Cellulose acetate membrane improves some aspects of red blood cell function in haemodialysis patients

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.

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.

Supercritical fluid assisted process for the generation of cellulose acetate loaded structures, potentially useful for tissue engineering applications

Supercritical CO2 phase inversion offers an alternative to obtain solvent free structures with short processing times and preservation of the morphology. We prepared cellulose acetate structures loaded with drug (ibuprofen) to perform experiments at pressures and temperatures ranging between 150 and 250 bars and 35 and 55 °C. The structures were properly characterized by SEM, EDX and DSC; drug controlled release experiments were also performed. Analyses showed that the operating conditions strongly influenced the structure morphology, porosity and drug release profiles. Indeed, connected microparticles, nanofibrous networks and cellular membranes were produced, which have generated different drug release profiles.

The Internal Structure of Macroporous Membranes and Transport of Surface-Modified Nanoparticles

Understanding the morphological structure of membranes is essential to improve performance of membrane-based applications. In this paper, macroporous membranes were investigated and two methods introduced as an alternative for characterization of stereo-structure of the membranes. We combined the use of synchrotron X-ray nanotomography and small-angle X-ray scattering to examine the internal structure of cellulose acetate membranes with studies of the capture of surface-modified gold nanoparticles within these membranes. Finally, the morphological structures of macroporous membranes were visualized and their relationships with penetration tendency of surface-modified gold nanoparticles were explained.

Synthesis and in vitro characterizations of porous carboxymethyl cellulose-poly(ethylene oxide) hydrogel film

BACKGROUND

Cellulose and its derivatives such as carboxymethyl cellulose (CMC) have been employed as a biomaterial for their diverse applications such as tissue engineering, drug delivery and other medical materials. Porosity of the scaffolds has advantages in their applications to tissue engineering such as more cell adhesion and migration leading to better tissue regeneration. After synthesis of CMC-poly(ethylene oxide) (PEO) hydrogel by mixing the solutions of both CMC-acrylate and PEO-hexa-thiols, fabrication and evaluation of a CMC-PEO gel and its film in porous form have been made for its possible applications to tissue regeneration. Physicochemical and biological properties of both CMC-PEO hydrogel and porous films have been evaluated by using physicochemical assays by SEM, FTIR and swelling behaviors as well as in vitro assays of MTT, Neutral red, BrdU, gel covering and tissue ingrowth into the pores of the CMC-PEO gel films. Degradation of CMC-PEO hydrogel was also evaluated by treating with esterase over time.

RESULTS

Chemical grafting of acrylate to CMC was verified by analyses of both FTIR and NMR. CMC-PEO hydrogel was obtained by mixing two precursor polymer solutions of CMC-acrylate and PEO-hexa-thiols and by transforming into a porous CMC-PEO gel film by gas forming of ammonium bicarbonate particles. The fabricated hydrogel has swollen in buffer to more than 6 times and degraded by esterase. The results of in vitro assays of live and dead, MTT, BrdU, Neutral red and gel covering on the cells showed excellent cell compatibility of CMC-PEO hydrogel and porous gel films. Furthermore the porous films showed excellent in vitro adhesion and migration of cells into their pore channels as observed by H&E and MT stains.

CONCLUSIONS

Both CMC-PEO hydrogel and porous gel films showed excellent biocompatibility and were expected to be a good candidate scaffold for tissue engineering.

Characterization of TEMPO-oxidized cellulose nanofibers in aqueous suspension by small-angle X-ray scattering

Cellulose nanofibers, extracted from wood pulps using the (2,2,6,6-tetramethylpiperidine-1-yl)oxyl (TEMPO)-mediated oxidation method, are low-cost, sustainable and high-performance materials with potential usage in many applications. The structural information of these cellulose nanofibers in aqueous suspension was characterized by synchrotron small-angle X-ray scattering (SAXS). A simplified ribbon model having a near rectangular cross section was found to give the best fit to the SAXS results. The analytical expression of the ribbon model also led to a higher calculation efficiency compared with the more conventional parallelepiped model. The extracted structural information included the cross-section size and size distribution of the cellulose nanofibers. For example, for nanofibers prepared from the dried pulp of the maritime pine, the size-weighted averages of thickness and width were 3.2 and 12.7 nm, respectively, and the corresponding standard deviations were 2.2 and 5.5 nm, respectively. The scattering results of the size-weighted average of the nanofiber width are also consistent with those determined directly from transmission electron microscopy.

High-flux versus low-flux membranes for end-stage kidney disease

BACKGROUND

Clinical practice guidelines regarding the use of high-flux haemodialysis membranes vary widely.

OBJECTIVES

We aimed to analyse the current evidence reported for the benefits and harms of high-flux and low-flux haemodialysis.

SEARCH METHODS

We searched Cochrane Renal Group's specialised register (July 2012), the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (1948 to March 2011), and EMBASE (1947 to March 2011) without language restriction.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that compared high-flux haemodialysis with low-flux haemodialysis in people with end-stage kidney disease (ESKD) who required long-term haemodialysis.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by two authors for study characteristics (participants and interventions), risks of bias, and outcomes (all-cause mortality and cause-specific mortality, hospitalisation, health-related quality of life, carpal tunnel syndrome, dialysis-related arthropathy, kidney function, and symptoms) among people on haemodialysis. Treatment effects were expressed as a risk ratio (RR) or mean difference (MD), with 95% confidence intervals (CI) using the random-effects model.

MAIN RESULTS

We included 33 studies that involved 3820 participants with ESKD. High-flux membranes reduced cardiovascular mortality (5 studies, 2612 participants: RR 0.83, 95% CI 0.70 to 0.99) but not all-cause mortality (10 studies, 2915 participants: RR 0.95, 95% CI 0.87 to 1.04) or infection-related mortality (3 studies, 2547 participants: RR 0.91, 95% CI 0.71 to 1.14). In absolute terms, high-flux membranes may prevent three cardiovascular deaths in 100 people treated with haemodialysis for two years. While high-flux membranes reduced predialysis beta-2 microglobulin levels (MD -12.17 mg/L, 95% CI -15.83 to -8.51 mg/L), insufficient data were available to reliably estimate the effects of membrane flux on hospitalisation, carpal tunnel syndrome, or amyloid-related arthropathy. Evidence for effects of high-flux membranes was limited by selective reporting in a few studies. Insufficient numbers of studies limited our ability to conduct subgroup analyses for membrane type, biocompatibility, or reuse. In general, the risk of bias was either high or unclear in the majority of studies.

AUTHORS' CONCLUSIONS

High-flux haemodialysis may reduce cardiovascular mortality in people requiring haemodialysis by about 15%. A large well-designed RCT is now required to confirm this finding.

Modulating human connective tissue progenitor cell behavior on cellulose acetate scaffolds by surface microtextures

Soft lithography techniques are used to fabricate cellulose acetate (CA) scaffolds with surface microtextures to observe growth characteristics of the progeny of human marrow-derived connective tissue progenitor cells (CTPs). Human CTPs were collected and cultured on CA scaffolds comprised postmicrotextures and smooth surfaces for up to 30 days. Cells on the smooth surfaces migrated without any preferred orientation for up to 30 days. On microtextures, cells tended to direct their processes toward posts and other cells on day 9. By day 30, cells on microtextures covered the surface with extracellular matrix. DNA quantification revealed approximately threefold more cells on microtextures than on the smooth surfaces. The alkaline phosphatase (AP) mRNA expression was slightly higher on smooth surfaces on day 9. However, by day 30, AP mRNA showed higher expression on microtextures. The mRNA expression of collagen type I was increased on microtextures by day 30, whereas smooth surfaces demonstrated similar expression. The osteocalcin mRNA expression was increased on postmicrotextures relative to smooth surfaces by day 30.

Photoreactive cellulose membrane—A novel matrix for covalent immobilization of biomolecules

We report a simple and mild procedure for the preparation of a photoreactive cellulose membrane capable of forming a covalent bond with a biomolecule in presence of 365 nm UV light. Photoreactive cellulose membrane was prepared by the reaction of fluoro group of 1-fluoro-2-nitro-4-azidobenzene (FNAB) and hydroxyl group of the cellulose in an alkaline medium. X-ray photoelectron spectroscopy (XPS) of the photoreactive cellulose confirmed the incorporation of FNAB moiety. Azido group of the photoreactive membrane on exposure to UV light transforms into highly reactive nitrene which binds with a protein. The efficacy of the activated membrane was checked by immobilizing glucose oxidase (GOD) onto it in presence of light. Immobilized GOD was found to have improved thermal, pH and storage stability. Photoreactive cellulose membrane was successfully used in enzyme-linked immunosorbent assay (ELISA) technique. The antibody immobilized onto such support by UV irradiation in 30 min showed similar ELISA value than the antibody immobilized onto a polystyrene ELISA plate in 12h incubation at 4 degrees C by conventional method.

Functional cardiac cell constructs on cellulose-based scaffolding

Cellulose and its derivatives have been successfully employed as biomaterials in various applications, including dialysis membranes, diffusion-limiting membranes in biosensors, in vitro hollow fibers perfusion systems, surfaces for cell expansion, etc. In this study, we tested the potential of cellulose acetate (CA) and regenerated cellulose (RC) scaffolds for growing functional cardiac cell constructs in culture. Specifically, we demonstrate that CA and RC surfaces are promoting cardiac cell growth, enhancing cell connectivity (gap junctions) and electrical functionality. Being optically clear and essentially non-autofluorescent, CA scaffolds did not interfere with functional optical measurements in the cell constructs. Molding to follow fine details or complex three-dimensional shapes are additional important characteristics for scaffold design in tissue engineering. Biodegradability can be controlled by hydrolysis, de-acetylization of CA and cytocompatible enzyme (cellulase) action, with glucose as a final product. Culturing of cardiac cells and growth of tissue-like cardiac constructs in vitro could benefit from the versatility and accessibility of cellulose scaffolds, combining good adhesion (comparable to the standard tissue-culture treated polystyrene), molding capabilities down to the nanoscale (comparable to the current favorite in soft lithography-polydimethylsiloxane) with controlled biodegradability.

The effect of different dialysis membranes on oxidative stress and selenium status

BACKGROUND

Oxidative stress is an important risk factor for the development and progression of several complications in hemodialysis patients. The aim of this study was to evaluate the effects of two different dialysis membranes on oxidative stress and selenium status.

METHODS

Forty long-term dialysis patients and 20 age-matched healthy controls were enrolled into our study. Serum malondialdehyde (MDA) and selenium (Se) concentrations, and glutathione peroxidase (GSH-Px) activities were determined before and after hemodialysis (HD) using a hemophan (H) or a polysulfone (PS) membrane.

RESULTS

MDA levels in the HD patients were significantly higher than those in the control group (p < 0.001). GSH-Px activity and selenium concentrations were significantly lower in HD patients compared to the control group (p < 0.001). MDA levels were significantly increased (p < 0.05); GSH-Px activity and selenium concentrations were significantly reduced (p < 0.001) in the PS membrane group compared to H membrane group after HD.

CONCLUSIONS

Comparing with H membrane, PS membrane caused more oxidative stress and lower levels of Se in HD patients.

Effect of different dialysis membranes on erythrocyte antioxidant enzyme levels and scavenger systems related to free hemoglobin in serum of hemodialysis patients

The main objective of the present study was to analyze some aspects of the function and structure of erythrocytes with respect to hemodialysis membrane biocompatibility throughout the erythrocyte and serum antioxidant levels. The study included 36 hemodialysis patients (14 female and 22 male, age 22-79 years, median 55) treated at the Department of Nephrology and Dialysis, Split Clinical Hospital in Split, and 30 control subjects matched for age and sex. Hemodialysis was performed three times a week for 4 hours with cellulose diacetate (n = 17; 6 females and 11 males) or polysulfone (n = 19; 8 females and 11 males) membranes. The aim of the study was to assess the level of oxidative stress in these patients by measuring catalytic concentrations of superoxide dismutase and glutathione peroxidase in erythrocyte lysate and scavenger systems related to free hemoglobin in serum (haptoglobin, hemopexin and bilirubin). In comparison with control values, the mean catalytic concentrations of superoxide dismutase were increased and catalytic concentrations of glutathione peroxidase decreased in patients before hemodialysis irrespective of the membrane used. Immediately after hemodialysis with either membrane, the mean catalytic concentrations of superoxide dismutase returned to the control range, while those of glutathione peroxidase were still decreased compared to control values, without any significant difference between the cellulose diacetate and polysulfone membranes. The predialysis and postdialysis values of haptoglobin, hemopexin and bilirubin in patient sera were within the range of control values. Comparison of the cellulose diacetate and polysulfone membranes showed no significant differences in the erythrocyte content of antioxidant enzymes and the scavenger system related to free hemoglobin in serum before and after hemodialysis.

Influence of different hemodialysis membranes on red blood cell susceptibility to oxidative stress

Oxidative stress is crucial in red blood cell (RBC) damage induced by activated neutrophils in in vitro experiments. The aim of the study was to evaluate whether the bioincompatibility phenomena occurring during hemodialysis (HD) (where neutrophil activation with increased free radical production is well documented) may have detrimental effects on RBC. We evaluated RBC susceptibility to oxidative stress before and after HD in 15 patients using Cuprophan, cellulose triacetate, and polysulfone membrane. RBC were incubated with t-butyl hydroperoxide as an oxidizing agent both in the presence and in the absence of the catalase inhibitor sodium azide. The level of malonaldehyde (MDA), a product of lipid peroxidation, was measured at 0, 5, 10, 15, and 30 min of incubation. When Cuprophan membrane was used, the MDA production was significantly higher after HD, indicating an increased susceptibility to oxidative stress in comparison to pre-HD. The addition of sodium azide enhanced this phenomenon. Both cellulose triacetate and polysulfone membranes did not significantly influence RBC susceptibility to oxidative stress. Neither the level of RBC reduced glutathione nor the RBC glutathione redox ratio changed significantly during HD with any of the membranes used. The RBC susceptibility to oxidative stress was influenced in different ways according to the dialysis membrane used, being increased only when using the more bioincompatible membrane Cuprophan, where neutrophil activation with increased free radical production is well documented. The alterations found in this study might contribute to the reduced RBC longevity of HD patients where a bioincompatible membrane is used.

Haemodialyser biocompatibility and erythrocyte structure and function

There is controversy as to the clinical importance of providing haemodialysis (HD) with biocompatible versus non-biocompatible membranes. The effects of both acute and chronic dialysis with a biocompatible membrane (polyacrylonitrile, PAN) and a non-biocompatible membrane (cuprophane, CU) on the structural and functional properties of human erythrocytes have been examined. All 27 studied HD patients had increased erythrocyte osmotic fragility (OF) compared to controls; a single CU HD decreased mean OF (% lysis) by 13% without altering cell cholesterol. A single PAN HD decreased OF by a significantly greater amount (24%) and was associated with a 20% reduction in cell cholesterol. Chronic PAN HD for 6 months was associated with a sustained reduction in osmotic fragility compared to chronic CU HD (mean lysis 16% vs 45%) with no differences in mean pre-HD cell cholesterol. A single CU HD was associated with increased mean erythrocyte malonyldialdehyde (MDA) and reduced membrane content of spectrin and band 3 and this was significantly different from the effects of PAN. A single CU or PAN HD had no significant action on reduced glutathione (GSH), ankyrin, actin or sodium pump activity. Chronic HD was associated with increased GSH, and decreased ankyrin and band 3 protein compared with controls but the results for CU and PAN were not different. There was a non-significant tendency for higher MDA levels after chronic CU HD compared to PAN. These results indicate that the structural integrity of erythrocytes is improved by PAN HD with respect to CU but this difference cannot easily be ascribed to gross changes in structural proteins, ionic homeostasis or oxidation status.