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

New polymethylmethacrylate membrane, NF-U, improves nutritional status and reduces patient-reported symptoms in older dialysis patients

Introduction

We previously reported the nutritional advantage of polymethylmethacrylate (PMMA) membranes to prevent the progression of malnutrition in dialysis patients. In this study, we examined whether a new PMMA dialyzer, NF-U, has advantages to improve the nutritional condition, patient-reported symptoms, and other clinical parameters in older dialysis patients.

Methods

We selected ten older chronic dialysis patients who were treated with NF-U for improving their worsening nutritional parameters and retrospectively evaluated nutrition and patient-reported symptoms. Patient-reported symptoms were surveyed by our original questionnaire including 20 items of symptom.

Results

Serum albumin concentration, geriatric nutritional risk index, and percent creatinine generation rate increased from 3.01 ± 0.16 to 3.25 ± 0.17 g/dL, 87.7 ± 5.8 to 91.4 ± 6.2, 100.2 ± 21.6 to 111.9 ± 20.9% at 1 and 4 months after switching to NF-U, respectively. For patient-reported outcomes, fatigue and the total score of patient-reported outcomes were improved after switching to NF-U.

Conclusion

Our results suggest that NF-U is a good choice for older dialysis patients to ameliorate their nutritional status and patient-reported outcomes.

Clinical advantages of a newly launched anti-thrombotic PMMA membrane for the nutritional status and dialysis-related symptoms in older chronic dialysis patients: a multicenter pilot study

Background

Malnutrition that is associated with inflammation is a key factor of poor outcome in chronic hemodialysis patients, especially in older dialysis patients. Polymethyl methacrylate (PMMA) membrane has been reported to improve the inflammatory status by removing pro-inflammatory cytokines via adsorption. However, older dialysis patients occasionally have multiple uncomfortable dialysis-related symptoms, which decrease their quality of life and survival rate. We investigated whether a new PMMA membrane, Filtryzer NF, can improve malnutrition and dialysis-related symptoms in older hemodialysis patients.

Methods

Patients over 70 years of age who were dialyzed using a polysulfone (PS) membrane were enrolled and randomly allocated into one of two groups: control or NF. In the NF group, the PS dialyzers were changed to NF, whereas in the control group, the PS membrane was continuously used. The primary outcome was the malnutrition–inflammation score (MIS). Secondary outcomes were C-reactive protein, normalized protein catabolism rate, percent of creatinine generation rate, arm circumference, and eight dialysis-related symptoms. The primary and secondary outcomes were measured every 3 months for 1 year.

Results

Fifty-four hemodialysis patients were randomly assigned to the NF group (n = 28) or the control group (n = 26). During the 12-month study period, 11 and 10 patients were withdrawn from the NF and control groups, respectively. There was no significant difference in the MIS between the groups during the study or between the beginning and the end of the study within each group. For the secondary outcomes, there was a significant reduction in the total score of dialysis-related symptoms in the NF group but not in the control group. During the study period, the total dialysis-related symptoms score in the NF group was significantly decreased from 6 (range, 1–16) to 3 (range, 0–11) (median [minimum–maximum], p < 0.05). Other secondary outcomes were not different between the groups or between the beginning and the end of the study.

Conclusions

This study showed no advantage for the nutritional status in older hemodialysis patients using NF compared with PS. However, our results indicated that NF may improve several dialysis-related symptoms. To clarify this clinical finding, large-scale prospective randomized clinical trials are required.

Trial registration

This study was registered with the Clinical Trials Registry of the University Hospital Medical Information Network (registration ID, UMIN000032990).

Reduction of protein-bound uraemic toxins in plasma of chronic renal failure patients: A systematic review

BACKGROUND

Protein-bound uraemic toxins (PBUTs) accumulate in patients with chronic kidney disease and impose detrimental effects on the vascular system. However, a unanimous consensus on the most optimum approach for the reduction of plasma PBUTs is still lacking.

METHODS

In this systematic review, we aimed to identify the most efficient clinically available plasma PBUT reduction method reported in the literature between 1980 and 2020. The literature was screened for clinical studies describing approaches to reduce the plasma concentration of known uraemic toxins. There were no limits on the number of patients studied or on the duration or design of the studies.

RESULTS

Out of 1274 identified publications, 101 studies describing therapeutic options aiming at the reduction of PBUTs in CKD patients were included in this review. We stratified the studies by the PBUTs and the duration of the analysis into acute (data from a single procedure) and longitudinal (several treatment interventions) trials. Reduction ratio (RR) was used as the measure of plasma PBUTs lowering efficiency. For indoxyl sulphate and p-cresyl sulphate, the highest RR in the acute studies was demonstrated for fractionated plasma separation, adsorption and dialysis system. In the longitudinal trials, supplementation of haemodialysis patients with AST-120 (Kremezin®) adsorbent showed the highest RR. However, no superior method for the reduction of all types of PBUTs was identified based on the published studies.

CONCLUSIONS

Our study shows that there is presently no technique universally suitable for optimum reduction of all PBUTs. There is a clear need for further research in this field.

Elevated plasma free thiols are associated with early and one-year graft function in renal transplant recipients

Background

Reduced free thiols in plasma are indicative of oxidative stress, which is an important contributor to ischaemia-reperfusion injury (IRI) in kidney transplantation leading to kidney damage and possibly delayed graft function (DGF). In a post-hoc, exploratory analysis of the randomised controlled CONTEXT trial, we investigated whether higher (i.e. less oxidised) plasma levels of free thiols as a biomarker of reduced oxidative stress are associated with a better initial graft function or a higher GFR.

Methods

Free thiol levels were measured in plasma at baseline, 30 and 90 minutes after reperfusion of the kidney as well as at Day 1, Day 5 and twelve months after kidney transplantation in 217 patients from the CONTEXT study. Free thiol levels were compared to the kidney graft function measured as the estimated time to a 50% reduction in plasma creatinine (tCr50), the risk of DGF and measured GFR (mGFR) at Day 5 and twelve months after transplantation.

Results

Higher levels of free thiols at Day 1 and Day 5 are associated with higher mGFR at Day 5 (p<0.001, r²_adj. = 0.16; p<0.001, r²_adj. = 0.25), as well as with mGFR at twelve months (p<0.001, r²_adj. = 0.20; p<0.001, r²_adj. = 0.16). However, plasma levels of free thiols at 30 minutes and 90 minutes, but not Day 1, were significantly higher among patients experiencing DGF.

Conclusion

Higher levels of plasma free thiols at Day 1 and Day 5, which are reflective of lower levels of oxidative stress, are associated with better early and late graft function in recipients of a kidney graft from deceased donors.

Trial registration

ClinicalTrials.gov Identifier:NCT01395719.

Relation of kidney function and homocysteine in patients with hypothyroidism

OBJECTIVE

It has been found that both serum homocysteine (Hcy) and serum creatinine levels were increased in hypothyroidism patients. The aim of this study was to investigate the correlation between serum Hcy and kidney function in patients with subclinical hypothyroidism or hypothyroidism.

METHODS

A total of 448 subjects were enrolled and divided into three groups: hypothyroidism (n = 129), subclinical hypothyroidism (n = 141), and control group (n = 168). Anthropometric information, metabolic parameters, serum Hcy and creatinine levels, and estimated glomerular filtration rate (eGFR) were analyzed.

RESULTS

Compared with healthy subjects, patients with subclinical hypothyroidism or hypothyroidism had significantly higher serum Hcy and creatinine levels and lower eGFR level (all P < 0.001). Serum Hcy was negatively correlated with eGFR in subclinical hypothyroidism patients (r = -0.220, P = 0.009), and in hypothyroidism patients (r = -0.422, P < 0.001). After adjusting for age, sex and BMI, eGFR was still significantly correlated with serum Hcy in subclinical hypothyroidism or hypothyroidism patients (both P < 0.05). Levothyroxine treatment resulted in significantly decreased Hcy and increased eGFR in hypothyroidism patients (both P < 0.001). The decrease in Hcy was correlated with the increased eGFR after treatment (P = 0.001).

CONCLUSION

Serum Hcy was negatively correlated with eGFR in subclinical hypothyroidism or hypothyroidism patients. After levothyroxine treatment, a correlation was found between the decrease in serum Hcy and the increase in eGFR in hypothyroidism patients.

The age-dependent decline of the extracellular thiol-disulfide balance and its role in SARS-CoV-2 infection

SARS-CoV-2 (COVID-19) infection can cause a severe respiratory distress syndrome. The risk of severe manifestations and mortality characteristically increase in the elderly and in the presence of non-COVID-19 comorbidity. We and others previously demonstrated that the low molecular weight (LMW) and protein thiol/disulfide ratio declines in human plasma with age and such decline is even more rapid in the case of inflammatory and premature aging diseases, which are also associated with the most severe complications of COVID-19 infection. The same decline with age of the LMW thiol/disulfide ratio observed in plasma appears to occur in the extracellular fluids of the respiratory tract and in association with many pulmonary diseases that characteristically reduce the concentrations and adaptive stress response of the lung glutathione. Early evidence in literature suggests that the thiol to disulfide balance of critical Cys residues of the COVID-19 spike protein and the ACE-2 receptor may influence the risk of infection and the severity of the disease, with a more oxidizing environment producing the worst prognosis. With this hypothesis paper we propose that the age-dependent decline of LMW thiol/disulfide ratio of the extracellular fluids, could play a role in promoting the physical (protein-protein) interaction of CoV-2 and the host cell in the airways. Therefore, this redox-dependent interaction is expected to affect the risk of severe infection in an age-dependent manner. The hypothesis can be verified in experimental models of in vitro CoV-2 infection and at the clinical level in that LMW thiols and protein thiolation can now be investigated with standardized, reliable and versatile laboratory protocols. Presenting the verification strategy of our hypothesis, we also discuss available nutritional and ancillary pharmacological strategies to intervene on the thiol/disulfide ratio of extracellular fluids of subjects at risk of infection and COVID-19 patients.

Albumin handling in different hemodialysis modalities

Hypoalbuminemia is a major risk factor for morbidity and mortality in dialysis patients. With increasing interest in highly permeable membranes and convective therapies to improve removal of middle molecules, transmembrane albumin loss increases accordingly. Currently, the acceptable upper limit of albumin loss for extracorporeal renal replacement therapies is unknown. In theory, any additional albumin loss should be minimized because it may contribute to hypoalbuminemia and adversely affect the patient's prognosis. However, hypoalbuminemia-associated mortality may be a consequence of inflammation and malnutrition, rather than low albumin levels per se. The purpose of this review is to give an overview of albumin handling with different extracorporeal renal replacement strategies. We conclude that the acceptable upper limit of dialysis-related albumin loss remains unknown. Whether enhanced middle molecule removal outweighs the potential adverse effects of increased albumin loss with novel highly permeable membranes and convective therapies is yet to be determined.

Moving beyond small solute clearance: What evidence is there for more permeable dialyzers and haemodiafiltration?

Dialyzers were initially developed for diffusive clearance of uraemic toxins. Diffusion most effectively clears small uncharged solutes from plasma water, such as urea. Sessional urea clearance targets have been shown to be important for short-term patient survival, but over the longer term, although low-flux dialysis can prolong patient survival, accumulation of middle-sized uraemic toxins, such as β2 microglobulin can lead to disabling arthropathy. Although the introduction of high-flux dialyzers, designed to increase β2 microglobulin clearance, has reduced the prevalence of arthropathy; this has not been translated into a demonstrable significant improvement in patient survival. However, analysis of individual patients recruited into trials of haemo-diafiltration reported that greater convective clearance was associated with better survival, although the individual trials reported mixed outcomes. Most haemodiafiltration trials were not designed to study the effect of convective dose, so although reported patient survival was greater for those receiving greater convective volume exchange, these results could potentially be confounded by patient or center effects. An alternative approach to increasing middle-sized solute clearances would be to use more permeable dialyzers, but as yet there are no trials reporting survival with larger cutoff dialyzers. As such, although there is increasing evidence that increasing middle-sized molecular uraemic solute clearance is associated with improved patient survival, further prospective trials are required to determine whether as with Kt/Vurea there is a threshold effect of how much convective or middle-sized solute clearance is required to improve patient survival.

Current approaches to middle molecule removal: room for innovation

Aggressive removal of middle molecules or larger low-molecular-weight proteins (LMWPs) has been a growing concern following studies on their harmful effects on the mortality and morbidity of chronic dialysis patients. To remove larger LMWPs and some protein-bound uremic toxins (PBUTs), high- and medium-cutoff (HCOs and MCOs, respectively) membranes, convective therapy and protein adsorptive membranes are available. When we use HCO or MCO membranes for convective therapy, we have to take care to avoid massive albumin leakage during a dialysis session. Convection volume is an important element to increase middle molecule removal; however, a larger convection volume has a risk of larger leakage of albumin. Predilution hemodiafiltration is a useful measurement to increase larger LMWPs without massive albumin leakage. β2-microglobulin (B2M), α1-microglobulin (A1M) and albumin leakage during a dialysis session are useful parameters for assessing middle-molecule removal. Reduction ratios of B2M >80% and of A1M >35% are favorable to improve severe dialysis-related symptoms. The efficacy of middle molecule removal should be evaluated in comparison with clinical outcomes, mortality, morbidity and the improvement of dialysis-related symptoms. Recently some dialysis-related symptoms such as sleep disturbance, skin itchiness and dialysis hypotension have been recognized as good surrogate makers for mortality. Further studies to evaluate the relationship between middle molecule or PBUTs removal and the improvement of patient symptoms should be performed in well-designed randomized controlled trials.

Enhancing dialyser clearance-from target to development

Products of metabolism accumulate in kidney failure and potentially have toxic effects. Traditionally these uraemic toxins are classified as small, middle-sized and protein-bound toxins, and clearance during dialysis is affected by diffusion, convection and adsorption. As current dialysis practice effectively clears small solutes, increasing evidence supports a toxic effect for middle-sized and protein-bound toxins. Therefore, newer approaches to standard dialysis practice are required to look beyond urea clearance. Current dialysers have been developed to effectively clear small solutes and secondly to increase middle-sized toxin clearances. However, there is no ideal dialyser which can effectively clear all uraemic toxins. Advances in nanotechnology have led to improvements in manufacturing, with the production of smoother membrane surfaces and uniformity of pore size. The introduction of haemodiafiltration has led to changes in dialyser design to improve convective clearances. Both diffusional and convectional clearances can be increased by changing dialyser designs to alter blood and dialysate flows, and novel dialyser designs using microfluidics offer more efficient solute clearances. Adjusting surface hydrophilicity and charge alter adsorptive properties, and greater clearance of protein-bound toxins can be achieved by adding carbon or other absorptive monoliths into the circuit or by developing composite dialyser membranes. Other strategies to increase protein-bound toxins clearances have centred on disrupting binding and so displacing toxins from proteins. Just as the hollow fibre design replaced the flat plate dialyser, we are now entering a new era of dialyser designs aimed to increase the spectrum of uraemic toxins which can be cleared by dialysis.

Increasing Haemodialytic Clearances as Residual Renal Function Declines: An Incremental Approach

Many patients with chronic kidney disease start undergoing thrice-weekly haemodialysis (HD), aiming for an HD sessional dialyzer urea clearance target, irrespective of whether they have residual renal function (RRF). While increasing sessional dialyzer urea clearance above a target of 1.2 has not been shown to improve patient survival, it has been shown that the preservation of RRF improves patient self-reported outcomes and survival. Observational studies have suggested that initiating twice-weekly HD schedules leads to greater preservation of RRF. This has led to the concept of following an incremental approach to initiating HD, steadily increasing the amount of weekly dialyzer clearance as RRF decreases. Incremental dialysis practice requires the regular assessment of RRF to prevent inadequate delivery of dialysis treatment. Once RRF is lost, then the dialysis schedule and modality need to be adjusted to try to increase the middle-sized solute clearance and protein-bound toxins.

Are all Dialyzers Compatible with the Convective Volumes Suggested for Postdilution Online Hemodiafiltration?

Introduction

The recent analysis of 4 randomized controlled trials has confirmed the lower mortality risk for postdilution online hemodiafiltration (OL-HDF) compared to hemodialysis, and above all for patients with the highest delivered body surface area standardized convective volume (CV/BSA >23 L/1.73 m2/session). Since the impact of the dialyzers used in these trials has never been studied, we retrospectively analyzed clinical tests carried out with 19 commonly used dialyzers. The aim was to provide information on their performances and behavior to aid in an objective choice for therapies associated with OL-HDF.

Methods

“Efficiency” was evaluated by measuring the reduction ratio of beta-2 microglobulin (RRß2M) and myoglobin (RRmyo) for a CV/BSA between 0 and 30 L, extrapolating them at CV/BSA = 23 L “Safety” was defined by the safe CV (CVsafe), corresponding to the CV/BSA above which albumin loss is >5 g/session. Results: With CV/BSA = 23 L, all the dialyzers ensure an optimal ß2M extraction (RRß2M: 76%–84.5%). For myoglobin, efficiency disparities are bigger (RRmyo: 40%–85%). Above all, 4/19 dialyzers lose more than 5 g albumin and should not be used under these conditions.

Conclusions

It is recommended to prescribe dialyzers that are above all safe. Moreover, if one considers that the removal of middle molecule solutes prevails over the CV necessary for their transmembrane transport, some dialyzers that are more efficient with CV/BSA <23 L than others with CV/BSA >= 23 L might then be prescribed when the conditions do not permit the suggested CV/BSA goal to be achieved.

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.

Adsorption techniques: dialysis sorbents and membranes

Adsorption is based on the attraction between the sorbent and the solute through hydrophobic interactions, ionic or electrostatic forces, hydrogen bonding or van der Waals forces. Adsorption is the adherence of molecules by the above-mentioned forces not only to the surface of the membrane but also to its interior. Since polymethylmethacrylate membranes have a much higher inside effective exchange surface than polysulfone membranes, these membranes are able to ensure a high level of adsorption, and therefore reduce the concentration of high-molecular-weight molecules and protein-bound uremic toxins.

Polymethylmethacrylate membrane and serum free light chain removal: enhancing adsorption properties

INTRODUCTION

Polymethylmethacrylate (PMMA) membranes can adsorb a wide variety of uremic toxins including serum free light chains (sFLC). However, limited data are available regarding the clinical use of PMMA in multiple myeloma patients and its maximum adsorption capacity in this setting.

AIM

This study aimed to measure the capacity of PMMA to adsorb sFLC and identify strategies to improve its efficiency in clinical practice.

METHODS

Ten patients with dialysis-dependent renal failure and high levels of sFLC were included in the study. Five patients received standard PMMA hemodialysis (HD; n = 18), while in the other 5 patients a new technique called enhanced adsorption dialysis (EAD) was used, which involves PMMA dialyzer replacement after 2 h (n = 19). In all patients, sFLC were measured at the beginning and at the end of each dialysis session to calculate the difference between start and end of treatment and the percentage removal.

RESULTS

PMMA membranes reduced sFLC in both the PMMA HD and EAD groups. PMMA HD showed similar efficiency on κ and λ percentage removal (22.3 and 21.0%, respectively, n.s.) but, in contrast, had a significantly greater effect on the delta of sFLC in κ [1,555 mg/l (-511 to +6,027)] versus λ [390 mg/l (120-650)] treatments (p = 0.007). EAD treatments only partially increased percentage removal of κ sFLC (22.3-31.0%, p = 0.38), while they had a significantly great effect on λ (21.0-53.1%, p = 0.003). A positive linear correlation was found between delta sFLC and pre-HD sFLC concentrations in PMMA HD κ treatments (r = 0.68, p < 0.02) but not for λ treatments (r = 0.54, p = 0.21), while the analysis of patients receiving EAD demonstrated a strong positive correlation for both κ and λ subtypes (r = 0.81 and r = 0.85, respectively, p < 0.008). In EAD sessions, a positive linear correlation was shown between blood flow during treatment and percentage removal of sFLC (r = 0.58, p = 0.02); however, with PMMA HD such a correlation was not observed (r = 0.28, p = 0.25).

CONCLUSIONS

PMMA membranes can efficiently adsorb sFLC, but the process is limited by membrane saturation and is different between κ and λ sFLC. The new EAD technique can greatly improve λ removal but only partially act on κ sFLC. Therefore, EAD should be considered a valid economic treatment option without side effects in particular subsets of patients for the removal of sFLC.

Homocysteine-lowering therapy does not lead to reduction in cardiovascular outcomes in chronic kidney disease patients: a meta-analysis of randomised, controlled trials

The efficacy of homocysteine (Hcy)-lowering therapy in reducing the risk of CVD among patients with chronic kidney disease (CKD) remains controversial. We performed a meta-analysis to determine whether pooling the data from the few small randomised, controlled trials that address this topic would improve the statistical power of the analysis and resolve some of the inconsistencies in the results. Randomised, controlled clinical trials (RCT) were identified from MEDLINE, EMBASE, www.clinicaltrials.gov, the Cochrane Controlled Clinical Trials Register Database and Nephrology Filters. Independent extraction of articles was performed using predefined data fields. The primary outcome was relative risk (RR) of CVD, CHD, stroke and all-cause mortality for the pooled trials. A stratified analysis was planned, assessing the RR for cardiovascular events between the patients on and not on dialysis. Overall, ten studies met the inclusion criteria. The estimated RR were not significantly different for any outcomes, including CHD (RR 1·00, 95 % CI 0·75, 1·31, P = 0·97), CVD (RR 0·94, 95 % CI 0·84, 1·05, P = 0·30), stroke (RR 0·83, 95 % CI 0·57, 1·19, P = 0·31) and all-cause mortality (RR 1·00, 95 % CI 0·92, 1·09, P = 0·98). In the stratified analysis, the estimated RR were not significantly different for cardiovascular events regardless of dialysis or in combination with vitamin B therapy or the degree of reduction in Hcy levels. Our meta-analysis of RCT supports the conclusion that Hcy-lowering therapy was not associated with a significant decrease in the risk for CVD events, stroke and all-cause mortality among patients with CKD.

Potential role of the soluble form of CD40 in deficient immunological function of dialysis patients: new findings of its amelioration using polymethylmethacrylate (PMMA) membrane

Even though numerous studies have helped to better delineate abnormalities of either innate or adaptive immune system in end-stage renal disease (ESRD) patients, understanding immune dysfunctions in ESRD patients remains a very complex puzzle with missing pieces. In this context, we showed that the soluble form of CD40 (sCD40) is elevated in ESRD patients and is associated with a lack of response to hepatitis B vaccination. Interestingly, although most dialysis membranes are unable to clear sCD40, we demonstrated that polymethylmethacrylate (PMMA) BK-F membranes (Toray Medical Company, Japan) allow a dramatic diminution of the molecule. We took advantage of this observation to address the question of the potential usefulness of PMMA membrane (BK-F series) in the improvement of humoral immune response of ESRD patients. We, thus, present our recent data highlighting the potential role of BK-F membrane in the improvement of hepatitis B vaccination of ESRD patients who failed to mount a protective immune response despite one or more well-conducted anterior vaccination.

Taken as a whole, our findings reinforced the concept of seeing dialysis membranes not just as a simple diffusive device but as a tool to tailor dialysis procedure to improve the global quality of life of ESRD patients. This opens a wide area of investigation, notably for the management of immunological dysfunction of ESRD patients.

Bare and protein-conjugated Fe(3)O(4) ferromagnetic nanoparticles for utilization in magnetically assisted hemodialysis: biocompatibility with human blood cells

Magnetically assisted hemodialysis is a development of conventional hemodialysis and is based on the circulation of ferromagnetic nanoparticle-targeted binding substance conjugates (FN-TBS Cs) in the bloodstream of the patient and their eventual removal by means of a 'magnetic dialyzer'. Presented here is an in vitro investigation on the biocompatibility of bare Fe(3)O(4) FNs and Fe(3)O(4)-bovine serum albumin Cs with blood cells, namely red blood cells (RBCs), white blood cells (WBCs) and platelets (Plts). Atomic force microscopy (AFM) and optical microscopy (OM) enabled the examination of blood cells at the nanometer and micrometer level, respectively. The observations made on FN- and C-maturated blood samples are contrasted to those obtained on FN- and C-free reference blood samples subjected to exactly the same maturation procedure. Qualitatively, both AFM and OM revealed no changes in the overall shape of RBCs, WBCs and Plts. Incidents where bare FNs or Cs were bound onto the surface of RBCs or internalized by WBCs were very rare. Detailed examination by means of OM proved that impaired coagulation of Plts is not initiated/promoted either by FNs or Cs. Quantitatively, the statistical analysis of the obtained AFM images from RBC surfaces clearly revealed that the mean surface roughness of RBCs maturated with bare FNs or Cs was identical to the one of reference RBCs.

Oxidatively-modified and glycated proteins as candidate pro-inflammatory toxins in uremia and dialysis patients

End stage renal disease (ESRD) patients accumulate blood hallmarks of protein glycation and oxidation. It is now well established that these protein damage products may represent a heterogeneous class of uremic toxins with pro-inflammatory and pro-oxidant properties. These toxins could be directly involved in the pathogenesis of the inflammatory syndrome and vascular complications, which are mainly sustained by the uremic state and bioincompatibility of dialysis therapy. A key underlying event in the toxicity of these proteinaceous solutes has been identified in scavenger receptor-dependent recognition and elimination by inflammatory and endothelial cells, which once activated generate further and even more pronounced protein injuries by a self-feeding mechanism based on inflammation and oxidative stress-derived events. This review examines the literature and provides original information on the techniques for investigating proteinaceous pro-inflammatory toxins. We have also evaluated therapeutic - either pharmacological or dialytic - strategies proposed to alleviate the accumulation of these toxins and to constrain the inflammatory and oxidative burden of ESRD.

Proteomic analysis of serum, outflow dialysate and adsorbed protein onto dialysis membranes (polysulfone and pmma) during hemodialysis treatment using SELDI-TOF-MS

AIMS

Alterations in the profiling of peptides and proteins in the serum, outflow dialysate and adsorbed protein on the dialysis membrane were investigated.

METHODS

Alterations in the protein profiling of routine hemodialysis using polysulfone (TS-UL) and PMMA (moderate flux membrane of polymethylmethacrylate: BK-U) in 8 patients and that of adsorption onto polysulfone and PMMA membranes in 4 patients were evaluated by SELDI-TOF-MS and ProteinChip array. Mass-to-charge ratios (m/z) between 2,000 and 120,000 were analyzed.

RESULTS

The protein with a relative intensity of m/z 11,730 measured by SELDI-TOF-MS was present in a small amount in the outflow dialysate and in a large amount in adsorption (identified as beta2-microglobulin) onto PMMA membrane. Unexpectedly, 68 molecular masses of peptides that were adsorbed more onto polysulfone than onto PMMA membrane were observed. There were more peptides less than m/z 11,730 adsorbed onto polysulfone membrane than onto PMMA membrane. Dominant peaks, m/z 6,629 and 6,431 adsorbed onto polysulfone membrane were identified as apolipoprotein CI and truncated apolipoprotein CI, respectively. 37 proteins with molecular weights larger than m/z 11,730 showed greater filtration through PMMA membrane than through polysulfone membrane. 149 molecular masses that were adsorbed onto PMMA or more onto PMMA membrane than onto polysulfone membrane were observed.

CONCLUSION

This experiment suggests that membrane adsorption is an important mechanism for the removal of middle-molecular-weight proteins by hemodialysis using not only PMMA membrane but also polysulfone membrane. Adsorption of peptide or protein onto a dialysis membrane may depend not only on the membrane material, but also on the peptide or protein.

Extracorporeal strategies for the removal of middle molecules

Uremic toxins with a molecular weight of less than 500 Da are classified as small nitrogenous waste products. They are highly water soluble, relatively homogeneous, and have no protein binding. Other uremic retention toxins differ significantly from the small nitrogenous metabolite class in molecular weight, heterogeneity, protein binding, and hydrophobicity. The European Uremic Toxin Work Group subdivided molecules into two categories: protein-bound solutes and middle molecules. Middle molecules were defined as toxins in the molecular weight range of 500-60,000 Da, which exceeds the molecular weight of 2000 Da defined in the original middle molecule hypothesis. Under this new proposed definition, most of these middle molecules are low molecular weight peptides and proteins (LMWPs). This concise review focuses on LMWPs. The metabolism of LMWPs is described, including molecular weight, physical conformation, and charge. Factors influencing dialytic removal of LMWPs such as membrane characteristics, protein-membrane interactions, and solute removal mechanisms, as well as strategies to enhance clearance of these compounds are discussed.

Beta2-microglobulin removal by extracorporeal renal replacement therapies

There is increasing evidence that end-stage renal disease patients with lower beta(2)-microglobulin plasma levels and patients on convective renal replacement therapy are at lower mortality risk. Therefore, an enhanced beta(2)-microglobulin removal by renal replacement procedures has to be regarded as a contribution to a more adequate dialysis therapy. In contrast to high-flux dialysis, low-flux hemodialysis is not qualified to eliminate substantial amounts of beta(2)-microglobulin. In hemodialysis using modern high-flux dialysis membranes, a beta(2)-microglobulin removal similar to that obtained in hemofiltration or hemodiafiltration can be achieved. Several of these high-flux membranes are protein-leaking, making them suitable only for hemodialysis due to a high albumin loss when used in more convective therapy procedures. On-line hemodiafiltration infusing large substitution fluid volumes represents the most efficient and innovative renal replacement therapy form. To maximize beta(2)-microglobulin removal, modifications of this procedure have been proposed. These modifications ensure safer operating conditions, such as mixed hemodiafiltration, or control albumin loss at maximum purification from beta(2)-microglobulin, such as mid-dilution hemodiafiltration, push/pull hemodiafiltration or programmed filtration. Whether these innovative hemodiafiltration options will become accepted in clinical routine use needs to be proven in future.

Uremic toxins: a new focus on an old subject

The uremic syndrome is characterized by an accumulation of uremic toxins due to inadequate kidney function. The European Uremic Toxin (EUTox) Work Group has listed 90 compounds considered to be uremic toxins. Sixty-eight have a molecular weight less than 500 Da, 12 exceed 12,000 Da, and 10 have a molecular weight between 500 and 12,000 Da. Twenty-five solutes (28%) are protein bound. The kinetics of urea removal is not representative of other molecules such as protein-bound solutes or the middle molecules, making Kt/V misleading. Clearances of urea, even in well-dialyzed patients, amount to only one-sixth of physiological clearance. In contrast to native kidney function, the removal of uremic toxins in dialysis is achieved by a one-step membrane-based process and is intermittent. The resulting sawtooth plasma concentrations of uremic toxins contrast with the continuous function of native kidneys, which provides constant solute clearances and mass removal rates. Our increasing knowledge of uremic toxins will help guide future treatment strategies to remove them.

Randomized trial of FX high flux vs standard high flux dialysis for homocysteine clearance

BACKGROUND

Cardiovascular disease is the major cause of death in the end-stage renal disease population. Novel risk factors such as homocysteine (Hcy) are of considerable interest in this group as hyperhomocysteinaemia is highly prevalent in the setting of renal impairment. Folic acid-vitamin B group therapies are only partially effective treatments. Hcy is highly protein-bound and thus poorly dialysed. Dialyzers with albumin-leaking properties have been shown to result in lowering of plasma Hcy. As the FX-class (Advanced Fresenius Polysulfone dialyzer) has greater clearance of larger molecular weight substances but is non-albumin-leaking, we explored the capacity of this new technology membrane to reduce plasma Hcy levels.

METHODS

A prospective randomized cross-over trial in 35 prevalent haemodialysis patients, one group receiving 12 weeks dialysis using FX dialyzer then 12 weeks with standard high flux dialysis (SHF) and the other group SHF followed by FX dialyzer. All patients received vitamin B(6) 25 mg and folic acid 5 mg daily throughout the study.

RESULTS

The primary outcome was plasma Hcy pre-dialysis at week 12. FX vs SHF showed no significant difference, 25+/-6.6 vs 25.9+/-5.8 microg/l, Delta95% CI = -2.77 to 4.59, P = 0.31. There was a non-significant trend toward a decrease in Hcy in both groups (27.43+/-7.68 to 25.91+/-5.78 micromol/l for SHF, P = 0.23 and 26.0+/-4.58 to 25.0+/-6.61 micromol/l for FX, P = 0.28). Analysis by repeated measures method demonstrated a statistically significantly lower Hcy with FX vs SHF dialyzer (adjusted beta = -1.30, 95% CI = -2.41 to -0.19, P = 0.022). K(t)/V(urea) was higher in FX vs SHF (1.35+/-0.18 vs 1.22+/-0.2; P = 0.013). Folate and B(6) levels did not change.

CONCLUSIONS

The primary outcome analysis did not show any significant difference in pre-Hcy comparing FX and SHF membranes. Although our secondary analysis demonstrated a statistically significant difference between membranes, the magnitude of the difference (1.3 mumol/l) is not clinically significant. Thus the use of the FX dialyzer did not result in a clinically significant benefit in relation to improving pre-dialysis Hcy compared with standard high-flux dialysis.

Protein-Leaking Membranes for Hemodialysis: A New Class of Membranes in Search of an Application?

A new class of membranes that leak protein has been developed for hemodialysis. These membranes provide greater clearances of low molecular weight proteins and small protein-bound solutes than do conventional high-flux dialysis membranes but at the cost of some albumin loss into the dialysate. Protein-leaking membranes have been used in a small number of clinical trials. The results of these trials suggest that protein-leaking membranes improve anemia correction, decrease plasma total homocysteine concentrations, and reduce plasma concentrations of glycosylated and oxidized proteins. However, it is not clear yet that routine use of protein-leaking membranes is warranted. Specific uremic toxins that are removed by protein-leaking membranes but not conventional high-flux membranes have not been identified. It is also unclear whether protein-leaking membranes offer benefits beyond those obtained with conventional high-flux membranes used in convective therapies, such as hemofiltration and hemodiafiltration. Finally, the amount of albumin loss that can be tolerated by hemodialysis patients in a long-term therapy has yet to be determined. Protein-leaking membranes offer a new approach to improving outcomes in hemodialysis, but whether their benefits will outweigh their disadvantages will require more basic and clinical research.

Neurological complications in renal failure: a review

Neurological complications whether due to the uremic state or its treatment, contribute largely to the morbidity and mortality in patients with renal failure. Despite continuous therapeutic advances, many neurological complications of uremia, like uremic encephalopathy, atherosclerosis, neuropathy and myopathy fail to fully respond to dialysis. Moreover, dialytic therapy or kidney transplantation may even induce neurological complications. Dialysis can directly or indirectly be associated with dialysis dementia, dysequilibrium syndrome, aggravation of atherosclerosis, cerebrovascular accidents due to ultrafiltration-related arterial hypotension, hypertensive encephalopathy, Wernicke's encephalopathy, hemorrhagic stroke, subdural hematoma, osmotic myelinolysis, opportunistic infections, intracranial hypertension and mononeuropathy. Renal transplantation itself can give rise to acute femoral neuropathy, rejection encephalopathy and neuropathy in graft versus host disease. The use of immunosuppressive drugs after renal transplantation can cause encephalopathy, movement disorders, opportunistic infections, neoplasms, myopathy and progression of atherosclerosis. We address the clinical, pathophysiological and therapeutical aspects of both central and peripheral nervous system complications in uremia.

Glycoxidation and inflammatory markers in patients on treatment with PMMA-based protein-leaking dialyzers

BACKGROUND

High-molecular-weight solutes such as glycation and oxidation protein products are putative proinflammatory mediators found in the uremic blood. The elimination of these and other large solutes by protein-leaking dialyzers (PLD) might help to correct the inflammatory status of maintenance hemodialysis (HD) patients.

METHODS

Two matched groups of 13 standard 3 times/week HD patients were treated for 6 months with PMMA-based PLD and non-protein-leaking dialyzers (NPLD), respectively. At baseline, 1, 3, and 6 months, we measured the blood levels of the inflammatory cytokines IL-1beta, TNF-alpha, IL-6, the acute-phase protein C-reactive protein (CRP), the adhesion molecules ICAM-1, VCAM-1, and selectine-E, the chemotaxis factors MCP-1, and the glycation and oxidation protein end products pentosidine, protein carbonyls, and AOPP.

RESULTS

In all the patients at baseline, pre-HD levels of glycation and oxidation protein markers, and inflammatory parameters were significantly higher than in healthy control subjects (P < 0.01 or greater). After 6 months, in the group on treatment with PLD, but not in that on NPLD, there was a significant decrease (P < 0.05 or greater) of pre-HD values of total pentosidine (mainly represented by pentosidine in serum albumin; -43%), protein carbonyls (-42%), AOPP (-38%), and the inflammatory cytokines IL-1beta (-49%), IL-6 (-39%), and TNF-alpha (-20%), while IL-10 and INF-gamma increased by 67% and 37%, respectively. Proinflammatory cytokines, and particularly IL-6, showed a positive correlation with the levels of circulating pentosidine. Protidemia was not significantly modified at the end of the study in both the groups.

CONCLUSION

The results in this pilot study show that the removal of large solutes by PLD can improve some indices of chronic inflammation in HD patients. Further studies are required to determine the relevance of the individual solutes removed with PLD as proinflammatory mediators in the uremic environment.

Controversies and Issues in Hemodiafiltration Therapy

Hemodiafiltration appears to be the most effective technique of renal replacement therapy but several drawbacks are not counterbalanced by significant advantages. Although optimal transfer for both small and middle molecules can be achieved, there is no difference in mortality risk between HDF and HD patients. The infusion of a large amount of dialysate containing residual acetate of 2-7 mmol/l could lead to impaired cardiac contractile functions and carbonyl stress whereas loss of amino acids and water-soluble vitamins along with high UF rate could lead to malnutrition. Moreover, as substitution fluid is prepared on-line, contaminated fluid could be inadvertently infused to patients. Stringent maintenance rules are required for the production of sterile and non-pyrogenic dialysis solutions. Finally, daily hemodialysis could be the most promising mode of renal replacement therapy since it leads to a more stable 'milieu interieur' than other techniques whatever the mode of solutes removal when performed three times a week.

Oxidative stress and uremia

Oxidative stress is a pathogenic element of great importance in uremic patients, with a great impact on their survival. The cause of oxidative stress in patients on hemodialysis is traditionally attributed to the recurrent activation of polymorphonucleate neutrophils and monocytes. The effects of oxidative stress are evident on all biochemical components of biological tissues: lipids, proteins, carbohydrates, and nucleic acids. This study briefly reviews the effects of different dialytic techniques and of kidney transplant on several parameters of oxidative stress. Many different modalities of pharmaceutical intervention are then analyzed, and the clinical evidences reported.

Clinical cross-over comparison of mid-dilution hemodiafiltration using a novel dialyzer concept and post-dilution hemodiafiltration

BACKGROUND

Several studies have indicated that the improved elimination of middle molecules by convective renal replacement procedures might be associated with a better outcome in end-stage renal disease (ESRD). On-line mid-dilution hemodiafiltration (HDF) with the Nephros OLpur MD 190 hemodiafilter represents a novel extracorporeal renal replacement therapy concept to increase the removal of middle molecules.

METHODS

In a prospective cross-over study in 10 ESRD patients, this technique was compared to on-line post-dilution HDF with a conventional synthetic high-flux dialyzer, operated at its technical limit, concerning small and middle molecular solute removal. Each patient was treated 3 times for 4.0 +/- 0.4 hours with both filters. Blood flow was 400 mL/min, substitution flow (Q(S)) during mid-dilution HDF 200 mL/min, and during post-dilution HDF 100 mL/min, and effective dialysate flow of 700 - Q(S) mL/min. Instantaneous clearances, reduction ratios (RR), and middle molecule mass transfer in continuously collected dialysate were determined.

RESULTS

While urea and creatinine clearances were significantly lower (6.4% and 3.9%, respectively), middle molecule removal was much more efficient in mid-dilution HDF over the whole range of investigated proteins: compared to post-dilution HDF, beta(2)-microglobulin (11.8 kD) clearance (165.8 +/- 26.59 vs. 201.9 +/- 20.63 mL/min; P < 0.001), RR (80.0 +/- 5.4% vs. 82.2 +/- 5.7%; P < 0.001), and dialysate mass transfer (53% higher; P < 0.001) were significantly higher. For the larger middle molecules, cystatin C (13.4 kD) and retinol-binding protein (21.2 kD), mid-dilution HDF resulted in an even more superior performance, indicated by significantly higher values of all investigated parameters.

CONCLUSION

On-line mid-dilution HDF with the Nephros OLpur MD 190 hemodiafilter appears to be a true technologic step ahead in terms of improved middle molecule removal. This efficient procedure gives hope to play a role in preventing or at least retarding dialysis-related long-term complications, such as beta(2)m amyloidosis, in ESRD patients, and may contribute to a more adequate dialysis therapy.

Biochemical and Clinical Evidence for Uremic Toxicity

The uremic syndrome is a mix of clinical features resulting from multiple organ dysfunctions which develop when kidney failure progresses, and is attributed to the retention of solutes, which under normal conditions are excreted by the healthy kidneys into the urine. The most practical classification of uremic solutes is based on their physicochemical characteristics that influence their dialytic removal, in (1) small water soluble compounds, (2) the larger "middle molecules," and (3) the protein bound compounds. Hence, uremic retention is much more complex than originally believed. Among the small water soluble compounds, urea exerts not much toxic activity and is not very representative in its kinetic behavior for many other uremic solutes. Among the middle molecules, many have been recognized to exert biological activity and hence to contribute to the uremic syndrome. Specific dialysis strategies apply large pore membranes to remove those middle molecules and have a beneficial impact on uremic morbidity and mortality. A substantial number of uremic solutes are protein bound. Only recently, a relation between their concentration and clinical status could be demonstrated. Likewise, it was only recently possible to demonstrate more than standard removal with super-flux dialysis membranes. To further improve characterization of uremic solutes and to develop directed therapeutic approaches, further concerted action among various groups of researchers will be needed.

Middle molecules and small-molecular-weight proteins in ESRD: properties and strategies for their removal

Molecular weight has traditionally been the parameter most commonly used to classify uremic toxins, with a value of approximately 500 Da frequently used as a demarcation point below which the molecular weights of small nitrogenous waste products fall. This toxin group, the most extensively studied from a clinical perspective, is characterized by a high degree of water solubility and the absence of protein binding. However, uremia is mediated by the retention of a plethora of other compounds having characteristics that differ significantly from those of the previously mentioned group. As opposed to the relative homogeneity of the nitrogenous metabolite class, other uremic toxins collectively are a very heterogeneous group, not only with respect to molecular weight but also other characteristics, such as protein binding and hydrophobicity. A recently proposed classification scheme by the European Uraemic Toxin Work Group subdivides the remainder of molecules into 2 categories: protein-bound solutes and middle molecules. For the latter group, the Work Group proposes a molecular weight range (500-60,000 Da) that incorporates many toxins identified since the original middle molecule hypothesis, for which the upper molecular weight limit was approximately 2,000 Da. In fact, low-molecular-weight peptides and proteins (LMWPs) comprise nearly the entire middle molecule category in the new scheme. The purpose of this article is to provide an overview of the middle molecule class of uremic toxins, with the focus on LMWPs. A brief review of LMWP metabolism under conditions of normal (and in a few cases, abnormal) renal function will be presented. The physical characteristics of several LMWPs will also be presented, including molecular weight, conformation, and charge. Specific LMWPs to be covered will include beta 2-microglobulin, complement proteins (C3a and Factor D), leptin, and proinflammatory cytokines. The article will also include a discussion of the treatment-related factors influencing dialytic removal of middle molecules. Once these factors, which include membrane characteristics, protein-membrane interactions, and solute removal mechanisms, are discussed, an overview of the different therapeutic strategies used to enhance clearance of these compounds is provided.