N-glucuronidation of carcinogenic aromatic amines catalyzed by rat hepatic microsomal preparations and purified rat liver uridine 5'-diphosphate-glucuronosyltransferases.

The N-glucuronidation of three carcinogenic aromatic amines (4-aminobiphenyl, alpha-naphthylamine, and beta-naphthylamine) was investigated in hepatic microsomal preparations from two rat strains. In preparations from Wistar rats, individual variability was observed for the glucuronidation of the arylamines. This variability correlated with high and low levels of 3 alpha-hydroxysteroid UDP-glucuronosyltransferase (UDPGT) in hepatic microsomal preparations from Wistar rats. This individual variability was not observed in Sprague-Dawley rat hepatic microsomal preparations because hepatic 3 alpha-hydroxysteroid UDPGT levels do not vary in this strain of rats. Five highly purified rat liver UDPGTs were investigated for their ability to catalyze the conjugation of the aromatic amines. Of the purified enzymes investigated, only 3 alpha-hydroxysteroid UDPGT catalyzed the glucuronidation of 4-aminobiphenyl. alpha-Naphthylamine and beta-naphthylamine conjugations were catalyzed by 3 alpha-hydroxysteroid, 17 beta-hydroxysteroid, and 3-methylcholanthrene-inducible p-nitrophenol UDPGTs. The three aromatic amines did not serve as substrates for purified digitoxigenin monodigitoxoside or phenobarbital-inducible morphine UDPGTs. The results show that N-glucuronide formation can be catalyzed by UDPGT isoforms which also catalyze the formation of O-glucuronides. In addition, variable levels of 3 alpha-hydroxysteroid UDPGT in Wistar rat liver may have toxicological significance for substrates of this isoenzyme.