Inhibition of airway hyper-responsiveness by TRPV1 antagonists (SB-705498 and PF-04065463) in the unanaesthetized, ovalbumin-sensitized guinea pig

TRPV1: Receptor structure, activation, modulation and role in neuro-immune interactions and pain

In the 1990s, the identification of a non-selective ion channel, especially responsive to capsaicin, revolutionized the studies of somatosensation and pain that were to follow. The TRPV1 channel is expressed mainly in neuronal cells, more specifically, in sensory neurons responsible for the perception of noxious stimuli. However, its presence has also been detected in other non-neuronal cells, such as immune cells, β- pancreatic cells, muscle cells and adipocytes. Activation of the channel occurs in response to a wide range of stimuli, such as noxious heat, low pH, gasses, toxins, endocannabinoids, lipid-derived endovanilloid, and chemical agents, such as capsaicin and resiniferatoxin. This activation results in an influx of cations through the channel pore, especially calcium. Intracellular calcium triggers different responses in sensory neurons. Dephosphorylation of the TRPV1 channel leads to its desensitization, which disrupts its function, while its phosphorylation increases the channel's sensitization and contributes to the channel's rehabilitation after desensitization. Kinases, phosphoinositides, and calmodulin are the main signaling pathways responsible for the channel's regulation. Thus, in this review we provide an overview of TRPV1 discovery, its tissue expression as well as on the mechanisms by which TRPV1 activation (directly or indirectly) induces pain in different disease models.

The Role of Cannabinoid-1 Receptor Ligands in the Ovalbumin-Induced Mouse Model of Allergic Asthma: Is It Related to Transient Receptor Potential Vanilloid-1 Channels?

Objectives: The aim of this study was to investigate the role of cannabinoid (CB1) receptors on airway inflammation and hypersensitivity in allergic asthma and the potential interactions with TRPV1 channels. Materials and Methods: BALB/c mice were sensitized and provoked with ovalbumin to create a model of allergic asthma. CB1 selective agonist arachidonoyl 2'-chloroethylamide (ACEA) was administered intraperitoneally at doses of 0.5, 3, and 5 mg/kg. Receptor antagonism studies were performed utilizing selective CB1 antagonists AM251 at a dose of 3 mg/kg. TRPV1 channel was selectively blocked by capsazepine at a dose of 2.5 mg/kg. Penh values were recorded in vivo by a whole-body plethysmograph under methacholine challenge. Inflammatory cell count was performed in bronchoalveolar lavage fluid (BALF). Serum levels of proinflammatory cytokines were measured by Enzyme-Linked ImmunoSorbent Assay (ELISA). Inflammation in the lung tissue was scored histopathologically. Statistical significance was determined using one-way analysis of variance or Kruskal-Wallis test and expressed as p<0.05. Results: In sensitized animals, provocation with inhaled ovalbumin increased Penh values, serum interleukin (IL)-4, IL-5, IL-13 levels, eosinophil, neutrophil, lymphocyte, macrophage counts in BALF, and inflammation in the lung tissue. ACEA applications did not significantly alter Penh values, BALF inflammatory cell levels, and histological changes related to inflammation in the lung tissue according to the disease group; however, only at a dose of 5 mg/kg, it reduced the levels of the inflammatory cytokine IL-4. AM251 decreased Penh values, eosinophil and neutrophil migration in BALF, and inflammation score of lung tissue compared with the disease group. Although BALF inflammatory cell levels and Penh values were higher in the AM251+ACEA group than in the AM251 group, the differences were insignificant. In the CPZ+ACEA group, Penh values were significantly higher, and serum IL-4 and IL-13 levels and BALF eosinophil counts were lower than that in the CPZ group. Conclusions: This study demonstrated an important role of the CB1 receptors in allergic asthma. CB1 antagonism reduced airway hyperresponsiveness and inflammation and showed immunomodulatory effects. The effect of the CB1 agonist ACEA on asthma does not appear to be related to TRPV1 channels.

The Expression of Semaphorin3E in Vagal Ganglion and Lung Tissue Is Related to Airway Hyperresponsiveness in Murine Asthma Model

Objective

Semaphorin3E (Sema3E) mediates reorganization of the actin cytoskeleton, and plays an important role in ensuring the specificity of synapse formation and angiogenesis. However, the role of Sema3E in allergic asthma (AS) and eosinophilic bronchitis (EB) is still elusive. This study aimed to investigate the relationship between Sema3E in vagal ganglion and lung tissue, airway reactivity, and eosinophilic inflammation.

Methods

The frequency of coughs and airway reactivity as well as the airway inflammation were observed in ovalbumin- (OVA-) induced AS and EB mouse models. The expression of Sema3E was examined in the vagal ganglion and lung tissues by immunofluorescence staining and western blotting analyses. In the Sema3E treatment protocol, exogenous Sema3E was administrated intranasally before challenge in AS model to study the effect of Sema3E on airway hyperresponsiveness, airway inflammation, mucus production, and collagen deposition.

Results

The similar higher frequency of coughs and airway eosinophilic inflammation could be seen in AS and EB groups compared with nasal saline (NS) and dexamethasone (DXM) groups. The absence of the airway hyperresponsiveness was observed in EB and DXM group, while AS group showed increase in airway reactivity to methacholine. The expression of Sema3E in vagal ganglion and lung tissue was remarkably decreased in AS and DXM group compared with EB group. Sema3E-treated asthma mice displayed ameliorated airway hyperresponsiveness, mucus production, and collagen deposition.

Conclusion

Sema3E in lungs and vagal ganglia is related to eosinophilic inflammation and has a protective effect on OVA-induced AHR in asthma.

Potential applications of P2X3 receptor antagonists in the treatment of refractory cough

Refractory chronic cough is defined as a clinical condition in which the cause of the cough remains unclear after comprehensive examination and treatment, or the cause is clear but symptomatic treatment is ineffective. Patients with refractory chronic cough experience a variety of physiological and psychological issues that significantly lower their quality of life and place a significant socio-economic burden on society. As a result, research both domestically and internationally has turned heavily toward these patients. Recently, several studies have identified P2X3 receptor antagonists for the treatment of refractory chronic cough, and this paper reviews the background, mechanism of action, evidence-based proof and application prospects of this class of drugs. KEY MESSAGE: There were plenty of studies about P2X3 receptor antagonists in the past, and in recent years this series of drugs are effective in refractory chronic cough. Although review articles summarizing have been published previously, most have focused on their chemical properties rather than their clinical aspects, with some omitting drugs that have been in clinical studies for nearly two years such as Eliapixant and Sivopixant. Focusing on four P2X3 receptor antagonists with proven efficacy in clinical studies, we analyzed the characteristics and disadvantages of each drug by comparing their clinical results of them and theoretically explained the common side effects of these drugs, as well as their potential for treating refractory chronic cough. This article can be used as a reference for the follow-up studies of P2X3 receptor antagonists in chronic cough. Additionally, it also has implications for the clinical focus of the drug and the approaches to relieve some side effects.

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

INTRODUCTION

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

METHODS AND ANALYSIS

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

DISCUSSION

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

TRIAL REGISTRATION

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

Interactions between calcium regulatory pathways and mechanosensitive channels in airways

INTRODUCTION

Asthma is a chronic lung disease influenced by environmental and inflammatory triggers and involving complex signaling pathways across resident airway cells such as epithelium, airway smooth muscle, fibroblasts, and immune cells. While our understanding of asthma pathophysiology is continually progressing, there is a growing realization that cellular microdomains play critical roles in mediating signaling relevant to asthma in the context of contractility and remodeling. Mechanosensitive pathways are increasingly recognized as important to microdomain signaling, with Piezo and transient receptor protein (TRP) channels at the plasma membrane considered important for converting mechanical stimuli into cellular behavior. Given their ion channel properties, particularly Ca2+ conduction, a question becomes whether and how mechanosensitive channels contribute to Ca2+ microdomains in airway cells relevant to asthma.

AREAS COVERED

Mechanosensitive TRP and Piezo channels regulate key Ca2+ regulatory proteins such as store operated calcium entry (SOCE) involving STIM and Orai channels, and sarcoendoplasmic (SR) mechanisms such as IP3 receptor channels (IP3Rs), and SR Ca2+ ATPase (SERCA) that are important in asthma pathophysiology including airway hyperreactivity and remodeling.

EXPERT OPINION

Physical and/or functional interactions between Ca2+ regulatory proteins and mechanosensitive channels such as TRP and Piezo can toward understanding asthma pathophysiology and identifying novel therapeutic approaches.

Investigating Potential TRPV1 Positive Feedback to Explain TRPV1 Upregulation in Airway Disease States

OBJECTIVE

The airway epithelium is a potential source of pathophysiology through activation of transient potential receptor vallinoid type 1 (TRPV1) channel. A positive feedback cycle caused by TRPV1 activity is hypothesised to induce upregulation and production of inflammatory cytokines, leading to exacerbations of chronic airway diseases. These cytokine and protein regulation effects were investigated in this study.

METHODS

Healthy (BEAS-2B) and cancer-derived (Calu-3) airway epithelial cell lines were assessed for changes to TRPV1 protein expression and mRNA expression following exposure to capsaicin (5 µM to 50 µM), and TRPV1 modulators including heat (43 °C), and hydrochloric acid (pH 3.4 to pH 6.4). Cytotoxicity was measured to determine the working concentration ranges of treatment. Subsequent bronchoconstriction by TRPV1 activation with capsaicin was measured on guinea pig airway tissue to confirm locally mediated activity without the action of known neuronal inputs.

RESULTS

TRPV1 protein expression was not different for all capsaicin, acidity, and heat exposures (P > 0.05), and was replicated in mRNA protein expression (P > 0.05). IL-6 and IL-8 expression were lower in BEAS-2B and Calu-3 cell lines exposed with acidity and heat (P < 0.05), but not consistently with capsaicin exposure, with potential cytotoxic effects possible.

CONCLUSIONS

TRPV1 expression was present in airway epithelial cells but its expression was not changed after activation by TRPV1 activators. Thus, it was not apparent the reason for reported TRPV1 upregulation in patients with airway disease states. More complex mechanisms are likely involved and will require further investigation.

Transient receptor potential cation channel subfamily V (TRPV) and its importance in asthma

Transient receptor potential (TRP) ion channels play critical roles in physiological and pathological conditions. Increasing evidence has unveiled the contribution of TRP vanilloid (TRPV) family in the development of asthma. The TRPV family is a group (TRPV1-TRPV6) of polymodal channels capable of sensing thermal, acidic, mechanical stress, and osmotic stimuli. TRPVs can be activated by endogenous ligands including, arachidonic acid derivatives or endocannabinoids. While TRPV1-TRPV4 are non-selective cation channels showing a predominance for Ca2+ over Na + influx, TRPV5 and TRPV6 are only Ca2+ permeable selective channels. Asthma is a chronic inflammatory bronchopulmonary disorder involving airway hyperresponsiveness (AHR) and airway remodeling. Patients suffering from allergic asthma display an inflammatory pattern driven by cytokines produced in type-2 helper T cells (Th2) and type 2 innate lymphoid cells (ILC2s). Ion channels are essential regulators in airway smooth muscle (ASM) and immune cells physiology. In this review, we summarize the contribution of TRPV1, TRPV2, and TRPV4 to the pathogenesis of asthma. TRPV1 is associated with hypersensitivity to environmental pollutants and chronic cough, inflammation, AHR, and remodeling. TRPV2 is increased in peripheral lymphocytes of asthmatic patients. TRPV4 contributes to ASM cells proliferation, and its blockade leads to a reduced eosinophilia, neutrophilia, as well as an abolished AHR. In conclusion, TRPV2 may represent a novel biomarker for asthma in children; meanwhile, TRPV1 and TRPV4 seem to be essential contributors to the development and exacerbations of asthma. Moreover, these channels may serve as novel therapeutic targets for this ailment.

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.

Thermosensory Transient Receptor Potential Ion Channels and Asthma

Asthma is a widespread chronic disease of the bronchopulmonary system with a heterogeneous course due to the complex etiopathogenesis. Natural-climatic and anthropogenic factors play an important role in the development and progression of this pathology. The reception of physical and chemical environmental stimuli and the regulation of body temperature are mediated by thermosensory channels, members of a subfamily of transient receptor potential (TRP) ion channels. It has been found that genes encoding vanilloid, ankyrin, and melastatin TRP channels are involved in the development of some asthma phenotypes and in the formation of exacerbations of this pathology. The review summarizes modern views on the role of high and low temperatures in airway inflammation in asthma. The participation of thermosensory TRP channels (vanilloid, ankyrin, and melastatin TRP channels) in the reaction to high and low temperatures and air humidity as well as in the formation of bronchial hyperreactivity and respiratory symptoms accompanying asthma is described. The genetic aspects of the functioning of thermosensory TRP channels are discussed. It is shown that new methods of treatment of asthma exacerbations caused by the influence of temperature and humidity should be based on the regulation of channel activity.

The emerging role of neuroimmune interactions in atopic dermatitis and itch

Millions of people globally suffer from allergic diseases, and the cases have been rising in the past decades. One of the major manifestations of allergic diseases is itch, which is an unpleasant symptom that triggers the urge to scratch and greatly affects the quality of life. Thus, research on how sensation of itch is detected/transmitted from the contact of the allergen to the nervous system is crucial in mitigating itch. Recent studies have attempted to elucidate the mechanisms of itch in allergic diseases. Here, we aim to review the endogenous mediators released from immune/nonimmune skin cells (that are indirectly involved in the propagation of itch) and the sensory neurons that express receptors for these itch mediators that are associated with direct transmission of itch in cutaneous allergic diseases. As the mechanisms for allergic itch become clearer, new therapeutic approaches to relieve itch are likely to be developed. Recent clinical trials are testing numerous compounds that target the endogenous mediators and their receptors. These studies provide the possibility of more effective itch treatment for allergic diseases.

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.

Onion Bulb Extract Downregulates EGFR/ERK1/2/AKT Signaling Pathway and Synergizes With Steroids to Inhibit Allergic Inflammation

The treatment of allergic diseases, such as asthma, with both conventional and novel therapies presents a challenge both in terms of optimal effect and cost. On the other hand, traditional therapies utilizing natural products such as onion have been in use for centuries with demonstrated efficacy and safety but without much knowledge of their mechanims of action. In this study, we investigated if the anti-inflammatory effects of onion bulb extract (OBE) are mediated via the modulation of the EGFR/ERK1/2/AKT signaling pathway, and whether OBE can synergise with steroids to produce greater anti-inflammatory actions. Treatment with OBE inhibited the house dust mite (HDM)-induced increased phosphorylation of EGFR, ERK1/2 and AKT which resulted in the inhibition of HDM-induced increase in airway cellular influx, perivascular and peribronchial inflammation, goblet cell hyper/metaplasia, and also inhibited ex vivo eosinophil chemotaxis. Moreover, treatment with a combination of a low dose OBE and low dose dexamethasone resulted in a significant inhibition of the HDM-induced cellular influx, perivascular and peribronchial inflammation, goblet cell hyper/metaplasia, and increased the pERK1/2 levels, whereas neither treatment, when given alone, had any discernible effects. This study therefore shows that inhibition of the EGFR/ERK1/2/AKT-dependent signaling pathway is one of the key mechanisms by which OBE can mediate its anti-inflammatory effects in diseases such as asthma. Importantly, this study also demonstrates that combining OBE with steroids results in significantly enhanced anti-inflammatory effects. This action may have important potential implications for future asthma therapy.

The role of ATP in cough hypersensitivity syndrome: new targets for treatment

Clinically, chronic cough can be effectively controlled in most patients by etiological treatment; however, there remain a small number of patients whose cough has unidentifiable etiology or where treatment efficacy is poor following etiology identification, whose condition is described as unexplained chronic cough or refractory chronic cough. Patients with refractory chronic or unexplained chronic cough commonly have increased cough reflex sensitivity, which has been described as cough hypersensitivity syndrome. The adenosine triphosphate (ATP)-gated P2X₃ receptor may be a key link in the activation of sensory neurons that regulate cough reflexes and has recently draw attention as a potential target for the treatment of refractory chronic cough, with a number of clinical studies validating the therapeutic effects of P2X₃ receptor antagonists in patients with this condition. As the energy source for various cells in vivo, ATP localizes within cells under normal physiological conditions, and has physiological functions, including in metabolism; however, under some pathological circumstances, ATP can act as a neuromodulator and is released into the extracellular space in large quantities as a signal transduction molecule. In addition, ATP is involved in regulation of airway inflammation and the cough reflex. Here, we review the generation, release, and regulation of ATP during airway inflammation and its role in the etiology of cough hypersensitivity syndrome, including the potential underlying mechanism.

Formation of flavorant-propylene Glycol Adducts With Novel Toxicological Properties in Chemically Unstable E-Cigarette Liquids

INTRODUCTION

"Vaping" electronic cigarettes (e-cigarettes) is increasingly popular with youth, driven by the wide range of available flavors, often created using flavor aldehydes. The objective of this study was to examine whether flavor aldehydes remain stable in e-cigarette liquids or whether they undergo chemical reactions, forming novel chemical species that may cause harm to the user.

METHODS

Gas chromatography was used to determine concentrations of flavor aldehydes and reaction products in e-liquids and vapor generated from a commercial e-cigarette. Stability of the detected reaction products in aqueous media was monitored by ultraviolet spectroscopy and nuclear magnetic resonance spectroscopy, and their effects on irritant receptors determined by fluorescent calcium imaging in HEK-293T cells.

RESULTS

Flavor aldehydes including benzaldehyde, cinnamaldehyde, citral, ethylvanillin, and vanillin rapidly reacted with the e-liquid solvent propylene glycol (PG) after mixing, and upward of 40% of flavor aldehyde content was converted to flavor aldehyde PG acetals, which were also detected in commercial e-liquids. Vaping experiments showed carryover rates of 50%-80% of acetals to e-cigarette vapor. Acetals remained stable in physiological aqueous solution, with half-lives above 36 hours, suggesting they persist when inhaled by the user. Acetals activated aldehyde-sensitive TRPA1 irritant receptors and aldehyde-insensitive TRPV1 irritant receptors.

CONCLUSIONS

E-liquids are potentially reactive chemical systems in which new compounds can form after mixing of constituents and during storage, as demonstrated here for flavor aldehyde PG acetals, with unexpected toxicological effects. For regulatory purposes, a rigorous process is advised to monitor the potentially changing composition of e-liquids and e-vapors over time, to identify possible health hazards.

IMPLICATIONS

This study demonstrates that e-cigarette liquids can be chemically unstable, with reactions occurring between flavorant and solvent components immediately after mixing at room temperature. The resulting compounds have toxicological properties that differ from either the flavorants or solvent components. These findings suggest that the reporting of manufacturing ingredients of e-liquids is insufficient for a safety assessment. The establishment of an analytical workflow to detect newly formed compounds in e-liquids and their potential toxicological effects is imperative for regulatory risk analysis.

Coughing in Small Animal Patients

Cough is one of the most common complaints in human medicine. In veterinary medicine cough is equally frequent and plays a significant role in an owner's perception of their pet's quality of life. In human and veterinary medicine, therapy for chronic cough is often ineffective. The complexity of the cough pathway and species differences have made it difficult to develop an effective antitussive agent for veterinary patients. The few effective antitussive agents currently available are associated with significant adverse effects. Fortunately, several promising drugs currently being studied in human clinical trials may offer options for use of novel antitussive therapies in small animal patients. This article reviews current understanding about cough pathophysiology, diagnostic strategies used to uncover underlying etiology of cough, and examines available options for controlling cough, including novel antitussive therapies used in human medicine.

Ang-(1-7)/ MAS1 receptor axis inhibits allergic airway inflammation via blockade of Src-mediated EGFR transactivation in a murine model of asthma

The angiotensin-(1–7) [Ang-(1–7)]/MAS1 receptor signaling axis is a key endogenous anti-inflammatory signaling pathway. However, the mechanisms by which its mediates the anti-inflammatory effects are not completely understood. Using an allergic murine model of asthma, we investigated whether Ang-1(1–7)/MAS1 receptor axis a): inhibits allergic inflammation via modulation of Src-dependent transactivation of the epidermal growth factor receptor (EGFR) and downstream signaling effectors such as ERK1/2, and b): directly inhibits neutrophil and/or eosinophil chemotaxis ex vivo. Ovalbumin (OVA)-induced allergic inflammation resulted in increased phosphorylation of Src kinase, EGFR, and ERK1/2. In addition, OVA challenge increased airway cellular influx, perivascular and peribronchial inflammation, fibrosis, goblet cell hyper/metaplasia and airway hyperresponsiveness (AHR). Treatment with Ang-(1–7) inhibited phosphorylation of Src kinase, EGFR, ERK1/2, the cellular and histopathological changes and AHR. Ang-(1–7) treatment also inhibited neutrophil and eosinophil chemotaxis ex vivo. These changes were reversed following pre-treatment with A779. These data show that the anti-inflammatory actions of Ang-(1–7)/ MAS1 receptor axis are mediated, at least in part, via inhibition of Src-dependent transactivation of EGFR and downstream signaling molecules such as ERK1/2. This study therefore shows that inhibition of the Src/EGRF/ERK1/2 dependent signaling pathway is one of the mechanisms by which the Ang-(1–7)/ MAS1 receptor axis mediates it anti-inflammatory effects in diseases such as asthma.

The Role of Transient Receptor Potential Vanilloid 1 in Common Diseases of the Digestive Tract and the Cardiovascular and Respiratory System

Transient receptor potential vanilloid subtype 1 (TRPV1), a member of the transient receptor potential vanilloid (TRPV) channel family, is a nonselective cation channel that is widely expressed in sensory nerve fibers and nonneuronal cells, including certain vascular endothelial cells and smooth muscle cells. The activation of TRPV1 may be involved in the regulation of various physiological functions, such as the release of inflammatory mediators in the body, gastrointestinal motility function, and temperature regulation. In recent years, a large number of studies have revealed that TRPV1 plays an important role in the physiological and pathological conditions of the digestive system, cardiovascular system, and respiratory system, but there is no systematic report on TRPV1. The objective of this review is to explain the function and effects of TRPV1 on specific diseases, such as irritable bowel syndrome, hypertension, and asthma, and to further investigate the intrinsic relationship between the expression and function of TRPV1 in those diseases to find new therapeutic targets for the cure of related diseases.

Airway Innervation and Plasticity in Asthma

Airway nerves represent a mechanistically and therapeutically important aspect that requires better highlighting in the context of diseases such as asthma. Altered structure and function (plasticity) of afferent and efferent airway innervation can contribute to airway diseases. We describe established anatomy, current understanding of how plasticity occurs, and contributions of plasticity to asthma, focusing on target-derived growth factors (neurotrophins). Perspectives toward novel treatment strategies and future research are provided.

TRPV1 and TRPA1 in Lung Inflammation and Airway Hyperresponsiveness Induced by Fine Particulate Matter (PM2.5)

Exposure to fine particulate matter (PM_2.5) has been associated with lung inflammation and airway hyperresponsiveness (AHR). Transient receptor potential (TRP) vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1) both may play important roles in lung inflammation and AHR. We investigated whether PM_2.5-induced lung inflammation and AHR could be prevented by blocking TRPV1 and TRPA1 channels. Mice were injected intraperitoneally with AMG9810 (30 mg/kg, a TRPV1 antagonist) or A967079 (30 mg/kg, a TRPA1 antagonist) or their combination or vehicle (PBS) one hour before intranasal instillation of PM_2.5 (7.8 mg/kg) or vehicle (PBS) for two consecutive days, and then the mice were studied 24 h later. All pretreatments inhibited PM_2.5-induced AHR and inflammatory infiltration in the lung tissue and decreased inflammatory cytokine levels in the bronchoalveolar lavage fluid, together with oxidant levels in the lung. AMG9810 inhibited MFF expression and increased MFN2 expression while A967079 inhibited DRP1 expression and increased OPA1 expression; combined pretreatment reduced MFF and DPR1 expression and increased MFN2 and OPA1 expression. All pretreatments inhibited the activation of the TLR4/NF-κB pathway, while A967079 alone, and combined with AMG9810 also reduced the activation of the NLRP3/caspase-1 pathway. Both TRPV1 and TRPA1 channels play an important role in PM_2.5-induced lung inflammation and AHR. However, inhibition of the TRPA1 channel or combined inhibition of TRPA1 and TRPV1 channels resulted in greater inhibitory effect on PM_2.5-induced lung injury through regulating the mitochondrial fission/fusion proteins and inhibiting the TLR4/NF-κB and NLRP3/caspase-1 pathways.

Modulators of Transient Receptor Potential (TRP) Channels as Therapeutic Options in Lung Disease

The lungs are essential for gas exchange and serve as the gateways of our body to the external environment. They are easily accessible for drugs from both sides, the airways and the vasculature. Recent literature provides evidence for a role of Transient Receptor Potential (TRP) channels as chemosensors and essential members of signal transduction cascades in stress-induced cellular responses. This review will focus on TRP channels (TRPA1, TRPC6, TRPV1, and TRPV4), predominantly expressed in non-neuronal lung tissues and their involvement in pathways associated with diseases like asthma, cystic fibrosis, chronic obstructive pulmonary disease (COPD), lung fibrosis, and edema formation. Recently identified specific modulators of these channels and their potential as new therapeutic options as well as strategies for a causal treatment based on the mechanistic understanding of molecular events will also be evaluated.

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.

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.

Transient receptor potential (TRP) channels as molecular targets in lung toxicology and associated diseases

The lungs as the gateways of our body to the external environment are essential for gas exchange. They are also exposed to toxicants from two sides, the airways and the vasculature. Apart from naturally produced toxic agents, millions of human made chemicals were produced since the beginning of the industrial revolution whose toxicity still needs to be determined. While the knowledge about toxic substances is increasing only slowly, a paradigm shift regarding the proposed mechanisms of toxicity at the plasma membrane emerged. According to their broad-range chemical reactivity, the mechanism of lung injury evoked by these agents has long been described as rather unspecific. Consequently, therapeutic options are still restricted to symptomatic treatment. The identification of molecular down-stream effectors in cells was a major step forward in the mechanistic understanding of the action of toxic chemicals and will pave the way for more causal and specific toxicity testing as well as therapeutic options. In this context, the involvement of Transient Receptor Potential (TRP) channels as chemosensors involved in the detection and effectors of toxicant action is an attractive concept intensively discussed in the scientific community. In this review we will summarize recent evidence for an involvement of TRP channels (TRPA1, TRPC4, TRPC6, TRPV1, TRPV4, TRPM2 and TRPM8) expressed in the lung in pathways of toxin sensing and as mediators of lung inflammation and associated diseases like asthma, COPD, lung fibrosis and edema formation. Specific modulators of these channels may offer new therapeutic options in the future and will endorse strategies for a causal, specifically tailored treatment based on the mechanistic understanding of molecular events induced by lung-toxic agents.

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

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

[Role of transient receptor potential vanilloid 1 in airway inflammation in asthmatic mice]

OBJECTIVE

To study the effects of the change in transient receptor potential vanilloid 1 (TRPV1) channel activity on the degree of airway inflammation in asthmatic mice.

METHODS

BALB/c mice were randomly divided into control, asthma, capsaicin (TRPV1 agonist), capsazepine (TRPV1 antagonist), and dexamethasone groups. The asthmatic mouse model was established by intraperitoneal injection of mixed ovalbumin-aluminium hydroxide solution and ultrasonic atomization with OVA for sensitization and challenge. The capsaicin, capsazepine, and dexamethasone groups were given intraperitoneal injection of capsaicin (30 μg/kg), capsazepine (10 μmol/kg), and dexamethasone (2 mg/kg) respectively, at 30 minutes before challenge. Hematoxylin and eosin staining was used to observe the degree of pulmonary inflammation. ELISA was used to measure the content of interleukin-8 (IL-8) and interleukin-13 (IL-13) in bronchoalveolar lavage fluid (BALF). Real-Time PCR was used to measure the relative content of TRPV1 mRNA in lung tissue.

RESULTS

Compared with the asthma group, the capsazepine and dexamethasone groups showed reduced pulmonary inflammation, while the capsaicin group showed aggravated pulmonary inflammation. Compared with the control group, the asthma and capsaicin groups showed increases in the content of IL-13 and IL-8 in BALF and the mRNA expression of TRPV1 in lung tissue (P<0.05). Compared with the asthma group, the capsazepine and dexamethasone groups showed reductions in the content of IL-13 and IL-8 in BALF and the mRNA expression of TRPV1 in lung tissue (P<0.05). The capsaicin group showed increases in the content of IL-13 and IL-8 in BALF (P<0.05).

CONCLUSIONS

TRPV1 channel agonist and antagonist can influence the degree of airway inflammation in asthmatic mice. Dexamethasone may reduce airway inflammation through regulating TRPV1 level.

[Role of transient receptor potential vanilloid 1 in airway inflammation in asthmatic mice]

OBJECTIVE

To study the effects of the change in transient receptor potential vanilloid 1 (TRPV1) channel activity on the degree of airway inflammation in asthmatic mice.

METHODS

BALB/c mice were randomly divided into control, asthma, capsaicin (TRPV1 agonist), capsazepine (TRPV1 antagonist), and dexamethasone groups. The asthmatic mouse model was established by intraperitoneal injection of mixed ovalbumin-aluminium hydroxide solution and ultrasonic atomization with OVA for sensitization and challenge. The capsaicin, capsazepine, and dexamethasone groups were given intraperitoneal injection of capsaicin (30 μg/kg), capsazepine (10 μmol/kg), and dexamethasone (2 mg/kg) respectively, at 30 minutes before challenge. Hematoxylin and eosin staining was used to observe the degree of pulmonary inflammation. ELISA was used to measure the content of interleukin-8 (IL-8) and interleukin-13 (IL-13) in bronchoalveolar lavage fluid (BALF). Real-Time PCR was used to measure the relative content of TRPV1 mRNA in lung tissue.

RESULTS

Compared with the asthma group, the capsazepine and dexamethasone groups showed reduced pulmonary inflammation, while the capsaicin group showed aggravated pulmonary inflammation. Compared with the control group, the asthma and capsaicin groups showed increases in the content of IL-13 and IL-8 in BALF and the mRNA expression of TRPV1 in lung tissue (P<0.05). Compared with the asthma group, the capsazepine and dexamethasone groups showed reductions in the content of IL-13 and IL-8 in BALF and the mRNA expression of TRPV1 in lung tissue (P<0.05). The capsaicin group showed increases in the content of IL-13 and IL-8 in BALF (P<0.05).

CONCLUSIONS

TRPV1 channel agonist and antagonist can influence the degree of airway inflammation in asthmatic mice. Dexamethasone may reduce airway inflammation through regulating TRPV1 level.

Role of the ion channel, transient receptor potential cation channel subfamily V member 1 (TRPV1), in allergic asthma

BACKGROUND

Asthma prevalence has increased world-wide especially in children; thus there is a need to develop new therapies that are safe and effective especially for patients with severe/refractory asthma. CD4(+) T cells are thought to play a central role in disease pathogenesis and associated symptoms. Recently, TRPV1 has been demonstrated to regulate the activation and inflammatory properties of CD4(+) cells. The aim of these experiments was to demonstrate the importance of CD4(+) T cells and the role of TRPV1 in an asthma model using a clinically ready TRPV1 inhibitor (XEN-D0501) and genetically modified (GM) animals.

METHODS

Mice (wild type, CD4 (-/-) or TRPV1 (-/-)) and rats were sensitised with antigen (HDM or OVA) and subsequently topically challenged with the same antigen. Key features associated with an allergic asthma type phenotype were measured: lung function (airway hyperreactivity [AHR] and late asthmatic response [LAR]), allergic status (IgE levels) and airway inflammation.

RESULTS

CD4(+) T cells play a central role in both disease model systems with all the asthma-like features attenuated. Targeting TRPV1 using either GM mice or a pharmacological inhibitor tended to decrease IgE levels, airway inflammation and lung function changes.

CONCLUSION

Our data suggests the involvement of TRPV1 in allergic asthma and thus we feel this target merits further investigation.

TRP channels and traffic-related environmental pollution-induced pulmonary disease

Environmental pollutant exposures are major risk factors for adverse health outcomes, with increased morbidity and mortality in humans. Diesel exhaust (DE) is one of the major harmful components of traffic-related air pollution. Exposure to DE affects several physiological systems, including the airways, and pulmonary diseases are increased in highly populated urban areas. Hence, there are urgent needs to (1) create newer and lesser polluting fuels, (2) improve exhaust aftertreatments and reduce emissions, and (3) understand mechanisms of actions for toxic effects of both conventional and cleaner diesel fuels on the lungs. These steps could aid the development of diagnostics and interventions to prevent the negative impact of traffic-related air pollution on the pulmonary system. Exhaust from conventional, and to a lesser extent, clean fuels, contains particulate matter (PM) and more than 400 additional chemical constituents. The major toxic constituents are nitrogen oxides (NOx) and polycyclic aromatic hydrocarbons (PAHs). PM and PAHs could potentially act via transient receptor potential (TRP) channels. In this review, we will first discuss the associations between DE from conventional as well as clean fuel technologies and acute and chronic airway inflammation. We will then review possible activation and/or potentiation of TRP vanilloid type 1 (TRPV1) and ankyrin 1 (TRPA1) channels by PM and PAHs. Finally, we will discuss and summarize recent findings on the mechanisms whereby TRPs could control the link between DE and airway inflammation, which is a primary determinant leading to pulmonary disease.

Neural Abnormalities in Nonallergic Rhinitis

Sensory nerve endings within the airway epithelial cells and the solitary chemoreceptor cells, synapsing with sensory nerves, respond to airborne irritants. Transient receptor potential (TRP) channels (A1 and V1 subtypes, specifically) on these nerve endings initiate local antidromic reflexes resulting in the release of neuropeptides such as substance P and calcitonin G-related peptides. These neuropeptides dilate epithelial submucosal blood vessels and may therefore increase transudation across these vessels resulting in submucosal edema, congestion, and rhinitis. Altered expression or activity of these TRP channels can therefore influence responsiveness to irritants. Besides these pathogenic mechanisms, additional mechanisms such as dysautonomia resulting in diminished sympathetic activity and comparative parasympathetic overactivity have also been suggested as a probable mechanism. Therapeutic effectiveness for this condition has been demonstrated through desensitization of TRPV1 channels with typical agonists such as capsaicin. Other agents effective in treating nonallergic rhinitis (NAR) such as azelastine have been demonstrated to exhibit TRPV1 channel activity through the modulation of Ca(2+) signaling on sensory neurons and in nasal epithelial cells. Roles of antimuscarinic agents such as tiotropium in NAR have been suggested by associations of muscarinic cholinergic receptors with TRPV1. The associations between these channels have also been suggested as mechanisms of airway hyperreactivity in asthma. The concept of the united airway disease hypothesis suggests a significant association between rhinitis and asthma. This concept is supported by the development of late-onset asthma in about 10-40 % of NAR patients who also exhibit a greater severity in their asthma. The factors and mechanisms associating NAR with nonallergic asthma are currently unknown. Nonetheless, free immunoglobulin light chains and microRNA alteration as mediators of these inflammatory conditions may play key roles in this association.

Transient receptor potential channels and itch: how deep should we scratch?

Over the past 30 years, transient receptor potential (TRP) channels have evolved from a somewhat obscure observation on how fruit flies detect light to become the center of drug discovery efforts, triggering a heated debate about their potential as targets for therapeutic applications in humans. In this review, we describe our current understanding of the diverse mechanism of action of TRP channels in the itch pathway from the skin to the brain with focus on the peripheral detection of stimuli that elicit the desire to scratch and spinal itch processing and sensitization. We predict that the compelling basic research findings on TRP channels and pruritus will be translated into the development of novel, clinically useful itch medications.

Guinea pig models of asthma

Described in this unit are methods for establishing guinea pig models of asthma. Sufficient detail is provided to enable investigators to study bronchoconstriction, cough, airway hyperresponsiveness, inflammation, and remodeling.

TRPV4: an exciting new target to promote alveolocapillary barrier function

Transient receptor potential (TRP) channels are emerging as important players and drug targets in respiratory disease. Amongst the vanilloid-type TRP channels (which includes the six members of the TRPV family), target diseases include cough, asthma, cancer, and more recently, pulmonary edema associated with acute respiratory distress syndrome. Here, we critically evaluate a recent report that addresses TRPV4 as a candidate target for the management of acute lung injury that develops as a consequence of aspiration of gastric contents, or acute chlorine gas exposure. By use of two new TRPV4 inhibitors (GSK2220691 or GSK2337429A) and a trpv4(-/-) mouse strain, TRPV4 was implicated as a key mediator of pulmonary inflammation after direct chemical insult. Additionally, applied therapeutically, TRPV4 inhibitors exhibited vasculoprotective effects after chlorine gas exposure, inhibiting vascular leakage, and improving blood oxygenation. These observations underscore TRPV4 channels as candidate therapeutic targets in the management of lung injury, with the added need to balance these against the potential drawbacks of TRPV4 inhibition, such as the danger of limiting the immune response in settings of pathogen-provoked injury.

TRPV1 Antagonism: From Research to Clinic

The capsaicin receptor, TRPV1, has been one of the most extensively studied molecules in sensory research. Its contribution to the sensation of pain in numerous pre-clinical inflammatory and neuropathic paradigms has been well-established and expression analysis suggests a potential role clinically in pain and bladder conditions. The field has now reached an exciting point in time with the development of a number of high quality TRPV1 antagonist drug candidates and the release of clinical data. What has become apparent from this work is that inhibition of TRPV1 function brings with it the potential liabilities of increased body temperature and altered thermal perception. However, there is cause for optimism because it appears that not all antagonists have the same properties and compounds can be identified that lack significant on-target side-effects whilst retaining efficacy, at least pre-clinically. What is perhaps now more critical to address is the question of how effective the analgesia provided by a TRPV1 antagonist will be. Although tantalizing clinical data showing effects on experimentally-induced pain or pain following molar extraction have been reported, no clear efficacy in a chronic pain condition has yet been demonstrated making it difficult to perform an accurate risk-benefit analysis for TRPV1 antagonists. Here we provide an overview of some of the most advanced clinical candidates and discuss the approaches being taken to avoid the now well established on-target effects of TRPV1 antagonists.

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.

TRPV1

TRPV1 is a well-characterised channel expressed by a subset of peripheral sensory neurons involved in pain sensation and also at a number of other neuronal and non-neuronal sites in the mammalian body. Functionally, TRPV1 acts as a sensor for noxious heat (greater than ~42 °C). It can also be activated by some endogenous lipid-derived molecules, acidic solutions (pH < 6.5) and some pungent chemicals and food ingredients such as capsaicin, as well as by toxins such as resiniferatoxin and vanillotoxins. Structurally, TRPV1 subunits have six transmembrane (TM) domains with intracellular N- (containing 6 ankyrin-like repeats) and C-termini and a pore region between TM5 and TM6 containing sites that are important for channel activation and ion selectivity. The N- and C- termini have residues and regions that are sites for phosphorylation/dephosphorylation and PI(4,5)P2 binding, which regulate TRPV1 sensitivity and membrane insertion. The channel has several interacting proteins, some of which (e.g. AKAP79/150) are important for TRPV1 phosphorylation. Four TRPV1 subunits form a non-selective, outwardly rectifying ion channel permeable to monovalent and divalent cations with a single-channel conductance of 50-100 pS. TRPV1 channel kinetics reveal multiple open and closed states, and several models for channel activation by voltage, ligand binding and temperature have been proposed. Studies with TRPV1 agonists and antagonists and Trpv1 (-/-) mice have suggested a role for TRPV1 in pain, thermoregulation and osmoregulation, as well as in cough and overactive bladder. TRPV1 antagonists have advanced to clinical trials where findings of drug-induced hyperthermia and loss of heat sensitivity have raised questions about the viability of this therapeutic approach.

Transient receptor potential (TRP) channels: a clinical perspective

Transient receptor potential (TRP) channels are important mediators of sensory signals with marked effects on cellular functions and signalling pathways. Indeed, mutations in genes encoding TRP channels are the cause of several inherited diseases in humans (the so-called 'TRP channelopathies') that affect the cardiovascular, renal, skeletal and nervous systems. TRP channels are also promising targets for drug discovery. The initial focus of research was on TRP channels that are expressed on nociceptive neurons. Indeed, a number of potent, small-molecule TRPV1, TRPV3 and TRPA1 antagonists have already entered clinical trials as novel analgesic agents. There has been a recent upsurge in the amount of work that expands TRP channel drug discovery efforts into new disease areas such as asthma, cancer, anxiety, cardiac hypertrophy, as well as obesity and metabolic disorders. A better understanding of TRP channel functions in health and disease should lead to the discovery of first-in-class drugs for these intractable diseases. With this review, we hope to capture the current state of this rapidly expanding and changing field.

Effect of chirality and lipophilicity in the functional activity of evodiamine and its analogues at TRPV1 channels

BACKGROUND AND PURPOSE

Evodiamine, a racemic quinazolinocarboline alkaloid isolated from the traditional Chinese medicine Evodiae fructus, has been reported to act as an agonist of the transient receptor potential vanilloid type-1 (TRPV1) cation channel both in vitro and in vivo. Evodiamine is structurally different from all known TRPV1 activators, and has significant clinical potential as a thermogenic agent. Nevertheless, the molecular bases for its actions are still poorly understood.

EXPERIMENTAL APPROACH

To investigate the structure-activity relationships of evodiamine, the natural racemate was resolved, and a series of 23 synthetic analogues was prepared, using as the end point the intracellular Ca(2+) elevation in HEK-293 cells stably overexpressing either the human or the rat recombinant TRPV1.

KEY RESULTS

S-(+) evodiamine was more efficacious and potent than R-(-) evodiamine, and a new potent lead (Evo30) was identified, more potent than the reference TRPV1 agonist, capsaicin. In general, potency and efficacy correlated with the lipophilicity of the analogues. Like other TRPV1 agonists, several synthetic analogues could efficiently desensitize TRPV1 to activation by capsaicin.

CONCLUSIONS AND IMPLICATIONS

Evodiamine qualifies as structurally unique lead structure to develop new potent TRPV1 agonists/desensitizers.

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.

Tiotropium modulates transient receptor potential V1 (TRPV1) in airway sensory nerves: A beneficial off-target effect?

Background

Recent studies have suggested that the long-acting muscarinic receptor antagonist tiotropium, a drug widely prescribed for its bronchodilator activity in patients with chronic obstructive pulmonary disease and asthma, improves symptoms and attenuates cough in preclinical and clinical tussive agent challenge studies. The mechanism by which tiotropium modifies tussive responses is not clear, but an inhibition of vagal tone and a consequent reduction in mucus production from submucosal glands and bronchodilation have been proposed.

Objective

The aim of this study was to investigate whether tiotropium can directly modulate airway sensory nerve activity and thereby the cough reflex.

Methods

We used a conscious cough model in guinea pigs, isolated vagal sensory nerve and isolated airway neuron tissue– and cell-based assays, and in vivo single-fiber recording electrophysiologic techniques.

Results

Inhaled tiotropium blocked cough and single C-fiber firing in the guinea pig to the transient receptor potential (TRP) V1 agonist capsaicin, a clinically relevant tussive stimulant. Tiotropium and ipratropium, a structurally similar muscarinic antagonist, inhibited capsaicin responses in isolated guinea pig vagal tissue, but glycopyrrolate and atropine did not. Tiotropium failed to modulate other TRP channel–mediated responses. Complementary data were generated in airway-specific primary ganglion neurons, demonstrating that tiotropium inhibited capsaicin-induced, but not TRPA1-induced, calcium movement and voltage changes.

Conclusion

For the first time, we have shown that tiotropium inhibits neuronal TRPV1-mediated effects through a mechanism unrelated to its anticholinergic activity. We speculate that some of the clinical benefit associated with taking tiotropium (eg, in symptom control) could be explained through this proposed mechanism of action.

TRPV1 and SP: key elements for sepsis outcome?

Sensory neurons play important roles in many disorders, including inflammatory diseases, such as sepsis. Sepsis is a potentially lethal systemic inflammatory reaction to a local bacterial infection, affecting thousands of patients annually. Although associated with a high mortality rate, sepsis outcome depends on the severity of systemic inflammation, which can be directly influenced by several factors, including the immune response of the patient. Currently, there is a lack of effective drugs to treat sepsis, and thus there is a need to develop new drugs to improve sepsis outcome. Several mediators involved in the formation of sepsis have now been identified, but the mechanisms underlying the pathology remain poorly understood. The transient receptor potential vanilloid 1 (TRPV1) receptor and the neuropeptide substance P (SP) have recently been demonstrated as important targets for sepsis and are located on sensory neurones and non-neuronal cells. Herein, we highlight and review the importance of sensory neurones for the modulation of sepsis, with specific focus on recent findings relating to TRPV1 and SP, with their distinct abilities to alter the transition from local to systemic inflammation and also modify the overall sepsis outcome. We also emphasize the protective role of TRPV1 in this context.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Perivagal antagonist treatment in rats selectively blocks the reflex and afferent responses of vagal lung C fibers to intravenous agonists

The terminals of vagal lung C fibers (VLCFs) express various types of pharmacological receptors that are important to the elicitation of airway reflexes and the development of airway hypersensitivity. We investigated the blockade of the reflex and afferent responses of VLCFs to intravenous injections of agonists using perivagal treatment with antagonists (PAT) targeting the transient receptor potential vanilloid 1, P2X, and 5-HT(3) receptors in anesthetized rats. Blockading these responses via perivagal capsaicin treatment (PCT), which blocks the neural conduction of C fibers, was also studied. We used capsaicin, α,β-methylene-ATP, and phenylbiguanide as the agonists, and capsazepine, iso-pyridoxalphosphate-6-azophenyl-2',5'-disulfonate, and tropisetron as the antagonists of transient receptor potential vanilloid 1, P2X, and 5-HT(3) receptors, respectively. We found that each of the PATs abolished the VLCF-mediated reflex apnea evoked by the corresponding agonist, while having no effect on the response to other agonists. Perivagal vehicle treatment failed to produce any such blockade. These blockades had partially recovered at 3 h after removal of the PATs. In contrast, PCT abolished the reflex apneic response to all three agonists. Both PATs and PCT did not affect the myelinated afferent-mediated apneic response to lung inflation. Consistently, our electrophysiological studies revealed that each of the PATs prevented the VLCF responses to the corresponding agonist, but not to any other agonist. PCT inevitably prevented the VLCF responses to all three agonists. Thus these PATs selectively blocked the stimulatory action of corresponding agonists on the VLCF terminals via mechanisms that are distinct from those of PCT. PAT may become a novel intervention for studying the pharmacological modulation of VLCFs.

TRPA1: A gatekeeper for inflammation

Tissue damage evokes an inflammatory response that promotes the removal of harmful stimuli, tissue repair, and protective behaviors to prevent further damage and encourage healing. However, inflammation may outlive its usefulness and become chronic. Chronic inflammation can lead to a host of diseases, including asthma, itch, rheumatoid arthritis, and colitis. Primary afferent sensory neurons that innervate target organs release inflammatory neuropeptides in the local area of tissue damage to promote vascular leakage, the recruitment of immune cells, and hypersensitivity to mechanical and thermal stimuli. TRPA1 channels are required for neuronal excitation, the release of inflammatory neuropeptides, and subsequent pain hypersensitivity. TRPA1 is also activated by the release of inflammatory agents from nonneuronal cells in the area of tissue injury or disease. This dual function of TRPA1 as a detector and instigator of inflammatory agents makes TRPA1 a gatekeeper of chronic inflammatory disorders of the skin, airways, and gastrointestinal tract.