Derivation and elimination of uremic toxins from kidney-gut axis

Uremic toxins are chemicals, organic or inorganic, that accumulate in the body fluids of individuals with acute or chronic kidney disease and impaired renal function. More than 130 uremic solutions are included in the most comprehensive reviews to date by the European Uremic Toxins Work Group, and novel investigations are ongoing to increase this number. Although approaches to remove uremic toxins have emerged, recalcitrant toxins that injure the human body remain a difficult problem. Herein, we review the derivation and elimination of uremic toxins, outline kidney-gut axis function and relative toxin removal methods, and elucidate promising approaches to effectively remove toxins.

The prognostic value of URR equals that of Kt/V for all-cause mortality in Taiwan after 10-year follow-up

Kt/V and URR (urea reduction ratio) measurements represent dialysis adequacy. Single-pool Kt/V is theoretically a superior method and is recommended by the Kidney Disease Outcomes Quality Initiative guidelines. However, the prognostic value of URR compared with Kt/V for all-cause mortality is unknown. The effect modifiers and cut-off values of the two parameters have not been compared. We investigated 2615 incident hemodialysis patients with URR of 72% and Kt/V (Daugirdas) of 1.6. The average patient age was 59 years, 50.7% were female, and 1113 (40.2%) died within 10 years. URR and Kt/V were both positively associated with nutrition factors and female sex and negatively associated with body weight and heart failure. In Cox regression mod-els for all-cause mortality, the hazard ratios (HRs) of high URR groups (65-70%, 70-75%, and > 75%) and the URR < 65% group were 0.748 (0.623-0.898), 0.693 (0.578-0.829), and 0.640 (0.519-0.788), respectively. The HRs of high Kt/V groups (Kt/V 1.2-1.4, 1.4-1.7, and > 1.7) and the Kt/V < 1.2 group were 0.711 (0.580-0.873), 0.656 (0.540-0.799), and 0.623 (0.498-0.779), respec-tively. In subgroup analysis, Kt/V was not associated with all-cause mortality in women. The prognostic value of URR for all-cause mortality is as great as that of Kt/V. URR > 70% and Kt/V > 1.4 were associated with a higher survival rate. Kt/V may have weaker prognostic value for women.

Strategies for optimizing urea removal to enable portable kidney dialysis: A reappraisal

BACKGROUND

Portable hemodialysis has the potential to improve health outcomes and quality of life for patients with kidney failure at reduced costs. Urea removal, required for dialysate regeneration, is a central function of any existing/potential portable dialysis device. Urea in the spent dialysate coexists with non-urea uremic toxins, nutrients, and electrolytes, all of which will interfere with the urea removal efficiency, regardless of whether the underlying urea removal mechanism is based on urease conversion, direct urea adsorption, or oxidation. The aim of the current review is to identify the amount of the most prevalent chemicals being removed during a single dialysis session and evaluate the potential benefits of an urea-selective membrane for portable dialysis.

METHODS

We have performed a literature search using Web of Science and PubMed databases to find available articles reporting (or be able to calculate from blood plasma concentration) > 5 mg of individually quantified solutes removed during thrice-weekly hemodialysis sessions. If multiple reports of the same solute were available, the reported values were averaged, and the geometric mean of standard deviations was taken. Further critical literature analysis of reported dialysate regeneration methods was performed using Web of Science and PubMed databases.

RESULTS

On average, 46.0 g uremic retention solutes are removed in a single conventional dialysis session, out of which urea is only 23.6 g. For both urease- and sorbent-based urea removal mechanisms, amino acids, with 7.7 g removal per session, could potentially interfere with urea removal efficiency. Additionally for the oxidation-based urea removal system, plentiful nutrients such as glucose (24.0 g) will interfere with urea removal by competition. Using a nanofiltration membrane between dialysate and oxidation unit with a molecular weight cutoff (MWCO) of ~200 Da, 67.6 g of non-electrolyte species will be removed in a single dialysis session, out of which 44.0 g are non-urea molecules. If the membrane MWCO is further decreased to 120 Da, the mass of non-electrolyte non-urea species will drop to 9.3 g. Reverse osmosis membranes have been shown to be both effective at blocking the transport of non-urea species (creatinine for example with ~90% rejection ratio), and permissive for urea transport (~20% rejection ratio), making them a promising urea selective membrane to increase the efficiency of the oxidative urea removal system.

CONCLUSIONS

Compiled are quantified solute removal amounts greater than 5 mg per session during conventional hemodialysis treatments, to act as a guide for portable dialysis system design. Analysis shows that multiple chemical species in the dialysate interfere with all proposed portable urea removal systems. This suggests the need for an additional protective dialysate loop coupled to urea removal system and an urea-selective membrane.

Proactive Risk Assessment Through Failure Mode and Effect Analysis (FMEA) for Haemodialysis Facilities: A Pilot Project

Haemodialysis (HD) is one of the methods for renal replacement therapy in the management of advanced chronic kidney disease through an osmosis process that allows purification of blood in the dialysis machine. The complexity of the dialytic procedure often requires the presence of a multi-specialist, multi-disciplinary team. The dialysis process is an important target for clinical risk management. Failure Mode and Effect Analysis (FMEA) is a proactive technique, considered a purposeful and dynamic tool for clinical risk management. FMEA is noted in five phases that allow a preliminary assessment of a definite process through identification and classification of risk priorities. This study represents the first of a two-phase project where FMEA is applied to HD in the setting of San Feliciano Hospital. The dialysis center performs ~12,000 dialysis sessions per year. The dialysis process is divided into different stages. A total of 31 failure modes were identified in the whole dialysis stages; more than 2/3 of the failure modes were related to the only connecting of the patient to the dialysis machine. The first phase of the study clearly remarked that the most critical step of the dialytic process is represented by the connection between the patient and the machine, as expected. Indeed, in order to have the dialysis set up, an arteriovenous fistula must be surgically created prior to the procedure and it is one of the most important issues in the HD process because of the necessity of a constant revision of it. FMEA application to HD is a useful tool, easy to be implemented and it is likely to nimbly reveal the practical and potential solutions to the critical steps of the procedure.

Design and Development of a Computational Tool for a Dialyzer by Using Computational Fluid Dynamic (CFD) Model

In order to reduce the hemodialysis cost and duration, an investigation of the effect of dialyzer design and process variables on the solute clearance rate is required. It is not easy to translate the in vivo transfer process with in vitro experiments, as it involves a high cost to produce various designs and membranes for the dialyzer. The primary objective of this study was the design and development of a computational tool for a dialyzer by using a computational fluid dynamic (CFD) model. Due to their complexity, only researchers with expertise in computational analysis can use dialyzer models. Therefore, COMSOL Inc. (Stockholm, Sweden) has made an application on membrane dialysis to study the impact of different design and process parameters on dialyzed liquid concentration. Still, membrane mathematical modeling is not considered in this application. This void hinders an investigation of the impact of membrane characteristics on the solute clearance rate. This study has developed a stand-alone computational tool in COMSOL Multiphysics 5.4 to fill this void. A review of the literature conducted shows that there are no suitable stand-alone computational tools for kidney dialysis. Very little work has been undertaken to validate the stand-alone computational tool. Medical staff in the hospitals require a computational tool that can be installed quickly and provide results with limited knowledge of dialysis. This work aims to construct a user-friendly computational tool to solve this problem. The development of a user-friendly stand-alone computational tool for the dialyzer is described thoroughly. This application simulates a mathematical model with the Finite Element Method using the COMSOL Multiphysics solver. The software tool is converted to a stand-alone version with the COMSOL compiler. The stand-alone computational tool provides the clearance rate of six different toxins and module packing density. Compared with the previous application, the stand-alone computational tool of membrane dialysis enables the user to investigate the impact of membrane characteristics and process parameters on the clearance rate of different solutes. The results are also inconsistent with the literature data, and the differences ranges are 0.09–6.35% and 0.22–2.63% for urea clearance rate and glucose clearance rate, respectively. Statistical analysis of the results is presented as mean with 95% confidence intervals (CIs) and p values 0.9472 and 0.833 of the urea and glucose clearance rates, respectively.

Improved Formula for Predicting Hemodialyzability of Intravenous and Oral Drugs

BACKGROUND

The rate of drug removal by hemodialysis needs to be considered when designing drug dosage regimens for patients on hemodialysis. We previously developed a simplified equation to predict the removal rates of intravenously administered drugs by hemodialysis. Here, we addressed shortcomings of this equation and developed a more accurate equation that can also predict the removal rates of orally administered drugs.

METHODS

A total of 70 drugs with known pharmacokinetic and physical parameters and drug removal rates that were measured during hemodialysis in clinical cases were randomly assigned at a 4:1 ratio to a training data group or a test data group. A prediction equation was developed by performing stepwise multiple regression analyses using the training data (i.e., the removal rate by hemodialysis) as the objective variable and pharmacokinetic parameters as the explanatory variables. The equation was validated using the test data.

RESULTS

Multiple regression analyses revealed that molecular weight (MW), protein binding rate, and fraction excreted unchanged in urine relative to the volume of distribution (Vd) were independently correlated with the drug clearance rate (adjusted coefficient of determination, 0.83; p = 2.2e-16). The following equation was obtained: drug removal rate by hemodialysis (%) = -17.32 × [log (MW)] - 0.39 × [protein binding rate (%)] + 0.06 × [fraction excreted unchanged in urine (%)/Vd (L/kg)] + 83.34. Validation of the equation using the test data showed a very high correlation between predicted and measured reduction rate (R = 0.93, p = 1.87e-6). Mean error was -3.34 (95% confidence interval: -10.03, 3.35), mean absolute error was 9.59, and root mean square error was 16.48.

CONCLUSION

The modified equation derived in this study using pharmacokinetic and physical parameters as variables precisely predicted the removal rates of both intravenous and oral drugs by hemodialysis.

Challenges of reducing protein-bound uremic toxin levels in chronic kidney disease and end stage renal disease

The prevalence of chronic kidney disease (CKD) in the worldwide population is currently estimated between 11% and 13%. Adequate renal clearance is compromised in these patients and the accumulation of a large number of uremic retention solutes results in an irreversible worsening of renal function which can lead to end stage renal disease (ESRD). Approximately three million ESRD patients currently receive renal replacement therapies (RRTs), such as hemodialysis, which only partially restore kidney function, as they are only efficient in removing mainly small, unbound solutes from the circulation while leaving larger and protein-bound uremic toxins (PBUTs) untouched. The accumulation of PBUTs in patients highly increases the risk of cardiovascular events and is associated with higher mortality and morbidity in CKD and ESRD. In this review, we address several strategies currently being explored toward reducing PBUT concentrations, including clinical and medical approaches, therapeutic techniques, and recent developments in RRT technology. These include preservation of renal function, limitation of colon derived PBUTs, oral sorbents, adsorbent RRT technology, and use of albumin displacers. Despite the promising results of the different approaches to promote enhanced removal of a small percentage of the more than 30 identified PBUTs, on their own, none of them provide a treatment with the required efficiency, safety and cost-effectiveness to prevent CKD-related complications and decrease mortality and morbidity in ESRD.

The impact of intradialytic cycling on the removal of protein-bound uraemic toxins: A randomised cross-over study

The evidence on impact of intradialytic exercise on the removal of urea, is conflictive. Impact of exercise on kinetics of serum levels of protein-bound uraemic toxins, known to exert toxicity and to have kinetics dissimilar of those of urea, has so far not been explored. Furthermore, if any effect, the most optimal intensity, time point and/or required duration of intradialytic exercise to maximise removal remain obscure. We therefore studied the impact of different intradialytic cycling schedules on the removal of protein-bound uraemic toxins during haemodialysis (HD).This randomised cross-over study included seven stable patients who were dialysed with an FX800 dialyser during three consecutive midweek HD sessions of 240 min: (A) without cycling; (B) cycling for 60 min between 60th and 120th minutes of dialysis; and (C) cycling for 60 min between 150th and 210th minutes, with the same cycling load as in session B. Blood and dialysate flows were respectively 300 and 500 mL/min. Blood was sampled from the blood inlet at different time points, and dialysate was partially collected (300 mL/h). Small water soluble solutes and protein-bound toxins were quantified and intradialytic reduction ratios (RR) and overall removal were calculated per solute.Total solute removal and reduction ratios were not different between the three test sessions, except for the reduction ratios RR_60-120 and RR_150-210 for potassium.In conclusion, we add evidence to the existing literature that, regardless of the timing within the dialysis session, intradialytic exercise has no impact on small solute clearance, and demonstrated also a lack of impact for protein-bound solutes.

Advanced organ support (ADVOS) in the critically ill: first clinical experience in patients with multiple organ failure

Background

Prevalence of multiple organ failure (MOF) in critically ill patients is increasing and associated mortality remains high. Extracorporeal organ support is a cornerstone in the management of MOF. We report data of an advanced hemodialysis system based on albumin dialysis (ADVOS multi device) that can regulate acid–base balance in addition to the established properties of renal replacement therapy and albumin dialysis systems in critically ill patients with MOF.

Methods

34 critically ill patients with MOF received 102 ADVOS treatment sessions in the Department of Intensive Care Medicine of the University Medical Center Hamburg-Eppendorf. Markers of metabolic detoxification and acid–base regulation were collected and blood gas analyses were performed. A subgroup analyses were performed in patients with severe acidemia (pH < 7.2).

Results

Median number of treatment sessions was 2 (range 1–9) per patient. Median duration of treatment was 17.5 (IQR 11–23) hours per session. Treatment with the ADVOS multi-albumin dialysis device caused a significant decrease in bilirubin levels, serum creatinine, BUN and ammonia levels. The relative elimination rate of bilirubin was concentration dependent. Furthermore, a significant improvement in blood pH, HCO₃⁻ and PaCO₂, was achieved during ADVOS treatment including six patients that suffered from severe metabolic acidosis refractory to continuous renal replacement therapy. Delta pH, HCO₃⁻ and PaCO₂ were significantly affected by the ADVOS blood flow rate and pH settings. This improvement in the clinical course during ADVOS treatments allowed a reduction in norepinephrine during ADVOS therapy. Treatments were well tolerated. Mortality rates were 50% and 62% for 28 and 90 days, respectively.

Conclusions

In this case series in patients with MOF, ADVOS was able to eliminate water-soluble and albumin-bound substances. Furthermore, the device corrected severe metabolic and respiratory acid–base disequilibrium. No major adverse events associated with the ADVOS treatments were observed.

Ex vivo evaluation of the blood compatibility of mixed matrix haemodialysis membranes

The patients with end stage kidney disease need haemodialysis therapies, using an artificial kidney. Nevertheless, the current therapies cannot remove a broad range of uremic toxins compared to the natural kidney. Adsorption therapies, using sorbent-based columns, can improve the clearance of uremic toxins, but the sorbent particles often require polymeric coatings to improve their haemocompatibility leading to mass transfer limitations and to lowering of their performance. Earlier, we have developed a dual layer Mixed Matrix fiber Membrane (MMM) based on polyethersulfone/polyvinylpyrrolidone (PES/PVP) polymer blends. There, the sorbent activated carbon particles are embedded in the outer membrane layer for achieving higher removal whereas the inner blood contacting selective membrane layer should achieve optimal blood compatibility. In this work, we evaluate in detail the haemocompatibility of the MMM following the norm ISO 10993-4. We study two generations of MMM having different dimensions and transport characteristics; one with low flux and no albumin leakage and another with high flux but some albumin leakage. The results are compared to those of home-made PES/PVP single layer hollow fiber and to various control fibers already applied in the clinic. Our results show that the low flux MMM successfully avoids contact of blood with the activated carbon and has good haemocompatibility, comparable to membranes currently used in the clinic. STATEMENT OF SIGNIFICANCE: Haemodialysis is a life-sustaining extracorporeal treatment for renal disease, however a broad range of uremic toxins cannot still be removed. In our previous works we showed that a double layer Mixed Matrix Membrane (MMM) composed of polyethersulfone/polyvinylpyrrolidone and activated carbon can achieve higher removal of uremic toxics compared to commercial haemodialysers. In this work we evaluate the haemocompatibility profile of the MMM in order to facilitate its clinical implementation. The lumen particle-free layer of the MMM successfully avoids the contact of blood with the poorly blood-compatible activated carbon. Moreover, thanks to the high amount of polyvinylpyrrolidone and to the smoothness of the lumen layer, the MMM has very good haemocompatibility, comparable to membranes currently used in the clinic.

Haemodiafiltration does not lower protein-bound uraemic toxin levels compared with haemodialysis in a paediatric population

Background

Haemodiafiltration (HDF) is accepted to effectively lower plasma levels of middle molecules in the long term, while data are conflicting with respect to the additive effect of convection on lowering protein-bound uraemic toxins (PBUTs). Here we compared pre-dialysis β2-microglobulin (β2M) and PBUT levels and the percentage of protein binding (%PB) in children on post-dilution HDF versus conventional high- (hf) or low-flux (lf) haemodialysis (HD) over 12 months of treatment.

Methods

In a prospective multicentre, non-randomized parallel-arm intervention study, pre-dialysis levels of six PBUTs and β2M were measured in children (5–20 years) on post-HDF (n = 37), hf-HD (n = 42) and lf-HD (n = 18) at baseline and after 12 months. Analysis of variance was used to compare levels and %PB in post-HDF versus conventional hf-HD and lf-HD cross-sectionally at 12 months and longitudinal from baseline to 12 months.

Results

For none of the PBUTs, no difference was found in either total and free plasma levels or %PB between post-HDF versus the hf-HD and lf-HD groups. Children treated with post-HDF had lower pre-dialysis β2M levels [median 23.2 (21.5; 26.6) mg/dL] after 12 months versus children on hf-HD [P&lt;0.01; 35.2 (29.3; 41.2) mg/dL] and children on lf-HD [P&lt;0.001; 47.2 (34.3; 53.0) mg/dL]. While β2M levels remained steady in the hf-HD and lf-HD group, a decrease in β2M was demonstrated for children on post-HDF (P&lt;0.01).

Conclusions

While post-HDF successfully decreased β2M, no additive effect on PBUT over 12 months of treatment was found. PBUT removal is complex and hampered by several factors. In children, these factors might be different from adults and should be explored in future research.

A swan song for Kt/Vurea

Dialyzer clearance of urea multiplied by dialysis time and normalized for urea distribution volume (Kt/V_urea or simply Kt/V) has been used as an index of dialysis adequacy since more than 30 years. This article reviews the flaws of Kt/V, starting with a lack of proof of concept in three randomized controlled hard outcome trials (RCTs), and continuing with a long list of conditions where the concept of Kt/V was shown to be flawed. This information leaves little room for any conclusion other than that Kt/V, as an indicator of dialysis adequacy, is obsolete. The dialysis patient might benefit more if, instead, the nephrology community concentrates in the future on pursuing the optimal dialysis dose that conforms with adequate quality of life and on factors that are likely to affect outcomes more than Kt/V. These include residual renal function, volume status, dialysis length, ultrafiltration rate, the number of intra-dialytic hypotensive episodes, interdialytic blood pressure, serum potassium and phosphate, serum albumin, and C reactive protein.

Prevention of hypophosphatemia during continuous renal replacement therapy-An overlooked problem

Hypophosphatemia is a common and potentially serious complication occurring during continuous renal replacement therapy (CRRT). Phosphate supplementation is required in the vast majority of patients undergoing CRRT, particularly beyond the first 48 hours. Supplementation can be provided either as a standalone oral or parenteral treatment or as an additive to CRRT solutions. Each approach has advantages and disadvantages, and clinicians must weigh the individual factors most relevant in their practice setting. Currently there are no consensus protocols for phosphate replacement in CRRT, and many centers replete phosphate in response to hypophosphatemia as opposed to pre-emptively. Repletion protocols have also been challenged in recent years by shortages in injectable phosphate solutions. More recently a commercially available phosphate-containing CRRT solution was approved in the United States, but there has been limited clinical experience with this product. In this review, we present recommendations for phosphate repletion in CRRT to prevent hypophosphatemia, and describe our experience using phosphate-containing CRRT solutions.

Carbon Adsorbents With Dual Porosity for Efficient Removal of Uremic Toxins and Cytokines from Human Plasma

The number of patients with chronic kidney disease increases while the number of available donor organs stays at approximately the same level. Unavoidable accumulation of the uremic toxins and cytokines for these patients comes as the result of malfunctioning kidneys and their high levels in the blood result in high morbidity and mortality. Unfortunately, the existing methods, like hemodialysis and hemofiltration, provide only partial removal of uremic toxins and/or cytokines from patients' blood. Consequently, there is an increasing need for the development of the extracorporeal treatments which will enable removal of broad spectrum of uremic toxins that are usually removed by healthy kidneys. Therefore, in this work we developed and tested ordered mesoporous carbons as new sorbents with dual porosity (micro/meso) that provide selective and efficient removal of a broad range of uremic toxins from human plasma. The new sorbents, CMK-3 are developed by nanocasting methods and have two distinct pore domains, i.e. micropores and mesopores, therefore show high adsorption capacity towards small water soluble toxins (creatinine), protein-bound molecules (indoxyl sulfate and hippuric acid), middle molecules (β-2-microglobulin) and cytokines of different size (IL-6 and IL-8). Our results show that small amounts of CMK-3 could provide selective and complete blood purification.

Binding of bromocresol green and bromocresol purple to albumin in hemodialysis patients

Background:

Colorimetric albumin assays based on binding to bromocresol purple (BCP) and bromocresol green (BCG) yield different results in chronic kidney disease. Altered dye binding of carbamylated albumin has been suggested as a cause. In the present study, a detailed analysis was carried out in which uremic toxins, acute phase proteins and Kt/V, a parameter describing hemodialysis efficiency, were compared with colorimetrically assayed (BCP and BCG) serum albumin.

Methods:

Albumin was assayed using immunonephelometry on a BN II nephelometer and colorimetrically based on, respectively, BCP and BCG on a Modular P analyzer. Uremic toxins were assessed using high-performance liquid chromatography. Acute phase proteins (C-reactive protein and α1-acid glycoprotein) and plasma protein α2-macroglobulin were assayed nephelometrically. In parallel, Kt/V was calculated.

Results:

Sixty-two serum specimens originating from hemodialysis patients were analyzed. Among the uremic toxins investigated, total para-cresyl sulfate (PCS) showed a significant positive correlation with the BCP/BCG ratio. The serum α1-acid glycoprotein concentration correlated negatively with the BCP/BCG ratio. The BCP/BCG ratio showed also a negative correlation with Kt/V.

Conclusions:

In renal insufficiency, the BCP/BCG ratio of serum albumin is affected by multiple factors: next to carbamylation, uremic toxins (total PCS) and α1-acid glycoprotein also play a role.

New low-flux mixed matrix membranes that offer superior removal of protein-bound toxins from human plasma

Hemodialysis is a widely available and well-established treatment for patients with End Stage Renal Disease (ESRD). However, although life-sustaining, patient mortality rates are very high. Several recent studies corroborated the link between dialysis patients' outcomes and elevated levels of protein-bound uremic toxins (PBUT) that are poorly removed by conventional hemodialysis. Therefore, new treatments are needed to improve their removal. Recently, our group showed that the combination of dialysis and adsorption on one membrane, the mixed matrix membrane (MMM), can effectively remove those toxins from human plasma. However, these first MMMs were rather large in diameter and their mass transport characteristics needed improvement before application in the clinical setting. Therefore, in this study we developed a new generation of MMMs that have a smaller diameter and optimized characteristics offering superior ability in removing the PBUT indoxyl sulfate (IS) and p-cresyl sulfate (pCS) in comparison to first generation MMMs (30 and 125% respectively), as well as, a commercial dialysis membrane (more than 100% better removal).

Revisiting the Middle Molecule Hypothesis of Uremic Toxicity: A Systematic Review of Beta 2 Microglobulin Population Kinetics and Large Scale Modeling of Hemodialysis Trials In Silico

Background

Beta-2 Microglobulin (β2M) is a prototypical “middle molecule” uremic toxin that has been associated with a higher risk of death in hemodialysis patients. A quantitative description of the relative importance of factors determining β2M concentrations among patients with impaired kidney function is currently lacking.

Methods

Herein we undertook a systematic review of existing studies reporting patient level data concerning generation, elimination and distribution of β₂M in order to develop a population model of β₂M kinetics. We used this model and previously determined relationships between predialysis β₂M concentration and survival, to simulate the population distribution of predialysis β₂M and the associated relative risk (RR) of death in patients receiving conventional thrice-weekly hemodialysis with low flux (LF) and high flux (HF) dialyzers, short (SD) and long daily (LD) HF hemodialysis sessions and on-line hemodiafiltration at different levels of residual renal function (RRF).

Results

We identified 9 studies of 106 individuals and 156 evaluations of or more compartmental kinetic parameters of β₂M. These studies used a variety of experimental methods to determine β₂M kinetics ranging from isotopic dilution to profiling of intra/inter dialytic concentration changes. Most of the patients (74/106) were on dialysis with minimal RRF, thus facilitating the estimation of non-renal elimination kinetics of β₂M. In large scale (N = 10000) simulations of individuals drawn from the population of β₂M kinetic parameters, we found that, higher dialytic removal materially affects β₂M exposures only when RRF (renal clearance of β₂M) was below 2 ml/min. In patients initiating conventional HF hemodialysis, total loss of RRF was predicted to be associated with a RR of death of more than 20%. Hemodiafiltration and daily dialysis may decrease the high risk of death of anuric patients by 10% relative to conventional, thrice weekly HF dialysis. Only daily long sessions of hemodialysis consistently reduced mortality risk between 7–19% across the range of β₂M generation rate.

Conclusions

Preservation of RRF should be considered one of the therapeutic goals of hemodialysis practice. Randomized controlled trials of novel dialysis modalities may require large sample sizes to detect an effect on clinical outcomes even if they enroll anuric patients. The developed population model for β₂M may allow personalization of hemodialysis prescription and/or facilitate the design of such studies by identifying patients with higher β₂M generation rate.

Modifications to bicarbonate conductivity: A way to increase phosphate removal during hemodialysis? Proof of concept

Introduction Hyperphosphatemia and cardiovascular mortality are associated particularly with end-stage renal disease. Available therapeutic strategies (i.e., diet restriction, calcium [or not]-based phosphate binders, calcimimetics) are associated with extrarenal blood purification. Compartmentalization of phosphate limits its depuration during hemodialysis. Several studies suggest that plasmatic pH is involved in the mobilization of phosphate from intracellular to extracellular compartments. Consequently, the efficiency of modified bicarbonate conductivity to purify blood phosphate was tested. Methods Ten hemodialysis patients with chronic hyperphosphatemia (>2.1 mmol/L) were included in the two three-sessions-per week periods. Bicarbonate concentration was fixed at 40 mmol/L and 30 mmol/L in the first and second periods, respectively. Phosphate depuration was evaluated by phosphate mobilization clearance (K_M ). Findings Although bicarbonatemia was lower during the second period (21.0 ± 2.7 vs. 24.4 ± 3.1 mmol/L, P < 0.01), no difference was observed in phosphatemia (2.4 ± 0.5 vs. 2.3 ± 0.4 mmol/L, P = NS). The in-session variation of phosphate was lower (-1.45 ± 0.42 vs. -1.58 ± 0.44 mmol/L, P < 0.05) and K_M was higher during the second period (82.94 ± 38.00 vs. 69.74 ± 24.48 mL/min, P < 0.05). Discussion The decrease of in-session phosphate and the increase in K_M reflect phosphate refilling during hemodialysis. Thus, modulation of serum bicarbonate may play a role in controlling the phosphate pool. Even though correcting metabolic acidosis during hemodialysis remains important, alkaline excess can impair phosphate mobilization clearance. Clinical trials are needed to test the efficiency and relevance of a strategy where bicarbonatemia is corrected less at the beginning of sessions.

Novel iron-containing phosphate binders for treatment of hyperphosphatemia

INTRODUCTION

Hyperphosphatemia is a frequent complication of chronic kidney disease and is associated with increased mortality. Despite side effects, risk of accumulation and high costs, phosphate binders (PBs) have become the crucial cornerstone of therapy. The iron-containing PB sucroferric oxyhydroxide (SO) and ferric citrate hydrate (FCH) have entered the market and other candidates are prior market entry.

AREAS COVERED

A literature search was performed using MEDLINE and EMBASE databases to identify references on iron-containing PB with particular regard to efficacy, safety and potential benefits. Additional hand searches were conducted along with a full-text review of any citation that appeared relevant.

EXPERT OPINION

On the highly competitive market, where the 'ideal' PB is still unknown, novel substances that offer clear benefits over available drugs are desired. Although SO and FCH showed similar efficacy and safety compared to sevelamer, head-to-head studies with lanthanum carbonate are absent. Clinical 1-year data in a limited patient cohort suggested improved adherence for SO and a large randomized controlled trial showed significant reduction in hospitalizations and costs for FCH. Additional large randomized controlled trials have now to prove these possible advantages. Cost-effectiveness in comparison to other PB and the exclusion of significant harms under long-term treatment will determine the future use of both drugs.

Dialyzer Reuse and Outcomes of High Flux Dialysis

Background

The bulk of randomized trial evidence for the expanding use of High Flux (HF) hemodialysis worldwide comes from two randomized controlled trials, one of which (HEMODIALYSIS, HEMO) allowed, while the other (Membrane Outcomes Permeability, MPO) excluded, the reuse of membranes. It is not known whether dialyzer reuse has a differential impact on outcomes with HF vs low flyx (LF) dialyzers.

Methods

Proportional Hazards Models and Joint Models for longitudinal measures and survival outcomes were used in HEMO to analyze the relationship between β2-microglobulin (β2M) concentration, flux, and reuse. Meta-analysis and regression techniques were used to synthesize the evidence for HF dialysis from HEMO and MPO.

Findings

In HEMO, minimally reused (< 6 times) HF dialyzers were associated with a hazard ratio (HR) of 0.67 (95% confidence interval, 95%CI: 0.48–0.92, p = 0.015), 0.64 (95%CI: 0.44 – 0.95, p = 0.03), 0.61 (95%CI: 0.41 – 0.90, p = 0.012), 0.53 (95%CI: 0.28 – 1.02, p = 0.057) relative to minimally reused LF ones for all cause, cardiovascular, cardiac and infectious mortality respectively. These relationships reversed for extensively reused membranes (p for interaction between reuse and flux < 0.001, p = 0.005) for death from all cause and cardiovascular causes, while similar trends were noted for cardiac and infectious mortality (p of interaction between reuse and flux of 0.10 and 0.08 respectively). Reduction of β2M explained only 1/3 of the effect of minimally reused HF dialyzers on all cause mortality, while non-β2M related factors explained the apparent attenuation of the benefit with more extensively reused dialyzers. Meta-regression of HEMO and MPO estimated an adjusted HR of 0.63 (95% CI: 0.51–0.78) for non-reused HF dialyzers compared with non-reused LF membranes.

Conclusions

This secondary analysis and synthesis of two large hemodialysis trials supports the widespread use of HF dialyzers in clinical hemodialysis over the last decade. A mechanistic understanding of the effects of HF dialysis and the reuse process on dialyzers may suggest novel biomarkers for uremic toxicity and may accelerate membrane technology innovations that will improve patient outcomes.

Free Levels of Selected Organic Solutes and Cardiovascular Morbidity and Mortality in Hemodialysis Patients: Results from the Retained Organic Solutes and Clinical Outcomes (ROSCO) Investigators

Background and Objectives

Numerous substances accumulate in the body in uremia but those contributing to cardiovascular morbidity and mortality in dialysis patients are still undefined. We examined the association of baseline free levels of four organic solutes that are secreted in the native kidney — p-cresol sulfate, indoxyl sulfate, hippurate and phenylacetylglutamine — with outcomes in hemodialysis patients.

Design, Setting, Participants and Measurements

We measured these solutes in stored specimens from 394 participants of a US national prospective cohort study of incident dialysis patients. We examined the relation of each solute and a combined solute index to cardiovascular mortality and morbidity (first cardiovascular event) using Cox proportional hazards regression adjusted for demographics, comorbidities, clinical factors and laboratory tests including Kt/V_UREA.

Results

Mean age of the patients was 57 years, 65% were white and 55% were male. In fully adjusted models, a higher p-cresol sulfate level was associated with a greater risk (HR per SD increase; 95% CI) of cardiovascular mortality (1.62; 1.17–2.25; p=0.004) and first cardiovascular event (1.60; 1.23–2.08; p<0.001). A higher phenylacetylglutamine level was associated with a greater risk of first cardiovascular event (1.37; 1.18–1.58; p<0.001). Patients in the highest quintile of the combined solute index had a 96% greater risk of cardiovascular mortality (1.96; 1.05–3.68; p=0.04) and 62% greater risk of first cardiovascular event (1.62; 1.12–2.35; p=0.01) compared with patients in the lowest quintile. Results were robust in sensitivity analyses.

Conclusions

Free levels of uremic solutes that are secreted by the native kidney are associated with a higher risk of cardiovascular morbidity and mortality in incident hemodialysis patients.

Improving outcomes by changing hemodialysis practice patterns

PURPOSE OF REVIEW

This review examines recent advances in understanding of how clinical outcomes for hemodialysis patients may be improved by achieving longer or more frequent treatment times, lower ultrafiltration rates (UFRs), improving nutritional status, and individualizing dialysate composition. This review also discusses the controversy related to timing of dialysis initiation.

RECENT FINDINGS

Many observational studies and several randomized controlled trials indicate longer dialysis treatment times, particularly nocturnal dialysis, and/or more frequent dialysis improve morbidity and mortality. Recent evidence also suggests that lower UFR and more consistent achievement of 'dry weight' may help minimize the damage from myocardial stunning and chronic volume overload that occurs in the majority of patients who receive conventional hemodialysis during the day with a standard schedule of 3-5 h, 3 times a week. Other aspects of the dialysis procedure such as appropriate estimated glomerular filtration rate for dialysis initiation and individualizing dialysate composition may also minimize cardiovascular risk. Finally, several studies have highlighted the benefits of oral nutritional supplementation (ONS) during dialysis.

SUMMARY

Greater treatment times per week with slower UFR, consistent attainment of 'dry weight', individualized dialysate prescriptions, and administration of ONS to malnourished patients are likely to reduce hospitalizations and improve survival in this high-risk population of end-stage renal disease patients.

Comparison of cystatin C and Beta-2-microglobulin kinetics in children on maintenance hemodialysis

Middle-molecules (MM) are not monitored in children on hemodialysis (HD), but are accumulated and increase the risk of cardiovascular disease and mortality. Molecular properties of Cystatin C (CyC), 13 kDa, potentially make it a preferred MM marker over Beta-2-Microglobulin (B2M), 12 kDa. We compared CyC and B2M kinetics to investigate if CyC can be used as preferred MM marker. CyC (mg/L) and B2M (μg/mL) were measured in 21 low-flux HD sessions in seven children. Blood samples were taken at HD start (pre), 1 and 2 hours into HD and at end of HD (post) for all sessions and 60 minutes after the first HD (Eq). PreCyC (9.85 ± 2.15) did not differ (P > 0.05) from postCyC (10.04 ± 2.83). PostB2M (38.87 ± 7.12) was higher (P < 0.05) than preHD B2M (33.27 ± 7.41). There was no change in CyC at 1 and 2 hours into HD, while B2M progressively increased. CyC or B2M changes did not significantly correlate with spKt/V (2.09 ± 0.86), ultrafiltration (4.61 ± 1.98%) or HD duration (218 ± 20 minutes). EqCyC was not different from postCyC (11.07 ± 3.14 vs. 10.71 ± 2.85, P > 0.05), while EqB2M was lower than postB2M (36.48 ± 7.68 vs. 41.09 ± 8.99, P < 0.05). MMs as represented by B2M and CyC are elevated in children on standard HD. Intensified HD modalities would be needed for their removal. B2M is affected by the dialytic process with a rise during HD independent of ultrafiltration and decrease 1 hour after, while CyC remains unchanged. We suggest that CyC be used as preferred marker of MM removal and as a marker of adequacy of intensified HD regimens.