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Mortari MR, Cunha AOS, Ferreira LB, dos Santos WF. Neurotoxins from invertebrates as anticonvulsants: From basic research to therapeutic application. Pharmacol Ther 2007; 114:171-83. [PMID: 17399793 DOI: 10.1016/j.pharmthera.2007.01.009] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2007] [Revised: 01/19/2007] [Accepted: 01/19/2007] [Indexed: 12/21/2022]
Abstract
Invertebrate venoms have attracted considerable interest as a potential source of bioactive substances, especially neurotoxins. These molecules have proved to be extremely useful tools for the understanding of synaptic transmission events, and they have contributed to the design of novel drugs for the treatment of neurological disorders and pain. In this context, as epilepsy involves neuronal substrates, which are sites of action of many neurotoxins; venoms may be particularly useful for antiepileptic drug (AED) research. Epilepsy is a chronic disease whose treatment consists of controlling seizures with antiepileptics that very often induce strong undesirable side effects that may limit treatment. Here, we review the vast, but yet unexplored, world of neurotoxins from invertebrates used as probes in pharmacological screening for novel and less toxic antiepileptics. We briefly review (1) the molecular basis of epilepsy, as well as the sites of action of commonly used anticonvulsants (we bring a comprehensive review of the elements from invertebrate venoms which are mostly studied in neuroscience research and may be useful for drug development); (2) peptides from conus snails; (3) peptides and polyamine toxins from spiders and wasps; and (4) peptides from scorpions.
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Affiliation(s)
- Márcia Renata Mortari
- Neurobiology and Venoms Laboratory, Department of Biology, School of Philosophy, Sciences and Literature, University of São Paulo Ribeirão Preto, Brazil
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2
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Bennett PB, Guthrie HRE. Trends in ion channel drug discovery: advances in screening technologies. Trends Biotechnol 2003; 21:563-9. [PMID: 14624866 DOI: 10.1016/j.tibtech.2003.09.014] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Affiliation(s)
- Paul B Bennett
- Department of Molecular Pharmacology, Merck Research Laboratories, West Point, PA 19486, USA.
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3
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Abstract
Lethargic mutant mice carry a mutation in the CCHB4 gene, which encodes the beta4 subunit of voltage-regulated calcium channels. These mutants have been shown to display a complex neurobehavioral phenotype that includes EEG discharges suggestive of absence epilepsy, chronic ataxia, and hypoactivity. The current studies demonstrate a fourth element of their phenotype, consisting of transient attacks of severe dyskinetic motor behavior. These attacks can be triggered by specific environmental and chemical influences, particularly those that stimulate locomotor activity. Behavioral and EEG analyses indicate that the attacks do not reflect motor epilepsy, but instead resemble a paroxysmal dyskinesia. The lethargic mutants provide additional evidence that calcium channelopathies can produce paroxysmal dyskinesias and provide a novel model for studying this unusual movement disorder.
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Lawson K. Tricyclic antidepressants and fibromyalgia: what is the mechanism of action? Expert Opin Investig Drugs 2002; 11:1437-45. [PMID: 12387704 DOI: 10.1517/13543784.11.10.1437] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Fibromyalgia is a chronic pain disorder of which other clinical features, such as persistent fatigue and disordered sleep, may be a secondary consequence. The initial pharmacological approach to treating the disorder is the management of the pain. Tricyclic antidepressants are the most effective drugs in use so far, especially when administered in combination with other therapies (e.g., selective serotonin re-uptake inhibitors), which suggests modulation of the neurotransmitters serotonin and noradrenaline. The effectiveness of amitriptyline and related tricyclic antidepressants, however, is consistent with the involvement of mechanisms, such as potassium channel modulation and NMDA receptor antagonism, in addition to or in place of the modulation of monoamine neurotransmitters. Investigation of the importance of each of the pharmacological properties of amitriptyline and related molecules in the management of fibromyalgia could provide clues for the rational design of new drugs.
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Affiliation(s)
- Kim Lawson
- Biomedical Research Centre and Division of Biomedical Sciences, Sheffield Hallam University, School of Science and Mathematics, City Campus, UK.
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5
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Abstract
Ion channels are complex proteins that span the lipid bilayer of the cell membrane, where they orchestrate the electrical signals necessary for normal function of the central nervous system, peripheral nerve, and both skeletal and cardiac muscle. The role of ion channel defects in the pathogenesis of numerous disorders, many of them neuromuscular, has become increasingly apparent over the last decade. Progress in molecular biology has allowed cloning and expression of genes that encode channel proteins, while comparable advances in biophysics, including patch-clamp electrophysiology and related techniques, have made the study of expressed proteins at the level of single channel molecules possible. Understanding the molecular basis of ion channel function and dysfunction will facilitate both the accurate classification of these disorders and the rational development of specific therapeutic interventions. This review encompasses clinical, genetic, and pathophysiological aspects of ion channels disorders, focusing mainly on those with neuromuscular manifestations.
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Affiliation(s)
- Kleopas A Kleopa
- Department of Neurology, University of Pennsylvania School of Medicine, 122 College Hall, Philadelphia, PA 19104, USA
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6
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Abstract
The periodic paralyses are rare disorders of skeletal muscle characterized by episodic attacks of weakness due to intermittent failure of electrical excitability. Familial forms of periodic paralysis are all caused by mutations in genes coding for voltage-gated ion channels. New discoveries in the past 2 years have broadened our views on the diversity of phenotypes produced by mutations of a single channel gene and have led to the identification of potassium channel mutations, in addition to those previously found in sodium and calcium channels. This review focuses on the clinical features, molecular genetic defects, and pathophysiologic mechanisms that underlie familial periodic paralysis.
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Affiliation(s)
- Stephen C Cannon
- Department of Neurology, Massachusetts General Hospital/Wellman 423, 50 Blossom Street, Boston, MA 02114, USA.
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Lawson K, Dunne MJ. Peripheral channelopathies as targets for potassium channel openers. Expert Opin Investig Drugs 2001; 10:1345-59. [PMID: 11772256 DOI: 10.1517/13543784.10.7.1345] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Potassium channel openers (KCOs) are important tools that are often used to gain a greater understanding of K(+) channels. Agents that can induce or maintain the opening of K(+) channels also offer a therapeutic approach to controlling of cell excitability and offer a means of producing stability in biological systems. The pathogenesis of a broad range of peripheral disorders (e.g., LQT syndrome, hypokalemic periodic paralysis, hyperinsulinism in infancy and erectile dysfunction) are associated with dysfunctional K(+) channels due to mutations in genes encoding channel proteins. The therapeutic potential of KCOs in peripheral K(+) channelopathies is discussed. The identification of K(+) channel subtype-specific openers offers discrete modulation of cellular systems creating a realistic therapeutic advance in the treatment of K(+) channelopathies.
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Affiliation(s)
- K Lawson
- Division of Biomedical Sciences, Sheffield Hallam University, School of Science and Mathematics, City Campus, Sheffield, S1 1WB, UK.
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Abstract
In the past decade, nine new drugs have been licensed for the treatment of epilepsy. With limited clinical experience of these agents, the mechanisms of action of antiepileptic drugs may be an important criterion in the selection of the most suitable treatment regimens for individual patients. At the cellular level, three basic mechanisms are recognised: modulation of voltage-dependent ion channels, enhancement of inhibitory neurotransmission, and attenuation of excitatory transmission. In this review, we will attempt to introduce the concepts of ion channel and neurotransmitter modulation and, thereafter, group currently used antiepileptic drugs according to their principal mechanisms of action.
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Affiliation(s)
- P Kwan
- Epilepsy Unit, University Department of Medicine and Therapeutics, Western Infirmary, Glasgow G11 6NT, Scotland, UK
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Lawson K. Is there a role for potassium channel openers in neuronal ion channel disorders? Expert Opin Investig Drugs 2000; 9:2269-80. [PMID: 11060806 DOI: 10.1517/13543784.9.10.2269] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Malfunction in ion channels, due to mutations in genes encoding channel proteins or the presence of autoantibodies, are increasing being implicated in causing disease conditions, termed channelopathies. Dysfunction of potassium (K(+)) channels has been associated with the pathophysiology of a number of neurological, as well as peripheral, disorders (e.g., episodic ataxia, epilepsy, neuromyotonia, Parkinson's disease, congenital deafness, long QT syndrome). K(+) channels, which demonstrate a high degree of diversity and ubiquity, are fundamental in the control of membrane depolarisation and cell excitability. A common feature of K(+) channelopathies is a reduction or loss of membrane potential repolarisation. The identification of K(+) channel subtype specific openers will allow the recovery of the mechanism(s) responsible for counteraction of uncontrolled cellular depolarisation. Synthetic agents that demonstrate K(+) channel opening properties are available for a variety of K(+) channel subtypes (e.g., K(ATP), BK(Ca), GIRK and M-channel). This study reviews the realistic therapeutic potential that may be gained in a broad spectrum of clinical conditions by K(+) channel openers. K(+) channel openers would therefore identify dysfunctional K(+) channel as therapeutic targets for clinical benefit, in addition being able to modulate normally functioning K(+) channels to gain clinical management of pathophysiological events irrespective of the cause.
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Affiliation(s)
- K Lawson
- Biomedical Research Centre, Sheffield Hallam University, School of Science and Mathematics, City Campus, Sheffield, S1 1WB, UK.
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The polyglutamine expansion in spinocerebellar ataxia type 6 causes a beta subunit-specific enhanced activation of P/Q-type calcium channels in Xenopus oocytes. J Neurosci 2000. [PMID: 10964945 DOI: 10.1523/jneurosci.20-17-06394.2000] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Spinocerebellar ataxia type 6 (SCA6) is a dominantly inherited degenerative disorder of the cerebellum characterized by nearly selective and progressive death of Purkinje cells. The underlying mutation in SCA6 consists of an expansion of a trinucleotide CAG repeat in the 3' region of the gene, CACNA1A, encoding the alpha(1A) subunit of the neuronal P/Q-type voltage-gated calcium channel. Although it is known that this mutation results in an expanded tract of glutamine residues in some alpha(1A) splice forms, the distribution of these splice forms and the role of this mutation in the highly selective Purkinje cell degeneration seen in SCA6 have yet to be elucidated. Using specific antisera we demonstrate that the pathological expansion in SCA6 can potentially be expressed in multiple isoforms of the alpha(1A) subunit, and that these isoforms are abundantly expressed in the cerebellum, particularly in the Purkinje cell bodies and dendrites. Using alpha(1A) subunit chimeras expressing SCA6 mutations, we show that the SCA6 polyglutamine expansion shifts the voltage dependence of channel activation and rate of inactivation only when expressed with beta(4) subunits and impairs normal G-protein regulation of P/Q channels. These findings suggest the possibility that SCA6 is a channelopathy, and that the underlying mutation in SCA6 causes Purkinje cell degeneration through excessive entry of calcium ions.
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Abstract
Autosomal-dominant cerebellar ataxias (ADCA) may present as progressive or paroxysmal disorders. While the progressive ataxias have been named spinocerebellar ataxias (SCA), the paroxysmal disorders are designated episodic ataxias (EA). Until now, three different mutational mechanisms resulting in distinctive pathogenesis have been identified. The first type of mutation present in SCA1, SCA2, SCA3, and SCA7 is an expanded CAG repeat in genes of unknown function that are translated into proteins with expanded polyglutamine tracts. A common ultrastructural feature of these disorders is the formation of neuronal intranuclear inclusions (NII) harboring the expanded disease proteins and a variety of other proteins. The pathogenic role of these inclusions has yet to be clarified. A second group of disorders is the result of mutations in genes that code for ion channels. In EA-1, a disorder characterized by episodes of ataxia provoked by movement and startle, missense mutations in a potassium channel gene, KCNA1, have been found. Patients with EA-2, another form of paroxysmal ataxia, carry nonsense mutations of the gene encoding the alpha1A voltage-dependent calcium channel subunit, CACNA1A, that are predicted to result in truncated channel proteins. In SCA6, a progressive ataxia, an expanded CAG repeat in the 3' translated region of the CACNA1A gene, has been found. The third type of mutation is an untranslated CTG expansion resembling the mutation found in myotonic dystrophy. It is associated with a progressive ataxia, SCA8.
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Affiliation(s)
- T Klockgether
- Department of Neurology, University of Bonn, Germany
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12
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Abstract
Systemic administration of the L-type calcium channel agonists +/-Bay K 8644 or FPL 64176 causes a characteristic pattern of motor dysfunction in normal C57BL/6J mice that resembles generalized dystonia. There is no associated change in the electroencephalogram, confirming that the motor disorder does not reflect epileptic seizures. However, the electromyogram reveals an increase in baseline motor unit activity with prolonged phasic discharges consistent with dystonia. The duration and severity of dystonia is dependent on the dose administered and the age of the animal at testing. The effects are transient, with the return of normal motor behavior 1-4 hours after treatment. Similar effects can be provoked by intracerebral administration of small amounts of the drugs, indicating a centrally mediated response. Dystonia can be attenuated by co-administration of dihydropyridine L-type calcium channel antagonists (nifedipine, nimodipine, and nitrendipine) but not by non-dihydropyridine antagonists (diltiazem, verapamil, and flunarizine). These results implicate abnormal function of L-type calcium channels in the expression of dystonia in this model.
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Affiliation(s)
- H A Jinnah
- Department of Neurology, Johns Hopkins Hospital, Baltimore, Maryland 21287, USA
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Gribkoff VK, Starrett JE. An assessment of the present and future roles of non-ligand gated ion channel modulators as CNS therapeutics. Expert Opin Pharmacother 1999; 1:61-70. [PMID: 11249565 DOI: 10.1517/14656566.1.1.61] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Few approved drugs have, as their primary known mechanism of action, modulation of non-ligand gated ion channels. However, these proteins are important regulators of neuronal function through their control of sodium, potassium, calcium and chloride flux, and are ideal candidates as drug discovery targets. Recent progress in the molecular biology and pharmacology of ion channels suggests that many will be associated with specific pharmacological profiles that will include both activators and inhibitors. Ion channels, through their regulation by G-proteins, are a major component of the final common pathway of many drugs acting at classical neuronal receptors. Thus, targeting of the ion channels themselves may confer different profiles of efficacy and specificity to drug action in the brain and spinal cord. Three areas for drug discovery are profiled that the authors consider prime targets for ion channel based therapies, anticonvulsant drugs, cognition enhancing drugs and drugs for improving neurone survival following ischaemia.
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Affiliation(s)
- V K Gribkoff
- Neuroscience and Genitourinary Drug Discovery, Bristol-Myers Squibb Pharmaceutical Research Institute, 5 Research Parkway, Wallingford, CT 06492, USA.
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Inshasi JS, Jose VP, van der Merwe CA, Gledhill RF. Dysfunction of sensory nerves during attacks of hypokalemic periodic paralysis. Neuromuscul Disord 1999; 9:227-31. [PMID: 10399749 DOI: 10.1016/s0960-8966(98)00129-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Reversible electrophysiologic abnormalities of sensory nerve function were found by chance in three patients with hypokalemic periodic paralysis, a disorder previously considered to affect the function of muscle membranes only. A formal, prospective study was therefore conducted. Serial nerve conduction studies were done in ten additional patients. Amplitude of sensory action potentials was significantly smaller during paralytic attacks, but did not differ from controls after normalization of serum potassium concentration. These apparently novel findings might be explained by previous electrodiagnostic studies either not involving the testing of sensory nerves at all, or not being repeated after recovery from an attack. Involvement of sensory nerves in hypokalemic periodic paralysis is suggested to arise through dorsal root ganglia having an incomplete blood-nerve barrier and sensory neurons being particularly vulnerable to derangements affecting nerve cell metabolism. Neuronal inexcitability is postulated to occur consequent upon possible inactivation of the sodium-potassium pump by the low concentration of extracellular potassium. In patients with acute areflexic limb weakness, the diagnosis of hypokalemic periodic paralysis should not be excluded by abnormal results of sensory nerve conduction studies.
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Affiliation(s)
- J S Inshasi
- Neurosciences Department, Rashid Hospital, Dubai, United Arab Emirates
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