Novel Therapies to Inhibit Mucus Synthesis and Secretion in Airway Hypersecretory Diseases.

BACKGROUND: In asthma and chronic obstructive pulmonary disease (COPD), airway mucus hypersecretion contributes to impaired mucociliary clearance, mucostasis and, potentially, the development of mucus plugging of the airways. SUMMARY: Excess mucus production can be targeted via therapies that focus on inhibition mucin synthesis, via reducing expression of mucin (MUC) genes, and/or inhibition of mucin secretion into the airways. KEY MESSAGES: This review discusses a number of therapeutic approaches to reduce airway mucus in asthma and COPD, including the use of synthetic and natural products. In particular, it highlights areas where clinical trials of inhibitors of particular target molecules are lacking. Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors are an example of a targeted therapy that has been researched to reduce mucus synthesis, as have inhibitors of EGFR's downstream signalling pathways, for example, mitogen-activated protein kinase-13 and hypoxia inducible factor-1. However, their efficacy and safety profiles are currently not up to the mark. There is clinical potential in Bio-11006, which reduces mucus secretion via the inhibition of myristoylated alanine-rich C-kinase substrate and is currently in Phase IIb trial.

Therapeutic options for hydrating airway mucus in cystic fibrosis.

BACKGROUND: In cystic fibrosis (CF), genetic mutations in the CF transmembrane conductance regulator (CFTR) gene cause reduced chloride efflux from ciliated airway epithelial cells. This results in a reduction in periciliary liquid (PCL) depth of the airway surface liquid due to associated reduced water efflux. PCL layer dehydration reduces mucociliary clearance (MCC), leading to airway obstruction (reduced airflow and inflammation due to pathogen invasion) with mucus plug formation. SUMMARY: Rehydrating mucus increases MCC. Mucus hydration can be achieved by direct hydration (administering osmotic agents to set up an osmotic gradient), using CFTR modulators to correct dysfunctional CFTR, or it can be achieved pharmacologically (targeting other ion channels on airway epithelial cells). Key Messages: The molecular mechanisms of several therapies are discussed in the context of pre-clinical and clinical trial studies. Currently, only the osmotic agent 7% hypertonic saline and the CFTR 'potentiator' VX-770 (ivacaftor) are used clinically to hydrate mucus. Emerging therapies include the osmotic agent mannitol (Bronchitol), the intracellular Ca(2+)-raising agent Moli1901/lancovutide, the CFTR potentiator sildenafil [phosphodiesterase type 5 (PDE5) inhibitor] and the CFTR 'corrector' VX-809 (lumacaftor). Other CFTR correctors (e.g. 'chemical chaperones') are also showing pre-clinical promise.

Effects of guaifenesin, N-acetylcysteine, and ambroxol on MUC5AC and mucociliary transport in primary differentiated human tracheal-bronchial cells.

BACKGROUND: Therapeutic intervention in the pathophysiology of airway mucus hypersecretion is clinically important. Several types of drugs are available with different possible modes of action. We examined the effects of guaifenesin (GGE), N-acetylcysteine (NAC) and ambroxol (Amb) on differentiated human airway epithelial cells stimulated with IL-13 to produce additional MUC5AC. METHODS: After IL-13 pre-treatment (3 days), the cultures were treated with GGE, NAC or Amb (10-300 µM) in the continued presence of IL-13. Cellular and secreted MUC5AC, mucociliary transport rates (MTR), mucus rheology at several time points, and the antioxidant capacity of the drugs were assessed. RESULTS: IL-13 increased MUC5AC content (~25%) and secretion (~2-fold) and decreased MTR, but only slightly affected the G' (elastic) or G" (viscous) moduli of the secretions. GGE significantly inhibited MUC5AC secretion and content in the IL-13-treated cells in a concentration-dependent manner (IC50s at 24 hr ~100 and 150 µM, respectively). NAC or Amb were less effective. All drugs increased MTR and decreased G' and G" relative to IL-13 alone. Cell viability was not affected and only NAC exhibited antioxidant capacity. CONCLUSIONS: Thus, GGE effectively reduces cellular content and secretion of MUC5AC, increases MTR, and alters mucus rheology, and may therefore be useful in treating airway mucus hypersecretion and mucostasis in airway diseases.

Proteomic analysis of polymeric salivary mucins: no evidence for MUC19 in human saliva.

MUC5B is the predominant polymeric mucin in human saliva [Thornton, Khan, Mehrotra, Howard, Veerman, Packer and Sheehan (1999) Glycobiology 9, 293-302], where it contributes to oral cavity hydration and protection. More recently, the gene for another putative polymeric mucin, MUC19, has been shown to be expressed in human salivary glands [Chen, Zhao, Kalaslavadi, Hamati, Nehrke, Le, Ann and Wu (2004) Am. J. Respir. Cell Mol. Biol. 30, 155-165]. However, to date, the MUC19 mucin has not been isolated from human saliva. Our aim was therefore to purify and characterize the MUC19 glycoprotein from human saliva. Saliva was solubilized in 4 M guanidinium chloride and the high-density mucins were purified by density-gradient centrifugation. The presence of MUC19 was investigated using tandem MS of tryptic peptides derived from this mucin preparation. Using this approach, we found multiple MUC5B-derived tryptic peptides, but were unable to detect any putative MUC19 peptides. These results suggest that MUC19 is not a major component in human saliva. In contrast, using the same experimental approach, we identified Muc19 and Muc5b glycoproteins in horse saliva. Moreover, we also identified Muc19 from pig, cow and rat saliva; the saliva of cow and rat also contained Muc5b; however, due to the lack of pig Muc5b genomic sequence data, we were unable to identify Muc5b in pig saliva. Our results suggest that unlike human saliva, which contains MUC5B, cow, horse and rat saliva are a heterogeneous mixture of Muc5b and Muc19. The functional consequence of these species differences remains to be elucidated.

The non-neuronal cholinergic system in the airways: an unappreciated regulatory role in pulmonary inflammation?

The parasympathetic neurotransmitter acetylcholine is also synthesised and secreted by non-neuronal cells and modifies their behaviour. This is termed the "non-neuronal cholinergic system" and is present in airway inflammatory cells. Acetylcholine is predominantly pro-inflammatory for lymphocytes and epithelial cells, anti-inflammatory for mast cells and macrophages, both pro- and anti-inflammatory for monocytes, and variable in neutrophils and eosinophils. Expression and function of components of the non-neuronal cholinergic system, for example cholinoceptors, can be modified by nicotine in cigarette smoke, the inflammation of asthma and chronic obstructive pulmonary disease (COPD), and the drugs used in clinical management of these diseases. The non-neuronal cholinergic system of airway inflammatory cells represents a previously unappreciated regulatory pathway, with immunomodulatory effects that potentially influence the inflammation of asthma and COPD.

Physiology of airway mucus secretion and pathophysiology of hypersecretion.

Mucus secretion is the first-line defense against the barrage of irritants that inhalation of approximately 500 L of air an hour brings into the lungs. The inhaled soot, dust, microbes, and gases can all damage the airway epithelium. Consequently, mucus secretion is extremely rapid, occurring in tens of milliseconds. In addition, mucus is held in cytoplasmic granules in a highly condensed state in which high concentrations of Ca(2+) nullify the repulsive forces of the highly polyanionic mucin molecules. Upon initiation of secretion and dilution of the Ca(2+), the repulsion forces of the mucin molecules cause many-hundred-fold swelling of the secreted mucus, to cover and protect the epithelium. Secretion is a highly regulated process, with coordination by several molecules, including soluble N-ethyl-maleimide-sensitive factor attachment protein receptor (SNARE) proteins, myristoylated alanine-rich C kinase substrate (MARCKS), and Munc proteins, to dock the mucin granules to the secretory cell membrane prior to exocytosis. Because mucus secretion appears to be such a fundamental airway homeostatic process, virtually all regulatory and inflammatory mediators and interventions that have been investigated increase secretion acutely. When given longer-term, many of these same mediators also increase mucin gene expression and mucin synthesis, and induce goblet cell hyperplasia. These responses induce (in contrast to the protective effects of acute secretion) long-term, chronic hypersecretion of airway mucus, which contributes to respiratory disease. In this case the homeostatic, protective function of airway mucus secretion is lost, and, instead, mucus hypersecretion contributes to pathophysiology of a number of severe respiratory conditions, including asthma, chronic obstructive pulmonary disease, and cystic fibrosis.

Mucoactive agents for airway mucus hypersecretory diseases.

Airway mucus hypersecretion is a feature of a number of severe respiratory diseases, including asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF). However, each disease has a different airway inflammatory response, with consequent, and presumably linked, mucus hypersecretory phenotype. Thus, it is possible that optimal treatment of the mucus hypersecretory element of each disease should be disease-specific. Nevertheless, mucoactive drugs are a longstanding and popular therapeutic option, and numerous compounds (eg, N-acetylcysteine, erdosteine, and ambroxol) are available for clinical use worldwide. However, rational recommendation of these drugs in guidelines for management of asthma, COPD, or CF has been hampered by lack of information from well-designed clinical trials. In addition, the mechanism of action of most of these drugs is unknown. Consequently, although it is possible to categorize them according to putative mechanisms of action, as expectorants (aid and/or induce cough), mucolytics (thin mucus), mucokinetics (facilitate cough transportability), and mucoregulators (suppress mechanisms underlying chronic mucus hypersecretion, such as glucocorticosteroids), it is likely that any beneficial effects are due to activities other than, or in addition to, effects on mucus. It is also noteworthy that the mucus factors that favor mucociliary transport (eg, thin mucus gel layer, "ideal" sol depth, and elasticity greater than viscosity) are opposite to those that favor cough effectiveness (thick mucus layer, excessive sol height, and viscosity greater than elasticity), which indicates that different mucoactive drugs would be required for treatment of mucus obstruction in proximal versus distal airways, or in patients with an impaired cough reflex. With the exception of mucoregulatory agents, whose primary action is unlikely to be directed against mucus, well-designed clinical trials are required to unequivocally determine the effectiveness, or otherwise, of expectorant, mucolytic, and mucokinetic agents in airway diseases in which mucus hypersecretion is a pathophysiological and clinical issue. It is noteworthy that, of the more complex molecules in development, it is simple inhaled hypertonic saline that is currently receiving the greatest attention as a mucus therapy, primarily in CF.

Pharmacological regulation of the neuronal control of airway mucus secretion.

The dominant neural control of human airway mucus secretion is cholinergic. There is no adrenergic control and sensory-efferent control is equivocal. Recent advances have identified several mechanisms that inhibit neurogenic mucus secretion. Muscarinic M3 receptor antagonists and tachykinin NK1 receptor antagonists inhibit neurogenic secretion. Muscarinic M2 receptors, nitric oxide and vasoactive intestinal peptide are inhibitory and regulate the magnitude of neurogenic secretion. The opening of large-conductance calcium-activated potassium channels is a common endogenous inhibitory mechanism and may represent the best therapeutic target. None of these inhibitory options are currently being targeted specifically for therapy of airway hypersecretion.

Airway mucus hypersecretion in asthma: an undervalued pathology?

Airway mucus hypersecretion is a feature of many patients with asthma. It is indicative of poor asthma control and contributes to morbidity and mortality. Excess mucus not only obstructs airways but also contributes to airway hyperresponsiveness. Furthermore, asthma might have a specific mucus hypersecretory phenotype. Goblet cell hyperplasia and submucosal gland hypertrophy are shared with other hypersecretory diseases, such as chronic obstructive pulmonary disease; however, some features are different, including mucus plugging, mucus "tethering" to goblet cells, plasma exudation, and increased amounts of a low charge glycoform of mucin (MUC)5B and the presence of MUC2 in secretions. Experimentally, most of the inflammatory mediators and neural mechanisms implicated in the pathophysiology of asthma impact upon the mucus hypersecretory phenotype. There is currently huge research interest in identifying targets involved in inducing mucus abnormalities, which should lead to the rational design of anti-hypersecretory drugs for treatment of airway mucus hypersecretion in asthma.

The airway goblet cell.

The two principal features of airway goblet cells are rapid secretion of mucin onto the airway surface and increase in number (hyperplasia) with chronic inhaled 'insult'. The first is associated with homeostasis, the latter with pathophysiology. Myristoylated alanine-rich C kinase (MARCKS) is a key molecule regulating mucin exocytosis, a process also involving cooperative interaction between protein kinase (PK) C and PKG. The epidermal growth factor (EGF) cascade and calcium activated chloride channels (CLCA) are key signalling molecules involved in development of goblet cell hyperplasia, with Bcl-2, an inhibitor of apoptosis, involved in maintenance of hyperplasia. Goblet cell hyperplasia and associated mucus hypersecretion is a pathophysiological feature of asthma and chronic obstructive pulmonary disease (COPD). Novel therapeutic strategies to prevent or reverse goblet cell hyperplasia include inhibitors of EGF receptor tyrosine kinase and CLCA, of which viable pharmaceutical molecules are now available for clinical trial in hypersecretory conditions of the airways.

Therapy for chronic obstructive pulmonary disease in the 21st century.

Chronic obstructive pulmonary disease (COPD) is a common, smoking-related, severe respiratory condition characterised by progressive, irreversible airflow limitation. Current treatment of COPD is symptomatic, with no drugs capable of halting the relentless progression of airflow obstruction. Better understanding of the airway inflammation, oxidative stress and alveolar destruction that characterise COPD has delineated new disease targets, with consequent identification of novel compounds with therapeutic potential. These new drugs include aids to smoking cessation (e.g. bupropion) and improvements to existing therapies, for example long-acting rather than short-acting bronchodilators, as well as combination therapy. New antiproteases include acyl-enzyme and transition state inhibitors of neutrophil elastase (e.g. sivelestat and ONO-6818), matrix metalloprotease inhibitors (e.g. batimastat), cathepsin inhibitors and peptide protease inhibitors (e.g. DX-890 [EPI-HNE-4] and trappin-2). New antioxidants include superoxide dismutase mimetics (e.g. AEOL-10113) and spin trap compounds (e.g. N-tert-butyl-alpha-phenylnitrone). New anti-inflammatory interventions include phosphodiesterase-4 inhibitors (e.g. cilomilast), inhibitors of tumour necrosis factor-alpha (e.g. humanised monoclonal antibodies), adenosine A(2a) receptor agonists (e.g. CGS-21680), adhesion molecule inhibitors (e.g. bimosiamose [TBC1269]), inhibitors of nuclear factor-kappaB (e.g. the naturally occurring compounds hypoestoxide and (-)-epigallocatechin-3-gallate) and activators of histone deacetylase (e.g. theophylline). There are also selective inhibitors of specific extracellular mediators such as chemokines (e.g. CXCR2 and CCR2 antagonists) and leukotriene B(4) (e.g. SB201146), and of intracellular signal transduction molecules such as p38 mitogen activated protein kinase (e.g. RWJ67657) and phosphoinositide 3-kinase. Retinoids may be one of the few potential treatments capable of reversing alveolar destruction in COPD, and a number of compounds are in clinical trial (e.g. all-trans-retinoic acid). Talniflumate (MSI-1995), an inhibitor of human calcium-activated chloride channels, has been developed to treat mucous hypersecretion. In addition, the purinoceptor P2Y(2) receptor agonist diquafosol (INS365) is undergoing clinical trials to increase mucus clearance. The challenge to transferral of these new compounds from preclinical research to disease management is the design of effective clinical trials. The current scarcity of well characterised surrogate markers predicts that long-term studies in large numbers of patients will be needed to monitor changes in disease progression.

Mucoactive drugs for asthma and COPD: any place in therapy?

Airway mucus hypersecretion is a clinical and pathophysiological feature of a number of severe respiratory conditions, including asthma and chronic obstructive pulmonary disease (COPD). The importance of mucus hypersecretion to the morbidity and mortality of asthma is acknowledged, whereas in COPD it appears to affect only certain groups of patients, particularly the elderly and those prone to chest infections. Treatment with compounds that alter mucus is perceived as a therapeutic option, in particular in continental Europe, and numerous compounds have been developed and are available for clinical use worldwide. However, acceptance (or otherwise) of these drugs in guidelines for management of asthma or COPD has been hampered by lack of information from well designed clinical trials. In addition, the mechanism of action of most of these drugs is unknown and is it likely that any beneficial effects are due to activities other than, or in addition to, effects on mucus. Current information indicates that the most effective use of mucolytic drugs is long-term therapy for reduction of exacerbations of COPD. Cost-effective treatment would be in patients with poor lung function who have frequent or prolonged exacerbations or are repeatedly admitted to hospital.

Comparison of the effects of salmeterol and formoterol in patients with severe asthma.

STUDY OBJECTIVE: Several studies have demonstrated the superiority of salmeterol and formoterol to either regular treatment with albuterol or placebo. However, to date there have been no trials comparing the efficacy of salmeterol and formoterol in patients with severe asthma. DESIGN: We undertook a randomized, placebo-controlled, crossover study to compare 4 weeks of treatment with inhaled formoterol (12 microg twice daily) or salmeterol (50 microg twice daily) in patients with severe asthma whose conditions were not being adequately controlled by therapy with high doses of inhaled corticosteroids (i.e., > or = 1,500 microg daily) or with regular oral corticosteroid treatment. Morning pretreatment peak expiratory flow (PEF) during the last 14 days of the treatment period was the primary outcome variable. Patients recorded morning and evening pretreatment PEF, daytime and nighttime symptom scores, and any use of rescue medication. Spirometry and bronchial reversibility were performed after each treatment. RESULTS: Forty-two nonsmoking patients (29 women; mean age, 45 +/- 2 years; mean [+/- SEM] FEV(1), 61.8 +/- 3.4% of predicted) took part in the trial, and 27 patients completed the trial. The mean morning PEF was greater in patients receiving formoterol (mean increase, 14.4 L/min; 95% confidence interval [CI]. 0.2 to 28.6) or salmeterol (mean increase, 14.8 L/min; 95% CI, 0.5 to 29.1) compared with those receiving placebo, but there was no difference between these treatments. There were no significant treatment effects for any of the secondary outcome variables (i.e., FEV(1,) FVC, mean evening PEF, mean daytime symptom score, or nighttime symptom score). CONCLUSION: We conclude that the long-acting beta(2)-agonists salmeterol and formoterol improve morning PEF in patients with severe asthma, but that there is no difference in efficacy between the two drugs.

Pulmonary mucus: Pediatric perspective.

Airway mucus hypersecretion is a clinical feature of a number of childhood diseases, including asthma and bronchitis-associated conditions. However, compared with adults, there is relatively scarce information concerning mucus pathophysiology in respiratory diseases in children. The available evidence indicates many similarities between adult and childhood respiratory hypersecretory conditions, including goblet-cell hyperplasia and submucosal gland hypertrophy, and airway mucus plugging in asthma. Consequently, it is likely that treatments that are effective in adults would be effective in children. Numerous therapeutic targets are linked to the pathophysiology of airway mucus hypersecretion in experimental models and adults with respiratory disease. Whether or not these same targets are relevant in children is for the most part unclear. These targets include the inflammatory cells mediating the inflammatory response that generates the hypersecretory phenotype, and highly specific cellular elements such as epidermal growth factor receptor tyrosine kinase and calcium-activated chloride (CACL) channels. Identification of these factors is linked with the development of different classes of pharmacotherapeutic molecules directed at these targets. Compounds with a broader spectrum of anti-inflammatory activity are likely to be more effective than compounds with restricted activity. However, certain highly specific targets, such as human CACL1 channels, appear to be strongly associated with the development of an airway hypersecretory phenotype. Data from current clinical trials in adults with blockers of these specific targets are awaited with great interest. The hope is that, if effective, pediatric trials with these compounds could be initiated with a view to alleviation of the clinical impact of airway mucus hypersecretion in children. A significant challenge to the therapeutic progression of these new compounds is effective delivery to the airways in children, with the research effort into development of new compounds matched by advances in inhaler design.

New pharmacotherapy for airway mucus hypersecretion in asthma and COPD: targeting intracellular signaling pathways.

Airway mucus hypersecretion is a pathophysiological feature of asthma and chronic obstructive pulmonary disease (COPD). The hypersecretion is associated with phenotypic changes in the airways, notably, increases in the number of surface epithelial goblet cells (hyperplasia) and in the size of the submucosal glands (hypertrophy). The hyperplasia and hypertrophy are associated with increased production of mucin, the gel-forming component of mucus. The excess mucus production contributes to morbidity and mortality in many patients, particularly in those with more severe disease. Although current pharmacotherapy is effective in clinical management of patients with stable asthma, severe asthma is poorly treated and there is no current drug treatment for COPD. In neither disease is there specific, effective pharmacotherapy for the hypersecretion. Consequently, identification of potential drug targets for treatment of hypersecretion in asthma and COPD is warranted. The inflammatory mediators and the associated intracellular signaling pathways underlying upregulation of mucin synthesis and development of goblet cell hyperplasia are gradually being elucidated. These include Th2 cytokines (predominantly IL-9 and IL-13), and IL-1 beta, tumor necrosis factor-alpha (TNF-alpha) and cyclooxygenase (COX)-2. IL-9 may act predominantly via calcium-activated chloride channels (CLCA), IL-13 via STAT-6 and FOXA2, TNF-alpha via NF-kappaB, and IL-1 beta via COX-2. Epidermal growth factor receptor (EGF-R) signaling and FOXA2 appear to be convergent intracellular pathways for a number of inflammatory mediators, with EGF-R upregulated in the airways of asthmatic and COPD patients. Thus, preclinical studies have clearly identified a number of intracellular signaling pathways as possible targets for pharmacotherapy of airway mucus hypersecretion in asthma and COPD. Of these, the EGF-R and Th2 cytokine pathways may have the greatest potential for inhibition of excessive mucus production. However, because these targets are so often intimately involved with different aspects of airway (and systemic) homeostasis, there is potential for development of unwanted side effects with drug intervention. Thus, translation of the promising preclinical studies to the clinic will depend on development of drug moieties with low off-target activity. This may be accomplished by maximizing airway selectivity, which may be facilitated by appropriate delivery device design.

Mucus hypersecretion in asthma: intracellular signalling pathways as targets for pharmacotherapy.

PURPOSE OF REVIEW: Airway mucus hypersecretion is a pathophysiological feature of asthma and, in many patients, contributes to morbidity and mortality. Although current pharmacotherapy is effective in patients with stable disease, severe asthma is poorly treated, and there is no specific treatment for the hypersecretion. Consequently, identification of potential targets for pharmacotherapy of hypersecretion in asthma is warranted. This review identifies intracellular signalling pathways as rational targets for treatment of excessive airway mucus production. RECENT FINDINGS: The inflammatory mediators and the associated intracellular signalling pathways underlying development of goblet cell hyperplasia, an index of mucus hypersecretion, are becoming ever clearer, and include T-helper type 2 (Th2) cytokines, in particular interleukin (IL)-9 and IL-13, as well as IL-1beta, tumour necrosis factor (TNF)-alpha and cyclooxygenase (COX)-2. IL-9 may act predominantly via calcium-activated chloride channels (CLCAs), IL-13 via STAT-6 and FOXA2, TNF-alpha via nuclear factor (NF)-kappaB, and IL-1beta via COX-2. Epidermal growth factor receptor (EGF-R) and FOXA2 appear to be convergent pathways for a number of mediator signals, with EGF-R up-regulated in the airways of asthmatic patients. SUMMARY: Although many potential intracellular signalling pathways have been identified as possible targets for pharmacotherapy of airway mucus hypersecretion in asthma, the EGF-R and Th2 cytokine pathways offer the greatest potential for inhibition of excessive mucus production.

Phytoceuticals: the new 'physic garden' for asthma and chronic obstructive pulmonary disease.

Phytoceuticals (non-nutritional but beneficial plant chemicals) merit investigation as pharmacotherapy for asthma and chronic obstructive pulmonary disease (COPD). Although asthma is mostly treated adequately, COPD is not. Thus, there is a need for new drugs with improved therapeutic benefit, especially in COPD. Recent interest in herbal remedies has redirected attention towards plants as sources of improved treatments for lung disease. Phytoceuticals from a variety of plants and plant products, including butterbur, English ivy, apples, chocolate, green tea and red wine, demonstrate broad-spectrum pharmacotherapeutic activities that could be exploited in the clinic. Well-designed clinical trials are required to determine whether these beneficial activities are reproduced in patients, with the prospect that phytoceuticals are the new physic garden for asthma and COPD.

Treatment of airway mucus hypersecretion.

Airway mucus hypersecretion is now recognized as a key pathophysiological feature in many patients with asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis. Consequently, it is important to develop drugs that inhibit mucus hypersecretion in these susceptible patients. Conventional therapies, including anticholinergics, ss2-adrenoceptor agonists, corticosteroids, mucolytics and macrolide antibiotics, have variable efficacy in inhibiting airway mucus hypersecretion, and are less effective in COPD than in asthma. Novel pharmacotherapeutic targets are being investigated, including inhibitors of nerve activity (e.g. large conductance calcium-activated potassium, BKCa, channel activators), tachykinin receptor antagonists, epoxygenase inducers (e.g. benzafibrate), inhibitors of mucin exocytosis (e.g. anti-myristoylated alanine-rich C kinase substrate (MARCKS), peptide and Munc-18B blockers), inhibitors of mucin synthesis and goblet cell hyperplasia (e.g. epidermal growth factor (EGF), receptor tyrosine kinase inhibitors, p38 mitogen-activated protein (MAP), kinase inhibitors, MAP kinase kinase/extracellular signal-regulated kinase (MEK/ERK), inhibitors, human calcium-activated chloride (hCACL2), channel blockers and retinoic acid receptor-a antagonists), inducers of goblet cell apoptosis (e.g. Bax inducers or Bcl-2 inhibitors), and purinoceptor P(2Y2) antagonists to inhibit mucin secretion or P(2Y2) agonists to hydrate secretions. However, real and theoretical differences delineate the mucus hypersecretory phenotype in asthma from that in COPD. More information is required on these differences to identify specific therapeutic targets which, in turn, should lead to rational design of anti-hypersecretory drugs for treatment of airway mucus hypersecretion in asthma and COPD.

The role of airway secretions in COPD: pathophysiology, epidemiology and pharmacotherapeutic options.

Often considered an aggravating but otherwise benign component of chronic obstructive pulmonary disease (COPD), airway mucus hypersecretion is now recognised as a potential risk factor for an accelerated loss of lung function in COPD and is a key pathophysiological feature in many patients, particularly those prone to respiratory tract infection. Consequently, it is important to develop drugs that inhibit mucus hypersecretion in these susceptible patients. Conventional therapy including anticholinergics, beta2-adrenoceoptor agonists, alone or in combination with corticosteroids, mucolytics and macrolide antibiotics are not entirely or consistently effective in inhibiting airway mucus hypersecretion in COPD. Novel pharmacotherapeutic targets are being investigated, including inhibitors of nerve activity (e.g., BK(Ca) channel activators), tachykinin receptor antagonists, epoxygenase inducers (e.g., benzafibrate), inhibitors of mucin exocytosis (e.g., anti-MARCKS peptide and Munc-18B blockers), inhibitors of mucin synthesis and goblet cell hyperplasia (e.g., EGF receptor tyrosine kinase inhibitors, p38 MAP kinase inhibitors, MEK/ERK inhibitors, hCACL2 blockers and retinoic acid receptor-alpha antagonists), inducers of goblet cell apoptosis (e.g., Bax inducers or Bcl-2 inhibitors), and purinoceptor P(2Y2) antagonists to inhibit mucin secretion or P(2Y2) agonists to hydrate secretions. However, real and theoretical differences delineate the mucus hypersecretory phenotype in COPD from that in other hypersecretory diseases of the airways. More information is required on these differences to identify therapeutic targets pertinent to COPD which, in turn, should lead to rational design of anti-hypersecretory drugs for specific treatment of airway mucus hypersecretion in COPD.