Atherosclerosis and folic acid supplementation trial in chronic renal failure: Baseline results

The Effect of Folic Acid Supplementation on Endothelial Function and Arterial Stiffness Markers in Adults: A Systematic Review and Meta-Analysis

Folic acid might improve endothelial function, but the results are inconclusive. This systematic review evaluated the effect of folic acid supplementation on endothelial parameters and arterial stiffness in adults. The study protocol was registered with the PROSPERO database (CRD42021290195). The PubMed, Web of Sciences, Cochrane and Scopus databases were searched to identify English-language randomised controlled trials of the effect of folate supplementation on arterial stiffness and endothelial function markers in adults. There were significant differences between the effect of folic acid and placebo on flow-mediated dilation (random-effects model, standardized mean differences (SMD): 0.888, 95% confidence interval (CI): 0.447, 1.329, p < 0.001) and monocyte chemotactic protein 1 (random-effects model, SMD: -1.364, 95% CI: -2.164, -0.563, p < 0.001), but there was no significant difference in the central pulse wave velocity (fixed-effects model, SMD: -0.069, 95% CI: -0.264, 0.125, p = 0.485) and peripheral pulse wave velocity (fixed-effects model, SMD: -0.093, 95% CI: -0.263, 0.077, p = 0.284). In conclusion, folic acid might have a favourable effect on endothelial function but may not affect arterial stiffness. Further studies are needed to confirm these results.

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.

Folic Acid Attenuates Vascular Endothelial Cell Injury Caused by Hypoxia via the Inhibition of ERK1/2/NOX4/ROS Pathway

Coronary artery disease is a disease with high morbidity and mortality, in which vascular endothelial dysfunction plays an important role. Hypoxia leads to the inflammation and oxidative stress in endothelial cells, which results in the endothelial injury. The present study was designed to investigate the protective effect and mechanism of folic acid on hypoxia-induced injury in human umbilical vein endothelial cells (HUVEC). Cell counting Kit was used to detect cell survival rate, and apoptotic cells were detected by Hoechst 33258 staining. Intracellular reactive oxygen species (ROS) level was measured using dichloro-dihydro-fluorescein diacetate staining. Western blot was used to determine the protein expressions of extracellular signal protein kinase 1/2 (ERK1/2) and phosphorylated ERK1/2 (p-ERK1/2), NOX4 subunit of NAPDH and endothelial nitric oxide synthase (eNOS). Folic acid significantly increased the cell survival rate and decreased the apoptosis of HUVECs treated with folic acid compared with hypoxia-treated HUVEC. Folic acid also decreased ROS level, while it increased the nitrite content in HUVECs. In addition, folic acid decreased protein expressions of NOX4 and p-ERK1/2, while it increased the protein expression of eNOS in HUVECs. Furthermore, N-acetyl cysteine (NAC), the antioxidant, had similar effect on the cell survival rate and the apoptosis. In addition, DPI (NOX4 inhibitor) and U0126 (ERK1/2 inhibitor) rather than NAC decreased the protein expression of NOX4. NAC, DPI, and U0126 increased the protein expression of eNOS. Furthermore, U0126 rather than DPI and NAC decreased the protein expression of p-ERK1/2. Taken together, the results suggested that hypoxia decreased the cell survival rate and induced apoptosis via ERK1/2/NOX4/ROS pathway, which could be the target of folic acid in protecting the HUVECs from injury caused by hypoxia.

Intima-media thickness is a useful marker of the extent of coronary artery disease in patients with impaired renal function

OBJECTIVE

The aim of the study was the assessment of intima-media thickness (IMT) in peripheral arteries (the carotid and the femoral artery) and its correlation with the extent of coronary artery disease (CAD). The second task was the analysis of the renal function's influence within IMT complex.

METHODS

231 patients (men, mean age 52.8), who had undergone coronary angiography due to symptoms of CAD were enrolled. The ultrasound measurement of IMT in the common carotid artery (CCA), carotid bulb and common femoral artery (CFA) was performed. The relationship between IMT, renal function and the extent of CAD was evaluated.

RESULTS

Significantly higher values of IMT in the peripheral arteries were observed in patients with CAD than in those without (CCA-0.91 vs 0.61 mm, carotid bulb-1.31 vs 0.67, CFA-1.38 vs 0.63 respectively, p<0.0001). The GFR values in the CAD patients significantly negatively correlated with IMT complex in CCA (p<0.001) and carotid bulb (p<0.05). Lower values of GFR in patients with three-vessel disease were observed than in those patients with one- or two-vessel disease (p<0.05). In multifactoral analysis (post-hoc NIR test) we found that glomerular filtration rate (GFR) is strongly determined by age (p<0.0001), BMI (p<0.0001), value of carotid intima-media thickness (p<0.001), value of IMT in the carotid bulb (p<0.02) and the treatment with ACE-I (p<0.05). In multifactoral analysis we did not find any statistical influence of lipid profile and glucose disturbances on GFR.

CONCLUSIONS

Higher peripheral artery IMTs in patients with CAD than in those without and patients with three-vessel disease indicate that IMT may be used as an early marker of atherosclerosis and reflect the severity of CAD. A significant negative correlation between the value of a GFR and the IMT confirmed the usefulness of this noninvasive method for the estimation of preclinical stages of atherosclerotic changes' development in patients with impaired renal function.

Homocysteine and asymmetric dimethylarginine (ADMA): biochemically linked but differently related to vascular disease in chronic kidney disease

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is formed by methylation of arginine residues in proteins and released after proteolysis. In this reaction, S-adenosylmethionine is methyldonor and S-adenosylhomocysteine the demethylated product. ADMA and homocysteine are thus biochemically linked. Both plasma homocysteine and ADMA concentrations are increased in patients with renal dysfunction, probably as a result of an impairment in their metabolic, but not urinary, clearance. Hyperhomocysteinemia has been associated with an increased risk of cardiovascular disease in end-stage renal disease, especially in patients without malnutrition and inflammation. Also, plasma ADMA levels have been associated with cardiovascular disease in renal failure patients. Both homocysteine and ADMA are thought to mediate their adverse vascular effects by impairing endothelial, nitric oxide-dependent function resulting in decreased vasodilatation, increased smooth muscle cell proliferation, platelet dysfunction and increased monocyte adhesion. At the same time, it has been shown that the correlation between plasma ADMA and homocysteine is weak and that, in renal patients, the association of plasma ADMA carotid intima-media thickness, cardiovascular events and overall mortality is independent of homocysteine. This indicates that the negative vascular effects of ADMA and homocysteine have a different etiology. Treatment with folic acid substantially lowers homocysteine, but not ADMA concentration. So far, homocysteine-lowering therapy has not been very successful in decreasing cardiovascular disease. In patients with renal failure, ADMA reduction may be an interesting new goal in the prevention of cardiovascular disease.

Association of Carotid Intima-Medial Thickness and Indices of Arterial Stiffness With Cardiovascular Disease Outcomes in CKD

BACKGROUND

Indices of arterial structure and stiffness are proposed as surrogate markers of cardiovascular disease in patients with chronic kidney disease (CKD), but no study examined multiple markers in the same population.

STUDY DESIGN

Prospective observational study.

SETTING & PARTICIPANTS

315 subjects with stages 4 to 5 CKD, aged 24 to 79 years (mean age, 56.6 +/- 13.6 [SD] years), enrolled in the Atherosclerosis and Folic Acid Supplementation Trial.

PREDICTORS

Carotid arterial intima-medial thickness (IMT; n = 315) and indices of arterial stiffness (n = 207), including aortofemoral pulse wave velocity (PWV[a-f]), systemic arterial compliance (SAC), and carotid-derived augmentation index.

OUTCOMES

The primary outcome was a composite of all fatal and nonfatal cardiovascular events.

RESULTS

During follow-up (median, 3.6 years), 95 cardiovascular events occurred. On Cox proportional-hazard modeling, mean maximum IMT, PWV(a-f), and SAC were predictive of the composite clinical end point of all cardiovascular events, but carotid-derived augmentation index was not (hazard ratio [HR] for every 0.01-mm increase in IMT, 1.09; P = 0.001; 95% confidence interval [CI], 1.03 to 1.14; HR for every 1-m/s increase in PWV(a-f), 1.18; P < 0.001; 95% CI, 1.12 to 1.25; HR for every 0.01-U/mm Hg decrease in SAC, 0.98; P = 0.01; 95% CI, 0.97 to 0.99). After adjustment for age, sex, blood pressure, diabetes, past cardiovascular disease, cholesterol level, and smoking, PWV(a-f) remained a significant independent predictor of cardiovascular events (adjusted HR, 1.12; P = 0.001; 95% CI, 1.05 to 1.20), but IMT and SAC did not.

LIMITATIONS

Study power to analyze differences between predialysis and dialysis stages of CKD.

CONCLUSIONS

PWV(a-f) is the only arterial index independently associated with cardiovascular outcome in patients with CKD.

Folic acid 5 or 15 mg/d similarly reduces plasma homocysteine in patients with moderate-advanced chronic renal failure

BACKGROUND

Hyperhomocysteinaemia is an independent risk factor for cardiovascular disease with a remarkable prevalence in patients with chronic renal failure (CRF). Low doses of folic acid (FA) with or without vitamin B6 and B12 has been shown to effectively reduce plasma homocysteine (Hcy). The aim of this study was to compare the short-term effects of two different oral doses of FA (5 vs 15 mg/d) on plasma Hcy levels in subjects suffering from moderate-severe CRF.

METHODS

A double-blind, double-dummy, comparative, two-stage randomised study was performed. Seventeen patients aged 45-71 years, with glomerular filtration rates between 15.4-50 mL/min 1.73/m2 were randomly assigned to receive FA 5 mg/d (FA-5, n: 8) or FA 15 mg/d (FA-15, n: 9) for 30 days. At the end of this 30-day double-blind period, all the participants were placed on FA 5 mg/d (open period), for 5 additional months. Both groups were also supplemented with vitamins B1, B6 and B12 throughout the trial. Blood samples were drawn at 0, 15, 30, 90 and 180 days to assess Hcy, complete blood count (CBC) and sequential multichannel analysis (SMA). Chest X-ray and a 12-lead electrocardiogram (ECG) were also performed.

RESULTS

Plasma Hcy (mean +/- SEM) decreased from 27.9 +/- 1.4 (baseline) to 15.1 +/- 0.6, 13.3 +/- 0.9, 14.1 +/- 0.5 and 13.8 +/- 0.5 micromol/L (FA-5) and from 28.8 +/- 2.7 to 15.6 +/- 1.2, 14.4 +/- 1.3, 13.0 +/- 0.7 and 13.1 +/- 0.6 micromol/L (FA-15) at days 15, 30, 90 and 180, respectively. (P < 0.01 from day 15 to 180 vs baseline for both groups with no differences between them). Renal function remained stable throughout the entire period of the study in all but one patient in whom it deteriorated to pre-end stage disease. No adverse cardiovascular events developed during the trial.

CONCLUSION

Both folic acid doses induced a significant and similar decrease in plasma Hcy in subjects with moderate-severe chronic renal failure. The possible dose-related effect of this approach in reducing the risk of accelerated sclerotic vascular disease and cardiovascular events in this especially vulnerable population should be a matter of further investigation.

Cardiovascular morbidity and mortality in the Atherosclerosis and Folic Acid Supplementation Trial (ASFAST) in chronic renal failure: a multicenter, randomized, controlled trial

OBJECTIVES

The Atherosclerosis and Folic Acid Supplementation Trial (ASFAST) aimed to establish whether high-dose folic acid would slow the progression of atherosclerosis and reduce cardiovascular events in patients with chronic renal failure (CRF).

BACKGROUND

Hyperhomocysteinemia is a potential contributor to the high rates of cardiovascular morbidity and mortality in patients with CRF.

METHODS

A total of 315 subjects with CRF, mean age 57 years (range 24 to 79 years) were randomized to 15 mg folic acid daily or placebo and followed for a median of 3.6 years. The primary intima-media thickness (IMT) and clinical end points were: rate of progression of mean maximum carotid IMT and a composite of myocardial infarction (MI), stroke, and cardiovascular death. Secondary end points included all cardiovascular events and change in pulse wave velocity, systemic arterial compliance and augmentation index. Data were analyzed by intention-to-treat.

RESULTS

Plasma total homocysteine was reduced by 19% in the folic acid group. There was no significant difference between the treatment groups in rate of change of IMT or any measure of artery function. Seventy-seven events occurred in the folic acid group (14.9 per 100 patient-years) as compared with 86 in the placebo group (16.3 per 100 patient-years). The rates of the primary and secondary clinical end points at five years were not significantly different after adjustment for baseline differences between the groups (adjusted hazard ratio for MI, stroke, and cardiovascular death: 0.98 [95% confidence interval: 0.66 to 1.47]; p = 0.94; for all cardiovascular events: 0.95 [95% confidence interval: 0.69 to 1.30]; p = 0.75).

CONCLUSIONS

High-dose folic acid does not slow atheroma progression or improve cardiovascular morbidity or mortality in patients with CRF.

Association between carotid artery intima-media thickness and cardiovascular risk factors in CKD

BACKGROUND

Common carotid artery intima-media thickness (CCA-IMT) correlates with cardiovascular events in the general population and is an independent predictor of cardiovascular mortality in the hemodialysis population. It has not been evaluated extensively in patients with chronic kidney disease.

METHODS

CCA-IMT was measured by using high-resolution B-mode ultrasonography, and glomerular filtration rate (GFR) was measured by means of EDTA clearance. Cardiovascular risk factors assessed included homocysteine and lipoprotein(a) levels, as well as smoking, blood pressure, and cholesterol level.

RESULTS

One hundred fourteen patients were studied; mean measured GFR was 29.6 +/- 18.4 mL/min/1.73 m2 (0.49 +/- 0.31 mL/s). CCA-IMT was significantly elevated (0.59 +/- 0.22 cm) compared with a control group (0.44 +/- 0.08 cm; P = 0.0012). CCA-IMT increases with age (P < 0.0001) and low-density lipoprotein level (P = 0.048) and decreases with high-density lipoprotein level (P = 0.001) and being white (P = 0.014).

CONCLUSION

This study suggests that arterial changes occur early in the course of renal disease progression and may be related to dyslipidemia in the early stages.

Young Hemodialysis Patients Are Exposed to Hyperhomocysteinemia

OBJECTIVE

Homocysteine is one of the cardiovascular risk factors in hemodialysis (HD) patients. Studies were performed to assess the effects of folic acid on pulse wave velocity (PWV) in HD patients.

METHODS

In a cross-sectional study, plasma total homocysteine (tHcy) was measured in 49 patients on maintenance HD. Ten HD patients younger than 45 years old entered the prospective study. Monthly changes in PWV were compared before and during folic acid treatment.

RESULTS

Younger HD patients had higher tHcy (r = -0.53, n = 49, P < .001). Patients who manifested myocardial ischemia (37 +/- 3 nmol/mL) possessed higher tHcy than those who did not (30 +/- 3 nmol/mL, P < .05). In prospective study, folic acid treatment (10 to 20 mg/d) failed to alter blood pressure and biochemical parameters, including lipids, calcium, phosphate, and parathormone. However, in association with a decrease in tHcy (46 +/- 5 to 27 +/- 3 nmol/mL, n = 10, P < .005), progressive increases in PWV (33 +/- 8 to 3 +/- 6 cm/sec/month, P < .01) were stopped.

CONCLUSIONS

The present findings indicate that young HD patients are exposed to severe hyperhomocysteinemia, and suggest that relatively large doses of folic acid attenuate progressive increases in PWV of young or middle-age HD patients.

Folic acid supplementation to prevent adverse events in individuals with chronic kidney disease and end stage renal disease

PURPOSE OF REVIEW

This review summarizes our current understanding of the role of folate in the treatment of hyperhomocysteindemia and the prevention of cardiovascular disease in patients with chronic kidney disease and end stage renal disease. Relevant papers published between 2003 and 2004 are referenced.

RECENT FINDINGS

With the exception of one paper, recent therapeutic studies supported previous findings that folate therapy achieves only a modest reduction in plasma homocysteine and seldom normalizes homocysteine. Large prospective studies are under way to evaluate the causal relationship between homocysteine and cardiovascular risk. Recent work supports earlier data that suggested that homocysteine inflicts its damage by oxidative stress. A newly described consequence of hyperhomocysteindemia is DNA hypomethylation and alteration of gene expression. A recent study in the general population suggested that while folate may lower homocysteine it does not improve endothelial function in individuals without cardiovascular disease.

SUMMARY

The causes of hyperhomocysteindemia in renal failure remain obscure. The possibilities include impairment of both renal and extrarenal metabolic pathways by uraemia. Hyperhomocysteindemia is associated in some but not all studies with an increased risk for cardiovascular disease. A low homocysteine may reflect malnutrition and predict a poor outcome. Folate achieves modest reductions of homocysteine in some but not all studies. There are no data to support therapy with very high-dose folic acid. Hyperhomocysteindemia impairs endothelial function which is not adequately reversed by folate.