Extracellular DNA and histones: double-edged swords in immunothrombosis

Targeting extranuclear histones to alleviate acute and chronic inflammation

Extracellular histones instigate an inflammatory triad - centered on cytotoxicity, immune cell stimulation, and coagulation - ultimately shaping the dynamics and outcome of various inflammatory pathologies. Given the virtual absence of beneficial functions of histones in the extracellular space, in recent years a number of interference strategies have emerged. In this review we summarize pathogenic functions of extracellular histones and highlight current developments of therapeutic interference. Finally, we elaborate on the current status of preclinical attempts to interfere with extracellular histones in the context of a focus on sepsis and cardiovascular diseases, both of which are leading causes of mortality worldwide.

Immunological alterations in the endothelial barrier: a new predictive and therapeutic paradigm for sepsis

INTRODUCTION

Despite the fact incidence and mortality vary widely among regions, sepsis remains a major cause of morbidity and cost worldwide. The importance of the endothelial barrier in sepsis and infectious diseases is increasingly recognized; however, the underlying pathophysiology of the endothelial barrier in sepsis remains poorly understood.

AREAS COVERED

Here we review the advances in basic and clinical research for relevant papers in PubMed database. We attempt to provide an updated overview of immunological alterations in endothelial dysfunction, discussing the central role of endothelial barrier involved in sepsis to provide new predictive and therapeutic paradigm for sepsis.

EXPERT OPINION

Given its physiological and immunological functions in infectious diseases, the endothelial barrier has been dramatically altered in sepsis, suggesting that endothelial dysfunction may play a critical role in the pathogenesis of sepsis. Although many reliable biomarkers have been investigated to monitor endothelial activation and injury in an attempt to find diagnostic and therapeutic tools, there are no specific therapies to treat sepsis due to its complex pathophysiology. Since sepsis is initiated by both hyperinflammation and immunoparalysis occurring simultaneously, a 'one-treatment-fits-all' strategy for sepsis-induced immune injury and immunoparalysis is bound to fail, and an individualized 'precision medicine' approach is required.

Leukocyte filtration and leukocyte modulation therapy during extracorporeal cardiopulmonary resuscitation in a porcine model of prolonged cardiac arrest

Extracorporeal cardiopulmonary resuscitation (ECPR) is emerging as a feasible and effective rescue strategy for prolonged cardiac arrest (CA). However, prolonged total body ischemia and reperfusion can cause microvascular occlusion that prevents organ reperfusion and recovery of function. One hypothesized mechanism of microvascular "no-reflow" is leukocyte adhesion and formation of neutrophil extracellular traps. In this study we tested the hypothesis that a leukocyte filter (LF) or leukocyte modulation device (L-MOD) could reduce NETosis and improve recovery of heart and brain function in a swine model of prolonged cardiac arrest treated with ECPR. Thirty-six swine (45.5 ± 2.5 kg, evenly distributed sex) underwent 8 min of untreated ventricular fibrillation CA followed by 30 min of mechanical CPR with subsequent 8 h of ECPR. Two females were later excluded from analysis due to CPR complications. Swine were randomized to standard care (Control group), LF, or L-MOD at the onset of CPR. NET formation was quantified by serum dsDNA and citrullinated histone as well as immunofluorescence staining of the heart and brain for citrullinated histone in the microvasculature. Primary outcomes included recovery of cardiac function based on cardiac resuscitability score (CRS) and recovery of neurologic function based on the somatosensory evoked potential (SSEP) N20 cortical response. In this model of prolonged CA treated with ECPR we observed significant increases in serum biomarkers of NETosis and immunohistochemical evidence of microvascular NET formation in the heart and brain that were not reduced by LF or L-MOD therapy. Correspondingly, there were no significant differences in CRS and SSEP recovery between Control, LF, and L-MOD groups 8 h after ECPR onset (CRS = 3.1 ± 2.7, 3.7 ± 2.6, and 2.6 ± 2.6 respectively; p = 0.606; and SSEP = 27.9 ± 13.0%, 36.7 ± 10.5%, and 31.2 ± 9.8% respectively, p = 0.194). In this model of prolonged CA treated with ECPR, the use of LF or L-MOD therapy during ECPR did not reduce microvascular NETosis or improve recovery of myocardial or brain function. The causal relationship between microvascular NETosis, no-reflow, and recovery of organ function after prolonged cardiac arrest treated with ECPR requires further investigation.

Neutrophil extracellular traps and active myeloperoxidase concentrate in lamellar tissue of equids with naturally occurring laminitis

Laminitis is a pathology of the equine digit ultimately leading to a failure of the dermo-epidermal interface. Neutrophil activation is recognized as a major factor in SIRS-associated laminitis and has recently been described in induced endocrinopathic laminitis evidenced by the presence of myeloperoxidase (MPO). Neutrophil extracellular traps (NET) are released with neutrophil activation. This study aimed to investigate the presence and activity of MPO and NET in the lamellar tissue of equids presented with naturally occurring laminitis. Samples of lamellar tissue of five horses and five donkeys presented with laminitis, as well as eight control horses without laminitis, were collected. Lamellar tissue extracts were submitted to ELISA and specific immuno-extraction followed by enzymatic detection (SIEFED) assays to confirm the presence and activity of both MPO and NET. Lamellar sections were also immunohistopathologically stained for MPO and NET. Analysis of lamellar tissue extracts revealed that laminitis cases had significantly higher levels of total MPO concentration, MPO activity, and NET-bound MPO activity in comparison to control horses. Moreover, a strong correlation was identified between the activity of NET-bound MPO and the total MPO activity, which suggests that MPO activity partly originates from NET-bound MPO. Immunohistochemical staining showed that MPO and NET labelling in laminitis cases was moderate to marked, primarily in the epidermis and in inflammatory infiltrates containing neutrophils, while labelling in control horses was minimal. This article constitutes the first indication of the presence and activity of NET-bound MPO in the lamellar tissue of horses and donkeys with naturally occurring laminitis. Targeting these substances may provide new treatment possibilities for this debilitating disease.

A Fully Integrated Microfluidic Device with Immobilized Dyes for Simultaneous Detection of Cell-Free DNA and Histones from Plasma Using Dehydrated Agarose Gates

Sepsis, a life-threatening condition resulting from a failing host response to infection, causes millions of deaths annually, necessitating rapid and simple prognostic assessments. A variety of genomic and proteomic biomarkers have been developed for sepsis. For example, it has been shown that the level of plasma cell-free DNA (cfDNA) and circulating histones increases considerably during sepsis, and they are linked with sepsis severity and mortality. Developing a diagnostic tool that is capable of assessing such diverse biomarkers is challenging as the detection methodology is quite different for each. Here, a fully integrated microfluidic device capable of detecting a genomic biomarker (cfDNA) and a proteomic biomarker (total circulating histones) using a common detection platform has been demonstrated. The microfluidic device utilizes dehydrated agarose gates loaded with pH-specific agarose to electrophoretically trap cfDNA and histones at their respective isoelectric points. It also incorporates fluorescent dyes within the device, eliminating the need for off-chip sample preparation and allowing the direct testing of plasma samples without the need for labeling DNA and histones with fluorescent dyes beforehand. Xurography, which is a low-cost and rapid method for fabrication of microfluidics, is used in all the fabrication steps. Experimental results demonstrate the effective accumulation and separation of cfDNA and histones in the agarose gates in a total processing time of 20 min, employing 10 and 30 Volts for cfDNA and histone accumulation and detection, respectively. The device can potentially be used to distinguish between the survivors and non-survivors of sepsis. The integration of the detection of both biomarkers into a single device and dye immobilization enhances its clinical utility for rapid point-of-care assessment of sepsis prognosis.

Impact of age on the host response to sepsis in a murine model of fecal-induced peritonitis

INTRODUCTION

Despite older adults being more vulnerable to sepsis, most preclinical research on sepsis has been conducted using young animals. This results in decreased scientific validity since age is an independent predictor of poor outcome. In this study, we explored the impact of aging on the host response to sepsis using the fecal-induced peritonitis (FIP) model developed by the National Preclinical Sepsis Platform (NPSP).

METHODS

C57BL/6 mice (3 or 12 months old) were injected intraperitoneally with rat fecal slurry (0.75 mg/g) or a control vehicle. To investigate the early stage of sepsis, mice were culled at 4 h, 8 h, or 12 h to investigate disease severity, immunothrombosis biomarkers, and organ injury. Mice received buprenorphine at 4 h post-FIP. A separate cohort of FIP mice were studied for 72 h (with buprenorphine given at 4 h, 12 h, and then every 12 h post-FIP and antibiotics/fluids starting at 12 h post-FIP). Organs were harvested, plasma levels of Interleukin (IL)-6, IL-10, monocyte chemoattract protein (MCP-1)/CCL2, thrombin-antithrombin (TAT) complexes, cell-free DNA (CFDNA), and ADAMTS13 activity were quantified, and bacterial loads were measured.

RESULTS

In the 12 h time course study, aged FIP mice demonstrated increased inflammation and injury to the lungs compared to young FIP mice. In the 72 h study, aged FIP mice exhibited a higher mortality rate (89%) compared to young FIP mice (42%) (p < 0.001). Aged FIP non-survivors also exhibited a trend towards elevated IL-6, TAT, CFDNA, CCL2, and decreased IL-10, and impaired bacterial clearance compared to young FIP non-survivors.

CONCLUSION

To our knowledge, this is the first study to investigate the impact of age on survival using the FIP model of sepsis. Our model includes clinically-relevant supportive therapies and inclusion of both sexes. The higher mortality rate in aged mice may reflect increased inflammation and worsened organ injury in the early stage of sepsis. We also observed trends in impaired bacterial clearance, increase in IL-6, TAT, CFDNA, CCL2, and decreased IL-10 and ADAMTS13 activity in aged septic non-survivors compared to young septic non-survivors. Our aging model may help to increase the scientific validity of preclinical research and may be useful for identifying mechanisms of age-related susceptibility to sepsis as well as age-specific treatment strategies.

Tumor-derived cell-free DNA and circulating tumor cells: partners or rivals in metastasis formation?

The origin of metastases is a topic that has sparked controversy. Despite recent advancements, metastatic disease continues to pose challenges. The first admitted model of how metastases develop revolves around cells breaking away from the primary tumor, known as circulating tumor cells (CTCs). These cells survive while circulating through the bloodstream and subsequently establish themselves in secondary organs, a process often referred to as the "metastatic cascade". This intricate and dynamic process involves various steps, but all the mechanisms behind metastatic dissemination are not yet comprehensively elucidated. The "seed and soil" theory has shed light on the phenomenon of metastatic organotropism and the existence of pre-metastatic niches. It is now established that these niches can be primed by factors secreted by the primary tumor before the arrival of CTCs. In particular, exosomes have been identified as important contributors to this priming. Another concept then emerged, i.e. the "genometastasis" theory, which challenged all other postulates. It emphasizes the intriguing but promising role of cell-free DNA (cfDNA) in metastasis formation through oncogenic formation of recipient cells. However, it cannot be ruled out that all these theories are intertwined. This review outlines the primary theories regarding the metastases formation that involve CTCs, and depicts cfDNA, a potential second player in the metastasis formation. We discuss the potential interrelationships between CTCs and cfDNA, and propose both in vitro and in vivo experimental strategies to explore all plausible theories.

Neutrophil extracellular traps induce persistent lung tissue damage via thromboinflammation without altering virus resolution in a mouse coronavirus model

BACKGROUND

During infection, neutrophil extracellular traps (NETs) are associated with severity of pulmonary diseases such as acute respiratory disease syndrome. NETs induce subsequent immune responses, are directly cytotoxic to pulmonary cells, and are highly procoagulant. Anticoagulation treatment was shown to reduce in-hospital mortality, indicating thromboinflammatory complications. However, data are sparsely available on the involvement of NETs in secondary events after virus clearance, which can lead to persistent lung damage and postacute sequelae with chronic fatigue and dyspnea.

OBJECTIVES

This study focuses on late-phase events using a murine model of viral lung infection with postacute sequelae after virus resolution.

METHODS

C57BL/6JRj mice were infected intranasally with the betacoronavirus murine coronavirus (MCoV, strain MHV-A95), and tissue samples were collected after 2, 4, and 10 days. For NET modulation, mice were pretreated with OM-85 or GSK484 and DNase I were administered intraperitoneally between days 2 to 5 and days 4 to 7, respectively.

RESULTS

Rapid, platelet-attributed thrombus formation was followed by a second, late phase of thromboinflammation. This phase was characterized by negligible virus titers but pronounced tissue damage, apoptosis, oxidative DNA damage, and presence of NETs. Inhibition of NETs during the acute phase did not impact virus burden but decreased lung cell apoptosis by 67% and oxidative stress by 94%. Prevention of neutrophil activation by immune training before virus infection reduced damage by 75%, NETs by 31%, and pulmonary thrombi by 93%.

CONCLUSION

NETs are detrimental inducers of tissue damage during respiratory virus infection but do not contribute to virus clearance.

Neutrophil extracellular traps formation is associated with postoperative complications in neonates and infants undergoing congenital cardiac surgery

Pediatric patients with congenital heart diseases (CHD) often undergo surgical repair on cardiopulmonary bypass (CPB). Despite a significant medical and surgical improvement, the mortality of neonates and infants remains high. Damage-associated molecular patterns (DAMPs) are endogenous molecules released from injured/damaged tissues as danger signals. We examined 101 pediatric patients who underwent congenital cardiac surgery on CPB. The mortality rate was 4.0%, and the complication rate was 31.6%. We found that neonates/infants experienced multiple complications most, consistent with the previous knowledge. Neonates and infants in the complication group had received more transfusion intraoperatively than the non-complication arm with lower maximum amplitude (MA) on rewarming CPB thromboelastography (TEG). Despite TEG profiles were comparable at ICU admission between the two groups, the complication arm had higher postoperative chest tube output, requiring more blood transfusion. The complication group showed greater neutrophil extracellular traps (NETs) formation at the end of CPB and postoperatively. Plasma histones and high mobility group box 1 (HMGB1) levels were significantly higher in the complication arm. Both induced NETs in vitro and in vivo . As histones and HMGB1 target Toll-like receptor (TLR)2 and TLR4, their mRNA expression in neutrophils was upregulated in the complication arm. Taken together, NETs play a major role in postoperative complication in pediatric cardiac surgery and would be considered a target for intervention.

Key points

Neonates and infants showed highest postoperative complications with more upregulation of inflammatory transcriptomes of neutrophils.Neonates and infants with organ dysfunction had more NETs formation with higher plasma histones and HMGB1 levels.

Blood Plasma Circulating DNA-Protein Complexes: Involvement in Carcinogenesis and Prospects for Liquid Biopsy of Breast Cancer

Circulating DNA (cirDNA) is a promising tool in translational medicine. However, studies of cirDNA have neglected its association with proteins, despite ample evidence that this interaction may affect the fate of DNA in the bloodstream and its molecular functions. The goal of the current study is to shed light on the differences between the proteomic cargos of histone-containing nucleoprotein complexes (NPCs) from healthy female (HFs) and breast cancer patients (BCPs), and to reveal the proteins involved in carcinogenesis. NPCs were isolated from the blood samples of HFs and BCPs using affinity chromatography. A total of 177 and 169 proteins were identified in NPCs from HFs and BCPs using MALDI-TOF mass spectrometry. A bioinformatics analysis revealed that catalytically active proteins, as well as proteins that bind nucleic acids and regulate the activity of receptors, are the most represented among the unique proteins of blood NPCs from HFs and BCPs. In addition, the proportion of proteins participating in ion channels and proteins binding proteins increases in the NPCs from BCP blood. However, the involvement in transport and signal transduction was greater in BCP NPCs compared to those from HFs. Gene ontology term (GO) analysis revealed that the NPC protein cargo from HF blood was enriched with proteins involved in the negative regulation of cell proliferation, and in BCP blood, proteins involved in EMT, invasion, and cell migration were observed. The combination of SPG7, ADRB1, SMCO4, PHF1, and PSMG1 NPC proteins differentiates BCPs from HFs with a sensitivity of 100% and a specificity of 80%. The obtained results indirectly indicate that, in tandem with proteins, blood cirDNA is an important part of intercellular communication, playing a regulatory and integrating role in the physiology of the body.

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.

Extracellular histones as damage-associated molecular patterns in neuroinflammatory responses

The four core histones H2A, H2B, H3, H4, and the linker histone H1 primarily bind DNA and regulate gene expression within the nucleus. Evidence collected mainly from the peripheral tissues illustrates that histones can be released into the extracellular space by activated or damaged cells. In this article, we first summarize the innate immune-modulatory properties of extracellular histones and histone-containing complexes, such as nucleosomes, and neutrophil extracellular traps (NETs), described in peripheral tissues. There, histones act as damage-associated molecular patterns (DAMPs), which are a class of endogenous molecules that trigger immune responses by interacting directly with the cellular membranes and activating pattern recognition receptors (PRRs), such as toll-like receptors (TLR) 2, 4, 9 and the receptor for advanced glycation end-products (RAGE). We then focus on the available evidence implicating extracellular histones as DAMPs of the central nervous system (CNS). It is becoming evident that histones are present in the brain parenchyma after crossing the blood-brain barrier (BBB) or being released by several types of brain cells, including neurons, microglia, and astrocytes. However, studies on the DAMP-like effects of histones on CNS cells are limited. For example, TLR4 is the only known molecular target of CNS extracellular histones and their interactions with other PRRs expressed by brain cells have not been observed. Nevertheless, extracellular histones are implicated in the pathogenesis of a variety of neurological disorders characterized by sterile neuroinflammation; therefore, detailed studies on the role these proteins and their complexes play in these pathologies could identify novel therapeutic targets.

Fibrinolysis Shutdown and Hypofibrinolysis Are Not Synonymous Terms: The Clinical Significance of Differentiating Low Fibrinolytic States

Low fibrinolytic activity has been associated with pathologic thrombosis and multiple-organ failure. Low fibrinolytic activity has two commonly associated terms, hypofibrinolysis and fibrinolysis shutdown. Hypofibrinolysis is a chronic state of lack of ability to generate an appropriate fibrinolytic response when anticipated. Fibrinolysis shutdown is the shutdown of fibrinolysis after systemic activation of the fibrinolytic system. There has been interchanging of these terms to describe critically ill patients in multiple settings. This is problematic in understanding the pathophysiology of disease processes related to these conditions. There is also a lack of research on the cellular mediators of these processes. The purpose of this article is to review the on and off mechanisms of fibrinolysis in the context of low fibrinolytic states to define the importance in differentiating hypofibrinolysis from fibrinolysis shutdown. In many clinical scenarios, the etiology of a low fibrinolytic state cannot be determined due to ambiguity if a preceding fibrinolytic activation event occurred. In this scenario, the term "low fibrinolytic activity" or "fibrinolysis resistance" is a more appropriate descriptor, rather than using assumptive of hypofibrinolysis and fibrinolysis shutdown, particularly in the acute setting of infection, injury, and surgery.

Development of a High-Throughput Urosepsis Mouse Model

Murine sepsis models are typically polymicrobial, and are associated with high mortality. We aimed to develop a high-throughput murine model that mimics a slow-paced, monomicrobial sepsis originating from the urinary tract. A total of 23 male C57Bl/6 mice underwent percutaneous insertion of a 4 mm catheter into the bladder using an ultrasound-guided method, previously developed by our group. The following day, Proteus mirabilis (PM) was introduced percutaneously in the bladder in three groups: g1-50 µL 1 × 10⁸ CFU/mL solution (n = 10); g2-50 µL 1 × 10⁷ CFU/mL solution (n = 10); and g3 (sham mice)-50 µL sterile saline (n = 3). On day 4, mice were sacrificed. The number of planktonic bacteria in urine, adherent to catheters, and adherent to/invaded into the bladder and spleen was assessed. Cell-free DNA, D-dimer, thrombin-antithrombin complex (TAT), and 32 pro-/anti-inflammatory cytokines/chemokines were quantified in the blood. All mice survived the 4 day postinterventional period. Mean weight loss was 11% in g1, 9% in g2, and 3% in the control mice. Mean urine CFU counts were highest in group 1. All catheters showed high catheter-adhered bacterial counts. Of the infected mice, 17/20 had CFU counts in the splenic tissue, indicating septicemia. Plasma levels of cell-free DNA, D-dimer, and the proinflammatory cytokines IFN-γ, IL-6, IP-10, MIG, and G-CSF were significantly elevated in infected mice versus controls. We present a reproducible, monomicrobial murine model of urosepsis that does not lead to rapid deterioration and death, and is useful for studying prolonged urosepsis.

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.

NETs promote ROS production to induce human amniotic epithelial cell apoptosis via ERK1/2 signaling in spontaneous preterm birth

PROBLEM

Premature birth is a common obstetric complication but its pathogenesis is unclear. Inflammation at the maternal-fetal interface in preterm labor leads to the infiltration of neutrophils, which promotes inflammatory responses and induces the degradation of extracellular matrix and cell apoptosis, thus contributing to preterm labor. It is unclear whether neutrophil extracellular traps (NETs), a functional form of neutrophils, are involved in preterm labor.

METHODS OF STUDY

After collecting amniotic membranes from research objects, we localized NETs by immunofluorescence and evaluated the expression of matrix metalloproteinase (MMP)-9 and MMP-2 by western blotting. Primary human amniotic epithelial cells (hAECs) subjected to treatment with NETs, 5-ethynyl-20-deoxyuridine cell proliferation assay, lactate dehydrogenase (LDH) assay, western blotting, and flow cytometry apoptosis assay were used to determine the effects of NETs on hAECs. We also elucidated possible mechanisms underlying the effects.

RESULTS

Compared with normal term women, NETs infiltration and MMP-9 expression in the amniotic membrane from preterm women had increased. Thereafter, NETs might suppress the proliferation and promote the apoptosis of hAECs. Furthermore, after NETs treatment, the mitochondrial membrane potential was significantly decreased, ERK1/2 phosphorylation expression was upregulated and reactive oxygen species (ROS) production was increased in hAECs. Changes in cell proliferation, LDH release, and cell apoptosis level due to NETs could be reversed by ROS inhibitor or ERK phosphorylation inhibitors.

CONCLUSIONS

NETs can promote the apoptosis of hAECs via ERK1/2 pathways dependent on ROS release.

Crosstalk between Inflammation and Hemorrhage/Coagulation Disorders in Primary Blast Lung Injury

Primary blast lung injury (PBLI), caused by exposure to high-intensity pressure waves from explosions in war, terrorist attacks, industrial production, and life explosions, is associated with pulmonary parenchymal tissue injury and severe ventilation insufficiency. PBLI patients, characterized by diffused intra-alveolar destruction, including hemorrhage and inflammation, might deteriorate into acute respiratory distress syndrome (ARDS) with high mortality. However, due to the absence of guidelines about PBLI, emergency doctors and rescue teams treating PBLI patients rely on experience. The goal of this review is to summarize the mechanisms of PBLI and their cross-linkages, exploring potential diagnostic and therapeutic targets of PBLI. We summarize the pathophysiological performance and pharmacotherapy principles of PBLI. In particular, we emphasize the crosstalk between hemorrhage and inflammation, as well as coagulation, and we propose early control of hemorrhage as the main treatment of PBLI. We also summarize several available therapy methods, including some novel internal hemostatic nanoparticles to prevent the vicious circle of inflammation and coagulation disorders. We hope that this review can provide information about the mechanisms, diagnosis, and treatment of PBLI for all interested investigators.

Secretory proteins in the orchestration of microbial virulence: The curious case of Staphylococcus aureus

Microbial virulence showcases an excellent model for adaptive changes that enable an organism to survive and proliferate in a hostile environment and exploit host resources to its own benefit. In Staphylococcus aureus, an opportunistic pathogen of the human host, known for the diversity of the disease conditions it inflicts and the rapid evolution of antibiotic resistance, virulence is a consequence of having a highly plastic genome that is amenable to quick reprogramming and the ability to express a diverse arsenal of virulence factors. Virulence factors that are secreted to the host milieu effectively manipulate the host conditions to favor bacterial survival and growth. They assist in colonization, nutrient acquisition, immune evasion, and systemic spread. The structural and functional characteristics of the secreted virulence proteins have been shaped to assist S. aureus in thriving and disseminating effectively within the host environment and exploiting the host resources to its best benefit. With the aim of highlighting the importance of secreted virulence proteins in bacterial virulence, the present chapter provides a comprehensive account of the role of the major secreted proteins of S. aureus in orchestrating its virulence in the human host.

Clinical Evidence of Circulating Tumor DNA Application in Aggressive Breast Cancer

Breast cancer is clinically and biologically heterogeneous and is classified into different subtypes according to the molecular landscape of the tumor. Triple-negative breast cancer is a subtype associated with higher tumor aggressiveness, poor prognosis, and poor response to treatment. In metastatic breast cancer, approximately 6% to 10% of new breast cancer cases are initially staged IV (de novo metastatic disease). The number of metastatic recurrences is estimated to be 20-30% of all existing breast tumor cases, whereby the need to develop specific genetic markers to improve the prognosis of patients suffering from these deadly forms of breast cancer. As an alternative, liquid biopsy methods can minutely identify the molecular architecture of breast cancer, including aggressive forms, which provides new perspectives for more precise diagnosis and more effective therapeutics. This review aimed to summarize the current clinical evidence for the application of circulating tumor DNA in managing breast cancer by detailing the increased usefulness of this biomarker as a diagnostic, prognostic, monitoring, and surveillance marker for breast cancer.

Cell-free DNA Release in the Plasma of Patients with Cardiac Disease is Associated with Cell Death Processes

Cell-free DNA (cfDNA) is released into the plasma of patients with cardiac disease. Here, the source and mechanism of plasma cfDNA release in patients with myocardial infarction (MI) and other cardiac diseases (n = 59) were investigated. Plasma levels of various markers including M30 (apoptosis), M65 (apoptosis and necrosis), cyclophilin A (CyPA) (necrosis), and myeloperoxidase (MPO) (neutrophil activation) were assayed. The plasma cfDNA concentrations in MI and other cardiac diseases were significantly higher than that in the healthy control subjects. Significant differences were not observed among the cardiac disease patients (MI and other cardiac diseases) and healthy control subjects in M30, M65, and CyPA levels. In contrast,the MPO levels were significantly elevated in cardiac disease patients when compared to control groups, and MPO levels in MI patients were significantly higher than other cardiac diseases patients. These results suggest that cfDNA is mainly released by neutrophils via NETosis in addition to apoptosis except for epithelial apoptosis in patients with cardiac disease and the degree is greater in MI patients. The results from this study provide basic information for diagnosis marker of MI.

S100A8/A9 drives the formation of procoagulant platelets through GPIbα

S100A8/A9, also known as "calprotectin" or "MRP8/14," is an alarmin primarily secreted by activated myeloid cells with antimicrobial, proinflammatory, and prothrombotic properties. Increased plasma levels of S100A8/A9 in thrombo-inflammatory diseases are associated with thrombotic complications. We assessed the presence of S100A8/A9 in the plasma and lung autopsies from patients with COVID-19 and investigated the molecular mechanism by which S100A8/A9 affects platelet function and thrombosis. S100A8/A9 plasma levels were increased in patients with COVID-19 and sustained high levels during hospitalization correlated with poor outcomes. Heterodimeric S100A8/A9 was mainly detected in neutrophils and deposited on the vessel wall in COVID-19 lung autopsies. Immobilization of S100A8/A9 with collagen accelerated the formation of a fibrin-rich network after perfusion of recalcified blood at venous shear. In vitro, platelets adhered and partially spread on S100A8/A9, leading to the formation of distinct populations of either P-selectin or phosphatidylserine (PS)-positive platelets. By using washed platelets, soluble S100A8/A9 induced PS exposure but failed to induce platelet aggregation, despite GPIIb/IIIa activation and alpha-granule secretion. We identified GPIbα as the receptor for S100A8/A9 on platelets inducing the formation of procoagulant platelets with a supporting role for CD36. The effect of S100A8/A9 on platelets was abolished by recombinant GPIbα ectodomain, platelets from a patient with Bernard-Soulier syndrome with GPIb-IX-V deficiency, and platelets from mice deficient in the extracellular domain of GPIbα. We identified the S100A8/A9-GPIbα axis as a novel targetable prothrombotic pathway inducing procoagulant platelets and fibrin formation, in particular in diseases associated with high levels of S100A8/A9, such as COVID-19.

Neutrophil extracellular traps and complications of liver transplantation

Many end-stage liver disease etiologies are attributed to robust inflammatory cell recruitment. Neutrophils play an important role in inflammatory infiltration and neutrophil phagocytosis, oxidative burst, and degranulation. It has also been suggested that neutrophils may release neutrophil extracellular traps (NETs) to kill pathogens. It has been proven that neutrophil infiltration within the liver contributes to an inflammatory microenvironment and immune cell activation. Growing evidence implies that NETs are involved in the progression of numerous complications of liver transplantation, including ischemia-reperfusion injury, acute rejection, thrombosis, and hepatocellular carcinoma recurrence. NETs are discussed in this comprehensive review, focusing on their effects on liver transplantation complications. Furthermore, we discuss NETs as potential targets for liver transplantation therapy.

PAD4 and Its Inhibitors in Cancer Progression and Prognosis

The systemic spread of malignancies and the risk of cancer-associated thrombosis are major clinical challenges in cancer therapy worldwide. As an important post-translational modification enzyme, peptidyl arginine deiminase 4 (PAD4) could mediate the citrullination of protein in different components (including nucleus and cytoplasm, etc.) of a variety of cells (tumor cells, neutrophils, macrophages, etc.), thus participating in gene regulation, neutrophil extracellular trap (NET) and macrophage extracellular trap (MET). Thereby, PAD4 plays an important role in enhancing the growth of primary tumors and facilitating the distant metastasis of cancer cells. In addition, it is related to the formation of cancer-associated thrombosis. Therefore, the development of PAD4-specific inhibitors may be a promising strategy for treating cancer, and it may improve patient prognosis. In this review, we describe PAD4 involvement in gene regulation, protein citrullination, and NET formation. We also discuss its potential role in cancer and cancer-associated thrombosis, and we summarize the development and application of PAD4 inhibitors.

Expanding role of deoxyribonucleic acid-sensing mechanism in the development of lifestyle-related diseases

In lifestyle-related diseases, such as cardiovascular, metabolic, respiratory, and kidney diseases, chronic inflammation plays a causal role in their pathogenesis; however, underlying mechanisms of sterile chronic inflammation are not well-understood. Previous studies have confirmed the damage of cells in these organs in the presence of various risk factors such as diabetes, dyslipidemia, and cigarette smoking, releasing various endogenous ligands for pattern recognition receptors. These studies suggested that nucleic acids released from damaged tissues accumulate in these tissues, acting as an endogenous ligand. Undamaged DNA is an integral factor for the sustenance of life, whereas, DNA fragments, especially those from pathogens, are potent activators of the inflammatory response. Recent studies have indicated that inflammatory responses such as the production of type I interferon (IFN) induced by DNA-sensing mechanisms which contributes to self-defense system in innate immunity participates in the progression of inflammatory diseases by the recognition of nucleic acids derived from the host, including mitochondrial DNA (mtDNA). The body possesses several types of DNA sensors. Toll-like receptor 9 (TLR9) recognizes DNA fragments in the endosomes. In addition, the binding of DNA fragments in the cytosol activates cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase (cGAS), resulting in the synthesis of the second messenger cyclic GMP-AMP (cGAMP). The binding of cGAMP to stimulator of interferon genes (STING) activates NF-κB and TBK-1 signaling and consequently the production of many inflammatory cytokines including IFNs. Numerous previous studies have demonstrated the role of DNA sensors in self-defense through the recognition of DNA fragments derived from pathogens. Beyond the canonical role of TLR9 and cGAS-STING, this review describes the role of these DNA-sensing mechanism in the inflammatory responses caused by endogenous DNA fragments, and in the pathogenesis of lifestyle-related diseases.

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.

Damage associated molecular patterns and neutrophil extracellular traps in acute pancreatitis

Previous researches have emphasized a trypsin-centered theory of acute pancreatitis (AP) for more than a century. With additional studies into the pathogenesis of AP, new mechanisms have been explored. Among them, the role of immune response bears great importance. Pro-inflammatory substances, especially damage-associated molecular patterns (DAMPs), play an essential role in activating, signaling, and steering inflammation. Meanwhile, activated neutrophils attach great importance to the immune defense by forming neutrophil extracellular traps (NETs), which cause ductal obstruction, premature trypsinogen activation, and modulate inflammation. In this review, we discuss the latest advances in understanding the pathological role of DAMPs and NETs in AP and shed light on the flexible crosstalk between these vital inflammatory mediators. We, then highlight the potentially promising treatment for AP targeting DAMPs and NETs, with a focus on novel insights into the mechanism, diagnosis, and management of AP.

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.

Proteomic Profiling of Saliva and Tears in Radiated Head and Neck Cancer Patients as Compared to Primary Sjögren's Syndrome Patients

Patients with head and neck cancer (HNC) and patients with primary Sjögren's syndrome (pSS) may exhibit similar symptoms of dry mouth and dry eyes, as a result of radiotherapy (RT) or a consequence of disease progression. To identify the proteins that may serve as promising disease biomarkers, we analysed saliva and tears from 29 radiated HNC patients and 21 healthy controls, and saliva from 14 pSS patients by mass spectrometry-based proteomics. The study revealed several upregulated, and in some instances overlapping, proteins in the two patient groups. Histone H1.4 and neutrophil collagenase were upregulated in whole saliva of both patient groups, while caspase-14, histone H4, and protein S100-A9 were upregulated in HNC saliva only. In HCN tear fluid, the most highly upregulated protein was mucin-like protein 1. These overexpressed proteins in saliva and tears play central roles in inflammation, host cell injury, activation of reactive oxygen species, and tissue repair. In conclusion, the similarities and differences in overexpressed proteins detected in saliva from HNC and pSS patients may contribute to the overall understanding of the different pathophysiological mechanisms inducing dry mouth. Thus, the recurring proteins identified could possibly serve as future promising biomarkers.

Diagnostic and Prognostic Value of Neutrophil Extracellular Trap Levels in Patients With Acute Aortic Dissection

Background

Acute aortic dissection (AAD) is a fatal disease demanding prompt diagnosis and proper treatment. There is a lack of serum markers that can effectively assist diagnosis and predict prognosis of AAD patients.

Methods

Ninety-six AAD patients were enrolled in this study, and 249 patients with chest pain due to acute myocardial infarction, pulmonary embolism, intramural hematoma, angina or other causes and 80 healthy controls were included as control group and healthy control group. Demographics, biochemical and hematological data and risk factors were recorded as baseline characteristics. The 1-year follow-up data were collected and analyzed. The diagnostic performance and ability to predict disease severity and prognosis of NET components in serum and aortic tissue were evaluated.

Results

Circulating NET markers, citH3 (citrullination of histone 3), cell-free DNA (cfDNA) and nucleosomes, had good diagnostic value for AAD, with superior diagnostic performance to D-dimer in discriminating patients with chest pain due to other reasons in the emergency department. Circulating NET marker levels (i.e., citH3, cfDNA and nucleosomes) of AAD patients were significantly higher than that of control group and healthy control group. In addition, circulating NET markers levels were closely associated with the disease severity, in-hospital death and 1-year survival of AAD patients. Systolic blood pressure < 90 mmHg and serum citH3 levels were identified as independent risk factors for 1-year survival of AAD patients. Excessive NET components (i.e., neutrophil elastase and citH3) in the aortic tissue of AAD patient were significantly higher than that of healthy donor aortic tissue. The expression levels of granules and nuclear NET components were significantly higher in aortic tissue from AAD patients than controls.

Conclusions

Circulating NET markers, citH3, cfDNA and nucleosomes, have significant diagnostic value and predictive value of disease severity and prognosis of AAD patients. The NETs components may constitute a useful diagnostic and prognostic marker in AAD patients.

NET-Mediated Pathogenesis of COVID-19: The Role of NETs in Hepatic Manifestations

Some coronavirus disease-2019 (COVID-19) patients exhibit multi-organ failure, which often includes the liver. Indeed, liver disease appears to be an emerging feature of COVID-19 infections. However, the exact mechanism behind this remains unknown. Neutrophil extracellular traps (NETs) have increasingly been attributed as major contributors to various liver pathologies, including sepsis, ischemic-reperfusion (I/R) injury, and portal hypertension in the setting of chronic liver disease. Although vital in normal immunity, excessive NET formation can drive inflammation, particularly of the endothelium. Collectively, we propose that NETs observed to be elevated in severe COVID-19 infection play principal roles in liver injury in addition to acute lung injury. Herein, we discuss the potential mechanisms underlying COVID-induced liver injury including cytopathic effects from direct liver infection, systemic inflammatory response syndrome, and hypoxic injury, encompassing I/R injury and coagulopathy. Further research is required to further elucidate the role of NETs in COVID. This holds potential therapeutic significance, as inhibition of NETosis could alleviate the symptoms of acute respiratory distress syndrome and liver injury, as well as other organs.

The Emerging Role of Neutrophil Extracellular Traps in Arterial, Venous and Cancer-Associated Thrombosis

Neutrophils play a vital role in the formation of arterial, venous and cancer-related thrombosis. Recent studies have shown that in a process known as NETosis, neutrophils release proteins and enzymes complexed to DNA fibers, collectively called neutrophil extracellular traps (NETs). Although NETs were originally described as a way for the host to capture and kill bacteria, current knowledge indicates that NETs also play an important role in thrombosis. According to recent studies, the destruction of vascular microenvironmental homeostasis and excessive NET formation lead to pathological thrombosis. In vitro experiments have found that NETs provide skeletal support for platelets, red blood cells and procoagulant molecules to promote thrombosis. The protein components contained in NETs activate the endogenous coagulation pathway to promote thrombosis. Therefore, NETs play an important role in the formation of arterial thrombosis, venous thrombosis and cancer-related thrombosis. This review will systematically summarize and explain the study of NETs in thrombosis in animal models and in vivo experiments to provide new targets for thrombosis prevention and treatment.

Mechanistic Studies of DNase I Activity: Impact of Heparin Variants and PAD4

Background

Excessive production of neutrophil extracellular traps (NETs) in sepsis contributes to vascular occlusion by acting as a scaffold and stimulus for thrombus formation. Removal of extracellular DNA, the major structural component of NETs, by DNase I may reduce host injury.

Objectives

(1) To determine how heparin variants (unfractionated heparin, enoxaparin, Vasoflux, and fondaparinux) affect DNase I activity, (2) to measure temporal changes in circulating DNA and DNase I in septic patients.

Methods

DNA–histone complexes were treated with DNase I ± heparin variants and visualized via agarose gels. We compared the ability of DNase I ± heparin variants to digest NETs released by phorbol 12-myristate 13-acetate-stimulated neutrophils versus DNA–histone complexes released by necrotic HEK293 cells. Plasma DNA and DNase I levels were measured longitudinally in 76 septic patients.

Results

Heparin enhances DNase I-mediated digestion of DNA–histone complexes in a size-dependent manner that does not require the antithrombin-binding region. In contrast, DNase I alone was able to degrade the DNA–histone component of NETs presumably due to peptidylarginine deiminase 4 (PAD4)-mediated histone citrullination that weakens DNA–histone interactions. In purified systems, PAD4 treatment of DNA–histone complexes enhanced the ability of DNase I to degrade histone-bound DNA. In septic patients, endogenous DNase I levels remained persistently low over 28 days, and there were no significant correlations between DNA and DNase I levels.

Conclusion

Heparin enhances DNA-mediated digestion of DNA–histone complexes in a size-dependent manner that is independent of its anticoagulant properties. Citrullination of histones by PAD4 renders DNA–histone complexes susceptible to DNase I digestion. Endogenous DNase I levels are persistently decreased in septic patients, which supports the potential utility of DNase I as a therapy for sepsis.

Neutrophil Extracellular Traps Exacerbate Ischemic Brain Damage

Most acute strokes are ischemic, and subsequent neuroinflammation promotes further damage leading to cell death but also plays a beneficial role by promoting cellular repair. Neutrophils are forerunners to brain lesions after ischemic stroke and exert elaborate functions. While neutrophil extracellular traps (NETs) possess a fundamental antimicrobial function within the innate immune system under physiological circumstances, increasing evidence indicates that NETosis, the release process of NETs, occurs in the pathogenic process of stroke. In this review, we focus on the processes of NET formation and clearance, the temporal and spatial alterations of neutrophils and NETs after ischemic damage, and how NETs are involved in several stroke-related phenomena. Generally, NET formation and release processes depend on the generation of reactive oxygen species (ROS) and the activation of nuclear peptidylarginine deiminase-4 (PAD4). The acid-base environment, oxygen concentration, and iron ions around the infarct may also impact NET formation. DNase 1 has been identified as the primary degrader of NETs in serum, while reactive microglia are expected to inhibit the formation of NETs around ischemic lesions by phagocytosis of neutrophils. The neutrophils and NETs are present in the perivascular space ipsilateral to the infarct arising after ischemic damage, peaking between 1 and 3 days postischemia, but their location in the brain parenchyma remains controversial. After the ischemic injury, NETs are involved in the destruction of neurological function primarily by disrupting the blood-brain barrier and promoting thrombosis. The potential effects of NETs on various ischemic nerve cells need to be further investigated, especially in the chronic ischemic phase.

Extracellular Histones Bind Vascular Glycosaminoglycans and Inhibit the Anti-Inflammatory Function of Antithrombin

BACKGROUND/AIMS

Binding of histones to molecular pattern recognition receptors on endothelial cells and leukocytes provokes proinflammatory responses and promotes activation of coagulation. Histones also bind therapeutic heparins, thereby neutralizing their anticoagulant functions. The aim of this study was to test the hypothesis that histones can interact with the antithrombin (AT)-binding vascular glycosaminoglycans (GAGs) to induce inflammation and inhibit the anti-inflammatory function of AT.

METHODS

We evaluated the heparin-binding function of histones by an AT-dependent protease-inhibition assay. Furthermore, we treated endothelial cells with histones in the absence and presence of AT and monitored cellular phenotypes employing established signaling assays.

RESULTS

Histones neutralized AT-dependent anticoagulant function of heparin in both purified protease-inhibition and plasma-based assays. Histones also disrupted endothelial cell barrier-permeability function by a GAG-dependent mechanism as evidenced by the GAG-antagonist, surfen, abrogating their disruptive effects. Further studies revealed histones and AT compete for overlapping binding-sites on GAGs, thus increasing concentrations of one protein abrogated effects of the other. Histones elicited proapoptotic effects by inducing nuclear localization of PKC-δ in endothelial cells and barrier-disruptive effects by destabilizing VE-cadherin, which were inhibited by AT, but not by a D-helix mutant of AT incapable of interacting with GAGs. Finally, histones induced release of Weibel-Palade body contents, VWF and angiopoietin-2, and promoted expression of cell adhesion molecules on endothelial cells, which were all downregulated by AT but not by D-helix mutant of AT.

CONCLUSION

We conclude that histones and AT compete for overlapping binding sites on vascular GAGs to modulate coagulation and inflammation.

Plasma tumor DNA is associated with increased risk of venous thromboembolism in metastatic castration-resistant cancer patients

Cancer is a risk factor for venous thromboembolism (VTE). Plasma tumor DNA (ptDNA) is an independent predictor of outcome in metastatic castration-resistant prostate cancer (mCRPC). We aimed to investigate the association between ptDNA and VTE in mCRPC. This prospective biomarker study included 180 mCRPC patients treated with abiraterone and enzalutamide from April 2013 to December 2018. We excluded patients with a previous VTE history and/or ongoing anticoagulation therapy. Targeted next-generation sequencing was performed to determine ptDNA fraction from pretreatment plasma samples. VTE risk based on survival analysis was performed using cumulative incidence function and estimating sub-distributional hazard ratio (SHR). At a median follow-up of 58 months (range 0.5-111.0), we observed 21 patients who experienced VTE with a cumulative incidence at 12 months of 17.1% (95% confidence interval [CI] 10.3-23.9). Elevated ptDNA, visceral metastasis, prior chemotherapy and lactate dehydrogenase (LDH) were significantly associated with higher VTE incidence compared to patients with no thrombosis (12-month estimate, 18.6% vs 3.5%, P = .0003; 44.4% vs 14.8%, P = .015; 24.7% vs 4.5%, P = .006; and 30.0% vs 13.5%, P = .05, respectively). In the multivariate analysis including ptDNA level, visceral metastases, number of lesions and serum LDH, high ptDNA fraction was the only independent factor associated with the risk of thrombosis (HR 5.78, 95% CI 1.63-20.44, P = .006). These results first suggest that baseline ptDNA fraction in mCRPC patients treated with abiraterone or enzalutamide may be associated with increased VTE risk. These patients may be followed-up more closely for the VTE risk, and the need for a primary thromboprophylaxis should be taken into account in mCRPC with elevated ptDNA.

Immunothrombosis and new-onset atrial fibrillation in the general population: the Rotterdam Study

Background

Atrial fibrillation (AF) is the most common age-related cardiac arrhythmia. The etiology underlying AF is still largely unknown. At the intersection of the innate immune system and hemostasis, immunothrombosis may be a possible cause of atrial remodeling, and therefore be an underlying cause of AF.

Methods

From 1990 to 2014, we followed participants aged 55 and over, free from AF at inclusion. Immunothrombosis factors fibrinogen, von Willebrand factor, ADAMTS13, and neutrophil extracellular traps (NETs) levels were measured at baseline. Participants were followed until either onset of AF, loss-to-follow-up, or reaching the end-date of 01-01-2014. Cox proportional hazard modelling was used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs), adjusted for cardiovascular risk factors.

Results

We followed 6174 participants (mean age 69.1 years, 57% women) for a median follow-up time of 12.8 years. 364 men (13.7%, incidence rate 13.0/1000 person-years) and 365 women (10.4%, incidence rate 8.9/1000 person-years) developed AF. We found no significant association between markers of immunothrombosis and new-onset AF after adjusting for cardiovascular risk factors [HR 1.00 (95% CI 0.93–1.08) for fibrinogen, 1.04 (0.97–1.12) for von Willebrand factor, 1.00 (1.00–1.01) for ADAMTS13, and 1.01 (0.94–1.09) for NETs]. In addition, we found no differences in associations between men and women.

Conclusion

We found no associations between markers of immunothrombosis and new-onset AF in the general population. Inflammation and immunothrombosis may be associated with AF through other cardiovascular risk factors or predisposing conditions of AF. Our findings challenge the added value of biomarkers in AF risk prediction.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00392-021-01938-4.

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

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

Scientific premise for the involvement of neutrophil extracellular traps (NETs) in vaccine-induced thrombotic thrombocytopenia (VITT)

Following on from the devastating spread of COVID‐19, a major global priority has been the production, procurement, and distribution of effective vaccines to ensure that the global pandemic reaches an end. However, concerns were raised about worrying side effects, particularly the occurrence of thrombosis and thrombocytopenia after administration of the Oxford/AstraZeneca and Johnson & Johnson's Janssen COVID‐19 vaccine, in a phenomenon being termed vaccine‐induced thrombotic thrombocytopenia (VITT). Similar to heparin‐induced thrombocytopenia (HIT), this condition has been associated with the development of anti‐platelet factor 4 antibodies, purportedly leading to neutrophil‐platelet aggregate formation. Although thrombosis has also been a common association with COVID‐19, the precise molecular mechanisms governing its occurrence are yet to be established. Recently, increasing evidence highlights the NLRP3 (NOD‐like, leucine‐rich repeat domains, and pyrin domain‐containing protein) inflammasome complex along with IL‐1β and effete neutrophils producing neutrophil extracellular traps (NETs) through NETosis. Herein, we propose and discuss that perhaps the incidence of VITT may be due to inflammatory reactions mediated via IL‐1β/NLRP3 inflammasome activation and consequent overproduction of NETs, where similar autoimmune mechanisms are observed in HIT. We also discuss avenues by which such modalities could be treated to prevent the occurrence of adverse events and ensure vaccine rollouts remain safe and on target to end the current pandemic.

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.

COVID-19 and immunothrombosis: emerging understanding and clinical management

The COVID-19 pandemic has been the most significant health crisis in recent global history. Early studies from Wuhan highlighted COVID-19-associated coagulopathy and a significant association with mortality was soon recognised. As research continues across the world, more evidence is emerging of the cross-talk between the innate immune system, coagulation activation and inflammation. Immunothrombosis has been demonstrated to play a key role in the pathophysiology of severe COVID-19, with extracellular histones and neutrophil extracellular traps detected in the plasma and cardiopulmonary tissues of critically ill patients. Targeting the components of immunothrombosis is becoming an important factor in the treatment of patients with COVID-19 infection. Recent studies report outcomes of intermediate and therapeutic anticoagulation in hospitalised patients with varying severities of COVID-19 disease, including optimal dosing and associated bleeding risks. Immunomodulatory therapies, including corticosteroids and IL-6 receptor antagonists, have been demonstrated to significantly reduce mortality in COVID-19 patients. As the pandemic continues, more studies are required to understand the driving factors and upstream mechanisms for coagulopathy and immunothrombosis in COVID-19, and thus potentially develop more targeted therapies for SARS-CoV-2 infection, both in the acute phase and in those who develop longer-term symptom burden.

Emerging Roles of the Innate Immune System Regulated by DNA Sensors in the Development of Vascular and Metabolic Diseases

Sterile chronic inflammation causes cardiometabolic disorders; however, the mechanisms are not fully understood. Previous studies have demonstrated the degradation of cells/tissues in the vasculature and metabolic organs in lifestyle-associated diseases, such as diabetes and hyperlipidemia, suggesting the release and/or accumulation of nucleic acids from damaged cells. DNA is indispensable for life; however, DNA fragments, especially those from pathogens, strongly induce inflammation by the activation of DNA sensors. Growing evidence suggests that DNA-sensing mechanisms, which are normally involved in self-defense against pathogens as the innate immune system, are associated with the progression of inflammatory diseases in response to endogenous DNA fragments. There are several types of DNA sensors in our bodies. Toll-like receptor 9 (TLR9)—one of the most studied DNA sensors—recognizes DNA fragments in endosome. In addition, stimulator of interferon genes (STING), which has recently been extensively investigated, recognizes cyclic GMP-AMP (cGAMP) generated from DNA fragments in the cytosol. Both TLR9 and STING are known to play pivotal roles in host defense as the innate immune system. However, recent studies have indicated that the activation of these DNA sensors in immune cells, such as macrophages, promotes inflammation leading to the development of vascular and metabolic diseases associated with lifestyle. In this review, we discuss recent advances in determining the roles of DNA sensors in these disease contexts. Revealing a novel mechanism of sterile chronic inflammation regulated by DNA sensors might facilitate clinical interventions for these health conditions.

Overexpression of Replication-Dependent Histone Signifies a Subset of Dedifferentiated Liposarcoma with Increased Aggressiveness

Liposarcoma (LPS) is an adult soft tissue malignancy that arises from fat tissue, where well-differentiated (WD) and dedifferentiated (DD) forms are the most common. DDLPS represents the progression of WDLPS into a more aggressive high-grade and metastatic form. Although a few DNA copy-number amplifications are known to be specifically found in WD- or DDLPS, systematic genetic differences that signify subtype determination between WDLPS and DDLPS remain unclear. Here, we profiled the genome and transcriptome of 38 LPS tumors to uncover the genetic signatures of subtype differences. Replication-dependent histone (RD-HIST) mRNAs were highly elevated and their regulation was disrupted in a subset of DDLPS, increasing cellular histone molecule levels, as measured using RNA-seq (the averaged fold change of 53 RD-HIST genes between the DD and WD samples was 10.9) and immunohistochemistry. The change was not observed in normal tissues. Integrated whole-exome sequencing, RNA-seq, and methylation analyses revealed that the overexpressed HMGA2 (the fold change between DD and WD samples was 7.3) was responsible for the increased RD-HIST level, leading to aberrant cell proliferation. Therefore, HMGA2-mediated elevation of RD-HISTs were crucial events in determining the aggressiveness of DDLPS, which may serve as a biomarker for prognosis prediction for liposarcoma patients.

Genetic and epigenetic regulation of cancer coagulome - lessons from heterogeneity of cancer cell populations

Cancer-associated thrombosis (CAT) is a morbid, potentially life threatening and biologically impactful paraneoplastic state. At least in part, CAT is likely driven by cancer-specific mechanisms the nature of which is still poorly understood, hampering diagnostic, prophylactic and therapeutic efforts. It is increasingly appreciated that cancer-specific drivers of CAT include a constellation of oncogenic mutations and their superimposed epigenetic states that shape the transcriptome, phenotype and secretome of cancer cell populations, including the repertoire of genes impacting the vascular and coagulation systems. High-grade brain tumours, such as glioblastoma multiforme (GBM) represent a paradigm of locally initiated haemostatic abnormalities that propagate systemically, likely through circulating mediators, such as extracellular vesicles and soluble factors. Reciprocally, CAT impacts the biology of cancer cells and may drive tumour evolution. The constituent, oncogene-transformed cancer cell populations form complex ecosystems, the intricate architecture of which has been recently revealed by single cell sequencing technologies. Amidst this phenotypic heterogeneity, several alternative pathways of CAT may exist both between and within individual tumours and their subtypes, including GBM. Indeed, different contributions of cells expressing key coagulant mediators, such as tissue factor, or podoplanin, have been identified in GBM subtypes driven by oncogenic mutations in EGFR, IDH1 and other transforming genes. Thus, a better understanding of cellular sources of CAT, including dominant cancer cell phenotypes and their dynamic shifts, may help design more personalised approaches to thrombosis in cancer patients to improve outcomes.

Circulating Histones in Sepsis: Potential Outcome Predictors and Therapeutic Targets

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection and is associated with high morbidity and mortality. Circulating histones (CHs), a group of damage-associated molecular pattern molecules mainly derived from neutrophil extracellular traps, play a crucial role in sepsis by mediating inflammation response, organ injury and death through Toll-like receptors or inflammasome pathways. Herein, we first elucidate the molecular mechanisms of histone-induced inflammation amplification, endothelium injury and cascade coagulation activation, and discuss the close correlation between elevated level of CHs and disease severity as well as mortality in patients with sepsis. Furthermore, current state-of-the-art on anti-histone therapy with antibodies, histone-binding proteins (namely recombinant thrombomodulin and activated protein C), and heparin is summarized to propose promising approaches for sepsis treatment.

Targeting the AnxA1/Fpr2/ALX pathway regulates neutrophil function, promoting thromboinflammation resolution in sickle cell disease

Neutrophils play a crucial role in the intertwined processes of thrombosis and inflammation. An altered neutrophil phenotype may contribute to inadequate resolution, which is known to be a major pathophysiological contributor of thromboinflammatory conditions such as sickle cell disease (SCD). The endogenous protein annexin A1 (AnxA1) facilitates inflammation resolution via formyl peptide receptors (FPRs). We sought to comprehensively elucidate the functional significance of targeting the neutrophil-dependent AnxA1/FPR2/ALX pathway in SCD. Administration of AnxA1 mimetic peptide AnxA1Ac2-26 ameliorated cerebral thrombotic responses in Sickle transgenic mice via regulation of the FPR2/ALX (a fundamental receptor involved in resolution) pathway. We found direct evidence that neutrophils with SCD phenotype play a key role in contributing to thromboinflammation. In addition, AnxA1Ac2-26 regulated activated SCD neutrophils through protein kinase B (Akt) and extracellular signal-regulated kinases (ERK1/2) to enable resolution. We present compelling conceptual evidence that targeting the AnxA1/FPR2/ALX pathway may provide new therapeutic possibilities against thromboinflammatory conditions such as SCD.

Protective Role of Activated Protein C against Viral Mimetic Poly(I:C)-Induced Inflammation

Activated protein C (APC) is an anticoagulant plasma serine protease which exhibits potent cytoprotective and anti-inflammatory activities. Here, we studied protective effects of APC on the proinflammatory function of polyinosinic:polycytidylic acid [poly(I:C)], a synthetic analog of viral double-stranded RNA, in cellular and animal models. Poly(I:C) induced histone H3 extranuclear translocation via interaction with toll-like receptor 3 in two established endothelial cell lines. Furthermore, poly(I:C) induced histone H3 extranuclear translocation in J774A.1 macrophages and human neutrophils and formation of macrophage and neutrophil extracellular traps (ETs). Mechanistically, poly(I:C) was found to upregulate expression of peptidylarginine deiminase 4 and enhance its interaction with histone H3, thereby leading to increased histone citrullination and neutrophil ET formation. Poly(I:C) elicited proinflammatory signaling responses by inducing nuclear factor kappa B activation and disrupting endothelial cell permeability. In vivo, poly(I:C) enhanced cell surface expression of Mac-1 on neutrophils in mice and facilitated their infiltration to lung tissues. Poly(I:C) also downregulated thrombomodulin expression in mouse tissues and reduced its circulating soluble level in plasma. We demonstrate in this study that APC and a signaling-selective mutant of APC effectively inhibit proinflammatory signaling effects of poly(I:C) in both cellular and animal models. We further demonstrate that unlike the requirement for endothelial protein C receptor on endothelial cells, the integrin Mac-1 is involved in the protease-activated receptor 1-dependent APC inhibition of macrophage ET formation in J774A.1 cells. Taken together, these results support a key role for APC signaling in inhibiting the viral mimetic-induced proinflammatory signaling responses and histone translocation-associated formation of ETs by innate immune cells.

Cytokine Storm as a Cellular Response to dsDNA Breaks: A New Proposal

Pathogenesis of cytokine storm is poorly understood. In this article we propose a new mechanism and suggest innovative therapeutic avenues for its prevention. We have reported that particles of cell-free chromatin (cfCh) that are released from the billions of cells that die in the body everyday can illegitimately integrate into genomes of healthy cells to trigger dsDNA breaks. The latter leads to apoptosis and/or intense activation of inflammatory cytokines in the affected cells. We hypothesise that a similar phenomenon of dsDNA breaks and inflammation is involved in cytokine storm. The abundant cfCh particles that are released from dying host cells following viral/microbial invasion initiate a cascading effect of more cell death resulting in a vicious cycle of further DNA damage, apoptosis and hyper-inflammation which culminate in cytokine storm. We propose that this unrelenting vicious cycle of cellular DNA damage and cytokine storm may be the underlying cause of high mortality from severe COVID-19. We discuss results of our preclinical studies wherein we have shown that endotoxin induced cytokine storm in mice can be reversed by three different agents that have the ability to inactivate cfCh. These agents may be worthy of investigation in clinical trials to reduce mortality from COVID-19.

NETosis in Rheumatic Diseases

PURPOSE OF REVIEW

Neutrophils are the most numerous and the first responder cells of the innate immune system. Evidence suggests that neutrophils may play an essential role in the pathogenesis of multiple systemic diseases. A novel mechanism of neutrophil extracellular traps (NETs) leading to breaking of self-tolerance and generation of autoimmune responses in predisposed individuals has been described in various autoimmune conditions. The purpose of the review is to identify these important mechanisms of NETs leading to autoimmunity in various rheumatic diseases.

RECENT FINDINGS

NETs contain histone and chromatin, which contain important autoantigens. Many autoimmune conditions are associated with increased NET-generating capacity, unique low-density granulocyte population, and impaired NET degradation leading to persistent inflammation and tissue damage. NETs can also activate other immune cells, and their components may amplify the inflammatory response by activation of complement pathways and inflammasomes. NETs can also contribute to autoantibody formation in disorders such as rheumatoid arthritis, ANCA-associated vasculitis, and systemic lupus erythematosus by providing a constant source of autoantigens. NETs can also serve as biomarkers providing insights into disease diagnosis and therapeutics. NETs seem to play a primary role in inflammatory disease pathogenesis. Identification of different NET pathogenic pathways in various rheumatic conditions could provide new insights into disease pathogenesis and therapeutic targets could be developed towards the future treatment of inflammatory autoimmune diseases.

Association of cfDNA levels and bothrops envenomation

In the Amazon, around 90% of snakebites are caused by the Bothrops genus. Complications arising from Bothrops envenomations result from the inflammatory and coagulotoxic activities of the venom. The aim of this study was to investigate the potential of cell-free DNA (cfDNA) as a biomarker of severity in Bothrops snakebites. Patients were treated at the Fundação de Medicina Tropical Dr. Heitor Vieira Dourado (FMT-HVD), Manaus, in the Brazilian Amazon. cfDNA plasma levels were measured by amplifying the human telomerase reverse transcriptase (hTERT) sequence using quantitative RT-PCR. Median levels of cfDNA were compared between envenomed and healthy volunteers and among patients presenting different complications, such as renal failure, bleeding and infection. Of the 76 patients included, 82.9% were male, with a mean age of 32.8 years, and envenomations were mainly classified as severe (39.5%). ROC curve analysis showed a good accuracy of cfDNA levels (AUROC of 0.745) in envenomation diagnosis. A correlation analysis using laboratory variables showed positive correlation with lactate dehydrogenase (p = 0.033) and platelet count (p = 0.003). When cfDNA levels were compared with clinical complications, significant statistical differences were only found among individuals with mild and severe pain (p < 0.05). In summary, our results demonstrated that cfDNA levels are sufficiently accurate for discriminating between envenomed and non-envenomed patients, but are not able to distinguish different complications and the level of severity among envenomed patients. Thus, the role of cfDNA in the pathogenesis of the snakebite envenomations needs to be further investigated.