Mechanisms of biomaterial-induced superoxide release by neutrophils

A barrier against reactive oxygen species: chitosan/acellular dermal matrix scaffold enhances stem cell retention and improves cutaneous wound healing

Background

Stem cell therapies have gained great attention for providing novel solutions for treatment of various injuries and diseases due to stem cells’ self-renewal, ability to differentiate into various cell types, and favorite paracrine function. Nevertheless, the low retention of transplanted stem cell still limits their clinical applications such as in wound healing in view of an induced harsh microenvironment rich in reactive oxygen species (ROS) during inflammatory reactions.

Methods

Herein, a novel chitosan/acellular dermal matrix (CHS/ADM) stem cell delivery system is developed, which is of great ROS scavenging activity and significantly attenuates inflammatory response.

Result

Under ROS microenvironment, this stem cell delivery system acts as a barrier, effectively scavenging an amount of ROS and protecting mesenchymal stem cells (MSCs) from the oxidative stress. It notably regulates intracellular ROS level in MSCs and reduces ROS-induced cellular death. Most importantly, such MSCs delivery system significantly enhances in vivo transplanted stem cell retention, promotes the vessel growth, and accelerates wound healing.

Conclusions

This novel delivery system, which overcomes the limitations of conventional plain collagen-based delivery system in lacking of ROS-environmental responsive mechanisms, demonstrates a great potential use in stem cell therapies in wound healing.

The Role of In Vitro Immune Response Assessment for Biomaterials

Grafts are required to restore tissue integrity and function. However, current gold standard autografting techniques yield limited harvest, with high rates of complication. In the search for viable substitutes, the number of biomaterials being developed and studied has increased rapidly. To date, low clinical uptake has accompanied inherently high failure rates, with immune rejection a specific and common end result. The objective of this review article was to evaluate published immune assays evaluating biomaterials, and to stress the value that incorporating immune assessment into evaluations carries. Immunogenicity assays have had three areas of focus: cell viability, maturation and activation, with the latter being the focus in the majority of the literature due to its relevance to functional outcomes. With recent studies suggesting poor correlation between current in vitro and in vivo testing of biomaterials, in vitro immune response assays may be more relevant and enhance ability in predicting acceptance prior to in vivo application. Uptake of in vitro immune response assessment will allow for substantial reductions in experimental time and resources, including unnecessary and unethical animal use, with a simultaneous decrease in inappropriate biomaterials reaching clinic. This improvement in bench to bedside safety is paramount to reduce patient harm.

Measurements for Sulfide-Mediated Inhibition of Myeloperoxidase Activity

Oxidative stress-alleviating and inflammation-mediatory functions of hydrogen sulfide were reported to be key features of its biological actions. However, the underlying molecular mechanisms of these biological observations are not fully understood. In conditions where sulfide was proposed to be protective against oxidative stress- or inflammation-induced tissue damage (e.g., reperfusion injury, atherosclerosis, vascular inflammation), the reactive oxidant-producing function of a key neutrophil enzyme, myeloperoxidase, was reported to be a protagonist on the detrimental side. We recently described favorable interactions between sulfide and myeloperoxidase and proposed that the potent inhibition of myeloperoxidase activities could contribute to sulfide's beneficial functions in a number of cardiovascular pathologies. Our chapter is dedicated to aid future studies and drug development endeavors in this area by providing methodological guidance on how to assess the inhibitory potential of sulfide on myeloperoxidase enzymatic activities in isolated protein systems, in neutrophil homogenates, and in live neutrophil preparations.

A systems approach to modeling drug release from polymer microspheres to accelerate in vitro to in vivo translation

Mathematical models of controlled release that span the in vitro to in vivo transition are needed to speed the development and translation of clinically-relevant controlled release drug delivery systems. Fully mechanistic approaches are often challenged due to the use of highly-parameterized mathematically complex structures to capture the release mechanism. The simultaneous scarcity of in vivo data to inform these models and parameters leads to a situation where overfitting to capture observed phenomena is common. A data-driven approach to model development for controlled drug release from polymeric microspheres is taken herein, where physiological mechanisms impacting controlled release are incorporated to capture observed changes between in vitro release profiles and in vivo device dynamics. The model is generalizable, using non-specific binding to capture drug-polymer interactions via charge and molecular structure, and it has the ability to describe both inhibited (slowed) and accelerated release resulting from electrostatic or steric interactions. Reactive oxygen species (ROS)-induced degradation of biodegradable polymers was incorporated via a reaction-diffusion formalism, and this suggests that ROS may be the primary effector of the oft-observed accelerated in vivo release of polymeric drug delivery systems. Model performance is assessed through comparisons between model predictions and controlled release of several drugs from various-sized microparticles in vitro and in vivo.

Free Radical Production in Immune Cell Systems Induced by Ti, Ti6Al4V and SS Assessed by Chemiluminescence Probe Pholasin Assay

The oxidative burst of human blood cells in the presence of different metal materials was investigated using chemiluminescence assay. Commercial pure titanium (Ti), titanium alloy (Ti6Al4V), and stainless steel 316L (SS) in particulate form with <20 μm in size were used. The effect of particulate materials opsonisation on the upregulation of the respiratory burst production by blood cells was also assessed. The largest chemiluminescence response was achieved after simultaneous injection of the stimulants fMLP+PMA. Moreover, Ti and SS induced a greater inflammatory reaction compared to Ti6Al4V, since the respiratory burst mounted was higher for both materials after opsonisation treatment. These results suggest that in vitro chemiluminescence response and respiratory burst measurements proved to be composition and treatment dependent.

N-acetyl cysteine improves affinity of beta-tricalcium phosphate granules for cultured osteoblast-like cells

Enhancement of bone substitute's biocompatibility may accelerate healing of surrounding bone. Although widely used as a biodegradable alloplastic bone substitute for alveolar bone augmentation, the osteocompatibility of beta-tricalcium phosphate (β-TCP) remains to be proven. The adverse cellular response to biomaterials is associated with oxidative stress. We hypothesized that commercially available β-TCP granules for clinical use, caused oxidative stress and was not optimal in osteocompatibility and that application of antioxidant amino acid derivative N-acetyl cysteine (NAC) would improve osteoblastic responses to the material. Only 20% of rat calvarial osteoblasts cultured on β-TCP granules remained viable at 24 h after seeding as opposed to 90% on polystyrene. Cell death on β-TCP granules was characterized by necrosis. However, the percentage of viable osteoblasts cultured on β-TCP granules showed a 100% increase with pre-treatment with NAC. NAC restored suppressed alkaline phosphatase activity on β-TCP granules at day 5. Intracellular ROS level on β-TCP granules was 16-fold greater than that on polystyrene, but decreased by half with pre-treatment with NAC. Cell death and intracellular ROS elevation were also induced in polystyrene culture under β-TCP granules even when the osteoblasts were not in direct contact with the β-TCP granules. NAC, however, prevented induction of cell death and elevation of intracellular ROS under β-TCP granules. These results indicate that commercially available β-TCP granules negatively affect cultured osteoblastic viability and function via oxidative stress and that NAC improves these negative responses to the material. This implies enhanced bone regeneration around biodegradable calcium phosphate-based bone substitute by NAC.

The role of multiple toll-like receptor signalling cascades on interactions between biomedical polymers and dendritic cells

Biomaterials are used in several health-related applications ranging from tissue regeneration to antigen-delivery systems. Yet, biomaterials often cause inflammatory reactions suggesting that they profoundly alter the homeostasis of host immune cells such as dendritic cells (DCs). Thus, there is a major need to understand how biomaterials affect the function of these cells. In this study, we have analysed the influence of chemically and physically diverse biomaterials on DCs using several murine knockouts. DCs can sense biomedical polymers through a mechanism, which involves multiple TLR/MyD88-dependent signalling pathways, in particular TLR2, TLR4 and TLR6. TLR-biomaterial interactions induce the expression of activation markers and pro-inflammatory cytokines and are sufficient to confer on DCs the ability to activate antigen-specific T cells. This happens through a direct biomaterial-DC interaction although, for degradable biomaterials, soluble polymer molecules can also alter DC function. Finally, the engagement of TLRs by biomaterials profoundly alters DC adhesive properties. Our findings could be useful for designing structure-function studies aimed at developing more bioinert materials. Moreover, they could also be exploited to generate biomaterials for studying the molecular mechanisms of TLR signalling and DC activation aiming at fine-tuning desired and pre-determined immune responses.

N-acetyl cysteine alleviates cytotoxicity of bone substitute

Lack of cytocompatibility in bone substitutes impairs healing in surrounding bone. Adverse biological events around biomaterials may be associated with oxidative stress. We hypothesized that a clinically used inorganic bone substitute is cytotoxic to osteoblasts due to oxidative stress and that N-acetyl cysteine (NAC), an antioxidant amino acid derivative, would detoxify such material. Only 20% of rat calvaria osteoblasts were viable when cultured on commercial deproteinized bovine bone particles for 24 hr, whereas this percentage doubled on bone substitute containing NAC. Intracellular ROS levels markedly increased on and under bone substitutes, which were reduced by prior addition of NAC to materials. NAC restored suppressed alkaline phosphatase activity in the bone substitute. Proinflammatory cytokine levels from human osteoblasts on the bone substitute decreased by one-third or more with addition of NAC. NAC alleviated cytotoxicity of the bone substitute to osteoblastic viability and function, implying enhanced bone regeneration around NAC-treated inorganic biomaterials.

Phagocyte responses to degradable polymers

Although many biodegradable polymers, such as poly-L-lactic acid and poly-L-glycolic acid, are preferentially composed of biological residues normally present in the human body, implants made of these materials often trigger inflammatory and fibrotic responses. Unfortunately, the mechanisms involved in degradable material-mediated tissue responses remain largely unknown. Using animal implantation and cell culture system models, we found a strong correlation between the rate of material degradation and the degree of inflammatory response to material implants. Furthermore, we have identified that both water-soluble and water-insoluble degradation products are potent triggers of phagocyte activation, including at the least, superoxide production. These results support a new concept that slow degradation may improve the biocompatibility of degradable drug-releasing particles and tissue engineering scaffolds.

Understanding the biodegradation of polyurethanes: from classical implants to tissue engineering materials

After almost half a century of use in the health field, polyurethanes (PUs) remain one of the most popular group of biomaterials applied for medical devices. Their popularity has been sustained as a direct result of their segmented block copolymeric character, which endows them with a wide range of versatility in terms of tailoring their physical properties, blood and tissue compatibility, and more recently their biodegradation character. While they became recognized in the 1970s and 1980s as the blood contacting material of choice in a wide range of cardiovascular devices their application in long-term implants fell under scrutiny with the failure of pacemaker leads and breast implant coatings containing PUs in the late 1980s. During the next decade PUs became extensively researched for their relative sensitivity to biodegradation and the desire to further understand the biological mechanisms for in vivo biodegradation. The advent of molecular biology into mainstream biomedical engineering permitted the probing of molecular pathways leading to the biodegradation of these materials. Knowledge gained throughout the 1990s has not only yielded novel PUs that contribute to the enhancement of biostability for in vivo long-term applications, but has also been translated to form a new class of bioresorbable materials with all the versatility of PUs in terms of physical properties but now with a more integrative nature in terms of biocompatibility. The current review will briefly survey the literature, which initially identified the problem of PU degradation in vivo and the subsequent studies that have led to the field's further understanding of the biological processes mediating the breakdown. An overview of research emerging on PUs sought for use in combination (drug + polymer) products and tissue regeneration applications will then be presented.

Biomaterial-associated thrombosis: roles of coagulation factors, complement, platelets and leukocytes

Our failure to produce truly non-thrombogenic materials may reflect a failure to fully understand the mechanisms of biomaterial-associated thrombosis. The community has focused on minimizing coagulation or minimizing platelet adhesion and activation. We have infrequently considered the interactions between the two although we are generally familiar with these interactions. However, we have rarely considered in the context of biomaterial-associated thrombosis the other major players in blood: complement and leukocytes. Biomaterials are known agonists of complement and leukocyte activation, but this is frequently studied only in the context of inflammation. For us, thrombosis is a special case of inflammation. Here we summarize current perspectives on all four of these components in thrombosis and with biomaterials and cardiovascular devices. We also briefly highlight a few features of biomaterial-associated thrombosis that are not often considered in the biomaterials literature: The importance of tissue factor and the extrinsic coagulation system. Complement activation as a prelude to platelet activation and its role in thrombosis. The role of leukocytes in thrombin formation. The differing time scales of these contributions.

Molecular responses of vascular smooth muscle cells and phagocytes to curcumin-eluting bioresorbable stent materials

A major complication of coronary stenting is restenosis, often accompanied by inflammatory reactions and smooth muscle cell proliferation. Curcumin has been shown to possess anti-inflammatory and anti-proliferative properties, thus we hypothesize that locally released curcumin by coronary stent would diminish in-stent restenosis. As a first test of this hypothesis, curcumin-eluting PLLA films (C-PLLA) were produced and the anti-inflammatory and anti-proliferative properties were then tested using peritoneal phagocytes and human coronary artery smooth muscle cell (hCASMCs) culture systems. We find that the addition of curcumin reduced phagocyte accumulation and activation on C-PLLA films. On the other hand, C-PLLA significantly reduced the proliferation, but not the adhesion, of hCASMCs. The molecular responses of hCASMCs to C-PLLA were further assessed by cDNA microarray analysis. Curcumin up-regulated genes related to apoptosis and enhanced the expression of anti-proliferative and anti-inflammatory factors, and of antioxidants. Equally important, C-PLLA inhibited the cell cycle progression of adherent hCASMCs. The results suggest that curcumin regulates gene expression and cell function through the protein kinase (PK) and mitogen-activated protein kinase (MAPK) pathways. These results support the use of curcumin to inhibit in-stent restenosis.

Nanoporous aluminum oxide affects neutrophil behaviour

This study evaluates neutrophil responses on aluminum oxide membranes. Using an in vitro cell culture system, we have found that the pore size (20 and 200 nm in diameter) of alumina membranes have a significant effect on leukocyte morphology and activation. Specifically, our results show that 20-nm pore-size membranes were more potent in triggering PMN spreading and extending of pseudopodia than 200-nm pore-size membranes. The morphological changes are also associated with cell activation. In fact, adherent neutrophils on 20-nm pore-size membranes elicit much stronger initial oxygen free radical production. Overall, our results point out that membrane pore size significantly affects the extent of cellular responses of adherent neutrophils.

Histologic Evaluation of the Tissue Seal and Biologic Response Around Cochlear Implant Electrodes in the Human

HYPOTHESIS

Histopathologic study of the tissue seal and biologic response around cochlear implant electrodes in patients who had received a cochlear implant during life could provide clues concerning the pathogenesis of meningitis after cochlear implantation.

BACKGROUND

Bacterial meningitis has been reported as an infrequent complication of cochlear implantation using a variety of electrode designs. The cause of meningitis in cochlear implant recipients has not been firmly established. In an analogous surgical situation, namely stapedectomy, delayed meningitis could occur as a complication of ipsilateral acute suppurative otitis media in which there was open communication between the middle ear and perilymph.

METHODS

Twenty-one temporal bones from 20 individuals who had undergone cochlear implantation during life were studied by light microscopy. All sections passing through the cochleostomy site and electrode track were examined to evaluate the tissue seal at the cochleostomy, the presence or absence of an extracochlear electrode sheath, and finally, to seek evidence of a cellular inflammatory response near the electrode. These data were compared with clinical data, including electrode system used, the number of years between implantation and death, type of tissue used at surgery, and the age and sex of the patients.

RESULTS

The 21 specimens included cases implanted with the Symbion Ineraid, Cochlear Corporation Nucleus 22-channel, Cochlear Corporation Nucleus 24-channel, a Cochlear Corporation Nucleus single channel, and Advanced Bionics Clarion C1 devices. At the cochleostomy site, and just within the cochlea, there was a robust fibrous and bony tissue response in all 21 ears and in most cases, there was a fibrous sheath surrounding the electrode in the middle ear. No recognizable open communication or potential communication between the middle ear and the inner ear was seen in any of the 21 ears. An inflammatory cellular response, including mononuclear leukocytes, histiocytes, and foreign body giant cells, were present in 12 of the 21 temporal bones (57%) and was most intense at the cochleostomy site. No statistically significant relationship was found between the presence or absence of inflammatory cells and the type of tissue graft used at surgery.

CONCLUSIONS

The histologic evidence presented in this study does not support open communication between the middle and the inner ear as part of the pathogenesis of bacterial meningitis as a late complication after cochlear implantation. Rather, the finding of a cellular inflammatory response in 12 of 21 temporal bones suggests that late hematogenous contamination and colonization of the implant is a much more likely pathogenic mechanism. This putative mechanism has implications for possible strategies to prevent meningitis after cochlear implantation.

Neutrophil survival on biomaterials is determined by surface topography

PURPOSE

Cardiovascular device-centered infections are a major cause of hospital morbidity, mortality, and expense. Caused by opportunistic bacteria, this phenomenon is thought to arise because of a defect in neutrophil bacterial killing. We have shown that neutrophils that adhere to polystyrene remain viable, whereas neutrophils that adhere to the vascular biomaterials expanded polytetrafluoroethylene (ePTFE) and Dacron undergo a rapid nonapoptotic death. This study was designed to test the hypothesis that surface topography is a determinant of the nonapoptotic death response of neutrophils to biomaterials.

METHODS

We took advantage of the ease with which a polystyrene surface can be manipulated to examine the effect of surface topography on neutrophil viability. Neutrophils were exposed to smooth or roughened polystyrene surfaces both in vivo and in vitro. Changes in cell membrane permeability and production of reactive oxygen species by individual cells were monitored with fluorescent dyes.

RESULTS

Host cells and isolated human neutrophils died rapidly after adhesion to roughened polystyrene. Neutrophils adherent to roughened surfaces produced more reactive oxygen intermediates than those adherent to smooth surfaces and were first to die. The cell death response precipitated by expanded polytetrafluoroethylene, Dacron, or the roughened surfaces was significantly reduced with treatment of the neutrophils with catalase, diphenylene iodonium, or the src kinase inhibitor PP2 before adhesion.

CONCLUSIONS

Neutrophil adhesion to roughened materials triggers rapid production of reactive oxygen species and precipitates a nonapoptotic cell death. Understanding the material properties that trigger these responses is essential to development of the next generation of implantable biomaterials.

The influence of plasma proteins and platelets on oxygen radical production and F-actin distribution in neutrophils adhering to polymer surfaces

It is well known that blood cell interactions with artificial surfaces might have deleterious effects on host tissue, however, the mechanisms involved are far from understood. In this study, neutrophil-platelet interaction on uncoated or protein-coated polymer surfaces was investigated. Cell spreading, reorganization of actin filaments and release of oxygen metabolites (measured as luminol-amplified chemiluminescence) were used as criteria for cell activation on positively charged, hydrophilic 1,2-diaminocyclohexane, and negatively charged, hydrophobic hexamethylene-disiloxane. The model surfaces were made by radio frequency plasma discharge polymerization. Neutrophil contact with the uncoated polymers induced a prolonged generation of oxygen radicals. Precoating of the polymer surfaces with human serum albumin (HSA) or fibrinogen, markedly reduced neutrophil activation, whereas coating with human immunoglobulin G (IgG), a well-known opsonin, resulted in significantly higher levels of cell activation. Consequently, protein coating overruled the activating effects of the polymer surfaces. The presence of unstimulated or thrombin-stimulated platelets markedly increased the reactivity of neutrophils against fibrinogen- and IgG-coated surfaces. However, neutrophils remained relatively unreactive in the presence of platelets on HSA-treated surfaces. Comparison of the different types of surfaces used, reveals a correlation between the degree of cell spreading, reorganization of the actin cytoskeleton and the amount of oxygen radicals produced. Our results suggest that the acute inflammatory reaction on a biomaterial surface is highly dependent on the nature and composition of the first adsorbed protein layer and the extent of platelet activation.

Simultaneous measurement of biopolymer-mediated Mac-1 up-regulation and adherence of neutrophils: a novel flow cytometric approach for predicting initial inflammatory interaction with foreign materials

Implantation of any medical device normally causes an inflammatory cell interaction with the foreign material. In vitro cell activation of human neutrophils (Mac-1 upregulation) has been taken as one measure to assess the attributable risk of inflammation due to biopolymers before their clinical application. Mac-1 expression has generally been measured by flow cytometric assays, whereas quantification of neutrophil adhesion to the biopolymer surfaces has been performed by separate and time-consuming assays, e.g. microscopically by differential cell counting. However, due to an increasing number of surface-modified novel biopolymers entering clinical usage, effective testing of their inflammatory potential is now mandatory. To facilitate these analyses, we have developed a novel flow cytometric assay permitting simultaneous measurement of biopolymer-mediated neutrophil activation and adhesion. The biopolymers were used as beads (diameter 25+/-10 microm), and were demonstrated to be non-phagocytosable and non-fluorescent before being co-incubated with whole human blood (range of ratio granulocytes/beads from 5:1 to 1:1). Besides flow cytometric measurement of Mac-1 up-regulated neutrophils as fluorescing events, a fluorescence of the bead population indicates the adherence of activated neutrophils to the biopolymer surface.After establishing this assay, we evaluated it by comparing six different biopolymers. We observed high levels of Mac-1 expression (>70% of positive control) accompanied by increased adhesiveness (>60% of neutrophils) for polyurethane (PUR), polymethylmetacrylate (PMMA), and poly-DL-lactide (PDLLA) beads. Low Mac-1 expression levels (<10%) accompanied by a low percentage of adhering neutrophils (<10%) were observed for polyethylene (PE), polyisoprene (PI), and silicone (SI) beads.

Effect of plasma and matrix proteins on defensin-induced impairment of phagocytic killing by adherent neutrophils

Infection is too often associated with prosthetic devices. Increased susceptibility to infection at these surgical sites appears to be associated with defective local phagocytic killing. The mechanisms for neutrophil down-regulation, however, continue to be obscure. We have recently demonstrated that cytotoxic substances are released from granulocytes associated with materials. One group of releasants, the cationic human neutrophil peptide(s) (also called defensins) not only impairs the antimicrobial capacity of the granulocyte that releases it but also impairs bystander phagocytes. Because plasma or matrix proteins soon become associated with implants, we investigated the interactive effect of adding these proteins, singly and in combination, on the microbicidal effect of bystander cells. Some plasma/matrix proteins (whole plasma, albumin, fibrinogen, and fibronectin) strongly interfered with the anti-microbicidal effects generated by neutrophil-polystyrene interaction. Other proteins (vitronectin and laminin) were without effect. These results suggest that protein composition at the prosthetic implant site could have a significant effect on infectivity, depending on whether neutrophils releasants were attenuated. In the absence of attenuation, the local environment would be hostile to host defenses, permitting bacterial survival and proliferation.

Interactions between human whole blood and modified TiO2-surfaces: influence of surface topography and oxide thickness on leukocyte adhesion and activation

An in vitro model (Nygren et al., J Lab Clin Med 129 (1997) 35-46) was used to investigate interactions between leukocytes and four modified TiO2-surfaces. Surface topography was measured using scanning electron microscopy and optical profilometry while Auger electron spectroscopy was used to determine surface composition and oxide thickness. The surfaces were either smooth or rough with either thin or thick oxides. All surfaces consisted of TiO2 covered by a carbonaceous layer. The surfaces were incubated with capillary blood for time periods of between 8 min and 32 h. Immunofluorescence techniques together with computer aided image analysis and chemiluminescence technique were used to detect cell adhesion, expression of adhesion receptors and the zymosan-stimulated respiratory burst response. Leukocyte adhesion to the surfaces increased during the first hours of blood-material contact and then decreased. Polymorphonuclear granulocytes were the dominating leukocytes on all surfaces followed by monocytes. Cells adhering to rough surfaces had higher normalized expression of adhesive receptors than cells on smooth surfaces. Maximum respiratory burst response occurred earlier on the smooth than on the rough surfaces. In conclusion, topography had a greater impact than oxide thickness on most cellular reactions investigated, but the latter often had a dampening effect on the responses.

Immunoglobulin enhances the bioactive-glass-induced chemiluminescence response of human polymorphonuclear leukocytes

Bioactive glasses are bone substitutes that chemically bind to bone. Implanted materials always elicit a response from surrounding tissues and thereby can activate inflammatory cells, with subsequent release of biomaterial and tissue-damaging agents. Bioactive glasses can activate polymorphonuclear leukocytes (PMNL) and induce a release of reactive oxygen metabolites (ROM). Adsorption of proteins on the surface of the implanted material may influence the subsequent inflammatory cell response. The effect of Sandoglobulin(R) (SG) and albumin on the ROM release by PMNLs induced by a bioactive glass was studied by a chemiluminescence (CL) assay. An enhanced effect for SG and inhibitory effect for albumin on the CL response of PMNLs was observable. The CL response of the PMNLs was dependent on the incubation time of the glass in solution.

Adhesion receptors of polymorphonuclear granulocytes on titanium in contact with whole blood

Titanium sheets were exposed to whole blood, and the TiO(2) surface was investigated regarding the presence of cells, receptor expression on adherent polymorphonuclear (PMN) granulocytes, and the ability of these cells to mount a respiratory burst when challenged with opsonized zymosan. The techniques used were immunofluorescence with computer-aided image analysis and chemiluminescence. Surface coverage of erythrocytes (9% to 10%), granulocytes (9% to 14%), and platelets (1% to 4%) dominated during the first 2 hours of blood contact. PMN granulocyte adhesion to titanium was associated with a rapid decrease in L-selectin expression within 16 minutes. Initially FcgammaIII receptor (CD16) expression dominated on the adherent cells. After 30 minutes, a shift toward integrin expression (CD11b) was found on the adherent cells. All investigated receptors were down-regulated within 1 hour of blood-titanium contact. Attempts were made to inhibit the initial adhesion of PMN granulocytes to titanium by adding specific antibodies or 2,3-diphosphoglyceric acid (phospholipase D inhibitor) to blood before surface contact. Adding anti-CD16 resulted in a 67% reduction in cell adhesion, whereas a 35% reduction was found with 2,3-diphosphoglyceric acid. No spontaneous respiratory burst was detected from adherent PMN granulocytes residing on the TiO(2) surface. The cells were, however, able to mount a respiratory burst in response to opsonized zymosan.

Neutrophil activation by plasma opsonized polymeric microspheres: inhibitory effect of pluronic F127

The phagocytosis of drug-loaded polymeric microspheres by white blood cells, such as neutrophils or mononuclear cells, represents the major clearance mechanism by which this foreign material is eliminated from the body. The process of phagocytosis requires the activation of the white blood cells by the microsphere surface, followed by binding and engulfment. Phagocytosis may result in the removal of the microspheres from the blood or the disease site and an inflammatory response. Therefore, we have studied the level of neutrophil activation by microspheres ( +/- opsonization) manufactured from various biomaterials or polymers. Polymer microspheres with equivalent size distributions were made from poly (DL-lactic acid) (PLA), poly(epsilon-caprolactone) (PCL), poly(methyl methacrylate) (PMMA) or a 50 : 50 blend of PLA: poly(ethylene-co-vinyl acetate) (PLA: EVA). Neutrophils were isolated from human blood and activation of these cells by microspheres was measured by chemiluminescence (CL). All four types of microspheres induced only low levels of CL, however these levels were enhanced significantly if the microspheres were pretreated with plasma or IgG suggesting an opsonization effect. The adsorption of IgG or proteins from plasma was confirmed by polyacrylamide gel electrophoresis (SDS-PAGE). The poloxamer Pluronic F127 inhibited the opsonization effect of IgG and plasma on all four types of microspheres and inhibited protein adsorption as measured by SDS-PAGE. Since neutrophil activation is part of the inflammation process in vivo, these in vitro data suggest that all four types of microspheres are likely to be inflammatory if injected into body compartments containing plasma-derived fluids. Pretreatment of the microspheres with Pluronic F127 may reduce the inflammatory potential of the microspheres.

Secretion of IL-1 and H2O2 by human mononuclear cells in vitro

The secretion of hydrogen peroxide (H2O2) and interleukin-1alpha (IL-1alpha) was evaluated during in vitro culturing of human monocytes. The oxidative metabolism and cytokine secretion were correlated to the cell distribution (number of surface-associated cells), the DNA content and their integrity, evaluated by lactate dehydrogenase (LDH) assay. The differentiation of cultured monocytes was determined by the expression of CD14, 27E10 and RM3/1. After 24 h cultivation, unstimulated cells had a low production of H2O2 and IL-1alpha. A four-fold increase in the production of H2O2 was detected with 5 and 10 microg/ml of lipopolysaccharide (LPS) and polystyrene (PS) particles. PS particles induced a concentration-dependent increase in IL-1alpha after 24 h. In contrast, cultivation for 48 h, did not result in any measurable production of H2O2, irrespective of the type of stimulus. A decreased viability of monocytes was shown after stimulation with PS particles in high concentrations. Our results indicate that the phenotype expression, adhesion, integrity and secretory pattern of human monocytes is dependent on the culture time and the type and concentration of stimulus.

Neutrophil adhesion to vascular prosthetic surfaces triggers nonapoptotic cell death

OBJECTIVE

To test the hypothesis that neutrophil adhesion to expanded polytetrafluoroethylene (ePTFE) and Dacron triggers cell death.

SUMMARY BACKGROUND DATA

Vascular prosthetic infections are intransigent clinical dilemmas associated with excessive rates of death and complications. Impaired neutrophil function has been implicated in the infection of implanted cardiovascular devices. ePTFE and Dacron are potent neutrophil stimuli able to elicit activation responses such as reactive oxygen species production independent of exogenous/soluble agonists. Reactive oxygen species that are released into the medium when neutrophils are challenged by soluble agonists are known to cause self-destruction. The authors therefore sought to examine whether neutrophil adhesion to prosthetic graft materials decreases neutrophil viability by means of reactive oxygen species production.

METHODS

Neutrophils were adhered to surfaces for up to 6 hours. Cell viability was monitored with propidium iodide staining and lactate dehydrogenase release.

RESULTS

Within 6 hours of adhesion to ePTFE and Dacron, respectively, 59% +/- 11% and 44% +/- 5% (n = 7) of the neutrophils were stained by propidium iodide. Indistinguishable results were obtained with plasma-coated ePTFE and Dacron. In contrast, less than 2% of the neutrophils adherent to fibrinogen-, immunoglobin-, or fetal bovine serum-coated polystyrene surfaces for 6 hours were positive for propidium iodide. The increase in membrane permeability to propidium iodide was accompanied by a two- to threefold increase in lactate dehydrogenase release. Pretreatment of neutrophils with N-acetyl-L-cysteine, cytochalasin D, or cyclosporin A significantly reduced the number of propidium iodide-positive ePTFE and Dacron adherent neutrophils.

CONCLUSIONS

Neutrophil adhesion to ePTFE and Dacron triggers a rapid nonapoptotic cell death. The effect of ePTFE and Dacron on neutrophil viability appears to be caused by reactive oxygen species production. The premature death of graft-adherent neutrophils provides a novel explanation of the defect in neutrophil bacterial killing associated with vascular prosthetic grafts.

Inflammatory cell recruitment, distribution, and chemiluminescence response at IgG precoated- and thiol functionalized gold surfaces

The role of complement activation by artificial surfaces relative to inflammatory response is not well understood. This study was performed to evaluate the inflammatory cell recruitment, distribution, and ex vivo metabolic activation of surfaces with different plasma protein adsorption and complement activation properties in vitro. The implants were (1) pure gold (reference), (2) albumin-precoated (3) IgG-precoated gold, and (4) 3-mercapto-1, 2-propanediol [mercaptoglycerol (MG)] and (5) glutathione (GSH) immobilized to gold. The implant disks were inserted subcutaneously in rats for 24 h, and the number of inflammatory cells that were recruited to the implant adjacent to the surrounding fluid phase (exudate) and the surfaces were quantified by DNA measurements. The oxidative burst was analyzed ex vivo using spontaneous and phorbol myristate acetate (PMA)-stimulated, luminol-enhanced chemiluminescence (CL). The in vitro surface-induced anti-rat C3 binding was evaluated by ellipsometry and antibody techniques after plasma incubations for 1 and 30 min. The ellipsometric results showed that immobilized mercaptoglycerol and IgG-coated, but not the immobilized glutathione or the reference Au, bound anti-C3. The in vivo results revealed that the largest amount of cells was associated with the IgG-coated surfaces, followed by immobilized GSH and MG, albumin-coated, and gold surfaces, respectively. No spontaneous ex vivo luminol-enhanced CL was recorded from the cells irrespective of surface functionality or localization. A down-regulation of surface-associated and exudate leukocyte CL was observed ex vivo, irrespective of surface functionality. The results do not indicate a clear relationship between the degree of complement activation in vitro and leukocyte recruitment and adhesion in vivo for differently functionalized surfaces.

In vivo cell recruitment, cytokine release and chemiluminescence response at gold, and thiol functionalized surfaces

Hydroxylated and methylated surfaces were prepared by the self-assembled monolayer technique (SAM) of alkane thiols on gold. The surfaces were used to evaluate the influence of implant surface chemistry on protein deposition and inflammatory cell response. Implants were inserted subcutaneously in the rat for 3 and 24 h. The surface chemical properties influenced the in vitro rat plasma protein adsorption (ellipsometry/antibody) with few exceptions (albumin not found and fibrinogen always found). The number of recruited cells and their distribution (DNA from implant versus from exudate) was influenced by the different chemistries at 24 h, but not at 3 h. HIS48+, ED1+, ED2+ and small numbers of CD5+ cells were present in the exudate at both time periods (flow cytometry). The cellular oxidative metabolism was low, although cells on -OH surfaces responded with the highest phorbol ester-stimulated chemiluminescence (CL)/DNA. The levels of cytokines IL-1alpha, IL-1beta and TNFalpha (ELISA) were not influenced by material surface chemistry. Sham operated sites had a higher cytokine concentration/DNA compared with exudates from an implant milieu. The results of this study show that surface chemical functionalization modifies specific events in the inflammatory response around implants in soft tissues.

Defensins impair phagocytic killing by neutrophils in biomaterial-related infection

The implantation of foreign material carries a risk of infection which frequently is resistant to all treatment short of removing the implant. We have previously shown that these materials activate neutrophils by contact, leading to production of oxygen free radicals accompanied by release of granule products. Such activation further results in depletion of local host defenses, including the capacity of biomaterial-activated neutrophils to kill bacteria. Among the granule products released from neutrophils are small cationic antibacterial peptides (human neutrophil peptides [HNP]) known as defensins. Here we tested the hypothesis that defensins, released from activated neutrophils onto the surface of biomaterials, might play a role in the deactivation of subsequent neutrophil populations. Incubation of neutrophils with purified HNP resulted in a dose-related impairment of stimulus-induced oxygen radical production and of phagocytic killing. Furthermore, fresh neutrophils added to biomaterial-associated neutrophils exhibited impaired phagocytic killing. This impairment could be abrogated by antibody to HNP but not by an irrelevant antibody. Taken together, these observations support the idea that neutrophils activated at a material surface can create, by means of HNP release, an environment hostile to their microbicidal function and that of their infiltrating brethren.

Flow cytometric study of in vitro neutrophil activation by biomaterials

Neutrophil activation for adherent and nonadherent cells, as measured by flow cytometry, was not strongly dependent on material surface chemistry. We had hypothesized that material-induced neutrophil activation was an important parameter associated with material failure. All materials tested [cellophane, an acrylonitrile copolymer (AN69), Pellethane, nylon, polyethylene terephthalate, low density polyethylene, and polydimethylsiloxane] activated isolated human neutrophils, which were resuspended in plasma or serum, to similar extents based on L-selectin shedding, CD11b upregulation, and stimulation of the oxidative burst after 30-min exposure. Inhibition of complement activation by sCR1 unexpectedly had little effect if any on nonadherent neutrophils. However, neutrophil adhesion, but not the level of activation of the adherent cells, was strongly dependent on complement activation. Pretreatment with albumin did not inhibit adhesion or reduce neutrophil activation, but plasma pretreatment resulted in increased activation for nonadherent and adherent cells. More adhesion and a higher level of activation of adherent cells was observed following pretreatment with fibrinogen, a ligand of CD11b. Taken together these results suggest that upon contact with a material, neutrophil activation may occur though mechanisms that are not mediated by complement. For example, the presence of plasma proteins such as fibrinogen at the interface may trigger activation and the release of other activating agents. Although the material differences are small, the extent of activation may be significant and warrant further study of the mechanism and consequences of that activation.

Fluorescent microplate assay for respiratory burst of PMNs challenged in vitro with orthopedic metals

This report describes a simple, rapid, automated microassay for measuring in vitro changes of oxidative burst of phagocytes following challenge with metals for orthopedic devices. The production of reactive oxygen species (ROS) by polymorphonuclear leukocytes (PMNs) was measured using 2',7'-dichlorofluorescin-diacetate (DCFH-DA) as fluorescent probe. DCFH-DA enters the cells and is oxidized by ROS to fluorescent DCF. The DCF generated was directly proportional to ROS produced intracellularly: The fluorescence intensity was read and converted to an index of ROS production by cells. In our experimental system, granulocytes (PMNs) were isolated from normal human blood and seeded in microplates. To verify if metals could influence ROS production, chromium, cobalt, nickel, molybdenum, titanium, aluminum, and vanadium prepared as aqueous extracts in phosphate-buffered saline were tested onto PMNs using phorbolmyristate acetate (PMA) as positive control. Molybdenum, aluminum, and vanadium increased ROS generation by PMNs, while signals not different from unstimulated PMNs were recorded for chromium, cobalt, nickel, and titanium. The DCFH-DA microplate-based assay provides an in vitro tool for the detection of oxygen-reactive species generated by PMNs as a response to metals.

Material-induced up-regulation of leukocyte CD11b during whole blood contact: material differences and a role for complement

Material-induced thrombogenicity is in part a consequence of leukocyte activation. To evaluate and compare material-induced platelet damage, we have expanded our in vitro flow cytometric immunoassay to include assessment of leukocyte activation. We have used a very simple system whereby fresh, heparinized whole blood contacts materials for 1 h at 37 degrees C under low shear. Unlike other tests that focus on adherent leukocytes, this assay evaluates the leukocytes in the whole blood drained from the tube (1.57 mm internal diameter, 25 cm length) after material contact. We demonstrate that whole blood contact with a polyvinyl alcohol (PVA) hydrogel surface leads to a twofold up-regulation in CD11b surface expression of all monocytes and neutrophils. The activation is metal-ion dependent and highly material dependent in that blood contact with polyethylene and Silastic surface leads to minimal activation. The shedding of L-selection as a marker of leukocyte activation was found to be unsuitable in our assay given it ease of shedding in resting heparinized whole blood. Further, plasma levels of complement components Bb and sC5b-9 (ELISA assays) were significantly elevated only after blood contact with PVA hydrogel surfaces (9.4 micrograms/mL sC5b-9 and 9.6 micrograms/mL Bb). Use of recombinant soluble human CR1 (sCR1) to inhibit the action of the C3 and C5 convertases completely inhibited sC5b-9 levels in whole blood after contact with PVA hydrogel surfaces and inhibited CD11b up-regulation by over 70%, suggesting that material-induced leukocyte activation is partially mediated by C5a production.

Ex vivo analysis of leukocyte hydrogen peroxide production using a bi-plate model in mice

Implantation of artificial materials is followed by inflammation and wound healing, where phagocytic cells play an important role. The mechanisms whereby the implant surface may elicit and modulate leukocyte functions in vivo are not understood, partly due to the technical difficulties of examining the local inflammatory events in vicinity of the material-tissue interface with conventional biochemical and immunological techniques. In the present study a newly developed biplate implant was inserted subcutaneously in the mouse. Leukocytes from the local inflammatory exudate and leukocytes associated to the surface of the implants were retrieved after 1 and 6 days and separately assayed with respect to hydrogen peroxide (H2O2) production ex vivo. Implantation caused a local accumulation of predominantly mononuclear cells in the surrounding subcutaneous tissue. The H2O2 production was found to be low in both the subcutaneous exudate and the implant-associated leukocytes, irrespective of implant material and implantation times. However, ex vivo-stimulation with phorbol myristate acetate (PMA) caused an enhanced H2O2 production. These observations show that biplate implants do not maximally activate the oxidative metabolism of the recruited leukocytes. The exudate leukocytes were more responsive to PMA stimulation in comparison with implant-associated leukocytes, indicating that properties of the implant surface and possibly surface-associated proteins could modify the responsiveness of the phagocytic cells at the implant site. Our results suggest that the present biplate model may be suitable for further studies on local production of oxygen metabolites and function of leukocytes at implanted biomaterials.

Regulation of superoxide anion generation in bovine alveolar macrophages by bacterial lipopolysaccharide, serum proteins, and modulators of signal transduction

The respiratory burst of phagocytes in an important leukocyte function which results in generation of oxygen species that are both microbicidal and potentially damaging to host tissues. We investigated regulation of the respiratory burst of alveolar macrophages in response to lipopolysaccharide (LPS) derived from gram-negative bacteria, serum proteins, and several modulators of signal transduction. When employed as a single stimulus, LPS (E. coli 055:B5, 10 ng/ml-1 microgram/ml) was a weak stimulus for generation of superoxide anion (O2-) as compared to the potent effect of the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA; 500 ng/ml). However, when LPS was combined with fetal bovine serum (FBS; 0.4-1.0% vol/vol, equivalent to 128-320 micrograms protein/ml), O2- generation was enhanced approximately two-fold over LPS alone. A chromatographically-derived bovine serum fraction which contained bovine lipopolysaccharide-binding protein (bLBP; 0.25-1.0 microgram/ml) was an effective substitute for FBS at a much lower protein concentration than whole FBS, and a similar synergistic effect with LPS on O2- generation was observed. Stimulation of macrophages for generation of O2- either with LPS alone or with LPS plus serum/serum fraction was suppressed by the protein tyrosine kinase inhibitor heribimycin A (0.2 ng/ml), and the calcium chelator BAPTA (12 microM), but not by modulators of G-proteins, including pertussis toxin (10 ng/ml) and cholera toxin (5 micrograms/ml protein). Essentially complete inhibition of O2- synthesis by herbimycin A and BAPTA occurred in the presence of LPS and the bLBP-containing serum fraction (1 microgram/ml protein), but only partial inhibition (46.7% and 64.1%, respectively) was observed in the presence of LPS plus FBS (256 micrograms/ml protein). These results indicate that when LPS is used as a sole stimulus it induces modest respiratory burst activity. However, when LPS is combined with appropriate serum components, it stimulates alveolar macrophages to generate larger amounts of O2-. Cellular signaling pathways important in stimulation of macrophages by LPS and serum components are protein tyrosine kinase- and Ca(++)-dependent, but do not relay on G-protein-mediated signaling.

The chemiluminescence response of neutrophils on polymer surfaces made by glow discharge plasma polymerization

Polypropylene tubes were coated with different polymers made by glow discharge plasma polymerization. Isolated human blood neutrophils were allowed to interact with the polymer surface and the chemiluminescence response of the cells was recorded as a measure of oxidative activation. The polymers represented surfaces that differed markedly with respect to charge, hardness, and wettability. We found that all polymers stimulated the chemiluminescence response in neutrophils differently; when preincubation with human serum albumin (HSA) there was a general reduction of the chemiluminescence response particularly on one of the positively charged surface 1,2-diamino-cyclohexane (DACH). Addition of a soluble stimulus, the chemoattractant formylmethionyl-leucylphenylalanine (FMLP), to the cells caused a dramatic increase in the response on one of the hydrophobic surface hexamethylene-disiloxane (HMDSO). However, there was also a pronounced reduction in the response on polymers with acrylic acid (AA). The response was normalized after addition of HSA. Taken together, the chemiluminescence response of the neutrophils interacting with the polymer surfaces differed with regard to the type of surfaces. When HSA and FMLP were added a larger difference in the response was found. Our results showed that the activation of human neutrophil granulocytes influenced by different polymer surfaces, followed unspecific different patterns which were someway related to the specific characteristics of the polymer and from this point we came to similar conclusions made by Kaplan et al. (J. Biomater. Res. 28, 377 (1994)), that it is difficult to extrapolate any activation mechanisms from one material to another.(ABSTRACT TRUNCATED AT 250 WORDS)