Induction of a high spin form of microsomal cytochrome P-448 in rat liver by 4-aminoazobenzene derivatives.

Male Sprague-Dawley rats were treated with 4-aminoazobenzene derivatives or other drug metabolizing enzyme inducers such as phenobarbital, 3-methylcholanthrene and isosafrole. The expression of hepatic microsomal cytochrome P-450 of the rats, principally that of a high spin form of cytochrome P-448 (cytochrome P-448H), was assessed by a bacterial mutation test and by immunological methods. The results of the mutation test with use of Salmonella typhimurium TA9 and 3 aromatic amine substrates showed that 2-methoxyl, 3-methoxyl and 2',3-dimethoxyl derivatives of AAB and methyl derivatives of AAB such as o-aminoazotoluene, N-methyl-4-aminoazobenzene and N,N-dimethyl-4-aminoazobenzene have a large capacity for the selective induction of cytochrome P-448H. Activity of the cytochrome increased by 6 hr after an azo dye treatment, reached a maximum after 24 hr, and then declined. In contrast, 4'-methoxy-AAB has a small, and AAB has no, capacity for the cytochrome induction. The aminoazo dye-induced enzymes differ in their substrate specificities from those induced with 3-methylcholanthrene or phenobarbital, and the induced enzyme was identified to be cytochrome P-448H, as determined by an enzyme-linked immunosorbent assay and immunoblotting with use of anti-cytochrome P-448 monoclonal antibodies. These observations indicate that several methoxyl and methyl derivatives of 4-aminoazobenzene are potent and selective inducers of cytochrome P-448H in the rat.