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Koniuszewski F, Vogel FD, Dajić I, Seidel T, Kunze M, Willeit M, Ernst M. Navigating the complex landscape of benzodiazepine- and Z-drug diversity: insights from comprehensive FDA adverse event reporting system analysis and beyond. Front Psychiatry 2023; 14:1188101. [PMID: 37457785 PMCID: PMC10345211 DOI: 10.3389/fpsyt.2023.1188101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Accepted: 06/05/2023] [Indexed: 07/18/2023] Open
Abstract
Introduction Medications which target benzodiazepine (BZD) binding sites of GABAA receptors (GABAARs) have been in widespread use since the nineteen-sixties. They carry labels as anxiolytics, hypnotics or antiepileptics. All benzodiazepines and several nonbenzodiazepine Z-drugs share high affinity binding sites on certain subtypes of GABAA receptors, from which they can be displaced by the clinically used antagonist flumazenil. Additional binding sites exist and overlap in part with sites used by some general anaesthetics and barbiturates. Despite substantial preclinical efforts, it remains unclear which receptor subtypes and ligand features mediate individual drug effects. There is a paucity of literature comparing clinically observed adverse effect liabilities across substances in methodologically coherent ways. Methods In order to examine heterogeneity in clinical outcome, we screened the publicly available U.S. FDA adverse event reporting system (FAERS) database for reports of individual compounds and analyzed them for each sex individually with the use of disproportionality analysis. The complementary use of physico-chemical descriptors provides a molecular basis for the analysis of clinical observations of wanted and unwanted drug effects. Results and Discussion We found a multifaceted FAERS picture, and suggest that more thorough clinical and pharmacoepidemiologic investigations of the heterogenous side effect profiles for benzodiazepines and Z-drugs are needed. This may lead to more differentiated safety profiles and prescription practice for particular compounds, which in turn could potentially ease side effect burden in everyday clinical practice considerably. From both preclinical literature and pharmacovigilance data, there is converging evidence that this very large class of psychoactive molecules displays a broad range of distinctive unwanted effect profiles - too broad to be explained by the four canonical, so-called "diazepam-sensitive high-affinity interaction sites". The substance-specific signatures of compound effects may partly be mediated by phenomena such as occupancy of additional binding sites, and/or synergistic interactions with endogenous substances like steroids and endocannabinoids. These in turn drive the wanted and unwanted effects and sex differences of individual compounds.
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Affiliation(s)
- Filip Koniuszewski
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Florian D. Vogel
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Irena Dajić
- Department of Psychiatry and Psychotherapy, Medical University of Vienna, Vienna, Austria
| | - Thomas Seidel
- Department of Pharmaceutical Sciences, University of Vienna, Vienna, Austria
| | - Markus Kunze
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Matthäus Willeit
- Department of Psychiatry and Psychotherapy, Medical University of Vienna, Vienna, Austria
| | - Margot Ernst
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
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2
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Shu HJ, Lu X, Bracamontes J, Steinbach JH, Zorumski CF, Mennerick S. Pharmacological and Biophysical Characteristics of Picrotoxin-Resistant, δSubunit-Containing GABA A Receptors. Front Synaptic Neurosci 2021; 13:763411. [PMID: 34867260 PMCID: PMC8636460 DOI: 10.3389/fnsyn.2021.763411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Accepted: 10/26/2021] [Indexed: 11/21/2022] Open
Abstract
GABAA receptors (GABAARs) play a crucial role in inhibition in the central nervous system. GABAARs containing the δ subunit mediate tonic inhibition, have distinctive pharmacological properties and are associated with disorders of the nervous system. To explore this receptor sub-class, we recently developed mice with δ-containing receptors rendered resistant to the common non-competitive antagonist picrotoxin (PTX). Resistance was achieved with a knock-in point mutation (T269Y; T6’Y) in the mouse genome. Here we characterize pharmacological and biophysical features of GABAARs containing the mutated subunit to contextualize results from the KI mice. Recombinant receptors containing δ T6’Y plus WT α4 and WT β2 subunits exhibited 3-fold lower EC50 values for GABA but not THIP. GABA EC50 values in native receptors containing the mutated subunit were in the low micromolar range, in contrast with some published results that have suggested nM sensitivity of recombinant receptors. Rectification properties of δ-containing GABAARs were similar to γ2-containing receptors. Receptors containing δ T6’Y had marginally weaker sensitivity to positive allosteric modulators, likely a secondary consequence of differing GABA sensitivity. Overexpression of δT6’Y in neurons resulted in robust PTX-insensitive IPSCs, suggesting that δ-containing receptors are readily recruited by synaptically released GABA. Overall, our results give context to the use of δ receptors with the T6’Y mutation to explore the roles of δ-containing receptors in inhibition.
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Affiliation(s)
- Hong-Jin Shu
- Department of Psychiatry, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States
| | - Xinguo Lu
- Department of Psychiatry, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States
| | - John Bracamontes
- Department of Anesthesiology, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States
| | - Joe Henry Steinbach
- Department of Anesthesiology, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States
| | - Charles F Zorumski
- Department of Psychiatry, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States.,Department of Neuroscience, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States
| | - Steven Mennerick
- Department of Psychiatry, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States.,Department of Neuroscience, Washington University in St. Louis, School of Medicine, St. Louis, MO, United States
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3
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Sexton CA, Penzinger R, Mortensen M, Bright DP, Smart TG. Structural determinants and regulation of spontaneous activity in GABA A receptors. Nat Commun 2021; 12:5457. [PMID: 34526505 PMCID: PMC8443696 DOI: 10.1038/s41467-021-25633-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Accepted: 08/24/2021] [Indexed: 11/25/2022] Open
Abstract
GABAA receptors are vital for controlling neuronal excitability and can display significant levels of constitutive activity that contributes to tonic inhibition. However, the mechanisms underlying spontaneity are poorly understood. Here we demonstrate a strict requirement for β3 subunit incorporation into receptors for spontaneous gating, facilitated by α4, α6 and δ subunits. The crucial molecular determinant involves four amino acids (GKER) in the β3 subunit's extracellular domain, which interacts with adjacent receptor subunits to promote transition to activated, open channel conformations. Spontaneous activity is further regulated by β3 subunit phosphorylation and by allosteric modulators including neurosteroids and benzodiazepines. Promoting spontaneous activity reduced neuronal excitability, indicating that spontaneous currents will alter neural network activity. This study demonstrates how regional diversity in GABAA receptor isoform, protein kinase activity, and neurosteroid levels, can impact on tonic inhibition through the modulation of spontaneous GABAA receptor gating.
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Affiliation(s)
- Craig A Sexton
- Department of Neuroscience, Physiology & Pharmacology, UCL, London, UK
| | - Reka Penzinger
- Department of Neuroscience, Physiology & Pharmacology, UCL, London, UK
| | - Martin Mortensen
- Department of Neuroscience, Physiology & Pharmacology, UCL, London, UK
| | - Damian P Bright
- Department of Neuroscience, Physiology & Pharmacology, UCL, London, UK
| | - Trevor G Smart
- Department of Neuroscience, Physiology & Pharmacology, UCL, London, UK.
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4
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Luo Y, Kusay AS, Jiang T, Chebib M, Balle T. Delta-containing GABA A receptors in pain management: Promising targets for novel analgesics. Neuropharmacology 2021; 195:108675. [PMID: 34153311 DOI: 10.1016/j.neuropharm.2021.108675] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2020] [Revised: 06/01/2021] [Accepted: 06/11/2021] [Indexed: 12/26/2022]
Abstract
Communication between nerve cells depends on the balance between excitatory and inhibitory circuits. GABA, the major inhibitory neurotransmitter, regulates this balance and insufficient GABAergic activity is associated with numerous neuropathological disorders including pain. Of the various GABAA receptor subtypes, the δ-containing receptors are particularly interesting drug targets in management of chronic pain. These receptors are pentameric ligand-gated ion channels composed of α, β and δ subunits and can be activated by ambient levels of GABA to generate tonic conductance. However, only a few ligands preferentially targeting δ-containing GABAA receptors have so far been identified, limiting both pharmacological understanding and drug-discovery efforts, and more importantly, understanding of how they affect pain pathways. Here, we systemically review and discuss the known drugs and ligands with analgesic potential targeting δ-containing GABAA receptors and further integrate the biochemical nature of the receptors with clinical perspectives in pain that might generate interest among researchers and clinical physicians to encourage analgesic discovery efforts leading to more efficient therapies.
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Affiliation(s)
- Yujia Luo
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia; Brain and Mind Centre, The University of Sydney, Camperdown, NSW, 2050, Australia
| | - Ali Saad Kusay
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia; Brain and Mind Centre, The University of Sydney, Camperdown, NSW, 2050, Australia
| | - Tian Jiang
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia; Brain and Mind Centre, The University of Sydney, Camperdown, NSW, 2050, Australia
| | - Mary Chebib
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia; Brain and Mind Centre, The University of Sydney, Camperdown, NSW, 2050, Australia
| | - Thomas Balle
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia; Brain and Mind Centre, The University of Sydney, Camperdown, NSW, 2050, Australia.
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5
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Falk-Petersen CB, Rostrup F, Löffler R, Buchleithner S, Harpsøe K, Gloriam DE, Frølund B, Wellendorph P. Molecular Determinants Underlying Delta Selective Compound 2 Activity at δ-Containing GABA A Receptors. Mol Pharmacol 2021; 100:46-56. [PMID: 33990405 DOI: 10.1124/molpharm.121.000266] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Accepted: 04/22/2021] [Indexed: 11/22/2022] Open
Abstract
Delta selective compound 2 (DS2; 4-chloro-N-[2-(2-thienyl)imidazo[1,2-a]pyridin-3-yl]benzamide) is one of the most widely used tools to study selective actions mediated by δ-subunit-containing GABAA receptors. DS2 was discovered over 10 years ago, but despite great efforts, the precise molecular site of action has remained elusive. Using a combination of computational modeling, site-directed mutagenesis, and cell-based pharmacological assays, we probed three potential binding sites for DS2 and analogs at α 4 β 1 δ receptors: an α 4 (+) δ (-) interface site in the extracellular domain (ECD), equivalent to the diazepam binding site in αβγ 2 receptors, and two sites in the transmembrane domain (TMD) - one in the α 4 (+) β 1 (-) and one in the α 4 (-) β 1 (+) interface, with the α 4 (-) β 1 (+) site corresponding to the binding site for etomidate and a recently disclosed low-affinity binding site for diazepam. We show that mutations in the ECD site did not abrogate DS2 modulation. However, mutations in the TMD α 4 (+) β 1 (-) interface, either α 4(S303L) of the α 4 (+) side or β 1(I289Q) of the β 1 (-) side, convincingly disrupted the positive allosteric modulation by DS2. This was consistently demonstrated both in an assay measuring membrane potential changes and by whole-cell patch-clamp electrophysiology and rationalized by docking studies. Importantly, general sensitivity to modulators was not compromised in the mutated receptors. This study sheds important light on the long-sought molecular recognition site for DS2, refutes the misconception that the selectivity of DS2 for δ-containing receptors is caused by a direct interaction with the δ-subunit, and instead points toward a functional selectivity of DS2 and its analogs via a surprisingly well conserved binding pocket in the TMD. SIGNIFICANCE STATEMENT: δ-Containing GABAA receptors represent potential drug targets for the treatment of several neurological conditions with aberrant tonic inhibition, yet no drugs are currently in clinical use. With the identification of the molecular determinants responsible for positive modulation by the known compound delta selective compound 2, the ground is laid for design of ligands that selectively target δ-containing GABAA receptor subtypes, for better understanding of tonic inhibition, and ultimately, for rational development of novel drugs.
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Affiliation(s)
- Christina B Falk-Petersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Frederik Rostrup
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Rebekka Löffler
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Stine Buchleithner
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Kasper Harpsøe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - David E Gloriam
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Bente Frølund
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Petrine Wellendorph
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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6
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Liao VWY, Chebib M, Ahring PK. Efficient expression of concatenated α1β2δ and α1β3δ GABA A receptors, their pharmacology and stoichiometry. Br J Pharmacol 2021; 178:1556-1573. [PMID: 33491192 DOI: 10.1111/bph.15380] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Revised: 12/28/2020] [Accepted: 01/11/2021] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE GABAA receptors containing δ-subunits are notorious for being difficult to study in vitro due to heterogeneity of expressed receptor populations and low GABA-evoked current amplitudes. Thus, there are some published misconceptions and contradictory conclusions made regarding the pharmacology and stoichiometry of δ-containing receptors. The aim of this study was to obtain robust homogenous expression of α1βδ receptors for in-depth investigation. EXPERIMENTAL APPROACH Novel δ-containing pentameric concatenated constructs were designed. The resulting α1β2δ and α1β3δ GABAA receptor concatemers were investigated by two-electrode voltage-clamp electrophysiology using Xenopus laevis oocytes. KEY RESULTS First, while homogenous α1βδ GABAA receptor pools could not be obtained by manipulating the ratio of injected cRNAs of free α1, β2/3, and δ subunits, concatenated pentameric α1β2δ and α1β3δ constructs resulted in robust expression levels of concatemers. Second, by using optimised constructs that give unidirectional assembly of concatemers, we found that the δ subunit cannot directly participate in GABA binding and receptor activation. Hence, functional δ-containing receptors are likely to all have a conventional 2α:2β:1δ stoichiometry arranged as βαβαδ when viewed counterclockwise from the extracellular side. Third, α1β2/3δ receptors were found to express efficiently in X. laevis oocytes but have a low estimated open probability of ~0.5% upon GABA activation. Because of this, these receptors are uniquely susceptible to positive allosteric modulation by, for example, neurosteroids. CONCLUSION AND IMPLICATIONS Our data answer important outstanding questions regarding the pharmacology and stoichiometry of α1δ-containing GABAA receptors and pave the way for future analysis and drug discovery efforts.
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Affiliation(s)
- Vivian Wan Yu Liao
- Brain and Mind Centre, Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
| | - Mary Chebib
- Brain and Mind Centre, Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
| | - Philip Kiaer Ahring
- Brain and Mind Centre, Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
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7
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Vega Alanis BA, Iorio MT, Silva LL, Bampali K, Ernst M, Schnürch M, Mihovilovic MD. Allosteric GABA A Receptor Modulators-A Review on the Most Recent Heterocyclic Chemotypes and Their Synthetic Accessibility. Molecules 2020; 25:E999. [PMID: 32102309 PMCID: PMC7070463 DOI: 10.3390/molecules25040999] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 02/18/2020] [Accepted: 02/19/2020] [Indexed: 11/17/2022] Open
Abstract
GABAA receptor modulators are structurally almost as diverse as their target protein. A plethora of heterocyclic scaffolds has been described as modulating this extremely important receptor family. Some made it into clinical trials and, even on the market, some were dismissed. This review focuses on the synthetic accessibility and potential for library synthesis of GABAA receptor modulators containing at least one heterocyclic scaffold, which were disclosed within the last 10 years.
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Affiliation(s)
- Blanca Angelica Vega Alanis
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/193, 1060 Vienna, Austria; (B.A.V.A.); (M.T.I.); (M.D.M.)
| | - Maria Teresa Iorio
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/193, 1060 Vienna, Austria; (B.A.V.A.); (M.T.I.); (M.D.M.)
| | - Luca L. Silva
- Department of Anesthesiology and Intensive Care Medicine, Charité–Universitätsmedizin, Charitéplatz 1, 10117 Berlin, Germany;
| | - Konstantina Bampali
- Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Spitalgasse 4, 1090 Vienna, Austria;
| | - Margot Ernst
- Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Spitalgasse 4, 1090 Vienna, Austria;
| | - Michael Schnürch
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/193, 1060 Vienna, Austria; (B.A.V.A.); (M.T.I.); (M.D.M.)
| | - Marko D. Mihovilovic
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/193, 1060 Vienna, Austria; (B.A.V.A.); (M.T.I.); (M.D.M.)
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8
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Kent DE, Savechenkov PY, Bruzik KS, Miller KW. Binding site location on GABA A receptors determines whether mixtures of intravenous general anaesthetics interact synergistically or additively in vivo. Br J Pharmacol 2019; 176:4760-4772. [PMID: 31454409 DOI: 10.1111/bph.14843] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 07/24/2019] [Accepted: 08/14/2019] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND AND PURPOSE General anaesthetics can act on synaptic GABAA receptors by binding to one of three classes of general anaesthetic sites. Canonical drugs that bind selectively to only one class of site are etomidate, alphaxalone, and the mephobarbital derivative, R-mTFD-MPAB. We tested the hypothesis that the general anaesthetic potencies of mixtures of such site-selective agents binding to the same or to different sites would combine additively or synergistically respectively. EXPERIMENTAL APPROACH The potency of general anaesthetics individually or in combinations to cause loss of righting reflexes in tadpoles was determined, and the results were analysed using isobolographic methods. KEY RESULTS The potencies of combinations of two or three site-selective anaesthetics that all acted on a single class of site were strictly additive, regardless of which single site was involved. Combinations of two or three site-selective anaesthetics that all bound selectively to different sites always interacted synergistically. The strength of the synergy increased with the number of separate sites involved such that the percentage of each agent's EC50 required to cause anaesthesia was just 35% and 14% for two or three sites respectively. Propofol, which binds non-selectively to the etomidate and R-mTFD-MPAB sites, interacted synergistically with each of these agents. CONCLUSIONS AND IMPLICATIONS The established pharmacology of the three anaesthetic binding sites on synaptic GABAA receptors was sufficient to predict whether a mixture of anaesthetics interacted additively or synergistically to cause loss of righting reflexes in vivo. The principles established here have implications for clinical practice.
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Affiliation(s)
- Daniel E Kent
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Department of Anaesthesia, Harvard Medical School, Boston, Massachusetts.,Department of Health Sciences, Northeastern University, Boston, Massachusetts
| | | | - Karol S Bruzik
- Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois
| | - Keith W Miller
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Department of Anaesthesia, Harvard Medical School, Boston, Massachusetts
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9
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Pierce SR, Senneff TC, Germann AL, Akk G. Steady-state activation of the high-affinity isoform of the α4β2δ GABA A receptor. Sci Rep 2019; 9:15997. [PMID: 31690811 PMCID: PMC6831628 DOI: 10.1038/s41598-019-52573-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Accepted: 10/18/2019] [Indexed: 12/18/2022] Open
Abstract
Activation of GABAA receptors consisting of α4, β2 (or β3), and δ subunits is a major contributor to tonic inhibition in several brain regions. The goal of this study was to analyze the function of the α4β2δ receptor in the presence of GABA and other endogenous and clinical activators and modulators under steady-state conditions. We show that the receptor has a high constitutive open probability (~0.1), but is only weakly activated by GABA that has a maximal peak open probability (POpen,peak) of 0.4, taurine (maximal POpen,peak = 0.4), or the endogenous steroid allopregnanolone (maximal POpen,peak = 0.2). The intravenous anesthetic propofol is a full agonist (maximal POpen,peak = 0.99). Analysis of currents using a cyclic three-state Resting-Active-Desensitized model indicates that the maximal steady-state open probability of the α4β2δ receptor is ~0.45. Steady-state open probability in the presence of combinations of GABA, taurine, propofol, allopregnanolone and/or the inhibitory steroid pregnenolone sulfate closely matched predicted open probability calculated assuming energetic additivity. The results suggest that the receptor is active in the presence of physiological concentrations of GABA and taurine, but, surprisingly, that receptor activity is only weakly potentiated by propofol.
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Affiliation(s)
- Spencer R Pierce
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Thomas C Senneff
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Allison L Germann
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Gustav Akk
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, 63110, USA. .,The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, 63110, USA.
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10
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Sieghart W, Savić MM. International Union of Basic and Clinical Pharmacology. CVI: GABAA Receptor Subtype- and Function-selective Ligands: Key Issues in Translation to Humans. Pharmacol Rev 2018; 70:836-878. [DOI: 10.1124/pr.117.014449] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
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11
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Yayeh T, Leem YH, Kim KM, Jung JC, Schwarz J, Oh KW, Oh S. Administration of Alpha s1-Casein Hydrolysate Increases Sleep and Modulates GABA A Receptor Subunit Expression. Biomol Ther (Seoul) 2018; 26:268-273. [PMID: 29316237 PMCID: PMC5933893 DOI: 10.4062/biomolther.2017.083] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Revised: 08/29/2017] [Accepted: 09/19/2017] [Indexed: 12/28/2022] Open
Abstract
Sleep is the most basic and essential physiological requirement for mental health, and sleep disorders pose potential risks of metabolic and neurodegenerative diseases. Tryptic hydrolysate of αS1-casein (αS1-CH) has been shown to possess stress relieving and sleep promoting effects. However, the differential effects of αS1-CH on electroencephalographic wave patterns and its effects on the protein levels of γ-aminobutyric acid A (GABAA) receptor subtypes in hypothalamic neurons are not well understood. We found αS1-CH (120, 240 mg/kg) increased sleep duration in mice and reduced sleep-wake cycle numbers in rats. While αS1-CH (300 mg/kg) increased total sleeping time in rats, it significantly decreased wakefulness. In addition, electroencephalographic theta (θ) power densities were increased whereas alpha (α) power densities were decreased by αS1-CH (300 mg/kg) during sleep-wake cycles. Furthermore, protein expressions of GABAA receptor β1 subtypes were elevated in rat hypothalamus by αS1-CH. These results suggest αS1-CH, through GABAA receptor modulation, might be useful for treating sleep disorders.
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Affiliation(s)
- Taddesse Yayeh
- Department of Molecular Medicine and TIDRC, School of Medicine, Ewha Womans University, Seoul 07985, Republic of Korea
| | - Yea-Hyun Leem
- Department of Molecular Medicine and TIDRC, School of Medicine, Ewha Womans University, Seoul 07985, Republic of Korea
| | - Kyung-Mi Kim
- Life Science Research Institute, Novarex Co., Ltd, Ochang, Cheongwon 28126, Republic of Korea
| | - Jae-Chul Jung
- Life Science Research Institute, Novarex Co., Ltd, Ochang, Cheongwon 28126, Republic of Korea
| | | | - Ki-Wan Oh
- Department of Pharmacy, College of Pharmacy, Chungbuk National University, Cheongju 28160, Republic of Korea
| | - Seikwan Oh
- Department of Molecular Medicine and TIDRC, School of Medicine, Ewha Womans University, Seoul 07985, Republic of Korea
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12
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13
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Delineation of the functional properties and the mechanism of action of AA29504, an allosteric agonist and positive allosteric modulator of GABA A receptors. Biochem Pharmacol 2018; 150:305-319. [DOI: 10.1016/j.bcp.2018.02.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Accepted: 02/13/2018] [Indexed: 11/22/2022]
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14
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Milanos S, Kuenzel K, Gilbert DF, Janzen D, Sasi M, Buettner A, Frimurer TM, Villmann C. Structural changes at the myrtenol backbone reverse its positive allosteric potential into inhibitory GABAA receptor modulation. Biol Chem 2018; 399:549-563. [DOI: 10.1515/hsz-2017-0262] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Accepted: 01/24/2018] [Indexed: 02/07/2023]
Abstract
Abstract
GABAA receptors are ligand-gated anion channels that form pentameric arrangements of various subunits. Positive allosteric modulators of GABAA receptors have been reported as being isolated either from plants or synthesized analogs of known GABAA receptor targeting drugs. Recently, we identified monoterpenes, e.g. myrtenol as a positive allosteric modulator at α1β2 GABAA receptors. Here, along with pharmacophore-based virtual screening studies, we demonstrate that scaffold modifications of myrtenol resulted in the loss of modulatory activity. Two independent approaches, fluorescence-based compound analysis and electrophysiological recordings in whole-cell configurations were used for analysis of transfected cells. C-atoms 1 and 2 of the myrtenol backbone were identified as crucial to preserve positive allosteric potential. A modification at C-atom 2 and lack of the hydroxyl group at C-atom 1 exhibited significantly reduced GABAergic currents at α1β2, α1β2γ, α2β3, α2β3γ and α4β3δ receptors. This effect was independent of the γ2 subunit. A sub-screen with side chain length and volume differences at the C-atom 1 identified two compounds that inhibited GABAergic responses but without receptor subtype specificity. Our combined approach of pharmacophore-based virtual screening and functional readouts reveals that side chain modifications of the bridged six-membered ring structure of myrtenol are crucial for its modulatory potential at GABAA receptors.
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Affiliation(s)
- Sinem Milanos
- Institute for Clinical Neurobiology , Julius-Maximilians-Universität Würzburg , Versbacherstr. 5 , D-97078 Würzburg , Germany
- Department of Chemistry and Pharmacy, Food Chemistry, Emil-Fischer-Center , Friedrich-Alexander-Universität Erlangen-Nürnberg , D-90154 Erlangen , Germany
| | - Katharina Kuenzel
- Institute of Medical Biotechnology , Friedrich-Alexander-Universität Erlangen-Nürnberg , D-91052 Erlangen , Germany
| | - Daniel F. Gilbert
- Institute of Medical Biotechnology , Friedrich-Alexander-Universität Erlangen-Nürnberg , D-91052 Erlangen , Germany
| | - Dieter Janzen
- Institute for Clinical Neurobiology , Julius-Maximilians-Universität Würzburg , Versbacherstr. 5 , D-97078 Würzburg , Germany
| | - Manju Sasi
- Institute for Clinical Neurobiology , Julius-Maximilians-Universität Würzburg , Versbacherstr. 5 , D-97078 Würzburg , Germany
| | - Andrea Buettner
- Department of Chemistry and Pharmacy, Food Chemistry, Emil-Fischer-Center , Friedrich-Alexander-Universität Erlangen-Nürnberg , D-90154 Erlangen , Germany
- Department of Sensory Analytics , Fraunhofer-Institute for Process Engineering and Packaging , D-85354 Freising , Germany
| | - Thomas M. Frimurer
- Section for Metabolic Receptology, Novo Nordisk Foundation Center for Basic Metabolic Research , University of Copenhagen , Copenhagen , Denmark
| | - Carmen Villmann
- Institute for Clinical Neurobiology , Julius-Maximilians-Universität Würzburg , Versbacherstr. 5 , D-97078 Würzburg , Germany
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15
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Zhou X, Desai R, Zhang Y, Stec WJ, Miller KW, Jounaidi Y. High-level production and purification in a functional state of an extrasynaptic gamma-aminobutyric acid type A receptor containing α4β3δ subunits. PLoS One 2018; 13:e0191583. [PMID: 29352320 PMCID: PMC5774841 DOI: 10.1371/journal.pone.0191583] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Accepted: 01/08/2018] [Indexed: 11/18/2022] Open
Abstract
The inhibitory γ-aminobutyric acid type A receptors are implicated in numerous physiological processes, including cognition and inhibition of neurotransmission, rendering them important molecular targets for many classes of drugs. Functionally, the entire GABAAR family of receptors can be subdivided into phasic, fast acting synaptic receptors, composed of α-, β- and γ-subunits, and tonic extrasynaptic receptors, many of which contain the δ-subunit in addition to α- and β-subunits. Whereas the subunit arrangement of the former group is agreed upon, that of the αβδ GABAARs remains unresolved by electrophysiological and pharmacological research. To resolve such issues will require biophysical techniques that demand quantities of receptor that have been previously unavailable. Therefore, we have engineered a stable cell line with tetracycline inducible expression of human α4-, β3- and N-terminally Flag-tagged δ-subunits. This cell line achieved a specific activity between 15 and 20 pmol [3H]muscimol sites/mg of membrane protein, making it possible to obtain 1 nmole of purified α4β3δ GABAAR from sixty 15-cm culture dishes. When induced, these cells exhibited agonist-induced currents with characteristics comparable to those previously reported for this receptor and a pharmacology that included strong modulation by etomidate and the δ-subunit-specific ligand, DS2. Immunoaffinity purification and reconstitution in CHAPS/asolectin micelles resulted in the retention of equilibrium allosteric interactions between the separate agonist, anesthetic and DS2 sites. Moreover, all three subunits retained glycosylation. The establishment of this well-characterized cell line will allow molecular level studies of tonic receptors to be undertaken.
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Affiliation(s)
- Xiaojuan Zhou
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Rooma Desai
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Yinghui Zhang
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Wojciech J. Stec
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Keith W. Miller
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
- * E-mail:
| | - Youssef Jounaidi
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
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16
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Feng HJ, Forman SA. Comparison of αβδ and αβγ GABA A receptors: Allosteric modulation and identification of subunit arrangement by site-selective general anesthetics. Pharmacol Res 2017; 133:289-300. [PMID: 29294355 DOI: 10.1016/j.phrs.2017.12.031] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 12/28/2017] [Accepted: 12/29/2017] [Indexed: 12/27/2022]
Abstract
GABAA receptors play a dominant role in mediating inhibition in the mature mammalian brain, and defects of GABAergic neurotransmission contribute to the pathogenesis of a variety of neurological and psychiatric disorders. Two types of GABAergic inhibition have been described: αβγ receptors mediate phasic inhibition in response to transient high-concentrations of synaptic GABA release, and αβδ receptors produce tonic inhibitory currents activated by low-concentration extrasynaptic GABA. Both αβδ and αβγ receptors are important targets for general anesthetics, which induce apparently different changes both in GABA-dependent receptor activation and in desensitization in currents mediated by αβγ vs. αβδ receptors. Many of these differences are explained by correcting for the high agonist efficacy of GABA at most αβγ receptors vs. much lower efficacy at αβδ receptors. The stoichiometry and subunit arrangement of recombinant αβγ receptors are well established as β-α-γ-β-α, while those of αβδ receptors remain controversial. Importantly, some potent general anesthetics selectively bind in transmembrane inter-subunit pockets of αβγ receptors: etomidate acts at β+/α- interfaces, and the barbiturate R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid (R-mTFD-MPAB) acts at α+/β- and γ+/β- interfaces. Thus, these drugs are useful as structural probes in αβδ receptors formed from free subunits or concatenated subunit assemblies designed to constrain subunit arrangement. Although a definite conclusion cannot be drawn, studies using etomidate and R-mTFD-MPAB support the idea that recombinant α1β3δ receptors may share stoichiometry and subunit arrangement with α1β3γ2 receptors.
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Affiliation(s)
- Hua-Jun Feng
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, and Department of Anesthesia, Harvard Medical School, Boston, MA 02114, USA.
| | - Stuart A Forman
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, and Department of Anesthesia, Harvard Medical School, Boston, MA 02114, USA.
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17
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Fedotova J, Kubatka P, Büsselberg D, Shleikin AG, Caprnda M, Dragasek J, Rodrigo L, Pohanka M, Gasparova I, Nosal V, Opatrilova R, Qaradakhi T, Zulli A, Kruzliak P. Therapeutical strategies for anxiety and anxiety-like disorders using plant-derived natural compounds and plant extracts. Biomed Pharmacother 2017; 95:437-446. [PMID: 28863384 DOI: 10.1016/j.biopha.2017.08.107] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Revised: 08/13/2017] [Accepted: 08/23/2017] [Indexed: 01/20/2023] Open
Abstract
Anxiety and anxiety-like disorders describe many mental disorders, yet fear is a common overwhelming symptom often leading to depression. Currently two basic strategies are discussed to treat anxiety: pharmacotherapy or psychotherapy. In the pharmacotherapeutical clinical approach, several conventional synthetic anxiolytic drugs are being used with several adverse effects. Therefore, studies to find suitable safe medicines from natural sources are being sought by researchers. The results of a plethora experimental studies demonstrated that dietary phytochemicals like alkaloids, terpenes, flavonoids, phenolic acids, lignans, cinnamates, and saponins or various plant extracts with the mixture of different phytochemicals possess anxiolytic effects in a wide range of animal models of anxiety. The involved mechanisms of anxiolytics action include interaction with γ-aminobutyric acid A receptors at benzodiazepine (BZD) and non-BZD sites with various affinity to different subunits, serotonergic 5-hydrodytryptamine receptors, noradrenergic and dopaminergic systems, glutamate receptors, and cannabinoid receptors. This review focuses on the use of both plant-derived natural compounds and plant extracts with anxiolytic effects, describing their biological effects and clinical application.
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Affiliation(s)
- Julia Fedotova
- Laboratory of Neuroendocrinology, I.P. Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg, Russia; Laboratory of Comparative Somnology and Neuroendocrinology, I.M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia; Department of Chemistry and Molecular Biology, ITMO University, St. Petersburg, Russia
| | - Peter Kubatka
- Department of Medical Biology, Jessenius Faculty of Medicine, Comenius University in Bratislava, Martin, Slovakia; Division of Oncology, Biomedical Center Martin, Jessenius Faculty of Medicine, Comenius University in Bratislava, Martin, Slovakia
| | | | - Alexander G Shleikin
- Department of Chemistry and Molecular Biology, ITMO University, St. Petersburg, Russia
| | - Martin Caprnda
- 2nd Department of Internal Medicine, Faculty of Medicine, Comenius University, Bratislava, Slovakia
| | - Jozef Dragasek
- Department of Psychiatry, Faculty of Medicine, Pavol Jozef Safarik University and University Hospital, Kosice, Slovakia
| | - Luis Rodrigo
- Faculty of Medicine, University of Oviedo, Central University Hospital of Asturia (HUCA), Oviedo, Spain
| | - Miroslav Pohanka
- Facultpy of Military Health Sciences, University of Defence, Hradec Kralove, Czech Republic
| | - Iveta Gasparova
- Institute of Biology, Genetics and Medical Genetics, Faculty of Medicine, Comenius University and University Hospital, Bratislava, Slovakia
| | - Vladimir Nosal
- Clinic of Neurology, Jessenius Faculty of Medicine, Comenius University and University Hospital in Martin, Martin, Slovakia
| | - Radka Opatrilova
- Department of Chemical Drugs, Faculty of Pharmacy, University of Veterinary and Pharmaceutical Sciences, Brno, Czech Republic
| | - Tawar Qaradakhi
- The Centre for Chronic Disease, College of Health & Biomedicine, Victoria University, Melbourne, Werribee Campus, Victoria, Australia
| | - Anthony Zulli
- The Centre for Chronic Disease, College of Health & Biomedicine, Victoria University, Melbourne, Werribee Campus, Victoria, Australia
| | - Peter Kruzliak
- Department of Chemical Drugs, Faculty of Pharmacy, University of Veterinary and Pharmaceutical Sciences, Brno, Czech Republic.
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18
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Martenson JS, Yamasaki T, Chaudhury NH, Albrecht D, Tomita S. Assembly rules for GABA A receptor complexes in the brain. eLife 2017; 6:27443. [PMID: 28816653 PMCID: PMC5577914 DOI: 10.7554/elife.27443] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Accepted: 08/04/2017] [Indexed: 12/15/2022] Open
Abstract
GABAA receptor (GABAAR) pentamers are assembled from a pool of 19 subunits, and variety in subunit combinations diversifies GABAAR functions to tune brain activity. Pentamers with distinct subunit compositions localize differentially at synaptic and non-synaptic sites to mediate phasic and tonic inhibition, respectively. Despite multitudes of theoretical permutations, limited subunit combinations have been identified in the brain. Currently, no molecular model exists for combinatorial GABAAR assembly in vivo. Here, we reveal assembly rules of native GABAAR complexes that explain GABAAR subunit subcellular distributions using mice and Xenopus laevis oocytes. First, α subunits possess intrinsic signals to segregate into distinct pentamers. Second, γ2 is essential for GABAAR assembly with Neuroligin-2 (NL2) and GARLHs, which localize GABAARs at synapses. Third, δ suppresses α6 synaptic localization by preventing assembly with GARLHs/NL2. These findings establish the first molecular model for combinatorial GABAAR assembly in vivo and reveal an assembly pathway regulating GABAAR synaptic localization.
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Affiliation(s)
- James S Martenson
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States.,Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, United States
| | - Tokiwa Yamasaki
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States.,Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, United States
| | - Nashid H Chaudhury
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States.,Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, United States
| | - David Albrecht
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States.,Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, United States
| | - Susumu Tomita
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States.,Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, United States
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19
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Baur R, Sigel E. Low Expression in Xenopus Oocytes and Unusual Functional Properties of α1β2γ2 GABAA Receptors with Non-Conventional Subunit Arrangement. PLoS One 2017; 12:e0170572. [PMID: 28114407 PMCID: PMC5256883 DOI: 10.1371/journal.pone.0170572] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Accepted: 01/07/2017] [Indexed: 11/25/2022] Open
Abstract
The major subunit isoform of GABAA receptors is α1β2γ2. The subunits are thought to surround an ion pore with the counterclockwise arrangement α1γ2β2α1β2 as seen from the outside of the neuron. These receptors have two agonist sites and one high affinity drug binding site specific for benzodiazepines. Recently, this receptor was postulated to assume alternative subunit stoichiometries and arrangements resulting in only one agonist site and one or even two sites for benzodiazepines. In order to force a defined subunit arrangement we expressed a combination of triple and dual concatenated subunits. Here we report that these unconventional receptors express only small current amplitudes in Xenopus oocytes. We determined agonist properties and modulation by diazepam of two of these receptors that resulted in currents large enough for a characterization, that is, β2-α1-γ2/α1-γ2 and β2-α1-γ2/β2-γ2. The first pentamer predicted to have two benzodiazepine binding sites shows similar response to diazepam as the standard receptor. As expected for both receptors with a single predicted agonist site the concentration response curves for GABA were characterized by a Hill coefficient < 1. β2-α1-γ2/β2-γ2 displayed a mM apparent GABA affinity for channel opening instead of the expected μM affinity. Based on their subunit and binding site stoichiometry, that contradicts all previous observations, their unusual functional properties and their very low expression levels in oocytes, we consider it unlikely that these unconventional receptors are expressed in neurons to an appreciable extent.
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Affiliation(s)
- Roland Baur
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - Erwin Sigel
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
- * E-mail:
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20
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Chua HC, Chebib M. GABA A Receptors and the Diversity in their Structure and Pharmacology. ADVANCES IN PHARMACOLOGY 2017; 79:1-34. [DOI: 10.1016/bs.apha.2017.03.003] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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21
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Maldifassi MC, Wongsamitkul N, Baur R, Sigel E. Xenopus Oocytes: Optimized Methods for Microinjection, Removal of Follicular Cell Layers, and Fast Solution Changes in Electrophysiological Experiments. J Vis Exp 2016. [PMID: 28117773 DOI: 10.3791/55034] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The Xenopus oocyte as a heterologous expression system for proteins, was first described by Gurdon et al.1 and has been widely used since its discovery (References 2 - 3, and references therein). A characteristic that makes the oocyte attractive for foreign channel expression is the poor abundance of endogenous ion channels4. This expression system has proven useful for the characterization of many proteins, among them ligand-gated ion channels. The expression of GABAA receptors in Xenopus oocytes and their functional characterization is described here, including the isolation of oocytes, microinjections with cRNA, the removal of follicular cell layers, and fast solution changes in electrophysiological experiments. The procedures were optimized in this laboratory5,6 and deviate from the ones routinely used7-9. Traditionally, denuded oocytes are prepared with a prolonged collagenase treatment of ovary lobes at RT, and these denuded oocytes are microinjected with mRNA. Using the optimized methods, diverse membrane proteins have been expressed and studied with this system, such as recombinant GABAA receptors10-12, human recombinant chloride channels13, Trypanosome potassium channels14, and a myo-inositol transporter15, 16. The methods detailed here may be applied to the expression of any protein of choice in Xenopus oocytes, and the rapid solution change can be used to study other ligand-gated ion channels.
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Affiliation(s)
| | - Nisa Wongsamitkul
- Institute of Biochemistry and Molecular Medicine, University of Bern
| | - Roland Baur
- Institute of Biochemistry and Molecular Medicine, University of Bern
| | - Erwin Sigel
- Institute of Biochemistry and Molecular Medicine, University of Bern;
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22
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Chiara DC, Jounaidi Y, Zhou X, Savechenkov PY, Bruzik KS, Miller KW, Cohen JB. General Anesthetic Binding Sites in Human α4β3δ γ-Aminobutyric Acid Type A Receptors (GABAARs). J Biol Chem 2016; 291:26529-26539. [PMID: 27821594 PMCID: PMC5159512 DOI: 10.1074/jbc.m116.753335] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Revised: 10/14/2016] [Indexed: 01/08/2023] Open
Abstract
Extrasynaptic γ-aminobutyric acid type A receptors (GABAARs),which contribute generalized inhibitory tone to the mammalian brain, are major targets for general anesthetics. To identify anesthetic binding sites in an extrasynaptic GABAAR, we photolabeled human α4β3δ GABAARs purified in detergent with [3H]azietomidate and a barbiturate, [3H]R-mTFD-MPAB, photoreactive anesthetics that bind with high selectivity to distinct but homologous intersubunit binding sites in the transmembrane domain of synaptic α1β3γ2 GABAARs. Based upon 3H incorporation into receptor subunits resolved by SDS-PAGE, there was etomidate-inhibitable labeling by [3H]azietomidate in the α4 and β3 subunits and barbiturate-inhibitable labeling by [3H]R-mTFD-MPAB in the β3 subunit. These sites did not bind the anesthetic steroid alphaxalone, which enhanced photolabeling, or DS-2, a δ subunit-selective positive allosteric modulator, which neither enhanced nor inhibited photolabeling. The amino acids labeled by [3H]azietomidate or [3H]R-mTFD-MPAB were identified by N-terminal sequencing of fragments isolated by HPLC fractionation of enzymatically digested subunits. No evidence was found for a δ subunit contribution to an anesthetic binding site. [3H]azietomidate photolabeling of β3Met-286 in βM3 and α4Met-269 in αM1 that was inhibited by etomidate but not by R-mTFD-MPAB established that etomidate binds to a site at the β3+-α4- interface equivalent to its site in α1β3γ2 GABAARs. [3H]Azietomidate and [3H]R-mTFD-MPAB photolabeling of β3Met-227 in βM1 established that these anesthetics also bind to a homologous site, most likely at the β3+-β3- interface, which suggests a subunit arrangement of β3α4β3δβ3.
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Affiliation(s)
| | - Youssef Jounaidi
- the Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts 02114, and
| | - Xiaojuan Zhou
- the Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts 02114, and
| | - Pavel Y Savechenkov
- the Department of Medicinal Chemistry and Pharmacognosy, University of Illinois, Chicago, Illinois 60612
| | - Karol S Bruzik
- the Department of Medicinal Chemistry and Pharmacognosy, University of Illinois, Chicago, Illinois 60612
| | - Keith W Miller
- the Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts 02114, and
- Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115
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