To elucidate the interactions of catechins with the cellular antioxidative system, human hepatorna HepG2 cells were incubated in a serum-free medium with catechins, and the level of thiobarbituric acid-reactive substances (TBARS) as a marker of lipid peroxidation was determined, as well as the contents of α-tocopherol (α-Toc) and glutathione (GSH) and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). TBARS was promptly decreased by the incubation with epigallocatechin 3-
O-gallate (EGCG), and 12 h later TBARS in the cells with 10μM EGCG was about 15% (
p<0.05) of that in the controls (without catechins). Epigallocatechin, epicatechin 3-
O-gallate, and epicatechin also had an antioxidative activity, but a higher concentration was required to induce the same effect as EGCG. In the cells incubated with EGCG, the consumption of α-Toc and the formation of the oxidized form of GSH were suppressed. Although EGCG showed no effects on the Cu/Zn-SOD activity, the Mn-SOD activity in the cells was enhanced (
p<0.05) by the incubation with EGCG. Moreover, the GSH-Px activity was maintained at a higher level (
p<0.05) in the cells with EGCG, compared with that in the controls. when the cells were preincubated with EGCG, the cytotoxicity of H
2O
2 was significantly reduced. Furthermore, the decrease of cellular α-Toc content induced by exposure to H
2O
2 was prevented by the pretreatment of EGCG. These results suggest that EGCG taken up into HepG2 cells is preferentially used as an antioxidant, rather than α-Toc and GSH, to suppress lipid neroxidation and to protect these cells from oxidative damages.
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