Muco-obstructive Lung Diseases Research Articles

The in vitro effect of nebulised hypertonic saline on human bronchial epithelium.

Inhaled hypertonic saline (HS) is an effective therapy for muco-obstructive lung diseases. However, the mechanism of action and principles pertinent to HS administration remain unclear.An in vitro system aerosolised HS to epithelial cells at rates comparable to in vivo conditions. Airway surface liquid (ASL) volume and cell height responses were measured by confocal microscopy under normal and hyperconcentrated mucus states.Aerosolised HS produced a rapid increase in ASL height and decrease in cell height. Added ASL volume was quickly reabsorbed following termination of nebulisation, although cell height did not recover within the same time frame. ASL volume responses to repeated HS administrations were blunted, but could be restored by a hypotonic saline bolus interposed between HS administrations. HS-induced ASL hydration was prolonged with hyperconcentrated mucus on the airway surface, with more modest reductions in cell volume.Aerosolised HS produced osmotically induced increases in ASL height that were limited by active sodium absorption and cell volume-induced reductions in cell water permeability. Mucus on airway surfaces prolonged the effect of HS via mucus-dependent osmotic forces, suggesting that the duration of action of HS is increased in patients with hyperconcentrated mucus.

Airway Mucin Concentration as a Marker of Chronic Bronchitis

BackgroundChronic obstructive pulmonary disease (COPD) is characterized by chronic bronchitic and emphysematous components. In one biophysical model, the concentration of mucin on the airway surfaces is hypothesized to be a key variable that controls mucus transport in healthy persons versus cessation of transport in persons with muco-obstructive lung diseases. Under this model, it is postulated that a high mucin concentration produces the sputum and disease progression that are characteristic of chronic bronchitis.MethodsWe characterized the COPD status of 917 participants from the Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS) using questionnaires administered to participants, chest tomography, spirometry, and examination of induced sputum. Total mucin concentrations in sputum were measured with the use of size-exclusion chromatography and refractometry. In 148 of these participants, the respiratory secreted mucins MUC5AC and MUC5B were quantitated by means of mass spectrometry. Data from chronic-bronchitis questionnaires and data on total mucin concentrations in sputum were also analyzed in an independent 94-participant cohort.ResultsMean (±SE) total mucin concentrations were higher in current or former smokers with severe COPD than in controls who had never smoked (3166±402 vs. 1515±152 μg per milliliter) and were higher in participants with two or more respiratory exacerbations per year than in those with zero exacerbations (4194±878 vs. 2458±113 μg per milliliter). The absolute concentrations of MUC5B and MUC5AC in current or former smokers with severe COPD were approximately 3 times as high and 10 times as high, respectively, as in controls who had never smoked. Receiver-operating-characteristic curve analysis of the association between total mucin concentration and a diagnosis of chronic bronchitis yielded areas under the curve of 0.72 (95% confidence interval [CI], 0.65 to 0.79) for the SPIROMICS cohort and 0.82 (95% CI, 0.73 to 0.92) for the independent cohort.ConclusionsAirway mucin concentrations may quantitate a key component of the chronic bronchitis pathophysiologic cascade that produces sputum and mediates disease severity. Studies designed to explore total mucin concentrations in sputum as a diagnostic biomarker and therapeutic target for chronic bronchitis appear to be warranted. (Funded by the National Heart, Lung, and Blood Institute and others.)

Airway mucus, inflammation and remodeling: emerging links in the pathogenesis of chronic lung diseases.

Airway mucus obstruction is a hallmark of many chronic lung diseases including rare genetic disorders such as cystic fibrosis (CF) and primary ciliary dyskinesia, as well as common lung diseases such as asthma and chronic obstructive pulmonary disease (COPD), which have emerged as a leading cause of morbidity and mortality worldwide. However, the role of excess airway mucus in the in vivo pathogenesis of these diseases remains poorly understood. The generation of mice with airway-specific overexpression of epithelial Na+ channels (ENaC), exhibiting airway surface dehydration (mucus hyperconcentration), impaired mucociliary clearance (MCC) and mucus plugging, led to a model of muco-obstructive lung disease that shares key features of CF and COPD. In this review, we summarize recent progress in the understanding of causes of impaired MCC and in vivo consequences of airway mucus obstruction that can be inferred from studies in βENaC-overexpressing mice. These studies confirm that mucus hyperconcentration on airway surfaces plays a critical role in the pathophysiology of impaired MCC, mucus adhesion and airway plugging that cause airflow obstruction and provide a nidus for bacterial infection. In addition, these studies support the emerging concept that excess airway mucus per se, probably via several mechanisms including hypoxic epithelial necrosis, retention of inhaled irritants or allergens, and potential immunomodulatory effects, is a potent trigger of chronic airway inflammation and associated lung damage, even in the absence of bacterial infection. Finally, these studies suggest that improvement of mucus clearance may be a promising therapeutic strategy for a spectrum of muco-obstructive lung diseases.

Generation and functional characterization of epithelial cells with stable expression of SLC26A9 Cl- channels.

Recent studies identified the SLC26A9 Cl(-) channel as a modifier and potential therapeutic target in cystic fibrosis (CF). However, understanding of the regulation of SLC26A9 in epithelia remains limited and cellular models with stable expression for biochemical and functional studies are missing. We, therefore, generated Fisher rat thyroid (FRT) epithelial cells with stable expression of HA-tagged SLC26A9 via retroviral transfection and characterized SLC26A9 expression and function using Western blotting, immunolocalization, whole cell patch-clamp, and transepithelial bioelectric studies in Ussing chambers. We demonstrate stable expression of SLC26A9 in transfected FRT (SLC26A9-FRT) cells on the mRNA and protein level. Immunolocalization and Western blotting detected SLC26A9 in different intracellular compartments and to a lesser extent at the cell surface. Whole cell patch-clamp recordings demonstrated significantly increased constitutive Cl(-) currents in SLC26A9-FRT compared with control-transduced FRT (Control-FRT) cells (P < 0.01). Similar, transepithelial measurements showed that the basal short circuit current was significantly increased in SLC26A9-FRT vs. Control-FRT cell monolayers (P < 0.01). SLC26A9-mediated Cl(-) currents were increased by cAMP-dependent stimulation (IBMX and forskolin) and inhibited by GlyH-101, niflumic acid, DIDS, and 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), as well as RNAi knockdown of WNK1 implicated in epithelial osmoregulation. Our results support that these novel epithelial cells with stable expression of SLC26A9 will be a useful model for studies of pharmacological regulation including the identification of activators of SLC26A9 Cl(-) channels that may compensate deficient cystic fibrosis transmembrane regulator (CFTR)-mediated Cl(-) secretion and serve as an alternative therapeutic target in patients with CF and potentially other muco-obstructive lung diseases.

On the Pathogenesis of Acute Exacerbations of Mucoobstructive Lung Diseases.

Mucoobstructive lung diseases have highlighted the importance of a proper description of the normal mucus clearance system. A useful description of the normal mucus clearance apparatus requires the presence of two gels on the airway surface (i.e., a mucus layer gel and a periciliary gel). Importantly, most mucoobstructive lung diseases are distributed heterogeneously in the lung, and exacerbations may reflect spread of the disease to previously normal areas. The spread may reflect disturbances in the balance of water between the two gel layers, producing heterogeneous mucus adhesion and infection within the lung. Ultimately, spread can produce losses of lung function that may be associated with acute exacerbation frequency.

IL-1 receptor anatagonist anakinra reduces neutrophilic airway inflammation in mice with cystic fibrosis-like lung disease

Hypoxic degeneration and necrosis of epithelial cells associated with airway mucus obstruction precedes neutrophilic airway inflammation in βENaC-overexpressing (βENaC-Tg) mice with cystic fibrosis (CF)-like lung disease (Mall MA et al., Am J Respir Crit Care Med., 2008). In many organs sterile neutrophilic inflammation is triggered by necrosis via release of Interleukin-1 alpha (IL-1α) and IL-1 receptor (IL-1R) signaling (Chen CJ et al., Nat Med., 2007). Recently we demonstrated that lack of IL-1R improved survival and reduced neutrophilic airway inflammation, structural lung damage and mucus obstruction in βENaC-Tg mice (Zhou-Suckow Z et al., Pediatr Pulmonol., Suppl 2013). In the present day, we hypothesized that treatment with the IL-1R antagonist anakinra may reduce neutrophilic airway inflammation and ameliorate CF-like lung disease in βENaC-Tg mice. To test this hypothesis, we treated 4 to 6 week old βENaC-Tg mice in established lung disease and wild-type littermates with anakinra (200 mg/kg body weight) or vehicle (NaCl 0.9%) alone by subcutaneous injection twice per day for one week. At the endpoint, we performed bronchoalveolar lavage (BAL) to determine differential cell counts and KC levels, and analyzed histology and morphometry for airway epithelial necrosis, airway mucus obstruction and emphysema. As expected from previous studies of βENaC-Tg mice with genetic deletion of IL-1R, treatment with anakinra had no effect on hypoxic epithelial degeneration. However, anakinra treatment significantly reduced neutrophilic inflammation and KC levels in BAL. Furthermore, mean linear intercepts and destructive index were also reduced by anakinra indicating less structural lung damage in βENaC-Tg mice. These results demonstrate that inhibition of IL-1R signalling provides an effective therapy of CF-like lung disease in mice and suggest anakinra as a potential anti-inflammatory therapy to limit neutrophilic inflammation and associated lung damage in patients with CF and potentially other muco-obstructive lung diseases.

WS06.5 SLC26A9 chloride channels: Generation and functional characterization of stably-overexpressing FRT epithelial cells

Objectives Previous findings in mice revealed that SLC26A9, a recently identified epithelial chloride channel, is essential for preventing airway obstruction associated with IL13-induced airway inflammation. These results suggest that SLC26A9 may be a promising alternative Cl − channel in mucoobstructive lung diseases [e.g. cystic fibrosis (CF)]. Thus, we functionally characterized a newly generated epithelial cell line with stable expression of SLC26A9 to investigate molecular regulation. Methods Fisher rat thyroid (FRT) cells were stably transduced with a HA-tagged SLC26A9 construct. Transepithelial Cl − currents were measured by applying a Cl − gradient in Ussing chambers. Whole-cell patch clamp experiments were performed. Results SLC26A9 expression in transduced FRT (FRT-SLC) cells was found at high levels. Transepithelial measurements revealed that the basal short circuit current (I sc ) was significantly increased in FRT-SLC (12.3±2.0 µA/cm 2 P 2 ) cell monolayers. CAMP (IBMX/forskolin)-stimulated Cl − secretion was significantly increased in FRT-SLC compared to FRT-CTL cells (ΔI sc = 4.9±0.5 vs. ΔI sc = 0.7±0.2 µA/cm 2 P − current in FRT-SLC cells and a similar inhibitor selectivity. Conclusion In FRT-SLC cells, SLC26A9 contributes to constitutive and cAMP-stimulated Cl − currents. This established epithelial cell model overexpressing SLC26A9 may be useful for further studies of the regulation and pharmacological activation of SLC26A9 as an alternative Cl − channel in CF.

On the pathogenesis of acute exacerbations of mucoobstructive lung diseases

On the pathogenesis of acute exacerbations of mucoobstructive lung diseases

Pulmonary hypoplasia: lung weight and radial alveolar count as criteria of diagnosis.

A working definition of pulmonary hypoplasia (PH) was established by retrospective assessment of lung growth both in recognised and hypothetical PH-associated conditions. Lung weight: body weight ratios (LW:BW) were calculated, and morphometry was determined by the radial alveolar count (RAC) (Emery and Mithal, 1960). Both parameters were reduced compared with those of normal controls in diaphragmatic hernia, anencephalus, anuric renal anomalies, chondrodystrophies, and osteogenesis inperfecta. Comparison of LW:BW ratio and RAC indicated that the RAC was the more reliable criterion of PH, LW:BW ratio of less than or equal to 0.012 (67%) of mean normal ratio) and/or RAC of less than or equal to 4.1 (75% of mean normal count) are suggested as diagnostic criteria of PH. Evidence of PH was incidentally discovered in a number of clinically unsuspected cases and retrospectively clarified the clinical and radiological findings. Routine assessment of lung growth should be an essential part of the neonatal necropsy.