Formation of urothelial and hepatic DNA adducts from carcinogen 2-naphthylamine

The carcinogen, 2-naphthylamine (2-NA), induces tumor formation in the urinary bladder but not the liver of several species, including humans and dogs. Since its proximate carcinogenic metabolite, N-hydroxy-2-NA, was known to react directly with DNA in vitro to give specific carcinogen-base adducts, we investigated the in vivo formation and persistence of (2-NA)-DNA adducts in the bladder and liver and attempted to determine whether or not these lesions correlated with tissue susceptibility. Male beagle dogs were administered [3H]2-NA and sacrificed after 2 or 7 days. The DNA was isolated from the liver and urothelium and hydrolyzed enzymatically. The (2-NA)-deoxyribonucleoside adducts, which were quantitated by high pressure liquid chromatographic analysis, were the same as those found in vitro, namely 1-(deoxyguanosin-N2-yl)-2-NA, 1-(deoxyadenosin-N6-yl)-2-NA, and an imidazole ring-opened derivative of N-(deoxyguanosin-8-yl)-2-NA. The major difference detected between target and non-target tissues was in the total level of binding to DNA, which was 4-fold higher in the urothelium at 2 days and 8-fold higher at 7 days after 2-NA dosing. Analysis of specific adducts suggested that this difference may be due to the relative persistence of the C-8-guanine adduct in the urothelium as compared to the liver. Similar experiments with the non-carcinogen, 1-naphthylamine, failed to reveal binding in urothelial DNA and indicated a 20-fold lower binding level in hepatic DNA. Evidence for binding of 2-NA to glycogen is also presented and problems associated with measuring total radioactivity in glycogen-contaminated DNA fractions are discussed. The data obtained in this study, through from a necessarily limited number of animals, are consistent with the hypothesis that the formation and persistence of DNA-carcinogen adducts may be important in the initiation of the neoplastic process.