Supplementation with vitamin B-12 decreases homocysteine and methylmalonicacid but also serum folate in patients with end-stage renal disease

Hyperhomocysteinemia is frequently found in patients with end-stage renal d isease (ESRD). Plasma total homocysteine (tHcy) concentrations may be reduc ed by supplementation with folic acid or combinations of folic acid, vitami n B-12, and vitamin B-6. Supplementation studies with vitamin B-12 alone in patients with ESRD have not yet been published. In this study, we investig ated the effects of intravenous injection of cyanocobalamin (1 mg/wk for 4 weeks) in ESRD patients (N = 14) with low serum cobalamin concentrations (< 180 pmol/L). All patients had elevated levels of plasma tHcy, methylmalonic acid (MMA), and cystathionine before supplementation. After supplementatio n, plasma tHcy and MMA decreased 35% and 48%, respectively; however, cystat hionine levels were unchanged. The extent of the plasma tHcy reduction tend ed to be influenced by the C677T polymorphism of methylenetetrahydrofolate reductase (MTHFR). Serum cobalamin increased significantly upon supplementa tion, whereas serum folate levels were substantially reduced by 47%. In con trast, red blood cell (RBC) folate was unchanged. This study shows that vit amin B-12 supplementation effectively decreases both MMA and plasma tHcy in ESRD patients with low B-12 levels. Furthermore, it illustrates the close interrelation between vitamin B-12 and folate metabolism. Copyright (C) 199 9 by W.B. Saunders Company.