A sensory neuronal ion channel essential for airway inflammation and hyperreactivity in asthma

An NT4/TrkB-dependent increase in innervation links early-life allergen exposure to persistent airway hyperreactivity

Children who are exposed to environmental respiratory insults often develop asthma that persists into adulthood. In this study, we used a neonatal mouse model of ovalbumin (OVA)-induced allergic airway inflammation to understand the long-term effects of early childhood insults on airway structure and function. We showed that OVA sensitization and challenge in early life led to a 2-fold increase in airway smooth muscle (ASM) innervation (P<0.05) and persistent airway hyperreactivity (AHR). In contrast, OVA exposure in adult life elicited short-term AHR without affecting innervation levels. We found that postnatal ASM innervation required neurotrophin (NT)-4 signaling through the TrkB receptor and that early-life OVA exposure significantly elevated NT4 levels and TrkB signaling by 5- and 2-fold, respectively, to increase innervation. Notably, blockade of NT4/TrkB signaling in OVA-exposed pups prevented both acute and persistent AHR without affecting baseline airway function or inflammation. Furthermore, biophysical assays using lung slices and isolated cells demonstrated that NT4 was necessary for hyperreactivity of ASM induced by early-life OVA exposure. Together, our findings show that the NT4/TrkB-dependent increase in innervation plays a critical role in the alteration of the ASM phenotype during postnatal growth, thereby linking early-life allergen exposure to persistent airway dysfunction.

Channelopathies

Channelopathies are a heterogeneous group of disorders resulting from the dysfunction of ion channels located in the membranes of all cells and many cellular organelles. These include diseases of the nervous system (e.g., generalized epilepsy with febrile seizures plus, familial hemiplegic migraine, episodic ataxia, and hyperkalemic and hypokalemic periodic paralysis), the cardiovascular system (e.g., long QT syndrome, short QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia), the respiratory system (e.g., cystic fibrosis), the endocrine system (e.g., neonatal diabetes mellitus, familial hyperinsulinemic hypoglycemia, thyrotoxic hypokalemic periodic paralysis, and familial hyperaldosteronism), the urinary system (e.g., Bartter syndrome, nephrogenic diabetes insipidus, autosomal-dominant polycystic kidney disease, and hypomagnesemia with secondary hypocalcemia), and the immune system (e.g., myasthenia gravis, neuromyelitis optica, Isaac syndrome, and anti-NMDA [N-methyl-D-aspartate] receptor encephalitis). The field of channelopathies is expanding rapidly, as is the utility of molecular-genetic and electrophysiological studies. This review provides a brief overview and update of channelopathies, with a focus on recent advances in the pathophysiological mechanisms that may help clinicians better understand, diagnose, and develop treatments for these diseases.

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

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

TRP channels and pain

Nociception is the process whereby primary afferent nerve fibers of the somatosensory system detect noxious stimuli. Pungent irritants from pepper, mint, and mustard plants have served as powerful pharmacological tools for identifying molecules and mechanisms underlying this initial step of pain sensation. These natural products have revealed three members of the transient receptor potential (TRP) ion channel family--TRPV1, TRPM8, and TRPA1--as molecular detectors of thermal and chemical stimuli that activate sensory neurons to produce acute or persistent pain. Analysis of TRP channel function and expression has validated the existence of nociceptors as a specialized group of somatosensory neurons devoted to the detection of noxious stimuli. These studies are also providing insight into the coding logic of nociception and how specification of nociceptor subtypes underlies behavioral discrimination of noxious thermal, chemical, and mechanical stimuli. Biophysical and pharmacological characterization of these channels has provided the intellectual and technical foundation for developing new classes of analgesic drugs.

The endogenous Th17 response in NO2-promoted allergic airway disease is dispensable for airway hyperresponsiveness and distinct from Th17 adoptive transfer

Severe, glucocorticoid-resistant asthma comprises 5-7% of patients with asthma. IL-17 is a biomarker of severe asthma, and the adoptive transfer of Th17 cells in mice is sufficient to induce glucocorticoid-resistant allergic airway disease. Nitrogen dioxide (NO2) is an environmental toxin that correlates with asthma severity, exacerbation, and risk of adverse outcomes. Mice that are allergically sensitized to the antigen ovalbumin by exposure to NO2 exhibit a mixed Th2/Th17 adaptive immune response and eosinophil and neutrophil recruitment to the airway following antigen challenge, a phenotype reminiscent of severe clinical asthma. Because IL-1 receptor (IL-1R) signaling is critical in the generation of the Th17 response in vivo, we hypothesized that the IL-1R/Th17 axis contributes to pulmonary inflammation and airway hyperresponsiveness (AHR) in NO2-promoted allergic airway disease and manifests in glucocorticoid-resistant cytokine production. IL-17A neutralization at the time of antigen challenge or genetic deficiency in IL-1R resulted in decreased neutrophil recruitment to the airway following antigen challenge but did not protect against the development of AHR. Instead, IL-1R-/- mice developed exacerbated AHR compared to WT mice. Lung cells from NO2-allergically inflamed mice that were treated in vitro with dexamethasone (Dex) during antigen restimulation exhibited reduced Th17 cytokine production, whereas Th17 cytokine production by lung cells from recipient mice of in vitro Th17-polarized OTII T-cells was resistant to Dex. These results demonstrate that the IL-1R/Th17 axis does not contribute to AHR development in NO2-promoted allergic airway disease, that Th17 adoptive transfer does not necessarily reflect an endogenously-generated Th17 response, and that functions of Th17 responses are contingent on the experimental conditions in which they are generated.

Rhinovirus upregulates transient receptor potential channels in a human neuronal cell line: implications for respiratory virus-induced cough reflex sensitivity

BACKGROUND

The mechanism underlying respiratory virus-induced cough hypersensitivity is unknown. Upregulation of airway neuronal receptors responsible for sensing physical and chemical stimuli is one possibility, and the transient receptor potential (TRP) channel family are potential candidates. We have used an in vitro model of sensory neurons and human rhinovirus (HRV-16) to study the effect of virus infection on TRP expression.

METHODS

IMR-32 neuroblastoma cells were differentiated in culture to express three TRP channels: TRPV1, TRPA1 and TRPM8. Flow cytometry and qRT-PCR were used to measure TRP channel protein and mRNA levels following inoculation with live virus, inactivated virus, virus-induced soluble factors or pelleted virus particles. Multiplex bioassay was used to determine nerve growth factor (NGF), interleukin (IL)-1β, IL-6 and IL-8 levels in response to infection.

RESULTS

Early upregulation of TRPA1 and TRPV1 expression occurred 2-4 h post infection. This was independent of replicating virus as virus-induced soluble factors alone were sufficient to increase channel expression 50-fold and 15-fold, respectively. NGF, IL-6 and IL-8 levels, increased in infected cell supernatants, represent possible candidates. In contrast, TRPM8 expression was maximal at 48 h (9.6-fold) and required virus replication rather than soluble factors.

CONCLUSIONS

We show for the first time that rhinovirus can infect neuronal cells. Furthermore, infection causes upregulation of TRP channels by channel-specific mechanisms. The increase in TRPA1 and TRPV1 levels can be mediated by soluble factors induced by infection whereas TRPM8 requires replicating virus. TRP channels may be novel therapeutic targets for controlling virus-induced cough.

Linoleic acid metabolite drives severe asthma by causing airway epithelial injury

Airway epithelial injury is the hallmark of various respiratory diseases, but its mechanisms remain poorly understood. While 13-S-hydroxyoctadecadienoic acid (13-S-HODE) is produced in high concentration during mitochondrial degradation in reticulocytes little is known about its role in asthma pathogenesis. Here, we show that extracellular 13-S-HODE induces mitochondrial dysfunction and airway epithelial apoptosis. This is associated with features of severe airway obstruction, lung remodeling, increase in epithelial stress related proinflammatory cytokines and drastic airway neutrophilia in mouse. Further, 13-S-HODE induced features are attenuated by inhibiting Transient Receptor Potential Cation Channel, Vanilloid-type 1 (TRPV1) both in mouse model and human bronchial epithelial cells. These findings are relevant to human asthma, as 13-S-HODE levels are increased in human asthmatic airways. Blocking of 13-S-HODE activity or disruption of TRPV1 activity attenuated airway injury and asthma mimicking features in murine allergic airway inflammation. These findings indicate that 13-S-HODE induces mitochondrial dysfunction and airway epithelial injury.

TRPM8 is the principal mediator of menthol-induced analgesia of acute and inflammatory pain

Menthol, the cooling natural product of peppermint, is widely used in medicinal preparations for the relief of acute and inflammatory pain in sports injuries, arthritis, and other painful conditions. Menthol induces the sensation of cooling by activating TRPM8, an ion channel in cold-sensitive peripheral sensory neurons. Recent studies identified additional targets of menthol, including the irritant receptor, TRPA1, voltage-gated ion channels and neurotransmitter receptors. It remains unclear which of these targets contribute to menthol-induced analgesia, or to the irritating side effects associated with menthol therapy. Here, we use genetic and pharmacological approaches in mice to probe the role of TRPM8 in analgesia induced by L-menthol, the predominant analgesic menthol isomer in medicinal preparations. L-menthol effectively diminished pain behavior elicited by chemical stimuli (capsaicin, acrolein, acetic acid), noxious heat, and inflammation (complete Freund's adjuvant). Genetic deletion of TRPM8 completely abolished analgesia by L-menthol in all these models, although other analgesics (acetaminophen) remained effective. Loss of L-menthol-induced analgesia was recapitulated in mice treated with a selective TRPM8 inhibitor, AMG2850. Selective activation of TRPM8 with WS-12, a menthol derivative that we characterized as a specific TRPM8 agonist in cultured sensory neurons and in vivo, also induced TRPM8-dependent analgesia of acute and inflammatory pain. L-menthol- and WS-12-induced analgesia was blocked by naloxone, suggesting activation of endogenous opioid-dependent analgesic pathways. Our data show that TRPM8 is the principal mediator of menthol-induced analgesia of acute and inflammatory pain. In contrast to menthol, selective TRPM8 agonists may produce analgesia more effectively, with diminished side effects.

TRPA1 controls inflammation and pruritogen responses in allergic contact dermatitis

Allergic contact dermatitis is a common skin disease associated with inflammation and persistent pruritus. Transient receptor potential (TRP) ion channels in skin-innervating sensory neurons mediate acute inflammatory and pruritic responses following exogenous stimulation and may contribute to allergic responses. Genetic ablation or pharmacological inhibition of TRPA1, but not TRPV1, inhibited skin edema, keratinocyte hyperplasia, nerve growth, leukocyte infiltration, and antihistamine-resistant scratching behavior in mice exposed to the haptens, oxazolone and urushiol, the contact allergen of poison ivy. Hapten-challenged skin of TRPA1-deficient mice contained diminished levels of inflammatory cytokines, nerve growth factor, and endogenous pruritogens, such as substance P (SP) and serotonin. TRPA1-deficient sensory neurons were defective in SP signaling, and SP-induced scratching behavior was abolished in Trpa1(-/-) mice. SP receptor antagonists, such as aprepitant inhibited both hapten-induced cutaneous inflammation and scratching behavior. These findings support a central role for TRPA1 and SP in the integration of immune and neuronal mechanisms leading to chronic inflammatory responses and pruritus associated with contact dermatitis.

Role of transient receptor potential ion channels and evoked levels of neuropeptides in a formaldehyde-induced model of asthma in BALB/c mice

OBJECTIVE

Asthma is a complex pulmonary inflammatory disease characterized by the hyper-responsiveness, remodeling and inflammation of airways. Formaldehyde is a common indoor air pollutant that can cause asthma in people experiencing long-term exposure. The irritant effect and adjuvant effect are the two possible pathways of formaldehyde promoted asthma.

METHODOLOGY/PRINCIPAL FINDINGS

To explore the neural mechanisms and adjuvant effect of formaldehyde, 48 Balb/c mice in six experimental groups were exposed to (a) vehicle control; (b) ovalbumin; (c) formaldehyde (3.0 mg/m(3)); (d) ovalbumin+formaldehyde (3.0 mg/m(3)); (e) ovalbumin+formaldehyde (3.0 mg/m(3))+HC-030031 (transient receptor potential ankyrin 1 antagonist); (f) ovalbumin+formaldehyde (3.0 mg/m(3))+ capsazepine (transient receptor potential vanilloid 1 antagonist). Experiments were conducted after 4 weeks of combined exposure and 1-week challenge with aerosolized ovalbumin. Airway hyper-responsiveness, pulmonary tissue damage, eosinophil infiltration, and increased levels of interleukin-4, interleukin-6, interleukin-1β, immunoglobulin E, substance P and calcitonin gene-related peptide in lung tissues were found in the ovalbumin+formaldehyde (3.0 mg/m(3)) group compared with the values seen in ovalbumin -only immunized mice. Except for interleukin-1β levels, other changes in the levels of biomarker could be inhibited by HC-030031 and capsazepine.

CONCLUSIONS/SIGNIFICANCE

Formaldehyde might be a key risk factor for the rise in asthma cases. Transient receptor potential ion channels and neuropeptides have important roles in formaldehyde promoted-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.

Activation of transient receptor potential ankyrin-1 (TRPA1) in lung cells by wood smoke particulate material

Cigarette smoke, diesel exhaust, and other combustion-derived particles activate the calcium channel transient receptor potential ankyrin-1 (TRPA1), causing irritation and inflammation in the respiratory tract. It was hypothesized that wood smoke particulate and select chemical constituents thereof would also activate TRPA1 in lung cells, potentially explaining the adverse effects of wood and other forms of biomass smoke on the respiratory system. TRPA1 activation was assessed using calcium imaging assays in TRPA1-overexpressing HEK-293 cells, mouse primary trigeminal neurons, and human adenocarcinoma (A549) lung cells. Particles from pine and mesquite smoke were less potent agonists of TRPA1 than an equivalent mass concentration of an ethanol extract of diesel exhaust particles; pine particles were comparable in potency to cigarette smoke condensate, and mesquite particles were the least potent. The fine particulate (PM < 2.5 μm) of wood smoke were the most potent TRPA1 agonists and several chemical constituents of wood smoke particulate, 3,5-ditert-butylphenol, coniferaldehyde, formaldehyde, perinaphthenone, agathic acid, and isocupressic acid, were TRPA1 agonists. Pine particulate activated TRPA1 in mouse trigeminal neurons and A549 cells in a concentration-dependent manner, which was inhibited by the TRPA1 antagonist HC-030031. TRPA1 activation by wood smoke particles occurred through the electrophile/oxidant-sensing domain (i.e., C621/C641/C665/K710), based on the inhibition of cellular responses when the particles were pretreated with glutathione; a role for the menthol-binding site of TRPA1 (S873/T874) was demonstrated for 3,5-ditert-butylphenol. This study demonstrated that TRPA1 is a molecular sensor for wood smoke particulate and several chemical constituents thereof, in sensory neurons and A549 cells, suggesting that TRPA1 may mediate some of the adverse effects of wood smoke in humans.

Role of arginase 1 from myeloid cells in th2-dominated lung inflammation

Th2-driven lung inflammation increases Arginase 1 (Arg1) expression in alternatively-activated macrophages (AAMs). AAMs modulate T cell and wound healing responses and Arg1 might contribute to asthma pathogenesis by inhibiting nitric oxide production, regulating fibrosis, modulating arginine metabolism and restricting T cell proliferation. We used mice lacking Arg1 in myeloid cells to investigate the contribution of Arg1 to lung inflammation and pathophysiology. In six model systems encompassing acute and chronic Th2-mediated lung inflammation we observed neither a pathogenic nor protective role for myeloid-expressed Arg1. The number and composition of inflammatory cells in the airways and lungs, mucus secretion, collagen deposition, airway hyper-responsiveness, and T cell cytokine production were not altered if AAMs were deficient in Arg1 or simultaneously in both Arg1 and NOS2. Our results argue that Arg1 is a general feature of alternative activation but only selectively regulates Th2 responses. Therefore, attempts to experimentally or therapeutically inhibit arginase activity in the lung should be examined with caution.

Emerging roles of TRPA1 in sensation of oxidative stress and its implications in defense and danger

Transient receptor potential ankyrin subtype 1 (TRPA1) is a well-known ion channel that play a central role for pain sensation. In the peripheral sensory nerve terminals innervating the body tegument or organs, TRPA1 detects and is activated by diverse harmful environmental and internal stimuli. The TRPA1 activation results in neuronal firing, which finally sends a warning signal to our brain. However, sensitization or sustained activation of TRPA1 often causes plastic changes both in the neural pathway and in the peripheral tissues, leading to a pathologic state in tissue health and pain mediation. Recently, a unique covalent detection mode for reactive biological attacks was uncovered in the sensory mechanisms of TRPA1. Notably, the pool of the newly found reactive stimulators for TRPA1 includes oxidative stress. Here, we overview the nature of this interaction, and try to find biological meanings of the participation of such a rapid ionotrophic component in disease exacerbations. Acutely, its relatively rapid response can be understood in terms of efficiency for avoiding harmful milieu as quickly as possible, as implicated in the raison d'etre of the pain mechanism. Nonetheless, complex situations in a chronic disease progress may occur. As well, multiple interplays with known molecules on the redox defense mechanism are anticipated. At a therapeutic angle, how to control TRPA1 for promoting body's defensive potential will be a practical question but remains to be answered. Future investigations will likely give more detailed insights to understand the roles and target validity of TRPA1.

Acute Asthma Models to Ovalbumin in the Mouse

Human asthma is defined as a chronic inflammatory disease of the airways. Animal models are required to study asthma pathophysiology and identify and/or evaluate new therapeutic strategies. Several models of asthma have been developed in mice to mimic asthma symptoms, and can be divided in two groups as acute and chronic models. They are characterized by airway hyperresponsiveness (AHR), inflammation, and remodeling. Several experimental procedures have been implemented, the one mostly used being acute asthma models to ovalbumin. It comprises a sensitization step in the presence of aluminum hydroxide as an adjuvant, and a second step where mice are challenged with the allergen introduced directly into the airways to induce the modeled asthma features. This article describes procedures to efficiently and reproducibly obtain acute asthma features in mice, with ovalbumin as the allergen, which allow group comparisons and/or assessment of the activity of drug candidates. Curr. Protoc. Mouse Biol. 3:31-37 © 2013 by John Wiley & Sons, Inc.

Hyaluronan activation of the Nlrp3 inflammasome contributes to the development of airway hyperresponsiveness

BACKGROUND

The role of the Nlrp3 inflammasome in nonallergic airway hyperresponsiveness (AHR) has not previously been reported. Recent evidence supports both interleukin (IL) 1β and short fragments of hyaluronan (HA) as contributors to the biological response to inhaled ozone.

OBJECTIVE

Because extracellular secretion of IL-1β requires activation of the inflammasome, we investigated the role of the inflammasome proteins ASC, caspase1, and Nlrp3 in the biological response to ozone and HA.

METHODS

C57BL/6J wild-type mice and mice deficient in ASC, caspase1, or Nlrp3 were exposed to ozone (1 ppm for 3 hr) or HA followed by analysis of airway resistance, cellular inflammation, and total protein and cytokines in bronchoalveolar lavage fluid (BALF). Transcription levels of IL-1β and IL-18 were determined in two populations of lung macrophages. In addition, we examined levels of cleaved caspase1 and cleaved IL-1β as markers of inflammasome activation in isolated alveolar macrophages harvested from BALF from HA-treated mice.

RESULTS

We observed that genes of the Nlrp3 inflammasome were required for development of AHR following exposure to either ozone or HA fragments. These genes are partially required for the cellular inflammatory response to ozone. The expression of IL-1β mRNA in alveolar macrophages was up-regulated after either ozone or HA challenge and was not dependent on the Nlrp3 inflammasome. However, soluble levels of IL-1β protein were dependent on the inflammasome after challenge with either ozone or HA. HA challenge resulted in cleavage of macrophage-derived caspase1 and IL-1β, suggesting a role for alveolar macrophages in Nlrp3-dependent AHR.

CONCLUSIONS

The Nlrp3 inflammasome is required for the development of ozone-induced reactive airways disease.

1,8-cineole, a TRPM8 agonist, is a novel natural antagonist of human TRPA1

BACKGROUND

Essential oils are often used in alternative medicine as analgesic and anti-inflammatory remedies. However, the specific compounds that confer the effects of essential oils and the molecular mechanisms are largely unknown. TRPM8 is a thermosensitive receptor that detects cool temperatures and menthol whereas TRPA1 is a sensor of noxious cold. Ideally, an effective analgesic compound would activate TRPM8 and inhibit TRPA1.

RESULTS

We screened essential oils and fragrance chemicals showing a high ratio of human TRPM8-activating ability versus human TRPA1-activating ability using a Ca2+-imaging method, and identified 1,8-cineole in eucalyptus oil as particularly effective. Patch-clamp experiments confirmed that 1,8-cineole evoked inward currents in HEK293T cells expressing human TRPM8, but not human TRPA1. In addition, 1,8-cineole inhibited human TRPA1 currents activated by allyl isothiocyanate, menthol, fulfenamic acid or octanol in a dose-dependent manner. Furthermore, in vivo sensory irritation tests showed that 1,8-cineole conferred an analgesic effect on sensory irritation produced by TRPA1 agonists octanol and menthol. Surprisingly, 1,4-cineole, which is structurally similar and also present in eucalyptus oil, activated both human TRPM8 and human TRPA1.

CONCLUSIONS

1,8-cineole is a rare natural antagonist of human TRPA1 that has analgesic and anti-inflammatory effects possibly due to its inhibition of TRPA1.

1,8-cineole, a TRPM8 agonist, is a novel natural antagonist of human TRPA1

Background

Essential oils are often used in alternative medicine as analgesic and anti-inflammatory remedies. However, the specific compounds that confer the effects of essential oils and the molecular mechanisms are largely unknown. TRPM8 is a thermosensitive receptor that detects cool temperatures and menthol whereas TRPA1 is a sensor of noxious cold. Ideally, an effective analgesic compound would activate TRPM8 and inhibit TRPA1.

Results

We screened essential oils and fragrance chemicals showing a high ratio of human TRPM8-activating ability versus human TRPA1-activating ability using a Ca²⁺-imaging method, and identified 1,8-cineole in eucalyptus oil as particularly effective. Patch-clamp experiments confirmed that 1,8-cineole evoked inward currents in HEK293T cells expressing human TRPM8, but not human TRPA1. In addition, 1,8-cineole inhibited human TRPA1 currents activated by allyl isothiocyanate, menthol, fulfenamic acid or octanol in a dose-dependent manner. Furthermore, in vivo sensory irritation tests showed that 1,8-cineole conferred an analgesic effect on sensory irritation produced by TRPA1 agonists octanol and menthol. Surprisingly, 1,4-cineole, which is structurally similar and also present in eucalyptus oil, activated both human TRPM8 and human TRPA1.

Conclusions

1,8-cineole is a rare natural antagonist of human TRPA1 that has analgesic and anti-inflammatory effects possibly due to its inhibition of TRPA1.

Novel antitussive strategies

Acute and chronic cough represent one of the most common symptoms of medical importance but effective pharmacotherapy is, to all intents and purposes, absent. Numerous initiatives targeting the recently discovered tussive pathways are in progress. Here, we review the current antitussive armamentarium and provide an update on the novel strategies and compounds in development.

Hypersensitivity of lung vagal C fibers induced by acute intermittent hypoxia in rats: role of reactive oxygen species and TRPA1

Obstructive sleep apnea, manifested by intermittent hypoxia and excess production of reactive oxygen species (ROS) in airways, is associated with hyperreactive airway diseases, but the mechanism remains unclear. Sensitization of lung vagal C fibers (LVCFs) contributes to the airway hypersensitivity. We investigated the mechanisms underlying the sensitization of LVCFs with acute intermittent hypoxia (AIH), by 10 episodes of exposure to 30 s of hypoxic air (0%, 5%, or 10% O(2)) followed by 30 s of room air in anesthetized, open-chest, and artificially ventilated rats. Reflex apneic response to intravenous capsaicin (an LVCF stimulant), as measured by phrenic nerve activity, was concentration dependently augmented by AIH. Similarly, reflex apneic response to intravenous α,β-methylene-ATP (another LVCF stimulant) was augmented by AIH (0% O(2)). The reflex apnea evoked by these two stimulants was abolished by bilateral vagotomy, which suggests the involvement of lung vagal afferents. The AIH-augmented apneic response to these two stimulants was prevented by pretreatment with dimethylthiourea (a hydroxyl radical scavenger), N-acetyl-l-cysteine (an antioxidant) and HC-030031 [a transient receptor potential ankyrin 1 (TRPA1) receptor antagonist]. Consistently, electrophysiological study revealed the afferent responses of LVCFs to capsaicin or α,β-methylene-ATP were augmented by AIH, and this sensitization of LVCFs was prevented by dimethylthiourea, N-acetyl-l-cysteine, and HC-030031. In contrast, AIH did not alter the afferent response of LVCFs to mechanical stimulation by lung hyperinflation. We concluded that AIH sensitizes LVCFs in rats, thus resulting in exaggerated airway reflexogenic responses to chemical stimulants, possibly by ROS action and activation of TRPA1 receptors.

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.

Current perspectives on the modulation of thermo-TRP channels: new advances and therapeutic implications

The thermo transient receptor potential (TRP) ion channels, a recently discovered family of ion channels activated by temperature, are expressed in primary sensory nerve terminals, where they provide information regarding thermal changes in the environment. Six thermo-TRPs have been characterized to date: TRPV1-4, which respond to different levels of warmth and heat, and TRPM8 and TRPA1, which respond to cool temperatures. We review the current state of knowledge of thermo-TRPs, and of the modulation of their thermal thresholds by a range of inflammatory mediators. Blockers of these channels are likely to have therapeutic uses as novel analgesics but may also cause unacceptable side effects. Controlling the modulation of thermo-TRPs by inflammatory mediators may be a useful alternative strategy in developing novel analgesics.

Transient receptor potential ankyrin 1 channel localized to non-neuronal airway cells promotes non-neurogenic inflammation

Background

The transient receptor potential ankyrin 1 (TRPA1) channel, localized to airway sensory nerves, has been proposed to mediate airway inflammation evoked by allergen and cigarette smoke (CS) in rodents, via a neurogenic mechanism. However the limited clinical evidence for the role of neurogenic inflammation in asthma or chronic obstructive pulmonary disease raises an alternative possibility that airway inflammation is promoted by non-neuronal TRPA1.

Methodology/Principal Findings

By using Real-Time PCR and calcium imaging, we found that cultured human airway cells, including fibroblasts, epithelial and smooth muscle cells express functional TRPA1 channels. By using immunohistochemistry, TRPA1 staining was observed in airway epithelial and smooth muscle cells in sections taken from human airways and lung, and from airways and lung of wild-type, but not TRPA1-deficient mice. In cultured human airway epithelial and smooth muscle cells and fibroblasts, acrolein and CS extract evoked IL-8 release, a response selectively reduced by TRPA1 antagonists. Capsaicin, agonist of the transient receptor potential vanilloid 1 (TRPV1), a channel co-expressed with TRPA1 by airway sensory nerves, and acrolein or CS (TRPA1 agonists), or the neuropeptide substance P (SP), which is released from sensory nerve terminals by capsaicin, acrolein or CS), produced neurogenic inflammation in mouse airways. However, only acrolein and CS, but not capsaicin or SP, released the keratinocyte chemoattractant (CXCL-1/KC, IL-8 analogue) in bronchoalveolar lavage (BAL) fluid of wild-type mice. This effect of TRPA1 agonists was attenuated by TRPA1 antagonism or in TRPA1-deficient mice, but not by pharmacological ablation of sensory nerves.

Conclusions

Our results demonstrate that, although either TRPV1 or TRPA1 activation causes airway neurogenic inflammation, solely TRPA1 activation orchestrates an additional inflammatory response which is not neurogenic. This finding suggests that non-neuronal TRPA1 in the airways is functional and potentially capable of contributing to inflammatory airway diseases.

Neurogenic inflammation and the peripheral nervous system in host defense and immunopathology

The peripheral nervous and immune systems are traditionally thought of as serving separate functions. The line between them is, however, becoming increasingly blurred by new insights into neurogenic inflammation. Nociceptor neurons possess many of the same molecular recognition pathways for danger as immune cells, and, in response to danger, the peripheral nervous system directly communicates with the immune system, forming an integrated protective mechanism. The dense innervation network of sensory and autonomic fibers in peripheral tissues and high speed of neural transduction allows rapid local and systemic neurogenic modulation of immunity. Peripheral neurons also seem to contribute to immune dysfunction in autoimmune and allergic diseases. Therefore, understanding the coordinated interaction of peripheral neurons with immune cells may advance therapeutic approaches to increase host defense and suppress immunopathology.

TRPA1 agonist activity of probenecid desensitizes channel responses: consequences for screening

The transient receptor potential channel subtype A member 1 (TRPA1) is a nonselective cation channel widely viewed as having therapeutic potential, particularly for pain-related indications. Realization of this potential will require potent, selective modulators; however, currently the pharmacology of TRPA1 is poorly defined. As TRPA1 is calcium permeable, calcium indicators offer a simple assay format for high-throughput screening. In this report, we show that probenecid, a uricosuric agent used experimentally in screening to increase loading of calcium-sensitive dyes, activates TRPA1. Prolonged probenecid incubation during the dye-loading process reduces agonist potency upon subsequent challenge. When Chinese Hamster Ovary (CHO)-hTRPA1 or STC-1 cells, which endogenously express TRPA1, were dye loaded in the presence of 2 mM probenecid TRPA1, agonists appeared less potent; EC(50) for allyl isothiocyante agonists in CHO-hTRPA1 was increased from 1.5±0.19 to 7.32±1.20 μM (P<0.01). No significant effect on antagonist potency was observed when using the agonist EC(80) concentration determined under the appropriate dye-loading conditions. We suggest an alternative protocol for calcium imaging using another blocker of anion transport, sulfinpyrazone. This blocker significantly augments indicator dye loading and the screening window, but is not a TRPA1 agonist and has no effect on agonist potency.

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.

TRPA1 contributes to the acute inflammatory response and mediates carrageenan-induced paw edema in the mouse

Transient receptor potential ankyrin 1 (TRPA1) is an ion channel involved in thermosensation and nociception. TRPA1 is activated by exogenous irritants and also by oxidants formed in inflammatory reactions. However, our understanding of its role in inflammation is limited. Here, we tested the hypothesis that TRPA1 is involved in acute inflammatory edema. The TRPA1 agonist allyl isothiocyanate (AITC) induced inflammatory edema when injected intraplantarly to mice, mimicking the classical response to carrageenan. Interestingly, the TRPA1 antagonist HC-030031 and the cyclo-oxygenase (COX) inhibitor ibuprofen inhibited not only AITC but also carrageenan-induced edema. TRPA1-deficient mice displayed attenuated responses to carrageenan and AITC. Furthermore, AITC enhanced COX-2 expression in HEK293 cells transfected with human TRPA1, a response that was reversed by HC-030031. This study demonstrates a hitherto unknown role of TRPA1 in carrageenan-induced inflammatory edema. The results also strongly suggest that TRPA1 contributes, in a COX-dependent manner, to the development of acute inflammation.

Transient receptor potential genes, smoking, occupational exposures and cough in adults

Background

Transient receptor potential (TRP) vanilloid and ankyrin cation channels are activated by various noxious chemicals and may play an important role in the pathogenesis of cough. The aim was to study the influence of single nucleotide polymorphisms (SNPs) in TRP genes and irritant exposures on cough.

Methods

Nocturnal, usual, and chronic cough, smoking, and job history were obtained by questionnaire in 844 asthmatic and 2046 non-asthmatic adults from the Epidemiological study on the Genetics and Environment of Asthma (EGEA) and the European Community Respiratory Health Survey (ECRHS). Occupational exposures to vapors, gases, dusts, and/or fumes were assessed by a job-exposure matrix. Fifty-eight tagging SNPs in TRPV1, TRPV4, and TRPA1 were tested under an additive model.

Results

Statistically significant associations of 6 TRPV1 SNPs with cough symptoms were found in non-asthmatics after correction for multiple comparisons. Results were consistent across the eight countries examined. Haplotype-based association analysis confirmed the single SNP analyses for nocturnal cough (7-SNP haplotype: p-global = 4.8 × 10^-6) and usual cough (9-SNP haplotype: p-global = 4.5 × 10^-6). Cough symptoms were associated with exposure to irritants such as cigarette smoke and occupational exposures (p < 0.05). Four polymorphisms in TRPV1 further increased the risk of cough symptoms from irritant exposures in asthmatics and non-asthmatics (interaction p < 0.05).

Conclusions

TRPV1 SNPs were associated with cough among subjects without asthma from two independent studies in eight European countries. TRPV1 SNPs may enhance susceptibility to cough in current smokers and in subjects with a history of workplace exposures.

Effects of (±)-praeruptorin A on airway inflammation, airway hyperresponsiveness and NF-κB signaling pathway in a mouse model of allergic airway disease

The root of Peucedanum praeruptorum Dunn is a traditional Chinese medicine commonly used to treat asthma in China. (±)-praeruptorin A (PA) is the most abundant constituent of P. praeruptorum Dunn, the effects of which on asthma were investigated using a murine model of allergic airway disease. BALB/c mice were sensitized and challenged by ovalbumin to induce airway inflammation. PA was administered intragastrically before every OVA challenge. Airway responsiveness was measured by a lung function analysis system. The number of total leukocytes in bronchoalveolar lavage fluid was counted using a hemocytometer, and differential cell counts were determined using Diff-Quick-stained smears. Histopathology of lung tissue was analyzed by hematoxylin-eosin and Congo red staining. Levels of inflammatory mediators in bronchoalveolar lavage fluid and immunoglobulins in serum were measured by enzyme-linked immunosorbent assay. The expression of pulmonary eotaxin was detected by immunohistochemistry and reverse transcription polymerase chain reaction. The activation of NF-κB was evaluated by electrophoretic mobility shift assay and western blot analysis. Compared with model group, PA significantly reduced airway hyperresponsiveness and airway eosinophilic inflammation, improved pathologic lesion of the lungs, reduced levels of interleukin (IL)-4, IL-5, IL-13 and LTC₄ in bronchoalveolar lavage fluid and immunoglobulin (Ig) E in serum, and inhibited eotaxin protein and mRNA expression, IκBα degradation, NF-κB nuclear translocation, NF-κB DNA-binding activity and RelA/p65 phosphorylation in lung, which suggested that PA can significantly suppress OVA-induced airway inflammation and airway hyperresponsiveness in mice, showing great therapeutic potential for the treatment of allergic asthma.

The thermo-TRP ion channel family: properties and therapeutic implications

The thermo-transient receptor potentials (TRPs), a recently discovered family of ion channels activated by temperature, are expressed in primary sensory nerve terminals where they provide information about thermal changes in the environment. Six thermo-TRPs have been characterised to date: TRP vanilloid (TRPV) 1 and 2 are activated by painful levels of heat, TRPV3 and 4 respond to non-painful warmth, TRP melastatin 8 is activated by non-painful cool temperatures, while TRP ankyrin (TRPA) 1 is activated by painful cold. The thermal thresholds of many thermo-TRPs are known to be modulated by extracellular mediators, released by tissue damage or inflammation, such as bradykinin, PG and growth factors. There have been intensive efforts recently to develop antagonists of thermo-TRP channels, particularly of the noxious thermal sensors TRPV1 and TRPA1. Blockers of these channels are likely to have therapeutic uses as novel analgesics, but may also cause unacceptable side effects. Controlling the modulation of thermo-TRPs by inflammatory mediators may be a useful alternative strategy in developing novel analgesics.

Pathogenesis and disease mechanisms of occupational asthma

Occupational asthma (OA) is one of the most common forms of work-related lung disease in all industrialized nations. The clinical management of patients with OA depends on an understanding of the multifactorial pathogenetic mechanisms that can contribute to this disease. This article discusses the various immunologic and nonimmunologic mechanisms and genetic susceptibility factors that drive the inflammatory processes of OA.

Chemesthesis and the chemical senses as components of a "chemofensor complex"

An important function of the chemical senses is to warn against dangerous biological and chemical agents in the environment. The discovery in recent years of "taste" receptor cells outside the oral cavity that appear to have protective functions has raised new questions about the nature and scope of the chemical senses in general and of chemesthesis in particular. The present paper briefly reviews these findings within the context of what is currently known about the body's chemically sensitive protective mechanisms, including nonsensory processes that help to expel or neutralize threatening agents once they have been encountered. It is proposed that this array of defense mechanisms constitutes a "chemofensor complex" in which chemesthesis is the most ubiquitous, functionally diverse, and interactive chemosensory component.

Properties and therapeutic potential of transient receptor potential channels with putative roles in adversity: focus on TRPC5, TRPM2 and TRPA1

Mammals contain 28 genes encoding Transient Receptor Potential (TRP) proteins. The proteins assemble into cationic channels, often with calcium permeability. Important roles in physiology and disease have emerged and so there is interest in whether the channels might be suitable therapeutic drug targets. Here we review selected members of three subfamilies of mammalian TRP channel (TRPC5, TRPM2 and TRPA1) that show relevance to sensing of adversity by cells and biological systems. Summarized are the cellular and tissue distributions, general properties, endogenous modulators, protein partners, cellular and tissue functions, therapeutic potential, and pharmacology. TRPC5 is stimulated by receptor agonists and other factors that include lipids and metal ions; it heteromultimerises with other TRPC proteins and is involved in cell movement and anxiety control. TRPM2 is activated by hydrogen peroxide; it is implicated in stress-related inflammatory, vascular and neurodegenerative conditions. TRPA1 is stimulated by a wide range of irritants including mustard oil and nicotine but also, controversially, noxious cold and mechanical pressure; it is implicated in pain and inflammatory responses, including in the airways. The channels have in common that they show polymodal stimulation, have activities that are enhanced by redox factors, are permeable to calcium, and are facilitated by elevations of intracellular calcium. Developing inhibitors of the channels could lead to new agents for a variety of conditions: for example, suppressing unwanted tissue remodeling, inflammation, pain and anxiety, and addressing problems relating to asthma and stroke.

Transient receptor potential A1 channels: insights into cough and airway inflammatory disease

Cough is a common symptom of diseases such as asthma and COPD and also presents as a disease in its own right. Treatment options are limited; a recent meta-analysis concluded that over-the-counter remedies are ineffective, and there is increasing concern about their use in children. Transient receptor potential cation channel, subfamily A, member 1 (TRPA1) channels are nonselective cation channels that are activated by a range of natural products (eg, allyl isothiocyanate), a multitude of environmental irritants (eg, acrolein, which is present in air pollution, vehicle exhaust, and cigarette smoke), and inflammatory mediators (eg, cyclopentenone prostaglandins). TRPA1 is primarily expressed in small-diameter, nociceptive neurons where its activation probably contributes to the perception of noxious stimuli. Inhalational exposure to irritating gases, fumes, dusts, vapors, chemicals, and endogenous mediators can lead to the development of cough. The respiratory tract is innervated by primary sensory afferent nerves, which are activated by mechanical and chemical stimuli. Recent data suggest that activation of TRPA1 on these vagal sensory afferents by these irritant substances could lead to central reflexes, including dyspnea, changes in breathing pattern, and cough, which contribute to the symptoms and pathophysiology of respiratory diseases.

TRPV1, TRPA1, and CB1 in the isolated vagus nerve--axonal chemosensitivity and control of neuropeptide release

Vagal sensory afferents innervating airways and abdominal tissues express TRPV1 and TRPA1, two depolarizing calcium permeable ion channels playing a major role in sensing environmental irritants and endogenous metabolites which cause neuropeptide release and neurogenic inflammation. Here we have studied axonal chemosensitivity and control of neuropeptide release from the isolated rat and mouse vagus nerve by using prototypical agonists of these transduction channels - capsaicin, mustard oil and the specific endogenous activators, anandamide (methyl arachidonyl ethanolamide, mAEA), and acrolein, respectively. Capsaicin evoked iCGRP release from the rat vagus nerve with an EC₅₀ of 0.12 μM. Co-application of mAEA had a dual effect: nanomolar concentrations of mAEA (0.01 μM) significantly reduced capsaicin-evoked iCGRP release while concentrations ≥ 1 μM mAEA had sensitizing effects. Only 100 μM mAEA directly augmented iCGRP release by itself. In the mouse, 310 μM mAEA increased release in wildtype and TRPA1-/- mice which could be inhibited by capsazepine (10 μM) and was completely absent in TRPV1-/- mice. CB1-/- and CB1/CB2 double -/- mice equally displayed increased sensitivity to mAEA (100 μM) and a sensitizing effect to capsaicin, in contrast to wildtypes. Acrolein and mustard oil (MO)--at μM concentrations--induced a TRPA1-dependent iCGRP release; however, millimolar concentrations of mustard oil (>1mM) evoked iCGRP release by activating TRPV1, confirming recent evidence for TRPV1 agonism of high mustard oil concentrations. Taken together, we present evidence for functional expression of excitatory TRPV1, TRPA1, and inhibitory CB1 receptors along the sensory fibers of the vagus nerve which lend pathophysiological relevance to the axonal membrane and the control of neuropeptide release that may become important in cases of inflammation or neuropathy. Sensitization and possible ectopic discharge may contribute to the development of autonomic dysregulation in visceral tissues that are innervated by the vagus nerve.

TRP Channels as Sensors and Signal Integrators of Redox Status Changes

Proteins are capable of sensing the redox status of cells. Cysteine residues, which react with oxidants, reductants, and electrophiles, have been increasingly recognized as the mediators of this redox sensitivity. Cation channels encoded by the transient receptor potential (trp) gene superfamily are characterized by a wide variety of activation triggers that act from outside and inside the cell. Recent studies have revealed that a class of TRP channels is sensitive to changes in redox status and is notably susceptible to modifications of cysteine residues, such as oxidation, electrophilic reaction, and S-nitrosylation of sulfhydryls. In this review, we focus on TRP channels, which directly sense redox status, and discuss the biological significance of cysteine modifications and the consequences of this chemical reaction for physiological responses.

Pathophysiology of allergic inflammation

Allergic inflammation is due to a complex interplay between several inflammatory cells, including mast cells, basophils, lymphocytes, dendritic cells, eosinophils, and sometimes neutrophils. These cells produce multiple inflammatory mediators, including lipids, purines, cytokines, chemokines, and reactive oxygen species. Allergic inflammation affects target cells, such as epithelial cells, fibroblasts, vascular cells, and airway smooth muscle cells, which become an important source of inflammatory mediators. Sensory nerves are sensitized and activated during allergic inflammation and produce symptoms. Allergic inflammatory responses are orchestrated by several transcription factors, particularly NF-κB and GATA3. Inflammatory genes are also regulated by epigenetic mechanisms, including DNA methylation and histone modifications. There are several endogenous anti-inflammatory mechanisms, including anti-inflammatory lipids and cytokines, which may be defective in allergic disease, thus amplifying and perpetuating the inflammation. Better understanding of the pathophysiology of allergic inflammation has identified new therapeutic targets but developing effective novel therapies has been challenging. Corticosteroids are highly effective with a broad spectrum of anti-inflammatory effects, including epigenetic modulation of the inflammatory response and suppression of GATA3.

TRPA1 and substance P mediate colitis in mice

BACKGROUND & AIMS

The neuropeptides calcitonin gene-related peptide (CGRP) and substance P, and calcium channels, which control their release from extrinsic sensory neurons, have important roles in experimental colitis. We investigated the mechanisms of colitis in 2 different models, the involvement of the irritant receptor transient receptor potential of the ankyrin type-1 (TRPA1), and the effects of CGRP and substance P.

METHODS

We used calcium-imaging, patch-clamp, and neuropeptide-release assays to evaluate the effects of 2,4,6-trinitrobenzene-sulfonic-acid (TNBS) and dextran-sulfate-sodium-salt on neurons. Colitis was induced in wild-type, knockout, and desensitized mice.

RESULTS

TNBS induced TRPA1-dependent release of colonic substance P and CGRP, influx of Ca2+, and sustained ionic inward currents in colonic sensory neurons and transfected HEK293t cells. Analysis of mutant forms of TRPA1 revealed that TNBS bound covalently to cysteine (and lysine) residues in the cytoplasmic N-terminus. A stable sulfinic acid transformation of the cysteine-SH group, shown by mass spectrometry, might contribute to sustained sensitization of TRPA1. Mice with colitis had increased colonic neuropeptide release, mediated by TRPA1. Endogenous products of inflammatory lipid peroxidation also induced TRPA1-dependent release of colonic neuropeptides; levels of 4-hydroxy-trans-2-nonenal increased in each model of colitis. Colitis induction by TNBS or dextran-sulfate-sodium-salt was inhibited or reduced in TRPA1-/- mice and by 2-(1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7H-purin-7-yl)-N-(4-isopro-pylphenyl)-acetamide, a pharmacologic inhibitor of TRPA1. Substance P had a proinflammatory effect that was dominant over CGRP, based on studies of knockout mice. Ablation of extrinsic sensory neurons prevented or attenuated TNBS-induced release of neuropeptides and both forms of colitis.

CONCLUSIONS

Neuroimmune interactions control intestinal inflammation. Activation and sensitization of TRPA1 and release of substance P induce and maintain colitis in mice.