Complement the hemostatic system: an intimate relationship

Monoclonal Gammopathy of Thrombotic Significance

The current review provides an overview of the thrombotic risk observed in patients with MG who do not otherwise require treatment. We discuss clinical and biomarker studies that highlight the heterogenous hemostatic profile observed in these patients and how knowledge has evolved over the past 20 years. Biomarker studies suggest shared biologic features between multiple myeloma and monoclonal gammopathy of undetermined significance (MGUS), which involves both hypercoagulability and platelet activation. Hemostatic abnormalities identified in MGUS patients cannot be translated into clinical practice as they lack correlation to clinical events. The prothrombotic phenotype of MGUS patients has not been ascertained yet, but novel data on coagulation markers are promising. We also review rare conditions associated with the thrombogenic properties of the monoclonal protein that predispose to arterial, venous or microthrombotic events and demonstrate that the M-protein can be linked to clinically significant thrombotic events. Cryoglobulinemia, cryofibrinogenemia, cryo-crystaloglobulinemia and MG-related antiphospholipid syndrome are reviewed. We propose the new umbrella term "monoclonal gammopathy of thrombotic significance" (MGTS) to refer to significant, recurrent thrombotic events in patients with MGUS that provide a rationale for targeting the underlying plasma cell clone. Identifying MGUS patients at high risk for thrombotic events is currently a challenge.

Exploratory Prognostic Biomarkers of Complement-Mediated Thrombotic Microangiopathy (CM-TMA) in Adults with Atypical Hemolytic Uremic Syndrome (aHUS): Analysis of a Phase III Study of Ravulizumab

BACKGROUND

Clinically validated biomarkers for monitoring of patients with complement-mediated thrombotic microangiopathy (CM-TMA) including atypical hemolytic uremic syndrome (aHUS) are unavailable. Improved characterization of biomarkers in patients with aHUS may inform treatment and monitoring for patients with CM-TMA.

METHODS

This analysis used data collected from 55/56 (98.2 %) adult patients with aHUS enrolled in the global Phase III study of ravulizumab (NCT02949128). Baseline (pre-treatment) patient serum, plasma and urine biomarker levels were compared with the maximum observed levels in normal donors and evaluated for associations with pre-treatment plasma exchange/infusion and dialysis status. Biomarkers were also assessed for associations with key clinical measures at baseline and with changes at 26 and 52 weeks from treatment initiation via linear regression analyses.

RESULTS

Complement-specific urine levels (factor Ba and sC5b-9) were elevated in >85 % of patients and are significantly associated with pre-treatment kidney dysfunction. Baseline levels of other evaluated biomarkers were elevated in >70 % of patients with aHUS, except for plasma sC5b-9 and serum sVCAM-1. Lower levels of urine complement markers at baseline are significantly associated with improvements in total urine protein and estimated glomerular filtration rate at 26 and 52 weeks of treatment. Clinical assessment of complement activation by a receiver operating characteristic analysis of Ba and sC5b-9 was more sensitive and specific in urine matrix than plasma.

CONCLUSION

This analysis identified a set of biomarkers that may show utility in the prognosis of CM-TMA, including their potential for measuring and predicting response to anti-C5 therapy. Further studies are required to enhance patient risk stratification and improve management of these vulnerable patients.

CLINICAL TRIALS REGISTRATION

NCT02949128, ClinicalTrials.gov.

Elevated levels of C3, C4, and CH50 of the complement system in ICU and non-ICU patients with COVID-19

PURPOSE

SARS-CoV-2 infection has spread in each corner of the world. Many health systems have dealt with it intensively. The complement system is an instrumental component in the inflammatory immune response and plays a role in the activation of blood coagulation. Our understanding of the pathophysiology of SARS-CoV-2 is still limited but is constantly expanding. This study aimed to determine changes in the complement system in intensive care unit (ICU) and non-ICU patients with COVID-19.

METHODS

In a cross-sectional study, plasma levels of C3, C4, and CH50 were determined in two groups of ICU and non-ICU patients with COVID-19 to understand the potential effects of SARS-CoV-2 on the innate immune system. The assays of C3 and C4 were conducted using turbidimetry method. The CH50 test was conducted using the functional method.

RESULTS

The present study revealed that the C3, C4, and CH50 plasma levels were 142.48 ± 30.38 mg/dL, 32.58 ± 8.78 mg/dL, and 61.74 ± 19.54%, respectively. These results indicate high levels of complement components C3 and C4 and complement function (CH50) in patients with COVID-19 than normal ranges. Plasma levels of C3, C4, and CH50 were higher in ICU patients than in non-ICU COVID-19 groups.

CONCLUSION

These results indicate that the innate immune system was activated in both ICU and non-ICU patients in response to SARS-CoV-2 infection. Further studies with a larger number of COVID-19 patients and additional testing of complement components (C3a and C5a) may reveal the role of COVID-19 infection in the activation of the complement system.

Mechanisms of immunothrombosis and vasculopathy in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune thrombophilia propelled by circulating antiphospholipid antibodies that herald vascular thrombosis and obstetrical complications. Antiphospholipid antibodies recognize phospholipids and phospholipid-binding proteins and are not only markers of disease but also key drivers of APS pathophysiology. Thrombotic events in APS can be attributed to various conspirators including activated endothelial cells, platelets, and myeloid-lineage cells, as well as derangements in coagulation and fibrinolytic systems. Furthermore, recent work has especially highlighted the role of neutrophil extracellular traps (NETs) and the complement system in APS thrombosis. Beyond acute thrombosis, patients with APS can also develop an occlusive vasculopathy, a long-term consequence of APS characterized by cell proliferation and infiltration that progressively expands the intima and leads to organ damage. This review will highlight known pathogenic factors in APS and will also briefly discuss similarities between APS and the thrombophilic coagulopathy of COVID-19.

Genetic justification of severe COVID-19 using a rigorous algorithm

Recent studies suggest excessive complement activation in severe coronavirus disease-19 (COVID-19). The latter shares common characteristics with complement-mediated thrombotic microangiopathy (TMA). We hypothesized that genetic susceptibility would be evident in patients with severe COVID-19 (similar to TMA) and associated with disease severity. We analyzed genetic and clinical data from 97 patients hospitalized for COVID-19. Through targeted next-generation-sequencing we found an ADAMTS13 variant in 49 patients, along with two risk factor variants (C3, 21 patients; CFH,34 patients). 31 (32%) patients had a combination of these, which was independently associated with ICU hospitalization (p = 0.022). Analysis of almost infinite variant combinations showed that patients with rs1042580 in thrombomodulin and without rs800292 in complement factor H did not require ICU hospitalization. We also observed gender differences in ADAMTS13 and complement-related variants. In light of encouraging results by complement inhibitors, our study highlights a patient population that might benefit from early initiation of specific treatment.

Increased risk of thrombotic events in cold agglutinin disease: A 10-year retrospective analysis

BACKGROUND

Cold agglutinin disease (CAD) is a rare autoimmune hemolytic anemia mediated by IgM autoantibodies that trigger hemolysis via classical complement pathway. Increased incidence of thrombotic events (TEs) has been reported in patients with other forms of hemolysis. The incidence of TEs in patients with CAD is unknown.

OBJECTIVE

Evaluate TE risk in patients with CAD.

PATIENTS/METHODS

This is a matched cohort comparison study evaluating the risk of TEs in patients with CAD and without CAD over a 10-year period. A total of 608 patients with CAD were identified in the Optum Claims-Clinical data set by reviewing clinical notes for CAD terms and matched with up to 10 patients without CAD (N = 5873). TEs were defined as the first medical claim for a TE using International Classification of Diseases, Ninth and Tenth Revision codes. Cox regression models were used to estimate time to first TE. Sensitivity analyses were conducted to estimate TE risk among patients with primary CAD.

RESULTS

At least 1 TE occurred in 29.6% of patients with CAD and 17.6% of patients without CAD. The proportion of patients experiencing venous, arterial, and cerebral TEs were each higher among CAD patients. The overall risk of having TEs was higher in patients with CAD (adjusted hazard ratio [aHR], 1.94; 95% confidence interval [CI], 1.64-2.30). Patients with presumed primary CAD also demonstrated an increased risk of TEs (aHR, 1.80; 95% CI, 1.46-2.22). Patients with CAD with the fewest comorbidities had 2.44-fold higher risk of having a TE (95% CI, 1.70-3.52).

CONCLUSIONS

Patients with CAD have an increased risk of TEs when compared with a matched non-CAD population.

Eculizumab decreases the procoagulant activity of extracellular vesicles in paroxysmal nocturnal hemoglobinuria: A pilot prospective longitudinal clinical study

INTRODUCTION

Paroxysmal nocturnal hemoglobinuria (PNH) is a disease characterized by the susceptibility of blood cells to attack by the complement system, inducing extracellular vesicle (EV) production. Thromboembolism is the leading cause of death in this condition. Eculizumab, a humanized monoclonal antibody which inhibits the C5 protein of the complement, reduces the thrombotic risk in PNH.

MATERIALS AND METHOD

We conducted a pilot, prospective, open-label, longitudinal clinical study with six PNH patients treated with eculizumab. The aim was to measure, by flow cytometry, the EVs' production in the patients' platelet-free plasma (PFP) before and during the treatment. We also assessed the procoagulant activity in PFP using STA®-Procoag-PPL and thrombin generation assays (TGA). A high-sensitive version of TGA was also used to study the procoagulant profile induced by the EVs using EVs pelleted from PFP.

RESULTS

We observed a decrease in platelet EV count with eculizumab treatment (p<0.05). STA®-Procoag-PPL assay showed a decrease of the procoagulant profile induced by procoagulant phospholipids (PL) during treatment. These results were not confirmed by TGA on PFP, due to a lack of sensitivity. Thus, we used a high-sensitive version of TGA that enabled us to observe variation in the procoagulant profile induced by the EVs with eculizumab (p<0.05).

CONCLUSIONS

Eculizumab has an impact on the extent of EV production and on the procoagulant profile induced by the procoagulant PL and the EVs. One factor in the antithrombotic action of eculizumab is its ability to decrease EV production and the procoagulant profile induced by PL and EVs.

Complement inhibition by hydroxychloroquine prevents placental and fetal brain abnormalities in antiphospholipid syndrome

Placental ischemic disease and adverse pregnancy outcomes are frequently observed in patients with antiphospholipid syndrome (APS). Despite the administration of conventional antithrombotic treatment a significant number of women continue to experience adverse pregnancy outcomes, with uncertain prevention and management. Efforts to develop effective pharmacological strategies for refractory obstetric APS cases will be of significant clinical benefit for both mothers and fetuses. Although the antimalarial drug, hydroxychloroquine (HCQ) is increasingly used to treat pregnant women with APS, little is known about its efficacy and mechanism of action of HCQ. Because complement activation plays a crucial and causative role in placental ischemia and abnormal fetal brain development in APS we hypothesised that HCQ prevents these pregnancy complications through inhibition of complement activation. Using a mouse model of obstetric APS that closely resembles the clinical condition, we found that HCQ prevented fetal death and the placental metabolic changes -measured by proton magnetic resonance spectroscopy in APS-mice. Using 111In labelled antiphospholipid antibodies (aPL) we identified the placenta and the fetal brain as the main organ targets in APS-mice. Using this same method, we found that HCQ does not inhibit aPL binding to tissues as was previously suggested from in vitro studies. While HCQ did not affect aPL binding to fetal brain it prevented fetal brain abnormal cortical development. HCQ prevented complement activation in vivo and in vitro. Complement C5a levels in serum samples from APS patients and APS-mice were lower after treatment with HCQ while the antibodies titres remained unchanged. HCQ prevented not only placental insufficiency but also abnormal fetal brain development in APS. By inhibiting complement activation, HCQ might also be an effective antithrombotic therapy.

Eculizumab reduces complement activation, inflammation, endothelial damage, thrombosis, and renal injury markers in aHUS

Atypical hemolytic uremic syndrome (aHUS) is a genetic, life-threatening disease characterized by uncontrolled complement activation, systemic thrombotic microangiopathy (TMA), and vital organ damage. We evaluated the effect of terminal complement blockade with the anti-C5 monoclonal antibody eculizumab on biomarkers of cellular processes involved in TMA in patients with aHUS longitudinally, during up to 1 year of treatment, compared with in healthy volunteers. Biomarker levels were elevated at baseline in most patients, regardless of mutational status, plasma exchange/infusion use, platelet count, or lactate dehydrogenase or haptoglobin levels. Eculizumab reduced terminal complement activation (C5a and sC5b-9) and renal injury markers (clusterin, cystatin-C, β2-microglobulin, and liver fatty acid binding protein-1) to healthy volunteer levels and reduced inflammation (soluble tumor necrosis factor receptor-1), coagulation (prothrombin fragment F1+2 and d-dimer), and endothelial damage (thrombomodulin) markers to near-normal levels. Alternative pathway activation (Ba) and endothelial activation markers (soluble vascular cell adhesion molecule-1) decreased but remained elevated, reflecting ongoing complement activation in aHUS despite complete terminal complement blockade. These results highlight links between terminal complement activation and inflammation, endothelial damage, thrombosis, and renal injury and underscore ongoing risk for systemic TMA and progression to organ damage. Further research regarding underlying complement dysregulation is warranted. This trial was registered at www.clinicaltrials.gov as #NCT01194973.

A common immunopathogenesis mechanism for infectious diseases: the protein-homeostasis-system hypothesis

It was once believed that host cell injury in various infectious diseases is caused solely by pathogens themselves; however, it is now known that host immune reactions to the substances from the infectious agents and/or from the injured host cells by infectious insults are also involved. All biological phenomena in living organisms, including biochemical, physiological and pathological processes, are performed by the proteins that have various sizes and shapes, which in turn are controlled by an interacting network within the living organisms. The author proposes that this network is controlled by the protein homeostasis system (PHS), and that the immune system is one part of the PHS of the host. Each immune cell in the host may recognize and respond to substances, including pathogenic proteins (PPs) that are toxic to target cells of the host, in ways that depend on the size and property of the PPs. Every infectious disease has its own set of toxic substances, including PPs, associated with disease onset, and the PPs and the corresponding immune cells may be responsible for the inflammatory processes that develop in those infectious diseases.

Extra-renal manifestations of complement-mediated thrombotic microangiopathies

Thrombotic microangiopathies (TMA) are rare but severe disorders, characterized by endothelial cell activation and thrombus formation leading to hemolytic anemia, thrombocytopenia, and organ failure. Complement over activation in combination with defects in its regulation is described in an increasing number of TMA and if primary for the disease denominated as atypical hemolytic-uremic syndrome. Although TMA predominantly affects the renal microvasculature, extra-renal manifestations are observed in 20% of patients including involvement of the central nerve system, cardiovascular system, lungs, skin, skeletal muscle, and gastrointestinal tract. Prompt diagnosis and treatment initiation are therefore crucial for the prognosis of disease acute phase and the long-term outcome. This review summarizes the available evidence on extra-renal TMA manifestations and discusses the role of acute and chronic complement activation by highlighting its complex interaction with inflammation, coagulation, and endothelial homeostasis.