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Review
. 2010 Sep 1;501(1):65-72.
doi: 10.1016/j.abb.2010.06.013. Epub 2010 Jun 15.

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

Joshua D Lambert  1 , Ryan J Elias
Affiliations
Review

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

Joshua D Lambert et al. Arch Biochem Biophys. .

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.

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Figures

Figure 1
Figure 1
Structures of the major tea polyphenols.
Figure 2
Figure 2
Resonance stabilization of unpaired eectrons by the gallate ring found in tea catechins.
Figure 3
Figure 3
Oxidative reaction between EGCG, superoxide, and ferric iron resulting in the production of oxidative stress, EGCG dimers, and EGCG-cysteine conjugates (EGCG-SR). PhO = semiquinone radical.
Figure 4
Figure 4
Proposed model for the mechanism by which the antioxidant and/or pro-oxidant effects tea polyphenols inhibit the carcinogenic process. ROS = reactive oxygen species, ARE = antioxidant response element, GST = glutathione S transferase, γGT = gamma glutamyltransferase.
See this image and copyright information in PMC

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