Evaluation of rat in vivo fetal-to-maternal transfer clearances of various xenobiotics by umbilical perfusion

It is important to address the tissue permeability of drugs, particularly in tissues that have a blood-tissue barrier, in terms of both lipophilicity and the contribution of transporters. Here, we employed umbilical perfusion in rats to evaluate in vivo fetal-to-maternal transfer clearances of various xenobiotics. We measured fetal-to-maternal clearance (CLfm ) of 23 compounds, which have a broad range of lipophilicity. Drugs for which CLfm was more than 300 µL/(mL min) belonged exclusively to Biopharmaceutical Drug Disposition Classification System (BDDCS) class 1 (highly permeable) and those for which CLfm was less than 50 µL/(mL min) belonged exclusively to BDDCS class 3 (poorly permeable). For most drugs, CLfm values were broadly consistent with lipophilicity. However, CLfm of digoxin was saturable and was inhibited by verapamil, suggesting that P-glycoprotein (P-gp)-mediated efflux has a substantially effect on measured clearance. CLfm of mitoxantrone continued to increase slightly at high concentrations of mitoxantrone, but placental-to-maternal clearance of mitoxantrone was saturable, implying that Bcrp1 contributes to mitoxantrone efflux across the placenta. Thus, we measured CLfm by umbilical perfusion and examined the relationship between CLfm and lipophilicity of xenobiotics. Fetal-to-maternal transport clearances measured in this study will be helpful to understand the characteristics of the blood-placental barrier.

Organic cation transporter 3 (OCT3/SLC22A3) and multidrug and toxin extrusion 1 (MATE1/SLC47A1) transporter in the placenta and fetal tissues: expression profile and fetus protective role at different stages of gestation

In our previous study, we described synchronized activity of organic cation transporter 3 (OCT3/SLC22A3) and multidrug and toxin extrusion 1 (MATE1/SLC47A1) transporter in the passage of organic cations across the rat placenta and the role of these transporters in fetal defense; in this study, we hypothesized that changes in placental levels of OCT3 and MATE1 throughout gestation might affect the fetal protection and detoxification. Using quantitative RT-PCR, Western blot analysis, and immunohistochemistry, we were able to detect Oct3/OCT3 and Mate1/MATE1 expression in the rat placenta as early as on Gestation Day (gd) 12 with increasing tendency toward the end of pregnancy. Comparing first versus third trimester human placenta, we observed stable expression of OCT1 and decreasing expression of OCT2 and OCT3 isoforms. Contrary to the current literature, we were able to detect also MATE1/MATE2 isoforms in the human placenta, however, with considerable inter- and intraindividual variability. Using infusion of 1-methyl-4-phenylpyridinium (MPP(+)), a substrate of OCT and MATE transporters, into pregnant dams, we investigated the protective function of the placenta against organic cations at different gds. The highest amount of MPP(+) reached the fetus on gd 12 while from gd 15 onward, maternal-to-fetal transport of MPP(+) decreased significantly. We conclude that increased expression of placental OCT3 and MATE1 along with general maturation of the placental tissues results in significantly lower transport of MPP(+) from mother to fetus. In contrast, decreasing expression of OCT3 and MATE1 in human placenta indicates these transporters may play a role in fetal protection preferentially at earlier stages of gestation.