Characterization of the NADPH-Dependent Metabolism of 17β-Estradiol to Multiple Metabolites by Human Liver Microsomes and Selectively Expressed Human Cytochrome P450 3A4 and 3A5
- 1Department of Basic Pharmaceutical Sciences, College of Pharmacy, University of South Carolina, Columbia, South Carolina (A.J.L., J.W.K., B.T.Z.); and 2Department of Chemical Biology, College of Pharmacy, Rutgers—The State University of New Jersey, Piscataway, New Jersey (A.H.C.)
- Bao Ting Zhu, Ph.D., Department of Basic Pharmaceutical Sciences, College of Pharmacy, University of South Carolina, Coker Life Sciences Building, 700 Sumter St., Columbia, SC 29208. E-mail: BTZhu{at}cop.sc.edu
Abstract
We characterized the NADPH-dependent metabolism of 17β-estradiol (E2) by liver microsomes from 21 male and 12 female human subjects. A large number of radioactive estrogen metabolite peaks were detected following incubations of [3H]E2 with male or female human liver microsomes in the presence of NADPH. The structures of 18 hydroxylated or keto estrogen metabolites formed by these microsomes were identified by gas chromatography/mass spectrometry analysis. 2-Hydroxylation (the formation of 2-OH-E2 and 2-OH-E1) was the dominant metabolic pathway with all human liver microsomes tested. The average ratio of 4-OH-E2 to 2-OH-E2 formation was ∼1:6. A new monohydroxylated E2 metabolite (chemical structure unidentified) was found to be one of the major metabolites formed by human liver microsomes of both genders. 6β-OH-E2 and 16β-OH-E2 were also formed in significant quantities, but products of estrogen 16α-hydroxylation (16α-OH-E2 + 16α-OH-E1) were quantitatively minor metabolites. In addition, many other estrogen metabolites such as 6-keto-E2, 6α-OH-E2, 7α-OH-E2, 12β-OH-E2, 15α-OH-E2, 15β-OH-E2, 16β-OH-E1, and 16-keto-E2 were also formed in relatively small quantities. The overall profiles for the E2 metabolites formed by male and female human liver microsomes were similar, and their average rates were not significantly different. The activity of testosterone 6β-hydroxylation (a selective probe for CYP3A4/5 activity) strongly correlated with the rate of formation of 2-OH-E2, 4-OH-E2, and several other hydroxyestrogen metabolites by both male and female liver microsomes. The dominant role of hepatic CYP3A4 and CYP3A5 in the formation of these hydroxyestrogen metabolites was further confirmed by incubations of selectively expressed human CYP3A4 or CYP3A5 with [3H]E2 and NADPH.
Footnotes
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This study was supported by Grant CA 74787 from the National Institutes of Health. This study was presented in preliminary form at the 91st Annual Meeting of the American Association for Cancer Research, San Francisco, CA, April 2000 [Lee AJ, Conney AH and Zhu BT (2000) NADPH-Dependent metabolism of 17β-estradiol and estrone by microsomes from twenty-four human liver samples. Proc Am Assoc Cancer Res41:743].
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1William M. and Myrle W. Garbe Professor of Cancer and Leukemia Research.
- Abbreviations:
- E2
- 17β-estradiol
- E1
- estrone
- E3
- estriol
- OH
- hydroxy
- CYP
- cytochrome P450
- NADPH
- β-nicotinamide adenine dinucleotide phosphate (reduced form)
- HPLC
- high-performance liquid chromatography
- GC/MS
- gas chromatography/mass spectrometry
- TMS
- trimethylsilyl
- BSTFA
- N,O-bis(trimethylsilyl)trifluoroacetamide
- TMCS
- trimethylchlorosilane
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- Received January 9, 2001.
- Accepted April 17, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
