The role of airway secretions in COPD--clinical applications

Physiology and pathophysiology of human airway mucus

The mucus clearance system is the dominant mechanical host defense system of the human lung. Mucus is cleared from the lung by cilia and airflow, including both two-phase gas-liquid pumping and cough-dependent mechanisms, and mucus transport rates are heavily dependent on mucus concentration. Importantly, mucus transport rates are accurately predicted by the gel-on-brush model of the mucociliary apparatus from the relative osmotic moduli of the mucus and periciliary-glycocalyceal (PCL-G) layers. The fluid available to hydrate mucus is generated by transepithelial fluid transport. Feedback interactions between mucus concentrations and cilia beating, via purinergic signaling, coordinate Na+ absorptive vs Cl- secretory rates to maintain mucus hydration in health. In disease, mucus becomes hyperconcentrated (dehydrated). Multiple mechanisms derange the ion transport pathways that normally hydrate mucus in muco-obstructive lung diseases, e.g., cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), non-CF bronchiectasis (NCFB), and primary ciliary dyskinesia (PCD). A key step in muco-obstructive disease pathogenesis is the osmotic compression of the mucus layer onto the airway surface with the formation of adherent mucus plaques and plugs, particularly in distal airways. Mucus plaques create locally hypoxic conditions and produce airflow obstruction, inflammation, infection, and, ultimately, airway wall damage. Therapies to clear adherent mucus with hydrating and mucolytic agents are rational, and strategies to develop these agents are reviewed.

ICON: chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is a public health problem that has a significant socio-economic impact. Moreover, the complexity of this disease due to its heterogeneous nature based on the underlying pathophysiology - leading to different disease variants - further complicates our understanding and directions for the most appropriate targeted treatment strategies. Several International/national guidelines/position papers and/or consensus documents are available that present the current knowledge and treatment strategies for CRS. Yet there are many challenges to the management of CRS especially in the case of the more severe and refractory forms of disease. Therefore, the International Collaboration in Asthma, Allergy and Immunology (iCAALL), a collaboration between EAACI, AAAAI, ACAAI, and WAO, has decided to propose an International Consensus (ICON) on Chronic Rhinosinusitis. The purpose of this ICON on CRS is to highlight the key common messages from the existing guidelines, the differences in recommendations as well as the gaps in our current knowledge of CRS, thus providing a concise reference. In this document we discuss the definition of the disease, its relevance, pharmacoeconomics, pathophysiology, phenotypes and endotypes, genetics and risk factors, natural history and co-morbidities as well as clinical manifestations and treatment options in both adults and children comprising pharmacotherapy, surgical interventions and more recent biological approaches. Finally, we have also highlighted the unmet needs that wait to be addressed through future research.

Clinical application of expectorant therapy in chronic inflammatory airway diseases (Review)

Airway mucus hypersecretion is a significant clinical and pathological feature of chronic inflammatory airway diseases. Its clinical presentations include recurrent coughing and phlegm. Airway mucus is closely associated with the occurrence, development and prognosis of chronic inflammatory airway diseases and critically affects the lung function, quality of life, hospitalization rate and mortality of patients with chronic inflammatory airway diseases. Therefore, expectorant therapies targeting the potential mechanisms of mucus hypersecretion have been the focus of numerous studies. Conventional expectorants are mainly mucoactive medicines, including nausea-stimulating expectorants, mucolytics, mucokinetics, and proteases and nucleases. In addition, certain traditional Chinese herbal medicines and non-mucoactive agents, including muscarinic acetylcholine receptor antagonists, corticosteroids, leukotriene receptor antagonists and macrolide antibiotics, have also shown expectorant effects. Several novel medicines for expectorant therapy have emerged, including cholesterol-lowering statins, epidermal growth factor receptor tyrosine kinase inhibitors, phosphodiesterase-4 inhibitors, stanozolol, surfactants, flavonoids, tachykinin receptor antagonists, protease inhibitors, cytokine antagonists and purinergic agonists. With the increasing number of multidisciplinary studies, the effectiveness of expectorant therapy for the treatment of chronic inflammatory airway diseases has been confirmed. Therefore, the development of novel expectorants and the standardization of expectorant therapy are the direction and focus of future studies, thus benefiting patients who have a chronic inflammatory airway disease.

Managing older patients with coexistent asthma and chronic obstructive pulmonary disease: diagnostic and therapeutic challenges

Asthma and chronic obstructive pulmonary disease (COPD) are common obstructive airway diseases, especially among older people. These conditions are associated with a significant and increasing disease burden. The diagnosis and management of asthma and COPD in older populations are complex, and consequently clinicians are faced with many therapeutic and diagnostic challenges. Both aging and obstructive airway diseases are associated with complex co-morbidities and these coexisting illnesses confound management. Moreover, the age-related physiological changes that occur in the lungs may lead to airflow limitation, and this may be difficult to distinguish from an active disease state. In practice, management of asthma and COPD is informed by disease-specific clinical practice guidelines; however, most older people with these conditions are excluded from clinical trials that are designed to inform practice, creating major evidence gaps. Furthermore, seldom do clinical practice guidelines consider the complexities of management in older populations. The problems experienced by older people are complex and multifactorial and our approach to management must reflect these challenges. Opportunities exist to improve the management and outcomes for older people with obstructive airway disease and there is an urgent need for clinical trials to test management approaches in this population; current research must consider the challenges and evidence gaps that exist.

Role of Epithelial Cells in Chronic Inflammatory Lung Disease

Airborne pathogens entering the lungs first encounter the mucus layer overlaying epithelial cells as a first line of host defense [1, 2]. In addition to serving as the physical barrier to these toxic agents, intact epithelia also are major sources of various macromolecules including antimicrobial agents, antioxidants and antiproteases [3, 4] as well as proinflammatory cytokines and chemokines that initiate and amplify host defensive responses to these toxic agents [5]. Airway epithelial cells can be categorized as either ciliated or secretory [6]. Secretory cells, such as goblet cells and Clara cells, are responsible for the production and secretion of mucus along the apical epithelial surface and, in conjunction with ciliated cells, for the regulation of airway surface liquid viscosity. In addition, submucosal mucus glands connect to the airway lumen through a ciliated duct that propels mucins outward. These glands are present in the larger airways between bands of smooth muscle and cartilage. See Fig. 1.

Effect of verapamil on bronchial goblet cells of asthma: an experimental study on sensitized animals

INTRODUCTION

Goblet cell hyperplasia (GCH) and mucus hypersecretion in the airway is recognized as an important contributor to morbidity and mortality in asthma and COPD. Verapamil is a calcium channel blocker that binds to the alpha-subunit of L-type calcium channels and inhibits the mucin gene via the calmodulin and CaM kinase pathway. The objective of this study was to determine the in vivo effect of verapamil on GCH and eosinophilic inflammation in sensitized mice.

METHODS

Male BALB/c mice were sensitized to ovalbumin using the standard method. Two groups of animals were received verapamil via an intramuscular injection: 1-low dose (0.5 mg/kg/day for two weeks), 2-high dose (1.5 mg/kg/day for two weeks). Serum and bronchoalveolar lavage fluid (BALF) was collected and analyzed for inflammatory cells, interferon-γ and IL-4. The left lung was sent for histopathological evaluation, especially for periodic acid-Schiff (PAS), to identify goblet cells in the epithelium. The degree of inflammatory cell infiltration, including eosinophils, mucus plugging, and smooth muscle thickness of the airways were classified on a semi quantitative scale.

RESULTS

Inflammatory cell infiltration in peribronchial and perivascular areas was observed in all sensitized groups. Eosinophils percentage in the BALF significantly decreased in verapamil-treated mice compared with sensitized mice (from 19.8% in asthmatic to 5.4% for low dose and 4.4% for high dose). The ratio of airway goblet cells per epithelial cells were significantly lower in verapamil-treated mice versus sensitized mice (1.57±1.30% for low dose; 1.50±0.93% for high dose versus 12.93±7.55%, P<0.05, respectively). Mucus production of goblet cells decreased significantly in verapamil-treated mice versus sensitized mice (mean score was 1.45±0.30 for low dose; 0.81±1.00 for high dose versus 2.85±0.86 in the sensitized control group, P<0.05, respectively). The concentration of serum and BALF-IFN-γ in verapamil-treated mice markedly increased by the verapamil treatment when compared to sensitized mice (15.1±0.43 versus 4.7±0.96, P<0.05 and 91.8±47.7 versus 14.8±4.6, P<0.01, respectively).

CONCLUSION

Verapamil is a useful drug with therapeutic targeting on GCH and a potential way to limit mucous production and improve bronchial inflammation.

The frequency of chronic rhinosinusitis/nasal polyp in COPD and its effect on the severity of COPD

This study aimed to investigate the effect of chronic rhinosinusitis/nasal polyposis on the severity of COPD and to find out whether the 'united airway disease' hypothesis is valid for COPD. The study enrolled 90 patients diagnosed and staged according to criteria of an international guideline for diagnosis and management of COPD. The patients in stages I and II were classified as Group 1 and the patients in stages III and IV as Group 2. All the patients were questioned about the presence of major and minor criteria of sinusitis, underwent paranasal sinus computed tomography (PNS-CT) scans, and answered a questionnaire based on a quality of life test for sinusitis (SNOT-20). Sinusitis was present in 48 (53%) patients according to criteria of major and minor symptoms, and in 58 (64%) patients according to Lund-Mackay scoring system of PNS-CT. There was no significant difference in CT score between Group 1 and Group 2 (2.3 +/- 0.5 vs. 2.1 +/- 0.4, p > 0.05). However, the frequency of minor symptoms was greater in Group 2. SNOT-20 score was significantly higher in Group 2 than in Group 1 (28.7 +/- 1.7 and 22.2 +/- 1.9, respectively, p = 0.014). A significant correlation was determined between Lund-Mackay and SNOT-20 scores. The presence of CRS should be assessed in COPD patients, especially in those with severe disease. Further research is needed to disclose possible common immunopathological mechanisms in the pathogeneses of COPD and CRS.

Distinct roles of FOXA2 and FOXA3 in allergic airway disease and asthma

RATIONALE

Increased production of mucus is a prominent feature of asthma. IL-13-driven mucous cell metaplasia is associated with decreased expression of the transcription factor FOXA2 and increased expression of the related transcription factor FOXA3 in animal and cell culture models.

OBJECTIVES

Establish how changes in FOXA2 and FOXA3 expression contribute to mucous metaplasia and determine whether FOXA2 and FOXA3 expression is altered in asthma.

METHODS

Mice expressing a Foxa2 transgene in airway epithelial cells and mice deficient in Foxa3 were analyzed after allergen sensitization and challenge. Expression of FOXA2, FOXA3, MUC5AC, and the highly IL-13-inducible gene CLCA1 was analyzed in airway biopsies from subjects with asthma and control subjects.

MEASUREMENTS AND MAIN RESULTS

Expression of a Foxa2 transgene reduced allergen-induced mucous metaplasia by 45% compared with control transgenic mice (P < 0.05) whereas inactivation of Foxa3 had no detectable effects on mucous metaplasia. Expression of FOXA2 was reduced in subjects with asthma and was negatively correlated with MUC5AC and CLCA1 levels in subjects with asthma. In contrast, FOXA3 expression was not significantly correlated with MUC5AC and was positively correlated with CLCA1.

CONCLUSIONS

Increasing Foxa2 expression reduced mucous metaplasia in an allergic mouse model. Subjects with asthma had decreased FOXA2 expression, suggesting that therapeutic approaches that increase FOXA2 expression or function could be beneficial for reducing mucus production in asthma. Unlike FOXA2, FOXA3 did not regulate mucous metaplasia.

Chronic Pseudomonas aeruginosa infection in chronic obstructive pulmonary disease

BACKGROUND

Pseudomonas aeruginosa infections are increasingly associated with acute exacerbations in chronic obstructive pulmonary disease (COPD). We aimed to determine whether an underlying chronic infection might be behind this process and to determine the epidemiological characteristics of the isolates involved, to implement useful protocols for preventing and treating these infections.

METHODS

P. aeruginosa isolates obtained from respiratory samples of 13 patients with COPD and from blood samples of 10 patients in intensive care units were investigated. In 8 patients with COPD, isolates were obtained during sequential exacerbation episodes. Five patients presented a single infection episode. Production of virulence determinants and genetic relationships were analyzed in all isolates.

RESULTS

Patients with COPD were usually infected with 1 P. aeruginosa clone that remained in the lung for years, without evidence of interpatient transmission. During chronic infection, each clone diversified, which led to the coexistence of isolates with different morphotypes and antibiotic susceptibility. Overall, P. aeruginosa evolved toward an increased mutation rate, increased antibiotic resistance, and reduced production of proteases. Isolates from samples of infected lungs tend to be less cytotoxic and motile and to produce more biofilm, compared with isolates from blood samples.

CONCLUSION

These results provide the first evidence supporting the hypothesis that P. aeruginosa causes chronic infections in COPD, with patterns of infection and evolution that resemble those observed in cystic fibrosis. Experience gained from treating cystic fibrosis might be useful for implementing new procedures for the prevention, diagnosis, and treatment of infection due to P. aeruginosa in COPD.

Nasal and sinus inflammation in chronic obstructive pulmonary disease

Epidemiologic studies suggest that as many as 75% of patients with COPD have concomitant nasal symptoms and more than 1/3 of patients with sinusitis also have lower airway symptoms of asthma or COPD. Because the inflammatory response of the upper and lower airways are similar, and both sites have a similar exposure to allergens and irritants, it is not surprising that rhinitis or sinusitis would coexist with COPD. Possible mechanisms of combined upper and lower airway dysfunction include the so-called nasal-bronchial reflex, inflammation caused by smoking, mouth breathing caused by nasal obstruction, and pulmonary aspiration of nasal contents. Patients with chronic sinusitis commonly have nonspecific bronchial hyperresponsiveness, suggesting a neural reflex. Postnasal drainage of nasal inflammatory mediators during sleep also may increase lower airway responsiveness. Therapy of nasal and sinus disease is associated with improved pulmonary function in patients with COPD.

MUC5AC and MUC5B mucins increase in cystic fibrosis airway secretions during pulmonary exacerbation

RATIONALE

Cystic fibrosis (CF) is believed to be associated with mucus hypersecretion; thus, the principal airway gel-forming mucins, MUC5AC and MUC5B, are also expected to be increased relative to non-CF secretions. However, we have shown that these mucins are decreased during stable CF disease.

OBJECTIVES

In this study, we determine if these mucins increase during a pulmonary exacerbation of CF.

METHODS

Expectorated sputum was collected from 11 adults with CF during stable disease and then during a pulmonary exacerbation and from 12 healthy control subjects. MUC5AC and MUC5B proteins were measured by Western blot. DNA content was measured using microfluorimetry.

RESULTS

MUC5AC protein increased by 908% and MUC5B by 59% (p < 0.05 for both) during an exacerbation compared with periods of stable disease. During stable disease, the vol/vol quantity of MUC5AC protein was 89% less than normal mucus, and the mucin-associated sugars, measured using a lectin binding assay, were 46% less compared with normal mucus. The concentration of DNA in CF sputum did not increase during an exacerbation.

CONCLUSIONS

During a CF exacerbation, concentration of secreted mucin increased to the amount found in mucus from normal subjects, suggesting that the capacity to secrete mucin in response to an infection or inflammatory stimulus is preserved in CF airways. This might help to protect the airway from injury.

Other medications for aerosol delivery

Although aerosol therapy is most commonly used to treat asthma and COPD, there are a large number of aerosol medications now used or in development for other diseases. Mucoactive agents have long been available by aerosol, but now we have truly effective drugs to improve effective airway clearance including dornase alfa, hyperosmolar saline, and aerosol surfactant. Inhaled antibiotics are available for the treatment of cystic fibrosis, bronchiectasis and other chronic airway infections. With the development of devices that can target aerosol to the deep lung, the opportunity to deliver medications systemically by the aerosol route has become a reality. Insulin, recently approved in the US as aerosol therapy, and other peptides are systemically absorbed from the distal airway and alveolus. Aerosol gene transfer therapy to correct abnormalities associated with cystic fibrosis, primary ciliary dyskinesia and other airway diseases also holds great potential.