Pregnancy-Induced Changes in Blood-Brain-Barrier and Placental Transporters and Blood-Brain and Maternal-Fetal Drug Distribution

Abstract

Pregnancy is a dynamic process in which both the mother's and fetus' physiological systems change continuously throughout gestation. Moreover, efflux transporters such as P-glycoprotein (P-gp) play a critical role in the maternal-to-fetal and blood-to-brain transfer of many drugs. Previous studies indicate that placental P-gp expression is altered during pregnancy. Furthermore, some central nervous system (CNS) acting drugs exhibit altered efficacy in the mother and fetal toxicity profiles when taken during pregnancy. Thus, it is important to characterize the distribution of agents routinely taken by pregnant women in this population. The objective of this work is to evaluate the effect of pregnancy on transporter expression and maternal blood-brain and maternal-fetal drug transport using in vitro cell models and an in vivo pregnant mouse model. To that end, the effect of progesterone (P4) and estradiol (E2) treatment on the expression and function of P-gp was evaluated in the placental JAR cells and P-gp over-expressing cells, NCI-ADR-RES. Using a mouse model, the effects of gestational age on P-gp and MRP expression in the placenta and brain were evaluated along with the brain, placental and fetal distribution of various P-gp and non P-gp substrates. Treatment with either E2 or P4 resulted in a significant increase in P-gp protein levels in both JAR and NCI-ADR-RES cells with the placental JAR cells more sensitive to E2, requiring 100-fold lower concentrations for P-gp induction. Furthermore, E2 or P4 treatment resulted in significant decreases in cellular uptake of select P-gp substrates indicating that the induced P-gp is functional. In vivo, P-gp protein levels in the placenta and brain were greater at mid- (gd 13) than late-gestation (gd 18). Likewise, brain MRP1 levels were greater in mice at gd 13, whereas, placental levels were greater at gd 18. To evaluate the effect of altered P-gp expression on drug disposition, the placenta, fetal and brain uptake of the P-gp substrates, saquinavir and methadone, and the non P-gp substrates; buprenorphine and paracellular markers, mannitol and sucrose was evaluated in mice. Following i.v. dosing, [3H]saquinavir placenta-to-plasma and fetal-to-plasma ratios were significantly greater in late-gestation mice versus mid-gestation. Furthermore, late-gestation mice experienced significant increases in the [3H]saquinavir and [3H]methadone brain-to-plasma ratios 60 min after dosing relative to mid-gestation. No significant differences were observed in tissue-to-plasma ratios for buprenorphine, mannitol or sucrose. Repeated dosing (3 doses, once daily) decreased the differential uptake of [3H]saquinavir in brain but potentiated it in the fetus. In conclusion, P4 or E2 increase P-gp expression and function in NCI-ADR-RES and JAR cells with the placental JAR more sensitive to E2. Furthermore, differential expression of P-gp in the brain and placenta likely contributes to the gestational-induced changes in brain and fetal uptake of saquinavir. These observed gestational-induced differences in brain and fetal uptake of saquinavir may have important implications for clinical dosing and efficacy of this compound as well as other P-gp substrates.