TRP channels: emerging targets for respiratory disease

Medicinal Chemistry, Pharmacology, and Clinical Implications of TRPV1 Receptor Antagonists

Transient receptor potential vanilloid 1 (TRPV1) is an ion channel expressed on sensory neurons triggering an influx of cations. TRPV1 receptors function as homotetramers responsive to heat, proinflammatory substances, lipoxygenase products, resiniferatoxin, endocannabinoids, protons, and peptide toxins. Its phosphorylation increases sensitivity to both chemical and thermal stimuli, while desensitization involves a calcium-dependent mechanism resulting in receptor dephosphorylation. TRPV1 functions as a sensor of noxious stimuli and may represent a target to avoid pain and injury. TRPV1 activation has been associated to chronic inflammatory pain and peripheral neuropathy. Its expression is also detected in nonneuronal areas such as bladder, lungs, and cochlea where TRPV1 activation is responsible for pathology development of cystitis, asthma, and hearing loss. This review offers a comprehensive overview about TRPV1 receptor in the pathophysiology of chronic pain, epilepsy, cough, bladder disorders, diabetes, obesity, and hearing loss, highlighting how drug development targeting this channel could have a clinical therapeutic potential. Furthermore, it summarizes the advances of medicinal chemistry research leading to the identification of highly selective TRPV1 antagonists and their analysis of structure-activity relationships (SARs) focusing on new strategies to target this channel.

TRPM8 genetic variations associated with COPD risk in the Chinese Han population

TRPM8 plays a key role in COPD. The development of pulmonary hypertension (PH) in COPD adversely affects survival and exercise capacity. Thus, the aim of this study was to evaluate the possible association between single nucleotide polymorphisms (SNPs) in TRPM8 and COPD or PH in COPD among the Chinese Han population. A total of 513 COPD patients and 506 controls were enrolled in the study. Six tag SNPs (tSNPs) were genotyped. The relationship between COPD or PH in COPD and the six tSNPs was evaluated using the χ² test and genetic model analysis. In the rs9789398 polymorphism, the T/C genotype was associated with an increased risk for COPD (P=0.005). Under the assumption of models of inheritance, there was an association between the rs9789398 polymorphism and COPD. In the rs9789675 polymorphism, the G/A genotype was associated with an increased risk for COPD (P=0.021). Furthermore, by the χ² test, we found that the minor allele “A” of rs9789675 (odds ratio [OR] =0.63, 95% confidence interval [CI], 0.42–0.97, P=0.034) and the minor allele “C” of rs9789398 (OR =1.59, 95% CI, 1.03–2.44, P=0.034) were associated with a decreased risk of PH in COPD in allele models. In genetic models, the genotypes “GA” and “AA” of rs9789675 were associated with a decreased risk of PH in COPD. The genotypes “TC” and “CC” of rs9789398 were associated with a decreased risk of PH in COPD. Moreover, “CG” of rs1004478 was significantly associated with a decreased risk of PH in COPD. There was a significant association between the five SNPs (rs2362290, rs9789675, rs9789398, rs1003540, and rs104478) in the TRPM8 gene and the risk of PH in COPD. Our findings indicated that rs9789398 in the TRPM8 gene was significantly associated with the risk of COPD in the Chinese Han population. Moreover, rs9789675, rs9789398, and rs1004478 were significantly associated with the risk of PH in COPD. This study provides a novel insight into COPD and PH in the development of COPD.

Inundation of asthma target research: Untangling asthma riddles

Asthma is an inveterate inflammatory disorder, delineated by the airway inflammation, bronchial hyperresponsiveness (BHR) and airway wall remodeling. Although, asthma is a vague term, and is recognized as heterogenous entity encompassing different phenotypes. Targeting single mediator or receptor did not prove much clinical significant, as asthma is complex disease involving myriad inflammatory mediators. Asthma may probably involve a large number of different types of molecular and cellular components interacting through complex pathophysiological pathways. This review covers the past, present, and future therapeutic approaches and pathophysiological mechanisms of asthma. Furthermore, review describe importance of targeting several mediators/modulators and receptor antagonists involved in the physiopathology of asthma. Novel targets for asthma research include Galectins, Immunological targets, K ⁺ Channels, Kinases and Transcription Factors, Toll-like receptors, Selectins and Transient receptor potential channels. But recent developments in asthma research are very promising, these include Bitter taste receptors (TAS2R) abated airway obstruction in mouse model of asthma and Calcium-sensing receptor obliterate inflammation and in bronchial hyperresponsiveness allergic asthma. All these progresses in asthma targets, and asthma phenotypes exploration are auspicious in untangling of asthma riddles.

The role of stretch-activated ion channels in acute respiratory distress syndrome: finally a new target?

Mechanical ventilation (MV) and oxygen therapy (hyperoxia; HO) comprise the cornerstones of life-saving interventions for patients with acute respiratory distress syndrome (ARDS). Unfortunately, the side effects of MV and HO include exacerbation of lung injury by barotrauma, volutrauma, and propagation of lung inflammation. Despite significant improvements in ventilator technologies and a heightened awareness of oxygen toxicity, besides low tidal volume ventilation few if any medical interventions have improved ARDS outcomes over the past two decades. We are lacking a comprehensive understanding of mechanotransduction processes in the healthy lung and know little about the interactions between simultaneously activated stretch-, HO-, and cytokine-induced signaling cascades in ARDS. Nevertheless, as we are unraveling these mechanisms we are gathering increasing evidence for the importance of stretch-activated ion channels (SACs) in the activation of lung-resident and inflammatory cells. In addition to the discovery of new SAC families in the lung, e.g., two-pore domain potassium channels, we are increasingly assigning mechanosensing properties to already known Na(+), Ca(2+), K(+), and Cl(-) channels. Better insights into the mechanotransduction mechanisms of SACs will improve our understanding of the pathways leading to ventilator-induced lung injury and lead to much needed novel therapeutic approaches against ARDS by specifically targeting SACs. This review 1) summarizes the reasons why the time has come to seriously consider SACs as new therapeutic targets against ARDS, 2) critically analyzes the physiological and experimental factors that currently limit our knowledge about SACs, and 3) outlines the most important questions future research studies need to address.

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.

Biomass smoke as a risk factor for chronic obstructive pulmonary disease: effects on innate immunity

Chronic obstructive pulmonary disease (COPD), a major cause of mortality and morbidity worldwide, is considered an archetypical disease of innate immunity, where inhaled particles and gases trigger an inflammatory response, favoring tissue proliferation in small airways and tissue destruction in lung parenchyma, in addition to the recruitment of immune cells to these compartments. Although cigarette smoking is still considered the main risk factor for developing COPD, the trend of proposing biomass smoke (BS) exposure as a principal risk factor is gaining importance, as around 3 billion people worldwide are exposed to this pollutant daily. A considerable amount of evidence has shown the potential of BS as an enhancer of lung inflammation. However, an impairment of some innate immune responses after BS exposure has also been described. Regarding the mechanisms by which biomass smoke alters the innate immune responses, three main classes of cell surface receptors-the TLRs, the scavenger receptors and the transient receptor potential channels-have shown the ability to transduce signals initiated after BS exposure. This article is an updated and comprehensive review of the immunomodulatory effects described after the interaction of BS components with these receptors.

Development of therapeutic antibodies to G protein-coupled receptors and ion channels: Opportunities, challenges and their therapeutic potential in respiratory diseases

The development of recombinant antibody therapeutics continues to be a significant area of growth in the pharmaceutical industry with almost 50 approved monoclonal antibodies on the market in the US and Europe. Therapeutic drug targets such as soluble cytokines, growth factors and single transmembrane spanning receptors have been successfully targeted by recombinant monoclonal antibodies and the development of new product candidates continues. Despite this growth, however, certain classes of important disease targets have remained intractable to therapeutic antibodies due to the complexity of the target molecules. These complex target molecules include G protein-coupled receptors and ion channels which represent a large target class for therapeutic intervention with monoclonal antibodies. Although these targets have typically been addressed by small molecule approaches, the exquisite specificity of antibodies provides a significant opportunity to provide selective modulation of these important regulators of cell function. Given this opportunity, a significant effort has been applied to address the challenges of targeting these complex molecules and a number of targets are linked to the pathophysiology of respiratory diseases. In this review, we provide a summary of the importance of GPCRs and ion channels involved in respiratory disease and discuss advantages offered by antibodies as therapeutics at these targets. We highlight some recent GPCRs and ion channels linked to respiratory disease mechanisms and describe in detail recent progress made in the strategies for discovery of functional antibodies against challenging membrane protein targets such as GPCRs and ion channels.

Modulating Innate and Adaptive Immunity by (R)-Roscovitine: Potential Therapeutic Opportunity in Cystic Fibrosis

(R)-Roscovitine, a pharmacological inhibitor of kinases, is currently in phase II clinical trial as a drug candidate for the treatment of cancers, Cushing's disease and rheumatoid arthritis. We here review the data that support the investigation of (R)-roscovitine as a potential therapeutic agent for the treatment of cystic fibrosis (CF). (R)-Roscovitine displays four independent properties that may favorably combine against CF: (1) it partially protects F508del-CFTR from proteolytic degradation and favors its trafficking to the plasma membrane; (2) by increasing membrane targeting of the TRPC6 ion channel, it rescues acidification in phagolysosomes of CF alveolar macrophages (which show abnormally high pH) and consequently restores their bactericidal activity; (3) its effects on neutrophils (induction of apoptosis), eosinophils (inhibition of degranulation/induction of apoptosis) and lymphocytes (modification of the Th17/Treg balance in favor of the differentiation of anti-inflammatory lymphocytes and reduced production of various interleukins, notably IL-17A) contribute to the resolution of inflammation and restoration of innate immunity, and (4) roscovitine displays analgesic properties in animal pain models. The fact that (R)-roscovitine has undergone extensive preclinical safety/pharmacology studies, and phase I and II clinical trials in cancer patients, encourages its repurposing as a CF drug candidate.

TRPC6 channel translocation into phagosomal membrane augments phagosomal function

Defects in the innate immune system in the lung with attendant bacterial infections contribute to lung tissue damage, respiratory insufficiency, and ultimately death in the pathogenesis of cystic fibrosis (CF). Professional phagocytes, including alveolar macrophages (AMs), have specialized pathways that ensure efficient killing of pathogens in phagosomes. Phagosomal acidification facilitates the optimal functioning of degradative enzymes, ultimately contributing to bacterial killing. Generation of low organellar pH is primarily driven by the V-ATPases, proton pumps that use cytoplasmic ATP to load H(+) into the organelle. Critical to phagosomal acidification are various channels derived from the plasma membrane, including the anion channel cystic fibrosis transmembrane conductance regulator, which shunt the transmembrane potential generated by movement of protons. Here we show that the transient receptor potential canonical-6 (TRPC6) calcium-permeable channel in the AM also functions to shunt the transmembrane potential generated by proton pumping and is capable of restoring microbicidal function to compromised AMs in CF and enhancement of function in non-CF cells. TRPC6 channel activity is enhanced via translocation to the cell surface (and then ultimately to the phagosome during phagocytosis) in response to G-protein signaling activated by the small molecule (R)-roscovitine and its derivatives. These data show that enhancing vesicular insertion of the TRPC6 channel to the plasma membrane may represent a general mechanism for restoring phagosome activity in conditions, where it is lost or impaired.

Transient receptor potential (TRP) channels as a therapeutic target for intervention of respiratory effects and lethality from phosgene

Phosgene (CG), a toxic inhalation and industrial hazard, causes bronchoconstriction, vasoconstriction and associated pathological effects that could be life threatening. Ion channels of the transient receptor potential (TRP) family have been identified to act as specific chemosensory molecules in the respiratory tract in the detection, control of adaptive responses and initiation of detrimental signaling cascades upon exposure to various toxic inhalation hazards (TIH); their activation due to TIH exposure may result in broncho- and vasoconstriction. We studied changes in the regulation of intracellular free Ca(2+) concentration ([Ca(2+)]i) in cultures of human bronchial smooth muscle cells (BSMC) and human pulmonary microvascular endothelial cells (HPMEC) exposed to CG (16ppm, 8min), using an air/liquid interface exposure system. CG increased [Ca(2+)]i (p<0.05) in both cell types, The CG-induced [Ca(2+)]i was blocked (p<0.05) by two types of TRP channel blockers, SKF-96365, a general TRP channel blocker, and RR, a general TRPV (vanilloid type) blocker, in both BSMC and HPMEC. These effects correlate with the in vivo efficacies of these compounds to protect against lung injury and 24h lethality from whole body CG inhalation exposure in mice (8-10ppm×20min). Thus the TRP channel mechanism appears to be a potential target for intervention in CG toxicity.

The TRPV1 receptor agonist capsaicin is an ineffective bronchoprovocant in an experimental model of feline asthma

OBJECTIVES

Airway hyper-responsiveness (AHR), a key feature of feline asthma, can be measured using bronchoprovocation testing. Limitations of both direct and indirect bronchoprovocants evaluated to date in experimental feline asthma have led to a search for a more specific indirect bronchoprovocant (ie, one which relies on existing inflammatory cells or activated neural pathways in diseased but not healthy airways). We hypothesized that capsaicin, a transient receptor potential cation channel subfamily V member 1 agonist, would lead to dose-responsive increases in airway resistance as measured by ventilator-acquired pulmonary mechanics in experimentally asthmatic cats.

METHODS

Five cats induced to have asthma using Bermuda grass allergen (BGA) were studied. Twenty-four hours after aerosol challenge of BGA, cats were anesthetized and underwent neuromuscular blockade for ventilator-acquired pulmonary mechanics. Cats were monitored with pulse oximetry for hemoglobin desaturation. Parameters recorded on a breath-by-breath basis on the ventilator included airway resistance (Raw) and compliance. Saline at baseline and 10-fold increasing concentrations of capsaicin (0.4-4000.0 µM) were aerosolized for 30 s and data collected for 4 mins between doses. The intended endpoint of the study was a doubling in baseline airway resistance, halving of compliance or oxygen desaturation <75%.

RESULTS

All cats completed the trial, reaching the highest dose of capsaicin without reaching any of the aforementioned endpoints. No biologically significant alteration in any other pulmonary mechanics parameter was noted.

CONCLUSIONS AND RELEVANCE

Capsaicin does not appear to be an effective bronchoprovocant in a feline asthma model.

Essential oils in the treatment of respiratory tract diseases highlighting their role in bacterial infections and their anti-inflammatory action: a review

The appearance of multidrug resistant bacteria and growing antibiotic resistance is leading to a continuous need for discovering new drugs and alternative treatments against infections. The investigation of the antibacterial effect of essential oils (EOs), which are commonly used nowadays in cosmetics, health care, traditional medicine and food industry, could be one of the promising solutions for this worldwide problem. EOs have a complex mode of action due to their multiple composition. Respiratory tract diseases (RTDs) associated with bacterial infection and inflammation affect a large number of people from every age group worldwide. Because of volatility, EOs can easily reach the upper and lower parts of the respiratory tract via inhalation. Moreover, due to their antimicrobial and anti-inflammatory potency, they offer an effective treatment in respiratory tract infections (RTIs). The purpose of this review is to describe the most frequently developing infections of the upper and lower respiratory tract and to show methods used for the determination of the antibacterial activity of EOs by gaseous contact. The mode of action of EOs on bacterial cells and their anti-inflammatory action are also discussed. Results coming from recently performed in vivo animal studies as well as human trials are also reported. Patents deal with the role of EOs and their volatile constituents in the treatment of RTIs are also introduced. On the whole, this review aimed at showing EOs as potential antimicrobials and as anti-inflammatory agents to alleviate symptoms and signs of RTDs including RTIs. Copyright © 2015 John Wiley & Sons, Ltd.

The role of sports and exercise in allergic disease: drawbacks and benefits

Although training and exercise have several benefits, overdoing it might not necessarily be a good thing. For instance, elite athletes have an increased risk for asthma and allergy. Several mechanisms can be implicated for this risk, which include the interplay between environmental training factors and athlete's personal risk factors, such as genetic susceptibility, neurogenic-mediated inflammation, and epithelial sensitivity. However, an overwhelming amount of scientific evidence shows the positive effects of sports as part of a healthy lifestyle. Training reduces breathlessness and asthma symptoms and attenuates Th2-mediated inflammatory responses. Taken together, the benefits far outweigh the potential hazards of training. An easily administered therapeutic healthy lifestyle intervention, which could be used alongside current treatment, must be developed.

Mechanotransduction via TRPV4 regulates inflammation and differentiation in fetal mouse distal lung epithelial cells

Background

Mechanical ventilation plays a central role in the injury of premature lungs. However, the mechanisms by which mechanical signals trigger an inflammatory cascade to promote lung injury are not well-characterized. Transient receptor potential vanilloid 4 (TRPV4), a calcium-permeable mechanoreceptor channel has been shown to be a major determinant of ventilator-induced acute lung injury in adult models. However, the role of these channels as modulators of inflammation in immature lungs is unknown. In this study, we tested the hypothesis that TRPV4 channels are important mechanotransducers in fetal lung injury.

Methods

Expression of TRPV4 in the mouse fetal lung was investigated by immunohistochemistry, Western blot and qRT-PCR. Isolated fetal epithelial cells were exposed to mechanical stimulation using the Flexcell Strain Unit and inflammation and differentiation were analyzed by ELISA and SP-C mRNA, respectively.

Results

TRPV4 is developmentally regulated in the fetal mouse lung; it is expressed in the lung epithelium and increases with advanced gestation. In contrast, in isolated epithelial cells, TRPV4 expression is maximal at E17-E18 of gestation. Mechanical stretch increases TRPV4 in isolated fetal epithelial cells only during the canalicular stage of lung development. Using the TRPV4 agonist GSK1016790A, the antagonist HC-067047, and the cytokine IL-6 as a marker of inflammation, we observed that TRPV4 regulates release of IL-6 via p38 and ERK pathways. Interestingly, stretch-induced differentiation of fetal epithelial cells was also modulated by TRPV4.

Conclusion

These studies demonstrate that TRPV4 may play an important role in the transduction of mechanical signals in the fetal lung epithelium by modulating not only inflammation but also the differentiation of fetal epithelial cells.

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.

TRP channels and temperature in airway disease-clinical significance

Temperatures above and below what is generally regarded as "comfortable" for the human being have long been known to induce various airway symptoms, especially in combination with exercise in cold climate with temperatures below 0°C, which is naturally since exercise is followed by enhanced ventilation and thus greater amounts of inhaled cold air. The aim was to highlight the knowledge we have today on symptoms from the airways (here also including the eyes) arisen from various temperatures; the mechanisms, the pathophysiology and their clinical significance. The most common eye and airway conditions related to temperature changes are dry eye disease, rhinitis, laryngeal dysfunction, asthma, chronic obstructive pulmonary disease and chronic cough. Transient receptor potential (TRP) ion channels are probably involved in all temperature induced airway symptoms but via different pathways, which are now beginning to be mapped out. In asthma, the most persuasive hypothesis today is that cold-induced asthmatic bronchoconstriction is induced by dehydration of the airway mucosa, from which it follows that provocations with osmotic stimuli like hypertonic saline and mannitol can be used as a surrogate for exercise provocation as well as dry air inhalation. In chronic unexplained cough there seems to be a direct influence of cold air on the TRP ion channels followed by coughing and increased cough sensitivity to inhaled capsaicin. Revelations in the last decades of the ability of several airway TRP ion channels to sense and react to ambient air temperature have opened new windows for the understanding of the pathogenesis in a diversity of airway reactions appearing in many common respiratory diseases.

Exploratory study comparing dysautonomia between asthmatic and non-asthmatic elite swimmers

BACKGROUND

Dysautonomia has been independently associated with training and exercise-induced bronchoconstriction. In addition, neurogenic airway inflammation was recently associated with swimmers-asthma. We aimed to assess the relation between autonomic nervous system and airway responsiveness of asthmatic elite swimmers.

METHODS

Twenty-seven elite swimmers, 11 of whom had asthma, were enrolled in this exploratory cross-sectional study. All performed spirometry with bronchodilation, skin prick tests and methacholine challenge according to the guidelines. Pupillometry was performed using PLR-200™ Pupillometer. One pupil light response curve for each eye was recorded and the mean values of pupil's maximal and minimal diameters, percentage of constriction, average and maximum constriction velocities (parasympathetic parameters), dilation velocity, and total time to recover 75% of the initial size (sympathetic parameters) were used for analysis. Asthma was defined using IOC-MC criteria; subjects were divided into airway hyperesponsiveness (AHR) severity according to methacholine PD20 in: no AHR, borderline, mild, moderate and severe AHR. Differences for pupillary parameters between groups and after categorization by AHR severity were assessed using SPSS 20.0 (p ≤ 0.05). In individuals with clinically relevant AHR, correlation between PD20 and pupillary parameters was investigated with Spearman's correlation test.

RESULTS

No statistically significant differences were observed between asthmatic and non-asthmatic swimmers regarding parasympathetic parameters. When stratified by AHR, maximal and minimal diameters and percentage of constriction were significantly lower among those with severe AHR. Among swimmers with clinically relevant AHR (n = 18), PD20 correlated with parasympathetic activity: maximal (r = 0.67, p = 0.002) and minimal diameters (r = 0.75, p<0.001), percentage of constriction (r = -0.59, p = 0.011) and latency (r = 0.490, p = 0.039).

CONCLUSIONS

No significant differences were observed between asthmatic and non-asthmatic swimmers regarding parasympathetic parameters, but among those with relevant AHR an association was found. Although limited by the sample size, these findings support the relation between dysautonomia and AHR in asthmatic swimmers.

The G protein-coupled receptor-transient receptor potential channel axis: molecular insights for targeting disorders of sensation and inflammation

Sensory nerves are equipped with receptors and ion channels that allow them to detect and respond to diverse chemical, mechanical, and thermal stimuli. These sensory proteins include G protein-coupled receptors (GPCRs) and transient receptor potential (TRP) ion channels. A subclass of peptidergic sensory nerves express GPCRs and TRP channels that detect noxious, irritant, and inflammatory stimuli. Activation of these nerves triggers protective mechanisms that lead to withdrawal from danger (pain), removal of irritants (itch, cough), and resolution of infection (neurogenic inflammation). The GPCR-TRP axis is central to these mechanisms. Signals that emanate from the GPCR superfamily converge on the small TRP family, leading to channel sensitization and activation, which amplify pain, itch, cough, and neurogenic inflammation. Herein we discuss how GPCRs and TRP channels function independently and synergistically to excite sensory nerves that mediate noxious and irritant responses and inflammation in the skin and the gastrointestinal and respiratory systems. We discuss the signaling mechanisms that underlie the GPCR-TRP axis and evaluate how new information about the structure of GPCRs and TRP channels provides insights into their functional interactions. We propose that a deeper understanding of the GPCR-TRP axis may facilitate the development of more selective and effective therapies to treat dysregulated processes that underlie chronic pain, itch, cough, and inflammation.

TRP Channels in Respiratory Pathophysiology: the Role of Oxidative, Chemical Irritant and Temperature Stimuli

There is rapidly growing evidence indicating multiple and important roles of Ca(2+)- permeable cation TRP channels in the airways, both under normal and disease conditions. The aim of this review was to summarize the current knowledge of TRP channels in sensing oxidative, chemical irritant and temperature stimuli by discussing expression and function of several TRP channels in relevant cell types within the respiratory tract, ranging from sensory neurons to airway smooth muscle and epithelial cells. Several of these channels, such as TRPM2, TRPM8, TRPA1 and TRPV1, are discussed in much detail to show that they perform diverse, and often overlapping or contributory, roles in airway hyperreactivity, inflammation, asthma, chronic obstructive pulmonary disease and other respiratory disorders. These include TRPM2 involvement in the disruption of the bronchial epithelial tight junctions during oxidative stress, important roles of TRPA1 and TRPV1 channels in airway inflammation, hyperresponsiveness, chronic cough, and hyperplasia of airway smooth muscles, as well as TRPM8 role in COPD and mucus hypersecretion. Thus, there is increasing evidence that TRP channels not only function as an integral part of the important endogenous protective mechanisms of the respiratory tract capable of detecting and ensuring proper physiological responses to various oxidative, chemical irritant and temperature stimuli, but that altered expression, activation and regulation of these channels may also contribute to the pathogenesis of respiratory diseases.

Dose-dependent cytotoxic effects of menthol on human malignant melanoma A-375 cells: correlation with TRPM8 transcript expression

BACKGROUND

Transient receptor potential melastatin 8 (TRPM8), a principle membrane receptor involved in calcium ion influx and cell signal transduction, has been found to be up-regulated in some cancer types, including melanomas. Efficiency of menthol, an agonist of TRPM8, in killing melanoma cancer cells has been reported previously, but the mechanisms remain unclear. We here determined whether in vitro cytotoxic effects of menthol on A-375 human malignant melanoma cells might be related to TRPM8 transcript expression.

MATERIALS AND METHODS

The PrestoBlue® cell viability assay was used to assess the in vitro cytotoxic effect of menthol after 24h of treatment. RT-PCR was used to quantify TRPM8 transcript expression levels in normal and menthol- treated cells. Cell morphology was observed under inverted phase contrast light microscopy.

RESULTS

TRPM8 transcript expression was found at low levels in A-375 cells and down-regulated in a potentially dose-dependent manner by menthol. Menthol exerted in vitro cytotoxic effects on A-375 cells with an IC50 value of 11.8 μM, which was at least as effective as 5-fluorouracil (IC50=120 μM), a commonly applied chemotherapeutic drug. Menthol showed no dose-dependent cytotoxicity on HeLa cells, a TRPM8 non-expressing cell line.

CONCLUSIONS

The cytotoxic effects on A-375 cells caused by menthol might be related to reduction of the TRPM8 transcript level. This suggests that menthol might activate TRPM8 to increase cytosolic Ca2+ levels, which leads to cytosolic Ca2+ imbalance and triggers cell death.

The low PLC-δ1 expression in cystic fibrosis bronchial epithelial cells induces upregulation of TRPV6 channel activity

Increase of Ca(2+) influx in Cystic Fibrosis (CF) cells has been reported to be related to Transient Receptor Potential Canonical (TRPC6) channel, which is implicated in a functional coupling with Cystic Fibrosis Transmembrane conductance Regulator (CFTR). Several members of the Transient Receptor Potential Vanilloid (TRPV) channels family have already been described as emerging target for respiratory diseases. Two specific isoforms, TRPV5 and TRPV6 are of particular interest in the context of CF Ca(2+) homeostasis as they are highly selective toward Ca(2+) and constitutively activated. Thus, we investigated the involvement of these channels in Ca(2+) influx in CF and non-CF human bronchial epithelial cell lines. 16HBE14o-, CFBE41o- cell lines, primary human airway epithelial cells (hAEC) and freshly isolated human airway epithelial cells from CF and non-CF individuals were used. We showed that both channels are expressed in CF and non-CF cells and constitutive Ca(2+) influx was significantly higher (85%) in cells from CF individuals compared to cells from non-CF ones. Using the selective inhibitor of TRPV6 channel SOR-C27 and a siRNA strategy, our results revealed that TRPV6 was mostly involved in the increase of Ca(2+) influx. TRPV6 channel is negatively regulated by the PLC-PIP2 pathway. We measured the Ca(2+) influx in the presence of the non-specific PLC inhibitor, U73122, in non-CF human bronchial epithelial cells. Ca(2+) influx was increased by 33% with U73122 and this increase was largely reduced in the presence of SOR-C27. PLC inhibition in CF cells by U73122 had no effect on Ca(2+) influx. These results showed that PLC-PIP2 pathway is dysregulated in CF cells and leads to the increase of TRPV6 activity. The regulation of TRPV6 by PLC-PIP2 pathway implicates the specific PLC isoform, PLC-δ1. Immunoblot experiments revealed that expression of PLC-δ1 was decreased by 70% in CF cells. TRPV6 activity was normalized but not the level of expression of PLC-δ1 protein after F508del-CFTR rescue by low temperature for 48 h or treated for 24 h by 10 μM VX-809 in CF cells. This study revealed TRPV6 and PLC-δ1 as critical actor of Ca(2+) homeostasis in CF human bronchial epithelial cells.

Recent additions in the treatment of cough

BACKGROUND

Worldwide, cough is regarded as a challenging clinical problem due to its frequency and often limited therapeutic options. Chronic cough that remains refractory to usual medical treatment causes significant quality of life impairment in people with this problem.

METHODS

We have examined current evidence on recent additions in the treatment of cough, specifically treatment of refractory chronic cough with speech pathology and gabapentin. Relevant randomised control trials, reviews and case reports were identified through a PubMed and SCOPUS search of English-language literature referring to these concepts over the last eight years.

SUMMARY

Of the one hundred and two articles comprising this review the majority investigated the role of the transient receptor potential (TRP) receptors TRP Vanilloid 1 (TRPV1) and TRPA1 in cough and the potential of TRP antagonists as effective anti-tussives. However, these have only been tested in the laboratory and therefore their clinical effectiveness is unknown. Behavioural treatments such as speech pathology have gained momentum and this was evident in the increasing number of articles investigating its positive effect on cough. Investigation on the effectiveness of neuromodulating medications in the treatment of cough have been supported primarily through case series reports and prospective reviews however; their use (particularly gabapentin) has been significantly advanced through recently conducted randomised controlled trials.

CONCLUSIONS

Recent additions in the treatment of chronic cough have been significant as they consider cough to have a unifying diagnosis of cough hypersensitivity with or without the presence of a neuropathic basis. Primarily, effective treatments for chronic cough target these areas and include behavioural treatment such as speech pathology and pharmaceutical treatment with neuromodulating medications such as gabapentin.

Ionotropic and metabotropic proton-sensing receptors involved in airway inflammation in allergic asthma

An acidic microenvironment has been shown to evoke a variety of airway responses, including cough, bronchoconstriction, airway hyperresponsiveness (AHR), infiltration of inflammatory cells in the lung, and stimulation of mucus hyperproduction. Except for the participation of transient receptor potential vanilloid-1 (TRPV1) and acid-sensing ion channels (ASICs) in severe acidic pH (of less than 6.0)-induced cough and bronchoconstriction through sensory neurons, the molecular mechanisms underlying extracellular acidic pH-induced actions in the airways have not been fully understood. Recent studies have revealed that ovarian cancer G protein-coupled receptor 1 (OGR1)-family G protein-coupled receptors, which sense pH of more than 6.0, are expressed in structural cells, such as airway smooth muscle cells and epithelial cells, and in inflammatory and immune cells, such as eosinophils and dendritic cells. They function in a variety of airway responses related to the pathophysiology of inflammatory diseases, including allergic asthma. In the present review, we discuss the roles of ionotropic TRPV1 and ASICs and metabotropic OGR1-family G protein-coupled receptors in the airway inflammation and AHR in asthma and respiratory diseases.

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.

WITHDRAWN: Exploratory study comparing dysautonomia between asthmatic and non-asthmatic elite swimmers

This article has been withdrawn for editorial reasons because the journal will be published only in English. In order to avoid duplicated records, this article can be found at http://dx.doi.org/10.1016/j.rppnen.2014.05.004. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Novel drug targets for asthma and COPD: lessons learned from in vitro and in vivo models

Asthma and chronic obstructive pulmonary disease (COPD) are highly prevalent respiratory diseases characterized by airway inflammation, airway obstruction and airway hyperresponsiveness. Whilst current therapies, such as β-agonists and glucocorticoids, may be effective at reducing symptoms, they do not reduce disease progression. Thus, there is a need to identify new therapeutic targets. In this review, we summarize the potential of novel targets or tools, including anti-inflammatories, phosphodiesterase inhibitors, kinase inhibitors, transient receptor potential channels, vitamin D and protease inhibitors, for the treatment of asthma and COPD.

Transient receptor potential (TRP) channels in the airway: role in airway disease

Over the last few decades, there has been an explosion of scientific publications reporting the many and varied roles of transient receptor potential (TRP) ion channels in physiological and pathological systems throughout the body. The aim of this review is to summarize the existing literature on the role of TRP channels in the lungs and discuss what is known about their function under normal and diseased conditions. The review will focus mainly on the pathogenesis and symptoms of asthma and chronic obstructive pulmonary disease and the role of four members of the TRP family: TRPA1, TRPV1, TRPV4 and TRPM8. We hope that the article will help the reader understand the role of TRP channels in the normal airway and how their function may be changed in the context of respiratory disease.

Role of extracellular proton-sensing OGR1 in regulation of insulin secretion and pancreatic β-cell functions

Insulin secretion with respect to pH environments has been investigated for a long time but its mechanism remains largely unknown. Extracellular pH is usually maintained at around 7.4 and, its change has been thought to occur in non-physiological situations. Acidification takes place under ischemic and inflammatory microenvironments, where stimulation of anaerobic glycolysis results in the production of lactic acid. In addition to ionotropic ion channels, such as transient receptor potential V1 (TRPV1) and acid-sensing ion channels (ASICs), metabotropic proton-sensing G protein-coupled receptors (GPCRs) have also been identified recently as proton-sensing machineries. While ionotropic ion channels usually sense strong acidic pH, proton-sensing GPCRs sense pH of 7.6 to 6.0 and have been shown to mediate a variety of biological actions in neutral and mildly acidic pH environments. Studies with receptor knockout mice have revealed that proton-sensing receptors, including ovarian cancer G protein-coupled receptor 1 (OGR1), a proton-sensing GPCRs, play a role in the regulation of insulin secretion and glucose metabolism under physiological conditions. Small molecule 3,5-disubstituted isoxazoles have recently been identified as OGR1 agonists working at neutral pH and have been shown to stimulate pancreatic β-cell differentiation and insulin synthesis. Thus, proton-sensing OGR1 may be an important player for insulin secretion and a potential target for improving β-cell function.

Functional expression of the transient receptor potential channel TRPA1, a sensor for toxic lung inhalants, in pulmonary epithelial cells

The cation channel TRPA1 functions as a chemosensory protein and is directly activated by a number of noxious inhalants. A pulmonary expression of TRPA1 has been described in sensory nerve endings and its stimulation leads to the acceleration of inflammatory responses in the lung. Whereas the function of TRPA1 in neuronal cells is well defined, only few reports exist suggesting a role in epithelial cells. The aim of the present study was therefore (1) to evaluate the expression of TRPA1 in pulmonary epithelial cell lines, (2) to characterize TRPA1-promoted signaling in these cells, and (3) to study the extra-neuronal expression of this channel in lung tissue sections. Our results revealed that the widely used alveolar type II cell line A549 expresses TRPA1 at the mRNA and protein level. Furthermore, stimulating A549 cells with known TRPA1 activators (i.e., allyl isothiocyanate) led to an increase in intracellular calcium levels, which was sensitive to the TRPA1 blocker ruthenium red. Investigating TRPA1 coupled downstream signaling cascades it was found that TRPA1 activation elicited a stimulation of ERK1/2 whereas other MAP kinases were not affected. Finally, using epithelial as well as neuronal markers in immunohistochemical approaches, a non-neuronal TRPA1 protein expression was detected in distal parts of the porcine lung epithelium, which was also found examining human lung sections. TRPA1-positive staining co-localized with both epithelial and neuronal markers underlining the observed epithelial expression pattern. Our findings of a functional expression of TRPA1 in pulmonary epithelial cells provide causal evidence for a non-neuronal TRPA1-mediated control of inflammatory responses elicited upon TRPA1-mediated registration of toxic inhalants in vivo.

TRPC3 regulates release of brain-derived neurotrophic factor from human airway smooth muscle

Exogenous brain-derived neurotrophic factor (BDNF) enhances Ca(2+) signaling and cell proliferation in human airway smooth muscle (ASM), especially with inflammation. Human ASM also expresses BDNF, raising the potential for autocrine/paracrine effects. The mechanisms by which ASM BDNF secretion occurs are not known. Transient receptor potential channels (TRPCs) regulate a variety of intracellular processes including store-operated Ca(2+) entry (SOCE; including in ASM) and secretion of factors such as cytokines. In human ASM, we tested the hypothesis that TRPC3 regulates BDNF secretion. At baseline, intracellular BDNF was present, and BDNF secretion was detectable by enzyme linked immunosorbent assay (ELISA) of cell supernatants or by real-time fluorescence imaging of cells transfected with GFP-BDNF vector. Exposure to the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFα) (20ng/ml, 48h) or a mixture of allergens (ovalbumin, house dust mite, Alternaria, and Aspergillus extracts) significantly enhanced BDNF secretion and increased TRPC3 expression. TRPC3 knockdown (siRNA or inhibitor Pyr3; 10μM) blunted BDNF secretion, and prevented inflammation effects. Chelation of extracellular Ca(2+) (EGTA; 1mM) or intracellular Ca(2+) (BAPTA; 5μM) significantly reduced secreted BDNF, as did the knockdown of SOCE proteins STIM1 and Orai1 or plasma membrane caveolin-1. Functionally, secreted BDNF had autocrine effects suggested by phosphorylation of high-affinity tropomyosin-related kinase TrkB receptor, prevented by chelating extracellular BDNF with chimeric TrkB-Fc. These data emphasize the role of TRPC3 and Ca(2+) influx in the regulation of BDNF secretion by human ASM and the enhancing effects of inflammation. Given the BDNF effects on Ca(2+) and cell proliferation, BDNF secretion may contribute to altered airway structure and function in diseases such as asthma.

TRPM2 channels are not required for acute airway inflammation in OVA-induced severe allergic asthma in mice

Background

Airway inflammation and asthma have been linked to oxidative stress and the melastatin-related transient receptor potential cation channel, member 2 (TRPM2), which can be activated by reactive oxygen species (ROS), has emerged as a potential therapeutic target for inflammatory diseases.

Objective

Using TRPM2 deficient (TRPM2^-/-) mice, we investigated whether the TRPM2 ion channel, which mediates calcium (Ca²⁺) influx and lysosomal Ca²⁺ release, plays a role in the pathophysiology of severe allergic asthma in mouse.

Methods

Severe allergic asthma was initiated in wild type (WT) and TRPM2^-/- mice by repeated sensitization with ovalbumin (OVA)/aluminum hydroxide on Days 0, 7 and 14, followed by intranasal challenge on Days 21, 22 and 23. Mice were investigated for the presence of airway responsiveness, airway inflammation, production of allergen-specific antibodies, cytokine response and lung pathology.

Results

The absence of TRPM2 channels has no obvious effect on major etiologic markers of severe allergic asthma in this mouse model. Neither airway resistance nor mucus production are affected in TRPM2^-/- mice. TRPM2 channel ablation also does not alter airway inflammation or immunocyte infiltration and does not affect antibody response or cytokine levels.

Conclusions

TRPM2 is not required for airway inflammation in OVA-induced severe allergic asthma in mice. Accordingly, TRPM2 might not be a suitable therapeutic target for airway inflammation caused by allergens in humans.

Work-related allergic respiratory disease and asthma in spice mill workers is associated with inhalant chili pepper and garlic exposures

OBJECTIVE

The aim of the study was to determine the prevalence and risk factors for allergic respiratory disease in spice mill workers.

METHODS

A cross-sectional study of 150 workers used European Community Respiratory Health Survey questionnaires, Phadiatop, serum specific IgE (garlic, chili pepper), spirometry and fractional exhaled nitric oxide (FeNO). Personal air samples (n=62) collected from eight-hour shifts were analysed for inhalable particulate mass. Novel immunological assays quantified airborne garlic and chili pepper allergen concentrations.

RESULTS

Mean dust particulate mass (geometric mean (GM)=2.06 mg/m(3)), chili pepper (GM=0.44 µg/m(3)) and garlic allergen (GM=0.24 µg/m(3)) were highest in blending and were highly correlated. Workers' mean age was 33 years, 71% were men, 46% current smokers and 45% atopic. Spice-dust-related asthma-like symptoms (17%) were common, as was garlic sensitisation (19%), with 13% being monosensitised and 6% cosensitised to chili pepper. Airflow reversibility and FeNO>50 ppb was present in 4% and 8% of workers respectively. Spice-dust-related ocular-nasal (OR 2.40, CI 1.09 to 5.27) and asthma-like (OR 4.15, CI 1.09 to 15.72) symptoms were strongly associated with airborne garlic in the highly exposed (>0.235 µg/m(3)) workers. Workers monosensitised to garlic were more likely to be exposed to higher airborne chili pepper (>0.92 µg/m(3)) (OR 11.52, CI 1.17 to 113.11) than garlic allergens (OR 5.08, CI 1.17 to 22.08) in this mill. Probable asthma was also more strongly associated with chili pepper than with garlic sensitisation.

CONCLUSIONS

Exposure to inhalable spice dust (GM >2.06 mg/m(3)) containing garlic (GM>0.24 µg/m&sup3;) and chili pepper (GM >0.44 µg/m(3)) allergens increase the risk of allergic respiratory disease and asthma.

Knockout of the Trpc1 gene reveals that TRPC1 can promote recovery from anaphylaxis by negatively regulating mast cell TNF-α production

Antigen-mediated mast cell (MC) degranulation is the critical early event in the induction of allergic reactions. Transient receptor potential channels (TRPC), particularly TRPC1, are thought to contribute to such MC activation. To explore the contribution of TRPC1 in MC-driven allergic reactions, we examined antigen-mediated anaphylaxis in Trpc1⁻/⁻ and WT mice, and TRPC1 involvement in the activation of MCs derived from the bone marrow (BMMCs) of these mice. In vivo, we observed a similar induction of passive systemic anaphylaxis in the Trpc1⁻/⁻ mice compared to WT controls. Nevertheless, there was delayed recovery from this response in Trpc1⁻/⁻ mice. Furthermore, contrary to expectations, Trpc1⁻/⁻ BMMCs responded to antigen with enhanced calcium signaling but with little defect in degranulation or associated signaling. In contrast, antigen-mediated production of TNF-α, and other cytokines, was enhanced in the Trpc1⁻/⁻ BMMCs, as were calcium-dependent events required for these responses. Additionally, circulating levels of TNF-α in response to antigen were preferentially elevated in the Trpc1⁻/⁻ mice, and administration of an anti-TNF-α antibody blocked the delay in recovery from anaphylaxis in these mice. These data thus provide evidence that, in this model, TRPC1 promotes recovery from the anaphylactic response by repressing antigen-mediated TNF-α release from MCs.

A review on the mechanism of sore throat in tonsillitis

BACKGROUND

Sore throat is a common condition associated with acute upper respiratory tract infection, and recurrent episodes of infection may result in chronic tonsillitis. The current UK and USA guidelines for tonsillectomy use the incidence of sore throat episodes as an indication for surgery. However, the mechanism of sore throat is poorly described in the literature.

OBJECTIVES

This review will provide basic information for the clinician regarding: the causes, pathophysiology and neurophysiology of sore throat; the mechanism of inflammation; and the role of transient receptor potential ion channels as nociceptors involved in sore throat. The review will present new ideas on the mechanism of ice therapy as an analgesic for post-tonsillectomy pain, and the role of vanilloid and cold receptors.

Transient receptor potential vanilloid 2 (TRPV2), a potential novel biomarker in childhood asthma

BACKGROUND

The presence of transient receptor potential vanilloid 2 (TRPV2) in human peripheral blood cells may suggest a role under pathological conditions. The aim of this study was to explore the relationship between the expression profile of TRPV2 gene and childhood asthma in the north of China. The effects of allergens exposure on the expression of TRPV2 gene were also investigated.

METHODS

Sixty asthmatics children confirmed by physician diagnosis and 60 healthy children as a control group were recruited. Serum total IgE and specific IgE were measured. Using quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR), TRPV2 was detected in total RNA extracted from peripheral blood lymphocytes. Student's t-test and chi-square test were used to analyze the relationship between TRPV2 transcript and different parameter variables on susceptibility of childhood asthma. Multiple logistic regression was used to analyze the associations between TRPV2 gene and allergens.

RESULTS

The expression level of TRPV2 gene was increased 2.6 times in asthmatic children compared with controls (p < .01). The up-regulation of TRPV2 gene and sensitization to one of three the allergens-spring pollen, dust mite, and dog and cat hair-were correlated with childhood asthma. In addition, the hypersensitivity to spring pollen, cockroach, and dust mite and up-regulation of TRPV2 gene expression may be the risk factors for the childhood asthma in Beijing.

CONCLUSIONS

The increased expression of TRPV2 gene in peripheral lymphocytes is closely correlated with childhood asthma in the north of China. This study provides a potential new biomarker of childhood asthma and lays the basis for further clarification of the pathogenesis underlying asthma.

Inhalation of menthol reduces capsaicin cough sensitivity and influences inspiratory flows in chronic cough

INTRODUCTION

Chronic cough is a common clinical problem and there is a shortage of effective treatments for it. Within the group of transient receptor potential ion channels a receptor for the cooling substance menthol has been identified. This study aimed to assess whether pre-inhalation of dissolved, nebulised menthol could increase capsaicin cough thresholds and influence spirometric values.

METHODS

Fourteen patients with chronic cough and airway sensitivity to environmental irritants and 15 control subjects were tested on three occasions. Each one inhaled a 1 mL of nebulised menthol solution of 0.5% or 1% or placebo (saline with 0.05% menthol) at each visit in a randomized and double-blind order. They were then provoked by capsaicin inhalation.

RESULTS

Patients' cough thresholds differed significantly from the controls' on all three provocations (P < 0.0001). After inhalation of 1% menthol, the patients' cough thresholds were significantly higher (P < 0.02) compared to after placebo inhalation and to after 0.5% menthol inhalation (P < 0.05). The patients' peak inspiratory flows were significantly reduced after inhalation of the placebo (saline) (P < 0.05) but not after inhalation of 0.5% or 1% menthol. Forced inspiratory flows 50% were lowered after inhalation of placebo and of 0.5% menthol (P < 0.05) but not after 1% menthol. Among the controls, forced inspiratory flows 50% were lowered after only placebo inhalation (P < 0.05).

CONCLUSIONS

In patients with chronic cough, pre-inhalation of menthol reduces cough sensitivity to inhaled capsaicin and influences inspiratory flows. The findings may provide scientific support for the common practice of using menthol as a reliever for variant airway discomfort. The use of menthol in different cigarette brands could be questioned since it could conceal the natural irritation following smoking.

TRP channels as therapeutic targets in airway disorders: a patent review

INTRODUCTION

Chronic respiratory diseases, such as asthma and chronic obstructive pulmonary disease, affect millions of patients worldwide. New therapeutic approaches to these conditions are urgently needed since current treatment options provide only symptomatic relief. Transient receptor potential (TRP) ion channels are emerging molecular target candidates for the development of novel, disease-modifying drugs addressing airway diseases.

AREAS COVERED

The authors review the patent literature on novel molecules targeting TRP channels (in particular TRPA1, TRPV1, TRPM8 and TRPC6) that are currently studied in clinical trials or are candidates for future clinical evaluation in the management of respiratory diseases.

EXPERT OPINION

The patent literature highlights TRPA1 and TRPV1 channels as the most advanced therapeutic targets in respiratory disorders. TRPV1 antagonists relieve cough in preclinical studies. TRPA1 antagonists not only are anti-tussive but also show efficacy in allergic asthma models. However, to date, only minimal clinical data are available regarding the effects of selective, small-molecule TRPV1 and TRPA1 blockers in respiratory disorders. Clearly, long-term clinical studies are required to confirm the expectations based on preclinical data. In conclusion, the current status of this rapidly expanding research area raises cautious optimism for TRPA1 (and possibly also TRPV1) antagonists as promising anti-tussive/anti-asthma drug candidates.

Modulation of thermoreceptor TRPM8 by cooling compounds

ThermoTRPs, a subset of the Transient Receptor Potential (TRP) family of cation channels, have been implicated in sensing temperature. TRPM8 and TRPA1 are both activated by cooling. TRPM8 is activated by innocuous cooling (<30 °C) and contributes to sensing unpleasant cold stimuli or mediating the effects of cold analgesia and is a receptor for menthol and icilin (mint-derived and synthetic cooling compounds, respectively). TRPA1 (Ankyrin family) is activated by noxious cold (<17 °C), icilin, and a variety of pungent compounds. Extensive amount of medicinal chemistry efforts have been published mainly in the form of patent literature on various classes of cooling compounds by various pharmaceutical companies; however, no prior comprehensive review has been published. When expressed in heterologous expression systems, such as Xenopus oocytes or mammalian cell lines, TRPM8 mediated currents are activated by a number of cooling compounds in addition to menthol and icilin. These include synthetic p-menthane carboxamides along with other class of compounds such as aliphatic/alicyclic alcohols/esters/amides, sulphones/sulphoxides/sulphonamides, heterocyclics, keto-enamines/lactams, and phosphine oxides. In the present review, the medicinal chemistry of various cooling compounds as activators of thermoTRPM8 channel will be discussed according to their chemical classes. The potential of these compounds to emerge as therapeutic agents is also discussed.