Comparative study of response to treatment with supraphysiologic doses of B-vitamins in hyperhomocysteinemic hemodialysis patients.

BACKGROUND: Hyperhomocysteinemia is a well-recognized risk factor for accelerated atherosclerosis in hemodialysis patients. OBJECTIVES: To examine the effects of two doses of vitamins B6 and B12 and folic acid on homocysteine levels in hemodialysis patients and assess the functional impact of the methylenetetrahydrofolate reductase genotype on the response to treatment. METHODS: In a randomized prospective study, we assessed the effects of folic acid and two doses of B-vitamins in 50 hemodialysis patients with hyperhomocysteinemia. Patients were divided into two groups: 26 patients (group A) who received 25 mg of vitamin B6 daily and one monthly injection of 200 microg vitamin B12, and 24 patients (group B) who received 100 mg of vitamin B6 daily and one monthly injection of 1,000 microg vitamin B12. In addition, both groups received 15 mg folic acid daily. Patients were evaluated for homocysteine levels as well as for coagulation and a thorough lipid profile. Baseline Hcy levels were determined after at least 4 weeks washout from all folic acid and B-vitamins that were given. MFTHR alleles were analyzed, as were activated protein C resistance, von Willebrand factor and lupus anticoagulant. RESULTS: Basal plasma Hcy levels were significantly elevated in hemodialysis patients compared with normal subjects (33.8 +/- 4.3 vs. 4.5 to 14.0 micromol/L). Following treatment, Hcy levels were significantly reduced to 21.2 +/- 1.6 in group A and 18.6 +/- 1.4 micromol/L in group B (P < 0.01). There was no difference in Hcy reduction following the administration of either high or low dosage of vitamins B6 and B12 utilized in the present study. There was no correlation between Hcy levels or thrombophilia and high incidence of thrombotic episodes in hemodialysis patients. Genotypic evaluation of MTHFR revealed that the presence of homozygous thermolabile MTHFR (n = 5) was associated with higher Hcy levels and better response to treatment (Hcy levels decreased by 58%, from 46.2 +/- 14.6 to 19.48 + 4.1 micromol/ L following treatment). In patients with heterozygous thermolabile MTHFR (n = 25), Hcy levels decreased by 34%, from 31.2 +/- 3.7 to 18.1 +/- 1.1 micromol/L following treatment. The efficacy of high and low doses of B-vitamins on the reduction of homocysteine levels was comparable. CONCLUSIONS: Treatment with B-vitamins in combination with folic acid significantly decreased homocysteine levels in hemodialysis patients, independently of the tested doses. In addition, mutations in MTHFR were associated with elevated plasma levels of Hcy. Neither vascular access nor the presence of diabetes was associated with higher pre- or post-treatment homocysteine level.

High glucose-induced replicative senescence: point of no return and effect of telomerase.

Primary human cells enter senescence after a characteristic number of population doublings (PDs). In the current study, human skin fibroblasts were propagated in culture under 5.5mM glucose (normoglycemia); addition of 16.5mM D-glucose to a concentration of 22 mM (hyperglycemia); and addition of 16.5mM L-glucose (osmotic control). Hyperglycemia induced premature replicative senescence after 44.42+/-1.5 PDs compared to 57.9+/-3.83 PDs under normoglycemia (p<0.0001). L-Glucose had no effect, suggesting that the effect of hyperglycemia was not attributed to hyperosmolarity. Activated caspase-3 measurement showed a significantly higher percentage of apoptotic cells in high glucose medium. Telomerase overexpression circumvented the effects of hyperglycemia on replicative capacity and apoptosis. The "point of no return," beyond which hyperglycemia resulted in irreversible progression to premature replicative senescence, occurred after exposure to hyperglycemia for as few as 20 PDs. These results may provide a biochemical basis for the relationship between hyperglycemia and those complications of diabetes, which are reminiscent of accelerated senescence.