Preventive effect of epicatechin and ginsenoside Rb2 on the inhibition of gap junctional intercellular communication by TPA and H2O2

The anticarcinogenic effects of epicatechin (EC) and ginsenoside Rb2 (Rb2), which are major components of green tea and Korea ginseng, respectively, were investigated using a model system of gap junctional intercellular communication (GJIC) in WB-F344 rat liver epithelial cells. 12-O-tetradecanoylphorbol-13-acetate (TPA) and hydrogen peroxide, known as cancer promoters, inhibited GJIC in the epithelial cells as determined by the scrape loading/dye transfer assay, fluorescence redistribution assay after photobleaching, and immunofluorescent staining of connexin 43 using a laser confocal microscope. The inhibition of GJIC by TPA and H2O2 was prevented with treatment of Rb2 or EC. The effect of EC on GJIC was stronger in TPA-treated cells than in H2O2-treated cells, while the effect of Rb2 was opposite to that of EC. EC, at the concentration of 27.8 μg/ml, prevented the TPA-induced GJIC inhibition by about 60%. Rb2, at the concentration of 277 μg/ml, recovered the H2O2-induced GJIC inhibition by about 60%. These results suggest that Rb2 and EC may prevent human cancers by preventing the down-regulation of GJIC during the cancer promotion phase and that the anticancer effect of green tea and Korea ginseng may come from the major respective components, EC and Rb2.