Protease-activated receptor 2 sensitizes the capsaicin receptor transient receptor potential vanilloid receptor 1 to induce hyperalgesia

Inflammatory proteases (mast cell tryptase and trypsins) cleave protease-activated receptor 2 (PAR2) on spinal afferent neurons and cause persistent inflammation and hyperalgesia by unknown mechanisms. We determined whether transient receptor potential vanilloid receptor 1 (TRPV1), a cation channel activated by capsaicin, protons, and noxious heat, mediates PAR2-induced hyperalgesia. PAR2 was coexpressed with TRPV1 in small- to medium-diameter neurons of the dorsal root ganglia (DRG), as determined by immunofluorescence. PAR2 agonists increased intracellular [Ca2+] ([Ca2+]i) in these neurons in culture, and PAR2-responsive neurons also responded to the TRPV1 agonist capsaicin, confirming coexpression of PAR2 and TRPV1. PAR2 agonists potentiated capsaicin-induced increases in [Ca2+]i in TRPV1-transfected human embryonic kidney (HEK) cells and DRG neurons and potentiated capsaicin-induced currents in DRG neurons. Inhibitors of phospholipase C and protein kinase C (PKC) suppressed PAR2-induced sensitization of TRPV1-mediated changes in [Ca2+]i and TRPV1 currents. Activation of PAR2 or PKC induced phosphorylation of TRPV1 in HEK cells, suggesting a direct regulation of the channel. Intraplantar injection of a PAR2 agonist caused persistent thermal hyperalgesia that was prevented by antagonism or deletion of TRPV1. Coinjection of nonhyperalgesic doses of PAR2 agonist and capsaicin induced hyperalgesia that was inhibited by deletion of TRPV1 or antagonism of PKC. PAR2 activation also potentiated capsaicin-induced release of substance P and calcitonin gene-related peptide from superfused segments of the dorsal horn of the spinal cord, where they mediate hyperalgesia. We have identified a novel mechanism by which proteases that activate PAR2 sensitize TRPV1 through PKC. Antagonism of PAR2, TRPV1, or PKC may abrogate protease-induced thermal hyperalgesia.

Neurogenic responses mediated by vanilloid receptor-1 (TRPV1) are blocked by the high affinity antagonist, iodo-resiniferatoxin

(1) Stimulation of the vanilloid receptor-1 (TRPV1) results in the activation of nociceptive and neurogenic inflammatory responses. Poor specificity and potency of TRPV1 antagonists has, however, limited the clarification of the physiological role of TRPV1. (2) Recently, iodo-resiniferatoxin (I-RTX) has been reported to bind as a high affinity antagonist at the native and heterologously expressed rat TRPV1. Here we have studied the ability of I-RTX to block a series of TRPV1 mediated nociceptive and neurogenic inflammatory responses in different species (including transfected human TRPV1). (3) We have demonstrated that I-RTX inhibited capsaicin-induced mobilization of intracellular Ca(2+) in rat trigeminal neurons (IC(50) 0.87 nM) and in HEK293 cells transfected with the human TRPV1 (IC(50) 0.071 nM). (4) Furthermore, I-RTX significantly inhibited both capsaicin-induced CGRP release from slices of rat dorsal spinal cord (IC(50) 0.27 nM) and contraction of isolated guinea-pig and rat urinary bladder (pK(B) of 10.68 and 9.63, respectively), whilst I-RTX failed to alter the response to high KCl or SP. (5) Finally, in vivo I-RTX significantly inhibited acetic acid-induced writhing in mice (ED(50) 0.42 micro mol kg(-1)) and plasma extravasation in mouse urinary bladder (ED(50) 0.41 micro mol kg(-1)). (6) In in vitro and in vivo TRPV1 activated responses I-RTX was approximately 3 log units and approximately 20 times more potent than capsazepine, respectively. This high affinity antagonist, I-RTX, may be an important tool for future studies in pain and neurogenic inflammatory models.

Ethanol elicits and potentiates nociceptor responses via the vanilloid receptor-1

The vanilloid receptor-1 (VR1) is a heat-gated ion channel that is responsible for the burning sensation elicited by capsaicin. A similar sensation is reported by patients with esophagitis when they consume alcoholic beverages or are administered alcohol by injection as a medical treatment. We report here that ethanol activates primary sensory neurons, resulting in neuropeptide release or plasma extravasation in the esophagus, spinal cord or skin. Sensory neurons from trigeminal or dorsal root ganglia as well as VR1-expressing HEK293 cells responded to ethanol in a concentration-dependent and capsazepine-sensitive fashion. Ethanol potentiated the response of VR1 to capsaicin, protons and heat and lowered the threshold for heat activation of VR1 from approximately 42 degrees C to approximately 34 degrees C. This provides a likely mechanistic explanation for the ethanol-induced sensory responses that occur at body temperature and for the sensitivity of inflamed tissues to ethanol, such as might be found in esophagitis, neuralgia or wounds.

Nonthermal activation of transient receptor potential vanilloid-1 channels in abdominal viscera tonically inhibits autonomic cold-defense effectors

An involvement of the transient receptor potential vanilloid (TRPV) 1 channel in the regulation of body temperature (T b) has not been established decisively. To provide decisive evidence for such an involvement and determine its mechanisms were the aims of the present study. We synthesized a new TRPV1 antagonist, AMG0347 [(E)-N-(7-hydroxy-5,6,7,8-tetrahydronaphthalen-1- yl)-3-(2-(piperidin-1-yl)-6-(trifluoromethyl)pyridin-3-yl)acrylamide], and characterized it in vitro. We then found that this drug is the most potent TRPV1 antagonist known to increase T b of rats and mice and showed (by using knock-out mice) that the entire hyperthermic effect of AMG0347 is TRPV1 dependent. AMG0347-induced hyperthermia was brought about by one or both of the two major autonomic cold-defense effector mechanisms (tail-skin vasoconstriction and/or thermogenesis), but it did not involve warmth-seeking behavior. The magnitude of the hyperthermic response depended on neither T b nor tail-skin temperature at the time of AMG0347 administration, thus indicating that AMG0347-induced hyperthermia results from blockade of tonic TRPV1 activation by nonthermal factors. AMG0347 was no more effective in causing hyperthermia when administered into the brain (intracerebroventricularly) or spinal cord (intrathecally) than when given systemically (intravenously), which indicates a peripheral site of action. We then established that localized intra-abdominal desensitization of TRPV1 channels with intraperitoneal resiniferatoxin blocks the T b response to systemic AMG0347; the extent of desensitization was determined by using a comprehensive battery of functional tests. We conclude that tonic activation of TRPV1 channels in the abdominal viscera by yet unidentified nonthermal factors inhibits skin vasoconstriction and thermogenesis, thus having a suppressive effect on T b. Copyright © 2007 Society for Neuroscience.

Protease-activated receptor 2 sensitizes TRPV1 by protein kinase Cepsilon- and A-dependent mechanisms in rats and mice

Proteases that are released during inflammation and injury cleave protease-activated receptor 2 (PAR2) on primary afferent neurons to cause neurogenic inflammation and hyperalgesia. PAR2-induced thermal hyperalgesia depends on sensitization of transient receptor potential vanilloid receptor 1 (TRPV1), which is gated by capsaicin, protons and noxious heat. However, the signalling mechanisms by which PAR2 sensitizes TRPV1 are not fully characterized. Using immunofluorescence and confocal microscopy, we observed that PAR2 was colocalized with protein kinase (PK) Cepsilon and PKA in a subset of dorsal root ganglia neurons in rats, and that PAR2 agonists promoted translocation of PKCepsilon and PKA catalytic subunits from the cytosol to the plasma membrane of cultured neurons and HEK 293 cells. Subcellular fractionation and Western blotting confirmed this redistribution of kinases, which is indicative of activation. Although PAR2 couples to phospholipase Cbeta, leading to stimulation of PKC, we also observed that PAR2 agonists increased cAMP generation in neurons and HEK 293 cells, which would activate PKA. PAR2 agonists enhanced capsaicin-stimulated increases in [Ca2+]i and whole-cell currents in HEK 293 cells, indicating TRPV1 sensitization. The combined intraplantar injection of non-algesic doses of PAR2 agonist and capsaicin decreased the latency of paw withdrawal to radiant heat in mice, indicative of thermal hyperalgesia. Antagonists of PKCepsilon and PKA prevented sensitization of TRPV1 Ca2+ signals and currents in HEK 293 cells, and suppressed thermal hyperalgesia in mice. Thus, PAR2 activates PKCepsilon and PKA in sensory neurons, and thereby sensitizes TRPV1 to cause thermal hyperalgesia. These mechanisms may underlie inflammatory pain, where multiple proteases are generated and released.

Anxiogenic-like effect induced by TRPV1 receptor activation within the dorsal periaqueductal gray matter in mice

Pharmacological manipulation of TRPV1 (Transient Receptor Potential Vanilloid type-1) receptors has been emerging as a novel target in the investigation of anxiety states. Here, we attempt to show the role played by the TRPV1 receptors within the dorsal periaqueductal gray matter (dPAG), a midbrain structure strongly involved in the modulation of anxiety. Anxiety was assessed by recording spatiotemporal [percent open arm entries (%OE) and percent open arm time (%OT)] and ethological [e.g., head dipping (HD), stretched-attend postures (SAP)] measures in mice exposed to the elevated plus-maze (EPM). Mice received an intra-dPAG injection of the TRPV1 agonist capsaicin (0, 0.01, 0.1 or 1.0. nmol/0.2. μL; Experiment 1) or antagonist capsazepine (0, 10, 30 or 60. nmol/0.2. μL; Experiment 2), or combined injections of capsazepine (30. nmol) and capsaicin (1.0. nmol) (Experiment 3), and were exposed to the EPM to record spatiotemporal and ethological measures. While capsaicin produced an anxiogenic-like effect (it reduced %OE and %OT and frequency of SAP and HD in the open arms), capsazepine did not change any behavior in the EPM. However, when injected before capsaicin (1.0. nmol), intra-dPAG capsazepine (30. nmol-a dose devoid of intrinsic effects) antagonized completely the anxiogenic-like effect of the TRPV1 agonist. These results suggest that the anxiogenic-like effect produced by capsaicin is primarily due to TRPV1 activation within the dPAG in mice, but that dPAG TRPV1 receptors do not exert a tonic control over defensive behavior in mice exposed to the EPM. © 2013 Elsevier B.V.

Potentiation of capsaicin receptor activity by metabotropic ATP receptors as a possible mechanism for ATP-evoked pain and hyperalgesia

The capsaicin (vanilloid) receptor, VR1, is a sensory neuron-specific ion channel that serves as a polymodal detector of pain-producing chemical and physical stimuli. It has been proposed that ATP, released from different cell types, initiates the sensation of pain by acting predominantly on nociceptive ionotropic purinoceptors located on sensory nerve terminals. In this study, we examined the effects of extracellular ATP on VR1. In cells expressing VR1, ATP increased the currents evoked by capsaicin or protons through activation of metabotropic P2Y1 receptors in a protein kinase C-dependent pathway. The involvement of Gq/11-coupled metabotropic receptors in the potentiation of VR1 response was confirmed in cells expressing both VR1 and M1 muscarinic acetylcholine receptors. In the presence of ATP, the temperature threshold for VR1 activation was reduced from 42°C to 35°C, such that normally nonpainful thermal stimuli (i.e., normal body temperature) were capable of activating VR1. This represents a novel mechanism through which the large amounts of ATP released from damaged cells in response to tissue trauma might trigger the sensation of pain.

Étude des tachykinines et de leurs dérivés peptidiques associés à la douleur neuropathique grâce à l’utilisation de modèles animaux et de la chromatographie en phase liquide couplée à la spectrométrie de masse

Thèse réalisée en co-tutelle avec l'Université Claude Bernard de Lyon 1, en France.

TRPV1 receptors modulate retinal development

We investigated the possible participation of TRPV1 channels in retinal apoptosis and overall development. Retinas from newborn, male albino rats were treated in vitro with capsazepine, a TRPV1 antagonist. The expression of cell cycle markers was not changed after TRPV1 blockade, whereas capsazepine reduced the number of apoptotic cells throughout the retina,increased ERK1/2 and p38 phosphorylation and slightly reduced JNK phosphorylation. The expression of BAD, Bcl-2, as well as integral and cleaved capsase-3 were similar in all experimental conditions. Newborn rats were kept for 2 months after receiving high doses of capsazepine. In their retinas, calbindin and parvalbumin protein levels were upregulated, but only the number of amacrine-like, parvalbumin-positive cells was increased. The numbers of calretinin, calbindin, ChAT, vimentin, PKC-alpha and GABA-positive cells were similar in both conditions. Protein expression of synapsin Ib was also increased in the retinas of capsazepine-treated rats. Calretinin, vimentin, GFAP, synapsin Ia, synaptophysin and light neurofilament protein levels were not changed when compared to control values. Our results indicate that TRPV1 channels play a role in the control of the early apoptosis that occur during retinal development, which might be dependent on MAPK signaling. Moreover, it seems that TRPV1 function might be important for neuronal and synaptic maturation in the retina. (C) 2011 ISDN. Published by Elsevier Ltd. All rights reserved.

Byrsonima intermedia A. Juss.: Gastric and duodenal anti-ulcer, antimicrobial and antidiarrheal effects in experimental rodent models

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Antinociceptive profile of (-)-spectaline: A piperidine alkaloid from Cassia leptophylla

The antinociceptive activity of (-)-spectaline (1), a piperidine alkaloid isolated from Cassia leptophylla Vog. (Leguminosae), was investigated. We have also studied the acute oral toxicity of 1 in mice and it did not show any signals of toxicity in doses lower than 400 mumol/kg. The antinociceptive effect of 1 was evaluated on chemical (acetic acid, formalin and capsaicin) and thermal (hot plate and tail flick) pain models in mice, using classical standard drugs. Dipyrone ID50 = 14.68 mumol/kg (4.8 mg/kg), in-domethacin ID50 = 0.78 mumol/kg (0.28 mg/kg) and (-)-spectaline ID50 = 48.49 mumol/kg (15.75 mg/kg), all produced a significant inhibition of acetic acid-induced abdominal writhing in mice. (-)-Spectaline was inactive in the hyperalgesic model of formalin and did not show any central analgesic activity (hot plate and tail flick models). In the capsaicin-induced neurogenic pain model, (-)-spectaline presented an important inhibitory effect with an ID50 = 20.81 mug/paw and dipyrone ID50 = 19.89 mug/ paw. The ensemble of results permitted us to identify 1 as an antinociceptive compound. The mechanism underlying this antinociceptive effect of 1 remains unknown, but the results suggest that such an effect could be related to pathways associated to vanilloid receptor systems.

Citral: A monoterpene with prophylactic and therapeutic anti-nociceptive effects in experimental models of acute and chronic pain

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Does the gastroprotective action of a medicinal plant ensure healing effects? An integrative study of the biological effects of Serjania marginata Casar. (Sapindaceae) in rats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Expression der pronozizeptiven Vanilloidrezeptoren TRPV1 und TRPV2 und des antinozizeptiven Cannabinoidrezeptors CB1 in Spinalganglienneuronen der Ratte

Nozizeptive Spinalganglienneurone detektieren mit einer Vielzahl liganden- und spannungsgesteuerter Ionenkanäle noxische Reize, d.h. Reize, die eine Gewebeschädigung bewirken können, wandeln sie in Aktionspotenzialentladungen um und leiten sie über das Rückenmark zum Gehirn weiter, wo eine Schmerzempfindung ausgelöst wird. Die pronozizeptiven transienten Rezeptor-Potenzial-Kanäle der Vanilloidrezeptorfamilie, TRPV1 und TRPV2, sind die klassischen Transduktionsmoleküle für noxische Hitzereize in den Spinalganglien und werden von Reiztemperaturen über 43°C bzw. 52°C aktiviert. Daneben finden sich auch antinozizeptive Membranproteine, wie z.B. der metabotrope Cannabinoidrezeptor CB1. Er koppelt an spannungsgesteuerte Kaliumkanäle, die neben Natrium- und Kalziumkanälen ebenfalls an der neuronalen Erregbarkeit beteiligt sind. Von den spannungsgesteuerten Kaliumkanälen könnte der Kv1.4, der einen schnell inaktivierenden A-Strom vermittelt, an antinozizeptiven Signalwegen beteiligt sein. Um die molekulare Physiologie der Regulation von Nozizeption und Antinozizeption zu charakterisieren, wurde die Expression bzw. Ko-Expression dieser Membranproteine auf der einen als auch die funktionelle Charakterisierung von TRPV1 auf der anderen Seite im Soma der Spinalganglienneurone und im heterologen Expressionssystem untersucht. TRPV1 wurde in je einem Drittel und TRPV2 in je einem Zehntel aller Spinalganglienneurone nachgewiesen. Das Expressionsmuster veränderte sich nicht zwischen verschiedenen Präparationsmethoden, die zur Aufarbeitung der Zellen für unterschiedliche experimentelle Ansätze notwendig sind. Somit können die aus Expressionsanalysen und funktionellen Untersuchungen gewonnenen Ergebnisse miteinander verglichen werden. Obwohl TRPV1 und TRPV2 in unterschiedlich großen Zellen exprimiert werden, überlappen dennoch ihre Größenverteilungen. Durch Ko-Expressionsanalysen konnten hier erstmalig TRPV1-TRPV2-ko-exprimierende Neurone detektiert werden. Mit dem neu entwickelten N-terminalen Antikörper gegen TRPV1 (3C11) konnte gezeigt werden, dass für TRPV1 verschiedene Splice-Varianten existieren. Neben den bereits bekannten Splice-Varianten wurde hier die neue Variante Vr.3’sv isoliert. Diese besitzt zwischen Exon 15 und 16 eine Insertion aus 104 Basen und exprimiert daher einen veränderten C-Terminus. Trotz dieser Veränderung bildeten sich im heterologen Expressionssystem funktionelle Kanäle aus, die im Gegensatz zu den anderen Varianten immer noch durch Capsaicin aktivierbar waren. Vr.3’sv könnte als Homo- oder Heterotetramer die Eigenschaften TRPV1-positiver Neurone beeinflussen. Bei der Bestimmung der Häufigkeit von TRPV1 in einem Gewebe ist somit die Wahl des Antikörpers von entscheidender Bedeutung. Für TRPV2 dagegen gibt es hier keine Hinweise auf Splice-Varianten. TRPV1 wird durch das Vanilloid Capsaicin aktiviert, wobei diese Substanz neurotoxisch ist und eine Degeneration von Neuronen und epidermalen Nervenfasern bewirkt. Hier wurde nun gezeigt, dass unabhängig von den Splice-Varianten nicht alle TRPV1-positiven Neurone bei langer Inkubationszeit absterben. Funktionelle Untersuchungen belegten, dass auch Capsaicin-sensitive Zellen unter dem Einfluss des Agonisten überleben können. Dieser Schutzmechanismus wird möglicherweise von den verschiedenen Splice-Varianten vermittelt. Ko-Expressionsanalysen zeigten, dass der spannungsgesteuerte Kaliumkanal Kv1.4 in nahezu allen TRPV1- aber nicht TRPV2-positiven Neuronen exprimiert wird. Desweiteren ko-exprimierten nahezu alle TRPV1-positiven Neurone auch den Cannabinoidrezeptor CB1. Diese fast vollständige Ko-Lokalisation von CB1 und Kv1.4 in nozizeptiven Spinalganglienneuronen spricht für eine funktionell synergistische Aktivität. Der Kaliumkanal kann unter der regulativen Kontrolle von CB1 als Vermittler von A-Typ-Kaliumströmen an der Kontrolle der repetitiven Entladungen in der Peripherie und der Transmitterausschüttung zentral beteiligt sein. Es ergeben sich daraus Ansatzpunkte für die Entwicklung neuer Medikamente. Mit Kv1.4-Aktivatoren und/oder peripher wirkenden Cannabinoiden könnten die Nebenwirkungen der Cannabinoide im zentralen Nervensystem umgangen werden.

Ion channels gated by heat

All animals need to sense temperature to avoid hostile environments and to regulate their internal homeostasis. A particularly obvious example is that animals need to avoid damagingly hot stimuli. The mechanisms by which temperature is sensed have until recently been mysterious, but in the last couple of years, we have begun to understand how noxious thermal stimuli are detected by sensory neurons. Heat has been found to open a nonselective cation channel in primary sensory neurons, probably by a direct action. In a separate study, an ion channel gated by capsaicin, the active ingredient of chili peppers, was cloned from sensory neurons. This channel (vanilloid receptor subtype 1, VR1) is gated by heat in a manner similar to the native heat-activated channel, and our current best guess is that this channel is the molecular substrate for the detection of painful heat. Both the heat channel and VR1 are modulated in interesting ways. The response of the heat channel is potentiated by phosphorylation by protein kinase C, whereas VR1 is potentiated by externally applied protons. Protein kinase C is known to be activated by a variety of inflammatory mediators, including bradykinin, whereas extracellular acidification is characteristically produced by anoxia and inflammation. Both modulatory pathways are likely, therefore, to have important physiological correlates in terms of the enhanced pain (hyperalgesia) produced by tissue damage and inflammation. Future work should focus on establishing, in molecular terms, how a single ion channel can detect heat and how the detection threshold can be modulated by hyperalgesic stimuli.