Does green tea antioxidant fraction prevent cytotoxicity and inhibition of intercellular communication in cultured mouse hepatocytes and human keratinocytes?
Green tea antioxidant fraction prevents cytotoxicity and inhibition of intercellular communication induced by pro-oxidant compounds in vitro, suggesting a mechanism for its anti-tumor promotion effects.
An antioxidant fraction of Chinese green tea (green tea antioxidant; GTA), containing several catechins, has been previously shown to inhibit 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced tumor promotion in mouse skin. In the present study, GTA was shown to have antioxidative activity toward hydrogen peroxide (H2O2) and the superoxide radical (O2-). GTA also prevented oxygen radical and H2O2-induced cytotoxicity and inhibition of intercellular communication in cultured B6C3F1 mouse hepatocytes and human keratinocytes (NHEK cells). GTA (0.05-50 micrograms/ml) prevented the killing of hepatocytes (measured by lactate dehydrogenase release) by paraquat (1-10 mM) and glucose oxidase (0.8-40 micrograms/ml) in a concentration-dependent fashion. GTA (50 micrograms/ml) also prevented the inhibition of hepatocyte intercellular communication by paraquat (5 mM), glucose oxidase (0.8 micrograms/ml), and phenobarbital (500 micrograms/ml). In addition, GTA (50 micrograms/ml) prevented the inhibition of intercellular communication in human keratinocytes by TPA (100 ng/ml). Cytotoxicity and inhibition of intercellular communication, two possible mechanisms by which tumor promoters may produce their promoting effects were therefore prevented by GTA. The inhibition of these two effects of pro-oxidant compounds may suggest a mechanism by which GTA inhibits tumor promotion in vivo.
Ruch et al. (Sun,) studied this question.