Effects of capsazepine, a transient receptor potential vanilloid type 1 antagonist, on morphine-induced antinociception, tolerance, and dependence in mice

The effect of cannabinoid type 2 receptor agonist on morphine tolerance

Pain highly impacts the quality of life of patients. Morphine is used for pain treatment; however, its side effects, especially morphine tolerance, limit its use in the clinic. The problem of morphine tolerance has plagued health workers and patients for years. Unfortunately, the exact mechanism of morphine tolerance has not been fully clarified. The mechanisms of morphine tolerance that are currently being studied may include μ-opioid receptor (MOR) desensitization and internalization, mitogen-activated protein kinase (MAPK) pathway activation and crosstalk, the effects of microglia and the increase in inflammatory factors. Morphine tolerance can be alleviated by improving the pathophysiological changes that lead to morphine tolerance. Previous studies have shown that a cannabinoid type 2 (CB2) receptor agonist could attenuate morphine tolerance in a variety of animal models. Many studies have shown an interaction between the cannabinoid system and the opioid system. The CB2 receptor may modulate the effect of morphine through a pathway that is common to the MOR, since both receptors are G protein-coupled receptors (GPCRs). This study introduces the potential mechanism of morphine tolerance and the effect of CB2 receptor agonists on reducing morphine tolerance, which can provide new ideas for researchers studying morphine and provide beneficial effects for patients suffering from morphine tolerance.

The Role of Cannabinoid-1 Receptor Ligands in the Ovalbumin-Induced Mouse Model of Allergic Asthma: Is It Related to Transient Receptor Potential Vanilloid-1 Channels?

Objectives: The aim of this study was to investigate the role of cannabinoid (CB1) receptors on airway inflammation and hypersensitivity in allergic asthma and the potential interactions with TRPV1 channels. Materials and Methods: BALB/c mice were sensitized and provoked with ovalbumin to create a model of allergic asthma. CB1 selective agonist arachidonoyl 2'-chloroethylamide (ACEA) was administered intraperitoneally at doses of 0.5, 3, and 5 mg/kg. Receptor antagonism studies were performed utilizing selective CB1 antagonists AM251 at a dose of 3 mg/kg. TRPV1 channel was selectively blocked by capsazepine at a dose of 2.5 mg/kg. Penh values were recorded in vivo by a whole-body plethysmograph under methacholine challenge. Inflammatory cell count was performed in bronchoalveolar lavage fluid (BALF). Serum levels of proinflammatory cytokines were measured by Enzyme-Linked ImmunoSorbent Assay (ELISA). Inflammation in the lung tissue was scored histopathologically. Statistical significance was determined using one-way analysis of variance or Kruskal-Wallis test and expressed as p<0.05. Results: In sensitized animals, provocation with inhaled ovalbumin increased Penh values, serum interleukin (IL)-4, IL-5, IL-13 levels, eosinophil, neutrophil, lymphocyte, macrophage counts in BALF, and inflammation in the lung tissue. ACEA applications did not significantly alter Penh values, BALF inflammatory cell levels, and histological changes related to inflammation in the lung tissue according to the disease group; however, only at a dose of 5 mg/kg, it reduced the levels of the inflammatory cytokine IL-4. AM251 decreased Penh values, eosinophil and neutrophil migration in BALF, and inflammation score of lung tissue compared with the disease group. Although BALF inflammatory cell levels and Penh values were higher in the AM251+ACEA group than in the AM251 group, the differences were insignificant. In the CPZ+ACEA group, Penh values were significantly higher, and serum IL-4 and IL-13 levels and BALF eosinophil counts were lower than that in the CPZ group. Conclusions: This study demonstrated an important role of the CB1 receptors in allergic asthma. CB1 antagonism reduced airway hyperresponsiveness and inflammation and showed immunomodulatory effects. The effect of the CB1 agonist ACEA on asthma does not appear to be related to TRPV1 channels.

STAT3 signaling in prostate cancer progression and therapy resistance: An oncogenic pathway with diverse functions

The categorization of cancers demonstrates that prostate cancer is the most common malignancy in men and it causes high death annually. Prostate cancer patients are diagnosed mainly via biomarkers such as PSA test and patients show poor prognosis. Prostate cancer cells rapidly diffuse into different parts of body and their metastasis is also a reason for death. Current therapies for prostate cancer patients include chemotherapy, surgery and radiotherapy as well as targeted therapy. The progression of prostate cancer cells is regulated by different factors that STAT3 signaling is among them. Growth factors and cytokines such as IL-6 can induce STAT3 signaling and it shows carcinogenic impact. Activation of STAT3 signaling occurs in prostate cancer and it promotes malignant behavior of tumor cells. Induction of STAT3 signaling increases glycolysis and proliferation of prostate cancer cells and prevents apoptosis. Furthermore, STAT3 signaling induces EMT mechanism in increasing cancer metastasis. Activation of STAT3 signaling stimulates drug resistance and the limitation of current works is lack of experiment related to role of STAT3 signaling in radio-resistance in prostate tumor. Calcitriol, capsazepine and β-elemonic are among the compounds capable of targeting STAT3 signaling and its inhibition in prostate cancer therapy. In addition to natural products, small molecules targeting STAT3 signaling have been developed in prostate cancer therapy.

Novel dual-target μ‑opioid and TRPV1 ligands as potential pharmacotherapeutics for pain management

Currently, the development of effective analgesic drugs with few side effects remains a great challenge. Studies have suggested that multi-target drug treatments show high efficacy and reduced side effects compared to single-target drug therapies. In this work, we designed and synthesized two series of novel MOR/TRPV1 dual active ligands in which the phenylpiperidine group or the N-phenyl-N-(piperidin-4-yl) propionamide group as the MOR pharmacophore was fused to the benzylpiperazinyl urea-based TRPV1 pharmacophore. In particular, compound 5a exhibited promising dual pharmacological activity for MOR (EC₅₀ = 53.7 nM) and TRPV1 (IC₅₀ = 32.9 nM) in vitro. In formalin tests, compound 5a showed potent, dose-dependent in vivo analgesic activity in both the 1st and 2nd phases. Gratifyingly, compound 5a did not cause the side effects of hyperthermia and analgesic tolerance. Consistent with its in vitro activity, compound 5a also simultaneously agonized MOR and antagonized TRPV1 in vivo. Further studies on compound 5a showed acceptable pharmacokinetic properties and brain permeability. Furthermore, molecular docking studies showed that compound 5a tightly bound to the active pockets of hMOR and hTRPV1, respectively. Overall, this work shows the promise in discovering new analgesic treatments through the strategy of simultaneously targeting MOR and TRPV1 with a single molecule.

The distinctive role of menthol in pain and analgesia: Mechanisms, practices, and advances

Menthol is an important flavoring additive that triggers a cooling sensation. Under physiological condition, low to moderate concentrations of menthol activate transient receptor potential cation channel subfamily M member 8 (TRPM8) in the primary nociceptors, such as dorsal root ganglion (DRG) and trigeminal ganglion, generating a cooling sensation, whereas menthol at higher concentration could induce cold allodynia, and cold hyperalgesia mediated by TRPM8 sensitization. In addition, the paradoxical irritating properties of high concentrations of menthol is associated with its activation of transient receptor potential cation channel subfamily A member 1 (TRPA1). Under pathological situation, menthol activates TRPM8 to attenuate mechanical allodynia and thermal hyperalgesia following nerve injury or chemical stimuli. Recent reports have recapitulated the requirement of central group II/III metabotropic glutamate receptors (mGluR) with endogenous κ-opioid signaling pathways for menthol analgesia. Additionally, blockage of sodium channels and calcium influx is a determinant step after menthol exposure, suggesting the possibility of menthol for pain management. In this review, we will also discuss and summarize the advances in menthol-related drugs for pathological pain treatment in clinical trials, especially in neuropathic pain, musculoskeletal pain, cancer pain and postoperative pain, with the aim to find the promising therapeutic candidates for the resolution of pain to better manage patients with pain in clinics.

Ambient ozone, and urban PM2.5 co-exposure, aggravate allergic asthma via transient receptor potential vanilloid 1-mediated neurogenic inflammation

Allergic asthma is the most common pulmonary inflammatory disease, and epidemiological studies have revealed that PM_2.5 or ambient ozone (O₃) exposure contribute to the higher prevalence of allergic asthma. Current experimental evidence focus principally on the pathogenic effect of exposure to a single air pollutant, ignoring the possible synergistic effect of combined exposure to a mix of these pollutants, which is a more realistic scenario. In this study, allergic mice and a nociceptor antagonist were used to explore the mechanisms of co-exposure to these two important air pollutants. Compared with exposure to either PM_2.5 or O₃, combined exposure to both greatly aggravated allergic asthma in a dose dependent manner, including increased airway hyperresponsiveness, goblet cell metaplasia, more severe airway inflammation and higher oxidative stress levels. In addition, co-exposure in the allergic mice resulted in elevation of the expression of transient receptor potential vanilloid 1 (TRPV1), and of the production of substance P (SP), which exacerbated lung inflammation by neurogenic inflammation. TRPV1 antagonist (capsazepine, CPZ) treatment for the co-exposed allergic mice, markedly attenuated TRPV1 expression and SP release, and reduced airway inflammation and oxidative damage, further alleviating airway hyperresponsiveness. We conclude that neuro-immune interactions might be involved in PM_2.5 and O₃ co-exposure aggravated allergic asthma.

Repeated Morphine Administration Increases TRPV1 mRNA Expression and Autoradiographic Binding at Supraspinal Sites in the Pain Pathway

Repeated morphine administration induces tolerance to its analgesic effects. A previous study reported that repeated morphine treatment activates transient receptor potential vanilloid type 1 (TRPV1) expression in the sciatic nerve, dorsal root ganglion, and spinal cord, contributing to morphine tolerance. In the present study, we analyzed TRPV1 expression and binding sites in supraspinal pain pathways in morphine-tolerant mice. The TRPV1 mRNA levels and binding sites were remarkably increased in the cortex and thalamus of these animals. Our data provide additional insights into the effects of morphine on TRPV1 in the brain and suggest that changes in the expression of, and binding to TRPV1 in the brain are involved in morphine tolerance.

Side Effects of Opioids Are Ameliorated by Regulating TRPV1 Receptors

Humans have used opioids to suppress moderate to severe pain for thousands of years. However, the long-term use of opioids has several adverse effects, such as opioid tolerance, opioid-induced hyperalgesia, and addiction. In addition, the low efficiency of opioids in controlling neuropathic pain limits their clinical applications. Combining nonopioid analgesics with opioids to target multiple sites along the nociceptive pathway may alleviate the side effects of opioids. This study reviews the feasibility of reducing opioid side effects by regulating the transient receptor potential vanilloid 1 (TRPV1) receptors and summarizes the possible underlying mechanisms. Blocking and activating TRPV1 receptors can improve the therapeutic profile of opioids in different manners. TRPV1 and μ-opioid receptors are bidirectionally regulated by β-arrestin2. Thus, drug combinations or developing dual-acting drugs simultaneously targeting μ-opioid and TRPV1 receptors may mitigate opioid tolerance and opioid-induced hyperalgesia. In addition, TRPV1 receptors, especially expressed in the dorsal striatum and nucleus accumbens, participate in mediating opioid reward, and its regulation can reduce the risk of opioid-induced addiction. Finally, co-administration of TRPV1 antagonists and opioids in the primary action sites of the periphery can significantly relieve neuropathic pain. In general, the regulation of TRPV1 may potentially ameliorate the side effects of opioids and enhance their analgesic efficacy in neuropathic pain.

Cannabinoid Receptor Type 2 Agonist Reduces Morphine Tolerance via Mitogen Activated Protein Kinase Phosphatase Induction and Mitogen Activated Protein Kinase Dephosphorylation

Morphine is an opioid drug often used in treating moderate to severe pain. However, morphine tolerance in patients limits its used in clinical settings. Our previous study showed that a cannabinoid type 2 (CB2) receptor agonist attenuated morphine tolerance. However, the exact mechanism by which CB2 agonists reduce morphine tolerance remains unclear. In this study, we investigated the effect of mitogen activated protein kinase (MAPK) and mitogen activated protein kinase phosphatases 1 and 3 (MKP-1 and MKP-3) on the regulation of morphine tolerance by CB2 receptor agonist. Chronic morphine treatments for 7 days reduced the protein expression of MKP-1 and MKP-3 in the spinal cord and increased the phosphorylation of p38, ERK1/2 and the level of proinflammatory mediator, such as IL-1β, IL-6 and TNF-α. Coadministration of CB2 receptor agonist AM1241 alleviated the inhibition of MKP-1 and MKP-3 by chronic morphine administration and reduced the expression of phosphorylated MAPK and proinflammatory factors. The effect of the CB2 receptor agonist on morphine-induced downregulation of MKP-1 and MKP-3 was reversed by the MKP-1 and MKP-3 antagonist triptolide. Our findings suggested that CB2 receptor agonist may induce the expression of MKP-1 and MKP-3 to promote MAPK dephosphorylation and reduce the production of downstream cytokine, thereby reducing morphine tolerance. This finding suggested that MKPs may serve as a new target for alleviating morphine tolerance.

Role of TRPV1 channels on glycogen synthase kinase-3β and oxidative stress in ouabain-induced bipolar disease

Bipolar disorder (BD) is a multifactorial chronic and refractory disease characterized by manic, depressive, and mixed mood episodes. Although epidemiological, and pathophysiological studies demonstrated a strong correlation between bipolar disorder and oxidative stress, precise etiology is still missing. Recent studies suggested the possible role of transient receptor potential channels (TRP) in the BD but, current knowledge is limited. Therefore, the current study investigates the possible role of TRPV1 in the ouabain-induced model of BD. The model was created with intracerebroventricular single dose ouabain (10^-3 M) administration. Animals were treated with capsaicin, capsazepine, and lithium for seven days. Mania and depressive-like states were investigated with open-field, sucrose preference, and elevated plus maze tests. Oxidative stress was assessed by measuring total antioxidant and oxidant states, spectrophotometrically. The phosphorylation Glycogen synthase kinase-3β (GSK-3β) evaluated by western blotting. Our results demonstrated that capsaicin dose-dependently inhibited the ouabain-induced hyperlocomotion and depression. Although capsazepine exacerbated behavioral impairment, it did not show a significant effect on the antioxidant and oxidant states, and the effects of capsazepine on behaviors were abolished by combination with capsaicin. Additionally, capsaicin potently prevented the ouabain-induced decrease in GSK-3β phosphorylation. In contrast, capsazepine potentiated ouabain-induced decrease in GSK-3β phosphorylation and combination with capsaicin, suppressed the effect of capsazepine on GSK-3β phosphorylation. The effects of TRPV1 activation on oxidative stress and mania-like behaviors in the ouabain-induced BD model might be regulated by GSK-3β phosphorylation.

Role and Modulation of TRPV1 in Mammalian Spermatozoa: An Updated Review

Based on the abundance of scientific publications, the polymodal sensor TRPV1 is known as one of the most studied proteins within the TRP channel family. This receptor has been found in numerous cell types from different species as well as in spermatozoa. The present review is focused on analyzing the role played by this important channel in the post-ejaculatory life of spermatozoa, where it has been described to be involved in events such as capacitation, acrosome reaction, calcium trafficking, sperm migration, and fertilization. By performing an exhaustive bibliographic search, this review gathers, for the first time, all the modulators of the TRPV1 function that, to our knowledge, were described to date in different species and cell types. Moreover, all those modulators with a relationship with the reproductive process, either found in the female tract, seminal plasma, or spermatozoa, are presented here. Since the sperm migration through the female reproductive tract is one of the most intriguing and less understood events of the fertilization process, in the present work, chemotaxis, thermotaxis, and rheotaxis guiding mechanisms and their relationship with TRPV1 receptor are deeply analyzed, hypothesizing its (in)direct participation during the sperm migration. Last, TRPV1 is presented as a pharmacological target, with a special focus on humans and some pathologies in mammals strictly related to the male reproductive system.

Role of TRPV1/TRPV3 channels in olanzapine-induced metabolic alteration: Possible involvement in hypothalamic energy-sensing, appetite regulation, inflammation and mesolimbic pathway

Atypical antipsychotics (AAPs) have the tendency of inducing severe metabolic alterations like obesity, diabetes mellitus, insulin resistance, dyslipidemia and cardiovascular complications. These alterations have been attributed to altered hypothalamic appetite regulation, energy sensing, insulin/leptin signaling, inflammatory reactions and active reward anticipation. Line of evidence suggests that transient receptor potential vanilloid type 1 and 3 (TRPV1 and TRPV3) channels are emerging targets in treatment of obesity, diabetes mellitus and could modulate feed intake. The present study was aimed to investigate the putative role TRPV1/TRPV3 in olanzapine-induced metabolic alterations in mice. Female BALB/c mice were treated with olanzapine for six weeks to induce metabolic alterations. Non-selective TRPV1/TRPV3 antagonist (ruthenium red) and selective TRPV1 (capsazepine) and TRPV3 antagonists (2,2-diphenyltetrahydrofuran or DPTHF) were used to investigate the involvement of TRPV1/TRPV3 in chronic olanzapine-induced metabolic alterations. These metabolic alterations were differentially reversed by ruthenium red and capsazepine, while DPTHF didn't show any significant effect. Olanzapine treatment also altered the mRNA expression of hypothalamic appetite-regulating and nutrient-sensing factors, inflammatory genes and TRPV1/TRPV3, which were reversed with ruthenium red and capsazepine treatment. Furthermore, olanzapine treatment also increased expression of TRPV1/TRPV3 in nucleus accumbens (NAc), TRPV3 expression in ventral tegmental area (VTA), which were reversed by the respective antagonists. However, DPTHF treatment showed reduced feed intake in olanzapine treated mice, which might be due to TRPV3 specific antagonism and reduced hedonic feed intake. In conclusion, our results suggested the putative role TRPV1 in hypothalamic dysregulations and TRPV3 in the mesolimbic pathway; both regulate feeding in olanzapine treated mice.

Inhibition of fatty acid amide hydrolase in the CNS prevents and reverses morphine tolerance in male and female mice

BACKGROUND AND PURPOSE

Fatty acid amide hydrolase (FAAH) is an intracellular serine amidase that terminates the signalling of various lipid messengers involved in pain regulation, including anandamide and palmitoylethanolamide. Here, we investigated the effects of pharmacological or genetic FAAH removal on tolerance to the anti-nociceptive effects of morphine.

EXPERIMENTAL APPROACH

We induced tolerance in male and female mice by administering twice-daily morphine for 7 days while monitoring nociceptive thresholds by the tail immersion test. The globally active FAAH inhibitor URB597 (1 and 3 mg·kg^-1 , i.p.) or the peripherally restricted FAAH inhibitor URB937 (3 mg·kg^-1 , i.p.) were administered daily 30 min prior to morphine, alone or in combination with the cannabinoid CB₁ receptor antagonist AM251 (3 mg·kg^-1 , i.p.), the CB₂ receptor antagonist AM630 (3 mg·kg^-1 , i.p.), or the PPAR-α antagonist GW6471 (4 mg·kg^-1 , i.p.). Spinal levels of FAAH-regulated lipids were quantified by LC/MS-MS. Gene transcription was assessed by RT-qPCR.

KEY RESULTS

URB597 prevented and reversed morphine tolerance in both male and female mice. This effect was mimicked by genetic FAAH deletion, but not by URB937. Treatment with AM630 suppressed, whereas treatment with AM251 or GW6471, attenuated the effects of URB597. Anandamide mobilization was enhanced in the spinal cord of morphine-tolerant mice. mRNA levels of the anandamide-producing enzyme N-acyl-phosphatidylethanolamine PLD (NAPE-PLD) and the palmitoylethanolamide receptor PPAR-α, but not those for CB₂ , CB₁ receptors or FAAH, were elevated in spinal cord CONCLUSION AND IMPLICATIONS: FAAH-regulated lipid signalling in the CNS modulated opiate tolerance, suggesting FAAH as a potential target for opiate-sparing medications.

Replacement of current opioid drugs focusing on MOR-related strategies

The scarcity and limited risk/benefit ratio of painkillers available on the market, in addition to the opioid crisis, warrant reflection on new innovation strategies. The pharmacopoeia of analgesics is based on products that are often old and derived from clinical empiricism, with limited efficacy or spectrum of action, or resulting in an unsatisfactory tolerability profile. Although they are reference analgesics for nociceptive pain, opioids are subject to the same criticism. The use of opium as an analgesic is historical. Morphine was synthesized at the beginning of the 19th century. The efficacy of opioids is limited in certain painful contexts and these drugs can induce potentially serious and fatal adverse effects. The current North American opioid crisis, with an ever-rising number of deaths by opioid overdose, is a tragic illustration of this. It is therefore legitimate to develop research into molecules likely to maintain or increase opioid efficacy while improving their tolerability. Several avenues are being explored including targeting of the mu opioid receptor (MOR) splice variants, developing biased agonists or targeting of other receptors such as heteromers with MOR. Ion channels acting as MOR effectors, are also targeted in order to offer compounds without MOR-dependent adverse effects. Another route is to develop opioid analgesics with peripheral action or limited central nervous system (CNS) access. Finally, endogenous opioids used as drugs or compounds that modify the metabolism of endogenous opioids (Dual ENKephalinase Inhibitors) are being developed. The aim of the present review is to present these various targets/strategies with reference to current indications for opioids, concerns about their widespread use, particularly in chronic non-cancer pains, and ways of limiting the risk of opioid abuse and misuse.

Antinociceptive and genotoxic assessments of the antagonist TRPV1 receptor SB-366791 on morphine-induced tolerance in mice

Chronic pain is mainly treated with opioid analgesics such as morphine. However, the use of these substances can cause adverse effects, including dependence and tolerance, necessitating the discovery of a new approach to analgesic therapies. The transient receptor potential vanilloid 1 (TRPV1) is linked to thermal sensibility and has been considered as a new therapeutic option for pain treatment. This study aims to investigate the antinociceptive effect and toxicity of SB-366791, a TRPV1 antagonist. Morphine-tolerant and morphine non-tolerant Swiss mice were submitted to the hot plate and thermal tail flick tests. Toxicological evaluations of the genotoxic and mutagenic activities of SB-366791 were assessed using a comet assay and micronucleus test, and the Salmonella/microsome mutagenicity assay. In the hot plate test, intrathecal injection of SB-366791 or morphine resulted in significantly increased antinociception in non-tolerant mice. SB-366791 also led to an analgesic effect in the tail flick test. Tolerant mice that received SB-366791 demonstrated a central antinociceptive effect in both thermal tests. No genotoxic effects were observed in the comet assay and no mutagenic effects were detected in the micronucleus test or in the Salmonella/microsome assay. Behavioral results of the thermal nociception tests show that SB-366791 has antinociceptive potential in both morphine-tolerant and non-tolerant mice and does not cause genotoxic or mutagenic effects. Nevertheless, new studies should be performed to clarify the activity and participation of vanilloid channels in the antinociception of SB-366791.

Neuropsychiatric implications of transient receptor potential vanilloid (TRPV) channels in the reward system

Neuropsychiatric disorders (NPDs) exert a devastating impact on an individual's personal and social well-being, encompassing various conditions and brain anomalies that influence affect, cognition, and behavior. Because the pathophysiology of NPDs is multifactorial, the precise mechanisms underlying the development of such disorders remain unclear, representing a unique challenge in current neuropsychopharmacotherapy. Transient receptor potential vanilloid (TRPV) type channels are a family of ligand-gated ion channels that mainly include sensory receptors that respond to thermal, mechanical and chemical stimuli. TRPV channels are abundantly present in dopaminergic neurons, thus playing a pivotal role in the modulation of the reward system and in pathophysiology of diseases such as stress, anxiety, depression, schizophrenia, neurodegenerative disorders and substance abuse/addiction. Recent evidence has highlighted TRPV channels as potential targets for understanding modulation of the reward system and various forms of addiction (opioids, cocaine, amphetamines, alcohol, nicotine, cannabis). In this review, we discuss the distribution, physiological roles, ligands and therapeutic importance of TRPV channels with regard to NPDs and addiction biology.

Capsaicinoids: Multiple effects on angiogenesis, invasion and metastasis in human cancers

Cancer progression is a complex multistep process comprising of angiogenesis of the primary tumor, its invasion into the surrounding stroma and its migration to distant organs to produce metastases. Nutritional compounds of the "capsaicinoid" family regulate angiogenesis, invasion and metastasis of tumors. Capsaicinoids display robust anti-angiogenic activity in both cell culture and mice models. However, conflicting reports exist about the effect of capsaicinoids on invasion of metastasis of cancers. While some published reports have described an anti-invasive and anti-metastatic role for capsaicinoids, others have argued that capsaicinoids stimulate invasion and metastasis of cancers. The present review article summarizes these findings involving the bioactivity of capsaicin in angiogenesis, invasion and metastasis of cancer. A survey of literature indicate that they are several articles summarizing the growth-inhibitory activity of capsaicinoids but few describe its effects on angiogenesis, invasion and metastasis in detail. Our review article fills this gap of knowledge. The discovery of a second generation of natural and synthetic capsaicin analogs (with anti-tumor activity) will pave the way to improved strategies for the treatment of several human cancers.

The role of IRAS/Nischarin involved in the development of morphine tolerance and physical dependence

Morphine is a potent opioid analgesic used to alleviate moderate or severe pain, but the development of drug tolerance and dependence limits its use in pain management. Our previous studies showed that the candidate protein for I1 imidazoline receptor, imidazoline receptor antisera-selected (IRAS)/Nischarin, interacts with μ opioid receptor (MOR) and modulates its trafficking. However, there is no report of the effect of IRAS on morphine tolerance and physical dependence. In the present study, we found that IRAS knockout (KO) mice showed exacerbated analgesic tolerance and physical dependence compared to wild-type (WT) mice by chronic morphine treatment. Chronic morphine treatment down-regulated the expression of MOR in spinal cord of IRAS KO mice, while had no significant effect on MOR expression in WT mice. We observed the compensatory increase of cAMP accumulation in spinal cord after morphine tolerance, and this change was more significant in KO mice than WT mice. Furthermore, KO mice showed more elevation in the phosphorylation of AMPA receptor GluR1-S845 than WT mice, while the total expression of GluR1 remained unchanged after morphine dependence. Altogether, these data suggest that IRAS may play an important role in the development of morphine tolerance and physical dependence in vivo through modulating MOR expression, as well as AMPA GluR1-S845 phosphorylation, which might be one of the mechanisms underlying the development of opiate addiction.

Pleiotropic Pharmacological Actions of Capsazepine, a Synthetic Analogue of Capsaicin, against Various Cancers and Inflammatory Diseases

Capsazepine is a synthetic analogue of capsaicin that can function as an antagonist of TRPV1. Capsazepine can exhibit diverse effects on cancer (prostate cancer, breast cancer, colorectal cancer, oral cancer, and osteosarcoma) growth and survival, and can be therapeutically used against other major disorders such as colitis, pancreatitis, malaria, and epilepsy. Capsazepine has been reported to exhibit pleiotropic anti-cancer effects against numerous tumor cell lines. Capsazepine can modulate Janus activated kinase (JAK)/signal transducer and activator of the transcription (STAT) pathway, intracellular Ca²⁺ concentration, and reactive oxygen species (ROS)-JNK-CCAAT/enhancer-binding protein homologous protein (CHOP) pathways. It can inhibit cell proliferation, metastasis, and induce apoptosis. Moreover, capsazepine can exert anti-inflammatory effects through the downregulation of lipopolysaccharide (LPS)-induced nuclear transcription factor-kappa B (NF-κB), as well as the blockage of activation of both transient receptor potential cation channel subfamily V member 1 (TRPV1) and transient receptor potential cation channel, subfamily A, and member 1 (TRPA1). This review briefly summarizes the diverse pharmacological actions of capsazepine against various cancers and inflammatory conditions.

α7 Nicotinic acetylcholine receptor contributes to the alleviation of lung ischemia-reperfusion injury by transient receptor potential vanilloid type 1 stimulation

BACKGROUND

Activation of transient receptor potential vanilloid type 1 (TRPV1) decreases lung ischemia-reperfusion injury (LIRI) in rabbits and rats. Stimulation of α7 nicotinic acetylcholine receptors (α7nAChRs) protects against lung injury. Here we examined whether α7nAChRs contribute to TRPV1-mediated protection against LIRI.

METHODS

Wild-type (WT) and TRPV1-knockout (KO) mice were subjected to 1-h lung ischemia by clamping left hilum, followed by 2-h reperfusion. WT or KO mice were pretreated with vehicle, TRPV1 agonist capsaicin, TRPV1 antagonist capsazepine, α7nAChR antagonist methyllycaconitine, or α7nAChR agonist PNU-282987. Arterial blood and lung tissues were obtained for blood gas, lung wet-to-dry weight ratio, interleukin (IL)1β, IL6, tumor necrosis factor-α (TNF-α), apoptosis-related proteins (caspases, Bax, Fas), and pathologic scoring.

RESULTS

Capsaicin pretreatment reduced wet-to-dry ratio, pathologic score, alveolar-arterial oxygen gradient (A-aDO₂), and IL1β, IL6, and TNFα levels in WT mice, with no effects in KO mice. This reduction was reversed by TRPV1 blockade. Furthermore, α7nAChR blockade before capsaicin exacerbated LIRI as evidenced by enhanced alveolar-arterial oxygen gradient, pathologic score, and IL1β, IL6, and TNFα levels, while α7nAChR agonist pretreatment under TRPV1 blockade showed opposite changes. Capsaicin also decreased cleaved caspase-3, caspase-3/9, and Bax protein expression, effects abolished by TRPV1 blockade. Similarly, α7nAChR blockade diminished capsaicin-induced downregulation of apoptotic proteins, and α7nAChR activation decreased expression levels even under TRPV1 blockade.

CONCLUSIONS

TRPV1 activation alleviates LIRI, partially dependent on α7nAChR activity. The α7nAChR stimulation with or without existence of TRPV1 alleviates LIRI. Thus, α7nAChR is involved in the pathway of TRPV1-mediated protection against LIRI and the specific mechanism remains to be revealed.

Effects of Cannabinoid Type 2 Receptor Agonist AM1241 on Morphine-Induced Antinociception, Acute and Chronic Tolerance, and Dependence in Mice

Morphine is a potent opioid analgesic used to alleviate moderate or severe pain, but the development of drug tolerance and dependence limits its use in pain management. Previous studies showed that cannabinoid type 2 (CB₂) receptor ligands may modulate opioid effects. However, there is no report of the effect of CB₂ receptor agonist on acute morphine tolerance and physical dependence. We therefore investigated the effect of a CB₂ receptor agonist (AM1241) on morphine-induced morphine tolerance and physical dependence in mice. Repeated coadministration of AM1241 (1 or 3mg/kg intraperitoneally) and morphine (10mg/kg subcutaneously) for 7days increased the mechanical paw withdrawal threshold in mice as measured by the von Frey filament test, and 3mg/kg AM1241 in combination with morphine increased the thermal paw withdrawal latency as measured by the hot-plate test. Combination with 3mg/kg AM1241 and morphine increased acute morphine antinociception. Coadministration of 1 or 3mg/kg AM1241 and morphine reduced acute morphine tolerance, and 3mg/kg AM1241 reduced chronic morphine tolerance. Coadministration of 1 or 3mg/kg AM1241 and morphine reduced naloxone-precipitated withdrawal jumping, but not diarrhea. Coadministration of AM1241 and morphine did not inhibit spontaneous locomotor activity. Pretreatment with 3mg/kg AM1241 decreased the chronic morphine-induced Iba1 expression in spinal cord. Coadministration of AM1241 (3 mg/kg) reduced the production of interleukin-1β, tumor necrosis factor-α, and interleukin-6 induced by long-term and acute morphine treatment. Our findings suggest that the coadministration of the CB₂ receptor agonist and morphine could increase morphine antinociception and reduce morphine tolerance and physical dependence in mice.

PERSPECTIVE

The combination of a CB₂ agonist and morphine may provide a new strategy for better treatment of acute and chronic pain and prevention of opioid tolerance and dependence. This finding may also provide a clue for the treatment of opioid tolerance and dependence in clinics.

Blockade of TRPV1 Inhibits Methamphetamine-induced Rewarding Effects

Methamphetamine (MAP) is the most widely used psychostimulant in the world, but the exact mechanisms underlying MAP addiction are not yet fully understood. Recent studies have identified the distribution of TRPV1 in several brain regions that are related to drug addiction, including nucleus accumbens (NAc) and dorsal striatum (DSt). In the present study, we performed conditioned place preference (CPP) and self-administration tests to examine the effects of capsazepine (CPZ) and SB366791 (SB) on MAP reward. We found that both CPZ and SB significantly inhibited MAP-induced CPP and self-administration; in contrast, TRPV1 knock-out (KO) mice did not develop MAP-induced CPP. Real-time RT-PCR, Western blot and quantitative autoradiographic tests showed up-regulation of TRPV1 mRNA and protein expression in the NAc and/or DSt regions of mice exhibiting MAP-induced CPP. In addition, an in vivo microdialysis experiment showed that CPZ dramatically reduced dopamine (DA) levels in the NAc region of MAP-treated mice. Furthermore, attenuated dopamine transporter (DAT) binding levels in the NAc and DSt regions of MAP-induced CPP mice were reversed by CPZ. Together, these data suggest that TRPV1 plays an important role in MAP reward via the modulation of DA release and DAT density, thereby providing a novel therapeutic target for MAP addiction.

Impairment of opiate-mediated behaviors by the selective TRPV1 antagonist SB366791

Transient receptor potential vanilloid type 1 (TRPV1), the archetypal member of the vanilloid TRP family, was initially identified as the receptor for capsaicin, the pungent ingredient in hot chili peppers. We previously demonstrated that TRPV1 in the dorsal striatum significantly contributes to morphine reward by using the conditioned place preference paradigm in mice; however, it is unknown whether TRPV1 has the same effect in other reward models. In this study, we investigated the role of TRPV1 in morphine reward by using a self-administration paradigm in rats. We found that treatment with a selective TRPV1 antagonist, SB366791, significantly decreased morphine self-administration on a fixed-ratio 1 schedule or a progressive ratio schedule of reinforcement. In addition, treatment with another selective TRPV1 antagonist, AMG9810, not only significantly prevented morphine self-administration but also prevented morphine-induced c-fos expression in the nucleus accumbens. Furthermore, administration of SB366791 decreased an anxiolytic-like effect during the morphine abstinence period. Moreover, treatment with SB366791 significantly decreased morphine-priming reinstatement. Taken together, our findings suggest that blockade of TRPV1 receptors could provide an approach to limiting morphine addiction.

Transient Receptor Potential Vanilloid 1 Antagonists Prevent Anesthesia-induced Hypothermia and Decrease Postincisional Opioid Dose Requirements in Rodents

Background

Intraoperative hypothermia and postoperative pain control are two important clinical challenges in anesthesiology. Transient receptor potential vanilloid 1 has been implicated both in thermoregulation and pain. Transient receptor potential vanilloid 1 antagonists were not advanced as analgesics in humans in part due to a side effect of hyperthermia. This study tested the hypothesis that a single, preincision injection of a transient receptor potential vanilloid 1 antagonist could prevent anesthesia-induced hypothermia and decrease the opioid requirement for postsurgical hypersensitivity.

Methods

General anesthesia was induced in rats and mice with either isoflurane or ketamine, and animals were treated with transient receptor potential vanilloid 1 antagonists (AMG 517 or ABT-102). The core body temperature and oxygen consumption were monitored during anesthesia and the postanesthesia period. The effect of preincision AMG 517 on morphine-induced reversal of postincision hyperalgesia was evaluated in rats.

Results

AMG 517 and ABT-102 dose-dependently prevented general anesthesia-induced hypothermia (mean ± SD; from 1.5° ± 0.1°C to 0.1° ± 0.1°C decrease; P &lt; 0.001) without causing hyperthermia in the postanesthesia phase. Isoflurane-induced hypothermia was prevented by AMG 517 in wild-type but not in transient receptor potential vanilloid 1 knockout mice (n = 7 to 11 per group). The prevention of anesthesia-induced hypothermia by AMG 517 involved activation of brown fat thermogenesis with a possible contribution from changes in vasomotor tone. A single preincision dose of AMG 517 decreased the morphine dose requirement for the reduction of postincision thermal (12.6 ± 3.0 vs. 15.6 ± 1.0 s) and mechanical (6.8 ± 3.0 vs. 9.5 ± 3.0 g) withdrawal latencies.

Conclusions

These studies demonstrate that transient receptor potential vanilloid 1 antagonists prevent anesthesia-induced hypothermia and decrease opioid dose requirements for the reduction of postincisional hypersensitivity in rodents.

Capsazepine inhibits JAK/STAT3 signaling, tumor growth, and cell survival in prostate cancer

Persistent STAT3 activation is seen in many tumor cells and promotes malignant transformation. Here, we investigated whether capsazepine (Capz), a synthetic analogue of capsaicin, exerts anticancer effects by inhibiting STAT3 activation in prostate cancer cells. Capz inhibited both constitutive and induced STAT3 activation in human prostate carcinoma cells. Capz also inhibited activation of the upstream kinases JAK1/2 and c-Src. The phosphatase inhibitor pervanadate reversed Capz-induced STAT3 inhibition, indicating that the effect of Capz depends on a protein tyrosine phosphatase. Capz treatment increased PTPε protein and mRNA levels. Moreover, siRNA-mediated knockdown of PTPε reversed the Capz-induced induction of PTPε and inhibition of STAT3 activation, indicating that PTPε is crucial for Capz-dependent STAT3 dephosphorylation. Capz also decreased levels of the protein products of various oncogenes, which in turn inhibited proliferation and invasion and induced apoptosis. Finally, intraperitoneal Capz administration decreased tumor growth in a xenograft mouse prostate cancer model and reduced p-STAT3 and Ki-67 expression. These data suggest that Capz is a novel pharmacological inhibitor of STAT3 activation with several anticancer effects in prostate cancer cells.

Interaction Between the Cannabinoid and Vanilloid Systems on Anxiety in Male Rats

Introduction:

Previous studies have shown that the cannabinoid system is involved in anxiety. In addition, transient receptor potential vanilloid type-1 (TRPV1) channels are new targets for the development of anxiolytics. The present study investigated the possible interaction between the cannabinoid and vanilloid systems on anxiety-like behavior in rats.

Methods:

Four different groups of male Wistar rats received intraperitoneal (IP) injections of (1) vehicle (DMSO+saline), (2) cannabinoid receptor agonist WIN55212-2 (WIN) (1 mg/kg), (3) TRPV1 receptor antagonist capsazepine (CPZ) (5 mg/kg), or (4) combined WIN (1 mg/kg) and CPZ (5 mg/kg) treatment 30 minutes before testing in the elevated plus maze.

Results:

The results showed that compared to the control (vehicle), both WIN and CPZ increased the time spent and number of entries on the open arms. Co-administration of WIN and CPZ had a synergistic effect, i.e., the number of entries and time spent on the open arms was greater than that in the groups administered the two compounds alone. The total distance travelled by rats and total number of entries on to the arms did not significantly differ between groups.

Conclusion:

Acute neuropharmacological blockade of the TRPV1 receptor or stimulation of the CB1 receptor produced an anxiolytic effect. It seems that antagonism of the vanilloid system modulates cannabinoid gain that rises the anxiolytic effect. TRPV1 antagonism may amend generation of endocannabinoids, which in turn increases anxiolytic impact. These results suggest that two systems could act on or share a common signaling pathway affecting the expression of anxiety.

Enhanced ability of TRPV1 channels in regulating glutamatergic transmission after repeated morphine exposure in the nucleus accumbens of rat

Glutamatergic projections to nucleus accumbens (NAc) drive drug-seeking behaviors during opioids withdrawal. Modulating glutamatergic neurotransmission provides a novel pharmacotherapeutic avenue for treatment of opioids dependence. Great deals of researches have verified that transient receptor potential vanilloid 1 (TRPV1) channels alters synaptic transmitter release and regulate neural plasticity. In the present study, whole-cell patch clamp recordings were adopted to examine the activity of TRPV1 Channels in regulating glutamate-mediated excitatory postsynaptic currents (EPSCs) in NAc of rat during morphine withdrawal for 3days and 3weeks. The data showed that the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) and the amplitudes of evoked excitatory postsynaptic currents (eEPSCs) were increased during morphine withdrawal after applied with capsaicin (TRPV1 agonist). Capsaicin decreased the paired pulse ratio (PPR) and increased sEPSCs frequency but not their amplitudes suggesting a presynaptic locus of action during morphine withdrawal. All these effects were fully blocked by the TRPV1 antagonist Capsazepine. Additionally, In the presence of AM251 (CB1 receptor antagonist), depolarization-induced release of endogenous cannabinoids activated TRPV1 channels to enhance glutamatergic neurotransmission during morphine withdrawal. The functional enhancement of TRPV1 Channels in facilitating glutamatergic transmission was not recorded in dorsal striatum. Our findings demonstrate the ability of TRPV1 in regulating excitatory glutamatergic transmission is enhanced during morphine withdrawal in NAc, which would deepen our understanding of glutamatergic modulation during opioids withdrawal.

Mitochondrial aldehyde dehydrogenase protects against doxorubicin cardiotoxicity through a transient receptor potential channel vanilloid 1-mediated mechanism

Cardiotoxicity is one of the major life-threatening effects encountered in cancer chemotherapy with doxorubicin and other anthracyclines. Mitochondrial aldehyde dehydrogenase (ALDH2) may alleviate doxorubicin toxicity although the mechanism remains elusive. This study was designed to evaluate the impact of ALDH2 overexpression on doxorubicin-induced myocardial damage with a focus on mitochondrial injury. Wild-type (WT) and transgenic mice overexpressing ALDH2 driven by chicken β-actin promoter were challenged with doxorubicin (15mg/kg, single i.p. injection, for 6days) and cardiac mechanical function was assessed using the echocardiographic and IonOptix systems. Western blot analysis was used to evaluate intracellular Ca(2+) regulatory and mitochondrial proteins, PKA and its downstream signal eNOS. Doxorubicin challenge altered cardiac geometry and function evidenced by enlarged left ventricular end systolic and diastolic diameters, decreased factional shortening, cell shortening and intracellular Ca(2+) rise, prolonged relengthening and intracellular Ca(2+) decay, the effects of which were attenuated by ALDH2. Doxorubicin challenge compromised mitochondrial integrity and upregulated 4-HNE and UCP-2 levels while downregulating levels of TRPV1, SERCA2a and PGC-1α, the effects of which were alleviated by ALDH2. Doxorubicin-induced cardiac functional defect and apoptosis were reversed by the TRPV1 agonist SA13353 and the ALDH-2 agonist Alda-1 whereas the TRPV1 antagonist capsazepine nullified ALDH2/Alda-1-induced protection. Doxorubicin suppressed phosphorylation of PKA and eNOS, the effect of which was reversed by ALDH2. Moreover, 4-HNE mimicked doxorubicin-induced cardiomyocyte anomalies, the effect of which was ablated by SA13353. Taken together, our results suggested that ALDH2 may rescue against doxorubicin cardiac toxicity possibly through a TRPV1-mediated protection of mitochondrial integrity.

Blockade and reversal of spinal morphine tolerance by P2X3 receptor antagonist

In recent years, studies have substantiated the view that P2X3 receptors play a part in the generation and transmission of purinergic signals in inflammatory and chronic neuropathic pain. Data have also been presented to suggest that the process of P2X3 receptor antagonism inhibits inflammatory hyperalgesia, involving the spinal opioid system. The aim of this study was to investigate the effect of the selective P2X3 receptor antagonist A-317491 on the development of antinociceptive tolerance to chronic morphine administration in mice. Daily systemic injection of A-317491 attenuated the morphine-induced antinociceptive tolerance to von Frey and thermal stimuli. Repeated morphine injections alone led to a significant rightward shift in the morphine dose-response curve compared with that with A-317491. A single dose of A-317491 also showed a reversal effect in morphine-tolerant mice. In a withdrawal test, co-administration of A-317491 and morphine also reduced the naloxone-induced withdrawal symptoms compared with the morphine-alone group. Thus, we propose that the P2X3 receptor is involved in the process of morphine antinociceptive tolerance and may be a new therapeutic target in the prevention of tolerance to morphine-induced antinociception.

Role of transient receptor potential vanilloid subetype 1 in the increase of thermal pain threshold by moxibustion

OBTECTIVE: To explore the role of transient receptor potential vanilloid subetype 1 (TRPV1) in the increase of the thermal pain threshold by moxibustion.

METHODS

Forty Kunming mice (20 ± 2) g were randomized into control group, capsaicin group, capsazepine group, moxibustion group and moxibustion + capsazepine (MC) group with 8 mice in each, and 16 C57BL/6 wild-type mice (18 ± 2) g were randomized into wild-type (WT) control group and WT moxibustion group with 8 mice in each, and 14 TRPV1 knockout mice (18 ± 2) g were randomized into knockout (KO) control group and KO moxibustion-group with 7 in each. Each mouse in the capsaicin group was subcutaneously injected with the amount of 0.1 mL/10 g into L5 and L6 spinal cords; each mouse in the capsazepine group was intraperitoneally injected with the amount of 0.1 mL/10 g. Similarly, each mouse in the moxibustion group was given a suspended moxibustion with specially-made moxa-stick for 20 min on L5 and L6 spinal cords. Each mouse in MC group was intraperitoneally injected with the amount of 0.1 mL/1 0 g first, then after 15 min was given a suspended moxibustion for 20 min on L5 and L6 spinal cords. Each mouse in WT moxibustion group and KO moxibustion group was given a suspended moxibustion with specially-made moxa-stick for 20 min on L5 and L6 spinal cords. The control group, WT control group and KO control group were of no treatment in any way. After all treatments were completed, the digital-display measurement instrument for thermal pain was used to measure the threshold of thermal pain in each group respectively.

RESULTS

Compared with the control group, the thresholds of thermal pain in the moxibustion group and MC group were significantly increased (P <0.01); no significant changes in the thresholds in the capsaicin group and the capsazepine group (P > 0.05); compared with moxibustion group, he threshold of thermal in MC group was obviously decreased (P < 0.01). Compared with WT control group, the threshold of thermal pain in WT moxibustion group was significantly increased (P < 0.01); compared with KO control group, no changes in the threshold in KO moxibustion group (P > 0.05).

CONCLUSION

TRPV1 participated in the process of increasing the threshold of thermal pain by stimulating L5 and L6 of mice spinal cord with burning mosa-stick.

Opioids and TRPV1 in the peripheral control of neuropathic pain--Defining a target site in the injured nerve

Targeting peripheral neuropathic pain at its origin may prevent the development of hypersensitivity. Recently we showed this can be mediated by opioid receptors at the injured nerve trunk. Here, we searched for the most relevant peripheral site to block transient receptor potential vanilloid 1 (TRPV1), and investigated analgesic interactions between TRPV1 and opioids in neuropathy. In a chronic constriction injury (CCI) of the sciatic nerve in mice, we assessed the effects of μ-, δ- and κ-opioid receptor agonists and TRPV1 antagonist (SB366791) injected at the CCI site or into the injured nerve-innervated paw on spontaneous paw lifting, heat and mechanical sensitivity. We also examined TRPV1 expression in total membrane and plasma membrane fractions from nerves and paws. We found that opioids and SB366791 co-injected in per se nonanalgesic doses at the CCI site or into the paw diminished heat and mechanical sensitivity. SB366791 alone dose-dependently alleviated heat and mechanical sensitivity. TRPV1 blockade in the paw was more effective than at the CCI site. None of the treatments diminished spontaneous paw lifting. TRPV1 expression analysis suggests that the levels of functional TRPV1 do not critically determine the TRPV1 antagonist-mediated analgesia. Together, the identification of the primary action site in damaged nerves is crucial for effective pain control. Contrary to opioids, the TRPV1 blockade in the injured nerve peripheral terminals, rather than at the nerve trunk, appears promising against heat pain. Opioid/TRPV1 antagonist combinations at both locations partially reduced neuropathy-triggered heat and mechanical pain.

The mechanism of μ-opioid receptor (MOR)-TRPV1 crosstalk in TRPV1 activation involves morphine anti-nociception, tolerance and dependence

Initiated by the activation of various nociceptors, pain is a reaction to specific stimulus modalities. The μ-opioid receptor (MOR) agonists, including morphine, remain the most potent analgesics to treat patients with moderate to severe pain. However, the utility of MOR agonists is limited by the adverse effects associated with the use of these drugs, including analgesic tolerance and physical dependence. A strong connection has been suggested between the expression of the transient receptor potential vanilloid type 1 (TRPV1) ion channel and the development of inflammatory hyperalgesia. TRPV1 is important for thermal nociception induction, and is mainly expressed on sensory neurons. Recent reports suggest that opioid or TRPV1 receptor agonist exposure has contrasting consequences for anti-nociception, tolerance and dependence. Chronic morphine exposure modulates TRPV1 activation and induces the anti-nociception effects of morphine. The regulation of many downstream targets of TRPV1 plays a critical role in this process, including calcitonin gene-related peptide (CGRP) and substance P (SP). Additional factors also include capsaicin treatment blocking the anti-nociception effects of morphine in rats, as well as opioid modulation of TRPV1 responses through the cAMP-dependent PKA pathway and MAPK signaling pathways. Here, we review new insights concerning the mechanism underlying MOR-TRPV1 crosstalk and signaling pathways and discuss the potential mechanisms of morphine-induced anti-nociception, tolerance and dependence associated with the TRPV1 signaling pathway and highlight how understanding these mechanisms might help find therapeutic targets for the treatment of morphine induced antinociception, tolerance and dependence.

Interference of TRPV1 function altered the susceptibility of PTZ-induced seizures

Transient receptor potential vanilloid 1 (TRPV1) is widely distributed in the central nervous system (CNS) including hippocampus, and regulates the balance of excitation and inhibition in CNS, which imply its important role in epilepsy. We used both pharmacological manipulations and transgenic mice to disturb the function of TRPV1 and then studied the effects of these alterations on the susceptibility of pentylenetetrazol (PTZ)-induced seizures. Our results showed that systemic administration of TRPV1 agonist capsaicin (CAP, 40 mg/kg) directly induced tonic-clonic seizures (TCS) without PTZ induction. The severity of seizure was increased in lower doses of CAP groups (5 and 10 mg/kg), although the latency to TCS was delayed. On the other hand, systemic administration of TRPV1 antagonist capsazepine (CPZ, 0.05 and 0.5 mg/kg) and TRPV1 knockout mice exhibited delayed latency to TCS and reduced mortality. Furthermore, hippocampal administration of CPZ (10 and 33 nmol/μL/side) was firstly reported to increase the latency to TCS, decrease the maximal grade of seizure and mortality. It is worth noting that decreased susceptibility of PTZ-induced seizures was observed in hippocampal TRPV1 overexpression mice and hippocampal CAP administration (33 nmol/μL/side), which is opposite from results of systemic agonist CAP. Our findings suggest that the systemic administration of TRPV1 antagonist may be a novel therapeutic target for epilepsy, and alteration of hippocampal TRPV1 function exerts a critical role in seizure susceptibility.

Transient receptor potential vanilloid type 1 channel may modulate opioid reward

Transient receptor potential vanilloid type 1 (TRPV1), a nonselective cation channel, is a well-known pain-related receptor. TRPV1 involvement in morphine-induced antinociception, tolerance, and withdrawal symptoms has been previously reported. Emerging evidence indicates that TRPV1 may be related to both the cellular and behavioral effects of addictive drugs. In the present study, we investigated the role of TRPV1 in morphine reward using the conditioned place preference (CPP) paradigm in mice. Repeated morphine treatments upregulated TRPV1 expression in the dorsal striatum (DSt). Treatment with a TRPV1 agonist potentiated morphine reward, and pretreatment with TRPV1 antagonists attenuated these effects. Microinjection of a selective TRPV1 antagonist into the DSt significantly inhibited morphine-CPP. In addition, treatment with a TRPV1 antagonist suppressed morphine-induced increases in μ-opioid receptor binding, adenylyl cyclase 1 (AC1), p38 mitogen-activated protein kinase (p38 MAPK), and nuclear factor kappa B (NF-κB) expression in the DSt. Administering a p38 inhibitor not only prevented morphine-CPP, but also prevented morphine-induced NF-κB and TRPV1 activation in the DSt. Furthermore, injecting an NF-κB inhibitor significantly blocked morphine-CPP. Our findings suggest that TRPV1 in the DSt contribute to morphine reward via AC1, p38 MAPK, and NF-κB. Brain TRPV1 may serve as a novel therapeutic target to treat morphine-addictive disorders.

Blocking TRPV1 in nucleus accumbens inhibits persistent morphine conditioned place preference expression in rats

The function of TRPV1 (transient receptor potential vanilloid subfamily, member 1) in the central nervous system is gradually elucidated. It has been recently proved to be expressed in nucleus accumbens (NAc), a region playing an essential role in mediating opioid craving and taking behaviors. Based on the general role of TRPV1 antagonist in blocking neural over-excitability by both pre- and post-synaptic mechanisms, TRPV1 antagonist capsazepine (CPZ) was tested for its ability to prohibit persistent opioid craving in rats. In the present study, we assessed the expression of TRPV1 in nucleus accumbens and investigated the effect of CPZ in bilateral nucleus accumbens on persistent morphine conditioned place preference (mCPP) in rats. We also evaluated the side-effect of CPZ on activity by comparing cross-beam times between groups. We found that morphine conditioned place preference increased the TRPV1 expression and CPZ attenuated morphine conditioned place preference in a dose-dependent and target-specific manner after both short- and long-term spontaneous withdrawal, reflected by the reduction of the increased time in morphine-paired side. CPZ (10 nM) could induce prolonged and stable inhibition of morphine conditioned place preference expression. More importantly, CPZ did not cause dysfunction of activity in the subjects tested, which indicates the inhibitory effect was not obtained at the sacrifice of regular movement. Collectively, these results indicated that injection of TRPV1 antagonist in nucleus accumbens is capable of attenuating persistent morphine conditioned place preference without affecting normal activity. Thus, TRPV1 antagonist is one of the promising therapeutic drugs for the treatment of opioid addiction.

Effects of dexmedetomidine and midazolam on motor coordination and analgesia: a comparative analysis

Objective

We compared the effects of 2 sedative drugs, dexmedetomidine and midazolam, on motor performance and analgesic efficacy in a rat model.

Materials and methods

Rats were randomly divided into the following 4 groups on the basis of the treatment received. The first group received 83 µg/kg/min midazolam; the second, 1 µg/kg/min dexmedetomidine; the third, 83 µg/kg/min morphine; and the fourth was a control group. The rats were measured motor coordination and pain reflexes by using rotarod, accelerod, hot plate, and tail flick tests.

Results

At all the tested speeds, the midazolam-injected rats remained on the rotarod longer than did the dexmedetomidine-injected rats. Furthermore, in the 10-minute accelerod test, the midazolam-injected rats remained for a longer duration than did the dexmedetomidine-injected rats. The latency time for the hot plate test was significantly higher at 10 minutes and 20 minutes in the dexmedetomidine group than in the midazolam group. Further, the latency time at 10 minutes for the tail flick test was greater in the dexmedetomidine group than in the midazolam group.

Conclusions

In this rat model, midazolam results in faster recovery of motor coordination performance when compared with dexmedetomidine.

Antinociceptive curcuminoid, KMS4034, effects on inflammatory and neuropathic pain likely via modulating TRPV1 in mice

BACKGROUND

Curcumin, the active ingredient of turmeric (Curcuma longa), has a wide range of beneficial effects including anti-inflammation and analgesia. However, poor bioavailability of curcumin hinders its clinical application. To overcome this limitation, we modified the structure of curcumin and synthesized new derivatives with favourable pharmacokinetic profiles. Recently, curcumin has been shown to have an antagonizing effect on transient receptor potential vanilloid type 1 (TRPV1) ion channels. We investigated the antinociceptive activity of KMS4034 which had the most favourable pharmacokinetics among the tested curcumin derivatives.

METHODS

To evaluate the mechanism of the antinociceptive effects of KMS4034, capsaicin (I(CAP))- and heat (I(heat))-induced currents in TRPV1 expressing HEK293 cells were observed after the application of KMS4034. Nociceptive behavioural measurement using the hot-plate test, formalin test, and chronic constriction injury (CCI) model were evaluated in mice. Also, calcitonin gene-related peptide (CGRP) was stained immunohistochemically in the L4/5 dorsal horns in mice with neuropathic pain.

RESULTS

I(CAP) (P<0.01) and I(heat) (P<0.05) of TRPV1 were significantly blocked by 10 μM KMS4034. Behaviourally, noticeable antinociceptive effects after 10 mg kg(-1) of KMS4034 treatment were observed in the first (P<0.05) and second phases (P<0.05) of the formalin and hot-plate tests. The mechanical threshold of CCI mice treated with 10 mg kg(-1) KMS4034 was significantly increased compared with control. Immunohistochemical CGRP expression was decreased in the lamina I-II of the lumbar dorsal horns in KMS4034-treated CCI mice compared with the control (P<0.05).

CONCLUSIONS

KMS4034 may be an effective analgesic for various pain conditions.

Cardiac-specific knockout of ET(A) receptor mitigates low ambient temperature-induced cardiac hypertrophy and contractile dysfunction

Cold exposure is associated with oxidative stress and cardiac dysfunction. The endothelin (ET) system, which plays a key role in myocardial homeostasis, may participate in cold exposure-induced cardiovascular dysfunction. This study was designed to examine the role of ET-1 in cold stress-induced cardiac geometric and contractile responses. Wild-type (WT) and ET(A) receptor knockout (ETAKO) mice were assigned to normal or cold exposure (4°C) environment for 2 and 5 weeks prior to evaluation of cardiac geometry, contractile, and intracellular Ca(2+) properties. Levels of the temperature sensor transient receptor potential vanilloid (TRPV1), mitochondrial proteins for biogenesis and oxidative phosphorylation, including UCP2, HSP90, and PGC1α were evaluated. Cold stress triggered cardiac hypertrophy, depressed myocardial contractile capacity, including fractional shortening, peak shortening, and maximal velocity of shortening/relengthening, reduced intracellular Ca(2+) release, prolonged intracellular Ca(2+) decay and relengthening duration, generation of ROS and superoxide, as well as apoptosis, the effects of which were blunted by ETAKO. Western blotting revealed downregulated TRPV1 and PGC1α as well as upregulated UCP2 and activation of GSK3β, GATA4, and CREB in cold-stressed WT mouse hearts, which were obliterated by ETAKO. Levels of HSP90, an essential regulator for thermotolerance, were unchanged. The TRPV1 agonist SA13353 attenuated whereas TRPV1 antagonist capsazepine mimicked cold stress- or ET-1-induced cardiac anomalies. The GSK3β inhibitor SB216763 ablated cold stress-induced cardiac contractile (but not remodeling) changes and ET-1-induced TRPV1 downregulation. These data suggest that ETAKO protects against cold exposure-induced cardiac remodeling and dysfunction mediated through TRPV1 and mitochondrial function.

Endogenous opiates and behavior: 2010

This paper is the thirty-third consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2010 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).