Long-term use of vitamin E-coated polysulfone membrane reduces oxidative stress markers in haemodialysis patients

Continuous renal replacement therapy with vitamin E-coated polysulfone hemofilter reduces inflammatory responses in a porcine lipopolysaccharide-treated model

INTRODUCTION

Biological invasions may promote the onset of systemic inflammatory response syndrome in patients eligible for continuous renal replacement therapy (CRRT), leading to poor prognosis. Hence, we aimed to examine the inflammatory reactions in circulation using vitamin E-coated polysulfone hollow fiber membrane (ViLIFE).

METHODS

Lipopolysaccharides were intravenously administered to pigs (2 μg/kg/30 min) to establish an acute inflammation model. Extracorporeal circulation was performed for 6 h in continuous venovenous hemodiafiltration mode using a hemofilter for CRRT filled with a polysulfone hollow fiber membrane or ViLIFE, and the differences in inflammatory reactions were evaluated.

RESULTS

The ViLIFE group exhibited low platelet and cytokine levels (p < 0.05 vs. sham-CRRT group). Additionally, the ViLIFE group had lower lactate and high mobility group box 1 levels than the other groups.

CONCLUSION

ViLIFE represents a promising CRRT modality that can inhibit the inflammatory response in circulation and inhibit further biological invasions.

Design of the Functional Dialysis Membrane with a Catalase Pseudoactive Center on the Surface

Here, we have designed a functional dialysis membrane with a catalase pseudoactive center on the surface. To make the catalase pseudoactive center, we have modified the regenerated cellulose dialysis membrane with methylated or octylated poly(1-vinylimidazole) (PVIm-Me or PVIm-Oc), followed by manganese or iron tetrakis(4-carboxyphenyl)porphyrin (Mn- or Fe-TCPP), using the layer-by-layer (LbL) method. As a result of the optimization, the dialysis membrane modified with 25 mol % methylated poly(1-vinylimidazole) [PVIm-Me(25)] and Mn-TCPP produced the highest amount of oxygen (O2) from hydrogen peroxide (H2O2) without the decomposition of Mn-TCPP. Conversely, Mn- and Fe-TCPP were decomposed under other experimental conditions in the presence of H2O2. These results suggest the conversion of H2O2 to O2 by catalase catalytic activity on the surface coated with PVIm-Me(25) and Mn-TCPP.

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.

Standardization of Nomenclature for the Mechanisms and Materials Utilized for Extracorporeal Blood Purification

In order to develop a standardized nomenclature for the mechanisms and materials utilized during extracorporeal blood purification, a consensus expert conference was convened in November 2022. Standardized nomenclature serves as a common language for reporting research findings, new device development, and education. It is also critically important to support patient safety, allow comparisons between techniques, materials, and devices, and be essential for defining and naming innovative technologies and classifying devices for regulatory approval. The multidisciplinary conference developed detailed descriptions of the performance characteristics of devices (membranes, filters, and sorbents), solute and fluid transport mechanisms, flow parameters, and methods of treatment evaluation. In addition, nomenclature for adsorptive blood purification techniques was proposed. This report summarizes these activities and highlights the need for standardization of nomenclature in the future to harmonize research, education, and innovation in extracorporeal blood purification therapies.

Engineering Antioxidative Cascade Metal-Phenolic Nanozymes for Alleviating Oxidative Stress during Extracorporeal Blood Purification

Oxidative stress is a compelling risk factor in chronic kidney diseases and is further aggravated for individuals during extracorporeal blood purification, ultimately leading to multiple complications. Herein, antioxidative cascade metal-phenolic nanozymes (metal-tannic acid nanozymes, M-TA NMs) are synthesized via metal ions-mediated oxidative coupling of polyphenols; then M-TA NMs engineered hemoperfusion microspheres (Cu-TAn@PMS) are constructed for alleviating oxidative stress. M-TA NMs show adjustable broad-spectrum antioxidative activities toward multiple reactive nitrogen and oxygen species (RNOS) due to the adjustable catalytic active centers. Importantly, M-TA NMs could mimic the cascade processes of superoxide dismutase and catalase to maintain intracellular redox balance. Detailed structural and spectral analyses reveal that the existence of a transition metal could decrease the electronic energy band gaps of M-TA NMs to offer better electron transfers for RNOS scavenging. Notably, dynamic blood experiments demonstrate that Cu-TAn@PMS could serve as an antioxidant defense system for blood in hemoperfusion to scavenge intracellular reactive oxygen species (ROS) effectively even in the complex blood environment and further protect endogenous antioxidative enzymes and molecules. In general, this work developed antioxidative cascade nanozymes engineered microspheres with excellent therapeutic efficacy for the treatment of oxidative stress-related diseases, which exhibited potential for clinical blood purification and extended the biomedical applications of nanozymes.

In vitro blood compatibility evaluation method: incubating while rotating hemodialyzers filled with fresh human blood

One of the often-used methods for in vitro evaluation of the blood compatibility of hemodialysis membranes is the circulation of human blood through a miniaturized hemodialyzer. The use of a rather small amount of human blood in its evaluation is one advantage of this method. However, because it is manufactured by a different process than actual ones, a miniaturized hemodialyzer membrane cannot always preserve the properties of actual hemodialyzers. To address this problem, we established a new experimental method that uses a relatively small amount of human blood and actual dialyzers. In this method, a test hemodialyzer and a control hemodialyzer filled with human blood obtained from the same donor is slowly rotated to prevent spontaneous blood cell sedimentation for 4 h at 37 °C. By use of this method, we were able to compare blood compatibility between a polysulfone (PS) membrane and a vitamin E (VE)-bonded PS membrane in terms of their relative antithrombotic, antioxidative, and anti-inflammatory properties. Consistent with many previous reports, the results clearly showed that compared with the PS membrane, VE-bonded PS membrane is more blood compatible. These findings suggest that our method is applicable, at least to in vitro blood compatibility evaluation of PS type dialysis membranes.

Application and Efficacy of Vitamin E-Bonded Polysulfone Membrane in Acute Blood Purification Therapy

INTRODUCTION

Acute blood purification therapy (BPT) has been evaluated in the context of intensive care for serious conditions related to systemic inflammation, but its mechanism and efficacy are not fully understood.

OBJECTIVE

This study examined the feasibility of using vitamin E-bonded polysulfone membranes (VEPS) for BPT in a LPS-induced rat model of systemic inflammation.

METHODS

To evaluate the efficacy of BPT with a VEPS membrane, polysulfone (PS) membranes conventionally used in intensive care were bonded with the antioxidant vitamin E and used in a rat model of lipopolysaccharide (LPS)-induced systemic inflammation. BPT using a PS membrane (PS group) or a VEPS membrane (VEPS group) was performed 6 h after administration of LPS. Extracorporeal circulation was established in normal rats as a control (sham group). Survival rates, histology of lung specimens, and levels of myeloperoxidase (MPO) and high mobility group box-1 (HMGB-1) were examined in each group.

RESULTS

Survival rates at 24 h after LPS administration were 100% in the VEPS group and 50% in the PS group. Pulmonary architecture was largely maintained and the level of infiltration of inflammatory cells remained moderate in the VEPS group. Levels of active MPO before and after BPT were significantly higher in the PS and VEPS groups than in the sham group, with no significant differences between the PS and VEPS groups. HMGB-1 levels were significantly elevated after BPT in the PS group.

CONCLUSIONS

This study demonstrated that use of the VEPS membrane for BPT increased survival rate and reduced lung injury in a rat model of systemic inflammatory response syndrome (SIRS), suggesting the possible use of VEPS membranes in the treatment of serious conditions related to systemic inflammation.

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.

Oxidative stress in hemodialysis: Causative mechanisms, clinical implications, and possible therapeutic interventions

Oxidative stress (OS) is the result of prooxidant molecules overwhelming the antioxidant defense mechanisms. Hemodialysis (HD) constitutes a state of elevated inflammation and OS, due to loss of antioxidants during dialysis and activation of white blood cells triggering production of reactive oxygen species. Dialysis vintage, dialysis methods, and type and condition of vascular access, biocompatibility of dialyzer membrane and dialysate, iron administration, and anemia all can play a role in aggravating OS, which in turn has been associated with increased morbidity and mortality. Oral or intravenous administration of antioxidants may detoxify the oxidative molecules and at least in part repair OS-mediated tissue damage. Lifestyle interventions and optimization of a highly biocompatible HD procedure might ameliorate OS development in dialysis.

Effect of Vitamin E-Coated Dialysis Membranes on Anemia in Patients with Chronic Kidney Disease: An Italian Multicenter Study

Background

Increased oxidant stress is increasingly recognized as a crucial factor in anemia in patients with chronic kidney disease. Vitamin E-coated membranes (VECMs) consist of a multilayer membrane with liposoluble vitamin E on the blood surface allowing direct free radical scavenging at the membrane site, which is of potential clinical benefit. Our objective was to examine the effect of VECMs on anemia in chronic hemodialysis (HD).

Methods

We enrolled 172 stable chronic HD patients (94 men, 78 women, age 65.4 ± 13.4 years) in an open-label multicenter study. They were shifted from their previous dialyzer to VECM for 1 year. Hemoglobin (Hb) levels and recombinant human erythropoietin (rHuEpo) dosage were analyzed after 4, 8, and 12 months on the VECM and compared with baseline values using paired tests.

Results

Hb significantly increased from 10.9 ± 1.2 g/dL at baseline to 11.7 ± 1.2 g/dL after 12 months (p<0.001) on VECMs. Conversely, the rHuEpo dosage decreased from 7,762 ± 5,865 IU/week at baseline to 6,390 ± 5,679 IU/week after 12 months (p<0.001). The proportion of patients who were at target Hb levels (European Best Practice Guidelines) increased from 49.4% at baseline to 80% after 12 months (p<0.001).

Conclusions

Dialysis with VECM in stable chronic HD patients was associated with significantly improved Hb levels and lower rHuEpo requirements. These results suggest that the antioxidant properties of VECMs may impact favorably on anemia management in chronic HD patients. Possible mechanisms include enhanced membrane biocompatibility, reduced oxidative stress and inflammation with VECMs, resulting in improved red blood cell survival and/or rHuEpo responsiveness. This therapy may potentially contribute to more effective anemia management in hemodialysis patients, and merits further rigorous study.

Oxidative Stress in Patients Undergoing Peritoneal Dialysis: A Current Review of the Literature

Peritoneal dialysis (PD) patients manifest excessive oxidative stress (OS) compared to the general population and predialysis chronic kidney disease patients, mainly due to the composition of the PD solution (high-glucose content, low pH, elevated osmolality, increased lactate concentration and glucose degradation products). However, PD could be considered a more biocompatible form of dialysis compared to hemodialysis (HD), since several studies showed that the latter results in an excess accumulation of oxidative products and loss of antioxidants. OS in PD is tightly linked with chronic inflammation, atherogenesis, peritoneal fibrosis, and loss of residual renal function. Although exogenous supplementation of antioxidants, such as vitamins E and C, N-acetylcysteine, and carotenoids, in some cases showed potential beneficial effects in PD patients, relevant recommendations have not been yet adopted in everyday clinical practice.

Oxidative Stress in Hemodialysis Patients: A Review of the Literature

Hemodialysis (HD) patients are at high risk for all-cause mortality and cardiovascular events. In addition to traditional risk factors, excessive oxidative stress (OS) and chronic inflammation emerge as novel and major contributors to accelerated atherosclerosis and elevated mortality. OS is defined as the imbalance between antioxidant defense mechanisms and oxidant products, the latter overwhelming the former. OS appears in early stages of chronic kidney disease (CKD), advances along with worsening of renal failure, and is further exacerbated by the HD process per se. HD patients manifest excessive OS status due to retention of a plethora of toxins, subsidized under uremia, nutrition lacking antioxidants and turn-over of antioxidants, loss of antioxidants during renal replacement therapy, and leukocyte activation that leads to accumulation of oxidative products. Duration of dialysis therapy, iron infusion, anemia, presence of central venous catheter, and bioincompatible dialyzers are several factors triggering the development of OS. Antioxidant supplementation may take an overall protective role, even at early stages of CKD, to halt the deterioration of kidney function and antagonize systemic inflammation. Unfortunately, clinical studies have not yielded unequivocal positive outcomes when antioxidants have been administered to hemodialysis patients, likely due to their heterogeneous clinical conditions and underlying risk profile.

Vitamin E-Coated and Heparin-Coated Dialyzer Membranes for Heparin-Free Hemodialysis: A Multicenter, Randomized, Crossover Trial

BACKGROUND

Hemodialysis requires effective anticoagulation to avoid blood circuit clotting. In patients at high risk for bleeding, several alternative methods have been developed.

STUDY DESIGN

Multicenter, prospective, randomized, crossover study evaluating the noninferiority of vitamin E-coated compared with heparin-coated dialyzers in a 4-hour heparin-free hemodialysis strategy.

SETTINGS & PARTICIPANTS

32 adult long-term hemodialysis patients from 2 French hemodialysis units with well-functioning fistulas or double-lumen catheters.

INTERVENTION

Patients were randomly allocated to a first period using either vitamin E- or heparin-coated dialyzers. After a washout period of 2 hemodialysis sessions, each patient was switched to the alternative dialyzer for a second period. Each study period started with 2 hemodialysis sessions with reduced heparin dose (50% and 25% of usual heparin dose, respectively, for sessions 1 and 2) followed by 2 heparin-free sessions.

OUTCOMES

The primary end point was the percentage of successful study periods, defined as no circuit-clotting event leading to premature interruption of any of the 4 dialysis sessions. Secondary end points included total number and cumulative duration of hemodialysis sessions without clotting, number of saline solution flushes, dialysis circuit bubble trap status and dialyzer membrane status by visual inspection, and dialysis adequacy.

RESULTS

The percentage of success with vitamin E-coated dialyzers (25/32 study periods [78%]) was not inferior to that with heparin-coated dialyzers (26/32 study periods [81%]). Visual inspection showed equal numbers of clean dialysis circuit bubble traps (vitamin E-coated, 34/121; heparin-coated, 32/120), whereas clean fiber bundles were more frequently noted with the vitamin E-coated compared with heparin-coated dialyzers (25/121 vs 2/120; P=0.002).

LIMITATIONS

Results may not extrapolate to critically ill patients. Differences in dialyzer transparency may account for visual inspection scores.

CONCLUSIONS

The success rate of 4-hour heparin-free hemodialysis sessions is lower than that previously claimed in uncontrolled studies. Vitamin E-coated and heparin-coated dialyzers exposed patients to similar and unacceptable high failure rates. Further studies are required to improve heparin-free hemodialysis.

Effects of glucose on cell viability and antioxidant and anti-inflammatory properties of phytochemicals and phytochemically modified membranes

By virtue of antioxidant and anti-inflammable properties, plant-derived phytochemicals such as mangiferin and genistein have attracted considerable attention for functionalization of polymeric hemodialysis (HD) membranes via solution blending. In-vitro dihydrorhodamine (DHR) assay of the genistein-modified membranes revealed drastic reduction in the level of the reactive oxygen species (ROS). In contrast, mangiferin-modified HD membrane manifested the pro-oxidant activity. We suspected that such difference in ROS generation may be attributed to the glucose unit on the xanthone backbone of mangiferin. This hypothesis was confirmed by comparing the ROS levels of genistein versus genistin, and mangiferin versus xanthone and 3,4,5,6-tetrahydroxyxanthone. Phytochemicals without the glucose unit show better antioxidant property related to the glycosides. Anti-inflammatory property was further conducted by measuring the level of TNF-α in blood after contacting with the same selected phytochemicals. Of particular interest is that the glucose unit promotes the generation of TNF-α.

In vitro investigation of antioxidant, anti-Inflammatory, and antiplatelet adhesion properties of genistein-modified poly(ethersulfone)/poly(vinylpyrrolidone) hemodialysis membranes

Hemocompatibility of genistein-modified poly(ethersulfone)/poly(vinylpyrrolidone) (PES/PVP) hemodialysis (HD) membranes has been investigated in vitro with emphasis on evaluation of cell viability, antioxidant, anti-inflammatory, and antiplatelet adhesion properties. Genistein modified PES/PVP membranes reveal significant reduction of the reactive oxygen species and also considerable suppression of interleukin-1β and tumor necrosis factor-α levels in whole blood, but to a lesser extent ininterleukin-6. The incorporation of PVP into the HD membrane reduces platelet adhesion by virtue of its hydrophilicity. Of particular importance is that platelet adhesion of the genistein modified membranes declines noticeably at low concentrations of genistein for about 5-10%, beyond which it raises the number of adhered platelets. The initial decline in the platelet adhesion is attributable to genistein's ability to inhibit intercellular and/or vascular cell adhesion, whereas the reversal of this adhesion trend with further increase of genistein loading is ascribed to the inherent hydrophobicity of the genistein modified HD membrane.

A randomized controlled trial evaluating the erythropoiesis stimulating agent sparing potential of a vitamin E-bonded polysulfone dialysis membrane

Background

Vitamin E (VE) bonded polysulfone dialysis membranes have putative erythropoiesis stimulating agent (ESA)-sparing and anti-inflammatory properties based on data from a small number of studies. We sought to investigate this in a large, prospective 12-month randomized controlled trial.

Methods

Two-hundred and sixty prevalent haemodialysis (HD) patients were randomized to dialysis with VE-bonded polysulfone membranes or non-VE-bonded equivalents. All ESA-dosing was performed by means of a computer-based anaemia management decision support system. Monthly data were used to calculate the ESA resistance index (ERI) and blood tests were performed at baseline, 6 and 12 months for measurement of C-reactive protein (CRP) levels.

Results

Of the 260 patients, 123 were randomized to dialysis with the VE-membrane and 12-month data was available for 220 patients. At the study population level, no beneficial effect of the VE membranes on the ERI or CRP levels was observed. Post hoc analyses indicated that there was a significant fall in ERI for patients with the highest baseline ESA resistance dialysed with the VE (9.28 [7.70–12.5] versus 7.70 [5.34–12.7] IU/week/kg/g/dL Hb, P = 0.01) but not the control membranes (9.45 [7.62–12.3] versus 8.14 [4.44–15.6] IU/week/kg/g/dL Hb, P = 0.41); this was not attributable to changes in CRP levels.

Conclusions

Wholesale switching of all chronic HD patients to dialysis with VE-bonded polysulfone membranes appears not to be associated with improvements in ESA-responsiveness or CRP. These membranes may have utility in patients with heightened ESA resistance.

Role of alpha-lipoic acid in the management of anemia in patients with chronic renal failure undergoing hemodialysis

Introduction

Anemia associated with chronic kidney disease is a serious complication necessitating expenditure of huge medical efforts and resources. This study investigates the role of alpha-lipoic acid (ALA) in end stage renal disease patients undergoing hemodialysis. By the virtue of its antioxidative effects, ALA is expected to act as an erythropoietin (EPO) adjuvant, and also has extended beneficial effects on endothelial dysfunction.

Methods

Forty-four patients undergoing hemodialysis and receiving EPO were randomized into two groups: the first group received ALA 600 mg once daily for 3 months; while the other group represented the control group. Parameters measured at baseline and at end of study were hemoglobin, EPO doses, EPO resistance index (ERI), iron store indices, malondialdehyde, oxidized low-density lipoprotein (ox-LDL), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and asymmetric dimethylarginine (ADMA), as well as routine laboratory follow-up.

Results

EPO doses and ERI were significantly decreased in the treatment group, while they did not change in the control group. Hemoglobin, iron store indices, malondialdehyde, oxidized ox-LDL, IL-6, TNF-α, and ADMA were similar in both treatment and control groups at baseline, and did not change by the end of study period. Likewise, routine laboratory measures were not affected by the treatment.

Conclusion

ALA could be used in hemodialysis patients to reduce requirements for EPO. However, larger and longer term studies are required to clarify the exact role of ALA in hemodialysis as well as in pre-hemodialysis patients.

The effect of vitamin E-bonded polysulfone membrane dialyzer on a new oxidative lipid marker

The use of vitamin E-bonded cellulose membrane dialyzers has been reported to cause a decrease in oxidative lipid marker levels (Nakai et al., Ther Apher Dial 14:505-540, 1; Nakai et al., J Jpn Soc Dial Ther 45:1-47, 2; Mashiba et al., Arterioscler Thromb Vasc Biol 21:1801-1808, 3). However, few studies have identified this effect with vitamin E-bonded polysulfone membranes, and no studies report the same effect on alpha (1) antitrypsin-LDL complex, a new oxidative lipid marker. This prompted us to examine the influence of use of VPS-HA vitamin E-bonded polysulfone high-flux membrane dialyzers on this new oxidative lipid marker. The subjects were 17 patients who had been dialyzed with VPS-HA for 12 months. The subjects' baseline characteristics were as follows. Their average age was 65.6 ± 13.1 years, comprising 8 males and 9 females; hemodialysis vintage was 83.8 ± 85.4 months. Eight had chronic glomerular nephropathy and five had diabetic nephropathy. The primary outcome was defined as alpha (1) antitrypsin-LDL complex level after 12 months, as a post-study using VPS-HA. Secondary outcomes included triglycerides, total cholesterol, HDL cholesterol and LDL cholesterol levels. The data were analyzed pre-study and after 3, 6, 9 and 12 months for alpha (1) antitrypsin-LDL complex, and pre-study and post-study for the other indicators. Twelve months after switching to VPS-HA, alpha (1) antitrypsin-LDL complex, total cholesterol and LDL cholesterol had significantly decreased. Triglycerides and HDL cholesterol had not significantly changed. Hemodialysis therapy with VPS-HA was shown to decrease alpha (1) antitrypsin-LDL complex, an index of oxidative stress, and also to decrease some lipid markers.

Activation of platelets upon contact with a vitamin E-coated/non-coated surface

The purpose of this study was to determine the effects of a vitamin E-coated surface on platelet activation, focusing on the interactions among the vitamin E-coated surface, platelets and leukocytes. Platelet-rich plasma (PRP) or PRP containing leukocytes (LPRP) was used. No difference was observed in platelet activation between PRP and LPRP for a vitamin E-coated membrane, meaning that platelet activation triggered by leukocytes was suppressed in plasma coming in contact with a vitamin E-coated membrane, while the membrane itself directly induced platelet activation. The antioxidant capacity of the vitamin E-coated membrane in contact with PRP or LPRP was partially reduced, but sufficient residual capacity remained. The in vitro experiments using an oxidized vitamin E-coated surface revealed that P-selectin expression and superoxide anion production in the platelets and platelet adhesion were induced by contact with the oxidized vitamin E-coated surface. We conclude that contact with a vitamin E-coated surface reduces platelet activation mediated by superoxide anions, probably by reducing superoxide anions, but during the process of the reduction, the vitamin E-coated surface itself becomes oxidized, which again causes platelet activation. The beneficial effects of a vitamin E-coated dialyzer in respect of platelet activation were counteracted by the formation of oxidized vitamin E.

Vitamin E-derived copolymers continue the challenge to hemodialysis biomaterials

Improving material biocompatibility has been a continuous effort and remains a major goal of dialysis therapy. In this respect, vitamin E-modified copolymers have been used to produce a generation of biomaterials that has offered new clinical challenges and the chance of further improving the quality of synthetic hemodialyser membranes. This mini review article describes the evolution of these copolymers that only recently have been adopted to develop new vitamin E-modified polysulfone hemodialysers. Biomaterial characteristics and clinical aspects of these membranes are discussed, starting from the most recent contributions that have appeared in the literature that are of interest for the community of nephrology and dialysis specialists, as well as biomaterial scientists.

Role of the human erythrocyte in generation and storage of asymmetric dimethylarginine

Proteolytic activity in whole blood may lead to release of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA). We investigated the role of the human erythrocyte in storage and generation of ADMA in healthy controls (n = 36) and critically ill patients (n = 38). Both free and total (sum of free and protein-incorporated) ADMA were measured. Upon incubation of intact erythrocytes with extracellular ADMA (0 to 40 μmol/l), equilibrium between intra- and extracellular ADMA was reached within 3 h. Compared with controls, patients had significantly higher basal concentrations of ADMA in plasma (0.88 ± 0.75 vs. 0.41 ± 0.07 μmol/l) and erythrocytes (1.28 ± 0.55 vs. 0.57 ± 0.14 μmol/l). Intracellular and plasma ADMA were significantly correlated in the patient group only (r = 0.834). Upon lysis, followed by incubation at 37°C for 2 h, free ADMA increased sevenfold (to 8.60 ± 3.61 μmol/l in patients and 3.90 ± 0.78 μmol/l in controls). In lysates of controls, free ADMA increased further to 9.85 ± 1.35 μmol/l after 18 h. Total ADMA was 15.43 ± 2.44 μmol/l and did not change during incubation. The increase of free ADMA during incubation corresponded to substantial release of ADMA from the erythrocytic protein-incorporated pool (21.9 ± 4.6% at 2 h and 60.8 ± 7.6% at 18 h). ADMA was released from proteins other than hemoglobin, which only occurred after complete lysis and was blocked by combined inhibition of proteasomal and protease activity. Neither intact nor lysed erythrocytes mediated degradation of free ADMA. We conclude that intact erythrocytes play an important role in storage of ADMA, whereas upon erythrocyte lysis large amounts of free ADMA are generated by proteolysis of methylated proteins, which may affect plasma levels in hemolysis-associated diseases.

Oxidative stress and inflammation: Implications in uremia and hemodialysis

Oxidative response and inflammation constitute a major defense against infections, but if not properly regulated they could also lead to a number of deleterious effects. Patients affected by different stages of acute and chronic kidney disease, particularly patients on hemodialysis, present a marked activation of oxidative and inflammatory processes. This condition exposes these patients to an elevated risk of morbidity and mortality. This Review is up to date and it analyses the newest notions about pathophysiological mechanisms of oxidative stress and inflammation in patients with renal diseases, also considering the different strategies studied to counterbalance this high risk state.

Evaluation of the impact of a new synthetic vitamin E-bonded membrane on anemia and rHuEPO requirement in ESRD patients with central venous catheters: a pilot study

In the last years, the number of hemodialysis (HD) patients with erythropoietin (rHuEPO) resistance is increasing. Probably, central venous catheters (CVCs) contribute to this resistance by inducing inflammation and oxidative stress. This study was aimed to compare vitamin E-bonded dialyzer (PSVE) versus polyethersulfone membrane. Sixteen subjects with CVCs were included in a prospective two-arm crossover 12-month study. The primary endpoints were the rHuEPO requirement and the erythropoiesis-stimulating agents (ESA) index, which was defined by the ratio between weekly EPO dosage (IU/kg/week) and Hb levels (g/dl). The mean dosages of rHuEPO to maintain hemoglobin between 10.5 and 12 g/dl were 135 ± 59 and 101 ± 57 IU/kg/week with polysulfone and PSVE, respectively (P = 0.14). The ESA indexes were 12.1 ± 5.2 and 8.7 ± 5.2 (P < 0.0001) with polysulfone and PSVE, respectively. A trend towards consensual changes in protein glycoxidation, antioxidant, and inflammatory markers was observed. In conclusion, the study suggests a role for PSVE in the reduction of ESA index in HD patients with CVCs.

Enhancement of the blood compatibility of dialyzer membranes by the physical adsorption of human thrombomodulin (ART-123)

ART-123 is a recombinant soluble human thrombomodulin (hTM) with excellent anticoagulant activity. We focused on improving the blood compatibility of the polysulfone-polyvinylpyrrolidone dialyzer surface by the physical adsorption of ART-123 onto the surface. The blood compatibility of the dialyzer with the hTM adsorbed membrane was evaluated by measuring the differential pressure between the arterial and the venous pressures and by blood parameters during blood circulation. The hTM adsorbed dialyzer membrane inhibited blood clot formation without heparin administration due to the anticoagulant activity of hTM for over 4 h. The physically adsorbed hTM was stable during blood circulation, and it did not affect activated clotting time, which is significant drawback of heparin administration, and blood cell counts of RBC, WBC, or platelets. The physical adsorption of hTM onto the dialyzer membrane will be a simple and safe method to prevent blood coagulation during dialysis instead of heparin administration.

Asymmetric dimethylarginine in hemodialysis, hemodiafiltration, and peritoneal dialysis

Asymmetric dimethylarginine (ADMA) is a mediator of endothelial dysfunction. Production and elimination of ADMA may be affected by the type of renal replacement therapy used and oxidative stress. Plasma ADMA, advanced glycation end products (AGE), and homocysteine were assessed in 59 subjects: 20 hemodialysis (HD) patients, 19 patients undergoing peritoneal dialysis (PD), and 20 controls. Results were compared between the groups. The effect of 8 weeks of HD and high-volume predilution hemodiafiltration (HDF) was compared in a randomized study. HD patients showed higher ADMA (1.20 [0.90-1.39 micromol/L]) compared to controls (0.89 [0.77-0.98], P < 0.01), while ADMA in PD did not differ from controls (0.96 [0.88-1.28]). AGE and homocysteine were highest in HD, lower in PD (P < 0.01 vs. HD), and lowest in controls (P < 0.001 vs. HD and PD). PD patients had higher residual renal function than HD (P < 0.01). The decrease in ADMA at the end of HD (from 1.25 [0.97-1.33] to 0.66 [0.57-0.73], P < 0.001) was comparable to that of HDF. Switching from HD to HDF led to a decrease in predialysis homocysteine level in 8 weeks (P < 0.05), while ADMA and AGE did not change. Increased ADMA levels in patients undergoing HD, as compared to PD, may be caused by higher oxidative stress and lower residual renal function in HD. Other factors, such as diabetes and statin therapy, may also be at play. The decrease in ADMA at the end of HD and HDF is comparable. Switching from HD to HDF decreases in 8 weeks the predialysis levels of homocysteine without affecting ADMA.

Improved management of intradialytic hypotension (IDH) using vitamin E-bonded polysulfone membrane dialyzer

BACKGROUND

Intradialytic hypotension (IDH) is a common clinical trait in hemodialysis (HD) which is caused by poor biocompatibility of the dialyzer membrane. Aiming to improve IDH, vitamin E-bonded polysulfone dialyzer (VPS-H) was evaluated in a pilot study.

METHODS

Eight IDH patients on standard HD were switched from their conventional high-flux dialyzers to VPS-H, and intradialytic blood pressure (BP) was monitored regularly for 10 months.

RESULTS

The results showed that hypotension of systolic BP (SBP), diastolic BP (DBP) and pulse pressure (PP) during the session were improved after changing the dialyzer. Notably, almost all the values recorded from 120 minutes into the session until the end of the treatment in the period between the second and tenth month after treatment were significantly different from the corresponding baseline values. Moreover, after 8 to 10 months, the SBP prior to a dialysis session was significantly reduced compared with baseline values. On the other hand, the pulse rate showed no difference throughout the study period.

CONCLUSIONS

This study provides early evidence of the beneficial role that vitamin E-bonded dialyzers may have in preventing IDH. Larger controlled trials are needed to confirm this original finding.

The role of oxidative stress in chronic kidney disease

New, reliable circulating oxidative stress markers have become available in chronic kidney disease (CKD) patients and have confirmed the long held belief that CKD is a pro-oxidant state. However, several questions related to this state of oxidative stress remain largely unresolved. First, the relative importance of each type of oxidant involved has been insufficiently evaluated. Only two recent studies have addressed this issue, and both suggested that chlorinated stress played a central role. Second, as only few population-based studies are available, the prevalence of oxidative stress among CKD patients remains undetermined. Third, although the link between oxidative stress and inflammation in CKD is emerging as a key process contributing to the genesis of oxidative stress in these patients, its pathogenesis remains poorly defined. Fourth, data favoring the involvement of oxidative stress in uremic toxicity are still limited. Finally, while two recent pilot studies have demonstrated that treatment of CKD patients with antioxidants is able to reduce cardiovascular events, information related to the pharmacokinetic characteristics of antioxidants, as well as their efficacy to prevent oxidative stress, is still limited in this patient group. Thus, although existing data suggest a prominent role of CKD-associated oxidative stress in uremic toxicity, further studies are required to definitively prove this concept.

Antiatherogenic effects of vitamin E: the search for the Holy Grail

Vitamin E, a naturally occurring antioxidant, has been found to reduce atherosclerotic lesion formation in animal models as well as cardiovascular morbidity in several observational studies. However, a number of case-control and prospective cohort studies failed to confirm its value in the primary and secondary prevention of morbidity and mortality from coronary artery disease. Several small or larger randomized interventional trials completed to date failed to resolve the conflict. Notably, even in large, well-conducted prospective epidemiologic studies, the potential effects of residual confounding may be on the same order of magnitude as the reported benefit. The response to vitamin E supplementation in specific patient subpopulations with chronic inflammation and/or higher degrees of oxidative stress has not been studied as yet. Therefore, further large randomized interventional trials are warranted to clarify accurately the role of vitamin E in the primary and secondary prevention of atherosclerotic coronary disease in these patient groups.

Alpha-tocopherol supplementation decreases electronegative low-density lipoprotein concentration [LDL(-)] in haemodialysis patients

BACKGROUND

Oxidative stress is a significant contributor to cardiovascular diseases (CVD) in haemodialysis (HD) patients, predisposing to the generation of oxidized low-density lipoprotein (oxLDL) or electronegatively charged LDL subfraction. Antioxidant therapy such as alpha-tocopherol acts as a scavenger of lipid peroxyl radicals attenuating the oxidative stress, which decreases the formation of oxLDL. The present study was designed to investigate the influence of the alpha-tocopherol supplementation on the concentration of electronegative low-density lipoprotein [LDL(-)], a minimally oxidized LDL, which we have previously described to be high in HD patients.

METHODS

Blood samples were collected before and after 120 days of supplementation by alpha-tocopherol (400 UI/day) in 19 stable HD patients (50 +/- 7.8 years; 9 males). The concentrations of LDL(-) in blood plasma [using an anti-LDL- human monoclonal antibody (mAb)] and the anti-LDL(-) IgG auto-antibodies were determined by ELISA. Calculation of body mass index (BMI) and measurements of waist circumference (WC), triceps skin folds (TSF) and arm muscle area (AMA) were performed.

RESULTS

The plasma alpha-tocopherol levels increased from 7.9 microM (0.32-18.4) to 14.2 microM (1.22-23.8) after the supplementation (P = 0.02). The mean concentration of LDL(-) was reduced from 570.9 microg/mL (225.6-1241.0) to 169.1 microg/mL (63.6-621.1) (P < 0.001). The anti-LDL(-) IgG auto-antibodies did not change significantly after the supplementation. The alpha-tocopherol supplementation also reduced the total cholesterol and LDL-C levels in these patients, from 176 +/- 42.3 mg/dL to 120 +/- 35.7 mg/dL (P < 0.05) and 115.5 +/- 21.4 mg/dL to 98.5 +/- 23.01 mg/dL (P < 0.001), respectively.

CONCLUSION

The oral administration of alpha-tocopherol in HD patients resulted in a significant decrease in the LDL(-), total cholesterol and LDL-C levels. This effect may favour a reduction in cardiovascular risk in these patients, but a larger study is required to confirm an effect in this clinical setting.

Hemodialysis improves endothelial venous function in end-stage renal disease

The objective of the present study was to determine the acute effect of hemodialysis on endothelial venous function and oxidative stress. We studied 9 patients with end-stage renal disease (ESRD), 36.8 +/- 3.0 years old, arterial pressure 133.8 +/- 6.8/80.0 +/- 5.0 mmHg, time on dialysis 55.0 +/- 16.6 months, immediately before and after a hemodialysis session, and 10 healthy controls matched for age and gender. Endothelial function was assessed by the dorsal hand vein technique using graded local infusion of acetylcholine (endothelium-dependent venodilation, EDV) and sodium nitroprusside (endothelium-independent venodilation). Oxidative stress was evaluated by measuring protein oxidative damage (carbonyls) and antioxidant defense (total radical trapping antioxidant potential - TRAP) in blood samples. All patients were receiving recombinant human erythropoietin for at least 3 months and were not taking nitrates or a-receptor antagonists. EDV was significantly lower in ESRD patients before hemodialysis (65.6 +/- 10.5) vs controls (109.6 +/- 10.8; P = 0.010) and after hemodialysis (106.6 +/- 15.7; P = 0.045). Endothelium-independent venodilation was similar in all comparisons performed. The hemodialysis session significantly decreased TRAP (402.0 +/- 53.5 vs 157.1 +/- 28.3 U Trolox/microL plasma; P = 0.001). There was no difference in protein damage comparing ESRD patients before and after hemodialysis. The magnitude of change in the EDV was correlated negatively with the magnitude of change in TRAP (r = -0.70; P = 0.037). These results suggest that a hemodialysis session improves endothelial venous function, in association with an antioxidant effect.

Randomized placebo-controlled trial assessing a treatment strategy consisting of pravastatin, vitamin E, and homocysteine lowering on plasma asymmetric dimethylarginine concentration in mild to moderate CKD

BACKGROUND

Chronic kidney disease (CKD) is associated with an increased incidence of cardiovascular disease (CVD). The Anti-oxidant Therapy In Chronic Renal Insufficiency (ATIC) Study showed that a multistep treatment strategy improved carotid intima-media thickness, endothelial function, and microalbuminuria in patients with stages 2 to 4 CKD. Increased plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, have been linked to greater CVD risk in patients with CKD. The aim of this study is to assess effects of the multistep intervention on plasma ADMA concentrations in the ATIC Study.

STUDY DESIGN

Secondary analysis of a randomized double-blind placebo-controlled trial.

SETTING & PARTICIPANTS

93 patients with creatinine clearance of 15 to 70 mL/min/1.73 m(2) (according to the Cockcroft-Gault equation) from 7 outpatient clinics in Amsterdam, The Netherlands.

INTERVENTION

The treatment group received sequential treatment consisting of pravastatin, 40 mg/d. After 6 months, vitamin E, 300 mg/d, was added, and after another 6 months, homocysteine-lowering therapy (folic acid, 5 mg/d; pyridoxine, 100 mg/d; and vitamin B(12), 1 mg/d, all in 1 tablet) were added and continued for another year. The control group received matching placebos.

OUTCOME & MEASURES

Plasma ADMA levels.

RESULTS

36 participants (77%) in the treatment group and 38 (83%) in the placebo group completed the study. Mean ADMA and symmetric dimethylarginine concentrations in the total study population were 0.53 +/- 0.07 (SD) and 1.14 +/- 0.46 mumol/L, respectively. After 24 months, there was no overall effect of the treatment strategy on ADMA concentrations (beta = -0.006; P = 0.27). Analysis of separate treatment effects suggested that vitamin E significantly decreased ADMA levels by 4% in the treatment group compared with the placebo group (multiple adjusted P = 0.02).

LIMITATIONS

The study was a secondary analysis, power calculation was based on the primary end point of carotid intima-media thickness, mean plasma ADMA levels were relatively low.

CONCLUSION

Overall, a multistep treatment strategy consisting of pravastatin, vitamin E, and B vitamins had no effect on plasma ADMA levels in a stage 2 to 4 CKD population. This suggests that the beneficial effects of the intervention were not mediated by changes in ADMA levels. Possible ADMA-lowering effects of vitamin E deserve further attention.

Comparative effects of dietary supplementation with red grape juice and vitamin E on production of superoxide by circulating neutrophil NADPH oxidase in hemodialysis patients

BACKGROUND

Atherosclerotic cardiovascular disease is the most common cause of death among hemodialysis patients; it has been attributed to increased oxidative stress, dyslipidemia, malnutrition, and chronic inflammation. Activation of neutrophils is a well-recognized feature in dialysis patients, and superoxide-anion production by neutrophil NADPH oxidase may contribute significantly to oxidative stress.

OBJECTIVE

The aim of the study was to compare the effects of dietary supplementation with concentrated red grape juice (RGJ), a source of polyphenols, and vitamin E on neutrophil NADPH oxidase activity and other cardiovascular risk factors in hemodialysis patients.

DESIGN

Thirty-two patients undergoing hemodialysis were recruited and randomly assigned to groups to receive dietary supplementation with RGJ, vitamin E, or both or a control condition without supplementation or placebo. Blood was obtained at baseline and on days 7 and 14 of treatment.

RESULTS

RGJ consumption but not vitamin E consumption reduced plasma concentrations of total cholesterol and apolipoprotein B and increased those of HDL cholesterol. Both RGJ and vitamin E reduced plasma concentrations of oxidized LDL and ex vivo neutrophil NADPH oxidase activity. These effects were intensified when the supplements were used in combination; in that case, reductions in the inflammatory biomarkers intercellular adhesion molecule 1 and monocyte chemoattractant protein 1 also were observed.

CONCLUSIONS

Regular ingestion of concentrated RGJ by hemodialysis patients reduces neutrophil NADPH-oxidase activity and plasma concentrations of oxidized LDL and inflammatory biomarkers to a greater extent than does that of vitamin E. This effect of RGJ consumption may favor a reduction in cardiovascular risk.

Cardiovascular disease in dialysis patients: do some antihypertensive drugs have specific antioxidant effects or is it just blood pressure reduction? Does antioxidant treatment reduce the risk for cardiovascular disease?

PURPOSE OF REVIEW

Patients with end-stage renal disease have an extremely high cardiovascular disease mortality. Oxidative stress is one of the 'nontraditional' risk factors for cardiovascular disease mortality in dialysis patients. This review discusses antioxidant activity of the commonly prescribed antihypertensive agents and the effects of antioxidant interventions on cardiovascular disease mortality in patients with end-stage renal disease.

RECENT FINDINGS

Several lines of evidence confirm antioxidant activity of the renin-angiotensin-aldosterone antagonists, some of the calcium channel blockers, carvedilol, and hydralazine. This appears to be independent of their antihypertensive activity. Clinical evidence of their superiority in improving cardiovascular disease endpoints in end-stage renal disease, however, is lacking. There are no randomized trials that have examined the effect of correcting oxidative stress on clinical endpoints. One randomized study in patients on hemodialysis reported a reduction in oxidative stress and the plasma methylarginines with valsartan and amlodipine but no clinical endpoints were examined.

SUMMARY

The effects of the antihypertensive agents with antioxidant activity on cardiovascular disease mortality in end-stage renal disease have not been examined in randomized clinical trials. These agents may offer specific clinical advantage in addition to lowering the blood pressure, but this remains to be proven. Two studies show a reduction in cardiovascular disease events with vitamin E and N-acetylcysteine in patients on hemodialysis without an effect on overall mortality.

Asymmetrical dimethylarginine in renal disease: limits of variation or variation limits? A systematic review

Asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is increasingly recognized as a putative biomarker in cardiovascular and renal disease. Elevated plasma levels of ADMA are the consequence of increased synthesis, reduced renal clearance or reduced enzymatic degradation. Based upon the metabolic fate the highest plasma concentrations of ADMA have been reported in patients with renal failure in whom this molecule accumulates. However, the range of published ADMA levels in patients with chronic renal failure as well as in patients with end-stage renal failure undergoing maintenance hemodialysis, peritoneal dialysis or kidney transplant recipients is widely scattered and overlaps with the levels reported in healthy individuals. This wide distribution can in part be explained by different bioanalytical techniques and the lack of standardization of such assays. This review summarizes available literature on ADMA in patients with kidney disease and stresses the urgent need for a consensus regarding reference values for different analytical methods in order to appreciate the prognostic significance of elevated ADMA levels. At present, one cannot advocate this molecule for risk assessment or individual patient prognosis in the clinical work-up of patients with renal impairment.