PRODUCTION OF REACTIVE OXYGEN SPECIES BY MICROSOMES ENRICHED IN SPECIFIC HUMAN CYTOCHROME-P450 ENZYMES

Few studies have evaluated the production of reactive oxygen intermedi ates by human microsomes, especially the influence of the specific for m of cytochrome P450. Experiments were carried out to evaluate the abi lity of CYP1A1, 1A2, 2B6, and 3A4 to consume NADPH, reduce iron, and c atalyze production of reactive oxygen species. Microsomes enriched in each of these CYPs were obtained from commercial +/- lymphoblast cells that had been transfected with cDNA encoding the specific human CYP. On a per nanomole cytochrome P450 basis, CYP3A4 was the must active P4 50 evaluated in catalyzing NADPH oxidation, production of superoxide a nion radical, NADPH-dependent chemiluminescence, oxidation of dichloro fluorescein diacetate, and reduction of either ferric-EDTA or ferric-c itrate. CYP1A1 was the next most reactive CYP, whereas CYP1A2 and 2B6 displayed a comparable, lower activity. Nitric oxide, which reacts wit h and inactivates hemoproteins, inhibited superoxide production by all the CYPs to a similar extent. Because CYP3A4 is present in high amoun ts in human liver microsomes and is active in catalyzing the formation of reactive oxygen species, this CYP may make an important contributi on in the overall ability of human liver microsomes to generate active oxygen species. (C) 1998 Elsevier Science Inc.