Transient Receptor Potential Vanilloid 1 Antagonist Research Articles

Effects of an intrathecal TRPV1 antagonist, SB366791, on morphine-induced itch, body temperature, and antinociception in mice.

PurposeTransient receptor potential vanilloid 1 (TRPV1) not only is activated by multiple stimuli but also is involved with histamine-induced itch. The effects of TRPV1 on morphine-induced itch are unknown. We examined the effects of intrathecal administration of TRPV1 antagonist on morphine-induced itch, body temperature, and antinociception for mice.MethodsEach C57/BL6j mouse was intrathecally administered with one of the following solutions: morphine, SB366791 (as the TRPV1 antagonist), morphine + SB366791, saline, or vehicle. For each mouse, each instance of observed scratching behavior was counted, the body temperature was measured, and the nociceptive threshold was determined using the tail-immersion test.ResultsSB366791 dose-dependently reduced the scratching behavior induced by the administration of morphine. SB366791 and the morphine + SB366791 groups did not manifest an increase in body temperature. Antinociceptive effects were observed to occur dose-dependently for morphine but not for SB366791. Compared with morphine alone, the administration of morphine + SB366791 did not reduce significant antinociceptive effects.ConclusionWe propose that an intrathecal TRPV1 antagonist, SB366791, reduced morphine-induced itch without causing hyperthermia and did not suppress morphine-induced antinociception for mice.

Blocking the transient receptor potential vanilloid-1 does not reduce the exercise pressor reflex in healthy rats.

Controversy exists regarding the role played by transient receptor potential vanilloid-1 (TRPV1) in evoking the exercise pressor reflex. Here, we determine the role played by TRPV1 in evoking this reflex while assessing possible confounding factors arising from TRPV1 antagonists or from the vehicle in which they were dissolved. The exercise pressor reflex was evoked in decerebrated, anesthetized Sprague-Dawley rats by electrical stimulation of the tibial nerve to contract the triceps surae muscles statically. This procedure was repeated before and after injection of the TRPV1 blockers: capsazepine (100 μg/100 μL), ruthenium red (100 μg/100 μL), or iodoresiniferatoxin (IRTX; 1 μg/100 μL). We found that capsazepine decreased the exercise pressor reflex when the drug was dissolved in DMSO (-10 ± 9 mmHg; P = 0.015; n = 7). However, similar reduction was found when DMSO alone was injected (-8 ± 5 mmHg; P = 0.023; n = 5). Capsazepine, dissolved in ethanol (2 ± 6 mmHg; P = 0.49; n = 7), ruthenium red (-4 ± 12 mmHg; P = 0.41; n = 7), or IRTX (4 ± 18 mmHg; P = 0.56; n = 7), did not significantly decrease the exercise pressor reflex. In addition, we found that capsazepine and ruthenium red had "off-target" effects. Capsazepine decreased the pressor response evoked by intra-arterial injection of bradykinin (500 ng/kg; -12 ± 13 mmHg; P = 0.028; n = 9) and α-β-methylene ATP (10 μg/kg; -7 ± 8 mmHg; P = 0.019; n = 10), whereas ruthenium red decreased the ability of the muscle to produce and sustain force (-99 ± 83 g; P = 0.020; n = 7). Our data therefore suggest that TRPV1 does not play a role in evoking the exercise pressor reflex. Additionally, given their strong off-target effects, capsazepine and ruthenium red should not be used for studying the role played by TRPV1 in evoking the exercise pressor reflex.

TRPV1 Antagonists as Novel Anti-Diabetic Agents: Regulation of Oral Glucose Tolerance and Insulin Secretion Through Reduction of Low-Grade Inflammation?

With a global prevalence among adults over 18 years of age approaching 9%, Type 2 diabetes mellitus (T2DM) has reached pandemic proportions and represents a major unmet medical need. To date, no disease modifying treatment is available for T2DM patients. Accumulating evidence suggest that the sensory nervous system is involved in the progression of T2DM by maintaining low-grade inflammation via the vanilloid (capsaicin) receptor, Transient Receptor Potential Vanilloid-1 (TRPV1). In this study, we tested the hypothesis that TRPV1 is directly involved in glucose homeostasis in rodents. TRPV1 receptor knockout mice (Trpv1−/−) and their wild-type littermates were kept on high-fat diet for 15 weeks. Moreover, Zucker obese rats were given the small molecule TRPV1 antagonist, N-(4-Tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide (BCTC), per os twice-a-day or vehicle for eight days. Oral glucose tolerance and glucose-stimulated insulin secretion was improved by both genetic inactivation (Trpv1−/− mice) and pharmacological blockade (BCTC) of TRPV1. In the obese rat, the improved glucose tolerance was accompanied by a reduction in inflammatory markers in the mesenteric fat, suggesting that blockade of low-grade inflammation contributes to the positive effect of TRPV1 antagonism on glucose metabolism. We propose that TRPV1 could be a promising therapeutic target in T2DM by improving glucose intolerance and correcting dysfunctional insulin secretion.

PGE2/EP4 receptor and TRPV1 channel are involved in repeated restraint stress-induced prolongation of sensitization pain evoked by subsequent PGE2 challenge

Prevalence of prior stressful experience is linked to high incidence of chronic pain. Stress, particularly repeated stress, is known to induce maladaptive neuroplasticity along peripheral and central pain transmission pathways. These maladaptive neuroplastic events facilitate sensitization of nociceptive neurons and transition from acute to chronic pain. Pro-inflammatory and pain mediators are involved in inducing neuroplasticity. Pain mediators such as prostaglandin E2 (PGE2), EP4 receptor and transient receptor potential vanilloid-1 (TRPV1) contribute to the genesis of chronic pain. In this study, we examined the role of PGE2/EP4 signaling and TRPV1 signaling in repeated restraint stress-induced prolongation of sensitization pain, a model for transition from acute to chronic pain, in both in vivo and in vitro models. We found that pre-exposure to single restraint stress induced analgesia that masked sensitization pain evoked by subsequent PGE2 challenge. However, pre-exposure to 3d consecutive restraint stress not only prolonged sensitization pain, but also increased stress hormone corticosterone (CORT) in serum, COX2 levels in paw skin, and EP4 and TRPV1 levels in dorsal root ganglion (DRG) and paw skin. Pre-exposure to CORT for 3d, not 1d, also prolonged sensitization pain evoked by PGE2. Co-injection of glucocorticoid receptor (GR) antagonist RU486, COX2 inhibitor NS-398, EP4 receptor antagonist L161,982 or TRPV1 antagonist capsazepine prevented 3d restraint stress prolonged sensitization pain evoked by PGE2. In DRG cultures, CORT increased EP4 and TRPV1 protein levels through GR activation. These data suggest that PGE2/EP4 signaling and TRPV1 signaling in peripheral pain pathway contribute to repeated stress-predisposed transition from acute to chronic pain.

Electroacupuncture Pretreatment Elicits Neuroprotection Against Cerebral Ischemia-Reperfusion Injury in Rats Associated with Transient Receptor Potential Vanilloid 1-Mediated Anti-Oxidant Stress and Anti-Inflammation.

Electroacupuncture (EA) pretreatment, electrical stimulation using metal needle at specific acupoints in advance, possesses the potential to prevent cerebral ischemia-reperfusion injury (CIRI). Transient receptor potential vanilloid 1 (TRPV-1) has been indicated to take part in cerebral protection of EA; however, the detailed mechanisms remain unclear. The aim of this study was to investigate whether neuroprotection of EA pretreatment against CIRI is associated with TRPV-1 and explore the underlying mechanisms. Middle cerebral artery occlusion (MCAO) was performed to induce CIRI after EA pretreatment at Baihui (GV20), bilateral Shenshu (BL23), and Sanyinjiao (SP6) acupoints in rats. Neurological deficit scores, infarct volumes, oxidative stress damage, inflammatory cytokine production, MAPK signaling activation, and the expression of TRPV-1 were assessed. EA pretreatment lowered neurological deficit scores, reduced infarct volumes, impeded oxidative stress injury, inhibited inflammatory cytokine production, curbed P38 phosphorylation, and suppressed TRPV-1 expression in MCAO rats. Attributing to inhibition of TRPV-1 expression, AMG-517 (TRPV-1 antagonist) showed the synergistic effect with EA pretreatment on the neuroprotection against ischemia-reperfusion injury. However, TRPV-1 agonists capsaicin significantly abrogated the neuroprotective effects of EA pretreatment in MCAO rats accompanying enhancement of TRPV-1 expression. These findings indicated EA pretreatment exerted neuroprotection in rats with cerebral ischemia-reperfusion injury, which at least partially were associated with TRPV1-mediated anti-oxidant stress and anti-inflammation via inhibiting P38 MAPK activation.

TRPV1 and TRPA1 in Lung Inflammation and Airway Hyperresponsiveness Induced by Fine Particulate Matter (PM2.5).

Exposure to fine particulate matter (PM2.5) has been associated with lung inflammation and airway hyperresponsiveness (AHR). Transient receptor potential (TRP) vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1) both may play important roles in lung inflammation and AHR. We investigated whether PM2.5-induced lung inflammation and AHR could be prevented by blocking TRPV1 and TRPA1 channels. Mice were injected intraperitoneally with AMG9810 (30 mg/kg, a TRPV1 antagonist) or A967079 (30 mg/kg, a TRPA1 antagonist) or their combination or vehicle (PBS) one hour before intranasal instillation of PM2.5 (7.8 mg/kg) or vehicle (PBS) for two consecutive days, and then the mice were studied 24 h later. All pretreatments inhibited PM2.5-induced AHR and inflammatory infiltration in the lung tissue and decreased inflammatory cytokine levels in the bronchoalveolar lavage fluid, together with oxidant levels in the lung. AMG9810 inhibited MFF expression and increased MFN2 expression while A967079 inhibited DRP1 expression and increased OPA1 expression; combined pretreatment reduced MFF and DPR1 expression and increased MFN2 and OPA1 expression. All pretreatments inhibited the activation of the TLR4/NF-κB pathway, while A967079 alone, and combined with AMG9810 also reduced the activation of the NLRP3/caspase-1 pathway. Both TRPV1 and TRPA1 channels play an important role in PM2.5-induced lung inflammation and AHR. However, inhibition of the TRPA1 channel or combined inhibition of TRPA1 and TRPV1 channels resulted in greater inhibitory effect on PM2.5-induced lung injury through regulating the mitochondrial fission/fusion proteins and inhibiting the TLR4/NF-κB and NLRP3/caspase-1 pathways.

Analgesic transient receptor potential vanilloid-1-active compounds inhibit native and recombinant T-type calcium channels.

T-type calcium (Cav 3) and transient receptor potential vanilloid-1 (TRPV1) channels play central roles in the control of excitability in the peripheral nervous system and are regarded as potential therapeutic pain targets. Modulators that either activate or inhibit TRPV1-mediated currents display analgesic properties in various pain models despite opposing effects on their connate target, TRPV1. We explored the effects of TRPV1-active compounds on Cav 3-mediated currents. Whole-cell patch clamp recordings were used to examine the effects of TRPV1-active compounds on rat dorsal root ganglion low voltage-activated calcium currents and recombinant Cav 3 isoforms in expression systems. The classical TRPV1 agonist capsaicin as well as TRPV1 antagonists A-889425, BCTC, and capsazepine directly inhibited Cav 3 channels. These compounds altered the voltage-dependence of activation and inactivation of Cav 3 channels and delayed their recovery from inactivation, leading to a concomitant decrease in T-type current availability. The TRPV1 antagonist capsazepine potently inhibited Cav 3.1 and 3.2 channels (KD <120nM), as demonstrated by its slow off rate. In contrast, neither the TRPV1 agonists, Palvanil and resiniferatoxin, nor the TRPV1 antagonist AMG9810 modulated Cav 3-mediated currents. Analgesic TRPV1-active compounds inhibit Cav 3 currents in native and heterologous systems. Hence, their analgesic effects may not be exclusively attributed to their actions on TRPV1, which has important implications in the current understanding of nociceptive pathways. Importantly, our results highlight the need for attention in the experimental design used to address the analgesic properties of Cav 3 channel inhibitors.

TRPV1 Contributes to Cerebral Malaria Severity and Mortality by Regulating Brain Inflammation

Transient receptor potential vanilloid 1 (TRPV1) is a Ca+2-permeable channel expressed on neuronal and nonneuronal cells, known as an oxidative stress sensor. It plays a protective role in bacterial infection, and recent findings indicate that this receptor modulates monocyte populations in mice with malaria; however, its role in cerebral malaria progression and outcome is unclear. By using TRPV1 wild-type (WT) and knockout (KO) mice, the importance of TRPV1 to this cerebral syndrome was investigated. Infection with Plasmodium berghei ANKA decreased TRPV1 expression in the brain. Mice lacking TRPV1 were protected against Plasmodium-induced mortality and morbidity, a response that was associated with less cerebral swelling, modulation of the brain expression of endothelial tight-junction markers (junctional adhesion molecule A and claudin-5), increased oxidative stress (via inhibition of catalase activity and increased levels of H2O2, nitrotyrosine, and carbonyl residues), and diminished production of cytokines. Plasmodium load was not significantly affected by TRPV1 ablation. Repeated subcutaneous administration of the selective TRPV1 antagonist SB366791 after malaria induction increased TRPV1 expression in the brain tissue and enhanced mouse survival. These data indicate that TRPV1 channels contribute to the development and outcome of cerebral malaria.

Protective effects of TRPV1 inhibition against sevoflurane-induced cell death

Sevoflurane is a widely used inhalational anesthetic that can induce developmental neurotoxicity, leading to cognitive dysfunction. In this study, we assessed the role of transient receptor potential vanilloid 1 (TRPV1) in mediating sevoflurane activation and whether the TRPV1 antagonist could prevent anesthesia-induced cell death. Here, we demonstrated that the expression of TRPV1 was increased after sevoflurane treatment, and pretreatment with TRPV1 antagonist SB366791 could attenuate the effect of sevoflurane on TRPV1 expression. Moreover, the inhibition of TRPV1 could prevent sevoflurane-induced cell death. The findings of this study provide novel insights into the treatment of general anesthesia-induced developmental neurotoxicity and even cognitive impairment.

A Single Injection of N-Oleoyldopamine, an Endogenous Agonist for Transient Receptor Potential Vanilloid-1, Induced Brain Hypothermia, but No Neuroprotective Effects in Experimentally Induced Cerebral Ischemia in Rats.

Targeted temperature management, or therapeutic hypothermia, is a potent neuroprotective approach after ischemic brain injury. Hypothermia should be induced as soon as possible after the onset of acute stroke to assure better outcomes. Accordingly, drugs with a fast-acting hypothermic effect sustainable through the period of emergency transportation to hospital would have clinical advantages. Activation of the transient receptor potential vanilloid-1 (TRPV1) can induce hypothermia. Our immunohistochemical investigations confirmed that TRPV1 was distributed to perivascular and periventricular regions of the rat brain, where TRPV1 can be easily detected by TRPV1 agonists. An endogenous TRPV1 selective agonist, N-oleoyldopamine (OLDA), and a synthetic antagonist, AMG 9810, were injected intraperitoneally into healthy adult male Wister rats, and brain and core temperatures and gross motor activities were monitored. Comparison with baseline temperatures showed that TRPV1 injection immediately induced mild hypothermia (p < 0.05 in brain and p < 0.01 in body), and AMG 9810 induced immediate mild hyperthermia (not significant). However, the OLDA-induced hypothermia did not decrease lesion volume after middle carotid artery occlusion in rats. Relative to vehicle, OLDA yielded poorer outcomes and AMG 9810 yielded better outcomes in neurological scores and lesion size. Our study showed that, as an agonist of TRPV1, OLDA has suitable hypothermia-inducing properties, but did not decrease lesion volume. Therefore, the search for novel TRPV1 agonists and/or antagonists providing hypothermia and neuroprotection should continue. Further investigations should also target OLDA-induced transient hypothermia combined with long-term hypothermia maintenance with surface cooling, which mimics the anticipated clinical use of this class of drug.

Dry eye sensitizes cool cells to capsaicin-induced changes in activity via TRPV1.

Corneal cool cells are sensitive to the ocular fluid status of the corneal surface and may be responsible for the regulation of basal tear production. Previously, we have shown that dry eye, induced by lacrimal gland excision (LGE) in rats, sensitized corneal cool cells to the transient receptor potential melastatin 8 (TRPM8) agonist menthol and to cool stimulation. In the present study, we examined the effect of dry eye on the sensitivity of cool cells to the transient receptor potential vanilloid 1 (TRPV1) agonist capsaicin. Single-unit recordings in the trigeminal ganglion were performed 7-10 days after LGE. At a concentration of 0.3 μM, capsaicin did not affect ongoing or cool-evoked activity in control animals yet facilitated ongoing activity and suppressed cool-evoked activity in LGE animals. At higher concentrations (3 μM), capsaicin continued to facilitate ongoing activity in LGE animals but suppressed ongoing activity in control animals. Higher concentrations of capsaicin also suppressed cool-evoked activity in both groups of animals, with an overall greater effect in LGE animals. In addition to altering cool-evoked activity, capsaicin enhanced the sensitivity of cool cells to heat in LGE animals. Capsaicin-induced changes were prevented by the application of the TRPV1 antagonist capsazepine. With the use of fluorescent in situ hybridization, TRPV1 and TRPM8 expression was examined in retrograde tracer-identified corneal neurons. The coexpression of TRPV1 and TRPM8 in corneal neurons was significantly greater in LGE-treated animals when compared with sham controls. These results indicate that LGE-induced dry eye increases TRPV1-mediated responses in corneal cool cells at least in part through the increased expression of TRPV1. NEW & NOTEWORTHY Corneal cool cells are known to detect drying of the ocular surface. Our study is the first to report that dry eye induced alterations in cool cell response properties, including the increased responsiveness to noxious heat and activation by capsaicin. Along with the changes in cell response properties, it is possible these neurons also function differently in dry eye, relaying information related to the perception of ocular irritation in addition to regulating tearing and blinking.

Effects of intrathecal transient receptor potential vanilloid 1 blocker on cervical distension induced visceral pain response

Objective: With the aid of an acute visceral pain model of uterine cervical distension (UCD), the present study aimed to observe the effects of intrathecal administration of transient receptor potential vanilloid 1 (TRPV1) antagonist SB-366791 on UCD induced-visceral nociception as well as its involved molecular mechanisms. Methods: A total of 30 Sprague-Dawley-derived adult virgin female rats were used. UCD model was established under isoflurane inhalation anesthesia. Briefly, a lower abdominal incision at midline was made to expose the uteral cervix, two metal rods were inserted through both sides of the cervix separately, one rod was fixed and the other one was connected to a pulley system with application of manual weighted traction (0, 25, 50, 75 or 100 g) for simulating 1 h of cervical distension. In addition, 12 Sprague-Dawley-derived adult virgin female rats were subjected to intrathecal catheter implantation, and UCD was established 7 days later. The rats were divided randomly into two groups; one group was administrated with intrathecal SB-366791 while the other was administrated with the same volume of saline as control. The 75 g distension force was then applied for an hour and the electromyographic (EMG) of musculus rectus abdominis, heart rate as well as respiratory frequency were measured continuously during the surgery. The spinal cord (T(12)-L(2)) was collected 30 minutes after UCD for the detection of changes of c-FOS and TRPV1 expression. Results: UCD increased EMG activity (P<0.05) and c-FOS expression (P<0.05) in the deep dorsal horn region and central canal of the spinal cord (T(12)-L(2)) in a stimuli-dependent manner, the expression of TRPV1 in the T(12)-L(2) spinal cord also increased in response to UCD stimulation (P<0.05). Compared with the saline group, intrathecal SB-366791 significantly decreased EMG activity (P<0.05) as well as spinal c-FOS (P<0.05) expression induced by UCD. Conclusions: UCD in rats increases EMG activity of musculus rectus abdominis as well as spinal c-FOS and TRPV1 expression. Intrathecal administration of TRPV1 antagonist SB-366791 significantly decreases the visceral nociception induced by UCD.

TRPV1 Exaggerates Cardiovascular Responses to Physical Exercise in Normotensive but Not in Hypertensive Rats

IntroductionThe transient receptor potential vanilloid‐1 (TRPV1) is an ion channel involved in several physiological responses, including arterial pressure regulation. This channel seems to have an important role in endothelium‐dependent and ‐independent vasodilation. In spontaneously hypertensive rats (SHRs), chronic treatment with a TRPV1 agonist decreases mean arterial pressure, which makes the TRPV1 a potential target for hypertension treatment. We have already shown that in normotensive rats, the acute blockage of TRPV1 channels leads to an exaggerated increase in mean arterial pressure and heart rate during physical exercise. Therefore, in this study we investigated whether the role of TRPV1 channels in cardiovascular responses during physical exercise is affected by arterial hypertension.MethodsMale Wistar normotensive and Wistar‐Kyoto SHRs (16–19 wk) were implanted with an intra‐arterial (ascending aorta) catheter to measure arterial pressure. The rats received an intra‐arterial injection of a TRPV1 antagonist N‐(4‐[6‐(4‐trifluoromethyl‐phenyl)‐pyrimidin‐4‐yloxy]‐benzothiazol‐2‐yl)‐acetamide (AMG 517, 60 μg/kg) or vehicle (20% ethanol in saline) and then were subjected to an incremental‐speed treadmill running at 24°C until fatigue. The pulsatile arterial pressure (which allowed the determination of mean, systolic and diastolic arterial pressures and the heart rate) was measured throughout the exercise period.ResultsIn both normotensive rats and SHR, the incremental exercise increased mean, systolic and diastolic arterial pressures and the heart rate (for mean arterial pressure, fatigue: Normotensive: 126 ± 3 mmHg; SHR: 165 ± 4 mmHg versus beginning of exercise: Normotensive: 108 ± 4 mmHg; SHR: 158 ± 5 mmHg). As expected, in the normotensive rats, the AMG 517 led to a greater exercise‐induced increases in the mean, systolic and diastolic arterial pressures and in the heart rate. In contrast, the TRPV1 antagonist had no effect on any of the cardiovascular variables evaluated in the SHRs (for mean arterial pressure, min 19: AMG 517: 161 ± 5 mmHg; Vehicle 164 ± 4 mmHg). The changes (values at fatigue minus values at the beginning of exercise) in the mean arterial pressure (Normotensive: 20.1 ± 1.8 mmHg versus SHR 10.5 ± 3.3 mmHg; p &lt; 0.05) as well as in the heart rate (Normotensive: 196 ± 13 bpm versus SHR: 149 ± 9 bpm, p &lt; 0.05) were greater in normotensive rats than in SHRs when the incremental exercise was performed after the TRPV1 antagonist injection.ConclusionsDespite inducing marked alterations in blood pressure regulation in the normotensive rats, the TRPV1 antagonist injection did not modify the cardiovascular responses to exercise in the SHRs, which suggests that the arterial hypertension affects the TRPV1‐mediated mechanism involved in arterial pressure regulation during exercise.Support or Funding InformationCAPES, CNPq and FAPEMIG.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Role of TRPV1 and TRPA1 Ion Channels in Inflammatory Bowel Diseases: Potential Therapeutic Targets?

Inflammatory bowel diseases (IBD) have long been recognized to be accompanied by pain resulting in high morbidity. Transient receptor potential vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1) ion channels located predominantly on the capsaicin-sensitive sensory neurons play a complex role in hyperalgesia and neurogenic inflammation. This review provides an overview of their expression and role in intestinal inflammation, in particular colitis, that appears to be virtually inconsistent based on the thorough investigations of the last twenty years. However, preclinical results with pharmacological interventions, as well as scarcely available human studies, more convincingly point out the potential therapeutic value of TRPV1 and TRPA1 antagonists in colitis and visceral hypersensitivity providing future therapeutical perspectives through a complex, unique mechanism of action for drug development in IBD.

Transient receptor potential Vanilloid 1-based gene therapy alleviates orthodontic pain in rats

Orthodontic pain that is induced by tooth movement is an important sequela of orthodontic treatment and has a significant effect on patient quality of life. Studies have shown that the high expression of transient receptor potential vanilloid 1 (TRPV1) in trigeminal ganglions plays a vital role in the transmission and modulation of orofacial pain. However, little is known about the role of TRPV1 in orthodontic pain. In this study, male Sprague–Dawley rats were randomly assigned to six groups to study the role of TRPV1 in the modulation of tooth-movement pain. The expression levels of TRPV1 mRNA and protein were determined by real-time PCR and western blot, respectively. Moreover, pain levels were assessed using the rat grimace scale (RGS). The role of TRPV1 in modulating tooth-movement pain was examined by injecting a TRPV1 antagonist into the trigeminal ganglia of rats. A lentivirus containing a TRPV1 shRNA sequence was constructed and transduced into the rats’ trigeminal ganglia. The results showed that the expression levels of TRPV1 protein and mRNA were elevated following tooth-movement pain. Pain levels increased rapidly on the 1st day, peaked on the 3rd day and returned to baseline on the 14th day. The TRPV1 antagonist significantly reduced tooth-movement pain. The lentivirus containing a TRPV1 shRNA sequence was able to inhibit the expression of TRPV1 and relieved tooth-movement pain. In conclusion, TRPV1-based gene therapy may be a treatment strategy for the relief of orthodontic pain.

Chondroitin sulfate attenuates acid-induced augmentation of the mechanical response in rat thin-fiber muscle afferents in vitro.

Exercise-induced tissue acidosis augments the exercise pressor reflex (EPR). One reason for this may be acid-induced mechanical sensitization in thin-fiber muscle afferents, which is presumably related to EPR. Acid-induced sensitization to mechanical stimulation has been reported to be attenuated in cultured primary-sensory neurons by exogenous chondroitin sulfate (CS) and chondroitinase ABC, suggesting that the extracellular matrix CS proteoglycan is involved in this sensitization. The purpose of this study was to clarify whether acid-induced sensitization of the mechanical response in the thin-fiber muscle afferents is also suppressed by exogenous CS and chondroitinase ABC using a single-fiber recording technique. A total of 88 thin fibers (conduction velocity <15.0 m/s) dissected from 86 male Sprague-Dawley rats were identified. A buffer solution at pH 6.2 lowered their mechanical threshold and increased their response magnitude. Five minutes after CS (0.3 and 0.03%) injection near the receptive field, these acid-induced changes were significantly reduced. No significant difference in attenuation was detected between the two CS concentrations. Chondroitinase ABC also significantly attenuated this sensitization. The control solution (0% CS) did not significantly alter the mechanical sensitization. Furthermore, no significant differences were detected in this sensitization and CS-based suppression between fibers with and without acid-sensitive channels [transient receptor potential vanilloid 1 (TRPV1), acid-sensing ion channel (ASIC)]. In addition, this mechanical sensitization was not changed by TRPV1 and ASIC antagonists, suggesting that these ion channels are not involved in the acid-induced mechanical sensitization of muscle thin-fiber afferents. In conclusion, CS administration has a potential to attenuate the acidosis-induced exaggeration of muscle mechanoreflex. NEW & NOTEWORTHY We found that exogenous chondroitin sulfate attenuated acid-induced mechanical sensitization in thin-fiber muscle afferents that play a crucial role in the exercise pressor reflex. This finding suggests that extracellular matrix chondroitin sulfate proteoglycans may be involved in the mechanism of acid-induced mechanical sensitization and that daily intake of chondroitin sulfate may potentially attenuate this amplification of muscle mechanoreflex and therefore reduce muscle pain related to acidic muscle conditions.

Attenuation of glutamatergic and nitrergic system contributes to the antidepressant-like effect induced by capsazepine in the forced swimming test.

The transient receptor potential vanilloid 1 (TRPV1) can modulate stress-related behaviours, thus representing an interesting target for new antidepressant drugs. TRPV1 can trigger glutamate release and nitric oxide synthesis in the brain, mechanisms also involved in the neurobiology of depression. However, it is not known if these mechanisms are involved in TRPV1-induced behavioural effects. Therefore, the aim of this study was to verify if the antidepressant-like effect induced by a TRPV1 antagonist in mice submitted to the forced swimming test (FST) would be facilitated by combined treatment with neuronal nitric oxide synthase (nNOS) inhibition and N-methyl-D-aspartate (NMDA) blockade. Male Swiss mice were given (intracerebroventricular) injections of capsazepine (CPZ) (TRPV1 antagonist - 0.05/0.1/0.3/0.6 nmol/µl), and AP7 (NMDA antagonist - 1/3/10 nmol/µl) or N-propyl-L-arginine (NPA, nNOS inhibitor - 0.001/0.01/0.1 nmol/µl), and 10 min later, submitted to an open field test, and immediately afterwards, to the FST. An additional group received coadministration of CPZ and AP7 or CPZ and NPA, in subeffective doses. The results demonstrated that CPZ (0.1 nmol/µl), AP7 (3 nmol/µl) and NPA (0.01/0.1 nmol/µl) induced antidepressant-like effects. Moreover, coadministration of subeffective doses of CPZ and AP7 or CPZ and NPA induced significant antidepressant-like effects. Altogether, the data indicate that blockade of TRPV1 receptors by CPZ induces antidepressant-like effects and that both nNOS inhibition and NMDA blockade facilitate CPZ effects in the FST.

TRPV1 variants impair intracellular Ca2+ signaling and may confer susceptibility to malignant hyperthermia

PurposeMalignant hyperthermia (MH) is a pharmacogenetic disorder arising from uncontrolled muscle calcium release due to an abnormality in the sarcoplasmic reticulum (SR) calcium-release mechanism triggered by halogenated inhalational anesthetics. However, the molecular mechanisms involved are still incomplete. MethodsWe aimed to identify transient receptor potential vanilloid 1(TRPV1) variants within the entire coding sequence in patients who developed sensitivity to MH of unknown etiology. In vitro and in vivo functional studies were performed in heterologous expression system, trpv1−/− mice, and a murine model of human MH. ResultsWe identified TRPV1 variants in two patients and their heterologous expression in muscles of trpv1−/− mice strongly enhanced calcium release from SR upon halogenated anesthetic stimulation, suggesting they could be responsible for the MH phenotype. We confirmed the in vivo significance by using mice with a knock-in mutation (Y524S) in the type I ryanodine receptor (Ryr1), a mutation analogous to the Y522S mutation associated with MH in humans. We showed that the TRPV1 antagonist capsazepine slows the heat-induced hypermetabolic response in this model. ConclusionWe propose that TRPV1 contributes to MH and could represent an actionable therapeutic target for prevention of the pathology and also be responsible for MH sensitivity when mutated.

Differences in the effects of TRPV1 antagonists on energy metabolism in mice.

Transient receptor potential vanilloid 1 (TRPV1) is a nociceptive cation channel that is activated by heat, protons and chemical ligands such as capsaicin. We investigated the roles of the capsaicin receptor, TRPV1, in controlling the energy metabolism of the whole body. It has been reported that the activation of TRPV1 by its agonists enhances energy metabolism. In this study, we used a respiratory gas analysis system to examine whether the inhibition of TRPV1 changes energy metabolism in mice. In addition, we examined the contributions of different modes of TRPV1 activation (heat, protons and capsaicin) to determine the influence of 3 different TRPV1 antagonists on energy metabolism. Here, we showed that intragastric administration of AMG517, a nonselective antagonist of TRPV1 (for heat, protons and capsaicin), enhanced energy metabolism as much as did intraperitoneal administration. On the other hand, intraperitoneal administration of AMG9810, a nonselective antagonist like AMG517, enhanced energy expenditure more than intragastric administration. However, the administration of JYL1421, a TRPV1 antagonist that very strongly inhibits TRPV1 activated by capsaicin, did not change energy metabolism. Taken together, these results suggest that the type of TRPV1 antagonists and the routes of its administration have different effects on energy metabolism in a normal body. Surprisingly, co-administration of JYL1421 and capsaicin significantly enhanced the energy metabolism more than administration of capsaicin alone. These results support the possibility that an unconventional mechanism is responsible for the increase in energy metabolism that occurs via TRPV1 inhibition.

258 - The transient receptor potential vanilloid 1 (TRPV1) channel is a critical factor in allergen-induced innate immune responses in the airway epithelium

The airway epithelium plays a critical role in innate responses to asthma-relevant protease allergens, such as house dust mite (HDM) or Alternaria alternata (ALT), by rapid secretion of IL-1 family alarmins, such as interleukin (IL)-1α and IL-33, that orchestrate appropriate type 2 immune responses. Previous studies indicate that allergen-induced IL-33 secretion is mediated by protease-activated receptors (PAR2) and type 2 purinergic receptors (P2RY2), which induce Ca2+-dependent signaling and activation of the NADPH oxidase dual oxidase 1 (DUOX1). Transient receptor potential (TRP) Ca2+ channels such as TRP Vanilloid 1 (TRPV1) are important in e.g. pain responses, often in coordination with PAR2 and P2YR2 activation, and TRPV1 has recently been implicated in asthma pathology. Using a panel of pharmacological inhibitors and activators of P2YR2, PAR2, and TRPV1, we observed that each of these receptors can provoke activation of DUOX1 and secretion of IL-33 in primary human nasal epithelial (HNE) cells. Further mechanistic studies using primary mouse tracheal epithelial cells (MTECs) or human bronchial epithelial cells (HBE1) confirmed these findings, and showed that TRPV1 contributes importantly to innate responses to HDM and ALT, and the danger signal ATP which activates P2YR2, as shown by activation of DUOX1-dependent H2O2 production, activation of epidermal growth factor receptor signaling, and rapid secretion of IL-33, which were prevented using TRPV1 antagonists or TRPV1-siRNA. Strikingly, inhibition or siRNA silencing of P2YR2 also prevented innate responses to the TRPV1 activator capsaicin, highlighting a close functional relationship of these airway epithelial surface receptors in the innate allergen responses. Finally, airway IL-33 secretion and subsequent type 2 cytokine production in mice in response to acute airway HDM challenge were markedly impaired in TRPV1-deficient mice. Overall, our studies indicate a complex relationship between various receptor types in epithelial responses to environmental triggers, and highlight the importance of TRPV1 in such epithelial responses.