DNA, histones and neutrophil extracellular traps exert anti-fibrinolytic effects in a plasma environment

Ischaemic Stroke, Thromboembolism and Clot Structure

Ischaemic stroke is a major cause of morbidity and mortality worldwide. Blood clotting and thromboembolism play a central role in the pathogenesis of ischaemic stroke. An increasing number of recent studies indicate changes in blood clot structure and composition in patients with ischaemic stroke. In this review, we aim to summarise and discuss clot structure, function and composition in ischaemic stroke, including its relationships with clinical diagnosis and treatment options such as thrombolysis and thrombectomy. Studies are summarised in which clot structure and composition is analysed both in vitro from patients' plasma samples and ex vivo in thrombi obtained through interventional catheter-mediated thrombectomy. Mechanisms that drive clot composition and architecture such as neutrophil extracellular traps and clot contraction are also discussed. We find that, while in vitro clot structure in plasma samples from ischaemic stroke patients are consistently altered, showing denser clots that are more resistant to fibrinolysis, current data on the composition and architecture of ex vivo clots obtained by thrombectomy are more variable. With the potential of advances in technologies underpinning both the imaging and retrieving of clots, we expect that future studies in this area will generate new data that is of interest for the diagnosis, optimal treatment strategies and clinical management of patients with ischaemic stroke.

Acute Ischemic Stroke Thrombus Composition

Ischemic stroke is caused by a thrombus blocking one or multiple arteries in the brain, resulting in irreversible damage in the associated brain tissue. The aim of therapy is to restore the blood flow as fast as possible. Two recanalization strategies are currently available: pharmacological thrombolysis using recombinant tissue plasminogen activator (rt-PA) and mechanical removal of the thrombus. Despite recent advancements, achieving efficient recanalization remains a challenge. The precise causes of therapy failure are not fully understood but thrombus composition is likely a key factor in successful recanalization. This review explores acute ischemic stroke thrombus composition, its recently identified components, and how it affects stroke treatment. It also discusses how new insights could enhance current recanalization strategies for ischemic stroke patients.

Association between thrombus composition and first-pass recanalization after thrombectomy in acute ischemic stroke

BACKGROUND

Achieving first-pass recanalization (FPR) has become the primary procedural objective during thrombectomy in acute ischemic stroke patients as it correlates with the best clinical outcome. Understanding factors contributing to FPR failures is essential to enhance FPR success rates. As the central target of thrombectomy, the thrombus itself may be a significant factor influencing FPR.

OBJECTIVES

This study aimed to investigate the association between thrombus composition and FPR success rates.

METHODS

In total, thrombi from 267 ischemic stroke patients were collected in the AZ Groeninge Hospital (Kortrijk, Belgium). Thrombus composition was determined via detailed histologic analysis of red blood cells (RBCs), fibrin, von Willebrand factor, platelets, leukocytes, citrullinated histone 3 (marker for neutrophil extracellular traps), and intracellular and extracellular DNA. FPR was defined as obtaining a modified thrombolysis in cerebral infarction (mTICI) score of 2c/3 after the first pass.

RESULTS

An mTICI score of 2c/3 was obtained in 180 patients, which was achieved via a successful FPR procedure in 126 cases or after multiple passes in 54 cases. Interestingly, thrombi from FPR cases had a different composition from thrombi that needed multiple passes to obtain an mTICI score of 2c/3. FPR thrombi contained significantly more RBCs (P = .0264), less fibrin (P = .0196), and less extracellular DNA (P = .0457).

CONCLUSION

Our results indicate that thrombi characterized by lower RBC content, higher fibrin levels, and increased extracellular DNA are less likely to result in an FPR. These results are important to guide future research aiming at improving procedures or technologies to obtain FPR rates in RBC-poor thrombi.

R-tPA Resistance Is Specific for Platelet-Rich Stroke Thrombi and Can Be Overcome by Targeting Nonfibrin Components

BACKGROUND

Resistance to r-tPA (recombinant tissue-type plasminogen activator) is a well-known but poorly understood phenomenon that hampers successful recanalization in patients with acute ischemic stroke. Using clinically relevant thrombi from patients with acute ischemic stroke, we investigated if and how thrombus composition impacts r-tPA-mediated lysis. In addition, we explored strategies to overcome r-tPA resistance.

METHODS

Thrombi were split into 2 parts, 1 of which was used for thrombolysis and the other for detailed histological analysis. Thrombolysis was performed in normal human plasma using r-tPA alone, using r-tPA in combination with DNase-1 or using r-tPA in combination with N,N'-diacetyl-l-cystine. Thrombus lysis was calculated as the percentage of residual thrombus weight compared with its initial weight and the degree of lysis was linked to thrombus composition determined via histology.

RESULTS

Interestingly, we found that the efficacy of r-tPA-mediated thrombolysis was strongly correlated with the composition of the thrombi. Thrombi containing high amounts of red blood cells and low amounts of DNA and von Willebrand Factor were efficiently degraded by r-tPA, whereas thrombi containing low amounts of red blood cells and higher amounts of DNA and von Willebrand Factor were resistant to r-tPA. Importantly, combination of r-tPA with DNase-1 or N,N'-diacetyl-l-cystine significantly and specifically improved the lysis of these r-tPA-resistant thrombi.

CONCLUSIONS

Using patient thrombus material, our results for the first time show that the composition of stroke thrombi largely determines their susceptibility to r-tPA-mediated thrombolysis. Red blood cell-poor thrombi have a specific resistance to r-tPA, which can be overcome by targeting nonfibrin components using DNase-1 or N,N'-diacetyl-l-cystine.

A promising frontier: targeting NETs for stroke treatment breakthroughs

Stroke is a prevalent global acute cerebrovascular condition, with ischaemic stroke being the most frequently occurring type. After a stroke, neutrophils accumulate in the brain and subsequently generate and release neutrophil extracellular traps (NETs). The accumulation of NETs exacerbates the impairment of the blood‒brain barrier (BBB), hampers neovascularization, induces notable neurological deficits, worsens the prognosis of stroke patients, and can facilitate the occurrence of t-PA-induced cerebral haemorrhage subsequent to ischaemic stroke. Alternative approaches to pharmacological thrombolysis or endovascular thrombectomy are being explored, and targeting NETs is a promising treatment that warrants further investigation.

Neutrophil Extracellular Traps in Cardiovascular and Aortic Disease: A Narrative Review on Molecular Mechanisms and Therapeutic Targeting

Neutrophil extracellular traps (NETs), composed of DNA, histones, and antimicrobial proteins, are released by neutrophils in response to pathogens but are also recognized for their involvement in a range of pathological processes, including autoimmune diseases, cancer, and cardiovascular diseases. This review explores the intricate roles of NETs in different cardiovascular conditions such as thrombosis, atherosclerosis, myocardial infarction, COVID-19, and particularly in the pathogenesis of abdominal aortic aneurysms. We elucidate the mechanisms underlying NET formation and function, provide a foundational understanding of their biological significance, and highlight the contribution of NETs to inflammation, thrombosis, and tissue remodeling in vascular disease. Therapeutic strategies for preventing NET release are compared with approaches targeting components of formed NETs in cardiovascular disease. Current limitations and potential avenues for clinical translation of anti-NET treatments are discussed.

Neutrophils and Neutrophil Extracellular Traps Cause Vascular Occlusion and Delayed Cerebral Ischemia After Subarachnoid Hemorrhage in Mice

BACKGROUND

After subarachnoid hemorrhage (SAH), neutrophils are deleterious and contribute to poor outcomes. Neutrophils can produce neutrophil extracellular traps (NETs) after ischemic stroke. Our hypothesis was that, after SAH, neutrophils contribute to delayed cerebral ischemia (DCI) and worse outcomes via cerebrovascular occlusion by NETs.

METHODS

SAH was induced via endovascular perforation, and SAH mice were given either a neutrophil-depleting antibody, a PAD4 (peptidylarginine deiminase 4) inhibitor (to prevent NETosis), DNAse-I (to degrade NETs), or a vehicle control. Mice underwent daily neurological assessment until day 7 and then euthanized for quantification of intravascular brain NETs (iNETs). Subsets of mice were used to quantify neutrophil infiltration, NETosis potential, iNETs, cerebral perfusion, and infarction. In addition, NET markers were assessed in the blood of aneurysmal SAH patients.

RESULTS

In mice, SAH led to brain neutrophil infiltration within 24 hours, induced a pro-NETosis phenotype selectively in skull neutrophils, and caused a significant increase in iNETs by day 1, which persisted until at least day 7. Neutrophil depletion significantly reduced iNETs, improving cerebral perfusion, leading to less neurological deficits and less incidence of DCI (16% versus 51.9%). Similarly, PAD4 inhibition reduced iNETs, improved neurological outcome, and reduced incidence of DCI (5% versus 30%), whereas degrading NETs marginally improved outcomes. Patients with aneurysmal SAH who developed DCI had elevated markers of NETs compared with non-DCI patients.

CONCLUSIONS

After SAH, skull-derived neutrophils are primed for NETosis, and there are persistent brain iNETs, which correlated with delayed deficits. The findings from this study suggest that, after SAH, neutrophils and NETosis are therapeutic targets, which can prevent vascular occlusion by NETs in the brain, thereby lessening the risk of DCI. Finally, NET markers may be biomarkers, which can predict which patients with aneurysmal SAH are at risk for developing DCI.

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.

Ultrasound elastography predicts anticoagulation in lower extremity deep vein thrombosis

OBJECTIVE

To investigate predictors of anticoagulation efficacy in deep venous thrombosis (DVT) by ultrasound elastography (UE).

METHODS

The basic clinical, laboratory and ultrasound treatment data of fifty-eight patients with DVT were collected and analyzed. Then the results of ultrasound after 3-month anticoagulation treatment were compared among different groups. Multiple logistic regression analysis was used to identify independent risk factors that affected anticoagulation efficacy. The predictive efficacy of each independent risk factor was accessed by drawing operating characteristic (ROC) curves.

RESULTS

According to the regression analysis, the elastic modulus (OR = 0.631, P = 0.001) and strain rate ratio (OR = 0.332, P = 0.006) were identified as independent risk factors for the effectiveness of anticoagulation therapy in patients with DVT. According to the ROC curves, elastic modulus and strain rate ratio could predict effective anticoagulation therapy for DVT, and the optimal threshold values were 22.10 kPa and 1.80 respectively. The corresponding AUC values were 0.879 and 0.854, with a sensitivity of 71.4% and 59.5%, a specificity of 93.7%, and a Youden index of 65.1% and 62.7%, respectively.

CONCLUSIONS

The elastic modulus (≤22.10 kPa) or strain rate ratio (≤1.80) of the thrombus were independent predictors for the effectiveness of anticoagulation therapy.

[Value of the expression levels of complement-3a receptor 1 and neutrophil extracellular traps in predicting sepsis-induced coagulopathy]

OBJECTIVES

To investigate the clinical value of complement-3a receptor 1 (C3aR1) and neutrophil extracellular traps (NETs) in predicting sepsis-induced coagulopathy (SIC).

METHODS

A prospective study was conducted among 78 children with sepsis who attended Xuzhou Children's Hospital Affiliated to Xuzhou Medical University from June 2022 to June 2023. According to the presence or absence of SIC, they were divided into two groups: SIC (n=36) and non-SIC (n=42) . The two groups were compared in terms of clinical data and the levels of C3aR1 and NETs. The factors associated with the occurrence of SIC were analyzed. The receiver operating characteristic (ROC) curve was used to evaluate the performance of C3aR1 and NETs in predicting SIC.

RESULTS

Compared with the non-SIC group, the SIC group had significantly higher levels of C-reactive protein, interleukin-6 (IL-6), interleukin-10, C3aR1, and NETs (P<0.05). The multivaiate logistic regression analysis showed that the increases in C3aR1, NETs, and IL-6 were closely associated with the occurrence of SIC (P<0.05). The ROC curve analysis showed that C3aR1 combined with NETs had an area under the curve (AUC) of 0.913 in predicting SIC (P<0.05), which was significantly higher than the AUC of C3aR1 or IL-6 (P<0.05), while there was no significant difference in AUC between C3aR1 combined with NETs and NETs alone (P>0.05).

CONCLUSIONS

There are significant increases in the expression levels of C3aR1 and NETs in the peripheral blood of children with SIC, and the expression levels of C3aR1 and NETs have a high clinical value in predicting SIC.

The fibrinolysis renaissance

Fibrinolysis is the system primarily responsible for removal of fibrin deposits and blood clots in the vasculature. The terminal enzyme in the pathway, plasmin, is formed from its circulating precursor, plasminogen. Fibrin is by far the most legendary substrate, but plasmin is notoriously prolific and is known to cleave many other proteins and participate in the activation of other proteolytic systems. Fibrinolysis is often overshadowed by the coagulation system and viewed as a simplistic poorer relation. However, the primordial plasminogen activators evolved alongside the complement system, approximately 70 million years before coagulation saw the light of day. It is highly likely that the plasminogen activation system evolved with its roots in primordial immunity. Almost all immune cells harbor at least one of a dozen plasminogen receptors that allow plasmin formation on the cell surface that in turn modulates immune cell behavior. Similarly, numerous pathogens express their own plasminogen activators or contain surface proteins that provide binding sites for host plasminogen. The fibrinolytic system has been harnessed for clinical medicine for many decades with the development of thrombolytic drugs and antifibrinolytic agents. Our refined understanding and appreciation of the fibrinolytic system and its alliance with infection and immunity and beyond are paving the way for new developments and interest in novel therapeutics and applications. One must ponder as to whether the nomenclature of the system hampered our understanding, by focusing on fibrin, rather than the complex myriad of interactions and substrates of the plasminogen activation system.

Low-grade endotoxemia in acute pulmonary embolism: Links with prothrombotic plasma fibrin clot phenotype

BACKGROUND

Lipopolysaccharide (LPS) can traverse the intestinal barrier and enter bloodstream, causing endotoxemia and triggering inflammation. Increased circulating LPS was reported in arterial thromboembolism. We investigated whether increased LPS levels occur in acute pulmonary embolism (PE) and if it is associated with a prothrombotic state.

METHODS

We studied 120 normotensive PE patients (aged 59 [48-68] years) on admission, after 5-7 days, and after a 3-month anticoagulation. Serum LPS levels, along with zonulin, a marker of gut permeability, endogenous thrombin potential (ETP), fibrin clot permeability (Ks), clot lysis time (CLT), fibrinolysis proteins, and platelet markers were assessed.

RESULTS

Median LPS concentration on admission was 70.5 (61.5-82) pg/mL (min-max, 34-134 pg/mL), in association with C-reactive protein (r = 0.22, p = 0.018), but not with fibrinogen, D-dimer or platelet markers. Patients with more severe PE had higher LPS levels compared with the remainder. Median zonulin level was 3.26 (2.74-4.08) ng/mL and correlated with LPS (r = 0.66, p < 0.0001). Patients with baseline LPS levels in the top quartile (≥82 pg/mL; n = 29) compared to lower quartiles had 18.6 % increased ETP, 14.5 % reduced Ks, and 25.3 % prolonged CLT, related to higher plasminogen activator inhibitor type 1 (PAI-1) levels. LPS decreased by 23.4 % after 5-7 days and by 40.4 % after 3-month anticoagulation together with reduced zonulin by 18.4 % and 22.3 %, respectively, compared to baseline (all p < 0.001). LPS levels were not related with fibrin characteristics and other variables assessed at 3 months.

CONCLUSIONS

Low-grade endotoxemia is detectable in patients with acute PE and may contribute to increased thrombin generation and PAI-1-mediated hypofibrinolysis.

NLRP3-Induced NETosis: A Potential Therapeutic Target for Ischemic Thrombotic Diseases?

Ischemic thrombotic disease, characterized by the formation of obstructive blood clots within arteries or veins, is a condition associated with life-threatening events, such as stroke, myocardial infarction, deep vein thrombosis, and pulmonary embolism. The conventional therapeutic strategy relies on treatments with anticoagulants that unfortunately pose an inherent risk of bleeding complications. These anticoagulants primarily target clotting factors, often overlooking upstream events, including the release of neutrophil extracellular traps (NETs). Neutrophils are integral components of the innate immune system, traditionally known for their role in combating pathogens through NET formation. Emerging evidence has now revealed that NETs contribute to a prothrombotic milieu by promoting platelet activation, increasing thrombin generation, and providing a scaffold for clot formation. Additionally, NET components enhance clot stability and resistance to fibrinolysis. Clinical and preclinical studies have underscored the mechanistic involvement of NETs in the pathogenesis of thrombotic complications, since the clots obtained from patients and experimental models consistently exhibit the presence of NETs. Given these insights, the inhibition of NETs or NET formation is emerging as a promising therapeutic approach for ischemic thrombotic diseases. Recent investigations also implicate a role for the nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome as a mediator of NETosis and thrombosis, suggesting that NLRP3 inhibition may also hold potential for mitigating thrombotic events. Therefore, future preclinical and clinical studies aimed at identifying and validating NLRP3 inhibition as a novel therapeutic intervention for thrombotic disorders are imperative.

Polyphosphate as an antithrombotic target and hemostatic agent

Polyphosphate (PolyP) is a polymer comprised of linear phosphate units connected by phosphate anhydride bonds. PolyP exists in a diverse range of eukaryotes and prokaryotes with varied chain lengths ranging from six to thousands of phosphate units. Upon activation, human platelets and neutrophils release short-chain PolyP, along with other components, to initiate the coagulation pathway. Long-chain PolyP derived from cellular or bacterial organelles exhibits higher proinflammatory and procoagulant effects compared to short-chain PolyP. Notably, PolyP has been identified as a low-hemorrhagic antithrombotic target since neutralizing plasma PolyP suppresses the thrombotic process without impairing the hemostatic functions. As an inorganic polymer without uniform steric configuration, PolyP is typically targeted by cationic polymers or recombinant polyphosphatases rather than conventional antibodies, small-molecule compounds, or peptides. Additionally, because of its procoagulant property, PolyP has been incorporated in wound-dressing materials to facilitate blood hemostasis. This review summarizes current studies on PolyP as a low-hemorrhagic antithrombotic target and the development of hemostatic materials based on PolyP.

Neutrophil extracellular traps mediate deep vein thrombosis: from mechanism to therapy

Deep venous thrombosis (DVT) is a part of venous thromboembolism (VTE) that clinically manifests as swelling and pain in the lower limbs. The most serious clinical complication of DVT is pulmonary embolism (PE), which has a high mortality rate. To date, its underlying mechanisms are not fully understood, and patients usually present with clinical symptoms only after the formation of the thrombus. Thus, it is essential to understand the underlying mechanisms of deep vein thrombosis for an early diagnosis and treatment of DVT. In recent years, many studies have concluded that Neutrophil Extracellular Traps (NETs) are closely associated with DVT. These are released by neutrophils and, in addition to trapping pathogens, can mediate the formation of deep vein thrombi, thereby blocking blood vessels and leading to the development of disease. Therefore, this paper describes the occurrence and development of NETs and discusses the mechanism of action of NETs on deep vein thrombosis. It aims to provide a direction for improved diagnosis and treatment of deep vein thrombosis in the near future.

Pathophysiology of Disseminated Intravascular Coagulation in Sepsis: A Clinically Focused Overview

Sepsis is a major global health problem that results from a dysregulated and uncontrolled host response to infection, causing organ failure. Despite effective anti-infective therapy and supportive treatments, the mortality rate of sepsis remains high. Approximately 30-80% of patients with sepsis may develop disseminated intravascular coagulation (DIC), which can double the mortality rate. There is currently no definitive treatment approach for sepsis, with etiologic treatment being the cornerstone of therapy for sepsis-associated DIC. Early detection, diagnosis, and treatment are critical factors that impact the prognosis of sepsis-related DIC. Over the past several decades, researchers have made continuous efforts to better understand the mechanisms of DIC in sepsis, as well as improve its quantitative diagnosis and treatment. This article aims to provide a comprehensive overview of the current understanding of sepsis-related DIC, focusing on common causes and diagnoses, with the goal of guiding healthcare providers in the care of patients with sepsis.

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.

SARS-CoV-2 Spike Proteins and Cell-Cell Communication Induce P-Selectin and Markers of Endothelial Injury, NETosis, and Inflammation in Human Lung Microvascular Endothelial Cells and Neutrophils: Implications for the Pathogenesis of COVID-19 Coagulopathy

COVID-19 progression often involves severe lung injury, inflammation, coagulopathy, and leukocyte infiltration into pulmonary tissues. The pathogenesis of these complications is unknown. Because vascular endothelium and neutrophils express angiotensin-converting enzyme-2 and spike (S)-proteins, which are present in bodily fluids and tissues of SARS-CoV-2-infected patients, we investigated the effect of S-proteins and cell-cell communication on human lung microvascular endothelial cells and neutrophils expression of P-selectin, markers of coagulopathy, NETosis, and inflammation. Exposure of endothelial cells or neutrophils to S-proteins and endothelial-neutrophils co-culture induced P-selectin transcription and expression, significantly increased expression/secretion of IL-6, von Willebrand factor (vWF, pro-coagulant), and citrullinated histone H3 (cit-H3, NETosis marker). Compared to the SARS-CoV-2 Wuhan variant, Delta variant S-proteins induced 1.4-15-fold higher P-selectin and higher IL-6 and vWF. Recombinant tissue factor pathway inhibitor (rTFPI), 5,5'-dithio-bis-(2-nitrobenzoic acid) (thiol blocker), and thrombomodulin (anticoagulant) blocked S-protein-induced vWF, IL-6, and cit-H3. This suggests that following SARS-CoV-2 contact with the pulmonary endothelium or neutrophils and endothelial-neutrophil interactions, S-proteins increase adhesion molecules, induce endothelial injury, inflammation, NETosis and coagulopathy via the tissue factor pathway, mechanisms involving functional thiol groups, and/or the fibrinolysis system. Using rTFPI, effectors of the fibrinolysis system and/or thiol-based drugs could be viable therapeutic strategies against SARS-CoV-2-induced endothelial injury, inflammation, NETosis, and coagulopathy.

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.

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.

An in vitro model for Extracellular DNA Traps (ETs)-rich Human Thrombus Analogs

BACKGROUND

Extracellular DNA traps (ETs) have important implications in both thrombosis and thrombolysis. Thus, developing benchtop thrombus analogs that recapitulate clinical ETs is potentially of great value for preclinical development and testing of thrombolytic agents and thrombectomy devices. In this study, we aimed to develop ETs-rich thrombus analogs for preclinical testing.

METHODS

Red blood cell (RBC)-rich, fibrin-rich, and platelet-rich thrombus analogs were created using human whole blood, platelet-poor plasma, and platelet-rich plasma obtained from the blood bank following institutional approval. Peripheral blood mononuclear cells (9.9×106 cells/mL) isolated from human whole blood and lipopolysaccharide (1 µg/mL) were added to induce ETs. Histochemical, immunohistochemistry and immunofluorescence were used to identify thrombus components and ETs. Scanning electronic microscopy was used to investigate the ultrastructure of the thrombus analogs. The thrombus compositions, morphologic features of ETs and citrullinated histone H3 (H3Cit) expression were compared with those of thrombi retrieved from patients by thrombectomy.

RESULTS

ETs-rich thrombus analogs were more compacted th-an the ETs-poor thrombus analogs. ETs were identified in both ETs-rich thrombus analogs and patient thrombi showing morphologic features including nuclear lobulation, nuclear swelling, diffused chromatin within cytoplasm, DNA/chromatin extending intracellularly and extracellularly, and extracellular chromatin patches and bundles. In the ETs-poor thrombus analogs, ETs were not observed and H3Cit expression was absent to minimal. The compositions and H3Cit expression in the ETs-rich thrombus analogs fell in the range of patient thrombi.

CONCLUSIONS

ETs-rich thrombus analogs can be consistently created in vitro and may benefit the preclinical development and testing of new thrombolytic agents and thrombectomy devices.

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.

Fibrin clot properties in cardiovascular disease: from basic mechanisms to clinical practice

Fibrinogen conversion into insoluble fibrin and the formation of a stable clot is the final step of the coagulation cascade. Fibrin clot porosity and its susceptibility to plasmin-mediated lysis are the key fibrin measures, describing the properties of clots prepared ex vivo from citrated plasma. Cardiovascular disease (CVD), referring to coronary heart disease, heart failure, stroke, and hypertension, has been shown to be associated with the formation of dense fibrin networks that are relatively resistant to lysis. Denser fibrin mesh characterized acute patients at the onset of myocardial infarction or ischaemic stroke, while hypofibrinolysis has been identified as a persistent fibrin feature in patients following thrombotic events or in those with stable coronary artery disease. Traditional cardiovascular risk factors, such as smoking, diabetes mellitus, hyperlipidaemia, obesity, and hypertension, have also been linked with unfavourably altered fibrin clot properties, while some lifestyle modifications and pharmacological treatment, in particular statins and anticoagulants, may improve fibrin structure and function. Prospective studies have suggested that prothrombotic fibrin clot phenotype can predict cardiovascular events in short- and long-term follow-ups. Mutations and splice variants of the fibrinogen molecule that have been proved to be associated with thrombophilia or increased cardiovascular risk, along with fibrinogen post-translational modifications, prothrombotic state, inflammation, platelet activation, and neutrophil extracellular traps formation, contribute also to prothrombotic fibrin clot phenotype. Moreover, about 500 clot-bound proteins have been identified within plasma fibrin clots, including fibronectin, α2-antiplasmin, factor XIII, complement component C3, and histidine-rich glycoprotein. This review summarizes the current knowledge on the mechanisms underlying unfavourable fibrin clot properties and their implications in CVD and its thrombo-embolic manifestations.

Heparin, Heparan Sulphate and Sepsis: Potential New Options for Treatment

Sepsis is a life-threatening hyperreaction to infection in which excessive inflammatory and immune responses cause damage to host tissues and organs. The glycosaminoglycan heparan sulphate (HS) is a major component of the cell surface glycocalyx. Cell surface HS modulates several of the mechanisms involved in sepsis such as pathogen interactions with the host cell and neutrophil recruitment and is a target for the pro-inflammatory enzyme heparanase. Heparin, a close structural relative of HS, is used in medicine as a powerful anticoagulant and antithrombotic. Many studies have shown that heparin can influence the course of sepsis-related processes as a result of its structural similarity to HS, including its strong negative charge. The anticoagulant activity of heparin, however, limits its potential in treatment of inflammatory conditions by introducing the risk of bleeding and other adverse side-effects. As the anticoagulant potency of heparin is largely determined by a single well-defined structural feature, it has been possible to develop heparin derivatives and mimetic compounds with reduced anticoagulant activity. Such heparin mimetics may have potential for use as therapeutic agents in the context of sepsis.

Vitronectin promotes immunothrombotic dysregulation in the venular microvasculature

Microvascular immunothrombotic dysregulation is a critical process in the pathogenesis of severe systemic inflammatory diseases. The mechanisms controlling immunothrombosis in inflamed microvessels, however, remain poorly understood. Here, we report that under systemic inflammatory conditions the matricellular glycoproteinvitronectin (VN) establishes an intravascular scaffold, supporting interactions of aggregating platelets with immune cells and the venular endothelium. Blockade of the VN receptor glycoprotein (GP)IIb/IIIa interfered with this multicellular interplay and effectively prevented microvascular clot formation. In line with these experimental data, particularly VN was found to be enriched in the pulmonary microvasculature of patients with non-infectious (pancreatitis-associated) or infectious (coronavirus disease 2019 (COVID-19)-associated) severe systemic inflammatory responses. Targeting the VN-GPIIb/IIIa axis hence appears as a promising, already feasible strategy to counteract microvascular immunothrombotic dysregulation in systemic inflammatory pathologies.

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.

Neutrophil extracellular traps are increased after extracorporeal membrane oxygenation support initiation and present in thrombus: A preclinical study using sheep as an animal model

BACKGROUND

The balance between thrombosis and hemostasis is a difficult issue during extracorporeal membrane oxygenation (ECMO) support. The pathogenesis leading to thrombotic complications during ECMO support is not well understood. Neutrophil extracellular traps (NETs) were reported to participate in thrombosis and have a key role in inflammation. This study aimed to explore the role of NETs in thrombosis during ECMO support and investigate NETs as a predictive biomarker for thrombotic complications during ECMO assistance.

METHODS

Ten ovine models of ECMO support were established. Animals were then randomly divided into 2 groups (5 sheep/group): venoarterial (VA) ECMO group and venovenous (VV) ECMO group. The venous blood samples were collected at different time points. Markers of NETs were detected in plasma, neutrophils, and thrombi from the vessels and membrane. Moreover, circulating NETs levels in 8 adults treated in the intensive care unit (ICU) who received VA-ECMO and 8 healthy controls were detected; patient survival was also recorded.

RESULTS

In vivo study showed that neutrophils and NETs markers (dsDNA and citH3) levels were significantly elevated 6 h after ECMO compared to baseline. Isolated neutrophils from fresh blood at 6 h could release more NETs. dsDNA and citH3 levels were significantly higher in the VA mode than in the VV mode. NETs were found in thrombi from the vessel and membrane. Clinical data further revealed that dsDNA, citH3, and nucleosomes were higher in patients who received ECMO than in healthy controls.

CONCLUSIONS

These data suggest NETs might be associated with thrombus during ECMO support, especially in the VA mode. These findings provide new insight into preventing thrombotic complications by targeting NETs. Also, NETs may potentially become an early warning biomarker for thrombosis under ECMO assistance.

Role of neutrophil extracellular traps in inflammatory evolution in severe acute pancreatitis

ABSTRACT

Severe acute pancreatitis (SAP) is a life-threatening acute abdominal disease with two peaks of death: the first in the early stage, characterized by systemic inflammatory response-associated organ failure; and the second in the late stage, characterized by infectious complications. Neutrophils are the main immune cells participating in the whole process of SAP. In addition to the traditional recognition of neutrophils as the origination of chemokine and cytokine cascades or phagocytosis and degranulation of pathogens, neutrophil extracellular traps (NETs) also play an important roles in inflammatory reactions. We reviewed the role of NETs in the occurrence and development of SAP and its fatal complications, including multiple organs injury, infected pancreatic necrosis, and thrombosis. This review provides novel insights into the involvement of NETs throughout the entire process of SAP, showing that targeting NETs might be a promising strategy in SAP treatment. However, precision therapeutic options targeting NETs in different situations require further investigation.

“Going with the flow” in modeling fibrinolysis

The formation of thrombi is shaped by intravascular shear stress, influencing both fibrin architecture and the cellular composition which has downstream implications in terms of stability against mechanical and fibrinolytic forces. There have been many advancements in the development of models that incorporate flow rates akin to those found in vivo. Both thrombus formation and breakdown are simultaneous processes, the balance of which dictates the size, persistence and resolution of thrombi. Therefore, there is a requirement to have models which mimic the physiological shear experienced within the vasculature which in turn influences the fibrinolytic degradation of the thrombus. Here, we discuss various assays for fibrinolysis and importantly the development of novel models that incorporate physiological shear rates. These models are essential tools to untangle the molecular and cellular processes which govern fibrinolysis and can recreate the conditions within normal and diseased vessels to determine how these processes become perturbed in a pathophysiological setting. They also have utility to assess novel drug targets and antithrombotic drugs that influence thrombus stability.

Citrullinated fibrinogen forms densely packed clots with decreased permeability

BACKGROUND

Fibrin, the main scaffold of thrombi, is susceptible to citrullination by PAD (peptidyl arginine deiminase) 4, secreted from neutrophils during the formation of neutrophil extracellular traps. Citrullinated fibrinogen (citFg) has been detected in human plasma as well as in murine venous thrombi, and it decreases the lysability and mechanical resistance of fibrin clots.

OBJECTIVE

To investigate the effect of fibrinogen citrullination on the structure of fibrin clots.

METHODS

Fibrinogen was citrullinated with PAD4 and clotted with thrombin. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to measure fiber thickness, fiber height/width ratio, and fiber persistence length in clots containing citFg. Fiber density was measured with laser scanning microscopy (LSM) and permeability measurements were carried out to estimate the porosity of the clots. The intra-fiber structure of fibrin was analyzed with small-angle X-ray scattering (SAXS).

RESULTS

SEM images revealed a decrease in the median fiber diameter that correlated with the fraction of citFg in the clot, while the fiber width/length ratio remained unchanged according to AFM. With SAXS we observed that citrullination resulted in the formation of denser clots in line with increased fiber density shown by LSM. The permeability constant of citrullinated fibrin decreased more than 3-fold indicating significantly decreased porosity. SAXS also showed largely preserved periodicity in the longitudinal assembly of fibrin monomers.

CONCLUSION

The current observations of thin fibers combined with dense packing and low porosity in the presence of citFg can provide a structural framework for the mechanical fragility and lytic resistance of citrullinated fibrin.

Clinical significance of neutrophil extracellular traps biomarkers in thrombosis

Neutrophil extracellular traps (NETs) may be associated with the development of thrombosis. Experimental studies have confirmed the presence of NETs in thrombi specimens and potential role of NETs in the mechanisms of thrombosis. Clinical studies also have demonstrated significant changes in the levels of serum or plasma NETs biomarkers, such as citrullinated histones, myeloperoxidase, neutrophil elastase, nucleosomes, DNA, and their complexes in patients with thrombosis. This paper aims to comprehensively review the currently available evidence regarding the change in the levels of NETs biomarkers in patients with thrombosis, summarize the role of NETs and its biomarkers in the development and prognostic assessment of venous thromboembolism, coronary artery diseases, ischemic stroke, cancer-associated thromboembolism, and coronavirus disease 2019-associated thromboembolism, explore the potential therapeutic implications of NETs, and further discuss the shortcomings of existing NETs biomarkers in serum and plasma and their detection methods.

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.

Coagulation and complement: Key innate defense participants in a seamless web

In 1969, Dr. Oscar Ratnoff, a pioneer in delineating the mechanisms by which coagulation is activated and complement is regulated, wrote, “In the study of biological processes, the accumulation of information is often accelerated by a narrow point of view. The fastest way to investigate the body’s defenses against injury is to look individually at such isolated questions as how the blood clots or how complement works. We must constantly remind ourselves that such distinctions are man-made. In life, as in the legal cliché, the devices through which the body protects itself form a seamless web, unwrinkled by our artificialities.” Our aim in this review, is to highlight the critical molecular and cellular interactions between coagulation and complement, and how these two major component proteolytic pathways contribute to the seamless web of innate mechanisms that the body uses to protect itself from injury, invading pathogens and foreign surfaces.

Investigations of the effectiveness of heparin variants as inhibitors of histones

BACKGROUND

Extracellular histones exert cytotoxic and procoagulant effects which contribute to immunothrombosis in vascular diseases such as sepsis. Heparin has been shown to neutralize the pathologic effects of histones in vitro and in animal models.

OBJECTIVES

To compare the effectiveness of unfractionated heparin (UFH), low-molecularweight heparin (LMWH), Vasoflux (lacks anticoagulant activity), and fondaparinux in neutralizing the cytotoxic and procoagulant activities of histones METHODS: Binding affinities between heparin variants and histone subunits were determined by Bio-layer Interferometry. The ability of heparin variants to diminish the cytotoxic and procoagulant effects of histones was studied by treating endothelial cells or monocytic THP-1 cells with histones ± heparin variants.

RESULTS

Unfractionated heparin, LMWH, and Vasoflux bind histone subunits with high affinities (Kd <1 pM-66.7 nM) whereas fondaparinux exhibited a low affinity (Kd of 3.06 µM-81.1 mM). UFH, LMWH, and Vasoflux neutralize histone-mediated cytotoxicity as well as monocytic procoagulant activity (as assessed by cell surface tissue factor and phosphatidylserine). In contrast, fondaparinux has no effect on these activities. All four heparin variants reverse histone-mediated impairment of APC generation in a dose-dependent manner.

CONCLUSIONS

The ability of heparin to neutralize the cytotoxic and procoagulant effects of histones require heparin fragments >1.7 kDa and is independent of the antithrombin-binding pentasaccharide. In contrast, the ability of heparin to neutralize histone-mediated impairment of APC generation is independent of size and anticoagulant activity. These findings suggest that heparin variants may have differential therapeutic potential in vascular diseases associated with elevated levels of histones.

Polyphosphate nanoparticles enhance the fibrin stabilization by histones more efficiently than linear polyphosphates

Introduction

Beyond the three-dimensional fibrin network, the mechanical and lytic stability of thrombi is supported by the matrix of neutrophil extracellular traps (NETs) composed of polyanionic DNA meshwork with attached proteins including polycationic histones. Polyphosphates represent another type of polyanions, which in their linear form are known to enhance the fibrin stabilizing effects of DNA and histones. However, in vivo polyphosphates are also present in the form of nanoparticles (PolyP-NP), the interference of which with the fibrin/NET matrix is poorly characterized.

Aims

To compare the effects of linear and nanoparticulate polyphosphates, and their combinations with relevant NET components (DNA, histone H3) on fibrin formation, structure, and lysis in in vitro assays focusing on histone-polyphosphate interactions.

Methods

Transmission electron microscopy and dynamic light scattering for stability of the PolyP-NP preparations. Turbidimetry for kinetics of fibrinogen clotting by thrombin and fibrin dissolution by tissue-type plasminogen activator/plasminogen. Scanning electron microscopy for fibrin structure. Surface plasmon resonance for strength of histone-PolyP interactions.

Results

Both linear PolyP and PolyP-NP accelerated the fibrin formation and slowed down its dissolution and these effects were strongly dependent on the number of individual PolyP particles and not on their size. Addition of DNA did not modify significantly the PolyP-NP effects on fibrin formation and lysis. Both linear and nanoparticulate PolyP counteracted the effect of histone in the acceleration of fibrinogen clotting by thrombin. PolyP-NP, but not linear PolyP enhanced the prolongation of lysis time in fibrin containing histone and caused more pronounced thickening of the fibrin fibers than the linear form. Finally, PolyP-NP bound weaker to histone than the linear form.

Conclusions

The interaction of PolyP with histone was a stronger modulator of fibrin formation and lysis than its interaction with DNA. In addition, the PolyP nanoparticles enhanced the thrombus stabilizing effects of histone more effectively than linear PolyP.

Cardiovascular disease risk in antiphospholipid syndrome: Thrombo-inflammation and atherothrombosis

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by the presence of antiphospholipid antibodies (aPL) (lupus anticoagulant, anticardiolipin antibodies and anti-beta2glycoprotein I (anti-β2GPI) antibodies) and a plethora of macro- and micro-vascular manifestations, affecting predominantly young adults. Cardiovascular events are the leading causes of morbidity and mortality in APS. APL-mediated thrombo-inflammation and atherothrombosis are emerging pathogenetic mechanisms of cardiovascular disease (CVD) in APS, involving endothelial cell and monocyte activation, cytokines and adhesion molecules expression, complement and neutrophils activation, neutrophil extracellular traps formation, platelet cell activation and aggregation, and subsequent thrombin generation, in parallel with an oxidized low-density lipoprotein (oxLDL)-β2GPI complex induced macrophage differentiation to foam cells. High risk aPL profile, especially the presence of lupus anticoagulant and triple aPL positivity (all three aPL subtypes), co-existence with Systemic Lupus Erythematosus (SLE), as well as traditional risk factors such as smoking, hypertension, hyperlipemia and obesity are associated with both subclinical atherosclerosis and cardiovascular events in APS. Increased awareness of CVD risk by the physicians and patients, regular assessment and strict control of traditional risk factors, and lifestyle modifications are recommended. Use of low-dose aspirin should be considered for cardiovascular prevention in asymptomatic aPL carriers or SLE patients with high-risk aPL profile. The role of older agents such as hydroxychloroquine and statins or new potential targeted treatments against immuno- and athero-thrombosis has been demonstrated by experimental and some clinical studies and needs to be further evaluated by randomized controlled studies. This review summarizes the available evidence about the pathogenetic mechanisms and prevalence of cardiovascular events and subclinical atherosclerosis, the interrelationship between traditional and disease-related CVD risk factors, and the cardiovascular risk assessment and management in APS.

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.

Diverse thrombus composition in thrombectomy stroke patients with longer time to recanalization

BACKGROUND AND PURPOSE

Delayed time to recanalization is associated with reduced recanalization success of mechanical thrombectomy (MT) and thrombolysis in acute ischemic stroke (AIS). The reasons for this are unclear. We hypothesized that alterations in thrombus structure and composition could be responsible for this.

METHODS

Retrieved thrombi from AIS patients who underwent MT less than 8 h from symptom onset to groin puncture (SOGP) were evaluated. Patients were divided into early (≤4 h.) vs delayed (> 4 h) groups based SOGP timing. Thrombi were histologically analysed using Martius Scarlett Blue and immunohistochemistry staining for von Willebrand Factor (vWF), anti-citrullinated H3 (H3Cit; NETs [neutrophil extracellular traps] marker). We used inferential statistics including, t-test, artificial neural network (ANN) to interpret the data.

RESULTS

A total of 137 thrombi were collected. The overall average percentage of red blood cells (RBC), white blood cells (WBC), platelet, fibrin, H3Cit, and vWF components in thrombi was 45.83%, 3.58%, 22.23%, 28.27%, 19.97% and 16.23% respectively. Delayed group had higher WBCs, (p = 0.02), fibrin (p = 0.02), H3Cit (p = 0.04) and vWF (p = 0.03) thrombus fractions compared to early group. Based on ANN model, the most important factors for predicting the number of passes required for successful recanalization are fibrin and RBC contents of the thrombus followed by vWF and H3Cit contents.

CONCLUSIONS

Longer time to recanalization was associated with increased WBCs, fibrin, H3Cit and vWF fractions of thrombi reflecting possible in situ maturation of thrombus components. Increased fibrin, NETs and vWF composition may reduce likelihood of revascularization by altering thrombus mechanical properties.

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.

An Untapped Resource: Characteristics of Thrombus Recovered from Intermediate or High Risk Pulmonary Embolus Patients

INTRODUCTION

Response to anticoagulation varies during management of acute hospitalized pulmonary embolism. We aimed to study thrombus histology in pulmonary embolism samples removed during acute surgical embolectomy to evaluate whether thrombus morphology was similar between patients and whether there was an association with duration of symptoms and/or resolution on follow up imaging.

METHODS

This was a retrospective observational single center study at the University of Rochester Medical Center. We evaluated patients that underwent acute surgical embolectomy and followed up in our clinic 2-4 months after the event with Ventilation/Perfusion (V/Q) scan obtained for all regardless of symptoms. Thromboemboli were formalin fixed and processed for light microscopy in the hospital histopathology laboratory. Four-micron thick sections were stained with hematoxylin and eosin, Masson trichrome, and Verhoeff elastic tissue stains. Immunohistochemistry was performed using anti-CD31 and anti-CD68. Slides were independently evaluated for time-dependent microscopic changes using Irniger's classification by two blinded pathologists.

RESULTS

Sixteen patients underwent embolectomy with fifteen having V/Q imaging at follow up. The majority of patients were female. Samples showed a generally similar overall architecture that included a central core composed primarily of red blood cells and fibrin and an outer layer of platelets and monocytes. Two samples had evidence of fibrosis and recanalization.

CONCLUSIONS

We found heterogeneous histopathology in samples obtained during acute embolectomy. Further prospective studies should systematically characterize clot morphology and evaluate treatment response and outcomes. Careful thrombus specimen measurement and consistent sampling for sections will be required to draw firm conclusions.

The role of cell-free DNA in fibrinolysis for intraventricular hemorrhage

OBJECTIVE

Tissue plasminogen activator (tPA) fibrinolysis did not improve functional outcomes of patients with intraventricular hemorrhage (IVH), largely because of the unsatisfactory clot clearance. The presence of neutrophil extracellular traps (NETs) within the clot has been confirmed to impair tPA fibrinolysis, but the mechanism has been unclear. The authors hypothesized that cell-free DNA (cfDNA), the main framework of NETs, might be the important reason for the fibrinolysis resistance, and they validated the hypothesis, hoping to provide a new target to promote intraventricular fibrinolysis.

METHODS

First, cfDNA was detected in IVH clots by immunofluorescence staining in a rat model of IVH. Second, after blood (with or without exogenous cfDNA) intraventricular injection, IVH rats were given intraventricular infusion of 2 μl of saline, tPA, or tPA + DNase1 randomly. Then, the ventricular volume, animal behavior, and reactive astrocyte proliferation were assessed. Third, the IVH clots were collected for fibrinolysis assay in vitro. Finally, the effects of exogenous cfDNA in IVH were evaluated.

RESULTS

The presence of cfDNA in clots was observed as early as 1 hour after IVH. Compared with the whole-blood model, blood + cfDNA caused more severe ventricular dilation (day 7: blood 32.47 ± 2.096 mm3 vs blood + DNA 40.09 ± 2.787 mm3, p < 0.05), increased fibrinolysis resistance to tPA (day 7: tPA + DNA 26.04 ± 1.318 mm3 vs tPA 22.15 ± 1.706 mm3, p < 0.05), and further deteriorated the functional defects in rats (blood vs blood + DNA, p < 0.05). Degradation of cfDNA by DNase1 further enhanced the fibrinolysis effects on relieving the ventricular dilation (day 7: tPA + DNase1 11.67 ± 2.023 mm3 vs tPA, p < 0.05), improving the functional outcome (tPA vs tPA + DNase1, p < 0.05) and reducing periventricular astrocyte proliferation.

CONCLUSIONS

cfDNA impaired tPA fibrinolysis for IVH, and degradation of cfDNA may be a new target to improve this condition.

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.

The Prothrombotic State Associated with SARS-CoV-2 Infection: Pathophysiological Aspects

Severe coronavirus disease-2019 (COVID-19) is frequently associated with microvascular thrombosis, especially in the lung, or macrovascular thrombosis, mainly venous thromboembolism, which significantly contributes to the disease mortality burden. COVID-19 patients also exhibit distinctive laboratory abnormalities that are compatible with a prothrombotic state. The key event underlying COVID-19-associated thrombotic complications is an excessive host inflammatory response to severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection generating multiple inflammatory mediators, mainly cytokines and complement activation products. The latter, along with the virus itself, the increased levels of angiotensin II and hypoxia, drive the major cellular changes promoting thrombosis, which include: (1) aberrant expression of tissue factor by activated alveolar epithelial cells, monocytes-macrophages and neutrophils, and production of other prothrombotic factors by activated endothelial cells (ECs) and platelets; (2) reduced expression of physiological anticoagulants by dysfunctional ECs, and (3) suppression of fibrinolysis by the endothelial overproduction of plasminogen activator inhibitor-1 and, likely, by heightened thrombin-mediated activation of thrombin-activatable fibrinolysis inhibitor. Moreover, upon activation or death, neutrophils and other cells release nuclear materials that are endowed with potent prothrombotic properties. The ensuing thrombosis significantly contributes to lung injury and, in most severe COVID-19 patients, to multiple organ dysfunction. Insights into the pathogenesis of COVID-19-associated thrombosis may have implications for the development of new diagnostic and therapeutic tools.

Psoriatic disease is associated with systemic inflammation, endothelial activation, and altered haemostatic function

Psoriasis is a chronic, immune-mediated inflammatory skin disease, affecting approximately 2% of the general population, which can be accompanied by psoriatic arthritis (PsA). The condition has been associated with an increased cardiovascular burden. Hypercoagulability is a potential underlying mechanism that may contribute to the increased risk of major cardiovascular events in psoriatic individuals. Whole blood samples were collected from 20 PsA patients and 20 healthy individuals. The concentrations of inflammatory molecules (C-reactive protein, serum amyloid A, soluble intercellular adhesion molecule-1, soluble vascular cell adhesion molecule-1, and soluble P-selectin) were determined by enzyme-linked immunosorbent assays. In addition, clotting efficiency was evaluated by thromboelastography. The fibrin network architecture was also assessed by scanning electron microscopy. Elevated levels of circulating inflammatory molecules were significantly associated with the presence of psoriatic disease. Furthermore, an increased tendency towards thrombus formation was significantly predictive of disease presence. Scanning electron microscopy revealed that fibrin clots were denser in psoriatic individuals, compared to healthy controls, with an increased fibrin fibre diameter associated with psoriatic disease. Our results add to the accumulating evidence of the systemic nature of psoriasis and the subsequent risk of cardiovascular comorbidities, potentially due to an acquired hypercoagulability. We suggest that haemostatic function should be monitored carefully in psoriatic patients that present with severe disease, due to the pre-eminent risk of developing thrombotic complications.

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.

Inflammation, Infection and Venous Thromboembolism

The association between inflammation, infection, and venous thrombosis has long been recognized; yet, only in the last decades have we begun to understand the mechanisms through which the immune and coagulation systems interact and reciprocally regulate one another. These interconnected networks mount an effective response to injury and pathogen invasion, but if unregulated can result in pathological thrombosis and organ damage. Neutrophils, monocytes, and platelets interact with each other and the endothelium in host defense and also play critical roles in the formation of venous thromboembolism. This knowledge has advanced our understanding of both human physiology and pathophysiology, as well as identified mechanisms of anticoagulant resistance and novel therapeutic targets for the prevention and treatment of thrombosis. In this review, we discuss the contributions of inflammation and infection to venous thromboembolism.

The Fibrinolytic System: Mysteries and Opportunities

The deposition and removal of fibrin has been the primary role of coagulation and fibrinolysis, respectively. There is also little doubt that these 2 enzyme cascades influence each other given they share the same serine protease family ancestry and changes to 1 arm of the hemostatic pathway would influence the other. The fibrinolytic system in particular has also been known for its capacity to clear various non-fibrin proteins and to activate other enzyme systems, including complement and the contact pathway. Furthermore, it can also convert a number of growth factors into their mature, active forms. More recent findings have extended the reach of this system even further. Here we will review some of these developments and also provide an account of the influence of individual players of the fibrinolytic (plasminogen activating) pathway in relation to physiological and pathophysiological events, including aging and metabolism.

Fibrinolysis in Platelet Thrombi

The extent and duration of occlusive thrombus formation following an arterial atherothrombotic plaque disruption may be determined by the effectiveness of endogenous fibrinolysis. The determinants of endogenous fibrinolysis are the subject of much research, and it is now broadly accepted that clot composition as well as the environment in which the thrombus was formed play a significant role. Thrombi with a high platelet content demonstrate significant resistance to fibrinolysis, and this may be attributable to an augmented ability for thrombin generation and the release of fibrinolysis inhibitors, resulting in a fibrin-dense, stable thrombus. Additional platelet activators may augment thrombin generation further, and in the case of coronary stenosis, high shear has been shown to strengthen the attachment of the thrombus to the vessel wall. Neutrophil extracellular traps contribute to fibrinolysis resistance. Additionally, platelet-mediated clot retraction, release of Factor XIII and resultant crosslinking with fibrinolysis inhibitors impart structural stability to the thrombus against dislodgment by flow. Further work is needed in this rapidly evolving field, and efforts to mimic the pathophysiological environment in vitro are essential to further elucidate the mechanism of fibrinolysis resistance and in providing models to assess the effects of pharmacotherapy.