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 Rb-2 (Rb-2), 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 Rbl or EC. The effect of EC on GJIC was stronger in TPA-treated cells than in H2O2-treated cells, while the effect of Rb-2 was opposite to that of EC. EC, at the concentration of 27.8 mug/ml, prevented the TPA-induced GJIC inhibition by about 60%. Rb-2 at the concentration of 277 mug/ml, recovered the H2O2-induced GJIC inhibition by about 60%. These results suggest that Rb-2 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 Rb-2. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.