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Background: Proteases have been shown to degrade airway mucin proteins and to damage the epithelium impairing mucociliary clearance. There are increased proteases in the COPD airway but changes in protease-antiprotease balance and mucin degradation have not been investigated during the course of a COPD exacerbation. We hypothesized that increased protease levels would lead to mucin degradation in acute COPD exacerbations., Methods: We measured neutrophil elastase (NE) and alpha 1 protease inhibitor (A1-PI) levels using immunoblotting, and conducted protease inhibitor studies, zymograms, elastin substrate assays and cigarette smoke condensate experiments to evaluate the stability of the gel-forming mucins, MUC5AC and MUC5B, before and 5-6 weeks after an acute pulmonary exacerbation of COPD (n = 9 subjects)., Results: Unexpectedly, mucin concentration and mucin stability were highest at the start of the exacerbation and restored to baseline after 6 weeks. Consistent with these data, immunoblots and zymograms confirmed decreased NE concentration and activity and increased A1-PI at the start of the exacerbation. After recovery there was an increase in NE activity and a decrease in A1-PI levels. In vitro, protease inhibitor studies demonstrated that serine proteases played a key role in mucin degradation. Mucin stability was further enhanced upon treating with cigarette smoke condensate (CSC)., Conclusion: There appears to be rapid consumption of secreted proteases due to an increase in antiproteases, at the start of a COPD exacerbation. This leads to increased mucin gel stability which may be important in trapping and clearing infectious and inflammatory mediators, but this may also contribute acutely to mucus retention.

The term bronchial hyperresponsiveness is generally used to describe a heightened airway smooth muscle bronchoconstrictor response measured by bronchoprovocation testing. However, the airway also responds to inflammation or bronchoprovocation with increased mucus secretion. We use the term "secretory hyperresponsiveness" to mean increased mucus secretion either intrinsically or in response to bronchoprovocation. This is not the same as retained phlegm or sputum. Unlike smooth muscle contraction, which is rapidly reversible using a bronchodilator, mucus hypersecretion produces airflow limitation that reverses more slowly and depends upon secretion clearance from the airway. Certain groups of patients appear to have greater mucus secretory response, including those with middle lobe syndrome, cough-dominant ("cough-variant") asthma, and severe asthma. Secretory hyperresponsiveness also is a component of forms of lung cancer associated with bronchorrhea. An extreme form of secretory hyperresponsiveness may lead to plastic bronchitis, a disease characterized by rigid branching mucus casts that obstruct the airway. Secretory hyperresponsiveness and mucus hypersecretion appear to be related to activation of the extracellular-regulated kinase 1/2, signaling through the epidermal growth factor receptor, or secretory phospholipases A2. Recognizing secretory hyperresponsiveness as a distinct clinical entity may lead to more effective and targeted therapy for these diseases.

Objective: It has been assumed that cystic fibrosis (CF) lung disease is due in part to abnormal airway mucus. Primary ciliary dyskinesia (PCD) is a form of bronchiectasis that is similar to CF in many ways but is caused by congenital defects in mucociliary clearance. Our objective was to compare the biophysical and transport properties of CF and PCD sputa in subjects matched for age and degree of lung function impairment., Design, Setting, Participants: PCD patients (n = 19; mean age, 9.5 +/- 3.0 years [+/- SD]; FEV1, 65.0 +/- 7.8 L) were recruited from the clinic at the Royal Brompton Hospital. Patients with CF (n = 30, mean age, 10.8 +/- 2.6 years; FEV1, 61.8 +/- 22.8 L) were identified from the Wake Forest University School of Medicine CF Center. Pulmonary function testing and sputum collection were performed as part of routine, scheduled clinic visits., Measurements: Pulmonary function was measured by spirometry, and sputum was collected during the pulmonary function test maneuver. Some patients were longitudinally assessed at visits during the course of 3 years. Sputum properties measured were dynamic viscoelasticity, wettability, cohesivity, interfacial (surface) tension, solids composition, DNA and interleukin (IL)-8 concentration, in vitro mucociliary transportability, and cough transportability., Results: Inflammation as measured by IL-8 concentration was three times greater in the PCD sputa (p < 0.0001). There were no significant differences in the sputum biophysical or transport properties comparing CF with PCD sputum., Conclusions: It is unlikely that established CF lung disease is principally due to abnormal sputum properties, and it is more likely that the biophysical and transport properties reflect disease severity regardless of whether bronchiectasis is due to CF or PCD.

It has been established that mucus hypersecretion and decreased mucus clearance contribute to the morbidity of chronic obstructive pulmonary disease (COPD). Indeed, the classic definition of chronic bronchitis relies on determining the frequency and duration of sputum expectoration. Despite the well recognized importance of this symptom, there are few therapies routinely used to decrease the sputum production or to improve clearance. There are fewer well conducted clinical trials of existing medications and this has led many regulatory agencies, notably the Food and Drug Administration (FDA), to refuse to register these medications or approve their sale. Similarly, airway clearance devices and chest physical therapy have not been well studied in COPD. Carefully conducted studies of interventions to improve airway clearance, similar to those done in cystic fibrosis (CF), may help us to identify effective therapies and possibly novel diagnostic tests for the management of COPD.

Cystic fibrosis (CF) is characterized by progressive airway obstruction. Although it has been postulated that this is due in part to mucus hypersecretion, there are no published data showing an increase in the gel-forming mucins MUC5AC or MUC5B in CF secretions. We used confocal microscopy to assess the amount of mucin-like glycoprotein and DNA in CF sputum and found more mucin in bronchitis sputum and a much greater amount of DNA in CF sputum. We then used antibodies to MUC5AC and MUC5B with Western gels and dot-blot to quantify mucin in sputum from 12 patients with CF and 11 subjects without lung disease. There was a 70% decrease in MUC5B and a 93% decrease in MUC5AC in CF sputum (P < 0.005 for both). We conclude that the vol/vol concentration of MUC5AC and MUC5B are decreased in the CF airways relative to normal mucus. This may be due to a relative increase in other components of sputum in the CF airway or to a primary defect in mucin secretion in CF.

Mucus clearance is the first line of pulmonary defense against inhaled irritants, microorganisms, and allergens. In health, the gel-forming mucins are the principal polymeric components of airway mucus but in cystic fibrosis (CF), the necrotic death of inflammatory and epithelial cells releases a network of copolymerized extracellular DNA and filamentous (F-) actin-producing secretions that are similar to pus and difficult to clear by cilia or airflow. The large amounts of F-actin in CF sputum suggested that thymosin β4 (Tβ4) or gelsolin could depolymerize the secondary polymer network of CF sputum. Dose-dependent CF sputum rheology and polymer structure were measured before and after the addition of excipient, dornase alfa, Tβ4, gelsolin, and Tβ4 or gelsolin with dornase for 30 min. Sputum was also incubated with Tβ4 30 μg/mL, gelsolin 10 μg/mL or excipient for 0, 5, 10, 15, 20, or 60 min. There was a dose-dependent decrease in cohesivity with Tβ4 and a time-dependent decrease in cohesivity at 30 μg/mL. With the combination of dornase alfa and Tβ4 at 1.5 μg/mL, there was a 65% decrease in elasticity ( P= 0.013). There was a time-dependent decrease in cohesivity ( P= 0.0004) and elasticity ( P= 0.047) with gelsolin and a dose-dependent fall in cohesivity ( P= 0.0008). An apparent synergy of Tβ4 or gelsolin on actin and dornase on DNA may be explained by the combined effect of actin depolymerization and DNA filament severing or by virtue of actin depolymerization increasing the effectiveness of dornase alfa. [ABSTRACT FROM AUTHOR]

Summary: Mucus accumulation in the lower airways is a key feature of cystic fibrosis (CF) lung disease. The major component of mucus in CF is not mucin derived from mucus producing cells but rather pus that includes viscous material such as polymerized DNA derived from degraded neutrophils. This has important implications for mucolytic therapy aiming to improve mucus clearance from the airways, since degradation of mucin may not be a suitable treatment strategy. In addition, thinning of secretions may not always be beneficial, since it may negatively affect certain aspects of mucus transport such as cough clearance. While inhaled N-acetylcysteine has been used as a mucolytic drug in CF for decades, there is little evidence that it has any beneficial effect. Dornase alfa has been shown to reduce pulmonary exacerbations and improve lung function and is currently the only mucolytic agent with proven efficacy in CF. Newer agents targeting other components of CF mucus, such as filamentous actin, are currently in development. Ultimately, drugs that are mucokinetic, which preserve viscoelasticity, rather than mucolytic may prove to be beneficial for CF lung disease in the future. [Copyright &y& Elsevier]