Enhanced cough response to hyperpnea with cold air challenge in chronic cough patients showing increased cough sensitivity to inhaled capsaicin

Recurrent Cough in the Elderly: A Forgotten Entity

INTRODUCTION

Recurrent cough is little researched in adults. We investigated the prevalence, risk factors, and consequences of recurrent cough, and compared the results to those of isolated chronic cough.

METHODS

Cross-sectional email survey in an elderly community-based population. Recurrent cough was defined as ≥ 3 cough episodes within one year (each lasting ≥ 1 week) and no current chronic cough. Isolated chronic cough was defined as current cough lasting ≥ 8 weeks and no recurrent cough.

RESULTS

The prevalence of recurrent cough was 3.8% among all respondents (n = 5983). Recurrent cough was associated with asthma (aOR 3.32 (95% CI 2.13-5.18)), chronic rhinosinusitis (2.91 (1.89-4.46)), family history of chronic cough (2.59 (1.88-3.56)), analgesic intolerance (2.13 (1.27-3.57)), male gender (1.92 (1.39-2.66)), gastro-esophageal reflux disease (1.73 (1.21-2.47)), obstructive sleep apnoea (1.69 (1.23-2.32)), symptom sum (1.12 per symptom (1.03-1.22)), and younger age (0.96 per year (0.93-1.00)). Isolated chronic cough was associated with chronic rhinosinusitis (3.45 (2.39-4.97)), asthma (2.17 (1.38-3.41), gastro-esophageal reflux disease (1.80 (1.32-2.47)), family history of chronic cough (1.80 (1.35-2.41)), obstructive sleep apnoea (1.49 (1.12-2.00)), symptom sum (1.18 per symptom (1.10-1.27)), and body mass index (0.96 per unit (0.93-1.00)). Among subjects with recurrent and isolated chronic cough, the prevalence of depressive symptoms were 7.7% and 4.2%, p = 0.11, the Leicester Cough Questionnaire total scores 15.2 (14.6-15.8) and 16.3 (16.0-16.6), P = 0.001, and the mean number of yearly cough-related doctor`s visits 0.58 (0.45-0.71) and 0.36 (0.19-0.53), P = 0.007, respectively.

CONCLUSION

The risk factors and consequences of recurrent and isolated chronic cough were comparable. Recurrent cough seems beneficial to address in cough evaluation.

A Cold Environment Aggravates Cough Hyperreactivity in Guinea Pigs With Cough by Activating the TRPA1 Signaling Pathway in Skin

Cough exacerbation in cold environments is a characteristic feature of patients with chronic cough. There is consensus that inhalation of cold air stimulates cough receptors but this idea is not consistent with the fact that cold air is usually unable to directly enter the lower airway. To elucidate the effects of cold environments and transient receptor potential ankyrin 1 (TRPA1) on cough, we compared cough reactivity, airway inflammation, and TRPA1 expression in guinea pigs with chronic cough induced by the repeated inhalation of citric acid for 15 days. The guinea pigs were exposed to cold environments for three consecutive days from day 13 to 15. Repeated inhalation of citric acid increased cough reactivity to inhaled cinnamaldehyde. We found that exposure to cold environments further aggravated cough hyperreactivity in guinea pigs with chronic cough, but not in normal guinea pigs. Cough hyperreactivity was promoted when the whole body and trunk-limbs, but not the heads, of the guinea pigs were exposed to cold environments, and abolished by pretreating the skin through immersion in the TRPA1 antagonist, HC-030031. Substance P levels in bronchoalveolar lavage fluid, and TRPA1 expression in the trachea and skin, were increased in guinea pigs when the whole body and trunk-limbs, rather than the head, were exposed to cold environments. However, this trend was also abolished by pretreatment of the skin via immersion in HC-030031. Similar changes in TRPA1 expression were also detected in the sensory fibers of the trachea and skin, as identified by immunofluorescence and laser-scanning confocal microscopy analysis. These results suggest that exaggerated cough hyperreactivity induced by cold environments may be related to activation of the cold-sensing TRPA1 signaling pathway in the skin, rather than the inhalation of cold air.

Cough-provocation tests with hypertonic aerosols

Recent advances in cough research suggest a more widespread use of cough-provocation tests to demonstrate the hypersensitivity of the cough reflex arc. Cough-provocation tests with capsaicin or acidic aerosols have been used for decades in scientific studies. Several factors have hindered their use in everyday clinical work: i.e. lack of standardisation, the need for special equipment and the limited clinical importance of the response. Cough-provocation tests with hypertonic aerosols (CPTHAs) involve provocations with hypertonic saline, hypertonic histamine, mannitol and hyperpnoea. They probably act via different mechanisms than capsaicin and acidic aerosols. They are safe and well tolerated and the response is repeatable. CPTHAs can assess not only the sensitivity of the cough reflex arc but also the tendency of the airway smooth muscles to constrict (airway hyper-responsiveness). They can differentiate between subjects with asthma or chronic cough and healthy subjects. The responsiveness to CPTHAs correlates with the cough-related quality of life among asthmatic subjects. Furthermore, the responsiveness to them decreases during treatment of chronic cough. A severe response to CPTHAs may indicate poor long-term prognosis in chronic cough. The mannitol test has been stringently standardised, is easy to administer with simple equipment, and has regulatory approval for the assessment of airway hyper-responsiveness. Manual counting of coughs during a mannitol challenge would allow the measurement of the function of the cough reflex arc as a part of clinical routine.

Cough-provocation tests with hypertonic aerosols offer the possibility to measure the function of the cough reflex arc even in everyday clinical workhttp://bit.ly/2RTOfMI

Comparison of mannitol and citric acid cough provocation tests

RATIONALE

Citric acid has been used as a cough provocation test for decades. However, the methods of administration have not been standardized. Inhaled mannitol is a novel cough provocation test, which has regulatory approval and can be performed utilizing a simple disposable inhaler in a standardized manner.

OBJECTIVE

To compare the mannitol and citric acid cough provocation tests with respect to their ability to identify subjects with chronic cough and their tolerability.

METHODS

Subjects with chronic cough (n = 36) and controls (n = 25) performed provocation tests with mannitol and citric acid. Both tests were video recorded. Cough sensitivity was expressed as coughs-to-dose ratios (CDR) and the cumulative doses to mannitol or concentration to citric acid evoking 5 coughs (C5). Forced expiratory volume in 1 s (FEV₁), visual analogue scales (VAS), test completion rates and the total cough frequencies were analysed.

RESULTS

Mannitol and citric acid CDR both effectively separated those with cough and the control subjects (AUC 0.847 and 0.803, respectively) as did C5 (AUC 0.823 and 0.763, respectively). There was a good correlation between the cough sensitivity provoked by the two stimuli, either expressed as CDR (r = 0.65, p < 0.001) or C5 (r = 0.53, p = 0.001). Both tests were similarly tolerated in terms of VAS, although more patients discontinued the mannitol test early, primarily due to cough.

CONCLUSIONS

Mannitol and citric acid tests correlated well, equally identified subjects with chronic cough and their tolerability was similar. The feasibility issues, strict standardisation and regulatory approval may favour mannitol to be used in clinical cough research.

Heterogeneity of cough hypersensitivity mediated by TRPV1 and TRPA1 in patients with chronic refractory cough

Background

The differential sensitivity of cough to antitussive therapies implies the existence of heterogeneity in cough hypersensitivity, but how such heterogeneity is expressed across individual patients is poorly understood. We investigated the phenotypes of cough hypersensitivity by examining transient receptor potential ankyrin 1 (TRPA1)- and transient receptor potential vanilloid 1 (TRPV1)-mediated cough sensitivity in patients with chronic refractory cough.

Methods

Using a selective TRPA1 agonist, allyl isothiocyanate (AITC), we established an AITC cough challenge as a measure of TRPA1-mediated cough sensitivity. The AITC cough challenge and the widely used capsaicin (a selective TRPV1 agonist) cough challenge were performed with 250 patients with chronic refractory cough and 56 healthy subjects. The concentration of AITC or capsaicin solution causing at least two (C2) and five coughs (C5) was recorded. Cough sensitivity was expressed as the mean (95% confidence interval) of log C5, and cough hypersensitivity was defined as a log C5 value lower than that of healthy subjects.

Results

A distinct concentration–response effect of inhaled AITC was identified both in patients with chronic refractory cough and in healthy subjects. Cough sensitivity to AITC and capsaicin was significantly higher in patients than in healthy subjects (AITC: 2.42 [2.37–2.48] vs 2.72 [2.66–2.78] mM, p = 0.001; capsaicin: 1.87 [1.75–1.98] vs 2.53 [2.36–2.70] μM, p = 0.001) and was higher in females than in males for both healthy subjects and patients (all p < 0.05). Among the 234 patients who completed both challenges, 25 (10.7%) exhibited hypersensitivity to both AITC and capsaicin, 44 (18.8%) showed hypersensitivity to AITC only, 28 (11.9%) showed hypersensitivity to capsaicin only, and 137 (58.6%) exhibited hypersensitivity to neither. Those with TRPA1- and/or TRPV1-mediated hypersensitivity were predominantly female, while those without TRPA1- and TRPV1-mediated hypersensitivity were mainly male.

Conclusions

Four phenotypes of cough hypersensitivity were identified by the activation of TRPV1 and TRPA1 channels, which supports the existence of heterogeneity in cough pathways and provides a new direction for personalized management of chronic refractory cough.

Trial registration

ClinicalTrials.gov NCT02591550.

Effects of indole alkaloids from leaf of Alstonia scholaris on post-infectious cough in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Leaf of Alstonia scholaris (L.) R. Br. (Apocynaceae), a wide used ethic-medicine in many Asia and Africa counties, has also been recorded as the common traditional Chinese medicine for treatment of illnesses in respiratory system by Dai people.

AIM OF THE STUDY

To provide experimental data of clinical adaption of total indole alkaloids (TA) from leaf of A. scholaris for treating post-infectious cough in phase II clinical trial.

MATERIALS AND METHODS

To model post-infectious cough, all animals except control group were instilled intra-tracheal with lipopolysaccharide (LPS) (80 μg/50 µL/mouse), followed by subsequent exposure to cigarette smoke (CS) for 30 min per day for a total of 30 days. Mice were orally given TA at dose of 10, 25, 50 mg/kg, and four main alkaloids (Sch: scholaricine, Epi: 19-epischolaricine, Val: vallesamine, Pic: picrinine) once daily. Cellular infiltration was assessed in the broncho-alveolar lavage fluid (BALF). Expression of interleukin-6 (IL-6) and C-reactive protein (CRP) in the serum was determined, the superoxide dismutase (SOD) activity as well as malondialdehyde (MDA) content in the serum and homogenate were examined. Finally, histopathological examination in the lungs was assessed by H. E. staining.

RESULTS

After administration of TA and four major alkaloids respectively, the symptoms of cough in mice were obviously attenuated. Total white blood cells (WBC) and neutrophils (NEU) amounts in BALF were reduced obviously and the pathological damage of lung was also attenuated. There was also significant reduction in IL-6, CRP, MDA and a marked improvement in SOD.

CONCLUSIONS

The efficacy of indole alkaloids against post-infectious cough (PIC) was shown in the down-regulation of inflammatory cells, cytokines, and the balance of antioxidants. What's more, the pharmacological effects of TA were better than single indole alkaloid, which might be related to the synergic effect of four major alkaloids.

Curative Effects of Suhuang Zhike Capsule on Postinfectious Cough: A Meta-Analysis of Randomized Trials

Objective. In this paper, we intended to systematically evaluate the efficacy of Suhuang Zhike Capsule (SZC) on postinfectious cough (PIC) in adults (age > 18). Methods. MEDLINE (PubMed), Chinese National Knowledge Infrastructure (CNKI), Cqvip Database (VIP), and Wanfang Database were researched for the randomized controlled trials (RCTs) of SZC for PIC. The search was limited to human studies, using the search keywords or free-text terms “cough,” “post-infectious cough,” “postinfectious cough,” “post-cold cough,” “postviral cough,” “postcold cough,” “Suhuang Zhike capsule,” “Chinese Medicine,” and “randomized clinical trials”. Two reviewers individually extracted data from the included RCTs and then the extracted data were analyzed using Review Manager 5.3 software. Results. Seven RCTs involving 573 patients entered the inclusion criteria. Findings suggested that, compared with western conventional medicine (WCM) and other Chinese medicine, SZC could effectively improve the efficacy rate (OR 2.68, 95%  CI, 1.48–4.84, P = 0.001; OR 4.86, 95%  CI, 1.50–15.73, P = 0.008, separately). Moreover, SZC could also improve the efficacy rate of Chinese medicine symptom (MD −0.74, 95%  CI, −1.46~−0.02, P = 0.04). However, in terms of cough relief time, more evidence is needed to prove that SZC have an earlier antitussive effect (MD −1.31, 95%  CI, −3.06~0.45, P = 0.14). Conclusion. The current evidence shows that SZC is effective in the treatment of PIC in adults and can significantly improve the effective rate of Chinese medicine symptoms.

Chinese herbal medicine for postinfectious cough: a systematic review of randomized controlled trials

Chinese herbal medicine has been commonly used in the treatment of postinfectious cough. The aim of this review is to systematically evaluate the efficacy and safety of Chinese herbal medicine for postinfectious cough. An extensive search for RCTs was performed using multiple electronic databases, supplemented with a manual search. All studies included were confirmed with specific inclusion criteria. Methodological quality of each study was examined according to the Cochrane risk of bias assessment. Quality of evidence was evaluated using rating approach developed by GRADE working group. The literature search yielded 352 results, of which 12 RCTs satisfied the inclusion criteria, offering moderate-to-high levels of evidence. Methodological quality was considered high in three trials, while in the other nine studies the unclear risk of bias was in the majority. Findings suggested that, compared with western conventional medicine or placebo, Chinese herbal medicine could effectively improve core symptoms of postinfectious cough, act better and have earlier antitussive effect, and enhance patients' quality of life. No serious adverse event was reported.

Capsaicin-induced apoptosis of FaDu human pharyngeal squamous carcinoma cells

PURPOSE

To investigate the anti-tumor effect of capsaicin on human pharyngeal squamous carcinoma cells (FaDu).

MATERIALS AND METHODS

The expression of apoptosis/cell cycle-related proteins (or genes) was examined by reverse transcriptase- polymerase chain reaction, western blotting and ELISA methods, while the apoptotic cell population, cell morphology and DNA fragmentation levels were assessed using flow cytometry, fluorescence microscopy and agarose gel electrophoresis.

RESULTS

Capsaicin was found to inhibit the growth and proliferation of FaDu cells in a dose- and time-dependent manner. Apoptotic cell death was confirmed by observing increases in nuclear condensation, nuclear DNA fragmentation and sub-G1 DNA content. The observed increase in cytosolic cytochrome c, activation of caspase 3 and PARP (p85) levels following capsaicin treatment indicated that the apoptotic response was mitochondrial pathway-dependent. Gene/protein expression analysis of Bcl-2, Bad and Bax further revealed decreased anti-apoptotic Bcl-2 protein and increased pro-apoptotic Bad/Bax expression. Furthermore, capsaicin suppressed the cell cycle progression at the G1/S phase in FaDu cells by decreasing the expression of the regulators of cyclin B1 and D1, as well as cyclin-dependent protein kinases cdk-1, cdk-2 and cdk-4.

CONCLUSION

Our current data show that capsaicin induces apoptosis in FaDu cells and this response is associated with mitochondrial pathways, possibly by mediating cell cycle arrest at G1/S.

Dyspnea from exercise in cold air is not always asthma

In the absence of other explanations, exercise-induced dyspnea is often labeled as a manifestation of asthma. The aim of this study was to use exercise provocation in cold air among patients with exercise-induced dyspnea, but without any bronchoconstriction, in order to study induced symptoms and different physiological parameters and to measure the possible influence of exercise in cold air on capsaicin cough sensitivity. Eleven patients with exercise-induced dyspnea but no asthma, along with 11 healthy controls, performed a capsaicin inhalation provocation on two occasions. One of these provocations was preceded by an exercise provocation in a cold chamber. Number of coughs, airway symptoms, spirometry, respiratory rate, pulse rate, end-tidal CO(2), and PSaO(2) were registered. During exercise, the patients coughed more than the controls and also had more airway symptoms. After exercise provocation, spirometry values remained unchanged, but capsaicin cough sensitivity was increased and end-tidal CO(2) decreased among the patients, both in comparison to the controls and in comparison to the patients themselves prior to exercise. Exercise-induced dyspnea may be associated with hypocapnia from hyperventilation and increased capsaicin cough sensitivity. The diagnosis of exercise-induced asthma should be questioned when the patient has no signs of bronchoconstriction.

Cold air-provoked respiratory symptoms: the mechanisms and management

OBJECTIVES

To describe the mechanisms and management of cold air-provoked respiratory symptoms.

STUDY DESIGN

A literature review.

METHODS

The review includes human epidemiological studies, human and animal experimental studies, as well as human studies about management of the cold air-provoked respiratory symptoms.

RESULTS

Cold air is unlikely to be a causal factor initiating respiratory diseases but a symptom trigger. In the present review, the airway responses beyond these symptoms were divided into three types. The short-term responses are those that develop within minutes in response to sudden cooling of the airways. Subjects with asthma or rhinitis are especially prone to these responses. The long-term responses are those that develop in response to repeated and long-standing cooling and drying of the airways, usually in endurance athletes. Finally, there are the physiological, reflex-mediated lower-airway responses to cooling of the skin or upper airways.

CONCLUSIONS

The mechanisms beyond cold air-provoked respiratory symptoms vary considerably and mainly depend on the individual's susceptibility and the ventilation level during the cold exposure. An understanding of these mechanisms is essential for successful management of the symptoms.

Safety of capsaicin cough challenge testing

BACKGROUND

Capsaicin, the pungent extract of red peppers, has achieved widespread use in clinical research because it induces cough in a dose-dependent and reproducible manner. Although > 2 decades of experience has led investigators to consider capsaicin cough challenge testing a safe diagnostic modality, this issue has not been specifically addressed in the literature.

STUDY OBJECTIVES

To review the published experience with capsaicin inhalation challenge testing in terms of safety.

DESIGN

Literature review and personal communication with study authors.

SETTING

Academic medical center.

RESULTS

One hundred twenty-two published studies since 1984 described 4,833 subjects (4,374 adults, 459 children) undergoing capsaicin cough challenge, with no serious adverse events reported. Subjects included healthy volunteers as well as patients with asthma, COPD, pathologic cough, and other respiratory conditions. Minor complaints described in a small fraction of studies consisted mainly of transient throat irritation. Personal communication with the authors of > 90% of the studies confirmed an absence of any serious adverse events. Furthermore, these investigators have performed thousands of additional capsaicin challenge studies not reported in the literature, also without any associated serious adverse events.

CONCLUSIONS

A review of the 20-year clinical experience has failed to uncover a single serious adverse event associated with capsaicin cough challenge testing in humans. Given the need for better antitussive therapies, capsaicin represents a vital component of future scientific inquiry in the field of cough.

Cough induced by airway vibration as a model of airway hyperreactivity in patients with acute upper respiratory tract infection

Patients with acute upper respiratory tract infection (URTI) have been shown to be hyperreactive to inhaled tussigens such as citric acid and capsaicin, and the authors propose that this may be due to an increased sensitivity of airway receptors that mediate cough. In recent studies we have demonstrated that cough may be induced by vibration of the airway at the level of the throat or chest in patients with URTI but that the same stimuli induce little or no cough in healthy subjects. The difference between the patients with URTI and healthy subjects in their response to airway vibration may be explained on the basis of hyperreactivity of airway sensory receptors. We propose that the model of cough induced by airway vibration may be useful for studies on the pathophysiology and pharmacology of airway hyperreactivity in acute cough. The airway vibration model of cough may have some advantages over inhaled tussigens as the stimulus is easily controlled and the method is safe for use in children.