tea extracts have been reported to be beneficial in treating UV-induced photodamage.
EGCG's and polyphenols
In a study by Elmets et al,6 1% to 10% green tea polyphenolic (GTP) fractionsin ethanol and water vehicle were applied onto the backs of 6 volunteers. Thirty minutes after GTP application, patients were exposed to twice the minimal erythema dose of UV radiation from a solar simulator. The minimal erythema dose was determined for each patient by exposing skin to graded doses of UV radiation from the solar simulator. Green tea extracts resulted in a dose-dependent reduction of UV-induced erythema as measured by chromatometry and visual evaluation. The (-)-epigallocatechin-3-gallate and (-)-epicatechin-3-gallate polphenolic fractions were most effective, while the (-)-epigallocatechin (EGC) and (-)-epicatechin fractions had little effect. Histologic examination showed a decrease in sunburn cells in GTP-treated skin. Epidermal Langerhans cells, the antigen-presenting cells involved in the skin immune response, were significantly protected against UV damage. Finally, GTP fractions reduced UV-induced mutations in DNA, as detected by means of a phosphorus 32 postlabeling technique. Spectrophotometric analysis indicated that GTP fractions did not absorb UV-B light, implying a mechanism of action different from that of sunscreens. This study demonstrates the potential benefit of GTP extracts in preventing UV-induced immunosuppression and erythema.
The use of GTP extracts was also found to be beneficial in treating UV-induced immunosuppression in mice. The GTP extracts, fruits and vegetables, and quercetin and chrysin significantly prevented the UV-induced suppression of contact hypersensitivity to picryl chloride when compared with irradiated, untreated control (P<.05). Increased ear thickness measurements were used to evaluate the response. The GTP was administered in concentrations of 0.1% and 0.01%.17 Green tea extracts have been beneficial in preventing early signs of photochemical damage to mouse and human skin treated with psoralen–UV-A therapy. Psoralen–UV-A, a treatment for psoriasis, increases the patient's risk of developing melanoma and squamous cell carcinoma. Pretreatment and posttreatment with the green tea extracts in mouse and human skin significantly decreased markers of this photochemical damage, namely hyperplasia and hyperkeratosis, c-fos and p53, and erythema, (P<.05), when compared with vehicle controls (water given before and after treatment).34 The effects of green tea on skin are further discussed by Katiyar et al.35
Oral and topical standardized black tea extracts also decreased photochemical damage to the skin. In one study, standardized black tea extracts significantly reduced erythema and skinfold thickness associated with UV-B–induced carcinogenesis in cultured keratinocytes and mouse and human skin (P<.05). In topically treated mice, a 64% reduction in severity of erythema and a 50% decrease in skinfold thickness were observed when compared with vehicle control. A decrease in the expression of c-fos, c-jun, and p53 in mouse skin and keratinocytes pretreated with standardized black tea extracts was also noted. This study indicates that when green tea is oxidized to black tea, the extracts remain beneficial in preventing the early signs of UV-B–induced phototoxic effects, namely, sunburn and skin thickness.
J Biol Chem. 2007 May 4;282(18):13736-45. Epub 2007 Mar 15. Links
Epigallocatechin gallate, a green tea polyphenol, mediates NO-dependent vasodilation using signaling pathways in vascular endothelium requiring reactive oxygen species and Fyn.
Kim JA, Formoso G, Li Y, Potenza MA, Marasciulo FL, Montagnani M, Quon MJ.
Diabetes Unit, NCCAM, National Institutes of Health, Bethesda, Maryland 20892, USA.
Green tea consumption is associated with reduced cardiovascular mortality in some epidemiological studies. Epigallocatechin gallate (EGCG), a bioactive polyphenol in green tea, mimics metabolic actions of insulin to inhibit gluconeogenesis in hepatocytes. Because signaling pathways regulating metabolic and vasodilator actions of insulin are shared in common, we hypothesized that EGCG may also have vasodilator actions to stimulate production of nitric oxide (NO) from endothelial cells. Acute intra-arterial administration of EGCG to mesenteric vascular beds isolated ex vivo from WKY rats caused dose-dependent vasorelaxation. This was inhibitable by L-NAME (NO synthase inhibitor), wortmannin (phosphatidylinositol 3-kinase inhibitor), or PP2 (Src family kinase inhibitor). Treatment of bovine aortic endothelial cells (BAEC) with EGCG (50 microm) acutely stimulated production of NO (assessed with NO-specific fluorescent dye DAF-2) that was inhibitable by l-NAME, wortmannin, or PP2. Stimulation of BAEC with EGCG also resulted in dose- and time-dependent phosphorylation of eNOS that was inhibitable by wortmannin or PP2 (but not by MEK inhibitor PD98059). Specific knockdown of Fyn (but not Src) with small interfering RNA inhibited both EGCG-stimulated phosphorylation of Akt and eNOS as well as production of NO in BAEC. Treatment of BAEC with EGCG generated intracellular H(2)O(2) (assessed with H(2)O(2)-specific fluorescent dye CM-H(2)DCF-DA), whereas treatment with N-acetylcysteine inhibited EGCG-stimulated phosphorylation of Fyn, Akt, and eNOS. We conclude that EGCG has endothelial-dependent vasodilator actions mediated by intracellular signaling pathways requiring reactive oxygen species and Fyn that lead to activation of phosphatidylinositol 3-kinase, Akt, and eNOS. This mechanism may explain, in part, beneficial vascular and metabolic health effects of green tea consumption.
Studies:
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