Tetrahydroisoquinolines: New Inhibitors of Neutrophil Extracellular Trap (NET) Formation

Resveratrol and tetrahydroisoquinoline effects on neutrophil sensitivity to NETosis formation in low-risk essential thrombocythemia patients

INTRODUCTION

Recent studies scrutinize how NETosis (a unique cell death mechanism of neutrophil), impacts thrombosis patients with essential thrombocythemia (ET). This research evaluates the susceptibility of ET neutrophils to form NETs and tests two potential inhibitors, resveratrol (RSV) and tetrahydroisoquinoline (THIQ), in vitro.

METHODS

Platelet-rich plasma from low-risk ET patients was used, along with neutrophils from both patients and controls. NET formation assays, with or without RSV and THIQ treatment after LPS stimulation, were conducted in a CO2 incubator. Evaluation included flow cytometry and fluorescence microscopy for NET formation and ELISA for TNFα, IL8, and vWF:Ag levels in patient and control plasma.

RESULTS

Neutrophils from ET patients released more NETs than controls, confirmed by flow cytometry and fluorescence microscopy. Additionally, patients had significantly higher plasma levels of IL8 and TNFα compared to controls, while RSV was more effective than THIQ in reducing NETosis rates in these patients.

CONCLUSIONS

In ET patients, a platelet counts over 1 million indicates the need for preventive treatment against thrombotic events. Similarly, in this study, RSV and THIQ significantly reduced the rate of NETosis in ET patients with higher platelet counts, and this role was more prominent in the case of the second inhibitor (RSV).

Targeting neutrophil extracellular traps: A novel strategy in hematologic malignancies

Neutrophil extracellular traps (NETs) have emerged as a critical factor in malignant hematologic disease pathogenesis. These structures, comprising DNA, histones, and cytoplasmic proteins, were initially recognized for their role in immune defense against microbial threats. Growing evidence suggests that NETs contribute to malignant cell progression and dissemination, representing a double-edged sword. However, there is a paucity of reports on its involvement in hematological disorders. A comprehensive understanding of the intricate relationship between malignant cells and NETs is necessary to explore effective therapeutic strategies. This review highlights NET formation and mechanisms underlying disease pathogenesis. Moreover, we discuss recent advancements in targeted inhibitor development for selective NET disruption, empowering precise design and efficacious therapeutic interventions for malignant hematologic diseases.

Mitochondria-induced formation of neutrophil extracellular traps is enhanced in the elderly via Toll-like receptor 9

Neutrophil extracellular traps are potent antimicrobial weapons; however, their formation during sterile inflammation is detrimental, and the mechanism of induction is still unclear. Since advanced age is the primary clinical risk factor for poor outcomes in inflammatory diseases, we hypothesized that sterile stimuli, represented by mitochondria, would induce neutrophil extracellular trap formation in an age-dependent manner. Therefore, we analyzed induction of neutrophil extracellular traps in patients grouped according to age or immune status and observed that neutrophils from elderly patients responded to the presence of mitochondria with enhanced neutrophil extracellular trap formation. These neutrophil extracellular traps were also found to be more oxidized and exhibited higher resistance to DNase I degradation. Additionally, a higher concentration of residual neutrophil extracellular traps was detected in the plasma of the elderly. This plasma was capable of priming neutrophils through TLR9-mediated signaling, leading to further neutrophil extracellular trap formation, which was successfully inhibited with chloroquine. Finally, in a mouse model of mitochondria-induced acute lung injury, we observed that neutrophils from aged mice displayed impaired chemotactic activity but exhibited a trend of higher neutrophil extracellular trap formation. Thus, we propose that residual neutrophil extracellular traps circulating in the elderly preactivate neutrophils, making them more prone to enhanced neutrophil extracellular trap formation when exposed to mitochondria during sterile inflammation. Further investigation is needed to determine whether this vicious circle could be a suitable therapeutic target.

Role and Therapeutic Targeting Strategies of Neutrophil Extracellular Traps in Inflammation

Neutrophil extracellular traps (NETs) are large DNA reticular structures secreted by neutrophils and decorated with histones and antimicrobial proteins. As a key mechanism for neutrophils to resist microbial invasion, NETs play an important role in the killing of microorganisms (bacteria, fungi, and viruses). Although NETs are mostly known for mediating microbial killing, increasing evidence suggests that excessive NETs induced by stimulation of physical and chemical components, microorganisms, and pathological factors can exacerbate inflammation and organ damage. This review summarizes the induction and role of NETs in inflammation and focuses on the strategies of inhibiting NETosis and the mechanisms involved in pathogen evasion of NETs. Furthermore, herbal medicine inhibitors and nanodelivery strategies improve the efficiency of inhibition of excessive levels of NETs.

Diabetes-associated neutrophil NETosis: pathogenesis and interventional target of diabetic complications

Neutrophil extracellular traps (NETs) are known as extracellular fibers networks consisting of antimicrobial proteins and decondensated chromatin DNA released by activated neutrophils. NETosis is a NETs-induced neutrophilic cell death which is unique from necrosis or apoptosis. Besides its neutralizing pathogen, NETosis plays a crucial role in diabetes and diabetes-related complications. In patients with diabetes, NETs-releasing products are significantly elevated in blood, and these findings confirm the association of NETosis and diabetic complications, including diabetic wound healing, diabetic retinopathy, and atherosclerosis. This article briefly summarizes the mechanisms of NETosis and discusses its contribution to the pathogenesis of diabetes-related complications and suggests new therapeutic targets by some small molecule compounds.

Neutrophil Extracellular Traps in Asthma: Friends or Foes?

Asthma is a chronic inflammatory disease characterized by variable airflow limitation and airway hyperresponsiveness. A plethora of immune and structural cells are involved in asthma pathogenesis. The roles of neutrophils and their mediators in different asthma phenotypes are largely unknown. Neutrophil extracellular traps (NETs) are net-like structures composed of DNA scaffolds, histones and granular proteins released by activated neutrophils. NETs were originally described as a process to entrap and kill a variety of microorganisms. NET formation can be achieved through a cell-death process, termed NETosis, or in association with the release of DNA from viable neutrophils. NETs can also promote the resolution of inflammation by degrading cytokines and chemokines. NETs have been implicated in the pathogenesis of various non-infectious conditions, including autoimmunity, cancer and even allergic disorders. Putative surrogate NET biomarkers (e.g., double-strand DNA (dsDNA), myeloperoxidase-DNA (MPO-DNA), and citrullinated histone H3 (CitH3)) have been found in different sites/fluids of patients with asthma. Targeting NETs has been proposed as a therapeutic strategy in several diseases. However, different NETs and NET components may have alternate, even opposite, consequences on inflammation. Here we review recent findings emphasizing the pathogenic and therapeutic potential of NETs in asthma.

Molecular mechanisms and therapeutic target of NETosis in diseases

Evidence shows that neutrophils can protect the host against pathogens in multiple ways, including the formation and release of neutrophil extracellular traps (NETs). NETs are web‐like structures composed of fibers, DNA, histones, and various neutrophil granule proteins. NETs can capture and kill pathogens, including bacteria, viruses, fungi, and protozoa. The process of NET formation is called NETosis. According to whether they depend on nicotinamide adenine dinucleotide phosphate (NADPH), NETosis can be divided into two categories: “suicidal” NETosis and “vital” NETosis. However, NET components, including neutrophil elastase, myeloperoxidase, and cell‐free DNA, cause a proinflammatory response and potentially severe diseases. Compelling evidence indicates a link between NETs and the pathogenesis of a number of diseases, including sepsis, systemic lupus erythematosus, rheumatoid arthritis, small‐vessel vasculitis, inflammatory bowel disease, cancer, COVID‐19, and others. Therefore, targeting the process and products of NETosis is critical for treating diseases linked with NETosis. Researchers have discovered that several NET inhibitors, such as toll‐like receptor inhibitors and reactive oxygen species scavengers, can prevent uncontrolled NET development. This review summarizes the mechanism of NETosis, the receptors associated with NETosis, the pathology of NETosis‐induced diseases, and NETosis‐targeted therapy.

New Insights into Neutrophil Extracellular Trap (NETs) Formation from Porcine Neutrophils in Response to Bacterial Infections

Actinobacillus pleuropneumoniae (A.pp, Gram negative) and Streptococcus (S.) suis (Gram positive) can cause severe diseases in pigs. During infection, neutrophils infiltrate to counteract these pathogens with phagocytosis and/or neutrophil extracellular traps (NETs). NETs consist of a DNA-backbone spiked with antimicrobial components. The NET formation mechanisms in porcine neutrophils as a response to both of the pathogens are not entirely clear. The aim of this study was to investigate whether A.pp (serotype 2, C3656/0271/11) and S. suis (serotype 2, strain 10) induce NETs by NADPH oxidase- or CD18-dependent mechanisms and to characterize phenotypes of NETs in porcine neutrophils. Therefore, we investigated NET induction in porcine neutrophils in the presence and absence of NET inhibitors and quantified NETs after 3 h. Furthermore, NETosis and phagocytosis were investigated by transmission electron microscopy after 30 min to characterize different phenotypes. A.pp and S. suis induce NETs that are mainly ROS-dependent. A.pp induces NETs that are partially CD18-dependent. Thirty minutes after infection, both of the pathogens induced a vesicular NET formation with only slight differences. Interestingly, some neutrophils showed only NET-marker positive phagolysosomes, but no NET-marker positive vesicles. Other neutrophils showed vesicular NETs and only NET-marker negative phagolysosomes. In conclusion, both of the pathogens induce ROS-dependent NETs. Vesicular NETosis and phagocytosis occur in parallel in porcine neutrophils in response to S. suis serotype 2 and A.pp serotype 2.

Itaconate Suppresses Formation of Neutrophil Extracellular Traps (NETs): Involvement of Hypoxia-Inducible Factor 1α (Hif-1α) and Heme Oxygenase (HO-1)

Neutrophil extracellular traps (NETs) immobilize pathogens during early stages of systemic inflammation but as the reaction progresses they become detrimental to endothelial cells and the organ-specific cells. For this reason it would be of importance to control their formation by either physiological or pharmacological means. Endogenously, formation of NETs is under control of cellular and whole organism metabolism as shown previously in the course of bacterial systemic inflammation, obesity or the combination of the two. Numerous leukocytes are subjected to immunometabolic regulation and in macrophages exposure to lipopolysaccharide (LPS) leads to two breaks in the Krebs cycle that impact this cell functioning. As a consequence of the first break, anti-microbial itaconic acid (itaconate) is produced whereas the second break activates hypoxia-inducible factor-1α (Hif-1α). In turn, itaconate activates transcription of the anti-inflammatory nuclear factor erythroid 2-related factor 2 (Nrf2) which upregulates cyto-protective heme oxygenase (HO-1). Here we report that exogenously added derivative of the itaconic acid, 4-octyl itaconate (4-OI), diminishes formation of NETs by neutrophils of either normal (lean) or obese mice, and independently of the age of the animals or immunoaging. Elucidating the mechanism of this inhibition we unravel that although Nrf2/HO-1 expression itself is not altered by 4-OI, it is up-regulated when compared against the NET formation while Hif-1α is downregulated in 4-OI-pre-treated LPS-stimulated neutrophils in either way. We further show that blockage of Hif-1α by its specific inhibitor diminishes NET release as does inhibition by 4-OI. Also inhibition of HO-1 activity correlates with diminished LPS-induced NET release upon pre-treatment with 4-OI albeit LPS alone induced NETs are not HO-1-dependent. In summary, we unravel that 4-OI inhibits NET formation by murine neutrophils independently of their origin (health vs. metabolically challenged animals) and the age of individuals/immunosenescence via inhibition of Hif-1α and induction of HO-1.

Inhibition of NETosis for treatment purposes: friend or foe?

Active neutrophils participate in innate and adaptive immune responses through various mechanisms, one of the most important of which is the formation and release of neutrophil extracellular traps (NETs). The NETs are composed of network-like structures made of histone proteins, DNA and other released antibacterial proteins by activated neutrophils, and evidence suggests that in addition to the innate defense against infections, NETosis plays an important role in the pathogenesis of several other non-infectious pathological states, such as autoimmune diseases and even cancer. Therefore, targeting NET has become one of the important therapeutic approaches and has been considered by researchers. NET inhibitors or other molecules involved in the NET formation, such as the protein arginine deiminase 4 (PAD4) enzyme, an arginine-to-citrulline converter, participate in chromatin condensation and NET formation, is the basis of this therapeutic approach. The important point is whether complete inhibition of NETosis can be helpful because by inhibiting this mechanism, the activity of neutrophils is suppressed. In this review, the biology of NETosis and its role in the pathogenesis of some important diseases have been summarized, and the consequences of treatment based on inhibition of NET formation have been discussed.

Effect of quercetin on formation of porcine neutrophil extracellular trap

Neutrophil extracellular trap (NET) formation is an immune response to the invasion of external microorganisms. Quercetin, a member of the flavonoid family found in fruits and vegetables, has been examined in multiple biological contexts. The objective of this study was to examine the effect of quercetin on porcine NET formation. We measured NET formation by peripheral blood polymorphonuclear cells (PMNs) using propidium iodide (PI) dye. The amount of tumor necrosis factor (TNF)-α in culture supernatants was quantified by ELISA, and TNF-α mRNA expression was measured by RT-PCR. Direct treatment of PMNs with quercetin did not affect NET formation; however, NET formation was inhibited by exposure to culture supernatant from peripheral blood mononuclear cells (PBMCs) treated with quercetin. By contrast, culture supernatant from PBMCs treated with lipopolysaccharide (LPS) induced high levels of NET formation of PMNs, and this effect was reduced by co-treatment with LPS and quercetin. In addition, treatment of PMNs with recombinant porcine (rp) TNF-α induced high levels of NET formation. PBMCs treated with LPS increased higher levels of TNF-α mRNA and protein, but this effect was weakened when they were co-treated with quercetin. These findings indicated that quercetin inhibits NET formation of PMNs by suppressing production of TNF-α from LPS-stimulated PBMCs. These results suggest that quercetin exerts an anti-inflammatory effect, mediated by down-regulation of TNF-α production from LPS-stimulated PBMCs, which inhibits NET formation in PMNs.

The Role of Neutrophil NETosis in Organ Injury: Novel Inflammatory Cell Death Mechanisms

NETosis is a type of regulated cell death dependent on the formation of neutrophil extracellular traps (NET), where net-like structures of decondensed chromatin and proteases are produced by polymorphonuclear (PMN) granulocytes. These structures immobilise pathogens and restrict them with antimicrobial molecules, thus preventing their spread. Whilst NETs possess a fundamental anti-microbial function within the innate immune system under physiological circumstances, increasing evidence also indicates that NETosis occurs in the pathogenic process of other disease type, including but not limited to atherosclerosis, airway inflammation, Alzheimer’s and stroke. Here, we reviewed the role of NETosis in the development of organ injury, including injury to the brain, lung, heart, kidney, musculoskeletal system, gut and reproductive system, whilst therapeutic agents in blocking injuries induced by NETosis in its primitive stages were also discussed. This review provides novel insights into the involvement of NETosis in different organ injuries, and whilst potential therapeutic measures targeting NETosis remain a largely unexplored area, these warrant further investigation.

Neutrophil extracellular traps in gastrointestinal cancer

Gastrointestinal (GI) cancer is a high-risk malignancy and is characterized by high mortality and morbidity worldwide. Neutrophil extracellular traps (NETs), a weblike structure consisting of chromatin DNA with interspersed cytoplasmic and granule proteins, are extruded by activated neutrophils to entrap and kill bacteria and fungi. However, accumulating evidence shows that NETs are related to the progression and metastasis of cancer. In clinical studies, NETs infiltrate primary GI cancer tissues and are even more abundant in metastatic lesions. The quantity of NETs in peripheral blood is revealed to be associated with ascending clinical tumour stages, indicating the role of NETs as a prognostic markers in GI cancer. Moreover, several inhibitors of NETs or NET-related proteins have been discovered and used to exert anti-tumour effects in vitro or in vivo, suggesting that NETs can be regarded as targets in the treatment of GI cancer. In this review, we will focus on the role of NETs in gastric cancer and colorectal cancer, generalizing their effects on tumour-related thrombosis, invasion and metastasis. Recent reports are also listed to show the latest evidences of how NETs affect GI cancer. Additionally, notwithstanding the scarcity of systematic studies elucidating the underlying mechanisms of the interaction between NETs and cancer cells, we highlight the potential importance of NETs as biomarkers and anti-tumour therapeutic targets.

New Insight Into Neutrophils: A Potential Therapeutic Target for Cerebral Ischemia

Ischemic stroke is one of the main issues threatening human health worldwide, and it is also the main cause of permanent disability in adults. Energy consumption and hypoxia after ischemic stroke leads to the death of nerve cells, activate resident glial cells, and promote the infiltration of peripheral immune cells into the brain, resulting in various immune-mediated effects and even contradictory effects. Immune cell infiltration can mediate neuronal apoptosis and aggravate ischemic injury, but it can also promote neuronal repair, differentiation and regeneration. The central nervous system (CNS), which is one of the most important immune privileged parts of the human body, is separated from the peripheral immune system by the blood-brain barrier (BBB). Under physiological conditions, the infiltration of peripheral immune cells into the CNS is controlled by the BBB and regulated by the interaction between immune cells and vascular endothelial cells. As the immune response plays a key role in regulating the development of ischemic injury, neutrophils have been proven to be involved in many inflammatory diseases, especially acute ischemic stroke (AIS). However, neutrophils may play a dual role in the CNS. Neutrophils are the first group of immune cells to enter the brain from the periphery after ischemic stroke, and their exact role in cerebral ischemia remains to be further explored. Elucidating the characteristics of immune cells and their role in the regulation of the inflammatory response may lead to the identification of new potential therapeutic strategies. Thus, this review will specifically discuss the role of neutrophils in ischemic stroke from production to functional differentiation, emphasizing promising targeted interventions, which may promote the development of ischemic stroke treatments in the future.

Neutrophil Extracellular Traps (NETs) and Vasculitis

Background: Neutrophil extracellular traps (NETs) have been implicated in host immune responses. Attempts have been made to examine how NETs affect the pathogenesis of complications such as autoimmune and vascular disorders. Aim: This study aimed to explore the relationship between NETs and vasculitis. Material and Methods: The current study entailed the searching of PsycINFO, PubMed, Web of Science, and CINAHL for articles related to the research topic. The search terms and phrases included "vasculitis," "NETs," "neutrophil extracellular traps," "NETosis," and "pathogenesis." The search was limited to articles published between 2009 and 2019. Results: Researchers have shown that NETs contribute to the pathogenesis of vasculitis through different mechanisms and processes, including renal failure and vascular damage. The protective effects of NETs have also been highlighted. Discussion: Overall, some scholars have shown the effectiveness of using DNase I and the PAD4 inhibitor Cl-amidine to treat vasculitis by restricting NET formation. However, observations have been noted in only animal experimental models. Conclusion: Neutrophil hyperactivity and its role in vasculitis are not yet fully understood. More studies aiming to determine the accurate function of NETs in vasculitis pathogenesis, particularly in humans, should be undertaken. Intensive research on NETs and vasculitis can increase the knowledge of medical practitioners and contribute to the development of new treatment methods to enhance patient outcomes in the future.

The molecular mechanisms of MLKL-dependent and MLKL-independent necrosis

Necrosis, a type of unwanted and passive cell demise, usually occurs under the excessive external stress and is considered to be unregulated. However, under some special conditions such as caspase inhibition, necrosis is regulable in a well-orchestrated way. The term 'regulated necrosis' has been proposed to describe such programed necrosis. Recently, several forms of necrosis, including necroptosis, pyroptosis, ferroptosis, parthanatos, oxytosis, NETosis, and Na+/K+-ATPase-mediated necrosis, have been identified, and some crucial regulators governing regulated necrosis have also been discovered. Mixed lineage kinase domain-like pseudokinase (MLKL), a core regulator in necroptosis, acts as an executioner in response to ligands of death receptor family. Its activation requires the receptor-interacting protein kinases, RIP1 and RIP3. However, MLKL is only involved in necroptosis, i.e. MLKL is dispensable for necrosis. Therefore, this review is aimed at summarizing the molecular mechanisms of MLKL-dependent and MLKL-independent necrosis.

Long non-coding RNA X-inactive specific transcript silencing ameliorates primary graft dysfunction following lung transplantation through microRNA-21-dependent mechanism

Background

Primary graft dysfunction (PGD) is a known acute lung injury (ALI) and a major cause of fatality post-lung transplantation. Though some long non-coding RNAs (lncRNAs) have been studied in ALI through regulation of microRNAs (miRNAs), their effects on PGD remain undefined. The present study aims to explore the underlying mechanism of lncRNA X-inactive specific transcript (XIST) in PGD after lung transplantation.

Methods

Initially, the expression of miR-21, IL-12A and XIST was determined by RT-qPCR and western blot analysis. The dual luciferase reporter assay, RNA pull-down and RIP assay were performed to identify the targeting relationship between miR-21 and IL-12A and the binding relationship between miR-21 and XIST. Loss- and gain-of-function investigations were conducted in rats treated with prolonged cold ischemia and polymorphonuclear neutrophils (PMNs).

Findings

miR-21 was decreased, whilst XIST and IL-12A were increased in the bronchoalveolar lavage fluid of PGD patients after lung transplantation. Enhanced miR-21 expression in rats and PMNs resulted in downregulated expression of pro-inflammatory factors and chemokines, and enhanced the apoptosis of PMNs. XIST was found to upregulate IL-12A expression in a miR-21-dependent manner. Additionally, XIST silencing enhanced the apoptosis of PMNs and inhibited the neutrophil extracellular trap (NET) formation through upregulation of miR-21 but downregulation of IL-12A in vivo.

Interpretation

In summary, lncRNA XIST upregulates IL-12A by binding to miR-21, thereby inducing NET formation and accelerating PGD after lung transplantation. This suggests that inhibition of XIST and NET may be beneficial for the treatment of PGD.

Cell death mechanisms in eukaryotes

Like the organism they constitute, the cells also die in different ways. The death can be predetermined, programmed, and cleanly executed, as in the case of apoptosis, or it can be traumatic, inflammatory, and sudden as many types of necrosis exemplify. Nevertheless, there are a number of cell deaths-some of them bearing a resemblance to apoptosis and/or necrosis, and many, distinct from each-that serve a multitude of roles in either supporting or disrupting the homoeostasis. Apoptosis is coordinated by death ligands, caspases, b-cell lymphoma-2 (Bcl-2) family proteins, and their downstream effectors. Events that can lead to apoptosis include mitotic catastrophe and anoikis. Necrosis, although it has been considered an abrupt and uncoordinated cell death, has many molecular events associated with it. There are cell death mechanisms that share some standard features with necrosis. These include methuosis, necroptosis, NETosis, pyronecrosis, and pyroptosis. Autophagy, generally a catabolic pathway that operates to ensure cell survival, can also kill the cell through mechanisms such as autosis. Other cell-death mechanisms include entosis, ferroptosis, lysosome-dependent cell death, and parthanatos.

High-Content Screening Identifies Vanilloids as a Novel Class of Inhibitors of NET Formation

Neutrophils migrate to sites of infection where they phagocytose, degranulate, and/or, in the presence of appropriate stimuli, release decondensed chromatin strands (called neutrophil extracellular traps, NETs) for trapping and possibly killing microorganisms. NET formation is characterized by marked morphological cell changes, in particular within the nucleus. Lytic NET formation can be observed in neutrophils undergoing cell death, which is referred to as NETosis. Dysregulation of NET production and/or degradation can exert pathogenic effects, contributing to the pathogenesis of various diseases, including cystic fibrosis, autoimmune diseases and inflammatory conditions. By employing a phenotypic assay based on high-content imaging and analysis, we screened a library of biologically active compounds and identified vanilloids as a novel class of chemical compounds able to hinder NETosis induction and NET release. Vanilloids also markedly decrease cytosolic ROS production. The identification of novel vanilloid NET inhibitors, able to stop excessive or aberrant NET production might offer new therapeutic options for those disorders displaying NET overproduction.

Advancements in Host-Based Interventions for Influenza Treatment

Influenza is a major acute respiratory infection that causes mortality and morbidity worldwide. Two classes of conventional antivirals, M2 ion channel blockers and neuraminidase inhibitors, are mainstays in managing influenza disease to lessen symptoms while minimizing hospitalization and death in patients with severe influenza. However, the development of viral resistance to both drug classes has become a major public health concern. Vaccines are prophylaxis mainstays but are limited in efficacy due to the difficulty in matching predicted dominant viral strains to circulating strains. As such, other potential interventions are being explored. Since viruses rely on host cellular functions to replicate, recent therapeutic developments focus on targeting host factors involved in virus replication. Besides controlling virus replication, potential targets for drug development include controlling virus-induced host immune responses such as the recently suggested involvement of innate lymphoid cells and NADPH oxidases in influenza virus pathogenesis and immune cell metabolism. In this review, we will discuss the advancements in novel host-based interventions for treating influenza disease.

Neutrophil extracellular traps in vasculitis, friend or foe?

PURPOSE OF REVIEW

Neutrophil extracellular traps (NETs) can be found at the sites of vascular lesions and in the circulation of patients with active small vessel vasculitis. Neutrophils from vasculitis patients release more NETs in vitro, and NETs have properties that can harm the vasculature both directly and indirectly. There are several ways to interfere with NET formation, which open for new therapeutic options. However, there are several types of NETs and different mechanisms of NET formation, and these might have different effects on inflammation. Here we review recent findings regarding the pathogenesis and therapeutic potentials of NETs in vasculitis.

RECENT FINDINGS

Experimental mouse models support a role for NETs in promoting vascular damage, where histones and mitochondrial DNA appear to be driving forces. Impaired formation of NETs, however, in an SLE-like mouse model leads to more severe disease, suggesting that NETs can be important in limiting inflammation. Studies on drug-induced vasculitis reveal that levamisole can induce NETosis via muscarinic receptors, predisposing for the generation of autoantibodies, including antineutrophil cytoplasmic autoantibodies (ANCA). This supports the notion that NETs can bridge the innate and adaptive immune systems.

SUMMARY

NETs can participate in the pathogenesis of vasculitis, but in some models there also seem to be protective effects of NETs. This complexity needs further evaluation with experimental models that are as specific as possible for human primary vasculitis.

Development and Application of High-Content Biological Screening for Modulators of NET Production

Neutrophil extracellular traps (NETs) are DNA-based antimicrobial web-like structures whose release is predominantly mediated by reactive oxygen species (ROS); their purpose is to combat infections. However, unbalanced NET production and clearance is involved in tissue injury, circulation of auto-antibodies and development of several chronic diseases. Currently, there is lack of agreement regarding the high-throughput methods available for NET investigation. This study, therefore, aimed to develop and optimize a high-content analysis (HCA) approach, which can be applied for the assay of NET production and for the screening of compounds involved in the modulation of NET release. A suitable paraformaldehyde fixation protocol was established to enable HCA of neutrophils and NETs. Bespoke and in-built bioinformatics algorithms were validated by comparison with standard low-throughput approaches for application in HCA of NETs. Subsequently, the optimized protocol was applied to high-content screening (HCS) of a pharmaceutically derived compound library to identify modulators of NETosis. Of 56 compounds assessed, 8 were identified from HCS for further characterization of their effects on NET formation as being either inducers, inhibitors or biphasic modulators. The effects of these compounds on naïve neutrophils were evaluated by using specific assays for the induction of ROS and NET production, while their modulatory activity was validated in phorbol 12-myristate 13-acetate-stimulated neutrophils. Results indicated the involvement of glutathione reductase, Src family kinases, molecular-target-of-Rapamycin, and mitogen-activated-protein-kinase pathways in NET release. The compounds and pathways identified may provide targets for novel therapeutic approaches for treating NET-associated pathologies.