Heterocyclic arylamines (HAAs) are formed in meats such as beef, chicken and fish upon cooking at normal, household temperature. These compounds are potent promutagens in the Ames Salmonella mutagenicity assay and a number of these compounds have been shown to be carcinogenic in rodent bioassays. 2-Amino-3methylimidazo[4,5-f]quinoline (IQ) has been recently shown to be carcinogenic in cynomolgus monkeys. We have previously shown, using recombinant cytochromes P450 expressed in human cells, that cytochrome P45OIA2 is the predominant cytochrome P450 responsible for the activation of these compounds via N-oxidation. Further studies have shown that N-hydroxy-IQ covalently binds to DNA directly and following further activation by 0-acetyl- and sulfotransferases. Adducts of IQ have been examined in rodents and monkeys and found to be identical to those formed in vitro upon reaction of N-hydroxy-IQ with DNA, and those found in Salmonella. In addition to in vitro studies of HAA metabolism we are studying the in vivo metabolism and distribution of HAAs in monkeys. 2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) is extensively metabolized in monkeys and excreted into urine and feces as metabolites. N-Sulfation, glucuronidation and N-demethylation play important roles in the detoxification and excretion of this compound. Metabolic processing also appears to be influenced by the dose of IQ. In light of this finding, we have begun to examine HAA-DNA adducts, and the distribution and excretion of HAA metabolites at food-equivalent doses by accelerator mass spectrometry. This is a highly sensitive method for counting 14-C atoms following administration of low levels of radiolabeled compound. Studies concerning repair in specific genes using the UvrABC excinuclease and alkaline hydrolysis are also underway. Studies are being carried out in isolated genomic DNA, plasmids and cultured cells. With this methodology we are seeing heterogeneity in initial adduct formation in different gene regions and differences in adduct levels with N-hydroxy-IQ and N-hydroxy-MeIQx.
