Emerging Targets for the Management of Osteoarthritis Pain

Worldwide, osteoarthritis (OA) is one of the leading causes of chronic pain, for which adequate relief is not available. Ongoing peripheral input from the affected joint is a major factor in OA-associated pain. Therefore, this review focuses predominantly on peripheral targets emerging in the preclinical and clinical arena. Nerve growth factor is the most advanced of these targets, and its blockade has shown tremendous promise in clinical trials in knee OA. A number of different types of ion channels, including voltage-gated sodium channels and calcium channels, transient receptor potential channels, and acid-sensing ion channels, are important for neuronal excitability and play a role in pain genesis. Few channel blockers have been tested in preclinical models of OA, with varying results. Finally, we discuss some examples of G-protein coupled receptors, which may offer attractive therapeutic strategies for OA pain, including receptors for bradykinin, calcitonin gene-related peptide, and chemokines. Since many of the pathways described above can be selectively and potently targeted, they offer an exciting opportunity for pain management in OA, either systemically or locally.

Effects of ginger and its pungent constituents on transient receptor potential channels

Ginger extract is used as an analeptic in herbal medicine and has been reported to exert antioxidant effects. Transient receptor potential (TRP) canonical 5 (TRPC5), TRP cation channel, subfamily M, member 7 (TRPM7; melastatin 7), and TRP cation channel, subfamily A, member 1 (TRPA1; ankyrin 1) are non-selective cation channels that are modulated by reactive oxygen/nitrogen species (ROS/RNS) and subsequently control various cellular processes. The aim of this study was to evaluate whether ginger and its pungent constituents modulate these channels and exert antioxidant effects. It was found that TRPC5 and TRPA1 currents were modulated by ginger extract and by its pungent constituents, [6]-gingerol, zingerone and [6]-shogaol. In particular, [6]-shogaol markedly and dose-dependently inhibited TRPC5 currents with an IC50 of value of ~18.3 µM. Furthermore, the strong dose-dependent activation of TRPA1 currents by [6]-shogaol was abolished by A‑967079 (a selective TRPA1 inhibitor). However, ginger extract and its pungent constituents had no effect on TRPM7 currents. These results suggest the antioxidant effects of ginger extract and its pungent constituents are mediated through TRPC5 and TRPA1, and that [6]-shogaol is predominantly responsible for the regulation of TRPC5 and TRPA1 currents by ginger extract.

Cannabinoid receptors and TRPA1 on neuroprotection in a model of retinal ischemia

Retinal ischemia is a pathological event present in several retinopathies such as diabetic retinopathy and glaucoma, leading to partial or full blindness with no effective treatment available. Since synthetic and endogenous cannabinoids have been studied as modulators of ischemic events in the central nervous system (CNS), the present study aimed to investigate the involvement of cannabinoid system in the cell death induced by ischemia in an avascular (chick) retina. We observed that chick retinal treatment with a combination of WIN 55212-2 and cannabinoid receptor antagonists (either AM251/O-2050 or AM630) decreased the release of lactate dehydrogenase (LDH) induced by retinal ischemia in an oxygen and glucose deprivation (OGD) model. Further, the increased availability of endocannabinoids together with cannabinoid receptor antagonists also had a neuroprotective effect. Surprisingly, retinal exposure to any of these drugs alone did not prevent the release of LDH stimulated by OGD. Since cannabinoids may also activate transient receptor potential (TRP) channels, we investigated the involvement of TRPA1 receptors (TRPA1) in retinal cell death induced by ischemic events. We demonstrated the presence of TRPA1 in the chick retina, and observed an increase in TRPA1 content after OGD, both by western blot and immunohistochemistry. In addition, the selective activation of TRPA1 by mustard oil (MO) did not worsen retinal LDH release induced by OGD, whereas the blockage of TRPA1 completely prevented the extravasation of cellular LDH in ischemic condition. Hence, these results show that during the ischemic event there is an augment of TRPA1, and activation of this receptor is important in cell death induction. The data also indicate that metabotropic cannabinoid receptors, both type 1 and 2, are not involved with the cell death found in the early stages of ischemia. Therefore, the study points to a potential role of TRPA1 as a target for neuroprotective approaches in retinal ischemia.

Coding and Plasticity in the Mammalian Thermosensory System

Perception of the thermal environment begins with the activation of peripheral thermosensory neurons innervating the body surface. To understand how temperature is represented in vivo, we used genetically encoded calcium indicators to measure temperature-evoked responses in hundreds of neurons across the trigeminal ganglion. Our results show how warm, hot, and cold stimuli are represented by distinct population responses, uncover unique functional classes of thermosensory neurons mediating heat and cold sensing, and reveal the molecular logic for peripheral warmth sensing. Next, we examined how the peripheral somatosensory system is functionally reorganized to produce altered perception of the thermal environment after injury. We identify fundamental transformations in sensory coding, including the silencing and recruitment of large ensembles of neurons, providing a cellular basis for perceptual changes in temperature sensing, including heat hypersensitivity, persistence of heat perception, cold hyperalgesia, and cold analgesia.

Oxidized Phospholipid OxPAPC Activates TRPA1 and Contributes to Chronic Inflammatory Pain in Mice

Oxidation products of the naturally occurring phospholipid 1-palmitoyl-2-arachidonoyl-sn-glycerol-3-phosphatidylcholine (PAPC), which are known as OxPAPC, accumulate in atherosclerotic lesions and at other sites of inflammation in conditions such as septic inflammation and acute lung injury to exert pro- or anti-inflammatory effects. It is currently unknown whether OxPAPC also contributes to inflammatory pain and peripheral neuronal excitability in these conditions. Here, we observed that OxPAPC dose-dependently and selectively activated human TRPA1 nociceptive ion channels expressed in HEK293 cells in vitro, without any effect on other TRP channels, including TRPV1, TRPV4 and TRPM8. OxPAPC agonist activity was dependent on essential cysteine and lysine residues within the N-terminus of the TRPA1 channel protein. OxPAPC activated calcium influx into a subset of mouse sensory neurons which were also sensitive to the TRPA1 agonist mustard oil. Neuronal OxPAPC responses were largely abolished in neurons isolated from TRPA1-deficient mice. Intraplantar injection of OxPAPC into the mouse hind paw induced acute pain and persistent mechanical hyperalgesia and this effect was attenuated by the TRPA1 inhibitor, HC-030031. More importantly, we found levels of OxPAPC to be significantly increased in inflamed tissue in a mouse model of chronic inflammatory pain, identified by the binding of an OxPAPC-specific antibody. These findings suggest that TRPA1 is a molecular target for OxPAPC and OxPAPC may contribute to chronic inflammatory pain through TRPA1 activation. Targeting against OxPAPC and TRPA1 signaling pathway may be promising in inflammatory pain treatment.

Glucose and GTP-binding protein-coupled receptor cooperatively regulate transient receptor potential-channels to stimulate insulin secretion [Review]

In pancreatic β-cells, glucose-induced closure of the ATP-sensitive K⁺ (KATP) channel is an initial process triggering glucose-stimulated insulin secretion (GSIS). This KATP-channel dependent pathway has been believed to be a central mechanism for GSIS. However, since the resting membrane potential of cells is determined by the balance of the net result of current amplitudes in outward and inward directions, it must be taken into consideration that not only KATP channel inhibition but also inward current via the basal opening of non-selective cation channels (NSCCs) plays a crucial role in membrane potential regulation. The basal activity of NSCCs is essential to effectively evoke depolarization in concert with KATP channel closure that is dependent on glucose metabolism. The present study summarizes recent findings regarding the roles of NSCCs in GSIS and GTP-binding protein coupled receptor-(GPCR) operated potentiation of GSIS.

Orexin A modulates INS-1E cell proliferation and insulin secretion via extracellular signal-regulated kinase and transient receptor potential channels

Orexins A (OXA) and B (OXB) control energy homeostasis by regulating food intake, energy expenditure and sleep-wake cycle. Several studies showed that OXA stimulates insulin secretion and proliferation of beta cells. However, mechanisms of action are still not well understood. Here, we investigated whether ERK and transient receptor potential channels (TRPs) play a role in mediating the effect of OXA on cell growth, insulin production, and secretion using the established INS-1E cell line. Cell proliferation was measured using BrdU assay. Insulin mRNA expression was detected by real-time PCR. Insulin secretion was assessed using ELISA. Intracellular calcium levels were measured using fluorescence calcium imaging (fura-2/AM). Extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation was detected by Western blot. TRP channel activity was blocked by lanthanum (III) chloride (La³⁺; 100 - 300 μM) or ruthenium red (RuR; 10 μM). OXA (100 nM) stimulated INS-1E cell proliferation, insulin secretion, intracellular Ca²⁺ concentration and ERK1/2 phosphorylation, without changing insulin mRNA expression. Inhibition of ERK1/2 by 10 μM U0126 attenuated OXA-stimulated INS-1E cell proliferation. Blockade of TRP channel activity by La³⁺ or RuR rendered OXA ineffective at modulating Ca²⁺ regulation and insulin release. In contrast, the L-type channel blocker nifedipine (10 μM) failed to affect OXA-stimulated insulin release. Taken together, OXA increases INS-1E cell proliferation via ERK1/2-dependent mechanism. Furthermore, OXA stimulates insulin secretion from INS-1E cells. TRPs are relevant for OXA-stimulated insulin secretion and intracellular calcium regulation.

TRPA1 and TRPV1 contribute to iodine antiseptics-associated pain and allergy

Iodine antiseptics exhibit superior antimicrobial efficacy and do not cause acquired microbial resistance. However, they are underused in comparison with antibiotics in infection treatments, partly because of their adverse effects such as pain and allergy. The cause of these noxious effects is not fully understood, and no specific molecular targets or mechanisms have been discovered. In this study, we show that iodine antiseptics cause pain and promote allergic contact dermatitis in mouse models, and iodine stimulates a subset of sensory neurons that express TRPA1 and TRPV1 channels. In vivo pharmacological inhibition or genetic ablation of these channels indicates that TRPA1 plays a major role in iodine antiseptics-induced pain and the adjuvant effect of iodine antiseptics on allergic contact dermatitis and that TRPV1 is also involved. We further demonstrate that iodine activates TRPA1 through a redox mechanism but has no direct effects on TRPV1. Our study improves the understanding of the adverse effects of iodine antiseptics and suggests a means to minimize their side effects through local inhibition of TRPA1 and TRPV1 channels.

Modulation of Human Neutrophil Responses by the Essential Oils from Ferula akitschkensis and Their Constituents

Essential oils were obtained by hydrodistillation of the umbels+seeds and stems of Ferula akitschkensis (FAEOu/s and FAEOstm, respectively) and analyzed by gas chromatography and gas chromatography-mass spectrometry. Fifty-two compounds were identified in FAEOu/s; the primary components were sabinene, α-pinene, β-pinene, terpinen-4-ol, eremophilene, and 2-himachalen-7-ol, whereas the primary components of FAEOstm were myristicin and geranylacetone. FAEOu/s, β-pinene, sabinene, γ-terpinene, geranylacetone, isobornyl acetate, and (E)-2-nonenal stimulated [Ca(2+)]i mobilization in human neutrophils, with the most potent being geranylacetone (EC50 = 7.6 ± 1.9 μM) and isobornyl acetate 6.4 ± 1.7 (EC50 = 7.6 ± 1.9 μM). In addition, treatment of neutrophils with β-pinene, sabinene, γ-terpinene, geranylacetone, and isobornyl acetate desensitized the cells to N-formyl-Met-Leu-Phe (fMLF)- and interleukin-8 (IL-8)-induced [Ca(2+)]i flux and inhibited fMLF-induced chemotaxis. The effects of β-pinene, sabinene, γ-terpinene, geranylacetone, and isobornyl acetate on neutrophil [Ca(2+)]i flux were inhibited by transient receptor potential (TRP) channel blockers. Furthermore, the most potent compound, geranylacetone, activated Ca(2+) influx in TRPV1-transfected HEK293 cells. In contrast, myristicin inhibited neutrophil [Ca(2+)]i flux stimulated by fMLF and IL-8 and inhibited capsaicin-induced Ca(2+) influx in TRPV1-transfected HEK293 cells. These findings, as well as pharmacophore modeling of TRP agonists, suggest that geranylacetone is a TRPV1 agonist, whereas myristicin is a TRPV1 antagonist. Thus, at least part of the medicinal properties of Ferula essential oils may be due to modulatory effects on TRP channels.

PIKfyve Regulates Vacuole Maturation and Nutrient Recovery following Engulfment

The scavenging of extracellular macromolecules by engulfment can sustain cell growth in a nutrient-depleted environment. Engulfed macromolecules are contained within vacuoles that are targeted for lysosome fusion to initiate degradation and nutrient export. We have shown that vacuoles containing engulfed material undergo mTORC1-dependent fission that redistributes degraded cargo back into the endosomal network. Here we identify the lipid kinase PIKfyve as a regulator of an alternative pathway that distributes engulfed contents in support of intracellular macromolecular synthesis during macropinocytosis, entosis, and phagocytosis. We find that PIKfyve regulates vacuole size in part through its downstream effector, the cationic transporter TRPML1. Furthermore, PIKfyve promotes recovery of nutrients from vacuoles, suggesting a potential link between PIKfyve activity and lysosomal nutrient export. During nutrient depletion, PIKfyve activity protects Ras-mutant cells from starvation-induced cell death and supports their proliferation. These data identify PIKfyve as a critical regulator of vacuole maturation and nutrient recovery during engulfment.

Hydrogen sulfide activates TRPA1 and releases 5-HT from epithelioid cells of the chicken thoracic aorta

Epithelioid cells in the chicken thoracic aorta are chemoreceptor cells that release 5-HT in response to hypoxia. It is likely that these cells play a role in chemoreception similar to that of glomus cells in the carotid bodies of mammals. Recently, H2S was reported to be a key mediator of carotid glomus cell responses to hypoxia. The aim of the present study was to reveal the mechanism of action of H2S on 5-HT outflow from chemoreceptor cells in the chicken thoracic aorta. The 5-HT outflow induced by NaHS, an H2S donor, and Na2S3, a polysulfide, was measured by using a HPLC equipped with an electrochemical detector. NaHS (0.3-3mM) caused a concentration-dependent increase in 5-HT outflow, which was significantly inhibited by the removal of extracellular Ca(2+). 5-HT outflow induced by NaHS (0.3mM) was also significantly inhibited by voltage-dependent L- and N-type Ca(2+) channel blockers and a selective TRPA1 channel blocker. Cinnamaldehyde, a TRPA1 agonist, mimicked the secretory response to H2S. 5-HT outflow induced by Na2S3 (10μM) was also inhibited by the TRPA1 channel blocker. Furthermore, the expression of TRPA1 was localized to 5-HT-containing chemoreceptor cells in the aortic wall. These findings suggest that the activation of TRPA1 and voltage-dependent Ca(2+) channels is involved in H2S-evoked 5-HT release from chemoreceptor cells in the chicken aorta.

Cardamonin, a Novel Antagonist of hTRPA1 Cation Channel, Reveals Therapeutic Mechanism of Pathological Pain

The increasing demand for safe and effective treatments of chronic pain has promoted the investigation of novel analgesic drugs. Some herbals have been known to be able to relieve pain, while the chemical basis and target involved in this process remained to be clarified. The current study aimed to find anti-nociceptive candidates targeting transient receptor potential ankyrin 1 (TRPA1), a receptor that implicates in hyperalgesia and neurogenic inflammation. In the current study, 156 chemicals were tested for blocking HEK293/TRPA1 ion channel by calcium-influx assay. Docking study was conducted to predict the binding modes of hit compound with TRPA1 using Discovery Studio. Cytotoxicity in HEK293 was conducted by Cell Titer-Glo assay. Additionally, cardiotoxicity was assessed via xCELLigence RTCA system. We uncovered that cardamonin selectively blocked TRPA1 activation while did not interact with TRPV1 nor TRPV4 channel. A concentration-dependent inhibitory effect was observed with IC₅₀ of 454 nM. Docking analysis of cardamonin demonstrated a compatible interaction with A-967079-binding site of TRPA1. Meanwhile, cardamonin did not significantly reduce HEK293 cell viability, nor did it impair cardiomyocyte constriction. Our data suggest that cardamonin is a selective TRPA1 antagonist, providing novel insight into the target of its anti-nociceptive activity.

Mustard vesicant-induced lung injury: Advances in therapy

Most mortality and morbidity following exposure to vesicants such as sulfur mustard is due to pulmonary toxicity. Acute injury is characterized by epithelial detachment and necrosis in the pharynx, trachea and bronchioles, while long-term consequences include fibrosis and, in some instances, cancer. Current therapies to treat mustard poisoning are primarily palliative and do not target underlying pathophysiologic mechanisms. New knowledge about vesicant-induced pulmonary disease pathogenesis has led to the identification of potentially efficacious strategies to reduce injury by targeting inflammatory cells and mediators including reactive oxygen and nitrogen species, proteases and proinflammatory/cytotoxic cytokines. Therapeutics under investigation include corticosteroids, N-acetyl cysteine, which has both mucolytic and antioxidant properties, inducible nitric oxide synthase inhibitors, liposomes containing superoxide dismutase, catalase, and/or tocopherols, protease inhibitors, and cytokine antagonists such as anti-tumor necrosis factor (TNF)-α antibody and pentoxifylline. Antifibrotic and fibrinolytic treatments may also prove beneficial in ameliorating airway obstruction and lung remodeling. More speculative approaches include inhibitors of transient receptor potential channels, which regulate pulmonary epithelial cell membrane permeability, non-coding RNAs and mesenchymal stem cells. As mustards represent high priority chemical threat agents, identification of effective therapeutics for mitigating toxicity is highly significant.

Acid-sensing ion channels and transient-receptor potential ion channels in zebrafish taste buds

Sensory information from the environment is required for life and survival, and it is detected by specialized cells which together make up the sensory system. The fish sensory system includes specialized organs that are able to detect mechanical and chemical stimuli. In particular, taste buds are small organs located on the tongue in terrestrial vertebrates that function in the perception of taste. In fish, taste buds occur on the lips, the flanks, and the caudal (tail) fins of some species and on the barbels of others. In fish taste receptor cells, different classes of ion channels have been detected which, like in mammals, presumably participate in the detection and/or transduction of chemical gustatory signals. However, since some of these ion channels are involved in the detection of additional sensory modalities, it can be hypothesized that taste cells sense stimuli other than those specific for taste. This mini-review summarizes current knowledge on the presence of transient-receptor potential (TRP) and acid-sensing (ASIC) ion channels in the taste buds of teleosts, especially adult zebrafish. Up to now ASIC4, TRPC2, TRPA1, TRPV1 and TRPV4 ion channels have been found in the sensory cells, while ASIC2 was detected in the nerves supplying the taste buds.

Tear gas: an epidemiological and mechanistic reassessment

Deployments of tear gas and pepper spray have rapidly increased worldwide. Large amounts of tear gas have been used in densely populated cities, including Cairo, Istanbul, Rio de Janeiro, Manama (Bahrain), and Hong Kong. In the United States, tear gas was used extensively during recent riots in Ferguson, Missouri. Whereas tear gas deployment systems have rapidly improved-with aerial drone systems tested and requested by law enforcement-epidemiological and mechanistic research have lagged behind and have received little attention. Case studies and recent epidemiological studies revealed that tear gas agents can cause lung, cutaneous, and ocular injuries, with individuals affected by chronic morbidities at high risk for complications. Mechanistic studies identified the ion channels TRPV1 and TRPA1 as targets of capsaicin in pepper spray, and of the tear gas agents chloroacetophenone, CS, and CR. TRPV1 and TRPA1 localize to pain-sensing peripheral sensory neurons and have been linked to acute and chronic pain, cough, asthma, lung injury, dermatitis, itch, and neurodegeneration. In animal models, transient receptor potential inhibitors show promising effects as potential countermeasures against tear gas injuries. On the basis of the available data, a reassessment of the health risks of tear gas exposures in the civilian population is advised, and development of new countermeasures is proposed.

Zinc directly stimulates cholecystokinin secretion from enteroendocrine cells and reduces gastric emptying in rats

Zinc, an essential mineral element, regulates various physiological functions such as immune responses and hormone secretion. Cholecystokinin (CCK), a gut hormone, has a role in protective immunity through the regulation of gastrointestinal motility, appetite, and inflammatory response. Here, we examined the effect of zinc on CCK secretion in STC-1 cells, an enteroendocrine cell line derived from murine duodenum, and in rats. Extracellular zinc triggered CCK secretion accompanied with increased intracellular Ca(2+) and Zn(2+) mobilization in STC-1 cells. Zinc-induced CCK secretion was abolished in the absence of intracellular Zn(2+) or extracellular calcium. Upon inhibition of transient receptor potential ankyrin 1 (TRPA1), extracellular zinc failed to increase intracellular Ca(2+) and subsequent CCK secretion. In rats, oral zinc administration decreased gastric emptying through the activation of CCK signaling. These results suggest that zinc is a novel stimulant for CCK secretion through the activation of TRPA1 related to intracellular Zn(2+) and Ca(2+) mobilization.

The Transient Receptor Potential (TRP) Channel Family in Colletotrichum graminicola: A Molecular and Physiological Analysis

Calcium (Ca2+) is a universal second messenger in all higher organisms and centrally involved in the launch of responses to environmental stimuli. Ca2+ signals in the cytosol are initiated by the activation of Ca2+ channels in the plasma membrane and/or in endomembranes. Yeast (Saccharomyces cerevisiae) contains a Ca2+-permeable channel of the TRP family, TRPY1, which is localized in the vacuolar membrane and contributes to cytosolic free Ca2+ ([Ca2+]cyt) elevations, for example in response to osmotic upshock. A TRPY1 homologue in the rice blast fungus is known to be important for growth and pathogenicity. To determine the role of the TRP channel family in the maize pathogen Colletotrichum graminicola, proteins homologous to TRPY1 were searched. This identified not one, but four genes in the C. graminicola genome, which had putative orthologs in other fungi, and which we named CgTRPF1 through 4. The topology of the CgTRPF proteins resembled that of TRPY1, albeit with a variable number of transmembrane (TM) domains additional to the six-TM-domain core and a diverse arrangement of putatively Ca2+-binding acidic motifs. All CgTRPF genes were expressed in axenic culture and throughout the infection of maize. Like TRPY1, all TRPF proteins of C. graminicola were localized intracellularly, albeit three of them were found not in large vacuoles, but co-localized in vesicular structures. Deletion strains for the CgTRPF genes were not altered in processes thought to involve Ca2+ release from internal stores, i.e. spore germination, the utilization of complex carbon sources, and the generation of tip-focussed [Ca2+]cyt spikes. Heterologous expression of CgTRPF1 through 4 in a tryp1Δ yeast mutant revealed that none of the channels mediated the release of Ca2+ in response to osmotic upshock. Accordingly, aequorin-based [Ca2+]cyt measurements of C. graminicola showed that in this fungus, osmotic upshock-triggered [Ca2+]cyt elevations were generated entirely by influx of Ca2+ from the extracellular space. Cgtrpf mutants did not show pathogenicity defects in leaf infection assays. In summary, our study reveals major differences between different fungi in the contribution of TRP channels to Ca2+-mediated signal transduction.

Transient Receptor Potential Channels in Microglia: Roles in Physiology and Disease

Microglia modulate the nervous system cellular environment and induce neuroprotective and neurotoxic effects. Various molecules are involved in these processes, including families of ion channels expressed in microglial cells, such as transient receptor potential (TRP) channels. TRP channels comprise a family of non-selective cation channels that can be activated by mechanical, thermal, and chemical stimuli, and which contribute to the regulation of intracellular calcium concentrations. TRP channels have been shown to be involved in cellular processes such as osmotic regulation, cytokine production, proliferation, activation, cell death, and oxidative stress responses. Given the significance of these processes in microglial activity, studies of TRP channels in microglia have focused on determining their roles in both neuroprotective and neurotoxic processes. TRP channel activity has been proposed to play an important function in neurodegenerative diseases, ischemia, inflammatory responses, and neuropathic pain. Modulation of TRP channel activity may thus be considered as a potential therapeutic strategy for the treatment of various diseases associated with alterations of the central nervous system (CNS). In this review, we describe the expression of different subfamilies of TRP channels in microglia, focusing on their physiological and pathophysiological roles, and consider their potential use as therapeutic targets in CNS diseases.

Gingerol activates noxious cold ion channel TRPA1 in gastrointestinal tract

TRPA1 channels are non-selective cation channels that could be activated by plant-derived pungent products, including gingerol, a main active constituent of ginger. Ginger could improve the digestive function; however whether ginger improves the digestive function through activating TRPA1 receptor in gastrointestinal tract has not been investigated. In the present study, gingerol was used to stimulate cell lines (RIN14B or STC-1) while depletion of extracellular calcium. TRPA1 inhibitor (rethenium red) and TRPA1 gene silencing via TRPA1-specific siRNA were also used for mechanistic studies. The intracellular calcium and secretion of serotonin or cholecystokinin were measured by fura-2/AM and ELISA. Stimulation of those cells with gingerol increased intracellular calcium levels and the serotonin or cholecystokinin secretion. The gingerol-induced intracellular calcium increase and secretion (serotonin or cholecystokinin) release were completely blocked by ruthenium red, EGTA, and TRPA1-specific siRNA. In summary, our results suggested that gingerol derived from ginger might improve the digestive function through secretion releasing from endocrine cells of the gut by inducing TRPA1-mediated calcium influx.

Antinociceptive effect of hydroalcoholic extract and isoflavone isolated from Polygala molluginifolia in mice: evidence for the involvement of opioid receptors and TRPV1 and TRPA1 channels

PURPOSE

The plants of the genus Polygala (Polygalaceae) have been used for a long time in folk medicine to treat pain and inflammation. The species Polygala molluginifolia is native to southern Brazil and is popularly known as "cânfora". The presented study analyzes the antinociceptive effect of hydroalcoholic extract from Polygala molluginifolia (HEPm) and an isoflavone (ISO) isolated from the extract, in behavioral models of pain in mice, as well as the mechanism underlying this effect.

MATERIALS AND METHODS

The phytochemical analysis of HEPm was performed through a capillary electrophoresis analysis and colorimetric test. The antinociceptive effects of HEPm and ISO (10-1000 mg/kg, i.g.) were evaluated by applying the formalin test; mechanical and thermal hyperalgesia to postoperative pain in mice. The possible involvement of opioid receptors, TRPV1 and TRPA1 channels in the antinociceptive effect of HEPm and ISO were also evaluated. Finally, the nonspecific effects of HEPm and ISO were evaluated by measuring locomotor activity (Open-field Test) and corporal temperature.

RESULTS

The 5,3',4'-trihydroxy-6″,6″-dimethylpyrano[2″,3″:7,6] isoflavone (ISO) was identified in HEPm by capillary electrophoresis analysis and selected for the experimental tests. The oral administration of HEPm or of ISO significantly inhibited the neurogenic and inflammatory phases of formalin-induced pain, edema formation and local hyperemia, without causing any change to locomotor activity. Acute and repeated treatment of animals with HEPm reduced mechanical and thermal (heat and cold) hyperalgesia in the postoperative pain. In addition, administering HEPm or ISO markedly reduced nociceptive behavior induced by the peripheral and central injection of TRPV1 and TRPA1 channels activators. Finally, the antinociception provided by the administration of HEPm or ISO was reversed by the preadministration of naloxone.

CONCLUSIONS

Taken together, these results provide the first experimental evidence of the significant antinociceptive effect of HEPm and ISO in animal models of acute pain without causing sedation or locomotor dysfunction. This effect appears to be mediated, at least in part, by the activation of opioid receptors and/or by the inhibition of TRPV1 and TRPA1 channels. Moreover, this study adds new scientific evidence and highlights the therapeutic potential of the medicinal plant Polygala molluginifolia in the development of phytomedicines with analgesic properties.

Menthol Modulates Pacemaker Potentials through TRPA1 Channels in Cultured Interstitial Cells of Cajal from Murine Small Intestine

BACKGROUND/AIMS

ICCs are the pacemaker cells responsible for slow waves in gastrointestinal (GI) smooth muscle, and generate periodic pacemaker potentials in current-clamp mode.

METHODS

The effects of menthol on the pacemaker potentials of cultured interstitial cells of Cajal (ICCs) from mouse small intestine were studied using the whole cell patch clamp technique.

RESULTS

Menthol (1 - 10 μM) was found to induce membrane potential depolarization in a concentration-dependent manner. The effects of various TRP channel antagonists were examined to investigate the receptors involved. The addition of the TRPM8 antagonist, AMTB, did not block menthol-induced membrane potential depolarizations, but TRPA1 antagonists (A967079 or HC-030031) blocked the effects of menthol, as did intracellular GDPβS. Furthermore, external and internal Ca2+ levels were found to depolarize menthol-induced membrane potentials, whereas external Na+ was not. Y-27632 (a Rho kinase inhibitor), SC-560 (a selective COX 1 inhibitor), NS-398 (a selective COX 2 inhibitor), ozagrel (a thromboxane A2 synthase inhibitor) and SQ-29548 (highly selective thromboxane receptor antagonist) were used to investigate the involvements of Rho-kinase, cyclooxygenase (COX), and the thromboxane pathway in menthol-induced membrane potential depolarizations, and all inhibitors were found to block the effect of menthol.

CONCLUSIONS

These results suggest that menthol-induced membrane potential depolarizations occur in a G-protein-, Ca2+-, Rho-kinase-, COX-, and thromboxane A2-dependent manner via TRPA1 receptor in cultured ICCs in murine small intestine. The study shows ICCs are targeted by menthol and that this interaction can affect intestinal motility.

Potential therapeutic value of TRPV1 and TRPA1 in diabetes mellitus and obesity

Diabetes mellitus and obesity, which is a major risk factor in the development of type 2 diabetes mellitus, have reached epidemic proportions worldwide including the USA. The current statistics and forecasts, both short- and long-term, are alarming and predict severe problems in the near future. Therefore, there is a race for developing new compounds, discovering new receptors, or finding alternative solutions to prevent and/or treat the symptoms and complications related to obesity and diabetes mellitus. It is well demonstrated that members of the transient receptor potential (TRP) superfamily play a crucial role in a variety of biological functions both in health and disease. In the recent years, transient receptor potential vanilloid type 1 (TRPV1) and transient receptor potential ankyrin 1 (TRPA1) were shown to have beneficial effects on whole body metabolism including glucose homeostasis. TRPV1 and TRPA1 have been associated with control of weight, pancreatic function, hormone secretion, thermogenesis, and neuronal function, which suggest a potential therapeutic value of these channels. This review summarizes recent findings regarding TRPV1 and TRPA1 in association with whole body metabolism with emphasis on obese and diabetic conditions.

Trp channels and itch

Itch is a unique sensation associated with the scratch reflex. Although the scratch reflex plays a protective role in daily life by removing irritants, chronic itch remains a clinical challenge. Despite urgent clinical need, itch has received relatively little research attention and its mechanisms have remained poorly understood until recently. The goal of the present review is to summarize our current understanding of the mechanisms of acute as well as chronic itch and classifications of the primary itch populations in relationship to transient receptor potential (Trp) channels, which play pivotal roles in multiple somatosensations. The convergent involvement of Trp channels in diverse itch signaling pathways suggests that Trp channels may serve as promising targets for chronic itch treatments.

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

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

Neuronal cell lines as model dorsal root ganglion neurons: A transcriptomic comparison

BACKGROUND

Dorsal root ganglion neuron-derived immortal cell lines including ND7/23 and F-11 cells have been used extensively as in vitro model systems of native peripheral sensory neurons. However, while it is clear that some sensory neuron-specific receptors and ion channels are present in these cell lines, a systematic comparison of the molecular targets expressed by these cell lines with those expressed in intact peripheral neurons is lacking.

RESULTS

In this study, we examined the expression of RNA transcripts in the human neuroblastoma-derived cell line, SH-SY5Y, and two dorsal root ganglion hybridoma cell lines, F-11 and ND7/23, using Illumina next-generation sequencing, and compared the results with native whole murine dorsal root ganglions. The gene expression profiles of these three cell lines did not resemble any specific defined dorsal root ganglion subclass. The cell lines lacked many markers for nociceptive sensory neurons, such as the Transient receptor potential V1 gene, but expressed markers for both myelinated and unmyelinated neurons. Global gene ontology analysis on whole dorsal root ganglions and cell lines showed similar enrichment of biological process terms across all samples.

CONCLUSIONS

This paper provides insights into the receptor repertoire expressed in common dorsal root ganglion neuron-derived cell lines compared with whole murine dorsal root ganglions, and illustrates the limits and potentials of these cell lines as tools for neuropharmacological exploration.