Potential TRPV1 Research Articles

Natural Products and some Semi-synthetic Analogues as Potential TRPV1 Ligands for Attenuating Neuropathic Pain.

Natural products and leads inspired by them have acted as a probe for successful drug discovery for many decades. Pain is an obnoxious sensory and emotional experience associated with potential tissue damage. It affects the quality of life of patients to a greater extent. Despite the availability of several agents targeting TRP receptors, none of them can proficiently alleviate neuropathic pain. TRPV1 is a prospective target for treating neuropathic pain as it is recognized to modulate the pain circuitry at the periphery and the central level. In this review, we have discussed several natural molecules, such as Capsaicinoids, Capsinoids, Piperine, Eugenol, Scutigeral, Ginsenosides, Cinnamaldehyde, Camphor, Shogaol, Gingerols, Zingerone, Allicin, Evodiamine, Allylisothiocyanate, Cannabidiol, Ricinoleic acid, Isovelleral, Capsazepine, Thapsigargin, Pellitorine, Yohimbine, Curcumin and some semi-synthetic analogues that activate TRPV1 channels and consequently, can be further harnessed for the treatment of neuropathic pain.

Toxic Peptide From Palythoa caribaeorum Acting on the TRPV1 Channel Prevents Pentylenetetrazol-Induced Epilepsy in Zebrafish Larvae.

PcActx peptide, identified from the transcriptome of zoantharian Palythoa caribaeorum, was clustered into the phylogeny of analgesic polypeptides from sea anemone Heteractis crispa (known as APHC peptides). APHC peptides were considered as inhibitors of transient receptor potential cation channel subfamily V member 1 (TRPV1). TRPV1 is a calcium-permeable channel expressed in epileptic brain areas, serving as a potential target for preventing epileptic seizures. Through in silico and in vitro analysis, PcActx peptide was shown to be a potential TRPV1 channel blocker. In vivo studies showed that the linear and oxidized PcActx peptides caused concentration-dependent increases in mortality of zebrafish larvae. However, monotreatment with PcActx peptides below the maximum tolerated doses (MTD) did not affect locomotor behavior. Moreover, PcActx peptides (both linear and oxidized forms) could effectively reverse pentylenetetrazol (PTZ)-induced seizure-related behavior in zebrafish larvae and prevent overexpression of c-fos and npas4a at the mRNA level. The excessive production of ROS induced by PTZ was markedly attenuated by both linear and oxidized PcActx peptides. It was also verified that the oxidized PcActx peptide was more effective than the linear one. In particular, oxidized PcActx peptide notably modulated the mRNA expression of genes involved in calcium signaling and γ-aminobutyric acid (GABA)ergic-glutamatergic signaling, including calb1, calb2, gabra1, grm1, gria1b, grin2b, gat1, slc1a2b, gad1b, and glsa. Taken together, PcActx peptide, as a novel neuroactive peptide, exhibits prominent anti-epileptic activity, probably through modulating calcium signaling and GABAergic-glutamatergic signaling, and is a promising candidate for epilepsy management.

Abnormal Pain Sensation in Mice Lacking the Prokineticin Receptor PKR2: Interaction of PKR2 with Transient Receptor Potential TRPV1 and TRPA1

The amphibian Bv8 and the mammalian prokineticin 1 (PROK1) and 2 (PROK2) are new chemokine-like protein ligands acting on two G protein-coupled receptors, prokineticin receptor 1 (PKR1) and 2 (PKR2), participating to the mediation of diverse physiological and pathological processes. Prokineticins (PKs), specifically activating the prokineticin receptors (PKRs) located in several areas of the central and peripheral nervous system associated with pain, play a fundamental role in nociception. In this paper, to improve the understanding of the prokineticin system in the neurobiology of pain, we investigated the role of PKR2 in pain perception using pkr2 gene-deficient mice. We observed that, compared to wildtype, pkr2-null mice were more resistant to nociceptive sensitization to temperatures ranging from 46 to 48 °C, to capsaicin and to protons, highlighting a positive interaction between PKR2 and the non-selective cation channels TRPV1. Moreover, PKR2 knock-out mice showed reduced nociceptive response to cold temperature (4 °C) and to mustard oil-induced inflammatory hyperalgesia, suggesting a functional interaction between PKR2 and transient receptor potential ankyrin 1 ion (TRPA1) channels. This notion was supported by experiments in dorsal root ganglia (DRG) cultures from pkr1 and–pkr2-null mice, demonstrating that the percentage of Bv8-responsive DRG neurons which were also responsive to mustard oil was much higher in PKR1−/− than in PKR2−/− mice. Taken together, these findings suggest a functional interaction between PKR2 and TRP channels in the development of hyperalgesia. Drugs able to directly or indirectly block these targets and/or their interactions may represent potential analgesics.

Novobiocin, a Newly Found TRPV1 Inhibitor, Attenuates the Expression of TRPV1 in Rat Intestine and Intestinal Epithelial Cell Line IEC-6.

Background and Purpose: Novobiocin (NOVO), an ABC transporter inhibitor, decreases intestinal wall permeability of capsaicin (CAP), an ABC transporter substrate. However, the mechanism of this effect is not consistent with the action of NOVO as an ABC transporter inhibitor. We previously found that CAP can also be transported via TRPV1, which was site-specific in the permeability of CAP across the intestine. We explored the regulation by NOVO of TRPV1 in the present study.Methods: Rats and transfected IEC-6 cells were used as the models to assess intestinal permeability and expression of TRPV1. Ussing chamber and intracellular accumulation were used to evaluate the influence of NOVO on the transport of CAP in vitro. The expression of TRPV1 was detected after administration of NOVO by qRT-PCR, western blot and immunofluorescent imaging. In addition, MTT and lactate dehydrogenase (LDH) were used to evaluate the cytotoxicity of NOVO in both rat and cell models. Finally, the effect of NOVO on the absorption of CAP in vivo was studied by LC-MS/MS.Results: In vitro data showed that there existed a dose-dependent relationship in the range of concentration between 5 and 50 μM, and even 5 μM NOVO could decrease intestinal permeability of CAP across the intestine. Meanwhile, cytosolic accumulation of CAP decreased when NOVO was used simultaneously or 24 h in advance. NOVO exhibited an inhibition level similar to that of ruthenium red (RR) or SB-705498, a TRPV1-specific inhibitor. NOVO down-regulated TRPV1 expression in the intestine and in transfected cells in a concentration-dependent fashion, hinting that its inhibition of the permeability of CAP is due to its inhibition of TRPV1 expression. Immunofluorescent imaging data showed that the fluorescence intensity of TRPV1 was reduced after pre-treatment with NOVO and SB-705498. In vivo data further demonstrated that oral co-administration of NOVO decreased Cmax and AUC of CAP in dosage-dependent ways, consistent with its role as a TRPV1 inhibitor.Conclusion: NOVO could be a potential TRPV1 inhibitor by attenuating the expression of TRPV1 and may be used to attenuate permeability of TRPV1 substrates.

New transient receptor potential TRPV1, TRPM8 and TRPA1 channel antagonists from a single linear β,γ-diamino ester scaffold

Incorporation of minor changes in the structure of a single β,γ-diaminoester linear scaffold resulted in selective hits for TRPV1, TRPM8 and TRPA1 blockade, as well as some dual antagonists.​

Compartment-specific modulation of GABAergic synaptic transmission by TRPV1 channels in the dentate gyrus.

The transient receptor potential TRPV1 or vanilloid receptor is a nonselective ligand-gated channel highly expressed in primary sensory neurons where it mediates nociception. TRPV1 is also expressed in the brain where its activation depresses excitatory synaptic transmission. Whether TRPV1 also regulates inhibitory synapses in the brain is unclear. Here, using a combination of pharmacology, electrophysiology, and an in vivo knockdown strategy, we report that TRPV1 activation by capsaicin or by the endocannabinoid anandamide depresses somatic, but not dendritic inhibitory transmission in both rat and mouse dentate gyrus. The effect on somatic inhibition was absent in TRPV1 knock-out mice and was also eliminated by two different TRPV1 shRNAs expressed in dentate granule cells, strongly supporting a functional role for TRPV1 in modulating GABAergic synaptic function. Moreover, TRPV1-mediated depression occurs independently of GABA release, requires postsynaptic Ca(2+) rise and activation of calcineurin, and is likely due to clathrin-dependent internalization of GABA receptors. Altogether, these findings reveal a novel form of compartment-specific regulation whereby TRPV1 channels can modify synaptic function in the brain.

Identification of voltage-gated K+ channel beta 2 (Kvβ2) subunit as a novel interaction partner of the pain transducer Transient Receptor Potential Vanilloid 1 channel (TRPV1)

The Transient Receptor Potential Vanilloid 1 (TRPV1, vanilloid receptor 1) ion channel plays a key role in the perception of thermal and inflammatory pain, however, its molecular environment in dorsal root ganglia (DRG) is largely unexplored. Utilizing a panel of sequence-directed antibodies against TRPV1 protein and mouse DRG membranes, the channel complex from mouse DRG was detergent-solubilized, isolated by immunoprecipitation and subsequently analyzed by mass spectrometry. A number of potential TRPV1 interaction partners were identified, among them cytoskeletal proteins, signal transduction molecules, and established ion channel subunits. Based on stringent specificity criteria, the voltage-gated K+ channel beta 2 subunit (Kvβ2), an accessory subunit of voltage-gated K+ channels, was identified of being associated with native TRPV1 channels. Reverse co-immunoprecipitation and antibody co-staining experiments confirmed TRPV1/Kvβ2 association. Biotinylation assays in the presence of Kvβ2 demonstrated increased cell surface expression levels of TRPV1, while patch-clamp experiments resulted in a significant increase of TRPV1 sensitivity to capsaicin. Our work shows, for the first time, the association of a Kvβ subunit with TRPV1 channels, and suggests that such interaction may play a role in TRPV1 channel trafficking to the plasma membrane.

TRPV1 activation by endogenous anandamide triggers postsynaptic long-term depression in dentate gyrus

The transient receptor potential TRPV1 is a nonselective cation channel that mediates pain sensations and is commonly activated by a wide variety of exogenous and endogenous, physical and chemical stimuli. While TRPV1 receptors are mainly found in nociceptive neurons of the peripheral nervous system, these receptors have also been described in the brain where their role is far less understood. Activation of TRPV1 reportedly regulates neurotransmitter release at several central synapses. Here we show, however, that TRPV1 suppresses excitatory transmission in rat and mouse dentate gyrus by regulating postsynaptic function in an input-specific manner. This suppression is due to a Ca2+-calcineurin and clathrin-dependent internalization of AMPA receptors. Moreover, synaptic activation of TRPV1 triggers a form of long-term depression (TRPV1-LTD) mediated by the endocannabinoid anandamide in a type 1 cannabinoid receptor-independent manner. Thus, our findings reveal a novel form of endocannabinoid- and TRPV1-mediated regulation of synaptic strength at central synapses.

Activation and Regulation of Nociceptive Transient Receptor Potential (TRP) Channels, TRPV1 and TRPA1

TRP channels are well recognized for their contributions to sensory transduction, responding to a wide variety of stimuli including temperature, nociceptive stimuli, touch, osmolarity and pheromones. In particular, the involvement of TRP channels in nociception has been extensively studied following the cloning of the capsaicin receptor, TRPV1. Painful diabetic peripheral neuropathy is described as a superficial burning pain, and it is one of the most commonly encountered neuropathic pain syndromes in clinical practice. We found that hypoxic and high glucose conditions commonly observed in diabetes potentiate TRPV1 activity without affecting TRPV1 expression both in native rat sensory neurons and HEK293 cells expressing rat TRPV1. The potentiation seems to be caused by phosphorylation of the serine residues of TRPV1 by PKC. These data indicate that PKC-dependent potentiation of TRPV1 activities under hypoxia and hyperglycemia might be involved in early diabetic neuropathy. Mechanisms for the detection of alkaline pH by sensory neurons are not well understood, although it is well accepted that acidic pH monitoring can be attributed to several ion channels, including TRPV1 and ASICs. We found that alkaline pH activates TRPA1 and that the TRPA1 activation is involved in nociception, using Ca(2+)-imaging and patch-clamp methods. In addition, intracellular alkalization activated TRPA1 at the whole-cell level, and single-channel openings were observed in the inside-out configuration. Furthermore, intraplantar injection of ammonium chloride into the mouse hind paw caused pain-related behaviors, which were not observed in TRPA1-deficient mice. These results suggest that alkaline pH causes pain sensation through activation of TRPA1.

Spiro-piperidine azetidinones as potent TRPV1 antagonists

A series of spiro-piperidine azetidinone were synthesized and evaluated as potential TRPV1 antagonists. An important issue of plasma stability was investigated and resolved. Further focused SAR study lead to the discovery of a potent antagonist with good oral pharmacokinetic profile in rat.