MUTAGENIC ACTIVATION OF 4-AMINOBIPHENYL AND ITS N-HYDROXY DERIVATIVES BY MICROSOMES FROM CULTURED HUMAN UROEPITHELIAL CELLS

Activation of the human bladder carcinogen 4-aminobiphenyl (ABP) and its N-hydroxy derivatives was investigated using lysates and subcellular enzyme preparations from cultured human uroepithelial cells (HUC). Mutagenic activation was determined using Salmonella typhimurium strains TA98; TA98/1,8-DNP6, a derivative deficient in acetyl coenzyme A:N-hydroxyarylamine 0-acetyltransferase (OAT); and YG1024, a derivative of TA98 with elevated OAT activity and enhanced sensitivity to mutation by N-hydroxyarylamines. Mutagenicity of ABP catalyzed by HUC microsomes was detected in YG1024 but not in the parent strain TA98. HUC microsomes also catalyzed the mutagenic activation of N-hydroxy-4-acetylaminobiphenyl (N-OH-AABP) and the relative sensitivity of the tester strains was YG1024 > TA98 > TA98/1,8-DNP6, indicating N-hydroxy-4-aminobiphenyl (N-OH-ABP) as the mutagenic intermediate. In contrast, the mutagenic activity of N-acetoxy-4-acetylaminobiphenyl incubated with HUC microsomes was approximately equal in TA98 and YG1024, and may involve N-acetoxy-4-aminobiphenyl (N-OAc-ABP) as the intermediate. High pressure liquid chromatography (HPLC) of the DNA hydrolysate obtained after incubation of [H-3]N-OH-ABP with YG1024, showed N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG - ABP) as the primary adduct, based on mobility of the radioactivity in comparison with the synthetic standard. Additionally, HUC microsomes catalyzed the binding of [H-3]N-OH-ABP to RNA in the presence of 4-acetylaminobiphenyl (AABP), N-OH-AABP and acetyl coenzyme A as acetyl donors, and this binding was blocked by paraoxon. The hydrolysate obtained from incubation of DNA with [H-3]N-OH-ABP and HUC microsomes, with AABP as acetyl donor, revealed the formation of dG - ABP adduct. P-32-post-labeling of adducted DNA from N-OH-ABP, N-OH-AABP and N-OAC-AABP showed similar adduct profiles, suggesting that the aryl nitrenium ion, arising from N-OAc-ABP, might be the reactive species responsible for the mutagenic activity.