The role of trigeminal nasal TRPM8-expressing afferent neurons in the antitussive effects of menthol

Profile of cough triggers and their relationship with capsaicin cough sensitivity in chronic cough

BACKGROUND

Cough hypersensitivity is an important part of the neurophysiology of cough, which presents with increased cough response to a lower level of stimuli or triggers. Classification of stimuli might bring about additional insight into the underlying mechanisms and management.

OBJECTIVES

This study investigated the profile of cough triggers in chronic cough patients and their relationship with capsaicin cough sensitivity.

DESIGN

This was a cross-sectional observational study.

METHODS

We enrolled patients with different causes of chronic cough from 2006 to 2021. Cough triggers were defined as cough response to chemical triggers, mechanical triggers, meal triggers, or thermal trigger. Cough sensitivity to capsaicin was evaluated by the capsaicin challenge test, which was expressed as the lowest concentration of capsaicin inducing 5 or more coughing (C5).

RESULTS

Among 1211 patients with chronic cough, 1107 (91.4%) patients reported at least one cough trigger. Chemical triggers (66.9%) were the most common cough triggers, followed by thermal exposure (50.6%), mechanical triggers (48.2%), and meal triggers (21.2%). There was no difference in the proportion of chemical triggers among different etiologies. Patients with refractory chronic cough reported the highest prevalence of cough triggers (97.1%). A higher number of meal triggers (34.9%) was associated with gastroesophageal reflux-related cough, and meal triggers and mechanical triggers were more common in refractory chronic cough. Among 254 patients who completed capsaicin challenge test, both the number of total triggers and the number of chemical triggers had a significant but mild correlation with capsaicin cough sensitivity.

CONCLUSION

Cough hypersensitivity as reflected by a variety of cough triggers is a common feature in chronic cough patients, but different etiologies present specific profiles of cough triggers, which could not be evaluated comprehensively by capsaicin cough sensitivity.

Ingredients of Vicks VapoRub inhibit rhinovirus-induced ATP release

Background

Over-the-counter therapies, such as Vicks VapoRub, are frequently used in the management of upper respiratory tract infection symptoms. Of these, acute cough is the most bothersome; however, the mechanisms involved have not been fully elucidated. The temperature-sensitive transient receptor potential (TRP) channels, including TRPA1, TRPV1, TRPM8 and TRPV4, are potential candidates. TRPV4 is also thought to be involved in cough through the TRPV4-ATP-P2X3 pathway. Here, we hypothesise that Vicks VapoRub ingredients (VVRIs) modulate the TRP cough channels.

Methods

Stably transfected HEK cells expressing TRP channels were challenged with VVRIs, individually or in combination, and the agonist and antagonist effects were measured using calcium signalling responses. In addition, rhinovirus serotype-16 (RV16)-infected A549 airway epithelial cells were pre-incubated with individual or combinations of VVRIs prior to hypotonic challenge and extracellular ATP release analysis.

Results

Calcium signalling reconfirmed some previously defined activation of TRP channels by specific VVRIs. The combined VVRIs containing menthol, camphor and eucalyptus oil activated TRPV1, TRPV4, TRPM8 and untransfected wild-type HEK293 cells. However, pre-incubation with VVRIs did not significantly inhibit any of the channels compared with the standard agonist responses. Pre-incubation of RV16-infected A549 cells with individual or combined VVRIs, except menthol, resulted in a 0.45-0.55-fold reduction in total ATP release following hypotonic stimulation, compared with infected cells not treated with VVRIs.

Conclusion

These findings suggest that some VVRIs may reduce symptoms associated with upper respiratory tract infection by modulating specific TRP receptors and by reducing RV16-induced ATP release.

L-Menthol Olfactory Stimulation Reduced Dyspnea Sensation during the 6 min Walk Test in Patients with Chronic Breathlessness Syndrome: A Pilot Study

There are very limited methods of relieving dyspnea that are independent of the causative disease. L-menthol olfactory stimulation is reported to be effective for dyspnea during exercise and inspiratory resistance. Therefore, we examined the effects of L-menthol olfactory stimulation on exertional dyspnea during the 6 min walking distance test (6MWT) in patients with chronic breathlessness syndrome. The subjects who consented to the study were divided into two groups. In Group A, the first 6MWT was performed as usual (placebo) while wearing a surgical mask, and the second 6MWT was performed under the L-menthol condition. In Group B, the first 6MWT was performed under the L-menthol condition, and the second 6MWT was performed as a placebo. A total of 16 subjects (70.8 ± 9.5 years) were included in the analysis. As for the effect of reducing dyspnea, a significant difference was observed in Group A patients who underwent the L-menthol condition in the second 6MWT (p = 0.034). In the comparison of the 6 min walking test under the L-menthol condition and the placebo, the modified Borg scale gain was significantly different between the L-menthol condition and the placebo (p = 0.007). Our results suggested that the L-menthol olfactory stimulation reduced dyspnea on exertion in patients with chronic breathlessness syndrome.

The treatment of mild upper respiratory tract infections - a position paper with recommendations for best practice

Following the waning severity of COVID-19 due to vaccination and the development of immunity, the current variants of SARS-CoV-2 often lead to mild upper respiratory tract infections (MURTIs), suggesting it is an appropriate time to review the pathogenesis and treatment of such illnesses. The present article reviews the diverse causes of MURTIs and the mechanisms leading to symptomatic illness. Different symptoms of MURTIs develop in a staggered manner and require targeted symptomatic treatment. A wide variety of remedies for home treatment is available, including over-the-counter drugs and plant-derived substances. Recent pharmacological research has increased the understanding of molecular effects, and clinical studies have shown the efficacy of certain herbal remedies. However, the use of subjective endpoints in these clinical studies may suggest limited validity of the results. In this position paper, the importance of patient-centric outcomes, including a subjective perception of improved well-being, is emphasized. A best practice approach for the management of MURTIs, in which pharmacists and physicians create an improved multi-professional healthcare setting and provide healthcare education to patients, is proposed. Pharmacists act as first-line consultants and provide patients with remedies, considering the individual patient's preferences towards chemical or plant-derived drugs and providing advice for self-monitoring. Physicians act as second-line consultants if symptoms worsen and subsequently initiate appropriate therapies. In conclusion, general awareness of MURTIs should be increased amongst medical professionals and patients, thus improving their management.

TRP (transient receptor potential) ion channel family: structures, biological functions and therapeutic interventions for diseases

Transient receptor potential (TRP) channels are sensors for a variety of cellular and environmental signals. Mammals express a total of 28 different TRP channel proteins, which can be divided into seven subfamilies based on amino acid sequence homology: TRPA (Ankyrin), TRPC (Canonical), TRPM (Melastatin), TRPML (Mucolipin), TRPN (NO-mechano-potential, NOMP), TRPP (Polycystin), TRPV (Vanilloid). They are a class of ion channels found in numerous tissues and cell types and are permeable to a wide range of cations such as Ca²⁺, Mg²⁺, Na⁺, K⁺, and others. TRP channels are responsible for various sensory responses including heat, cold, pain, stress, vision and taste and can be activated by a number of stimuli. Their predominantly location on the cell surface, their interaction with numerous physiological signaling pathways, and the unique crystal structure of TRP channels make TRPs attractive drug targets and implicate them in the treatment of a wide range of diseases. Here, we review the history of TRP channel discovery, summarize the structures and functions of the TRP ion channel family, and highlight the current understanding of the role of TRP channels in the pathogenesis of human disease. Most importantly, we describe TRP channel-related drug discovery, therapeutic interventions for diseases and the limitations of targeting TRP channels in potential clinical applications.

Impact of trigeminal and/or olfactory nerve stimulation on measures of inspiratory neural drive: Implications for breathlessness

The perception of breathlessness is mechanistically linked to the awareness of increased inspiratory neural drive (IND). Stimulation of upper airway cold receptors on the trigeminal nerve (TGN) with TGN agonists such as menthol or cool air to the face/nose has been hypothesized to reduce breathlessness by decreasing IND. The aim of this systematic scoping review was to identify and summarize the results of studies in animals and humans reporting on the impact of TGN stimulation or blockade on measures of IND. Thirty-one studies were identified, including 19 in laboratory animals and 12 in human participants. Studies in laboratory animals consistently reported that as TGN activity increased, measures of IND decreased (e.g., phrenic nerve activity). In humans, stimulation of the TGN with a stream of cool air to the face/nose decreased the sensitivity of the ventilatory chemoreflex response to hypercapnia. Otherwise, TGN stimulation with menthol or cool air to the face/note had no effect on measures of IND in humans. This review provides new insight into a potential neural mechanism of breathlessness relief with selected TGN agonists.

Current pharmacological strategies for symptomatic reduction of persistent breathlessness - a literature review

INTRODUCTION

Persistent breathlessness is a debilitating symptom that is prevalent in the community, particularly in people with chronic and life-limiting illnesses. Treatment includes different steps, including pharmacological treatment aiming to improve the symptom and optimize people's wellbeing.

AREAS COVERED

PubMed and Google Scholar were screened using 'chronic breathlessness' OR 'persistent breathlessness,' AND 'pharmacological treatment,' OR 'opioids.' This review focuses on pharmacological treatments to reduce persistent breathlessness and discusses possible mechanisms involved in the process of breathlessness reduction through pharmacotherapy. Research gaps in the field of persistent breathlessness research are outlined, and future research directions are suggested.

EXPERT OPINION

Regular, low-dose (≤30 mg/day), sustained-release morphine is recommended as the first-line pharmacological treatment for persistent breathlessness. Inter-individual variation in response needs to be investigated in future studies in order to optimize clinical outcomes. This includes 1) better understanding the centrally mediated mechanisms associated with persisting breathlessness and response to pharmacological therapies, 2) understanding benefit from the perspective of people experiencing persistent breathlessness, small and meaningful gains in physical activity.

Irritant-evoked reflex tachyarrhythmia in spontaneously hypertensive rats is reduced by inhalation of TRPM8 agonists l-menthol and WS-12

Inhalation of noxious irritants activates nociceptive sensory afferent nerves innervating the airways, inducing reflex regulation of autonomic networks and the modulation of respiratory drive and cardiovascular (CV) parameters such as heart rate and blood pressure. In healthy mammals, irritant-evoked pulmonary-cardiac reflexes cause parasympathetic-mediated bradycardia. However, in spontaneously hypertensive (SH) rats, irritant inhalation also increases sympathetic drive to the heart. This remodeled pulmonary-cardiac reflex may contribute to cardiovascular risk caused by inhalation of air pollutants/irritants in susceptible individuals with cardiovascular disease (CVD). Previous studies have shown that the cooling mimic l-menthol, an agonist for the cold-sensitive transient receptor potential melastatin 8 (TRPM8), can alleviate nasal inflammatory symptoms and respiratory reflexes evoked by irritants. Here, we investigated the impact of inhalation of TRPM8 agonists l-menthol and WS-12 on pulmonary-cardiac reflexes evoked by inhalation of the irritant allyl isothiocyanate (AITC) using radiotelemetry. l-Menthol, but not its inactive analog d-menthol, significantly reduced the AITC-evoked reflex tachycardia and premature ventricular contractions (PVCs) in SH rats but had no effect on the AITC-evoked bradycardia in either SH or normotensive Wistar-Kyoto (WKY) rats. WS-12 reduced AITC-evoked tachycardia and PVCs in SH rats, but this more potent TRPM8 agonist also reduced AITC-evoked bradycardia. l-Menthol had no effect on heart rate when given alone, whereas WS-12 evoked a minor bradycardia in WKY rats. We conclude that stimulation of TRPM8-expressing afferents within the airways reduces irritant-evoked pulmonary-cardiac reflexes, especially the aberrant reflex tachyarrhythmia in SH rats. Airway menthol treatment may be an effective therapy for reducing pollution-associated CV exacerbations.NEW & NOTEWORTHY Irritant-evoked pulmonary-cardiac reflexes are remodeled in spontaneously hypertensive (SH) rats-causing de novo sympathetic reflexes that drive tachyarrhythmia. This remodeling may contribute to air pollution-associated risk in susceptible individuals with cardiovascular disease. We found that inhalation of TRPM8 agonists, l-menthol and WS-12, but not the inactive analog d-menthol, selectively reduces the reflex tachyarrhythmia evoked by allyl isothiocyanate (AITC) inhalation in SH rats. Use of menthol may protect susceptible individuals from pollution-associated CV exacerbations.

Modulation of transient receptor potential (TRP) channels by plant derived substances used in over-the-counter cough and cold remedies

BACKGROUND

Upper respiratory tract infections (URTIs) impact all age groups and have a significant economic and social burden on society, worldwide. Most URTIs are mild and self-limiting, but due to the wide range of possible causative agents, including Rhinovirus (hRV), Adenovirus, Respiratory Syncytial Virus (RSV), Coronavirus and Influenza, there is no single and effective treatment. Over-the-counter (OTC) remedies, including traditional medicines and those containing plant derived substances, help to alleviate symptoms including inflammation, pain, fever and cough.

PURPOSE

This systematic review focuses on the role of the major plant derived substances in several OTC remedies used to treat cold symptoms, with a particular focus on the transient receptor potential (TRP) channels involved in pain and cough.

METHODS

Literature searches were done using Pubmed and Web of Science, with no date limitations, using the principles of the PRISMA statement. The search terms used were 'TRP channel AND plant compound', 'cough AND plant compound', 'cough AND TRP channels AND plant compound', 'cough AND P2X3 AND plant compound' and 'P2X3 AND plant compound' where plant compound represents menthol or camphor or eucalyptus or turpentine or thymol.

RESULTS

The literature reviewed showed that menthol activates TRPM8 and may inhibit respiratory reflexes reducing irritation and cough. Menthol has a bimodal action on TRPA1, but inhibition may have an analgesic effect. Eucalyptus also activates TRPM8 and inhibits TRPA1 whilst down regulating P2X3, aiding in the reduction of cough, pain and airway irritation. Camphor inhibits TRPA1 and the activation of TRPM8 may add to the effects of menthol. Activation of TRPV1 by camphor, may also have an analgesic effect.

CONCLUSIONS

The literature suggests that these plant derived substances have multifaceted actions and can interact with the TRP 'cough' receptors. The plant derived substances used in cough and cold medicines have the potential to target multiple symptoms experienced during a cold.

The distinctive role of menthol in pain and analgesia: Mechanisms, practices, and advances

Menthol is an important flavoring additive that triggers a cooling sensation. Under physiological condition, low to moderate concentrations of menthol activate transient receptor potential cation channel subfamily M member 8 (TRPM8) in the primary nociceptors, such as dorsal root ganglion (DRG) and trigeminal ganglion, generating a cooling sensation, whereas menthol at higher concentration could induce cold allodynia, and cold hyperalgesia mediated by TRPM8 sensitization. In addition, the paradoxical irritating properties of high concentrations of menthol is associated with its activation of transient receptor potential cation channel subfamily A member 1 (TRPA1). Under pathological situation, menthol activates TRPM8 to attenuate mechanical allodynia and thermal hyperalgesia following nerve injury or chemical stimuli. Recent reports have recapitulated the requirement of central group II/III metabotropic glutamate receptors (mGluR) with endogenous κ-opioid signaling pathways for menthol analgesia. Additionally, blockage of sodium channels and calcium influx is a determinant step after menthol exposure, suggesting the possibility of menthol for pain management. In this review, we will also discuss and summarize the advances in menthol-related drugs for pathological pain treatment in clinical trials, especially in neuropathic pain, musculoskeletal pain, cancer pain and postoperative pain, with the aim to find the promising therapeutic candidates for the resolution of pain to better manage patients with pain in clinics.

Changes of the airway reactivity in patients with rhinosinusitis

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

Chemosensory Contributions of E-Cigarette Additives on Nicotine Use

While rates of smoking combustible cigarettes in the United States have trended down in recent years, use of electronic cigarettes (e-cigarettes) has dramatically increased, especially among adolescents. The vast majority of e-cigarette users consume "flavored" products that contain a variety of chemosensory-rich additives, and recent literature suggests that these additives have led to the current "teen vaping epidemic." This review, covering research from both human and rodent models, provides a comprehensive overview of the sensory implications of e-cigarette additives and what is currently known about their impact on nicotine use. In doing so, we specifically address the oronasal sensory contributions of e-cigarette additives. Finally, we summarize the existing gaps in the field and highlight future directions needed to better understand the powerful influence of these additives on nicotine use.

Cough hypersensitivity and chronic cough

Chronic cough is globally prevalent across all age groups. This disorder is challenging to treat because many pulmonary and extrapulmonary conditions can present with chronic cough, and cough can also be present without any identifiable underlying cause or be refractory to therapies that improve associated conditions. Most patients with chronic cough have cough hypersensitivity, which is characterized by increased neural responsivity to a range of stimuli that affect the airways and lungs, and other tissues innervated by common nerve supplies. Cough hypersensitivity presents as excessive coughing often in response to relatively innocuous stimuli, causing significant psychophysical morbidity and affecting patients' quality of life. Understanding of the mechanisms that contribute to cough hypersensitivity and excessive coughing in different patient populations and across the lifespan is advancing and has contributed to the development of new therapies for chronic cough in adults. Owing to differences in the pathology, the organs involved and individual patient factors, treatment of chronic cough is progressing towards a personalized approach, and, in the future, novel ways to endotype patients with cough may prove valuable in management.

The Severity of Acute Kidney and Lung Injuries Induced by Cecal Ligation and Puncture Is Attenuated by Menthol: Role of Proliferating Cell Nuclear Antigen and Apoptotic Markers

Objective

Sepsis-induced acute lung injury (ALI) and acute kidney injury (AKI) are major causes of mortality. Menthol is a natural compound that has anti-inflammatory and antioxidative actions. Since exaggerated inflammatory and oxidative stress are characteristics of sepsis, the aim of this study was to evaluate the effect of menthol against sepsis-induced mortality, ALI, and AKI.

Methods

The cecal ligation and puncture (CLP) procedure was employed as a model of sepsis. Rats were grouped into sham, sham-Menthol, CLP, and CLP-Menthol (100 mg/kg, p.o).

Key Findings

A survival study showed that menthol enhanced the survival after sepsis from 0% in septic group to 30%. Septic rats developed histological evidence of ALI and AKI. Menthol markedly suppressed sepsis induced elevation of tissue TNF-a, ameliorated sepsis-induced cleavage of caspase-3 and restored the antiapoptotic marker Bcl2.

Significance

We introduced a role of the proliferating cell nuclear antigen (PCNA) in these tissues with a possible link to the damage induced by sepsis. PCNA level was markedly reduced in septic animals and menthol ameliorated this effect. Our data provide novel evidence that menthol protects against organ damage and decreases mortality in experimental sepsis.

A Review on the Role of TRP Channels and Their Potential as Drug Targets_An Insight Into the TRP Channel Drug Discovery Methodologies

Transient receptor potential (TRP) proteins are a large group of ion channels that control many physiological functions in our body. These channels are considered potential therapeutic drug targets for various diseases such as neurological disorders, cancers, cardiovascular disease, and many more. The Nobel Prize in Physiology/Medicine in the year 2021 was awarded to two scientists for the discovery of TRP and PIEZO ion channels. Improving our knowledge of technologies for their study is essential. In the present study, we reviewed the role of TRP channel types in the control of normal physiological functions as well as disease conditions. Also, we discussed the current and novel technologies that can be used to study these channels successfully. As such, Flux assays for detecting ionic flux through ion channels are among the core and widely used tools for screening drug compounds. Technologies based on these assays are available in fully automated high throughput set-ups and help detect changes in radiolabeled or non-radiolabeled ionic flux. Aurora’s Ion Channel Reader (ICR), which works based on label-free technology of flux assay, offers sensitive, accurate, and reproducible measurements to perform drug ranking matching with patch-clamp (gold standard) data. The non-radiolabeled trace-based flux assay coupled with the ICR detects changes in various ion types, including potassium, calcium, sodium, and chloride channels, by using appropriate tracer ions. This technology is now considered one of the very successful approaches for analyzing ion channel activity in modern drug discovery. It could be a successful approach for studying various ion channels and transporters, including the different members of the TRP family of ion channels.

Evidence for Alpha7 Nicotinic Receptor Activation During the Cough Suppressing Effects Induced by Nicotine and Identification of ATA-101 as a Potential Novel Therapy for the Treatment of Chronic Cough

Studies performed in healthy smokers have documented a diminished responsiveness to tussive challenges, and several lines of experimental evidence implicate nicotine as an antitussive component in both cigarette smoke and the vapors generated by electronic cigarettes (eCigs). We set out to identify the nicotinic receptor subtype involved in the antitussive actions of nicotine and to further evaluate the potential of nicotinic receptor-selective agonists as cough-suppressing therapeutics. We confirmed an antitussive effect of nicotine in guinea pigs. We additionally observed that the alpha-4 beta-2 (α ₄ β ₂)-selective agonist Tc-6683 was without effect on evoked cough responses in guinea pigs, while the α ₇-selective agonist PHA 543613 dose-dependently inhibited evoked coughing. We subsequently describe the preclinical evidence in support of ATA-101, a potent and highly selective (α ₇) selective nicotinic receptor agonist, as a potential candidate for antitussive therapy in humans. ATA-101, formerly known as Tc-5619, was orally bioavailable and moderately central nervous system (CNS) penetrant and dose-dependently inhibited coughing in guinea pigs evoked by citric acid and bradykinin. Comparing the effects of airway targeted administration versus systemic dosing and the effects of repeated dosing at various times prior to tussive challenge, our data suggest that the antitussive actions of ATA-101 require continued engagement of α ₇ nicotinic receptors, likely in the CNS. Collectively, the data provide the preclinical rationale for α ₇ nicotinic receptor engagement as a novel therapeutic strategy for cough suppression. The data also suggest that α ₇ nicotinic acetylcholine receptor (nAChR) activation by nicotine may be permissive to nicotine delivery in a way that may promote addiction. SIGNIFICANCE STATEMENT: This study documents the antitussive actions of nicotine and identifies the α₇ nicotinic receptor subtype as the target for nicotine during cough suppression described in humans. We additionally present evidence suggesting that ATA-101 and other α₇ nicotinic receptor-selective agonists may be promising candidates for the treatment of chronic refractory cough.

l-Menthol - a new treatment for breathlessness?

PURPOSE OF REVIEW

In patients with advanced chronic obstructive pulmonary disease (COPD), it is challenging to treat breathlessness. In addition, novel palliative interventions are required for multiple perspectives of breathlessness that may still be present after disease-specific therapies. This review provides an overview of the mechanisms and effects of l-menthol on breathlessness by covering the latest relevant papers.

RECENT FINDINGS

A literature review identified one randomized controlled trial assessing the effect of l-menthol on relieving breathlessness in patients with COPD. It has been reported that the mechanism of relieving breathlessness partly involves stimulation of the trigeminal nerve by the cooling sensation of l-menthol, which gives a cognitive illusion of inspiratory flow perception. The effect of l-menthol on breathlessness caused by exertion has been reported in healthy subjects but not yet in patients with breathlessness.

SUMMARY

The effect of l-menthol on the sensory-emotional dimensions of laboratory-induced breathlessness in patients with COPD has been described in a clinical trial. Further studies are warranted to investigate its application to inspiratory muscle training and its effects in combination with exercise training.

Advances in TRP channel drug discovery: from target validation to clinical studies

Transient receptor potential (TRP) channels are multifunctional signalling molecules with many roles in sensory perception and cellular physiology. Therefore, it is not surprising that TRP channels have been implicated in numerous diseases, including hereditary disorders caused by defects in genes encoding TRP channels (TRP channelopathies). Most TRP channels are located at the cell surface, which makes them generally accessible drug targets. Early drug discovery efforts to target TRP channels focused on pain, but as our knowledge of TRP channels and their role in health and disease has grown, these efforts have expanded into new clinical indications, ranging from respiratory disorders through neurological and psychiatric diseases to diabetes and cancer. In this Review, we discuss recent findings in TRP channel structural biology that can affect both drug development and clinical indications. We also discuss the clinical promise of novel TRP channel modulators, aimed at both established and emerging targets. Last, we address the challenges that these compounds may face in clinical practice, including the need for carefully targeted approaches to minimize potential side-effects due to the multifunctional roles of TRP channels.

Animal models of cough

Cough is a vital airway reflex that keeps the respiratory tract wisely protected. It is also a sign of many diseases of the respiratory system and it may become a disease in its own right. Even though the efficacy of antitussive compounds is extensively studied in animal models with promising results, the treatment of pathological cough in humans is insufficient at the moment. The limited translational potential of animal models used to study cough causes, mechanisms and possible therapeutic targets stems from multiple sources. First of all, cough induced in the laboratory by mechanical or chemical stimuli is far from natural cough present in human disease. The main objective of this review is to provide a comprehensive summary of animal models currently used in cough research and to address their advantages and disadvantages. We also want to encourage cough researchers to call for precision is research by addressing the sex bias which has existed in basic cough research for decades and discuss the role of specific pathogen-free (SPF) animals.

TRP channels in airway sensory nerves

Transient Receptor Potential (TRP) channels expressed in specific subsets of airway sensory nerves function as transducers and integrators of a diverse range of sensory inputs including chemical, mechanical and thermal signals. These TRP sensors can detect inhaled irritants as well as endogenously released chemical substances. They play an important role in generating the afferent activity carried by these sensory nerves and regulating the centrally mediated pulmonary defense reflexes. Increasing evidence reported in recent investigations has revealed important involvements of several TRP channels (TRPA1, TRPV1, TRPV4 and TRPM8) in the manifestation of various symptoms and pathogenesis of certain acute and chronic airway diseases. This mini-review focuses primarily on these recent findings of the responses of these TRP sensors to the biological stresses emerging under the pathophysiological conditions of the lung and airways.

The Prospect for Potent Sodium Voltage-Gated Channel Blockers to Relieve an Excessive Cough

An excessive, irritable, productive or non-productive coughing associated with airway inflammation belongs to pathological cough. Increased activation of airway vagal nociceptors in pathological conditions results from dysregulation of the neural pathway that controls cough. A variety of mediators associated with airway inflammation overstimulate these vagal airway fibers including C-fibers leading to hypersensitivity and hyperreactivity. Because current antitussives have limited efficacy and unwanted side effects there is a continual demand for the development of a novel more effective antitussives for a new efficacious and safe cough treatment. Therefore, inhibiting the activity of these vagal C-fibers represents a rational approach to the development of effective antitussive drugs. This may be achieved by blocking inflammatory mediator receptors or by blocking the generator potential associated with the specific ion channels. Because voltage-gated sodium channels (NaVs) are absolutely required for action potentials initiation and conduction irrespective of the stimulus, NaVs become a promising neural target. There is evidence that NaV1.7, 1.8 and 1.9 subtypes are predominantly expressed in airway cough-triggering nerves. The advantage of blocking these NaVs is suppressing C-fiber irrespective to stimuli, but the disadvantage is that by suppressing the nerves is may also block beneficial sensations and neuronal reflex behavior. The concept is that new antitussive drugs would have the benefit of targeting peripheral airway nociceptors without inhibiting the protective cough reflex.

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.

Mechanisms and Rationale for Targeted Therapies in Refractory and Unexplained Chronic Cough

Chronic cough, defined as a cough lasting > 8 weeks, is a common medical condition that exerts a substantial physical, mental, and social burden on patients. A subset of patients with chronic cough are troubled with a cough that persists despite optimal treatment of presumed associated common and uncommon conditions (refractory chronic cough; RCC) or in which no diagnosable cause for cough can be identified despite extensive assessment (unexplained chronic cough; UCC). Many of these patients exhibit clinical features of cough hypersensitivity, including laryngeal paresthesia, hypertussia, and allotussia. Over-the-counter cough remedies are ineffective and can lead to intolerable side effects when used for RCC/UCC, and the lack of approved treatments indicated for these conditions reflects a major unmet need. An increased understanding of the anatomy and neurophysiology of protective and pathologic cough has fostered a robust clinical development pipeline of several targeted therapies for RCC/UCC. This manuscript reviews the mechanisms presumed to underly RCC/UCC together with the rationale and clinical evidence for several targeted therapies currently under clinical investigation, including transient receptor potential channel antagonists, P2X3-receptor antagonists, voltage-gated sodium channel blockers, neuromodulators, and neurokinin-1-receptor antagonists. Finally, we provide an overview of targets that have been investigated in preclinical models of cough and other airway diseases that may hold future promise for clinical studies in RCC/UCC. Development of targeted therapies with different sites of action may foster a precision medicine approach to treat this heterogeneous, underserved patient population.

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.

Fan therapy for cough: case report and literature review

This case report describes the care of a 59-year-old woman with metastatic small cell lung cancer and chronic obstructive pulmonary disease who was highly symptomatic with an intractable cough. The patient reported a subjective benefit from a table fan. The authors observed an objective improvement with a marked reduction in cough frequency when the fan was in use. A literature review was undertaken and identified one randomised controlled trial assessing the use of fan for cough. The proposed underlying mechanism of cough relief is stimulation of the trigeminal nerve, possibly by cooling. This mechanism is well described in breathlessness. It presents the possibility of a novel therapeutic approach to managing cough. Further studies of both the role of nasal receptors in cough pathophysiology and the role of fan therapy in cough, where there is no concern of an airborne infectious pathogen such as COVID-19, are warranted.

TRPM8 channels: A review of distribution and clinical role

Ion channels are important therapeutic targets due to their plethoric involvement in physiological and pathological consequences. The transient receptor potential cation channel subfamily M member 8 (TRPM8) is a nonselective cation channel that controls Ca²⁺ homeostasis. It has been proposed to be the predominant thermoreceptor for cellular and behavioral responses to cold stimuli in the transient receptor potential (TRP) channel subfamilies and exploited so far to reach the clinical-stage of drug development. TRPM8 channels can be found in multiple organs and tissues, regulating several important processes such as cell proliferation, migration and apoptosis, inflammatory reactions, immunomodulatory effects, pain, and vascular muscle tension. The related disorders have been expanded to new fields ranging from cancer and migraine to dry eye disease, pruritus, irritable bowel syndrome (IBS), and chronic cough. This review is aimed to summarize the distribution of TRPM8 and disorders related to it from a clinical perspective, so as to broaden the scope of knowledge of researchers to conduct more studies on this subject.

Biosynthetic pathways and metabolic engineering of spice flavors

Historically, spices have played an important economic role, due to their large applications and unique flavor. The supply and cost of spice materials and their corresponding natural products are often affected by environmental, geopolitical and climatic conditions. Secondary metabolite composition, including certain flavor compounds in spice plants, is recognized and considered closely related to plant classification. Both genes and enzymes involved in the biosynthesis of spice flavors are constantly identified, which provides insight into metabolic engineering of flavor compounds (i.e. aroma and pungent compounds) from spice plants. In this review, a systematic meta-analysis was carried out based on a comprehensive literature survey of the flavor profiles of 36 spice plants from nine families. We also reviewed typical biosynthetic pathways and metabolic engineering of most representative aroma and pungent compounds that may assist in the future study of spice plants as biosynthetic factories facing a new challenge in creating spice products.

Effect of facial skin cooling induced by a handheld fan on the cough reflex threshold and urge to cough induced by citric acid

Chronic cough is a condition that impairs the quality of life of affected patients and may persist despite optimal intervention. Thus, a novel therapeutic approach with broad clinical utility based on the nature of the cough reflex is required.

Facial skin cooling induced by a handheld fan alleviates the cough reflex and the urge to cough induced by citric acidhttp://bit.ly/2m1kzAP

Pharmacokinetics behaviors of l-menthol after inhalation and intravenous injection in rats and its inhibition effects on CYP450 enzymes in rat liver microsomes

1. l-Menthol, as a kind of monocyclic terpene, is widely used in inhalation formulations, food and tobacco. The purpose of this study was to investigate the pharmacokinetic behavior of l-menthol as well as its influence on the activities of cytochrome P450 enzymes. 2. The pharmacokinetic behaviors of l-menthol after inhalation (50 mg/kg) and intravenous injection (10 mg/kg) were investigated. A rat liver microsomal model was adopted to elucidate the inhibitory effect of l-menthol on CYP1A2, CYP2C11, CYP2D1/2, CYP2D4, CYP2E1 and CYP3A1 using phenacetin, tolbutamide, omeprazole, dextromethorphan, chlorzoxazone and testosterone as probe drugs, respectively. 3. The plasma concentration reached the C_max within 1.0 h (inhalation) and descended with the T_1/2 of 8.53 and 6.69 h for inhalation and i.v. administration, respectively. IC₅₀ for inhibition of l-menthol on CYP 450 enzymes were 4.35 μM for 2D4, 8.67 μM for 1A2, 13.02 μM for 3A1, 14.78 μM for 2D1/2, 234.9 μM for 2C11 and 525.4 μM for 2E1, respectively. 4. The results illustrate the pharmacokinetic process of l-menthol in rats and provide information for further rational applications. l-Menthol had moderate inhibitions on CYP2D4 and 1A2, which might affect the disposition of medicines primarily dependent on these pathways.

Involvement of Glucagon in Preventive Effect of Menthol Against High Fat Diet Induced Obesity in Mice

Glucagon mediated mechanisms have been shown to play clinically significant role in energy expenditure. The present study was designed to understand whether pharmacological mimicking of cold using menthol (TRPM8 modulator) can induce glucagon-mediated energy expenditure to prevent weight gain and related complications. Acute oral and topical administration of TRPM8 agonists (menthol and icilin) increased serum glucagon concentration which was prevented by pre-treatment with AMTB, a TRPM8 blocker. Chronic administration of menthol (50 and 100 mg/kg/day for 12 weeks) to HFD fed animals prevented weight gain, insulin resistance, adipose tissue hypertrophy and triacylglycerol deposition in liver. These effects were not restricted to oral administration, but also observed upon the topical application of menthol (10% w/v). The metabolic alterations caused by menthol in liver and adipose tissue mirrored the known effects of glucagon, such as increased glycogenolysis and gluconeogenesis in the liver, and enhanced thermogenic activity of white and brown adipose tissue. Correlation analysis suggests a strong correlation between glucagon dependent changes and energy expenditure markers. Interestingly, in-vitro treatment of the serum of menthol treated mice increased energy expenditure markers in mature 3T3L1 adipocytes, which was prevented in the presence of non-competitive glucagon receptor antagonist, L-168,049, indicating that menthol-induced increase in serum glucagon is responsible for increase in energy expenditure phenotype. In conclusion, the present work provides evidence that glucagon plays an important role in the preventive effect of menthol against HFD-induced weight gain and related complications.

Transient Receptor Potential Channels and Chronic Airway Inflammatory Diseases: A Comprehensive Review

Chronic airway inflammatory diseases remain a major problem worldwide, such that there is a need for additional therapeutic targets and novel drugs. Transient receptor potential (TRP) channels are a group of non-selective cation channels expressed throughout the body that are regulated by various stimuli. TRP channels have been identified in numerous cell types in the respiratory tract, including sensory neurons, airway epithelial cells, airway smooth muscle cells, and fibroblasts. Different types of TRP channels induce cough in sensory neurons via the vagus nerve. Permeability and cytokine production are also regulated by TRP channels in airway epithelial cells, and these channels also contribute to the modulation of bronchoconstriction. TRP channels may cooperate with other TRP channels, or act in concert with calcium-dependent potassium channels and calcium-activated chloride channel. Hence, TRP channels could be the potential therapeutic targets for chronic airway inflammatory diseases. In this review, we aim to discuss the expression profiles and physiological functions of TRP channels in the airway, and the roles they play in chronic airway inflammatory diseases.

Activation of TRPV3 by Wood Smoke Particles and Roles in Pneumotoxicity

Wood/biomass smoke particulate materials (WBSPM) are pneumotoxic, but the mechanisms by which these materials affect lung cells are not fully understood. We previously identified transient receptor potential (TRP) ankyrin-1 as a sensor for electrophiles in WBSPM and hypothesized that other TRP channels expressed by lung cells might also be activated by WBSPM, contributing to pneumotoxicity. Screening TRP channel activation by WBSPM using calcium flux assays revealed TRPV3 activation by materials obtained from burning multiple types of wood under fixed conditions. TRPV3 activation by WBSPM was dependent on the chemical composition, and the pattern of activation and chemical components of PM agonists was different from that of TRPA1. Chemical analysis of particle constituents by gas chromatography–mass spectrometry and principal component analysis indicated enrichment of cresol, ethylphenol, and xylenol analogues, plus several other chemicals among the most potent samples. 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-xylenol, 2-, 3-, and 4-ethylphenol, 2-methoxy-4-methylphenol, and 5,8-dihydronaphthol were TRPV3 agonists exhibiting preferential activation versus TRPA1, M8, V1, and V4. The concentration of 2,3- and 3,4-xylenol in the most potent samples of pine and mesquite smoke PM (<3 μm) was 0.1–0.3% by weight, while that of 5,8-dihydronaphthol was 0.03%. TRPV3 was expressed by several human lung epithelial cell lines, and both pine PM and pure chemical TRPV3 agonists found in WBSPM were more toxic to TRPV3-over-expressing cells via TRPV3 activation. Finally, mice treated sub-acutely with pine particles exhibited an increase in sensitivity to inhaled methacholine involving TRPV3. In summary, TRPV3 is activated by specific chemicals in WBSPM, potentially contributing to the pneumotoxic properties of certain WBSPM.

l-Menthol alleviates cigarette smoke extract induced lung injury in rats by inhibiting oxidative stress and inflammation via nuclear factor kappa B, p38 MAPK and Nrf2 signalling pathways

l-Menthol is the main ingredient of peppermint which affects various pharmacological effects such as anti-inflammation and anti-oxidative activity.

Cough and airway disease: The role of ion channels

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

Opposing effects of bronchopulmonary C-fiber subtypes on cough in guinea pigs

We have addressed the hypothesis that the opposing effects of bronchopulmonary C-fiber activation on cough are attributable to the activation of C-fiber subtypes. Coughing was evoked in anesthetized guinea pigs by citric acid (0.001-2 M) applied topically in 100-µl aliquots to the tracheal mucosa. In control preparations, citric acid evoked 10 ± 1 coughs cumulatively. Selective activation of the pulmonary C fibers arising from the nodose ganglia with either aerosols or continuous intravenous infusion of adenosine or the 5-HT₃ receptor-selective agonist 2-methyl-5-HT nearly abolished coughing evoked subsequently by topical citric acid challenge. Delivering adenosine or 2-methyl-5-HT directly to the tracheal mucosa (where few if any nodose C fibers terminate) was without effect on citric acid-evoked cough. These actions of pulmonary administration of adenosine and 2-methyl-5-HT were accompanied by an increase in respiratory rate, but it is unlikely that the change in respiratory pattern caused the decrease in coughing, as the rapidly adapting receptor stimulant histamine also produced a marked tachypnea but was without effect on cough. In awake guinea pigs, adenosine failed to evoke coughing but reduced coughing induced by the nonselective C-fiber stimulant capsaicin. We conclude that bronchopulmonary C-fiber subtypes in guinea pigs have opposing effects on cough, with airway C fibers arising from the jugular ganglia initiating and/or sensitizing the cough reflex and the intrapulmonary C fibers arising from the nodose ganglia actively inhibiting cough upon activation.

Electronic Cigarettes: Their Constituents and Potential Links to Asthma

PURPOSE OF REVIEW

Vaping is gaining popularity in the USA, particularly among teens and young adults. While e-cigs are commonly represented as safer alternatives to tobacco cigarettes, little is known regarding the health effects of their short- or long-term use, especially in individuals with pre-existing respiratory diseases such as asthma. Flavored e-cig liquids (e-liquids) and e-cig aerosols contain airway irritants and toxicants that have been implicated in the pathogenesis and worsening of lung diseases. In this review, we will summarize existing data on potential health effects of components present in e-cig aerosols, such as propylene glycol, vegetable glycerin, nicotine, and flavorings, and discuss their relevance in the context of asthma.

RECENT FINDINGS

Recent survey data indicate that adolescents with asthma had a higher prevalence of current e-cig use (12.4%) compared to their non-asthmatics peers (10.2%) and conveyed positive beliefs about tobacco products, especially e-cigs. Similarly, a study conducted among high school students from Ontario, Canada, indicated a greater likelihood of e-cig use in asthmatics as compared to their non-asthmatic peers. Availability of different flavorings is often cited as the main reason among youth/adolescents for trying e-cigs or switching from cigarettes to e-cigs. Occupational inhalation of some common food-safe flavoring agents is reported to cause occupational asthma and worsen asthmatic symptoms. Moreover, workplace inhalation exposures to the flavoring agent diacetyl have caused irreversible obstructive airway disease in healthy workers. Additionally, recent studies report that thermal decomposition of propylene glycol (PG) and vegetable glycerin (VG), the base constituents of e-liquids, produces reactive carbonyls, including acrolein, formaldehyde, and acetaldehyde, which have known respiratory toxicities. Furthermore, recent nicotine studies in rodents reveal that prenatal nicotine exposures lead to epigenetic reprogramming in the offspring, abnormal lung development, and multigenerational transmission of asthmatic-like symptoms. Comparisons of the toxicity and health effects of e-cigs and conventional cigarettes often focus on toxicants known to be present in cigarette smoke (CS) (i.e., formaldehyde, nitrosamines, etc.), as well as smoking-associated clinical endpoints, such as cancer, bronchitis, and chronic obstructive pulmonary disease (COPD). However, this approach disregards potential toxicity of components unique to flavored e-cigs, such as PG, VG, and the many different flavoring chemicals, which likely induce respiratory effects not usually observed in cigarette smokers.

Drugs Affecting TRP Channels

Chronic obstructive pulmonary disease (COPD) and asthma are both common respiratory diseases that are associated with airflow reduction/obstruction and pulmonary inflammation. Whilst drug therapies offer adequate symptom control for many mild to moderate asthmatic patients, severe asthmatics and COPD patients symptoms are often not controlled, and in these cases, irreversible structural damage occurs with disease progression over time. Transient receptor potential (TRP) channels, in particular TRPV1, TRPA1, TRPV4 and TRPM8, have been implicated with roles in the regulation of inflammation and autonomic nervous control of the lungs. Evidence suggests that inflammation elevates levels of activators and sensitisers of TRP channels and additionally that TRP channel expression may be increased, resulting in excessive channel activation. The enhanced activity of these channels is thought to then play a key role in the propagation and maintenance of the inflammatory disease state and neuronal symptoms such as bronchoconstriction and cough. For TRPM8 the evidence is less clear, but as with TRPV1, TRPA1 and TRPV4, antagonists are being developed by multiple companies for indications including asthma and COPD, which will help in elucidating their role in respiratory disease.

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.

Pilot Experiment: The Effect of Added Flavorants on the Taste and Pleasantness of Mixtures of Glycerol and Propylene Glycol

Introduction

The US Food and Drug Administration banned most "sweet" flavorants for use in cigarettes due to the concern that sweet flavors appeal to young, beginning smokers. However, many of the same flavors, including fruity and confection-associated aromas (e.g. vanilla) are still used in e-cigarettes. Sweet flavors may have a number of effects, including enhancement of the taste of other ingredients. The current work focused on the impact of model flavorants on the taste of a mixture of propylene glycol and vegetable glycerine, solvents used in most e-cigarettes and related products.

Methods

A device delivered mixtures of propylene glycol and vegetable glycerine into the mouth in parallel with puffs of clean air (control) or odorized air. Aromas included two "fruity" esters ("pineapple" and "banana"), two confection-associated aromas ("vanilla" and "caramel/malty"), menthol (not a "sweet" aroma, but commonly used in e-cigarettes), and a "burnt" aroma not expected enhance flavor. Twenty young adults, aged 18-25, rated the sweetness, bitterness, and pleasantness of all stimuli (within-subjects design).

Results

Both fruity aromas significantly enhanced sweetness, both confection-associated aromas significantly enhanced pleasantness, and the caramel/malty aroma significantly reduced bitterness. Menthol and the "burnt" aroma had no measurable effects on the taste of solvent mixtures.

Conclusion

Some flavorants modulated the taste of solvents commonly used in e-cigarettes in ways consistent with an enhanced sensory profile.

Implications

If similar effects occur in actual products, improved flavor profiles could facilitate continued use, particularly in non-smokers experimenting with e-cigarettes and related products.

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.

Puerarin transport across a Calu-3 cell monolayer - an in vitro model of nasal mucosa permeability and the influence of paeoniflorin and menthol

Nasal administration is a high-potential delivery system, particularly because it can provide a pathway from the nose to the brain. The objective of this research is to characterize puerarin transport across a Calu-3 cell monolayer used as a model of the nasal mucosa and to evaluate the influence of puerarin in combination with paeoniflorin and menthol to explore the enhanced mechanism of the permeability at the cell level. The apparent permeability coefficients (P_app) of puerarin bidirectional transport were both <1.5×10⁻⁶ cm/s, and the efflux ratio was <1.5, indicating that puerarin alone exhibited poor absorption and that its transport primarily occurred by passive diffusion through the cell monolayer. When puerarin was coad ministered with paeoniflorin, the P_app was not changed (P>0.05). However, the addition of menthol significantly (P<0.05) improved the P_app of puerarin in both directions. Moreover, based on immunofluorescence experiments and transepithelial electrical resistance measurements, the data indicated that the drug compatibility opened tight junctions and weakened the barrier capabilities of epithelial cells, thereby promoting the permeability of puerarin.

Role of reactive oxygen species and TRP channels in the cough reflex

The cough reflex is evoked by noxious stimuli in the airways. Although this reflex is essential for health, it can be triggered chronically in inflammatory and infectious airway disease. Neuronal transient receptor potential (TRP) channels such as ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1) are polymodal receptors expressed on airway nociceptive afferent nerves. Reactive oxygen species (ROS) and other reactive compounds are associated with inflammation, from either NADPH oxidase or mitochondria. These reactive compounds cause activation and hyperexcitability of nociceptive afferents innervating the airways, and evidence suggests key contributions of TRPA1 and TRPV1.

Cough reflex sensitization from esophagus and nose

The diseases of the esophagus and nose are among the major factors contributing to chronic cough although their role in different patient populations is debated. Studies in animal models and in humans show that afferent C-fiber activators applied on esophageal or nasal mucosa do not initiate cough, but enhance cough induced by inhaled irritants. These results are consistent with the hypothesis that activation of esophageal and nasal C-fibers contribute to cough reflex hypersensitivity observed in chronic cough patients with gastroesophageal reflux disease (GERD) and chronic rhinitis, respectively. The afferent nerves mediating cough sensitization from the esophagus are probably the neural crest-derived vagal jugular C-fibers. In addition to their responsiveness to high concentration of acid typical for gastroesophageal reflux (pH < 5), esophageal C-fibers also express receptors for activation by weakly acidic reflux such as receptors highly sensitive to acid and receptors for bile acids. The nature of sensory pathways from the nose and their activators relevant for cough sensitization are less understood. Increased cough reflex sensitivity was also reported in many patients with GERD or rhinitis who do not complain of cough indicating that additional endogenous or exogenous factors may be required to develop chronic coughing in these diseases.

Transient receptor potential melastatin 8 gene polymorphism is associated with cold-induced airway hyperresponsiveness in bronchial asthma

BACKGROUND AND OBJECTIVE

Cold-induced airway hyperresponsiveness (CAH) is common in bronchial asthma (BA) patients and represents a problem for those living in cold climate. Transient receptor potential melastatin 8 (TRPM8) channel is the main cold temperature sensor in humans that could mediate cold response in asthmatics with CAH. No associations between TRPM8 gene polymorphisms and CAH have been reported.

METHODS

The present study involved 123 BA patients. CAH was assessed by 3-min isocapnic (5% CO2 ) cold air (-20°C) hyperventilation challenge. The c.750G > C (rs11562975), c.1256G > A (rs7593557), c.3048C > T (rs11563208) and c.3174C > G (rs11563071) polymorphisms of TRPM8 gene were genotyped by allele-specific polymerase chain reaction (PCR) and PCR with subsequent restriction fragment length polymorphism analysis.

RESULTS

GC genotype and C allele carriers of the c.750G > C (rs11562975) polymorphism were more frequently observed to exhibit CAH. The estimated odds ratio for the GC genotype was 3.73 95%CI (1.48; 9.37), P = 0.005. Furthermore, GC heterozygotes had a prominent decrease in forced expiratory volume in 1 s after the challenge as compared to GG homozygotes (-12% (-16; -8.1) vs -6.45% (-11; -2.1), P < 0.001). GC carriers also had a marked reduction in other spirometric parameters.

CONCLUSIONS

The GC variant of the TRPM8:c.750G > C (rs11562975) polymorphism is associated with CAH in patients with BA, which suggests a potential role of TRPM8 in CAH development.