Application Of Capsaicin Research Articles

Reflex regulation of breathing by the paratrigeminal nucleus via multiple bulbar circuits.

Sensory neurons of the jugular vagal ganglia innervate the respiratory tract and project to the poorly studied medullary paratrigeminal nucleus. In the present study, we used neuroanatomical tracing, pharmacology and physiology in guinea pig to investigate the paratrigeminal neural circuits mediating jugular ganglia-evoked respiratory reflexes. Retrogradely traced laryngeal jugular ganglia neurons were largely (> 60%) unmyelinated and expressed the neuropeptide substance P and calcitonin gene-related peptide, although a population (~ 30%) of larger diameter myelinated jugular neurons was defined by the expression of vGlut1. Within the brainstem, vagal afferent terminals were confined to the caudal two-thirds of the paratrigeminal nucleus. Electrical stimulation of the laryngeal mucosa evoked a vagally mediated respiratory slowing that was mimicked by laryngeal capsaicin application. These laryngeal reflexes were modestly reduced by neuropeptide receptor antagonist microinjections into the paratrigeminal nucleus, but abolished by ionotropic glutamate receptor antagonists. D,L-Homocysteic acid microinjections into the paratrigeminal nucleus mimicked the laryngeal-evoked respiratory slowing, whereas capsaicin microinjections evoked a persistent tachypnoea that was insensitive to glutamatergic inhibition but abolished by neuropeptide receptor antagonists. Extensive projections from paratrigeminal neurons were anterogradely traced throughout the pontomedullary respiratory column. Dual retrograde tracing from pontine and ventrolateral medullary termination sites, as well as immunohistochemical staining for calbindin and neurokinin 1 receptors, supported the existence of different subpopulations of paratrigeminal neurons. Collectively, these data provide anatomical and functional evidence for at least two types of post-synaptic paratrigeminal neurons involved in respiratory reflexes, highlighting an unrecognised complexity in sensory processing in this region of the brainstem.

Therapeutic Applications of Capsaicin in Upper Airways.

Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is the substance responsible of the irritation caused by the contact of chili peppers with the skin or mucous membranes. This protoalkaloid acts by stimulating the transient receptor potential cation channel subfamily V member 1 (TRPV1), which is mainly expressed by nociceptive fibers of peripheral sensory neurons, but is also present in the central nervous system, and in some non-neuronal cells. Following the initial, intense neuronal excitation, a brief refractory period occurs. However, repeated and massive exposures to capsaicin can impair nociceptive fiber function for weeks or months. During this lapse of time, disorders related to the hyperreactivity of peripheral nociceptors are abolished or greatly reduced. Capsaicin has been utilized to treat several diseases of upper airways. The objective of this review was to report the latest findings on the use of Capsaicin in the treatment of upper airway diseases. Capsaicin effectiveness has been proved in non allergic rhinitis. Some studies suggest that this substance may be also effective in nasal polyposis and in the burning mouth syndrome. No clear evidence has been obtained about its use in allergic rhinitis. To date, the use of capsaicin to treat upper airway diseases is still limited in clinical practice. This may originate by the lack of strong, conclusive evidences of its effectiveness, by the variety of therapeutic schemes used in literature, and finally by the unpleasant effects of the exposure to capsaicin, which are only partly relieved by the pretreatment with local anesthetics.

Orexin-1 receptors in the rostral ventromedial medulla are involved in the modulation of capsaicin evoked pulpal nociception and impairment of learning and memory.

To investigate the role of rostral ventromedial medulla orexin-1 receptors in the modulation of orofacial nociception as well as nociception-induced learning and memory impairment in adult male rats. Pulpal nociception was induced by intradental application of capsaicin (100μg) into the incisors of rats. Orexin-1 receptors agonist (orexin-A, 10, 25 and 50pmolL-1 rat-1 ) and antagonist (SB-334867-A, 40 and 80nmolL-1 rat-1 ) were microinjected into the rostral ventromedial medulla prior to capsaicin administration. Total time spent on nocifensive behaviour was recorded by direct visualization of freely moving rats whilst learning and memory were evaluated by the Morris water maze test. One-way analysis of variance and repeated-measures were used for the statistical analysis. Capsaicin-treated rats had a significant increase of nocifensive behaviours (P<0.001), as well as learning and memory impairment (P< 0.001). However, intraventromedial medulla prior micro-injection of orexin-A (50pmolL-1 rat-1 ) significantly reduced the nociceptive behaviour (P<0.001). This effect was blocked by pre-treatment with SB334867-A (80nmolL-1 rat-1 ). Orexin-A (50pmolL-1 rat-1 ) also inhibited nociception-induced learning and memory deficits. Moreover, administration of SB-334867-A (80nmolL-1 rat-1 ) plus orexin-A (50pmolL-1 rat-1 ) had no effect on learning and memory deficits induced by capsaicin. The data suggest that rostral ventromedial medulla orexin-A receptors are involved in pulpal nociceptive modulation and improvement of learning and memory deficits induced by intradental application of capsaicin.

Expression of TRPV1 channels by Cajal-Retzius cells and layer-specific modulation of synaptic transmission by capsaicin in the mouse hippocampus.

By taking advantage of calcium imaging and electrophysiology, we provide direct pharmacological evidence for the functional expression of TRPV1 channels in hippocampal Cajal-Retzius cells. Application of the TRPV1 activator capsaicin powerfully enhances spontaneous synaptic transmission in the hippocampal layers that are innervated by the axons of Cajal-Retzius cells. Capsaicin-triggered calcium responses and membrane currents in Cajal-Retzius cells, as well as layer-specific modulation of spontaneous synaptic transmission, are absent when the drug is applied to slices prepared from TRPV1- /- animals. We discuss the implications of the functional expression of TRPV1 channels in Cajal-Retzius cells and of the observed TRPV1-dependent layer-specific modulation of synaptic transmission for physiological and pathological network processing. The vanilloid receptor TRPV1 forms complex polymodal channels that are expressed by sensory neurons and play a critical role in nociception. Their distribution pattern and functions in cortical circuits are, however, much less understood. Although TRPV1 reporter mice have suggested that, in the hippocampus, TRPV1 is predominantly expressed by Cajal-Retzius cells (CRs), direct functional evidence is missing. As CRs powerfully excite GABAergic interneurons of the molecular layers, TRPV1 could play important roles in the regulation of layer-specific processing. Here, we have taken advantage of calcium imaging with the genetically encoded indicator GCaMP6s and patch-clamp techniques to study the responses of hippocampal CRs to the activation of TRPV1 by capsaicin, and have compared the effect of TRPV1 stimulation on synaptic transmission in layers innervated or non-innervated by CRs. Capsaicin induced both calcium responses and membrane currents in ∼50% of the cell tested. Neither increases of intracellular calcium nor whole-cell currents were observed in the presence of the TRPV1 antagonists capsazepine/Ruthenium Red or in slices prepared from TRPV1 knockout mice. We also report a powerful TRPV1-dependent enhancement of spontaneous synaptic transmission onto interneurons with dendritic trees confined to the layers innervated by CRs. In conclusion, our work establishes that functional TRPV1 is expressed by a significant fraction of CRs and we propose that TRPV1 activity may regulate layer-specific synaptic transmission in the hippocampus. Lastly, as CR density decreases during postnatal development, we also propose that functional TRPV1 receptors may be related to mechanisms involved in CR progressive reduction by calcium-dependent toxicity/apoptosis.

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.

RENAL SYMPATHETIC AND SENSORY NERVES DO NOT DRIVE HYPERTENSION IN A POLYCYSTIC KIDNEY DISEASE RAT MODEL

Objective: Catheter-based renal denervation (RDN) is used to treat hypertension however recent clinical trials have cast doubt on previously reported effects. This study aims to determine if RDN improves systolic blood pressure, renal function and autonomic dysfunction in a hypertensive rodent model due to polycystic kidney disease (PKD).Design and method: Lewis polycystic kidney rats (LPK) underwent total, selective sensory or sham RDN by periaxonal application of phenol, capsaicin or normal saline, respectively, at 6-weeks-old. Animals then underwent 1) euthanasia at 7-weeks-old, 10-weeks-old or 14-weeks-old or 2) repeat procedure at 10-weeks-old and euthanasia at 14-weeks-old. Blood pressure was measured by radiotelemetry and treatment efficacy determined using renal immunohistochemistry for sensory [calcitonin gene-related peptide [(CGRP)] and sympathetic nerve [tyrosine hydroxylase (TH)] markers. Renal function was determined by plasma creatinine and urea. Autonomic function was assessed using baroreflex sensitivity (BRS at low frequency, αLF and high frequency, αHF). Results: Cortical TH labelling was significantly depleted at 1-week, but returned to ∼23% and ∼32% of control levels by 4-week and 8-week post-total RDN respectively. Pelvic CGRP labelling was largely abolished by 1-week, but returned to ∼43% and ∼80% of control levels by 4-week and 8-week post-total RDN, and to 67% and 97% by 4-week and 8-week post-sensory RDN. Neither total RDN nor sensory RDN reduced SBP in the LPK rats (total vs. sensory vs. sham, 202 ± 22 vs. 213 ± 7 vs. 205 ± 12 mmHg, P = 0.5) between 7–10 weeks. Repeat total RDN did not have any additional impact on SBP compared to a single procedure or shams between 11–14 weeks (P = 0.48). Neither total nor sensory RDN affected αLF (total vs. sensory vs. sham, 1.1 ± 0.1 vs. 1.1 ± 0.0 vs. 1.2 ± 0.0 ms/mmHg, P = 0.6) or αHF (total vs. sensory vs. sham, 2.2 ± 0.2 vs. 1.8 ± 0.1 vs. 2.1 ± 0.1 ms/mmHg, P = 0.1) between 7–10 weeks. Between 11–14 weeks, there was no significant difference in BRS between all groups. Neither procedure worsened plasma creatinine or urea. Conclusions: We conclude that renal sympathetic and sensory nerves do not drive hypertension or autonomic dysfunction in the LPK model of PKD. Furthermore, PKD patients as a cohort might not benefit from the RDN procedure.

Sympatho-excitatory response to pulmonary chemosensitive spinal afferent activation in anesthetized, vagotomized rats.

The sensory innervation of the lung is well known to be innervated by nerve fibers of both vagal and sympathetic origin. Although the vagal afferent innervation of the lung has been well characterized, less is known about physiological effects mediated by spinal sympathetic afferent fibers. We hypothesized that activation of sympathetic spinal afferent nerve fibers of the lung would result in an excitatory pressor reflex, similar to that previously characterized in the heart. In this study, we evaluated changes in renal sympathetic nerve activity (RSNA) and hemodynamics in response to activation of TRPV1‐sensitive pulmonary spinal sensory fibers by agonist application to the visceral pleura of the lung and by administration into the primary bronchus in anesthetized, bilaterally vagotomized, adult Sprague‐Dawley rats. Application of bradykinin (BK) to the visceral pleura of the lung produced an increase in mean arterial pressure (MAP), heart rate (HR), and RSNA. This response was significantly greater when BK was applied to the ventral surface of the left lung compared to the dorsal surface. Conversely, topical application of capsaicin (Cap) onto the visceral pleura of the lung, produced a biphasic reflex change in MAP, coupled with increases in HR and RSNA which was very similar to the hemodynamic response to epicardial application of Cap. This reflex was also evoked in animals with intact pulmonary vagal innervation and when BK was applied to the distal airways of the lung via the left primary bronchus. In order to further confirm the origin of this reflex, epidural application of a selective afferent neurotoxin (resiniferatoxin, RTX) was used to chronically ablate thoracic TRPV1‐expressing afferent soma at the level of T1–T4 dorsal root ganglia pleura. This treatment abolished all sympatho‐excitatory responses to both cardiac and pulmonary application of BK and Cap in vagotomized rats 9–10 weeks post‐RTX. These data suggest the presence of an excitatory pulmonary chemosensitive sympathetic afferent reflex. This finding may have important clinical implications in pulmonary conditions inducing sensory nerve activation such as pulmonary inflammation and inhalation of chemical stimuli.

Psychophysical and vasomotor evidence for interdependency of TRPA1 and TRPV1-evoked nociceptive responses in human skin: an experimental study.

The TRPA1 and TRPV1 receptors are important pharmaceutical targets for antipruritic and analgesic therapy. Obtaining further knowledge on their roles and interrelationship in humans is therefore crucial. Preclinical results are contradictory concerning coexpression and functional interdependency of TRPV1 and TRPA1, but no human evidence exists. This human experimental study investigated whether functional responses from the subpopulation of TRPA1 nociceptors could be evoked after defunctionalization of TRPV1 nociceptors by cutaneous application of high-concentration capsaicin. Two quadratic areas on each forearm were randomized to pretreatment with an 8% topical capsaicin patch or vehicle for 24 hours. Subsequently, areas were provoked by transdermal 1% topical capsaicin (TRPV1 agonist) or 10% topical allyl isothiocyanate ("AITC," a TRPA1 agonist), delivered by 12 mm Finn chambers. Evoked pain intensities were recorded during pretreatments and chemical provocations. Quantitative sensory tests were performed before and after provocations to assess changes of heat pain sensitivity. Imaging of vasomotor responses was used to assess neurogenic inflammation after the chemical provocations. In the capsaicin-pretreated areas, both the subsequent 1% capsaicin- and 10% AITC-provoked pain was inhibited by 92.9 ± 2.5% and 86.9 ± 5.0% (both: P < 0.001), respectively. The capsaicin-ablated skin areas showed significant heat hypoalgesia at baseline (P < 0.001) as well as heat antihyperalgesia, and inhibition of neurogenic inflammation evoked by both 1% capsaicin and 10% AITC provocations (both: P < 0.001). Ablation of cutaneous capsaicin-sensitive afferents caused consistent and equal inhibition of both TRPV1- and TRPA1-provoked responses assessed psychophysically and by imaging of vasomotor responses. This study suggests that TRPA1 nociceptive responses in human skin strongly depend on intact capsaicin-sensitive, TRPV1 fibers.

T83. Characterization of pain evoked potentials and skin innervations in capsaicin-induced reversible focal neuropathy

Introduction This study aimed to investigate the temporal alterations of contact heat evoked potential (CHEP) in capsaicin-induced nerve degeneration and regeneration and its relationship to skin innervation density and thermal thresholds, in particular, whether the relationship between these parameters remained the same during different time points after topical capsaicin treatment. Methods We enrolled 14 normal subjects (7 men, age = 24.3 ± 2.5 years) to investigate intraepidermal nerve fiber (IENF) density, contact heat evoked potential (CHEP), and thermal thresholds at four time points including baseline, and first day, 3 weeks and 10 weeks after 2-weeks capsaicin application. Results After 2-weeks capsaicin treatment, IENF density was reduced with decreased amplitude and prolonged latency of CHEP, and increased warm and heat pain thresholds. Repeated measures ANOVA comparing the time course of IENF density, CHEP, pain rating and thermal threshold showed a significant effect of time on IENF density (F = 8.31, p Conclusion There was differential restoration of IENF density, CHEP and thermal thresholds, and discordant relationship between nociceptive nerve terminals and brain responses during the skin reinnervation after capsaicin-induced focal neuropathy.

Behavioral characteristics of capsaicin mediated cutaneous, myogenic, and arthrogenic orofacial nociception in rats

ObjectiveTo assess changes in orofacial tactile sensitivity and gnawing related to capsaicin-mediated cutaneous, myogenic, and arthrogenic nociception in the rat. DesignAfter recovery from anesthesia, orofacial tactile sensitivity and gnawing were assessed using operant testing methods following capsaicin application. Twenty female CD-Hairless rats were tested with bilateral capsaicin cream application to the cheek or with isoflurane anesthesia alone. Following several weeks of recovery, animals (n = 20) received either 10 μL unilateral masseter injections of vehicle, or phosphate buffered saline (PBS) to assess injection sensitization. After several weeks, masseter capsaicin (1.0%) injections (10 μL) were assessed compared to vehicle and PBS (n = 13). Weeks later capsaicin TMJ injections were evaluated. Animals (n = 11) received either 10 μL unilateral TMJ injections of capsaicin solution (1%) or vehicle. ResultsCapsaicin cream to the skin significantly altered gnawing activity (increased puncture time by 248 s (p = 0.0002)) and tactile sensitivity (decreased tolerated bottle distance by 0.980 cm compared to isoflurane only (p = 0.0001)). Similarly, capsaicin masseter injection increased puncture time (339.6 s, p = 0.07) and decreased tolerated bottle distance (1.04 cm, p = 0.005) compared to vehicle. However, intra-articular capsaicin in the TMJ only modified gnawing (increased puncture time by 133 s), with no changes found in tactile sensitivity compared to vehicle. ConclusionApplication of capsaicin to the skin and masseter had similar behavioral effects; however, intra-articular injections to the TMJ only affected gnawing. These data indicate the behavioral changes in rodent models of myogenic and cutaneous pain may be markedly different than models of arthrogenic pain originating from the TMJ.

Chronic adriamycin treatment impairs CGRP-mediated functions of meningeal sensory nerves

Adriamycin is a potent anthracycline-type antitumor agent, but it also exerts potentially serious side effects due to its cardiotoxic and neurotoxic propensity. Multiple impairments in sensory nerve functions have been recently reported in various rat models. The present experiments were initiated in an attempt to reveal adriamycin-induced changes in sensory effector functions of chemosensitive meningeal afferents.Meningeal blood flow was measured with laser Doppler flowmetry in the parietal dura mater of adult male Wistar rats. The dura mater was repeatedly stimulated by topical applications of capsaicin, a transient receptor potential vanilloid 1 (TRPV1) receptor agonist, or acrolein, a transient receptor potential ankyrin 1 (TRPA1) receptor agonist, which induce the release of calcitonin gene-related peptide (CGRP) from meningeal afferents. The blood flow increasing effects of CGRP, histamine, acetylcholine and forskolin were also measured. Capsaicin- and acrolein-induced CGRP release was measured with enzyme-linked immunoassay in an ex vivo dura mater preparation. TRPV1 content of trigeminal ganglia and TRPV1-, CGRP- and CGRP receptor component-immunoreactive structures were examined in dura mater samples obtained from control and adriamycin-treated rats.The vasodilator effects of capsaicin, acrolein and CGRP were significantly reduced in adriamycin-treated animals while histamine-, acetylcholine- and forskolin-induced vasodilatation were unaffected. Measurements of CGRP release in an ex vivo dura mater preparation revealed an altered dynamic upon repeated stimulations of TRPV1 and TRPA1 receptors. In whole-mount dura mater preparations immunohistochemistry revealed altered CGRP receptor component protein (RCP)-immunoreactivity in adriamycin-treated animals, while CGRP receptor activity modifying protein (RAMP1)-, TRPV1- and CGRP-immunostaining were left apparently unaltered. Adriamycin-treatment slightly reduced TRPV1 protein content of trigeminal ganglia.The present findings demonstrate that adriamycin-treatment alters the function of the trigeminovascular system leading to reduced meningeal sensory neurogenic vasodilatation that may affect the local regulatory and protective mechanisms of chemosensitive afferents leading to alterations in tissue integrity.

Anti‐cancer activity of non‐pungent capsaicin analogs: A Structure‐Activity Study

The nutritional compound capsaicin is the major spicy ingredient of chili peppers. Although traditionally associated with analgesic activity, recent studies have shown that capsaicin has profound anti‐neoplastic effects in several types of human cancers. However, the applications of capsaicin as a clinically viable drug are limited by its unpleasant side effects, such as gastric irritation, stomach cramps and burning sensation. This has led to extensive research focused on the identification and rational design of second‐generation capsaicin analogs. Previous studies have shown that addition of long‐chain unsaturated groups after the amide group of capsaicin were non‐pungent and retained the bioactivity of capsaicin. The chemical nature of these compounds are unsaturated N‐acylvanillamides (uN‐AVAMs). However, a majority of these uN‐AVAMs have been studied for their pain‐relieving activity. We synthesized a panel of uN‐AVAMs with 0–4 double bonds in the side chain of capsaicin. We investigated the growth‐inhibitory activity of these compounds with an MTT‐based screening assay. We selected our “hit compound” Arvanil for further studies. Next, we compared the apoptotic activity of arvanil and capsaicin in a panel of human small cell lung cancer (SCLC) cells. We observed that the non‐pungent capsaicin‐analog arvanil displayed greater magnitude of apoptosis than capsaicin. The pro‐apoptotic activity of arvanil and capsaicin was mediated by the intracellular calcium pathway. We measured the uN‐AVAM‐induced levels of intracellular calcium in SCLC cells. The pattern of uN‐AVAM‐induced intracellular calcium was analogous to the results obtained in the MTT assay. Therefore, the measurement of intracellular calcium may be used as a screening tool for capsaicin‐mimetics with anti‐cancer activity.Support or Funding InformationFunding for our study was supported by a NIH R15‐AREA Grant (2R15CA161491‐02). Furthermore, this study was supported in part by an Institutional Development Award (IDeA) Grant number P20GM104932 from the National Institute of General Medical Sciences (NIGMS) and the Research Core B of COBRE, a component of the National Institutes of Health (NIH).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Opposing vasomotor roles of TRPV1 and TRPV2 channels in the Human Adipose Microcirculation

Mechanosensitive, Ca2+‐permeable channels of the transient receptor potential vanilloid (TRPV) family, especially TRPV4, have emerged as important regulators of vascular tone. Within the vasculature, TRPV channels are expressed in smooth muscle cells, endothelial cells and perivascular nerves. We have previously demonstrated that Ca2+ influx through endothelial TRPV4 channels mediates flow‐induced dilation (FID) of human coronary arterioles (HCAs) from subjects with coronary artery disease (CAD). Recent unpublished studies from our lab show that FID is not affected by TRPV4 inhibition in HCAs of subjects without CAD (non‐CAD), even though TRPV4 channels are similarly expressed in non‐CAD and CAD HCAs. Interestingly, FID of non‐CAD HCAs is inhibited by ruthenium red, a non‐selective TRPV channel blocker, suggesting the involvement of other TRPV channel subtypes. Moreover, endothelial TRPV1 channels have been previously shown to mediate FID in rodent arteries; whereas a functional role for endothelial TRPV2 channels has yet to be determined. Together, these data have led us to hypothesize that endothelial TRPV1/TRPV2 channels mediate FID of non‐CAD human coronary and adipose arterioles. The objective of the current study was to characterize the expression and vasomotor function of TRPV1 and TRPV2 channels in HCAs and human adipose arterioles (HAAs) from non‐CAD subjects. RT‐PCR analysis revealed the presence of TRPV1 and TRPV2 transcripts in HCAs and HAAs isolated from multiple subjects. Consistent with mRNA expression, both proteins were detected in membrane fractions of HCAs and HAAs using immunoblotting. We next examined the vasomotor effect of capsaicin, a TRPV1‐ selective agonist and cannabidiol, a TRPV2‐selective agonist, on freshly isolated HAAs. HAAs (100–250 μm) were cannulated under 60 mmHg and examined for diameter changes using videomicroscopy. Bath application of cannabidiol (10−7 – 10−5 M) induced dose‐dependent dilation of endothelium‐intact and surprisingly, endothelium‐denuded HAAs (% dilation at 10−5 M, 95.3 ± 1.4%, n=9 intact; 95.4 ± 2.6%, n=6 denuded HAAs), suggesting a vasomotor role for both endothelial and smooth muscle TRPV2 channels. In contrast, bath application of capsaicin (10−10 – 10−6 M) induced constriction of both endothelium‐intact and denuded HAAs at concentrations of 10−7 M (−55 ± 8%; n=5) and 10−6 M (−50.8 ± 12.9%; n=5). Moreover, capsaicin (10−6 M) induced a prolonged increase in intracellular calcium concentration ([Ca2+]i) in smooth muscle cells of HAAs, consistent with vasoconstriction observed in functional studies; whereas cannabidiol (10−7 – 10−5 M) induced a dose‐dependent increase in endothelial [Ca2+]i, consistent with vasodilation observed in functional studies. These results suggest that TRPV1 and TRPV2 channels are functionally expressed in human arterioles and upon activation, produce opposing vasomotor responses in HAAs. Further studies are required to determine the precise mechanisms responsible for such contrasting vasomotor effects of TRPV1 and TRPV2 activation.Support or Funding InformationSupport for this research was provided by the National Heart, Lung and BloodInstitute Grant R01‐HL 096647.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Anti‐metastatic activity of capsaicin and natural capsaicin‐like compounds in human lung adenocarcinoma

Lung adenocarcinoma (LAC) accounts for 65% of all non‐small cell lung cancer (NSCLC) cases. A substantial proportion of LAC present with extrapulmonary and distant metastasis at the time of their diagnosis. One of the earliest events of the metastatic process is the invasion of malignant cells through the surrounding extracellular basement membrane into the blood and lymph. The long‐term goal of our laboratory is to identify nutrition‐based agents which will suppress the growth and progression of human LACs. Capsaicin is the pungent ingredient of chili peppers. Published reports have revealed that capsaicin inhibits the invasion and metastasis of several types of human cancers including melanoma, prostate cancer, and cholangiosarcoma. However, the clinical application of capsaicin as an anti‐cancer drug is limited by its unpleasant side‐effect profile. This led us to compare the anti‐metastatic activity of capsaicin with natural non‐pungent capsaicin‐like compounds, namely capsiate and capsiconiate. The structure and bioactivity of capsaicin closely resembles capsiate. There are no published reports involving the biological activity of capsiconiate. We measured the anti‐invasive activity of these compounds by two independent invasion assays, namely the Boyden chamber assay and spherical invasion assay. We found that capsaicin and capsiate displayed anti‐invasive activity in three human LAC cell lines. In contrast, capsiconiate did not suppress the invasion of any LAC cell lines. Furthermore, we tested the anti‐metastatic activity of capsaicin in a syngeneic mouse model of metastasis. We observed that the daily dietary administration of capsaicin in AIN‐76A diet (with 5% lipid level) robustly decreased the area metastatic foci (in the lung) relative to vehicle‐treated mice. The results of our studies may foster the development of novel anti‐metastatic therapies for human LAC.Support or Funding InformationFunding for our study was supported by an NIH R15‐AREA Grant (2R15CA161491‐02) and a NASA Undergraduate Fellowship to NANThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Machine-learned analysis of the association of next-generation sequencing-based human TRPV1 and TRPA1 genotypes with the sensitivity to heat stimuli and topically applied capsaicin.

Heat pain and its modulation by capsaicin varies among subjects in experimental and clinical settings. A plausible cause is a genetic component, of which TRPV1 ion channels, by their response to both heat and capsaicin, are primary candidates. However, TRPA1 channels can heterodimerize with TRPV1 channels and carry genetic variants reported to modulate heat pain sensitivity. To address the role of these candidate genes in capsaicin-induced hypersensitization to heat, pain thresholds acquired before and after topical application of capsaicin and TRPA1/TRPV1 exomic sequences derived by next-generation sequencing were assessed in n = 75 healthy volunteers and the genetic information comprised 278 loci. Gaussian mixture modeling indicated 2 phenotype groups with high or low capsaicin-induced hypersensitization to heat. Unsupervised machine learning implemented as swarm-based clustering hinted at differences in the genetic pattern between these phenotype groups. Several methods of supervised machine learning implemented as random forests, adaptive boosting, k-nearest neighbors, naive Bayes, support vector machines, and for comparison, binary logistic regression predicted the phenotype group association consistently better when based on the observed genotypes than when using a random permutation of the exomic sequences. Of note, TRPA1 variants were more important for correct phenotype group association than TRPV1 variants. This indicates a role of the TRPA1 and TRPV1 next-generation sequencing-based genetic pattern in the modulation of the individual response to heat-related pain phenotypes. When considering earlier evidence that topical capsaicin can induce neuropathy-like quantitative sensory testing patterns in healthy subjects, implications for future analgesic treatments with transient receptor potential inhibitors arise.

Capsaicin 8% patch reversibly reduces A-delta fiber evoked potential amplitudes.

The capsaicin 8% patch is a treatment option in patients with localized peripheral neuropathic pain. Better understanding of its mechanisms of action and knowledge on predictive biomarkers for a treatment response is warranted. To use electrically evoked pain-related potentials for investigation of A-delta fiber conduction after capsaicin 8% patch treatment. We studied 11 healthy controls at the dorsal hand and the foot and 12 patients with neuropathic pain at the area affected by neuropathic pain before and 2 hours after application of a capsaicin 8% patch (Qutenza). Patients were additionally phenotyped using quantitative sensory testing and skin biopsy. Peak-to-peak N1-P1 amplitudes (PPA) were reduced after Qutenza application by a median of 60% in 6/11 controls and by 33% in patients with neuropathic pain compared with baseline; they were increased in 3 controls that did not develop capsaicin-induced pain. Patients with elevated cold detection thresholds more often had reduced PPA after Qutenza than those with normal cold detection threshold. Patients with reduced PPA after capsaicin application and with capsaicin-induced pain were more likely to achieve pain reduction on Qutenza. The capsaicin 8% patch induces a reduction in A-delta PPA in healthy persons and in patients with neuropathic pain adding to the mechanistic understanding of its effect.

Effect of a novel TRPV1 antagonist on capsaicin nociceptors

Effect of a novel TRPV1 antagonist on capsaicin nociceptors

Micro electrode arrays to investigate neuron-glia crosstalk in neuropathic pain in-vitro models

Micro electrode arrays to investigate neuron-glia crosstalk in neuropathic pain in-vitro models

Involvement of TRPV1-ANO1 Interactions in Pain-Enhancing Mechanisms.

Primary sensory neurons detect potentially dangerous environmental situations via many "sensor" proteins located on the plasma membrane. Although receptor-type cation channels are thought to be the major sensors in sensory neurons, anion channels are also important players in the peripheral nervous system. Recently, we showed that transient receptor potential vanilloid 1 (TRPV1) interacts with anoctamin 1 (ANO1, also called TMEM16A) in primary sensory neurons and that this interaction enhanced TRPV1-mediated pain sensation. In that study, we induced ANO1 currents by application of capsaicin to small DRG neurons and showed that ANO1-dependent depolarization following TRPV1 activation could evoke more action potentials. Furthermore, capsaicin-evoked pain-related behaviors in mice were strongly inhibited by a selective ANO1 blocker. Together these findings indicate that selective ANO1 inhibition can reduce pain sensation. We also investigated non-specific inhibitory effects on ion channel activities to control ion dynamics via the TRPV1-ANO1 complex. We found that 4-isopropylcyclohexanol (4-iPr-CyH-OH) had an analgesic effect on burning pain sensations through its inhibition of TRPV1 and ANO1 together. Additionally, 4-iPr-CyH-OH did not have clear agonistic effects on TRPV1, TRPA1, and ANO1 activity individually. These results indicate that 4-iPr-CyH-OH could function globally to mediate TRP-ANO1 complex functions to reduce skin hypersensitivity and could form the basis for novel analgesic agents.

Role of medullary astroglial glutamine synthesis in tooth pulp hypersensitivity associated with frequent masseter muscle contraction.

BackgroundThe mechanisms underlying tooth pulp hypersensitivity associated with masseter muscle hyperalgesia remain largely underinvestigated. In the present study, we aimed to determine whether masseter muscle contraction induced by daily electrical stimulation influences the mechanical head-withdrawal threshold and genioglossus electromyography activity caused by the application of capsaicin to the upper first molar tooth pulp. We further investigated whether astroglial glutamine synthesis is involved in first molar tooth pulp hypersensitivity associated with masseter muscle contraction.MethodsThe first molar tooth pulp was treated with capsaicin or vehicle in masseter muscle contraction or sham rats, following which the astroglial glutamine synthetase inhibitor methionine sulfoximine or Phosphate buffered saline (PBS) was applied. Astroglial activation was assessed via immunohistochemistry.ResultsThe mechanical head-withdrawal threshold of the ipsilateral masseter muscle was significantly decreased in masseter muscle contraction rats than in sham rats. Genioglossus electromyography activity was significantly higher in masseter muscle contraction rats than sham rats. Glial fibrillary acidic protein-immunoreactive cell density was significantly higher in masseter muscle contraction rats than in sham rats. Administration of methionine sulfoximine induced no significant changes in the density of glial fibrillary acidic protein-immunoreactive cells relative to PBS treatment. However, mechanical head-withdrawal threshold was significantly higher in masseter muscle contraction rats than PBS-treated rats after methionine sulfoximine administration. Genioglossus electromyography activity following first molar tooth pulp capsaicin treatment was significantly lower in methionine sulfoximine-treated rats than in PBS-treated rats. In the ipsilateral region, the total number of phosphorylated extracellular signal-regulated protein kinase immunoreactive cells in the medullary dorsal horn was significantly smaller upon first molar tooth pulp capsaicin application in methionine sulfoximine-treated rats than in PBS-treated rats.ConclusionsOur results suggest that masseter muscle contraction induces astroglial activation, and that this activation spreads from caudal to the obex in the medullary dorsal horn, resulting in enhanced neuronal excitability associated with astroglial glutamine synthesis in medullary dorsal horn neurons receiving inputs from the tooth pulp. These findings provide significant insight into the mechanisms underlying tooth pulp hypersensitivity associated with masseter muscle contraction.