CYP2E1 level in rat liver injured by the interaction between carbon tetrachloride and chloroform

The toxic interaction between carbon tetrachloride (CCl₄) and chloroform (CHCl₃) was investigated in rats chronically pretreated with ethanol, and in rat liver microsomes. A combined exposure to 10 ppm CCl₄ and 50 ppm CHCl₃ increased plasma alanine aminotransferase (ALT) activity to a level similar to that by a single exposure to 50 ppm CCl₄. The single exposure decreased liver reduced glutathione (GSH) and cytochrome P450 (CYP) content, and N-nitrosodimethylamine N-demethylase (NDMAD) activity. The effects of combined exposure, however, were little or less than those of the single exposure. Immunoblot analysis with monoclonal antibody to CYP2E1 indicated that CYP2E1 was appreciably decreased after the single exposure but the enzyme remained after the combined exposure. The antibody inhibited CCl₄-induced lipid peroxidation in microsomes from ethanol-treated rats. Ethanol pretreatment increased the metabolic rate of CCl₄ and CCl₄-induced lipid peroxidation, but the coexistence of CHCl₃ and other hydrocarbons such as trichloroethylene and 1,1,1-trichloroethane did not increase the in vitro metabolic rate or the lipid peroxidation. The addition of GSH decreased CCl₄-induced lipid peroxidation, and the effect reached its maximum at 0.3 mM of GSH, so that the hepatotoxic interaction between CCl₄ and CHCl₃ at low dose exposure is more than additive when judged by the plasma ALT activity, but this is not true of the changes in drug-metabolizing enzyme activity and GSH depletion.