Abstract
The purpose of this study was to quantify the oxidative metabolism of dehydroepiandrosterone (3β-hydroxy-androst-5-ene-17-one; DHEA) by liver microsomal fractions from various species and identify the cytochrome P450 (P450) enzymes responsible for production of individual hydroxylated DHEA metabolites. A gas chromatography-mass spectrometry method was developed for identification and quantification of DHEA metabolites. 7α-Hydroxy-DHEA was the major oxidative metabolite formed by rat (4.6 nmol/min/mg), hamster (7.4 nmol/min/mg), and pig (0.70 nmol/min/mg) liver microsomal fractions. 16α-Hydroxy-DHEA was the next most prevalent metabolite formed by rat (2.6 nmol/min/mg), hamster (0.26 nmol/min/mg), and pig (0.16 nmol/min/mg). Several unidentified metabolites were formed by hamster liver microsomes, and androstenedione was produced only by pig microsomes. Liver microsomal fractions from one human demonstrated that DHEA was oxidatively metabolized at a total rate of 7.8 nmol/min/mg, forming 7α-hydroxy-DHEA, 16α-hydroxy-DHEA, and a previously unidentified hydroxylated metabolite, 7β-hydroxy-DHEA. Other human microsomal fractions exhibited much lower rates of metabolism, but with similar metabolite profiles. Recombinant P450s were used to identify the cytochrome P450s responsible for DHEA metabolism in the rat and human. CYP3A4 and CYP3A5 were the cytochromes P450 responsible for production of 7α-hydroxy-DHEA, 7β-hydroxy-DHEA, and 16α-hydroxy-DHEA in adult liver microsomes, whereas the fetal/neonatal form CYP3A7 produced 16α-hydroxy and 7β-hydroxy-DHEA. CYP3A23 uniquely formed 7α-hydroxy-DHEA, whereas other P450s, CYP2B1, CYP2C11, and CYP2D1, were responsible for 16α-hydroxy-DHEA metabolite production in rat liver microsomal fractions. These results indicate that the stereo- and regioselectivity of hydroxylation by different P450s account for the diverse DHEA metabolites formed among various species.
Footnotes
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↵2 Abbreviations used are: DHEA, dehydroepiandrosterone (3β-hydroxy-androst-5-ene-17-one); DHEA-S, DHEA 3β-sulfate; ADIONE, androstenedione (androst-5-ene-3,17-dione); BSTFA-TMS, N,O-bis(trimethylsilyl)trifluoroacetamide; P450, cytochrome P450; P450 oxidoreductase, NADPH/cytochrome P450 oxidoreductase; 7α-OH-DHEA, 7α-hydroxy-DHEA; 7β-OH-DHEA, 7β-hydroxy-DHEA; 16α-OH-DHEA, 16α-hydroxy-DHEA; 7-oxo-DHEA, 3β-hydroxy-androst-5-ene-7,17-dione; GC/MS, gas chromatography-mass spectrometry; LC/MS, liquid chromatography-mass spectrometry; MOX, methoxyamine · HCl.
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This work was presented in part at the International Society for the Study of Xenobiotics national meeting [Drug Metab Rev (2002) 34 (suppl 1):54]. This research was supported by National Institutes of Health Grant R01 DK54774 (R.A.P.), National Research Service Award Fellowship F32 ES05927 (S.L.R.), and American Heart Association Predoctoral Fellowship 0110109 (K.K.M.M.)
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↵1 Current address: Pfizer Global Research and Development, Eastern Point Rd., Groton, CT 06340.
- Received August 7, 2003.
- Accepted November 25, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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