Effect of Carbon Monoxide or of 3-Aminotriazole on C- and N-Hydroxylation of the Carcinogen N-2-Fluorenylacetamide by Liver Microsomes of Hamsters Pretreated with 3-Methylcholanthrene

Abstract

1. Incubation of a liver microsomal fraction from male hamsters with the carcinogen N-2-fluorenylacetamide, a polycyclic aromatic amide, led to the formation of several carbon-hydroxylated and the N-hydroxylated metabolites. In decreasing amounts the 7-hydroxy, N-hydroxy, 5-hydroxy and 3-hydroxy derivatives were thus found. Incubation in the presence of carbon monoxide reduced mainly hydroxylation on the 7-carbon, and least on the N-atom.

2. With the microsomal fraction of livers of hamsters treated 24 h previously with 3-methylcholanthrene the amount of cytochrome P-450 was higher, and hydroxylation at all positions studied was enhanced very appreciably, most on the nitrogen. Incubation of such microsomal fractions in the presence of carbon monoxide reduced all hydroxylation reactions, most on the 3-position, and least on the nitrogen.

3. Three injections of 3-amino-1H-1,2,4-triazole prior to the preparation of the microsomal fraction from normal hamster liver failed to affect cytochrome P-450, reduced 3- and 5-hydroxylation, but increased N-hydroxylation.

4. 3-Aminotriazole injection together with 3-methylcholanthrene pretreatment reduced hydroxylation at all positions, compared to methylcholanthrene controls, most at the 3- and least at the 7-carbon.

5. The data are interpreted to reflect operation of a family of hydroxylating microsomal enzymes. N-2-Fluorenylacetamide, being hydroxylated simultaneously at several stereochemically and electronically different ring carbons and also on the nitrogen, is a useful substrate for exploration of the mechanisms of aromatic hydroxylation.