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Smith PA. Neuropathic pain; what we know and what we should do about it. FRONTIERS IN PAIN RESEARCH 2023; 4:1220034. [PMID: 37810432 PMCID: PMC10559888 DOI: 10.3389/fpain.2023.1220034] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Accepted: 09/05/2023] [Indexed: 10/10/2023] Open
Abstract
Neuropathic pain can result from injury to, or disease of the nervous system. It is notoriously difficult to treat. Peripheral nerve injury promotes Schwann cell activation and invasion of immunocompetent cells into the site of injury, spinal cord and higher sensory structures such as thalamus and cingulate and sensory cortices. Various cytokines, chemokines, growth factors, monoamines and neuropeptides effect two-way signalling between neurons, glia and immune cells. This promotes sustained hyperexcitability and spontaneous activity in primary afferents that is crucial for onset and persistence of pain as well as misprocessing of sensory information in the spinal cord and supraspinal structures. Much of the current understanding of pain aetiology and identification of drug targets derives from studies of the consequences of peripheral nerve injury in rodent models. Although a vast amount of information has been forthcoming, the translation of this information into the clinical arena has been minimal. Few, if any, major therapeutic approaches have appeared since the mid 1990's. This may reflect failure to recognise differences in pain processing in males vs. females, differences in cellular responses to different types of injury and differences in pain processing in humans vs. animals. Basic science and clinical approaches which seek to bridge this knowledge gap include better assessment of pain in animal models, use of pain models which better emulate human disease, and stratification of human pain phenotypes according to quantitative assessment of signs and symptoms of disease. This can lead to more personalized and effective treatments for individual patients. Significance statement: There is an urgent need to find new treatments for neuropathic pain. Although classical animal models have revealed essential features of pain aetiology such as peripheral and central sensitization and some of the molecular and cellular mechanisms involved, they do not adequately model the multiplicity of disease states or injuries that may bring forth neuropathic pain in the clinic. This review seeks to integrate information from the multiplicity of disciplines that seek to understand neuropathic pain; including immunology, cell biology, electrophysiology and biophysics, anatomy, cell biology, neurology, molecular biology, pharmacology and behavioral science. Beyond this, it underlines ongoing refinements in basic science and clinical practice that will engender improved approaches to pain management.
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Affiliation(s)
- Peter A. Smith
- Neuroscience and Mental Health Institute and Department of Pharmacology, University of Alberta, Edmonton, AB, Canada
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Calderon-Rivera A, Gomez K, Loya-López S, Wijeratne EK, Stratton H, Tang C, Duran P, Masterson K, Alsbiei O, Gunatilaka AL, Khanna R. Betulinic acid analogs inhibit N- and T-type voltage-gated calcium channels to attenuate nerve-injury associated neuropathic and formalin models of pain. NEUROBIOLOGY OF PAIN (CAMBRIDGE, MASS.) 2023; 13:100116. [PMID: 36687466 PMCID: PMC9853350 DOI: 10.1016/j.ynpai.2023.100116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 01/10/2023] [Accepted: 01/11/2023] [Indexed: 01/15/2023]
Abstract
Over the past three decades, there has been a significant growth in the use of natural products, with approximately 80% of individuals using them for some aspect of primary healthcare. Our laboratories have identified and studied natural compounds with analgesic effects from dry land plants or their associated fungus during the past ten years. Here, we isolated and characterized thirteen betulin analogs and fifteen betulinic acid analogs for their capacity to prevent calcium influx brought on by depolarization in sensory neurons. The in vitro inhibition of voltage-gated calcium channels by the top drugs was then assessed using whole cell patch clamp electrophysiology. In vivo experiments, conducted at two sites, evaluated the best compound in acute and tonic, neuropathic, inflammatory, post-operative and visceral models of pain. We found that the betulinic acid analog 8 inhibited calcium influx in rat dorsal root ganglion neurons by inhibiting N- (CaV2.2) and T- (CaV3) type voltage-gated calcium channels. Moreover, intrathecal delivery of analog 8 had analgesic activity in both spared nerve injury model of neuropathic pain and acute and tonic pain induced by formalin. The results presented herein highlight the potential antinociceptive properties of betulinic acid analog 8 and set the stage for the development of novel non-opioid pain therapeutics based on the triterpenoid scaffold of betulinic acid.
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Affiliation(s)
- Aida Calderon-Rivera
- Department of Molecular Pathobiology, College of Dentistry, New York University, New York, NY, United States
- NYU Pain Research Center, New York University, New York, NY, United States
| | - Kimberly Gomez
- Department of Molecular Pathobiology, College of Dentistry, New York University, New York, NY, United States
- NYU Pain Research Center, New York University, New York, NY, United States
| | - Santiago Loya-López
- Department of Molecular Pathobiology, College of Dentistry, New York University, New York, NY, United States
- NYU Pain Research Center, New York University, New York, NY, United States
| | - E.M. Kithsiri Wijeratne
- Natural Products Center, School of Natural Resources and the Environment, College of Agriculture and Life Sciences, The University of Arizona, Tucson, AZ, United States
| | - Harrison Stratton
- Department of Pharmacology, College of Medicine, The University of Arizona, Tucson, AZ, United States
| | - Cheng Tang
- Department of Molecular Pathobiology, College of Dentistry, New York University, New York, NY, United States
- NYU Pain Research Center, New York University, New York, NY, United States
| | - Paz Duran
- Department of Molecular Pathobiology, College of Dentistry, New York University, New York, NY, United States
- NYU Pain Research Center, New York University, New York, NY, United States
| | - Kyleigh Masterson
- NYU Pain Research Center, New York University, New York, NY, United States
| | - Omar Alsbiei
- NYU Pain Research Center, New York University, New York, NY, United States
| | - A.A. Leslie Gunatilaka
- Natural Products Center, School of Natural Resources and the Environment, College of Agriculture and Life Sciences, The University of Arizona, Tucson, AZ, United States
| | - Rajesh Khanna
- Department of Molecular Pathobiology, College of Dentistry, New York University, New York, NY, United States
- NYU Pain Research Center, New York University, New York, NY, United States
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Alles SRA, Smith PA. Peripheral Voltage-Gated Cation Channels in Neuropathic Pain and Their Potential as Therapeutic Targets. FRONTIERS IN PAIN RESEARCH 2022; 2:750583. [PMID: 35295464 PMCID: PMC8915663 DOI: 10.3389/fpain.2021.750583] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 11/10/2021] [Indexed: 11/25/2022] Open
Abstract
The persistence of increased excitability and spontaneous activity in injured peripheral neurons is imperative for the development and persistence of many forms of neuropathic pain. This aberrant activity involves increased activity and/or expression of voltage-gated Na+ and Ca2+ channels and hyperpolarization activated cyclic nucleotide gated (HCN) channels as well as decreased function of K+ channels. Because they display limited central side effects, peripherally restricted Na+ and Ca2+ channel blockers and K+ channel activators offer potential therapeutic approaches to pain management. This review outlines the current status and future therapeutic promise of peripherally acting channel modulators. Selective blockers of Nav1.3, Nav1.7, Nav1.8, Cav3.2, and HCN2 and activators of Kv7.2 abrogate signs of neuropathic pain in animal models. Unfortunately, their performance in the clinic has been disappointing; some substances fail to meet therapeutic end points whereas others produce dose-limiting side effects. Despite this, peripheral voltage-gated cation channels retain their promise as therapeutic targets. The way forward may include (i) further structural refinement of K+ channel activators such as retigabine and ASP0819 to improve selectivity and limit toxicity; use or modification of Na+ channel blockers such as vixotrigine, PF-05089771, A803467, PF-01247324, VX-150 or arachnid toxins such as Tap1a; the use of Ca2+ channel blockers such as TTA-P2, TTA-A2, Z 944, ACT709478, and CNCB-2; (ii) improving methods for assessing “pain” as opposed to nociception in rodent models; (iii) recognizing sex differences in pain etiology; (iv) tailoring of therapeutic approaches to meet the symptoms and etiology of pain in individual patients via quantitative sensory testing and other personalized medicine approaches; (v) targeting genetic and biochemical mechanisms controlling channel expression using anti-NGF antibodies such as tanezumab or re-purposed drugs such as vorinostat, a histone methyltransferase inhibitor used in the management of T-cell lymphoma, or cercosporamide a MNK 1/2 inhibitor used in treatment of rheumatoid arthritis; (vi) combination therapy using drugs that are selective for different channel types or regulatory processes; (vii) directing preclinical validation work toward the use of human or human-derived tissue samples; and (viii) application of molecular biological approaches such as clustered regularly interspaced short palindromic repeats (CRISPR) technology.
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Affiliation(s)
- Sascha R A Alles
- Department of Anesthesiology and Critical Care Medicine, University of New Mexico School of Medicine, Albuquerque, NM, United States
| | - Peter A Smith
- Department of Pharmacology, Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
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Anselmi L, Kim JS, Kaufman MP, Zhou S, Ruiz-Velasco V. Serotonin (5-HT)-mediated activation of 5-HT1 receptors oppositely modulates CaV2.2 currents in rat sensory neurons innervating hindlimb muscle. Mol Pharmacol 2022; 101:309-321. [PMID: 35184045 PMCID: PMC9092463 DOI: 10.1124/molpharm.121.000419] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 02/05/2022] [Indexed: 11/22/2022] Open
Abstract
Serotonin (5-HT) is a multifaceted neurotransmitter that has been described to play a role as a peripheral inflammatory mediator when released in ischemic or injured muscle. Dorsal root ganglia (DRG) neurons are key sensors of noxious stimuli that are released under inflammatory conditions or mechanical stress. Little information is available on the specific 5-HT receptor subtypes expressed in primary afferents that help regulate reflex pressor responses. In the present study, the whole-cell patch-clamp technique was employed to examine the modulation of voltage-gated calcium channel (CaV) 2.2 currents by 5-HT and to identify the 5-HT receptor subtype(s) mediating this response in acutely dissociated rat DRG neurons innervating triceps surae muscle. Our results indicate that exposure of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-labeled DRG neurons to 5-HT can exert three modulatory effects on CaV currents: high inhibition, low inhibition, and enhancement. Both 5-HT-mediated inhibition responses were blocked after pretreatment with pertussis toxin (PTX), indicating that 5-HT receptors are coupled to CaV2.2 via Gα i/o protein subunits. Application of selective serotonin receptor type 1 (5-HT1) agonists revealed that modulation of CaV2.2 currents occurs primarily after 5-HT1A receptor subtype stimulation and minimally from 5-HT1D activation. Finally, the intrathecal administration of the selective 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), significantly (P < 0.05) decreased the pressor response induced by intra-arterial administration of lactic acid. This suggests that 5-HT1A receptors are expressed presynaptically on primary afferent neurons innervating triceps surae muscle. Our findings indicate that preferential stimulation of 5-HT1 receptors, expressed on thin fiber muscle afferents, serves to regulate the reflex pressor response to metabolic stimuli. SIGNIFICANCE STATEMENT: The monoamine serotonin (5-HT), released under ischemic conditions, can contribute to the development of inflammation that negatively affects the exercise pressor reflex. The 5-HT receptor subtype and signaling pathway that underlies calcium channel modulation in dorsal root ganglia afferents, innervating hindlimb muscles, are unknown. We show that 5-HT can either block (primarily via serotonin receptor type 1 (5-HT1)A subtypes) or enhance voltage-gated calcium channel (CaV2.2) currents. Our findings suggest 5-HT exhibits receptor subtype selectivity, providing a complexity of cellular responses.
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Affiliation(s)
- Laura Anselmi
- Department of Anesthesiology and Perioperative Medicine (L.A., V.R.-V.) and Heart and Vascular Institute (J.S.K., M.P.K.), Penn State College of Medicine, Hershey, Pennsylvania; and Department of Public Health Sciences Division of Biostatistics and Bioinformatics, Penn State Cancer Institute, Next-Generation Therapies, Hershey, Pennsylvania (S.Z.)
| | - Joyce S Kim
- Department of Anesthesiology and Perioperative Medicine (L.A., V.R.-V.) and Heart and Vascular Institute (J.S.K., M.P.K.), Penn State College of Medicine, Hershey, Pennsylvania; and Department of Public Health Sciences Division of Biostatistics and Bioinformatics, Penn State Cancer Institute, Next-Generation Therapies, Hershey, Pennsylvania (S.Z.)
| | - Marc P Kaufman
- Department of Anesthesiology and Perioperative Medicine (L.A., V.R.-V.) and Heart and Vascular Institute (J.S.K., M.P.K.), Penn State College of Medicine, Hershey, Pennsylvania; and Department of Public Health Sciences Division of Biostatistics and Bioinformatics, Penn State Cancer Institute, Next-Generation Therapies, Hershey, Pennsylvania (S.Z.)
| | - Shouhao Zhou
- Department of Anesthesiology and Perioperative Medicine (L.A., V.R.-V.) and Heart and Vascular Institute (J.S.K., M.P.K.), Penn State College of Medicine, Hershey, Pennsylvania; and Department of Public Health Sciences Division of Biostatistics and Bioinformatics, Penn State Cancer Institute, Next-Generation Therapies, Hershey, Pennsylvania (S.Z.)
| | - Victor Ruiz-Velasco
- Department of Anesthesiology and Perioperative Medicine (L.A., V.R.-V.) and Heart and Vascular Institute (J.S.K., M.P.K.), Penn State College of Medicine, Hershey, Pennsylvania; and Department of Public Health Sciences Division of Biostatistics and Bioinformatics, Penn State Cancer Institute, Next-Generation Therapies, Hershey, Pennsylvania (S.Z.)
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Marler TL, Wright AB, Elmslie KL, Heier AK, Remily E, Kim-Han JS, Ramachandra R, Elmslie KS. Na V1.9 channels in muscle afferent neurons and axons. J Neurophysiol 2018; 120:1032-1044. [PMID: 29847236 DOI: 10.1152/jn.00573.2017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The exercise pressor reflex (EPR) is activated by muscle contractions to increase heart rate and blood pressure during exercise. While this reflex is beneficial in healthy individuals, the reflex activity is exaggerated in patients with cardiovascular disease, which is associated with increased mortality. Group III and IV afferents mediate the EPR and have been shown to express both tetrodotoxin-sensitive (TTX-S, NaV1.6, and NaV1.7) and -resistant (TTX-R, NaV1.8, and NaV1.9) voltage-gated sodium (NaV) channels, but NaV1.9 current has not yet been demonstrated. Using a F--containing internal solution, we found a NaV current in muscle afferent neurons that activates at around -70 mV with slow activation and inactivation kinetics, as expected from NaV1.9 current. However, this current ran down with time, which resulted, at least in part, from increased steady-state inactivation since it was slowed by both holding potential hyperpolarization and a depolarized shift of the gating properties. We further show that, following NaV1.9 current rundown (internal F-), application of the NaV1.8 channel blocker A803467 inhibited significantly more TTX-R current than we had previously observed (internal Cl-), which suggests that NaV1.9 current did not rundown with that internal solution. Using immunohistochemistry, we found that the majority of group IV somata and axons were NaV1.9 positive. The majority of small diameter myelinated afferent somata (putative group III) were also NaV1.9 positive, but myelinated muscle afferent axons were rarely labeled. The presence of NaV1.9 channels in muscle afferents supports a role for these channels in activation and maintenance of the EPR. NEW & NOTEWORTHY Small diameter muscle afferents signal pain and muscle activity levels. The muscle activity signals drive the cardiovascular system to increase muscle blood flow, but these signals can become exaggerated in cardiovascular disease to exacerbate cardiac damage. The voltage-dependent sodium channel NaV1.9 plays a unique role in controlling afferent excitability. We show that NaV1.9 channels are expressed in muscle afferents, which supports these channels as a target for drug development to control hyperactivity of these neurons.
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Affiliation(s)
- Tyler L Marler
- The Baker Laboratory of Pharmacology, Department of Pharmacology, Kirksville College of Osteopathic Medicine, A. T. Still University of Health Sciences, Kirksville, Missouri
| | - Andrew B Wright
- The Baker Laboratory of Pharmacology, Department of Pharmacology, Kirksville College of Osteopathic Medicine, A. T. Still University of Health Sciences, Kirksville, Missouri
| | - Kristina L Elmslie
- The Baker Laboratory of Pharmacology, Department of Pharmacology, Kirksville College of Osteopathic Medicine, A. T. Still University of Health Sciences, Kirksville, Missouri
| | - Ankeeta K Heier
- The Baker Laboratory of Pharmacology, Department of Pharmacology, Kirksville College of Osteopathic Medicine, A. T. Still University of Health Sciences, Kirksville, Missouri
| | - Ethan Remily
- The Baker Laboratory of Pharmacology, Department of Pharmacology, Kirksville College of Osteopathic Medicine, A. T. Still University of Health Sciences, Kirksville, Missouri
| | - Jeong Sook Kim-Han
- The Baker Laboratory of Pharmacology, Department of Pharmacology, Kirksville College of Osteopathic Medicine, A. T. Still University of Health Sciences, Kirksville, Missouri
| | - Renuka Ramachandra
- The Baker Laboratory of Pharmacology, Department of Pharmacology, Kirksville College of Osteopathic Medicine, A. T. Still University of Health Sciences, Kirksville, Missouri
| | - Keith S Elmslie
- The Baker Laboratory of Pharmacology, Department of Pharmacology, Kirksville College of Osteopathic Medicine, A. T. Still University of Health Sciences, Kirksville, Missouri
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Inhibition of α9α10 nicotinic acetylcholine receptors prevents chemotherapy-induced neuropathic pain. Proc Natl Acad Sci U S A 2017; 114:E1825-E1832. [PMID: 28223528 DOI: 10.1073/pnas.1621433114] [Citation(s) in RCA: 124] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Opioids are first-line drugs for moderate to severe acute pain and cancer pain. However, these medications are associated with severe side effects, and whether they are efficacious in treatment of chronic nonmalignant pain remains controversial. Medications that act through alternative molecular mechanisms are critically needed. Antagonists of α9α10 nicotinic acetylcholine receptors (nAChRs) have been proposed as an important nonopioid mechanism based on studies demonstrating prevention of neuropathology after trauma-induced nerve injury. However, the key α9α10 ligands characterized to date are at least two orders of magnitude less potent on human vs. rodent nAChRs, limiting their translational application. Furthermore, an alternative proposal that these ligands achieve their beneficial effects by acting as agonists of GABAB receptors has caused confusion over whether blockade of α9α10 nAChRs is the fundamental underlying mechanism. To address these issues definitively, we developed RgIA4, a peptide that exhibits high potency for both human and rodent α9α10 nAChRs, and was at least 1,000-fold more selective for α9α10 nAChRs vs. all other molecular targets tested, including opioid and GABAB receptors. A daily s.c. dose of RgIA4 prevented chemotherapy-induced neuropathic pain in rats. In wild-type mice, oxaliplatin treatment produced cold allodynia that could be prevented by RgIA4. Additionally, in α9 KO mice, chemotherapy-induced development of cold allodynia was attenuated and the milder, temporary cold allodynia was not relieved by RgIA4. These findings establish blockade of α9-containing nAChRs as the basis for the efficacy of RgIA4, and that α9-containing nAChRs are a critical target for prevention of chronic cancer chemotherapy-induced neuropathic pain.
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Wormuth C, Lundt A, Henseler C, Müller R, Broich K, Papazoglou A, Weiergräber M. Review: Ca v2.3 R-type Voltage-Gated Ca 2+ Channels - Functional Implications in Convulsive and Non-convulsive Seizure Activity. Open Neurol J 2016; 10:99-126. [PMID: 27843503 PMCID: PMC5080872 DOI: 10.2174/1874205x01610010099] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Revised: 05/16/2016] [Accepted: 06/24/2016] [Indexed: 11/22/2022] Open
Abstract
Background: Researchers have gained substantial insight into mechanisms of synaptic transmission, hyperexcitability, excitotoxicity and neurodegeneration within the last decades. Voltage-gated Ca2+ channels are of central relevance in these processes. In particular, they are key elements in the etiopathogenesis of numerous seizure types and epilepsies. Earlier studies predominantly targeted on Cav2.1 P/Q-type and Cav3.2 T-type Ca2+ channels relevant for absence epileptogenesis. Recent findings bring other channels entities more into focus such as the Cav2.3 R-type Ca2+ channel which exhibits an intriguing role in ictogenesis and seizure propagation. Cav2.3 R-type voltage gated Ca2+ channels (VGCC) emerged to be important factors in the pathogenesis of absence epilepsy, human juvenile myoclonic epilepsy (JME), and cellular epileptiform activity, e.g. in CA1 neurons. They also serve as potential target for various antiepileptic drugs, such as lamotrigine and topiramate. Objective: This review provides a summary of structure, function and pharmacology of VGCCs and their fundamental role in cellular Ca2+ homeostasis. We elaborate the unique modulatory properties of Cav2.3 R-type Ca2+ channels and point to recent findings in the proictogenic and proneuroapoptotic role of Cav2.3 R-type VGCCs in generalized convulsive tonic–clonic and complex-partial hippocampal seizures and its role in non-convulsive absence like seizure activity. Conclusion: Development of novel Cav2.3 specific modulators can be effective in the pharmacological treatment of epilepsies and other neurological disorders.
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Affiliation(s)
- Carola Wormuth
- Department of Neuropsychopharmacology, Federal Institute for Drugs and Medical Devices (BfArM), Kurt-Georg-Kiesinger-Allee 3, 53175 Bonn, Germany
| | - Andreas Lundt
- Department of Neuropsychopharmacology, Federal Institute for Drugs and Medical Devices (BfArM), Kurt-Georg-Kiesinger-Allee 3, 53175 Bonn, Germany
| | - Christina Henseler
- Department of Neuropsychopharmacology, Federal Institute for Drugs and Medical Devices (BfArM), Kurt-Georg-Kiesinger-Allee 3, 53175 Bonn, Germany
| | - Ralf Müller
- Department of Psychiatry and Psychotherapy, University of Cologne, Faculty of Medicine, Cologne, Germany
| | - Karl Broich
- Department of Neuropsychopharmacology, Federal Institute for Drugs and Medical Devices (BfArM), Kurt-Georg-Kiesinger-Allee 3, 53175 Bonn, Germany
| | - Anna Papazoglou
- Department of Neuropsychopharmacology, Federal Institute for Drugs and Medical Devices (BfArM), Kurt-Georg-Kiesinger-Allee 3, 53175 Bonn, Germany
| | - Marco Weiergräber
- Department of Neuropsychopharmacology, Federal Institute for Drugs and Medical Devices (BfArM), Kurt-Georg-Kiesinger-Allee 3, 53175 Bonn, Germany
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Abstract
Ion channels are critical for all aspects of cardiac function, including rhythmicity and contractility. Consequently, ion channels are key targets for therapeutics aimed at cardiac pathophysiologies such as atrial fibrillation or angina. At the same time, off-target interactions of drugs with cardiac ion channels can be the cause of unwanted side effects. This manuscript aims to review the physiology and pharmacology of key cardiac ion channels. The intent is to highlight recent developments for therapeutic development, as well as elucidate potential mechanisms for drug-induced cardiac side effects, rather than present an in-depth review of each channel subtype.
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Cloning, synthesis, and characterization of αO-conotoxin GeXIVA, a potent α9α10 nicotinic acetylcholine receptor antagonist. Proc Natl Acad Sci U S A 2015; 112:E4026-35. [PMID: 26170295 DOI: 10.1073/pnas.1503617112] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We identified a previously unidentified conotoxin gene from Conus generalis whose precursor signal sequence has high similarity to the O1-gene conotoxin superfamily. The predicted mature peptide, αO-conotoxin GeXIVA (GeXIVA), has four Cys residues, and its three disulfide isomers were synthesized. Previously pharmacologically characterized O1-superfamily peptides, exemplified by the US Food and Drug Administration-approved pain medication, ziconotide, contain six Cys residues and are calcium, sodium, or potassium channel antagonists. However, GeXIVA did not inhibit calcium channels but antagonized nicotinic AChRs (nAChRs), most potently on the α9α10 nAChR subtype (IC50 = 4.6 nM). Toxin blockade was voltage-dependent, and kinetic analysis of toxin dissociation indicated that the binding site of GeXIVA does not overlap with the binding site of the competitive antagonist α-conotoxin RgIA. Surprisingly, the most active disulfide isomer of GeXIVA is the bead isomer, comprising, according to NMR analysis, two well-resolved but uncoupled disulfide-restrained loops. The ribbon isomer is almost as potent but has a more rigid structure built around a short 310-helix. In contrast to most α-conotoxins, the globular isomer is the least potent and has a flexible, multiconformational nature. GeXIVA reduced mechanical hyperalgesia in the rat chronic constriction injury model of neuropathic pain but had no effect on motor performance, warranting its further investigation as a possible therapeutic agent.
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Hassan B, Kim JS, Farrag M, Kaufman MP, Ruiz-Velasco V. Alteration of the mu opioid receptor: Ca2+ channel signaling pathway in a subset of rat sensory neurons following chronic femoral artery occlusion. J Neurophysiol 2014; 112:3104-15. [PMID: 25231620 DOI: 10.1152/jn.00630.2014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The exercise pressor reflex, a crucial component of the cardiovascular response under physiological and pathophysiological states, is activated via metabolic and mechanical mediators that originate from contracting muscles and stimulate group III and IV afferents. We reported previously that stimulation of mu opioid receptors (MOR), expressed in both afferents, led to a significant attenuation of the reflex in rats whose femoral arteries had been occluded for 72 h. The present study examined the effect of arterial occlusion on the signaling components involved in the opioid-mediated modulation of Ca(2+) channels in rat dorsal root ganglion neurons innervating the triceps surae muscles. We focused on neurons that were transfected with cDNA coding for enhanced green fluorescent protein whose expression is driven by the voltage-gated Na(+) channel 1.8 (Na(V)1.8) promoter region, a channel expressed primarily in nociceptive neurons. With the use of a small interference RNA approach, our results show that the pertussis toxin-sensitive Gα(i3) subunit couples MOR with Ca(2+) channels. We observed a significant leftward shift of the MOR agonist [D-Ala2-N-Me-Phe4-Glycol5]-enkephalin concentration-response relationship in neurons isolated from rats with occluded arteries compared with those that were perfused freely. Femoral occlusion did not affect Ca(2+) channel density or the fraction of the main Ca(2+) channel subtype. Furthermore, Western blotting analysis indicated that the leftward shift did not result from either increased Gα(i3) or MOR expression. Finally, all neurons from both groups exhibited an inward current following exposure of the transient potential receptor vanilloid 1 (TRPV1) agonist, 8-methyl-N-vanillyl-6-nonenamide. These findings suggest that sensory neurons mediating the exercise pressor reflex express Na(V)1.8 and TRPV1 channels, and femoral occlusion alters the MOR pharmacological profile.
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Affiliation(s)
- Bassil Hassan
- Department of Anesthesiology, Penn State College of Medicine, Hershey, Pennsylvania; and
| | - Joyce S Kim
- Heart and Vascular Institute, Penn State College of Medicine, Hershey, Pennsylvania
| | - Mohamed Farrag
- Department of Anesthesiology, Penn State College of Medicine, Hershey, Pennsylvania; and
| | - Marc P Kaufman
- Heart and Vascular Institute, Penn State College of Medicine, Hershey, Pennsylvania
| | - Victor Ruiz-Velasco
- Department of Anesthesiology, Penn State College of Medicine, Hershey, Pennsylvania; and
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