Folate absorption in alcoholic pigs: in vitro hydrolysis and transport at the intestinal brush border membrane

Periconceptional alcohol exposure causes female-specific perturbations to trophoblast differentiation and placental formation in the rat

The development of pathologies during pregnancy, including pre-eclampsia, hypertension and fetal growth restriction (FGR), often originates from poor functioning of the placenta. In vivo models of maternal stressors, such as nutrient deficiency, and placental insufficiency often focus on inadequate growth of the fetus and placenta in late gestation. These studies rarely investigate the origins of poor placental formation in early gestation, including those affecting the pre-implantation embryo and/or the uterine environment. The current study characterises the impact on blastocyst, uterine and placental outcomes in a rat model of periconceptional alcohol exposure, in which 12.5% ethanol is administered in a liquid diet from 4 days before until 4 days after conception. We show female-specific effects on trophoblast differentiation, embryo-uterine communication, and formation of the placental vasculature, resulting in markedly reduced placental volume at embryonic day 15. Both sexes exhibited reduced trophectoderm pluripotency and global hypermethylation, suggestive of inappropriate epigenetic reprogramming. Furthermore, evidence of reduced placental nutrient exchange and reduced pre-implantation maternal plasma choline levels offers significant mechanistic insight into the origins of FGR in this model.

Gastrointestinal Handling of Water-Soluble Vitamins

Nine compounds are classified as water-soluble vitamins, eight B vitamins and one vitamin C. The vitamins are mandatory for the function of numerous enzymes and lack of one or more of the vitamins may lead to severe medical conditions. All the vitamins are supplied by food in microgram to milligram quantities and in addition some of the vitamins are synthesized by the intestinal microbiota. In the gastrointestinal tract, the vitamins are liberated from binding proteins and for some of the vitamins modified prior to absorption. Due to their solubility in water, they all require specific carriers to be absorbed. Our current knowledge concerning each of the vitamins differs in depth and focus and is influenced by the prevalence of conditions and diseases related to lack of the individual vitamin. Because of that we have chosen to cover slightly different aspects for the individual vitamins. For each of the vitamins, we summarize the physiological role, the steps involved in the absorption, and the factors influencing the absorption. In addition, for some of the vitamins, the molecular base for absorption is described in details, while for others new aspects of relevance for human deficiency are included. © 2018 American Physiological Society. Compr Physiol 8:1291-1311, 2018.

Reduced SP1-mediated transcriptional activation decreases expression of intestinal folate transporters in response to ethanol exposure

SCOPE

The study was designed to identify the regulatory mechanisms underlying the effects of ethanol exposure on intestinal folate transport and to investigate the reversibility of such effects.

METHODS AND RESULTS

Caco-2 cells were grown in control and ethanol containing medium for 96 h. Thereafter, one subgroup of cells was shifted on ethanol free medium and grown for next 72 h. For in vivo studies, rats were given 1g ethanol/kg body weight/day either for 3 or 5 months and after 3 months of ethanol treatment, one group of rats received no ethanol for 2 months. A significant decrease in folic acid transport as well as expression of folate transporters was observed on ethanol treatment and the effects were reversible upon removal of ethanol. Ethanol exposure had no impact on CpG island methylation of the folate transporters however, an increase in their mRNA half-life was observed that seems to be a homeostatic mechanism. Chromatin immunoprecipitation assay revealed a decrease in binding of SP1 transcription factor to the promoter regions of folate transporters.

CONCLUSION

Reduced binding of SP1 to the promoter region of folate transporters may be a part of the regulatory mechanism resulting in decreased expression of folate transporters on ethanol exposure.

B-Vitamin dependent methionine metabolism and alcoholic liver disease

Convincing evidence links aberrant B-vitamin dependent hepatic methionine metabolism to the pathogenesis of alcoholic liver disease (ALD). This review focuses on the essential roles of folate and vitamins B6 and B12 in hepatic methionine metabolism, the causes of their deficiencies among chronic alcoholic persons, and how their deficiencies together with chronic alcohol exposure impact on aberrant methionine metabolism in the pathogenesis of ALD. Folate is the dietary transmethylation donor for the production of S-adenosylmethionine (SAM), which is the substrate for all methyltransferases that regulate gene expressions in pathways of liver injury, as well as a regulator of the transsulfuration pathway that is essential for production of glutathione (GSH), the principal antioxidant for defense against oxidative liver injury. Vitamin B12 regulates transmethylation reactions for SAM production and vitamin B6 regulates transsulfuration reactions for GSH production. Folate deficiency accelerates the experimental development of ALD in ethanol-fed animals while reducing liver SAM levels with resultant abnormal gene expression and decreased production of antioxidant GSH. Through its effects on folate metabolism, reduced SAM also impairs nucleotide balance with resultant increased DNA strand breaks, oxidation, hepatocellular apoptosis, and risk of carcinogenesis. The review encompasses referenced studies on mechanisms for perturbations of methionine metabolism in ALD, evidence for altered gene expressions and their epigenetic regulation in the pathogenesis of ALD, and clinical studies on potential prevention and treatment of ALD by correction of methionine metabolism with SAM.

Folate malabsorption and its influence on DNA methylation during cancer development

The folate transport across the epithelial of the intestine, colon, kidney, and liver is essential for folate homeostasis. The relative localization of transporters in membranes is an important determinant for the vectorial flow of substrates across the epithelia. Folate deficiency is a highly prevalent vitamin deficiency in the world, and alcohol ingestion has been the major contributor. It can develop because of folate malabsorption in tissues, increased renal excretion dietary inadequacy, and altered hepatobiliary metabolism. Additionally, folate-mediated one-carbon metabolism is important for various cellular processes, including DNA synthesis and methylation. In this regard, the contribution of alcohol-associated and dietary folate deficiency to methylation patterns is under intense investigation, especially in cancer. The epigenetic events have increasing relevance in the development of strategies for early diagnosis, prevention, and treatment of cancer.

Alcohol-associated folate disturbances result in altered methylation of folate-regulating genes

Folate plays a critical role in maintaining normal metabolic, energy, differentiation and growth status of all mammalian cells. The steady-state accumulation of folate seems to depend on the activity of two enzymes: folylpolyglutamate synthetase (FPGS), which adds glutamate residues, and gamma-glutamyl hydrolase (GGH), which removes them, enabling it to be transported across the biological membranes. Overexpression of GGH and downregulation of FPGS would be expected to decrease intracellular folate in its polyglutamylated form, thereby increasing efflux of folate and its related molecules, which might lead to resistance to drugs or folate deficiency. The study was sought to delineate the activity of GGH and expression FPGS in tissues involved in folate homeostasis during alcoholism and the epigenetic regulation of these enzymes and transporters regulating intracellular folate levels. We determined the activity of GGH and expression of FPGS in tissues after 3 months of ethanol feeding to rats at 1 g/kg body weight/day. The results showed that there was not any significant change in the activity of folate hydrolyzing enzyme GGH in ethanol-fed rats while there was significant down regulation in the expression of FPGS. Ethanol feeding decreased the total as well as polyglutamated folate levels. There was tissue-specific hyper/hypo methylation of folate transporter genes viz. PCFT and RFC by chronic ethanol feeding. Moreover, hypermethylation of FPGS gene was observed in intestine and kidney without any change in methylation levels of GGH in the ethanol-fed rats. In conclusion, the initial deconjugation of polyglutamylated folate by GGH was not impaired in ethanol-fed rats while the conversion of monoglutamylated folate to polyglutamylated form might be impaired. There was tissue-specific altered methylation of folate transporter genes by chronic ethanol feeding.

Evaluation of the kinetic properties of the folate transport system in intestinal absorptive epithelium during experimental ethanol ingestion

Folate plays a critical role in maintaining normal metabolic, energy, differentiation and growth status of all mammalian cells. The disturbances in body folate homeostasis such as intestinal malabsorption in alcoholism are well-known contributor to folate deficiency associated disorders. The study was sought to delineate the kinetic features of folate transport in intestinal absorptive epithelium that could highlight insights of malabsorption during alcoholism. We studied [(3)H]-folic acid transport in intestinal brush border membrane (BBM) after 3 months of ethanol administration at 1 g/kg body weight/day to rats. The results showed that the folate transport exhibited saturable kinetics and was pH, Na(+), temperature, divalent cation sensitive, besides -SH group(s) was/were found important in the folate transport system to be efficiently operative. Importantly, the decreased intestinal BBM folate transport in chronic alcoholism was associated with increased K (m) and decreased V (max) during alcoholism. In addition, S-S group status of the transporter and presence of Na(+ )at the absorptive site seems to be perturbed during ethanol ingestion. However, H(+)/folate(-) coupled transport provided the driving force for transport as pH optimum in acidic range was not altered during alcoholism. The inhibition constants of methotrexate and unlabelled folic acid revealed that the two analogues are handled differently by the folate transport system. In addition, the low activity of folate transport system during chronic ethanol exposure was associated with low RBC folate levels. Overall, these findings suggest that the deregulated folate transport kinetics might contribute to intestinal folate malabsorption in alcoholism.

Effect of red wine on the intestinal absorption of thiamine and folate in the rat: comparison with the effect of ethanol alone

BACKGROUND

This work aimed to investigate, in the rat, the acute in vitro effect of red wine and the effect of chronic red wine ingestion on the intestinal absorption of thiamine and folate and to compare them with the effects of ethanol alone.

METHODS

The effects of red wine and of an ethanol solution (same ethanol concentration as that in the red wine, i.e., 12% [v/v]) on rat jejunal apparent permeability (Papp) to H-thiamine and H-folate in the mucosal-to-serosal direction were investigated. Red wine and ethanol were tested both chronically (21-day consumption) and acutely in vitro.

RESULTS

Acutely, both red wine and ethanol 12% (v/v) (both diluted 1:5) reduced (to 65 and 60% of control, respectively) the mucosal-to-serosal Papp to H-thiamine across rat jejunum. Chronic (21-day) ethanol (12% [v/v]) consumption also decreased the Papp to H-thiamine (to 33% of control), but red wine consumption for the same period did not change it. Mucosal-to-serosal Papp to H-folate across rat jejunum was not changed by chronic ingestion of red wine or ethanol. Similarly, it was not affected by acute exposition of the tissue to red wine or ethanol. Acute ethanol (0.05% [v/v]) did not affect the Papp to H-thiamine or H-folate in jejunal tissues obtained from control and red wine-treated rats, but it significantly increased the Papp to both H-thiamine and H-folate (to 183 and 197% of control, respectively) in tissues from chronically ethanol-treated rats.

CONCLUSIONS

Acute and chronic red wine or ethanol had no effect on the intestinal absorption of folate. However, ethanol, both acutely and chronically, decreased the jejunal absorption of thiamine, and red wine reduced the jejunal absorption of thiamine, but only when tested acutely. These findings show that it is not correct to extrapolate from results obtained with ethanol alone on intestinal permeability to the effect of alcoholic beverage consumption.

Effects of alcohol on folate metabolism: implications for carcinogenesis

Epidemiologic observations implicate excess ethanol ingestion as well as low dietary folate intake as risk factors for several cancers. Moreover, the epidemiologic observations support the concept of a synergistic effect between these two factors. Such a relation is biologically plausible because ethanol impedes the bioavailability of dietary folate and is known to inhibit select folate-dependent biochemical reactions. For example, alcohol ingestion in animals is known to inhibit folate-mediated methionine synthesis and thereby may interrupt critical methylation processes that are mediated by the activated form of methionine that provides substrate for biologic methylation, S-adenosylmethionine. Consistent with this observed inhibition of methionine synthesis is the observation that chronic alcohol ingestion in laboratory animals is known to produce hypomethylation of DNA in the colonic mucosa, a constant feature of early colorectal neoplasia. Inhibition of methionine synthase also creates a "methylfolate trap," analogous to what occurs in vitamin B12 deficiency. In addition, some evidence indicates that alcohol may redirect the utilization of folate toward serine synthesis and thereby may interfere with a critical function of methylenetetrahydrofolate, thymidine synthesis. Although a mechanistic link between alcohol and impaired folate metabolism in the genesis of cancer is still not definitively established, such a link should be pursued in future studies because of the intimate metabolic relation between alcohol and folate metabolism.

Relationship of tobacco smoking with serum vitamin B12, folic acid and haematological indices in healthy adults

OBJECTIVES

To investigate the effects of tobacco smoking on serum vitamin B12, folic acid and haematological parameters in healthy Thai smokers and non-smokers.

DESIGN

Cross-sectional study of smokers and non-smokers in a military unit in Bangkok, Thailand.

SETTING

A military unit in Thailand.

SUBJECTS

One hundred and twenty-three male smokers from a military unit in Bangkok, who participated voluntarily in the study, were investigated. Sixty-six male non-smokers from the same unit were selected as controls. Fasting blood samples were collected for investigation of vitamin B12, folic acid and haematological variables.

RESULTS

The serum folic acid concentration of smokers was lower than that of non-smokers, but was not statistically significantly different. Haemoglobin was lower in smokers than in non-smokers; 16.3% of smokers were anaemic compared with only 3.0% of non-smokers. Anaemia was not related to folate deficiency. The white blood cell count was found to be higher in smokers than in non-smokers.

CONCLUSION

The results of this study suggest that there were low serum folic acid concentrations in smokers compared with non-smokers, which might contribute to the development of vascular and cardiovascular diseases. The higher white blood cell count might be indicative alterations in the immune functions of smokers.

Metabolic interactions of alcohol and folate

The goals and objectives of these studies, conducted over the past 30 y, were to determine: a) how chronic alcoholism leads to folate deficiency and b) how folate deficiency contributes to the pathogenesis of alcoholic liver disease (ALD). The intestinal absorption of folic acid was decreased in binge drinking alcoholics and, prospectively, in volunteers fed alcohol with low folate diets. Monkeys fed alcohol for 2 y developed decreased hepatic folate stores, folic acid malabsorption and decreased hepatic uptake but increased urinary excretion of labeled folic acid. Micropigs fed alcohol for 1 y developed features of ALD in association with decreased translation and activity of intestinal reduced folate carrier. Another study in ethanol-fed micropigs demonstrated abnormal hepatic methionine and DNA nucleotide imbalance and increased hepatocellular apoptosis. When alcohol feeding was combined with folate deficiency, micropigs developed typical histological features of ALD in 14 wk, together with elevated plasma homocysteine levels, reduced liver S-adenosylmethionine and glutathione and increased markers for DNA and lipid oxidation. In summary, chronic alcohol exposure impairs folate absorption by inhibiting expression of the reduced folate carrier and decreasing the hepatic uptake and renal conservation of circulating folate. At the same time, folate deficiency accelerates alcohol-induced changes in hepatic methionine metabolism while promoting enhanced oxidative liver injury and the histopathology of ALD.

Dietary monoglutamate and polyglutamate folate are associated with plasma folate concentrations in Dutch men and women aged 20-65 years

Dietary folate consists of monoglutamate and polyglutamate folate species. In the small intestine, folate polyglutamate is deconjugated to the monoglutamate form before absorption takes place. This enzymatic deconjugation might limit the bioavailability of polyglutamate folate. Until now, no data have been available on dietary intake of both folate forms and their associations with folate status. Therefore, we estimated the intake of monoglutamate and polyglutamate folate in the Dutch population and studied whether the association with plasma folate is different for these two folate forms. Dietary intake of monoglutamate and polyglutamate folate from nonfortified foods was estimated for 2435 subjects (1275 men; 1160 women) aged 20-65 y. The intake of monoglutamate folate was about one third of total folate intake, derived mainly from bread (approximately 20%) and meat (approximately 18%), whereas two thirds consisted of polyglutamates, derived mainly from vegetables (approximately 25%). The predictive power of the regression model with total folate intake as the independent variable adjusted for age, smoking and alcohol intake, did not increase when including the ratio of monoglutamate to polyglutamate folate intake. In addition, linear regression models showed that both monoglutamate and polyglutamate folate intake were associated positively with plasma folate levels. However, in men, the monoglutamate folate form appeared to be a threefold stronger determinant of plasma folate levels than polyglutamate folate, whereas in women, both folate forms were equally strong determinants. This might be explained by different food intake patterns of men and women, including alcohol intake. At present, it does not seem necessary to distinguish between food folate forms in advising an increase in folate intake from nonfortified foods.

ALCOHOL: its metabolism and interaction with nutrients

In the past, alcoholic liver disease was attributed exclusively to dietary deficiencies, but experimental and judicious clinical studies have now established alcohol's hepatotoxicity. Despite an adequate diet, it can contribute to the entire spectrum of liver diseases, mainly by generating oxidative stress through its microsomal metabolism via cytochrome P4502E1 (CYP2E1). It also interferes with nutrient activation, resulting in changes in nutritional requirements. This is exemplified by methionine, one of the essential amino acids for humans, which needs to be activated to S-adenosylmethionine (SAMe), a process impaired by liver disease. Thus, SAMe rather than methionine is the compound that must be supplemented in the presence of significant liver disease. In baboons, SAMe attenuated mitochondrial lesions and replenished glutathione; it also significantly reduced mortality in patients with Child A or B cirrhosis. Similarly, decreased phosphatidylethanolamine methyltransferase activity is associated with alcoholic liver disease, resulting in phosphatidylcholine depletion and serious consequences for the integrity of membranes. This can be offset by polyenylphosphatidylcholine (PPC), a mixture of polyunsaturated phosphatidylcholines comprising dilinoleoylphosphatidylcholine (DLPC), which has high bioavailability. PPC (and DLPC) opposes major toxic effects of alcohol, with down-regulation of CYP2E1 and reduction of oxidative stress, deactivation of hepatic stellate cells, and increased collagenase activity, which in baboons, results in prevention of ethanol-induced septal fibrosis and cirrhosis. Corresponding clinical trials are ongoing.

Hyperhomocysteinemia in chronic alcoholism: relations to folic acid and vitamins B(6) and B(12) status

The objective of this review is to present and discuss the current perspectives of homocysteine and one carbon metabolism in chronic alcoholism. Chronic alcoholics frequently suffer from specific micronutrient deficiencies, including vitamins involved in one carbon metabolism, i.e., folate, vitamin B(6) and vitamin B(12). The possible link between homocysteine and alcoholism stems from the fact that homocysteine metabolism is closely linked to the metabolism of these three vitamins. In fact, homocysteine stands at the intersection of two pathways: methylation and transsulfuration. In methylation, homocysteine acquires a methyl group from N-5-methyltetrahydrofolate in a vitamin B(12) dependent reaction, whereas in the transsulfuration pathway, homocysteine condenses with serine to form cystathionine in an irreversible reaction catalyzed by the pyridoxal-5'-phosphate-containing enzyme, cystathionine-beta-synthase. Due to these relationships, nutritional deficiency of one of these vitamins, as a consequence of chronic alcohol intake, could lead to metabolic disruption and potentially to hyperhomocysteinemia. Consistent with an interference of alcohol in these metabolic pathways, a previous study performed in chronic alcoholics in whom hyperhomocysteinemia was observed along with disturbed vitamin status, DNA hypomethylation in peripheral lymphocytes was demonstrated as well. Because all these alterations were observed in the absence of clinically overt disease, one might speculate whether these metabolic abnormalities could be involved in the pathogenesis of organic diseases associated to chronic alcoholism.

Membrane and tissue distribution of folate binding protein in pig

Folate binding protein may participate in folate homeostasis by regulating monoglutamyl folate transport across relevant cell membranes. We compared the activity, immunoreactivity, and transcripts of folate binding protein in pig liver, kidney, and jejunal mucosa and their relevant cell membranes. Binding of [3H]folic acid was sixfold greater to pig liver plasma membranes than to kidney brush-border membranes, whereas there was no binding to jejunal brush-border membranes. The IgG fraction of rabbit antibody detected pig recombinant folate binding protein at 30 kDa and stained pig liver plasma membranes and kidney brush-border membranes but did not react with jejunal brush-border membranes. Folate binding protein transcripts were present in threefold greater abundance in pig liver than in kidney. Species comparisons showed folate binding protein transcripts in rat and human kidney but not in liver. Thus folate binding protein participates in folate homeostasis by regulating uptake by renal tubular membranes and uniquely by pig liver plasma membranes, but it is not involved in jejunal folate absorption.