Ex vivo sputum analysis reveals impairment of protease-dependent mucus degradation by plasma proteins in acute asthma

Eosinophilic mucus diseases

Eosinophilic inflammation is primarily characterized by type 2 immune responses against parasitic organisms. In the contemporary human being especially in developed countries, eosinophilic inflammation is strongly associated with allergic/sterile inflammation, and constitutes an undesired immune reaction. This situation is in stark contrast to neutrophilic inflammation, which is indispensable for the host defense against bacterial infections. Among eosinophilic inflammatory disorders, massive accumulation of eosinophils within mucus is observed in certain cases, and is often linked to the distinctive clinical finding of mucus with high viscosity. Eosinophilic mucus is found in a variety of diseases, including chronic allergic keratoconjunctivitis, chronic rhinosinusitis encompassing allergic fungal sinusitis, eosinophilic otitis media, eosinophilic sialodochitis, allergic bronchopulmonary aspergillosis/mycosis, eosinophilic plastic bronchitis, and eosinophilic asthma. In these pathological conditions, chronic inflammation and tissue remodeling coupled with irreversible organ damage due to persistent adhesion of toxic substances and luminal obstruction may impose a significant burden on the body. Eosinophils aggregate in the hyperconcentrated mucus together with cell-derived crystals, macromolecules, and polymers, thereby affecting the biophysical properties of the mucus. This review focuses on the clinically significant challenges of mucus and discusses the consequences of activated eosinophils on the mucosal surface that impact mucus and persistent inflammation.

Emerging cell and molecular targets for treating mucus hypersecretion in asthma

Mucus provides a protective barrier that is crucial for host defense in the lungs. However, excessive or abnormal mucus can have pathophysiological consequences in many pulmonary diseases, including asthma. Patients with asthma are treated with agents that relax airway smooth muscle and reduce airway inflammation, but responses are often inadequate. In part, this is due to the inability of existing therapeutic agents to directly target mucus. Accordingly, there is a critical need to better understand how mucus hypersecretion and airway plugging are affected by the epithelial cells that synthesize, secrete, and transport mucus components. This review highlights recent advances in the biology of mucin glycoproteins with a specific focus on MUC5AC and MUC5B, the chief macromolecular components of airway mucus. An improved mechanistic understanding of key steps in mucin production and secretion will help reveal novel potential therapeutic strategies.

How Does Airway Surface Liquid Composition Vary in Different Pulmonary Diseases, and How Can We Use This Knowledge to Model Microbial Infections?

Growth environment greatly alters many facets of pathogen physiology, including pathogenesis and antimicrobial tolerance. The importance of host-mimicking environments for attaining an accurate picture of pathogen behaviour is widely recognised. Whilst this recognition has translated into the extensive development of artificial cystic fibrosis (CF) sputum medium, attempts to mimic the growth environment in other respiratory disease states have been completely neglected. The composition of the airway surface liquid (ASL) in different pulmonary diseases is far less well characterised than CF sputum, making it very difficult for researchers to model these infection environments. In this review, we discuss the components of human ASL, how different lung pathologies affect ASL composition, and how different pathogens interact with these components. This will provide researchers interested in mimicking different respiratory environments with the information necessary to design a host-mimicking medium, allowing for better understanding of how to treat pathogens causing infection in these environments.

Mucus Structure, Viscoelastic Properties, and Composition in Chronic Respiratory Diseases

The respiratory mucus, a viscoelastic gel, effectuates a primary line of the airway defense when operated by the mucociliary clearance. In chronic respiratory diseases (CRDs), such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF), the mucus is overproduced and its solid content augments, changing its structure and viscoelastic properties and determining a derangement of essential defense mechanisms against opportunistic microbial (virus and bacteria) pathogens. This ensues in damaging of the airways, leading to a vicious cycle of obstruction and infection responsible for the harsh clinical evolution of these CRDs. Here, we review the essential features of normal and pathological mucus (i.e., sputum in CF, COPD, and asthma), i.e., mucin content, structure (mesh size), micro/macro-rheology, pH, and osmotic pressure, ending with the awareness that sputum biomarkers (mucins, inflammatory proteins and peptides, and metabolites) might serve to indicate acute exacerbation and response to therapies. There are some indications that old and novel treatments may change the structure, viscoelastic properties, and biomarker content of sputum; however, a wealth of work is still needed to embrace these measures as correlates of disease severity in association with (or even as substitutes of) pulmonary functional tests.

The role of airway mucus and diseased pulmonary epithelium on the absorption of inhaled antibodies

Inhaled antibody therapy for the treatment of respiratory diseases is a promising strategy to maximize pulmonary exposure and reduce side effects associated with parenteral administration. However, the development of inhaled antibodies is often challenging due to a poor understanding of key mechanisms governing antibody absorption and clearance in healthy and diseased pulmonary epithelium. Here, we utilize well established Human Bronchial Epithelial Cell (HBEC) models grown at air-liquid interface to study the absorption process of antibodies and antibody fragments. With these cellular models, we recapitulate the morphology and function of healthy and diseased pulmonary epithelium, and incorporate the mucosal barrier to enable the investigation of both cellular permeability as well as mucodiffusion. We studied the saturation of antibody transport across the HBEC barriers and estimated the impact of disease-like epithelial barriers on antibody paracellular transport. Additionally, we identified a potential role of neonatal Fc receptor (FcRn)-independent and target-mediated transcytosis in the transport of Fragment antigen-binding (Fab) and F(ab)2 antibody fragments. Lastly, our models were able to pinpoint an impaired antibody diffusion across mucus gels. These mechanistic cellular models are promising in vitro tools to inform Physiologically-based Pharmacokinetic (PBPK) computational models for dose prediction toward de-risking the development of inhaled biologics.

Engineered lipid liquid crystalline nanoparticles as an inhaled nanoplatform for mucus penetration enhancement

Nanocarrier-assisted pulmonary drug delivery system has been widely employed for lung local disease treatment due to its enhanced drug lesion accumulation and reduced systematical side effects. However, the mucus barriers covered on the epithelia of trachea and bronchial tree construct a dense barrier for inhaled nanocarrier transport, which compromises the therapeutical effects. In this study, a lipid liquid crystalline nanoparticle NLP@Z with surface zwitterion material hexadecyl betaine (HB) modification and N-acetylcysteine (NAC) encapsulation was presented to exert the combination strategy of mucus-inert surface and mucus degradation. The HB modification endowed NLP@Z mucus-inert surface to inhibit the interaction between NLP@Z and mucins, and the encapsulated NAC could effectively degrade the mucins and further decrease the mucus viscosity. This combination strategy was proved to significantly promote the mucus penetration performance and enhance epithelial cell uptake. In addition, the proposed NLP@Z was equipped with desired nebulization property, which could be served as a potential pulmonary delivery nanoplatform. In summary, the proposed NLP@Z highlights the employment of the combination strategy for mucus penetration enhancement in pulmonary delivery, which may become a versatile platform for lung disease therapy.

Engineering in vitro models of cystic fibrosis lung disease using neutrophil extracellular trap inspired biomaterials

Cystic fibrosis (CF) is a muco-obstructive lung disease where inflammatory responses due to chronic infection result in the accumulation of neutrophil extracellular traps (NETs) in the airways. NETs are web-like complexes comprised mainly of decondensed chromatin that function to capture and kill bacteria. Prior studies have established excess release of NETs in CF airways increases viscoelasticity of mucus secretions and reduces mucociliary clearance. Despite the pivotal role of NETs in CF disease pathogenesis, current in vitro models of this disease do not account for their contribution. Motivated by this, we developed a new approach to study the pathobiological effects of NETs in CF by combining synthetic NET-like biomaterials, composed of DNA and histones, with an in vitro human airway epithelial cell culture model. To determine the impact of synthetic NETs on airway clearance function, we incorporated synthetic NETs into mucin hydrogels and cell culture derived airway mucus to assess their rheological and transport properties. We found that the addition of synthetic NETs significantly increases mucin hydrogel viscoelasticity. As a result, mucociliary transport in vitro was significantly reduced with the addition of mucus containing synthetic NETs. Given the prevalence of bacterial infection in the CF lung, we also evaluated the growth of Pseudomonas aeruginosa in mucus with or without synthetic NETs. We found mucus containing synthetic NETs promoted microcolony growth and prolonged bacterial survival. Together, this work establishes a new biomaterial enabled approach to study innate immunity mediated airway dysfunction in CF.

The Dual Role of the Airway Epithelium in Asthma: Active Barrier and Regulator of Inflammation

Chronic airway inflammation is the cornerstone on which bronchial asthma arises, and in turn, chronic inflammation arises from a complex interplay between environmental factors such as allergens and pathogens and immune cells as well as structural cells constituting the airway mucosa. Airway epithelial cells (AECs) are at the center of these processes. On the one hand, they represent the borderline separating the body from its environment in order to keep inner homeostasis. The airway epithelium forms a multi-tiered, self-cleaning barrier that involves an unstirred, discontinuous mucous layer, the dense and rigid mesh of the glycocalyx, and the cellular layer itself, consisting of multiple, densely interconnected cell types. On the other hand, the airway epithelium represents an immunologically highly active tissue once its barrier has been penetrated: AECs play a pivotal role in releasing protective immunoglobulin A. They express a broad spectrum of pattern recognition receptors, enabling them to react to environmental stressors that overcome the mucosal barrier. By releasing alarmins-proinflammatory and regulatory cytokines-AECs play an active role in the formation, strategic orientation, and control of the subsequent defense reaction. Consequently, the airway epithelium is of vital importance to chronic inflammatory diseases, such as asthma.

Sputum handling for rheology

The rheology of sputum is viewed as a powerful emerging biophysical marker for monitoring muco-obstructive pulmonary diseases such as cystic fibrosis (CF) and non-CF bronchiectasis (NCFB). However, there is no unified practice to process sputa from collection to analysis, which can lead to highly variable, and sometimes inconsistent results. The main objective of this study is to bring light into the handling of sputum samples to establish a standardised and robust protocol before rheological measurements. Sputum collected from 22 CF and 10 NCFB adults, was divided into control (vortexed and fresh: non-heated and non-frozen) and three treated conditions (either non-vortexed, heated or frozen). In addition, 6 CF expectorations were used to study the dynamics of ageing over 24 h. Sputum's mechanical properties were measured with a rotational rheometer to obtain their properties at rest, elastic ([Formula: see text]) and viscous moduli ([Formula: see text]), and at the onset of flow, critical deformation ([Formula: see text]) and critical stress ([Formula: see text]). We demonstrate that heating sputum is completely destructive while freezing sputa at [Formula: see text] has no discernible effect on their rheology. We also show that the variability of rheological measurements largely resulted from the sample's macroscopic heterogeneity, and can be greatly reduced by non-destructive vortex homogenisation. Finally, we observed contrasted ageing effects as a fonction of purulence: while the viscoelasticity of purulent samples reduced by half within 6 h after collection, semi-purulent samples did not evolve. These results guide towards a robust unified protocol for simple sputum handling in rheometry. We therefore suggest to vortex and snap freeze sputum samples immediately after collection when direct testing is not possible.

The effects of benralizumab on airway geometry and dynamics in severe eosinophilic asthma: a single-arm study design exploring a functional respiratory imaging approach

BACKGROUND

Severe eosinophilic asthma (SEA) is characterised by elevated blood/sputum eosinophil counts and airway inflammation, which can lead to mucus plug-mediated airway obstruction, increased exacerbation frequency, declines in lung function, and death. Benralizumab targets the alpha-subunit of the interleukin-5 receptor found on eosinophils, leading to rapid and near complete eosinophil depletion. This is expected to result in reduced eosinophilic inflammation, reduced mucus plugging and improved airway patency and airflow distribution.

METHODS

BURAN is an interventional, single-arm, open-label, uncontrolled, prospective, multicentre study during which participants will receive three 30 mg subcutaneous doses of benralizumab at 4-week intervals. This study will use functional respiratory imaging (FRI), a novel, quantitative method of assessing patients' lung structure and function based on detailed, three-dimensional models of the airways, with direct comparison of images taken at Weeks 0 and 13. Patients aged ≥ 18 years with established SEA who may be receiving oral corticosteroids and/or other asthma controller medications, who are inadequately controlled on inhaled corticosteroid-long-acting β₂-agonist therapies and who have had ≥ 2 asthma exacerbations in the previous 12 months will be included. The objectives of BURAN are to describe changes in airway geometry and dynamics, measured by specific image-based airway volume and other FRI endpoints, following benralizumab therapy. Outcomes will be evaluated using descriptive statistics. Changes in FRI parameters, mucus plugging scores and central/peripheral ratio will be quantified as mean percent change from baseline (Week 0) to Week 13 (± 5 days) and statistical significance will be evaluated using paired t-tests. Relationships between FRI parameters/mucus plugging scores and conventional lung function measurements at baseline will be assessed with linear regression analyses for associations between outcomes, scatterplots to visualise the relationship, and correlation coefficients (Spearman's rank and Pearson's) to quantify the strength of these associations.

CONCLUSIONS

The BURAN study will represent one of the first applications of FRI-a novel, non-invasive, highly sensitive method of assessing lung structure, function and health-in the field of biologic respiratory therapies. Findings from this study will increase understanding of cellular-level eosinophil depletion mechanisms and improvements in lung function and asthma control following benralizumab treatment. Trial registration EudraCT: 2022-000152-11 and NCT05552508.

A novel thiol-saccharide mucolytic for the treatment of muco-obstructive lung diseases

BACKGROUND

Mucin disulfide cross-links mediate pathologic mucus formation in muco-obstructive lung diseases. MUC-031, a novel thiol-modified carbohydrate compound, cleaves disulfides to cause mucolysis. The aim of this study was to determine the mucolytic and therapeutic effects of MUC-031 in sputum from patients with cystic fibrosis (CF) and mice with muco-obstructive lung disease (βENaC-Tg mice).

METHODS

We compared the mucolytic efficacy of MUC-031 and existing mucolytics (N-acetylcysteine (NAC) and recombinant human deoxyribonuclease I (rhDNase)) using rheology to measure the elastic modulus (G') of CF sputum, and we tested effects of MUC-031 on airway mucus plugging, inflammation and survival in βENaC-Tg mice to determine its mucolytic efficacy in vivo.

RESULTS

In CF sputum, compared to the effects of rhDNase and NAC, MUC-031 caused a larger decrease in sputum G', was faster in decreasing sputum G' by 50% and caused mucolysis of a larger proportion of sputum samples within 15 min of drug addition. Compared to vehicle control, three treatments with MUC-031 in 1 day in adult βENaC-Tg mice decreased airway mucus content (16.8±3.2 versus 7.5±1.2 nL·mm-2, p<0.01) and bronchoalveolar lavage cells (73 833±6930 versus 47 679±7736 cells·mL-1, p<0.05). Twice-daily treatment with MUC-031 for 2 weeks also caused decreases in these outcomes in adult and neonatal βENaC-Tg mice and reduced mortality from 37% in vehicle-treated βENaC-Tg neonates to 21% in those treated with MUC-031 (p<0.05).

CONCLUSION

MUC-031 is a potent and fast-acting mucolytic that decreases airway mucus plugging, lessens airway inflammation and improves survival in βENaC-Tg mice. These data provide rationale for human trials of MUC-031 in muco-obstructive lung diseases.

Relationship Between Intra-Abdominal pressure and microaspiration of gastric contents in critically ill mechanically ventilated patients

The relationship between increased intra-abdominal pressure (IAP) and microaspiration of oro-gastric content in mechanically-ventilated patients has not yet been established. Microaspiration is proposed as one of the causes of ventilator-associated pneumonia (VAP). We aimed to investigate whether mechanically-ventilated patients with increased IAP present evidence of lung microaspiration by assessing pepsin levels in bronchial secretions and evaluated the relationship between pepsin and VAP. 68 mechanically-ventilated patients and 10 control subjects were recruited from an academic ICU in Greece. IAP, pH, pepsin and total protein levels, in bronchial secretions, were assessed within 14 days. Patients underwent assessment for timely VAP diagnosis based on clinical, radiological and laboratory criteria. Pepsin and total protein levels were significantly elevated in patients compared to controls. Pepsin values correlated significantly with IAP (r = 0.61, ***p < 0.001). Multivariate regression analysis showed that IAP was an independent risk factor for increased pepsin values in bronchial secretions [OR95%CI 1.463(1.061-1.620), *p = 0.014]. Pepsin values were higher in patients with VAP, while IAP was independently associated with VAP. There was an indication towards increased VAP in patients with increased pepsin. In conclusion, our results show that pepsin in bronchial secretions may be elevated when IAP is increased, indicating microaspiration and potentially VAP.

Airway mucus in pulmonary diseases: Muco-adhesive and muco-penetrating particles to overcome the airway mucus barriers

Airway mucus is a complex viscoelastic gel that provides a defensive physical barrier and shields the airway epithelium by trapping inhaled foreign pathogens and facilitating their removal via mucociliary clearance (MCC). In patients with respiratory diseases, such as chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), non-CF bronchiectasis, and asthma, an increase in crosslinking and physical entanglement of mucin polymers as well as mucus dehydration often alters and typically reduces mucus mesh network pore size, which reduces neutrophil migration, decreases pathogen capture, sustains bacterial infection, and accelerates lung function decline. Conventional aerosol particles containing hydrophobic drugs are rapidly captured and removed by MCC. Therefore, it is critical to design aerosol delivery systems with the appropriate size and surface chemistry that can improve drug retention and absorption with the goal of increased efficacy. Biodegradable muco-adhesive particles (MAPs) and muco-penetrating particles (MPPs) have been engineered to achieve effective pulmonary delivery and extend drug residence time in the lungs. MAPs can be used to target mucus as they get trapped in airway mucus by steric obstruction and/or adhesion. MPPs avoid muco-adhesion and are designed to have a particle size smaller than the mucus network, enhancing lung retention of particles as well as transport to the respiratory epithelial layer and drug absorption. In this review, we aim to provide insight into the composition of airway mucus, rheological characteristics of airway mucus in healthy and diseased subjects, the most recent techniques to study the flow dynamics and particle diffusion in airway mucus (in particular, multiple particle tracking, MPT), and the advancements in engineering MPPs that have contributed to improved airway mucus penetration, lung distribution, and retention.

The Pathology of Asthma: What Is Obstructing Our View?

Despite the advent of sophisticated and efficient new biologics to treat inflammation in asthma, the disease persists. Even following treatment, many patients still experience the well-known symptoms of wheezing, shortness of breath, and coughing. What are we missing? Here we examine the evidence that mucus plugs contribute to a substantial portion of disease, not only by physically obstructing the airways but also by perpetuating inflammation. In this way, mucus plugs may act as an immunogenic stimulus even in the absence of allergen or with the use of current therapeutics. The alterations of several parameters of mucus biology, driven by type 2 inflammation, result in sticky and tenacious sputum, which represents a potent threat, first due to the difficulties in expectoration and second by acting as a platform for viral, bacterial, or fungal colonization that allows exacerbations. Therefore, in this way, mucus plugs are an overlooked but critical feature of asthmatic airway disease.

Modeling mucus physiology and pathophysiology in human organs-on-chips

The surfaces of human internal organs are lined by a mucus layer that ensures symbiotic relationships with commensal microbiome while protecting against potentially injurious environmental chemicals, toxins, and pathogens, and disruption of this layer can contribute to disease development. Studying mucus biology has been challenging due to the lack of physiologically relevant human in vitro models. Here we review recent progress that has been made in the development of human organ-on-a-chip microfluidic culture models that reconstitute epithelial tissue barriers and physiologically relevant mucus layers with a focus on lung, colon, small intestine, cervix and vagina. These organ-on-a-chip models that incorporate dynamic fluid flow, air-liquid interfaces, and physiologically relevant mechanical cues can be used to study mucus composition, mechanics, and structure, as well as investigate its contributions to human health and disease with a level of biomimicry not possible in the past.

MUC5B mobilizes and MUC5AC spatially aligns mucociliary transport on human airway epithelium

Secreted mucus is a frontline defense against respiratory infection, enabling the capture and swift removal of infectious or irritating agents from the lungs. Airway mucus is composed of two mucins: mucin 5B (MUC5B) and 5AC (MUC5AC). Together, they form a hydrogel that can be actively transported by cilia along the airway surface. In chronic respiratory diseases, abnormal expression of these mucins is directly implicated in dysfunctional mucus clearance. Yet, the role of each mucin in supporting normal mucus transport remains unclear. Here, we generate human airway epithelial tissue cultures deficient in either MUC5B or MUC5AC to understand their individual contributions to mucus transport. We find that MUC5B and MUC5AC deficiency results in impaired and discoordinated mucociliary transport, respectively, demonstrating the importance of each mucin to airway clearance.

Mucus-Inspired Dynamic Hydrogels: Synthesis and Future Perspectives

Mucus hydrogels at biointerfaces are crucial for protecting against foreign pathogens and for the biological functions of the underlying cells. Since mucus can bind to and host both viruses and bacteria, establishing a synthetic model system that can emulate the properties and functions of native mucus and can be synthesized at large scale would revolutionize the mucus-related research that is essential for understanding the pathways of many infectious diseases. The synthesis of such biofunctional hydrogels in the laboratory is highly challenging, owing to their complex chemical compositions and the specific chemical interactions that occur throughout the gel network. In this perspective, we discuss the basic chemical structures and diverse physicochemical interactions responsible for the unique properties and functions of mucus hydrogels. We scrutinize the different approaches for preparing mucus-inspired hydrogels, with specific examples. We also discuss recent research and what it reveals about the challenges that must be addressed and the opportunities to be considered to achieve desirable de novo synthetic mucus hydrogels.

An optimized protocol for assessment of sputum macrorheology in health and muco-obstructive lung disease

Background: Airway mucus provides important protective functions in health and abnormal viscoelasticity is a hallmark of muco-obstructive lung diseases such as cystic fibrosis (CF). However, previous studies of sputum macrorheology from healthy individuals and patients with CF using different experimental protocols yielded in part discrepant results and data on a systematic assessment across measurement settings and conditions remain limited.

Objectives: The aim of this study was to develop an optimized and reliable protocol for standardized macrorheological measurements of airway mucus model systems and native human sputum from healthy individuals and patients with muco-obstructive lung disease.

Methods: Oscillatory rheological shear measurements were performed using bovine submaxillary mucin (BSM) at different concentrations (2% and 10% solids) and sputum samples from healthy controls (n = 10) and patients with CF (n = 10). Viscoelastic properties were determined by amplitude and frequency sweeps at 25°C and 37°C with or without solvent trap using a cone-plate geometry.

Results: Under saturated atmosphere, we did not observe any temperature-dependent differences in 2% and 10% BSM macrorheology, whereas in the absence of evaporation control 10% BSM demonstrated a significantly higher viscoelasticity at 37°C. Similarly, during the measurements without evaporation control at 37°C we observed a substantial increase in the storage modulus G′ and the loss modulus G″ of the highly viscoelastic CF sputum but not in the healthy sputum.

Conclusion: Our data show systematically higher viscoelasticity of CF compared to healthy sputum at 25°C and 37°C. For measurements at the higher temperature using a solvent trap to prevent evaporation is essential for macrorheological analysis of mucus model systems and native human sputum. Another interesting finding is that the viscoelastic properties are not much sensitive to the applied experimental deformation and yield robust results despite their delicate consistency. The optimized protocol resulting from this work will facilitate standardized quantitative assessment of abnormalities in viscoelastic properties of airway mucus and response to muco-active therapies in patients with CF and other muco-obstructive lung diseases.

Mucoadhesive, Antibacterial, and Reductive Nanogels as a Mucolytic Agent for Efficient Nebulized Therapy to Combat Allergic Asthma

Asthma is an intractable disease involving the infiltration of inflammatory cells and mucus plugging. Despite small molecular mucolytics having the ability to break the disulfide bonds of mucins, offering a potential way to overcome the airflow obstruction and airway infection, these mucolytics have limited therapeutic effects in vivo. Therefore, in this work, arginine-grafted chitosan (CS-Arg) is ionically cross-linked with tris(2-carboxyethyl)phosphine (TCEP) to obtain nanogels as a mucolytic agent. The positively charged nanogels effectively inhibit the formation of large aggregates of mucin in vitro, probably thanks to the formation of an ionic interaction between CS-Arg and mucin, as well as the breakage of disulfide bonds in mucin by the reductive TCEP. Moreover, the nanogels show good cytocompatibility at concentrations up to 5 mg mL^-1, exhibiting effective inhibitory effects against the proliferation of both Staphylococcus aureus and Escherichia coli at 5 mg mL^-1. After the administration of the nanogels by nebulization into a Balb/c mouse model with allergic asthma, they can efficiently reduce the mucus obstruction in bronchioles and alveoli and relieve airway inflammation. Therefore, these CS-Arg/TCEP nanogels potentially represent a promising mucolytic agent for the efficient treatment of allergic asthma and other muco-obstructive diseases.

Pulmonary delivery nanomedicines towards circumventing physiological barriers: Strategies and characterization approaches

Pulmonary delivery of nanomedicines is very promising in lung local disease treatments whereas several physiological barriers limit its application via the interaction with inhaled nanomedicines, namely bio-nano interactions. These bio-nano interactions may affect the pulmonary fate of nanomedicines and impede the distribution of nanomedicines in its targeted region, and subsequently undermine the therapeutic efficacy. Pulmonary diseases are under worse scenarios as the altered physiological barriers generally induce stronger bio-nano interactions. To mitigate the bio-nano interactions and regulate the pulmonary fate of nanomedicines, a number of manipulating strategies were established based on size control, surface modification, charge tuning and co-delivery of mucolytic agents. Visualized and non-visualized characterizations can be employed to validate the robustness of the proposed strategies. This review provides a guiding overview of the physiological barriers affecting the in vivo fate of inhaled nanomedicines, the manipulating strategies, and the validation methods, which will assist with the rational design and application of pulmonary nanomedicine.

Asthma and Post-Asthmatic Fibrosis: A Search for New Promising Molecular Markers of Transition from Acute Inflammation to Pulmonary Fibrosis

Asthma is a heterogeneous pulmonary disorder, the progression and chronization of which leads to airway remodeling and fibrogenesis. To understand the molecular mechanisms of pulmonary fibrosis development, key genes forming the asthma-specific regulome and involved in lung fibrosis formation were revealed using a comprehensive bioinformatics analysis. The bioinformatics data were validated using a murine model of ovalbumin (OVA)-induced asthma and post-asthmatic fibrosis. The performed analysis revealed a range of well-known pro-fibrotic markers (Cat, Ccl2, Ccl4, Ccr2, Col1a1, Cxcl12, Igf1, Muc5ac/Muc5b, Spp1, Timp1) and a set of novel genes (C3, C3ar1, Col4a1, Col4a2, Cyp2e1, Fn1, Thbs1, Tyrobp) mediating fibrotic changes in lungs already at the stage of acute/subacute asthma-driven inflammation. The validation of genes related to non-allergic bleomycin-induced pulmonary fibrosis on asthmatic/fibrotic lungs allowed us to identify new universal genes (Col4a1 and Col4a2) associated with the development of lung fibrosis regardless of its etiology. The similarities revealed in the expression profiles of nodal fibrotic genes between asthma-driven fibrosis in mice and nascent idiopathic pulmonary fibrosis in humans suggest a tight association of identified genes with the early stages of airway remodeling and can be considered as promising predictors and early markers of pulmonary fibrosis.

Mucus-producing epithelial models for investigating the activity of gene delivery systems in the lung

Inhaled transfection particles have to penetrate the mucus layer lining the airways to successfully deliver their therapeutic nucleic acid payload to target cells in the underlying epithelium. However, the in vitro models used for evaluating gene carrier efficiency often disregard this viscous defensive barrier. In this study, the two mucus-secreting cell lines NCI-H292 and Calu-3 were selected to develop a series of epithelial models displaying gradual mucus production. In NCI-H292 models, a gradual increase in the MUC5AC mucin was obtained after cell exposure to inducers. In Calu-3 models, MUC5AC production increased as a function of culture duration (3, 7, 14 days) at the air-liquid interface (ALI). Six DOPC-derived cationic lipids were designed and their pDNA delivery activity was evaluated to validate these cellular models. The strongest impairment of the lipid delivery activity was observed in the Calu-3 14-d ALI model. The MUC5AC production in this model was the greatest and the mucus layer was 20 µm thick. The mucus exhibited a solid viscoelastic behaviour, and represented a major hindrance to lipoplex diffusion. The Calu-3 14-d ALI model will be highly useful for accurate evaluation of gene carriers intended for airway administration and characterization of their interactions with the mucus.

A bioinspired synthetic soft hydrogel for the treatment of dry eye

Natural soft hydrogels are unique elastic soft materials utilized by living organisms for protecting delicate tissues. Under a theoretical framework derived from the Blob model, we chemically crosslinked high molecular weight hyaluronic acid at a concentration close to its overlap concentration (c*), and created synthetic soft hydrogels that exhibited unique rheological properties similar to a natural soft hydrogel: being dominantly elastic under low shear stress while being viscous when the stress is above a small threshold. We explored a potential application of the hyaluronic acid-based soft hydrogel as a long-acting ocular surface lubricant and evaluated its therapeutic effects for dry eye. The soft hydrogel was found to be biocompatible after topical instillation on experimental animals' and companion dogs' eyes. In a canine clinical study, twice-a-day ocular instillation of the soft hydrogel in combination with cyclosporine for 1 month improved the clinical signs in more than 65% of dog patients previously unresponsive to cyclosporine treatment.

Forgotten but not gone: Particulate matter as contaminations of mucosal systems

A decade ago, environmental issues, such as air pollution and the contamination of the oceans with microplastic, were prominently communicated in the media. However, these days, political topics, as well as the ongoing COVID-19 pandemic, have clearly taken over. In spite of this shift in focus regarding media representation, researchers have made progress in evaluating the possible health risks associated with particulate contaminations present in water and air. In this review article, we summarize recent efforts that establish a clear link between the increasing occurrence of certain pathological conditions and the exposure of humans (or animals) to airborne or waterborne particulate matter. First, we give an overview of the physiological functions mucus has to fulfill in humans and animals, and we discuss different sources of particulate matter. We then highlight parameters that govern particle toxicity and summarize our current knowledge of how an exposure to particulate matter can be related to dysfunctions of mucosal systems. Last, we outline how biophysical tools and methods can help researchers to obtain a better understanding of how particulate matter may affect human health. As we discuss here, recent research has made it quite clear that the structure and functions of those mucosal systems are sensitive toward particulate contaminations. Yet, our mechanistic understanding of how (and which) nano- and microparticles can compromise human health via interacting with mucosal barriers is far from complete.

The role of eosinophils in sepsis and acute respiratory distress syndrome: a scoping review

PURPOSE

Septic shock and acute respiratory distress syndrome (ARDS) are characterized by a dysregulated immune host response that may respond to steroid therapy. Eosinophils contribute to type 2 inflammation that often responds to steroid therapy; their role in immune dysregulation and outcomes in sepsis and ARDS is unclear.

SOURCE

A systematic search of Cochrane Library, MEDLINE, and EMBASE was performed from inception to 9 September 2020. The search comprised the following terms: eosinophils, sepsis, septic shock, and ARDS. Two reviewers independently screened abstracts and texts and extracted data on disease severity and clinical outcomes.

PRINCIPAL FINDINGS

Thirty-nine studies were identified: 30 evaluated serum eosinophil count in sepsis, one evaluated eosinophil activity in sepsis, three assessed bronchoalveolar lavage (BAL) eosinophil count in ARDS, four assessed eosinophil activity in ARDS, and one assessed peripheral eosinophil count in ARDS. Eleven studies showed an association between eosinopenia and sepsis, and eight studies found persistent eosinopenia at > 48 hr of intensive care unit admission to predict mortality and readmission in septic patients. Three studies found BAL eosinophil count to be low in ARDS, although one found that levels rose in late-phase ARDS. Three studies found eosinophil activity markers in BAL to be high in ARDS and correlate with ARDS severity.

CONCLUSION

Persistent peripheral eosinopenia is a marker of bacterial sepsis and is independently associated with poor outcomes. Bronchoalveolar lavage eosinophil counts are low in early-phase ARDS, but increase in late-phase ARDS, while elevated markers of eosinophil activity correlate with ARDS severity. Further studies understanding the mechanisms leading to eosinopenia in sepsis and increased eosinophil activity in ARDS are needed.

Modeling Airway Dysfunction in Asthma Using Synthetic Mucus Biomaterials

As asthma worsens, occlusion of airways with mucus significantly contributes to airflow obstruction and reduced lung function. Recent evidence from clinical studies has shown mucus obtained from adults and children with asthma possesses altered mucin composition. However, how these changes alter the functional properties of the mucus gel is not yet fully understood. To study this, we have engineered a synthetic mucus biomaterial to closely mimic the properties of native mucus in health and disease. We demonstrate that this model possesses comparable biophysical and transport properties to native mucus ex vivo collected from human subjects and in vitro isolated from human airway epithelial (HAE) tissue cultures. We found by systematically varying mucin composition that mucus gel viscoelasticity is enhanced when predominantly composed of mucin 5AC (MUC5AC), as is observed in asthma. As a result, asthma-like synthetic mucus gels are more slowly transported on the surface of HAE tissue cultures and at a similar rate to native mucus produced by HAE cultures stimulated with type 2 cytokine IL-13, known to contribute to airway inflammation and MUC5AC hypersecretion in asthma. We also discovered that the barrier function of asthma-like synthetic mucus toward influenza A virus was impaired as evidenced by the increased frequency of infection in MUC5AC-rich hydrogel-coated HAE cultures. Together, this work establishes a biomaterial-based approach to understand airway dysfunction in asthma and related muco-obstructive lung diseases.

Human Laryngeal Mucus from the Vocal Folds: Rheological Characterization by Particle Tracking Microrheology and Oscillatory Shear Rheology

Mucus consistency affects voice physiology and is connected to voice disorders. Nevertheless, the rheological characteristics of human laryngeal mucus from the vocal folds remain unknown. Knowledge about mucus viscoelasticity enables fabrication of artificial mucus with natural properties, more realistic ex-vivo experiments and promotes a better understanding and improved treatment of dysphonia with regard to mucus consistency. We studied human laryngeal mucus samples from the vocal folds with two complementary approaches: 19 samples were successfully applied to particle tracking microrheology (PTM) and five additional samples to oscillatory shear rheology (OSR). Mucus was collected by experienced laryngologists from patients together with demographic data. The analysis of the viscoelasticity revealed diversity among the investigated mucus samples according to their rigidity (absolute G′ and G″). Moreover some samples revealed throughout solid-like character (G′ > G″), whereas some underwent a change from solid-like to liquid-like (G′ < G″). This led to a subdivision into three groups. We assume that the reason for the differences is a variation in the hydration level of the mucus, which affects the mucin concentration and network formation factors of the mucin mesh. The demographic data could not be correlated to the differences, except for the smoking behavior. Mucus of predominant liquid-like character was associated with current smokers.

EGFR activation-induced decreases in claudin1 promote MUC5AC expression and exacerbate asthma in mice

Claudin1 plays a critical role in maintaining the epithelial barrier, and mucus hypersecretion induced by epidermal growth factor receptor (EGFR) activation is a pivotal pathological feature of asthma. The relationship between claudin1 expression and mucus hypersecretion and EGFR activation is still poorly understood. In this report, we showed that claudin1 expression correlated with asthma stage, in both patients with asthma and in the house dust mite (HDM)-induced mouse asthma model. Claudin1 knockdown induced MUC5AC overexpression both in 16HBE cells and in mouse airways. In addition, claudin1 expression negatively correlated with asthma severity as demonstrated by significantly higher MUC5AC expression, more severe airway inflammation, and increased airway hyperreactivity in mouse lungs with claudin1 knockdown following HDM challenge. EGFR activation reduced claudin1 expression and increased MUC5AC expression, both in vitro and in vivo. Erlotinib alleviated murine allergic airway inflammation, restored claudin1 expression and decreased MUC5AC expression. These results suggest that EGFR activation-induced decreases in claudin1 promote goblet-cell metaplasia, and restoring claudin1 to maintain barrier integrity by EGFR antagonism may provide a novel therapeutic strategy for asthma.

Leveraging 3D Model Systems to Understand Viral Interactions with the Respiratory Mucosa

Respiratory viruses remain a significant cause of morbidity and mortality in the human population, underscoring the importance of ongoing basic research into virus-host interactions. However, many critical aspects of infection are difficult, if not impossible, to probe using standard cell lines, 2D culture formats, or even animal models. In vitro systems such as airway epithelial cultures at air-liquid interface, organoids, or 'on-chip' technologies allow interrogation in human cells and recapitulate emergent properties of the airway epithelium-the primary target for respiratory virus infection. While some of these models have been used for over thirty years, ongoing advancements in both culture techniques and analytical tools continue to provide new opportunities to investigate airway epithelial biology and viral infection phenotypes in both normal and diseased host backgrounds. Here we review these models and their application to studying respiratory viruses. Furthermore, given the ability of these systems to recapitulate the extracellular microenvironment, we evaluate their potential to serve as a platform for studies specifically addressing viral interactions at the mucosal surface and detail techniques that can be employed to expand our understanding.

Mucin Biopolymers and Their Barrier Function at Airway Surfaces

In the lung, the airway epithelium produces secreted and tethered mucin biopolymers to form a mucus hydrogel layer and a surface-attached polymer brush layer. These layers work in concert to facilitate the cilia-mediated transport of mucus for the capture and clearance of inhaled materials to prevent lung damage. The mechanisms by which mucin biopolymers protect the lung from injury have been an intense area of study in airway biology for the past several decades. In this feature article, we will discuss how airway mucins achieve these protective barrier functions. We will present the key findings, rooted in polymer and surface science, that have aided in understanding mucin barrier function. In addition, we will describe how this work may influence the design of nanoparticles to overcome the mucus barrier to effective drug delivery.

An anti-siglec-8 antibody depletes sputum eosinophils from asthmatic subjects and inhibits lung mast cells

BACKGROUND

Sialic acid-binding immunoglobulin-like lectin (Siglec)-8 is expressed on mast cells and eosinophils, but information about Siglec-8 expression and function in the lung is limited. A humanized antibody, AK002, targeting Siglec-8 is undergoing development for treatment of diseases associated with mast cell and eosinophil-driven inflammation.

OBJECTIVE

To characterize Siglec-8 expression in the airway in asthma and determine whether antibodies that target Siglec-8 (S8mAbs) can decrease airway eosinophils in asthma or inhibit lung mast cell activation.

METHODS

Gene expression profiling and flow cytometry were used to characterize Siglec-8 expression in sputum cells from stable asthma. An antibody-dependent cellular cytotoxicity (ADCC) assay was used to determine whether an S8mAb can decrease eosinophils in sputum from asthma patients ex vivo. A mast cell activation assay was used to determine whether an S8mAb can inhibit mast cell activation in human lung tissue ex vivo.

RESULTS

Gene expression for Siglec-8 is increased in sputum cells in asthma and correlates with gene expression for eosinophils and mast cells. Gene expression for Siglec-8 is inversely and significantly correlated with measures of airflow obstruction in asthma patients. Siglec-8 is prominently expressed on the surface of eosinophils and mast cells in sputum. S8mAbs decrease eosinophils in sputum from patients with asthma and inhibit FcεR1-activated mast cells in lung tissues.

CONCLUSIONS AND CLINICAL RELEVANCE

Siglec-8 is highly expressed on eosinophils and mast cells in asthmatic sputum and targeting Siglec-8 with an antibody is a plausible strategy to decrease sputum eosinophils and inhibit lung mast cells in asthma.

More Than Just a Barrier: The Immune Functions of the Airway Epithelium in Asthma Pathogenesis

Allergic bronchial asthma is a chronic disease of the airways that is characterized by symptoms like respiratory distress, chest tightness, wheezing, productive cough, and acute episodes of broncho-obstruction. This symptom-complex arises on the basis of chronic allergic inflammation of the airway wall. Consequently, the airway epithelium is central to the pathogenesis of this disease, because its multiple abilities directly have an impact on the inflammatory response and thus the formation of the disease. In turn, its structure and functions are markedly impaired by the inflammation. Hence, the airway epithelium represents a sealed, self-cleaning barrier, that prohibits penetration of inhaled allergens, pathogens, and other noxious agents into the body. This barrier is covered with mucus that further contains antimicrobial peptides and antibodies that are either produced or specifically transported by the airway epithelium in order to trap these particles and to remove them from the body by a process called mucociliary clearance. Once this first line of defense of the lung is overcome, airway epithelial cells are the first cells to get in contact with pathogens, to be damaged or infected. Therefore, these cells release a plethora of chemokines and cytokines that not only induce an acute inflammatory reaction but also have an impact on the alignment of the following immune reaction. In case of asthma, all these functions are impaired by the already existing allergic immune response that per se weakens the barrier integrity and self-cleaning abilities of the airway epithelium making it more vulnerable to penetration of allergens as well as of infection by bacteria and viruses. Recent studies indicate that the history of allergy- and pathogen-derived insults can leave some kind of memory in these cells that can be described as imprinting or trained immunity. Thus, the airway epithelium is in the center of processes that lead to formation, progression and acute exacerbation of asthma.

Humoral First-Line Mucosal Innate Defence in vivo

Based on observations in vivo in guinea-pig and human airways, this review presents plasma exudation as non-sieved transmission of bulk plasma across an unperturbed mucosa that maintains its normal barrier functions. Several steps have led to the present understanding of plasma exudation as a non-injurious response to mucosal challenges. The implication of a swift appearance of all circulating multipotent protein systems (also including antimicrobial peptides that now are viewed as being exclusively produced by local cells) on challenged, but intact, mucosal surfaces cannot be trivial. Yet, involvement of early plasma exudation responses in innate mucosal immunology has dwelled below the radar. Admittedly, exploration of physiological plasma exudation mechanisms requires in vivo approaches beyond mouse studies. Plasma exudation also lacks the specificity that is a hallmark of biological revelations. These aspects separate plasma exudation from mainstream progress in immunology. The whole idea, presented here, thus competes with strong paradigms currently entertained in the accepted research front. The present focus on humoral innate immunity in vivo further deviates from most discussions, which concern cell-mediated innate defence. Indeed, plasma exudation has emerged as sole in vivo source of major mucosal defence proteins that now are viewed as local cell produce. In conclusion, this review highlights opportunities for complex actions and interactions provided by non-sieved plasma proteins/peptides on the surface of intact mucosal barriers in vivo.

Changes in airway diameter and mucus plugs in patients with asthma exacerbation

Background

Airway obstruction due to decreased airway diameter and increased incidence of mucus plugs has not been directly observed in asthma exacerbation. We studied the changes in the inner diameter of the airway (Din) and the frequency of mucus plugs by airway generation in patients with asthma exacerbation. We compared these patients to those in a stable phase using high-resolution computed tomography (HRCT).

Methods and findings

Thirteen patients with asthma were studied by HRCT during asthma exacerbation and in a stable period. The HRCT study was performed on patients who could safely hold their breath for a short while in a supine position 1 hour after initial treatment for asthma exacerbation. Using a curved multiplanar reconstruction (MPR) software, we reconstructed the longitudinal airway images and the images exactly perpendicular to the airway axis to measure the Din and mucus plugs from the second- (segmental) to sixth-generation bronchi in all segments of the lungs.The ratios of Din (exacerbation/stable) were 0.91(P = 0.016), 0.88 (P = 0.002), 0.83 (P = 0.001), 0.80 (P = 0.001), and 0.87 (NS) in the second-, third-, fourth-, fifth-, and sixth-generation bronchi, respectively. The percentages of airway obstruction due to mucus plugs were notably higher in the fourth- and fifth-generation bronchi (17.9%/18.1% in stable phase and 43.2%/45.9% in the exacerbation phase, respectively) than in the other generations of bronchi.

Conclusions

Among the bronchi examined, the fourth- and fifth-generation bronchi were significantly obstructed during asthma exacerbation compared with the stable phase in terms of a decreased airway diameter and mucus plugs.

Modulation of protective reflex cough by acute immune driven inflammation of lower airways in anesthetized rabbits

Chronic irritating cough in patients with allergic disorders may reflect behavioral or reflex response that is inappropriately matched to the stimulus present in the respiratory tract. Such dysregulated response is likely caused by sensory nerve damage driven by allergic mediators leading to cough hypersensitivity. Some indirect findings suggest that even acid-sensitive, capsaicin-insensitive A-δ fibers called “cough receptors” that are likely responsible for protective reflex cough may be modulated through immune driven inflammation. The aim of this study was to find out whether protective reflex cough is altered during acute allergic airway inflammation in rabbits sensitized to ovalbumin. In order to evaluate the effect of such inflammation exclusively on protective reflex cough, C-fiber mediated cough was silenced using general anesthesia. Cough provocation using citric acid inhalation and mechanical stimulation of trachea was realized in 16 ovalbumin (OVA) sensitized, anesthetized and tracheotomised rabbits 24h after OVA (OVA group, n = 9) or saline challenge (control group, n = 7). Number of coughs provoked by citric acid inhalation did not differ between OVA and control group (12,2 ±6,1 vs. 17,9 ± 6,9; p = 0.5). Allergic airway inflammation induced significant modulation of cough threshold (CT) to mechanical stimulus. Mechanically induced cough reflex in OVA group was either up-regulated (subgroup named “responders” CT: 50 msec (50–50); n = 5 p = 0.003) or down-regulated (subgroup named “non responders”, CT: 1200 msec (1200–1200); n = 4 p = 0.001) when compared to control group (CT: 150 msec (75–525)). These results advocate that allergen may induce longer lasting changes of reflex cough pathway, leading to its up- or down-regulation. These findings may be of interest as they suggest that effective therapies for chronic cough in allergic patients should target sensitized component of both, reflex and behavioral cough.

Development of new in vitro models of lung protease activity for investigating stability of inhaled biological therapies and drug delivery systems

Proteases play a vital role in lung health and are critically important to the metabolic clearance of inhaled protein-based therapeutics after inhalation. Surprisingly little is known about lung fluid protease composition and there is a consequent lack of biorelevant experimental models, which limits research and development in the burgeoning field of inhaled biologics. The aim of this study was to quantify proteases in human lung fluid and to use this data to design novel in vitro experimental models of lung lining fluid possessing biorelevant lung protease activity for use in biopharmaceutical stability studies. As a proof of concept, these novel models were used to investigate the effect of proteolytic activity on the stability of albumin nanoparticles, a biologic nanoparticle formulation widely investigated as a pulmonary drug delivery system. Bronchoalveolar lavage fluid was collected from healthy human volunteers and proteomic analysis was used to quantify the predominant proteases. Based on these data, four new lung protease models were constructed based on: (i) trypsin as a sole protease, (ii) dipeptidyl peptidase IV, cathepsin D, cathepsin H, and angiotensin converting enzyme in ratio and concentration to mimic the protease concentration in healthy lungs. Neutrophil elastase was used to model protease activity in inflammation. Albumin nanoparticles of 100 nm diameter remained intact over 48 h in phosphate buffered saline, but were degraded more rapidly in trypsin (50% reduction in 10 min) compared to the healthy lung protease model (50% reduction in 150 min). The addition of neutrophil elastase to the healthy lung protease model resulted in a similar, but more variable degradation profile. Nanoparticle degradation was associated with concomitant appearance of small fragments and aggregates. In conclusion, we have characterised the protease concentration in the lungs of healthy humans, designed models of lung protease activity and demonstrated their utility in studying albumin nanoparticle degradation. These methods and models have wide application to study the influence of proteases in lung disease, expression of proteases in respiratory cell culture models, stability of peptide and protein-based drugs and inhaled drug delivery systems.

Endotracheal tube mucus as a source of airway mucus for rheological study

Muco-obstructive lung diseases (MOLDs), like cystic fibrosis and chronic obstructive pulmonary disease, affect a spectrum of subjects globally. In MOLDs, the airway mucus becomes hyperconcentrated, increasing osmotic and viscoelastic moduli and impairing mucus clearance. MOLD research requires relevant sources of healthy airway mucus for experimental manipulation and analysis. Mucus collected from endotracheal tubes (ETT) may represent such a source with benefits, e.g., in vivo production, over canonical sample types such as sputum or human bronchial epithelial (HBE) mucus. Ionic and biochemical compositions of ETT mucus from healthy human subjects were characterized and a stock of pooled ETT samples generated. Pooled ETT mucus exhibited concentration-dependent rheologic properties that agreed across spatial scales with reported individual ETT samples and HBE mucus. We suggest that the practical benefits compared with other sample types make ETT mucus potentially useful for MOLD research.

Endotracheal tube mucus as a source of airway mucus for rheological study

Muco-obstructive lung diseases (MOLDs), like cystic fibrosis and chronic obstructive pulmonary disease, affect a spectrum of subjects globally. In MOLDs, the airway mucus becomes hyperconcentrated, increasing osmotic and viscoelastic moduli and impairing mucus clearance. MOLD research requires relevant sources of healthy airway mucus for experimental manipulation and analysis. Mucus collected from endotracheal tubes (ETT) may represent such a source with benefits, e.g., in vivo production, over canonical sample types such as sputum or human bronchial epithelial (HBE) mucus. Ionic and biochemical compositions of ETT mucus from healthy human subjects were characterized and a stock of pooled ETT samples generated. Pooled ETT mucus exhibited concentration-dependent rheologic properties that agreed across spatial scales with reported individual ETT samples and HBE mucus. We suggest that the practical benefits compared with other sample types make ETT mucus potentially useful for MOLD research.

Natural inhibitors on airway mucin: Molecular insight into the therapeutic potential targeting MUC5AC expression and production

Airway mucin overproduction is the hallmark risk factor of asthma, which is associated with the reduction of lung function. An aberrant mucin expression is responsible for airway obstruction due to its high viscous characteristics. Among the mucins discovered, MUC5AC is the prime mucin of airway epithelia. Nowadays, mucins induced asthma and chronic obstructive pulmonary disease (COPD) are a great concern all over the world. This review focuses on the effects of natural compounds that can be beneficial to explore new drugs to halt MUC5AC secretion and production in airway epithelial, and also their underlying molecular mechanisms based on recent studies. Several researchers are seeking natural sources to identify a new potent MUC5AC inhibitory agent for clinical applications, because of countable limitations of existing synthetic drugs. Currently, flavonoids, glycoside and steroids like natural compounds have acquired great attention due to their anti-inflammatory and mucoregulatory effects. Most importantly, many natural compounds have shown their potential effects as the modulator of mucin expression, secretion, and production. Therefore, targeting airway MUC5AC expression and production represents an auspicious area of research for the development of drugs against various respiratory diseases.

A Nanosensor Toolbox for Rapid, Label-Free Measurement of Airway Surface Liquid and Epithelial Cell Function

Ciliated lung epithelial cells and the airway surface liquid (ASL) comprise one of the body's most important protective systems. This system is finely tuned, and perturbations to ASL rheology, ASL depth, ASL pH, the transepithelial potential, and the cilia beat frequency are all associated with disease pathology. Further, these apparently distinct properties interact with each other in a complex manner. For example, changes in ASL rheology can result from altered mucin secretion, changes in ASL pH, or changes in ASL depth. Thus, one of the great challenges in trying to understand airway pathology is that the properties of the ASL/epithelial cell system need to be assessed near-simultaneously and without perturbing the sample. Here, we show that nanosensor probes mounted on a scanning ion conductance microscope make this possible for the first time, without any need for labeling. We also demonstrate that ASL from senescence-retarded human bronchial epithelial cells retains its native properties. Our results demonstrate that by using a nanosensor approach, it is possible to pursue faster, more accurate, more coherent, and more informative studies of ASL and airway epithelia in health and disease.

The enigmatic role of the neutrophil in asthma: Friend, foe or indifferent?

Whilst severe asthma has classically been categorized as a predominantly Th2-driven pathology, there has in recent years been a paradigm shift with the realization that it is a heterogeneous disease that may manifest with quite disparate underlying inflammatory and remodelling profiles. A subset of asthmatics, particularly those with a severe, corticosteroid refractory disease, present with a prominent neutrophilic component. Given the potential of neutrophils to impart extensive tissue damage and promote inflammation, it has been anticipated that these cells are closely implicated in the underlying pathophysiology of severe asthma. However, uncertainty persists as to why the neutrophil is present in the asthmatic lung and what precisely it is doing there, with evidence supporting its role as a protagonist of pathology being primarily circumstantial. Furthermore, our view of the neutrophil as a primitive, indiscriminate killer has evolved with the realization that neutrophils can exhibit a marked anti-inflammatory, pro-resolving and wound healing capacity. We suggest that the neutrophil likely exhibits pleiotropic and potentially conflicting roles in defining asthma pathophysiology-some almost certainly detrimental and some potentially beneficial-with context, timing and location all critical confounders. Accordingly, indiscriminate blockade of neutrophils with a broad sword approach is unlikely to be the answer, but rather we should first seek to understand their complex and multifaceted roles in the disease state and then target them with the same subtleties and specificity that they themselves exhibit.

Airways exudation of plasma macromolecules: Innate defense, epithelial regeneration, and asthma

This review discusses in vivo airway aspects of plasma exudation in relation to current views on epithelial permeability and epithelial regeneration in health and disease. Microvascular-epithelial exudation of bulk plasma proteins characteristically occurs in asthmatic patients, being especially pronounced in those with severe and exacerbating asthma. Healthy human and guinea pig airways challenged by noninjurious histamine-leukotriene–type autacoids also respond through prompt mucosal exudation of nonsieved plasma macromolecules. Contrary to current beliefs, epithelial permeability in the opposite direction (ie, absorption of inhaled molecules) has not been increased in patients with asthma and allergic rhinitis or in acutely exuding healthy airways. A slightly increased subepithelial hydrostatic pressure produces such unidirectional outward perviousness to macromolecules. Lack of increased absorption permeability in asthmatic patients can further be reconciled with occurrence of epithelial shedding, leaving small patches of denuded basement membrane. Counteracting escalating barrier breaks, plasma exudation promptly covers the denuded patches. Here it creates and sustains a biologically active barrier involving a neutrophil-rich, fibrin-fibronectin net. Furthermore, in the plasma-derived milieu, all epithelial cell types bordering the denuded patch dedifferentiate and migrate from all sides to cover the denuded basement membrane. However, this speedy epithelial regeneration can come at a cost. Guinea pig in vivo studies demonstrate that patches of epithelial denudation regeneration are exudation hot spots evoking asthma-like features, including recruitment/activation of granulocytes, proliferation of fibrocytes/smooth muscle cells, and basement membrane thickening. In conclusion, nonsieved plasma macromolecules can operate on the intact airway mucosa as potent components of first-line innate immunity responses. Exuded plasma also takes center stage in epithelial regeneration. When exaggerated, epithelial regeneration can contribute to the inception and development of asthma.

Meta-analysis of airway epithelium gene expression in asthma

Differential gene expression in the airway epithelium of patients with asthma versus controls has been reported in several studies. However, there is no consensus on which genes are reproducibly affected in asthma. We sought to identify a consensus list of differentially expressed genes (DEGs) using a meta-analysis approach.We identified eight studies with data that met defined inclusion criteria. These studies comprised 355 cases and 193 controls and involved sampling either bronchial or nasal epithelium. We conducted study-level analyses, followed by a meta-analysis. Likewise, we applied a meta-analysis framework to the results of study-level pathway enrichment.We identified 1273 DEGs, 431 of which had not been identified in previous studies. 450 DEGs exhibited large effect sizes and were robust to study population differences in age, sex, race/ethnicity, medication use, smoking status and exacerbations. The magnitude of differential expression of these 450 genes was highly similar in bronchial and nasal airway epithelia. Meta-analysis of pathway enrichment revealed a number of consistently dysregulated biological pathways, including putative transcriptional and post-transcriptional regulators.In total, we identified a set of genes that is consistently dysregulated in asthma, that links to known and novel biological pathways, and that will inform asthma subtype identification.

Mucus plugs in patients with asthma linked to eosinophilia and airflow obstruction

BACKGROUND

The link between mucus plugs and airflow obstruction has not been established in chronic severe asthma, and the role of eosinophils and their products in mucus plug formation is unknown.

METHODS

In clinical studies, we developed and applied a bronchopulmonary segment-based scoring system to quantify mucus plugs on multidetector computed tomography (MDCT) lung scans from 146 subjects with asthma and 22 controls, and analyzed relationships among mucus plug scores, forced expiratory volume in 1 second (FEV1), and airway eosinophils. Additionally, we used airway mucus gel models to explore whether oxidants generated by eosinophil peroxidase (EPO) oxidize cysteine thiol groups to promote mucus plug formation.

RESULTS

Mucus plugs occurred in at least 1 of 20 lung segments in 58% of subjects with asthma and in only 4.5% of controls, and the plugs in subjects with asthma persisted in the same segment for years. A high mucus score (plugs in ≥ 4 segments) occurred in 67% of subjects with asthma with FEV1 of less than 60% of predicted volume, 19% with FEV1 of 60%-80%, and 6% with FEV1 greater than 80% (P < 0.001) and was associated with marked increases in sputum eosinophils and EPO. EPO catalyzed oxidation of thiocyanate and bromide by H2O2 to generate oxidants that crosslink cysteine thiol groups and stiffen thiolated hydrogels.

CONCLUSION

Mucus plugs are a plausible mechanism of chronic airflow obstruction in severe asthma, and EPO-generated oxidants may mediate mucus plug formation. We propose an approach for quantifying airway mucus plugging using MDCT lung scans and suggest that treating mucus plugs may improve airflow in chronic severe asthma.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01718197, NCT01606826, NCT01750411, NCT01761058, NCT01761630, NCT01759186, NCT01716494, and NCT01760915.

FUNDING

NIH grants P01 HL107201, R01 HL080414, U10 HL109146, U10 HL109164, U10 HL109172, U10 HL109086, U10 HL109250, U10 HL109168, U10 HL109257, U10 HL109152, and P01 HL107202 and National Center for Advancing Translational Sciences grants UL1TR0000427, UL1TR000448, and KL2TR000428.

ATP12A promotes mucus dysfunction during Type 2 airway inflammation

Allergic airway disease is known to cause significant morbidity due to impaired mucociliary clearance, however the mechanism that leads to the mucus dysfunction is not entirely understood. Interleukin 13 (IL-13), a key mediator of Type 2 (T2) inflammation, profoundly alters the ion transport properties of airway epithelium. However, these electrophysiological changes cannot explain the thick, tenacious airway mucus that characterizes the clinical phenotype. Here we report that IL-13 dramatically increases the airway surface liquid (ASL) viscosity in cultured primary human bronchial epithelial cells and thereby inhibits mucus clearance. These detrimental rheological changes require ATP12A, a non-gastric H⁺/K⁺-ATPase that secretes protons into the ASL. ATP12A knockdown or inhibition prevented the IL-13 dependent increase in ASL viscosity but did not alter the ASL pH. We propose that ATP12A promotes airway mucus dysfunction in individuals with T2 inflammatory airway diseases and that ATP12A may be a novel therapeutic target to improve mucus clearance.