Vitamin B12 decreases, but does not normalize, homocysteine and methylmalonic acid in end-stage renal disease: a link with glycine metabolism and possible explanation of hyperhomocysteinemia in end-stage renal disease.

The genetic and environmental factors influencing catabolism of homocysteine in end-stage renal disease (ESRD) patients remain poorly understood. This study investigated how genetic and nutritional influences affect the response to high-dose vitamin B(12) and folate treatment in ESRD patients with hyperhomocysteinemia. We studied 81 hemodialysis patients with hyperhomocysteinemia (> 16 micromol/L) on varied doses of a multivitamin containing 1 mg of folic acid per day. After screening blood work, all patients were switched to daily multivitamin therapy including 1 mg of folic acid for 4 weeks. Vitamin B(12), 1 mg/d, was added for an additional 4 weeks. Patients were then randomized to receive folic acid or placebo. The influence of the 3 methylenetetrahydrofolate reductase (MTHFR) 677 C-->T genotypes on the efficacy of vitamin therapy was assessed. In addition, we investigated how the metabolic complications of ESRD, including the relationship between methylmalonic acid (MMA) and circulating glycine, may contribute to hyperhomocysteinemia. There was no significant difference in total homocysteine (tHcy) levels between the MTHFR 677 C-->T genotypes during the screening phase of the trial. Treatment with a daily multivitamin containing 1 mg folate significantly lowered tHcy levels in all patients by 19.2%. Further supplementation with 1 mg vitamin B(12) resulted in greater tHcy reduction among subjects with the MTHFR 677 T/T genotype (P<.01, T/T v C/C or C/T) while lowering MMA equally in all MTHFR genotypes. There was a significant positive correlation between plasma glycine levels and MMA (P <.05). High-dose vitamin therapy significantly lowers, but does not normalize, MMA and tHcy levels. The MTHFR genotype, while influencing homocysteine levels, was not responsible for the majority of the elevation in plasma tHcy.

Hyndman ME ，Manns BJ ，Snyder FF ，Bridge PJ ，Scott-Douglas NW ，Fung E ，Parsons HG ... -  《METABOLISM-CLINICAL AND EXPERIMENTAL》

Methylenetetrahydrofolate reductase genotype, vitamin B12, and folate influence plasma homocysteine in hemodialysis patients.

Hyperhomocysteinemia, a well-recognized cardiovascular risk factor, is frequent in hemodialysis (HD) patients. A common polymorphism in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene, C-->T substitution at nucleotide 677, is associated with homocysteine (Hcy) level elevation. We examined whether three factors involved in the methionine cycle could influence plasma Hcy concentrations in HD patients: MTHFR polymorphism; vitamin B12, an essential cofactor; and folate, the substrate. In a cross-sectional study, serum vitamin B12, folate, and plasma Hcy were measured and MTHFR genotyping was performed in 534 HD patients. Effects of MTHFR genotypes, vitamin B12, and folate on plasma Hcy levels were examined in 450 HD patients not administered vitamin B12 or folate. To examine the effect of vitamin B12 on plasma Hcy concentrations, we compared plasma Hcy concentrations in HD patients with and without vitamin B12 supplementation. To examine whether functional vitamin B12 deficiency exists even in HD patients with normal vitamin B12 concentrations, 15 HD patients (serum vitamin B12 concentrations, 250 to 2,100 pg/mL) were treated with vitamin B12 (mecobalamin, 1.5 mg/d) for 8 weeks. Serum concentrations of methylmalonic acid (MMA) and vitamin B12 were measured. Hcy levels were higher and folate levels were lower in patients with the TT and CT genotypes compared with patients with the CC genotype. Analysis of covariance to determine independent predictors of high Hcy levels identified low serum vitamin B12 and folate levels and high albumin (Alb) levels in CC-genotype patients, low folate levels and high Alb levels in CT-genotype patients, and low folate levels in TT-genotype patients. Plasma Hcy levels were lower in CC- and CT-genotype patients with vitamin B12 supplementation than in those without supplementation. Vitamin B12 supplementation for 8 weeks significantly reduced MMA concentrations in HD patients with normal serum vitamin B12 concentrations. These results indicate that MTHFR genotype influences the correlation of Hcy level with vitamin B12 and folate levels in HD patients. Functional vitamin B12 deficiency may exist, even in HD patients with normal vitamin B12 concentrations. The efficacy of vitamin B12 and folate supplementation on plasma Hcy levels may depend on MTHFR genotype.

Nakamura T ，Saionji K ，Hiejima Y ，Hirayama H ，Tago K ，Takano H ，Tajiri M ，Hayashi K ，Kawabata M ，Funamizu M ，Makita Y ，Hata A ... -  《-》

Controlled trials of very high dose folic acid, vitamins B12 and B6, intravenous folinic acid and serine for treatment of hyperhomocysteinemia in ESRD.

Gonin JM ，Nguyen H ，Gonin R ，Sarna A ，Michels A ，Masri-Imad F ，Bommareddy G ，Chassaing C ，Wainer I ，Loya A ，Cary D ，Barker LF ，Assefi A ，Greenspan R ，Mahoney D ，Wilcox CS ... -  《JOURNAL OF NEPHROLOGY》

Supplementation with vitamin B12 decreases homocysteine and methylmalonic acid but also serum folate in patients with end-stage renal disease.

Dierkes J ，Domröse U ，Ambrosch A ，Schneede J ，Guttormsen AB ，Neumann KH ，Luley C ... -  《-》

[Frequency of hyperhomocysteinemia in hemodialysis patients with folic acid supplementation].

Kárpáti I ，Balla J ，Szóke G ，Bereczky Z ，Páll D ，Ben T ，Toma K ，Katona E ，Mohácsi A ，Paragh G ，Varga Z ，Kakuk G ，Muszbek L ... -  《ORVOSI HETILAP》