Halomethane hepatotoxicity: Induction of lipid peroxidation and inactivation of cytochrome P-450 in rat liver microsomes under low oxygen partial pressures

Abstract

Halomethane-induced lipid peroxidation and inactivation of cytochrome P-450 were studied in liver microsomes from pheno-barbital-pretreated rats in the presence of NADPH at steady-state O 2 partial pressures ( PO in2). As indicated by the formation of thiobarbituric acid-reactive material and the stimulation of O 2 uptake, significant lipid peroxidation was induced by those halomethanes containing more than two Cl, Br, or I atoms. Lipid peroxidation decisively depended on the PO 2 present, showing distinct maxima at PO 2 between 1 and 10 mm Hg. Those halomethanes inducing lipid peroxidation also led to inactivation of microsomal cytochrome P-450, as indicated by a loss of cytochrome P-450 detectable as ferrous CO complex and an equimolar loss of microsomal heme. Under anaerobic conditions inactivation of cytochrome P-450 presumably resulted solely from an attack of halomethane radicals on its heme moiety. Under aerobic conditions lipid peroxidation made an additional contribution to the inactivation of cytochrome P-450. These results suggest that the reductive activation to free radicals, catalyzed by cytochrome P-450, and thus the induction of lipid peroxidation at low but physiological PO 2 are characteristic not only of CCl 4 but also of other polyhalogenated methanes, especially CBrCl 3, CBr 4, CHI 3, CHBr 3, and CHBr 2Cl.