Treatment of hyperhomocysteinemia in end-stage renal disease

Novel options for failing allograft in kidney transplanted patients to avoid or defer dialysis therapy

PURPOSE OF REVIEW

Despite improvement in short-term renal allograft survival in recent years, renal transplant recipients (RTR) have poorer long-term allograft outcomes. Allograft function slowly declines with periods of stable function similar to natural progression of chronic kidney disease in nontransplant population. Nearly all RTR transitions to failing renal allograft (FRG) period and require transition to dialysis. Conservative chronic kidney disease management before transition to end-stage renal disease is an increasingly important topic; however, there is limited data in RTR regarding how to delay dialysis initiation with conservative management.

RECENT FINDINGS

Since immunological and nonimmunological factors unique to RTR contribute to decline in allograft function, therapies to slow progression of FRG should take both sets of factors into account. Renal replacement therapy either incremental dialysis or rekidney transplantation should be explored. This required taking benefits and risks of continuing immunosuppressive medications into account when allograft nephrectomy may be necessary.

SUMMARY

FRG may benefit from various interventions to slow progression of worsening allograft function. Until there are stronger evidence to guide interventions to preserve renal function, extrapolating evidence from nontransplant patients and clinical judgment are necessary. The goal is to provide individualized care for conservative management of RTR with FRG.

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.

Cardiovascular Risk Markers in Hemodialysis Patients

Cardiovascular events are the main cause of death in hemodialysis patients. Nevertheless, acute myocardial infarction may be misdiagnosed in uremic patients, because typical markers have a high rate of false positivity. A recent two-year prospective study showed that predialytic high serum concentrations of troponin T and CK-MB mass were associated with high mortality, cardiac mortality, myocardial infarction and unstable angina (MACEs). We studied 16 uremic patients (13 M; 3 W) on standard HD and 6 patients (4 M; 2 W) on on-line HDF, who had been taking folic acid for at least three months. Patients who suffered from acute or chronic cardiac ischemic disease were excluded. Anthropometric parameters, pre and post-dialytic pH, HCO3 and electrolytes did not differ between the two groups. Kt/V and URR % were lower in conventional HD vs on-line HDF (p<0.04; p<0.04). ORR % was strongly elevated in on-line HDF compared with HD (p<0.005). In conventional HD, ORR % was directly correlated with Kt/V and URR% (r = 0.49, p<0.04; r = 0.48, p<0.04, respectively). Even in on-line HDF ORR % was directly correlated with Kt/V and URR % (r = 0.79, p<0.04; r = 0.76, p<0.05, respectively). Troponin I and CK-MB mass were not significantly different in pre vs post-dialysis, both in standard HD and on-line HDF. Nevertheless, in standard HD postdialytic troponin I correlated with serum sodium concentration (r = 0.93, p < 0.000), potassium (r = 0.67, p < 0.004) and serum chlorine (r = 0.92, p < 0.92, p < 0.000). CK-MB mass showed a correlation with serum chlorine (r = 0.49, p < 0.05). Postdialytic CK-MB mass correlated with serum potassium in on-line HDF (r = 0.83, p < 0.03). Our data suggest that hemodialytic treatments, both standard HD and on-line HDF, do not modify serum troponin I and CK-MB mass. Consequently, we can use these parameters for the diagnostic approach in acute or chronic ischemic heart disease in hemodialysis 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.

Interventions for lowering plasma homocysteine levels in kidney transplant recipients

BACKGROUND

Elevated homocysteine levels have been shown to be an independent risk factor for cardiovascular disease. However studies of homocysteine lowering in general and end-stage kidney disease (ESKD) populations have not demonstrated a reduction in cardiovascular event rates. Kidney transplant recipients have high homocysteine levels, high cardiovascular event rates and, unlike the ESKD population, may achieve normalisation of homocysteine levels with homocysteine lowering therapies. Thus may benefit from homocysteine lowering therapy.

OBJECTIVES

To evaluate the effects of established homocysteine lowering therapy on cardiovascular mortality in patients with functioning kidney transplants.

SEARCH METHODS

We searched the Cochrane Renal Group's Specialised Register to 16 March 2015 through contact with the Trials' Search Co-ordinator using search terms relevant to this review.

SELECTION CRITERIA

Randomised controlled trials of any therapy that has been shown to significantly lower homocysteine levels conducted in people with functioning kidney transplants. Studies were to be included if they compared homocysteine lowering therapy with placebo or usual care, or compare higher versus lower doses of homocysteine lowering therapy.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study quality and extracted data. Results were to be expressed as the risk ratio (RR) for dichotomous outcomes or mean difference (MD) for continuous outcomes with 95% confidence intervals (CI). Data was to be pooled using the random effects model.

MAIN RESULTS

The literature search yielded 359 reports of which only one study was identified that met our inclusion criteria and reported relevant clinical endpoints. This study randomised 4110 adult participants with a functioning kidney transplant and elevated homocysteine levels to folic acid plus high dose B multivitamins or low dose multivitamins who were followed for a mean 4.0 years. Despite effectively lowering homocysteine levels) in homocysteine levels at follow-up (MD -4.40 μmol/L, 95% CI -5.98 to -2.82) there was no evidence the intervention impacted on any of the outcomes reported including cardiovascular mortality (RR 0.91, 95% CI 0.69 to 1.20), all-cause mortality (RR 1.04, 95% CI 0.88 to 1.22), myocardial infarction (RR 1.02, 95% CI 0.77 to 1.35), stroke (RR 1.08, 95% CI 0.69 to 1.71), commencement of renal replacement therapy (RR 1.12, 95% CI 0.91 to 1.37) or all reported adverse events (RR 1.02, 95% CI 0.87 to 1.20). There was no evidence the intervention impacted on the primary endpoint of the study, a cardiovascular event composite (RR 0.99, 95% CI 0.85 to 1.15). The study was of high quality.

AUTHORS' CONCLUSIONS

There is no current evidence to support the use of homocysteine lowering therapy for cardiovascular disease prevention in kidney transplant recipients.

Correlations of MTHFR 677C>T polymorphism with cardiovascular disease in patients with end-stage renal disease: a meta-analysis

OBJECTIVE

This meta-analysis was conducted to evaluate the correlations of a common polymorphism (677C>T) in the methylenetetrahydrofolate reductase (MTHFR) gene with risk of cardiovascular disease (CVD) in patients with end-stage renal disease (ESRD).

METHOD

The following electronic databases were searched without language restrictions: Web of Science (1945∼2013), the Cochrane Library Database (Issue 12, 2013), MEDLINE (1966∼2013), EMBASE (1980∼2013), CINAHL (1982∼2013) and the Chinese Biomedical Database (CBM) (1982∼2013). Meta-analysis was performed using STATA statistical software. Odds ratios (ORs) with their 95% confidence intervals (95%CIs) were calculated.

RESULTS

Eight cohort studies met all inclusion criteria and were included in this meta-analysis. A total of 2,292 ESRD patients with CVD were involved in this meta-analysis. Our meta-analysis results revealed that the MTHFR 677C>T polymorphism might increase the risk of CVD in ESRD patients (TT vs. CC: OR = 2.75, 95%CI = 1.35∼5.59, P = 0.005; CT+TT vs. CC: OR = 1.39, 95%CI = 1.09∼1.78, P = 0.008; TT vs. CC+CT: OR = 2.52, 95%CI = 1.25∼5.09, P = 0.010; respectively). Further subgroup analysis by ethnicity suggested that the MTHFR 677C>T polymorphism was associated with an elevated risk for CVD in ESRD patients among Asians (TT vs. CC: OR = 3.38, 95%CI = 1.11∼10.28, P = 0.032; CT+TT vs. CC: OR = 1.44, 95%CI = 1.05∼1.97, P = 0.022; TT vs. CC+CT: OR = 3.15, 95%CI = 1.02∼9.72, P = 0.046; respectively), but not among Africans or Caucasians (all P>0.05).

CONCLUSION

Our findings indicate that the MTHFR 677C>T polymorphism may be associated with an elevated risk for CVD in ESRD patients, especially among Asians.

Obesity and adiponectin after kidney transplantation

Obesity and hyperlipidaemia are found very frequently after kidney transplantation (Tx) and may represent independent risk factors for development of atherosclerosis and chronic allograft nephropathy. In a prospective metabolic study, we monitored, a total of 68 obese transplant patients [body mass index (BMI) > 30 kg/m2] with dyslipidaemia over a period of 24 months. We compared the findings of a new therapeutic regimen 1 year (start of the study) and 2 years after renal transplantation. Based on a Subjective Global Assessment Scoring Sheet, we started at the end of the first year with an individualized hypoenergic-hypolipidaemic diet (IHHD). Subsequently, after corticoid withdrawal, IHHD was supplemented regularly with statins (atorvastatin 10-20 mg/day)) and followed-up for 2 years. All patients were on a regimen of cyclosporin A or tacrolimus and mycophenolate mofetil. During the study period, there was a significant decrease in BMI (p < 0.025) and an increase of the adiponectin level (p < 0.01). Long-term therapy was associated with a significant decrease in serum leptin (p < 0.01) and lipid metabolism parameters (p < 0.01). Inulin clearance, mean systolic and diastolic blood pressure, proteinuria, lipoprotein(a) and apo-lipoprotein E isoforms did not differ significantly. Based on our results, we assume that obesity and hyperlipidaemia after renal transplantation can be treated effectively by modified immunosuppression (corticosteroid withdrawal), statins and long-term diet (IHHD). The increased level of adiponectin may be a marker of reducing atherosclerotic and chronic allograft nephropathy processes.

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.

Total homocysteine concentration and associated cardiovascular and renal implications in adults

Hyperhomocysteinemia has been linked to an increased risk for cardiovascular (CV) disease since 1969. Recent epidemiological and cohort observations continue to confirm this relationship, provided the homocysteine concentration is elevated. This elevation in homocysteine concentration and increased CV disease risk are particularly strong in patients with renal disease. Hyperhomocysteinemia is also related to declining status of vitamins B6 and B12, folate, and in some cases riboflavin. This relationship between vitamins and homocysteine concentration has provided the basis for clinical trials targeting CV risk reduction by vitamin supplementation. This review describes the evidence behind vitamin supplementation as it pertains to homocysteine status and make recommendations for vitamin intake management in patients with hyperhomocysteinemia, including those patients with renal disease.

Preliminary Results of the Effect of Treatment of Hyperhomocysteinemia and Its Relationship With Inflammation, Coagulation Status, and Endothelial Function After Renal Transplantation

The aim of this study was to assess the relationship between total plasma homocysteine (tHC) and several markers of endothelial function, coagulation, and pro-inflammatory status in renal transplant recipients. Our own previous study demonstrated the efficacy of folic acid (FA) and vitamin B(12) (B(12)) treatment to reduce tHC. Using 70 stable recipients, 56 of whom showed hyperhomocisteinemia (HHC) (tHC > or = 14 micromol/L) and a control group (n = 14, tHC < 14 micromol/L), we treated 29 patients in the HHC group (10 mg FA and 500 mg B(12) daily) and determined their endothelial function, inflammatory activity, and coagulation status. We assessed plasma levels of von Willebrand Factor and fibrinogen as the prothrombotic profile and C-reactive protein and plasma albumin as inflammation markers. We performed Doppler sonography of the brachial artery to assess endothelial function. The mean value of plasma tHC of 19.05 +/- 3.70 micromol/L before treatment decreased to 13.45 +/- 3.25 micromol/L after 3 months of treatment (P < .001). The vWF was significantly correlated with tHC (P < .05) and was higher in the HHC patients (P < .05). The fibrinogen mean level was also significantly higher in HHC patients (P < .05). The C-reactive protein level was significantly higher and the albumin level was lower among patients with HHC. The endothelium-dependent dilation (EDD) correlated with baseline tHC (P < .05). In preliminary data we observed that homocysteine-lowering therapy may provide cardiovascular protection by enhancing endothelial function, limiting oxidative stress, and reducing procoagulation status.

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.

Evaluation and treatment of coronary artery disease in patients with end-stage renal disease

Evaluation and treatment of coronary artery disease in patients with end-stage renal disease. Patients with end-stage renal disease (ESRD) are at increased risk of death from coronary artery disease (CAD). The metabolic milieu that results from renal dysfunction appears to accelerate the atherosclerotic process by decades in patients with ESRD. The extremely high prevalence of atherosclerosis in patients with ESRD mandates risk factor identification and treatment. Traditionally, CAD in this patient population has been treated conservatively. Analysis of large databases has highlighted the scope and complexity of this problem; nonetheless, there is a paucity of randomized, controlled trials of CAD in patients with ESRD. In this paper the following issues related to evaluation and treatment of patients with chronic kidney disease are addressed: (1) optimal CAD risk management; (2) evaluation for CAD in patients with ESRD, including the identification of coronary calcification; (3) treatment of CAD with medical therapy and revascularization; (4) relative merits of percutaneous coronary intervention versus bypass surgery. In general, an aggressive approach to medical management of CAD is warranted, even in the setting of subclinical CAD. A low threshold for diagnostic testing should be employed in patients with ESRD. When significant CAD is identified, ESRD patients appear to benefit more from revascularization compared to conservative medical management. Thus, if clinically reasonable, patients with ESRD and CAD should be managed aggressively to improve survival and reduce the incidence of future cardiac events.

Homocysteine in chronic kidney disease: Effect of low protein diet and repletion with B vitamins

BACKGROUND

Data are limited on the determinants of homocysteine (tHcy) and its relationship with nutritional indices, and dietary protein intake, in the earlier stages of chronic kidney disease (CKD).

METHODS

Levels of tHcy were assayed at baseline (N= 804) and 1 year postrandomization (N= 678) in the Modification of Diet in Renal Disease (MDRD) Study [study A, glomerular filtration rate (GFR) 25 to 55 mL/min/1.73 m(2) and study B GFR 13 to 24 mL/min/1.73 m(2)]. Participants were randomly assigned to different blood pressure targets and protein diets and all subjects received a multivitamin supplement containing 1 mg of folic acid, 10 mg pyridoxal 5'-phosphate (PLP) and 6 mug of vitamin B(12). Multivariable analyses were used to evaluate determinants of tHcy at baseline and 1 year.

RESULTS

The prevalence of hyperhomocysteinemia (tHcy >15 mumol/L) at baseline was 56% in study A and 85% in study B. Baseline tHcy was negatively correlated with measures of body fat and dietary protein intake. Folate, vitamin B(12), and GFR were the major determinants of tHcy levels. Of the patients with hyperhomocysteinemia at baseline, 49% and 24% reduced their tHcy levels at 1 year to < or =15 micromol/L in study A and study B, respectively. There was no association between dietary protein intake and odds of developing hyperhomocysteinemia at 1 year in study A (P= 0.94) or study B (P= 0.10).

CONCLUSION

Hyperhomocysteinemia is partly amenable to correction by vitamin supplementation in CKD stages 3 and 4. There is insufficient evidence to suggest that low tHcy is associated with poor nutritional status in the MDRD Study cohort. B vitamins and GFR, but not dietary protein, are the major determinants of tHcy in this patient population.

Cardiovascular disease in chronic kidney disease from a cardiologist's perspective

PURPOSE OF REVIEW

Cardiovascular disease accounts for the majority of morbidity and mortality in patients with chronic kidney disease (CKD). This review therefore concentrates on CKD from the viewpoint of the cardiologist.

RECENT FINDINGS

Studies have identified several explanations for this observation, including high rates of risk factors for cardiovascular disease, lesser use of cardioprotective strategies, adverse outcomes with cardiovascular drugs and procedures, and accelerated atherosclerosis and myocardial disease in CKD. Because recent studies have rigorously controlled for confounding factors, there is an emerging recognition that CKD is an independent cardiovascular risk state. Conversely, CKD appears to be the result of systemic atherosclerosis. The relative under-utilization of cardioprotective therapies has been an increasingly reported finding in the literature. It appears that conventional cardiovascular risk factor reduction in both the chronic and acute care settings has a greater relative benefit in those patients with CKD than in those with normal renal function.

SUMMARY

CKD is an independent cardiovascular risk state. Hence, there is a strong rationale for research in CKD patients into the pathogenesis of CVD. In addition, there are multiple opportunities for improving cardiovascular outcomes in patients with CKD, including both chronic and acute cardiovascular risk reduction.

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.

Association between serum homocysteine and markers of impaired kidney function in adults in the United States

BACKGROUND

Circulating homocysteine, a risk factor for cardiovascular disease (CVD), is often elevated in chronic kidney disease and end-stage renal disease (ESRD) patients. Little is known about the risk of elevated homocysteine associated with less advanced renal insufficiency in the community.

METHODS

Serum homocysteine concentration measures (umol/L) from the National Health and Nutrition Examination Survey (NHANES) 1991-1994 participants who were aged >/=40 years and fasted >/=6 hours (1558 men and 1829 women) were categorized as <9, 9 to 11.9, 12 to 14.9, and >/=15. Renal function levels were determined by Modified Diet in Renal Disease (MDRD) estimated glomerular filtration rate (GFRest) (mL/min/1.73 m(2)) and the urinary albumin-to-creatinine ratio (ACR) (mg/g). Cumulative odds ratios (OR) of exceeding any given homocysteine cut point were computed by gender, using ordinal logistic regression. Each model included GFRest (<60, 60 to 90, >/=90), ACR (<15, 15 to <30, >/=30), age, race/ethnicity, red blood cell folate, serum vitamin B(12), and dietary vitamin B(6) intake as independent variables.

RESULTS

The adjusted ORs for elevated homocysteine risk were 9 to 11 times greater in adults with the lowest GFRest levels (<60 mL/min/1.73 m(2)) compared to those with normal GFRest levels. Association measures for marginal GFRest levels (60 to 90 mL/min/1.73 m(2)) were weaker but significant. Albuminuria (ACR >/=30 mg/g) was a significant, independent renal risk factor for elevated homocysteine in men and women (adjusted OR = 1.78, 95% CI 1.08-2.93, and adjusted OR = 1.83, 95% CI 1.21-2.76, respectively) relative to those with low normal albumin excretion, but high normal albuminuria (ACR = 15-30 mg/g) was not.

CONCLUSION

In the general population, renal insufficiency is strongly associated with an increased risk of elevated circulating homocysteine, independent of B vitamin status. These results raise the possibility that elevated homocysteine may be an important risk factor to explain the heavy burden of CVD associated with kidney disease.

Opportunities for improvement in the cardiovascular care of patients with end-stage renal disease

Cardiovascular disease accounts for the majority of morbidity and mortality in patients with end-stage renal disease (ESRD). Studies have identified several explanations for this observation, such as high rates of cardiovascular risk factors, lesser use of cardioprotective strategies, adverse outcomes with cardiovascular drugs and procedures, and accelerated atherosclerosis and myocardial disease in ESRD. Based on these findings, this article addresses the critical opportunities for improvement in cardiovascular outcomes in patients with ESRD. These improvements include prevention of cardiovascular events, management of acute coronary syndromes and heart failure, and the prevention of sudden death.

Comparative kinetics of the uremic toxin p-cresol versus creatinine in rats with and without renal failure

BACKGROUND

p-cresol, which is extensively metabolized into p-cresylglucuronide in the rat, is related to several biochemical and physiologic alterations in uremia and is not removed adequately by current hemodialysis strategies. The knowledge of its in vivo kinetic behavior could be helpful to improve the current removal strategies.

METHODS

We investigated the kinetic behavior of intravenously injected p-cresol (10 mg/kg) in rats with normal and decreased renal function, and compared the results with those obtained for creatinine (60 mg/kg) under similar conditions. Renal failure was obtained by 5/6 nephrectomy. Both p-cresol and p-cresylglucuronide were analyzed using reversed-phase high-performance liquid chromatography (RP-HPLC). The relation between the p-cresylglucuronide peak height and the underlying amount of p-cresol was determined after hydrolysis of the glucuronide with beta-glucuronidase. We calculated urinary excretion of p-cresol with and without taking p-cresylglucuronide into account. In addition, total, renal, and non-renal clearance, half-life, and volume of distribution were calculated for p-cresol.

RESULTS

Over a 4-hour period, p-cresol serum concentration showed only a minimal decline in rats with decreased renal function (t1/2 = 11.7 +/- 0.4 hours), compared to rats with normal renal function (t1/2 = 1.4 +/- 0.7 hours). A similar observation was made for p-cresylglucuronide. In rats with normal renal function, 21.0 +/- 10.0% of the injected p-cresol was excreted in urine as p-cresol and 60.7 +/- 25.0% as p-cresylglucuronide; in rats with renal failure, the respective amounts were 6.7 +/- 7.5% and 32.0 +/- 25.3% (P < 0.05 vs. normal renal function) (total recovery 81.81 +/- 31.07% vs. 38.50 +/- 32.09%, P < 0.05). The volume of distribution of p-cresol was approximately 4 times larger than that of creatinine, but was not significantly affected by renal failure. Not only renal, but also non-renal and total clearance, were much lower in rats with decreased renal function.

CONCLUSION

The present data sheds a light on the kinetic behavior of p-cresol in uremic patients; the large volume of distribution, especially, might explain the inadequate dialytic removal of p-cresol. In addition, a substantial amount of p-cresol is removed by metabolism, and both renal and non-renal clearance are disturbed in uremia.

The effect of PMMA-based protein-leaking dialyzers on plasma homocysteine levels

BACKGROUND

Hyperhomocysteinemia is a well-recognized independent risk factor for cardiovascular disease in end-stage renal disease (ESRD) patients. Since homocysteine (Hcy) largely binds to serum proteins (80 to 90%), in this study we investigated the possibility that polymethylmethacrylate (PMMA)-based protein-leaking dialyzers could reduce total plasma Hcy (tHcy) levels in ESRD patients.

METHODS

Two matched groups of patients (N = 13) showing mild to intermediate hyperhomocysteinemia on standard hemodialysis (HD) with conventional non-protein-leaking dialyzers were included. In the control group membranes were maintained the same, while the study group was switched to protein-leaking dialyzers (BK-F series; Toray, Japan) and studied for 6 months. tHcy was measured by high performance liquid chromatography (HPLC) at baseline and after 1, 3, and 6 months. Proteins and Hcy were also measured in the spent dialysate.

RESULTS

The pre-HD levels of tHcy in the control group remained close to baseline values (26.6 +/- 5.0 micromol/L), while in the study group at 1, 3, and 6 months they decreased from a baseline value (in micrormol/L) of 25.3 +/- 5.9 to 21.5 +/- 4.5, 16.9 +/- 4.0, and 17.2 +/- 4.2, respectively (P < 0.01 for values at 3 and 6 months vs. baseline). The intra-HD drop of tHcy (Delta HDHcy) slightly but progressively decreased during the 3 steps on protein-leaking dialyzers and a positive correlation was found between Delta HDHcy and pre-HD levels of tHcy. In spent dialysate samples from protein-leaking dialyzer-treated patients, the amount of protein-bound Hcy (bHcy) was approximately 10 times higher than in non-protein-leaking dialyzers, but the Delta HDHcy observed in non-protein-leaking dialyzers and protein-leaking dialyzers was comparable. Serum proteins and albumin were only slightly affected by protein-leaking dialyzers.

CONCLUSION

This study demonstrates that protein-leaking dialyzers used with a pure diffusive technique significantly lower pre-HD tHcy (approximately 33% of starting levels after 3 months of treatment) in ESRD patients. A possible underlying mechanism for this effect could be the removal of large molecular weight solutes responsible for a defective metabolism of the Hcy, as the removal of bHcy with protein-leaking dialyzers seems not sufficient, per se, to explain this steady reduction of tHcy levels in pre-HD.

Methylenetetrahydrofolate reductase gene polymorphism and susceptibility to diabetic nephropathy in type 1 diabetes

BACKGROUND

The T allele of the C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene is associated with elevated plasma homocysteine levels, and it has been postulated to be a risk factor for the development of diabetic nephropathy. We examined this hypothesis in both a case-control and a follow-up study in individuals with type 1 diabetes.

METHODS

In the case-control study, the control group included 310 subjects with normoalbuminuria and diabetes duration of 15 years or greater, and the case group included 88 prevalent cases with end-stage renal disease (ESRD). The follow-up study included 235 subjects with overt proteinuria followed up for 6 years (on average), during which time ESRD developed in 69 subjects. DNA from each individual was genotyped for the C677T MTHFR polymorphism.

RESULTS

The frequency of TT homozygotes did not vary significantly among the four groups: 10% in controls, 15% in prevalent cases of ESRD, 13% in cases with new-onset ESRD, and 11% in those who remained proteinuric during follow-up (P = 0.9, 6 df). Similarly, frequency of the T allele varied little among the same groups (range, 33% to 36%; P = 0.9, 3 df) During follow-up, 52 of 323 individuals with diabetic nephropathy died. Total mortality rates were 4.3/100 person-years in TT homozygotes, 2.4/100 person-years in CT heterozygotes, and 3.0/100 person-years in CC homozygotes (P = 0.55, 2 df).

CONCLUSION

Using both a large case-control and a follow-up study, we found no evidence that the C677T MTHFR polymorphism has a significant role in the development of diabetic nephropathy in type 1 diabetes.

Hyperhomocysteinemia and its relationship to cardiovascular disease in ESRD: influence of hypoalbuminemia, malnutrition, inflammation, and diabetes mellitus

BACKGROUND

In the general population, a mildly elevated plasma total homocysteine (tHcy) level is an independent and graded risk factor for cardiovascular disease (CVD). In patients with end-stage renal disease (ESRD), CVD is highly prevalent and a major cause of premature mortality, and plasma tHcy levels are as much as three to four times greater than in the general population. Several other risk factors, such as diabetes mellitus (DM), inflammation, and malnutrition, also are prevalent and contribute to CVD in patients with ESRD, and there are strong associations between inflammation, malnutrition, and hypoalbuminemia in these patients. Several investigations in patients with ESRD have shown the important role of vitamin status for plasma tHcy, but little attention has been given to the influence of nutritional status. However, it is obvious that hypoalbuminemia is of interest because a substantial fraction of tHcy (>70%) is protein bound, mainly to albumin.

RESULTS

In studies of patients with ESRD in whom the prevalence of hyperhomocysteinemia was very high (>90%), tHcy level was strongly related to serum albumin level, and patients with malnutrition had lower levels of both tHcy and serum albumin than those with normal nutritional status. Furthermore, inflammation, DM, and CVD are associated with hypoalbuminemia and therefore a lower degree of hyperhomocysteinemia. In our studies, in different groups of patients with ESRD, we showed that greater tHcy levels were associated with lower CVD mortality. However, this apparently paradoxical association between lower CVD mortality and lower plasma tHcy levels (although still abnormally high) does not refute the concept that hyperhomocysteinemia is a risk factor for CVD because almost all patients may have had long-standing elevated plasma tHcy levels within a range that makes them prone to develop atherosclerosis. Instead, a potentially detrimental effect of hyperhomocysteinemia on CVD in patients with ESRD may be obscured by the influence of hypoalbuminemia, whatever the cause, because hypoalbuminemia and its causes are strong predictors of mortality.

CONCLUSION

Our findings imply that nutritional status and serum albumin level, as well as the presence of inflammation and DM, should be taken into consideration when evaluating tHcy as a risk factor for CVD in patients with ESRD.

Uremia-related metabolic cardiac risk factors in chronic kidney disease

Growing evidence has been gathered over the last 15 years regarding the role of nontraditional or uremia-related risk factors in the pathogenesis of atherosclerosis in subjects with renal failure. Among those factors, dyslipidemia, inflammation, hyperhomocysteinemia, and oxidant stress have been extensively studied. However, the clinical significance of many of these factors remains controversial in light of reported studies. In this article, the existing evidence regarding the role of uremia-related risk factors in the pathogenesis of atherosclerosis is reviewed, with special emphasis on prevalence, cardiac risk, and management in patients with chronic kidney disease (CKD). Consensus treatment recommendations are provided for risk factors for which there is evidence to support preventive or therapeutic interventions.