DIFFERENT CONTRIBUTIONS OF CYTOCHROME-P450 2E1 AND P450 2B1 2 TO CHLOROFORM HEPATOTOXICITY IN RAT/

The contribution of cytochrome P450 isozymes CYP2E1 and CYP2B1/2 to ch loroform-induced hepatotoxicity taken at 18 hr after the treatment was investigated in rats treated with n-hexane as an inducer of CYP2E1, 2 -hexanone as an inducer of CYP2E1 and CYP2B1/2, and phenobarbital (PB) as an inducer of CYP2B1/2, Hepatic damage was evaluated by gross meas urement of plasma alanine aminotransferase activity and histopathologi cal examination. All treatments potentiated chloroform-induced hepatic damage, In n-hexane-pretreated rats, the damage was maximal with the middle dose of chloroform (0.2 ml/kg), whereas the damage increased wi th dose in rats treated with 2-hexanone or PB, The degree of hepatic d amage induced with the three pretreatments was in the following order: n-hexane > 2-hexanone = PB with the middle dose of chloroform and PB much greater than 2-hexanone > n-hexane with the high dose (0.5 ml/kg) ; little difference among the pretreatments was seen with the low dose (0.1 ml/kg), These findings suggest that CYP2E1 is a low K-m isoform and CYP2B1/2 a high K-m isoform for chloroform activation, CYP2E1-depe ndent hepatic damage was characterized by ballooned hepatocytes, which were restricted to the centrilobular area; with CYP2B1/2, more necrot ic than ballooned hepatocytes were seen and the necrotic hepatocytes w ere found not only in the centrilobular but also in the midzonal and p eriportal areas. Chloroform treatment did not affect the activity of N -nitrosodimethylamine N-demethylase in pretreated rats; the high dose increased the activity in control rats. In contrast, the high dose of chloroform decreased the activity of 7-pentoxyresorufin O-depentylase in all induced rats but not in controls, Immunoinhibition and immunobl ot analyses showed that the high dose of chloroform induced CYP2E1 in control rats but decreased CYP2B1/2 in all pretreated rats. These resu lts suggest that although both CYP2E1 and CYP2B1/2 contribute to chlor oform-induced hepatic damage, they do so quite differently. (C) 1995 A cademic Press, Inc.