Monoclonal antibody-directed characterization of benzene, ethoxyresorufin and pentoxyresorufin metabolism in rat liver microsomes.

The contribution of cytochrome P450IA, P450IIB, P450IICII and P450IIEI to the oxidative metabolism of benzene, 7-ethoxyresorufin and 7-pentoxyresorufin was investigated using monoclonal antibodies (MAb) in liver microsomes from fed, one-day fasted, phenobarbital (PB)-, 3-methylcholanthrene (MC)- and ethanol-treated rats. Overall catalytic activity varied with different pretreatments and thereby the contribution of different P450s. MAb 1-91-3 against P450IIE1 did not influence alkoxyresorufin dealkylation but inhibited benzene aromatic hydroxylase (BAH) in relation to its increasing inducibility as follows: MC, PB (less than or equal to 48%) less than fed (less than or equal to 59%) less than fasted (less than or equal to 70%) less than ethanol (less than or equal to 91%). MAbs 2-66-3, 4-7-1 and 4-29-5, all against P450IIB, had no effect on 7-ethoxyresorufin O-deethylase (EROD) but inhibited the activities of high-Km BAH (greater than or equal to 58%) and 7-pentoxyresorufin O-depentylase (PROD) (greater than or equal to 96%) in PB-treated microsomes. MAb 1-7-1 against P450IA inhibited EROD (79%), PROD (50%) and high-Km BAH (42%) activities in MC-microsomes. MAb 1-68-11 against P450IIC11 inhibited EROD, PROD and high-Km BAH activities. Thus, P450IIE1 contributed to benzene metabolism as a low-Km BAH but not to alkoxyresorufin metabolism. P450IIB was responsible besides for the major part of 7-pentoxyresorufin metabolism also, selectively, for benzene hydroxylation at high benzene concentrations. P450IA contributed primarily to 7-ethoxyresorufin metabolism and only slightly to PROD and high-Km BAH activities. P450IIC11 contributed slightly to high-Km BAH and to alkoxyresorufin metabolism.