Structural changes in the airways: cause or effect of chronic cough?

The role of neutrophils in chronic cough

Chronic cough is a common disorder lasting more than 8 weeks and affecting all age groups. The evidence supporting the role of neutrophils in chronic cough pathology is based on many patients with chronic cough developing airway neutrophilia. How neutrophils influence the development of chronic cough is unknown. However, they are likely involved in multiple aspects of cough etiology, including promoting airway inflammation, airway remodeling, hyper-responsiveness, local neurogenic inflammation, and other possible mechanisms. Neutrophilic airway inflammation is also associated with refractory cough, poor control of underlying diseases (e.g., asthma), and insensitivity to cough suppressant therapy. The potential for targeting neutrophils in chronic cough needs exploration, including developing new drugs targeting one or more neutrophil-mediated pathways or altering the neutrophil phenotype to alleviate chronic cough. How the airway microbiome differs, plays a role, and interacts with neutrophils in different cough etiologies is poorly understood. Future studies should focus on understanding the relationship between the airway microbiome and neutrophils.

Changes of the airway reactivity in patients with rhinosinusitis

Rhinosinusitis is one of the most common conditions in primary and secondary care all over the world. Rhinosinusitis together with asthma and gastroesophageal reflux disease represent the most common causes of chronic cough. The relationship between rhinosinusitis and cough is still not completely understood, however, direct stimulation of nasal mucosa, upper airway cough syndrome, inflammation of the airways, and cough reflex sensitisation play the crucial role in the pathogenesis of chronic cough.

Narrative Review: how long should patients with cough variant asthma or non-asthmatic eosinophilic bronchitis be treated?

The causes of chronic cough can be categorized into eosinophilic and noneosinophilic disorders, and approximately 30% to 50% of people with chronic cough have eosinophilic airway inflammation, the presence of which can be confirmed by sputum eosinophilia or elevated exhaled nitric-oxide levels. Cough variant asthma (CVA) is a phenotype of asthma which lacks wheezing or dyspnea, and consistently one of the most common causes of chronic cough worldwide. CVA and non-asthmatic eosinophilic bronchitis (NAEB) shares common feature such as chronic dry cough, eosinophilic inflammation, and development of chronic airflow obstruction (CAO) and asthma in a subset of patients. The distinctive characteristic of these conditions is the presence of airway hyperresponsiveness in CVA but not in NAEB. Coughing is responsive to bronchodilators such as beta-agonists in CVA, but such feature has not been clarified in NAEB. Inhaled corticosteroids (ICSs) are the first-line treatment, and leukotriene receptor antagonists are also effective, in patients with both CVA and NAEB. This review will give an outline of clinical and physiological features, and prognosis and its determinants of CVA and EBNA. Further, the rationale and evidence, despite limited, for the need of long-term treatment will be discussed. The development of airway remodeling due to mechanical stress to the airways exerted by long-standing coughing will also be discussed.

Upper Airway Cough Syndrome in Pathogenesis of Chronic Cough

Cough is one of the most important defensive reflexes. However, extensive non- productive cough is a harmful mechanism leading to the damage of human airways. Cough is initiated by activation of vagal afferents in the airways. The site of their convergence is particularly the nucleus of the solitary tract (nTS). The second-order neurons terminate in the pons, medulla and spinal cord and there is also the cortical and subcortical control of coughing.Upper airway cough syndrome (UACS) - previously postnasal drip syndrome - is one of the most common causes of chronic cough together with asthma and gastroesophageal reflux. The main mechanisms leading to cough in patients with nasal and sinus diseases are postnasal drip, direct irritation of nasal mucosa, inflammation in the lower airways, upper airway inflammation and the cough reflex sensitization. The cough demonstrated by UACS patients is probably due to hypersensitivity of the upper airways sensory nerve or lower airways sensory nerve, or a combination of both. Further studies are needed to clarify this mechanism.

Establishment of a mouse model with all four clinical features of eosinophilic bronchitis

Eosinophilic bronchitis (EB) is a clinical disease characterized by chronic cough, airway eosinophil infiltration, and responsive to steroid therapy but with the absence of airway hyperreactivity (AHR). This study established an EB mouse model with all the above features. First, 42 mice were divided into 7 groups to investigate the optimal time interval between cough and AHR detections. Afterward, 28 mice were divided into the asthma, EB, normal saline (NS), and dexamethasone (DXM) groups. Mice were challenged using nasal drops of 200 µg ovalbumin (OVA), 10 µg OVA, NS, or intraperitoneal injections of 5 mg/kg of DXM one hour prior to 10 µg OVA challenge. Airway reactivity was measured 6 h after cough was observed. The frequency of coughs in the asthma and EB groups increased significantly compared to mice in the NS group. After DXM administration, frequency of coughs was significantly decreased compared to mice in the asthma and EB groups. Lung resistance in the asthma group was significantly higher compared to mice in the NS, EB, and DXM groups. Obvious airway eosinophilic inflammation in BALF and lung tissues were observed in the asthma and EB groups, while DXM administration could attenuate airway inflammatory infiltration. In summary, we developed a mouse EB model with all four clinical features of EB by the administration of 10 µg OVA nasal drops.

The role of ATP in cough hypersensitivity syndrome: new targets for treatment

Clinically, chronic cough can be effectively controlled in most patients by etiological treatment; however, there remain a small number of patients whose cough has unidentifiable etiology or where treatment efficacy is poor following etiology identification, whose condition is described as unexplained chronic cough or refractory chronic cough. Patients with refractory chronic or unexplained chronic cough commonly have increased cough reflex sensitivity, which has been described as cough hypersensitivity syndrome. The adenosine triphosphate (ATP)-gated P2X₃ receptor may be a key link in the activation of sensory neurons that regulate cough reflexes and has recently draw attention as a potential target for the treatment of refractory chronic cough, with a number of clinical studies validating the therapeutic effects of P2X₃ receptor antagonists in patients with this condition. As the energy source for various cells in vivo, ATP localizes within cells under normal physiological conditions, and has physiological functions, including in metabolism; however, under some pathological circumstances, ATP can act as a neuromodulator and is released into the extracellular space in large quantities as a signal transduction molecule. In addition, ATP is involved in regulation of airway inflammation and the cough reflex. Here, we review the generation, release, and regulation of ATP during airway inflammation and its role in the etiology of cough hypersensitivity syndrome, including the potential underlying mechanism.

Repeated bronchoconstriction attenuates the cough response to bronchoconstriction in naïve guinea pigs

BACKGROUND

Cough variant asthma (CVA) is recognized as a precursor of bronchial asthma (BA). However, the cough response to bronchoconstriction differs between these similar diseases. Repeated bronchoconstriction and the resulting imbalance of endogenous lipid mediators may impact the cough response.

METHODS

We investigated the influence of repeated bronchoconstriction on the cough response to bronchoconstriction using naïve guinea pigs. Bronchoconstriction was induced for 3 consecutive days and changes in the cough response and lipid mediators, such as PGE₂, PGI₂, and cysteinyl-LTs (Cys-LTs), in BAL fluid (BALF) were assessed. We investigated the effect of endogenous PGI₂ on the cough response by employing a PGI₂ receptor antagonist. In order to investigate the cough response over a longer period, we re-evaluated the cough response 2 weeks after repeated bronchoconstriction.

RESULTS

The number of coughs induced by bronchoconstriction were significantly decreased by repeated bronchoconstriction. The levels of PGE₂, PGI₂, and Cys-LTs, and the ratio of PGI₂/PGE₂ were significantly increased, following repeated bronchoconstriction. This decrease in the cough response was suppressed by pretreatment with a PGI₂ receptor antagonist. Two weeks after repeated bronchoconstriction, the cough response returned to the same level as before repeated bronchoconstriction along with a concomitant return of lipid mediators, such as PGE₂, PGI₂, and Cys-LTs and the ratio of PGI₂/PGE₂.

CONCLUSIONS

Our results suggest that repeated bronchoconstriction and the resulting imbalance of endogenous lipid mediators contribute to the difference in cough responses to bronchoconstriction in CVA and BA.

Association of cough hypersensitivity with tracheal TRPV1 activation and neurogenic inflammation in a novel guinea pig model of citric acid-induced chronic cough

Objective

This study was performed to establish a novel model of citric acid-induced chronic cough in guinea pigs and to investigate the pathogenesis of cough hypersensitivity.

Methods

Healthy conscious guinea pigs inhaled citric acid (0.4 M) for 3 minutes twice daily for 25 days. Cough reactivity was evaluated, substance P (SP) and calcitonin gene-related peptide (CGRP) in bronchoalveolar lavage fluid were detected, and transient receptor potential cation channel subfamily V member 1 (TRPV1) protein expression in the trachea and bronchus was determined. Tracheal and bronchial tissues were examined for TRPV1.

Results

Inhalation of 0.4 M citric acid increased coughing in a time-dependent manner: coughing peaked at 15 days and reached the lowest level at 25 days. This was accompanied by similar changes in SP, CGRP, and TRPV1 protein expression. TRPV1 was mainly observed in the mucosal and submucosal layer of the trachea and bronchi. The areas of TRPV1 positivity in the trachea and bronchi of citric acid-treated animals were significantly larger than in the control group.

Conclusions

Repeated inhalation of citric acid can be employed to establish a chronic cough model in guinea pigs. Cough hypersensitivity in this model is related to tracheal TRPV1 activation and neurogenic inflammation.

Impaired innate immune gene profiling in airway smooth muscle cells from chronic cough patients

Chronic cough is associated with airway inflammation and remodelling. Abnormal airway smooth muscle cell (ASMC) function may underlie mechanisms of chronic cough. Our objective was to examine the transcriptome and focused secretome of ASMCs from chronic cough patients and healthy non-cough volunteers. ASMC gene expression profiling was performed at baseline and/or after stimulation with polyinosinic:polycytidylic acid (poly(I:C)) to mimic viral infection. Supernatants were collected for multiplex analysis. Our results showed no significant differentially expressed genes (DEGs, false discovery rate (FDR) <0.05) between chronic cough and healthy non-cough ASMCs at baseline. Poly(I:C) stimulation resulted in 212 DEGs (>1.5 fold-change, FDR <0.05) in ASMCs from chronic cough patients compared with 1674 DEGs in healthy non-cough volunteers. The top up-regulated genes included chemokine (C–X–C motif) ligand (CXCL) 11 (CXCL11), CXCL10, chemokine (C–C motif) ligand (CCL) 5 (CCL5) and interferon-induced protein 44 like (IFI44L) corresponding with inflammation and innate immune response pathways. ASMCs from cough subjects had enhanced activation of viral response pathways in response to poly(I:C) compared with healthy non-cough subjects, reduced activation of pathways involved in chronic inflammation and equivalent activation of neuroregulatory genes. The poly(I:C)-induced release of inflammatory mediators, including CXCL8, interleukin (IL)-6 and CXCL1, from ASMCs from cough patients was significantly impaired compared with healthy non-cough subjects. Addition of fluticasone propionate (FP) to poly(I:C)-treated ASMCs resulted in greater gene expression changes in healthy non-cough ASMCs. FP had a differential effect on poly(I:C)-induced mediator release between chronic cough and healthy non-cough volunteers. In conclusion, altered innate immune and inflammatory gene profiles within ASMCs, rather than infiltrating cells or nerves, may drive the cough response following respiratory viral infection.

Cough in exercise and athletes

Cough is the most common respiratory symptom reported by athletes and can significantly impact on health status, ability to train and athletic performance. The presence of cough in an athlete is typically taken to indicate exercise-induced bronchoconstriction (EIB), yet in many athletes with chronic cough there is no objective evidence of airway hyper-responsiveness (AHR) or heightened airway inflammation. Moreover, cough in athletes often fails to respond to a therapeutic asthma strategy, thus further work is urgently needed to progress our understanding of the pathophysiology of exercise-associated cough in this unique population. This article provides an overview of the current state of knowledge of exercise-associated cough in athletes. The article summarises our understanding of pathophysiological basis of cough in this context and provides a pragmatic clinical approach to this problem.

Chronic cough: clinical characteristics and etiologies of 510 cases

BACKGROUND/AIM

To investigate the clinical features and underlying etiologies of chronic cough (CC).

MATERIALS AND METHODS

Five hundred and ten CC patients were enrolled. The phases, characteristics and associated clinical manifestations of CC among the gastroesophageal reflux cough (GERC), cough-variant asthma (CVA), and upper airway cough syndrome (UACS) groups were compared, and the diagnostic values of each group were evaluated by multiple regression analysis.

RESULTS

In the 510 patients, 404 had CC with single etiology-GERC (n = 175), CVA (n = 134), and UACS (n = 95). The characteristic features of GERC included gastric acid backflow symptoms such as sour-tasting regurgitation, heartburn, endoscopic esophagitis, poststimulation cough, frequent throat clearing, daytime mono-cough, and feelings of heaviness and pain in the chest. Patients with CVA typically exhibited sensitivity to smog and other irritants; the cough occurred mostly at night, and was associated with positive bronchodilator and provocation test results. The typical features of UACS included a history and/or symptoms of rhinitis, retropharyngeal postnasal drip, and wet cough occurring mostly during the daytime. The diagnostic specificities of above factors were >70%.

CONCLUSION

The most common causes of CC include GERC, CVA, and UACS, and their diagnosis is based on the characteristics of the underlying disease.

Airway remodeling associated with cough hypersensitivity as a consequence of persistent cough: An experimental study

BACKGROUND

Chronic cough involves airway remodeling associated with cough reflex hypersensitivity. Whether cough itself induces these features remains unknown.

METHODS

Guinea pigs were assigned to receive treatment with citric acid (CA), saline (SA), or CA+dextromethorphan (DEX). All animals were exposed to 0.5M CA on days 1 and 22. On days 4-20, the CA and CA+DEX groups were exposed to CA, and the SA group to saline thrice weekly, during which the CA+DEX group was administered DEX pretreatment to inhibit cough. The number of coughs was counted during each 10-min CA or SA exposure. Terbutaline premedication was started to prevent bronchoconstriction. Bronchoalveolar lavage and pathology were examined on day 25. Average cough number for 10 CA exposures was examined as "cough index" in the CA group, which was divided into frequent (cough index>5) and infrequent (<5) cough subgroups for lavage and pathology analysis.

RESULTS

The number of coughs significantly increased in the CA group from day 13 onwards. In the CA+DEX and SA groups, the number of coughs did not differ between days 1 and 22, while average number of coughs during days 4-20 was significantly lower than at days 1 and 22. Bronchoalveolar cell profiles were similar among the four groups. The smooth muscle area of small airways was significantly greater in the frequent-cough subgroup than in the other groups (in which it was similar), and highly correlated with cough index in CA group.

CONCLUSION

Repeated cough induces airway smooth muscle remodeling associated with cough reflex hypersensitivity.

Airway inflammation, cough and athlete quality of life in elite female cross-country skiers: A longitudinal study

The aim of this study was to investigate the effect of a season of cross-country training and racing on airway inflammation, cough symptoms, and athlete quality of life in female skiers. Eighteen elite female skiers performed sputum induction and completed the Leicester Cough Questionnaire (LCQ) and the Recovery-Stress Questionnaire (REST-Q) at three time points (T1 - May/Jun, T2 - Oct/Nov, T3 - Jan-Mar) during the year. No changes were observed between T1 and T2. However, an increase in sputum eosinophils and lymphocytes (P < 0.05) and a significant change in all three domains of the LCQ were observed between T1 and T3 (P < 0.05). A significant association was found between the total yearly hours of training and the change in the total cell count (r(2)  = 0.74; P = 0.006), and a number of other sputum cell counts between T1 and T3. No changes were observed for any domain of the REST-Q. The results of this study demonstrate that airway inflammation and cough symptoms are significantly increased in elite female cross-country skiers across a year of training and racing. The increase in airway inflammation is related to the total amount of training and is worse during the winter months when athletes are training and racing in cold, dry air.

Olodaterol attenuates citric acid-induced cough in naïve and ovalbumin-sensitized and challenged guinea pigs

Excessive coughing is a common feature of airway diseases. Different G-protein coupled receptors, including β2-adrenergic receptors (β2-AR), have been implicated in the molecular mechanisms underlying the cough reflex. However, the potential antitussive property of β2-AR agonists in patients with respiratory disease is a matter of ongoing debate. The aim of our study was to test the efficacy of the long-acting β2-AR agonist olodaterol with regard to its antitussive property in a pre-clinical model of citric acid-induced cough in guinea pigs and to compare the results to different clinically relevant β2-AR agonists. In our study β2-AR agonists were intratracheally administered, as dry powder, into the lungs of naïve or ovalbumin-sensitized guinea pigs 15 minutes prior to induction of cough by exposure to citric acid. Cough events were counted over 15 minutes during the citric acid exposure. Olodaterol dose-dependently inhibited the number of cough events in naïve and even more potently and with a greater maximal efficacy in ovalbumin-sensitized guinea pigs (p < 0.01). Formoterol and salmeterol showed a trend towards reducing cough. On the contrary, indacaterol demonstrated pro-tussive properties as it significantly increased the number of coughs, both in naïve and ovalbumin-sensitized animals (p < 0.001). In conclusion, olodaterol, at doses eliciting bronchodilation, showed antitussive properties in a model of citric acid-induced cough in naïve and ovalbumin-sensitized guinea pigs. This is in agreement with pre-clinical and clinical studies showing antitussive efficacy of β2-AR agonists. Indacaterol increased the number of coughs in this model, which concurs with clinical data where a transient cough has been observed after indacaterol inhalation. While the antitussive properties of β2-AR agonists can be explained by their ability to lead to the cAMP-induced hyperpolarization of the neuron membrane thereby inhibiting sensory nerve activation and the cough reflex, the mechanism underlying the pro-tussive property of indacaterol is not known.

Advances in upper airway cough syndrome

Upper airway cough syndrome (UACS), previously referred to as postnasal drip syndrome, is one of the most common causes of chronic cough. However, the pathogenesis of UACS/postnasal drip syndrome remains unclear, and physicians in countries throughout the world have different definitions and ways of treating this disease. The various proposed pathogeneses of UACS include the early postnasal drip theory, subsequent chronic airway inflammation theory, and a recent sensory neural hypersensitivity theory. Additionally, some researchers suggest that UACS is a clinical phenotype of cough hypersensitivity syndrome. While the general principles involved in treating UACS are similar throughout the world, the specific details of treatment differ. This review summarizes the various definitions, pathogenic mechanisms, treatments, and other aspects of UACS, to aid clinicians in expanding their knowledge of how to diagnose and treat this syndrome.

Matrix metalloproteinase 9 is involved in airway inflammation in cough variant asthma

Previous studies have revealed the role of matrix metalloproteinase 9 (MMP9) in asthma and chronic obstructive pulmonary disease (COPD). However, its role in airway inflammation in cough variant asthma (CVA) remains unknown. In the present study, variations in the levels of MMP9 and interleukin (IL)-5 in the induced sputum of patients with CVA prior to and following therapy with inhaled corticosteroid and long-acting β2-agonist (ICS/LABA), were detected. The levels of IL-5 and percentage of eosinophils (EOS) in the induced sputum from patients with CVA were significantly higher than those in the control group of healthy individuals. The levels of MMP9 in the induced sputum from patients with CVA were also significantly higher than those in the control group. Following treatment with ICS/LABA for 6-9 months, the levels of MMP9 and IL-5, as well as the percentage of EOS, in the induced sputum from patients with CVA had significantly decreased. Thus, MMP9 may be an important biomarker in the airway inflammation of CVA.

EAACI Position Paper on assessment of cough in the workplace

Cough is a nonspecific and relatively common symptom that can present difficulties in diagnosis and management, particularly when it is reported to be associated with the workplace. The present consensus document, prepared by a taskforce of the Interest Group on Occupational Allergy of the European Academy of Allergy and Clinical Immunology by means of a nonsystematic review of the current literature, is intended to provide a definition and classification of work-related chronic cough (WRCC) to assist the daily practice of physicians facing with this symptom. The review demonstrates that several upper and lower airway work-related diseases may present with chronic cough; hence, the possible link with the workplace should always be considered. Due to the broad spectrum of underlying diseases, a multidisciplinary approach is necessary to achieve a definite diagnosis. Nevertheless, more epidemiological studies are necessary to estimate the real prevalence and risk factors for WRCC, the role of exposure to environmental and occupational sensitizers and irritants in its pathogenesis and the interaction with both upper and lower airways. Finally, the best management option should be evaluated in order to achieve the best outcome without adverse social and financial consequences for the worker.

Cough in asthma is due to eosinophilic airway inflammation: a pro/con debate

Multiple prospective studies have demonstrated that asthma is among the most common etiologies of chronic cough, along with upper-airway cough syndrome (formerly known as postnasal drip syndrome) and gastroesophageal reflux disease. More recently, the entity of nonasthmatic eosinophilic bronchitis has been appreciated as a significant cause of chronic cough worldwide. Chronic cough associated with both of these conditions typically responds well to therapy with systemic or inhaled corticosteroids, thus leading to a general assumption that the suppression of eosinophilic airway inflammation explains the improvement in cough. However, some recent studies challenge a causal relationship between eosinophilic airway inflammation and cough in asthmatics. The 4th American Cough Conference, held in New York in June 2013, provided an ideal forum for discussion and debate of this issue between two internationally recognized experts in the field of asthma and chronic cough.