scholarly journals The Positive Allosteric Modulator of Alpha-2/3-Containing γ-Aminobutyric Acid Type A Receptors, KRM-II-81, Is Active in Pharmacoresistant Models of Epilepsy and in Human Epileptic Tissue

Neurosurgery ◽  
2019 ◽  
Vol 66 (Supplement_1) ◽  
Author(s):  
Jodi L Smith ◽  
Xingie Ping ◽  
Xiaoming Jin ◽  
Lalit K Golani ◽  
Guanguan Li ◽  
...  
Keyword(s):  
Antiepileptic Drug ◽  
Antiepileptic Drugs ◽  
Temporal Lobe ◽  
Gabaa Receptors ◽  
Type A ◽  
Network Activity ◽  
Aminobutyric Acid ◽  
Acid Type ◽  
Gabaa Receptor Antagonist ◽  
Mesial Temporal Lobe

Abstract INTRODUCTION Epilepsy patients continue to suffer from the lack of efficacious medications. Recent attention has been directed toward the potential advantages of developing positive allosteric modulators of alpha-2/3-containing γ-aminobutyric acid type A (GABAA) receptors as antiepileptic drugs. A proof of principle has been reported with one such molecule in patients with photosensitive epilepsy. KRM-II-81 (5- (8-ethynyl-6- (pyridin-2-yl)-4H-benzo[f]imidazole[1,5-alpha][1,4]diazepin-3-yl)oxazole) is an orally-bioavailable compound recently designed for selectivity at alpha-2/3-containing GABAA receptors over the alpha-1-subtype involved in motor-impairing effects. KRM-II-81 has recently been reported to dampen seizure activity in rodents induced by acute and chronic seizure provocation. KRM-II-81 was often more efficacious than diazepam as an anticonvulsant while producing less motor impairment than diazepam. The reduced motor impact of KRM-II-81 is hypothesized to enable higher central target exposure and hence increased efficacy. METHODS The effects of KRM-II-81 were investigated in a mouse mesial temporal lobe model and a rat lamotrigine-resistant kindling model. We also explored the antiepileptic electrophysiological effects of KRM-II-81 in cortical slices from epileptic pediatric patients to help guide the development of novel compounds that might be valuable against antiepileptic drug-resistant epilepsies. RESULTS Mice with kainate-induced mesial temporal lobe seizures exhibited spontaneous recurrent hippocampal paroxysmal discharges (16.8 +/–2.5). KRM-II-81 significantly reduced the discharge frequency to 5.5 +/–1.4 after oral dosing at 15 mg/kg. KRM-II-81 also decreased convulsions in rats undergoing amygdala kindling in the presence of lamotrigine. In slices of epileptic cortex, KRM-II-81 produced a concentration-dependent dampening of network activity engendered by the GABAA receptor antagonist picrotoxin or the K+-channel modulator 4-aminopyridine. CONCLUSION This study provides increased levels of confidence regarding the unique anticonvulsant profile of KRM-II-81 and its potential as an improved antiepileptic drug. The data also help to solidify the veracity of alpha-2/3-containing GABAA receptors as a novel molecular target for antiepileptic drugs.

scholarly journals Differential Regulation of the Postsynaptic Clustering of γ-Aminobutyric Acid Type A (GABAA) Receptors by Collybistin Isoforms

2011 ◽  
Vol 286 (25) ◽  
pp. 22456-22468 ◽  
Author(s):  
Tzu-Ting Chiou ◽  
Bevan Bonhomme ◽  
Hongbing Jin ◽  
Celia P. Miralles ◽  
Haiyan Xiao ◽  
...  
Keyword(s):  
Gabaa Receptors ◽  
Type A ◽  
Differential Regulation ◽  
Aminobutyric Acid ◽  
Acid Type

Classic Benzodiazepines Modulate the Open–Close Equilibrium in α1β2γ2Lγ-Aminobutyric Acid Type A Receptors

2005 ◽  
Vol 102 (4) ◽  
pp. 783-792 ◽  
Author(s):  
Dirk Rüsch ◽  
Stuart A. Forman
Keyword(s):  
Gabaa Receptors ◽  
Sulfonic Acid ◽  
Site Occupancy ◽  
Type A ◽  
Aminobutyric Acid ◽  
Clinical Effects ◽  
Gamma Aminobutyric Acid ◽  
Wild Type ◽  
Acid Type ◽  
Benzodiazepine Site

Background Classic benzodiazepine agonists induce their clinical effects by binding to a site on gamma-aminobutyric acid type A (GABAA) receptors and enhancing receptor activity. There are conflicting data regarding whether the benzodiazepine site is allosterically coupled to gamma-aminobutyric acid binding versus the channel open-close (gating) equilibrium. The authors tested the hypothesis that benzodiazepine site ligands modulate alpha1beta2gamma2L GABAA receptor gating both in the absence of orthosteric agonists and when the orthosteric sites are occupied. Methods GABAA receptors were recombinantly expressed in Xenopus oocytes and studied using two-microelectrode voltage clamp electrophysiology. To test gating effects in the absence of orthosteric agonist, the authors used spontaneously active GABAA receptors containing a leucine-to-threonine mutation at residue 264 on the alpha1 subunit. To examine effects on gating when orthosteric sites were fully occupied, they activated wild-type receptors with high concentrations of a partial agonist, piperidine-4-sulfonic acid. Results In the absence of orthosteric agonists, the channel activity of alpha1L264Tbeta2gamma2L receptors was increased by diazepam and midazolam and reduced by the inverse benzodiazepine agonist FG7142. Flumazenil displayed very weak agonism and blocked midazolam from further activating mutant channels. In wild-type receptors activated with saturating concentrations of piperidine-4-sulfonic acid, midazolam increased maximal efficacy. Conclusions Independent of orthosteric site occupancy, classic benzodiazepines modulate the gating equilibrium in alpha1beta2gamma2L GABAA receptors and are therefore allosteric coagonists. A Monod-Wyman-Changeux coagonist gating model quantitatively predicts these effects, suggesting that benzodiazepines minimally alter orthosteric ligand binding.

scholarly journals A Cysteine Substitution Probes β3H267 Interactions with Propofol and Other Potent Anesthetics in α1β3γ2L γ-Aminobutyric Acid Type A Receptors

2016 ◽  
Vol 124 (1) ◽  
pp. 89-100 ◽  
Author(s):  
Alex T. Stern ◽  
Stuart A. Forman
Keyword(s):  
Gabaa Receptors ◽  
Barbituric Acid ◽  
Type A ◽  
Homology Model ◽  
Aminobutyric Acid ◽  
Mammalian Brain ◽  
Cysteine Substitution ◽  
Acid Type ◽  
Study Results ◽  
Contact Residues

Abstract Background Anesthetic contact residues in γ-aminobutyric acid type A (GABAA) receptors have been identified using photolabels, including two propofol derivatives. O-propofol diazirine labels H267 in β3 and α1β3 receptors, whereas m-azi-propofol labels other residues in intersubunit clefts of α1β3. Neither label has been studied in αβγ receptors, the most common isoform in mammalian brain. In αβγ receptors, other anesthetic derivatives photolabel m-azi-propofol-labeled residues, but not βH267. The authors’ structural homology model of α1β3γ2L receptors suggests that β3H267 may abut some of these sites. Methods Substituted cysteine modification–protection was used to test β3H267C interactions with four potent anesthetics: propofol, etomidate, alphaxalone, and R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirinylphenyl) barbituric acid (mTFD-MPAB). The authors expressed α1β3γ2L or α1β3H267Cγ2L GABAA receptors in Xenopus oocytes. The authors used voltage clamp electrophysiology to assess receptor sensitivity to γ-aminobutyric acid (GABA) and anesthetics and to compare p-chloromercuribenzenesulfonate modification rates with GABA versus GABA plus anesthetics. Results Enhancement of low GABA (eliciting 5% of maximum) responses by equihypnotic concentrations of all four anesthetics was similar in α1β3γ2L and α1β3H267Cγ2L receptors (n > 3). Direct activation of α1β3H267Cγ2L receptors, but not α1β3γ2L, by mTFD-MPAB and propofol was significantly greater than the other anesthetics. Modification of β3H267C by p-chloromercuribenzenesulfonate (n > 4) was rapid and accelerated by GABA. Only mTFD-MPAB slowed β3H267C modification (approximately twofold; P = 0.011). Conclusions β3H267 in α1β3γ2L GABAA receptors contacts mTFD-MPAB, but not propofol. The study results suggest that β3H267 is near the periphery of one or both transmembrane intersubunit (α+/β− and γ+/β−) pockets where both mTFD-MPAB and propofol bind.

Structure–Function Evaluation of Imidazopyridine Derivatives Selective for δ-Subunit-Containing γ-Aminobutyric Acid Type A (GABAA) Receptors

2018 ◽  
Vol 61 (5) ◽  
pp. 1951-1968 ◽  
Author(s):  
Kirsten Yakoub ◽  
Sascha Jung ◽  
Christian Sattler ◽  
Helen Damerow ◽  
Judith Weber ◽  
...  
Keyword(s):  
Structure Function ◽  
Gabaa Receptors ◽  
Type A ◽  
Aminobutyric Acid ◽  
Function Evaluation ◽  
Acid Type ◽  
Imidazopyridine Derivatives

scholarly journals Etomidate and Etomidate Analog Binding and Positive Modulation of γ-Aminobutyric Acid Type A Receptors

2018 ◽  
Vol 129 (5) ◽  
pp. 959-969 ◽  
Author(s):  
Megan McGrath ◽  
Zhiyi Yu ◽  
Selwyn S. Jayakar ◽  
Celena Ma ◽  
Mansi Tolia ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
Gabaa Receptors ◽  
Binding Sites ◽  
Phenyl Ring ◽  
Type A ◽  
Binding Pocket ◽  
Aminobutyric Acid ◽  
Substituent Group ◽  
Acid Type ◽  
Site Selective

Abstract Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New Background Naphthalene-etomidate, an etomidate analog containing a bulky phenyl ring substituent group, possesses very low γ-aminobutyric acid type A (GABAA) receptor efficacy and acts as an anesthetic-selective competitive antagonist. Using etomidate analogs containing phenyl ring substituents groups that range in volume, we tested the hypothesis that this unusual pharmacology is caused by steric hindrance that reduces binding to the receptor’s open state. Methods The positive modulatory potencies and efficacies of etomidate and phenyl ring–substituted etomidate analogs were electrophysiology defined in oocyte-expressed α1β3γ2L GABAA receptors. Their binding affinities to the GABAA receptor’s two classes of transmembrane anesthetic binding sites were assessed from their abilities to inhibit receptor labeling by the site-selective photolabels 3[H]azi-etomidate and tritiated R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid. Results The positive modulatory activities of etomidate and phenyl ring–substituted etomidate analogs progressively decreased with substituent group volume, reflecting significant decreases in both potency (P = 0.005) and efficacy (P < 0.0001). Affinity for the GABAA receptor’s two β+ − α– anesthetic binding sites similarly decreased with substituent group volume (P = 0.003), whereas affinity for the receptor’s α+ – β–/γ+ – β– sites did not (P = 0.804). Introduction of the N265M mutation, which is located at the β+ − α– binding sites and renders GABAA receptors etomidate-insensitive, completely abolished positive modulation by naphthalene-etomidate. Conclusions Steric hindrance selectively reduces phenyl ring–substituted etomidate analog binding affinity to the two β+ − α– anesthetic binding sites on the GABAA receptor’s open state, suggesting that the binding pocket where etomidate’s phenyl ring lies becomes smaller as the receptor isomerizes from closed to open.

Pharmacological Characterisation of Cortical γ-Aminobutyric Acid Type A (GABAA) Receptors in Two Wistar Rat Lines Selectively Bred for High and Low Anxiety-Related Behaviour

2000 ◽  
Vol 1 (3) ◽  
pp. 137-143 ◽  
Author(s):  
Bettina Hermann ◽  
Rainer Landgraf ◽  
Martin E Keck ◽  
Alexandra Wigger ◽  
A. Leslie Morrow ◽  
...  
Keyword(s):  
Gabaa Receptors ◽  
Type A ◽  
Wistar Rat ◽  
Aminobutyric Acid ◽  
Acid Type

Multiple assembly signals in γ-aminobutyric acid (type A) receptor subunits combine to drive receptor construction and composition

2003 ◽  
Vol 31 (4) ◽  
pp. 875-879 ◽  
Author(s):  
K. Bollan ◽  
L.A. Robertson ◽  
H. Tang ◽  
C.N. Connolly
Keyword(s):  
Gabaa Receptor ◽  
Gabaa Receptors ◽  
Type A ◽  
Aminobutyric Acid ◽  
Single Amino Acid ◽  
Functional Surface ◽  
Surface Receptors ◽  
Acid Type ◽  
Absolute Requirement ◽  
Receptor Assembly

Mammalian γ-aminobutyric acid type A (GABAA) receptors are constructed from a large repertoire of subunits (α1–α6, β1–β3, γ1–γ3, δ, ∊, θ and π) into a pentameric ion channel. GABAA receptor assembly occurs within the endoplasmic reticulum (ER) and involves interactions with chaperone molecules. Only specific subunit combinations can produce functional surface receptors (with a fixed stoichiometry); other subunit combinations are retained within the ER and degraded. Thus, receptor assembly occurs by defined pathways to limit the diversity of GABAA receptors. The key to understanding how receptor diversity is achieved and controlled is the identification of assembly signals capable of distinguishing between other subunit partners. Analysis of an assembly box in α1 (residues 57–68) has revealed an absolute requirement for this region in the assembly of αβ receptors. Furthermore, a selective requirement for a single amino acid (R66) is observed for the assembly of α1β2, but not α1β1 or α1β3, receptors. In addition, we have characterized an assembly signal in the β3 subunit that is capable of driving the assembly of β3, γ2β3 and α1β3 receptors. Interestingly, this signal does not appear to utilize the α1 assembly box, suggesting the presence of alternative assembly signals within the α1 subunit. Although this β3 signal is sufficient to permit the formation of βγ receptors it is not necessary, suggesting that alternative assembly signals also exist within the β3 subunit. These findings support the belief that GABAA receptor assembly occurs via multiple defined pathways that may be determined by subunit availability.

Sign in / Sign up

Export Citation Format

Share Document