Protection of rat liver microsomes against carbon tetrachloride-induced lipid peroxidation by red ginseng saponin through cytochrome P450 inhibition

A possible role of cytochrome P450 (P450) inhibition by red ginseng saponins in carbon tetrachloride (CCI4)-induced lipid peroxidation was investigated in liver microsomes prepared from male Sprague Dawley rats. The total saponin of red ginseng standardized on ginsenosides-Rbl, -Rb2, -Rc, -Rd, -Re, and -Rg1 whose composition was studied in our previous report was used in the present study. The standardized saponin of red ginseng showed inhibitory effects on P450-associated monooxygenase activities in a dose-dependent manner, particularly p-nitrophenol hydroxylase activity which has been known to represent CCl4-activating P450 2E1 enzyme. Meanwhile, silymarin enhanced the activity of P450 2E1 enzyme in liver microsomes. When the lipid peroxidation was induced by incubating rat liver microsomes with CCI4 in the presence of NADPH, the standardized saponin significantly blocked the formation of thiobarbituric acid-reactive substances at the same concentrations showing P450 inhibition in liver microsomes. Silymarin revealed more potent protection against CCI4-induced lipid peroxidation. When the lipid peroxidation was induced by FeCl3, in which metabolic activation may not be required, only silymarin could protect the lipid peroxidation in liver microsomes. Taken together, our present results indicated that the inhibitory effects of red ginseng saponin on P450 enzymes may have a critical role in CCl4-induced lipid peroxidation in rat liver microsomes and that the mechanism of hepatoprotection by red ginseng saponin may be distinct from that of silymarin.