Evaluation of the Impact of a New Synthetic Vitamin E-Bonded Membrane on the Hypo-Responsiveness to the Erythropoietin Therapy in Hemodialysis Patients: A Multicenter Study

A chronic intermittent haemodialysis pig model for functional evaluation of dialysis membranes

Performance evaluation of new dialysis membranes is primarily performed in vitro, which can lead to differences in clinical results. Currently, data on dialysis membrane performance and safety are available only for haemodialysis patients. Herein, we aimed to establish an in vivo animal model of dialysis that could be extrapolated to humans. We created a bilateral nephrectomy pig model of renal failure, which placed a double-lumen catheter with the hub exposed dorsally. Haemodialysis was performed in the same manner as in humans, during which clinically relevant physiologic data were evaluated. Next, to evaluate the utility of this model, the biocompatibility of two kinds of membranes coated with or without vitamin E used in haemodiafiltration therapy were compared. Haemodialysis treatment was successfully performed in nephrectomized pigs under the same dialysis conditions (4 h per session, every other day, for 2 weeks). In accordance with human clinical data, regular dialysis alleviated renal failure in pigs. The vitamin E-coated membrane showed a significant reduction rate of advanced oxidation protein products during dialysis than non-coated membrane. In conclusion, this model mimics the pathophysiology and dialysis condition of patients undergoing haemodialysis. This dialysis treatment model of renal failure will be useful for evaluating the performance and safety of dialysis membranes.

Alleviation of Oxidative Stress during Hemodialysis Sessions by Hemodialysis Membrane Innovation: A Multidisciplinary Perspective

Oxidative stress is prevalent in end-stage kidney disease patients receiving chronic hemodialysis and is associated with heavy cardiovascular disease burdens and increased mortality risks. Hemoincompatible hemodialysis membranes per se contribute to the activation of oxidative reactions and the generation of oxygen free radicals. Since the early 1990s, vitamin E-coated membranes have been extensively used in hemodialysis patients to reduce oxidative stress during hemodialysis sessions. However, the beneficial effects of vitamin E-coated membranes versus unmodified synthetic membranes on long-term patient-centered outcomes, such as survival, quality of life, and prevalence of cardiovascular diseases, remain controversial. Accordingly, novel antioxidant hemodialysis membranes were prepared to replace the use of vitamin E-coated membranes despite the translational research on these membranes unfortunately coming to a standstill. In this review, we first summarize the state-of-the-art on the use of vitamin E-coated membranes in hemodialysis patients to highlight their strengths and limitations. Then, we discuss the latest advances in fabricating antioxidant hemodialysis membranes and provide perspectives to bridge knowledge gaps between laboratorial investigations and clinical practice in fabricating antioxidant hemodialysis membranes.

Vitamin E (Alpha-Tocopherol) Metabolism and Nutrition in Chronic Kidney Disease

Vitamin E (alpha-tocopherol) is an essential micronutrient and fat-soluble antioxidant with proposed role in protecting tissues from uncontrolled lipid peroxidation. This vitamin has also important protein function and gene modulation effects. The metabolism of vitamin E depends on hepatic binding proteins that selectively retain food alpha-tocopherol for incorporation into nascent VLDL and tissue distribution together with esterified cholesterol and triglycerides. Chronic kidney disease (CKD) is a condition of oxidative stress and increased lipid peroxidation, that are associated with alterations of alpha-tocopherol metabolism and function. Specific changes have been reported for the levels of its enzymatic metabolites, including both short-chain and long-chain metabolites, the latter being endowed with regulatory functions on enzymatic and gene expression processes important for the metabolism of lipids and xenobiotics detoxification, as well as for the control of immune and inflammatory processes. Vitamin E therapy has been investigated in CKD using both oral vitamin E protocols and vitamin E-coated hemodialyzers, showing promising results in the secondary prevention of cardiovascular disease, as well as of immune and hematological complications. These therapeutic approaches are reviewed in the present article, together with a narrative excursus on the main findings indicating CKD as a condition of relative deficiency and impaired metabolism of vitamin E.

Biocompatibility of Surface-Modified Membranes for Chronic Hemodialysis Therapy

Hemodialysis is a life-sustaining therapy for millions of people worldwide. However, despite considerable technical and scientific improvements, results are still not fully satisfactory in terms of morbidity and mortality. The membrane contained in the hemodialyzer is undoubtedly the main determinant of the success and quality of hemodialysis therapy. Membrane properties influence solute removal and the interactions with blood components that define the membrane’s biocompatibility. Bioincompatibility is considered a potential contributor to several uremic complications. Thus, the development of more biocompatible polymers used as hemodialyzer membrane is of utmost importance for improving results and clinical patient outcomes. Many different surface-modified membranes for hemodialysis have been manufactured over recent years by varying approaches in the attempt to minimize blood incompatibility. Their main characteristics and clinical results in hemodialysis patients were reviewed in the present article.

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.

Vitamin E-Bonded Membranes Do Not Influence Markers of Oxidative Stress in Hemodialysis Patients with Homozygous Glutathione Transferase M1 Gene Deletion

BACKGROUND

Increased oxidative stress is a hallmark of end-stage renal disease. Hemodialysis (HD) patients lacking glutathione transferase M1 (GSTM1) enzyme activity exhibit enhanced oxidative DNA damage and higher mortality rate than those with active GSTM1 enzyme. To our knowledge, this is the first study to use the vitamin E-bonded membranes (VEM) in patients with homozygous GSTM1 gene deletion, and we aimed to determine the effect of VEM on oxidative and inflammatory status in HD patients with homozygous GSTM1 gene deletion.

METHODS

GSTM1 genotypes were determined by polymerase chain reaction (PCR) in 170 chronic HD patients. Those with GSTM1-null genotype were randomized and 80 were included in the study. Forty of them were dialyzed for three months with VEM, while the other forty were dialyzed with high-flux same-surface polysulfone dialyzers. Markers of protein and lipid oxidative damage and inflammation (thiol groups, malondialdehyde (MDA), Interleukin-6 (IL-6)), together with plasma antioxidant activity (glutathione peroxidase (GPX), superoxide dismutase (SOD)) were determined.

RESULTS

Seventy-five patients finished the study. There were no differences at baseline in markers of protein and lipid oxidative damage, inflammation and plasma antioxidant activity. After three months of therapy, GPX, MDA, and thiol groups increased significantly in both groups, but without statistical significance between groups. SOD and C reactive protein (CRP) did not change significantly during the three-month period. IL-6 increased in the control group, and at the same time, decreased in the VEM group, but without statistical significance. Hemoglobin (Hb) value, red blood cells, erythropoiesis resistance index (ERI), serum ferritin and iron did not change significantly within or between groups. Regarding other laboratory parameters, proteins, albumins, triglycerides, serum phosphorus, serum bicarbonate and Kt/V showed significant improvements within groups but with no significant difference between groups.

CONCLUSIONS

Our data shows that therapy with VEM over three months had no benefit over standard polysulfone membrane in decreasing by-products of oxidative stress and inflammation in dialysis patients lacking GSTM1 enzyme activity.

Darbepoetin Alfa in Patients with Advanced CKD without Diabetes: Randomized, Controlled Trial

BACKGROUND AND OBJECTIVES

Large, randomized, controlled trials targeting higher hemoglobin level with erythropoiesis-stimulating agents for Western patients with CKD showed harm. However, the effect of anemia correction using erythropoiesis-stimulating agents may differ between CKD subpopulations. The Prevention of ESKD by Darbepoetin Alfa in CKD Patients with Non-diabetic Kidney Disease study, a multicenter, randomized, open-label, parallel-group study, aimed to examine the effect of targeting hemoglobin levels of 11-13 g/dl using darbepoetin alfa with reference to a low-hemoglobin target of 9-11 g/dl on kidney outcome in patients with advanced CKD without diabetes in Japan.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We enrolled 491 patients with CKD without diabetes, and an eGFR of 8-20 ml/min per 1.73 m². Of these 491 patients, 239 and 240 were ultimately assigned to the high- and low-hemoglobin groups, respectively (12 patients were excluded). The primary outcome was a kidney composite end point (starting maintenance dialysis, kidney transplantation, eGFR≤6 ml/min per 1.73 m², and 50% reduction in eGFR).

RESULTS

Mean hemoglobin levels were 11.2±1.1 and 10.0±0.9 g/dl in the high- and low-hemoglobin groups, respectively, during the mean study period of 73.5±29.7 weeks. The kidney composite end point occurred in 105 (44%) and 116 (48%) patients in the high- and low-hemoglobin groups, respectively (log-rank test; P=0.32). The adjusted Cox proportional hazards model showed that the hazard ratio for the high- versus low-hemoglobin group was 0.78 (95% confidence interval, 0.60 to 1.03; P=0.08). Cardiovascular events occurred in 19 (8%) and 16 (7%) patients in each group, respectively, with no significant between-group difference (log-rank test; P=0.66).

CONCLUSIONS

Targeting a higher hemoglobin level (11-13 g/dl) with darbepoetin alfa did not improve kidney outcome compared with targeting a lower hemoglobin level (9-11 g/dl) in patients with advanced CKD without diabetes.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Prevention of ESKD by Darbepoetin Alfa in CKD Patients with Non-diabetic Kidney Disease (PREDICT), NCT01581073.

Oxidative Stress in Hemodialysis Patients: Pathophysiological Mechanisms, Clinical Consequences and Basic Principles of Treatment

Cardiovascular diseases are the leading cause of death in patients who undergo regular hemodialysis. Oxidative stress is a non-traditional risk factor for the development of cardiovascular diseases in this population of patients. It is defined as tissue damage caused by balance disturbance between the formation of free radicals and the function of protective antioxidative systems. The superoxide anion and hydrogen peroxide are precursors in the formation of stronger oxidants, such as: hydroxyl radical, peroxynitrite and hypochloric acid. Superoxide dismutase is the first line of antioxidant protection while catalase, glutathione peroxidase, trace elements, vitamin C, vitamin E, N-acetylcysteine and coenzyme Q10 also have a significant antioxidative role. Hemo-dialysis is itself a trigger for the increased formation of oxygen free radicals. The two main pathophysiological mechanisms of the increased formation of free oxygen radicals during the hemo-dialysis session are: bionicompatibility of the dialysis membrane and the presence of endotoxins in the hemodialysis solution. The measurement of myeloperoxidase concentration in a patient’s serum during hemodialysis is an indicator of the severity of oxidative stress induced by the dialysis membrane (an indicator of the biocompatibility of the dialysis membrane). The main clinical consequences of oxidative stress include: atherosclerosis, erythropoietin resistance, malnutrition and amyloidosis associated with hemodialysis. The evaluation of oxidative stress in patients undergoing hemodialysis is performed by measuring the concentration of lipid peroxidation products (malonyldialdehyde, 4-hydroxynonenal, TBARS, F2-isoprostane, oxLDL), protein oxidation (AOPP), protein gelling (AGE), and oxidation of nucleic acids (8-OHdG). The antioxidant treatment strategy consists of replenishing vitamin C, vitamin E, selenium, N-acetylcysteine and coenzyme Q10. On-line hemodialysis, a biocompatible vitamin E-coated dialysis membrane, an ultra-pure solution for hemodialysis, prevent oxidative stress, reduce the rate of cardiovascular morbidity and mortality and improve life quality of patients treated with regular hemodialysis.

Clinical evaluation of performance, biocompatibility, and safety of vitamin E-bonded polysulfone membrane hemodialyzer compared to non-vitamin E-bonded hemodialyzer

The vitamin E-bonded polysulfone membrane hemodialyzer (ViE™-21) was evaluated in a clinical study for regulatory submission. Seventeen patients on hemodialysis were treated with conventional high-flux hemodialyzers for 2 weeks (Pre-ViE phase) and switched to the ViE-21 for 36 sessions (ViE phase) followed by an additional 2 weeks on conventional hemodialyzers (Post-ViE phase). Reduction ratios of urea, creatinine, beta-2-microglobulin, albumin, and ultrafiltration coefficients (KUF) were measured once during the Pre-ViE phase and twice during the ViE phase. Moreover, biocompatibility markers [leucocyte count, platelet count, and activated complement factor (C3a) levels] were evaluated pre-dialysis, 15 min after initiation, and post-dialysis. During the study, type and number of adverse events (AEs), and device malfunctions were recorded. ViE-21 reduction ratios and KUF were not noticeably different than those of conventional hemodialyzers. Fluctuations of leucocyte counts and C3a concentrations were similar using ViE-21 and conventional hemodialyzers; however, the platelet count fluctuation was lower in ViE-21 sessions. The frequency of episodes of hypotension occurring during the ViE phase was lower than that occurring during the Pre- and Post-ViE phases. In conclusion, this study provided performance and safety data of the ViE-21 for regulatory application. The data suggest that vitamin E-bonded hemodialyzers are beneficial in lowering platelet activation and frequency of intradialytic hypotension. Larger randomized controlled trials are needed to confirm these findings.

Antioxidant Supplementation in Renal Replacement Therapy Patients: Is There Evidence?

The disruption of balance between production of reactive oxygen species and antioxidant systems in favor of the oxidants is termed oxidative stress (OS). To counteract the damaging effects of prooxidant free radicals, all aerobic organisms have antioxidant defense mechanisms that are aimed at neutralizing the circulating oxidants and repair the resulting injuries. Antioxidants are either endogenous (the natural defense mechanisms produced by the human body) or exogenous, found in supplements and foods. OS is present at the early stages of chronic kidney disease, augments progressively with renal function deterioration, and is further exacerbated by renal replacement therapy. End-stage renal disease patients, on hemodialysis (HD) or peritoneal dialysis (PD), suffer from accelerated OS, which has been associated with increased risk for mortality and cardiovascular disease. During HD sessions, the bioincompatibility of dialyzers and dialysate trigger activation of white blood cells and formation of free radicals, while a significant loss of antioxidants is also present. In PD, the bioincompatibility of solutions, including high osmolality, elevated lactate levels, low pH, and accumulation of advanced glycation end-products trigger formation of prooxidants, while there is significant loss of vitamins in the ultrafiltrate. A number of exogenous antioxidants have been suggested to ameliorate OS in dialysis patients. Vitamins B, C, D, and E, coenzyme Q10, L-carnitine, a-lipoic acid, curcumin, green tea, flavonoids, polyphenols, omega-3 polyunsaturated fatty acids, statins, trace elements, and N-acetylcysteine have been studied as exogenous antioxidant supplements in both PD and HD patients.

A Retrospective Study on Erythropoiesis Stimulating Agent Dose Reducing Potential of an Anti-Platelet Activation Membrane Dialyzer in Hemodialysis Patients

Our previous small‐scale trial demonstrated an erythropoiesis stimulating agent (ESA)‐sparing potential of the TORAYLIGHT NV (NV) dialyzer in hemodialysis patients with high interleukin‐6 levels. We now retrospectively explored this ESA‐sparing potential of the NV dialyzer in 122 and 129 prevalent dialysis patients who were on the NV and conventional polysulfone (PS) dialyzers, respectively, for 12 months. ESA resistance index (ERI) increased with the PS dialyzers whereas neither ERI nor ESA dose changed with the NV dialyzer. Analyses of baseline ERI or ESA dose‐based subgroups revealed a decrease in ERI and ESA dose with the NV dialyzer in patients with a baseline ERI ≥12 IU·dL/week·kg·g Hb (P < 0.05) and in those with a baseline ESA dose >6000 IU/week (P < 0.001), respectively. Neither ERI nor ESA dose improved in the corresponding subgroups on the PS dialyzers. These findings suggest that NV dialyzer can improve ESA responsiveness in hemodialysis patients with advanced ESA resistance.

Choosing a dialyzer: What clinicians need to know

The objectives of hemodialysis have moved from the diffusive clearance of small molecular weight uremic toxins and achieving dialyzer urea adequacy targets to emphasis on improving clinical outcomes in end stage renal failure patients by increasing larger sized uremic toxin clearance. Clinical emphasis in the last few decades has focused on increasing middle molecule weight toxin clearance by hemodiafiltration. Although long-term data is still lacking, short-term outcomes appear promising. Advancements in nanotechnology have now introduction a new generation of medium cut-off membrane dialyzers which allow diffusive clearance of similar middle molecular weight uremia toxin clearance as hemodiafiltration, without increased albumin losses. As these dialyzers have only recently been introduced into clinical practice, no long-term outcomes are available to determine the relative benefits or advantages of this approach. As dialyzers are now designed to maximize diffusive or convective clearance, or provide a combination, then clinicians can now choose dialyzers tailored to the individual patient needs depending on clinical circumstances. We review the key important features in choosing a dialyzer for patients with end stage renal failure and acute kidney injury.