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Golub V, Ramakrishnan S, Reddy DS. Isobolographic analysis of adjunct antiseizure activity of the FDA-approved cannabidiol with neurosteroids and benzodiazepines in adult refractory focal onset epilepsy. Exp Neurol 2023; 360:114294. [PMID: 36493860 PMCID: PMC9884179 DOI: 10.1016/j.expneurol.2022.114294] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2022] [Revised: 11/27/2022] [Accepted: 12/04/2022] [Indexed: 12/12/2022]
Abstract
Epilepsy is a serious neurological disorder associated with recurrent and unpredictable seizures and extensive neuropsychiatric comorbidities. There is no cure for epilepsy, and over one third of epileptic patients have been diagnosed with drug-refractory epilepsy, indicating the critical need for novel antiseizure medications (ASMs). Cannabidiol (CBD) has been shown to decrease seizures in pediatric epilepsies, such as Dravet and Lennox-Gastaut syndromes; however, it has not been rigorously tested for adult seizures or in models of refractory focal epilepsy. Although the exact mechanism is unknown, it is likely to act in a way that is unique to certain GABA-A receptor-modulating drugs, such as neurosteroids and benzodiazepines. In this study, we sought to determine the adjunct antiseizure activity of a clinical CBD product in an adult 6-Hz model of focal refractory epilepsy. CBD was evaluated alone in both a dose-response and time-course manner and in an adjunct combination with two ASMs ganaxolone (neurosteroid) and midazolam (benzodiazepine) against 6-Hz-induced refractory focal onset, generalized seizures. In pharmacological studies, CBD produced dose-dependent protection against seizures (ED50, 53 mg/kg, i.p.) without any side effects. CBD significantly reduced both electrographic activity and behavioral ictal responses with no apparent sex differences. CBD was evaluated in an isobologram design in conjunction with ganaxolone or midazolam at three standard ratios (1:1, 1:3, 3:1). Isobolographic analysis shows the combination regimens of CBD + ganaxolone and CBD + midazolam exerted combination index of 0.313 and 0.164, indicating strong synergism for seizure protection, with little to no toxicity. Together, these results demonstrate the therapeutic potential of CBD monotherapy and as an adjunct therapy for adult focal refractory epilepsy in combination with GABAergic ASMs.
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Affiliation(s)
- Victoria Golub
- Department of Neuroscience and Experimental Therapeutics, School of Medicine, Texas A&M University Health Science Center, Bryan, TX, USA
| | - Sreevidhya Ramakrishnan
- Department of Neuroscience and Experimental Therapeutics, School of Medicine, Texas A&M University Health Science Center, Bryan, TX, USA; Texas A&M Health Institute of Pharmacology and Neurotherapeutics, Texas A&M University, Bryan, TX, USA
| | - Doodipala Samba Reddy
- Department of Neuroscience and Experimental Therapeutics, School of Medicine, Texas A&M University Health Science Center, Bryan, TX, USA; Texas A&M Health Institute of Pharmacology and Neurotherapeutics, Texas A&M University, Bryan, TX, USA.
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2
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Roy A, Geetha RV, Magesh A, Vijayaraghavan R, Ravichandran V. Autoinjector - A smart device for emergency cum personal therapy. Saudi Pharm J 2021; 29:1205-1215. [PMID: 34703373 PMCID: PMC8523323 DOI: 10.1016/j.jsps.2021.09.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Accepted: 09/11/2021] [Indexed: 12/18/2022] Open
Abstract
Autoinjectors are self-injectable devices; they are important class of medical devices which can deliver drugs through subcutaneous or intramuscular route. They enclose prefilled syringes or cartridges which are driven by a spring system. The major benefits of this device are easy self-administration, improved patient compliance, reduced anxiety, and dosage accuracy. Immediate treatment during emergency conditions such as anaphylaxis, migraine, and status epilepticus or for chronic conditions like psoriasis, diabetes, multiple sclerosis, and rheumatoid arthritis, Reformulation of first-generation biologics, technical advancements, innovative designs, patient compliance, overwhelming interest for self-administration all these made entry of more and more autoinjectors into use. In this review, intensive efforts have been made for exploring the different types of currently available autoinjectors for the management of emergency and chronic diseases.
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Affiliation(s)
- Anitha Roy
- Department of Pharmacology, Saveetha Dental College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India
| | - Royapuram Veeraragavan Geetha
- Department of Microbiology, Saveetha Dental College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India
| | - Anitha Magesh
- Department of Research and Development, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India
| | - Rajagopalan Vijayaraghavan
- Department of Research and Development, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India
| | - Veerasamy Ravichandran
- Pharmaceutical Chemistry Unit, Faculty of Pharmacy, AIMST University, Semeling-08100, Bedong, Malaysia.,Centre of Excellence for Biomaterials Engineering, AIMST University, Semeling-08100, Bedong, Malaysia.,Saveetha Dental College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India
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3
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Mundy PC, Pressly B, Carty DR, Yaghoobi B, Wulff H, Lein PJ. The efficacy of γ-aminobutyric acid type A receptor (GABA AR) subtype-selective positive allosteric modulators in blocking tetramethylenedisulfotetramine (TETS)-induced seizure-like behavior in larval zebrafish with minimal sedation. Toxicol Appl Pharmacol 2021; 426:115643. [PMID: 34265354 PMCID: PMC8514104 DOI: 10.1016/j.taap.2021.115643] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 07/02/2021] [Accepted: 07/05/2021] [Indexed: 11/19/2022]
Abstract
The chemical threat agent tetramethylenedisulfotetramine (TETS) is a γ-aminobutyric acid type A receptor (GABA AR) antagonist that causes life threatening seizures. Currently, there is no specific antidote for TETS intoxication. TETS-induced seizures are typically treated with benzodiazepines, which function as nonselective positive allosteric modulators (PAMs) of synaptic GABAARs. The major target of TETS was recently identified as the GABAAR α2β3γ2 subtype in electrophysiological studies using recombinantly expressed receptor combinations. Here, we tested whether these in vitro findings translate in vivo by comparing the efficacy of GABAAR subunit-selective PAMs in reducing TETS-induced seizure behavior in larval zebrafish. We tested PAMs targeting α1, α2, α2/3/5, α6, ß2/3, ß1/2/3, and δ subunits and compared their efficacy to the benzodiazepine midazolam (MDZ). The data demonstrate that α2- and α6-selective PAMs (SL-651,498 and SB-205384, respectively) were effective at mitigating TETS-induced seizure-like behavior. Combinations of SB-205384 and MDZ or SL-651,498 and 2–261 (ß2/3-selective) mitigated TETS-induced seizure-like behavior at concentrations that did not elicit sedating effects in a photomotor behavioral assay, whereas MDZ alone caused sedation at the concentration required to stop seizure behavior. Isobologram analyses suggested that SB-205384 and MDZ interacted in an antagonistic fashion, while the effects of SL-651,498 and 2–261 were additive. These results further elucidate the molecular mechanism by which TETS induces seizures and provide mechanistic insight regarding specific countermeasures against this chemical convulsant.
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Affiliation(s)
- Paige C Mundy
- Department of Molecular Biosciences, University of California, School of Veterinary Medicine, Davis, CA 95616, United States.
| | - Brandon Pressly
- Department of Pharmacology, University of California, School of Medicine, Davis, CA 95616, United States.
| | - Dennis R Carty
- Department of Molecular Biosciences, University of California, School of Veterinary Medicine, Davis, CA 95616, United States
| | - Bianca Yaghoobi
- Department of Molecular Biosciences, University of California, School of Veterinary Medicine, Davis, CA 95616, United States.
| | - Heike Wulff
- Department of Pharmacology, University of California, School of Medicine, Davis, CA 95616, United States.
| | - Pamela J Lein
- Department of Molecular Biosciences, University of California, School of Veterinary Medicine, Davis, CA 95616, United States.
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4
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Therapeutic effect of intravenous levetiracetam in status epilepticus: A meta-analysis and systematic review. Seizure 2020; 74:49-55. [DOI: 10.1016/j.seizure.2019.11.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2019] [Revised: 11/15/2019] [Accepted: 11/21/2019] [Indexed: 11/19/2022] Open
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5
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Abstract
Patients with prolonged seizures that do not respond to intravenous benzodiazepines and a second-line anticonvulsant suffer from refractory status epilepticus and those with seizures that do not respond to continuous intravenous anesthetic anticonvulsants suffer from super-refractory status epilepticus. Both conditions are associated with significant morbidity and mortality. A strict pharmacological treatment regimen is urgently required, but the level of evidence for the available drugs is very low. Refractory complex focal status epilepticus generally does not require anesthetics, but all intravenous non-anesthetizing anticonvulsants may be used. Most descriptive data are available for levetiracetam, phenytoin and valproate. Refractory generalized convulsive status epilepticus is a life-threatening emergency, and long-term clinical consequences are eminent. Administration of intravenous anesthetics is mandatory, and drugs acting at the inhibitory gamma-aminobutyric acid (GABA)A receptor such as midazolam, propofol and thiopental/pentobarbital are recommended without preference for one of those. One in five patients with anesthetic treatment does not respond and has super-refractory status epilepticus. With sustained seizure activity, excitatory N-methyl-d-aspartate (NMDA) receptors are increasingly expressed post-synaptically. Ketamine is an antagonist at this receptor and may prove efficient in some patients at later stages. Neurosteroids such as allopregnanolone increase sensitivity at GABAA receptors; a Phase 1/2 trial demonstrated safety and tolerability, but randomized controlled data failed to demonstrate efficacy. Adjunct ketogenic diet may contribute to termination of difficult-to-treat status epilepticus. Randomized controlled trials are needed to increase evidence for treatment of refractory and super-refractory status epilepticus, but there are multiple obstacles for realization. Hitherto, prospective multicenter registries for pharmacological treatment may help to improve our knowledge.
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Affiliation(s)
- Martin Holtkamp
- Epilepsy-Center Berlin-Brandenburg, Department of Neurology, Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Charitéplatz 1, 10117, Berlin, Germany.
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6
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Elgarf A, Siebert DCB, Steudle F, Draxler A, Li G, Huang S, Cook JM, Ernst M, Scholze P. Different Benzodiazepines Bind with Distinct Binding Modes to GABA A Receptors. ACS Chem Biol 2018; 13:2033-2039. [PMID: 29767950 PMCID: PMC6102643 DOI: 10.1021/acschembio.8b00144] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2018] [Accepted: 05/16/2018] [Indexed: 01/20/2023]
Abstract
Benzodiazepines are clinically relevant drugs that bind to GABAA neurotransmitter receptors at the α+/γ2- interfaces and thereby enhance GABA-induced chloride ion flux leading to neuronal hyperpolarization. However, the structural basis of benzodiazepine interactions with their high-affinity site at GABAA receptors is controversially debated in the literature, and in silico studies led to discrepant binding mode hypotheses. In this study, computational docking of diazepam into α+/γ2- homology models suggested that a chiral methyl group, which is known to promote preferred binding to α5-containing GABAA receptors (position 3 of the seven-membered diazepine ring), could possibly provide experimental evidence that supports or contradicts the proposed binding modes. Thus, we investigated three pairs of R and S isomers of structurally different chemotypes, namely, diazepam, imidazobenzodiazepine, and triazolam derivatives. We used radioligand displacement studies as well as two-electrode voltage clamp electrophysiology in α1β3γ2-, α2β3γ2-, α3β3γ2-, and α5β3γ2-containing GABAA receptors to determine the ligand binding and functional activity of the three chemotypes. Interestingly, both imidazobenzodiazepine isomers displayed comparable binding affinities, while for the other two chemotypes, a discrepancy in binding affinities of the different isomers was observed. Specifically, the R isomers displayed a loss of binding, whereas the S isomers remained active. These findings are in accordance with the results of our in silico studies suggesting the usage of a different binding mode of imidazobenzodiazepines compared to those of the other two tested chemotypes. Hence, we conclude that different chemically related benzodiazepine ligands interact via distinct binding modes rather than by using a common binding mode.
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Affiliation(s)
- Alshaimaa
A. Elgarf
- Department
of Pathobiology of the Nervous System, Center for Brain Research, Medical University of Vienna, 1090 Vienna, Austria
- Department
of Pharmacology and Therapeutics, Faculty of Medicine, Ain Shams University, Cairo, Egypt
| | | | - Friederike Steudle
- Department
of Pathobiology of the Nervous System, Center for Brain Research, Medical University of Vienna, 1090 Vienna, Austria
- Department
of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, 1090 Vienna, Austria
| | - Angelika Draxler
- Department
of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, 1090 Vienna, Austria
| | - Guanguan Li
- Department
of Chemistry and Biochemistry, University
of Wisconsin—Milwaukee, Milwaukee, Wisconsin 53211, United States
| | - Shengming Huang
- Department
of Chemistry and Biochemistry, University
of Wisconsin—Milwaukee, Milwaukee, Wisconsin 53211, United States
| | - James M. Cook
- Department
of Chemistry and Biochemistry, University
of Wisconsin—Milwaukee, Milwaukee, Wisconsin 53211, United States
| | - Margot Ernst
- Department
of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, 1090 Vienna, Austria
| | - Petra Scholze
- Department
of Pathobiology of the Nervous System, Center for Brain Research, Medical University of Vienna, 1090 Vienna, Austria
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7
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Siebert DCB, Bampali K, Puthenkalam R, Varagic Z, Sarto-Jackson I, Scholze P, Sieghart W, Mihovilovic MD, Schnürch M, Ernst M. Engineered Flumazenil Recognition Site Provides Mechanistic Insight Governing Benzodiazepine Modulation in GABA A Receptors. ACS Chem Biol 2018; 13:2040-2047. [PMID: 29989390 DOI: 10.1021/acschembio.8b00145] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The anxiolytic, anticonvulsant, muscle-relaxant, and sedative-hypnotic effects of benzodiazepine site ligands are mainly elicited by allosteric modulation of GABAA receptors via their extracellular αx+/γ2- ( x = 1, 2, 3, 5) interfaces. In addition, a low affinity binding site at the homologous α+/β- interfaces was reported for some benzodiazepine site ligands. Classical benzodiazepines and pyrazoloquinolinones have been used as molecular probes to develop structure-activity relationship models for benzodiazepine site activity. Considering all possible α+/β- and α+/γ- interfaces, such ligands potentially interact with as many as 36 interfaces, giving rise to undesired side effects. Understanding the binding modes at their binding sites will enable rational strategies to design ligands with desired selectivity profiles. Here, we compared benzodiazepine site ligand interactions in the high affinity α1+/γ2- site with the homologous α1+/β3- site using a successive mutational approach. We incorporated key amino acids known to contribute to high affinity benzodiazepine binding of the γ2- subunit into the β3- subunit, resulting in a quadruple mutant β3(4mut) with high affinity flumazenil (Ro 15-1788) binding properties. Intriguingly, some benzodiazepine site ligands displayed positive allosteric modulation in the tested recombinant α1β3(4mut) constructs while diazepam remained inactive. Consequently, we performed in silico molecular docking in the wildtype receptor and the quadruple mutant. The results led to the conclusion that different benzodiazepine site ligands seem to use distinct binding modes, rather than a common binding mode. These findings provide structural hypotheses for the future optimization of both benzodiazepine site ligands, and ligands that interact with the homologous α+/β- sites.
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Affiliation(s)
- David C. B. Siebert
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/163, 1060 Vienna, Austria
| | - Konstantina Bampali
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Roshan Puthenkalam
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Zdravko Varagic
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | | | - Petra Scholze
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University of Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Werner Sieghart
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Marko D. Mihovilovic
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/163, 1060 Vienna, Austria
| | - Michael Schnürch
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/163, 1060 Vienna, Austria
| | - Margot Ernst
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
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8
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Olsen RW. GABA A receptor: Positive and negative allosteric modulators. Neuropharmacology 2018; 136:10-22. [PMID: 29407219 PMCID: PMC6027637 DOI: 10.1016/j.neuropharm.2018.01.036] [Citation(s) in RCA: 178] [Impact Index Per Article: 29.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2017] [Revised: 01/23/2018] [Accepted: 01/25/2018] [Indexed: 12/11/2022]
Abstract
gamma-Aminobutyric acid (GABA)-mediated inhibitory neurotransmission and the gene products involved were discovered during the mid-twentieth century. Historically, myriad existing nervous system drugs act as positive and negative allosteric modulators of these proteins, making GABA a major component of modern neuropharmacology, and suggesting that many potential drugs will be found that share these targets. Although some of these drugs act on proteins involved in synthesis, degradation, and membrane transport of GABA, the GABA receptors Type A (GABAAR) and Type B (GABABR) are the targets of the great majority of GABAergic drugs. This discovery is due in no small part to Professor Norman Bowery. Whereas the topic of GABABR is appropriately emphasized in this special issue, Norman Bowery also made many insights into GABAAR pharmacology, the topic of this article. GABAAR are members of the ligand-gated ion channel receptor superfamily, a chloride channel family of a dozen or more heteropentameric subtypes containing 19 possible different subunits. These subtypes show different brain regional and subcellular localization, age-dependent expression, and potential for plastic changes with experience including drug exposure. Not only are GABAAR the targets of agonist depressants and antagonist convulsants, but most GABAAR drugs act at other (allosteric) binding sites on the GABAAR proteins. Some anxiolytic and sedative drugs, like benzodiazepine and related drugs, act on GABAAR subtype-dependent extracellular domain sites. General anesthetics including alcohols and neurosteroids act at GABAAR subunit-interface trans-membrane sites. Ethanol at high anesthetic doses acts on GABAAR subtype-dependent trans-membrane domain sites. Ethanol at low intoxicating doses acts at GABAAR subtype-dependent extracellular domain sites. Thus GABAAR subtypes possess pharmacologically specific receptor binding sites for a large group of different chemical classes of clinically important neuropharmacological agents. This article is part of the "Special Issue Dedicated to Norman G. Bowery".
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Affiliation(s)
- Richard W Olsen
- Department of Molecular & Medical Pharmacology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
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9
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Amundarain MJ, Viso JF, Zamarreño F, Giorgetti A, Costabel M. Orthosteric and benzodiazepine cavities of the α 1β 2γ 2 GABA A receptor: insights from experimentally validated in silico methods. J Biomol Struct Dyn 2018; 37:1597-1615. [PMID: 29633901 DOI: 10.1080/07391102.2018.1462733] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
γ-aminobutyric acid-type A (GABAA) receptors mediate fast synaptic inhibition in the central nervous system of mammals. They are modulated via several sites by numerous compounds, which include GABA, benzodiazepines, ethanol, neurosteroids and anaesthetics among others. Due to their potential as targets of novel drugs, a detailed knowledge of their structure-function relationships is needed. Here, we present the model of the α1β2γ2 subtype GABAA receptor in the APO state and in complex with selected ligands, including agonists, antagonists and allosteric modulators. The model is based on the crystallographic structure of the human β3 homopentamer GABAA receptor. The complexes were refined using atomistic molecular dynamics simulations. This allowed a broad description of the binding modes and the detection of important interactions in agreement with experimental information. From the best of our knowledge, this is the only model of the α1β2γ2 GABAA receptor that represents altogether the desensitized state of the channel and comprehensively describes the interactions of ligands of the orthosteric and benzodiazepines binding sites in agreement with the available experimental data. Furthermore, it is able to explain small differences regarding the binding of a variety of chemically divergent ligands. Finally, this new model may pave the way for the design of focused experimental studies that will allow a deeper description of the receptor.
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Affiliation(s)
- María Julia Amundarain
- a Departamento de Física, Instituto de Física del Sur (IFISUR) , Universidad Nacional del Sur (UNS), CONICET , Bahía Blanca , Argentina
| | - Juan Francisco Viso
- a Departamento de Física, Instituto de Física del Sur (IFISUR) , Universidad Nacional del Sur (UNS), CONICET , Bahía Blanca , Argentina
| | - Fernando Zamarreño
- a Departamento de Física, Instituto de Física del Sur (IFISUR) , Universidad Nacional del Sur (UNS), CONICET , Bahía Blanca , Argentina
| | - Alejandro Giorgetti
- b Faculty of Mathematical, Physical and Natural Sciences, Department of Biotechnology , University of Verona , Verona , Italy.,c Computational Biomedicine, Institute for Advanced Simulation IAS-5 and Computational Biomedicine, Institute of Neuroscience and Medicine INM-9 , Forschungszentrum Jülich , Jülich , Germany
| | - Marcelo Costabel
- a Departamento de Física, Instituto de Física del Sur (IFISUR) , Universidad Nacional del Sur (UNS), CONICET , Bahía Blanca , Argentina
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10
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Molecular tools for GABA A receptors: High affinity ligands for β1-containing subtypes. Sci Rep 2017; 7:5674. [PMID: 28720884 PMCID: PMC5516028 DOI: 10.1038/s41598-017-05757-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Accepted: 06/05/2017] [Indexed: 12/15/2022] Open
Abstract
γ-Aminobutyric acid type A (GABAA) receptors are pentameric GABA-gated chloride channels that are, in mammalians, drawn from a repertoire of 19 different genes, namely α1-6, β1-3, γ1-3, δ, ε, θ, π and ρ1-3. The existence of this wide variety of subunits as well as their diverse assembly into different subunit compositions result in miscellaneous receptor subtypes. In combination with the large number of known and putative allosteric binding sites, this leads to a highly complex pharmacology. Recently, a novel binding site at extracellular α+/β- interfaces was described as the site of modulatory action of several pyrazoloquinolinones. In this study we report a highly potent ligand from this class of compounds with pronounced β1-selectivity that mainly lacks α-subunit selectivity. It constitutes the most potent β1-selective positive allosteric modulatory ligand with known binding site. In addition, a proof of concept pyrazoloquinolinone ligand lacking the additional high affinity interaction with the benzodiazepine binding site is presented. Ultimately, such ligands can be used as invaluable molecular tools for the detection of β1-containing receptor subtypes and the investigation of their abundance and distribution.
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11
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Sivilotti MLA. Flumazenil, naloxone and the 'coma cocktail'. Br J Clin Pharmacol 2016; 81:428-36. [PMID: 26469689 PMCID: PMC4767210 DOI: 10.1111/bcp.12731] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Revised: 07/29/2015] [Accepted: 07/31/2015] [Indexed: 01/14/2023] Open
Abstract
Flumazenil and naloxone are considered to be pharmacologically ideal antidotes. By competitive binding at the molecular target receptors, they are highly specific antagonists of two important drug classes, the benzodiazepines and opioids, respectively. Both antidotes enjoy rapid onset and short duration after parenteral administration, are easily titrated and are essentially devoid of agonist effects. Yet only naloxone is widely used as a component of the 'coma cocktail', a sequence of empirical treatments to correct altered mental status, while experts discourage the use of flumazenil for such patients. This review contrasts the history, indications, published evidence and novel applications for each antidote in order to explain this disparity in the clinical use of these 'ideal' antidotes.
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Affiliation(s)
- Marco L A Sivilotti
- Emergency Medicine and Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario
- Ontario Poison Centre, Hospital for Sick Children, Toronto, Ontario, Canada
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12
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Kuver A, Smith SS. Flumazenil decreases surface expression of α4β2δ GABAA receptors by increasing the rate of receptor internalization. Brain Res Bull 2015; 120:131-43. [PMID: 26592470 DOI: 10.1016/j.brainresbull.2015.11.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2015] [Revised: 11/15/2015] [Accepted: 11/18/2015] [Indexed: 11/25/2022]
Abstract
Increases in expression of α4βδ GABAA receptors (GABARs), triggered by fluctuations in the neurosteroid THP (3α-OH-5α[β]-pregnan-20-one), are associated with changes in mood and cognition. We tested whether α4βδ trafficking and surface expression would be altered by in vitro exposure to flumazenil, a benzodiazepine ligand which reduces α4βδ expression in vivo. We first determined that flumazenil (100 nM-100 μM, IC50=∼1 μM) acted as a negative modulator, reducing GABA (10 μM)-gated current in the presence of 100 nM THP (to increase receptor efficacy), assessed with whole cell patch clamp recordings of recombinant α4β2δ expressed in HEK-293 cells. Surface expression of recombinant α4β2δ receptors was detected using a 3XFLAG reporter at the C-terminus of α4 (α4F) using confocal immunocytochemical techniques following 48 h exposure of cells to GABA (10 μM)+THP (100 nM). Flumazenil (10 μM) decreased surface expression of α4F by ∼60%, while increasing its intracellular accumulation, after 48 h. Reduced surface expression of α4β2δ after flumazenil treatment was confirmed by decreases in the current responses to 100 nM of the GABA agonist gaboxadol. Flumazenil-induced decreases in surface expression of α4β2δ were prevented by the dynamin blocker, dynasore, and by leupeptin, which blocks lysosomal enzymes, suggesting that flumazenil is acting to increase endocytosis and lysosomal degradation of the receptor. Flumazenil increased the rate of receptor removal from the cell surface by 2-fold, assessed using botulinum toxin B to block insertion of new receptors. These findings may suggest new therapeutic strategies for regulation of α4β2δ expression using flumazenil.
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Affiliation(s)
- Aarti Kuver
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave, Brooklyn, NY 11203, USA
| | - Sheryl S Smith
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, 450 Clarkson Ave, Brooklyn, NY 11203, USA.
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13
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Reddy SD, Reddy DS. Midazolam as an anticonvulsant antidote for organophosphate intoxication--A pharmacotherapeutic appraisal. Epilepsia 2015; 56:813-21. [PMID: 26032507 DOI: 10.1111/epi.12989] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/05/2015] [Indexed: 12/11/2022]
Abstract
OBJECTIVE This review summarizes the therapeutic potential of midazolam as an anticonvulsant antidote for organophosphate (OP) intoxication. METHODS Benzodiazepines are widely used to treat acute seizures and status epilepticus (SE), a neurologic emergency of persistent seizures that can lead to severe neuronal damage or death. Midazolam is a benzodiazepine hypnotic with a rapid onset and short duration of action. RESULTS Midazolam is considered the new drug of choice for persistent acute seizures and SE, including those caused by neurotoxic OPs and nerve agents. Midazolam is a positive allosteric modulator of synaptic γ-aminobutyric acid (GABA)A receptors in the brain. It potentiates GABAergic inhibition and thereby controls hyperexcitability and seizures. Midazolam is administered intravenously or intramuscularly to control acute seizures and SE. Due to its favorable pharmacokinetic features, midazolam is being considered as a replacement anticonvulsant for diazepam in the antidote kit for nerve agents. Clinical studies such as the recent Rapid Anticonvulsant Medication Prior to Arrival Trial (RAMPART) trial have confirmed the anticonvulsant efficacy of midazolam in SE in prehospital settings. SIGNIFICANCE In experimental models, midazolam is effective when given at the onset of seizures caused by nerve agents. However, benzodiazepines are less effective at terminating seizures when given 30 min or later after OP exposure or seizure onset, likely because of internalization or downregulation of synaptic, but not extrasynaptic, GABAA receptors, which can lead to diminished potency and seizure recurrence.
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Affiliation(s)
- Sandesh D Reddy
- Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas, U.S.A
| | - Doodipala Samba Reddy
- Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas, U.S.A
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Reddy SD, Younus I, Clossen BL, Reddy DS. Antiseizure Activity of Midazolam in Mice Lacking δ-Subunit Extrasynaptic GABA(A) Receptors. J Pharmacol Exp Ther 2015; 353:517-28. [PMID: 25784648 DOI: 10.1124/jpet.114.222075] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2014] [Accepted: 03/16/2015] [Indexed: 12/31/2022] Open
Abstract
Midazolam is a benzodiazepine anticonvulsant with rapid onset and short duration of action. Midazolam is the current drug of choice for acute seizures and status epilepticus, including those caused by organophosphate nerve agents. The antiseizure activity of midazolam is thought to result from its allosteric potentiation of synaptic GABA(A) receptors in the brain. However, there are indications that benzodiazepines promote neurosteroid synthesis via the 18-kDa cholesterol transporter protein (TSPO). Therefore, we investigated the role of neurosteroids and their extrasynaptic GABA(A) receptor targets in the antiseizure activity of midazolam. Here, we used δ-subunit knockout (DKO) mice bearing a targeted deletion of the extrasynaptic receptors to investigate the contribution of the extrasynaptic receptors to the antiseizure activity of midazolam using the 6-Hz and hippocampus kindling seizure models. In both models, midazolam produced rapid and dose-dependent protection against seizures (ED50, 0.4 mg/kg). Moreover, the antiseizure potency of midazolam was undiminished in DKO mice compared with control mice. Pretreatment with PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide], a TSPO blocker, or finasteride, a 5α-reductase neurosteroid inhibitor, did not affect the antiseizure effect of midazolam. The antiseizure activity of midazolam was significantly reversed by pretreatment with flumazenil, a benzodiazepine antagonist. Plasma and brain levels of the neurosteroid allopregnanolone were not significantly greater in midazolam-treated animals. These studies therefore provide strong evidence that neurosteroids and extrasynaptic GABA(A) receptors are not involved in the antiseizure activity of midazolam, which mainly occurs through synaptic GABA(A) receptors via direct binding to benzodiazepine sites. This study reaffirms midazolam's use for controlling acute seizures and status epilepticus.
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Affiliation(s)
- Sandesh D Reddy
- Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas
| | - Iyan Younus
- Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas
| | - Bryan L Clossen
- Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas
| | - Doodipala Samba Reddy
- Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas
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15
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Microwave-assisted synthesis of 4H-benzo[f]imidazo[1,4]diazepin-6-ones via a post-Ugi copper-catalyzed intramolecular Ullmann coupling. Tetrahedron Lett 2014. [DOI: 10.1016/j.tetlet.2014.02.023] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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16
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Wallner M, Hanchar HJ, Olsen RW. Alcohol selectivity of β3-containing GABAA receptors: evidence for a unique extracellular alcohol/imidazobenzodiazepine Ro15-4513 binding site at the α+β- subunit interface in αβ3δ GABAA receptors. Neurochem Res 2014; 39:1118-26. [PMID: 24500446 DOI: 10.1007/s11064-014-1243-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Revised: 01/13/2014] [Accepted: 01/17/2014] [Indexed: 01/08/2023]
Abstract
GABAA receptors (GABARs) have long been the focus for acute alcohol actions with evidence for behaviorally relevant low millimolar alcohol actions on tonic GABA currents and extrasynaptic α4/6, δ, and β3 subunit-containing GABARs. Using recombinant expression in oocytes combined with two electrode voltage clamp, we show with chimeric β2/β3 subunits that differences in alcohol sensitivity among β subunits are determined by the extracellular N-terminal part of the protein. Furthermore, by using point mutations, we show that the β3 alcohol selectivity is determined by a single amino acid residue in the N-terminus that differs between GABAR β subunits (β3Y66, β2A66, β1S66). The β3Y66 residue is located in a region called "loop D" which in γ subunits contributes to the imidazobenzodiazepine (iBZ) binding site at the classical α+γ2- subunit interface. In structural homology models β3Y66 is the equivalent of γ2T81 which is one of three critical residues lining the benzodiazepine binding site in the γ2 subunit loop D, opposite to the "100H/R-site" benzodiazepine binding residue in GABAR α subunits. We have shown that the α6R100Q mutation at this site leads to increased alcohol-induced motor in-coordination in alcohol non-tolerant rats carrying the α6R100Q mutated allele. Based on the identification of these two amino acid residues α6R100 and β66 we propose a model in which β3 and δ containing GABA receptors contain a unique ethanol site at the α4/6+β3- subunit interface. This site is homologous to the classical benzodiazepine binding site and we propose that it not only binds ethanol at relevant concentrations (EC50-17 mM), but also has high affinity for a few selected benzodiazepine site ligands including alcohol antagonistic iBZs (Ro15-4513, RY023, RY024, RY80) which have in common a large moiety at the C7 position of the benzodiazepine ring. We suggest that large moieties at the C7-BZ ring compete with alcohol for its binding pocket at a α4/6+β3- EtOH/Ro15-4513 site. This model reconciles many years of alcohol research on GABARs and provides a plausible explanation for the competitive relationship between ethanol and iBZ alcohol antagonists in which bulky moieties at the C7 position compete with ethanol for its binding site. We conclude with a critical discussion to suggest that much of the controversy surrounding this issue might be due to fundamental species differences in alcohol and alcohol antagonist responses in rats and mice.
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Affiliation(s)
- M Wallner
- Department of Molecular and Medical Pharmacology, University of California Los Angeles, Room 23-338 CHS, Charles Young Drive South, Los Angeles, CA, 90095-1735, USA,
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17
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Robust photoregulation of GABA(A) receptors by allosteric modulation with a propofol analogue. Nat Commun 2013; 3:1095. [PMID: 23033071 PMCID: PMC4023869 DOI: 10.1038/ncomms2094] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Accepted: 08/29/2012] [Indexed: 01/09/2023] Open
Abstract
Photochemical switches represent a powerful method for improving pharmacological therapies and controlling cellular physiology. Here we report the photo-regulation of GABAA receptors (GABAARs) by a derivative of propofol (2,6-diisopropylphenol), a GABAAR allosteric modulator, that we have modified to contain photo-isomerizable azobenzene. Using α1β2γ2 GABAARs expressed in Xenopus laevis oocytes and native GABAARs of isolated retinal ganglion cells, we show that the trans-azobenzene isomer of the new compound (trans-MPC088), generated by visible light (wavelengths ~440 nm), potentiates the GABA-elicited response and at higher concentrations directly activates the receptors. cis-MPC088, generated from trans-MPC088 by UV light (~365 nm), produces little if any receptor potentiation/activation. In cerebellar slices, MPC088 co-applied with GABA affords bidirectional photo-modulation of Purkinje cell membrane current and spike-firing rate. The findings demonstrate photo-control of GABAARs by an allosteric ligand and open new avenues for fundamental and clinically oriented research on GABAARs, a major class of neurotransmitter receptors in the central nervous system.
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18
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Lemoine D, Jiang R, Taly A, Chataigneau T, Specht A, Grutter T. Ligand-gated ion channels: new insights into neurological disorders and ligand recognition. Chem Rev 2012; 112:6285-318. [PMID: 22988962 DOI: 10.1021/cr3000829] [Citation(s) in RCA: 115] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Damien Lemoine
- Laboratoire de Biophysicochimie des Récepteurs Canaux, UMR 7199 CNRS, Conception et Application de Molécules Bioactives, Faculté de Pharmacie, Université de Strasbourg , 67400 Illkirch, France
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Dhir A, Rogawski MA. Role of neurosteroids in the anticonvulsant activity of midazolam. Br J Pharmacol 2012; 165:2684-91. [PMID: 22014182 DOI: 10.1111/j.1476-5381.2011.01733.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE Midazolam is a short-acting benzodiazepine that is widely used as an i.v. sedative and anticonvulsant. Besides interacting with the benzodiazepine site associated with GABA(A) receptors, some benzodiazepines act as agonists of translocator protein (18 kDa) (TSPO) to enhance the synthesis of steroids, including neurosteroids with positive modulatory actions on GABA(A) receptors. We sought to determine if neurosteroidogenesis induced by midazolam contributes to its anticonvulsant action. EXPERIMENTAL APPROACH Mice were pretreated with neurosteroid synthesis inhibitors and potentiators followed by midazolam or clonazepam, a weak TSPO ligand. Anticonvulsant activity was assessed with the i.v. pentylenetetrazol (PTZ) threshold test. KEY RESULTS Midazolam (500-5000 µg·kg(-1) , i.p.) caused a dose-dependent increase in seizure threshold. Pretreatment with the neurosteroid synthesis inhibitors finasteride, a 5α-reductase inhibitor, and a functional TSPO antagonist PK 11195, reduced the anticonvulsant action of midazolam. The anticonvulsant action of midazolam was enhanced by the neurosteroidogenic drug metyrapone, an 11β-hydroxylase inhibitor. In contrast, the anticonvulsant action of clonazepam (100 µg·kg(-1) ) was reduced by finasteride but not by PK 11195, indicating a possible contribution of neurosteroids unrelated to TSPO. CONCLUSION AND IMPLICATIONS Enhanced endogenous neurosteroid synthesis, possibly mediated by an interaction with TSPO, contributed to the anticonvulsant action of midazolam. Enhanced neurosteroidogenesis may also be a factor in the actions of other benzodiazepines, even those that only weakly interact with TSPO.
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Affiliation(s)
- Ashish Dhir
- Department of Neurology, School of Medicine, University of California, Davis, Sacramento, CA 95817, USA
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20
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Richter L, de Graaf C, Sieghart W, Varagic Z, Mörzinger M, de Esch IJP, Ecker GF, Ernst M. Diazepam-bound GABAA receptor models identify new benzodiazepine binding-site ligands. Nat Chem Biol 2012; 8:455-64. [PMID: 22446838 DOI: 10.1038/nchembio.917] [Citation(s) in RCA: 151] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2011] [Accepted: 02/02/2012] [Indexed: 11/09/2022]
Abstract
Benzodiazepines exert their anxiolytic, anticonvulsant, muscle-relaxant and sedative-hypnotic properties by allosterically enhancing the action of GABA at GABA(A) receptors via their benzodiazepine-binding site. Although these drugs have been used clinically since 1960, the molecular basis of this interaction is still not known. By using multiple homology models and an unbiased docking protocol, we identified a binding hypothesis for the diazepam-bound structure of the benzodiazepine site, which was confirmed by experimental evidence. Moreover, two independent virtual screening approaches based on this structure identified known benzodiazepine-site ligands from different structural classes and predicted potential new ligands for this site. Receptor-binding assays and electrophysiological studies on recombinant receptors confirmed these predictions and thus identified new chemotypes for the benzodiazepine-binding site. Our results support the validity of the diazepam-bound structure of the benzodiazepine-binding pocket, demonstrate its suitability for drug discovery and pave the way for structure-based drug design.
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Affiliation(s)
- Lars Richter
- Department of Medicinal Chemistry, University of Vienna, Vienna, Austria
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21
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Tan KR, Rudolph U, Lüscher C. Hooked on benzodiazepines: GABAA receptor subtypes and addiction. Trends Neurosci 2011; 34:188-97. [PMID: 21353710 DOI: 10.1016/j.tins.2011.01.004] [Citation(s) in RCA: 202] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2010] [Revised: 01/04/2011] [Accepted: 01/14/2011] [Indexed: 12/21/2022]
Abstract
Benzodiazepines are widely used clinically to treat anxiety and insomnia. They also induce muscle relaxation, control epileptic seizures, and can produce amnesia. Moreover, benzodiazepines are often abused after chronic clinical treatment and also for recreational purposes. Within weeks, tolerance to the pharmacological effects can develop as a sign of dependence. In vulnerable individuals with compulsive drug use, addiction will be diagnosed. Here we review recent observations from animal models regarding the cellular and molecular basis that might underlie the addictive properties of benzodiazepines. These data reveal how benzodiazepines, acting through specific GABA(A) receptor subtypes, activate midbrain dopamine neurons, and how this could hijack the mesolimbic reward system. Such findings have important implications for the future design of benzodiazepines with reduced or even absent addiction liability.
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Affiliation(s)
- Kelly R Tan
- Department of Basic Neurosciences, Medical Faculty, University of Geneva, Geneva, Switzerland
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22
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Saari TI, Uusi-Oukari M, Ahonen J, Olkkola KT. Enhancement of GABAergic activity: neuropharmacological effects of benzodiazepines and therapeutic use in anesthesiology. Pharmacol Rev 2011; 63:243-67. [PMID: 21245208 DOI: 10.1124/pr.110.002717] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
GABA is the major inhibitory neurotransmitter in the central nervous system (CNS). The type A GABA receptor (GABA(A)R) system is the primary pharmacological target for many drugs used in clinical anesthesia. The α1, β2, and γ2 subunit-containing GABA(A)Rs located in the various parts of CNS are thought to be involved in versatile effects caused by inhaled anesthetics and classic benzodiazepines (BZD), both of which are widely used in clinical anesthesiology. During the past decade, the emergence of tonic inhibitory conductance in extrasynaptic GABA(A)Rs has coincided with evidence showing that these receptors are highly sensitive to the sedatives and hypnotics used in anesthesia. Anesthetic enhancement of tonic GABAergic inhibition seems to be preferentially increased in regions shown to be important in controlling memory, awareness, and sleep. This review focuses on the physiology of the GABA(A)Rs and the pharmacological properties of clinically used BZDs. Although classic BZDs are widely used in anesthesiological practice, there is a constant need for new drugs with more favorable pharmacokinetic and pharmacodynamic effects and fewer side effects. New hypnotics are currently developed, and promising results for one of these, the GABA(A)R agonist remimazolam, have recently been published.
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Affiliation(s)
- Teijo I Saari
- Department of Anesthesiology, Intensive Care, Emergency Care and Pain Medicine, Turku University Hospital, P.O. Box 52 (Kiinamyllynkatu 4-8), FI-20520 Turku, Finland.
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23
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Mechanism of Allosteric Modulation of the Cys-loop Receptors. Pharmaceuticals (Basel) 2010; 3:2592-2609. [PMID: 27713368 PMCID: PMC4033940 DOI: 10.3390/ph3082592] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2010] [Revised: 07/30/2010] [Accepted: 08/09/2010] [Indexed: 11/18/2022] Open
Abstract
The cys-loop receptor family is a major family of neurotransmitter-operated ion channels. They play important roles in fast synaptic transmission, controlling neuronal excitability, and brain function. These receptors are allosteric proteins, in that binding of a neurotransmitter to its binding site remotely controls the channel function. The cys-loop receptors also are subject to allosteric modulation by many pharmaceutical agents and endogenous modulators. By binding to a site of the receptor distinct from the neurotransmitter binding site, allosteric modulators alter the response of the receptors to their agonists. The mechanism of allosteric modulation is traditionally believed to be that allosteric modulators directly change the binding affinity of receptors for their agonists. More recent studies support the notion that these allosteric modulators are very weak agonists or antagonists by themselves. They directly alter channel gating, and thus change the distribution of the receptor across multiple different affinity states, indirectly influencing receptors’ sensitivity to agonists. There are two major locations of allosteric modulator binding sites. One is in subunit interfaces of the amino-terminal domain. The other is in the transmembrane domain close to the channel gating machinery. In this review, we also give some examples of well characterized allosteric binding pockets.
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24
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Meera P, Olsen RW, Otis TS, Wallner M. Alcohol- and alcohol antagonist-sensitive human GABAA receptors: tracking δ subunit incorporation into functional receptors. Mol Pharmacol 2010; 78:918-24. [PMID: 20699325 DOI: 10.1124/mol.109.062687] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
GABA(A) receptors (GABA(A)Rs) have long been a focus as targets for alcohol actions. Recent work suggests that tonic GABAergic inhibition mediated by extrasynaptic δ subunit-containing GABA(A)Rs is uniquely sensitive to ethanol and enhanced at concentrations relevant for human alcohol consumption. Ethanol enhancement of recombinant α4β3δ receptors is blocked by the behavioral alcohol antagonist 8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester (Ro15-4513), suggesting that EtOH/Ro15-4513-sensitive receptors mediate important behavioral alcohol actions. Here we confirm alcohol/alcohol antagonist sensitivity of α4β3δ receptors using human clones expressed in a human cell line and test the hypothesis that discrepant findings concerning the high alcohol sensitivity of these receptors are due to difficulties incorporating δ subunits into functional receptors. To track δ subunit incorporation, we used a functional tag, a single amino acid change (H68A) in a benzodiazepine binding residue in which a histidine in the δ subunit is replaced by an alanine residue found at the homologous position in γ subunits. We demonstrate that the δH68A substitution confers diazepam sensitivity to otherwise diazepam-insensitive α4β3δ receptors. The extent of enhancement of α4β3δH68A receptors by 1 μM diazepam, 30 mM EtOH, and 1 μM β-carboline-3-carboxy ethyl ester (but not 1 μM Zn(2+) block) is correlated in individual recordings, suggesting that δ subunit incorporation into recombinant GABA(A)Rs varies from cell to cell and that this variation accounts for the variable pharmacological profile. These data are consistent with the notion that δ subunit-incorporation is often incomplete in recombinant systems yet is necessary for high ethanol sensitivity, one of the features of native δ subunit-containing GABA(A)Rs.
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Affiliation(s)
- Pratap Meera
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095-1735, USA
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25
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Hanek AP, Lester HA, Dougherty DA. Photochemical proteolysis of an unstructured linker of the GABAAR extracellular domain prevents GABA but not pentobarbital activation. Mol Pharmacol 2010; 78:29-35. [PMID: 20363860 DOI: 10.1124/mol.109.059832] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The GABA type A receptor (GABA(A)R) is the major inhibitory receptor in the mammalian central nervous system and the target of numerous pharmaceuticals. The alpha-subunit of these pentameric Cys-loop neurotransmitter-gated ion channels contributes to the binding of both GABA and allosteric modulators such as the benzodiazepines, suggesting a role for this subunit in the conformational changes associated with activation of the receptor. Herein we use the nonsense suppression methodology to incorporate a photoactivatable unnatural amino acid and photochemically cleave the backbone of the alpha subunit of the alpha(1)beta(2) GABA(A)R in a linker region that is believed to span the subunit. Proteolytic cleavage impairs GABA but not pentobarbital activation, strongly suggesting that conformational changes involving this linker region are critical to the GABA activation pathway.
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Affiliation(s)
- Ariele P Hanek
- Division of Chemistry and Chemical Engineering, Division of Biology, California Institute of Technology, Pasadena, California, USA
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26
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Berezhnoy D, Gibbs TT, Farb DH. Docking of 1,4-benzodiazepines in the alpha1/gamma2 GABA(A) receptor modulator site. Mol Pharmacol 2009; 76:440-50. [PMID: 19483108 DOI: 10.1124/mol.109.054650] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Positive allosteric modulation of the GABA(A) receptor (GABA(A)R) via the benzodiazepine recognition site is the mechanism whereby diverse chemical classes of therapeutic agents act to reduce anxiety, induce and maintain sleep, reduce seizures, and induce conscious sedation. The binding of such therapeutic agents to this allosteric modulatory site increases the affinity of GABA for the agonist recognition site. A major unanswered question, however, relates to how positive allosteric modulators dock in the 1,4-benzodiazepine (BZD) recognition site. In the present study, the X-ray structure of an acetylcholine binding protein from the snail Lymnea stagnalis and the results from site-directed affinity-labeling studies were used as the basis for modeling of the BZD binding pocket at the alpha(1)/gamma(2) subunit interface. A tethered BZD was introduced into the binding pocket, and molecular simulations were carried out to yield a set of candidate orientations of the BZD ligand in the binding pocket. Candidate orientations were refined based on known structure-activity and stereospecificity characteristics of BZDs and the impact of the alpha(1)H101R mutation. Results favor a model in which the BZD molecule is oriented such that the C5-phenyl substituent extends approximately parallel to the plane of the membrane rather than parallel to the ion channel. Application of this computational modeling strategy, which integrates site-directed affinity labeling with structure-activity knowledge to create a molecular model of the docking of active ligands in the binding pocket, may provide a basis for the design of more selective GABA(A)R modulators with enhanced therapeutic potential.
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Affiliation(s)
- D Berezhnoy
- Laboratory of Molecular Neurobiology, Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, MA 02118, USA
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27
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Hanson SM, Morlock EV, Satyshur KA, Czajkowski C. Structural requirements for eszopiclone and zolpidem binding to the gamma-aminobutyric acid type-A (GABAA) receptor are different. J Med Chem 2009; 51:7243-52. [PMID: 18973287 DOI: 10.1021/jm800889m] [Citation(s) in RCA: 148] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
The sleep-aids zolpidem and eszopiclone exert their effects by binding to and modulating gamma-aminobutyric acid type-A receptors (GABA(A)Rs), but little is known about the structural requirements for their actions. We made 24 cysteine mutations in the benzodiazepine (BZD) binding site of alpha(1)beta(2)gamma(2) GABA(A)Rs and measured zolpidem, eszopiclone, and BZD-site antagonist binding. Mutations in gamma(2)loop D and alpha(1)loops A and B altered the affinity of all ligands tested, indicating that these loops are important for BZD pocket structural integrity. In contrast, gamma(2)loop E and alpha(1)loop C mutations differentially affected ligand affinity, suggesting that these loops are important for ligand selectivity. In agreement with our mutagenesis data, eszopiclone docking yielded a single model stabilized by several hydrogen bonds. Zolpidem docking yielded three equally populated orientations with few polar interactions, suggesting that unlike eszopiclone, zolpidem relies more on shape recognition of the binding pocket than on specific residue interactions and may explain why zolpidem is highly alpha(1)- and gamma(2)-subunit selective.
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Affiliation(s)
- Susan M Hanson
- Department of Physiology and Program in Molecular and Cellular Pharmacology, University of Wisconsin Madison, Madison, Wisconsin 53711, USA
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28
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Anzini M, Braile C, Valenti S, Cappelli A, Vomero S, Marinelli L, Limongelli V, Novellino E, Betti L, Giannaccini G, Lucacchini A, Ghelardini C, Norcini M, Makovec F, Giorgi G, Ian Fryer R. Ethyl 8-Fluoro-6-(3-nitrophenyl)-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate as Novel, Highly Potent, and Safe Antianxiety Agent. J Med Chem 2008; 51:4730-43. [DOI: 10.1021/jm8002944] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Maurizio Anzini
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Carlo Braile
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Salvatore Valenti
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Andrea Cappelli
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Salvatore Vomero
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Luciana Marinelli
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Vittorio Limongelli
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Ettore Novellino
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Laura Betti
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Gino Giannaccini
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Antonio Lucacchini
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Carla Ghelardini
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Monica Norcini
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Francesco Makovec
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - Gianluca Giorgi
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
| | - R. Ian Fryer
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy, Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Psichiatria, Neurobiologia Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy, Dipartimento di Farmacologia Preclinica e Clinica “M. Aiazzi Mancini”,
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29
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Guerrini G, Ciciani G, Cambi G, Bruni F, Selleri S, Melani F, Montali M, Martini C, Ghelardini C, Norcini M, Costanzo A. Novel 3-aroylpyrazolo[5,1-c][1,2,4]benzotriazine 5-oxides 8-substituted, ligands at GABAA/benzodiazepine receptor complex: Synthesis, pharmacological and molecular modeling studies. Bioorg Med Chem 2008; 16:4471-89. [DOI: 10.1016/j.bmc.2008.02.058] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2007] [Revised: 02/13/2008] [Accepted: 02/19/2008] [Indexed: 11/29/2022]
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Eriksson O, Josephsson R, Långstrom B, Bergström M. Positron emission tomography and target-controlled infusion for precise modulation of brain drug concentration. Nucl Med Biol 2008; 35:299-303. [PMID: 18355685 DOI: 10.1016/j.nucmedbio.2007.12.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2007] [Revised: 12/07/2007] [Accepted: 12/11/2007] [Indexed: 11/29/2022]
Abstract
INTRODUCTION There are several instances when it is desirable to control brain concentration of pharmaceuticals, e.g., to modulate the concentration of anesthetic agents to different desired levels fitting to different needs during the course of surgery. This has so far only been possible using indirect estimates of drug concentration such as assuming constant relation between tissue and blood including extrapolations from animals. METHODS A system for controlling target tissue concentration (UIPump) was used to regulate whole-brain concentrations of a central benzodiazepine receptor antagonist at therapeutic levels with input from brain kinetics as determined with PET. The system was tested by using pharmacological doses of flumazenil mixed with tracer amounts of [11C]flumazenil. Flumazenil was used as a model compound for anesthesia. An infusion scheme to produce three different steady-state levels in sequence was designed based on kinetic curves obtained after bolus injection. The subjects (Sprague-Dawley rats, n=6) were monitored in a microPET scanner during the whole experiment to verify resulting brain kinetic curves. RESULTS A steady-state brain concentration was rapidly achieved corresponding to a whole-brain concentration of 118+/-6 ng/ml. As the infusion rate decreased to lower the exposure by a factor of 2, the brain concentration decreased to 56+/-4 ng/ml. A third increased steady-state level of anesthesia corresponding to a whole-brain concentration of 107+/-7 ng/ml was rapidly achieved. CONCLUSION The experimental setup with computerized pump infusion and PET supervision enables accurate setting of target tissue drug concentration.
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31
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Hsiao B, Mihalak KB, Magleby KL, Luetje CW. Zinc potentiates neuronal nicotinic receptors by increasing burst duration. J Neurophysiol 2007; 99:999-1007. [PMID: 18094103 DOI: 10.1152/jn.01040.2007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Micromolar zinc potentiates neuronal nicotinic acetylcholine receptors (nAChRs) in a subtype-dependent manner. Zinc potentiates receptor function even at saturating agonist concentrations, without altering the receptor desensitization rate. Potentiation could occur through an increase in the number of available receptors, an increase in single-channel current amplitude, or an increase in single-channel open probability. To distinguish among these possibilities, we examined rat neuronal nAChRs expressed in Xenopus oocytes. Blockade of a large fraction of ACh activated alpha4beta4 or alpha4beta2 receptors by the open channel blocker hexamethonium failed to change the extent of potentiation by zinc, suggesting that zinc does not change the number of available receptors. The single-channel amplitudes of ACh (1 microM) activated alpha4beta4 receptors in outside-out patches were similar in the absence and the presence of 100 microM zinc (3.0 +/- 0.1 and 2.9 +/- 0.1 pA, respectively). To determine the effect of zinc on single-channel open probability, we examined alpha4beta4 receptors in cell-attached patches. The open probability at 100 nM ACh (0.011 +/- 0.002) was increased 4.5-fold by 100 microM zinc (0.050 +/- 0.008), accounting for most of the potentiation observed at the whole cell level. The increase in open probability was due to an increase in burst duration, which increased from 207 +/- 38 ms in the absence of zinc to 830 +/- 189 ms in the presence of zinc. Our results suggest that potentiation of neuronal nAChRs by zinc is due to a stabilization of the bursting states of the receptor.
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Affiliation(s)
- Bernard Hsiao
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33101, USA
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32
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Mokrab Y, Bavro VN, Mizuguchi K, Todorov NP, Martin IL, Dunn SMJ, Chan SL, Chau PL. Exploring ligand recognition and ion flow in comparative models of the human GABA type A receptor. J Mol Graph Model 2007; 26:760-74. [PMID: 17544304 DOI: 10.1016/j.jmgm.2007.04.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Accepted: 04/29/2007] [Indexed: 11/25/2022]
Abstract
We present two comparative models of the GABA(A) receptor. Model 1 is based on the 4-A resolution structure of the nicotinic acetylcholine receptor from Torpedo marmorata and represents the unliganded receptor. Two agonists, GABA and muscimol, two benzodiazepines, flunitrazepam and alprazolam, together with the general anaesthetic halothane, have been docked to this model. The ion flow is also explored in model 1 by evaluating the interaction energy of a chloride ion as it traverses the extracellular, transmembrane and intracellular domains of the protein. Model 2 differs from model 1 only in the extracellular domain and represents the liganded receptor. Comparison between the two models not only allows us to explore commonalities and differences with comparative models of the nicotinic acetylcholine receptor, but also suggests possible protein sub-domain interactions with the GABA(A) receptor not previously addressed.
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Affiliation(s)
- Younes Mokrab
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, United Kingdom
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33
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He Y, Kudo M, Kudo T, Kushikata T, Li E, Hirota K. The Effects of Benzodiazepines on Orexinergic Systems in Rat Cerebrocortical Slices. Anesth Analg 2007; 104:338-40. [PMID: 17242090 DOI: 10.1213/01.ane.0000252413.62821.2e] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND As orexinergic (OXergic) neurons have been reported to mediate emotional changes, benzodiazepines might interact with OXergic neurons. METHODS We examined the interactions between OXergic neurons and benzodiazepine receptors in orexin-A (100 nM) and K+ (25 mM)-evoked norepinephrine release from rat cerebrocortical slices. RESULTS Midazolam, diazepam, and flunitrazepam concentration-dependently inhibited both OX-A- and K+-evoked norepinephrine release. The IC50 of midazolam for orexin-A-evoked release (0.87 microM, P < 0.01), which was insensitive to flumazenil, was significantly lower than that of diazepam and flunitrazepam (around 60 microM), whereas the IC50s for K+-evoked release were not different among the benzodiazepines. CONCLUSION There may be no interaction between OXergic neurons and central benzodiazepine receptors.
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Affiliation(s)
- Ying He
- Department of Anesthesiology, University of Hirosaki School of Medicine, Hirosaki, Japan
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34
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Venkatachalan SP, Bushman JD, Mercado JL, Sancar F, Christopherson KR, Boileau AJ. Optimized expression vector for ion channel studies in Xenopus oocytes and mammalian cells using alfalfa mosaic virus. Pflugers Arch 2006; 454:155-63. [PMID: 17146677 PMCID: PMC2574422 DOI: 10.1007/s00424-006-0183-1] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2006] [Accepted: 10/28/2006] [Indexed: 10/23/2022]
Abstract
Plasmid vectors used for mammalian expression or for in vitro cRNA translation can differ substantially and are rarely cross-compatible. To make comparisons between mammalian and Xenopus oocyte expression systems, it would be advantageous to use a single vector without the need for shuttle vectors or subcloning. We have designed such a vector, designated pUNIV for universal, with elements that will allow for in vitro or ex vivo expression in multiple cell types. We tested the expression of pUNIV-based cDNA cassettes using enhanced green fluorescent protein and two forms of the type A gamma-aminobutyric acid receptor (GABA(A)R) and compared pUNIV to vectors optimized for expression in either Xenopus oocytes or mammalian cells. In HEK293 cells, radioligand binding was robust, and patch clamp experiments showed that subtle macroscopic GABA(A)R kinetics were indistinguishable from our previous results. In Xenopus oocytes, agonist median effective concentration measurements matched previous work using a vector optimized for oocyte expression. Furthermore, we found that expression using pUNIV was significantly enhanced in oocytes and was remarkably long-lasting in both systems.
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Affiliation(s)
- Srinivasan P. Venkatachalan
- Department of Physiology, University of Wisconsin-Madison, 601 Science Drive, Madison, WI 53711, USA e-mail:
| | - Jeremy D. Bushman
- Department of Physiology, University of Wisconsin-Madison, 601 Science Drive, Madison, WI 53711, USA e-mail:
| | - José L. Mercado
- Neuroscience Training Program, University of Wisconsin-Madison, 601 Science Drive, Madison, WI 53711, USA
| | - Feyza Sancar
- Neuroscience Training Program, University of Wisconsin-Madison, 601 Science Drive, Madison, WI 53711, USA
| | - Kelly R. Christopherson
- Molecular and Cellular Pharmacology Program, University of Wisconsin-Madison, 601 Science Drive, Madison, WI 53711, USA
| | - Andrew J. Boileau
- Department of Physiology, University of Wisconsin-Madison, 601 Science Drive, Madison, WI 53711, USA e-mail:
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35
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Primofiore G, Da Settimo F, Marini AM, Taliani S, La Motta C, Simorini F, Novellino E, Greco G, Cosimelli B, Ehlardo M, Sala A, Besnard F, Montali M, Martini C. Refinement of the benzodiazepine receptor site topology by structure-activity relationships of new N-(heteroarylmethyl)indol-3-ylglyoxylamides. J Med Chem 2006; 49:2489-95. [PMID: 16610792 DOI: 10.1021/jm0511841] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
N-(heteroarylmethyl)indol-3-ylglyoxylamides (1-26) were synthesized and evaluated as ligands of the benzodiazepine receptor (BzR) to probe the hydrogen bonding properties of the so-called S(1) site of the BzR by means of suitable heterocyclic side chains. SARs were developed in light of our hypothesis of binding modes A and B. Pyrrole and furan derivatives adopting mode A (2, 8, 10, 20, 22) turned out to be more potent (K(i) values < 35 nM) than their analogues lacking hydrogen bonding heterocyclic side chains. These data suggest that the most potent indoles interact with a hydrogen bond acceptor/donor (HBA/D) group located within the S(1) site of the BzR. Compounds 1, 2, 8, 19, 20, and 22, tested at recombinant rat alpha(1)beta(2)gamma(2), alpha(2)beta(2)gamma(2), and alpha(5)beta(3)gamma(2) BzRs, elicited selectivity for the alpha(1)beta(2)gamma(2) isoform. On the basis of published mutagenesis studies and the present SARs, we speculate that the S(1) HBA/D group might be identified as the hydroxyl of alpha(1)-Tyr209 or of other neighboring amino acids.
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Affiliation(s)
- Giampaolo Primofiore
- Dipartimento di Scienze Farmaceutiche, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy
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Szárics E, Riedl Z, Nyikos L, Hajós G, Kardos J. Interaction of novel condensed triazine derivatives with central and peripheral type benzodiazepine receptors: synthesis, in vitro pharmacology and modelling. Eur J Med Chem 2006; 41:445-56. [PMID: 16530296 DOI: 10.1016/j.ejmech.2005.10.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2004] [Revised: 10/18/2005] [Accepted: 10/26/2005] [Indexed: 11/28/2022]
Abstract
Structurally related sets of triazino-quinoline, triazino-isoquinoline and pyrido-triazine derivatives were synthesised and their binding interactions with central (CBR)- and peripheral-type (PBR) benzodiazepine binding sites have been characterised. Of 33 compounds tested, a new compound, 2-(4-methylphenyl)-3H- [1,2,4] triazino [2, 3-a] quinolin-3-one (1 g) showed the lowest CBR binding inhibition constant (K(i) = 42 +/- 9 nM) and the highest CBR over PBR selectivity (>1300). All but the 4-methylphenyl (1 g) structural modifications decreased the affinity and selectivity of the parent compound, 2-phenyl-3H- [1,2,4]triazino[2,3-a]quinolin-3-one (1d) (K(i) = 69 +/- 9 nM, selectivity >890). Molecular interactions between selected ligands (standards and triazine derivatives) and alpha(1)gamma(2) subunit-interface residues in a GABA(A) receptor extracellular domain homology model have been calculated. Comparing data with calculations confirmed hydrogen bonding to gamma(2)Thr142 and hydrophobic interaction with alpha(1)His101 as being essential for high-affinity CBR binding.
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Affiliation(s)
- Eva Szárics
- Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest
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37
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Hanchar HJ, Chutsrinopkun P, Meera P, Supavilai P, Sieghart W, Wallner M, Olsen RW. Ethanol potently and competitively inhibits binding of the alcohol antagonist Ro15-4513 to alpha4/6beta3delta GABAA receptors. Proc Natl Acad Sci U S A 2006; 103:8546-51. [PMID: 16581914 PMCID: PMC1482528 DOI: 10.1073/pnas.0509903103] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Although GABA(A) receptors have long been implicated in mediating ethanol (EtOH) actions, receptors containing the "nonsynaptic" delta subunit only recently have been shown to be uniquely sensitive to EtOH. Here, we show that delta subunit-containing receptors bind the imidazo-benzodiazepines (BZs) flumazenil and Ro15-4513 with high affinity (K(d) < 10 nM), contrary to the widely held belief that these receptors are insensitive to BZs. In immunopurified native cerebellar and recombinant delta subunit-containing receptors, binding of the alcohol antagonist [(3)H]Ro15-4513 is inhibited by low concentrations of EtOH (K(i) approximately 8 mM). Also, Ro15-4513 binding is inhibited by BZ-site ligands that have been shown to reverse the behavioral alcohol antagonism of Ro15-4513 (i.e., flumazenil, beta-carbolinecarboxylate ethyl ester (beta-CCE), and N-methyl-beta-carboline-3-carboxamide (FG7142), but not including any classical BZ agonists like diazepam). Experiments that were designed to distinguish between a competitive and allosteric mechanism suggest that EtOH and Ro15-4513 occupy a mutually exclusive binding site. The fact that only Ro15-4513, but not flumazenil, can inhibit the EtOH effect, and that Ro15-4513 differs from flumazenil by only a single group in the molecule (an azido group at the C7 position of the BZ ring) suggest that this azido group in Ro15-4513 might be the area that overlaps with the alcohol-binding site. Our findings, combined with previous observations that Ro15-4513 is a behavioral alcohol antagonist, suggest that many of the behavioral effects of EtOH at relevant physiological concentrations are mediated by EtOH/Ro15-4513-sensitive GABA(A) receptors.
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Affiliation(s)
| | - Panida Chutsrinopkun
- Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok 10 400, Thailand; and
| | - Pratap Meera
- Neurobiology, University of California, Los Angeles, CA 90095
| | - Porntip Supavilai
- Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok 10 400, Thailand; and
| | - Werner Sieghart
- Center for Brain Research, Division of Biochemistry and Molecular Biology and Section of Biochemical Psychiatry, Medical University of Vienna, A-1090 Vienna, Austria
| | - Martin Wallner
- Departments of *Molecular and Medical Pharmacology and
- To whom correspondence may be addressed at:
Department of Molecular and Medical Pharmacology, University of California, Room 23-120 CHS, Charles Young Drive South, Los Angeles, CA 90095-1735. E-mail:
or
| | - Richard W. Olsen
- Departments of *Molecular and Medical Pharmacology and
- To whom correspondence may be addressed at:
Department of Molecular and Medical Pharmacology, University of California, Room 23-120 CHS, Charles Young Drive South, Los Angeles, CA 90095-1735. E-mail:
or
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38
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Sieghart W. Structure, pharmacology, and function of GABAA receptor subtypes. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2006; 54:231-63. [PMID: 17175817 DOI: 10.1016/s1054-3589(06)54010-4] [Citation(s) in RCA: 224] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Werner Sieghart
- Division of Biochemistry and Molecular Biology, Center for Brain Research, and Section of Biochemical Psychiatry, University Clinic for Psychiatry, Medical University Vienna, Austria
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39
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Hsiao B, Mihalak KB, Repicky SE, Everhart D, Mederos AH, Malhotra A, Luetje CW. Determinants of zinc potentiation on the alpha4 subunit of neuronal nicotinic receptors. Mol Pharmacol 2005; 69:27-36. [PMID: 16189299 DOI: 10.1124/mol.105.015164] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have shown previously that the function of neuronal nicotinic acetylcholine receptors can be modulated by zinc. This modulation varies from potentiation to inhibition, depending on receptor subunit composition and zinc concentration, with the alpha4beta2 and alpha4beta4 receptors displaying the most dramatic potentiation. In this study, we used site-directed mutagenesis to identify glutamate 59 and histidine 162 on the rat alpha4 subunit as potential mediators of zinc potentiation. By modeling the extracellular domain of the receptor pentamer, we locate these residues to two subunit-subunit interfaces that alternate with the two acetylcholine-binding interfaces. Substitution of a cysteine at either position allows additional reduction of zinc potentiation upon treatment with the methanethiosulfonate reagents N-biotinoylaminoethyl methanethiosulfonate (MTSEA-biotin) and [2-(trimethylammonium)ethyl] methanethiosulfonate. Mutagenesis and methanethiosulfonate treatment are most effective at position 162, and the presence of zinc hinders the reaction of MTSEA-biotin with the substituted cysteine at this position, suggesting that alpha4His162 participates in forming a coordination site for zinc. Mutagenesis and methanethiosulfonate treatment are less effective at position 59, suggesting that whereas alpha4Glu59 may be near the zinc coordination site, it may not be participating in coordination of the zinc ion. It is noteworthy that the position of alpha4Glu59 within the neuronal nAChR is identical to that of a residue that lines the benzodiazepine-binding site on GABA(A) receptors. We suggest that the zinc potentiation sites on neuronal nAChRs are structurally and functionally similar to the benzodiazepine-binding sites on GABA(A) receptors.
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Affiliation(s)
- Bernard Hsiao
- Department of Molecular and Cellular Pharmacology, Miller School of Medicine, University of Miami, Miami, FL 33101, USA
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40
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Ogris W, Pöltl A, Hauer B, Ernst M, Oberto A, Wulff P, Höger H, Wisden W, Sieghart W. Affinity of various benzodiazepine site ligands in mice with a point mutation in the GABA(A) receptor gamma2 subunit. Biochem Pharmacol 2005; 68:1621-9. [PMID: 15451405 DOI: 10.1016/j.bcp.2004.07.020] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2004] [Accepted: 07/07/2004] [Indexed: 11/26/2022]
Abstract
The benzodiazepine binding site of GABA(A) receptors is located at the interface of the alpha and gamma subunits. Certain point mutations in these subunits have been demonstrated to dramatically reduce the affinity of benzodiazepine binding site ligands for these receptors. Recently, mice were generated with a phenylalanine (F) to isoleucine (I) substitution at position 77 in the gamma2 subunit of GABA(A) receptors. Here we tested the potency of 24 benzodiazepine binding site ligands from 16 different structural classes for inhibition of [(3)H]flunitrazepam binding to brain membranes of these gamma2F77I mice. Results indicate that the potency of the classical 1,4-benzodiazepines, of the 1,4-thienodiazepine clotiazepam, the 1,5-benzodiazepine clobazam, or the pyrazoloquinoline CGS 9896 is only 2-7-fold reduced by this gamma2F77I point mutation. The potency of the imidazopyrimidines Ru 32698, Ru 33203, and Ru 33356, of the imidazoquinoline Ru 31719, or the pyrazolopyridine CGS 20625 is reduced 10-20-fold, whereas the potency of some imidazobenzodiazepines, beta-carbolines, cyclopyrrolones, imidazopyridines, triazolopyridazines, or quinolines is 100-1000-fold reduced. Interestingly, the extent of potency reduction induced by the gamma2F77I point mutation varied within the structural classes of compounds. Results support and significantly extend previous observations indicating that the residue gamma2F77 is important for high affinity binding of some, but not all benzodiazepine site ligands.
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Affiliation(s)
- Waltraud Ogris
- Division of Biochemistry and Molecular Biology, Brain Research Institute, Medical University of Vienna, Spitalgasse 4, A-1090 Vienna, Austria
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41
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Derry JMC, Dunn SMJ, Davies M. Identification of a residue in the γ-aminobutyric acid type A receptor α subunit that differentially affects diazepam-sensitive and -insensitive benzodiazepine site binding. J Neurochem 2004; 88:1431-8. [PMID: 15009644 DOI: 10.1046/j.1471-4159.2003.02264.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
GABAA receptors that contain either the alpha4- or alpha6-subunit isoform do not recognize classical 1,4-benzodiazepines (BZDs). However, other classes of BZD site ligands, including beta-carbolines, bind to these diazepam-insensitive receptor subtypes. Some beta-carbolines [e.g. ethyl beta-carboline-3-carboxylate (beta-CCE) and methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM)] display a higher affinity for alpha4- compared to alpha6-containing receptors. In order to identify the structural determinants that underlie these affinity differences, we constructed chimeric alpha6/alpha4 subunits and co-expressed these with wild-type rat beta2 and gamma2L subunits in tsA201 cells for radioligand binding analysis. After identification of candidate regions, site-directed mutagenesis was used to narrow the ligand selectivity to a single amino acid residue (alpha6N204/alpha4I203). Substitutions at alpha6N204 did not alter the affinity of the imidazobenzodiazepine Ro15-4513. A homologous mutation in the diazepam-sensitive alpha1 subunit (S205N) resulted in a 7-8-fold reduction in affinity for the beta-carbolines examined. Although the binding of the classical agonist flunitrazepam was relatively unaffected by this mutation in the alpha1 subunit, the affinity for Ro15-1788 and Ro15-4513 was decreased by approximately 19-fold and approximately 38-fold respectively. The importance of this residue, located in the Loop C region of the extracellular N-terminus of the subunit protein, emphasizes the differential interaction of ligands with the alpha subunit in diazepam-sensitive and -insensitive receptors.
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Affiliation(s)
- Jason M C Derry
- Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
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42
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Berezhnoy D, Nyfeler Y, Gonthier A, Schwob H, Goeldner M, Sigel E. On the benzodiazepine binding pocket in GABAA receptors. J Biol Chem 2003; 279:3160-8. [PMID: 14612433 DOI: 10.1074/jbc.m311371200] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Benzodiazepines are used for their sedative/hypnotic, anxiolytic, muscle relaxant, and anticonvulsive effects. They exert their actions through a specific high affinity binding site on the major inhibitory neurotransmitter receptor, the gamma-aminobutyric acid, type A (GABA(A)) receptor channel, where they act as positive allosteric modulators. To start to elucidate the relative positioning of benzodiazepine binding site ligands in their binding pocket, GABA(A) receptor residues thought to reside in the site were individually mutated to cysteine and combined with benzodiazepine analogs carrying substituents reactive to cysteine. Direct apposition of such reactive partners is expected to lead to an irreversible site-directed reaction. We describe here the covalent interaction of alpha(1)H101C with a reactive group attached to the C-7 position of diazepam. This interaction was studied at the level of radioactive ligand binding and at the functional level using electrophysiological methods. Covalent reaction occurs concomitantly with occupancy of the binding pocket. It stabilizes the receptor in its allosterically stimulated conformation. Covalent modification is not observed in wild type receptors or when using mutated alpha(1)H101C-containing receptors in combination with the reactive ligand pre-reacted with a sulfhydryl group, and the modification rate is reduced by the binding site ligand Ro15-1788. We present in addition evidence that gamma(2)Ala-79 is probably located in the access pathway of the ligand to its binding pocket.
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Affiliation(s)
- Dmytro Berezhnoy
- Department of Pharmacology, University of Bern, CH-3010 Bern, Switzerland
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43
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Ernst M, Brauchart D, Boresch S, Sieghart W. Comparative modeling of GABA(A) receptors: limits, insights, future developments. Neuroscience 2003; 119:933-43. [PMID: 12831854 DOI: 10.1016/s0306-4522(03)00288-4] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
GABA(A) receptors are chloride ion channels that mediate fast synaptic transmission and belong to a superfamily of pentameric ligand-gated ion channels. The recently published crystal structure of the acetylcholine binding protein can be used as a template for comparative modeling of the extracellular domain of GABA(A) receptors. In this commentary, difficulties with comparative modeling at low sequence identity are discussed, the degree of structural conservation to be expected within the superfamily is analyzed and numerical estimates of model uncertainties in functional regions are provided. Topography of the binding sites at subunit-interfaces is examined and possible targets for rational mutagenesis studies are suggested. Allosteric motions are considered and a mechanism for mediation of positive cooperativity at the benzodiazepine site is proposed.
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Affiliation(s)
- M Ernst
- Brain Research Institute of the University of Vienna, Biochemistry and Molecular Biology Department, Spitalgasse 4, 1090, Vienna, Austria
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