Neutrophil apoptosis: A target for enhancing the resolution of inflammation

Leveraging a neutrophil-derived PCD signature to predict and stratify patients with acute myocardial infarction: from AI prediction to biological interpretation

BACKGROUND

Programmed cell death (PCD) has recently been implicated in modulating the removal of neutrophils recruited in acute myocardial infarction (AMI). Nonetheless, the clinical significance and biological mechanism of neutrophil-related PCD remain unexplored.

METHODS

We employed an integrative machine learning-based computational framework to generate a predictive neutrophil-derived PCD signature (NPCDS) within five independent microarray cohorts from the peripheral blood of AMI patients. Non-negative matrix factorization was leveraged to develop an NPCDS-based AMI subtype. To elucidate the biological mechanism underlying NPCDS, we implemented single-cell transcriptomics on Cd45+ cells isolated from the murine heart of experimental AMI. We finally conducted a Mendelian randomization (MR) study and molecular docking to investigate the therapeutic value of NPCDS on AMI.

RESULTS

We reported the robust and superior performance of NPCDS in AMI prediction, which contributed to an optimal combination of random forest and stepwise regression fitted on nine neutrophil-related PCD genes (MDM2, PTK2B, MYH9, IVNS1ABP, MAPK14, GNS, MYD88, TLR2, CFLAR). Two divergent NPCDS-based subtypes of AMI were revealed, in which subtype 1 was characterized as inflammation-activated with more vibrant neutrophil activities, whereas subtype 2 demonstrated the opposite. Mechanically, we unveiled the expression dynamics of NPCDS to regulate neutrophil transformation from a pro-inflammatory phase to an anti-inflammatory phase in AMI. We uncovered a significant causal association between genetic predisposition towards MDM2 expression and the risk of AMI. We also found that lidoflazine, isotetrandrine, and cepharanthine could stably target MDM2.

CONCLUSION

Altogether, NPCDS offers significant implications for prediction, stratification, and therapeutic management for AMI.

Insight into the mechanism of melatonin in attenuating PCB126-induced liver injury: Resistance to ROS-dependent NETs formation to alleviate inflammation and lipid metabolism dysfunction

3,3',4',4',5-Polychlorinated biphenyls (PCB126) is classified as a persistent organic environmental pollutant that can cause liver damage by producing excessive reactive oxygen species (ROS). ROS also can stimulate neutrophil extracellular traps (NETs) formation, which cause damage to organism if NETs are produced in excess. Melatonin is generally considered to possess strong antioxidant and anti-inflammation prosperities, but it is unclear whether it can alleviate PCB126-induced injury. To explore whether PCB126-induced liver injury is related to the formation of NETs and whether melatonin has a potent protective effect, we established PCB126 exposure/ PCB126 and melatonin co-treatment mouse models by gavage. To further clarify the specific mechanism, we also cultured neutrophils and AML12 cells to replicate in vivo model. Here, we found PCB126 exposure resulted in an elevation in the activities of MDA, LPO, PCO, and 8-OHdG, and a reduction in the activities of CAT, GSH-PX and SOD. We found that PCB126 exposure led to an elevation in the expression levels of chemokines (CCL2, CCL3, CCL4, CXCL12, and CXCL8) and marker factors for NETs formation (MPO, NE, NOX2, PKCα, and PKCζ) in the PCB126 group. IF, SYTOX staining, and SEM results also revealed that PCB126 could stimulate NETs formation. In addition, results of a co-culture system of PBNs and AML12 cells revealed that the expression levels of inflammatory cytokines (IL-1β, IL-6, and TNF-α) significantly decreased and the expression levels of metabolism factors (Fas, Acc, and Srebp) slightly decreased for scavenging NETs, indicating NETs formation aggravated PCB126-induced hepatic damages. Noteworthy, treatment with melatonin reversed these results. In summary, our findings revealed that melatonin alleviated hepatic damage aggravated by PCB126-induced ROS-dependent NETs formation through suppressing excessive ROS production. This finding not only enriches toxicological mechanism of PCB126, but more importantly extends biological effects of melatonin and its potential application values.

Therapeutic potential for targeting Annexin A1 in fibrotic diseases

Annexin A1, a well-known endogenous anti-inflammatory mediator, plays a critical role in a variety of pathological processes. Fibrosis is described by a failure of tissue regeneration and contributes to the development of many diseases. Accumulating evidence supports that Annexin A1 participates in the progression of tissue fibrosis. However, the fundamental mechanisms by which Annexin A1 regulates fibrosis remain elusive, and even the functions of Annexin A1 in fibrotic diseases are still paradoxical. This review focuses on the roles of Annexin A1 in the development of fibrosis of lung, liver, heart, and other tissues, with emphasis on the therapy potential of Annexin A1 in fibrosis, and presents future research interests and directions in fibrotic diseases.

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.

Increased Neutrophil-Subset Associated With Severity/Mortality In ARDS And COVID19-ARDS Expresses The Dual Endothelin-1/VEGFsignal-Peptide Receptor (DEspR): An Actionable Therapeutic Target

Neutrophil-mediated secondary tissue injury underlies acute respiratory distress syndrome (ARDS) and progression to multi-organ-failure (MOF) and death, processes linked to severe COVID19. This 'innocent bystander' tissue injury arises in dysregulated hyperinflammatory states from neutrophil functions and neutrophil extracellular traps (NETs) intended to kill pathogens, but injure cells instead, causing MOF. Insufficiency of prior therapeutic approaches suggest need to identify dysregulated neutrophil-subset(s) and induce subset-specific apoptosis critical for neutrophil function-shutdown and clearance. We hypothesized that neutrophils expressing the pro-survival dual endothelin-1/signal peptide receptor, DEspR, are apoptosis-resistant just like DEspR+ cancer cells, hence comprise a consequential pathogenic neutrophil-subset in ARDS and COVID19-ARDS. Here, we report correlation of circulating DEspR+CD11b+ activated neutrophils (DESpR+actNs) and NETosing-neutrophils with severity in ARDS and in COVID19-ARDS, increased DEspR+ neutrophils and monocytes in post-mortem ARDS-patient lung sections, and neutrophil DEspR/ET1 receptor/ligand autocrine loops in severe COVID19. Unlike DEspR[-] neutrophils, ARDS patient DEspR+actNs exhibit apoptosis-resistance, which decreased upon ex vivo treatment with humanized anti-DEspR-IgG4S228P antibody, hu6g8. Ex vivo live-cell imaging of non-human primate DEspR+actNs showed hu6g8 target-engagement, internalization, and induction of apoptosis. Altogether, data differentiate DEspR+actNs as a targetable neutrophil-subset associated with ARDS and COVID19-ARDS severity, and suggest DEspR-inhibition as a potential therapeutic paradigm.

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.

Resolvin D1 ameliorates Inflammation-Mediated Blood-Brain Barrier Disruption After Subarachnoid Hemorrhage in rats by Modulating A20 and NLRP3 Inflammasome

Inflammation is typically related to dysfunction of the blood-brain barrier (BBB) that leads to early brain injury (EBI) after subarachnoid hemorrhage (SAH). Resolvin D1 (RVD1), a lipid mediator derived from docosahexaenoic acid, possesses anti-inflammatory and neuroprotective properties. This study investigated the effects and mechanisms of RVD1 in SAH. A Sprague-Dawley rat model of SAH was established through endovascular perforation. RVD1was injected through the femoral vein at 1 and 12 h after SAH induction. To further explore the potential neuroprotective mechanism, a formyl peptide receptor two antagonist (WRW4) was intracerebroventricularly administered 1 h after SAH induction. The expression of endogenous RVD1 was decreased whereas A20 and NLRP3 levels were increased after SAH. An exogenous RVD1 administration increased RVD1 concentration in brain tissue, and improved neurological function, neuroinflammation, BBB disruption, and brain edema. RVD1 treatment upregulated the expression of A20, occludin, claudin-5, and zona occludens-1, as well as downregulated nuclear factor-κBp65, NLRP3, matrix metallopeptidase 9, and intercellular cell adhesion molecule-1 expression. Furthermore, RVD1 inhibited microglial activation and neutrophil infiltration and promoted neutrophil apoptosis. However, the neuroprotective effects of RVD1 were abolished by WRW4. In summary, our findings reveal that RVD1 provides beneficial effects against inflammation-triggered BBB dysfunction after SAH by modulating A20 and NLRP3 inflammasome.

Therapeutic potential of the FPR2/ALX agonist AT-01-KG in the resolution of articular inflammation

The resolution of inflammation is a dynamic process, characterized by the biosynthesis of pro-resolving mediators, including the lipid Lipoxin A4 (LXA₄). LXA₄ acts on the N-formyl peptide receptor 2 (FPR2/ALX) to mediate anti-inflammatory and pro-resolving effects. In order to exploit the therapeutic potential of endogenous LXA₄ in the context of inflammation we have recently developed synthetic LXA₄ mimetics (sLXms) including a dimethyl-imidazole-containing FPR2/ALX agonist designated AT-01-KG. Here, we have investigated the effect of treatment with AT-01-KG in established models of articular inflammation. In a model of gout, mice were injected with MSU crystals and treated with AT-01-KG at the peak of inflammatory response. The treatment decreased the number of neutrophils in the knee exudate, an effect which was accompanied by low levels of myeloperoxidase, CXCL1 and IL-1β in periarticular tissue. AT-01-KG treatment led to reduced tissue damage and hypernociception. The effects of AT-01-KG on neutrophil accumulation were not observed in MSU treated FPR2/3^-/-mice. Importantly, AT-01-KG induced resolution of articular inflammation by increasing neutrophil apoptosis and subsequent efficient efferocytosis. In a model of antigen-induced arthritis, AT-01-KG treatment also attenuated inflammatory responses. These data suggest that AT-01-KG may be a potential new therapy for neutrophilic inflammation of the joints.

Molecular Mechanisms for Regulation of Neutrophil Apoptosis under Normal and Pathological Conditions

Neutrophils are one of the main cells of innate immunity that perform a key effector and regulatory function in the development of the human inflammatory response. Apoptotic forms of neutrophils are important for regulating the intensity of inflammation and restoring tissue homeostasis. This review summarizes current data on the molecular mechanisms of modulation of neutrophil apoptosis by the main regulatory factors of the inflammatory response-cytokines, integrins, and structural components of bacteria. Disturbances in neutrophil apoptosis under stress are also considered, molecular markers of changes in neutrophil lifespan associated with various diseases and pathological conditions are presented, and data on pharmacological agents for modulating apoptosis as potential therapeutics are also discussed.

Immune Dysfunction in Uremia 2020

Cardiovascular disease and infections are major causes for the high incidence of morbidity and mortality of patients with chronic kidney disease. Both complications are directly or indirectly associated with disturbed functions or altered apoptotic rates of polymorphonuclear leukocytes, monocytes, lymphocytes, and dendritic cells. Normal responses of immune cells can be reduced, leading to infectious diseases or pre-activated/primed, giving rise to inflammation and subsequently to cardiovascular disease. This review summarizes the impact of kidney dysfunction on the immune system. Renal failure results in disturbed renal metabolic activities with reduced renin, erythropoietin, and vitamin D production, which adversely affects the immune system. Decreased kidney function also leads to reduced glomerular filtration and the retention of uremic toxins. A large number of uremic toxins with detrimental effects on immune cells have been identified. Besides small water-soluble and protein-bound compounds originating from the intestinal microbiome, several molecules in the middle molecular range, e.g., immunoglobulin light chains, retinol-binding protein, the neuropeptides Met-enkephalin and neuropeptide Y, endothelin-1, and the adipokines leptin and resistin, adversely affect immune cells. Posttranslational modifications such as carbamoylation, advanced glycation products, and oxidative modifications contribute to uremic toxicity. Furthermore, high-density lipoprotein from uremic patients has an altered protein profile and thereby loses its anti-inflammatory properties.

Marine omega-3 (n-3) phospholipids: A comprehensive review of their properties, sources, bioavailability, and relation to brain health

For several decades, there has been considerable interest in marine-derived long chain n-3 fatty acids (n-3 LCPUFAs) due to their outstanding health benefits. n-3 LCPUFAs can be found in nature either in triglycerides (TAGs) or in phospholipid (PL) form. From brain health point of view, PL n-3 is more bioavailable and potent compared to n-3 in TAG form, as only PL n-3 is able to cross the blood-brain barrier and can be involved in brain biochemical reactions. However, PL n-3 has been ignored in the fish oil industry and frequently removed as an impurity during degumming processes. As a result, PL products derived from marine sources are very limited compared to TAG products. Commercially, PLs are being used in pharmaceutical industries as drug carriers, in food manufacturing as emulsifiers and in cosmetic industries as skin care agents, but most of the PLs used in these applications are produced from vegetable sources that contain less (without EPA, DPA, and DHA) or sometimes no n-3 LCPUFAs. This review provides a comprehensive account of the properties, structures, and major sources of marine PLs, and provides focussed discussion of their relationship to brain health. Epidemiological, laboratory, and clinical studies on n-3 LCPUFAs enriched PLs using different model systems in relation to brain and mental health that have been published over the past few years are discussed in detail.

Effect of Curcumin on Serum Cathepsin D in Patients with Metabolic Syndrome

BACKGROUND

Inflammation has been shown to accompany Metabolic Syndrome (MetS) and its features. Cathepsin D is one of a proinflammatory mediator. In the current study, we aimed to investigate the effect of curcumin supplementation on serum cathepsin D levels in patients with MetS.

METHODS

The current study was conducted on 18-65 years old individuals with MetS diagnosed according to the International Diabetes Federation guidelines. A total of 80 participants were randomly divided into treatment and control groups. The first group (n=40) was given 2 capsules containing 500 mg of phosphatidylcholine complex of curcumin, and the other group (n=40) was given two 500 mg placebo capsules for 6 weeks. Before (week 0) and after (week 6) the intervention, anthropometric indices and blood pressure were measured and blood samples were taken. Serum cathepsin D was measured using an ELISA kit.

RESULTS

There was no significant difference between treatment and control groups in terms of weight, body mass index, waist circumference and serum cathepsin D levels before and after the intervention. In addition, there was no significant difference between pre- and post-trial values of serum cathepsin D.

CONCLUSION

The present results do not suggest any effect of curcumin on cathepsin D levels in patients with MetS.

Anhydroglucitol-core gallotannins from red maple buds modulate viability of human blood neutrophils

Apoptosis of neutrophils is an essential checkpoint for the resolution of inflammation by shutting down the deleterious functions of these immune cells. This study investigated the role of anhydroglucitol-core gallotannins (ACGs) in apoptosis increase of human blood neutrophils treated by the hot water extract from red maple buds (RMB). Fractions obtained by liquid-liquid partitioning (ethyl acetate, butanol and water-remaining fractions) of the hot water extract from RMB were assessed for their effects on neutrophil viability by using flow cytometry. These fractions were then phytochemically analyzed to investigate the ability of major compounds to induce neutrophil apoptosis individually. Ethyl acetate and butanol fractions that contained the major ACGs ginnalin A, ginnalin 3,6 and ginnalin C stimulated the apoptosis of neutrophils. The three ACGs at 100 μM significantly increased the rate of the late apoptotic cells. When differentially combined, these ACGs have additive or antagonist effects. These effects are related to the concentrations of the constituents in the mixtures studied, especially so for ginnalin C. GinA increased FADD, phospho-Rad17, SMAC/Diablo and cytochrome C, while decreasing the anti-apoptotic protein catalase. These compounds could be useful for the development of novel therapeutic approaches that facilitate resolution of neutrophil-mediated inflammatory diseases.

Adoption of in vitro systems and zebrafish embryos as alternative models for reducing rodent use in assessments of immunological and oxidative stress responses to nanomaterials

Assessing the safety of engineered nanomaterials (NMs) is paramount to the responsible and sustainable development of nanotechnology, which provides huge societal benefits. Currently, there is no evidence that engineered NMs cause detrimental health effects in humans. However, investigation of NM toxicity using in vivo, in vitro, in chemico, and in silico models has demonstrated that some NMs stimulate oxidative stress and inflammation, which may lead to adverse health effects. Accordingly, investigation of these responses currently dominates NM safety assessments. There is a need to reduce reliance on rodent testing in nanotoxicology for ethical, financial and legislative reasons, and due to evidence that rodent models do not always predict the human response. We advocate that in vitro models and zebrafish embryos should have greater prominence in screening for NM safety, to better align nanotoxicology with the 3Rs principles. Zebrafish are accepted for use by regulatory agencies in chemical safety assessments (e.g. developmental biology) and there is growing acceptance of their use in biomedical research, providing strong foundations for their use in nanotoxicology. We suggest that investigation of the response of phagocytic cells (e.g. neutrophils, macrophages) in vitro should also form a key part of NM safety assessments, due to their prominent role in the first line of defense. The development of a tiered testing strategy for NM hazard assessment that promotes the more widespread adoption of non-rodent, alternative models and focuses on investigation of inflammation and oxidative stress could make nanotoxicology testing more ethical, relevant, and cost and time efficient.

c-Abl tyrosine kinase regulates neutrophil crawling behavior under fluid shear stress via Rac/PAK/LIMK/cofilin signaling axis

The excessive recruitment and improper activation of polymorphonuclear neutrophils (PMNs) often induces serious injury of host tissues, leading to inflammatory disorders. Therefore, to understand the molecular mechanism on neutrophil recruitment possesses essential pathological and physiological importance. In this study, we found that physiological shear stress induces c-Abl kinase activation in neutrophils, and c-Abl kinase inhibitor impaired neutrophil crawling behavior on ICAM-1. We further identified Vav1 was a downstream effector phosphorylated at Y174 and Y267. Once activated, c-Abl kinase regulated the activity of Vav1, which further affected Rac1/PAK1/LIMK1/cofilin signaling pathway. Here, we demonstrate a novel signaling function and critical role of c-Abl kinase during neutrophil crawling under physiological shear by regulating Vav1. These findings provide a promising treatment strategy for inflammation-related disease by inactivation of c-Abl kinase to restrict neutrophil recruitment.

CD47 overexpression is associated with decreased neutrophil apoptosis/phagocytosis and poor prognosis in non-small-cell lung cancer patients

Background:

Non-small-cell lung cancer (NSCLC) patients often exhibit neutrophilia, which has been associated with poor clinical outcomes. However, the mechanisms that lead to neutrophilia have not been fully established. CD47 is an antiphagocytic molecule that promotes neutrophil recruitment.

Methods:

Blood was collected from 50 treatment-naive patients with advanced NSCLC and from 25 healthy subjects. The frequency of CD66b⁺ cells and the expression of CD47 were determined by flow cytometry. Neutrophil apoptosis was determined by 7-amino-actinomycin D/Annexin V-APC staining. Phagocytosis was assessed by flow cytometry. Reactive oxygen species production after phorbol 12-myristate 13-acetate treatment was quantified by 2′,7′-dichlorofluorescein fluorescence. Pro-inflammatory plasma cytokines were quantified using a cytometric bead array assay.

Results:

The percentage of circulating neutrophils was significantly higher in patients than in controls (P<0.001). Patient-derived neutrophils had a higher oxidative potential than those of controls (P=0.0286). The number of neutrophils in late apoptosis/necrosis was lower in patients than in controls (P=0.0317). Caspase 3/7 activation was also lower in patients than in controls (P=0.0079). CD47 expression in whole-blood samples and in the neutrophil fraction was higher in NSCLC patients than in controls (P=0.0408 and P<0.001). Patient-derived neutrophils were phagocytosed at a lower rate than those of controls (P=0.0445). CD47 expression in neutrophils negatively correlated with their ingestion by macrophages (P=0.0039). High CD47 expression was associated with a lower overall survival.

Conclusions:

Increased CD47 expression on the surface of neutrophils was associated with a delay in neutrophil apoptosis and with an impairment in their phagocytic clearance by macrophages, suggesting that CD47 overexpression may be one of the underlying mechanisms leading to neutrophilia in NSCLC patients.

The critical role of myeloperoxidase in Streptococcus pneumoniae clearance and tissue damage during mouse acute otitis media

We have recently reported that neutrophils play a pivotal role in innate defense against Streptococcus pneumoniae ( Spn) during mouse acute otitis media (AOM). However, the underlying mechanism remains unclear. By constructing models of pneumococcal AOM in C57BL/6 mice and using a specific inhibitor in vivo, we investigated the role of myeloperoxidase (MPO), one of the most important protein components of neutrophils. Experiment results showed a significant increase in MPO production of the recruited neutrophils in Spn-infected mice. Neutrophils killed Spn in a MPO-dependent manner. MPO facilitated the generation of reactive oxygen species (ROS), and consequently promoted Spn clearance at an early stage and exacerbated tissue damage. Moreover, MPO induced neutrophil apoptosis and necrosis, which, in turn, worsened tissue damage. In summary, our study demonstrates that neutrophil MPO plays a paradoxical role in bacterial clearance and tissue damage in pneumococcal AOM.

Neutrophil serine proteases and their endogenous inhibitors in coronary artery ectasia patients

Objective:

Proteolytic enzymes possibly contribute to coronary artery ectasia (CAE). This study aimed to determine whether neutrophils, neutrophil serine proteases (NSPs), and their endogenous inhibitors participated in the pathological process of CAE.

Methods:

The study consisted of 30 patients with CAE, 30 patients with coronary artery disease (CAD), and 29 subjects with normal coronary arteries (Control). The following circulating items were measured: the main NSPs, including human neutrophil elastase (HNE), cathepsin G (CG), and proteinase 3 (PR3); soluble elastin (sElastin), which was a degradation product of elastin fibres; NSP inhibitors such as α1-protease inhibitor (α1-PI), α2-macroglobulin (α2-MG), secretory leucoprotease inhibitor (SLPI), and elafin; as well as two neutrophil activation markers (myeloperoxidase and lactoferrin) and three classic neutrophil activators [tumor necrosis factor-α (TNF-α), interleukin-8 (IL-8), and bacterial endotoxin].

Results:

The levels of HNE, CG, and sElastin were elevated in the CAE group. The levels of α1-PI and α2-MG were also significantly increased in the CAE group. The levels of myeloperoxidase and lactoferrin were higher in the CAE group. The levels of TNF-α, IL-8, and endotoxin were unchanged in the CAE group compared with those in the CAD group.

Conclusion:

Neutrophils may participate in the process of vessel extracellular matrix destruction and coronary ectasia by releasing NSPs in a non-classical manner.

Understanding the molecular mechanisms of NETs and their role in antiviral innate immunity

Polymorphonuclear neutrophils (PMNs) are the most abundant cells in the context of innate immunity; they are one of the first cells to arrive at the site of viral infection constituting the first line of defense in response to invading pathogens. Indeed, neutrophils are provided with several defense mechanisms including release of cytokines, cytotoxic granules and the last recently described neutrophil extracellular traps (NETs). The main components of NETs are DNA, granular antimicrobial peptides, and nuclear and cytoplasmic proteins, that together play an important role in the innate immune response. While NETs were first described as a mechanism against bacteria and fungi, recently, several studies are beginning to elucidate how NETs are involved in the host antiviral response and the prominent characteristics of this new mechanism are discussed in the present review.

In Vitro effects of tamoxifen on equine neutrophils

Neutrophils participate in innate immunity as the first line of host defense against microorganisms. However, exacerbated neutrophil activity can be harmful to surrounding tissues; this is important in a range of diseases, including allergic asthma and chronic obstructive pulmonary disease in humans, and equine asthma (also known as recurrent airway obstruction (RAO). Tamoxifen (TX) is a non-steroidal estrogen receptor modulator with effects on cell growth and survival. Previous preliminary studies showed that TX treatment in horses with induced acute pulmonary inflammation promoted early apoptosis of blood and BALF neutrophils, reduction of BALF neutrophils, and improvement in animals' clinical status. The aim of this study was to evaluate the in vitro effect of TX on functional tests in equine peripheral blood neutrophils. Chemotaxis, respiratory burst production and phagocytosis assays were performed on neutrophils isolated from peripheral blood samples from 10 healthy horses. Results showed that IL-8 stimulated cells decrease their chemotactic index when treated with TX (1 and 10μM). Respiratory burst production was also dampened after treatment with TX. In conclusion, these results confirm that tamoxifen has a direct action on equine peripheral blood neutrophils. However, more in vivo and in vitro studies are required to fully understand the mechanisms of action of TX on neutrophils, in order to elucidate if it can be used as treatment in disorders such as allergic asthma in humans and horses.

Effect of dietary antioxidant supplementation (Cuminum cyminum) on bacterial susceptibility of diabetes-induced rats

Diabetic patients are at risk of acquiring infections. Chronic low-grade inflammation is an important factor in the pathogenesis of diabetic complication. Diabetes causes generation of reactive oxygen species that increases oxidative stress, which may play a role in the development of complications as immune-deficiency and bacterial infection. The study aimed to investigate the role of a natural antioxidant, cumin, in the improvement of immune functions in diabetes. Diabetes was achieved by interperitoneal injection of streptozotocin (STZ). Bacterial infection was induced by application of Staphylococcus aureus suspension to a wound in the back of rats. The antioxidant was administered for 6 weeks. Results revealed a decrease in blood glucose levels in diabetic rats (p < 0.001), in addition to improving immune functions by decreasing total IgE approaching to the normal control level. Also, inflammatory cytokine (IL-6, IL-1β and TNF) levels, as well as total blood count decreased in diabetic rats as compared to the control group. Thus, cumin may serve as anti-diabetic treatment and may help in attenuating diabetic complications by improving immune functions. Therefore, a medical dietary antioxidant supplementation is important to improve the immune functions in diabetes.

Annexin A1 and the Resolution of Inflammation: Modulation of Neutrophil Recruitment, Apoptosis, and Clearance

Neutrophils (also named polymorphonuclear leukocytes or PMN) are essential components of the immune system, rapidly recruited to sites of inflammation, providing the first line of defense against invading pathogens. Since neutrophils can also cause tissue damage, their fine-tuned regulation at the inflammatory site is required for proper resolution of inflammation. Annexin A1 (AnxA1), also known as lipocortin-1, is an endogenous glucocorticoid-regulated protein, which is able to counterregulate the inflammatory events restoring homeostasis. AnxA1 and its mimetic peptides inhibit neutrophil tissue accumulation by reducing leukocyte infiltration and activating neutrophil apoptosis. AnxA1 also promotes monocyte recruitment and clearance of apoptotic leukocytes by macrophages. More recently, some evidence has suggested the ability of AnxA1 to induce macrophage reprogramming toward a resolving phenotype, resulting in reduced production of proinflammatory cytokines and increased release of immunosuppressive and proresolving molecules. The combination of these mechanisms results in an effective resolution of inflammation, pointing to AnxA1 as a promising tool for the development of new therapeutic strategies to treat inflammatory diseases.

Antiinflammatory and Antimicrobial Effects of Thiocyanate in a Cystic Fibrosis Mouse Model

Thiocyanate (SCN) is used by the innate immune system, but less is known about its impact on inflammation and oxidative stress. Granulocytes oxidize SCN to evolve the bactericidal hypothiocyanous acid, which we previously demonstrated is metabolized by mammalian, but not bacterial, thioredoxin reductase (TrxR). There is also evidence that SCN is dysregulated in cystic fibrosis (CF), a disease marked by chronic infection and airway inflammation. To investigate antiinflammatory effects of SCN, we administered nebulized SCN or saline to β epithelial sodium channel (βENaC) mice, a phenotypic CF model. SCN significantly decreased airway neutrophil infiltrate and restored the redox ratio of glutathione in lung tissue and airway epithelial lining fluid to levels comparable to wild type. Furthermore, in Pseudomonas aeruginosa-infected βENaC and wild-type mice, SCN decreased inflammation, proinflammatory cytokines, and bacterial load. SCN also decreased airway neutrophil chemokine keratinocyte chemoattractant (also known as C-X-C motif chemokine ligand 1) and glutathione sulfonamide, a biomarker of granulocyte oxidative activity, in uninfected βENaC mice. Lung tissue TrxR activity and expression increased in inflamed lung tissue, providing in vivo evidence for the link between hypothiocyanous acid metabolism by TrxR and the promotion of selective biocide of pathogens. SCN treatment both suppressed inflammation and improved host defense, suggesting that nebulized SCN may have important therapeutic utility in diseases of both chronic airway inflammation and persistent bacterial infection, such as CF.

Glycyrrhizic Acid Prevents Sepsis-Induced Acute Lung Injury and Mortality in Rats

Glycyrrhizic acid (GA), an active ingredient in licorice, has multiple pharmacological activities. However, the effects of GA on sepsis-induced acute lung injury (ALI) have not been determined. Tthe aim of this study was to investigate the molecular mechanism involved in the effects of GA against sepsis-induced ALI in rats. We found that GA alleviated sepsis-induced ALI through improvements in various pathological changes, as well as decreases in the lung wet/dry weight ratio and total protein content in bronchoalveolar lavage fluid, and a significant increase in the survival rate of treated rats. Additionally, GA markedly inhibited sepsis-induced pulmonary inflammatory responses. Moreover, we found that treatment with GA inhibited oxidative stress damage and apoptosis in lung tissue induced by ALI. Finally, GA treatment significantly inhibited NF-κ B, JNK and P38 MAPK activation. Our data indicate that GA has a protective effect against sepsis-induced ALI by inhibiting the inflammatory response, damage from oxidative stress, and apoptosis via inactivation of NF-κB and MAPK signaling pathways, providing a molecular basis for a new medical treatment for sepsis-induced ALI.

Arbutin and decrease of potentially toxic substances generated in human blood neutrophils

Neutrophils, highly motile phagocytic cells, constitute the first line of host defense and simultaneously they are considered to be central cells of chronic inflammation. In combination with standard therapeutic procedures, natural substances are gaining interest as an option for enhancing the effectiveness of treatment of inflammatory diseases. We investigated the effect of arbutin and carvedilol and of their combination on 4β-phorbol-12β-myristate-13α-acetate- stimulated functions of human isolated neutrophils. Cells were preincubated with the drugs tested and subsequently stimulated. Superoxide (with or without blood platelets, in the rate close to physiological conditions [1:50]) and HOCl generation, elastase and myeloperoxidase release were determined spectrophotometrically and phospholipase D activation spectrofluorometrically. The combined effect of arbutin and carvedilol was found to be more effective than the effect of each compound alone.

Our study provided evidence supporting the potential beneficial effect of arbutin alone or in combination with carvedilol in diminishing tissue damage by decreasing phospholipase D, myeloperoxidase and elastase activity and by attenuating the generation of superoxide and the subsequently derived reactive oxygen species. The presented data indicate the ability of arbutin to suppress the onset and progression of inflammation.

Effects of Glucocorticoids in the Immune System

Glucocorticoids (GCs) are steroid hormones with widespread effects. They control intermediate metabolism by stimulating gluconeogenesis in the liver, mobilize amino acids from extra hepatic tissues, inhibit glucose uptake in muscle and adipose tissue, and stimulate fat breakdown in adipose tissue. They also mediate stress response. They exert potent immune-suppressive and anti-inflammatory effects particularly when administered pharmacologically. Understanding these diverse effects of glucocorticoids requires a detailed knowledge of their mode of action. Research over the years has uncovered several details on the molecular action of this hormone, especially in immune cells. In this chapter, we have summarized the latest findings on the action of glucocorticoids in immune cells with a view of identifying important control points that may be relevant in glucocorticoid therapy.

Gene expression during the generation and activation of mouse neutrophils: implication of novel functional and regulatory pathways

As part of the Immunological Genome Project (ImmGen), gene expression was determined in unstimulated (circulating) mouse neutrophils and three populations of neutrophils activated in vivo, with comparison among these populations and to other leukocytes. Activation conditions included serum-transfer arthritis (mediated by immune complexes), thioglycollate-induced peritonitis, and uric acid-induced peritonitis. Neutrophils expressed fewer genes than any other leukocyte population studied in ImmGen, and down-regulation of genes related to translation was particularly striking. However, genes with expression relatively specific to neutrophils were also identified, particularly three genes of unknown function: Stfa2l1, Mrgpr2a and Mrgpr2b. Comparison of genes up-regulated in activated neutrophils led to several novel findings: increased expression of genes related to synthesis and use of glutathione and of genes related to uptake and metabolism of modified lipoproteins, particularly in neutrophils elicited by thioglycollate; increased expression of genes for transcription factors in the Nr4a family, only in neutrophils elicited by serum-transfer arthritis; and increased expression of genes important in synthesis of prostaglandins and response to leukotrienes, particularly in neutrophils elicited by uric acid. Up-regulation of genes related to apoptosis, response to microbial products, NFkB family members and their regulators, and MHC class II expression was also seen, in agreement with previous studies. A regulatory model developed from the ImmGen data was used to infer regulatory genes involved in the changes in gene expression during neutrophil activation. Among 64, mostly novel, regulatory genes predicted to influence these changes in gene expression, Irf5 was shown to be important for optimal secretion of IL-10, IP-10, MIP-1α, MIP-1β, and TNF-α by mouse neutrophils in vitro after stimulation through TLR9. This data-set and its analysis using the ImmGen regulatory model provide a basis for additional hypothesis-based research on the importance of changes in gene expression in neutrophils in different conditions.

Prevention of neutrophil extravasation by α2-adrenoceptor-mediated endothelial stabilization

Adrenergic receptors are expressed on the surface of inflammation-mediating cells, but their potential role in the regulation of the inflammatory response is still poorly understood. The objectives of this work were to study the effects of α2-adrenergic agonists on the inflammatory response in vivo and to determine their mechanism of action. In two mouse models of inflammation, zymosan air pouch and thioglycolate-induced peritonitis models, the i.m. treatment with xylazine or UK14304, two α2-adrenergic agonists, reduced neutrophil migration by 60%. The α2-adrenergic antagonist RX821002 abrogated this effect. In flow cytometry experiments, the basal surface expression of L-selectin and CD11b was modified neither in murine nor in human neutrophils upon α2-agonist treatment. Similar experiments in HUVEC showed that UK14304 prevented the activation-dependent upregulation of ICAM-1. In contrast, UK14304 augmented electrical resistance and reduced macromolecular transport through a confluent HUVEC monolayer. In flow chamber experiments, under postcapillary venule-like flow conditions, the pretreatment of HUVECs, but not neutrophils, with α2-agonists decreased transendothelial migration, without affecting neutrophil rolling. Interestingly, α2-agonists prevented the TNF-α-mediated decrease in expression of the adherens junctional molecules, VE-cadherin, β-catenin, and plakoglobin, and reduced the ICAM-1-mediated phosphorylation of VE-cadherin by immunofluorescence and confocal analysis and Western blot analysis, respectively. These findings indicate that α2-adrenoceptors trigger signals that protect the integrity of endothelial adherens junctions during the inflammatory response, thus pointing at the vascular endothelium as a therapeutic target for the management of inflammatory processes in humans.

Inflammatory responses and side effects generated by several adjuvant-containing vaccines in turbot

Several of the adjuvants used in fish vaccines cause adhesions in internal organs when they are injected intraperitoneally. We describe the damage caused by vaccines containing different adjuvants in the turbot Scophthalmus maximus and show that internal adhesions can be greatly reduced by injecting the fish in a specific way. Injection of fish with the needle directed towards the anterior part of the peritoneal cavity induced formation of a single cell-vaccine mass (CVM) that became attached to the parietal peritoneum. However, injection of the fish with the needle pointing in the opposite direction generated many small CVM that became attached to the visceral and parietal peritoneum and in some cases caused internal adhesions. We describe the structural and cellular changes in the adjuvant-induced CVMs. The CVMs mainly comprised neutrophils and macrophages, although most of the former underwent apoptosis, which was particularly evident from day 3 post-injection. The apoptotic cells were phagocytosed by macrophages, which were the dominant cell type from the first days onwards. All of the vaccines induced angiogenesis in the area of contact between the CVM and the mesothelium. Vaccines containing oil-based adjuvants or microspheres induced the formation of granulomas in the CVM; however, no granulomas were observed in the CVM induced by vaccines containing aluminium hydroxide or Matrix-Q(®) as adjuvants. All of the vaccines induced strong migration of cells to the peritoneal cavity. Although some of these cells remained unattached in the peritoneal cavity, most of them formed part of the CVM. We also observed migration of the cells from the peritoneal cavity to lymphoid organs, indicating bidirectional traffic of cells between the inflamed areas and these organs.

On the molecular pharmacology of resveratrol on oxidative burst inhibition in professional phagocytes

Resveratrol—3,5,4′-trihydroxystilbene—possesses antioxidant activities in vitro. It dose-dependently inhibited the generation of peroxyl, hydroxyl, peroxides, and lipid peroxidation products in cell free systems. Oxidative burst of whole human blood stimulated with PMA, fMLP, OpZ, and A23187 was inhibited in a concentration-dependent way, indicating suppression of both receptor and nonreceptor activated chemiluminescence by resveratrol. Results from isolated human neutrophils revealed that resveratrol was active extracellularly as well as intracellularly in inhibiting the generation of reactive oxygen species. Liberation of ATP and analysis of apoptosis showed that in the concentration of 100 μM, resveratrol did not change the viability and integrity of isolated neutrophils. Western blot analysis documented that resveratrol in concentrations of 10 and 100 μM significantly decreased PMA-induced phosphorylation of PKC α/βII. Dose-dependent inhibition of nitrite production and iNOS protein expression in RAW 264.7 cells indicated possible interference of resveratrol with reactive nitrogen radical generation in professional phagocytes. The results suggest that resveratrol represents an effective naturally occurring substance with potent pharmacological effect on oxidative burst of human neutrophils and nitric oxide production by macrophages. It should be further investigated for its pharmacological activity against oxidative stress in ischaemia reperfusion, inflammation, and other pathological conditions, particularly neoplasia.

The natural stilbenoid piceatannol decreases activity and accelerates apoptosis of human neutrophils: involvement of protein kinase C

Neutrophils are able to release cytotoxic substances and inflammatory mediators, which, along with their delayed apoptosis, have a potential to maintain permanent inflammation. Therefore, treatment of diseases associated with chronic inflammation should be focused on neutrophils; formation of reactive oxygen species and apoptosis of these cells represent two promising targets for pharmacological intervention. Piceatannol, a naturally occurring stilbenoid, has the ability to reduce the toxic action of neutrophils. This substance decreased the amount of oxidants produced by neutrophils both extra- and intracellularly. Radicals formed within neutrophils (fulfilling a regulatory role) were reduced to a lesser extent than extracellular oxidants, potentially dangerous for host tissues. Moreover, piceatannol did not affect the phosphorylation of p40^phox—a component of NADPH oxidase, responsible for the assembly of functional oxidase in intracellular (granular) membranes. The stilbenoid tested elevated the percentage of early apoptotic neutrophils, inhibited the activity of protein kinase C (PKC)—the main regulatory enzyme in neutrophils, and reduced phosphorylation of PKC isoforms α, βII, and δ on their catalytic region. The results indicated that piceatannol may be useful as a complementary medicine in states associated with persisting neutrophil activation and with oxidative damage of tissues.

Increased saturated fatty acids in obesity alter resolution of inflammation in part by stimulating prostaglandin production

Extensive evidence indicates that nutrient excess associated with obesity and type 2 diabetes activates innate immune responses that lead to chronic, sterile low-grade inflammation, and obese and diabetic humans also have deficits in wound healing and increased susceptibility to infections. Nevertheless, the mechanisms that sustain unresolved inflammation during obesity remain unclear. In this study, we report that saturated free fatty acids that are elevated in obesity alter resolution of acute sterile inflammation by promoting neutrophil survival and decreasing macrophage phagocytosis. Using a targeted mass spectrometry-based lipidomics approach, we found that in db/db mice, PGE2/D2 levels were elevated in inflammatory exudates during the development of acute peritonitis. Moreover, in isolated macrophages, palmitic acid stimulated cyclooxygenase-2 induction and prostanoid production. Defects in macrophage phagocytosis induced by palmitic acid were mimicked by PGE2 and PGD2 and were reversed by cyclooxygenase inhibition or prostanoid receptor antagonism. Macrophages isolated from obese-diabetic mice expressed prostanoid receptors, EP2 and DP1, and contained significantly higher levels of downstream effector, cAMP, compared with wild-type mice. Therapeutic administration of EP2/DP1 dual receptor antagonist, AH6809, decreased neutrophil accumulation in the peritoneum of db/db mice, as well as the accumulation of apoptotic cells in the thymus. Taken together, these studies provide new insights into the mechanisms underlying altered innate immune responses in obesity and suggest that targeting specific prostanoid receptors may represent a novel strategy for resolving inflammation and restoring phagocyte defects in obese and diabetic individuals.

Targeting neutrophil apoptosis for enhancing the resolution of inflammation

Resolution of acute inflammation is an active process that requires inhibition of further leukocyte recruitment and removal of leukocytes from inflamed sites. Emigrated neutrophils undergo apoptosis before being removed by scavenger macrophages. Recent studies using a variety of gene knockout, transgenic and pharmacological strategies in diverse models of inflammation established neutrophil apoptosis as a critical control point in resolving inflammation. Analysis of death mechanisms revealed distinct features in executing the death program in neutrophils, which can be exploited as targets for controlling the lifespan of neutrophils. Indeed, anti-inflammatory and pro-resolution lipid mediators derived from essential fatty acids, such as lipoxin A₄ and resolvin E1, autacoids and proteins, such as annexin A1 and TRAIL, and cyclin-dependent kinase inhibitors, can enhance the resolution of inflammation through induction of neutrophil apoptosis and promoting their removal by efferocytosis. In this review, we discuss recent advances in understanding the molecular basis of these actions, highlighting the potential of therapeutic induction of neutrophil apoptosis for dampening neutrophil-mediated tissue injury and inflammation underlying a variety of diseases.

Modulation of Neutrophil Apoptosis and the Resolution of Inflammation through β2 Integrins

Precise control of the neutrophil death program provides a balance between their defense functions and safe clearance, whereas impaired regulation of neutrophil death is thought to contribute to a wide range of inflammatory pathologies. Apoptosis is essential for neutrophil functional shutdown, removal of emigrated neutrophils, and timely resolution of inflammation. Neutrophils receive survival and pro-apoptosis cues from the inflammatory microenvironment and integrate these signals through surface receptors and common downstream mechanisms. Among these receptors are the leukocyte-specific membrane receptors β2 integrins that are best known for regulating adhesion and phagocytosis. Accumulating evidence indicate that outside-in signaling through the β2 integrin Mac-1 can generate contrasting cues in neutrophils, leading to promotion of their survival or apoptosis. Binding of Mac-1 to its ligands ICAM-1, fibrinogen, or the azurophilic granule enzyme myeloperoxidase suppresses apoptosis, whereas Mac-1-mediated phagocytosis of bacteria evokes apoptotic cell death. Mac-1 signaling is also target for the anti-inflammatory, pro-resolving mediators, including lipoxin A4, aspirin-triggered lipoxin A4, and resolvin E1. This review focuses on molecular mechanisms underlying Mac-1 regulation of neutrophil apoptosis and highlights recent advances how hierarchy of survival and pro-apoptosis signals can be harnessed to facilitate neutrophil apoptosis and the resolution of inflammation.

Effects of different electroacupuncture scheduling regimens on murine bone tumor-induced hyperalgesia: sex differences and role of inflammation

Previous studies have shown that electroacupuncture (EA) is able to reduce hyperalgesia in rodent models of persistent pain, but very little is known about the analgesic effects and potential sex differences of different EA treatment regimens. In the present study, we examined the effects of five different EA treatments on tumor-induced hyperalgesia in male and female mice. EA applied to the ST-36 acupoint either twice weekly (EA-2X/3) beginning on postimplantation day (PID) 3 or prophylactically three times prior to implantation produced the most robust and longest lasting antinociceptive effects. EA treatment given once per week beginning at PID 7 only produced an antinociceptive effect in female animals. The analgesic effect of EA-2X/3 began earlier in males, but lasted longer in females indicating sex differences in EA. We further demonstrate that EA-2X/3 elicits a marked decrease in tumor-associated inflammation as evidenced by a significant reduction in tumor-associated neutrophils at PID 7. Moreover, EA-2X/3 produced a significant reduction in tumor-associated PGE₂ as measured in microperfusate samples. Collectively, these data provide evidence that EA-2X/3 treatment reduces tumor-induced hyperalgesia, which is associated with a decrease in tumor-associated inflammation and PGE₂ concentration at the tumor site suggesting possible mechanisms by which EA reduces tumor nociception.

Characteristics of an autologous leukocyte and platelet-rich fibrin patch intended for the treatment of recalcitrant wounds

We have investigated the physical, biochemical, and cellular properties of an autologous leukocyte and platelet-rich fibrin patch. This was generated in an automated device from a sample of a patient's blood at the point of care. Using microscopy, cell counting, enzyme-linked immunosorbent assay, antibody arrays, and cell culture assays, we show that the patch is a three-layered membrane comprising a fibrin sheet, a layer of platelets, and a layer of leukocytes. Mean recovery of platelets from the donated blood was 98% (±95%CI 0.8%). Mean levels of platelet-derived growth factor AB, human transforming growth factor beta 1, and vascular endothelial growth factor extracted from the patch were determined as 127 ng (±95% CI 20), 92 ng (±95%CI 17), and 1.35 ng (±95%CI 0.37), respectively. We showed a continued release of PDGF-AB over several days, the rate of which was increased by the addition of chronic wound fluid. By comparison with traditional platelet-rich plasma, differences in immune components were found. The relevance of these findings was assessed by showing a mitogenic and migratory effect on cultured human dermal fibroblasts. Further, we showed that fibrocytes, a cell type important for acute wound healing, could be grown from the patch. The relevance of these findings in relation to the use of the patch for treating recalcitrant wounds is discussed.

The uraemic toxin phenylacetic acid contributes to inflammation by priming polymorphonuclear leucocytes

BACKGROUND

The activation of polymorphonuclear leucocytes (PMNLs) causes inflammation and as a result cardiovascular disease, which is a main risk factor for increased morbidity and mortality in patients with chronic kidney disease. Toxins accumulating in uraemic patients play a major role in modulating essential PMNL functions and apoptosis, the latter being crucial for a coordinated resolution of inflammation. One uraemic toxin is phenylacetic acid (PAA). We therefore investigated whether PAA contributes to the deranged immune response in uraemia by modulating PMNL activities.

METHODS

PMNL oxidative burst, phagocytosis and surface expression of the activation markers CD11b and CD18 were measured by flow cytometry in whole blood from healthy subjects in the presence and absence of PAA. Spontaneous apoptosis of isolated PMNLs was assessed by evaluating morphological features under the fluorescence microscope and by measuring the DNA content by flow cytometry. PMNL chemotaxis was tested by the under-agarose method.

RESULTS

PAA significantly enhanced the stimulation of PMNL oxidative burst by Escherichia coli, phagocytosis of E. coli by PMNLs and the expression of CD11b and CD18 at the PMNL surface. PAA significantly decreased PMNL apoptosis resulting in an increased percentage of viable cells. PAA affected neither the oxidative burst stimulated by phorbol-12-myristate-13-acetate nor PMNL chemotaxis.

CONCLUSIONS

PAA increases the activation of various PMNL functions and the expression of surface activation markers, while it attenuates PMNL apoptotic cell death. Therefore, PAA may contribute to the inflammatory state and consequently to increased cardiovascular risk in uraemic patients.

The role of water in activation mechanism of human N-formyl peptide receptor 1 (FPR1) based on molecular dynamics simulations

The Formyl Peptide Receptor 1 (FPR1) is an important chemotaxis receptor involved in various aspects of host defense and inflammatory processes. We constructed a model of FPR1 using as a novel template the chemokine receptor CXCR4 from the same branch of the phylogenetic tree of G-protein-coupled receptors. The previously employed template of rhodopsin contained a bulge at the extracellular part of TM2 which directly influenced binding of ligands. We also conducted molecular dynamics (MD) simulations of FPR1 in the apo form as well as in a form complexed with the agonist fMLF and the antagonist tBocMLF in the model membrane. During all MD simulation of the fMLF-FPR1 complex a water molecule transiently bridged the hydrogen bond between W254(6.48) and N108(3.35) in the middle of the receptor. We also observed a change in the cytoplasmic part of FPR1 of a rotamer of the Y301(7.53) residue (tyrosine rotamer switch). This effect facilitated movement of more water molecules toward the receptor center. Such rotamer of Y301(7.53) was not observed in any crystal structures of GPCRs which can suggest that this state is temporarily formed to pass the water molecules during the activation process. The presence of a distance between agonist and residues R201(5.38) and R205(5.42) on helix TM5 may suggest that the activation of FPR1 is similar to the activation of β-adrenergic receptors since their agonists are separated from serine residues on helix TM5. The removal of water molecules bridging these interactions in FPR1 can result in shrinking of the binding site during activation similarly to the shrinking observed in β-ARs. The number of GPCR crystal structures with agonists is still scarce so the designing of new ligands with agonistic properties is hampered, therefore homology modeling and docking can provide suitable models. Additionally, the MD simulations can be beneficial to outline the mechanisms of receptor activation and the agonist/antagonist sensing.

Decreased activity and accelerated apoptosis of neutrophils in the presence of natural polyphenols

Prolonged or excessive formation and liberation of cytotoxic substances from neutrophils intensifies inflammation and the risk of tissue damage. From this perspective, administration of substances which are able to reduce activity of neutrophils and to enhance apoptosis of these cells may improve the therapy of pathological states connected with persistent inflammation. In this short review, neutrophil oxidative burst and apoptosis are presented as potential targets for pharmacological intervention. Effects of natural polyphenols (resveratrol, pterostilbene, pinosylvin, piceatannol, curcumin, N-feruloylserotonin) are summarised, considering the ability of these compounds to affect inflammation and particularly neutrophil activity. The intended neutrophil inhibition is introduced as a part of a new strategy for pharmacological modulation of chronic inflammatory processes, focused on supporting innate anti-inflammatory mechanisms and enhancing resolution of inflammation.

Apolipoproteins and apolipoprotein mimetic peptides modulate phagocyte trafficking through chemotactic activity

The plasma lipoprotein-associated apolipoproteins (apo) A-I and apoE have well described anti-inflammatory actions in the cardiovascular system, and mimetic peptides that retain these properties have been designed as therapeutics. The anti-inflammatory mechanisms of apolipoprotein mimetics, however, are incompletely defined. Whether circulating apolipoproteins and their mimetics regulate innate immune responses at mucosal surfaces, sites where transvascular emigration of leukocytes is required during inflammation, remains unclear. Herein, we report that Apoai(-/-) and Apoe(-/-) mice display enhanced recruitment of neutrophils to the airspace in response to both inhaled lipopolysaccharide and direct airway inoculation with CXCL1. Conversely, treatment with apoA-I (L-4F) or apoE (COG1410) mimetic peptides reduces airway neutrophilia. We identify suppression of CXCR2-directed chemotaxis as a mechanism underlying the apolipoprotein effect. Pursuing the possibility that L-4F might suppress chemotaxis through heterologous desensitization, we confirmed that L-4F itself induces chemotaxis of human PMNs and monocytes. L-4F, however, fails to induce a calcium flux. Further exploring structure-function relationships, we studied the alternate apoA-I mimetic L-37pA, a bihelical analog of L-4F with two Leu-Phe substitutions. We find that L-37pA induces calcium and chemotaxis through formyl peptide receptor (FPR)2/ALX, whereas its D-stereoisomer (i.e. D-37pA) blocks L-37pA signaling and induces chemotaxis but not calcium flux through an unidentified receptor. Taken together, apolipoprotein mimetic peptides are novel chemotactic agents that possess complex structure-activity relationships to multiple receptors, displaying anti-inflammatory efficacy against innate immune responses in the airway.

Neutrophils are not less sensitive than other blood leukocytes to the genomic effects of glucocorticoids

Background

Neutrophils are generally considered less responsive to glucocorticoids compared to other inflammatory cells. The reported increase in human neutrophil survival mediated by these drugs partly supports this assertion. However, it was recently shown that dexamethasone exerts potent anti-inflammatory effects in equine peripheral blood neutrophils. Few comparative studies of glucocorticoid effects in neutrophils and other leukocytes have been reported and a relative insensitivity of neutrophils to these drugs could not be ruled out.

Objective

We assessed glucocorticoid-responsiveness in equine and human peripheral blood neutrophils and neutrophil-depleted leukocytes.

Methods

Blood neutrophils and neutrophil-depleted leukocytes were isolated from 6 healthy horses and 4 human healthy subjects. Cells were incubated for 5 h with or without LPS (100 ng/mL) alone or combined with hydrocortisone, prednisolone or dexamethasone (10⁻⁸ M and 10⁻⁶ M). IL-1β, TNF-α, IL-8, glutamine synthetase and GR-α mRNA expression was quantified by qPCR. Equine neutrophils were also incubated for 20 h with or without the three glucocorticoids and cell survival was assessed by flow cytometry and light microscopy on cytospin preparations.

Results

We found that glucocorticoids down-regulated LPS-induced pro-inflammatory mRNA expression in both cell populations and species. These drugs also significantly increased glutamine synthetase gene expression in both equine cell populations. The magnitude of glucocorticoid response between cell populations was generally similar in both species. We also showed that dexamethasone had a comparable inhibitory effect on pro-inflammatory gene expression in both human and equine neutrophils. As reported in other species, glucocorticoids significantly increase the survival in equine neutrophils.

Conclusions

Glucocorticoids exert genomic effects of similar magnitude on neutrophils and on other blood leukocytes. We speculate that the poor response to glucocorticoids observed in some chronic neutrophilic diseases such as severe asthma or COPD is not explained by a relative lack of inhibition of these drugs on pro-inflammatory cytokines expression in neutrophils.

Common genetic variations in the NALP3 inflammasome are associated with delayed apoptosis of human neutrophils

Background

Neutrophils are key-players in the innate host defense and their programmed cell death and removal are essential for efficient resolution of inflammation. These cells recognize a variety of pathogens, and the NOD-like receptors (NLRs) have been suggested as intracellular sensors of microbial components and cell injury/stress. Some NLR will upon activation form multi-protein complexes termed inflammasomes that result in IL-1β production. NLR mutations are associated with auto-inflammatory syndromes, and our previous data propose NLRP3 (Q705K)/CARD-8 (C10X) polymorphisms to contribute to increased risk and severity of inflammatory disease by acting as genetic susceptibility factors. These gene products are components of the NALP3 inflammasome, and approximately 6.5% of the Swedish population are heterozygote carriers of these combined gene variants. Since patients carrying the Q705K/C10X polymorphisms display leukocytosis, the aim of the present study was to find out whether the inflammatory phenotype was related to dysfunctional apoptosis and impaired clearance of neutrophils by macrophages.

Methods and Findings

Patients carrying the Q705K/C10X polymorphisms displayed significantly delayed spontaneous as well as microbe-induced apoptosis compared to matched controls. Western blotting revealed increased levels and phosphorylation of Akt and Mcl-1 in the patients' neutrophils. In contrast to macrophages from healthy controls, macrophages from the patients produced lower amounts of TNF; suggesting impaired macrophage clearance response.

Conclusions

The Q705K/C10X polymorphisms are associated with delayed apoptosis of neutrophils. These findings are explained by altered involvement of different regulators of apoptosis, resulting in an anti-apoptotic profile. Moreover, the macrophage response to ingestion of microbe-induced apoptotic neutrophils is altered in the patients. Taken together, the patients display impaired turnover and clearance of apoptotic neutrophils, pointing towards a dysregulated innate immune response that influences the resolution of inflammation. The future challenge is to understand how microbes affect the activation of inflammasomes, and why this interaction will develop into severe inflammatory disease in certain individuals.

Vitronectin inhibits neutrophil apoptosis through activation of integrin-associated signaling pathways

Vitronectin is present in large concentrations in serum and the extracellular matrix. Although vitronectin is known to modulate neutrophil adhesion and chemotaxis, and to contribute to neutrophil-associated proinflammatory processes, a role in apoptosis has not been demonstrated. In the present studies, we found that neutrophils demonstrated more rapid progression to spontaneous or TNF-related apoptosis-inducing ligand-induced apoptosis when incubated under vitronectin-free conditions than when vitronectin was present. The ability of native vitronectin to delay neutrophil apoptosis was not recapitulated by the vitronectin somatomedin B domain. In contrast, inclusion of the cyclo[Arg-Gly-Asp-D-Phe-Val] peptide in cultures containing vitronectin resulted in enhanced neutrophil apoptosis, showing that the vitronectin RGD motif (Arg-Gly-Asp motif) was responsible for the antiapoptotic effects of vitronectin. Addition of antibodies to β(1), β(3), or β(5), but not to β(2) or β(4) integrins, reversed the ability of vitronectin to diminish neutrophil apoptosis. The ability of vitronectin to enhance neutrophil viability was dependent on activation of phosphatidylinositol 3-kinase and extracellular signal-regulated kinase 1/2 kinases, but not on the p38 kinase. Increased numbers of apoptotic neutrophils were present in the lungs of LPS-treated transgenic vitronectin-deficient mice, as compared with control mice. These results demonstrate a novel antiapoptotic function for vitronectin.

Activation of the annexin A1 pathway underlies the protective effects exerted by estrogen in polymorphonuclear leukocytes

OBJECTIVE

The anti-inflammatory properties of the female sex hormone estrogen have been linked to a reduced incidence of cardiovascular disease. In the present study, we addressed whether estrogen could activate vasculoprotective mechanisms via annexin A1 (AnxA1) mobilization in human polymorphonuclear cells (PMNs).

METHODS AND RESULTS

Using whole-blood flow cytometry, we demonstrated that premenopausal women expressed higher levels of surface AnxA1 on circulating PMNs compared with males. This correlated with high plasma estrogen during the menstrual cycle. The addition of estrogen in vitro to male PMNs induced rapid mobilization of AnxA1, optimal at 5 ng/mL and a 30-minute incubation period; this effect was abolished in the presence of the estrogen receptor antagonist ICI182780. Estrogen addition to human PMNs induced a distinct AnxA1(hi) CD62L(lo) CD11b(lo) phenotype, and this was associated with lower cell activation as measured by microparticle formation. Treatment of human PMNs with E(2) inhibited cell adhesion to an endothelial cell monolayer under shear, which was absent when endogenous AnxA1 was neutralized. Of interest, addition of estrogen to PMNs flowed over the endothelial monolayer amplified its upregulation of AnxA1 localization on the cell surface. Finally, in a model of intravital microscopy, estrogen inhibition of white blood cell adhesion to the postcapillary venule was absent in mice nullified for AnxA1.

CONCLUSION

We unveil a novel AnxA1-dependent mechanism behind the inhibitory properties of estrogen on PMN activation, describing a novel phenotype with a conceivable impact on the vasculoprotective effects of this hormone.

Molecular docking of 2-(benzimidazol-2-ylthio)-N-phenylacetamide-derived small-molecule agonists of human formyl peptide receptor 1

Human N-formyl peptide receptor 1 (FPR1) is a G protein-coupled receptor (GPCR) involved in host defense and sensing cellular damage. Since structure-based ligand design for many GPCRs, including FPR1, is restricted by the lack of experimental three dimensional structures, homology modeling has been widely used to study GPCR-ligand binding. Indeed, receptor-ligand binding mode predictions can be derived from homology modeling with supporting ligand information. In the present work, we report comparative docking studies of 2-(benzimidazol-2-ylthio)-N-phenylacetamide derived FPR1 agonists, identified here and previously, with several known FPR1 peptide agonists in a FPR1 homology model that is based on the crystal structure of bovine rhodopsin. We found that the binding pocket of the most active molecules shares some common features with high affinity FPR1 peptide agonists, suggesting that they may bind to similar binding sites. Classification tree analysis led to the derivation of a good recognition model based on four amino acid descriptors for distinguishing FPR1 ligands from inactive analogs. Hence, the corresponding residues (Thr199, Arg201, Gly202, and Ala261) can be considered as markers of important areas in the ligand binding site. Concurrently, we identified several unique binding features of benzimidazole derivatives and showed that alkoxy-substituents of the benzimidazole ring are located within a FPR1 hole bounded by Thr199, Thr265, Ile268, and Leu271 or in a groove in the vicinity of Leu198, Arg201, Gly202, and Arg205. The understanding of these molecular features will likely prove beneficial in future design of novel FPR1 agonists based on the benzimidazole scaffold.