Comparison of folic acid uptake characteristics by human placental choriocarcinoma cells at acidic and physiological pH

Endocytosis at the maternal-fetal interface: balancing nutrient transport and pathogen defense

Endocytosis represents a category of regulated active transport mechanisms. These encompass clathrin-dependent and -independent mechanisms, as well as fluid phase micropinocytosis and macropinocytosis, each demonstrating varying degrees of specificity and capacity. Collectively, these mechanisms facilitate the internalization of cargo into cellular vesicles. Pregnancy is one such physiological state during which endocytosis may play critical roles. A successful pregnancy necessitates ongoing communication between maternal and fetal cells at the maternal-fetal interface to ensure immunologic tolerance for the semi-allogenic fetus whilst providing adequate protection against infection from pathogens, such as viruses and bacteria. It also requires transport of nutrients across the maternal-fetal interface, but restriction of potentially harmful chemicals and drugs to allow fetal development. In this context, trogocytosis, a specific form of endocytosis, plays a crucial role in immunological tolerance and infection prevention. Endocytosis is also thought to play a significant role in nutrient and toxin handling at the maternal-fetal interface, though its mechanisms remain less understood. A comprehensive understanding of endocytosis and its mechanisms not only enhances our knowledge of maternal-fetal interactions but is also essential for identifying the pathogenesis of pregnancy pathologies and providing new avenues for therapeutic intervention.

Recent Advances in Folates and Autoantibodies against Folate Receptors in Early Pregnancy and Miscarriage

Though firstly identified in cerebral folate deficiency, autoantibodies against folate receptors (FRAbs) have been implicated in pregnancy complications such as miscarriage; however, the underlying mechanism needs to be further elaborated. FRAbs can be produced via sensitization mediated by folate-binding protein as well as gene mutation, aberrant modulation, or degradation of folate receptors (FRs). FRAbs may interfere with folate internalization and metabolism through blocking or binding with FRs. Interestingly, different types of FRs are expressed on trophoblast cells, decidual epithelium or stroma, and macrophages at the maternal-fetal interface, implying FRAbs may be involved in the critical events necessary for a successful pregnancy. Thus, we propose that FRAbs may disturb pregnancy establishment and maintenance by modulating trophoblastic biofunctions, placental development, decidualization, and decidua homeostasis as well as the functions of FOLR2+ macrophages. In light of these findings, FRAbs may be a critical factor in pathological pregnancy, and deserve careful consideration in therapies involving folic acid supplementation for pregnancy complications.

Endocytosis in the placenta: An undervalued mediator of placental transfer

Endocytosis is an essential mechanism for cellular uptake in many human tissues. A range of endocytic mechanisms occur including clathrin-dependent and -independent mechanisms. However, the role of endocytosis in the placenta and the spatial localisation of individual mechanisms is not well understood. The two principal cell layers that comprise the placental barrier to maternal-fetal transfer are the syncytiotrophoblast and fetal capillary endothelium. Endocytic uptake into the syncytiotrophoblast has been demonstrated for physiological maternal molecules such as transferrin-bound iron and low density lipoprotein (LDL) and may play an important role in the uptake of several other micronutrients, serum proteins, and therapeutics at both major placental cell barriers. These mechanisms may also mediate placental uptake of some viruses and nanoparticles. This review introduces the mechanisms of cargo-specific endocytosis and what is known about their localisation in the placenta, focussing predominantly on the syncytiotrophoblast. A fuller understanding of placental endocytosis is necessary to explain both fetal nutrition and the properties of the placental barrier. Characterising placental endocytic mechanisms and their regulation may allow us to identify their role in pregnancy pathologies and provide new avenues for therapeutic intervention.

Folate and Borneol Modified Bifunctional Nanoparticles for Enhanced Oral Absorption

Oral delivery is considered the preferred route of administration due to its convenience and favorable compliance. Here, docetaxel (DTX) loaded polylactic-co-glycolic acid (PLGA) nanoparticles, coated with polyethyleneimine⁻folic acid (PEI-FA) and polyethyleneimine⁻borneol (PEI-BO), were designed to enhance oral absorption (FA/BO-PLGA-NPs). The FA/BO-PLGA-NPs were spherical and smooth with an average size of (137.0 ± 2.1) nm. Encapsulation efficiency (EE%) and drug loading (DL%) were (80.3 ± 1.8)% and (2.3 ± 0.3)%, respectively. In vitro release studies showed that approximately 62.1% of DTX was released from FA/BO-PLGA-NPs in media at pH 7.4. The reverted gut sac method showed that the absorption of FA/BO-PLGA-NPs in the intestines was approximately 6.0 times that of DTX. Moreover, cellular uptake suggested that the obtained FA/BO-PLGA-NPs could be efficiently internalized into Caco-2 cells via FA-mediated active targeting and BO-mediated P-glycoprotein (P-gp) inhibition. Pharmacokinetics study demonstrated that after oral administration of DTX at a dose of 10 mg/kg in FA/BO-PLGA-NPs, the bioavailability of FA/BO-PLGA-NPs was enhanced by approximately 6.8-fold compared with that of DTX suspension. FA/BO-PLGA-NPs caused no obvious irritation to the intestines. Overall, the FA/BO-PLGA-NP formulation remarkably improved the oral bioavailability of DTX and exhibited a promising perspective in oral drug delivery.

Identification of placental nutrient transporters associated with intrauterine growth restriction and pre-eclampsia

Background

Gestational disorders such as intrauterine growth restriction (IUGR) and pre-eclampsia (PE) are main causes of poor perinatal outcomes worldwide. Both diseases are related with impaired materno-fetal nutrient transfer, but the crucial transport mechanisms underlying IUGR and PE are not fully elucidated. In this study, we aimed to identify membrane transporters highly associated with transplacental nutrient deficiencies in IUGR/PE.

Results

In silico analyses on the identification of differentially expressed nutrient transporters were conducted using seven eligible microarray datasets (from Gene Expression Omnibus), encompassing control and IUGR/PE placental samples. Thereby 46 out of 434 genes were identified as potentially interesting targets. They are involved in the fetal provision with amino acids, carbohydrates, lipids, vitamins and microelements. Targets of interest were clustered into a substrate-specific interaction network by using Search Tool for the Retrieval of Interacting Genes. The subsequent wet-lab validation was performed using quantitative RT-PCR on placentas from clinically well-characterized IUGR/PE patients (IUGR, n = 8; PE, n = 5; PE+IUGR, n = 10) and controls (term, n = 13; preterm, n = 7), followed by 2D-hierarchical heatmap generation. Statistical evaluation using Kruskal-Wallis tests was then applied to detect significantly different expression patterns, while scatter plot analysis indicated which transporters were predominantly influenced by IUGR or PE, or equally affected by both diseases. Identified by both methods, three overlapping targets, SLC7A7, SLC38A5 (amino acid transporters), and ABCA1 (cholesterol transporter), were further investigated at the protein level by western blotting. Protein analyses in total placental tissue lysates and membrane fractions isolated from disease and control placentas indicated an altered functional activity of those three nutrient transporters in IUGR/PE.

Conclusions

Combining bioinformatic analysis, molecular biological experiments and mathematical diagramming, this study has demonstrated systematic alterations of nutrient transporter expressions in IUGR/PE. Among 46 initially targeted transporters, three significantly regulated genes were further investigated based on the severity and the disease specificity for IUGR and PE. Confirmed by mRNA and protein expression, the amino acid transporters SLC7A7 and SLC38A5 showed marked differences between controls and IUGR/PE and were regulated by both diseases. In contrast, ABCA1 may play an exclusive role in the development of PE.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4518-z) contains supplementary material, which is available to authorized users.

The effect of oxidative stress induced by tert-butylhydroperoxide under distinct folic acid conditions: An in vitro study using cultured human trophoblast-derived cells

Preeclampsia is a pregnancy disorder characterized by high maternal blood pressure, fetal growth restriction and intrauterine hypoxia. Folic acid is a vitamin required during pregnancy. In this work, we investigated the relationship between preeclampsia and the intake of distinct doses of folic acid during pregnancy. Considering that preeclampsia is associated with increased placental oxidative stress levels, we investigated the effect of oxidative stress induced by tert-butylhydroperoxide (TBH) in human trophoblast-derived cells cultured upon deficient/low, physiological and supra-physiological folic acid levels. The negative effect of TBH upon thiobarbituric acid reactive substances (TBARS), total, reduced and oxidized glutathione, cell viability, cell proliferation, culture growth and cell migration was more marked under folic acid excess. This study suggests more attention on the dose administered, and ultimately, on the overall folic acid levels during pregnancy, in the context of preeclampsia risk.

Ion-transfer voltammetric determination of folic acid at meso-liquid–liquid interface arrays

Voltammetric studies on the simple ion transfer (IT) behaviors of an important water-soluble B-vitamin, folic acid (FA), at the liquid–liquid (L–L) interface were firstly performed and applied as a novel detection method for FA under physiological conditions. This work provides a new and attractive strategy for the detection of FA⁻ and other biological anions.

Methotrexate enhances 3T3-L1 adipocytes hypertrophy

Methotrexate (MTX) is broadly used in the treatment of chronic inflammatory diseases such as rheumatoid arthritis (RA). The prevalence of metabolic syndrome (MeS) in patients with this condition is relatively high. Given the importance of adipose tissue in the development of obesity metabolic complications, this study aimed to investigate the effect of methotrexate on preadipocyte proliferation, adipogenesis, and glucose uptake by adipocytes. 3T3-L1 preadipocytes proliferation was evaluated by sulforhodamine B staining and (3)H-thymidine incorporation, after 24 or 48 h of treatment with MTX (0.1 and 10 μM). Preadipocytes were induced to differentiate with an appropriate adipogenic cocktail in the presence or absence of MTX. Adipogenesis was determined by measuring lipid accumulation after staining with oil red O. (3)H-Deoxyglucose ((3)H-DG) uptake was determined by liquid scintillation counting. MTX treatment reduced culture protein content in a concentration-dependent manner and (3)H-thymidine incorporation (P < 0.05). MTX (0.1 μM) treatment increased lipid accumulation and basal (3)H-DG uptake by adipocytes (P < 0.05). In 0.1 μM MTX-treated adipocytes, insulin stimulation did not result in an increase of (3)H-DG uptake, contrarily to what was observed in control cells. These results demonstrate that methotrexate interferes with adipocyte proliferation and promotes the hypertrophic growth of adipocytes. These molecular effects may have implications on metabolic profile of RA patients treated with MTX.

Folic acid uptake by the human syncytiotrophoblast is affected by gestational diabetes, hyperleptinemia, and TNF-α

BACKGROUND

The mechanisms whereby gestational diabetes mellitus (GDM) increases the risk of fetal overgrowth and development of metabolic diseases later in life are likely to involve changes in nutrient supply to the fetus. Hence, in this work, we hypothesize that GDM may affect folic acid (FA) supply to the placenta and fetus.

METHODS

We compared (3)H-FA uptake by human cytotrophoblasts isolated from normal pregnancies (normal trophoblasts; NTB cells) and GDM pregnancies (diabetic trophoblasts; DTB cells) and investigated the effect of GDM hallmarks on (3)H-FA uptake by BeWo cells.

RESULTS

(3)H-FA uptake by NTB and DTB cells was time dependent and acidic pH stimulated. When compared with NTB, (3)H-FA uptake by DTB cells was more sensitive to acidic pH changes and to 5-methyltetrahydrofolate and pemetrexed (PTX) inhibition, indicating a proportionally greater involvement of the proton-coupled folate transporter (PCFT). A 4-h exposure of BeWo cells to lipopolysaccharide (LPS, 1-10 μg/ml) or to high levels of tumor necrosis factor-α (TNF-α, 300 ng/l) significantly reduced (3)H-FA uptake. Moreover, hyperleptinemic conditions (100 ng/ml leptin) decreased (3)H-FA uptake by BeWo cells in a time-dependent manner when compared with normoleptinemic conditions (1 ng/ml leptin).

CONCLUSION

GDM modulates (3)H-FA uptake by the syncytiotrophoblast, and leptin as well as TNF-α downregulate it.

Effect of polyphenols on the intestinal and placental transport of some bioactive compounds

Polyphenols are a group of widely distributed phytochemicals present in most foods of vegetable origin. A growing number of biological effects have been attributed to these molecules in the past few years and only recently has their interference with the transport capacity of epithelial barriers received attention. This review will present data obtained concerning the effect of polyphenols upon the transport of some compounds (organic cations, glucose and the vitamins thiamin and folic acid) at the intestinal and placental barriers. Important conclusions can be drawn: (i) different classes of polyphenols affect transport of these bioactive compounds at the intestinal epithelia and the placenta; (ii) different compounds belonging to the same phenolic family often possess opposite effects upon transport of a given molecule; (iii) the acute and chronic/short-term and long-term exposures to polyphenols do not produce parallel results and, therefore, care should be taken when extrapolating results; (iv) the effect of polyphenolics in combination may be very different from the expected ones taking into account the effect of each of these compounds alone, and so care should be taken when speculating on the effect of a drink based on the effect of one component only; (v) care should be taken in drawing conclusions for alcoholic beverages from results obtained with ethanol alone. Although most of the data reviewed in the present paper refer to in vitro experiments with cell-culture systems, these studies raise a concern about possible changes in the bioavailability of substrates upon concomitant ingestion of polyphenols.

Membrane transporters and folate homeostasis: intestinal absorption and transport into systemic compartments and tissues

Members of the family of B9 vitamins are commonly known as folates. They are derived entirely from dietary sources and are key one-carbon donors required for de novo nucleotide and methionine synthesis. These highly hydrophilic molecules use several genetically distinct and functionally diverse transport systems to enter cells: the reduced folate carrier, the proton-coupled folate transporter and the folate receptors. Each plays a unique role in mediating folate transport across epithelia and into systemic tissues. The mechanism of intestinal folate absorption was recently uncovered, revealing the genetic basis for the autosomal recessive disorder hereditary folate malabsorption, which results from loss-of-function mutations in the proton-coupled folate transporter gene. It is therefore now possible to piece together how these folate transporters contribute, both individually and collectively, to folate homeostasis in humans. This review focuses on the physiological roles of the major folate transporters, with a brief consideration of their impact on the pharmacological activities of antifolates.

The mechanism of carrier-mediated transport of folates in BeWo cells: the involvement of heme carrier protein 1 in placental folate transport

The aim of this study was to elucidate the mechanism of folate transport in the placenta. A study of folate was carried out to determine which carriers transport folates in the human choriocarcinoma cell line BeWo, a model cell line for the placenta. We investigated the effects of buffer pH and various compounds on folate uptake. In the first part of the study, the expression levels of the mRNA of the folate receptor alpha (FRalpha), the reduced folate carrier (RFC), and heme carrier protein 1 (HCP1) were determined in BeWo cells by RT-PCR analysis. Folate uptake into BeWo cells was greater under an acidic buffer condition than under a neutral one. Structure analogs of folates inhibited folate uptake under all buffer pH conditions, but anion drugs (e.g., pravastatin) inhibited folate uptake only under an acidic buffer condition. Although thiamine pyrophosphate (TPP), a substrate of RFC, had no effect on folate uptake, hemin (a weak inhibitor of folate uptake via HCP1) decreased folate uptake to about 80% of the control level under an acidic buffer condition. Furthermore, kinetic analysis showed that hemin inhibited the low-affinity phase of folate uptake under an acidic buffer condition. We conclude that pH-dependent folate uptake in BeWo cells is mediated by at least two carriers. RFC is not involved in folate uptake, but FRalpha (high affinity phase) and HCP1 (low affinity phase) transport folate in BeWo cells.

Progesterone Inhibits Folic Acid Transport in Human Trophoblasts

The aim of this work was to test the putative involvement of members of the ABC superfamily of transporters on folic acid (FA) cellular homeostasis in the human placenta. [(3)H]FA uptake and efflux in BeWo cells were unaffected or hardly affected by multidrug resistance 1 (MDR1) inhibition (with verapamil), multidrug resistance protein (MRP) inhibition (with probenecid) or breast cancer resistance protein (BCRP) inhibition (with fumitremorgin C). However, [(3)H]FA uptake and efflux were inhibited by progesterone (200 microM). An inhibitory effect of progesterone upon [(3)H]FA uptake and efflux was also observed in human cytotrophoblasts. Moreover, verapamil and ss-estradiol also reduced [(3)H]FA efflux in these cells. Inhibition of [(3)H]FA uptake in BeWo cells by progesterone seemed to be very specific since other tested steroids (beta-estradiol, corticosterone, testosterone, aldosterone, estrone and pregnanediol) were devoid of effect. However, efflux was also inhibited by beta-estradiol and corticosterone and stimulated by estrone. Moreover, the effect of progesterone upon the uptake of [(3)H]FA by BeWo cells was concentration-dependent (IC(50 )= 65 [range 9-448] microM) and seems to involve competitive inhibition. Also, progesterone (1-400 microM) did not affect either [(3)H]FA uptake or efflux at an external acidic pH. Finally, inhibition of [(3)H]FA uptake by progesterone was unaffected by either 4-acetamido-4'-isothiocyanato-2,2'-stilbenedisulfonic acid (SITS), a known inhibitor of the reduced folate carrier (RFC), or an anti-RFC antibody. These results suggest that progesterone inhibits RFC. In conclusion, our results show that progesterone, a sterol produced by the placenta, inhibits both FA uptake and efflux in BeWo cells and primary cultured human trophoblasts.

The molecular identity and characterization of a Proton-coupled Folate Transporter--PCFT; biological ramifications and impact on the activity of pemetrexed

Membrane transport of folates is essential for the survival of all mammalian cells and transport of antifolates is an important determinant of antifolate activity. While a major focus of attention has been on transport mediated by the reduced folate carrier and folate receptors, a very prominent carrier-mediated folate transport activity has been recognized for decades with a low-pH optimum and substrate specificity distinct from that of the reduced folate carrier which operates most efficiently at neutral pH. This low-pH transporter represents the mechanism by which folates are absorbed in the small intestine and it is also widely expressed in other human tissues and solid tumors. Recently, this laboratory discovered the molecular identity of this transporter which is genetically unrelated to the reduced folate carrier. This transporter is proton-coupled, electrogenic, and manifests a substrate specificity that is similar to that of the low-pH transport activity previously described in mammalian cells. The key role this transporter plays in intestinal folate absorption has been confirmed by the demonstration of a mutation in this gene in the rare autosomal recessive disorder, hereditary folate malabsorption. This article reviews (1) the characteristics and prevalence of the low-pH folate transport activity, (2) its relationship to, and properties of, the recently identified Proton-Coupled Folate Transporter (PCFT), (3) the physiological and pharmacological roles of this transporter, particularly with respect to pemetrexed, and (4) the historical controversy, now resolved, on the mechanism of intestinal folate absorption.

Acute and chronic effects of some dietary bioactive compounds on folic acid uptake and on the expression of folic acid transporters by the human trophoblast cell line BeWo

Folic acid (FA) is a vitamin that acts as a coenzyme in the biosynthesis of purine and pyrimidine precursors of nucleic acids, which are critically important during pregnancy. Our group has previously shown that both reduced folate carrier (RFC1) and folate receptor alpha (FRalpha) seem to be involved in the uptake of [3H]folic acid ([3H]FA) by a human trophoblast cell line (BeWo) and by human primary cultured cytotrophoblasts. Our aim was to study the interaction between FA and some nutrients/bioactive substances. For this, we tested the acute and chronic effects of some dietary compounds on [3H]FA apical uptake and on the expression of both RFC1 and FRalpha mRNA in BeWo cells. Our results show that [3H]FA uptake was significantly reduced by acute exposure to epicatechin, isoxanthohumol (1-400 microM) or theophylline (0.1-100 microM); isoxanthohumol seemed to act as a competitive inhibitor, whereas epicatechin and theophylline caused an increase in both Km and Vmax. On the other hand, [3H]FA uptake was significantly increased by chronic exposure to xanthohumol, quercetin or isoxanthohumol (0.1-10 microM), and this increase does not seem to result from changes in the level of RFC1 or FRalpha gene expression. Moreover, [3H]FA uptake was significantly reduced by chronic exposure to ethanol (0.01%). This reduction seems to be, at least in part, due to a reduction in FRalpha expression. These results are compatible with an association between a deficient FA supply to the placenta/fetus and ethanol toxicity in pregnancy.