Folate Abstracts 7

©

The folic acid metabolite L-5-methyltetrahydrofolate effectively reduces total serum homocysteine level in orthotopic liver transplant recipients: a double-blind placebo-controlled study.
            (Akoglu et al., 2008) Download
OBJECTIVE: Hyperhomocysteinemia is a described risk factor of cardiovascular diseases. The aim of this study was the treatment of hyperhomocysteinemia in liver transplant recipients with L-5-methyltetrahydrofolate (L-5-MTHF; 1 mg) vs folic acid (1 mg) vs placebo in a double-blind placebo-controlled study and to compare the relative responsiveness of these patients to L-5-MTHF and folic acid. SUBJECTS/METHODS: Patients were recruited from Hepatology-Transplantation-Unit at Johann Wolfgang Goethe-University, Frankfurt. Sixty patients were included in this study and 12 patients dropped out for different reasons. The patients were treated over 8 weeks with supplemental L-5-MTHF or folic acid or placebo. Serum homocysteine (HCY) was analyzed with high-performance liquid chromatography (HPLC) beside routine lab tests. RESULTS: We observed only a significant decrease of total serum HCY in the L-5-MTHF group during the study period (at week 0: 15+/-7.7 microM; after 8 weeks treatment: 9.41+/-2.6 microM, P<0.001). There was no significant decrease of total serum HCY neither in the folic acid group nor in the placebo group. CONCLUSION: The effects of L-5-MTHF are significantly more potent than folic acid itself. Therefore, lowering serum HCY in liver transplant recipients is effective with L-5-MTHF.

Folic acid safety and toxicity: a brief review.
            (Butterworth and Tamura, 1989) Download
Oral folic acid (pteroylglutamic acid) is generally regarded as not toxic for normal humans but it may cause neurological injury when given to patients with undiagnosed pernicious anemia. The vitamin should be given with caution to drug-treated epileptic patients because seizure control may be affected. Some studies suggest that folic acid supplements interfere with intestinal zinc absorption in humans and animals but others do not confirm such an effect. The weight of current evidence favors the view that daily supplements of 5-15 mg folic acid do not have significant adverse effects on Zn nutriture in healthy nonpregnant subjects. Because antifolate medications are now being used to treat a wide range of malignant and nonmalignant disorders, further investigation is needed concerning folate metabolism and the safety of supplements in patients with these disorders.

High folic acid consumption leads to pseudo-MTHFR deficiency, altered lipid metabolism, and liver injury in mice.
            (Christensen et al., 2015) Download
BACKGROUND: Increased consumption of folic acid is prevalent, leading to concerns about negative consequences. The effects of folic acid on the liver, the primary organ for folate metabolism, are largely unknown. Methylenetetrahydrofolate reductase (MTHFR) provides methyl donors for S-adenosylmethionine (SAM) synthesis and methylation reactions. OBJECTIVE: Our goal was to investigate the impact of high folic acid intake on liver disease and methyl metabolism. DESIGN: Folic acid-supplemented diet (FASD, 10-fold higher than recommended) and control diet were fed to male Mthfr(+/+) and Mthfr(+/-) mice for 6 mo to assess gene-nutrient interactions. Liver pathology, folate and choline metabolites, and gene expression in folate and lipid pathways were examined. RESULTS: Liver and spleen weights were higher and hematologic profiles were altered in FASD-fed mice. Liver histology revealed unusually large, degenerating cells in FASD Mthfr(+/-) mice, consistent with nonalcoholic fatty liver disease. High folic acid inhibited MTHFR activity in vitro, and MTHFR protein was reduced in FASD-fed mice. 5-Methyltetrahydrofolate, SAM, and SAM/S-adenosylhomocysteine ratios were lower in FASD and Mthfr(+/-) livers. Choline metabolites, including phosphatidylcholine, were reduced due to genotype and/or diet in an attempt to restore methylation capacity through choline/betaine-dependent SAM synthesis. Expression changes in genes of one-carbon and lipid metabolism were particularly significant in FASD Mthfr(+/-) mice. The latter changes, which included higher nuclear sterol regulatory element-binding protein 1, higher Srepb2 messenger RNA (mRNA), lower farnesoid X receptor (Nr1h4) mRNA, and lower Cyp7a1 mRNA, would lead to greater lipogenesis and reduced cholesterol catabolism into bile. CONCLUSIONS: We suggest that high folic acid consumption reduces MTHFR protein and activity levels, creating a pseudo-MTHFR deficiency. This deficiency results in hepatocyte degeneration, suggesting a 2-hit mechanism whereby mutant hepatocytes cannot accommodate the lipid disturbances and altered membrane integrity arising from changes in phospholipid/lipid metabolism. These preliminary findings may have clinical implications for individuals consuming high-dose folic acid supplements, particularly those who are MTHFR deficient.


Serum folate and vitamin B12 concentrations in relation to prostate cancer risk--a Norwegian population-based nested case-control study of 3000 cases and 3000 controls within the JANUS cohort.
            (de Vogel et al., 2013) Download
BACKGROUND: Although individual studies have been inconsistent, meta-analyses of epidemiological data suggest that high folate and vitamin B12 levels may be associated with increased prostate cancer risk. METHODS: Within JANUS, a prospective cohort in Norway (n = 317 000) with baseline serum samples, we conducted a nested case-control study among 3000 prostate cancer cases and 3000 controls, matched on age and time at serum sampling, and county of residence. Using conditional logistic regression, odds ratios (OR) and 95% confidence intervals (CI) for prostate cancer risk were estimated according to quintiles of serum folate, vitamin B12, methylmalonic acid (MMA), total homocysteine (tHcy) and methionine, and according to MTHFR 677C-->T genotypes. To correct for degradation during sample storage, folate concentration was measured as p-aminobenzoylglutamate (pABG) equivalents following oxidation and acid hydrolysis. RESULTS: We observed a weak positive association between folate concentration and prostate cancer risk [OR highest vs lowest quintile = 1.15 (0.97-1.37), P-trend = 0.04], which was more pronounced among individuals >/= 50 years at inclusion [OR 1.40 (1.07-1.84), P-trend = 0.02]. tHcy showed an inverse trend with risk [OR 0.92 (0.77-1.10), P-trend = 0.03]. Vitamin B12, MMA and methionine concentrations were not associated with prostate cancer risk. Compared with the MTHFR 677CC genotype, the CT and TT variants, both of which were related to lower folate concentrations, were associated with reduced prostate cancer risk [OR 0.82 (0.72-0.94) and OR 0.78 (0.64-0.94), respectively]. CONCLUSION: This large-scale population-based study suggests that high serum folate concentration may be associated with modestly increased prostate cancer risk. We did not observe an association between vitamin B12 status and prostate cancer risk.

Association of the MTHFR A1298C variant with unexplained severe male infertility
            (Eloualid et al., 2012) Download
The methylenetetrahydrofolate reductase (MTHFR) gene is one of the main regulatory enzymes involved in folate metabolism, DNA synthesis and remethylation reactions. The influence of MTHFR variants on male infertility is not completely understood. The objective of this study was to analyze the distribution of the MTHFR C677T and A1298C variants using PCR-Restriction Fragment Length Polymorphism (RFLP) in a case group consisting of 344 men with unexplained reduced sperm counts compared to 617 ancestry-matched fertile or normozoospermic controls. The Chi square test was used to analyze the genotype distributions of MTHFR polymorphisms. Our data indicated a lack of association of the C677T variant with infertility. However, the homozygous (C/C) A1298C polymorphism of the MTHFR gene was present at a statistically high significance in severe oligozoospermia group compared with controls (OR = 3.372, 95% confidence interval CI = 1.27-8.238; p = 0.01431). The genotype distribution of the A1298C variants showed significant deviation from the expected Hardy-Weinberg equilibrium, suggesting that purifying selection may be acting on the 1298CC genotype. Further studies are necessary to determine the influence of the environment, especially the consumption of diet folate on sperm counts of men with different MTHFR variants.

Strong association of 677 C>T substitution in the MTHFR gene with male infertility--a study on an indian population and a meta-analysis
            (Gupta et al., 2011) Download
BACKGROUND: Methylenetetrahydrofolate reductase (MTHFR) is an important enzyme of folate and methionine metabolism, making it crucial for DNA synthesis and methylation. The objective of this study was to analyze MTHFR gene 677C>T polymorphism in infertile male individuals from North India, followed by a meta-analysis on our data and published studies. METHODOLOGY/PRINCIPAL FINDINGS: We undertook genotyping on a total of 837 individuals including well characterized infertile (N = 522) and confirmed fertile (N = 315) individuals. The SNP was typed by direct DNA sequencing. Chi square test was done for statistical analysis. Published studies were searched using appropriate keywords. Source of data collection for meta-analysis included 'Pubmed', 'Ovid' and 'Google Scholar'. Those studies analyzing 677C>T polymorphism in male infertility and presenting all relevant data were included in meta-analysis. The genotype data for infertile subjects and fertile controls was extracted from each study. Chi square test was done to obtain odds ratio (OR) and p-value. Meta-analysis was performed using Comprehensive Meta-analysis software (Version 2). The frequency of mutant (T) allele (p = 0.0025) and genotypes (CT+TT) (p = 0.0187) was significantly higher in infertile individuals in comparison to fertile controls in our case-control study. The overall summary estimate (OR) for allele and genotype meta-analysis were 1.304 (p = 0.000), 1.310 (p = 0.000), respectively, establishing significant association of 677C>T polymorphism with male infertility. CONCLUSIONS/SIGNIFICANCE: 677C>T substitution associated strongly with male infertility in Indian population. Allele and genotype meta-analysis also supported its strong correlation with male infertility, thus establishing it as a risk factor.


 

Riboflavin lowers blood pressure in cardiovascular disease patients homozygous for the 677C-->T polymorphism in MTHFR
            (Horigan et al., 2010) Download
OBJECTIVE: The purpose was to examine the effect of intervention with riboflavin (a cofactor for MTHFR) on blood pressure in patients homozygous (TT genotype) for the common 677C-->T polymorphism in MTHFR. METHODS: We investigated 197 premature cardiovascular disease patients, prescreened for the MTHFR 677C-->T polymorphism, from an original cohort of 404 to select those with the TT genotype (n = 60) and a similar number with heterozygous (CT; n = 85) or wild-type (CC; n = 75) genotypes. Of these, 181 completed an intervention in which participants were randomized within each genotype group to receive 1.6 mg per day riboflavin or placebo for 16 weeks. RESULTS: Among patients taking one or more antihypertensive drugs at recruitment (82%), we observed that target blood pressure (<140/90 mmHg) had been achieved in only 37% patients with the TT genotype compared with 59% with the CT and 64% with the CC genotype (P < 0.001). Riboflavin intervention reduced mean blood pressure specifically in those with the TT genotype (from 144/87 to 131/80 mmHg; P < 0.05 systolic; P < 0.05 diastolic), with no response observed in the other genotype groups. CONCLUSION: Riboflavin is effective in reducing blood pressure specifically in patients with the MTHFR 677 TT genotype. The findings, if confirmed, may have important implications for the prevention and treatment of hypertension.

MTHFR polymorphisms and breast cancer risk
            (Hosseini et al., 2011) Download
INTRODUCTION: Two functional single nucleotide polymorphisms (SNPs) in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene, C677T and A1298C, lead to decreased enzyme activity and affect chemosensitivity of tumour cells. MATERIAL AND METHODS: We evaluated these two common polymorphisms and breast cancer risk association in an Iranian sporadic breast cancer population-based case-control study of 294 breast cancer cases and 306 controls using a PCR-RFLP-based assay. RESULTS: Analyses of affected and controls show that homozygote genotype MTHFR 677CC has the highest frequency in both groups (28.3% in patients and 25.3% in control group). Genotype MTHFR 677CT and genotype MTHFR 1298AC were found to be statistically significant risk factors in our population (odds ratio: 1.6, 95% CI: 1.019-2.513, p = 0.041; and odds ratio: 2.575, 95% CI: 1.590-4.158, p = 0.001 respectively). CONCLUSIONS: We can conclude based on the results of our study that a significant association between breast cancer and C677T and A1298C polymorphism might exist.


Folate-mediated one-carbon metabolism and its effect on female fertility and pregnancy viability
            (Laanpere et al., 2010) Download
This review summarizes current knowledge of the effect of folate-mediated one-carbon metabolism and related genetic variants on female fertility and pregnancy viability. Insufficient folate status disrupts DNA methylation and integrity and increases blood homocysteine levels. Elevated levels of follicular fluid homocysteine correlate with oocyte immaturity and poor early embryo quality, while methylenetetrahydrofolate reductase (MTHFR) gene variants are associated with lower ovarian reserves, diminished response to follicular stimulation, and reduced chance of live birth after in vitro fertilization. Embryos carrying multiple MTHFR variants appear to have a selective disadvantage; however, the heterozygous MTHFR 677CT genotype in the mother and fetus provides the greatest chance for a viable pregnancy and live birth, possibly due to a favorable balance in folate cofactor distribution between methyl donor and nucleotide synthesis. The results of previous studies clearly emphasize that imbalances in folate metabolism and related gene variants may impair female fecundity as well as compromise implantation and the chance of a live birth.

Red blood cell folate concentrations increase more after supplementation with [6S]-5-methyltetrahydrofolate than with folic acid in women of childbearing age
            (Lamers et al., 2006) Download
BACKGROUND: For the primary prevention of neural tube defects (NTDs), public health authorities recommend women of childbearing age to take 400 mug folic acid/d 4 wk before conception and during the first trimester. The biologically active derivate [6S]-5-methyltetrahydrofolate ([6S]-5-MTHF) could be an alternative to folic acid. OBJECTIVE: We investigated the effect of supplementation with [6S]-5-MTHF compared with that of folic acid on red blood cell folate concentration, an indicator of folate status. DESIGN: The study was designed as a double-blind, randomized, placebo-controlled intervention trial. Healthy women (n = 144) aged 19-33 y received 400 microg folic acid, the equimolar amount of [6S]-5-MTHF (416 microg), 208 microg [6S]-5-MTHF, or placebo as a daily supplement for 24 wk. Red blood cell and plasma folate concentrations were measured at baseline and at 4-wk intervals. RESULTS: The increase in red blood cell folate over time was significantly higher in the group receiving 416 microg [6S]-5-MTHF/d than in the groups receiving 400 microg folic acid/d or 208 microg [6S]-5-MTHF/d (P < 0.001). No plateau was reached in red blood cell folate concentration in the 3 treatment groups during 24 wk of intervention; however, plasma folate plateaued after 12 wk. CONCLUSIONS: We showed that administration of [6S]-5-MTHF is more effective than is folic acid supplementation at improving folate status. In addition, the study indicates that the recommended period for preconceptional folic acid supplementation should be extended to >4 wk for maximal prevention of NTDs based on folate concentrations. [6S]-5-MTHF might be an efficient and safe alternative to folic acid.

Might erectile dysfunction be due to the thermolabile variant of methylenetetrahydrofolate reductase?
            (Lombardo et al., 2004) Download
Hyperhomocysteinemia is considered one of the most important cardiovascular risk factors increasing considerably the risk of stroke and myocardial infarction. With respect to endothelial function, direct effects of hyperhomocysteinemia on vascular endothelial cells have been demonstrated through the reduction of endothelial nitric oxide production. In this paper, we report the case of a young man with homozygote genotype mutated with 5-methylenetetrahydrofolate reductase (MTHFR) thermolabile variant who, in the absence of relational stress, developed an erectile dysfunction (ED) refractory to the vasoactive type-V phosphodiesterase (PDE5) inhibitor therapy. After one month of treatment with 5 mg/day folic acid and 1000 microg/day cyanocobalamin, the patient restarted the assumption of 50 mg sildenafil, obtaining satisfying erections during sexual intercourse. We suggest that hyperhomocysteinemia may interfere with penile blood supply and, thus, be responsible for ED. If this relationship is confirmed, plasma levels and urinary homocysteine (HCy) should be evaluated in selected young patients with vascular ED. Furthermore, careful attention should be given to the risk of ED when dealing with this metabolic disturbance.

Treatment of erectile dysfunction due to C677T mutation of the MTHFR gene with vitamin B6 and folic acid in patients non responders to PDE5i
            (Lombardo et al., 2010) Download
INTRODUCTION: Epidemiological studies conducted on erectile dysfunction (ED) have demonstrated its close correlation with cardiovascular disease. Since hyperhomocysteinemia is considered an important cardiovascular risk factor, it could also be involved in the pathogenesis of ED. AIM: To study the role of the C677T MTHFR mutation with subsequent hyperhomocysteinemia in the determination of ED. METHODS: We studied 75 consecutive patients presenting with ED. Patients were interviewed using the International Index of Erectile Function. Blood samples were drawn for determination of MTHFR gene C677T mutation, homocysteine (Hcy) and folate levels. Penile color Doppler was also performed. MAIN OUTCOME METHODS: Patients were administered sildenafil citrate for 2 months. The nonresponders were treated with combination of sildenafil, vitamin B6, and folic acid for 6 weeks. Patients were split into three groups, A, B, and C on the basis on their MTHFR genotype, and in a further group defined as "sildenafil nonresponders" (NR). RESULTS: We found 20 patients homozygous for mutant MTHFR 677T, 36 heterozygous, and 19 wild type. Difference in baseline values for Hcy and folic acid was found between groups A and B, and A and C. The NR group (18 patients from group A and B), presented high levels of Hcy and low levels of folic acid. After combination treatment 16 of them (88.9%) revealed an improvement in the IIEF questionnaire. Moreover, it was measured a significant difference between the values of Hcy and folic acid at the baseline and at the end of the study for the nonresponders. CONCLUSIONS: Hyperhomocysteinemia in patients homozygotes for the C677T mutation may interfere with erection mechanisms and thus be responsible for ED. In case of hyperhomocysteinemia associated with low levels of folates, the administration of PDE5 inhibitors may fail if not preceded by the correction of the alterated levels of Hcy and folates.

Methylenetetrahydrofolate reductase: a common human polymorphism and its biochemical implications.
            (Matthews, 2002) Download
Methlenetetrahydrofolate (CH2-H4folate) is required for the conversion of homocysteine to methionine and of dUMP to dTMP in support of DNA synthesis, and also serves as a major source of one carbon unit for purine biosynthesis. This review presents biochemical studies of a human polymorphism in methylenetetrahydrofolate reductase, which catalyzes the reaction shown below. The mutation decreases the flux of CH2-H4folate into CH3-H4folate, and is associated with both beneficial and deleterious effects that can be traced to the molecular effect of the substitution of alanine 222 by valine.

Folic acid and L-5-methyltetrahydrofolate: comparison of clinical pharmacokinetics and pharmacodynamics
            (Pietrzik et al., 2010) Download
There is a large body of evidence to suggest that improving periconceptional folate status reduces the risk of neonatal neural tube defects. Thus increased folate intake is now recommended before and during the early stages of pregnancy, through folic acid supplements or fortified foods. Furthermore, there is growing evidence that folic acid may have a role in the prevention of other diseases, including dementia and certain types of cancer. Folic acid is a synthetic form of the vitamin, which is only found in fortified foods, supplements and pharmaceuticals. It lacks coenzyme activity and must be reduced to the metabolically active tetrahydrofolate form within the cell. L-5-methyl-tetrahydrofolate (L-5-methyl-THF) is the predominant form of dietary folate and the only species normally found in the circulation, and hence it is the folate that is normally transported into peripheral tissues to be used for cellular metabolism. L-5-methyl-THF is also available commercially as a crystalline form of the calcium salt (Metafolin(R)), which has the stability required for use as a supplement. Studies comparing L-5-methyl-THF and folic acid have found that the two compounds have comparable physiological activity, bioavailability and absorption at equimolar doses. Bioavailability studies have provided strong evidence that L-5-methyl-THF is at least as effective as folic acid in improving folate status, as measured by blood concentrations of folate and by functional indicators of folate status, such as plasma homocysteine. Intake of L-5-methyl-THF may have advantages over intake of folic acid. First, the potential for masking the haematological symptoms of vitamin B(12) deficiency may be reduced with L-5-methyl-THF. Second, L-5-methyl-THF may be associated with a reduced interaction with drugs that inhibit dihydrofolate reductase.

MTHFR C677T and MTR A2756G polymorphisms and the homocysteine lowering efficacy of different doses of folic acid in hypertensive Chinese adults
            (Qin et al., 2012) Download
ABSTRACT: BACKGROUND: This study aimed to investigate if the homocysteine-lowering efficacy of two commonly used physiological doses (0.4 mg/d and 0.8 mg/d) of folic acid (FA) can be modified by individual methylenetetrahydrofolate reductase (MTHFR) C677T and/or methionine synthase (MTR) A2756G polymorphisms in hypertensive Chinese adults. METHODS: A total of 480 subjects with mild or moderate essential hypertension were randomly assigned to three treatment groups: 1) enalapril only (10 mg, control group); 2) enalapril-FA tablet [10:0.4 mg (10 mg enalapril combined with 0.4 mg of FA), low FA group]; and 3) enalapril-FA tablet (10:0.8 mg, high FA group), once daily for 8 weeks. RESULTS: After 4 or 8 weeks of treatment, homocysteine concentrations were reduced across all genotypes and FA dosage groups, except in subjects with MTR 2756AG /GG genotype in the low FA group at week 4. However, compared to subjects with MTHFR 677CC genotype, homocysteine concentrations remained higher in subjects with CT or TT genotype in the low FA group (P < 0.05 for either of these genotypes) and TT genotype in the high FA group (P < 0.05). Furthermore, subjects with TT genotype showed a greater homocysteine-lowering response than did subjects with CC genotype in the high FA group (mean percent reduction of homocysteine at week 8: CC 10.8% vs. TT: 22.0%, P = 0.005), but not in the low FA group (CC 9.9% vs. TT 11.2%, P = 0.989). CONCLUSIONS: This study demonstrated that MTHFR C677T polymorphism can not only affect homocysteine concentration at baseline and post-FA treatment, but also can modify therapeutic responses to various dosages of FA supplementation.


 

Consequences of dietary methyl donor supplements: Is more always better?
            (Shorter et al., 2015) Download
Epigenetic mechanisms are now recognized to play roles in disease etiology. Several diseases increasing in frequency are associated with altered DNA methylation. DNA methylation is accomplished through metabolism of methyl donors such as folate, vitamin B12, methionine, betaine (trimethylglycine), and choline. Increased intake of these compounds correlates with decreased neural tube defects, although this mechanism is not well understood. Consumption of these methyl donor pathway components has increased in recent years due to fortification of grains and high supplemental levels of these compounds (e.g. vitamins, energy drinks). Additionally, people with mutations in one of the enzymes that assists in the methyl donor pathway (5-MTHFR) are directed to consume higher amounts of methyl donors to compensate. Recent evidence suggests that high levels of methyl donor intake may also have detrimental effects. Individualized medicine may be necessary to determine the appropriate amounts of methyl donors to be consumed, particularly in women of child bearing age.

Folic acid supplementation does not reduce intracellular homocysteine, and may disturb intracellular one-carbon metabolism.
            (Smith et al., 2013) Download
BACKGROUND: In randomized trails, folic acid (FA) lowered plasma homocysteine, but failed to reduce cardiovascular risk. We hypothesize this is due to a discrepancy between plasma and intracellular effects of FA. METHODS: In a double-blind trial, 50 volunteers were randomized to received 500 microg FA daily for 8 weeks, or placebo. Plasma and peripheral blood mononuclear cell (PBMC) concentrations of homocysteine, S-adenosylmethionine (SAM), S-adenosylhomocysteine, methionine, cystathionine and 5-methyltetrahydrofolate (bioactive folate) were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). PBMCs were used as a cellular model since they display the full spectrum of one-carbon (1C) enzymes and reactions. RESULTS: At baseline, plasma concentrations were a poor reflection of intracellular concentrations for most 1C metabolites, except 5-methyltetrahydrofolate (R=0.33, p=0.02), homocysteine (Hcy) (R=0.35, p=0.01), and cystathionine (R=0.45, p=0.001). FA significantly lowered plasma homocysteine (p=0.00), but failed to lower intracellular homocysteine or change the concentrations of any of the other PBMC 1C metabolites. At baseline, PBMC homocysteine concentrations correlated to PBMC SAM. After FA supplementation, PBMC homocysteine no longer correlated with PBMC SAM, suggesting a loss of SAM's regulatory function. In vitro experiments in lymphoblasts confirmed that at higher folate substrate concentrations, physiological concentrations of SAM no longer effectively inhibit the key regulatory enzyme methylenetetrahydrofolate reductase (MTHFR). CONCLUSIONS: FA supplementation does not reduce intracellular concentrations of Hcy or any of its closely related substances. Rather, FA may disturb physiological regulation of intracellular 1C metabolism by interfering with SAM's inhibitory effect on MTHFR activity.

Molecular mechanisms underlying the potentially adverse effects of folate.
            (Strickland et al., 2013) Download
The importance of proper consumption of dietary folate for human health has been highlighted by an extensive number of publications over several decades. Fortification of grain products with folic acid was initiated with the specific intent to prevent neural tube defects, and the scope of this endeavor is unique in that its target population (women of the periconceptional period) is many times smaller than the population it affects (everyone who ingests fortified grain products). Folate fortification has been wildly successful in terms of its goal; since its inception, the incidence of neural tube defects has markedly decreased. In the wake of this public health triumph, it is important to catalog both the serendipitous benefits and potential side effects of folic acid supplementation. The vitamin is generally regarded as a harmless nutrient based on studies evaluating the safe upper limits of folate intake. In recent years, however, a concern has been raised with respect to a potential downside to folate supplementation; namely, its proposed ability to enhance proliferation of malignant tumors. The current review summarizes the available literature on the effects of folate supplementation and the molecular mechanisms by which high doses of folate may have negative consequences on human health, especially with regard to cancer.

Methylenetetrahydrofolate reductase: biochemical characterization and medical significance
            (Trimmer, 2013) Download
Methylenetetrahydrofolate reductase (MTHFR) catalyzes the reduction of 5,10-methylenetetrahydofolate (CH2-H4folate) to 5-methyltetrahydrofolate (CH3-H4folate). The enzyme employs a noncovalently-bound flavin adenine dinucleotide (FAD), which accepts reducing equivalents from NAD(P)H and transfers them to CH2-H4folate. The reaction provides the sole source of CH3-H4folate, which is utilized by methionine synthase in the synthesis of methionine from homocysteine. MTHFR plays a key role in folate metabolism and in the homeostasis of homocysteine; mutations in the enzyme lead to hyperhomocyst(e)inemia. A common C677T polymorphism in MTHFR has been associated with an increased risk for the development of cardiovascular disease, Alzheimer's disease, and depression in adults, and of neural tube defects in the fetus. The mutation also confers protection for certain types of cancers. This review presents the current knowledge of the enzyme, its biochemical characterization, and medical significance.

Impact of MTHFR C677T gene polymorphism and vitamins intake on homocysteine concentration in the Polish adult population
            (Waskiewicz et al., 2011) Download
BACKGROUND: Homocysteine (Hcy) levels are modulated by nutritional and genetic factors, among which is the enzyme 5,10-methylenetetrahydrofolate reductase (MTHFR). AIM: To determine the effects of the MTHTR C677T polymorphism, as well as the intake of folate, vitamins B(6) and B(12) on serum Hcy concentration in the Polish population. METHODS: Within the framework of the National Multicentre Health Survey (WOBASZ), a representative sample of the whole Polish population aged 20-74 was screened in 2003-2005. Vitamins intake, Hcy level and known MTHTR C677T genotype were available for 1,561 men and 1,712 women. RESULTS: In the Polish population, T/T, C/T and C/C genotype frequencies were 10%, 43% and 47%, respectively in men, and 9%, 42% and 49%, respectively in women. The T/T genotype was associated with increased levels of Hcy (13.14 mumol/L in men, and 9.77 mmol/L in women) compared to the C/C and C/T genotypes (10.18 and 8.77, respectively), after adjustment for age, methionine, coffee and alcohol intake, smoking and drugs used. In a multivariable linear regression model, among subjects with the T/T genotype, the only factor influencing Hcy was age in women. In the case of the other groups (C/C and C/T), there was a relationship between Hcy and age, alcohol consumption, drugs used, folate and vitamin B(6) in men, and age, smoking, coffee consumption, drugs used, folate and vitamin B(12) in women. CONCLUSIONS: The T/T genotype is associated with higher levels of Hcy (29% in men, and 11% in women) compared to other genotypes. Nutritional factors affect Hcy levels only in the C/C and C/T MTHFR genotypes.

Riboflavin offers a targeted strategy for managing hypertension in patients with the MTHFR 677TT genotype: a 4-y follow-up
            (Wilson et al., 2012) Download
BACKGROUND: We recently reported that the elevated blood pressure (BP) observed in patients with cardiovascular disease who are homozygous for the 677C-->T polymorphism (TT genotype) in the gene encoding methylenetetrahydrofolate reductase (MTHFR) was responsive to supplementation with riboflavin-the cofactor for MTHFR. Objective: The objective was to investigate the effect of riboflavin on BP targeted at patients with the TT genotype 4 y after initial investigation, during which time major changes in the clinical guidelines for antihypertensive therapy were introduced. DESIGN: A total of 83 patients (representing all 3 genotypes) who participated in a placebo-controlled riboflavin intervention for 16 wk in 2004 agreed to take part. Nested within this follow-up, those with the TT genotype (n = 31) proceeded to intervention with riboflavin (1.6 mg/d for 16 wk) or placebo, conducted in a crossover style whereby the 2004 treatment groups were reversed. Results: At follow-up in 2008, as in 2004, patients with the TT genotype had higher systolic BP (P < 0.01), with a nonsignificant trend noted for higher diastolic BP (P = 0.051). Despite the marked changes in antihypertensive therapy that had occurred, BP remained unchanged in patients with the TT genotype at the time of follow-up. Riboflavin supplementation (administered in 2004 and 2008) produced an overall decrease in systolic (-9.2 +/- 12.8 mm Hg; P = 0.001) and diastolic (-6.0 +/- 9.9 mm Hg; P = 0.003) BP. CONCLUSIONS: Optimizing riboflavin status offers a low-cost targeted strategy for managing elevated BP in this genetically at-risk group. These findings, if confirmed in the general population, could have important implications for the prevention of hypertension.

Idiopathic male infertility is strongly associated with aberrant promoter methylation of methylenetetrahydrofolate reductase (MTHFR)
            (Wu et al., 2010) Download
BACKGROUND: Abnormal germline DNA methylation in males has been proposed as a possible mechanism compromising spermatogenesis of some men currently diagnosed with idiopathic infertility. Previous studies have been focused on imprinted genes with DNA methylation in poor quality human sperms. However, recent but limited data have revealed that sperm methylation abnormalities may involve large numbers of genes or shown that genes that are not imprinted are also affected. METHODOLOGY/PRINCIPAL FINDINGS: Using the methylation-specific polymerase chain reaction and bisulfite sequencing method, we examined methylation patterns of the promoter of methylenetetrahydrofolate reductase (MTHFR) gene (NG_013351: 1538-1719) in sperm DNA obtained from 94 idiopathic infertile men and 54 normal fertile controls. Subjects with idiopathic infertility were further divided into groups of normozoospermia and oligozoospermia. Overall, 45% (41/94) of idiopathic infertile males had MTHFR hypermethylation (both hemimethylation and full methylation), compared with 15% of fertile controls (P<0.05). Subjects with higher methylation level of MTHFR were more likely to have idiopathic male infertility (P-value for trend = 0.0007). Comparing the two groups of idiopathic infertile subjects with different sperm concentrations, a higher methylation pattern was found in the group with oligozoospermia. CONCLUSIONS: Hypermethylation of the promoter of MTHFR gene in sperms is associated with idiopathic male infertility. The functional relevance of hypermathylation of MTHFR to male fertility warrants further investigation.


 

References

Akoglu, B, et al. (2008), ‘The folic acid metabolite L-5-methyltetrahydrofolate effectively reduces total serum homocysteine level in orthotopic liver transplant recipients: a double-blind placebo-controlled study.’, Eur J Clin Nutr, 62 (6), 796-801. PubMedID: 17522618
Butterworth, CE Jr and T Tamura (1989), ‘Folic acid safety and toxicity: a brief review.’, Am J Clin Nutr, 50 (2), 353-58. PubMedID: 2667316
Christensen, KE, et al. (2015), ‘High folic acid consumption leads to pseudo-MTHFR deficiency, altered lipid metabolism, and liver injury in mice.’, Am J Clin Nutr, 101 (3), 646-58. PubMedID: 25733650
de Vogel, S, et al. (2013), ‘Serum folate and vitamin B12 concentrations in relation to prostate cancer risk--a Norwegian population-based nested case-control study of 3000 cases and 3000 controls within the JANUS cohort.’, Int J Epidemiol, 42 (1), 201-10. PubMedID: 23508410
Eloualid, A., et al. (2012), ‘Association of the MTHFR A1298C variant with unexplained severe male infertility’, PLoS One, 7 (3), e34111. PubMedID: 22457816
Gupta, N., et al. (2011), ‘Strong association of 677 C>T substitution in the MTHFR gene with male infertility--a study on an indian population and a meta-analysis’, PLoS One, 6 (7), e22277. PubMedID: 21799811
Horigan, G., et al. (2010), ‘Riboflavin lowers blood pressure in cardiovascular disease patients homozygous for the 677C-->T polymorphism in MTHFR’, J Hypertens, 28 (3), 478-86. PubMedID: 19952781
Hosseini, M., M. Houshmand, and A. Ebrahimi (2011), ‘MTHFR polymorphisms and breast cancer risk’, Arch Med Sci, 7 (1), 134-37. PubMedID: 22291746
Laanpere, M., et al. (2010), ‘Folate-mediated one-carbon metabolism and its effect on female fertility and pregnancy viability’, Nutr Rev, 68 (2), 99-113. PubMedID: 20137055
Lamers, Y., et al. (2006), ‘Red blood cell folate concentrations increase more after supplementation with [6S]-5-methyltetrahydrofolate than with folic acid in women of childbearing age’, Am J Clin Nutr, 84 (1), 156-61. PubMedID: 16825690
Lombardo, F., et al. (2004), ‘Might erectile dysfunction be due to the thermolabile variant of methylenetetrahydrofolate reductase?’, J Endocrinol Invest, 27 (9), 883-85. PubMedID: 15648556
Lombardo, F., et al. (2010), ‘Treatment of erectile dysfunction due to C677T mutation of the MTHFR gene with vitamin B6 and folic acid in patients non responders to PDE5i’, J Sex Med, 7 (1 Pt 1), 216-23. PubMedID: 19694922
Matthews, RG (2002), ‘Methylenetetrahydrofolate reductase: a common human polymorphism and its biochemical implications.’, Chem Rec, 2 (1), 4-12. PubMedID: 11933257
Pietrzik, K., L. Bailey, and B. Shane (2010), ‘Folic acid and L-5-methyltetrahydrofolate: comparison of clinical pharmacokinetics and pharmacodynamics’, Clin Pharmacokinet, 49 (8), 535-48. PubMedID: 20608755
Qin, X., et al. (2012), ‘MTHFR C677T and MTR A2756G polymorphisms and the homocysteine lowering efficacy of different doses of folic acid in hypertensive Chinese adults’, Nutr J, 11 2. PubMedID: 22230384
Shorter, KR, MR Felder, and PB Vrana (2015), ‘Consequences of dietary methyl donor supplements: Is more always better?’, Prog Biophys Mol Biol, 118(1-2) (1-2), 14-20. PubMedID: 25841986
Smith, DE, et al. (2013), ‘Folic acid supplementation does not reduce intracellular homocysteine, and may disturb intracellular one-carbon metabolism.’, Clin Chem Lab Med, 51 (8), 1643-50. PubMedID: 23740686
Strickland, KC, NI Krupenko, and SA Krupenko (2013), ‘Molecular mechanisms underlying the potentially adverse effects of folate.’, Clin Chem Lab Med, 51 (3), 607-16. PubMedID: 23241610
Trimmer, E. E. (2013), ‘Methylenetetrahydrofolate reductase: biochemical characterization and medical significance’, Curr Pharm Des, 19 (14), 2574-93. PubMedID: 23116396
Waskiewicz, A., et al. (2011), ‘Impact of MTHFR C677T gene polymorphism and vitamins intake on homocysteine concentration in the Polish adult population’, Kardiol Pol, 69 (12), 1259-64. PubMedID: 22219102
Wilson, C. P., et al. (2012), ‘Riboflavin offers a targeted strategy for managing hypertension in patients with the MTHFR 677TT genotype: a 4-y follow-up’, Am J Clin Nutr, 95 (3), 766-72. PubMedID: 22277556
Wu, W., et al. (2010), ‘Idiopathic male infertility is strongly associated with aberrant promoter methylation of methylenetetrahydrofolate reductase (MTHFR)’, PLoS One, 5 (11), e13884. PubMedID: 21085488