Progesterone Metabolites Produced by Cytochrome P450 3A Modulate Uterine Contractility in a Murine Model

Abstract

We seek to characterize the effect of progesterone metabolites on spontaneous and oxytocin-induced uterine contractility. Study Design: Spontaneous contractility was studied in mouse uterine horns after treatment with progesterone, 2a-hydroxyprogesterone, 6b-hydroxyprogesterone (6b-OHP), 16a-hydroxyprogesterone (16a-OHP), or 17-hydroxyprogesterone caproate (17-OHPC) at 10 À9 to 10 À6 mol/L. Uterine horns were exposed to progestins (10 À6 mol/L), followed by increasing concentrations of oxytocin (1-100 nmol/L) to study oxytocin-induced contractility. Contraction parameters were compared for each progestin and matched vehicle control using repeated measures 2-way analysis of variance. In vitro metabolism of progesterone by recombinant cytochrome P450 3A (CYP3A) microsomes (3A5, 3A5, and 3A7) identified major metabolites. Results: Oxytocininduced contractile frequency was decreased by 16a-OHP (P ¼ .03) and increased by 6b-OHP (P ¼ .05). Progesterone and 17-OHPC decreased oxytocin-induced contractile force (P ¼ .02 and P ¼ .04, respectively) and frequency (P ¼ .02 and P ¼ .03, respectively). Only progesterone decreased spontaneous contractile force (P ¼ .02). Production of 16a-OHP and 6b-OHP metabolites were confirmed in all CYP3A isoforms tested. Conclusion: Progesterone metabolites produced by maternal or fetal CYP3A enzymes influence uterine contractility.

Characterization of Maternal and Fetal CYP3A-Mediated Progesterone Metabolism

“…While fetal clearance of progesterone is minute with respect to overall clearance, fetuses who express an active CYP3A5 were estimated to form ~3-times more 6β-OHP than nonexpressers. Based on our prior in vitro work indicating pro-contractility effects of 6β-OHP and anti-contractility effects of 16α-OHP (10), we hypothesize that the higher 6β-OHP/16α-OHP ratio in CYP3A5 expressers may contribute to increased preterm labor risk in CYP3A5 expressers. Additional studies are needed to evaluate this hypothesis.…”

“…(37, 38) We have recently reported that the primary metabolites of progesterone, 6β-OHP and 16α-OHP, have contradictory effects on oxytocin-induced contractile frequency. (10) While previous studies have shown that progesterone is metabolized in the liver by CYP3A enzymes, the relative importance of the three human isozymes CYP3A4, CYP3A5, and CYP3A7 had not been described. (12, 13, 39) Therefore, we undertook the current study to examine the CYP3A isozyme specific metabolic formation of 6β-OHP and 16α-OHP in vitro .…”

“…Progesterone and its metabolites appear to elicit characteristic effects on oxytocin-induced uterine contractility, suggesting that relative amounts of each compound may alter myometrial contractility. (10) Our study identifies the primary sources of progesterone metabolite formation and describes the influence of CYP3A isoforms on the relative amounts of 6β-OHP and 16α-OHP produced from progesterone. While our in vitro in vivo extrapolation does not indicate that maternal CYP3A5 genotype will influence formation of progesterone metabolism, it is unknown whether increased 6β-OHP by fetal liver will influence localized 6β-OHP/16α-OHP ratio and whether this will effect uterine contractility.…”

“…The opposing effects of these progesterone metabolites on oxytocin-induced uterine contractility suggests that the relative amounts of the metabolites may influence myometrial contractility. (10)…”

“…(10) To our knowledge, the contribution of CYP3A5, CYP3A7, or placental CYP19A1 to the production of 6β-OHP and 16α-OHP has not been evaluated in detail. Therefore, the objectives of this in vitro drug metabolism study were to evaluate the ability of hepatic CYP450’s and CYP19A1 to form 6β-OHP and 16α-OHP from progesterone and to determine the Michaelis-Menten kinetic parameters for these metabolites for individual CYP3A isoforms.…”