Anticlastogenic, antigenotoxic and apoptotic activity of epigallocatechin gallate: a green tea polyphenol

Modulation of events characteristic of carcinogenesis or of cancer cells is being emphasized as a rational strategy to control cancer. Green tea polyphenol epigallocatechin gallate (EGCG) has been shown to be highly active as a cancer chemopreventive agent. Certain cellular and molecular events relevant to carcinogenesis are also modified by EGCG. The present investigation was carried out to examine the effects of EGCG on the cytogenetic change and DNA damage induced by toxicant H2O2 and carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in Chinese hamster V-79 cells in culture. Cytogenetic change as evident by the formation of micronuclei and DNA damage in the form of comet tail length during single cell gel electrophoresis was found to be significantly suppressed by EGCG in a dose dependent manner. Cells preincubated with EGCG were protected from subsequent damage by the genotoxic agents. Apoptosis, a highly organized physiological mechanism to eliminate injured or abnormal cells, is also implicated in multistage carcinogenesis. Initiated cells, cells at promotional stage or fully transformed cells can be eliminated through apoptosis. It was observed that EGCG suppressed growth and proliferation of K-562 cells derived from human chronic myelogenic leukemia. Morphological features of treated cells and characteristic DNA fragmentation revealed that the cytotoxicity was due to induction of apoptosis. This was mediated by activation of caspase 3 and caspase 8. Results show that EGCG not only protects normal cells against genotoxic hazard but also eliminate cancer cells through induction of apoptosis