Raised sputum extracellular DNA confers lung function impairment and poor symptom control in an exacerbation-susceptible phenotype of neutrophilic asthma

Physiology and pathophysiology of mucus and mucolytic use in critically ill patients

Airway mucus is a highly specialised secretory fluid which functions as a physical and immunological barrier to pathogens whilst lubricating the airways and humifying atmospheric air. Dysfunction is common during critical illness and is characterised by changes in production rate, chemical composition, physical properties, and inflammatory phenotype. Mucociliary clearance, which is determined in part by mucus characteristics and in part by ciliary function, is also dysfunctional in critical illness via disease related and iatrogenic mechanisms. The consequences of mucus dysfunction are potentially devastating, contributing to prolonged ventilator dependency, increased risk of secondary pneumonia, and worsened lung injury. Mucolytic therapies are designed to decrease viscosity, improve expectoration/suctioning, and thereby promote mucus removal. Mucolytics, including hypertonic saline, dornase alfa/rhDNase, nebulised heparin, carbocisteine/N-Acetyl cysteine, are commonly used in critically ill patients. This review summarises the physiology and pathophysiology of mucus and the existing evidence for the use of mucolytics in critically ill patients and speculates on journey to individualised mucolytic therapy.

Progress in research on induced sputum in asthma: a narrative review

OBJECTIVE

To explore the clinical significance of induced sputum in asthma through a retrospective analysis of induced sputum in patients with asthma.

DATA SOURCES

The data and references cited in this article were obtained from PubMed, Sci-Hub, and Web of Science.

STUDY SELECTION

Observational studies with reliable data were selected.

CONCLUSIONS

The cytological count, -omics, and pathogen detection of induced sputum are helpful for the clinical diagnosis of asthma and in guiding medication choices.

Anti-IL-5 treatment, but not neutrophil interference, attenuates inflammation in a mixed granulocytic asthma mouse model, elicited by air pollution

INTRODUCTION

Diesel exhaust particles (DEP) have been proven to aggravate asthma pathogenesis. We previously demonstrated that concurrent exposure to house dust mite (HDM) and DEP in mice increases both eosinophils and neutrophils in bronchoalveolar lavage fluid (BALF) and also results in higher levels of neutrophil-recruiting chemokines and neutrophil extracellular trap (NET) formation compared to sole HDM, sole DEP or saline exposure. We aimed to evaluate whether treatment with anti-IL-5 can alleviate the asthmatic features in this mixed granulocytic asthma model. Moreover, we aimed to unravel whether neutrophils modulate the DEP-aggravated eosinophilic airway inflammation.

MATERIAL AND METHODS

Female C57BL6/J mice were intranasally exposed to saline or HDM and DEP for 3 weeks (subacute model). Interference with eosinophils was performed by intraperitoneal administration of anti-IL-5 (TRFK5), which neutralizes IL-5. Interference with neutrophils and neutrophil elastase was performed by intraperitoneal anti-Ly6G and sivelestat administration, respectively. Outcome parameters included eosinophils subsets (homeostatic EOS and inflammatory EOS), proinflammatory cytokines, goblet cell hyperplasia and airway hyperresponsiveness.

RESULTS

The administration of anti-IL-5 significantly decreased eosinophilic responses, affecting both inflammatory and homeostatic eosinophil subsets, upon subacute HDM + DEP exposure while BAL neutrophils, NET formation and other asthma features remained present. Neutrophils were significantly reduced after anti-Ly6G administration in BALF, lung and blood without affecting the eosinophilic inflammation upon HDM + DEP exposure. Sivelestat treatment tended to decrease BALF inflammation, including eosinophils, upon HDM + DEP exposure, but did not affect lung inflammation.

CONCLUSION

Inhibition of IL-5 signalling, but not neutrophil interventions, significantly attenuates eosinophilic inflammation in a mouse model of mixed granulocytic asthma, elicited by air pollution exposure.

Targeted DNase treatment of obstructive lung disease: a pilot randomised controlled trial

Background

Sputum extracellular DNA (eDNA) is associated with disease severity in asthma and COPD and therefore emerging as a potential therapeutic target. The aim of this study was to investigate the effect of 10 days of recombinant human DNase (rhDNase) treatment of eDNA-high asthma and COPD on sputum eDNA levels, neutrophil-related inflammation, lung function and symptoms.

Methods

Adults with asthma (n=80) or COPD (n=66) were screened for the presence of high (>20 µg·mL-1) sputum eDNA and those eligible (n=18 asthma, n=17 COPD) were randomised to a two-period crossover controlled trial consisting of daily nebulised rhDNase (2.5 mg/2.5 mL) or placebo (5 mL 0.9% saline) for 10 days, with a 2-week washout period. The primary outcome was sputum eDNA, and secondary outcomes included sputum neutrophil extracellular trap (NET)-related biomarkers, inflammatory cell counts, lung function and respiratory symptoms.

Results

At screening, high eDNA was associated with significantly higher sputum total cell count, sputum colour score and inflammation (HNP1-3, LL-37 and interleukin-1β) in both asthma and COPD compared to low eDNA groups. In asthma, participants with high eDNA were older and had poorer lung function and asthma control compared to low eDNA. Administration of nebulised rhDNase significantly reduced sputum eDNA levels in both asthma (median (Q1-Q3) Pre: 48.4 (22.1-74.1); Post: 17.0 (5.0-31.0) µg·mL-1; p=0.022) and COPD (median (Q1-Q3) Pre: 39.3 (36.7-55.6); Post: 25.4 (11.3-38.6) µg·mL-1; p=0.044) compared to placebo. Symptoms, lung function and NET biomarkers remained unchanged. In asthma, there was a reduction in banded blood neutrophils (3.2 (0-7.7) to 0.0 (0.0-1.5); p=0.044).

Conclusion

Targeted rhDNase treatment for 10 days effectively reduced sputum eDNA in eDNA-high asthma and COPD.

Molecular Pathways and Potential Therapeutic Targets of Refractory Asthma

Asthma is a chronic inflammatory lung disease. Refractory asthma poses a significant challenge in management due to its resistance to standard therapies. Key molecular pathways of refractory asthma include T2 inflammation mediated by Th2 and ILC2 cells, eosinophils, and cytokines including IL-4, IL-5, and IL-13. Additionally, non-T2 mechanisms involving neutrophils, macrophages, IL-1, IL-6, and IL-17 mediate a corticosteroid resistant phenotype. Mediators including alarmins (IL-25, IL-33, TSLP) and OX40L have overlap between T2 and non-T2 inflammation and may signify unique pathways of asthma inflammation. Therapies that target these pathways and mediators have proven to be effective in reducing exacerbations and improving lung function in subsets of severe asthma patients. However, there are patients with severe asthma who do not respond to approved therapies. Small molecule inhibitors, such as JAK-inhibitors, and monoclonal antibodies targeting mast cells, IL-1, IL-6, IL-33, TNFα, and OX40L are under investigation for their potential to modulate inflammation involved in refractory asthma. Understanding refractory asthma heterogeneity and identifying mediators involved are essential in developing therapeutic interventions for patients unresponsive to currently approved biologics. Further investigation is needed to develop personalized treatments based on these molecular insights to potentially offer more effective treatments for this complex disease.

8-Iso-prostaglandin F2α as a biomarker of type 2 low airway inflammation and remodeling in adult asthma

BACKGROUND

Although 8-iso-prostaglandin F2a has been proposed as a potential biomarker for oxidative stress in airway diseases, its specific role in asthma remains poorly understood.

OBJECTIVE

To evaluate the diagnostic potential of 8-iso-prostaglandin F2a in assessing airway inflammation, airway remodeling, airway hyperresponsiveness, and oxidative stress in asthma.

METHODS

Blood and urine concentrations of 8-iso-prostaglandin F2a were quantified using liquid chromatography-tandem mass spectrometry in 128 adults with asthma who had maintained antiasthma medications. Their correlations with clinical data, sputum cell counts, lung function parameters, and serum markers of epithelial/neutrophil activity and airway remodeling were then analyzed.

RESULTS

The urinary 8-iso-prostaglandin F2a concentrations were significantly higher in patients with noneosinophilic asthma than in those with eosinophilic asthma (P < .05). The area under the curve was 0.678, indicating moderate diagnostic accuracy for noneosinophilic asthma. There were significant correlations with neutrophilic inflammation markers and airway remodeling markers (all P < .05). Negative correlations were observed with forced expiratory volume in 1 second (%), forced expiratory volume in 1 second/forced vital capacity, forced expiratory flow at 25% to 75% of forced vital capacity, and serum club cell protein 16 levels (all P < .05). High 8-iso-prostaglandin F2a concentrations were also noted in obese and smoking subgroups (all P < .05). However, the serum 8-iso-prostaglandin F2a concentrations were not correlated with these asthma-related parameters.

CONCLUSION

Urinary 8-iso-prostaglandin F2a concentrations are a potential biomarker for phenotyping severe asthma, particularly noneosinophilic asthma, offering oxidative stress-induced epithelial inflammation/remodeling as an additional target in asthma management.

Intranasal PAMAM-G3 scavenges cell-free DNA attenuating the allergic airway inflammation

Allergic airway inflammation (AAI), including allergic rhinitis (AR) and allergic asthma, is driven by epithelial barrier dysfunction and type 2 inflammation. However, the underlying mechanism remains uncertain and available treatments are constrained. Consequently, we aim to explore the role of cell-free DNA (cfDNA) in AAI and assess the potential alleviating effects of cationic polymers (CPs) through cfDNA elimination. Levels of cfDNA were evaluated in AR patients, allergen-stimulated human bronchial epithelium (BEAS-2B cells) and primary human nasal epithelium from both AR and healthy control (HC), and AAI murine model. Polyamidoamine dendrimers-generation 3 (PAMAM-G3), a classic type of cationic polymers, were applied to investigate whether the clearance of cfDNA could ameliorate airway epithelial dysfunction and inhibit AAI. The levels of cfDNA in the plasma and nasal secretion from AR were higher than those from HC (P < 0.05). Additionally, cfDNA levels in the exhaled breath condensate (EBC) were positively correlated with Interleukin (IL)-5 levels in EBC (R = 0.4191, P = 0.0001). Plasma cfDNA levels negatively correlated with the duration of allergen immunotherapy treatment (R = -0.4297, P = 0.006). Allergen stimulated cfDNA secretion in vitro (P < 0.001) and in vivo (P < 0.0001), which could be effectively scavenged with PAMAM-G3. The application of PAMAM-G3 inhibited epithelial barrier dysfunction in vitro and attenuated the development of AAI in vivo. This study elucidates that cfDNA, a promising biomarker for monitoring disease severity, aggravates AAI and the application of intranasal PAMAM-G3 could potentially be a novel therapeutic intervention for AAI. Allergen stimulates the secretion of cell-free DNA (cfDNA) in both human and mouse airway. Intranasal polyamidoamine dendrimers-generation 3 (PAMAM-G3) scavenges cfDNA and alleviates allergic airway inflammation.

Bronchial epithelial transcriptomics and experimental validation reveal asthma severity-related neutrophilc signatures and potential treatments

Airway epithelial transcriptome analysis of asthma patients with different severity was used to disentangle the immune infiltration mechanisms affecting asthma exacerbation, which may be advantageous to asthma treatment. Here we introduce various bioinformatics methods and develop two models: an OVA/CFA-induced neutrophil asthma mouse model and an LPS-induced human bronchial epithelial cell damage model. Our objective is to investigate the molecular mechanisms, potential targets, and therapeutic strategies associated with asthma severity. Multiple bioinformatics methods identify meaningful differences in the degree of neutrophil infiltration in asthma patients with different severity. Then, PTPRC, TLR2, MMP9, FCGR3B, TYROBP, CXCR1, S100A12, FPR1, CCR1 and CXCR2 are identified as the hub genes. Furthermore, the mRNA expression of 10 hub genes is determined in vivo and in vitro models. Reperixin is identified as a pivotal drug targeting CXCR1, CXCR2 and MMP9. We further test the potential efficiency of Reperixin in 16HBE cells, and conclude that Reperixin can attenuate LPS-induced cellular damage and inhibit the expression of them. In this study, we successfully identify and validate several neutrophilic signatures and targets associated with asthma severity. Notably, Reperixin displays the ability to target CXCR1, CXCR2, and MMP9, suggesting its potential therapeutic value for managing deteriorating asthma.

Neutrophil extracellular traps and their implications in airway inflammatory diseases

Neutrophil extracellular traps (NETs) are essential for immune defense and have been increasingly recognized for their role in infection and inflammation. In the context of airway inflammatory diseases, there is growing evidence suggesting the involvement and significance of NETs. This review aims to provide an overview of the formation mechanisms and components of NETs and their impact on various airway inflammatory diseases, including acute lung injury/ARDS, asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis. By understanding the role of NETs in airway inflammation, we can gain valuable insights into the underlying pathogenesis of these diseases and identify potential targets for future therapeutic strategies that either target NETs formation or modulate their harmful effects. Further research is warranted to elucidate the complex interactions between NETs and airway inflammation and to develop targeted therapies that can effectively mitigate their detrimental effects while preserving their beneficial functions in host defense.

Eosinophils and tissue remodeling: Relevance to airway disease

The ability of human tissue to reorganize and restore its existing structure underlies tissue homeostasis in the healthy airways, but in disease can persist without normal resolution, leading to an altered airway structure. Eosinophils play a cardinal role in airway remodeling both in health and disease, driving epithelial homeostasis and extracellular matrix turnover. Physiological consequences associated with eosinophil-driven remodeling include impaired lung function and reduced bronchodilator reversibility in asthma, and obstructed airflow in chronic rhinosinusitis with nasal polyps. Given the contribution of airway remodeling to the development and persistence of symptoms in airways disease, targeting remodeling is an important therapeutic consideration. Indeed, there is early evidence that eosinophil attenuation may reduce remodeling and disease progression in asthma. This review provides an overview of tissue remodeling in both health and airway disease with a particular focus on eosinophilic asthma and chronic rhinosinusitis with nasal polyps, as well as the role of eosinophils in these processes and the implications for therapeutic interventions. Areas for future research are also noted, to help improve our understanding of the homeostatic and pathological roles of eosinophils in tissue remodeling, which should aid the development of targeted and effective treatments for eosinophilic diseases of the airways.

Window of opportunity for respiratory oscillometry: A review of recent research

Oscillometry has been around for almost 70 years, but there are still many unknowns. The test is performed during tidal breathing and is therefore free from patient-dependent factors that could influence the results. The Forced Oscillation Technique (FOT), which requires minimal patient cooperation, is gaining ground, particularly with elderly patients and children. In pulmonology, it is a valuable tool for assessing obstructive conditions (with a distinction between central and peripheral obstruction) and restrictive disorders (intrapulmonary and extrapulmonary). Its sensitivity allows the assessment of bronchodilator and bronchoconstrictor responses. Different lung diseases show different patterns of changes in FOT, especially studied in asthma and chronic obstructive pulmonary disease. Because of these differences, many studies have analysed the usefulness of this technique in different areas of medicine. In this paper, the authors would like to present the basics of oscillometry with the areas of its most recent clinical applications.

Role and Therapeutic Targeting Strategies of Neutrophil Extracellular Traps in Inflammation

Neutrophil extracellular traps (NETs) are large DNA reticular structures secreted by neutrophils and decorated with histones and antimicrobial proteins. As a key mechanism for neutrophils to resist microbial invasion, NETs play an important role in the killing of microorganisms (bacteria, fungi, and viruses). Although NETs are mostly known for mediating microbial killing, increasing evidence suggests that excessive NETs induced by stimulation of physical and chemical components, microorganisms, and pathological factors can exacerbate inflammation and organ damage. This review summarizes the induction and role of NETs in inflammation and focuses on the strategies of inhibiting NETosis and the mechanisms involved in pathogen evasion of NETs. Furthermore, herbal medicine inhibitors and nanodelivery strategies improve the efficiency of inhibition of excessive levels of NETs.

The Unified Airway Hypothesis: Evidence From Specific Intervention With Anti-IL-5 Biologic Therapy

The unified airway hypothesis proposes that upper and lower airway diseases reflect a single pathological process manifesting in different locations within the airway. Functional, epidemiological, and pathological evidence has supported this well-established hypothesis for some time. However, literature on the pathobiologic roles/therapeutic targeting of eosinophils and IL-5 in upper and lower airway diseases (including asthma, chronic rhinosinusitis with nasal polyps [CRSwNP], and nonsteroidal anti-inflammatory drug-exacerbated respiratory disease) has recently emerged. This narrative review revisits the unified airway hypothesis by searching the scientific literature for recent learnings and clinical trial/real-world data that provide a novel perspective on its relevance for clinicians. According to the available literature, eosinophils and IL-5 have important pathophysiological roles in both the upper and lower airways, although the impact of eosinophils and IL-5 may vary in asthma and CRSwNP. Some differential effects of anti-IL-5 and anti-IL-5-receptor therapies in CRSwNP have been observed, requiring further investigation. However, pharmaceutical targeting of eosinophils and IL-5 in patients with upper, lower, and comorbid upper and lower airway inflammation has led to clinical benefit, supporting the hypothesis that these are linked conditions manifesting in different locations. Consideration of this approach may improve patient care and aid clinical decision making.

Blockade of neutrophil extracellular traps ameliorates toluene diisocyanate-induced steroid-resistant asthma

BACKGROUND AND PURPOSE

Toluene diisocyanate (TDI)-induced asthma is characterized by mixed inflammation dominated by neutrophils, and is refractory to steroid treatment. Neutrophil extracellular traps (NETs) play an important role in severe asthma, but their role in TDI-induced asthma models is unclear. This study focused on the role and mechanism of NETs in steroid-resistant TDI-induced asthma.

METHODS

Induced sputum was collected from 85 asthmatic patients and 25 healthy controls to detect eDNA. A murine TDI-induced asthma model was prepared, and asthmatic mice were given dexamethasone or DNase I. In vitro, the human bronchial epithelial cell line HBE was stimulated with NETs or TDI-human serum albumin (TDI-HSA).

RESULTS

Asthma patients had higher sputum eDNA compared to healthy subjects. In asthma patients, eDNA was positively correlated with sputum neutrophils, and negatively correlated with FEV1%predicted. Airway inflammation, airway reactivity, Th2 cytokine levels in lymph supernatant, and levels of NETs were significantly increased in the TDI-induced asthmatic mice. These increases were suppressed by DNase I, but not by dexamethasone. Inhibition of NETs improved interleukin (IL)-8 and MKP1 mRNA expression, and reduced phosphorylation of GR-S226 induced by TDI. Inhibition of NETs improved airway epithelial barrier disruption, as well as p38 and ERK signaling pathways in TDI-induced asthmatic mice. In vitro, NETs promoted the expression of IL-8 mRNA in HBE cells, and reduced the expression of MKP1. IL-8 elevation induced by NETs was suppressed by a p38 inhibitor or ERK inhibitor, but not by dexamethasone. Pretreatment with RAGE inhibitor reduced NETs induced p38/ERK phosphorylation and IL-8 levels in HBE cells.

CONCLUSION

Our data suggest that targeting NETs might effectively improved TDI-induced airway inflammation and airway epithelial barrier function. This may potentially be a treatment for patients with steroid-resistance asthma.

Extracellular Traps: A Novel Therapeutic Target for Severe Asthma

Asthma is a complicated disease defined by a combination of clinical symptoms and physiological characteristics. Typically, asthma is diagnosed by the presence of episodic cough, wheezing, or dyspnea triggered by variable environmental factors (allergens and respiratory infections), and reversible airflow obstruction. To date, the majority of asthmatic patients have been adequately controlled by anti-inflammatory/bronchodilating agents, but those with severe asthma (SA) have not been sufficiently controlled by high-dose inhaled corticosteroids-long-acting beta-agonists plus additional controllers including leukotriene modifiers. Accordingly, these uncontrolled patients provoke a special issue, because they consume high healthcare resources, requiring innovative precision medicine solutions. Recently, phenotyping based on biomarkers of airway inflammation has led to elucidating the pathophysiological mechanism of SA, where emerging evidence has highlighted the significance of eosinophil or neutrophil extracellular traps contributing to the development of SA. Here, we aimed to provide current findings about extracellular traps as a novel therapeutic target for asthma to address medical unmet needs.

Longitudinal Impact of Sputum Inflammatory Phenotypes on Small Airway Dysfunction and Disease Outcomes in Asthma

BACKGROUND

Little is known about the relationship between airway inflammatory phenotypes and some important asthma features such as small airway dysfunction (SAD).

OBJECTIVE

To describe the longitudinal impact of airway inflammatory phenotypes on SAD and asthma outcomes.

METHODS

We measured eosinophil and neutrophil counts in induced sputum at baseline and 1 year later to stratify 197 adult patients with asthma into 4 inflammatory phenotypes. We conducted a comprehensive assessment of lung function using spirometry, body plethysmography, impulse oscillometry, and inert gas single and multiple breath washouts. We compared lung function, asthma severity, exacerbation frequency, and symptom control between the phenotypes. We studied the longitudinal impact of persistent sputum inflammatory phenotypes and the change of sputum cell counts on lung function.

RESULTS

Patients were stratified into eosinophilic (23%, n = 45), neutrophilic (33%, n = 62), mixed granulocytic (22%, n = 43), and paucigranulocytic (24%, n = 47) phenotypes. Patients with eosinophilic and mixed granulocytic asthma had higher rates of airflow obstruction and severe exacerbation as well as poorer symptom control than patients with paucigranulocytic asthma. All SAD measures were worse in patients with eosinophilic and mixed asthma than in those with paucigranulocytic asthma (all P values <.05). Eosinophilic asthma also indicated worse distal airflow obstruction, increased ventilation inhomogeneity (all P values <.05), and higher tendency for severe exacerbation (P = .07) than neutrophilic asthma. Longitudinally, persistent mixed granulocytic asthma was associated with the worst follow-up measures of SAD compared with persistent neutrophilic, persistent paucigranulocytic, or nonpersistent asthma phenotypes. In patients with stable forced expiratory volume in 1 second (FEV1), the mean increase in small airway resistance (R5-20) was greater in patients with persistent mixed granulocytic asthma (+103%) than in patients with persistent neutrophilic (+26%), P = .040, or persistent paucigranulocytic asthma (-41%), P = .028. Multivariate models adjusted for confounders and treatment with inhaled or oral corticosteroids or antieosinophilic biologics indicated that the change of sputum eosinophil rather than neutrophil counts is an independent predictor for the longitudinal change in FEV1, forced expiratory flow at 25% to 75% of forced vital capacity, specific effective airway resistance, residual lung volume, and lung clearance index.

CONCLUSIONS

In asthma, airway eosinophilic inflammation is the main driver of lung function impairment and poor disease outcomes, which might also be aggravated by the coexistence of airway neutrophilia to confer a severe mixed granulocytic asthma phenotype. Persistent airway eosinophilia might be associated with dynamic SAD even in patients with stable FEV1.