Arylamine-DNA adducts in vitro and in vivo: their role in bacterial mutagenesis and urinary bladder carcinogenesis

Hepatic N-oxidation, followed by N-glucuronidation, has been proposed as a route of metabolic activation for arylamine bladder carcinogens. It is postulated that the N-glucuronides are transported to the bladder lumen where they are hydrolyzed under slightly acidic conditions to release direct-acting carcinogenic and mutagenic N-hydroxyarylamines. In this study, 4-aminobiphenyl (ABP), 1-naphthylamine (1-NA), 2-naphthylamine (2-NA), 2-acetylaminofluorene (AAF), 4-nitrobiphenyl (NBP), benzidine (BZ), and N-acetylbenzidine (ABZ) were administered to male beagle dogs (60 μmole/kg), and the bladder epithelium DNA adducts were quantified at various times after treatment. At 24-48 hr after administration, the order of binding to bladder epithelium DNA was: ABP >> AAF > NBP ≅ 2-NA≅BZ ≅ ABZ >> 1-NA. The level of DNA modification by ABP remained constant for 7 days, whereas 2-NA and AAF residues decreased by 35% and 80%, respectively. The extent and relative persistence of total DNA binding correlated with the compounds' ability to induce bladder tumors in dogs. ABP, AAF, NBP, 2-NA and ABZ administration resulted in DNA binding sufficient for adduct analysis. Enzymatic hydrolysis of the DNA and examination of the adducts by high pressure liquid chromatography indicated that arylamine substitution at C8 of deoxyguanosine was the dominant product. Additional adducts were detected in animals treated with ABP, NBP, and 2-NA. Furthermore, the profiles of adducts obtained in vivo were remarkably similar to the profiles obtained when the N-hydroxy arylamine metabolites of these carcinogens were reacted with DNA in vitro at pH 5.0. To evaluate the mutagenic potential of these arylamine-DNA adducts, Salmonella typhimurium strains TA 1535 and TA 1538 were incubated with N-hydroxy-2-NA, N-hydroxy-2-aminofluorene (AF), N-hydroxy-ABP, and N-hydroxy-ABZ and the resulting DNA adducts and reversions were quantified. Arylamine-C8-deoxyguanosine substitution was correlated with frameshift reversions induced by these agents, with the lesions showing a relative order of mutagenic efficiency of ABZ>AF≅2-NA>ABP. These data suggest that mutagenic N-hydroxyarylamines may be ultimate carcinogens for the bladder epithelium. Furthermore, if one assumes that a mutagenic lesion is important for tumor initiation, then C8-deoxyguanosine substitution by these compounds may be significant for urinary bladder carcinogenesis.