Received for publication April 23, 2004.
Revised August 9, 2004.
Accepted for publication August 9, 2004.

The Involvement of CYP3A4 and CYP2C9 in the metabolism of 17-Ethinylestradiol

Abstract

The role of specific cytochrome P450 (CYP) isoforms in the metabolism of ethinylestradiol (EE) was evaluated. The recombinant human P450 (rCYP) isozymes CYP1A1, CYP1A2, CYP2C9, CYP2C19, and CYP3A4 were found to be capable of catalyzing the metabolism of EE (1 µM). Without exception, the major metabolite was 2-hydroxy-EE. The highest catalytic efficiency (V_max/K_m) was observed with rCYP1A1, followed by rCYP3A4, rCYP2C9 and rCYP1A2. The CYP isoforms 3A4 and 2C9 were shown to play a significant role in the formation of 2-hydroxy-EE in pool of human liver microsomes by using isoform-specific monoclonal antibodies, where the inhibition of formation was ~54 and 24%, respectively. The involvement of CYP3A4 and CYP2C9 were further confirmed by using selective chemical inhibitors (i.e. ketoconazole and sulfaphenazole). The relative contribution of each CYP isoform to the 2-hydroxylation pathway were obtained from the catalytic efficiency of each isoform normalized by its relative abundance in the same pool of human liver microsomes, as determined by quantitative Western blot analysis. Collectively, these results suggested that multiple CYP isoforms were involved in the oxidative metabolism of EE in human liver microsomes, with CYP3A4 and CYP2C9 as the major contributing enzymes.

Key words: CYP induction, drug-drug interactions, human CYP enzymes, microsomes, monoclonal antibody

This article has been cited by other articles:

				H.-l. Lin and P. F. Hollenberg The Inactivation of Cytochrome P450 3A5 by 17{alpha}-Ethynylestradiol Is Cytochrome b5-Dependent: Metabolic Activation of the Ethynyl Moiety Leads to the Formation of Glutathione Conjugates, a Heme Adduct, and Covalent Binding to the Apoprotein J. Pharmacol. Exp. Ther., April 1, 2007; 321(1): 276 - 287. [Abstract] [Full Text] [PDF]

				L. A. Henriquez-Hernandez, A. Flores-Morales, R. Santana-Farre, M. Axelson, P. Nilsson, G. Norstedt, and L. Fernandez-Perez Role of Pituitary Hormones on 17{alpha}-Ethinylestradiol-Induced Cholestasis in Rat J. Pharmacol. Exp. Ther., February 1, 2007; 320(2): 695 - 705. [Abstract] [Full Text] [PDF]

				H. V. Gelboin and K. Krausz Monoclonal antibodies and multifunctional cytochrome p450: drug metabolism as paradigm. J. Clin. Pharmacol., March 1, 2006; 46(3): 353 - 372. [Abstract] [Full Text] [PDF]