Effects of folinic acid on forearm blood flow in patients with end-stage renal disease

Interventions for lowering plasma homocysteine levels in dialysis patients

BACKGROUND

People with end-stage kidney disease (ESKD) have high rates of cardiovascular events. Randomised controlled trials (RCTs) of homocysteine-lowering therapies have not shown reductions in cardiovascular event rates in the general population. However, people with kidney disease have higher levels of homocysteine and may have different mechanisms of cardiovascular disease. We performed a systematic review of the effect of homocysteine-lowering therapies in people with ESKD.

OBJECTIVES

To evaluate the benefits and harms of established homocysteine lowering therapy (folic acid, vitamin B6, vitamin B12) on all-cause mortality and cardiovascular event rates in patients with ESKD.

SEARCH METHODS

We searched Cochrane Kidney and Transplant's Specialised Register to 25 January 2016 through contact with the Information Specialist using search terms relevant to this review.

SELECTION CRITERIA

Studies conducted in people with ESKD that reported at least 100 patient-years of follow-up and assessed the effect of therapies that are known to have homocysteine-lowering properties were included.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data using a standardised form. The primary outcome was cardiovascular mortality. Secondary outcomes included all-cause mortality, incident cardiovascular disease (fatal and nonfatal myocardial infarction and coronary revascularisation), cerebrovascular disease (stroke and cerebrovascular revascularisation), peripheral vascular disease (lower limb amputation), venous thromboembolic disease (deep vein thrombosis and pulmonary embolism), thrombosis of dialysis access, and adverse events. The effects of homocysteine-lowering therapies on outcomes were assessed with meta-analyses using random-effects models. Prespecified subgroup and sensitivity analyses were conducted.

MAIN RESULTS

We included six studies that reported data on 2452 participants with ESKD. Interventions investigated were folic acid with or without other vitamins (vitamin B6, vitamin B12). Participants' mean age was 48 to 65 years, and proportions of male participants ranged from 50% to 98%.Homocysteine-lowering therapy probably leads to little or no effect on cardiovascular mortality (4 studies, 1186 participants: RR 0.93, 95% CI 0.70 to 1.22). There was no evidence of heterogeneity among the included studies (I² = 0%). Homocysteine-lowering therapy had little or no effect on all-cause mortality or any other of this review's secondary outcomes. All prespecified subgroup and sensitivity analyses demonstrated little or no difference. Reported adverse events were mild and there was no increase in the incidence of adverse events from homocysteine-lowering therapies (3 studies, 1248 participants: RR 1.12, 95% CI 0.51 to 2.47; I(2) = 0%). Overall, studies were assessed as being at low risk of bias and there was no evidence of publication bias.

AUTHORS' CONCLUSIONS

Homocysteine-lowering therapies were not found to reduce mortality (cardiovascular and all-cause) or cardiovascular events among people with ESKD.

Folate administration decreases oxidative status and blood pressure in postmenopausal women

PURPOSE

The purpose of this study was to evaluate whether folate exerts antioxidant effects in postmenopausal women and whether this effect is related to folate-induced modification of 24-h ambulatory blood pressure (BP).

METHODS

Double-blind placebo-controlled study performed in 30 apparently healthy postmenopausal women recruited at the outpatient service of University Hospital. Women, free from hormones or substances possibly interfering with the investigated parameters, were randomized to receive orally for 3 weeks placebo (n = 15) or 15 mg/day of 5-methyltetrahydrofolate (5-MTHF; n = 15). Whole-blood free oxygen radicals test (FORT), free oxygen radical defence (FORD), lipids, glucose, insulin, insulin resistance [homeostatic model assessment for insulin resistance (HOMA-IR)], homocysteine and 24-h ambulatory BP values were evaluated.

RESULTS

In the entire group of women, FORT was independently and inversely related to the day-night difference of diastolic (r = 0.420; p = 0.03) and mean BP (r = 0.497; p = 0.01). Placebo did not affect any biochemical or BP parameter. 5-MTHF reduced FORT (-71.5 ± 98.2; p = 0.02) and increased FORD (0.5 ± 0.9; p = 0.05), decreased insulin (p = 0.01), HOMA-IR (p = 0.0002) and homocysteine (p = 0.008). During 5-MTHF, night-time mean (p = 0.001) and diastolic BP (p = 0.002) decreased of about 5 mmHg and the day-night difference of mean (p = 0.001) and diastolic BP (p = 0.002) contemporaneously increased. FORT reduction was related to the amplification of the nocturnal decline of mean (0.697; p = 0.006) and diastolic BP (r = 0.777; p = 0.002) and to the amplification of the day-night difference of diastolic BP (r = 0.63; p = 0.015).

CONCLUSIONS

Present data show a clear reduction of oxidative stress during 5-MTHF administration and a strong correlation between this decrease and the nocturnal decline of BP. The possible link between the two is worthy to be explored.