Capsaicin-induced Activation Research Articles

Effective suppression of Ih and INa caused by capsazepine, known to be a blocker of TRPV1 receptor

A synthetic inhibitor of capsaicin-induced TRPV1 channel activation is called capsazepine (CPZ). In this study, we aimed to explore the effects of CPZ on hyperpolarization-activated cationic current (Ih) and voltage-gated Na + current (INa) in pituitary tumor (GH3) cells. Through patch-clamp recordings, we found that CPZ concentration-dependently inhibited Ih amplitude and slowed its activation time course. The IC50 and KD values were 3.1 and 3.16 μM, respectively. CPZ also shifted the steady-state activation curve of Ih towards a more hyperpolarized potential. However, there was no change in the gating charge of the curve. A modified Markovian model predicted the CPZ-induced decrease in the voltage-dependent hysteresis of Ih. CPZ suppressed INa in GH3 cells, without altering its activation or inactivation time course. Additionally, exposure to CPZ reduced spontaneous firing. These findings suggest that CPZ’s inhibitory effects on Ih and INa are direct and not dependent on vanilloid receptor binding. This could provide light on an unidentified ionic mechanism influencing the membrane excitability of neurons and endocrine or neuroendocrine cells in vivo.

Capsaicin indirectly regulates TRPA1 via the arachidonic acid cascade, resulting in TJ opening.

Capsaicin induces the reversible opening of tight junctions (TJs) and enhances the delivery of hydrophilic macromolecules through a paracellular route. We previously revealed that TRPA1 is involved in the capsaicin-induced Ca2+ influx and TJ permeability increase, although there are no reports that capsaicin directly activates TRPA1. In this study, we investigated the upstream factors of TRPA1 using RNA-seq analysis, and found that the cyclooxygenase 2 (COX2) gene was upregulated by capsaicin. Cyclooxygenase 2 converts arachidonic acid (AA), a metabolite by phospholipase A2 (PLA2), to prostaglandins. Prostaglandin E2 (PGE2) production was stimulated by capsaicin, and capsaicin-induced Ca2+ influx was effectively inhibited by PLA2 and COX2 inhibitors. The AA-induced TJ permeability increase was inhibited by a TRPA1 antagonist, but the capsaicin- and AA-induced TJ permeability increases were hardly inhibited by a COX2 inhibitor. These results suggest that capsaicin-induced PLA2 activation and AA production are the important steps for the TJ permeability increase.

Activation of transient receptor potential vanilloid 1 ameliorates tau accumulation-induced synaptic damage and cognitive dysfunction via autophagy enhancement.

The autophagy-lysosomal pathway is important for maintaining cellular proteostasis, while dysfunction of this pathway has been suggested to drive the aberrant intraneuronal accumulation of tau protein, leading to synaptic damage and cognitive impairment. Previous studies have demonstrated that the activation of transient receptor potential vanilloid 1 (TRPV1) by capsaicin has a positive impact on cognition and AD-related biomarkers. However, the effect and mechanism of TPRV1 activation on neuronal tau homeostasis remain elusive. A mouse model of tauopathy was established by overexpressing full-length human tau in the CA3 area. Mice were fed capsaicin diet (0.0125%) or normal diet for 9 weeks. The cognitive ability, synaptic function, tau phosphorylation levels, and autophagy markers were detected. In vitro, capsaicin-induced alterations in cellular autophagy and tau degradation were characterized using two cell models. Besides, various inhibitors were applied to validate the role of TRPV1-mediated autophagy enhancement in tau clearance. We observed that TRPV1 activation by capsaicin effectively mitigates hippocampal tau accumulation-induced synaptic damages, gliosis, and cognitive impairment in vivo. Capsaicin promotes the degradation of abnormally accumulated tau through enhancing autophagic function in neurons, which is dependent on TRPV1-mediated activation of AMP-activated protein kinase (AMPK) and subsequent inhibition of the mammalian target of rapamycin (mTOR). Blocking AMPK activation abolishes capsaicin-induced autophagy enhancement and tau degradation in neurons. Our findings reveal that capsaicin-induced TRPV1 activation confers neuroprotection by restoring neuronal tau homeostasis via modulating cellular autophagy and provides additional evidence to support the potential of TRPV1 as a therapeutic target for tauopathies.

Capsaicin: A Potential Treatment to Improve Cerebrovascular Function and Cognition in Obesity and Ageing.

Impaired cognition is the primary symptom of dementia, which can lead to functional disability and reduced quality of life among an increasingly ageing population. Ageing is associated with increased oxidative stress, chronic low-grade systemic inflammation, and endothelial dysfunction, which reduces cerebrovascular function leading to cognitive decline. Chronic low-grade systemic inflammatory conditions, such as obesity, exacerbate this decline beyond normal ageing and predispose individuals to neurodegenerative diseases, such as dementia. Capsaicin, the major pungent molecule of chilli, has recently demonstrated improvements in cognition in animal models via activation of the transient receptor potential vanilloid channel 1 (TRPV1). Capsaicin-induced TRPV1 activation reduces adiposity, chronic low-grade systemic inflammation, and oxidative stress, as well as improves endothelial function, all of which are associated with cerebrovascular function and cognition. This review examines the current literature on capsaicin and Capsimax, a capsaicin supplement associated with reduced gastrointestinal irritation compared to capsaicin. Acute and chronic capsaicin treatment can improve cognition in animals. However, studies adequately assessing the effects of capsaicin on cerebrovascular function, and cognition in humans do not exist. Capsimax may be a potentially safe therapeutic intervention for future clinical trials testing the effects of capsaicin on cerebrovascular function and cognition.

Characterization of trigeminal C-fiber reactivity through capsaicin-induced release of calcitonin gene-related peptide.

We hypothesized that the response of trigeminal dermal blood flow (DBF) in the trigeminal system and consecutive expansion of flare response to capsaicin would differ from the somatosensory system (arm). We also investigated whether there are differences between patients with migraine and healthy controls (HC). Functional differences between the trigeminal and extracephalic somatosensory systems may partly explain the susceptibility for headaches in patients with migraine. Capsaicin-induced activation of nociceptive C-fibers in the skin is mainly mediated by calcitonin gene-related peptide (CGRP) and induces cutaneous vessel dilatation and flare response. Female patients with migraine (n=38) and age-matched HC (n=35) underwent DBF measurement at baseline and after topical capsaicin administration using laser speckle imaging. DBF before and after capsaicin stimulation was analyzed over ophthalmic nerve/maxillary nerve/mandibular nerve (V1/V2/V3) dermatomes and the forearm as an extracephalic control. Capsaicin-induced DBF increased more in the trigeminal dermatomes than on the forearm. The V1 dermatome showed a smaller increase of DBF in patients with migraine compared to HC. Our results suggest that the trigeminovascular system reacts differently from extracephalic areas, which may explain the trigeminal susceptibility to CGRP-mediated pain attacks. By demonstrating a different reactivity of the V1 dermatome in patients with migraine, our finding suggests that the first trigeminal branch is functionally different from the second and third branches; however, only in patients with migraine.

Decreased heat sensitivity of lungfish TRPV1 revealed by the heterologous expression system

In this study, we focused on TRPV1 of African lungfish, Protopterus annectens. During drought at high temperature, African lungfish can survive by undergoing into aestivation in mud cocoons. Therefore, lungfish is considered to have some specialized heat-sensor, TRPV1, for heat tolerance. Further, lungfish which shares similarities with fishes and amphibians, is one of important species for investigating the fish-tetrapod transition. Since fish TRPV1 and tetrapod TRPV1 have some differences, character of lungfish TRPV1 attracts attention. Here, we first cloned TRPV1 paralogue from lungfish, Protopterus annectens (lfTRPV1) and determined the chemical and thermal sensitivities of lfTRPV1 by two-electrode voltage clamp method using frog oocytes. We detected activation of lfTRPV1 by acid and 2-APB, but capsaicin-induced activation was not observed. The sensitivity to acid of lfTRPV1 was similar to that of rat TRPV1 (rTRPV1), but the 2-APB sensitivity of lfTRPV1 was relatively weaker than rTRPV1. Heat stimulation up to 44 °C did not activate lfTRPV1 and the heat-activation was not detected even on acid condition of pH6. This dramatically decreased heat-sensitivity of TRPV1 may contribute the heat tolerance of African lungfish. Moreover, this might be the property of ancient tetrapod-type TRPV1 gene.

The Natural Chemotherapeutic Capsaicin Activates AMPK through LKB1 Kinase and TRPV1 Receptors in Prostate Cancer Cells.

The natural bioactive compound capsaicin has been reported to have anticancer activity, although the underlying mechanism of action has not been completely clarified. Herein, we investigated the mechanism whereby capsaicin exerts antitumor effects on prostate cancer cells. We found that capsaicin activated AMP-activated kinase (AMPK) and promoted cell death in the LKB1-expressing prostate cancer cell lines LNCaP and PC3, but not in the liver kinase B1 (LKB1)-null cell line DU-145. Capsaicin treatment stimulated LKB1 phosphorylation and activated AMPK in LKB1-expressing cells. In addition, LKB1 silencing in LNCaP and PC3 cells abrogated capsaicin-induced AMPK activation, while the overexpression of LKB1 by lentiviral infection in DU-145 cells induced capsaicin-triggered AMPK phosphorylation. Moreover, the calcium/calmodulin-dependent kinase kinase 2 (CaMKK2) inhibitor STO-609 did not modify the activation of AMPK induced by capsaicin, suggesting a CaMKK2-independent mechanism. Capsaicin-induced LKB1 phosphorylation was dependent on the transient receptor potential cation channel subfamily V member 1 (TRPV1), since TRPV1 knocked down by shRNA abolished LKB1 and AMPK phosphorylation in LKB1-expressing cells. Altogether, our results showed that capsaicin affected AMPK activity in an LKB1- and TRPV1-dependent fashion, linking TRPV1 with cell fate. These data also suggest that capsaicin may be a rational chemotherapeutic option for prostate tumors.

Acute High-glucose Exposure Potentiates The Response To Capsaicin-induced Trpv1 Activation In Group Iv Muscle Afferents.

Acute High-glucose Exposure Potentiates The Response To Capsaicin-induced Trpv1 Activation In Group Iv Muscle Afferents.

Probing temperature and capsaicin-induced activation of TRPV1 channel via computationally guided point mutations in its pore and TRP domains

In a recent computational study, we revealed some mechanistic aspects of TRPV1 (transient receptor potential channel 1) thermal activation and gating and proposed a set of probable functionally important residues — “hot spots” that have not been characterized experimentally yet. In this work, we analyzed TRPV1 point mutants G643A, I679A + A680G, and K688G/P combining molecular modeling, biochemistry, and electrophysiology. The substitution G643A reduced maximal conductivity that resulted in a normal response to moderate stimuli, but a relatively weak response to more intensive activation. I679A + A680G channel was severely toxic for oocytes most probably due to abnormally increased basal activity of the channel (“always open” gates). The replacement K688G presumably facilitated movements of TRP domain and disturbed its coupling to the pore, thus leading to spontaneous activation and enhanced desensitization of the channel. Finally, mutation K688P was suggested to impair TRP domain directed movement, and the mutated channel showed ~100-fold less sensitivity to the capsaicin, enhanced desensitization and weaker activation by the heat. Our results provide a better understanding of TRPV1 thermal and capsaicin-induced activation and gating. These observations provide a structural basis for understanding some aspects of TRPV1 channel functioning and depict potentially pathogenic mutations.

Modulation of the extrinsic tongue muscle activity in response to bronchopulmonary C-fiber activation following midcervical contusion in the rat.

This study was designed to investigate extrinsic tongue muscle activity in response to bronchopulmonary C-fiber activation following midcervical spinal contusion in the rat. Esophageal pressure and electromyogram of the extrinsic tongue muscles (genioglossus and hyoglossus) were monitored before and after inhalation of capsaicin (25 and 100 µg/mL) at the acute (3 days), subchronic (12-16 days), and chronic (52-65 days) injured stages following unilateral midcervical spinal contusion. Three days after injury, the preinspiratory burst amplitude of the extrinsic tongue muscle at baseline was significantly greater in midcervical spinal-contused animals than in sham animals. At this time, capsaicin induced a significant reduction in both preinspiratory and inspiratory activity of the extrinsic tongue muscle in sham but not contused animals at the acute stage. During the chronic injured stage, capsaicin at 100 µg/mL induced stronger suppression of preinspiratory genioglossus muscle activity in the contused animals than in sham animals. These results demonstrated that cervical spinal cord injury alters upper airway motor outputs and their reflex modulation by bronchopulmonary C-fibers. The compensatory increase in respiratory activity of the extrinsic tongue muscle early after cervical spinal cord injury may help to maintain upper airway patency. However, under the condition of chronic cervical spinal cord injury, the increased suppression of genioglossus muscle activity by bronchopulmonary C-fiber activation may increase the risk of airway obstruction following chronic cervical spinal cord injury.NEW & NOTEWORTHY Tongue muscle activity plays an important role in the regulation of upper airway patency. This study aimed to investigate the respiratory activity of the extrinsic tongue muscle in response to capsaicin-induced bronchopulmonary C-fiber activation following cervical spinal cord contusion. Midcervical spinal-contused animals exhibited a greater baseline preinspiratory burst amplitude of the extrinsic tongue muscle and were resistant to inhaled capsaicin-induced reduction of respiratory tongue muscle activity at the acute injured stage. However, inhalation of capsaicin caused a more severe attenuation of preinspiratory activity of the extrinsic tongue muscle at the chronic injured stage. These results suggest that the upper airway may be predisposed to collapse in response to bronchopulmonary C-fiber activation following chronic cervical spinal cord injury.

Short- and Long-Distance Allosteric Coupling in Capsaicin-Induced TRPV1 Activation

Short- and Long-Distance Allosteric Coupling in Capsaicin-Induced TRPV1 Activation

Heat attenuates sensitivity of mammalian cells to capsaicin.

The transient receptor potential (TRP) channels are thermo-sensors, and transient receptor potential vanilloid (TRPV)1 and V4 are widely expressed in primary afferent neurons and nonneuronal cells. Although heat acclimation is considered as changes of thermoregulatory responses by thermo-effectors to heat, functional changes of TRP channels in heat acclimation has not been fully elucidated. Here, we investigated whether heat acclimation induces capsaicin tolerance. NIH3T3 cells were incubated at 39.5°C. We determined the expression level of TRPV1 and TRPV4 messenger RNA (mRNA), performed cellular staining of TRPV1 and TRPV4, and investigated actin assembly and activation of the extracellular signal-regulated kinase (ERK). Exposure to moderate heat decreased the levels of TRPV1 but not TRPV4 mRNA. It also induced stress fiber formation and the intensity of TRPV1 seemed to be decreased by chronic heat stimuli. In addition, heat acclimation attenuated the capsaicin-induced activation of ERK. Heat acclimation may induce capsaicin tolerance via the downregulation of TRPV1.

Activation of temperature-sensitive TRPV1-like receptors in ARC POMC neurons reduces food intake

Proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARC) respond to numerous hormonal and neural signals, resulting in changes in food intake. Here, we demonstrate that ARC POMC neurons express capsaicin-sensitive transient receptor potential vanilloid 1 receptor (TRPV1)-like receptors. To show expression of TRPV1-like receptors in ARC POMC neurons, we use single-cell reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, electrophysiology, TRPV1 knock-out (KO), and TRPV1-Cre knock-in mice. A small elevation of temperature in the physiological range is enough to depolarize ARC POMC neurons. This depolarization is blocked by the TRPV1 receptor antagonist and by Trpv1 gene knockdown. Capsaicin-induced activation reduces food intake that is abolished by a melanocortin receptor antagonist. To selectively stimulate TRPV1-like receptor-expressing ARC POMC neurons in the ARC, we generate an adeno-associated virus serotype 5 (AAV5) carrying a Cre-dependent channelrhodopsin-2 (ChR2)–enhanced yellow fluorescent protein (eYFP) expression cassette under the control of the two neuronal POMC enhancers (nPEs). Optogenetic stimulation of TRPV1-like receptor-expressing POMC neurons decreases food intake. Hypothalamic temperature is rapidly elevated and reaches to approximately 39 °C during treadmill running. This elevation is associated with a reduction in food intake. Knockdown of the Trpv1 gene exclusively in ARC POMC neurons blocks the feeding inhibition produced by increased hypothalamic temperature. Taken together, our findings identify a melanocortinergic circuit that links acute elevations in hypothalamic temperature with acute reductions in food intake.

Novel capsaicin-induced parameters of microcirculation in migraine patients revealed by imaging photoplethysmography

BackgroundThe non-invasive biomarkers of migraine can help to develop the personalized medication of this disorder. In testing of the antimigraine drugs the capsaicin-induced skin redness with activated TRPV1 receptors in sensory neurons associated with the release of the migraine mediator CGRP has already been widely used.MethodsFourteen migraine patients (mean age 34.6 ± 10.2 years) and 14 healthy volunteers (mean age 29.9 ± 9.7 years) participated in the experiment. A new arrangement of imaging photoplethysmography recently developed by us was used here to discover novel sensitive parameters of dermal blood flow during capsaicin applications in migraine patients.ResultsBlood pulsation amplitude (BPA) observed as optical-intensity waveform varying synchronously with heartbeat was used for detailed exploration of microcirculatory perfusion induced by capsicum patch application. The BPA signals, once having appeared after certain latent period, were progressively rising until being saturated. Capsaicin-induced high BPA areas were distributed unevenly under the patch, forming “hot spots.” Interestingly the hot spots were much more variable in migraine patients than in the control group. In contrast to BPA, a slow component of waveforms related to the skin redness changed significantly less than BPA highlighting the latter parameter as the potential sensitive biomarker of capsaicin-induced activation of the blood flow. Thus, in migraine patients, there is a non-uniform (both in space and in time) reaction to capsaicin, resulting in highly variable openings of skin capillaries.ConclusionBPA dynamics measured by imaging photoplethysmography could serve as a novel sensitive non-invasive biomarker of migraine-associated changes in microcirculation.

Parathyroid hormone-related peptide activates and modulates TRPV1 channel in human DRG neurons.

Parathyroid hormone-related peptide (PTHrP) is associated with advanced tumor growth and metastasis, especially in breast, prostate and myeloma cancers that metastasize to bones, resulting in debilitating chronic pain conditions. Our recent studies revealed that the receptor for PTHrP, PTH1R, is expressed in mouse DRG sensory neurons, and its activation leads to flow-activation and modulation of TRPV1 channel function, resulting in peripheral heat and mechanical hypersensitivity. In order to verify the translatability of our findings in rodents to humans, we explored whether this signalling axis operates in primary human DRG sensory neurons. Analysis of gene expression data from recently reported RNA deep sequencing experiments performed on mouse and human DRGs reveals that PTH1R is expressed in DRG and tibial nerve. Furthermore, exposure of cultured human DRG neurons to PTHrP leads to slow-sustained activation of TRPV1 and modulation of capsaicin-induced channel activation. Both activation and modulation of TRPV1 by PTHrP were dependent on PKC activity. Our findings suggest that functional PTHrP/PTH1R-TRPV1 signalling exists in human DRG neurons, which could contribute to local nociceptor excitation in the vicinity of metastatic bone tumor microenvironment.

Activation of temperature-sensitive TRPV1-like receptors in ARC POMC neurons reduces food intake.

Proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARC) respond to numerous hormonal and neural signals, resulting in changes in food intake. Here, we demonstrate that ARC POMC neurons express capsaicin-sensitive transient receptor potential vanilloid 1 receptor (TRPV1)-like receptors. To show expression of TRPV1-like receptors in ARC POMC neurons, we use single-cell reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, electrophysiology, TRPV1 knock-out (KO), and TRPV1-Cre knock-in mice. A small elevation of temperature in the physiological range is enough to depolarize ARC POMC neurons. This depolarization is blocked by the TRPV1 receptor antagonist and by Trpv1 gene knockdown. Capsaicin-induced activation reduces food intake that is abolished by a melanocortin receptor antagonist. To selectively stimulate TRPV1-like receptor-expressing ARC POMC neurons in the ARC, we generate an adeno-associated virus serotype 5 (AAV5) carrying a Cre-dependent channelrhodopsin-2 (ChR2)–enhanced yellow fluorescent protein (eYFP) expression cassette under the control of the two neuronal POMC enhancers (nPEs). Optogenetic stimulation of TRPV1-like receptor-expressing POMC neurons decreases food intake. Hypothalamic temperature is rapidly elevated and reaches to approximately 39 °C during treadmill running. This elevation is associated with a reduction in food intake. Knockdown of the Trpv1 gene exclusively in ARC POMC neurons blocks the feeding inhibition produced by increased hypothalamic temperature. Taken together, our findings identify a melanocortinergic circuit that links acute elevations in hypothalamic temperature with acute reductions in food intake.

A synthetic peptide blocking TRPV1 activation inhibits UV-induced skin responses

BackgroundTransient receptor potential type 1 (TRPV1) can be activated by ultraviolet (UV) irradiation, and mediates UV-induced matrix metalloproteinase (MMP)-1 and proinflammatory cytokines in keratinocytes. Various chemicals and compounds targeting TRPV1 activation have been developed, but are not in clinical use mostly due to their safety issues. ObjectiveWe aimed to develop a novel TRPV1-targeting peptide to inhibit UV-induced responses in human skin. MethodsWe designed and generated a novel TRPV1 inhibitory peptide (TIP) which mimics the specific site in TRPV1 (aa 701-709: Gln-Arg-Ala-Ile-Thr-Ile-Leu-Asp-Thr, QRAITILDT), Thr705, and tested its efficacy of blocking UV-induced responses in HaCaT, mouse, and human skin. ResultsTIP effectively inhibited capsaicin-induced calcium influx and TRPV1 activation. Treatment of HaCaT with TIP prevented UV-induced increases of MMP-1 and pro-inflammatory cytokines such as interleukin (IL)-6 and tumor necrosis factor-α. In mouse skin in vivo, TIP inhibited UV-induced skin thickening and prevented UV-induced expression of MMP-13 and MMP-9. Moreover, TIP attenuated UV-induced erythema and the expression of MMP-1, MMP-2, IL-6, and IL-8 in human skin in vivo. ConclusionThe novel synthetic peptide targeting TRPV1 can ameliorate UV-induced skin responses in vitro and in vivo, providing a promising therapeutic approach against UV-induced inflammation and photoaging.

A novel form of capsaicin-modified amygdala LTD mediated by TRPM1

Recently we have shown that capsaicin attenuates the strength of LTP in the lateral amygdala (LA) and demonstrated that this effect is mediated by the transient receptor potential (TRP) channel TRPV1. Here we further show that capsaicin, which is thought to act primarily through TRPV1, modifies long term depression (LTD) in the LA. Yet the application of various TRPV1 antagonists does not reverse this effect and it remains in TRPV1-deficient mice. In addition, voltage gated calcium channels, nitric oxide and CB1 receptors are not involved. Using pharmacology and TRPM1−/− mice, our electrophysiological data indicate that capsaicin-induced activation of TRPM1 channels contribute to the induction of LA-LTD. Whereas LA-LTD in general depends on the acitvation of NMDA receptors- and group II metabotropic glutamate receptors (mGluR), the modifying effect of capsaicin on LA-LTD via TRPM1 appears to be specifically mediated by group I mGluRs and in interaction with another member of the TRP family, TRPC5. Additionally, intact GABAergic transmission is required for the capsaicin-effect to take place. This is the first documentation that beside their function in the retina TRPM1 proteins are expressed in the brain and have a functional relevance in modifying synaptic plasticity.

Distinct BOLD fMRI Responses of Capsaicin-Induced Thermal Sensation Reveal Pain-Related Brain Activation in Nonhuman Primates.

BackgroundApproximately 20% of the adult population suffer from chronic pain that is not adequately treated by current therapies, highlighting a great need for improved treatment options. To develop effective analgesics, experimental human and animal models of pain are critical. Topically/intra-dermally applied capsaicin induces hyperalgesia and allodynia to thermal and tactile stimuli that mimics chronic pain and is a useful translation from preclinical research to clinical investigation. Many behavioral and self-report studies of pain have exploited the use of the capsaicin pain model, but objective biomarker correlates of the capsaicin augmented nociceptive response in nonhuman primates remains to be explored.MethodologyHere we establish an aversive capsaicin-induced fMRI model using non-noxious heat stimuli in Cynomolgus monkeys (n = 8). BOLD fMRI data were collected during thermal challenge (ON:20 s/42°C; OFF:40 s/35°C, 4-cycle) at baseline and 30 min post-capsaicin (0.1 mg, topical, forearm) application. Tail withdrawal behavioral studies were also conducted in the same animals using 42°C or 48°C water bath pre- and post- capsaicin application (0.1 mg, subcutaneous, tail).Principal FindingsGroup comparisons between pre- and post-capsaicin application revealed significant BOLD signal increases in brain regions associated with the ‘pain matrix’, including somatosensory, frontal, and cingulate cortices, as well as the cerebellum (paired t-test, p<0.02, n = 8), while no significant change was found after the vehicle application. The tail withdrawal behavioral study demonstrated a significant main effect of temperature and a trend towards capsaicin induced reduction of latency at both temperatures.ConclusionsThese findings provide insights into the specific brain regions involved with aversive, ‘pain-like’, responses in a nonhuman primate model. Future studies may employ both behavioral and fMRI measures as translational biomarkers to gain deeper understanding of pain processing and evaluate the preclinical efficacy of novel analgesics.

A novel 3-(4,5-diphenyl-1,3-oxazol-2-yl)propanal oxime compound is a potent Transient Receptor Potential Ankyrin 1 and Vanilloid 1 (TRPA1 and V1) receptor antagonist

Transient Receptor Potential Ankyrin 1 and Vanilloid 1 (TRPA1, TRPV1) ion channels expressed on nociceptive primary sensory neurons are important regulators of pain and inflammation. TRPA1 is activated by several inflammatory mediators including formaldehyde and methylglyoxal that are products of the semicarbazide-sensitive amine-oxidase enzyme (SSAO). SZV-1287 is a new 3-(4,5-diphenyl-1,3-oxazol-2-yl)propanal oxime SSAO inhibitor, its chemical structure is similar to other oxime derivatives described as TRPA1 antagonists. Therefore, we investigated its effects on TRPA1 and TRPV1 receptor activation on the cell bodies and peripheral terminals of primary sensory neurons and TRPA1 or TRPV1 receptor-expressing cell lines.Calcium influx in response to the TRPA1 agonist allyl-isothiocyanate (AITC) (200μM) and the TRPV1 stimulator capsaicin (330nM) in rat trigeminal neurons or TRPA1 and TRPV1 receptor-expressing cell lines was measured by microfluorimetry or radioactive 45Ca2+ uptake experiments. Calcitonin gene-related peptide (CGRP) release as the indicator of 100μM AITC – or 100nM capsaicin-induced peripheral sensory nerve terminal activation was measured by radioimmunoassay.SZV-1287 (100, 500 and 1000nM) exerted a concentration-dependent significant inhibition on both AITC- and capsaicin-evoked calcium influx in trigeminal neurons and TRPA1 or TRPV1 receptor-expressing cell lines. It also significantly inhibited the TRPA1, but not the TRPV1 activation-induced CGRP release from the peripheral sensory nerve endings in a concentration-dependent manner. In contrast, the reference SSAO inhibitor LJP 1207 with a different structure had no effect on TRPA1 or TRPV1 activation in either model system.This is the first evidence that our novel oxime compound SZV-1287 originally developed as a SSAO inhibitor has a potent dual antagonistic action on TRPA1 and TRPV1 ion channels on primary sensory neurons.