THE METABOLISM AND DNA-BINDING OF THE COOKED-FOOD MUTAGEN, 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE (PHIP) IN PRECISION-CUT RAT-LIVER SLICES

Precision-cut liver slices prepared from Aroclor 1254 pretreated male rats were used to investigate the metabolism of 2-amino-1-methyl-6-phe nylimidazo [4,5-b]pyridine (PhIP). The acetyltransferase and sulfotran sferase inhibitors, pentachlorophenol (PCP) and 2,6-dichlaro-4-nitroph enol (DCNP), and the cytochrome P450 inhibitor, alpha-naphthoflavone ( ANF), were used to modulate PhIP metabolism and DNA and protein adduct formation. PCP and DCNP had similar effects on the formation of some PhIP metabolites, PCP and DCNP decreased the formation of 4'-(2-amino- 1-methylimidazo [4,5-b]pyrid-6-yl)phenyl sulfate (4'-PhIP-sulfate) and roxyamino)-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-hydroxy-PhIP)-g lucuronide to 10% and 55% of controls, respectively. 1-methyl-4'-hydro xy-6-phenylimidazo[4,5-b]pyridine (4'-hydroxy-PhIP) was increased by 5 0% relative to control levels due to PCP and DCNP treatment. PCP and D CNP had different effects on the formation of other PhIP metabolites. Metabolite formation as percent of control for the uncharacterized met abolite, 'Peak A', was 50% and 100% in incubations with PCP and DCNP, respectively. Formation of 4'-hydroxy-PhIP-glucuronide was decreased t o 10% of controls with PCP and increased to 147% of controls with DCNP . PCP and DCNP had no effect on the formation of an unidentified metab olite, 'Peak B'. ANF decreased metabolite formation by 60-95%. None of the enzyme inhibitors had a statistically significant effect on PhIP- DNA binding. Covalent binding of PhIP to protein was slightly decrease d in incubations containing DCNP or PCP. The lack of significant chang es in covalent binding to either DNA or protein suggests that addition al pathways may be important in PhIP bioactivation in rat liver slices . With ANF, there was a significant decrease (35%) in protein binding. These observations on the effects of PCP, DCNP and ANF on PhIP metabo lism as well as on covalent binding of PhIP to tissue macromolecules a re in close agreement with what was reported earlier in hepatocytes. T his indicates that tissue slices from various target tissues for tumor igenesis will be a useful in vitro tool for future studies on heterocy clic amine metabolism. This study provides another important example o f the utility of precision-cut tissue slices to investigate xenobiotic metabolism and toxicity.