The Role of Sulfation and/or Acetylation in the Metabolism of the Cooked-Food Mutagen 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in Salmonella typhimurium and Isolated Rat Hepatocytes

• Published in: Chemical research in toxicology Vol. 7; no. 2; pp. 139 - 147
• Main Authors: Malfatti, Michael A, Buonarati, Michael H, Turteltaub, Kenneth W, Shen, Nancy H, Felton, James S
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-03-1994
• Subjects: 550200 - Biochemistry; 550500 - Metabolism; Acetylation; Acetyltransferases - antagonists & inhibitors; ADDUCTS; ANIMAL CELLS; ANIMALS; AZINES; BACTERIA; BASIC BIOLOGICAL SCIENCES; BIOCHEMICAL REACTION KINETICS; Biological and medical sciences; BIOLOGICAL PATHWAYS; Cells, Cultured; Chemical mutagenesis; CYTOCHROMES; DNA ADDUCTS; ENZYME INHIBITORS; HETEROCYCLIC COMPOUNDS; Imidazoles - metabolism; KINETICS; Liver - cytology; Liver - metabolism; LIVER CELLS; Male; MAMMALS; Medical sciences; METABOLIC ACTIVATION; MICROORGANISMS; MUTAGENESIS; Mutagenicity Tests; Mutagens - metabolism; Nitrophenols - pharmacology; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; Pentachlorophenol - pharmacology; PICOLINES; PIGMENTS; PROTEINS; PYRIDINES; RATS; Rats, Sprague-Dawley; REACTION KINETICS; RODENTS; SALMONELLA; SALMONELLA TYPHIMURIUM; Salmonella typhimurium - metabolism; SOMATIC CELLS; Sulfates - metabolism; Sulfotransferases - antagonists & inhibitors; Toxicology; VERTEBRATES; Bakery product; Rat; Toxicity; Cytochrome P450; Rodentia; Metabolism toxicity relation; Mutagen; In vitro; Sulfatation; Vertebrata; Mammalia; Hepatocyte; Animal; Metabolic activation; Acetylation; Mechanism of action; Food
• ISSN: 0893-228X; 1520-5010
• DOI: 10.1021/tx00038a005

Mutagenic activity of the cooked-food mutagen/carcinogen 2-amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine (PhIP) is highly dependent upon cytochrome P450 activation to the N-hydroxylated intermediate. In the present study the bioactivation pathways of PhIP were investigated in Salmonella typhimurium and isolated rat hepatocyte preparations. In the Ames/S. typhimurium assay, the acetyltransferase and sulfotransferase enzyme inhibitors pentachlorophenol (PCP) and 2,6-dichloro-4-nitrophenol (DCNP) were used to modulate mutagenicity. DCNP, but not PCP, produced a concentration-dependent decrease in mutagenic activity of 2-(hydroxyamino)-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-hydroxy-PhIP). In rat hepatocyte preparations, PCP and DCNP, as well as the cytochrome P450 IA1 and IA2 inhibitor alpha-naphthoflavone (ANF), were used to modulate metabolite, protein adduct, and DNA adduct formation. Incubations of [3H]PhIP (100 microM) with Aroclor 1254-induced or uninduced hepatocytes resulted in the formation of several metabolites, including 4'-(2-amino-1-methylimidazo[4,5-b]pyrid-6-yl)phenyl sulfate (4'-PhIP-sulfate), 2-amino-1-methyl-4'-hydroxy-6- phenylimidazo[4,5-b]pyridine (4'-hydroxy-PhIP), a glucuronide conjugate of 2-(hydroxyamino)-1-methyl-6-phenylimidazo[4,5-b]pyridine, and other uncharacterized metabolites. While PCP or DCNP pretreatment produced a significant decline in sulfate-dependent conjugation of 4'-hydroxy-PhIP to 4'-PhIP-sulfate, these inhibitors produced only slight decreases in PhIP-dependent covalent binding to proteins in hepatocytes derived from either Aroclor 1254-induced or uninduced rats. PhIP DNA adduct levels were relatively unchanged by PCP or DCNP pretreatment of Aroclor 1254-induced hepatocytes. DNA adducts from hepatocytes dosed with N-hydroxy-PhIP, however, resulted in a decrease in adduct levels from cells pretreated with PCP or DCNP.