Folate transporter expression decreases in the human placenta throughout pregnancy and in pre-eclampsia

Altered Expression of BCRP Impacts Fetal Accumulation of Rosuvastatin in a Rat Model of Preeclampsia

Expression of the breast cancer resistance protein (BCRP/ABCG2) transporter is downregulated in placentas from women with preeclampsia (PE) and in an immunological rat model of PE. While many drugs are substrates of this important efflux transporter, the impact of PE associated BCRP downregulation on maternal and fetal drug exposure has not been investigated. Using the PE rat model, we performed a pharmacokinetic study with rosuvastatin (RSV), a BCRP substrate, to investigate this impact. PE was induced in rats during gestational days (GD) 13 to 16 with daily low-dose endotoxin. On GD18, RSV (3 mg/kg) was administrated intravenously, and rats were sacrificed at time intervals between 0.5 and 6 h. As compared to controls, placental expression of Bcrp and Oatp2b1 significantly decreased in PE rats. A corresponding increase in RSV levels was seen in fetal tissues and amniotic fluid of the PE group (p < 0.05), while maternal plasma concentrations remained unchanged from the controls. An increase in Bcrp expression and decreased RSV concentration were seen in the livers of PE dams. This suggests that PE-mediated transporter dysregulation leads to significant changes in the maternal and fetal RSV disposition. Overall, our findings demonstrate that altered placental expression of transporters in PE can increase fetal accumulation of their substrates.

Effects of valproate, an HDAC inhibitor, on the expression of folate carriers and folate metabolism-related genes in the placenta of rats

Valproate (VPA), an antiepileptic drug, is known to inhibit histone deacetylases (HDACs). Exposure to VPA during pregnancy increases several fetal risks. The maintenance of folate level during pregnancy is essential for adequate fetal development, and the placenta plays a critical role in supplying nutrients to the fetus. The aim of this study was to elucidate the effects of VPA on the gene expression of folate carriers and metabolizing enzymes in the rat placenta at both mid and late gestation periods. Pregnant rats were orally administered VPA on a single day or 4 days (repeated administration). Gene expression of folate carriers (Folr1, Slc19a1, Slc46a1) and metabolizing enzymes (Cth, Mtr, Mtrr, Mthfr, Dhfr) was assessed in the placenta on gestational day (GD) 13 or GD20. In the control rats, the expression of Folr1, Slc46a1, Cth, and Mthfr tended to be upregulated, whereas that of Mtrr and Dhfr was downregulated during gestation; the expression of Slc19a1 and Mtr did not change. Repeated VPA administration reduced the placental expression of Folr1and Mtr on GD20 and increased the expression of Dhfr on GD13 compared with the control. These findings indicate that administration of VPA alters the placental gene expression of folate carriers and metabolism-related enzymes.

Epigenetic regulation of folate receptor-α (FOLR1) in human placenta of preterm newborns

INTRODUCTION

Folates are essential nutrients for fetal development and pregnancy outcomes; they are transported to the fetus during gestation through specific folate transporters located in the placenta. In preterm newborns, we previously showed a lower placental mRNA expression of FOLR1 along with higher folate and lower vitamin B12 cord blood levels. Thereby we aimed to explore FOLR1 methylation in placentas of preterm newborns and hypothesized an increased FOLR1 methylation associated with cord blood folates and vitamin B12 concentrations.

METHODS

FOLR1 methylation and mRNA were determined by methylation sensitive - high resolution melting (MS-HRM) and by real-time PCR respectively, in two placental sides of placental tissues: maternal (basal, BP) and fetal plates (chorionic, CP) of moderate preterm infants (32-36 gestational age) and term birth (37-41 gestational weeks). Folates and vitamin B12 were determined by electrochemiluminescence in umbilical cord blood samples from term and preterm newborns.

RESULTS

We found that in preterm newborns, FOLR1 mRNA was lower in both plates of placenta compared with term newborns (p < 0,05) and was negatively associated with methylation of FOLR1 in CP. Preterm newborns presented higher folate and lower vitB12 concentrations in cord blood which correlated with increased placental FOLR1 methylation.

DISCUSSION

In preterm newborns, placental FOLR1 expression is regulated by epigenetic mechanisms and presumably by maternal concentrations of folate and vitamin B12.

Contributions of Drug Transporters to Blood-Placental Barrier

The placenta is the only organ linking two different individuals, mother and fetus, termed as blood-placental barrier. The functions of the blood-placental barrier are to regulate material transfer between the maternal and fetal circulation. The main functional units are the chorionic villi within which fetal blood is separated by only three or four cell layers (placental membrane) from maternal blood in the surrounding intervillous space. A series of drug transporters such as P-glycoprotein (P-GP), breast cancer resistance protein (BCRP), multidrug resistance-associated proteins (MRP1, MRP2, MRP3, MRP4, and MRP5), organic anion-transporting polypeptides (OATP4A1, OATP1A2, OATP1B3, and OATP3A1), organic anion transporter 4 (OAT4), organic cation transporter 3 (OCT3), organic cation/carnitine transporters (OCTN1 and OCTN2), multidrug and toxin extrusion 1 (MATE1), and equilibrative nucleoside transporters (ENT1 and ENT2) have been demonstrated on the apical membrane of syncytiotrophoblast, some of which also expressed on the basolateral membrane of syncytiotrophoblast or fetal capillary endothelium. These transporters are involved in transport of most drugs in the placenta, in turn, affecting drug distribution in fetus. Moreover, expressions of these transporters in the placenta often vary along with the gestational ages and are also affected by pathophysiological factor. This chapter will mainly illustrate function and expression of these transporters in placentas, their contribution to drug distribution in fetus, and their clinical significance.

Value of ABCG2 Q141K and Q126X genotyping in predicting risk of preeclampsia in Chinese Han women population

Hyperuricemia (HUA) in women with preeclampsia (PE) not only indicates a reminder of severity but also contributes directly to the pathogenesis of PE. ATP-binding cassette subfamily G member 2 (ABCG2) has a very strong effect on the serum urate concentrations. Our aim was to investigate the association between polymorphisms of ABCG2 with PE in Chinese Han female population. A cohort of 793 preeclamptic women (466 PE with HUA and 327 PE without HUA) and 744 normal pregnant women recruited in this study were genotyped for genetic distribution of Q141K (rs2231142) and Q126X (72552713) in ABCG2 by the TaqMan allelic discrimination real-time PCR. There was no statistically significant difference of genotypic and allelic frequencies between PE and the normal pregnant women in Q141K (Χ² = 1.11, P = 0.58 by genotype; Χ² = 0.32, P = 0.57 by allele) and Q126X (P = 0.33 by genotype; P = 0.33 by allele), and no significant difference was found in the genetic distribution of Q141K and Q126X between PE with HUA, PE without HUA and controls. Additionally, this study observed no significant difference in genotypic and allelic distribution between early/late-onset PE with/without HUA or mild/severe PE with/without HUA and control subgroups. Based on our findings, the ABCG2 Q141K and Q126X polymorphisms may not be associated with PE in Chinese Han women.

Placental transporter localization and expression in the Human: the importance of species, sex, and gestational age differences†

The placenta is a critical organ during pregnancy, essential for the provision of an optimal intrauterine environment, with fetal survival, growth, and development relying on correct placental function. It must allow nutritional compounds and relevant hormones to pass into the fetal bloodstream and metabolic waste products to be cleared. It also acts as a semipermeable barrier to potentially harmful chemicals, both endogenous and exogenous. Transporter proteins allow for bidirectional transport and are found in the syncytiotrophoblast of the placenta and endothelium of fetal capillaries. The major transporter families in the human placenta are ATP-binding cassette (ABC) and solute carrier (SLC), and insufficiency of these transporters may lead to deleterious effects on the fetus. Transporter expression levels are gestation-dependent and this is of considerable clinical interest as levels of drug resistance may be altered from one trimester to the next. This highlights the importance of these transporters in mediating correct and timely transplacental passage of essential compounds but also for efflux of potentially toxic drugs and xenobiotics. We review the current literature on placental molecular transporters with respect to their localization and ontogeny, the influence of fetal sex, and the relevance of animal models. We conclude that a paucity of information exists, and further studies are required to unlock the enigma of this dynamic organ.

Relationship between folate transporters expression in human placentas at term and birth weights

BACKGROUND

Adequate folate levels are essential for successful pregnancy outcomes. We aimed to study the relationship between placental mRNA and protein levels of folate transporters to birth weight.

METHODS

Placental folate transporters (FOLR1, RFC1 and HCP1/PCFT) mRNA and protein levels in basal (BP) and chorionic plate (CP) of small (SGA), appropriate (AGA) and large (LGA) for gestational age term infants (≥37 weeks gestation, n = 111) were determined by real-time PCR and Western blot respectively.

RESULTS

FOLR1 and HCP1/PCFT mRNA were lower in both plates of SGA and LGA placentas compared to AGA (p < 0.01) and RFC1 mRNA was lower only in CP (p < 0.02). RFC1 protein levels were lower in BP of SGA (p < 0.05) and LGA (p < 0.01), and FOLR1 protein levels were lower in CP of SGA (p < 0.02) and LGA (p < 0.01) groups compared to AGA. HCP1/PCFT protein levels remained unchanged in all groups.

CONCLUSION

Placentas of SGA and LGA groups showed a reduced mRNA expression and protein levels of folate transporters, with some differences depending on the location within the placenta (BP or CP). This suggests the presence of specific placental regulation mechanisms in gene expression that may be associated to birth weight.