Cardiovascular morbidity and endothelial dysfunction in chronic haemodialysis patients: is homocyst(e)ine the missing link?

BACKGROUND: Haemodialysis patients exhibit an excessive burden of atherothrombotic disease, which is not explained adequately by traditional risk factors. Hyperhomocyst(e)inaemia, a consistent finding in uraemic patients, is now widely recognized as an independent risk factor for vascular disease. The aim of this study was to examine the hypothesis that hyperhomocyst(e)inaemia is associated with cardiovascular complications in dialysed patients.
METHODS: In a cohort of 63 stable chronic haemodialysis patients, we examined the causal relationship between hyperhomocyst(e)inaemia and vascular endothelial and haemostatic function. All their markers were determined before and after an 8-week course of a 10 mg per day oral folate supplementation, a manoeuvre known to decrease hyperhomocyst(e)inaemia in uraemic patients.
RESULTS: History of at least one cardiovascular atherothrombotic event was present in 47.6% of the haemodialysed patients, and radiographic evidence of vascular calcifications in 70%. Hyperhomocyst(e)inaemia was found in all patients, averaging 3.5-fold the upper limit of normal values (P<0.001), despite the lack of clinical and biological evidence of malnutrition. Fibrinogen, von Willebrand factor and plasminogen activator inhibitor type 1, but not endothelin 1, were significantly higher in haemodialysis patients than in controls. After adjustment for all variables, past history of cardiovascular events was independently associated with higher levels of homocyst(e)inaemia only (odds ratio (OR) 1.06; 95% confidence interval (CI) 1.01-1.12; P<0.026). The presence of aortic calcifications was independently and significantly associated with age (OR 1.37; 95% CI 1.07-1.75; P<0.025), homocyst(e)inaemia (OR 1.14; 95% CI 1.02-1.27; P<0.05) and fibrinogen concentration only (OR 9.74; 95% CI 1.25-75.2; P<0.05). None of the endothelial haemostatic factors was, however, related to homocyst(e)ine levels. Mid-term folate supplementation decreased plasma homocyst(e)ine levels significantly without achieving normal values. No significant change of endothelial-haemostatic markers was observed, however, despite the drop in plasma homocyst(e)ine.
CONCLUSIONS: Hyperhomocyst(e)inaemia is associated with increased cardiovascular risk in haemodialysis patients. Folate supplementation was partially effective in lowering hyperhomocyst(e)inaemia, but its usefulness in terms of reduction in cardiovascular morbidity and mortality remains to be determined in prospective trials.