Evaluation of the impact of two C5 genetic variants on C5-eculizumab complex stability at the molecular level

Complement C5 is the target of the monoclonal antibody eculizumab, used in complement dysregulating disorders, like the rare disease Paroxysmal Nocturnal Hemoglobinuria (PNH). PNH is an acquired hematopoietic stem cell condition characterized by aberrant destruction of erythrocytes, chronic hemolytic anemia, and thromboembolism propensity. C5 is a protein component of the complement system which is part of the immune system of the body and plays a prominent role in the destruction of red blood cells, misidentifying them as a threat. This work describes the application of molecular dynamics simulations to the study of the underlying interactions between complement C5 and eculizumab. This study also reveals the importance of single nucleotide polymorphisms on C5 protein concerning the effective inhibition of the mAB, involving the mechanistic events taking place at the interface spots of the complex. The predicted conformational change in the C5 Arg885/His/Cys mutation has implications on the protein's interaction with eculizumab, compromising their compatibility. The acquired insights into the conformational changes, dynamics, flexibility, and interactions shed light on the knowledge of the function of this biomolecule providing answers about the poor response to the treatment in PNH patient carriers of the mutations. By investigating the intricate dynamics, significant connections between C5 and eculizumab can be uncovered. Such insights may aid in the creation of novel compounds or lead to the enhancement of eculizumab's efficacy.Communicated by Ramaswamy H. Sarma.

Discrepancy in clinical and laboratory profiles of NMOSD patients between AQP4 antibody positive and negative: can NMOSD be diagnosed without AQP4 antibody?

AQP4-IgG has been considered as the pathogenic factor leading to NMOSD. However, about 20-30% of patients lack AQP4-IgG. So far, all therapeutic medicines are ineffective for NMOSD patients without AQP4 IgG. Thus AQP4-IgG is the pathogenic factor of NMOSD has been suspected and challenged. In addition, lack of efficacy of immunotherapy in NMOSD without AQP4 IgG has been a serious problem in the neurology. Identifying the clinical and laboratory characteristics and diversities between NMOSD patients with and without AQP4-IgG can be helpful to further explore the pathogenesis of NMOSD and guide clinical treatment. This is a single-centre retrospective study in The First Hospital of Jilin University, China including 92 patients diagnosed as NMOSD from January 2013 to January 2015. The characteristics of clinic, blood, cerebrospinal fluid (CSF), and image between AQP4-IgG negative (AQP4-IgG-) and AQP4-IgG positive (AQP4-IgG+) NMOSDs were compared. Our results showed that in the AQP4-IgG+ group, the ratio of women to men was 5.55, while in AQP4-IgG- group was 1.54 (P = 0.0092). In the AQP4-IgG+ patients, the expanded disability status scale (EDSS) was from 0 to 8.5, with an average of 5.550 ± 0.25, and the AQP4-IgG- patients had the EDSS score from 0 to 9, with an average of 4.032 ± 0.36 (P = 0.0006), which mainly affected movement system (P < 0.05) and superficial sensory impairment (P < 0.05). In the AQP4-IgG+ group, the blood brain barrier (BBB) permeability (P = 0.0210) and myelin basic protein (MBP) were increased (P = 0.0310) when compared to AQP4-IgG- group. Higher level IL-17 was seen in AQP4-IgG+ group than AQP4-IgG- group (P= 0.0066). Our results demonstrated that the NMOSD with AQP4-IgG more likely occurred in women and presented more severe clinical symptoms as well as significant BBB damage and increased MBP and IL-17 in CSF and blood, respectively compared with NMOSD without AQP4-IgG group. The differences in clinical and laboratory profiles between NMOSD with and without AQP4-IgG indicate the heterogeneity of NMOSD, in which AQP4-IgG may not be the only pathogenic molecule. It is necessary to find more pathogenic factors and to explore the new pathogenesis of NMOSD and therapeutic methods in the future.

Complement inhibition can decrease the haemostatic response in a microvascular bleeding model at multiple levels

Background

Haemostasis is a crucial process by which the body stops bleeding. It is achieved by the formation of a platelet plug, which is strengthened by formation of a fibrin mesh mediated by the coagulation cascade. In proinflammatory and prothrombotic conditions, multiple interactions of the complement system and the coagulation cascade are known to aggravate thromboinflammatory processes and increase the risk of arterial and venous thrombosis. Whether those interactions also play a relevant role during the physiological process of haemostasis is not yet completely understood. The aim of this study was to investigate the potential role of complement components and activation during the haemostatic response to mechanical vessel injury.

Methods

We used a microvascular bleeding model that simulates a blood vessel, featuring human endothelial cells, perfusion with fresh human whole blood, and an inducible mechanical injury to the vessel. We studied the effects of complement inhibitors against components of the lectin (MASP-1, MASP-2), classical (C1s), alternative (FD) and common pathways (C3, C5), as well as a novel triple fusion inhibitor of all three complement pathways (TriFu). Effects on clot formation were analysed by recording of fibrin deposition and the platelet activation marker CD62P at the injury site in real time using a confocal microscope.

Results

With the inhibitors targeting MASP-2 or C1s, no significant reduction of fibrin formation was observed, while platelet activation was significantly reduced in the presence of the FD inhibitor. Both common pathway inhibitors targeting C3 or C5, respectively, were associated with a substantial reduction of fibrin formation, and platelet activation was also reduced in the presence of the C3 inhibitor. Triple inhibition of all three activation pathways at the C3-convertase level by TriFu reduced both fibrin formation and platelet activation. When several complement inhibitors were directly compared in two individual donors, TriFu and the inhibitors of MASP-1 and C3 had the strongest effects on clot formation.

Conclusion

The observed impact of complement inhibition on reducing fibrin clot formation and platelet activation suggests a role of the complement system in haemostasis, with modulators of complement initiation, amplification or effector functions showing distinct profiles. While the interactions between complement and coagulation might have evolved to support haemostasis and protect against bleeding in case of vessel injury, they can turn harmful in pathological conditions when aggravating thromboinflammation and promoting thrombosis.

Results of a phase 1/2 study of cemdisiran in healthy subjects and patients with paroxysmal nocturnal hemoglobinuria

Complement dysregulation underpins the physiopathology of paroxysmal nocturnal hemoglobinuria (PNH). Cemdisiran, an RNA interference investigational treatment, silences complement component 5 (C5) expression in the liver. Previously reported results showed sustained reduction in C5 levels following cemdisiran monotherapy, with >90% reduction in patients with PNH. This phase 1/2 study evaluated single (Part A, n = 32; 50-900 mg) or multiple (Part B, n = 24; 100-600 mg) ascending doses of cemdisiran or placebo (double-blind, randomized 3:1) in healthy adults, or cemdisiran in patients with PNH who were naive to, or receiving, eculizumab (Part C, n = 6; 200 or 400 mg weekly; open-label). The primary objective was to assess the safety and tolerability of cemdisiran. Other assessments included change in complement activity, lactate dehydrogenase levels, and inhibition of hemolysis following cemdisiran treatment. Cemdisiran was generally well tolerated in this study. Overall, 75%, 89%, and 100% of subjects in Parts A, B, and C, respectively, experienced ≥1 non-serious adverse event (AE). Most events were Grade 1 or 2 in severity and the most common AEs included nasopharyngitis and headache. Cemdisiran elicited robust, sustained reductions in the complement activity in healthy adults and patients with PNH. In Part C, exploratory analyses showed that cemdisiran monotherapy was insufficient to prevent hemolysis in patients with PNH as measured by serum lactate dehydrogenase levels. Cemdisiran and eculizumab combination therapy reduced the dose of eculizumab required to provide adequate control of intravascular hemolysis. These results demonstrate a potential benefit of cemdisiran coadministration in patients who are inadequate responders to eculizumab alone.

Crovalimab treatment in patients with paroxysmal nocturnal haemoglobinuria: Long-term results from the phase I/II COMPOSER trial

OBJECTIVES

This study reports long-term outcomes from the open-label extension (OLE) period of the Phase I/II COMPOSER trial (NCT03157635) that evaluated crovalimab in patients with paroxysmal nocturnal haemoglobinuria, who were treatment-naive or switched from eculizumab at enrolment.

METHODS

COMPOSER consists of four sequential parts followed by the OLE. The primary OLE objective was to assess long-term crovalimab safety, with a secondary objective to assess crovalimab pharmacokinetics and pharmacodynamics. Exploratory efficacy endpoints included change in lactate dehydrogenase (LDH), transfusion avoidance, haemoglobin stabilisation and breakthrough haemolysis (BTH).

RESULTS

A total 43 of 44 patients entered the OLE after completing the primary treatment period. Overall, 14 of 44 (32%) experienced treatment-related adverse events. Steady state exposure levels of crovalimab and terminal complement inhibition were maintained over the OLE. During the OLE, mean normalised LDH was generally maintained at ≤1.5× upper limit of normal, transfusion avoidance was achieved in 83%-92% of patients and haemoglobin stabilisation was reached in 79%-88% of patients across each 24-week interval. Five BTH events occurred with none leading to withdrawal.

CONCLUSIONS

Over a 3-year median treatment duration, crovalimab was well tolerated and sustained C5 inhibition was achieved. Intravascular haemolysis control, haemoglobin stabilisation and transfusion avoidance were maintained, signifying long-term crovalimab efficacy.

Complement C5 is a novel biomarker for liver metastasis of colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is one of the most prominent malignant diseases, with a high incidence and a dismal prognosis. Metastasis to the liver is the leading cause of death in CRC patients. This study aimed to identify accurate metastatic biomarkers of CRC and investigate the potential molecular mechanisms of liver metastasis of colorectal cancer (LMCRC).

METHODS

Three independent datasets were screened and downloaded from the Gene Expression Omnibus (GEO) database. The GEO2R tool was used to identify differentially expressed genes (DEGs) in CRC tissues and liver metastases. Next, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were conducted using the Database for Annotation, Visualization, and Integrated Discovery (DAVID). Furthermore, the protein-protein interactions (PPIs) of the DEGs were analyzed using the Search Tool for the Retrieval of Interacting Genes (STRING) database, Cytoscape, and Molecular Complex Detection (MCODE). Next, the expression levels and Kaplan-Meier survival analysis of the target gene between normal colon and CRC tissues were performed by UALCAN. The expression of the target gene in tissues and cell lines was verified by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), western blot, and immunohistochemistry (IHC) assay. The impact of the target gene on the proliferation, invasion, and migration ability of COAD cells was explored in vitro.

RESULTS

A total of 92 common DEGs were found in the three independent datasets. GO/KEGG enrichment analysis showed that the DEGs were mainly involved in 14 different pathways. The protein-protein interaction (PPI) network revealed that complement 5 (C5), the upstream gene of C8A in the complement system, was associated with C8 and other key hub genes. Meanwhile, the online UALCAN resource showed that C5 was up-regulated and facilitated malignant progression in COAD samples. Next, we confirmed that C5 remarkably increased and promoted cell proliferation, migration, and invasion in CRC cell lines, SW620 and SW480. The IHC assay showed C5 was also highly expressed in a majority of LMCRC tissues compared with paired CRC tissues.

CONCLUSIONS

The findings of our integrated bioinformatics study suggest that complement C5 might serve as a potential therapeutic target in patients with CRC.

A Novel Cleavage Pattern of Complement C5 Induced by Chlamydia trachomatis Infection via the Chlamydial Protease CPAF

Urogenital Chlamydia trachomatis infection is one of the most common bacterial sexually transmitted diseases globally. Untreated C. trachomatis infections can ascend to the upper genital tract and establish a series of severe complications. Previous studies using C3^−/− and C5^−/− mice models demonstrated that C3-independent activation of C5 occurred during C. trachomatis infection. However, the mechanism of how chlamydial infection activates C5 in the absence of C3 has yet to be elucidated. To delineate interactions between C5 and chlamydial infection, cleavage products in a co-incubation system containing purified human C5 and C. trachomatis-HeLa229 cell lysates were analyzed, and a novel cleavage pattern of C5 activation induced by C. trachomatis infection was identified. C5 was cleaved efficiently at the previously unidentified site K970, but was cleaved poorly at site R751. C5b was modified to C5b_Ct, which later formed C5b_Ct-9, which had enhanced lytic ability compared with C5b-9. The chlamydial serine protease CPAF contributed to C3-independent C5 activation during C. trachomatis infection. Nafamostat mesylate, a serine protease inhibitor with a good safety profile, had a strong inhibitory effect on C5 activation induced by chlamydial infection. These discoveries reveal the mechanism of C3-independent C5 activation induced by chlamydial infection, and furthermore provide a potential therapeutic target and drug for preventing tubal fibrosis caused by chlamydial infection.

Complement activation and regulation in preeclampsia and hemolysis, elevated liver enzymes, and low platelet count syndrome

The complement system is critical to human health owing to its central role in host defense and innate immunity. During pregnancy, the complement system must be appropriately regulated to allow for immunologic tolerance to the developing fetus and placenta. Although some degree of complement activation can be seen in normal pregnancy, the fetus seems to be protected in part through the placental expression of complement regulatory proteins, which inhibit complement activation at different steps along the complement activation cascade. In women who develop preeclampsia and hemolysis, elevated liver enzymes, and low platelet count syndrome, there is a shift toward increased complement activation and decreased complement regulation. There is an increase in placental deposition of C5b-9, which is the terminal effector of classical, lectin, and alternative complement pathways. C5b-9 deposition stimulates trophoblasts to secrete soluble fms-like tyrosine kinase-1, which sequesters vascular endothelial growth factor and placental growth factor. Pathogenic mutations or deletions in complement regulatory genes, which predispose to increased complement activation, have been detected in women with preeclampsia and hemolysis, elevated liver enzymes, and low platelet count syndrome. Before the disease, biomarkers of alternative complement pathway activation are increased; during active disease, biomarkers of terminal complement pathway activation are increased. Urinary excretion of C5b-9 is associated with preeclampsia with severe features and distinguishes it from other hypertensive disorders of pregnancy. Taken together, existing data link preeclampsia and hemolysis, elevated liver enzymes, and low platelet count syndrome with increased activation of the terminal complement pathway that, in some cases, may be influenced by genetic alterations in complement regulators. These findings suggest that the inhibition of the terminal complement pathway, possibly through C5 blockade, may be an effective strategy to treat preeclampsia and hemolysis, elevated liver enzymes, and low platelet count syndrome, but this strategy warrants further evaluation in clinical trials.

C5 Variant rs10985126 is Associated with Mortality in Patients with Symptomatic Coronary Artery Disease

BACKGROUND

Complement component 5a (C5a) is a highly potent anaphylatoxin with a variety of pro-inflammatory effects. C5a contributes to progression of atherosclerosis and inhibition of the receptor (C5aR) might offer a therapeutic strategy in this regard. Single nucleotide polymorphisms (SNPs) of the C5 gene may modify protein expression levels and therefore function of C5a and C5aR. This study aimed to examine associations between clinically relevant C5a SNPs and the prognosis of patients with symptomatic coronary artery disease (CAD). Furthermore, we sought to investigate the influence of C5 SNPs on C5aR platelet surface expression and circulating C5a levels.

METHODS

C5 variants (rs25681, rs17611, rs17216529, rs12237774, rs41258306, and rs10985126) were analyzed in a consecutive cohort of 833 patients suffering from symptomatic coronary artery disease (CAD). Circulating C5a levels were determined in 116 patients whereas C5aR platelet surface expression was measured in 473 CAD patients. Endpoints included all-cause mortality, myocardial infarction (MI), and ischemic stroke (IS). Homozygous carriers (HC) of the minor allele (rs10985126) showed significantly higher all-cause mortality than major allele carriers. While we could not find significant associations between rs10985126 allele frequency and C5aR platelet surfazl ce expression, significantly elevated levels of circulating C5a were found in HC of the minor allele of the respective genotype. rs17216529 allele frequency correlated with the composite combined endpoint and bleeding events. However, since the number of HC of the minor allele of this genotype was low, we cannot draw a robust conclusion about the observed associations.

CONCLUSION

In this study, we provide evidence for the prognostic relevance of rs10985126 in CAD patients. C5 rs10985126 may serve as a prognostic biomarker for risk stratification in high-risk CAD patients and consequently promote tailored therapies.

Zilucoplan: An Investigational Complement C5 Inhibitor for the Treatment of Acetylcholine Receptor Autoantibody-Positive Generalized Myasthenia Gravis

INTRODUCTION

Generalized myasthenia gravis (gMG) is an autoimmune disorder in which pathogenic autoantibodies damage the neuromuscular junction, causing disabling or life-threatening muscle weakness. Most treatments nonspecifically inhibit aspects of the immune system, do not directly address the causal mechanisms of tissue damage, and often have side-effect profiles that negatively impact patients. Understanding of the central pathogenic role of the complement cascade in gMG is advancing, and a new complement-targeting treatment is under investigation.

AREAS COVERED

We provide an overview of gMG etiology, the complement cascade, current treatments, and the investigational gMG therapy zilucoplan. Zilucoplan is a small, subcutaneously administered, macrocyclic peptide that inhibits cleavage of complement component C5 and the subsequent formation of the membrane attack complex.

EXPERT OPINION

In a randomized, double-blind, placebo-controlled, phase 2 clinical trial, zilucoplan demonstrated clinically meaningful complement inhibition in patients with acetylcholine receptor-positive gMG. Zilucoplan, a first-of-its-kind cyclic peptide targeting C5, appears to be a therapeutic option for the treatment of gMG based on available pharmacokinetic/pharmacodynamic data and phase 1 and 2 efficacy, safety, and tolerability data with limited long-term follow-up. Zilucoplan use earlier in the treatment paradigm would be suitable in this population should phase 3 efficacy and safety data be equally favorable.

The allosteric modulation of complement C5 by knob domain peptides

Bovines have evolved a subset of antibodies with ultra-long heavy chain complementarity determining regions that harbour cysteine-rich knob domains. To produce high-affinity peptides, we previously isolated autonomous 3–6 kDa knob domains from bovine antibodies. Here, we show that binding of four knob domain peptides elicits a range of effects on the clinically validated drug target complement C5. Allosteric mechanisms predominated, with one peptide selectively inhibiting C5 cleavage by the alternative pathway C5 convertase, revealing a targetable mechanistic difference between the classical and alternative pathway C5 convertases. Taking a hybrid biophysical approach, we present C5-knob domain co-crystal structures and, by solution methods, observed allosteric effects propagating >50 Å from the binding sites. This study expands the therapeutic scope of C5, presents new inhibitors, and introduces knob domains as new, low molecular weight antibody fragments, with therapeutic potential.

Antibodies are proteins produced by the immune system that can selectively bind to other molecules and modify their behaviour. Cows are highly equipped at fighting-off disease-causing microbes due to the unique shape of some of their antibodies. Unlike other jawed vertebrates, cows’ antibodies contain an ultra-long loop region that contains a ‘knob domain’ which sticks out from the rest of the antibody. Recent research has shown that when detached, the knob domain behaves like an antibody fragment, and can independently bind to a range of different proteins.

Antibody fragments are commonly developed in the laboratory to target proteins associated with certain diseases, such as arthritis and cancer. But it was unclear whether the knob domains from cows’ antibodies could also have therapeutic potential. To investigate this, Macpherson et al. studied how knob domains attach to complement C5, a protein in the inflammatory pathway which is a drug target for various diseases, including severe COVID-19.

The experiments identified various knob domains that bind to complement C5 and inhibits its activity by altering its structure or movement. Further tests studying the structure of these interactions, led to the discovery of a common mechanism by which inhibitors can modify the behaviour of this inflammatory protein.

Complement C5 is involved in numerous molecular pathways in the immune system, which means many of the drugs developed to inhibit its activity can also leave patients vulnerable to infection. However, one of the knob domains identified by Macpherson et al. was found to reduce the activity of complement C5 in some pathways, whilst leaving other pathways intact. This could potentially reduce the risk of bacterial infections which sometimes arise following treatment with these types of inhibitors.

These findings highlight a new approach for developing drug inhibitors for complement C5. Furthermore, the ability of knob domains to bind to multiple sites of complement C5 suggests that this fragment could be used to target proteins associated with other diseases.

Complement C5 activation promotes type 2 diabetic kidney disease via activating STAT3 pathway and disrupting the gut-kidney axis

Diabetic kidney disease (DKD) is a severe DM complication. While complement C5 up-regulation and gut dysbiosis are found in T2DM, their roles in DKD are unclear. Here, we investigated the effect of C5 on the gut microbiota during DKD development. Renal C5a/C5a receptor (C5aR) expression changes were measured in T2DM patients and db/db mice. Db/db mice were treated with a C5aR antagonist (C5aRA), and renal function, gut microbiota and renal genome changes were analysed. The effects of C5a and short-chain fatty acids (SCFAs) on the signal transducer and activator of transcription 3 (STAT3) pathway were examined in vitro. C5a was up-regulated in glomerular endothelial cells (GECs) of T2DM patients and db/db mice. Although glucose and lipid metabolism were unchanged, C5aR blockade alleviated renal dysfunction, ECM deposition, macrophage infiltration and proinflammatory factor expression in db/db mice. C5aRA partly reversed the declines in gut microbiota diversity and abundance and gut SCFA levels in db/db mice. C5aRA down-regulated the expression of many immune response-related genes, such as STAT3, in db/db mouse kidneys. C5aRA and SCFAs suppressed C5a-induced STAT3 activation in human renal glomerular endothelial cells (HRGECs). Based on our results, C5 hyperactivation promotes DKD by activating STAT3 in GECs and impairing the gut-kidney axis, suggesting that this hyperactivation is a potential target for the treatment of DKD.

COVID-19: A collision of complement, coagulation and inflammatory pathways

COVID-19 is frequently accompanied by a hypercoagulable inflammatory state with microangiopathic pulmonary changes that can precede the diffuse alveolar damage characteristic of typical acute respiratory distress syndrome (ARDS) seen in other severe pathogenic infections. Parallels with systemic inflammatory disorders such as atypical hemolytic uremic syndrome (aHUS) have implicated the complement pathway in the pathogenesis of COVID-19, and particularly the anaphylatoxins C3a and C5a released from cleavage of C3 and C5, respectively. C5a is a potent cell signalling protein that activates a cytokine storm-a hyper-inflammatory phenomenon-within hours of infection and the innate immune response. However, excess C5a can result in a pro-inflammatory environment orchestrated through a plethora of mechanisms that propagate lung injury, lymphocyte exhaustion, and an immune paresis. Furthermore, disruption of the homeostatic interactions between complement and extrinsic and intrinsic coagulation pathways contributes to a net pro-coagulant state in the microvasculature of critical organs. Fatal COVID-19 has been associated with a systemic inflammatory response accompanied by a pro-coagulant state and organ damage, particularly microvascular thrombi in the lungs and kidneys. Pathologic studies report strong evidence of complement activation. C5 blockade reduces inflammatory cytokines and their manifestations in animal studies, and has shown benefits in patients with aHUS, prompting investigation of this approach in the treatment of COVID-19. This review describes the role of the complement pathway and particularly C5a and its aberrations in highly pathogenic virus infections, and therefore its potential as a therapeutic target in COVID-19.

Pharmacokinetic and pharmacodynamic effects of ravulizumab and eculizumab on complement component 5 in adults with paroxysmal nocturnal haemoglobinuria: results of two phase 3 randomised, multicentre studies

Ravulizumab, a novel long‐acting complement component 5 (C5) inhibitor administered every 8 weeks (q8w), was non‐inferior to eculizumab for all efficacy outcomes in two randomised, open‐label, phase 3 trials in C5 inhibitor‐naïve (Study 301) and eculizumab‐experienced (Study 302) adult patients with paroxysmal nocturnal haemoglobinuria (PNH). This pre‐specified analysis characterised ravulizumab pharmacokinetics (PK), pharmacodynamics (PD; free C5 levels), and PD differences between medications (Study 301, n = 246; Study 302, n = 195). Ravulizumab PK parameters were determined using non‐compartmental analysis. Serum free C5 was quantified with a Gyros‐based fluorescence assay (ravulizumab) and an electrochemiluminescence ligand‐binding assay (eculizumab). Ravulizumab PK parameters were numerically comparable in both studies; the median time to maximum concentrations ranged from 2·3 to 2·8 and 2·3 to 2·6 h in studies 301 and 302, respectively. Ravulizumab steady‐state serum concentrations were achieved immediately after the first dose and sustained throughout treatment. For ravulizumab, the mean (SD) post hoc terminal elimination half‐life was 49·7 (8·9) days. Serum free C5 concentrations <0·5 µg/ml were achieved after the first ravulizumab dose and sustained throughout treatment in both studies. In a minority of patients, free C5 concentrations <0·5 µg/ml were not consistently achieved with eculizumab in either study. Ravulizumab q8w was more consistent in providing immediate, complete, sustained C5 inhibition than eculizumab every‐2‐weeks in patients with PNH.

Complement component 5 does not interfere with physiological hemostasis but is essential for Escherichia coli-induced coagulation accompanied by Toll-like receptor 4

There is a close cross-talk between complement, Toll-like receptors (TLRs) and coagulation. The role of the central complement component 5 (C5) in physiological and pathophysiological hemostasis has not, however, been fully elucidated. This study examined the effects of C5 in normal hemostasis and in Escherichia coli-induced coagulation and tissue factor (TF) up-regulation. Fresh whole blood obtained from six healthy donors and one C5-deficient individual (C5D) was anti-coagulated with the thrombin inhibitor lepirudin. Blood was incubated with or without E. coli in the presence of the C5 inhibitor eculizumab, a blocking anti-CD14 monoclonal antibody (anti-CD14) or the TLR-4 inhibitor eritoran. C5D blood was reconstituted with purified human C5. TF mRNA was measured by quantitative polymerase chain reaction (qPCR) and monocyte TF and CD11b surface expression by flow cytometry. Prothrombin fragment 1+2 (PTF1·2) in plasma and microparticles exposing TF (TF-MP) was measured by enzyme-linked immunosorbent assay (ELISA). Coagulation kinetics were analyzed by rotational thromboelastometry and platelet function by PFA-200. Normal blood with eculizumab as well as C5D blood with or without reconstitution with C5 displayed completely normal biochemical hemostatic patterns. In contrast, E. coli-induced TF mRNA and TF-MP were significantly reduced by C5 inhibition. C5 inhibition combined with anti-CD14 or eritoran completely inhibited the E. coli-induced monocyte TF, TF-MP and plasma PTF1·2. Addition of C5a alone did not induce TF expression on monocytes. In conclusion, C5 showed no impact on physiological hemostasis, but substantially contributed to E. coli-induced procoagulant events, which were abolished by the combined inhibition of C5 and CD14 or TLR-4.

Alternative Pathway Is Essential for Glomerular Complement Activation and Proteinuria in a Mouse Model of Membranous Nephropathy

Membranous nephropathy is an immune kidney disease caused by IgG antibodies that form glomerular subepithelial immune complexes. Proteinuria is mediated by complement activation, as a result of podocyte injury by C5b-9, but the role of specific complement pathways is not known. Autoantibodies-mediating primary membranous nephropathy are predominantly of IgG4 subclass, which cannot activate the classical pathway. Histologic evidence from kidney biopsies suggests that the lectin and the alternative pathways may be activated in membranous nephropathy, but the pathogenic relevance of these pathways remains unclear. In this study, we evaluated the role of the alternative pathway in a mouse model of membranous nephropathy. After inducing the formation of subepithelial immune complexes, we found similar glomerular IgG deposition in wild-type mice and in factor B-null mice, which lack a functional alternative pathway. Unlike wild-type mice, mice lacking factor B did not develop albuminuria nor exhibit glomerular deposition of C3c and C5b-9. Albuminuria was also reduced but not completely abolished in C5-deficient mice. Our results provide the first direct evidence that the alternative pathway is necessary for pathogenic complement activation by glomerular subepithelial immune complexes and is, therefore, a key mediator of proteinuria in experimental membranous nephropathy. This knowledge is important for the rational design of new therapies for membranous nephropathy.

Sexual dimorphism of liver metastasis by murine pancreatic neuroendocrine tumors is affected by expression of complement C5

In a mouse model for neuroendocrine tumors of the pancreas (PanNETs), liver metastasis occurred at a higher frequency in males. Male mice also had higher serum and intratumoral levels of the innate immunity protein complement C5. In mice that lost the ability to express complement C5, there was a lower frequency of metastasis, and males no longer had a higher frequency of metastasis than females. Treatment with PMX53, a small molecule antagonist of C5aR1/CD88, the receptor for complement C5a, also reduced metastasis. Mice lacking a functional gene for complement C5 had smaller primary tumors, which were less invasive and lacked the CD68+ macrophages that have previously been associated with metastasis in this type of tumor. This is the first report of a gene that causes sexual dimorphism of metastasis in a mouse model. In the human disease, which also shows sexual dimorphism for metastasis, clinically advanced tumors expressed more complement C5 than less advanced tumors.