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

High cut-off membranes in patients requiring renal replacement therapy: a systematic review and meta-analysis

BACKGROUND

Whether high cut-off (HCO) membranes are more effective than high-flux (HF) membranes in patients requiring renal replacement therapy (RRT) remains controversial. The aim of this systematic review was to investigate the efficacy of HCO membranes regarding the clearance of inflammation-related mediators, β2-microglobulin and urea; albumin loss; and all-cause mortality in patients requiring RRT.

METHODS

We searched all relevant studies on PubMed, Embase, Web of Science, the Cochrane Library, and China National Knowledge Infrastructure, with no language or publication year restrictions. Two reviewers independently selected studies and extracted data using a prespecified extraction instrument. Only randomized controlled trials (RCTs) were included. Summary estimates of standardized mean differences (SMDs) or weighted mean differences (WMDs) and risk ratios (RRs) were obtained by fixed-effects or random-effects models. Sensitivity analyses and subgroup analyses were performed to determine the source of heterogeneity.

RESULTS

Nineteen RCTs involving 710 participants were included in this systematic review. Compared with HF membranes, HCO membranes were more effective in reducing the plasma level of interleukin-6 (IL-6) (SMD -0.25, 95% confidence interval (CI) -0.48 to -0.01, P   =  0.04, I2  = 63.8%); however, no difference was observed in the clearance of tumor necrosis factor-α (TNF-α) (SMD 0.03, 95% CI -0.27 to 0.33, P  = 0.84, I2  = 4.3%), IL-10 (SMD 0.22, 95% CI -0.12 to 0.55, P  = 0.21, I2  = 0.0%), or urea (WMD -0.27, 95% CI -2.77 to 2.23, P  = 0.83, I2  = 19.6%). In addition, a more significant reduction ratio of β 2 -microglobulin (WMD 14.8, 95% CI 3.78 to 25.82, P  = 0.01, I2  = 88.3%) and a more obvious loss of albumin (WMD -0.25, 95% CI -0.35 to -0.16, P  < 0.01, I2  = 40.8%) could be observed with the treatment of HCO membranes. For all-cause mortality, there was no difference between the two groups (risk ratio [RR] 1.10, 95% CI 0.87 to 1.40, P  = 0.43, I2  = 0.0%).

CONCLUSIONS

Compared with HF membranes, HCO membranes might have additional benefits on the clearance of IL-6 and β 2-microglobulin but not on TNF-α, IL-10, and urea. Albumin loss is more serious with the treatment of HCO membranes. There was no difference in all-cause mortality between HCO and HF membranes. Further larger high-quality RCTs are needed to strengthen the effects of HCO membranes.

Influence of Modified Carbon Black on Nylon 6 Nonwoven Fabric and Performance as Adsorbent Material

The number of chronic kidney disease (CKD) persons continues to rise in Mexico. They require renal replacement therapy, and in the absence of it, hemodialysis is the major option for their survival. The uremic toxins present in the blood are removed by hemodialysis, which involve membranes. In this study, nonwoven fabrics with modified carbon black nanoparticles in a matrix polymer of Nylon 6 were obtained and evaluated as an adsorbent material of uremic toxins. All nonwoven fabrics were characterized by FTIR, XRD, TGA, SEM, and contact angle measurements and were evaluated as an adsorbent material for the urea toxin and as an albumin retainer. The findings suggest their potential application as a hemodialysis membrane. Nanocomposites had a higher hydrophilic characteristic compared to pure Nylon 6. The average diameter size of the fibers was in the range of 5 to 50 μm. All nanocomposites nonwoven fabrics showed high removal percentages of inulin in a range of 80-85% at 15 min of contact. Most Ny6 Zytel/CB nanocomposites showed a high percentage of urea removal (80 to 90%).

Light Chain Cast Nephropathy in Multiple Myeloma: Prevalence, Impact and Management Challenges

“Cast nephropathy” (CN) is a pathological feature of myeloma kidney, also seen to a lesser extent in the context of severe nephrotic syndrome from non-haematological diseases. The name relates to obstruction of distal tubules by “casts” of luminal proteins concentrated by intensive water reabsorption resulting from dehydration or high-dose diuretics. Filtered proteins form complexes with endogenous tubular Tamm-Horsfall glycoprotein. The resulting gel further slows or stops luminal flow upon complete obstruction of distal convoluted tubules and collecting ducts. Thus, a tubular obstructive form of acute kidney injury (AKI) is a common consequence of CN. The pathogenesis of CN will be reviewed in light of recent advances in the understanding of monoclonal disorders of B lymphocytes, leading to the release of immunoglobulin components (free light chains, FLC) into the bloodstream and their filtration across the glomerular basement membrane. Treatment aiming at reduction of the circulating burden of FLC may help recovery of renal function in a fraction of these patients, besides filling the void between the onset of AKI, histopathological diagnosis, and full response to pharmacologic treatment.

Point your SmartPhone at the code above. If you have a QR code reader the video abstract will appear. Or use:

https://youtu.be/-LOd4bqJsIo

Effects of Expanded Hemodialysis with Medium Cut-Off Membranes on Maintenance Hemodialysis Patients: A Review

Kidney failure is associated with high morbidity and mortality. Hemodialysis, the most prevalent modality of renal replacement therapy, uses the principle of semipermeable membranes to remove solutes and water in the plasma of patients with kidney failure. With the evolution of hemodialysis technology over the last half century, the clearance of small water-soluble molecules in such patients is adequate. However, middle molecules uremic toxins are still retained in the plasma and cause cardiovascular events, anemia, and malnutrition, which significantly contribute to poor quality of life and high mortality in maintenance hemodialysis patients. A new class of membrane, defined as a medium cut-off (MCO) membrane, has emerged in recent years. Expanded hemodialysis with MCO membranes is now recognized as the artificial kidney model closest to natural kidney physiology. This review summarizes the unique morphological characteristics and internal filtration–backfiltration mechanism of MCO membranes, and describes their effects on removing uremic toxins, alleviating inflammation and cardiovascular risk, and improving quality of life in maintenance hemodialysis patients.

Influence of Dialysis Membranes on Clinical Outcomes: From History to Innovation

Dialysis membranes were traditionally classified according to their material compositions (i.e., as cellulosic or synthetic) and on the basis of the new concept of the sieving coefficient (determined by the molecular weight retention onset and molecular weight cut-off). The advantages of synthetic polymer membranes over cellulose membranes are also described on the basis of their physical, chemical, and structural properties. Innovations of dialysis membrane in recent years include the development of medium cutoff membranes; graphene oxide membranes; mixed-matrix membranes; bioartificial kidneys; and membranes modified with vitamin E, lipoic acid, and neutrophil elastase inhibitors. The current state of research on these membranes, their effects on clinical outcomes, the advantages and disadvantages of their use, and their potential for clinical use are outlined and described.

Flummoxed by flux: the indeterminate principles of haemodialysis

In haemodialysis (HD), unwanted substances (uraemic retention solutes or ‘uraemic toxins’) that accumulate in uraemia are removed from blood by transport across the semipermeable membrane. Like all membrane separation processes, the transport requires driving forces to facilitate the transfer of molecules across the membrane. The magnitude of the transport is quantified by the phenomenon of ‘flux’, a finite parameter defined as the volume of fluid (or permeate) transferred per unit area of membrane surface per unit time. In HD, as transmembrane pressure is applied to facilitate fluid flow or flux across the membrane to enhance solute removal, flux is defined by the ultrafiltration coefficient (KUF; mL/h/mmHg) reflecting the hydraulic permeability of the membrane. However, in HD, the designation of flux has come to be used in a much broader sense and the term is commonly used interchangeably and erroneously with other measures of membrane separation processes, resulting in considerable confusion. Increased flux is perceived to reflect more ‘porous’ membranes having ‘larger’ pores, even though other membrane and therapy attributes determine the magnitude of flux achieved during HD. Adjectival designations of flux (low-, mid-, high-, super-, ultra-) have found indiscriminate usage in the scientific literature to qualify a parameter that influences clinical decision making and prescription of therapy modalities (low-flux or high-flux HD). Over the years the concept and definition of flux has undergone arbitrary and periodic adjustment and redefinition by authors in publications, regulatory bodies (US Food and Drug Administration) and professional association guidelines (European Renal Association, Kidney Disease Outcomes Quality Initiative), with little consensus. Industry has stretched the boundaries of flux to derive marketing advantages, justify increased reimbursement or contrive new classes of therapy modalities when in fact flux is just one of several specifications that determine membrane or dialyser performance. Membranes considered as high-flux previously are today at the lower end of the flux spectrum. Further, additional parameters unrelated to the rate of diffusive or convective transport (flux) are used in conjunction with or in place of KUF to allude to flux: clearance (mL/min, e.g. of β₂-microglobulin) or sieving coefficients (dimensionless). Considering that clinical trials in nephrology, designed to make therapy recommendations and guide policy with economic repercussions, are based on the parameter flux they merit clarification—by regulatory authorities and scientists alike—to avoid further misappropriation.

Clinical relevance of abstruse transport phenomena in haemodialysis

Haemodialysis (HD) utilizes the bidirectional properties of semipermeable membranes to remove uraemic toxins from blood while simultaneously replenishing electrolytes and buffers to correct metabolic acidosis. However, the nonspecific size-dependent transport across membranes also means that certain useful plasma constituents may be removed from the patient (together with uraemic toxins), or toxic compounds, e.g. endotoxin fragments, may accompany electrolytes and buffers of the dialysis fluids into blood and elicit severe biological reactions. We describe the mechanisms and implications of these undesirable transport processes that are inherent to all HD therapies and propose approaches to mitigate the effects of such transport. We focus particularly on two undesirable events that are considered to adversely affect HD therapy and possibly impact patient outcomes. Firstly, we describe how loss of albumin (and other essential substances) can occur while striving to eliminate larger uraemic toxins during HD and why hypoalbuminemia is a clinical condition to contend with. Secondly, we describe the origins and mode of transport of biologically active substances (from dialysis fluids with bacterial contamination) into the blood compartment and biological reactions they elicit. Endotoxin fragments activate various proinflammatory pathways to increase the underlying inflammation associated with chronic kidney disease. Both phenomena involve the physical as well as chemical properties of membranes that must be selected judiciously to balance the benefits with potential risks patients may encounter, in both the short and long term.

A Review of Commercial Developments and Recent Laboratory Research of Dialyzers and Membranes for Hemodialysis Application

Dialyzers have been commercially used for hemodialysis application since the 1950s, but progress in improving their efficiencies has never stopped over the decades. This article aims to provide an up-to-date review on the commercial developments and recent laboratory research of dialyzers for hemodialysis application and to discuss the technical aspects of dialyzer development, including hollow fiber membrane materials, dialyzer design, sterilization processes and flow simulation. The technical challenges of dialyzers are also highlighted in this review, which discusses the research areas that need to be prioritized to further improve the properties of dialyzers, such as flux, biocompatibility, flow distribution and urea clearance rate. We hope this review article can provide insights to researchers in developing/designing an ideal dialyzer that can bring the best hemodialysis treatment outcomes to kidney disease patients.

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.

Acute Kidney Injury in Monoclonal Gammopathies

Monoclonal gammopathies (MG) encompass a variety of disorders related to clonal expansion and/or malignant transformation of B lymphocytes. Deposition of free immunoglobulin (Ig) components (light or heavy chains, LC/HC) within the kidney during MG may result over time in multiple types and degrees of injury, including acute kidney injury (AKI). AKI is generally a consequence of tubular obstruction by luminal aggregates of LC, a pattern known as “cast nephropathy”. Monoclonal Ig LC can also be found as intracellular crystals in glomerular podocytes or proximal tubular cells. Proliferative glomerulonephritis with monoclonal Ig deposits is another, less frequent form of kidney injury with a sizable impact on renal function. Hypercalcemia (in turn related to bone reabsorption triggered by proliferating plasmacytoid B cells) may lead to AKI via functional mechanisms. Pharmacologic treatment of MG may also result in additional renal injury due to local toxicity or the tumor lysis syndrome. The present review focuses on AKI complicating MG, evaluating predictors, risk factors, mechanisms of damage, prognosis, and options for treatment.

Slipping Through the Pores: Hypoalbuminemia and Albumin Loss During Hemodialysis

Hypoalbuminemia results when compensatory mechanisms are unable to keep pace with derangements in catabolism/loss and/or decreased synthesis of albumin. Across many disease states, including chronic kidney disease (CKD), hypoalbuminemia is a well-established, independent risk factor for adverse outcomes, including mortality. In the setting of CKD, reduced serum albumin concentrations are often a manifestation of protein-energy wasting, a state of metabolic and nutritional alterations resulting in reduced protein and energy stores. The progression of CKD to kidney failure and the initiation of maintenance hemodialysis (HD) further predisposes an already at-risk population toward hypoalbuminemia such that approximately 60% of HD patients have albumin concentrations <4.0 g/dl. Albumin loss into the dialysate through the dialyzer appears to be a potentially modifiable cause of hypoalbuminemia in some patients. A group of newer dialyzers for maintenance HD-sometimes termed protein-leaking or medium cut-off membranes-aim to improve clearance of middle molecules (vs high flux dialyzers) but are associated with increased albumin losses. In this article, we will examine the impact of dialyzer selection on albumin losses during conventional HD, including the clinical relevance of such losses on serum albumin levels. Data on the clinical relevance of albumin losses during dialysis and current gaps in the evidence base are also discussed.

Effect of high cut-off dialysis for acute kidney injury secondary to cast nephropathy in patients with multiple myeloma: a systematic review and meta-analysis

Background

Acute kidney injury (AKI) caused by cast nephropathy is associated with increased morbidity and mortality among patients with multiple myeloma (MM). High cut-off haemodialysis (HCO-HD) has proven to be effective in the removal of serum light chains but the effect on clinical outcomes, especially renal recovery, remains uncertain.

Methods

A systematic review and meta-analysis were performed examining all randomized controlled trials (RCTs) and observational studies (OBSs) assessing the effect of HCO-HD on clinical outcomes of patients with MM complicated by cast nephropathy–induced severe AKI. The primary outcome was all-cause mortality at the end of the study. The secondary outcomes included all-cause mortality at 12 months, HD independence and serum kappa and lambda light chain reduction. Pooled analysis was performed using random effects models.

Results

We identified five studies, comprising two RCTs and three retrospective cohort studies, including 276 patients with a mean follow-up of 18.7 months. The majority of the studies were of suboptimal quality and underpowered. Compared with patients treated with conventional HD, HCO-HD was not associated with a survival benefit at 12 months {five studies, 276 patients, relative risk [RR] 1.02 [95% confidence interval (CI) 0.76–1.35], I² = 33.9%} or at the end of the studies at an average of 34 months [five studies, 276 patients, RR 1.32 (95% CI 0.71–2.45), I² = 62.0%]. There was no difference in HD independence at 90 days [two trials, 78 patients, RR 2.23 (95% CI 1.09–4.55)], 6 months [two studies, 188 patients, RR 1.19 (95% CI 0.68–2.06)] or 12 months [two studies, 188 patients, RR 1.14 (95% CI 0.58–2.26)]. Patients receiving HCO dialysis, however, had a greater reduction in serum kappa [two studies, 188 patients, weighted mean difference (WMD) 46.7 (95% CI 38.6–54.7), I² =  52.0%] and lambda [two studies, 188 patients, WMD 50.3 (95% CI 21.4–79.3), I² = 95.1%] light chain levels.

Conclusion

Current evidence from RCTs and OBSs suggests HCO dialysis is able to reduce serum free light chains but makes no significant improvement in all-cause mortality and renal outcomes compared with conventional HD for patients with myeloma cast nephropathy. However, there is a trend towards better renal outcomes with the use of HCO dialysis. The lack of long-term data and the small sample sizes of the included studies limit this analysis. Therefore further large-scale RCTs with longer follow-up are needed to assess the effect of HCO dialysis on clinical outcomes in patients with myeloma cast nephropathy.

Modeling the transfer of low molecular weight plasma proteins during hemodialysis and online hemodiafiltration

Replacing the renal excretion of low molecular weight proteins (LMWP) by extracorporeal dialysis (dialysis) treatment poses technological challenges. Hemodialyzers with sieving coefficients for LMWP that match or even exceed those of the glomerular membrane barrier are commercially available; however, the associated losses of albumin are much higher than physiological levels of renal albumin excretion. A unidimensional, convection-diffusion model of solute transfer has been developed to analyze and quantitate LMWP extraction and albumin loss during dialysis treatment. The model is applicable to any extracorporeal dialysis technique and any type of hemodialyzer. Clinical extraction data for beta 2 microglobin (β2M, 11.6 kDa), myoglobin (16.7 kDa) and interleukin 6 (IL6, 21-30 kDa) from 15 patients on hemodiafiltration (HDF) using a Nipro Elisio H series high flux hemodialyzer were analyzed using the model and values for the convection and mass transfer coefficients were derived. The model predicts that under normal clinical operating conditions, given equal amounts of β2M removal, albumin losses are higher using pre-dilution rather than post-dilution HDF. The model can be used to provide estimates of the internal filtration rates of hemodialyzers operating in vivo.

Doping Polysulfone Membrane with Alpha-Tocopherol and Alpha-Lipoic Acid for Suppressing Oxidative Stress Induced by Hemodialysis Treatment

The reduction of free radicals by bioactive membranes used for hemodialysis treatment is an important topic due to the constant rise of oxidative stress-associated cardiovascular mortality by hemodialysis patients. Therefore, it is urgent to find an effective solution that helps to solve this problem. Polysulfone membranes enriched with α-lipoic acid, α-tocopherol, and with both components are fabricated by spin coating. The antioxidant properties of these membranes are evaluated in vitro by determining the lipid-peroxidation level and the total antioxidant status of the blood plasma. The biocompatibility is assessed by quantifying the protein adsorption, platelet adhesion, complement activation, and hemolytic effect. All types of membranes show in vitro antioxidant activity and a trend to reduce oxidative stress in vivo; the best results show membranes prepared with a combination of both compounds and prove to be nonhemolytic and hemocompatible. Moreover, the membrane specific separation ability for the main waste products is not affected by antioxidants incorporation.

Super high-flux hemodialysis provides comparable effectiveness with high-volume postdilution online hemodiafiltration in removing protein-bound and middle-molecule uremic toxins: A prospective cross-over randomized controlled trial

Although high-volume postdilution online hemodiafiltration (ol-HDF) is superior to high-flux HD in removing all kinds of uremic toxins and improving survival, this treatment is not available in most HD centers. The present study was conducted to compare the effectiveness in removals of protein-bound (indoxyl sulfate [IS]), middle-molecule [beta-2 microglobulin (B2M) and alpha-1 microglobulin (A1MG)], and small-molecule uremic toxins between super high-flux HD (SHF-HD), HD with a novel SHF dialyzer and high-volume postdilution ol-HDF in a noninferiority fashion. Fifteen prevalent HD patients were randomly allocated into two sequences of 12-week treatment periods of SHF-HD treatment and later high-volume postdilution ol-HDF period or vice versa. Each treatment period was divided by a wash-out phase of 4-week high-flux HD. Twelve of 15 patients could complete the study. When compared with high-volume postdilution ol-HDF (convective volume of 24.4 ± 3.52 L), SHF-HD provided comparable reduction ratio values of IS, B2M, and A1MG with mean difference of 5.87 (95% confidence interval [CI] -1.63, 13.37), 1.98 (95% CI,-0.21, 4.18), and 22.96 (95% CI, -1.91, 47.83), respectively. The spKt/Vurea was not different. The predialysis levels of all uremic toxins at baseline and after 12-week treatment did not differ between both groups. Although albumin loss in dialysate in SHF-HD was greater than high-volume postdilution ol-HDF, the serum albumin levels after 12-week SHF-HD treatment were significantly higher than baseline. In conclusion, SHF-HD provides noninferior effectiveness to high-volume postdilution ol-HDF in removing various uremic toxins with significantly increased serum albumin levels despite higher albumin loss. SHF-HD might be an effectively alternative treatment when high-volume postdilution ol-HDF is not available.

Hypoalbuminemia: a price worth paying for improved dialytic removal of middle-molecular-weight uremic toxins?

Hemodiafiltration (HDF) increases the removal of middle-molecular-weight uremic toxins and may improve outcomes in patients with end-stage kidney disease (ESKD), but it requires complex equipment and comes with risks associated with infusion of large volumes of substitution solution. New high-flux hemodialysis membranes with improved diffusive permeability profiles do not have these limitations and offer an attractive alternative to HDF. However, both strategies are associated with increased albumin loss into the dialysate, raising concerns about the potential for decreased serum albumin concentrations that have been associated with poor outcomes in ESKD. Many factors can contribute to hypoalbuminemia in ESKD, including protein energy wasting, inflammation, volume expansion, renal loss and loss into the dialysate; of these factors, loss into the dialysate is not necessarily the most important. Furthermore, recent studies suggest that mild hypoalbuminemia per se is not an independent predictor of increased mortality in dialysis patients, but in combination with inflammation it is a poor prognostic sign. Thus, whether hypoalbuminemia predisposes to increased morbidity and mortality may depend on the presence or absence of inflammation. In this review we summarize recent findings on the role of dialysate losses in hypoalbuminemia and the importance of concomitant inflammation on outcomes in patients with ESKD. Based on these findings, we discuss whether hypoalbuminemia may be a price worth paying for increased dialytic removal of middle-molecular-weight uremic toxins.

Albumin losses during hemodiafiltration: all dialyzers are not created equal - a case report

Background

Online hemodiafiltration (OL-HDF) is associated with better removal of both small and middle molecules and might improve survival compared to conventional hemodialysis (HD). Nevertheless, hemodiafiltration (HDF) can lead to an increase in albumin loss across the dialyzer, especially with high permeability membrane and high convective volume (CV). We present the case of a patient treated by OL-HDF who developed severe hypoalbuminemia resulting from massive albumin loss into dialysate.

Case presentation

A 71-year-old woman with ESRD started renal replacement therapy in December 2016. She was treated by high volume post-dilution OL-HDF, 4 h, 3 times per week. The dialyzer was the Phylther HF20SD (a 2.0m² heat sterilized high flux (HF) polyphenylene membrane from Bellco). At the initiation of dialysis, the serum albumin was 4.0 g/dl. During the following months, the patient developed severe hypoalbuminemia. The lowest value observed was 2.26 g/dl in July 2017. Diagnostic workup excluded nephrotic syndrome, hepatic failure and malabsorption. The patient was shifted from OL-HDF to standard HF HD, keeping the same dialyzer and dialysis schedule. During the following months, we observed a progressive correction of the hypoalbuminemia (3.82 g/dl at last follow-up). To precise the impact of the epuration technique on the albumin losses in this patient, we measured the amount of albumin in dialysate during one session with the Phylther HF20SD on OL-HDF and one session with the same filter but on standard HD. The CV was 29.0 l for the HDF session. The total albumin losses were 23.6 g on OL-HDF and 4.6 g on HD.

Conclusion

OL-HDF can lead to significant albumin loss into the dialysate, especially with high permeability membrane and high CV. When prescribing post-dilutional OL-HDF, the choice of the dialyzer membrane should be made with caution. Users of the steam sterilized polyphenylene membrane, the Phylther SD, should be informed of the risk of large albumin loss with this membrane during post-dilution OL-HDF.

The Inability of Podocytes to Proliferate: Cause, Consequences, and Origin

This study presents a theoretical analysis of the problems related to the inability of podocytes to proliferate. The basis of these problems is the very high rate of glomerular filtration. Podocytes do not in general die by apoptosis or necrosis but are lost by detachment from the glomerular basement membrane (GBM) as viable cells. Podocytes situated on the outside of the filtration barrier and attached to the GBM only by their foot processes are permanently exposed to the flow dynamic forces of the high filtration rate tending to detach them from the GBM. The major challenge seems to consist of the high shear stresses on the foot processes within the filtration slits due to filtrate flow. Healthy podocytes are able to resist this challenge, injured podocytes are not, and may undergo foot process detachment, leading to a gap in the podocyte cover of the GBM. This represents a mortal event. Like a dam break, such a leak cannot be repaired. The ongoing exposure to filtrate flow prevents any attempt to close the gap, thus preventing any regeneration including cell proliferation. An improvement of this precarious situation consists of healing by scarring that may involve only one lobule of the glomerulus, permitting the remaining lobules to maintain filtration. An answer to the question of which waste product requires such a high filtration rate for its excretion may be in the huge quantity of circulating peptides, a problem that dates far back in evolution.

Expanded haemodialysis: from operational mechanism to clinical results

Recent advances in chemical composition and new production techniques resulted in improved biocompatibility and permeability of dialysis membranes. Among these, the creation of a new class of membranes called medium cut-off (MCO) represents an important step towards improvement of clinical outcomes. Such membranes have been developed to improve the clearance of medium to high molecular weight (MW) solutes (i.e. uraemic toxins in the range of 5–50 kDa). MCO membranes have peculiar retention onset and cut-off characteristics. Due to a modified sieving profile, MCO membranes have also been described as high-retention onset. The significant internal filtration achieved in MCO haemodialysers provides a remarkable convective clearance of medium to high MW solutes. The marginal loss of albumin observed in MCO membranes compared with high cut-off membranes is considered acceptable, if not beneficial, producing a certain clearance of protein-bound solutes. The application of MCO membranes in a classic dialysis modality characterizes a new technique called expanded haemodialysis. This therapy does not need specific software or dedicated hardware, making its application possible in every setting where the quality of dialysis fluid meets current standards.

Membrane innovation: closer to native kidneys

Modern methods in analytical biochemistry have established that uraemia is associated with the retention of proteins, both in their native state and post-translationally modified, over a wide range of molecular weights up to 60 kDa. Evidence is accumulating that these higher molecular weight retention solutes are important uraemic toxins, and therapies such as online haemodiafiltration (HDF), which enhance their removal, are associated with improved outcomes. However, HDF has limitations regarding cost, clinical implementation and the need for an external source of sterile substitution solution to maintain fluid balance. New membranes that have a solute removal profile more closely approaching that of the glomerular filtration barrier when used for conventional haemodialysis, while at the same time not allowing the passage of clinically significant amounts of beneficial proteins, are needed to address these limitations. Tighter control of the molecular characteristics of the polymers used for membrane fabrication, along with the introduction of additives and improvements in the manufacturing process, has led to membranes with a tighter pore size distribution that allows the use of an increased absolute pore size without leaking substantial amounts of albumin. At the same time, the wall thickness and internal diameter of membrane fibres have been decreased, enhancing convective transport within the dialyser without the need for an external source of substitution solution. These new expanded range membranes provide a solute removal profile more like that of the native kidney than currently available membranes when used in conventional haemodialysis.

Extracorporeal Treatment in the Management of Acute Poisoning: What an Intensivist Should Know?

Extracorporeal treatment (ECTR) represents a treatment modality promoting removal of endogenous or exogenous poisons and supporting or temporarily replacing a vital organ. This article aims to provide a brief overview of the technical aspects and the potential indications and limitations of the different ECTRs, highlighting the important characteristics of poison amenable to ECTR and the most appropriate prescriptions used in the setting of acute poisoning. The various principles that govern poison elimination by ECTR (diffusion, convection, adsorption, and centrifugation) and how components of the ECTR can be adjusted to maximize clearance have also being discussed.

Antithrombotic properties of hemofilter coated with polymer having a hydrophilic blood-contacting layer

OBJECTIVE:

Extracorporeal circulation devices are coated with a biocompatible polymer coating agent (BPCA) that has a hydrophilic blood-contacting layer, but hemofilters are not. We aimed to investigate the antithrombotic properties of a BPCA-coated hemofilter.

METHODS:

Four experiments using BPCA-coated circuits and non-coated hemofilters and four experiments using BPCA-coated circuits and BPCA-coated hemofilters were performed with whole human blood and compared by measuring the circuit pressure every 5 min, antithrombin activity every 40 min, and thrombin-antithrombin complex every 40 min, for a total of 240 min of recirculation.

RESULTS:

The mean time required for the pressure at the inlet of the hemofilter to increase sharply was longer in BPCA-coated than in non-coated hemofilters (66 ± 11 min vs 25 ± 9 min, p < 0.01). The mean antithrombin activity value at 200 and 240 min of recirculation was significantly higher in the experiments with BPCA-coated versus non-coated hemofilters (43.3 ± 2.87 vs 33.3 ± 5.74, p = 0.04; 42.8 ± 3.59 vs 31.0 ± 5.35, p = 0.01, respectively); the antithrombin activity values at the other time points were not significantly different. Furthermore, all thrombin-antithrombin complex values in experiments with the BPCA-coated hemofilters achieved overrange at 80 min of recirculation, whereas those with the non-coated hemofilter achieved overrange at 40 min.

CONCLUSION:

This study suggests that BPCA-coated hemofilters can inhibit antithrombin consumption, contributing to antithrombotic effects in extracorporeal circulation circuits.

Treatment of multiple myeloma with renal involvement: the nephrologist's view

Renal injury is a common complication in multiple myeloma (MM). In fact, as many as 10% of patients with MM develop dialysis-dependent acute kidney injury related to increased free light chain (FLC) production by a plasma cell clone. Myeloma cast nephropathy (MCN) is the most prevalent pathologic diagnosis associated with renal injury, followed by light chain deposition disease and light chain amyloidosis. Several FLC removal techniques have been explored to improve kidney disease in MM but their impact on renal clinical outcomes remains unclear. According to the evidence, high cut-off haemodialysis should be restricted to MM patients on chemotherapy with histological diagnosis of MCN and haemodialysis requirements. From our perspective, more efforts are needed to improve kidney outcomes in patients with MM and renal failure.

Quantification of Internal Filtration in Hollow Fiber Hemodialyzers with Medium Cut-Off Membrane

Background: Inadequate removal of molecules between 5 and 50 KDa may cause long-term complication in chronic hemodialysis. Medium cut-off (MCO) is a new class of membranes with enhanced sieving properties and negligible albumin loss. MCO membrane makes it possible to perform expanded hemodialysis (HDx), a technique based on high internal filtration (IF).The present study is designed to quantify IF in 2 MCO dialyzers (Theranova 400 and 500, Baxter, Deerfield, USA) using a nuclear imaging technique previously validated. Methods: Blood and dialysate compartment pressure drop along with transmembrane pressure; they were measured in a closed in vitro circuit with human blood (blood flow [QB] = 300 and 400 mL/min; dialysate flow 500 mL/min; net ultrafiltration rate 0 mL/min). A non-diffusible marker molecule (albumin macro-aggregates labeled with 99Tc metastable) was injected in the blood compartment and nuclear emission was recorded by a gamma camera. Relative variations in the concentration of the marker molecule along the length of the filter were used to calculate local cross filtration. Results: Based on marker concentration profiles, IF was estimated. For Theranova 400, IF were 29.7 and 41.6 mL/min for QB of 300 and 400 mL/min. For Theranova 500, IF were 31.6 and 53.1 mL/min for QB of 300 and 400 mL/min respectively. Conclusions: MCO membrane provides significant amounts of IF due to the particular combination between hydraulic permeability of the membrane and reduced inner diameter of the fibers. High IF combined with enhanced sieving profile of MCO membrane leads to improved removal of a wider spectrum of uremia retention molecules in HDx, without requiring complex equipment.

Leptin and β2-Microglobulin Kinetics with Three Different Dialysis Modalities

Background

Leptin is a protein produced by fat cells and involved in body weight regulation. In patients with normal kidney function, leptin has been considered an independent predictor of cardiovascular events. In uremic patients, leptin in plasma serum was assumed to be associated with malnutrition, inflammation and atherosclerosis. Because of its molecular weight and characteristics, leptin can be considered as a protein-bound uremic retention solute. Some authors have reported the possibility of decreasing the serum leptin concentration with high flux membranes, but limited data are available on the elimination with medium-flux membranes or alternative dialysis strategies such as hemodiafiltration.

Methods

We evaluated the kinetics of leptin and β2m in a study of 18 chronic hemodialysis patients using low-flux, medium-flux and high-flux biocompatible membranes, the last one used in hemodiafiltration (HDF). Blood samples for leptin and β2m were collected pre- and post-treatment and 30 minutes after the end of treatment, over a 1-week period that included 3 dialysis sessions. Clearances of leptin and β2m across the dialyzer were also determined directly from the arterial and venous blood concentrations 60 and 210 minutes after starting dialysis.

Results

At baseline, all groups showed similar leptin (18.8±4.4 ng/mL) and β2m concentrations (29.2±7.1 ng/mL). After a single dialysis session, a reduction of both solutes was observed with HDF (39.8±1.9%, 78.1±4.9) and medium flux membranes (18.2±0.9%, 52.2±1.7%), whereas the concentrations remained unchanged with the low-flux membranes. After one-week period, a trend of reduction of plasma pre dialysis leptin and β2m were observed with HDF and medium flux membranes. At 60 minutes, HDF showed the best instantaneous clearance across the filter for leptin (56.2±10.1 ml/min) and β2m (75.3±4.4 ml/min). The magnitude of post dialysis rebound of leptin at 30 min was variable and strongly correlated with the instantaneous clearance of the solute (r2= 0.88).

Conclusions

Leptin serum concentration can be influenced by dialysis modalities and membrane permeability; data on rebound suggest a multicompartimental kinetic of leptin similar to β2m. Leptin removal, as measured by the reduction rate, can be considered as an index of dialysis efficiency for protein-bound uremic retention solutes.

Precise Quantitative Assessment of the Clinical Performances of Two High-Flux Polysulfone Hemodialyzers in Hemodialysis: Validation of a Blood-Based Simple Kinetic Model Versus Direct Dialysis Quantification

Highly permeable dialysis membranes with better design filters have contributed to improved solute removal and dialysis efficacy. However, solute membrane permeability needs to be well controlled to avoid increased loss of albumin that is considered to be detrimental for dialysis patients. A novel high-flux dialyzer type (FX CorDiax; Fresenius Medical Care) incorporating an advanced polysulfone membrane modified with nano-controlled spinning technology to enhance the elimination of a broader spectrum of uremic toxins has been released. The aim of this study was to compare in the clinical setting two dialyzer types having the same surface area, the current (FX dialyzer) and the new dialyzer generation (FX CorDiax), with respect to solute removal capacity over a broad spectrum of markers, including assessment of albumin loss based on a direct dialysis quantification method. We performed a crossover study following an A1-B-A2 design involving 10 patients. Phase A1 was 1 week of thrice-weekly bicarbonate hemodialysis with the FX dialyzer, 4 h per treatment; phase B was performed with a similar treatment regimen but with a new FX CorDiax dialyzer and finally the phase A2 was repeated with FX dialyzer as the former phase. Solute removal markers of interest were assessed from blood samples taken before and after treatment and from total spent dialysate collection (direct dialysis quantification) permitting a mass transfer calculation (mg/session into total spent dialysate/ultrafiltrate). On the blood side, there were no significant differences in the solute percent reduction between FX CorDiax 80 and FX 80. On the dialysate side, no difference was observed regarding eliminated mass of different solutes including β₂ -microglobulin (143.1 ± 33.6 vs. 138.3 ± 41.9 mg, P = 0.8), while the solute mass removal of total protein (1.65 ± 0.51 vs. 2.14 ± 0.75 g, P = 0.04), and albumin (0.41 ± 0.21 vs. 1.22 ± 0.51 g, P < 0.001) were significantly less for FX CorDiax 80 compared to the FX 80 dialyzer. The results of this cross-over study indicate that the new FX CorDiax dialyzer has highly effective removal of middle molecules, without any concomitant increase in total protein and albumin loss. The clinical relevance and potential benefit of this finding needs to be determined.

Hemodialysis membrane coated with a polymer having a hydrophilic blood-contacting layer can enhance diffusional performance

Purpose

Currently, the foreign surfaces of various extracorporeal circulation devices are coated with a biocompatible polymer coating agent (BPA), which creates a hydrophilic blood-contacting layer to reduce thrombogenicity, while the membranes in hemodialyzers are not. We aimed to clarify other side effects of BPA-coated membranes by examining the diffusion performance in in vitro experiments.

Methods

We used a polyethersulfone membrane (sieving coefficient of albumin is ≤0.01) coated with BPA product, SEC-1™ (Toyobo), in a hemodialyzer. To estimate the diffusion rates of a wide range of molecules, 2 L of saline containing vancomycin, lysozyme, and albumin were recirculated in the circuit configured with a hemodialyzer, and dialyzed continuously using water. The concentrations of sodium, vancomycin, lysozyme, and albumin were measured every 5 minutes for 30 minutes and compared in experiments with BPA-coated (n = 4) and BPA-noncoated (n = 4) membranes.

Results

The removal rates of sodium and vancomycin after 5 minutes of dialysis (n = 24) were significantly higher in BPA-coated than noncoated membranes, while those of lysozyme and albumin were not significantly different. The removal rates of sodium and vancomycin after 30 minutes of dialysis (n = 4) were significantly higher, and those of lysozyme were significantly lower in BPA-coated than noncoated membranes, while those of albumin were not significantly different.

Conclusions

The preliminary study suggests that BPA-coated membranes enhanced the diffusion rate of molecules with low and middle molecular weight without affecting the sieving coefficient of albumin. Thus, BPA coating can enhance the dialysis performance of membranes.

Performance of hemodialysis with novel medium cut-off dialyzers

Background. Compared to high-flux dialysis membranes, novel medium cut-off (MCO) membranes show greater permeability for larger middle molecules.

Methods. In two prospective, open-label, controlled, randomized, crossover pilot studies, 39 prevalent hemodialysis (HD) patients were studied in four dialysis treatments as follows: study 1, three MCO prototype dialyzers (AA, BB and CC with increasing permeability) and one high-flux dialyzer in HD; and study 2, two MCO prototype dialyzers (AA and BB) in HD and high-flux dialyzers in HD and hemodiafiltration (HDF). Primary outcome was lambda free light chain (λFLC) overall clearance. Secondary outcomes included overall clearances and pre-to-post-reduction ratios of middle and small molecules, and safety of MCO HD treatments.

Results. MCO HD provided greater λFLC overall clearance [least square mean (standard error)] as follows: study 1: MCO AA 8.5 (0.54), MCO BB 11.3 (0.51), MCO CC 15.0 (0.53) versus high-flux HD 3.6 (0.51) mL/min; study 2: MCO AA 10.0 (0.58), MCO BB 12.5 (0.57) versus high-flux HD 4.4 (0.57) and HDF 6.2 (0.58) mL/min. Differences between MCO and high-flux dialyzers were consistently significant in mixed model analysis (each P < 0.001). Reduction ratios of λFLC were greater for MCO. Clearances of α1-microglobulin, complement factor D, kappa FLC (κFLC) and myoglobin were generally greater with MCO than with high-flux HD and similar to or greater than clearances with HDF. Albumin loss was moderate with MCO, but greater than with high-flux HD and HDF.

Conclusions. MCO HD removes a wide range of middle molecules more effectively than high-flux HD and even exceeds the performance of high-volume HDF for large solutes, particularly λFLC.

The Rise of Expanded Hemodialysis

The low water permeability feature of original cellulosic membranes was considered an advantage in the absence of dialysis equipment that are capable of controlling water removal. The advent of ultrafiltration control systems led to the development and use of high-flux (HF) membranes that allowed improved middle molecule removal including β-2 microglobulin. Further advances in technology allowed better control over the structure and permeability of membranes. Different polymers and improved spinning modalities led to significant advances in solute removal and hemocompatibility. Inner surface modification produced a reduction in membrane thrombogenicity and protein-membrane interaction with a less tendency to fouling and permeability decay. Further evolution in technology led to the development of a new class of membranes referred to as protein-leaking membranes or super-flux or high cutoff (HCO). These membranes are more permeable than conventional HF membranes and allow some passage of proteins, including albumin. The rationale for these membranes is the need for increased clearance of low molecular weight proteins and protein-bound solutes. However, albumin loss in protein-leaking HCO membranes represents a limitation whose effect in patients is still controversial. The last evolution in the field of membranes is the development of a new class defined as "high retention onset" (HRO) due to the peculiar high sieving value in the middle to high molecular weight range. The introduction of HRO membranes in the clinical routine has enabled the development of a new concept therapy called "expanded hemodialysis." Its simple set up and application offer the possibility to use it even in patients with suboptimal vascular access or even with an indwelling catheter. The system does not require particular hardware or unusual nursing skill. The quality of dialysis fluid is, however, mandatory to ensure a safe conduction of the dialysis session. This new therapy is likely to modify the outcome of end-stage kidney disease patients, thanks to the enhanced removal of molecules traditionally retained by current dialysis techniques.

[Online hemodiafiltration: Practical aspects, safety and efficacy]

Purification of high molecular uremic toxins by conventional hemodialysis is limited. It remains associated with a high morbidity and excessively high mortality. Online hemodiafiltration using a high permeability hemodiafilter, an ultrapure dialysate, and which tends to maximize substitution volumes, provides a high efficiency and low bio-incompatibility renal supplementation. Regular use of online hemodiafiltration is associated with reduced morbidity (reduction of intradialytic hypotension episodes, improved blood pressure control, reduced inflammatory profile, better anemia correction and prevention of β₂-microglobulin-associated amyloidosis). Recently, several cohort studies have shown that hemodiafiltration with high substitution volume was associated with a significant reduction in mortality. Randomized studies have been conducted in Europe to confirm these facts. The high safety of online hemodiafiltration has been confirmed in clinical practice by prospective studies. Online hemodiafiltration has reached its full maturity phase and is expected to represent the new standard of renal replacement therapy.

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.

Hemodiafiltration improves free light chain removal and normalizes κ/λ ratio in hemodialysis patients

BACKGROUND/AIMS

Serum free light chain (FLC) levels are correlated with chronic kidney disease (CKD) stages and are highest in patients on hemodialysis (HD). Aim of this study was to assess the FLC removal efficiency of Elisio™-210H dialyzer using either high-flux HD or on line high efficiency hemodiafiltration (HDF) modalities in CKD-5D patients.

METHODS

In this prospective and comparative study, 20 CKD-5D patients free from multiple myeloma were randomized in two groups: HD versus on line HDF. All patients were dialyzed with Elisio™-210H dialyzer. Serum samples were collected before and after the midweek dialysis session, before randomization and at the end of the study to measure κ and λ FLC concentrations. Reduction ratios were corrected for net ultrafiltration.

RESULTS

For both HD and HDF mode, κ and λ FLC concentrations were significantly lower after dialysis than before but median reductions in κ and λ FLC levels were significantly higher in HDF versus HD groups (κ 73.5 vs. 65.5 %, p = 0.04 and λ 51.0 vs. 36.6 %, p = 0.07). After dialysis, all κ/λ ratio values were between 0.26 and 1.65 which is the reference range described in subjects with normal kidney function, for both HD and HDF groups (median κ/λ ratios were 0.80 [0.47-1.22] and 0.67 [0.50-0.79] respectively).

CONCLUSION

This study shows the superiority of on line HDF compared with HD to remove both κ and λ FLC. Moreover, all post-dialysis κ/λ ratios reached normal reference range.

Principles and operational parameters to optimize poison removal with extracorporeal treatments

A role for nephrologists in the management of a poisoned patient involves evaluating the indications for, and methods of, enhancing the elimination of a poison. Nephrologists are familiar with the various extracorporeal treatments (ECTRs) used in the management of impaired kidney function, and their respective advantages and disadvantages. However, these same skills and knowledge may not always be considered, or applicable, when prescribing ECTR for the treatment of a poisoned patient. Maximizing solute elimination is a key aim of such treatments, perhaps more so than in the treatment of uremia, because ECTR has the potential to reverse clinical toxicity and shorten the duration of poisoning. This manuscript reviews the various principles that govern poison elimination by ECTR (diffusion, convection, adsorption, and centrifugation) and how components of the ECTR can be adjusted to maximize clearance. Data supporting these recommendations will be presented, whenever available.

Is there a future for electrochemically assisted hemodialysis? Focus on the application of polypyrrole–nanocellulose composites

This work summarizes the various aspects of using electrochemically assisted solute removal techniques in hemodialysis with a focus on blood electrodialysis and electrochemically controlled uremic retention solute removal using polypyrrole. In particular, the feasibility of using highly porous conductive polypyrrole–Cladophora cellulose membranes for hemodialysis are overviewed as a part of our dedicated research efforts during the past 4 years. The potential benefits and the current limitations associated with using the electrochemically controlled uremic retention solute removal techniques are discussed in detail.

A stepwise approach for the management of poisoning with extracorporeal treatments

The use of an extracorporeal treatment (ECTR) in a poisoned patient may be life-saving in a limited number of scenarios. The decision-processes surrounding the use of ECTR in poisoning is complex: most nephrologists are not trained to assess a poisoned patient while clinical toxicologists rarely prescribe ECTRs. Deciding on which ECTR is most appropriate for a poison requires a good understanding of the poison's physicochemical and pharmacokinetic properties. Further, a detailed understanding of the capabilities and limitations of the different ECTRs can be useful to select the most appropriate ECTR for a given clinical situation. This manuscript provides a stepwise approach to assess the usefulness of ECTRs in poisoning.

Extended characterization of a new class of membranes for blood purification: the high cut-off membranes

High cut-off membranes are a new class of blood purification membranes whose particular characteristics present challenges for commonly-used characterization methods. Dextran sieving curves for representative blood purification membranes of the high-flux and high cut-off types were measured and compared to curves for the glomerular filtration barrier (GFB). The performance was also determined after blood exposure for the most permeable synthetic membranes. High cut-off membranes were observed to be more open than the GFB before blood exposure, but become tighter and more selective after the exposure, keeping the permeation for low and middle molecules while restraining the filtration of large species. Based on dextran sieving experiments for a variety of commercially available blood purification membranes, we present a novel method for classifying blood purification membranes. By using a well-established technique and introducing a new characteristic parameter for the sieving curve--the molecular weight retention onset (MWRO)--a graph of molecular weight cut-off versus molecular weight retention onset provides the landscape of dialysis membrane types. This meaningful representation is based on only one in vitro method, and allows the membrane classification by indirectly considering two structural parameters: pore size and pore size distribution. In this way, the families of low-flux, high-flux, protein leaking, and high cut-off membranes are clearly differentiated. The differentiation allows for the definition of MWCO/MWRO regions for the different types, so that further classification of newly developed membranes can be easily achieved.

Cardiorenal syndrome: the emerging role of protein-bound uremic toxins

Cardiorenal syndrome is a condition in which a complex interrelationship between cardiac dysfunction and renal dysfunction exists. Despite advances in treatment of both cardiovascular and kidney disease, cardiorenal syndrome remains a major global health problem. Characteristic of the pathophysiology of cardiorenal syndrome is bidirectional cross-talk; mediators/substances activated by the disease state of 1 organ can play a role in worsening dysfunction of the other by exerting their biologically harmful effects, leading to the progression of the syndrome. Accumulation of uremic toxins is a hallmark of renal excretory dysfunction. Removal of some toxins by conventional dialysis is particularly problematic because of their high protein binding. In this review, we demonstrate that protein-bound uremic toxins may play an important role in progression of cardiovascular disease in the setting of chronic kidney disease. The highly protein-bound uremic toxin indoxyl sulfate has emerged as a potent toxin adversely affecting both the kidney and heart. Direct cardiac effects of this toxin have been recently demonstrated both in vitro and in vivo. Specifically, potent fibrogenic and prohypertrophic effects, as well as oxidative stress-inducing effects, appear to play a central role in both renal and cardiac pathology. Many of these adverse effects can be suppressed by use of a gut adsorbent, AST-120. Potential mechanisms underlying indoxyl sulfate-induced cardiorenal fibrosis are discussed. Future research and clinical implications conclude this review.

Morphological Characterization of the Polyflux 210H Hemodialysis Filter Pores

Background. Morphological characterization of hemodialysis membranes is necessary to improve pore design. Aim. To delineate membrane pore structure of a high flux filter, Polyflux 210H. Methods. We used a Joel JSM-6010LV scanning electron microscope (SEM) and a SU6600 Hitachi field emission scanning electron microscope (FESEM) to characterize the pore and fiber morphology. The maximal diameters of selected uremic toxins were calculated using the macromolecular modeling Crystallographic Object-Oriented Toolkit (COOT) software. Results. The mean pore densities on the outermost and innermost surfaces of the membrane were 36.81% and 5.45%, respectively. The membrane exhibited a tortuous structure with poor connection between the inner and outer pores. The aperture's width in the inner surface ranged between 34 and 45 nm, which is 8.76-11.60 times larger than the estimated maximum diameter of β2-microglobulin (3.88 nm). Conclusion. The results suggest that the diameter size of inner pore apertures is not a limiting factor to middle molecules clearance, the extremely diminished density is. Increasing inner pore density and improving channel structure are strategies to improve clearance of middle molecules.

Theoretical Application of Irreversible (Nonequilibrium) Thermodynamic Principles to Enhance Solute Fluxes across Nanofabricated Hemodialysis Membranes

Objective. Nanotechnology has the potential to improve hemodialysis membrane technology. Thus, a major objective is to understand how to enhance toxic solute fluxes across these membranes. The aim of this concept building study is to review the application of irreversible thermodynamic (IT) to solute fluxes. Methods. We expanded the application of the Nernst-Planck equation to include the Kedem-Katchalsky equation, pH, membrane thickness, pore size, and electric potential as variables. Results. (1) Reducing the membrane's thickness from 25 μm to 25 nm increased the flux of creatinine, β₂-microglobulin, and tumor necrosis factor-α (TNF-α) by a thousand times but prevented completely albumin flux, (2) applying an electric potential of 50–400 mV across the membrane enhanced the flux of the respective molecules by 71.167 × 10⁻³, 38.7905 × 10⁻⁸, and 0.595 × 10⁻¹³ mol/s, and (3) changing the pH from 7.35 to 7.42 altered the fluxes minimally. Conclusions. The results supported an argument to investigate the application of IT to study forces of fluxes across membranes. Reducing the membrane's thickness—together with the application of an electrical potential—qualities achievable by nanotechnology, can enhance the removal of uremic toxins by many folds. However, changing the pH at a specific membrane thickness does not affect the flux significantly.

The rationale and evidence base for the direct removal of serum-free light chains in the management of myeloma kidney

Myeloma kidney (cast nephropathy) causing severe acute kidney injury occurs in up to 10% of patients with multiple myeloma. The lesion is caused by exposure of the kidneys to high serum levels of free clonal immunoglobulin light chains (LCs) and is associated with very high morbidity and mortality. The current focus on the management of this complication is on early and aggressive treatment to rapidly reduce the serum levels of the immunoglobulin LC clone and protect the kidneys from continuing injury. This has promoted intense interest in the role of direct (extracorporeal) removal of free LCs from serum by plasma exchange or high cut-off (protein permeable) hemodialysis. However, it remains uncertain whether direct removal provides an additional measurable clinical benefit over the current standard of care; rapid institution of treatment with a dexamethasone- and bortezomib-based chemotherapy regime. In this article, we review the rationale for direct removal of free LCs and the current clinical evidence base for plasma exchange and high cut-off hemodialysis.

High cut-off membrane hemodiafiltration in myoglobinuric acute renal failure: a case series

Acute renal failure is a major complication of rhabdomyolysis. New membranes for hemodialysis have been developed with a high cut-off pore size allowing efficient removal of myoglobin. We report on six patients treated by hemodiafiltration with a high cut-off membrane (HCO-HDF) for myoglobinuric acute renal failure. Rhabdomyolysis was caused by infection in two patients, by a statin in one patient and a non-traumatic crush in another, and followed cardiovascular surgery in two others. Ten HCO-HDF procedures were performed. A high cut-off hemofilter was used, with citrate anticoagulation and postdilutional fluid substitution of 2-3 L/h, dialysate flow 500 mL/min, and blood flow within 250-300 mL/min. Albumin losses were replaced by infusion of human albumin solution, and the mean myoglobin reduction ratio was 77% (range, 62-89%). An excellent clearance of 81 mL/min (range 42-131 mL/min) was achieved. Nearly 5 g of myoglobin was removed into the dialysate collected in one of the procedures. A high rebound in serum myoglobin, on average to 244% of the post-procedure myoglobin level, was observed. The four patients alive at the time remained anuric for a week. Slow myoglobin elimination with a mean half-time of 39 h (range 19-59 h) was observed in that period. Highly efficient myoglobin removal by high cut-off membrane hemodiafiltration was demonstrated in our patients. Rapid redistribution from the extracellular fluid and sustained myoglobin release were suggested by the high rebound observed. Elimination of myoglobin within the body was shown in our study to occur slowly during the period of anuria.