title: Metabolism of the food-borne mutagen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in humans.
abstract: The metabolism of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was investigated in five human volunteers given a dietary equivalent of 14C-labeled MeIQx. The amount of the dose excreted in urine ranged from 20.2% to 58.6%, with unmetabolized MeIQx accounting for 0.7-2.8% of the dose. Five principal metabolites were detected in urine, and four of the derivatives were characterized by on-line UV spectroscopy and by HPLC-MS following immunoaffinity chromatography. Two metabolites were identified as the phase II conjugates N2-(3,8-dimethylimidazo[4,5-f]quinoxalin-2-yl)sulfamic acid (MeIQx-N2-SO3(-)) and N2-(beta-1-glucosiduronyl)-2-amino-3,8-dimethylimidazo[4,5-f ]quinoxaline (MeIQx-N2-Gl). Two other metabolites were the cytochrome P450-mediated (P450) oxidation products 2-amino-8-(hydroxymethyl)-3-methylimidazo[4,5-f]quinoxaline (8-CH2OH-MeIQx), and N2-(beta-1-glucosiduronyl)-N-hydroxy-2-amino-3,8-dimethylimidaz o[4,5-f]quinoxaline (NOH-MeIQx-N2-Gl). The latter product is a conjugate of the genotoxic metabolite 2-(hydroxyamino)-3,8-dimethylimidazo-[4,5-f]quinoxaline (NHOH-MeIQx). A large interindividual variation was observed in the metabolism and disposition of MeIQx; these four metabolites and unchanged MeIQx combined accounted for 6.3-26.7% of the total dose. The remaining principal metabolite found in all subjects accounted for 7.6-28% of the dose. It has not been previously identified in rodents or nonhuman primates, and its structure remains unknown. P450-mediated ring oxidation of MeIQx at the C-5 position, a major pathway of detoxication in rodents, was not detected in humans. Both 8-CH2OH-MeIQx formation and NHOH-MeIQx formation are catalyzed by P450 1A2 and may be useful biomarkers of P450 1A2 activity in humans. The levels of NHOH-MeIQx-N2-Gl found in human urine ranged from 1.4% to 10.0% of the dose, which is significantly higher than that formed in rodents and nonhuman primates undergoing cancer bioassays. Thus, bioactivation of MeIQx by P450-mediated N-oxidation is extensive in humans.
authors.affiliation: Nestlé Research Center, Nestec Ltd., Lausanne, Switzerland. Turesky@CHLSNR.NESTRD.CH
authors.forename: R J
authors.initials: RJ
authors.lastname: Turesky
authors.forename: R C
authors.initials: RC
authors.lastname: Garner
authors.forename: D H
authors.initials: DH
authors.lastname: Welti
authors.forename: J
authors.initials: J
authors.lastname: Richoz
authors.forename: S H
authors.initials: SH
authors.lastname: Leveson
authors.forename: K H
authors.initials: KH
authors.lastname: Dingley
authors.forename: K W
authors.initials: KW
authors.lastname: Turteltaub
authors.forename: L B
authors.initials: LB
authors.lastname: Fay
mesh_terms: D000284:Administration, Oral; D000368:Aged; D000369:Aged, 80 and over; D002851:Chromatography, High Pressure Liquid; D005260:Female; D005506:Food Contamination; D006801:Humans; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D008875:Middle Aged; D009153:Mutagens / Q000378:metabolism*; D011810:Quinoxalines / Q000378:metabolism* / Q000652:urine; D012015:Reference Standards; D012907:Smoking
chemical_list: D009153:Mutagens; D011810:Quinoxalines; C036990:2-amino-3,8-dimethylimidazo(4,5-f)quinoxaline