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Arias HR, Pierce SR, Germann AL, Xu SQ, Ortells MO, Sakamoto S, Manetti D, Romanelli MN, Hamachi I, Akk G. Chemical, Pharmacological, and Structural Characterization of Novel Acrylamide-Derived Modulators of the GABA A Receptor. Mol Pharmacol 2023; 104:115-131. [PMID: 37316350 PMCID: PMC10441626 DOI: 10.1124/molpharm.123.000692] [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: 03/01/2023] [Revised: 05/22/2023] [Accepted: 06/01/2023] [Indexed: 06/16/2023] Open
Abstract
Acrylamide-derived compounds have been previously shown to act as modulators of members of the Cys-loop transmitter-gated ion channel family, including the mammalian GABAA receptor. Here we have synthesized and functionally characterized the GABAergic effects of a series of novel compounds (termed "DM compounds") derived from the previously characterized GABAA and the nicotinic α7 receptor modulator (E)-3-furan-2-yl-N-p-tolyl-acrylamide (PAM-2). Fluorescence imaging studies indicated that the DM compounds increase apparent affinity to the transmitter by up to 80-fold in the ternary αβγ GABAA receptor. Using electrophysiology, we show that the DM compounds, and the structurally related (E)-3-furan-2-yl-N-phenylacrylamide (PAM-4), have concurrent potentiating and inhibitory effects that can be isolated and observed under appropriate recording conditions. The potentiating efficacies of the DM compounds are similar to those of neurosteroids and benzodiazepines (ΔG ∼ -1.5 kcal/mol). Molecular docking, functionally confirmed by site-directed mutagenesis experiments, indicate that receptor potentiation is mediated by interactions with the classic anesthetic binding sites located in the transmembrane domain of the intersubunit interfaces. Inhibition by the DM compounds and PAM-4 was abolished in the receptor containing the α1(V256S) mutation, suggestive of similarities in the mechanism of action with that of inhibitory neurosteroids. Functional competition and mutagenesis experiments, however, indicate that the sites mediating inhibition by the DM compounds and PAM-4 differ from those mediating the action of the inhibitory steroid pregnenolone sulfate. SIGNIFICANCE STATEMENT: We have synthesized and characterized the actions of novel acrylamide-derived compounds on the mammalian GABAA receptor. We show that the compounds have concurrent potentiating effects mediated by the classic anesthetic binding sites, and inhibitory actions that bear mechanistic resemblance to but do not share binding sites with, the inhibitory steroid pregnenolone sulfate.
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Affiliation(s)
- Hugo R Arias
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Spencer R Pierce
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Allison L Germann
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Sophia Q Xu
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Marcelo O Ortells
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Seiji Sakamoto
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Dina Manetti
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Maria Novella Romanelli
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Itaru Hamachi
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Gustav Akk
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
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Pierce SR, Germann AL, Xu SQ, Menon SL, Ortells MO, Arias HR, Akk G. Mutational Analysis of Anesthetic Binding Sites and Their Effects on GABA A Receptor Activation and Modulation by Positive Allosteric Modulators of the α7 Nicotinic Receptor. Biomolecules 2023; 13:698. [PMID: 37189445 PMCID: PMC10135968 DOI: 10.3390/biom13040698] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Revised: 04/16/2023] [Accepted: 04/18/2023] [Indexed: 05/17/2023] Open
Abstract
The positive allosteric modulators (PAMs) of the α7 nicotinic receptor N-(5-Cl-2-hydroxyphenyl)-N'-[2-Cl-5-(trifluoromethyl)phenyl]-urea (NS-1738) and (E)-3-(furan-2-yl)-N-(p-tolyl)-acrylamide (PAM-2) potentiate the α1β2γ2L GABAA receptor through interactions with the classic anesthetic binding sites located at intersubunit interfaces in the transmembrane domain of the receptor. In the present study, we employed mutational analysis to investigate in detail the involvement and contributions made by the individual intersubunit interfaces to receptor modulation by NS-1738 and PAM-2. We show that mutations to each of the anesthetic-binding intersubunit interfaces (β+/α-, α+/β-, and γ+/β-), as well as the orphan α+/γ- interface, modify receptor potentiation by NS-1738 and PAM-2. Furthermore, mutations to any single interface can fully abolish potentiation by the α7-PAMs. The findings are discussed in the context of energetic additivity and interactions between the individual binding sites.
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Affiliation(s)
- Spencer R. Pierce
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Allison L. Germann
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Sophia Q. Xu
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Saumith L. Menon
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Marcelo O. Ortells
- Facultad de Medicina, Universidad de Morón, CONICET, Morón 1708, Argentina
| | - Hugo R. Arias
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, OK 74464, USA
| | - Gustav Akk
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
- The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO 63110, USA
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Pence A, Hoyt H, McGrath M, Forman SA, Raines DE. Competitive Interactions Between Propofol and Diazepam: Studies in GABA A Receptors and Zebrafish. J Pharmacol Exp Ther 2022; 383:238-245. [PMID: 36167415 PMCID: PMC9667980 DOI: 10.1124/jpet.122.001337] [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: 06/02/2022] [Revised: 08/25/2022] [Accepted: 09/16/2022] [Indexed: 01/07/2023] Open
Abstract
Although propofol is among the most commonly administered general anesthetics, its mechanism of action is not fully understood. It has been hypothesized that propofol acts via a similar mechanism as (R)-ethyl 1-(1-phenylethyl)-1H-imidazole-5-carboxylate (etomidate) by binding within the GABAA receptor transmembrane receptor domain at the two β +/α - subunit interfaces with resultant positive allosteric modulation. To test this hypothesis, we leveraged the ability of diazepam to bind to those sites and act as a competitive antagonist. We used oocyte-expressed α 1 β 3 γ 2L GABAA receptors to define the actions of diazepam (± flumazenil) on currents activated or potentiated by propofol and a zebrafish activity assay to define the impact of diazepam and flumazenil on propofol-induced anesthesia. We found that diazepam increased the amplitudes of GABAA receptor-mediated currents at nanomolar concentrations but reduced them at micromolar concentrations. The current amplitude changes produced by nanomolar diazepam concentrations were inhibited by flumazenil whereas those produced by micromolar diazepam concentrations were not. Studies of agonist potentiation showed that the micromolar inhibitory action of diazepam was surmountable by high concentrations of propofol and produced a rightward shift in the propofol concentration-response curve characterized by a Schild slope not statistically significantly different from 1, consistent with competition between diazepam and propofol. Although micromolar concentrations of diazepam (plus flumazenil) similarly reduced GABAA receptor currents modulated by propofol and etomidate, it only reduced the anesthetic actions of etomidate. We conclude that while both propofol and etomidate can modulate GABAA receptors by binding to the β +/α - subunit interfacial sites, propofol-induced anesthesia likely involves additional target sites. SIGNIFICANCE STATEMENT: Although the drug combination of diazepam and flumazenil reverses the GABAA receptor positive modulatory actions of both propofol and (R)-ethyl 1-(1-phenylethyl)-1H-imidazole-5-carboxylate (etomidate), it only reverses the in vivo anesthetic actions of etomidate. These results strongly suggest that distinct mechanisms of action account for the anesthetic actions of these two commonly administered anesthetic agents.
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Affiliation(s)
- Andrea Pence
- Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Helen Hoyt
- Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Megan McGrath
- Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Stuart A Forman
- Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Douglas E Raines
- Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
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Arias HR, Germann AL, Pierce SR, Sakamoto S, Ortells MO, Hamachi I, Akk G. Modulation of the mammalian GABA A receptor by type I and type II positive allosteric modulators of the α7 nicotinic acetylcholine receptor. Br J Pharmacol 2022; 179:5323-5337. [PMID: 36082615 PMCID: PMC9669183 DOI: 10.1111/bph.15948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Revised: 08/29/2022] [Accepted: 09/06/2022] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Positive allosteric modulators of the α7 nicotinic acetylcholine (nACh) receptor (α7-PAMs) possess promnesic and procognitive properties and have potential in the treatment of cognitive and psychiatric disorders including Alzheimer's disease and schizophrenia. Behavioural studies in rodents have indicated that α7-PAMs can also produce antinociceptive and anxiolytic effects that may be associated with positive modulation of the GABAA receptor. The overall goal of this study was to investigate the modulatory actions of selected α7-PAMs on the GABAA receptor. EXPERIMENTAL APPROACH We employed a combination of cell fluorescence imaging, electrophysiology, functional competition and site-directed mutagenesis to investigate the functional and structural mechanisms of modulation of the GABAA receptor by three representative α7-PAMs. KEY RESULTS We show that the α7-PAMs at micromolar concentrations enhance the apparent affinity of the GABAA receptor for the transmitter and potentiate current responses from the receptor. The compounds were equi-effective at binary αβ and ternary αβγ GABAA receptors. Functional competition and site-directed mutagenesis indicate that the α7-PAMs bind to the classic anaesthetic binding sites in the transmembrane region in the intersubunit interfaces, which results in stabilization of the active state of the receptor. CONCLUSION AND IMPLICATIONS We conclude that the tested α7-PAMs are micromolar-affinity, intermediate- to low-efficacy allosteric potentiators of the mammalian αβγ GABAA receptor. Given the similarities in the in vitro sensitivities of the α7 nACh and α1β2γ2L GABAA receptors to α7-PAMs, we propose that doses used to produce nACh receptor-mediated behavioural effects in vivo are likely to modulate GABAA receptor function.
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Affiliation(s)
- Hugo R. Arias
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, OK, USA
| | - Allison L. Germann
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Spencer R. Pierce
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Seiji Sakamoto
- Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan
| | - Marcelo O. Ortells
- Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina
| | - Itaru Hamachi
- Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan
| | - Gustav Akk
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
- The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA
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Goldschen-Ohm MP. Benzodiazepine Modulation of GABA A Receptors: A Mechanistic Perspective. Biomolecules 2022; 12:biom12121784. [PMID: 36551212 PMCID: PMC9775625 DOI: 10.3390/biom12121784] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 11/23/2022] [Accepted: 11/26/2022] [Indexed: 12/05/2022] Open
Abstract
Benzodiazepines (BZDs) are a class of widely prescribed psychotropic drugs that target GABAA receptors (GABAARs) to tune inhibitory synaptic signaling throughout the central nervous system. Despite knowing their molecular target for over 40 years, we still do not fully understand the mechanism of modulation at the level of the channel protein. Nonetheless, functional studies, together with recent cryo-EM structures of GABAA(α1)2(βX)2(γ2)1 receptors in complex with BZDs, provide a wealth of information to aid in addressing this gap in knowledge. Here, mechanistic interpretations of functional and structural evidence for the action of BZDs at GABAA(α1)2(βX)2(γ2)1 receptors are reviewed. The goal is not to describe each of the many studies that are relevant to this discussion nor to dissect in detail all the effects of individual mutations or perturbations but rather to highlight general mechanistic principles in the context of recent structural information.
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Hoyt H, Fantasia RJ, Bhave K, Yang X, Forman SA. Photomotor Responses in Zebrafish and Electrophysiology Reveal Varying Interactions of Anesthetics Targeting Distinct Sites on γ-Aminobutyric Acid Type A Receptors. Anesthesiology 2022; 137:568-585. [PMID: 36018576 PMCID: PMC9588801 DOI: 10.1097/aln.0000000000004361] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND Etomidate, barbiturates, alfaxalone, and propofol are anesthetics that allosterically modulate γ-aminobutyric acid type A (GABAA) receptors via distinct sets of molecular binding sites. Two-state concerted coagonist models account for anesthetic effects and predict supra-additive interactions between drug pairs acting at distinct sites. Some behavioral and molecular studies support these predictions, while other findings suggest potentially complex anesthetic interactions. We therefore evaluated interactions among four anesthetics in both animals and GABAA receptors. METHODS The authors used video assessment of photomotor responses in zebrafish larvae and isobolography to evaluate hypnotic drug pair interactions. Voltage clamp electrophysiology and allosteric shift analysis evaluated coagonist interactions in α1β3γ2L receptors activated by γ-aminobutyric acid (GABA) versus anesthetics [log(d, AN):log(d, GABA) ratio]. Anesthetic interactions at concentrations relevant to zebrafish were assessed in receptors activated with low GABA. RESULTS In zebrafish larvae, etomidate interacted additively with both propofol and the barbiturate R-5-allyl-1-methyl m-trifluoromethyl mephobarbital (R-mTFD-MPAB; mean ± SD α = 1.0 ± 0.07 and 0.96 ± 0.11 respectively, where 1.0 indicates additivity), while the four other drug pairs displayed synergy (mean α range 0.76 to 0.89). Electrophysiologic allosteric shifts revealed that both propofol and R-mTFD-MPAB modulated etomidate-activated receptors much less than GABA-activated receptors [log(d, AN):log(d, GABA) ratios = 0.09 ± 0.021 and 0.38 ± 0.024, respectively], while alfaxalone comparably modulated receptors activated by GABA or etomidate [log(d) ratio = 0.87 ± 0.056]. With low GABA activation, etomidate combined with alfaxalone was supra-additive (n = 6; P = 0.023 by paired t test), but etomidate plus R-mTFD-MPAB or propofol was not. CONCLUSIONS In both zebrafish and GABAA receptors, anesthetic drug pairs interacted variably, ranging from additivity to synergy. Pairs including etomidate displayed corresponding interactions in animals and receptors. Some of these results challenge simple two-state coagonist models and support alternatives where different anesthetics may stabilize distinct receptor conformations, altering the effects of other drugs. EDITOR’S PERSPECTIVE
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Affiliation(s)
- Helen Hoyt
- Department of Anesthesia Critical Care & Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Ryan J Fantasia
- School of Biologic Sciences, University of California-San Diego, San Diego, California
| | - Kieran Bhave
- Department of Anesthesia Critical Care & Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Xiaoxuan Yang
- Department of Anesthesiology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
| | - Stuart A Forman
- Department of Anesthesia Critical Care & Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
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7
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Pressly B, Lee RD, Singh V, Pessah IN, Wulff H. The seizure-inducing plastic explosive RDX inhibits the α1β2γ2 GABA A receptor. Ann Clin Transl Neurol 2022; 9:600-609. [PMID: 35324073 PMCID: PMC9082378 DOI: 10.1002/acn3.51536] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 02/21/2022] [Accepted: 02/23/2022] [Indexed: 12/20/2022] Open
Abstract
Objective Royal demolition explosive (RDX) can induce seizures in wildlife and humans following release into the environment or after voluntary consumption. During the Vietnam War, RDX intoxication was the most common cause of generalized seizures in US service personnel, and in some sections of the armed forces, eating of RDX has continued as “a dare” to this day. After its mechanism of action was long unknown, RDX was recently shown to be a GABAA receptor antagonist. We here determined the GABAA receptor subtype‐selectivity of RDX and mapped its functional binding site. Methods We used whole‐cell patch‐clamp to determine the potency of RDX on 10 recombinantly expressed GABAA receptors and mapped the RDX binding site using a combination of Rosetta molecular modeling and site‐directed mutagenesis. Results RDX was found to reversibly inhibit the α1β2γ2 GABAA receptor with an IC50 of 23 μmol/L (95% CI 15.1–33.3 μmol/L), whereas α4 and α6 containing GABAA receptor combinations were 4–10‐fold less sensitive. RDX is binding to the noncompetitive antagonist (NCA) site in the pore. In a molecular model based on the cryo‐EM structure of the resting state of the α1β2γ2 receptor, RDX forms two hydrogen bonds with the threonines at the T6’ ring and makes hydrophobic interactions with the valine and alanine in 2′ position of the α1 or β2 subunits. Interpretation Our findings characterize the mechanism of action of RDX at the atomistic level and suggest that RDX‐induced seizures should be susceptible to treatment with GABAA modulating drugs such as benzodiazepines, barbiturates, propofol, or neurosteroids.
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Affiliation(s)
- Brandon Pressly
- Department of Pharmacology, School of Medicine, University of California, Davis, California, USA
| | - Ruth D Lee
- Department of Pharmacology, School of Medicine, University of California, Davis, California, USA
| | - Vikrant Singh
- Department of Pharmacology, School of Medicine, University of California, Davis, California, USA
| | - Isaac N Pessah
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, California, USA
| | - Heike Wulff
- Department of Pharmacology, School of Medicine, University of California, Davis, California, USA
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Arias HR, Borghese CM, Germann AL, Pierce SR, Bonardi A, Nocentini A, Gratteri P, Thodati TM, Lim NJ, Adron Harris R, Akk G. (+)-Catharanthine potentiates the GABA A receptor by binding to a transmembrane site at the β(+)/α(-) interface near the TM2-TM3 loop. Biochem Pharmacol 2022; 199:114993. [PMID: 35304861 PMCID: PMC9178925 DOI: 10.1016/j.bcp.2022.114993] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Revised: 03/09/2022] [Accepted: 03/10/2022] [Indexed: 11/17/2022]
Abstract
(+)-Catharanthine, a coronaridine congener, potentiates the γ-aminobutyric acid type A receptor (GABAAR) and induces sedation through a non-benzodiazepine mechanism, but the specific site of action and intrinsic mechanism have not beendefined. Here, we describe GABAAR subtype selectivity and location of the putative binding site for (+)-catharanthine using electrophysiological, site-directed mutagenesis, functional competition, and molecular docking experiments. Electrophysiological and in silico experiments showed that (+)-catharanthine potentiates the responses to low, subsaturating GABA at β2/3-containing GABAARs 2.4-3.5 times more efficaciously than at β1-containing GABAARs. The activity of (+)-catharanthine is reduced by the β2(N265S) mutation that decreases GABAAR potentiation by loreclezole, but not by the β3(M286C) or α1(Q241L) mutations that reduce receptor potentiation by R(+)-etomidate or neurosteroids, respectively. Competitive functional experiments indicated that the binding site for (+)-catharanthine overlaps that for loreclezole, but not those for R(+)-etomidate or potentiating neurosteroids. Molecular docking experiments suggested that (+)-catharanthine binds at the β(+)/α(-) intersubunit interface near the TM2-TM3 loop, where it forms H-bonds with β2-D282 (TM3), β2-K279 (TM2-TM3 loop), and β2-N265 and β2-R269 (TM2). Site-directed mutagenesis experiments supported the in silico results, demonstrating that the K279A and D282A substitutions, that lead to a loss of H-bonding ability of the mutated residue, and the N265S mutation, impair the gating efficacy of (+)-catharanthine. We infer that (+)-catharanthine potentiates the GABAAR through several H-bond interactions with a binding site located in the β(+)/α(-) interface in the transmembrane domain, near the TM2-TM3 loop, where it overlaps with loreclezole binding site.
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Affiliation(s)
- Hugo R Arias
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, OK, USA.
| | - Cecilia M Borghese
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, TX, USA.
| | - Allison L Germann
- Department of Anesthesiology, the Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA.
| | - Spencer R Pierce
- Department of Anesthesiology, the Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA.
| | - Alessandro Bonardi
- Department of Neurosciences, Psychology, Drug Research and Child Health (NEUROFARBA), Section of Pharmaceutical and Nutraceutical Sciences, Laboratory of Molecular Modeling Cheminformatics & QSAR, University of Florence, Florence, Italy.
| | - Alessio Nocentini
- Department of Neurosciences, Psychology, Drug Research and Child Health (NEUROFARBA), Section of Pharmaceutical and Nutraceutical Sciences, Laboratory of Molecular Modeling Cheminformatics & QSAR, University of Florence, Florence, Italy.
| | - Paola Gratteri
- Department of Neurosciences, Psychology, Drug Research and Child Health (NEUROFARBA), Section of Pharmaceutical and Nutraceutical Sciences, Laboratory of Molecular Modeling Cheminformatics & QSAR, University of Florence, Florence, Italy.
| | - Thanvi M Thodati
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, TX, USA.
| | - Natalie J Lim
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, TX, USA.
| | - R Adron Harris
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, TX, USA.
| | - Gustav Akk
- Department of Anesthesiology, the Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA.
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9
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McGrath M, Hoyt H, Pence A, Forman SA, Raines DE. Selective actions of benzodiazepines at the transmembrane anaesthetic binding sites of the GABA A receptor: In vitro and in vivo studies. Br J Pharmacol 2021; 178:4842-4858. [PMID: 34386973 PMCID: PMC8637433 DOI: 10.1111/bph.15662] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Revised: 07/14/2021] [Accepted: 07/21/2021] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE In addition to binding to the classical high-affinity extracellular benzodiazepine binding site of the GABAA receptor, some benzodiazepines occupy transmembrane inter-subunit anaesthetic sites that bind etomidate (β+ /α- sites) or the barbiturate derivative R-mTFD-MPAB (α+ /β- and γ+ /β- sites). We aimed to define the functional effects of these interactions on GABAA receptor activity and animal behaviour. EXPERIMENTAL APPROACH With flumazenil blocking classical high-affinity extracellular benzodiazepine site effects, modulation of GABA-activated currents by diazepam, midazolam and flurazepam was measured electrophysiologically in wildtype and M2-15' mutant α1 β3 γ2L GABAA receptors. Zebrafish locomotive activity was also assessed in the presence of each benzodiazepine plus flumazenil. KEY RESULTS In the presence of flumazenil, micromolar concentrations of diazepam and midazolam both potentiated and inhibited wildtype GABAA receptor currents. β3 N265M (M2-15' in the β+ /α- sites) and α1 S270I (M2-15' in the α+ /β- site) mutations reduced or abolished potentiation by these drugs. In contrast, the γ2 S280W mutation (M2-15' in the γ+ /β- site) abolished inhibition. Flurazepam plus flumazenil only inhibited wildtype receptor currents, an effect unaltered by M2-15' mutations. In the presence of flumazenil, zebrafish locomotion was enhanced by diazepam at concentrations up to 30 μM and suppressed at 100 μM, suppressed by midazolam and enhanced by flurazepam. CONCLUSIONS AND IMPLICATIONS Benzodiazepine binding to transmembrane anaesthetic binding sites of the GABAA receptor can produce positive or negative modulation manifesting as decreases or increases in locomotion, respectively. Selectivity for these sites may contribute to the distinct GABAA receptor and behavioural actions of different benzodiazepines, particularly at high (i.e. anaesthetic) concentrations.
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Affiliation(s)
- Megan McGrath
- Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, USA
| | - Helen Hoyt
- Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, USA
| | - Andrea Pence
- Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, USA
| | - Stuart A Forman
- Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, USA
| | - Douglas E Raines
- Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, USA
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10
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Knoflach F, Bertrand D. Pharmacological modulation of GABA A receptors. Curr Opin Pharmacol 2021; 59:3-10. [PMID: 34020139 DOI: 10.1016/j.coph.2021.04.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Accepted: 04/13/2021] [Indexed: 10/21/2022]
Abstract
Ligand-gated ion channels are integral membrane proteins that activate through a change in conformation upon transmitter binding and were identified as key players of brain function. GABAA receptors are major inhibitory ligand-gated ion channels of this protein family. They are the target of many therapeutic compounds widely used in the clinic and continue to attract the attention of academic and pharmaceutical laboratories. Advances in the knowledge of the structure of GABAA receptors at the molecular level with unprecedented resolution enabled the determination of the binding sites of many allosteric modulators revealing the nature of their interactions with the receptors. Herein, we review the latest findings on allosteric modulation of GABAA receptors and their relevance to drug discovery.
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Affiliation(s)
- Frédéric Knoflach
- F. Hoffmann-La Roche Ltd., Neuroscience & Rare Diseases (NRD) Research, Roche Innovation Center Basel, Basel, 4070, Switzerland
| | - Daniel Bertrand
- HiQScreen Sàrl, 6 rte de Compois, Vésenaz, Geneva, 1222, Switzerland.
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11
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Germann AL, Pierce SR, Tateiwa H, Sugasawa Y, Reichert DE, Evers AS, Steinbach JH, Akk G. Intrasubunit and Intersubunit Steroid Binding Sites Independently and Additively Mediate α1 β2 γ2L GABA A Receptor Potentiation by the Endogenous Neurosteroid Allopregnanolone. Mol Pharmacol 2021; 100:19-31. [PMID: 33958479 DOI: 10.1124/molpharm.121.000268] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Accepted: 04/22/2021] [Indexed: 12/18/2022] Open
Abstract
Prior work employing functional analysis, photolabeling, and X-ray crystallography have identified three distinct binding sites for potentiating steroids in the heteromeric GABAA receptor. The sites are located in the membrane-spanning domains of the receptor at the β-α subunit interface (site I) and within the α (site II) and β subunits (site III). Here, we have investigated the effects of mutations to these sites on potentiation of the rat α1β2γ2L GABAA receptor by the endogenous neurosteroid allopregnanolone (3α5αP). The mutations were introduced alone or in combination to probe the additivity of effects. We show that the effects of amino acid substitutions in sites I and II are energetically additive, indicating independence of the actions of the two steroid binding sites. In site III, none of the mutations tested reduced potentiation by 3α5αP, nor did a mutation in site III modify the effects of mutations in sites I or II. We infer that the binding sites for 3α5αP act independently. The independence of steroid action at each site is supported by photolabeling data showing that mutations in either site I or site II selectively change steroid orientation in the mutated site without affecting labeling at the unmutated site. The findings are discussed in the context of linking energetic additivity to empirical changes in receptor function and ligand binding. SIGNIFICANCE STATEMENT: Prior work has identified three distinct binding sites for potentiating steroids in the heteromeric γ-aminobutyric acid type A receptor. This study shows that the sites act independently and additively in the presence of the steroid allopregnanolone and provide estimates of energetic contributions made by steroid binding to each site.
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Affiliation(s)
- Allison L Germann
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Spencer R Pierce
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Hiroki Tateiwa
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Yusuke Sugasawa
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - David E Reichert
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Alex S Evers
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Joe Henry Steinbach
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Gustav Akk
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
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12
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Fantasia RJ, Nourmahnad A, Halpin E, Forman SA. Substituted Cysteine Modification and Protection with n-Alkyl- Methanethiosulfonate Reagents Yields a Precise Estimate of the Distance between Etomidate and a Residue in Activated GABA Type A Receptors. Mol Pharmacol 2021; 99:426-434. [PMID: 33766924 DOI: 10.1124/molpharm.120.000224] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Accepted: 03/10/2021] [Indexed: 11/22/2022] Open
Abstract
The anesthetic etomidate modulates synaptic α1β2/3γ2 GABAA receptors via binding sites located in transmembrane β+/α- interfaces. Various approaches indicate that etomidate binds near β2/3M286 side chains, including recent cryogenic electron microscopy images in α1β2γ2L receptors under nonphysiologic conditions with ∼3.5-Å resolution. We hypothesized that substituted cysteine modification and protection experiments using variably sized n-alkyl-methanethiosulfonate (MTS) reagents could precisely estimate the distance between bound etomidate and β3M286 side chains in activated functional receptors. Using voltage-clamp electrophysiology in Xenopus oocytes expressing α1β3M286Cγ2L GABAA receptors, we measured functional changes after exposing GABA-activated receptors to n-alkyl-MTS reagents, from methyl-MTS to n-decyl-MTS. Based on previous studies using a large sulfhydryl reagent, we anticipated that cysteine modifications large enough to overlap etomidate sites would cause persistently increased GABA sensitivity and decreased etomidate modulation and that etomidate would hinder these modifications, reducing effects. Based on altered GABA or etomidate sensitivity, ethyl-MTS and larger n-alkyl-MTS reagents modified GABA-activated α1β3M286Cγ2L GABAA receptors. Receptor modification by n-propyl-MTS or larger reagents caused persistently increased GABA sensitivity and decreased etomidate modulation. Receptor-bound etomidate blocked β3M286C modification by n-propyl-MTS, n-butyl-MTS, and n-hexyl-MTS. In contrast, GABA sensitivity was unaltered by receptor exposure to methyl-MTS or ethyl-MTS, and ethyl-MTS modification uniquely increased etomidate modulation. These results reveal a "cut-on" between ethyl-MTS and n-propyl-MTS, from which we infer that -S-(n-propyl) is the smallest β3M286C appendage that overlaps with etomidate sites. Molecular models of the native methionine and -S-ethyl and -S-(n-propyl) modified cysteines suggest that etomidate is located between 1.7 and 3.0 Å from the β3M286 side chain. SIGNIFICANCE STATEMENT: Precise spatial relationships between drugs and their receptor sites are essential for mechanistic understanding and drug development. This study combined electrophysiology, a cysteine substitution, and n-alkyl-methanethiosulfonate modifiers, creating a precise molecular ruler to estimate the distance between a α1β3γ2L GABA type A receptor residue and etomidate bound in the transmembrane β+/α- interface.
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Affiliation(s)
- Ryan J Fantasia
- Beecher-Mallinckrodt Laboratories, Department of Anesthesia Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Anahita Nourmahnad
- Beecher-Mallinckrodt Laboratories, Department of Anesthesia Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Elizabeth Halpin
- Beecher-Mallinckrodt Laboratories, Department of Anesthesia Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Stuart A Forman
- Beecher-Mallinckrodt Laboratories, Department of Anesthesia Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
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13
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Prevost MS, Bouchenaki H, Barilone N, Gielen M, Corringer PJ. Concatemers to re-investigate the role of α5 in α4β2 nicotinic receptors. Cell Mol Life Sci 2021; 78:1051-1064. [PMID: 32472188 PMCID: PMC11071962 DOI: 10.1007/s00018-020-03558-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 05/15/2020] [Accepted: 05/22/2020] [Indexed: 01/08/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are pentameric ion channels expressed in the central nervous systems. nAChRs containing the α4, β2 and α5 subunits are specifically involved in addictive processes, but their functional architecture is poorly understood due to the intricacy of assembly of these subunits. Here we constrained the subunit assembly by designing fully concatenated human α4β2 and α4β2α5 receptors and characterized their properties by two-electrodes voltage-clamp electrophysiology in Xenopus oocytes. We found that α5-containing nAChRs are irreversibly blocked by methanethiosulfonate (MTS) reagents through a covalent reaction with a cysteine present only in α5. MTS-block experiments establish that the concatemers are expressed in intact form at the oocyte surface, but that reconstitution of nAChRs from loose subunits show inefficient and highly variable assembly of α5 with α4 and β2. Mutational analysis shows that the concatemers assemble both in clockwise and anticlockwise orientations, and that α5 does not contribute to ACh binding from its principal (+) site. Reinvestigation of suspected α5-ligands such as galantamine show no specific effect on α5-containing concatemers. Analysis of the α5-D398N mutation that is linked to smoking and lung cancer shows no significant effect on the electrophysiological function, suggesting that its effect might arise from alteration of other cellular processes. The concatemeric strategy provides a well-characterized platform for mechanistic analysis and screening of human α5-specific ligands.
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Affiliation(s)
- Marie S Prevost
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France
| | - Hichem Bouchenaki
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France
| | - Nathalie Barilone
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France
| | - Marc Gielen
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France.
- Sorbonne Université, 21, rue de l'école de médecine, 75006, Paris, France.
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14
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Shalabi AR, Yu Z, Zhou X, Jounaidi Y, Chen H, Dai J, Kent DE, Feng HJ, Forman SA, Cohen JB, Bruzik KS, Miller KW. A potent photoreactive general anesthetic with novel binding site selectivity for GABA A receptors. Eur J Med Chem 2020; 194:112261. [PMID: 32247113 DOI: 10.1016/j.ejmech.2020.112261] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Revised: 03/18/2020] [Accepted: 03/19/2020] [Indexed: 12/27/2022]
Abstract
The pentameric γ-aminobutyric acid type A receptors (GABAARs) are the major inhibitory ligand-gated ion channels in the central nervous system. They mediate diverse physiological functions, mutations in them are associated with mental disorders and they are the target of many drugs such as general anesthetics, anxiolytics and anti-convulsants. The five subunits of synaptic GABAARs are arranged around a central pore in the order β-α-β-α-γ. In the outer third of the transmembrane domain (TMD) drugs may bind to five homologous intersubunit binding sites. Etomidate binds between the pair of β - α subunit interfaces (designated as β+/α-) and R-mTFD-MPAB binds to an α+/β- and an γ+/β- subunit interface (a β- selective ligand). Ligands that bind selectively to other homologous sites have not been characterized. We have synthesized a novel photolabel, (2,6-diisopropyl-4-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenyl)methanol or pTFD-di-iPr-BnOH). It is a potent general anesthetic that positively modulates agonist and benzodiazepine binding. It enhances GABA-induced currents, shifting the GABA concentration-response curve to lower concentrations. Photolabeling-protection studies show that it has negligible affinity for the etomidate sites and high affinity for only one of the two R-mTFD-MPAB sites. Exploratory site-directed mutagenesis studies confirm the latter conclusions and hint that pTFD-di-iPr-BnOH may bind between the α+/β- and α+/γ- subunits in the TMD, making it an α+ ligand. The latter α+/γ- site has not previously been implicated in ligand binding. Thus, pTFD-di-iPr-BnOH is a promising new photolabel that may open up a new pharmacology for synaptic GABAARs.
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Affiliation(s)
- Abdelrahman R Shalabi
- Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, 833 South Wood Street, Chicago, IL, 60612, USA
| | - Zhiyi Yu
- Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, MA, 02115, USA.
| | - Xiaojuan Zhou
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA
| | - Youssef Jounaidi
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA
| | - Hanwen Chen
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA.
| | - Jiajia Dai
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA.
| | - Daniel E Kent
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA; Department of Health Science, Northeastern University, 360 Huntington Ave, Boston, MA, 02115, USA
| | - Hua-Jun Feng
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA
| | - Stuart A Forman
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA
| | - Jonathan B Cohen
- Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, MA, 02115, USA
| | - Karol S Bruzik
- Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, 833 South Wood Street, Chicago, IL, 60612, USA
| | - Keith W Miller
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA.
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15
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Drug-selective Anesthetic Insensitivity of Zebrafish Lacking γ-Aminobutyric Acid Type A Receptor β3 Subunits. Anesthesiology 2020; 131:1276-1291. [PMID: 31567362 DOI: 10.1097/aln.0000000000002963] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
BACKGROUND Transgenic mouse studies suggest that γ-aminobutyric acid type A (GABAA) receptors containing β3 subunits mediate important effects of etomidate, propofol, and pentobarbital. Zebrafish, recently introduced for rapid discovery and characterization of sedative-hypnotics, could also accelerate pharmacogenetic studies if their transgenic phenotypes reflect those of mammals. The authors hypothesized that, relative to wild-type, GABAA-β3 functional knock-out (β3) zebrafish would show anesthetic sensitivity changes similar to those of β3 mice. METHODS Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 mutagenesis was used to create a β3 zebrafish line. Wild-type and β3 zebrafish were compared for fertility, growth, and craniofacial development. Sedative and hypnotic effects of etomidate, propofol, pentobarbital, alphaxalone, ketamine, tricaine, dexmedetomidine, butanol, and ethanol, along with overall activity and thigmotaxis were quantified in 7-day postfertilization larvae using video motion analysis of up to 96 animals simultaneously. RESULTS Xenopus oocyte electrophysiology showed that the wild-type zebrafish β3 gene encodes ion channels activated by propofol and etomidate, while the β3 zebrafish transgene does not. Compared to wild-type, β3 zebrafish showed similar morphology and growth, but more rapid swimming. Hypnotic EC50s (mean [95% CI]) were significantly higher for β3 versus wild-type larvae with etomidate (1.3 [1.0 to 1.6] vs. 0.6 [0.5 to 0.7] µM; P < 0.0001), propofol (1.1 [1.0 to 1.4] vs. 0.7 [0.6 to 0.8] µM; P = 0.0005), and pentobarbital (220 [190 to 240] vs. 130 [94 to 179] μM; P = 0.0009), but lower with ethanol (150 [106 to 213] vs. 380 [340 to 420] mM; P < 0.0001) and equivalent with other tested drugs. Comparing β3 versus wild-type sedative EC50s revealed a pattern similar to hypnosis. CONCLUSIONS Global β3 zebrafish are selectively insensitive to the same few sedative-hypnotics previously reported in β3 transgenic mice, indicating phylogenetic conservation of β3-containing GABAA receptors as anesthetic targets. Transgenic zebrafish are potentially valuable models for sedative-hypnotic mechanisms research.
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Kent DE, Savechenkov PY, Bruzik KS, Miller KW. Binding site location on GABA A receptors determines whether mixtures of intravenous general anaesthetics interact synergistically or additively in vivo. Br J Pharmacol 2019; 176:4760-4772. [PMID: 31454409 DOI: 10.1111/bph.14843] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 07/24/2019] [Accepted: 08/14/2019] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND AND PURPOSE General anaesthetics can act on synaptic GABAA receptors by binding to one of three classes of general anaesthetic sites. Canonical drugs that bind selectively to only one class of site are etomidate, alphaxalone, and the mephobarbital derivative, R-mTFD-MPAB. We tested the hypothesis that the general anaesthetic potencies of mixtures of such site-selective agents binding to the same or to different sites would combine additively or synergistically respectively. EXPERIMENTAL APPROACH The potency of general anaesthetics individually or in combinations to cause loss of righting reflexes in tadpoles was determined, and the results were analysed using isobolographic methods. KEY RESULTS The potencies of combinations of two or three site-selective anaesthetics that all acted on a single class of site were strictly additive, regardless of which single site was involved. Combinations of two or three site-selective anaesthetics that all bound selectively to different sites always interacted synergistically. The strength of the synergy increased with the number of separate sites involved such that the percentage of each agent's EC50 required to cause anaesthesia was just 35% and 14% for two or three sites respectively. Propofol, which binds non-selectively to the etomidate and R-mTFD-MPAB sites, interacted synergistically with each of these agents. CONCLUSIONS AND IMPLICATIONS The established pharmacology of the three anaesthetic binding sites on synaptic GABAA receptors was sufficient to predict whether a mixture of anaesthetics interacted additively or synergistically to cause loss of righting reflexes in vivo. The principles established here have implications for clinical practice.
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Affiliation(s)
- Daniel E Kent
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Department of Anaesthesia, Harvard Medical School, Boston, Massachusetts.,Department of Health Sciences, Northeastern University, Boston, Massachusetts
| | | | - Karol S Bruzik
- Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois
| | - Keith W Miller
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Department of Anaesthesia, Harvard Medical School, Boston, Massachusetts
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17
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Germann AL, Pierce SR, Senneff TC, Burbridge AB, Steinbach JH, Akk G. Steady-state activation and modulation of the synaptic-type α1β2γ2L GABA A receptor by combinations of physiological and clinical ligands. Physiol Rep 2019; 7:e14230. [PMID: 31549483 PMCID: PMC6757177 DOI: 10.14814/phy2.14230] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2019] [Revised: 08/22/2019] [Accepted: 08/23/2019] [Indexed: 11/24/2022] Open
Abstract
The synaptic α1β2γ2 GABAA receptor is activated phasically by presynaptically released GABA. The receptor is considered to be inactive between synaptic events when exposed to ambient GABA because of its low resting affinity to the transmitter. We tested the hypothesis that a combination of physiological and/or clinical positive allosteric modulators of the GABAA receptor with ambient GABA generates measurable steady-state activity. Recombinant α1β2γ2L GABAA receptors were expressed in Xenopus oocytes and activated by combinations of low concentrations of orthosteric (GABA, taurine) and allosteric (the steroid allopregnanolone, the anesthetic propofol) agonists, in the absence and presence of the inhibitory steroid pregnenolone sulfate. Steady-state activity was analyzed using the three-state cyclic Resting-Active-Desensitized model. We estimate that the steady-state open probability of the synaptic α1β2γ2L GABAA receptor in the presence of ambient GABA (1 μmol/L), taurine (10 μmol/L), and physiological levels of allopregnanolone (0.01 μmol/L) and pregnenolone sulfate (0.1 μmol/L) is 0.008. Coapplication of a clinical concentration of propofol (1 μmol/L) increases the steady-state open probability to 0.03. Comparison of total charge transfer for phasic and tonic activity indicates that steady-state activity can contribute strongly (~20 to >99%) to integrated activity from the synaptic GABAA receptor.
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Affiliation(s)
- Allison L. Germann
- Department of AnesthesiologyWashington University School of MedicineSt. LouisMissouri
| | - Spencer R. Pierce
- Department of AnesthesiologyWashington University School of MedicineSt. LouisMissouri
| | - Thomas C. Senneff
- Department of AnesthesiologyWashington University School of MedicineSt. LouisMissouri
| | - Ariel B. Burbridge
- Department of AnesthesiologyWashington University School of MedicineSt. LouisMissouri
| | - Joe Henry Steinbach
- Department of AnesthesiologyWashington University School of MedicineSt. LouisMissouri
- Taylor Family Institute for Innovative Psychiatric ResearchWashington University School of MedicineSt. LouisMissouri
| | - Gustav Akk
- Department of AnesthesiologyWashington University School of MedicineSt. LouisMissouri
- Taylor Family Institute for Innovative Psychiatric ResearchWashington University School of MedicineSt. LouisMissouri
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Germann AL, Pierce SR, Burbridge AB, Steinbach JH, Akk G. Steady-State Activation and Modulation of the Concatemeric α1 β2 γ2L GABA A Receptor. Mol Pharmacol 2019; 96:320-329. [PMID: 31263018 DOI: 10.1124/mol.119.116913] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Accepted: 06/21/2019] [Indexed: 12/19/2022] Open
Abstract
The two-state coagonist model has been successfully used to analyze and predict peak current responses of the γ-aminobutyric acid type A (GABAA) receptor. The goal of the present study was to provide a model-based description of GABAA receptor activity under steady-state conditions after desensitization has occurred. We describe the derivation and properties of the cyclic three-state resting-active-desensitized (RAD) model. The relationship of the model to receptor behavior was tested using concatemeric α1β2γ2 GABAA receptors expressed in Xenopus oocytes. The receptors were activated by the orthosteric agonists GABA or β-alanine, the allosteric agonist propofol, or combinations of GABA, propofol, pentobarbital, and the steroid allopregnanolone, and the observed steady-state responses were compared with those predicted by the model. A modified RAD model was employed to analyze and describe the actions on steady-state current of the inhibitory steroid pregnenolone sulfate. The findings indicate that the steady-state activity in the presence of multiple active agents that interact with distinct binding sites follows standard energetic additivity. The derived equations enable prediction of peak and steady-state activity in the presence of orthosteric and allosteric agonists, and the inhibitory steroid pregnenolone sulfate. SIGNIFICANCE STATEMENT: The study describes derivation and properties of a three-state resting-active-desensitized model. The model and associated equations can be used to analyze and predict peak and steady-state activity in the presence of one or more active agents.
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Affiliation(s)
- Allison L Germann
- Department of Anesthesiology (A.L.G., S.R.P., A.B.B., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Spencer R Pierce
- Department of Anesthesiology (A.L.G., S.R.P., A.B.B., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Ariel B Burbridge
- Department of Anesthesiology (A.L.G., S.R.P., A.B.B., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Joe Henry Steinbach
- Department of Anesthesiology (A.L.G., S.R.P., A.B.B., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Gustav Akk
- Department of Anesthesiology (A.L.G., S.R.P., A.B.B., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
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