Transient receptor potential ankyrin 1 (TRPA1) modulators: Recent update and future perspective

Identification of isoxazole-based TRPA1 inhibitors with analgesic effects in vivo

The transient receptor potential ankyrin 1 (TRPA1) channel has been extensively studied as a potential therapeutic target for the treatment of different pain types, with better efficacy and safety profiles compared to current therapies. Because TRPA1 is implicated in different pathophysiological processes, selective antagonists of this channel could provide therapeutic benefits beyond pain relief. In this study, we report the design and synthesis of a novel series of carboxamide derivatives incorporating an isoxazole moiety, which were evaluated for their ability to inhibit TRPA1-mediated signalling. Among these, we identified the TRPA1 antagonists 12 and 13 displaying nanomolar potency in vitro and significant analgesic effects against the TRPA1 agonist, allyl isothiocyanate and in the formalin test in mice. Docking analyses were also conducted to explore the binding modes of the most representative compounds with the proposed pharmacological target.

Discovery of non-electrophilic TRPA1 channel agonists with anti-nociceptive effects via rapid current desensitization

Desensitizing transient receptor potential ankyrin 1 (TRPA1) cation channel through agonists emerges as an effective strategy for developing analgesics. Many TRPA1 agonists are electrophilic irritants, including BITC and iodoacetamide (IA), which covalently bind to cysteine residues in the cytoplasmic region of the channel. The electrophile JT010 is also recognized as a potent TRPA1 agonist via covalent modification of Cys621, whose irritant effects have been confirmed in humans, highlighting a commonly undesirable property of these electrophilic agonists. Cryo-electron microscopy (cryo-EM) structures have shown that these electrophiles induce a strong driving force for conformational change through electrophilic modification of TRPA1. However, the stable activated conformation induced by electrophiles might delay subsequent desensitization, leading to prolonged TRPA1-mediated nociception responses in vivo. Therefore, developing non-electrophilic TRPA1 agonists may mitigate the irritation associated with electrophilic agonists by accelerating the desensitizing process. To test this hypothesis, we designed and synthesized a series of novel TRPA1 agonists by removing the electrophilic functional group of JT010. Among these synthetic compounds, whole-cell patch clamp recording assays identified compound 21 as a selective TRPA1 agonist with an EC50 of 25.47 ± 1.56 μM for hTRPA1, exhibiting faster desensitization (τ = 20.02 ± 1.66 s) of mTRPA1 compared to electrophiles JT010 (41.71 ± 4.10 s) and BITC (68.05 ± 5.57 s). Importantly, compound 21 demonstrated effective analgesic properties without irritation in mice. Our findings support the hypothesis that facilitating rapid desensitization of TRPA1 by non-electrophilic channel agonists enhances anti-nociceptive effects. Compound 21 may serve as a promising lead for further optimization.

Colonic mucosal TRPA1 expression profiles in irritable bowel syndrome and its correlation to symptom severity: An exploratory study

INTRODUCTION

Visceral hypersensitivity is a hallmark of irritable bowel syndrome (IBS). A putative involvement of the Transient Receptor Potential Ankyrin-1 (TRPA1) cation channel has been suggested by several animal studies. Main objective of this study is to assess location-specific TRPA1 expression in the colonic mucosa and its correlation with symptom severity in IBS patients.

METHODS

Biopsies were obtained from the sigmoid of 30 IBS patients (Rome III; median age 39.0 years, 80 % female) and 23 healthy controls (median age 22.7 years, 43.5 % female). Additional biopsies of the proximal colon were obtained in 24 IBS patients. TRPA1 expression levels were measured in duplicate by quantitative reverse-transcriptase-polymerase-chain-reaction, normalized to GAPDH, and assessed as relative mRNA values using the -2ΔCt method. In IBS patients, symptoms were assessed and correlated with TRPA1 expression.

RESULTS

Relative TRPA1 expression in the sigmoid was significantly higher in IBS patients compared to healthy controls (P < 0.001). Within IBS patients TRPA1 expression of sigmoid biopsies was significantly higher compared to proximal colon samples (p < 0.001). No significant correlation was found between TRPA1 expression in sigmoid or proximal colon samples and the symptom severity (abdominal discomfort, abdominal pain and bloating).

CONCLUSION

These findings suggest a potential role for the TRPA1 related pathway as a target for IBS treatment in the future. Since there was no correlation found in the current exploratory study between TRPA1 expression and symptom severity, further research towards the clinical relevance of the increased TRPA1 expression in IBS-patients along with its location-specific expression is warranted.

Pinosylvin: A Multifunctional Stilbenoid with Antimicrobial, Antioxidant, and Anti-Inflammatory Potential

Stilbenoids are a category of plant compounds exhibiting notable health-related benefits. After resveratrol, perhaps the most well-known stilbenoid is pinosylvin, a major phytochemical constituent of most plants characterised by the pine spines among others. Pinosylvin and its derivatives have been found to exert potent antibacterial and antifungal effects, while their antiparasitic and antiviral properties are still a subject of ongoing research. The antioxidant properties of pinosylvin are mostly based on its scavenging of free radicals, inhibition of iNOS and protein kinase C, and promotion of HO-1 expression. Its anti-inflammatory properties are based on a variety of mechanisms, such as COX-2 inhibition, NF-κB and TRPA1 activation inhibition, and reduction in IL-6 levels. Its anticancer properties are partly associated with its antioxidant and anti-inflammatory potential, although a number of other mechanisms are described, such as apoptosis induction and matrix metalloproteinase inhibition. A couple of experiments have also suggested a neuroprotective potential. A multitude of ethnomedical and ethnobotanical effects of pinosylvin-containing plants are reported, like antimicrobial, antioxidant, anti-inflammatory, hepatoprotective, and prokinetic actions; many of these are corroborated by recent research. The advent of novel methods of artificial pinosylvin synthesis may facilitate its mass production and adoption as a medical compound. Finally, pinosylvin may be a tool in promoting environmentally friendly pesticide and insecticide policies and be used in land remediation schemes.

NCX1 interacts with TRPA1 to promote cell proliferation and tumor growth of colon cancer via disruption of calcium homeostasis

INTRODUCTION

Aberrant Ca2+ signaling plays a critical role in the hallmark of cancer, but its regulatory mechanisms in tumorigenesis remain largely unclear. Na+/Ca2+ exchanger 1 (NCX1) functions as a bidirectional Na+ and Ca2+ transporter, operating in either Ca2+ entry or exit mode, while the transient receptor potential ankyrin 1 (TRPA1) serves as a Ca2+-permeable channel. Both play crucial roles in maintaining normal homeostasis of cytosolic Ca2+ ([Ca2+]cyt). Although each of them has been implicated in some tumorigenesis, the potential coordination between NCX1 and TRPA1 in the pathogenesis of colon cancer (CC) remains unexplored.

OBJECTIVES

We investigated the impact of NCX1- and TRPA1-mediated Ca2+ signaling on CC and the underlying mechanisms.

METHODS

The cell experiments were conducted using the human normal colonic epithelial cell line (HCoEpiC) and human colon cancer cell lines (Caco-2, SW620, and DLD-1). We performed stable transfection to knock down NCX1 or TRPA1 genes and employed CCK8, colony formation, and flow cytometry assays to assess cell proliferation. We employed RT-qPCR, Western blotting, immunofluorescence and co-immunoprecipitation assays to explore the expression and regulatory relationship between NCX1 and TRPA1. Calcium and sodium assays were used to determine [Ca2+]cyt and [Na+]cyt. Finally, we used the xenografted tumor model to verify their impact on CC development in vivo.

RESULTS

NCX1 and TRPA1 were parallelly over-expressed, co-localized, and bound, and their functional activities were enhanced in human CC cells. NCX1 functions in Ca2+ exit mode to expel [Ca2+]cyt, in which TRPA1 function was clearly verified as well. Moreover, when the Ca2+ exit mode of NCX1 was inhibited, TRPA1 activation resulted in a larger amount of [Ca2+]cyt to suppress cell proliferation through inhibiting ERK1/2 and β-catenin phosphorylation. NCX1 or TRPA1 knockdown significantly diminished tumor growth in vivo.

CONCLUSION

TRPA1 channels couple with the Ca2+ exit mode of NCX1 to maintain a moderate increase in [Ca2+]cyt in CC cells, thereby promoting CC cell proliferation and tumor growth through ERK1/2 and β-catenin phosphorylation. Consequently, the NCX1/TRPA1 coupling may serve as an innovative target for preventing and treating CC.

A fluorescent protein C-terminal fusion knock-in is functional with TRPA1 but not TRPC5

OBJECTIVE

Transgenic mice with fluorescent protein (FP) reporters take full advantage of new in vivo imaging technologies. Therefore, we generated a TRPC5- and a TRPA1-reporter mouse based on FP C-terminal fusion, providing us with better alternatives for studying the physiology, interaction and coeffectors of these two TRP channels at the cellular and tissue level.

METHODS

We generated transgenic constructs of the murine TRPC5- and TRPA1-gene with a 3*GGGGS linker and C-terminal fusion to mCherry and mTagBFP, respectively. We microinjected zygotes to generate reporter mice. Reporter mice were examined for visible fluorescence in trigeminal ganglia with two-photon microscopy, immunohistochemistry and calcium imaging.

RESULTS

Both TRPC5-mCherry and TRPA1-mTagBFP knock-in mouse models were successful at the DNA and RNA level. However, at the protein level, TRPC5 resulted in no mCherry fluorescence. In contrast, sensory neurons derived from the TRPA1-reporter mice exhibited visible mTag-BFP fluorescence, although TRPA1 had apparently lost its ion channel function.

CONCLUSIONS

Creating transgenic mice with a TRP channel tagged at the C-terminus with a FP requires detailed investigation of the structural and functional consequences in a given cellular context and fine-tuning the design of specific constructs for a given TRP channel subtype. Different degrees of functional impairment of TRPA1 and TRPC5 constructs suggest a specific importance of the distal C-terminus for the regulation of these two channels in trigeminal neurons.

Damsin and neoambrosin: Two sesquiterpene lactones with affinity and different activity for PPAR and TRPA1 receptors

Ambrosia maritima L. (family Asteraceae) is an annual herb widely distributed throughout the Mediterranean region and Africa. The herb is employed in folk medicine for the treatment of many ailments. Herein, we report a comprehensive investigation of the diverse biological potential of two sesquiterpene lactones, damsin and neoambrosin, isolated from Ambrosia maritima. 1D and 2D NMR and HR-ESI-MS/MS were employed to characterize the chemical structures of both compounds. In order to identify biological targets of both compounds we investigated their potential affinity for peroxisome proliferator-activated receptors (PPARs) and transient receptor potential (TRP) channels, which are pleiotropic classes of receptors implicated in essential functions of the body. This was investigated using a luciferase assay and a calcium fluorometric assay. A carbonic anhydrase inhibition assay was also performed using stopped flow CO2 hydrase spectrophotometric assay. Our analysis revealed that unlike damsin, neoambrosin showed a selective partial agonist effect on PPARγ receptors and TRPA1 channels. Its binding mode was investigated through in silico analysis. Both compounds showed no affinity for the tested carbonic anhydrases. Overall, our study details the chemical properties of neoambrosin and damsin and highlights neoambrosin as novel, cost-effective partial agonist of PPARɣ and TRPA1 receptors despite additional in vivo studies are needed to elucidate its biological and pharmacological properties.

Sulfide and polysulfide as pronociceptive mediators: Focus on Cav3.2 function enhancement and TRPA1 activation

Reactive sulfur species including sulfides, polysulfides and cysteine hydropersulfide play extensive roles in health and disease, which involve modification of protein functions through the interaction with metals bound to the proteins, cleavage of cysteine disulfide (S-S) bonds and S-persulfidation of cysteine residues. Sulfides over a wide micromolar concentration range enhance the activity of Cav3.2 T-type Ca2+ channels by eliminating Zn2+ bound to the channels, thereby promoting somatic and visceral pain. Cav3.2 is under inhibition by Zn2+ in physiological conditions, so that sulfides function to reboot Cav3.2 from Zn2+ inhibition and increase the excitability of nociceptors. On the other hand, polysulfides generated from sulfides activate TRPA1 channels via cysteine S-persulfidation, thereby facilitating somatic, but not visceral, pain. Thus, Cav3.2 function enhancement by sulfides and TRPA1 activation by polysulfides, synergistically accelerate somatic pain signals. The increased activity of the sulfide/Cav3.2 system, in particular, appears to have a great impact on pathological pain, and may thus serve as a therapeutic target for treatment of neuropathic and inflammatory pain including visceral pain.

Implication of the endocannabidiome and metabolic pathways in fragile X syndrome pathophysiology

Fragile X Syndrome (FXS) results from the silencing of the FMR1 gene and is the most prevalent inherited cause of intellectual disability and the most frequent monogenic cause of autism spectrum disorder. It is well established that Fragile X individuals are subjected to a wide array of comorbidities, ranging from cognitive, behavioural, and medical origin. Furthermore, recent studies have also described metabolic impairments in FXS individuals. However, the molecular mechanisms linking FMRP deficiency to improper metabolism are still misunderstood. The endocannabinoidome (eCBome) is a lipid-based signalling system that regulates several functions across the body, ranging from cognition, behaviour and metabolism. Alterations in the eCBome have been described in FXS animal models and linked to neuronal hyperexcitability, a core deficit of the disease. However, the potential link between dysregulation of the eCBome and altered metabolism observed in FXS remains unexplored. As such, this review aims to overcome this issue by describing the most recent finding related to eCBome and metabolic dysfunctions in the context of FXS. A better comprehension of this association will help deepen our understanding of FXS pathophysiology and pave the way for future therapeutic interventions.

Serum TRPA1 mediates the association between olfactory function and cognitive function

Background

Olfactory dysfunction was associated with poorer cognition. However, the association between transient receptor potential cation channel subfamily A member 1 (TRPA1) and cognitive function have not been studied. This study aimed to evaluate the mediation effect of TRPA1 on the association between olfactory and cognitive function among Chinese older adults.

Methods

We recruited 121 participants with cognitive impairment (CI) and 135 participants with normal cognition (NC) from a memory clinic and the "Shanghai Aging Study." Olfactory identification of each participant was measured by the Sniffin' Sticks Screening Test 12 (SSST-12). Serum TRPA1 were quantified using the Enzyme-Linked Immunosorbent Assay. The mediation effects of TRPA1 on the association between olfactory function and cognitive function were explored using mediation analysis.

Results

The CI group had a significantly higher proportion of the high level of serum TRPA1 (58.7%) than the NC group (42.2%) (p = 0.0086). After adjusted for gender, age, and years of education, mediation analysis verified that TRPA1 partially mediated the association between SSST-12 and Mini Mental State Examination (MMSE). It also verified that TRPA1 partially mediated the association between the identification of peppermint and MMSE.

Conclusion

Our study emphasizes the mediation role of TRPA1 in the relationship between olfactory and cognitive function among older adults. Further research is necessary to explore the mechanism of TRPA1 on the relationship between olfactory and cognitive decline.

TRPA1 Covalent Ligand JT010 Modifies T Lymphocyte Activation

Transient Receptor Potential Ankyrin 1 (TRPA1) is a non-selective cation channel involved in sensitivity to a plethora of irritating agents and endogenous mediators of oxidative stress. TRPA1 influences neuroinflammation and macrophage and lymphocyte functions, but its role is controversial in immune cells. We reported earlier a detectable, but orders-of-magnitude-lower level of Trpa1 mRNA in monocytes and lymphocytes than in sensory neurons by qRT-PCR analyses of cells from lymphoid organs of mice. Our present goals were to (a) further elucidate the expression of Trpa1 mRNA in immune cells by RNAscope in situ hybridization (ISH) and (b) test the role of TRPA1 in lymphocyte activation. RNAscope ISH confirmed that Trpa1 transcripts were detectable in CD14+ and CD4+ cells from the peritoneal cavity of mice. A selective TRPA1 agonist JT010 elevated Ca2+ levels in these cells only at high concentrations. However, a concentration-dependent inhibitory effect of JT010 was observed on T-cell receptor (TcR)-induced Ca2+ signals in CD4+ T lymphocytes, while JT010 neither modified B cell activation nor ionomycin-stimulated Ca2+ level. Based on our present and past findings, TRPA1 activation negatively modulates T lymphocyte activation, but it does not appear to be a key regulator of TcR-stimulated calcium signaling.

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.

Targeting Transient Receptor Potential (TRP) Channels, Mas-Related G-Protein-Coupled Receptors (Mrgprs), and Protease-Activated Receptors (PARs) to Relieve Itch

Itch (pruritus) is a sensation in the skin that provokes the desire to scratch. The sensation of itch is mediated through a subclass of primary afferent sensory neurons, termed pruriceptors, which express molecular receptors that are activated by itch-evoking ligands. Also expressed in pruriceptors are several types of Transient Receptor Potential (TRP) channels. TRP channels are a diverse class of cation channels that are responsive to various somatosensory stimuli like touch, pain, itch, and temperature. In pruriceptors, TRP channels can be activated through intracellular signaling cascades initiated by pruritogen receptors and underly neuronal activation. In this review, we discuss the role of TRP channels TRPA1, TRPV1, TRPV2, TRPV3, TRPV4, TRPM8, and TRPC3/4 in acute and chronic pruritus. Since these channels often mediate itch in association with pruritogen receptors, we also discuss Mas-related G-protein-coupled receptors (Mrgprs) and protease-activated receptors (PARs). Additionally, we cover the exciting therapeutic targets amongst the TRP family, as well as Mrgprs and PARs for the treatment of pruritus.

The conducting state of TRPA1 modulates channel lateral mobility

We have studied Danio rerio (Zebrafish) TRPA1 channel using a method that combines single channel electrophysiological and optical recordings to evaluate lateral mobility and channel gating simultaneously in single channels. TRPA1 channel activation by two distinct chemical ligands: allyl isothiocyanate (AITC) and TRPswitch B, results in substantial reduction of channel lateral mobility at the plasma membrane. Incubation with the cholesterol sequestering agent methyl-β-cyclodextrin (MβCD), prevents the reduction on lateral mobility induced by the two chemical agonists. This results strongly suggest that the open conformation of TRPA1 modulates channel lateral mobility probably by facilitating the insertion of the channel into cholesterol-enriched domains at the plasma membrane.