Neutrophil Oxygen Radical Production by Dialysis Membranes

The ability of different dialysis membranes to activate polymorphonuclearneutrophil oxygen radical production was investigated with chemiluminescence.All the six membranes, namely cuprophan, cellulose acetate,polycarbonate, polysulphone, polyacrilonitrile and polymethylmethacrylatewere able to interact with neutrophils and stimulate their oxygenradical production, the highest responses being seen with polyacrilonitrile,polymethylmethacrylate and polycarbonate. To analyse the roleof complement in this interaction, fresh plasma, heat inactivatedand zymosan-activated plasma were added: with fresh plasma oxygenradical production was stimulated on cuprophan, cellulose acetateand polysulphone, not modified on polycarbonate, and decreasedon polyacrilonitrile and polymethylmethacrylate. With heat-inactivatedplasma, the responses were decreased or abrogated on all themembranes except polycarbonate and polymethylmethacrylate, whereaswith zymosanactivated plasma similar responses to fresh plasmawere observed. In addition, when plasma was used to precoatthe membrane, cuprophan, cellulose acetate and polysulphonedisclosed an enhanced neutrophil oxidative burst, while precoatedpolyacrilonitrile and polymethylmethacrylate were less stimulatorythan uncoated membranes. In contrast the precoating of polycarbonatedid not modify oxygen radical production. These data suggestthat neutrophil activation occurs by direct membrane neutrophilinteraction. Plasmatic factors modulate this interaction butcomplement seems involved on cellulosic and polysulphone membranesonly. Therefore, it appears that oxygen radicals produced fromcontact of neutrophils with the dialysis membrane might playan initial and/or additional role in the events occurring atthe initiation of haemodialysis.     

Hemodialysis with Cellulose Membranes Primes the Neutrophil Oxidative Burst

Abstract: Hemodialysis with cellulose membranes causes a complement-mediated neutropenia. Changes in neutrophil function have also been reported; however, it is unclear if these changes indicate a direct effect of the membrane on neutrophils or if they are a consequence of the neutropenia. We tested the hypothesis that neutrophil oxidative burst activity is enhanced during dialysis with cellulose membranes. Resting and Staphylococcus aureus -stimulated H₂O₂ production were determined predialysis and in blood entering and leaving the dialyzer during the first 30 min of dialysis and in blood leaving the membrane module in a single-pass on-line model of hemodialysis. Resting H₂O₂ production increased slightly but significantly during the first 30 min of dialysis. Transit of neutrophils through the dialyzer caused a marked increase in stimulated H₂O₂ production, indicating priming of the oxidative burst. However, priming was limited to the first 5 min of dialysis before the onset of neutropenia. In contrast, stimulation and priming of H₂O₂ production persisted throughout 30 min of single-pass on-line perfusion. These results indicate that cellulose membranes both stimulate and prime neutrophil oxidative burst activity but that these effects are partially obscured by neutropenia.     

Complement Activation During Hemodialysis: Laboratory Evaluation of Hemodialyzers

A laboratory method that facilitates delineation of the complement-activating characteristics of various dialyzers under defined conditions has been developed. Results obtained by circulating reconstituted human serum through these devices and measuring time-dependent production of both C3a and C5a antigens are entirely consistent with previous clinical observations. For example, the complement-activating potential of dialyzer membranes could be described as high (cuprammonium cellulose), moderate (cellulose acetate), or low (polycarbonate or polyacrylonitrile). Furthermore, these techniques provided the opportunity to identify membrane characteristics that are not readily defined by clinical studies alone. Specifically, membranes that transported and absorbed C5a antigen were readily identified by these methods. Additionally, laboratory evaluation provided the unique ability to define the efficiency of complement activation taking place on the membrane surface. Results of these investigations are compatible with a hypothetical model that not only describes the properties of a typical dialyzer membrane but may be generally applicable to other biomaterials as well.     

Adsorption of Nafamostat Mesilate by Hemodialysis Membranes

The adsorption of the anticoagulant nafamostat mesilate (FUT-175) by five different hemodialysis membranes was studied in vivo and in vitro. In vivo, FUT-175 was adsorbed strongly by a polyacrylonitrile (AN69) membrane and slightly by another polyacrylonitrile (J-PAN) membrane but not by Cuprophan (CU), hemophan (HE), or polymethylmethacrylate (PMMA) membranes during hemodialysis performed in 4 patients in whom FUT-175 was used as an anticoagulant. Only during hemodialysis using the AN69 membrane did FUT-175 not induce a significant prolongation of celite-activated coagulation time. In vitro studies showed that FUT-175 was adsorbed by the AN69, J-PAN, and PMMA membranes but not by the CU and HE membranes. Methylene blue, a dye that possesses a cationic portion in its chemical structure, stained AN69, J-PAN, and PMMA membranes. Since FUT-175 also possesses a cationic portion, we conclude that FUT-175 is adsorbed by negatively charged membranes via an ionic bond and is unsuited for use as an anticoagulant in hemodialysis using an AN69 membrane because of that membrane's marked capacity to adsorb FUT-175.     

Activation of Basophils Is a New and Sensitive Marker of Biocompatibility in Hemodialysis

The hemodialysis procedure involves contact between peripheral blood and the surface of dialyzer membranes, which may lead to alterations in the pathways of innate and adaptive immunity. We aimed to study the effect of blood–membrane interaction on human peripheral basophils and neutrophils in hemodialysis with high‐ and low‐permeability polysulfone dialyzers. The surface expression of CD203c (basophil selection marker) and CD63 (activation marker) after activation by the bacterial peptide formyl‐methionyl‐leucyl‐phenylalanine (fMLP) or anti‐Fcε receptor I (FcεRI) antibody and the absolute number of basophils was investigated before and after hemodialysis with each of the dialyzers. Moreover, the expression on neutrophils of CD11b, the CD11b active epitope, and CD88 was analyzed in the same groups of individuals. The expression of CD63 in basophils following activation by fMLP was significantly higher in the patient group compared with that in healthy controls, but no differences were observed after activation by anti‐FcεRI. During the hemodialysis procedure, the low‐flux membrane induced up‐regulation of CD63 expression on basophils, while passage through the high‐flux membrane did not significantly alter the responsiveness. In addition, the absolute number of basophils was unchanged after hemodialysis with either of the dialyzers and compared with healthy controls. We found no significant differences in the expression of the neutrophil activation markers (CD11b, the active epitope of CD11b, and CD88) comparing the two different dialyzers before and after dialysis and healthy controls. Together, these findings suggest that alterations in basophil activity may be a useful marker of membrane bioincompatibility in hemodialysis.     

Extraction of Serum Proteins Adsorbed on the Surface of Dialysis Membranes

Abstract: Extraction of adsorbed proteins from dialysis membranes that had been used during actual hemodialysis procedures was performed. The condition of extraction with SDS plus 2–mercaptoethanol at 95°C is more efficient than with only PBS or with SDS solution without 2–mercaptoethanol at 37°C.     

The Effects of Endotoxin–Contaminated Dialysate and Polysulfone or Cellulosic Membranes on the Release of TNFα during Simulated Dialysis

Abstract: Simulated dialysis of whole blood was used to determine whether membrane factors (biocompatibility), endotoxin (ET) membrane diffusion, or transmembrane monocyte–ET interactions would stimulate tumor necrosis factor (TNFα) release. Whole blood containing EDTA and aprotinin was recirculated in the blood compartment of hollow fiber dialyzers containing either regenerated cellulose or polysulfone membranes. ET–free and ET–spiked dialysate were recirculated consecutively in the dialysate compartment for 30 min each. Blood and dialysate samples were collected at t _o and after each 30 min of simulated dialysis for determination of TNFa and ET concentrations. TNFa was not detected in any blood samples collected after simulated dialysis with regenerated cellulose (RC) membranes and ET–free or ET–spiked dialysate. However, blood ET concentrations, as determined by the Limulus amebocyte lysate (LAL) assay, increased in RC dialyzers after each 30 min of simulated dialysis even with ET–free dialysate. Since TNFa was not detected in these blood samples, the material detected by the LAL assay probably was not ET but an LAL–reactive material. After simulated dialysis with polysulfone dialyzers and ET–free dialysate, TNFa and ET were not detected in blood samples. ET also was not detected in blood samples after dialysis with ET–spiked dialysate. However, TNFa was detected in 7 of 13 (54%) of the blood samples following the 500 ng/ml of ET dialysate spike. TNFα release during simulated dialysis with polysulfone membranes and ET–contaminated dialysate may be due to transmembrane stimulation of circulating mononuclear cells and not diffusion of ET across the membrane.     

Soluble TNFα Receptors Are Increased in Chronic Renal Insufficiency and Hemodialysis and Inhibit Neutrophil Priming by TNFα

Abstract: The oxidative burst of neutrophils from azotemic patients is refractory to priming by tumor necrosis factor-α (TNFα). Soluble TNFα binding proteins (TNFR) accumulate in the plasma of azotemic patients. To test the hypothesis that these increased sTNFR concentrations inhibit TNFa priming of oxidative burst activity, we measured plasma sTNFR concentrations in nondialyzed azotemic patients, hemodialysis patients, and normal subjects, and determined TNFa priming of fMet-Leu-Phe-stimulated superoxide production in neutrophils incubated in plasma with differing levels of sTNFR. These sTNFR concentrations increased significantly as creatinine clearance decreased and were significantly greater in hemodialysis patients than could be accounted for by loss of renal function alone. TNFα primed superoxide production by normal neutrophils in normal plasma, but this effect was significantly reduced in plasma with increased concentrations of sTNFR. Neutrophils from azotemic and hemodialysis patients were refractory to priming by TNFα in autologous plasma, and incubation in normal plasma only partially corrected this defect. We conclude that sTNFR accumulate as a result of the loss of renal function and hemodialysis and inhibit TNFα priming of neutrophils in azotemic and hemodialysis patients, but that these cells also have an intrinsic functional defect.     

Influence of Hemodialysis Membranes on Gene Expression and Plasma Levels of Interleukin-iβ

Abstract: Plasma levels of interleukin-iβ (IL-iβ) were measured in 10 normal subjects, in 11 nondialyzed end-stage renal failure (ESRD) patients, and in 22 hemodialysis (HD) patients. Of the HD patients, 7 were dialyzed with Cuprophan (CU), 7 with polymethylmethacrylate (PMMA), and 8 with polysulphone (PS) dialyzers. In normal controls, nondialyzed ESRD patients, and HD equipped with CU, PAMM, and PS dialyzers, plasma levels of IL-iβ were 10.73 ± 5.24 pg/ml, 9.97 ± 3.61 pg/ml, 13.17 ± 4.04 pg/ml, 15.16 ± 6.16 pg/ml, and 13.96 ± 5.47 pg/ml, respectively. There were no statistically significant differences among the groups (p ≥ 0.05). In contrast, the gene expression of IL-iβ for peripheral blood mononu-clear cells (PBMC) by in situ hybridization showed differences among the groups. The gene for IL-iβ for PBMC appears in HD equipped with different membranes, but not in cases of nondialyzed uremic patients and normal subjects. With computer imaging analysis, we carried out quantitative analysis of cells in in situ hybridization with an area of positive spots to an area of total cells. In HD with CU, PMMA, and PS, the results were 10.64 ± 1.07, 3.34 ± 0.74, and 3.27 ± 0.64%, respectively. The levels of IL-iβ gene expression in CU were higher than that in PMMA or PS. There were statistically significant differences (p ≤ 0.001) between CU and PMMA or PS and no significant difference between the PMMA and PS (p ≥ 0.05). We suggest measuring the gene expression of cy-tokines for PBMC and which may be better than measuring cytokine levels only for investigating the blood compatibility of dialyzers, which may help in understanding chronic complications of the dialysis procedure.     

Dialyzer Membranes: Effect of Surface Area and Chemical Modification of Cellulose on Complement and Platelet Activation

Using an ex vivo model, the effects of membrane composition and surface area on both the complement system (as reflected by plasma C3a levels) and platelets [as indicated by plasma concentrations of thromboxane B2 (TXB2) and platelet factor 4 (PF4)] were studied. In this model, polyacrylonitrile (PAN) was associated with less complement activation than cuprammonium cellulose (CC). A new "modified cellulose" (MC) membrane, in which a small number of the free hydroxyl groups on cellulose are substituted with a tertiary amino compound, was also associated with a low degree of complement activation, similar to that with PAN. However, the extent of hydroxyl group substitution in four MC membrane subtypes did not correlate with the reduction in complement activation. In studies using CC, the amount of generated C3a correlated with the membrane surface area, although the relationship was curvilinear. Plasma concentrations at the "dialyzer" outlet of TXB2 and PF4 were similar with CC, PAN, and MC. In studies with the MC subtypes, increasing the extent of hydroxyl group substitution paradoxically increased, albeit slightly, the amount of TXB2 generation. In studies with CC, a linear relationship between membrane surface area and TXB2 generation was found. The results suggest a dissociation between platelet and complement effects among different dialyzer membranes, and underline the importance of membrane surface area.     

Study on Adsorption Mechanism of Proteins Onto Synthetic Calcium Hydroxyapatites Through Ionic Concentration Measurements

To clarify the adsorption mechanism of proteins onto calcium hydroxyapatite (Hap), the kinetic studies of dissolution and ion-exchange properties of synthetic Hap particles in the absence and presence of proteins were examined at 15°C. In the absence of proteins, Hap particles slightly dissolved to give low amounts of calcium ([Ca²⁺] = 0.09-0.14 mol m^-2) and phosphate [PO₄^3-] = 0.01-0.08 mol m^-2) ions in KCl, CaCl₂, BaCl₂ and AlCl₃ solutions. The [Ca²⁺] increased with increase in the Ca/P ratio of Hap, while the [PO₄^3-] decreased. The[ Ca²⁺] and [ PO₄^3-] were independent of the ionic strength. Ba²⁺ and AI³⁺ ions were completely ion-exchanged with calcium ions in Hap lattice within 2 hr. The solution pH was increased by 1.1-1.8 after the dissolution of OH^- ions on the Hap surface. In the presence of bovine serum albumin (BSA), the Hap particles dissolved slightly faster than the systems without protein. This fact was explained by a complexation of dissolved ions to functional groups of BSA. The adsorption of BSA induced a reduction of [Ca²⁺] and [ PO₄^3-] in the aqueous medium and minima appeared on [Ca²⁺] and [PO₄^3-] profiles before the BSA adsorption reached a saturation. This result suggests that the adsorption of BSA onto Hap is governed by [Ca²⁺] ions complexing to BSA molecules (binding effect) together with the operation of [Ca²⁺] ions exposing on the Hap surfaces by dissolution of OH^- ions, so-called C-sites. The addition of BaCl₂ and AlCl₃ steeply increased the amounts of adsorbed BSA (n^BSA) at the initial adsorption step by the strong binding effect of these di- and tri-valent cations between BSA and Hap. However, after eliminating these cations from the Hap surface by the ion-exchange reaction, the binding effects disappeared and n^BSA decreased. Since the number of functional groups is small, the binding effect of the counter ions was only slightly detected for the systems with di- and trivalent ions on the adsorption systems of lysozyme (LSZ).