5-Methyltetrahydrofolate

by Marie-France Leroux ND.A., naturopath

This article was originally published in the Naturomag magazine (an ÉESNQ publication) in February 2016.

Introduction

Folate is an essential micronutrient that is vital for normal cellular function and a critical factor in one-carbon metabolism. Mammals cannot synthesize folate and depend on external sources to maintain normal levels. Folate is the generic term given to a family of chemically similar compounds that have been recognized as beneficial for the prevention of a range of conditions.

This family includes folic acid and its derivatives: 5- methyltetrahydrofolate (5-MTHF), 5-formyltetrahydrofolate (1).

Folic acid is the synthetic, parent compound of this family. It is an oxidized synthetic water-soluble member of the vitamin-B complex family which does not exist in nature, although oxidation of folates to folic acid is seen in stored or cooked foods (2). Folic acid itself is not active as a coenzyme and has to undergo several metabolic steps within the cell in order to be converted into the metabolically active THF form.

Folinic acid is a 5-formyl derivative of THF. Unlike the synthetic folate, folinic acid is naturally found in food. It is readily converted to THF without requiring the action of the enzyme dihydrofolate reductase (DHFR). Therefore its function as a vitamin is unaffected by drugs inhibiting this enzyme, such as methotrexate. 5-MTHF is a biologically active form of folate and is the most abundant form found in plasma, representing >90% of folate and is the predominant active metabolite of ingested folic acid (1).

Good food sources of folate include mushrooms and green vegetables such as spinach, brussels sprouts, broccoli, asparagus, and turnip greens, okra, among others, as well as peanuts, legumes (especially lima, pinto, and kidney beans), lentils, fruits (especially strawberries and oranges) and their juices, and liver. Raw foods typically are higher in folate than cooked foods because of folate losses incurred with cooking. Fortification of flours, grains, and cereals with folic acid (140 μg folic acid per 100 g of product) was initiated in 1998 in the USA and Canada. Thus, fortified cereals, breads, and grain products now represent major sources of the vitamin in those countries. Some juices also are now fortified with folic acid. (3) In most countries, the recommended dietary allowance (RDA) for folate is 300 ug /day for adults and 400 ug / day for women of childbearing age. (1)

Function

Intracellular folate metabolism is at the branch of two major inter-related metabolic cycles: synthesis of thymidylate and purines and synthesis of methionine from homocysteine. 5-Methyl-THF acts as a methyl donor for homocysteine remethylation which is catalysed by the vitamin B12-dependent enzyme methionine synthase. (1)

THF functions in the body as a coenzyme in both the mitochondria and cytoplasm to accept one-carbon groups typically generated from amino acid metabolism. These THF derivatives then serve as donors of one-carbon units in a variety of synthetic reactions, such as amino acid synthesis and purine and pyrimidine synthesis. (3)

The reaction catalysed by the enzyme MTHFR is crucial for the regulation of available 5-methyl- THF, which is required for methionine synthesis. Methionine, in turn can be metabolized to S_adenosyl methionine (SAMe), which acts as the principal methyl donor in many reactions, including methylation of DNA, histones and other proteins. These methylation reactions play important roles in development, gene expression and genomic stability (4).

5-MTHF is needed for the remethylation of homocysteine to form methionine. This reaction, which occurs when SAMe concentrations are low, requires folate as 5-methyl THF as a methyl donor and vitamin B12 in the form of methylcobalamin as a prosthetic group for homocyste- ine methyltransferase (also called methionine synthase). (3).

SAMe is an important compound, serving as a methyl donor in many reactions in the body. For example, DNA and RNA methylation, myelin maintenance, neural function, and polyamine, carnitine, and catecholamine synthesis, among other processes, are dependent on methylation reactions using SAM. (3)

Deficiency:

Causes of deficiency

Deficiency of folate can be a direct result of low dietary intake, poor absorption of ingested folate by the intestine and increased use (i.e. physical activity, pregnancy); it can also be caused by pathological liver conditions (5, 6) and folate dysmetabolism, due to genetic defects or drug interactions. (1)

Polyglutamate folates ingested with the diet must be converted to the monoglutamate form by the conjugase enzymes in order to be absorbed. Since these enzymes have an optimum activity at pH 6–7, alteration of the intestinal pH may determine an incomplete deconjugation of folate thus leading to reduced absorption. There are several conditions in which the luminal pH changes, such as atrophic gastritis and situations with altered biliary–pancreatic secretions. In addition, treatment with drugs such as proton pump inhibitors (PPI) and H2-antagonists and ingestion of foods rich in citrate, malate and ascorbate may lead to alteration of luminal pH (7). In all these conditions, supplementation with folates is effective and generally recommended (8). Moreover, there are conditions in which drug treatment causes defects in folate metabolism thus impairing its conversion to the active form. This is the case for treatment with drugs such as methotrexate, aminopterine, pyrimethamine and trimethoprim which inhibit DHFR. In these conditions, folic acid supplementation is ineffective and 5-MTHF can be a good alternative to folic acid (1).

Genetic polymorphisms in some of the folate-dependent enzymes have been identified. Several mutations in methylene THF reductase (abbreviated MTHFR) have been demonstrated. MTHFR converts 5,10-methylene THF to 5-methyl THF. Mutations in MTHFR impair 5-methyl THF formation and thus reduce remethylation of homocysteine, resulting in hyperhomocysteinemia. (3)

Genetic alterations of genes codifying for key enzymes of folate metabolism increase folate requirement and contribute to the risk of several disease conditions linked to folate status, such as neural tube defect (NTD) and cardiovascular diseases (9-10). A variant of MTHFR is due to a polymorphism of the MTHFR gene (677C > T polymorphism) and this polymorphism has been associated with increased risk of NTD and increased cardio- vascular risk (11-12).

Testing:

Folate can be measured in plasma, but since plasma folate levels change rapidly according to supply, it is an indication of a short-term folate status. Red blood cells contain more folate than does plasma, however, RBC folate is attained during erythropoiesis. Folate is not taken up by mature red blood cells. Thus, RBC folate concentrations represent an index of longer-term (2 to 3 months) folate status than does plasma. (3)

The methionine cycle is highly sensitive to inadequate folate status. When folate status is poor, the ability of the cell to remethylate cellular homocysteine is impaired and this results in increased plasma homocysteine levels. Therefore, plasma homocysteine levels are an indirect indicator of folate level (13), although low folate level is not the only possible cause of high homocysteine.

Effects of deficiency

Folate deficiency has been linked with an increased risk of neural tube defect, cardio-vascular disease, cancer and cognitive dysfunction (1).

Cardio-vascular health

For the last 2 decades, studies and meta-analysis yielded consistant results: Hcy can be considered as an independent risk factor for cardio-vascular disease. (14) High homocystein levels can be caused by folate deficiency, although many factors can cause or contribute to homocysteinemia: poor diet, B12 or B6 deficiency, heterozygosity for cystathionine synthase defects, hypothyroidism, impaired renal function, or use of drugs affecting homocysteine, folate or cobalamin levels (15).

High Hcy levels have been found to be associated with atherosclerosis, increased reactive oxygen species and reactive nitrogen species production (16), increased activation of pro-inflammatory mediators (17), detrimental effect on endothelial function, and vascular thrombosis. However, Hcy’s role in these mechanisms are not well elucidated, and it is therefore uncertain if Hcy is the cause of these phenomena or not. (14)

A recent study on patients undergoing coronary bypass revealed the importance of 5-MTHF, and not homocysteine, in the regulation of vascular redox state and endothelial function. It revealed that vascular endothelium circulation and systemic circulation behave as independent compartments regarding the metabolism of homocyteine. MTHFR 677C>T polymorphism has a strong impact on vascular and plasma 5-MTHF and on Hcy, but has a minor role in the regulation of vascular Hcy levels in humans. Plasma or circulating 5-MTHF and the MTHFR 677C>T polymorphsm exert a direct effect on vascular BH4 levels, NO availability, and eNOS coupling in human vessels in vivo. 5-MTHF have independent effects on the vascular redox state by affecting different enzymatic sources of superoxyde such as uncoupled eNOS or NADPH-oxydase. (18)

Cognition

Another condition being investigated as possibly linked to poor folate status is dementia, including Alzheimer’s dementia (19). Memory and abstract thinking appear to be influenced by folate. Cognitive dysfunction and dementia have been shown to correlate with plasma homocysteine concentrations, which in turn are influenced in part by folate status (20-21). However, it is not sure if homocysteinemia in Alzheimer disease is contributing to the disease process or if it is a consequence of neurodegeneration. In a study on mice, researchers concluded that folate reduction and hyperhomocysteinemia may contribute to neurodegeneration and may also be triggered by neurodegenerative processes. In other words, they could represent both a cause and a consequence of neurodegeneration. Researchers suggest that such a vicious cycle may be breakable by dietary or supplementation strategies increasing the availability of 5-MTHF (22).

Depression

Many studies found a greater number of depressed patients had folic acid deficiency than non-depressed patients (23), and these studies suggest that folate deficiency may be present in one-third or more of patients with major depression. In another study in elderly women, low plasma folate status was associated with doubling of risk of depression, compared to women with the highest levels. Another study on people aged 60 to 64 found low serum folate and high plasma homocysteine were associated with increased risk of depression (24). A recent meta-analysis found a significant relationship between the risk of depression and low serum folate (25). Many studies also have found a connection between high homocysteine levels and depression (24). Studies have also found that depressed individuals with low serum folate levels are significantly less likely to respond favorably to some SSRI drugs (fluoxetine, sertraline) or a tricyclic anti-depressant (nortriptynine) and more likely to relapse during treatment. (26-27-28)

As discussed earlier, folate is needed for the remethylation of homocysteine to form methionine. This reaction requires folate as 5-methyl THF as a methyl donor and vitamin B12 in the form of methylcobalamin. Methionine is essential in the synthesis of SAM, an important compound, serving as a methyl donor in many reactions in the body. Catecholamine (epinephrine, norepinephrin and dopamine) and serotonin synthesis, among other processes, are dependent on methylation reactions using SAM. This could explain the effect of folate deficiency on mood and brain function.

Increased homocysteine and / or decreased serum folate results in lower levels of SAM in cerebrospinal fluid(29).

Cancer

Folate deficiency or poor folate status is also suspected in the development of some cancers, especially colon cancer. Folate deficiency in cells and tissues is thought to increase the potential for neoplastic changes in normal cells during the early stages of cancer (30). Some evidence suggests that decreased methylation of DNA, especially tumor suppression genes, or increased DNA strand breaks (asso- ciated with misincorporation of uridylate for thymidylate in DNA, caused by folate deficiency) may alter gene expression and thus promote cancer (31). Lower folate intakes have been associated with some cancers, and conversely higher folate intakes have been associated with reduced risks for some cancers (32, 33). Polymorphisms in methylenetetrahydrofolate reductase can increase the likelihood for colorectal cancers (34) and are also associated with breast cancer risk (35)

Two main mechanisms appear to link folate deficiency to cancer: a reduced synthesis of SAMe, which results in aberrations in DNA methylation and a reduced synthesis of the pyrimidine thymidylate, which results in the misincorporation of uracil into DNA. A third possible mechanism involves an impaired purine synthesis and subsequent changes in DNA (36).

Therapeutics

Several studies have focused on comparing the efficacy of folic acid and 5-MTHF in modulating folate-related parameters. One study compared administration of equimolar amounts of 5-MTHF to folic acid for 24 weeks in increasing RBC folate in healthy women of childbearing age. After treatment, increases in RBC and plasma folate concentrations were significantly higher in the group receiving 5-MTHF compared with the folic acid group (37).

The results this study support the use of 5-MTHF as an effective and safe alternative to synthetic folic acid.

In another study, equimolar amounts of folic acid and 5- MTHF were administered for 8 weeks to 160 healthy women of child- bearing age. After treatment, folate plasma concentrations were significantly higher in the 5-MTHF group compared with the folic acid group, whereas the increase in RBC folate was similar in both treatment groups (38) which is not surprising since RBC folate is an indicator of long term folate status. Similarly, Houghton et al. conducted a 16-week trial to evaluate the effectiveness of folic acid versus 5-MTHF on RBC folate concentration during lactation. At the end of the study, the RBC folate concentration in the 5-MTHF group was higher than that in the folic acid group (39).

Other advantages of 5-MTHF over folic acid: The reaction catalysed by DHFR, which is required to reduce folic acid to THF, is slow and easily reaches saturation. Bailey & Ayling (2009) have shown that the reduction of folic acid by DHFR per gram of human liver is on average, less that 2% of that in rat liver. Moreover, in contrast to rats, there was almost a five-fold variation of DHFR activity among the human samples. The great variation of DHFR activity among the human samples and the low rate of conversion of folic acid suggests that the benefit of its use in high doses will be limited by saturation of DHFR, especially in individuals possessing lower than average activity. Thus with the ever-increasing exposure to folic acid from fortification of foods and the use of supplements a total folic acid intake >1mg is now not uncommon in USA and the low activity of DHFR in human liver is the fundamental cause of exposure to relatively high transients of plasma unmetabolized folic acid at doses greater than the RDA (40).

Finally, a major risk of folic acid supplementation is that it may mask vitamin B12 deficiency (41) predisposing people to irreversible neurological damage. In this respect, 5-MTHF would reduce this risk because, unlike folic acid, it is not able to induce a haematological response in cells from patients with vitamin B12 deficiency (42). Folic acid might also be involved in reduced natural killer cell cytotoxicity, but this is still under discussion. Another advantage of 5-MTHF over folic acid is that it is significantly more effective at increasing plasma folate compared with the same dose of folic acid people with 677 C>T polymorphism of MTHFR (43).

Cardio-vascular health

Despite the fact that homocysteinemia appears to be an independent risk factor fo cardio-vascular disease, and that the flour fortification program with folate was followed by an accelerated reduction of stroke mortality in North America, several trials have failed to report improvement of the elastic properties of the arteries after Hcy lowering treatment, generally using folate, B6 and B12. Taking into account all the conflicting results, some researchers conclude that current data does not support pharmacological treatment with folic acid and B vitamins. In contrast, they state that homocysteine-lowering treatment should be considered when moderate homocysteinemia is present. Homocysteinemia is classified according to fasting plasme Hcy levels, as moderate (15-30 umol/L), intermideiate (30-100 umol/L), or severe (>100 umol/L) (15). When the cause of homocysteinemia is established, the best treatment is the reversal of this cause. In the case of increased homocysteine levels due to folate deficiency, the presence of MTHFR 677TT genotype, or renal failure, then 5-MTHF treatment should be considered. Eventhough it is unclear if folate treatment improves clinical outcomes, it is at least not harmfull (14).

Aside from its implications in homocysteine metabolism, 5-MTHF appears to have direct beneficial effects on cardiovascular health. A study on patients undergoing coronary artery by-pass grafting revealed that administration of 5-MTHF has a striking beneficial effect on NO-mediated endothelial function and on super-oxyde production in human vessels from patients with atherosclerosis, both in vivo and ex-vivo. According to this study, 5-MTHF may prevent the peroxynitrite-induced oxidation of BH4, leading to an improvement in eNOS coupling and an enhancement of eNOS activity (44).

Psychiatric disorders

Many studies reported positive effects of 5-MTHF in psychiatric disorders, including depression and schizophrenia. In a 6 weeks, open trail, a high dose 5-MTHF (50 mg daily)was conducted on depressed elderly patients, a significant improvements in depressive symptoms was seen in 81 % of patients (46). Another study (double-blind) was done with 50 mg / day 5-MTHF in depressed elderly patients with concomitant dementia, with normal folate levels at baseline. 5-MTHF group showed significant reduction in the Hamilton Depression Rating Scale (HDRS). The results were equivalent to the group taking anti-depressant drug trazodone (47).

In another study, patients being treated for major depressive disorder and schizophrenia were given 15 mg daily of 5-MTHF for 6 months along the psychotropic medications. Treatment resulted in significant improvements in the HDRS and in social recovery (48).

Athor forms of folate also appeared to benefit in depression. Folic acid (500 mcg/day) given to depressed patients on fluoxetine significantly improved the response rate, compared to the fluoxetine and placebo group (49). In a study on patients unresponsive to SSRIs, 15-30 mg of folinic aid was given along with the anti-depressant for eight weeks: 31 % of patients had a 50% reduction in HRDS scores and 19% achieved remission of depression symptoms (50).

5-MTHF also shows efficacy as adjunctive therapy or monotherapy in reducing depressive symptoms in patients with normal and low folate levels, improving cognitive function and reducing depressive symptoms in elderly patients with dementia and folate deficiency, and reducing depressive and somatic symptoms in patients with depression and alcoholism (51).

Based on existing data, supplementation with various formulations of folates appears to be efficacious and well tolerated in reducing depressive symptoms. Compared with other forms of folates, 5-methyltetrahydrofolate may represent a preferable treatment option for major depressive disorder given its greater bioavailability in patients with a genetic polymorphism, and the lower risk of specific side effects associated with folic acid (52). Although further randomized controlled trials in this area appear warranted, 5-MTHF may represent a useful addition to the anti-depressant pharmacotherapy.

Alzheimer’s disease

There seems to be a link between homocysteinemia and Alzheimer’s disease, although the exact implication of homocysteine in the disease process has not yet been elucidated. In a study done on mice, researchers conclude that folate reduction and hyperhomocysteinemia may contribute to neurodegeneration and may also be triggered by neurodegenerative processes. In other words, they represent both a cause and a consequence of neurodegeneration. Researchers suggest that such a vicious cycle may be breakable by dietary or supplementation strategies increasing the availability of 5-MTHF(53).

In a recent clinical trial, data showed that high-dose B-vitamin treatment (folic acid 0.8 mg, vitamin B6 20 mg, vitamin B12 0.5 mg) in elderly subjects with increased dementia risk (mild cognitive impairment according to 2004 Petersen criteria) slowed shrinkage of the whole brain volume over 2 y. These results show that B-vitamin supplementation can slow the atrophy of specific brain regions that are a key component of the AD process and that are associated with cognitive decline (54).

Cancer

In several studies, higher folate intake from diet and /or supplement was associated with a lower risk of cancer, especially breast and colon cancer (55).

In an in vitro study, dihydrofolate and 5-MTHF were shown to be potent inhibitors of cell growth in colon cancer cells, inhibiting cell proliferation moderately within 24 h. Data suggested that 5-MTHF, being the key metabolite in both the folate and homocysteine metabolic pathway, is the main modulator of growth-promoting actions of homocysteine as well as antiproliferative effects of folate in colon cancer cells (56). This is very promising in regard to colon cancer treatment, considering the bad prognosis of colon cancer and the very low risk of side effects of 5-MTHF.

End-stage renal disease (ESRD)

Recent studies showed potential benefit of 5-MTHF for patients with chronic renal failure. Hemodialysis patients show a 20-fold increase in cardio-vascular disease in comparison to the general population (57). They also have a high prevalence of hyperhomocysteinemia, which tends to be resistant to treatment with usual therapy.

In a clinical study, 15 mg 5-MTHF was given daily to uraemic patients on peritoneal dialysis, compared to a placebo group, for 12 weeks. 5-MTHF admnistration lowered Hcy and improved endothelial dysfunction and this effect appeared to be independent of the reduction in Hcy plasma levels. Previous studies done with folic acid administration was ineffective in improving endothelial function in these patients(58). (Improvement of endothelial function in uraemic patients: possible role fo 5-MTHF – NTD 2007)

In another study on end-stage renal disease (ESRD) patients, two groups received either 5-MTHF (50 mg i.v. after each HD session) or 5 mg/ day oral folic acid for . The results showed that only CRP (a marker of inflammation), and not homocysteine or genotype, was an independent risk factor for mortality in these patients; there was an statistically significant improvement in survival rate of patients treated with 5-MTHF compared with folic acid; a significant reduction of CRP was observed in patients treated with 5-MTHF. These results support the hypothesis that a reduction of homocysteine plasma levels is not associated with decreased mortality risk, and that treatment with 5-MTHF seems to induce an increase in survival rate probably by inducing a lower inflammatory state (59).

Cystic fibrosis

One study has shown preliminary evidence of benefit of 5-MTHF with vitamin B12 supplementation in children with cystic fibrosis. It was observed in this study that CF children had higher RBC intracellular folates than healthy controls, with associated abnormalities of red cell membranes, suggesting that intracellular floats might be metabolically inactive. The hypothesis that was retained as a cause for this, is a reduced activity of the MTHFR. After supplementation for 24 weeks with 5-MTHF (7,5 mg/day) along with vitamin B12 (0,5 mg / day), researchers observed an increased amount of PUFAs , in particular AA, in CF red cell membrane associated with increased unsaturation index. This improves cellular membrane fluidity, and also suggests a reduced release of AA from phospholipids to form eicosanoids that may contribute to inflammation in CF patients. 5-MTHF and vitamin B12 supplementation increased the bioavailability of active form of folate and reduced free radical cell injury. In addition, supplementation normalized CF red cell Na+ content and increased red cell K+ content towards values similar to those observed in normal controls, indicating an amelioration of membrane trafficking. Considering the results of this study and of previous studies on both animals and humans suggesting that besides the CFTR gene mutation, other defects such as altered activity of various membrane cation transport systems, abnormal membrane phospholipid composition, elevated turnover of EFAs, and oxidant-antioxidant imbalance can contribute to clinical manifestations of CF, 5-MTHF and vitamin B12 supplementation might represent a new tool to ameliorate membrane features in CF patients (60). More studies are need to evaluate the potential benefit of 5-MTHF and vitamin B12 on clinical outcomes of CF patients.

Dosage

In the studies on 5-MTHF, dosage used ranged from 500 ug to 50 mg daily. It was used orally in most studies, and used intra-veinously for end-stage renal disease patients. The highest dosages have been used in studies on patients with psychiatric disorders (50 mg daily, with good clinical results), although dosages as low as 500 ug daily of folic acid has shown good results in one study. High dosage has also been used for ESRD patients and cardio-vascular health. More clinical trials are needed in order to identify the most appropriate dosage for each condition.

Conclusion

Although the clinical benefits of supplemental folic acid have been know for a long time to prevent neural tube defect in new borns, it is only in the last 2 decades that studies revealed the potential benefits of 5-MTHF in the prevention and treatment of several diseases. In the cases of depression, cardio-vascular disease and end-stage renal disease, positive effects on clinical outcomes were confirmed by studies. In the case of cancer, Alzheimer’s disease and cystic fibrosis, more studies and clinical trials are still needed to better understand the mechanism of action and evaluate the effect on the clinical outcome of those diseases. But existing studies are promising.

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