Artificial surface-induced cytokine synthesis: effect of heparin coating and complement inhibition

Crosstalk of Inflammation and Coagulation in Bothrops Snakebite Envenoming: Endogenous Signaling Pathways and Pathophysiology

Snakebite envenoming represents a major health problem in tropical and subtropical countries. Considering the elevated number of accidents and high morbidity and mortality rates, the World Health Organization reclassified this disease to category A of neglected diseases. In Latin America, Bothrops genus snakes are mainly responsible for snakebites in humans, whose pathophysiology is characterized by local and systemic inflammatory and degradative processes, triggering prothrombotic and hemorrhagic events, which lead to various complications, organ damage, tissue loss, amputations, and death. The activation of the multicellular blood system, hemostatic alterations, and activation of the inflammatory response are all well-documented in Bothrops envenomings. However, the interface between inflammation and coagulation is still a neglected issue in the toxinology field. Thromboinflammatory pathways can play a significant role in some of the major complications of snakebite envenoming, such as stroke, venous thromboembolism, and acute kidney injury. In addition to exacerbating inflammation and cell interactions that trigger vaso-occlusion, ischemia-reperfusion processes, and, eventually, organic damage and necrosis. In this review, we discuss the role of inflammatory pathways in modulating coagulation and inducing platelet and leukocyte activation, as well as the inflammatory production mediators and induction of innate immune responses, among other mechanisms that are altered by Bothrops venoms.

Effect of Intraperitoneal 224Radium-Labelled Microparticles on Compartmentalized Inflammation After Cytoreductive Surgery and Hypertherm Intraperitoneal Chemotherapy

Despite extensive treatment with surgery and chemotherapy many patients with peritoneal metastases from colorectal cancer experience intraperitoneal disease relapse. The α-emitting 224radium-labelled microparticle radionuclide therapeutic Radspherin® is being explored as a novel treatment option for these patients. Radspherin® is specially designed to give local radiation to the surface of the peritoneal cavity and potentially kill remaining attached micrometastases as well as free-floating cancer cells, thus preventing future relapse. The effect of Radspherin® on the immune system is not known. Systemic and local inflammatory responses were analyzed in plasma, intraperitoneal fluid and urine collected prospectively as part of a phase 1 dose-escalation study of intraperitoneal instillation of the α-emitting therapeutic radiopharmaceutical Radspherin®, at baseline and the first 7 postoperative days from nine patients undergoing cytoreductive surgery and hyperthermic intraperitoneal chemotherapy. All patients additionally received intraperitoneal instillation of Radspherin® on postoperative day 2. Complement activation products C3bc and the terminal complement complex were analyzed using enzyme-linked immunosorbent assay. Cytokines (n = 27), including interleukins, chemokines, interferons and growth factors, were analyzed using multiplex technique. The time course and magnitude of the postoperative cytokine response after cytoreductive surgery and hyperthermic intraperitoneal chemotherapy displayed a modest systemic response in plasma, in contrast to a substantial local intraperitoneal response. After administration of Radspherin®, a significant increase (P < 0.05) in TNF and MIP-1β was observed in both plasma and peritoneal fluid, whereas IL-9 increased only in plasma and IFNγ and IL1-RA only in peritoneal fluid. Only minor changes were seen for the majority of the inflammatory markers after Radspherin® administration. Our study showed a predominately local rather than systemic inflammatory response to cytoreductive surgery and hyperthermic intraperitoneal chemotherapy. Radspherin® had overall modest impact on the inflammation.

Neuroinflammatory Gene Expression Analysis Reveals Pathways of Interest as Potential Targets to Improve the Recording Performance of Intracortical Microelectrodes

Intracortical microelectrodes are a critical component of brain-machine interface (BMI) systems. The recording performance of intracortical microelectrodes used for both basic neuroscience research and clinical applications of BMIs decreases over time, limiting the utility of the devices. The neuroinflammatory response to the microelectrode has been identified as a significant contributing factor to its performance. Traditionally, pathological assessment has been limited to a dozen or so known neuroinflammatory proteins, and only a few groups have begun to explore changes in gene expression following microelectrode implantation. Our initial characterization of gene expression profiles of the neuroinflammatory response to mice implanted with non-functional intracortical probes revealed many upregulated genes that could inform future therapeutic targets. Emphasis was placed on the most significant gene expression changes and genes involved in multiple innate immune sets, including Cd14, C3, Itgam, and Irak4. In previous studies, inhibition of Cluster of Differentiation 14 (Cd14) improved microelectrode performance for up to two weeks after electrode implantation, suggesting CD14 can be explored as a potential therapeutic target. However, all measures of improvements in signal quality and electrode performance lost statistical significance after two weeks. Therefore, the current study investigated the expression of genes in the neuroinflammatory pathway at the tissue-microelectrode interface in Cd14-/- mice to understand better how Cd14 inhibition was connected to temporary improvements in recording quality over the initial 2-weeks post-surgery, allowing for the identification of potential co-therapeutic targets that may work synergistically with or after CD14 inhibition to improve microelectrode performance.

Avoiding ambient air in test tubes during incubations of human whole-blood minimizes complement background activation

BACKGROUND

In vitro, the complement system can be studied in test tubes incubated with anticoagulated human whole-blood. Background activation of complement may mask inflammatory signals. Air bubbles are known to activate complement. We examined if removing ambient air from test tubes before incubation reduced background complement activation.

METHODS

Blood from twelve donors was anticoagulated with the thrombin inhibitor lepirudin and incubated with either no air, ambient air or air bubbles in polypropylene tubes at 37 °C for 180 min on a roller mixer. After incubation, EDTA was added, plasma isolated and analyzed for seven complement activation products using ELISA. Results are presented as means with 95% confidence intervals.

RESULTS

Blood incubated without air had significantly lower complement activation compared to blood incubated with ambient air; C4d 273 (192-364) vs. 379 (263-494) ng/mL (p = 0.002), C4bc 8.2 (4.1-13) vs. 12 (3.2-21) CAU/mL (p = 0.01), C3a 1351 (873-1838) vs. 2944 (2315-3572) ng/mL (p = 0.0005), C3bc 31 (17-46) vs. 68 (52-84) CAU/mL (p = 0.002), C3bBbP 134 (97-171) vs. 427 (358-506) CAU/mL (p < 0.0001), C5a 3.5 (1.9-5 0.2) vs. 15 (1.8-27)) ng/mL (p = 0.003), TCC 4.6 (2.8-6.3) vs. 9.9 (7.3-12) CAU/mL (p = 0.006). At the end of the experiment blood incubated with air bubbles had a higher complement activation than blood incubated with ambient air with an average 26 fold increase (range 1.6-59) from baseline of all activation products; C4d 551 (337-766) ng/mL, C4bc 21 (5.0-36) CAU/mL, C3a 3983 (3518-4448) ng/mL, C4bc 103 (86-121) CAU/mL, C3bBbP 626 (543-708) CAU/mL, C5a 10 (2.8-18) ng/mL and TCC 10 (6.0-14) CAU/mL.

CONCLUSION

Avoiding air in test tubes during whole-blood experiments reduced background complement activation substantially and represents an important improvement to the lepirudin whole-blood model. This could also apply to other in vitro models.

Heparin molecularly imprinted surfaces for the attenuation of complement activation in blood

Heparin molecularly imprinted polymer films limit complement activation in whole blood.

Complement C5a potentiates uric acid crystal-induced IL-1β production

Anaphylatoxin C5a released upon complement activation is associated with both acute and chronic inflammations such as gout. The pathogenesis of gout was identified as uric acid crystal deposition in the joints that activates inflammasome, leading to IL-1β release. However, little is known about the interaction between complement activation and monosodium urate/uric acid (MSU) crystal-induced inflammasome activation or IL-1β production. Here, we report that MSU crystal-induced proinflammatory cytokines/chemokines in human whole blood is predominantly regulated by C5a through its interaction with C5a receptor. C5a induces pro-IL-1β and IL-1β production in human primary monocytes, and potentiates MSU or cholesterol crystals in IL-1β production. This potentiation is caspase-1 dependent and requires intracellular Ca(2+) mobilization, K(+) efflux, and cathepsin B activity. Our results provide insight into the role of C5a as an endogenous priming signal that is required for the initiation of uric acid crystal-induced IL-1β production. C5a could potentially be a therapeutic target together with IL-1β antagonists for the treatment of complement-dependent and inflammasome-associated diseases.

History, ethics, advantages and limitations of experimental models for hepatic ablation

Numerous techniques developed in medicine require careful evaluation to determine their indications, limitations and potential side effects prior to their clinical use. At present this generally involves the use of animal models which is undesirable from an ethical standpoint, requires complex and time-consuming authorization, and is very expensive. This process is exemplified in the development of hepatic ablation techniques, starting experiments on explanted livers and progressing to safety and efficacy studies in living animals prior to clinical studies. The two main approaches used are ex vivo isolated non-perfused liver models and in vivo animal models. Ex vivo non perfused models are less expensive, easier to obtain but not suitable to study the heat sink effect or experiments requiring several hours. In vivo animal models closely resemble clinical subjects but often are expensive and have small sample sizes due to ethical guidelines. Isolated perfused ex vivo liver models have been used to study drug toxicity, liver failure, organ transplantation and hepatic ablation and combine advantages of both previous models.

Do blood components affect the production of reactive oxygen species (ROS) by equine synovial cells in vitro?

Blood-derived products are commonly administered to horses and humans to treat many musculoskeletal diseases, due to their potential antioxidant and anti-inflammatory effects. Nevertheless, antioxidant effects have never been shown upon horse synovial fluid cells in vitro. If proved, this could give a new perspective to justify the clinical application of blood-derived products. The aim of the present study was to investigate the antioxidant effects of two blood-derived products - plasma (unconditioned blood product - UBP) and a commercial blood preparation (conditioned blood product - CBP)¹ - upon stimulated equine synovial fluid cells. Healthy tarsocrural joints (60) were tapped to obtain synovial fluid cells; these cells were pooled, processed, stimulated with lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA), and evaluated by flow cytometry for the production of reactive oxygen species (ROS). Upon addition of any blood-derived product here used - UBP and CBP - there was a significant decrease in the oxidative burst of synovial fluid cells (P<0.05). There was no difference between UBP and CBP effects. In conclusion, treatment of stimulated equine synovial cells with either UBP or CBP efficiently restored their redox equilibrium.

Activation of coagulation and platelets by candidate membranes of implantable devices in a whole blood model without soluble anticoagulant

Implantable devices are challenged with thrombus formation at their biomaterial interface. Thus the importance of identifying compatible biomaterials that will help to improve the performance of these devices are becoming increasingly paramount. The aim of this study was to evaluate the activation of coagulation and platelets by candidate membranes considered for use in implantable devices on the basis of an adapted whole blood model without soluble anticoagulants. Evaluated materials were incubated with whole blood without soluble anticoagulant in wells coated with heparin. Prothrombin fragment 1+2 (PTF 1+2), thrombin-antithrombin complex (TAT), and β-thromboglobulin (BTG) were analyzed in plasma samples using enzyme immunoassays. The C5 inhibitor eculizumab was used to evaluate the role of complement. Incubation of two of the polyamide membranes PAR and PATF led to an increase in concentration of PTF 1+2 and TAT (p < 0.01 for PAR, ns for PATF). The BTG concentration was significantly increased for five materials [PAR, PATF, polycarbonate (PC), and two polyarylethersulphone membranes PAES-1 and PAES-2]. Complement inhibition had no effect on coagulation or platelet activation induced by PAR and PATF. In conclusion, PAR and PATF were not compatible with blood and should be avoided for use in implantable devices.

Complement activation and cardiac surgery: a novel target for improving outcomes

Complement activation and the resulting inflammatory response is an important potential mechanism for multisystem organ injury in cardiac surgery. Novel therapeutic strategies using complement inhibitors may hold promise for improving outcomes for cardiac surgical patients by attenuating complement activation or its biologically active effector molecules. Recent clinical trials evaluating complement inhibitors have provided important data to further delineate the impact of complement activation and its inhibition on clinical outcomes. In this review we examine the role of complement activation and its inhibition as a therapeutic approach in cardiac surgery.

DEHP and its active metabolites: leaching from different tubing types, impact on proinflammatory cytokines and adhesion molecule expression. Is there a subsumable context?

Introduction: Di(2-ethylhexyl)phthalate (DEHP) is suspected to be toxic for several reasons. During contact with a lipophilic medium, DEHP leaks from polyvinylchloride (PVC), but its influence on inflammatory reactions remains unknown. We examined specific DEHP leaching out of different tubing types, the possibly modulated liberation of proinflammatory cytokines and the induction of adhesion molecule expression in primary endothelial cells.

Materials and Methods: Blood samples were circulated in traditional PVC, nodioctyl phthalate (DOP) PVC and heparin-coated PVC tubing within a Chandler loop model. The blood was tested for the concentration of DEHP and its active metabolites as well as the liberation of the proinflammatory cytokines TNFα and IL1ß. Furthermore, we exposed human endothelial cells to circulated blood and analysed them for the expression of the adhesion molecules ICAM-1, VCAM-1 and E-selectin.

Results: In contrast to the other tubing, PVC tubing showed significantly elevated DEHP levels, but no alteration was observed concerning a potential up-regulation of the cytokines or activation of the endothelial adhesion molecule receptors.

Conclusions: Our data conclude that there is no correlation between DEHP leaching and the inflammatory response after ECC support, but this study showed that even DEHP-free material is leaching DEHP and its toxic metabolites.

Alginate microbeads are complement compatible, in contrast to polycation containing microcapsules, as revealed in a human whole blood model

Alginate microbeads and microcapsules are presently under evaluation for future cell-based therapy. Defining their inflammatory properties with regard to humans is therefore essential. A lepirudine-based human whole blood model was used as an inflammation predictor by measuring complement and leukocyte stimulation. Alginate microbeads were complement-compatible since they did not activate complement as measured by the soluble terminal complement complex (sTCC), Bb or the anaphylatoxins C3a and C5a. In addition, alginate microbeads were free of surface adherent leukocytes. In contrast, microcapsules containing poly-L-lysine (PLL) induced elevated levels of sTCC, Bb, C3a and C5a, surface active C3 convertase and leukocyte adhesion. The soluble PLL induced elevated levels of sTCC and up-regulated leukocyte CD11b expression. PMCG microcapsules containing poly(methylene-co-guanidine) complexed with sodium alginate and cellulose sulfate triggered a fast sTCC response and C3 deposition. The PMCG microcapsules were still less activating than PLL-containing microcapsules as a function of time. The amounts of anaphylatoxins C3a and C5a were diminished by the PMCG microcapsules, whereas leukocyte adherence demonstrated surface activating properties. We propose the whole blood model as an important tool for measuring bioincompatibility of microcapsules and microbeads for future applications as well as determining the mechanisms leading to inflammatory reactions.

Artificial surface-induced inflammation relies on complement factor 5: proof from a deficient person

BACKGROUND

Exposing blood to artificial surfaces results in an inflammatory response, including complement activation and cytokine release. The aim of this investigation was to study complement-dependency and independency in artificial surface-induced inflammation in human whole blood from a patient with a genetic deficiency of complement factor 5 (C5).

METHODS

Whole blood from a C5-deficient patient, C5 protein reconstituted blood, and blood from a control subject was used. The complement inhibitor compstatin (C3 inhibitor) and a C5a receptor antagonist were used to block complement. Blood was circulated in closed loops of polyvinyl chloride tubing. Leukocyte CD11b expression and release of granule enzymes (myeloperoxidase, elastase, lactoferrin), cytokines (interleukins, chemokines, and growth factors; n = 27) as well as complement activation were measured after incubation.

RESULTS

In C5-deficient blood, there was no formation of the terminal complement complex, as opposed to reconstituted or control blood. Release of granule enzymes was partly dependent on C3, revealed by a compstatin-dependent effect in C5-deficient blood, and partly C5a-dependent as evident from the reconstitution and control blood. The chemokines interleukin-8 and monocyte chemoattractant protein-1 were also highly complement dependent, the effect being C5a-mediated, whereas platelet-derived and vascular endothelial growth factors were partly complement dependent. Interferon-γ increased in a complement-independent manner, whereas the rest of the cytokines did not respond to the surface. Leukocyte expression of CD11b was only marginally increased in deficient blood exposed to the surface, whereas reconstitution induced a considerable, C5a-dependent increase, comparable with that of the control.

CONCLUSIONS

The polyvinyl chloride surface induced a defined inflammatory response, which largely depended on C5.

Bioengineering of improved biomaterials coatings for extracorporeal circulation requires extended observation of blood-biomaterial interaction under flow

Extended use of cardiopulmonary bypass (CPB) systems is often hampered by thrombus formation and infection. Part of these problems relates to imperfect hemocompatibility of the CPB circuitry. The engineering of biomaterial surfaces with genuine long-term hemocompatibility is essentially virgin territory in biomaterials science. For example, most experiments with the well-known Chandler loop model, for evaluation of blood-biomaterial interactions under flow, have been described for a maximum duration of 2 hours only. This study reports a systematic evaluation of two commercial CPB tubings, each with a hemocompatible coating, and one uncoated control. The experiments comprised (i) testing over 5 hours under flow, with human whole blood from 4 different donors; (ii) measurement of essential blood parameters of hemocompatibility; (iii) analysis of the luminal surfaces by scanning electron microscopy and thrombin generation time measurements. The dataset indicated differences in hemocompatibility of the tubings. Furthermore, it appeared that discrimination between biomaterial coatings can be made only after several hours of blood-biomaterial contact. Platelet counting, myeloperoxidase quantification, and scanning electron microscopy proved to be the most useful methods. These findings are believed to be relevant with respect to the bioengineering of extracorporeal devices that should function in contact with blood for extended time.

Comparable biocompatibility of Phisio- and Bioline-coated cardiopulmonary bypass circuits indicated by the inflammatory response

Background: The biocompatibility of cardiopulmonary bypass surfaces has been improved by heparin and polymer surface modifications. The present study compared the effect of two such coatings on the inflammatory reactions after open heart surgery.

Methods:Thirty patients undergoing elective heart surgery were randomly assigned to receive one of two types of coated circuits: Bioline (n=15) or phosphorylcholine (Phisio, n=15). The platelet and leukocyte counts, neutrophil activation (myeloperoxidase), complement activation (C3a and TCC), concentrations of lactate dehydrogenase, 27 cytokines (including interleukins, chemokines and growth factors), thrombin-antithrombin complexes, and the endothelial cell marker syndecan-1 were analyzed at five predetermined time points until 24 hrs post operatively.

Results: Most measurements were comparable in both groups. However, myeloperoxidase was significantly higher in the Bioline group (p < 0.001). Postoperative lactate dehydrogenase concentrations were significantly higher in the Phisio group (p<0.01) and the maximal concentration of thrombin-antithrombin complexes 2 hours postoperatively tended to be higher in the Phisio group (p=0.08), consistent with a longer aortic cross-clamp and cardiopulmonary bypass time. Conclusions: The two circuits exhibited a comparable degree of in vivo biocompatibility.

Evaluation of blood components exposed to coated arterial filters in extracorporeal circuits

Background: Biocompatible surfaces play an important role in the inflammatory response during cardiopulmonary bypass (CBP), with the arterial filter contributing a large surface area of the circuit. Different filter-coating materials designed to improve blood-filter biocompatibility are currently used in CPB circuits. This study evaluates eight biocompatible coatings used for arterial filters and their effects on blood components during circulation. Methods: Arterial filters were randomly assigned in eight independent heparin-bonded tubing loops and perfused by a single swine (n=8). Arterial blood was routed simultaneously, but separately, into each circuit and circulated for 30 minutes at 37°C. Blood samples were drawn for CBC, ACT, and TAT III measurements at baseline, post-heparinization and post-circulation. At study completion, filters were imaged using multiphoton microscopy. Results: RBC, platelet, and WBC counts, and TAT III complex were all decreased after 30 minutes of circulation; however, WBC count was the only parameter that showed statistically significant differences between the filters. Circulating WBC reduction ranged from 6% (Carmeda and Trillium) to 41% (Terumo-X-coating) with corresponding microscopic confirmation of increased WBC entrapment. Conclusion: All eight filter coatings altered the blood components to varying degrees. Selection of the most effective filter, in conjunction with a heparin-bonded circuit for CPB, may decrease the intraoperative foreign-surface activation of blood cells.

The artificial surface-induced whole blood inflammatory reaction revealed by increases in a series of chemokines and growth factors is largely complement dependent

Exposing blood to an artificial surface results in a systemic inflammatory response, including cytokine release and complement activation. We studied the artificial surface-induced inflammation in human whole blood using an extensive panel of inflammatory mediators including proinflammatory cytokines, chemokines and growth-factors and investigated the role of the complement system in the induction of this response. Using multiplex technology, 27 different inflammatory mediators were measured after circulating blood for 4 hours in polyvinyl chloride tubing. The C3 inhibitor compstatin was used to block complement activation. A significant (p < 0.05) increase in 14 of the 27 mediators was induced by the surface, of which 7 were chemokines (IL-8, MCP-1, MIP-1alpha, MIP-1beta, RANTES, eotaxin and IP-10) and 5 were growth-factors (G-CSF, GM-CSF, VEGF, PDGF and FGF). The traditional proinflammatory cytokines like IL-1beta, TNFalpha and IL-6 were not induced, although IL-6, as well as IL-15 and IL-17 increased if the surface was coated with highly bioincompatible laminaran. Inhibition of complement activation with compstatin significantly (p < 0.05) reduced the formation of 12 of the 14 mediators. For 10 of the 12 mediators, the inhibition was by 2/3 or more, for the remaining two the inhibition was more moderate. A highly biocompatible heparin-coated PVC surface was used as negative control and completely abolished the whole inflammatory response. The artificial surface PVC markedly induced a broad spectrum of chemokines and growth-factors, which was largely dependent on activation of complement.

Heparin and EDTA as anticoagulant differentially affect cytokine mRNA level of cultured porcine blood cells

Cytokine mRNA expression profiles serve to characterize immune cell activation in different test systems. Both, diluted whole blood and isolated PBMC are widely applied for these studies. Comprehensive data regarding the suitability of different anticoagulants for profiling cytokine expression are not available for the pig. Therefore the aim of this study was to compare the effect of two commonly used anticoagulants (heparin and EDTA) on the cytokine expression pattern of porcine blood cells. IL-1alpha, IL-2, IL-4, IL-6, IL-10 and IFN-gamma mRNA levels were detected ex-vivo and upon in-vitro stimulation in diluted porcine whole blood and isolated PBMC by real-time PCR. The cells were stimulated with ConA or LPS, known to act on different target cells and implying different signalling pathways. Additionally the integrity of the isolated RNA was investigated. Ex-vivo cytokine expression pattern of fresh whole blood were not affected by the investigated anticoagulants. In contrast, stimulation of cultured diluted whole blood or PBMC resulted in significant differences depending on the applied anticoagulant. Using EDTA we found a significantly decreased capacity of whole blood to express cytokines. However, isolated PBMC from EDTA anticoagulated blood showed a higher cytokine expression capacity than PBMC from heparinized blood. Comparing diluted whole blood and PBMC we found that cultured porcine whole blood responded better to bacterial products than isolated PBMC, probably because sufficient auxiliary plasma derived factors such as LPS-binding protein, are present. However, isolated PBMC showed a higher T-cell response than diluted whole blood. In conclusion, our findings underline that each application demands a specific assay system.

Leukocyte effects of C5a-receptor blockade during simulated extracorporeal circulation

BACKGROUND

Distinct pathways of leukocyte activation during simulated cardiopulmonary bypass are mediated by the complement C5a anaphylatoxin. We hypothesized that a human C5a receptor antagonist would specifically inhibit the inflammatory response of neutrophils to simulated extracorporeal circulation, while preserving the C5b-9 pathway for innate immunity.

METHODS

An in vitro extracorporeal circuit recirculated fresh heparinized whole blood through a membrane oxygenator with and without addition of a small molecule human C5a receptor antagonist. Samples were periodically drawn over 90 minutes for complement and leukocyte activation studies.

RESULTS

Addition of the C5a receptor antagonist to simulated extracorporeal circulation abrogated both neutrophil CD11b upregulation and interleukin 8 release (p < 0.01 for both), despite full generation of C3a and C5b-9; however, elastase release from neutrophils was unaffected. Although C5a receptor blockade only trended toward inhibiting monocyte CD11b upregulation (p = 0.09), circuit clearance of both monocytes (p = 0.04) and neutrophils (p = 0.01) was significantly decreased. In addition, the C5a receptor antagonist completely blocked both neutrophil-platelet and monocyte-platelet conjugate formation (p < 0.001 for both), without affecting platelet P-selectin expression.

CONCLUSIONS

C5a receptor blockade during simulated extracorporeal circulation completely blocked neutrophil beta2 integrin upregulation and induction of plasma interleukin 8, suggesting an acute downregulatory effect on neutrophil chemotaxis-related pathways, while preserving terminal complement generation and neutrophil elastase release. Inhibition of leukocyte-platelet conjugate formation suggests a novel function for leukocyte adhesive receptors, possibly related to preservation of elastase generation.

The role of complement in biomaterial-induced inflammation

Biomaterials are regularly used in various types of artificial tissues and organs, such as oxygenators, plasmapheresis equipment, hemodialysers, catheters, prostheses, stents, vascular grafts, miniature pumps, sensors and heart aids. Although progress has been made regarding bioincompatibility, many materials and procedures are associated with side effects, in particular bioincompatibility-induced inflammation, infections and subsequent loss of function. After cardiopulmonary bypass, coagulopathies can occur and lead to cognitive disturbances, stroke and extended hospitalization. Hemodialysis is associated with anaphylatoid reactions that cause whole-body inflammation and may contribute to accelerated arteriosclerosis. Stents cause restenosis and, in severe cases, thrombotic reactions. This situation indicates that there is still a need to try to understand the mechanisms involved in these incompatibility reactions in order to be able to improve the biomaterials and to develop treatments that attenuate the reactions and thereby reduce patients' discomfort, treatment time and cost. This overview deals with the role of complement in the incompatibility reactions that occur when biomaterials come in contact with blood and other body fluids.

Loss of ecto-5'nucleotidase from porcine endothelial cells after exposure to human blood: Implications for xenotransplantation

The endothelial cell surface expression of ecto-5'-nucleotidase (E5'N, CD73) is thought to be essential for the extracellular formation of cytoprotective, anti-thrombotic and immunosuppressive adenosine. Decreased E5'N activity may play a role in xenograft acute vascular rejection, preventing accommodation and tolerance mechanisms. We investigated the extent of changes in E5'N activity and other enzymes of purine metabolism in porcine hearts or endothelial cells when exposed to human blood or plasma and studied the role of humoral immunity in this context. Pig hearts, wild type (WT, n = 6) and transgenic (T, n = 5) for human decay accelerating factor (hDAF), were perfused ex vivo with fresh human blood for 4 h. Pig aortic endothelial cells (PAEC) were exposed for 3 h to autologous porcine plasma (PP), normal (NHP) or heat inactivated human plasma (HHP), with and without C1-inhibitor. Enzyme activities were measured in heart or endothelial cell homogenates with an HPLC based procedure. The baseline activity of E5'N in WT and T porcine hearts were 6.60 +/- 0.33 nmol/min/mg protein and 8.54 +/- 2.10 nmol/min/mg protein respectively (P < 0.01). Ex vivo perfusion of pig hearts with fresh human blood for 4 h resulted in a decrease in E5'N activity to 4.01 +/- 0.32 and 4.52 +/- 0.52 nmol/min/mg protein (P < 0.001) in WT and T hearts respectively, despite attenuation of hyperacute rejection in transgenic pigs. The initial PAEC activity of E5'N was 9.10 +/- 1.40 nmol/min/mg protein. Activity decreased to 6.76 +/- 0.57 and 4.58 +/- 0.47 nmol/min/mg protein (P < 0.01) after 3 h exposure of HHP and NHP respectively (P < 0.05), whereas it remained unchanged at 9.62 +/- 0.88 nmol/min/mg protein when incubated with PP controls. C1-inhibitor partially preserved E5'N activity, similar to the effect of HHP. Adenosine deaminase, adenosine kinase and AMP deaminase (other enzymes of purine metabolism) showed a downward trend in activity, but none were statistically significant. We demonstrate a specific decrease in E5'N activity in pig hearts following exposure to human blood which impairs adenosine production resulting in a loss of a cytoprotective phenotype, contributing to xenograft rejection. This effect is triggered by human humoral immune responses, and complement contributes but does not fully mediate E5'N depletion.

Differential Effect of Heparin Coating and Complement Inhibition on Artificial Surface-Induced Eicosanoid Production

BACKGROUND

Contact between blood and artificial surfaces induces an inflammatory response including activation of leukocytes and platelets, as well as complement and other plasma cascade systems. In the present study we investigated the roles of complement and surface modification in polyvinyl chloride-induced synthesis of eicosanoids (arachidonic acid metabolites).

METHODS

Human whole blood was incubated in rotating loops of polyvinyl chloride or heparin-coated polyvinyl chloride tubing for 4 hours. Plasma concentrations of the eicosanoids leukotriene B4, prostaglandin E2 and thromboxane B2 were quantified.

RESULTS

Polyvinyl chloride induced a substantial increase in leukotriene B4, prostaglandin E2, and thromboxane B2. Inhibition of complement activation by the complement factor 3 binding peptide compstatin or blockade of the complement factor 5a receptor with a specific antagonist significantly and specifically inhibited the synthesis of leukotriene B4, whereas thromboxane B2 and prostaglandin E2 synthesis were apparently complement independent. The increase in all three mediators was significantly reduced by the heparin coating. Indomethacin abolished the increase of the cyclooxygenase products prostaglandin E2 and thromboxane B2, but had no effect on the increase of the lipoxygenase product leukotriene B4, consistent with the specificity of indomethacin for the cyclooxygenase and confirming the specificity of complement inhibition.

CONCLUSIONS

Polyvinyl chloride-induced increase in all three eicosanoids was attenuated by heparin coating, whereas complement inhibition selectively reduced the synthesis of leukotriene B4.

Role of granulocytes and monocytes in the polyvinyl chloride-induced synthesis of interleukin 8, monocyte chemoattractant protein 1, and leukotriene B4

In an in vitro whole blood model of artificial surface-induced inflammation, we have studied the contribution of leukocyte populations in the synthesis of inflammatory mediators. This was done by depleting the blood of specific cell types using magnetic beads coated with monoclonal antibodies against leukocyte surface antigens. Synthesis of interleukin 8 (IL-8) was highly dependent on CD15+ cells and was reduced by 80% when these cells were removed from the blood. Correspondingly, IL-8 production showed a high correlation with the concentration of granulocytes (r = 0.77, p < 0.0001). Synthesis of monocyte chemoattractant protein 1 (MCP-1) was dependent on CD14+ cells and was reduced by 35% when these cells were removed from the blood. Correspondingly, MCP-1 production correlated with the concentration of monocytes (r = 0.39, p < 0.0001). Synthesis of leukotriene B4 (LTB4) was highly dependent on CD15+ cells and was reduced by 75% when these cells were removed from the blood. Correspondingly, LTB4 production correlated strongly with the granulocyte concentration (r = 0.54, p < 0.0001). As expected, complement activation was not affected by cell depletion and did not correlate with the concentration of any of the cell types. Thus, artificial surface-induced IL-8 and LTB4 synthesis was almost exclusively granulocyte dependent. However, MCP-1 synthesis was mainly a product of monocytes, although granulocytes and other subpopulations may partly contribute. (c) 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005.