Homocysteine and cardiovascular disease: current evidence and future prospects

Novel cardiovascular risk factors

In addition to the well-established cardiovascular risk factors of elevated total and low-density lipoprotein cholesterol, hypertension, and cigarette smoking, multiple additional factors are suspected culprits in both the development and progression of atherothrombosis. It is key for the clinician to critically review research findings utilizing an organized framework in order to credibly advise the patient with cardiovascular disease or at risk for its development. The current evidence and recommendations regarding the following "novel"or "emerging" risk factors will be reviewed: lipoprotein(a), hyperhomocysteinemia, C-reactive protein, infectious processes, fibrinogen, and microalbuminuria.

Total plasma homocysteine and restenosis after percutaneous coronary angioplasty: current evidence

BACKGROUND

Restenosis after percutaneous coronary angioplasty (PTCA) remains an important limitation of this procedure.

AIM

To assess the relationship between homocysteine levels and restenosis after PTCA, and discuss the potential benefit of homocysteine-lowering therapy.

METHOD

MEDLINE-based literature review.

RESULTS

The conflicting literature on the association between homocysteine levels and restenosis after PTCA can partially be explained by differences in methodology. Depending on the type of studies considered, a pooling of data resulted in a 22%-36% risk reduction of restenosis in lesions exposed to low homocysteine levels. The strongest reduction was found in balloon-only treated lesions (42%), while only a trend (14%) was seen in stented lesions. Based on the only available trial, homocysteine-lowering therapy yielded a 54% restenosis rate reduction, 76% in balloon-only treated lesions and 31% in stented lesions. Furthermore, homocysteine-lowering therapy provided a significant clinical benefit with a 40% relative reduction in major adverse events at 6 months' follow-up.

CONCLUSIONS

This review suggests that plasma homocysteine is a modifiable risk factor for restenosis, which when lowered improves outcome after PTCA. This inexpensive treatment with virtually no side-effects could therefore be considered as adjunctive therapy for patients undergoing PTCA, while awaiting results from further studies.

Niacin extended-release/lovastatin: combination therapy for lipid disorders

The new combination of niacin extended-release (ER) and lovastatin (Advicor, Kos pharmaceuticals), is a powerful lipid modifying agent and takes advantage of the different mechanisms of action of its two components. Niacin decreases hepatic atherogenic apolipoprotein (apo) B production whereas lovastatin increases apoB removal. Whereas niacin potently increases high density lipoprotein (HDL) levels by decreasing hepatic removal of antiatherogenic apoA-I particles, 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase inhibitors ('statins') appear to increase production of apoA-I. Although there is no outcome data with this combination product, each component has been independently associated with a reduction of cardiovascular event risk by approximately 25 - 35%. The results of a long-term trial in 814 patients, where > 600 had been treated for 6 months and > 200 for 1 year, found reductions of 45 and 42% in low density lipoprotein cholesterol and triglycerides, respectively, at the maximum dose (niacin ER 2000 mg/ lovastatin 40 mg). HDL cholesterol increased by 41%. In addition, the combination decreased lipoprotein (a) by 25% and C-reactive protein by 24%. The niacin ER/lovastatin combination was generally well-tolerated. Flushing was the most common side effect, with approximately 10% of patients intolerant to niacin ER/lovastatin. Hepatotoxicity in this study was 0.5% and myopathy did not occur. Recent studies indicate that niacin can be used safely in diabetic patients who have good glucose control (HbA(1c) < 9%). Once-daily niacin ER/lovastatin exhibits potent synergistic actions on multiple lipid risk factors and represents an effective new agent in the clinical management of dyslipidaemia. Outcome studies are needed to evaluate if combination therapy would result in additive effects on morbidity and mortality.

Folic acid enhances endothelial function and reduces blood pressure in smokers: a randomized controlled trial

OBJECTIVE

Cigarette smoking is associated with increased plasma homocysteine concentrations, endothelial dysfunction and arterial stiffening. Homocysteine per se induces endothelial dysfunction and arterial stiffening and might account, at least partly, for the vascular abnormalities observed in smokers. We sought to determine whether folic acid supplementation, by reducing plasma homocysteine concentrations, enhanced endothelial function and reduced arterial stiffness in smokers.

DESIGN

Double-blind, randomized controlled, parallel-group, trial.

SETTING

Academic medical centre.

SUBJECTS

A consecutive sample of 24 healthy cigarette smokers (age 37.8 +/- 2.5 years, mean +/- SEM).

INTERVENTION

Subjects were randomly assigned to 4-week folic acid 5 mg day-1 or placebo.

MAIN OUTCOME MEASURES

The following were measured before and after treatment: (i) peripheral vasoreactivity (forearm arterial blood flow, FABF) during intra-arterial administration of endothelium-dependent (acetylcholine 1.5, 4.5 and 15 microg min-1) and endothelium-independent (sodium nitroprusside 1, 2 and 4 microg min-1) vasodilators; (ii) carotid-femoral pulse-wave velocity (PWV); (iii) blood pressure (BP).

RESULTS

Folic acid reduced homocysteine concentrations (10.8 +/- 0.6 vs. 8.2 +/- 0.5 micromol L-1, P < 0.001) and enhanced endothelium-dependent vasodilatation during each acetylcholine infusion rate (ratio between the FABF in the infused and control arm during increasing infusion rates at baseline 1.09 +/- 0.03 vs. 1.41 +/- 0.09 after treatment, P < 0.01; 1.39 +/- 0.07 vs. 1.83 +/- 0.12, P < 0.01; 1.65 +/- 0.16 vs. 2.72 +/- 0.36, P < 0.05) whilst endothelium-independent vasodilatation was unaffected. A significant fall in BP was also observed (mean BP 88 +/- 2 vs. 83 +/- 1 mmHg, P < 0.01). By contrast, PWV did not significantly change (8.4 +/- 0.3 vs. 7.8 +/- 0.4 m s-1). No significant changes in plasma homocysteine concentrations, FABF, BP, and PWV were observed in the placebo group. A multiple regression analysis showed that changes in folic acid plasma concentrations independently predicted both FABF changes during maximal acetylcholine-mediated vasodilatation (P < 0.01) and BP changes (P = 0.01).

CONCLUSIONS

Short-term folic acid supplementation significantly enhanced endothelial function and reduced BP in young chronic smokers. These effects were largely independent from the homocysteine lowering effects. Thus, a simple, nontoxic, and relatively inexpensive vitamin intervention might be useful in primary cardiovascular prevention in this high-risk group.