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Sieghart W, Savić MM. International Union of Basic and Clinical Pharmacology. CVI: GABAA Receptor Subtype- and Function-selective Ligands: Key Issues in Translation to Humans. Pharmacol Rev 2018; 70:836-878. [DOI: 10.1124/pr.117.014449] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
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Bader BM, Steder A, Klein AB, Frølund B, Schroeder OHU, Jensen AA. Functional characterization of GABAA receptor-mediated modulation of cortical neuron network activity in microelectrode array recordings. PLoS One 2017; 12:e0186147. [PMID: 29028808 PMCID: PMC5640229 DOI: 10.1371/journal.pone.0186147] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Accepted: 09/26/2017] [Indexed: 12/11/2022] Open
Abstract
The numerous γ-aminobutyric acid type A receptor (GABAAR) subtypes are differentially expressed and mediate distinct functions at neuronal level. In this study we have investigated GABAAR-mediated modulation of the spontaneous activity patterns of primary neuronal networks from murine frontal cortex by characterizing the effects induced by a wide selection of pharmacological tools at a plethora of activity parameters in microelectrode array (MEA) recordings. The basic characteristics of the primary cortical neurons used in the recordings were studied in some detail, and the expression levels of various GABAAR subunits were investigated by western blotting and RT-qPCR. In the MEA recordings, the pan-GABAAR agonist muscimol and the GABABR agonist baclofen were observed to mediate phenotypically distinct changes in cortical network activity. Selective augmentation of αβγ GABAAR signaling by diazepam and of δ-containing GABAAR (δ-GABAAR) signaling by DS1 produced pronounced changes in the majority of the activity parameters, both drugs mediating similar patterns of activity changes as muscimol. The apparent importance of δ-GABAAR signaling for network activity was largely corroborated by the effects induced by the functionally selective δ-GABAAR agonists THIP and Thio-THIP, whereas the δ-GABAAR selective potentiator DS2 only mediated modest effects on network activity, even when co-applied with low THIP concentrations. Interestingly, diazepam exhibited dramatically right-shifted concentration-response relationships at many of the activity parameters when co-applied with a trace concentration of DS1 compared to when applied alone. In contrast, the potencies and efficacies displayed by DS1 at the networks were not substantially altered by the concomitant presence of diazepam. In conclusion, the holistic nature of the information extractable from the MEA recordings offers interesting insights into the contributions of various GABAAR subtypes/subgroups to cortical network activity and the putative functional interplay between these receptors in these neurons.
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Affiliation(s)
| | - Anne Steder
- NeuroProof GmbH, Friedrich-Barnewitz-Str. 4, Rostock, Germany
| | - Anders Bue Klein
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen Ø, Denmark
| | - Bente Frølund
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen Ø, Denmark
| | | | - Anders A. Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen Ø, Denmark
- * E-mail:
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Yuan NY, Poe MM, Witzigmann C, Cook JM, Stafford D, Arnold LA. Characterization of GABA A receptor ligands with automated patch-clamp using human neurons derived from pluripotent stem cells. J Pharmacol Toxicol Methods 2016; 82:109-114. [PMID: 27544543 DOI: 10.1016/j.vascn.2016.08.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 05/31/2016] [Accepted: 08/14/2016] [Indexed: 11/16/2022]
Abstract
INTRODUCTION Automated patch clamp is a recent but widely used technology to assess pre-clinical drug safety. With the availability of human neurons derived from pluripotent stem cells, this technology can be extended to determine CNS effects of drug candidates, especially those acting on the GABAA receptor. METHODS iCell Neurons (Cellular Dynamics International, A Fujifilm Company) were cultured for ten days and analyzed by patch clamp in the presence of agonist GABA or in combination with positive allosteric GABAA receptor modulators. Both efficacy and affinity were determined. In addition, mRNA of GABAA receptor subunits were quantified by qRT-PCR. RESULTS We have shown that iCell Neurons are compatible with the IonFlux microfluidic system of the automated patch clamp instrument. Resistance ranging from 15 to 25MΩ was achieved for each trap channel of patch clamped cells in a 96-well plate format. GABA induced a robust change of current with an EC50 of 0.43μM. Positive GABAA receptor modulators diazepam, HZ-166, and CW-04-020 exhibited EC50 values of 0.42μM, 1.56μM, and 0.23μM, respectively. The α2/α3/α5 selective compound HZ-166-induced the highest potentiation (efficacy) of 810% of the current induced by 100nM GABA. Quantification of GABAA receptor mRNA in iCell Neurons revealed high levels of α5 and β3 subunits and low levels of α1, which is similar to the configuration in human neonatal brain. DISCUSSION iCell Neurons represent a new cellular model to characterize GABAergic compounds using automated patch clamp. These cells have excellent representation of cellular GABAA receptor distribution that enable determination of total small molecule efficacy and affinity as measured by cell membrane current change.
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Affiliation(s)
- Nina Y Yuan
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
| | - Michael M Poe
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
| | - Christopher Witzigmann
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
| | - James M Cook
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
| | - Douglas Stafford
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
| | - Leggy A Arnold
- Department of Chemistry and Biochemistry and Milwaukee Institute for Drug Discovery, University of Wisconsin - Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211, United States.
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Hammer H, Ebert B, Jensen HS, Jensen AA. Functional characterization of the 1,5-benzodiazepine clobazam and its major active metabolite N-desmethylclobazam at human GABA(A) receptors expressed in Xenopus laevis oocytes. PLoS One 2015; 10:e0120239. [PMID: 25798598 PMCID: PMC4370687 DOI: 10.1371/journal.pone.0120239] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2014] [Accepted: 02/04/2015] [Indexed: 12/13/2022] Open
Abstract
The 1,5-benzodiazepine clobazam is indicated for the adjunctive treatment of seizures associated with Lennox-Gastaut syndrome in patients 2 years of age or older in the United States, and for treatment of anxiety and various forms of epilepsy elsewhere. Clobazam has been reported to exhibit different in vivo adverse effects and addiction liability profile than the classic 1,4-benzodiazepines. In this study, it was investigated whether the in vitro pharmacological properties of clobazam and its major active metabolite N-desmethylclobazam could explain some of these clinical differences. The functional properties of the two 1,5-benzodiazepines were characterized at the human γ-aminobutyric acid type A receptor (GABAAR) subtypes α1β2γ2S, α2β2γ2S, α3β2γ2S, α5β2γ2S and α6β2δ expressed in Xenopus laevis oocytes by use of two-electrode voltage-clamp electrophysiology and compared to those exhibited by the 1,4-benzodiazepine clonazepam. All three compounds potentiated GABA EC20-evoked responses through the α1,2,3,5β2γ2S GABAARs in a reversible and concentration-dependent manner, with each displaying similar EC50 values at the four subtypes. Furthermore, the degrees of potentiation of the GABA EC20 currents through the four receptors mediated by saturating modulator concentrations did not differ substantially for any of the three benzodiazepines. The three compounds were substantially less potent (200-3900 fold) as positive allosteric modulators at the α6β2δ GABAAR than at the α1,2,3,5β2γ2S receptors. Interestingly, however, clobazam and especially N-desmethylclobazam were highly efficacious potentiators of α6β2δ receptor signaling. Although this activity component is unlikely to contribute to the in vivo effects of clobazam/N-desmethylclobazam, the 1,5-benzodiazepine could constitute an interesting lead for novel modulators targeting this low-affinity binding site in GABAARs. In conclusion, the non-selective modulation exerted by clobazam, N-desmethylclobazam and clonazepam at the α1β2γ2S, α2β2γ2S, α3β2γ2S and α5β2γ2S GABAARs indicate that the observed clinical differences between clobazam and 1,4-benzodiazepines are likely to arise from factors other than their respective pharmacological properties at the GABAARs as investigated here.
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Affiliation(s)
- Harriet Hammer
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | | | | | - Anders A. Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- * E-mail:
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Obradović AL, Joksimović S, Poe MM, Ramerstorfer J, Varagic Z, Namjoshi O, Batinić B, Radulović T, Marković B, Roth BL, Sieghart W, Cook JM, Savić MM. Sh-I-048A, an in vitro non-selective super-agonist at the benzodiazepine site of GABAA receptors: the approximated activation of receptor subtypes may explain behavioral effects. Brain Res 2014; 1554:36-48. [PMID: 24472579 DOI: 10.1016/j.brainres.2014.01.036] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 12/19/2013] [Accepted: 01/20/2014] [Indexed: 12/24/2022]
Abstract
Enormous progress in understanding the role of four populations of benzodiazepine-sensitive GABAA receptors was paralleled by the puzzling findings suggesting that substantial separation of behavioral effects may be accomplished by apparently non-selective modulators. We report on SH-I-048A, a newly synthesized chiral positive modulator of GABAA receptors characterized by exceptional subnanomolar affinity, high efficacy and non-selectivity. Its influence on behavior was assessed in Wistar rats and contrasted to that obtained with 2mg/kg diazepam. SH-I-048A reached micromolar concentrations in brain tissue, while the unbound fraction in brain homogenate was around 1.5%. The approximated electrophysiological responses, which estimated free concentrations of SH-I-048A or diazepam are able to elicit, suggested a similarity between the 10mg/kg dose of the novel ligand and 2mg/kg diazepam; however, SH-I-048A was relatively more active at α1- and α5-containing GABAA receptors. Behaviorally, SH-I-048A induced sedative, muscle relaxant and ataxic effects, reversed mechanical hyperalgesia 24h after injury, while it was devoid of clear anxiolytic actions and did not affect water-maze performance. While lack of clear anxiolytic actions may be connected with an enhanced potentiation at α1-containing GABAA receptors, the observed behavior in the rotarod, water maze and peripheral nerve injury tests was possibly affected by its prominent action at receptors containing the α5 subunit. The current results encourage further innovative approaches aimed at linking in vitro and in vivo data in order to help define fine-tuning mechanisms at four sensitive receptor populations that underlie subtle differences in behavioral profiles of benzodiazepine site ligands.
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Affiliation(s)
- Aleksandar Lj Obradović
- Department of Physiology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Srđan Joksimović
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Michael M Poe
- Department of Chemistry and Biochemistry, University of Wisconsin - Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA
| | - Joachim Ramerstorfer
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Zdravko Varagic
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Ojas Namjoshi
- Department of Chemistry and Biochemistry, University of Wisconsin - Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA
| | - Bojan Batinić
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Tamara Radulović
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Bojan Marković
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Brian L Roth
- Department of Pharmacology, University of North Carolina Chapel Hill Medical School, Chapel Hill, NC 27514, USA; Division of Chemical Biology and Medicinal Chemistry, University of North Carolina Chapel Hill Medical School, Chapel Hill, NC 27514, USA
| | - Werner Sieghart
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - James M Cook
- Department of Chemistry and Biochemistry, University of Wisconsin - Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA
| | - Miroslav M Savić
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia.
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Rundfeldt C, Löscher W. The pharmacology of imepitoin: the first partial benzodiazepine receptor agonist developed for the treatment of epilepsy. CNS Drugs 2014; 28:29-43. [PMID: 24357084 DOI: 10.1007/s40263-013-0129-z] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Although benzodiazepines (BZDs) offer a wide spectrum of antiepileptic activity against diverse types of epileptic seizures, their use in the treatment of epilepsy is limited because of adverse effects, loss of efficacy (tolerance), and development of physical and psychological dependence. BZDs act as positive allosteric modulators of the inhibitory neurotransmitter GABA by binding to the BZD recognition site ("BZD receptor") of the GABAA receptor. Traditional BZDs such as diazepam or clonazepam act as full agonists at this site, so that one strategy to resolve the disadvantages of these compounds would be the development of partial agonists with lower intrinsic efficacy at the BZD site of the GABAA receptor. Several BZD site partial or subtype selective compounds, including bretazenil, abecarnil, or alpidem, have been developed as anxioselective anxiolytic drugs, but epilepsy was not a target indication for such compounds. More recently, the imidazolone derivatives imepitoin (ELB138) and ELB139 were shown to act as low-affinity partial agonists at the BZD site of the GABAA receptor, and imepitoin was developed for the treatment of epilepsy. Imepitoin displayed a broad spectrum of anticonvulsant activity in diverse seizure and epilepsy models at tolerable doses, and, as expected from its mechanism of action, lacked tolerance and abuse liability in rodent and primate models. The more favorable pharmacokinetic profile of imepitoin in dogs versus humans led to the decision to develop imepitoin for the treatment of canine epilepsy. Based on randomized controlled trials that demonstrated antiepileptic efficacy and high tolerability and safety in epileptic dogs, the drug was recently approved for this indication in Europe. Hopefully, the favorable profile of imepitoin for the treatment of epilepsy in dogs will reactivate the interest in partial BZD site agonists as new treatments for human epilepsy.
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Ghisdal P, Noel N, Pacico N, Martini M, Foerch P, Hanon E, Wolff C. Determining the Relative Efficacy of Positive Allosteric Modulators of the GABAA Receptor. ACTA ACUST UNITED AC 2013; 19:462-7. [DOI: 10.1177/1087057113501555] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Gamma amino butyric acid receptors (GABA) are major therapeutic targets for the development of drugs in neurological and psychiatric disorders. The new generation of GABAA modulators is targeting subtype selectivity and low/partial efficacy on the receptor to potentially overcome the adverse effects described for drugs with full agonist profile. We evaluated a screening approach to measure the relative efficacy of GABAA positive allosteric modulators (PAM) using automated patch clamp and fluorescence membrane potential assays. We determined that the use of an internal comparator (zolpidem), tested on each cell in parallel to the test compound, provides a reliable approach to measure and compare the relative efficacy of PAM ligands. Patch clamp recordings on recombinant GABAA receptors, using a multiple drug addition protocol, allows us to rank PAM ligands with different levels of efficacies. We observed that fluorescence membrane potential assays are not predictive of the relative efficacies of GABAA PAM ligands.
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Masneuf S, Buetler J, Koester C, Crestani F. Role of α1- and α2-GABA(A) receptors in mediating the respiratory changes associated with benzodiazepine sedation. Br J Pharmacol 2012; 166:339-48. [PMID: 22044283 DOI: 10.1111/j.1476-5381.2011.01763.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND AND PURPOSE The molecular substrates underlying the respiratory changes associated with benzodiazepine sedation are unknown. We examined the effects of different doses of diazepam and alprazolam on resting breathing in wild-type (WT) mice and clarified the contribution of α1- and α2-GABA(A) receptors, which mediate the sedative and muscle relaxant action of diazepam, respectively, to these drug effects using point-mutated mice possessing either α1H101R- or α2H101R-GABA(A) receptors insensitive to benzodiazepine. EXPERIMENTAL APPROACH Room air breathing was monitored using whole-body plethysmography. Different groups of WT mice were injected i.p. with diazepam (1-100 mg·kg(-1) ), alprazolam (0.3, 1 or 3 mg·kg(-1) ) or vehicle. α1H101R and α2H101R mice received 1 or 10 mg·kg(-1) diazepam or 0.3 or 3 mg·kg(-1) alprazolam. Respiratory frequency, tidal volume, time of expiration and time of inspiration before and 20 min after drug injection were analysed. KEY RESULTS Diazepam (10 mg·kg(-1) ) decreased the time of expiration, thereby increasing the resting respiratory frequency, in WT and α2H101R mice, but not in α1H101R mice. The time of inspiration was shortened in WT and α1H101R mice, but not in α2H101R mice. Alprazolam (1-3 mg·kg(-1) ) stimulated the respiratory frequency by shortening expiration and inspiration duration in WT mice. This tachypnoeic effect was partially conserved in α1H101R mice while absent in α2H101R mice. CONCLUSIONS AND IMPLICATIONS These results identify a specific role for α1-GABA(A) receptors and α2-GABA(A) receptors in mediating the shortening by benzodiazepines of the expiratory and inspiratory phase of resting breathing respectively.
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Affiliation(s)
- S Masneuf
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
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Karim N, Gavande N, Wellendorph P, Johnston GAR, Hanrahan JR, Chebib M. 3-Hydroxy-2'-methoxy-6-methylflavone: a potent anxiolytic with a unique selectivity profile at GABA(A) receptor subtypes. Biochem Pharmacol 2011; 82:1971-83. [PMID: 21924247 DOI: 10.1016/j.bcp.2011.09.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Revised: 09/01/2011] [Accepted: 09/02/2011] [Indexed: 11/30/2022]
Abstract
Genetic and pharmacological studies have demonstrated that α2- and α4-containing GABA(A) receptors mediate the anxiolytic effects of a number of agents. Flavonoids are a class of ligands that act at GABA(A) receptors and possess anxiolytic effects in vivo. Here we demonstrate that the synthetic flavonoid, 3-hydroxy-2'-methoxy-6-methylflavone (3-OH-2'MeO6MF) potentiates GABA-induced currents at recombinant α1/2β2, α1/2/4/6β1-3γ2L but not α3/5β1-3γ2L receptors expressed in Xenopus oocytes. The enhancement was evident at micromolar concentrations (EC(50) values between 38 and 106 μM) and occurred in a flumazenil-insensitive manner. 3-OH-2'MeO6MF displayed preference for β2/3- over β1-containing receptors with the highest efficacy observed at α2β2/3γ2L, displaying a 4-11-fold increase in efficacy over α2β1γ2L and α1/4/6-containing subtypes. In contrast, 3-OH-2'MeO6MF acted as a potent bicuculline-sensitive activator, devoid of potentiation effects at extrasynaptic α4β2/3δ receptors expressed in oocytes. The affinity of 3-OH-2'MeO6MF for α4β2/3δ receptors (EC(50) values between 1.4 and 2.5 μM) was 10-fold higher than at α4β1δ GABA(A) receptors. 3-OH-2'MeO6MF acted as a full agonist at α4β2/3δ (105% of the maximal GABA response) but as a partial agonist at α4β1δ (61% of the maximum GABA response) receptors. In mice, 3-OH-2'MeO6MF (1-100 mg/kg i.p.) induced anxiolytic-like effects in two unconditioned models of anxiety: the elevated plus maze and light/dark paradigms. No sedative or myorelaxant effects were detected using holeboard, actimeter and horizontal wire tests and only weak barbiturate potentiating effects on the loss of righting reflex test. Taken together, these data suggest that 3-OH-2'MeO6MF is an anxiolytic without sedative and myorelaxant effects acting through positive allosteric modulation of the α2β2/3γ2L and direct activation of α4β2/3δ GABA(A) receptor subtypes.
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Leppä E, Linden AM, Rabe H, Vekovischeva OY, Wulff P, Lüddens H, Wisden W, Korpi ER. Actions of two GABAA receptor benzodiazepine-site ligands that are mediated via non-γ2-dependent modulation. Eur J Pharmacol 2011; 666:111-21. [PMID: 21616065 DOI: 10.1016/j.ejphar.2011.05.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2010] [Revised: 05/03/2011] [Accepted: 05/10/2011] [Indexed: 12/12/2022]
Abstract
The potent sedative-hypnotic zolpidem and the convulsant methyl-6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM) act primarily by binding to the benzodiazepine site of the main inhibitory neurotransmitter receptor, the pentameric γ-aminobutyric acid type A receptor (GABA(A)). This binding depends critically on the wild-type F77 residue of the GABA(A) receptor γ2 subunit. Mice with γ2 subunit F77I point mutation (γ2I77 mouse line) lose the high-affinity nanomolar binding of these ligands as well as their most robust behavioral actions at low doses. Interestingly, the γ2I77 mice offer a tool to study the actions of these substances mediated via other possible binding sites of the GABA(A) receptor. In ligand autoradiographic experiments, we discovered in γ2I77 mouse brain sections a significant amount of residual non-γ2 subunit-dependent benzodiazepine site binding enriched to the striatum and septum. Zolpidem only weakly affected this residual binding at micromolar concentrations, and only a high zolpidem dose (≥ 40 mg/kg) caused sedation and deficits in motor coordination in γ2I77 mice. DMCM had an agonistic action through a secondary, low-affinity non-benzodiazepine binding site of the GABA(A) receptor in the forebrain of γ2I77 mice, and this drug also fully displaced the residual benzodiazepine-site labeling. In behavioral tests, a high dose (20mg/kg) of DMCM was sedative and modulated fear learning. DMCM, but not zolpidem, acted as an agonist in recombinant GABA(A) α1/6β3 receptors studied using ligand binding and electrophysiological assays. Our results highlight the less well-known actions of high doses of DMCM and zolpidem that are not mediated via the γ2 subunit-containing benzodiazepine site of the GABA(A) receptor.
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Affiliation(s)
- Elli Leppä
- Institute of Biomedicine, Pharmacology, POB 63 (Haartmaninkatu 8), FI-00014 University of Helsinki, Finland.
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Vinkers CH, Mirza NR, Olivier B, Kahn RS. The inhibitory GABA system as a therapeutic target for cognitive symptoms in schizophrenia: investigational agents in the pipeline. Expert Opin Investig Drugs 2011; 19:1217-33. [PMID: 20812877 DOI: 10.1517/13543784.2010.513382] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
IMPORTANCE OF THE FIELD Cognitive impairments associated with schizophrenia include neuropsychological deficits in attention, working memory, learning and executive function. Because these cognitive deficits precede the onset of psychosis, are present in non-affected relatives and constitute the best predictor of functional outcome, they are a cardinal clinical feature in schizophrenia. Currently, no effective treatment for the cognitive symptoms in schizophrenia exists. AREAS COVERED IN THIS REVIEW There is evidence that the inhibitory GABA system is affected in schizophrenia, suggesting that cognitive impairments associated with schizophrenia may be effectively treated by drugs that modulate the GABA(A) receptor. However, classical benzodiazepines produce cognitive impairments and are associated with numerous side effects. The recent development of compounds with selective efficacy for different α subunits at the benzodiazepine site of the GABA(A) receptor has renewed interest for the therapeutic potential of GABAergic drugs. WHAT THE READER WILL GAIN This review summarizes the involvement of the inhibitory GABA system in the cognitive abnormalities of schizophrenia and discusses putative (selective) GABAergic cognition-enhancing drugs for schizophrenia. TAKE HOME MESSAGE If cognitive abnormalities in schizophrenic individuals are the result of GABAergic dysfunction, selectively modulating the GABA system could comprise a promising therapeutic intervention for cognitive symptoms in schizophrenia.
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Affiliation(s)
- Christiaan H Vinkers
- Department of Psychiatry, University Medical Center Utrecht, Rudolf Magnus Institute of Neuroscience, Utrecht, The Netherlands
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Flavan-3-ol derivatives are positive modulators of GABAA receptors with higher efficacy for the α2 subtype and anxiolytic action in mice. Neuropharmacology 2008; 55:900-7. [DOI: 10.1016/j.neuropharm.2008.06.069] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2008] [Revised: 06/30/2008] [Accepted: 06/30/2008] [Indexed: 11/19/2022]
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Reynolds DS. The value of genetic and pharmacological approaches to understanding the complexities of GABAA receptor subtype functions: The anxiolytic effects of benzodiazepines. Pharmacol Biochem Behav 2008; 90:37-42. [DOI: 10.1016/j.pbb.2008.03.015] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/17/2007] [Revised: 03/02/2008] [Accepted: 03/24/2008] [Indexed: 11/16/2022]
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Landmark CJ, Johannessen SI. Modifications of Antiepileptic Drugs for Improved Tolerability and Efficacy. PERSPECTIVES IN MEDICINAL CHEMISTRY 2008. [DOI: 10.1177/1177391x0800200001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Introduction A large number of antiepileptic drugs (AEDs) are available today, but they may not be satisfactory regarding clinical efficacy, tolerance, toxicity or pharmacokinetic properties. The purpose of this review is to focus upon the rationale behind the chemical modifications of several recently marketed AEDs or drugs in development and to categorize them according to the main purposes for the improvements: better efficacy or tolerability accompanied by improved pharmacokinetic properties. Material and Method AEDs that have been chemically modified to new derivatives during the last years are reviewed based on recent publications and PubMed-searches. Results and Discussion Improvement in pharmacokinetic parameters may affect both tolerability and efficacy. Modifications to improve tolerability include various valproate analogues, divided into aliphatic amides, cyclic derivatives or amino acid conjugates. Furthermore, there are the carbamazepine analogues oxcarbazepine and eslicarbazepine, the felbamate analogues fluorofelbamate and carisbamate (RWJ 33369), and the lamotrigine analogue JZP-4. The levetiracetam analogues brivaracetam and seletracetam and the derivatives of gabapentin, pregabalin and XP13512, have improved selectivity compared to their parent compounds. Other new drugs have new mechanisms of action related to GABA and glutamate receptors; the glutamate antagonists like topiramate (talampanel and NS-1209), and GABAA receptor agonists, benzodiazepine or progesterone analogues (ELB-139 and ganaxolone). Conclusion Further challenges for development of new AEDs include investigations of target molecules affected by pathophysiological processes and detailed structure-activity relationships with focus on stereoselectivity. These potential drugs may become of importance in future drug therapy in epilepsy and other CNS disorders.
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Affiliation(s)
| | - Svein I. Johannessen
- National Center for Epilepsy, Sandvika, Division of Clinical Neuroscience, Rikshospitalet University Hospital, Oslo, Norway
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Saarelainen KS, Ranna M, Rabe H, Sinkkonen ST, Möykkynen T, Uusi-Oukari M, Linden AM, Lüddens H, Korpi ER. Enhanced behavioral sensitivity to the competitive GABA agonist, gaboxadol, in transgenic mice over-expressing hippocampal extrasynaptic alpha6beta GABA(A) receptors. J Neurochem 2007; 105:338-50. [PMID: 18021290 DOI: 10.1111/j.1471-4159.2007.05136.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The behavioral and functional significance of the extrasynaptic inhibitory GABA(A) receptors in the brain is still poorly known. We used a transgenic mouse line expressing the GABA(A) receptor alpha6 subunit gene in the forebrain under the Thy-1.2 promoter (Thy1alpha6) mice ectopically expressing alpha6 subunits especially in the hippocampus to study how extrasynaptically enriched alphabeta(gamma2)-type receptors alter animal behavior and receptor responses. In these mice extrasynaptic alpha6beta receptors make up about 10% of the hippocampal GABA(A) receptors resulting in imbalance between synaptic and extrasynaptic inhibition. The synthetic GABA-site competitive agonist gaboxadol (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol; 3 mg/kg) induced remarkable anxiolytic-like response in the light : dark exploration and elevated plus-maze tests in Thy1alpha6 mice, while being almost inactive in wild-type mice. The transgenic mice also lost quicker and for longer time their righting reflex after 25 mg/kg gaboxadol than wild-type mice. In hippocampal sections of Thy1alpha6 mice, the alpha6beta receptors could be visualized autoradiographically by interactions between gaboxadol and GABA via [(35)S]TBPS binding to the GABA(A) receptor ionophore. Gaboxadol inhibition of the binding could be partially prevented by GABA. Electrophysiology of recombinant GABA(A) receptors revealed that GABA was a partial agonist at alpha6beta3 and alpha6beta3delta receptors, but a full agonist at alpha6beta3gamma2 receptors when compared with gaboxadol. The results suggest strong behavioral effects via selective pharmacological activation of enriched extrasynaptic alphabeta GABA(A) receptors, and the mouse model represents an example of the functional consequences of altered balance between extrasynaptic and synaptic inhibition.
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Affiliation(s)
- Kati S Saarelainen
- Institute of Biomedicine, Pharmacology, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland
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Langen B, Rundfeldt C. ELB139 an agonist at the benzodiazepine binding site increases 5-HT in the striatum and prefrontal cortex of rats: a microdialysis study. Pharmacol Biochem Behav 2007; 86:79-85. [PMID: 17257662 DOI: 10.1016/j.pbb.2006.12.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2006] [Revised: 12/08/2006] [Accepted: 12/15/2006] [Indexed: 11/23/2022]
Abstract
Benzodiazepines induce an immediate anxiolytic activity at the expense of side effects such as sedation, tolerance and withdrawal. In contrast, selective serotonin receptor uptake inhibitors (SSRIs) are known to offer long-term symptom improvement without inducing tolerance and withdrawal, but with a delayed onset of the anxiolytic effect. ELB139 is a novel agonist at the benzodiazepine binding site with pronounced anxiolytic and anticonvulsant activity without inducing tolerance to both effects after chronic administration. ELB139 shows a selectivity for alpha-3-subunit containing GABA(A) receptors. In the present study the effect of the compound on monoaminergic neurotransmitter levels were investigated by microdialysis. ELB139 induced a significant increase of extracellular 5-HT in the striatum and the medial prefrontal cortex of rats without affecting dopamine levels in these areas. The increase of 5-HT in the striatum was reversed by systemic and by local administration of the benzodiazepine antagonist flumazenil in the dorsal raphe nucleus by a microdialysis probe, suggesting that the increase in 5-HT was mediated by the activity of ELB139 at the benzodiazepine binding site. As the dorsal raphe nucleus is rich in alpha-3 subunits, this effect of ELB139 may be mediated by its subtype selectivity. Thus, ELB139 seems to combine effects seen with benzodiazepine agonists and SSRIs in one compound.
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Affiliation(s)
- Barbara Langen
- elbion AG, Pharmacology Department, Meissner Str. 191, 01445 Radebeul, Germany.
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