Эпигаллокатехин egcg лечебные эффекты Кожные болезни Сахарный диабет Ожирение Научные исследования Укрепления здоровья эффекты зеленого чая




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Repair of UVB-induced DNA damage by green tea polyphenols leads to a reduction in UVB-induced inflammation in the skin


Exposure of the skin to UV radiation induces inflammation, and there is increasing evidence that chronic inflammation promotes the initiation of various skin diseases, including the development of skin cancers [16, and reviewed in 71]. Both UV-induced inflammatory responses and UV-induced skin tumorigenesis are causally related to UV-induced DNA damage. Therefore, it was of interest to explore the effects of green tea polyphenols on DNA repair and their relationship with inflammatory effects. CPDs are formed immediately after the exposure of the skin to UV radiation, and inflammation develops thereafter. Following UV exposure, it was observed that UV-induced DNA damage in the form of CPDs was repaired or removed more rapidly in the skin of mice that had been treated either with topical application of EGCG or orally administered GTPs. Subsequently, the levels of UVB-induced inflammation was lower in the treated mice than the non-treated mice with the levels of inflammation in the mouse skin from the different treatment groups being assessed through analysis of biomarkers of inflammation, such as COX-2 expression, PGE2 production and the levels of pro-inflammatory cytokines. Interestingly, this effect of EGCG or GTPs was not observed in IL-12-deficient or knockout mice. This may be due to the fact that the treatment with EGCG or GTPs was not able to repair UV-induced DNA damage significantly in the IL-12 knockout mice, as detailed [59]. This new information supports the concept that UV-induced DNA damage and inflammatory responses are causally related with the increased risk of photocarcinogenesis. This in vivo experimental evidence indicates that the prevention of UVB-induced skin cancer by GTPs or EGCG is mediated through inhibition of UVB-induced inflammation, which in turn is mediated, at least in part, through rapid repair of damaged DNA. The outcome of this study therefore suggests that regular consumption of green tea or green tea polyphenols may be considered as an effective strategy for the prevention of inflammation-associated skin diseases including skin cancers.

Bioavailability and metabolism of polyphenols


The bioavailability and metabolism of polyphenols may influence their effectiveness. The considerable structural diversity among the polyphenols can influence 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, 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. Such reactions facilitate their excretion and limit their potential toxicity, if any [77]. During digestion in the intestine, the large polyphenolic molecules break into multiple small molecules or metabolites and these may systemically induce beneficial effects in the body. Polymeric proanthocyanidins are not absorbed as such in the gut. Detection of proanthocyanidin dimers B1 and B2 in human plasma indicated that the absorption of these dimers was ~100-fold lower than that of the monomeric flavanols. In the case of topical delivery of the polyphenols, the penetration of polyphenols into the skin is limited and successful delivery of plant polyphenols requires cream-based, organic solvent-based or lipid soluble topical formulations that can enhance the penetration of the polyphenols.

Conclusion


The polyphenols discussed in this review article show significant anti-inflammatory, anti-oxidant and anti-DNA damaging effects. These protective effects of polyphenols may contribute to their anti-photocarcinogenic effects and act to abrogate the various biochemical processes induced or mediated by solar UV radiation. Based on the epidemiological evidence and laboratory studies conducted using in vitro and in vivo systems, it is suggested that routine consumption or topical treatment of these polyphenols may provide efficient protection against the harmful effects of solar ultraviolet radiation in humans. For appropriate conversion of drug or chemopreventive agent doses from animal studies to human studies, the body surface area normalization method has been prescribed [reviewed in 75]. Based on this reference, the human equivalent dose (HED) of any chemopreventive agent can be calculated using the following formula:

HED(mg/kg)=Animal dose(mg/kg)×AnimalKmfactorHumanKmfactor

(Km factor for mouse = 3; Km factor for adult human = 37).

Further, the use of polyphenols in combination with sunscreens or skin care lotions 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 exposures.



Эпигаллокатехин-3-галлат (EGCG): химической и медико-биологической точек зрения.

Соединение (-)-эпигаллокатехин-3-галлат (EGCG) является основной катехин, содержащийся в зеленых чая [Camellia sinensis L.) Ktze. (Theaceae)]. Это полифенольные соединения и нескольких связанных катехины, как считается, ответственны за пользы для здоровья, связанных с потреблением зеленого чая. Потенциальные выгоды для здоровья, приписываемые зеленый чай и EGCG включает антиоксидантное действие, проведение химиопрофилактики рака, улучшения сердечно-сосудистых заболеваний, повышение веса, защищая кожу от повреждений, вызванных ионизирующей радиации, и другие. Соединение EGCG было показано, регулируют десятки болезнь-специфические молекулярные мишени. Многие из этих молекулярных мишеней, которые зависят только от концентрации EGCG, что гораздо выше уровня достигнуто либо пить зеленый чай или потребление умеренных доз экстракта зеленого чая на основе биологически активных добавок. Несмотря на это, хорошо продуманные двойных слепых контролируемых клинических исследований в последнее время показана эффективность экстракты зеленого чая и очищенной EGCG продукции в пациентов. Поэтому, этот отзыв основные результаты от того, что авторы считают одними из наиболее клинически значимых последних исследований и описывает текущие события в стереоселективного полный синтез EGCG.



Phytochemistry. 2006 Sep;67(17):1849-55. Epub 2006 Jul 31.
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