Emerging potassium channel targets for the treatment of pain

Associations Between Preoperative Shortness of Breath and Potassium Channels Gene Variations in Women With Breast Cancer

OBJECTIVES

Shortness of breath is a common symptom in patients with cancer. However, the mechanisms that underlie this troublesome symptom are poorly understood. Therefore, this study aimed to determine the prevalence of and associated risk factors for shortness of breath in women prior to breast cancer surgery and identify associations between shortness of breath and polymorphisms for potassium channel genes.

METHODS

Patients were recruited prior to breast cancer surgery and completed a self-report questionnaire on the occurrence of shortness of breath. Genotyping of single nucleotides polymorphism (SNPs) in potassium channel genes was performed using a custom array. Multiple logistic regression analyses were done to identify associations between the occurrence of shortness of breath and SNPs in ten candidate genes.

RESULTS

Of the 398 patients, 11.1% reported shortness of breath. These patients had a lower annual household income, a higher comorbidity burden, and a lower functional status. After controlling for functional status, comorbidity burden, genomic estimates of ancestry and self-reported race and ethnicity, the genetic associations that remained significant in the multiple regression analyses were for potassium voltage-gated channel subfamily D (KCND2) rs12673992, potassium voltage-gated channel modifier subfamily S (KCNS1) rs4499491, and potassium two pore channel subfamily K (KCNK2) rs4411107.

CONCLUSIONS

While these findings warrant replication, they suggest that alterations in potassium channel function may contribute to the occurrence of shortness of breath in women prior to breast cancer surgery.

Kv7 Channel Activators Flupirtine and ML213 Alleviate Neuropathic Pain Behavior in the Streptozotocin Rat Model of Diabetic Neuropathy

Background & Objective

Chronic peripheral neuropathic pain (PNP) is a debilitating condition that is associated with many types of injury/diseases, including diabetes mellitus. Patients with longstanding diabetes develop diabetic PNP (DPNP), which is resilient to currently available drugs. The underlying molecular mechanisms of DPNP are still illusive, but Kv7 channels that have been implicated in the pathogenesis of various types of chronic pain are likely to be involved. Indeed, using the streptozotocin (STZ) rat model of DPNP, we have previously shown that Kv7 activation with their non-selective activator retigabine attenuated neuropathic pain behavior suggesting that these channels are implicated in DPNP pathogenesis. Here, we evaluated, in the same STZ model, whether the more potent and more selective Kv7 channel openers flupirtine and ML213 attenuate STZ-induced pain hypersensitivity.

Methods

Male Sprague Dawley rats (250-300 g) were used. The STZ model involved a single injection of STZ (60 mg/kg, i.p.). Behavioral testing for mechanical and heat pain sensitivity was performed using a dynamic plantar aesthesiometer and Hargreaves analgesiometer, respectively.

Results

STZ rats exhibited behavioral signs of mechanical and heat hypersensitivity as indicated by significant decreases in the mean paw withdrawal threshold (PWT) and mean paw withdrawal latency (PWL), respectively, at 35 days post-STZ treatment. Single injections of flupirtine (10 mg/kg, i.p.) and ML213 (5 mg/kg, i.p.) to STZ rats (35-days after STZ treatment) caused significant increases in the mean PWT, but not PWL, indicating attenuation of mechanical, but not heat hypersensitivity. Both flupirtine and ML213 were as effective as the positive control gabapentin (10/kg, i.p.), and their anti-allodynic effects were prevented by the Kv7 channel-specific blocker XE991 (3 mg/kg, i.p.).

Conclusion

The findings suggest that Kv7 channels are involved in the mechanisms of mechanical but not heat hypersensitivity associated with DPNP, and that their activation may prove to be effective in alleviating DPNP symptoms.

Novel Targets and Drug Delivery System in the Treatment of Postoperative Pain: Recent Studies and Clinical Advancement

Pain is generated by a small number of peripheral targets. These can be made more sensitive by inflammatory mediators. The number of opioids prescribed to the patients can be reduced dramatically with better pain management. Any therapy that safely and reliably provides extended analgesia and is flexible enough to facilitate a diverse array of release profiles would be useful for improving patient comfort, quality of care, and compliance after surgical procedures. Comparisons are made between new and traditional methods, and the current state of development has been discussed; taking into account the availability of molecular and cellular level data, preclinical and clinical data, and early post-market data. There are a number of benefits associated with the use of nanotechnology in the delivery of analgesics to specific areas of the body. Nanoparticles are able to transport drugs to inaccessible bodily areas because of their small molecular size. This review focuses on targets that act specifically or primarily on sensory neurons, as well as inflammatory mediators that have been shown to have an analgesic effect as a side effect of their anti- inflammatory properties. New, regulated post-operative pain management devices that use existing polymeric systems were presented in this article, along with the areas for potential development. Analgesic treatments, both pharmacological and non-pharmacological, have also been discussed.

Genetic Architecture and Functional Implications of the CSF-Contacting Nucleus

We previously identified a unique nucleus, the cerebrospinal fluid (CSF)-contacting nucleus. This study aims to understand its gene architecture and preliminarily suggest its functions. The results showed that there were about 19,666 genes in this nucleus, of which 913 were distinct from the dorsal raphe nucleus (non-CSF contacting). The top 40 highly-expressed genes are mainly related to energy metabolism, protein synthesis, transport, secretion, and hydrolysis. The main neurotransmitter is 5-HT. The receptors of 5-HT and GABA are abundant. The channels for Cl-, Na+, K+, and Ca2+ are routinely expressed. The signaling molecules associated with the CaMK, JAK, and MAPK pathways were identified accurately. In particular, the channels of transient receptor potential associated with nociceptors and the solute carrier superfamily members associated with cell membrane transport were significantly expressed. The relationship between the main genes of the nucleus and life activities is preliminarily verified.

An anchor-tether 'hindered' HCN1 inhibitor is antihyperalgesic in a rat spared nerve injury neuropathic pain model

BACKGROUND

Neuropathic pain impairs quality of life, is widely prevalent, and incurs significant costs. Current pharmacological therapies have poor/no efficacy and significant adverse effects; safe and effective alternatives are needed. Hyperpolarisation-activated cyclic nucleotide-regulated (HCN) channels are causally implicated in some forms of peripherally mediated neuropathic pain. Whilst 2,6-substituted phenols, such as 2,6-di-tert-butylphenol (26DTB-P), selectively inhibit HCN1 gating and are antihyperalgesic, the development of therapeutically tolerable, HCN-selective antihyperalgesics based on their inverse agonist activity requires that such drugs spare the cardiac isoforms and do not cross the blood-brain barrier.

METHODS

In silico molecular dynamics simulation, in vitro electrophysiology, and in vivo rat spared nerve injury methods were used to test whether 'hindered' variants of 26DTB-P (wherein a hydrophilic 'anchor' is attached in the para-position of 26DTB-P via an acyl chain 'tether') had the desired properties.

RESULTS

Molecular dynamics simulation showed that membrane penetration of hindered 26DTB-Ps is controlled by a tethered diol anchor without elimination of head group rotational freedom. In vitro and in vivo analysis showed that BP4L-18:1:1, a variant wherein a diol anchor is attached to 26DTB-P via an 18-carbon tether, is an HCN1 inverse agonist and an orally available antihyperalgesic. With a CNS multiparameter optimisation score of 2.25, a >100-fold lower drug load in the brain vs blood, and an absence of adverse cardiovascular or CNS effects, BP4L-18:1:1 was shown to be poorly CNS penetrant and cardiac sparing.

CONCLUSIONS

These findings provide a proof-of-concept demonstration that anchor-tethered drugs are a new chemotype for treatment of disorders involving membrane targets.

Downregulation of ciRNA-Kat6b in dorsal spinal horn is required for neuropathic pain by regulating Kcnk1 in miRNA-26a-dependent manner

AIMS

Nerve injury-induced maladaptive changes in gene expression in the spinal neurons are essential for neuropathic pain genesis. Circular RNAs (ciRNA) are emerging as key regulators of gene expression. Here, we identified a nervous-system-tissues-specific ciRNA-Kat6 with conservation in humans and mice. We aimed to investigate whether and how spinal dorsal horn ciRNA-Kat6b participates in neuropathic pain.

METHODS

Unilateral sciatic nerve chronic constrictive injury (CCI) surgery was used to prepare the neuropathic pain model. The differentially expressed ciRNAs were obtained by RNA-Sequencing. The identification of nervous-system-tissues specificity of ciRNA-Kat6b and the measurement of ciRNA-Kat6b and microRNA-26a (miRNA-26a) expression level were carried out by quantitative RT-PCR. The ciRNA-Kat6b that targets miRNA-26a and miRNA-26a that targets Kcnk1 were predicted by bioinformatics analysis and verified by in vitro luciferase reports test and in vivo experiments including Western-blot, immunofluorescence, and RNA-RNA immunoprecipitation. The correlation between neuropathic pain and ciRNA-Kat6b, miRNA-26a, or Kcnk1 was examined by the hypersensitivity response to heat and mechanical stimulus.

RESULTS

Peripheral nerve injury downregulated ciRNA-Kat6b in the dorsal spinal horn of male mice. Rescuing this downregulation blocked nerve injury-induced increase of miRNA-26a, reversed the miRNA-26a-triggered decrease of potassium channel Kcnk1, a key neuropathic pain player, in the dorsal horn, and alleviates CCI-induced pain hypersensitivities. On the contrary, mimicking this downregulation increased the miRNA-26a level and decreased Kcnk1 in the spinal cord, resulting in neuropathic pain-like syndrome in naïve mice. Mechanistically, the downregulation of ciRNA-Kat6b reduced the accounts of miRNA-26a binding to ciRNA-Kat6b, and elevated the binding accounts of miRNA-26a to the 3' untranslated region of Kcnk1 mRNA and degeneration of Kcnk1 mRNA, triggering in the reduction of KCNK1 protein in the dorsal horn of neuropathic pain mice.

CONCLUSION

The ciRNA-Kat6b/miRNA-26a/Kcnk1 pathway in dorsal horn neurons regulates the development and maintenance of neuropathic pain, ciRNA-Kat6b may be a potential new target for analgesic and treatment strategies.

Pain in Huntington's disease and its potential mechanisms

Pain is common and frequent in many neurodegenerative diseases, although it has not received much attention. In Huntington's disease (HD), pain is often ignored and under-researched because attention is more focused on motor and cognitive decline than psychiatric symptoms. In HD progression, pain symptoms are complex and involved in multiple etiologies, particularly mental issues such as apathy, anxiety and irritability. Because of psychiatric issues, HD patients rarely complain of pain, although their bodies show severe pain symptoms, ultimately resulting in insufficient awareness and lack of research. In HD, few studies have focused on pain and pain-related features. A detailed and systemic pain history is crucial to assess and explore pain pathophysiology in HD. This review provides an overview concentrating on pain-related factors in HD, including neuropathology, frequency, features, affecting factors and mechanisms. More attention and studies are still needed in this interesting field in the future.

Nerve Injury-Induced γH2AX Reduction in Primary Sensory Neurons Is Involved in Neuropathic Pain Processing

Phosphorylation of the serine 139 of the histone variant H2AX (γH2AX) is a DNA damage marker that regulates DNA damage response and various diseases. However, whether γH2AX is involved in neuropathic pain is still unclear. We found the expression of γH2AX and H2AX decreased in mice dorsal root ganglion (DRG) after spared nerve injury (SNI). Ataxia telangiectasia mutated (ATM), which promotes γH2AX, was also down-regulated in DRG after peripheral nerve injury. ATM inhibitor KU55933 decreased the level of γH2AX in ND7/23 cells. The intrathecal injection of KU55933 down-regulated DRG γH2AX expression and significantly induced mechanical allodynia and thermal hyperalgesia in a dose-dependent manner. The inhibition of ATM by siRNA could also decrease the pain threshold. The inhibition of dephosphorylation of γH2AX by protein phosphatase 2A (PP2A) siRNA partially suppressed the down-regulation of γH2AX after SNI and relieved pain behavior. Further exploration of the mechanism revealed that inhibiting ATM by KU55933 up-regulated extracellular-signal regulated kinase (ERK) phosphorylation and down-regulated potassium ion channel genes, such as potassium voltage-gated channel subfamily Q member 2 (Kcnq2) and potassium voltage-gated channel subfamily D member 2 (Kcnd2) in vivo, and KU559333 enhanced sensory neuron excitability in vitro. These preliminary findings imply that the down-regulation of γH2AX may contribute to neuropathic pain.

Peripheral Ion Channel Genes Screening in Painful Small Fiber Neuropathy

Neuropathic pain is a characteristic feature of small fiber neuropathy (SFN), which in 18% of the cases is caused by genetic variants in voltage-gated sodium ion channels. In this study, we assessed the role of fifteen other ion channels in neuropathic pain. Patients with SFN (n = 414) were analyzed for ANO1, ANO3, HCN1, KCNA2, KCNA4, KCNK18, KCNN1, KCNQ3, KCNQ5, KCNS1, TRPA1, TRPM8, TRPV1, TRPV3 and TRPV4 variants by single-molecule molecular inversion probes-next-generation sequencing. These patients did not have genetic variants in SCN3A, SCN7A-SCN11A and SCN1B-SCN4B. In twenty patients (20/414, 4.8%), a potentially pathogenic heterozygous variant was identified in an ion-channel gene (ICG). Variants were present in seven genes, for two patients (0.5%) in ANO3, one (0.2%) in KCNK18, two (0.5%) in KCNQ3, seven (1.7%) in TRPA1, three (0.7%) in TRPM8, three (0.7%) in TRPV1 and two (0.5%) in TRPV3. Variants in the TRP genes were the most frequent (n = 15, 3.6%), partly in patients with high mean maximal pain scores VAS = 9.65 ± 0.7 (n = 4). Patients with ICG variants reported more severe pain compared to patients without such variants (VAS = 9.36 ± 0.72 vs. VAS = 7.47 ± 2.37). This cohort study identified ICG variants in neuropathic pain in SFN, complementing previous findings of ICG variants in diabetic neuropathy. These data show that ICG variants are central in neuropathic pain of different etiologies and provides promising gene candidates for future research.

Increased nociceptive sensitivity is associated with periodontal inflammation and expression of chronic pain genes in gingival tissues of male rats

OBJECTIVE

This study aimed to evaluate the inflammatory response, hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2), and voltage-gated potassium (Kv) 9.1 channel expression in rats with paclitaxel-induced neuropathic pain-like behavior.

METHODS

Sixteen male Sprague Dawley rats were divided equally into two groups: control and paclitaxel-induced pain (PTX). The attachment loss and inflammatory cell infiltrate levels were analyzed histometrically and immunohistochemically. The gene expression of HCN2 and KCNS1 was analyzed by qPCR in the brain and gingival tissues.

RESULTS

The attachment loss and prominent infiltration of inflammatory cells were significantly higher in the PTX group than in the control groups. In gingival tissues; the expression levels of HCN2 (p = 0,0011) were significantly higher and KCNS1 (p = 0,0003) were significantly lower in the PTX group than in the control groups.

CONCLUSION

Increased nociceptive sensitivity, may play a role in periodontal inflammation. KCNS1 may decrease and HCN2 expression may increase in periodontium in permanent chronic pain states. The results of the present study may be helpful in developing new approaches to alleviate pain and maintain periodontal health in patients suffering from orofacial pain.

Glial-derived neurotrophic factor regulates the expression of TREK2 in rat primary sensory neurons leading to attenuation of axotomy-induced neuropathic pain

TREK2 is a member of the 2-pore domain family of K+ channels (K2P) preferentially expressed by unmyelinated, slow-conducting and non-peptidergic isolectin B4-binding (IB4+) primary sensory neurons of the dorsal root ganglia (DRG). IB4+ neurons depend on the glial-derived neurotrophic factor (GDNF) family of ligands (GFL's) to maintain their phenotype. In our previous work, we demonstrated that 7 days after spinal nerve axotomy (SNA) of the L5 DRG, TREK2 moves away from the cell membrane resulting in a more depolarised resting membrane potential (Em). Given that axotomy deprives DRG neurons from peripherally-derived GFL's, we hypothesized that they might control the expression of TREK2. Using a combination of immunohistochemistry, immunocytochemistry, western blotting, in vivo pharmacological manipulation and behavioral tests we examined the ability of the GFL's (GDNF, neurturin and artemin) and their selective receptors (GFRα1, GFRα2 and GFRα3) to regulate the expression and function of TREK2 in the DRG. We found that TREK2 correlated strongly with the three receptors normally and ipsilaterally for all GFR's after SNA. GDNF, but not NGF, neurturin or artemin up-regulated the expression of TREK2 in cultured DRG neurons. In vivo continuous, subcutaneous administration of GDNF restored the subcellular distribution of TREK2 ipsilaterally and reversed mechanical and cold allodynia 7 days after SNA. This is the first demonstration that GDNF controls the expression of a K2P channel in nociceptors. As TREK2 controls the Em of C-nociceptors affecting their excitability, our finding has therapeutic potential in the treatment of chronic pain.

Quantitative proteomic analysis of oxaliplatin induced peripheral neurotoxicity

Oxaliplatin (OXA)-induced peripheral neurotoxicity (OIPN) is a high-incidence and dose-dependent adverse reaction during OXA treatment. Its underlying mechanisms remain unclear, and no effective treatment or prevention therapies are currently available. Here, we employed a data independent acquisition (DIA)-based quantitative proteomic strategy to investigate the global proteome alterations in the dorsal root ganglion (DRG) tissues from mice injected with OXA for different periods. We identified 1128 differentially regulated proteins that were divided into six subclusters according to their alteration trends. Interestingly, these proteins were involved in cellular processes such as cell cycle, ribosomal stress, metabolism, and ion transport. In addition, OXA administration induced abundance changes of ion channels and proteins associated with mitochondrial function and reactive oxygen species production. Furthermore, we investigated the effects of diroximel fumarate (DRF), an FDA-approved oral fumarate drug for the treatment of relapsing forms of multiple sclerosis. Our findings showed that DRF could effectively ameliorate symptoms of OIPN and reduce the level of oxidative stress in mice. Taken together, our study systematically mapped the proteome alteration associated with the neural toxicity of OXA, and the findings could be leveraged to better understand the mechanisms of OIPN and to develop more effect treatment therapies. SIGNIFICANCE: Oxaliplatin (OXA)-induced peripheral neurotoxicity (OIPN) is a high-incidence and dose-dependent adverse reaction with unclear mechanism. Here we employed a data independent acquisition (DIA)-based quantitative proteomic strategy to explore the proteome changes in dorsal root ganglion (DRG) tissues from mice treated by OXA. The findings provided novel insights regarding the mechanisms of OIPN. For example, our data showed that OXA induced a broad disturbance in metabolism, particularly in glycolysis and amino acid metabolism. Additionally, we observed abundance changes of many ion channels and proteins associated with mitochondrial function and reactive oxygen species production. Furthermore, this study provided the first evidence for the possibility of repositioning diroximel fumarate (DRF) for treating OIPN.

SUMOylation of Kir7.1 participates in neuropathic pain through regulating its membrane expression in spinal cord neurons

Aims

Potassium (K⁺) channels have been demonstrated to play a prominent involvement in nociceptive processing. Kir7.1, the newest members of the Kir channel family, has not been extensively studied in the CNS, and its function remains largely unknown. The present study investigated the role of spinal Kir7.1 in the development of pathological pain.

Methods and Results

Neuropathic pain was induced by spared nerve injury (SNI). The mechanical sensitivity was assessed by von Frey test. Immunofluorescence staining assay revealed that Kir7.1 was predominantly expressed in spinal neurons but not astrocytes or microglia in normal rats. Western blot results showed that SNI markedly decreased the total and membrane expression of Kir7.1 in the spinal dorsal horn accompanied by mechanical hypersensitivity. Blocking Kir7.1 with the specific antagonist ML418 or knockdown kir7.1 by siRNA led to mechanical allodynia. Co‐IP results showed that the spinal kir7.1 channels were decorated by SUMO‐1 but not SUMO‐2/3, and Kir7.1 SUMOylation was upregulated following SNI. Moreover, inhibited SUMOylation by GA (E1 inhibitor) or 2‐D08 (UBC9 inhibitor) can increase the spinal surface Kir7.1 expression.

Conclusion

SUMOylation of the Kir7.1 in the spinal cord might contribute to the development of SNI‐induced mechanical allodynia by decreasing the Kir7.1 surface expression in rats.

Cdyl Deficiency Brakes Neuronal Excitability and Nociception through Promoting Kcnb1 Transcription in Peripheral Sensory Neurons

Epigenetic modifications are involved in the onset, development, and maintenance of pain; however, the precise epigenetic mechanism underlying pain regulation remains elusive. Here it is reported that the epigenetic factor chromodomain Y-like (CDYL) is crucial for pain processing. Selective knockout of CDYL in sensory neurons results in decreased neuronal excitability and nociception. Moreover, CDYL facilitates histone 3 lysine 27 trimethylation (H3K27me3) deposition at the Kcnb1 intron region thus silencing voltage-gated potassium channel (Kv ) subfamily member Kv 2.1 transcription. Loss function of CDYL enhances total Kv and Kv 2.1 current density in dorsal root ganglia and knockdown of Kv 2.1 reverses the pain-related phenotypes of Cdyl deficiency mice. Furthermore, focal administration of a novel potent CDYL antagonist blunts nociception and attenuates neuropathic pain. These findings reveal that CDYL is a critical regulator of pain sensation and shed light on the development of novel analgesics targeting epigenetic mechanisms.

Targeting Chemokines and Chemokine GPCRs to Enhance Strong Opioid Efficacy in Neuropathic Pain

Neuropathic pain (NP) originates from an injury or disease of the somatosensory nervous system. This heterogeneous origin and the possible association with other pathologies make the management of NP a real challenge. To date, there are no satisfactory treatments for this type of chronic pain. Even strong opioids, the gold-standard analgesics for nociceptive and cancer pain, display low efficacy and the paradoxical ability to exacerbate pain sensitivity in NP patients. Mounting evidence suggests that chemokine upregulation may be a common mechanism driving NP pathophysiology and chronic opioid use-related consequences (analgesic tolerance and hyperalgesia). Here, we first review preclinical studies on the role of chemokines and chemokine receptors in the development and maintenance of NP. Second, we examine the change in chemokine expression following chronic opioid use and the crosstalk between chemokine and opioid receptors. Then, we examine the effects of inhibiting specific chemokines or chemokine receptors as a strategy to increase opioid efficacy in NP. We conclude that strong opioids, along with drugs that block specific chemokine/chemokine receptor axis, might be the right compromise for a favorable risk/benefit ratio in NP management.

Circulating Concentration of Chemical Elements During Exercise-Induced Muscle Damage and the Repeated Bout Effect

The objective of the study was to evaluate the circulating levels of chemical elements after exercise-induced muscle damage (EIMD) followed by the repeated bout effect (RBE). Seven physically active subjects (26.5 ± 4.0 years) performed two sessions of EIMD (5 sets of 20 drop jumps), the second session 14 days after the first for RBE assessment. Blood collections, countermovement jump (CMJ), squat jump (SJ), and delayed-onset muscle soreness (DOMS) were performed before (Pre), after (Post), and 24, 48, and 72 h after the exercise session. Creatine kinase (CK) was detected by biochemical analysis and the concentration of chemical elements by total reflection X-ray fluorescence (TXRF). Differences between time points and sessions were assessed with two-way ANOVA and the effect size (ES). EIMD induced a reduction in the CMJ at 24 h (P < 0.05) and an increase in DOMS at 24 h (P < 0.01) and 48 h (P < 0.01), and CK at 72 h (P < 0.05). RBE alleviated all symptoms of EIMD in the second session (P > 0.05). EIMD induced a large to very large ES for Zn reduction at 24 h (- 1.37) and 72 h (- 0.93) and Br (- 0.83) at 72 h. RBE presented large to very large ES for the increase in P at 48 h (0.92); Cl at 24 h (1.04); K at 24 h (0.91), 48 h (1.10), and 72 h (0.96); Ca at 72 h (0.92); and Fe at 24 h (0.85). RBE influenced the concentration of elements associated with fatigue (K, Ca, Cl), inflammatory response, and glucose metabolism (Zn).

Astaxanthin engages the l-arginine/NO/cGMP/KATP channel signaling pathway toward antinociceptive effects

One of the main functions of the sensory system in our body is to maintain somatosensory homeostasis. Recent reports have led to a significant advance in our understanding of pain signaling mechanisms; however, the exact mechanisms of pain transmission have remained unclear. There is an urgent need to reveal the precise signaling mediators of pain to provide alternative therapeutic agents with more efficacy and fewer side effects. Accordingly, although the anti-inflammatory, antioxidative and anti-neuropathic effects of astaxanthin (AST) have been previously highlighted, its peripheral antinociceptive mechanisms are not fully understood. In this line, considering the engagement of l-arginine/nitric oxide (NO)/cyclic GMP (cGMP)/potassium channel (KATP) signaling pathway in the antinociceptive responses, the present study evaluated its associated role in the antinociceptive activity of AST. Male mice were intraperitoneally (i.p.) injected with l-arginine (100 mg/kg), SNAP (1 mg/kg), L-NAME (30 mg/kg), sildenafil (5 mg/kg), and glibenclamide (10 mg/kg) alone and prior to the most effective dose of AST. Following AST administration, intraplantarly (i.pl) injection of formalin was done, and pain responses were evaluated in mice during the primary (acute) and secondary (inflammatory) phases of formalin test. The results highlighted that 10 mg/kg i.p. dose of AST showed the greatest antinociceptive effect. Besides, while L-NAME and glibenclamide reduced the antinociceptive effect of AST, it was significantly increased by l-arginine, SNAP and sildenafil during both the primary and secondary phases of formalin test. These data suggest that the antinociceptive activity of AST is passing through the l-arginine/NO/cGMP/KATP pathway.

Contribution of Neuronal and Glial Two-Pore-Domain Potassium Channels in Health and Neurological Disorders

Two-pore-domain potassium (K2P) channels are widespread in the nervous system and play a critical role in maintaining membrane potential in neurons and glia. They have been implicated in many stress-relevant neurological disorders, including pain, sleep disorder, epilepsy, ischemia, and depression. K2P channels give rise to leaky K⁺ currents, which stabilize cellular membrane potential and regulate cellular excitability. A range of natural and chemical effectors, including temperature, pressure, pH, phospholipids, and intracellular signaling molecules, substantially modulate the activity of K2P channels. In this review, we summarize the contribution of K2P channels to neuronal excitability and to potassium homeostasis in glia. We describe recently discovered functions of K2P channels in glia, such as astrocytic passive conductance and glutamate release, microglial surveillance, and myelin generation by oligodendrocytes. We also discuss the potential role of glial K2P channels in neurological disorders. In the end, we discuss current limitations in K2P channel researches and suggest directions for future studies.

Glabridin Relaxes Vascular Smooth Muscles by Activating BKCa Channels and Inhibiting Phosphodiesterase in Human Saphenous Vein

The aim of the current study was to investigate the pharmacological activity of glabridin on the isolated human saphenous vein (SV) and explore the underlying mechanisms. Samples of patients' SVs were removed during bypass surgery, and 4-mm lengths of the vessels were placed in Krebs solution at +4°C and hung in an isolated organ bath to assess their contraction/relaxation responses. The contraction/relaxation responses were recorded to observe if the cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) pathway mediates the relaxant effect of glabridin after treatment with blockers like ODQ (a guanylate cyclase inhibitor), KT5823 (a PKG inhibitor), isobutylmethylxanthine [IBMX, a phosphodiesterase (PDE) inhibitor], and cantharidin [Cant, a myosin light-chain phosphatase (MLCP) inhibitor]. Moreover, nitric oxide (NO), cGMP, and PKG levels in SV tissues were determined by ELISA after incubation with glabridin, N(ω)-nitro-L-arginine methyl ester (L-Name, a NO synthetase inhibitor), phenylephrine (PE), ODQ, IBMX, and KT5823. The results showed that glabridin relaxed the vascular smooth muscle of human SV pretreated with PE in a dose-dependent manner, which was independent of the endothelium. The vasorelaxant effect of glabridin was only inhibited by iberiotoxin (IbTX), Cant, and KT5823. Glabridin increased cGMP and PKG levels in SV homogenates, whereas it did not alter the NO level. The enhancing effects of cGMP and PKG levels by glabridin were abolished by ODQ and KT5823. In conclusion, glabridin has a vasorelaxant effect, which is associated with the activation of BK_Ca channels and inhibition of PDE.

Alternate thermal stimulation ameliorates thermal sensitivity and modulates calbindin-D 28K expression in lamina I and II and dorsal root ganglia in a mouse spinal cord contusion injury model

Neuropathic pain (NP) is a common complication that negatively affects the lives of patients with spinal cord injury (SCI). The disruption in the balance of excitatory and inhibitory neurons in the spinal cord dorsal horn contributes to the development of SCI and induces NP. The calcium-binding protein (CaBP) calbindin-D 28K (CaBP-28K) is highly expressed in excitatory interneurons, and the CaBP parvalbumin (PV) is present in inhibitory neurons in the dorsal horn. To better define the changes in the CaBPs contributing to the development of SCI-induced NP, we examined the changes in CaBP-28K and PV staining density in the lumbar (L4-6) lamina I and II, and their relationship with NP after mild spinal cord contusion injury in mice. We additionally examined the effects of alternate thermal stimulation (ATS). Compared with sham mice, injured animals developed mechanical allodynia in response to light mechanical stimuli and exhibited mechanical hyporesponsiveness to noxious mechanical stimuli. The decreased response latency to heat stimuli and increased response latency to cold stimuli at 7 days post injury suggested that the injured mice developed heat hyperalgesia and cold hypoalgesia, respectively. Temperature preference tests showed significant warm allodynia after injury. Animals that underwent ATS (15-18 and 35-40°C; +5 minutes/stimulation/day; 5 days/week) displayed significant amelioration of heat hyperalgesia, cold hypoalgesia, and warm allodynia after 2 weeks of ATS. In contrast, mechanical sensitivity was not influenced by ATS. Analysis of the CaBP-28K positive signal in L4-6 lamina I and II indicated an increase in staining density after SCI, which was associated with an increase in the number of CaBP-28K-stained L4-6 dorsal root ganglion (DRG) neurons. ATS decreased the CaBP-28K staining density in L4-6 spinal cord and DRG in injured animals, and was significantly and strongly correlated with ATS alleviation of pain behavior. The expression of PV showed no changes in lamina I and II after ATS in SCI animals. Thus, ATS partially decreases the pain behavior after SCI by modulating the changes in CaBP-associated excitatory-inhibitory neurons.

Identification of Novel Targets of Knee Osteoarthritis Shared by Cartilage and Synovial Tissue

Arthritis is the leading cause of disability among adults, while osteoarthritis (OA) is the most common form of arthritis that results in cartilage loss. However, accumulating evidence suggests that the protective hyaline cartilage should not be the sole focus of OA treatment. Particularly, synovium also plays essential roles in OA’s initiation and progression and warrants serious consideration when battling against OA. Thus, biomarkers with similar OA-responsive expressions in cartilage and synovium should be the potential targets for OA treatment. On the other hand, molecules with a distinguished response during OA in cartilage and synovium should be ruled out as OA therapeutic(s) to avoid controversial effects in different tissues. Here, to pave the path for developing a new generation of OA therapeutics, two published transcriptome datasets of knee articular cartilage and synovium were analyzed in-depth. Genes with statistically significantly different expression in OA and healthy cartilage were compared with those in the synovium. Thirty-five genes with similar OA-responsive expression in both tissues were identified while recognizing three genes with opposite OA-responsive alteration trends in cartilage and synovium. These genes were clustered based on the currently available knowledge, and the potential impacts of these clusters in OA were explored.

Novel Analgesics with Peripheral Targets

A limited number of peripheral targets generate pain. Inflammatory mediators can sensitize these. The review addresses targets acting exclusively or predominantly on sensory neurons, mediators involved in inflammation targeting sensory neurons, and mediators involved in a more general inflammatory process, of which an analgesic effect secondary to an anti-inflammatory effect can be expected. Different approaches to address these systems are discussed, including scavenging proinflammatory mediators, applying anti-inflammatory mediators, and inhibiting proinflammatory or facilitating anti-inflammatory receptors. New approaches are contrasted to established ones; the current stage of progress is mentioned, in particular considering whether there is data from a molecular and cellular level, from animals, or from human trials, including an early stage after a market release. An overview of publication activity is presented, considering a IuPhar/BPS-curated list of targets with restriction to pain-related publications, which was also used to identify topics.

Intercellular communication and ion channels in neuropathic pain chronicization

BACKGROUND

Neuropathic pain is caused by primary lesion or dysfunction of either peripheral or central nervous system. Due to its complex pathogenesis, often related to a number of comorbidities, such as cancer, neurodegenerative and neurovascular diseases, neuropathic pain still represents an unmet clinical need, lacking long-term effective treatment and complex case-by-case approach.

AIM AND METHODS

We analyzed the recent literature on the role of selective voltage-sensitive sodium, calcium and potassium permeable channels and non-selective gap junctions (GJs) and hemichannels (HCs) in establishing and maintaining chronic neuropathic conditions. We finally focussed our review on the role of extracellular microenvironment modifications induced by resident glial cells and on the recent advances in cell-to-cell and cell-to-extracellular environment communication in chronic neuropathies.

CONCLUSION

In this review, we provide an update on the current knowledge of neuropathy chronicization processes with a focus on both neuronal and glial ion channels, as well as on channel-mediated intercellular communication.

Selected pathobiological features and principles of pharmacological pain management

Pain induced by inflammation and nerve injury arises from abnormal neural activity of primary afferent nociceptors in response to tissue damage, which causes long-term elevation of the sensitivity and responsiveness of spinal cord neurons. Inflammatory pain typically resolves following resolution of inflammation; however, nerve injury-either peripheral or central-may cause persistent neuropathic pain, which frequently manifests as hyperalgesia or allodynia. Neuralgias, malignant metastatic bone disease, and diabetic neuropathy are some of the conditions associated with severe, often unremitting chronic pain that is both physically and psychologically debilitating or disabling. Therefore, optimal pain management for patients with chronic neuropathic pain requires a multimodal approach that comprises pharmacological and psychological interventions. Non-opioid analgesics (e.g., paracetamol, aspirin, or other non-steroidal anti-inflammatory drugs) are first-line agents used in the treatment of mild-to-moderate acute pain, while opioids of increasing potency are indicated for the treatment of persistent, moderate-to-severe inflammatory pain. N-methyl D-aspartate receptor antagonists, antidepressants, anticonvulsants, or a combination of these should be considered for the treatment of chronic neuropathic pain. This review discusses the various neural signals that mediate acute and chronic pain, as well as the general principles of pain management.

Characteristics of voltage-gated potassium currents in monosodium urate induced gouty arthritis in mice

OBJECTIVE

To evaluate the role of K⁺ channels in pain following gouty arthritis.

METHODS

The model of acute gouty arthritis was induced by monosodium urate (MSU) in mice. The swelling degree was determined by measuring the circumference of the ankle joint. Mechanical hyperalgesia was detected by von Frey filaments. Two types of K⁺ currents, A-type currents (I_A) and delayed rectifier currents (I_K), were recorded in dorsal root ganglion (DRG) neurons using patch-clamp techniques.

RESULTS

The swelling degree reached its maximum at 10 h and the minimum pain threshold was maintained between 8 and 48 h after MSU treatment in mice. The amplitudes of I_A and I_K in DRG neurons were moderately increased on day 1 after MSU treatment, and then, they were gradually decreased with times and reached their minimums on day 4 (for I_A) or 5 (for I_K). Compared with control group, the activation curve of I_A was significantly shifted to more positive potential and the recovery time of I_A from inactivation was markedly prolonged, but inactivation and frequency dependence of I_A appeared unaffected in MSU-treated group. Additionally, no change was observed in the activation curve of I_K after MSU treatment. The excitability was significantly higher in the MSU group than in the control group.

CONCLUSIONS

MSU-induced gout pain may be related to the hyperexcitability of DRG neurons elicited by decreasing K⁺ currents.

Noncanonical Ion Channel Behaviour in Pain

Ion channels contribute fundamental properties to cell membranes. Although highly diverse in conductivity, structure, location, and function, many of them can be regulated by common mechanisms, such as voltage or (de-)phosphorylation. Primarily considering ion channels involved in the nociceptive system, this review covers more novel and less known features. Accordingly, we outline noncanonical operation of voltage-gated sodium, potassium, transient receptor potential (TRP), and hyperpolarization-activated cyclic nucleotide (HCN)-gated channels. Noncanonical features discussed include properties as a memory for prior voltage and chemical exposure, alternative ion conduction pathways, cluster formation, and silent subunits. Complementary to this main focus, the intention is also to transfer knowledge between fields, which become inevitably more separate due to their size.

Mice lacking Kcns1 in peripheral neurons show increased basal and neuropathic pain sensitivity

Voltage-gated potassium (Kv) channels are increasingly recognised as key regulators of nociceptive excitability. Kcns1 is one of the first potassium channels to be associated with neuronal hyperexcitability and mechanical sensitivity in the rat, as well as pain intensity and risk of developing chronic pain in humans. Here, we show that in mice, Kcns1 is predominantly expressed in the cell body and axons of myelinated sensory neurons positive for neurofilament-200, including Aδ-fiber nociceptors and low-threshold Aβ mechanoreceptors. In the spinal cord, Kcns1 was detected in laminae III to V of the dorsal horn where most sensory A fibers terminate, as well as large motoneurons of the ventral horn. To investigate Kcns1 function specifically in the periphery, we generated transgenic mice in which the gene is deleted in all sensory neurons but retained in the central nervous system. Kcns1 ablation resulted in a modest increase in basal mechanical pain, with no change in thermal pain processing. After neuropathic injury, Kcns1 KO mice exhibited exaggerated mechanical pain responses and hypersensitivity to both noxious and innocuous cold, consistent with increased A-fiber activity. Interestingly, Kcns1 deletion also improved locomotor performance in the rotarod test, indicative of augmented proprioceptive signalling. Our results suggest that restoring Kcns1 function in the periphery may be of some use in ameliorating mechanical and cold pain in chronic states.

Genetic polymorphisms and their association with the prevalence and severity of chronic postsurgical pain: a systematic review

BACKGROUND

Although several patient characteristic, clinical, and psychological risk factors for chronic postsurgical pain (CPSP) have been identified, genetic variants including single nucleotide polymorphisms have also become of interest as potential risk factors for the development of CPSP. The aim of this review is to summarize the current evidence on genetic polymorphisms associated with the prevalence and severity of CPSP in adult patients.

METHODS

A systematic review of the literature was performed, and additional literature was obtained by reference tracking. The primary outcome was CPSP, defined as pain at least 2 months after the surgery. Studies performed exclusively in animals were excluded.

RESULTS

Out of the 1001 identified studies, 14 studies were selected for inclusion. These studies described 5269 participants in 17 cohorts. A meta-analysis was not possible because of heterogeneity of data and data analysis. Associations with the prevalence or severity of CPSP were reported for genetic variants in the COMT gene, OPRM1, potassium channel genes, GCH1, CACNG, CHRNA6, P2X7R, cytokine-associated genes, human leucocyte antigens, DRD2, and ATXN1 CONCLUSIONS: Research on the topic of genetic variants associated with CPSP is still in its initial phase. Hypothesis-free, genome-wide association studies on large cohorts are needed in this field. In addition, future studies may also integrate genetic risk factors and patient characteristic, clinical, and psychological predictors for CPSP.

Role of L-arginine/NO/cGMP/KATP channel signaling pathway in the central and peripheral antinociceptive effect of thymoquinone in rats

Objective(s):

Growing evidence demonstrates that L-arginine/NO/cGMP/K_ATP channel pathway has a modulatory role in pain perception. Previous studies have shown that thymoquinone exerts antinociceptive effects; however, the mechanisms underlying antinociception induced by thymoquinone have not been fully clarified. The aim of the present study was to evaluate the role of L-arginine/NO/cGMP/K_ATP channel pathway in the central and peripheral antinociceptive effect of thymoquinone in rats.

Materials and Methods:

Rats were pretreated intraplantarly (IPL) or intracerebroventricularly (ICV) with L-arginine (the NO precursor), l-NAME (an NO synthase inhibitor), SNAP (an NO donor), methylene blue (a guanylyl cyclase inhibitor), glibenclamide (the blocker of K_ATP channel), and tetraethylammonium (TEA, a K_v channel blocker) before the injection of thymoquinone.

Results:

Local ipsilateral (20 and 40 μg, IPL) but not contralateral and ICV (4 and 8 μg) administration of thymoquinone caused a dose-dependent and significant antinociception in both early and late phases of the formalin test. Pretreatment of rats with L-arginine (100 μg, IPL or ICV) and SNAP (200 μg, IPL or ICV) increased while l-NAME (100 μg, IPL or 1 μg, ICV) and methylene blue (400 μg, IPL or ICV) decreased the antinociceptive effects of thymoquinone in the formalin test. The administration of TEA (IPL or ICV) did not modify but glibenclamide (50 μg, IPL or ICV) significantly abolished the peripheral and central antinociceptive effects of thymoquinone in both phases of the formalin test.

Conclusion:

The results of the present study indicate that L-arginine/NO/cGMP/K_ATP channel pathway participates in the central and peripheral antinociceptive effect of thymoquinone.

Role of l-arginine/SNAP/NO/cGMP/KATP channel signalling pathway in antinociceptive effect of α-terpineol in mice

OBJECTIVES

The main purpose of this study was to assess the role of l-arginine/SNAP/NO/cGMP/K_ATP channel pathway in analgesic effects of α-terpineol in mice.

METHODS

Male NMRI mice were pretreated intraperitoneally with NO precursor (l-arginine, 100 mg/kg), NO synthase inhibitor (l-NAME, 30 mg/kg), NO donor (SNAP, 1 mg/kg), guanylyl cyclase inhibitor (methylene blue, 20 mg/kg), PDE inhibitor (sildenafil, 0.5 mg/kg), K_ATP channel blocker (glibenclamide, 10 mg/kg) and naloxone (2 mg/kg) 20 min before the administration of α-terpineol. The formalin test was performed 20 min after the administration of α-terpineol, and nociceptive responses of mice were recorded during 30 min.

KEY FINDINGS

A significant and dose-dependent antinociception was produced by α-terpineol (40 and 80 mg/kg) in both the phases of formalin test. The antinociceptive effect of α-terpineol was significantly potentiated by l-arginine in the second phase while significantly antagonized by l-NAME in both phases of formalin test. Also, SNAP and sildenafil non-significantly enhanced-while methylene blue significantly diminished-the antinociceptive effect of α-terpineol in both phases of formalin test. Glibenclamide significantly reversed the α-terpineol-induced antinociception, indicating the involvement of K_ATP channels in antinociceptive effect of α-terpineol.

CONCLUSIONS

These results indicate that the antinociceptive effect of α-terpineol is mediated through l-arginine/SNAP/NO/cGMP/K_ATP channel pathway.

Pain-Causing Venom Peptides: Insights into Sensory Neuron Pharmacology

Venoms are produced by a wide variety of species including spiders, scorpions, reptiles, cnidarians, and fish for the purpose of harming or incapacitating predators or prey. While some venoms are of relatively simple composition, many contain hundreds to thousands of individual components with distinct pharmacological activity. Pain-inducing or "algesic" venom compounds have proven invaluable to our understanding of how physiological nociceptive neural networks operate. In this review, we present an overview of some of the diverse nociceptive pathways that can be modulated by specific venom components to evoke pain.

The Kv7 Channel and Cardiovascular Risk Factors

Potassium channels play a pivotal role in the regulation of excitability in cells such as neurons, cardiac myocytes, and vascular smooth muscle cells. The KCNQ (Kv7) family of voltage-activated K⁺ channels hyperpolarizes the cell and stabilizes the membrane potential. Here, we outline how Kv7 channel activity may contribute to the development of the cardiovascular risk factors such as hypertension, diabetes, and obesity. Questions and hypotheses regarding previous and future research have been raised. Alterations in the Kv7 channel may contribute to the development of cardiovascular disease (CVD). Pharmacological modification of Kv7 channels may represent a possible treatment for CVD in the future.

Basic/Translational Development of Forthcoming Opioid- and Nonopioid-Targeted Pain Therapeutics

Opioids represent an efficacious therapeutic modality for some, but not all pain states. Singular reliance on opioid therapy for pain management has limitations, and abuse potential has deleterious consequences for patient and society. Our understanding of pain biology has yielded insights and opportunities for alternatives to conventional opioid agonists. The aim is to have efficacious therapies, with acceptable side effect profiles and minimal abuse potential, which is to say an absence of reinforcing activity in the absence of a pain state. The present work provides a nonexclusive overview of current drug targets and potential future directions of research and development. We discuss channel activators and blockers, including sodium channel blockers, potassium channel activators, and calcium channel blockers; glutamate receptor-targeted agents, including N-methyl-D-aspartate, α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid, and metabotropic receptors. Furthermore, we discuss therapeutics targeted at γ-aminobutyric acid, α2-adrenergic, and opioid receptors. We also considered antagonists of angiotensin 2 and Toll receptors and agonists/antagonists of adenosine, purine receptors, and cannabinoids. Novel targets considered are those focusing on lipid mediators and anti-inflammatory cytokines. Of interest is development of novel targeting strategies, which produce long-term alterations in pain signaling, including viral transfection and toxins. We consider issues in the development of druggable molecules, including preclinical screening. While there are examples of successful translation, mechanistically promising preclinical candidates may unexpectedly fail during clinical trials because the preclinical models may not recapitulate the particular human pain condition being addressed. Molecular target characterization can diminish the disconnect between preclinical and humans' targets, which should assist in developing nonaddictive analgesics.

Chronic post-amputation pain: peri-operative management - Review

Study design

Narrative review.

Method

Eight bibliographic databases were searched for studies published in the (last five years up until Feb 2017). For the two database searches (Cochrane and DARE), the time frame was unlimited. The review involved keyword searches of the term 'Amputation' AND 'chronic pain'. Studies selected were interrogated for any association between peri-operative factors and the occurrence of chronic post amputation pain (CPAP).

Results

Heterogeneity of study populations and outcome measures prevented a systematic review and hence a narrative synthesis of results was undertaken. The presence of variation in two gene alleles (GCH1 and KCNS1) may be relevant for development of CPAP. There was little evidence to draw conclusions on the association between age, gender and CPAP. Pre-operative anxiety and depression influenced pain intensity post operatively and long-term post amputation pain (CPAP). The presence of pre-amputation pain is correlated to the development of acute and chronic post amputation pain while evidence for the association of post-operative pain with CPAP is modest. Regional anaesthesia and peri-neural catheters improve acute postoperative pain relief but evidence on their efficacy to prevent CPAP is limited. A suggested whole system pathway based on current evidence to optimize peri-operative amputation pain is described.

Conclusion

The current evidence suggests that optimized peri-operative analgesia reduces the incidence of acute peri-operative pain but no firm conclusion can be drawn on reducing risk for CPAP.

Breaking barriers to novel analgesic drug development

Acute and chronic pain complaints, although common, are generally poorly served by existing therapies. This unmet clinical need reflects a failure to develop novel classes of analgesics with superior efficacy, diminished adverse effects and a lower abuse liability than those currently available. Reasons for this include the heterogeneity of clinical pain conditions, the complexity and diversity of underlying pathophysiological mechanisms, and the unreliability of some preclinical pain models. However, recent advances in our understanding of the neurobiology of pain are beginning to offer opportunities for developing novel therapeutic strategies and revisiting existing targets, including modulating ion channels, enzymes and G-protein-coupled receptors.

Hopes for the Future of Pain Control

Here we aim to present an accessible review of the pharmacological targets for pain management, and succinctly discuss the newest trends in pain therapy. A key task for current pain pharmacotherapy is the identification of receptors and channels orchestrating nociception. Notwithstanding peripheral alterations in the receptors and channels following pathophysiological events, the modulatory mechanisms in the central nervous system are also fundamental to the regulation of pain perception. Bridging preclinical and clinical studies of peripheral and central components of pain modulation, we present the different types of pain and relate these to pharmacological interventions. We firstly highlight the roles of several peripheral nociceptors, such as NGF, CGRP, sodium channels, and TRP-family channels that may become novel targets for therapies. In the central nervous system, the roles of calcium channels and gabapentinoids as well as NMDA receptors in generating excitability are covered including ideas on central sensitization. We then turn to central modulatory systems and discuss opioids and monoamines. We aim to explain the importance of central sensitization and the dialogue of the spinal circuits with the brain descending modulatory controls before discussing a mechanism-based effectiveness of antidepressants in pain therapy and their potential to modulate the descending controls. Emphasizing the roles of conditioned pain modulation and its animal's equivalent, diffuse noxious inhibitory controls, we discuss these unique descending modulations as a potential tool for understanding mechanisms in patients suffering from pain. Mechanism-based therapy is the key to picking the correct treatments and recent clinical studies using sensory symptoms of patients as surrogates for underlying mechanisms can be used to subgroup patients and reveal actions of drugs that may be lost when studying heterogenous groups of patients. Key advances in the understanding of basic pain principles will impact our thinking about therapy targets. The complexity of pain syndromes will require tailored pharmacological drugs, often in combination or through drugs with more than one action, and often psychotherapy, to fully control pain.

Centipede venom peptide SsmTX-I with two intramolecular disulfide bonds shows analgesic activities in animal models

Pain is a major symptom of many diseases and results in enormous pressures on human body or society. Currently, clinically used analgesic drugs, including opioids and nonsteroidal anti-inflammatory drugs, have adverse reactions, and thus, the development of new types of analgesic drug candidates is urgently needed. Animal venom peptides have proven to have potential as new types of analgesic medicine. In this research, we describe the isolation and characterization of an analgesic peptide from the crude venom of centipede, Scolopendra subspinipes mutilans. The amino acid sequence of this peptide was identical with SsmTX-I that was previously reported as a specific Kv2.1 ion channel blocker. Our results revealed that SsmTX-I was produced by posttranslational processing of a 73-residue prepropeptide. The intramolecular disulfide bridge motifs of SsmTX-I was Cys1-Cys3 and Cys2-Cys4. Functional assay revealed that SsmTX-I showed potential analgesic activities in formalin-induced paw licking, thermal pain, and acetic acid-induced abdominal writhing mice models. Our research provides the first report of cDNA sequences, disulfide motif, successful synthesis, and analgesic potential of SsmTX-I for the development of pain-killing drugs. It indicates that centipede peptide toxins could be a treasure trove for the search of novel analgesic drug candidates. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

HCN2 ion channels: basic science opens up possibilities for therapeutic intervention in neuropathic pain

Nociception — the ability to detect painful stimuli — is an invaluable sense that warns against present or imminent damage. In patients with chronic pain, however, this warning signal persists in the absence of any genuine threat and affects all aspects of everyday life. Neuropathic pain, a form of chronic pain caused by damage to sensory nerves themselves, is dishearteningly refractory to drugs that may work in other types of pain and is a major unmet medical need begging for novel analgesics. Hyperpolarisation-activated cyclic nucleotide (HCN)-modulated ion channels are best known for their fundamental pacemaker role in the heart; here, we review data demonstrating that the HCN2 isoform acts in an analogous way as a ‘pacemaker for pain’, in that its activity in nociceptive neurons is critical for the maintenance of electrical activity and for the sensation of chronic pain in pathological pain states. Pharmacological block or genetic deletion of HCN2 in sensory neurons provides robust pain relief in a variety of animal models of inflammatory and neuropathic pain, without any effect on normal sensation of acute pain. We discuss the implications of these findings for our understanding of neuropathic pain pathogenesis, and we outline possible future opportunities for the development of efficacious and safe pharmacotherapies in a range of chronic pain syndromes.

Nociceptive transmission and modulation via P2X receptors in central pain syndrome

Painful sensations are some of the most frequent complaints of patients who are admitted to local medical clinics. Persistent pain varies according to its causes, often resulting from local tissue damage or inflammation. Central somatosensory pathway lesions that are not adequately relieved can consequently cause central pain syndrome or central neuropathic pain. Research on the molecular mechanisms that underlie this pathogenesis is important for treating such pain. To date, evidence suggests the involvement of ion channels, including adenosine triphosphate (ATP)-gated cation channel P2X receptors, in central nervous system pain transmission and persistent modulation upon and following the occurrence of neuropathic pain. Several P2X receptor subtypes, including P2X2, P2X3, P2X4, and P2X7, have been shown to play diverse roles in the pathogenesis of central pain including the mediation of fast transmission in the peripheral nervous system and modulation of neuronal activity in the central nervous system. This review article highlights the role of the P2X family of ATP receptors in the pathogenesis of central neuropathic pain and pain transmission. We discuss basic research that may be translated to clinical application, suggesting that P2X receptors may be treatment targets for central pain syndrome.