Metabolic activation of aromatic amines and dialkylnitrosamines.

Metabolic activation steps involved in carcinogenesis by several aromatic amines, their N-acetylated derivatives, and dialkylnitrosamines are reviewed. N-Hydroxylation is the first activation step in the carcinogenesis by 2-acetylaminofluorene (AAF), other aromatic amides and amines. The cytochrome P-450 enzyme system is involved in AAF N-hydroxylation. Reconstitution studies indicate that the specificity of AAF N-hydroxylation is determined by the source of cytochrome P-450. Further metabolic activations of aromatic N-hydroxy amines and amides via sulfate, acetyl, and glucuronyl transfer reactions in the hepatic and extrahepatic tissue carcinogenesis by AAF, 4-aminobiphenyl, 2-naphthylamine, and aminoazo dyes are discussed. Dialkylnitrosamines are shown to be activated by oxidative dealkylation via cytochrome P-450 enzyme systems. Other microsomal enzymes are also believed to be involved in oxidation of these compounds. Tissue and species show specificity in oxidative metabolism of these carcinogens. During oxidation of these compounds, reactive alkylating species are generated which interact covalently with cellular macromolecules. DNA methylation does occur during NADPH dependent oxidation of dimethylnitrosamine by liver microsomes. High pressure liquid chromatography separation of acid hydrolyzed DNA indicates the presence of methylated bases including N-7 methylguanine and O6-methylguanine. It is believed that the presence of O6-alkylguanine in DNA may be responsible for the initiation of carcinogenesis by dialkylnitrosamines.