Effect of high dose folic acid therapy on hyperhomocysteinemia in hemodialysis patients: results of the Vienna multicenter study

The effect of B-vitamins on the prevention and treatment of cardiovascular diseases: a systematic review and meta-analysis

CONTEXT

Previous research evaluating the effects in B-vitamins on the prevention and treatment of cardiovascular disease (CVD) has substantial limitations and lacks recently published large prospective studies; hence, conducting an updated meta-analysis is needed.

OBJECTIVE

We investigated the association between vitamin B status and human CVD development in order to provide more specific advice about vitamin B intake for those at risk of CVD.

DATA SOURCES

Relevant articles were identified by JSTOR, PubMed, and ProQuest databases.

DATA EXTRACTION

Key words used to identify the studies included the different combinations of B-vitamins, folate, folic acid, vitamin B6, vitamin B12, homocysteine, cardiovascular disease, stroke, coronary disease, myocardial infarction, and cerebrovascular and transient ischemic attack. The database search was supplemented by hand-searching of reference lists of selected articles.

DATA ANALYSIS

Pooled estimates were calculated from the mean differences using a random-effects model.

RESULTS

Supplementation with folic acid was reported to have a clinical benefit of significantly reducing carotid intima-media thickness. Higher intakes of folic acid, vitamin B6, and vitamin B12 were generally associated with a lower risk of CVD in the general population, except in those without normal renal function and those with unstable angina or past non-ST-elevation myocardial infarction.

CONCLUSION

Vitamin B supplementation resulted in the greatest cardiovascular benefit in those with normal renal function and without unstable angina or non-ST-elevation myocardial infarction recently. Factors such as age, gender, and genetic polymorphisms contribute to varying effects.

Homocysteine exchange across skeletal muscle in patients with chronic kidney disease

Sites and mechanisms regulating the supply of homocysteine (Hcy) to the circulation are unexplored in humans. We studied the exchange of Hcy across the forearm in CKD patients (n = 17, eGFR 20 ± 2 ml/min), in hemodialysis (HD)-treated patients (n = 14) and controls (n = 9). Arterial Hcy was ~ 2.5 folds increased in CKD and HD patients (p < 0.05-0.03 vs. controls). Both in controls and in patients Hcy levels in the deep forearm vein were consistently greater (+~7%, p < 0.05-0.01) than the corresponding arterial levels, indicating the occurrence of Hcy release from muscle. The release of Hcy from the forearm was similar among groups. In all groups arterial Hcy varied with its release from muscle (p < 0.03-0.02), suggesting that muscle plays an important role on plasma Hcy levels. Forearm Hcy release was inversely related to folate plasma level in all study groups but neither to vitamin B12 and IL-6 levels nor to muscle protein net balance. These data indicate that the release of Hcy from peripheral tissue metabolism plays a major role in influencing its Hcy plasma levels in humans and patients with CKD, and that folate is a major determinant of Hcy release.

Food-Derived Uremic Toxins in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) have a higher cardiovascular risk compared to the average population, and this is partially due to the plasma accumulation of solutes known as uremic toxins. The binding of some solutes to plasma proteins complicates their removal via conventional therapies, e.g., hemodialysis. Protein-bound uremic toxins originate either from endogenous production, diet, microbial metabolism, or the environment. Although the impact of diet on uremic toxicity in CKD is difficult to quantify, nutrient intake plays an important role. Indeed, most uremic toxins are gut-derived compounds. They include Maillard reaction products, hippurates, indoles, phenols, and polyamines, among others. In this review, we summarize the findings concerning foods and dietary components as sources of uremic toxins or their precursors. We then discuss their endogenous metabolism via human enzyme reactions or gut microbial fermentation. Lastly, we present potential dietary strategies found to be efficacious or promising in lowering uremic toxins plasma levels. Aligned with current nutritional guidelines for CKD, a low-protein diet with increased fiber consumption and limited processed foods seems to be an effective treatment against uremic toxins accumulation.

A Hypertrophic Spinal Pachymeningitis Patient With Factor V Leiden (G1691A), MTHFR C677T, MTHFR A1298C, PAI-1 4G-5G, Glycoprotein IIIa L33P Gene Mutations

Hypertrophic pachymeningitis (HP) is a rare clinical entity of diverse etiology, characterized by a chronic inflammation that causes dura thickening. Reports of Idiopathic hypertrophic cranial pachymeningitis (IHCP) were related to infections, trauma, tumors, and rheumatologic conditions. It was first described by Charcot and Joffroy regarding spinal meninges in 1869. HP has three stages; progressive radicular symptoms begin first, then muscle weakness and atrophy start. Findings such as paraplegia, loss of bladder and bowel control, and respiratory distress caused by intercostal and diaphragmatic denervation are considered the third stage of the disease. Especially in the cranial form of the disease, nerve ischemia and various cranial neuropathic findings may occur.

Factor V Leiden (G1691A), MTHFR C677T, MTHFR A1298C, and PAI-1 4G-5G gene mutation analysis were measured with an ABI Prism. In this case report, the authors present a case of hypertrophic mutations pachymeningitis with Factor V Leiden (G1691A), MTHFR C677T, MTHFR A1298C, PAI-1 4G-5G, Glycoprotein IIIa L33P gene.

In conclusion, we report a case of HP with Factor V Leiden (G1691A), MTHFR C677T, MTHFR A1298C, PAI-1 4G-5G, and Glycoprotein IIIa L33P gene mutations. We emphasize that the identification of pachymeningitis can be easily bypassed with the application of limited laboratory techniques. As in this case report, we think that these mutations should be analyzed in patients diagnosed with pachymeningitis.

Effective Homocysteine-Lowering Vitamin B Treatment in Peritoneal Dialysis Patients

Background

Hyperhomocysteinemia, a risk factor for atherosclerosis, is frequently detected in patients with renal failure. Vitamin B supplementation reduces but rarely normalizes homocysteine (Hcy) levels in hemodialysis patients. There are no data about the effects of vitamin B therapy on Hcy levels in patients on peritoneal dialysis (PD).

Aims

We performed this trial both to observe baseline plasma Hcy levels in PD patients and to assess the effects of vitamin B therapy on Hcy levels in continuous ambulatory PD patients.

Methods

We conducted a 6-month prospective study of the effects of vitamin B therapy on plasma Hcy levels. Biochemical analyses were obtained at baseline and after every phase of treatment with folic acid, folic acid plus vitamin B12, and folic acid plus vitamin B12plus vitamin B6. Eighteen of the 25 enrolled patients finished the study.

Results

Hyperhomocysteinemia was present in 83% of PD patients. We detected a trend toward a significant inverse relationship between baseline Hcy and folate levels. There were no significant correlations between baseline Hcy and vitamin B12, peritoneal membrane permeability, dialytic efficiency, or computed peritoneal Hcy clearance. We obtained an effective decrease in mean Hcy concentration from 20 to 14.8 μmol/L after folic acid and vitamin B12treatment. We observed a further reduction in mean Hcy level to 12.8 μmol/L using the triple therapy; 72% of patients normalized their Hcy value.

Conclusions

High doses of folic acid, vitamin B6, and vitamin B12normalize Hcy values in the majority of PD patients. This treatment may be important in reducing cardiovascular morbidity and mortality.

Undertreatment of Cardiac Risk Factors in Adolescents with Renal Failure

Cardiovascular disease (CVD) is the most common cause of death in adults with end-stage renal disease and after renal transplantation, and the relative excess of mortality is greatest in the young. The most likely explanation is the dramatic accumulation of both classical and uremic risk factors leading to atherosclerosis, uremic vasculopathy, and uremic cardiomyopathy. Prospective studies have established the significance of classical and uremic risk factors for the occurrence of CVD in the normal population and in the population with chronic renal disease alike. However, whether and to what degree modification of risk factors by therapeutic intervention can lower morbidity and mortality rates is as yet unknown.

Effect of Folic Acid therapy on Homocysteine Level in patients with Atherosclerosis or Buerger's Disease and in Healthy individuals: A clinical trial

Background

Hyperhomocysteinemia is considered a risk factor for atherosclerosis and some other vascular diseases such as Buerger’s disease.

Objective

The aim of this study was to measure the Homocysteine levels in 3 different groups of participants (Buerger’s disease, atherosclerosis patients, and healthy cases) and determine the therapeutic effect of folic acid therapy on homocysteine levels for these three groups

Methods

This nonrandomized clinical trial study was conducted in the vascular and endovascular surgery research center of Mashhad University of Medical Sciences in Mashhad, Iran. This interventional study consisted of 44 participants of which 22 patients had Buerger’s disease and a control group of 22 healthy individuals, all of which were enrolled in this study. All of the study’s participants had their serum homocysteine levels measured both before and after 12 weeks of folic acid (5mg/day) therapy. The data analysis used fo data analysis was a Chi square and t-test or their non-parametrical equivalents for data analysis by means of Statistical Package for the Social Sciences (SPSS) version 16

Results

The homocysteine levels were found to be significantly higher in patients with Buerger’s disease as compared to other groups before treatment with folic acid (Buerger = 21.8 ± 8.5 Mm/L, atherosclerosis = 17.3 ± 6.9, healthy = 13.8 ± 3.1; p < 0.001). After treatment with folic acid at 5 mg/daily for 12 weeks, the new plasma homocysteine levels did not show any significant difference (p = 0.38) between the Buerger’s disease group (14.6 ± 4.5 Mm/L) and atherosclerosis group (13.9 ± 4.7), but it was found to besignificantly higher in both groups when compared to the healthy group (10.7 ± 3.9, p<0.05). The plasma homocysteine level was reduced significantly when compared to its initial level in all 3 groups. The comparison of differences among three groups was found not to be significant (p=0.41)

Conclusions

It seems that supplementary therapy with folic acid at a dose of 5 mg daily may reduce the serum homocysteine levels significantly and may have a role in the development of vascular diseases such as Buerger’s disease. We suggest that folic acid should be considered as a routine agent in the Buerger’s disease therapeutic regime

Clinical trial registration

The trial was registered at the Thai Clinical Trials Registry (http://www.clinicaltrials.in.th) with the ID: TCTR20160601003.

Funding

This study was not funded by any organization.

Design and statistical issues in the homocysteinemia in kidney and end stage renal disease (HOST) study

The Homocysteine Study (HOST) Veterans Affairs Cooperative Studies Program No. 453, is a prospective, randomized, two arm, double blind study of patients with end stage renal disease (ESRD) or advanced chronic kidney disease (ACKD, defined as an estimated creatinine clearance of 30 ml/min or less). Its primary objective is to determine whether administration of high doses of three vitamins, folic acid, vitamin B6 and vitamin B12, to lower the high plasma homocysteine levels, will reduce all cause mortality. The secondary objectives are to examine whether the treatment lowers the incidence of myocardial infarction, stroke, amputation of a lower extremity, a composite of death and the foregoing three events, the plasma homocysteine level, and, in ESRD patients undergoing hemodialysis, thrombosis of the vascular access. A unique feature of this trial is that after initial evaluation at enrollment and one return visit the follow up is exclusively by phone (or, if necessary, by mail). The subject is contacted every three months throughout the duration of the study from a central location. The study drug is shipped to the patient from a central location rather supplied locally. In a two year enrollment period, 2006 patients are to be enrolled. The duration of the observation period is four to six years. Data will be stored and analyzed at a coordinating center. The study design has the power to detect a reduction in all cause mortality rate of 17%. Issues related to the unique features of the design of this study are discussed.

High doses of oral folate and sublingual vitamin B12 in dialysis patients with hyperhomocysteinemia

INTRODUCTION

Folic acid and vitamin B12, alone or in combination have been used to reduce homocysteine (Hcy) levels in dialysis patients.

OBJECTIVES

We aimed to assess the efficacy of high doses of oral folate and vitamin B12 in reducing plasma Hcy levels after a 12-week treatment.

PATIENTS AND METHODS

Thirty-two dialysis patients aged 10-324 months screened for hyperhomocysteinuria. Then cases with hyperhomocysteinemia received oral folate 10 mg/day with sublingual methylcobalamin 1 mg/day for 12 weeks. In pre- and post-intervention phases plasma Hcy concentration, serum folate, and vitamin B12 levels were measured. Changes in plasma Hcy, serum folate, and vitamin B12 concentrations were analyzed by paired t tests, and P values < 0.05 were considered significant.

RESULTS

Eighteen (56.2%) patients had hyperhomocysteinuria. Vitamin B12 and folate levels were normal or high in all cases. Two patients were lost due to transplant or irregular drugs consumption. Plasma Hcy levels were reduced in all, and reached normal values in 50%. A statistically significant differences between first Hcy levels with levels after intervention was found (95% CI, 5.1-8.9, P = 0.0001).

CONCLUSION

Oral folate 10 mg/day in combination with sublingual vitamin B12, 1 mg/day can be considered as a favorable treatment for hyperhomocysteinemia in dialysis patients.

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.

B vitamin supplementation improves cognitive function in the middle aged and elderly with hyperhomocysteinemia

OBJECTIVE

An intervention study was performed to determine if supplement containing folic acid, vitamin B₆, and vitamin B₁₂ could improve cognitive function and lower homocysteine in middle-aged and elderly patients with hyperhomocysteinemia.

METHODS

One hundred and four participants with hyperhomocysteinemia were recruited in Tianjin, China, aged 55-94 years old. Fifty-seven individuals with hyperhomocysteinemia were included in the intervention group (vitamin B group, which received 800 µg/day of folate, with 10 mg of vitamin B₆ and 25 µg of vitamin B₁₂) and 47 patients in the placebo group. The endpoint was the improvement in cognitive function as evaluated by Basic Cognitive Aptitude Tests (BCATs). All parameters were measured before and after the treatment period of 14 weeks.

RESULTS

The BCAT total score and four sub-tests scores (digit copy, Chinese character rotation, digital working memory, and recognition of meaningless figure) of BCAT at 14 weeks significantly increased only for the vitamin B group. Serum total homocysteine (tHcy) levels significantly decreased in the intervention group, while serum concentrations of folate, vitamin B₆, and vitamin B₁₂ significantly increased in the intervention group.

CONCLUSION

The results demonstrated that supplement containing folate, vitamin B₆, and vitamin B₁₂ in middle-aged and elderly patients with hyperhomocysteinemia could improve their cognitive function partly and reduce serum tHcy levels.

Altered folate receptor 2 expression in uraemic patients on haemodialysis: implications for folate resistance

BACKGROUND

Folate therapy reduces, but does not normalize homocysteine (Hcy) levels, frequently elevated in chronic kidney disease (CKD). The mechanisms of this folate resistance are unknown. Cellular acquisition of folate is mediated by folate receptors (FRs), whose expression is also modulated by folate status, through an Hcy-dependent regulation mechanism involving heterogeneous nuclear ribonucleoprotein-E1 (hnRNP-E1). Our objective was to evaluate whether an alteration of the FR2 (the form present in nucleated blood cells) expression is present in CKD patients on haemodialysis (HD), and its susceptibility to folate treatment.

METHODS

A population of chronic uraemic patients on HD was enrolled, along with a control group, and studies on FR2 receptor expression and related items were performed in plasma and mononuclear cells from peripheral blood. A subgroup of patients was treated with methyltetrahydrofolate for 1 month.

RESULTS

In HD, there was a significant reduction in FR2 protein expression compared with controls, not correlated with Hcy concentrations, while its mRNA levels were significantly increased. After folate treatment, there was a significant mRNA decrease, in the absence of significant changes in receptor protein expression. hnRNP-E1 gene and protein expression levels increased pre-treatment, while decreased post-treatment.

CONCLUSIONS

In HD, FR2 expression is altered in peripheral mononuclear cells, since its levels are decreased and are not responsive to variations in Hcy concentration, while the intracellular machinery (receptor mRNA and hnRNP-E1), possibly triggering its regulation, is conserved. These findings provide insight into the mechanisms of folate resistance in uraemia.

Management of hyperhomocysteinemia

Hyperhomocysteinemia is an established risk factor for cardiovascular disease. The modification of traditional cardiovascular risk factors has resulted in better morbidity and mortality outcomes, so the treatment of hyperhomocysteinemia is explored for a similar benefit. Vitamin B(6), vitamin B(12) and folate, as co-factors in the metabolism of homosyteine, are used in the treatment of hyperhomocysteinemia. Betaine, a methyl-donor in a separate homocysteine metabolism pathway, is also used to treat hyperhomocysteinemia. These supplements have been used in various doses and combinations for different periods of time, with favorable outcomes. There is still no concensus whether hyperhomocysteinemia can be treated with folic acid alone, or in combination with vitamin B(6) and vitamin B(12). The dose of the supplements required to normalize fasting homocysteine remains to be determined, especially in diabetic nephropathy, hemodialysis and renal transplant patients. The benefits from lowering homocysteine levels have mainly been demonstrated in surrogate cardiovascular outcomes. The treatment of hyperhomocysteinemia cannot be firmly advocated until there are trials that demonstrate a beneficial clinical endpoint. In patients who have cardiovascular disease in the absence of more established risk factors, investigation and treatment of hyperhomocysteinemia should be considered.

Therapy of hyperhomocysteinemia in hemodialysis patients: effects of folates and N-acetylcysteine

OBJECTIVE

Uremia represents a state where hyperhomocysteinemia is resistant to folate therapy, thus undermining intervention trials' efficacy. N-acetylcysteine (NAC), an antioxidant, in addition to folates (5-methyltetrahydrofolate, MTHF), was tested in a population of hemodialysis patients.

DESIGN

The study is an open, parallel, intervention study.

SETTING

Ambulatory chronic hemodialysis patients.

SUBJECTS

Clinically stable chronic hemodialysis patients, on hemodialysis since more than 3 months, undergoing a folate washout. Control group on standard therapy (n = 50).

INTERVENTION

One group was treated with intravenous MTHF (MTHF group, n = 48). A second group was represented by patients treated with MTHF, and, during the course of 10 hemodialysis sessions, NAC was administered intravenous (MTHF + NAC group, n = 47).

MAIN OUTCOME MEASURE

Plasma homocysteine measured before and after dialysis at the first and the last treatment.

RESULTS

At the end of the study, there was a significant decrease in predialysis plasma homocysteine levels in the MTHF group and MTHF + NAC group, compared with the control group, but no significant difference between the MTHF group and MTHF + NAC group. A significant decrease in postdialysis plasma homocysteine levels in MTHF + NAC group (10.27 ± 0.94 μmol/L, 95% confidence interval: 8.37-12.17) compared with the MTHF group (16.23 ± 0.83, 95% confidence interval: 14.55-17.90) was present. In the MTHF + NAC group, 64% of patients reached a postdialysis homocysteine level <12 μmol/L, compared with 19% in the MTHF group and 16% in the control group.

CONCLUSIONS

NAC therapy induces a significant additional decrease in homocysteine removal during dialysis. The advantage is limited to the time of administration.

Effect of folic acid supplementation on the progression of carotid intima-media thickness: a meta-analysis of randomized controlled trials

OBJECTIVES

We conducted a meta-analysis of relevant randomized trials to assess whether folic acid supplementation reduces the progression of atherosclerosis as measured by carotid intima-media thickness (CIMT).

METHODS

This analysis included 2052 subjects from ten folic acid randomized trials with the change in CIMT reported as one of the end points. Summary estimates of weighted mean differences (WMDs) and 95% CIs were obtained by using random-effect models. Meta-regression and subgroup analyses were performed to identify the source of heterogeneity.

RESULTS

Our analysis showed that folic acid supplementation significantly reduces the progression of CIMT (WMD: -0.04 mm; 95%CI: -0.07, -0.02; P<0.001), particularly in subjects with chronic kidney disease (CKD) (WMD: -0.16 mm; 95%CI: -0.26, -0.07; P=0.0006) or high cardiovascular disease (CVD) risk (WMD: -0.05 mm; 95%CI: -0.11, 0.00; P=0.06) but not in subjects who were generally healthy with only elevated homocysteine concentrations (WMD:0.00 mm; 95%CI: -0.01, 0.01; P=0.35). Furthermore, meta-regression analysis of the data showed that the baseline CIMT levels (P=0.011) and the percent reduction of homocysteine (P<0.001) were positively related to the effect size. Consistently, a greater beneficial effect was seen in those trials with baseline CIMT levels ≥0.8 mm (WMD: -0.14 mm; 95%CI: -0.19, -0.08; P<0.0001), and a reduction in the homocysteine concentration ≥30% (WMD: -0.22 mm; 95%CI: -0.38, -0.06; P=0.009). In the corresponding comparison groups, the effect sizes were attenuated and insignificant.

CONCLUSIONS

Our findings indicate that folic acid supplementation is effective in reducing the progression of CIMT, particularly in subjects with CKD or high CVD risk and among trials with higher baseline CIMT levels or a larger homocysteine reduction.

Medication adherence assessment in a clinical trial with centralized follow-up and direct-to-patient drug shipments

BACKGROUND

Assessment of adherence to study medications is a common challenge in clinical research. Counting unused study medication is the predominant method by which adherence is assessed in outpatient clinical trials but it has limitations that include questionable validity and burdens on research personnel.

PURPOSE

To compare capsule counts, patient questionnaire responses, and plasma drug levels as methods of determining adherence in a clinical trial that had 2056 participants and used centralized drug distribution and patient follow-up.

METHODS

Capsule counts from study medication bottles returned by participants and responses to questions regarding adherence during quarterly telephone interviews were averaged and compared. Both measures were compared to plasma drug levels obtained at the 3-month study visit of patients in the treatment group. Counts and questionnaire responses were converted to adherence rates (doses taken divided by days elapsed) and were categorized by stringent (≥85.7%) and liberal (≥71.4%) definitions. We calculated the prevalence-adjusted bias-adjusted kappa to assess agreement between the two measures.

RESULTS

Using a pre-paid mailer, participants returned 76.0% of study medication bottles to the central pharmacy. Both capsule counts and questionnaire responses were available for 65.8% of participants and were used to assess adherence. Capsule counts identified more patients who were under-adherent (18.8% by the stringent definition and 7.5% by the liberal definition) than self-reports did (10.4% by the stringent definition and 2.1% by the liberal definition). The prevalence-adjusted bias-adjusted kappa was 0.58 (stringent) and 0.83 (liberal), indicating fair and very good agreement, respectively. Both measures were also in agreement with plasma drug levels determined at the 3-month visit (capsule counts: p = 0.005 for the stringent and p = 0.003 for the liberal definition; questionnaire: p = 0.002 for both adherence definitions).

LIMITATIONS

Inconsistent bottle returns and incomplete notations of medication start and stop dates resulted in missing data but exploratory missing data analyses showed no reason to believe that the missing data resulted in systematic bias.

CONCLUSIONS

Depending upon the definition of adherence, there was fair to very good agreement between questionnaire results and capsule counts among returned study bottles, confirmed by plasma drug levels. We conclude that a self-report of medication adherence is potentially comparable to capsule counts as a method of assessing adherence in a clinical trial, if a relatively low adherence threshold is acceptable, but adherence should be confirmed by other measures if a high adherence threshold is required.

B Vitamins and the Risk of Total Mortality and Cardiovascular Disease in End-Stage Renal Disease

Background— In observational studies, hyperhomocysteinemia has been found to be a risk factor for total mortality and cardiovascular events in patients with end-stage renal disease. These patients have grossly elevated homocysteine levels that can be lowered by supplementation with folic acid and vitamin B 12 . We conducted a randomized clinical trial with B vitamins to reduce homocysteine levels and therefore cardiovascular events and total mortality.

Methods and Results— This randomized, double-blind multicenter study was conducted in 33 dialysis centers in north and east Germany between July 2002 and July 2008. We randomly assigned 650 patients with end-stage renal disease who were undergoing hemodialysis to 2 postdialysis treatments: 5 mg folic acid, 50 μg vitamin B 12 , and 20 mg vitamin B 6 (active treatment) or 0.2 mg folic acid, 4 μg vitamin B 12 , and 1.0 mg vitamin B 6 (placebo) given 3 times per week for an average of 2 years. The primary outcome was total mortality; the secondary outcome was fatal and nonfatal cardiovascular events. The primary outcome occurred in 102 patients (31%) receiving the active treatment and in 92 (28%) receiving placebo (hazard ratio, 1.13; 95% confidence interval, 0.85 to 1.50; P =0.51). The secondary outcome occurred in 83 patients (25%) receiving the active treatment and in 98 (30%) receiving placebo (hazard ratio, 0.80; 95% confidence interval, 0.60 to 1.07; P =0.13).

Conclusions— Increased intake of folic acid, vitamin B 12 , and vitamin B 6 did not reduce total mortality and had no significant effect on the risk of cardiovascular events in patients with end-stage renal disease.

Clinical Trial Registration— URL: www.anzctr.org.au. Unique identifier: ACTRN12609000911291. URL: www.cochrane-renal.org. Unique identifier: CRG010600027.

Folic acid supplementation and cardiac and stroke mortality among hemodialysis patients

OBJECTIVE

We sought to assess whether the use of folic acid vitamin supplements reduced cardiac and stroke mortality in hemodialysis patients. Further, we examined whether the consumption of folic acid from vitamin supplements >1000 microg compared with the standard 1000 microg, and 1000 microg compared with either a lower dose or no consumption, were associated with reduced cardiac and stroke mortality risk.

DESIGN

We performed a secondary analysis of data from the Hemodialysis Study, a randomized clinical trial examining dialysis treatment regimens over a 3-year follow-up.

PARTICIPANTS

Participants included 1846 hemodialysis patients previously participating in the Hemodialysis Study.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURE

Cardiac and stroke mortality were our main outcome measures.

RESULTS

Based on time-dependent Cox proportional hazard regression models, folic acid consumption from vitamin supplements, above or below the standard 1000-microg dose, was not associated with a decrease or increase in cardiac mortality (P = .53, above vs. standard dose; P = .46, below vs. standard dose). There was also no association between folic acid consumption and mortality from stroke (P = .27, above vs. standard dose; P = .64, below vs. standard dose).

CONCLUSION

The consumption of higher than the standard 1000-microg prescribed dose of folic acid was not beneficial in reducing cardiac or stroke mortality in hemodialysis patients. Similarly, the consumption of less than the standard dose was not associated with an increase in either cardiac or stroke mortality.

Homocysteine as a risk factor for cardiovascular disease in patients treated by dialysis: a meta-analysis

BACKGROUND

In the general population, increased homocysteine concentrations are a risk factor for cardiovascular disease and mortality. However, it is not known whether this also applies to patients with end-stage renal disease.

STUDY DESIGN

Meta-analysis of retrospective (11 studies including 1,506 individuals), prospective observational studies (12 studies including 1,975 individuals), and intervention trials (5 studies including 1,642 dialysis patients). Analyses were carried out separately, according to the study design.

SETTING & POPULATION

Studies of patients with end-stage renal disease treated by means of hemodialysis or peritoneal dialysis.

SELECTION CRITERIA FOR STUDIES

Studies investigating the association between total homocysteine level and cardiovascular disease or total mortality or the influence of vitamin supplementation on cardiovascular or mortality risk.

INTERVENTION

In intervention studies, vitamin preparations with folic acid alone or in combination with other vitamins, such as vitamin B(12) and B(6), were used.

OUTCOMES

In retrospective studies, cases are patients with cardiovascular diseases. Outcomes for prospective observational and intervention studies are cardiovascular events and total mortality.

RESULTS

In retrospective studies, there was no significant overall difference in homocysteine concentrations between cases and controls (weighted mean difference in homocysteine, 2.82 micromol/L; 95% confidence interval [CI], -2.22 to 7.86; P = 0.3). The pooled overall risk estimate for prospective observational studies suggests no association between homocysteine level (5-micromol/L increase) and total mortality (hazard ratio [HR], 1.02; 95% CI, 0.93 to 1.12; P = 0.7), but there was an association with cardiovascular events (HR, 1.09; 95% CI, 1.03 to 1.14; P = 0.001). In subgroup analysis of patients not receiving vitamins, an increase in homocysteine level was associated with increased mortality (HR, 1.07; 95% CI, 1.02 to 1.13; P = 0.01). For intervention trials with B vitamins, there was a significant risk reduction for cardiovascular disease (relative risk, 0.73; 95% CI, 0.56 to 0.94; P = 0.02), but no risk reduction for total mortality or the composite end point including total mortality (relative risk, 1.01; 95% CI, 0.88 to 1.15; P = 0.9).

LIMITATIONS

Many studies are small, which may lead to the observed heterogeneity. Some intervention trials are neither placebo controlled nor randomized. Separate analyses for specific end points and patients treated by means of hemodialysis or peritoneal dialysis were not possible.

CONCLUSION

Total homocysteine level may be a risk factor for cardiovascular events and total mortality in patients with end-stage renal disease not receiving vitamin supplementation or folic acid food fortification. There may be a potential for reducing cardiovascular disease in this population by folic acid supplementation.

Prognostic factors influencing the patency of hemodialysis vascular access: literature review and novel therapeutic modality by far infrared therapy

In Taiwan, more than 85% of patients with end-stage renal disease undergo maintenance hemodialysis (HD). The native arteriovenous fistula (AVF) accounts for a prevalence of more than 80% of the vascular access in our patients. Some mechanical factors may affect the patency of hemodialysis vascular access, such as surgical skill, puncture technique and shear stress on the vascular endothelium. Several medical factors have also been identified to be associated with vascular access prognosis in HD patients, including stasis, hypercoagulability, endothelial cell injury, medications, red cell mass and genotype polymorphisms of transforming growth factor-beta1 and methylene tetrahydrofolate reductase. According to our previous study, AVF failure was associated with a longer dinucleotide (GT)n repeat (n > or = 30) in the promoter of the heme oxygenase-1 (HO-1) gene. Our recent study also demonstrated that far-infrared therapy, a noninvasive and convenient therapeutic modality, can improve access flow, inflammatory status and survival of the AVF in HD patients through both its thermal and non-thermal (endothelial-improving, anti-inflammatory, antiproliferative, antioxidative) effects by upregulating NF-E2-related factor-2-dependent HO-1 expression, leading to the inhibition of expression of E-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1.

5-methyltetrahydrofolate administration is associated with prolonged survival and reduced inflammation in ESRD patients

BACKGROUND

Hemodialysis (HD) patients have a greatly increased risk of cardiovascular morbidity and mortality. For this reason, attempts are often made to normalize hyperhomocysteinemia. This randomized prospective study sought to determine which risk factors are predictors of mortality and whether high doses of folates or 5-methyltetrahydrofolate (5-MTHF) could improve hyperhomocysteinemia and survival in HD patients.

METHODS

341 patients were divided into two groups: group A was treated with 50 mg i.v. 5-MTHF, and group B was treated with 5 mg/day oral folic acid. Both groups received i.v. vitamin B(6) and B(12). By dividing patients into C-reactive protein (CRP) quartiles, group A had the highest survival for CRP <12 mg/l, whereas no survival difference was found for group B. CRP was the only predictive risk factor for death (RR 1.17, range 1.04-1.30, p = 0.02). Dialysis age, hyperhomocysteinemia, methylenetetrahydrofolate reductase polymorphism, albumin, lipoprotein (a) and folate did not influence mortality risk. Survival in group A was higher than that in group B, namely 36.2 +/- 20.9 vs. 26.1 +/- 22.2 months (p = 0.003).

RESULTS

Our results suggest that CRP, but not hyperhomocysteinemia, is the main risk factor for mortality in HD patients receiving vitamin supplements. Intravenous 5-MTHF seems to improve survival in HD patients independent from homocysteine lowering.

Mathematical models of folate-mediated one-carbon metabolism

Folate-mediated one-carbon metabolism is an unusually complex metabolic network, consisting of several interlocking cycles, and compartmentation between cytosol and mitochondria. The cycles have diverse functions, the primary being thymidylate synthesis (the rate limiting step in DNA synthesis), the initial steps in purine synthesis, glutathione synthesis, and a host of methyl transfer reactions that include DNA and histone methylation. Regulation within the network is accomplished by numerous allosteric interactions in which metabolites in one part of the network affect the activity of enzymes elsewhere in the network. Although a large body of experimental work has elucidated the details of the mechanisms in every part of the network, the multitude of complex and non-linear interactions within the network makes it difficult to deduce how the network as a whole operates. Understanding the operation of this network is further complicated by the fact that human populations maintain functional polymorphisms for several enzymes in the network, and that the network is subject to continual short and long-term fluctuations in its inputs as well as in demands on its various outputs. Understanding how such a complex system operates is possible only by means of mathematical models that take account of all the reactions and interactions. Simulations with such models can be used as an adjunct to laboratory experimentation to test ideas and alternative hypotheses and interpretations quickly and inexpensively. A number of mathematical models have been developed over the years, largely motivated by the need to understand the complex mechanisms by which anticancer drugs like methotrexate inhibit nucleotide synthesis and thus limit the ability of cells to divide. More recently, mathematical models have been used to investigate the regulatory and homeostatic mechanisms that allow the system to accommodate large fluctuations in one part of the network without affecting critical functions elsewhere in the network.

Intravenous N-acetylcysteine during haemodialysis reduces the plasma concentration of homocysteine in patients with end-stage renal disease

BACKGROUND

Hyperhomocysteinaemia is an independent cardiovascular risk factor in patients with renal disease. The current study aimed to determine the effect of intravenous N-acetylcysteine on plasma homocysteine levels when administered during haemodialysis in patients with end-stage renal failure.

PATIENTS AND METHODS

Sixty patients with end-stage renal failure were randomised to receive a 4-hour intravenous infusion of N-acetylcysteine or placebo during a 4-hour haemodialysis session. Plasma homocysteine levels were measured before and after haemodialysis. Haemodynamic parameters, including pulse pressure, were also measured.

RESULTS

After haemodialysis in the placebo treatment group, plasma homocysteine was reduced by 23.7% from the pre-dialysis level, whereas patients treated with N-acetylcysteine exhibited an 88.3% decrease (p < 0.001). Reduction of plasma homocysteine concentration was significantly correlated with a reduction of pulse pressure (p = 0.001). A 10% decrease in plasma homocysteine concentration was associated with a 1.45mm Hg decrease in pulse pressure.

CONCLUSIONS

Intravenous administration of N-acetylcysteine during haemodialysis normalises plasma homocysteine concentration, and this is associated with improved pulse pressure in patients with end-stage renal failure. Intravenous administration of N-acetylcysteine during haemodialysis may be a promising approach to help reduce cardiovascular risk in this vulnerable group of patients.

Homocysteine-Lowering Vitamin B Treatment Decreases Cardiovascular Events in Hemodialysis Patients

BACKGROUND

Dialysis patients have higher cardiovascular events rate than patients with normal renal function. Hyperhomocysteinemia, a risk factor for cardiovascular disease, is frequently detected in dialysis patients. Vitamin B supplementation lowers hyperhomocysteinemia, but it is unknown whether it reduces cardiovascular events rate. We planned a long-term study to analyze the effects of homocysteine-lowering vitamin B therapy on cardiovascular disease in hemodialysis patients.

METHODS

We performed a single center open prospective trial. Patients, just on folate therapy at enrolment, were left out from randomization and maintained folate therapy according to study's protocol (group A). Patients, untreated with folic acid at recruitment, were randomly assigned to other 2 groups: patients submitted to folate supplementation according to study's protocol (group B), and untreated ones (group C). We instructed patients to take 5 mg oral daily folic acid or 5 mg every other day whether serum folate levels were up the normal high limit. We measured homocysteine, folate and vitamin B12 plasma levels at baseline and every 4 months. We chose the appearance of fatal and nonfatal cardiovascular events as end-points.

RESULTS

We analyzed data of 114 patients for a median follow-up time of 871 days. Stepwise regression analysis demonstrated that baseline homocysteine levels were related to folate (coefficient: -1.02; F: 64.5), creatinine (coefficient: 0.98; F: 11.3), and C reactive protein (coefficient: -0.64; F: 4.3). Patients ended the study for the following reasons: cardiovascular morbidity (n = 44), death (n = 25), renal transplant (n = 9), moved away (n = 4). Cardiovascular events occurred in 58 of 114 patients (51%), in 26 of 63 (41%) treated patients (both group A and group B) and in 32 of 51 (63%; chi2 = 6.0; p = 0.05) untreated patients (group C). Kaplan-Meier survival analysis showed that cardiovascular events were less frequent in treated patients with low homocysteine levels (chi2 24.1; p < 0.0001). Cox regression analysis showed that cardiovascular events were explained by homocysteine, dialysis vintage, past cardiovascular accidents, and age. We noticed not only lower homocysteine levels, but also higher protein catabolic rate values in events-free patients as compared with patients with nonfatal cardiovascular events. After having divided patients into 4 subgroups according to high and low, split at median, Hcy and protein catabolic rate values, we observed in Kaplan-Meier survival curves for cardiovascular events by these subgroups that patients with low Hcy and high protein catabolic rate values showed a significant lower hazard rate than patients with high Hcy and low protein catabolic rate levels (chi2 = 21.7; p < 0.0001).

CONCLUSIONS

This trial shows for the first time that homocysteine-lowering folate therapy decreases cardiovascular events in dialysis patients. It is necessary to perform large prospective studies to confirm our results.

Testing the homocysteine hypothesis in end-stage renal disease: Problems and a possible solution

The homocysteine hypothesis states that circulating homocysteine is a vascular toxin in concentrations that occur in the general population and in renal failure. This hypothesis is currently being tested in the Kidney and End State Renal Disease Study (HOST), but data have emerged since the HOST began that suggest its results will be inconclusive. The crucial treatment component in the HOST is folic acid, but its effect is likely to be lost because the American food supply is now fortified with folic acid. A second concern is that the very high doses of folic acid and pyridoxine being used in the HOST may confound the results. Finally, confounding due to 'reverse epidemiology' was not considered when the HOST was designed. Parenteral vitamin B(12) is a highly promising therapy for homocysteine reduction in end-stage renal disease that merits careful investigation. Clinical trials using it to test the homocysteine hypothesis will avoid the problems inherent in the HOST.

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.

Comparative effects of hydroxocobalamin and cyanocobalamin on plasma homocysteine concentrations in end-stage renal disease

End-stage renal disease (ESRD) is associated with marked hyperhomocysteinemia which is only partially corrected by folic acid and pyridoxine supplementation. We and others have reported that various forms of parenteral cobalamin reduce plasma total homocysteine (tHcy) concentrations of patients with ESRD substantially below the lowest levels attainable with folic acid. We here report a 16-week randomized controlled crossover trial which directly compared the Hcy-lowering effect of intravenous hydroxocobalamin (HC) with that of cyanocobalamin (CC). Folic acid- and vitamin B12-replete maintenance hemodialysis patients were randomly assigned to receive either 1 mg intravenous HC weekly for 8 weeks followed by CC for a further 8 weeks, or CC for 8 weeks followed by HC for 8 weeks. Hydroxocobalamin increased serum cobalamin concentrations 40-fold, whereas CC increased them only 10-fold, but both treatments reduced plasma tHcy concentrations similarly by 33% (P < .001). Crossover to the alternate form of the vitamin greatly affected the serum cobalamin concentration but was without further effect on the plasma tHcy concentration. These results confirm that weekly cobalamin injections lower plasma tHcy concentrations of hemodialysis patients well below the level attainable with folic acid. Hydroxocobalamin and CC are equipotent despite producing very different serum cobalamin concentrations.

Hyperhomocysteinemia in patients with mild chronic renal failure

BACKGROUND

The aim of this study was to evaluate the prevalence of high plasma levels of homocysteine in patients with mild renal failure.

METHODS

Forty-six chronic renal failure patients (25 males and 21 females, mean age 55.6+/-14.4 years) were recruited for the study. Mean plasma creatinine was 2.1+/-1.0 mg/dl and mean creatinine clearance was 50.6+/-26.3 ml/min. Patients with severe renal failure were excluded. Patients were compared with a control group with normal renal function (n=35, 22 men and 13 women, mean age 50.0+/-11.5 years). Plasma homocysteine values were measured in both groups at baseline and after an oral overload of methionine.

RESULTS

Baseline homocysteine levels of patients were higher than those of controls (16.5+/-7.3 vs. 10.4+/-4.2 micromol/l, p<0.0001). Some 34 patients and 4 controls had increased plasma homocysteine levels at baseline. After the oral overload, 4 more patients had abnormally increased homocysteine levels, meaning that 83% of the patients with chronic renal failure had hyperhomocysteinemia.

CONCLUSIONS

Hyperhomocysteinemia is a very common finding among patients with mild renal failure. The need for vitamin supplementation should be evaluated in the first stage of chronic renal failure.

Cobalamin dose regimen for maximum homocysteine reduction in end-stage renal disease

Plasma total homocysteine (tHcy) concentrations are markedly increased in end-stage renal disease and only partially corrected by folic acid supplementation. We and others have reported that cobalamin, administered parenterally, reduces plasma tHcy substantially below the lowest concentrations attainable with folic acid. We have now carried out a randomized controlled clinical trial to compare the plasma Hcy-lowering effect of 3 intravenous cyanocobalamin dose regimens in maintenance hemodialysis patients: 1 mg postdialysis every 28, 14, and 7 days in addition to routine oral vitamin B supplementation. All patients in the hemodialysis unit where the study was carried out routinely received 1 mg intravenous cyanocobalamin every month, so participants who were randomized to receive the vitamin every 28 days simply continued with their existing treatment program. Serum cobalamin and plasma tHcy concentrations in the control group did not change over the course of the study. As measured after 8 weeks of therapy, intravenous cyanocobalamin every 14 days increased serum cobalamin approximately 2.5-fold and reduced plasma tHcy by 11.5% ( P = .035) below the concentration previously attained with monthly administration, whereas treatment every 7 days increased serum cobalamin concentrations approximately 5-fold and reduced plasma tHcy by 11.0% ( P = .013). These results show that intravenous cyanocobalamin at 7- or 14-day intervals reduces plasma tHcy concentrations of hemodialysis patients below the levels brought about by prior long-term administration every 4 weeks and confirms that plasma tHcy lowering with parenteral cobalamin is a true pharmacological effect and not merely correction of a latent deficiency state.

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.

Traditional and nontraditional cardiovascular risk factors in chronic kidney disease

Chronic kidney disease (CKD) is public health problem, with as many as 20 million individuals affected in the United States. Patients with CKD should be considered in the highest-risk group for development of cardiovascular disease (CVD), and aggressive treatment of traditional and nontraditional risk factors should be instituted. Additional randomized controlled trials are urgently needed to evaluate potential treatments in this population. This article focuses attention on the major modifiable cardiovascular risk factors in CKD.

Hiperhomocisteinemia na insuficiência renal crônica

A homocisteína é um aminoácido sulfurado proveniente do metabolismo da metionina, cujo acúmulo anormal no plasma é um fator de risco para doenças vasculares, tanto na população em geral como nos pacientes com insuficiência renal crônica. Nestes, a prevalência de indivíduos com hiperhomocisteinemia é bastante elevada, mesmo na fase não dialítica da doença, em que a função renal está diminuída, mas ainda não é necessário tratamento dialítico. O principal fator que parece estar implicado na elevação dos níveis de homocisteína nestes pacientes com insuficiência renal crônica é a perda da massa renal, já que esta exerce uma importante função no metabolismo desse aminoácido. O tratamento da hiperhomocisteinemia na população em geral consiste na suplementação com as vitaminas envolvidas no seu metabolismo (folato, B6 e B12). Porém, em pacientes com insuficiência renal crônica, este tratamento não é completamente eficaz, pois apesar de promover a redução dos níveis de homocisteína, não alcança a normalização dos mesmos na maioria dos pacientes. Este estudo compreende uma revisão da etiologia da hiperhomocisteinemia na insuficiência renal crônica, sua relação com as doenças vasculares, seus principais determinantes e as formas de tratamento.

Determinación y utilización de la concentración plasmática de homocisteína en la práctica clínica

Homocysteine is a methionine-derived amino acid and its metabolism depends on B12, B6 and B2 vitamins and folic acid. The total homocysteine plasmatic concentration can be measured in most laboratories by means of enzymeimmunoassays. Hyperhomocysteinemia may be caused by genetic defects of the enzymes involved in its metabolism, nutritional deficiencies or absorption deficiencies of the vitamin cofactors of these enzymes, chronic diseases or administration of some drugs. An increase in the total plasmatic concentration of homocysteine represents a sensitive marker of folate and cobalamin deficiencies as well as an independent risk factor of cardiovascular disease. Furthermore, total plasmatic concentrations of homocysteine are related to the development of congenital malformations, pregnancy complications, psychiatric diseases and to cognitive impairment in the elderly. Therefore, the measurement of the concentration of homocysteine has a notable clinical interest, which may increase in future if it is confirmed that the association with these disorders is causal and that they can be prevented by treating hyperhomocysteinemia.

Intravenous treatment of hyperhomocysteinemia in patients on chronic hemodialysis--a pilot study

BACKGROUND

Treatment of hyperhomocysteinemia in patients with end-stage renal disease (ESRD) can be performed with the oral application of vitamins. However, this therapy rarely normalizes total homocysteine (tHcy) levels. Frequently, a rebound is observed after the end of treatment. Currently, no data are available about intravenous combination therapy with folic acid, pyridoxine (B6), and cyanocobalamin (B12).

METHODS

We conducted a prospective pilot study comprising 13 patients on chronic hemodialysis treatment (63.7+/-4.9 years; 6 female, 7 male) for 27 weeks. The patients received 10 mg folic acid and 100 mg pyridoxine intravenously (IV) after each dialysis plus 1000 microg vitamin B12 IV once a week for 9 weeks. Between weeks 10 and 18 the patients received 10 mg folic acid, 100 mg vitamin B6 once a week, and 1000 microg vitamin B12 bimonthly IV.

RESULTS

The therapy regimen decreased tHcy concentration (baseline: 30.5+/-2.2 micromol/L) significantly to 17.4+/-1.2 micromol/L, 15.6+/-1.0 micromol/L, and 16.4+/-0.1 micromol/L after 3, 6, and 9 weeks, respectively (p<0.01 vs. baseline concentration). The maximum reduction (-47.5+/-3.3%) of tHcy concentration was measured after 6 weeks of therapy. During the following maintenance therapy, tHcy-levels did not increase and no rebound of tHcy was detected during follow-up (week 27:16.5+/-1.97 micromol/L).

CONCLUSION

The concept of a short, high-dose induction therapy with intravenous folic acid, pyridoxine, cyanocobalamin, and a subsequent low-dose maintenance regimen is effective in the treatment of hyperhomocysteinemia in patients with ESRD.

Response of Homocysteine, Cystathionine, and Methylmalonic Acid to Vitamin Treatment in Dialysis Patients

Background: Hyperhomocysteinemia is observed in &gt;80% of hemodialysis patients and is considered a risk factor for cardiovascular disease. Vitamin treatment lowers total homocysteine (tHcy) concentrations in plasma and may therefore reduce the associated risk. Current treatment strategies have not achieved normalization of tHcy in the majority of dialysis patients.

Methods: We administered folic acid (5 mg) plus vitamin B6 (50 mg) and B12 (0.7 mg) intravenously to 38 hyperhomocysteinemic patients (tHcy &gt;18 μmol/L) after each dialysis treatment. The treatment phase lasted 1 month, and serum concentrations of tHcy, methylmalonic acid (MMA), and cystathionine were measured at weeks 0, 2, 4, 6, 8, and 24.

Results: The median serum tHcy concentration decreased significantly, from 26.1 μmol/L at baseline to 13.2 μmol/L at week 4. The median change in tHcy after 4 weeks was 13.4 μmol/L (−51%) compared with baseline. Serum MMA and cystathionine concentrations were reduced by 28% and 26%, respectively, but neither was normalized at 4 weeks. Backward-elimination stepwise regression analysis revealed that higher concentrations of tHcy, MMA, and cystathionine and lower folate at baseline predict changes of tHcy after treatment. Twenty weeks after vitamin withdrawal, tHcy concentrations returned to values comparable to baseline (median, 24.8 μmol/L).

Conclusions: The combination of folic acid, vitamin B12, and vitamin B6 used in this study normalized serum concentrations of tHcy in almost all of our hyperhomocysteinemic dialysis patients. This regimen may be used to investigate the effects of homocysteine normalization on cardiovascular outcomes in hemodialysis patients.

Hyperhomocysteinemia and response of methionine cycle intermediates to vitamin treatment in renal patients

The role of hyperhomocysteinemia (HHcy) as a risk marker for cardiovascular diseases in renal patients is a matter of controversy. The remethylation of homocysteine (Hcy) to methionine in the kidneys is of great importance for Hcy clearance. Hcy remethylation is markedly decreased in patients on hemodialysis, but transsulfuration remains mostly unaffected. Markedly increased concentrations of methylmalonic acid (MMA), as a metabolic marker of vitamin B

Dialysis Outcomes and Practice Patterns Study (DOPPS) data on medications in hemodialysis patients

BACKGROUND

Medications affect many measures of hemodialysis patients' well-being.

METHODS

The Dialysis Outcomes and Practice Patterns Study (DOPPS) has evaluated the use of hydroxymethyl glutaryl coenzyme A reductase inhibitors (statins), analgesics, antidepressants, and multivitamins. Additionally, DOPPS has reported on the associations between vascular access outcomes and related medications.

RESULTS

Prescription of statins varied widely across countries, with the highest use in the United States. Patients prescribed statins had lower risk of cardiac and noncardiac causes of mortality than those who were not prescribed statins. DOPPS data also show that statins are underprescribed relative to recent Kidney Disease Outcomes Quality Initiative guidelines. No guidelines have been established for analgesic use, but high pain levels self-reported by hemodialysis patients suggest opportunities for improved pain management strategies. Guidelines for analgesic use in dialysis patients may help balance improved quality of life against potential side effects of analgesics. Medical and patient questionnaires show that depression in hemodialysis patients is common, frequently underdiagnosed, usually untreated, and associated with increased rates of mortality and hospitalization. Calcium channel blockers were associated with improved primary graft patency, aspirin with improved secondary graft patency, and angiotensin-converting enzyme inhibitors with improved secondary fistula patency. All 3 medications were associated with significantly decreased relative risk for access failure. There is large country variation in multivitamin use, with significantly higher use in the United States compared with Europe and Japan. Patients taking multivitamins had lower mortality risk than patients not taking multivitamins.

CONCLUSION

DOPPS findings on medications indicate that prospective trials are needed before guidelines can be developed for appropriate medication use in these different therapeutic categories.

Hyperhomocysteinemia and cardiovascular disease in uremia: The newest evidence in epidemiology and mechanisms of action

In the general population, hyperhomocysteinemia is an independent risk factor for cardiovascular disease (ischemic disease, such as stroke and myocardial infarction, and arterial and venous thrombosis). We can presume that the association is causal, based on the example of homocystinuria, and on the evidence put forward by several basic science and epidemiologic studies. However, the results of large intervention trials, which may grant further support to this hypothesis, are not yet available. In chronic renal failure and in uremia, the evidence that is offered by carefully performed prospective studies also indicate the presence of an association, although some studies suggest reverse epidemiology. The mechanisms underlying the association, and able to explain the several toxic effects of homocysteine, related or not to cardiovascular disease, are unclear. Oxidation, nitrosylation, and hypomethylation are among the postulated mechanisms. In uremia, protein hypomethylation interferes with protein repair; DNA hypomethylation impairs regulation of gene expression, whereas folate treatment reverts such alterations. Acylation, another structural modification able to impair protein function, is a possible mediator of homocysteine toxicity.

International variation in vitamin prescription and association with mortality in the dialysis outcomes and practice patterns study (DOPPS)

BACKGROUND

The prevalence of water-soluble vitamin use among hemodialysis (HD) patients and whether mortality and hospitalization are associated with water-soluble vitamin use by HD patients have not previously been reported. The present study investigates patterns of water-soluble vitamin use among HD patients in the Dialysis Outcomes and Practice Patterns Study (DOPPS) I and evaluates outcomes associated with vitamin use.

METHODS

The study sample came from the DOPPS I, a prospective observational study of adult HD patients (N = 16,345) randomly selected from 308 representative dialysis facilities in France, Germany, Italy, Japan, Spain, the United Kingdom, and the United States. Time-dependent Cox regression models were used to assess relative risk (RR) for mortality and hospitalization for patients administered water-soluble vitamins versus those not administered water-soluble vitamins.

RESULTS

There was large variation by region in the percentage of patients administered water-soluble vitamins: Europe ranged from a low of 3.7% in the United Kingdom to a high of 37.9% in Spain; 5.6% in Japan; and 71.9% in the United States. Patient use of water-soluble vitamins was associated with a substantially and significantly lower risk for mortality (RR, 0.84; P = 0.001). Lower RR for facility-level mortality also was associated with greater water-soluble vitamin use (RR, 0.98; P = 0.05 per 10% more patients administered water-soluble vitamins at the facility).

CONCLUSION

Although only a randomized trial could prove that water-soluble vitamins improve outcomes, use of water-soluble vitamins is a minimal-risk practice pattern associated with improved outcomes in this prospective observational study.

Medical factors affecting patency of arteriovenous access

Arteriovenous access failure is multifactorial in nature with contributions from both medical and surgical etiologies. Medical causes of arteriovenous access failure are rare, and therefore infrequently identified as a major contributing source of malfunction. Although they account for only 10-15% of all cases of access failure, their importance should not be underestimated, especially in cases where a surgical source cannot be identified. Most medical causes are derived from Virchow's triad of endothelial cell injury, stasis, and hypercoaguability. Endothelial cell injury occurs through oxidative stress, activated platelets, increased levels of circulating tumor necrosis factor-alpha, and preexisting intimal hyperplasia. Stasis can occur through prolonged access compression, hypotension, or hypoalbuminemia. Finally, patients with renal failure requiring hemodialysis are frequently at increased risk for hypercoaguable states, except for situations of platelet dysfunction, and therefore access failure. Potential treatments include identifying and removing the offending source, as well as innovative, new medications to prevent their reoccurrence. Treatment is aimed at improving quality of life, as well as decreasing morbidity and hospital admissions in this difficult patient population.

Acetylcysteine Reduces Plasma Homocysteine Concentration and Improves Pulse Pressure and Endothelial Function in Patients With End-Stage Renal Failure

Background— Increased oxidative stress, elevated plasma homocysteine concentration, increased pulse pressure, and impaired endothelial function constitute risk factors for increased mortality in patients with end-stage renal failure.

Methods and Results— We investigated the metabolic and hemodynamic effects of intravenous administration of acetylcysteine, a thiol-containing antioxidant, during a hemodialysis session in a prospective, randomized, placebo-controlled crossover study in 20 patients with end-stage renal failure. Under control conditions, a hemodialysis session reduced plasma homocysteine concentration to 58±22% predialysis (mean±SD), whereas in the presence of acetylcysteine, the plasma homocysteine concentration was significantly more reduced to 12±7% predialysis ( P <0.01). The reduction of plasma homocysteine concentration was significantly correlated with a reduction of pulse pressure. A 10% decrease in plasma homocysteine concentration was associated with a decrease of pulse pressure by 2.5 mm Hg. Analysis of the second derivative of photoplethysmogram waveform showed changes of arterial wave reflectance during hemodialysis in the presence of acetylcysteine, indicating improved endothelial function.

Conclusions— Acetylcysteine-dependent increase of homocysteine removal during a hemodialysis session improves plasma homocysteine concentration, pulse pressure, and endothelial function in patients with end-stage renal failure.

Facts and Recommendations about Total Homocysteine Determinations: An Expert Opinion

Background: Measurement of plasma total homocysteine has become common as new methods have been introduced. A wide range of disorders are associated with increased concentrations of total homocysteine. The purpose of this review is to provide an international expert opinion on the practical aspects of total homocysteine determinations in clinical practice and in the research setting and on the relevance of total homocysteine measurements as diagnostic or screening tests in several target populations.

Methods: Published data available on Medline were used as the basis for the recommendations. Drafts of the recommendations were critically discussed at meetings over a period of 3 years.

Outcome: This review is divided into two sections: (a) determination of homocysteine (methods and their performance, sample collection and handling, biological determinants, reference intervals, within-person variability, and methionine loading test); and (b) risk assessment and disease diagnosis (homocystinuria, folate and cobalamin deficiencies, cardiovascular disease, renal failure, psychiatric disorders and cognitive impairment, pregnancy complications and birth defects, and screening of elderly and newborns). Each of these subsections concludes with a separate series of recommendations to assist the clinician and the research scientist in making informed decisions. The review concludes with a list of unresolved questions.