Neutrophil extracellular traps and organ dysfunction in sepsis

Spatiotemporal regulation of neutrophil heterogeneity in health and disease

Neutrophils are the most abundant leukocytes in humans and are indispensable for innate immunity. They are short-lived, terminally differentiated cells. However, mounting evidence indicates that neutrophils are heterogeneous in health and disease: they are young or aged in a steady state, while their heterogeneity becomes more diverse in disease conditions, such as cancer, sepsis, and thromboinflammation. Although the presence of distinct neutrophil subsets is well recognized, it is not fully understood how neutrophils have functional and phenotypic heterogeneity and what mechanisms control it. This review will focus on our current understanding of the molecular basis for neutrophil heterogeneity in pathophysiological conditions. In addition, we will discuss the possibility of targeting a specific subset of neutrophils to attenuate inflammation and tissue damage without compromising innate immune responses.

Transcriptomic and metabolomic insights into neutrophil activity in COPD complicated by metabolic syndrome

OBJECTIVES

Chronic obstructive pulmonary disease (COPD) frequently coexists with metabolic syndrome (MS), compounding its impact on patients' health and quality of life. This study aimed to elucidate the immune and metabolic response characteristics in COPD patients with and without MS.

METHODS

A total of 11,315 COPD patients admitted to the Department of Respiratory and Critical Care Medicine at the Third People's Hospital of Chengdu between January 1, 2013, and May 1, 2023, were selected. Multivariate logistic regression was conducted to identify the risk factors for acute exacerbation of chronic obstructive pulmonary disease. Moreover, from this cohort, 30 patients (18 with COPD and 12 with COPD-MS) were recruited for a further study to investigate the underlying mechanisms of COPD and COPD-MS. Blood samples were collected from these participants to perform transcriptomic and metabolomic analyses, aiming to explore the differences in immune responses and metabolic alterations between the two groups.

RESULTS

Our findings indicate a significant enhancement of neutrophil-mediated immune responses in COPD-MS patients. Transcriptomic analysis revealed 327 differentially expressed genes (DEGs) significantly involved in neutrophil-mediated immunity. Key metabolic pathways were disrupted, with 39 differential metabolites identified. Notably, metabolites, such as L-homoarginine and diethanolamine, which were elevated in COPD-MS patients, showed strong correlations with DEGs involved in neutrophil pathways and immune checkpoint regulation. The study also found decreased levels of IL4 and IL5RA in COPD-MS patients, suggesting a shift from Th2 to Th1 inflammatory responses, potentially contributing to glucocorticoid resistance.

CONCLUSIONS

COPD patients with metabolic syndrome exhibit a heightened neutrophil-mediated inflammatory response and significant metabolic disturbances, which underscores the need for precise therapeutic strategies targeting both metabolic and inflammatory pathways to improve patient outcomes and manage COPD-MS complexities effectively.

Decoding Inflammation: The Role of Neutrophil-to-Lymphocyte Ratio and Platelet-to-Lymphocyte Ratio in Predicting Critical Outcomes in COVID-19 Patients

Background and Objectives: The neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) are novel biomarkers that provide insight into systemic inflammation and how the immune system responds to stress or infection. These ratios have been associated with predicting clinical outcomes in various diseases, including COVID-19. This study aims to evaluate the prognostic value of NLR and PLR in anticipating ICU admission, acute respiratory failure, and disease severity in COVID-19 patients. Materials and Methods: We conducted a retrospective, observational study that included 536 patients diagnosed with COVID-19. We analyzed the NLR and PLR values at admission and correlated them with ICU admission, the onset of acute respiratory failure, and clinical outcomes. Results: Statistical correlations were identified between elevated NLR and PLR values and the development of complications during hospitalization (p = 0.04 and p = 0.00), acute hypoxemic respiratory failure (p = 0.00), and admission to the intensive care unit (ICU) (p = 0.04). No correlations were found between the values of these ratios and mortality (p = 0.46 and p = 0.32) nor with the development of hepatic cytolysis (p = 0.79 and p = 0.87). Conclusions: NLR and PLR are reliable, easily obtainable biomarkers that can aid in the early prediction of ICU admission and disease severity in COVID-19 patients, offering valuable insights for risk stratification and clinical management. Further prospective studies are needed to validate these biomarkers as part of a broader predictive model for critical care in COVID-19.

Disrupting the dangerous alliance: Dual anti-inflammatory and anticoagulant strategy targets platelet-neutrophil crosstalk in sepsis

Sepsis is a life-threatening disease characterized by excessive systemic inflammation and coagulopathy. Platelets and neutrophils form a "dangerous alliance" through crosstalk, promoting the inflammatory cytokine storm and coagulation disorders during sepsis. Platelet-neutrophil crosstalk leads to the formation of platelet-neutrophil complexes (PNCs), which are the central "protagonists" of this "dangerous alliance." These PNCs further enhance the crosstalk between platelets and neutrophils, amplifying immune and coagulation responses through positive feedback loops. Although some targeted therapies have been reported recently, they primarily focus on inducing neutrophil apoptosis or degrading existing neutrophil extracellular traps (NETs). Limited strategies are available for targeting platelets and suppressing sepsis-associated PNCs. Herein, we propose a two-pronged approach to intercept platelet-neutrophil crosstalk by simultaneously targeting drugs to both platelets and neutrophils of the "dangerous alliance." This strategy not only effectively alleviates inflammation induced by platelet-neutrophil crosstalk but also reduces PNC formation, thereby dismantling the structural scaffold of microthrombi. In a sepsis mouse model, this approach significantly decreased markers of platelet-neutrophil crosstalk, reduced the cytokine storm, and lowered the risk of thrombosis. Moreover, it alleviated organ damage caused by PNC infiltration and prolonged the survival of septic mice. Overall, this work combines anti-inflammatory and anticoagulant therapies to effectively disrupt the "dangerous alliance" between platelets and neutrophils, offering a promising strategy for treating sepsis.

IL-6 and PD-1 antibody blockade combination therapy regulate inflammation and T lymphocyte apoptosis in murine model of sepsis

BACKGROUND

Interleukin-6 (IL-6) plays a central role in sepsis-induced cytokine storm involving immune hyperactivation and early neutrophil activation. Programmed death protein-1 (PD-1) is associated with sepsis-induced immunosuppression and lymphocyte apoptosis. However, the effects of simultaneous blockade of IL-6 and PD-1 in a murine sepsis model are not well understood.

RESULTS

In this study, sepsis was induced in male C57BL/6 mice through cecal ligation and puncture (CLP). IL-6 blockade, PD-1 blockade, or combination of both was administered 24 h after CLP. Peripheral blood count, cytokine level, lymphocyte apoptosis in the spleen, neutrophil infiltration in the lungs and liver, and survival rate were measured. The mortality rate of the IL-6/PD-1 group was lower, though not statistically significant (p = 0.164), than that of CLP mice (75.0% vs. 91.7%). The IL-6/PD-1 group had lower neutrophil percentage and platelet count compared with the CLP group; no significant difference was observed in other cytokine levels. The IL-6/PD-1 group also showed reduced T lymphocyte apoptosis in the spleen and decreased neutrophil infiltration in the liver and lungs.

CONCLUSIONS

IL-6/PD-1 dual blockade reduces neutrophil infiltration, lymphocyte apoptosis, and bacterial burden while preserving tissue integrity in sepsis. Although the improvement in survival was not statistically significant, these findings highlight its potential as a therapeutic approach in sepsis.

Neutrophil Extracellular Traps (NETs) as a Potential Target for Anti-Aging: Role of Therapeutic Apheresis

Neutrophil extracellular traps (NETs) are large structures composed of chromatin, histones and granule-derived proteins released extracellularly by neutrophils. They are generally considered to be a part of the antimicrobial defense strategy, preventing the dissemination of pathogens. However, overproduction of NETs or their ineffective clearance can drive various pathologies, many of which are associated with advanced age and involve uncontrolled inflammation, oxidative, cardiovascular and neurodegenerative stress as underlying mechanisms. Targeting NETs in the elderly as an anti-aging therapy seems to be a very attractive therapeutic approach. Therapeutic apheresis with a specific filter to remove NETs could be a promising strategy worth considering.

Immunopharmacological Insights into Cordyceps spp.: Harnessing Therapeutic Potential for Sepsis

Cordyceps spp. (CS), a well-known medicinal mushroom that belongs to Tibetan medicine and is predominantly found in the high altitudes in the Himalayas. CS is a rich reservoir of various bioactive substances including nucleosides, sterols flavonoids, peptides, and phenolic compounds. The bioactive compounds and CS extract have antibacterial, antioxidant, immunomodulatory, and inflammatory properties in addition to organ protection properties across a range of disease states. The study aimed to review the potential of CS, a medicinal mushroom, as a treatment for sepsis. While current sepsis drugs have side effects, CS shows promise due to its anti-inflammatory, antioxidant, and antibacterial properties. We have performed an extensive literature search based on published original and review articles in Scopus and PubMed. The keywords used were Cordyceps, sepsis, and inflammation. Studies indicate that CS extract and bioactive compounds target free radicals including oxidative as well as nitrosative stress, lower inflammation, and modulate the immune system, all of which are critical components in sepsis. The brain, liver, kidneys, lungs, and heart are among the organs that CS extracts may be able to shield against harm during sepsis. Traditional remedies with anti-inflammatory and protective qualities, such as Cordyceps mushrooms, are promising in sepsis. However, more research including clinical trials is required to validate the usefulness of CS metabolites in terms of organ protection and fight infections in sepsis.

CircIRAK3 Promotes Neutrophil Extracellular Trap Formation by Improving the Stability of ELANE mRNA in Sepsis

Excessive formation of neutrophil extracellular traps (NETs) has been shown to exacerbate inflammatory injury and organ damage in patients with sepsis. Circular RNAs (circRNAs) abnormally expressed in immune cells of sepsis patients, and play an important role in the pathogenesis of dysregulated immune responses. However, the functions of circRNAs in NET formation during sepsis remain unknown. Here, we identified circIRAK3, a novel circRNA that was upregulated in peripheral blood neutrophils of sepsis patients. Combining clinical data, we revealed that elevated circIRAK3 was positively correlated with blood NET levels. Furthermore, knockdown and overexpression in differentiated HL-60 (dHL-60) neutrophil-like cells demonstrated that circIRAK3 promoted NET formation. In addition, we found that circIRAK3 promoted NET formation via positively regulating elastase expression in dHL-60 cells when treated with inflammatory stimuli. Mechanistically, circIRAK3 directly interacted with ELAVL1 to improve ELANE mRNA stability and consequently promote elastase protein expression. In summary, our study reveals that circIRAK3 promotes NET formation in sepsis by increasing ELANE mRNA levels.

MiRNAs and Neutrophil-Related Membrane Proteins from Plasma-Derived Extracellular Vesicles for Early Prediction of Organ Dysfunction and Prognosis in Septic Patients

Purpose

The pathogenesis of sepsis-induced organ dysfunction remains elusive, and the mortality remains alarmingly high. We sought to investigate the profile of extracellular vesicles (EVs)-mediated communication between plasma and polymorphonuclear neutrophils (PMNs) in sepsis, and to elucidate whether miRNAs and PMN-related membrane proteins from plasma-derived EVs (plasma-EVs) are associated with sepsis-induced organ dysfunction and prognosis.

Methods

PMN-derived EVs (PMN-EVs) were isolated from the blood samples of healthy controls (N=3) and patients with septic shock (N=3) after ICU admission. We performed miRNA sequencing of the isolated EVs, followed by bioinformatic analysis. A miRNA model for comparing PMN-EVs and plasma-EVs was successfully established in the training cohort. Furthermore, miRNAs and PMN-related membrane proteins from the plasma-EV model were confirmed in the validation cohort. A logistic regression model, receiver operating characteristic (ROC) curves, and Kaplan-Meier analyses were performed to evaluate the efficiency of diagnostic and/or prognostic performance. Further, in vivo and in vitro experiments were conducted to explore the involvement of plasma-EVs in PMNs autophagy.

Results

Fifty-five miRNAs from PMN-EVs differed significantly between the healthy controls and patients with septic shock. Furthermore, the plasma-EV model (six miRNAs and eight PMN-related membrane proteins) was confirmed in the validation cohort, demonstrating that miR-34a-5p, miR-503-5p, miR-4772-3p, ITGAM, MPO, and MMP9 serve as sepsis biomarkers for distinguishing lung, liver, and kidney dysfunction. Kaplan-Meier survival analysis showed that miR-34a-5p, miR-4772-3p, ITGAM, and MMP9 were potential prognostic predictors. Finally, we found that plasma-EVs from sepsis patients exert an inhibitory effect on PMNs autophagy, which can be reversed by EV inhibitors such as GW4869 and enoxaparin.

Conclusion

These findings suggest that miRNAs and PMN-related membrane proteins from plasma-EVs could be valuable diagnostic tools for identifying sepsis-induced organ dysfunction and predicting prognosis, enabling proactive management of sepsis by physicians and improving the prognosis of sepsis patients.

Neutrophil extracellular traps - an a-list-actor in a variety of diseases

Neutrophil extracellular traps (NETs) represent a response mechanism in which activated neutrophils release DNA-based webs, adorned with histones and neutrophil proteases, to capture and eliminate invasive microorganisms. However, when these neutrophils become excessively activated, much more proteases associated with NETs are liberated into surrounding tissues or bloodstreams, thereby altering the cellular milieu and causing tissue damage. Recent research has revealed that NETs may play significant roles in the emergence and progression of various diseases, spanning from infections, inflammation to autoimmune disorders and cancers. In this review, we delve deeply into the intricate and complex mechanisms that underlie the formation of NETs and their profound interplay with various clinical pathologies. We aim to describe the application perspectives of NETs related proteins in specific disease diagnosis and treatment.

The toxic effects of neutrophil extracellular traps on mesenchymal stem cells

Sepsis, a systemic inflammatory response syndrome resulting from an uncontrolled inflammatory reaction to infection, remains without a definitive cure despite therapeutic advancements. Mesenchymal stem cells (MSCs), renowned for their capacity to alleviate inflammation and modulate the immune system, have emerged as a potential treatment avenue for sepsis. In sepsis pathophysiology, hyperactivated neutrophils release extracellular neutrophil traps (NETs). NETs are essential for eradicating pathogens; however, excessive formation leads to tissue damage. Given the limited knowledge regarding the impact of NETs on MSCs used in sepsis therapy and the established interaction between MSCs and NETs, this study investigates the effects of NETs on MSCs in vitro. NETs were isolated from stimulated neutrophils, and MSCs were sourced from umbilical cord blood. After co-culturing MSCs with isolated NETs, MSCs' viability, migration, intracellular antioxidant capacity, and changes in gene expression were analyzed. Following exposure to NETs, MSCs exhibited obvious apoptosis and necrosis. NETs disrupt MSCs' mitochondrial activity. Also, NETs upregulate the pro-apoptotic gene BAX and downregulate the anti-apoptotic gene BCL2 in MSCs. Additionally, NETs reduce MSCs' intracellular antioxidant capacity. Furthermore, MSC migration is significantly impaired by NETs. This study collectively demonstrates that NETs have toxic and detrimental effects on MSCs. These effects on MSCs indicate a potential barrier to their functionality and therapeutic efficacy. Therefore, it appears that reducing the undesirable effects of NETs could serve as a novel target to enhance the therapeutic efficacy of MSCs in septic patients.

Bay-117082 treats sepsis by inhibiting neutrophil extracellular traps (NETs) formation through down-regulating NLRP3/N-GSDMD

During the inflammatory storm of sepsis, a significant quantity of neutrophil extracellular traps (NETs) are generated, which act as a double-edged sword and not only impede the invasion of foreign microorganisms but also exacerbate organ damage. This study provides evidence that NETs can cause damage to alveolar epithelial cells in vitro. The sepsis model developed in this study showed a significant increase in NETs in the bronchoalveolar lavage fluid (BALF). The development of NETs has been shown to increase the lung inflammatory response and aggravate injury to alveolar epithelial cells. Bay-117082, a well-known NF-κB suppressor, is used to modulate inflammation. This analysis revealed that Bay-117082 efficiently reduced total protein concentration, myeloperoxidase activity, and inflammatory cytokines in BALF. Moreover, Bay-117082 inhibited the formation of NETs, which in turn prevented the activation of the pore-forming protein gasdermin D (GSDMD). In summary, these results indicated that excessive NET production during sepsis exacerbated the onset and progression of acute lung injury (ALI). Therefore, Bay-117082 could serve as a novel therapeutic approach for ameliorating sepsis-associated ALI.

Understanding the complex chromatin dynamics in primary human neutrophils during PMA-induced NET formation

Background

Primary human neutrophils play a pivotal role in innate immunity, mainly through the formation of neutrophil extracellular traps (NETs) in a process known as NETosis. This cell-death pathway is crucial for combating infections but is also implicated in many inflammatory diseases, such as sepsis, systemic lupus erythematosus, and rheumatoid arthritis.

Methods

The study presented here investigates chromatin dynamics during NET formation by stimulating primary human neutrophils with phorbol 12-myristate 13-acetate (PMA). We adapt the ATAC-Seq (assay for transposase-accessible chromatin using sequencing) method to isolated neutrophils and characterize a time-dependent chromatin response.

Results

We found that chromatin accessibility patterns are consistent across individual donors and most chromatin changes occur within 30 min, with many continuing across the 90 min assessed in this study. Regulatory regions gaining accessibility were associated with the activity of pathways that have been implicated in NOX-dependent NET formation.

Conclusions

Our findings increase the understanding of the chromatin changes underlying NET formation and also identify potential early-acting targets for modulating this process in inflammatory diseases.

Neutrophil activation, acute lung injury and disease severity in Plasmodium knowlesi malaria

The risk of severe malaria from the zoonotic parasite Plasmodium knowlesi approximates that from P. falciparum. In severe falciparum malaria, neutrophil activation contributes to inflammatory pathogenesis, including acute lung injury (ALI). The role of neutrophil activation in the pathogenesis of severe knowlesi malaria has not been examined. We evaluated 213 patients with P. knowlesi mono-infection (138 non-severe, 75 severe) and 49 Plasmodium-negative controls from Malaysia. Markers of neutrophil activation (soluble neutrophil elastase [NE], citrullinated histone [CitH3] and circulating neutrophil extracellular traps [NETs]) were quantified in peripheral blood by microscopy and immunoassays. Findings were correlated with malaria severity, ALI clinical criteria, biomarkers of parasite biomass, haemolysis, and endothelial activation. Neutrophil activation increased with disease severity, with median levels higher in severe than non-severe malaria and controls for NE (380[IQR:210-930]ng/mL, 236[139-448]ng/mL, 218[134-307]ng/mL, respectively) and CitH3 (8.72[IQR:3.0-23.1]ng/mL, 4.29[1.46-9.49]ng/mL, 1.53[0.6-2.59]ng/mL, respectively)[all p<0.01]. NETs were higher in severe malaria compared to controls (126/μL[IQR:49-323] vs 51[20-75]/μL, p<0.001). In non-severe malaria, neutrophil activation fell significantly upon discharge from hospital (p<0.03). In severe disease, NETs, NE, and CitH3 were correlated with parasitaemia, cell-free haemoglobin and angiopoietin-2 (all Pearson's r>0.24, p<0.05). Plasma NE and angiopoietin-2 were higher in knowlesi patients with ALI than those without (p<0.008); neutrophilia was associated with an increased risk of ALI (aOR 3.27, p<0.01). In conclusion, neutrophil activation is increased in ALI and in proportion to disease severity in knowlesi malaria, is associated with endothelial activation, and may contribute to disease pathogenesis. Trials of adjunctive therapies to regulate neutrophil activation are warranted in severe knowlesi malaria.

Augmenting Neutrophil Extracellular Traps with Carbonized Polymer Dots: A Potential Treatment for Bacterial Sepsis

Sepsis is a life-threatening condition that can progress to septic shock as the body's extreme response to pathogenesis damages its own vital organs. Staphylococcus aureus (S. aureus) accounts for 50% of nosocomial infections, which are clinically treated with antibiotics. However, methicillin-resistant strains (MRSA) have emerged and can withstand harsh antibiotic treatment. To address this problem, curcumin (CCM) is employed to prepare carbonized polymer dots (CPDs) through mild pyrolysis. Contrary to curcumin, the as-formed CCM-CPDs are highly biocompatible and soluble in aqueous solution. Most importantly, the CCM-CPDs induce the release of neutrophil extracellular traps (NETs) from the neutrophils, which entrap and eliminate microbes. In an MRSA-induced septic mouse model, it is observed that CCM-CPDs efficiently suppress bacterial colonization. Moreover, the intrinsic antioxidative, anti-inflammatory, and anticoagulation activities resulting from the preserved functional groups of the precursor molecule on the CCM-CPDs prevent progression to severe sepsis. As a result, infected mice treated with CCM-CPDs show a significant decrease in mortality even through oral administration. Histological staining indicates negligible organ damage in the MRSA-infected mice treated with CCM-CPDs. It is believed that the in vivo studies presented herein demonstrate that multifunctional therapeutic CPDs hold great potential against life-threatening infectious diseases.

GSDMD in regulated cell death: A novel therapeutic target for sepsis

Sepsis is a life-threatening multi-organ dysfunction syndrome caused by an abnormal host response to infection. Regulated cell death is essential for maintaining tissue homeostasis and eliminating damaged, infected, or aging cells in multicellular organisms. Gasdermin D, as a member of the gasdermin family, plays a crucial role in the formation of cytoplasmic membrane pores. Research has found that GSDMD plays important roles in various forms of regulated cell death such as pyroptosis, NETosis, and necroptosis. Therefore, through mediating regulated cell death, GSDMD regulates different stages of disease pathophysiology. This article mainly summarizes the concept of GSDMD, its role in regulated cell death, its involvement in organ damage associated with sepsis-related injuries mediated by regulated cell death via GSDMD activation and introduces potential drugs targeting GSDMD that may provide more effective treatment options for sepsis patients through drug modification.

Neutrophil Depletion Changes the N-Glycosylation Pattern of IgG in Experimental Murine Sepsis

Sepsis is a life-threatening condition with a rising disease burden worldwide. It is a multifactorial disease and is defined as a dysregulated host response to infection. Neutrophils have been shown to be involved in the pathogenesis of sepsis by exacerbating inflammation. However, the exact effector mechanism of action still remains a mystery. Changes in the glycosylation pattern of the immunoglobulin G (IgG) Fc region are described for several diseases including meningococcal sepsis. In this study, we investigated the possible contribution of neutrophils and neutrophil implication, potentially related to degranulation or neutrophil extracellular trap (NET) formation in changing the IgG Fc N-glycosylation pattern in a murine sepsis model. We have measured the serum level of cytokines/chemokines and immunoglobulins, the serum activity of neutrophil elastase (NE), and analyzed the IgG Fc glycosylation pattern by Liquid Chromatography-Electrospray Ionization-Mass Spectrometry (LC-ESI-MS) and Lectin enzyme-linked immunosorbent assay (ELISA). We observed an increased activity of NE- and neutrophil-associated cytokines such as keratinocyte chemoattractant (KC) with the development of sepsis. Regarding the IgG Fc N-glycosylation, we observed an increase in fucosylation and α1,3-galactosylation and a decrease for sialyation. Interestingly, these changes were not uniform for all IgG subclasses. After depletion of neutrophils, we saw a change in the exposure of fucose and α2,6-linked sialic acid during the time course of our experimental sepsis model. In conclusion, neutrophils can influence changes in the IgG glycosylation pattern in experimental sepsis.

Ferritin-mediated neutrophil extracellular traps formation and cytokine storm via macrophage scavenger receptor in sepsis-associated lung injury

BACKGROUND

Sepsis is a severe systemic inflammatory disorder manifested by a dysregulated immune response to infection and multi-organ failure. Numerous studies have shown that elevated ferritin levels exist as an essential feature during sepsis and are able to suggest patients' prognoses. At the same time, the specific mechanism of ferritin-induced inflammatory injury remains unclear.

METHODS

Hyper-ferritin state during inflammation was performed by injecting ferritin into a mouse model and demonstrated that injection of ferritin could induce a systemic inflammatory response and increase neutrophil extracellular trap (NET) formation.Padi4-/-, Elane-/- and Cybb-/- mice were used for the NETs formation experiment. Western blot, immunofluorescence, ELISA, and flow cytometry examined the changes in NETs, inflammation, and related signaling pathways.

RESULTS

Ferritin induces NET formation in a peptidylarginine deiminase 4 (PAD4), neutrophil elastase (NE), and reactive oxygen species (ROS)-dependent manner, thereby exacerbating the inflammatory response. Mechanistically, ferritin induces the expression of neutrophil macrophage scavenger receptor (MSR), which promotes the formation of NETs. Clinically, high levels of ferritin in patients with severe sepsis correlate with NETs-mediated cytokines storm and are proportional to the severity of sepsis-induced lung injury.

CONCLUSIONS

In conclusion, we demonstrated that hyper-ferritin can induce systemic inflammation and increase NET formation in an MSR-dependent manner. This process relies on PAD4, NE, and ROS, further aggravating acute lung injury. In the clinic, high serum ferritin levels are associated with elevated NETs and worse lung injury, which suggests a poor prognosis for patients with sepsis. Our study indicated that targeting NETs or MSR could be a potential treatment to alleviate lung damage and systemic inflammation during sepsis. Video Abstract.

Dietary exposure to polystyrene microplastics exacerbates liver damage in fulminant hepatic failure via ROS production and neutrophil extracellular trap formation

With the increasing influx of microplastics (MPs) into the environment, their potential toxicity represents an increasing threat to human health. However, there is a lack of relevant research surrounding the biological toxicity associated with pre-exposure to MPs under pathological conditions. To fill this gap, we established a mouse model of fulminant hepatic failure after 14 days of pre-exposure to polystyrene (PS) MPs and investigated its biological response process under combined stimulation with lipopolysaccharide (LPS)/d-galactosamine (d-GalN) and PS-MPs. The results indicated that the stress response from exposure to PS-MPs exacerbated the death induced by LPS/d-GalN and reinforced the potential of liver damage in mice. The dominant roles of inflammation promotion, reactive oxygen species (ROS), and neutrophil extracellular traps in this process were confirmed by cellular reactive oxygen species assays and experiments on oxidative stress and inflammatory responses in the liver. Transcriptomic analysis revealed that PS-MPs exacerbated the expression levels of neutrophil extracellular traps in mice treated with LPS/d-GalN, and weakened the expression of genes involved in pathways related to peroxisome, taurine, and hypotaurine metabolism, which was further validated by reverse-transcription quantitative polymerase chain reaction. This study addresses the knowledge gap regarding the adverse effects caused by a pathological state upon exposure to MPs and provides a theoretical reference for further assessment of the underlying health risks of MPs.

Free Radicals, Mitochondrial Dysfunction and Sepsis-induced Organ Dysfunction: A Mechanistic Insight

Sepsis is a complex clinical condition and a leading cause of death worldwide. During Sepsis, there is a derailment in the host response to infection, which can progress to severe sepsis and multiple organ dysfunction or failure, which leads to death. Free radicals, including reactive oxygen species (ROS) generated predominantly in mitochondria, are one of the key players in impairing normal organ function in sepsis. ROS contributing to oxidative stress has been reported to be the main culprit in the injury of the lung, heart, liver, kidney, gastrointestinal, and other organs. Here in the present review, we describe the generation, and essential properties of various types of ROS, their effect on macromolecules, and their role in mitochondrial dysfunction. Furthermore, the mechanism involved in the ROS-mediated pathogenesis of sepsis-induced organ dysfunction has also been discussed.

Neutrophil extracellular traps in influenza infection

Despite recent progress in developing novel therapeutic approaches and vaccines, influenza is still considered a global health threat, with about half a million mortality worldwide. This disease is caused by Influenza viruses, which are known for their rapid evolution due to different genetical mechanisms that help them develop new strains with the ability to evade therapies and immunization. Neutrophils are one of the first immune effectors that act against pathogens. They use multiple mechanisms, including phagocytosis, releasing the reactive oxygen species, degranulation, and the production of neutrophil extracellular traps. Neutrophil extracellular traps are used to ensnare pathogens; however, their dysregulation is attributed to inflammatory and infectious diseases. Here, we discuss the effects of these extracellular traps in the clinical course of influenza infection and their ability to be a potential target in treating influenza infection.

Acute respiratory distress syndrome heterogeneity and the septic ARDS subgroup

Acute respiratory distress syndrome (ARDS) is an acute diffuse inflammatory lung injury characterized by the damage of alveolar epithelial cells and pulmonary capillary endothelial cells. It is mainly manifested by non-cardiogenic pulmonary edema, resulting from intrapulmonary and extrapulmonary risk factors. ARDS is often accompanied by immune system disturbance, both locally in the lungs and systemically. As a common heterogeneous disease in critical care medicine, researchers are often faced with the failure of clinical trials. Latent class analysis had been used to compensate for poor outcomes and found that targeted treatment after subgrouping contribute to ARDS therapy. The subphenotype of ARDS caused by sepsis has garnered attention due to its refractory nature and detrimental consequences. Sepsis stands as the most predominant extrapulmonary cause of ARDS, accounting for approximately 32% of ARDS cases. Studies indicate that sepsis-induced ARDS tends to be more severe than ARDS caused by other factors, leading to poorer prognosis and higher mortality rate. This comprehensive review delves into the immunological mechanisms of sepsis-ARDS, the heterogeneity of ARDS and existing research on targeted treatments, aiming to providing mechanism understanding and exploring ideas for accurate treatment of ARDS or sepsis-ARDS.

Caspase-3/GSDME mediated pyroptosis: A potential pathway for sepsis

The inflammatory response is one of the host's mechanisms to combat pathogens. Normal and controlled inflammation can accelerate the clearance of pathogens. However, in sepsis, the host often exhibits an excessive inflammatory response to infection, leading to tissue and organ damage. Therefore, studying the mechanisms underlying the occurrence and development of sepsis is of significant importance. Pyroptosis is a form of programmed cell death (PCD) executed by the gasdermins (GSDMs) family, and its pro-inflammatory characteristics are considered a crucial component of the sepsis mechanism. Previous research on pyroptosis in sepsis has mainly focused on the caspase-1/4/5/11-GSDMD pathway, which has made significant progress. However, there is a lack of research on the roles of other GSDMs family members in sepsis. New research has revealed that the caspase-3/GSDME pathway can also mediate pyroptosis, playing important roles in cancer, other inflammatory diseases, and even some sepsis-related conditions. This discovery suggests the potential value of investigating caspase-3/GSDME in sepsis research. This review provides an overview of the role of the GSDMs family in infectious diseases, summarizes current research on the caspase-1/4/5/11-GSDMD pathway, describes the role of caspase-3 in sepsis, and discusses the research findings related to pyroptosis mediated by the caspase-3/GSDME pathway in cancer, inflammatory diseases, and sepsis-related conditions. The aim of this article is to propose the concept of caspase-3/GSDME as a potential target in sepsis research. Considering the role of this pathway in other diseases, including inflammatory conditions, and given the unique nature of sepsis as an inflammatory disease, the article suggests that this pathway may also play a role in sepsis. This hypothesis provides new insights and options for future sepsis research, although direct experiments are needed to validate this hypothesis.

Machine learning-based identification of CYBB and FCAR as potential neutrophil extracellular trap-related treatment targets in sepsis

Objective

Sepsis related injury has gradually become the main cause of death in non-cardiac patients in intensive care units, but the underlying pathological and physiological mechanisms remain unclear. The Third International Consensus Definitions for Sepsis and Septic Shock (SEPSIS-3) definition emphasized organ dysfunction caused by infection. Neutrophil extracellular traps (NETs) can cause inflammation and have key roles in sepsis organ failure; however, the role of NETs-related genes in sepsis is unknown. Here, we sought to identify key NETs-related genes associate with sepsis.

Methods

Datasets GSE65682 and GSE145227, including data from 770 patients with sepsis and 54 healthy controls, were downloaded from the GEO database and split into training and validation sets. Differentially expressed genes (DEGs) were identified and weighted gene co-expression network analysis (WGCNA) performed. A machine learning approach was applied to identify key genes, which were used to construct functional networks. Key genes associated with diagnosis and survival of sepsis were screened out. Finally, mouse and human blood samples were collected for RT-qPCR verification and flow cytometry analysis. Multiple organs injury, apoptosis and NETs expression were measured to evaluated effects of sulforaphane (SFN).

Results

Analysis of the obtained DEGs and WGCNA screened a total of 3396 genes in 3 modules, and intersection of the results of both analyses with 69 NETs-related genes, screened out seven genes (S100A12, SLC22A4, FCAR, CYBB, PADI4, DNASE1, MMP9) using machine learning algorithms. Of these, CYBB and FCAR were independent predictors of poor survival in patients with sepsis. Administration of SFN significantly alleviated murine lung NETs expression and injury, accompanied by whole blood CYBB mRNA level.

Conclusion

CYBB and FCAR may be reliable biomarkers of survival in patients with sepsis, as well as potential targets for sepsis treatment. SFN significantly alleviated NETs-related organs injury, suggesting the therapeutic potential by targeting CYBB in the future.

Transcriptomic profiles of multiple organ dysfunction syndrome phenotypes in pediatric critical influenza

Background

Influenza virus is responsible for a large global burden of disease, especially in children. Multiple Organ Dysfunction Syndrome (MODS) is a life-threatening and fatal complication of severe influenza infection.

Methods

We measured RNA expression of 469 biologically plausible candidate genes in children admitted to North American pediatric intensive care units with severe influenza virus infection with and without MODS. Whole blood samples from 191 influenza-infected children (median age 6.4 years, IQR: 2.2, 11) were collected a median of 27 hours following admission; for 45 children a second blood sample was collected approximately seven days later. Extracted RNA was hybridized to NanoString mRNA probes, counts normalized, and analyzed using linear models controlling for age and bacterial co-infections (FDR q<0.05).

Results

Comparing pediatric samples collected near admission, children with Prolonged MODS for ≥7 days (n=38; 9 deaths) had significant upregulation of nine mRNA transcripts associated with neutrophil degranulation (RETN, TCN1, OLFM4, MMP8, LCN2, BPI, LTF, S100A12, GUSB) compared to those who recovered more rapidly from MODS (n=27). These neutrophil transcripts present in early samples predicted Prolonged MODS or death when compared to patients who recovered, however in paired longitudinal samples, they were not differentially expressed over time. Instead, five genes involved in protein metabolism and/or adaptive immunity signaling pathways (RPL3, MRPL3, HLA-DMB, EEF1G, CD8A) were associated with MODS recovery within a week.

Conclusion

Thus, early increased expression of neutrophil degranulation genes indicated worse clinical outcomes in children with influenza infection, consistent with reports in adult cohorts with influenza, sepsis, and acute respiratory distress syndrome.

Immune dysregulation and RNA N6-methyladenosine modification in sepsis

Sepsis is defined as life-threatening organ dysfunction caused by the host immune dysregulation to infection. It is a highly heterogeneous syndrome with complex pathophysiological mechanisms. The host immune response to sepsis can be divided into hyper-inflammatory and immune-suppressive phases which could exist simultaneously. In the initial stage, systemic immune response is activated after exposure to pathogens. Both innate and adaptive immune cells undergo epigenomic, transcriptomic, and functional reprogramming, resulting in systemic and persistent inflammatory responses. Following the hyper-inflammatory phase, the body is in a state of continuous immunosuppression, which is related to immune cell apoptosis, metabolic failure, and epigenetic reprogramming. Immunosuppression leads to increased susceptibility to secondary infections in patients with sepsis. RNA N6-Methyladenosine (m6A) has been recognized as an indispensable epitranscriptomic modification involved in both physiological and pathological processes. Recent studies suggest that m6A could reprogram both innate and adaptive immune cells through posttranscriptional regulation of RNA metabolism. Dysregulated m6A modifications contribute to the pathogenesis of immune-related diseases. In this review, we summarize immune cell changes and the potential role of m6A modification in sepsis. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > RNA Editing and Modification.

Polyunsaturated fatty acids drive neutrophil extracellular trap formation in nonalcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is the hepatic manifestation of metabolic syndrome. Non-resolving inflammation, triggered by sustained accumulation of lipids, is an important driving force of NASH. Thus, unveiling metabolic immune regulation could help better understand the pathology and intervention of NASH. In this study, we found the recruitment of neutrophils is an early inflammatory event in NASH mice, following the formation of neutrophil extracellular traps (NETs). NET is an initiating factor which exacerbates inflammatory responses in macrophages. Inhibition of NETs using DNase I significantly alleviated inflammation in NASH mice. We further carried out a metabolomic study to identify possible metabolic triggers of NETs, and linoleic acid (LA) metabolic pathway was the most altered pathway. We re-analyzed published clinical data and validated that LA metabolism was highly correlated with NASH. Consistently, both LA and γ-linolenic acid (GLA) were active in triggering NETs formation by oxidative burst. Furthermore, we identified silybin, a hepatoprotective agent, as a potent NETosis inhibitor, which effectively blocked NETs formation both in vitro and in vivo. Together, this study not only provide new insights into metabolism-immune causal link in NASH progression, but also demonstrate silybin as an important inhibitor of NETs and its therapeutical potential in treating NETosis-related diseases.

Fast Track Diagnostic Tools for Clinical Management of Sepsis: Paradigm Shift from Conventional to Advanced Methods

Sepsis is one of the deadliest disorders in the new century due to specific limitations in early and differential diagnosis. Moreover, antimicrobial resistance (AMR) is becoming the dominant threat to human health globally. The only way to encounter the spread and emergence of AMR is through the active detection and identification of the pathogen along with the quantification of resistance. For better management of such disease, there is an essential requirement to approach many suitable diagnostic techniques for the proper administration of antibiotics and elimination of these infectious diseases. The current method employed for the diagnosis of sepsis relies on the conventional culture of blood suspected infection. However, this method is more time consuming and generates results that are false negative in the case of antibiotic pretreated samples as well as slow-growing microbes. In comparison to the conventional method, modern methods are capable of analyzing blood samples, obtaining accurate results from the suspicious patient of sepsis, and giving all the necessary information to identify the pathogens as well as AMR in a short period. The present review is intended to highlight the culture shift from conventional to modern and advanced technologies including their limitations for the proper and prompt diagnosing of bloodstream infections and AMR detection.

Nomogram and risk calculator for severe hypoxemia after heart valve surgery

Background

Hypoxemia is a very common issue in patients undergoing heart valve surgery (HVS), related to poor clinical outcomes. However, studies on severe hypoxemia (SH) after HVS have not been reported. The aims of this study were to identify predictors for SH in patients undergoing HVS and to develop and validate a risk prediction model.

Methods

Patients undergoing HVS between 2016 and 2019 in a cardiovascular center were enrolled and were assigned to training and validation sets by a 7:3 ratio. Based on whether patients developed SH, they were divided into two groups. By univariate and multivariate analysis, predictors for SH were identified. Based on the predictors and logistic rule, a nomogram and a risk calculator were generated. The model was evaluated using calibration, discrimination and clinical utility.

Results

The incidence rates of SH, moderate hypoxemia and mild hypoxemia were respectively 2.4, 23.9, and 58.2%. By multivariate analysis, seven independent risk factors for SH after HVS were identified, including body mass index, chronic obstructive pulmonary disease, renal insufficiency, white blood cell count, serum globulin, cardiopulmonary bypass time, and surgical types. The logistic model demonstrated satisfactory discrimination, calibration and clinical utility in both the training and validation sets. A nomogram and a risk calculator based on the logistic model were generated for easy application. Risk stratification was performed and three risk intervals were defined according to the nomogram and clinical practice. In addition, compared to patients without SH, patients with SH had significantly poorer clinical outcomes.

Conclusions

Postoperative hypoxemia was prevalent after HVS, related to poor clinical outcomes. A logistic model including seven independent predictors for SH after HVS were established and validated, which demonstrated satisfactory discrimination, calibration and clinical utility. The results of this study may provide help to individualized risk assessment, early prevention and perioperative management.

Incidence, Risk Factors, and Outcomes of Severe Hypoxemia After Cardiac Surgery

Background

Hypoxemia is common in patients undergoing cardiac surgery, however, few studies about severe hypoxemia (SH) after cardiac surgery exist. The objectives of this study were to clarify the incidence, risk factors, and outcomes of SH after cardiac surgery.

Methods

Patients undergoing cardiac surgery from 2016 to 2019 in a single center were enrolled and were divided into two groups based on whether postoperative SH developed. Independent risk factors for SH were identified by univariate and multivariate analysis. Model selection statistics were applied to help determine the most parsimonious final model.

Results

Severe hypoxemia developed in 222 of the 5,323 included patients (4.2%), was associated with poorer clinical outcomes. Six independent risk factors for SH after cardiac surgery were identified by multivariate analysis, such as surgical types, white blood cell (WBC) count, body mass index (BMI), serum albumin, cardiopulmonary bypass (CPB) time, and intraoperative transfusion of red blood cells (RBCs). After comprehensively considering the discrimination, calibration, and simplicity, the most appropriate and parsimonious model was finally established using four predictors, such as WBC count, BMI, CPB time, and intraoperative transfusion of RBCs. A nomogram and a web-based risk calculator based on the final model were constructed to facilitate clinical practice. Patients were stratified into three risk groups based on the nomogram and clinical practice.

Conclusion

Severe hypoxemia was common after cardiac surgery and was associated with poorer clinical outcomes. A parsimonious final model with good discrimination, calibration, and clinical utility was constructed, which may be helpful for personalized risk assessment and targeted intervention.

Neutrophils in COVID-19: Not Innocent Bystanders

Unusually for a viral infection, the immunological phenotype of severe COVID-19 is characterised by a depleted lymphocyte and elevated neutrophil count, with the neutrophil-to-lymphocyte ratio correlating with disease severity. Neutrophils are the most abundant immune cell in the bloodstream and comprise different subpopulations with pleiotropic actions that are vital for host immunity. Unique neutrophil subpopulations vary in their capacity to mount antimicrobial responses, including NETosis (the generation of neutrophil extracellular traps), degranulation and de novo production of cytokines and chemokines. These processes play a role in antiviral immunity, but may also contribute to the local and systemic tissue damage seen in acute SARS-CoV-2 infection. Neutrophils also contribute to complications of COVID-19 such as thrombosis, acute respiratory distress syndrome and multisystem inflammatory disease in children. In this Progress review, we discuss the anti-viral and pathological roles of neutrophils in SARS-CoV-2 infection, and potential therapeutic strategies for COVID-19 that target neutrophil-mediated inflammatory responses.

Integrated Single Cell and Bulk RNA-Seq Analysis Revealed Immunomodulatory Effects of Ulinastatin in Sepsis: A Multicenter Cohort Study

Sepsis is a leading cause of morbidity and mortality in the intensive care unit, which is caused by unregulated inflammatory response leading to organ injuries. Ulinastatin (UTI), an immunomodulatory agent, is widely used in clinical practice and is associated with improved outcomes in sepsis. But its underlying mechanisms are largely unknown. Our study integrated bulk and single cell RNA-seq data to systematically explore the potential mechanisms of the effects of UTI in sepsis. After adjusting for potential confounders in the negative binomial regression model, there were more genes being downregulated than being upregulated in the UTI group. These down-regulated genes were enriched in the neutrophil involved immunity such as neutrophil activation and degranulation, indicating the immunomodulatory effects of UTI is mediated via regulation of neutrophil activity. By deconvoluting the bulk RNA-seq samples to obtain fractions of cell types, the Myeloid-derived suppressor cells (MDSC) were significantly expanded in the UTI treated samples. Further cell-cell communication analysis revealed some signaling pathways such as ANEEXIN, GRN and RESISTIN that might be involved in the immunomodulatory effects of UTI. The study provides a comprehensive reference map of transcriptional states of sepsis treated with UTI, as well as a general framework for studying UTI-related mechanisms.

Cell-Free DNA, Neutrophil extracellular traps (NETs), and Endothelial Injury in Coronavirus Disease 2019– (COVID-19–) Associated Acute Kidney Injury

Introduction: Neutrophil extracellular traps (NETs) release (i.e., NETosis) has been recently implicated in the pathomechanism underlying severe end-organ damage in Coronavirus Disease 2019 (COVID-19) and could present a novel therapeutic target. We aimed to determine whether circulating levels of cell-free DNA (cfDNA), a surrogate for NETosis, may be associated with the development of acute kidney injury (AKI), a major contributor to poor outcomes and mortality in COVID-19. Methods: Blood samples were collected prospectively from adult patients infected with SARS-CoV-2 presenting to the emergency department (ED). Circulating levels of cfDNA were quantified from patients' serum. Further assessment of correlations between cfDNA levels and markers of AKI (i.e., serum creatinine (SCr), cystatin C, neutrophil gelatinase–associated lipocalin (NGAL)), biomarkers of thrombotic microangiopathy and of inflammation in patients' serum was performed. Results: Fifty-one COVID-19 patients were enrolled. cfDNA levels were found to be significantly higher in those who developed severe AKI (p < 0.001) and those needing renal replacement therapy (p = 0.020). cfDNA positively correlated with ED SCr, NGAL, cystatin C, neutrophil count, neutrophil-to-lymphocyte ratio, C3a, C5a, Scb5-9, IL-6, IL-8, IL-10, TNF-α, LDH, CRP, ferritin, and fibrinogen and negatively correlated with ADAMTS13/von-Willebrand factor ratio and lymphocyte count. In a multivariate logistic regression, a one-unit increase in cfDNA value was associated with 4.6% increased odds of severe AKI (OR = 1.046; p = 0.040). Finally, cfDNA significantly correlated with established NETs components, myeloperoxidase, and neutrophil elastase. Conclusion: Intravascular NETosis could be an important contributing factor in the development of microthrombosis and COVID-19-associated AKI. Further research is urgently needed to understand the role of NETosis in COVID-19 and evaluate therapeutic avenues for targeting this process.

Do Circulating Histones Represent the Missing Link among COVID-19 Infection and Multiorgan Injuries, Microvascular Coagulopathy and Systemic Hyperinflammation?

Several studies shed light on the interplay among inflammation, thrombosis, multi-organ failures and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Increasing levels of both free and/or circulating histones have been associated to coronavirus disease 2019 (COVID-19), enhancing the risk of heart attack and stroke with coagulopathy and systemic hyperinflammation. In this view, by considering both the biological and clinical rationale, circulating histones may be relevant as diagnostic biomarkers for stratifying COVID-19 patients at higher risk for viral sepsis, and as predictive laboratory medicine tool for targeted therapies.

Role of Neutrophils and NETs in Animal Models of Thrombosis

Thrombosis is one of the major causes of mortality worldwide. Notably, it is not only implicated in cardiovascular diseases, such as myocardial infarction (MI), stroke, and pulmonary embolism (PE), but also in cancers. Understanding the cellular and molecular mechanisms involved in platelet thrombus formation is a major challenge for scientists today. For this purpose, new imaging technologies (such as confocal intravital microscopy, electron microscopy, holotomography, etc.) coupled with animal models of thrombosis (mouse, rat, rabbit, etc.) allow a better overview of this complex physiopathological process. Each of the cellular components is known to participate, including the subendothelial matrix, the endothelium, platelets, circulating cells, and, notably, neutrophils. Initially known as immune cells, neutrophils have been considered to be part of the landscape of thrombosis for more than a decade. They participate in this biological process through their expression of tissue factor (TF) and protein disulfide isomerase (PDI). Moreover, highly activated neutrophils are described as being able to release their DNA and thus form chromatin networks known as “neutrophil extracellular traps” (NETs). Initially, described as “dead sacrifices for a good cause” that prevent the dissemination of bacteria in the body, NETs have also been studied in several human pathologies, such as cardiovascular and respiratory diseases. Many articles suggest that they are involved in platelet thrombus formation and the activation of the coagulation cascade. This review presents the models of thrombosis in which neutrophils and NETs are involved and describes their mechanisms of action. We have even highlighted the medical diagnostic advances related to this research.