Inhibition of neutrophil exocytosis ameliorates acute lung injury in rats

Neutrophil heterogeneity and plasticity: unveiling the multifaceted roles in health and disease

Neutrophils, the most abundant circulating leukocytes, have long been recognized as key players in innate immunity and inflammation. However, recent discoveries unveil their remarkable heterogeneity and plasticity, challenging the traditional view of neutrophils as a homogeneous population with a limited functional repertoire. Advances in single-cell technologies and functional assays have revealed distinct neutrophil subsets with diverse phenotypes and functions and their ability to adapt to microenvironmental cues. This review provides a comprehensive overview of the multidimensional landscape of neutrophil heterogeneity, discussing the various axes along which diversity manifests, including maturation state, density, surface marker expression, and functional polarization. We highlight the molecular mechanisms underpinning neutrophil plasticity, focusing on the complex interplay of signaling pathways, transcriptional regulators, and epigenetic modifications that shape neutrophil responses. Furthermore, we explore the implications of neutrophil heterogeneity and plasticity in physiological processes and pathological conditions, including host defense, inflammation, tissue repair, and cancer. By integrating insights from cutting-edge research, this review aims to provide a framework for understanding the multifaceted roles of neutrophils and their potential as therapeutic targets in a wide range of diseases.

Local Drug Delivery Systems as Novel Approach for Controlling NETosis in Periodontitis

Periodontitis is a chronic inflammation caused by periodontopathogenic bacteria in the dental biofilm, and also involves the inflammatory-immune response of the host. Polymorphonuclear neutrophils (PMNs) play essential roles in bacterial clearance by multiple mechanisms, including the formation of neutrophil extracellular traps (NETs) that retain and destroy pathogens. During PD progression, the interaction between PMNs, NETs, and bacteria leads to an exaggerated immune response and a prolonged inflammatory state. As a lesion matures, PMNs accumulate in the periodontal tissues and die via NETosis, ultimately resulting in tissue injury. A better understanding of the role of NETs, the associated molecules, and the pathogenic pathways of NET formation in periodontitis, could provide markers of NETosis as reliable diagnostic and prognostic tools. Moreover, an assessment of NET biomarker levels in biofluids, particularly in saliva or gingival crevicular fluid, could be useful for monitoring periodontitis progression and treatment efficacy. Preventing excessive NET accumulation in periodontal tissues, by both controlling NETs' formation and their appropriate removal, could be a key for further development of more efficient therapeutic approaches. In periodontal therapy, local drug delivery (LDD) systems are more targeted, enhancing the bioavailability of active pharmacological agents in the periodontal pocket and surrounding tissues for prolonged time to ensure an optimal therapeutic outcome.

Aged-Signal-Eliciting Nanoparticles Stimulated Macrophage-Mediated Programmed Removal of Inflammatory Neutrophils

Excessive infiltration of activated neutrophils is regarded as a predominant cause of tissue injury in neutrophilic inflammation. Although programmed cell death like apoptosis maintains the homeostasis of activated neutrophils, this process is disrupted by an abnormal inflammatory response. Unlike endogenous calreticulin exposed during apoptosis, exogenous calreticulin acts as an "aged" signal and initiates premature macrophage-mediated programmed cell removal (PrCR), which is independent of apoptosis. Here, we report a nano-mediated strategy to stimulate the precise clearance of activated neutrophils initiated with artificial aged signal and alleviated inflammation. Polymeric nanoparticles PC@PLGA were fabricated by cloaking poly(lactic-co-glycolic acid) (PLGA) with a hybrid membrane derived from platelet-derived extracellular vesicles (PEVs, denoted by P) and the calreticulin-expressed membrane obtained from doxorubicin-treated cells (denoted by C). P-selectin in PEVs favors PC@PLGA to anchor activated neutrophils, while calreticulin mimics exogenous "aged" signal secreted by macrophages to trigger PrCR. We showed that PC@PLGA specifically targeted activated neutrophils and misled macrophages to recognize them as "aged" neutrophils and then initiated premature PrCR and prevented proinflammatory response and tissue damage in a mouse model of acute lung injury and severe acute pancreatitis. The collective findings indicate the efficiency of specific elimination of activated neutrophils with exogenous aged signal in improving inflammation therapy.

Neutrophils in the periodontium: Interactions with pathogens and roles in tissue homeostasis and inflammation

Neutrophils are of key importance in periodontal health and disease. In their absence or when they are functionally defective, as occurs in certain congenital disorders, affected individuals develop severe forms of periodontitis in early age. These observations imply that the presence of immune-competent neutrophils is essential to homeostasis. However, the presence of supernumerary or hyper-responsive neutrophils, either because of systemic priming or innate immune training, leads to imbalanced host-microbe interactions in the periodontium that culminate in dysbiosis and inflammatory tissue breakdown. These disease-provoking imbalanced interactions are further exacerbated by periodontal pathogens capable of subverting neutrophil responses to their microbial community's benefit and the host's detriment. This review attempts a synthesis of these findings for an integrated view of the neutrophils' ambivalent role in periodontal disease and, moreover, discusses how some of these concepts underpin the development of novel therapeutic approaches to treat periodontal disease.

Myeloperoxidase: Regulation of Neutrophil Function and Target for Therapy

Neutrophils, the most abundant white blood cells in humans, are critical for host defense against invading pathogens. Equipped with an array of antimicrobial molecules, neutrophils can eradicate bacteria and clear debris. Among the microbicide proteins is the heme protein myeloperoxidase (MPO), stored in the azurophilic granules, and catalyzes the formation of the chlorinating oxidant HOCl and other oxidants (HOSCN and HOBr). MPO is generally associated with killing trapped bacteria and inflicting collateral tissue damage to the host. However, the characterization of non-enzymatic functions of MPO suggests additional roles for this protein. Indeed, evolving evidence indicates that MPO can directly modulate the function and fate of neutrophils, thereby shaping immunity. These actions include MPO orchestration of neutrophil trafficking, activation, phagocytosis, lifespan, formation of extracellular traps, and MPO-triggered autoimmunity. This review scrutinizes the multifaceted roles of MPO in immunity, focusing on neutrophil-mediated host defense, tissue damage, repair, and autoimmunity. We also discuss novel therapeutic approaches to target MPO activity, expression, or MPO signaling for the treatment of inflammatory and autoimmune diseases.

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.

Roles of neutrophil granule proteins in orchestrating inflammation and immunity

Neutrophil granulocytes form the first line of host defense against invading pathogens and tissue injury. They are rapidly recruited from the blood to the affected sites, where they deploy an impressive arsenal of effectors to eliminate invading microbes and damaged cells. This capacity is endowed in part by readily mobilizable proteins acquired during granulopoiesis and stored in multiple types of cytosolic granules with each granule type containing a unique cargo. Once released, granule proteins contribute to killing bacteria within the phagosome or the extracellular milieu, but are also capable of inflicting collateral tissue damage. Neutrophil-driven inflammation underlies many common diseases. Research over the last decade has documented neutrophil heterogeneity and functional versatility far beyond their antimicrobial function. Emerging evidence indicates that neutrophils utilize granule proteins to interact with innate and adaptive immune cells and orchestrate the inflammatory response. Granule proteins have been identified as important modulators of neutrophil trafficking, reverse transendothelial migration, phagocytosis, neutrophil life span, neutrophil extracellular trap formation, efferocytosis, cytokine activity, and autoimmunity. Hence, defining their roles within the inflammatory locus is critical for minimizing damage to the neighboring tissue and return to homeostasis. Here, we provide an overview of recent advances in the regulation of degranulation, granule protein functions, and signaling in modulating neutrophil-mediated immunity. We also discuss how targeting granule proteins and/or signaling could be harnessed for therapeutic benefits.

Acute Lung Injury: Disease Modelling and the Therapeutic Potential of Stem Cells

Acute lung injury (ALI) is a severe clinical condition with high morbidity and mortality that usually results in the development of multiple organ dysfunction. The complex pathophysiology of ALI seems to provide a wide range of targets that offer numerous therapeutic options. However, despite extensive studies of ALI pathophysiology and treatment, no effective pharmacotherapy is available. Increasing evidence from both preclinical and clinical studies supports the preventive and therapeutic effects of mesenchymal stem cells (MSCs) for treating ALI. As cell-based therapy poses the risk of occlusion in microvasculature or unregulated growth, MSC-derived extracellular vesicles (MSC-EVs) have been extensively studied as a new therapeutic strategy for non-cell based therapy. It is widely accepted that the therapeutic properties of MSCs are derived from soluble factors with paracrine or endocrine effects, and EVs are among the most important paracrine or endocrine vehicles that can deliver various soluble factors with a similar phenotype as the parent cell. Therapeutic effects of MSCs have been reported for various delivery approaches, diverse doses, multiple origins, and different times of administration, and MSC-EVs treatment may include but is not limited to these choices. The mechanisms by which MSCs and MSC-EVs may contribute to ALI treatment remain elusive and need further exploration. This review provides an overview of preclinical studies that support the application of MSC-EVs for treating ALI, and it discusses emerging opportunities and their associated challenges.

Neutrophils produce proinflammatory or anti-inflammatory extracellular vesicles depending on the environmental conditions

Extracellular vesicles (EVs) are important elements of intercellular communication. A plethora of different, occasionally even opposite, physiologic and pathologic effects have been attributed to these vesicles in the last decade. A direct comparison of individual observations is however hampered by the significant differences in the way of elicitation, collection, handling, and storage of the investigated vesicles. In the current work, we carried out a careful comparative study on 3, previously characterized types of EVs produced by neutrophilic granulocytes. We investigated in parallel the modulation of multiple blood-related cells and functions by medium-sized vesicles. We show that EVs released from resting neutrophils exert anti-inflammatory action by reducing production of reactive oxygen species (ROS) and cytokine release from neutrophils. In contrast, vesicles generated upon encounter of neutrophils with opsonized particles rather promote proinflammatory processes as they increase production of ROS and cytokine secretion from neutrophils and activate endothelial cells. EVs released from apoptosing cells were mainly active in promoting coagulation. We thus propose that EVs are “custom made,” acquiring selective capacities depending on environmental factors prevailing at the time of their biogenesis.

Therapeutic targeting of neutrophil exocytosis

Dysregulation of neutrophil activation causes disease in humans. Neither global inhibition of neutrophil functions nor neutrophil depletion provides safe and/or effective therapeutic approaches. The role of neutrophil granule exocytosis in multiple steps leading to recruitment and cell injury led each of our laboratories to develop molecular inhibitors that interfere with specific molecular regulators of secretion. This review summarizes neutrophil granule formation and contents, the role granule cargo plays in neutrophil functional responses and neutrophil-mediated diseases, and the mechanisms of granule release that provide the rationale for development of our exocytosis inhibitors. We present evidence for the inhibition of granule exocytosis in vitro and in vivo by those inhibitors and summarize animal data indicating that inhibition of neutrophil exocytosis is a viable therapeutic strategy.

Supercritical Fluid-Assisted Porous Microspheres for Efficient Delivery of Insulin and Inhalation Therapy of Diabetes

Pulmonary delivery of drugs has attracted increasing attention in healthcare, as the lungs are an easily accessible site for noninvasive systemic delivery of drugs. Although pulmonary inhalation of porous microparticles has been shown to sustain drug delivery, there are limited reports on efficient delivery of insulin and inhalation therapy of diabetes based on supercritical carbon dioxide (SC-CO₂ ) technology. Herein, this study reports the fabrication of insulin-loaded poly-l-lactide porous microspheres (INS-PLLA PMs) by using the SC-CO₂ technology, and their use as an inhalation delivery system potentially for diabetes therapy. Biocompatibility and delivery efficiency of the PLLA PMs in the lungs are investigated. The PLLA PMs show negligible toxicity to lung-derived cells, resulting in no significant reduction in cell viability, as well as levels of various inflammatory mediators such as interleukin (IL)-6, IL-8, and tumor necrosis factor-α, compared with the negative control group. INS-PLLA PMs are further efficiently deposited in the trachea and the bronchi of superior lobes of the lungs, which exhibit pronounced hypoglycemic activity in induced diabetic rats. Together, the results demonstrate that the INS-PLLA PMs have a strong potential as an effective strategy for inhalation treatment of diabetes.

Priming and de-priming of neutrophil responses in vitro and in vivo

The activation status of neutrophils can cycle from basal through primed to fully activated ("green-amber-red"), and at least in vitro, primed cells can spontaneously revert to a near basal phenotype. This broad range of neutrophil responsiveness confers extensive functional flexibility, allowing neutrophils to respond rapidly and appropriately to varied and evolving threats throughout the body. Primed and activated cells display dramatically enhanced bactericidal capacity (including augmented respiratory burst activity, degranulation and longevity), but this enhancement also confers the capacity for significant unintended tissue injury. Neutrophil priming and its consequences have been associated with adverse outcomes in a range of disease states, hence understanding the signalling processes that regulate the transition between basal and primed states (and back again) may offer new opportunities for therapeutic intervention in pathological settings. A wide array of host- and pathogen-derived molecules is able to modulate the functional status of these versatile cells. Reflecting this extensive repertoire of potential mediators, priming can be established by a range of signalling pathways (including mitogen-activated protein kinases, phosphoinositide 3-kinases, phospholipase D and calcium transients) and intracellular processes (including endocytosis, vesicle trafficking and the engagement of adhesion molecules). The signalling pathways engaged, and the exact cellular phenotype that results, vary according to the priming agent(s) to which the neutrophil is exposed and the precise environmental context. Herein we describe the signals that establish priming (in particular for enhanced respiratory burst, degranulation and prolonged lifespan) and describe the recently recognised process of de-priming, correlating in vitro observations with in vivo significance.

Gingival Exudatome Dynamics Implicate Inhibition of the Alternative Complement Pathway in the Protective Action of the C3 Inhibitor Cp40 in Nonhuman Primate Periodontitis

Periodontitis is a prevalent chronic inflammatory disease associated with dysbiosis. Although complement inhibition has been successfully used to treat periodontitis in animal models, studies globally analyzing inflamed tissue proteins to glean insight into possible mechanisms of action are missing. Using quantitative shotgun proteomics, we aimed to investigate differences in composition of inflammatory gingival tissue exudate ("gingival crevicular fluid"; GCF), before and after local administration of an inhibitor of the central complement component, C3, in nonhuman primates. The C3 inhibitor, Cp40 (also known as AMY-101) was administered locally in the maxillary gingival tissue of cynomolgus monkeys with established periodontitis, either once a week (1×-treatment; n = 5 animals) or three times per week (3×-treatment; n = 10 animals), for 6 weeks followed by another 6 weeks of observation in the absence of treatment. 45 GCF samples were processed for FASP digestion and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Data were processed using the ProgenesisQI software. The statistical significance of differences between the groups was determined by RM-ANOVA, and a protein expression change was considered as a true regulation at >2-fold and p < 0.05. The human orthologues were subjected to Gene Ontology analyses using PANTHER. Data are available via ProteomeXchange with identifier PXD009502. 573 proteins with >2 peptides were longitudinally quantified. Both 3× and 1× administration of Cp40 resulted in significant down-regulation of dozens of proteins during the 6-week course of treatment as compared to baseline. Following drug withdrawal at 6 weeks, more than 50% of the down-regulated proteins showed increased levels at week 12. The top scored pathway was "complement activation, alternative pathway", and several proteins involved in this pathway were down-regulated at 6 weeks. We mapped the proteomic fingerprint changes in local tissue exudate of cynomolgus monkey periodontitis in response to C3 inhibition and identified the alternative pathway of complement activation and leukocyte degranulation as main targets, which are thus likely to play significant roles in periodontal disease pathogenesis. Label-free quantitative proteomics strategies utilizing GCF are powerful tools for the identification of treatment targets and providing insights into disease mechanisms.

Neutrophil exocytosis induces podocyte cytoskeletal reorganization and proteinuria in experimental glomerulonephritis

Acute glomerulonephritis is characterized by rapid glomerular neutrophil recruitment, proteinuria, and glomerular hypercellularity. The current study tested the hypothesis that the release of neutrophil granule contents plays a role in both the loss of filtration barrier leading to proteinuria and the increase in glomerular cells. Inhibition of neutrophil exocytosis with a peptide inhibitor prevented proteinuria and attenuated podocyte and endothelial cell injury but had no effect on glomerular hypercellularity in an experimental acute glomerulonephritis model in mice. Cultivation of podocytes with neutrophil granule contents disrupted cytoskeletal organization, an in vitro model for podocyte effacement and loss of filtration barrier. Activated, cultured podocytes released cytokines that stimulated neutrophil chemotaxis, primed respiratory burst activity, and stimulated neutrophil exocytosis. We conclude that crosstalk between podocytes and neutrophils contributes to disruption of the glomerular filtration barrier in acute glomerulonephritis. Neutrophil granule products induce podocyte injury but do not participate in the proliferative response of intrinsic glomerular cells.

ABIN1 Determines Severity of Glomerulonephritis via Activation of Intrinsic Glomerular Inflammation

Transcription factor NF-κB regulates expression of numerous genes that control inflammation and is activated in glomerular cells in glomerulonephritis (GN). We previously identified genetic variants for a NF-κB regulatory, ubiquitin-binding protein ABIN1 as risk factors for GN in systemic autoimmunity. The goal was to define glomerular inflammatory events controlled by ABIN1 function in GN. Nephrotoxic serum nephritis was induced in wild-type (WT) and ubiquitin-binding deficient ABIN1[D485N] mice, and renal pathophysiology and glomerular inflammatory phenotypes were assessed. Proteinuria was also measured in ABIN1[D485N] mice transplanted with WT mouse bone marrow. Inflammatory activation of ABIN1[D472N] (D485N homolog) cultured human-derived podocytes, and interaction with primary human neutrophils were also assessed. Disruption of ABIN1 function exacerbated proteinuria, podocyte injury, glomerular NF-κB activity, glomerular expression of inflammatory mediators, and glomerular recruitment and retention of neutrophils in antibody-mediated nephritis. Transplantation of WT bone marrow did not prevent the increased proteinuria in ABIN1[D845N] mice. Tumor necrosis factor-stimulated enhanced expression and secretion of NF-κB-targeted proinflammatory mediators in ABIN1[D472N] cultured podocytes compared with WT cells. Supernatants from ABIN1[D472N] podocytes accelerated chemotaxis of human neutrophils, and ABIN1[D472N] podocytes displayed a greater susceptibility to injurious morphologic findings induced by neutrophil granule contents. These studies define a novel role for ABIN1 dysfunction and NF-κB in mediating GN through proinflammatory activation of podocytes.

Development of Protein-Protein Interaction Inhibitors for the Treatment of Infectious Diseases

Protein-protein interaction (PPI) inhibitors are a rapidly expanding class of therapeutics. Recent advances in our understanding of PPIs and success of early examples of PPI inhibitors demonstrate the feasibility of targeting PPIs. This review summarizes the techniques used for the discovery and optimization of a diverse set PPI inhibitors, focusing on the development of PPI inhibitors as new antibacterial and antiviral agents. We close with a summary of the advances responsible for making PPI inhibitors realistic targets for therapeutic intervention and brief outlook of the field.

Molecular mechanisms regulating secretory organelles and endosomes in neutrophils and their implications for inflammation

Neutrophils constitute the first line of cellular defense against invading microorganisms and modulate the subsequent innate and adaptive immune responses. In order to execute a rapid and precise response to infections, neutrophils rely on preformed effector molecules stored in a variety of intracellular granules. Neutrophil granules contain microbicidal factors, the membrane-bound components of the respiratory burst oxidase, membrane-bound adhesion molecules, and receptors that facilitate the execution of all neutrophil functions including adhesion, transmigration, phagocytosis, degranulation, and neutrophil extracellular trap formation. The rapid mobilization of intracellular organelles is regulated by vesicular trafficking mechanisms controlled by effector molecules that include small GTPases and their interacting proteins. In this review, we focus on recent discoveries of mechanistic processes that are at center stage of the regulation of neutrophil function, highlighting the discrete and selective pathways controlled by trafficking modulators. In particular, we describe novel pathways controlled by the Rab27a effectors JFC1 and Munc13-4 in the regulation of degranulation, reactive oxygen species and neutrophil extracellular trap production, and endolysosomal signaling. Finally, we discuss the importance of understanding these molecular mechanisms in order to design novel approaches to modulate neutrophil-mediated inflammatory processes in a targeted fashion.

Re-Examining Neutrophil Participation in GN

Significant advances in understanding the pathogenesis of GN have occurred in recent decades. Among those advances is the finding that both innate and adaptive immune cells contribute to the development of GN. Neutrophils were recognized as key contributors in early animal models of GN, at a time when the prevailing view considered neutrophils to function as nonspecific effector cells that die quickly after performing antimicrobial functions. However, advances over the past two decades have shown that neutrophil functions are more complex and sophisticated. Specifically, research has revealed that neutrophil survival is regulated by the inflammatory milieu and that neutrophils demonstrate plasticity, mediate microbial killing through previously unrecognized mechanisms, demonstrate transcriptional activity leading to the release of cytokines and chemokines, interact with and regulate cells of the innate and adaptive immune systems, and contribute to the resolution of inflammation. Therefore, neutrophil participation in glomerular diseases deserves re-evaluation. In this review, we describe advances in understanding classic neutrophil functions, review the expanded roles of neutrophils in innate and adaptive immune responses, and summarize current knowledge of neutrophil contributions to GN.

Over-expression of insulin-response element binding protein-1 (IRE-BP1) in mouse pancreatic islets increases expression of RACK1 and TCTP: Beta cell markers of high glucose sensitivity

BACKGROUND

A targeted analysis of the 50kDa C-terminal fragment of insulin-response element binding protein-1 (IRE-BP1) activation of target genes through the insulin receptor substrate receptor/PI-3 kinase/Akt pathway has been demonstrated for the insulin growth factor-1 receptor. The broader effects of 50kDa C-terminal IRE-BP1 fragment over-expression on protein abundance in pancreatic islet beta cells have not been determined.

RESULTS

Liquid-chromatography coupled to tandem mass spectrometry (LC-MS/MS) analyses of replicate lysates of pancreatic islets isolated from background strain animals and transgenic animals, overexpressing IRE-BP1 in pancreatic islet beta cells, demonstrated statistically significant increases in the expression of proteins involved in protein synthesis, endoplasmic reticulum (ER) stress and scaffolding proteins important for protein kinase C signaling; some of which were confirmed by immunoblot analyses. Bioinformatic analysis of protein expression network patterns suggested IRE-BP1 over-expression leads to protein expression patterns indicative of activation of functional protein networks utilized for protein post-translational modification, protein folding, and protein synthesis. Co-immunoprecipitation experiments demonstrate a novel interaction between two differentially regulated proteins receptor for activated protein kinase C (RACK1) and translationally controlled tumor protein (TCTP).

CONCLUSIONS

Proteomic analysis of IRE-BP1 over-expression in pancreatic islet beta cells suggest IRE-BP1 (a) directly or indirectly through establishing hyperglycemia results in increased expression of ribosomal proteins and markers of ER stress and (b) leads to the enhanced and previously un-described interaction of RACK1 and TCTP.

SIGNIFICANCE

This study identified C-terminal 50kDa domain of IRE-BP1 over-expression results in increased markers of ER-stress and a novel interaction between the scaffolding proteins RACK1 and TCTP.

Identification of Neutrophil Exocytosis Inhibitors (Nexinhibs), Small Molecule Inhibitors of Neutrophil Exocytosis and Inflammation: DRUGGABILITY OF THE SMALL GTPase Rab27a

Neutrophils constitute the first line of cellular defense in response to bacterial and fungal infections and rely on granular proteins to kill microorganisms, but uncontrolled secretion of neutrophil cargos is injurious to the host and should be closely regulated. Thus, increased plasma levels of neutrophil secretory proteins, including myeloperoxidase and elastase, are associated with tissue damage and are hallmarks of systemic inflammation. Here, we describe a novel high-throughput screening approach to identify small molecule inhibitors of the interaction between the small GTPase Rab27a and its effector JFC1, two central regulators of neutrophil exocytosis. Using this assay, we have identified small molecule inhibitors of Rab27a-JFC1 binding that were also active in cell-based neutrophil-specific exocytosis assays, demonstrating the druggability of Rab GTPases and their effectors. These compounds, named Nexinhibs (neutrophil exocytosis inhibitors), inhibit exocytosis of azurophilic granules in human neutrophils without affecting other important innate immune responses, including phagocytosis and neutrophil extracellular trap production. Furthermore, the compounds are reversible and potent inhibitors of the extracellular production of superoxide anion by preventing the up-regulation of the granule membrane-associated subunit of the NADPH oxidase at the plasma membrane. Nexinhibs also inhibit the up-regulation of activation signature molecules, including the adhesion molecules CD11b and CD66b. Importantly, by using a mouse model of endotoxin-induced systemic inflammation, we show that these inhibitors have significant activity in vivo manifested by decreased plasma levels of neutrophil secretory proteins and significantly decreased tissue infiltration by inflammatory neutrophils. Altogether, our data present the first neutrophil exocytosis-specific inhibitor with in vivo anti-inflammatory activity, supporting its potential use as an inhibitor of systemic inflammation.

Dopamine D1 receptor agonist A-68930 inhibits NLRP3 inflammasome activation and protects rats from spinal cord injury-induced acute lung injury

STUDY DESIGN

Randomized experimental study.

OBJECTIVES

The study aimed to investigate the therapeutic efficacy and molecular mechanisms of A-68930 in a rat model of spinal cord injury (SCI)-induced acute lung injury (ALI).

SETTING

China.

METHODS

The influences of A-68930 on the pulmonary edema, histological changes, proinflammatory cytokines levels, myeloperoxidase (MPO) activity and NLRP3 inflammasome protein expression were estimated.

RESULTS

SCI significantly promoted NLRP3 inflammasome activation, increased proinflammatory cytokine productions and MPO activity, and induced pulmonary edema and tissue damage in the SCI group as compared with the control group. A-68930 administration significantly inhibited NLRP3 inflammasome activation and reduced inflammatory cytokines levels and MPO activity. Moreover, A-68930 administration attenuated pulmonary edema and histopathology.

CONCLUSION

Our experimental findings indicated that A-68930 exhibited a protective effect on SCI-induced ALI by the alleviations of inflammatory response with the inhibition NLRP3 inflammasome activation 72 h post injury. The present study indicated that A-68930 could be a potentially efficient therapeutic strategy for the treatment of SCI-induced ALI.

Therapeutic targeting of acute lung injury and acute respiratory distress syndrome

There is no Food and Drug Administration-approved treatment for acute respiratory distress syndrome (ARDS), in spite of the relatively large number of patients with the diagnosis. In this report, we provide an overview of preclinical studies and a description of completed and future clinical trials in humans with ARDS. Preclinical studies dealing with acute lung injury have suggested roles for complement and complement receptors, as well as the evolving role of histones, but details of these pathways are inadequately understood. Anti-inflammatory interventions have not been convincingly effective. Various cell growth factors are being considered for clinical study. Interventions to block complement activation or its products are under consideration. Stem cell therapies have shown efficacy in preclinical studies, which have motivated phase I/II trials in humans with ARDS.

Anti-inflammatory effects of Perilla frutescens in activated human neutrophils through two independent pathways: Src family kinases and Calcium

The leaves of Perilla frutescens (L.) Britt. have been traditionally used as an herbal medicine in East Asian countries to treat a variety diseases. In this present study, we investigated the inhibitory effects of P. frutescens extract (PFE) on N-formyl-Met-Leu-Phe (fMLF)-stimulated human neutrophils and the underlying mechanisms. PFE (1, 3, and 10 μg/ml) inhibited superoxide anion production, elastase release, reactive oxygen species formation, CD11b expression, and cell migration in fMLF-activated human neutrophils in dose-dependent manners. PFE inhibited fMLF-induced phosphorylation of the Src family kinases (SFKs), Src (Tyr416) and Lyn (Tyr396), and reduced their enzymatic activities. Both PFE and PP2 (a selective inhibitor of SFKs) reduced the phosphorylation of Burton’s tyrosine kinases (Tyr223) and Vav (Tyr174) in fMLF-activated human neutrophils. Additionally, PFE decreased intracellular Ca²⁺ levels ([Ca²⁺]_i), whereas PP2 prolonged the time required for [Ca²⁺]_i to return to its basal level. Our findings indicated that PFE effectively regulated the inflammatory activities of fMLF-activated human neutrophils. The anti-inflammatory effects of PFE on activated human neutrophils were mediated through two independent signaling pathways involving SFKs (Src and Lyn) and mobilization of intracellular Ca²⁺.

Baclofen, a GABABR agonist, ameliorates immune-complex mediated acute lung injury by modulating pro-inflammatory mediators

Immune-complexes play an important role in the inflammatory diseases of the lung. Neutrophil activation mediates immune-complex (IC) deposition-induced acute lung injury (ALI). Components of gamma amino butyric acid (GABA) signaling, including GABA B receptor 2 (GABA_BR2), GAD65/67 and the GABA transporter, are present in the lungs and in the neutrophils. However, the role of pulmonary GABA_BR activation in the context of neutrophil-mediated ALI has not been determined. Thus, the objective of the current study was to determine whether administration of a GABA_BR agonist, baclofen would ameliorate or exacerbate ALI. We hypothesized that baclofen would regulate IC-induced ALI by preserving pulmonary GABA_BR expression. Rats were subjected to sham injury or IC-induced ALI and two hours later rats were treated intratracheally with saline or 1 mg/kg baclofen for 2 additional hours and sacrificed. ALI was assessed by vascular leakage, histology, TUNEL, and lung caspase-3 cleavage. ALI increased total protein, tumor necrosis factor α (TNF-α and interleukin-1 receptor associated protein (IL-1R AcP), in the bronchoalveolar lavage fluid (BALF). Moreover, ALI decreased lung GABA_BR2 expression, increased phospho-p38 MAPK, promoted IκB degradation and increased neutrophil influx in the lung. Administration of baclofen, after initiation of ALI, restored GABA_BR expression, which was inhibited in the presence of a GABA_BR antagonist, CGP52432. Baclofen administration activated pulmonary phospho-ERK and inhibited p38 MAPK phosphorylation and IκB degradation. Additionally, baclofen significantly inhibited pro-inflammatory TNF-α and IL-1βAcP release and promoted BAL neutrophil apoptosis. Protective effects of baclofen treatment on ALI were possibly mediated by inhibition of TNF-α- and IL-1β-mediated inflammatory signaling. Interestingly, GABA_BR2 expression was regulated in the type II pneumocytes in lung tissue sections from lung injured patients, further suggesting a physiological role for GABA_BR2 in the repair process of lung damage. GABA_BR2 agonists may play a potential therapeutic role in ALI.

Complement C5a exacerbates acute lung injury induced through autophagy-mediated alveolar macrophage apoptosis

Intestinal ischemia has a high mortality and often causes acute lung injury (ALI), which is a serious complication, and is accompanied by high mortality up to 40%. An intense local and systemic inflammation occurs during intestinal ischemia/reperfusion (IR)-induced lung injury resulting from activation of immune responses. It has been reported that one component of complement, C5a, is indispensable for the full development of IR-induced lung injury, whereas the detailed molecular mechanism remains to be elucidated. In this study, we found that intestinal IR induced ALI-like symptoms, and C5a receptor (C5aR) expression was upregulated in alveolar macrophages, which are resident macrophages in lung tissue and are important in pulmonary homeostasis. C5a produced during lung injury binds to C5aR in alveolar macrophages, initiates downstream signaling that promotes autophagy, leading to apoptosis of alveolar macrophages. Using Mφ-ATG5^−/− mice, in which the atg5 is deficient specifically in macrophages and autophagy is inhibited, we confirmed that in vivo C5a interacting with C5aR induced autophagy in alveolar macrophages, which promoted alveolar macrophage apoptosis. Further study indicated that autophagy was induced through C5aR-mediated degradation of bcl-2. Taken together, our results demonstrated that C5aR-mediated autophagy induced apoptosis in alveolar macrophages, disrupting pulmonary homeostasis and contributing to the development of ALI. This novel mechanism suggests new therapeutic potential of autophagy regulation in ALI.

Neutrophil-derived microparticles induce myeloperoxidase-mediated damage of vascular endothelial cells

BACKGROUND

Upon activation neutrophil releases microparticles - small plasma membrane vesicles that contain cell surface proteins and cytoplasmic matter, with biological activities. In this study we investigated the potential role of myeloperoxidase in the endothelial cell injury caused by neutrophil-derived microparticles.

RESULTS

Microparticles were produced by activating human neutrophils with a calcium ionophore and characterized by flow cytometry and transmission and scanning electron microscopy. Myeloperoxidase activity was measured by luminol-dependent chemiluminescence. Neutrophil microparticles-induced injuries and morphological alterations in human umbilical vein endothelial cells (HUVECs) were evaluated by microscopy and flow cytometry. Neutrophil microparticles were characterized as structures bounded by lipid bilayers and were less than 1 μm in diameter. The microparticles also expressed CD66b, CD62L and myeloperoxidase, which are all commonly expressed on the surface of neutrophils, as well as exposition of phosphatidylserine. The activity of the myeloperoxidase present on the microparticles was confirmed by hypochlorous acid detection. This compound is only catalyzed by myeloperoxidase in the presence of hydrogen peroxide and chloride ion. The addition of sodium azide or taurine inhibited and reduced enzymatic activity, respectively. Exposure of HUVEC to neutrophil microparticles induced a loss of cell membrane integrity and morphological changes. The addition of sodium azide or myeloperoxidase-specific inhibitor-I consistently reduced the injury to the endothelial cells. Taurine addition reduced HUVEC morphological changes.

CONCLUSIONS

We have demonstrated the presence of active myeloperoxidase in neutrophil microparticles and that the microparticle-associated myeloperoxidase cause injury to endothelial cells. Hence, the microparticle-associated myeloperoxidase-hydrogen peroxide-chloride system may contribute to widespread endothelial cell damage in conditions of neutrophil activation as observed in vasculitis and sepsis.

Growth arrest-specific protein 6 attenuates neutrophil migration and acute lung injury in sepsis

Sepsis is an acute inflammatory condition that can result in multiple organ failure and acute lung injury. Growth arrest-specific protein 6 (Gas6) is a broad regulator of the innate immune response involved with the nuclear factor κB signaling pathway. We hypothesized that Gas6 could have a protective role in attenuating the severity of acute lung injury and sepsis. Male mice were subjected to sepsis by cecal ligation and puncture (CLP) after which recombinant murine Gas6 (rmGas6; 5 μg/mouse) or normal saline (vehicle) was administered intravenously. Blood and lung tissues were collected at 20 h after CLP for various measurements. Treatment with rmGas6 significantly reduced serum levels of the injury markers aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase, as well as proinflammatory cytokines interleukin 6 (IL-6) and IL-17, compared with the vehicle group (P < 0.05). The parenchyma of the lungs damaged by CLP was attenuated by rmGas6 treatment. Lung mRNA levels of tumor necrosis factor α, IL-1β, IL-6, IL-17, and macrophage inflammatory protein 2 (MIP-2) were decreased by 60%, 86%, 82%, 93%, and 82%, respectively, with rmGas6 treatment as determined by real-time reverse transcriptase-polymerase chain reaction (P < 0.05). The degradation of IκB-α induced by CLP in the lungs was inhibited by rmGas6 treatment. The number of neutrophils and myeloperoxidase activity in the lungs were significantly reduced in the rmGas6 group. Moreover, rmGas6 reduced the in vitro migration of differentiated human promyelocytic HL60 cells by 64%. Finally, the 10-day survival rate of mice subjected to CLP was increased from 31% in the vehicle group to 67% in the rmGas6 group (P < 0.05). Thus, Gas6 has potential to be developed as a novel therapeutic agent to treat patients with sepsis and acute lung injury.

Myristoylated Alanine Rich C Kinase Substrate (MARCKS) is essential to β2-integrin dependent responses of equine neutrophils

Neutrophil infiltration is a prominent feature in a number of pathologic conditions affecting horses including recurrent airway obstruction, ischemia-reperfusion injury, and laminitis. Cell signaling components involved in neutrophil migration represent targets for novel anti-inflammatory therapies. In order to migrate into tissue, neutrophils must respond to chemoattractant signals in their external environment through activation of adhesion receptors (i.e. integrins) and reorganization of the actin cytoskeleton. Myristoylated Alanine-Rich C-Kinase Substrate (MARCKS), a highly conserved actin-binding protein, has a well demonstrated role in cytoskeletal dependent cellular functions (i.e. adhesion, spreading, and migration), but the details of MARCKS involvement in these processes remain vague. We hypothesized that MARCKS serves as a link between the actin cytoskeleton and integrin function in neutrophils. Using a MARCKS-specific inhibitor peptide known as MANS on equine neutrophils in vitro, we demonstrate that inhibition of MARCKS function significantly attenuates β2-integrin-dependent neutrophil functions including migration, adhesion, and immune complex-mediated respiratory burst. The MANS peptide did not, however, inhibit the β2-integrin-independent PMA mediated respiratory burst. These results attest to the essential role of MARCKS function in regulating neutrophil responses, and strongly implicate MARCKS as a potential regulator of β2-integrins in neutrophils.

TAT-SNAP-23 treatment inhibits the priming of neutrophil functions contributing to shock and/or sepsis-induced extra-pulmonary acute lung injury

Respiratory burst function of neutrophils is thought to play a pivotal role in the development of pathologies such as indirect (extra-pulmonary) acute lung injury (iALI), as well as sepsis. The current study was conducted to determine the effect of an HIV transactivator of transcription (TAT)-fusion protein containing a soluble N-ethylmaleimide-sensitive factor attachment protein receptor domain from synaptosome-associated protein-23 (SNAP-23) on the shock/sepsis- and sepsis-enhanced neutrophil burst capacity using the clinical relevant two-hit iALI mouse model and the classical cecal ligation and puncture (CLP) septic model. TAT-SNAP-23 significantly decreased the blood neutrophil respiratory burst in vitro, and also in vivo in CLP and hemorrhaged mice. We found that the neutrophil influx to the lung tissue, as measured by myeloperoxidase levels and neutrophil-specific esterase(+) cells, was also decreased in the TAT-SNAP-23-treated group. Consistent with this, treatment of TAT-SNAP-23 significantly reduced the disruption of lung tissue architecture and protein concentration of bronchoalveolar lavage fluid in iALI mice compared with vehicle-treated iALI mice. In addition, although TAT-SNAP-23 did not alter the extent of local cytokine/chemokine expression, the in vitro migration capacity of neutrophils was blunted from septic and hemorrhagic mice. These data support our hypothesis that TAT-SNAP-23 reduces neutrophil dysfunction in iALI and sepsis by inhibiting neutrophil respiratory burst.