Rat liver microsomal metabolites of 7-methylbenz[c]acridine

Application of synchronous luminescence to the separate determination of cochromatographing metabolites of the carcinogen, 7-methylbenz[c]acridine

A synchronous fluorescence assay for the cochromatographing metabolites of 7-methylbenz[c]acridine, 7-hydroxymethylbenz[c]acridine and trans-7-methylbenz[c]-acridine-10,11-dihydrodiol is described and applied to the analysis of these metabolites formed by rat liver microsomes.

Metabolism of the carcinogen 7-methylbenz[c]-acridine in the rat

The biliary excretion of radioactivity by adult Wistar rats given i.v. 7-methyl-[7-14C]benz[c]acridine(14C-7-MBAC) and [methyl-3H]-7-methylbenz[c]acridine (3H-7-MBAC) (2 mg/kg) was 61% and 48%, respectively, in males in six hours. Females excreted 33% of a 2 mg/kg dose of 3H-7-MBAC in the same time-period. For male rats, the urinary and faecal excretions were about 10% and 61% of the dose of 14C-7-MBAC, respectively, in seven days. No enterohepatic circulation could be demonstrated in control male rats. The biliary excretion of radioactivity by phenobarbital- and 3-methylcholanthrene-induced male rats given 14C-7-MBAC was similar to or greater than that of control male rats. The organo-soluble biliary metabolites after beta-glucuronidase/arylsulphatase hydrolysis were separated by h.p.l.c., and quantitative metabolite distributions were obtained for induced and control rats by comparison with metabolite standards. The mutagenicity of bile from carcinogen-dosed control rats was greater than that of equivalent bile from carcinogen-dosed 3-methylcholanthrene-pretreated animals.

The metabolism of the carcinogen 7-methylbenz[c]acridine by hepatocytes isolated from untreated and induced rats

The metabolic fate of the carcinogenic aza-aromatic hydrocarbon 7-methyl[7-(14)C]benz[c]acridine (14C-7MBAC) was studied in hepatocytes freshly isolated from untreated, phenobarbital-pretreated and 3-methylcholanthrene-pretreated rats. 14C-7MBAC (4-200 microM) was metabolized in a concentration-dependent manner; Michaelis-Menten kinetics were not followed. Using 100 microM 14C-7MBAC, the bulk of the ethyl acetate-extractable metabolites were found in the incubation medium; about 50% of the total metabolites were not extractable into ethyl acetate. The nature of the water-soluble metabolites was examined by enzyme hydrolysis of glucuronides and sulphates, and by glutathione-depletion experiments. Organo-extractable metabolites were examined by reverse-phase h.p.l.c. and quantified by co-chromatography with standards. pretreatment of the rats with mixed-function oxidase inducers, phenobarbital and 3-methylcholanthrene resulted in 2.85- and 5.70-fold increases, respectively, in total metabolism of 14C-7MBAC. Major metabolites for all three hepatocyte preparations co-chromatographed with 7-hydroxymethylbenz[c]acridine, trans-5,6-dihydro-5,6-dihydroxy-7-methylbenz[c]acridine and trans-8,9-dihydro-8,9-dihydroxy-7-methylbenz[c]acridine.