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Do HQ, Pirayesh E, Ferreira G, Pandhare A, Gallardo ZR, Jansen M. A bupropion modulatory site in the Gloeobacter violaceus ligand-gated ion channel. Biophys J 2024; 123:2185-2198. [PMID: 38678367 PMCID: PMC11309978 DOI: 10.1016/j.bpj.2024.04.027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Revised: 01/27/2024] [Accepted: 04/25/2024] [Indexed: 04/29/2024] Open
Abstract
Bupropion is an atypical antidepressant and smoking cessation drug that causes adverse effects such as insomnia, irritability, and anxiety. Bupropion inhibits dopamine and norepinephrine reuptake transporters and eukaryotic cation-conducting pentameric ligand-gated ion channels, such as nicotinic acetylcholine and serotonin type 3A receptors, at clinically relevant concentrations. Here, we demonstrate that bupropion also inhibits a prokaryotic homolog of pentameric ligand-gated ion channels, the Gloeobacter violaceus ligand-gated ion channel (GLIC). Using the GLIC as a model, we used molecular docking to predict binding sites for bupropion. Bupropion was found to bind to several sites within the transmembrane domain, with the predominant site being localized to the interface between transmembrane segments M1 and M3 of two adjacent subunits. Residues W213, T214, and W217 in the first transmembrane segment, M1, and F267 and I271 in the third transmembrane segment, M3, most frequently reside within a 4 Å distance from bupropion. We then used single amino acid substitutions at these positions and two-electrode voltage-clamp recordings to determine their impact on bupropion inhibitory effects. The substitution T214F alters bupropion potency by shifting the half-maximal inhibitory concentration to a 13-fold higher value compared to wild-type GLIC. Residue T214 is found within a previously identified binding pocket for neurosteroids and lipids in the GLIC. This intersubunit binding pocket is structurally conserved and almost identical to a binding pocket described for neurosteroids in γ-aminobutyric acid type A receptors. Our data thus suggest that the T214 that lines a previously identified lipophilic binding pocket in GLIC and γ-aminobutyric acid type A receptors is also a modulatory site for bupropion interaction with the GLIC.
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Affiliation(s)
- Hoa Quynh Do
- Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Elham Pirayesh
- Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Garren Ferreira
- Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Akash Pandhare
- Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Zackary Ryan Gallardo
- Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Michaela Jansen
- Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas.
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2
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Menzikov SA, Zaichenko DM, Moskovtsev AA, Morozov SG, Kubatiev AA. Phenols and GABA A receptors: from structure and molecular mechanisms action to neuropsychiatric sequelae. Front Pharmacol 2024; 15:1272534. [PMID: 38303988 PMCID: PMC10831359 DOI: 10.3389/fphar.2024.1272534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Accepted: 01/03/2024] [Indexed: 02/03/2024] Open
Abstract
γ-Aminobutyric acid type A receptors (GABAARs) are members of the pentameric ligand-gated ion channel (pLGIC) family, which are widespread throughout the invertebrate and vertebrate central nervous system. GABAARs are engaged in short-term changes of the neuronal concentrations of chloride (Cl-) and bicarbonate (HCO3 -) ions by their passive permeability through the ion channel pore. GABAARs are regulated by various structurally diverse phenolic substances ranging from simple phenols to complex polyphenols. The wide chemical and structural variability of phenols suggest similar and different binding sites on GABAARs, allowing them to manifest themselves as activators, inhibitors, or allosteric ligands of GABAAR function. Interest in phenols is associated with their great potential for GABAAR modulation, but also with their subsequent negative or positive role in neurological and psychiatric disorders. This review focuses on the GABAergic deficit hypotheses during neurological and psychiatric disorders induced by various phenols. We summarize the structure-activity relationship of general phenol groups concerning their differential roles in the manifestation of neuropsychiatric symptoms. We describe and analyze the role of GABAAR subunits in manifesting various neuropathologies and the molecular mechanisms underlying their modulation by phenols. Finally, we discuss how phenol drugs can modulate GABAAR activity via desensitization and resensitization. We also demonstrate a novel pharmacological approach to treat neuropsychiatric disorders via regulation of receptor phosphorylation/dephosphorylation.
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Bhave K, Forman SA. Substituted Cysteine Modification and Protection with n-Alkyl-MTS Reagents Quantifies Steric Changes Induced by a Mutation in Anesthetic Binding Sites on GABA Type A Receptors. Mol Pharmacol 2023; 104:266-274. [PMID: 37586749 PMCID: PMC10658906 DOI: 10.1124/molpharm.123.000719] [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: 05/08/2023] [Revised: 08/11/2023] [Accepted: 08/14/2023] [Indexed: 08/18/2023] Open
Abstract
Multiple approaches, including cryogenic electron microscopy (cryo-EM), indicate that the anesthetics etomidate and propofol modulate α1β2/3γ2 GABAA receptors by binding in overlapping transmembrane inter-subunit sites near βM286 and αL232 sidechains. High-precision approaches in functional receptors are needed for comparisons with cryo-EM. We previously used substituted cysteine modification and protection (SCAMP) with n-alkyl-methanethiosulfonate (MTS) reagents and electrophysiology in α1β3M286Cγ2L receptors to estimate the distance from etomidate to β3M286 with precision near 1.3 Å. Here, we address three more aims using this approach: (i) SCAMP with etomidate was tested in α1L232Cβ3γ2L receptors; (ii) studies in α1L232Wβ3M286Cγ2L receptors assessed whether α1L232W displaces etomidate relative to β3M286C; and (iii) results with propofol were compared with those with etomidate. Voltage-clamp electrophysiology in Xenopus oocytes was used to assess persistent functional changes after exposing cysteine-substituted receptors to methyl-MTS through n-decyl-MTS. Overlap of modified cysteine sidechains with bound anesthetic was inferred when anesthetic co-application with alkyl-MTS reagent blocked the development of persistent effects. In α1L232Cβ3γ2L receptors, only pentyl-MTS and hexyl-MTS induced persistent effects that were unaltered by etomidate co-application, precluding a direct estimate of intermolecular distance. In α1L232Wβ3M286Cγ2L receptors, sidechain overlap with bound etomidate was inferred for modifications with ethyl-MTS through n-pentyl-MTS, with unambiguous cut-on and cut-off. Comparison with results in α1β3M286Cγ2L reveals that α1L232W, which increases maximal sidechain length by 2.1 Å, displaces etomidate closer to β3M286C by about 1.3 Å. Propofol results largely mirrored those with etomidate. These findings indicate that both etomidate and propofol bind within 1 Å of α1L232, consistent with cryo-EM structures. SIGNIFICANCE STATEMENT: We combined electrophysiology, cysteine substitutions, and n-alkyl-methanethiosulfonate modifiers in functional GABAA receptors to enable precise estimates of the distance between β3M286C sidechains and anesthetics (etomidate and propofol) bound in transmembrane β+/α- inter-subunit pockets. Comparing results in α1β3M286Cγ2L and α1L232Wβ3M286Cγ2L receptors reveals that α1L232W mutations displace both anesthetics toward β3M286C, indicating that these anesthetics bind within 1 Å of the α1L232 sidechain in functional receptors, consistent with cryogenic electron microscopy structures derived under nonphysiologic conditions.
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Affiliation(s)
- Kieran Bhave
- 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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Munir R, Zahoor AF, Javed S, Parveen B, Mansha A, Irfan A, Khan SG, Irfan A, Kotwica-Mojzych K, Mojzych M. Simmons-Smith Cyclopropanation: A Multifaceted Synthetic Protocol toward the Synthesis of Natural Products and Drugs: A Review. Molecules 2023; 28:5651. [PMID: 37570621 PMCID: PMC10420228 DOI: 10.3390/molecules28155651] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2023] [Revised: 07/16/2023] [Accepted: 07/20/2023] [Indexed: 08/13/2023] Open
Abstract
Simmons-Smith cyclopropanation is a widely used reaction in organic synthesis for stereospecific conversion of alkenes into cyclopropane. The utility of this reaction can be realized by the fact that the cyclopropane motif is a privileged synthetic intermediate and a core structural unit of many biologically active natural compounds such as terpenoids, alkaloids, nucleosides, amino acids, fatty acids, polyketides and drugs. The modified form of Simmons-Smith cyclopropanation involves the employment of Et2Zn and CH2I2 (Furukawa reagent) toward the total synthesis of a variety of structurally complex natural products that possess broad range of biological activities including anticancer, antimicrobial and antiviral activities. This review aims to provide an intriguing glimpse of the Furukawa-modified Simmons-Smith cyclopropanation, within the year range of 2005 to 2022.
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Affiliation(s)
- Ramsha Munir
- Medicinal Chemistry Research Lab, Department of Chemistry, Government College University Faisalabad, Faisalabad 38000, Pakistan; (R.M.); (B.P.); (A.M.); (S.G.K.); (A.I.)
| | - Ameer Fawad Zahoor
- Medicinal Chemistry Research Lab, Department of Chemistry, Government College University Faisalabad, Faisalabad 38000, Pakistan; (R.M.); (B.P.); (A.M.); (S.G.K.); (A.I.)
| | - Sadia Javed
- Department of Biochemistry, Government College University Faisalabad, Faisalabad 38000, Pakistan;
| | - Bushra Parveen
- Medicinal Chemistry Research Lab, Department of Chemistry, Government College University Faisalabad, Faisalabad 38000, Pakistan; (R.M.); (B.P.); (A.M.); (S.G.K.); (A.I.)
| | - Asim Mansha
- Medicinal Chemistry Research Lab, Department of Chemistry, Government College University Faisalabad, Faisalabad 38000, Pakistan; (R.M.); (B.P.); (A.M.); (S.G.K.); (A.I.)
| | - Ahmad Irfan
- Department of Chemistry, College of Science, King Khalid University, Abha 61413, Saudi Arabia;
| | - Samreen Gul Khan
- Medicinal Chemistry Research Lab, Department of Chemistry, Government College University Faisalabad, Faisalabad 38000, Pakistan; (R.M.); (B.P.); (A.M.); (S.G.K.); (A.I.)
| | - Ali Irfan
- Medicinal Chemistry Research Lab, Department of Chemistry, Government College University Faisalabad, Faisalabad 38000, Pakistan; (R.M.); (B.P.); (A.M.); (S.G.K.); (A.I.)
| | - Katarzyna Kotwica-Mojzych
- Laboratory of Experimental Cytology, Medical University of Lublin, Radziwiłłowska 11, 20-080 Lublin, Poland;
| | - Mariusz Mojzych
- Department of Chemistry, Siedlce University of Natural Sciences and Humanities, 3-go Maja 54, 08-110 Siedlce, Poland
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Chuang CM, Chen CY, Yen PS, Wu CH, Shiao LR, Wong KL, Chan P, Leung YM. Propofol Causes Sustained Ca2+ Elevation in Endothelial Cells by Stimulating Ryanodine Receptor and Suppressing Plasmalemmal Ca2+ Pump. J Cardiovasc Pharmacol 2022; 79:749-757. [PMID: 35239284 DOI: 10.1097/fjc.0000000000001246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2021] [Accepted: 01/23/2022] [Indexed: 11/25/2022]
Abstract
ABSTRACT Propofol, a general anesthetic administered intravenously, may cause pain at the injection site. The pain is in part due to irritation of vascular endothelial cells. We here investigated the effects of propofol on Ca2+ transport and pain mediator release in human umbilical vein endothelial cells (EA.hy926). Propofol mobilized Ca2+ from cyclopiazonic acid (CPA)-dischargeable pool but did not cause Ca2+ release from the lysosomal Ca2+ stores. Propofol-elicited Ca2+ release was suppressed by 100 μM ryanodine, suggesting the participation of ryanodine receptor channels. Propofol did not affect ATP-triggered Ca2+ release but abolished the Ca2+ influx triggered by ATP; in addition, propofol also suppressed store-operated Ca2+ entry elicited by CPA. Ca2+ clearance during CPA-induced Ca2+ discharge was unaffected by a low Na+ (50 mM) extracellular solution, but strongly suppressed by 5 mM La3+ (an inhibitor of plasmalemmal Ca2+ pump), suggesting Ca2+ extrusion was predominantly through the plasmalemmal Ca2+ pump. Propofol mimicked the effect of La3+ in suppressing Ca2+ clearance. Propofol also stimulated release of pain mediators, namely, reactive oxygen species and bradykinin. Our data suggest propofol elicited Ca2+ release and repressed Ca2+ clearance, causing a sustained cytosolic [Ca2+]i elevation. The latter may cause reactive oxygen species and bradykinin release, resulting in pain.
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Affiliation(s)
- Chin-Min Chuang
- Department of Emergency Medicine, China Medical University Hospital, Taichung, Taiwan
| | - Cing-Yu Chen
- Department of Physiology, China Medical University, Taichung, Taiwan
| | - Pao-Sheng Yen
- Department of Radiology, Kuang Tien General Hospital, Shalu, Taichung, Taiwan
| | - Cheng-Hsun Wu
- Department of Anatomy, China Medical University, Taichung, Taiwan
| | - Lian-Ru Shiao
- Department of Physiology, China Medical University, Taichung, Taiwan
| | - Kar-Lok Wong
- Department of Anesthesiology, Kuang Tien General Hospital, Shalu, Taichung, Taiwan
- Department of Anesthesiology, University of Hong Kong, Hong Kong, China; and
| | - Paul Chan
- Division of Cardiovascular Medicine, Department of Internal Medicine, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan
| | - Yuk-Man Leung
- Department of Physiology, China Medical University, Taichung, Taiwan
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Zhang X, Yu S, Liu Z, Long Y, Zhao J, Xu W, Zhang H, Zhang H. Development of a Kilogram-Scale Route for Clinical Sample Production of the Intravenous Anesthetic Cipepofol. Org Process Res Dev 2022. [DOI: 10.1021/acs.oprd.1c00306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Xiaowei Zhang
- Sichuan Haisco Pharmaceutical Co. Ltd., 136 Baili Road, Wenjiang District, Chengdu 611130, China
| | - Shuowen Yu
- Sichuan Haisco Pharmaceutical Co. Ltd., 136 Baili Road, Wenjiang District, Chengdu 611130, China
| | - Zhaojun Liu
- Sichuan Haisco Pharmaceutical Co. Ltd., 136 Baili Road, Wenjiang District, Chengdu 611130, China
| | - Yuanqiang Long
- Sichuan Haisco Pharmaceutical Co. Ltd., 136 Baili Road, Wenjiang District, Chengdu 611130, China
| | - Jinwei Zhao
- Sichuan Haisco Pharmaceutical Co. Ltd., 136 Baili Road, Wenjiang District, Chengdu 611130, China
| | - Wei Xu
- Sichuan Haisco Pharmaceutical Co. Ltd., 136 Baili Road, Wenjiang District, Chengdu 611130, China
| | - Haifeng Zhang
- Sichuan Haisco Pharmaceutical Co. Ltd., 136 Baili Road, Wenjiang District, Chengdu 611130, China
| | - Haijun Zhang
- Sichuan Haisco Pharmaceutical Co. Ltd., 136 Baili Road, Wenjiang District, Chengdu 611130, China
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7
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Kono M, Ozoe F, Asahi M, Ozoe Y. State-dependent inhibition of GABA receptor channels by the ectoparasiticide fluralaner. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2022; 181:105008. [PMID: 35082031 DOI: 10.1016/j.pestbp.2021.105008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Revised: 11/15/2021] [Accepted: 12/07/2021] [Indexed: 06/14/2023]
Abstract
γ-Aminobutyric acid (GABA) receptors (GABARs) are ligand-gated Cl- channels, which cause an influx of Cl- that inhibits excitation in postsynaptic cells upon activation. GABARs are important targets for drugs and pest control chemicals. We previously reported that the isoxazoline ectoparasiticide fluralaner inhibits GABA-induced currents in housefly (Musca domestica) GABARs by binding to the putative binding site in the transmembrane subunit interface. In the present study, we investigated whether fluralaner inhibits the GABA response in the GABAR activated state, the resting state, or both, using two-electrode voltage clamp electrophysiology protocols. We found that inhibition progresses over time to steady-state levels by repeated short applications of GABA during fluralaner perfusion. The GABA response was not impaired by fluralaner treatment in the GABAR resting state. However, once inhibited, the GABA response was not restored by repeated applications of GABA. These findings suggest that fluralaner might reach the binding site of the activated conformation of GABARs in a stepwise fashion and tightly bind to it.
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Affiliation(s)
- Miku Kono
- Faculty of Life and Environmental Sciences, Shimane University, Matsue, Shimane 690-8504, Japan
| | - Fumiyo Ozoe
- Interdisciplinary Institute for Science Research, Organization for Research and Academic Information, Shimane University, Matsue, Shimane 690-8504, Japan
| | - Miho Asahi
- Biological Research Laboratories, Nissan Chemical Corporation, Shiraoka, Saitama 349-0294, Japan
| | - Yoshihisa Ozoe
- Faculty of Life and Environmental Sciences, Shimane University, Matsue, Shimane 690-8504, Japan; Interdisciplinary Institute for Science Research, Organization for Research and Academic Information, Shimane University, Matsue, Shimane 690-8504, Japan.
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Platholi J, Hemmings HC. Effects of general anesthetics on synaptic transmission and plasticity. Curr Neuropharmacol 2021; 20:27-54. [PMID: 34344292 PMCID: PMC9199550 DOI: 10.2174/1570159x19666210803105232] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 07/26/2021] [Accepted: 08/02/2021] [Indexed: 11/22/2022] Open
Abstract
General anesthetics depress excitatory and/or enhance inhibitory synaptic transmission principally by modulating the function of glutamatergic or GABAergic synapses, respectively, with relative anesthetic agent-specific mechanisms. Synaptic signaling proteins, including ligand- and voltage-gated ion channels, are targeted by general anesthetics to modulate various synaptic mechanisms, including presynaptic neurotransmitter release, postsynaptic receptor signaling, and dendritic spine dynamics to produce their characteristic acute neurophysiological effects. As synaptic structure and plasticity mediate higher-order functions such as learning and memory, long-term synaptic dysfunction following anesthesia may lead to undesirable neurocognitive consequences depending on the specific anesthetic agent and the vulnerability of the population. Here we review the cellular and molecular mechanisms of transient and persistent general anesthetic alterations of synaptic transmission and plasticity.
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Affiliation(s)
- Jimcy Platholi
- Cornell University Joan and Sanford I Weill Medical College Ringgold standard institution - Anesthesiology New York, New York. United States
| | - Hugh C Hemmings
- Cornell University Joan and Sanford I Weill Medical College Ringgold standard institution - Anesthesiology New York, New York. United States
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9
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Bregestovski PD, Ponomareva DN. Photochromic Modulation of Cys-loop
Ligand-gated Ion Channels. J EVOL BIOCHEM PHYS+ 2021. [DOI: 10.1134/s0022093021020162] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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10
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Yuan X, Zhang D, Mao S, Wang Q. Filling the Gap in Understanding the Mechanism of GABA AR and Propofol Using Computational Approaches. J Chem Inf Model 2021; 61:1889-1901. [PMID: 33823589 DOI: 10.1021/acs.jcim.0c01290] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
γ-Aminobutyric acid type-A receptors (GABAARs) play a critical role in neural transmission by mediating the inhibitory neural firing and are the target of many psychiatric drugs. Among them, propofol is one of the most widely used and important general anesthetics in clinics. Recent advances in structural biology revealed the structure of a human GABAAR in both open and closed states. Yet, the detailed mechanism of the receptor and propofol remains to be fully understood. Therefore, in this study, based on the previous successes in structural biology, a variety of computational techniques were applied to fill the gap between previous experimental studies. This study investigated the ion-conducting mechanism of GABAAR, predicted the possible binding mechanism of propofol, and revealed a new motion mechanism of transmembrane domain (TMD) helices. We hope that this study may contribute to future studies on ion-channel receptors, general anesthetics, and drug development.
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Affiliation(s)
- Xinghang Yuan
- Key Laboratory of Drug-Targeting and Drug Delivery System of the Education Ministry and Sichuan Province, Sichuan Engineering Laboratory for Plant-Sourced Drug and Sichuan Research Center for Drug Precision Industrial Technology, West China School of Pharmacy, Sichuan University, Chengdu 610041, China
| | - Di Zhang
- Key Laboratory of Drug-Targeting and Drug Delivery System of the Education Ministry and Sichuan Province, Sichuan Engineering Laboratory for Plant-Sourced Drug and Sichuan Research Center for Drug Precision Industrial Technology, West China School of Pharmacy, Sichuan University, Chengdu 610041, China
| | - Shengjun Mao
- Key Laboratory of Drug-Targeting and Drug Delivery System of the Education Ministry and Sichuan Province, Sichuan Engineering Laboratory for Plant-Sourced Drug and Sichuan Research Center for Drug Precision Industrial Technology, West China School of Pharmacy, Sichuan University, Chengdu 610041, China
| | - Qiantao Wang
- Key Laboratory of Drug-Targeting and Drug Delivery System of the Education Ministry and Sichuan Province, Sichuan Engineering Laboratory for Plant-Sourced Drug and Sichuan Research Center for Drug Precision Industrial Technology, West China School of Pharmacy, Sichuan University, Chengdu 610041, China
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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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12
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Jin W, Zucker M, Pralle A. Membrane nanodomains homeostasis during propofol anesthesia as function of dosage and temperature. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1863:183511. [PMID: 33245892 DOI: 10.1016/j.bbamem.2020.183511] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Revised: 11/01/2020] [Accepted: 11/12/2020] [Indexed: 12/12/2022]
Abstract
Some anesthetics bind and potentiate γ-aminobutyric-acid-type receptors, but no universal mechanism for general anesthesia is known. Furthermore, often encountered complications such as anesthesia induced amnesia are not understood. General anesthetics are hydrophobic molecules easily dissolving into lipid bilayers. Recently, it was shown that general anesthetics perturb phase separation in vesicles extracted from fixed cells. Unclear is whether under physiological conditions general anesthetics induce perturbation of the lipid bilayer, and whether this contributes to the transient loss of consciousness or anesthesia side effects. Here we show that propofol perturbs lipid nanodomains in the outer and inner leaflet of the plasma membrane in intact cells, affecting membrane nanodomains in a concentration dependent manner: 1 μM to 5 μM propofol destabilize nanodomains; however, propofol concentrations higher than 5 μM stabilize nanodomains with time. Stabilization occurs only at physiological temperature and in intact cells. This process requires ARP2/3 mediated actin nucleation and Myosin II activity. The rate of nanodomain stabilization is potentiated by GABAA receptor activity. Our results show that active nanodomain homeostasis counteracts the initial disruption causing large changes in cortical actin. SIGNIFICANCE STATEMENT: General anesthesia is a routine medical procedure with few complications, yet a small number of patients experience side-effects that persist for weeks and months. Very young children are at risk for effects on brain development. Elderly patients often exhibit subsequent amnesia. Here, we show that the general anesthetic propofol perturbs the ultrastructure of the lipid bilayer of the cell membrane in intact cells. Initially propofol destabilized lipid nanodomains. However, with increasing incubation time and propofol concentration, the effect is reversed and nanodomains are further stabilized. We show that this stabilization is caused by the activation of the actin cortex under the membrane. These perturbations of membrane bilayer and cortical actin may explain how propofol affects neuronal plasticity at synapses.
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Affiliation(s)
- Weixiang Jin
- Dept. of Physics, University at Buffalo, SUNY, Buffalo, NY 14260-1500, USA
| | - Michael Zucker
- Dept. of Physics, University at Buffalo, SUNY, Buffalo, NY 14260-1500, USA
| | - Arnd Pralle
- Dept. of Physics, University at Buffalo, SUNY, Buffalo, NY 14260-1500, USA.
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Tortosa V, Pietropaolo V, Brandi V, Macari G, Pasquadibisceglie A, Polticelli F. Computational Methods for the Identification of Molecular Targets of Toxic Food Additives. Butylated Hydroxytoluene as a Case Study. Molecules 2020; 25:E2229. [PMID: 32397407 PMCID: PMC7248939 DOI: 10.3390/molecules25092229] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 05/06/2020] [Accepted: 05/07/2020] [Indexed: 11/24/2022] Open
Abstract
Butylated hydroxytoluene (BHT) is one of the most commonly used synthetic antioxidants in food, cosmetic, pharmaceutical and petrochemical products. BHT is considered safe for human health; however, its widespread use together with the potential toxicological effects have increased consumers concern about the use of this synthetic food additive. In addition, the estimated daily intake of BHT has been demonstrated to exceed the recommended acceptable threshold. In the present work, using BHT as a case study, the usefulness of computational techniques, such as reverse screening and molecular docking, in identifying protein-ligand interactions of food additives at the bases of their toxicological effects has been probed. The computational methods here employed have been useful for the identification of several potential unknown targets of BHT, suggesting a possible explanation for its toxic effects. In silico analyses can be employed to identify new macromolecular targets of synthetic food additives and to explore their functional mechanisms or side effects. Noteworthy, this could be important for the cases in which there is an evident lack of experimental studies, as is the case for BHT.
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Affiliation(s)
- Valentina Tortosa
- Department of Sciences, Roma Tre University, 00146 Rome, Italy; (V.T.); (V.P.); (V.B.); (G.M.); (A.P.)
| | - Valentina Pietropaolo
- Department of Sciences, Roma Tre University, 00146 Rome, Italy; (V.T.); (V.P.); (V.B.); (G.M.); (A.P.)
| | - Valentina Brandi
- Department of Sciences, Roma Tre University, 00146 Rome, Italy; (V.T.); (V.P.); (V.B.); (G.M.); (A.P.)
| | - Gabriele Macari
- Department of Sciences, Roma Tre University, 00146 Rome, Italy; (V.T.); (V.P.); (V.B.); (G.M.); (A.P.)
| | - Andrea Pasquadibisceglie
- Department of Sciences, Roma Tre University, 00146 Rome, Italy; (V.T.); (V.P.); (V.B.); (G.M.); (A.P.)
| | - Fabio Polticelli
- Department of Sciences, Roma Tre University, 00146 Rome, Italy; (V.T.); (V.P.); (V.B.); (G.M.); (A.P.)
- National Institute of Nuclear Physics, Roma Tre University, 00146 Rome, Italy
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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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Chen L, Yang ZL, Cheng J, Zhang PP, Zhang LS, Liu XS, Wang LC. Propofol decreases the excitability of cholinergic neurons in mouse basal forebrain via GABA A receptors. Acta Pharmacol Sin 2019; 40:755-761. [PMID: 30367153 PMCID: PMC6786414 DOI: 10.1038/s41401-018-0168-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 08/31/2018] [Indexed: 12/23/2022] Open
Abstract
Propofol is an intravenous anesthetic that can active γ-aminobutyric acid A (GABAA) receptors and generate sedative-hypnotic effects. Propofol has been widely applied clinically to achieve sedation comparable to sleep in humans. The basal forebrain (BF) is a brain region that plays an important role in sleep-wake regulation. Previous studies suggest that propofol affects the sleep-wake circuit via the BF; however, the mechanism remains elusive. In the current study we investigated the effects of propofol on the inherent properties of cholinergic neurons and their ability to convert excitatory inputs into spikes in mouse BF slices using whole-cell patch clamp recordings. Bath application of propofol (10 μM) significantly elevated the threshold potentials (Vts), decreased the number of spikes in response to a depolarizing current injection, and augmented the inter-spike intervals (ISIs), energy barrier (Vts-Vrs), and absolute refractory periods (ARPs). These effects were eliminated by co-application of a GABAA receptor antagonist picrotoxin (50 μM). Altogether, our results reveal that propofol decreases the excitability of cholinergic neurons in mouse BF via GABAA receptors.
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Affiliation(s)
- Lei Chen
- Department of Pharmacology and Physiology, School of Basic Medical Sciences, Anhui Medical University, Hefei, 230032, China
| | - Zhi-Lai Yang
- Department of Anesthesiology, First Affiliated Hospital of Anhui Medical University, Hefei, 230022, China
| | - Juan Cheng
- Department of Pharmacology and Physiology, School of Basic Medical Sciences, Anhui Medical University, Hefei, 230032, China
| | - Ping-Ping Zhang
- Department of Pharmacology and Physiology, School of Basic Medical Sciences, Anhui Medical University, Hefei, 230032, China
| | - Le-Sha Zhang
- Department of Pharmacology and Physiology, School of Basic Medical Sciences, Anhui Medical University, Hefei, 230032, China
| | - Xue-Sheng Liu
- Department of Anesthesiology, First Affiliated Hospital of Anhui Medical University, Hefei, 230022, China.
| | - Lie-Cheng Wang
- Department of Pharmacology and Physiology, School of Basic Medical Sciences, Anhui Medical University, Hefei, 230032, China.
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16
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Jayakar SS, Zhou X, Chiara DC, Jarava-Barrera C, Savechenkov PY, Bruzik KS, Tortosa M, Miller KW, Cohen JB. Identifying Drugs that Bind Selectively to Intersubunit General Anesthetic Sites in the α1 β3 γ2 GABA AR Transmembrane Domain. Mol Pharmacol 2019; 95:615-628. [PMID: 30952799 DOI: 10.1124/mol.118.114975] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Accepted: 03/29/2019] [Indexed: 12/19/2022] Open
Abstract
GABAA receptors (GABAARs) are targets for important classes of clinical agents (e.g., anxiolytics, anticonvulsants, and general anesthetics) that act as positive allosteric modulators (PAMs). Previously, using photoreactive analogs of etomidate ([3H]azietomidate) and mephobarbital [[3H]1-methyl-5-allyl-5-(m-trifluoromethyl-diazirynylphenyl)barbituric acid ([3H]R-mTFD-MPAB)], we identified two homologous but pharmacologically distinct classes of general anesthetic binding sites in the α1β3γ2 GABAAR transmembrane domain at β +-α - (β + sites) and α +-β -/γ +-β - (β - sites) subunit interfaces. We now use competition photolabeling with [3H]azietomidate and [3H]R-mTFD-MPAB to identify para-substituted propofol analogs and other drugs that bind selectively to intersubunit anesthetic sites. Propofol and 4-chloro-propofol bind with 5-fold selectivity to β +, while derivatives with bulkier lipophilic substitutions [4-(tert-butyl)-propofol and 4-(hydroxyl(phenyl)methyl)-propofol] bind with ∼10-fold higher affinity to β - sites. Similar to R-mTFD-MPAB and propofol, these drugs bind in the presence of GABA with similar affinity to the α +-β - and γ +-β - sites. However, we discovered four compounds that bind with different affinities to the two β - interface sites. Two of these bind with higher affinity to one of the β - sites than to the β + sites. We deduce that 4-benzoyl-propofol binds with >100-fold higher affinity to the γ +-β - site than to the α +-β - or β +-α - sites, whereas loreclezole, an anticonvulsant, binds with 5- and 100-fold higher affinity to the α +-β - site than to the β + and γ +-β - sites. These studies provide a first identification of PAMs that bind selectively to a single intersubunit site in the GABAAR transmembrane domain, a property that may facilitate the development of subtype selective GABAAR PAMs.
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Affiliation(s)
- Selwyn S Jayakar
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (S.S.J., D.C.C., J.B.C.); Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (X.Z., K.W.M.); Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois (P.Y.S., K.S.B.); and the Departamento de Quimica Orgánica, Universidad Autónoma de Madrid, Madrid, Spain (C.J.-B., M.T.)
| | - Xiaojuan Zhou
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (S.S.J., D.C.C., J.B.C.); Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (X.Z., K.W.M.); Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois (P.Y.S., K.S.B.); and the Departamento de Quimica Orgánica, Universidad Autónoma de Madrid, Madrid, Spain (C.J.-B., M.T.)
| | - David C Chiara
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (S.S.J., D.C.C., J.B.C.); Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (X.Z., K.W.M.); Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois (P.Y.S., K.S.B.); and the Departamento de Quimica Orgánica, Universidad Autónoma de Madrid, Madrid, Spain (C.J.-B., M.T.)
| | - Carlos Jarava-Barrera
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (S.S.J., D.C.C., J.B.C.); Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (X.Z., K.W.M.); Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois (P.Y.S., K.S.B.); and the Departamento de Quimica Orgánica, Universidad Autónoma de Madrid, Madrid, Spain (C.J.-B., M.T.)
| | - Pavel Y Savechenkov
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (S.S.J., D.C.C., J.B.C.); Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (X.Z., K.W.M.); Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois (P.Y.S., K.S.B.); and the Departamento de Quimica Orgánica, Universidad Autónoma de Madrid, Madrid, Spain (C.J.-B., M.T.)
| | - Karol S Bruzik
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (S.S.J., D.C.C., J.B.C.); Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (X.Z., K.W.M.); Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois (P.Y.S., K.S.B.); and the Departamento de Quimica Orgánica, Universidad Autónoma de Madrid, Madrid, Spain (C.J.-B., M.T.)
| | - Mariola Tortosa
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (S.S.J., D.C.C., J.B.C.); Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (X.Z., K.W.M.); Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois (P.Y.S., K.S.B.); and the Departamento de Quimica Orgánica, Universidad Autónoma de Madrid, Madrid, Spain (C.J.-B., M.T.)
| | - Keith W Miller
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (S.S.J., D.C.C., J.B.C.); Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (X.Z., K.W.M.); Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois (P.Y.S., K.S.B.); and the Departamento de Quimica Orgánica, Universidad Autónoma de Madrid, Madrid, Spain (C.J.-B., M.T.)
| | - Jonathan B Cohen
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (S.S.J., D.C.C., J.B.C.); Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (X.Z., K.W.M.); Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois (P.Y.S., K.S.B.); and the Departamento de Quimica Orgánica, Universidad Autónoma de Madrid, Madrid, Spain (C.J.-B., M.T.)
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17
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Abstract
Neurosteroids (NS) are the main modulators of γ-aminobutyric acid type A receptors (GABAARs), which are the ligand-gated channels target of the major inhibitory neurotransmitter in vertebrates. As a consequence of their ability to modify inhibitory functions in the brain, NS have high physiological and clinical relevance. Accumulated evidence has strongly suggested that NS binding sites were located in the GABAAR transmembrane domain; however the specific localization of these sites has remained an enigma for decades. Fortunately, recent resolution of GABAARs crystal structures, together with computational strategies applied to investigate the NS binding, has paved the way to rationalizing the molecular basis of NS modulation. This work reviews from a historical perspective the road followed for establishing the GABAAR/NS binding mode, from their initial molecular modeling to the latest findings. Furthermore, a comparative analysis describing the NS binding is provided, plus a preliminary analysis of putative NS sites in other assemblies.
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Affiliation(s)
- Lautaro D Alvarez
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales , Universidad de Buenos Aires , Ciudad Universitaria , Buenos Aires C1428EGA , Argentina.,UMYMFOR , CONICET-Universidad de Buenos Aires , Ciudad Universitaria , Buenos Aires C1428EGA , Argentina
| | - Adali Pecci
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales , Universidad de Buenos Aires , Ciudad Universitaria , Buenos Aires C1428EGA , Argentina.,IFIBYNE , CONICET-Universidad de Buenos Aires , Ciudad Universitaria , Buenos Aires C1428EGA , Argentina
| | - Dario A Estrin
- Departamento de Química Inorgánica Analítica y Química Física, Facultad de Ciencias Exactas y Naturales , Universidad de Buenos Aires , Ciudad Universitaria , Buenos Aires C1428EGA , Argentina.,INQUIMAE , CONICET-Universidad de Buenos Aires , Ciudad Universitaria , Buenos Aires C1428EGA , Argentina
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18
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Menzikov SA, Morozov SG. Involvement of brain GABA AR-coupled Cl -/HCO 3--ATPase in phenol-induced the head-twitching and tremor responses in rats. Neurotoxicology 2018; 71:122-131. [PMID: 30590068 DOI: 10.1016/j.neuro.2018.12.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Revised: 12/19/2018] [Accepted: 12/21/2018] [Indexed: 11/26/2022]
Abstract
Phenol-induced neurotoxicity manifests as twitching/tremor and convulsions, but its molecular mechanisms underlying the behavioral responses remain unclear. We assessed the role of the brain Cl-/HCO3--ATPase in behavioral responses in rats following an in vivo intraperitoneal injection of phenol (20-160 mg/kg). Low concentrations of phenol (20-80 mg/kg) increased the ATPase activity as well as the head twitching responses in rat, whereas higher phenol concentrations (>60 mg/kg) increased the tremor but reduced the ATPase activity. At phenol concentrations >120 mg/kg, no ATPase activity was detected. Phenobarbital (10 mg/kg) and picrotoxin (1 mg/kg) as well as o-vanadate (2 mg/kg), significantly prevented (˜55-70%) the phenol-induced change in the behavioral responses and completely restored the enzyme activity. In vitro experiments confirmed that phenol stimulated the Cl-/HCO3--ATPase activity at low concentrations, but had no stimulating effect on other transport ATPases. Low doses of phenol increased the formation of phosphoprotein and the rate of ATP-consuming Cl- transport by the reconstituted enzyme. The present findings provide evidence that phenol-induced neurotoxicity involves the Cl-/HCO3--ATPase in the behavioral responses in mammals and indicate the potential benefit of this enzyme as a target for the treatment of head twitching and other types of tremor diseases.
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Affiliation(s)
- Sergey A Menzikov
- Institute of General Pathology and Pathological Physiology, 8, Baltiyskaya st., Moscow, 125315, Russia.
| | - Sergey G Morozov
- Institute of General Pathology and Pathological Physiology, 8, Baltiyskaya st., Moscow, 125315, Russia
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19
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Xiong M, Zheng ZX, Hu ZR, He J, Madubuko U, Grech D, Zhang XA, Xu B. Propofol-sparing effect of different concentrations of dexmedetomidine : Comparison of gender differences. Anaesthesist 2018; 68:15-21. [PMID: 30406275 PMCID: PMC6342900 DOI: 10.1007/s00101-018-0506-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 10/02/2018] [Accepted: 10/09/2018] [Indexed: 11/30/2022]
Abstract
Background The pharmacodynamics of propofol are closely linked to gender. Dexmedetomidine can decrease propofol needs during propofol anesthesia. The aim of this study was to compare the gender differences on the calculated effect site median effective concentration (EC50) of propofol for loss of consciousness (LOC) after pretreatment with different concentrations of dexmedetomidine. Methods In this study 60 male and 60 female patients were randomly allocated to receive dexmedetomidine at target plasma concentrations of 0.0 ng/ml (0.0 group), 0.4 ng/ml (0.4 group), 0.6 ng/ml (0.6 group) and 0.8 ng/ml (0.8 group). Propofol was administered after dexmedetomidine had been intravenously infused for 15 min. The propofol infusion was targeted to provide an initial effect-site concentration of 1.0 μg/ml, followed by increments by 0.2 μg/ml when the effect-site concentration and target concentration of propofol were in equilibrium until LOC was established, where LOC was defined by the observer’s assessment of alertness/sedation scale (OAA/S) score < 2. Results The calculated effect-site EC50 of propofol LOC was higher in males than in females in the 0.0, 0.4, 0.6, and 0.8 groups (2.43 vs. 2.17, 1.99 vs. 1.82, 1.72 vs. 1.56 and 1.50 vs. 1.32 μg/ml, respectively, all p < 0.05). The hypnotic interaction between dexmedetomidine and propofol could be described with an additive model of pharmacodynamic interaction. Conclusion Gender significantly influenced the calculated effect-site EC50 of propofol for LOC after pretreatment with different concentrations of intravenous dexmedetomidine. It was concluded that an additive interaction could describe the results seen. Thus, gender has to be considered when these drugs are co-administered.
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Affiliation(s)
- Ming Xiong
- Department of Anesthesiology, General Hospital of Southern Theatre Command of PLA, 510010, Guangzhou, China.,Department of Anesthesiology & Peri-Operative Medicine, New Jersey Medical School, Rutgers, NJ, USA
| | - Zhao -Xin Zheng
- Department of Anesthesiology, General Hospital of Southern Theatre Command of PLA, 510010, Guangzhou, China.,Department of Anesthesiology, Zhongshan Hospital Affiliated to Xiamen University, Xiamen, China
| | - Zu-Rong Hu
- Department of Anesthesiology, General Hospital of Southern Theatre Command of PLA, 510010, Guangzhou, China.,Department of Anesthesiology, Guangdong Province Hospital for Women and Children Health Care, Guangzhou, China
| | - Jing He
- Department of Anesthesiology, General Hospital of Southern Theatre Command of PLA, 510010, Guangzhou, China
| | - Uchenna Madubuko
- Department of Anesthesiology & Peri-Operative Medicine, New Jersey Medical School, Rutgers, NJ, USA
| | - Dennis Grech
- Department of Anesthesiology & Peri-Operative Medicine, New Jersey Medical School, Rutgers, NJ, USA
| | - Xing-An Zhang
- Department of Anesthesiology, General Hospital of Southern Theatre Command of PLA, 510010, Guangzhou, China
| | - Bo Xu
- Department of Anesthesiology, General Hospital of Southern Theatre Command of PLA, 510010, Guangzhou, China.
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20
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Liu Y, Liao C, Zhou J, Liu C, Li Q, Jiang Y, Qian H. Novel benzodiazepines derivatives as analgesic modulating for Transient receptor potential vanilloid 1. Bioorg Med Chem 2018; 26:4567-4573. [PMID: 30093345 DOI: 10.1016/j.bmc.2018.08.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Revised: 07/28/2018] [Accepted: 08/01/2018] [Indexed: 11/16/2022]
Abstract
A new series of derivatives of 3-(7-chloro-5-(2-fluorophenyl)-2-oxo-2,3-dihydro-1H-benzo[e][1,4]diazepin-3-yl)propanoic acid were designed and synthesized as analgesic modulating for Transient receptor potential vanilloid 1. They were investigated for TRPV1 antagonistic activity in vitro, analgesic activity and sedative activity in vivo and aqueous solubility. Preliminary studies identified 3-(7-chloro-5-(2-fluorophenyl)-2-oxo-2,3-dihydro-1H-benzo[e][1,4]diazepin-3-yl)-N,N-dimethylpropanamide(Compound 11), as a potent analgesic modulating for TRPV1 with potent activity and good aqueous solubility.
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Affiliation(s)
- Yan Liu
- School of Pharmacy, Chongqing Medical University, 1 Yixueyuan Road, Chongqing 400016, PR China.
| | - Chen Liao
- Center of Drug Discovery, State Key Laboratory of Natural Medicines, China Pharmaceutical University, 24 Tongjiaxiang, Nanjing 210009, PR China
| | - Jiaqi Zhou
- Center of Drug Discovery, State Key Laboratory of Natural Medicines, China Pharmaceutical University, 24 Tongjiaxiang, Nanjing 210009, PR China
| | - Chunxia Liu
- Center of Drug Discovery, State Key Laboratory of Natural Medicines, China Pharmaceutical University, 24 Tongjiaxiang, Nanjing 210009, PR China
| | - Qifei Li
- Center of Drug Discovery, State Key Laboratory of Natural Medicines, China Pharmaceutical University, 24 Tongjiaxiang, Nanjing 210009, PR China
| | - Yue Jiang
- School of Pharmacy, Chongqing Medical University, 1 Yixueyuan Road, Chongqing 400016, PR China
| | - Hai Qian
- Center of Drug Discovery, State Key Laboratory of Natural Medicines, China Pharmaceutical University, 24 Tongjiaxiang, Nanjing 210009, PR China; Jiangsu Key Laboratory of Drug Discovery for Metabolic Disease, China Pharmaceutical University, 24 Tongjiaxiang, Nanjing 210009, PR China.
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21
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Alphaxalone Binds in Inner Transmembrane β+-α- Interfaces of α1β3γ2 γ-Aminobutyric Acid Type A Receptors. Anesthesiology 2018; 128:338-351. [PMID: 29210709 DOI: 10.1097/aln.0000000000001978] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
BACKGROUND Neurosteroids like alphaxalone are potent anxiolytics, anticonvulsants, amnestics, and sedative-hypnotics, with effects linked to enhancement of γ-aminobutyric acid type A (GABAA) receptor gating in the central nervous system. Data locating neurosteroid binding sites on synaptic αβγ GABAA receptors are sparse and inconsistent. Some evidence points to outer transmembrane β-α interfacial pockets, near sites that bind the anesthetics etomidate and propofol. Other evidence suggests that steroids bind more intracellularly in β-α interfaces. METHODS The authors created 12 single-residue β3 cysteine mutations: β3T262C and β3T266C in β3-M2; and β3M283C, β3Y284C, β3M286C, β3G287C, β3F289C, β3V290C, β3F293C, β3L297C, β3E298C, and β3F301C in β3-M3 helices. The authors coexpressed α1 and γ2L with each mutant β3 subunit in Xenopus oocytes and electrophysiologically tested each mutant for covalent sulfhydryl modification by the water-soluble reagent para-chloromercuribenzenesulfonate. Then, the authors assessed whether receptor-bound alphaxalone, etomidate, or propofol blocked cysteine modification, implying steric hindrance. RESULTS Eleven mutant β3 subunits, when coexpressed with α1 and γ2L, formed functional channels that displayed varied sensitivities to the three anesthetics. Exposure to para-chloromercuribenzenesulfonate produced irreversible functional changes in ten mutant receptors. Protection by alphaxalone was observed in receptors with β3V290C, β3F293C, β3L297C, or β3F301C mutations. Both etomidate and propofol protected receptors with β3M286C or β3V290C mutations. Etomidate also protected β3F289C. In α1β3γ2L structural homology models, all these protected residues are located in transmembrane β-α interfaces. CONCLUSIONS Alphaxalone binds in transmembrane β-α pockets of synaptic GABAA receptors that are adjacent and intracellular to sites for the potent anesthetics etomidate and propofol.
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Olsen RW. GABA A receptor: Positive and negative allosteric modulators. Neuropharmacology 2018; 136:10-22. [PMID: 29407219 PMCID: PMC6027637 DOI: 10.1016/j.neuropharm.2018.01.036] [Citation(s) in RCA: 189] [Impact Index Per Article: 31.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2017] [Revised: 01/23/2018] [Accepted: 01/25/2018] [Indexed: 12/11/2022]
Abstract
gamma-Aminobutyric acid (GABA)-mediated inhibitory neurotransmission and the gene products involved were discovered during the mid-twentieth century. Historically, myriad existing nervous system drugs act as positive and negative allosteric modulators of these proteins, making GABA a major component of modern neuropharmacology, and suggesting that many potential drugs will be found that share these targets. Although some of these drugs act on proteins involved in synthesis, degradation, and membrane transport of GABA, the GABA receptors Type A (GABAAR) and Type B (GABABR) are the targets of the great majority of GABAergic drugs. This discovery is due in no small part to Professor Norman Bowery. Whereas the topic of GABABR is appropriately emphasized in this special issue, Norman Bowery also made many insights into GABAAR pharmacology, the topic of this article. GABAAR are members of the ligand-gated ion channel receptor superfamily, a chloride channel family of a dozen or more heteropentameric subtypes containing 19 possible different subunits. These subtypes show different brain regional and subcellular localization, age-dependent expression, and potential for plastic changes with experience including drug exposure. Not only are GABAAR the targets of agonist depressants and antagonist convulsants, but most GABAAR drugs act at other (allosteric) binding sites on the GABAAR proteins. Some anxiolytic and sedative drugs, like benzodiazepine and related drugs, act on GABAAR subtype-dependent extracellular domain sites. General anesthetics including alcohols and neurosteroids act at GABAAR subunit-interface trans-membrane sites. Ethanol at high anesthetic doses acts on GABAAR subtype-dependent trans-membrane domain sites. Ethanol at low intoxicating doses acts at GABAAR subtype-dependent extracellular domain sites. Thus GABAAR subtypes possess pharmacologically specific receptor binding sites for a large group of different chemical classes of clinically important neuropharmacological agents. This article is part of the "Special Issue Dedicated to Norman G. Bowery".
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Affiliation(s)
- Richard W Olsen
- Department of Molecular & Medical Pharmacology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
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Ishiguro M, Kobayashi S, Matsuyama K, Nagamine T. Effects of propofol on IPSCs in CA1 and dentate gyrus cells of rat hippocampus: Propofol effects on hippocampal cells' IPSCs. Neurosci Res 2018; 143:13-19. [PMID: 29778809 DOI: 10.1016/j.neures.2018.05.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2017] [Revised: 04/06/2018] [Accepted: 05/14/2018] [Indexed: 11/28/2022]
Abstract
Propofol (2, 6-diisopropylphenol) is one of the most popular intravenous anesthetic agents. In this study, we compared the effects of propofol on inhibitory postsynaptic currents (IPSCs) induced by single and paired electrical stimulations in CA1 pyramidal cells (CA1-PCs) and dentate gyrus granule cells (DG-GCs) in rat hippocampal slices using the whole cell patch-clamp technique. In the absence of propofol, the amplitude of evoked IPSC by single stimulation and decay time constants were stable in both CA1-PCs and DG-GCs for 30 min. Propofol (1 μM and 10 μM) increased both IPSC amplitude in CA1-PCs, but not in DG-GCs. Further, using a paired pulse stimulation protocol, the ratio of IPSC amplitudes (the second response: A2/the first response: A1) was increased by propofol in CA1, but not in DG-GCs. These results suggest that propofol selectively affects IPSCs in CA1-PCs, which is similar to previously reported actions of benzodiazepines.
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Affiliation(s)
- Masanori Ishiguro
- Department of Systems Neuroscience, Sapporo Medical University School of Medicine, South 1, West 17, Chuo-ku, Sapporo, 060-8556, Japan.
| | - Suguru Kobayashi
- Laboratory of Functional Biology, Kagawa School of Pharmaceutical Sciences, Tokushima Bunri University, South 1, West 17, Chuo-ku, Sapporo, 060-8556, Japan
| | - Kiyoji Matsuyama
- Department of Occupational Therapy, Sapporo Medical University School of Health Sciences, South 1, West 17, Chuo-ku, Sapporo, 060-8556, Japan
| | - Takashi Nagamine
- Department of Systems Neuroscience, Sapporo Medical University School of Medicine, South 1, West 17, Chuo-ku, Sapporo, 060-8556, Japan
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Delineation of the functional properties and the mechanism of action of AA29504, an allosteric agonist and positive allosteric modulator of GABA A receptors. Biochem Pharmacol 2018; 150:305-319. [DOI: 10.1016/j.bcp.2018.02.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Accepted: 02/13/2018] [Indexed: 11/22/2022]
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Forman SA. Combining Mutations and Electrophysiology to Map Anesthetic Sites on Ligand-Gated Ion Channels. Methods Enzymol 2018; 602:369-389. [PMID: 29588039 DOI: 10.1016/bs.mie.2018.01.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2023]
Abstract
General anesthetics are known to act in part by binding to and altering the function of pentameric ligand-gated ion channels such as nicotinic acetylcholine and γ-aminobutyric acid type A receptors. Combining heterologous expression of the subunits that assemble to form these ion channels, mutagenesis techniques and voltage-clamp electrophysiology have enabled a variety of "structure-function" approaches to questions of where anesthetic binds to these ion channels and how they enhance or inhibit channel function. Here, we review the evolution of concepts and experimental strategies during the last three decades, since molecular biological and electrophysiological tools became widely used. Topics covered include: (1) structural models as interpretive frameworks, (2) various electrophysiological approaches and their limitations, (3) Monod-Wyman-Changeux allosteric models as functional frameworks, (4) structural strategies including chimeras and point mutations, and (5) methods based on cysteine substitution and covalent modification. We discuss in particular depth the experimental design considerations for substituted cysteine modification-protection studies.
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Affiliation(s)
- Stuart A Forman
- Massachusetts General Hospital, Boston, MA, United States; Harvard Medical School, Boston, MA, United States.
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Functional properties and mechanism of action of PPTQ, an allosteric agonist and low nanomolar positive allosteric modulator at GABAA receptors. Biochem Pharmacol 2018; 147:153-169. [DOI: 10.1016/j.bcp.2017.11.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Accepted: 11/13/2017] [Indexed: 11/23/2022]
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Bademosi AT, Steeves J, Karunanithi S, Zalucki OH, Gormal RS, Liu S, Lauwers E, Verstreken P, Anggono V, Meunier FA, van Swinderen B. Trapping of Syntaxin1a in Presynaptic Nanoclusters by a Clinically Relevant General Anesthetic. Cell Rep 2018; 22:427-440. [DOI: 10.1016/j.celrep.2017.12.054] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 10/27/2017] [Accepted: 12/15/2017] [Indexed: 12/12/2022] Open
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Feng HJ, Forman SA. Comparison of αβδ and αβγ GABA A receptors: Allosteric modulation and identification of subunit arrangement by site-selective general anesthetics. Pharmacol Res 2017; 133:289-300. [PMID: 29294355 DOI: 10.1016/j.phrs.2017.12.031] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 12/28/2017] [Accepted: 12/29/2017] [Indexed: 12/27/2022]
Abstract
GABAA receptors play a dominant role in mediating inhibition in the mature mammalian brain, and defects of GABAergic neurotransmission contribute to the pathogenesis of a variety of neurological and psychiatric disorders. Two types of GABAergic inhibition have been described: αβγ receptors mediate phasic inhibition in response to transient high-concentrations of synaptic GABA release, and αβδ receptors produce tonic inhibitory currents activated by low-concentration extrasynaptic GABA. Both αβδ and αβγ receptors are important targets for general anesthetics, which induce apparently different changes both in GABA-dependent receptor activation and in desensitization in currents mediated by αβγ vs. αβδ receptors. Many of these differences are explained by correcting for the high agonist efficacy of GABA at most αβγ receptors vs. much lower efficacy at αβδ receptors. The stoichiometry and subunit arrangement of recombinant αβγ receptors are well established as β-α-γ-β-α, while those of αβδ receptors remain controversial. Importantly, some potent general anesthetics selectively bind in transmembrane inter-subunit pockets of αβγ receptors: etomidate acts at β+/α- interfaces, and the barbiturate R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid (R-mTFD-MPAB) acts at α+/β- and γ+/β- interfaces. Thus, these drugs are useful as structural probes in αβδ receptors formed from free subunits or concatenated subunit assemblies designed to constrain subunit arrangement. Although a definite conclusion cannot be drawn, studies using etomidate and R-mTFD-MPAB support the idea that recombinant α1β3δ receptors may share stoichiometry and subunit arrangement with α1β3γ2 receptors.
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Affiliation(s)
- Hua-Jun Feng
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, and Department of Anesthesia, Harvard Medical School, Boston, MA 02114, USA.
| | - Stuart A Forman
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, and Department of Anesthesia, Harvard Medical School, Boston, MA 02114, USA.
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Amin J, Subbarayan MS. Orthosteric- versus allosteric-dependent activation of the GABA A receptor requires numerically distinct subunit level rearrangements. Sci Rep 2017; 7:7770. [PMID: 28798394 PMCID: PMC5552871 DOI: 10.1038/s41598-017-08031-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 07/07/2017] [Indexed: 12/05/2022] Open
Abstract
Anaesthetic molecules act on synaptic transmission via the allosteric modulation of ligand-gated chloride channels, such as hetero-oligomeric α1β2γ2 GABAA receptors. To elucidate the overall activation paradigm via allosteric versus orthosteric sites, we used highly homologous, but homo-oligomeric, ρ1 receptors that are contrastingly insensitive to anaesthetics and respond partially to several full GABA α1β2γ2 receptor agonists. Here, we coexpressed varying ratios of RNAs encoding the wild-type and the mutated ρ1 subunits, which are anaesthetic-sensitive and respond with full efficacy to partial GABA agonists, to generate distinct ensembles of receptors containing five, four, three, two, one, or zero mutated subunits. Using these experiments, we then demonstrate that, in the pentamer, three anaesthetic-sensitive ρ1 subunits are needed to impart full efficacy to the partial GABA agonists. By contrast, five anaesthetic-sensitive subunits are required for direct activation by anaesthetics alone, and only one anaesthetic-sensitive subunit is sufficient to confer the anaesthetic-dependent potentiation to the GABA current. In conclusion, our data indicate that GABA and anaesthetics holistically activate the GABAA ρ1 receptor through distinct subunit level rearrangements and suggest that in contrast to the global impact of GABA via orthosteric sites, the force of anaesthetics through allosteric sites may not propagate to the neighbouring subunits and, thus, may have only a local and limited effect on the ρ1 GABAA receptor model system.
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Affiliation(s)
- Jahanshah Amin
- Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, Florida, 33612, USA.
| | - Meena S Subbarayan
- Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, Florida, 33612, USA
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Zheng Y, Liu H, Liang Y. Genistein exerts potent antitumour effects alongside anaesthetic, propofol, by suppressing cell proliferation and nuclear factor-κB-mediated signalling and through upregulating microRNA-218 expression in an intracranial rat brain tumour model. J Pharm Pharmacol 2017; 69:1565-1577. [PMID: 28776680 DOI: 10.1111/jphp.12781] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 06/11/2017] [Indexed: 12/20/2022]
Abstract
Abstract
Objective
This study was implemented to evaluate the effect of genistein and propofol on intracranial tumour model.
Methods
Male Fischer 344 rats were subjected to intracranial implantation of 9L gliosarcoma cells. Genistein (100 or 200 mg/kg b.wt) was administered orally regularly from 3rd day after implantation to 25th day. Propofol (20 mg/kg; i.p.) was administered once every 5 days till 25th day and was administered 2 h after genistein.
Key findings
Human gliosarcoma cells (U251) exposed to genistein (12.5–200 μg) for 24 h exhibited reduced cell viability as assessed by MTT assay and Hoechst staining. In intracranial tumour model, genistein treatment either with or without administration of propofol significantly reduced tumour volume and extended survival time of tumour-bearing rats. Genistein, either alone or with propofol upregulated pro-apoptotic proteins (Bad and Bax) and miRNA-218 expression and also had induced activation of cleaved caspase-3. Activated NF-κB signalling and overproduction of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) were reduced.
Conclusions
Genistein and propofol effectively inhibited growth of gliosarcoma cells and induced apoptosis. Genistein administration with propofol was found to be more effective than propofol or genistein alone suggesting the positive effects of genistein on propofol-mediated antitumour effects and vice versa.
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Affiliation(s)
- Yuzhen Zheng
- Department of Anesthesiology, Tianjin Huanhu Hospital, Tianjin, China
- Tianjin Cerebral Vascular and Neural Degenerative Diseases Key Laboratory, TianjinHuanhu Hospital, Tianjin, China
| | - Haigen Liu
- Department of Anesthesiology, Tianjin Huanhu Hospital, Tianjin, China
| | - Yu Liang
- Department of Anesthesiology, Tianjin Huanhu Hospital, Tianjin, China
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Heil LBB, Silva PL, Pelosi P, Rocco PRM. Immunomodulatory effects of anesthetics in obese patients. World J Crit Care Med 2017; 6:140-152. [PMID: 28828299 PMCID: PMC5547428 DOI: 10.5492/wjccm.v6.i3.140] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Revised: 04/27/2017] [Accepted: 07/10/2017] [Indexed: 02/06/2023] Open
Abstract
Anesthesia and surgery have an impact on inflammatory responses, which influences perioperative homeostasis. Inhalational and intravenous anesthesia can alter immune-system homeostasis through multiple processes that include activation of immune cells (such as monocytes, neutrophils, and specific tissue macrophages) with release of pro- or anti-inflammatory interleukins, upregulation of cell adhesion molecules, and overproduction of oxidative radicals. The response depends on the timing of anesthesia, anesthetic agents used, and mechanisms involved in the development of inflammation or immunosuppression. Obese patients are at increased risk for chronic diseases and may have the metabolic syndrome, which features insulin resistance and chronic low-grade inflammation. Evidence has shown that obesity has adverse impacts on surgical outcome, and that immune cells play an important role in this process. Understanding the effects of anesthetics on immune-system cells in obese patients is important to support proper selection of anesthetic agents, which may affect postoperative outcomes. This review article aims to integrate current knowledge regarding the effects of commonly used anesthetic agents on the lungs and immune response with the underlying immunology of obesity. Additionally, it identifies knowledge gaps for future research to guide optimal selection of anesthetic agents for obese patients from an immunomodulatory standpoint.
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Forman SA, Miller KW. Mapping General Anesthetic Sites in Heteromeric γ-Aminobutyric Acid Type A Receptors Reveals a Potential For Targeting Receptor Subtypes. Anesth Analg 2017; 123:1263-1273. [PMID: 27167687 DOI: 10.1213/ane.0000000000001368] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
IV general anesthetics, including propofol, etomidate, alphaxalone, and barbiturates, produce important actions by enhancing γ-aminobutyric acid type A (GABAA) receptor activation. In this article, we review scientific studies that have located and mapped IV anesthetic sites using photoaffinity labeling and substituted cysteine modification protection. These anesthetics bind in transmembrane pockets between subunits of typical synaptic GABAA receptors, and drugs that display stereoselectivity also show remarkably selective interactions with distinct interfacial sites. These results suggest strategies for developing new drugs that selectively modulate distinct GABAA receptor subtypes.
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Affiliation(s)
- Stuart A Forman
- From the Department of Anesthesia Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
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Kumar M, Kumar M, Freund JM, Dillon GH. A Single Amino Acid Residue at Transmembrane Domain 4 of the α Subunit Influences Carisoprodol Direct Gating Efficacy at GABA A Receptors. J Pharmacol Exp Ther 2017. [PMID: 28642232 DOI: 10.1124/jpet.117.242156] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The muscle relaxant carisoprodol has recently been controlled at the federal level as a Schedule IV drug due to its high abuse potential and consequences of misuse, such as withdrawal syndrome, delusions, seizures, and even death. Recent work has shown that carisoprodol can directly gate and allosterically modulate the type A GABA (GABAA) receptor. These actions are subunit-dependent; compared with other GABAA receptors, carisoprodol has nominal direct gating effects in α3β2γ2 receptors. Here, using site-directed mutagenesis and whole-cell patch-clamp electrophysiology in transiently transfected human embryonic kidney 293 cells, we examined the role of GABAA receptor α subunit transmembrane domain 4 (TM4) amino acids in direct gating and allosteric modulatory actions of carisoprodol. Mutation of α3 valine at position 440 to leucine (present in the equivalent position in the α1 subunit) significantly increased the direct gating effects of carisoprodol without affecting its allosteric modulatory effects. The corresponding reverse mutation, α1(L415V), decreased carisoprodol direct gating potency and efficacy. Analysis of a series of amino acid mutations at the 415 position demonstrated that amino acid volume correlated positively with carisoprodol efficacy, whereas polarity inversely correlated with carisoprodol efficacy. We conclude that α1(415) of TM4 is involved in the direct gating, but not allosteric modulatory, actions of carisoprodol. In addition, the orientation of alkyl or hydroxyl groups at this position influences direct gating effects. These findings support the likelihood that the direct gating and allosteric modulatory effects of carisoprodol are mediated via distinct binding sites.
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Affiliation(s)
- Manoj Kumar
- Department of Physiology and Pharmacology, Center for Neuroscience, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia (Mo.K., Mi.K., J.M.F., G.H.D.); and Center for Neuroscience Discovery, Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, Texas (Mi.K., G.H.D.)
| | - Manish Kumar
- Department of Physiology and Pharmacology, Center for Neuroscience, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia (Mo.K., Mi.K., J.M.F., G.H.D.); and Center for Neuroscience Discovery, Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, Texas (Mi.K., G.H.D.)
| | - John M Freund
- Department of Physiology and Pharmacology, Center for Neuroscience, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia (Mo.K., Mi.K., J.M.F., G.H.D.); and Center for Neuroscience Discovery, Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, Texas (Mi.K., G.H.D.)
| | - Glenn H Dillon
- Department of Physiology and Pharmacology, Center for Neuroscience, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia (Mo.K., Mi.K., J.M.F., G.H.D.); and Center for Neuroscience Discovery, Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, Texas (Mi.K., G.H.D.)
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Tryptophan and Cysteine Mutations in M1 Helices of α1β3γ2L γ-Aminobutyric Acid Type A Receptors Indicate Distinct Intersubunit Sites for Four Intravenous Anesthetics and One Orphan Site. Anesthesiology 2017; 125:1144-1158. [PMID: 27753644 DOI: 10.1097/aln.0000000000001390] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND γ-Aminobutyric acid type A (GABAA) receptors mediate important effects of intravenous general anesthetics. Photolabel derivatives of etomidate, propofol, barbiturates, and a neurosteroid get incorporated in GABAA receptor transmembrane helices M1 and M3 adjacent to intersubunit pockets. However, photolabels have not been consistently targeted at heteromeric αβγ receptors and do not form adducts with all contact residues. Complementary approaches may further define anesthetic sites in typical GABAA receptors. METHODS Two mutation-based strategies, substituted tryptophan sensitivity and substituted cysteine modification-protection, combined with voltage-clamp electrophysiology in Xenopus oocytes, were used to evaluate interactions between four intravenous anesthetics and six amino acids in M1 helices of α1, β3, and γ2L GABAA receptor subunits: two photolabeled residues, α1M236 and β3M227, and their homologs. RESULTS Tryptophan substitutions at α1M236 and positional homologs β3L231 and γ2L246 all caused spontaneous channel gating and reduced γ-aminobutyric acid EC50. Substituted cysteine modification experiments indicated etomidate protection at α1L232C and α1M236C, R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirinylphenyl) barbituric acid protection at β3M227C and β3L231C, and propofol protection at α1M236C and β3M227C. No alphaxalone protection was evident at the residues the authors explored, and none of the tested anesthetics protected γ2I242C or γ2L246C. CONCLUSIONS All five intersubunit transmembrane pockets of GABAA receptors display similar allosteric linkage to ion channel gating. Substituted cysteine modification and protection results were fully concordant with anesthetic photolabeling at α1M236 and β3M227 and revealed overlapping noncongruent sites for etomidate and propofol in β-α interfaces and R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirinylphenyl) barbituric acid and propofol in α-β and γ-β interfaces. The authors' results identify the α-γ transmembrane interface as a potentially unique orphan modulator site.
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Eaton MM, Germann AL, Arora R, Cao LQ, Gao X, Shin DJ, Wu A, Chiara DC, Cohen JB, Steinbach JH, Evers AS, Akk G. Multiple Non-Equivalent Interfaces Mediate Direct Activation of GABAA Receptors by Propofol. Curr Neuropharmacol 2017; 14:772-80. [PMID: 26830963 PMCID: PMC5050400 DOI: 10.2174/1570159x14666160202121319] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 05/08/2016] [Accepted: 05/16/2016] [Indexed: 11/28/2022] Open
Abstract
Abstract: Background Propofol is a sedative agent that at clinical concentrations acts by allosterically activating or potentiating the γ-aminobutyric acid type A (GABAA) receptor. Mutational, modeling, and photolabeling studies with propofol and its analogues have identified potential interaction sites in the transmembrane domain of the receptor. At the “+” of the β subunit, in the β-α interface, meta-azipropofol labels the M286 residue in the third transmembrane domain. Substitution of this residue with tryptophan results in loss of potentiation by propofol. At the “-” side of the β subunit, in the α-β interface (or β-β interface, in the case of homomeric β receptors), ortho-propofol diazirine labels the H267 residue in the second transmembrane domain. Structural modeling indicates that the β(H267) residue lines a cavity that docks propofol with favorable interaction energy. Method We used two-electrode voltage clamp to determine the functional effects of mutations to the
“+” and “-” sides of the β subunit on activation of the α1β3 GABAA receptor by propofol. Results We found that while the individual mutations had a small effect, the combination of the M286W mutation with tryptophan mutations of selected residues at the α-β interface leads to strong reduction in gating efficacy for propofol. Conclusion We conclude that α1β3 GABAA receptors can be activated by propofol interactions with the β-β, α-β, and β-α interfaces, where distinct, non-equivalent regions control channel gating. Any interface can mediate activation, hence substitutions at all interfaces are required for loss of activation by propofol.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | - Gustav Akk
- Department of Anesthesiology, Washington University, Campus Box 8054, 660 South Euclid Ave, St. Louis, MO 63110
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Chua HC, Chebib M. GABA A Receptors and the Diversity in their Structure and Pharmacology. ADVANCES IN PHARMACOLOGY 2017; 79:1-34. [DOI: 10.1016/bs.apha.2017.03.003] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Zalucki O, van Swinderen B. What is unconsciousness in a fly or a worm? A review of general anesthesia in different animal models. Conscious Cogn 2016; 44:72-88. [PMID: 27366985 DOI: 10.1016/j.concog.2016.06.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Revised: 05/31/2016] [Accepted: 06/20/2016] [Indexed: 12/14/2022]
Abstract
All animals are rendered unresponsive by general anesthetics. In humans, this is observed as a succession of endpoints from memory loss to unconsciousness to immobility. Across animals, anesthesia endpoints such as loss of responsiveness or immobility appear to require significantly different drug concentrations. A closer examination in key model organisms such as the mouse, fly, or the worm, uncovers a trend: more complex behaviors, either requiring several sub-behaviors, or multiple neural circuits working together, are more sensitive to volatile general anesthetics. This trend is also evident when measuring neural correlates of general anesthesia. Here, we review this complexity hypothesis in humans and model organisms, and attempt to reconcile these findings with the more recent view that general anesthetics potentiate endogenous sleep pathways in most animals. Finally, we propose a presynaptic mechanism, and thus an explanation for how these drugs might compromise a succession of brain functions of increasing complexity.
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Affiliation(s)
- Oressia Zalucki
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Bruno van Swinderen
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
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A Cysteine Substitution Probes β3H267 Interactions with Propofol and Other Potent Anesthetics in α1β3γ2L γ-Aminobutyric Acid Type A Receptors. Anesthesiology 2016; 124:89-100. [PMID: 26569173 DOI: 10.1097/aln.0000000000000934] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
BACKGROUND Anesthetic contact residues in γ-aminobutyric acid type A (GABAA) receptors have been identified using photolabels, including two propofol derivatives. O-propofol diazirine labels H267 in β3 and α1β3 receptors, whereas m-azi-propofol labels other residues in intersubunit clefts of α1β3. Neither label has been studied in αβγ receptors, the most common isoform in mammalian brain. In αβγ receptors, other anesthetic derivatives photolabel m-azi-propofol-labeled residues, but not βH267. The authors' structural homology model of α1β3γ2L receptors suggests that β3H267 may abut some of these sites. METHODS Substituted cysteine modification-protection was used to test β3H267C interactions with four potent anesthetics: propofol, etomidate, alphaxalone, and R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirinylphenyl) barbituric acid (mTFD-MPAB). The authors expressed α1β3γ2L or α1β3H267Cγ2L GABAA receptors in Xenopus oocytes. The authors used voltage clamp electrophysiology to assess receptor sensitivity to γ-aminobutyric acid (GABA) and anesthetics and to compare p-chloromercuribenzenesulfonate modification rates with GABA versus GABA plus anesthetics. RESULTS Enhancement of low GABA (eliciting 5% of maximum) responses by equihypnotic concentrations of all four anesthetics was similar in α1β3γ2L and α1β3H267Cγ2L receptors (n > 3). Direct activation of α1β3H267Cγ2L receptors, but not α1β3γ2L, by mTFD-MPAB and propofol was significantly greater than the other anesthetics. Modification of β3H267C by p-chloromercuribenzenesulfonate (n > 4) was rapid and accelerated by GABA. Only mTFD-MPAB slowed β3H267C modification (approximately twofold; P = 0.011). CONCLUSIONS β3H267 in α1β3γ2L GABAA receptors contacts mTFD-MPAB, but not propofol. The study results suggest that β3H267 is near the periphery of one or both transmembrane intersubunit (α+/β- and γ+/β-) pockets where both mTFD-MPAB and propofol bind.
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Chowdhury L, Croft CJ, Goel S, Zaman N, Tai ACS, Walch EM, Smith K, Page A, Shea KM, Hall CD, Jishkariani D, Pillai GG, Hall AC. Differential Potency of 2,6-Dimethylcyclohexanol Isomers for Positive Modulation of GABAA Receptor Currents. J Pharmacol Exp Ther 2016; 357:570-9. [PMID: 27029583 DOI: 10.1124/jpet.115.228890] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 03/22/2016] [Indexed: 11/22/2022] Open
Abstract
GABAA receptors meet all of the pharmacological requirements necessary to be considered important targets for the action of general anesthetic agents in the mammalian brain. In the following patch-clamp study, the relative modulatory effects of 2,6-dimethylcyclohexanol diastereomers were investigated on human GABAA (α1β3γ2s) receptor currents stably expressed in human embryonic kidney cells. Cis,cis-, trans,trans-, and cis,trans-isomers were isolated from commercially available 2,6-dimethylcyclohexanol and were tested for positive modulation of submaximal GABA responses. For example, the addition of 30 μM cis,cis-isomer resulted in an approximately 2- to 3-fold enhancement of the EC20 GABA current. Coapplications of 30 μM 2,6-dimethylcyclohexanol isomers produced a range of positive enhancements of control GABA responses with a rank order for positive modulation: cis,cis > trans,trans ≥ mixture of isomers > > cis,trans-isomer. In molecular modeling studies, the three cyclohexanol isomers bound with the highest binding energies to a pocket within transmembrane helices M1 and M2 of the β3 subunit through hydrogen-bonding interactions with a glutamine at the 224 position and a tyrosine at the 220 position. The energies for binding to and hydrogen-bond lengths within this pocket corresponded with the relative potencies of the agents for positive modulation of GABAA receptor currents (cis,cis > trans,trans > cis,trans-2,6-dimethylcyclohexanol). In conclusion, the stereochemical configuration within the dimethylcyclohexanols is an important molecular feature in conferring positive modulation of GABAA receptor activity and for binding to the receptor, a consideration that needs to be taken into account when designing novel anesthetics with enhanced therapeutic indices.
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Affiliation(s)
- Luvana Chowdhury
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - Celine J Croft
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - Shikha Goel
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - Naina Zaman
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - Angela C-S Tai
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - Erin M Walch
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - Kelly Smith
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - Alexandra Page
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - Kevin M Shea
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - C Dennis Hall
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - D Jishkariani
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - Girinath G Pillai
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
| | - Adam C Hall
- Neuroscience Program, Departments of Biological Sciences (L.C., C.J.C., S.G., N.Z., A.C.-S.T., E.M.W., A.C.H.) and Chemistry (K.S., A.P., K.M.S.), Smith College, Northampton, Massachusetts; Department of Chemistry, University of Florida, Gainesville, Florida (C.D.H., D.J., G.G.P.); and Department of Chemistry, University of Tartu, Ravila, Estonia (G.G.P.)
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Functional sites involved in modulation of the GABAA receptor channel by the intravenous anesthetics propofol, etomidate and pentobarbital. Neuropharmacology 2016; 105:207-214. [PMID: 26767954 DOI: 10.1016/j.neuropharm.2016.01.003] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Revised: 12/15/2015] [Accepted: 01/03/2016] [Indexed: 11/22/2022]
Abstract
GABAA receptors are the major inhibitory neurotransmitter receptors in the brain and are the target for many clinically important drugs. Among the many modulatory compounds are also the intravenous anesthetics propofol and etomidate, and barbiturates. The mechanism of receptor modulation by these compounds is of mayor relevance. The site of action of these compounds has been located to subunit interfaces in the intra-membrane region of the receptor. In α1β2γ2 GABAA receptors there are five such interfaces, two β+/α- and one each of α+/β-, α+/γ- and γ+/β- subunit interfaces. We have used reporter mutations located in the second trans-membrane region in different subunits to probe the effects of changes at these subunit interfaces on modulation by propofol, etomidate and pentobarbital. We provide evidence for the fact that each of these compounds either modulates through a different set of subunit interfaces or through the same set of subunit interfaces to a different degree. As a GABAA receptor pentamer harbors two β+/α- subunit interfaces, we used concatenated receptors to dissect the contribution of individual interfaces and show that only one of these interfaces is important for receptor modulation by etomidate.
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Chen HY, Albertson TE, Olson KR. Treatment of drug-induced seizures. Br J Clin Pharmacol 2015; 81:412-9. [PMID: 26174744 DOI: 10.1111/bcp.12720] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2015] [Revised: 07/03/2015] [Accepted: 07/07/2015] [Indexed: 01/01/2023] Open
Abstract
Seizures are a common complication of drug intoxication, and up to 9% of status epilepticus cases are caused by a drug or poison. While the specific drugs associated with drug-induced seizures may vary by geography and change over time, common reported causes include antidepressants, stimulants and antihistamines. Seizures occur generally as a result of inadequate inhibitory influences (e.g., gamma aminobutyric acid, GABA) or excessive excitatory stimulation (e.g. glutamate) although many other neurotransmitters play a role. Most drug-induced seizures are self-limited. However, status epilepticus occurs in up to 10% of cases. Prolonged or recurrent seizures can lead to serious complications and require vigorous supportive care and anticonvulsant drugs. Benzodiazepines are generally accepted as the first line anticonvulsant therapy for drug-induced seizures. If benzodiazepines fail to halt seizures promptly, second line drugs include barbiturates and propofol. If isoniazid poisoning is a possibility, pyridoxine is given. Continuous infusion of one or more anticonvulsants may be required in refractory status epilepticus. There is no role for phenytoin in the treatment of drug-induced seizures. The potential role of ketamine and levetiracetam is promising but not established.
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Affiliation(s)
- Hsien-Yi Chen
- California Poison Control System, Department of Clinical Pharmacy, University of California, San Francisco, USA.,Department of Emergency Medicine, Chang-Gung Memorial Hospital, Taoyuan, Taiwan.,Division of Clinical Pharmacology & Toxicology, San Francisco General Hospital, San Francisco, USA
| | - Timothy E Albertson
- California Poison Control System, Department of Clinical Pharmacy, University of California, San Francisco, USA.,Department of Internal Medicine, University of California Davis School of Medicine and Veterans Administration Northern California Health Care System, California
| | - Kent R Olson
- California Poison Control System, Department of Clinical Pharmacy, University of California, San Francisco, USA.,Division of Clinical Pharmacology & Toxicology, San Francisco General Hospital, San Francisco, USA
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Syntaxin1A-mediated Resistance and Hypersensitivity to Isoflurane in Drosophila melanogaster. Anesthesiology 2015; 122:1060-74. [PMID: 25738637 DOI: 10.1097/aln.0000000000000629] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
BACKGROUND Recent evidence suggests that general anesthetics activate endogenous sleep pathways, yet this mechanism cannot explain the entirety of general anesthesia. General anesthetics could disrupt synaptic release processes, as previous work in Caenorhabditis elegans and in vitro cell preparations suggested a role for the soluble NSF attachment protein receptor protein, syntaxin1A, in mediating resistance to several general anesthetics. The authors questioned whether the syntaxin1A-mediated effects found in these reductionist systems reflected a common anesthetic mechanism distinct from sleep-related processes. METHODS Using the fruit fly model, Drosophila melanogaster, the authors investigated the relevance of syntaxin1A manipulations to general anesthesia. The authors used different behavioral and electrophysiological endpoints to test the effect of syntaxin1A mutations on sensitivity to isoflurane. RESULTS The authors found two syntaxin1A mutations that confer opposite general anesthesia phenotypes: syxH3-C, a 14-amino acid deletion mutant, is resistant to isoflurane (n = 40 flies), and syxKARRAA, a strain with two amino acid substitutions, is hypersensitive to the drug (n = 40 flies). Crucially, these opposing effects are maintained across different behavioral endpoints and life stages. The authors determined the isoflurane sensitivity of syxH3-C at the larval neuromuscular junction to assess effects on synaptic release. The authors find that although isoflurane slightly attenuates synaptic release in wild-type animals (n = 8), syxH3-C preserves synaptic release in the presence of isoflurane (n = 8). CONCLUSION The study results are evidence that volatile general anesthetics target synaptic release mechanisms; in addition to first activating sleep pathways, a major consequence of these drugs may be to decrease the efficacy of neurotransmission.
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Eaton MM, Cao LQ, Chen Z, Franks NP, Evers AS, Akk G. Mutational Analysis of the Putative High-Affinity Propofol Binding Site in Human β3 Homomeric GABAA Receptors. Mol Pharmacol 2015. [PMID: 26206487 DOI: 10.1124/mol.115.100347] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Propofol is a sedative and anesthetic agent that can both activate GABA(A) receptors and potentiate receptor activation elicited by submaximal concentrations of the transmitter. A recent modeling study of the β3 homomeric GABA(A) receptor postulated a high-affinity propofol binding site in a hydrophobic pocket in the middle of a triangular cleft lined by the M1 and M2 membrane-spanning domains of one subunit and the M2 domain of the neighboring subunit. The goal of the present study was to gain functional evidence for the involvement of this pocket in the actions of propofol. Human β3 and α1β3 receptors were expressed in Xenopus oocytes, and the effects of substitutions of selected residues were probed on channel activation by propofol and pentobarbital. The data demonstrate the vital role of the β3(Y143), β3(F221), β3(Q224), and β3(T266) residues in the actions of propofol but not pentobarbital in β3 receptors. The effects of β3(Y143W) and β3(Q224W) on activation by propofol are likely steric because propofol analogs with less bulky ortho substituents activated both wild-type and mutant receptors. The T266W mutation removed activation by propofol in β3 homomeric receptors; however, this mutation alone or in combination with a homologous mutation (I271W) in the α1 subunit had almost no effect on activation properties in α1β3 heteromeric receptors. We hypothesize that heteromeric α1β3 receptors can be activated by propofol interactions with β3-β3, α1-β3, and β3-α1 interfaces, but the exact locations of the binding site and/or nature of interactions vary in different classes of interfaces.
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Affiliation(s)
- Megan M Eaton
- Department of Anesthesiology (M.M.E., L.Q.C., Z.C., A.S.E., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (Z.C., A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Life Sciences, Imperial College London, South Kensington, United Kingdom (N.P.F.)
| | - Lily Q Cao
- Department of Anesthesiology (M.M.E., L.Q.C., Z.C., A.S.E., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (Z.C., A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Life Sciences, Imperial College London, South Kensington, United Kingdom (N.P.F.)
| | - Ziwei Chen
- Department of Anesthesiology (M.M.E., L.Q.C., Z.C., A.S.E., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (Z.C., A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Life Sciences, Imperial College London, South Kensington, United Kingdom (N.P.F.)
| | - Nicholas P Franks
- Department of Anesthesiology (M.M.E., L.Q.C., Z.C., A.S.E., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (Z.C., A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Life Sciences, Imperial College London, South Kensington, United Kingdom (N.P.F.)
| | - Alex S Evers
- Department of Anesthesiology (M.M.E., L.Q.C., Z.C., A.S.E., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (Z.C., A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Life Sciences, Imperial College London, South Kensington, United Kingdom (N.P.F.)
| | - Gustav Akk
- Department of Anesthesiology (M.M.E., L.Q.C., Z.C., A.S.E., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (Z.C., A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Life Sciences, Imperial College London, South Kensington, United Kingdom (N.P.F.)
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Structural comparisons of ligand-gated ion channels in open, closed, and desensitized states identify a novel propofol-binding site on mammalian γ-aminobutyric acid type A receptors. Anesthesiology 2015; 122:787-94. [PMID: 25575161 DOI: 10.1097/aln.0000000000000588] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
BACKGROUND Most anesthetics, particularly intravenous agents such as propofol and etomidate, enhance the actions of the neurotransmitter γ-aminobutyric acid (GABA) at the GABA type A receptor. However, there is no agreement as where anesthetics bind to the receptor. A novel approach would be to identify regions on the receptor that are state-dependent, which would account for the ability of anesthetics to affect channel opening by binding differentially to the open and closed states. METHODS The open and closed structures of the GABA type A receptor homologues Gloeobacter ligand-gated ion channel and glutamate-gated chloride channel were compared, and regions in the channels that move on channel opening and closing were identified. Docking calculations were performed to investigate possible binding of propofol to the GABA type A β3 homomer in this region. RESULTS A comparison between the open and closed states of the Gloeobacter ligand-gated ion channel and glutamate-gated chloride channel channels identified a region at the top of transmembrane domains 2 and 3 that shows maximum movement when the channels transition between the open and closed states. Docking of propofol into the GABA type A β3 homomer identified two putative binding cavities in this same region, one with a high affinity and one with a lower affinity. Both cavities were adjacent to a histidine residue that has been photolabeled by a propofol analog, and both sites would be disrupted on channel closing. CONCLUSIONS These calculations support the conclusion of a recent photolabeling study that propofol acts at a site at the interface between the extracellular and transmembrane domains, close to the top of transmembrane domain 2.
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Hammer H, Bader BM, Ehnert C, Bundgaard C, Bunch L, Hoestgaard-Jensen K, Schroeder OHU, Bastlund JF, Gramowski-Voß A, Jensen AA. A Multifaceted GABAA Receptor Modulator: Functional Properties and Mechanism of Action of the Sedative-Hypnotic and Recreational Drug Methaqualone (Quaalude). Mol Pharmacol 2015; 88:401-20. [PMID: 26056160 DOI: 10.1124/mol.115.099291] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2015] [Accepted: 06/08/2015] [Indexed: 01/09/2023] Open
Abstract
In the present study, we have elucidated the functional characteristics and mechanism of action of methaqualone (2-methyl-3-o-tolyl-4(3H)-quinazolinone, Quaalude), an infamous sedative-hypnotic and recreational drug from the 1960s-1970s. Methaqualone was demonstrated to be a positive allosteric modulator at human α1,2,3,5β2,3γ2S GABAA receptors (GABAARs) expressed in Xenopus oocytes, whereas it displayed highly diverse functionalities at the α4,6β1,2,3δ GABAAR subtypes, ranging from inactivity (α4β1δ), through negative (α6β1δ) or positive allosteric modulation (α4β2δ, α6β2,3δ), to superagonism (α4β3δ). Methaqualone did not interact with the benzodiazepine, barbiturate, or neurosteroid binding sites in the GABAAR. Instead, the compound is proposed to act through the transmembrane β((+))/α((-)) subunit interface of the receptor, possibly targeting a site overlapping with that of the general anesthetic etomidate. The negligible activities displayed by methaqualone at numerous neurotransmitter receptors and transporters in an elaborate screening for additional putative central nervous system (CNS) targets suggest that it is a selective GABAAR modulator. The mode of action of methaqualone was further investigated in multichannel recordings from primary frontal cortex networks, where the overall activity changes induced by the compound at 1-100 μM concentrations were quite similar to those mediated by other CNS depressants. Finally, the free methaqualone concentrations in the mouse brain arising from doses producing significant in vivo effects in assays for locomotion and anticonvulsant activity correlated fairly well with its potencies as a modulator at the recombinant GABAARs. Hence, we propose that the multifaceted functional properties exhibited by methaqualone at GABAARs give rise to its effects as a therapeutic and recreational drug.
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Affiliation(s)
- Harriet Hammer
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (H.H., L.B., K.H.-J., A.A.J.); NeuroProof, Rostock, Germany (B.M.B., C.E., O.H.-U.S., A.G.-V.); and H. Lundbeck A/S, Valby, Denmark (C.B., J.F.B.)
| | - Benjamin M Bader
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (H.H., L.B., K.H.-J., A.A.J.); NeuroProof, Rostock, Germany (B.M.B., C.E., O.H.-U.S., A.G.-V.); and H. Lundbeck A/S, Valby, Denmark (C.B., J.F.B.)
| | - Corina Ehnert
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (H.H., L.B., K.H.-J., A.A.J.); NeuroProof, Rostock, Germany (B.M.B., C.E., O.H.-U.S., A.G.-V.); and H. Lundbeck A/S, Valby, Denmark (C.B., J.F.B.)
| | - Christoffer Bundgaard
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (H.H., L.B., K.H.-J., A.A.J.); NeuroProof, Rostock, Germany (B.M.B., C.E., O.H.-U.S., A.G.-V.); and H. Lundbeck A/S, Valby, Denmark (C.B., J.F.B.)
| | - Lennart Bunch
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (H.H., L.B., K.H.-J., A.A.J.); NeuroProof, Rostock, Germany (B.M.B., C.E., O.H.-U.S., A.G.-V.); and H. Lundbeck A/S, Valby, Denmark (C.B., J.F.B.)
| | - Kirsten Hoestgaard-Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (H.H., L.B., K.H.-J., A.A.J.); NeuroProof, Rostock, Germany (B.M.B., C.E., O.H.-U.S., A.G.-V.); and H. Lundbeck A/S, Valby, Denmark (C.B., J.F.B.)
| | - Olaf H-U Schroeder
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (H.H., L.B., K.H.-J., A.A.J.); NeuroProof, Rostock, Germany (B.M.B., C.E., O.H.-U.S., A.G.-V.); and H. Lundbeck A/S, Valby, Denmark (C.B., J.F.B.)
| | - Jesper F Bastlund
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (H.H., L.B., K.H.-J., A.A.J.); NeuroProof, Rostock, Germany (B.M.B., C.E., O.H.-U.S., A.G.-V.); and H. Lundbeck A/S, Valby, Denmark (C.B., J.F.B.)
| | - Alexandra Gramowski-Voß
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (H.H., L.B., K.H.-J., A.A.J.); NeuroProof, Rostock, Germany (B.M.B., C.E., O.H.-U.S., A.G.-V.); and H. Lundbeck A/S, Valby, Denmark (C.B., J.F.B.)
| | - Anders A Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (H.H., L.B., K.H.-J., A.A.J.); NeuroProof, Rostock, Germany (B.M.B., C.E., O.H.-U.S., A.G.-V.); and H. Lundbeck A/S, Valby, Denmark (C.B., J.F.B.)
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Naito A, Muchhala KH, Trang J, Asatryan L, Trudell JR, Homanics GE, Alkana RL, Davies DL. Manipulations of extracellular Loop 2 in α1 GlyR ultra-sensitive ethanol receptors (USERs) enhance receptor sensitivity to isoflurane, ethanol, and lidocaine, but not propofol. Neuroscience 2015; 297:68-77. [PMID: 25827497 DOI: 10.1016/j.neuroscience.2015.03.034] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2015] [Revised: 03/16/2015] [Accepted: 03/17/2015] [Indexed: 11/18/2022]
Abstract
We recently developed ultra-sensitive ethanol receptors (USERs) as a novel tool for investigation of single receptor subunit populations sensitized to extremely low ethanol concentrations that do not affect other receptors in the nervous system. To this end, we found that mutations within the extracellular Loop 2 region of glycine receptors (GlyRs) and γ-aminobutyric acid type A receptors (GABAARs) can significantly increase receptor sensitivity to micro-molar concentrations of ethanol resulting in up to a 100-fold increase in ethanol sensitivity relative to wild-type (WT) receptors. The current study investigated: (1) Whether structural manipulations of Loop 2 in α1 GlyRs could similarly increase receptor sensitivity to other anesthetics; and (2) If mutations exclusive to the C-terminal end of Loop 2 are sufficient to impart these changes. We expressed α1 GlyR USERs in Xenopus oocytes and tested the effects of three classes of anesthetics, isoflurane (volatile), propofol (intravenous), and lidocaine (local), known to enhance glycine-induced chloride currents using two-electrode voltage clamp electrophysiology. Loop 2 mutations produced a significant 10-fold increase in isoflurane and lidocaine sensitivity, but no increase in propofol sensitivity compared to WT α1 GlyRs. Interestingly, we also found that structural manipulations in the C-terminal end of Loop 2 were sufficient and selective for α1 GlyR modulation by ethanol, isoflurane, and lidocaine. These studies are the first to report the extracellular region of α1 GlyRs as a site of lidocaine action. Overall, the findings suggest that Loop 2 of α1 GlyRs is a key region that mediates isoflurane and lidocaine modulation. Moreover, the results identify important amino acids in Loop 2 that regulate isoflurane, lidocaine, and ethanol action. Collectively, these data indicate the commonality of the sites for isoflurane, lidocaine, and ethanol action, and the structural requirements for allosteric modulation on α1 GlyRs within the extracellular Loop 2 region.
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Affiliation(s)
- A Naito
- Department of Pharmacology and Pharmaceutical Sciences, University of Southern California, School of Pharmacy, 1985 Zonal Avenue, Los Angeles, CA 90089, USA
| | - K H Muchhala
- Department of Pharmacology and Pharmaceutical Sciences, University of Southern California, School of Pharmacy, 1985 Zonal Avenue, Los Angeles, CA 90089, USA
| | - J Trang
- Department of Pharmacology and Pharmaceutical Sciences, University of Southern California, School of Pharmacy, 1985 Zonal Avenue, Los Angeles, CA 90089, USA
| | - L Asatryan
- Titus Family Department of Clinical Pharmacy and Pharmaceutical Economics and Policy, University of Southern California, School of Pharmacy, 1985 Zonal Avenue, Los Angeles, CA 90089, USA
| | - J R Trudell
- Department of Anesthesia, Beckman Program for Molecular and Genetic Medicine, Stanford University, Stanford University Medical Center, Stanford, CA 94305, USA
| | - G E Homanics
- Department of Anesthesiology, University of Pittsburgh, 6060 Biomedical Science Tower 3, Pittsburgh, PA 15261, USA; Department of Pharmacology and Chemical Biology, University of Pittsburgh, 6060 Biomedical Science Tower 3, Pittsburgh, PA 15261, USA
| | - R L Alkana
- Department of Pharmacology and Pharmaceutical Sciences, University of Southern California, School of Pharmacy, 1985 Zonal Avenue, Los Angeles, CA 90089, USA
| | - D L Davies
- Titus Family Department of Clinical Pharmacy and Pharmaceutical Economics and Policy, University of Southern California, School of Pharmacy, 1985 Zonal Avenue, Los Angeles, CA 90089, USA.
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Olsen RW. Allosteric ligands and their binding sites define γ-aminobutyric acid (GABA) type A receptor subtypes. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2015; 73:167-202. [PMID: 25637441 DOI: 10.1016/bs.apha.2014.11.005] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
GABAA receptors (GABA(A)Rs) mediate rapid inhibitory transmission in the brain. GABA(A)Rs are ligand-gated chloride ion channel proteins and exist in about a dozen or more heteropentameric subtypes exhibiting variable age and brain regional localization and thus participation in differing brain functions and diseases. GABA(A)Rs are also subject to modulation by several chemotypes of allosteric ligands that help define structure and function, including subtype definition. The channel blocker picrotoxin identified a noncompetitive channel blocker site in GABA(A)Rs. This ligand site is located in the transmembrane channel pore, whereas the GABA agonist site is in the extracellular domain at subunit interfaces, a site useful for low energy coupled conformational changes of the functional channel domain. Two classes of pharmacologically important allosteric modulatory ligand binding sites reside in the extracellular domain at modified agonist sites at other subunit interfaces: the benzodiazepine site and the high-affinity, relevant to intoxication, ethanol site. The benzodiazepine site is specific for certain GABA(A)R subtypes, mainly synaptic, while the ethanol site is found at a modified benzodiazepine site on different, extrasynaptic, subtypes. In the transmembrane domain are allosteric modulatory ligand sites for diverse chemotypes of general anesthetics: the volatile and intravenous agents, barbiturates, etomidate, propofol, long-chain alcohols, and neurosteroids. The last are endogenous positive allosteric modulators. X-ray crystal structures of prokaryotic and invertebrate pentameric ligand-gated ion channels, and the mammalian GABA(A)R protein, allow homology modeling of GABA(A)R subtypes with the various ligand sites located to suggest the structure and function of these proteins and their pharmacological modulation.
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Affiliation(s)
- Richard W Olsen
- Department of Molecular & Medical Pharmacology, David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
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48
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Sieghart W. Allosteric modulation of GABAA receptors via multiple drug-binding sites. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2014; 72:53-96. [PMID: 25600367 DOI: 10.1016/bs.apha.2014.10.002] [Citation(s) in RCA: 135] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
GABAA receptors are ligand-gated ion channels composed of five subunits that can be opened by GABA and be modulated by multiple pharmacologically and clinically important drugs. Over the time, hundreds of compounds from different structural classes have been demonstrated to modulate, directly activate, or inhibit GABAA receptors, and most of these compounds interact with more than one binding site at these receptors. Crystal structures of proteins and receptors homologous to GABAA receptors as well as homology modeling studies have provided insights into the possible location of ligand interaction sites. Some of these sites have been identified by mutagenesis, photolabeling, and docking studies. For most of these ligands, however, binding sites are not known. Due to the high flexibility of GABAA receptors and the existence of multiple drug-binding sites, the unequivocal identification of interaction sites for individual drugs is extremely difficult. The existence of multiple GABAA receptor subtypes with distinct subunit composition, the contribution of distinct subunit sequences to binding sites of different receptor subtypes, as well as the observation that even subunits not directly contributing to a binding site are able to influence affinity and efficacy of drugs, contribute to a unique pharmacology of each GABAA receptor subtype. Thus, each receptor subtype has to be investigated to identify a possible subtype selectivity of a compound. Although multiple binding sites make GABAA receptor pharmacology even more complicated, the exploitation of ligand interaction with novel-binding sites also offers additional possibilities for a subtype-selective modulation of GABAA receptors.
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Affiliation(s)
- Werner Sieghart
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Vienna, Austria.
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49
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Mutations at beta N265 in γ-aminobutyric acid type A receptors alter both binding affinity and efficacy of potent anesthetics. PLoS One 2014; 9:e111470. [PMID: 25347186 PMCID: PMC4210246 DOI: 10.1371/journal.pone.0111470] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Accepted: 10/02/2014] [Indexed: 11/19/2022] Open
Abstract
Etomidate and propofol are potent general anesthetics that act via GABAA receptor allosteric co-agonist sites located at transmembrane β+/α- inter-subunit interfaces. Early experiments in heteromeric receptors identified βN265 (M2-15') on β2 and β3 subunits as an important determinant of sensitivity to these drugs. Mechanistic analyses suggest that substitution with serine, the β1 residue at this position, primarily reduces etomidate efficacy, while mutation to methionine eliminates etomidate sensitivity and might prevent drug binding. However, the βN265 residue has not been photolabeled with analogs of either etomidate or propofol. Furthermore, substituted cysteine modification studies find no propofol protection at this locus, while etomidate protection has not been tested. Thus, evidence of contact between βN265 and potent anesthetics is lacking and it remains uncertain how mutations alter drug sensitivity. In the current study, we first applied heterologous α1β2N265Cγ2L receptor expression in Xenopus oocytes, thiol-specific aqueous probe modification, and voltage-clamp electrophysiology to test whether etomidate inhibits probe reactions at the β-265 sidechain. Using up to 300 µM etomidate, we found both an absence of etomidate effects on α1β2N265Cγ2L receptor activity and no inhibition of thiol modification. To gain further insight into anesthetic insensitive βN265M mutants, we applied indirect structure-function strategies, exploiting second mutations in α1β2/3γ2L GABAA receptors. Using α1M236C as a modifiable and anesthetic-protectable site occupancy reporter in β+/α- interfaces, we found that βN265M reduced apparent anesthetic affinity for receptors in both resting and GABA-activated states. βN265M also impaired the transduction of gating effects associated with α1M236W, a mutation that mimics β+/α- anesthetic site occupancy. Our results show that βN265M mutations dramatically reduce the efficacy/transduction of anesthetics bound in β+/α- sites, and also significantly reduce anesthetic affinity for resting state receptors. These findings are consistent with a role for βN265 in anesthetic binding within the β+/α- transmembrane sites.
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50
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Jayakar SS, Zhou X, Chiara DC, Dostalova Z, Savechenkov PY, Bruzik KS, Dailey WP, Miller KW, Eckenhoff RG, Cohen JB. Multiple propofol-binding sites in a γ-aminobutyric acid type A receptor (GABAAR) identified using a photoreactive propofol analog. J Biol Chem 2014; 289:27456-68. [PMID: 25086038 DOI: 10.1074/jbc.m114.581728] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Propofol acts as a positive allosteric modulator of γ-aminobutyric acid type A receptors (GABAARs), an interaction necessary for its anesthetic potency in vivo as a general anesthetic. Identifying the location of propofol-binding sites is necessary to understand its mechanism of GABAAR modulation. [(3)H]2-(3-Methyl-3H-diaziren-3-yl)ethyl 1-(phenylethyl)-1H-imidazole-5-carboxylate (azietomidate) and R-[(3)H]5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl)barbituric acid (mTFD-MPAB), photoreactive analogs of 2-ethyl 1-(phenylethyl)-1H-imidazole-5-carboxylate (etomidate) and mephobarbital, respectively, have identified two homologous but pharmacologically distinct classes of intersubunit-binding sites for general anesthetics in the GABAAR transmembrane domain. Here, we use a photoreactive analog of propofol (2-isopropyl-5-[3-(trifluoromethyl)-3H-diazirin-3-yl]phenol ([(3)H]AziPm)) to identify propofol-binding sites in heterologously expressed human α1β3 GABAARs. Propofol, AziPm, etomidate, and R-mTFD-MPAB each inhibited [(3)H]AziPm photoincorporation into GABAAR subunits maximally by ∼ 50%. When the amino acids photolabeled by [(3)H]AziPm were identified by protein microsequencing, we found propofol-inhibitable photolabeling of amino acids in the β3-α1 subunit interface (β3Met-286 in β3M3 and α1Met-236 in α1M1), previously photolabeled by [(3)H]azietomidate, and α1Ile-239, located one helical turn below α1Met-236. There was also propofol-inhibitable [(3)H]AziPm photolabeling of β3Met-227 in βM1, the amino acid in the α1-β3 subunit interface photolabeled by R-[(3)H]mTFD-MPAB. The propofol-inhibitable [(3)H]AziPm photolabeling in the GABAAR β3 subunit in conjunction with the concentration dependence of inhibition of that photolabeling by etomidate or R-mTFD-MPAB also establish that each anesthetic binds to the homologous site at the β3-β3 subunit interface. These results establish that AziPm as well as propofol bind to the homologous intersubunit sites in the GABAAR transmembrane domain that binds etomidate or R-mTFD-MPAB with high affinity.
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Affiliation(s)
| | - Xiaojuan Zhou
- the Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts 02114
| | | | - Zuzana Dostalova
- the Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts 02114
| | - Pavel Y Savechenkov
- the Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois 60612, and
| | - Karol S Bruzik
- the Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois 60612, and
| | | | - Keith W Miller
- the Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts 02114, Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115
| | - Roderic G Eckenhoff
- Department of Anesthesiology and Critical Care, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104
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