Steroid-resistant neutrophilic inflammation in a mouse model of an acute exacerbation of asthma

The Efficacy & Molecular Mechanisms of a Terpenoid Compound Ganoderic Acid C1 on Corticosteroid-Resistant Neutrophilic Airway Inflammation: In vivo and in vitro Validation

Introduction

Neutrophil predominant airway inflammation is associated with severe and steroid-resistant asthma clusters. Previously, we reported efficacy of ASHMI, a three-herb TCM asthma formula in a steroid-resistant neutrophil-dominant murine asthma model and further identified Ganoderic Acid C1 (GAC1) as a key ASHMI active compound in vitro. The objective of this study is to investigate GAC1 effect on neutrophil-dominant, steroid-resistant asthma in a murine model.

Methods

In this study, Balb/c mice were systematically sensitized with ragweed (RW) and alum and intranasally challenged with ragweed. Unsensitized/PBS challenged mice served as normal controls. Post sensitization, mice were given 4 weeks of oral treatment with GAC1 or acute dexamethasone (Dex) treatment at 48 hours prior to challenge. Pulmonary cytokines were measured by ELISA, and lung sections were processed for histology by H&E staining. Furthermore, GAC1 effect on MUC5AC expression and on reactive oxygen species (ROS) production in human lung epithelial cell line (NCI-H292) was determined by qRT-PCR and ROS assay kit, respectively. Computational analysis was applied to select potential targets of GAC1 in steroid-resistant neutrophil-dominant asthma. Molecular docking was performed to predict binding modes between GAC1 and Dex with TNF-α.

Results

The result of the study showed that chronic GAC1 treatment, significantly reduced pulmonary inflammation (P < 0.01-0.001 vs Sham) and airway neutrophilia (P < 0.01 vs Sham), inhibited TNF-α, IL-4 and IL-5 levels (P < 0.05-0.001 vs Sham). Acute Dex treatment reduced eosinophilic inflammation and IL-4, IL-5 levels, but had no effect on neutrophilia and TNF-α production. GAC1 treated H292 cells showed decreased MUC5AC gene expression and production of ROS (P < 0.001 vs stimulated/untreated cells). Molecular docking results showed binding energy of complex GAC1-TNF was -10.8 kcal/mol.

Discussion

GAC1 may be a promising anti-asthma botanical drug for treatment of steroid-resistant asthma.

Impact of obesity in asthma: Possible future therapies

Obesity is one of the factors associated with the severity of asthma. Obesity is associated with aggravation of the pathophysiology of asthma, including exacerbations, airway inflammation, decreased pulmonary function, and airway hyperresponsiveness. The present review addresses the characteristics of asthma with obesity, focusing especially on the heterogeneity caused by the degree of type 2 inflammation, sex differences, the onset of asthma, and race differences. To understand the severity mechanisms in asthma and obesity, such as corticosteroid resistance, fatty acids, gut microbiome, and cytokines, several basic research studies are evaluated. Finally, possible future therapies, including weight reduction, microbiome-targeted therapies, and other molecular targeted therapies are addressed. We believe that the present review will contribute to better understanding of the severity mechanisms and the establishment of novel treatments for severe asthma patients with obesity.

Intravascular Leukocyte Labeling Refines the Distribution of Myeloid Cells in the Lung in Models of Allergen-induced Airway Inflammation

Innate immune cell populations are critical in asthma with different functional characteristics based on tissue location, which has amplified the importance of characterizing the precise number and location of innate immune populations in murine models of asthma. In this study, we performed premortem intravascular (IV) labeling of leukocytes in mice in two models of asthma to differentiate innate immune cell populations within the IV compartment versus those residing in the lung tissue or airway lumen. We performed spectral flow cytometry analysis of the blood, suspensions of digested lung tissue, and bronchoalveolar lavage fluid. We discovered that IV labeled leukocytes do not contaminate analysis of bronchoalveolar lavage fluid but represent a significant proportion of cells in digested lung tissue. Exclusion of IV leukocytes significantly improved the accuracy of the assessments of myeloid cells in the lung tissue and provided important insights into ongoing trafficking in both eosinophilic and neutrophilic asthma models.

Bioinformatic analysis and experimental validation of the potential gene in the airway inflammation of steroid-resistant asthma

Steroid-resistant asthma is a troublesome clinical problem in public health. The pathogenesis of steroid-resistant asthma is complex and remains to be explored. In our work, the online Gene Expression Omnibus microarray dataset GSE7368 was used to explore differentially expressed genes (DEGs) between steroid-resistant asthma patients and steroid-sensitive asthma patients. Tissue-specific gene expression of DEGs was analyzed using BioGPS. The enrichment analyses were performed using GO, KEGG, and GSEA analysis. The protein-protein interaction network and key gene cluster were constructed using STRING, Cytoscape, MCODE, and Cytohubba. A steroid-resistant neutrophilic asthma mouse model was established using lipopolysaccharide (LPS) and ovalbumin (OVA). An LPS-stimulated J744A.1 macrophage model was prepared to validate the underlying mechanism of the interesting DEG gene using the quantitative reverse transcription-polymerase chain reaction (qRT-PCR). A total of 66 DEGs were identified, most of which were present in the hematologic/immune system. Enrichment analysis displayed that the enriched pathways were the IL-17 signaling pathway, MAPK signal pathway, Toll-like receptor signaling pathway, and so on. DUSP2, as one of the top upregulated DEGs, has not been clearly demonstrated in steroid-resistant asthma. In our study, we observed that the salubrinal administration (DUSP2 inhibitor) reversed neutrophilic airway inflammation and cytokine responses (IL-17A, TNF-α) in a steroid-resistant asthma mouse model. We also found that salubrinal treatment reduced inflammatory cytokines (CXCL10 and IL-1β) in LPS-stimulated J744A.1 macrophages. DUSP2 may be a candidate target for the therapy of steroid-resistant asthma.

Bruton's tyrosine kinase inhibition suppresses neutrophilic inflammation and restores histone deacetylase 2 expression in myeloid and structural cells in a mixed granulocytic mouse model of asthma

Asthmatic inflammation is not a single homogenous inflammation but may be categorized into several phenotypes/endotypes. Severe asthma is characterized by mixed granulocytic inflammation in which there is increased presence of neutrophilic numbers and unresponsiveness to corticosteroids. Neutrophilic oxidative stress and histone deacetylase 2 (HDAC2) dysregulation in the pulmonary compartment are thought to lead to corticosteroid insensitivity in severe asthma with mixed granulocytic inflammation. Bruton's tyrosine kinase (BTK) is a no-receptor tyrosine kinase which is expressed in innate immune cells such as neutrophils and dendritic cells (DCs) where it is incriminated in balancing of inflammatory signaling. We hypothesized in this study that BTK inhibition strategy could be utilized to restore corticosteroid responsiveness in mixed granulocytic asthma. Therefore, combined therapy of BTK inhibitor (ibrutinib) and corticosteroid, dexamethasone was administered in cockroach allergen extract (CE)-induced mixed granulocyte airway inflammation model in mice. Our data show that CE-induced neutrophilic inflammation was concomitant with HDAC2 expression and upregulation of p-NFkB expression in airway epithelial cells (AECs), myeloid cells and pulmonary tissue. Further, there were increased expression/release of inflammatory and oxidative mediators such as MUC5AC, TNF-α, GM-CSF, MCP-1, iNOS, nitrotyrosine, MPO, lipid peroxides in AECs/myeloid cells/pulmonary tissue. Dexamethasone alone significantly attenuated eosinophilic inflammation and inflammatory cytokines but was not able to control oxidative inflammation. Ibrutinib alone markedly reduced neutrophilic infiltration and oxidative inflammation, and restored HDAC2 without having any significant effect on eosinophilic inflammation. These data suggest that BTK inhibition strategy may be used in conjunction with dexamethasone to treat both neutrophilic and eosinophilic inflammation, i.e. mixed granulocytic asthma.

Ketamine Attenuates Airway Inflammation via Inducing Inflammatory Cells Apoptosis and Activating Nrf2 Pathway in a Mixed-Granulocytic Murine Asthma Model

Purpose

The use of ketamine, an anesthetic, as a treatment for asthma has been investigated in numerous studies. However, how ketamine affects asthma is unclear. The present study examined the effects of ketamine on a murine model of mixed-granulocytic asthma, and the role of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway.

Methods

The murine model of mixed-granulocytic asthma was established using ovalbumin (OVA) for sensitization and the combination of OVA and lipopolysaccharides (LPS) for challenge. The main characteristics of asthma, oxidative stress biomarkers, and the expression of the Nrf2 pathway were examined. ML385 was administered to verify the role of the Nrf2 pathway.

Results

Mice in the OVA +LPS group developed asthmatic characteristics, including airway hyperresponsiveness, mixed-granulocytic airway inflammation, mucus overproduction, as well as increased levels of oxidative stress and impaired apoptosis of inflammatory cells. Among the three concentrations, ketamine at 75mg/kg effectively attenuated these asthmatic symptoms, activated the Nrf2 pathway, decreased oxidative stress, and induced apoptosis of eosinophils and neutrophils in bronchoalveolar lavage fluid (BALF) with a reducing level of myeloid cell leukemia 1(Mcl-1). ML385 (an Nrf2 inhibitor) eliminated the protective effects of ketamine on the mixed-granulocytic asthma model.

Conclusion

The study concluded that ketamine reduced oxidative stress and attenuated asthmatic symptoms (neutrophilic airway inflammation) by activating the Nrf2-Keap1 pathway, with 75 mg/kg ketamine showing the best results. Ketamine administration also increased neutrophil and eosinophil apoptosis in BALF, which may contribute to the resolution of inflammation. The use of ketamine as a treatment for asthma may therefore be beneficial.

Quercetin alleviates ferroptosis accompanied by reducing M1 macrophage polarization during neutrophilic airway inflammation

Ferroptosis is a kind of regulated cell death, supporting the pathological process of lung inflammation, including asthma. Quercetin (QCT), a kind of natural dietary flavonoid, exerts anti-inflammatory and anti-ferroptosis effects in various diseases. However, the role of QCT in ferroptosis-associated airway inflammation of neutrophilic asthma remains to be described. Our study aimed to investigate the therapeutic effects of QCT on neutrophilic airway inflammation of asthma. Ferrostatin-1 (Fer-1), as a kind of ferroptosis inhibitor, was used to demonstrate whether neutrophilic airway inflammation of asthma relied on ferroptosis. In our study, the alleviation effect of QCT on neutrophilic airway inflammation was similar to Fer-1. Moreover, the significantly decreased levels of ferroptosis anti-oxidant protein (GPX4 and SLC7A11), increased malondialdehyde (MDA) levels, upregulated levels of 4-hydroxynonenal (4-HNE) expression by immunohistochemistry, and distorted mitochondria morphological changes in the lung tissues suggested lung ferroptosis in neutrophilic airway inflammation, which could be reversed by QCT treatment. In vitro experiments showed that QCT reduced LPS-induced ferroptosis through upregulating cell viability and levels of ferroptosis anti-oxidant protein (SLC7A11 and GPX4), reducing inflammatory cytokines, and decreasing the levels of MDA. Furthermore, ferroptosis was accompanied by enhancing M1 phenotype in neutrophilic airway inflammation, and QCT suppressed ferroptosis by inhibiting the pro-inflammatory M1 profile in vitro and in vivo, just as Fer-1 did. In conclusion, our study found that QCT ameliorated ferroptosis-associated neutrophilic airway inflammation accompanied by inhibiting M1 macrophage polarization. QCT may be a promising ferroptosis inhibitor for neutrophilic airway inflammation.

Neuroimmune Responses in a New Experimental Animal Model of Cerebral Aspergillosis

Exposure of immunosuppressed individuals to the opportunistic fungal pathogen Aspergillus fumigatus may result in invasive pulmonary aspergillosis (IPA), which can lead to the development of cerebral aspergillosis (CA), a highly lethal infection localized in the central nervous system (CNS). There are no experimental models of CA that effectively mimic human disease, resulting in a considerable knowledge gap regarding mechanisms of neurological pathogenicity and neuroimmune responses during infection. In this report, immunosuppressed mice (via acute, high-dose corticosteroid administration) challenged with A. fumigatus resting conidia intranasally, followed a day later by a 70-fold lower inoculum of pre-swollen conidia intravenously (IN + IV + steroid), demonstrated increased weight loss, signs of severe clinical disease, increased fungal burden in the brain, and significant reduction in survival compared to immunosuppressed mice challenged intranasally only (IN + steroid) or non-immunosuppressed mice challenged both intranasally and intravenously (IN + IV). The IN + IV + steroid group demonstrated significant decreases in monocytes, eosinophils, dendritic cells (DCs), and invasive natural killer T (iNKT) cells, but not neutrophils or γδ T cells, in the brain compared to the IN + IV group. Likewise, the IN + IV + steroid group had significantly lower levels of interleukin (IL)-1β, IL-6, IL-17A, CC motif chemokine ligand 3 (CCL3), CXC chemokine ligand 10 (CXCL10), and vascular endothelial growth factor (VEGF) in the brain compared to the IN + IV group. IN + IV + steroid was superior to both IN + IV + chemotherapy (cytarabine + daunorubicin) and IN + IV + neutropenia for the development of CA. In conclusion, we have developed a well-defined, physiologically relevant model of disseminated CA in corticosteroid-induced immunosuppressed mice with a primary pulmonary infection. This model will serve to advance understanding of disease mechanisms, identify immunopathogenic processes, and help define the protective neuroinflammatory response to CA. IMPORTANCE Invasive fungal infections (IFIs) result in significant mortality in immunosuppressed individuals. Of these, invasive pulmonary aspergillosis (IPA), caused by the opportunistic mold Aspergillus fumigatus, is the most lethal. Lethality in IPA is due to two main factors: destruction of the lung leading to compromised pulmonary function, and dissemination of the organism to extrapulmonary organs. Of these, the CNS is the most common site of dissemination. However, very little is known regarding the pathogenesis of or immune response during cerebral aspergillosis, which is directly due to the lack of an animal model that incorporates immunosuppression, lung infection, and consistent dissemination to the CNS/brain. In this report, we have developed a new experimental animal model of CA which includes the above parameters and characterized the neuroimmune response. We further compared this disseminated CA model to two additional immunosuppressive strategies. Overall, this model of disseminated CA following IPA in an immunosuppressed host provides a novel platform for studying the efficacy of antifungal drugs and immunotherapies for improving disease outcomes.

Coadministration of Stigmasterol and Dexamethasone (STIG+DEX) Modulates Steroid-Resistant Asthma

Airway inflammation in asthma is managed with anti-inflammatory steroids such as dexamethasone (DEX). However, about 20% of asthmatics do not respond to this therapy and are classified as steroid-resistant. Currently, no effective therapy is available for steroid-resistant asthma. This work therefore evaluated the effect of a plant sterol, stigmasterol (STIG), and stigmasterol-dexamethasone combination (STIG+DEX) in LPS-ovalbumin-induced steroid-resistant asthma in Guinea pigs. To do this, the effect of drugs on inflammatory features such as airway hyperreactivity and histopathology of lung tissue was evaluated. Additionally, the possible pathway of drug action was assessed by measuring events such neutrophil levels, oxidative and nitrative stress, and histone deacetylase 2 (HDAC2) and interleukin 17 (IL-17) levels. STIG alone did not affect inflammatory features, although it caused some changes in the molecular events associated with steroid-resistant asthma. However, STIG+DEX caused significant modulation of inflammatory features by protecting against destruction of lung tissue. The modulation of inflammatory features was associated with significant inhibition of neutrophilia and oxidative and nitrative stress, decrease in HDAC2, and increase in IL-17 levels that are usually associated with steroid-resistant asthma. Our findings show that although STIG and DEX individually do not protect against steroid-resistant asthma, their coadministration results in significant modulation of inflammatory features and the associated molecular events that lead to steroid-resistant asthma.

Function-specific IL-17A and dexamethasone interactions in primary human airway epithelial cells

Asthmatics have elevated levels of IL-17A compared to healthy controls. IL-17A is likely to contribute to reduced corticosteroid sensitivity of human airway epithelium. Here, we aimed to investigate the mechanistic underpinnings of this reduced sensitivity in more detail. Differentiated primary human airway epithelial cells (hAECs) were exposed to IL-17A in the absence or presence of dexamethasone. Cells were then collected for RNA sequencing analysis or used for barrier function experiments. Mucus was collected for volume measurement and basal medium for cytokine analysis. 2861 genes were differentially expressed by IL-17A (Padj < 0.05), of which the majority was not sensitive to dexamethasone (< 50% inhibition). IL-17A did inhibit canonical corticosteroid genes, such as HSD11B2 and FKBP5 (p < 0.05). Inflammatory and goblet cell metaplasia markers, cytokine secretion and mucus production were all induced by IL-17A, and these effects were not prevented by dexamethasone. Dexamethasone did reverse IL-17A-stimulated epithelial barrier disruption, and this was associated with gene expression changes related to cilia function and development. We conclude that IL-17A induces function-specific corticosteroid-insensitivity. Whereas inflammatory response genes and mucus production in primary hAECs in response to IL-17A were corticosteroid-insensitive, corticosteroids were able to reverse IL-17A-induced epithelial barrier disruption.

Identification of ANXA2 on epithelial cells as a new receptor for secretory IgA using immunoprecipitation and mass spectrometry

Secretory immunoglobulin A plays an important role in the protection against exogenous pathogens and antigens, but it has also been reported to have pathogenic potential. We previously found that secretory immunoglobulin A accumulated in the peripheral lungs during idiopathic pulmonary fibrosis and that transferrin receptor/CD71 was partially involved in secretory immunoglobulin A-induced inflammatory cytokine production in A549 cells. This study aimed to identify the receptor responsible for the induction of cytokine production by secretory immunoglobulin A-stimulated airway epithelial cells. To this end, immunoprecipitation followed by time-of-flight mass spectrometry and peptide mass fingerprinting were performed and Annexin A2 was detected as a novel receptor for secretory immunoglobulin A. Enzyme-linked immunosorbent assay demonstrated binding of secretory immunoglobulin A to Annexin A2, and flow cytometry showed robust expression of Annexin A2 on the surface of BEAS-2B cells, A549 cells, and normal human bronchial/tracheal epithelial cells. Experiments in A549 cells using Annexin A2 small interfering RNA and neutralizing antibodies suggested that Annexin A2 was partially involved in the production of interleukin-8/CXCL8 and C-C motif chemokine ligand 2/monocyte chemoattractant protein-1 induced by secretory immunoglobulin A. Immunohistochemistry using lung sections revealed clear expression of Annexin A2 on airway epithelial cells, although the staining remained equivalent in idiopathic pulmonary fibrosis, asthma, and healthy control lungs. In conclusion, we identified that Annexin A2 expressed in airway epithelial cells is a novel receptor for secretory immunoglobulin A, which is involved in cytokine synthesis.

Murine model of steroid-resistant neutrophilic bronchial asthma as an attempt to simulate human pathology

Bronchial asthma (BA) is a heterogeneous chronic inflammatory disease of the airways. The majority of patients with mild to moderate BA develop Th2-biased eosinophilic pulmonary inflammation and respond well to corticosteroid treatment. However up to 10% of BA patients develop severe pathology, which is associated with neutrophilic inflammation and resistant to conventional corticosteroid therapy. Contrary to eosinophil-predominant airway inflammation neutrophilic BA is developed through Th1- and Th17-immune responses. However, the etiology of corticoid insensitive neutrophilic BA is still remains unclear. Therefore, in the current study we developed a mouse model of BA with predominant neutrophilic rather than eosinophilic pulmonary inflammation. BALB/c mice were immunized with the mixture of the ovalbumin allergen and Freund's adjuvant, followed by aerosol challenge with the same allergen mixed with E. coli lipopolysaccharide. As a result, mice developed the main BA manifestations: production of allergen specific IgE, development of airway hyperreactivity, airway remodeling and pulmonary neutrophilic inflammation. Moreover, this pathology developed through Th1- and Th17-dependent mechanisms and mice with induced neutrophilic BA phenotype responded poorly to dexamethasone treatment, that coincide to clinical observations. The established mouse model could be useful both for studying the pathogenesis and for testing novel approaches to control neutrophilic BA.

Different Phenotypes in Asthma: Clinical Findings and Experimental Animal Models

Asthma is a respiratory allergic disease presenting a high prevalence worldwide, and it is responsible for several complications throughout life, including death. Fortunately, asthma is no longer recognized as a unique manifestation but as a very heterogenic manifestation. Its phenotypes and endotypes are known, respectively, as pathologic and molecular features that might not be directly associated with each other. The increasing number of studies covering this issue has brought significant insights and knowledge that are constantly expanding. In this review, we intended to summarize this new information obtained from clinical studies, which not only allowed for the creation of patient clusters by means of personalized medicine and a deeper molecular evaluation, but also created a connection with data obtained from experimental models, especially murine models. We gathered information regarding sensitization and trigger and emphasizing the most relevant phenotypes and endotypes, such as Th2-^high asthma and Th2-^low asthma, which included smoking and obesity-related asthma and mixed and paucigranulocytic asthma, not only in physiopathology and the clinic but also in how these phenotypes can be determined with relative similarity using murine models. We also further investigated how clinical studies have been treating patients using newly developed drugs focusing on specific biomarkers that are more relevant according to the patient's clinical manifestation of the disease.

Pharmacological Rationale for Targeting IL-17 in Asthma

Asthma is a respiratory disease that currently affects around 300 million people worldwide and is defined by coughing, shortness of breath, wheezing, mucus overproduction, chest tightness, and expiratory airflow limitation. Increased levels of interleukin 17 (IL-17) have been observed in sputum, nasal and bronchial biopsies, and serum of patients with asthma compared to healthy controls. Patients with higher levels of IL-17 have a more severe asthma phenotype. Biologics are available for T helper 2 (Th2)-high asthmatics, but the Th17-high subpopulation has a relatively low response to these treatments, rendering it a rather severe asthma phenotype to treat. Several experimental models suggest that targeting the IL-17 pathway may be beneficial in asthma. Moreover, as increased activation of the Th17/IL-17 axis is correlated with reduced inhaled corticosteroids (ICS) sensitivity, targeting the IL-17 pathway might reverse ICS unresponsiveness. In this review, we present and discuss the current knowledge on the role of IL-17 in asthma and its interaction with the Th2 pathway, focusing on the rationale for therapeutic targeting of the IL-17 pathway.

Asthma-COPD overlap: current understanding and the utility of experimental models

Pathological features of both asthma and COPD coexist in some patients and this is termed asthma-COPD overlap (ACO). ACO is heterogeneous and patients exhibit various combinations of asthma and COPD features, making it difficult to characterise the underlying pathogenic mechanisms. There are no controlled studies that define effective therapies for ACO, which arises from the lack of international consensus on the definition and diagnostic criteria for ACO, as well as scant in vitro and in vivo data. There remain unmet needs for experimental models of ACO that accurately recapitulate the hallmark features of ACO in patients. The development and interrogation of such models will identify underlying disease-causing mechanisms, as well as enabling the identification of novel therapeutic targets and providing a platform for assessing new ACO therapies. Here, we review the current understanding of the clinical features of ACO and highlight the approaches that are best suited for developing representative experimental models of ACO.

Understanding the pathogenesis of asthma-COPD overlap is critical for improving therapeutic approaches. We present current knowledge on asthma-COPD overlap and the requirements for developing an optimal animal model of disease.https://bit.ly/3lsjyvm

Local drug delivery systems for inflammatory diseases: Status quo, challenges, and opportunities

Inflammation that is not resolved in due course becomes a chronic disease. The treatment of chronic inflammatory diseases involves a long-term use of anti-inflammatory drugs such as corticosteroids and nonsteroidal anti-inflammatory drugs, often accompanied by dose-dependent side effects. Local drug delivery systems have been widely explored to reduce their off-target side effects and the medication frequency, with several products making to the market or in development over the years. However, numerous challenges remain, and drug delivery technology is underutilized in some applications. This review showcases local drug delivery systems in different inflammatory diseases, including the targets well-known to drug delivery scientists (e.g., joints, eyes, and teeth) and other applications with untapped opportunities (e.g., sinus, bladder, and colon). In each section, we start with a brief description of the disease and commonly used therapy, introduce local drug delivery systems currently on the market or in the development stage, focusing on polymeric systems, and discuss the remaining challenges and opportunities in future product development.

Virus-Induced Asthma Exacerbations: SIRT1 Targeted Approach

The prevalence of asthma has increased worldwide. Asthma exacerbations triggered by upper respiratory tract viral infections remain a major clinical problem and account for hospital admissions and time lost from work. Virus-induced asthma exacerbations cause airway inflammation, resulting in worsening asthma and deterioration in the patients’ quality of life, which may require systemic corticosteroid therapy. Despite recent advances in understanding the cellular and molecular mechanisms underlying asthma exacerbations, current therapeutic modalities are inadequate for complete prevention and treatment of these episodes. The pathological role of cellular senescence, especially that involving the silent information regulator 2 homolog sirtuin (SIRT) protein family, has recently been demonstrated in stable and exacerbated chronic respiratory disease states. This review discusses the role of SIRT1 in the pathogenesis of bronchial asthma. It also discusses the role of SIRT1 in inflammatory cells that play an important role in virus-induced asthma exacerbations. Recent studies have hypothesized that SIRT1 is one of major contributors to cellular senescence. SIRT1 levels decrease in Th2 and non-Th2-related airway inflammation, indicating the role of SIRT1 in several endotypes and phenotypes of asthma. Moreover, several models have demonstrated relationships between viral infection and SIRT1. Therefore, targeting SIRT1 is a novel strategy that may be effective for treating virus-induced asthma exacerbations in the future.

Regeneration and repair in the healing lung

The lung achieves an efficient gas exchange between a complex non‐sterile atmosphere and the body via a delicate and extensive epithelial surface, with high efficiency because of elastic deformation allowing for an increase and decrease in volume during the process of breathing and because of an extensive vasculature which aids rapid gas diffusion. The lungs’ large surface area exposes the organ to a continual risk of damage from pathogens, toxins or irritants; however, lung damage can be rapidly healed via regenerative processes that restore its structure and function. In response to sustained and extensive damage, the lung is healed via a non‐regenerative process resulting in scar tissue which locally stiffens its structure, which over time leads to a serious loss of lung function and to increasing morbidities. This review discusses what is known about the factors which influence whether a lung is healed by regeneration or repair and what potential new therapeutic approaches may positively influence lung healing.

Granulocyte-targeted therapies for airway diseases

The average respiration rate for an adult is 12-20 breaths per minute, which constantly exposes the lungs to allergens and harmful particles. As a result, respiratory diseases, which includes asthma, chronic obstructive pulmonary disease (COPD) and acute lower respiratory tract infections (LTRI), are a major cause of death worldwide. Although asthma, COPD and LTRI are distinctly different diseases with separate mechanisms of disease progression, they do share a common feature - airway inflammation with intense recruitment and activation of granulocytes and mast cells. Neutrophils, eosinophils, basophils, and mast cells are crucial players in host defense against pathogens and maintenance of lung homeostasis. Upon contact with harmful particles, part of the pulmonary defense mechanism is to recruit these cells into the airways. Despite their protective nature, overactivation or accumulation of granulocytes and mast cells in the lungs results in unwanted chronic airway inflammation and damage. As such, understanding the bright and the dark side of these leukocytes in lung physiology paves the way for the development of therapies targeting this important mechanism of disease. Here we discuss the role of granulocytes in respiratory diseases and summarize therapeutic strategies focused on granulocyte recruitment and activation in the lungs.

Bergenin-activated SIRT1 inhibits TNF-α-induced proinflammatory response by blocking the NF-κB signaling pathway

BACKGROUND

Bergenin, a type of polyphenol compound, exhibits antiulcerogenic, anti-inflammatory, antitussive, and burn wound-healing properties. However, its therapeutic effect on tumor necrosis factor α (TNF-α)-induced proinflammatory responses in the airway and potential mechanisms of actions are still unclear. This study aimed to investigate the anti-inflammatory effects and mechanism of bergenin in TNF-α-stimulated human bronchial epithelial (16-HBE) cells.

METHODS

Cell Counting Kit-8 was used to evaluate cytotoxicity. Cytokine expression was analyzed by reverse transcription-quantitative PCR (RT-qPCR) and enzyme-linked immunosorbent assay. Immunofluorescence, western blot, and sirtuin-1 (SIRT1) activity assays were employed to investigate potential molecular mechanisms.

RESULTS

Bergenin obviously decreased both mRNA and protein expression levels of interleukins 6 and 8 (IL-6 and IL-8) in TNF-α-stimulated 16-HBE cells. Bergenin blocked TNF-α-mediated activation of nuclear factor κB (NF-κB) signaling and NF-κB nuclear translocation. Interestingly, RT-qPCR and western blotting results revealed that bergenin did not affect SIRT1 expression, but significantly increased its activity. Bergenin-mediated SIRT1 activation was further confirmed by results indicating decreased acetylation levels of NF-κB-p65 and p53. Moreover, the inhibitory effects of bergenin on mRNA and protein expression levels of IL-6 and IL-8 were reversed by a SIRT1 inhibitor. In addition, combining bergenin and dexamethasone (DEX) yielded additive effects on the reduction of IL-6 and IL-8 expression.

CONCLUSIONS

These findings demonstrate that bergenin could suppress TNF-α-induced proinflammatory responses by augmenting SIRT1 activity to block the NF-κB signaling pathway, which may provide beneficial effects for the treatment of airway inflammation associated with asthma.

Independent roles of beta-adrenergic and glucocorticoid receptors in systemic and pulmonary effects of ozone

Background: The release of catecholamines is preceded by glucocorticoids during a stress response. We have shown that ozone-induced pulmonary responses are mediated through the activation of stress hormone receptors.Objective: To examine the interdependence of beta-adrenergic (βAR) and glucocorticoid receptors (GRs), we inhibited βAR while inducing GR or inhibited GR while inducing βAR and examined ozone-induced stress response.Methods: Twelve-week-old male Wistar-Kyoto rats were pretreated daily with saline or propranolol (PROP; βAR-antagonist; 10 mg/kg-i.p.; starting 7-d prior to exposure) followed-by saline or dexamethasone (DEX) sulfate (GR-agonist; 0.02 mg/kg-i.p.; starting 1-d prior to exposure) and exposed to air or 0.8 ppm ozone (4 h/d × 2-d). In a second experiment, rats were similarly pretreated with corn-oil or mifepristone (MIFE; GR-antagonist, 30 mg/kg-s.c.) followed by saline or clenbuterol (CLEN; β₂AR-agonist; 0.02 mg/kg-i.p.) and exposed.Results: DEX and PROP + DEX decreased adrenal, spleen and thymus weights in all rats. DEX and MIFE decreased and increased corticosterone, respectively. Ozone-induced pulmonary protein leakage, inflammation and IL-6 increases were inhibited by PROP or PROP + DEX and exacerbated by CLEN or CLEN + MIFE. DEX and ozone-induced while MIFE reversed lymphopenia (MIFE > CLEN + MIFE). DEX exacerbated while PROP, MIFE, or CLEN + MIFE inhibited ozone-induced hyperglycemia and glucose intolerance. Ozone inhibited glucose-mediated insulin release.Conclusions: In summary, 1) activating βAR, even with GR inhibition, exacerbated and inhibiting βAR, even with GR activation, attenuated ozone-induced pulmonary effects; and 2) activating GR exacerbated ozone systemic effects, but with βAR inhibition, this exacerbation was less remarkable. These data suggest the independent roles of βAR in pulmonary and dependent roles of βAR and GR in systemic effects of ozone.

Mammalian Target of Rapamycin Signaling Enhances Ovalbumin-Induced Neutrophilic Airway Inflammation by Promoting Th17 Cell Polarization in Murine Noneosinophilic Asthma Model

Background: T helper 17 (Th17) is regarded as key immune cell in the pathogenesis of noneosinophilic asthma (NEA) due to the recruitment of neutrophils into the airways. The mammalian target of rapamycin (mTOR) is an important signaling molecule that plays a critical role in immune regulation. This study focused on mTOR signaling pathway in the regulation of Th17-mediated neutrophilic airway inflammation. Methods: Ovalbumin (OVA) T cell receptor transgenic DO11.10 mice (DO11.10 mice) were used to establish NEA model, and few mice received specific mTORC1 inhibitor rapamycin (RAPA) before intranasal administration of OVA. The severity of airway inflammation was determined by differential cell counts in bronchoalveolar lavage (BAL) fluids and histopathologic lung analysis. The levels of various cytokines in BAL fluids and lung tissues were measured. To determine the role of mTORC1 signaling in Th17 differentiation, naive T cells from wild-type (WT) and TSC1 knockout (KO) mice were cultured in Th17 skewing condition with or without RAPA in vitro and the production of IL-17A was compared. Results: Treatment with RAPA markedly attenuated OVA-induced neutrophilic airway inflammation in DO11.10 mice. Also the production of IL-17A was inhibited without affecting the production of interferon-γ (IFN-γ) and IL-4 in lungs. Furthermore, RAPA suppressed differentiation of Th17 cells in vitro, whereas enhanced activity of mTORC1 promoted Th17 cell differentiation and increased the expression of Th17-related transcription factors RORγt and RORα. Conclusion: These results suggested that mTOR promoted Th17 cell polarization and enhanced OVA-induced neutrophilic airway inflammation in experimental NEA.

CCR5 attenuates neutrophilic airway inflammation exacerbated by infection with rhinovirus

Human rhinovirus (hRV) is the most common cause of asthma exacerbation characterized by clinical and pathophysiological heterogeneity. Steroid-sensitive, Th2 type-eosinophilic asthma has been somewhat studied, but hRV-induced neutrophilic asthma exacerbation is poorly understood. Here, CCR5 was found to play a role in attenuating neutrophilic airway inflammation in hRV-induced asthma exacerbation using chicken ovalbumin (OVA)-based model. CCR5 deficiency resulted in exacerbated neutrophilic asthmatic responses in airways following hRV infection. CCR5-deficient mice showed enhanced mucus expression and altered expression of tight junction proteins in lung tissues. CCR5-deficient mice were also manifested with influx of CD45⁺CD11b⁺Siglec-F⁺Gr-1⁺ neutrophils, along with enhanced production of IL-17A, IFN-γ, IL-6, IL-1β cytokines in inflamed tissues. In contrast, CCR5-deficient mice elicited down-regulation of Th2-related cytokine proteins following hRV infection. More interestingly, the lack of CCR5 altered the equilibrium of CD4⁺FoxP3⁺ Tregs and IL-17⁺CD4⁺ Th17 in inflamed tissues. CCR5-deficient mice showed increased frequency and absolute number of IL-17-producing CD4⁺ Th17 cells in lung tissues compared to wild-type mice, whereas the reduced infiltration of CD4⁺FoxP3⁺ Treg cells was observed. CCR5 deficiency resulted in the skewed production of Th17 and Th1 cytokines in lymph nodes and lungs upon OVA stimulation. Likewise, CCR5-deficient mice showed enhanced expression of Th17-inducing cytokines (IL-1β, IL-6, and TNF-α) in lung tissues. These results imply that CCR5 deficiency facilitates Th17 airway inflammation during hRV-induced asthma exacerbation, along with suppressing Th2 responses. Furthermore, our results suggest that CCR5 attenuates hRV-induced neutrophilic airway inflammation through conserving the equilibrium of CD4⁺Foxp3⁺ Treg cells and IL-17⁺CD4⁺ Th17 cells in hRV-induced asthma exacerbation.

Nrf2 Activator RTA-408 Protects Against Ozone-Induced Acute Asthma Exacerbation by Suppressing ROS and γδT17 Cells

Ozone is a strong oxidant in air pollution that exacerbates respiratory disorders and is a major risk factor for acute asthma exacerbation. Ozone can induce reactive oxygen species (ROS) and airway neutrophilic inflammation. In addition, γδT17 cells contribute to IL-17A production upon ozone challenge, resulting in neutrophilic inflammation. It is known, however, that Nrf2 can ameliorate oxidative stress. We therefore investigated whether RTA-408, an Nrf2 activator, can attenuate airway inflammation and inhibit ROS production and whether this effect involves γδT17 cells. Balb/c mice were sensitized/challenged with ovalbumin (OVA) and followed by ozone exposure. We investigated the effect of Nrf2 activator RTA-408 on airway hyperresponsiveness, neutrophilic airway inflammation, cytokine/chemokine production, and OVA-specific IgE level in a mouse model of O3 induced asthma exacerbation. Furthermore, malondialdehyde (MDA) and glutathione (GSH) levels in lung and intracellular ROS were measured. IL-17⁺ γδT cell percentage by flow cytometer was determined. Nrf2 protein expression by western blot was also examined. We observed that RTA-408 attenuated ROS release during ozone-induced asthma exacerbation and suppressed neutrophil lung infiltration. RTA-408 decreased pro-inflammatory cytokine production and reduced the percentage of IL-17⁺ γδT cells. Thus, our results suggest that RTA-408 does attenuate airway inflammation in a murine model of ozone-induced asthma exacerbation.

Maternal Obesity in Mice Exacerbates the Allergic Inflammatory Response in the Airways of Male Offspring

It was previously demonstrated that non-allergen-sensitized rodents born to mothers exposed to a high-fat diet (HFD) spontaneously develop lower respiratory compliance and higher respiratory resistance. In the present study, we sought to determine if mice born to mothers consuming HFD would exhibit changes in inflammatory response and lung remodeling when subjected to ovalbumin (OVA) sensitization/challenge in adult life. Mice born to dams consuming either HFD or standard chow had increased bronchoalveolar lavage (BAL) levels of IL-1β, IL-4, IL-5, IL-10, IL-13, TNF-α and TGF-β1 after challenge with OVA. IL-4, IL-13, TNF-α and TGF-β1 levels were further increased in the offspring of HFD-fed mothers. Mice born to obese dams also had exacerbated values of leukocyte infiltration in lung parenchyma, eosinophil and neutrophil counts in BAL, mucus overproduction and collagen deposition. The programming induced by maternal obesity was accompanied by increased expression of miR-155 in peripheral-blood mononuclear cells and reduced miR-133b in trachea and lung tissue in adult life. Altogether, the present data support the unprecedented notion that the progeny of obese mice display exacerbated responses to sensitization/challenge with OVA, leading to the intensification of the morphological changes of lung remodeling. Such changes are likely to result from long-lasting changes in miR-155 and miR-133b expression.

The Role of Leukotrienes as Potential Therapeutic Targets in Allergic Disorders

Leukotrienes (LTs) are lipid mediators that play pivotal roles in acute and chronic inflammation and allergic diseases. They exert their biological effects by binding to specific G-protein-coupled receptors. Each LT receptor subtype exhibits unique functions and expression patterns. LTs play roles in various allergic diseases, including asthma (neutrophilic asthma and aspirin-sensitive asthma), allergic rhinitis, atopic dermatitis, allergic conjunctivitis, and anaphylaxis. This review summarizes the biology of LTs and their receptors, recent developments in the area of anti-LT strategies (in settings such as ongoing clinical studies), and prospects for future therapeutic applications.

Sulforaphane treatment reverses corticosteroid resistance in a mixed granulocytic mouse model of asthma by upregulation of antioxidants and attenuation of Th17 immune responses in the airways

Sulforaphane has received considerable attention in recent years due to its antioxidant and anti-inflammatory properties. Its preventive effect in the inhibition of airway inflammation is known; however, whether it affects mixed granulocyte asthma (corticosteroid resistance phenotype) is largely undiscovered. Therefore, we assessed the effect of pharmacological activation of Nrf2, a redox-sensitive transcription factor, using sulforaphane in a mouse model of mixed granulocyte airway inflammation. Mice were sensitized and challenged with cockroach allergen extract (CE), and airway inflammatory parameters and markers of steroid resistance [Nrf2 activity, oxidant-antioxidant balance in airway epithelial cells (AECs)/lung, and IL-17A-related pathway in Th17 cells and dendritic cells (DCs)] were investigated. Our results show that sulforaphane administration reduced neutrophilic airway inflammation, myeloperoxidase (MPO) activity, and Th17 immune responses in a mixed granulocyte mouse model of asthma through Nrf2 activation. On the other hand, corticosteroid treatment decreased Th2/eosinophilic immune responses but had little on Th17/neutrophilic immune responses. However, combined treatment with both almost completely blocked both neutrophilic/eosinophilic and Th17/Th2 immune responses in the lung. Sulforaphane treatment led to induction of antioxidant enzymes (SOD, GPx) in AECs and pulmonary non-enzymatic antioxidants. Further, it led to reduction in inflammatory cytokines (IL-6/IL-23/IL-17A) in Th17 cells/CD11c + DCs during mixed granulocytic inflammation. Collectively, our study presents the evidence that activation of Nrf2 by sulforaphane reduces neutrophilic airway inflammation by upregulation of antioxidants and downregulation of inflammatory cytokines in airways. This is possibly the basis for reversal of corticosteroid resistance in this model. This shows the therapeutic potential of sulforaphane in mixed granulocyte asthma.

Targeting the phosphorylation site of myristoylated alanine-rich C kinase substrate alleviates symptoms in a murine model of steroid-resistant asthma

BACKGROUND AND PURPOSE

Myristoylated alanine-rich C kinase substrate (MARCKS), a PKC substrate, facilitates mucus production and neutrophil migration. However, the effects of therapeutic procedures targeting the phosphorylation site of MARCKS on steroid-resistant asthma and the mechanisms underlying such effects have not yet been investigated. We designed a peptide that targets the MARCKS phosphorylation site (MPS peptide) and assessed its therapeutic potential against steroid-resistant asthma.

EXPERIMENTAL APPROACH

Mice were sensitized with ovalbumin (OVA), alum, and challenged with aerosolized OVA five times a week for 1 month. The mice were intratracheally administered MPS peptides three times a week, 1 hr before OVA challenge. Asthma symptoms and cell profiles in the bronchoalveolar lavage were assessed, and key proteins were analysed using Western blotting.

KEY RESULTS

Phosphorylated (p)-MARCKS was highly expressed in inflammatory and bronchial epithelial cells in OVA-immunized mice. MPS peptide reduced eosinophils, neutrophils, mucus production, collagen deposition, and airway hyper-responsiveness. Dexamethasone (Dexa) did not alleviate steroid-resistant asthma symptoms. MPS peptide caused a decrease in p-MARCKS, nitrotyrosine and the expression of oxidative stress enzymes, NADPH oxidase dual oxidase 1 and inducible NOS, in lung tissues. Compared to Dexa, MPS peptides inhibited C5a production and attenuated IL-17A and KC production in the airway more effectively, thus suppressing asthma symptoms.

CONCLUSIONS AND IMPLICATIONS

Our findings indicate that targeting MARCKS phosphorylation through MPS treatment may inhibit neutrophilic inflammation and relieve asthma symptoms, thereby highlighting its potential as a therapeutic agent for steroid-resistant asthma.

Drug Repurposing: The Anthelmintics Niclosamide and Nitazoxanide Are Potent TMEM16A Antagonists That Fully Bronchodilate Airways

There is an unmet need in severe asthma where approximately 40% of patients exhibit poor β-agonist responsiveness, suffer daily symptoms and show frequent exacerbations. Antagonists of the Ca2+-activated Cl- channel, TMEM16A, offers a new mechanism to bronchodilate airways and block the multiple contractiles operating in severe disease. To identify TMEM16A antagonists we screened a library of ∼580,000 compounds. The anthelmintics niclosamide, nitazoxanide, and related compounds were identified as potent TMEM16A antagonists that blocked airway smooth muscle depolarization and contraction. To evaluate whether TMEM16A antagonists resist use- and inflammatory-desensitization pathways limiting β-agonist action, we tested their efficacy under harsh conditions using maximally contracted airways or airways pretreated with a cytokine cocktail. Stunningly, TMEM16A antagonists fully bronchodilated airways, while the β-agonist isoproterenol showed only partial effects. Thus, antagonists of TMEM16A and repositioning of niclosamide and nitazoxanide represent an important additional treatment for patients with severe asthma and COPD that is poorly controlled with existing therapies. It is of note that drug repurposing has also attracted wide interest in niclosamide and nitazoxanide as a new treatment for cancer and infectious disease. For the first time we identify TMEM16A as a molecular target for these drugs and thus provide fresh insights into their mechanism for the treatment of these disorders in addition to respiratory disease.

Mouse models of severe asthma for evaluation of therapeutic cytokine targeting

Severe asthma is a heterogeneous inflammatory disease of the airways, which requires treatment with high-dose inhaled corticosteroids or their systemic administration, yet often remains uncontrolled despite this therapy. Over the past decades, research efforts into phenotyping of severe asthma and defining the pathological mechanisms of this disease were successful largely due to the development of appropriate animal models. Recent identification of distinct inflammatory patterns of severe asthma endotypes led to novel treatment approaches, including targeting specific cytokines or their receptors with neutralizing antibodies. Here we discuss how different experimental mouse models contributed to generation of clinically relevant findings concerning pathogenesis of severe asthma and to identification of potential targets for biologic therapy.

Oxidative stress and macrophages: driving forces behind exacerbations of asthma and chronic obstructive pulmonary disease?

Oxidative stress is a common feature of obstructive airway diseases like asthma and chronic obstructive pulmonary disease (COPD). Lung macrophages are key innate immune cells that can generate oxidants and are known to display aberrant polarization patterns and defective phagocytic responses in these diseases. Whether these characteristics are linked in one way or another and whether they contribute to the onset and severity of exacerbations in asthma and COPD remain poorly understood. Insight into oxidative stress, macrophages, and their interactions may be important in fully understanding acute worsening of lung disease. This review therefore highlights the current state of the art regarding the role of oxidative stress and macrophages in exacerbations of asthma and COPD. It shows that oxidative stress can attenuate macrophage function, which may result in impaired responses toward exacerbating triggers and may contribute to exaggerated inflammation in the airways.

Effect of Syringic acid on antioxidant biomarkers and associated inflammatory markers in mice model of asthma

Asthma is termed as the induction of chronic inflammation in the airway lumen of lungs due to accumulation of inflammatory cells which affects normal breathing process. Prolonged accumulation of inflammatory cells leads to oxidative stress and suppression of antioxidant activities. Therefore, in our present investigation, a potential phenolic compound, Syringic acid was tested for the suppression of inflammatory markers toward an antiasthmatic activity in ovalbumin (OVA)-induced asthmatic mice model. As a result, the Syringic acid treatment was found to suppress the inflammatory cells; eosinophil, neutrophil, macrophage, lymphocyte, and other inflammatory markers including IL-4, IL-5, IL-13, and TNF-α in the BALF of OVA-induced asthmatic mice. Similarly, IgE levels were significantly reduced in the blood serum of Syringic acid treated mice groups. In this context, the IFN-γ levels were found enhanced in the BALF of Syringic acid treated asthmatic mice groups, expressing an anti-inflammatory response. Enzymatic and nonenzymatic antioxidants such as SOD, CAT, and GSH levels were found high in the Syringic acid treatment than the asthmatic control group, which depicts the antioxidant response of Syringic acid on asthmatic groups. Intriguingly, the ROS, NO₂ , NO₃ , and MDA levels were inhibited in the BALF of Syringic acid treated mice groups. The airway hyper-reactivity (AHR) was comparatively normal in the Syringic acid treatment as it was severe in the case of asthmatic control group. Consequently, the effect of Syringic acid is prominent in the treatment of asthma by controlling the accumulation of inflammatory cells, other inflammatory markers along with enhancement of antioxidant markers, suppression of ROS and controlling airway hyperreactivity. Hence, Syringic acid may be recommended for clinical trials in the treatment of asthma.

Inhibition of BET bromodomains restores corticosteroid responsiveness in a mixed granulocytic mouse model of asthma

Asthma is a heterogeneous disease characterized by different endotypes/phenotypes. Th2/Th17 driven mixed granulocytic asthma is one of them and shows resistance to corticosteroid therapy. Bromodomain and extra-terminal (BET) proteins are required for differentiation of Th17 cells which play a pivotal role in neutrophilic inflammation. Therefore, we sought to characterize the differential effects of BET inhibitor versus corticosteroids, and their potential synergism in cockroach allergen extract (CE)-induced mixed granulocytic (eosinophilic and neutrophilic) mouse model of asthma having Th2/Th17 endotype. Effects of BET inhibitor, (+)JQ-1 alone and in combination with dexamethasone (Dexa) were assessed on airway inflammation as well as Th2/Th17 related airway immune responses in CE-induced mixed granulocytic asthma. Markers of steroid resistance [histone deacetylase 2 (HDAC2), and oxidative stress] were also assessed in the lungs of mice and primary human bronchial epithelial cells (HBECs). BET inhibitor, (+)JQ-1 abolished Th17 driven neutrophilic inflammation in CE-induced mixed granulocytic asthma. Dexa had limited effect on overall airway inflammation despite having significant reductions in Th2 driven immune responses. However, combination of (+)JQ-1 with Dexa completely blocked both Th2 and /Th17 driven immune responses in the lung which led to significant reductions in eosinophils, neutrophils, and mucin secretion. (+)JQ-1 also reversed CE- and IL-17A-induced decrease in HDAC2 expression in murine and human airway epithelial cells respectively.

Modeling TH 2 responses and airway inflammation to understand fundamental mechanisms regulating the pathogenesis of asthma

In this review, we highlight experiments conducted in our laboratories that have elucidated functional roles for CD4⁺ T-helper type-2 lymphocytes (T_H 2 cells), their associated cytokines, and eosinophils in the regulation of hallmark features of allergic asthma. Notably, we consider the complexity of type-2 responses and studies that have explored integrated signaling among classical T_H 2 cytokines (IL-4, IL-5, and IL-13), which together with CCL11 (eotaxin-1) regulate critical aspects of eosinophil recruitment, allergic inflammation, and airway hyper-responsiveness (AHR). Among our most important findings, we have provided evidence that the initiation of T_H 2 responses is regulated by airway epithelial cell-derived factors, including TRAIL and MID1, which promote T_H 2 cell development via STAT6-dependent pathways. Further, we highlight studies demonstrating that microRNAs are key regulators of allergic inflammation and potential targets for anti-inflammatory therapy. On the background of T_H 2 inflammation, we have demonstrated that innate immune cells (notably, airway macrophages) play essential roles in the generation of steroid-resistant inflammation and AHR secondary to allergen- and pathogen-induced exacerbations. Our work clearly indicates that understanding the diversity and spatiotemporal role of the inflammatory response and its interactions with resident airway cells is critical to advancing knowledge on asthma pathogenesis and the development of new therapeutic approaches.

PARP-1 inhibition ameliorates elastase induced lung inflammation and emphysema in mice

COPD is associated with high morbidity and mortality and no effective treatment is available till date. We have previously reported that PARP-1 plays an important role in the establishment of airway inflammation associated with asthma and ALI. In the present work, we have evaluated the beneficial effects of PARP-1 inhibition on COPD pathogenesis utilizing elastase induced mouse model of the disease. Our data show that PARP-1 inhibition by olaparib significantly reduced the elastase-induced recruitment of inflammatory cells particularly neutrophils in the lungs of mice when administered at a dose of 5 mg/kg b.wt (i.p.). Reduction in the lung inflammation was associated with suppressed myeloperoxidase activity. Further, the drug restored the redox status in the lung tissues towards normal as reflected by the levels of ROS, GSH and MDA. Olaparib administration prior to elastase instillation blunted the phosphorylation of P65-NF-κB at Ser 536 without altering phosphorylation of its inhibitor IκBα in the lungs. Furthermore, olaparib down regulated the elastase-induced expression of NF-κB dependent pro-inflammatory cytokines (TNF-A, IL-6), chemokine (MIP-2) and growth factor (GCSF) severely both at the mRNA and protein levels. Additionally, PARP-1 heterozygosity suppressed the recruitment of inflammatory cells and production of TNF-A, IL-6, MIP-2 and GCSF in the BALF to the similar extent as exhibited by olaparib administration. Finally, PARP-1 inhibition by olaparib or gene deletion protected against elastase-induced emphysema markedly. Overall, our data strongly suggest that PARP-1 plays a critical role in elastase induced lung inflammation and emphysema, and thus may be a new drug target candidate in COPD.

The interplay between neuroendocrine activity and psychological stress-induced exacerbation of allergic asthma

Psychological stress is recognized as a key factor in the exacerbation of allergic asthma, whereby brain responses to stress act as immunomodulators for asthma. In particular, stress-induced enhanced type 2 T-helper (Th2)-type lung inflammation is strongly associated with asthma pathogenesis. Psychological stress leads to eosinophilic airway inflammation through activation of the hypothalamic-pituitary-adrenal pathway and autonomic nervous system. This is followed by the secretion of stress hormones into the blood, including glucocorticoids, epinephrine, and norepinephrine, which enhance Th2 and type 17 T-helper (Th17)-type asthma profiles in humans and rodents. Recent evidence has shown that a defect of the μ-opioid receptor in the brain along with a defect of the peripheral glucocorticoid receptor signaling completely disrupted stress-induced airway inflammation in mice. This suggests that the stress response facilitates events in the central nervous and endocrine systems, thus exacerbating asthma. In this review, we outline the recent findings on the interplay between stress and neuroendocrine activities followed by stress-induced enhanced Th2 and Th17 immune responses and attenuated regulatory T (Treg) cell responses that are closely linked with asthma exacerbation. We will place a special focus on our own data that has emphasized the continuity from central sensing of psychological stress to enhanced eosinophilic airway inflammation. The mechanism that modulates psychological stress-induced exacerbation of allergic asthma through neuroendocrine activities is thought to involve a series of consecutive pathological events from the brain to the lung, which implies there to be a "neuropsychiatry phenotype" in asthma.

Effects of Macrolide and Corticosteroid in Neutrophilic Asthma Mouse Model

BACKGROUND

Asthma is a disease of chronic airway inflammation with heterogeneous features. Neutrophilic asthma is corticosteroid-insensitive asthma related to absence or suppression of TH2 process and increased TH1 and/or TH17 process. Macrolides are immunomodulatory drug that reduce airway inflammation, but their role in asthma is not fully known. The purpose of this study was to evaluate the role of macrolides in neutrophilic asthma and compare their effects with those of corticosteroids.

METHODS

C57BL/6 female mice were sensitized with ovalbumin (OVA) and lipopolysaccharides (LPS). Clarithromycin (CAM) and/or dexamethasone (DXM) were administered at days 14, 15, 21, 22, and 23. At day 24, the mice were sacrificed.

RESULTS

Airway resistance in the OVA+LPS exposed mice was elevated but was more attenuated after treatment with CAM+DXM compared with the monotherapy group (p<0.05 and p<0.01). In bronchoalveolar lavage fluid study, total cells and neutrophil counts in OVA+LPS mice were elevated but decreased after CAM+DXM treatment. In hematoxylin and eosin stain, the CAM+DXM-treated group showed less inflammation additively than the monotherapy group. There was less total protein, interleukin 17 (IL-17), interferon γ, and tumor necrosis factor α in the CAM+DXM group than in the monotherapy group (p<0.001, p<0.05, and p<0.001). More histone deacetylase 2 (HDAC2) activity was recovered in the DXM and CAM+DXM challenged groups than in the control group (p<0.05).

CONCLUSION

Decreased IL-17 and recovered relative HDAC2 activity correlated with airway resistance and inflammation in a neutrophilic asthma mouse model. This result suggests macrolides as a potential corticosteroid-sparing agent in neutrophilic asthma.

House dust mite allergen causes certain features of steroid resistant asthma in high fat fed obese mice

Obesity is a high risk factor for diseases such as cardiovascular, metabolic syndrome and asthma. Obese-asthma is another emerging phenotype in asthma which is typically refractive to steroid treatment due to its non-classical features such as non-eosinophilic cellular inflammation. The overall increased morbidity, mortality and economical burden in asthma is mainly due to steroid resistant asthma. In the present study, we used high fat diet induced obese mice which when sensitized with house dust mite (HDM) showed steroid resistant features. While the steroid, dexamethasone (DEX), treatment to high fat fed naïve mice could not reduce the airway hyperresponsiveness (AHR) induced by high fat, DEX treatment to high fat fed allergic mice could not reduce the HDM allergen induced airway remodeling features though it reduced airway inflammation. Further, these HDM induced high fat fed mice with or without DEX treatment had shown the increased activity and expression of arginase as well as the inducible nitric oxide synthase (iNOS) expression. However, DEX treatment had reduced the expressions of high iNOS and arginase I in control chow diet fed mice. Thus, we speculate that the steroid resistance seen in human obese asthmatics could be stemming from altered NO metabolism and its induced airway remodeling and with further investigations, it would encourage new treatments specific to obese-asthma phenotype.

Pathological Roles of Neutrophil-Mediated Inflammation in Asthma and Its Potential for Therapy as a Target

Asthma is a chronic inflammatory disease that undermines the airways. It is caused by dysfunction of various types of cells, as well as cellular components, and is characterized by recruitment of inflammatory cells, bronchial hyperreactivity, mucus production, and airway remodelling and narrowing. It has commonly been considered that airway inflammation is caused by the Th2 immune response, or eosinophilia, which is a hallmark of bronchial asthma pathogenesis. Some patients display a neutrophil-dominant presentation and are characterized with low (or even absent) Th2 cytokines. In recent years, increasing evidence has also suggested that neutrophils play a key role in the development of certain subtypes of asthma. This review discusses neutrophils in asthma and potentially related targeted therapies.

Lung-Infiltrating Foxp3+ Regulatory T Cells Are Quantitatively and Qualitatively Different during Eosinophilic and Neutrophilic Allergic Airway Inflammation but Essential To Control the Inflammation

Understanding functions of Foxp3⁺ regulatory T cells (Tregs) during allergic airway inflammation remains incomplete. In this study, we report that, during cockroach Ag-induced allergic airway inflammation, Foxp3⁺ Tregs are rapidly mobilized into the inflamed lung tissues. However, the level of Treg accumulation in the lung was different depending on the type of inflammation. During eosinophilic airway inflammation, ∼30% of lung-infiltrating CD4 T cells express Foxp3, indicative of Tregs. On the contrary, only ∼10% of infiltrating CD4 T cells express Foxp3 during neutrophilic airway inflammation. Despite the different accumulation, the lung inflammation and inflammatory T cell responses were aggravated following Treg depletion, regardless of the type of inflammation, suggesting regulatory roles for Tregs. Interestingly, however, the extent to which inflammatory responses are aggravated by Treg depletion was significantly greater during eosinophilic airway inflammation. Indeed, lung-infiltrating Tregs exhibit phenotypic and functional features associated with potent suppression. Our results demonstrate that Tregs are essential regulators of inflammation, regardless of the type of inflammation, although the mechanisms used by Tregs to control inflammation may be shaped by environmental cues available to them.

Linoleic acid metabolite leads to steroid resistant asthma features partially through NF-κB

Studies have highlighted the role of nutritional and metabolic modulators in asthma pathobiology. Steroid resistance is an important clinical problem in asthma but lacks good experimental models. Linoleic acid, a polyunsaturated fatty acid, has been linked to asthma and glucocorticoid sensitivity. Its 12/15–lipoxygenase metabolite, 13-S-hydroxyoctadecadienoic acid (HODE) induces mitochondrial dysfunction, with severe airway obstruction and neutrophilic airway inflammation. Here we show that HODE administration leads to steroid unresponsiveness in an otherwise steroid responsive model of allergic airway inflammation (AAI). HODE treatment to allergic mice further increased airway hyperresponsiveness and goblet metaplasia. Treatment with dexamethasone was associated with increased neutrophilic inflammation in HODE treated allergic mice; unlike control allergic mice that showed resolution of inflammation. HODE induced loss of steroid sensitivity was associated with increased p-NFkB in mice and reduced GR-α transcript levels in cultured human bronchial epithelia. In summary, HODE modifies typical AAI to recapitulate many of the phenotypic features seen in severe steroid unresponsive asthma. We speculate that since HODE is a natural metabolite, it may be relevant to the increased asthma severity and steroid insensitivity in patients who are obese or consume high fat diets. Further characterization of HODE induced steroid insensitivity may clarify the mechanisms.

Adenosine Triphosphate Promotes Allergen-Induced Airway Inflammation and Th17 Cell Polarization in Neutrophilic Asthma

Adenosine triphosphate (ATP) is a key mediator to alert the immune dysfunction by acting on P2 receptors. Here, we found that allergen challenge caused an increase of ATP secretion in a murine model of neutrophilic asthma, which correlated well with neutrophil counts and interleukin-17 production. When ATP signaling was blocked by intratracheal administration of the ATP receptor antagonist suramin before challenge, neutrophilic airway inflammation, airway hyperresponsiveness, and Th17-type responses were reduced significantly. Also, neutrophilic inflammation was abrogated when airway ATP levels were locally neutralized using apyrase. Furthermore, ATP promoted the Th17 polarization of splenic CD4⁺ T cells from DO11.10 mice in vitro. In addition, ovalbumin (OVA) challenge induced neutrophilic inflammation and Th17 polarization in DO11.10 mice, whereas administration of suramin before challenge alleviated these parameters. Thus, ATP may serve as a marker of neutrophilic asthma, and local blockade of ATP signaling might provide an alternative method to prevent Th17-mediated airway inflammation in neutrophilic asthma.

Mouse models of severe asthma: Understanding the mechanisms of steroid resistance, tissue remodelling and disease exacerbation

Severe asthma has significant disease burden and results in high healthcare costs. While existing therapies are effective for the majority of asthma patients, treatments for individuals with severe asthma are often ineffective. Mouse models are useful to identify mechanisms underlying disease pathogenesis and for the preclinical assessment of new therapies. In fact, existing mouse models have contributed significantly to our understanding of allergic/eosinophilic phenotypes of asthma and facilitated the development of novel targeted therapies (e.g. anti-IL-5 and anti-IgE). These therapies are effective in relevant subsets of severe asthma patients. Unfortunately, non-allergic/non-eosinophilic asthma, steroid resistance and disease exacerbation remain areas of unmet clinical need. No mouse model encompasses all features of severe asthma. However, mouse models can provide insight into pathogenic pathways that are relevant to severe asthma. In this review, as examples, we highlight models relevant to understanding steroid resistance, chronic tissue remodelling and disease exacerbation. Although these models highlight the complexity of the immune pathways that may underlie severe asthma, they also provide insight into new potential therapeutic approaches.

STAT6 Regulates the Development of Eosinophilic versus Neutrophilic Asthma in Response to Alternaria alternata

Human asthma is a heterogeneous disease characterized by the expression of both Th2 and Th17 cytokines. In vitro and in vivo studies have shown a reciprocal regulation between Th2 and Th17 pathways, suggesting a potential induction of neutrophil-promoting Th17 inflammation in the absence of a Th2 response. Alternaria alternata is a clinically relevant allergen that is associated with severe and fatal asthma exacerbations. Exposure to A. alternata is characterized by a predominant Th2 response, but can also induce the production of factors associated with Th17 responses (e.g., CXCL8) from epithelial cells. Using a mouse model, we found that wild-type mice develop an eosinophilic Th2 airway disease in response to A. alternata exposure, whereas IL-4-, IL-13-, and STAT6-deficient mice exhibit a primarily neutrophilic response. Neutrophilic asthma in STAT6-/- mice was accompanied by elevated lung levels of TNF-α, CXCL1, CXCL2, and CXCL5, and was steroid resistant. Neutralization of Th17 signaling only partially reduced neutrophil numbers and total airway inflammation. Airway neutrophilia developed in RAG-deficient and CD4-depleted BALB/c mice, suggesting that the suppression of neutrophil responses is dependent on Th2 cytokine production by T cells and that airway neutrophilia is primarily an innate response to allergen. These results highlight the importance of combination therapies for treatment of asthma and establish a role for factors other than IL-17 as targets for neutrophilic asthma.

Tollip SNP rs5743899 modulates human airway epithelial responses to rhinovirus infection

BACKGROUND

Rhinovirus (RV) infection in asthma induces varying degrees of airway inflammation (e.g. neutrophils), but the underlying mechanisms remain unclear.

OBJECTIVE

The major goal was to determine the role of genetic variation [e.g. single nucleotide polymorphisms (SNPs)] of Toll-interacting protein (Tollip) in airway epithelial responses to RV in a type 2 cytokine milieu.

METHODS

DNA from blood of asthmatic and normal subjects was genotyped for Tollip SNP rs5743899 AA, AG and GG genotypes. Human tracheobronchial epithelial (HTBE) cells from donors without lung disease were cultured to determine pro-inflammatory and antiviral responses to IL-13 and RV16. Tollip knockout and wild-type mice were challenged with house dust mite (HDM) and infected with RV1B to determine lung inflammation and antiviral response.

RESULTS

Asthmatic subjects carrying the AG or GG genotype (AG/GG) compared with the AA genotype demonstrated greater airflow limitation. HTBE cells with AG/GG expressed less Tollip. Upon IL-13 and RV16 treatment, cells with AG/GG (vs. AA) produced more IL-8 and expressed less antiviral genes, which was coupled with increased NF-κB activity and decreased expression of LC3, a hallmark of the autophagic pathway. Tollip co-localized and interacted with LC3. Inhibition of autophagy decreased antiviral genes in IL-13- and RV16-treated cells. Upon HDM and RV1B, Tollip knockout (vs. wild-type) mice demonstrated higher levels of lung neutrophilic inflammation and viral load, but lower levels of antiviral gene expression.

CONCLUSIONS AND CLINICAL RELEVANCE

Our data suggest that Tollip SNP rs5743899 may predict varying airway response to RV infection in asthma.

Inducible and naturally occurring regulatory T cells enhance lung allergic responses through divergent transcriptional pathways

BACKGROUND

Regulatory T cells attenuate development of asthma in wild-type (WT) mice, with both naturally occurring regulatory T (nTreg) cells and inducible regulatory T (iTreg) cells exhibiting suppressive activity. When transferred into CD8-deficient (CD8^-/-) recipients, both cell types enhanced development of allergen-induced airway hyperresponsiveness.

OBJECTIVE

We sought to determine whether the pathways leading to enhancement of lung allergic responses by transferred nTreg and iTreg cells differed.

METHODS

nTreg cells (CD4⁺CD25⁺) were isolated from WT mice and iTreg cells were generated from WT CD4⁺CD25^- T cells after activation in the presence of TGF-β and transferred into sensitized CD8^-/- recipients before challenge. Development of airway hyperresponsiveness, cytokine levels, and airway inflammation were monitored.

RESULTS

Transfer of nTreg cells enhanced lung allergic responses, as did transfer of iTreg cells. Although anti-IL-13 reduced nTreg cell-mediated enhancement, it was ineffective in iTreg cell-mediated enhancement; conversely, anti-IL-17, but not anti-IL-13, attenuated the enhancement by iTreg cells. Recovered iTreg cells from the lungs of CD8^-/- recipients were capable of IL-17 production and expressed high levels of signature genes of the T_H17 pathway, RORγt and Il17, whereas reduced expression of the Treg cell key transcription factor forkhead box p3 (Foxp3) was observed. In vitro exogenous IL-6-induced IL-17 production in iTreg cells, and in vivo conversion of transferred iTreg cells was dependent on recipient IL-6.

CONCLUSIONS

iTreg cells, similar to nTreg cells, exhibit functional plasticity and can be converted from suppressor cells to pathogenic effector cells, enhancing lung allergic responses, but these effects were mediated through different pathways.

Elucidating novel disease mechanisms in severe asthma

Corticosteroids are broadly active and potent anti-inflammatory agents that, despite the introduction of biologics, remain as the mainstay therapy for many chronic inflammatory diseases, including inflammatory bowel diseases, nephrotic syndrome, rheumatoid arthritis, chronic obstructive pulmonary disease and asthma. Significantly, there are cohorts of these patients with poor sensitivity to steroid treatment even with high doses, which can lead to many iatrogenic side effects. The dose-limiting toxicity of corticosteroids, and the lack of effective therapeutic alternatives, leads to substantial excess morbidity and healthcare expenditure. We have developed novel murine models of respiratory infection-induced, severe, steroid-resistant asthma that recapitulate the hallmark features of the human disease. These models can be used to elucidate novel disease mechanisms and identify new therapeutic targets in severe asthma. Hypothesis-driven studies can elucidate the roles of specific factors and pathways. Alternatively, 'Omics approaches can be used to rapidly generate new targets. Similar approaches can be used in other diseases.

BCL-2 protects human and mouse Th17 cells from glucocorticoid-induced apoptosis

BACKGROUND

Glucocorticoid resistance has been associated with Th17-driven inflammation, the mechanisms of which are not clear. We determined whether human and mouse Th17 cells are resistant to glucocorticoid-induced apoptosis.

METHODS

Freshly isolated human blood Th17 cells and in vitro differentiated Th17 cells from IL-17F red fluorescent protein reporter mice were treated with dexamethasone, a potent glucocorticoid. Apoptosis was measured using annexin V and DAPI staining. Screening of apoptosis genes was performed using the apoptosis PCR array. Levels of molecules involved in apoptosis were measured using quantitative RT-PCR, flow cytometry, and Western blotting. Knockdown of BCL-2 in murine Th17 cells was performed via retroviral transduction. Cytokines were measured using ELISA. A murine Th17-driven severe asthma model was examined for Th17 glucocorticoid sensitivity in vivo.

RESULTS

Human and mouse Th17 cells and mouse Th2 cells were resistant to glucocorticoid-induced apoptosis. Th17 cells had glucocorticoid receptors levels comparable to those in other T effectors cells. Th17 cells had high levels of BCL-2, knockdown of which sensitized Th17 cells to dexamethasone-induced apoptosis. Production of IL-22, but not IL-17A and IL-17F, was suppressed by glucocorticoids. STAT3 phosphorylation in Th17 cells was insensitive to glucocorticoid inhibition. Lung Th17 cells in the murine severe asthma model were enhanced, rather than suppressed, by glucocorticoids.

CONCLUSION

Th17 cells are resistant to glucocorticoid-induced apoptosis and cytokine suppression, at least in part due to high levels of BCL-2. These findings support a role of Th17 cells in glucocorticoid-resistant inflammatory conditions such as certain endotypes of asthma.