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.
Roberts
Dean W
DW
Division of Biochemical Toxicology, National Center for Toxicological Research, 3900 NCTR Road, Jefferson, Arkansas 72079, USA.
Doerge
Daniel R
DR
Churchwell
Mona I
MI
Gamboa da Costa
Gonçalo
G
Marques
M Matilde
MM
Tolleson
William H
WH
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