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Inhibition of extrahepatic human cytochromes P450 1A1 and 1B1 by metabolism of isoflavones found in Trifolium pratense (red clover)
- Roberts, D.W., Doerge, D.R., Churchwell, M.I., Gamboa da Costa, G., Marques, M.M., Tolleson, W.H.
- Journal of agricultural and food chemistry 2004 v.52 no.21 pp. 6623-6632
- metabolism, humans, medicinal properties, formononetin, cytochrome P-450, Trifolium pratense, genistein, daidzein, liver microsomes, enzyme inhibition
- Biochanin A and formononetin are the predominant isoflavones in red clover. In a previous study (J. Agric. Food Chem. 2002, 50, 4783-4790), it was demonstrated that human liver microsomes converted biochanin A and formononetin to genistein and daidzein. This paper now shows CYP1B1-catalyzed O-demethylation of biochanin A and formononetin to produce genistein and daidzein, respectively, which inhibit CYP1B1. Recombinant human CYP1A1 or CYP1B1 was incubated with biochanin A or formononetin. CYP1A1 catalyzed isoflavone 4'-O-demethylation and hydroxylations with similar efficiency, whereas CYP1B1 favored 4'-O-demethylation over hydroxylations. Three of the biochanin A metabolites (5,7,3'-trihydroxy-4'-methoxyisoflavone, 5,7,8-trihydroxy-4'-methoxyisoflavone, and 5,6,7-trihydroxy-4'-methoxyisoflavone) were characterized by 1H NMR spectroscopy and mass spectrometry. Daidzein (K(i) = 3.7 micromolar) exhibited competitive inhibition of CYP1B1 7-ethoxyresorufin O-deethylase activity, and genistein (K(i) = 1.9 micromolar) exhibited mixed inhibition. Biochanin A and/or formononetin may exert anticarcinogenic effects directly by acting as competitive substrates for CYP1B1 or indirectly through their metabolites daidzein and genistein, which inhibit CYP1B1.