Inhibition of extrahepatic human cytochromes P450 1A1 and 1B1 by metabolism of isoflavones found in Trifolium pratense (red clover).
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 (Ki = 3.7 microM) exhibited competitive inhibition of CYP1B1 7-ethoxyresorufin O-deethylase activity, and genistein (Ki = 1.9 microM) 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.
Division of Biochemical Toxicology, National Center for Toxicological Research, 3900 NCTR Road, Jefferson, Arkansas 72079, USA.
Dean W
DW
Roberts
Daniel R
DR
Doerge
Mona I
MI
Churchwell
Gonçalo
G
Gamboa da Costa
M Matilde
MM
Marques
William H
WH
Tolleson
D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors*; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors*; D065633:Cytochrome P-450 CYP1B1; D004791:Enzyme Inhibitors / Q000378:metabolism* / Q000494:pharmacology*; D019833:Genistein / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D007529:Isoflavones / Q000378:metabolism* / Q000494:pharmacology; D029921:Trifolium / Q000737:chemistry*
D004791:Enzyme Inhibitors; D007529:Isoflavones; C007768:formononetin; C004742:daidzein; D019833:Genistein; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1; C004541:biochanin A