Knut Tore Lappegård

Cholesterol Crystals Induce Complement-Dependent Inflammasome Activation and Cytokine Release

Inflammation is associated with development of atherosclerosis, and cholesterol crystals (CC) have long been recognized as a hallmark of atherosclerotic lesions. CC appear early in the atheroma development and trigger inflammation by NLRP3 inflammasome activation. In this study we hypothesized whether CC employ the complement system to activate inflammasome/caspase-1, leading to release of mature IL-1β, and whether complement activation regulates CC-induced cytokine production. In this study we describe that CC activated both the classical and alternative complement pathways, and C1q was found to be crucial for the activation. CC employed C5a in the release of a number of cytokines in whole blood, including IL-1β and TNF. CC induced minimal amounts of cytokines in C5-deficient whole blood, until reconstituted with C5. Furthermore, C5a and TNF in combination acted as a potent primer for CC-induced IL-1β release by increasing IL-1β transcripts. CC-induced complement activation resulted in upregulation of complement receptor 3 (CD11b/CD18), leading to phagocytosis of CC. Also, CC mounted a complement-dependent production of reactive oxygen species and active caspase-1. We conclude that CC employ the complement system to induce cytokines and activate the inflammasome/caspase-1 by regulating several cellular responses in human monocytes. In light of this, complement inhibition might be an interesting therapeutic approach for treatment of atherosclerosis.

Human genetic deficiencies reveal the roles of complement in the inflammatory network: Lessons from nature

Complement component C5 is crucial for experimental animal inflammatory tissue damage; however, its involvement in human inflammation is incompletely understood. The responses to Gram-negative bacteria were here studied taking advantage of human genetic complement-deficiencies—natures own knockouts—including a previously undescribed C5 defect. Such deficiencies provide a unique tool for investigating the biological role of proteins. The experimental conditions allowed cross-talk between the different inflammatory pathways using a whole blood model based on the anticoagulant lepirudin, which does not interfere with the complement system. Expression of tissue factor, cell adhesion molecules, and oxidative burst depended highly on C5, mediated through the activation product C5a, whereas granulocyte enzyme release relied mainly on C3 and was C5a-independent. Release of cytokines and chemokines was mediated to varying degrees by complement and CD14; for example, interleukin (IL)-1β and IL-8 were more dependent on complement than IFN-γ and IL-6, which were highly dependent on CD14. IL-1 receptor antagonist (IL-1ra) and IFN-γ inducible protein 10 (IP-10) were fully dependent on CD14 and inversely regulated by complement, that is, complement deficiency and complement inhibition enhanced their release. Granulocyte responses were mainly complement-dependent, whereas monocyte responses were more dependent on CD14. Notably, all responses were abolished by combined neutralization of complement and CD14. The present study provides important insight into the comprehensive role of complement in human inflammatory responses to Gram-negative bacteria.

Effect of complement inhibition and heparin coating on artificial surface-induced leukocyte and platelet activation.

BACKGROUND Exposure of blood to artificial surfaces, as in cardiopulmonary bypass, induces an inflammatory response involving complement, leukocyte and platelet activation. To elucidate the specific role of complement in this process, studies were performed on blood circulated in polyvinyl chloride tubing in the absence and presence of complement inhibitors. Parallel experiments were performed with heparin-coated polyvinyl chloride tubing, which is known to prevent complement and cell activation. METHODS A novel experimental model was used, based on human whole blood anticoagulated with lepirudin. Complement activation products, myeloperoxidase, lactoferrin, and thrombospondin were quantified in enzyme immunoassays. Leukocyte CD11b expression and leukocyte-platelet conjugates were detected by flow cytometry. RESULTS Increased levels of C3 activation products, alternative pathway convertase, and the terminal SC5b-9 complex, combined with unchanged levels of C1rs-C1-inhibitor complexes and marginal changes in C4 activation demonstrated that complement was activated through the alternative pathway. Granulocyte and monocyte CD11b expression and granulocyte-platelet conjugate formation were efficiently attenuated by blocking either factor D, C3, C5, or C5a receptor. In contrast, monocyte-platelet conjugate formation and release of myeloperoxidase, lactoferrin, and thrombospondin were not reduced by complement inhibition. Heparin-coated polyvinyl chloride tubing efficiently reduced all inflammatory markers studied, except for C1rs-C1-inhibitor complexes, which increased, consistent with the enhancing effect of heparin on C1-inhibitor function. This effect did not, however, reduce fluid-phase classic pathway activation induced by heat-aggregated immunoglobulin G. CONCLUSIONS Leukocyte and platelet activation in response to artificial materials occur by mechanisms that vary in their dependence on complement. Heparin coating precludes both the complement-dependent and complement-independent reactions.

Plasma Lipopolysaccharide Is Closely Associated With Glycemic Control and Abdominal Obesity: Evidence from bariatric surgery

OBJECTIVE It is of vital importance to elucidate the triggering factors of obesity and type 2 diabetes to improve patient care. Bariatric surgery has been shown to prevent and even cure diabetes, but the mechanism is unknown. Elevated levels of lipopolysaccharide (LPS) predict incident diabetes, but the sources of LPS are not clarified. The objective of the current study was to evaluate the potential impact of plasma LPS on abdominal obesity and glycemic control in subjects undergoing bariatric surgery. RESEARCH DESIGN AND METHODS This was a prospective observational study involving a consecutive sample of 49 obese subjects undergoing bariatric surgery and 17 controls. Main assessments were plasma LPS, HbA1c, adipose tissue volumes (computed tomography), and quantified bacterial DNA in adipose tissue compartments. RESULTS Plasma levels of LPS were elevated in obese individuals compared with controls (P < 0.001) and were reduced after bariatric surgery (P = 0.010). LPS levels were closely correlated with HbA1c (r = 0.56; P = 0.001) and intra-abdominal fat volumes (r = 0.61; P < 0.001), but only moderately correlated with subcutaneous fat volumes (r = 0.33; P = 0.038). Moreover, there was a decreasing gradient (twofold) in bacterial DNA levels going from mesenteric via omental to subcutaneous adipose tissue compartments (P = 0.041). Finally, reduced LPS levels after bariatric surgery were directly correlated with a reduction in HbA1c (r = 0.85; P < 0.001). CONCLUSIONS Our findings support a hypothesis of translocated gut bacteria as a potential trigger of obesity and diabetes, and suggest that the antidiabetic effects of bariatric surgery might be mechanistically linked to, and even the result of, a reduction in plasma levels of LPS.

A Novel Enzyme Immunoassay for Plasma Thrombospondin: Comparison with Beta-Thromboglobulin as Platelet Activation Marker in Vitro and in Vivo

A novel enzyme immunoassay for plasma thrombospondin (TSP) based on commercially available monoclonal antibodies was established. The following conditions for correct collection and preservation of blood samples were required: venipuncture directly into a vacutainer containing citrate, theophylline, adenosine and dipyridamole, storage on ice, and separation of plasma within 30 minutes. Thereafter, the plasma TSP concentration remained constant at room temperature and after five times of freezing and thawing. Both inter- and intraassay variation coefficients were 5%. The lower detection limit was 20 microg/L. Median TSP concentration among 40 healthy blood donors was 43 microg/L, slightly lower than previously published. The assay is valid, reliable, and has certain advantages compared with previously published methods. TSP and beta-thromboglobulin (BTG) were then compared as platelet activation and biocompatibility markers in vivo: 23 patients undergoing cardiopulmonary bypass (CPB); and in vitro: effect of coating polyvinyl chloride with heparin. The kinetic patterns of TSP and BTG were markedly different in vivo but virtually identical in vitro, explained by different in vivo clearance mechanisms during CPB. We conclude that BTG is superior to TSP for evaluation of platelet activation during in vivo CPB, whereas TSP and BTG are virtually identical as markers in vitro.

Different inflammatory responses induced by three LDL-lowering apheresis columns.

Low‐density lipoprotein (LDL) apheresis is well‐established in selected patients with uncontrolled LDL levels. As such treatment affects biomarkers important in atherosclerosis and acute coronary syndromes, we systematically compared the inflammatory response induced by three LDL apheresis columns. Three patients with heterozygous familial hypercholesterolemia participated in a cross‐over study with six consecutive treatments with three different LDL apheresis columns: DL‐75 (whole blood adsorption), LA‐15 (plasma adsorption), and EC‐50W (plasma filtration). Biochemical parameters and inflammatory biomarkers, including complement activation products and 27 cytokines, chemokines, and growth factors were measured before and after treatment. Complement was activated through the alternative pathway. The final end product sC5b‐9 increased significantly (P < 0.01) and equally with all devices, whereas the anaphylatoxins C3a and C5a were lower by use of the adsorption columns. Hs‐CRP was reduced by 77% (DL‐75), 72% (LA‐15), and 43% (EC‐50W). The cytokines were consistently either increased (IL‐1ra, IP‐10, MCP‐1), decreased (IFN‐γ, TNF‐α, RANTES, PDGF, VEGF), or hardly changed (including IL‐6, IL8, MIP‐1αβ) during treatment. The changes were in general less pronounced with the adsorption columns. All columns reduced LDL significantly and to the same extent. In conclusion, three LDL‐apheresis devices with equal cholesterol‐lowering effect differed significantly with respect to the inflammatory response. J. Clin. Apheresis, 2009.

Anti-Inflammatory Effect of Cardiac Resynchronization Therapy

Background: Congestive heart failure (CHF) is associated with persistent immune activation. Medical therapy has been shown to exert only limited anti‐inflammatory effects. Cardiac resynchronization therapy (CRT) reduces morbidity and mortality in a subset of patients with heart failure, but it is not known whether this treatment affects the immune system as well. To test this hypothesis, eight patients with heart failure scheduled for CRT were investigated for immune activation before and 6 months after CRT treatment.

The complement system and toll-like receptors as integrated players in the pathophysiology of atherosclerosis

Despite recent medical advances, atherosclerosis is a global burden accounting for numerous deaths and hospital admissions. Immune-mediated inflammation is a major component of the atherosclerotic process, but earlier research focus on adaptive immunity has gradually switched towards the role of innate immunity. The complement system and toll-like receptors (TLRs), and the crosstalk between them, may be of particular interest both with respect to pathogenesis and as therapeutic targets in atherosclerosis. Animal studies indicate that inhibition of C3a and C5a reduces atherosclerosis. In humans modified LDL-cholesterol activate complement and TLRs leading to downstream inflammation, and histopathological studies indicate that the innate immune system is present in atherosclerotic lesions. Moreover, clinical studies have demonstrated that both complement and TLRs are upregulated in atherosclerotic diseases, although interventional trials have this far been disappointing. However, based on recent research showing an intimate interplay between complement and TLRs we propose a model in which combined inhibition of both complement and TLRs may represent a potent anti-inflammatory therapeutic approach to reduce atherosclerosis.

Changes in serum levels of E-selectin correlate to improved glycaemic control and reduced obesity in subjects with the metabolic syndrome

Objective. Inflammation plays an essential role in the atherosclerotic process. Cellular adhesion molecules (CAMs) such as E‐selectin, intercellular adhesion molecule‐1 (ICAM‐1) and vascular cell adhesion molecule‐1 (VCAM‐1) are involved in the rolling, adhesion and extravasation of monocytes and T‐lymphocytes into the atherosclerotic plaque. In the present study the effect of physical exercise and pravastatin (40 mg daily) on serum levels of CAMs and a possible role of adipose tissue in regulating serum levels of CAMs were investigated. Material and methods. The study was designed as an unmasked randomized 2×2 factorial trial of 12 weeks duration in 32 subjects with the metabolic syndrome. Changes from baseline were studied, and correlations between changes in CAMs, anthropometric measures, regional fat distribution, glycaemic control and the adipocytokine tumour necrosis factor‐α (TNF‐α) and adiponectin were investigated. Results. No significant changes in CAMs were observed in any of the intervention groups. However, when examining the whole study population regardless of intervention, changes in serum E‐selectin were significantly correlated to changes in body mass index (r = 0.48, p = 0.006), waist circumference (r = 0.48, p = 0.006), fasting glucose (r = 0.43, p = 0.02) and HbA1c (r = 0.45, p = 0.01), but not to changes in visceral fat, subcutaneous fat, TNF‐α or adiponectin. Conclusion. Changes in glycaemic control and obesity, rather than regional fat distribution, seem to influence the levels of E‐selectin in subjects with the metabolic syndrome.

Critical roles of complement and antibodies in host defense mechanisms against Neisseria meningitidis as revealed by human complement genetic deficiencies.

ABSTRACT Certain complement defects are associated with an increased propensity to contract Neisseria meningitidis infections. We performed detailed analyses of complement-mediated defense mechanisms against N. meningitidis 44/76 with whole blood and serum from two adult patients who were completely C2 or C5 deficient. The C5-deficient patient and the matched control were also deficient in mannose-binding lectin (MBL). The proliferation of meningococci incubated in freshly drawn whole blood was estimated by CFU and quantitative DNA real-time PCR. The serum bactericidal activity and opsonophagocytic activity by granulocytes were investigated, including heat-inactivated postvaccination sera, to examine the influence of antimeningococcal antibodies. The meningococci proliferated equally in C2- and C5-deficient blood, with a 2 log10 increase of CFU and 4- to 5-log10 increase in DNA copies. Proliferation was modestly decreased in reconstituted C2-deficient and control blood. After reconstitution of C5-deficient blood, all meningococci were killed, which is consistent with high antibody titers being present. The opsonophagocytic activity was strictly C2 dependent, appeared with normal serum, and increased with postvaccination serum. Serum bactericidal activity was strictly dependent on C2, C5, and high antibody titers. MBL did not influence any of the parameters observed. Complement-mediated defense against meningococci was thus dependent on the classical pathway. Some opsonophagocytic activity occurred despite low levels of antimeningococcal antibodies but was more efficient with immune sera. Serum bactericidal activity was dependent on C2, C5, and immune sera. MBL did not influence any of the parameters observed.