Metabolism of Genistein by Rat and Human Cytochrome P450s

The metabolism of gemstein (4ʹ,5,7-trihydroxyisoflavone), a phytoestrogen derived from soy products, was investigated using rat and human liver microsomes and recombinant human cytochrome P450 enzymes. Metabolism ofgemstein by microsomes obtained from rats treated with pyridine, phenobarbital, beta-naphthoflavone, isosafrole, pregnenolone-16alpha(.-carbonitrile, or 3-methylcholanthrene resulted in very different product profiles consisting of five different NADPH- and time-dependent metabolites as observed by HPLC reverse-phase analysis at 260 nm. The metabolism of genistein was also investigated with recombinant human cytochrome P450 1A1, 1A2, 1B1, 2B6, 2C8, 2E1, or 3A4. P450s 1A, 1A2, 1B1, and 2E1 metabolized genistein to form predominantly one product (peak 3) with smaller amounts of peaks 1 and 2. P450 3A4 produced two different products (peaks 4 and 5). Product peaks 1-3 eluted off the HPLC column prior to the parent compound genistein, and the UV/vis spectra, GC/MS, and ESI/MS/MS analyses support the conclusion that these products result from hydroxylation of genistein. The product peak 3 has been identified by tandem mass spectrometry as 3ʹ,4ʹ,5,7tetrahydroxyisoflavone, also known as orobol, and peaks I and 2 appear to be hydroxylated at position 6 or 8.