Pre-clinical studies in cough research: role of Transient Receptor Potential (TRP) channels

Zhisou powder suppresses airway inflammation in LPS and CS-induced post-infectious cough model mice via TRPA1/TRPV1 channels

ETHNOPHARMACOLOGICAL RELEVANCE

Zhisou Powder (ZSP), a traditional Chinese medicine (TCM) prescription, has been widely used in the clinic for the treatment of post-infectious cough (PIC). However, the exact mechanism is not clear.

AIM OF THE STUDY

The aim of this study was to investigate the ameliorative effect of ZSP on PIC in mice. The possible mechanisms of action were screened based on network pharmacology, and the potential mechanisms were explored through molecular docking and in vivo experimental validation.

MATERIALS AND METHODS

Lipopolysaccharide (LPS) (80μg/50 μL) was used to induce PIC in mice, followed by daily exposure to cigarette smoke (CS) for 30 min for 30 d to establish PIC model. The effects of ZSP on PIC mice were observed by detecting the number of coughs and cough latency, peripheral blood and bronchoalveolar lavage fluid (BALF) inflammatory cell counts, enzyme-linked immunosorbent assay (ELISA), and histological analysis. The core targets and key pathways of ZSP on PIC were analyzed using network pharmacology, and TRPA1 and TRPV1 were validated using RT-qPCR and western blotting assays.

RESULTS

ZSP effectively reduced the number of coughs and prolonged the cough latency in PIC mice. Airway inflammation was alleviated by reducing the expression levels of the inflammatory mediators TNF-α and IL-1β. ZSP modulated the expression of Substance P, Calcitonin gene-related peptide (CGRP), and nerve growth factor (NGF) in BALF. Based on the results of network pharmacology, the mechanism of action of ZSP may exert anti-neurogenic airway-derived inflammation by regulating the expression of TRPA1 and TRPV1 through the natural active ingredients α-spinastero, shionone and didehydrotuberostemonine.

CONCLUSION

ZSP exerts anti-airway inflammatory effects through inhibition of TRPA1/TRPV1 channels regulating neuropeptides to alleviate cough hypersensitivity and has a favorable therapeutic effect on PIC model mice. It provides theoretical evidence for the clinical application of ZSP.

Xingbei antitussive granules ameliorate cough hypersensitivity in post-infectious cough guinea pigs by regulating tryptase/PAR2/TRPV1 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Xingbei antitussive granules (XB) is a classic Chinese Medicine prescription for treating post-infectious cough(PIC), based on the Sanao Decoction from Formularies of the Bureau of People's Welfare Pharmacies in the Song Dynasty and Jiegeng decoction from Essentials of the Golden Chamber in the Han Dynasty. However, the therapeutic effects and pharmacological mechanisms are still ambiguous. In the present study, we endeavored to elucidate these underlying mechanisms.

AIMS OF THE STUDY

This study aimed to explore the potential impact and mechanism of XB on PIC, and provide a scientific basis for its clinical application.

MATERIALS AND METHODS

Cigarette smoking (CS) combined with lipopolysaccharide (LPS) nasal drops were administered to induce the PIC guinea pig with cough hypersensitivity status. Subsequently, the model guinea pigs were treated with XB and the cough frequency was observed by the capsaicin cough provocation test. The pathological changes of lung tissue were assessed by HE staining, and the levels of inflammatory mediators, mast cell degranulating substances, and neuropeptides were detected. The protein and mRNA expression of transient receptor potential vanilloid type 1(TRPV1), proteinase-activated receptor2(PAR2), and protein kinase C (PKC) were measured by Immunohistochemical staining, Western blot, and RT-qPCR. Changes in the abundance and composition of respiratory bacterial microbiota were determined by 16S rRNA sequencing.

RESULTS

After XB treatment, the model guinea pigs showed a dose-dependent decrease in cough frequency, along with a significant alleviation in inflammatory infiltration of lung tissue and a reduction in inflammatory mediators. In addition, XB high-dose treatment significantly decreased the levels of mast cell Tryptase as well as β-hexosaminidase (β-Hex) and downregulated the expression of TRPV1, PAR2, and p-PKC. Simultaneously, levels of neuropeptides like substance P (SP), calcitonin gene-related peptide (CGRP), neurokinin A (NKA), and nerve growth factor (NGF) were improved. Besides, XB also can modulate the structure of respiratory bacterial microbiota and restore homeostasis.

CONCLUSION

XB treatment alleviates cough hypersensitivity and inflammatory responses, inhibits the degranulation of mast cells, and ameliorates neurogenic inflammation in PIC guinea pigs whose mechanism may be associated with the inhibition of Tryptase/PAR2/PKC/TRPV1 and the recovery of respiratory bacterial microbiota.

Neural Mechanisms Underlying the Coughing Reflex

Breathing is an intrinsic natural behavior and physiological process that maintains life. The rhythmic exchange of gases regulates the delicate balance of chemical constituents within an organism throughout its lifespan. However, chronic airway diseases, including asthma and chronic obstructive pulmonary disease, affect millions of people worldwide. Pathological airway conditions can disrupt respiration, causing asphyxia, cardiac arrest, and potential death. The innervation of the respiratory tract and the action of the immune system confer robust airway surveillance and protection against environmental irritants and pathogens. However, aberrant activation of the immune system or sensitization of the nervous system can contribute to the development of autoimmune airway disorders. Transient receptor potential ion channels and voltage-gated Na+ channels play critical roles in sensing noxious stimuli within the respiratory tract and interacting with the immune system to generate neurogenic inflammation and airway hypersensitivity. Although recent studies have revealed the involvement of nociceptor neurons in airway diseases, the further neural circuitry underlying airway protection remains elusive. Unraveling the mechanism underpinning neural circuit regulation in the airway may provide precise therapeutic strategies and valuable insights into the management of airway diseases.

Association of lower plasma citric acid with prolonged cough: the Nagahama study

Little is known about the association of prolonged cough, a common and troublesome symptom, with metabolic pathways. We aimed to clarify this association using data from the Nagahama cohort, a prospective study of participants from the general population. Self-report questionnaires on prolonged cough were collected at baseline and 5-year follow-up assessments. Blood tests at follow-up were used for gas chromatography-mass spectrometry-based metabolomics. The association between metabolites and prolonged cough was examined using the partial least squares discriminant analysis and multiple regression analysis. Among the 7432 participants, 632 had newly developed prolonged cough at follow-up, which was defined as "new-onset prolonged cough". Low plasma citric acid was significantly associated with new-onset prolonged cough, even after the adjustment of confounding factors including the presence of asthma, upper airway cough syndrome (UACS), and gastroesophageal reflux disease (GERD). A similar association was observed for isocitric acid, 3-hydroxybutyric acid, and 3-hydroxyisobutyric acid. The analysis of these four metabolites revealed that citric acid had the strongest association with new-onset prolonged cough. This significant association remained even when the analysis was confined to participants with UACS or GERD at baseline or follow-up, and these associations were also observed in participants (n = 976) who had prolonged cough at follow-up regardless of baseline status. In conclusion, low blood citric acid may be associated with prolonged cough.

Alterations in Pulmonary Physiology with Lung Transplantation

Lung transplant is a treatment option for patients with end-stage lung diseases; however, survival outcomes continue to be inferior when compared to other solid organs. We review the several anatomic and physiologic changes that result from lung transplantation surgery, and their role in the pathophysiology of common complications encountered by lung recipients. The loss of bronchial circulation into the allograft after transplant surgery results in ischemia-related changes in the bronchial artery territory of the allograft. We discuss the role of bronchopulmonary anastomosis in blood circulation in the allograft posttransplant. We review commonly encountered complications related to loss of bronchial circulation such as allograft airway ischemia, necrosis, anastomotic dehiscence, mucociliary dysfunction, and bronchial stenosis. Loss of dual circulation to the lung also increases the risk of pulmonary infarction with acute pulmonary embolism. The loss of lymphatic drainage during transplant surgery also impairs the management of allograft interstitial fluid, resulting in pulmonary edema and early pleural effusion. We discuss the role of lymphatic drainage in primary graft dysfunction. Besides, we review the association of late posttransplant pleural effusion with complications such as acute rejection. We then review the impact of loss of afferent and efferent innervation from the allograft on control of breathing, as well as lung protective reflexes. We conclude with discussion about pulmonary function testing, allograft monitoring with spirometry, and classification of chronic lung allograft dysfunction phenotypes based on total lung capacity measurements. We also review factors limiting physical exercise capacity after lung transplantation, especially impairment of muscle metabolism. © 2023 American Physiological Society. Compr Physiol 13:4269-4293, 2023.

TRPV4 Promotes Metastasis in Melanoma by Regulating Cell Motility through Cytoskeletal Rearrangement

The abnormal expression of Transient Receptor Potential cation channel subfamily V member 4 (TRPV4) is closely related to the progression of multiple tumors. In addition, TRPV4 is increasingly being considered a potential target for cancer therapy, especially in tumor metastasis prevention. However, the biological correlation between TRPV4 and tumor metastasis, as well as the specific role of TRPV4 in malignant melanoma metastasis, is poorly understood. In this study, we aimed to examine the role of TRPV4 in melanoma metastasis through experiments and clinical data analysis, and the underlying anticancer mechanism of Baicalin, a natural compound, and its inhibitory effect on TRPV4 with in vivo and in vitro experiments. Our findings suggested that TRPV4 promotes metastasis in melanoma by regulating cell motility via rearranging the cytoskeletal, and Baicalin can inhibit cancer metastasis, whose mechanisms reverse the recruitment of activated cofilin to leading-edge protrusion and the increasing phosphorylation level of cortactin, which is provoked by TRPV4 activation.

Non-Specific Targets for Correction of Pneumonia Caused by Aerosols Containing Damaging Factors of Various Nature

This review article provides data on the current state of the pathogenesis peculiarities of body and lung inflammation (pneumonia) under the influence of damaging factors of various nature: infectious agents, chemical toxicants, as well as incorporated radionuclides, etc. The peculiarities of inflammation itself, as a typical pathological process, are considered. Information on mediators that induce the so-called pro-resolving phase of inflammation manifestations is given. Approaches to the neuroimmune correction of non-specific inflammation are substantiated. Data on the following alternative approaches to the correction of nonspecific inflammation are summarized: factors of the coagulation system, modulators of the integrated stress response, and modulators of sigma-1 receptors. Based on the data presented, general directions for the treatment of nonspecific pneumonia are formulated, including reflexogenic and anti-inflammatory therapy in combination with multimodal drugs, as well as pro-resolving therapy in combination with drugs that prevent fibrosis.

WAO-ARIA consensus on chronic cough - Part 1: Role of TRP channels in neurogenic inflammation of cough neuronal pathways

BACKGROUND

Cough features a complex peripheral and central neuronal network. The function of the chemosensitive and stretch (afferent) cough receptors is well described but partly understood. It is speculated that chronic cough reflects a neurogenic inflammation of the cough reflex, which becomes hypersensitive. This is mediated by neuromediators, cytokines, inflammatory cells, and a differential expression of neuronal (chemo/stretch) receptors, such as transient receptor potential (TRP) and purinergic P2X ion channels; yet the overall interaction of these mediators in neurogenic inflammation of cough pathways remains unclear.

OBJECTIVES

The World Allergy Organization/Allergic Rhinitis and its Impact on Asthma (WAO/ARIA) Joint Committee on Chronic Cough reviewed the current literature on neuroanatomy and pathophysiology of chronic cough. The role of TRP ion channels in pathogenic mechanisms of the hypersensitive cough reflex was also examined.

OUTCOMES

Chemoreceptors are better studied in cough neuronal pathways compared to stretch receptors, likely due to their anatomical overabundance in the respiratory tract, but also their distinctive functional properties. Central pathways are important in suppressive mechanisms and behavioral/affective aspects of chronic cough. Current evidence strongly suggests neurogenic inflammation induces a hypersensitive cough reflex marked by increased expression of neuromediators, mast cells, and eosinophils, among others. TRP ion channels, mainly TRP V1/A1, are important in the pathogenesis of chronic cough due to their role in mediating chemosensitivity to various endogenous and exogenous triggers, as well as a crosstalk between neurogenic and inflammatory pathways in cough-associated airways diseases.

Prostaglandin E2 sensitizes the cough reflex centrally via EP3 receptor-dependent activation of NaV 1.8 channels

Background

Cough hypersensitivity is a major characteristic feature associated with several types of cough, including chronic cough, but its underlying mechanisms remain to be fully understood. Inflammatory mediators, such as prostaglandin E₂ (PGE₂), have been implicated in both peripheral induction and sensitization of the cough reflex. In this study, using a conscious guinea pig model of cough, we investigated whether PGE₂ can sensitize the cough reflex via central actions and, if so, via which mechanisms.

Methods

All drugs were administered by intracerebroventricular (i.c.v.) route and whole-body plethysmograph set-up was used for both induction, using aerosolized citric acid (0.2 M), and recording of cough. Immunohistochemistry was performed to confirm the expression of NaV 1.8 channels in the nucleus tractus solitarius (nTS).

Results

We show that both PGE₂ and the non-selective EP1/EP3 agonist, sulprostone, dose-dependently enhanced the citric acid-induced cough (P ≤ 0.001, P ≤ 0.01, respectively). Pretreatment with the EP1 antagonist, ONO-8130, did not affect the sulprostone-induced cough sensitization, whilst the EP3 antagonist, L-798,106, dose-dependently inhibited this effect (P ≤ 0.05). Furthermore, treatment with either the EP2 agonist, butaprost or the EP4 agonist, L-902,688, had no effect on cough sensitization. Additionally, pretreatment with either the TRPV1 antagonist, JNJ-17203212 or the TRPA1 antagonist, HC-030031, alone or in combination, nor with the NaV 1.1, 1.2, 1.3, 1.4, 1.6 and 1.7 channel blocker, tetrodotoxin, had any effect on the cough. In contrast, pretreatment with the NaV 1.8 antagonist, A-803467, dose-dependently inhibited this effect (P ≤ 0.05). Furthermore, NaV 1.8 channels were shown to be expressed in the nTS.

Conclusion

Collectively, our findings show that PGE₂ sensitizes the cough reflex centrally via EP3 receptor-dependent activation of NaV 1.8 but independently of TRPV1,TRPA1 and TTX-sensitive sodium channel activation. These results indicate that PGE₂ plays an important role in central sensitization of the cough reflex and suggest that central EP3 receptors and/or NaVv 1.8 channels may represent novel antitussive molecular targets.

Graphical Abstract

Phosphodiesterase-4 Inhibitors for Non-COPD Respiratory Diseases

Selective phosphodiesterase (PDE) inhibitors are a class of nonsteroid anti-inflammatory drugs for treating chronic inflammatory diseases. Modulation of systemic and airway inflammation is their pivotal mechanism of action. Furthermore, PDE inhibitors modulate cough reflex and inhibit airway mucus secretion. Roflumilast, a selective PDE4 inhibitor, has been extensively studied for the efficacy and safety in chronic obstructive pulmonary disease (COPD) patients. According to the mechanisms of action, the potential roles of PDE inhibitors in treating chronic respiratory diseases including severe asthma, asthma-COPD overlap (ACO), noncystic fibrosis bronchiectasis, and chronic cough are discussed. Since roflumilast inhibits airway eosinophilia and neutrophilia in COPD patients, it reduces COPD exacerbations in the presence of chronic bronchitis in addition to baseline therapies. The clinical studies in asthma patients have shown the comparable efficacy of roflumilast to inhaled corticosteroids for improving lung function. However, the clinical trials of roflumilast in severe asthma have been limited. Although ACO is common and is also associated with poor outcomes, there is no clinical trial regarding its efficacy in patients with ACO despite a promising role in reducing COPD exacerbation. Since mucus hypersecretion is a result of neutrophil secretagogue in patients with chronic bronchitis, experimental studies have shown that PDE4s are regulators of the cystic fibrosis transmembrane conductance regulator (CFTR) in human airway epithelial cells. Besides, goblet cell hyperplasia is associated with an increased expression of PDE. Bronchiectasis and chronic bronchitis are considered neutrophilic airway diseases presenting with mucus hypersecretion. They commonly coexist and thus lead to severe disease. The role of roflumilast in noncystic fibrosis bronchiectasis is under investigation in clinical trials. Lastly, PDE inhibitors have been shown modulating cough from bronchodilation, suppressing transient receptors potential (TRP), and anti-inflammatory properties. Hence, there is the potential role of the drug in the management of unexplained cough. However, clinical trials for examining its antitussive efficacy are pivotal. In conclusion, selective PDE4 inhibitors may be potential treatment options for chronic respiratory diseases apart from COPD due to their promising mechanisms of action.

The Cough Reflex: The Janus of Respiratory Medicine

In clinical practice, we commonly face adversity when encountering dysfunction of the cough reflex. Similar to ancient Roman deity Janus, it often presents with one of two opposing "faces". Continual aberrant activation of the cough reflex, also known as chronic cough, can cause great detriment to quality of life and many of these patients are left misdiagnosed and undertreated. In contrast, loss of normal functioning of the cough reflex is the cause of a significant proportion of mortality in the elderly, primarily through the development of aspiration pneumonia. In this review we discuss both hyper- and hypo-activation of the cough reflex and how airway reflux and chronic aspiration may be involved in the aetiology and sequalae of both disease states. We detail the physiological and pharmacological mechanisms involved in cough, and how the recent development of P2X3 receptor antagonists may lead to the first pharmaceutical agent licensed for chronic cough. The treatment and prevention of loss of the cough reflex, which has been largely neglected, is also discussed as novel low-cost interventions could help prevent a number of hospital and domiciliary deaths from both acute and chronic aspiration.

The role of TRPA1 and TRPV4 channels in bronchoconstriction and plasma extravasation in airways of rats treated with captopril

Angiotensin-converting enzyme inhibitors (ACEis) may cause adverse airway events, such as cough and angioedema, due to a reduction in bradykinin breakdown and consequent activation of bradykinin type 2 receptor (B₂ receptor). Recent studies have shown that bradykinin can also sensitize pro-inflammatory receptors such as the transient receptor potential ankyrin 1 (TRPA1) and vanilloid 4 (TRPV4), which are implicated in several inflammatory airway diseases. Based on these considerations, the aim of this study was to understand the role of TRPA1 and TRPV4 channels in the bronchoconstrictive response and plasma extravasation in the trachea of rats pretreated with captopril. Using methods to detect alterations in airway resistance and plasma extravasation, we found that intravenous (i.v.) administration of bradykinin (0.03-0.3 μmol/kg, B₂ receptor agonist), allyl isothiocyanate (100-1000 μmol/kg, TRPA1 agonist) or GSK1016790A (0.01-0.1 μmol/kg, TRPV4 agonist), but not des-arg⁹-bradykinin (DABK; 100-300 μmol/kg, B₁ receptor agonist), induced bronchoconstriction in anaesthetized rats. In doses that did not cause significant bronchoconstriction, bradykinin (0.03 μmol/kg) or allyl isothiocyanate (100 μmol/kg), but not GSK1016790A (0.01 μmol/kg) or DABK (300 μmol/kg) induced an increased bronchoconstrictive response in rats pretreated with captopril (2.5 mg/kg, i.v.). On the other hand, in rats pretreated with captopril (5 mg/kg, i.v.), an increased bronchoconstrictive response to GSK1016790A (0.01 μmol/kg) was observed. The bronchoconstrictive response induced by bradykinin in captopril-pretreated rats was inhibited by intratracheal treatment (i.t.) with HC030031 (300 μg/50 μl; 36 ± 9%) or HC067047 (300 μg/50 μl; 35.1 ± 16%), for TRPA1 and TRPV4 antagonists, respectively. However, the co-administration of both antagonists did not increase this inhibition. The bronchoconstriction induced by allyl isothiocyanate in captopril-pretreated rats (2.5 mg/kg) was inhibited (58.3 ± 8%) by the B₂ receptor antagonist HOE140 (10 nmol/50 μl, i.t.). Similarly, the bronchoconstriction induced by GSK1016790A in captopril-pretreated rats (5 mg/kg) was also inhibited (84.2 ± 4%) by HOE140 (10 nmol/50 μl, i.t.). Furthermore, the plasma extravasation induced by captopril on the trachea of rats was inhibited by pretreatment with HC030031 (47.2 ± 8%) or HC067047 (38.9 ± 8%). Collectively, these findings support the hypothesis that TRPA1 and TRPV4, via a B₂ receptor activation-dependent pathway, are involved in the plasma extravasation and bronchoconstriction induced by captopril, making them possible pharmacological targets to prevent or remediate ACEi-induced adverse respiratory reactions.

Effect of San'ao decoction with scorpio and bombyx batryticatus on CVA mice model via airway inflammation and regulation of TRPA1/TRPV1/TRPV5 channels

ETHNOPHARMACOLOGICAL RELEVANCE

Cough variant asthma (CVA) is characterized with its long-lasting cough symptom on clinic. The mechanism of CVA is related to chronic persistent airway inflammation, airway hyperresponsiveness, etc. The traditional Chinese prescription has achieved good curative effect on CVA treatment through reducing cough counts, decreasing airway hyperresponsiveness and alleviating airway inflammation. The mechanism is associated with reducing IL4, IL-13, NGF and CGRP levels, as well as down-regulating TRPA1/TRPV1/TRPV5 channels in both lung and brain tissues.

AIM OF THE STUDY

The Chinese prescription, San'ao decoction with scorpio and bombyx batryticatus (SSB), is well known in treating cough in asthmatic patients. In this study, the anti-tussive and anti-asthmatic role of SSB, as well as its mechanism on CVA mice model were explored and evaluated via alleviating airway inflammation and regulation of TRP channels.

MATERIALS AND METHODS

The major chemical components in SSB were detected and analyzed by UPLC-QTOF-MS under an optimized chromatographic and MS condition. 60 BALB/c mice were randomly divided into six groups: normal group, model group, dexamethasone group (0.1178 mg/kg/d), SSB high dose group (9.74 g/kg/d), SSB middle dose group (4.87 g/kg/d) and SSB low dose group (2.435 g/kg/d). The cough variant asthma mice model was established by ovalbumin sensitization and challenge. The protective role of SSB on CVA mice model was studied through inducing cough counts by capsaicin, assessing inflammatory cells in peripheral blood and bronchoalveolar lavage fluid (BALF), measuring airway responsiveness, detecting histopathological changes in lung tissues, analyzing cytokines and neuropeptides levels in BALF, as well as examining the mRNA and protein expressions of TRPA1, TRPV1 and TRPV5 in both lung and brain tissues.

RESULTS

17 signal peaks of the chemical components in SSB were identified by using UPLC-QTOF-MS. SSB (especially the high dose and middle dose), showed significantly effects on mice model by reducing mice cough counts (P ＜ 0.01), decreasing eosinophil (EOS) counts in blood (P ＜ 0.01) and inflammatory cell numbers in BALF (P ＜ 0.01), decreasing airway hyperresponsiveness (P ＜ 0.05), reducing the levels of IL-4 (P ＜ 0.05), IL-13 (P ＜ 0.01), NGF (P ＜ 0.01) and CGRP (P ＜ 0.01) in BALF, as well as down regulating the mRNA and protein expressions of TRPA1, TRPV1 and TRPV5 in both lung and brain tissues (P ＜ 0.01).

CONCLUSIONS

SSB showed anti-tussive and anti-asthmatic effects on cough variant asthma mice model by reducing cough counts, improving lung function, alleviating lung injury and airway inflammation. The mechanism of SSB might be associated with the regulation of cytokines and neuropeptides in BALF, as well as the regulation of TRPA1, TRPV1, TRPV5 channels in both lung and brain tissues.

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.

Exploring the 'cold/hot' properties of traditional Chinese medicine by cell temperature measurement

Context: It is common sense that chewing a mint leaf can cause a cooling feeling, while chewing ginger root will produce a burning feeling. In Traditional Chinese Medicine (TCM), this phenomenon is referred to as 'cold/hot' properties of herbs. Herein, it is reported that TCM with different "cold/hot" properties have different effects on the variation of cells.Objective: To explore the intrinsic 'cold/hot' properties of TCM from the perspective of cellular and molecular biology.Materials and methods: A375 cells were selected using Cancer Cell Line Encyclopaedia (CCLE) analysis and western blots. Hypaconitine and baicalin were selected by structural similarity analysis from 56 and 140 compounds, respectively. A wireless thermometry system was used to measure cellular temperature change induced by different compounds. Alteration of intracellular calcium influx was investigated by means of calcium imaging.Results: The IC₅₀ values of GSK1016790A, HC067047, hypaconitine, and baicalin for A375 cells are 8.363 nM, 816.4 μM, 286.4 μM and 29.84 μM, respectively. And, 8 μM hypaconitine induced obvious calcium influx while 8 μM baicalin inhibited calcium influx induced by TRPV4 activation. Cellular temperature elevated significantly when treated with GSK1016790A or hypaconitine, while the results were reversed when cells were treated with HC067047 or baicalin.Discussion and conclusions: The changes in cellular temperature are speculated to be caused by the alteration of intracellular calcium influx mediated by TRPV4. In addition, the 'cold/hot' properties of compounds in TCM can be classified by using cellular temperature detection.

Methods for assessing cough sensitivity

Cough sensitivity can be described as the reaction intensity of the cough reflex to different stimuli which activate chemically and mechanically sensitive vagal afferent nerves innervating airways and lungs. Measurement of cough reflex sensitivity plays an important role in revealing the underlying mechanisms of cough and evaluating the effects of pharmacological interventions. Besides, different responses to cough suppression therapies indicate the existence of cough hypersensitivity. In consideration of these factors stated above, cough sensitivity should therefore be assessed with a variety of cough challenge tests. Based on the neuroanatomical characteristics of the cough reflex, chemical challenge tests have been developed to objectively assess cough sensitivity. In cough inhalation challenges, capsaicin and citric acid are commonly used as the tussive agents to induce cough, which are validated for describing a profile of cough sensitivity to chemical irritants. Recently, mechanical methodologies have also been tried to measure the mechanical sensitivity of the cough reflex. Methodological consideration and selection are necessary for the reasonable assessment of cough sensitivity while employing cough challenges in clinical trials. Thus, in this review, we will focus on describing various methodologies of cough sensitivity measurement and, detailing some factors influencing on the accuracy of outcomes in the experimentally induced cough.

Effects of Heating-Conduction Dry Needling Therapy on Rats with Chronic Myofascial Pain Syndrome

OBJECTIVE

This study aimed to investigate the effect of dry needling (DN) with 44°C heating on the pressure pain threshold (PPT) of rats with chronic myofascial pain syndrome (MPS) by regulating the transient receptor potential V1 channel.

METHODS

A total of 80 rats were divided into 5 groups: A, B, C, D, and E (16 in each group). The rats in Group A recovered naturally, while those in other groups received the DN treatment. The needles were heated to 40°C for the rats in Groups B and E and 44°C for the rats in Groups C and D. In addition, both Groups D and E received local capsaicin injection. PPTs of the gastrocnemius muscle and tolerance time of the plantar hot plate were measured before modeling, 1 day before the intervention, 24 hours after the intervention, and 7 days after the intervention.

RESULTS

PPTs of the gastrocnemius muscle for rats with MPS increased 7 days after DN and heating to 40°C. For the rats receiving DN at 44°C heating, PPTs increased 24 hours and 7 days after the intervention. Further, 44°C heating and capsaicin injection improved PPT. DN and 40°C heating followed by capsaicin injection improved PPT.

CONCLUSION

DN and 44°C heating had therapeutic effects on rats with MPS at 24 hours and at 7 days after the intervention. DN and 40°C heating had therapeutic effects 7 days after the intervention. DN and 44°C heating might exert therapeutic effects by regulating the transient receptor potential V1 channel.

Modulation of TRPV-1 by prostaglandin-E2 and bradykinin changes cough sensitivity and autonomic regulation of cardiac rhythm in healthy subjects

A neurogenic pathway, involving airway TRPV-1, has been implicated in acute cardiovascular events occurring after peaks of air pollution. We tested whether inhaled prostaglandin-E₂ (PGE₂) and bradykinin (BK) regulate TRPV-1 activity in vivo by changing cough response to capsaicin (CPS) and affecting heart rate variability (HRV), while also taking into account the influence of TRPV-1 polymorphisms (SNPs). Moreover, we assessed the molecular mechanism of TRPV-1 modulation in vitro. Seventeen healthy volunteers inhaled 100 μg PGE₂, 200 μg BK or diluent in a randomized double-blind fashion. Subsequently, the response to CPS was assessed by cough challenge and the sympathetic activity by HRV, expressed by low (nLF) and high (nHF) normalized frequency components, as well as nLF/nHF ratio. Intracellular [Ca²⁺] was measured in HeLa cells, transfected with wild-type TRPV-1, pre-treated with increasing doses of PGE₂, BK or diesel exhaust particulate (DEP), after CPS stimulation. Six functional TRPV-1 SNPs were characterized in DNA from each subject. Inhalation of PGE₂ and BK was associated with significant increases in cough response induced by 30 μM of CPS (cough number after PGE₂ = 4.20 ± 0.42; p < 0.001, and after BK = 3.64 ± 0.37; p < 0.01), compared to diluent (2.77 ± 0.29) and in sympathetic activity (nLF/nHF ratio after PGE₂ = 6.1; p < 0.01, and after BK = 4.2; p < 0.05), compared to diluent (2.5–3.3). No influence of SNPs was observed on autonomic regulation and cough sensitivity. Unlike PGE₂ and BK, DEP directly activated TRPV-1. Inhalation of PGE₂ and BK sensitizes TRPV-1 and is associated with autonomic dysregulation of cardiac rhythm in healthy subjects.

Looking ahead to novel therapies for chronic cough. Part 1 - peripheral sensory nerve targeted treatments

INTRODUCTION

Due to a relatively high prevalence and negative impact on quality of life chronic cough (CC) is a challenge for both patients and clinicians. There is ongoing research to address the unmet need and develop more effective antitussive treatment options. This is the first part of a series of two reviews of new antitussive medications. Medical databases (Medline, Embase and SCOPUS) and trial registries (ClinicalTrials.gov and EudraCT) were searched for studies on antitussive drugs targeting peripheral sensory nerves.

AREAS COVERED

This review presents current knowledge of peripheral receptors that are not only involved in evoking the cough reflex, but are also potentially responsible for more sustained neural alterations. Blockage of the receptors and ion channels is discussed in terms of its potential antitussive effect.

EXPERT OPINION

Although better understanding of CC mechanisms has facilitated the development of novel treatments including P2X2/3 receptor inhibitors (e.g. gefapixant), there remain several gaps in the knowledge about the mechanisms and treatment of CC. These include the lack of tests to diagnose cough hypersensitivity syndrome and predictors of response to specific treatments. Further research into cough phenotypes and endotypes will yield important insights and a personalized approach to cough management.

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.

Upper Respiratory Tract Infection-Associated Acute Cough and the Urge to Cough: New Insights for Clinical Practice

Upper respiratory tract infection (URTI)-associated acute cough is the most common symptom both in children and adults worldwide and causes economic and social problems with significant implications for the patient, the patient's family, and the health care system. New pathogenic mechanisms in acute cough, including the urge to cough (UTC) mechanisms, have been recently identified. The brainstem neural network, pharyngeal sensory innervation, airway mechanical stimulation, inflammatory mediators, and postnasal drip actively participate in the onset and maintenance of acute cough and the urge to cough phenomenon. However, there is still no effective pharmacological treatment capable of interfering with the pathophysiologic mechanisms involved in URTI-associated acute cough. Moreover, severe adverse events frequently occur in administering such cough medications, mainly in children. New evidence has been provided concerning polysaccharides, resins, and honey as potential cough relievers with high antitussive efficiency, effect on the UTC, and minimal side effects.

Mechanisms underlying the stimulatory effect of inhaled sulfur dioxide on vagal bronchopulmonary C-fibres

KEY POINTS

Brief inhalation of SO₂ of concentration >500 p.p.m. triggered a pronounced stimulatory effect on vagal bronchopulmonary C-fibres in anaesthetized rats. This stimulatory effect was drastically diminished by a pretreatment with NaHCO₃ that raised the baseline arterial pH, suggesting a possible involvement of acidification of airway fluid and/or tissue generated by inhaled SO₂ . The stimulation was completely abolished by pretreatment with antagonists of both acid-sensing ion channels and transient receptor potential vanilloid type-1 receptors, indicating that this effect was caused by acid activation of these cation channels expressed in airway sensory nerves. This conclusion was further supported by the results obtained from studies in isolated rat vagal bronchopulmonary sensory neurones and also in the cough response to SO₂ inhalation challenge in awake mice. These results provide new insight into the underlying mechanism of harmful irritant effects in the respiratory tract caused by accidental exposure to a high concentration of SO₂ .

ABSTRACT

Inhalation of sulfur dioxide (SO₂ ) triggers coughs and reflex bronchoconstriction, and stimulation of vagal bronchopulmonary C-fibres is primarily responsible. However, the mechanism underlying this stimulatory effect is not yet fully understood. In this study, we tested the hypothesis that the C-fibre stimulation was caused by SO₂ -induced local tissue acidosis in the lung and airways. Single-unit activities of bronchopulmonary C-fibres in response to inhalation challenges of SO₂ (500-1500 p.p.m., 10 breaths) were measured in anaesthetized rats. Inhalation of SO₂ reproducibly induced a pronounced and sustained stimulation (lasting for 15-60 s) of pulmonary C-fibres in a concentration-dependent manner. This stimulatory effect was significantly attenuated by an increase in arterial pH generated by infusion of sodium bicarbonate (NaHCO₃ ), and completely abrogated by a combined pretreatment with amiloride (an antagonist of acid-sensing ion channels, ASICs) and AMG8910 (a selective antagonist of the transient receptor potential vanilloid type-1 receptor, TRPV1). Furthermore, in isolated rat vagal pulmonary sensory neurones, perfusion of an aqueous solution of SO₂ evoked a transient increase in the intracellular Ca²⁺ concentration; this response was also markedly diminished by a pretreatment with amiloride and AMG8910. In addition, inhalation of SO₂ consistently evoked coughs in awake mice; responses were significantly smaller in TRPV1^-/- mice than in wild-type mice, and almost completely abolished after a pretreatment with amiloride in TRPV1^-/- mice. These results suggested that the stimulatory effect of inhaled SO₂ on bronchopulmonary C-fibres was generated by acidification of fluid and/or tissue in the lung and airways, which activated both ASICs and TRPV1 expressed in these sensory nerves.

Increased Cough Receptor Sensitivity to Capsaicin Predicts a Positive Bronchial Thermoplasty Response: A Single-center Retrospective Study

BACKGROUND

Bronchial thermoplasty (BT) is a novel bronchoscopic therapy for severe uncontrolled asthma unresponsive to standard pharmacological treatments, including inhaled corticosteroids and long-acting beta-2 agonists. Although several studies have shown that BT improves asthma control, the optimal predictors of BT response remain unknown.

PATIENTS AND METHODS

We reviewed 10 consecutive asthma patients treated with BT at Kanazawa University Hospital between January 2016 and March 2018 and attempted to identify factors that correlated with a positive BT response.

RESULTS

All patients had the most severe persistent asthma according to the 2017 Japanese guidelines for adult asthma and were uncontrolled despite adequate treatments including high-dose inhaled corticosteroids and long-acting beta-2 agonists. Six patients had significant improvement in asthma control evaluated with the Asthma Control Questionnaire-6. Eight patients showed a significant improvement in asthma-specific health-related quality of life evaluated with the Asthma Quality of Life Questionnaire. The number of severe asthma exacerbations decreased in 6 patients. The maintenance dose of oral corticosteroids decreased in 1 patient. There were no severe adverse events related to the procedure. Six patients showed a positive BT response, and all 4 patients with increased cough receptor sensitivity to capsaicin responded to BT. No other factors, including age, smoking status, body mass index, age of asthma onset, disease duration, blood eosinophil count, total serum immunoglobulin E, prebronchodilator forced expiratory volume in 1 second, reversibility to beta-2 agonist, or fractional exhaled nitric oxide, were associated with a positive BT response.

CONCLUSION

Increased cough receptor sensitivity to capsaicin may predict a positive BT response.

Why chronic cough in children is different

Recently, there have been robust changes in our knowledge of the neurophysiology of cough and novel clinical etiologies. Specifically, cough hypersensitivity in adults and protracted bacterial bronchitis (PBB) in children have been increasingly investigated, and differences between chronic cough in children and adults have been widely reported. In young children, postinfectious cough, bronchiectasis, airway malacia, PBB, and asthma appear to be the main causes of cough; however, by adolescence, the causes of cough are more likely to become those common in adults, namely, gastroesophageal reflux, asthma, and upper airway syndrome. These differences are attributed to changes in various characteristics of the respiratory tract, immune system, and nervous system between children and adults. New knowledge about the neural aspects of cough has revealed a complex network of pathways that initiate cough. The effect of inflammation on cough neural processing occurs at multiple peripheral and central sites within the nervous system. Evidence exists that direct or indirect neuroimmune interaction induces a complex response, which can be altered by mediators released by the sensory or parasympathetic neurons and vice versa. During childhood, the respiratory tract and the nervous system undergo a series of anatomical and physiological maturation processes that produce the cough neural circuits. Alterations provoked by various pathological processes, noxious agents, infection, and inflammation during the developmental period can lead to persistent or irreversible modifications, which may explain why many adult patients, in addition to expressing high cough sensitivity, remain refractive to disease-specific therapies.

Small and large airway reactions to osmotic stimuli in asthma and chronic idiopathic cough

BACKGROUND

Chronic cough is a common symptom and related to several pulmonary, airway and heart diseases. When all likely medical explanations for the coughing are excluded, there remains a large group of patients with chronic coughing, which is mostly a cough reflex easily triggered by environmental irritants and noxious stimuli. The main aim of this study was to improve the diagnostic ability to differentiate chronic idiopathic cough (CIC) from asthma.

METHODS

Twenty-three patients with CIC, 16 patients with mild asthma and 21 control participants were included. The study consisted of three randomised bronchial provocations with osmotic stimuli: mannitol, eucapnic dry air and hypertonic saline. At each provocation lung function was assessed by spirometry and impulse oscillometry (IOS).

RESULTS

In a comparison of the groups, while the FEV₁ measurements did not differ, the CIC group had increased airway resistance and reactance after provocation with hypertonic saline compared to the control subjects. After mannitol provocation the patients with asthma had significantly increased airway resistance compared to the controls and from eucapnic dry air provocations these patients had a significant reduction in spirometry values and increased airway resistance compared to both the patients with CIC and the controls.

CONCLUSION

The asthma group reacted in a predictable way with impaired lung function from osmotic provocations, whereas the patients with CIC demonstrated peripheral airway changes from hypertonic saline, also known to be a noxious stimulus. The IOS method uncovers differences between patients with CIC and control participants that contribute to our ability to provide a correct diagnosis.

The emerging role of transient receptor potential channels in chronic lung disease

Chronic lung diseases such as asthma, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis are a major and increasing global health burden with a high unmet need. Drug discovery efforts in this area have been largely disappointing and so new therapeutic targets are needed. Transient receptor potential ion channels are emerging as possible therapeutic targets, given their widespread expression in the lung, their role in the modulation of inflammatory and structural changes and in the production of respiratory symptoms, such as bronchospasm and cough, seen in chronic lung disease.

Modulation of the TRPV4 ion channel as a therapeutic target for disease

Transient Receptor Potential Vanilloid 4 (TRPV4) is a broadly expressed, polymodally gated ion channel that plays an important role in many physiological and pathophysiological processes. TRPV4 knockout mice and several synthetic pharmacological compounds that selectively target TRPV4 are now available, which has allowed detailed investigation in to the therapeutic potential of this ion channel. Results from animal studies suggest that TRPV4 antagonism has therapeutic potential in oedema, pain, gastrointestinal disorders, and lung diseases such as cough, bronchoconstriction, pulmonary hypertension, and acute lung injury. A lack of observed side-effects in vivo has prompted a first-in-human trial for a TRPV4 antagonist in healthy participants and stable heart failure patients. If successful, this would open up an exciting new area of research for a multitude of TRPV4-related pathologies. This review will discuss the known roles of TRPV4 in disease, and highlight the possible implications of targeting this important cation channel for therapy.

Blocking TRPA1 in Respiratory Disorders: Does It Hold a Promise?

Transient Receptor Potential Ankyrin 1 (TRPA1) ion channel is expressed abundantly on the C fibers that innervate almost entire respiratory tract starting from oral cavity and oropharynx, conducting airways in the trachea, bronchi, terminal bronchioles, respiratory bronchioles and upto alveolar ducts and alveoli. Functional presence of TRPA1 on non-neuronal cells got recognized recently. TRPA1 plays a well-recognized role of “chemosensor”, detecting presence of exogenous irritants and endogenous pro-inflammatory mediators that are implicated in airway inflammation and sensory symptoms like chronic cough, asthma, chronic obstructive pulmonary disease (COPD), allergic rhinitis and cystic fibrosis. TRPA1 can remain activated chronically due to elevated levels and continued presence of such endogenous ligands and pro-inflammatory mediators. Several selective TRPA1 antagonists have been tested in animal models of respiratory disease and their performance is very promising. Although there is no TRPA1 antagonist in advanced clinical trials or approved on market yet to treat respiratory diseases, however, limited but promising evidences available so far indicate likelihood that targeting TRPA1 may present a new therapy in treatment of respiratory diseases in near future. This review will focus on in vitro, animal and human evidences that strengthen the proposed role of TRPA1 in modulation of specific airway sensory responses and also on preclinical and clinical progress of selected TRPA1 antagonists.

The role of TRPV1 in the CD4+ T cell-mediated inflammatory response of allergic rhinitis

Transient receptor potential vanilloid 1 (TRPV1), which has been identified as a molecular target for the activation of sensory neurons by various painful stimuli, was reported to regulate the signaling and activation of CD4⁺ T cells. However, the role of TRPV1 in CD4⁺ T cell in allergic rhinitis remains poorly understood. In this study, TRPV1 expression was localized in CD4⁺ T cells. Both knockout and chemical inhibition of TRPV1 suppressed Th2/Th17 cytokine production in CD4 T cells and Jurkat T cells, respectively, and can suppress T cell receptor signaling pathways including NF-κB, MAP kinase, and NFAT. In TRPV1 knockout allergic rhinitis (AR) mice, eosinophil infiltration, Th2/Th17 cytokines in the nasal mucosa, and total and ova-specific IgE levels in serum decreased, compared with wild-type AR mice. The TRPV1 antagonists, BCTC or theobromine, showed similar inhibitory immunologic effects on AR mice models. In addition, the number of TRPV1⁺/CD4⁺ inflammatory cells increased in the nasal mucosa of patients with AR, compared with that of control subjects. Thus, TRPV1 activation on CD4⁺ T cells is involved in T cell receptor signaling, and it could be a novel therapeutic target in AR.

TRPV1 and TRPM8 in Treatment of Chronic Cough

Chronic cough is common in the population, and among some there is no evident medical explanation for the symptoms. Such a refractory or idiopathic cough is now often regarded as a neuropathic disease due to dysfunctional airway ion channels, though the knowledge in this field is still limited. Persistent coughing and a cough reflex easily triggered by irritating stimuli, often in combination with perceived dyspnea, are characteristics of this disease. The patients have impaired quality of life and often reduced work capacity, followed by social and economic consequences. Despite the large number of individuals suffering from such a persisting cough, there is an unmet clinical need for effective cough medicines. The cough treatment available today often has little or no effect. Adverse effects mostly follow centrally acting cough drugs comprised of morphine and codeine, which demands the physician's awareness. The possibilities of modulating airway transient receptor potential (TRP) ion channels may indicate new ways to treat the persistent cough "without a reason". The TRP ion channel vanilloid 1 (TRPV1) and the TRP melastin 8 (TRPM8) appear as two candidates in the search for cough therapy, both as single targets and in reciprocal interaction.

Impact of Air Pollution on Age and Gender Related Increase in Cough Reflex Sensitivity of Healthy Children in Slovakia

BACKGROUND

Numerous studies show higher cough reflex sensitivity (CRS) and cough outcomes in children compared to adults and in females compared to males. Despite close link that exists between cough and environment the potential influence of environmental air pollution on age- and gender -related differences in cough has not been studied yet.

PURPOSE

The purpose of our study was to analyse whether the effects of exposure to environmental tobacco smoke (ETS) from parental smoking and PM10 from living in urban area are implied in age- and gender-related differences in cough outcomes of healthy, non-asthmatic children. Assessment of CRS using capsaicin and incidence of dry and wet cough was performed in 290 children (mean age 13.3 ± 2.6 years (138 females/152 males).

RESULTS

CRS was significantly higher in girls exposed to ETS [22.3 μmol/l (9.8-50.2 μmol/l)] compared to not exposed girls [79.9 μmol/l (56.4-112.2 μmol/l), p = 0.02] as well as compared to exposed boys [121.4 μmol/l (58.2-253.1 μmol/l), p = 0.01]. Incidence of dry cough lasting more than 3 weeks was significantly higher in exposed compared to not exposed girls. CRS was significantly higher in school-aged girls living in urban area [22.0 μmol/l (10.6-45.6 μmol/l)] compared to school-aged girls living in rural area [215.9 μmol/l (87.3-533.4 μmol/l); p = 0.003], as well as compared to teenage girls living in urban area [108.8 μmol/l (68.7-172.9 μmol/l); p = 0.007]. No CRS differences were found between urban and rural boys when controlled for age group. No CRS differences were found between school-aged and teenage boys when controlled for living area.

CONCLUSIONS

Our results have shown that the effect of ETS on CRS was gender specific, linked to female gender and the effect of PM10 on CRS was both gender and age specific, related to female gender and school-age. We suggest that age and gender related differences in incidence of cough and CRS might be, at least partially, ascribed to the effect of environmental pollutants. The role of age and gender in the effect of air pollution on cough strongly suggest some interplay of development with biological and behavioral factors.

How does rhinovirus cause the common cold cough?

Cough is a protective reflex to prevent aspiration and can be triggered by a multitude of stimuli. The commonest form of cough is caused by upper respiratory tract infection and has no benefit to the host. The virus hijacks this natural defence mechanism in order to propagate itself through the population. Despite the resolution of the majority of cold symptoms within 2 weeks, cough can persist for some time thereafter. Unfortunately, the mechanism of infectious cough brought on by pathogenic viruses, such as human rhinovirus, during colds, remains elusive despite the extensive work that has been undertaken. For socioeconomic reasons, it is imperative we identify the mechanism of cough. There are several theories which have been proposed as the causative mechanism of cough in rhinovirus infection, encompassing a range of different processes. Those of which hold most promise are physical disruption of the epithelial lining, excess mucus production and an inflammatory response to rhinovirus infection which may be excessive. And finally, neuronal modulation, the most convincing hypothesis, is thought to potentiate cough long after the original stimulus has been cleared. All these hypotheses will be briefly covered in the following sections.

Implications of Human Transient Receptor Potential Melastatin 8 (TRPM8) Channel Gating from Menthol Binding Studies of the Sensing Domain

The transient receptor potential melastatin 8 (TRPM8) ion channel is the primary cold sensor in humans. TRPM8 is gated by physiologically relevant cold temperatures and chemical ligands that induce cold sensations, such as the analgesic compound menthol. Characterization of TRPM8 ligand-gated channel activation will lead to a better understanding of the fundamental mechanisms that underlie TRPM8 function. Here, the direct binding of menthol to the isolated hTRPM8 sensing domain (transmembrane helices S1-S4) is investigated. These data are compared with two mutant sensing domain proteins, Y745H (S2 helix) and R842H (S4 helix), which have been previously identified in full length TRPM8 to be menthol insensitive. The data presented herein show that menthol specifically binds to the wild type, Y745H, and R842H TRPM8 sensing domain proteins. These results are the first to show that menthol directly binds to the TRPM8 sensing domain and indicates that Y745 and R842 residues, previously identified in functional studies as crucial to menthol sensitivity, do not affect menthol binding but instead alter coupling between the sensing domain and the pore domain.

Eight International London Cough Symposium 2014: Cough hypersensitivity syndrome as the basis for chronic cough

At the Eighth International London Cough Conference held in London in July 2014, the focus was on the relatively novel concept of cough hypersensitivity syndrome (CHS) as forming the basis of chronic cough. This concept has been formulated following understanding of the neuronal pathways for cough and a realisation that not all chronic cough is usually associated with a cause. The CHS is defined by troublesome coughing triggered by low level of thermal, mechanical or chemical exposure. It also encompasses other symptoms or sensations such as laryngeal hypersensitivity, nasal hypersensitivity and possibly also symptoms related to gastrooesopahgeal reflux. The pathophysiologic basis of the CHS is now being increasingly linked to an enhancement of the afferent pathways of the cough reflex both at the peripheral and central levels. Mechanisms involved include the interactions of inflammatory mechanisms with cough sensors in the upper airways and with neuronal pathways of cough, associated with a central component. Tools for assessing CHS in the clinic need to be developed. New drugs may be developed to control CHS. A roadmap is suggested from the inception of the CHS concept towards the development of newer antitussives at the Symposium.

Cough hypersensitivity as a neuro-immune interaction

Cough is an intrinsic protective reflex. However, chronic cough affects a considerable proportion of general population and has a major impact on quality of life. A recent paradigm shift to ‘cough hypersensitivity syndrome’ suggests that chronic cough arises from hypersensitivity of the airway sensory nerves. As cough reflex is determined by interaction of the nervous system with immune system, persistent dysregulation of one or both of these systems may lead to chronic cough hypersensitivity. Here we review the current evidence for the neuro-immune interactions that underlie cough hypersensitivity and discuss future therapeutic strategies.

Targeting TRP channels for chronic cough: from bench to bedside

Cough is currently the most common reason for patients to visit a primary care physician in the UK, yet it remains an unmet medical need. Current therapies have limited efficacy or have potentially dangerous side effects. Under normal circumstances, cough is a protective reflex to clear the lungs of harmful particles; however, in disease, cough can become excessive, dramatically impacting patients' lives. In many cases, this condition is linked to inflammatory diseases such as asthma and chronic obstructive pulmonary disease (COPD), but can also be refractory to treatment and idiopathic in nature. Therefore, there is an urgent need to develop therapies, and targeting the sensory afferent arm of the reflex which initiates the cough reflex may uncover novel therapeutic targets. The cough reflex is initiated following activation of ion channels present on vagal sensory afferents. These ion channels include the transient receptor potential (TRP) family of cation-selective ion channels which act as cellular sensors and respond to changes in the external environment. Many direct activators of TRP channels, including arachidonic acid derivatives, a lowered airway pH, changes in temperature, and altered airway osmolarity are present in the diseased airway where responses to challenge agents which activate airway sensory nerve activity are known to be enhanced. Furthermore, the expression of some TRP channels is increased in airway disease. Together, this makes them promising targets for the treatment of chronic cough. This review will cover the current understanding of the role of the TRP family of ion channels in the activation of airway sensory nerves and cough, focusing on four members, transient receptor potential vanilloid (TRPV) 1, transient receptor potential ankyrin (TRPA) 1, TRPV4, and transient receptor potential melastatin (TRPM) 8 as these represent the channels where most information has been gathered with relevance to the airways. We will describe recent data and highlight the possible therapeutic utility of specific TRP channel antagonists as antitussives in the clinic.

Human TRPM8 and TRPA1 pain channels, including a gene variant with increased sensitivity to agonists (TRPA1 R797T), exhibit differential regulation by SRC-tyrosine kinase inhibitor

TRPM8 (transient receptor potential M8) and TRPA1 (transient receptor potential A1) are cold-temperature-sensitive nociceptors expressed in sensory neurons but their behaviour in neuronal cells is poorly understood. Therefore DNA expression constructs containing human TRPM8 or TRPA1 cDNAs were transfected into HEK (human embryonic kidney cells)-293 or SH-SY5Y neuroblastoma cells and G418 resistant clones analysed for effects of agonists and antagonists on intracellular Ca²⁺ levels. Approximately 51% of HEK-293 and 12% of SH-SY5Y cell clones expressed the transfected TRP channel. TRPM8 and TRPA1 assays were inhibited by probenecid, indicating the need to avoid this agent in TRP channel studies. A double-residue mutation in ICL-1 (intracellular loop-1) of TRPM8 (SV762,763EL, mimicking serine phosphorylation) or one in the C-terminal tail region (FK1045,1046AG, a lysine knockout) retained sensitivity to agonists (WS 12, menthol) and antagonist {AMTB [N-(3-Aminopropyl)-2-[(3-methylphenyl)methoxy]-N-(2-thienylmethyl)benzamide]}. SNP (single nucleotide polymorphism) variants in TRPA1 ICL-1 (R797T, S804N) and TRPA1 fusion protein containing C-terminal (His)₁₀ retained sensitivity to agonists (cinnamaldehyde, allyl-isothiocyanate, carvacrol, eugenol) and antagonists (HC-030031, A967079). One SNP variant, 797T, possessed increased sensitivity to agonists. TRPA1 became repressed in SH-SY5Y clones but was rapidly rescued by Src-family inhibitor PP2 [4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine]. Conversely, TRPM8 in SH-SY5Y cells was inhibited by PP2. Further studies utilizing SH-SY5Y may identify structural features of TRPA1 and TRPM8 involved in conferring differential post-translational regulation.

Transient receptor potential channels M8 and A1 sense the cellular environment and activate entry of Ca²⁺ into the cytoplasm. We identified a TRPA1 (transient receptor potential A1) variant with increased sensitivity and differential modulation of channels by a tyrosine kinase inhibitor in neuroblastoma cells.

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.

Changing the paradigm for cough: does 'cough hypersensitivity' aid our understanding?

Chronic cough is a common reason for patients to seek medication attention. Over the last few decades, we have experienced significant clinical success by applying the paradigm of 'evaluating and treating the causes for chronic cough'. However, we still ask ourselves 'what underlies chronic cough. Indeed in a considerable proportion of patients cough is idiopathic, or unexplained despite vigorous evaluation. Commonly associated conditions such as rhinitis, eosinophilic bronchitis, asthma, or gastroesophageal acidic reflux may not be fundamental to cough, and thus may be triggers rather than causes. The cardinal feature of chronic cough is persistent upregulation the cough reflex, which may be driven by complex interactions between biologic, neurologic, immunologic, genetic, comorbid, and environmental factors. We suggest the new paradigm 'cough hypersensitivity syndrome' should finally bring us further advances in understanding and management of chronic cough.