Comparison of acyltransferase-mediated mutagenicity and nucleic acid binding of N-acetoxy-4-acetylaminobiphenyl by hepatic and bladder microsomes from rats and dogs.
Acyltransferase-mediated mutagenic and metabolic activation of N-acetoxy-4-acetylaminobiphenyl (N-OAc-AABP) by hepatic tissues of rats and dogs were compared. N-OAc-AABP was mutagenic in Salmonella typhimurium TA98 even in the absence of exogenous enzyme(s). However, supplementation with hepatic microsomes from dogs showed a dose-dependent increase in mutagenicity of N-OAc-AABP, whereas under the same conditions, rat microsomes were inactive. Incubation of liver microsomes with RNA showed that 46.4 and 11.2 nmole of [3H]N-OAc-AABP were bound/mg RNA/mg protein with dogs and rats, respectively. The hepatic microsome-mediated binding and mutagenicities of N-OAc-AABP were blocked by paraoxon, suggesting the involvement of deacetylase(s) in the activation process. Analyses of the in vitro incubates of N-OAc-AABP with rat and dog liver microsomes revealed the O-deacetylation product N-hydroxy-4-acetylaminobiphenyl (N-OH-AABP) as the major metabolite. The ratios of O-deacetylation of N-O[14C]Ac-AABP versus N-deacetylation of N-OAc-[14C]AABP for hepatic microsomes from dogs and rats were 2.9 and 7.2, respectively. The O- and N-deacetylases are also distributed in bladder tissues and their activities in comparison to the hepatic tissues were lower and amounted to 14.2 and 5.0 nmoles (O/N-deacetylation ratio 2.8) for dogs and 14.8 and 1.7 nmoles per mg protein per min (O/N-ratio of 8.7) for rats. The microsomes from bladder tissues also catalyzed the binding of [3H]N-OAc-AABP to RNA and enhanced its mutagenic response in TA98, both of which were blocked by paraoxon. The occurrence of deacetylase(s) in the target tissues of the bladder carcinogen 4-acetylaminobiphenyl (AABP) suggests that metabolic activation of some of the proximate metabolites could occur within these target organs. Furthermore, since the O-deacetylation product N-OH-AABP is relatively innocuous compared to the N-deacetylation product N-acetoxy-4-aminobiphenyl, these results imply that the refractiveness of rats for 4-aminobiphenyl or AABP-induced bladder carcinogenesis might in part be associated with the higher ratios of microsomal O/N-deacetylase activities. Thus susceptibility to arylamine or arylacetamide-induced liver and bladder carcinogenesis might be influenced by the microsomal deacetylases.
Swaminathan
S
S
Department of Human Oncology, University of Wisconsin Comprehensive Cancer Center, Madison.
Hatcher
J F
JF
D000217:Acyltransferases / Q000378:metabolism*; D000611:Aminobiphenyl Compounds / Q000378:metabolism* / Q000633:toxicity*; D000818:Animals; D004247:DNA / Q000378:metabolism*; D004285:Dogs; D004789:Enzyme Activation / Q000187:drug effects; D004950:Esterases / Q000378:metabolism; D008297:Male; D008861:Microsomes / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism*; D009153:Mutagens / Q000378:metabolism / Q000633:toxicity; D010261:Paraoxon / Q000494:pharmacology; D012313:RNA / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D001743:Urinary Bladder / Q000378:metabolism*
D000611:Aminobiphenyl Compounds; D009153:Mutagens; C022916:N-acetoxy-4-acetylaminobiphenyl; D012313:RNA; D004247:DNA; D000217:Acyltransferases; D004950:Esterases; D010261:Paraoxon