title: Role of cytochrome P-450IIE1 in N-nitroso-N-methylaniline induced hepatocyte cytotoxicity.
abstract: 1. The cytotoxicity of N-nitrosomethylaniline (NMA) towards hepatocytes isolated from rats was prevented by acetone or ethanol (inhibitors for cytochrome P-450IIE1) but not by metyrapone or SKF525A (inhibitors for cytochrome P-450IIB1/2). Various alcohols, secondary ketones and isothiocyanates that induced cytochrome P-450IIE1 were also found to be protective. Various aromatic and chlorinated hydrocarbon solvents that are substrates or inducers of cytochrome P-450IIE1 also prevented NMA cytotoxicity. Nitrogen-containing heterocycles that induced cytochrome P-450IIE1 were less effective. Further evidence that cytochrome P-450IIE1 was responsible for the activation of NMA was the marked increase in hepatocyte susceptibility if hepatocytes from pyrazole-induced rats were used. 2. NMA was more cytotoxic to hepatocytes isolated from phenobarbital-pretreated rats than uninduced rats. However, metyrapone now prevented and SKF525A delayed the cytotoxicity whereas ethanol, acetone, allyl isocyanate, isoniazid or trichloroethylene had no effect on the susceptibility of phenobarbital-induced hepatocytes. Furthermore, microsomes isolated from phenobarbital-pretreated rats had higher NMA-N-demethylase activity which was more inhibited by metyrapone and SKF525A than that of uninduced microsomal activity. By contrast the N-demethylase activity of phenobarbital induced microsomes was more resistant to acetone, ethanol, hexanal, trichloroethylene and toluene than uninduced microsome. 3. The above results suggest that cytochrome P-450IIE1 catalyses the cytotoxic activation of NMA in normal or pyrazole-induced hepatocytes whereas cytochrome P-450IIB1/2 is responsible for cytotoxicity in phenobarbital-induced hepatocytes.
authors.affiliation: Faculty of Pharmacy, University of Toronto, Ontario, Canada.
authors.forename: Z
authors.initials: Z
authors.lastname: Quan
authors.forename: S
authors.initials: S
authors.lastname: Khan
authors.forename: P J
authors.initials: PJ
authors.lastname: O'Brien
mesh_terms: D000438:Alcohols / Q000494:pharmacology; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D002470:Cell Survival / Q000187:drug effects; D002725:Chloroform / Q000494:pharmacology; D019392:Cytochrome P-450 CYP2E1; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000378:metabolism; D004790:Enzyme Induction; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D009602:Nitrosamines / Q000037:antagonists & inhibitors / Q000633:toxicity*; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D010634:Phenobarbital; D011720:Pyrazoles; D051381:Rats; D011919:Rats, Inbred Strains; D013250:Steroid Hydroxylases / Q000378:metabolism
chemical_list: D000438:Alcohols; D065607:Cytochrome P-450 Enzyme Inhibitors; D009602:Nitrosamines; D011720:Pyrazoles; C031280:pyrazole; D002725:Chloroform; D003577:Cytochrome P-450 Enzyme System; C014102:N-methyl-N-nitrosoaniline; D013250:Steroid Hydroxylases; D019392:Cytochrome P-450 CYP2E1; D001189:Aryl Hydrocarbon Hydroxylases; C025619:steroid 16-beta-hydroxylase; D010089:Oxidoreductases, N-Demethylating; D010634:Phenobarbital