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Renal tubular reabsorption of filtered folate is essential for the conservation and normal homeostasis of this important vitamin. Different molecular mechanisms have been implicated in epithelial folate transport, including folate receptors. Defective expression or antibody inactivation of these is associated with embryonic defects also correlated with low folate intake; however, their contribution to renal tubular folate reabsorption has not been established. With the use of targeted inactivation of the folate binding protein 1 (folbp1) and folate binding protein 2 (folbp2) genes in mice, the role of folate receptors in renal epithelial folate reabsorption was evaluated during low and normal folate intake. Inactivation of folbp1 was associated with (1) loss of 3 H-folic acid binding to crude kidney membranes, (2) increase in renal folate clearance, and (3) increase in urinary excretion and decrease in renal uptake of injected 3 H-methyltetrahydrofolate. No changes in renal folate handling were observed as a result of folbp2 inactivation. Thus, folbp1 is essential for normal renal tubular folate reabsorption, preventing excessive urinary folate loss. Folbp1 is heavily expressed in choroid plexus, yolk sac, and placenta, supporting a role of folbp1 in folate transport in other tissues. The greatest significance of folbp1 for renal folate uptake was observed at conditions of low folate intake, providing a possible explanation for the ability of folate supplementation to prevent developmental defects associated with folbp1 inactivation.

Inactivation of folate binding protein-1 (Folbp1) adversely impacts murine embryonic development, as nullizygous embryos (Folbp1 -/-) die in utero. Administration of folinic acid (N5-formyl-tetrahydrofolate) to Folbp1-deficient dams before and throughout gestation rescues the majority of embryos from premature death; however, a portion of surviving embryos develop structural malformations, including neural tube defects. We examined whether maternal supplementation with L-N5-methyl-tetrahydrofolate (L-5M-THF) has superior protective effects on embryonic development of Folbp1 -/-fetuses compared with L-N5-formyl-tetrahydrofolate (L-5F-THF). We also examined the critical period during gestation when folate supplementation is most beneficial to the developing Folbp1 -/-embryos. Folbp1 -/-pups presented with a range of malformations involving the neural tube, craniofacies, eyes, and abdominal wall. The frequencies of these malformations decreased with increasing folate dose, regardless of the form used. There was no additional benefit provided by L-5M-THF compared with L-5F-THF. Despite rescuing the phenotype in Folbp1 -/-embryos, no significant elevation of Folbp1 -/-maternal folate levels was observed with supplementation.

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Summary:Purpose: Neural tube defects (NTDs), including spina bifida and anencephaly, are common congenital malformations that occur when the neural tube fails to achieve proper closure during early embryogenesis. Based on epidemiological and clinical data obtained over the last few decades, it is apparent that these multifactorial defects have a significant genetic component to their etiology that interacts with specific environmental risk factors. The purpose of this review article is to synthesize the existing literature on the genetic factors contributing to NTD risk.Results: To date, there is evidence that closure of the mammalian neural tube initiates and fuses intermittently at four discrete locations. Disruption of this process at any of these four sites may lead to an NTD, possibly arising through closure sitespecific genetic mechanisms. Candidate genes involved in neural tube closure include genes of the folate metabolic pathway, as well as those involved in folate transport.Conclusions: Although extensive efforts have focused on elucidating the genetic risk factors contributing to the etiology of NTDs, the population burden for these malformations remains unknown. One group at high risk for having children with NTDs is epileptic women receiving antiepileptic medications during pregnancy. Efforts to better understand the genetic factors that may contribute to their heightened risk, as well as the pathogenesis of neural tube closure defects, are reviewed herein.

Administration of Albu-BChE at single doses of 50, 100, and 300 mg safely resulted in long-lasting decreases in cocaine exposure in recreational cocaine users.

Periconceptional folic acid supplementation has been shown to prevent up to 70% of neural tube and other birth defects in humans; however, the mechanism is still unknown. In this study, we tested whether defective intracellular folate transport, as achieved by inactivation of the murine folate-binding protein 1 (Folbp1), affects global DNA methylation in the liver and brain from gestational day (GD) 15 embryos. Complete Folbp1 inactivation is embryolethal but can be reversed by maternal folinic acid (FA) supplementation, and thus we also tested the effect of FA supplementation on DNA methylation in Folbp1 fetuses. Overall, the extent of global DNA methylation seems to be similar across all genotypes in unsupplemented control Folbp1 mice; however, explicit conclusions regarding Folbp1(-/-) fetuses were not possible because only a single living unsupplemented fetus was viable at GD 15. FA supplementation induced global DNA hypomethylation across all genotypes. FA-induced hypomethylation is most likely due to its ability to inhibit the enzyme glycine hydroxymethyltransferase, thereby inhibiting the homocysteine remethylation cycle necessary to regenerate S-adenosylmethionine, the methyl donor for DNA methyltransferases. Our hypothesis was that due to defective folate transport in Folbp1(-/-) embryos and fetuses, DNA would be hypomethylated, thereby altering the temporal expression of critical genes necessary for normal embryonic development. However, these results suggest that an extended examination of changes in DNA methylation prior to GD 15 is required to unequivocally prove or disprove the hypothesis.

Summary:Purpose: The purpose of this study was to test the teratogenic potential of the antiepileptic drug (AED) levetiracetam (LEV), its major metabolite in humans, 2-pyrrolidone-Nbutyric acid (PBA), and enantiomer, (R)-α-ethyl-oxo-pyrrolidine acetamide (REV), in a well-established mouse model.Methods: All compounds were administered by intraperitoneal injections once daily to SWV/Fnn mice on gestational days 8 1 2 to 12 1 2 . LEV was administered at doses of 600, 1,200, and 2,000 mg/kg/day, piracetam (PIR) and PBA, at 600 and 1,200 mg/kg/day, and REV, at 600 mg/kg/day. On gestational day 18 1 2 , fetuses were examined for gross external malformations and prepared for skeletal analysis by using Alizarin Red S staining.Results: No significant gross external malformations were observed in any of the study groups. Fetal weights were significantly reduced in most study groups. Resorption rates were significantly increased only in the 2,000-mg/kg/day LEV group. The overall incidence of skeletal abnormalities and specifically of hypoplastic phalanges was significantly increased in both PBA treatments and in the intermediate 1,200-mg/kg/day LEV group. In contrast to that in humans, 24-h urinary excretion analysis in mice showed that 65-100% of the LEV doses were excreted unchanged, whereas only 4% was excreted as the metabolite PBA. Conclusions:Results of this study demonstrate that both LEV and its major metabolite in humans, PBA, do not induce major structural malformations in developing SWV/Fnn embryos and suggest that they provide a margin of reproductive safety for the pregnant epileptic population when compared with other AEDs tested in this mouse model.