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Mortensen M, Bright DP, Fagotti J, Dorovykh V, Cerna B, Smart TG. Forty Years Searching for Neurosteroid Binding Sites on GABA A Receptors. Neuroscience 2024:S0306-4522(24)00257-4. [PMID: 38852898 DOI: 10.1016/j.neuroscience.2024.06.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2024] [Revised: 05/31/2024] [Accepted: 06/03/2024] [Indexed: 06/11/2024]
Abstract
Brain inhibition is a vital process for controlling and sculpting the excitability of the central nervous system in healthy individuals. This level of control is provided over several timescales and involves the neurotransmitter GABA acting at inhibitory synapses to: rapidly inhibit neurons by activating the GABAA receptor; over a slower timescale, to tonically activate extrasynaptic GABAA receptors to provide a low level of background inhibition; and finally, to activate G-protein coupled GABAB receptors to control transmitter release by inhibiting presynaptic Ca2+ channels whilst providing postsynaptic inhibition via K+ channel activation. From this plethora of roles for GABA and its receptors, the GABAA receptor isoform is of major interest due to its dynamic functional plasticity, which in part, is due to being targeted by modulatory brain neurosteroids derived from sex and stress hormones. This family of neurosteroids can, depending on their structure, potentiate, activate and also inhibit the activity of GABAA receptors to affect brain inhibition. This review tracks the methods that have been deployed in probing GABAA receptors, and charts the sterling efforts made by several groups to locate the key neurosteroid binding sites that affect these important receptors. Increasing our knowledge of these binding sites will greatly facilitate our understanding of the physiological roles of neurosteroids and will help to advance their use as novel therapeutics to combat debilitating brain diseases.
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Affiliation(s)
- Martin Mortensen
- University College London, Dept Neuroscience, Physiology & Pharmacology, Gower Street, London WC1E 6BT, United Kingdom
| | - Damian P Bright
- University College London, Dept Neuroscience, Physiology & Pharmacology, Gower Street, London WC1E 6BT, United Kingdom
| | - Juliane Fagotti
- University College London, Dept Neuroscience, Physiology & Pharmacology, Gower Street, London WC1E 6BT, United Kingdom
| | - Valentina Dorovykh
- University College London, Dept Neuroscience, Physiology & Pharmacology, Gower Street, London WC1E 6BT, United Kingdom
| | - Barbora Cerna
- University College London, Dept Neuroscience, Physiology & Pharmacology, Gower Street, London WC1E 6BT, United Kingdom
| | - Trevor G Smart
- University College London, Dept Neuroscience, Physiology & Pharmacology, Gower Street, London WC1E 6BT, United Kingdom.
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2
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Germann AL, Xu Y, Covey DF, Evers AS, Akk G. Comparison of Behavioral Effects of GABAergic Low- and High-Efficacy Neuroactive Steroids in the Zebrafish Larvae Assay. ACS Chem Neurosci 2024; 15:909-915. [PMID: 38386612 PMCID: PMC10953468 DOI: 10.1021/acschemneuro.3c00836] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2024] Open
Abstract
Activation of the GABAA receptor is associated with numerous behavioral end points ranging from anxiolysis to deep anesthesia. The specific behavioral effect of a GABAergic compound is considered to correlate with the degree of its functional effect on the receptor. Here, we tested the hypothesis that a low-efficacy allosteric potentiator of the GABAA receptor may act, due to a ceiling effect, as a sedative with reduced and limited action. We synthesized a derivative, named (3α,5β)-20-methyl-pregnane-3,20-diol (KK-235), of the GABAergic neurosteroid 5β-pregnane-3α,20α-diol. Using electrophysiology, we showed that KK-235 is a low-efficacy potentiator of the synaptic-type α1β2γ2L GABAA receptor. In the zebrafish larvae behavioral assay, KK-235 was found to only partially block the inverted photomotor response (PMR) and to weakly reduce swimming behavior, whereas the high-efficacy GABAergic steroid (3α,5α,17β)-3-hydroxyandrostane-17-carbonitrile (ACN) fully blocked PMR and spontaneous swimming. Coapplication of KK-235 reduced the potentiating effect of ACN in an electrophysiological assay and dampened its sedative effect in behavioral experiments. We propose that low-efficacy GABAergic potentiators may be useful as sedatives with limited action.
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Affiliation(s)
- Allison L. Germann
- Departments of Anesthesiology (ALG, ASE, GA) and Developmental Biology (YX, DFC), and the Taylor Family Institute for Innovative Psychiatric Research (DFC, ASE, GA), Washington University School of Medicine, St Louis, MO 63110, USA
| | - Yuanjian Xu
- Departments of Anesthesiology (ALG, ASE, GA) and Developmental Biology (YX, DFC), and the Taylor Family Institute for Innovative Psychiatric Research (DFC, ASE, GA), Washington University School of Medicine, St Louis, MO 63110, USA
| | - Douglas F. Covey
- Departments of Anesthesiology (ALG, ASE, GA) and Developmental Biology (YX, DFC), and the Taylor Family Institute for Innovative Psychiatric Research (DFC, ASE, GA), Washington University School of Medicine, St Louis, MO 63110, USA
| | - Alex S. Evers
- Departments of Anesthesiology (ALG, ASE, GA) and Developmental Biology (YX, DFC), and the Taylor Family Institute for Innovative Psychiatric Research (DFC, ASE, GA), Washington University School of Medicine, St Louis, MO 63110, USA
| | - Gustav Akk
- Departments of Anesthesiology (ALG, ASE, GA) and Developmental Biology (YX, DFC), and the Taylor Family Institute for Innovative Psychiatric Research (DFC, ASE, GA), Washington University School of Medicine, St Louis, MO 63110, USA
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3
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Vaitkevicius H, Ramsay RE, Swisher CB, Husain AM, Aimetti A, Gasior M. Intravenous ganaxolone for the treatment of refractory status epilepticus: Results from an open-label, dose-finding, phase 2 trial. Epilepsia 2022; 63:2381-2391. [PMID: 35748707 PMCID: PMC9796093 DOI: 10.1111/epi.17343] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Revised: 06/22/2022] [Accepted: 06/22/2022] [Indexed: 12/30/2022]
Abstract
OBJECTIVE Patients with refractory status epilepticus (RSE) have failed treatment with benzodiazepines and ≥1 second-line intravenous (IV) antiseizure medication (ASM). Guidelines recommend IV anesthesia when second-line ASMs have failed, but potential harms can outweigh the benefits. Novel treatments are needed to stop and durably control RSE without escalation to IV anesthetics. Ganaxolone is an investigational neuroactive steroid in development for RSE treatment. This study's objective was to determine the appropriate dosing for IV ganaxolone in RSE and obtain a preliminary assessment of efficacy and safety. METHODS This was an open-label, phase 2 trial conducted from February 19, 2018 to September 18, 2019, at three sites in the United States. Patients were aged ≥12 years, had convulsive or nonconvulsive SE, and failed to respond to ≥1 second-line IV ASM. Twenty-one patients were screened; 17 were enrolled. Patients received IV ganaxolone added to standard-of-care ASMs. Ganaxolone infusion was initiated as an IV bolus (over 3 min) with continuous infusion of decreasing infusion rates for 48-96 h followed by an 18-h taper. There were three ganaxolone dosing cohorts: low, 500 mg/day; medium, 650 mg/day; and high, 713 mg/day. The primary end point was the number of patients not requiring escalation to IV anesthetic treatment within 24 h of ganaxolone initiation. RESULTS Most of the 17 enrolled patients (65%) had nonconvulsive SE, and had failed a median of three prior ASMs, including first-line benzodiazepine and second-line IV ASM therapy. Median time to SE cessation following ganaxolone initiation was 5 min. No patient required escalation to third-line IV anesthetics during the 24-h period following ganaxolone initiation. Two treatment-related serious adverse events (sedation) were reported. Of the three deaths, none was considered related to ganaxolone; all occurred 9-22 days after completing ganaxolone. SIGNIFICANCE IV ganaxolone achieved rapid and durable seizure control in patients with RSE, and showed acceptable safety and tolerability.
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Affiliation(s)
- Henrikas Vaitkevicius
- Department of NeurologyBrigham and Women's HospitalBostonMassachusettsUSA,Marinus PharmaceuticalsRadnorPennsylvaniaUSA
| | - R. Eugene Ramsay
- International Center for EpilepsySt. Bernard HospitalNew OrleansLouisianaUSA
| | | | - Aatif M. Husain
- Department of NeurologyDuke UniversityDurhamNorth CarolinaUSA,Neurodiagnostic CenterVeterans Affairs Medical CenterDurhamNorth CarolinaUSA
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4
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Wang L, Covey DF, Akk G, Evers AS. Neurosteroid Modulation of GABA A Receptor Function by Independent Action at Multiple Specific Binding Sites. Curr Neuropharmacol 2022; 20:886-890. [PMID: 34856904 PMCID: PMC9881108 DOI: 10.2174/1570159x19666211202150041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Revised: 11/28/2021] [Accepted: 11/28/2021] [Indexed: 11/22/2022] Open
Abstract
Neurosteroids are endogenous modulators of GABAA receptors that mediate anxiety, pain, mood and arousal. The 3-hydroxyl epimers, allopregnanolone (3α-OH) and epiallopregnanolone (3β-OH) are both prevalent in the mammalian brain and produce opposite effects on GABAA receptor function, acting as positive and negative allosteric modulators, respectively. This Perspective provides a model to explain the actions of 3α-OH and 3β-OH neurosteroids. The model is based on evidence that the neurosteroid epimers bind to an overlapping subset of specific sites on GABAA receptors, with their net functional effect on channel gating being the sum of their independent effects at each site.
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Affiliation(s)
- Lei Wang
- Department of Anesthesiology (LW, DFC, GA, ASE),,Department of Anesthesiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Douglas F. Covey
- Department of Anesthesiology (LW, DFC, GA, ASE),,Department of Developmental Biology (Pharmacology);,Department of Psychiatry (DFC) and
| | - Gustav Akk
- Department of Anesthesiology (LW, DFC, GA, ASE),,The Taylor Institute for Innovative Psychiatric Research (DFC, GA, ASE), Washington University School of Medicine, St. Louis, MO63110; U.S.A
| | - Alex S. Evers
- Department of Anesthesiology (LW, DFC, GA, ASE),,Department of Developmental Biology (Pharmacology);,The Taylor Institute for Innovative Psychiatric Research (DFC, GA, ASE), Washington University School of Medicine, St. Louis, MO63110; U.S.A,Address correspondence to this author at the Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Ave, Box # 8054, St. Louis, MO 63110, USA; Tel: +1 314-362-8557; E-mail:
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5
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Akk G. Meet the Editorial Board Member. Curr Neuropharmacol 2022. [DOI: 10.2174/1570159x2004220328151242] [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
Affiliation(s)
- Gustav Akk
- Department of Anesthesiology
Washington University School of Medicine
St. Louis, MO
USA
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6
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Mazzoleni S, Bassani S. PCDH19 interplay with GABA(A) receptors: a window to DEE9 pathogenetic mechanisms. Neural Regen Res 2021; 17:803-805. [PMID: 34472478 PMCID: PMC8530141 DOI: 10.4103/1673-5374.322455] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Affiliation(s)
- Sara Mazzoleni
- Institute of Neuroscience, CNR, Milan; Department of Medical Biotechnology and Translational Medicine, University of Milan, Segrate (MI), Italy
| | - Silvia Bassani
- Institute of Neuroscience, CNR; NeuroMI Milan Center for Neuroscience, University of Milano-Bicocca, Milan, Italy
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7
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Akk G. Meet Our Editorial Board Member. Curr Neuropharmacol 2020. [PMCID: PMC7903496 DOI: 10.2174/1570159x1901201214092532] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Affiliation(s)
- Gustav Akk
- Department of Anesthesiology Washington University School of Medicine St. Louis, MO, United States
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Sugasawa Y, Cheng WW, Bracamontes JR, Chen ZW, Wang L, Germann AL, Pierce SR, Senneff TC, Krishnan K, Reichert DE, Covey DF, Akk G, Evers AS. Site-specific effects of neurosteroids on GABA A receptor activation and desensitization. eLife 2020; 9:55331. [PMID: 32955433 PMCID: PMC7532004 DOI: 10.7554/elife.55331] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 09/20/2020] [Indexed: 12/16/2022] Open
Abstract
This study examines how site-specific binding to three identified neurosteroid-binding sites in the α1β3 GABAA receptor (GABAAR) contributes to neurosteroid allosteric modulation. We found that the potentiating neurosteroid, allopregnanolone, but not its inhibitory 3β-epimer epi-allopregnanolone, binds to the canonical β3(+)–α1(-) intersubunit site that mediates receptor activation by neurosteroids. In contrast, both allopregnanolone and epi-allopregnanolone bind to intrasubunit sites in the β3 subunit, promoting receptor desensitization and the α1 subunit promoting effects that vary between neurosteroids. Two neurosteroid analogues with diazirine moieties replacing the 3-hydroxyl (KK148 and KK150) bind to all three sites, but do not potentiate GABAAR currents. KK148 is a desensitizing agent, whereas KK150 is devoid of allosteric activity. These compounds provide potential chemical scaffolds for neurosteroid antagonists. Collectively, these data show that differential occupancy and efficacy at three discrete neurosteroid-binding sites determine whether a neurosteroid has potentiating, inhibitory, or competitive antagonist activity on GABAARs.
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Affiliation(s)
- Yusuke Sugasawa
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Wayland Wl Cheng
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - John R Bracamontes
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Zi-Wei Chen
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, United States
| | - Lei Wang
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Allison L Germann
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Spencer R Pierce
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Thomas C Senneff
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Kathiresan Krishnan
- Department of Developmental Biology, Washington University in St. Louis, St. Louis, United States
| | - David E Reichert
- Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, United States.,Department of Radiology, Washington University in St. Louis, St. Louis, United States
| | - Douglas F Covey
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, United States.,Department of Developmental Biology, Washington University in St. Louis, St. Louis, United States.,Department of Psychiatry, Washington University in St. Louis, St. Louis, United States
| | - Gustav Akk
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, United States
| | - Alex S Evers
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, United States.,Department of Developmental Biology, Washington University in St. Louis, St. Louis, United States
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9
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Jayakar SS, Chiara DC, Zhou X, Wu B, Bruzik KS, Miller KW, Cohen JB. Photoaffinity labeling identifies an intersubunit steroid-binding site in heteromeric GABA type A (GABA A) receptors. J Biol Chem 2020; 295:11495-11512. [PMID: 32540960 DOI: 10.1074/jbc.ra120.013452] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Revised: 06/09/2020] [Indexed: 12/11/2022] Open
Abstract
Allopregnanolone (3α5α-P), pregnanolone, and their synthetic derivatives are potent positive allosteric modulators (PAMs) of GABAA receptors (GABAARs) with in vivo anesthetic, anxiolytic, and anti-convulsant effects. Mutational analysis, photoaffinity labeling, and structural studies have provided evidence for intersubunit and intrasubunit steroid-binding sites in the GABAAR transmembrane domain, but revealed only little definition of their binding properties. Here, we identified steroid-binding sites in purified human α1β3 and α1β3γ2 GABAARs by photoaffinity labeling with [3H]21-[4-(3-(trifluoromethyl)-3H-diazirine-3-yl)benzoxy]allopregnanolone ([3H]21-pTFDBzox-AP), a potent GABAAR PAM. Protein microsequencing established 3α5α-P inhibitable photolabeling of amino acids near the cytoplasmic end of the β subunit M4 (β3Pro-415, β3Leu-417, and β3Thr-418) and M3 (β3Arg-309) helices located at the base of a pocket in the β+-α- subunit interface that extends to the level of αGln-242, a steroid sensitivity determinant in the αM1 helix. Competition photolabeling established that this site binds with high affinity a structurally diverse group of 3α-OH steroids that act as anesthetics, anti-epileptics, and anti-depressants. The presence of a 3α-OH was crucial: 3-acetylated, 3-deoxy, and 3-oxo analogs of 3α5α-P, as well as 3β-OH analogs that are GABAAR antagonists, bound with at least 1000-fold lower affinity than 3α5α-P. Similarly, for GABAAR PAMs with the C-20 carbonyl of 3α5α-P or pregnanolone reduced to a hydroxyl, binding affinity is reduced by 1,000-fold, whereas binding is retained after deoxygenation at the C-20 position. These results provide a first insight into the structure-activity relationship at the GABAAR β+-α- subunit interface steroid-binding site and identify several steroid PAMs that act via other sites.
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Affiliation(s)
- Selwyn S Jayakar
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts
| | - David C Chiara
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts
| | - Xiaojuan Zhou
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Bo Wu
- Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois
| | - Karol S Bruzik
- Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois
| | - Keith W Miller
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts
| | - Jonathan B Cohen
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts
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10
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Zorumski CF, Paul SM, Covey DF, Mennerick S. Neurosteroids as novel antidepressants and anxiolytics: GABA-A receptors and beyond. Neurobiol Stress 2019; 11:100196. [PMID: 31649968 PMCID: PMC6804800 DOI: 10.1016/j.ynstr.2019.100196] [Citation(s) in RCA: 78] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Accepted: 09/24/2019] [Indexed: 01/22/2023] Open
Abstract
The recent FDA approval of the neurosteroid, brexanolone (allopregnanolone), as a treatment for women with postpartum depression, and successful trials of a related neuroactive steroid, SGE-217, for men and women with major depressive disorder offer the hope of a new era in treating mood and anxiety disorders based on the potential of neurosteroids as modulators of brain function. This review considers potential mechanisms contributing to antidepressant and anxiolytic effects of allopregnanolone and other GABAergic neurosteroids focusing on their actions as positive allosteric modulators of GABAA receptors. We also consider their roles as endogenous "stress" modulators and possible additional mechanisms contributing to their therapeutic effects. We argue that further understanding of the molecular, cellular, network and psychiatric effects of neurosteroids offers the hope of further advances in the treatment of mood and anxiety disorders.
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Affiliation(s)
- Charles F. Zorumski
- Department of Psychiatry, Washington University School of Medicine, St. Louis, MO, USA
- Department of Neuroscience, Washington University School of Medicine, St. Louis, MO, USA
- The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA
| | - Steven M. Paul
- Department of Psychiatry, Washington University School of Medicine, St. Louis, MO, USA
- Department of Neurology, Washington University School of Medicine, St. Louis, MO, USA
- The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA
| | - Douglas F. Covey
- Department of Psychiatry, Washington University School of Medicine, St. Louis, MO, USA
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO, USA
- The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA
| | - Steven Mennerick
- Department of Psychiatry, Washington University School of Medicine, St. Louis, MO, USA
- Department of Neuroscience, Washington University School of Medicine, St. Louis, MO, USA
- The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA
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11
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Chen ZW, Bracamontes JR, Budelier MM, Germann AL, Shin DJ, Kathiresan K, Qian MX, Manion B, Cheng WWL, Reichert DE, Akk G, Covey DF, Evers AS. Multiple functional neurosteroid binding sites on GABAA receptors. PLoS Biol 2019; 17:e3000157. [PMID: 30845142 PMCID: PMC6424464 DOI: 10.1371/journal.pbio.3000157] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Revised: 03/19/2019] [Accepted: 02/05/2019] [Indexed: 11/18/2022] Open
Abstract
Neurosteroids are endogenous modulators of neuronal excitability and nervous system development and are being developed as anesthetic agents and treatments for psychiatric diseases. While gamma amino-butyric acid Type A (GABAA) receptors are the primary molecular targets of neurosteroid action, the structural details of neurosteroid binding to these proteins remain ill defined. We synthesized neurosteroid analogue photolabeling reagents in which the photolabeling groups were placed at three positions around the neurosteroid ring structure, enabling identification of binding sites and mapping of neurosteroid orientation within these sites. Using middle-down mass spectrometry (MS), we identified three clusters of photolabeled residues representing three distinct neurosteroid binding sites in the human α1β3 GABAA receptor. Novel intrasubunit binding sites were identified within the transmembrane helical bundles of both the α1 (labeled residues α1-N408, Y415) and β3 (labeled residue β3-Y442) subunits, adjacent to the extracellular domains (ECDs). An intersubunit site (labeled residues β3-L294 and G308) in the interface between the β3(+) and α1(−) subunits of the GABAA receptor pentamer was also identified. Computational docking studies of neurosteroid to the three sites predicted critical residues contributing to neurosteroid interaction with the GABAA receptors. Electrophysiological studies of receptors with mutations based on these predictions (α1-V227W, N408A/Y411F, and Q242L) indicate that both the α1 intrasubunit and β3-α1 intersubunit sites are critical for neurosteroid action. Novel neurosteroid analogue photolabeling reagents identify three specific neurosteroid binding sites on α1β3 GABAA receptors, showing that a site between the α and β subunits, as well as a site within the α-subunit, contribute to neurosteroid-mediated enhancement of GABAA currents. Neurosteroids are cholesterol metabolites produced by neurons and glial cells that participate in central nervous system (CNS) development, regulate neuronal excitability, and modulate complex behaviors such as mood. Exogenously administered neurosteroid analogues are effective sedative hypnotics and are being developed as antidepressants and anticonvulsants. Gamma amino-butyric acid Type A (GABAA) receptors, the principal ionotropic inhibitory neurotransmitter receptors in the brain, are the primary functional target of neurosteroids. Understanding the molecular details of neurosteroid interactions with GABAA receptors is critical to understanding their mechanism of action and developing specific and effective therapeutic agents. In the current study, we developed a suite of neurosteroid analogue affinity labeling reagents, which we used to identify three distinct binding sites on GABAA receptors and to determine the orientation of neurosteroid binding in each site. Electrophysiological studies performed on receptors with mutations designed to disrupt the identified binding sites showed that two of the three sites contribute to neurosteroid modulation of GABAA currents. The distinct patterns of neurosteroid affinity, binding orientation, and effect provide the potential for the development of isoform-specific agonists, partial agonists, and antagonists with targeted therapeutic effects.
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Affiliation(s)
- Zi-Wei Chen
- Department of Anesthesiology, Washington University in St Louis, St Louis, Missouri, United States of America.,Taylor Family Institute for Innovative Psychiatric Research, St Louis, Missouri, United States of America
| | - John R Bracamontes
- Department of Anesthesiology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - Melissa M Budelier
- Department of Anesthesiology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - Allison L Germann
- Department of Anesthesiology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - Daniel J Shin
- Department of Anesthesiology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - Krishnan Kathiresan
- Department of Developmental Biology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - Ming-Xing Qian
- Department of Developmental Biology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - Brad Manion
- Department of Anesthesiology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - Wayland W L Cheng
- Department of Anesthesiology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - David E Reichert
- Taylor Family Institute for Innovative Psychiatric Research, St Louis, Missouri, United States of America.,Department of Radiology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - Gustav Akk
- Department of Anesthesiology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - Douglas F Covey
- Department of Anesthesiology, Washington University in St Louis, St Louis, Missouri, United States of America.,Taylor Family Institute for Innovative Psychiatric Research, St Louis, Missouri, United States of America.,Department of Developmental Biology, Washington University in St Louis, St Louis, Missouri, United States of America
| | - Alex S Evers
- Department of Anesthesiology, Washington University in St Louis, St Louis, Missouri, United States of America.,Taylor Family Institute for Innovative Psychiatric Research, St Louis, Missouri, United States of America.,Department of Developmental Biology, Washington University in St Louis, St Louis, Missouri, United States of America
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12
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Ratner MH, Kumaresan V, Farb DH. Neurosteroid Actions in Memory and Neurologic/Neuropsychiatric Disorders. Front Endocrinol (Lausanne) 2019; 10:169. [PMID: 31024441 PMCID: PMC6465949 DOI: 10.3389/fendo.2019.00169] [Citation(s) in RCA: 62] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2018] [Accepted: 02/28/2019] [Indexed: 12/24/2022] Open
Abstract
Memory dysfunction is a symptomatic feature of many neurologic and neuropsychiatric disorders; however, the basic underlying mechanisms of memory and altered states of circuitry function associated with disorders of memory remain a vast unexplored territory. The initial discovery of endogenous neurosteroids triggered a quest to elucidate their role as neuromodulators in normal and diseased brain function. In this review, based on the perspective of our own research, the advances leading to the discovery of positive and negative neurosteroid allosteric modulators of GABA type-A (GABAA), NMDA, and non-NMDA type glutamate receptors are brought together in a historical and conceptual framework. We extend the analysis toward a state-of-the art view of how neurosteroid modulation of neural circuitry function may affect memory and memory deficits. By aggregating the results from multiple laboratories using both animal models for disease and human clinical research on neuropsychiatric and age-related neurodegenerative disorders, elements of a circuitry level view begins to emerge. Lastly, the effects of both endogenously active and exogenously administered neurosteroids on neural networks across the life span of women and men point to a possible underlying pharmacological connectome by which these neuromodulators might act to modulate memory across diverse altered states of mind.
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Saporito MS, Gruner JA, DiCamillo A, Hinchliffe R, Barker-Haliski M, White HS. Intravenously Administered Ganaxolone Blocks Diazepam-Resistant Lithium-Pilocarpine–Induced Status Epilepticus in Rats: Comparison with Allopregnanolone. J Pharmacol Exp Ther 2018; 368:326-337. [DOI: 10.1124/jpet.118.252155] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Accepted: 12/12/2018] [Indexed: 11/22/2022] Open
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Cheng WWL, Chen ZW, Bracamontes JR, Budelier MM, Krishnan K, Shin DJ, Wang C, Jiang X, Covey DF, Akk G, Evers AS. Mapping two neurosteroid-modulatory sites in the prototypic pentameric ligand-gated ion channel GLIC. J Biol Chem 2018; 293:3013-3027. [PMID: 29301936 DOI: 10.1074/jbc.ra117.000359] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Revised: 12/21/2017] [Indexed: 12/20/2022] Open
Abstract
Neurosteroids are endogenous sterols that potentiate or inhibit pentameric ligand-gated ion channels (pLGICs) and can be effective anesthetics, analgesics, or anti-epileptic drugs. The complex effects of neurosteroids on pLGICs suggest the presence of multiple binding sites in these receptors. Here, using a series of novel neurosteroid-photolabeling reagents combined with top-down and middle-down mass spectrometry, we have determined the stoichiometry, sites, and orientation of binding for 3α,5α-pregnane neurosteroids in the Gloeobacter ligand-gated ion channel (GLIC), a prototypic pLGIC. The neurosteroid-based reagents photolabeled two sites per GLIC subunit, both within the transmembrane domain; one site was an intrasubunit site, and the other was located in the interface between subunits. By using reagents with photoreactive groups positioned throughout the neurosteroid backbone, we precisely map the orientation of neurosteroid binding within each site. Amino acid substitutions introduced at either site altered neurosteroid modulation of GLIC channel activity, demonstrating the functional role of both sites. These results provide a detailed molecular model of multisite neurosteroid modulation of GLIC, which may be applicable to other mammalian pLGICs.
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Affiliation(s)
| | - Zi-Wei Chen
- Department of Anesthesiology; Taylor Family Institute for Innovative Psychiatric Research, Washington University, St. Louis, Missouri 63110
| | | | | | | | | | | | | | - Douglas F Covey
- Department of Anesthesiology; Taylor Family Institute for Innovative Psychiatric Research, Washington University, St. Louis, Missouri 63110; Department of Developmental Biology; Department of Psychiatry
| | - Gustav Akk
- Department of Anesthesiology; Taylor Family Institute for Innovative Psychiatric Research, Washington University, St. Louis, Missouri 63110
| | - Alex S Evers
- Department of Anesthesiology; Taylor Family Institute for Innovative Psychiatric Research, Washington University, St. Louis, Missouri 63110; Department of Developmental Biology.
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Locci A, Pinna G. Neurosteroid biosynthesis down-regulation and changes in GABA A receptor subunit composition: a biomarker axis in stress-induced cognitive and emotional impairment. Br J Pharmacol 2017; 174:3226-3241. [PMID: 28456011 DOI: 10.1111/bph.13843] [Citation(s) in RCA: 95] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Revised: 04/05/2017] [Accepted: 04/12/2017] [Indexed: 12/26/2022] Open
Abstract
By rapidly modulating neuronal excitability, neurosteroids regulate physiological processes, such as responses to stress and development. Excessive stress affects their biosynthesis and causes an imbalance in cognition and emotions. The progesterone derivative, allopregnanolone (Allo) enhances extrasynaptic and postsynaptic inhibition by directly binding at GABAA receptors, and thus, positively and allosterically modulates the function of GABA. Allo levels are decreased in stress-induced psychiatric disorders, including depression and post-traumatic stress disorder (PTSD), and elevating Allo levels may be a valid therapeutic approach to counteract behavioural dysfunction. While benzodiazepines are inefficient, selective serotonin reuptake inhibitors (SSRIs) represent the first choice treatment for depression and PTSD. Their mechanisms to improve behaviour in preclinical studies include neurosteroidogenic effects at low non-serotonergic doses. Unfortunately, half of PTSD and depressed patients are resistant to current prescribed 'high' dosage of these drugs that engage serotonergic mechanisms. Unveiling novel biomarkers to develop more efficient treatment strategies is in high demand. Stress-induced down-regulation of neurosteroid biosynthesis and changes in GABAA receptor subunit expression offer a putative biomarker axis to develop new PTSD treatments. The advantage of stimulating Allo biosynthesis relies on the variety of neurosteroidogenic receptors to be targeted, including TSPO and endocannabinoid receptors. Furthermore, stress favours a GABAA receptor subunit composition with higher sensitivity for Allo. The use of synthetic analogues of Allo is a valuable alternative. Pregnenolone or drugs that stimulate its levels increase Allo but also sulphated steroids, including pregnanolone sulphate which, by inhibiting NMDA tonic neurotransmission, provides neuroprotection and cognitive benefits. In this review, we describe current knowledge on the effects of stress on neurosteroid biosynthesis and GABAA receptor neurotransmission and summarize available pharmacological strategies that by enhancing neurosteroidogenesis are relevant for the treatment of SSRI-resistant patients. Linked Articles This article is part of a themed section on Pharmacology of Cognition: a Panacea for Neuropsychiatric Disease? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.19/issuetoc.
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Affiliation(s)
- Andrea Locci
- The Psychiatric Institute, Department of Psychiatry, College of Medicine, University of Illinois at Chicago, Chicago, IL, USA
| | - Graziano Pinna
- The Psychiatric Institute, Department of Psychiatry, College of Medicine, University of Illinois at Chicago, Chicago, IL, USA
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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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17
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Chakrabarti S, Qian M, Krishnan K, Covey DF, Mennerick S, Akk G. Comparison of Steroid Modulation of Spontaneous Inhibitory Postsynaptic Currents in Cultured Hippocampal Neurons and Steady-State Single-Channel Currents from Heterologously Expressed α1β2γ2L GABA(A) Receptors. Mol Pharmacol 2016; 89:399-406. [PMID: 26769414 DOI: 10.1124/mol.115.102202] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Accepted: 01/13/2016] [Indexed: 12/18/2022] Open
Abstract
Neuroactive steroids are efficacious modulators of γ-aminobutyric acid type A receptor (GABA(A)) receptor function. The effects of steroids on the GABA(A) receptor are typically determined by comparing steady-state single-channel open probability or macroscopic peak responses elicited by GABA in the absence and presence of a steroid. Due to differences in activation conditions (exposure duration, concentration of agonist), it is not obvious whether modulation measured using typical experimental protocols can be used to accurately predict the effect of a modulator on native receptors under physiologic conditions. In the present study, we examined the effects of 14 neuroactive steroids and analogs on the properties of spontaneous inhibitory postsynaptic currents (sIPSCs) in cultured rat hippocampal neurons. The goal was to determine whether the magnitude of modulation of the decay time course of sIPSCs correlates with the extent of modulation and kinetic properties of potentiation as determined in previous single-channel studies. The steroids were selected to cover a wide range of efficacy on heterologously expressed rat α1β2γ2L GABA(A) receptors, ranging from essentially inert to highly efficacious (strong potentiators of single-channel and macroscopic peak responses). The data indicate a strong correlation between prolongation of the decay time course of sIPSCs and potentiation of single-channel open probability. Furthermore, changes in intracluster closed time distributions were the single best predictor of prolongation of sIPSCs. We infer that the information obtained in steady-state single-channel recordings can be used to forecast modulation of synaptic currents.
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Affiliation(s)
- Sampurna Chakrabarti
- Department of Anesthesiology (S.C., G.A.), Department of Developmental Biology (M.Q., K.K., D.F.C.), and Department of Psychiatry (S.M.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., S.M., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Mingxing Qian
- Department of Anesthesiology (S.C., G.A.), Department of Developmental Biology (M.Q., K.K., D.F.C.), and Department of Psychiatry (S.M.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., S.M., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Kathiresan Krishnan
- Department of Anesthesiology (S.C., G.A.), Department of Developmental Biology (M.Q., K.K., D.F.C.), and Department of Psychiatry (S.M.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., S.M., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Douglas F Covey
- Department of Anesthesiology (S.C., G.A.), Department of Developmental Biology (M.Q., K.K., D.F.C.), and Department of Psychiatry (S.M.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., S.M., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Steven Mennerick
- Department of Anesthesiology (S.C., G.A.), Department of Developmental Biology (M.Q., K.K., D.F.C.), and Department of Psychiatry (S.M.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., S.M., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Gustav Akk
- Department of Anesthesiology (S.C., G.A.), Department of Developmental Biology (M.Q., K.K., D.F.C.), and Department of Psychiatry (S.M.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., S.M., G.A.), Washington University School of Medicine, St. Louis, Missouri
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Taherianfard M, Taci AA. Effects of Bisphenol A and Learning on the Distribution of GABAAα1 Receptors in the Rat Hippocampus and Prefrontal Cortex. NEUROPHYSIOLOGY+ 2015. [DOI: 10.1007/s11062-015-9492-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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Bruun DA, Cao Z, Inceoglu B, Vito ST, Austin AT, Hulsizer S, Hammock BD, Tancredi DJ, Rogawski MA, Pessah IN, Lein PJ. Combined treatment with diazepam and allopregnanolone reverses tetramethylenedisulfotetramine (TETS)-induced calcium dysregulation in cultured neurons and protects TETS-intoxicated mice against lethal seizures. Neuropharmacology 2015; 95:332-42. [PMID: 25882826 DOI: 10.1016/j.neuropharm.2015.03.035] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Revised: 03/15/2015] [Accepted: 03/31/2015] [Indexed: 01/09/2023]
Abstract
Tetramethylenedisulfotetramine (TETS) is a potent convulsant GABAA receptor blocker. Mice receiving a lethal dose of TETS (0.15 mg/kg i.p.) are rescued from death by a high dose of diazepam (5 mg/kg i.p.) administered shortly after the second clonic seizure (∼20 min post-TETS). However, this high dose of diazepam significantly impairs blood pressure and mobility, and does not prevent TETS-induced neuroinflammation in the brain. We previously demonstrated that TETS alters synchronous Ca(2+) oscillations in primary mouse hippocampal neuronal cell cultures and that pretreatment with the combination of diazepam and allopregnanolone at concentrations having negligible effects individually prevents TETS effects on intracellular Ca(2+) dynamics. Here, we show that treatment with diazepam and allopregnanolone (0.1 μM) 20 min after TETS challenge normalizes synchronous Ca(2+) oscillations when added in combination but not when added singly. Similarly, doses (0.03-0.1 mg/kg i.p.) of diazepam and allopregnanolone that provide minimal protection when administered singly to TETS intoxicated mice increase survival from 10% to 90% when given in combination either 10 min prior to TETS or following the second clonic seizure. This therapeutic combination has negligible effects on blood pressure or mobility. Combined treatment with diazepam and allopregnanolone also decreases TETS-induced microglial activation. Diazepam and allopregnanolone have distinct actions as positive allosteric modulators of GABAA receptors that in combination enhance survival and mitigate neuropathology following TETS intoxication without the adverse side effects associated with high dose benzodiazepines. Combination therapy with a benzodiazepine and neurosteroid represents a novel neurotherapeutic strategy with potentially broad application.
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Affiliation(s)
- Donald A Bruun
- Department of Molecular Biosciences, School of Veterinary Medicine, Davis, CA 95616, USA
| | - Zhengyu Cao
- Department of Molecular Biosciences, School of Veterinary Medicine, Davis, CA 95616, USA
| | - Bora Inceoglu
- Department of Entomology, College of Agricultural and Environmental Sciences, University of California, Davis, Davis, CA 95616, USA
| | - Stephen T Vito
- Department of Entomology, College of Agricultural and Environmental Sciences, University of California, Davis, Davis, CA 95616, USA
| | | | - Susan Hulsizer
- Department of Molecular Biosciences, School of Veterinary Medicine, Davis, CA 95616, USA
| | - Bruce D Hammock
- Department of Entomology, College of Agricultural and Environmental Sciences, University of California, Davis, Davis, CA 95616, USA; Comprehensive Cancer Center, Sacramento, CA 95817, USA
| | | | - Michael A Rogawski
- Department of Neurology, School of Medicine, University of California, Davis, Sacramento, CA 95817, USA
| | - Isaac N Pessah
- Department of Molecular Biosciences, School of Veterinary Medicine, Davis, CA 95616, USA
| | - Pamela J Lein
- Department of Molecular Biosciences, School of Veterinary Medicine, Davis, CA 95616, USA.
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Feng HJ, Jounaidi Y, Haburcak M, Yang X, Forman SA. Etomidate produces similar allosteric modulation in α1β3δ and α1β3γ2L GABA(A) receptors. Br J Pharmacol 2014; 171:789-98. [PMID: 24199598 DOI: 10.1111/bph.12507] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Revised: 10/13/2013] [Accepted: 10/31/2013] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE Neuronal GABA(A) receptors are pentameric chloride ion channels, which include synaptic αβγ and extrasynaptic αβδ isoforms, mediating phasic and tonic inhibition respectively. Although the subunit arrangement of αβγ receptors is established as β-α-γ-β-α, that of αβδ receptors is uncertain and possibly variable. We compared receptors formed from free α1, β3 and δ or γ2L subunits and concatenated β3-α1-δ and β3-α1 subunit assemblies (placing δ in the established γ position) by investigating the effects of R-(+)-etomidate (ETO), an allosteric modulator that selectively binds to transmembrane interfacial sites between β3 and α1. EXPERIMENTAL APPROACH GABA-activated receptor-mediated currents in Xenopus oocytes were measured electrophysiologically, and ETO-induced allosteric shifts were quantified using an established model. KEY RESULTS ETO (3.2 μM) similarly enhanced maximal GABA (1 mM)-evoked currents in oocytes injected with 5 ng total mRNA and varying subunit ratios, for α1β3(1:1), α1β3δ(1:1:1) and α1β3δ(1:1:3), but this potentiation by ETO was significantly greater for β3-α1-δ/β3-α1(1:1) receptors. Reducing the amount of α1β3δ(1:1:3) mRNA mixture injected (0.5 ng) increased the modulatory effect of ETO, matching that seen with β3-α1-δ/β3-α1(1:1, 1 ng). ETO similarly reduced EC₅₀s and enhanced maxima of GABA concentration-response curves for both α1β3δ and β3-α1-δ/β3-α1 receptors. Allosteric shift parameters derived from these data depended on estimates of maximal GABA efficacy, and the calculated ranges overlap with allosteric shift values for α1β3γ2L receptors. CONCLUSION AND IMPLICATIONS Reducing total mRNA unexpectedly increased δ subunit incorporation into receptors on oocyte plasma membranes. Our results favour homologous locations for δ and γ2L subunits in α1β3γ2/δ GABA(A) receptors.
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Affiliation(s)
- H-J Feng
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
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21
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Chen ZW, Wang C, Krishnan K, Manion BD, Hastings R, Bracamontes J, Taylor A, Eaton MM, Zorumski CF, Steinbach JH, Akk G, Mennerick S, Covey DF, Evers AS. 11-trifluoromethyl-phenyldiazirinyl neurosteroid analogues: potent general anesthetics and photolabeling reagents for GABAA receptors. Psychopharmacology (Berl) 2014; 231:3479-91. [PMID: 24756762 PMCID: PMC4263769 DOI: 10.1007/s00213-014-3568-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Accepted: 03/28/2014] [Indexed: 11/25/2022]
Abstract
RATIONALE While neurosteroids are well-described positive allosteric modulators of gamma-aminobutyric acid type A (GABAA) receptors, the binding sites that mediate these actions have not been definitively identified. OBJECTIVES This study was conducted to synthesize neurosteroid analogue photolabeling reagents that closely mimic the biological effects of endogenous neurosteroids and have photochemical properties that will facilitate their use as tools for identifying the binding sites for neurosteroids on GABAA receptors. RESULTS Two neurosteroid analogues containing a trifluromethyl-phenyldiazirine group linked to the steroid C11 position were synthesized. These reagents, CW12 and CW14, are analogues of allopregnanolone (5α-reduced steroid) and pregnanolone (5β-reduced steroid), respectively. Both reagents were shown to have favorable photochemical properties with efficient insertion into the C-H bonds of cyclohexane. They also effectively replicated the actions of allopregnanolone and pregnanolone on GABAA receptor functions: they potentiated GABA-induced currents in Xenopus laevis oocytes transfected with α1β2γ2L subunits, modulated [(35)S]t-butylbicyclophosphorothionate binding in rat brain membranes, and were effective anesthetics in Xenopus tadpoles. Studies using [(3)H]CW12 and [(3)H]CW14 showed that these reagents covalently label GABAA receptors in both rat brain membranes and in a transformed human embryonal kidney (TSA) cells expressing either α1 and β2 subunits or β3 subunits of the GABAA receptor. Photolabeling of rat brain GABAA receptors was shown to be both concentration-dependent and stereospecific. CONCLUSIONS CW12 and CW14 have the appropriate photochemical and pharmacological properties for use as photolabeling reagents to identify specific neurosteroid-binding sites on GABAA receptors.
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Affiliation(s)
- Zi-Wei Chen
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of the Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Cunde Wang
- Department of Psychiatry, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Kathiresan Krishnan
- Department of Psychiatry, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Brad D. Manion
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Randy Hastings
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri 63110
| | - John Bracamontes
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Amanda Taylor
- Department of Psychiatry, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Megan M. Eaton
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Charles F. Zorumski
- Department of Psychiatry, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of Anatomy and Neurobiology, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of the Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Joseph H. Steinbach
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of Anatomy and Neurobiology, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of the Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Gustav Akk
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of the Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Steven Mennerick
- Department of Psychiatry, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of Anatomy and Neurobiology, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of the Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Douglas F. Covey
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of Developmental Biology, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of Psychiatry, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of the Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri 63110
| | - Alex S. Evers
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of Developmental Biology, Washington University in St. Louis, St. Louis, Missouri 63110
- Department of the Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri 63110
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Qian M, Krishnan K, Kudova E, Li P, Manion BD, Taylor A, Elias G, Akk G, Evers AS, Zorumski CF, Mennerick S, Covey DF. Neurosteroid analogues. 18. Structure-activity studies of ent-steroid potentiators of γ-aminobutyric acid type A receptors and comparison of their activities with those of alphaxalone and allopregnanolone. J Med Chem 2014; 57:171-90. [PMID: 24328079 PMCID: PMC3951241 DOI: 10.1021/jm401577c] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A model of the alignment of neurosteroids and ent-neurosteroids at the same binding site on γ-aminobutyric acid type A (GABAA) receptors was evaluated for its ability to identify the structural features in ent-neurosteroids that enhance their activity as positive allosteric modulators of this receptor. Structural features that were identified included: (1) a ketone group at position C-16, (2) an axial 4α-OMe group, and (3) a C-18 methyl group. Two ent-steroids were identified that were more potent than the anesthetic steroid alphaxalone in their threshold for and duration of loss of the righting reflex in mice. In tadpoles, loss of righting reflex for these two ent-steroids occurs with EC50 values similar to those found for allopregnanolone. The results indicate that ent-steroids have considerable potential to be developed as anesthetic agents and as drugs to treat brain disorders that are ameliorated by positive allosteric modulators of GABAA receptor function.
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Affiliation(s)
- Mingxing Qian
- Department of Developmental Biology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
| | - Kathiresan Krishnan
- Department of Developmental Biology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
| | - Eva Kudova
- Department of Developmental Biology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
- Department of Anesthesiology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
| | - Ping Li
- Department of Anesthesiology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
| | - Brad D. Manion
- Department of Anesthesiology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
| | - Amanda Taylor
- Department of Psychiatry, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
| | | | - Gustav Akk
- Department of Anesthesiology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
- Department of Radiology, The Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri, 63110, United States
| | - Alex S. Evers
- Department of Developmental Biology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
- Department of Anesthesiology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
- Department of Radiology, The Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri, 63110, United States
| | - Charles F. Zorumski
- Department of Psychiatry, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
- Department of Radiology, The Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri, 63110, United States
- Department of Anatomy and Neurobiology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
| | - Steven Mennerick
- Department of Psychiatry, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
- Department of Radiology, The Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri, 63110, United States
- Department of Anatomy and Neurobiology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
| | - Douglas F. Covey
- Department of Developmental Biology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
- Department of Anesthesiology, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
- Department of Psychiatry, Washington University in St. Louis School of Medicine, St. Louis, Missouri, 63110, United States
- Department of Radiology, The Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri, 63110, United States
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Inoue M, Harada K, Nakamura J, Matsuoka H. Regulation of α3-containing GABAA receptors in guinea-pig adrenal medullary cells by adrenal steroids. Neuroscience 2013; 253:245-55. [DOI: 10.1016/j.neuroscience.2013.08.046] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2013] [Revised: 08/23/2013] [Accepted: 08/24/2013] [Indexed: 12/14/2022]
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The benzodiazepine diazepam potentiates responses of α1β2γ2L γ-aminobutyric acid type A receptors activated by either γ-aminobutyric acid or allosteric agonists. Anesthesiology 2013; 118:1417-25. [PMID: 23407108 DOI: 10.1097/aln.0b013e318289bcd3] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND The γ-aminobutyric acid (GABA) type A receptor is a target for several anesthetics, anticonvulsants, anxiolytics, and sedatives. Neurosteroids, barbiturates, and etomidate both potentiate responses to GABA and allosterically activate the receptor. We examined the ability of a benzodiazepine, diazepam, to potentiate responses to allosteric agonists. METHODS The GABA type A receptors were expressed in human embryonic kidney 293 cells and studied using whole-cell and single-channel patch clamp. The receptors were activated by the orthosteric agonist GABA and allosteric agonists pentobarbital, etomidate, and alfaxalone. RESULTS Diazepam is equally potent at enhancing responses to orthosteric and allosteric agonists. Diazepam EC50s were 25 ± 4, 26 ± 6, 33 ± 6, and 26 ± 3 nm for receptors activated by GABA, pentobarbital, etomidate, and alfaxalone, respectively (mean ± SD, 5-6 cells at each condition). Mutations to the benzodiazepine-binding site (α1(H101C), γ2(R144C), γ2(R197C)) reduced or removed potentiation for all agonists, and an inverse agonist at the benzodiazepine site reduced responses to all agonists. Single-channel data elicited by GABA demonstrate that in the presence of 1 μm diazepam the prevalence of the longest open-time component is increased from 13 ± 7 (mean ± SD, n = 5 patches) to 27 ± 8% (n = 3 patches) and the rate of channel closing is decreased from 129 ± 28 s(-1) to 47 ± 6 s(-1) (mean ± SD) CONCLUSIONS: We conclude that benzodiazepines do not act by enhancing affinity of the orthosteric site for GABA but rather by increasing channel gating efficacy. The results also demonstrate the presence of interactions between allosteric activators and potentiators, raising a possibility of effects on dosage requirements or changes in side effects.
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Neurosteroids, stress and depression: potential therapeutic opportunities. Neurosci Biobehav Rev 2012; 37:109-22. [PMID: 23085210 DOI: 10.1016/j.neubiorev.2012.10.005] [Citation(s) in RCA: 146] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Revised: 09/28/2012] [Accepted: 10/02/2012] [Indexed: 12/19/2022]
Abstract
Neurosteroids are potent and effective neuromodulators that are synthesized from cholesterol in the brain. These agents and their synthetic derivatives influence the function of multiple signaling pathways including receptors for γ-aminobutyric acid (GABA) and glutamate, the major inhibitory and excitatory neurotransmitters in the central nervous system (CNS). Increasing evidence indicates that dysregulation of neurosteroid production plays a role in the pathophysiology of stress and stress-related psychiatric disorders, including mood and anxiety disorders. In this paper, we review the mechanisms of neurosteroid action in brain with an emphasis on those neurosteroids that potently modulate the function of GABA(A) receptors. We then discuss evidence indicating a role for GABA and neurosteroids in stress and depression, and focus on potential strategies that can be used to manipulate CNS neurosteroid synthesis and function for therapeutic purposes.
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Bracamontes JR, Li P, Akk G, Steinbach JH. A neurosteroid potentiation site can be moved among GABAA receptor subunits. J Physiol 2012; 590:5739-47. [PMID: 22988137 DOI: 10.1113/jphysiol.2012.237255] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Endogenous neurosteroids are among the most potent and efficacious potentiators of activation of GABA(A) receptors. It has been proposed that a conserved glutamine residue in the first membrane-spanning region (TM1 region) of the α subunits is required for binding of potentiating neurosteroids. Mutations of this residue can reduce or remove the ability of steroids to potentiate function. However, it is not known whether potentiation requires that a steroid interact with the α subunit, or not. To examine this question we mutated the homologous residue in the β2 and γ2L subunits to glutamine, and found that these mutations could not confer potentiation by allopregnanolone (3α5αP) when expressed in receptors containing ineffective α1 subunits. However, potentiation is restored when the entire TM1 region from the α1 subunit is transferred to the β2 or γ2L subunit. Mutations in the TM1 region that affect potentiation when made in the α1 subunit have similar effects when made in transferred TM1 region. Further, the effects of 3α5αP on single-channel kinetics are similar for wild-type receptors and receptors with moved TM1 regions. These results support the idea that steroids bind in the transmembrane regions of the receptor. The observations are consistent with previous work indicating that neurosteroid potentiation is mediated by an action that affects the receptor as a whole, rather than an individual subunit or pair of subunits, and in addition demonstrate that the mechanism is independent of the nature of the subunit that interacts with steroid.
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Affiliation(s)
- John R Bracamontes
- Department of Anesthesiology, Washington University School of Medicine, St Louis, MO 63110, USA
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Shu HJ, Bracamontes J, Taylor A, Wu K, Eaton MM, Akk G, Manion B, Evers AS, Krishnan K, Covey DF, Zorumski CF, Steinbach JH, Mennerick S. Characteristics of concatemeric GABA(A) receptors containing α4/δ subunits expressed in Xenopus oocytes. Br J Pharmacol 2012; 165:2228-43. [PMID: 21950777 DOI: 10.1111/j.1476-5381.2011.01690.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
BACKGROUND AND PURPOSE GABA(A) receptors mediate both synaptic and extrasynaptic actions of GABA. In several neuronal populations, α4 and δ subunits are key components of extrasynaptic GABA(A) receptors that strongly influence neuronal excitability and could mediate the effects of neuroactive agents including neurosteroids and ethanol. However, these receptors can be difficult to study in native cells and recombinant δ subunits can be difficult to express in heterologous systems. EXPERIMENTAL APPROACH We engineered concatemeric (fused) subunits to ensure δ and α4 subunit expression. We tested the pharmacology of the concatemeric receptors, compared with a common synaptic-like receptor subunit combination (α1 +β2 +γ2L), and with free-subunit α4/δ receptors, expressed in Xenopus oocytes. KEY RESULTS δ-β2 -α4 +β2-α4 cRNA co-injected into Xenopus oocytes resulted in GABA-gated currents with the expected pharmacological properties of α4/δ-containing receptors. Criteria included sensitivity to agonists of different efficacy, sensitivity to the allosteric activator pentobarbital, and modulation of agonist responses by DS2 (4-chloro-N-[2-(2-thienyl)imidazo[1,2-a]pyridine-3-yl benzamide; a δ-selective positive modulator), furosemide, and Zn(2+) . We used the concatemers to examine neurosteroid sensitivity of extrasynaptic-like, δ-containing receptors. We found no qualitative differences between extrasynaptic-like receptors and synaptic-like receptors in the actions of either negative or positive neurosteroid modulators of receptor function. Quantitative differences were explained by the partial agonist effects of the natural agonist GABA and by a mildly increased sensitivity to low steroid concentrations. CONCLUSIONS AND IMPLICATIONS The neurosteroid structure-activity profile for α4/δ-containing extrasynaptic receptors is unlikely to differ from that of synaptic-like receptors such as α1/β2/γ2-containing receptors.
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Affiliation(s)
- Hong-Jin Shu
- Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri, USA
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Chen ZW, Manion B, Townsend RR, Reichert DE, Covey DF, Steinbach JH, Sieghart W, Fuchs K, Evers AS. Neurosteroid analog photolabeling of a site in the third transmembrane domain of the β3 subunit of the GABA(A) receptor. Mol Pharmacol 2012; 82:408-19. [PMID: 22648971 DOI: 10.1124/mol.112.078410] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Accumulated evidence suggests that neurosteroids modulate GABA(A) receptors through binding interactions with transmembrane domains. To identify these neurosteroid binding sites directly, a neurosteroid-analog photolabeling reagent, (3α,5β)-6-azi-pregnanolone (6-AziP), was used to photolabel membranes from Sf9 cells expressing high-density, recombinant, His(8)-β3 homomeric GABA(A) receptors. 6-AziP inhibited (35)S-labeled t-butylbicyclophosphorothionate binding to the His(8)-β3 homomeric GABA(A) receptors in a concentration-dependent manner (IC(50) = 9 ± 1 μM), with a pattern consistent with a single class of neurosteroid binding sites. [(3)H]6-AziP photolabeled proteins of 30, 55, 110, and 150 kDa, in a concentration-dependent manner. The 55-, 110-, and 150-kDa proteins were identified as His(8)-β3 subunits through immunoblotting and through enrichment on a nickel affinity column. Photolabeling of the β3 subunits was stereoselective, with [(3)H]6-AziP producing substantially greater labeling than an equal concentration of its diastereomer [(3)H](3β,5β)-6-AziP. High-resolution mass spectrometric analysis of affinity-purified, 6-AziP-labeled His(8)-β3 subunits identified a single photolabeled peptide, ALLEYAF-6-AziP, in the third transmembrane domain. The identity of this peptide and the site of incorporation on Phe301 were confirmed through high-resolution tandem mass spectrometry. No other sites of photoincorporation were observed despite 90% sequence coverage of the whole β3 subunit protein, including 84% of the transmembrane domains. This study identifies a novel neurosteroid binding site and demonstrates the feasibility of identifying neurosteroid photolabeling sites by using mass spectrometry.
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Affiliation(s)
- Zi-Wei Chen
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
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Structural studies of the actions of anesthetic drugs on the γ-aminobutyric acid type A receptor. Anesthesiology 2012; 115:1338-48. [PMID: 21881491 DOI: 10.1097/aln.0b013e3182315d93] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The γ-aminobutyric acid type A receptor is the major transmitter-gated inhibitory channel in the central nervous system. The receptor is a target for anesthetics, anticonvulsants, anxiolytics, and sedatives whose actions facilitate the flow of chloride ions through the channel and enhance the inhibitory tone in the brain. Both the kinetic and structural aspects of the actions of modulators of the γ-aminobutyric acid type A receptor are of great importance to understanding the molecular mechanisms of general anesthesia. In this review, the structural rearrangements that take place in the γ-aminobutyric acid type A receptor during channel activation and modulation are described, focusing on data obtained using voltage-clamp fluorometry. Voltage-clamp fluorometry entails the binding of an environmentally sensitive fluorophore molecule to a site of interest in the receptor, and measurement of changes in the fluorescence signal resulting from activation- or modulation-elicited structural changes. Detailed investigations can provide a map of structural changes that underlie or accompany the functional effects of modulators.
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Use of concatemers of ligand-gated ion channel subunits to study mechanisms of steroid potentiation. Anesthesiology 2012; 115:1328-37. [PMID: 21926904 DOI: 10.1097/aln.0b013e318233046a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Synaptic receptors of the nicotinic receptor gene family are pentamers of subunits. This modular structure creates problems in studies of drug actions, related to the number of copies of a subunit that are present and their position. A separate issue concerns the mechanism of action of many anesthetics, which involves potentiation of responses to neurotransmitters. Potentiation requires an interaction between a transmitter and a potentiator, mediated through the target receptor. We have studied the mechanism by which neurosteroids potentiate transmitter responses, using concatemers of covalently linked subunits to control the number and position of subunits in the assembled receptor and to selectively introduce mutations into positionally defined copies of a subunit. We found that the steroid needs to interact with only one site to produce potentiation, that the native sites for steroid interaction have indistinguishable properties, and that steroid potentiation appears to result from a global effect on receptor function.
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Akk G, Covey DF, Evers AS, Mennerick S, Zorumski CF, Steinbach JH. Kinetic and structural determinants for GABA-A receptor potentiation by neuroactive steroids. Curr Neuropharmacol 2011; 8:18-25. [PMID: 20808543 PMCID: PMC2866458 DOI: 10.2174/157015910790909458] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Revised: 11/16/2009] [Accepted: 11/20/2009] [Indexed: 12/03/2022] Open
Abstract
Endogenous neurosteroids and synthetic neuroactive steroid analogs are among the most potent and efficacious potentiators of the mammalian GABA-A receptor. The compounds interact with one or more sites on the receptor leading to an increase in the channel open probability through a set of changes in the open and closed time distributions. The endogenous neurosteroid allopregnanolone potentiates the α1β2γ2L GABA-A receptor by enhancing the mean duration and prevalence of the longest-lived open time component and by reducing the prevalence of the longest-lived intracluster closed time component. Thus the channel mean open time is increased and the mean closed time duration is decreased, resulting in potentiation of channel function. Some of the other previously characterized neurosteroids and steroid analogs act through similar mechanisms while others affect a subset of these parameters. The steroids modulate the GABA-A receptor through interactions with the membrane-spanning region of the receptor. However, the number of binding sites that mediate the actions of steroids is unclear. We discuss data supporting the notions of a single site vs. multiple sites mediating the potentiating actions of steroids.
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Affiliation(s)
- Gustav Akk
- Departments of Anesthesiology (GA, ASE, JHS), Washington University School of Medicine, St. Louis, MO, USA.
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A mutant residue in the third transmembrane region of the GABA(A) alpha1 subunit causes increased agonistic neurosteroid responses. Neurochem Int 2011; 58:794-803. [PMID: 21397651 DOI: 10.1016/j.neuint.2011.03.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2010] [Revised: 03/02/2011] [Accepted: 03/05/2011] [Indexed: 11/24/2022]
Abstract
Pregnane derived steroids have agonistic and antagonistic actions at GABA(A) receptors. Putative binding sites for agonistic neurosteroids are located within the transmembrane (TM) regions. A mutation within the rat α(1) TM3 region, S299C, caused the expressed receptors to have unusual and extreme sensitivity to agonistic neurosteroids. For mutant α1S299C receptors, with wild type β and γ subunits, expressed in Xenopus oocytes, steroids activated the GABA(A) receptors in the absence of GABA. Maximal steroid induced currents were about half of maximal GABA currents. The steroid activation was biphasic with EC(50)'s much lower than wild type, in subnanomolar and nanomolar concentrations, while the wild type had only one activation peak with near micromolar EC(50). These currents could be blocked by both picrotoxin and an antagonist neurosteroid. The steroids did not seem to potentiate significantly submaximal GABA currents. The α1S299C mutation did not affect responses to the extracellularly acting partial agonist piperidine-4-sulfate. Substituted cysteine experiments indicate that this mutant can be modified by pCMBS(-) when the sulfhydryl reagent is added with the higher steroid concentration for activation but not the lower steroid concentration. The pCMBS(-) will also immediately block the high concentration steroid current. Taken together the data suggest that α1S299 is important in at least the in transduction of the steroid binding to the rest of the receptor.
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Wirth MM. Beyond the HPA Axis: Progesterone-Derived Neuroactive Steroids in Human Stress and Emotion. Front Endocrinol (Lausanne) 2011; 2:19. [PMID: 22649366 PMCID: PMC3355912 DOI: 10.3389/fendo.2011.00019] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Accepted: 07/28/2011] [Indexed: 12/13/2022] Open
Abstract
Stress and social isolation are well-known risk factors for psychopathology. However, more research is needed as to the physiological mechanisms by which social support buffers the impacts of stress. Research in animal models suggests important roles for progesterone (P) and its product, the neuroactive steroid allopregnanolone (ALLO), in stress and psychopathology. These hormones are produced in brain and periphery during stress in rodents, and down-regulate anxiety behavior and hypothalamic-pituitary-adrenal axis activity. Human clinical populations, including depressed patients, have alterations in ALLO levels, but it is unclear whether these basal hormone level differences have clinical import. To begin to address this question, this review examines the role of P and ALLO in stress physiology, and the impact of these hormones on mood, in healthy humans. Evidence largely supports that P and ALLO increase during stress in humans. However, P/ALLO administration appears to cause only mild effects on mood and subjective anxiety, while exerting effects consistent with gamma-aminobutyric acid receptor modulation. Additionally, P is linked to motivation for affiliation/social contact; P (and ALLO) release may be especially responsive to social rejection. These observations lead to the novel hypothesis that stress-related P/ALLO production functions not only to down-regulate stress and anxiety, but also to promote social contact as a long-term coping strategy. Malfunctioning of the P/ALLO system could therefore underlie depression partly by decreasing propensity to affiliate with others.
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Affiliation(s)
- Michelle M. Wirth
- Department of Psychology, University of Notre DameNotre Dame, IN, USA
- *Correspondence: Michelle M. Wirth, Department of Psychology, University of Notre Dame, 123B Haggar Hall, Notre Dame, IN 46556, USA. e-mail:
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Ramakrishnan L, Hess GP. Mechanism of Potentiation of a Dysfunctional Epilepsy-Linked Mutated GABAA Receptor by a Neurosteroid (3α, 21-Dihydroxy-5α-pregnan-20-one): Transient Kinetic Investigations. Biochemistry 2010; 49:7892-901. [DOI: 10.1021/bi901241g] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Latha Ramakrishnan
- Department of Molecular Biology and Genetics, 216 Biotechnology Building, Cornell University, Ithaca, New York 14853-2703
| | - George P. Hess
- Department of Molecular Biology and Genetics, 216 Biotechnology Building, Cornell University, Ithaca, New York 14853-2703
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Chisari M, Eisenman LN, Covey DF, Mennerick S, Zorumski CF. The sticky issue of neurosteroids and GABA(A) receptors. Trends Neurosci 2010; 33:299-306. [PMID: 20409596 DOI: 10.1016/j.tins.2010.03.005] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2009] [Revised: 03/10/2010] [Accepted: 03/25/2010] [Indexed: 01/01/2023]
Abstract
Endogenous neurosteroids and their synthetic analogs (neuroactive steroids) are potent modulators of GABA(A) receptors. Thus, they are of physiological and clinical relevance for their ability to modulate inhibitory function in the CNS. Despite their importance, fundamental issues of neurosteroid actions remain unresolved. Recent evidence suggests that glutamatergic principal neurons, rather than glia, are the major sources of neurosteroid synthesis. Other recent studies have identified putative neurosteroid binding sites on GABA(A) receptors. In this Opinion, we argue that neurosteroids require a membranous route of access to transmembrane-domain binding sites within GABA(A) receptors. This has implications for the design of future neuroactive steroids because the lipid solubility and related accessibility properties of the ligand are likely to be key determinants of receptor modulation.
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Affiliation(s)
- Mariangela Chisari
- Department of Psychiatry, Washington University School of Medicine, 660 S. Euclid Ave, St. Louis, MO 63110, USA
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36
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Evers AS, Chen ZW, Manion BD, Han M, Jiang X, Darbandi-Tonkabon R, Kable T, Bracamontes J, Zorumski CF, Mennerick S, Steinbach JH, Covey DF. A synthetic 18-norsteroid distinguishes between two neuroactive steroid binding sites on GABAA receptors. J Pharmacol Exp Ther 2010; 333:404-13. [PMID: 20124410 DOI: 10.1124/jpet.109.164079] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In the absence of GABA, neuroactive steroids that enhance GABA-mediated currents modulate binding of [35S]t-butylbicyclophosphorothionate in a biphasic manner, with enhancement of binding at low concentrations (site NS1) and inhibition at higher concentrations (site NS2). In the current study, compound (3alpha,5beta,17beta)-3-hydroxy-18-norandrostane-17-carbonitrile (3alpha5beta-18-norACN), an 18-norsteroid, is shown to be a full agonist at site NS1 and a weak partial agonist at site NS2 in both rat brain membranes and heterologously expressed GABAA receptors. 3alpha5beta-18-norACN also inhibits the action of a full neurosteroid agonist, (3alpha,5alpha,17beta)-3-hydroxy-17-carbonitrile (3alpha5alphaACN), at site NS2. Structure-activity studies demonstrate that absence of the C18 methyl group and the 5beta-reduced configuration both contribute to the weak agonist effect at the NS2 site. Electrophysiological studies using heterologously expressed GABAA receptors show that 3alpha5beta-18-norACN potently and efficaciously potentiates the GABA currents elicited by low concentrations of GABA but that it has low efficacy as a direct activator of GABAA receptors. 3alpha5beta-18-norACN also inhibits direct activation of GABAA receptors by 3alpha5alphaACN. 3alpha5beta-18-norACN also produces loss of righting reflex in tadpoles and mice, indicating that action at NS1 is sufficient to mediate the sedative effects of neurosteroids. These data provide insight into the pharmacophore required for neurosteroid efficacy at the NS2 site and may prove useful in the development of selective agonists and antagonists for neurosteroid sites on the GABAA receptor.
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Affiliation(s)
- Alex S Evers
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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Li P, Bandyopadhyaya AK, Covey DF, Steinbach JH, Akk G. Hydrogen bonding between the 17beta-substituent of a neurosteroid and the GABA(A) receptor is not obligatory for channel potentiation. Br J Pharmacol 2009; 158:1322-9. [PMID: 19702782 DOI: 10.1111/j.1476-5381.2009.00390.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND AND PURPOSE Potentiating neurosteroids are some of the most efficacious modulators of the mammalian GABA(A) receptor. One of the crucial interactions may be between the C20 ketone group (D-ring substituent at C17) of the neurosteroid, and the N407 and Y410 residues in the M4 domain of the receptor. In this study, we examined the contribution of hydrogen bonding between 17beta-substituents on the steroid D-ring and the GABA(A) receptor to potentiation by neurosteroids. EXPERIMENTAL APPROACH Whole-cell and single-channel recordings were made from HEK 293 cells transiently expressing wild-type and mutant alpha1beta2gamma2L GABA(A) receptors. KEY RESULTS A steroid with a 17beta-carbonitrile group (3alpha5alpha18nor17betaCN) was a potent and efficacious potentiator of the GABA(A) receptor. Potentiation was also shown by a cyclosteroid in which C21 and the C18 methyl group of (3alpha,5alpha)-3-hydroxypregnan-20-one are connected within a six-membered ring containing a double bond as a hydrogen bond acceptor (3alpha5alphaCDNC12), a steroid containing a 17beta-ethyl group on the D-ring (3alpha5alpha17betaEt) and a steroid lacking a 17beta-substituent on the D-ring (3alpha5alpha17H). Single-channel kinetic analysis indicates that the kinetic mechanism of action is the same for the neurosteroid 3alpha5alphaP, 3alpha5alpha18nor17betaCN, 3alpha5alphaCDNC12, 3alpha5alpha17betaEt and 3alpha5alpha17H. Interestingly, 3alpha5alpha17betaEt, at up to 3 microM, was incapable of potentiating the alpha1N407A/Y410F double mutant receptor. CONCLUSIONS AND IMPLICATIONS Hydrogen bonding between the steroid 17beta-substituent and the GABA(A) receptor is not a critical requirement for channel potentiation. The alpha1N407/Y410 residues are important for neurosteroid potentiation for reasons other than hydrogen bonding between steroid and receptor.
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Affiliation(s)
- Ping Li
- Department of Anesthesiology, Washington University in St Louis, St Louis, MO 63110, USA
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Akk G, Li P, Bracamontes J, Steinbach JH. Activation and modulation of concatemeric GABA-A receptors expressed in human embryonic kidney cells. Mol Pharmacol 2009; 75:1400-11. [PMID: 19289569 DOI: 10.1124/mol.108.054510] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have employed whole-cell and single-channel electrophysiology to examine the kinetic and pharmacological properties of GABA-A receptors consisting of gamma2L-beta2-alpha1 and beta2-alpha1 subunit concatemeric constructs expressed in human embryonic kidney cells. Concatemeric receptors activated by GABA exhibited the same single-channel conductance, channel opening rate constant, and basic open- and closed-time properties as receptors containing free subunits. However, the whole-cell GABA dose-response and the single-channel effective opening rate curves were shifted to higher GABA concentrations, suggesting that the concatemeric receptors have a lower affinity to GABA. Pharmacological tests demonstrated that the concatemeric receptors were potentiated by pentobarbital, diazepam, and the neurosteroid (3alpha,5alpha)-3-hydroxypregnan-20-one (3alpha5alphaP), and were insensitive to Zn(2+). Selective introduction of the alpha1Q241L mutation, previously shown to abolish alpha1beta2gamma2L channel potentiation by neurosteroids, into one of the two concatemeric constructs had a relatively small effect on receptor activation by GABA or macroscopic potentiation by the neurosteroid 3alpha5alphaP. Single-channel measurements showed that the kinetic mechanism of action of the steroid is unchanged when the mutation is introduced to the gamma2L-beta2-alpha1 concatemer. We infer that a single wild-type alpha subunit is capable of mediating the full set of kinetic effects in the presence of steroids. Introduction of the alpha1Q241W mutation, previously shown to mimic the effect of the steroid on alpha1beta2gamma2L channels, selectively into either concatemeric construct altered the mode of activity elicited by P4S, but the presence of mutations in both alpha subunits was required to affect open-time distributions. The data indicate that the alpha1Q241W mutation acts as a partial steroid modulator.
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Affiliation(s)
- Gustav Akk
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri, USA.
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Slavíková B, Krištofíková Z, Chodounská H, Buděšínský M, Durán FJ, Veleiro AS, Burton G, Kasal A. Allopregnanolone (3α-Hydroxy-5α-pregnan-20-one) Derivatives with a Polar Chain in Position 16α: Synthesis and Activity. J Med Chem 2009; 52:2119-25. [DOI: 10.1021/jm801454a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Barbora Slavíková
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Zdena Krištofíková
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Hana Chodounská
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Miloš Buděšínský
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Fernando J. Durán
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Adriana S. Veleiro
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Gerardo Burton
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Alexander Kasal
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
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Stastna E, Chodounska H, Pouzar V, Kapras V, Borovska J, Cais O, Vyklicky L. Synthesis of C3, C5, and C7 pregnane derivatives and their effect on NMDA receptor responses in cultured rat hippocampal neurons. Steroids 2009; 74:256-63. [PMID: 19071149 DOI: 10.1016/j.steroids.2008.11.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/23/2008] [Revised: 10/31/2008] [Accepted: 11/15/2008] [Indexed: 01/16/2023]
Abstract
The synthesis of several novel 5alpha- and 5beta-20-oxo-pregnane derivatives substituted in the position 3 and 7 of the steroid skeleton is described. Activity of synthesized compounds was studied in voltage-clamped cultured rat hippocampal neurons. Substituted derivatives inhibited NMDA-elicited neuronal activity. The relationship between biological activity and structure is discussed.
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Affiliation(s)
- Eva Stastna
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i.,166 10 Prague 6, Czech Republic
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Bracamontes JR, Steinbach JH. Steroid interaction with a single potentiating site is sufficient to modulate GABA-A receptor function. Mol Pharmacol 2009; 75:973-81. [PMID: 19176850 DOI: 10.1124/mol.108.053629] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neuroactive steroids are efficacious potentiators of GABA-A receptors. Recent work has identified a site in the alpha1 subunit of the GABA-A receptor, that is essential for potentiation by steroids. However, each receptor contains two copies of the alpha1 subunit. We generated concatemers of subunits so that the alpha1 subunits could be mutated separately and examined the consequences of mutations that remove potentiation by most neurosteroids (alpha1 Q241L, alpha1 Q241W). Concatemers were expressed in Xenopus laevis oocytes, and activation by GABA, potentiation by neurosteroids, and the agonist activity of piperidine-4-sulfonic acid (P4S) were determined. When the alpha1 Q241L mutation is present in alpha1 subunits the EC(50) for activation by GABA is shifted to higher concentration and potentiation by neurosteroids is diminished. When the alpha1 Q241W mutation is expressed, the EC(50) for GABA is shifted to lower concentration, the relative efficacy of P4S is increased, and potentiation by neurosteroids is diminished. Mutation of only one alpha1 subunit does not produce the full effect of mutating both sites. Overall, the data demonstrate that at a macroscopic level, the presence of a single wild-type steroid-binding site is sufficient to mediate responses to steroid, but both must be mutated to completely remove the effects of steroids. Differences between the two sites seem to be relatively subtle.
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Affiliation(s)
- John R Bracamontes
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
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Jin X, Covey DF, Steinbach JH. Kinetic analysis of voltage-dependent potentiation and block of the glycine alpha 3 receptor by a neuroactive steroid analogue. J Physiol 2009; 587:981-97. [PMID: 19124545 DOI: 10.1113/jphysiol.2008.159343] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We examined the actions of a carboxylated analogue of pregnanolone ((3alpha,5beta)-20-oxopregnane-3-carboxylic acid; 3alphaCOOH5betaP) on receptors composed of glycine receptor alpha3 subunits, expressed in Xenopus oocytes. This analogue both inhibits and potentiates this receptor; potentiation increases with more negative membrane potentials while block increases with less negative membrane potentials. We used a second analogue ((3alpha,5beta)-3-hydroxymethylpregnan-20-one; 3alphaCH(2)OH5betaP) to examine the mechanism for voltage-dependent potentiation. This analogue potentiates but does not block the glycine alpha3 receptor. Steady-state responses and current relaxations following voltage jumps support the idea that the voltage dependence of potentiation indirectly arises from a voltage dependence for channel activation by glycine, rather than an intrinsic voltage dependence for potentiation. Potentiation results from a slowing of the channel deactivation rate. In the absence of steroid, at a low [glycine] current relaxations after a voltage jump show two exponential components, with a weighted average time constant of approximately 425 ms (-50 mV, 22 degrees C). The rate for channel deactivation increases at more negative potentials (e-fold per 170 mV) whereas activation decreases (e-fold per 230 mV). The probability a channel is active at a high [glycine] is greater than 0.9. The addition of 10 microM 3alphaCH(2)OH5betaP decreases the deactivation rate by 6.3-fold (-50 mV). Voltage-dependent block by 3alphaCOOH5betaP is consistent with simple open-channel block, with voltage dependence reflecting interactions of the charge on the analogue with the electrical field. Block and unblock have equal but opposite dependence on membrane potential, and the charge on 3alphaCOOH5betaP senses approximately 70% of the membrane field at the blocking site. The apparent forward rate for block, however, is very slow (2 x 10(5) m(-1) s(-1)).
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Affiliation(s)
- Xiaochun Jin
- Department of Anesthesiology, Washington University, 660 South Euclid Ave, St Louis, MO 63110, USA
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The insecticide fipronil and its metabolite fipronil sulphone inhibit the rat alpha1beta2gamma2L GABA(A) receptor. Br J Pharmacol 2008; 155:783-94. [PMID: 18660823 DOI: 10.1038/bjp.2008.309] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
BACKGROUND AND PURPOSE Fipronil is the active ingredient in a number of widely used insecticides. Human exposure to fipronil leads to symptoms (headache, nausea and seizures) typically associated with the antagonism of GABA(A) receptors in the brain. In this study, we have examined the modulation of the common brain GABA(A) receptor subtype by fipronil and its major metabolite, fipronil sulphone. EXPERIMENTAL APPROACH Whole-cell and single-channel recordings were made from HEK 293 cells transiently expressing rat alpha1beta2gamma2L GABA(A) receptors. KEY RESULTS The major effect of fipronil was to increase the rate of current decay in macroscopic recordings. In single-channel recordings, the presence of fipronil resulted in shorter cluster durations without affecting the intracluster open and closed time distributions or the single-channel conductance. The alpha1V256S mutation, previously shown alleviate channel inhibition by inhibitory steroids and several insecticides, had a relatively small effect on channel block by fipronil. The mode of action of fipronil sulphone was similar to that of its parent compound but the metabolite was less potent at inhibiting the alpha1beta2gamma2L receptor. CONCLUSIONS AND IMPLICATIONS We conclude that exposure to fipronil induces accumulation of receptors in a novel, long-lived blocked state. This process proceeds in parallel with and independently of, channel desensitization. The lower potency of fipronil sulphone indicates that the conversion serves as a detoxifying process in mammalian brain.
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Akk G, Li P, Bracamontes J, Reichert DE, Covey DF, Steinbach JH. Mutations of the GABA-A receptor alpha1 subunit M1 domain reveal unexpected complexity for modulation by neuroactive steroids. Mol Pharmacol 2008; 74:614-27. [PMID: 18544665 DOI: 10.1124/mol.108.048520] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neuroactive steroids are among the most efficacious modulators of the mammalian GABA-A receptor. Previous work has proposed that receptor potentiation is mediated by steroid interactions with a site defined by the residues alpha1Asn407/Tyr410 in the M4 transmembrane domain and residue alpha1Gln241 in the M1 domain. We examined the role of residues in the alpha1 subunit M1 domain in the modulation of the rat alpha1beta2gamma2L GABA-A receptor by neuroactive steroids. The data demonstrate that the region is critical to the actions of potentiating neuroactive steroids. Receptors containing the alpha1Q241W or alpha1Q241L mutations were insensitive to (3alpha,5alpha)-3-hydroxypregnan-20-one (3alpha5alphaP), albeit with different underlying mechanisms. The alpha1Q241S mutant was potentiated by 3alpha5alphaP, but the kinetic mode of potentiation was altered by the mutation. It is noteworthy that the alpha1Q241L mutation had no effect on channel potentiation by (3alpha,5alpha)-3-hydroxymethyl-pregnan-20-one, but mutation of the neighboring residue, alpha1Ser240, prevented channel modulation. A steroid lacking an H-bonding group on C3 (5alpha-pregnan-20-one) potentiated the wild-type receptor but not the alpha1Q241L mutant. The findings are consistent with a model in which the alpha1Ser240 and alpha1Gln241 residues shape the surface to which steroid molecules bind.
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Affiliation(s)
- Gustav Akk
- Department of Anesthesiology, Washington University School of Medicine, Campus Box 8054, 660 S. Euclid Ave, St. Louis, MO 63110, USA.
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Scaglione JB, Jastrzebska I, Krishnan K, Li P, Akk G, Manion BD, Benz A, Taylor A, Rath NP, Evers AS, Zorumski CF, Mennerick S, Covey DF. Neurosteroid analogues. 14. Alternative ring system scaffolds: GABA modulatory and anesthetic actions of cyclopenta[b]phenanthrenes and cyclopenta[b]anthracenes. J Med Chem 2008; 51:1309-18. [PMID: 18275132 DOI: 10.1021/jm701128r] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Although the structural features of binding sites for neuroactive steroids on gamma-aminobutryic acid type A (GABA A) receptors are still largely unknown, structure-activity studies have established a pharmacophore for potent enhancement of GABA A receptor function by neuroactive steroids. This pharmacophore emphasizes the importance of the position and stereochemistry of hydrogen-bonding groups on the steroid. However, the importance of the steroid ring system in mediating hydrophobic interactions with the GABA A receptor is unclear. We have taken the cyclopenta[ b]phenanthrene (tetracyclic compounds with a nonlinear ring system different from that of steroids) and cyclopenta[ b]anthracene (tetracyclic molecules with a linear 6-6-6-5 carbocyclic ring system) ring systems and properly substituted them to satisfy the pharmacophore requirements of the critical hydrogen-bond donor and acceptor groups found in neuroactive steroids. We have found these cyclopenta[ b]phenanthrene and cyclopenta[ b]anthracene analogues to have potent activity at the GABA A receptor, rivaling that of the most potent steroid modulators. Single-channel analysis of electrophysiological data indicates that similarly substituted analogues in the different ring systems affect the kinetic components of macroscopic currents in different ways. Mutations to the hydrogen bonding amino acids at the putative steroid binding site (alpha1Q241L mutation and alpha1N407A/Y410F double mutation) produce similar effects on macroscopic current amplitude by the different ring system analogues suggesting that the different kinetic effects are explained by the precise interactions of each analogue with the same binding site(s).
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Affiliation(s)
- Jamie B Scaglione
- Department of Molecular Biology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Photo-activated azi-etomidate, a general anesthetic photolabel, irreversibly enhances gating and desensitization of gamma-aminobutyric acid type A receptors. Anesthesiology 2008; 108:103-12. [PMID: 18156888 DOI: 10.1097/01.anes.0000296074.33999.52] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND The general anesthetic etomidate acts via gamma-aminobutyric acid type A (GABA(A)) receptors, enhancing activation at low GABA and prolonging deactivation. Azi-etomidate is a photo-reactive etomidate derivative with similar pharmacological actions, which has been used to identify putative binding sites. The authors examine the irreversible effects of azi-etomidate photo-modification on functional GABA(A) receptors in cell membranes. METHODS GABA(A) receptors (alpha1beta2gamma2L) were expressed in both Xenopus oocytes and human embryonic kidney cells exposed to 365 nm light-activated azi-etomidate with or without GABA, then extensively washed. Receptor-mediated chloride currents were measured using voltage clamp electrophysiology to assess the ratio of peak responses at 10 microm and 1 mm GABA (I10/I1000) and deactivation time course. RESULTS After azi-etomidate photo-modification, I10/I1000 ratios were persistently enhanced and deactivation was prolonged, mimicking reversible azi-etomidate actions. Azi-etomidate and ultraviolet light were required to produce irreversible receptor modulation. Adding GABA during photo-modification greatly enhanced irreversible modulation. Azi-etomidate modification also dose-dependently reduced maximal GABA-activated currents, consistent with accumulation of permanently desensitized receptors. Excess etomidate during azi-etomidate photo-modification competitively reduced permanent desensitization. Persistent channel modulation was blocked by 320-fold excess etomidate but enhanced when 32-fold excess etomidate was present. CONCLUSIONS Azi-etomidate efficiently photo-modifies etomidate sites on GABA(A) receptors in intact cells, producing persistent functional changes that mimic its reversible effects. The results demonstrate sequential modification at more than one etomidate site per receptor. The sites display reciprocal positive cooperativity. In combination with focal photo-activation, azi-etomidate may prove useful for studies of anesthetic actions in neural circuits.
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alpha1beta2delta, a silent GABAA receptor: recruitment by tracazolate and neurosteroids. Br J Pharmacol 2008; 153:1062-71. [PMID: 18204487 DOI: 10.1038/sj.bjp.0707665] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
BACKGROUND AND PURPOSE This study investigated the alpha(1)beta(2)delta isoform of the GABA(A) receptor that is presumably expressed in the forebrain. The functional and pharmacological properties of this receptor combination are largely unknown. EXPERIMENTAL APPROACH We expressed alpha(1)beta(2)delta GABA(A) receptors in Xenopus laevis oocytes. GABA-activated currents, in the presence and absence of modulators, were recorded using the two-electrode voltage clamp technique. KEY RESULTS The alpha(1)beta(2)delta isoform of the GABA(A) receptor exhibited an extremely small GABA-mediated current. Tracazolate increased the current amplitude evoked by a half-maximal concentration (EC(50)) of GABA by 59-fold. The maximum current was increased 23-fold in the presence of a saturating GABA concentration. Concomitant with the increase in the maximum, was a 4-fold decrease in the EC(50). Finally, a mutation in the second transmembrane domain of the delta subunit that increases receptor efficacy (L286S), eliminated the increase in the maximum GABA-activated current. The endogenous neurosteroid, tetrahydrodeoxycorticosterone (THDOC), also decreased the EC(50) and increased the maximum current amplitude, although to a lesser degree than that of tracazolate. CONCLUSIONS AND IMPLICATIONS Taken all together, these findings indicate that the small GABA-mediated currents in the absence of the modulator are due to a low efficacy for activation. In the absence of modulators, alpha(1)beta(2)delta GABA receptors would be effectively silent and therefore contribute little to inhibition in the CNS. In the presence of tracazolate or endogenous neurosteroids however, this particular receptor isoform could exert a profound inhibitory influence on neuronal activity.
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Kelly EW, Solt K, Raines DE. Volatile aromatic anesthetics variably impact human gamma-aminobutyric acid type A receptor function. Anesth Analg 2007; 105:1287-92, table of contents. [PMID: 17959956 DOI: 10.1213/01.ane.0000282829.21797.97] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
BACKGROUND The gamma-aminobutyric acid type A (GABA(A)) and N-methyl-d-aspartate (NMDA) receptors are important inhibitory and excitatory neurotransmitter receptors, respectively, in the central nervous system. At the concentrations required to produce immobility in the face of a noxious stimulus, volatile aromatic anesthetics inhibit NMDA receptors to varying degrees, strongly suggesting that they also act at other targets to produce immobilization. In this study, we sought to assess the potential role that GABA(A) receptors play in mediating the behavioral actions of volatile aromatic anesthetics. METHODS Electrophysiological techniques were used to quantify the effects of eight volatile aromatic anesthetics and three clinical anesthetics on currents mediated by alpha1beta2gamma2L GABA(A) receptors expressed in Xenopus oocytes. RESULTS At equivalent minimal alveolar anesthetic concentration multiples, volatile aromatic anesthetics vary widely in the degrees to which they enhance GABA(A) receptor-mediated currents elicited by low concentrations of GABA. In general, anesthetics that inhibit NMDA receptors most, enhanced GABA(A) receptors least. This reciprocal relationship between anesthetic potency on GABA(A) versus NMDA receptors was also observed for the clinical anesthetics isoflurane, halothane, and cyclopropane. Studies using a range of GABA concentrations indicated that volatile aromatic anesthetics enhance GABA(A) receptor activity by shifting the open-close (gating) equilibrium towards the open channel state. CONCLUSIONS These findings suggest that GABA(A) receptors contribute variably to the behavioral actions of volatile anesthetics and imply that the molecular determinants of anesthetic action on NMDA and GABA(A) receptors are distinctly different.
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Affiliation(s)
- Elizabeth W Kelly
- Department of Anesthesia and Critical Care, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
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Peričić D, Štrac DŠ, Vlainić J. Interaction of diazepam and swim stress. Brain Res 2007; 1184:81-7. [DOI: 10.1016/j.brainres.2007.09.039] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2007] [Revised: 09/13/2007] [Accepted: 09/17/2007] [Indexed: 10/22/2022]
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Li P, Reichert DE, Rodríguez AD, Manion BD, Evers AS, Eterović VA, Steinbach JH, Akk G. Mechanisms of potentiation of the mammalian GABAA receptor by the marine cembranoid eupalmerin acetate. Br J Pharmacol 2007; 153:598-608. [PMID: 18037909 DOI: 10.1038/sj.bjp.0707597] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE Eupalmerin acetate (EPA) is a marine diterpene compound isolated from the gorgonian octocorals Eunicea succinea and Eunicea mammosa. The compound has been previously shown to modulate muscle-type and neuronal nicotinic acetylcholine receptors, which are inhibited in the presence of low micromolar concentrations of EPA. In this study, we examined the effect of EPA on another transmitter-gated ion channel, the GABA(A) receptor. EXPERIMENTAL APPROACH Whole-cell and single-channel recordings were made from HEK 293 cells transiently expressing rat wild-type and mutant alpha1beta2gamma2L GABA(A) receptors. KEY RESULTS Our findings demonstrate that, at micromolar concentrations, EPA potentiates the rat alpha1beta2gamma2L GABA(A) receptor. The analysis of single-channel currents recorded in the presence of EPA showed that the kinetic mode of action of EPA is similar to that of neuroactive steroids. Mutations to residues alpha1Q241 and alpha1N407/Y410, previously shown to affect receptor modulation by neurosteroids, also diminished potentiation by EPA. Exposure to a steroid antagonist, (3alpha,5alpha)-17-phenylandrost-16-en-3-ol, reduced potentiation by EPA. Additionally, exposure to EPA led to potentiation of GABA(A) receptors activated by very high concentrations (1-10 microM) of allopregnanolone. In tadpole behavioural assays, EPA caused loss of righting reflex and loss of swimming reflex. CONCLUSIONS AND IMPLICATIONS We conclude that EPA either interacts with the putative neurosteroid binding site on the GABA(A) receptor or shares with neurosteroids the key transduction elements involved in channel potentiation by steroids. The results indicate that cembranoids represent a novel class of GABA(A) receptor modulators.
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Affiliation(s)
- P Li
- Department of Anesthesiology, Washington University School of Medicine, St Louis, MO 63110, USA
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