Abstract
Tea and coffee are consumed worldwide and epidemiological and clinical studies have shown their health beneficial effects, including anti-cancer effects. Epigallocatechin gallate (EGCG) and chlorogenic acid (CGA) are the major components of green tea polyphenols and coffee polyphenols, respectively, and believed to be responsible for most of these effects. Although a large number of cell-based and animal experiments have provided convincing evidence to support the anti-cancer effects of green tea, coffee, EGCG, and CGA, human studies are still controversial and some studies have suggested even an increased risk for certain types of cancers such as esophageal and gynecological cancers with green tea consumption and bladder and lung cancers with coffee consumption. The reason for these inconsistent results may have been arisen from various confounding factors. Cell-based and animal studies have proposed several mechanisms whereby EGCG and CGA exert their anti-cancer effects. These components appear to share the common mechanisms, among which one related to reactive oxygen species is perhaps the most attractive. Meanwhile, EGCG and CGA have also different target molecules which might explain the site-specific differences of anti-cancer effects found in human studies. Further studies will be necessary to clarify what is the mechanism to cause such differences between green tea and coffee.
Highlights
Green tea is produced by processing of leaves of the plant Camellia sinensis (Theaceae) and is popularly consumed worldwide
This review focuses mechanisms related to anti-oxidant and pro-oxidant effects, anti-inflammatory effects, anti-angiogenic effects, induction of apoptosis, modulation of epigenetic pathways and Epigallocatechin gallate (EGCG)’s binding to cancer-related proteins which have been reviewed in many articles [26,34,35,36,37,38,39]
Expression in cultured E0771 cells. These findings indicate that EGCG exerts anti-cancer effect by inhibiting angiogenesis mediated by the downregulation of vascular endothelial growth factor (VEGF), HIF-1α and nuclear factor-κB (NF-κB) [60]
Summary
Green tea is produced by processing of leaves of the plant Camellia sinensis (Theaceae) and is popularly consumed worldwide. Coffee is consumed worldwide and has various health effects. It contains about 2000 different chemicals and the major polyphenols are chlorogenic acid (CGA, Figure 1) and its derivatives which amount to about 3% w/w of roasted coffee powder [2,5]. We discuss recent evidence from human studies to support the anti-cancer effects of consumption of green tea and coffee and mechanistic aspects of the actions of EGCG and CGA based on the results of cell-based and animal experiments. Caffeine is contained abundantly in tea and coffee and may contribute to the anti-cancer effects of these beverages. For the safe of clarity, the current review focuses on EGCG and CGA but excludes any discussion on caffeine, which has already been comprehensively reviewed [9,10,11,12]
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