Comparison of the Stimulatory and Inhibitory Effects of Steroid Hormones and alpha-Naphthoflavone on Steroid Hormone Hydroxylation Catalyzed by Human Cytochrome P450 3A Subfamilies

摘要

The inhibitory and stimulatory effects of steroid hormones and related compounds on the hydroxylation activity at the 6 beta-position of two steroid hormones, progesterone and testosterone, by CYP3A4, polymorphically expressed CYP3A5, and fetal CYP3A7 were compared to clarify the catalytic properties of the predominant forms of the human CYP3A subfamily. Hydroxylation activities of progesterone and testosterone by CYP3A4, CYP3A5, and CYP3A7 were estimated using HPLC. The Michaelis constants (K-m) for progesterone 6 beta-hydroxylation by CYP3A5 were markedly decreased in the presence of dehydroepiandrosterone (DHEA) and alpha-naphthoflavone (ANF), whereas progesterone and DHEA competitively inhibited testosterone 6 beta-hydroxylation mediated by CYP3A4, and progesterone competitively inhibited CYP3A5-mediated activity, which was weaker than that for CYP3A4. ANF noncompetitively inhibited testosterone 6 beta-hydroxylation mediated by both CYP3A4 and CYP3A5. Progesterone and testosterone 6 beta-hydroxylation mediated by CYP3A7 was inhibited or unaffected by DHEA, pregnenolone, and ANF. These results suggested that DHEA and ANF stimulated progesterone 6 beta-hydroxylation by CYP3A5 but not by CYP3A4 and CYP3A7; however, progesterone, DHEA, and ANF inhibited testosterone 6 beta-hydroxylation mediated by all CYP3A subfamily members. The inhibitory/stimulatory pattern of steroid-steroid interactions is different among CYP3A subfamily members and CYP3A5 is the most sensitive in terms of activation among the CYP3A subfamily members investigated.