Anti-Cancer Effects of Green Tea by Either Anti- or Pro- Oxidative Mechanisms.

Tea derived from the leaves and buds of Camellia sinensis (Theaceae) is consumed worldwide. Green tea contains various components with specific health-promoting effects, and is believed to exert protective effects against diseases including cancer, diabetes and hepatitis, as well as obesity. Of the various tea components, the polyphenol catechins have been the subject of extensive investigation and among the catechins, (-)-epigallocatechin gallate has the strongest bioactivity in most cases. Our research group has postulated that hepatocyte nuclear factor-4α, sterol regulatory element-binding proteins, and tumor necrosis factor-α are targets of green tea constituents including (-)-epigallocatechin gallate for their anti-diabetes, anti-obesity, and anti-hepatitis effects, respectively. Published papers were reviewed to determine whether the observed changes in these factors can be correlated with anti-cancer effects of green tea. Two major action mechanisms of (-)-epigallocatechin gallate have been proposed; one associated with its anti-oxidative properties and the other with its pro-oxidative activity. When reactive oxygen species are assumed to be involved, our findings that (-)-epigallocatechin gallate down- regulated hepatocyte nuclear factor-4α, sterol regulatory element-binding proteins, and tumor necrosis factor-α may explain the anti-cancer effect of green tea as well. However, further studies are required to elucidate which determinant directs (-)-epigallocatechin gallate action as an anti-oxidant or a pro-oxidant for favorable activity.