Repair synthesis of DNA induced by the urinary N-hydroxy metabolites of carcinogenic arylamines in urothelial cells of susceptible species.

Urinary N-hydroxy metabolites of the bladder carcinogens, 2-aminofluorene and 4-aminobiphenyl, were examined for the induction of unscheduled DNA synthesis (UDS) in urothelial cells of several susceptible species. N-Hydroxy-2-aminofluorene, N-hydroxy-2-acetylaminofluorene (N-OH-AAF), N-hydroxy-4-aminobiphenyl, N-hydroxy-4-acetylaminobiphenyl, and the N-glucuronides of these two hydroxylamines induced UDS in the urothelial cells of dogs, rats, and rabbits. N-Hydroxy-2-aminonaphthalene, N-hydroxy-2-acetylaminonaphthalene, and the N-glucuronide of the hydroxylamine were not active. The induction of UDS in dog cells by N-OH-AAF or N-acetoxy-2-acetylaminofluorene, but not by N-hydroxy-2-aminofluorene, was inhibited by paraoxon. The microsomal fraction of dog urothelial cells catalyzed the binding of N-OH-AAF to transfer ribonucleic acid; the enzyme activity was completely inhibited by paraoxon, suggesting that N-deacetylase, but not N-,O-acetyltransferase, was responsible for the binding. The O-glucuronide of N-OH-AAF did not induce UDS in the urothelial cells of dogs, rats, or rabbits, nor did it bind to tRNA in the presence of dog urothelial enzymes, which suggest that N-OH-AAF is detoxified by O-glucuronidation. These results are consistent with the hypothesis that nonacetylated, N-hydroxylated metabolites play a major role in arylamine-induced bladder carcinogenesis. The importance of arylacethydroxamic acid metabolites in bladder carcinogenesis for various species may be inversely related to the rate of hepatic O-glucuronidation.