Polymerized Salicylic Acid Microparticles Reduce the Progression and Formation of Human Neutrophil Extracellular Traps (NET)s

Neutrophils can contribute to inflammatory disease propagation via innate mechanisms intended for inflammation resolution. For example, neutrophil extracellular traps (NETs) are necessary for trapping pathogens but can contribute to clot formation and blood flow restriction, that is, ischemia. Currently, no therapeutics in the clinic directly target NETs despite the known involvement of NETs contributing to mortality and increased disease severity. Vascular-deployed particle-based therapeutics are a novel and robust alternative to traditional small-molecule drugs by enhancing drug delivery to cells of interest. This work designs a high-throughput assay to investigate the immunomodulatory behavior and functionality of salicylic acid-based polymer-based particle therapeutics against NETosis in human neutrophils. Briefly, this work finds that polymeric composition plays a role, and particle size can also influence rates of NETosis. Salicylate-based polymeric (Poly-SA) particles are found to functionally inhibit NETosis depending on the particle size and concentration exposed to neutrophils. This work demonstrates the high throughput method can help fast-track particle-based therapeutic optimization and design, more efficiently preparing this innovative therapeutics for the clinic.

Targeting Neutrophil Extracellular Trap Formation: Exploring Promising Pharmacological Strategies for the Treatment of Preeclampsia

Neutrophils, which constitute the most abundant leukocytes in human blood, emerge as crucial players in the induction of endothelial cell death and the modulation of endothelial cell responses under both physiological and pathological conditions. The hallmark of preeclampsia is endothelial dysfunction induced by systemic inflammation, in which neutrophils, particularly through the formation of neutrophil extracellular traps (NETs), play a pivotal role in the development and perpetuation of endothelial dysfunction and the hypertensive state. Considering the potential of numerous pharmaceutical agents to attenuate NET formation (NETosis) in preeclampsia, a comprehensive assessment of the extensively studied candidates becomes imperative. This review aims to identify mechanisms associated with the induction and negative regulation of NETs in the context of preeclampsia. We discuss potential drugs to modulate NETosis, such as NF-κβ inhibitors, vitamin D, and aspirin, and their association with mutagenicity and genotoxicity. Strong evidence supports the notion that molecules involved in the activation of NETs could serve as promising targets for the treatment of preeclampsia.

Neutrophil extracellular traps promote ΔNp63+ basal cell hyperplasia in chronic rhinosinusitis

BACKGROUND

Neutrophil extracellular traps (NETs) are observed in chronic rhinosinusitis (CRS), although their role remains unclear.

OBJECTIVES

This study aimed to investigate the influence of NETs on the CRS epithelium.

METHODS

Forty-five sinonasal biopsy specimens were immunofluorescence-stained to identify NETs and p63+ basal stem cells. Investigators treated human nasal epithelial cells with NETs and studied them with immunofluorescence staining, Western blotting, and quantitative real-time PCR. NET inhibitors were administered to a murine neutrophilic nasal polyp model.

RESULTS

NETs existed in tissues in patients with CRS with nasal polyps, especially in noneosinophilic nasal polyp tissues. p63+ basal cell expression had a positive correlation with the release of NETs. NETs induced the expansion of Ki-67+p63+ cells. We found that ΔNp63, an isoform of p63, was mainly expressed in the nasal epithelium and controlled by NETs. Treatment with deoxyribonuclease (DNase) I or Sivelestat (NET inhibitors) prevented the overexpression of ΔNp63+ epithelial stem cells and reduced polyp formation.

CONCLUSIONS

These results reveal that NETs are implicated in CRS pathogenesis via basal cell hyperplasia. This study suggests a novel possibility of treating CRS by targeting NETs.

A variety of death modes of neutrophils and their role in the etiology of autoimmune diseases

Neutrophils are important in the context of innate immunity and actively contribute to the progression of diverse autoimmune disorders. Distinct death mechanisms of neutrophils may exhibit specific and pivotal roles in autoimmune diseases and disease pathogenesis through the orchestration of immune homeostasis, the facilitation of autoantibody production, the induction of tissue and organ damage, and the incitement of pathological alterations. In recent years, more studies have provided in-depth examination of various neutrophil death modes, revealing nuances that challenge conventional understanding and underscoring their potential clinical utility in diagnosis and treatment. This review explores the multifaceted processes and characteristics of neutrophil death, with a focus on tailored investigations within various autoimmune diseases. It also highlights the potential interplay between neutrophil death and the landscape of autoimmune disorders. The review encapsulates the pertinent pathways implicated in various neutrophil death mechanisms across diverse autoimmune diseases while also charts possible avenues for future research.

Recent advances in the role of neutrophils and neutrophil extracellular traps in acute pancreatitis

Pancreatitis is an inflammatory disease, which is triggered by adverse events in acinar cells of the pancreas. After the initial injury, infiltration of neutrophils in pancreas is observed. In the initial stages of pancreatitis, the inflammation is sterile. It has been shown that the presence of neutrophils at the injury site can modulate the disease. Their depletion in experimental animal models of the acute pancreatitis has been shown to be protective. But information on mechanism of contribution to inflammation by neutrophils at the injury site is not clear. Once at injury site, activated neutrophils release azurophilic granules containing proteolytic enzymes and generate hypochlorous acid which is a strong microbicidal agent. Additionally, emerging evidence shows that neutrophil extracellular traps (NETs) are formed which consist of decondensed DNA decorated with histones, proteases and granular and cytosolic proteins. NETs are considered mechanical traps for microbes, but there is preliminary evidence to indicate that NETs, which constitute a special mechanism of the neutrophil defence system, play an adverse role in pancreatitis by contributing to the pancreatic inflammation and distant organ injury. This review presents the overall current information about neutrophils and their role including NETs in acute pancreatitis (AP). It also highlights current gaps in knowledge which should be explored to fully elucidate the role of neutrophils in AP and for therapeutic gains.

NETosis: an emerging therapeutic target in renal diseases

Introduction

Neutrophil extracellular traps (NETs) are web-like structures composed of nuclear and granular components. The primary role of NETS is to prevent the dissemination of microbes and facilitate their elimination. However, this process is accompanied by collateral proinflammatory adverse effects when the NET release becomes uncontrollable, or clearance is impaired. Although NET-induced organ damage is conducted primarily and indirectly via immune complexes and the subsequent release of cytokines, their direct effects on cells are also remarkable. NETosis plays a critical pathogenic role in several renal disorders, such as the early phase of acute tubular necrosis, anti-neutrophil cytoplasmic antibody-mediated renal vasculitis, lupus nephritis, thrombotic microangiopathies, anti-glomerular basement membrane disease, and diabetic nephropathy. Their substantial contribution in the course of these disorders makes them a desirable target in the therapeutic armamentarium. This article gives an in-depth review of the heterogeneous pathogenesis and physiological regulations of NETosis and its pivotal role in renal diseases. Based on the pathogenesis, the article also outlines the current therapeutic options and possible molecular targets in the treatment of NET-related renal disorders.

Methods

We carried out thorough literature research published in PubMed and Google Scholar, including a comprehensive review and analysis of the classification, pathomechanisms, and a broad spectrum of NET-related kidney disorders.

Conclusions

NETosis plays a pivotal role in certain renal diseases. It initiates and maintains inflammatory and autoimmune disorders, thus making it a desirable target for improving patient and renal outcomes. Better understanding and clinical translation of the pathogenesis are crucial aspects to treatment, for improving patient, and renal outcomes.

The central role of neutrophil extracellular traps (NETs) and by-products in COVID-19 related pulmonary thrombosis

Extracellular trap networks (neutrophil extracellular traps [NETs]) of polymorphonuclear neutrophils are mesh-like substances that prevent the spread of pathogens. They primarily consist of DNA skeletons, histones, granule components, and cytoplasmic proteins. NETs formation requires a certain environment and there are different pathways for NETs production. However, it is still not clear how severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) promotes NETs. NETs exert antiinflammatory effects through immune response, while they can also lead to certain adverse outcomes, such as the development of immunothrombosis. Coronavirus disease 2019 (COVID-19) is an inflammatory reaction affecting various organs caused by SARS-CoV-2, especially the lungs. NETs production and disease severity are linked with unique neutrophil clusters by single-cell RNA sequencing. NETs might exert an anti-inflammatory role in the initial stage of lung tissue inflammation. Nevertheless, numerous studies and cases have shown that they can also result in pulmonary thrombosis. There is mounting evidence that NETs are tightly related with COVID-19 pulmonary thrombosis, and many studies on the mechanisms are involved. The role and mechanism of NETs in the development of pulmonary thrombosis will be the main topics of this manuscript. Additionally, we address the potential targeting of NETs in COVID-19 patients.

Balancing the functions of DNA extracellular traps in intracellular parasite infections: implications for host defense, disease pathology and therapy

The release of DNA to the extracellular milieu is a biological process referred to as etosis, which is involved in both physiological and pathological functions. Although the release of DNA extracellular traps (ETs) was initially attributed to innate immune cells such as neutrophils, eosinophils, and macrophages, recent studies have shown that T cells, as well as non-immune cells, are capable of releasing ETs. These structures were described primarily for their potential to trap and kill pathogens, presenting an important strategy of host defense. Intriguingly, these functions have been associated with intracellular pathogens such as the parasites Leishmania sp. and Trypanosoma cruzi, causative agents of leishmaniasis and Chagas disease, respectively. These are two devastating tropical diseases that lead to thousands of deaths every year. In an apparent contradiction, ETs can also induce and amplify inflammation, which may lead to worsening disease pathology. This has prompted the concept of targeting ETs' release as a means of controlling tissue destruction to treat human diseases. What is the best approach to prevent disease severity: inducing ETs to kill pathogens or preventing their release? In this Perspective article, we will discuss the importance of understanding ETs released by different cell types and the need to balance their potentially complementary functions. In addition, we will explore other functions of ETs and their translational applications to benefit individuals infected with intracellular parasites and other pathogens. Ultimately, a better understanding of the role of ETs in disease pathogenesis will provide valuable insights into developing novel therapies for human diseases.

Mechanisms of neutrophil extracellular trap in chronic inflammation of endothelium in atherosclerosis

Cardiovascular diseases are a primary cause of morbidity and mortality around the world. In addition, atherosclerosis (AS)-caused cardiovascular disease is the primary cause of death in human diseases, and almost two billion people suffer from carotid AS worldwide. AS is caused by chronic inflammation of the arterial vessel and is initiated by dysfunction of vascular endothelial cells. Neutrophils protect against pathogen invasion because they function as a component of the innate immune system. However, the contribution of neutrophils to cardiovascular disease has not yet been clarified. Neutrophil extracellular traps (NETs) represent an immune defense mechanism that is different from direct pathogen phagocytosis. NETs are extracellular web-like structures activated by neutrophils, and they play important roles in promoting endothelial inflammation via direct or indirect pathways. NETs consist of DNA, histones, myeloperoxidase, matrix metalloproteinases, proteinase 3, etc. Most of the components of NETs have no direct toxic effect on endothelial cells, such as DNA, but they can damage endothelial cells indirectly. In addition, NETs play a critical role in the process of AS; therefore, it is important to clarify the mechanisms of NETs in AS because NETs are a new potential therapeutic target AS. This review summarizes the possible mechanisms of NETs in AS.

The effect of neutrophil extracellular traps in venous thrombosis

Neutrophil extracellular traps (NETs) as special release products of neutrophils have received extensive attention. They are composed of decondensed chromatin and coated with nucleoproteins, including histones and some granulosa proteins. NETs can form a network structure to effectively capture and eliminate pathogens and prevent their spread. Not only that, recent studies have shown that NETs also play an important role in venous thrombosis. This review provides the most important updated evidence regarding the mechanism of NETs formation and the role of NETs in the process of venous thrombosis. The potential prophylactic and therapeutic value of NETs in venous thrombotic disease will also be discussed.

Hypobaric Hypoxia Aggravates Renal Injury by Inducing the Formation of Neutrophil Extracellular Traps through the NF-κB Signaling Pathway

OBJECTIVE

The hypersensitivity of the kidney makes it susceptible to hypoxia injury. The involvement of neutrophil extracellular traps (NETs) in renal injury resulting from hypobaric hypoxia (HH) has not been reported. In this study, we aimed to investigate the expression of NETs in renal injury induced by HH and the possible underlying mechanism.

METHODS

A total of 24 SD male rats were divided into three groups (n=8 each): normal control group, hypoxia group and hypoxia+pyrrolidine dithiocarbamate (PDTC) group. Rats in hypoxia group and hypoxia+PDTC group were placed in animal chambers with HH which was caused by simulating the altitude at 7000 meters (oxygen partial pressure about 6.9 kPa) for 7 days. PDTC was administered at a dose of 100 mg/kg intraperitoneally once daily for 7 days. Pathological changes of the rat renal tissues were observed under a light microscope; the levels of serum creatinine (SCr), blood urea nitrogen (BUN), cell-free DNA (cf-DNA) and reactive oxygen species (ROS) were measured; the expression levels of myeloperoxidase (MPO), citrullinated histone H3 (cit-H3), B-cell lymphoma 2 (Bcl-2), Bax, nuclear factor kappa B (NF-κB) p65 and phospho-NF-κB p65 (p-NF-κB p65) in rat renal tissues were detected by qRT-qPCR and Western blotting; the localization of NF-κB p65 expression in rat renal tissues was observed by immunofluorescence staining and the expression changes of NETs in rat renal tissues were detected by multiplex fluorescence immunohistochemical staining.

RESULTS

After hypoxia, the expression of NF-κB protein in renal tissues was significantly increased, the levels of SCr, BUN, cf-DNA and ROS in serum were significantly increased, the formation of NETs in renal tissues was significantly increased, and a large number of tubular dilatation and lymphocyte infiltration were observed in renal tissues. When PDTC was used to inhibit NF-κB activation, NETs formation in renal tissue was significantly decreased, the expression level of Bcl-2 in renal tissues was significantly increased, the expression level of Bax was significantly decreased, and renal injury was significantly alleviated.

CONCLUSION

HH induces the formation of NETs through the NF-κB signaling pathway, and it promotes apoptosis and aggravates renal injury by decreasing Bcl-2 and increasing Bax expression.

Circulating neutrophil extracellular trap (NET)-forming 'rogue' neutrophil subset, immunotype [DEspR + CD11b +], mediate multi-organ failure in COVID-19-an observational study

Background

Cumulative research show association of neutrophils and neutrophil extracellular traps (NETs) with poor outcomes in severe COVID-19. However, to date, there is no curative intent therapy able to block neutrophil/NETs-mediated progression of multi-organ dysfunction. Because of emerging neutrophil heterogeneity, the study of subsets of circulating NET-forming neutrophils [NET + Ns] as mediators of multi-organ failure progression among patients with COVID-19 is critical to identification of therapeutic targets.

Methods

We conducted a prospective observational study of circulating levels of CD11b + [NET + N] immunotyped for dual endothelin-1/signal peptide receptor (DEspR ±) expression by quantitative immunofluorescence-cytology and causal mediation analysis. In 36 consented adults hospitalized with mod-severe COVID-19, May to September 2020, we measured acute multi-organ failure via SOFA-scores and respiratory failure via SaO2/FiO2 (SF)-ratio at time points t1 (average 5.5 days from ICU/hospital admission) and t2 (the day before ICU-discharge or death), and ICU-free days at day28 (ICUFD). Circulating absolute neutrophil counts (ANC) and [NET + N] subset-specific counts were measured at t1. Spearman correlation and causal mediation analyses were conducted.

Results

Spearman correlation analyses showed correlations of t1-SOFA with t2-SOFA (rho r S  = 0.80) and ICUFD (r S  = -0.76); circulating DEspR + [NET + Ns] with t1-SOFA (r S  = 0.71), t2-SOFA (r S  = 0.62), and ICUFD (r S  = -0.63), and ANC with t1-SOFA (r S  = 0.71), and t2-SOFA (r S  = 0.61).Causal mediation analysis identified DEspR + [NET + Ns] as mediator of 44.1% [95% CI:16.5,110.6] of the causal path between t1-SOFA (exposure) and t2-SOFA (outcome), with 46.9% [15.8,124.6] eliminated when DEspR + [NET + Ns] were theoretically reduced to zero. Concordantly, DEspR + [NET + Ns] mediated 47.1% [22.0,72.3%] of the t1-SOFA to ICUFD causal path, with 51.1% [22.8,80.4%] eliminated if DEspR + [NET + Ns] were reduced to zero. In patients with t1-SOFA > 1, the indirect effect of a hypothetical treatment eliminating DEspR + [NET + Ns] projected a reduction of t2-SOFA by 0.98 [0.29,2.06] points and ICUFD by 3.0 [0.85,7.09] days. In contrast, there was no significant mediation of SF-ratio through DEspR + [NET + Ns], and no significant mediation of SOFA-score through ANC.

Conclusions

Despite equivalent correlations, DEspR + [NET + Ns], but not ANC, mediated progression of multi-organ failure in acute COVID-19, and its hypothetical reduction is projected to improve ICUFD. These translational findings warrant further studies of DEspR + [NET + Ns] as potential patient-stratifier and actionable therapeutic target for multi-organ failure in COVID-19.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41231-023-00143-x.

Blockade of neutrophil extracellular traps ameliorates toluene diisocyanate-induced steroid-resistant asthma

BACKGROUND AND PURPOSE

Toluene diisocyanate (TDI)-induced asthma is characterized by mixed inflammation dominated by neutrophils, and is refractory to steroid treatment. Neutrophil extracellular traps (NETs) play an important role in severe asthma, but their role in TDI-induced asthma models is unclear. This study focused on the role and mechanism of NETs in steroid-resistant TDI-induced asthma.

METHODS

Induced sputum was collected from 85 asthmatic patients and 25 healthy controls to detect eDNA. A murine TDI-induced asthma model was prepared, and asthmatic mice were given dexamethasone or DNase I. In vitro, the human bronchial epithelial cell line HBE was stimulated with NETs or TDI-human serum albumin (TDI-HSA).

RESULTS

Asthma patients had higher sputum eDNA compared to healthy subjects. In asthma patients, eDNA was positively correlated with sputum neutrophils, and negatively correlated with FEV1%predicted. Airway inflammation, airway reactivity, Th2 cytokine levels in lymph supernatant, and levels of NETs were significantly increased in the TDI-induced asthmatic mice. These increases were suppressed by DNase I, but not by dexamethasone. Inhibition of NETs improved interleukin (IL)-8 and MKP1 mRNA expression, and reduced phosphorylation of GR-S226 induced by TDI. Inhibition of NETs improved airway epithelial barrier disruption, as well as p38 and ERK signaling pathways in TDI-induced asthmatic mice. In vitro, NETs promoted the expression of IL-8 mRNA in HBE cells, and reduced the expression of MKP1. IL-8 elevation induced by NETs was suppressed by a p38 inhibitor or ERK inhibitor, but not by dexamethasone. Pretreatment with RAGE inhibitor reduced NETs induced p38/ERK phosphorylation and IL-8 levels in HBE cells.

CONCLUSION

Our data suggest that targeting NETs might effectively improved TDI-induced airway inflammation and airway epithelial barrier function. This may potentially be a treatment for patients with steroid-resistance asthma.

Immunothrombosis: Molecular Aspects and New Therapeutic Perspectives

Thromboinflammation or immunothrombosis is a concept that explains the existing link between coagulation and inflammatory response present in many situations, such as sepsis, venous thromboembolism, or COVID-19 associated coagulopathy. The purpose of this review is to provide an overview of the current data regarding the mechanisms involved in immunothrombosis in order to understand the new therapeutic strategies focused in reducing thrombotic risk by controlling the inflammation.

Novel perception of neutrophil extracellular traps in gouty inflammation

The self-limiting nature of the inflammatory flare is a feature of gout. The effects of neutrophil extracellular traps (NETs) on gout have remarkably attracted researchers' attention. Aggregated NETs promote the resolution of gouty inflammation by packing monosodium urate (MSU) crystals, degrading cytokines and chemokines, and blocking neutrophil recruitment and activation. Deficiency of NETs aggravates experimental gout. Thus, aggregated NETs are assumed to be a possible mechanism for the spontaneous resolution of gout. It is feasible to envisage therapeutic strategies for targeting NETosis (NET formation process) in gout. However, recent studies have demonstrated that levels of NETs are not associated with disease activity and inflammation in human gout. Moreover, the process of MSU crystal trapping is not affected in the absence of neutrophils. This review has concentrated on the mechanisms and associations between NETs and gout.

The coming of age of neutrophil extracellular traps in thrombosis: Where are we now and where are we headed?

Thrombosis remains a major problem in our society, manifesting across multiple demographic groups and with high associated morbidity and mortality. Thrombus development is the result of a complex mechanism in which multiple cell types and soluble factors play a crucial role. One cell that has gained the most attention in recent years is the neutrophil. This key member of the innate immune system can form neutrophil extracellular traps (NETs) in response to activating stimuli in circulation. NETs form a scaffold for thrombus formation, both initiating the process and stabilizing the final product. As the first responders of the host immune system, neutrophils have the flexibility to recognize a variety of molecules and can quickly interact with a range of different cell types. This trait makes them sensitive to exogenous stimuli. NET formation in response to pathogens is well established, leading to immune-mediated thrombus formation or immunothrombosis. NETs can also be formed during sterile inflammation through the activation of neutrophils by fellow immune cells including platelets, or activated endothelium. In chronic inflammatory settings, NETs can ultimately promote the development of tissue fibrosis, with organ failure as an end-stage outcome. In this review, we discuss the different pathways through which neutrophils can be activated toward NET formation and how these processes can result in a shared outcome: thrombus formation. Finally, we evaluate these different interactions and mechanisms for their potential as therapeutic targets, with neutrophil-targeted therapies providing a future approach to treating thrombosis. In contrast to current practices, such treatment could result in reduced pathogenic blood clot formation without increasing the risk of bleeding.

Rituximab induces a flare-up of activated neutrophil extracellular traps under in vitro conditions

Purpose: During neutrophil extracellular traps (NET) formation granulocytes release a decondensed chromatin web that is studded with antimicrobial proteins. These NET engulf and kill pathogens like bacteria and fungi. NET formation is part of the innate immune response but can also contribute to the aggravation of autoimmune diseases, thrombosis, and cancer metastasis. Anti-NET therapeutics to prevent potentially harmful consequences of excessive NET formation are warranted.Materials and methods: Therefore, we stimulated NET formation with ionomycin in the peripheral blood of 25 healthy individuals and quantified NET with flow cytometry and fluorescence microscopy after exposure to five different anti-inflammatory and cytostatic drugs. NET were identified by their expression of myeloperoxidase, citrullinated histone H3, and (extracellular) DNA release.Results: The preliminary in vitro drug screening indicated that acetylsalicylic acid (ASA) might suppress (-3.82%), and rituximab might enhance (+10.52%) NET formation. To consolidate the screening results, we quantified NET after exposure to rituximab and ASA in the blood of nine additional healthy subjects. Rituximab showed a significant increased NET formation compared to the neutrophils treated with ASA (a mean of differences 3.96%; 95% CI 1.90-6.03%; p < .01) or compared to neutrophils without treatment (a mean of differences 4.39%; 95% CI 1.17-7.61%; p = .01). Contrary to the screening results ASA showed no significant suppression of NET formation in the consolidation experiments (a mean of differences 0.43%; 95% CI -1.27 to 2.12%; p = .58).Conclusions: We conclude that rituximab therapy might further trigger activated NET formation and should be applied with caution in patients with pro-inflammatory state and underlying autoimmune disease, thrombosis, or cancer.

Neutrophils as emerging protagonists and targets in chronic inflammatory diseases

INTRODUCTION

Neutrophils are the key cells of our innate immune system with a primary role in host defense. They rapidly arrive at the site of infection and display a range of effector functions including phagocytosis, degranulation, and NETosis to eliminate the invading pathogens. However, in recent years, studies focusing on neutrophil biology have revealed the highly adaptable nature and versatile functions of these cells which extend beyond host defense. Neutrophils are now referred to as powerful mediators of chronic inflammation. In several chronic inflammatory diseases, their untoward actions, such as immense infiltration, hyper-activation, dysregulation of effector functions, and extended survival, eventually contribute to disease pathogenesis. Therefore, a better understanding of neutrophils and their effector functions in prevalent chronic diseases will not only shed light on their role in disease pathogenesis but will also reveal them as novel therapeutic targets.

METHODS

We performed a computer-based online search using the databases, PubMed.gov and Clinical trials.gov for published research and review articles.

RESULTS AND CONCLUSIONS

This review provides an assessment of neutrophils and their crucial involvement in various chronic inflammatory disorders ranging from respiratory, neurodegenerative, autoimmune, and cardiovascular diseases. In addition, we also discuss the therapeutic approach for targeting neutrophils in disease settings that will pave the way forward for future research.

Selinexor, a selective inhibitor of nuclear export, inhibits human neutrophil extracellular trap formation in vitro

Neutrophils are central players in the innate immune system. To protect against invading pathogens, neutrophils can externalize chromatin to create neutrophil extracellular traps (NETs). While NETs are critical to host defense, they also have deleterious effects, and dysregulation of NETs formation has been implicated in autoimmune diseases, atherosclerosis and thrombotic conditions, cancer progression and dissemination, and acute respiratory distress syndrome. Here, we report that selinexor, a first-in-class selective inhibitor of nuclear export approved for the treatment of multiple myeloma and diffuse large B-cell lymphoma, markedly suppressed the release of NETs in vitro. Furthermore, we demonstrate a significant inhibitory effect of selinexor on NETs formation, but not on oxidative burst or enzymatic activities central to NETs release such as neutrophil elastase, myeloperoxidase or peptidyl arginine deiminase type IV. The inhibitory effect of selinexor was demonstrated in neutrophils activated by a variety of NETs-inducers, including PMA, TGF-β, TNF-α and IL-8. Maximal inhibition of NETs formation was observed using TGF-β, for which selinexor inhibited NETs release by 61.6%. These findings pave the way to the potential use of selinexor in an effort to reduce disease burden by inhibition of NETs.

Targeted delivery of an anti-inflammatory corticosteroid to Ly6C/G-positive cells abates severity of influenza A symptoms

The distribution of Ly6C/G-positive cells in response to an infection of the mouse respiratory tract with influenza A virus was followed noninvasively over time by immuno-positron emission tomography. We converted nanobodies that recognize Ly6C and Ly6G, markers of neutrophils and other myeloid cells, as well as an influenza hemagglutinin-specific nanobody, into ⁸⁹Zr-labeled PEGylated positron emission tomography (PET) imaging agents. The PET images showed strong accumulation of these imaging agents in the lungs of infected mice. Immunohistochemistry of influenza virus-infected mice and control mice, injected with a biotinylated and PEGylated version of the Ly6C/G-specific nanobody, showed the presence of abundant Ly6C/G-positive myeloid cells and positivity for Ly6C/G on bronchial epithelium in influenza virus-infected mice. This is consistent with focal inflammation in the lungs, a finding that correlated well with the immuno-PET results. No such signals were detected in control mice. Having shown by PET the accumulation of the Ly6C/G-specific nanobody in infected lungs, we synthesized conjugates of Ly6C/G-specific nanobodies with dexamethasone to enable targeted delivery of this immunosuppressive corticosteroid to sites of inflammation. Such conjugates reduced the weight loss that accompanies infection, while the equivalent amount of free dexamethasone was without effect. Nanobody-drug conjugates thus enable delivery of drugs to particular cell types at the appropriate anatomic site(s). By avoiding systemic exposure to free dexamethasone, this strategy minimizes its undesirable side effects because of the much lower effective dose of the nanobody-dexamethasone conjugate. The ability to selectively target inflammatory cells may find application in the treatment of other infections or other immune-mediated diseases.

Bibliometric and visual analysis of neutrophil extracellular traps from 2004 to 2022

Background

Neutrophil extracellular traps (NETs) are specialized structures formed by neutrophils that were initially found to be important in killing pathogenic bacteria during infection. With the development of related research, the relationship between NETs and diseases such as sepsis, cancer, and systemic lupus erythematosus has received close attention. However, there is a lack of reports that comprehensively and objectively present the current status of NETs-related studies. Therefore, this study aims to visually analyze the current status and trends of NETs-related research by means of bibliometrics and knowledge mapping.

Methods

NETs-related articles and reviews were retrieved using the Web of Science core collection subject search, and bibliometric analysis was performed in Excel 365, CiteSpace, VOSviewer, and Bibliometrix (R-Tool of R-Studio).

Results

A total of 4866 publications from 2004 to 2022 were included in the bibliometric analysis. The number of publications shows an increasing trend from year to year. Collaborative network analysis shows that the United States and Germany are the most influential countries in this field, with the highest number of publications and citations. The journal with the most publications is Frontiers in Immunology. Brinkmann Volker is an authoritative author in this field, and his publication "Neutrophil extracellular traps kill bacteria" is the most frequently cited. The literature and keyword analysis shows that the relationship between NETs and diseases (hematological diseases, sepsis, cancer, etc.) and cell death (apoptosis, necroptosis, pyroptosis, etc.) is a popular research topic. Currently, NETs and SARS-CoV-2-related studies are at the forefront of the field.

Conclusion

This study is the first to visualize the research in NETs-related fields using bibliometric methods, revealing the trends and frontiers of NETs research. This study will provide valuable references for scholars to find research focus questions and partners.

Neutrophil Activated by the Famous and Potent PMA (Phorbol Myristate Acetate)

This review will briefly outline the major signaling pathways in PMA-activated neutrophils. PMA is widely used to understand neutrophil pathways and formation of NETs. PMA activates PKC; however, we highlight some isoforms that contribute to specific functions. PKC α, β and δ contribute to ROS production while PKC βII and PKC ζ are involved in cytoskeleton remodeling. Actin polymerization is important for the chemotaxis of neutrophils and its remodeling is connected to ROS balance. We suggest that, although ROS and production of NETs are usually observed together in PMA-activated neutrophils, there might be a regulatory mechanism balancing both. Interestingly, we suggest that serine proteases might determine the PAD4 action. PAD4 could be responsible for the activation of the NF-κB pathway that leads to IL-1β release, triggering the cleavage of gasdermin D by serine proteases such as elastase, leading to pore formation contributing to release of NETs. On the other hand, when serine proteases are inhibited, NETs are formed by citrullination through the PAD4 pathway. This review puts together results from the last 31 years of research on the effects of PMA on the neutrophil and proposes new insights on their interpretation.

Neutrophil extracellular traps facilitate cancer metastasis: cellular mechanisms and therapeutic strategies

Background

The formation of neutrophil extracellular traps (NETs) was initially discovered as a novel immune response against pathogens. Recent studies have also suggested that NETs play an important role in tumor progression. This review summarizes the cellular mechanisms by which NETs promote distant metastasis and discusses the possible clinical applications targeting NETs.

Method

The relevant literature from PubMed and Google Scholar (2001–2021) have been reviewed for this article.

Results

The presence of NETs has been detected in various primary tumors and metastatic sites. NET-associated interactions have been observed throughout the different stages of metastasis, including initial tumor cell detachment, intravasation and extravasation, the survival of circulating tumor cells, the settlement and the growth of metastatic tumor cells. Several in vitro and in vivo studies proved that inhibiting NET formation resulted in anti-cancer effects. The biosafety and efficacy of some NET inhibitors have also been demonstrated in early phase clinical trials.

Conclusions

Considering the role of NETs in tumor progression, NETs could be a promising diagnostic and therapeutic target for cancer management. However, current evidence is mostly derived from experimental models and as such more clinical studies are still needed to verify the clinical significance of NETs in oncological settings.

Extracellular traps and the role in thrombosis

Thrombotic complications pose serious health risks worldwide. A significant change in our understanding of the pathophysiology of thrombosis has occurred since the discovery of extracellular traps (ETs) and their prothrombotic properties. As a result of immune cells decondensing chromatin into extracellular fibers, ETs promote thrombus formation by acting as a scaffold that activates platelets and coagulates them. The involvement of ETs in thrombosis has been reported in various thrombotic conditions including deep vein thrombosis (DVT), pulmonary emboli, acute myocardial infarction, aucte ischemic stroke, and abdominal aortic aneurysms. This review summarizes the existing evidence of ETs in human and animal model thrombi. The authors described studies showing the existence of ETs in venous or arterial thrombi. In addition, we studied potential novel therapeutic opportunities related to the resolution or prevention of thrombosis by targeting ETs.

The phytoactive constituents of Eugenia selloi B.D. Jacks (pitangatuba): Toxicity and elucidation of their anti-inflammatory mechanism(s) of action

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Purified subfraction from Eugenia selloi fruit, showed anti-inflammatory activity.

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It were identified isomers of quercetrin, vanillic acid, and coumaric acid.

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S8 reduced NF-κB, IL-1β, IL-6, IL-10, MDC and MCP-1 levels in macrophages.

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S8 reduced neutrophil migration and ICAM-1 expression in mice.

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S8 showed scavenging capacity against ROO^•, HOCl and NO^• biological radicals.

We determined the phytochemical composition, anti-inflammatory mechanism of action, ROS/RNS scavenging capacity and systemic toxicity of a purified subfraction (S8) of Eugenia selloi. The composition of S8 was assessed by LC-ESI-QTOF-MS; the anti-inflammatory activity in RAW264.7 macrophages through NF-κB activation and biomarkers by multiplex in THP-1 cells; neutrophil migration, intravital microscopy and ICAM-1 expression in mice; NETs formation and CD11b expression; S8 scavenging capacity of ROS/RNS; toxicity in Galleria mellonella larvae model. Coumaric acid, quercetrin and vanillic acid were identified. S8 decreased NF-κB activation, IL-1β, IL-6, IL-10, MDC and MCP-1 levels, reduced neutrophil migration and ICAM-1 expression in mice; S8 did not interfere NET formation and CD11b expression, exhibited high antioxidant and showed negligible toxicity. E. selloi proved to be a promising, yet underexplored source of bioactive compounds, which can be useful employed in agribusiness and in the pharmaceutical and food industry to develop new products or human health supplies.

The Fatal Circle of NETs and NET-Associated DAMPs Contributing to Organ Dysfunction

The innate immune system is the first line of defense against invading pathogens or sterile injuries. Pattern recognition receptors (PRR) sense molecules released from inflamed or damaged cells, or foreign molecules resulting from invading pathogens. PRRs can in turn induce inflammatory responses, comprising the generation of cytokines or chemokines, which further induce immune cell recruitment. Neutrophils represent an essential factor in the early immune response and fulfill numerous tasks to fight infection or heal injuries. The release of neutrophil extracellular traps (NETs) is part of it and was originally attributed to the capture and elimination of pathogens. In the last decade studies revealed a detrimental role of NETs during several diseases, often correlated with an exaggerated immune response. Overwhelming inflammation in single organs can induce remote organ damage, thereby further perpetuating release of inflammatory molecules. Here, we review recent findings regarding damage-associated molecular patterns (DAMPs) which are able to induce NET formation, as well as NET components known to act as DAMPs, generating a putative fatal circle of inflammation contributing to organ damage and sequentially occurring remote organ injury.

Association between plaque vulnerability and neutrophil extracellular traps (NETs) levels: The Plaque At RISK study

Carotid atherosclerotic plaque rupture and its sequelae are among the leading causes of acute ischemic stroke. The risk of rupture and subsequent thrombosis is, among others, determined by vulnerable plaque characteristics and linked to activation of the immune system, in which neutrophil extracellular traps (NETs) potentially play a role. The aim of this study was to investigate how plaque vulnerability is associated with NETs levels. We included 182 patients from the Plaque At RISK (PARISK) study in whom carotid imaging was performed to measure plaque ulceration, fibrous cap integrity, intraplaque hemorrhage, lipid-rich necrotic core, calcifications and plaque volume. Principal component analysis generated a ‘vulnerability index’ comprising all plaque characteristics. Levels of the NETs marker myeloperoxidase-DNA complex were measured in patient plasma. The association between the vulnerability index and low or high NETs levels (dependent variable) was assessed by logistic regression. No significant association between the vulnerability index and NETs levels was detected in the total population (odds ratio 1.28, 95% confidence interval 0.90–1.83, p = 0.18). However, in the subgroup of patients naive to statins or antithrombotic medication prior to the index event, this association was statistically significant (odds ratio 2.08, 95% confidence interval 1.04–4.17, p = 0.04). Further analyses revealed that this positive association was mainly driven by intraplaque hemorrhage, lipid-rich necrotic core and ulceration. In conclusion, plaque vulnerability is positively associated with plasma levels of NETs, but only in patients naive to statins or antithrombotic medication prior to the index event.

Endothelial Dysfunction Induced by Extracellular Neutrophil Traps Plays Important Role in the Occurrence and Treatment of Extracellular Neutrophil Traps-Related Disease

Many articles have demonstrated that extracellular neutrophil traps (NETs) are often described as part of the antibacterial function. However, since the components of NETs are non-specific, excessive NETs usually cause inflammation and tissue damage. Endothelial dysfunction (ED) caused by NETs is the major focus of tissue damage, which is highly related to many inflammatory diseases. Therefore, this review summarizes the latest advances in the primary and secondary mechanisms between NETs and ED regarding inflammation as a mediator. Moreover, the detailed molecular mechanisms with emphasis on the disadvantages from NETs are elaborated: NETs can use its own enzymes, release particles as damage-associated molecular patterns (DAMPs) and activate the complement system to interact with endothelial cells (ECs), drive ECs damage and eventually aggravate inflammation. In view of the role of NETs-induced ED in different diseases, we also discussed possible molecular mechanisms and the treatments of NETs-related diseases.

Extracellular DNA Traps: Origin, Function and Implications for Anti-Cancer Therapies

Extracellular DNA may serve as marker in liquid biopsies to determine individual diagnosis and prognosis in cancer patients. Cell death or active release from various cell types, including immune cells can result in the release of DNA into the extracellular milieu. Neutrophils are important components of the innate immune system, controlling pathogens through phagocytosis and/or the release of neutrophil extracellular traps (NETs). NETs also promote tumor progression and metastasis, by modulating angiogenesis, anti-tumor immunity, blood clotting and inflammation and providing a supportive niche for metastasizing cancer cells. Besides neutrophils, other immune cells such as eosinophils, dendritic cells, monocytes/macrophages, mast cells, basophils and lymphocytes can also form extracellular traps (ETs) during cancer progression, indicating possible multiple origins of extracellular DNA in cancer. In this review, we summarize the pathomechanisms of ET formation generated by different cell types, and analyze these processes in the context of cancer. We also critically discuss potential ET-inhibiting agents, which may open new therapeutic strategies for cancer prevention and treatment.

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

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

Neutrophil-Mediated Immunopathology and Matrix Metalloproteinases in Central Nervous System - Tuberculosis

Tuberculosis (TB) remains one of the leading infectious killers in the world, infecting approximately a quarter of the world’s population with the causative organism Mycobacterium tuberculosis (M. tb). Central nervous system tuberculosis (CNS-TB) is the most severe form of TB, with high mortality and residual neurological sequelae even with effective TB treatment. In CNS-TB, recruited neutrophils infiltrate into the brain to carry out its antimicrobial functions of degranulation, phagocytosis and NETosis. However, neutrophils also mediate inflammation, tissue destruction and immunopathology in the CNS. Neutrophils release key mediators including matrix metalloproteinase (MMPs) which degrade brain extracellular matrix (ECM), tumor necrosis factor (TNF)-α which may drive inflammation, reactive oxygen species (ROS) that drive cellular necrosis and neutrophil extracellular traps (NETs), interacting with platelets to form thrombi that may lead to ischemic stroke. Host-directed therapies (HDTs) targeting these key mediators are potentially exciting, but currently remain of unproven effectiveness. This article reviews the key role of neutrophils and neutrophil-derived mediators in driving CNS-TB immunopathology.

Neutrophil Extracellular Traps (NETs) and Covid-19: A new frontiers for therapeutic modality

Coronavirus disease 2019 (Covid-19) is a worldwide infectious disease caused by severe acute respiratory coronavirus 2 (SARS-CoV-2). In severe SARS-CoV-2 infection, there is severe inflammatory reactions due to neutrophil recruitments and infiltration in the different organs with the formation of neutrophil extracellular traps (NETs), which involved various complications of SARS-CoV-2 infection. Therefore, the objective of the present review was to explore the potential role of NETs in the pathogenesis of SARS-CoV-2 infection and to identify the targeting drugs against NETs in Covid-19 patients. Different enzyme types are involved in the formation of NETs, such as neutrophil elastase (NE), which degrades nuclear protein and release histones, peptidyl arginine deiminase type 4 (PADA4), which releases chromosomal DNA and gasdermin D, which creates pores in the NTs cell membrane that facilitating expulsion of NT contents. Despite of the beneficial effects of NETs in controlling of invading pathogens, sustained formations of NETs during respiratory viral infections are associated with collateral tissue injury. Excessive development of NETs in SARS-CoV-2 infection is linked with the development of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) due to creation of the NETs-IL-1β loop. Also, aberrant NTs activation alone or through NETs formation may augment SARS-CoV-2-induced cytokine storm (CS) and macrophage activation syndrome (MAS) in patients with severe Covid-19. Furthermore, NETs formation in SARS-CoV-2 infection is associated with immuno-thrombosis and the development of ALI/ARDS. Therefore, anti-NETs therapy of natural or synthetic sources may mitigate SARS-CoV-2 infection-induced exaggerated immune response, hyperinflammation, immuno-thrombosis, and other complications.

Dexamethasone, but Not Vitamin D or A, Dampens the Inflammatory Neutrophil Response to Protect At-risk COVID-19 Patients

Dexamethasone (DEX) was the first drug shown to save lives of critically ill coronavirus disease 2019 (COVID-19) patients suffering from respiratory distress. A hyperactivated state of neutrophils was found in COVID-19 patients compared to non-COVID pneumonia cases. Given the beneficial effects of DEX in COVID-19 patients, we investigated the effects of DEX and of other immunomodulatory drugs vitamin D3 (VD3) and retinoic acid (RA) on neutrophil function. DEX, but not VD3 or RA, significantly inhibited all tested aspects of neutrophil function, e.g., degranulation, intracellular ROS production, CXCL8 release and NETosis. Interestingly, RA displayed the opposite effect by significantly increasing both CXCL8 and NET release by neutrophils. Taken together, these data suggest that the lower COVID-19 mortality in DEX-treated patients may in part be due to the dampening effect of DEX on the inflammatory neutrophil response, which could prevent neutrophil plugs with NETS in the lungs and other inflamed organs of patients.

Aspirin as an Adjunctive Pharmacologic Therapy Option for COVID-19: Anti-Inflammatory, Antithrombotic, and Antiviral Effects All in One Agent

Introduction

Pharmacologic therapy options for COVID-19 should include antiviral, anti-inflammatory, and anticoagulant agents. With the limited effectiveness, currently available virus-directed therapies may have a substantial impact on global health due to continued reports of mutant variants affecting repeated waves of COVID-19 around the world.

Methods

We searched articles pertaining to aspirin, COVID-19, acute lung injury and pharmacology in PubMed and provide a comprehensive appraisal of potential use of aspirin in the management of patients with COVID-19. The scope of this article is to provide an overview of the rationale and currently available clinical evidence that supports aspirin as an effective therapeutic option in COVID-19.

Results

Experimental and clinical evidence are available for the potential use of aspirin in patients with COVID-19.

Discussion

Aspirin targets the intracellular signaling pathway that is essential for viral replication, and resultant inflammatory responses, hypercoagulability, and platelet activation. With these multiple benefits, aspirin can be a credible adjunctive therapeutic option for the treatment of COVID-19. In addition, inhaled formulation with its rapid effects may enhance direct delivery to the lung, which is the key organ damaged in COVID-19 during the critical initial course of the disease, whereas the 150-325 mg/day can be used for long-term treatment to prevent thrombotic event occurrences. Being economical and widely available, aspirin can be exploited globally, particularly in underserved communities and remote areas of the world to combat the ongoing COVID-19 pandemic.

A Review of Neutrophil Extracellular Traps (NETs) in Disease: Potential Anti-NETs Therapeutics

Activated neutrophils release neutrophil extracellular traps (NETs) in response to a variety of stimuli. NETosis is driven by protein-arginine deiminase type 4, with the release of intracellular granule components that function by capturing and destroying microbes, including viral, fungal, bacterial, and protozoal pathogens. The positive effects of pathogen control are countered by pro-inflammatory effects as demonstrated in a variety of diseases. Components of NETS are non-specific, and other than controlling microbes, they cause injury to surrounding tissue by themselves or by increasing the pro-inflammatory response. NETs can play a role in enhancement of the inflammation seen in autoimmune diseases including psoriasis, rheumatoid arthritis, and systemic lupus erythematosis. In addition, autoinflammatory diseases such as gout have been associated with NETosis. Inhibition of NETs may decrease the severity of many diseases improving survival. Herein, we describe NETosis in different diseases focusing on the detrimental effect of NETs and outline possible therapeutics that can be used to mitigate netosis. There is a need for more studies and clinical trials on these and other compounds that could prevent or destroy NETs, thereby decreasing damage to patients.

The cytokine storms of COVID-19, H1N1 influenza, CRS and MAS compared. Can one sized treatment fit all?

An analysis of published data appertaining to the cytokine storms of COVID-19, H1N1 influenza, cytokine release syndrome (CRS), and macrophage activation syndrome (MAS) reveals many common immunological and biochemical abnormalities. These include evidence of a hyperactive coagulation system with elevated D-dimer and ferritin levels, disseminated intravascular coagulopathy (DIC) and microthrombi coupled with an activated and highly permeable vascular endothelium. Common immune abnormalities include progressive hypercytokinemia with elevated levels of TNF-α, interleukin (IL)-6, and IL-1β, proinflammatory chemokines, activated macrophages and increased levels of nuclear factor kappa beta (NFκB). Inflammasome activation and release of damage associated molecular patterns (DAMPs) is common to COVID-19, H1N1, and MAS but does not appear to be a feature of CRS. Elevated levels of IL-18 are detected in patients with COVID-19 and MAS but have not been reported in patients with H1N1 influenza and CRS. Elevated interferon-γ is common to H1N1, MAS, and CRS but levels of this molecule appear to be depressed in patients with COVID-19. CD4+ T, CD8+ and NK lymphocytes are involved in the pathophysiology of CRS, MAS, and possibly H1N1 but are reduced in number and dysfunctional in COVID-19. Additional elements underpinning the pathophysiology of cytokine storms include Inflammasome activity and DAMPs. Treatment with anakinra may theoretically offer an avenue to positively manipulate the range of biochemical and immune abnormalities reported in COVID-19 and thought to underpin the pathophysiology of cytokine storms beyond those manipulated via the use of, canakinumab, Jak inhibitors or tocilizumab. Thus, despite the relative success of tocilizumab in reducing mortality in COVID-19 patients already on dexamethasone and promising results with Baricitinib, the combination of anakinra in combination with dexamethasone offers the theoretical prospect of further improvements in patient survival. However, there is currently an absence of trial of evidence in favour or contravening this proposition. Accordingly, a large well powered blinded prospective randomised controlled trial (RCT) to test this hypothesis is recommended.

A Fragile Balance: Does Neutrophil Extracellular Trap Formation Drive Pulmonary Disease Progression?

Neutrophils act as the first line of defense during infection and inflammation. Once activated, they are able to fulfil numerous tasks to fight inflammatory insults while keeping a balanced immune response. Besides well-known functions, such as phagocytosis and degranulation, neutrophils are also able to release "neutrophil extracellular traps" (NETs). In response to most stimuli, the neutrophils release decondensed chromatin in a NADPH oxidase-dependent manner decorated with histones and granule proteins, such as neutrophil elastase, myeloperoxidase, and cathelicidins. Although primarily supposed to prevent microbial dissemination and fight infections, there is increasing evidence that an overwhelming NET response correlates with poor outcome in many diseases. Lung-related diseases especially, such as bacterial pneumonia, cystic fibrosis, chronic obstructive pulmonary disease, aspergillosis, influenza, and COVID-19, are often affected by massive NET formation. Highly vascularized areas as in the lung are susceptible to immunothrombotic events promoted by chromatin fibers. Keeping this fragile equilibrium seems to be the key for an appropriate immune response. Therapies targeting dysregulated NET formation might positively influence many disease progressions. This review highlights recent findings on the pathophysiological influence of NET formation in different bacterial, viral, and non-infectious lung diseases and summarizes medical treatment strategies.

A Review of the Neutrophil Extracellular Traps (NETs) from Cow, Sheep and Goat Models

This review provides insight into the importance of understanding NETosis in cows, sheep, and goats in light of the importance to their health, welfare and use as animal models. Neutrophils are essential to innate immunity, pathogen infection, and inflammatory diseases. The relevance of NETosis as a conserved innate immune response mechanism and the translational implications for public health are presented. Increased understanding of NETosis in ruminants will contribute to the prediction of pathologies and design of strategic interventions targeting NETs. This will help to control pathogens such as coronaviruses and inflammatory diseases such as mastitis that impact all mammals, including humans. Definition of unique attributes of NETosis in ruminants, in comparison to what has been observed in humans, has significant translational implications for one health and global food security, and thus warrants further study.

Methylprednisolone Induces Extracellular Trap Formation and Enhances Bactericidal Effect of Canine Neutrophils

Methylprednisolone is a glucocorticoid and can negatively influence immune defense mechanisms. During bacterial infections in the dog, neutrophils infiltrate infected tissue and mediate antimicrobial effects with different mechanisms such as phagocytosis and neutrophil extracellular trap (NET) formation. Here, we investigated the influence of methylprednisolone on canine NET formation and neutrophil killing efficiency of Gram positive and Gram negative bacteria. Therefore, canine blood derived neutrophils were treated with different concentrations of methylprednisolone over time. The survival factor of Staphylococcus pseudintermedius, Streptococcus canis or Escherichia coli was determined in presence of stimulated neutrophils. Additionally, free DNA and nucleosomes as NET marker were analyzed in supernatants and neutrophils were assessed for NET formation by immunofluorescence microscopy. Methylprednisolone concentrations of 62.5 and 625 µg/mL enhanced the neutrophil killing of Gram positive bacteria, whereas no significant influence was detected for the Gram negative Escherichia coli. Interestingly, higher amounts of free DNA were detected under methylprednisolone stimulation in a concentration dependency and in the presence of Streptococcus canis and Escherichia coli. The nucleosome release by neutrophils is induced by bacterial infection and differs depending on the concentration of methylprednisolone. Furthermore, immunofluorescence microscopy analysis identified methylprednisolone at a concentration of 62.5 µg/mL as a NET inducer. In summary, methylprednisolone enhances NET-formation and time-dependent and concentration-dependent the bactericidal effect of canine neutrophils on Gram positive bacteria.

Cardiovascular Diseases: Consider Netosis

Neutrophil extracellular traps (NETs) are net-like chromatin fibers that are released from dying neutrophils during infections. NETs are a sort of scaffold, ideal to retain microbes. The main function of NETs is the trapping and killing pathogens, as such as bacteria, fungi, viruses (including SARS-CoV-2) and protozoa. The death of neutrophils via NETs formation is called "NETosis." Nevertheless, recent studies suggest that NETosis is involved in several diseases, other than infections. Very recently, it has been shown that NETs formation contributes to venous thromboembolism but also to atherosclerosis progression, creating a link between venous and arterial thrombosis. The presence of NETs in the luminal portion of human atherosclerotic vessels and coronary specimens obtained from patients after acute myocardial infarction has been detected. This review provides evidence of the most important updates about the role of NETs in myocardial infarction, in heart failure and in the process of atherosclerosis itself. The prognostic significance of NETs-related markers in cardiovascular diseases will be discussed, in order to assess targeted therapeutic strategies.

Raised sputum extracellular DNA confers lung function impairment and poor symptom control in an exacerbation-susceptible phenotype of neutrophilic asthma

Background

Extracellular DNA (e-DNA) and neutrophil extracellular traps (NETs) are linked to asthmatics airway inflammation. However, data demonstrating the characterization of airway inflammation associated with excessive e-DNA production and its impact on asthma outcomes are limited.

Objective

To characterize the airway inflammation associated with excessive e-DNA production and its association with asthma control, severe exacerbations and pulmonary function, particularly, air trapping and small airway dysfunction.

Methods

We measured e-DNA concentrations in induced sputum from 134 asthma patients and 28 healthy controls. We studied the correlation of e-DNA concentrations with sputum neutrophils, eosinophils and macrophages and the fractional exhaled nitric oxide (FeNO). Lung function was evaluated using spirometry, body plethysmography, impulse oscillometry and inert gas multiple breath washout. We stratified patients with asthma into low-DNA and high-DNA to compare lung function impairments and asthma outcomes.

Results

Patients with severe asthma had higher e-DNA concentration (54.2 ± 42.4 ng/µl) than patients with mild-moderate asthma (41.0 ± 44.1 ng/µl) or healthy controls (26.1 ± 16.5 ng/µl), (all p values < 0.05). E-DNA concentrations correlated directly with sputum neutrophils (R = 0.49, p < 0.0001) and negatively with sputum macrophages (R = − 0.36, p < 0.0001), but neither with sputum eosinophils (R = 0.10, p = 0.26), nor with FeNO (R = − 0.10, p = 0.22). We found that 29% of asthma patients (n = 39) had high e-DNA concentrations above the upper 95th percentile value in healthy controls (55.6 ng /μl). High-DNA was associated with broad lung function impairments including: airflow obstruction of the large (FEV₁) and small airways (FEF50%, FEF25–75), increased air trapping (RV, RV/TLC), increased small airway resistance (R5-20, sReff), decreased lung elasticity (X5Hz) and increased ventilation heterogeneity (LCI), (all P values < 0.05). We also found that high e-DNA was associated with nearly three-fold greater risk of severe exacerbations (OR 2·93 [95% CI 1.2–7.5]; p = 0·012), worse asthma control test (p = 0.03), worse asthma control questionnaire scores (p = 0.01) and higher doses of inhaled corticosteroids (p = 0.026).

Conclusion

Increased production of extracellular DNA in the airway characterizes a subset of neutrophilic asthma patients who have broad lung function impairments, poor symptom control and increased risk of severe exacerbations.

A Synergy Between Endotoxin and (1→3)-Beta-D-Glucan Enhanced Neutrophil Extracellular Traps in Candida Administered Dextran Sulfate Solution Induced Colitis in FcGRIIB-/- Lupus Mice, an Impact of Intestinal Fungi in Lupus

Introduction

The translocation of organismal molecules from gut into blood circulation might worsen the disease severity of lupus through the induction of neutrophil extracellular traps (NETs).

Methods

An impact of lipopolysaccharide (LPS) and (1→3)-β-D-glucan (BG), components of gut bacteria and fungi, respectively, on NETs formation, was explored in lupus models, Fc gamma receptor IIB deficiency (FcGRIIB-/-) and Pristane injection, using Candida-administered dextran sulfate solution induced colitis (Candida-DSS) model.

Results

Severity of Candida-DSS in FcGRIIB-/- mice was more prominent than wild-type (WT) and Pristane mice as indicated by (i) colonic NETs using immunofluorescence of Ly6G, myeloperoxidase (MPO) and neutrophil elastase (NE) together with expression of PAD4 and IL-1β, (ii) colonic immunoglobulin (Ig) deposition (immunofluorescence), (iii) gut-leakage by FITC-dextran assay, endotoxemia and serum BG, (iv) systemic inflammation (neutrophilia, serum cytokines, serum dsDNA and anti-dsDNA) and (v) renal injury (proteinuria, glomerular NETs and Ig deposition).

Discussion

The formation of NETs in Candida-DSS mice was more severe than non-Candida-DSS mice and NETs in Candida-DSS were more profound in FcGRIIB-/- mice than Pristane mice. Prominent NETs in Candida-DSS FcGRIIB-/- mice might be due to the profound responses against LPS+BG in FcGRIIB-/- neutrophils compared with WT cells. These data implied an impact of the inhibitory FcGRIIB in NETs formation and an influence of gut fungi in lupus exacerbation. Hence, gut fungi in a DSS-induced gut-leakage lupus model enhanced colonic NETs that facilitated gut translocation of organismal molecules and synergistically exacerbated lupus activity.

Neutrophil Extracellular Traps: Inflammation and Biomaterial Preconditioning for Tissue Engineering

Tissue injury initiates a tissue repair program, characterized by acute inflammation and recruitment of immune cells, dominated by neutrophils. Neutrophils prevent infection in the injured tissue through multiple effector functions, including the production of reactive oxygen species, the release of granules, the phagocytosis of invaders, and the extrusion of neutrophil extracellular traps (NETs). However, these canonical protective mechanisms can also have detrimental effects both in the context of infection and in response to sterile injuries. Of particular interest to biomaterials and tissue engineering is the release of NETs, which are extracellular structures composed of decondensed chromatin and various toxic nuclear and granular components. These structures and their dysregulated release can cause collateral tissue damage, uncontrolled inflammation, and fibrosis and prevent the neutrophil from exerting its prohealing functions. This review discusses our knowledge of NETs, including their composition and morphology, signaling pathways, inhibitors, and contribution to inflammatory pathologies, as well as their role in the resolution of inflammation. In addition, we summarize what is known about the release of NETs as a preconditioning event in the response to biomaterials and highlight future considerations to target the neutrophil response and enhance biomaterial-guided tissue repair and regeneration. Impact statement Neutrophil extracellular trap (NET) release is an active process programmed into the neutrophil's molecular machinery to prevent infection. However, the release of NETs on biomaterials appears to be a significant preconditioning event that influences the potential for tissue healing with largely detrimental consequences. Given their contribution to inflammatory pathologies, this review highlights the role of NETs in the response to biomaterials. Together, the studies discussed in this review suggest that biomaterials should be designed to regulate NET release to avoid maladaptive immune responses and improve the therapeutic potential of tissue-engineered biomaterials and their applications in the clinical setting.

Pathogenesis of cardiovascular events in BCR-ABL1-negative myeloproliferative neoplasms

Thrombosis, both in arterial and venous territories, is the major complication of myeloproliferative neoplasms and is responsible for a high rate of morbidity and mortality. The currently accepted risk factors are an age over 60 years and a history of thrombosis. However, many complex mechanisms contribute to this increased prothrombotic risk, with involvement of all blood cell types, plasmatic factors, and endothelial cells. Besides, some cardiovascular events may originate from arterial vasospasm that could contribute to thrombotic complications. In this review, we discuss recent results obtained in mouse models in the light of data obtained from clinical studies. We emphasize on actors of thrombosis that are currently not targeted with current therapeutics but could be promising targets, i.e, neutrophil extracellular traps and vascular reactivity.

[Neutrophil extracellular traps in the pathogenesis of chronic rhinosinusitis]

The review presents the current understanding of the pathogenesis of chronic rhinosinusitis. The causes of damage to the mucous membrane of the paranasal sinuses are most often the result of a combination of immunological, infectious and anatomical factors. This indicates the need for a multidisciplinary approach to the study of the pathogenesis of this pathology. There is no single universally recognized classification of chronic rhinosinusitis, which takes into account histological and immunological changes in the mucous membrane of the paranasal sinuses. The discovery of the mechanism of completion of the life cycle of neutrophils - the formation of a neutrophil extracellular trap or NETosis, different from necrosis and apoptosis, opened up new prospects in the study of the pathogenesis of inflammatory processes, including rhinosinusitis. Neutrophil extracellular traps reduce the permeability of the epithelial barrier in the mucous membrane of the paranasal sinuses. This determines their possible role in the etiopathogenesis of rhinosinusitis. In recent years, more and more attention has been paid to the feasibility, effectiveness and safety of therapy that affects the immune component of the inflammatory process, including NETosis. The data obtained in the study of extracellular traps can be used in clinical practice. It is neutrophil extracellular traps that can become a potential target in the treatment of patients with chronic rhinosinusitis.

Neutrophils in respiratory syncytial virus infection: From harmful effects to therapeutic opportunities

Respiratory syncytial virus (RSV) is an important infectious agent in infants and young children. In most cases, RSV infection only causes mild disease, but in some, it requires invasive ventilation. Although antiviral drugs are obvious candidates to treat viral illness, and some have shown antiviral effects in humans, antivirals such as GS-5806, ALX-0171 and ALS-8176 have not yet met their expectations. Since the inappropriate or dysregulated immune response against RSV leads to harmful immune pathology, a robust immune cascade is probably underway by the time patients reach the hospital. RSV infection is associated with a strong neutrophil influx into the airway. It not clear if these cells contribute to antiviral defence or to lung pathology. This article discusses the protective and harmful roles of neutrophils during RSV infection and provides an overview of mechanisms by which neutrophil function could be targeted to prevent tissue injury and preserve homeostasis.

Heparin induces neutrophil elastase-dependent vital and lytic NET formation

Heparin is used extensively as an anticoagulant in a broad range of diseases and procedures; however, its biological effects are not limited to coagulation and remain incompletely understood. Heparin usage can lead to the life-threatening complication known as heparin-induced thrombocytopenia (HIT), caused by the development of antibodies against heparin/PF4 complexes. Here, we demonstrate the ability of heparin to induce neutrophil extracellular traps (NETs). NETs occurred with cell lysis and death, but live neutrophils releasing extracellular DNA strands, known as vital NETs, also occurred abundantly. Formation of NETs was time and dose dependent, and required reactive oxygen species and neutrophil elastase. Other compounds related to heparin such as low molecular weight heparin, fondaparinux and heparan sulfate either failed to induce NETs, or did so to a much lesser extent. Our findings suggest the ability of heparin to directly induce NET formation should be considered in the context of heparin treatment and HIT pathogenesis.

NETs Are Double-Edged Swords with the Potential to Aggravate or Resolve Periodontal Inflammation

Periodontitis is a general term for diseases characterised by inflammatory destruction of tooth-supporting tissues, gradual destruction of the marginal periodontal ligament and resorption of alveolar bone. Early-onset periodontitis is due to disturbed neutrophil extracellular trap (NET) formation and clearance. Indeed, mutations that inactivate the cysteine proteases cathepsin C result in the massive periodontal damage seen in patients with deficient NET formation. In contrast, exaggerated NET formation due to polymorphonuclear neutrophil (PMN) hyper-responsiveness drives the pathology of late-onset periodontitis by damaging and ulcerating the gingival epithelium and retarding epithelial healing. Despite the gingival regeneration, periodontitis progression ends with almost complete loss of the periodontal ligament and subsequent tooth loss. Thus, NETs help to maintain periodontal health, and their dysregulation, either insufficiency or surplus, causes heavy periodontal pathology and edentulism.