Hepatocyte cytotoxicity induced by various hepatotoxins mediated by cytochrome P-450 IIE1: protection with diethyldithiocarbamate administration

Abstract

The objective of this study was to determine whether the thiol drug, diethyldithiocarbamate (DEDC) and its two metabolites, disulfiram (DS) and carbon disulfide (CS 2) could be used as inhibitors of cytochrome P-450 IIE1 to protect hepatocytes from cytotoxic xenobiotics. (1) Hepatocytes isolated from rats following pyrazole administration to induce cytochrome P-450 IIE1 were much more susceptible to carbon tetrachloride (CCl 4) and dimethylnitrosamine (DMN) than hepatocytes from untreated rats. Microsomes isolated from P-450 IIE1-induced liver were also much more effective at catalysing a NADPH-dependent metabolism of CCl 4 and DMN. The activities of aniline hydroxylase and p-nitroanisole- O-demethylase increased whereas ethoxyresorufin- O-dealkylase activity was much less induced and pentoxyresorufin- O-dealkylase activity was decreased. The P-450 IIE1 antibody markedly inhibited the NADPH-dependent metabolism of these compounds indicating that IIE1 is a major catalyst of the microsomal metabolism of CCl 4 and DMN. (2) Hepatocytes isolated from rats treated with DEDC or its metabolites, DS and CS 2, on the other hand, were resistant to CCl 4 and DMN. Microsomes isolated from the liver of animals treated with DEDC or DS or CS 2 were also much less effective at catalysing the NADPH-dependent metabolism of the above compounds. DEDC markedly decreased the activities of aniline hydroxylase, p-nitroanisole- O-demethylase and pentoxyresorufin- O-dealkylase but had no effect on ethoxyresorufin- O-dealkylase activity. (3) Hepatocytes isolated from pyrazole-treated rats were also more susceptible to bromobenzene (BB) and naphthalene-induced cytotoxicity than hepatocytes from untreated rats. Furthermore, DEDC or CS 2 administration beforehand significantly protected hepatocytes against both xenobiotics. (4) By contrast, hepatocytes isolated from P-450 IIE1 induced rats were not more susceptible to lactonitrile or cyclophosphamide. Instead, cyclophosphamide was activated by phenobarbital-induced P-450 isozymes whereas lactonitrile was activated by alcohol dehydrogenase. Hepatocytes isolated from DEDC-treated rats were also resistant to cyclophosphamide but not lactonitrile. (5) The above results suggest that P-450 IIE1 catalyses the cytotoxic activation of CCl 4, DMN, BB and naphthalene but not of lactonitrile or cyclophosphamide. Furthermore, the administration of DEDC and its metabolites, disulfiram or CS 2, inactivates P-450 IIE1 so that the hepatocytes become resistant to these hepatotoxins.