Absorption of folate by Caco-2 cells is not affected by high glucose concentration

Association of Altered Ratio of Maternal Folic Acid and Vitamin B12 during Pregnancy with Newborn Birth Weight, Head Circumference, and Chest Circumference

OBJECTIVE

This study evaluated the effect of an altered ratio of maternal RBC folate (MRF) to serum vitamin B12 (MB12) on pregnancy and newborn outcomes.

METHODS

Blood samples were collected from pregnant women and the umbilical cord at the time of delivery. Estimations of RBC folate and serum vitamin B12 from maternal and cord blood samples and total homocysteine (HCY) were performed. Maternal and newborn anthropometric parameters like placental weight (PW), head circumference (HC), chest circumference (CC), and body weight (BW) were measured in offsprings after birth. We stratified the pregnant women into six groups (a) vitamin B12 normal and folic acid normal (BNFN)-control group, (b) vitamin B12 normal and folic acid elevated (BNFE), (c) vitamin B12 normal and folic acid deficient (BNFD), (d) vitamin B12 deficient and folic acid normal (BDFN), (e) vitamin B12 deficient and folic acid elevated (BDFE) and (f) vitamin B12 deficient and folic acid deficient (BDFD) based on their levels of RBC folate (MRF) and vitamin B12 (MB12). The expression of the one-carbon metabolism genes (methionine synthase (MS), glycine N-methyltransferase (GNMT), and cystathionine β-synthase (CBS) was also studied in placental tissue by using real-time PCR.

RESULTS

Cord blood RBC folate was significantly reduced in groups BDFE and BDFD as compared to the control group (BNFN). The cord blood vitamin B12 levels were also reduced in the BDFE group as compared to the BDFD. All the newborn parameters viz. PW, HC, CC, and BW, were reduced in the altered MRF/MB12 ratio (low & high vs. normal ratio). Total HCY was significantly elevated in the groups with (BDFE & BDFN) an imbalance of maternal RBC folate and serum vitamin B12 as compared to the control group. Downregulation of one-carbon metabolism genes like MS (p < 0.001), GNMT (p < 0.05), and CBS (p < 0.01) in placental tissue was observed in the high MRF/MB12 ratio group as compared to the normal ratio group. A strong positive correlation was also observed between MRF, MB12, and newborn parameters.

CONCLUSIONS

The altered ratio of folate to vitamin B12 in the maternal blood is associated with adverse growth and development of the newborn.

Different dietary combinations of folic acid and vitamin B12 in parental diet results in epigenetic reprogramming of IGF2R and KCNQ1OT1 in placenta and fetal tissues in mice

Genomic imprinting is important for mammalian development and its dysregulation can cause various developmental defects and diseases. The study evaluated the effects of different dietary combinations of folic acid and B12 on epigenetic regulation of IGF2R and KCNQ1OT1 ncRNA in C57BL/6 mice model. Female mice were fed diets with nine combinations of folic acid and B12 for 4 weeks. They were mated and off-springs born (F1) were continued on the same diet for 6 weeks postweaning and were allowed to mate. The placenta and fetal (F2) tissues were collected at day 20 of gestation. Dietary deficiency of folate (BNFD and BOFD) and B12 (BDFN) with either state of other vitamin or combined deficiency of both vitamins (BDFD) in comparison to BNFN, were overall responsible for reduced expression of IGF2R in the placenta (F1) and the fetal liver (F2) whereas a combination of folate deficiency with different levels of B12 revealed sex-specific differences in kidney and brain. The alterations in the expression of IGF2R caused by folate-deficient conditions (BNFD and BOFD) and both deficient condition (BDFD) was found to be associated with an increase in suppressive histone modifications. Over-supplementation of either folate or B12 or both vitamins in comparison to BNFN, led to increase in expression of IGF2R and KCNQ1OT1 in the placenta and fetal tissues. The increase in the expression of IGF2R caused by folate over-supplementation (BNFO) was associated with decreased DNA methylation in fetal tissues. KCNQ1OT1 noncoding RNA (ncRNA), however, showed upregulation under deficient conditions of folate and B12 only in female fetal tissues which correlated well with hypomethylation observed under these conditions. An epigenetic reprograming of IGF2R and KCNQ1OT1 ncRNA in the offspring was evident upon different dietary combinations of folic acid and B12 in the mice.

Effect of imbalance in folate and vitamin B12 in maternal/parental diet on global methylation and regulatory miRNAs

DNA methylation, a central component of the epigenetic network is altered in response to nutritional influences. In one-carbon cycle, folate acts as a one-carbon carrier and vitamin B12 acts as co-factor for the enzyme methionine synthase. Both folate and vitamin B12 are the important regulators of DNA methylation which play an important role in development in early life. Previous studies carried out in this regard have shown the individual effects of these vitamins but recently the focus has been to study the combined effects of both the vitamins during pregnancy. Therefore, this study was planned to elucidate the effect of the altered dietary ratio of folate and B12 on the expression of transporters, related miRNAs and DNA methylation in C57BL/6 mice. Female mice were fed diets with 9 combinations of folate and B12 for 4 weeks. They were mated and off-springs born (F1) were continued on the same diet for 6 weeks post-weaning. Maternal and fetal (F2) tissues were collected at day 20 of gestation. Deficient state of folate led to an increase in the expression of folate transporters in both F1 and F2 generations, however, B12 deficiency (BDFN) also led to an increase in the expression in both the generations. B12 transporters/proteins were found to be increased with B12 deficiency in F1 and F2 generations except for TC-II in the kidney which was found to be decreased in the F1 generation. miR-483 was found to be increased with all conditions of folate and B12 in both F1 and F2 generations, however, deficient conditions of B12 led to an increase in the expression of miR-221 in both F1 and F2 generations. The level of miR-133 was found to be increased in BDFN group in F1 generation however; in F2 generation the change in expression was tissue and sex-specific. Global DNA methylation was decreased with deficiency of both folate and B12 in maternal tissues (F1) but increased with folate deficiency in placenta (F1) and under all conditions in fetal tissues (F2). DNA methyltransferases were overall found to be increased with deficiency of folate and B12 in both F1 and F2 generations. Results suggest that the dietary ratio of folate and B12 resulted in altered expression of transporters, miRNAs, and genomic DNA methylation in association with DNMTs.

The transport mechanism of monocarboxylate transporter on spinosin in Caco-2 cells

OBJECTIVES

The aim of this study was to determine the uptake mechanism of spinosin (SPI) by the monocarboxylic acid transporters (MCTs) in Caco-2 cells.

METHODS

The Caco-2 cells were pretreated with various monocarboxylic acids, and the uptake of spinosin from Caco-2 cells was measured by High Performance Liquid Chromatography (HPLC).

KEY FINDINGS

Preloading of various monocarboxylic acids enhanced the uptake of SPI, especially salicylic acid (a substrate of MCTs) had a 23.4 times increase in SPI uptake, indicating that the monocarboxylic acid transporters had an efflux effect on SPI uptake and salicylic acid had a strong inhibition on SPI efflux in Caco-2 cells. At the same time, the uptake of SPI through Caco-2 cells was Na(+)- and temperature-dependent, pretreatment without Na(+) significantly increased the uptake of SPI by 1.85 times and incubated at low temperature (4 °C) SPI uptake increased 20% than that of 37 °C. Furthermore, SPI was transported mainly via a carrier-mediated transport: [Vmax = 5.364 μg/mg protein, Km = 657.0 μg/mL].

CONCLUSION

The uptake of spinosin (SPI) in Caco-2 cells was mainly regulated by the monocarboxylic acid transporters along with Salicylic acid.

Reduced expression of folate transporters in kidney of a rat model of folate oversupplementation

Folic acid is the key one-carbon donor required for de novo nucleotide and methionine synthesis. Its deficiency is associated with megaloblastic anemia, cancer and various complications of pregnancy. However, its supplementation results in reduction of neural tube defects and prevention of several types of cancer. The intake of folic acid from fortified food together with the use of nutritional supplements creates a state of folate oversupplementation. Fortification of foods is occurring worldwide with little knowledge of the potential safety and physiologic consequences of intake of such high doses of folic acid. So, we planned to examine the effects of acute and chronic folate oversupplementation on the physiology of renal folate transport in rats. Male Wistar rats were procured and divided into two groups. Rats in group I were given semisynthetic diets containing 2 mg folic acid/kg diet (control) and those in group II were given folate-oversupplemented rat diet, i.e., 20 mg folic acid/kg diet (oversupplemented). Six animals from group I and group II received the treatment for 10 days (acute treatment) and remaining six for 60 days (chronic treatment). In acute folate-oversupplemented rats, 5-[(14)C]-methyltetrahydrofolate uptake was found to be significantly reduced, as compared to chronic folate-oversupplemented and control rats. This reduction in uptake was associated with a significant decrease in the mRNA and protein levels of the folate transporters. Results of the present investigation showed that acute oversupplementation led to a specific and significant down-regulation of renal folate uptake process mediated via transcriptional and translational regulatory mechanism(s).

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.

Uptake and fate of ganglioside GD3 in human intestinal Caco-2 cells

Ganglioside GD3 is a glycosphingolipid found in colostrum, developing tissues, and tumors and is known to regulate cell growth, differentiation, apoptosis, and inflammation. Feeding a GD3-enriched diet to rats increases GD3 in intestinal lipid rafts and blood. The mechanism, efficiency, and fate of ganglioside absorption by human enterocytes have not been investigated. A model to study GD3 uptake by human intestinal cells was developed to test the hypothesis that enterocyte GD3 uptake is time and concentration dependent, with uptake efficiency and fate influenced by route of delivery. Caco-2 cells were exposed to GD3 on the apical or basolateral membrane (BLM) side for 6, 24, and 48 h. GD3 uptake, retention, transfer, and metabolism was determined. GD3 uptake across the apical and BLM was time and concentration dependent and reached a plateau. GD3 uptake across the BLM was more efficient than apical delivery. Apical GD3 was metabolized with some cell retention and transfer, whereas basolateral GD3 was mostly metabolized. This study demonstrates efficient GD3 uptake by enterocytes and suggests that the route of delivery influences ganglioside uptake and fate.

The effect of high glucose on SERT, the human plasmalemmal serotonin transporter

The aim of this work was to investigate the effect of short- and long-term high-glucose exposure on the plasmalemmal serotonin transporter (SERT)-mediated uptake of [(3)H]-serotonin (5-HT) by Caco-2 cells. Short-term exposure of Caco-2 cells to high apical glucose levels (30 mM for 2 h or 40 mM for 1 h) decreased the uptake of [(3)H]-5-HT by 20-30%. On the other hand, long-term (21-24 weeks) exposure of the cells to high (25 mM) glucose caused a 30% increase in the uptake of [(3)H]5-HT. Under these conditions, the affinity of the transporter for 5-HT and noradrenaline was not significantly changed, and the inhibitory potencies of fluoxetine and desipramine were also unchanged. In conclusion, high-glucose levels modulate SERT activity. A short-term exposure of the cells to a high concentration of glucose decreases the activity of the transporter, whereas a longer exposure of the cells to a high concentration of glucose increases the activity of SERT, without interfering with its affinity.

Folate deprivation induces BCRP (ABCG2) expression and mitoxantrone resistance in Caco-2 cells

Folates can induce the expression and activity of the breast-cancer-resistance-protein (BCRP) and the multidrug-resistance-protein-1 (MRP1). Our aim was to study the time-dependent effect of folate deprivation/supplementation on (i) BCRP and MRP expression and (ii) on drug resistance mediated by these transporters. Therefore Caco-2 colon cancer cells usually grown in standard RPMI-medium containing supraphysiological folic acid (FA) concentrations (2.3 muM; high-folate, HF) were gradually adapted to more physiological folate concentrations (1 nM leucovorin (LV) or 1 nM FA; low-folate, LF), resulting in the sublines Caco-2-LF/LV and Caco-2-LF/FA. Caco-2-LF/LV and LF/FA cells exhibited a maximal increase of 5.2- and 9.6-fold for BCRP-mRNA and 3.9- and 5.7-fold for BCRP protein expression, respectively, but no major changes on MRP expression. Overexpression of BCRP in the LF-cells resulted in 3.6- to 6.3-fold resistance to mitoxantrone (MR), which was completely reverted by the BCRP inhibitor Ko143. On the other hand, LF-adapted cells were markedly more sensitive to methotrexate than the HF-counterpart, both after 4-hr (9,870- and 23,923-fold for Caco-2-LF/LV and LF/FA, respectively) and 72-hr (11- and 22-fold for Caco-2-LF/LV and LF/FA, respectively) exposure. Immunofluorescent staining observed with a confocal-laser-scan-microscope revealed that in Caco-2 cells (both HF and LF), BCRP is mainly located in the cytoplasm. In conclusion, folate deprivation induces BCRP expression associated with MR resistance in Caco-2 cells. The intracellular localization of BCRP in these cells suggests that this transporter is not primarily extruding its substrates out of the cell, but rather to an intracellular compartment where folates can be kept as storage.

Modulation of folate uptake in cultured human colon adenocarcinoma Caco-2 cells by dietary compounds

Folate is a water-soluble B vitamin with a crucial role in the synthesis and methylation of DNA and in the metabolism of several amino acids. In the present study we investigated whether beverages like wine, beer and tea, or some of their specific constituents, affect the intestinal uptake of (3)H-folic acid or (3)H-methotrexate (an antifolate). All tested beverages significantly inhibited the uptake of (3)H-folic acid by Caco-2 cells. Most of these beverages, with the exception of wines (not tested), also inhibited (3)H-methotrexate uptake in these cells. Additionally, ethanol, when tested separately, inhibited the uptake of both compounds. Some of the tested phenolic compounds, namely myricetin, epigallocatechin gallate (EGCG) and isoxanthohumol, markedly inhibited (3)H-folic acid uptake. Myricetin and EGCG also had a concentration-dependent inhibitory effect upon the uptake of (3)H-methotrexate by Caco-2 cells. Resveratrol, quercetin and kaempferol were able to inhibit the transport of both compounds, but only in the concentration of 100 microM. In conclusion, dietary constituents may impact on intestinal folate uptake, as here shown for phenolic compounds.