CYTOSOLIC ACTIVATION OF AROMATIC AND HETEROCYCLIC AMINES - INHIBITIONBY DICOUMAROL AND ENHANCEMENT IN VIRAL-HEPATITIS-B

The aromatic amines 2-aminofluorene (2AFI, 2-acetylaminofluorene, and 2-aminoanthracene, and the heterocyclic amines 2-amino-3-methylimidazo [4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinol and 3- amino-1-methyl-SH-pyrido[4,3-b]indole (Trp-P-2) were activated by rat liver cytosolic fractions to form mutagenic metabolites in Salmonella typhimurium strains TA98, TA98NR, and TA98/1,8-DNP6. In the case of th e Trp-P-2, the cytosolic activation was even more potent than the micr osomal activation, which is classically ascribed to N-hydroxylation an d subsequent esterification. The cytosolic activation was a) NADPH-dep endent, b) induced by pretreatment of rats with 3-methylcholanthrene a nd especially Aroclor 1254 but not by phenobarbital, and c) inhibited by dicoumarol. The hypothesis is that, following a preliminary oxidati ve step in the cytosol (pure cytosolic activation) or in microsomes vi a prostaglandin H synthase (mixed microsomal-cytosolic activation), an oxidized intermediate of amino compounds may serve as substrate for D T diaphorase activity and bielectronically reduced to the correspondin g N-hydroxyamino derivative. Purified DT diaphorase, in the presence o f either NADPH or NADH as electron donor, produced mutagenic derivativ es from IQ and Trp-P-2. An NADPH-dependent activation of Trp-P-2! also occurred in the liver cytosol of woodchucks (Marmota monax), but was not inhibited by dicoumarol. As previously demonstrated with liver S-1 2 fractions in both humans and woodchucks, the cytosolic activation of Trp-P-2 was enhanced in animals affected by hepatitis B virus infecti on. This enhanced metabolism, which persisted even after appearance of primary hepatocellular carcinoma in virus carriers, is likely to be a scribed to mechanisms other than DT diaphorase induction, such as glut athione depletion.