Recent Progress in the Discovery and Development of TRPA1 Modulators

TRPM8 and TRPA1 ideal targets for treating cold-induced pain

TRP channels are essential for detecting variations in external temperature and are ubiquitously expressed in both the peripheral and central nervous systems as integral channel proteins. They primarily mediate a range of sensory responses, including thermal sensations, nociception, mechanosensation, vision, and gustation, thus playing a critical role in regulating various physiological functions. In colder climates, individuals often experience pain associated with low temperatures, leading to significant discomfort. Within the TRP channel family, TRPM8 and TRPA1 ion channels serve as the primary sensors for cold temperature fluctuations and are integral to both cold nociception and neuropathic pain pathways. Recent advancements in the biosynthesis of inhibitors targeting TRPM8 and TRPA1 have prompted the need for a comprehensive review of their structural characteristics, biological activities, biosynthetic pathways, and chemical synthesis. This paper aims to delineate the distinct roles of TRPM8 and TRPA1 in pain perception, elucidate their respective protein structures, and compile various combinations of TRPM8 and TRPA1 antagonists and agonists. The discussion encompasses their chemical structures, structure-activity relationships (SARs), biological activities, selectivity, and therapeutic potential, with a particular focus on the conformational relationships between antagonists and the channels. This review seeks to provide in-depth insights into pharmacological strategies for managing pain associated with TRPM8 and TRPA1 activation and will pave the way for future investigations into pharmacotherapeutic approaches for alleviating cold-induced pain.

Discovery of Dual TRPA1 and TRPV1 Antagonists as Novel Therapeutic Agents for Pain

Pain management remains a major challenge in medicine, highlighting the need for the development of new therapeutic agents. The transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1) are ion channels that play key roles in pain perception. Targeting both TRPA1 and TRPV1 simultaneously with dual antagonists offers a promising approach to pain relief. In this study, we investigated a series of hybrid analogs of TRPA1 and TRPV1 antagonists to discover novel therapeutic agents for pain. Among these compounds synthesized by a condensation reaction forming 1,2,4-oxadiazole between the A- and C-regions, compound 50 exhibited substantial dual-acting antagonism to TRPA1 and TRPV1 with IC50 values of 1.42, 2.84, 2.13, and 5.02 μM for hTRPA1, mTRPA1, hTRPV1, and rTRPV1, respectively. In the formalin test, compound 50 demonstrated dose-dependent analgesic activity with an ED50 of 85.9 mg/kg in phase 1 and 21.6 mg/kg in phase 2, respectively, and was able to inhibit pain behavior completely at a dose of 100 mg/kg. This study presents the discovery and characterization of a novel dual TRPA1/TRPV1 antagonist, highlighting its potential as a therapeutic agent for pain management.

Widespread transcriptomic alterations of transient receptor potential channel genes in cancer

Ion channels, in particular transient-receptor potential (TRP) channels, are essential genes that play important roles in many physiological processes. Emerging evidence has demonstrated that TRP genes are involved in a number of diseases, including various cancer types. However, we still lack knowledge about the expression alterations landscape of TRP genes across cancer types. In this review, we comprehensively reviewed and summarised the transcriptomes from more than 10 000 samples in 33 cancer types. We found that TRP genes were widespreadly transcriptomic dysregulated in cancer, which was associated with clinical survival of cancer patients. Perturbations of TRP genes were associated with a number of cancer pathways across cancer types. Moreover, we reviewed the functions of TRP family gene alterations in a number of diseases reported in recent studies. Taken together, our study comprehensively reviewed TRP genes with extensive transcriptomic alterations and their functions will directly contribute to cancer therapy and precision medicine.

The Role of TRP Channels in Sepsis and Colitis

To date, several members of the transient receptor potential (TRP) channels which provide a wide array of roles have been found in the gastrointestinal tract (GI). The goal of earlier research was to comprehend the intricate signaling cascades that contribute to TRP channel activation as well as how these receptors' activity affects other systems. Moreover, there is a large volume of published studies describing the role of TRP channels in a number of pathological disorders, including inflammatory bowel disease (IBD) and sepsis. Nevertheless, the generalizability of these results is subject to certain limitations. For instance, the study of IBD relies on various animal models and experimental methods, which are unable to precisely imitate the multifactorial chronic disease. The diverse pathophysiological mechanisms and unique susceptibility of animals may account for the inconsistency of the experimental data collected. The main purpose of this study was to conduct a comprehensive review and analysis of existing studies on transient receptor potential (TRP) channels implicating specific models of colitis and sepsis, with particular emphasis on their involvement in pathological disorders such as IBD and sepsis. Furthermore, the text endeavors to evaluate the generalizability of experimental findings, taking into consideration the limitations posed by animal models and experimental methodologies. Finally, we also provide an updated schematic of the most important and possible molecular signaling pathways associated with TRP channels in IBD and sepsis.

Discovery of TRPA1 Antagonist : Derisking Preclinical Toxicity and Aldehyde Oxidase Metabolism with a Potential First-in-Class Therapy for Respiratory Disease

Transient receptor potential ankyrin 1 (TRPA1) is a nonselective calcium ion channel highly expressed in the primary sensory neurons, functioning as a polymodal sensor for exogenous and endogenous stimuli, and has been implicated in neuropathic pain and respiratory disease. Herein, we describe the optimization of potent, selective, and orally bioavailable TRPA1 small molecule antagonists with strong in vivo target engagement in rodent models. Several lead molecules in preclinical single- and short-term repeat-dose toxicity studies exhibited profound prolongation of coagulation parameters. Based on a thorough investigative toxicology and clinical pathology analysis, anticoagulation effects in vivo are hypothesized to be manifested by a metabolite─generated by aldehyde oxidase (AO)─possessing a similar pharmacophore to known anticoagulants (i.e., coumarins, indandiones). Further optimization to block AO-mediated metabolism yielded compounds that ameliorated coagulation effects in vivo, resulting in the discovery and advancement of clinical candidate GDC-6599, currently in Phase II clinical trials for respiratory indications.

Pharmacologic Inhibition of Transient Receptor Potential Ion Channel Ankyrin 1 Counteracts 2-Chlorobenzalmalononitrile Tear Gas Agent-Induced Cutaneous Injuries

Deployment of the tear gas agent 2-chlorobenzalmalononitrile (CS) for riot control has significantly increased in recent years. The effects of CS have been believed to be transient and benign. However, CS induces severe pain, blepharospasm, lachrymation, airway obstruction, and skin blisters. Frequent injuries and hospitalizations have been reported after exposure. We have identified the sensory neuronal ion channel, transient receptor potential ankyrin 1 (TRPA1), as a key CS target resulting in acute irritation and pain and also as a mediator of neurogenic inflammation. Here, we examined the effects of pharmacologic TRPA1 inhibition on CS-induced cutaneous injury. We modeled CS-induced cutaneous injury by applying 10 μl CS agent [200 mM in dimethyl sulfoxide (DMSO)] to each side of the right ears of 8- to 9-week-old C57BL/6 male mice, whereas left ears were applied with solvent only (DMSO). The TRPA1 inhibitor HC-030031 or A-967079 was administered after CS exposure. CS exposure induced strong tissue swelling, plasma extravasation, and a dramatic increase in inflammatory cytokine levels in the mouse ear skin. We also showed that the effects of CS were not transient but caused persistent skin injuries. These injury parameters were reduced with TRPA1 inhibitor treatment. Further, we tested the pharmacologic activity of advanced TRPA1 antagonists in vitro. Our findings showed that TRPA1 is a crucial mediator of CS-induced nociception and tissue injury and that TRPA1 inhibitors are effective countermeasures that reduce key injury parameters when administered after exposure. Additional therapeutic efficacy studies with advanced TRPA1 antagonists and decontamination strategies are warranted. SIGNIFICANCE STATEMENT: 2-Chlorobenzalmalononitrile (CS) tear gas agent has been deployed as a crowd dispersion chemical agent in recent times. Exposure to CS tear gas agents has been believed to cause transient acute toxic effects that are minimal at most. Here we found that CS tear gas exposure causes both acute and persistent skin injuries and that treatment with transient receptor potential ion channel ankyrin 1 (TRPA1) antagonists ameliorated skin injuries.

Human Transient Receptor Potential Ankyrin 1 Channel: Structure, Function, and Physiology

The transient receptor potential ion channel TRPA1 is a Ca2+-permeable nonselective cation channel widely expressed in sensory neurons, but also in many nonneuronal tissues typically possessing barrier functions, such as the skin, joint synoviocytes, cornea, and the respiratory and intestinal tracts. Here, the primary role of TRPA1 is to detect potential danger stimuli that may threaten the tissue homeostasis and the health of the organism. The ability to directly recognize signals of different modalities, including chemical irritants, extreme temperatures, or osmotic changes resides in the characteristic properties of the ion channel protein complex. Recent advances in cryo-electron microscopy have provided an important framework for understanding the molecular basis of TRPA1 function and have suggested novel directions in the search for its pharmacological regulation. This chapter summarizes the current knowledge of human TRPA1 from a structural and functional perspective and discusses the complex allosteric mechanisms of activation and modulation that play important roles under physiological or pathophysiological conditions. In this context, major challenges for future research on TRPA1 are outlined.

Research Progress on TRPA1 in Diseases

For a long time, the physiological activity of TRP ion channels and the response to various stimuli have been the focus of attention, and the physiological functions mediated by ion channels have subtle links with the occurrence of various diseases. Our group has been engaged in the study of ion channels. In recent years, the report rate of TRPA1, the only member of the TRPA subfamily in the newly described TRP channel, has been very high. TRPA1 channels are not only abundantly expressed in peptidergic nociceptors but are also found in many nonneuronal cell types and tissues, and through the regulation of Ca2+ influx, various neuropeptides and signaling pathways are involved in the regulation of nerves, respiration, circulation, and various diseases and inflammation throughout the body. In this review, we mainly summarize the effects of TRPA1 on various systems in the body, which not only allows us to have a more systematic and comprehensive understanding of TRPA1 but also facilitates more in-depth research on it in the future.

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

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

Discovery of , a Selective CNS Penetrant Chemical Probe as Transient Receptor Potential Ankyrin 1 (TRPA1) Antagonist

Transient receptor potential ankyrin 1 (TRPA1) is a voltage-dependent, ligand-gated ion channel, and activation thereof is linked to a variety of painful conditions. Preclinical studies have demonstrated the role of TRPA1 receptors in a broad range of animal models of acute, inflammatory, and neuropathic pain. In addition, a clinical study using the TRPA1 antagonist GRC-17536 (Glenmark Pharmaceuticals) demonstrated efficacy in a subgroup of patients with painful diabetic neuropathy. Consequently, there is an increasing interest in TRPA1 inhibitors as potential analgesics. Herein, we report the identification of a fragment-like hit from a high-throughput screening (HTS) campaign and subsequent optimization to provide a novel and brain-penetrant TRPA1 inhibitor (compound 18, BAY-390), which is now being made available to the research community as an open-source in vivo probe.

Analysis of Structural Determinants of Peptide MS 9a-1 Essential for Potentiating of TRPA1 Channel

The TRPA1 channel is involved in a variety of physiological processes and its activation leads to pain perception and the development of inflammation. Peptide Ms 9a-1 from sea anemone Metridium senile is a positive modulator of TRPA1 and causes significant analgesic and anti-inflammatory effects by desensitization of TRPA1-expressing sensory neurons. For structural and functional analysis of Ms 9a-1, we produced four peptides—Ms 9a-1 without C-terminal domain (abbreviated as N-Ms), short C-terminal domain Ms 9a-1 alone (C-Ms), and two homologous peptides (Ms 9a-2 and Ms 9a-3). All tested peptides possessed a reduced potentiating effect on TRPA1 compared to Ms 9a-1 in vitro. None of the peptides reproduced analgesic and anti-inflammatory properties of Ms 9a-1 in vivo. Peptides N-Ms and C-Ms were able to reduce pain induced by AITC (selective TRPA1 agonist) but did not decrease AITC-induced paw edema development. Fragments of Ms 9a-1 did not effectively reverse CFA-induced thermal hyperalgesia and paw edema. Ms 9a-2 and Ms 9a-3 possessed significant effects and anti-inflammatory properties in some doses, but their unexpected efficacy and bell-shape dose–responses support the hypothesis of other targets involved in their effects in vivo. Therefore, activity comparison of Ms 9a-1 fragments and homologues peptides revealed structural determinants important for TRPA1 modulation, as well as analgesic and anti-inflammatory properties of Ms9a-1.

Randomized, double-blind, placebo-controlled trial of ISC 17536, an oral inhibitor of transient receptor potential ankyrin 1, in patients with painful diabetic peripheral neuropathy: impact of preserved small nerve fiber function

ABSTRACT

Patients with chronic pain syndromes, such as those with painful peripheral neuropathy due to diabetes mellitus, have limited treatment options and suffer ongoing attrition of their quality of life. Safer and more effective treatment options are needed. One therapeutic approach encompasses phenotypic characterization of the neuropathic pain subtype, combined with the selection of agents that act on relevant mechanisms. ISC 17536 is a novel, orally available inhibitor of the widely expressed pain receptor, transient receptor potential ankyrin 1, which mediates nociceptive signaling in peripheral small nerve fibers. In this randomized, placebo-controlled, proof-of-concept trial, we assessed the safety and efficacy of 28-day administration of ISC 17536 in 138 patients with chronic, painful diabetic peripheral neuropathy and used quantitative sensory testing to characterize the baseline phenotype of patients. The primary end point was the change from baseline to end of treatment in the mean 24-hour average pain intensity score based on an 11-point pain intensity numeric rating scale. The study did not meet the primary end point in the overall patient population. However, statistically significant and clinically meaningful improvement in pain were seen with ISC 17536 in an exploratory hypothesis-generating subpopulation of patients with preserved small nerve fiber function defined by quantitative sensory testing. These results may provide a mechanistic basis for targeted therapy in specific pain phenotypes in line with current approaches of "precision medicine" or personalized pain therapeutics. The hypothesis is planned to be tested in a larger phase 2 study.

A fluorogenic probe for TRPA1 channel imaging based on a molecular rotation mechanism

A fluorescent probe for selectively visualizing the TRPA1 channel and rapidly screening its regulators.

Transient receptor potential ankyrin 1 and calcium: Interactions and association with disease (Review)

Calcium (Ca²⁺) is an essential signaling molecule in all cells. It is involved in numerous fundamental functions, including cell life and death. Abnormal regulation of Ca²⁺ homeostasis may cause human diseases. Usually known as a member of the transient receptor potential (TRP) family, TRP ankyrin 1 (TRPA1) is the only member of the ankyrin subfamily identified in mammals so far and widely expressed in cells and tissues. As it is involved in numerous sensory disorders such as pain and pruritus, TRPA1 is a potential target for the treatment of neuropathy. The functions of TRP family members are closely related to Ca²⁺. TRPA1 has a high permeability to Ca²⁺, sodium and potassium ions as a non-selective cation channel and the Ca²⁺ influx mediated by TRPA1 is involved in a variety of biological processes. In the present review, research on the relationship between the TRPA1 channel and Ca²⁺ ions and their interaction in disease-associated processes was summarised. The therapeutic potential of the TRPA1 channel is highlighted, which is expected to become a novel direction for the prevention and treatment of health conditions such as cancer and neurodegenerative diseases.

An automated computational approach to kinetic model discrimination and parameter estimation

We herein report experimental applications of a novel, automated computational approach to chemical reaction network (CRN) identification. This report shows the first chemical applications of an autonomous tool to identify the kinetic model and parameters of a process, when considering both catalytic species and various integer and non-integer orders in the model's rate laws. This kinetic analysis methodology requires only the input of the species within the chemical system (starting materials, intermediates, products, etc.) and corresponding time-series concentration data to determine the kinetic information of the chemistry of interest. This is performed with minimal human interaction and several case studies were performed to show the wide scope and applicability of this process development tool. The approach described herein can be employed using experimental data from any source and the code for this methodology is also provided open-source.

We herein report experimental applications of a novel, automated computational approach to chemical reaction network (CRN) identification.

A TRPA1 inhibitor suppresses neurogenic inflammation and airway contraction for asthma treatment

Despite the development of effective therapies, a substantial proportion of asthmatics continue to have uncontrolled symptoms, airflow limitation, and exacerbations. Transient receptor potential cation channel member A1 (TRPA1) agonists are elevated in human asthmatic airways, and in rodents, TRPA1 is involved in the induction of airway inflammation and hyperreactivity. Here, the discovery and early clinical development of GDC-0334, a highly potent, selective, and orally bioavailable TRPA1 antagonist, is described. GDC-0334 inhibited TRPA1 function on airway smooth muscle and sensory neurons, decreasing edema, dermal blood flow (DBF), cough, and allergic airway inflammation in several preclinical species. In a healthy volunteer Phase 1 study, treatment with GDC-0334 reduced TRPA1 agonist-induced DBF, pain, and itch, demonstrating GDC-0334 target engagement in humans. These data provide therapeutic rationale for evaluating TRPA1 inhibition as a clinical therapy for asthma.

Sanguinarine is an agonist of TRPA1 channel

Sanguinarine, a benzyl isoquinoline alkaloid extracted from the root of Papaveraceae plants, shows extensive pharmacological activities including anti-microbial, anti-trypanosoma, anti-tumor, anti-platelet, anti-hypertensive effects, as well as inhibition of osteoclast formation. Here we demonstrate that TRPA1 channel (Transient receptor potential cation channel, member A1) is a potential target for sanguinarine. Electrophysiological recordings show that sanguinarine activates TRPA1 channel potently with an EC50 0.09 (0.04-0.13) μM, but has no effects on other examined TRP channels. Sanguinarine increases the intracellular calcium levels and upregulates the excitability of mouse dorsal root ganglion (DRG) neurons in vitro significantly. Plantar injection of sanguinarine evokes nociceptive behaviors similar to that elicited by allyl isothiocyanate (AITC), a classic agonist of TRPA1. Both the enhancement of excitability of DRG neurons and the nociceptive behaviors can be attenuated by treatment of TRPA1 channel antagonist HC030031 or knockout of trpa1 gene. Taken together, our data demonstrate that sanguinarine is a potent and relatively selective agonist of TRPA1 channel.

Transient receptor potential channels in pulmonary chemical injuries and as countermeasure targets

The lung is highly sensitive to chemical injuries caused by exposure to threat agents in industrial or transportation accidents, occupational exposures, or deliberate use as weapons of mass destruction (WMD). There are no antidotes for the majority of the chemical threat agents and toxic inhalation hazards despite their use as WMDs for more than a century. Among several putative targets, evidence for transient receptor potential (TRP) ion channels as mediators of injury by various inhalational chemical threat agents is emerging. TRP channels are expressed in the respiratory system and are essential for homeostasis. Among TRP channels, the body of literature supporting essential roles for TRPA1, TRPV1, and TRPV4 in pulmonary chemical injuries is abundant. TRP channels mediate their function through sensory neuronal and nonneuronal pathways. TRP channels play a crucial role in complex pulmonary pathophysiologic events including, but not limited to, increased intracellular calcium levels, signal transduction, recruitment of proinflammatory cells, neurogenic inflammatory pathways, cough reflex, hampered mucus clearance, disruption of the integrity of the epithelia, pulmonary edema, and fibrosis. In this review, we summarize the role of TRP channels in chemical threat agents-induced pulmonary injuries and how these channels may serve as medical countermeasure targets for broader indications.

TRP Channel Cooperation for Nociception: Therapeutic Opportunities

Chronic pain treatment remains a sore challenge, and in our aging society, the number of patients reporting inadequate pain relief continues to grow. Current treatment options all have their drawbacks, including limited efficacy and the propensity of abuse and addiction; the latter is exemplified by the ongoing opioid crisis. Extensive research in the last few decades has focused on mechanisms underlying chronic pain states, thereby producing attractive opportunities for novel, effective and safe pharmaceutical interventions. Members of the transient receptor potential (TRP) ion channel family represent innovative targets to tackle pain sensation at the root. Three TRP channels, TRPV1, TRPM3, and TRPA1, are of particular interest, as they were identified as sensors of chemical- and heat-induced pain in nociceptor neurons. This review summarizes the knowledge regarding TRP channel-based pain therapies, including the bumpy road of the clinical development of TRPV1 antagonists, the current status of TRPA1 antagonists, and the future potential of targeting TRPM3.

Transient receptor potential ankyrin 1 (TRPA1) antagonists: a patent review (2015-2019)

INTRODUCTION

TRPA1 is a non-selective cation channel predominantly expressed in sensory neurons, and functions as an irritant sensor for a plethora of noxious external stimuli and endogenous ligands. Due to its involvement in pain, itch, and respiratory syndromes, TRPA1 has been pursued as a promising drug target.

AREAS COVERED

In this review, the small molecule patent literature of TRPA1 antagonists from 2015-2019 was surveyed. The patent applications are described with a focus on chemical structures, biochemical/pharmacological activities, and potential clinical applications. The development of TRPA1 antagonists in clinical trials has been highlighted.

EXPERT OPINION

During 2015-2019, significant progress was made toward the discovery of new TRPA1 antagonists. A total of 14 organizations published 28 patent applications disclosing several distinct classes of chemical matter and potential uses. During this period, three new molecules entered the clinic (ODM-108, HX-100, and GDC-0334) bringing the total number of TRPA1 antagonists to reach clinical trials to five (including earlier molecules CB-625 and GRC 17536); however, to our knowledge, development of all five molecules have been discontinued. Further clinical trials of recent TRPA1 antagonists with good pharmacokinetics would be needed to help understand TRPA1 involvement in human diseases and its potential as a therapeutic target.

Structural Insights into Electrophile Irritant Sensing by the Human TRPA1 Channel

Transient receptor potential channel subfamily A member 1 (TRPA1) is a Ca2+-permeable cation channel that serves as one of the primary sensors of environmental irritants and noxious substances. Many TRPA1 agonists are electrophiles that are recognized by TRPA1 via covalent bond modifications of specific cysteine residues located in the cytoplasmic domains. However, a mechanistic understanding of electrophile sensing by TRPA1 has been limited due to a lack of high-resolution structural information. Here, we present the cryoelectron microscopy (cryo-EM) structures of nanodisc-reconstituted ligand-free TRPA1 and TRPA1 in complex with the covalent agonists JT010 and BITC at 2.8, 2.9, and 3.1 Å, respectively. Our structural and functional studies provide the molecular basis for electrophile recognition by the extraordinarily reactive C621 in TRPA1 and mechanistic insights into electrophile-dependent conformational changes in TRPA1. This work also provides a platform for future drug development targeting TRPA1.

Insulin-like growth factor-1 inhibits spreading depression-induced trigeminal calcitonin gene related peptide, oxidative stress & neuronal activation in rat

Migraineurs can show brain hyperexcitability and oxidative stress that may promote headache. Since hyperexcitability can enhance oxidative stress which promotes hyperexcitability, ending this feed-back loop may reduce migraine. Neocortical spreading depression, an animal model of migraine begins with hyperexcitability and triggers oxidative stress in the neocortical area involved and in the trigeminal system, which is important to pain pathway nociceptive activation in migraine. Additionally, oxidative stress causes increased trigeminal ganglion calcitonin gene-related peptide release and oxidative stress can reduce spreading depression threshold. Insulin-like growth factor-1 significantly protects against spreading depression in vitro by reducing oxidative stress and it is effective against spreading depression after intranasal delivery to animals. Here, we used adult male rats and extend this work to study the trigeminal system where insulin-like growth factor-1 receptors are highly expressed. Recurrent neocortical spreading depression significantly increased surrogate markers of trigeminal activation - immunostaining for trigeminal ganglion oxidative stress, calcitonin gene related peptide levels and c-fos in the trigeminocervical complex versus sham. These effects were significantly reduced by intranasal delivery of insulin-like growth factor-1 a day before recurrent neocortical spreading depression. Furthermore, intranasal treatment with insulin-like growth factor-1 significantly reduced naïve levels of trigeminal ganglion calcitonin gene related peptide versus sham with no impact on blood glucose levels. Intranasal delivery of insulin-like growth factor-1 not only mitigates neocortical spreading depression, a cause of migraine hyperexcitability modeled in animals, but also when neocortical spreading depression is triggered by supra-threshold stimuli, insulin-like growth factor-1 effectively reduces nociceptive activation in the trigeminal system.

Transient receptor potential (TRP) channels: Biosensors for redox environmental stimuli and cellular status

Transient receptor potential (TRP) channels are a family of cation channels that depolarizes the membrane potential and regulates intracellular concentrations of cations such as Ca²⁺. TRP channels are also known to function as "biosensors" to detect changes of the surrounding environment and cellular status. Lines of evidence have unveiled that numerous proteins are subject to redox modification and subsequent signaling. For example, TRPM2, TRPC5, TRPV1, and TRPA1 are known as redox sensors activated by hydrogen peroxide (H₂O₂), nitric oxide (NO), and electrophiles. Thus, these channels facilitate the influx of cations which in turn triggers the appropriate cellular responses against environmental redox stimuli and cellular redox status. In this review, we focus on the recent findings regarding the functions of TRP channels in relation to other ion channels, and other proteins which also go through redox modification of cysteine (Cys) residues. We aim to understand the structural and molecular basis of the redox-sensing mechanisms of TRP channels in exerting various functions under physiological conditions as well as pathological conditions such as cancer malignancy. Their future potential as drug targets will also be discussed.

Identification and characterization of saikosaponins as antagonists of transient receptor potential A1 channel

Neuropathic pain is associated with an increased sensitivity to painful stimuli or abnormal sensitivity to otherwise innocuous stimuli. However, in addition to adverse effects, currently available drugs have shown limited response in patients with neuropathic pain, which provides a rationale to explore new drug classes acting on novel targets and with better efficacy and safety profiles. Here, we found that saikosaponins potently inhibit agonist-induced activation of the transient receptor potential A1 (TRPA1) channel, which has been reported to mediate neuropathic pain by sensing a variety of chemical irritants. Molecular docking and site-directed mutagenesis analyses suggested that saikosaponins bind to the hydrophobic pocket in TRPA1 near the Asn855 residue, which, when mutated to Ser, was previously associated with enhanced pain perception in humans. In support of these findings, saikosaponin D significantly attenuated agonist-induced nociceptive responses and vincristine-induced mechanical hypersensitivity in mice. These results indicate that saikosaponins are TRPA1 antagonists and provide a basis for further elaboration of saikosaponin derivatives for the development of new therapeutics for neuropathic pain.

Mammalian Transient Receptor Potential TRPA1 Channels: From Structure to Disease

The transient receptor potential ankyrin (TRPA) channels are Ca²⁺-permeable nonselective cation channels remarkably conserved through the animal kingdom. Mammals have only one member, TRPA1, which is widely expressed in sensory neurons and in non-neuronal cells (such as epithelial cells and hair cells). TRPA1 owes its name to the presence of 14 ankyrin repeats located in the NH₂ terminus of the channel, an unusual structural feature that may be relevant to its interactions with intracellular components. TRPA1 is primarily involved in the detection of an extremely wide variety of exogenous stimuli that may produce cellular damage. This includes a plethora of electrophilic compounds that interact with nucleophilic amino acid residues in the channel and many other chemically unrelated compounds whose only common feature seems to be their ability to partition in the plasma membrane. TRPA1 has been reported to be activated by cold, heat, and mechanical stimuli, and its function is modulated by multiple factors, including Ca²⁺, trace metals, pH, and reactive oxygen, nitrogen, and carbonyl species. TRPA1 is involved in acute and chronic pain as well as inflammation, plays key roles in the pathophysiology of nearly all organ systems, and is an attractive target for the treatment of related diseases. Here we review the current knowledge about the mammalian TRPA1 channel, linking its unique structure, widely tuned sensory properties, and complex regulation to its roles in multiple pathophysiological conditions.

Transient receptor potential ankyrin 1 (TRPA1)-mediated toxicity: friend or foe?

Transient receptor potential (TRP) channels have been widely studied during the last decade. New studies uncover new features and potential applications for these channels. TRPA1 has a huge distribution all over the human body and has been reported to be involved in different physiological and pathological conditions including cold, pain, and damage sensation. Considering its role, many studies have been devoted to evaluating the role of this channel in the initiation and progression of different toxicities. Accordingly, we reviewed the most recent studies and divided the role of TRPA1 in toxicology into the following sections: neurotoxicity, cardiotoxicity, dermatotoxicity, and pulmonary toxicity. Acetaminophen, heavy metals, tear gases, various chemotherapeutic agents, acrolein, wood smoke particulate materials, particulate air pollution materials, diesel exhaust particles, cigarette smoke extracts, air born irritants, sulfur mustard, and plasticizers are selected compounds and materials with toxic effects that are, at least in part, mediated by TRPA1. Considering the high safety of TRPA1 antagonists and their efficacy to resolve selected toxic or adverse drug reactions, the future of these drugs looks promising.

TRPA1 Channel as a Regulator of Neurogenic Inflammation and Pain: Structure, Function, Role in Pathophysiology, and Therapeutic Potential of Ligands

TRPA1 is a cation channel located on the plasma membrane of many types of human and animal cells, including skin sensory neurons and epithelial cells of the intestine, lungs, urinary bladder, etc. TRPA1 is the major chemosensor that also responds to thermal and mechanical stimuli. Substances that activate TRPA1, e.g., allyl isothiocyanates (pungent components of mustard, horseradish, and wasabi), cinnamaldehyde from cinnamon, organosulfur compounds from garlic and onion, tear gas, acrolein and crotonaldehyde from cigarette smoke, etc., cause burning, mechanical and thermal hypersensitivity, cough, eye irritation, sneezing, mucus secretion, and neurogenic inflammation. An increased activity of TRPA1 leads to the emergence of chronic pruritus and allergic dermatitis and is associated with episodic pain syndrome, a hereditary disease characterized by episodes of debilitating pain triggered by stress. TRPA1 is now considered as one of the targets for developing new anti-inflammatory and analgesic drugs. This review summarizes information on the structure, function, and physiological role of this channel, as well as describes known TRPA1 ligands and their significance as therapeutic agents in the treatment of inflammation-associated pain.

Study of Anti-inflammatory Activity of a New Non-opioid Analgesic on the Basis of a Selective Inhibitor of TRPA1 Ion Channels

INTRODUCTION

Nowadays, the group of NSAIDs is used the most widely in order to treat the inflammatory process. But its long-term administration increases the risk of complications of pharmacotherapy. Therefore, today it is urgent to search for new molecules that can selectively block biological targets that directly perceive inflammatory mediators. One of such targets is TRPA1. ZC02-0012, a compound from the group of substituted pyrazinopyrimidinones, which is a selective inhibitor of TRPA1 ion channel.

OBJECTIVE

The aim of our study was to study the anti-inflammatory activity of an innovative molecule under the laboratory code ZC02-0012 from the group of selective inhibitors of TRPA1 ion channel.

MATERIALS AND METHODS

Anti-inflammatory activity of ZC02-0012 was studied on the model of acute exudative inflammation of the paw in response to subplantar injection in the right hind paw of mice with 0.02 ml of 2% formaldehyde solution. The mass of the paw was measured after 4 hours (peak edema) after phlogistic injection. The test substance and the reference drug was administered intragastrically or intramuscularly 45 minutes before the injection of formaldehyde solution. The presence and intensity of antiinflammatory activity was judged by the inhibitory effect, represented in percent.

RESULTS AND DISCUSSION

Selective inhibitor of the TRPA1 ion channel ZC02-0012 revealed the anti-inflammatory activity at doses of 3 and 9 mg/kg, its intensity is comparable to diclofenac sodium.

CONCLUSION

The selective inhibitor of the ion channel TRPA1, a substance under code ZC02-0012, has an anti-inflammatory activity comparable with diclofenac sodium.

TRPA1 ankyrin repeat six interacts with a small molecule inhibitor chemotype

TRPA1, a member of the transient receptor potential channel (TRP) family, is genetically linked to pain in humans, and small molecule inhibitors are efficacious in preclinical animal models of inflammatory pain. These findings have driven significant interest in development of selective TRPA1 inhibitors as potential analgesics. The majority of TRPA1 inhibitors characterized to date have been reported to interact with the S5 transmembrane helices forming part of the pore region of the channel. However, the development of many of these inhibitors as clinical drug candidates has been prevented by high lipophilicity, low solubility, and poor pharmacokinetic profiles. Identification of alternate compound interacting sites on TRPA1 provides the opportunity to develop structurally distinct modulators with novel structure-activity relationships and more desirable physiochemical properties. In this paper, we have identified a previously undescribed potent and selective small molecule thiadiazole structural class of TRPA1 inhibitor. Using species ortholog chimeric and mutagenesis strategies, we narrowed down the site of interaction to ankyrinR #6 within the distal N-terminal region of TRPA1. To identify the individual amino acid residues involved, we generated a computational model of the ankyrinR domain. This model was used predictively to identify three critical amino acids in human TRPA1, G238, N249, and K270, which were confirmed by mutagenesis to account for compound activity. These findings establish a small molecule interaction region on TRPA1, expanding potential avenues for developing TRPA1 inhibitor analgesics and for probing the mechanism of channel gating.

Role of Chemosensory TRP Channels in Lung Cancer

Transient receptor potential (TRP) channels represent a large family of cation channels and many members of the TRP family have been shown to act as polymodal receptor molecules for irritative or potentially harmful substances. These chemosensory TRP channels have been extensively characterized in primary sensory and neuronal cells. However, in recent years the functional expression of these proteins in non-neuronal cells, e.g., in the epithelial lining of the respiratory tract has been confirmed. Notably, these proteins have also been described in a number of cancer types. As sensor molecules for noxious compounds, chemosensory TRP channels are involved in cell defense mechanisms and influence cell survival following exposure to toxic substances via the modulation of apoptotic signaling. Of note, a number of cytostatic drugs or drug metabolites can activate these TRP channels, which could affect the therapeutic efficacy of these cytostatics. Moreover, toxic inhalational substances with potential involvement in lung carcinogenesis are well established TRP activators. In this review, we present a synopsis of data on the expression of chemosensory TRP channels in lung cancer cells and describe TRP agonists and TRP-dependent signaling pathways with potential relevance to tumor biology. Furthermore, we discuss a possible role of TRP channels in the non-genomic, tumor-promoting effects of inhalational carcinogens such as cigarette smoke.