The antioxidant and pro-oxidant activities of green tea polyphenols: A role in cancer prevention

Abstract

Green tea (Camellia sinensis) is rich in catechins, of which (−)-epigallocatechin-3-gallate (EGCG) is the most abundant. Studies in animal models of carcinogenesis have shown that green tea and EGCG can inhibit tumorigenesis during the initiation, promotion and progression stages. Many potential mechanisms have been proposed including both antioxidant and pro-oxidant effects, but questions remain regarding the relevance of these mechanisms to cancer prevention. In the present review we will discuss the redox chemistry of the tea catechins and the current literature on the antioxidant and pro-oxidative effects of the green tea polyphenols as they relate to cancer prevention. We report that although the catechins are chemical antioxidants which can quench free radical species and chelate transition metals, there is evidence that some of the effects of these compounds may be related to induction of oxidative stress. Such pro-oxidant effects appear to be responsible for the induction of apoptosis in tumor cells. These pro-oxidant effects may also induce endogenous antioxidant systems in normal tissues that offer protection against carcinogenic insult. This review is meant point out understudied areas and stimulate research on the topic with the hope that insights into the mechanisms of cancer preventive activity of tea polyphenols will result.

Protictive effects of green tea and garlic on the morphological and oxidative stress changes of hippocampus in aged male and female albino rats

“…The previous studies of [33,34] reported that GT reduces oxidative stress by virtue of its antioxidant properties thus improving the structural integrity of cell membrane and eventually alleviates the histopathological changes as well as the biochemical perturbations. These results suggest that catechins, epicatechin (EC), epigallocatechin (EGC), epicatechin-3-gallate (ECG), and EGCG could have a direct (antioxidant) or indirect (increase of activity or expression) effect [35,36].…”

Green Tea Polyphenols Extend the Lifespan of MaleDrosophila melanogasterWhile Impairing Reproductive Fitness

“…49,50 In the case of green tea, its polyphenols have been shown to have pro-oxidant activities 46 and thus may actually be mildly toxic, consistent with hormesis as a plausible mechanism of action.…”

Effect of morin, a flavonoid against DOCA-salt hypertensive rats: a dose dependent study

“…Flavonoids are polyphenolic compounds that can be found in dietary components such as food products, beverages and herbal medicines with different health benefits shown in a large number of studies [13] . Most flavonoids have an antioxidant activity [14,15] .…”