Overactivation Of Complement Research Articles

Expansion of Anticomplement Therapy Indications from Rare Genetic Disorders to Common Kidney Diseases.

Complement constitutes a major part of the innate immune system. The study of complement in human health has historically focused on infection risks associated with complement protein deficiencies; however, recent interest in the field has focused on overactivation of complement as a cause of immune injury and the development of anticomplement therapies to treat human diseases. The kidneys are particularly sensitive to complement injury, and anticomplement therapies for several kidney diseases have been investigated. Overactivation of complement can result from loss-of-function mutations in complement regulators; gain-of-function mutations in key complement proteins such as C3 and factor B; or autoantibody production, infection, or tissue stresses, such as ischemia and reperfusion, that perturb the balance of complement activation and regulation. Here, we provide a high-level review of the status of anticomplement therapies, with an emphasis on the transition from rare diseases to more common kidney diseases.

A Dual-Targeted Metal-Organic Framework Based Nanoplatform for the Treatment of Rheumatoid Arthritis by Restoring the Macrophage Niche.

Inflammatory infiltration and bone destruction are important pathological features of rheumatoid arthritis (RA), which originate from the disturbed niche of macrophages. Here, we identified a niche-disrupting process in RA: due to overactivation of complement, the barrier function of VSIg4+ lining macrophages is disrupted and mediates inflammatory infiltration within the joint, thereby activating excessive osteoclastogenesis and bone resorption. However, complement antagonists have poor biological applications due to superphysiologic dose requirements and inadequate effects on bone resorption. Therefore, we developed a dual-targeted therapeutic nanoplatform based on the MOF framework to achieve bone-targeted delivery of the complement inhibitor CRIg-CD59 and pH-responsive sustained release. The surface-mineralized zoledronic acid (ZA) of ZIF8@CRIg-CD59@HA@ZA targets the skeletal acidic microenvironment in RA, and the sustained release of CRIg-CD59 can recognize and prevent the complement membrane attack complex (MAC) from forming on the surface of healthy cells. Importantly, ZA can inhibit osteoclast-mediated bone resorption, and CRIg-CD59 can promote the repair of the VSIg4+ lining macrophage barrier to achieve sequential niche remodeling. This combination therapy is expected to treat RA by reversing the core pathological process, circumventing the pitfalls of traditional therapy.

Persistently elevated complement alternative pathway biomarkers in COVID-19 correlate with hypoxemia and predict in-hospital mortality.

Mechanisms underlying the SARS-CoV-2-triggered hyperacute thrombo-inflammatory response that causes multi-organ damage in coronavirus disease 2019 (COVID-19) are poorly understood. Several lines of evidence implicate overactivation of complement. To delineate the involvement of complement in COVID-19, we prospectively studied 25 ICU-hospitalized patients for up to 21 days. Complement biomarkers in patient sera and healthy controls were quantified by enzyme-linked immunosorbent assays. Correlations with respiratory function and mortality were analyzed. Activation of complement via the classical/lectin pathways was variably increased. Strikingly, all patients had increased activation of the alternative pathway (AP) with elevated levels of activation fragments, Ba and Bb. This was associated with a reduction of the AP negative regulator, factor (F) H. Correspondingly, terminal pathway biomarkers of complement activation, C5a and sC5b-9, were significantly elevated in all COVID-19 patient sera. C5a and AP constituents Ba and Bb, were significantly associated with hypoxemia. Ba and FD at the time of ICU admission were strong independent predictors of mortality in the following 30 days. Levels of all complement activation markers were sustained throughout the patients’ ICU stays, contrasting with the varying serum levels of IL-6, C-reactive protein, and ferritin. Severely ill COVID-19 patients have increased and persistent activation of complement, mediated strongly via the AP. Complement activation biomarkers may be valuable measures of severity of lung disease and the risk of mortality. Large-scale studies will reveal the relevance of these findings to thrombo-inflammation in acute and post-acute COVID-19.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00430-021-00725-2.

Pharmacokinetic and Pharmacodynamic Evaluation of Ravulizumab in Adults with Severe Coronavirus Disease 2019.

IntroductionTerminal complement amplification is hypothesized to be a key contributor to the clinical manifestations of severe coronavirus disease 2019 (COVID-19). Ravulizumab, a humanized monoclonal antibody that binds with high affinity to complement protein C5 and inhibits terminal complement activation, is being evaluated as a treatment for COVID-19-related severe pneumonia, acute lung injury, and acute respiratory distress syndrome in an ongoing phase 3 randomized controlled trial (ALXN1210-COV-305). To address the overactivation of terminal complement in severe COVID-19 compared to the diseases in which ravulizumab is currently approved, a modified dosing regimen was adopted. This analysis evaluates preliminary pharmacokinetic/pharmacodynamic data to confirm the modified dosing regimen.MethodsWeight-based ravulizumab doses were administered on days 1, 5, 10, and 15. Serum levels of ravulizumab and free C5 were measured before and after administration of ravulizumab and any time on day 22. Free C5 levels < 0.5 μg/mL indicate complete C5 inhibition. The pharmacokinetic target was defined as ravulizumab concentrations at the end of the dosing interval > 175 μg/mL, the concentration above which C5 is completely inhibited.ResultsTwenty-two patients were included in this evaluation. At baseline, mean C5 concentration was 240 ± 67 μg/mL. In all patients and at all individual timepoints after the first dose was administered, ravulizumab concentrations remained > 175 μg/mL and free C5 concentrations remained < 0.5 μg/mL.ConclusionHigh levels of baseline C5 observed in patients with severe COVID-19 contribute to the growing body of evidence that suggests this disease is marked by amplification of terminal complement activation. Data from this preliminary pharmacokinetic/pharmacodynamic evaluation of 22 patients with severe COVID-19 show that the modified ravulizumab dosing regimen achieved immediate and complete terminal complement inhibition, which can be sustained for up to 22 days. These data support the continued use of this dosage regimen in the ongoing phase 3 study.Trial RegistrationClinicalTrials.gov identifier, NCT04369469

Broadly effective metabolic and immune recovery with C5 inhibition in CHAPLE disease.

Complement hyperactivation, angiopathic thrombosis, and protein-losing enteropathy (CHAPLE disease) is a lethal disease caused by genetic loss of the complement regulatory protein CD55 leading to overactivation of complement and innate immunity together with immunodeficiency due to immunoglobulin (Ig) wasting in the intestine. We report in vivo human data that we accumulated using the complement C5 inhibitor eculizumab for the medical treatment of CHAPLE patients and observed cessation of gastrointestinal pathology together with restoration of normal immunity and metabolism. We found that patients rapidly renormalized Ig concentrations and other serum proteins as revealed by aptamer profiling, re-established a healthy gut microbiome, discontinued Ig replacement and other treatments, and exhibited catch-up growth. Thus, we show blockade of C5 by eculizumab effectively re-establishes the regulation of the innate immune complement system to substantially reduce the pathophysiological manifestations of CD55 deficiency in humans.

The role and progress of complement activation in antiphospholipid syndrome

Antiphospholipid syndrome(APS) is a non-inflammatory autoimmune disease caused by anti-phospholipid antibodies. In recent years, it has been found that over-activation of complement is the key factor leading to the formation of thrombosis and pathological pregnancy in APS. With more understanding of the role of complement activation in the pathogenesis of APS, methods of complement inhibition therapy have emerged one after another. Therefore, the detection of complement components is of great significance for the early diagnosis, treatment and monitoring of APS. Key words: Complement activation; Antiphospholipid syndrome; Complement system proteins; Biomarkers

Complement Receptor C5aR1 Inhibition Reduces Pyroptosis in hDPP4-Transgenic Mice Infected with MERS-CoV.

Middle East respiratory syndrome coronavirus (MERS-CoV) is a highly pathogenic virus with a crude mortality rate of ~35%. Previously, we established a human DPP4 transgenic (hDPP4-Tg) mouse model in which we studied complement overactivation-induced immunopathogenesis. Here, to better understand the pathogenesis of MERS-CoV, we studied the role of pyroptosis in THP-1 cells and hDPP4 Tg mice with MERS-CoV infection. We found that MERS-CoV infection induced pyroptosis and over-activation of complement in human macrophages. The hDPP4-Tg mice infected with MERS-CoV overexpressed caspase-1 in the spleen and showed high IL-1β levels in serum, suggesting that pyroptosis occurred after infection. However, when the C5a-C5aR1 axis was blocked by an anti-C5aR1 antibody (Ab), expression of caspase-1 and IL-1β fell. These data indicate that MERS-CoV infection induces overactivation of complement, which may contribute to pyroptosis and inflammation. Pyroptosis and inflammation were suppressed by inhibiting C5aR1. These results will further our understanding of the pathogenesis of MERS-CoV infection.

Protective effects of ethyl pyruvate on lipopolysaccharide‑induced acute lung injury through inhibition of autophagy in neutrophils.

Among a number of clinical factors, bacterial infection is one of the most common causes of acute lung injury (ALI), a serious complication that carries a high risk of mortality (~40%). During the process of ALI, intense local and systemic inflammation is elicited, which exacerbates the injury. Neutrophil infiltration into airspace is observed in early stage of ALI, and is required for the full development of ALI through an array of mechanisms, including the release of granule contents and the production of pro-inflammatory cytokines, due to the overactivation of complement and cytokines. The present study noted that ethyl pyruvate alleviated ALI in lipopolysaccharide (LPS)-induced ALI mice. Increased autophagy in neutrophils from ALI mice was observed, while ethyl pyruvate diminished autophagy in neutrophils and constrained granule release, and therefore myeloperoxidase (MPO) in bronchoalveolar lavage fluid and the production of proinflammatory cytokines. Using neutrophil cells, it was identified that autophagy was required for neutrophil activation and granule release, and that ethyl pyruvate caused neutrophil autophagy, leading to the restriction of granule release, and thus contributing to the mitigation of ALI. If autophagy was obviated through knockdown of key regulator of autophagy Atg5, the effects of ethyl pyruvate on granule release by neutrophils disappeared. Taken together, the results demonstrated that ethyl pyruvate alleviates ALI through inhibition of autophagy-induced granule release by neutrophils, and this mechanism suggested a novel potential therapeutic target in autophagy regulation for ALI.

Inhibition of pre-existing natural periodontitis in non-human primates by a locally administered peptide inhibitor of complement C3.

Human periodontitis is associated with overactivation of complement, which is triggered by different mechanisms converging on C3, the central hub of the system. We assessed whether the C3 inhibitor Cp40 inhibits naturally occurring periodontitis in non-human primates (NHPs). Non-human primates with chronic periodontitis were intra-gingivally injected with Cp40 either once (5 animals) or three times (10 animals) weekly for 6weeks followed by a 6-week follow-up period. Clinical periodontal examinations and collection of gingival crevicular fluid and biopsies of gingiva and bone were performed at baseline and during the study. A one-way repeated-measures anova was used for data analysis. Whether administered once or three times weekly, Cp40 caused a significant reduction in clinical indices that measure periodontal inflammation (gingival index and bleeding on probing), tissue destruction (probing pocket depth and clinical attachment level) or tooth mobility. These clinical changes were associated with significantly reduced levels of pro-inflammatory mediators and decreased numbers of osteoclasts in bone biopsies. The protective effects of Cp40 persisted, albeit at reduced efficacy, for at least 6weeks following drug discontinuation. Cp40 inhibits pre-existing chronic periodontal inflammation and osteoclastogenesis in NHPs, suggesting a novel adjunctive anti-inflammatory therapy for treating human periodontitis.

AHUS in children: A severe disease with increasingly better diagnostic and treatment options

Atypical haemolytic uraemic syndrome (aHUS) accounts for around 10% of children presenting with haemolytic uremic syndrome, a triad of thrombocytopenia, haemolytic anaemia and renal failure. As opposed to diarrhoeal causes usually associated with E. coli infection producing the toxin STEC, aHUS generally presents without diarrhoea and is frequently associated with defects in the complement pathway leading to over-activation of complement.The major cause of paediatric aHUS is due to defects in complement factor H, a regulatory protein that limits complement activation. Mutations in CFH that are both dominant and recessive have been described. There are now over 10 other genes that have been described in aHUS with around 40% of sporadic cases of aHUS without an identified genetic cause.Clinically patients often present acutely with an infectious prodrome, and may require supportive haemodialysis and transfusion. Children occasionally have extra renal manifestations involving GI and CNS. Therapy involves plasma exchange to replace complement factors and more recently the use of C5 inhibitors that have been highly effective.In those who progress to end-stage renal failure, transplantation carries a high risk of disease recurrence and this is highest with CFH mutations.Exclusion of infectious HUS and of TTP, a similar adult disease due to defects in ADAMTS13, is important. Genetic diagnosis has been significantly aided by massively parallel sequencing that can sequence the 10 known genes in one run. Further analysis using MLPA to identify rearrangements and deletions is also increasingly of use. Genetic identification assists in risk stratification and in identifying those children who will benefit from C5 inhibitors. Atypical haemolytic uraemic syndrome (aHUS) accounts for around 10% of children presenting with haemolytic uremic syndrome, a triad of thrombocytopenia, haemolytic anaemia and renal failure. As opposed to diarrhoeal causes usually associated with E. coli infection producing the toxin STEC, aHUS generally presents without diarrhoea and is frequently associated with defects in the complement pathway leading to over-activation of complement. The major cause of paediatric aHUS is due to defects in complement factor H, a regulatory protein that limits complement activation. Mutations in CFH that are both dominant and recessive have been described. There are now over 10 other genes that have been described in aHUS with around 40% of sporadic cases of aHUS without an identified genetic cause. Clinically patients often present acutely with an infectious prodrome, and may require supportive haemodialysis and transfusion. Children occasionally have extra renal manifestations involving GI and CNS. Therapy involves plasma exchange to replace complement factors and more recently the use of C5 inhibitors that have been highly effective. In those who progress to end-stage renal failure, transplantation carries a high risk of disease recurrence and this is highest with CFH mutations. Exclusion of infectious HUS and of TTP, a similar adult disease due to defects in ADAMTS13, is important. Genetic diagnosis has been significantly aided by massively parallel sequencing that can sequence the 10 known genes in one run. Further analysis using MLPA to identify rearrangements and deletions is also increasingly of use. Genetic identification assists in risk stratification and in identifying those children who will benefit from C5 inhibitors.

Endoplasmic Reticulum Stress of Neutrophils Is Required for Ischemia/Reperfusion-Induced Acute Lung Injury.

Diverse clinical factors, including intestinal ischemia, contribute to acute lung injury (ALI), which has up to a 40% mortality rate. During the development of lung injury an immune response is elicited that exacerbates the lung insult. Neutrophils have been well studied in mediating the pulmonary insults through an assortment of mechanisms, such as release of granule contents and production of proinflammatory cytokines due to the overactivation of complement and cytokines. In this study, we found that enhanced endoplasmic reticulum (ER) stress was observed in infiltrated neutrophils in the early stage of an ALI mice model. In neutrophils, complement 5a (C5a) inspires strong ER stress through inositol-requiring kinase 1a and, to a less extent, the protein kinase R-like ER kinase signaling pathway. The granule release induced by C5a was ER stress mediated. Knowkdown of X-box-binding protein 1, a downstream signaling molecule of inositol-requiring kinase 1a, impaired granule release, based on myeloperoxidase production. Further analysis revealed that C5a induced ER stress by binding to C5a receptor in neutrophils. Using xbp(f/f) MRP8-cre mice in which X-box-binding protein 1 is deficient specifically in neutrophils and ER stress is deprived, we confirmed that ER stress in neutrophils was required for granule release in vivo and led to ALI, whereas dampening ER stress in neutrophils substantially alleviated ALI. Taken together, our results demonstrated that C5a receptor-mediated ER stress induced granule release in neutrophils, contributing to the development of ALI. This novel mechanism suggests a new potential therapeutic target in autophagy regulation for ALI.

Houttuyniacordata Thunb. polysaccharides ameliorates lipopolysaccharide-induced acute lung injury in mice

Ethnopharmacological relevanceHouttuynia cordata (HC) has been used as a folk therapy to treat pulmonary infections. This study aimed to determine the role and mechanism of action of polysaccharides isolated from HC (HCP) in lipopolysaccharide (LPS)-induced ALI in the mice. Materials and methodsLPS was delivered by the intratracheal route to Balb/c mice 2h before HCP (40, 80 and 160mg/kg) administration. ResultsThe number of total cells, protein and tumor necrosis factor-α (TNF-α) concentrations in bronchoalveolar lavage fluid, the wet/dry weight ratio (w/d) of lungs and pulmonary pathology of each mouse were analyzed, it was found that HCP significantly alleviated ALI induced by LPS. Moreover, in lungs of mice, it was found that the infiltration of inflammatory cells, the expression of Toll-like receptor 4 and complement deposition were significantly decreased by HCP treatment. In vitro assays showed that C5a, a complement activation product, induced significant macrophage migration and treatment with HCP prevented it. The in vitro results also proved that LPS increased nitric oxide and pro-inflammatory cytokines (TNF-α, interleukin-6, and interleukin-1β) production, and HCP antagonized these effects of LPS. It was also found that HCP alone augmented secretion of some pro-inflammatory cytokines. ConclusionThese results indicate that HCP may alleviate LPS induced lung inflammatory injury, which may be associated with its inhibitory effect on the over activation of complement and macrophages. This suggests a potential role to treat ALI.

Beneficial Effect of the Polysaccharides from Bupleurum smithii var. parvifolium on “Two-Hit” Acute Lung Injury in Rats

Radix Bupleuri is a traditional Chinese herb frequently used in the prescriptions for the treatment of inflammatory diseases. This study was to determine whether the crude polysaccharides isolated from the roots of Bupleurum smithii var. parvifolium (BPs) had beneficial effects on a "two-hit" acute lung injury model in rats. A two-hit lung injury model characterized by hemorrhagic shock followed by reperfusion and intratracheal lipopolysaccharide (1mgkg(-1)) administration was established in Wistar rats. Drugs and saline were administered 30min after the start of resuscitation. The two-hit acute lung injury model was successfully established. After oral administration, all BPs groups ameliorated pathological injury with lessened complement C3c deposit in lung. BPs 10 and 20mgkg(-1) diminished the ratio of wet-to-dry weight. In bronchoalveolar lavage (BAL) fluids, the protein concentration, the leukocytes counts, and the lung myeloperoxidase were significantly reduced. BPs also mediated the decreases in interleukin-6 and tumor necrosis factor-α in BAL fluids and in sera. Furthermore, BPs 20mgkg(-1) decreased the total complement hemolytic activity. BPs had beneficial effects on two-hit acute lung injury. The mechanisms of BPs on inflammatory disease might relate to its inhibitory effect on increased production of proinflammatory mediators and on overactivation of complement.

Transplantation in Atypical Hemolytic Uremic Syndrome

Atypical hemolytic uremic syndrome (aHUS) is a disease characterized by overactivation of complement. Recurrence following renal transplantation is determined by a genetic predisposition. Genetic screening of all individuals with aHUS should be performed prior to listing for transplantation. Individuals with isolated mutations in MCP have a low risk of recurrence and may be considered for kidney transplantation alone. In individuals with CFH and CFI mutations, the risk of recurrence following renal transplantation is high. Combined liver/kidney transplantation has been used successfully in individuals with CFH mutations following the introduction of perioperative plasma exchange; however, such a procedure is not without its risks. Liver/kidney transplantation has yet to be performed on individuals with CFI and C3 mutations but may be predicted to be successful. In individuals with CFH autoantibodies, a reduction in titer through plasma exchange and rituximab has been successful. Clinical trials of the complement C5 inhibitor eculizumab may improve prospects for isolated renal transplantation in individuals with complement protein mutations.

Pathogenesis of atherosclerosis: infectious versus immune pathogenesis. A new concept.

A novel concept for the pathogenesis of atherosclerosis is presented that obviates the need to search for a causative infectious agent. It is shown that LDL stranded in the subendothelium is transformed by enzymatic (non-oxidative) modification to yield an entity with complement- and macrophage-activating properties. This primarily serves to clear the stranded lipoprotein from tissues. However, sustained overactivation of complement and macrophages occurs when LDL-deposition is too extensive. A chronic inflammation then ensuing initiates and promotes the pathology of the atherosclerotic lesion. Atherosclerosis is thus a special form of an immunopathological disease which evolves through overactivation of the most archaic effector components of the immune system by altered self.

Identification of a novel complement-dependent serum-elicited inward current in the Xenopus oocyte provoking Ca 2+ influx and subsequent activation of Cl − channels

The membrane spanning complement channel is assumed to be a nonselective ion ‘pore’, although little evidence is available to support this hypothesis. In this paper we provide evidence that Ca 2+ entry and Cl − exit occur rapidly after complement activation and precede the development of a long-lasting complement-dependent inward current. Addition of rabbit serum (a source of heterologous complement) and mouse anti-human insulin receptor antibody to a single Xenopus oocyte expressing human insulin receptor was shown to stimulate an initial hyperpolarising current followed by a sustained depolarising current. On voltage clamping the oocyte, a novel long-lasting inward current generated by serum addition was detected. Complement classical pathway-stimulated calcium influx into the oocyte was directly demonstrated using 45Ca influx measurements. In addition, we found that Ca 2+ influx was required for the stimulation of the complement alternative pathway-dependent inward current. The novel conductance elicited by the classical pathway was outwardly rectifying, had a reversal potential of −35 ± 8 mV (or −52 ± 7 mV in the presence of chloride channel inhibitors), was inhibited by nifedipine, and was observed in the presence but not in the absence of the pore-forming complement component C9. As overactivation of complement does play a role in many inflammatory or autoimmune diseases, inhibition of early complement-mediated ion flux might restrict tissue damage and aid recovery from such diseases.