Chronic cough and pain: Janus faces in sensory neurobiology?

Optimal compatibility proportional screening of Trichosanthis Pericarpium - Trichosanthis Radix and its anti - Inflammatory components effect on experimental zebrafish and coughing mice

ETHNOPHARMACOLOGICAL RELEVANCE

The herbal pair of Trichosanthis Pericarpium (TP) - Trichosanthis Radix (TR) can be seen in the famous formula "Beimu Gualou San". It is a commonly selected combination of medicinal herbs for the treatment of cough with lung heat. Both drugs are derived from Trichosanthes kirilowii Maxim, a medicinal plant known for its ability to clear heat, resolve phlegm, produce saliva, and alleviate dryness. However, the optimal combination ratio and active ingredients of TP-TR have yet to be determined.

AIM OF THE STUDY

This study aims to investigate the optimal combination ratio of TP-TR and its anti-inflammatory active ingredients in cough treatment.

MATERIALS AND METHODS

A zebrafish (Danio rerio) inflammatory injury model and response surface method were applied in the present study to determine the appropriate proportion of TP-TR. Chemical constituents in TP-TR were identified using HPLC-ELSD and UPLC-MS/MS methods. Subsequently, a cough mouse model was created using an ammonia solution to evaluate the effectiveness of the optimal TP-TR ratio. Network pharmacology and intestinal flora sequencing were used to validate the anti-inflammatory components of TP-TR.

RESULTS

The herbal pair of TP - TR at the ratio of 1:2 showed an optimal anti-inflammatory effect, with a composite inflammatory factor score of 119.645 in the zebrafish experiment. TP-TR combination facilitated the dissolution of glutamine, inosine, cytosine, isoquercetin, and other substances. In the animal model, the TP-TR (1:2) treatment significantly reduced the frequency of coughs and prolonged cough latency compared to the model group. Results of the network pharmacology indicated that inflammatory-related factors such as TLR4, STAT3, EGFR, and AKT1 played crucial roles in cough treatment with TP-TR, consistent with the validation experiment. The 16s rDNA sequencing results revealed a significant increase in the abundance of Clostridia_UCG-014, Lachnospiraceae, Christenella, Ruminococcus, and other species in the intestinal tract of mice after modelling. TP-TR (1:2) reduced the abundance of pro-inflammatory flora such as Clostridium_UCG-014 and Lachnospira, which were closely associated with L-lysine and trans-4-hydroxy-L-proline present in TP-TR according to correlation analysis.

CONCLUSION

TP-TR may promote the dissolution of glutamine, thymidine, inosine, cytosine, isoquercetin, and other components through their combination, thereby regulating the abundance of Clostridium_UCG-014 and Lachnospira and exerting an antitussive effect. This study, for the first time, showed that TP-TR at a 1:2 ratio exhibits superior anti-inflammatory effects. In addition to inflammatory mediators like EGFR, TLR4, AKT1, and STAT3, gut microbes could also serve as potential regulatory targets of TP-TR in the treatment of cough. 2'-Deoxyguanosine monohydrate, L-lysine, L-leucine, γ-aminobutyric acid, L-valine, L-tryptophan, L-proline, trans-4-hydroxy-L-proline, L-methionine, uridine, 2'-deoxyinosine, guanosine, cucurbitacin B and cucurbitacin D were identified as its anti-inflammatory active ingredients.

Neural substrates of cough control during coughing

Cough is known as a protective reflex to keep the airway free from harmful substances. Although brain activity during cough was previously examined mainly by functional magnetic resonance imaging (fMRI) with model analysis, this method does not capture real brain activity during cough. To obtain accurate measurements of brain activity during cough, we conducted whole-brain scans during different coughing tasks while correcting for head motion using a restraint-free positron emission tomography (PET) system. Twenty-four healthy right-handed males underwent multiple PET scans with [15O]H2O. Four tasks were performed during scans: "resting"; "voluntary cough (VC)", which simply repeated spontaneous coughing; "induced cough (IC)", where participants coughed in response to an acid stimulus in the cough-inducing method with tartaric acid (CiTA); and "suppressed cough (SC)", where coughing was suppressed against CiTA. The whole brain analyses of motion-corrected data revealed that VC chiefly activated the cerebellum extending to pons. In contrast, CiTA-related tasks (IC and SC) activated the higher sensory regions of the cerebral cortex and associated brain regions. The present results suggest that brain activity during simple cough is controlled chiefly by infratentorial areas, whereas manipulating cough predominantly requires the higher sensory brain regions to allow top-down control of information from the periphery.

A randomized, double-blinded, placebo-controlled clinical trial of duloxetine hydrochloride enteric-coated tablets in the treatment of refractory chronic cough

INTRODUCTION

Refractory cough, a chronic cough with an unclear diagnosis or poor treatment response. The symptoms are often stubborn and persistent, causing serious complications and lowering the patient's quality of life. Cough hypersensitivity syndrome (CHS) is proposed as a potential cause, and reducing sensory nerve hyperresponsiveness is suggested as an effective treatment. However, current drugs have low efficacy and benefit rates and numerous side effects. This trail proposes using duloxetine, a selective 5-HT and norepinephrine reuptake inhibitor, as a potential treatment for refractory cough, which has shown promise in treating pain and depression. Duloxetine may inhibit pain conduction and oxidative stress in peripheral nerves by inhibiting the activity of TRPV1 channels, which play an important role in the peripheral afferent pathway of refractory cough. Meanwhile, the antidepressant effects of duloxetine may also play a role in the treatment of refractory cough.

METHODS AND ANALYSIS

This is a single-center, prospective, randomized, double-blind, and controlled trial. A total of 98 individuals will be randomized in a 1:1 ratio to duloxetine group and placebo control group (starting with 20 mg QD, increasing 20 mg daily until 20 mg TID). After a screening period, the second stage runs from baseline to the 42nd (last) day of treatment, with follow-up visits on the 3rd, 7th, 14th, 21st, 28th, 35th, 42nd and 49th days. The main end-stage observation indicators include objective cough frequency, cough visual analog scale (VAS), cough symptom score, Leicester Cough Questionnaire (LCQ), and cough evaluation test (CET); the secondary end-stage observation indicators include capsaicin cough sensitivity, Patient Health Questionnaire-9 (PHQ-9), Major Depression Inventory (MDI), the Generalized Anxiety Disorder-7 scale (GAD-7), Life Events Scale (LES-32), induced sputum supernatant. The safety measures will be AEs/SAEs, vital signs, liver and kidney function, fecal occult blood test.

DISCUSSION

This study is the first randomized, double-blind, and controlled clinical trial investigating the use of duloxetine in the treatment of refractory coughs. The study aims to provide a high-quality basis for evaluating the efficacy and safety of duloxetine for this condition.

TRIAL REGISTRATION

Our study was registered in the Chinese Clinical Trials Register ( www.chictr.org.cn/ ) (ChiCTR2000037429) in 28/08/2020.

Multiple Chemical Sensitivity: It's time to catch up to the science

Multiple chemical sensitivity (MCS) is a complex medical condition associated with low dose chemical exposures. MCS is characterized by diverse features and common comorbidities, including fibromyalgia, cough hypersensitivity, asthma, and migraine, and stress/anxiety, with which the syndrome shares numerous neurobiological processes and altered functioning within diverse brain regions. Predictive factors linked to MCS comprise genetic influences, gene-environment interactions, oxidative stress, systemic inflammation, cell dysfunction, and psychosocial influences. The development of MCS may be attributed to the sensitization of transient receptor potential (TRP) receptors, notably TRPV1 and TRPA1. Capsaicin inhalation challenge studies demonstrated that TRPV1 sensitization is manifested in MCS, and functional brain imaging studies revealed that TRPV1 and TRPA1 agonists promote brain-region specific neuronal variations. Unfortunately, MCS has often been inappropriately viewed as stemming exclusively from psychological disturbances, which has fostered patients being stigmatized and ostracized, and often being denied accommodation for their disability. Evidence-based education is essential to provide appropriate support and advocacy. Greater recognition of receptor-mediated biological mechanisms should be incorporated in laws, and regulation of environmental exposures.

ERS International Congress 2022: highlights from the Airway Diseases Assembly

The European Respiratory Society (ERS) celebrated the return of an in-person meeting in Barcelona, Spain, after 2 years of virtual congresses. The ERS Congress 2022 programme was replete with symposia, skills workshops and abstract presentations from all 14 assemblies, encompassing over 3000 abstracts presented in the form of thematic poster discussion and oral presentations. In this article, highlights from the ERS Congress 2022 (including from thematic poster sessions, oral presentations and symposia from keynote speakers), presented by Assembly 5 (Airway diseases, asthma, COPD and chronic cough), are reviewed by Early Career Members and experts in the field, with the aim of presenting key recent findings in the field.

Exhaled biomarkers in adults with non-productive cough

BACKGROUND

Chronic cough is a common condition but disease mechanisms are not fully understood. Our aim was to study respiratory biomarkers from the small airways in individuals with non-productive cough.

METHODS

A cohort of 107 participants answered detailed questionnaires, performed spirometry, exhaled NO measurement, impulse oscillometry, gave blood samples and particles in exhaled air (PEx) samples. Current smokers (N = 38) were excluded. A total of 14 participants reported non-productive cough (cases). A total of 55 participants reported no cough (control group). PEx samples, containing exhaled particles derived from small airways, were collected and analysed with the SOMAscan proteomics platform.

RESULTS

Participants with non-productive cough had similar age, sex, BMI, and inflammation markers in blood tests, as participants without cough. The proteomics analysis found 75 proteins significantly altered among participants with chronic cough compared to controls, after adjusting for sex and investigator performing the PExA measurement (all with p-value < 0.05 and q-value ≤ 0.13, thereof 21 proteins with a q-value < 0.05). These proteins were mostly involved in immune and inflammatory responses, complement and coagulation system, but also tight junction proteins and proteins involved in neuroinflammatory responses.

CONCLUSIONS

This exploratory study on proteomics of exhaled particles among individuals with chronic cough found alterations in relative abundance of 75 proteins. The proteins identified are implicated in both pathways known to be implicated in cough, but also potentially new pathways. Further studies are needed to explore the importance of these findings.

Polygenic risk score for ACE-inhibitor-associated cough based on the discovery of new genetic loci

AIMS

To search for sequence variants associated with ACEi discontinuation and to test their association with ACEi-associated adverse drug reactions (ADRs).

METHODS AND RESULTS

A genome-wide association study (GWAS) on ACEi discontinuation was conducted, including 33 959 ACEi-discontinuers and 44 041 controls. Cases were defined as persons who switched from an ACEi treatment to an angiotensin receptor blocker. Controls were defined as persons who continued ACEi treatment for at least 1 year. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were computed for ACEi discontinuation risk by mixed model regression analysis. Summary statistics from the individual cohorts were meta-analyzed with a fixed-effects model. To test for association with specific ACEi-associated ADRs, any genome-wide significant (P < 5 × 10-8) ACEi discontinuation variants was tested for association with ACEi-associated cough and angioedema. A polygenetic risk score (PRS) based on ACEi discontinuation GWAS data was constructed and tested for association with ACEi-associated cough and angioedema in two population-based samples. In total, seven genetic genome-wide loci were identified, of which six were previously unreported. The strongest association with ACEi discontinuation was at 20q13.3 (NTSR1; OR: 1.21; 95% CI: 1.17-1.24; P = 2.1 × 10-34). Five of seven lead variants were associated with ACEi-associated cough, whereas none were associated with ACEi-associated angioedema. The ACEi discontinuation PRS was associated with ACEi-associated cough in a dose-response manner but not with ACEi-associated angioedema. ACEi discontinuation was genetically correlated with important causes for cough, including gastro-esophageal reflux disease, allergic rhinitis, hay fever, and asthma, which indicates partly shared genetic underpinning between these traits.

CONCLUSION

This study showed the advantage of using prescription patterns to discover genetic links with ADRs. In total, seven genetic loci that associated with ACEi discontinuation were identified. There was evidence of a strong association between our ADR phenotype and ACEi-associated cough. Taken together, these findings increase insight into the pathophysiological processes that underlie ACEi-associated ADRs.

The Evolving Clinical Practice of Chronic Cough

Chronic cough, defined as a cough lasting for greater than 8 weeks, accounts for a substantial number of primary care and specialist consultations in the United States. Although cough can arise from a myriad number of serious respiratory diseases, attention has traditionally focused on diagnosing and treating gastroesophageal reflux, upper airway cough syndrome, and eosinophilic airway inflammation (asthma and nonasthmatic eosinophilic bronchitis) in patients with normal chest imaging. The newly described paradigm and entity of cough hypersensitivity syndrome (CHS) becomes useful when the etiology of cough remains elusive or when the cough remains refractory despite appropriate therapy for underlying causes. We present an update on the evolving understanding of refractory chronic cough and/or unexplained chronic cough as manifestations of laryngeal hypersensitivity and CHS. This includes a focus on understanding the pathophysiology underlying current and novel therapeutics for CHS, while also ensuring that common causes of chronic cough continue to be evaluated and treated in a systematic multidisciplinary manner.

Effects of transcranial direct current stimulation on cough reflex and urge-to-cough in healthy young adults

Background

Chronic cough is prevalent in the clinic. The existing therapies are mostly limited to medical treatment, with poor curative effects and serious side effects. Studies have suggested that the right dorsolateral prefrontal cortex (rDLPFC) may play an active role in the inhibitory pathway of cough elicitation. Thus, this study explored the effect of transcranial direct current stimulation (tDCS) on the rDLPFC activation in relation to cough reflex and urge-to-cough sensitivity.

Methods

Twenty-three healthy young adults completed the experiment. Participants randomly received tDCS anodal stimulation, cathodal stimulation, and sham stimulation, and the interval between every two stimuli was at least one week. The tDCS (2 mA, 30 min) stimulated brain rDLPFC region. After tDCS intervention, cough reflex threshold and urge-to-cough were evaluated immediately by inhalation of citric acid-saline solution.

Results

Compared with sham stimulation, the cough reflex thresholds logC₂ and logC₅ have increased under tDCS anodal stimulation (1.78 ± 0.55 g/L vs. 1.57 ± 0.57 g/L, p < 0.05; 1.92 ± 0.53 g/L vs. 1.67 ± 0.56 g/L, p < 0.05), accompanied by the increase of the urge-to-cough threshold LogC_u (0.76 ± 0.53 g/L vs. 0.47 ± 0.44 g/L, p < 0.05). In contrast, the urge-to-cough sensitivity expressed as UTC slope was not significantly changed (1.21 ± 0.86 point·L/g vs. 1.00 ± 0.37 point·L/g, p > 0.05), and there were no apparent changes in cough reflex thresholds Log C₂ and logC₅, urge-to-cough threshold LogC_u, and urge-to-cough sensitivity UTC slope under tDCS cathodal stimulation, compared with sham stimulation.

Conclusions

This study found that anodal tDCS stimulation of rDLPFC could significantly decrease cough reflex sensitivity, accompanied by the increase of urge-to-cough threshold. Further investigations targeting different brain regions using multiple central intervention techniques to explore the underlying mechanisms are warranted.

Trial registration The study protocol was registered for the clinical trial in China (registration number: ChiCTR2100045618)

Neural control of the lower airways: Role in cough and airway inflammatory disease

Airway function is under constant neurophysiological control, in order to maximize airflow and gas exchange and to protect the airways from aspiration, damage, and infection. There are multiple sensory nerve subtypes, whose disparate functions provide a wide array of sensory information into the CNS. Activation of these subtypes triggers specific reflexes, including cough and alterations in autonomic efferent control of airway smooth muscle, secretory cells, and vasculature. Importantly, every aspect of these reflex arcs can be impacted and altered by local inflammation caused by chronic lung disease such as asthma, bronchitis, and infections. Excessive and inappropriate activity in sensory and autonomic nerves within the airways is thought to contribute to the morbidity and symptoms associated with lung disease.

An open-label study of the tolerability and potential efficacy of memantine for treating refractory chronic cough

Refractory chronic cough (RCC) is defined as cough lasting longer than 8 weeks either in the absence of an identifiable underlying cause or that remains resistant to treating any potential underlying causes [1]. Affected patients have a poor quality of life and suffer from fatigue, disturbed sleep, incontinence, frustration, anxiety, and depression [2]. Despite being a debilitating condition, no licensed treatment is available.

Blocking NMDA receptors with memantine in refractory chronic cough patients is poorly tolerated and demonstrates no improvement in coughhttps://bit.ly/3kgx2g1

Association between chronic idiopathic cough and sensitive skin syndromes is a new argument in favor of common neuropathic pathways: results from a survey on 4050 subjects

Sensitive skin syndrome has a neuropathic origin, which is why it is frequently associated with irritable bowel syndrome. We have looked for a possible association with chronic cough, which is commonly maintained by neurogenic mechanisms, whatever the initial cause(s). A survey was carried out on a representative sample of the population over 15 years of age using the quota method. The questionnaire included sociodemographic data and questions about sensitive skin, the presence of chronic cough, smoking and possible causes of chronic cough. Chronic cough was assessed by the Leicester Cough Questionnaire, and 4050 subjects responded (mean age: 45 years). Overall, 12.2% of subjects with a chronic cough were compared to the 87.8% without any cough. Among them, 72.5% had sensitive skin (vs. 47.8%, p < 0.001); additionally, 17.4% of the subjects with sensitive skin had a chronic cough (vs. 6.9% if no sensitive skin). These proportions were higher if very sensitive skin was reported. The risk of having chronic cough was twice as high if sensitive skin was reported [OR = 1.9 (1.5-2.4), p < 0.001]. The risk of having sensitive skin was also twice as high for chronic cough. Thus, chronic cough and sensitive skin are frequently associated. This association represents a new argument in favor of a neuropathic nature of sensitive skin. Sensitive skin and chronic cough are both modes of overreaction to environmental factors, which tend to be autonomized by neurogenic mechanisms. Dermatologists should ask their patients if they have a chronic cough, and pneumologists should ask about the presence of sensitive skin.

Effects of pain on depression, sleep, exercise tolerance, and quality of life in patients with nontuberculous mycobacterial pulmonary disease

The experience and causes of pain in patients with nontuberculous mycobacterial pulmonary disease (NTM-PD) have not been clarified.This study aimed to determine the prevalence and severity of bodily pain (BP) in patients with NTM-PD. We also investigated the clinical indicators that contribute to pain.We used a retrospective cross-sectional study design. The participants were 114 NTM-PD patients (109 women) with a mean age of 65 years. The prevalence and severity of pain were measured using 2 items from the 36-Item Short Form Survey version 2 (SF-36), and the BP score was calculated. Functional limitation due to dyspnea was quantified using the Modified Medical Research Council Dyspnea Scale (mMRC), depression was assessed using the Center for Epidemiological Studies Depression Scale (CES-D), sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI); health-related quality of life was assessed using the Leicester Cough Questionnaire (LCQ), and exercise tolerance was measured using the Incremental Shuttle Walk Test (ISWT).Pain was reported by 70.2% of the patients (n = 80), and of these, 35.7% (n = 25) reported moderate to very severe pain. NTM-PD patients with high levels of pain had significantly higher scores on the mMRC, CES-D, and PSQI scores, and significantly lower performance on the ISWT and LCQ. Multiple regression analysis identified ISWT, CES-D, and PSQI as independent factors that affected BP scores.Our findings suggest that pain significantly impacts daily life associated with reduced exercise tolerance, the presence of depressive symptoms, and poor sleep quality in patients with NTM-PD.

Gender Difference in Chronic Cough: Are Women More Likely to Cough?

Chronic cough is a common complaint for patients to seek medical cares all over the world. Worldwide, about two thirds of chronic cough patients are females. However, in some regions of China the prevalence of chronic cough between sexes is roughly the same. Estrogen and progesterone can not only have an effect on transient receptor potential vanilloid 1 channel, eosinophils and mast cells, but also influence laryngeal dysfunction, gastroesophageal reflux disease and obstructive sleep apnea hypopnea syndrome, which may lead to increased cough sensitivity in women. On the other hand, the quality of life was adversely affected more in female patients with chronic cough. Both hormones possibly cause gender difference in chronic cough.

The interrelatedness of chronic cough and chronic pain

Since chronic cough has common neurobiological mechanisms and pathophysiology with chronic pain, both clinical disorders might be interrelated. Hence, we examined the association between chronic cough and chronic pain in adult subjects in the Rotterdam Study, a large prospective population-based cohort study.Using a standardised questionnaire, chronic pain was defined as pain lasting up to 6 months and grouped into a frequency of weekly/monthly or daily pain. Chronic cough was described as daily coughing for at least 3 months duration. The longitudinal and cross-sectional associations were investigated bi-directionally.Of 7141 subjects in the study, 54% (n=3888) reported chronic pain at baseline. The co-prevalence of daily chronic pain and chronic cough was 4.4%. Chronic cough was more prevalent in subjects with daily and weekly/monthly chronic pain compared with those without chronic pain (13.8% and 10.3% versus 8.2%; p<0.001). After adjustment for potential confounders, prevalent chronic pain was significantly associated with incident chronic cough (OR 1.47, 95% CI 1.08-1.99). The association remained significant in subjects with daily chronic pain (OR 1.49, 95% CI 1.06-2.11) with a similar effect estimate, albeit non-significant in those with weekly/monthly chronic pain (OR 1.43, 95% CI 0.98-2.10). After adjustment for covariables, subjects with chronic cough had a significant risk of developing chronic pain (OR 1.63, 95% CI 1.02-2.62) compared with those without chronic cough.Chronic cough and chronic pain confer risk on each other among adult subjects, indicating that both conditions might share common risk factors and/or pathophysiologic mechanisms.

Effect of pregabalin for the treatment of chronic refractory cough: A case report

RATIONALE

Chronic refractory cough (CRC) is a common clinical problem which is more likely associated with some physical problems. Although many patients have received satisfactory treatment, there were still many patients suffered from long-term cough symptoms after standardized treatment.

PATIENT CONCERNS

A patient suffered from postherpetic neuralgia (PHN) and also he complained CRC for more than 20 years.

DIAGNOSIS

The patient was diagnosed with PHN and CRC.

INTERVENTIONS

Pregabalin was originally administered to treat PHN.

OUTCOMES

pregabalin not only alleviated her pain of PHN but also relieved chronic cough.

LESSONS

This report demonstrated the surprising effect of pregabalin on the treatment of CRC.

An update and systematic review on drug therapies for the treatment of refractory chronic cough

INTRODUCTION

Chronic Cough (CC) is common and often associated with significant comorbidity and decreased quality of life. In up to 50% of cases, the cough is refractory despite extensive investigation and treatment trials. It is likely that the key abnormality in refractory CC is dysfunctional, hypersensitive sensory nerves, similar to conditions such as laryngeal hypersensitivity and neuropathic pain.

AREAS COVERED

The aim of this systematic review is to assess drug therapies for refractory CC. The authors review the current management of CC and provide discussion of the similarities between neuropathic pain and refractory CC. They review repurposed and new pharmacological treatments. Several meta-analyses were performed to compare the efficacy of treatments where possible.

EXPERT OPINION

Repurposed pain medications such as gabapentin and pregabalin reduce the frequency of cough and improve quality of life. Along with speech pathology, they are important and alternate treatments for refractory CC. However, more treatments are needed and the P2X3 ion channel receptor antagonists show the most promise. With a better understanding of neuronal activation and sensitisation and their signal processing in the brain, improved animal models of cough, and the use of validated cough measurement tools, more effective treatments will develop.

Risks and Cough-Aggravating Factors in Prolonged Cough. Epidemiological Observations from the Nagahama Cohort Study

RATIONALE

Chronic cough hypersensitivity, a potentially important concept of chronic or prolonged cough, is featured by heightened cough response to low-intensity stimuli, which may be generated in the absence of airflow limitations or allergic conditions. However, there is little epidemiological evidence to support this.

OBJECTIVES

In this large-scale community survey, we aimed to determine risks and cough-aggravating factors of prolonged cough while focusing on serum IgE levels.

METHODS

Prevalence of prolonged cough, defined as cough lasting 3 weeks or longer, was determined in 9,804 residents from a baseline measurement of the Nagahama Cohort Study, conducted from 2008 to 2010. Risk assessment of prolonged cough was confined to subjects without asthma (n = 9,402). A follow-up measurement of the Nagahama Study was successively conducted from 2013 to 2015, recruiting the same residents living in Nagahama City, Japan (n = 8,292). Validation analysis was performed in the follow-up measurement.

RESULTS

In a baseline measurement, prolonged cough was reported by 9.5% of subjects without asthma and 32.3% of subjects with asthma. In subjects without asthma, various cough-aggravating factors were associated with prolonged cough. On the multivariate analysis, several cough-aggravating factors, including nighttime or early morning, weather, pollen season, and common cold, were associated with prolonged cough, independent of female sex, younger age, chronic obstructive pulmonary disease, postnasal drip, daytime sputum, and lower serum total IgE. Serum-specific IgE levels against Japanese cedar pollen were significantly higher in subjects who responded "yes" to "cough in the pollen season" than in those who did not respond, whereas, among subjects who responded "yes" to "cough in the pollen season," prolonged coughers showed lower serum IgE levels against Japanese cedar pollen than temporal coughers. Validation analysis in a follow-up measurement confirmed the associations between prolonged cough and cough-aggravating factors observed in the baseline measurement.

CONCLUSIONS

The presence of several cough-aggravating factors in the absence of severe allergic conditions may support the presence of cough hypersensitivity.

Vagal Afferent Innervation of the Airways in Health and Disease

Vagal sensory neurons constitute the major afferent supply to the airways and lungs. Subsets of afferents are defined by their embryological origin, molecular profile, neurochemistry, functionality, and anatomical organization, and collectively these nerves are essential for the regulation of respiratory physiology and pulmonary defense through local responses and centrally mediated neural pathways. Mechanical and chemical activation of airway afferents depends on a myriad of ionic and receptor-mediated signaling, much of which has yet to be fully explored. Alterations in the sensitivity and neurochemical phenotype of vagal afferent nerves and/or the neural pathways that they innervate occur in a wide variety of pulmonary diseases, and as such, understanding the mechanisms of vagal sensory function and dysfunction may reveal novel therapeutic targets. In this comprehensive review we discuss historical and state-of-the-art concepts in airway sensory neurobiology and explore mechanisms underlying how vagal sensory pathways become dysfunctional in pathological conditions.

Advances in mechanisms and management of chronic cough: The Ninth London International Cough Symposium 2016

At the Ninth London International Cough Symposium held in June 2016, advances in chronic cough were presented. Chronic cough has been labelled as a cough hypersensitivity syndrome (CHS) with neuroinflammatory mechanisms likely to be the underlying mechanisms. The concept is that there is a stage of peripheral sensitisation induced by inflammatory factors setting up the scene for a central component that can be visualised by functional magnetic resonance imaging. There has also been progress in assessing CHS patients in the clinic in terms of measuring cough, with an increasing interest in assessing different types of cough associated with respiratory diseases such as asthma, COPD, bronchiectasis and pulmonary fibrosis. There is an emerging area of new antitussives in the form of neuromodulators. These advances have been paralleled by improvements in the management of patients with chronic cough. However, more work is needed but the future looks promising.

Ozone-Induced Hypertussive Responses in Rabbits and Guinea Pigs

Cough remains a major unmet clinical need, and preclinical animal models are not predictive for new antitussive agents. We have investigated the mechanisms and pharmacological sensitivity of ozone-induced hypertussive responses in rabbits and guinea pigs. Ozone induced a significant increase in cough frequency and a decrease in time to first cough to inhaled citric acid in both conscious guinea pigs and rabbits. This response was inhibited by the established antitussive drugs codeine and levodropropizine. In contrast to the guinea pig, hypertussive responses in the rabbit were not inhibited by bronchodilator drugs (β2 agonists or muscarinic receptor antagonists), suggesting that the observed hypertussive state was not secondary to bronchoconstriction in this species. The ozone-induced hypertussive response in the rabbit was inhibited by chronic pretreatment with capsaicin, suggestive of a sensitization of airway sensory nerve fibers. However, we could find no evidence for a role of TRPA1 in this response, suggesting that ozone was not sensitizing airway sensory nerves via activation of this receptor. Whereas the ozone-induced hypertussive response was accompanied by a significant influx of neutrophils into the airway, the hypertussive response was not inhibited by the anti-inflammatory phosphodiesterase 4 inhibitor roflumilast at a dose that clearly exhibited anti-inflammatory activity. In summary, our results suggest that ozone-induced hypertussive responses to citric acid may provide a useful model for the investigation of novel drugs for the treatment of cough, but some important differences were noted between the two species with respect to sensitivity to bronchodilator drugs.

Evidence for neuropathic processes in chronic cough

Chronic cough is a very common symptom for which patients seek medical attention but can often be difficult to manage, because associated causes may remain elusive and treatment of any associated causes does not always provide adequate relief. Current antitussives have limited efficacy and undesirable side-effects. Patients with chronic cough typically describe sensory symptoms suggestive of upper airway and laryngeal neural dysfunction. They often report cough triggered by low-level physical and chemical stimuli supporting the recently emerging concept of 'cough hypersensitivity syndrome'. Chronic cough is a neuropathic condition that could be secondary to sensory nerve damage caused by inflammatory, infective and allergic factors. Mechanisms underlying peripheral and central augmentation of the afferent cough pathways have been identified. Successful treatment of chronic cough with agents used for treating neuropathic pain, such as gabapentin and amitriptyline, would also support this concept. Further research of neuropathic cough may lead to the discovery of more effective antitussives in the future.

Neuroimmune interactions in itch: Do chronic itch, chronic pain, and chronic cough share similar mechanisms?

Itch and pain are closely related but also clearly distinct sensations. Pain is known to suppress itch, while analgesics such as morphine can provoke itch. However, in pathological and chronic conditions, pain and itch also have similarities. Dysfunction of the nervous system, as manifested by neural plastic changes in primary sensory neurons of the peripheral nervous system (peripheral sensitization) and spinal cord and brain stem neurons in the central nervous system (central sensitization) will result in chronic pain and itch. Importantly, these diseases also result from immune dysfunction, since inflammatory mediators can directly activate or sensitize nociceptive and pruriceptive neurons in the peripheral and central nervous system, leading to pain and itch hypersensitivity. In this mini-review, I discuss the roles of Toll-like receptors (TLRs), transient receptor potential ankyrin 1 (TRPA1) ion channel, and Nav1.7 sodium channel in regulating itch and inflammation, with special emphasis of neuronal TLR signaling and the interaction of TLR7 and TRPA1. Chronic pain and chronic itch are debilitating diseases and dramatically impact the life quality of patients. Targeting TLRs for the control of inflammation, neuroinflammation (inflammation restricted in the nervous system), and hyperexcitability of nociceptors and pruriceptors will lead to new therapeutics for the relief of chronic pain and chronic itch. Finally, given the shared mechanisms among chronic cough, chronic pain, and chronic itch and the demonstrated efficacy of the neuropathic pain drug gabapentin in treating chronic cough, novel therapeutics targeting TRPA1, Nav1.7, and TLRs may also help to alleviate refractory cough via modulating neuron-immune interaction.

Neural dysfunction following respiratory viral infection as a cause of chronic cough hypersensitivity

Respiratory viral infections are a common cause of acute coughing, an irritating symptom for the patient and an important mechanism of transmission for the virus. Although poorly described, the inflammatory consequences of infection likely induce coughing by chemical (inflammatory mediator) or mechanical (mucous) activation of the cough-evoking sensory nerves that innervate the airway wall. For some individuals, acute cough can evolve into a chronic condition, in which cough and aberrant airway sensations long outlast the initial viral infection. This suggests that some viruses have the capacity to induce persistent plasticity in the neural pathways mediating cough. In this brief review we present the clinical evidence of acute and chronic neural dysfunction following viral respiratory tract infections and explore possible mechanisms by which the nervous system may undergo activation, sensitization and plasticity.

Chronic cough: from a complex dysfunction of the neurological circuit to the production of persistent cough

Chronic cough or cough that lasts more than 8 weeks, once a chest x-ray and spirometry are confirmed normal, is caused by an alteration in a section of the route between peripheral receptors, mainly in the upper and lower airway and oesophagus, spinal cord and the cough centre in the brain stem involving the cortex. These mechanisms of cough have their homology in the circuit of chronic pain, and on that basis, should expand future research of chronic cough. Clinically chronic cough is easy to diagnose by an excessive response or hypertussia to low-intensity stimuli or banal stimuli, which we now call hypersensitivity cough syndrome, quantified by a positive reflex cough with capsaicin or citric acid. However, hypersensitivity cough syndrome can be impossible to quantify in the laboratory when the hyper-responsiveness originates in the central nervous system. This is normally caused by excessive peripheral input or convergence of stimuli from different sources. Once central hypersensitivity is acquired, peripheral input is not as important for activation of the cough.

Capsaicin cough sensitivity is related to the older female predominant feature in chronic cough patients

Purpose

The present study aimed to examine the age and gender distributions among chronic cough patients referred to a tertiary cough clinic in Korea, and to investigate clinical factors related to the demographic findings.

Methods

Study participants were unselectively recruited from adult chronic cough patients who attended the cough clinic for the first time during one year. To validate their representativeness, their age and gender distributions were compared to the entire chronic cough population, or with those presenting with other chronic disease. Data from the baseline investigations were analyzed to identify clinical factors related to the demographic findings.

Results

A total of 272 chronic cough patients were included. They had a middle-aged female predominant feature (mean age: 52.8±15.7 years and female 69.1%). Their age and gender distributions were almost identical to the entire chronic cough population, but were distinct from patients with hypertension. Among clinical factors, the older female predominance was associated with enhanced capsaicin cough sensitivity, and also with the presence of 'cough by cold air' symptom. Allotussia and laryngeal paresthesia were highly common in chronic cough patients, affecting 94.8% and 86.8% of them, respectively.

Conclusions

The present study demonstrated older female predominance among adult chronic cough patients attending a referral cough clinic in Korea. The demographic features were significantly associated with the capsaicin cough responses and also potentially with allotussia (particularly cold air as the trigger). These findings suggest a role of cough reflex sensitization in the pathophysiology of chronic cough in adults.

Development and validation of the Newcastle laryngeal hypersensitivity questionnaire

Background

Laryngeal hypersensitivity may be an important component of the common disorders of laryngeal motor dysfunction including chronic refractory cough, pdoxical vocal fold movement (vocal cord dysfunction), muscle tension dysphonia, and globus pharyngeus. Patients with these conditions frequently report sensory disturbances, and an emerging concept of the ‘irritable larynx’ suggests common features of a sensory neuropathic dysfunction as a part of these disorders. The aim of this study was to develop a Laryngeal Hypersensitivity Questionnaire for patients with laryngeal dysfunction syndromes in order to measure the laryngeal sensory disturbance occurring in these conditions.

Methods

The 97 participants included 82 patients referred to speech pathology for behavioural management of laryngeal dysfunction and 15 healthy controls. The participants completed a 21 item self administered questionnaire regarding symptoms of abnormal laryngeal sensation. Factor analysis was conducted to examine correlations between items. Discriminant analysis and responsiveness to change were evaluated.

Results

The final questionnaire comprised 14 items across three domains: obstruction, pain/thermal, and irritation. The questionnaire demonstrated significant discriminant validity with a mean difference between the patients with laryngeal disorders and healthy controls of 5.5. The clinical groups with laryngeal hypersensitivity had similar abnormal scores. Furthermore the Newcastle Laryngeal Hypersensitivity Questionnaire (LHQ) showed improvement following behavioural speech pathology intervention with a mean reduction in LHQ score of 2.3.

Conclusion

The Newcastle Laryngeal Hypersensitivity Questionnaire is a simple, non-invasive tool to measure laryngeal pesthesia in patients with laryngeal conditions such as chronic cough, pdoxical vocal fold movement (vocal cord dysfunction), muscle tension dysphonia, and globus pharyngeus. It can successfully differentiate patients from healthy controls and measure change following intervention. It is a promising tool for use in clinical research and practice.

Targeting voltage gated sodium channels NaV1.7, Na V1.8, and Na V1.9 for treatment of pathological cough

Recent advances in our understanding of voltage-gated sodium channels (NaVs) lead to the rational hypothesis that drugs capable of selective blockade of NaV subtypes may be a safe and effective strategy for the treatment of unwanted cough. Among the nine NaV subtypes (NaV1.1-NaV1.9), the afferent nerves involved in initiating cough, in common with nociceptive neurons in the somatosensory system, express mainly NaV1.7, NaV1.8, and NaV1.9. Although knowledge about the effect of selectively blocking these channels on the cough reflex is limited, their biophysical properties indicate that each may contribute to the hypertussive and allotussive state that typifies subacute and chronic nonproductive cough.