Interrupting the cough reflex in asthma

Discovery of TRPA1 Antagonist : Derisking Preclinical Toxicity and Aldehyde Oxidase Metabolism with a Potential First-in-Class Therapy for Respiratory Disease

Transient receptor potential ankyrin 1 (TRPA1) is a nonselective calcium ion channel highly expressed in the primary sensory neurons, functioning as a polymodal sensor for exogenous and endogenous stimuli, and has been implicated in neuropathic pain and respiratory disease. Herein, we describe the optimization of potent, selective, and orally bioavailable TRPA1 small molecule antagonists with strong in vivo target engagement in rodent models. Several lead molecules in preclinical single- and short-term repeat-dose toxicity studies exhibited profound prolongation of coagulation parameters. Based on a thorough investigative toxicology and clinical pathology analysis, anticoagulation effects in vivo are hypothesized to be manifested by a metabolite─generated by aldehyde oxidase (AO)─possessing a similar pharmacophore to known anticoagulants (i.e., coumarins, indandiones). Further optimization to block AO-mediated metabolism yielded compounds that ameliorated coagulation effects in vivo, resulting in the discovery and advancement of clinical candidate GDC-6599, currently in Phase II clinical trials for respiratory indications.

A TRPA1 inhibitor suppresses neurogenic inflammation and airway contraction for asthma treatment

Despite the development of effective therapies, a substantial proportion of asthmatics continue to have uncontrolled symptoms, airflow limitation, and exacerbations. Transient receptor potential cation channel member A1 (TRPA1) agonists are elevated in human asthmatic airways, and in rodents, TRPA1 is involved in the induction of airway inflammation and hyperreactivity. Here, the discovery and early clinical development of GDC-0334, a highly potent, selective, and orally bioavailable TRPA1 antagonist, is described. GDC-0334 inhibited TRPA1 function on airway smooth muscle and sensory neurons, decreasing edema, dermal blood flow (DBF), cough, and allergic airway inflammation in several preclinical species. In a healthy volunteer Phase 1 study, treatment with GDC-0334 reduced TRPA1 agonist-induced DBF, pain, and itch, demonstrating GDC-0334 target engagement in humans. These data provide therapeutic rationale for evaluating TRPA1 inhibition as a clinical therapy for asthma.

Role and Impact of Chronic Cough in Individuals with Asthma From the General Population

BACKGROUND

Cough is a well-recognized symptom in asthma, but the role and impact of chronic cough in individuals with asthma has not been described in the general population.

OBJECTIVE

We hypothesized that among individuals with asthma, those with chronic cough versus those without have a more severe disease phenotype.

METHODS

We identified individuals with asthma and chronic cough among 14,740 adults from the Copenhagen General Population Study, and investigated respiratory symptoms, health care utilizations, lung function, and biomarkers in blood.

RESULTS

A total of 855 (6%) individuals suffered from asthma, and 70 (8%) had chronic cough. Individuals with asthma and chronic cough had a Leicester Cough Questionnaire median total score of 16.8 (25th and 75th percentiles, 14.8-18.9), corresponding to 5.4 (4.6-6.0) for the physical domain, 5.7 (4.6-6.4) for the psychological domain, and 6.0 (5.3-6.8) for the social domain. Among individuals with asthma, those with chronic cough versus those without reported more often wheezing (70% vs 54%), dyspnea (74% vs 49%), night-time dyspnea (27% vs 11%), sputum production (59% vs 14%), chest pain/tightness (14% vs 4%), acute bronchitis/pneumonia episodes, and general practitioner visits. Furthermore, these individuals had more often FEV₁ predicted value of less than 60% (14% vs 7%) and higher levels of neutrophils, leukocytes, and fibrinogen in blood, but there were no differences with regard to levels of high-sensitive C-reactive protein, eosinophils, and IgE in blood.

CONCLUSIONS

Chronic cough in individuals with asthma is associated with a more severe disease phenotype in terms of worse respiratory symptoms, greater health care utilizations, lower lung function, and higher levels of systemic inflammatory biomarkers in blood.

Cough and airway disease: The role of ion channels

Cough is the most common reason for patients to visit a primary care physician, yet it remains an unmet medical need. It can be idiopathic in nature but can also be a troublesome symptom across chronic lung diseases such as asthma, COPD and idiopathic pulmonary fibrosis (IPF). Chronic cough affects up to 12% of the population and yet there are no safe and effective therapies. The cough reflex is regulated by vagal, sensory afferent nerves which innervate the airway. The Transient Receptor Potential (TRP) family of ion channels are expressed on sensory nerve terminals, and when activated can evoke cough. This review focuses on the role of 4 TRP channels; TRP Vannilloid 1 (TRPV1), TRP Ankyrin 1 (TRPA1), TRP Vannilloid 4 (TRPV4) and TRP Melastatin 8 (TRPM8) and the purinergic P2X3 receptor and their possible role in chronic cough. We conclude that these ion channels, given their expression profile and their role in the activation of sensory afferents and the cough reflex, may represent excellent therapeutic targets for the treatment of respiratory symptoms in chronic lung disease.

High prevalence of severe asthma in a large random population study

BACKGROUND

The prevalence of asthma severity is not well described at a population level.

OBJECTIVE

We sought to determine the prevalence of phenotypic signs of asthma severity among asthmatic patients in a general population and to describe risk factors for asthma severity.

METHODS

We performed an epidemiologic study conducted between 2008 and 2012 (West Sweden Asthma Study). A postal questionnaire was sent to a random population (n = 30,000) in west Sweden, with 18,087 responses. A total of 2,006 subjects were carefully phenotyped. Only subjects with "active asthma" (symptoms or medication in the last year, n = 744) were analyzed in this study to determine the degree of severity of the disease within an asthma cohort. Phenotypes of severity were calculated based on (1) multiple symptoms during the day despite ongoing use of asthma medications, (2) FEV₁ of less than 70% of predicted value, (3) daily or almost daily use of rescue medications, (4) nighttime symptoms once a week or more, and (5) oral corticosteroid use/emergency department visits. Asthmatic patients were grouped as having nonsevere disease, 1 sign of severity, or 2 or more signs of severity.

RESULTS

A total of 36.2% of asthmatic patients expressed at least 1 sign of asthma severity, and 13.2% had 2 or more signs. The group with 2 or more signs was older in age and had higher body mass index, a higher rate of tobacco smoking, and lower lung function. Bronchial hyperreactivity, airway inflammation, and sensitization were significantly different among the 3 groups. At a population level, the prevalence of asthma severity was 3.1% for 1 sign and 1.3% for at least 2 signs.

CONCLUSION

More than 1 in 3 asthmatic patients show at least 1 sign of asthma severity. The phenotypes of asthma severity are highly diverse, which is important to consider when implementing personalized medicine in asthmatic patients.

Bronchoprotective effect of deep inspirations in cough variant asthma: A distinguishing feature in the spectrum of airway disease?

PURPOSE

To assess the effect of deep inspirations (DIs) on airway behaviour in individuals with classic asthma (CA), cough variant asthma (CVA), and methacholine (MCh)-induced cough but normal airway sensitivity (COUGH) during bronchoprovocation.

METHODS

Twenty-five adults (18 female; 44.8 ± 12.3 years (Mean ± SD); n = 9 CA, n = 9 CVA, and n = 7 COUGH) completed two single-dose MCh challenges, with and without DIs. Bronchoprotection was assessed by comparing changes in bronchoconstriction (FEV₁, FVC, FEV₁/FVC, FEF₅₀, FEF_25-75), gas trapping (RV, RV/TLC) and impulse oscillometry (IOS) measurements.

RESULTS

The% changes in FEV₁ with and without DIs were not significantly different within any group. Decreases in FEF₅₀ and FEF_25-75 were greater in CA (p = 0.041 and p = 0.029), decreases in FVC (% predicted) and FEV₁/FVC(%) were less in CVA (p = 0.048 and p = 0.010), and increases in RV (L) and RV/TLC (% predicted) were less in COUGH (p = 0.007 and p = 0.028), respectively. No differences in IOS measurements were noted.

CONCLUSIONS

DIs triggered bronchoconstriction in CA, bronchoprotection in CVA, and prevented gas trapping in COUGH.

Bronchodilating effect of deep inspirations in asthma and chronic cough

The pathophysiologic processes distinguishing classic asthma (CA), cough-variant asthma (CVA), and methacholine (MCh)-induced cough but normal airway sensitivity (COUGH) are inadequately understood and may be a result of differences in the ability to bronchodilate following a deep inspiration (DI). The purpose of this study was to compare the bronchodilating effect of DIs in individuals with CA, CVA, and COUGH using high-dose MCh. Individuals aged 18-65 yr with CA or suspected CVA completed high-dose MCh testing to a maximum change in forced expiratory volume in 1 s (FEV1) of 50% from baseline (MAX). Impulse oscillometry (IOS) measurements and partial and maximal-flow volume curves (used to calculate a DI index) were recorded at baseline and at each dose of MCh. Body plethysmography was performed at baseline and MAX. Twenty-eight subjects [25 women, 39.8 ± 11.9 yr (means ± SD)] were studied (n = 11 CA, n = 10 CVA, and n = 7 COUGH). At MAX, the percent change in FEV1 was greater in subjects with CA compared with those with CVA (P < 0.001) and COUGH (P < 0.001), and the percent change in forced vital capacity was greater in those with CA than with COUGH (P = 0.017). Subjects with CA and CVA developed dynamic hyperinflation and gas trapping. In subjects with CA and CVA, all IOS parameters were significantly increased from baseline to MAX, except for central respiratory resistance (R20). In individuals with COUGH, total respiratory resistance, R20, and resonant frequency were significantly increased from baseline. At MAX, the DI index was positive in all groups, suggesting preserved bronchodilation (CA, 0.67 ± 0.97; CVA, 0.51 ± 0.73; COUGH, 0.01 ± 0.36; P = 0.211). We conclude that the bronchodilating effect of DIs is preserved in individuals with CA, CVA, and borderline with COUGH; however, hyperinflation and gas trapping are avoided in subjects with COUGH alone.

Frequent cough in unsatisfactory controlled asthma--results from the population-based West Sweden Asthma study

BACKGROUND

Asthma is a complex disease presenting with variable symptoms which are sometimes hard to control. The purpose of the study was to describe the prevalence of asthma symptoms, use of asthma medications and allergic sensitization in subjects with asthma. We also related those indices to the level of asthma control, lung function and in particular, cough.

METHODS

An extensive questionnaire was sent to randomly selected adults from the West Sweden region. Clinical examinations and interview were performed in a subset. Of the participants, 744 were defined as having an ongoing asthma - reported ever having asthma or physician diagnosed asthma and one of the following - use of asthma medications, recurrent wheeze or attacks of shortness of breath with or without wheeze in the last 12 months. A respiratory disease-free control group of 847 subjects was also described.

RESULTS

According to GINA guidelines, 40.6% of the asthmatics had partly controlled and 17.8% had uncontrolled asthma. Asthmatic subjects reported significantly more symptoms in the last 12 months than the control group - wheezing (79.4 vs 9.2%), shortness of breath (36.1 vs 2.5%), wheezing with shortness of breath (58.7 vs 1.3%). Important complaints were morning cough (42.5 vs 15.5%), cough with sputum production (36.1 vs 6.8%) and longstanding cough (32.5 vs 11.1%), which bothered two thirds of the uncontrolled and one third of partly controlled subjects. Asthma medications were used by 87.5% of the asthmatics, although around 30% of them who had insufficiently controlled disease used only short-acting beta-agonists. Asthmatics also had lower lung function, reacted to lower doses of methacholine that the controls and 13.6% of them had a FEV1/FVC ratio below 0.7. Allergic rhinitis was reported by 73.8% of the asthmatics and they were more frequently sensitized to several common allergens.

CONCLUSIONS

Approximately 60% of asthmatics from this population-based study had insufficiently controlled asthma and persistent complaints, despite a high use of asthma medications. These self-reported symptoms were supported by clinical examination data. Increased cough frequency is an indicator of a more severe and difficult to control disease and should be considered when asthma is characterized.

Asthmatic cough and airway oxidative stress

The mechanisms of cough in asthma are unclear. Asthma is associated with an oxidative stress. Many reactive oxygen species sensitize or activate sensory C-fibers which are capable to induce cough. It was hypothesized that oxidative stress in the airways might contribute to the cough severity in asthma. Exhaled breath condensate samples were collected in ten healthy and 26 asthmatic subjects. The concentration of 8-isoprostane was measured. In addition, the subjects filled in Leicester Cough Questionnaire and underwent cough provocation tests with dry air hyperpnoea and hypertonic saline, among other measurements. Among the asthmatic subjects, high 8-isoprostane was associated with severe cough response to hyperpnoea (p=0.001), low Leicester Cough Questionnaire values (indicating severe subjective cough, p=0.02), and usage of combination asthma drugs (p=0.03-0.04). However, the 8-isoprostane concentrations did not differ significantly between the healthy and the asthmatic subjects. Airway oxidative stress may be associated with experienced cough severity and measured cough sensitivity in asthma.

Cough in asthma

Asthma is one of the most common causes of chronic cough, and cough may be the sole or predominant symptom of asthma. The mechanisms of cough in asthma are complex and presumbably multi-factorial. In particular, the pathophysiologic basis of cough variant versus classic asthma is poorly understood. Recent research utilizing various inhalation challenge tests suggests that preservation of the bronchodilating and bronchoprotective effects of deep inspirations is a distinguishing feature of cough variant asthma. This review outlines the tussive agents used in cough research (including tussive and direct, indirect and combined bronchoconstrictive stimuli), their mechanisms of action, the receptors involved in eliciting cough, and characteristic responses in classic asthma and cough variant asthma.