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Łątka K, Jończyk J, Bajda M. γ-Aminobutyric acid transporters as relevant biological target: Their function, structure, inhibitors and role in the therapy of different diseases. Int J Biol Macromol 2020; 158:S0141-8130(20)32987-1. [PMID: 32360967 DOI: 10.1016/j.ijbiomac.2020.04.126] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Revised: 04/17/2020] [Accepted: 04/18/2020] [Indexed: 12/13/2022]
Abstract
γ-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the nervous system. It plays a crucial role in many physiological processes. Upon release from the presynaptic element, it is removed from the synaptic cleft by reuptake due to the action of GABA transporters (GATs). GATs belong to a large SLC6 protein family whose characteristic feature is sodium-dependent relocation of neurotransmitters through the cell membrane. GABA transporters are characterized in many contexts, but their spatial structure is not fully known. They are divided into four types, which differ in occurrence and role. Herein, the special attention was paid to these transporting proteins. This comprehensive review presents the current knowledge about GABA transporters. Their distribution in the body, physiological functions and possible utilization in the therapy of different diseases were fully discussed. The important structural features were described based on published data, including sequence analysis, mutagenesis studies, and comparison with known SLC6 transporters for leucine (LeuT), dopamine (DAT) and serotonin (SERT). Moreover, the most important inhibitors of GABA transporters of various basic scaffolds, diverse selectivity and potency were presented.
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Affiliation(s)
- Kamil Łątka
- Jagiellonian University Medical College, Faculty of Pharmacy, Department of Physicochemical Drug Analysis, 30-688 Cracow, Medyczna 9, Poland
| | - Jakub Jończyk
- Jagiellonian University Medical College, Faculty of Pharmacy, Department of Physicochemical Drug Analysis, 30-688 Cracow, Medyczna 9, Poland
| | - Marek Bajda
- Jagiellonian University Medical College, Faculty of Pharmacy, Department of Physicochemical Drug Analysis, 30-688 Cracow, Medyczna 9, Poland.
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Zaręba P, Gryzło B, Malawska K, Sałat K, Höfner GC, Nowaczyk A, Fijałkowski Ł, Rapacz A, Podkowa A, Furgała A, Żmudzki P, Wanner KT, Malawska B, Kulig K. Novel mouse GABA uptake inhibitors with enhanced inhibitory activity toward mGAT3/4 and their effect on pain threshold in mice. Eur J Med Chem 2020; 188:111920. [DOI: 10.1016/j.ejmech.2019.111920] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2019] [Revised: 11/16/2019] [Accepted: 11/27/2019] [Indexed: 12/12/2022]
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Kickinger S, Hellsberg E, Frølund B, Schousboe A, Ecker GF, Wellendorph P. Structural and molecular aspects of betaine-GABA transporter 1 (BGT1) and its relation to brain function. Neuropharmacology 2019; 161:107644. [PMID: 31108110 DOI: 10.1016/j.neuropharm.2019.05.021] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Revised: 04/14/2019] [Accepted: 05/16/2019] [Indexed: 01/09/2023]
Abstract
ɣ-aminobutyric-acid (GABA) functions as the principal inhibitory neurotransmitter in the central nervous system. Imbalances in GABAergic neurotransmission are involved in the pathophysiology of various neurological diseases such as epilepsy, Alzheimer's disease and stroke. GABA transporters (GATs) facilitate the termination of GABAergic signaling by transporting GABA together with sodium and chloride from the synaptic cleft into presynaptic neurons and surrounding glial cells. Four different GATs have been identified that all belong to the solute carrier 6 (SLC6) transporter family: GAT1-3 (SLC6A1, SLC6A13, SLC6A11) and betaine/GABA transporter 1 (BGT1, SLC6A12). BGT1 has emerged as an interesting target for treating epilepsy due to animal studies that reported anticonvulsant effects for the GAT1/BGT1 selective inhibitor EF1502 and the BGT1 selective inhibitor RPC-425. However, the precise involvement of BGT1 in epilepsy remains elusive because of its controversial expression levels in the brain and the lack of highly selective and potent tool compounds. This review gathers the current structural and functional knowledge on BGT1 with emphasis on brain relevance, discusses all available compounds, and tries to shed light on the molecular determinants driving BGT1 selectivity. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.
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Affiliation(s)
- Stefanie Kickinger
- University of Vienna, Department of Pharmaceutical Chemistry, Althanstrasse 14, 1090, Vienna, Austria
| | - Eva Hellsberg
- University of Vienna, Department of Pharmaceutical Chemistry, Althanstrasse 14, 1090, Vienna, Austria
| | - Bente Frølund
- University of Copenhagen, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Arne Schousboe
- University of Copenhagen, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Gerhard F Ecker
- University of Vienna, Department of Pharmaceutical Chemistry, Althanstrasse 14, 1090, Vienna, Austria
| | - Petrine Wellendorph
- University of Copenhagen, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, 2 Universitetsparken, 2100, Copenhagen, Denmark.
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Nowaczyk A, Fijałkowski Ł, Kowalska M, Podkowa A, Sałat K. Studies on the Activity of Selected Highly Lipophilic Compounds toward hGAT1 Inhibition. Part II. ACS Chem Neurosci 2019; 10:337-347. [PMID: 30222312 DOI: 10.1021/acschemneuro.8b00282] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
In this paper, we describe the latest results involving molecular modeling and pharmacodynamic studies of the selected highly lipophilic compounds acting by human GABA transporter 1 (hGAT1) inhibition. The chemical interaction of 17 GABA analogues with a model of hGAT1 is described using the molecular docking method. The biological role of GAT1 is related to the regulation of GABA level in the central nervous system and GAT1 inhibition plays an important role in the control of seizure threshold. To confirm that GAT1 can be also a molecular target for drugs used to treat other neurological and psychiatric diseases (e.g., pain and anxiety), in the in vivo part of this study, potential antinociceptive and anxiolytic-like properties of tiagabine, a selective GAT1 inhibitor, are described.
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Affiliation(s)
- Alicja Nowaczyk
- Department of Organic Chemistry, Faculty of Pharmacy, Collegium Medicum in Bydgoszcz, Nicolaus Copernicus University, 2 dr. A. Jurasza St., 85-094 Bydgoszcz, Poland
| | - Łukasz Fijałkowski
- Department of Organic Chemistry, Faculty of Pharmacy, Collegium Medicum in Bydgoszcz, Nicolaus Copernicus University, 2 dr. A. Jurasza St., 85-094 Bydgoszcz, Poland
| | - Magdalena Kowalska
- Department of Organic Chemistry, Faculty of Pharmacy, Collegium Medicum in Bydgoszcz, Nicolaus Copernicus University, 2 dr. A. Jurasza St., 85-094 Bydgoszcz, Poland
| | - Adrian Podkowa
- Chair of Inorganic and Analytical Chemistry, Jagiellonian University Medical College, 9 Medyczna St., 30-688 Kraków, Poland
| | - Kinga Sałat
- Department of Pharmacodynamics, Chair of Pharmacodynamics, Jagiellonian University Medical College, 9 Medyczna St., 30-688 Krakow, Poland
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Liberato JL, Godoy LD, Cunha AOS, Mortari MR, de Oliveira Beleboni R, Fontana ACK, Lopes NP, Dos Santos WF. Parawixin2 Protects Hippocampal Cells in Experimental Temporal Lobe Epilepsy. Toxins (Basel) 2018; 10:toxins10120486. [PMID: 30469496 PMCID: PMC6316435 DOI: 10.3390/toxins10120486] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 10/27/2018] [Accepted: 11/13/2018] [Indexed: 12/20/2022] Open
Abstract
Epilepsy is considered as one of the major disabling neuropathologies. Almost one third of adult patients with temporal lobe epilepsy (TLE) do not respond to current antiepileptic drugs (AEDs). Additionally, most AEDs do not have neuroprotective effects against the inherent neurodegenerative process underlying the hippocampal sclerosis on TLE. Dysfunctions in the GABAergic neurotransmission may contribute not only to the onset of epileptic activity but also constitute an important system for therapeutic approaches. Therefore, molecules that enhance GABA inhibitory effects could open novel avenues for the understanding of epileptic plasticity and for drug development. Parawixin2, a compound isolated from Parawixia bistriata spider venom, inhibits both GABA and glycine uptake and has an anticonvulsant effect against a wide range of chemoconvulsants. The neuroprotective potential of Parawixin2 was analyzed in a model of TLE induced by a long-lasting Status Epilepticus (SE), and its efficiency was compared to well-known neuroprotective drugs, such as riluzole and nipecotic acid. Neuroprotection was assessed through histological markers for cell density (Nissl), astrocytic reactivity (GFAP) and cell death labeling (TUNEL), which were performed 24 h and 72 h after SE. Parawixin2 treatment resulted in neuroprotective effects in a dose dependent manner at 24 h and 72 h after SE, as well as reduced reactive astrocytes and apoptotic cell death. Based on these findings, Parawixin2 has a great potential to be used as a tool for neuroscience research and as a probe to the development of novel GABAergic neuroprotective agents.
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Affiliation(s)
- José Luiz Liberato
- Neurobiology and Venoms Laboratory (LNP), Department of Biology, College of Philosophy, Sciences and Literature of Ribeirão Preto, University of São Paulo, Av. Bandeirantes, 3900, Ribeirão Preto, 14040-901 São Paulo, Brazil.
- Neuroscience Behavioral Institute (INEC), Av. do Café, 2450, Ribeirão Preto, 14050-220 São Paulo, Brazil.
| | - Lívea Dornela Godoy
- Neurobiology and Venoms Laboratory (LNP), Department of Biology, College of Philosophy, Sciences and Literature of Ribeirão Preto, University of São Paulo, Av. Bandeirantes, 3900, Ribeirão Preto, 14040-901 São Paulo, Brazil.
- Neuroscience Behavioral Institute (INEC), Av. do Café, 2450, Ribeirão Preto, 14050-220 São Paulo, Brazil.
| | - Alexandra Olimpio Siqueira Cunha
- Neurobiology and Venoms Laboratory (LNP), Department of Biology, College of Philosophy, Sciences and Literature of Ribeirão Preto, University of São Paulo, Av. Bandeirantes, 3900, Ribeirão Preto, 14040-901 São Paulo, Brazil.
| | - Marcia Renata Mortari
- Laboratory of Neuropharmacology, Department of Physiological Sciences, Institute of Biological Sciences, University of Brasília, DF 70910-900 Brasília, Brazil.
| | - Rene de Oliveira Beleboni
- Department of Biotechnology/School of Medicine, University of Ribeirão Preto, Av. Costábile Romano, 2201, Ribeirão Preto, 14096-900 São Paulo, Brazil.
| | - Andréia C K Fontana
- Department of Pharmacology and Physiology, Drexel University College of Medicine, 245 N. 15th Street, Philadelphia, PA 19102, USA.
| | - Norberto Peporine Lopes
- NPPNS, Department of Physics and Chemistry, College of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil, Av. do Cafe s/n, Ribeirão Preto, 14040-903 São Paulo, Brazil.
| | - Wagner Ferreira Dos Santos
- Neurobiology and Venoms Laboratory (LNP), Department of Biology, College of Philosophy, Sciences and Literature of Ribeirão Preto, University of São Paulo, Av. Bandeirantes, 3900, Ribeirão Preto, 14040-901 São Paulo, Brazil.
- Neuroscience Behavioral Institute (INEC), Av. do Café, 2450, Ribeirão Preto, 14050-220 São Paulo, Brazil.
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Sowa AR, Brooks AF, Shao X, Henderson BD, Sherman P, Arteaga J, Stauff J, Lee AC, Koeppe RA, Scott PJH, Kilbourn MR. Development of Positron Emission Tomography Radiotracers for the GABA Transporter 1. ACS Chem Neurosci 2018; 9:2767-2773. [PMID: 29763549 DOI: 10.1021/acschemneuro.8b00183] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
In vivo positron emission tomography (PET) imaging of the γ-aminobutyric acid (GABA) receptor complex has been accomplished using radiolabeled benzodiazepine derivatives, but development of specific presynaptic radioligands targeting the neuronal membrane GABA transporter type 1 (GAT-1) has been less successful. The availability of new structure-activity studies of GAT-1 inhibitors and the introduction of a GAT-1 inhibitor (tiagabine, Gabatril) into clinical use prompted us to reinvestigate the syntheses of PET ligands for this transporter. Initial synthesis and rodent PET studies of N-[11C]methylnipecotic acid confirmed the low brain uptake of that small and polar molecule. The common design approach to improve blood-brain barrier permeability of GAT-1 inhibitors is the attachment of a large lipophilic substituent. We selected an unsymmetrical bis-aromatic residue attached to the ring nitrogen by a vinyl ether spacer from a series recently reported by Wanner and coworkers. Nucleophilic aromatic substitution of an aryl chloride precursor with [18F]fluoride was used to prepare the desired candidate radiotracer ( R, E/ Z)-1-(2-((4-fluoro-2-(4-[18F]fluorobenzoyl)styryl)oxy)ethyl)piperidine-3-carboxylic acid (( R, E/ Z)-[18F]10). PET studies in rats showed no brain uptake, which was not altered by pretreatment of animals with the P-glycoprotein inhibitor cyclosporine A, indicating efflux by Pgp was not responsible. Subsequent PET imaging studies of ( R, E/ Z)-[18F]10 in rhesus monkey brain showed very low brain uptake. Finally, to test if the free carboxylic acid group was the likely cause of poor brain uptake, PET studies were done using the ethyl ester derivative of ( R, E/ Z)-[18F]10. Rapid and significant monkey brain uptake of the ester was observed, followed by a slow washout over 90 min. The blood-brain barrier permeability of the ester supports a hypothesis that the free acid function limits brain uptake of nipecotic acid-based GAT-1 radioligands, and future radiotracer efforts should investigate the use of carboxylic acid bioisosteres.
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Affiliation(s)
- Alexandra R. Sowa
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
- Department of Medicinal Chemistry, University of Michigan, Ann Arbor, Michigan 48105, United States
| | - Allen F. Brooks
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Xia Shao
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Bradford D. Henderson
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Philip Sherman
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Janna Arteaga
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Jenelle Stauff
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Adam C. Lee
- E.I. du Pont de Nemours and Company, DuPont Haskell Global Center for Health Sciences, P.O. Box 30, Newark, Delaware 19714, United States
| | - Robert A. Koeppe
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Peter J. H. Scott
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
- Department of Medicinal Chemistry, University of Michigan, Ann Arbor, Michigan 48105, United States
| | - Michael R. Kilbourn
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
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Astrocytic GABA Transporters: Pharmacological Properties and Targets for Antiepileptic Drugs. ADVANCES IN NEUROBIOLOGY 2017; 16:283-296. [PMID: 28828616 DOI: 10.1007/978-3-319-55769-4_14] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Inactivation of GABA-mediated neurotransmission is achieved by high-affinity transporters located at both GABAergic neurons and the surrounding astrocytes. Early studies of the pharmacological properties of neuronal and glial GABA transporters suggested that different types of transporters might be expressed in the two cell types, and such a scenario was confirmed by the cloning of four distinctly different GABA transporters from a number of different species. These GABA-transport entities have been extensively characterized using a large number of GABA analogues of restricted conformation, and several of these compounds have been shown to exhibit pronounced anticonvulsant activity in a variety of animal seizure models. As proof of concept of the validity of this drug development approach, one GABA-transport inhibitor, tiagabine, has been developed as a clinically active antiepileptic drug. This review provides a detailed account of efforts to design new subtype-selective GABA-transport inhibitors aiming at identifying novel antiepileptic drug candidates.
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Jiang Y, Liu Z, Holenz J, Yang H. Competitive Intelligence–based Lead Generation and Fast Follower Approaches. ACTA ACUST UNITED AC 2016. [DOI: 10.1002/9783527677047.ch08] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Vogensen SB, Jørgensen L, Madsen KK, Jurik A, Borkar N, Rosatelli E, Nielsen B, Ecker GF, Schousboe A, Clausen RP. Structure activity relationship of selective GABA uptake inhibitors. Bioorg Med Chem 2015; 23:2480-8. [DOI: 10.1016/j.bmc.2015.03.060] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 03/12/2015] [Accepted: 03/19/2015] [Indexed: 10/23/2022]
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Jurik A, Zdrazil B, Holy M, Stockner T, Sitte HH, Ecker GF. A binding mode hypothesis of tiagabine confirms liothyronine effect on γ-aminobutyric acid transporter 1 (GAT1). J Med Chem 2015; 58:2149-58. [PMID: 25679268 PMCID: PMC4360375 DOI: 10.1021/jm5015428] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
![]()
Elevating
GABA levels in the synaptic cleft by inhibiting its reuptake
carrier GAT1 is an established approach for the treatment of CNS disorders
like epilepsy. With the increasing availability of crystal structures
of transmembrane transporters, structure-based approaches to elucidate
the molecular basis of ligand–transporter interaction also
become feasible. Experimental data guided docking of derivatives of
the GAT1 inhibitor tiagabine into a protein homology model of GAT1
allowed derivation of a common binding mode for this class of inhibitors
that is able to account for the distinct structure–activity
relationship pattern of the data set. Translating essential binding
features into a pharmacophore model followed by in silico screening
of the DrugBank identified liothyronine as a drug potentially exerting
a similar effect on GAT1. Experimental testing further confirmed the
GAT1 inhibiting properties of this thyroid hormone.
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Affiliation(s)
- Andreas Jurik
- University of Vienna , Department of Pharmaceutical Chemistry, Division of Drug Design and Medicinal Chemistry, Althanstraße 14, 1090 Vienna, Austria
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Sałat K, Podkowa A, Kowalczyk P, Kulig K, Dziubina A, Filipek B, Librowski T. Anticonvulsant active inhibitor of GABA transporter subtype 1, tiagabine, with activity in mouse models of anxiety, pain and depression. Pharmacol Rep 2014; 67:465-72. [PMID: 25933955 DOI: 10.1016/j.pharep.2014.11.003] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2014] [Revised: 10/21/2014] [Accepted: 11/12/2014] [Indexed: 10/24/2022]
Abstract
BACKGROUND Tiagabine, a selective inhibitor of GABA transporter subtype 1 is used as an add-on therapy of partial seizures in humans but its mechanism of action suggests other potential medical indications for this drug. In this research we assess its pharmacological activity in several screening models of seizures, pain, anxiety and depression in mice. METHODS For pharmacological tests tiagabine was administered intraperitoneally 60 min before the assay. Behavioral tests were performed using models of chemically and electrically induced seizures, thermal acute pain and formalin-induced tonic pain. Anxiolytic-like properties were evaluated using the four plate test and the elevated plus maze test. Antidepressant-like activity was assessed in the forced swim test. In addition, to exclude false positive results in these assays, the influence of tiagabine on animals' locomotor activity and motor coordination was investigated, too. RESULTS Tiagabine demonstrated anticonvulsant properties in chemically induced seizures (pentylenetetrazole and pilocarpine seizures). At the dose of 100mg/kg it also elevated the seizure threshold for electrically induced seizures by 31.6% (p<0.01), but it had no activity in the maximal electroshock seizure test. Tiagabine showed anxiolytic-like and antidepressant-like effects. Although it apparently reduced animals' nociceptive responses in pain tests, these activities rather resulted from its sedative and motor-impairing properties demonstrated in the locomotor activity and the rotarod tests, respectively. CONCLUSIONS The results obtained in the present study suggest that tiagabine, apart its anticonvulsant effect, has anxiolytic-like, sedative and antidepressant-like properties. In view of this, it can be potentially used in the treatment of anxiety and mood disorders.
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Affiliation(s)
- Kinga Sałat
- Department of Pharmacodynamics, Jagiellonian University, Medical College, Kraków, Poland.
| | - Adrian Podkowa
- Department of Pharmacodynamics, Jagiellonian University, Medical College, Kraków, Poland
| | - Paula Kowalczyk
- Department of Physicochemical Drug Analysis, Chair of Pharmaceutical Chemistry, Jagiellonian University, Medical College, Kraków, Poland
| | - Katarzyna Kulig
- Department of Physicochemical Drug Analysis, Chair of Pharmaceutical Chemistry, Jagiellonian University, Medical College, Kraków, Poland
| | - Anna Dziubina
- Department of Pharmacodynamics, Jagiellonian University, Medical College, Kraków, Poland
| | - Barbara Filipek
- Department of Pharmacodynamics, Jagiellonian University, Medical College, Kraków, Poland
| | - Tadeusz Librowski
- Department of Radioligands, Jagiellonian University, Medical College, Kraków, Poland
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Kobayashi T, Suemasa A, Igawa A, Ide S, Fukuda H, Abe H, Arisawa M, Minami M, Shuto S. Conformationally Restricted GABA with Bicyclo[3.1.0]hexane Backbone as the First Highly Selective BGT-1 Inhibitor. ACS Med Chem Lett 2014; 5:889-93. [PMID: 25147609 DOI: 10.1021/ml500134k] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Accepted: 06/16/2014] [Indexed: 11/29/2022] Open
Abstract
On the basis of the three-dimensional diversity-oriented conformational restriction strategy using key chiral cyclopropane units, we previously identified 3 ((2S,3R)-4-amino-3,4-methanobutyric acid) with a chiral trans-cyclopropane structure as a γ-aminobutyric acid (GABA) transporter inhibitor selective for GABA transporter (GAT) subtypes GAT-3 and BGT-1 (betaine/GABA transporter-1). Further conformational restriction of 3 with the rigid bicyclo[3.1.0]hexane backbone led to the successful development of the first highly potent and selective BGT-1 inhibitor 4 (IC50 = 0.59 μM). The bioactive conformation of 3 for BGT-1 was also identified.
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Affiliation(s)
- Takaaki Kobayashi
- Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12,
Nishi-6, Kita-ku, Sapporo 060-0812, Japan
| | - Akihiro Suemasa
- Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12,
Nishi-6, Kita-ku, Sapporo 060-0812, Japan
| | - Arisa Igawa
- Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12,
Nishi-6, Kita-ku, Sapporo 060-0812, Japan
| | - Soichiro Ide
- Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12,
Nishi-6, Kita-ku, Sapporo 060-0812, Japan
| | - Hayato Fukuda
- Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12,
Nishi-6, Kita-ku, Sapporo 060-0812, Japan
| | - Hiroshi Abe
- Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12,
Nishi-6, Kita-ku, Sapporo 060-0812, Japan
| | - Mitsuhiro Arisawa
- Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12,
Nishi-6, Kita-ku, Sapporo 060-0812, Japan
| | - Masabumi Minami
- Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12,
Nishi-6, Kita-ku, Sapporo 060-0812, Japan
| | - Satoshi Shuto
- Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12,
Nishi-6, Kita-ku, Sapporo 060-0812, Japan
- Center for Research
and Education on Drug Discovery, Hokkaido University, Kita-ku, Sapporo 060-0812, Japan
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Kempson SA, Zhou Y, Danbolt NC. The betaine/GABA transporter and betaine: roles in brain, kidney, and liver. Front Physiol 2014; 5:159. [PMID: 24795654 PMCID: PMC4006062 DOI: 10.3389/fphys.2014.00159] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 04/04/2014] [Indexed: 12/18/2022] Open
Abstract
The physiological roles of the betaine/GABA transporter (BGT1; slc6a12) are still being debated. BGT1 is a member of the solute carrier family 6 (the neurotransmitter, sodium symporter transporter family) and mediates cellular uptake of betaine and GABA in a sodium- and chloride-dependent process. Most of the studies of BGT1 concern its function and regulation in the kidney medulla where its role is best understood. The conditions here are hostile due to hyperosmolarity and significant concentrations of NH4Cl and urea. To withstand the hyperosmolarity, cells trigger osmotic adaptation, involving concentration of a transcriptional factor TonEBP/NFAT5 in the nucleus, and accumulate betaine and other osmolytes. Data from renal cells in culture, primarily MDCK, revealed that transcriptional regulation of BGT1 by TonEBP/NFAT5 is relatively slow. To allow more acute control of the abundance of BGT1 protein in the plasma membrane, there is also post-translation regulation of BGT1 protein trafficking which is dependent on intracellular calcium and ATP. Further, betaine may be important in liver metabolism as a methyl donor. In fact, in the mouse the liver is the organ with the highest content of BGT1. Hepatocytes express high levels of both BGT1 and the only enzyme that can metabolize betaine, namely betaine:homocysteine –S-methyltransferase (BHMT1). The BHMT1 enzyme removes a methyl group from betaine and transfers it to homocysteine, a potential risk factor for cardiovascular disease. Finally, BGT1 has been proposed to play a role in controlling brain excitability and thereby represents a target for anticonvulsive drug development. The latter hypothesis is controversial due to very low expression levels of BGT1 relative to other GABA transporters in brain, and also the primary location of BGT1 at the surface of the brain in the leptomeninges. These issues are discussed in detail.
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Affiliation(s)
- Stephen A Kempson
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine Indianapolis, IN, USA
| | - Yun Zhou
- Department of Anatomy, Centre of Molecular Biology and Neuroscience, Institute of Basic Medical Sciences, University of Oslo Oslo, Norway
| | - Niels C Danbolt
- Department of Anatomy, Centre of Molecular Biology and Neuroscience, Institute of Basic Medical Sciences, University of Oslo Oslo, Norway
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Hiramatsu M. [Functional role for GABA transporters in the CNS]. Nihon Yakurigaku Zasshi 2014; 143:187-192. [PMID: 24717607 DOI: 10.1254/fpj.143.187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
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15
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Discovery of a subtype selective inhibitor of the human betaine/GABA transporter 1 (BGT-1) with a non-competitive pharmacological profile. Biochem Pharmacol 2013; 86:521-8. [DOI: 10.1016/j.bcp.2013.06.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2013] [Revised: 06/07/2013] [Accepted: 06/11/2013] [Indexed: 12/21/2022]
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Sałat K, Kulig K, Gajda J, Więckowski K, Filipek B, Malawska B. Evaluation of anxiolytic-like, anticonvulsant, antidepressant-like and antinociceptive properties of new 2-substituted 4-hydroxybutanamides with affinity for GABA transporters in mice. Pharmacol Biochem Behav 2013; 110:145-53. [PMID: 23850524 DOI: 10.1016/j.pbb.2013.06.013] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Revised: 06/14/2013] [Accepted: 06/28/2013] [Indexed: 01/01/2023]
Abstract
PURPOSE The inhibition of plasma membrane GABA transporters (GATs) is responsible for anxiolytic-like, anticonvulsant, antinociceptive and antidepressant-like effects in mice. It also influences animals' motor coordination and their sensitivity to ethanol. The aim of this study was to assess the pharmacological activity of two novel 2-substituted 4-hydroxybutanamides (BM 130 and BM 131) in some screening models. An attempt has been made to establish the relationship between the inhibition of GAT subtype and the observed in vivo activity. METHODS The affinity for GAT subtypes was evaluated by means of [(3)H]GABA uptake assay. It indicated that BM 130 inhibited GAT1 and GAT2, whereas BM 131 inhibited GAT1 and GAT3. In mice anxiolytic-like, antidepressant-like, anticonvulsant and antinociceptive properties of the test compounds were assessed. Their influence on motor coordination, locomotor activity and the ability to potentiate effects of subnarcotic doses of ethanol was also tested. RESULTS Both compounds administered intraperitoneally exerted a significant anxiolytic-like effect in the four plate test with ED50 values 3.4 and 7.9 mg/kg, respectively. At 30 mg/kg they reduced duration of immobility in the forced swim test for 33% and 19%, respectively. They had no effect on electroconvulsive threshold or pain reactivity in the hot plate assay but they were antinociceptive in the acetic acid-induced writhing test (ED50 values were 12.7 and 18.6 mg/kg, respectively) and in both phases of the formalin test (ED50 values in the first phase were 10.2 and 2.1 mg/kg for BM 130 and BM 131, respectively). No motor adverse effects were observed in mice pretreated with the test compounds in the rotarod or chimney tests but BM 131 caused a transient but statistically significant decrease of animals' locomotor activity. CONCLUSIONS In mice BM 130 and BM 131 have anxiolytic-like, antidepressant-like and antinociceptive properties which can be attributed to their affinity for not only mGAT1 but also mGAT2-4.
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Affiliation(s)
- Kinga Sałat
- Department of Pharmacodynamics, Jagiellonian University, Medical College, Medyczna 9, 30-688 Cracow, Poland.
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Sałat K, Więckowska A, Więckowski K, Höfner GC, Kamiński J, Wanner KT, Malawska B, Filipek B, Kulig K. Synthesis and pharmacological properties of new GABA uptake inhibitors. Pharmacol Rep 2013; 64:817-33. [PMID: 23087134 DOI: 10.1016/s1734-1140(12)70877-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Revised: 04/05/2012] [Indexed: 12/01/2022]
Abstract
BACKGROUND γ-Aminobutanoic acid (GABA) is the principal inhibitory neurotransmitter in the mammalian central nervous system. The identification and subsequent development of the GABA transport inhibitors which enhance the GABA-ergic transmission has shown the important role that GABA transporters play in the control of numerous functions of the nervous system. Compounds which inhibit GABA uptake are used as antiepileptic drugs (tiagabine - a selective GAT1 inhibitor), they are also being investigated for other indications, including treatment of psychosis, general anxiety, sleep disorders, drug addiction or acute and chronic pain. METHODS In this paper, the synthesis of 2-substituted-4-(1,3-dioxoisoindolin-2-ylo)-butanamides and 2-substituted-4-aminobutanoic acids derivatives is described. These compounds were tested in vitro for their ability to inhibit GABA uptake. The inhibitory potency towards murine plasma membrane GABA transporters (mGAT1-4) was performed as [(3)H]GABA uptake assay based on stably transfected HEK cells. Compound 18, which demonstrated the highest affinity for mGAT1-4 (pIC(50) ranged from 4.42 for mGAT1 to 5.07 for mGAT3), was additionally investigated in several behavioral tests in mice. RESULTS Compound 18 increased the locomotor activity (14-38%) and had anxiolytic-like properties in the four-plate test (ED(50) = 9.3 mg/kg). It did not show analgesic activity in acute pain model, namely the hot plate test, however, it was antinociceptive in the acetic acid-induced writhing test (ED(50) = 15.3 mg/kg) and in the formalin model of tonic pain. In the latter assay, it diminished nocifensive behavior in both phases and in the first (neurogenic) phase of this test the obtained ED(50) value (5.3 mg/kg) was similar to morphine (3.0 mg/kg). CONCLUSION Compound 18 exhibited significant anxiolytic-like properties and was antinociceptive in some models of pain in mice. Moreover, it did not impair animals' motor coordination in the chimney test. Some of the described pharmacological activities of compound 18 can be partly explained based on its affinity for plasma membrane GABA transporters.
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Affiliation(s)
- Kinga Sałat
- Department of Physicochemical Drug Analysis, Jagiellonian University, Medical College, Kraków, Poland
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Jurik A, Reicherstorfer R, Zdrazil B, Ecker GF. Classification of High-Activity Tiagabine Analogs by Binary QSAR Modeling. Mol Inform 2013; 32:415-419. [PMID: 23956803 PMCID: PMC3743161 DOI: 10.1002/minf.201300020] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2013] [Accepted: 03/28/2013] [Indexed: 12/01/2022]
Affiliation(s)
- Andreas Jurik
- University of Vienna, Department of Medicinal Chemistry Althanstraße 14, A-1090 Vienna, Austria phone/fax: +431-4277-55110/-9551
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Vogensen SB, Jørgensen L, Madsen KK, Borkar N, Wellendorph P, Skovgaard-Petersen J, Schousboe A, White HS, Krogsgaard-Larsen P, Clausen RP. Selective mGAT2 (BGT-1) GABA uptake inhibitors: design, synthesis, and pharmacological characterization. J Med Chem 2013; 56:2160-4. [PMID: 23398473 DOI: 10.1021/jm301872x] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
β-Amino acids sharing a lipophilic diaromatic side chain were synthesized and characterized pharmacologically on mouse GABA transporter subtypes mGAT1-4. The parent amino acids were also characterized. Compounds 13a, 13b, and 17b displayed more than 6-fold selectivity for mGAT2 over mGAT1. Compound 17b displayed anticonvulsive properties inferring a role of mGAT2 in epileptic disorders. These results provide new neuropharmacological tools and a strategy for designing subtype selective GABA transport inhibitors.
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Affiliation(s)
- Stine B Vogensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
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A steered molecular dynamics study of binding and translocation processes in the GABA transporter. PLoS One 2012; 7:e39360. [PMID: 22737235 PMCID: PMC3380839 DOI: 10.1371/journal.pone.0039360] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2012] [Accepted: 05/21/2012] [Indexed: 12/03/2022] Open
Abstract
The entire substrate translocation pathway in the human GABA transporter (GAT-1) was explored for the endogenous substrate GABA and the anti-convulsive drug tiagabine. Following a steered molecular dynamics (SMD) approach, in which a harmonic restraining potential is applied to the ligand, dissociation and re-association of ligands were simulated revealing events leading to substrate (GABA) translocation and inhibitor (tiagabine) mechanism of action. We succeeded in turning the transporter from the outward facing occluded to the open-to-out conformation, and also to reorient the transporter to the open-to-in conformation. The simulations are validated by literature data and provide a substrate pathway fingerprint in terms of which, how, and in which sequence specific residues are interacted with. They reveal the essential functional roles of specific residues, e.g. the role of charged residues in the extracellular vestibule including two lysines (K76 (TM1) and K448 (TM10)) and a TM6-triad (D281, E283, and D287) in attracting and relocating substrates towards the secondary/interim substrate-binding site (S2). Likewise, E101 is highlighted as essential for the relocation of the substrate from the primary substrate-binding site (S1) towards the cytoplasm.
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Analgesic and anticonvulsant activity of new derivatives of 2-substituted 4-hydroxybutanamides in mice. Pharmacol Rep 2012; 64:102-12. [DOI: 10.1016/s1734-1140(12)70736-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2011] [Revised: 09/15/2011] [Indexed: 01/18/2023]
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22
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Abstract
GABA, the principal inhibitory neurotransmitter in the cerebral cortex, maintains the inhibitory tone that counterbalances neuronal excitation. The identification and subsequent development of GABA-transport inhibitors has shown the important role that GABA transporters play in the control of the CNS. To date, four GABA transporters have been cloned (GAT1-4). Compounds that inhibit GABA uptake are targets for epilepsy treatment. Currently, they are also being investigated for other possible indications such as the treatment of psychosis, general anxiety and sleep disorders, drug addiction, acute and chronic pain. These and other issues are discussed in this article.
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Abstract
Since it was first reported approximately 40 years ago that putative amino acid neurotransmitters, including GABA, would likely be inactivated by synaptic high-affinity transporters, there has been an exponential increase in interest in delineating the pharmacological characteristics of these transporters. During the 1980s and 1990s a large series of publications was devoted to a detailed characterization of neuronal and astroglial GABA transporters demonstrating important differences between these, a notion that turned out to be of relevance for the development of anticonvulsants targeting GABA transporters. The cloning era, leading to the identification of four proteins capable of transporting GABA across plasma membranes, has further boosted this research. Ultimately the clinically active antiepileptic drug, tiagabine, was developed and it was established that its mechanism of action involved inhibition of the GABA transporter-1 (GAT1). Current and future research is directed towards a better understanding of how extrasynaptic GABA receptors may be regulated via manipulation of extrasynaptic GABA levels, possibly involving extrasynaptic GABA transporters, most likely non-GAT1 transporters.
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Kulig K, Więckowski K, Więckowska A, Gajda J, Pochwat B, Höfner GC, Wanner KT, Malawska B. Synthesis and biological evaluation of new derivatives of 2-substituted 4-hydroxybutanamides as GABA uptake inhibitors. Eur J Med Chem 2011; 46:183-90. [DOI: 10.1016/j.ejmech.2010.11.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2010] [Revised: 10/19/2010] [Accepted: 11/01/2010] [Indexed: 11/15/2022]
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A Possible Role of the Non-GAT1 GABA Transporters in Transfer of GABA From GABAergic to Glutamatergic Neurons in Mouse Cerebellar Neuronal Cultures. Neurochem Res 2010; 35:1384-90. [DOI: 10.1007/s11064-010-0196-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/13/2010] [Indexed: 10/19/2022]
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26
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García DA, Vendrell I, Galofré M, Suñol C. GABA released from cultured cortical neurons influences the modulation of t-[35S]butylbicyclophosphorothionate binding at the GABAA receptor. Eur J Pharmacol 2008; 600:26-31. [DOI: 10.1016/j.ejphar.2008.10.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2008] [Revised: 09/29/2008] [Accepted: 10/06/2008] [Indexed: 11/28/2022]
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Müller glia as an active compartment modulating nervous activity in the vertebrate retina: neurotransmitters and trophic factors. Neurochem Res 2008; 33:1466-74. [PMID: 18273703 DOI: 10.1007/s11064-008-9604-1] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2007] [Accepted: 01/23/2008] [Indexed: 01/13/2023]
Abstract
Müller cells represent the main type of glia present in the retina interacting with most, if not all neurons in this tissue. Müller cells have been claimed to function as optic fibers in the retina delivering light to photoreceptors with minimal distortion and low loss [Franze et al (2007) Proc Natl Acad Sci 104:8287-8292]. Most of the mediators found in the brain are also detected in the retinal tissue, and glia cells are active players in the synthesis, release, signaling and uptake of major mediators of synaptic function. Müller glia trophic factors may regulate many different aspects of neuronal circuitry during synaptogenesis, differentiation, neuroprotection and survival of photoreceptors, Retinal Ganglion Cells (RGCs) and other targets in the retina. Here we review the role of several transmitters and trophic factors that participate in the neuron-glia loop in the retina.
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Inhibition of the betaine-GABA transporter (mGAT2/BGT-1) modulates spontaneous electrographic bursting in the medial entorhinal cortex (mEC). Epilepsy Res 2008; 79:6-13. [PMID: 18262393 DOI: 10.1016/j.eplepsyres.2007.12.009] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2007] [Revised: 12/12/2007] [Accepted: 12/17/2007] [Indexed: 11/24/2022]
Abstract
Disruptions in GABAergic neurotransmission have been implicated in numerous CNS disorders, including epilepsy and neuropathic pain. Selective inhibition of neuronal and glial GABA transporter subtypes may offer unique therapeutic options for regaining balance between inhibitory and excitatory systems. The ability of two GABA transport inhibitors to modulate inhibitory tone via inhibition of mGAT1 (tiagabine) or mGAT2/BGT-1 (N-[4,4-bis(3-methyl-2-thienyl)-3-butenyl]-4-(methylamino-4,5,6,7-tetrahydrobenzo[d]isoxazol-3-ol), also known as EF1502) was evaluated using an in vitro model of spontaneous interictal-like bursting (SB). SBs were recorded extracellularly in combined mEC-HC horizontal brain slices (400 microm; 31+/-1 degrees C) obtained from KA-treated rats. Slice recordings demonstrated that EF1502 exhibited a concentration-dependent reduction in SB frequency. EF1502 significantly reduced SB rate to 32% of control at the 30 microM concentration, while reducing the area and duration of SB activity to 60% and 46% of control, respectively, at the 10 microM concentration. In contrast, the GAT1 selective inhibitor tiagabine (3, 10, and 30 microM) was unable to significantly reduce the frequency of SB activity in the mEC, despite significantly reducing both the duration (51% of control) and area (58% of control) of the SB at concentrations as low as 3 microM. The ability of EF1502, but not tiagabine, to inhibit SBs in the mEC suggests that this in vitro model of pharmacoresistant SB activity is useful to differentiate between novel anticonvulsants with similar mechanisms of action and suggests a therapeutic potential for non-GAT1 transport inhibitors.
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Christiansen B, Meinild AK, Jensen AA, Braüner-Osborne H. Cloning and Characterization of a Functional Human γ-Aminobutyric Acid (GABA) Transporter, Human GAT-2. J Biol Chem 2007; 282:19331-41. [PMID: 17502375 DOI: 10.1074/jbc.m702111200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Plasma membrane gamma-aminobutyric acid (GABA) transporters act to terminate GABA neurotransmission in the mammalian brain. Intriguingly four distinct GABA transporters have been cloned from rat and mouse, whereas only three functional homologs of these transporters have been cloned from human. The aim of this study therefore was to search for this fourth missing human transporter. Using a bioinformatics approach, we successfully identified and cloned the full-length cDNA of a so far uncharacterized human GABA transporter (GAT). The predicted protein displays high sequence similarity to rat GAT-2 and mouse GAT3, and in accordance with the nomenclature for rat GABA transporters, we therefore refer to the transporter as human GAT-2. We used electrophysiological and cell-based methods to demonstrate that this protein is a functional transporter of GABA. The transport was saturable and dependent on both Na(+) and Cl(-). Pharmacologically the transporter is distinct from the other human GABA transporters and similar to rat GAT-2 and mouse GAT3 with high sensitivity toward GABA and beta-alanine. Furthermore the GABA transport inhibitor (S)-SNAP-5114 displayed some inhibitory activity at the transporter. Expression analysis by reverse transcription-PCR showed that GAT-2 mRNA is present in human brain, kidney, lung, and testis. The finding of the human GAT-2 demonstrates for the first time that the four plasma membrane GABA transporters identified in several mammalian species are all conserved in human. Furthermore the availability of human GAT-2 enables the use of all human clones of the GABA transporters in drug development programs and functional characterization of novel inhibitors of GABA transport.
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Affiliation(s)
- Bolette Christiansen
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, DK-2100 Copenhagen, Denmark
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Abstract
This review considers how recent advances in the physiology of ion channels and other potential molecular targets, in conjunction with new information on the genetics of idiopathic epilepsies, can be applied to the search for improved antiepileptic drugs (AEDs). Marketed AEDs predominantly target voltage-gated cation channels (the alpha subunits of voltage-gated Na+ channels and also T-type voltage-gated Ca2+ channels) or influence GABA-mediated inhibition. Recently, alpha2-delta voltage-gated Ca2+ channel subunits and the SV2A synaptic vesicle protein have been recognized as likely targets. Genetic studies of familial idiopathic epilepsies have identified numerous genes associated with diverse epilepsy syndromes, including genes encoding Na+ channels and GABA(A) receptors, which are known AED targets. A strategy based on genes associated with epilepsy in animal models and humans suggests other potential AED targets, including various voltage-gated Ca2+ channel subunits and auxiliary proteins, A- or M-type voltage-gated K+ channels, and ionotropic glutamate receptors. Recent progress in ion channel research brought about by molecular cloning of the channel subunit proteins and studies in epilepsy models suggest additional targets, including G-protein-coupled receptors, such as GABA(B) and metabotropic glutamate receptors; hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channel subunits, responsible for hyperpolarization-activated current Ih; connexins, which make up gap junctions; and neurotransmitter transporters, particularly plasma membrane and vesicular transporters for GABA and glutamate. New information from the structural characterization of ion channels, along with better understanding of ion channel function, may allow for more selective targeting. For example, Na+ channels underlying persistent Na+ currents or GABA(A) receptor isoforms responsible for tonic (extrasynaptic) currents represent attractive targets. The growing understanding of the pathophysiology of epilepsy and the structural and functional characterization of the molecular targets provide many opportunities to create improved epilepsy therapies.
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Affiliation(s)
- Brian S Meldrum
- Centre for Neuroscience, Division of Biomedical and Health Sciences, School of Medicine, Kings College, London, United Kingdom
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Schousboe A, Waagepetersen HS. GABA: Homeostatic and pharmacological aspects. PROGRESS IN BRAIN RESEARCH 2007; 160:9-19. [PMID: 17499106 DOI: 10.1016/s0079-6123(06)60002-2] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The central nervous system (CNS) operates by a fine-tuned balance between excitatory and inhibitory signalling. In this context, the inhibitory neurotransmission may be of particular interest as it has been suggested that such neuronal pathways may constitute 'command pathways' and the principle of 'dis-inhibition' leading ultimately to excitation may play a fundamental role (Roberts, E. (1974). Adv. Neurol., 5: 127-143). The neurotransmitter responsible for this signalling is gamma-aminobutyrate (GABA) which was first discovered in the CNS as a curious amino acid (Roberts, E., Frankel, S. (1950). J. Biol. Chem., 187: 55-63) and later proposed as an inhibitory neurotransmitter (Curtis, D.R., Watkins, J.C. (1960). J. Neurochem., 6: 117-141; Krnjevic, K., Schwartz, S. (1967). Exp. Brain Res., 3: 320-336). The present review will describe aspects of GABAergic neurotransmission related to homeostatic mechanisms such as biosynthesis, metabolism, release and inactivation. Additionally, pharmacological and therapeutic aspects of this will be discussed.
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Affiliation(s)
- Arne Schousboe
- Department of Pharmacology and Pharmacotherapy, The Faculty of Pharmaceutical Sciences, University of Copenhagen, DK-2100 Copenhagen, Denmark.
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