Neutrophils in the initiation and resolution of acute pulmonary inflammation: understanding biological function and therapeutic potential

Semaphorin 7A coordinates neutrophil response during pulmonary inflammation and sepsis

ABSTRACT

Pulmonary defense mechanisms are critical for host integrity during pneumonia and sepsis. This defense is fundamentally dependent on the activation of neutrophils during the innate immune response. Recent work has shown that semaphorin 7A (Sema7A) holds significant impact on platelet function, yet its role on neutrophil function within the lung is not well understood. This study aimed to identify the role of Sema7A during pulmonary inflammation and sepsis. In patients with acute respiratory distress syndrome (ARDS), we were able to show a correlation between Sema7A and oxygenation levels. During subsequent workup, we found that Sema7A binds to the neutrophil PlexinC1 receptor, increasing integrins, and L-selectin on neutrophils. Sema7A prompted neutrophil chemotaxis in vitro and the formation of platelet-neutrophil complexes in vivo. We also observed altered adhesion and transmigration of neutrophils in Sema7A-/-animals in the lung during pulmonary inflammation. This effect resulted in increased number of neutrophils in the interstitial space of Sema7A-/- animals but reduced numbers of neutrophils in the alveolar space during pulmonary sepsis. This finding was associated with significantly worse outcome of Sema7A-/- animals in a model of pulmonary sepsis. Sema7A has an immunomodulatory effect in the lung, affecting pulmonary sepsis and ARDS. This effect influences the response of neutrophils to external aggression and might influence patient outcome. This trial was registered at www.ClinicalTrials.gov as #NCT02692118.

Zerumbone exhibits anti-inflammatory effects by suppressing eicosanoid signaling: Evidence from LPS-induced peripheral blood leukocytes

Zerumbone, a sesquiterpene isolated from Zingiber zerumbet, has many bioactivities, exhibiting anti-inflammatory properties. However, the effect of zerumbone on the eicosanoid signaling pathway has yet to be examined. Here, we deciphered the anti-eicosanoid properties of zerumbone isolated from ginger. The molecular interaction between zerumbone and eicosanoid metabolizing enzymes (COX-2, 5-LOX, FLAP, and LTA4-hydrolase) and receptors (EP-4, BLT-1, and ICAM-1) along with NOS-2 were assessed using Auto-Dock 4.2 and visualized by chimera and Liggplot+ software. Further, the leukocytes were treated with zerumbone (1-20 μM) and activated using bacterial lipopolysaccharide (LPS-10 nM). The oxidative stress (OS) markers, antioxidant enzymes, and the eicosanoid pathway mediators such as COX-2, 5-LOX, BLT-1, and EP-4 were assessed. The molecular interaction of zerumbone with eicosanoids showed a higher binding affinity with mPGES-1, followed by NOS-2, FLAP, COX-2, LTA-4-hydrolase, and BLT-1. The concentration of 5 μM zerumbone effectively prevented the generation of reactive oxygen species (ROS) and nitric oxide (NO). Likewise, zerumbone significantly (p<0.05) inhibited COX-2, 5-LOX, NOS-2, EP-4, BLT-1, and ICAM-1 expression in LPS-induced peripheral blood leukocytes from rats. Further, the zerumbone treatment on the human PBMCs activated with LPS showed significant inhibition in the expression of ICAM1, COX-2, 5-LOX, and the generation of inflammatory cytokines compared to the control. Overall, the data presented infers that zerumbone positively modulates critical enzymes and receptors of eicosanoids in leukocytes activated with lipopolysaccharides. Thus, zerumbone can be a potential anti-eicosanoid drug in managing inflammation.

Dose-dependent multi-organ injury following lipopolysaccharide gas inhalation

Lipopolysaccharide (LPS) is widely used to establish various animal models, including models of acute lung injury, cardiomyocyte damage, and acute kidney injury. Currently, there is no consensus on the diagnosis and treatment of LPS-induced disease. We herein present a case series of four patients who developed dose-dependent multi-organ injury, including acute lung injury and acute kidney injury, after inhaling LPS gas in a sealed room. These patients exhibited varying degrees of multi-organ injury characterized by inflammatory cell infiltration and secretion of proinflammatory cytokines. One patient showed progressive symptoms even with active treatment, leading to mild pulmonary fibrosis. This study emphasizes the importance of early diagnosis and treatment of significant LPS exposure and suggests personalized treatment approaches for managing LPS poisoning.

Hydrogen ameliorates endotoxin-induced acute lung injury through AMPK-mediated bidirectional regulation of Caspase3

Septic lung injury is characterized by uncontrollable inflammatory infiltrations and acute onset bilateral hypoxemia. Evidence has emerged of the beneficial effect of hydrogen in acute lung injury (ALI), but the underlying mechanism is unclear. In this research, the recovery action of hydrogen on lipopolysaccharide (LPS)-induced ALI in mice and A549 cells was investigated. The 7-day survival rate and body weight of mice were measured after intraperitoneal injection of LPS. Lung function was determined by a whole body plethysmography (WBP) system using the indicators respiratory rate and enhanced pause. Hematoxylin and eosin (HE) staining confirmed the signs of pulmonary edema and inflammatory ooze. Reverse transcription-polymerase chain reaction (RT-PCR) quantification was used to detect the expression of inflammatory factors. Western blotting analysis evaluated the expression levels of involved proteins in the AMP-activated protein kinase (AMPK) pathway. The experimental results confirmed that hydrogen provided an essential solution to the dissipative effects of LPS on survival rate, weight loss and lung function. The LPS-stimulated inflammatory factors, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were also suppressed by hydrogen in A549 cells. Western blot analysis showed that hydrogen significantly upregulated the levels of phosphorylated AMPK (p-AMPK) and lowered the LPS-induced increased expression of dynamin-related protein 1 (Drp1) and Caspase3. These findings prove that hydrogen attenuated LPS-treated ALI by activating the AMPK pathway, supporting the feasibility of hydrogen treatment for sepsis.

Hispidulin exerts a protective effect against oleic acid induced-ARDS in the rat via inhibition of ACE activity and MAPK pathway

This study investigates the protective role of Hispidulin on acute respiratory distress syndrome (ARDS) in rats. Rats were divided into three groups: control, ARDS, ARDS+ Hispidulin. The ARDS models were established by injecting rats with oleic acid. Hispidulin (100 mg/kg) was injected i.p. an hour before ARDS. Myeloperoxidase (MPO), Interleukin-8 (IL-8), Mitogen-activated protein kinases (MAPK), Lipid Peroxidation (LPO), Superoxide Dismutase (SOD), Glutathione (GSH), and Angiotensin-converting enzyme (ACE) were determined by ELISA. Tumor necrosis factor-alpha (TNF-α) expression was described by RT-qPCR. Caspase-3 immunostaining was performed to evaluate apoptosis. Compared with the model group, a significant decrease was observed in the MPO, IL-8, MAPK, ACE, LPO levels, and TNF-α expression in the ARDS+ Hispidulin group. Moreover, reduced caspase-3 immunoreactivity and activity of ACE were detected in the Hispidulin+ARDS group. The protective effect of Hispidulin treatment may act through inhibition of the ACE activity and then regulation of inflammatory cytokine level and alteration of apoptosis.

The proteolytic airway environment associated with pneumonia acts as a barrier for treatment with anti-infective antibodies

Like pneumonia, coronavirus disease 2019 (COVID-19) is characterized by a massive infiltration of innate immune cells (such as polymorphonuclear leukocytes) into the airways and alveolar spaces. These cells release proteases that may degrade therapeutic antibodies and thus limit their effectiveness. Here, we investigated the in vitro and ex vivo impact on anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) IgG1s and other IgG subclasses (IgG2 and IgG4) of the neutrophil elastase, proteinase 3 and cathepsin G (the three main neutrophil serine proteases) found in endotracheal aspirates from patients with severe COVID-19. Although the IgGs were sensitive to neutrophil serine proteases, IgG2 was most resistant to proteolytic degradation. The two anti-SARS CoV2 antibodies (casirivimab and imdevimab) were sensitive to the lung's proteolytic environment, although neutrophil serine protease inhibitors only partly limited the degradation. Overall, our results show that the pneumonia-associated imbalance between proteases and their inhibitors in the airways contributes to degradation of antiviral antibodies.

LC-QToF chemical profiling of Euphorbia grantii Oliv. and its potential to inhibit LPS-induced lung inflammation in rats via the NF-κB, CY450P2E1, and P38 MAPK14 pathways

Acute lung injury (ALI) is a life-threatening syndrome that causes high morbidity and mortality worldwide. The aerial parts of Euphorbia grantii Oliv. were extracted with methanol to give a total methanolic extract (TME), which was further fractionated into dichloromethane (DCMF) and the remaining mother liquor (MLF) fractions. Biological guided anti-inflammatory assays in vitro revealed that the DCMF showed the highest activity (IC50 6.9 ± 0.2 μg/mL and 0.29 ± 0.01 μg/mL) compared to. celecoxib (IC50 of 88.0 ± 1 μg/mL and 0.30 ± 0.01 μg/mL) on COX-1 and COX-2, respectively. Additionally, anti-LOX activity was IC50 = 24.0 ± 2.5 μg/mL vs. zileuton with IC50 of 40.0 ± 0.5 μg/mL. LC-DAD-QToF analysis of TME and the active DCMF resulted in the tentative identification and characterization of 56 phytochemical compounds, where the diterpenes were the dominated metabolites. An LPS-induced inflammatory model of ALI (10 mg/kg i.p) was used to assess the anti-inflammatory potential of DCMF in vivo at dose of 200 mg/kg and 300 mg/kg compared to dexamethasone (5 mg/kg i.p). Our treatments significantly reduced the pro-inflammatory cytokines (TNF-α, IL-1, IL-6, and MPO), increased the activity of antioxidant enzymes (SOD, CAT, and GSH), decreased the activity of oxidative stress enzyme (MDA), and reduced the expression of inflammatory genes (p38.MAPK14 and CY450P2E1). The western blotting of NF-κB p65 in lung tissues was inhibited after orally administration of the DCMF. Histopathological study of the lung tissues, scoring, and immunohistochemistry of transforming growth factor-beta 1 (TGF-β1) were also assessed. In both dose regimens, DCMF of E. grantii prevented further lung damage and reduced the side effects of LPS on acute lung tissue injury.

DPP-4 exacerbates LPS-induced endothelial cells inflammation via integrin-α5β1/FAK/AKT signaling

Endothelial dysfunction plays a pivotal role in the pathogenesis of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Dipeptidyl peptidase IV (DPP-4), a cell surface glycoprotein, has been implicated in endothelial inflammation and barrier dysfunction. In this study, the role of DPP-4 on lipopolysaccharide (LPS)-induced pulmonary microvascular endothelial cells (HPMECs) dysfunction and the underlying mechanism were investigated by siRNA-mediated knockdown of DPP-4. Our results indicated that LPS (1 μg/ml) challenge resulted in either the production and releasing of DPP-4, as well as the secretion of IL-6 and IL-8 in HPMECs. DPP-4 knockdown inhibited chemokine releasing and monolayer hyper-permeability in LPS challenged HPMECs. When cocultured with human polymorphonuclear neutrophils (PMNs), DPP4 knockdown suppressed LPS-induced neutrophil-endothelial adhesion, PMN chemotaxis and trans-endothelial migration. Western blotting showed that DPP-4 knockdown attenuated LPS-induced activation of TLR4/NF-κB pathway. Immunoprecipitation and liquid chromatography-tandem mass spectrometry revealed that DPP-4 mediated LPS-induced endothelial inflammation by interacting with integrin-α5β1. Moreover, exogenous soluble DPP-4 treatment sufficiently activated integrin-α5β1 downstream FAK/AKT/NF-κB signaling, thereafter inducing ICAM-1 upregulation in HPMECs. Collectively, our results suggest that endothelia synthesis and release DPP-4 under the stress of endotoxin, which interact with integrin-α5β1 complex in an autocrine or paracrine manner to exacerbate endothelial inflammation and enhance endothelial cell permeability. Therefore, blocking DDP-4 could be a potential therapeutic strategy to prevent endothelial dysfunction in ALI/ARDS.

Engineered Biomimetic Nanovesicles Based on Neutrophils for Hierarchical Targeting Therapy of Acute Respiratory Distress Syndrome

Acute Respiratory Distress Syndrome (ARDS) is a clinically severe respiratory disease that causes severe medical and economic burden. To improve therapeutic efficacy, effectively targeting delivery to the inflamed lungs and inflamed cells remains an ongoing challenge. Herein, we designed engineered biomimetic nanovesicles (DHA@ANeu-DDAB) by fusion of lung-targeting functional lipid, neutrophil membrane containing activated β2 integrins, and the therapeutic lipid, docosahexaenoic acid (DHA). By the advantage of lung targeting lipid and β2 integrin targeting adhesion, DHA@ANeu-DDAB can first target lung tissue and further target inflammatory vascular endothelial cells, to achieve "tissue first, cell second" hierarchical delivery. In addition, the β2 integrins in DHA@ANeu-DDAB could bind to the intercellular cell adhesion molecule-1/2 (ICAM-1/2) ligand on the endothelium in the inflamed blood vessels, thus inhibiting neutrophils' infiltration in the blood circulation. DHA administration to inflamed lungs could effectively regulate macrophage phenotype and promote its anti-inflammatory activity via enhanced biosynthesis of specialized pro-resolving mediators. In the lipopolysaccharide-induced ARDS mouse model, DHA@ANeu-DDAB afforded a comprehensive and efficient inhibition of lung inflammation and promoted acute lung damage repair. Through mimicking physiological processes, these engineered biomimetic vesicles as a delivery system possess good potential in targeting therapy for ARDS.

Hippophae rhamnoides Prevents Oleic Acid-Induced Acute Respiratory Distress Syndrome by Releasing Acetylcholinesterase Activity and Mitigation of Angiotensin-Converting Enzyme Level

Hippophae rhamnoides exhibit a wide variety of medicinal and pharmacological effects. The present study aims to determine the role of ethanol extract of H. rhamnoides on oleic acid (OA)-induced acute respiratory distress syndrome (ARDS) in rats. Male rats were randomly divided into the following groups: (I) Control, (II) OA, and (III) OA+H. rhamnoides. H. rhamnoides extract (500 mg/kg) was given orally for 2 weeks before OA in Group III. Levels of total antioxidant capacity, total oxidant status (TOS), myeloperoxidase (MPO), mitogen-activated protein kinase (MAPK), acetylcholinesterase (AChE), and angiotensin-converting enzyme (ACE) were quantified by enzyme-linked immunosorbent assay (ELISA). Real time quantitative polymerase chain reaction was utilized to evaluate the expression of nuclear factor kappa B (NF-κB), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and matrix metalloproteinase 2 (MMP2). Also, Caspase-3 immunostaining and expression were performed to evaluate apoptosis. Compared with the OA group, there was a significantly decrease in the levels of MPO, TOS, MAPK, and ACE and in the expression of NF-κB, TNF-α, IL-6, MMP2, and Caspase-3 in the H. rhamnoides administration group. Moreover, the activity of AChE and level of TAS were substantially higher in the H. rhamnoides administration compared with the OA group. The findings in the study suggest that the protective effect of H. rhamnoides pretreatment may act through inhibition of the ACE activity, releasing AChE, regulation of inflammatory cytokine levels, and suppression of apoptotic process in ARDS.

A guide to ERK dynamics, part 2: downstream decoding

Signaling by the extracellular signal-regulated kinase (ERK) pathway controls many cellular processes, including cell division, death, and differentiation. In this second installment of a two-part review, we address the question of how the ERK pathway exerts distinct and context-specific effects on multiple processes. We discuss how the dynamics of ERK activity induce selective changes in gene expression programs, with insights from both experiments and computational models. With a focus on single-cell biosensor-based studies, we summarize four major functional modes for ERK signaling in tissues: adjusting the size of cell populations, gradient-based patterning, wave propagation of morphological changes, and diversification of cellular gene expression states. These modes of operation are disrupted in cancer and other related diseases and represent potential targets for therapeutic intervention. By understanding the dynamic mechanisms involved in ERK signaling, there is potential for pharmacological strategies that not only simply inhibit ERK, but also restore functional activity patterns and improve disease outcomes.

Role of DCLK1/Hippo pathway in type II alveolar epithelial cells differentiation in acute respiratory distress syndrome

BACKGROUND

Delay in type II alveolar epithelial cell (AECII) regeneration has been linked to higher mortality in patients with acute respiratory distress syndrome (ARDS). However, the interaction between Doublecortin-like kinase 1 (DCLK1) and the Hippo signaling pathway in ARDS-associated AECII differentiation remains unclear. Therefore, the objective of this study was to understand the role of the DCLK1/Hippo pathway in mediating AECII differentiation in ARDS.

MATERIALS AND METHODS

AECII MLE-12 cells were exposed to 0, 0.1, or 1 μg/mL of lipopolysaccharide (LPS) for 6 and 12 h. In the mouse model, C57BL/6JNarl mice were intratracheally (i.t.) injected with 0 (control) or 5 mg/kg LPS and were euthanized for lung collection on days 3 and 7.

RESULTS

We found that LPS induced AECII markers of differentiation by reducing surfactant protein C (SPC) and p53 while increasing T1α (podoplanin) and E-cadherin at 12 h. Concurrently, nuclear YAP dynamic regulation and increased TAZ levels were observed in LPS-exposed AECII within 12 h. Inhibition of YAP consistently decreased cell levels of SPC, claudin 4 (CLDN-4), galectin 3 (LGALS-3), and p53 while increasing transepithelial electrical resistance (TEER) at 6 h. Furthermore, DCLK1 expression was reduced in isolated human AECII of ARDS, consistent with the results in LPS-exposed AECII at 6 h and mouse SPC-positive (SPC+) cells after 3-day LPS exposure. We observed that downregulated DCLK1 increased p-YAP/YAP, while DCLK1 overexpression slightly reduced p-YAP/YAP, indicating an association between DCLK1 and Hippo-YAP pathway.

CONCLUSIONS

We conclude that DCLK1-mediated Hippo signaling components of YAP/TAZ regulated markers of AECII-to-AECI differentiation in an LPS-induced ARDS model.

Role of Neutrophil Extracellular Traps in Health and Disease Pathophysiology: Recent Insights and Advances

Neutrophils are the principal trouper of the innate immune system. Activated neutrophils undergo a noble cell death termed NETosis and release a mesh-like structure called neutrophil extracellular traps (NETs) as a part of their defensive strategy against microbial pathogen attack. This web-like architecture includes a DNA backbone embedded with antimicrobial proteins like myeloperoxidase (MPO), neutrophil elastase (NE), histones and deploys in the entrapment and clearance of encountered pathogens. Thus NETs play an inevitable beneficial role in the host's protection. However, recent accumulated evidence shows that dysregulated and enhanced NET formation has various pathological aspects including the promotion of sepsis, pulmonary, cardiovascular, hepatic, nephrological, thrombotic, autoimmune, pregnancy, and cancer diseases, and the list is increasing gradually. In this review, we summarize the NET-mediated pathophysiology of different diseases and focus on some updated potential therapeutic approaches against NETs.

Granulocytes subsets and their divergent functions in host resistance to Mycobacterium tuberculosis - a 'tipping-point' model of disease exacerbation

Granulocytes are innate immune effector cells with essential functions in host resistance to bacterial infections. I will discuss emerging evidence that during Mycobacterium tuberculosis infection, counter-intuitively, eosinophils are host-protective while neutrophils are host detrimental. Additionally, I will propose a 'tipping-point' model in which neutrophils are an integral part of a feedforward loop driving tuberculosis disease exacerbation.

Discovery of Highly Selective and Orally Bioavailable PI3Kδ Inhibitors with Anti-Inflammatory Activity for Treatment of Acute Lung Injury

PI3Kδ is a promising target for the treatment of inflammatory disease; however, the application of PI3Kδ inhibitors in acute respiratory inflammatory diseases is rarely investigated. In this study, through scaffold hopping design, we report a new series of 1H-pyrazolo[3,4-d]pyrimidin-4-amine-tethered 3-methyl-1-aryl-1H-indazoles as highly selective and potent PI3Kδ inhibitors with significant anti-inflammatory activities for treatment of acute lung injury (ALI). There were 29 compounds designed, prepared, and subjected to PI3Kδ inhibitory activity evaluation and anti-inflammatory activity evaluation in macrophages. (S)-29 was identified as a candidate with high PI3Kδ inhibitory activity, isoform selectivity, and high oral bioavailability. The in vivo administration of (S)-29 at 10 mg/kg dosage could significantly ameliorate histopathological changes and attenuate lung inflammation in lung tissues of LPS-challenged mice. Molecular docking demonstrated the success of scaffold hopping design. Overall, (S)-29 is a potent PI3Kδ inhibitor which might be a promising candidate for the treatment of ALI.

Not all vaping is the same: differential pulmonary effects of vaping cannabidiol versus nicotine

RATIONALE

Vaping has become a popular method of inhaling various psychoactive substances. While evaluating respiratory effects of vaping have primarily focused on nicotine-containing products, cannabidiol (CBD)-vaping is increasingly becoming popular. It currently remains unknown whether the health effects of vaping nicotine and cannabinoids are similar.

OBJECTIVES

This study compares side by side the pulmonary effects of acute inhalation of vaporised CBD versus nicotine.

METHODS

In vivo inhalation study in mice and in vitro cytotoxicity experiments with human cells were performed to assess the pulmonary damage-inducing effects of CBD or nicotine aerosols emitted from vaping devices.

MEASUREMENTS AND MAIN RESULTS

Pulmonary inflammation in mice was scored by histology, flow cytometry, and quantifying levels of proinflammatory cytokines and chemokines. Lung damage was assessed by histology, measurement of myeloperoxidase activity and neutrophil elastase levels in the bronchoalveolar lavage fluid and lung tissue. Lung epithelial/endothelial integrity was assessed by quantifying BAL protein levels, albumin leak and pulmonary FITC-dextran leak. Oxidative stress was determined by measuring the antioxidant potential in the BAL and lungs. The cytotoxic effects of CBD and nicotine aerosols on human neutrophils and human small airway epithelial cells were evaluated using in vitro air-liquid interface system. Inhalation of CBD aerosol resulted in greater inflammatory changes, more severe lung damage and higher oxidative stress compared with nicotine. CBD aerosol also showed higher toxicity to human cells compared with nicotine.

CONCLUSIONS

Vaping of CBD induces a potent inflammatory response and leads to more pathological changes associated with lung injury than vaping of nicotine.

HSP47: A Therapeutic Target in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease characterized by a progressive decline in lung function and poor prognosis. The deposition of the extracellular matrix (ECM) by myofibroblasts contributes to the stiffening of lung tissue and impaired oxygen exchange in IPF. Type I collagen is the major ECM component and predominant collagen protein deposited in chronic fibrosis, suggesting that type I collagen could be a target of drugs for fibrosis treatment. Heat shock protein 47 (HSP47), encoded by the serpin peptidase inhibitor clade H, member 1 gene, is a stress-inducible collagen-binding protein. It is an endoplasmic reticulum-resident molecular chaperone essential for the correct folding of procollagen. HSP47 expression is increased in cellular and animal models of pulmonary fibrosis and correlates with pathological manifestations in human interstitial lung diseases. Various factors affect HSP47 expression directly or indirectly in pulmonary fibrosis models. Overall, understanding the relationship between HSP47 expression and pulmonary fibrosis may contribute to the development of novel therapeutic strategies.

Synthesis of Sialyl LewisX Mimetics with E- and P-Selectin Binding Properties and Immunosuppressive Activity

E- and P-selectins are adhesion proteins implicated in immune cell recruitment at sites of infection, making them important drug targets for diseases involving excessive and uncontrolled inflammation. In this study, we developed an efficient strategy to synthesize bicyclic galactopyranosides through a key stereoselective equatorial C4-propiolate addition and TMSCN axial C-glycosidation. The nitrile group can then be converted to the carboxyl and different bioisosteres at a late stage in the synthesis, allowing for various derivatizations to potentially enhance biological activity. The sialyl LewisX glycomimetic featuring this rigidified bicyclic galactopyranoside moiety prevents neutrophil adhesion to endothelial cells in vitro by binding to both E- and P-selectins. We show here that the axial carboxyl analogue blocks immune cell recruitment in vivo, demonstrating its potential as an immunomodulator.

A comprehensive overview of investigational elastase inhibitors for the treatment of acute respiratory distress syndrome

INTRODUCTION

Excessive activity of neutrophil elastase (NE), the main enzyme present in azurophil granules in the neutrophil cytoplasm, may cause tissue injury and remodeling in various lung diseases, including acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), in which it is crucial to the immune response and inflammatory process. Consequently, NE is a possible target for therapeutic intervention in ALI/ARDS.

AREAS COVERED

The protective effects of several NE inhibitors in attenuating ALI/ARDS in several models of lung injury are described. Some of these NE inhibitors are currently in clinical development, but only sivelestat has been evaluated as a treatment for ALI/ARDS.

EXPERT OPINION

Preclinical research has produced encouraging information about using NE inhibitors. Nevertheless, only sivelestat has been approved for this clinical indication, and only in Japan and South Korea because of the conflicting results of clinical trials and likely also because of the potential adverse events. Identifying subsets of patients with ARDS most likely to benefit from NE inhibitor treatment, such as the hyperinflammatory phenotype, and using a more advanced generation of NE inhibitors than sivelestat could enable better clinical results than those obtained with elastase inhibitors.

Liang-Ge-San: a classic traditional Chinese medicine formula, attenuates acute inflammation via targeting GSK3β

Sepsis is a serious life-threatening health disorder with high morbidity and mortality rates that burden the world, but there is still a lack of more effective and reliable drug treatment. Liang-Ge-San (LGS) has been shown to have anti-inflammatory effects and is a promising candidate for the treatment of sepsis. However, the anti-sepsis mechanism of LGS has still not been elucidated. In this study, a set of genes related to inflammatory chemotaxis pathways was downloaded from Encyclopedia of Genes and Genomes (KEGG) and integrated with sepsis patient information from the Gene Expression Omnibus (GEO) database to perform differential gene expression analysis. Glycogen synthase kinase-3β (GSK-3β) was found to be the feature gene after these important genes were examined using the three algorithms Random Forest, support vector machine recursive feature elimination (SVM-REF), and least absolute shrinkage and selection operator (LASSO), and then intersected with possible treatment targets of LGS found through the search. Upon evaluation, the receiver operating characteristic (ROC) curve of GSK-3β indicated an important role in the pathogenesis of sepsis. Immune cell infiltration analysis suggested that GSK-3β expression was associated with a variety of immune cells, including neutrophils and monocytes. Next, lipopolysaccharide (LPS)-induced zebrafish inflammation model and macrophage inflammation model was used to validate the mechanism of LGS. We found that LGS could protect zebrafish against a lethal challenge with LPS by down-regulating GSK-3β mRNA expression in a dose-dependent manner, as indicated by a decreased neutrophils infiltration and reduction of inflammatory damage. The upregulated mRNA expression of GSK-3β in LPS-induced stimulated RAW 264.7 cells also showed the same tendency of depression by LGS. Critically, LGS could induce M1 macrophage polarization to M2 through promoting GSK-3β inactivation of phosphorylation. Taken together, we initially showed that anti-septic effects of LGS is related to the inhibition on GSK-3β, both in vitro and in vivo.

Analysis of AT7519 as a pro-resolution compound in an acetaminophen-induced mouse model of acute inflammation by UPLC-MS/MS

BACKGROUND

Uncontrolled inflammation contributes to the progression of organ damage in acute conditions, such as acetaminophen-induced acute liver injury (APAP-ALI) and there are limited treatments for this condition. AT7519, a cyclic-dependent kinase inhibitor (CDKI), has been used successfully in several conditions, to resolve inflammation and return tissue homeostatic functions. AT7519 has not been assessed in APAP-ALI and its effect on APAP metabolism is unknown. Targeted chromatography and mass spectrometry can be used to assess multiple compounds simultaneously and this approach has not been applied yet to measure APAP and AT7519 in a mouse model.

RESULTS

We show an optimised simple and sensitive LC-MS/MS method for determining concentrations of AT7519 and APAP in low volumes of mouse serum. Using positive ion mode electrospray ionisation, separation of AT7519 and APAP and their corresponding isotopically labelled internal standards [2H]8-AT16043M (d8-AT7519) and [2H]8-APAP (d4-APAP), was achieved on an Acquity UPLC BEH C18 column (100 × 2.1 mm; 1.7μm). A gradient mobile phase system of water and methanol was delivered at a flow rate of 0.5 mL/min with a run time of 9 min. Calibration curves were linear, intra-day and inter-day precision and accuracy were acceptable and the covariates of all standards and quality control replicates were less than 15%. The method was successfully applied to evaluate AT7519 and APAP levels 20 h post AT7519 (10 mg/mg) in C57Bl6J wild type mouse serum treated with either vehicle or APAP. Serum AT7519 was significantly higher in mice that had received APAP compared to control, but there was no correlation between APAP and AT7519 quantification. There was also no correlation of AT7519 and hepatic damage or proliferation markers.

CONCLUSION

We optimised an LC-MS/MS method to quantify both AT7519 and APAP in mouse serum (50 µL), using labelled internal standards. Application of this method to a mouse model of APAP toxicity proved effective in accurately measuring APAP and AT7519 concentrations after i.p. dosing. AT7519 was significantly higher in mice with APAP toxicity, indicating hepatic metabolism of this CDKI, but there was no correlation with markers of hepatic damage or proliferation, demonstrating that this dose of AT7519 (10 mg/kg) does not contribute to hepatic damage or repair. This optimised method can be used for future investigations of AT7519 in APAP in mice.

An Inhalable Hybrid Biomimetic Nanoplatform for Sequential Drug Release and Remodeling Lung Immune Homeostasis in Acute Lung Injury Treatment

Interactions of lung macrophages and recruited neutrophils with the lung microenvironment continuously aggravate the dysregulation of lung inflammation in the pathogenesis of acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Either modulating macrophages or destroying neutrophil counts cannot guarantee a satisfactory outcome in ARDS treatment. Aimed at inhibiting the coordinated action of neutrophils and macrophages and modulating the hyper-inflammatory condition, an inhalable biomimetic sequential drug-releasing nanoplatform was developed for the combinatorial treatment of ALI. The nanoplatform (termed D-SEL) was made by conjugating DNase I, as outer cleavable arms, to a serum exosomal and liposomal hybrid nanocarrier (termed SEL) via a matrix metalloproteinase 9 (MMP-9)-cleavable peptide and then encapsulating methylprednisolone sodium succinate (MPS). In lipopolysaccharide (LPS) induced ALI in mice, the MPS/D-SEL moved through muco-obstructive airways and was retained in the alveoli for over 24 h postinhalation. DNase I was then released from the nanocarrier first after responding to MMP-9, resulting in inner SEL core exposure, which precisely delivered MPS into macrophages for promoting M2 macrophage polarization. Local and sustained DNase I release degraded dysregulated neutrophil extracellular traps (NETs) and suppressed neutrophil activation and the mucus plugging microenvironment, which in turn amplified M2 macrophage polarization efficiency. Such dual-stage drug release behavior facilitated down-regulation of pro-inflammatory cytokines in the lung but anti-inflammatory cytokine production through remodeling lung immune homeostasis, ultimately promoting lung tissue repair. This work presents a versatile hybrid biomimetic nanoplatform for the local pulmonary delivery of dual-drug therapeutics and displays potential in the treatment of acute inflammation.

Immunosuppressive reprogramming of neutrophils by lung mesenchymal cells promotes breast cancer metastasis

Neutrophils, the most abundant innate immune cells, function as crucial regulators of the adaptive immune system in diverse pathological conditions, including metastatic cancer. However, it remains largely unknown whether their immunomodulatory functions are intrinsic or acquired within the pathological tissue environment. Here, using mouse models of metastatic breast cancer in the lungs, we show that, although neutrophils isolated from bone marrow (BM) or blood are minimally immunosuppressive, lung-infiltrating neutrophils are robustly suppressive of both T cells and natural killer (NK) cells. We found that this tissue-specific immunosuppressive capacity of neutrophils exists in the steady state and is reinforced by tumor-associated inflammation. Acquisition of potent immunosuppression activity by lung-infiltrating neutrophils was endowed by the lung-resident stroma, specifically CD140a+ mesenchymal cells (MCs) and largely via prostaglandin-endoperoxide synthase 2 (PTGS2), the rate-limiting enzyme for prostaglandin E2 (PGE2) biosynthesis. MC-specific deletion of Ptgs2 or pharmacological inhibition of PGE2 receptors reversed lung neutrophil-mediated immunosuppression and mitigated lung metastasis of breast cancer in vivo. These lung stroma-targeting strategies substantially improved the therapeutic efficacy of adoptive T cell-based immunotherapy in treating metastatic disease in mice. Collectively, our results reveal that the immunoregulatory effects of neutrophils are induced by tissue-resident stroma and that targeting tissue-specific stromal factors represents an effective approach to boost tissue-resident immunity against metastatic disease.

THE ROLE OF NEUTROPHIL EXTRACELLULAR TRAPS (NETS) IN THE IMMUNOPATHOGENESIS OF SEVERE COVID-19: POTENTIAL IMMUNOTHERAPEUTIC STRATEGIES REGULATING NET FORMATION AND ACTIVITY

The role of neutrophil granulocytes (NG) in the pathogenesis of COVID-19 is associated with the recruitment of NG into inflammatory foci, activation of their functions and enhanced formation of neutrophil extracellular networks (NETs). In this review, we analyzed a fairly large volume of scientific literature devoted to the peculiarities of the formation of NETs, their role in the pathogenesis of COVID-19, participation in the occurrence of immunothrombosis, vasculitis, acute respiratory distress syndrome, cytokine storm syndrome, multi-organ lesions. Convincing data are presented that clearly indicate the significant involvement of NETs in the immunopathogenesis of COVID-19 and the associated severe complications resulting from the intensification of the inflammation process, which is key for the course of infection caused by the SARS-CoV-2 virus. The presented role of NG and NETs, along with the role of other immune system cells and pro-inflammatory cytokines, is extremely important in understanding the development of an overactive immune response in severe COVID-19. The obtained scientific results, available today, allow identifying the possibilities of regulatory effects on hyperactivated NG, on the formation of NETs at various stages and on limiting the negative impact of already formed NETs on various tissues and organs. All of the above should help in the creation of new, specialized immunotherapy strategies designed to increase the chances of survival, reduce the severity of clinical manifestations in patients with COVID-19, as well as significantly reduce mortality rates. Currently, it is possible to use existing drugs and a number of new drugs are being developed, the action of which can regulate the amount of NG, positively affect the functions of NG and limit the intensity of NETs formation. Continuing research on the role of hyperactive NG and netosis, as well as understanding the mechanisms of regulation of the phenomenon of formation and restriction of NETs activity in severe COVID-19, apparently, are a priority, since in the future the new data obtained could become the basis for the development of targeted approaches not only to immunotherapy aimed at limiting education and blocking negative effects already formed NETs in severe COVID-19, but also to immunotherapy, which could be used in the complex treatment of other netopathies, first of all, autoimmune diseases, auto-inflammatory syndromes, severe purulent-inflammatory processes, including bacterial sepsis and hematogenous osteomyelitis.

Human functional genomics reveals toxicological mechanism underlying genotoxicants-induced inflammatory responses under low doses exposure

Understanding the toxicological mechanisms of chemicals is essential for accurate assessments of environmental health risks. Inflammation could play a critical role in the adverse health outcomes caused by genotoxicants; however, the toxicological mechanisms underlying genotoxicants-induced inflammatory response are still limited. Here, functional genomics CRISPR screens were performed to enhance the mechanistic understanding of the genotoxicants-induced inflammatory response at low doses exposure. Key genes and pathways associated with the activities of immune cells and the production of cytokines were identified by CRISPR screens of 6 model genotoxicants. Gene network analysis revealed that three genes (TLR10, HCAR2 and TRIM6) were involved in the regulation of neutrophil apoptosis and cytokine release, and TLR10 shared a similar functional pattern with HCAR2 and TRIM6. Furthermore, adverse outcome pathway (AOP) network analysis revealed that TLR10 was involved in the molecular initiating events (MIEs) or key events (KEs) in the inflammatory response AOPs of all the 6 genotoxicants, which provided mechanistic links between TLR10 and genotoxicants-induced inflammation and respiratory diseases. Finally, functional validation tests demonstrated that TLR10 exhibited inhibitory effects on genotoxicants-induced inflammatory responses in both epithelial and immune cells. This study highlights the powerful utility of the integration of CRISPR screen and AOP network analysis in illuminating the toxicological causal mechanisms of environmental chemicals.

Acute respiratory distress syndrome enhances tumor metastasis into lungs: Role of BRD4 in the tumor microenvironment

Acute respiratory distress syndrome (ARDS) is associated with severe lung inflammation, edema, hypoxia, and high vascular permeability. The COVID-19-associated pandemic ARDS caused by SARS-CoV-2 has created dire global conditions and has been highly contagious. Chronic inflammatory disease enhances cancer cell proliferation, progression, and invasion. We investigated how acute lung inflammation activates the tumor microenvironment and enhances lung metastasis in LPS induced in vitro and in vivo models. Respiratory illness is mainly caused by cytokine storm, which further influences oxidative and nitrosative stress. The LPS-induced inflammatory cytokines made the conditions suitable for the tumor microenvironment in the lungs. In the present study, we observed that LPS induced the cytokine storm and promoted lung inflammation via BRD4, which further caused the nuclear translocation of p65 NF-κB and STAT3. The transcriptional activation additionally triggers the tumor microenvironment and lung metastasis. Thus, BRD4-regulated p65 and STAT3 transcriptional activity in ARDS enhances lung tumor metastasis. Moreover, LPS-induced ARDS might promote the tumor microenvironment and increase cancer metastasis into the lungs. Collectively, BRD4 plays a vital role in inflammation-mediated tumor metastasis and is found to be a diagnostic and molecular target in inflammation-associated cancers.

CIRCKLHL2 KNOCKDOWN ALLEVIATES SEPSIS-INDUCED ACUTE LUNG INJURY BY REGULATING MIR-29B-3P MEDIATED ROCK1 EXPRESSION DOWN-REGULATION

ABSTRACT

Background: Acute lung injury (ALI) induced by sepsis is distinguished by an inflammatory progression. Herein, we investigated the action of circular RNA kelch like family member 2 (circKlhl2) in sepsis-induced ALI. Methods: The animal or cell model of sepsis ALI was established by LPS stimulation. The contents of circKlhl2, microRNA-29b-3p (miR-29b-3p), rho-associated coiled-coil containing protein kinase 1 (ROCK1), CyclinD1, B-cell lymphoma-2 (Bcl-2), and cleaved-caspase 3 (C-caspase-3) were detected by quantitative real-time polymerase chain reaction and western blot, respectively. Cell viability was assessed by cell counting kit 8 assay. Cell cycle and apoptosis were evaluated by flow cytometry. The abundances of proinflammatory cytokines were detected by enzyme-linked immunosorbent assay. Besides, the targeted relationship between miR-29b-3p and circKlhl2 or ROCK1 was verified by dual-luciferase reporter assay, RNA immunoprecipitation assay and RNA pull-down assay. Results: Loss of circKlhl2 mitigated lung injury and proinflammatory cytokine expression in sepsis-ALI mice model and alleviated LPS-induced apoptosis and inflammatory response in microvascular endothelial cell (MPVECs) in vitro . The abundances of circKlhl2 and ROCK1 were boosted, while the miR-29b-3p level was diminished in the animal or cell model of sepsis-ALI. MiR-29b-3p inhibition abrogated circKlhl2 knockdown-mediated effects on MPVECs injury. Moreover, miR-29b-3p overexpression promoted cell proliferation and inhibited apoptosis and inflammation in LPS-treated MPVECs, while ROCK1 enhancement reversed these effects. Conclusion: CircKlhl2 expedited the sepsis-induced ALI by adjusting miR-29b-3p/ROCK1 axis.

Protection from acute lung injury by a peptide designed to inhibit the voltage-gated proton channel

There are no targeted medical therapies for Acute Lung Injury (ALI) or its most severe form acute respiratory distress syndrome (ARDS). Infections are the most common cause of ALI/ARDS and these disorders present clinically with alveolar inflammation and barrier dysfunction due to the influx of neutrophils and inflammatory mediator secretion. We designed the C6 peptide to inhibit voltage-gated proton channels (Hv1) and demonstrated that it suppressed the release of reactive oxygen species (ROS) and proteases from neutrophils in vitro. We now show that intravenous C6 counteracts bacterial lipopolysaccharide (LPS)-induced ALI in mice, and suppresses the accumulation of neutrophils, ROS, and proinflammatory cytokines in bronchoalveolar lavage fluid. Confirming the salutary effects of C6 are via Hv1, genetic deletion of the channel similarly protects mice from LPS-induced ALI. This report reveals that Hv1 is a key regulator of ALI, that Hv1 is a druggable target, and that C6 is a viable agent to treat ALI/ARDS.

Carnosic acid inhibits reactive oxygen species-dependent neutrophil extracellular trap formation and ameliorates acute respiratory distress syndrome

AIMS

Infiltration of activated neutrophils into the lungs is a hallmark of acute respiratory distress syndrome (ARDS). Neutrophilic inflammation, particularly neutrophil extracellular traps (NETs), is proposed as a useful target for treating ARDS. Carnosic acid (CA) is a food additive; however, its anti-neutrophilic activity in the treatment of ARDS has not been well established. The hypothesis of present study is to confirm that CA alleviates ARDS by suppressing neutrophilic inflammation and oxidative damage.

MAIN METHODS

Generation of superoxide anions and reactive oxygen species (ROS), induction of elastase degranulation, and formation of NETs by human neutrophils were assayed using spectrophotometry, flow cytometry, and immunofluorescent microscopy. Immunoblotting was performed to determine the cellular mechanisms involved. Cell-free radical systems were used to test antioxidant activities. The therapeutic effect of CA was evaluated in a lipopolysaccharide (LPS)-induced ARDS mouse model.

KEY FINDINGS

CA greatly reduced superoxide anion production, ROS production, elastase release, cluster of differentiation 11b expression, and cell adhesion in activated human neutrophils. Mechanistic studies have demonstrated that CA suppresses phosphorylation of extracellular regulated kinase and c-Jun N-terminal kinase in activated neutrophils. CA effectively scavenges reactive oxygen and nitrogen species, but not superoxide anions. This is consistent with the finding that CA is effective against ROS-dependent NET formation. CA treatment significantly improved pulmonary neutrophil infiltration, oxidative damage, NET formation, and alveolar damage in LPS-induced mice.

SIGNIFICANCE

Our data suggested the potential application of CA for neutrophil-associated ARDS therapy.

A Supraceliac Aortic Cross Clamping Model to Explore Remote Lung Injury and the Endothelial Glycocalyx

BACKGROUND

We hypothesized that supraceliac aortic cross clamping could induce lung injury mediated by an inflammatory ischemia-reperfusion (IR) trigger. We aimed to characterize glycocalyx (GCX), a component of endothelial membrane, participating to remote lung injury.

METHODS

Rats underwent supraceliac aortic cross clamping for 40 min and were sacrificed at 0, 3, 6, and 24 hr of reperfusion (n = 10/group). Each group was compared to sham (n = 6/group). GCX products (syndecan-1 [Sdc-1] and heparan sulfate [HS]), tumor necrosis factor-alpha (TNF-α), and interleukin-1β (IL-1β) were measured in plasma (enzyme-linked immunosorbent assay[ELISA]). Lungs were harvested for measurements of TNF-α, IL-1β (polymerase chain reaction) and Sdc-1 (western blotting [WB]). Histologic lung injury scoring and pulmonary gravimetry were analyzed in a blinded manner.

RESULTS

Plasmatic Sdc-1, HS, TNF-α, and IL-1β reached peak levels at 3 hr. Levels were significantly higher in clamping groups than sham at 6 hr for Sdc-1, at 0 and 3 hr for HS, at 3 and 6 hr for TNF-α, and at 3 hr for IL-1β. Lung TNF-α and Interleukin-1β reached peak levels at 6 hr. Levels were significantly higher than sham at 6 and 24 hr for TNF-α and at 6 hr for IL-1β. Lung Sdc-1 was lowest at 3 hr. Sdc-1 was not significantly different compared to sham at the different reperfusion times. At 3 hr, it was 0.27 ± 0.03 vs. 0.33 ± 0.02 (sham) (P = 0.09). Histopathologic scores at 6 and 24 hr were higher in clamping groups than sham. At 6 and 24 hr, it was higher for hemorrhage, polynuclear neutrophil (PNN) infiltration and intravascular leukocytes. Pulmonary edema was higher by gravimetry at 0 and 6 hr.

CONCLUSIONS

Supra celiac aortic clamping causes early lung injury in relation with a systemic inflammatory response associated with altered GCX structure.

Locally organised and activated Fth1hi neutrophils aggravate inflammation of acute lung injury in an IL-10-dependent manner

Acute respiratory distress syndrome (ARDS) is a common respiratory critical syndrome with no effective therapeutic intervention. Neutrophils function in the overwhelming inflammatory process of acute lung injury (ALI) caused by ARDS; however, the phenotypic heterogeneity of pulmonary neutrophils in ALI/ARDS remains largely unknown. Here, using single-cell RNA sequencing, we identify two transcriptionally and functionally heterogeneous neutrophil populations (Fth1^hi Neu and Prok2^hi Neu) with distinct locations in LPS-induced ALI mouse lungs. Exposure to LPS promotes the Fth1^hi Neu subtype, with more inflammatory factors, stronger antioxidant, and decreased apoptosis under the regulation of interleukin-10. Furthermore, prolonged retention of Fth1^hi Neu within lung tissue aggravates inflammatory injury throughout the development of ALI/ARDS. Notably, ARDS patients have high ratios of Fth1 to Prok2 expression in pulmonary neutrophils, suggesting that the Fth1^hi Neu population may promote the pathological development and provide a marker of poor outcome.

Thrombotic storm in coronavirus disease 2019: from underlying mechanisms to its management

Introduction. Coronavirus disease 2019 (COVID-19) identified in December 2019 in Wuhan, China, is associated with high mortality rates worldwide.

Hypothesis/Gap Statement. Thrombotic problems, such as coagulopathy, are common in COVID-19 patients. Despite anticoagulation, thrombosis is more common in patients in the intensive care unit and patients with more severe disease. Although the exact mechanisms of coagulopathy in COVID-19 patients are still unclear, studies showed that overactivation of the renin-angiotensin system (RAS), cytokine storm, endothelial damage, formation of neutrophil extracellular traps (NETs), and also extracellular vesicles (EVs) in response to COVID-19 induced inflammation can lead to systemic coagulation and thrombosis.

Aim. The management of COVID-19 patients requires the use of basic and readily available laboratory markers, both on admission and during hospitalization. Because it is critical to understand the pathophysiology of COVID-19 induced coagulopathy and treatment strategies, in this review we attempt to explain the underlying mechanism of COVID-19 coagulopathy, its diagnosis, and the associated successful treatment strategies.

Conclusion. The exact mechanisms behind COVID-19-related coagulopathy are still unclear, but several studies revealed some mechanisms. More research is needed to determine the best anticoagulant regimen and to study other therapeutic options.

Tumor Progression Locus 2 Protects against Acute Respiratory Distress Syndrome in Influenza A Virus-Infected Mice

Excessive inflammation in patients with severe influenza disease may lead to acute lung injury that results in acute respiratory distress syndrome (ARDS). ARDS is associated with alveolar damage and pulmonary edema that severely impair gas exchange, leading to hypoxia. With no existing FDA-approved treatment for ARDS, it is important to understand the factors that lead to virus-induced ARDS development to improve prevention, diagnosis, and treatment. We have previously shown that mice deficient in the serine-threonine mitogen-activated protein kinase, Tpl2 (MAP3K8 or COT), succumb to infection with a typically low-pathogenicity strain of influenza A virus (IAV; HKX31, H3N2 [x31]). The goal of the current study was to evaluate influenza A virus-infected Tpl2-/- mice clinically and histopathologically to gain insight into the disease mechanism. We hypothesized that Tpl2-/- mice succumb to IAV infection due to development of ARDS-like disease and pulmonary dysfunction. We observed prominent signs of alveolar septal necrosis, hyaline membranes, pleuritis, edema, and higher lactate dehydrogenase (LDH) levels in the lungs of IAV-infected Tpl2-/- mice compared to wild-type (WT) mice from 7 to 9 days postinfection (dpi). Notably, WT mice showed signs of regenerating epithelium, indicative of repair and recovery, that were reduced in Tpl2-/- mice. Furthermore, biomarkers associated with human ARDS cases were upregulated in Tpl2-/- mice at 7 dpi, demonstrating an ARDS-like phenotype in Tpl2-/- mice in response to IAV infection. IMPORTANCE This study demonstrates the protective role of the serine-threonine mitogen-activated protein kinase, Tpl2, in influenza virus pathogenesis and reveals that host Tpl2 deficiency is sufficient to convert a low-pathogenicity influenza A virus infection into severe influenza disease that resembles ARDS, both histopathologically and transcriptionally. The IAV-infected Tpl2-/- mouse thereby represents a novel murine model for studying ARDS-like disease that could improve our understanding of this aggressive disease and assist in the design of better diagnostics and treatments.

“Rogue” neutrophil-subset [DEspR+CD11b+/CD66b+] immunotype is an actionable therapeutic target for neutrophilic inflammation-mediated tissue injury – studies in human, macaque and rat LPS-inflammation models

Background and objective

The correlation (Rs > 0.7) of neutrophils expressing the dual endothelin1/signal peptide receptor (DEspR+CD11b+/CD66b+) with severity of hypoxemia (SF-ratio) and multi-organ failure (SOFA-score) in patients with acute respiratory distress syndrome (ARDS) suggest the hypothesis that the DEspR+ neutrophil-subset is an actionable therapeutic target in ARDS. To test this hypothesis, we conducted in vivo studies to validate DEspR+ neutrophil-subset as therapeutic target and test efficacy of DEspR-inhibition in acute neutrophilic hyperinflammation models.

Methods

We performed tests in lipopolysaccharide (LPS)-induced acute neutrophilic inflammation in three species – human, rhesus macaque, rat – with increasing dose-dependent severity. We measured DEspR+CD66b+ neutrophils in bronchoalveolar lavage fluid (BALF) in healthy volunteers (HVs) 24-hours after segmental LPS-challenge by ChipCytometry, and DEspR+CD11b+ neutrophils in whole blood and BALF in an LPS-induced transient acute lung injury (ALI) model in macaques. We determined anti-DEspR antibody efficacy in vivo in LPS-ALI macaque model and in high-mortality LPS-induced encephalopathy in hypertensive rats.

Results

ChipCytometry detected increased BALF total neutrophil and DEspR+CD66b+ neutrophil counts after segmental LPS-challenge compared to baseline (P =0.034), as well as increased peripheral neutrophil counts and neutrophil-lymphocyte ratio (NLR) compared to pre-LPS level (P <0.05). In the LPS-ALI macaque model, flow cytometry detected increased DEspR+ and DEspR[-] neutrophils in BALF, which was associated with moderate-severe hypoxemia. After determining pharmacokinetics of single-dose anti-DEspR[hu6g8] antibody, one-time pre-LPS anti-DEspR treatment reduced hypoxemia (P =0.03) and neutrophil influx into BALF (P =0.0001) in LPS-ALI vs vehicle mock-treated LPS-ALI macaques. Ex vivo live cell imaging of macaque neutrophils detected greater “intrinsic adhesion to hard-surface” in DEspR+ vs DEspR[-] neutrophils (P <0.001). Anti-DEspR[hu6g8] antibody abrogated intrinsic high adhesion in DEspR+ neutrophils, but not in DEspR[-] neutrophils (P <0.001). In the LPS-encephalopathy rat model, anti-DEspR[10a3] antibody treatment increased median survival (P =0.0007) and exhibited brain target engagement and bioeffects.

Conclusion

Detection of increased DEspR+ neutrophil-subset in human BALF after segmental LPS-challenge supports the correlation of circulating DEspR+ neutrophil counts with severity measure (SOFA-score) in ARDS. Efficacy and safety of targeted inhibition of DEspR+CD11b+ neutrophil-subset in LPS-induced transient-ALI and high-mortality encephalopathy models identify a potential therapeutic target for neutrophil-mediated secondary tissue injury.

Hybrid Biomimetic Nanovesicles to Drive High Lung Biodistribution and Prevent Cytokine Storm for ARDS Treatment

Acute respiratory distress syndrome (ARDS) has been a life threat for patients in ICUs. Vast efforts have been devoted, while no medication has proved viable, which may be ascribed to inadequate drug delivery to damaged tissues and insufficient control of lung inflammation. Given the anti-inflammatory role of M2-type macrophages, M2 macrophage-derived nanovesicles and lung-targeting liposomes are cofused to fabricate hybrid liposomes-nanovesicles (LNVs). Benefiting from the incorporated lung-homing moiety, LNVs demonstrate high pulmonary accumulation with a lung/liver ratio of 14.9, which is approximately 53.3-fold of free nanovesicles. Thus, M2 macrophage-derived nanovesicles can be delivered to lung tissues for executing immunoregulatory functions. LNVs display phagocytosis by the infiltrated neutrophils and macrophages, exhibiting sustained release of preloaded IKK-2 inhibitor (TPCA-1). The integrated nanosystems demonstrate multidimensional suppression of the overwhelming inflammation, such as decreasing infiltration of inflammatory cells, achieving restraint on cytokine storms and alleviating oxidative stress. Therefore, the improved therapeutic outcome in ARDS mice is obtained. Altogether, the hybrid nanoplatform provides a versatile drug delivery paradigm for integrating biological nanovesicles and therapeutic molecules by cofusion of nanovesicles with liposomes, improving lung biodistribution and accomplishing a boosted anti-inflammatory response for ARDS therapy.

D-tagatose protects against oleic acid-induced acute respiratory distress syndrome in rats by activating PTEN/PI3K/AKT pathway

Acute respiratory distress syndrome (ARDS) is characterized by disruption of the alveolar–capillary barrier, resulting in severe alveolar edema and inflammation. D-tagatose (TAG) is a low-calorie fructose isomer with diverse biological activities whose role in ARDS has never been explored. We found that TAG protects lung tissues from injury in the oleic acid-induced rat model of ARDS. Seventeen male Sprague–Dawley rats were randomly assigned to 3 groups: Sham (n = 5), ARDS (n = 6), and TAG + ARDS (n = 6). The treatment groups were injected with oleic acid to induce ARDS, and the TAG + ARDS group was given TAG 3 days before the induction. After the treatments, the effect of TAG was evaluated by blood gas analysis and observing the gross and histological structure of the lung. The results showed that TAG significantly improved the oxygenation function, reduced the respiratory acidosis and the inflammatory response. TAG also improved the vascular permeability in ARDS rats and promoted the differentiation of alveolar type II cells, maintaining the stability of the alveolar structure. This protective effect of TAG on the lung may be achieved by activating the PTEN/PI3K/AKT pathway. Thus, TAG protects against oleic acid-induced ARDS in rats, suggesting a new clinical strategy for treating the condition.

CircEXOC5 facilitates cell pyroptosis via epigenetic suppression of Nrf2 in septic acute lung injury

Acute lung injury (ALI) caused by sepsis is characterized by a destructive high inflammatory response in lungs, which is the ultimate cause of high mortality to patients diagnosed with sepsis. The objective of the present study is to explore the effect and related mechanisms of circEXOC5 on pyroptosis in septic ALI. Sepsis ALI mouse model was induced and established by CLP induction and sepsis MPVEC cell model by LPS. HE staining was used to detect lung tissue pathological changes. ELISA, flow cytometry, and Western blot were utilized to evaluate the release of inflammatory cytokines and cell pyroptosis, and RIP was applied to verify the binding relationship between EZH2 and circEXOC5 or Nrf2. Finally, the interaction between CircEXOC5 and EZH2, H3k27me3, and Nrf2 promoter regions was clarified using ChIP. CircEXOC5 levels were notably ascended in the lung tissues of septic ALI mice. And silencing circEXOC5 inhibited cell pyroptosis and the release of inflammatory cytokines in MPVEC stimulated by LPS. In addition, RIP and ChIP indicated that Nrf2 expression in MPVECs cells could be inhibited by circEXOC5 via recruiting EZH2. In addition, ML385 (a specific inhibitor of Nrf2) reversed the efficacy of Knockdown of circEXOC5 on the Inhibition of pyroptosis and inflammation of MPVEC cells stimulated by LPS. These results indicated that CircEXOC5 could promote cell pyroptosis through epigenetic inhibition of Nrf2 in septic ALI.

Regulated necrosis in COVID-19: A double-edged sword

COVID-19 caused by SARS-CoV-2 can cause various systemic diseases such as acute pneumonia with cytokine storm. Constituted of necroptosis, pyroptosis, and ferroptosis, regulated necrosis constitutes the cell death patterns under the low apoptosis condition commonly observed in COVID-19. Regulated necrosis is involved in the release of cytokines like TNF-α, IL-1 β, and IL-6 and cell contents such as alarmins, PAMPs, and DAMPs, leading to more severe inflammation. Uncontrolled regulated necrosis may explain the poor prognosis and cytokine storm observed in COVID-19. In this review, the pathophysiology and mechanism of regulated necrosis with the double-edged sword effect in COVID-19 are thoroughly discussed in detail. Furthermore, this review also focuses on the biomarkers and potential therapeutic targets of the regulated necrosis pathway in COVID-19, providing practical guidance to judge the severity, prognosis, and clinical treatment of COVID-19 and guiding the development of clinical anti-SARS-CoV-2 drugs.

Allyl methyl trisulfide protected against LPS-induced acute lung injury in mice via inhibition of the NF-κB and MAPK pathways

Allyl methyl trisulfide (AMTS) is one major lipid-soluble organosulfur compound of garlic. Previous studies have reported the potential therapeutic effect of garlic on acute lung injury (ALI) or its severe condition acute respiratory distress syndrome (ARDS), but the specific substances that exert the regulatory effects are still unclear. In this study, we investigate the protective effects of AMTS on lipopolysaccharide (LPS)-induced ALI mice and explored the underlying mechanisms. In vivo experiments, ICR mice were pretreated with 25–100 mg/kg AMTS for 7 days and followed by intratracheal instillation of LPS (1.5 mg/kg). The results showed that AMTS significantly attenuated LPS-induced deterioration of lung pathology, demonstrated by ameliorative edema and protein leakage, and improved pulmonary histopathological morphology. Meanwhile, the expression of inflammatory mediators and the infiltration of inflammation-regulation cells induced by LPS were also inhibited. In vitro experiments also revealed that AMTS could alleviate inflammation response and inhibit the exaggeration of macrophage M1 polarization in LPS-induced RAW264.7 cells. Mechanistically, we identified that AMTS treatment could attenuate the LPS-induced elevation of protein expression of p-IκBα, nuclear NF-κB-p65, COX2, iNOS, p-P38, p-ERK1/2, and p-JNK. Collectively, these data suggest that AMTS could attenuate LPS-induced ALI and the molecular mechanisms should be related to the suppression of the NF-κB and MAPKs pathways.

Interferon-β regulates proresolving lipids to promote the resolution of acute airway inflammation

Acute respiratory distress syndrome is characterized by aberrant inflammatory responses, including polymorphonuclear neutrophil granulocyte dysfunction and hyperactive Toll-like receptor signaling. Timely resolution of bacterial infections depends on efficient removal of neutrophils from the inflamed tissue. Here we show that the antiviral cytokine interferon-β is essential for the resolution of neutrophil-driven airway inflammation by countering Toll-like receptor 9–mediated suppression of phagocytosis, neutrophil apoptosis, and uptake by macrophages. We also report that the beneficial effects of interferon-β are, in part, mediated by production of proresolving lipid mediators, such as 15-epi-lipoxin A₄ and resolvin D1, which act through the lipoxin receptor ALX/FPR2. These findings uncover an interferon-β–initiated ALX/FPR2-centered resolution program as a potential target for facilitating the resolution of airway inflammation.

Aberrant immune responses, including hyperresponsiveness to Toll-like receptor (TLR) ligands, underlie acute respiratory distress syndrome (ARDS). Type I interferons confer antiviral activities and could also regulate the inflammatory response, whereas little is known about their actions to resolve aberrant inflammation. Here we report that interferon-β (IFN-β) exerts partially overlapping, but also cooperative actions with aspirin-triggered 15-epi-lipoxin A₄ (15-epi-LXA₄) and 17-epi-resolvin D1 to counter TLR9-generated cues to regulate neutrophil apoptosis and phagocytosis in human neutrophils. In mice, TLR9 activation impairs bacterial clearance, prolongs Escherichia coli–evoked lung injury, and suppresses production of IFN-β and the proresolving lipid mediators 15-epi-LXA₄ and resolvin D1 (RvD1) in the lung. Neutralization of endogenous IFN-β delays pulmonary clearance of E. coli and aggravates mucosal injury. Conversely, treatment of mice with IFN-β accelerates clearance of bacteria, restores neutrophil phagocytosis, promotes neutrophil apoptosis and efferocytosis, and accelerates resolution of airway inflammation with concomitant increases in 15-epi-LXA₄ and RvD1 production in the lungs. Pharmacological blockade of the lipoxin receptor ALX/FPR2 partially prevents IFN-β–mediated resolution. These findings point to a pivotal role of IFN-β in orchestrating timely resolution of neutrophil and TLR9 activation–driven airway inflammation and uncover an IFN-β–initiated resolution program, activation of an ALX/FPR2-centered, proresolving lipids-mediated circuit, for ARDS.

The Role of Inflammasomes in COVID-19: Potential Therapeutic Targets

The coronavirus 2019 disease (COVID-19) pandemic has caused massive morbidity and mortality worldwide. In severe cases, it is mainly associated with acute pneumonia, cytokine storm, and multi-organ dysfunction. Inflammasomes play a primary role in various pathological processes such as infection, injury, and cancer. However, their role in COVID-19-related complications has not been explored. In addition, the role of underlying medical conditions on COVID-19 disease severity remains unclear. Therefore, this review expounds on the mechanisms of inflammasomes following COVID-19 infection and provides recent evidence on the potential double-edged sword effect of inflammasomes during COVID-19 pathogenesis. The assembly and activation of inflammasomes are critical for inducing effective antiviral immune responses and disease resolution. However, uncontrolled activation of inflammasomes causes excessive production of proinflammatory cytokines (cytokine storm), increased risk of acute respiratory distress syndrome, and death. Therefore, discoveries in the role of the inflammasome in mediating organ injury are key to identifying therapeutic targets and treatment modifications to prevent or reduce COVID-19-related complications.

Network Pharmacology and Experimental Validation to Explore the Mechanism of Qing-Jin-Hua-Tan-Decoction Against Acute Lung Injury

Qing-Jin-Hua-Tan-Decoction (QJHTD), a classic famous Chinese ancient prescription, has been used for treatment of pulmonary diseases since Ming Dynasty. A total of 22 prototype compounds of QJHTD absorbed into rat blood were chosen as candidates for the pharmacological network analysis and molecular docking. The targets from the intersection of compound target and ALI disease targets were used for GO and KEGG enrichment analyses. Molecular docking was adopted to further verify the interactions between 22 components and the top 20 targets with higher degree values in the component–target–pathway network. In vitro experiments were performed to verify the results of network pharmacology using SPR experiments, Western blot experiments, and the PMA-induced neutrophils to produce neutrophil extracellular trap (NET) model. The compound–target–pathway network includes 176 targets and 20 signaling pathways in which the degree of MAPK14, CDK2, EGFR, F2, SRC, and AKT1 is higher than that of other targets and which may be potential disease targets. The biological processes in QJHTD for ALI mainly included protein phosphorylation, response to wounding, response to bacterium, regulation of inflammatory response, and so on. KEGG enrichment analyses revealed multiple signaling pathways, including lipid and atherosclerosis, HIF-1 signaling pathway, renin–angiotensin system, and neutrophil extracellular trap formation. The molecular docking results showed that baicalin, oroxylin A-7-glucuronide, hispidulin-7-O-β-D-glucuronide, wogonoside, baicalein, wogonin, tianshic acid, and mangiferin can be combined with most of the targets, which might be the core components of QJHTD in treatment of ALI. Direct binding ability of baicalein, wogonin, and baicalin to thrombin protein was all micromolar, and their K_D values were 11.92 μM, 1.303 μM, and 1.146 μM, respectively, revealed by SPR experiments, and QJHTD could inhibit Src phosphorylation in LPS-activated neutrophils by Western blot experiments. The experimental results of PMA-induced neutrophils to produce NETs indicated that QJHTD could inhibit the production of NETs. This study revealed the active compounds, effective targets, and potential pharmacological mechanisms of QJHTD acting on ALI.

Delayed neutrophil apoptosis may enhance NET formation in ARDS

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a neutrophil-associated disease. Delayed neutrophil apoptosis and increased levels of neutrophil extracellular traps (NETs) have been described in ARDS. We aimed to investigate the relationship between these phenomena and their potential as inflammation drivers. We hypothesized that delayed neutrophil apoptosis might enhance NET formation in ARDS.

METHOD

Our research was carried out in three aspects: clinical research, animal experiments, and in vitro experiments. First, we compared the difference between neutrophil apoptosis and NET levels in healthy controls and patients with ARDS and analyzed the correlation between neutrophil apoptosis and NET levels in ARDS. Then, we conducted animal experiments to verify the effect of neutrophil apoptosis on NET formation in Lipopolysaccharide-induced acute lung injury (LPS-ALI) mice. Furthermore, this study explored the relationship between neutrophil apoptosis and NETs at the cellular level. Apoptosis was assessed using morphological analysis, flow cytometry, and western blotting. NET formation was determined using immunofluorescence, PicoGreen assay, SYTOX Green staining, and western blotting.

RESULTS

ARDS neutrophils lived longer because of delayed apoptosis, and the cyclin-dependent kinase inhibitor, AT7519, reversed this phenomenon both in ARDS neutrophils and neutrophils in bronchoalveolar lavage fluid (BALF) of LPS-ALI mice. Neutrophils in a medium containing pro-survival factors (LPS or GM-CSF) form more NETs, which can also be reversed by AT7519. Tissue damage can be reduced by promoting neutrophil apoptosis.

CONCLUSIONS

Neutrophils with extended lifespan in ARDS usually enhance NET formation, which aggravates inflammation. Enhancing neutrophil apoptosis in ARDS can reduce the formation of NETs, inhibit inflammation, and consequently alleviate ARDS.

Early taurine administration as a means for halting the cytokine storm progression in COVID-19 patients

Around the world, more than 6.2 million individuals have died as a result of coronavirus disease 2019 (COVID-19). According to a recent survey conducted among immunologists, epidemiologists, and virologists, this disease is expected to become endemic. This implies that the disease could have a continuous presence and/or normal frequency in the population. Pharmacological interventions to prevent infection, as well as to treat the patients at an early phase of illness to avoid hospitalization are essential additions to the vaccines. Taurine is known to inhibit the generation of all inflammatory mediators linked to the cytokine storm. It can also protect against lung injury by suppressing increased oxidants production and promoting the resolution of the inflammatory process. Neutrophil lactoferrin degranulation stimulated by taurine may have antiviral effects against SARS-CoV-2, limiting viral replication. It is hypothesized that if taurine is administered early in the onset of COVID-19 disease, it may stop the cytokine storm from progressing, lowering morbidity and mortality.

Possible role of pannexin 1 channels and purinergic receptors in the pathogenesis and mechanism of action of SARS-CoV-2 and therapeutic potential of targeting them in COVID-19

Identifying signaling pathways and molecules involved in SARS-CoV-2 pathogenesis is pivotal for developing new effective therapeutic or preventive strategies for COVID-19. Pannexins (PANX) are ATP-release channels in the plasma membrane essential in many physiological and immune responses. Activation of pannexin channels and downstream purinergic receptors play dual roles in viral infection, either by facilitating viral replication and infection or inducing host antiviral defense. The current review provides a hypothesis demonstrating the possible contribution of the PANX1 channel and purinergic receptors in SARS-CoV-2 pathogenesis and mechanism of action. Moreover, we discuss whether targeting these signaling pathways may provide promising preventative therapies and treatments for patients with progressive COVID-19 resulting from excessive pro-inflammatory cytokines and chemokines production. Several inhibitors of this pathway have been developed for the treatment of other viral infections and pathological consequences. Specific PANX1 inhibitors could be potentially included as part of the COVID-19 treatment regimen if, in future, studies demonstrate the role of PANX1 in COVID-19 pathogenesis. Of note, any ATP therapeutic modulation for COVID-19 should be carefully designed and monitored because of the complex role of extracellular ATP in cellular physiology.

MAP2K2 Delays Recovery in Murine Models of Acute Lung Injury and Associates with Acute Respiratory Distress Syndrome Outcome

Acute respiratory distress syndrome (ARDS) remains a significant problem in need of new pharmaceutical approaches to improve its resolution. Studies comparing gene expression signatures in rodents and humans with lung injury reveal conserved pathways, including MAPK (mitogen-activated protein kinase)/ERK (extracellular signal-related protein kinase) activation. In preclinical acute lung injury (ALI) models, inhibition of MAP2K1 (MAPK kinase 1)/MAP2K2 (MAPK kinase 2) improves measures of ALI. Myeloid cell deletion of MAP2K1 results in sustained MAP2K2 activation and nonresolving ALI, suggesting that MAP2K2 deactivation may be a key driver of ALI resolution. We used human genomic data from the iSPAAR (Identification of SNPs Predisposing to Altered Acute Lung Injury Risk) Consortium to assess genetic variants in MAP2K1 and MAP2K2 for association with mortality from ARDS. To determine the role of MAP2K2 in ALI recovery, we studied mice deficient in Map2k2 (Mek2-/-) and wild-type control mice in ALI models. We identified a MAP2K2 variant that was associated with death in ARDS and MAP2K2 expression. In Pseudomonas aeruginosa ALI, Mek2-/- mice had similar early alveolar neutrophilic recruitment but faster resolution of alveolar neutrophilia and vascular leak. Gene expression analysis revealed a role for MAP2K2 in promoting and sustaining select proinflammatory pathway activation in ALI. Bone marrow chimera studies indicate that leukocyte MAP2K2 is the key regulator of ALI duration. These studies implicate a role for MAP2K2 in ALI duration via transcriptional regulation of inflammatory programming with potential relevance to ARDS. Targeting leukocyte MAP2K2 may be an effective strategy to promote ALI resolution.

A new mouse unilateral model of diffuse alveolar damage of the lung

Objective and design

The existing biological models of diffuse alveolar damage (DAD) in mice have many shortcomings. To offset these shortcomings, we have proposed a simple, nonsurgical, and reproducible method of unilateral total damage of the left lung in ICR mice. This model is based on the intrabronchial administration of a mixture of bacterial lipopolysaccharide (LPS) from the cell wall of S. enterica and α-galactosylceramide (inducing substances) to the left lung.

Methods

Using computer tomography of the lungs with endobronchial administration of contrast material, we have been able to perform an operative intravital verification of the targeted delivery of the inducer. The model presented is characterized by more serious and homogeneous damage of the affected lung compared to the existing models of focal pneumonia; at the same time, our model is characterized by longer animal survival since the right lung remains intact.

Results

The model is also characterized by diffuse alveolar damage of the left lung, animal survival of 100%, abrupt increases in plasma levels of TNFa, INFg, and IL-6, and significant myocardial overload in the right heart. It can be used to assess the efficacy of innovative drugs for the treatment of DAD and ARDS as the clinical manifestations that are developed in patients infected with SARS-CoV-2. Morphological patterns of lungs in the noninfectious (“sterile”) model of DAD induced by LPS simultaneously with α-galactosylceramide (presented here) and in the infectious model of DAD induced by SARS-CoV-2 have been compared.

Conclusion

The DAD model we have proposed can be widely used for studying the efficacy of candidate molecules for the treatment of infectious respiratory diseases, such as viral pneumonias of different etiology, including SARS-CoV-2.

Secretome of Mesenchymal Stem Cells from Consecutive Hypoxic Cultures Promotes Resolution of Lung Inflammation by Reprogramming Anti-Inflammatory Macrophages

The secretome from hypoxia-preconditioned mesenchymal stem cells (MSCs) has been shown to promote resolution of inflammation and alleviate acute lung injury (ALI) through its immunomodulatory function. However, the effects of consecutive hypoxic culture on immunomodulatory function of the MSCs secretome are largely unclarified. Here, we intend to investigate the effects of consecutive hypoxia on therapeutic efficacy of conditioned medium derived from MSCs (MSCs-CM) in alleviating ALI. Human umbilical cord-derived MSCs (UC-MSCs) were consecutively cultured in 21% O₂ (Nor-MSCs) or in 1% O₂ (Hypo-MSCs) from passage 0. Their conditioned medium (Nor-CM and Hypo-CM respectively) was collected and administered into ALI models. Our findings confirmed that Hypo-MSCs exhibited increased proliferation ability and decreased cell senescence compared with Nor-MSCs. Consecutive hypoxia promoted UC-MSCs to secrete immunomodulatory cytokines, such as insulin-like growth factor 1(IGF1), IL10, TNFα-stimulated gene 6(TSG6), TGFβ, and prostaglandin E2 (PGE2). Both Nor-CM and Hypo-CM could effectively limit lung inflammation, promote efferocytosis and modulate anti-inflammatory polarization of lung macrophages in ALI models. Moreover, the effects of Hypo-CM were more potent than Nor-CM. Taken together, our findings indicate that consecutive hypoxic cultures could not only promote both proliferation and quality of UC-MSCs, but also enhance the therapeutic efficacy of their secretome in mitigating lung inflammation by promoting efferocytosis and anti-inflammatory polarization of macrophages.

Targeting Neutrophils for Promoting the Resolution of Inflammation

Acute inflammation is a localized and self-limited innate host-defense mechanism against invading pathogens and tissue injury. Neutrophils, the most abundant immune cells in humans, play pivotal roles in host defense by eradicating invading pathogens and debris. Ideally, elimination of the offending insult prompts repair and return to homeostasis. However, the neutrophils` powerful weaponry to combat microbes can also cause tissue damage and neutrophil-driven inflammation is a unifying mechanism for many diseases. For timely resolution of inflammation, in addition to stopping neutrophil recruitment, emigrated neutrophils need to be disarmed and removed from the affected site. Accumulating evidence documents the phenotypic and functional versatility of neutrophils far beyond their antimicrobial functions. Hence, understanding the receptors that integrate opposing cues and checkpoints that determine the fate of neutrophils in inflamed tissues provides insight into the mechanisms that distinguish protective and dysregulated, excessive inflammation and govern resolution. This review aims to provide a brief overview and update with key points from recent advances on neutrophil heterogeneity, functional versatility and signaling, and discusses challenges and emerging therapeutic approaches that target neutrophils to enhance the resolution of inflammation.

A targetable ‘rogue’ neutrophil-subset, [CD11b+DEspR+] immunotype, is associated with severity and mortality in acute respiratory distress syndrome (ARDS) and COVID-19-ARDS

Neutrophil-mediated secondary tissue injury underlies acute respiratory distress syndrome (ARDS) and progression to multi-organ-failure (MOF) and death, processes linked to COVID-19-ARDS. This secondary tissue injury arises from dysregulated neutrophils and neutrophil extracellular traps (NETs) intended to kill pathogens, but instead cause cell-injury. Insufficiency of pleiotropic therapeutic approaches delineate the need for inhibitors of dysregulated neutrophil-subset(s) that induce subset-specific apoptosis critical for neutrophil function-shutdown. We hypothesized that neutrophils expressing the pro-survival dual endothelin-1/VEGF-signal peptide receptor, DEspR, are apoptosis-resistant like DEspR+ cancer-cells, hence comprise a consequential pathogenic neutrophil-subset in ARDS and COVID-19-ARDS. Here, we report the significant association of increased peripheral DEspR+CD11b+ neutrophil-counts with severity and mortality in ARDS and COVID-19-ARDS, and intravascular NET-formation, in contrast to DEspR[-] neutrophils. We detect DEspR+ neutrophils and monocytes in lung tissue patients in ARDS and COVID-19-ARDS, and increased neutrophil RNA-levels of DEspR ligands and modulators in COVID-19-ARDS scRNA-seq data-files. Unlike DEspR[-] neutrophils, DEspR+CD11b+ neutrophils exhibit delayed apoptosis, which is blocked by humanized anti-DEspR-IgG4^S228P antibody, hu6g8, in ex vivo assays. Ex vivo live-cell imaging of Rhesus-derived DEspR+CD11b+ neutrophils showed hu6g8 target-engagement, internalization, and induction of apoptosis. Altogether, data identify DEspR+CD11b+ neutrophils as a targetable ‘rogue’ neutrophil-subset associated with severity and mortality in ARDS and COVID-19-ARDS.