Biomonitoring of heterocyclic aromatic amine metabolites in human urine

Human exposure to heterocyclic aromatic amines such as MeIQx (2-amino-3,8-d imethylimidazo[4,5-f]quinoxaline) may be monitored by measuring the levels of the heterocyclic aromatic amine in urine. In order to investigate the co ntribution of N-oxidation to the metabolism of MeIQx in vivo, we developed a biomonitoring procedure for the analysis and quantification of the N-2-gl ucuronide conjugate of 2-hydroxyamino-3,8-dimethylimidazo[4,5-f]quinoxaline in human urine. Subjects (n = 66) in the dietary study ingested a uniform diet of cooked meat containing known amounts of MeIQx, and urine was collec ted after consumption of the test meal. A method based on solid-phase extra ction and immunoaffinity separation was used to isolate N-2-(beta-1-glucosi duronyl)-2-hydroxyamino-3,8-dimethylimidazo[4,5-f]quinoxaline and its stabl e isotope-labeled internal standard from urine. The isolated conjugate was converted to the deaminated product 2-hydroxy-3,8-dimethylimidazo[4,5-f]qui noxaline by treatment with acetic acid under moderate heating. 2-Hydroxy-3, 8-dimethylimidazo[4,5-f]quinoxaline and the [H-2(3)]methyl analog were deri vatized to form the corresponding 3,5-bis(trifluoromethyl)benzyl ether deri vatives and quantified by capillary gas chromatography-negative ion chemica l ionization mass spectrometry employing selected ion monitoring procedures . The amounts of N-2-(beta-1-glucosiduronyl)-2-hydroxyamino-3,8-dimethylimi dazo[4,5-f]quinoxaline recovered in urine collected 0-12 h after the test m eal accounted for 2.2-17.1% of the ingested dose, with a median value of 9. 5%. The variability in the proportion of the dose excreted among the subjec ts may be reflective of several factors, including interindividual variatio n in the enzymic activity of CYP1A2 and/or conjugation reactions of the N-h ydroxylamine metabolite with N-glucuronosyltransferase(s). (C) 1999 Elsevie r Science Ireland Ltd. All rights reserved.