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The transient receptor potential (TRP) ion channel family is composed of twenty-seven channel proteins that are ubiquitously expressed in the human body. The TRPV (vanilloid) subfamily has been a recent target of investigation within the cardiovascular field. TRPV1, which is sensitive to heat as well as vanilloids, is the best characterized TRPV channel and is the namesake for the subfamily that includes six members. Research into the function of TRPV2 has suggested that it plays an important role in cardiovascular function. Over the last twenty years a greater understanding of the differences among the TRPV channels has allowed for more precise experimentation and has opened various translational opportunities. TRPV2 has been found to be a both a mechanosensor and a mediator of calcium handling and has been found to play important roles in healthy and diseased cardiomyocytes. These roles have been translated into clinical studies in patients with muscular dystrophy (both agonism and antagonism) as well as in patients with cardiomyopathy and heart failure with reduced ejection fraction. Its role as a structural protein has also been elucidated, though the clinical significance of this finding has yet to be established. Despite the clinical progress that has been made there is still a need for large, prospective randomized studies with TRPV2 channel agonists and antagonists in order to bring these basic and translational science findings to the bedside.

Human monocytes and dendritic cells express transient receptor potential vanilloid 1 (TRPV1) which may play a role in mediating the inflammatory, immune and cancer surveillance responses of these cells. The aim of the present study was to investigate TRPV1 expression and function in THP-1 monocytic cells. RT-PCR and Western blot were used to detect TRPV1. The metabolic activity and viability of THP-1 cells following exposure to vanilloids was assessed using resorufin production from rezazurin. Cytokine release was measured using ELISA. TRPV1 was expressed in cultured THP-1 monocytic cells and naïve monocytes. Lower concentrations (250 μM) of capsaicin, but not other putative TRPV1 agonists, were shown to stimulate cell metabolic activity, whereas at concentrations250 μM, all agonists decreased metabolic activity. Capsaicin-stimulated THP-1 metabolic activity was blocked by the TRPV1 antagonist, 5-iodo-resiniferatoxin (5'-IRTX), whereas the decline in resorufin production by THP-1 cells at higher capsaicin concentrations (due to cell death), was not affected by 5'-IRTX. Finally, capsaicin (≤125 μM) significantly increased lipopolysaccharide-stimulated IL-6 and TNF-α release from THP-1 cells, whereas phytohaemagglutinin-stimulated IL-1β, TNF-α, MCP-1 and IL-6 release were concentration-dependently inhibited by capsaicin. Modulation of IL-1β release was not TRPV1 mediated. Overall, these results show that functional TRPV1 channels are present in naïve monocytes and THP-1 cells, and when activated, increase cell metabolic activity. In addition, capsaicin modifies cytokine release from THP-1 cells and induces cell death, most likely by a mechanism that is independent of TRPV1 activation.

Scope Grains of Paradise (GOP), the seeds of Aframomum melegueta, has anti-obesity effects. However, the mechanisms underlying the effects remain unclear. Methods and results We set up to study the anti-obesity impact and homeostatic effects of 6-paradol, a major vanilloid found in GOP, and investigated the physiological outputs and the lipometabolism-related gene in fat and liver in high-fat-induced obese mice with a comparison with structurally similar vanilloids (6-gingerol and 6-shogaol). The vanilloids were synthesized in adequate quantities for performing animal experiments and orally administered to six-week-old male mice over two weeks. We found that 6-paradol decreased body weight gain and visceral and subcutaneous fats in two weeks, whereas 6-gingerol and 6-shogaol had no effect. Additionally, 6-paradol suppressed the hepatic cholesterol and triglyceride and significantly decreased the gene expression related to fatty acid synthesis, lipid transportation, and adipocyte differentiation in both liver and adipose tissue. Moreover, phosphorylation of AMP-activated protein kinase (AMPK) that greatly contributes to lipometabolism was promoted by 6-gingerol but not 6-paradol. Conclusion These results suggest that 6-paradol regulates several obesity-related genes in an AMPK-independent manner. Therefore, it could be the principal active vanilloid in GOP giving it anti-obesity properties with a different mechanism. This article is protected by copyright. All rights reserved.

Transient receptor potential vanilloid 1 (TRPV1) is a calcium-permeable ion channel best known for its ability to be gated by the pungent constituent of red chili pepper, capsaicin, and related chemicals from the group of vanilloids as well as by noxious heat. As such, it is mostly expressed in sensory neurons to act as a detector of painful stimuli produced by pungent chemicals and high temperatures. Its activation is also sensitized by the numerous endogenous inflammatory mediators and second messengers, making it an important determinant of nociceptive signaling. Except for such signaling, though, neuronal TRPV1 activation may influence various organ functions by promoting the release of bioactive neuropeptides from sensory fiber innervation organs. However, TRPV1 is also found outside the sensory nervous system in which its activation and function is not that straightforward. Thus, TRPV1 expression is detected in skeletal muscle; in some types of smooth muscle; in epithelial and immune cells; and in adipocytes, where it can be activated by the combination of dietary vanilloids, endovanilloids, and pro-inflammatory factors while the intracellular calcium signaling that this initiates can regulate processes as diverse as muscle constriction, cell differentiation, and carcinogenesis. The purpose of the present review is to provide a clear-cut distinction between neurogenic TRPV1 effects in various tissues consequent to its activation in sensory nerve endings and non-neurogenic TRPV1 effects due to its expression in cell types other than sensory neurons.

Transient receptor potential vanilloid type 1 (TRPV1) channels are activated by heat, vanilloids, and extracellular protons. Cryo-EM has revealed various conformations of TRPV1, and these structures suggest an intramolecular twisting motion in response to ligand binding. However, limited experimental data support this observation. Here we analyzed the intramolecular motion of TRPV1 using diffracted X-ray tracking (DXT). DXT analyzes trajectories of Laue spots generated from attached gold nanocrystals, and provides picometer spatial and microsecond time scale information about intramolecular motion. We observed that both an agonist and a competitive antagonist evoked rotating bias in TRPV1, though these biases were in opposing directions. Furthermore, the rotational bias generated by capsaicin was reversed between the wild type and the capsaicin-insensitive Y511A mutant. Our findings bolster the understanding of the mechanisms used activation and modulation of TRP channels, and this knowledge can be exploited for pharmacological usage such as inhibitor design.

Moringa oleifera Lam. is a tropical plant widely used in traditional medicines and as a food supplement. It is characterized by the presence of glucosinolates and isothiocyanates, the stable isothiocyanate 4-[(&alpha, l-rhamnosyloxy)benzyl]isothiocyanate (moringin) has been widely studied for its bioactivity as hypoglycemic, antimicrobial, anticancer and in particular for its involvement in nociception and neurogenic pain. Moringa extracts and pure moringin were submitted to in vitro assays with the somatosensory TRPA1 ion channel, proving that moringin is a potent and effective agonist of this receptor involved in nociceptive function and pain states. Moringin do not activate or activates very weakly the vanilloids somatosensory channels TRPV1,2,3 and 4, and the melastatin cooling receptor TRPM8. The comparison of moringin&rsquo, s activity with other known agonists of natural origin is also discussed.

Despite the apparent abundance of ligand-gated transient receptor potential vanilloid type 1 (TRPV1) and possible cross talk between the endocannabinoid and endovanilloid systems in the central nervous system (CNS), it is unclear what role TRPV1 receptor activation in CNS plays in neurobehavioral development. We previously reported that capsaicin or WIN55212-2 induces risk aversion in the plus-maze test, which was dependent on the gender and mouse strain used. In this study, pregnant BALBc mice were administered capsaicin (1.0 or 4.0 mg/kg, i.p.) during the second week of gestation. Developmental effects of prenatal exposure to capsaicin were assessed in neonates, and behavioral effects were assessed in adult offspring. Gender- and dose-specific variations in ultrasonic vocalizations, weight gain, righting reflex, and general activity of the pups were observed. Prenatal exposure to capsaicin altered plus-maze performance, especially with further exogenous capsaicin challenge. Furthermore, dose- and gender-specific effects were evident in the conditioned place preference/aversion paradigm following conditioning with capsaicin in adult animals. The capsaicin-induced aversion in the plus-maze test was enhanced by WIN55212-2 and blocked by pretreatment with vanilloid antagonist capsazepine or the CB(1) receptor antagonist rimonabant, demonstrating an interaction between the endocannabinoid and endovanilloid systems in CNS. Taken together, the interaction between the endocannabinoid and endovanilloid signaling systems can be exploited for therapeutic applications in health and disease.

Neutrophils migrate to sites of infection where they phagocytose, degranulate, and/or, in the presence of appropriate stimuli, release decondensed chromatin strands (called neutrophil extracellular traps, NETs) for trapping and possibly killing microorganisms. NET formation is characterized by marked morphological cell changes, in particular within the nucleus. Lytic NET formation can be observed in neutrophils undergoing cell death, which is referred to as NETosis. Dysregulation of NET production and/or degradation can exert pathogenic effects, contributing to the pathogenesis of various diseases, including cystic fibrosis, autoimmune diseases and inflammatory conditions. By employing a phenotypic assay based on high-content imaging and analysis, we screened a library of biologically active compounds and identified vanilloids as a novel class of chemical compounds able to hinder NETosis induction and NET release. Vanilloids also markedly decrease cytosolic ROS production. The identification of novel vanilloid NET inhibitors, able to stop excessive or aberrant NET production might offer new therapeutic options for those disorders displaying NET overproduction.

Capsaicin is a natural protoalkaloid recognized as the main pungent component in hot peppers (Capsicum annuum L.). The capsaicin receptor is highly expressed in the unmyelinated type C nerve fibers originating from small diameter sensory neurons in dorsal root ganglia and cranial nerve ganglia correspondents. Capsaicin and related vanilloids have a variety of effects on primary sensory neurons function, from sensory neuron excitation characterized by local burning sensation and neurogenic inflammation, followed by conduction blockage accompanied by reversible ultrastructural changes of peripheral nociceptive endings (desensitization), going as far as irreversible degenerative changes (neurotoxicity). The main role in capsaicin-induced neurogenic inflammation relies on the capsaicin sensitive, small diameter primary sensory neurons, therefore its evaluation could be used as a diagnostic instrument in functional alterations of cutaneous sensory nerve fibers. Moreover, capsaicin-induced desensitization and neurotoxicity explain the analgesic/anti-nociceptive and anti-inflammatory effects of topical capsaicin and its potential use in the management of painful and inflammatory conditions. In this study, we describe the effects of capsaicin on neurogenic inflammation and nociception, as well as its potential diagnostic value and therapeutic impact in various conditions involving impairment of sensory nerve fibers.

The Transient Receptor Potential Vanilloid 1 (TRPV) channel is activated by an array of stimuli, including heat and vanilloid compounds. The TRPV1 homologues TRPV2 and TRPV3 are also activated by heat, but sensitivity to vanilloids and many other agonists is not conserved among TRPV subfamily members. It was recently discovered that four mutations in TRPV2 are sufficient to render the channel sensitive to the TRPV1-specific vanilloid agonist resiniferatoxin (RTx). Here we show that mutation of six residues in TRPV3 corresponding to the vanilloid site in TRPV1 is sufficient to engineer RTx binding. However, robust activation of TRPV3 by RTx requires facilitation of channel opening by introducing individual mutations in the pore, temperatures > 30°C, or co-stimulation with another agonist. Our results demonstrate that the energetics of channel activation can determine the apparent sensitivity to a stimulus and suggest that allosteric pathways for activation are conserved in the TRPV family.

Microvascular endothelial cells are an essential part of many biological barriers, such as the blood–brain barrier (BBB) and the endothelium of the arteries and veins. A reversible opening strategy to increase the permeability of drugs across the BBB could lead to improved therapies due to enhanced drug bioavailability. Vanilloids, such as capsaicin, are known to reversibly open tight junctions of epithelial and endothelial cells. In this study, we used several in vitro assays with the murine endothelial capillary brain cells (line cEND) as a BBB model to characterize the interaction between capsaicin and endothelial tight junctions.

Vanilloids including capsaicin and resiniferatoxin are potent transient receptor potential vanilloid type 1 (TRPV1) agonists. TRPV1 overstimulation selectively ablates capsaicin-sensitive sensory neurons in animal models in vivo. The cytotoxic mechanisms are based on strong Na⁺ and Ca2 + influx via TRPV1 channels, which leads to mitochondrial Ca2 + accumulation and necrotic cell swelling. Increased TRPV1 expression levels are also observed in breast and prostate cancer and derived cell lines. Here, we examined whether potent agonist- induced overstimulation mediated by TRPV1 might represent a means for the eradication of prostate carcinoma (PC-3, Du 145, LNCaP) and breast cancer (MCF7, MDA-MB-231, BT-474) cells in vitro. While rat sensory neurons were highly vanilloid- sensitive, normal rat prostate epithelial cells were resistant in vivo. We found TRPV1 to be expressed in all cancer cell lines at mRNA and protein levels, yet protein expression levels were significantly lower compared to sensory neurons. Treatment of all human carcinoma cell lines with capsaicin didn't lead to overstimulation cytotoxicity in vitro. We assume that the low vanilloid-sensitivity of prostate and breast cancer cells is associated with low expression levels of TRPV1, since ectopic TRPV1 expression rendered them susceptible to the cytotoxic effect of vanilloids evidenced by plateau- type Ca2 + signals, mitochondrial Ca2 + accumulation and Na⁺- and Ca2 +-dependent membrane disorganization. Moreover, long- term monitoring revealed that merely the ectopic expression of TRPV1 stopped cell proliferation and often induced apoptotic processes via strong activation of caspase-3 activity. Our results indicate that specific targeting of TRPV1 function remains a putative strategy for cancer treatment.

Treatment for overactive bladder (OAB) with oral pharmacologic therapy can be unsatisfactory, and alternative options should be considered when patients fail. Intravesical therapy with botulinum neurotoxin should be introduced as a third-line treatment option in those OAB patients refractory to oral therapy or intolerant to its systemic side effects. The popularity of intravesical therapy with botulinum toxin has continuously increased due to the literature-supported safety, effectiveness, facile administration, adaptable learning curve, and reproducible effect with repeated use. While vanilloids (capsaicin and resiniferatoxin) are also an available therapeutic option, they are not regularly utilized due to their lack of FDA approval and documented efficacy and safety. The aim of this chapter is to describe the clinical applications of injectable intravesical agents for OAB and discuss their mechanism of action, outcomes, and safety.

Vanilloid (4-hydroxy-3-methoxyphenyl benzenoid) containing foods are reported to possess many biological activities including anti-inflammatory properties. Homodimerisation of the Toll-like receptor-4 (TLR-4)/Myeloid differentiation factor 2 (MD-2) complex results in life-threatening complications in inflammatory disorders. In this study, we report activity of vanilloids in inhibition of TLR-4/MD-2 homodimersization and their molecular interactions with the receptor. The inhibitory activities of vanilloids were assessed in vitro by determining their antagonistic actions of lipopolysaccharide from Escherichia coli (LPSEc) in activation of TLR-4/MD-2 homodimerisation in TLR-4/MD-2/CD-14 transfected HEK-293 cells. The in vitro anti-inflammatory activity of vanilloids was also determined using RAW 264.7 cells. All the vanilloids were found to be active in the inhibition of TLR-4/MD-2 homodimersiation and nitric oxide production in RAW 264.7 cells. Rigid and flexible molecular docking studies were performed to gain insight into interactions between vanilloids and the binding site of the TLR-4/MD-2 complex.

In this chapter, evidence from the international literature is collected in support of a crucial role of exogenous DAMPs played in the “world of DAMPs.” The various exogenous compounds and molecules of this Category IV of DAMPs derive from different origins and possess different bioactive functions. The first subchapter is dedicated to the Class IVA DAMPs which are defined as being indirectly sensed by the NLRP3 inflammasome. The three subclasses (IVA-1–3 DAMPs) described refer to aluminum salt, asbestos fibers, and silica particles. Diseases mediated by these DAMPs include asbestosis and silicosis of the lung. The second subchapter deals with Class IVB DAMPs defined as exogenous molecules being sensed by nociceptors. Nociception is the process of transmission of painful signals by nociceptors, and modern notions hold that this process reflects a new branch of the innate immune defense system. Subclasses of these exogenous DAMPs include non-reactive compounds such as menthol and nicotine, reactive electrophilic compounds such as allicin in garlic, and vanilloids such as capsaicin, the pungent ingredient of the hot chilli pepper. Finally, the Class IVC of DAMPs referring to specific allergens is addressed by describing briefly the subclasses of metal allergens such as nickel, cobalt, and palladium. The chapter ends with a few remarks on the role of exogenous DAMPs in treatment options, on the one side, and certain disorders such as chronic respiratory and allergic diseases, on the other hand.

Control of the lower urinary tract is a complex, multilevel process that involves both the central and peripheral nervous system. Neurologic disease can impair these processes and lead to neurogenic lower urinary tract dysfunction (NLUTD). NLUTD is a chronic illness that affects millions of individuals worldwide, especially in regard to quality of life and economic burden. Intravesical therapy with botulinum neurotoxin and vanilloids (capsaicin and resiniferatoxin) is actively introduced as a second-line treatment in those NLUTD patients refractory to oral therapy or intolerant to its systemic side effects. The popularity of intravesical therapy has continuously increased due to the literature-supported safety, effectiveness, easy use, adaptable learning curve and reproducible effect on repeated use. The aim of this chapter is to describe the clinical applications of intravesical agents and discuss mechanism of action, outcomes, and safety.

Transient receptor potential vanilloid type 1 (TRPV1) is a polymodal receptor channel that responds to multiple types of stimuli, such as heat, acid, mechanical pressure and some vanilloids. Capsaicin is the most commonly used vanilloid to stimulate TRPV1. TRPV1 channels are expressed in dorsal root ganglion neurons that extend to Aδ- and C-fibers and have a role in the transduction of noxious inputs to the skin into the electrical signals of the sensory nerve. Although noradrenergic nervous systems, including the descending antinociceptive system and the sympathetic nervous system, are known to modulate pain sensation, the functional association between TRPV1 and noradrenaline in primary sensory neurons has rarely been examined. In the present study, we examined the effects of noradrenaline on capsaicin-evoked currents in cultured dorsal root ganglion neurons of the rat by the whole-cell voltage clamp method. Noradrenaline at concentrations higher than 0.1 pM significantly reduced the amplitudes of the inward capsaicin currents recorded at -60 mV holding potential. This inhibitory action was reversed by either yohimbine (an α2 antagonist, 10 nM) or propranolol (a β antagonist, 10 nM). The α2 agonists, clonidine (1 pM) and dexmedetomidine (1 pM) inhibited capsaicin currents, and yohimbine (1 nM) reversed the effects of clonidine. The inhibitory action of noradrenaline was not seen in the neurons pretreated with pertussis toxin (100 μg/ml for 24 h) and the neurons dialyzed intracellularly with guanosine 5'- [β-thio] diphosphate (GDPβS, 200 μM), the catalytic subunit of protein kinase A (250 U/ml) or okadaic acid (1 μM). These results suggest that noradrenaline directly acts on dorsal root ganglion neurons to inhibit the activity of TRPV1 depending on the activation of α2-adrenoceptors followed by the inhibition of the adenylate cyclase/cAMP/protein kinase A pathway.

Nociception is the sensory nervous system’s response to certain harmful or potentially harmful stimuli such as mechanical (crushing and cutting), thermal (heat and cold), and chemical (chili pepper in eyes or skin). Sensory nerve cells (nociceptors) when stimulated produce signals that travel along a chain of nerve fibers through the spinal cord to the brain. For example, most nociceptors are cation channels including transient receptor potential (TRP) channels. The TRP family consists of more than 30 cation channels, and most are permeable to monovalent and divalent cations such as Na+, Ca2+, and Mg2+. The transient receptor potential vanilloid 1 (TRPV1) is a member of the transient receptor potential (TRP) family of ion channels, which is a polymodal, nonselective cation channel and is highly expressed in sensory neurons, as well as in tissues such as the brain, bronchial epithelial cells, epidermal keratinocytes, and kidney. TRPV1 is the site of action of capsaicin, the pungent ingredient in red pepper, and nociceptor of the sensory afferent neurons. TRPV1 is modulated by signaling pathways in the cell, permitting it to respond in a holistic fashion to perturbations in the cellular environment, including the mammalian sensory system responding to a broad range of stimuli such as pain, temperature, taste, touch, osmolarity, and pheromones. TRPV1 is one of the best-characterized and widely validated members of the TRP family that play essential role in pain physiology, neurogenic inflammation, and also in non-neuronal cell types such as mast cells, epidermal and hair follicle keratinocytes, and dendritic cells. TRPV1 in keratinocytes has been implicated in proliferation, differentiation, homeostasis, and cutaneous immunological function that is related to pruritis and inflammation. TRPV1 is phosphorylated by protein kinase C, protein kinase A, protein kinase D, and Ca2+/calmodulin-dependent protein kinase II, which influences its sensitivity, desensitization, and functional ligand interaction. TRPV1 is activated or sensitized by a variety of endogenous stimuli, including bioactive lipids, noxious heat, and extracellular protons, which are generated as a result of tissue injury and inflammation. Thus, inhibition of TRPV1 receptor is modulated by desensitization (decrease TRPV1 activity by prolonged exposure to the agonist), which results in excessive calcium to enter the nerve fiber, initiating reversible impairment of nociceptor function, which provides relief from pain. TRPV1 is activated by exogenous stimuli such as capsaicin and resiniferatoxin (RTX). Capsaicin acts as an antipruritic, antipsoriatic, anti-inflammatory, and anti-itch agent. In addition, capsaicin is reported to cause apoptosis or inhibit proliferation of malignant cancer cells. However, the most notorious clinical limitation of capsaicin and related vanilloids is the TRPV1-coupled acute excitation, which results in marked burning sensation. In addition, capsaicin is very lipophilic and can reside in human skin relatively unchanged for a long period of time, leading to frequent erythema reactions and may cause cancer. However, TRPV1 antagonists, such as AMG9810 and capsazepine, block TRPV1 activity that cause reduction in pain signal. TRPV1 antagonists are effective in treatment of chronic intractable pain secondary to cancer, migraine, AIDS or diabetes, urinary urge incontinence, chronic cough, and irritable bowel syndrome. Nonetheless, TRPV1 antagonist like AMG9810 promotes mouse skin tumorigenesis. To alleviate the side effects, TRPV1 is modulated such that antagonists either block responses to capsaicin and lower the pH or only selectively antagonize capsaicin. Present vanilloid therapeutics focus on increasing the local concentration of TRPV1 agonists in injections or patches, minimization of agonist excitation, and utilization of pore permeable capsaicinoids that target only the hyperactive channels. However, of the more than 15 compounds that entered Phase 1 clinical trials, only five compounds have progressed into Phase 2 clinical trials, and none of these compounds advanced to Phase III due to their undesirable side effects. Capsaicin soft drugs applied or administered near the site of action are designed to undergo deactivation by the hydrolyzing activity of esterases after having exerted their biological activity. Soft drugs cover therapeutic areas, including anticholinergics, antimicrobials, corticosteroids, and ACE inhibitors. Compounds of this Patent Highlight are soft drugs, which are susceptible to be hydrolyzed by esterases and subsequently eliminated. Thus, these compounds may not accumulate in the body and show improved activity with minimal side effects compared to the irritant or potential carcinogenic effect of capsaicin.

Capsaicin is the main pungent in chili peppers, one of the most commonly used spices in the world; its analgesic and anti-inflammatory properties have been proven in various cultures for centuries. It is a lipophilic substance belonging to the class of vanilloids and an agonist of the transient receptor potential vanilloid 1 receptor. Taking into consideration the complex neuro-immune impact of capsaicin and the potential link between inflammation and carcinogenesis, the effect of capsaicin on muco-cutaneous cancer has aroused a growing interest. The aim of this review is to look over the most recent data regarding the connection between capsaicin and muco-cutaneous cancers, with emphasis on melanoma and muco-cutaneous squamous cell carcinoma.

Capsaicin, a well known vanilloid, has shown evidence of an ample variety of biological effects which make it the target of extensive research ever since its identification. In spite of the fact that capsaicin causes health hazards in quite a few ways, yet, the verity cannot be ignored that capsaicin has several therapeutic implications. In patients with hypersensitive bladders, vesical instillation of 1 mM capsaicin markedly improved urinary frequency and urge incontinence. Again, administration of capsaicin favors an augmentation in lipid mobilization and a decrease in adipose tissue mass. Topical capsaicin cream as well decreases postsurgical neuropathic pain and is preferred by patients over a placebo among other therapies. Several in vitro studies have revealed that capsaicin results in growth arrest in some transformed cell lines. Furthermore, capsaicin has been proven to be an undeniably exciting molecule and remains a valuable drug for alleviating pain and itch. It has been recognized that capsaicinoids are the most potential agonists of capsaicin receptor (TRPV1). However, vanilloids could exert the beneficial effects not only through the receptor-dependent pathway but also through the receptor-independent one. The involvement of serotonin, neuropeptide Substance P and somatostatin in the pharmacological actions of capsaicin has been expansively investigated. Better understanding of the established TRPV1 receptor mechanism as well as exploring other possible receptor mechanism may publicize other new clinical efficacies of capsaicin. Further, clinical studies are required in several of these conditions to establish the efficacy of capsaicin.

“Molecular neurosurgery” is emerging as a new medical concept, and is the combination of two partners: (i) a molecular neurosurgery agent, and (ii) the cognate receptor whose activation results in the selective elimination of a specific subset of neurons in which this receptor is endogenously expressed. In general, a molecular surgery agent is a selective and potent ligand, and the target is a specific cell type whose elimination is desired through the molecular surgery procedure. These target cells have the highest innate sensitivity to the molecular surgery agent usually due to the highest receptor density being in their plasma membrane. The interaction between the ligand and its receptor evokes an overactivity of the receptor. If the receptor is a ligand-activated non-selective cation channel, the overactivity of receptor leads to excess Ca2+ and Na+ influx into the cell and finally cell death. One of the best known examples of such an interaction is the effect of ultrapotent vanilloids on TRPV1- expressing pain-sensing neurons. One intrathecal resiniferatoxin (RTX) dose allows for the receptor-mediated removal of TRPV1+ neurons from the peripheral nervous system. The TRPV1 receptor-mediated ion influx induces necrotic processes, but only in pain-sensing neurons, and usually within an hour. Besides that, target-specific apoptotic processes are also induced. Thus, as a nano-surgery scalpel, RTX removes the neurons responsible for generating pain and inflammation from the peripheral nervous system providing an option in clinical management for the treatment of morphine-insensitive pain conditions. In the future, the molecular surgery concept can also be exploited in cancer research for selectively targeting the specific tumor cell.

Much of our knowledge of the endocannabinoid system in schizophrenia comes from behavioral measures in rodents, like prepulse inhibition of the acoustic startle and open-field locomotion, which are commonly used along with neurochemical approaches or drug challenge designs. Such methods continue to map fundamental mechanisms of sensorimotor gating, hyperlocomotion, social interaction, and underlying monoaminergic, glutamatergic, and GABAergic disturbances. These strategies will require, however, a greater use of neurophysiological tools to better inform clinical research. In this sense, electrophysiology and viral vector-based circuit dissection, like optogenetics, can further elucidate how exogenous cannabinoids worsen (e.g., tetrahydrocannabinol, THC) or ameliorate (e.g., cannabidiol, CBD) schizophrenia symptoms, like hallucinations, delusions, and cognitive deficits. Also, recent studies point to a complex endocannabinoid-endovanilloid interplay, including the influence of anandamide (endogenous CB1 and TRPV1 agonist) on cognitive variables, such as aversive memory extinction. In fact, growing interest has been devoted to TRPV1 receptors as promising therapeutic targets. Here, these issues are reviewed with an emphasis on the neurophysiological evidence. First, we contextualize imaging and electrographic findings in humans. Then, we present a comprehensive review on rodent electrophysiology. Finally, we discuss how basic research will benefit from further combining psychopharmacological and neurophysiological tools.

To examine the responses of mouse odontoblast-lineage cell line (OLC) cultures to xylitol-induced hypertonic stress.OLCs were treated with xylitol, sucrose, sorbitol, mannitol, arabinose and lyxose. Cell viability was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium assay. The expression of transient receptor potential vanilloids (TRPV) 1, 3 and 4 was detected using a reverse transcriptase-polymerase chain reaction (RT-PCR) assay. The expression of aquaporin (AQP) 2 was detected using immunofluorescence and Western blotting analysis. The expression of interleukin-6 (IL-6) under xylitol-induced hypertonic stress was assessed using an enzyme-linked immunosorbent assay (ELISA). Small interfering ribonucleic acid (siRNA) for AQP-2 was used to inhibition assay.Xylitol-induced hypertonic stress did not decrease OLC viability, unlike the other sugars tested. OLCs expressed TRPV1, 3 and 4 as well as AQP2. Xylitol inhibited lipopolysaccharide (LPS)-induced IL-6 expression after 3 h of hypertonic stress. TRPV1 mRNA expression was upregulated by xylitol. Costimulation with HgCl2 (AQP inhibitor) and Ruthenium red (TRPV1 inhibitor) decreased cell viability with xylitol stimulation. OLCs treated with siRNA against TRPV1 exhibited decreased cell viability with xylitol stimulation.OLCs have high-cell viability under xylitol-induced hypertonic stress, which may be associated with TRPV1 and AQP2 expressions.

Background and Purpose Evodiamine, a racemic quinazolinocarboline alkaloid isolated from the traditional Chinese medicine Evodiae fructus, has been reported to act as an agonist of the transient receptor potential vanilloid type-1 (TRPV1) cation channel both in vitro and in vivo. Evodiamine is structurally different from all known TRPV1 activators, and has significant clinical potential as a thermogenic agent. Nevertheless, the molecular bases for its actions are still poorly understood. Experimental Approach To investigate the structure-activity relationships of evodiamine, the natural racemate was resolved, and a series of 23 synthetic analogues was prepared, using as the end point the intracellular Ca2+ elevation in HEK-293 cells stably overexpressing either the human or the rat recombinant TRPV1. Key Results S-(+) evodiamine was more efficacious and potent than R-(−) evodiamine, and a new potent lead (Evo30) was identified, more potent than the reference TRPV1 agonist, capsaicin. In general, potency and efficacy correlated with the lipophilicity of the analogues. Like other TRPV1 agonists, several synthetic analogues could efficiently desensitize TRPV1 to activation by capsaicin. Conclusions and Implications Evodiamine qualifies as structurally unique lead structure to develop new potent TRPV1 agonists/desensitizers. Linked Articles This article is part of a themed section on the pharmacology of TRP channels. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-10

Capsaicinoids are the ‘hot’ compounds in placental tissues of Capsicum fruits that are responsible for capsicum’s pungency. Capsaicinoids belong to the broader class of vanilloids that activate the non-selective cation channel, transient receptor potential vanilloid-1 (TRPV1). Endogenous vanilloids include arachidonic acid derivatives that have different affinities for TRPV1 and are increasingly recognized as an important group of signaling molecules affecting tissue injury, pain and inflammation. Furthermore, some endogenous vanilloids have high affinity for cannabinoid receptors (CB1 and CB2), which are present in platelets. The most well-known and widely studied plant-derived vanilloid, capsaicin, is reported to have anti-platelet properties but the mechanism of action is uncertain. This article will briefly review the mechanisms involved in platelet activation and aggregation, discuss the properties of vanilloids and their receptor, TRPV1, and discuss whether the effects of vanilloids, and particularly capsaicinoids, on platelets may be exploited for therapeutic benefit.

Vanilloids are pain evoking molecules that serve as ligands of the "heat and capsaicin receptor" TRPV1. Binding of either endogenous or exogenous vanilloids evokes channel and subsequent neuronal activation, leading to pain sensation. Despite its pivotal physiological role, the molecular basis of TRPV1 activation and deactivation is not fully understood. The highly conserved tyrosine in position 511 (Tyr(511)) of the rat TRPV1 (rTRPV1) was the first residue to be identified as a necessary participant in the vanilloid-mediated response. rTRPV1 cryo-EM structures implicated rotation of this residue in the vanilloids bound state. Therefore, we hypothesize that the rTRPV1 Tyr(511) residue entraps vanilloids in their binding site, prolonging channel activity. To test our hypothesis, we generated an array of rTRPV1 mutants, containing the whole spectrum of Tyr(511) substitutions, and tested their response to both exo- and endovanilloids. Our data show that only substitutions of Tyr(511) to aromatic amino acids were able to mimic, albeit partially, the vanilloid-evoked activation pattern of the wt receptor. Although these substitutions reduced the channel sensitivity to vanilloids, a maximal open-channel lifetime could be achieved. Moreover, whereas their current activation rate remains intact, receptors with Tyr(511) substitutions exhibited a faster current deactivation. Our findings therefore suggest that the duration of channel activity evoked by vanilloids is regulated by the interaction between Tyr(511) and the agonist. To conclude, we suggest that Tyr(511)-mediated anchoring of vanilloids in their binding pocket is pivotal for TRPV1 activation and subsequent pain sensation.

The TRPV1 channel is a detector of noxious stimuli, including heat, acidosis, vanilloid compounds and lipids. The gating mechanisms of the related TRPV2 channel are poorly understood because selective high affinity ligands are not available, and the threshold for heat activation is extremely high (>50°C). Cryo-EM structures of TRPV1 and TRPV2 reveal that they adopt similar structures, and identify a putative vanilloid binding pocket near the internal side of TRPV1. Here we use biochemical and electrophysiological approaches to investigate the resiniferatoxin(RTx) binding site in TRPV1 and to explore the functional relationships between TRPV1 and TRPV2. Collectively, our results support the interaction of vanilloids with the proposed RTx binding pocket, and demonstrate an allosteric influence of a tarantula toxin on vanilloid binding. Moreover, we show that sensitivity to RTx can be engineered into TRPV2, demonstrating that the gating and permeation properties of this channel are similar to TRPV1. DOI: http://dx.doi.org/10.7554/eLife.16409.001, eLife digest Ion channels form pores in cell membranes and can open and close to allow specific ions to flow from one side of the membrane to the other. Humans and other mammals rely on an ion channel protein called TRPV1 to sense heat, and this protein is activated by the active ingredient in hot chili peppers, a chemical called capsaicin that belongs to a group of compounds called vanilloids. An ion channel called TRPV2 is related to TRPV1 and has a similar shape, but is less well understood. This is partly because there are no chemicals that are known to selectively activate this channel, and it is not activated by the vanilloids that activate TRPV1. Zhang, Hanson et al. have now investigated where vanilloid compounds bind to activate the rat TRPV1 channel and if the binding site can be created in the rat TRPV2 as well. Like all proteins, these channels are built from smaller units called amino acids. The results from an array of approaches identified four specific amino acids that can be exchanged between TRPV1 and TRPV2 to swap their ability to bind and be activated by resiniferatoxin (a vanilloid isolated from a cactus-like plant called resin spurge). When rat TRPV2 channels were engineered to contain these four amino acids, resiniferatoxin could easily open the channel. In addition, the engineered channel allowed ions to pass through in a way that is similar to TRPV1, which suggests that the channels are more similar than previously believed. Together the findings show how the TRPV2 channel can be made sensitive to vanilloids. This will help researchers to solve the structure of this ion channel when it is active and open. In addition, the findings may also allow the role of TRPV2 to be explored further in animals, such as mice. DOI: http://dx.doi.org/10.7554/eLife.16409.002

To assess the effectiveness of TRPV1 modulators in animal model of Chronic fatigue syndrome (CFS). To assess central and peripheral behavioral activity of TRPV1 modulators.CFS was induced by forcing the rats to swim for 10min for 21 consecutive days. The rats were treated with capsaicin (TRPV1 agonist, 2.5mg/kg) and n-tert-butylcyclohexanol (TRPV1 antagonist, 10mg/kg) for 21days 30min before the exposure to stress procedure. The behavioral consequence of CFS was measured in terms of immobility time, grip strength, locomotor activity, and anxiety level using Rota rod, Actophotometer, and Elevated plus maze model respectively. The other parameters include Plasma corticosterone, adrenal gland and spleen weight, complete blood count, blood urea niterogen (BUN), Lactate dehydrogenase (LDH), Lipid peroxidation, catalase and reduced glutathione (GSH).TRPV1 modulators reversed (p0.05) the increase in immobility period, anxiety, spleen weight, BUN and LDH levels, and MDA levels along with decrease in grip strength, locomotor activity, plasma corticosterone, adrenal gland weight, catalase, and GSH. There was also significant increase in total WBC count when compared with the disease control group. The reversal was attributed to modulation of HPA axis, oxidative stress, anaerobic respiration product, muscle degradation product.The present study reveals the effectiveness of n-tert-butylcyclohexanol and capsaicin against chronic fatigue syndrome. The mechanism of action can be attributed to inhibition of TRPV1 channel and thereby modulating pain perception, neuroendocrine function, oxidative stress and immune function.

Vanilloid-like agents, including capsaicin, N-arachidonoyl-dopamine and N-oleoyldopamine inhibit platelet aggregation, however little is known about the precise mechanism(s) of action. The authors have previously shown that blocking of the capsaicin receptor, transient receptor potential vanilloid-1 (TRPV1), does not interfere with capsaicin action during adenosine diphosphate (ADP)-induced aggregation. This research is extended to investigate the effect of these vanilloid-like-agents on platelet count, and to test whether the effect of these agents is mediated through TRPV1 and/or cannabinoid (CB1 and CB2) receptors in the presence of other agonists, including collagen and arachidonic acid. Incubation of platelets with each of the individual vanilloids, or with receptor antagonists of TRPV1 (SB452533), CB1 (AM251) and CB2 (AM630), for up to 2 h did not significantly affect the platelet count. Similarly, the effect of individual vanilloids on the inhibition of platelet aggregation was not significantly different in the presence of receptor agonists compared to control, irrespective of the agonist used, suggesting that the inhibitory effect of vanilloids on platelet aggregation is independent of TRPV1, CB1 and CB2 receptors. Further research on the antiplatelet activity of vanilloids should focus on mechanisms other than those associated with vanilloid receptors.

Capsaicin, the pungent ingredient of the hot chili pepper, is known to act on the transient receptor potential cation channel vanilloid subfamily member 1 (TRPV1). TRPV1 is involved in somatic and visceral peripheral inflammation, in the modulation of nociceptive inputs to spinal cord and brain stem centers, as well as the integration of diverse painful stimuli. In this review, we first describe the chemical and pharmacological properties of capsaicin and its derivatives in relation to their analgesic properties. We then consider the biochemical and functional characteristics of TRPV1, focusing on its distribution and biological effects within the somatosensory and viscerosensory nociceptive systems. Finally, we discuss the use of capsaicin as an agonist of TRPV1 to model acute inflammation in slices and other ex vivo preparations.

Transient receptor potential (TRP) channels belong to a superfamily of sensory-related ion channels responding to a wide variety of thermal, mechanical, or chemical stimuli. In an attempt to comprehend the piquancy and pain mechanism of the archetypal vanilloids, transient receptor potential vanilloid (TRPV) 1 was discovered. TRPV1, a well-established member of the TRP family, is implicated in a range of functions including inflammation, painful stimuli sensation, and mechanotransduction. TRPV1 channels are nonselective cation receptors that are gated by a broad array of noxious ligands. Such polymodal-sensor aspect makes the TRPV1 channel extremely versatile and important for its role in sensing burning pain. Besides ligands, TRPV1 signaling can also be modulated by lipids, secondary messengers, protein kinases, cytoskeleton, and several other proteins. Due to its central role in hyperalgesia transduction and inflammatory processes, it is considered as the primary pharmacological pain target. Moreover, understanding the structural and functional intricacies of the channel is indispensable for the therapeutic intervention of TRPV1 in pain and other pathological disorders. In this chapter, we seek to give a mechanistic outlook on the TRPV1 channel. Specifically, we will explore the TRPV1 structure, activation, modulation, ligands, and its therapeutic targeting. However, the major objective of this review is to highlight the fact that TRPV1 channel can be treated as an effective therapeutic target for treating several pain- and nonpain-related physiological and pathological states.

Transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel, is a receptor activated by high temperatures and chemical agonists such as the vanilloids and protons. Because of these properties, TRPV1 has emerged as a polymodal nocisensor of nociceptive afferent neurons. TRPV1 is thought to be a central transducer of hyperalgesia and a prime target for controlling pain pharmacologically because it is a point where many proalgesic pathways converge and it is upregulated and sensitized by inflammation and injury. However, whether TRPV1 agonists promote or inhibit inflammation remains unclear. We recently demonstrated that SA13353 (1-[2-(1-adamantyl)ethyl]-1-pentyl-3-[3-(4-pyridyl)propyl]urea), a novel TRPV1 agonist, inhibits tumor necrosis factor-a production by the activation of capsaicin-sensitive afferent neurons and reduces the severity of symptoms in kidney injury, lung inflammation, arthritis, and encephalomyelitis. These results suggest that TRPV1 agonists may act as anti-inflammatories in certain inflammatory and autoimmune conditions in vivo. Given the potential deleterious effects of inhibiting the population of channels with a protective function, caution should be taken in the use of potent TRPV1 antagonists as a general strategy to treat inflammation. Further studies are required to clarify the role of TRPV1 and neuropeptides, which are released because of TRPV1 activation in inflammation and autoimmune diseases.

The effect of the plant-derived vanilloid, capsaicin (CAP), on the metabolic activity of THP-1, U266B1 and U937 hematological malignancy cells was determined. CAP reduced metabolic activity in a concentration-dependent manner in the three cell lines. A biphasic effect was observed on THP-1 cells (EC50: IC50 (95% CI) 32.9 (19.9-54.3)/219 (144-246) µmol/l). U266B1 cells were more resistant to CAP than THP-1 and U937. Metabolic activity was significantly inhibited by CAP in U937 compared to U266B1 cells (IC50: 197 versus 431 µmol/l, respectively, p < 0.008). Transient receptor potential vanilloid-1 (TRPV1) and CB1 antagonists (SB452533 and AM251, respectively) suppressed the CAP-induced increase in THP-1 cell metabolic activity (p < 0.001). AM251 and SB452533 appeared to act as partial agonists and displayed a synergistic effect with CAP in U937 cells. CAP inhibits the metabolic activity of malignant hematological cells through non-TRPV1-dependent mechanisms.

The idea of selectively targeting nociceptive transmission at the level of the peripheral nervous system is attractive from multiple perspectives, particularly the potential lack of non-specific (non-targeted) CNS side effects. Out of the multiple TRP channels involved in nociception, TRPV1 is a strong candidate based on its biophysical conductance properties and its expression in inflammation-sensitive dorsal root ganglion neurons and their axons and central and peripheral nerve terminals. While TRPV1 antagonists have undergone extensive medicinal chemical and pharmacological investigation, for TRPV1 agonists nature has provided an optimized compound in RTX. RTX is not suitable for systemic administration, but it is highly adaptable to a variety of pain problems when used by local administration. This can include routes as diverse as subcutaneous, intraganglionic or intrathecal (CSF space around the spinal cord). The present review focuses on the molecular and preclinical animal experiments that form the underpinnings of our clinical trial of intrathecal RTX for pain in advanced cancer. As such this represents a new approach to pain control that emerges from a long line of research on capsaicin and other vanilloids, their physiological actions, and the molecular biology of the capsaicin receptor TRPV1.

Vanilloids including capsaicin and resiniferatoxin (RTX) have been identified as potential novel anti-inflammatory and analgesic compounds. We have previously shown that systemic capsaicin administration to neonatal rats evokes profound long-term alterations in transient receptor potential vanilloid 1 (TRPV1)- and neurokinin 1 (NK1) receptor-mediated respiratory responses in the commissural nucleus of the solitary tract (cNTS). Whether this effect of capsaicin is unique to developmentally immature animals is unknown. Therefore, in the present study, we investigated the effects of systemic capsaicin administration to adult rats on NK1 receptor binding sites, TRPV1 and NK1 immunoreactivity and function in the cNTS. Microinjection of capsaicin (1 nmol) or RTX (75 pmol) into the cNTS of vehicle-pretreated rats produced a profound bradypnoea (maximum change: –45 breaths·min–1) and a small increase in tidal volume (VT). Similarly, microinjection of the selective NK1 receptor agonists [Sar9, Met(O2)11]substance P (SP; 66 pmol) and septide (20 pmol) decreased respiratory frequency and increased VT. Thirteen to 18 days after systemic administration of capsaicin (125 mg·kg–1 s.c.), the bradypnoeic responses to both capsaicin and RTX were absent (p < 0.05), indicative of sensory neuron ablation/desensitisation. Systemic capsaicin pretreatment significantly (p < 0.05) reduced the density of both [125I]Bolton-Hunter SP binding sites (NK1 receptors) and NK1 receptor immunoreactivity in the cNTS, but did not alter the respiratory responses evoked by microinjection of [Sar9, Met(O2)11]SP and septide into this region. These studies show that systemic capsaicin administration reduces NK1 receptor density in the cNTS without adversely affecting NK1 receptor function at this site. We speculate that adult rats may be more resistant than neonatal rats to the neuroplastic effects of systemic capsaicin administration.

Capsaicin and other vanilloids selectively excite and subsequently desensitize pain-conducting nerve fibers (nociceptors) and this process contributes to the analgesic (and thus therapeutically relevant) effects of these compounds. Such a desensitization process is triggered by the activation of the transient receptor potential vanilloid subtype 1 receptor channels (TRPV1) that open their cationic pores, permeable to sodium, potassium and calcium (Ca(2+)) ions. Depending on the duration of capsaicin exposure and the external calcium concentration, the Ca(2+) influx via TRPV1 channels desensitizes the channels themselves, which, from the cellular point of view, represents a feedback mechanism protecting the nociceptive neuron from toxic Ca(2+) overload. The 'acute desensitization' accounts for most of the reduction in responsiveness occurring within the first few (~20) seconds after the vanilloids are administered to the cell for the first time. Another form of desensitization is 'tachyphylaxis', which is a reduction in the response to repeated applications of vanilloid. The wealth of pathways following TRPV1 activation that lead to increased intracellular Ca(2+) levels and both forms of desensitization is huge and they might utilise just about every known type of signalling molecule. This review will not attempt to cover all historical aspects of research into all these processes. Instead, it will try to highlight some new challenging thoughts on the important phenomenon of TRPV1 desensitization and will focus on the putative mechanisms that are thought to account for the acute phase of this process.

Quinone reductase (QR) inducing activity, a biomarker for Phase II enzyme induction, was detected in a crude ginger rhizome ethanolic extract using a murine hepatoma cell (Hepa 1c1c7) bioassay. An ethyl acetate-partitioned fraction became enriched in QR inducing activity with a CD value (concentration required to double QR specific activity) of 7 μg/ml and was further separated by silica flash chromatography. The four major fractions recovered exhibited CD values ranging 10–20 μg/mL for QR inducing activity. 1 H NMR analysis revealed an abundance of gingerols in the first 3 fractions, and this led to a comparative assessment of QR inducing and anti-inflammatory activities among [6]-gingerol and structurally related vanilloids from ginger and other spices. [6]-Dehydroshogaol (DHSG), a minor component of fresh ginger, had QR inducing activity (CD = 8.4 μM) of comparable potency to the well known cancer preventive agent, curcumin (CD = 4.3 μM). In contrast, [6]-gingerol the major pungent component of ginger showed less potent QR inducing activity (CD = 55 μM) and capsaicin exhibited the weakest inducing activity (CD = 103 μM). [6]-Shogaol, [6]-DHSG and curcumin were also potent inhibitors of nitric oxide (NO) synthesis, inhibiting 50% NO evolution in activated macrophages at levels of 10–12 μM (IC 50 values). Comparatively, IC 50 values for [6]-gingerol and capsaicin were about an order of magnitude greater (less potent) at 90 μM and 169 μM, respectively. This appears to be the first report of biological activities of [6]-DHSG, and Phase II enzyme-inducing ability of shogoal and gingerol.

Cannabinoids and vanilloids are two distinct groups of substances that share some pharmacological targets. Here we report that two cannabinoid type 1 receptor (CB1) agonists, WIN 55212-2 (WIN) and arachidonyl-2'-chloroethylamide (ACEA) have opposing effects on evoked quantal acetylcholine release - WIN decreased quantal content while ACEA increased quantal content. The decrease in quantal content by WIN was blocked by the CB1 antagonist AM 251. The increase in quantal content by ACEA was not blocked by AM 251, indicating it acts through a receptor other than CB1. As ACEA is also an agonist for the vanilloid receptor (TRPV1) we tested the effect of vanilloids on quantal content. Similar to ACEA, the vanilloid agonist capsaicin increased quantal content, and this effect was blocked by capsazepine, a TRPV1 antagonist. Capsazepine also blocked the increase in quantal content by ACEA. Together these data show an inhibitory effect of CB1 activation on evoked acetylcholine release and the first evidence for the presence of a vanilloid receptor at the neuromuscular junction.

Aim Thermoregulatory side effects hinder the development of transient receptor potential vanilloid-1 (TRPV1) antagonists as new painkillers. While many antagonists cause hyperthermia, a well-studied effect, some cause hypothermia. The mechanisms of this hypothermia are unknown and were studied herein. Methods Two hypothermia-inducing TRPV1 antagonists, the newly synthesized A-1165901 and the known AMG7905, were used in physiological experiments in rats and mice. Their pharmacological profiles against rat TRPV1 were studied in vitro. Results Administered peripherally, A-1165901 caused hypothermia in rats by either triggering tail-skin vasodilation (at thermoneutrality) or inhibiting thermogenesis (in the cold). A-1165901-induced hypothermia did not occur in rats with desensitized (by an intraperitoneal dose of the TRPV1 agonist resiniferatoxin) sensory abdominal nerves. The hypothermic responses to A-1165901 and AMG7905 (administered intragastrically or intraperitoneally) were absent in Trpv1-/- mice, even though both compounds evoked pronounced hypothermia in Trpv1+/+ mice. In vitro, both A-1165901 and AMG7905 potently potentiated TRPV1 activation by protons, while potently blocking channel activation by capsaicin. Conclusion TRPV1 antagonists cause hypothermia by an on-target action: on TRPV1 channels on abdominal sensory nerves. These channels are tonically activated by protons and drive the reflectory inhibition of thermogenesis and tail-skin vasoconstriction. Those TRPV1 antagonists that cause hypothermia further inhibit these cold defences, thus decreasing body temperature. Significance TRPV1 antagonists (of capsaicin activation) are highly unusual in that they can cause both hyper- and hypothermia by modulating the same mechanism. For drug development, this means that both side effects can be dealt with simultaneously, by minimizing these compounds' interference with TRPV1 activation by protons.

Background and purpose: ATP, released from urothelial cells, modulates afferent nerve firing from the urinary bladder. Here, we have characterized ATP release from the rat bladder mucosa in response to acid, capsaicin, electrical field stimulation (EFS) and stretch, using agonists and antagonists at transient receptor potential vanilloid receptor 1 (TRPV1) and acid-sensing ion channels (ASICs). Experimental approach: Rat mucosal strips (containing urothelium and lamina propria) in Perspex microbaths were superfused with Krebs solution. ATP was measured after exposure of matched strips to acid (pH 6.6–5.0), capsaicin (0.1–10 µM), EFS or stretch (150% of original length). Key results: Median basal ATP release was 3.46 nmol·g−1. The mucosal strips responded to stimuli with potency order (median, IQR): acid (pH 5.6–6.0) 286 (103–555) > 10 µM capsaicin 188 (117–431) > 10 Hz EFS 63.0 (13.3–96.4) > stretch 24.4 (6.73–55.1) nmol ATP g−1. ATP release in response to acid was pH dependent (P < 0.05). Responses to capsaicin did not desensitize nor were they concentration dependent. TRPV1 antagonist, capsazepine (10 µM) abolished capsaicin-evoked ATP release, and reduced acid-evoked (pH 6.5) release to 30% (P < 0.001). The ASIC channel antagonists gadolinium (0.1 mM) and amiloride (0.3 µM) reduced (P < 0.05) the acid-evoked (pH 6.5) release to 40 and 6.5% respectively. ASIC (ASIC1, ASIC2a, ASIC2b, ASIC3) and two TRPV1 gene products were detected in mucosal and detrusor extracts. Conclusions and implications: Capsaicin (at TRPV1) and acid (at both TRPV1 and ASIC) induce ATP release from the rat bladder mucosa. This ATP appears to be principally of urothelial origin. This study highlights the importance of ATP and acid as signalling molecules in modulating bladder function.

5.1. Dorsal Vagal Complex 3170 5.2. Vagal Afferents 3171 5.3. Enteric Nervous System 3171 5.4. Gastrointestinal Tissue 3172 5.5. Substance P and Emesis 3172 6. Cannabinoids and Vanilloids 3175 6.1. Dorsal Vagal Complex 3176 6.2. Vagal Afferents 3178 6.3. Enteric Nervous System 3178 6.4. Gastrointestinal Tissue 3179 6.5. Cannabinoids and Emesis 3179 7. Eicosanoids: Synthesis, Storage, Release, Degradation, And Receptors 3181

Small- to medium-sized neurons in the dorsal root ganglion (DRG) convey nociceptive information to the spinal cord. The co-expression of TRPV1 receptors (sensitive to vanilloids, heat and acidic pH) with P2X(3) receptors (sensitive to extracellular ATP) has been found in many DRG neurons. We investigated whether the co-activation of these two receptor classes in small-diameter cells leads to a modulation of the resulting current responses shaping the intensity of pain sensation. The whole-cell patch clamp method was used to record agonist-induced currents in cultured rat DRG neurons and in HEK293 cells transfected with the respective wild-type recombinant receptors or their mutants. Co-immunoprecipitation studies were used to demonstrate the physical association of TRPV1 and P2X(3) receptors. At a negative holding potential, the P2X(3) receptor agonist alpha,beta-meATP induced less current in the presence of the TRPV1 agonist capsaicin than that in its absence. This inhibitory interaction was not changed at a positive holding potential, in a Ba(2+)-containing superfusion medium, or when the buffering of intrapipette Ca(2+) was altered. The C-terminal truncation at Glu362 of P2X(3) receptors abolished the TRPV1/P2X(3) cross-talk in the HEK293 expression system. Co-immunoprecipitation studies with polyclonal antibodies generated against TRPV1 and P2X(3) showed a visible signal in HEK293 cells transfected with both receptors. It is concluded that the two pain-relevant receptors TRPV1 and P2X(3) interact with each other in an inhibitory manner probably by a physical association established by a motif located at the C-terminal end of the P2X(3) receptor distal to Glu362.

Preclinical studies suggest that the vanilloid receptor (TRPV1) is an important component of several disease areas such as pain (inflammatory, visceral, cancer and neuropathic), airway disease (including chronic cough), inflammatory bowel disease (IBD), interstitial cystitis, urinary incontinence, pancreatitis and migraine. TRPV1 is a member of a distinct subgroup of the transient receptor potential (TRP) family of ion channels. The neuronally expressed TRPV1 is a non-selective, Ca(2+)-preferring, cation channel. In addition to capsaicin, this channel is activated by a number of different stimuli including heat, acid, certain arachidonic acid derivatives and direct phosphorylation via protein kinase C (PKC). Moreover, there is also evidence that various inflammatory mediators such as adenosine triphosphate (ATP), bradykinin, nerve growth factor (NGF) or prostaglandin E(2) (PGE(2)) may indirectly lead to activation of the TRPV1 channel via activation of their respective receptors. There is strong experimental evidence that the combination of direct and indirect mechanisms finely tune the TRPV1 activity. Each of the different known modes of direct TRPV1 activation (protons, heat and vanilloids) is capable of sensitising the channel to other agonists. Similarly, inflammatory mediators from the external milieu found in disease conditions can indirectly sensitise the receptor. It is this sensitisation of the TRPV1 receptor in inflammatory disease that could hold the key and contribute to the transduction of noxious signalling for normally innocuous stimuli, i.e. either hyperalgesia in the case of chronic pain or airway hyperresponsivness/hypertussive responses in patients with chronic cough. It seems reasonable to suggest that the various mechanisms for sensitisation provide a scenario for TRPV1 to be tonically active and this activity may contribute to the underlying pathology -- providing an important convergence point of multiple pain producing stimuli in the somatosensory system and multiple cough-evoking irritants in the airways. The complex mechanisms and pathways that contribute to the pathophysiology of chronic pain and chronic cough have made it difficult for clinicians to treat patients with current therapies. There is an increasing amount of evidence supporting the hypothesis that the expression, activation and modulation of TRPV1 in sensory neurones appears to be an integral component of pain and cough pathways, although the precise contribution of TRPV1 to human disease has yet to be determined. So the question remains open as to whether TRPV1 therapeutics will be efficacious and safe in man and represent a much needed novel pain and cough therapeutic.

Agents that block the efferent function of micturition reflex, such as antimuscarinics, are currently first-line therapy for overactive bladder (OAB) and neurogenic detrusor overactivity. Many urologists believe that the actual “efferent” pharmacologic management of OAB is not completely satisfactory. Consequently, research is trying to address issues of efficacy, tolerability, and convenience of new therapeutic strategies targeting the “afferent” function. This article discusses the rationale underlying the development of new drugs and the use of electrical modulation to manage lower urinary tract dysfunctions. It also offers insight into the mechanism of action, efficacy, side effects, and market status of several drugs that target the afferent branch of micturition reflex (vanilloids, botulinum toxin, tachykinin, nociceptin/orphanin FQ) and sacral neuromodulation.

Intravesical therapy with botulinum toxin type A (BTX-A) and vanilloids (capsaicin and resiniferatoxin) are actively investigated as potential treatments for lower urinary tract symptoms refractory to conventional therapy in patients with neurogenic detrusor overactivity. BTX-A cleaves soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins in afferent and efferent nerve endings, impeding the fusion of synaptic vesicles with the neuronal membrane necessary for the release of neurotransmitters. Vanilloids desensitize the transient receptor potential vanilloid type 1 receptor and inactivate C-fibers. BTX-A intradetrusor injections are extremely effective for treating urinary incontinence, provide adequate protection of the upper urinary tract, and improve quality of life in patients with neurogenic detrusor overactivity. Therefore, BTX-A is currently the mainstay of intravesical therapy. However, despite promising results overall, the administration of these compounds, including BTX-A, remains an experimental procedure requiring further clinical studies.

This study investigated the effect of synthetic capsiate, a simplified analogue of capsiate, and vanillyl alcohol on the oxidative stress induced by tert-butyl hydroperoxide (TBH) in a line of fibroblasts derived from monkey kidney (Vero cells). In response to the TBH-mediated oxidative stress, a reduction of the levels of total unsaturated fatty acids and cholesterol was observed, and a rise in the concentrations of conjugated dienes fatty acids hydroperoxides and 7-ketocholesterol. Pretreatment with both synthetic capsiate and vanillyl alcohol preserved Vero cells from oxidative damage and showed a remarkable protective effect on the reduction of the levels of total unsaturated fatty acids and cholesterol, inhibiting the increase of MDA, conjugated dienes fatty acids hydroperoxides, and 7-ketocholesterol. Both compounds were effective against peroxidation of cell membrane lipids induced by TBH, with synthetic capsiate essentially acting as a pro-drug of vanillyl alcohol, its hydrophilic hydrolytic derivative.

OBJECTIVES To investigate the peripheral role of nitric oxide (NO) in capsaicin-induced detrusor overactivity (DO), as exogenously applied vanilloids can evoke NO release in urothelial cells but its functional role has not yet been reported. MATERIALS AND METHODS The effects of NG-nitro-l-arginine methyl ester (L-NAME), an inhibitor of NO synthase (NOS), on bladder activity during intravesical capsaicin (30 µm) instillation were examined by using continuous infusion cystometry in urethane-anaesthetized rats. L-NAME was administered intravenously (i.v., 20 mg/kg), intrathecally (i.t., 270 µg/rat), intracerebroventricularly (i.c.v., 270 µg/rat) or intravesically (10 mg/mL) before or during capsaicin instillation. RESULTS During cystometry with intravesical saline infusion, L-NAME injected i.v., i.t. and i.c.v., but not intravesically, significantly increased the intercontraction intervals (ICI) and L-NAME injected i.v., but not i.t., i.c.v. or intravesically, increased the maximum voiding pressure (MVP) without affecting the baseline pressure. Capsaicin instillation induced DO evidenced by a significant reduction in the ICI. L-NAME administered i.v. further decreased the ICI and increased the MVP and the baseline pressure during capsaicin instillation. Co-intravesical application of capsaicin and L-NAME also similarly enhanced capsaicin-induced DO. However, L-NAME injected i.t. or i.c.v. had no effect on capsaicin-induced DO. The excitatory effects of i.v and intravesical L-NAME on the ICI, MVP and baseline pressure during capsaicin infusion were significantly suppressed by desensitization of C-fibre afferent pathways by capsaicin pretreatment (125 mg/kg s.c., 4 days before cystometry). CONCLUSION These results indicate that locally released NO can suppress DO induced by capsaicin-mediated C-fibre activation and that central NO pathways are not involved in capsaicin-induced DO.

Background Perineural administration of the naturally occurring vanilloids (capsaicin, resiniferatoxin [RTX]) produces selective nociceptive blockade. Studies using perineural vanilloids in high concentrations suggest that they can cause a degeneration of unmyelinated fibers. However, electron microscopic studies of local vanilloid toxicity produced conflicting outcomes. In the present study, we sought to determine whether RTX-induced reversible sciatic nerve block results in the degenerative changes of unmyelinated fibers. Methods In rat experiments, RTX was administered percutaneously at the sciatic nerve. The effect of RTX was monitored by measuring the rat's response to noxious heat. The sciatic nerves were removed 48 h after the blockade initiation. Quantitative electron microscopic evaluation of the unmyelinated fibers was performed in three groups of animals: RTX 0.0001% (0.1 microg), RTX 0.001% (1 microg), and control (RTX vehicle, 0.1 mL). Results Cross-sections of the sciatic nerve 48 h after the initiation of RTX-induced reversible nerve blockade appeared essentially normal. One rarely observed finding was the irregularly compacted membranous deposits in the unmyelinated axons. The frequency of this finding was approximately one per thousand fibers with both concentrations of RTX. Conclusions The results of the study suggest that a selective and long-lasting sciatic nerve block (up to 2 wk) can be provided by RTX without any significant damage to the unmyelinated nerve fibers.

The transient receptor potential (TRP) vanilloid receptor subtype 1 (TRPV1) is a ligand-gated, Ca(2+)-permeable ion channel in the TRP superfamily of channels. We report the establishment of the first neuronal model expressing recombinant human TRPV1 (SH-SY5Y(hTRPV1)). SH-SY5Y human neuroblastoma cells were stably transfected with hTRPV1 using the Amaxa Biosystem (hTRPV1 in pIREShyg2 with hygromycin selection). Capsaicin, olvanil, resiniferatoxin and the endocannabinoid anandamide increased [Ca(2+)](i) with potency (EC(50)) values of 2.9 nmol/L, 34.7 nmol/L, 0.9 nmol/L and 4.6 micromol/L, respectively. The putative endovanilloid N-arachidonoyl-dopamine increased [Ca(2+)](i) but this response did not reach a maximum. Capsaicin, anandamide, resiniferatoxin and olvanil mediated increases in [Ca(2+)](i) were inhibited by the TRPV1 antagonists capsazepine and iodo-resiniferatoxin with potencies (K(B)) of approximately 70 nmol/L and 2 nmol/L, respectively. Capsaicin stimulated the release of pre-labelled [(3)H]noradrenaline from monolayers of SH-SY5Y(hTRPV1) cells with an EC(50) of 0.6 nmol/L indicating amplification between [Ca(2+)](i) and release. In a perfusion system, we simultaneously measured [(3)H]noradrenaline release and [Ca(2+)](i) and observed that increased [Ca(2+)](i) preceded transmitter release. Capsaicin treatment also produced a cytotoxic response (EC(50) 155 nmol/L) that was antagonist-sensitive and mirrored the [Ca(2+)](I) response. This model displays pharmacology consistent with TRPV1 heterologously expressed in standard non-neuronal cells and native neuronal cultures. The advantage of SH-SY5Y(hTRPV1) is the ability of hTRPV1 to couple to neuronal biochemical machinery and produce large quantities of cells.

Transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel with high Ca(2+) permeability, which functions as a polymodal nociceptor activated by heat, protons and several vanilloids, including capsaicin and anandamide. Although TRPV1 channels are widely distributed in the mammalian brain, their pathophysiological roles in the brain remain to be elucidated. In this study, we investigated whether TRPV1 is involved in cerebral ischemic injury using a middle cerebral artery (MCA) occlusion model in wild-type (WT) and TRPV1-knockout (KO) mice. For transient ischemia, the left MCA of C57BL/6 mice was occluded for 60 min and reperfused at 1 and 2 days after ischemia. We found that neurological and motor deficits, and infarct volumes in TRPV1-KO mice were lower than those of WT mice. Consistent with these results, intracerebroventricular injection of a TRPV1 antagonist, capsazepine (20 nmol), 30 min before the onset of ischemia attenuated neurological and motor deficits and improved infarct size without influencing cerebral blood flow in the occluded MCA territory. The protective effect of capsazepine on ischemic brain damage was not observed in TRPV1-KO mice. WT and TRPV1-KO mice did not show any differences with respect to the increased number of Iba1-positive microglia/macrophages, GFAP-positive astrocytes, and Gr1-positive neutrophils at 1 and 2 days after cerebral ischemia. Taken together, we conclude that brain TRPV1 channels are activated by ischemic stroke and cause neurological and motor deficits and infarction after brain ischemia.