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      Voltage gated sodium channels as therapeutic targets for chronic pain

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          Abstract

          Being maladaptive and frequently unresponsive to pharmacotherapy, chronic pain presents a major unmet clinical need. While an intact central nervous system is required for conscious pain perception, nociceptor hyperexcitability induced by nerve injury in the peripheral nervous system (PNS) is sufficient and necessary to initiate and maintain neuropathic pain. The genesis and propagation of action potentials is dependent on voltage-gated sodium channels, in particular, Nav1.7, Nav1.8 and Nav1.9. However, nerve injury triggers changes in their distribution, expression and/or biophysical properties, leading to aberrant excitability. Most existing treatment for pain relief acts through non-selective, state-dependent sodium channel blockage and have narrow therapeutic windows. Natural toxins and developing subtype-specific and molecular-specific sodium channel blockers show promise for treatment of neuropathic pain with minimal side effects. New approaches to analgesia include combination therapy and gene therapy. Here, we review how individual sodium channel subtypes contribute to pain, and the attempts made to develop more effective analgesics for the treatment of chronic pain.

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          Most cited references 123

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          Central mechanisms of pathological pain.

           Rohini Kuner (2010)
          Chronic pain is a major challenge to clinical practice and basic science. The peripheral and central neural networks that mediate nociception show extensive plasticity in pathological disease states. Disease-induced plasticity can occur at both structural and functional levels and is manifest as changes in individual molecules, synapses, cellular function and network activity. Recent work has yielded a better understanding of communication within the neural matrix of physiological pain and has also brought important advances in concepts of injury-induced hyperalgesia and tactile allodynia and how these might contribute to the complex, multidimensional state of chronic pain. This review focuses on the molecular determinants of network plasticity in the central nervous system (CNS) and discusses their relevance to the development of new therapeutic approaches.
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            Nociceptors are interleukin-1beta sensors.

            A cardinal feature of inflammation is heightened pain sensitivity at the site of the inflamed tissue. This results from the local release by immune and injured cells of nociceptor sensitizers, including prostaglandin E(2), bradykinin, and nerve growth factor, that reduce the threshold and increase the excitability of the peripheral terminals of nociceptors so that they now respond to innocuous stimuli: the phenomenon of peripheral sensitization. We show here that the proinflammatory cytokine interleukin-1beta (IL-1beta), in addition to producing inflammation and inducing synthesis of several nociceptor sensitizers, also rapidly and directly activates nociceptors to generate action potentials and induce pain hypersensitivity. IL-1beta acts in a p38 mitogen-activated protein kinase (p38 MAP kinase)-dependent manner, to increase the excitability of nociceptors by relieving resting slow inactivation of tetrodotoxin-resistant voltage-gated sodium channels and also enhances persistent TTX-resistant current near threshold. By acting as an IL-1beta sensor, nociceptors can directly signal the presence of ongoing tissue inflammation.
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              A tetrodotoxin-resistant voltage-gated sodium channel expressed by sensory neurons.

              Dorsal root ganglion sensory neurons associated with C-fibres, many of which are activated by tissue-damage, express an unusual voltage-gated sodium channel that is resistant to tetrodotoxin. We report here that we have identified a 1,957 amino-acid sodium channel in these cells that shows 65% identity with the rat cardiac tetrodotoxin-insensitive sodium channel, and is not expressed in other peripheral and central neurons, glia or non-neuronal tissues. In situ hybridization shows that the channel is expressed only by small-diameter sensory neurons in neonatal and adult dorsal root and trigeminal ganglia. The channel is resistant to tetrodotoxin when expressed in Xenopus oocytes. The electrophysiological and pharmacological properties of the expressed channel are similar to those described for the small-diameter sensory neuron tetrodotoxin-resistant sodium channels. As some noxious input into the spinal cord is resistant to tetrodotoxin, block of expression or function of such a C-fibre-restricted sodium channel may have a selective analgesic effect.
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                Author and article information

                Journal
                J Pain Res
                J Pain Res
                JPR
                jpainres
                Journal of Pain Research
                Dove
                1178-7090
                09 September 2019
                2019
                : 12
                : 2709-2722
                Affiliations
                [1 ]Department of Medicine, University of Cambridge , Cambridge, UK
                [2 ]Faculty of Medicine, University College London , London, UK
                [3 ]Faculty of Medicine, Imperial College London , London, UK
                Author notes
                Correspondence: Raihan MohammedSchool of Clinical Medicine, University of Cambridge , Hills Road, CambridgeCB2 0SP, UKTel +44 787 173 6004Email rm758@cam.ac.uk
                Article
                207610
                10.2147/JPR.S207610
                6743634
                © 2019 Ma et al.

                This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms ( https://www.dovepress.com/terms.php).

                Page count
                Tables: 2, References: 140, Pages: 14
                Categories
                Review

                Anesthesiology & Pain management

                pns, nociceptors, cns, electrogenesis, neuropathic, ttx

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