scholarly journals Propofol at Clinically Relevant Concentrations Increases Neuronal Differentiation But Is Not Toxic to Hippocampal Neural Precursor Cells In Vitro 

2012 ◽  
Vol 117 (5) ◽  
pp. 1080-1090 ◽  
Author(s):  
Jeffrey W. Sall ◽  
Greg Stratmann ◽  
Jason Leong ◽  
Elliott Woodward ◽  
Philip E. Bickler
Keyword(s):  
Cell Death ◽  
Lactate Dehydrogenase ◽  
Neuronal Differentiation ◽  
Cell Function ◽  
Type A ◽  
Receptor Activation ◽  
Aminobutyric Acid ◽  
Neural Precursor ◽  
Acid Type

Background Propofol in the early postnatal period has been shown to cause brain cell death. One proposed mechanism for cognitive dysfunction after anesthesia is alteration of neural stem cell function and neurogenesis. We examined the effect of propofol on neural precursor or stem cells (NPCs) grown in vitro. Methods Hippocampal-derived NPCs from postnatal day 2 rats were exposed to propofol or Diprivan. NPCs were then analyzed for bromodeoxyuridine incorporation to measure proliferation. Cell death was measured by lactate dehydrogenase release. Immunocytochemistry was used to evaluate the expression of neuronal and glial markers in differentiating NPCs exposed to propofol. Results Propofol dose dependently increases the release of lactate dehydrogenase from NPCs under both proliferating and differentiating conditions at supraclinical concentrations (more than 7.1 µM). Both Diprivan and propofol had the same effect on NPCs. Propofol-mediated release of lactate dehydrogenase is not inhibited by blocking the γ-aminobutyric acid type A receptor or extracellular calcium influx and is not mediated by caspase-3/7. Direct γ-aminobutyric acid type A receptor activation did not have the same effect. In differentiating NPCs, 6 h of propofol at 2.1 µM increased the number neurons but not glial cells 4 days later. Increased neuronal differentiation was not blocked by bicuculline. Conclusions Only supraclinical concentrations of propofol or Diprivan kill NPCs in culture by a non-γ-aminobutyric acid type A, noncaspase-3 mechanism. Clinically relevant doses of propofol increase neuronal fate choice by a non-γ-aminobutyric acid type A mechanism.

Droperidol Inhibits GABAAand Neuronal Nicotinic Receptor Activation

2002 ◽  
Vol 96 (4) ◽  
pp. 987-993 ◽  
Author(s):  
Pamela Flood ◽  
Kristen M. Coates
Keyword(s):  
Type A ◽  
Receptor Activation ◽  
Aminobutyric Acid ◽  
Hill Coefficient ◽  
High Dose ◽  
Gamma Aminobutyric Acid ◽  
Anesthetic Drugs ◽  
Gaba Inhibition ◽  
Acid Type ◽  
Anesthetic Action

Background Droperidol is used in neuroleptanesthesia and as an antiemetic. Although its antiemetic effect is thought to be caused by dopaminergic inhibition, the mechanism of droperidol's anesthetic action is unknown. Because gamma-aminobutyric acid type A (GABAA) and neuronal nicotinic acetylcholine receptors (nAChRs) have been implicated as putative targets of other general anesthetic drugs, the authors tested the ability of droperidol to modulate these receptors. Methods gamma-Aminobutyric acid type A alpha1beta1gamma2 receptor, alpha7 and alpha4beta2 nAChRs were expressed in Xenopus oocytes and studied with two-electrode voltage clamp recording. The authors tested the ability of droperidol at concentrations from 1 nm to 100 microm to modulate activation of these receptors by their native agonists. Results Droperidol inhibited the GABA response by a maximum of 24.7 +/- 3.0%. The IC50 for inhibition was 12.6 +/- 0.47 nm droperidol. At high concentrations, droperidol (100 microm) activates the GABAA receptor in the absence of GABA. Inhibition of the GABA response is significantly greater at hyperpolarized membrane potentials. The activation of the alpha7 nAChR is also inhibited by droperidol, with an IC50 of 5.8 +/- 0.53 microm. The Hill coefficient is 0.95 +/- 0.1. Inhibition is noncompetitive, and membrane voltage dependence is insignificant. Conclusions Droperidol inhibits activation of both the GABAA alpha1beta1gamma2 and alpha7 nAChR. The submaximal GABA inhibition occurs within a concentration range such that it might be responsible for the anxiety, dysphoria, and restlessness that limit the clinical utility of high-dose droperidol anesthesia. Inhibition of the alpha7 nAChR might be responsible for the anesthetic action of droperidol.

scholarly journals A Conserved Tyrosine in the β2Subunit M4 Segment Is a Determinant of γ-Aminobutyric Acid Type A Receptor Sensitivity to Propofol

2007 ◽  
Vol 107 (3) ◽  
pp. 412-418 ◽  
Author(s):  
James E. Richardson ◽  
Paul S. Garcia ◽  
Kate K. O'Toole ◽  
Jason M. C. Derry ◽  
Shannon V. Bell ◽  
...  
Keyword(s):  
Binding Site ◽  
Type A ◽  
Receptor Activation ◽  
Aminobutyric Acid ◽  
Gamma Aminobutyric Acid ◽  
General Anesthetics ◽  
Receptor Function ◽  
293 Cells ◽  
Acid Type ◽  
Normal Sensitivity

Background The gamma-aminobutyric acid type A receptor (GABAA-R) beta subunits are critical targets for the actions for several intravenous general anesthetics, but the precise nature of the anesthetic binding sites are unknown. In addition, little is known about the role the fourth transmembrane (M4) segment of the receptor plays in receptor function. The aim of this study was to better define the propofol binding site on the GABAA-R by conducting a tryptophan scan in the M4 segment of the beta2 subunit. Methods Seven tryptophan mutations were introduced into the C-terminal end of the M4 segment of the GABAA-R beta2 subunit. GABAA-R subunit complementary DNAs were transfected into human embryonic kidney 293 cells grown on glass coverslips. After transfection (36-72 h), coverslips were transferred to a perfusion chamber to assay receptor function. Cells were whole cell patch clamped and exposed to GABA, propofol, etomidate, and pregnenolone. Chemicals were delivered to the cells using two 10-channel infusion pumps and a rapid solution exchanger. Results All tryptophan mutations were well tolerated, and with one exception, all resulted in minimal changes in receptor activation by GABA. One mutation, beta2(Y444W), selectively suppressed the ability of propofol to enhance receptor function while retaining normal sensitivity to etomidate and pregnenolone. Conclusions This is the first report of a mutation that selectively reduces propofol sensitivity without altering the action of etomidate. The reduction in propofol sensitivity is consistent with the loss of a hydrogen bond within the propofol binding site. These results also suggest a possible orientation of the propofol molecule within its binding site.

scholarly journals An Allosteric Coagonist Model for Propofol Effects on α1β2γ2L γ-Aminobutyric Acid Type A Receptors

2012 ◽  
Vol 116 (1) ◽  
pp. 47-55 ◽  
Author(s):  
Dirk Ruesch ◽  
Elena Neumann ◽  
Hinnerk Wulf ◽  
Stuart A. Forman
Keyword(s):  
Type A ◽  
Receptor Activation ◽  
Convincing Evidence ◽  
Receptor Activity ◽  
Aminobutyric Acid ◽  
Single Class ◽  
Gaba A ◽  
Direct Activation ◽  
Receptor Sites ◽  
Acid Type

Background Propofol produces its major actions via γ-aminobutyric acid type A (GABA(A)) receptors. At low concentrations, propofol enhances agonist-stimulated GABA(A) receptor activity, and high propofol concentrations directly activate receptors. Etomidate produces similar effects, and there is convincing evidence that a single class of etomidate sites mediate both agonist modulation and direct GABA(A) receptor activation. It is unknown if the propofol binding site(s) on GABA(A) receptors that modulate agonist-induced activity also mediate direct activation. Methods GABA(A) α1β2γ2L receptors were heterologously expressed in Xenopus oocytes and activity was quantified using voltage clamp electrophysiology. We tested whether propofol and etomidate display the same linkage between agonist modulation and direct activation of GABA(A) receptors by identifying equiefficacious drug solutions for direct activation. We then determined whether these drug solutions produce equal modulation of GABA-induced receptor activity. We also measured propofol-dependent direct activation and modulation of low GABA responses. Allosteric coagonist models similar to that established for etomidate, but with variable numbers of propofol sites, were fitted to combined data. Results Solutions of 19 μM propofol and 10 μM etomidate were found to equally activate GABA(A) receptors. These two drug solutions also produced indistinguishable modulation of GABA-induced receptor activity. Combined electrophysiological data behaved in a manner consistent with allosteric coagonist models with more than one propofol site. The best fit was observed when the model assumed three equivalent propofol sites. Conclusions Our results support the hypothesis that propofol, like etomidate, acts at GABA(A) receptor sites mediating both GABA modulation and direct activation.

scholarly journals Methoxycarbonyl-etomidate

2009 ◽  
Vol 111 (2) ◽  
pp. 240-249 ◽  
Author(s):  
Joseph F. Cotten ◽  
S Shaukat Husain ◽  
Stuart A. Forman ◽  
Keith W. Miller ◽  
Elizabeth W. Kelly ◽  
...  
Keyword(s):  
Half Life ◽  
Human Liver ◽  
Type A ◽  
Aminobutyric Acid ◽  
Gamma Aminobutyric Acid ◽  
Loss Of Righting Reflex ◽  
Acid Type ◽  
Righting Reflex ◽  
S9 Fraction

Background Etomidate is a rapidly acting sedative-hypnotic that provides hemodynamic stability. It causes prolonged suppression of adrenocortical steroid synthesis; therefore, its clinical utility and safety are limited. The authors describe the results of studies to define the pharmacology of (R)-3-methoxy-3-oxopropyl1-(1-phenylethyl)-1H-imidazole-5-carboxylate (MOC-etomidate), the first etomidate analogue designed to be susceptible to ultra-rapid metabolism. Methods The gamma-aminobutyric acid type A receptor activities of MOC-etomidate and etomidate were compared by using electrophysiological techniques in human alpha1beta2gamma2l receptors. MOC-etomidate's hypnotic concentration was determined in tadpoles by using a loss of righting reflex assay. Its in vitro metabolic half-life was measured in human liver S9 fraction, and the resulting metabolite was provisionally identified by using high-performance liquid chromatography/mass spectrometry techniques. The hypnotic and hemodynamic actions of MOC-etomidate, etomidate, and propofol were defined in rats. The abilities of MOC-etomidate and etomidate to inhibit corticosterone production were assessed in rats. Results MOC-etomidate potently enhanced gamma-aminobutyric acid type A receptor function and produced loss of righting reflex in tadpoles. Metabolism in human liver S9 fraction was first-order, with an in vitro half-life of 4.4 min versus more than 40 min for etomidate. MOC-etomidate's only detectable metabolite was a carboxylic acid. In rats, MOC-etomidate produced rapid loss of righting reflex that was extremely brief and caused minimal hemodynamic changes. Unlike etomidate, MOC-etomidate produced no adrenocortical suppression 30 min after administration. Conclusions MOC-etomidate is an etomidate analogue that retains etomidate's important favorable pharmacological properties. However, it is rapidly metabolized, ultra-short-acting, and does not produce prolonged adrenocortical suppression after bolus administration.

scholarly journals Analogues of Etomidate

2014 ◽  
Vol 121 (2) ◽  
pp. 290-301 ◽  
Author(s):  
Ervin Pejo ◽  
Peter Santer ◽  
Spencer Jeffrey ◽  
Hilary Gallin ◽  
S. Shaukat Husain ◽  
...  
Keyword(s):  
Adrenocorticotropic Hormone ◽  
Type A ◽  
Chiral Center ◽  
Aminobutyric Acid ◽  
Adrenocortical Function ◽  
Receptor Subtypes ◽  
Structure Activity ◽  
Acid Type ◽  
Righting Reflex

Abstract Background: R-etomidate possesses unique desirable properties but potently suppresses adrenocortical function. Consequently, efforts are being made to define structure–activity relationships with the goal of designing analogues with reduced adrenocortical toxicity. The authors explored the pharmacological impact of modifying etomidate’s chiral center using R-etomidate, S-etomidate, and two achiral etomidate analogues (cyclopropyl etomidate and dihydrogen etomidate). Methods: The γ-aminobutyric acid type A receptor modulatory potencies of drugs were assessed in oocyte-expressed α1(L264T)β3γ2L and α1(L264T)β1γ2L γ-aminobutyric acid type A receptors (for each drug, n = 6 oocytes per subtype). In rats, hypnotic potencies and durations of action were measured using a righting reflex assay (n = 26 to 30 doses per drug), and adrenocortical potencies were quantified by using an adrenocorticotropic hormone stimulation test (n = 20 experiments per drug). Results: All four drugs activated both γ-aminobutyric acid type A receptor subtypes in vitro and produced hypnosis and suppressed adrenocortical function in rats. However, drug potencies in each model ranged by 1 to 2 orders of magnitude. R-etomidate had the highest γ-aminobutyric acid type A receptor modulatory, hypnotic, and adrenocortical inhibitory potencies. Respectively, R-etomidate, S-etomidate, and cyclopropyl etomidate were 27.4-, 18.9-, and 23.5-fold more potent activators of receptors containing β3 subunits than β1 subunits; however, dihydrogen etomidate’s subunit selectivity was only 2.48-fold and similar to that of propofol (2.08-fold). S-etomidate was 1/23rd as potent an adrenocortical inhibitor as R-etomidate. Conclusion: The linkage between the structure of etomidate’s chiral center and its pharmacology suggests that altering etomidate’s chiral center may be used as part of a strategy to design analogues with more desirable adrenocortical activities and/or subunit selectivities.

scholarly journals γ-Aminobutyric Acid Type A (GABAA) Receptor Activation Modulates Tau Phosphorylation

2012 ◽  
Vol 287 (9) ◽  
pp. 6743-6752 ◽  
Author(s):  
Niko-Petteri Nykänen ◽  
Kai Kysenius ◽  
Prasanna Sakha ◽  
Päivi Tammela ◽  
Henri J. Huttunen
Keyword(s):  
Gabaa Receptor ◽  
Type A ◽  
Receptor Activation ◽  
Tau Phosphorylation ◽  
Aminobutyric Acid ◽  
Acid Type

scholarly journals Effects of γ-Aminobutyric Acid Type A Receptor Modulation by Flumazenil on Emergence from General Anesthesia

2016 ◽  
Vol 125 (1) ◽  
pp. 147-158 ◽  
Author(s):  
Seyed A. Safavynia ◽  
Glenda Keating ◽  
Iris Speigel ◽  
Jonathan A. Fidler ◽  
Matthias Kreuzer ◽  
...  
Keyword(s):  
General Anesthesia ◽  
Expression System ◽  
Type A ◽  
Aminobutyric Acid ◽  
Clinical Effects ◽  
General Anesthetics ◽  
Isoflurane Anesthesia ◽  
Receptor Modulation ◽  
Acid Type

Abstract Background Transitions into conscious states are partially mediated by inactivation of sleep networks and activation of arousal networks. Pharmacologic hastening of emergence from general anesthesia has largely focused on activating subcortical monoaminergic networks, with little attention on antagonizing the γ-aminobutyric acid type A receptor (GABAAR). As the GABAAR mediates the clinical effects of many common general anesthetics, the authors hypothesized that negative GABAAR modulators would hasten emergence, possibly via cortical networks involved in sleep. Methods The authors investigated the capacity of the benzodiazepine rescue agent, flumazenil, which had been recently shown to promote wakefulness in hypersomnia patients, to alter emergence. Using an in vivo rodent model and an in vitro GABAAR heterologous expression system, they measured flumazenil’s effects on behavioral, neurophysiologic, and electrophysiologic correlates of emergence from isoflurane anesthesia. Results Animals administered intravenous flumazenil (0.4 mg/kg, n = 8) exhibited hastened emergence compared to saline-treated animals (n = 8) at cessation of isoflurane anesthesia. Wake-like electroencephalographic patterns occurred sooner and exhibited more high-frequency electroencephalography power after flumazenil administration (median latency ± median absolute deviation: 290 ± 34 s) compared to saline administration (473 ± 186 s; P = 0.042). Moreover, in flumazenil-treated animals, there was a decreased impact on postanesthesia sleep. In vitro experiments in human embryonic kidney-293T cells demonstrated that flumazenil inhibited isoflurane-mediated GABA current enhancement (n = 34 cells, 88.7 ± 2.42% potentiation at 3 μM). Moreover, flumazenil exhibited weak agonist activity on the GABAAR (n = 10 cells, 10.3 ± 3.96% peak GABA EC20 current at 1 μM). Conclusions Flumazenil can modulate emergence from isoflurane anesthesia. The authors highlight the complex role GABAARs play in mediating consciousness and provide mechanistic links between emergence from anesthesia and arousal.

scholarly journals Carboetomidate

2010 ◽  
Vol 112 (3) ◽  
pp. 637-644 ◽  
Author(s):  
Joseph F. Cotten ◽  
Stuart A. Forman ◽  
Joydev K. Laha ◽  
Gregory D. Cuny ◽  
S. Shaukat Husain ◽  
...  
Keyword(s):  
Critically Ill ◽  
Critically Ill Patients ◽  
Type A ◽  
Aminobutyric Acid ◽  
Adrenocortical Function ◽  
Gamma Aminobutyric Acid ◽  
Wild Type ◽  
High Affinity ◽  
Acid Type

Background Etomidate is a sedative hypnotic that is often used in critically ill patients because it provides superior hemodynamic stability. However, it also binds with high affinity to 11beta-hydroxylase, potently suppressing the synthesis of steroids by the adrenal gland that are necessary for survival. The authors report the results of studies to define the pharmacology of (R)-ethyl 1-(1-phenylethyl)-1H-pyrrole-2-carboxylate (carboetomidate), a pyrrole analog of etomidate specifically designed not to bind with high affinity to 11beta-hydroxylase. Methods The hypnotic potency of carboetomidate was defined in tadpoles and rats using loss of righting reflex assays. Its ability to enhance wild-type alpha1beta2gamma2l and etomidate-insensitive mutant alpha1beta2M286Wgamma2l human gamma-aminobutyric acid type A receptor activities was assessed using electrophysiologic techniques. Its potency for inhibiting in vitro cortisol synthesis was defined using a human adrenocortical cell assay. Its effects on in vivo hemodynamic and adrenocortical function were defined in rats. Results Carboetomidate was a potent hypnotic in tadpoles and rats. It increased currents mediated by wild-type but not etomidate-insensitive mutant gamma-aminobutyric acid type A receptors. Carboetomidate was a three orders of magnitude less-potent inhibitor of in vitro cortisol synthesis by adrenocortical cells than was etomidate. In rats, carboetomidate caused minimal hemodynamic changes and did not suppress adrenocortical function at hypnotic doses. Conclusions Carboetomidate is an etomidate analog that retains many beneficial properties of etomidate, but it is dramatically less potent as an inhibitor of adrenocortical steroid synthesis. Carboetomidate is a promising new sedative hypnotic for potential use in critically ill patients in whom adrenocortical suppression is undesirable.

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