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

Mesna for treatment of hyperhomocysteinemia in hemodialysis patients: a placebo-controlled, double-blind, randomized trial

BACKGROUND AND OBJECTIVES

Increased plasma total homocysteine is a graded, independent risk factor for the development of atherosclerosis and thrombosis. More than 90% of patients with end-stage renal disease have hyperhomocysteinemia despite vitamin supplementation. It was shown in previous studies that a single intravenous dose of mesna 5 mg/kg caused a drop in plasma total homocysteine that was significantly lower than predialysis levels 2 d after dosing. It was hypothesized 5 mg/kg intravenous mesna administered thrice weekly, before dialysis, for 8 wk would cause a significant decrease in plasma total homocysteine compared with placebo.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients with end-stage renal disease were randomly assigned to receive either intravenous mesna 5 mg/kg or placebo thrice weekly before dialysis. Predialysis plasma total homocysteine concentrations at weeks 4 and 8 were compared between groups by paired t test.

RESULTS

Mean total homocysteine at 8 wk in the placebo group was 24.9 micromol/L compared with 24.3 micromol/L in the mesna group (n = 22 [11 pairs]; mean difference 0.63). Interim analysis at 4 wk also showed no significant difference between mesna and placebo (n = 32 [16 pairs]; placebo 26.3 micromol/L, mesna 24.5 micromol/L; mean difference 1.88). Multivariable adjustments for baseline characteristics did not alter the analysis. Plasma mesna seemed to reach steady-state concentrations by 4 wk.

CONCLUSIONS

It is concluded that 5 mg/kg mesna does not lower plasma total homocysteine in hemodialysis patients and that larger dosages may be required.

Is homocysteine toxic in uremia?

High levels of homocysteine have been implicated as a cardiovascular risk factor in the general population and in patients with chronic renal failure, and particularly patients on hemodialysis. To classify a risk factor as causally related to a certain disease, both strong epidemiologic data and sound basic-science studies establishing a mechanism are needed. Among the latter, the hypomethylation of proteins and DNA, and protein homocysteinylation, have been investigated in uremia, providing for an array of toxic effects in this disease.

Homocysteinemia correlates with plasma thiol redox status in patients with end-stage renal disease

BACKGROUND/AIMS

In end-stage renal disease (ESRD), hyperhomocysteinemia is a common finding associated with increased cardiovascular risk. However, the pathogenic role of homocysteine is still unclear. In vitro studies show that thiol redox status affects endothelial cell functions. We therefore investigated the possible association between homocysteinemia and plasma thiol redox status in ESRD patients.

METHODS

Total plasma homocysteine (Hcy), cysteine (Cys) and free thiols (SH) were measured both before and after a dialytic session in 54 ESRD patients receiving (n = 15) or not receiving (n = 39) folate supplementation, and 17 control subjects.

RESULTS

High predialysis levels of both Hcy and Cys were found to be negatively correlated with low SH levels both in supplemented (r = -0.680, p < 0.01 and r = -0.624, p < 0.02, respectively) and unsupplemented (r = -0.698, p < 0.001 and r = -0.445, p < 0.01, respectively) patients. Following dialysis, SH values returned to normal and the above correlations were no longer appreciable.

CONCLUSION

A strong, folate therapy-insensitive association between homocysteinemia and plasma free thiol levels was found in ESRD patients. These results support a role for oxidative stress in ESRD-related hyperhomocysteinemia and suggest the plasma thiol redox status alteration as a possible pathogenic mechanism underlying the cardiovascular toxicity of hyperhomocysteinemia in these patients.

Impaired vascular reactivity in patients with chronic kidney disease

BACKGROUND

Patients with chronic kidney disease (CKD) show increased cardiovascular morbidity. We hypothesized that vascular properties which can be routinely evaluated noninvasively are related to different stages of CKD and their clinical and biochemical characteristics.

METHODS

Arterial vascular properties were quantified by the reflective index using digital photoplethysmography in 260 patients with CKD. Patients were grouped according to estimated glomerular filtration rate (eGFR). Additional measurements were performed in 50 healthy control subjects.

RESULTS

In patients with CKD stage 1 and 2 (n = 115; age 65 +/- 1 years) the reflective index was 30 +/- 1%, whereas in patients with CKD stage 3 and 4 (n = 60; age 72 +/- 1 years) the reflective index was 36 +/- 1%, and in patients with CKD stage 5 (n = 85; age 64 +/- 1 years) the reflective index was 36 +/- 1% (p < 0.01 by Kruskal-Wallis test) indicating increased arterial stiffness in advanced CKD. Arterial vascular reactivity was significantly impaired in patients with advanced stages of CKD (stage 1 and 2, 78 +/- 12%; stage 3 and 4, 32 +/- 12%; stage 5, 33 +/- 12%; p < 0.01). Univariate analysis showed a significant correlation of the reflective index and eGFR (Pearson r = -0.24; p < 0.0001). Multivariate regression analysis showed an independent association of the reflective index and eGFR (adjusted correlation coefficient, -0.24; p < 0.001).

CONCLUSION

The advanced stages of CKD are associated with increased vascular stiffness and impaired vascular reactivity and these changes are already present in CKD stage 3 and 4.

Homocysteine-lowering therapy: a role in stroke prevention?

On the basis of the results of several recent clinical trials, many researchers have concluded that vitamin therapy designed to lower total homocysteine concentrations is not effective in reducing the risk of cardiovascular events. However, whereas almost all myocardial infarctions are due to plaque rupture, stroke has many more pathophysiological mechanisms, and thrombosis-which is increased by raised total homocysteine concentrations-has an important role in many of these processes. Thus, stroke and myocardial infarction could respond differently to vitamin therapy. A detailed assessment of the results of the recent HOPE-2 trial and a reanalysis of the VISP trial restricted to patients capable of responding to vitamin therapy suggest that higher doses of vitamin B12 and perhaps new approaches to lowering total homocysteine besides routine vitamin therapy with folate, vitamin B6, and vitamin B12 could reduce the risk of stroke. Thus, therapy to lower homocysteine could still help to prevent stroke, if not other vascular outcomes.

Effect of N-Acetylcysteine on Endothelial Dysfunction in Dialysis Patients

BACKGROUND/AIMS

Patients with K/DOQI stage 5 chronic kidney disease (CKD) have higher incidence of cardiovascular events due to the oxidative stress and endothelial dysfunction (ED). The aim of this study is to evaluate the effects of N-acetylcysteine (NAC), which might prevent cardiovascular events by improving oxidative stress on endothelial cells in patients with CKD.

METHODS

Thirty uremic patients (age 40 +/- 12 years, 6 males) on hemodialysis (HD) were evaluated for ED by using high-resolution Doppler ultrasound of brachial artery before and after 6 weeks of oral NAC (2 x 600 mg) medication. Also, 13 healthy controls (35 +/- 9 years, 5 males) were included in the study. Reactive hyperemia following 5 min forearm ischemia was accepted as endothelium-dependent vasodilatation (flow-mediated dilatation; FMD) and compared to endothelium-independent vasodilatation in response to sublingual glyceril trinitrate (GTN).

RESULTS

Patients on HD had lower DeltaFMD (0.28 +/- 0.17 vs. 0.41 +/- 0.11, p < 0.05) and FMD% (7.5 +/- 5.05 vs. 11.33 +/- 2.95, p < 0.05) than the controls. Baseline DeltaGTN and GTN% were similar in two groups. NAC treatment significantly increased the DeltaFMD (0.41 +/- 0.11, p < 0.001 vs. baseline) and FMD% (10.59 +/- 3.22, p < 0.01 vs. baseline) of patients on HD, while it had no effect on DeltaGTN and GTN%.

CONCLUSION

These results suggest that NAC treatment could improve the ED by preventing the reduction of FMD in patients on HD.

Mesna as a nonvitamin intervention to lower plasma total homocysteine concentration: implications for assessment of the homocysteine theory of atherosclerosis

Elevated plasma total homocysteine is independently associated with atherosclerosis. Recent randomized trials show that vitamins lower total homocysteine but do not prevent cardiovascular events, suggesting the need for nonvitamin therapies to evaluate whether a causative relationship exists. Mesna (sodium 2-mercaptoethanesulfonate) is a thiol-containing drug capable of liberating homocysteine bound by disulfide bonds to proteins, facilitating its excretion. The effect of oral mesna on total homocysteine has not been evaluated and was the objective of this study. Eleven healthy volunteers received vehicle or 10 mg/kg mesna in random order, after which serial blood and urine samples were collected over 4 hours. Plasma total homocysteine decreased by 24.2% (P < .0001) following mesna. Urinary homocysteine excretion was significantly greater with mesna (3.9 +/- 2.4 mumol) compared to vehicle (0.4 +/- 0.1 mumol), P < .01. Oral mesna decreases plasma total homocysteine and is a potential nonvitamin treatment for assessing the homocysteine theory of atherosclerosis.

Phenylacetic acid and arterial vascular properties in patients with chronic kidney disease stage 5 on hemodialysis therapy

BACKGROUND

Phenylacetic acid (PAA) is a recently described uremic toxin that inhibits inducible nitric oxide synthase expression and plasma membrane calcium ATPase and may therefore also be involved in remodeling of arteries. Such vascular effects have not been evaluated yet in patients with chronic kidney disease stage 5.

METHOD

We prospectively measured the plasma concentrations of PAA using nuclear magnetic resonance spectroscopy in 50 patients with chronic kidney disease stage 5 (37 men, 13 women) on maintenance hemodialysis. Arterial vascular properties were quantified by the reflective index obtained from digital photoplethysmography.

RESULTS

During the hemodialysis session the plasma PAA concentration was reduced from 3.38 +/- 0.24 mmol/l (mean +/- SEM; median, 2.85 mmol/l; interquartile range, 2.02-4.52 mmol/l) to 2.25 +/- 0.11 mmol/l (median, 2.06 mmol/l; interquartile range, 1.62-2.86 mmol/l; n = 50; p < 0.001). There was a significant correlation between the PAA concentration and the reflective index before the start of the hemodialysis session.

CONCLUSION

The study demonstrates an association of PAA and arterial vascular properties in patients with chronic kidney disease stage 5.

Improvement in central arterial pressure waveform during hemodialysis is related to a reduction in asymmetric dimethylarginine (ADMA) levels

BACKGROUND

Cardiovascular mortality is high in hemodialysis (HD) patients. Early arterial pressure wave reflections, reflecting arterial stiffness and the endogenous nitric oxide synthesis inhibitor asymmetric dimethylarginine (ADMA) levels predict mortality in HD patients. Therefore, we aimed to study changes in ADMA levels and central arterial pressure waveform during HD.

METHODS

Thirty-two chronic HD patients were studied before and after a HD session. In a subset of 22 patients without arrhythmias, pulse wave analysis was performed on radial artery (SphygmoCor). Augmentation index (AIx), defined as difference between the second and first systolic peak divided by central pulse pressure, was used as a measure of arterial stiffness. ADMA was measured in plasma with the ELISA technique. Homocysteine was measured in plasma using the EIA technique.

RESULTS

HD reduced both AIx (19%; p = 0.003) and ADMA levels (17%; p < 0.001). The magnitudes of changes in AIx and ADMA during HD were correlated (r = 0.44; p = 0.045). Mean arterial pressure change was not significant. HD reduced homocysteine levels, but homocysteine was not related to ADMA or AIx.

CONCLUSION

The reduction in ADMA level seen after HD was associated with improvement in the central arterial pressure waveform, suggesting involvement of nitric oxide in the regulation of arterial stiffness in HD patients.

The uremic solute indoxyl sulfate induces oxidative stress in endothelial cells

BACKGROUND

Endothelial dysfunction and oxidative stress are matters of concern in patients with chronic renal failure (CRF). Uremic solutes retained in these patients could be involved in these processes. Notably, the protein-bound uremic solute indoxyl sulfate induces endothelial dysfunction in vitro, and has shown pro-oxidant effects.

OBJECTIVE

To demonstrate that indoxyl sulfate is a potential mediator of oxidative stress in endothelial cells in vitro.

METHODS

Indoxyl sulfate-induced oxidative stress in human umbilical vein endothelial cells (HUVEC) was studied by measuring reactive oxygen specie (ROS) production by cytofluorimetry, by analyzing the involvement of the pro-oxidative enzymes NAD(P)H oxidase, xanthine oxidase, and NO synthase, and by measuring the levels of the non-enzymatic antioxidant glutathione.

RESULTS

We showed that indoxyl sulfate induced a significant production of ROS in HUVEC, with or without human serum albumin. We then investigated the role of pro-oxidative enzymes and measured the levels of the antioxidant glutathione. The NAD(P)H oxidase inhibitors, DPI, and apocynin, inhibited ROS production, whereas inhibitors of xanthine oxidase, NO synthase, and mitochondrial ROS had no effect. Interestingly, indoxyl sulfate strongly decreased the levels of glutathione, one of the most active antioxidant systems of the cell. In addition, the ROS production mediated by indoxyl sulfate was inhibited by the antioxidants vitamin C, vitamin E, and NAC.

CONCLUSION

The uremic solute indoxyl sulfate enhances ROS production, increases NAD(P)H oxidase activity, and decreases glutathione levels in endothelial cells. Thus, indoxyl sulfate induces oxidative stress by modifying the balance between pro- and antioxidant mechanisms in endothelial cells.

Intensive management of risk factors for accelerated atherosclerosis: the role of multiple interventions

Patients at high risk of vascular events can reduce their risk by 75% to 80% through a combination of lifestyle changes and medical therapy. These include smoking cessation, a Mediterranean diet, daily exercise, maintaining a fit weight, moderate consumption of alcohol, effective control of blood pressure and diabetes, intensive treatment with lipid-lowering drugs and antiplatelet agents, and perhaps treatment with vitamins to lower homocysteine. Much of this is achieved primarily by the patient; physicians need to become better at assisting their patients in making lifestyle changes. Effective control of treatment-resistant hypertension can be improved by individualizing medical therapy to the underlying cause, based on measurement of plasma renin and aldosterone. Measurement of carotid plaque may be useful by providing feedback on the success of therapy.

Vascular sources of oxidative stress: implications for uremia-related cardiovascular disease

Chronic oxidative stress that characterizes uremia has potentially devastating effects on the vasculature and has been advocated in the pathogenesis of accelerated atherosclerosis in this disease. Recent advances have been made in our understanding of the molecular mechanisms that regulate expression and activity of key enzymes of vascular oxidative stress (eg, nicotinamide adenine dinucleotide phosphate [NAD{P}H] oxidase) and that dissect their interactions with signalling pathways of inflammation. The finding that NAD(P)H oxidase is upregulated in experimental uremia has important consequences from a physiologic and a therapeutic standpoint. In addition, identification of novel proteins involved in systemic oxidative stress has shed some new light on the pathogenesis of vascular disease. p66(shc) is a cytoplasmic protein that is expressed in a wide range of cell types. Initially believed to be involved in signalling pathways that regulate cell growth and oxidative stress, it has now been shown to play a pivotal role in promoting endothelial dysfunction and atherosclerosis. Although a specific role in uremia-related vascular disease has not yet been shown, available data in humans suggest involvement of p66(shc) in clinical conditions associated with increased oxidative stress.

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.

Modification of cardiovascular risk in hemodialysis patients: An evidence-based review

Cardiovascular disease accounts for 40% to 50% of deaths in dialysis populations. Overall, the risk of cardiac mortality is 10-fold to 20-fold greater in dialysis patients than in age and sex-matched controls without chronic kidney disease. The aim of this paper is to review critically the evidence that cardiac outcomes in dialysis patients are modified by cardiovascular risk factor interventions. There is limited, but as yet inconclusive controlled trial evidence that cardiovascular outcomes in dialysis populations may be improved by antioxidants (vitamin E or acetylcysteine), ensuring that hemoglobin levels do not exceed 120 g/L (especially in the setting of known cardiovascular disease), prescribing carvedilol in the setting of dilated cardiomyopathy, and by using cinacalcet in uncontrolled secondary hyperparathyroidism. Similarly, there are a number of negative controlled trials, which have demonstrated that statins, high-dose folic acid, angiotensin-converting enzyme inhibitors, multiple risk factor intervention via multidisciplinary clinics, and high-dose or high-flux dialysis are ineffective in preventing cardiovascular disease. Although none of these studies could be considered conclusive, the negative trials to date should raise significant concerns about the heavy reliance of current clinical practice guidelines on extrapolation of findings from cardiovascular intervention trials in the general population. It may be that cardiovascular disease in dialysis populations is less amenable to intervention, either because of the advanced stage of chronic kidney disease or because the pathogenesis of cardiovascular disease in dialysis patients is different from that in the general population. Large, well-conducted, multicenter randomized-controlled trials in this area are urgently required.

The Effect of Mesna on Plasma Total Homocysteine Concentration in Hemodialysis Patients

BACKGROUND

Plasma total homocysteine (tHcy) level is an independent risk factor for the development of atherosclerosis. The degree of risk in most of the population is decreased by using dietary vitamin supplementation; however, more than 90% of patients with end-stage renal disease have increased tHcy levels despite supplementation. Only a small fraction of tHcy is removed by hemodialysis because of extensive disulfide bonding to albumin. The objective of this study is to determine whether a single intravenous dose of mesna, a thiol-containing drug analogue of taurine, facilitates tHcy clearance during hemodialysis.

METHODS

Initial in vitro thiol exchange tests were performed with mesna in plasma from dialysis patients. Mesna, 300 micromol/L (49.2 mg/L), was incubated with plasma at 37 degrees C, and free homocysteine was measured at various times. In vivo, mesna activity was tested in 10 hemodialysis patients by administering 2.5 or 5.0 mg/kg of mesna intravenously at the beginning of a treatment cycle. Blood samples were drawn throughout dialysis, and plasma tHcy levels were compared with those obtained from a previous dialysis session in which mesna was not administered.

RESULTS

In vitro, mesna liberated 36.5% +/- 2.5% of protein-bound homocysteine in 30 minutes. In vivo, a single 2.5-mg/kg dose of mesna was ineffective; however, at 5.0 mg/kg, it caused a 55.2% +/- 3.9% decrease in plasma tHcy levels postdialysis compared with a 34.2% +/- 5.3% decrease with dialysis alone (P < 0.001).

CONCLUSION

Intravenous mesna causes a rapid decrease in plasma tHcy levels during hemodialysis.

Increased arterial vascular tone during the night in patients with essential hypertension

The time-dependent incidence of cardiovascular events points to an important role of chronobiology for arterial properties. To evaluate arterial properties in patients with essential hypertension, we assessed arterial vascular tone during sleep at night in patients with essential hypertension and normotensive control subjects. Vascular tone was continuously quantified by the reflective index obtained by non-invasive digital photoplethysmography and an algorithm for continuous, investigator-independent, automatic analysis of digital volume pulse. During the first half of the night, the reflective index was significantly higher in 31 patients with essential hypertension compared to 30 normotensive control subjects (30.0+/-0.2 vs 28.8+/-0.2; P=0.001). In patients with essential hypertension, the reflective index significantly increased from 30.0+/-0.2 in the first half (from 2301 to 0230) to 30.7+/-0.2 in the second half (from 0231 to 0600) of the night (n=31; P=0.027). In normotensive control subjects the reflective index also significantly increased from 28.8+/-0.2 in the first half of the night to 30.2+/-0.2 in the second half of the night (n=30; P=0.001). An increase of the reflective index tone indicated systemic vasoconstriction as confirmed by cold pressure tests and a significant correlation between arterial vascular tone and sympathetic nerve activity measured by microneurography from the peroneal nerve. Photoplethysmographic determination of arterial vascular tone demonstrated a significant increase of systemic arterial vascular tone in patients with essential hypertension during the first half of the night compared to normotensive control subjects.

Thiol exchange: An in vitro assay that predicts the efficacy of novel homocysteine lowering therapies

Elevated plasma total homocysteine (tHcy) is a risk factor for atherosclerosis. Hcy is 70-80% bound to albumin as a disulfide. Recent trials have evaluated ability of thiol-containing drugs to exchange with protein bound Hcy and consequently increase its renal clearance. The objective of this study was to develop an in vitro assay to predict the efficacy of thiol-containing drugs to lower tHcy in the clinical setting. The assay was used to test the effects of N-acetylcysteine (NAC), mesna, captopril, dimercaptosuccinic acid (DMSA), and penicillamine. Hcy was added in vitro to plasma of healthy subjects (n = 6) and equilibrated. Concentrations of thiol exchange agent were added and incubated at 37 degrees C. Aliquots were removed at selected intervals and free Hcy determined. Mesna, captopril, and NAC caused a concentration-dependent increase in free Hcy. Three-hundred micromolar mesna and captopril had a greater effect than equimolar NAC, increasing free Hcy by 33.9 +/- 5.0% and 32.0 +/- 2.6%, respectively compared to 22.3 +/- 2.4% for NAC, p < 0.001. Our in vitro results indicate that mesna, captopril, and NAC effectively exchange with covalently bound Hcy. This assay can act as screening tool for novel tHcy lowering therapies and should spare the expense of negative trials.

Serum myeloperoxidase and mortality in maintenance hemodialysis patients

BACKGROUND

During inflammation, myeloperoxidase (MPO) is released, for which its measurement in systemic circulation may be used as an index of leukocyte activation and oxidant stress. MPO levels correlate with angiographic evidence of coronary atherosclerosis and cardiovascular events in subjects with chest pain within the general population. We hypothesized that serum MPO levels are associated with adverse clinical outcomes in maintenance hemodialysis (MHD) patients.

METHODS

MPO levels were determined in serum samples from 356 MHD patients at the start of a 3-year cohort.

RESULTS

Patients (46% women, 28% blacks, 54% with diabetes) were 54.6 +/- 14.6 (SD) years old and had undergone MHD for a median period of 26 months. Measured serum MPO level was 2,005 +/- 1,877 pmol/L (median, 1,444 pmol/L; interquartile range, 861 to 2,490 pmol/L). MHD patients with greater total body fat had greater MPO levels. MPO level had statistically significant (P < 0.01) and positive correlations with values for serum C-reactive protein (CRP; r = +0.15), interleukin 6 (IL-6; r = +0.23), tumor necrosis factor alpha (TNF-alpha; r = +0.21), and white blood cell count (r = +0.21). A death hazard ratio for each 1,000-pmol/L increase in serum MPO level was 1.14 (95% confidence interval [CI], 1.03 to 1.26; P = 0.01) after controlling for age, race (black), diabetes mellitus, dialysis vintage, Charlson comorbidity score, history of previous cardiovascular disease, blood hemoglobin level, and serum concentrations of albumin, CRP, IL-6, and TNF-alpha. After dividing MPO values into 3 equal groups (tertiles), the death hazard ratio of the highest tertile (versus the middle tertile) was 1.82 (95% CI, 1.07 to 3.10; P = 0.03).

CONCLUSION

Serum MPO levels correlate with levels of markers of inflammation and prospective mortality risk in MHD patients.

Impaired renal allograft function is associated with increased arterial stiffness in renal transplant recipients

It is important whether impairment of renal allograft function may deteriorate arterial stiffness in renal transplant recipients. In a cross-sectional study, arterial vascular characteristics were non-invasively determined in 48 patients with renal allograft using applanation tonometry and digital photoplethysmography. Mean age was 51 +/- 2 years (mean +/- SEM), and studies were performed 17 +/- 1 months after transplantation. The stage of chronic kidney disease was based on the glomerular filtration rate. We observed a significant association between the stage of chronic kidney disease and arterial stiffness of large arteries S1 and small arteries S2 in renal transplant recipients (each p < 0.05 by non-parametric Kruskal-Wallis test between groups). Multivariate linear regression analysis showed that male gender of patients with renal allograft (p < 0.01) reduced glomerular filtration rate (p = 0.01), and older age of kidney donor (p = 0.04) were independently associated with an increase of large artery stiffness S1. Furthermore, a significant association between the stage of chronic kidney disease and arterial vascular reactivity during reactive hyperemia was observed (p < 0.05 by non-parametric Kruskal-Wallis test between groups). It is concluded that impairment of renal allograft function is associated with an increased arterial stiffness in renal transplant recipients.

Noninvasive continuous monitoring of digital pulse waves during hemodialysis

Intermittent hemodynamic instability during hemodialysis treatment is a frequent complication in patients with end-stage renal failure. A noninvasive method for continuous hemodynamic monitoring is needed. We used noninvasive digital photoplethysmography and an algorithm for continuous, investigator-independent, automatic analysis of digital volume pulse in 10 healthy subjects and in 20 patients with end-stage renal failure during the hemodialysis session. The reflective index was defined representing the diastolic component of the digital pulse wave. The properties of the reflective index were studied in healthy control subjects (n=10). An increased reflective index was due to increased peripheral pulse wave reflection (e.g., vasoconstriction). During a hemodialysis session, the reflective index increased significantly from 36+/-3 arbitrary units to 41+/-3 arbitrary units (n=20; p<0.05) measured using digital photoplethysmography. This increase appeared in 15 of the 20 patients with end-stage renal failure. Our data establish digital photoplethysmography as a noninvasive, reliable, and sensitive method for continuous monitoring during the hemodialysis session.

Homocysteine and risk in end-stage renal disease: a matter of context

Like blood pressure and cholesterol, homocysteine shows a paradoxical inverse relationship with cardiovascular complications in end-stage renal disease (ESRD). A paper by Ducloux et al. in this issue adds perhaps decisive evidence on malnutrition-hypoalbuminemia as the main factor explaining the counterintuitive association between homocysteine and clinical outcome reported in previous studies.

Biomarkers in chronic kidney disease: utility and issues towards better understanding

PURPOSE OF REVIEW

Biomarkers are substances that reflect the presence of a given disease, its pathophysiology or organ damage. These indicators are increasingly proposed to assess prognosis or the response to treatment. This review examines the value of a series of biomarkers which have been recently tested in prospective studies in chronic kidney disease and end-stage renal disease patients.

RECENT FINDINGS

C reactive protein has coherently emerged as an early marker of renal dysfunction. The usefulness of this measurement for predicting the evolution of chronic kidney disease or for monitoring the response to renoprotective treatment, however, still remains unproven. On the other hand the measurement of C reactive protein can be recommended for monitoring the risk of atherosclerotic complications in patients with chronic kidney disease and end-stage renal disease, particularly in those with evidence of coronary heart disease or other cardiovascular complications (i.e. in the vast majority of patients followed up in nephrology clinics). There is growing interest in homocysteine and asymmetric dimethyl arginine as biomarkers of cardiovascular and renal risk but the usefulness of these biomarkers in clinical practice remains to be proven. Brain natriuretic peptide and troponin T are strongly related to cardiovascular outcomes in end-stage renal disease patients but their value in this population still requires to be proper tested in specifically designed intervention studies.

SUMMARY

Among emerging biomarkers C reactive protein is the only one which is very near to fulfilling the methodological requirements for being recommended in clinical practice.

IL-10, IL-6, and TNF-alpha: central factors in the altered cytokine network of uremia--the good, the bad, and the ugly

It has been increasingly apparent that wasting and cardiovascular disease (CVD) is associated with a persistent systemic inflammatory response in end-stage renal disease (ESRD) patients. The reasons for the increased risk of inflammation in ESRD patients appear to be complex, including non-dialysis as well as dialysis-related factors. The combination of an impaired immune response coupled with persistent immune stimulation may have a role in the low-grade systemic inflammation and altered cytokine balance that characterizes the uremic state and which may translate into increased risk for vascular disease. The accelerated atherosclerotic process of ESRD may involve several interrelated processes, such as oxidative stress, endothelial dysfunction, and vascular calcification, in a milieu of constant low-grade inflammation with impaired function of neutrophils and T cells, as well as a dysregulated cytokine network. Although a large number of pro- and anti-inflammatory cytokines are of importance, available data suggest that the anti-inflammatory cytokine interleukin (IL)-10 and the mainly proinflammatory cytokines IL-6 and tumor necrosis factor-alpha (TNF-alpha) may play important roles in the development of Th imbalance, CVD and wasting in the uremic milieu. Given the strong association between proinflammatory cytokines and complications common in ESRD, such as vascular calcification and wasting, the potential role of both general and targeted anticytokine treatment strategies in ESRD patients needs further evaluation.

Correlation of plasma homocysteine level with arterial stiffness and pulse pressure in hemodialysis patients

Elevated plasma homocysteine, arterial stiffness, and increased pulse pressure (PP) are independently associated with higher cardiovascular risk in patients with end-stage renal disease. The aim of this study is to investigate the influence of plasma homocysteine on arterial stiffness and PP in hemodialysis (HD) patients. One hundred and nine HD patients were stratified into three groups by plasma homocysteine levels: low (11.2-20.8 micromol/L), middle (21.2-25.1 micromol/L), and high tertiles of plasma homocysteine (Hcy) group (25.2-43.9 micromol/L). Using a computerized oscillometry, we measured the arterial stiffness index (ASI) and blood pressure (BP) hemodynamic parameters in the brachial artery. The high Hcy group exhibited a higher ASI (110.4+/-129.5 versus 46.2+/-17.5, mean+/-S.E., P<0.01), PP (59.7+/-23.1 versus 43.3+/-16.3 mmHg, P<0.01), and age (57.8+/-14.1 versus 49.9+/-12.7 years, P<0.05) compared with the low Hcy group. Plasma homocysteine was significantly correlated with ASI (r=0.25, P<0.001), PP (r=0.33, P<0.001), systolic BP (r=0.31, P<0.001), and age (r=0.24, P<0.05). Serum ferritin was significantly correlated with ASI (r=0.24, P<0.05) and PP (r=0.23, P<0.05). ASI was also correlated with PP (r=0.64, P<0.001). Multiple regression analyses showed that both plasma homocysteine and serum ferritin had significant associations with ASI (beta=4.246, P=0.007 and beta=0.024, P=0.006, respectively), and with PP (beta=1.089, P=0.002 and beta=0.005, P=0.005, respectively) independent of other classic risk factors for atherosclerosis. In conclusion, plasma homocysteine, along with serum ferritin, may act as an important predictor for arterial stiffness and PP in HD patients.

The antioxidant N-acetylcysteine prevents accelerated atherosclerosis in uremic apolipoprotein E knockout mice

BACKGROUND

Cardiovascular disease is the most frequent cause of mortality in chronic renal failure (CRF). Therefore, it is important to identify appropriate treatment measures. The antioxidant N-acetylcysteine (NAC) has been shown to reduce cardiovascular events in hemodialysis patients. Here we examine a possible direct effect of NAC supplementation on uremia-enhanced atherosclerosis in apolipoprotein E-deficient (apoE(-/-)) mice.

METHODS

Uremia was induced surgically in 8-week-old female apoE(-/-) mice. Two weeks after creation of CRF mice were randomized to receive either NAC (daily oral gavage with 200 mg/kg for 8 weeks) or placebo. They were compared to a control group of sham-operated apoE(-/-) mice receiving placebo. After 8 weeks of treatment, the mice were sacrificed, and the cross-section surface area of atherosclerotic plaques was measured in aortic root and descending aorta.

RESULTS

At 10 weeks following surgery, atherosclerotic lesions were significantly larger in uremic apoE(-/-) mice than in nonuremic controls. This accelerated atherosclerosis was associated with an increase in aortic nitrotyrosine expression and collagen plaque content. NAC treatment inhibited the progression of atherosclerotic lesions and plaque collagen content compared with placebo treatment. In addition, plaques from NAC-treated uremic animals showed a significant decrease in nitrotyrosine expression whereas the degree of macrophage infiltration was comparable in both uremic groups. There was no difference in mean arterial blood pressure between the three groups.

CONCLUSION

We show for the first time that the antioxidant NAC is capable of reducing atheroma progression, in an animal model of uremia-enhanced atherosclerosis, probably via a decrease in oxidative stress.

Relevance of Oxidative Pathways in the Pathophysiology of Chronic Kidney Disease

Patients with uremia (whether requiring renal replacement therapy or not) have a greatly increased cardiovascular risk that cannot be explained entirely by traditional cardiovascular risk factors. An increase in oxidative stress has been proposed as a nontraditional cardiovascular risk factor in this patient population. Using a wide variety of different biomarkers of increased oxidative stress status, numerous laboratories around the world have now unequivocally demonstrated that uremia is a state of increased oxidative stress. Recent data also suggest linkages between oxidative stress inflammation, endothelial dysfunction, and malnutrition in the uremic population. These factors are probably synergistic in their effects on atherogenecity and risk of a cardiovascular event. The pathophysiology of increased oxidative stress in uremia is multifactorial, but the retention of oxidized solute by the loss of kidney function is probably a major contributor. Uremic oxidative stress can be characterized biologically by an increase in lipid per oxidation products and reactive aldehyde groups as well as by increased retention of oxidized thiols. Two recently published studies have suggested that antioxidative therapy may be particularly promising in reducing cardiovascular events in this patient population.Further definitive studies of antioxidant use are greatly needed.

Potential antiatherogenic and anti-inflammatory properties of sevelamer in maintenance hemodialysis patients

BACKGROUND

Patients affected by end-stage renal disease (ESRD) demonstrate a very high cardiovascular risk mediated by traditional cardiovascular risk factors as well as abnormal mineral metabolism and a state of chronic inflammation. Sevelamer is a nonabsorbable non-calcium-based hydrogel with potential antiatherosclerotic properties.

METHOD AND RESULTS

One hundred eight patients undergoing maintenance hemodialysis were randomized to sevelamer or calcium acetate as treatment for hyperphosphatemia. A coronary artery calcium score, as a measure of plaque burden, was calculated at baseline and 1 year, along with serial measurements of serum lipoproteins, beta2-microglobulin, and high-sensitivity C-reactive protein (hs-CRP). At 1 year, coronary artery calcium score progressed significantly from baseline in calcium acetate-treated subjects ( P < .001) but not in sevelamer-treated patients (P = NS). Total cholesterol (P < .0001), low-density lipoprotein cholesterol (P < .0001), apolipoprotein B (P < .0001), beta2-microglobulin (P = .018), and hs-CRP (P < .002) decreased, and high-density lipoprotein increased significantly (P = .036) from baseline in the sevelamer-treated subjects but not in subjects treated with calcium acetate despite the more frequent use of statins in the latter group (46% vs 22%, P < .05). The changes in total and low-density lipoprotein cholesterol, apolipoprotein B, and hs-CRP were significantly different between treatment groups (all P < .01).

CONCLUSIONS

Sevelamer leads to favorable changes in lipids and inflammatory markers with potentially useful antiatherogenic effects in hemodialysis patients.

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.

Linking oxidative stress and inflammation in kidney disease: which is the chicken and which is the egg?

For end-stage renal disease (ESRD) patients, cardiovascular disease remains the single most common cause of excess morbidity and mortality. Furthermore, although the prevalence of traditional cardiovascular risk factors is high in the dialysis population, the extent and severity of associated cardiovascular morbidity and mortality remain disproportionate to traditional risk factor profiles. Consequently, considerable effort has been focused on "nontraditional" risk factors for cardiovascular events in this patient population. Among the examined nontraditional risk factors, increased oxidative stress as well as increased acute phase inflammation are postulated to be important contributors to uremic cardiovascular risk. Additional important uremic cardiovascular risk factors include malnutrition and endothelial dysfunction, both of which may be directly linked to the processes that cause increased oxidative stress and inflammation in uremia. In this context I review available data linking the pathogenesis of oxidative stress to acute phase inflammation and uremia. I also review data suggesting that oxidative stress in uremia directly contributes to the development of acute phase inflammation and that patients with higher levels of inflammation have higher levels of oxidative stress biomarkers. Similarly I review emerging data on the potential effects of antioxidant therapy on inflammatory biomarkers, as well as data suggesting that strategies to lower acute phase inflammation may also improve biomarkers of oxidative stress. Theoretical constructs evaluating the linkage of oxidative stress and inflammation in uremia and their contribution to the pathogenesis of atherosclerosis are suggested.

Chronic Renal Dysfunction as an Independent Risk Factor for the Development of Cardiovascular Disease

Cardiac disease is the leading cause of death in patients having end-stage renal disease (ESRD). Patients with ESRD have a higher risk for developing coronary artery disease (CAD) than one would estimate from the presence of traditional risk factors such as hypertension, diabetes, hyperlipidemia, and cigarette smoking. Patients with milder forms of renal dysfunction who do not require dialysis also appear to have an increased risk for CAD. ESRD is associated with anemia, hyperhomocystinemia, increased calcium-phosphate product, hypoalbuminemia, increased troponin, increased markers of inflammation, increased oxidant stress, and decreased nitric oxide activity, factors that could contribute to increased CAD risk. Patients with ESRD require aggressive management of traditional risk factors for CAD, which include hypertension, hyperlipidemia, hyperhomocystinemia, and hypercoagulability. Milder forms of renal dysfunction could also be predictors of occult CAD and should be screened for in assessing cardiac risk in asymptomatic individuals.

Homocysteine in relation to cognitive performance in pathological and non-pathological conditions

Elevated serum homocysteine has been associated with increased risk of Alzheimer's disease. Furthermore, elevated homocysteine levels are related to cognitive dysfunction in the elderly. The aim of the present study was to explore the disease specificity of the relation between serum total homocysteine levels and cognitive function. For this, we summarize data from several studies on homocysteine levels in both normal and pathological conditions performed in our laboratories and evaluate possible mechanisms of effects of elevated homocysteine levels in the central nervous system. Total homocysteine levels were measured in serum of: 1) healthy aging individuals; 2) patients with Alzheimer's and Parkinson's disease and patients with other cognitive disorders; and 3) patients with multiple sclerosis. Increased serum homocysteine concentration was related to worse cognitive performance over a 6-year period in the normal aging population (r=−0.36 to −0.14, p<0.01 for the Word learning tests; r=0.76, p<0.05 for the Stroop Colored Word test). Homocysteine was only increased in patients with Parkinson's disease on L-Dopa therapy (18.9 vs. 16.5μmol/L in healthy controls), and not in dementia patients. Homocysteine was elevated in patients with progressive multiple sclerosis (15.0μmol/L, n=39, compared to 12.0 μmol/L in 45 controls) and correlated to both cognitive and motor function (r=−0.33 and −0.33, p<0.05, respectively). The relationship between homocysteine and cognitive function in non-pathological and pathological situations indicates that changes in its levels may play a role in cognitive functioning in a broad spectrum of conditions.

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

POOR NUTRITIONAL STATUS AND INFLAMMATION: Novel Approaches in an Integrated Therapy of Inflammatory-Associated Wasting in End-Stage Renal Disease

It is increasingly apparent that end-stage renal disease (ESRD) patients carry an inflammatory burden, which may play a pivotal role in the evolution of not only wasting, but also the massive increase in the relative risk of cardiovascular disease (CVD). Thus wasting is strongly associated with a persistent systemic inflammatory response, CVD, and impaired patient survival in end-stage renal disease (ESRD), as well as in other chronic diseases. Evidence suggests that a facilitative interaction between inflammatory cytokines and other factors such as poor appetite, comorbidity, acidosis, anemia, and hormonal derangements may cause wasting in this patient group. Clearly, isolated interventions in the form of nutritional energy and protein supplementation have seldom proven to be very effective in improving nutritional status and outcome in ESRD patients, presumably because of the need to attack other causative factors. Therefore, new treatment strategies must be evaluated. Strategies such as multiple appetite stimulants, various "anti-inflammatory diets," and new potentially useful anti-inflammatory pharmacologic agents may be tested alone, or in combination, to evaluate if these new therapeutic modalities can improve the outcome of ESRD patients. As the etiology of wasting in ESRD is multifactorial, we propose that its treatment must include not one, but a number of concomitant measures to provide an integrated therapy against this devastating complication.

N-Acetylcysteine in nephrology; contrast nephropathy and beyond

PURPOSE OF REVIEW

Since the first publication appeared in 2000 showing that prophylactic oral administration of the antioxidant acetylcysteine, along with adequate hydration, can prevent the reduction in renal function induced by non-ionic, low-osmolality contrast agents, acetylcysteine has rapidly become widely used in clinical practice. Meanwhile, other applications of acetylcysteine in nephrology have been reported. This review analyses recent literature on the effects of acetylcysteine on radiocontrast-induced nephropathy, on plasma homocysteine concentrations, and on cardiovascular events in patients with end-stage renal failure.

RECENT FINDINGS

At least 19 randomized trials evaluating acetylcysteine for the prevention of radiocontrast-induced nephropathy, at least five meta-analyses, and several reviews on that topic have been published within the past 4 years. The studies on radiocontrast-induced nephropathy showed remarkably mixed results, probably as a result of study heterogeneity. One study recently indicated that the administration of acetylcysteine during a haemodialysis session significantly lowered plasma homocysteine concentrations. Another study indicated that long-term antioxidative treatment with acetylcysteine significantly reduced cardiovascular events in patients with end-stage renal failure.

SUMMARY

Although there are controversies on dosing and timing, the use of acetylcysteine together with hydration should be considered to protect patients from radiographic contrast media-induced nephropathy. Long-term antioxidative treatment with acetylcysteine in patients with end-stage renal failure may also be useful to prevent adverse cardiovascular events.