Transient receptor potential vanilloid 4 blockade protects against experimental colitis in mice: a new strategy for inflammatory bowel diseases treatment?

Phenolic acids from Chicory roots ameliorate dextran sulfate sodium-induced colitis in mice by targeting TRP signaling pathways and the gut microbiota

BACKGROUND

Inflammatory bowel disease (IBD) is a type of immune-mediated condition associated with intestinal homeostasis. Our preliminary studies disclosed that Cichorium intybus L., a traditional medicinal plant, also known as Chicory in Western countries, contained substantial phenolic acids displaying significant anti-inflammatory activities. We recognized the potential of harnessing Chicory for the treatment of IBD, prompting a need for in-depth investigation into the underlying mechanisms.

METHODS

On the third day, mice were given 100, 200 mg/kg of total phenolic acids (PA) from Chicory and 200 mg/kg of sulfasalazine (SASP) via gavage, while dextran sodium sulfate (DSS) concentration was 2.5 % for one week. The study measured and evaluated various health markers including body weight, disease activity index (DAI), colon length, spleen index, histological score, serum concentrations of myeloperoxidase (MPO), nitric oxide (NO), superoxide dismutase (SOD), lipid oxidation (MDA), and inflammatory factors. We evaluated the TRP family and the NLRP3 inflammatory signaling pathways by Western blot, while 16S rDNA sequencing was used to track the effects of PA on gut microbes.

RESULTS

It was shown that PA ameliorated the weight loss trend, attenuated inflammatory damage, regulated oxidative stress levels, and repaired the intestinal barrier in DSS mice. Analyses of Western blots demonstrated that PA suppressed what was expressed of transient receptor potential family TRPV4, TRPA1, and the expression of NLRP3 inflammatory signaling pathway, NLRP3 and GSDMD. In addition, PA exerted therapeutic effects on IBD by regulating gut microbiota richness and diversity. Meanwhile, the result of the KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis showed that gut microbiota was mainly related to Membrane Transport, Replication and Repair, Carbohydrate Metabolism and Amino Acid Metabolism.

CONCLUSION

PA derived from Chicory may have therapeutic effects on IBD by regulating the TRPV4/NLRP3 signaling pathway and gut microbiome. This study provides new insights into the effects of phenolic acids from Chicory on TRP ion channels and gut microbiota, revealing previously unexplored modes of action.

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.

Roles of TRP and PIEZO receptors in autoimmune diseases

Autoimmune diseases are pathological autoimmune reactions in the body caused by various factors, which can lead to tissue damage and organ dysfunction. They can be divided into organ-specific and systemic autoimmune diseases. These diseases usually involve various body systems, including the blood, muscles, bones, joints and soft tissues. The transient receptor potential (TRP) and PIEZO receptors, which resulted in David Julius and Ardem Patapoutian winning the Nobel Prize in Physiology or Medicine in 2021, attracted people's attention. Most current studies on TRP and PIEZO receptors in autoimmune diseases have been carried out on animal model, only few clinical studies have been conducted. Therefore, this study aimed to review existing studies on TRP and PIEZO to understand the roles of these receptors in autoimmune diseases, which may help elucidate novel treatment strategies.

Non-electrophysiological techniques targeting transient receptor potential (TRP) gene of gastrointestinal tract

Transient receptor potential (TRP) channels are cation channels related to a wide range of physical and chemical stimuli, they are expressed all along the gastrointestinal system, and a myriad of diseases are often associated with aberrant expression or mutation of the TRP gene, suggesting that TRPs are promising targets for drug therapy. Therefore, a better understanding of the information of TRPs in health and disease could facilitate the development of effective drugs for the treatment of gastrointestinal diseases like IBD. But there are very few generalizations about the experimental techniques studied in this field. In view of the promise of TRP as a therapeutic target, we discuss experimental methods that can be used for TRPs including their distribution, function and interaction with other proteins, as well as some promising emerging technologies to provide experimental methods for future studies.

TRPV4 is expressed by enteric glia and muscularis macrophages of the colon but does not play a prominent role in colonic motility

Background

Mechanosensation is an important trigger of physiological processes in the gastrointestinal tract. Aberrant responses to mechanical input are associated with digestive disorders, including visceral hypersensitivity. Transient Receptor Potential Vanilloid 4 (TRPV4) is a mechanosensory ion channel with proposed roles in visceral afferent signaling, intestinal inflammation, and gut motility. While TRPV4 is a potential therapeutic target for digestive disease, current mechanistic understanding of how TRPV4 may influence gut function is limited by inconsistent reports of TRPV4 expression and distribution.

Methods

In this study we profiled functional expression of TRPV4 using Ca2+ imaging of wholemount preparations of the mouse, monkey, and human intestine in combination with immunofluorescent labeling for established cellular markers. The involvement of TRPV4 in colonic motility was assessed in vitro using videomapping and contraction assays.

Results

The TRPV4 agonist GSK1016790A evoked Ca2+ signaling in muscularis macrophages, enteric glia, and endothelial cells. TRPV4 specificity was confirmed using TRPV4 KO mouse tissue or antagonist pre-treatment. Calcium responses were not detected in other cell types required for neuromuscular signaling including enteric neurons, interstitial cells of Cajal, PDGFRα+ cells, and intestinal smooth muscle. TRPV4 activation led to rapid Ca2+ responses by a subpopulation of glial cells, followed by sustained Ca2+ signaling throughout the enteric glial network. Propagation of these waves was suppressed by inhibition of gap junctions or Ca2+ release from intracellular stores. Coordinated glial signaling in response to GSK1016790A was also disrupted in acute TNBS colitis. The involvement of TRPV4 in the initiation and propagation of colonic motility patterns was examined in vitro.

Conclusions

We reveal a previously unappreciated role for TRPV4 in the initiation of distension-evoked colonic motility. These observations provide new insights into the functional role of TRPV4 activation in the gut, with important implications for how TRPV4 may influence critical processes including inflammatory signaling and motility.

Mitochondrial dysfunctions in T cells: focus on inflammatory bowel disease

Mitochondria has emerged as a critical ruler of metabolic reprogramming in immune responses and inflammation. In the context of colitogenic T cells and IBD, there has been increasing research interest in the metabolic pathways of glycolysis, pyruvate oxidation, and glutaminolysis. These pathways have been shown to play a crucial role in the metabolic reprogramming of colitogenic T cells, leading to increased inflammatory cytokine production and tissue damage. In addition to metabolic reprogramming, mitochondrial dysfunction has also been implicated in the pathogenesis of IBD. Studies have shown that colitogenic T cells exhibit impaired mitochondrial respiration, elevated levels of mROS, alterations in calcium homeostasis, impaired mitochondrial biogenesis, and aberrant mitochondria-associated membrane formation. Here, we discuss our current knowledge of the metabolic reprogramming and mitochondrial dysfunctions in colitogenic T cells, as well as the potential therapeutic applications for treating IBD with evidence from animal experiments.

Research hotspots and trend analysis of abdominal pain in inflammatory bowel disease: a bibliometric and visualized analysis

Aims: The study aimed to provide a bibliometric and visual analysis of research on abdominal pain in inflammatory bowel disease and discuss the current status, research hotspots, and future developments. Methods: We used the Web of Science Core Collection to comprehensively search the literature on abdominal pain-related research in IBD published between 2003 and 2022. The bibliometric and visual analysis was performed through CiteSpace, VOSviewer software, R language, and the bibliometric online analysis platform, including authors, institutions, countries, journals, references, and keywords in the literature. Results: A total of 3,503 relevant articles are included, indicating that the number of articles in this field has increased in recent years. The United States leads the way with a dominant position in terms of article output, followed by China and JAPAN. United States (967 articles), University of Calgary (98 articles), and World Journal of Gastroenterology (127 articles) are the top publishing countries, institutions, and journals, respectively; keyword analysis shows that gut microbiota, depression, stress, visceral hypersensitivity, and multidisciplinary approach are the hot spots and trends in this research area. Conclusion: Abdominal pain-related studies in IBD have received increasing attention in the past two decades. This study provides the first bibliometric analysis of papers in this research area using visualization software and data information mining. It provides insights into this field's current status, hot spots, and trends. However, many outstanding issues in this research area still need further exploration to provide a theoretical basis for its clinical application.

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.

Management of Pelvic Pain in Patients with Crohn's Disease-Current Overview

Crohn's disease (CD) is a subtype of chronic inflammatory bowel diseases (IBD) with characteristic skip lesions and transmural inflammation that may affect the entire gastrointestinal tract from the mouth to the anus. Persistent pain is one of the main symptoms of CD. This pain has multifactorial pathogenesis, but most often arises from intestinal inflammation itself, as well as from gut distention or partial intestinal obstruction. Some current evidence also suggests sensitization of sensory pathways, as well as modulation of those signals by the central nervous system, which highlights the impact of biopsychosocial factors. To date, most studies have focused only on the pain located in the abdomen, while pelvic pain has rarely been explored, despite it being a common symptom. The aim of this study is to provide an abbreviated summary of the current state of knowledge on the origins and treatment of pelvic pain in CD.

Ion channel regulation of gut immunity

Mounting evidence indicates that gastrointestinal (GI) homeostasis hinges on communications among many cellular networks including the intestinal epithelium, the immune system, and both intrinsic and extrinsic nerves innervating the gut. The GI tract, especially the colon, is the home base for gut microbiome which dynamically regulates immune function. The gut's immune system also provides an effective defense against harmful pathogens entering the GI tract while maintaining immune homeostasis to avoid exaggerated immune reaction to innocuous food and commensal antigens which are important causes of inflammatory disorders such as coeliac disease and inflammatory bowel diseases (IBD). Various ion channels have been detected in multiple cell types throughout the GI tract. By regulating membrane properties and intracellular biochemical signaling, ion channels play a critical role in synchronized signaling among diverse cellular components in the gut that orchestrates the GI immune response. This work focuses on the role of ion channels in immune cells, non-immune resident cells, and neuroimmune interactions in the gut at the steady state and pathological conditions. Understanding the cellular and molecular basis of ion channel signaling in these immune-related pathways and initial testing of pharmacological intervention will facilitate the development of ion channel-based therapeutic approaches for the treatment of intestinal inflammation.

Abdominal Pain in Inflammatory Bowel Diseases: A Clinical Challenge

Up to 60% of inflammatory bowel disease (IBD) patients experience abdominal pain in their lifetime regardless of disease activity. Pain negatively affects different areas of daily life and particularly impacts the quality of life of IBD patients. This review provides a comprehensive overview of the multifactorial etiology implicated in the chronic abdominal pain of IBD patients including peripheral sensitization by inflammation, coexistent irritable bowel syndrome, visceral hypersensitivity, alteration of the brain–gut axis, and the multiple factors contributing to pain persistence. Despite the optimal management of intestinal inflammation, chronic abdominal pain can persist, and pharmacological and non-pharmacological approaches are necessary. Integrating psychological support in care models in IBD could decrease disease burden and health care costs. Consequently, a multidisciplinary approach similar to that used for other chronic pain conditions should be recommended.

Post-inflammatory Abdominal Pain in Patients with Inflammatory Bowel Disease During Remission: A Comprehensive Review

Patients with inflammatory bowel disease often experience ongoing pain even after achieving mucosal healing (i.e., post-inflammatory pain). Factors related to the brain-gut axis, such as peripheral and central sensitization, altered sympatho-vagal balance, hypothalamic-pituitary-adrenal axis activation, and psychosocial factors, play a significant role in the development of post-inflammatory pain. A comprehensive study investigating the interaction between multiple predisposing factors, including clinical psycho-physiological phenotypes, molecular mechanisms, and multi-omics data, is still needed to fully understand the complex mechanism of post-inflammatory pain. Furthermore, current treatment options are limited and new treatments consistent with the underlying pathophysiology are needed to improve clinical outcomes.

Efficient Attenuation of Dextran Sulfate Sodium-Induced Colitis by Oral Administration of 5,6-Dihydroxy-8Z,11Z,14Z,17Z-eicosatetraenoic Acid in Mice

5,6-dihydroxy-8Z,11Z,14Z,17Z-eicosatetraenoic acid (5,6-DiHETE) is an eicosapentaenoic acid-derived newly discovered bioactive anti-inflammatory lipid mediator having diverse functions. Here, we assessed the potential of orally administered 5,6-DiHETE in promoting healing of dextran sulfate sodium (DSS)-induced colitis in mice. We measured the plasma concentrations of 5,6-DiHETE in untreated mice before and 0.5, 1, 3, and 6 h after its oral administration (150 or 600 μg/kg) in mice. Mice developed colitis by DSS (2% in drinking water for 4 days), and 5,6-DiHETE (150 or 600 μg/kg/day) was orally administered from day 9 to 14. Next, the faecal hardness and bleeding were assessed, and the dissected colons on day 14 via H&E staining. The plasma concentration of 5,6-DiHETE reached 25.05 or 44.79 ng/mL 0.5 h after the administration of 150 or 600 μg/kg, respectively, followed by a gradual decrease. The half-life of 5,6-DiHETE was estimated to be 1.25-1.63 h. Diarrhoea deteriorated after day 3 and peaked on day 5, followed by a gradual recovery. Histological assessment on day 14 showed DSS-mediated granulocyte infiltration, mucosal erosion, submucosal edema, and cryptal abscesses in mice. Oral administration of 150 or 600 μg/kg/day of 5,6-DiHETE accelerated the recovery from the DSS-induced diarrhoea and significantly ameliorated colon inflammation. The therapeutic effect of 600 μg/kg/day 5,6-DiHETE was slightly stronger than that by 150 μg/kg/day. Our study reveals attenuation of DSS-induced colitis in mice by the oral administration of 5,6-DiHETE dose-dependently, thereby suggesting a therapeutic potential of 5,6-DiHETE for inflammatory bowel disease.

Activation of transient receptor potential vanilloid channel 4 contributes to the development of ethanol-induced gastric injury in mice

The transient receptor potential vanilloid channel 4 (TRPV4) is associated with the development of several pathologies, particularly gastric disorders. However, there are no studies associating this receptor with the pathophysiology of gastric erosions. The aim of this study was to investigate the role of TRPV4 in the development of ethanol-induced gastric damage in vivo. Gastric lesions were induced by ethanol in Swiss mice pretreated with TRPV4 antagonists, GSK2193874 (0.1; 0.3 and 0.9 mg/kg) or Ruthenium red (0.03; 0.1 or 0.3 mg/kg) or its agonist, GSK1016790A (0.9 mg/kg). Gastric mucosal samples were taken for histopathology, immunohistochemistry, atomic force microscopy and evaluation of antioxidant parameters. The gastric mucus content and TRPV4 mRNA expression were analyzed. Ethanol exposure induced upregulation of gastric mRNA and protein expression of TRPV4. TRPV4 blockade promoted gastroprotection against ethanol-induced injury on macro- and microscopic levels, leading to reduced hemorrhage, cell loss and edema and enhanced gastric mucosal integrity. Moreover, an increase in superoxide dismutase (SOD) and glutathione (GSH) activity was observed, followed by a decrease in malondialdehyde (MDA) levels. TRPV4 blockade during alcohol challenge reestablished gastric mucus content. The combination of TRPV4 agonist and ethanol revealed macroscopic exacerbation of gastric damage area. Our results confirmed the association of TRPV4 with the development of gastric injury, showing the importance of this receptor for further investigations in the field of gastrointestinal pathophysiology and pharmacology.

5,6-dihydroxy-8Z,11Z,14Z,17Z-eicosatetraenoic acid accelerates the healing of colitis by inhibiting transient receptor potential vanilloid 4-mediated signaling

5,6-dihydroxy-8Z,11Z,14Z,17Z-eicosatetraenoic acid (5,6-DiHETE) is an eicosapentaenoic acid-derived lipid metabolite, which we previously detected in inflamed mouse colon. In this study, we investigated the pathophysiological roles of 5,6-DiHETE in murine colitis and its underlying mechanisms of action, focusing on the effects on transient receptor potential vanilloid (TRPV) channel activity. Oral administration of dextran sodium sulfate (DSS, 2%, for 4 days) caused colon inflammation, which peaked on day 7 and gradually declined by day 18. 5,6-DiHETE concentration in colon tissue was significantly increased during the healing phase of colitis (days 9 to 18). In vitro study showed that pretreatment with 5,6-DiHETE (0.1-1 μM, 30 minutes) significantly inhibited endothelial barrier disruption induced by a TRPV4 agonist (GSK1016790A, 50 nM). Intracellular Ca²⁺ imaging also showed that pretreatment with 5,6-DiHETE (1 μM, 10 minutes) reduced GSK1016790A-induced intracellular Ca²⁺ increase in HEK293T cells overexpressing TRPV4. In vivo, intraperitoneal administration of 5,6-DiHETE (50 µg kg^-1  day^-1 ) during the healing phase accelerated the recovery from DSS-induced colitis. Pathological studies showed that the administration of 5,6-DiHETE inhibited edema formation and leukocyte infiltration in inflamed colon tissue. In conclusion, we identified 5,6-DiHETE as a novel endogenous TRPV4 antagonist, and we also demonstrated that its administration promotes the healing of colitis by inhibiting inflammatory responses.

Gene Expression of Transient Receptor Potential Channels in Peripheral Blood Mononuclear Cells of Inflammatory Bowel Disease Patients

We examined the expression profile of transient receptor potential (TRP) channels in peripheral blood mononuclear cells (PBMCs) from patients with inflammatory bowel disease (IBD). PBMCs were obtained from 41 ulcerative colitis (UC) patients, 34 Crohn's disease (CD) patients, and 30 normal subjects. mRNA levels of TRP channels were measured using the quantitative real-time polymerase chain reaction, and correlation tests with disease ranking, as well as laboratory parameters, were performed. Compared with controls, TRPV2 and TRPC1 mRNA expression was lower, while that of TRPM2, was higher in PBMCs of UC and CD patients. Moreover, TRPV3 mRNA expression was lower, while that of TRPV4 was higher in CD patients. TRPC6 mRNA expression was higher in patients with CD than in patients with UC. There was also a tendency for the expression of TRPV2 mRNA to be negatively correlated with disease activity in patients with UC and CD, while that of TRPM4 mRNA was negatively correlated with disease activity only in patients with UC. PBMCs from patients with IBD exhibited varying mRNA expression levels of TRP channel members, which may play an important role in the progression of IBD.

Translational research into the effects of cigarette smoke on inflammatory mediators and epithelial TRPV1 in Crohn's disease

Crohn's disease is a pathological condition of the gastro-intestinal tract, causing severe transmural inflammation in the ileum and/or colon. Cigarette smoking is one of the best known environmental risk factors for the development of Crohn's disease. Nevertheless, very little is known about the effect of prolonged cigarette smoke exposure on inflammatory modulators in the gut. We examined the effect of cigarette smoke on cytokine profiles in the healthy and inflamed gut of human subjects and in the trinitrobenzene sulphonic acid mouse model, which mimics distal Crohn-like colitis. In addition, the effect of cigarette smoke on epithelial expression of transient receptor potential channels and their concurrent increase with cigarette smoke-augmented cytokine production was investigated. Active smoking was associated with increased IL-8 transcription in ileum of controls (p < 0,001; n = 18-20/group). In the ileum, TRPV1 mRNA levels were decreased in never smoking Crohn's disease patients compared to healthy subjects (p <0,001; n = 20/group). In the colon, TRPV1 mRNA levels were decreased (p = 0,046) in smoking healthy controls (n = 20/group). Likewise, healthy mice chronically exposed to cigarette smoke (n = 10/group) showed elevated ileal Cxcl2 (p = 0,0075) and colonic Kc mRNA levels (p = 0,0186), whereas TRPV1 mRNA and protein levels were elevated in the ileum (p = 0,0315). Although cigarette smoke exposure prior to trinitrobenzene sulphonic acid administration did not alter disease activity, increased pro-inflammatory cytokine production was observed in the distal colon (Kc: p = 0,0273; Cxcl2: p = 0,104; Il1-β: p = 0,0796), in parallel with the increase of Trpv1 mRNA (p < 0,001). We infer that CS affects pro-inflammatory cytokine expression in healthy and inflamed gut, and that the simultaneous modulation of TRPV1 may point to a potential involvement of TRPV1 in cigarette smoke-induced production of inflammatory mediators.

TRPV Subfamily (TRPV2, TRPV3, TRPV4, TRPV5, and TRPV6) Gene and Protein Expression in Patients with Ulcerative Colitis

Introduction

TRPVs are a group of receptors with a channel activity predominantly permeable to Ca²⁺. This subfamily is involved in the development of gastrointestinal diseases such as ulcerative colitis (UC). The aim of the study was to characterize the gene and protein expression of the TRPV subfamily in UC patients and controls.

Methods

We determined by quantitative PCR the gene expression of TRPV2, TRPV3, TRPV4, TRPV5, and TRPV6 in 45 UC patients (29 active UC and 16 remission UC) and 26 noninflamed controls. Protein expression was evaluated in 5 μm thick sections of formalin-fixed, paraffin-embedded tissue from 5 customized severe active UC patients and 5 control surgical specimens.

Results

TRPV2 gene expression was increased in the control group compared with active UC and remission patients (P = 0.002 and P = 0.05, respectively). TRPV3 gene expression was significantly higher in controls than in active UC patients (P = 0.002). The gene expression of TRPV4 was significantly higher in colonic tissue from patients with remission UC compared with active UC patients (P = 0.05) and controls (P = 0.005). TRPV5 had significantly higher mRNA levels in a control group compared with active UC patients (P = 0.02). The gene expression of TRPV6 was significantly higher in the colonic tissue from patients with active UC compared with the control group (P = 0.05). The protein expression of TRPV2 was upregulated in the mucosa and submucosa from the controls compared with the UC patients (P ≤ 0.003). The protein expression of TRPV3 and TRPV4 was upregulated in all intestinal layers from the controls compared with the UC patients (P < 0.001). TRPV5 was upregulated in the submucosa and serosa from the controls vs. UC patients (P < 0.001). TRPV6 was upregulated in all intestinal layers from the UC patients vs. controls (P ≤ 0.001).

Conclusion

The TRPV subfamily clearly showed a differential expression in the UC patients compared with the controls, suggesting their role in the pathophysiology of UC.

Transient Receptor Potential Channels and Inflammatory Bowel Disease

The transient receptor potential (TRP) cation channels are present in abundance across the gastrointestinal (GI) tract, serving as detectors for a variety of stimuli and secondary transducers for G-protein coupled receptors. The activation of TRP channels triggers neurogenic inflammation with related neuropeptides and initiates immune reactions by extra-neuronally regulating immune cells, contributing to the GI homeostasis. However, under pathological conditions, such as inflammatory bowel disease (IBD), TRP channels are involved in intestinal inflammation. An increasing number of human and animal studies have indicated that TRP channels are correlated to the visceral hypersensitivity (VHS) and immune pathogenesis in IBD, leading to an exacerbation or amelioration of the VHS or intestinal inflammation. Thus, TRP channels are a promising target for novel therapeutic methods for IBD. In this review, we comprehensively summarize the functions of TRP channels, especially their potential roles in immunity and IBD. Additionally, we discuss the contradictory findings of prior studies and offer new insights with regard to future research.

The effect of transient receptor potential vanilloid 4 on the intestinal epithelial barrier and human colonic cells was affected by tyrosine-phosphorylated claudin-7

TRPV4 is a type of nonselective cation channel, and activation of TRPV4 in the gastrointestinal tract causes experimental colitis in mice. A previous study found that tyrosine-phosphorylated claudin-7 is increased in experimental colitis. The relationship between tyrosine-phosphorylated claudin-7 and TRPV4 remains undefined. In the present study, we developed a claudin-7 mutant by replacing tyrosine with glutamic acid at position 210, named cld7-Y210E colonic cells. We found that activation of TRPV4 by GSK1016790A increased the permeability of control colonic cell monolayers, which was decreased by the TRPV4 antagonist HC067047. In monolayers of cld7-Y210E colonic cells, no differences in permeability were found between GSK1016790A and HC067047 treatments. GSK1016790A increased the aggregation of claudin-7 at the cell membrane in control colonic cells, and the effect was diminished by HC067047. In cld7-Y210E colonic cells, neither GSK1016790A nor HC067047 apparently changed the aggregation of claudin-7. Neither GSK1016790A nor HC067047 altered the TRPV4 protein level in vector colonic cells. In cld7-wild colonic cells, GSK1016790A did not alter the TRPV4 protein level, while HC067047 increased the TRPV4 protein level. The TRPV4 protein level was increased in cld7-Y210E colonic cells, decreased by GSK1016790A and further decreased by HC067047. Calcium influx was not significantly changed in the control colonic cells treated with GSK1016790A. However, GSK1016790A significantly increased calcium influx in cld7-Y210E colonic cells. We concluded that tyrosine-phosphorylated claudin-7 affects the TRPV4-modulated intestinal epithelial barrier, TRPV4-mediated calcium influx, and the protein expression of TRPV4 in human colonic cells. We suggest that tyrosine-phosphorylated claudin-7 affects the TRPV4-modulated intestinal epithelial barrier, which might be related to TRPV4 expression and TRPV4-mediated calcium influx.

The Pivotal Role of TRP Channels in Homeostasis and Diseases throughout the Gastrointestinal Tract

The transient receptor potential (TRP) channels superfamily are a large group of proteins that play crucial roles in cellular processes. For example, these cation channels act as sensors in the detection and transduction of stimuli of temperature, small molecules, voltage, pH, and mechanical constrains. Over the past decades, different members of the TRP channels have been identified in the human gastrointestinal (GI) tract playing multiple modulatory roles. Noteworthy, TRPs support critical functions related to the taste perception, mechanosensation, and pain. They also participate in the modulation of motility and secretions of the human gut. Last but not least, altered expression or activity and mutations in the TRP genes are often related to a wide range of disorders of the gut epithelium, including inflammatory bowel disease, fibrosis, visceral hyperalgesia, irritable bowel syndrome, and colorectal cancer. TRP channels could therefore be promising drug targets for the treatment of GI malignancies. This review aims at providing a comprehensive picture of the most recent advances highlighting the expression and function of TRP channels in the GI tract, and secondly, the description of the potential roles of TRPs in relevant disorders is discussed reporting our standpoint on GI tract–TRP channels interactions.

Dietary fatty acid content influences the expression of genes involved in the lipid turnover and inflammation in mouse colon and spleen

BACKGROUND

Dietary interventions can improve gastrointestinal (GI) symptoms. We determined the effects of fatty acids (FAs) supplementation with medium- and long-chain saturated FAs on mouse GI motility and correlated them with the expression of genes for free FA receptors (FFAR)1-4, FA binding protein 4 (FABP4) and inflammation.

METHODS

Forty-eight BalbC were assigned to: standard diet (STD), diet rich in medium-chain saturated FAs (COCO) and long-chain saturated FAs (HF) (7% by weight). Body weight (BW) and food intake (FI) were monitored for 8-weeks. GI motility was determined by fecal pellet output (FPO) and colon bead expulsion tests. FABP4 inhibitor, BMS309403 (1mg/kg, ip) was injected to half of each group 2 days/week. mRNA expression of FABP4, (FFAR)1-4, and pro-inflammatory cytokines were measured in colonic and splenic tissues using real-time PCR.

RESULTS

COCO and HF decreased FI. COCO accelerated overall GI transit (p<0.05). COCO increased the mRNA expression of FFAR2 (p<0.001) and TNFα (p<0.01); HF increased the expression of FABP4 and FFAR4 (p<0.05), and FFAR2 (p<0.001) in the colon, and decreased FFAR1 and FFAR4 (p<0.001), TNFα (p<0.01) and IL-1β (p<0.05) in splenic tissues. BMS309403 decreased the FI and delayed colonic transit in STD+BMS and COCO+BMS vs. STD (p<0.05). HF+BMS increased colonic expression of FFAR3 (p<0.01), TNFα (p<0.01), IL-6 (p<0.01), and reduced FFAR4 (p<0.05); COCO+BMS decreased TNFα (p<0.01).

CONCLUSION

Diversification in the dietary lipid content affected GI motility in mice and the expression of FFARs and pro-inflammatory cytokines in vivo.

[Physiological and pathophysiological roles of TRPV4 channel in gastrointestinal tract]

Transient receptor potential vanilloid 4 (TRPV4) is a non-selective cation channel that responds to mechanical, thermal, and chemical stimuli in addition to various endogenous ligands, such as arachidonic acid metabolites. The present study aimed to elucidate the expression of TRPV4 in the gastrointestinal tract and the pathogenic roles of TRPV4 in dextran sulphate sodium (DSS)-induced colitis. TRPV4-immunoreactivity was detected in epithelial-like cells of the mouse tongue, esophagus, stomach, ileum, and colon; TRPV4 expression in the tongue was higher than other gastrointestinal tracts. TRPV4 colocalized with a type IV cell marker sonic hedgehog in circumvallate papillae. These findings suggest that TRPV4 contributes to sour taste sensing by regulating type III taste cell differentiation in mice. DSS-induced colitis was significantly attenuated in TRPV4-knockout (TRPV4KO) mice when compared to wild-type mice. DSS treatment upregulated TRPV4 expression in vascular endothelia of colonic mucosa and submucosa. DSS treatment increased vascular permeability, which was abolished in TRPV4KO mice. The activation of TRPV4 decreased VE-cadherin expression in mouse aortic endothelial cells exposed to TNF-α. These findings indicate that the upregulation of TRPV4 in vascular endothelial cells contributes to the progression of colonic inflammation via the activation of vascular permeability. Thus, TRPV4 is an attractive target for the treatment of inflammatory bowel diseases.

G protein-coupled estrogen receptor mediates anti-inflammatory action in Crohn's disease

Estrogens exert immunomodulatory action in many autoimmune diseases. Accumulating evidence highlights the meaningful impact of estrogen receptors in physiology and pathophysiology of the colon. However, the significance of G protein-coupled estrogen receptor (GPER) on Crohn's disease (CD), one of the inflammatory bowel disease (IBD) types, is still elusive. Our study revealed GPER overexpression at the mRNA and protein levels in patients with CD. To evaluate the effects of GPER activation/inhibition on colitis development, a murine 2, 4, 6-trinitrobenzene sulfonic acid (TNBS)-induced model of CD was used. We showed that activation of GPER reduces mortality, improves macroscopic and microscopic scores and lowers C-reactive protein (CRP) level. The impact of estrogen signaling on the suppression of the intestinal inflammation was proved by immunohistochemistry. It was demonstrated that GPER activation is accompanied by modulation of extracellular-signal regulated kinase (ERK) signaling pathway and expression level of genes involved in signal transmission and immune response as well as the expression of some microRNAs (miR-145, miR-148-5p and miR-592). Our study revealed that the membrane-bound estrogen receptor GPER mediates anti-inflammatory action and seems to be a potent therapeutic target in maintaining remission in CD.

Focus on current and future management possibilities in inflammatory bowel disease-related chronic pain

INTRODUCTION

Visceral pain is a symptom reported by over 70% of inflammatory bowel disease (IBD) sufferers. So far, a single, specific cause of this debilitating state has not been established. Chronic pain is one of the most important factors decreasing the quality of life in IBD course. Concurrently, management of pain is the most challenging issue encountered by clinicians in IBD treatment.

AREAS COVERED

This review focuses on pathophysiology of inflammatory bowel disease-caused visceral pain and explores currently available approaches to its management. We also covered recent pharmacological developments in the field.

CONCLUSIONS

Pain-related disability has major effects on quality of life and on functional and social outcomes in IBD patients. Currently, there is no one standardized method of managing chronic visceral pain in IBD. Therefore, future development, focusing primarily on alleviating the pain, but also on reducing inflammation, is essential.

The potential of Thymus vulgaris aqueous extract to protect against delayed gastric emptying and colonic constipation in rats

Thyme is a rich source of bioactive phytochemicals and it is frequently used in folk-medicine to treat gastroenteritis irritations. The current study was performed to examine the potential of Thymus vulgaris aqueous extract (TV-AE) to protect against delayed gastric emptying (DGE) and colonic constipation in rats. Stomach ulcer was caused by a single oral dose administration of indomethacin (INDO) (30 mg kg⁻¹ of body weight). Constipation was induced following intravenous intoxication of rats with vinblastine (VINB) (2 mg kg⁻¹ of body weight) for one week. The effect of TV-AE at two graduated doses (100 and 200 mg kg⁻¹) on DGE, gastrointestinal transit (GIT) and constipated rats and biochemical parameters was estimated using phenol red, charcoal meal test and colorimetric methods, respectively. The phytochemical-profile of TV-AE was explored using high-performance liquid chromatography coupled with photodiode array detection and electrospray ionization-mass spectrometry (HPLC-PDA/ESI-MS). INDO and VINB caused a significant reduction in (P < 0.05) DGE and GIT and colonic motility dysfunction. TV-AE consumption remarkably (P < 0.05) attenuated the DGE (from 58.56% to 69.871%) and difficulty in evacuating stools (from 48.5 to 55.5 fecal pellets per rat) and balanced the GIT (65% to 71%). These GI-ameliorative effects were accompanied by reversed INDO/VINB-related oxidative changes, lipid-metabolism alteration and intracellular pathway moderation. HPLC-PDA/ESI-MS-analysis identified several chemical constituents including rosmarinic acid, quinic acid, luteolin-7-o-glucoside, protocatechuic acid and trans-cinnamic acid. Thus, TV-AE bioactive components may be used as medicinal substances to regulate/attenuate gastrointestinal–physiological activities and disturbances, which support its pharmacological use.

Thyme is a rich source of bioactive phytochemicals and it is frequently used in folk-medicine to treat gastroenteritis irritations.

TRPV4 Inhibition Improved Myelination and Reduced Glia Reactivity and Inflammation in a Cuprizone-Induced Mouse Model of Demyelination

The inhibition of demyelination and the promotion of remyelination are both considerable challenges in the therapeutic process for many central nervous system (CNS) diseases. Increasing evidence has demonstrated that neuroglial activation and neuroinflammation are responsible for myelin sheath damage during demyelinating disorders. It has been revealed that the nonselective cation channel transient receptor potential vanilloid 4 (TRPV4) profoundly affects a variety of physiological processes, including inflammation. However, its roles and mechanisms in demyelination have remained unclear. Here, for the first time, we found that there was a significant increase in TRPV4 in the corpus callosum in a demyelinated mouse model induced by cuprizone (CPZ). RN-1734, a TRPV4-antagonist, clearly alleviated demyelination and inhibited glial activation and the production of tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) without altering the number of olig2-positive cells. In vitro, RN-1734 treatment clearly inhibited the influx of calcium and decreased the levels of IL-1β and TNF-α in lipopolysaccharide (LPS)-activated microglial cells by suppressing NF-κB P65 phosphorylation. Apoptosis of oligodendrocyte induced by LPS-activated microglia was also alleviated by RN-1734. The results suggest that activation of TRPV4 in microglia is involved in oligodendrocyte apoptosis through the activation of the NF-κB signaling pathway, thus revealing a new mechanism of CNS demyelination.

[TRPV4 regulates vascular endothelial permeability during colonic inflammation in dextran sulphate sodium-induced murine colitis]

The transient receptor potential vanilloid 4 (TRPV4) is a nonselective cation channel involved in physical sensing in various tissue types. The present study aimed to elucidate the function and expression of TRPV4 in colonic vascular endothelial cells during dextran sulphate sodium (DSS)-induced colitis. The role of TRPV4 in the progression of colonic inflammation was examined in the 2% DSS-induced murine colitis model using immunohistochemical analysis, Western blotting, and Evans blue dye extrusion assay. DSS-induced colitis was significantly attenuated in TRPV4-deficient (TRPV4 KO) mice when compared to wild-type mice. Repeated intrarectal administration of GSK1016790A, a TRPV4 agonist, exacerbated the severity of DSS-induced colitis. Bone marrow transfer experiments demonstrated a dominant role of TRPV4 in non-haematopoietic cells for DSS-induced colitis. DSS treatment upregulated TRPV4 expression in the vascular endothelia of colonic mucosa and submucosa. DSS treatment increased vascular permeability, which was abolished in TRPV4 KO mice. The DSS-induced increase in vascular permeability was further enhanced by intravenous administration of GSK1016790A, which was abrogated by a TRPV4 antagonist RN1734. TRPV4 was co-localized with vascular endothelial (VE)-cadherin, and VE-cadherin expression was decreased by repeated intravenous administration of GSK1016790A during colitis. Furthermore, TRPV4 activation by GSK106790A decreased VE-cadherin expression in mouse aortic endothelial cells exposed to TNF-α. These findings indicate that TRPV4 upregulation in vascular endothelial cells contributes to the progression of colonic inflammation via the activation of vascular permeability. Thus, TRPV4 is an attractive target for the treatment of inflammatory bowel diseases.

Newly developed serine protease inhibitors decrease visceral hypersensitivity in a post-inflammatory rat model for irritable bowel syndrome

BACKGROUND AND PURPOSE

Serine proteases have been re suggested as important mediators of visceral pain. We investigated their effect by using newly developed serine protease inhibitors with a well-characterized inhibitory profile in a rat model of post-inflammatory irritable bowel syndrome (IBS).

EXPERIMENTAL APPROACH

Colitis was induced in rats receiving intrarectal trinitrobenzenesulphonic acid; controls received 0.9% NaCl. Colonoscopies were performed on day 3, to confirm colitis, and later until mucosal healing. Visceral hypersensitivity was quantified by visceromotor responses (VMRs) to colorectal distension, 30 min after i.p. injection of the serine protease inhibitors nafamostat, UAMC-00050 or UAMC-01162. Serine proteases, protease-activated receptors (PARs) and TRP channels were quantified by qPCR and immunohistochemistry. Proteolytic activity was characterized using fluorogenic substrates.

KEY RESULTS

VMR was significantly elevated in post-colitis rats. Nafamostat normalized VMRs at the lowest dose tested. UAMC-00050 and UAMC-01162 significantly decreased VMR dose-dependently. Expression of mRNA for tryptase-αβ-1and PAR4, and tryptase immunoreactivity was significantly increased in the colon of post-colitis animals. Trypsin-like activity was also significantly increased in the colon but not in the faeces. PAR2 and TRPA1 immunoreactivity co-localized with CGRP-positive nerve fibres in control and post-colitis animals.

CONCLUSIONS AND IMPLICATIONS

Increased expression of serine proteases and activity together with increased expression of downstream molecules at the colonic and DRG level and in CGRP-positive sensory nerve fibres imply a role for serine proteases in post-inflammatory visceral hypersensitivity. Our results support further investigation of serine protease inhibitors as an interesting treatment strategy for IBS-related visceral pain.

Expression Profiling of the Transient Receptor Potential Vanilloid (TRPV) Channels 1, 2, 3 and 4 in Mucosal Epithelium of Human Ulcerative Colitis

The Transient Receptor Potential (TRP) family of selective and non-selective ion channels is well represented throughout the mammalian gastrointestinal track. Several members of the Transient Receptor Potential Vanilloid (TRPV) subfamily have been identified in contributing to modulation of mobility, secretion and sensitivity of the human intestine. Previous studies have focused on the detection of TRPV mRNA levels in colon tissue of patients with inflammatory bowel disease (IBD) whereas little information exists regarding TRPV channel expression in the colonic epithelium. The aim of this study was to evaluate the expression levels of TRPV1, TRPV2, TRPV3 and TRPV4 in mucosa epithelial cells of colonic biopsies from patients with ulcerative colitis (UC) in comparison to colonic resections from non-IBD patients (control group). Immunohistochemistry, using specific antibodies and quantitative analyses of TRPV-immunostained epithelial cells, was performed in semi-serial sections of the samples. TRPV1 expression was significantly decreased whereas TRPV4 expression was significantly increased in the colonic epithelium of UC patients compared to patients in the control group (p < 0.05). No significant difference for TRPV2 and TRPV3 expression levels between UC and control specimens was detected (p > 0.05). There was no correlation between TRPV channel expression and the clinical features of the disease (p > 0.05). Further investigation is needed to clarify the role of TRPV channels in human bowel inflammatory response.

Toward an effective peripheral visceral analgesic: responding to the national opioid crisis

This minireiew summarizes recent new developments in visceral analgesics. This promising field is important, as a new approach to address abdominal pain with peripheral visceral analgesics is considered a key approach to addressing the current opioid crisis. Some of the novel compounds address peripheral pain mechanisms through modulation of opioid receptors via biased ligands, nociceptin/orphanin FQ opioid peptide (NOP) receptor, or dual action on NOP and μ-opioid receptor, buprenorphine and morphiceptin analogs. Other compounds target nonopioid mechanisms, including cannabinoid (CB2), N-methyl-d-aspartate, calcitonin gene-related peptide, estrogen, and adenosine A_2B receptors and transient receptor potential (TRP) channels (TRPV1, TRPV4, and TRPM8). Although current evidence is based predominantly on animal models of visceral pain, early human studies also support the evidence from the basic and animal research. This augurs well for the development of nonaddictive, visceral analgesics for treatment of chronic abdominal pain, an unmet clinical need.

Transient receptor potential vanilloid 4 channel regulates vascular endothelial permeability during colonic inflammation in dextran sulphate sodium-induced murine colitis

BACKGROUND AND PURPOSE

The transient receptor potential vanilloid 4 (TRPV4) channel is a non-selective cation channel involved in physical sensing in various tissue types. The present study aimed to elucidate the function and expression of TRPV4 channels in colonic vascular endothelial cells during dextran sulphate sodium (DSS)-induced colitis.

EXPERIMENTAL APPROACH

The role of TRPV4 channels in the progression of colonic inflammation was examined in a murine DSS-induced colitis model using immunohistochemical analysis, Western blotting and Evans blue dye extrusion assay.

KEY RESULTS

DSS-induced colitis was significantly attenuated in TRPV4-deficient (TRPV4 KO) as compared to wild-type mice. Repeated intrarectal administration of GSK1016790A, a TRPV4 agonist, exacerbated the severity of DSS-induced colitis. Bone marrow transfer experiments demonstrated the important role of TRPV4 in non-haematopoietic cells for DSS-induced colitis. DSS treatment up-regulated TRPV4 expression in the vascular endothelia of colonic mucosa and submucosa. DSS treatment increased vascular permeability, which was abolished in TRPV4 KO mice. This DSS-induced increase in vascular permeability was further enhanced by i.v. administration of GSK1016790A, and this effect was abolished by the TRPV4 antagonist RN1734. TRPV4 was co-localized with vascular endothelial (VE)-cadherin, and VE-cadherin expression was decreased by repeated i.v. administration of GSK1016790A during colitis. Furthermore, GSK106790A decreased VE-cadherin expression in mouse aortic endothelial cells exposed to TNF-α.

CONCLUSION AND IMPLICATIONS

These findings indicate that an up-regulation of TRPV4 channels in vascular endothelial cells contributes to the progression of colonic inflammation by increasing vascular permeability. Thus, TRPV4 is an attractive target for the treatment of inflammatory bowel diseases.

Systemic Administration of Sialorphin Attenuates Experimental Colitis in Mice via Interaction With Mu and Kappa Opioid Receptors

BACKGROUND AND AIMS

Pharmacological treatment and/or maintenance of remission in inflammatory bowel disease [IBD] is currently one of the biggest challenges in the field of gastroenterology. Here we aimed to assess the anti-inflammatory effect and the mechanism of action of sialorphin, the natural blocker of the endogenous opioid peptide-degrading enzymes neprilysin [NEP] and aminopeptidase N [APN], in mouse models of IBD and the changes in the expression of these enzymes in IBD patients.

METHODS

We used two models of experimental colitis in mice [2,4,6-trinitrobenzene sulphonic acid [TNBS]- and dextran sulphate sodium [DSS]-induced]. Macroscopic score, ulcer score, colonic wall thickness, and myeloperoxidase [MPO] activity were recorded. Additionally, we measured the expression of NEP and APN in the colon of IBD patients and healthy controls.

RESULTS

We showed that sialorphin attenuated acute, semichronic, and relapsing TNBS-induced colitis in mice after systemic administration, and its anti-inflammatory action is associated with mu and kappa opioid receptors.

CONCLUSIONS

We show that indirect stimulation of opioid receptors by the blockade of NEP and APN is a promising pharmacological strategy for the treatment of IBD, and may become of greater importance than the use of classical opioid agonists.

Transient receptor potential vanilloid type 4 channels mediate Na-K-Cl-co-transporter-induced brain edema after traumatic brain injury

Na⁺ -K⁺ -2Cl^- co-transporter (NKCC1) plays an important role in traumatic brain injury (TBI)-induced brain edema via the MAPK cascade. The transient receptor potential vanilloid type 4 (TRPV4) channel participates in neurogenic inflammation, pain transmission, and edema. In this study, we investigated the relationship between NKCC1 and TRPV4 and the related signaling pathways in TBI-induced brain edema and neuronal damage. TBI was induced by the calibrated weight-drop device. Adult male Wistar rats were randomly assigned into sham and experimental groups for time-course studies of TRPV4 expression after TBI. Hippocampal TRPV4, NKCC1, MAPK, and PI-3K cascades were analyzed by western blot, and brain edema was also evaluated among the different groups. Expression of hippocampal TRPV4 peaked at 8 h after TBI, and phosphorylation of the MAPK cascade and Akt was significantly elevated. Administration of either the TRPV4 antagonist, RN1734, or NKCC1 antagonist, bumetanide, significantly attenuated TBI-induced brain edema through decreasing the phosphorylation of MEK, ERK, and Akt proteins. Bumetanide injection inhibited TRPV4 expression, which suggests NKCC1 activation is critical to TRPV4 activation. Our results showed that hippocampal NKCC1 activation increased TRPV4 expression after TBI and then induced severe brain edema and neuronal damage through activation of the MAPK cascade and Akt-related signaling pathway.

Transient receptor potential ion channel function in sensory transduction and cellular signaling cascades underlying visceral hypersensitivity

Visceral hypersensitivity is an important mechanism underlying increased abdominal pain perception in functional gastrointestinal disorders including functional dyspepsia, irritable bowel syndrome, and inflammatory bowel disease in remission. Although the exact pathophysiological mechanisms are poorly understood, recent studies described upregulation and altered functions of nociceptors and their signaling pathways in aberrant visceral nociception, in particular the transient receptor potential (TRP) channel family. A variety of TRP channels are present in the gastrointestinal tract (TRPV1, TRPV3, TRPV4, TRPA1, TRPM2, TRPM5, and TRPM8), and modulation of their function by increased activation or sensitization (decreased activation threshold) or altered expression in visceral afferents have been reported in visceral hypersensitivity. TRP channels directly detect or transduce osmotic, mechanical, thermal, and chemosensory stimuli. In addition, pro-inflammatory mediators released in tissue damage or inflammation can activate receptors of the G protein-coupled receptor superfamily leading to TRP channel sensitization and activation, which amplify pain and neurogenic inflammation. In this review, we highlight the present knowledge on the functional roles of neuronal TRP channels in visceral hypersensitivity and discuss the signaling pathways that underlie TRP channel modulation. We propose that a better understanding of TRP channels and their modulators may facilitate the development of more selective and effective therapies to treat visceral hypersensitivity.

TRPV4: Molecular Conductor of a Diverse Orchestra

Transient receptor potential vanilloid type 4 (TRPV4) is a calcium-permeable nonselective cation channel, originally described in 2000 by research teams led by Schultz (Nat Cell Biol 2: 695-702, 2000) and Liedtke (Cell 103: 525-535, 2000). TRPV4 is now recognized as being a polymodal ionotropic receptor that is activated by a disparate array of stimuli, ranging from hypotonicity to heat and acidic pH. Importantly, this ion channel is constitutively expressed and capable of spontaneous activity in the absence of agonist stimulation, which suggests that it serves important physiological functions, as does its widespread dissemination throughout the body and its capacity to interact with other proteins. Not surprisingly, therefore, it has emerged more recently that TRPV4 fulfills a great number of important physiological roles and that various disease states are attributable to the absence, or abnormal functioning, of this ion channel. Here, we review the known characteristics of this ion channel's structure, localization and function, including its activators, and examine its functional importance in health and disease.

Cannabinoids as gastrointestinal anti-inflammatory drugs

In this mini-review, we focus on the potential of the endocannabinoid system as a target for novel therapies to treat gastrointestinal (GI) inflammation. We discuss the organization of the endocannabinoid signaling and present possible pharmacological sites in the endocannabinoid system. We also refer to recent clinical findings in the field. Finally, we point at the potential use of cannabinoids at low, non-psychoactive doses to counteract non-inflammatory pathological events in the GI tract, like chemotherapy-induced diarrhea, as evidenced by Abalo et al. in the rat model.

Modulation of the TRPV4 ion channel as a therapeutic target for disease

Transient Receptor Potential Vanilloid 4 (TRPV4) is a broadly expressed, polymodally gated ion channel that plays an important role in many physiological and pathophysiological processes. TRPV4 knockout mice and several synthetic pharmacological compounds that selectively target TRPV4 are now available, which has allowed detailed investigation in to the therapeutic potential of this ion channel. Results from animal studies suggest that TRPV4 antagonism has therapeutic potential in oedema, pain, gastrointestinal disorders, and lung diseases such as cough, bronchoconstriction, pulmonary hypertension, and acute lung injury. A lack of observed side-effects in vivo has prompted a first-in-human trial for a TRPV4 antagonist in healthy participants and stable heart failure patients. If successful, this would open up an exciting new area of research for a multitude of TRPV4-related pathologies. This review will discuss the known roles of TRPV4 in disease, and highlight the possible implications of targeting this important cation channel for therapy.

Participation of peripheral TRPV1, TRPV4, TRPA1 and ASIC in a magnesium sulfate-induced local pain model in rat

We previously showed that magnesium sulfate (MS) has systemic antinociceptive and local peripheral pronociceptive effects. The role of transient receptor potential (TRP) channels and acid-sensing ion channels (ASICs) in the mechanism of action of MS has not been investigated in detail. The aim of this study was to explore the participation of TRP channels in the pronociceptive action of MS in rats after its intraplantar injection. The paw withdrawal threshold (PWT) to mechanical stimuli was measured by the electronic von Frey test. Drugs that were tested were either co-administered with an isotonic pH-unadjusted or pH-adjusted solution of MS intraplantarily, or to the contralateral paw to exclude systemic effects. We found that the subcutaneous administration of both pH-adjusted (7.4) and pH-unadjusted (about 6.0) isotonic (6.2% w/v in water) solutions of MS induce the pain at the injection site. The pH-unadjusted MS solution-induced mechanical hyperalgesia decreased in a dose-dependent manner as a consequence of co-injection of capsazepine, a selective TRPV1 antagonist (20, 100 and 500pmol/paw), RN-1734, a selective TRPV4 antagonist (1.55, 3.1 and 6.2μmol/paw), HC-030031, a selective TRPA1 antagonist (5.6, 28.1 and 140nmol/paw), and amiloride hydrochloride, a non-selective ASIC inhibitor (0.83, 2.5 and 7.55μmol/paw). In pH-adjusted MS-induced hyperalgesia, the highest doses of TRPV1, TRPV4 and TRPA1 antagonists displayed effects that were, respectively, either similar, less pronounced or delayed in comparison to the effect induced by administration of the pH-unadjusted MS solution; the ASIC antagonist did not have any effect. These results suggest that the MS-induced local peripheral mechanical hyperalgesia is mediated via modulation of the activity of peripheral TRPV1, TRPV4, TRPA1 and ASICs. Specific local inhibition of TRP channels represents a novel approach to treating local injection-related pain.

Transient receptor potential vanilloid 4-dependent calcium influx and ATP release in mouse and rat gastric epithelia

AIM: To explore the expression of transient receptor potential vanilloid 4 (TRPV4) and its physiological meaning in mouse and rat gastric epithelia.

METHODS: RT-PCR and immunochemistry were used to detect TRPV4 mRNA and protein expression in mouse stomach and a rat normal gastric epithelial cell line (RGE1-01), while Ca²⁺-imaging and electrophysiology were used to evaluate TRPV4 channel activity. ATP release was measured by a luciferin-luciferase assay. Gastric emptying was also compared between WT and TRPV4 knockout mice.

RESULTS: TRPV4 mRNA and protein were detected in mouse tissues and RGE1-01 cells. A TRPV4-specific agonist (GSK1016790A) increased intracellular Ca²⁺ concentrations and/or evoked TRPV4-like current activities in WT mouse gastric epithelial cells and RGE1-01 cells, but not TRPV4KO cells. GSK1016790A or mechanical stimuli induced ATP release from RGE1-01 cells while TRPV4 knockout mice displayed delayed gastric emptying in vivo.

CONCLUSION: TRPV4 is expressed in mouse and rat gastric epithelium and contributes to ATP release and gastric emptying.

What is the evidence for the role of TRP channels in inflammatory and immune cells?

A complex network of many interacting mechanisms orchestrates immune and inflammatory responses. Among these, the cation channels of the transient receptor potential (TRP) family expressed by resident tissue cells, inflammatory and immune cells and distinct subsets of primary sensory neurons, have emerged as a novel and interrelated system to detect and respond to harmful agents. TRP channels, by means of their direct effect on the intracellular levels of cations and/or through the indirect modulation of a large series of intracellular pathways, orchestrate a range of cellular processes, such as cytokine production, cell differentiation and cytotoxicity. The contribution of TRP channels to the transition of inflammation and immune responses from a defensive early response to a chronic and pathological condition is also emerging as a possible underlying mechanism in various diseases. This review discusses the roles of TRP channels in inflammatory and immune cell function and provides an overview of the effects of inflammatory and immune TRP channels on the pathogenesis of human diseases.

Understanding autoimmunity: The ion channel perspective

Ion channels are integral membrane proteins that orchestrate the passage of ions across the cell membrane and thus regulate various key physiological processes of the living system. The stringently regulated expression and function of these channels hold a pivotal role in the development and execution of various cellular functions. Malfunction of these channels results in debilitating diseases collectively termed channelopathies. In this review, we highlight the role of these proteins in the immune system with special emphasis on the development of autoimmunity. The role of ion channels in various autoimmune diseases is also listed out. This comprehensive review summarizes the ion channels that could be used as molecular targets in the development of new therapeutics against autoimmune disorders.

Protease-Activated Receptor-2 Up-Regulates Transient Receptor Potential Vanilloid 4 Function in Mouse Esophageal Keratinocyte

BACKGROUND

The reflux of pancreatic-duodenal fluids is implicated in the pathophysiology of proton-pump inhibitor-resistant gastroesophageal reflux disease (GERD). Protease-activated receptor-2 (PAR-2) is activated by proteases, the pancreatic enzyme, trypsin, and the activated PAR-2 enhances transient receptor potential vanilloid 4 (TRPV4) function in neurons. TRPV4 stimulates ATP exocytosis in conjunction with the vesicular nucleotide transporter, which mediates mechano-transduction and vagal stimulation. The aim of the present study was to verify whether the activated PAR-2 up-regulates TRPV4 function in mouse esophageal keratinocytes, which may link to the pathophysiology in PPI-resistant GERD.

METHODS

TRPV4 and PAR-2 expressions were detected by RT-PCR, immunostaining, and western blotting in mouse esophageal keratinocytes. The functional response of TRPV4 to esophageal keratinocytes was analyzed using a Ca(2+) imaging system. Cellular ATP release was examined by luciferase-luciferin reaction. TRPV4 phosphorylation was studied by immunoprecipitation and western blotting.

RESULTS

PAR-2 and TRPV4 mRNAs and proteins were expressed in esophageal keratinocytes. Pre-treatment with trypsin significantly increased the responses to TRPV4 activator in esophageal keratinocytes, probably via the phosphorylation of serine residue of TRPV4 by protein kinase C and resulted in cellular ATP release from the cells.

CONCLUSIONS

Activated PAR-2 with trypsin exposure up-regulated TRPV4 function and increased ATP release in mouse esophageal keratinocytes. This mechanism might be related to the pathophysiology of GERD, especially non-erosive GERD.

Alcohol and high fat induced chronic pancreatitis: TRPV4 antagonist reduces hypersensitivity

The pathogenesis of pain in chronic pancreatitis is poorly understood, and its treatment can be a major clinical challenge. Surgical and other invasive methods have variable outcomes that can be unsatisfactory. Therefore, there is a great need for further discovery of the pathogenesis of pancreatitis pain and new therapeutic targets. Human and animal studies indicate a critical role for oxidative stress and activation of transient receptor potential (TRP) cation channel subfamily members TRPV1 and TRPA1 on pancreatic nociceptors in sensitization mechanisms that result in pain. However, the in vivo role of transient receptor potential cation channel subfamily V member 4 (TRPV4) in chronic pancreatitis needs further evaluation. The present study characterized a rat alcohol/high fat diet (AHF)-induced chronic pancreatitis model with hypersensitivity, fibrotic pathology, and fat vacuolization consistent with the clinical syndrome. The rats with AHF-induced pancreatitis develop referred visceral pain-like behaviors, i.e. decreased hindpaw mechanical thresholds and shortened abdominal and hindpaw withdrawal latency to heat. In this study, oxidative stress was characterized as well as the role of TRPV4 in chronic visceral hypersensitivity. Lipid peroxidase and oxidative stress were indicated by increased plasma thiobarbituric acid reactive substances (TBARS) and diminished pancreatic manganese superoxide dismutase (MnSOD). The secondary sensitization associated with AHF-induced pancreatitis was effectively alleviated by the TRPV4 antagonist, HC 067047. Similarity of the results to those with the peripherally restricted μ-opiate receptor agonist, loperamide, suggested TRPV4 channel activated peripheral sensitization. This study using a reliable model that provides pre-clinical correlates of human chronic pancreatitis provides further evidence that TRPV4 channel is a potential therapeutic target for treatment of pancreatitis pain.