INVOLVEMENT OF P4503A IN THE METABOLISM OF 7,8-BENZOFLAVONE BY HUMAN LIVER-MICROSOMES

1. The metabolism of 7,8-benzoflavone (ANF) was studied in human liver microsomal fractions. Five metabolites were generated and tentatively identified as ANF 5,6-oxide, 5,6-dihydrodiol, 7,8-dihydrodiol, 6-hydr oxy ANF, and 7-hydroxy ANF based on UV and mass spectral analysis. 2. The involvement of P4503A in the metabolism of ANF was confirmed by th e following observations: (1) correlation of ANF 5,6-oxide formation w as noted with testosterone 6 beta-hydroxylation, an indicator of P4503 A, in human liver microsomal fractions; (2) metabolism of ANF was inhi bited by various selective P4503A enzyme inhibitors; (3) rabbit antibo dy raised against P4503A4 inhibited the ANF metabolism by > 80%; and ( 4) microsomal fractions that specifically expressed P4503A4 metabolize d ANF to oxidized metabolites. 3. These results indicate that P4503A i soform(s) mainly metabolize ANF to oxidized derivatives in human liver microsomal fractions.