Activation of the carcinogens N-hydroxy-N-2-fluorenylbenzamide and N-hydroxy-N-2-fluorenylacetamide via deacylations and acetyl transfers by rat peritoneal serosa and liver.
Intraperitoneally administered N-hydroxy-N-2-fluorenylbenzamide (N-OH-2-FBA) and N-hydroxy-N-2-fluorenylacetamide (N-OH-2-FAA) are carcinogenic for rat peritoneum. The potential of peritoneal serosa to activate these compounds via deacylations and acyl transfers was compared to that of liver. N-Deacylations of N-OH-2-FBA and N-OH-2-FAA to N-2-fluorenylhydroxylamine (N-OH-2-FA) were faster by liver than serosa and by microsomes than cytosols. N-Debenzoylations of N-OH-2-FBA were 73- to 123-fold faster than N-deacetylations of N-OH-2-FAA. The esters, N-benzoyloxy-2-FBA and N-acetoxy-2-FAA, were O- and N-deacylated to N-OH-2-FA by liver, and the benzoate by serosa. Inhibition by paraoxon of the above deacylations implicated a serine carboxylesterase. Liver and serosa cytosols catalyzed acetyl CoA-, but not benzoyl CoA-, dependent and iodoacetamide (IAA)-sensitive N-acylation of N-2-fluorenamine (2-FA), implicating an acetyltransferase. In hepatic microsomes this activity was IAA-insensitive and partially inhibited by paraoxon. Liver cytosol, but not microsomes, used N-OH-2-FAA as an acyl donor and neither used N-OH-2-FBA. Liver and serosa catalyzed binding to DNA of N-OH-2-[ring-3H]FBA which was paraoxon-sensitive and increased by acetyl CoA, but not benzoyl CoA. Binding to DNA of N-OH-2-[ring-3H]FAA catalyzed by cytosols was approximately 22-fold greater in liver than in serosa and was IAA-sensitive. Microsome-catalyzed binding of this compound in both tissues was increased approximately 2-fold by acetyl CoA. The results support a two-step activation of N-OH-2-FBA in the liver consisting of esterase-catalyzed N-debenzoylation to N-OH-2-FA and an acyltransferase-catalyzed O-acetylation to the putative electrophile N-acetoxy-2-FA. In the serosa, binding to DNA appears to be due to rapid N-debenzoylation to N-OH-2-FA, a fraction of which is O-acetylated. Whereas activation of N-OH-2-FAA by liver and serosa microsomes may also involve N-OH-2-FA and/or its O-acetate, activation by the cytosols is consistent with N,O-acetyltransfer of N-OH-2-FAA to yield N-acetoxy-2-FA. The study provides first evidence for activation of N-OH-2-FBA by rat liver and of both compounds by peritoneum in vitro.
Ritter
C L
CL
Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis 55455.
Malejka-Giganti
D
D
D000107:Acetylation; D000215:Acylation; D000818:Animals; D001711:Biotransformation; D002273:Carcinogens / Q000493:pharmacokinetics*; D004247:DNA / Q000378:metabolism; D005449:Fluorenes / Q000493:pharmacokinetics; D006881:Hydroxyacetylaminofluorene / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics*; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D010529:Peritoneal Cavity; D051381:Rats; D017207:Rats, Sprague-Dawley; D012704:Serous Membrane / Q000201:enzymology / Q000378:metabolism*
D002273:Carcinogens; D005449:Fluorenes; C007739:fluorenylhydroxamic acid; C077090:N-hydroxy-N-(2-fluorenyl)benzamide; D006881:Hydroxyacetylaminofluorene; D004247:DNA