Effect of low doses of 5-methyltetrahydrofolate and folic acid on plasma homocysteine in healthy subjects with or without the 677C-->T polymorphism of methylenetetrahydrofolate reductase

The effects of folinic acid and l-methylfolate supplementation on serum total homocysteine levels in healthy adults

BACKGROUND - AIM

Hyperhomocysteinemia is recognized as a risk factor for several diseases and conditions. The aim of this study was to investigate and compare the efficacy of two total homocysteine (tHcy)-lowering treatments including folinic acid or l-methylfolate in healthy Greek adults.

METHODS

Two hundred and seventy-two healthy Greek adults (143 men, 129 women; mean age±SD: 43.0 ± 15.3 years), with serum tHcy levels ≥10 μmol/L received randomized folinic acid ("Folinic acid Group") or l-methylfolate ("l-methylfolate Group") orally for three months. All subjects with serum cobalamin (Cbl) levels <300 pg/mL additionally received 1 mg hydroxycobalamine intramuscularly twice a week for the first month only. Serum folate, Cbl and tHcy levels were determined using immunoassays methods at the beginning and the end of the study period. The MTHFR C677T and MTHFR A1298C gene polymorphisms were genotyped using polymerase chain reaction and reverse hybridization.

RESULTS

At the end of the 3-month intervention period, the levels of serum folate and Cbl increased significantly, whereas the levels of serum tHcy decreased significantly in the two groups. The individuals with MTHFR 677TT genotype had a significantly higher reduction in serum tHcy levels than the individuals with the MTHFR 677CC or MTHFR 677CT genotypes. Although the "Folinic acid Group" had a considerably higher increase in their serum folate levels (but not Cbl) than the "l-methylfolate Group", the reduction of serum tHcy levels between the two groups was not substantially different. The individuals with MTHFR 677CT genotype had a statistically significant higher reduction in serum tHcy levels when supplemented with folinic acid rather than l-methylfolate.

CONCLUSIONS

The administration of folinic acid compared to l-methylfolate caused a higher increase of serum folate levels but no difference in the reduction of serum tHcy levels. The reduction of serum tHcy levels was influenced by the existence of MTHFR C677T and not MTHFR A1298C gene polymorphisms. The individuals with MTHFR 677CT genotype appear to benefit more by folinic acid than l-methylfolate supplementation.

Folinic Acid Increases Protein Arginine Methylation in Human Endothelial Cells

Elevated plasma total homocysteine (tHcy) is associated with increased risk of cardiovascular disease, but the mechanisms underlying this association are not completely understood. Cellular hypomethylation has been suggested to be a key pathophysiologic mechanism, since S-adenosylhomocysteine (AdoHcy), the Hcy metabolic precursor and a potent inhibitor of methyltransferase activity, accumulates in the setting of hyperhomocysteinemia. In this study, the impact of folate and methionine on intracellular AdoHcy levels and protein arginine methylation status was studied. Human endothelial cells were incubated with increasing concentrations of folinic acid (FnA), a stable precursor of folate, with or without methionine restriction. The levels of intracellular AdoHcy and AdoMet, tHcy in the cell culture medium, and protein-incorporated methylarginines were evaluated by suitable liquid chromatography techniques. FnA supplementation, with or without methionine restriction, reduced the level of tHcy and did not affect intracellular AdoMet levels. Interestingly, FnA supplementation reduced intracellular AdoHcy levels only in cells grown under methionine restriction. Furthermore, these cells also displayed increased protein arginine methylation status. These observations suggest that folic acid supplementation may enhance cellular methylation capacity under a low methionine status. Our results lead us to hypothesize that the putative benefits of folic acid supplementation in restoring endothelial homeostasis, thus preventing atherothrombotic events, should be reevaluated in subjects under a methionine restriction diet.

Cyclic supplementation of 5-MTHF is effective for the correction of hyperhomocysteinemia

Folic acid supplementation is the mainstay treatment of hyperhomocysteinemia (HHcy). However, no recommendations are currently available in regard to the optimal replacement therapy. Therefore, this prospective study hypothesized that a cyclic schedule (1 month of therapy followed by 2 months of withdrawal) of 5-methyltetrahydrofolate (5-MTHF) would reduce plasma levels of fasting total homocysteine (tHcy) in patients with mild/moderate HHcy. Patients with a new diagnosis of mild/moderate HHcy were evaluated for the methylenetetrahydrofolate reductase genotype and the presence of major features of metabolic syndrome. All enrolled subjects received a cyclic 5-MTHF oral supplementation and were reevaluated after each treatment cycle for a total of 2 years. In the 246 enrolled subjects, a significant reduction of tHcy levels occurred after the first cycle of treatment (from 31.6 ± 13.6 to 14.4 ± 5.77 μmol/L, P < .001) and during the whole 2-year follow-up (from 31.6 ± 13.6 to 12.18 ± 3.03 μmol/L, P < .001). The values of tHcy returned to reference range in 117 subjects (51.3%) after the first cycle and in 198 (86.8%) during the follow-up. The risk of failure in tHcy level normalization was increased in patients with metabolic syndrome (hazard ratio [HR], 3.49; 95% confidence interval [CI], 1.46-8.36), higher baseline tHcy levels (HR, 1.045; 95% CI, 1.018-1.073), or methylenetetrahydrofolate reductase homozygous mutation (HR, 6.59; 95% CI, 2.64-16.4). This study clearly shows that a cyclic schedule (1 month of therapy followed by 2 months of withdrawal) of 5-MTHF supplementation is able to significantly reduce tHcy levels in patients with mild/moderate HHcy.

Antioxidant activity comparison between [6S]-5-methyltetrahydrofolic acid calcium salt and the related racemate form

Folates, such as [6S]-5-methyltetrahydrofolic acid, have been introduced in the market both in vitamin pills and in fortified foods. Their antioxidant activity has been evaluated, but stereoisomer influence on activity has not been proven. In this study, a comparison between [6S]-5-methyltetrahydrofolic acid (5-MTHF) and its racemate [6R,S] form was made by TEAC assay at different pHs, FRAP assay, and ORAC assay. The results showed that the [6S] form had higher antioxidant activity than its racemate form in the TEAC assay at all pHs, with similar values in the FRAP and ORAC assays. Results suggest that stereoisomeric difference could influence the antioxidant activity of 5-MTHF and hence should be taken into account when folates are added to foodstuffs to improve their nutritional value.

Methods in assessing homocysteine metabolism

Homocysteine, a sulfur-containing amino acid, is a metabolite of the essential amino acid methionine. High blood levels of homocysteine result in far-reaching biochemical and life-threatening consequences. Homocysteine exists at a critical biochemical intersection in the methionine cycle between S-adenosylmethionine, the ubiquitous methyl donor, and vitamins B(12) and folic acid. Indirect and direct vascular damage can be caused by homocysteine, a putative atherothrombotic risk factor. Homocysteine has been associated with vascular disease, particularly in subjects with significant carotid stenosis. Increasing evidence for a connection between homocysteine metabolism and cognitive function is surfacing, and this includes from mild cognitive decline (age-related memory loss) to vascular dementia and Alzheimer's disease. In the elderly population increase in homocysteine is commonly seen due to significant deficiencies in cobalamin (B(12)), folate and vitamin B(6.) All of these disease associations are thought to be interrelated via increased homocysteine and S-adenosylhomocysteine and subsequent hypomethylation of numerous substances, including DNA and proteins, rendering vascular structures more susceptible to damage. Decreasing plasma homocysteine, by providing nutritional cofactors for its metabolism has been shown to reduce the risk of cardiovascular events. The current methods of evaluation of homocysteine metabolism include assessment of cobalamin (B(12)) and folate and vitamin B(6) status and screening for mutations in the genes encoding the enzymes of metabolism. An accurate method for the estimation of plasma and tissue levels of homocysteine would contribute greatly to a proper understanding of the metabolism. In the current review emphasis will be on the estimation of homocysteine, and evaluation of one of the common mutations encountered in the metabolism of this amino acid.

[6S]-5-methyltetrahydrofolate increases plasma folate more effectively than folic acid in women with the homozygous or wild-type 677C-->T polymorphism of methylenetetrahydrofolate reductase

BACKGROUND AND PURPOSE

5,10-Methylenetetrahydrofolate reductase (MTHFR) is responsible for the synthesis of 5-methyltetrahydrofolate (5-MTHF). The 677C-->T mutation of MTHFR reduces the activity of this enzyme. The aim of this study was, first, to compare pharmacokinetic parameters of [6S]-5-MTHF and folic acid (FA) in women with the homozygous (TT) and wild-type (CC) 677C-->T mutation, and second, to explore genotype differences. The metabolism of [6S]-5-MTHF and FA was evaluated by measuring plasma folate derivatives.

EXPERIMENTAL APPROACH

Healthy females (TT, n= 16; CC, n= 8) received a single oral dose of FA (400 microg) and [6S]-5-MTHF (416 microg) in a randomized crossover design. Plasma folate was measured up to 8 h after supplementation. Concentration-time-profile [area under the curve of the plasma folate concentration vs. time (AUC)], maximum concentration (C(max)) and time-to-reach-maximum (t(max)) were calculated.

KEY RESULTS

AUC and C(max) were significantly higher, and t(max) significantly shorter for [6S]-5-MTHF compared with FA in both genotypes. A significant difference between the genotypes was observed for t(max) after FA only (P < 0.05). Plasma folate consisted essentially of 5-MTHF irrespective of the folate form given. Unmetabolized FA in plasma occurs regularly following FA supplementation, but rarely with [6S]-5-MTHF.

CONCLUSIONS AND IMPLICATIONS

These data suggest that [6S]-5-MTHF increases plasma folate more effectively than FA irrespective of the 677C-->T mutation of the MTHFR. This natural form of folate could be an alternative to FA supplementation or fortification.

Homocysteine: role and implications in atherosclerosis

Hyperhomocysteinemia promotes atherosclerosis and is most commonly caused by B-vitamin deficiencies, especially folic acid, B(6), and B(12); genetic disorders; certain drugs; and renal impairment. Elevated homocysteine promotes atherosclerosis through increased oxidant stress, impaired endothelial function, and induction of thrombosis. Prospective studies have shown that elevated plasma homocysteine concentrations increase risk of cardiovascular disease by twofold and risk of cerebrovascular disease to a lesser degree. Hyperhomocysteinemia should be identified in patients with progressive or unexplained atherosclerosis and treated appropriately. Treatment of hyperhomocysteinemia is primarily through vitamin supplementation; folic acid and vitamins B(6) and B(12) are the mainstay of therapy. Betaine and 5-methyl tetrahydro-folate are also effective in lowering homocysteine levels. Treatment of moderately elevated plasma homocysteine in patients without atherosclerosis should be deferred until the completion of randomized outcome trials.

Reduced in vivo oxidative stress following 5-methyltetrahydrofolate supplementation in patients with early-onset thrombosis and 677TT methylenetetrahydrofolate reductase genotype

The protective role of folate in vascular disease has been related to antioxidant effects. In 45 patients with previous early-onset (at age <50 years) thrombotic episodes and the 677TT methylenetetrahydrofolate reductase genotype, we evaluated the effects of a 28 d-course (15 mg/d) of 5-methyltetrahydrofolate (MTHF) on homocysteine metabolism and on in vivo generation of 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a reliable marker of oxidative stress. At baseline, patients' fasting total homocysteine (tHcy) was 11.5 micromol/l (geometric mean) and urinary excretion of 8-iso-PGF2alpha was 304 pg/mg creatinine, with the highest metabolite levels in the lowest quartile of plasma folate distribution (P < 0.05). After 5-MTHF supplementation, plasma folate levels increased approximately 13-fold (P < 0.0001 versus baseline); tHcy levels (6.7 micromol/l, P < 0.0001) and urinary 8-iso-PGF2alpha (254 pg/mg creatinine, P < 0.001) were both significantly lowered, their reduction being proportional to baseline values (r = 0.98 and r = 0.77, respectively) and maximal in patients with the lowest pre-supplementation folate levels (P < 0.05). The effects on folate (P < 0.0001) and tHcy (P = 0.0004) persisted for at least up to 2 months after withdrawing 5-MTHF. In parallel with long-lasting tHcy-lowering effects, a short-course 5-MTHF supplementation reduces in vivo formation of 8-iso-PGF2alpha in this population, supporting the antioxidant protective effects of folate in vascular disease.

Folate and homocysteine interrelationships including genetics of the relevant enzymes

PURPOSE OF REVIEW

Inadequate folate status has been linked to risk of a wide range of adverse health conditions throughout life, from birth defects and complications of pregnancy to cardiovascular disease, cancer and cognitive dysfunction in the elderly. In many instances these risks are manifested through elevated plasma homocysteine. This review focuses on current research into the contribution of genetic variability to folate status and disease predisposition.

RECENT FINDINGS

Some dozen potentially important polymorphisms in folate-related genes have been examined for disease associations or for their role in determining the level of plasma homocysteine. In most instances, the effects are either modest, not significant, or undetectable. However, the mechanism by which the 677C-->T variant of methylenetetrahydrofolate reductase determines homocysteine status has become clearer with the elucidation of a critical role for riboflavin in modulating the plasma homocysteine of TT homozygotes. Moreover, several new metaanalyses have confirmed an association of this variant with vascular disease, probably through low folate status and elevated plasma homocysteine.

SUMMARY

There are enormous difficulties in attempting to assess the contribution of minor genetic variability to nutrient status, against major background differences due to ethnicity, age, gender, lifestyle, dietary habits and disease status. Nevertheless, this is an important goal in the future management of chronic multifactorial disease. The present research into the genetic components of folate and homocysteine variability is paving the way towards an eventual capacity to ensure optimal folate status in every individual and, consequently, to reduce their risk of developing such diseases.