Species differences in metabolism of heterocyclic aromatic amines, human exposure, and biomonitoring

Heterocyclic aromatic amines (HAAs) are animal carcinogens and suspected human carcinogens which are formed in cooked foods at the low parts per billion level. HAAs in cooked meats were purified by either immunoaffinity chromatography or solid phase tandem extraction, which allowed for the simultaneous analysis of 11 HAAs by HPLC. The metabolism of two prominent HAAs, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), was investigated in animal models and in vitro with human tissues to develop strategies for human biomonitoring. MeIQx and IQ are rapidly absorbed from the gastrointestinal tract of rodents and transformed into several detoxification products which are excreted in urine and feces. Metabolites result from cytochrome P450-mediated ring oxidation at the C-5 position followed by conjugation to sulfate or beta-glucuronic acid. Other major metabolites include the phase II conjugates, N2-glucuronide and N2-sulfamate. A metastable N2-glucuronide conjugate of the genotoxic metabolite of N-hydroxy-MeIQx was also detected in urine and bile. The binding of both carcinogens to blood proteins was low and suggests that human biomonitoring through protein adducts may be difficult. These metabolic pathways exist in nonhuman primates and several of these pathways also occur in vitro with human liver. The urinary excretion of MeIQx in seven human subjects following consumption of cooked beef or fish ranged between 2 and 22 ng in 12 hr when determined by negative ion chemical ionization GC-MS. After acid hydrolysis of urine, the amount of MeIQx increased 4- to 10-fold in 6 of the 7 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)