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A gain-of-function voltage-gated sodium channel 1.8 mutation drives intense hyperexcitability of A- and C-fiber neurons. Pain 2014; 155:896-905. [PMID: 24447515 DOI: 10.1016/j.pain.2014.01.012] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Revised: 12/27/2013] [Accepted: 01/14/2014] [Indexed: 12/12/2022]
Abstract
Therapeutic use of general sodium channel blockers, such as lidocaine, can substantially reduce the enhanced activity in sensory neurons that accompanies chronic pain after nerve or tissue injury. However, because these general blockers have significant side effects, there is great interest in developing inhibitors that specifically target subtypes of sodium channels. Moreover, some idiopathic small-fiber neuropathies are driven by gain-of-function mutations in specific sodium channel subtypes. In the current study, we focus on one subtype, the voltage-gated sodium channel 1.8 (Nav1.8). Nav1.8 is preferentially expressed in nociceptors, and gain-of-function mutations in Nav1.8 result in painful mechanical hypersensitivity in humans. Here, we used the recently developed gain-of-function Nav1.8 transgenic mouse strain, Possum, to investigate Nav1.8-mediated peripheral afferent hyperexcitability. This gain-of-function mutation resulted in markedly increased mechanically evoked action potential firing in subclasses of Aβ, Aδ, and C fibers. Moreover, mechanical stimuli initiated bursts of action potential firing in specific subpopulations that continued for minutes after removal of the force and were not susceptible to conduction failure. Surprisingly, despite the intense afferent firing, the behavioral effects of the Nav1.8 mutation were quite modest, as only frankly noxious stimuli elicited enhanced pain behavior. These data demonstrate that a Nav1.8 gain-of-function point mutation contributes to intense hyperexcitability along the afferent axon within distinct sensory neuron subtypes.
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Lee SK, Dawson J, Lee JA, Osman G, Levitin MO, Guzel RM, Djamgoz MB. Management of cancer pain: 1. Wider implications of orthodox analgesics. Int J Gen Med 2014; 7:49-58. [PMID: 24470767 PMCID: PMC3891517 DOI: 10.2147/ijgm.s42187] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
In this review, the first of two parts, we first provide an overview of the orthodox analgesics used commonly against cancer pain. Then, we examine in more detail the emerging evidence for the potential impact of analgesic use on cancer risk and disease progression. Increasing findings suggest that long-term use of nonsteroidal anti-inflammatory drugs, particularly aspirin, may reduce cancer occurrence. However, acetaminophen may raise the risk of some hematological malignancies. Drugs acting upon receptors of gamma-aminobutyric acid (GABA) and GABA “mimetics” (eg, gabapentin) appear generally safe for cancer patients, but there is some evidence of potential carcinogenicity. Some barbiturates appear to slightly raise cancer risks and can affect cancer cell behavior in vitro. For cannabis, studies suggest an increased risk of squamous cell carcinoma of the tongue, larynx, and possibly lung. Morphine may stimulate human microvascular endothelial cell proliferation and angiogenesis; it is not clear whether this might cause harm or produce benefit. The opioid, fentanyl, may promote growth in some tumor cell lines. Opium itself is an emerging risk factor for gastric adenocarcinoma and possibly cancers of the esophagus, bladder, larynx, and lung. It is concluded that analgesics currently prescribed for cancer pain can significantly affect the cancer process itself. More futuristically, several ion channels are being targeted with novel analgesics, but many of these are also involved in primary and/or secondary tumorigenesis. Further studies are needed to elucidate possible cellular and molecular effects of orthodox analgesics and their possible long-term impact, both positive and negative, and thus enable the best possible clinical gain for cancer patients.
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Affiliation(s)
| | - Jill Dawson
- Healthcare Communications Consultancy, Danville, CA, USA
| | - Jack A Lee
- College of Arts and Sciences, Vanderbilt University, Nashville, TN, USA
| | - Gizem Osman
- Department of Chemical Engineering, Loughborough University, Loughborough, UK
| | - Maria O Levitin
- Division of Cell and Molecular Biology, Neuroscience Solutions to Cancer Research Group, South Kensington Campus, Imperial College London, London, UK
| | - Refika Mine Guzel
- Division of Cell and Molecular Biology, Neuroscience Solutions to Cancer Research Group, South Kensington Campus, Imperial College London, London, UK
| | - Mustafa Ba Djamgoz
- Division of Cell and Molecular Biology, Neuroscience Solutions to Cancer Research Group, South Kensington Campus, Imperial College London, London, UK ; Cyprus International University, Biotechnology Research Centre, Haspolat, North Cyprus, Mersin, Turkey
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Probing functional properties of nociceptive axons using a microfluidic culture system. PLoS One 2013; 8:e80722. [PMID: 24278311 PMCID: PMC3835735 DOI: 10.1371/journal.pone.0080722] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 10/04/2013] [Indexed: 11/25/2022] Open
Abstract
Pathological changes in axonal function are integral features of many neurological disorders, yet our knowledge of the molecular basis of axonal dysfunction remains limited. Microfluidic chambers (MFCs) can provide unique insight into the axonal compartment independent of the soma. Here we demonstrate how an MFC based cell culture system can be readily adapted for the study of axonal function in vitro. We illustrate the ease and versatility to assay electrogenesis and conduction of action potentials (APs) in naïve, damaged or sensitized DRG axons using calcium imaging at the soma for pharmacological screening or patch-clamp electrophysiology for detailed biophysical characterisation. To demonstrate the adaptability of the system, we report by way of example functional changes in nociceptor axons following sensitization by neurotrophins and axotomy in vitro. We show that NGF can locally sensitize axonal responses to capsaicin, independent of the soma. Axotomizing neurons in MFC results in a significant increase in the proportion of neurons that respond to axonal stimulation, and interestingly leads to accumulation of Nav1.8 channels in regenerating axons. Axotomy also augmented AP amplitude following axotomy and altered activation thresholds in a subpopulation of regenerating axons. We further show how the system can readily be used to study modulation of axonal function by non-neuronal cells such as keratinocytes. Hence we describe a novel in vitro platform for the study of axonal function and a surrogate model for nerve injury and sensitization.
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Chen YW, Tzeng JI, Liu KS, Yu SH, Hung CH, Wang JJ. Systemic diphenidol reduces neuropathic allodynia and TNF-alpha overexpression in rats after chronic constriction injury. Neurosci Lett 2013; 552:62-5. [DOI: 10.1016/j.neulet.2013.07.030] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Revised: 06/17/2013] [Accepted: 07/21/2013] [Indexed: 01/20/2023]
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Black JA, Hoeijmakers JGJ, Faber CG, Merkies ISJ, Waxman SG. NaV1.7: stress-induced changes in immunoreactivity within magnocellular neurosecretory neurons of the supraoptic nucleus. Mol Pain 2013; 9:39. [PMID: 23924059 PMCID: PMC3750570 DOI: 10.1186/1744-8069-9-39] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Accepted: 08/06/2013] [Indexed: 02/07/2023] Open
Abstract
Background NaV1.7 is preferentially expressed, at relatively high levels, in peripheral neurons, and is often referred to as a “peripheral” sodium channel, and NaV1.7-specific blockers are under study as potential pain therapeutics which might be expected to have minimal CNS side effects. However, occasional reports of patients with NaV1.7 gain-of-function mutations and apparent hypothalamic dysfunction have appeared. The two sodium channels previously studied within the rat hypothalamic supraoptic nucleus, NaV1.2 and NaV1.6, display up-regulated expression in response to osmotic stress. Results Here we show that NaV1.7 is present within vasopressin-producing neurons and oxytocin-producing neurons within the rat hypothalamus, and demonstrate that the level of Nav1.7 immunoreactivity is increased in these cells in response to osmotic stress. Conclusions NaV1.7 is present within neurosecretory neurons of rat supraoptic nucleus, where the level of immunoreactivity is dynamic, increasing in response to osmotic stress. Whether NaV1.7 levels are up-regulated within the human hypothalamus in response to environmental factors or stress, and whether NaV1.7 plays a functional role in human hypothalamus, is not yet known. Until these questions are resolved, the present findings suggest the need for careful assessment of hypothalamic function in patients with NaV1.7 mutations, especially when subjected to stress, and for monitoring of hypothalamic function as NaV1.7 blocking agents are studied.
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Affiliation(s)
- Joel A Black
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
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106
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Nalamachu S, Nalamasu R, Jenkins J, Marriott T. An open-label pilot study evaluating the effectiveness of the heated lidocaine/tetracaine patch for the treatment of pain associated with carpal tunnel syndrome. Pain Pract 2013; 14:607-12. [PMID: 23906384 DOI: 10.1111/papr.12105] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2013] [Accepted: 05/29/2013] [Indexed: 12/23/2022]
Abstract
OBJECTIVES Carpal tunnel syndrome (CTS) is a common entrapment neuropathy of the median nerve at the wrist that is characterized by pain, paresthesias, weakness, and loss of dexterity. This pilot study was conducted to evaluate the heated lidocaine/tetracaine patch (HLT patch) as a conservative treatment for pain of CTS. METHODS Twenty adult patients (mean age = 44 ± 12 years) with pain secondary to unilateral CTS and electrodiagnostic evidence of mild-to-moderate CTS enrolled in this open-label study. Patients were treated with a single HLT patch placed over the junction of forearm and wrist on the palmar aspect of the wrist twice daily (morning and evening at 12-hour intervals) for 2 hours. At baseline and during the 2-week study, patients graded their pain intensity with an 11-point numerical rating scale (0 = no pain, 10 = worst imaginable pain). Pain interference with general activity, work, and sleep was evaluated with a similar 0-to-10-point scale. RESULTS Fifteen patients completed the 14-day treatment period. Mean average pain intensity score decreased from 5.1 ± 1.5 at baseline to 2.5 ± 1.6 at end of study in the per-protocol population (P < 0.001). Two-thirds of the patients demonstrated clinically meaningful pain relief (≥ 30% reduction in average pain score), with 40% of the patients reaching this threshold by the third treatment day. Similar improvements were observed for pain interference scores. The HLT patch was generally well tolerated. CONCLUSION The HLT patch resulted in clinically meaningful reduction in pain intensity in the majority of patients with mild-to-moderate CTS and may represent a targeted nonsurgical treatment for pain associated with CTS.
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Affiliation(s)
- Srinivas Nalamachu
- International Clinical Research Institute, Inc., Overland Park, Kansas, U.S.A
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107
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Laedermann CJ, Cachemaille M, Kirschmann G, Pertin M, Gosselin RD, Chang I, Albesa M, Towne C, Schneider BL, Kellenberger S, Abriel H, Decosterd I. Dysregulation of voltage-gated sodium channels by ubiquitin ligase NEDD4-2 in neuropathic pain. J Clin Invest 2013; 123:3002-13. [PMID: 23778145 DOI: 10.1172/jci68996] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Accepted: 04/19/2013] [Indexed: 12/22/2022] Open
Abstract
Peripheral neuropathic pain is a disabling condition resulting from nerve injury. It is characterized by the dysregulation of voltage-gated sodium channels (Navs) expressed in dorsal root ganglion (DRG) sensory neurons. The mechanisms underlying the altered expression of Na(v)s remain unknown. This study investigated the role of the E3 ubiquitin ligase NEDD4-2, which is known to ubiquitylate Navs, in the pathogenesis of neuropathic pain in mice. The spared nerve injury (SNI) model of traumatic nerve injury-induced neuropathic pain was used, and an Na(v)1.7-specific inhibitor, ProTxII, allowed the isolation of Na(v)1.7-mediated currents. SNI decreased NEDD4-2 expression in DRG cells and increased the amplitude of Na(v)1.7 and Na(v)1.8 currents. The redistribution of Na(v)1.7 channels toward peripheral axons was also observed. Similar changes were observed in the nociceptive DRG neurons of Nedd4L knockout mice (SNS-Nedd4L(-/-)). SNS-Nedd4L(-/-) mice exhibited thermal hypersensitivity and an enhanced second pain phase after formalin injection. Restoration of NEDD4-2 expression in DRG neurons using recombinant adenoassociated virus (rAAV2/6) not only reduced Na(v)1.7 and Na(v)1.8 current amplitudes, but also alleviated SNI-induced mechanical allodynia. These findings demonstrate that NEDD4-2 is a potent posttranslational regulator of Na(v)s and that downregulation of NEDD4-2 leads to the hyperexcitability of DRG neurons and contributes to the genesis of pathological pain.
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Affiliation(s)
- Cédric J Laedermann
- Pain Center, Department of Anesthesiology, University Hospital Center and University of Lausanne, Lausanne, Switzerland
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Pitcher GM, Ritchie J, Henry JL. Peripheral neuropathy induces cutaneous hypersensitivity in chronically spinalized rats. PAIN MEDICINE 2013; 14:1057-71. [PMID: 23855791 DOI: 10.1111/pme.12123] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
BACKGROUND/OBJECTIVES The present study was aimed at the issue of whether peripheral nerve injury-induced chronic pain is maintained by supraspinal structures governing descending facilitation to the spinal dorsal horn, or whether altered peripheral nociceptive mechanisms sustain central hyperexcitability and, in turn, neuropathic pain. We examined this question by determining the contribution of peripheral/spinal mechanisms, isolated from supraspinal influence(s), in cutaneous hypersensitivity in an animal model of peripheral neuropathy. METHODS Adult rats were spinalized at T8-T9; 8 days later, peripheral neuropathy was induced by implanting a 2-mm polyethylene cuff around the left sciatic nerve. Hind paw withdrawal responses to mechanical or thermal plantar stimulation were evaluated using von Frey filaments or a heat lamp, respectively. RESULTS Spinalized rats without cuff implantation exhibited a moderate decrease in mechanical withdrawal threshold on ~day 10 (P < 0.05) and in thermal withdrawal threshold on ~day 18 (P < 0.05). However, cuff-implanted spinalized rats developed a more rapid and significant decrease in mechanical (~day 4; P < 0.001) and thermal (~day 10; P < 0.05) withdrawal thresholds that remained significantly decreased through the duration of the study. CONCLUSIONS Our findings demonstrate an aberrant peripheral/spinal mechanism that induces and maintains thermal and to a greater degree tactile cutaneous hypersensitivity in the cuff model of neuropathic pain, and raise the prospect that altered peripheral/spinal nociceptive mechanisms in humans with peripheral neuropathy may have a pathologically relevant role in both inducing and sustaining neuropathic pain.
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Affiliation(s)
- Graham M Pitcher
- Departments of Physiology and Psychiatry, McGill University, Montreal, Quebec, Canada.
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109
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Alvarado S, Tajerian M, Millecamps M, Suderman M, Stone LS, Szyf M. Peripheral nerve injury is accompanied by chronic transcriptome-wide changes in the mouse prefrontal cortex. Mol Pain 2013; 9:21. [PMID: 23597049 PMCID: PMC3640958 DOI: 10.1186/1744-8069-9-21] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Accepted: 03/22/2013] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND Peripheral nerve injury can have long-term consequences including pain-related manifestations, such as hypersensitivity to cutaneous stimuli, as well as affective and cognitive disturbances, suggesting the involvement of supraspinal mechanisms. Changes in brain structure and cortical function associated with many chronic pain conditions have been reported in the prefrontal cortex (PFC). The PFC is implicated in pain-related co-morbidities such as depression, anxiety and impaired emotional decision-making ability. We recently reported that this region is subject to significant epigenetic reprogramming following peripheral nerve injury, and normalization of pain-related structural, functional and epigenetic abnormalities in the PFC are all associated with effective pain reduction. In this study, we used the Spared Nerve Injury (SNI) model of neuropathic pain to test the hypothesis that peripheral nerve injury triggers persistent long-lasting changes in gene expression in the PFC, which alter functional gene networks, thus providing a possible explanation for chronic pain associated behaviors. RESULTS SNI or sham surgery where performed in male CD1 mice at three months of age. Six months after injury, we performed transcriptome-wide sequencing (RNAseq), which revealed 1147 differentially regulated transcripts in the PFC in nerve-injured vs. control mice. Changes in gene expression occurred across a number of functional gene clusters encoding cardinal biological processes as revealed by Ingenuity Pathway Analysis. Significantly altered biological processes included neurological disease, skeletal muscular disorders, behavior, and psychological disorders. Several of the changes detected by RNAseq were validated by RT-QPCR and included transcripts with known roles in chronic pain and/or neuronal plasticity including the NMDA receptor (glutamate receptor, ionotropic, NMDA; grin1), neurite outgrowth (roundabout 3; robo3), gliosis (glial fibrillary acidic protein; gfap), vesicular release (synaptotagmin 2; syt2), and neuronal excitability (voltage-gated sodium channel, type I; scn1a). CONCLUSIONS This study used an unbiased approach to document long-term alterations in gene expression in the brain following peripheral nerve injury. We propose that these changes are maintained as a memory of an insult that is temporally and spatially distant from the initial injury.
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Affiliation(s)
- Sebastian Alvarado
- Department of Pharmacology and Therapeutics, McGill University, Faculty of Medicine, 3655 Promenade Sir William Osler, Montréal, Québec H3G 1Y6, Canada
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Copel C, Clerc N, Osorio N, Delmas P, Mazet B. The Nav1.9 channel regulates colonic motility in mice. Front Neurosci 2013; 7:58. [PMID: 23596386 PMCID: PMC3625748 DOI: 10.3389/fnins.2013.00058] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2012] [Accepted: 03/28/2013] [Indexed: 01/07/2023] Open
Abstract
The colonic migrating motor complex (CMMC) is a major pattern of motility that is entirely generated and organized by the enteric nervous system. We have previously demonstrated that the Nav1.9 channel underlies a tetrodotoxin-resistant sodium current which modulates the excitability of enteric neurons. The aim of this study was to observe the effect of loss of the Nav1.9 channel in enteric neurons on mouse colonic motility in vitro. The mechanical activity of the circular muscle was simultaneously recorded from three sites, namely, proximal, mid- and distal, along the whole colon of male, age-matched wild-type and Nav1.9 null mice. Spontaneous CMMCs were observed in all preparations. The mean frequency of CMMCs was significantly higher in the Nav1.9 null mice (one every 2.87 ± 0.1 min compared to one every 3.96 ± 0.23 min in the wild type). The mean duration of CMMCs was shorter and the mean area-under-contraction was larger in the Nav1.9 null mice compared to the wild type. In addition, CMMCs propagated preferentially in an aboral direction in the Nav1.9 null mice. Our study demonstrates that CMMCs do occur in mice lacking the Nav1.9 channel, but their characteristics are significantly different from controls. Up to now, the Nav1.9 channel was mainly associated with nociceptive neurons and involved in their hyperexcitability after inflammation. Our result shows for the first time a role for the Nav1.9 channel in a complex colonic motor pattern.
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Affiliation(s)
- Carine Copel
- Aix Marseille Université, CNRS, CRN2M UMR 7286 Marseille, France
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111
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Molet J, Pohl M. Gene-based approaches in pain research and exploration of new therapeutic targets and strategies. Eur J Pharmacol 2013; 716:129-41. [PMID: 23500201 DOI: 10.1016/j.ejphar.2013.01.073] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2012] [Revised: 01/17/2013] [Accepted: 01/29/2013] [Indexed: 12/18/2022]
Abstract
Large panel of gene-based techniques is used for many years specifically in the pain research field. From the first identification (cloning) of some "mythic" genes, such as those encoding opioid or capsaicin receptors allowing then the creation of first-generation knockout mice, to the today conditional (time, tissue, cell-type and even pathology-dependent) and regulatable modulation of a gene function, these approaches largely contributed to fundamental leaps forward in our understanding of the function of some proteins and of their interest as possible druggable targets. Perhaps one of the most remarkable evolution in the last years is the passage of these approaches from the bench to the patient; whether it concerns the identification of genes involved in inherited pain insensibility/susceptibility, the search for genetic markers of pain types, the individual pharmacogenomics or even the first gene therapy trials. From many possible variants of gene-grounded techniques used in pain research we focus here on gene knockouts and some recent developments, on viral vectors-based gene transfer and on transgenic models for the tracing of pain pathways. Through these selected examples we attempted to emphasize the immense potential of these approaches and their already well-recognized contribution in both the basic and clinical pain research.
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Affiliation(s)
- Jenny Molet
- INSERM UMRS 975, CNRS UMR 7225, UPMC, Equipe Douleurs , Faculté de Médecine Pitié-Salpêtrière, 91 Bd de l'Hôpital, 75013 Paris, France.
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Moldovan M, Alvarez S, Romer Rosberg M, Krarup C. Axonal voltage-gated ion channels as pharmacological targets for pain. Eur J Pharmacol 2013; 708:105-12. [PMID: 23500193 DOI: 10.1016/j.ejphar.2013.03.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Accepted: 03/04/2013] [Indexed: 12/19/2022]
Abstract
Upon peripheral nerve injury (caused by trauma or disease process) axons of the dorsal root ganglion (DRG) somatosensory neurons have the ability to sprout and regrow/remyelinate to reinnervate distant target tissue or form a tangled scar mass called a neuroma. This regenerative response can become maladaptive leading to a persistent and debilitating pain state referred to as chronic pain corresponding to the clinical description of neuropathic/chronic inflammatory pain. There is little agreement to what causes peripheral chronic pain other than hyperactivity of the nociceptive DRG neurons which ultimately depends on the function of voltage-gated ion channels. This review focuses on the pharmacological modulators of voltage-gated ion channels known to be present on axonal membrane which represents by far the largest surface of DRG neurons. Blockers of voltage-gated Na(+) channels, openers of voltage-gated K(+) channels and blockers of hyperpolarization-activated cyclic nucleotide-gated channels that were found to reduce neuronal activity were also found to be effective in neuropathic and inflammatory pain states. The isoforms of these channels present on nociceptive axons have limited specificity. The rationale for considering axonal voltage-gated ion channels as targets for pain treatment comes from the accumulating evidence that chronic pain states are associated with a dysregulation of these channels that could alter their specificity and make them more susceptible to pharmacological modulation. This drives the need for further development of subtype-specific voltage-gated ion channels modulators, as well as clinically available neurophysiological techniques for monitoring axonal ion channel function in peripheral nerves.
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Affiliation(s)
- Mihai Moldovan
- Institute of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
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Vastani N, Seifert B, Spahn DR, Maurer K. Preconditioning depolarizing ramp currents enhance the effect of sodium channel blockers in primary sensory afferents. Neuromodulation 2013; 16:336-44. [PMID: 23421867 DOI: 10.1111/ner.12031] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Revised: 12/14/2012] [Accepted: 01/03/2013] [Indexed: 11/30/2022]
Abstract
OBJECTIVES The conformational state of voltage-gated sodium channels is an important determinant for the efficacy of both local anesthesia and electrical neuromodulation techniques. This study investigated the role of subthreshold preconditioning ramp currents on axonal nerve excitability parameters in the presence of sodium channel blockers in myelinated A and unmyelinated C fibers. MATERIALS AND METHODS A- and C-fiber compound action potentials were recorded extracellularly in vitro in saphenous nerve from adult rats. Nerve fibers were stimulated with a supramaximal current pulse either alone or after a 300-msec conditioning polarizing ramp current (between -10% and +100% of the original threshold current) in the presence and absence of lidocaine and tetrodotoxin (TTX). A computerized threshold tracking program (QTRAC), Institute of Neurology, University College London, London, UK) was used to determine the membrane thresholds. RESULTS Preconditioning ramp currents of weak strengths increased membrane excitability. Stronger preconditioning ramp currents enhanced the potency of lidocaine and TTX to increase excitability thresholds. In A and C fibers stimulated with ramp currents of 110% (A fibers) and 40% (C fibers), lidocaine (80 μM) induced a 168 ± 15% (p < 0.001) and 302 ± 23% (p < 0.001) increase in threshold, respectively (no ramp current: 135 ± 9% and 124 ± 4%, respectively). TTX (16 nM) induced an increase in threshold of 455 ± 45% (p < 0.001) and 214 ± 22% (p = 0.005), respectively (no ramp current: 205 ± 12% and 128 ± 6%, respectively). CONCLUSIONS Slow preconditioning ramp stimuli inactivate sodium currents. In the presence of sodium channel blockers, stronger ramp stimuli cause an increase in threshold, which is larger than that caused by the sodium channel blocker alone. Therefore, we conclude that small depolarizing ramp currents could be used to increase excitability threshold in the presence of low concentrations of local anesthetics. These additive effects might represent a target to address with peripheral nerve stimulation in order to suppress afferent pain signaling.
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Affiliation(s)
- Nisha Vastani
- Institute of Anesthesiology, University Hospital of Zurich, Zurich, Switzerland
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Abstract
The somatic sensory system includes a variety of sensory modalities, such as touch, pain, itch, and temperature sensitivity. The coding of these modalities appears to be best explained by the population-coding theory, which is composed of the following features. First, an individual somatic sensory afferent is connected with a specific neural circuit or network (for simplicity, a sensory-labeled line), whose isolated activation is sufficient to generate one specific sensation under normal conditions. Second, labeled lines are interconnected through local excitatory and inhibitory interneurons. As a result, activation of one labeled line could modulate, or provide gate control of, another labeled line. Third, most sensory fibers are polymodal, such that a given stimulus placed onto the skin often activates two or multiple sensory-labeled lines; crosstalk among them is needed to generate one dominant sensation. Fourth and under pathological conditions, a disruption of the antagonistic interaction among labeled lines could open normally masked neuronal pathways, and allow a given sensory stimulus to evoke a new sensation, such as pain evoked by innocuous mechanical or thermal stimuli and itch evoked by painful stimuli. As a result of this, some sensory fibers operate along distinct labeled lines under normal versus pathological conditions. Thus, a better understanding of the neural network underlying labeled line crosstalk may provide new strategies to treat chronic pain and itch.
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Black JA, Frézel N, Dib-Hajj SD, Waxman SG. Expression of Nav1.7 in DRG neurons extends from peripheral terminals in the skin to central preterminal branches and terminals in the dorsal horn. Mol Pain 2012; 8:82. [PMID: 23134641 PMCID: PMC3517774 DOI: 10.1186/1744-8069-8-82] [Citation(s) in RCA: 140] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Accepted: 10/30/2012] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Sodium channel Nav1.7 has emerged as a target of considerable interest in pain research, since loss-of-function mutations in SCN9A, the gene that encodes Nav1.7, are associated with a syndrome of congenital insensitivity to pain, gain-of-function mutations are linked to the debiliting chronic pain conditions erythromelalgia and paroxysmal extreme pain disorder, and upregulated expression of Nav1.7 accompanies pain in diabetes and inflammation. Since Nav1.7 has been implicated as playing a critical role in pain pathways, we examined by immunocytochemical methods the expression and distribution of Nav1.7 in rat dorsal root ganglia neurons, from peripheral terminals in the skin to central terminals in the spinal cord dorsal horn. RESULTS Nav1.7 is robustly expressed within the somata of peptidergic and non-peptidergic DRG neurons, and along the peripherally- and centrally-directed C-fibers of these cells. Nav1.7 is also expressed at nodes of Ranvier in a subpopulation of Aδ-fibers within sciatic nerve and dorsal root. The peripheral terminals of DRG neurons within skin, intraepidermal nerve fibers (IENF), exhibit robust Nav1.7 immunolabeling. The central projections of DRG neurons in the superficial lamina of spinal cord dorsal horn also display Nav1.7 immunoreactivity which extends to presynaptic terminals. CONCLUSIONS The expression of Nav1.7 in DRG neurons extends from peripheral terminals in the skin to preterminal central branches and terminals in the dorsal horn. These data support a major contribution for Nav1.7 in pain pathways, including action potential electrogenesis, conduction along axonal trunks and depolarization/invasion of presynaptic axons. The findings presented here may be important for pharmaceutical development, where target engagement in the right compartment is essential.
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Affiliation(s)
- Joel A Black
- Department of Neurology and Paralyzed Veterans of America Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA.
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Peigneur S, Béress L, Möller C, Marí F, Forssmann W, Tytgat J. A natural point mutation changes both target selectivity and mechanism of action of sea anemone toxins. FASEB J 2012; 26:5141-51. [DOI: 10.1096/fj.12-218479] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Steve Peigneur
- Laboratory of ToxicologyUniversity of Leuven (Katholieke Universiteit Leuven)LeuvenBelgium
| | - László Béress
- Department of Immunology and RheumatologyHannover Medical UniversityHannoverGermany
- Pharis Biotec GmbHHannoverGermany
| | - Carolina Möller
- Department of Chemistry and BiochemistryFlorida Atlantic UniversityBoca RatonFloridaUSA
| | - Frank Marí
- Department of Chemistry and BiochemistryFlorida Atlantic UniversityBoca RatonFloridaUSA
| | - Wolf‐Georg Forssmann
- Department of Immunology and RheumatologyHannover Medical UniversityHannoverGermany
- Pharis Biotec GmbHHannoverGermany
| | - Jan Tytgat
- Laboratory of ToxicologyUniversity of Leuven (Katholieke Universiteit Leuven)LeuvenBelgium
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117
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Nardi A, Damann N, Hertrampf T, Kless A. Advances in targeting voltage-gated sodium channels with small molecules. ChemMedChem 2012; 7:1712-40. [PMID: 22945552 DOI: 10.1002/cmdc.201200298] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Revised: 07/30/2012] [Indexed: 12/19/2022]
Abstract
Blockade of voltage-gated sodium channels (VGSCs) has been used successfully in the clinic to enable control of pathological firing patterns that occur in conditions as diverse as chronic pain, epilepsy, and arrhythmias. Herein we review the state of the art in marketed sodium channel inhibitors, including a brief compendium of their binding sites and of the cellular and molecular biology of sodium channels. Despite the preferential action of this drug class toward over-excited cells, which significantly limits potential undesired side effects on other cells, the need to develop a second generation of sodium channel inhibitors to overcome their critical clinical shortcomings is apparent. Current approaches in drug discovery to deliver novel and truly innovative sodium channel inhibitors is next presented by surveying the most recent medicinal chemistry breakthroughs in the field of small molecules and developments in automated patch-clamp platforms. Various strategies aimed at identifying small molecules that target either particular isoforms of sodium channels involved in specific diseases or anomalous sodium channel currents, irrespective of the isoform by which they have been generated, are critically discussed and revised.
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Affiliation(s)
- Antonio Nardi
- Global Drug Discovery, Department of Medicinal Chemistry, Grünenthal, Zieglerstrasse 6, 52078 Aachen, Germany.
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118
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Silva AO, Peigneur S, Diniz MRV, Tytgat J, Beirão PSL. Inhibitory effect of the recombinant Phoneutria nigriventer Tx1 toxin on voltage-gated sodium channels. Biochimie 2012; 94:2756-63. [PMID: 22968173 DOI: 10.1016/j.biochi.2012.08.016] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2012] [Accepted: 08/20/2012] [Indexed: 11/19/2022]
Abstract
Phoneutria nigriventer toxin Tx1 (PnTx1, also referred to in the literature as Tx1) exerts inhibitory effect on neuronal (Na(V)1.2) sodium channels in a way dependent on the holding potential, and competes with μ-conotoxins but not with tetrodotoxin for their binding sites. In the present study we investigated the electrophysiological properties of the recombinant toxin (rPnTx1), which has the complete amino acid sequence of the natural toxin with 3 additional residues: AM on the N-terminal and G on the C-terminal. At the concentration of 1.5 μM, the recombinant toxin inhibits Na(+) currents of dorsal root ganglia neurons (38.4 ± 6.1% inhibition at -80 mV holding potential) and tetrodotoxin-resistant Na(+) currents (26.2 ± 4.9% at the same holding potential). At -50 mV holding potential the inhibition of the total current reached 71.3 ± 2.3% with 1.5 μM rPnTx1. The selectivity of rPnTx1 was investigated on ten different isoforms of voltage-gated sodium channels expressed in Xenopus oocytes. The order of potency for rPnTx1 was: rNa(V)1.2 > rNa(V)1.7 ≈ rNa(V)1.4 ≥ rNa(V)1.3 > mNa(V)1.6 ≥ hNa(V)1.8. No effect was seen on hNa(V)1.5 and on the arthropods isoforms (DmNa(V)1, BGNa(V)1.1a and VdNa(V)1). The IC(50) for Na(V)1.2 was 33.7 ± 2.9 nM with a maximum inhibition of 83.3 ± 1.9%. The toxin did not alter the voltage-dependence of channel gating and was effective on Na(V)1.2 channels devoid of inactivation. It was ineffective on neuronal calcium channels. We conclude that rPnTx1 has a promising selectivity, and that it may be a valuable model to achieve pharmacological activities of interest for the treatment of channelopathies and neuropathic pain.
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Affiliation(s)
- Anita O Silva
- Dept. of Biochemistry and Immunology, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais - UFMG, Av. Antonio Carlos 6627, 31270-901 Belo Horizonte, MG, Brazil
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119
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Samad OA, Tan AM, Cheng X, Foster E, Dib-Hajj SD, Waxman SG. Virus-mediated shRNA knockdown of Na(v)1.3 in rat dorsal root ganglion attenuates nerve injury-induced neuropathic pain. Mol Ther 2012; 21:49-56. [PMID: 22910296 DOI: 10.1038/mt.2012.169] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Neuropathic pain is a chronic condition that is often refractory to treatment with available therapies and thus an unmet medical need. We have previously shown that the voltage-gated sodium channel Na(v)1.3 is upregulated in peripheral and central nervous system (CNS) of rats following nerve injury, and that it contributes to nociceptive neuron hyperexcitability in neuropathic conditions. To evaluate the therapeutic potential of peripheral Na(v)1.3 knockdown at a specific segmental level, we constructed adeno-associated viral (AAV) vector expressing small hairpin RNA against rat Na(v)1.3 and injected it into lumbar dorsal root ganglion (DRG) of rats with spared nerve injury (SNI). Our data show that direct DRG injection provides a model that can be used for proof-of-principle studies in chronic pain with respect to peripheral delivery route of gene transfer constructs, high transduction efficiency, flexibility in terms of segmental localization, and limited behavioral effects of the surgical procedure. We show that knockdown of Na(v)1.3 in lumbar 4 (L4) DRG results in an attenuation of nerve injury-induced mechanical allodynia in the SNI model. Taken together, our studies support the contribution of peripheral Na(v)1.3 to pain in adult rats with neuropathic pain, validate Na(v)1.3 as a target, and provide validation for this approach of AAV-mediated peripheral gene therapy.
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Affiliation(s)
- Omar A Samad
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut, USA
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120
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Verkerk AO, Remme CA, Schumacher CA, Scicluna BP, Wolswinkel R, de Jonge B, Bezzina CR, Veldkamp MW. Functional Na
V
1.8 Channels in Intracardiac Neurons. Circ Res 2012; 111:333-43. [DOI: 10.1161/circresaha.112.274035] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Rationale:
The
SCN10A
gene encodes the neuronal sodium channel isoform Na
V
1.8. Several recent genome-wide association studies have linked
SCN10A
to PR interval and QRS duration, strongly suggesting an as-yet unknown role for Na
V
1.8 in cardiac electrophysiology.
Objective:
To demonstrate the functional presence of
SCN10A
/Nav1.8 in intracardiac neurons of the mouse heart.
Methods and Results:
Immunohistochemistry on mouse tissue sections showed intense Na
V
1.8 labeling in dorsal root ganglia and intracardiac ganglia and only modest Na
V
1.8 expression within the myocardium. Immunocytochemistry further revealed substantial Na
V
1.8 staining in isolated neurons from murine intracardiac ganglia but no Na
V
1.8 expression in isolated ventricular myocytes. Patch-clamp studies demonstrated that the Na
V
1.8 blocker A-803467 (0.5–2 μmol/L) had no effect on either mean sodium current (I
Na
) density or I
Na
gating kinetics in isolated myocytes but significantly reduced I
Na
density in intracardiac neurons. Furthermore, A-803467 accelerated the slow component of current decay and shifted voltage dependence of inactivation toward more negative voltages, as expected for blockade of Na
V
1.8-based I
Na
. In line with these findings, A-803467 did not affect cardiomyocyte action potential upstroke velocity but markedly reduced action potential firing frequency in intracardiac neurons, confirming a functional role for Na
V
1.8 in cardiac neural activity.
Conclusions:
Our findings demonstrate the functional presence of
SCN10A
/Na
V
1.8 in intracardiac neurons, indicating a novel role for this neuronal sodium channel in regulation of cardiac electric activity.
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Affiliation(s)
- Arie O. Verkerk
- From the Department of Clinical and Experimental Cardiology (C.A.R., C.A.S., B.P.S., R.W., C.R.B., M.W.V.) and the Department of Anatomy, Embryology, and Physiology (A.O.V., B.d.J.), Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Carol Ann Remme
- From the Department of Clinical and Experimental Cardiology (C.A.R., C.A.S., B.P.S., R.W., C.R.B., M.W.V.) and the Department of Anatomy, Embryology, and Physiology (A.O.V., B.d.J.), Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Cees A. Schumacher
- From the Department of Clinical and Experimental Cardiology (C.A.R., C.A.S., B.P.S., R.W., C.R.B., M.W.V.) and the Department of Anatomy, Embryology, and Physiology (A.O.V., B.d.J.), Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Brendon P. Scicluna
- From the Department of Clinical and Experimental Cardiology (C.A.R., C.A.S., B.P.S., R.W., C.R.B., M.W.V.) and the Department of Anatomy, Embryology, and Physiology (A.O.V., B.d.J.), Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Rianne Wolswinkel
- From the Department of Clinical and Experimental Cardiology (C.A.R., C.A.S., B.P.S., R.W., C.R.B., M.W.V.) and the Department of Anatomy, Embryology, and Physiology (A.O.V., B.d.J.), Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Berend de Jonge
- From the Department of Clinical and Experimental Cardiology (C.A.R., C.A.S., B.P.S., R.W., C.R.B., M.W.V.) and the Department of Anatomy, Embryology, and Physiology (A.O.V., B.d.J.), Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Connie R. Bezzina
- From the Department of Clinical and Experimental Cardiology (C.A.R., C.A.S., B.P.S., R.W., C.R.B., M.W.V.) and the Department of Anatomy, Embryology, and Physiology (A.O.V., B.d.J.), Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Marieke W. Veldkamp
- From the Department of Clinical and Experimental Cardiology (C.A.R., C.A.S., B.P.S., R.W., C.R.B., M.W.V.) and the Department of Anatomy, Embryology, and Physiology (A.O.V., B.d.J.), Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
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121
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Tate S, Derjean D, Rugiero F. Nav(1.8)igating the maze of sensory function. Pain 2012; 153:1985-1986. [PMID: 22738797 DOI: 10.1016/j.pain.2012.06.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Revised: 06/11/2012] [Accepted: 06/11/2012] [Indexed: 11/18/2022]
Affiliation(s)
- Simon Tate
- Convergence Pharmaceuticals Ltd., Babraham Research Campus, Cambridge CB22 3AT, UK
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122
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Nozaki C, Le Bourdonnec B, Reiss D, Windh RT, Little PJ, Dolle RE, Kieffer BL, Gavériaux-Ruff C. δ-Opioid mechanisms for ADL5747 and ADL5859 effects in mice: analgesia, locomotion, and receptor internalization. J Pharmacol Exp Ther 2012; 342:799-807. [PMID: 22700431 DOI: 10.1124/jpet.111.188987] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
N,N-diethyl-4-(5-hydroxyspiro[chromene-2,4'-piperidine]-4-yl) benzamide (ADL5859) and N,N-diethyl-3-hydroxy-4-(spiro[chromene-2,4'-piperidine]-4-yl)benzamide (ADL5747) are novel δ-opioid agonists that show good oral bioavailability and analgesic and antidepressive effects in the rat and represent potential drugs for chronic pain treatment. Here, we used genetic approaches to investigate molecular mechanisms underlying their analgesic effects in the mouse. We tested analgesic effects of ADL5859 and ADL5747 in mice by using mechanical sensitivity measures in both complete Freund's adjuvant and sciatic nerve ligation pain models. We examined their analgesic effects in δ-opioid receptor constitutive knockout (KO) mice and mice with a conditional deletion of δ-receptor in peripheral voltage-gated sodium channel (Nav)1.8-expressing neurons (cKO mice). Both ADL5859 and ADL5747, and the prototypical δ agonist 4-[(R)-[(2S,5R)-4-allyl-2,5-dimethyl-piperazin-1-yl]-(3-methoxyphenyl)methyl]-N,N-diethyl-benzamide (SNC80) as a control, significantly reduced inflammatory and neuropathic pain. The antiallodynic effects of all three δ-opioid agonists were abolished in constitutive δ-receptor KO mice and strongly diminished in δ-receptor cKO mice. We also measured two other well described effects of δ agonists, increase in locomotor activity and agonist-induced receptor internalization by using knock-in mice expressing enhanced green fluorescence protein-tagged δ receptors. In contrast to SNC80, ADL5859 and ADL5747 did not induce either hyperlocomotion or receptor internalization in vivo. In conclusion, both ADL5859 and ADL5747 showed efficient pain-reducing properties in the two models of chronic pain. Their effects were mediated by δ-opioid receptors, with a main contribution of receptors expressed on peripheral Nav1.8-positive neurons. The lack of in vivo receptor internalization and locomotor activation, typically induced by SNC80, suggests agonist-biased activity at the receptor for the two drugs.
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Affiliation(s)
- Chihiro Nozaki
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
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123
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Chattopadhyay M, Zhou Z, Hao S, Mata M, Fink DJ. Reduction of voltage gated sodium channel protein in DRG by vector mediated miRNA reduces pain in rats with painful diabetic neuropathy. Mol Pain 2012; 8:17. [PMID: 22439790 PMCID: PMC3388457 DOI: 10.1186/1744-8069-8-17] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2011] [Accepted: 03/22/2012] [Indexed: 01/08/2023] Open
Abstract
Background Painful neuropathy is a common complication of diabetes. Previous studies have identified significant increases in the amount of voltage gated sodium channel isoforms NaV1.7 and NaV1.3 protein in the dorsal root ganglia (DRG) of rats with streptozotocin (STZ)-induced diabetes. We found that gene transfer-mediated release of the inhibitory neurotransmitters enkephalin or gamma amino butyric acid (GABA) from DRG neurons in diabetic animals reduced pain-related behaviors coincident with a reduction in NaV1.7 protein levels in DRG in vivo. To further evaluate the role of NaVα subunit levels in DRG in the pathogenesis of pain in diabetic neuropathy, we constructed a non-replicating herpes simplex virus (HSV)-based vector expressing a microRNA (miRNA) against NaVα subunits. Results Subcutaneous inoculation of the miRNA-expressing HSV vector into the feet of diabetic rats to transduce DRG resulted in a reduction in NaVα subunit levels in DRG neurons, coincident with a reduction in cold allodynia, thermal hyperalgesia and mechanical hyperalgesia. Conclusions These data support the role of increased NaVα protein in DRG in the pathogenesis of pain in diabetic neuropathy, and provide a proof-of-principle demonstration for the development of a novel therapy that could be used to treat intractable pain in patients with diabetic neuropathy.
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Affiliation(s)
- Munmun Chattopadhyay
- Department of Neurology, University of Michigan and VA Ann Arbor Healthcare System, Ann Arbor, MI, USA
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124
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Tetrodotoxin (TTX) as a therapeutic agent for pain. Mar Drugs 2012; 10:281-305. [PMID: 22412801 PMCID: PMC3296997 DOI: 10.3390/md10020281] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2011] [Revised: 01/19/2012] [Accepted: 01/19/2012] [Indexed: 12/19/2022] Open
Abstract
Tetrodotoxin (TTX) is a potent neurotoxin that blocks voltage-gated sodium channels (VGSCs). VGSCs play a critical role in neuronal function under both physiological and pathological conditions. TTX has been extensively used to functionally characterize VGSCs, which can be classified as TTX-sensitive or TTX-resistant channels according to their sensitivity to this toxin. Alterations in the expression and/or function of some specific TTX-sensitive VGSCs have been implicated in a number of chronic pain conditions. The administration of TTX at doses below those that interfere with the generation and conduction of action potentials in normal (non-injured) nerves has been used in humans and experimental animals under different pain conditions. These data indicate a role for TTX as a potential therapeutic agent for pain. This review focuses on the preclinical and clinical evidence supporting a potential analgesic role for TTX. In addition, the contribution of specific TTX-sensitive VGSCs to pain is reviewed.
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125
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Dworkin RH, Turk DC. Accelerating the development of improved analgesic treatments: the ACTION public-private partnership. PAIN MEDICINE 2011; 12 Suppl 3:S109-17. [PMID: 21752182 DOI: 10.1111/j.1526-4637.2011.01159.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
There has been considerable progress identifying pathophysiologic mechanisms of neuropathic pain, but analgesic medications with improved efficacy, safety, and tolerability still represent an unmet public health need. Numerous treatments examined in recent randomized clinical trials (RCTs) have failed to show efficacy for neuropathic pain, including treatments that had previously demonstrated efficacy. This suggests that at least some negative results reflect limited assay sensitivity of RCTs to distinguish efficacious treatments from placebo. Patient characteristics, clinical trial research designs and methods, outcome measures, approaches to data analysis, and statistical power may all play a role in accounting for difficulties in demonstrating the benefits of efficacious analgesic treatments vs placebo. The identification of specific clinical trial characteristics associated with assay sensitivity in existing data has the potential to provide an evidence-based approach to the design of analgesic clinical trials. The US Food and Drug Administration recently launched the Analgesic Clinical Trial Innovations, Opportunities, and Networks (ACTION) public-private partnership, which is designed to facilitate the discovery and development of analgesics with improved efficacy, safety, and tolerability for acute and chronic pain conditions. ACTION will establish a collaborative effort to prioritize research objectives, develop a standardized analgesic database platform, and conduct methodologically focused studies to increase the assay sensitivity and efficiency of analgesic clinical trials. The results of these activities have the potential to inform and accelerate the development of improved pain management interventions of all types, not just pharmacologic treatments.
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Affiliation(s)
- Robert H Dworkin
- Departments of Anesthesiology and Neurology and Center for Human Experimental Therapeutics, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
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