URINARY-EXCRETION OF UNMETABOLIZED AND PHASE-II CONJUGATES OF 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE AND 2-AMINO-3,8-DIMETHYLIMIDAZO[4,5-F]QUINOXALINE IN HUMANS - RELATIONSHIP TO CYTOCHROME P4501A2 AND N-ACETYLTRANSFERASE ACTIVITY

Cooking meat, fish, or poultry at high temperature gives rise to heter ocyclic aromatic amines (HAAs), which may be metabolically activated t o mutagenic or carcinogenic intermediates, The enzymes cytochrome P450 1A2 (CYP1A2) and N-acetyltransferase (NAT2) are principally implicated in such biotransformations. We have determined the relationship betwe en the activity of these two enzymes and the urinary excretion of unme tabolized and Phase II conjugates of the two HAAs MeIQx (2-amino3,8-di methylimidazo[4,5-f]quinoxaline) and PhIP (2-amino-1-methyl-6-phenylim idazo[4,5-b]pyridine) in individuals fed a uniform diet containing hig h-temperature cooked meat, The subjects in the study ate meat containi ng known amounts of MeIQx and PhIP, and urine collections were made 0- 12 and 12-24 h after a meal. MeIQx and PhIP were measured in urine aft er acid treatment that quantitatively hydrolyzes the Phase II conjugat es to the respective parent amine, The extracts containing the HAAs me re purified by immunoaffinity chromatography and analyzed by liquid ch romatography using electrospray ionization-tandem mass spectrometry, T he MeIQx content in the 0-12 h urine increased after acid hydrolysis b y a factor of 3-21-fold, After acid treatment, the total amount of MeI Qx (unmetabolized plus the N-2-glucuronide and sulfamate metabolites) excreted in the 0-12 h urine was 10.5 +/- 3.5% (mean a SD) of the dose , whereas the total amount of PhIP [unmetabolized plus acid-labile con jugate(s)] in the 0-12 h period was 4.3 +/- 1.7% (mean +/- SD) of the dose, The total amount of PhIP in the 12-24 h urine after acid treatme nt was 0.9 +/- 0.4% (mean +/- SD) of the dose, Linear regression analy sis of the amounts of MeIQx and PhIP excreted in the 0-12 h period exp ressed as a percentage of the ingested dose, for all subjects, gave a low but significant correlation (r = 0.37, P = 0.005), Linear regressi on analyses showed that lower total MeIQx (unmetabolized plus the N-2- glucuronide and sulfamate metabolites) in urine was associated with hi gher CYP1A2 activity, whereas total PhIP (unmetabolized plus conjugate d) in urine showed no association to CYP1A2 activity, These results in dicate that in humans, MeIQx metabolism and disposition are more stron gly influenced by CYP1A2 activity than are those of PhIP, Linear regre ssion analysis found no association between NAT2 activity and the leve ls (unmetabolized plus acid-labile conjugates) of MeIQx or PhIP excret ed in urine.