Mechanisms by which pregnancy increases the clearance of the anti-HIV protease inhibitor, nelfinavir

Given standard doses, pregnant women achieve lower plasma concentrations of anti-HIV protease inhibitors (PIs) than non-pregnant women or men. The goal of this research was to determine the mechanistic basis of this phenomenon by using a representative animal model. Therefore, we investigated two animal models, the non-human primate, M. nemestrina and the mouse, including the CYP3A4-promoter-lucficerase-transgenic mouse.;We first tested and showed that the oral clearance of nelfinavir, a PI, was significantly increased (∼3-fold) in the pregnant macaque. This increased oral clearance was caused by increased systemic clearance (1.9-fold) and decreased bioavailability (∼45%) of the drug during pregnancy. In vitro studies showed that pregnancy significantly increased the rate of nelfinavir depletion in hepatic, but not intestinal S-9 fractions. These data suggested that increased hepatic activity of nelfinavir metabolizing enzymes (perhaps CYP3A enzymes) results in increased clearance of PIs during pregnancy in the macaque.;Because nelfinavir is cleared from the body predominantly by CYP3A and P-glycoprotein, we studied, if pregnancy affects the intestinal and hepatic CYP3A activity in M. nemestrina, using midazolam as a probe, and intestinal, hepatic and renal P-gp activity, using digoxin as a probe. Although systemic clearance of midazolam was significantly increased during pregnancy (perhaps due to increased hepatic blood flow), no significant difference in the oral clearance of the drug was observed. In vitro studies found no change in hepatic or intestinal CYP3A activity or expression during pregnancy. In addition, no change in digoxin pharmacokinetics was observed during pregnancy, indicating unchanged P-glycoprotein activity. Therefore, the activity of some other transporter(s) and/or enzyme(s), involved in the clearance of nelfinavir, must be increased during macaque pregnancy.;Though our macaque studies did not suggest that CYP3A activity was increased during pregnancy, our mouse studies do. We found that transcriptional activation of selective CYP3a isoforms leads to increased expression and activity of CYP3a in the pregnant mouse. That is, the pregnancy-related factors that transcriptionally activate mouse Cyp3a isoforms also activate the human CYP3A4 promoter in pregnant CYP3A4-promoter-luciferase-transgenic mice. We propose that the CYP3A4-promoter-luciferase-transgenic mouse should be studied to determine the molecular mechanisms of increased CYP3A activity during pregnancy.