Novel C5-dependent mechanism of neutrophil stimulation by bioincompatible dialyzer membranes

Immunological Effects of a Single Hemodialysis Treatment

Immune disorders, involving both innate and adaptive response, are common in patients with end-stage renal disease under chronic hemodialysis. Endogenous and exogenous factors, such as uremic toxins and the extracorporeal treatment itself, alter the immune balance, leading to chronic inflammation and higher risk of cardiovascular events. Several studies have previously described the immune effects of chronic hemodialysis and the possibility to modulate inflammation through more biocompatible dialyzers and innovative techniques. On the other hand, very limited data are available on the possible immunological effects of a single hemodialysis treatment. In spite of the lacking information about the immunological reactivity related to a single session, there is evidence to indicate that mediators of innate and adaptive response, above all complement cascade and T cells, are implicated in immune system modulation during hemodialysis treatment. Expanding our understanding of these modulations represents a necessary basis to develop pro-tolerogenic strategies in specific conditions, like hemodialysis in septic patients or the last session prior to kidney transplant in candidates for receiving a graft.

Mode of renal replacement therapy determines endotoxemia and neutrophil dysfunction in chronic kidney disease

Bacterial infection and sepsis are common complications of chronic kidney disease (CKD). A vicious cycle of increased gut permeability, endotoxemia, inadequate activation of the innate immune system and resulting innate immune dysfunction is hypothesized. We assessed endotoxemia, neutrophil function and its relation to oxidative stress, inflammation and gut permeability in patients with CKD grade 3–5 without renal replacement therapy (CKD group, n = 57), patients with CKD stage 5 undergoing haemodialysis (HD, n = 32) or peritoneal dialysis (PD, n = 28) and patients after kidney transplantation (KT, n = 67) in a cross-sectional observational study. In HD patients, endotoxin serum levels were elevated and neutrophil phagocytic capacity was decreased compared to all other groups. Patients on HD had a significantly higher mortality, due to infections during follow up, compared to PD (p = 0.022). Oxidative stress, neutrophil energy charge, systemic inflammation and gut permeability could not completely explain these differences. Our findings suggest that dialysis modality and not renal function per se determine the development of neutrophil dysfunction and endotoxemia in CKD-patients. HD patients are particularly prone to neutrophil dysfunction and endotoxemia whereas neutrophil function seems to improve after KT. Multi-target approaches are therefore warranted to improve neutrophil function and potentially reduce the rate of infections with patients undergoing haemodialysis.

Complement activation by neutrophil granulocytes

Complement plays a vital role in the body's defence systems. Cardiopulmonary bypass induces a detrimental inflammatory reaction in which the complement system is known to participate through direct effects as well as through activation of neutrophils, platelets and endothelial cells. On the other hand, it has been suggested that in the setting of cardiopulmonary bypass, complement may be activated by neutrophils, perhaps due to fragmentation caused by the heart-lung machine. We therefore investigated whether intact or fragmented neutrophils were able to activate the complement system, and whether neutrophil-platelet interaction could influence such complement activation. Lepirudin-anticoagulated plasma was incubated at 37 degrees C with resting or activated intact neutrophils or neutrophils combined with platelets, or increasing amounts of fragmented neutrophils. Complement activation was evaluated by measurement of C1rs-C1 inhibitor complexes, C4bc, C3bBbP, C3bc, C5a and sC5b-9. We found significant activation of complement only by unphysiological doses of fragmented neutrophils or supernatant from fragmented neutrophils, consistent with a limited clinical significance related to neutrophil destruction during cardiopulmonary bypass. Unstimulated neutrophils induced C3bPBb formation but little formation of other activation products, indicating an increased C3 hydrolysis which was kept under control by regulatory mechanisms. Neutrophils and platelets combined increased classical activation and decreased alternative activation, similar to the findings with platelets alone. Our data confirm that in the setting of acute neutrophil fragmentation or activation, complement activation is much more important in the inflammatory network as an event upstream to neutrophil activation than vice versa.

In vitro--transcriptional response of polymorphonuclear leukocytes following contact with different antigens

Background Human polymorphonuclear neutrophils (PMN) are activated and undergo apoptosis if brought into contact with cuprophane haemodialysis membranes, a phenomenon not observed if more 'biocompatible' polysulfone dialysers are used. It remains yet to be defined if this differential response is due to mechanisms regulated on a transcriptional or protein level. Furthermore, it is not clear if the contact of PMN with membranes ('frustrated' phagocytosis) activates the same response as phagocytosis of bacteria (complete phagocytosis). Materials and methods We performed a genome-wide differential gene expression study using cDNA microarrays to analyse the impact of different dialysis fibres on the transcriptional response of PMN of human healthy volunteers. These results were compared to transcriptional response of PMN during phagocytosis of Escherichia coli. Results We did not detect significant differences in gene expression between PMN stimulated with cuprophane or pulysulfone. Compared to unstimulated PMN the 'frustrated' phagocytosis of either dialysis membrane resulted in increased expression of 50 genes, with a marked up-regulation of FOS - and JUN - transcripts, but with only little activation of immune response genes, and virtually no activation of apoptosis related RNA transcripts. In contrast, phagocytosis of E.coli was associated with a striking up-regulation of 88 genes, most of them involved in pro- and antiapoptotic pathways, immune response and activation of nuclear factor kappa B and inhibitor of NF-kappa B. Conclusions Our results suggest that the response of PMN to artificial surfaces is not controlled on transcriptional level. Complete and 'frustrated' phagocytosis activate markedly distinct transcriptional regulatory pathways in PMN.

Expression of granzyme A in human polymorphonuclear neutrophils

Polymorphonuclear neutrophils (PMNs) are the first line of defence against invading pathogens. They contain a multitude of antimicrobial and potentially cytotoxic substances packed in granules and secretory vesicles. Here, we show that granzyme A (GzmA) is constitutively expressed in human PMNs, but not in the promyelocytic cell line HL-60, by performing flow cytometry, western blot, enzyme-linked immunosorbent assay and quantitative polymerase chain reaction. To further track the intracellular localization of GzmA, we performed subcellular fractionation and found GzmA to be present in peroxidase-negative granules. Finally, stimulation with opsonized Escherichia coli or the bioincompatible haemodialysis membrane cuprophane led to up-regulation of GzmA expression at the transcriptional level as well as at the translational level. In conclusion, we provide clear evidence that GzmA is constitutively expressed in human PMNs and can be up-regulated upon stimulation. These findings may also indicate a role for GzmA in PMNs in defence against invading pathogens.

Platelet activation through interaction with hemodialysis membranes induces neutrophils to produce reactive oxygen species

The intradialytic activation of leukocytes is one of the major causes of hemodialysis-associated complications. During hemodialysis, the formation of microaggregates consisting of platelets and neutrophils has been observed to accompany the production of reactive oxygen species (ROS) by leukocytes. In this study, we investigated the interaction of platelets and neutrophils with hemodialysis membranes in vitro to elucidate the mechanism underlying microaggregate formation and its relevance to leukocyte activation. The production of ROS in neutrophils was induced by the coincubation of neutrophils with polysulfone (PS) membranes, and was increased when platelets were present in the neutrophil suspension. Neutrophils that were incubated with polymethylmethacrylate (PMMA) membranes in the presence of platelets also produced significant levels of ROS, suggesting that the presence of platelets augmented ROS production in neutrophils. Platelets adhered more firmly to hydrophobic membranes such as PS and PMMA membranes than to hydrophilic membranes, such as those composed of regenerated cellulose (RC) or ethylene vinylalcohol copolymer (EVAL). The adhesion of platelets to dialysis membranes composed of different materials was correlated with those membranes' ability to induce platelet activation as assessed by the cell surface expression of P-selectin. Moreover, coincubation of neutrophils with platelets that had been treated with hydrophobic membranes induced a higher level of superoxide anion relative to those treated with hydrophilic membranes in association with the P-selectin-mediated microaggregate formation. These results suggest that platelets activated through interaction with hemodialysis membranes stimulate neutrophils to produce ROS via P-selectin-mediated adhesion, and that this property of adhesion to platelets is critical for the biocompatibility of hemodialysis membranes.

Complement inhibition reduces material-induced leukocyte activation with PEG modified polystyrene beads (Tentagel™) but not polystyrene beads

With isolated leukocytes, inhibiting complement reduced material-induced leukocyte activation (CD11b) with polyethylene glycol modified polystyrene beads (PS-PEG), but not with polystyrene beads (PS). The PS-PEG beads (TentaGel) were complement activating as measured by SC5b-9 levels consistent with the sensitivity of these beads to leukocyte inhibition with complement inhibitors. Following contact with PS and PS-PEG beads, isolated leukocytes in plasma and in the absence in platelets were found to significantly upregulate CD11b, while TF expression and exposure of phosphatidylserine remained at background levels. Complement inhibition by means of sCR1 partially reduced CD11b upregulation on PS-PEG beads, but had no effect with PS beads. Pyridoxal-5-phosphate (P5P) was able to significantly reduce both CD11b upregulation and exposure of phosphatidylserine with PS-PEG beads, although it did not appear to inhibit SC5b-9 production. Pentamidine and NAAGA inhibited complement and were effective in reducing CD11b upregulation with both PS and PS-PEG. However, they also had an inhibitory effect on leukocyte signaling mechanisms, precluding their utility for further study in this context. Leukocyte adhesion occurred to similar extents on both PS and PS-PEG beads. While sCR1 and P5P blocked adhesion and activation (for adherent leukocytes) on PS-PEG beads, they had no effect on leukocytes adherent to PS beads. The role of complement in leukocyte activation and adhesion was found to be material-dependent. Thus, leukocyte-material compatibility may be resolved by complement inhibition in some but not all cases. For these other materials (example here was PS), other mechanisms, such as fibrinogen adsorption and direct leukocyte release, may need exploitation to minimize leukocyte activation and adhesion.

Apoptosis of human polymorphonuclear neutrophils accelerated by dialysis membranes via the activation of the complement system

BACKGROUND

Haemodialysis (HD) with bioincompatible cellulosic membranes like Cuprophan (CU) is considered to influence negatively the clinical outcome of acute and chronic renal failure. In this effect, apart from the disturbance of phagocytosis or oxygen species production by leukocytes, increased apoptosis also has been implicated recently. The objective of this study was to study the effect of HD membranes on apoptosis induction in polymorphonuclear neutrophils (PMN).

METHODS

PMN from healthy donors and uraemic patients were isolated and apoptosis was induced by co-incubation with CU, Hemophan or polyamide hollow fibres in the presence of serum from healthy or uraemic humans. Apoptosis was quantified by flow cytometry using Annexin V-FITC and propidium iodide staining and was confirmed by the detection of DNA fragmentation on gel electrophoresis. The deposition of immunoglobulins (Ig) and complement factors on hollow fibres was detected by direct immunofluorescence.

RESULTS

Heat inactivation or the depletion of complement components or Ig significantly reduced apoptosis, indicating its dependence on classical complement activation. The detection of IgG on hollow CU fibres and the restored acceleration of apoptosis by the appropriate replenishment of Ig-deficient sera additionally confirmed these findings. Inhibition experiments revealed that caspases were necessary mainly, but not exclusively, for apoptosis to occur after complement activation. Uraemia led to increased PMN apoptosis in the presence of bioincompatible, but not biocompatible, membranes.

CONCLUSIONS

Our results suggest that the acceleration of PMN apoptosis in the presence of CU is mediated via an antibody-dependent activation of the classical complement pathway mobilizing both caspase-dependent and -independent pathways.

Hemodialysis Membranes: Interleukins, Biocompatibility, and Middle Molecules

ABSTRACT. Maintenance hemodialysis patients display evidence of elevated interleukin-1 (IL-1) and tumor necrosis factor alpha release after stimulation either by contaminated dialysate, bioincompatible membrane material, or both. This release is followed by the stimulated secretion of a large number of other interleukins, particularly IL-6, the cytokine principally responsible for acute-phase protein synthesis. It has been shown that high levels of the circulating proinflammatory cytokines IL-1, tumor necrosis factor alpha, IL-6, and IL-13 are associated with mortality in hemodialysis patients. Essential functions of polymorphonuclear leukocytes—that is, phagocytosis, oxygen species production, upregulation of specific cell surface receptor proteins, or apoptosis—are disturbed in patients with end-stage renal disease. These are further altered as a result of complement activation by the hemodialysis procedure, particularly if bioincompatible dialyzers are used. Polymorphonuclear leukocyte degranulation occurring during extracorporeal circulation does not depend on complement activation but rather on intracellular calcium and the presence or absence of the degranulation inhibitory proteins angiogenin and complement factor D. Clinical signs and symptoms of end-stage renal disease patients are at least in part related to the accumulation of middle molecules such as β2-microglobulin, parathyroid hormone, advanced glycation end products, advanced lipoxidation end products, advanced oxidation protein products (formed as a result of oxidative stress, carbonyl stress, or both), granulocyte inhibitory proteins, or leptin. Currently available membrane materials do not provide long-lasting, effective reduction of middle molecules in patients who require maintenance hemodialysis.

Specific inhibition of C3 to facilitate general complement inhibition on endotoxin affinity sorbents for apheresis applications

Complement activation, as a result of human blood exposure to biomaterial surfaces, continues to be a concern in medical applications. The purpose of this study was to identify sorbent(s) and surface modification(s) that allow specific removal of endotoxin, while minimizing complement activation. Maleic anhydride (MA) modification of Sepharose CL-4B, cellulose, and Toyopearl HW-65F resulted in reduced generation of C3a, a marker of complement activation, by two orders of magnitude over unmodified surfaces. Surfaces modified with both MA and polymyxin B (PMB), utilized for binding endotoxin, reduced complement activation in a similar manner. Western Blot analysis of the larger C3 cleavage product C3dg showed a similar reduction, for all MA-modified sorbents, as observed for C3a by ELISA. C3alpha43 levels (constituent of iC3b and C3c) were also reduced, although only MA-Sepharose CL-4B levels were similar to C3a. Activation of C5, measured as the SC5b-9 complex, was also reduced by two orders of magnitude after MA modification of Sepharose CL-4B; the decrease was similar to all chemical modifications tested. PMB immobilized via CNBr on MA-modified cellulose maintained its endotoxin-binding capacity, while the latter was eliminated when PMB was immobilized via CNBr to MA-modified Sepharose CL-4B and Toyopearl HW-65F.

Serum proteins modified by neutrophil-derived oxidants as mediators of neutrophil stimulation

Reactive oxygen intermediates (ROI) released during inflammation may act as important mediators of neutrophil effector functions. The objective of this investigation was to evaluate the influence of ROI generation on neutrophil adhesion molecule regulation and degranulation. Induction of the neutrophil oxidative burst via Fcgamma receptor cross-linking was accompanied by up-regulation of neutrophil surface CD11b, CD35, and CD66b only in the presence of selected serum proteins, such as purified human C4, C5, or human serum albumin (HSA). Scavenging of ROI attenuated protein-dependent receptor regulations. Moreover, exogenous hydrogen peroxide was effective to increase neutrophil CD11b expression in a protein-dependent way. HSA exposed to neutrophil-derived ROI displayed signs of oxidative modification in terms of carbonyl formation. Such modified HSA transferred to resting neutrophils bound readily to the cell surface and effected receptor modulation as well as cellular spreading. In contrast, neither native HSA nor HSA protected against oxidation by the tocopherol analog Trolox exhibited agonistic properties. In conclusion, we demonstrate that neutrophil-derived ROI modify selected serum proteins, which, in turn, act as proinflammatory mediators of neutrophil stimulation.

Effect of vitamin C on neutrophil function after high-intensity exercise

High-intensity exercise leads to an increased risk of upper respiratory tract infections in athletes, which had been related to an exercise-induced impairment of neutrophil function. In this study, several indices of neutrophil function were analysed before and after a biathlon and the effect of oral vitamin C on neutrophil function was determined. Six athletes took 2 g vitamin C daily for 1 week prior to a biathlon and four athletes did not take any supplementation. Neutrophil phagocytosis was analysed by fluorescence microscopy and flow cytometry. Cytosolic calcium kinetics were assessed fluorometrically and neutrophil bactericidal ability was assessed by fluorescence microscopy. Reactive oxygen production was analysed by flow cytometry. Catecholamines were analysed by high-performance liquid chromatography. After high-intensity exercise there were significant reductions in the number of phagocytosed Escherichia coli per neutrophil and in neutrophil bactericidal ability. There was a significant exercise-dependent increase of catecholamines. There was no difference between the two groups of athletes. These results do not support the concept that vitamin C supplementation corrects neutrophil dysfunction after strenuous exercise.

Complement-dependent acceleration of apoptosis in neutrophils by dialyzer membranes

Recently, we have shown that cuprophan (CU) causes receptor modulation by a C5-dependent mechanism, which is activated by neutrophil-derived reactive oxygen intermediates. The objective of our study was to evaluate the contribution of dialyzer membranes to the induction of apoptosis in human neutrophils [polymorphonuclear cells (PMNs)]. PMNs harvested from healthy donors were incubated with hollow fibers from a biocompatible membrane polysulfone (PS) and a bioincompatible membrane CU, all in the presence of 25% human serum. After 4, 8, and 12 hours of incubation at 37 degrees C, apoptosis was quantitated by counting the numbers of cells showing features of apoptosis on cytospins by light microscopy and also by flow cytometry using propidium iodide nuclear staining. Compared with PMNs incubated with serum alone, cells cultured with fibers of PS demonstrated a higher percentage of apoptosis. Fibers from CU dialyzers led to a more pronounced induction of apoptosis in PMNs, which was significantly higher compared with PS. This effect was partly mediated by heat-sensitive serum products and depended on the presence of divalent cations. In contrast to the recently described C5-dependent pathway in PMN receptor modulation by CU, this effect seemed to depend on the presence of the complement factor C3. In conclusion, our results indicate that besides the well-known accelerated apoptosis of PMNs in uremia, both biocompatible and bioincompatible dialyzer material itself can accelerate apoptosis in human PMNs.

Activation and control of complement, inflammation, and infection associated with the use of biomedical polymers

It is generally acknowledged that artificial biomaterials are much less immunologically active than transplants or tissue derived biomaterials. However, activation of both the coagulation cascade and the complement system is a common occurrence when human blood is exposed to biomaterial surfaces during extracorporeal procedures, such as renal hemodialysis or cardiopulmonary bypass. Both individual and collective activation of these cascades often produce local and systemic effects. A number of complement activation products function as the mediators of inflammation. They serve as ligands for specific receptors on polymorphonuclear leukocytes, monocytes, macrophages, mast cells, and other cells. Such an interaction leads to induction of cellular responses in adhered cells, including release of oxidative products, lysosomal enzymes, or both, which often contribute to a number of pathologic conditions. Most pathogens invading the human body are attacked by the immune system directly following entry, especially when they are in contact with blood. However, bacteria and parasites have developed a large number of specific strategies to overcome immune defense among others by avoiding either recognition or eradication by complement. In this aspect, of concern are several microorganisms responsible for formation of antibiotic resistant biofilms on biomaterial surfaces, namely Staphylococcus epidermidis, Staphylococcus aureus, and Pseudomonas aeruginosa.

Polymorphonuclear granulocyte stimulation by cellulose-based hemodialysis membranes

Hemodialysis with cellulose-based membranes is associated with an array of adverse reactions, including leukopenia, pulmonary sequestration and dysfunction of leukocytes. Activation of the alternative pathway of complement due to direct contact of plasma with dialysis membrane is considered to be responsible for the induction of these side effects. In recent years, evidence has accumulated that other neutrophil effector functions such as reactive oxygen intermediate production play an important role as well. Here the importance of burst formation in cooperation with other inflammatory effector functions in the mechanisms of hemodialysis-related adverse effects will be discussed.