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Blednov YA, Shawlot W, Homanics GE, Osterndorff-Kahanek EA, Mason S, Mayfield J, Smalley JL, Moss SJ, Messing RO. The PDE4 inhibitor apremilast modulates ethanol responses in Gabrb1-S409A knock-in mice via PKA-dependent and independent mechanisms. Neuropharmacology 2024; 257:110035. [PMID: 38876310 PMCID: PMC11387004 DOI: 10.1016/j.neuropharm.2024.110035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Revised: 06/05/2024] [Accepted: 06/10/2024] [Indexed: 06/16/2024]
Abstract
We previously showed that the PDE4 inhibitor apremilast reduces ethanol consumption in mice by protein kinase A (PKA) and GABAergic mechanisms. Preventing PKA phosphorylation of GABAA β3 subunits partially blocked apremilast-mediated decreases in drinking. Here, we produced Gabrb1-S409A mice to render GABAA β1 subunits resistant to PKA-mediated phosphorylation. Mass spectrometry confirmed the presence of the S409A mutation and lack of changes in β1 subunit expression or phosphorylation at other residues. β1-S409A male and female mice did not differ from wild-type C57BL/6J mice in expression of Gabrb1, Gabrb2, or Gabrb3 subunits or in behavioral characteristics. Apremilast prolonged recovery from ethanol ataxia to a greater extent in Gabrb1-S409A mice but prolonged recovery from zolpidem and propofol to a similar extent in both genotypes. Apremilast shortened recovery from diazepam ataxia in wild-type but prolonged recovery in Gabrb1-S409A mice. In wild-type mice, the PKA inhibitor H89 prevented apremilast modulation of ataxia by ethanol and diazepam, but not by zolpidem. In Gabrb1-S409A mice, inhibiting PKA or EPAC2 (exchange protein directly activated by cAMP) partially reversed apremilast potentiation of ethanol, diazepam, and zolpidem ataxia. Apremilast prevented acute tolerance to ethanol ataxia in both genotypes, but there were no genotype differences in ethanol consumption before or after apremilast. In contrast to results in Gabrb3-S408A/S409A mice, PKA phosphorylation of β1-containing GABAA receptors is not required for apremilast's effects on acute tolerance or on ethanol consumption but is required for its ability to decrease diazepam intoxication. Besides PKA we identified EPAC2 as an additional cAMP-dependent mechanism by which apremilast regulates responses to GABAergic drugs.
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Affiliation(s)
- Yuri A Blednov
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, TX, 78712, USA
| | - William Shawlot
- Center for Biomedical Research Support, Mouse Genetic Engineering Facility, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Gregg E Homanics
- Departments of Anesthesiology & Perioperative Medicine, Neurobiology, and Pharmacology & Chemical Biology, University of Pittsburgh, Pittsburgh, PA, 15261, USA
| | | | - Sonia Mason
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Jody Mayfield
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Joshua L Smalley
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, 02111, USA
| | - Stephen J Moss
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, 02111, USA
| | - Robert O Messing
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, TX, 78712, USA; Department of Neuroscience, The University of Texas at Austin, Austin, TX, 78712, USA; Department of Neurology, Dell Medical School, The University of Texas at Austin, Austin, TX, 78712, USA.
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Marcinkowska M, Fajkis-Zajączkowska N, Szafrańska K, Jończyk J, Siwek A, Mordyl B, Karcz T, Latacz G, Kolaczkowski M. 2-(4-Fluorophenyl)-1 H-benzo[ d]imidazole as a Promising Template for the Development of Metabolically Robust, α1β2γ2GABA-A Receptor-Positive Allosteric Modulators. ACS Chem Neurosci 2023; 14:1166-1180. [PMID: 36848624 PMCID: PMC10020958 DOI: 10.1021/acschemneuro.2c00800] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023] Open
Abstract
Modulation of α1β2γ2GABA-A receptor subpopulation expressed in the basal ganglia region is a conceptually novel mode of pharmacological strategy that offers prospects to tackle a variety of neurological dysfunction. Although clinical findings provided compelling evidence for the validity of this strategy, the current chemical space of molecules able to modulate the α1/γ2 interface of the GABA-A receptor is limited to imidazo[1,2-a]pyridine derivatives that undergo rapid biotransformation. In response to a deficiency in the chemical repertoire of GABA-A receptors, we identified a series of 2-(4-fluorophenyl)-1H-benzo[d]imidazoles as positive allosteric modulators (PAMs) with improved metabolic stability and reduced potential for hepatotoxicity, where lead molecules 9 and 23 displayed interesting features in a preliminary investigation. We further disclose that the identified scaffold shows a preference for interaction with the α1/γ2 interface of the GABA-A receptor, delivering several PAMs of the GABA-A receptor. The present work provides useful chemical templates to further explore the therapeutic potential of GABA-A receptor ligands and enriches the chemical space of molecules suitable for the interaction with the α1/γ2 interface.
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Affiliation(s)
- Monika Marcinkowska
- Department of Medicinal Chemistry, Faculty of Pharmacy, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
| | - Nikola Fajkis-Zajączkowska
- Department of Medicinal Chemistry, Faculty of Pharmacy, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
| | - Katarzyna Szafrańska
- Department of Medicinal Chemistry, Faculty of Pharmacy, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
| | - Jakub Jończyk
- Department of Medicinal Chemistry, Faculty of Pharmacy, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
| | - Agata Siwek
- Department of Pharmacobiology, Faculty of Pharmacy Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
| | - Barbara Mordyl
- Department of Pharmacobiology, Faculty of Pharmacy Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
| | - Tadeusz Karcz
- Department of Technology and Biotechnology of Drugs, Faculty of Pharmacy, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
| | - Gniewomir Latacz
- Department of Technology and Biotechnology of Drugs, Faculty of Pharmacy, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
| | - Marcin Kolaczkowski
- Department of Medicinal Chemistry, Faculty of Pharmacy, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
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Neumann E, Rudolph U, Knutson DE, Li G, Cook JM, Hentschke H, Antkowiak B, Drexler B. Zolpidem Activation of Alpha 1-Containing GABA A Receptors Selectively Inhibits High Frequency Action Potential Firing of Cortical Neurons. Front Pharmacol 2019; 9:1523. [PMID: 30687091 PMCID: PMC6333667 DOI: 10.3389/fphar.2018.01523] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 12/12/2018] [Indexed: 11/13/2022] Open
Abstract
Introduction: High frequency neuronal activity in the cerebral cortex can be induced by noxious stimulation during surgery, brain injury or poisoning. In this scenario, it is essential to block cortical hyperactivity to protect the brain against damage, e.g., by using drugs that act as positive allosteric modulators at GABAA receptors. Yet, cortical neurons express multiple, functionally distinct GABAA receptor subtypes. Currently there is a lack of knowledge which GABAA receptor subtypes would be a good pharmacological target to reduce extensive cortical activity. Methods: Spontaneous action potential activity was monitored by performing extracellular recordings from organotypic neocortical slice cultures of wild type and GABAAR-α1(H101R) mutant mice. Phases of high neuronal activity were characterized using peri-event time histograms. Drug effects on within-up state firing rates were quantified via Hedges' g. Results: We quantified the effects of zolpidem, a positive modulator of GABAA receptors harboring α1-subunits, and the experimental benzodiazepine SH-053-2'F-S-CH3, which preferably acts at α2/3/5- but spares α1-subunits. Both agents decreased spontaneous action potential activity but altered the firing patterns in different ways. Zolpidem reduced action potential firing during highly active network states. This action was abolished by flumazenil, suggesting that it was mediated by benzodiazepine-sensitive GABAA receptors. SH-053-2'F-S-CH3 also attenuated neuronal activity, but unlike zolpidem, failed to reduce high frequency firing. To confirm that zolpidem actions were indeed mediated via α1-dependent actions, it was evaluated in slices from wild type and α(H101R) knock-in mice. Inhibition of high frequency action potential firing was observed in slices from wild type but not mutant mice. Conclusion: Our results suggest that during episodes of scarce and high neuronal activity action potential firing of cortical neurons is controlled by different GABAA receptor subtypes. Exaggerated firing of cortical neurons is reduced by positive modulation of α1-, but not α2/3/5-subunit containing GABAA receptors.
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Affiliation(s)
- Elena Neumann
- Experimental Anesthesiology Section, Department of Anesthesiology and Intensive Care, Eberhard Karls Universität Tübingen, Tübingen, Germany
| | - Uwe Rudolph
- Department of Comparative Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Daniel E Knutson
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, United States
| | - Guanguan Li
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, United States
| | - James M Cook
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, United States
| | - Harald Hentschke
- Experimental Anesthesiology Section, Department of Anesthesiology and Intensive Care, Eberhard Karls Universität Tübingen, Tübingen, Germany
| | - Bernd Antkowiak
- Experimental Anesthesiology Section, Department of Anesthesiology and Intensive Care, Eberhard Karls Universität Tübingen, Tübingen, Germany.,Werner Reichardt Center for Integrative Neuroscience, Eberhard Karls Universität Tübingen, Tübingen, Germany
| | - Berthold Drexler
- Experimental Anesthesiology Section, Department of Anesthesiology and Intensive Care, Eberhard Karls Universität Tübingen, Tübingen, Germany
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Zhu S, Noviello CM, Teng J, Walsh RM, Kim JJ, Hibbs RE. Structure of a human synaptic GABA A receptor. Nature 2018; 559:67-72. [PMID: 29950725 PMCID: PMC6220708 DOI: 10.1038/s41586-018-0255-3] [Citation(s) in RCA: 325] [Impact Index Per Article: 54.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 05/17/2018] [Indexed: 11/08/2022]
Abstract
Fast inhibitory neurotransmission in the brain is principally mediated by the neurotransmitter GABA (γ-aminobutyric acid) and its synaptic target, the type A GABA receptor (GABAA receptor). Dysfunction of this receptor results in neurological disorders and mental illnesses including epilepsy, anxiety and insomnia. The GABAA receptor is also a prolific target for therapeutic, illicit and recreational drugs, including benzodiazepines, barbiturates, anaesthetics and ethanol. Here we present high-resolution cryo-electron microscopy structures of the human α1β2γ2 GABAA receptor, the predominant isoform in the adult brain, in complex with GABA and the benzodiazepine site antagonist flumazenil, the first-line clinical treatment for benzodiazepine overdose. The receptor architecture reveals unique heteromeric interactions for this important class of inhibitory neurotransmitter receptor. This work provides a template for understanding receptor modulation by GABA and benzodiazepines, and will assist rational approaches to therapeutic targeting of this receptor for neurological disorders and mental illness.
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Affiliation(s)
- Shaotong Zhu
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Colleen M Noviello
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jinfeng Teng
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Richard M Walsh
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jeong Joo Kim
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Ryan E Hibbs
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
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5
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Bader BM, Steder A, Klein AB, Frølund B, Schroeder OHU, Jensen AA. Functional characterization of GABAA receptor-mediated modulation of cortical neuron network activity in microelectrode array recordings. PLoS One 2017; 12:e0186147. [PMID: 29028808 PMCID: PMC5640229 DOI: 10.1371/journal.pone.0186147] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Accepted: 09/26/2017] [Indexed: 12/11/2022] Open
Abstract
The numerous γ-aminobutyric acid type A receptor (GABAAR) subtypes are differentially expressed and mediate distinct functions at neuronal level. In this study we have investigated GABAAR-mediated modulation of the spontaneous activity patterns of primary neuronal networks from murine frontal cortex by characterizing the effects induced by a wide selection of pharmacological tools at a plethora of activity parameters in microelectrode array (MEA) recordings. The basic characteristics of the primary cortical neurons used in the recordings were studied in some detail, and the expression levels of various GABAAR subunits were investigated by western blotting and RT-qPCR. In the MEA recordings, the pan-GABAAR agonist muscimol and the GABABR agonist baclofen were observed to mediate phenotypically distinct changes in cortical network activity. Selective augmentation of αβγ GABAAR signaling by diazepam and of δ-containing GABAAR (δ-GABAAR) signaling by DS1 produced pronounced changes in the majority of the activity parameters, both drugs mediating similar patterns of activity changes as muscimol. The apparent importance of δ-GABAAR signaling for network activity was largely corroborated by the effects induced by the functionally selective δ-GABAAR agonists THIP and Thio-THIP, whereas the δ-GABAAR selective potentiator DS2 only mediated modest effects on network activity, even when co-applied with low THIP concentrations. Interestingly, diazepam exhibited dramatically right-shifted concentration-response relationships at many of the activity parameters when co-applied with a trace concentration of DS1 compared to when applied alone. In contrast, the potencies and efficacies displayed by DS1 at the networks were not substantially altered by the concomitant presence of diazepam. In conclusion, the holistic nature of the information extractable from the MEA recordings offers interesting insights into the contributions of various GABAAR subtypes/subgroups to cortical network activity and the putative functional interplay between these receptors in these neurons.
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Affiliation(s)
| | - Anne Steder
- NeuroProof GmbH, Friedrich-Barnewitz-Str. 4, Rostock, Germany
| | - Anders Bue Klein
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen Ø, Denmark
| | - Bente Frølund
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen Ø, Denmark
| | | | - Anders A. Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen Ø, Denmark
- * E-mail:
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6
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Steinmann ME, Schmidt RS, Bütikofer P, Mäser P, Sigel E. TbIRK is a signature sequence free potassium channel from Trypanosoma brucei locating to acidocalcisomes. Sci Rep 2017; 7:656. [PMID: 28386071 PMCID: PMC5429665 DOI: 10.1038/s41598-017-00752-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Accepted: 03/13/2017] [Indexed: 12/26/2022] Open
Abstract
Potassium channels from prokaryotes and eukaryotes are usually recognized by a typical amino acid sequence TXTGY(F)G representing the ionic selectivity filter. Using a screening approach with ion channel family profiles but without the above motif, we identified a gene in Trypanosoma brucei that exhibits homology to inward rectifying potassium channels. We report here cloning of this ion channel named TbIRK. The protein is localized to acidocalcisomes in procyclic and in bloodstream form parasites. Functional properties of this channel were established after expression in Xenopus oocytes. Currents recorded in potassium medium show inward rectification and little time dependence. Surprisingly, this channel retains selectivity for potassium ions over sodium ions >7, in spite of the lack of the classical selectivity filter. The sequence GGYVG was predicted in silico to replace this filter motif. Point mutations of the corresponding glycine residues confirmed this at the functional level. The channel is inhibited by caesium ions but remains unaffected by barium ions up to 10 mM. TbIRK is to our knowledge the first potassium channel in T. brucei that localizes to the acidocalcisomes, organelles involved in the storage of phosphates and the response to osmotic stress that occurs during the life cycle of trypanosomes.
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Affiliation(s)
- Michael E Steinmann
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - Remo S Schmidt
- Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Peter Bütikofer
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - Pascal Mäser
- Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Erwin Sigel
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland.
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Zolpidem is a potent stoichiometry-selective modulator of α1β3 GABAA receptors: evidence of a novel benzodiazepine site in the α1-α1 interface. Sci Rep 2016; 6:28674. [PMID: 27346730 PMCID: PMC4921915 DOI: 10.1038/srep28674] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 06/06/2016] [Indexed: 12/16/2022] Open
Abstract
Zolpidem is not a typical GABAA receptor hypnotic. Unlike benzodiazepines, zolpidem modulates tonic GABA currents in the rat dorsal motor nucleus of the vagus, exhibits residual effects in mice lacking the benzodiazepine binding site, and improves speech, cognitive and motor function in human patients with severe brain injury. The receptor by which zolpidem mediates these effects is not known. In this study we evaluated binary α1β3 GABAA receptors in either the 3α1:2β3 or 2α1:3β3 subunit stoichiometry, which differ by the existence of either an α1-α1 interface, or a β3-β3 interface, respectively. Both receptor stoichiometries are readily expressed in Xenopus oocytes, distinguished from each other by using GABA, zolpidem, diazepam and Zn2+. At the 3α1:2β3 receptor, clinically relevant concentrations of zolpidem enhanced GABA in a flumazenil-sensitive manner. The efficacy of diazepam was significantly lower compared to zolpidem. No modulation by either zolpidem or diazepam was detected at the 2α1:3β3 receptor, indicating that the binding site for zolpidem is at the α1-α1 interface, a site mimicking the classical α1-γ2 benzodiazepine site. Activating α1β3 (3α1:2β3) receptors may, in part, mediate the physiological effects of zolpidem observed under distinct physiological and clinical conditions, constituting a potentially attractive drug target.
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Rufener L, Bedoni N, Baur R, Rey S, Glauser DA, Bouvier J, Beech R, Sigel E, Puoti A. acr-23 Encodes a monepantel-sensitive channel in Caenorhabditis elegans. PLoS Pathog 2013; 9:e1003524. [PMID: 23950710 PMCID: PMC3738477 DOI: 10.1371/journal.ppat.1003524] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Accepted: 06/12/2013] [Indexed: 11/19/2022] Open
Abstract
Monepantel is a member of the recently identified class of anthelmintics known as the amino-acetonitrile derivatives (AADs). Monepantel controls all major gastro-intestinal nematodes in sheep including those that are resistant to the classical anthelmintics. Previous studies have shown that the Caenorhabditis elegans acr-23 and the Haemonchus contortus Hco-mptl-1 genes may be prominent targets of monepantel. With this discovery it became possible to investigate the mode of action of monepantel in nematodes at the molecular level. In the present study, we show that a C. elegans mutant acr-23 strain is fully rescued by expressing the wild-type acr-23 gene. Moreover, we present a new mutant allele, and characterize acr-23 alleles genetically. We also show that acr-23 is expressed in body wall muscle cells, and provide therefore a possible explanation for the paralysis caused by monepantel. Furthermore, genetic evidence suggests that the chaperone RIC-3 is required for expression of full monepantel resistance. Finally, we present reconstitution of the C. elegans ACR-23 receptor in Xenopus laevis oocytes and provide direct evidence of its modulation by monepantel. Conversely, co-injection of the chaperone RIC-3 had no impact for channel reconstitution in X. laevis oocytes. These results reinforce the involvement of the ACR-23 family in the mode of action of monepantel and advance our understanding of this new class of anthelmintics. Worldwide, sheep and cattle farming are endangered by anthelmintic-resistant gastro-intestinal nematodes. Monepantel, a member of the recently identified class of anthelmintics known as the amino-acetonitrile derivatives (AADs) exhibits excellent efficacy against various species of livestock-pathogenic nematodes and, more importantly, overcomes existing resistances to the currently available anthelmintics. Previous studies conducted with the non-parasitic model nematode Caenorhabditis elegans have found that acr-23 mutants are fully resistant to monepantel. In this study, we confirm the role of acr-23 as a primary target of monepantel by 1) restoring monepantel sensitivity in the presence of extrachromosomal copies of wild-type acr-23, 2) finding that ACR-23 is mainly expressed in muscle cells, and 3) showing that acr-23 forms a monepantel-sensitive channel in Xenopus oocytes.
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Affiliation(s)
- Lucien Rufener
- Novartis Centre de Recherche Santé Animale, St. Aubin, Switzerland
- Institute of Parasitology, Macdonald College, McGill University, Ste Anne de Bellevue, Quebec, Canada
| | - Nicola Bedoni
- Department of Biology, University of Fribourg, Fribourg, Switzerland
| | - Roland Baur
- Institute for Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - Samantha Rey
- Department of Biology, University of Fribourg, Fribourg, Switzerland
| | | | - Jacques Bouvier
- Novartis Centre de Recherche Santé Animale, St. Aubin, Switzerland
| | - Robin Beech
- Institute of Parasitology, Macdonald College, McGill University, Ste Anne de Bellevue, Quebec, Canada
| | - Erwin Sigel
- Institute for Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - Alessandro Puoti
- Department of Biology, University of Fribourg, Fribourg, Switzerland
- * E-mail:
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9
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Baur R, Gertsch J, Sigel E. The cannabinoid CB1 receptor antagonists rimonabant (SR141716) and AM251 directly potentiate GABA(A) receptors. Br J Pharmacol 2012; 165:2479-84. [PMID: 21470203 DOI: 10.1111/j.1476-5381.2011.01405.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Rimonabant (SR141716) and the structurally related AM251 are widely used in pharmacological experiments as selective cannabinoid receptor CB(1) antagonists / inverse agonists. Concentrations of 0.5-10 µM are usually applied in in vitro experiments. We intended to show that these drugs did not act at GABA(A) receptors but found a significant positive allosteric modulation instead. EXPERIMENTAL APPROACH Recombinant GABA(A) receptors were expressed in Xenopus oocytes. Receptors were exposed to AM251 or rimonabant in the absence and presence of GABA. Standard electrophysiological techniques were used to monitor the elicited ionic currents. KEY RESULTS AM251 dose-dependently potentiated responses to 0.5 µM GABA at the recombinant α(1) β(2) γ(2) GABA(A) receptor with an EC(50) below 1 µM and a maximal potentiation of about eightfold. The Hill coefficient indicated that more than one binding site for AM251 was located in this receptor. Rimonabant had a lower affinity, but a fourfold higher efficacy. AM251 potentiated also currents mediated by α(1) β(2) , α(x) β(2) γ(2) (x = 2,3,5,6), α(1) β(3) γ(2) and α(4) β(2) δ GABA(A) receptors, but not those mediated by α(1) β(1) γ(2) . Interestingly, the CB(1) receptor antagonists LY320135 and O-2050 did not significantly affect α(1) β(2) γ(2) GABA(A) receptor-mediated currents at concentrations of 1 µM. CONCLUSIONS AND IMPLICATIONS This study identified rimonabant and AM251 as positive allosteric modulators of GABA(A) receptors. Thus, potential GABAergic effects of commonly used concentrations of these compounds should be considered in in vitro experiments, especially at extrasynaptic sites where GABA concentrations are low. LINKED ARTICLES This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.
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Affiliation(s)
- R Baur
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bühlstr, Bern, Switzerland
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10
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Kuhn-Nentwig L, Fedorova IM, Lüscher BP, Kopp LS, Trachsel C, Schaller J, Vu XL, Seebeck T, Streitberger K, Nentwig W, Sigel E, Magazanik LG. A venom-derived neurotoxin, CsTx-1, from the spider Cupiennius salei exhibits cytolytic activities. J Biol Chem 2012; 287:25640-9. [PMID: 22613721 DOI: 10.1074/jbc.m112.339051] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
CsTx-1, the main neurotoxic acting peptide in the venom of the spider Cupiennius salei, is composed of 74 amino acid residues, exhibits an inhibitory cysteine knot motif, and is further characterized by its highly cationic charged C terminus. Venom gland cDNA library analysis predicted a prepropeptide structure for CsTx-1 precursor. In the presence of trifluoroethanol, CsTx-1 and the long C-terminal part alone (CT1-long; Gly-45-Lys-74) exhibit an α-helical structure, as determined by CD measurements. CsTx-1 and CT1-long are insecticidal toward Drosophila flies and destroys Escherichia coli SBS 363 cells. CsTx-1 causes a stable and irreversible depolarization of insect larvae muscle cells and frog neuromuscular preparations, which seem to be receptor-independent. Furthermore, this membranolytic activity could be measured for Xenopus oocytes, in which CsTx-1 and CT1-long increase ion permeability non-specifically. These results support our assumption that the membranolytic activities of CsTx-1 are caused by its C-terminal tail, CT1-long. Together, CsTx-1 exhibits two different functions; as a neurotoxin it inhibits L-type Ca(2+) channels, and as a membranolytic peptide it destroys a variety of prokaryotic and eukaryotic cell membranes. Such a dualism is discussed as an important new mechanism for the evolution of spider venomous peptides.
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Affiliation(s)
- Lucia Kuhn-Nentwig
- Institute of Ecology and Evolution, University of Bern, Baltzerstrasse 6, CH-3012 Bern, Switzerland.
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Gonzalez-Salgado A, Steinmann ME, Greganova E, Rauch M, Mäser P, Sigel E, Bütikofer P. myo-Inositol uptake is essential for bulk inositol phospholipid but not glycosylphosphatidylinositol synthesis in Trypanosoma brucei. J Biol Chem 2012; 287:13313-23. [PMID: 22351763 DOI: 10.1074/jbc.m112.344812] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
myo-Inositol is an essential precursor for the production of inositol phosphates and inositol phospholipids in all eukaryotes. Intracellular myo-inositol is generated by de novo synthesis from glucose 6-phosphate or is provided from the environment via myo-inositol symporters. We show that in Trypanosoma brucei, the causative pathogen of human African sleeping sickness and nagana in domestic animals, myo-inositol is taken up via a specific proton-coupled electrogenic symport and that this transport is essential for parasite survival in culture. Down-regulation of the myo-inositol transporter using RNA interference inhibited uptake of myo-inositol and blocked the synthesis of the myo-inositol-containing phospholipids, phosphatidylinositol and inositol phosphorylceramide; in contrast, it had no effect on glycosylphosphatidylinositol production. This together with the unexpected localization of the myo-inositol transporter in both the plasma membrane and the Golgi demonstrate that metabolism of endogenous and exogenous myo-inositol in T. brucei is strictly segregated.
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Affiliation(s)
- Amaia Gonzalez-Salgado
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bühlstrasse 28, 3012 Bern, Switzerland
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Baur R, Tan KR, Lüscher BP, Gonthier A, Goeldner M, Sigel E. Covalent modification of GABAA receptor isoforms by a diazepam analogue provides evidence for a novel benzodiazepine binding site that prevents modulation by these drugs. J Neurochem 2008; 106:2353-63. [PMID: 18643789 DOI: 10.1111/j.1471-4159.2008.05574.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Classical benzodiazepines, for example diazepam, interact with alpha(x)beta(2)gamma(2) GABA(A) receptors, x = 1, 2, 3, 5. Little is known about effects of alpha subunits on the structure of the binding pocket. We studied here the interaction of the covalently reacting diazepam analog 7-Isothiocyanato-5-phenyl-1,3-dihydro-2H-1,4-benzodiazepin-2-one (NCS compound) with alpha(1)H101Cbeta(2)gamma(2) and with receptors containing the homologous mutation, alpha(2)H101Cbeta(2)gamma(2), alpha(3)H126Cbeta(2)gamma(2) and alpha(5)H105Cbeta(2)gamma(2). This comparison was extended to alpha(6)R100Cbeta(2)gamma(2) receptors as this mutation conveys to these receptors high affinity towards classical benzodiazepines. The interaction was studied at the ligand binding level and at the functional level using electrophysiological techniques. Results indicate that the geometry of alpha(6)R100Cbeta(2)gamma(2) enables best interaction with NCS compound, followed by alpha(3)H126Cbeta(2)gamma(2), alpha(1)H101Cbeta(2)gamma(2) and alpha(2)H101Cbeta(2)gamma(2), while alpha(5)H105Cbeta(2)gamma(2) receptors show little interaction. Our results allow conclusions about the relative apposition of alpha(1)H101 and homologous positions in alpha(2), alpha(3), alpha(5) and alpha(6) with the position occupied by -Cl in diazepam. During this study we found evidence for the presence of a novel site for benzodiazepines that prevents modulation of GABA(A) receptors via the classical benzodiazepine site. The novel site potentially contributes to the high degree of safety to some of these drugs. Our results indicate that this site may be located at the alpha/beta subunit interface pseudo-symmetrically to the site for classical benzodiazepines located at the alpha/gamma interface.
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Affiliation(s)
- Roland Baur
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
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