Biological basis and pathological relevance of microvascular thrombosis

The Combination of Natural Compounds Escin-Bromelain-Ginkgo Biloba-Sage Miltiorrhiza (EBGS) Reduces Platelet Adhesion to TNFα-Activated Vascular Endothelium through FAK Signaling

Thrombosis is a key process that determines acute coronary syndrome and ischemic stroke and is the leading cause of morbidity and mortality in the world, together with cancer. Platelet adhesion and subsequent activation and aggregation are critical processes that cause thrombus formation after endothelial damage. To date, high hopes are associated with compounds of natural origin, which show anticoagulant action without undesirable effects and can be proposed as supportive therapies. We investigated the effect of the new combination of four natural compounds, escin-bromelain-ginkgo biloba-sage miltiorrhiza (EBGS), on the initial process of the coagulation cascade, which is the adhesion of platelets to activated vascular endothelium. Our results demonstrated that EBGS pretreatment of endothelial cells reduces platelet adhesion even in the presence of the monocyte-lymphocyte population. Our data indicate that EBGS exerts its effects by inhibiting the transcription of adhesion molecules, including P-selectin, platelet membrane glycoprotein GP1b, integrins αV and β3, and reducing the secretion of the pro-inflammatory cytokines interleukin 6, interleukin 8, and the metalloproteinases MMP-2 and MMP-9. Furthermore, we demonstrated that EBGS inhibited the expression of focal adhesion kinase (FAK), strictly involved in platelet adhesion, and whose activity is correlated with that of integrin β3. The results shown in this manuscript suggest a possible inhibitory role of the new combination EBGS in the reduction in platelet adhesion to activated endothelium, thus possibly preventing coagulation cascade initiation.

Potential use of sodium glucose co-transporter 2 inhibitors during acute illness: a systematic review based on COVID-19

OBJECTIVE

SGLT-2i are increasingly recognized for their benefits in patients with cardiometabolic risk factors. Additionally, emerging evidence suggests potential applications in acute illnesses, including COVID-19. This systematic review aims to evaluate the effects of SGLT-2i in patients facing acute illness, particularly focusing on SARS-CoV-2 infection.

METHODS

Following PRISMA guidelines, a systematic search of PubMed, Scopus, medRxiv, Research Square, and Google Scholar identified 22 studies meeting inclusion criteria, including randomized controlled trials and observational studies. Data extraction and quality assessment were conducted independently.

RESULTS

Out of the 22 studies included in the review, six reported reduced mortality in DM-2 patients taking SGLT-2i, while two found a decreased risk of hospitalization. Moreover, one study demonstrated a lower in-hospital mortality rate in DM-2 patients under combined therapy of metformin plus SGLT-2i. However, three studies showed a neutral effect on the risk of hospitalization. No increased risk of developing COVID-19 was associated with SGLT-2i use in DM-2 patients. Prior use of SGLT-2i was not associated with ICU admission and need for MV. The risk of acute kidney injury showed variability, with inconsistent evidence regarding diabetic ketoacidosis.

CONCLUSION

Our systematic review reveals mixed findings on the efficacy of SGLT-2i use in COVID-19 patients with cardiometabolic risk factors. While some studies suggest potential benefits in reducing mortality and hospitalizations, others report inconclusive results. Further research is needed to clarify optimal usage and mitigate associated risks, emphasizing caution in clinical interpretation.

Platelets and Thrombotic Antiphospholipid Syndrome

Antiphospholipid antibody syndrome (APS) is an autoimmune disorder characterised by thrombosis and the presence of antiphospholipid antibodies (aPL): lupus anticoagulant and/or IgG/IgM anti-β2-glycoprotein I and anticardiolipin antibodies. APS carries significant morbidity for a relatively young patient population from recurrent thrombosis in any vascular bed (arterial, venous, or microvascular), often despite current standard of care, which is anticoagulation with vitamin K antagonists (VKA). Platelets have established roles in thrombosis at any site, and platelet hyperreactivity is clearly demonstrated in the pathophysiology of APS. Together with excess thrombin generation, platelet activation and aggregation are the common end result of all the pathophysiological pathways leading to thrombosis in APS. However, antiplatelet therapies play little role in APS, reserved as a possible option of low dose aspirin in addition to VKA in arterial or refractory thrombosis. This review outlines the current evidence and mechanisms for excessive platelet activation in APS, how it plays a central role in APS-related thrombosis, what evidence for antiplatelets is available in clinical outcomes studies, and potential future avenues to define how to target platelet hyperreactivity better with minimal impact on haemostasis.

Thrombosis and Hyperinflammation in COVID-19 Acute Phase Are Related to Anti-Phosphatidylserine and Anti-Phosphatidylinositol Antibody Positivity

Antiphospholipid antibodies (APLA) are strongly associated with thrombosis seen in patients with antiphospholipid syndrome. In COVID-19, thrombosis has been observed as one of the main comorbidities. In patients hospitalised for COVID-19, we want to check whether APLA positivity is associated with COVID-19-related thrombosis, inflammation, severity of disease, or long COVID-19. We enrolled 92 hospitalised patients with COVID-19 between March and April 2020 who were tested for 18 different APLAs (IgG and IgM) with a single line-immunoassay test. A total of 30 healthy blood donors were used to set the cut-off for each APLA positivity. Of the 92 COVID-19 inpatients, 30 (32.61%; 95% CI [23.41-43.29]) tested positive for APLA, of whom 10 (33.3%; 95% CI [17.94-52.86]) had more than one APLA positivity. Anti-phosphatidylserine IgM positivity was described in 5.4% of inpatients (n = 5) and was associated with the occurrence of COVID-19-related thrombosis (p = 0.046). Anti-cardiolipin IgM positivity was the most prevalent among the inpatients (n = 12, 13.0%) and was associated with a recorded thrombosis in their clinical history (p = 0.044); however, its positivity was not associated with the occurrence of thrombosis during their hospitalisation for COVID-19. Anti-phosphatidylinositol IgM positivity, with a prevalence of 5.4% (n = 5), was associated with higher levels of interleukin (IL)-6 (p = 0.007) and ferritin (p = 0.034). Neither of these APLA positivities was a risk factor for COVID-19 severity or a predictive marker for long COVID-19. In conclusion, almost a third of COVID-19 inpatients tested positive for at least one APLA. Anti-phosphatidylserine positivity in IgM class was associated with thrombosis, and anti-phosphatidylinositol positivity in IgM class was associated with inflammation, as noticed by elevated levels of IL-6. Thus, testing for non-criteria APLA to assess the risk of clinical complications in hospitalised COVID-19 patients might be beneficial. However, they were not related to disease severity or long COVID-19.

How to manage coagulopathies in critically ill patients

Coagulopathy is a severe and frequent complication in critically ill patients, for which the pathogenesis and presentation may be variable depending on the underlying disease. Based on the dominant clinical phenotype, the current review differentiates between hemorrhagic coagulopathies, characterized by a hypocoagulable and hyperfibrinolysis state, and thrombotic coagulopathies with a systemic prothrombotic and antifibrinolytic phenotype. We discuss the differences in pathogenesis and treatment of the common coagulopathies.

A review of pathophysiological mechanism, diagnosis, and treatment of thrombosis risk associated with COVID-19 infection

Severe coronavirus (COVID-19) infection has been reportedly associated with a high risk of thromboembolism. Developing macrovascular thrombotic complications, including myocardial injury/infarction, venous thromboembolism, and stroke have been observed in one-third of severe COVID-19 hospitalized patients, leading to an increase in mortality and morbidity. The diagnosis of COVID-19 associated coagulopathy may be challenging because there are close similarities between pulmonary embolism and severe COVID-19 disease. Therefore, a critical step in improving the clinical outcome of patients with hospitalized COVID-19 is the recognition of coagulation abnormalities and the identification of patients with poor prognoses, prophylactic guidance, or antithrombotic therapy. Prescribing anticoagulants in all patients hospitalized with COVID-19 and 2-6 weeks post-hospital discharge in the absence of contraindications is recommended by most consensus documents published on behalf of professional societies. However, a decision on some variable factors such as intensity and duration of anticoagulation may be made based on an individual case and needs future randomized trial studies. Regarding little information on this subject, this study aims to review how inflammation and thrombosis are related to COVID-19 patients, discuss the types of thrombosis in these patients, and summarize the diagnosis and treatment of thrombosis in COVID19 patients.

Circulating Small Extracellular Vesicles Profiling and Thrombin Generation as Potential Markers of Thrombotic Risk in Glioma Patients

Introduction

Patients with glioma (GM) are at a high risk of venous thromboembolism (VTE). The role of microvesiculation in the cancer-associated thrombosis mechanisms has been previously demonstrated. This study aimed to evaluate the relative abundance of extracellular vesicles (EVs) and thrombin generation (TG) in combination with standard laboratory tests in patients with newly diagnosed GM as potential prognostic markers in VTE.

Materials and Methods

In the present study, 11 patients with newly diagnosed GM and 10 healthy volunteers were analyzed. EVs were counted and their cellular origin was determined (CytoFlex B4-R2-V2, Beckman Coulter, United States), as well as thrombin generation test (TGT) (Diagnostica Stago SAS, France) was performed.

Results

In patients with GM, the relative abundance of the CD41 + EVs (platelet-derived)—and CD105 + EVs (endothelial-derived) was significantly higher than in the control group (44.3 [40.5; 52.4] vs. 27.2 [22.9; 31.0]%, p = 0.002, and 5.4 [4.8; 7.8] vs. 1.9 [1.5; 2.8]%, p = 0.0003, respectively). The D-dimer level was higher in patients with GM compared with the control group (0.46 [0.38; 1.85] vs. 0.36 [0.27; 0.40] μg/ml FEU, p = 0.03, respectively). There was a trend toward an increase in the peak thrombin and velocity index (VI) in the GM group (p = 0.06). During the follow-up period, two patients (18%) developed thrombosis, had tumor sizes of more than 5 cm, thrombocytopenia, increased VI, and D-dimer.

Conclusion

Analysis of platelet-derived EVs, platelet count, and TGT in combination with D-dimer assessment could improve the stratification of patients prone to VTE, which needs to be confirmed in a larger sample.

The thrombodynamic ratio as a predictor of 28-day mortality in sepsis patients

BACKGROUND

The thrombodynamic ratio (TDR) as a composite thromboelastography (TEG) parameter, has been proven to be valuable in multiple diseases. However, the association between TDR and mortality in sepsis has not been studied.

METHODS

One hundred forty-one patients were enrolled in this retrospectively study. TEG was performed immediately at admission. Two cox proportional hazards models were developed for the prediction of 28-day mortality. The C statistic, continuous net reclassification index (cNRI) and integrated discriminatory index (IDI) were calculated to compare the discrimination performance of clinical models with and without the TDR value. The integrated calibration index (ICI) and E50 were calculated to compare the calibration.

RESULTS

Patients with lower TDR were more likely to have organ impairments and increased 28-day mortality. The TDR value improved discrimination performance in both Model 1 (C statistic, 0.745 vs 0.735; cNRI 19.4%, p =0.044; IDI 5.6%, p =0.012) and Model 2 (C statistic, 0.761 vs 0.751; IDI, 5.1%, p = 0.012). Compared to the calibration curve of Model 1 without TDR, addition of TDR displayed better calibration (ICI, 0.023; E50, 0.021).

CONCLUSION

TDR value significantly predicts 28-day mortality in patients with sepsis and could improve the discrimination and calibration performance of clinical prediction models.

Evolution of Platelet Activation Parameters During Septic Shock in Intensive Care Unit

During severe sepsis, platelet activation may induce disseminate microvascular thrombosis, which play a key role in critical organ failure. Crucially, most of the studies in this field have explored platelet-leukocyte interactions in animal models, or explored platelets under the spectrum of thrombocytopenia or disseminated intravascular coagulation and have not taken into account the complex interplay that might exist between platelets and leukocytes during human septic shock nor the kinetics of platelet activation. Here, we assessed platelet activation parameters at the admission of patients with sepsis to the intensive care unit (ICU) and 48 hours later. Twenty-two patients were enrolled in the study, thirteen (59.1%) of whom were thrombocytopenic. The control group was composed of twelve infection-free patients admitted during the study period. The activation parameters studied included platelet-leukocyte interactions, assessed by flow cytometry in whole blood, as well as membrane surface and soluble platelet activation markers measured by flow cytometry and dedicated ELISA kits. We also investigated platelet aggregation and secretion responses of patients with sepsis following stimulation, compared to controls. At admission, the level of circulating monocyte-platelet and neutrophil-platelet heterotypic aggregates was significantly higher in sepsis patients compared to controls and returned to a level comparable to controls or even below 48 hours later. Basal levels of CD62P and CD63 platelet membrane exposure at admission and 48 hours later were low and similar to controls. In contrast, plasma level of soluble GPVI and soluble CD40 ligand was significantly increased in septic patients, at the two times of analysis, reflecting previous platelet activation. Platelet aggregation and secretion responses induced by specific agonists were significantly decreased in septic conditions, particularly 48 hours after admission. Hence, we have observed for the first time that critically ill septic patients compared to controls have both an early and durable platelet activation while their circulating platelets are less responsive to different agonists.

The Pathophysiology and Management of Hemorrhagic Shock in the Polytrauma Patient

The recognition and management of life-threatening hemorrhage in the polytrauma patient poses several challenges to prehospital rescue personnel and hospital providers. First, identification of acute blood loss and the magnitude of lost volume after torso injury may not be readily apparent in the field. Because of the expression of highly effective physiological mechanisms that compensate for a sudden decrease in circulatory volume, a polytrauma patient with a significant blood loss may appear normal during examination by first responders. Consequently, for every polytrauma victim with a significant mechanism of injury we assume substantial blood loss has occurred and life-threatening hemorrhage is progressing until we can prove the contrary. Second, a decision to begin damage control resuscitation (DCR), a costly, highly complex, and potentially dangerous intervention must often be reached with little time and without sufficient clinical information about the intended recipient. Whether to begin DCR in the prehospital phase remains controversial. Furthermore, DCR executed imperfectly has the potential to worsen serious derangements including acidosis, coagulopathy, and profound homeostatic imbalances that DCR is designed to correct. Additionally, transfusion of large amounts of homologous blood during DCR potentially disrupts immune and inflammatory systems, which may induce severe systemic autoinflammatory disease in the aftermath of DCR. Third, controversy remains over the composition of components that are transfused during DCR. For practical reasons, unmatched liquid plasma or freeze-dried plasma is transfused now more commonly than ABO-matched fresh frozen plasma. Low-titer type O whole blood may prove safer than red cell components, although maintaining an inventory of whole blood for possible massive transfusion during DCR creates significant challenges for blood banks. Lastly, as the primary principle of management of life-threatening hemorrhage is surgical or angiographic control of bleeding, DCR must not eclipse these definitive interventions.

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.

Neutrophil Extracellular Trap-Driven Occlusive Diseases

The enlightenment of the formation of neutrophil extracellular traps (NETs) as a part of the innate immune system shed new insights into the pathologies of various diseases. The initial idea that NETs are a pivotal defense structure was gradually amended due to several deleterious effects in consecutive investigations. NETs formation is now considered a double-edged sword. The harmful effects are not limited to the induction of inflammation by NETs remnants but also include occlusions caused by aggregated NETs (aggNETs). The latter carries the risk of occluding tubular structures like vessels or ducts and appear to be associated with the pathologies of various diseases. In addition to life-threatening vascular clogging, other occlusions include painful stone formation in the biliary system, the kidneys, the prostate, and the appendix. AggNETs are also prone to occlude the ductal system of exocrine glands, as seen in ocular glands, salivary glands, and others. Last, but not least, they also clog the pancreatic ducts in a murine model of neutrophilia. In this regard, elucidating the mechanism of NETs-dependent occlusions is of crucial importance for the development of new therapeutic approaches. Therefore, the purpose of this review is to address the putative mechanisms of NETs-associated occlusions in the pathogenesis of disease, as well as prospective treatment modalities.

Thrombotic Complications in Patients with COVID-19: Pathophysiological Mechanisms, Diagnosis, and Treatment

INTRODUCTION

Emerging evidence points to an association between severe clinical presentation of COVID-19 and increased risk of thromboembolism. One-third of patients hospitalized due to severe COVID-19 develops macrovascular thrombotic complications, including venous thromboembolism, myocardial injury/infarction and stroke. Concurrently, the autopsy series indicate multiorgan damage pattern consistent with microvascular injury.

PROPHYLAXIS, DIAGNOSIS AND TREATMENT

COVID-19 associated coagulopathy has distinct features, including markedly elevated D-dimers concentration with nearly normal activated partial thromboplastin time, prothrombin time and platelet count. The diagnosis may be challenging due to overlapping features between pulmonary embolism and severe COVID-19 disease, such as dyspnoea, high concentration of D-dimers, right ventricle with dysfunction or enlargement, and acute respiratory distress syndrome. Both macro- and microvascular complications are associated with an increased risk of in-hospital mortality. Therefore, early recognition of coagulation abnormalities among hospitalized COVID-19 patients are critical measures to identify patients with poor prognosis, guide antithrombotic prophylaxis or treatment, and improve patients' clinical outcomes.

RECOMMENDATIONS FOR CLINICIANS

Most of the guidelines and consensus documents published on behalf of professional societies focused on thrombosis and hemostasis advocate the use of anticoagulants in all patients hospitalized with COVID-19, as well as 2-6 weeks post hospital discharge in the absence of contraindications. However, since there is no guidance for deciding the intensity and duration of anticoagulation, the decision-making process should be made in individual-case basis.

CONCLUSIONS

Here, we review the mechanistic relationships between inflammation and thrombosis, discuss the macrovascular and microvascular complications and summarize the prophylaxis, diagnosis and treatment of thromboembolism in patients affected by COVID-19.

Potential Role of Antioxidant and Anti-Inflammatory Therapies to Prevent Severe SARS-Cov-2 Complications

The coronavirus disease 2019 (COVID-19) pandemic is caused by a novel severe acute respiratory syndrome (SARS)-like coronavirus (SARS-CoV-2). Here, we review the molecular pathogenesis of SARS-CoV-2 and its relationship with oxidative stress (OS) and inflammation. Furthermore, we analyze the potential role of antioxidant and anti-inflammatory therapies to prevent severe complications. OS has a potential key role in the COVID-19 pathogenesis by triggering the NOD-like receptor family pyrin domain containing 3 inflammasome and nuclear factor-kB (NF-kB). While exposure to many pro-oxidants usually induces nuclear factor erythroid 2 p45-related factor2 (NRF2) activation and upregulation of antioxidant related elements expression, respiratory viral infections often inhibit NRF2 and/or activate NF-kB pathways, resulting in inflammation and oxidative injury. Hence, the use of radical scavengers like N-acetylcysteine and vitamin C, as well as of steroids and inflammasome inhibitors, has been proposed. The NRF2 pathway has been shown to be suppressed in severe SARS-CoV-2 patients. Pharmacological NRF2 inducers have been reported to inhibit SARS-CoV-2 replication, the inflammatory response, and transmembrane protease serine 2 activation, which for the entry of SARS-CoV-2 into the host cells through the angiotensin converting enzyme 2 receptor. Thus, NRF2 activation may represent a potential path out of the woods in COVID-19 pandemic.

Recent advances in the research and management of sepsis-associated DIC

Disseminated intravascular coagulation (DIC) is a common and life-threatening complication in sepsis. Sepsis-associated DIC is recognized as the systemic activation in coagulation with suppressed fibrinolysis that leads to organ dysfunction in combination with systemic intravascular inflammation. In this process, thrombin contributes a key role in connecting both coagulation and inflammation. Endothelial injury, a result of sepsis, causes DIC due to the effect of multiple activated factors that include neutrophils, platelets, and damage-associated molecular patterns. Recent advances in the understanding of pathophysiology have made it possible to diagnose sepsis-associated DIC at earlier timing with better accuracy. However, progress in the treatment is still limited, and new therapeutics for sepsis-associated DIC are needed.

Preventing the development of severe COVID-19 by modifying immunothrombosis

BACKGROUND

COVID-19-associated acute respiratory distress syndrome (ARDS) is associated with significant morbidity and high levels of mortality. This paper describes the processes involved in the pathophysiology of COVID-19 from the initial infection and subsequent destruction of type II alveolar epithelial cells by SARS-CoV-2 and culminating in the development of ARDS.

MAIN BODY

The activation of alveolar cells and alveolar macrophages leads to the release of large quantities of proinflammatory cytokines and chemokines and their translocation into the pulmonary vasculature. The presence of these inflammatory mediators in the vascular compartment leads to the activation of vascular endothelial cells platelets and neutrophils and the subsequent formation of platelet neutrophil complexes. These complexes in concert with activated endothelial cells interact to create a state of immunothrombosis. The consequence of immunothrombosis include hypercoagulation, accelerating inflammation, fibrin deposition, migration of neutrophil extracellular traps (NETs) producing neutrophils into the alveolar apace, activation of the NLRP3 inflammazome, increased alveolar macrophage destruction and massive tissue damage by pyroptosis and necroptosis Therapeutic combinations aimed at ameliorating immunothrombosis and preventing the development of severe COVID-19 are discussed in detail.

Anticoagulant protein S in COVID-19: low activity, and associated with outcome

Introduction. COVID-19 disease was associated with both thrombo-embolic events and in-situ thrombi formation in small vessels. Antiphospholipidic antibodies were found in some studies.Aim. Assessment of protein S activity in patients with COVID-19 as a cause of this prothrombotic state, and of the association of protein S activity with worse outcome.Methods. All patients admitted for COVID-19 disease in a university hospital between 15^th of May and 15^th of July 2020 were prospectively enrolled into this cohort study. Patients treated with antivitamin K anticoagulants and with liver disease were excluded. All patients had protein S activity determined at admission. The main outcome was survival, while secondary outcomes were clinical severity and lung damage.Results. 91 patients were included, of which 21 (23.3%) died. Protein S activity was decreased in 65% of the patients. Death was associated with lower activity of protein S (median 42% vs. 58%, p < 0.001), and the association remained after adjustment for age, inflammation markers and ALAT. There was a dose-response relationship between protein S activity and clinical severity (Kendall_tau coefficient = -0.320, p < 0.001; Jonckheere-Terpstra for trend: p < 0.001) or pulmonary damage on CT scan (Kendall_tau coefficient = -0.290, p < 0.001; Jonckheere-Terpstra for trend: p < 0.001). High neutrophil count was also independently associated with death (p = 0.002).Conclusion. Protein S activity was lower in COVID-19 patients, and its level was associated with survival and disease severity, suggesting that it may have a role in the thrombotic manifestations of the disease.

Neutrophil extracellular traps and thrombosis in COVID-19

Studies of patients with COVID-19 have demonstrated markedly dysregulated coagulation and a high risk of morbid arterial and venous thrombotic events. Elevated levels of blood neutrophils and neutrophil extracellular traps (NETs) have recently been described in patients with COVID-19. However, their potential role in COVID-19-associated thrombosis remains incompletely understood. In order to elucidate the potential role of hyperactive neutrophils and NET release in COVID-19-associated thrombosis, we conducted a case–control study of patients hospitalized with COVID-19 who developed thrombosis, as compared with gender- and age-matched COVID-19 patients without clinical thrombosis. We found that remnants of NETs (cell-free DNA, myeloperoxidase-DNA complexes, and citrullinated histone H3) and neutrophil-derived S100A8/A9 (calprotectin) in patient sera were associated with higher risk of morbid thrombotic events in spite of prophylactic anticoagulation. These observations underscore the need for urgent investigation into the potential relationship between NETs and unrelenting thrombosis in COVID-19, as well as novel approaches for thrombosis prevention.

The pathophysiology of SARS-CoV-2: A suggested model and therapeutic approach

In this paper, a model is proposed of the pathophysiological processes of COVID-19 starting from the infection of human type II alveolar epithelial cells (pneumocytes) by SARS-CoV-2 and culminating in the development of ARDS. The innate immune response to infection of type II alveolar epithelial cells leads both to their death by apoptosis and pyroptosis and to alveolar macrophage activation. Activated macrophages secrete proinflammatory cytokines and chemokines and tend to polarise into the inflammatory M1 phenotype. These changes are associated with activation of vascular endothelial cells and thence the recruitment of highly toxic neutrophils and inflammatory activated platelets into the alveolar space. Activated vascular endothelial cells become a source of proinflammatory cytokines and reactive oxygen species (ROS) and contribute to the development of coagulopathy, systemic sepsis, a cytokine storm and ARDS. Pulmonary activated platelets are also an important source of proinflammatory cytokines and ROS, as well as exacerbating pulmonary neutrophil-mediated inflammatory responses and contributing to systemic sepsis by binding to neutrophils to form platelet-neutrophil complexes (PNCs). PNC formation increases neutrophil recruitment, activation priming and extraversion of these immune cells into inflamed pulmonary tissue, thereby contributing to ARDS. Sequestered PNCs cause the development of a procoagulant and proinflammatory environment. The contribution to ARDS of increased extracellular histone levels, circulating mitochondrial DNA, the chromatin protein HMGB1, decreased neutrophil apoptosis, impaired macrophage efferocytosis, the cytokine storm, the toll-like receptor radical cycle, pyroptosis, necroinflammation, lymphopenia and a high Th17 to regulatory T lymphocyte ratio are detailed.

Guidance on diagnosis, prevention and treatment of thromboembolic complications in COVID-19: a position paper of the Brazilian Society of Thrombosis and Hemostasis and the Thrombosis and Hemostasis Committee of the Brazilian Association of Hematology, Hemotherapy and Cellular Therapy

Hemostatic abnormalities and thrombotic risk associated with coronavirus disease 2019 (COVID-19) are among the most discussed topics in the management of this disease. The aim of this position paper is to provide the opinion of Brazilian experts on the thromboprophylaxis and management of thrombotic events in patients with suspected COVID-19, in the sphere of healthcare in Brazil. To do so, the Brazilian Society of Thrombosis and Hemostasis (BSTH) and the Thrombosis and Hemostasis Committee of the Brazilian Association of Hematology, Hemotherapy and Cellular Therapy (ABHH) have constituted a panel of experts to carefully review and discuss the available evidence about this topic. The data discussed in this document was reviewed by May 9, 2020. Recommendations and suggestions reflect the opinion of the panel and should be reviewed periodically as new evidence emerges.

Severe COVID-19 Is Marked by a Dysregulated Myeloid Cell Compartment

Coronavirus disease 2019 (COVID-19) is a mild to moderate respiratory tract infection, however, a subset of patients progress to severe disease and respiratory failure. The mechanism of protective immunity in mild forms and the pathogenesis of severe COVID-19 associated with increased neutrophil counts and dysregulated immune responses remain unclear. In a dual-center, two-cohort study, we combined single-cell RNA-sequencing and single-cell proteomics of whole-blood and peripheral-blood mononuclear cells to determine changes in immune cell composition and activation in mild versus severe COVID-19 (242 samples from 109 individuals) over time. HLA-DRhiCD11chi inflammatory monocytes with an interferon-stimulated gene signature were elevated in mild COVID-19. Severe COVID-19 was marked by occurrence of neutrophil precursors, as evidence of emergency myelopoiesis, dysfunctional mature neutrophils, and HLA-DRlo monocytes. Our study provides detailed insights into the systemic immune response to SARS-CoV-2 infection and reveals profound alterations in the myeloid cell compartment associated with severe COVID-19.

COVID-19-Associated Coagulopathy: An Exacerbated Immunothrombosis Response

Since the onset of the global pandemic in early 2020, coronavirus disease 2019 (COVID-19) has posed a multitude of challenges to health care systems worldwide. In order to combat these challenges and devise appropriate therapeutic strategies, it becomes of paramount importance to elucidate the pathophysiology of this illness. Coronavirus disease 2019, caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV2), is characterized by a dysregulated immune system and hypercoagulability. COVID-associated coagulopathy (CAC) was recognized based on profound d-dimer elevations and evidence of microthrombi and macrothrombi, both in venous and arterial systems. The underlying mechanisms associated with CAC have been suggested, but not clearly defined. The model of immunothrombosis illustrates the elaborate crosstalk between the innate immune system and coagulation. The rendering of a procoagulant state in COVID-19 involves the interplay of many innate immune pathways. The SARS-CoV2 virus can directly infect immune and endothelial cells, leading to endothelial injury and dysregulation of the immune system. Activated leukocytes potentiate a procoagulant state via release of intravascular tissue factor, platelet activation, NETosis, and inhibition of anticoagulant mechanisms. Additional pathways of specific relevance in CAC include cytokine release and complement activation. All these mechanisms have recently been reported in COVID-19. Immunothrombosis provides a comprehensive perspective of the several synergistic pathways pertinent to the pathogenesis of CAC.

Neutrophil extracellular traps in COVID-19

In severe cases of coronavirus disease 2019 (COVID-19), viral pneumonia progresses to respiratory failure. Neutrophil extracellular traps (NETs) are extracellular webs of chromatin, microbicidal proteins, and oxidant enzymes that are released by neutrophils to contain infections. However, when not properly regulated, NETs have the potential to propagate inflammation and microvascular thrombosis - including in the lungs of patients with acute respiratory distress syndrome. We now report that sera from patients with COVID-19 have elevated levels of cell-free DNA, myeloperoxidase-DNA (MPO-DNA), and citrullinated histone H3 (Cit-H3); the latter 2 are specific markers of NETs. Highlighting the potential clinical relevance of these findings, cell-free DNA strongly correlated with acute-phase reactants, including C-reactive protein, D-dimer, and lactate dehydrogenase, as well as absolute neutrophil count. MPO-DNA associated with both cell-free DNA and absolute neutrophil count, while Cit-H3 correlated with platelet levels. Importantly, both cell-free DNA and MPO-DNA were higher in hospitalized patients receiving mechanical ventilation as compared with hospitalized patients breathing room air. Finally, sera from individuals with COVID-19 triggered NET release from control neutrophils in vitro. Future studies should investigate the predictive power of circulating NETs in longitudinal cohorts and determine the extent to which NETs may be novel therapeutic targets in severe COVID-19.

Neutrophils promote venular thrombosis by shaping the rheological environment for platelet aggregation

In advanced inflammatory disease, microvascular thrombosis leads to the interruption of blood supply and provokes ischemic tissue injury. Recently, intravascularly adherent leukocytes have been reported to shape the blood flow in their immediate vascular environment. Whether these rheological effects are relevant for microvascular thrombogenesis remains elusive. Employing multi-channel in vivo microscopy, analyses in microfluidic devices, and computational modeling, we identified a previously unanticipated role of leukocytes for microvascular clot formation in inflamed tissue. For this purpose, neutrophils adhere at distinct sites in the microvasculature where these immune cells effectively promote thrombosis by shaping the rheological environment for platelet aggregation. In contrast to larger (lower-shear) vessels, this process in high-shear microvessels does not require fibrin generation or extracellular trap formation, but involves GPIbα-vWF and CD40-CD40L-dependent platelet interactions. Conversely, interference with these cellular interactions substantially compromises microvascular clotting. Thus, leukocytes shape the rheological environment in the inflamed venular microvasculature for platelet aggregation thereby effectively promoting the formation of blood clots. Targeting this specific crosstalk between the immune system and the hemostatic system might be instrumental for the prevention and treatment of microvascular thromboembolic pathologies, which are inaccessible to invasive revascularization strategies.

First visualization of circulating neutrophil extracellular traps using cell fluorescence during human septic shock-induced disseminated intravascular coagulation

Disseminated intravascular coagulation (DIC) is a severe complication of septic shock. Polymorphonuclear neutrophils (PMNs) may play a key role in septic shock-induced DIC via the release of neutrophils extracellular traps (NETs). NETs capture invading pathogens, but also act as a pro-coagulant surface at the interface between immunity and thrombosis. During septic shock-induced DIC, neutrophil activation may result in excessive NET formation. Herein, we originally report the presence of circulating NETs in human blood during septic shock-induced DIC. To investigate NET formation during shock-induced DIC neutrophils were isolated from patients in septic shock associated with (n = 3) or without (n = 3) DIC. Neutrophils from healthy donors (n = 3) were stimulated in vitro with ionomycin as NET formation positive controls. PMNs smears were stained with mouse anti-human FITC anti-myeloperoxidase antibody and the blue-fluorescent DAPI nucleic acid stain. NETs were identified as elongated extracellular DNA fibers associated to myeloperoxidase detected by immunofluorescence. NETs were unambiguously observed in PMNs from septic shock patients with DIC but not from patients without DIC. NETs features in DIC+ patients were undistinguishable from those observed in ionomycin-induced PMNs from healthy donors. Fluorescence images of NETs were associated to extracellular cytoplasmic expansions. Our data report for the first time the direct visualization of circulating NETs in patients with septic shock-induced DIC. The in vivo relevance of previously reported indirect markers of NETosis (neutrophil side fluorescence) is confirmed.

Platelets Are Critical Key Players in Sepsis

Host defense against infection is based on two crucial mechanisms: the inflammatory response and the activation of coagulation. Platelets are involved in both hemostasis and immune response. These mechanisms work together in a complex and synchronous manner making the contribution of platelets of major importance in sepsis. This is a summary of the pathophysiology of sepsis-induced thrombocytopenia, microvascular consequences, platelet-endothelial cells and platelet–pathogens interactions. The critical role of platelets during sepsis and the therapeutic implications are also reviewed.

Contrast Agent Enhanced Multimodal Photoacoustic Microscopy and Optical Coherence Tomography for Imaging of Rabbit Choroidal and Retinal Vessels in vivo

Multimodal imaging with photoacoustic microscopy (PAM) and optical coherence tomography (OCT) can be an effective method to evaluate the choroidal and retinal microvasculature. To improve the efficiency for visualizing capillaries, colloidal gold nanoparticles (AuNPs) have been applied as a multimodal contrast agent for both OCT and PAM imaging by taking advantage of the strong optical scattering and the strong optical absorption of AuNPs due to their surface plasmon resonance. Ultra-pure AuNPs were fabricated by femtosecond laser ablation, capped with polyethylene glycol (PEG), and administered to 13 New Zealand white rabbits and 3 Dutch Belted pigmented rabbits. The synthesized PEG-AuNPs (20.0 ± 1.5 nm) were demonstrated to be excellent contrast agents for PAM and OCT, and do not demonstrate cytotoxicity to bovine retinal endothelial cells in cell studies. The image signal from the retinal and choroidal vessels in living rabbits was enhanced by up to 82% for PAM and up to 45% for OCT, respectively, by the administered PEG-AuNPs, which enables detection of individual blood vessels by both imaging modalities. The biodistribution study demonstrated the AuNP accumulated primarily in the liver and spleen. Histology and TUNEL staining did not indicate cell injury or death in the lung, liver, kidney, spleen, heart, or eyes up to seven days after AuNP administration. PEG-AuNPs offer an efficient and safe contrast agent for multimodal ocular imaging to achieve improved characterization of microvasculature.

Neutrophil Activation During Septic Shock

In addition to their well-known role as the cellular mediators of immunity, key other roles have been identified for neutrophils during septic shock. Importantly, neutrophils indeed play a critical role in the recently described immunothrombosis concept and in septic shock-induced coagulopathy. Septic shock is one of the most severe forms of infection, characterized by an inadequate host response to the pathogenic organism. This host response involves numerous defense mechanisms with an intense cellular activation, including neutrophil activation. Neutrophils are key cells of innate immunity through complex interactions with vascular cells and their activation may participate in systemic tissue damages. Their activation also leads to the emission of neutrophil extracellular traps, which take part in both pathogen circumscription and phagocytosis, but also in coagulation activation. Neutrophils thus stand at the interface between hemostasis and immunity, called immunothrombosis.The present review will develop a cellular approach of septic shock pathophysiology focusing on neutrophils as key players of septic shock-induced vascular cell dysfunction and of the host response, associating immunity and hemostasis. We will therefore first develop the role of neutrophils in the interplay between innate and adaptive immunity, and will then highlight recent advances in our understanding of immunothrombosis septic shock-induced coagulopathy.

Enhancement of Tissue Factor Expression in Monocyte-Derived Dendritic Cells by Pentraxin 3 and Its Modulation by C1 Esterase Inhibitor

BACKGROUND

We have previously shown that human monocyte-derived dendritic cells (moDCs) may participate in immune system-mediated hypercoagulable state through enhanced tissue factor (TF) expression and that the complement system may be involved in this process.

OBJECTIVES

The aim of this study was to explore the role of pentraxin 3 (PTX3) and the complement system in enhanced TF expression in moDCs.

METHODS

moDCs were generated from isolated human monocytes. PTX3 levels in whole human blood supplemented with moDCs were determined after lipopolysaccharide (LPS) stimulation. PTX3 release by the generated moDCs upon LPS stimulation was also assessed. The effect of PTX3 on whole blood coagulation was investigated using thromboelastometric analysis. TF expression in stationary moDCs treated with LPS and/or PTX3 was determined by measuring TF activity. The effect of complement inhibitors on TF activity in moDCs treated with LPS and/or PTX3 under low-shear conditions was evaluated.

RESULTS

PTX3 levels were higher in whole blood supplemented with moDCs than in the presence of monocytes and were further elevated by LPS stimulation. PTX3 release from generated moDCs was also increased by LPS stimulation. PTX3 reduced whole blood coagulation time in a dose-dependent manner. However, PTX3 did not increase TF expression in stationary moDCs. Under low-shear conditions, PTX3 increased TF expression in moDCs. C1 esterase inhibitor (C1-inh) suppressed this effect.

CONCLUSIONS

PTX3 might have a thrombophilic activity and enhance TF expression in moDCs under low-shear conditions. Furthermore, suppression of moDC-associated hypercoagulability by C1-inh might be partly ascribed to its inhibitory effect on PTX3.

Thrombomodulin favors leukocyte microvesicle fibrinolytic activity, reduces NETosis and prevents septic shock-induced coagulopathy in rats

BACKGROUND

Septic shock-induced disseminated intravascular coagulation is responsible for increased occurrence of multiple organ dysfunction and mortality. Immunothrombosis-induced coagulopathy may contribute to hypercoagulability. We aimed at determining whether recombinant human thrombomodulin (rhTM) could control exaggerated immunothrombosis by studying procoagulant responses, fibrinolysis activity borne by microvesicles (MVs) and NETosis in septic shock.

METHODS

In a septic shock model after a cecal ligation and puncture-induced peritonitis (H0), rats were treated with rhTM or a placebo at H18, resuscitated and monitored during 4 h. At H22, blood was sampled to perform coagulation tests, to characterize MVs and to detect neutrophils extracellular traps (NETs). Lungs were stained with hematoxylin-eosin for inflammatory injury assessment.

RESULTS

Coagulopathy was attenuated in rhTM-treated septic rats compared to placebo-treated rats, as attested by a significant decrease in procoagulant annexin A5+-MVs and plasma procoagulant activity of phospholipids and by a significant increase in antithrombin levels (84 ± 8 vs. 64 ± 6%, p < 0.05), platelet count (582 ± 157 vs. 319 ± 91 × 109/L, p < 0.05) and fibrinolysis activity borne by MVs (2.9 ± 0.26 vs. 0.48 ± 0.29 U/mL urokinase, p < 0.05). Lung histological injury score showed significantly less leukocyte infiltration. Decreased procoagulant activity and lung injury were concomitant with decreased leukocyte activation as attested by plasma leukocyte-derived MVs and NETosis reduction after rhTM treatment (neutrophil elastase/DNA: 93 ± 33 vs. 227 ± 48 and citrullinated histones H3/DNA: 96 ± 16 vs. 242 ± 180, mOD for 109 neutrophils/L, p < 0.05).

CONCLUSION

Thrombomodulin limits procoagulant responses and NETosis and at least partly restores hemostasis control during immunothrombosis. Neutrophils might thus stand as a promising therapeutic target in septic shock-induced coagulopathy.

The importance of blood platelet lipid signaling in thrombosis and in sepsis

Blood platelets are the first line of defense against hemorrhages and are also strongly involved in the processes of arterial thrombosis, a leading cause of death worldwide. Besides their well-established roles in hemostasis, vascular wall repair and thrombosis, platelets are now recognized as important players in other processes such as inflammation, healing, lymphangiogenesis, neoangiogenesis or cancer. Evidence is accumulating they are key effector cells in immune and inflammatory responses to host infection. To perform their different functions platelets express a wide variety of membrane receptors triggering specific intracellular signaling pathways and largely use lipid signaling systems. Lipid metabolism is highly active in stimulated platelets including the phosphoinositide metabolism with the phospholipase C (PLC) and the phosphoinositide 3-kinase (PI3K) pathways but also other enzymatic systems producing phosphatidic acid, lysophosphatidic acid, platelet activating factor, sphingosine 1-phosphate and a number of eicosanoids. While several of these bioactive lipids regulate intracellular platelet signaling mechanisms others are released by activated platelets acting as autocrine and/or paracrine factors modulating neighboring cells such as endothelial and immune cells. These bioactive lipids have been shown to play important roles in hemostasis and thrombosis but also in vessel integrity and dynamics, inflammation, tissue remodeling and wound healing. In this review, we will discuss some important aspects of platelet lipid signaling in thrombosis and during sepsis that is an important cause of death in intensive care unit. We will particularly focus on the implication of the different isoforms of PI3Ks and on the generation of eicosanoids released by activated platelets.

The role of heparin in sepsis: much more than just an anticoagulant

Despite progress in antibiotic treatment, mechanical ventilation, fluid resuscitation and blood glucose maintenance, sepsis remains a cause of high mortality in the intensive care unit to date, there are no proven treatment strategies for the routine management of septic patients. The extensive interaction between inflammation and coagulation contributes to the basic pathophysiology of sepsis. Thus, the agents that attenuate the activation of both inflammation and coagulation may improve the outcome in sepsis. Apart from the well-known anticoagulant effects of heparin, it also possesses various immunomodulatory properties and protects glycocalyx from shedding. Hence, heparin seems to be such an agent. Immunothrombosis plays an important role in early host defence against bacterial dissemination, thus the proper timing for anticoagulant therapy should be determined. We review the available experimental and clinical data supporting the use of heparin in sepsis. At this time the use of heparin in the treatment of sepsis is conflicting. Future trials of heparin therapy for sepsis should concentrate on the very severely ill patients, in whom benefit is most likely to be demonstrated.

Low molecular weight heparins prevent the induction of autophagy of activated neutrophils and the formation of neutrophil extracellular traps

The protection exerted by neutrophils against invading microbes is partially mediated via the generation of neutrophil extracellular traps (NETs). In sterile conditions NETs are damaging species, enriched in autoantigens and endowed with the ability to damage the vessel wall and bystander tissues, to promote thrombogenesis, and to impair wound healing. To identify and reposition agents that can be used to modulate the formation of NETs is a priority in the research agenda. Low molecular weight heparins (LMWH) are currently used, mostly on an empirical basis, in conditions in which NETs play a critical role, such as pregnancy complications associated to autoimmune disease. Here we report that LMWHs induce a profound change in the ability of human neutrophils to generate NETs and to mobilize the content of the primary granules in response to unrelated inflammatory stimuli, such as IL-8, PMA and HMGB1. Autophagy consistently accompanies NET generation in our system and autophagy inhibitors, 3-MA and wortmannin, prevent NET generation. Pretreatment with LMWH in vitro critically jeopardizes neutrophil ability to activate autophagy, a mechanism that might contribute to neutrophil unresponsiveness. Finally, we verified that treatment of healthy volunteers with a single prophylactic dose of parnaparin abrogated the ability of neutrophils to activate autophagy and to generate NETs. Together, these results support the contention that neutrophils, and NET generation in particular, might represent a preferential target of the anti-inflammatory action of LMWH.

Biological basis of personalized anticoagulation in cancer: oncogene and oncomir networks as putative regulators of coagulopathy

Activation of stromal response pathways in cancer is increasingly viewed as both a local and systemic extension of molecular alterations driving malignant transformation. Rather than reflecting passive and unspecific responses to anatomical abnormalities, the coagulation system is a target of oncogenic deregulation, impacting the role of clotting and fibrinolytic proteins, and integrating hemostasis, inflammation, angiogenesis and cellular growth effects in cancer. These processes signify, but do not depend on, the clinically manifest coagulopathy and thrombosis. In this regard, the role of driver mutations affecting oncoprotein coding genes such as RAS, EGFR or MET and tumour suppressors (PTEN, TP53) are well described as regulators of tissue factor (TF), protease activated receptors (PAR-1/2) and ectopic coagulation factors (FVII). Indeed, in both adult and pediatric brain tumours the expression patterns of coagulation and angiogenesis regulators (coagulome and angiome, respectively) reflect the molecular subtypes of the underlying diseases (glioblastoma or medulloblastoma) as defined by their oncogenic classifiers and clinical course. This emerging understanding is still poorly established in relation to the transforming effects of non-coding genes, including those responsible for the expression of microRNA (miR). Indeed, several miRs have been recently found to regulate TF and other effectors. We recently documented that in the context of the aggressive embryonal tumour with multilayered rosettes (ETMR) the oncogenic driver miR (miR-520g) suppresses the expression of TF and correlates with hypocoagulant tumour characteristics. Unlike in adult cancers, the growth of pediatric embryonal brain tumour cells as spheres (to maintain stem cell properties) results in upregulation of miR-520g and downregulation of TF expression and activity. We postulate that oncogenic protein and miR coding genes form alternative pathways of coagulation system regulation in different tumour settings, a property necessitating more personalised and biologically-based approaches to anticoagulation.

Propagation of thrombosis by neutrophils and extracellular nucleosome networks

Neutrophils, early mediators of the innate immune defense, are recruited to developing thrombi in different types of thrombosis. They amplify intravascular coagulation by stimulating the tissue factor-dependent extrinsic pathway via inactivation of endogenous anticoagulants, enhancing factor XII activation or decreasing plasmin generation. Neutrophil-dependent prothrombotic mechanisms are supported by the externalization of decondensed nucleosomes and granule proteins that together form neutrophil extracellular traps. These traps, either in intact or fragmented form, are causally involved in various forms of experimental thrombosis as first indicated by their role in the enhancement of both microvascular thrombosis during bacterial infection and carotid artery thrombosis. Neutrophil extracellular traps can be induced by interactions of neutrophils with activated platelets; vice versa, these traps enhance adhesion of platelets via von Willebrand factor. Neutrophil-induced microvascular thrombus formation can restrict the dissemination and survival of blood-borne bacteria and thereby sustain intravascular immunity. Dysregulation of this innate immune pathway may support sepsis-associated coagulopathies. Notably, neutrophils and extracellular nucleosomes, together with platelets, critically promote fibrin formation during flow restriction-induced deep vein thrombosis. Neutrophil extracellular traps/extracellular nucleosomes are increased in thrombi and in the blood of patients with different vaso-occlusive pathologies and could be therapeutically targeted for the prevention of thrombosis. Thus, during infections and in response to blood vessel damage, neutrophils and externalized nucleosomes are major promoters of intravascular blood coagulation and thrombosis.

Extracellular signal-regulated kinase 5 promotes acute cellular and systemic inflammation

Inflammatory critical illness is a syndrome that is characterized by acute inflammation and organ injury, and it is triggered by infections and noninfectious tissue injury, both of which activate innate immune receptors and pathways. Although reports suggest an anti-inflammatory role for the mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase 5 (ERK5), we previously found that ERK5 mediates proinflammatory responses in primary human cells in response to stimulation of Toll-like receptor 2 (TLR2). We inhibited the kinase activities and reduced the abundances of ERK5 and MEK5, a MAPK kinase directly upstream of ERK5, in primary human vascular endothelial cells and monocytes, and found that ERK5 promoted inflammation induced by a broad range of microbial TLR agonists and by the proinflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). Furthermore, we found that inhibitors of MEK5 or ERK5 reduced the plasma concentrations of proinflammatory cytokines in mice challenged with TLR ligands or heat-killed Staphylococcus aureus, as well as in mice that underwent sterile lung ischemia-reperfusion injury. Finally, we found that inhibition of ERK5 protected endotoxemic mice from death. Together, our studies support a proinflammatory role for ERK5 in primary human endothelial cells and monocytes, and suggest that ERK5 is a potential therapeutic target in diverse disorders that cause inflammatory critical illness.

Global assays of hemostasis in the diagnostics of hypercoagulation and evaluation of thrombosis risk

Thrombosis is a deadly malfunctioning of the hemostatic system occurring in numerous conditions and states, from surgery and pregnancy to cancer, sepsis and infarction. Despite availability of antithrombotic agents and vast clinical experience justifying their use, thrombosis is still responsible for a lion’s share of mortality and morbidity in the modern world. One of the key reasons behind this is notorious insensitivity of traditional coagulation assays to hypercoagulation and their inability to evaluate thrombotic risks; specific molecular markers are more successful but suffer from numerous disadvantages. A possible solution is proposed by use of global, or integral, assays that aim to mimic and reflect the major physiological aspects of hemostasis process in vitro. Here we review the existing evidence regarding the ability of both established and novel global assays (thrombin generation, thrombelastography, thrombodynamics, flow perfusion chambers) to evaluate thrombotic risk in specific disorders. The biochemical nature of this risk and its detectability by analysis of blood state in principle are also discussed. We conclude that existing global assays have a potential to be an important tool of hypercoagulation diagnostics. However, their lack of standardization currently impedes their application: different assays and different modifications of each assay vary in their sensitivity and specificity for each specific pathology. In addition, it remains to be seen how their sensitivity to hypercoagulation (even when they can reliably detect groups with different risk of thrombosis) can be used for clinical decisions: the risk difference between such groups is statistically significant, but not large.

PAMPs and DAMPs as triggers for DIC

Thrombosis is generally considered harmful because it compromises the blood supply to organs. However, recent studies have suggested that thrombosis under certain circumstances plays a major physiological role in early immune defense against invading pathogens. This defensive role of thrombosis is now referred to as immunothrombosis. Activated monocytes and neutrophils are two major inducers of immunothrombosis. Monocytes and neutrophils are activated when they detect pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Detection of PAMPs and DAMPs triggers tissue factor expression on monocytes and neutrophil extracellular trap (NET) release by neutrophils, promoting immunothrombosis. Although tissue factor-mediated and NET-mediated immunothrombosis plays a role in early host defense against bacterial dissemination, uncontrolled immunothrombosis may lead to disseminated intravascular coagulation.

Microvascular thrombosis, fibrinolysis, ischemic injury, and death after cerebral thromboembolism are affected by levels of circulating α2-antiplasmin

OBJECTIVE

Ischemic stroke is primarily attributable to thrombotic vascular occlusion. Elevated α2-antiplasmin (a2AP) levels correlate with increased stroke risk, but whether a2AP contributes to the pathogenesis of stroke is unknown. We examined how a2AP affects thrombosis, ischemic brain injury, and survival after experimental cerebral thromboembolism.

APPROACH AND RESULTS

We evaluated the effects of a2AP on stroke outcomes in mice with increased, normal, or no circulating a2AP, as well as in mice given an a2AP-inactivating antibody. Higher a2AP levels were correlated with greater ischemic brain injury (rs=0.88, P<0.001), brain swelling (rs=0.82, P<0.001), and reduced middle cerebral artery thrombus dissolution (rs=-0.93, P<0.001). In contrast, a2AP deficiency enhanced thrombus dissolution, increased cerebral blood flow, reduced brain infarction, and decreased brain swelling. By comparison to tissue plasminogen activator (TPA), a2AP inactivation hours after thromboembolism still reduced brain infarction (P<0.001) and hemorrhage (P<0.05). Microvascular thrombosis, a process that enhances brain ischemia, was markedly reduced in a2AP-deficient or a2AP-inactivated mice compared with TPA-treated mice or mice with increased a2AP levels (all P<0.001). Matrix metalloproteinase-9 expression, which contributes to acute brain injury, was profoundly decreased in a2AP-deficient or a2AP-inactivated mice versus TPA-treated mice or mice with increased a2AP levels (all P<0.001). a2AP inactivation markedly reduced stroke mortality versus TPA (P<0.0001).

CONCLUSIONS

a2AP has profound, dose-related effects on ischemic brain injury, swelling, hemorrhage, and survival after cerebral thromboembolism. By comparison to TPA, the protective effects of a2AP deficiency or inactivation seem to be mediated through reductions in microvascular thrombosis and matrix metalloproteinase-9 expression.

In vivo characterization of neutrophil extracellular traps in various organs of a murine sepsis model

Neutrophil extracellular traps (NETs) represent extracellular microbial trapping and killing. Recently, it has been implicated in thrombogenesis, autoimmune disease, and cancer progression. The aim of this study was to characterize NETs in various organs of a murine sepsis model in vivo and to investigate their associations with platelets, leukocytes, or vascular endothelium. NETs were classified as two distinct forms; cell-free NETs that were released away from neutrophils and anchored NETs that were anchored to neutrophils. Circulating cell-free NETs were characterized as fragmented or cotton-like structures, while anchored NETs were characterized as linear, reticular, membranous, or spot-like structures. In septic mice, both anchored and cell-free NETs were significantly increased in postcapillary venules of the cecum and hepatic sinusoids with increased leukocyte-endothelial interactions. NETs were also observed in both alveolar space and pulmonary capillaries of the lung. The interactions of NETs with platelet aggregates, leukocyte-platelet aggregates or vascular endothelium of arterioles and venules were observed in the microcirculation of septic mice. Microvessel occlusions which may be caused by platelet aggregates or leukocyte-platelet aggregates and heterogeneously decreased blood flow were also observed in septic mice. NETs appeared to be associated with the formation of platelet aggregates or leukocyte-platelet aggregates. These observational findings may suggest the adverse effect of intravascular NETs on the host during a sepsis.