Cell-Free DNA Modulates Clot Structure and Impairs Fibrinolysis in Sepsis

Neutrophil extracellular traps mediate neuro-immunothrombosis

Neutrophil extracellular traps are primarily composed of DNA and histones and are released by neutrophils to promote inflammation and thrombosis when stimulated by various inflammatory reactions. Neutrophil extracellular trap formation occurs through lytic and non-lytic pathways that can be further classified by formation mechanisms. Histones, von Willebrand factor, fibrin, and many other factors participate in the interplay between inflammation and thrombosis. Neuro-immunothrombosis summarizes the intricate interplay between inflammation and thrombosis during neural development and the pathogenesis of neurological diseases, providing cutting-edge insights into post-neurotrauma thrombotic events. The blood-brain barrier defends the brain and spinal cord against external assaults, and neutrophil extracellular trap involvement in blood-brain barrier disruption and immunothrombosis contributes substantially to secondary injuries in neurological diseases. Further research is needed to understand how neutrophil extracellular traps promote blood-brain barrier disruption and immunothrombosis, but recent studies have demonstrated that neutrophil extracellular traps play a crucial role in immunothrombosis, and identified modulators of neuro-immunothrombosis. However, these neurological diseases occur in blood vessels, and the mechanisms are unclear by which neutrophil extracellular traps penetrate the blood-brain barrier to participate in immunothrombosis in traumatic brain injury. This review discusses the role of neutrophil extracellular traps in neuro-immunothrombosis and explores potential therapeutic interventions to modulate neutrophil extracellular traps that may reduce immunothrombosis and improve traumatic brain injury outcomes.

The convergent model of coagulation

It is increasingly apparent that the pathologic interplay between coagulation and innate immunity, ie, immunothrombosis, forms the common basis of many challenges across the boundaries of specialized medicine and cannot be fully explained by the conventional concepts of cascade and cell-based coagulation. To improve our understanding of coagulation, we propose a model of coagulation that converges with inflammation and innate immune activation as a unified response toward vascular injury. Evolutionarily integral to the convergent response are damage-associated molecular patterns, which are released as a consequence of injury. Damage-associated molecular patterns facilitate diverse interactions within and between systems, not only to complement and reinforce cell-based clot formation but also to steer the response toward clot resolution and wound healing. By extending coagulation beyond its current boundaries, the convergent model aims to deliver novel diagnostics and therapeutics for contemporary and unexpected challenges across medicine, as exposed by COVID-19 and vaccine-induced immune thrombotic thrombocytopenia.

The Role of Biomarkers in Diagnosis of Sepsis and Acute Kidney Injury

Sepsis and acute kidney injury (AKI) are two major public health concerns that contribute significantly to illness and death worldwide. Early diagnosis and prompt treatment are essential for achieving the best possible outcomes. To date, there are no specific clinical, imaging, or biochemical indicators available to diagnose sepsis, and diagnosis of AKI based on the KDIGO criterion has limitations. To improve the diagnostic process for sepsis and AKI, it is essential to continually evolve our understanding of these conditions. Delays in diagnosis and appropriate treatment can have serious consequences. Sepsis and AKI often occur together, and patients with kidney dysfunction are more prone to developing sepsis. Therefore, identifying potential biomarkers for both conditions is crucial. In this review, we talk about the main biomarkers that evolve the diagnostic of sepsis and AKI, namely neutrophil gelatinase-associated lipocalin (NGAL), proenkephalin (PENK), and cell-free DNA.

Overall haemostatic potential assay for prediction of outcomes in venous and arterial thrombosis and thrombo-inflammatory diseases

Thromboembolic diseases including arterial and venous thrombosis are common causes of morbidity and mortality globally. Thrombosis frequently recurs and can also complicate many inflammatory conditions through the process of 'thrombo-inflammation,' as evidenced during the COVID-19 pandemic. Current candidate biomarkers for thrombosis prediction, such as D-dimer, have poor predictive efficacy. This limits our capacity to tailor anticoagulation duration individually and may expose lower risk individuals to undue bleeding risk. Global coagulation assays, such as the Overall Haemostatic Potential (OHP) assay, that investigate fibrin generation and fibrinolysis, may provide a more accurate and functional assessment of hypercoagulability. We present a review of fibrin's critical role as a central modulator of thrombotic risk. The results of our studies demonstrating the OHP assay as a predictive biomarker in venous thromboembolism, chronic renal disease, diabetes mellitus, post-thrombotic syndrome, and COVID-19 are discussed. As a comprehensive and global measurement of fibrin generation and fibrinolytic capacity, the OHP assay may be a valuable addition to future multi-modal predictive tools in thrombosis.

Trauma-induced innate immune activation and disseminated intravascular coagulation

Dysregulated innate immunity participates in the pathomechanisms of disseminated intravascular coagulation (DIC) in trauma-induced coagulopathy. Accidental and regulated cell deaths and neutrophil extracellular traps release damage-associated molecular patterns (DAMPs), such as histones, nuclear and mitochondrial DNA, and high-mobility group box 1, into circulation immediately after trauma. DAMP-induced inflammation activation releases tissue factor-bearing procoagulant extracellular vesicles through gasdermin D-mediated pore formation and plasma membrane rupture by regulated cell death. DAMPs also evoke systemic inflammation, platelet, coagulation activation, and impaired fibrinolysis associated with endothelial injury, leading to the dysfunction of anticoagulation systems, which are the main pathophysiological mechanisms of DIC. All these processes induce systemic thrombin generation in vivo, not restricted to the injury sites immediately after trauma. Thrombin generation at the site of injury stops bleeding and maintains homeostasis. However, DIC associated with endothelial injury generates massive thrombin, enhancing protease-activated, receptor-mediated bidirectional interplays between inflammation and coagulation, aggravating the diverse actions of thrombin and disturbing homeostasis. Insufficiently regulated thrombin causes disseminated microvascular thrombosis, resulting in tissue hypoxia due to reduced oxygen delivery, and mitochondrial dysfunction due to DAMPs causes tissue dysoxia. In addition, DAMP-induced calcium influx and overload, as well as neutrophil activation, play a role in endothelial cell injury. Tissue hypoxia and cytotoxicity result in multiple organ dysfunction in DIC after trauma. Controls against dysregulated innate immunity evoking systemic inflammation, thrombin generation, and cytotoxicity are key issues in improving the prognosis of DIC in trauma-induced coagulopathy.

Rethinking coagulation: from enzymatic cascade and cell-based reactions to a convergent model involving innate immune activation

ABSTRACT

Advancements in the conceptual thinking of hemostasis and thrombosis have been catalyzed by major developments within health research over several decades. The cascade model of coagulation was first described in the 1960s, when biochemistry gained prominence through innovative experimentation and technical developments. This was followed by the cell-based model, which integrated cellular coordination to the enzymology of clot formation and was conceptualized during the growth period in cell biology at the turn of the millennium. Each step forward has heralded a revolution in clinical therapeutics, both in procoagulant and anticoagulant treatments to improve patient care. In current times, the COVID-19 pandemic may also prove to be a catalyst: thrombotic challenges including the mixed responses to anticoagulant treatment and the vaccine-induced immune thrombotic thrombocytopenia have exposed limitations in our preexisting concepts while simultaneously demanding novel therapeutic approaches. It is increasingly clear that innate immune activation as part of the host response to injury is not separate but integrated into adaptive clot formation. Our review summarizes current understanding of the major molecules facilitating such a cross talk between immunity, inflammation and coagulation. We demonstrate how such effects can be layered upon the cascade and cell-based models to evolve conceptual understanding of the physiology of immunohemostasis and the pathology of immunothrombosis.

Cell-free DNA reveals distinct pathology of multisystem inflammatory syndrome in children

Multisystem inflammatory syndrome in children (MIS-C) is a rare but life-threatening hyperinflammatory condition induced by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes pediatric COVID-19 (pCOVID-19). The relationship of the systemic tissue injury to the pathophysiology of MIS-C is poorly defined. We leveraged the high sensitivity of epigenomics analyses of plasma cell-free DNA (cfDNA) and plasma cytokine measurements to identify the spectrum of tissue injury and glean mechanistic insights. Compared with pediatric healthy controls (pHCs) and patients with pCOVID-19, patients with MIS-C had higher levels of cfDNA primarily derived from innate immune cells, megakaryocyte-erythroid precursor cells, and nonhematopoietic tissues such as hepatocytes, cardiac myocytes, and kidney cells. Nonhematopoietic tissue cfDNA levels demonstrated significant interindividual variability, consistent with the heterogenous clinical presentation of MIS-C. In contrast, adaptive immune cell-derived cfDNA levels were comparable in MIS-C and pCOVID-19 patients. Indeed, the cfDNA of innate immune cells in patients with MIS-C correlated with the levels of innate immune inflammatory cytokines and nonhematopoietic tissue-derived cfDNA, suggesting a primarily innate immunity-mediated response to account for the multisystem pathology. These data provide insight into the pathogenesis of MIS-C and support the value of cfDNA as a sensitive biomarker to map tissue injury in MIS-C and likely other multiorgan inflammatory conditions.

Neutrophil-Mediated Progression of Mild Cognitive Impairment to Dementia

Cognitive impairment is a serious condition that begins with amnesia and progresses to cognitive decline, behavioral dysfunction, and neuropsychiatric impairment. In the final stage, dysphagia and incontinence occur. There are numerous studies and developed drugs for cognitive dysfunction in neurodegenerative diseases, such as Alzheimer's disease (AD); however, their clinical effectiveness remains equivocal. To date, attempts have been made to overcome cognitive dysfunction and understand and delay the aging processes that lead to degenerative and chronic diseases. Cognitive dysfunction is involved in aging and the disruption of inflammation and innate immunity. Recent reports have indicated that the innate immune system is prevalent in patients with AD, and that peripheral neutrophil markers can predict a decline in executive function in patients with mild cognitive impairment (MCI). Furthermore, altered levels of pro-inflammatory interleukins have been reported in MCI, which have been suggested to play a role in the peripheral immune system during the process from early MCI to dementia. Neutrophils are the first responders of the innate immune system. Neutrophils eliminate harmful cellular debris via phagocytosis, secrete inflammatory factors to activate host defense systems, stimulate cytokine production, kill pathogens, and regulate extracellular proteases and inhibitors. This review investigated and summarized the regulation of neutrophil function during cognitive impairment caused by various degenerative diseases. In addition, this work elucidates the cellular mechanism of neutrophils in cognitive impairment and what is currently known about the effects of activated neutrophils on cognitive decline.

DNA and histones impair the mechanical stability and lytic susceptibility of fibrin formed by staphylocoagulase

Background

Staphylocoagulase (SCG) is a virulence factor of Staphylococcus aureus, one of the most lethal pathogens of our times. The complex of SCG with prothrombin (SCG/ProT) can clot fibrinogen, and SCG/ProT-induced fibrin and plasma clots have been described to show decreased mechanical and lytic resistance, which may contribute to septic emboli from infected cardiac vegetations. At infection sites, neutrophils can release DNA and histones, as parts of neutrophil extracellular traps (NETs), which in turn favor thrombosis, inhibit fibrinolysis and strengthen clot structure.

Objectives

To characterize the combined effects of major NET-components (DNA, histone H1 and H3) on SCG/ProT-induced clot structure, mechanical and lytic stability.

Methods

Recombinant SCG was used to clot purified fibrinogen and plasma. The kinetics of formation and lysis of fibrin and plasma clots containing H1 or core histones+/-DNA were followed by turbidimetry. Fibrin structure and mechanical stability were characterized with scanning electron microscopy, pressure-driven permeation, and oscillation rheometry.

Results

Histones and DNA favored the formation of thicker fibrin fibers and a more heterogeneous clot structure including high porosity with H1 histone, whereas low porosity with core histones and DNA. As opposed to previous observations with thrombin-induced clots, SCG/ProT-induced fibrin was not mechanically stabilized by histones. Similarly to thrombin-induced clots, the DNA-histone complexes prolonged fibrinolysis with tissue-type plasminogen activator (up to 2-fold). The anti-fibrinolytic effect of the DNA and DNA-H3 complex was observed in plasma clots too. Heparin (low molecular weight) accelerated the lysis of SCG/ProT-clots from plasma, even if DNA and histones were also present.

Conclusions

In the interplay of NETs and fibrin formed by SCG, DNA and histones promote structural heterogeneity in the clots, and fail to stabilize them against mechanical stress. The DNA-histone complexes render the SCG-fibrin more resistant to lysis and thereby less prone to embolization.

Plasminogen System in the Pathophysiology of Sepsis: Upcoming Biomarkers

Severe hemostatic disturbances and impaired fibrinolysis occur in sepsis. In the most serious cases, the dysregulation of fibrinolysis contributes to septic shock, disseminated intravascular coagulation (DIC), and death. Therefore, an analysis of circulating concentrations of pro- and anti-fibrinolytic mediators could be a winning strategy in both the diagnosis and the treatment of sepsis. However, the optimal cutoff value, the timing of the measurements, and their combination with coagulation indicators should be further investigated. The purpose of this review is to summarize all relevant publications regarding the role of the main components of the plasminogen activation system (PAS) in the pathophysiology of sepsis. In addition, the clinical value of PAS-associated biomarkers in the diagnosis and the outcomes of patients with septic syndrome will be explored. In particular, experimental and clinical trials performed in emergency departments highlight the validity of soluble urokinase plasminogen activator receptor (suPAR) as a predictive and prognostic biomarker in patients with sepsis. The measurements of PAI-I may also be useful, as its increase is an early manifestation of sepsis and may precede the development of thrombocytopenia. The upcoming years will undoubtedly see progress in the use of PAS-associated laboratory parameters.

INVESTIGATION OF THE PATHOLOGICAL EFFECTS OF HISTONES, DNA, AND NUCLEOSOMES IN A MURINE MODEL OF SEPSIS

ABSTRACT

Background: In sepsis, neutrophil extracellular traps (NETs) are an important interface between innate immunity and coagulation. The major structural component of neutrophil extracellular traps is nucleosomes (DNA-histone complexes). In vitro, DNA and histones exert procoagulant/cytotoxic effects whereas nucleosomes are not harmful. However, whether DNA, histones, and/or nucleosomes exert harmful effects in vivo remain unclear. Objectives: (1) The aims of the study are to investigate the cytotoxic effects of nucleosomes ± DNase I and heparin in vitro and (2) to investigate whether DNA, histones, and/or nucleosomes are harmful when injected into healthy and septic mice. Methods : The cytotoxic effects of DNA, histones, and nucleosomes (± DNaseI or ±heparin) were assessed in HEK293 cells. Mice underwent cecal ligation and puncture or sham surgery and then received injections of DNA (8 mg/kg), histones (8.5 mg/kg), or nucleosomes at 4 and 6 h. Organs and blood were harvested at 8 h. Cell-free DNA, IL-6, thrombin-anti-thrombin, and protein C were quantified from plasma. Results:In vitro , incubation of HEK293 cells with DNaseI-treated nucleosomes reduced cell survival compared with nucleosome-treated cells, suggesting that DNaseI releases cytotoxic histones from nucleosomes. Addition of heparin to DNaseI-treated nucleosomes rescued cell death. In vivo, administration of histones to septic mice increased markers of inflammation (IL-6) and coagulation (thrombin-anti-thrombin), which was not observed in sham or septic mice administered DNA or nucleosomes. Conclusions: Our studies suggest that DNA masks the harmful effects of histones in vitro and in vivo . Although administration of histones contributed to the pathogenesis of sepsis, administration of nucleosomes or DNA was not harmful in healthy or septic mice.

All tangled up: interactions of the fibrinolytic and innate immune systems

The hemostatic and innate immune system are intertwined processes. Inflammation within the vasculature promotes thrombus development, whilst fibrin forms part of the innate immune response to trap invading pathogens. The awareness of these interlinked process has resulted in the coining of the terms "thromboinflammation" and "immunothrombosis." Once a thrombus is formed it is up to the fibrinolytic system to resolve these clots and remove them from the vasculature. Immune cells contain an arsenal of fibrinolytic regulators and plasmin, the central fibrinolytic enzyme. The fibrinolytic proteins in turn have diverse roles in immunoregulation. Here, the intricate relationship between the fibrinolytic and innate immune system will be discussed.

Neutrophil extracellular traps (NETs), transfusion requirements and clinical outcomes in orthotopic liver transplantation

Inflammatory phenomena have a direct impact on the prognosis of orthotopic liver transplantation (OLT). Neutrophil extracellular traps (NETs) contribute to OLT inflammation and hemostasis imbalance in OLT. The association between NETosis, clinical outcomes and transfusion requirements is not determined. To evaluate NETs release during OLT and the effect of NETosis ontransfusion requirements and adverse outcomes in a prospective cohort of patients submitted to OLT. We quantified citrullinated histones (cit-H3) and circulating-free-DNA (cf-DNA) in ninety-three patients submitted to OLT in three periods: pre-transplant, after graft reperfusion and before discharge. NETs markers were compared between these periods using ANOVA test. The association of NETosis and adverse outcomes was evaluated using regression models adjusted for age, sex and corrected MELD. We observed a peak of circulating NETs following reperfusion, evidenced by a 2.4-fold increase in cit-H3 levels in the post-graft reperfusion period (median levels of cit-H3 pre transplant: 0.5 ng/mL, after reperfusion: 1.2 ng/mL and at discharge 0.5 ng/mL, p < 0.0001). We observed an association between increased levels of cit-H3 and in-hospital death (OR = 1.168, 95% CI 1.021-1.336, p = 0.024). No association was found between NETs markers and transfusion requirements. There is a prompt release of NETs after reperfusion that is associated with poorer outcomes and death. Intraoperative NETs release seems to be independent of transfusion requirements. These findings highlight the relevance of inflammation promoted by NETS and its impact on OLT adverse clinical outcomes.

Inhibitors of Polyphosphate and Neutrophil Extracellular Traps

The contact pathway of blood clotting has received intense interest in recent years as studies have linked it to thrombosis, inflammation, and innate immunity. Because the contact pathway plays little to no role in normal hemostasis, it has emerged as a potential target for safer thromboprotection, relative to currently approved antithrombotic drugs which all target the final common pathway of blood clotting. Research since the mid-2000s has identified polyphosphate, DNA, and RNA as important triggers of the contact pathway with roles in thrombosis, although these molecules also modulate blood clotting and inflammation via mechanisms other than the contact pathway of the clotting cascade. The most significant source of extracellular DNA in many disease settings is in the form of neutrophil extracellular traps (NETs), which have been shown to contribute to incidence and severity of thrombosis. This review summarizes known roles of extracellular polyphosphate and nucleic acids in thrombosis, with an emphasis on novel agents under current development that target the prothrombotic activities of polyphosphate and NETs.

NETs-Induced Thrombosis Impacts on Cardiovascular and Chronic Kidney Disease

Arterial and venous thrombosis constitute a major source of morbidity and mortality worldwide. Association between thrombotic complications and cardiovascular and other chronic inflammatory diseases are well described. Inflammation and subsequent initiation of thrombotic events, termed immunothrombosis, also receive growing attention but are still incompletely understood. Nevertheless, the clinical relevance of aberrant immunothrombosis, referred to as thromboinflammation, is evident by an increased risk of thrombosis and cardiovascular events in patients with inflammatory or infectious diseases. Proinflammatory mediators released from platelets, complement activation, and the formation of NETs (neutrophil extracellular traps) initiate and foster immunothrombosis. In this review, we highlight and discuss prominent and emerging interrelationships and functions between NETs and other mediators in immunothrombosis in cardiovascular disease. Also, with patients with chronic kidney disease suffering from increased cardiovascular and thrombotic risk, we summarize current knowledge on neutrophil phenotype, function, and NET formation in chronic kidney disease. In addition, we elaborate on therapeutic targeting of NETs-induced immunothrombosis. A better understanding of the functional relevance of antithrombotic mediators which do not increase bleeding risk may provide opportunities for successful therapeutic interventions to reduce thrombotic risk beyond current treatment options.

Endothelial dysfunction and immunothrombosis in sepsis

Sepsis is a life-threatening clinical syndrome characterized by multiorgan dysfunction caused by a dysregulated or over-reactive host response to infection. During sepsis, the coagulation cascade is triggered by activated cells of the innate immune system, such as neutrophils and monocytes, resulting in clot formation mainly in the microcirculation, a process known as immunothrombosis. Although this process aims to protect the host through inhibition of the pathogen’s dissemination and survival, endothelial dysfunction and microthrombotic complications can rapidly lead to multiple organ dysfunction. The development of treatments targeting endothelial innate immune responses and immunothrombosis could be of great significance for reducing morbidity and mortality in patients with sepsis. Medications modifying cell-specific immune responses or inhibiting platelet–endothelial interaction or platelet activation have been proposed. Herein, we discuss the underlying mechanisms of organ-specific endothelial dysfunction and immunothrombosis in sepsis and its complications, while highlighting the recent advances in the development of new therapeutic approaches aiming at improving the short- or long-term prognosis in sepsis.

THE EFFECTS OF DNASE I AND LOW-MOLECULAR-WEIGHT HEPARIN IN A MURINE MODEL OF POLYMICROBIAL ABDOMINAL SEPSIS

ABSTRACT

Introduction: Cell-free DNA (CFDNA) has emerged as a prognostic biomarker in patients with sepsis. Circulating CFDNA is hypothesized to be associated with histones in the form of nucleosomes. In vitro, DNA activates coagulation and inhibits fibrinolysis, whereas histones activate platelets and are cytotoxic to endothelial cells. Previous studies have targeted CFDNA or histones in animal models of sepsis using DNase I or heparins, respectively, which has reduced inflammatory and thrombosis markers, thereby improving survival. In this study, we explored the possibility that the combination of DNase I and a low-molecular weight heparin (LMWH) may be a better therapeutic approach than monotherapy in a murine model of abdominal sepsis. Methods: C57Bl/6 mice (8-12 weeks old, both sexes) were subjected to either cecal ligation and puncture or sham surgery. Mice were given antibiotics, fluids, and either saline, DNase I (intraperitoneally, 20 mg/kg/8 h), LMWH (dalteparin, subcutaneously 500 IU/kg/12 h), or a combination of both (n = 12-31). Mice were monitored over 72 h for survival. Organs and blood were harvested for analysis. Levels of LMWH, CFDNA, IL-6, citrullinated histone-H3, thrombin-antithrombin complexes, and protein C were measured in plasma. Results: Administration of either DNase I (81.8%) or LMWH (83.3%, prophylactic range of 0.12 ± 0.07 IU/mL achieved) improved the survival of septic mice compared with saline- (38.7%) and combination-treated mice (48.8%, P < 0.05). Combination-treated mice also showed a small but insignificant improvement in survival compared with saline-treated cecal ligation and puncture mice. Monotherapies may be improving survival by reducing blood bacterial loads, citrullinated histone-H3, and thrombin-antithrombin complexes, and improving protein C levels. Conclusions: Compared with saline- and combination-treated mice, administration of monotherapies to septic mice improved survival. These findings suggest that there may be a negative drug-drug interaction between DNase I and LMWH when DNase I is administered intraperitoneally in a murine model of polymicrobial abdominal sepsis.

Coagulation Disorders in Sepsis and COVID-19-Two Sides of the Same Coin? A Review of Inflammation-Coagulation Crosstalk in Bacterial Sepsis and COVID-19

Sepsis is a major cause of morbidity and mortality worldwide. Sepsis-associated coagulation disorders are involved in the pathogenesis of multiorgan failure and lead to a subsequently worsening prognosis. Alongside the global impact of the COVID-19 pandemic, a great number of research papers have focused on SARS-CoV-2 pathogenesis and treatment. Significant progress has been made in this regard and coagulation disturbances were once again found to underlie some of the most serious adverse outcomes of SARS-CoV-2 infection, such as acute lung injury and multiorgan dysfunction. In the attempt of untangling the mechanisms behind COVID-19-associated coagulopathy (CAC), a series of similarities with sepsis-induced coagulopathy (SIC) became apparent. Whether they are, in fact, the same disease has not been established yet. The clinical picture of CAC shows the unique feature of an initial phase of intravascular coagulation confined to the respiratory system. Only later on, patients can develop a clinically significant form of systemic coagulopathy, possibly with a consumptive pattern, but, unlike SIC, it is not a key feature. Deepening our understanding of CAC pathogenesis has to remain a major goal for the research community, in order to design and validate accurate definitions and classification criteria.

Beta 2 glycoprotein I and neutrophil extracellular traps: Potential bridge between innate and adaptive immunity in anti-phospholipid syndrome

Antiphospholipid syndrome (APS) is a systemic autoimmune disorder characterized by recurrent vascular thrombosis and miscarriages in the absence of known causes. Antibodies against phospholipid-binding proteins (aPL) are pathogenic players in both clotting and pregnancy APS manifestations. There is sound evidence that antibodies specific for beta2 glycoprotein I (β2GPI) trigger thrombotic and pregnancy complications by interacting with the molecule on the membranes of different cell types of the coagulation cascade, and in placenta tissues. In addition to the humoral response against β2GPI, both peripheral and tissue CD4⁺ β2GPI-specific T cells have been reported in primary APS as well as in systemic lupus erythematosus (SLE)-associated APS. While adaptive immunity plays a clear role in APS, it is still debated whether innate immunity is involved as well. Acute systemic inflammation does not seem to be present in the syndrome, however, there is sound evidence that complement activation is crucial in animal models and can be found also in patients. Furthermore, neutrophil extracellular traps (NETs) have been documented in arterial and venous thrombi with different etiology, including clots in APS models. Keeping in mind that β2GPI is a pleiotropic glycoprotein, acting as scavenger molecule for infectious agents and apoptotic/damaged body constituents and that self-molecules externalized through NETs formation may become immunogenic autoantigens, we demonstrated β2GPI on NETs, and its ability to stimulate CD4⁺β2GPI-specific T cells. The aim of this review is to elucidate the role of β2GPI in the cross-talk between the innate and adaptive immunity in APS.

Increased thrombin activatable fibrinolysis inhibitor activity is associated with hypofibrinolysis in dogs with sepsis

Introduction

Disorders of coagulation are well-recognized in dogs with sepsis, but data regarding fibrinolysis disorders are limited. We aimed to characterize fibrinolysis in dogs with sepsis compared to healthy controls. We hypothesized that dogs with sepsis would be hypofibrinolytic, and that hypofibrinolysis would be associated with non-survival.

Methods

This was a prospective observational cohort study. We enrolled 20 client-owned dogs with sepsis admitted to the Cornell University Hospital for Animals and 20 healthy pet dogs. Coagulation and fibrinolytic pathway proteins including antiplasmin activity (AP), antithrombin activity (AT), thrombin activatable fibrinolysis inhibitor activity (TAFI), D-dimer concentration, fibrinogen concentration, and plasminogen activity were measured and compared between groups. Overall coagulation potential, overall fibrinolysis potential, and overall hemostatic potential were calculated from the curve of fibrin clot formation and lysis over time.

Results

Compared to healthy controls, dogs with sepsis had lower AT (P = 0.009), higher AP (P = 0.002), higher TAFI (P = 0.0385), and higher concentrations of fibrinogen (P < 0.0001) and D-dimer (P = 0.0001). Dogs with sepsis also had greater overall coagulation potential (P = 0.003), overall hemostatic potential (P = 0.0015), and lower overall fibrinolysis potential (P = 0.0004). The extent of fibrinolysis was significantly negatively correlated with TAFI. No significant differences were observed between survivors and non-survivors.

Discussion

Dogs with sepsis were hypercoagulable and hypofibrinolytic compared to healthy dogs, suggesting potential utility of thromboprophylaxis in this patient population. The association between high TAFI and low overall fibrinolysis potential might provide a potential mechanism for this hypofibrinolysis.

Fibrin structure, viscoelasticity and lysis face the interplay of biorelevant polyions

PURPOSE OF REVIEW

In the past 5 decades, heparins have been widely used as anticoagulants in the prevention and treatment of thrombosis. Subsequent development of heparin variants of various size and charge facilitated the discovery of their multiple biological actions and nonanticoagulant benefits. Platelet-derived or microbial polyphosphates, as well as DNA released in the course of neutrophil extracellular trap-formation are additional polyanions, which can modulate the development and stability of thrombi associated with cancer or inflammation. In this review, we focus on the size-dependent and electric charge-dependent modulatory effects of the three polyanions of different chemical structure.

RECENT FINDINGS

The polycationic histones have been recognized as potential biomarkers and therapeutic targets in several diseases related to inflammation and thrombosis. Since combating histones with activated protein C or heparin could cause unwanted bleeding, the quest for nonanticoagulant histone-neutralizing agents is ongoing. Polyanions may neutralize or exaggerate certain histone-mediated effects depending on their electric charge, size and histone effects under investigation. Several prothrombotic effects of polyphosphates and DNA are also size-dependent.

SUMMARY

The efficiency of future therapeutics targeting prothrombotic polyanions or histones is not a simple matter of electric charge, but may rely on a delicate combination of size, charge and chemical composition.

Venous Thromboembolism in Sepsis: From Bench to Bedside

Septic patients were commonly affected by coagulation disorders; thus, they are at high risk of thrombotic complications. In the last decades, novel knowledge has emerged about the interconnected and reciprocal influence of immune and coagulation systems. This phenomenon is called immunothrombosis, and it indicates an effective response whereby immune cells and the coagulation cascade cooperate to limit pathogen invasion and endothelial damage. When this network becomes dysregulated due to a systemic inflammatory activation, as occurs during sepsis, it can result in pathological thrombosis. Endothelium, platelets and neutrophils are the main characters involved in this process, together with the TF and coagulation cascade, playing a critical role in both the host defense and in thrombogenesis. A deeper understanding of this relationship may allow us to answer the growing need for clinical instruments to establish the thrombotic risk and treatments that consider more the connection between coagulation and inflammation. Heparin remains the principal therapeutical response to this phenomenon, although not sufficiently effective. To date, no other significant alternatives have been found yet. In this review, we discuss the role of sepsis-related inflammation in the development and resolution of venous thromboembolism and its clinical implications, from bench to bedside.

Unveiling Leukocyte Extracellular Traps in Inflammatory Responses of the Central Nervous System

Over the past nearly two decades, increasing evidence has uncovered how immune cells can actively extrude genetic material to entrap invading pathogens or convey sterile inflammatory signals that contribute to shaping immune responses. Originally identified in neutrophils, the release of decondensed chromatin fibers decorated with antimicrobial proteins, called extracellular traps (ETs), has been recognized as a specific form of programmed inflammatory cell death, which is now known to occur in several other leukocytes. Subsequent reports have shown that self-DNA can be extruded from immune cells even in the absence of cell death phenomena. More recent data suggest that ETs formation could exacerbate neuroinflammation in several disorders of the central nervous system (CNS). This review article provides an overview of the varied types, sources, and potential functions of extracellular DNA released by immune cells. Key evidence suggesting the involvement of ETs in neurodegenerative, traumatic, autoimmune, and oncological disorders of the CNS will be discussed, outlining ongoing challenges and drawing potentially novel lines of investigation.

Aberrant Fibrin Clot Structure Visualized Ex Vivo in Critically Ill Patients With Severe Acute Respiratory Syndrome Coronavirus 2 Infection

OBJECTIVES

Disseminated fibrin-rich microthrombi have been reported in patients who died from COVID-19. Our objective is to determine whether the fibrin clot structure and function differ between critically ill patients with or without COVID-19 and to correlate the structure with clinical coagulation biomarkers.

DESIGN

A cross-sectional observational study. Platelet poor plasma was used to analyze fibrin clot structure; the functional implications were determined by quantifying clot turbidity and porosity.

SETTING

ICU at an academic medical center and an academic laboratory.

PATIENTS

Patients admitted from July 1 to August 1, 2020, to the ICU with severe acute respiratory syndrome coronavirus 2 infection confirmed by reverse transcription-polymerase chain reaction or patients admitted to the ICU with sepsis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Blood was collected from 36 patients including 26 ICU patients with COVID-19 and 10 ICU patients with sepsis but without COVID-19 at a median of 11 days after ICU admission (interquartile range, 3-16). The cohorts were similar in age, gender, body mass index, comorbidities, Sequential Organ Failure Assessment (SOFA) score, and mortality. More patients with COVID-19 (100% vs 70%; p = 0.003) required anticoagulation. Ex vivo fibrin clots formed from patients with COVID-19 appeared to be denser and to have smaller pores than those from patients with sepsis but without COVID-19 (percent area of fluorescent fibrin 48.1% [SD, 16%] vs 24.9% [SD, 18.8%]; p = 0.049). The turbidity and flow-through assays corroborated these data; fibrin clots had a higher maximum turbidity in patients with COVID-19 compared with patients without COVID-19 (0.168 vs 0.089 OD units; p = 0.003), and it took longer for buffer to flow through these clots (216 vs 103 min; p = 0.003). In patients with COVID-19, d-dimer levels were positively correlated with percent area of fluorescent fibrin (ρ = 0.714, p = 0.047). Denser clots (assessed by turbidity and thromboelastography) and higher SOFA scores were independently associated with delayed clot lysis.

CONCLUSIONS

We found aberrant fibrin clot structure and function in critically ill patients with COVID-19. These findings may contribute to the poor outcomes observed in COVID-19 patients with widespread fibrin deposition.

Impact of Neutrophil Extracellular Traps on Thrombosis Formation: New Findings and Future Perspective

Thrombotic diseases seriously endanger human health, neutrophils and neutrophil extracellular traps (NETs) play an important role in abnormal thrombus formation. NETs are extracellular structures released by neutrophils upon stimulation by pathogens. NETs include neutrophil elastase (NE), myeloperoxidase (MPO), cathepsin G and other active substances. The network structure provided by NETs can prevent the spread of pathogens and effectively kill and eliminate pathogens. However, the components of NETs can also abnormally activate the coagulation pathway and participate in the formation of pathological thrombi. This review aims to summarize the mechanisms of NETs formation in detail; the research progress of NETs in venous thrombosis, arterial thrombosis, acquired disease-associated thrombosis, sepsis coagulation disorder; as well as the strategies to target NETs in thrombosis prevention and treatment.

Autophagy-driven neutrophil extracellular traps: The dawn of sepsis

Sepsis is a systemic inflammatory syndrome caused by infection disorders. The core mechanism of sepsis is immune dysfunction. Neutrophils are the most abundant circulating white blood cells, which play a crucial role in mediating the innate immune response. Previous studies have shown that an effective way to treat sepsis is through the regulation of neutrophil functions. Autophagy, a highly conserved degradation process, is responsible for removing denatured proteins or damaged organelles within cells and protecting cells from external stimuli. It is a key homeostasis process that promotes neutrophil function and differentiation. Autophagy has been shown to be closely associated with inflammation and immunity. Neutrophils, the first line of innate immunity, migrate to inflammatory sites upon their activation. Neutrophil-mediated autophagy may participate in the clinical course of sepsis. In this review, we summarized and analyzed the latest research findings on the changes in neutrophil external traps during sepsis, the regulatory role of autophagy in neutrophil, and the potential application of autophagy-driven NETs in sepsis, so as to guide clinical treatment of sepsis.

The Citrullination-Neutrophil Extracellular Trap Axis in Chronic Diseases

Citrullination of proteins is crucial for the formation of neutrophil extracellular traps (NETs) − strands of nuclear DNA expulsed in the extracellular environment along with antimicrobial proteins in order to halt the spread of pathogens. Paradoxically, NETs may be immunogenic and contribute to inflammation. It is known that for the externalization of DNA, a group of enzymes called peptidyl arginine deiminases (PADs) is required. Current research often looks at citrullination, NET formation, PAD overexpression, and extracellular DNA (ecDNA) accumulation in chronic diseases as separate events. In contrast, we propose that citrullination can be viewed as the primary mechanism of autoimmunity, for instance by the formation of anti-citrullinated protein antibodies (ACPAs) but also as a process contributing to chronic inflammation. Therefore, citrullination could be at the center, connecting and impacting multiple inflammatory diseases in which ACPAs, NETs, or ecDNA have already been documented. In this review, we aimed to highlight the importance of citrullination in the etiopathogenesis of a number of chronic diseases and to explore the diagnostic, prognostic, and therapeutic potential of the citrullination-NET axis.

Staphylococcus aureus and Neutrophil Extracellular Traps: The Master Manipulator Meets Its Match in Immunothrombosis

Over the past 10 years, neutrophil extracellular traps (NETs) have become widely accepted as an integral player in immunothrombosis, due to their complex interplay with both pathogens and components of the coagulation system. While the release of NETs is an attempt by neutrophils to trap pathogens and constrain infections, NETs can have bystander effects on the host by inducing uncontrolled thrombosis, inflammation, and tissue damage. From an evolutionary perspective, pathogens have adapted to bypass the host innate immune response. Staphylococcus aureus (S. aureus), in particular, proficiently overcomes NET formation using several virulence factors. Here we review mechanisms of NET formation and how these are intertwined with platelet activation, the release of endothelial von Willebrand factor, and the activation of the coagulation system. We discuss the unique ability of S. aureus to modulate NET formation and alter released NETs, which helps S. aureus to escape from the host's defense mechanisms. We then discuss how platelets and the coagulation system could play a role in NET formation in S. aureus-induced infective endocarditis, and we explain how targeting these complex cellular interactions could reveal novel therapies to treat this disease and other immunothrombotic disorders.

DNase 1 Protects From Increased Thrombin Generation and Venous Thrombosis During Aging: Cross-Sectional Study in Mice and Humans

Background Human aging is associated with increased risk of thrombosis, but the mechanisms are poorly defined. We hypothesized that aging induces peroxide-dependent release of neutrophil extracellular traps that contribute to thrombin generation and thrombosis. Methods and Results We studied C57BL6J mice and littermates of glutathione peroxidase-1 transgenic and wild-type mice at young (4 month) and old (20 month) ages and a healthy cohort of young (18-39 years) or middle-aged/older (50-72 years) humans. In plasma, we measured thrombin generation potential and components of neutrophil extracellular traps (cell-free DNA and citrullinated histone). Aged wild-type mice displayed a significant increase in thrombin generation that was decreased in aged glutathione peroxidase-1 transgenic mice. Both aged wild-type and aged glutathione peroxidase-1 transgenic mice demonstrated similar elevation of plasma cell-free DNA compared with young mice. In contrast, plasma levels of citrullinated histone were not altered with age or genotype. Release of neutrophil extracellular traps from neutrophils in vitro was also similar between young and aged wild-type or glutathione peroxidase-1 transgenic mice. Treatment of plasma or mice with DNase 1 decreased age-associated increases in thrombin generation, and DNase 1 treatment blocked the development of experimental venous thrombi in aged C57BL6J mice. Similarly, thrombin generation potential and plasma cell-free DNA, but not citrullinated histone, were higher in middle-aged/older humans, and treatment of plasma with DNase 1 reversed the increase in thrombin generation. Conclusions We conclude that DNase 1 limits thrombin generation and protects from venous thrombosis during aging, likely by hydrolyzing cell-free DNA.

Altered fibrin clot structure and dysregulated fibrinolysis contribute to thrombosis risk in severe COVID-19

Elevated fibrinogen, in conjunction with accelerated formation of FXIIa, may promote compact fibrin clot architecture in COVID-19.

A dense fibrin network and dysregulated fibrinolysis collectively contribute to a high incidence of thrombotic events in COVID-19.

The high incidence of thrombotic events suggests a possible role of the contact system pathway in COVID-19 pathology. In this study, we determined the altered levels of factor XII (FXII) and its activation products in critically ill patients with COVID-19 in comparison with patients with severe acute respiratory distress syndrome related to the influenza virus (acute respiratory distress syndrome [ARDS]-influenza). Compatible with those data, we found rapid consumption of FXII in COVID-19 but not in ARDS-influenza plasma. Interestingly, the lag phase in fibrin formation, triggered by the FXII activator kaolin, was not prolonged in COVID-19, as opposed to that in ARDS-influenza. Confocal and electron microscopy showed that increased FXII activation rate, in conjunction with elevated fibrinogen levels, triggered formation of fibrinolysis-resistant, compact clots with thin fibers and small pores in COVID-19. Accordingly, clot lysis was markedly impaired in COVID-19 as opposed to that in ARDS-influenza. Dysregulated fibrinolytic system, as evidenced by elevated levels of thrombin-activatable fibrinolysis inhibitor, tissue-plasminogen activator, and plasminogen activator inhibitor-1 in COVID-19 potentiated this effect. Analysis of lung tissue sections revealed widespread extra- and intravascular compact fibrin deposits in patients with COVID-19. A compact fibrin network structure and dysregulated fibrinolysis may collectively contribute to a high incidence of thrombotic events in COVID-19.

Inhaled Edoxaban dry powder inhaler formulations: Development, characterization and their effects on the coagulopathy associated with COVID-19 infection

Herein, we demonstrated the development and characterization of a dry powder inhaler (DPI) formulation of edoxaban (EDX); and investigated the in-vitro anticoagulation effect for the management of pulmonary or cerebral coagulopathy associated with COVID-19 infection. The formulations were prepared by mixing the inhalable micronized drug with a large carrier lactose and dispersibility enhancers, leucine, and magnesium stearate. The drug-excipient interaction was studied using X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) methods. The drug and excipients showed no physical inter particulate interaction. The in-vitro drug aerosolization from the developed formulation was determined by a Twin Stage Impinger (TSI) at a flow rate of 60 ± 5 L /min. The amount of drug deposition was quantified by an established HPLC-UV method. The fine particle fraction (FPF) of EDX API from drug alone formulation was 7%, whereas the formulations with excipients increased dramatically to almost 7-folds up to 47%. The developed DPI formulation of EDX showed a promising in-vitro anticoagulation effect at a very low concentration. This novel DPI formulation of EDX could be a potential and effective inhalation therapy for managing pulmonary venous thromboembolism (VTE) associated with COVID-19 infection. Further studies are warranted to investigate the toxicity and clinical application of the inhaled EDX DPI formulation.

Neutrophil extracellular traps: a role in inflammation and dysregulated hemostasis as well as in patients with COVID-19 and severe obstetric pathology

Numerous studies have proven a close relationship between inflammatory diseases and the state of hypercoagulability. In fact, thromboembolic complications represent one of the main causes of disability and mortality in acute and chronic inflammatory diseases, cancer and obstetric complications. Despite this, the processes of hemostasis and immune responses have long been considered separately; currently, work is underway to identify the molecular basis for a relationship between such systems. It has been identified that various pro-inflammatory stimuli are capable of triggering a coagulation cascade, which in turn modulates inflammatory responses. Neutrophil extracellular traps (NETs) are the networks of histones of extracellular DNA generated by neutrophils in response to inflammatory stimuli. The hemostasis is activated against infection in order to minimize the spread of infection and, if possible, inactivate the infectious agent. Another molecular network is based on fibrin. Over the last 10 years, there has been accumulated a whole body of evidence that NETs and fibrin are able to form a united network within a thrombus, stabilizing each other. Similarities and molecular cross-reactions are also present in the processes of fibrinolysis and lysis of NETs. Both NETs and von Willebrand factor (vWF) are involved in thrombosis as well as inflammation. During the development of these conditions, a series of events occurs in the microvascular network, including endothelial activation, NETs formation, vWF secretion, adhesion, aggregation, and activation of blood cells. The activity of vWF multimers is regulated by the specific metalloproteinase ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). Studies have shown that interactions between NETs and vWF can lead to arterial and venous thrombosis and inflammation. In addition, the contents released from activated neutrophils or NETs result in decreased ADAMTS-13 activity, which can occur in both thrombotic microangiopathies and acute ischemic stroke. Recently, NETs have been envisioned as a cause of endothelial damage and immunothrombosis in COVID-19. In addition, vWF and ADAMTS-13 levels predict COVID-19 mortality. In this review, we summarize the biological characteristics and interactions of NETs, vWF, and ADAMTS-13, the effect of NETs on hemostasis regulation and discuss their role in thrombotic conditions, sepsis, COVID-19, and obstetric complications.

FM-CATH, A Novel Cathelicidin From Fejervarya Multistriata, Shows Therapeutic Potential for Treatment of CLP-Induced Sepsis

Sepsis is an exacerbated inflammatory reaction induced by severe infection. As important defensive molecules in innate immunity, several AMPs are reported to prevent septic shock. In this study, we characterized a novel cathelicidin, FM-CATH, from the frog skin of F. multistriata. FM-CATH was found to adopt an amphipathic α-helix structural in membrane-mimetic environments and possess favorable antimicrobial effects against bacteria and fungus. In addition, it triggered the agglutination of bacteria. It could also strongly bind to LPS and LTA. Additionally, FM-CATH affected the enzymatic activities of thrombin, plasmin, β-tryptase, and tPA, leading to coagulation inhibition in vitro and in vivo. Finally, we observed that FM-CATH improved survival rate and inhibited pathological alteration, bacterial count, serum biochemistry, and pro-inflammatory cytokine expression in the cecal ligation and puncture-induced sepsis mice. Taken together, these findings suggest that FM-CATH might be served as a promising agent for the treatment of sepsis.

The role of leukocytes in acute ischemic stroke-related thrombosis: a notable but neglected topic

Ischemic stroke is one of the most serious diseases today, and only a minority of patients are provided with effective clinical treatment. Importantly, leukocytes have gradually been discovered to play vital roles in stroke thrombosis, including promoting the activation of thrombin and the adhesion and aggregation of platelets. However, they have not received enough attention in the field of acute ischemic stroke. It is possible that we could not only prevent stroke-related thrombosis by inhibiting leukocyte activation, but also target leukocyte components to dissolve thrombi in the cerebral artery. In this review, we expound the mechanisms by which leukocytes are activated and participate in the formation of stroke thrombus, then describe the histopathology of leukocytes in thrombi of stroke patients and the influence of leukocyte composition on vascular recanalization effects and patient prognosis. Finally, we discuss the relevant antithrombotic strategies targeting leukocytes.

The Role of Neutrophil Extracellular Traps in Central Nervous System Diseases and Prospects for Clinical Application

Neutrophil extracellular traps (NETs) are complexes of decondensed DNA fibers and antimicrobial peptides that are released by neutrophils and play important roles in many noninfectious diseases, such as cystic fibrosis, systemic lupus erythematosus, diabetes, and cancer. Recently, the formation of NETs has been detected in many central nervous system diseases and is thought to play different roles in the occurrence and development of these diseases. Researchers have detected NETs in acute ischemic stroke thrombi, and these NETs are thought to promote coagulation and thrombosis. NETs in ischemic brain parenchyma were identified as the cause of secondary nerve damage. High levels of NETs were also detected in grade IV glioma tissues, where NETs were involved in the proliferation and invasion of glioma cells by activating a signaling pathway. Extracellular web-like structures have also recently been observed in mice with traumatic brain injury (TBI), and it was hypothesized that NETs contribute to the development of edema after TBI. This article reviews the effect of NETs on multiple diseases that affect the CNS and explores their clinical application prospects.

A modified in vitro clot lysis assay predicts outcomes and safety in acute ischemic stroke patients undergoing intravenous thrombolysis

The outcome of intravenous thrombolysis using recombinant tissue plasminogen activator (rt-PA) is only favorable in ≈ 40% of acute ischemic stroke (AIS) patients. Moreover, in ≈ 6-8% of cases, intracerebral hemorrhage (ICH) develops. We tested whether a modification of clot lysis assay (CLA), might predict therapy outcomes and safety. In this prospective observational study, blood samples of 231 AIS patients, all receiving intravenous rt-PA, were taken before thrombolysis. Cell-free DNA (cfDNA), CLA and CLA supplemented with cfDNA and histones (mCLA) were determined from the blood samples. Stroke severity was determined by NIHSS on admission. ICH was classified according to ECASSII. Short- and long-term outcomes were defined at 7 and 90 days post-event according to ΔNIHSS and by the modified Rankin Scale, respectively. Stroke severity demonstrated a step-wise positive association with cfDNA levels, while a negative association was found with the time to reach 50% lysis (50%CLT) parameter of CLA and mCLA. ROC analysis showed improved diagnostic performance of the mCLA. Logistic regression analysis proved that 50%CLT is a predictor of short-term therapy failure, while the AUC parameter predicts ICH occurrence. A modified CLA, supplemented with cfDNA and histones, might be a promising tool to predict short-term AIS outcomes and post-lysis ICH.

Biomarkers of coagulation, endothelial function, and fibrinolysis in critically ill patients with COVID-19: A single-center prospective longitudinal study

BACKGROUND

Immunothrombosis and coagulopathy in the lung microvasculature may lead to lung injury and disease progression in coronavirus disease 2019 (COVID-19). We aim to identify biomarkers of coagulation, endothelial function, and fibrinolysis that are associated with disease severity and may have prognostic potential.

METHODS

We performed a single-center prospective study of 14 adult COVID-19(+) intensive care unit patients who were age- and sex-matched to 14 COVID-19(-) intensive care unit patients, and healthy controls. Daily blood draws, clinical data, and patient characteristics were collected. Baseline values for 10 biomarkers of interest were compared between the three groups, and visualized using Fisher's linear discriminant function. Linear repeated-measures mixed models were used to screen biomarkers for associations with mortality. Selected biomarkers were further explored and entered into an unsupervised longitudinal clustering machine learning algorithm to identify trends and targets that may be used for future predictive modelling efforts.

RESULTS

Elevated D-dimer was the strongest contributor in distinguishing COVID-19 status; however, D-dimer was not associated with survival. Variable selection identified clot lysis time, and antigen levels of soluble thrombomodulin (sTM), plasminogen activator inhibitor-1 (PAI-1), and plasminogen as biomarkers associated with death. Longitudinal multivariate k-means clustering on these biomarkers alone identified two clusters of COVID-19(+) patients: low (30%) and high (100%) mortality groups. Biomarker trajectories that characterized the high mortality cluster were higher clot lysis times (inhibited fibrinolysis), higher sTM and PAI-1 levels, and lower plasminogen levels.

CONCLUSIONS

Longitudinal trajectories of clot lysis time, sTM, PAI-1, and plasminogen may have predictive ability for mortality in COVID-19.

PCSK9 Biology and Its Role in Atherothrombosis

It is now about 20 years since the first case of a gain-of-function mutation involving the as-yet-unknown actor in cholesterol homeostasis, proprotein convertase subtilisin/kexin type 9 (PCSK9), was described. It was soon clear that this protein would have been of huge scientific and clinical value as a therapeutic strategy for dyslipidemia and atherosclerosis-associated cardiovascular disease (CVD) management. Indeed, PCSK9 is a serine protease belonging to the proprotein convertase family, mainly produced by the liver, and essential for metabolism of LDL particles by inhibiting LDL receptor (LDLR) recirculation to the cell surface with the consequent upregulation of LDLR-dependent LDL-C levels. Beyond its effects on LDL metabolism, several studies revealed the existence of additional roles of PCSK9 in different stages of atherosclerosis, also for its ability to target other members of the LDLR family. PCSK9 from plasma and vascular cells can contribute to the development of atherosclerotic plaque and thrombosis by promoting platelet activation, leukocyte recruitment and clot formation, also through mechanisms not related to systemic lipid changes. These results further supported the value for the potential cardiovascular benefits of therapies based on PCSK9 inhibition. Actually, the passive immunization with anti-PCSK9 antibodies, evolocumab and alirocumab, is shown to be effective in dramatically reducing the LDL-C levels and attenuating CVD. While monoclonal antibodies sequester circulating PCSK9, inclisiran, a small interfering RNA, is a new drug that inhibits PCSK9 synthesis with the important advantage, compared with PCSK9 mAbs, to preserve its pharmacodynamic effects when administrated every 6 months. Here, we will focus on the major understandings related to PCSK9, from its discovery to its role in lipoprotein metabolism, involvement in atherothrombosis and a brief excursus on approved current therapies used to inhibit its action.

Size- and charge-dependent modulation of the lytic susceptibility and mechanical stability of fibrin-histone clots by heparin and polyphosphate variants

BACKGROUND

Neutrophil extracellular traps (NETs) containing DNA and histones are expelled from neutrophils in infection and thrombosis. Heparins, anticoagulant polyanions, can neutralize histones with a potential therapeutic advantage in sepsis. Polyphosphates, procoagulant polyanions, are released by platelets and microorganisms.

OBJECTIVES

To characterize the combined effects of NET components and polyanions on clot structure, mechanical properties and lytic susceptibility.

METHODS

Scanning electron microscopy, pressure-driven permeation, turbidimetry, and oscillation rheometry were used for the characterization of the structure, viscoelasticity, and kinetics of formation and lysis of fibrin and plasma clots containing histones+/-DNA in combination with unfractionated heparin, its desulfated derivatives, low molecular weight heparin (LMWH), pentasaccharide, and polyphosphates of different sizes.

RESULTS

Histones and DNA inhibited fibrin lysis by plasmin, but this behavior was not neutralized by negatively charged heparins or short polyphosphates. Rather, fibrin lysis was further inhibited by added polyanions. Histones inhibited plasma clot lysis by tissue plasminogen activator and the response to added heparin was size dependent. Unfractionated heparin, LMWH, and pentasaccharide had no effect, exacerbated, or reversed histone inhibition, respectively. Histones increased the mechanical strength of fibrin, which was exacerbated by smaller heparin and polyphosphate molecules. Histones increased fibrin diameter and pore size of fibrin clots and this effect was neutralized by all heparin variants but enhanced by polyphosphates.

CONCLUSIONS

Despite their common polyanionic character, heparins and polyphosphates exert distinct effects on fibrin mechanical and fibrinolytic stability. Anti-fibrinolytic effects of histones were more often enhanced by polyanions not counteracted. Careful selection of anti-histone strategies is required if they are to be combined with thrombolytic therapy.

It takes two to thrombosis: Hemolysis and complement

Thromboembolic events represent the most common complication of hemolytic anemias characterized by complement-mediated hemolysis such as paroxysmal nocturnal hemoglobinuria and autoimmune hemolytic anemia. Similarly, atypical hemolytic uremic syndrome is characterized by hemolysis and thrombotic abnormalities. The main player in the development of thrombosis in hemolytic diseases is suggested to be the complement system. However, the release of extracellular hemoglobin and heme by hemolysis itself can also drive procoagulant responses. Both, complement activation and hemolysis promote the activation of neutrophils resulting in the formation of neutrophil extracellular traps and induce inflammation and vascular damage which all together might (synergistically) lead to hypercoagulability. In this review we aim to summarize the current knowledge on the role of complement activation and hemolysis in the onset of thrombosis in hemolytic diseases. This review will discuss the interplay between different biological systems and neutrophil activation contributing to the pathogenesis of thrombosis. Finally, we will combine this fundamental knowledge and address the pathophysiology of hemolysis in prototypical complement-driven diseases.

Diagnostic Potential of Coagulation-Related Biomarkers for Sepsis in the Emergency Department: Protocol for a Pilot Observational Cohort Study

Background:

Between 75% and 80% of patients with sepsis arrive in the hospital through the emergency department. Early diagnosis is important to alter patient prognosis, but currently, there is no reliable biomarker. The innate immune response links inflammation and coagulation. Several coagulation -related biomarkers are associated with poor prognosis in the ICU. The role of coagulation biomarkers to aid in early sepsis diagnosis has not previously been investigated. The objective of our study is to determine the individual or combined accuracy of coagulation and inflammation biomarkers with standard biochemical tests to diagnose adult septic patients presenting to the emergency department.

Methods:

in the Emergency Department is a prospective, observational cohort study with a target enrolment of 250 suspected septic patients from two Canadian emergency departments. The emergency physicians will enroll patients with suspected sepsis. Blood samples will be collected at two time points (initial presentation and 4 hr following). Patients will be adjudicated into septic, infected, or not infected status in accordance with the Sepsis-3 definitions. Patient demographics, cultures, diagnosis, and biomarkers will be reported using descriptive statistics. Optimal cut off values with sensitivity and specificity for each biomarker will be determined using C-statistics to distinguish between septic and nonseptic patients. Stepwise multiple logistic regression analysis with exclusion of nonsignificant covariates from the final model will be used to establish a panel of biomarkers.

Conclusions:

Our protocol describes the processes and methods for a pragmatic observational biomarker study in the emergency department. This study will seek to determine the potential diagnostic importance of early coagulation abnormalities to identify additional tools for sepsis diagnosis.

Fibrinolytic Alterations in Sepsis: Biomarkers and Future Treatment Targets

Sepsis is a life-threatening condition which develops as a dysregulated immune response in the face of infection and which is associated with profound hemostatic disturbances and in the most extreme cases disseminated intravascular coagulation (DIC). In addition, the fibrinolytic system is subject to alterations during infection and sepsis, and impaired fibrinolysis is currently considered a key player in sepsis-related microthrombus formation and DIC. However, we still lack reliable biomarkers to assess fibrinolysis in the clinical setting. Furthermore, drugs targeting the fibrinolytic system have potential value in sepsis patients with severe fibrinolytic disturbances, but these are still being tested in the preclinical stage. The present review provides an overview of key fibrinolytic changes in sepsis, reviews the current literature on potential laboratory markers of altered fibrinolysis in adult sepsis patients, and discusses future perspectives for diagnosis and treatment of fibrinolytic disturbances in sepsis patients.

Myeloperoxidase has no effect on the low procoagulant activity of silica-free DNA

Blood coagulation and innate immunity are closely interrelated. At sites of inflammation, DNA and myeloperoxidase (MPO) are released from polymorphonuclear leukocytes (PMNs) as an integral component of neutrophil extracellular traps (NETs). NETs exert pleiotropic thrombogenic effects, with DNA-mediated contact activation of factor XII (FXII) likely playing a role. We have previously shown that MPO, a highly cationic protein, regulates coagulation through heteromolecular interactions with various negatively charged structures, including membrane phospholipids and low-molecular-weight heparin. The aims of our current study were to confirm that DNA activates coagulation and to investigate whether its procoagulant activity (PCA) is regulated by PMN-derived MPO. To this end, we used thrombin generation and FXIIa amidolytic activity assays to analyze the PCA of cell-free DNA isolated with silica membrane-based (cfDNA) or silica-free procedures (PaxDNA). cfDNA potently activated FXII and promoted thrombin generation in a concentration-dependent manner, but its PCA was largely attributable to contaminating silica particles. In contrast, pure, i.e. silica-free, PaxDNA was markedly less procoagulant. Although PaxDNA amplified thrombin generation in plasma, it was devoid of any direct FXII activating activity. MPO supershifted both cfDNA and PaxDNA in gel electrophoresis, but only silica-associated PCA of cfDNA was neutralized by MPO independently of its catalytic properties. Moreover, pretreatment with DNase I abolished silica-induced thrombin generation. In summary, we show that pure DNA has rather weak PCA, which is not further inhibited by heteromolecular complex formation with exogenous MPO. Our study thus provides novel mechanistic insights into the regulation of coagulation by extracellular DNA under inflammatory conditions.

Characterization and functional analysis of cathelicidin-MH, a novel frog-derived peptide with anti-septicemic properties

Antimicrobial peptides form part of the innate immune response and play a vital role in host defense against pathogens. Here we report a new antimicrobial peptide belonging to the cathelicidin family, cathelicidin-MH (cath-MH), from the skin of Microhyla heymonsivogt frog. Cath-MH has a single α-helical structure in membrane-mimetic environments and is antimicrobial against fungi and bacteria, especially Gram-negative bacteria. In contrast to other cathelicidins, cath-MH suppresses coagulation by affecting the enzymatic activities of tissue plasminogen activator, plasmin, β-tryptase, elastase, thrombin, and chymase. Cath-MH protects against lipopolysaccharide (LPS)- and cecal ligation and puncture-induced sepsis, effectively ameliorating multiorgan pathology and inflammatory cytokine through its antimicrobial, LPS-neutralizing, coagulation suppressing effects as well as suppression of MAPK signaling. Taken together, these data suggest that cath-MH is an attractive candidate therapeutic agent for the treatment of septic shock.

The Neutrophil Secretome as a Crucial Link between Inflammation and Thrombosis

Cardiovascular diseases are a leading cause of death. Blood–cell interactions and endothelial dysfunction are fundamental in thrombus formation, and so further knowledge of the pathways involved in such cellular crosstalk could lead to new therapeutical approaches. Neutrophils are secretory cells that release well-known soluble inflammatory signaling mediators and other complex cellular structures whose role is not fully understood. Studies have reported that neutrophil extracellular vesicles (EVs) and neutrophil extracellular traps (NETs) contribute to thrombosis. The objective of this review is to study the role of EVs and NETs as key factors in the transition from inflammation to thrombosis. The neutrophil secretome can promote thrombosis due to the presence of different factors in the EVs bilayer that can trigger blood clotting, and to the release of soluble mediators that induce platelet activation or aggregation. On the other hand, one of the main pathways by which NETs induce thrombosis is through the creation of a scaffold to which platelets and other blood cells adhere. In this context, platelet activation has been associated with the induction of NETs release. Hence, the structure and composition of EVs and NETs, as well as the feedback mechanism between the two processes that causes pathological thrombus formation, require exhaustive analysis to clarify their role in thrombosis.

Cell-free DNA maps COVID-19 tissue injury and risk of death and can cause tissue injury

INTRODUCTION

The clinical course of coronavirus 2019 (COVID-19) is heterogeneous, ranging from mild to severe multiorgan failure and death. In this study, we analyzed cell-free DNA (cfDNA) as a biomarker of injury to define the sources of tissue injury that contribute to such different trajectories.

METHODS

We conducted a multicenter prospective cohort study to enroll patients with COVID-19 and collect plasma samples. Plasma cfDNA was subject to bisulfite sequencing. A library of tissue-specific DNA methylation signatures was used to analyze sequence reads to quantitate cfDNA from different tissue types. We then determined the correlation of tissue-specific cfDNA measures to COVID-19 outcomes. Similar analyses were performed for healthy controls and a comparator group of patients with respiratory syncytial virus and influenza.

RESULTS

We found markedly elevated levels and divergent tissue sources of cfDNA in COVID-19 patients compared with patients who had influenza and/or respiratory syncytial virus and with healthy controls. The major sources of cfDNA in COVID-19 were hematopoietic cells, vascular endothelium, hepatocytes, adipocytes, kidney, heart, and lung. cfDNA levels positively correlated with COVID-19 disease severity, C-reactive protein, and D-dimer. cfDNA profile at admission identified patients who subsequently required intensive care or died during hospitalization. Furthermore, the increased cfDNA in COVID-19 patients generated excessive mitochondrial ROS (mtROS) in renal tubular cells in a concentration-dependent manner. This mtROS production was inhibited by a TLR9-specific antagonist.

CONCLUSION

cfDNA maps tissue injury that predicts COVID-19 outcomes and may mechanistically propagate COVID-19–induced tissue injury.

FUNDING

Intramural Targeted Anti–COVID-19 grant, NIH.

Traumatic injury is associated with reduced deoxyribonuclease activity and dysregulation of the actin scavenging system

Background

Traumatic injury is associated with increased concentrations of cell-free DNA (cfDNA) in the circulation, which contribute to post-injury complications. The endonuclease deoxyribonuclease 1 (DNase-1) is responsible for removing 90% of circulating cfDNA. Recently, DNase activity was reported to be significantly reduced following major non-traumatic brain injury (TBI), but the processes responsible were not investigated. Moreover, it is not known how quickly following injury DNase activity is reduced and whether this also occurs after TBI.

Methods

At 3 post-injury time points (≤1, 4–12 and 48–72 hours), blood samples were obtained from 155 adult trauma patients that had sustained an isolated TBI (n = 21), TBI with accompanying extracranial injury (TBI⁺) (n = 53) or an extracranial injury only (ECI) (n = 81). In addition to measuring cfDNA levels and the activity and expression of DNase, circulating concentrations of monomeric globular action (G-actin), an inhibitor of DNase-1, and the actin scavenging proteins gelsolin (GSN) and vitamin D binding protein (VDBP) were determined and values compared to a cohort of healthy controls.

Results

Significantly elevated concentrations of plasma cfDNA were seen in TBI, TBI⁺ and ECI patients at all study time points when compared to healthy controls. cfDNA levels were significantly higher at ≤1 hour post-injury in ECI patients who subsequently developed multiple organ dysfunction syndrome when compared to those who did not. Plasma DNase-1 protein was significantly elevated in all patient groups at all sampling time points. In contrast, DNase enzyme activity was significantly reduced, with this impaired function evident in TBI⁺ patients within minutes of injury. Circulating concentrations of G-actin were elevated in all patient cohorts in the immediate aftermath of injury and this was accompanied by a significant reduction in the levels of GSN and VDBP.

Conclusions

The post-traumatic increase in circulating cfDNA that occurs following extracranial trauma and TBI is accompanied by reduced DNase activity. We propose that, secondary to reduced GSN and VDBP levels, elevated circulating concentrations of G-actin underlie the post-injury reduction in DNase activity. Reducing circulating cfDNA levels via therapeutic restoration of DNase-1 activity may improve clinical outcomes post-injury.

Cell-free DNA beyond a biomarker for rejection: Biological trigger of tissue injury and potential therapeutics

Cell-free DNA, measured as donor-derived cell-free DNA is developed as a non-specific biomarker for allograft injury and transplant rejection. However, cell-free DNA characteristics are more specific, its fragment length, nucleotide content, and composition, as well as the tissue source of origin, are intrinsically linked to the underlying disease pathogenesis, showing distinct features in acute cellular rejection and antibody-mediated rejection for example. Further, cell-free DNA and cell-free mitochondrial DNA can directly trigger tissue injury as damage-associated molecular patterns through three major intracellular receptors, toll-like receptor 9 , cyclic guanosine monophosphate-adenosine monophosphate synthase, and inflammasomes (i.e., absent in melanoma 2: AIM2). Therefore, in addition to its role as a non-specific marker for allograft injury, cell-free DNA analysis may be used to phenotype transplant rejection, and to non-invasively point the underlying molecular mechanisms with allograft injury. Novel treatment approaches targeting these cell-free DNA pathways may be useful to treat transplant rejection and prevent end-organ dysfunction. In this review, we discuss the link between cell-free DNA characteristics and disease, the role of cell-free DNA as a damage-associated molecular pattern, and novel therapeutics targeting these cell-free DNA molecular pathways and their potential utility to treat transplant rejection.

Do all cardiac surgery patients benefit from antifibrinolytic therapy?

BACKGROUND

In trauma patients, the recognition of fibrinolysis phenotypes has led to a re-evaluation of the risks and benefits of antifibrinolytic therapy (AF). Many cardiac patients also receive AF, but the distribution of fibrinolytic phenotypes in that population is unknown. The purpose of this hypothesis-generating study was to fill that gap.

METHODS

Seventy-eight cardiac surgery patients were retrospectively reviewed. Phenotypes were defined as hypofibrinolytic (LY30 <0.8%), physiologic (0.8%-3.0%), and hyperfibrinolytic (>3%) based on thromboelastogram.

RESULTS

The population was 65 ± 10-years old, 74% male, average body mass index of 29 ± 5 kg/m² . Fibrinolytic phenotypes were distributed as physiologic = 45% (35 of 78), hypo = 32% (25 of 78), and hyper = 23% (18 of 78). There was no obvious effect of age, gender, race, or ethnicity on this distribution; 47% received AF. For AF versus no AF, the time with chest tube was longer (4 [1] vs. 3 [1] days, p = .037), and all-cause morbidity was more prevalent (51% vs. 25%, p = .017). However, when these two groups were further stratified by phenotypes, there were within-group differences in the percentage of patients with congestive heart failure (p = .022), valve disease (p = .024), on-pump surgery (p < .0001), estimated blood loss during surgery (p = .015), transfusion requirement (p = .015), and chest tube output (p = .008), which highlight other factors along with AF that might have affected all-cause morbidity.

CONCLUSION

This is the first description of the prevalence of three different fibrinolytic phenotypes and their potential influence on cardiac surgery patients. The use of AF was associated with increased morbidity, but because of the small sample size and treatment allocation bias, additional confirmatory studies are necessary. We hope these present findings open the dialog on whether it is safe to administer AFs to cardiac surgery patients who are normo- or hypofibrinolytic.