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Limited data are available on the determinants of homocysteinemia or the association between plasma homocysteine (Hcy) levels and prevalent cardiovascular disease (CVD) in maintenance dialysis patients. We assessed etiology of renal failure, residual renal function and dialysis adequacy-related variables, and vitamin status, as determinants of fasting total plasma homocysteine (Hcy) in 75 maintenance dialysis patients. We also assessed the potential interactive effect on plasma Hcy of folate status and a common mutation (ala to val; homozygous val-val frequency approximately 10%) in methylenetetrahydrofolate reductase (MTHFR), a folate-dependent enzyme crucial for the remethylation of homocysteine (Hcy) to methionine. Lastly, we evaluated whether the Hcy levels differed amongst these patients in the presence or absence of prevalent CVD, after adjustment for the traditional CVD risk factors. Fasting total plasma Hcy, folate, pyridoxal 5'-phosphate (PLP; active B6), B12, creatinine, glucose, total and HDL cholesterol levels, and presence of the ala to val MTHFR mutation were determined, and clinical CVD and CVD risk factor prevalence were ascertained. General linear modelling/analysis of covariance revealed: (1) folate status and serum creatinine were the only significant independent predictors of fasting Hcy; (2) there was a significant interaction between presence of the val mutation and folate status, i.e., among patients with plasma folate below the median (< 29.2 ng/ml), geometric mean Hcy levels were 33% greater (29.0 vs. 21.8 microM, P = 0.012) in the pooled homozygotes (val-val) and heterozygotes (ala-val) for the ala to val mutation, vs. normals (ala-ala); (3) there was no association between prevalent CVD and plasma Hcy. Given potentially intractable survivorship effects, prospective cohort studies will be required to clarify the relationship between plasma Hcy or any putative CVD risk factor, and incident CVD in dialysis patients. If a positive association between plasma Hcy and incident CVD can be established in maintenance dialysis patients, the current data provide a rationale for additional folic acid supplementation in this patient population.

Hyperhomocysteinemia is a common finding in dialysis-dependent end-stage renal disease (ESRD) patients, but its etiology and refractoriness to standard homocysteine-lowering B-vitamin therapy are poorly understood. In the absence of actual in vivo data, it has been hypothesized that loss of normal renal parenchymal uptake and metabolism of homocysteine is an important determinant of hyperhomocysteinemia in ESRD, given that urinary homocysteine excretion by healthy kidneys is trivial. We assessed net renal uptake and metabolism of homocysteine using an established rat model for measuring arteriovenous amino acid differences across the rat kidney, along with simultaneous determination of renal plasma flow, urine flow, and urinary homocysteine concentration. Substantial homocysteine uptake and metabolism by normal rat kidneys was demonstrated, and we also confirmed that urinary homocysteine excretion is minimal. These data suggest that loss of the sizable homocysteine metabolizing capacity of the intact kidneys may be an important determinant of the refractory, potentially atherothrombotic hyperhomocysteinemia frequently observed in ESRD.

Pharmacologic doses of folate, in the absence of clinical folate deficiency, can reduce plasma levels of the putatively atherothrombotic amino acid, homocysteine (H(e)). Data suggesting that H(e) may accumulate in experimental scurvy prompted us to explore the efficacy of high dose ascorbate supplementation as a H(e)-lowering treatment, in the absence of clinical ascorbate deficiency. A randomized, placebo-controlled trial of 12 weeks of high dose (4.5 g/day) ascorbate supplementation was completed by 44 patients with established coronary heart disease. No significant change in mean fasting total plasma H(e) levels was demonstrable despite a marked increase in mean fasting plasma Asorbate levels amongst those patients randomized to active treatment. Ascorbate supplementation to prevent the development of fasting hyperhomocysteinemia may only be relevant at scorbutic levels of plasma ascorbate.

Item does not contain fulltext The results of prospective studies on the relations between the plasma concentration of total homocysteine (tHcy) and B-vitamins, on the one hand, and coronary heart disease (CHD) mortality, on the other hand, are inconclusive and scarce considering the relation with B-vitamins. We prospectively determined these relations in a case-cohort study. The full-cohort existed in approximately 36,000 Dutch adults aged 20-59 years at baseline. The statistical analyses were done with a random sample from the cohort (n=630) complemented with all subjects who died of CHD (n=102) during a mean follow-up of 10.3 years. All subjects reported the absence of cardiovascular diseases (CVDs) at baseline. The plasma concentrations of tHcy, folate, PLP, and vitamin B12 were determined in samples obtained at baseline. Men with a tHcy concentration in the highest tertile (T3) compared with men in the lowest tertile (T1) had a relative risk (RR) of 1.14 for CHD (95% confidence interval (CI): 0.50, 2.61) after adjusting for age, study center, hypertension, HDL and total cholesterol, smoking, and creatinine. For women, this RR was 2.04 (95% CI: 0.48, 8.62). For each 5 micromol/l increase in tHcy, the RR of CHD was 1.03 (95% CI: 0.83-1.29) for men and women combined. In women only, high folate levels were associated with a statistically significant protection of fatal CHD (T3 versus T1; RR: 0.22, 95% CI: 0.06, 0.87). Plasma PLP (B6) and vitamin B12 concentrations were not associated with CHD risk. We conclude that elevated tHcy concentrations do not seem to be a risk factor for CHD mortality in these relatively young healthy Dutch subjects free of baseline CVD. Higher folate concentrations may be protective of CHD, but this needs confirmation.

Maintenance dialysis patients experience an exceedingly high incidence of arteriosclerotic cardiovascular disease (CVD) events that are poorly predicted by traditional CVD risk factor indices. We evaluated the prevalence of three non-traditional CVD risk factors, i.e. hyperhomocysteinemia, hyperfibrinogenemia, and lipoprotein (a) (Lp(a)) excess, and combined hyperhomocysteinemia, hyperfibrinogenemia, and Lp(a) excess, in maintenance dialysis patients. Fasting total plasma homocysteine (Hcy), fibrinogen, Lp(a), glucose, and total and HDL cholesterol levels, and traditional CVD risk factor (i.e. glucose tolerance, smoking, hypertension, dyslipidemia) prevalences were assessed in 71 dialysis patients and 71 age, sex, and race matched Framingham Study controls free of clinical renal disease, with normal serum creatinine (≤ 1.5 mg/dl). Mean plasma Hcy (23.7 vs. 9.9 μM, P = 0.0001), fibrinogen (457 vs. 309 mg/dl, P = 0.0001), and Lp(a) (30 vs. 17 mg/dl, P = 0.0070) levels were substantially increased in the dialysis patients. Matched odds ratios (with 95% confidence intervals), dialysis patients/controls, for hyperhomocysteinemia, hyperfibrinogenemia, and Lp(a) excess, alone or combined, were markedly greater in the dialysis patients, with no evidence of confounding by the traditional CVD risk factors: hyperhomocysteinemia, 105.0 (29.9–368.9); hyperfibrinogenemia, 16.6 (6.6–42.0); Lp(a) excess, 3.5 (1.5–8.4); all three combined 35.0 (5.7–199.8). Given in vitro evidence that Hcy, Lp(a), and fibrinogen interact to promote atherothrombosis, combined hyperhomocysteinemia, hyperfibrinogenemia, and Lp(a) excess may contribute to the high incidence of vascular disease sequelae experienced by dialysis patients, which is inadequately explained by traditional CVD risk factors. Controlled, prospective studies of well-characterized maintenance dialysis cohorts are urgently required to substantiate this hypothesis.

Hyperhomocysteinemia, either fasting or after oral methionine loading, appears to be an independent risk factor for coronary heart disease (CHD). It remains unclear whether fasting total homocysteine determination alone adequately detects the full spectrum of hyperhomocysteinemic individuals. We measured fasting and 4-h post methionine loading (0.1 g L-methionine/kg body weight) total plasma homocysteine in 274 participants in The NHLBI Family Heart Study, a population-based investigation of genetic and non-genetic determinants of CHD. Of the total number ( n = 47) of hyperhomocysteinemic persons, 43% (2047) were identified only by methionine loading, while 32% (1547) of the total number, and 75% of those with post-methionine loading hyperhomocysteinemia only (1520), had fasting total homocysteine concentrations below the 75th percentile (10.7 μmol/l). We conclude that fasting total plasma homocysteine determination alone fails to identify a sizable percentage (> 40%) of persons who may have clinically relevant hyperhomocysteinemia post methionine loading.

Hyperhomocysteinemia occurs frequently in end-stage renal disease (ESRD), but its prevalence in comparison with traditional cardiovascular disease (CVD) risk factors is unknown. Fasting total plasma homocysteine, potential determinants of plasma homocysteine (i.e., plasma B-vitamins and serine), total and HDL cholesterol, glucose, and creatinine, were determined in 24 ESRD patients on dialysis, and 24 age, gender, and race matched Framingham Offspring Study controls with normal renal function. Presence of clinical CVD and CVD risk factors was established by standardized methods. Mean plasma homocysteine was markedly higher in the ESRD patients versus controls (22.7 vs. 9.5 mumol/l). ESRD patients were 33 times more likely than controls to have hyperhomocysteinemia (> 15.8 mumol/l) (95% confidence interval, 5.7-189.6). Hyperhomocysteinemia persisted in the ESRD patients despite normal to supernormal B-vitamin status. Plasma serine levels below the tenth percentile of the control distribution were found in 75% of the ESRD patients. Oral serine supplementation caused a 37% increase in mean plasma serine, but had no effect on plasma homocysteine in four ESRD patients with supernormal plasma folate, low plasma serine, and hyperhomocysteinemia. Given its unusually high prevalence, improved management of hyperhomocysteinemia might reduce CVD sequelae in ESRD.