The general anesthetic etomidate and fenamate mefenamic acid oppositely affect GABAAR and GlyR: a structural explanation

Abstract

GABA and glycine act as inhibitory neurotransmitters in the CNS. Inhibitory neurotransmission is mediated via activation of ionotropic GABA A and glycine receptors. We used a modeling approach to explain the opposite effects of the general anesthetic etomidate (ETM) and fenamate mefenamic acid (MFA) on GABA-and glycine-activated currents recorded in isolated cerebellar Purkinje cells and hippocampal pyramidal neurons, respectively. These drugs potentiated GABA A Rs but blocked GlyRs. We built a homology model of α1β GlyR based on the cryo-EM structure of open α1 GlyR, used the α1β3γ2 GABA A R structure from the PDB, and applied Monte-Carlo energy minimization to optimize models of receptors and ligand-receptor complexes. In silico docking suggests that ETM/MFA bind at the transmembrane β(+)/α(−) intersubunit interface in GABA A R. Our models predict that the bulky side chain of the highly conserved Arg 19′ residue at the plus interface side wedges the interface and maintains the conducting receptor state. We hypothesized that MFA/ETM binding at the β(+)/α(−) interface leads to prolongation of receptor lifetime in the open state. Having analyzed different GABA A R and GlyR structures available in the PDB, we found that mutual arrangement of the Arg 19′ and Gln −26′ side chains at the plus and minus interface sides, respectively, plays an important role when the receptor switches from the open to closed state. We show that this process is accompanied by narrowing of the intersubunit interfaces, leading to extrusion of the Arg 19′ side chain from the interface. Our models allow us to explain the lack of GlyR potentiation in our electrophysiological experiments.

Structural insights into GABAA receptor potentiation by Quaalude

“…4b ). Finally, when comparing complexes where the ion channel is in a resting-like state, we observed another, distinct βR269 orientation that has been noted before 52 . In the receptor structures bound by the competitive antagonist bicuculline (6X3S, 6HUK) 28 , 30 , and by the pore blocker picrotoxin (6HUG, 6X40, 6HUJ) 28 , 30 , βR269 resides at the interface of M2 and M1 helices of the complementary subunits (Supplementary Fig.…”

“…These observations suggest three distinct conformations of the arginine located at the top of the β/α allosteric binding site, and its spatial orientation seems to be linked with the receptor state and/or the modulator occupancy of this interface. The βR269 residue, which is conserved across all (except for ρ) GABA A R and α GlyR subunits, has been suggested to play an important role in conformational changes of the receptor during gating [52][53][54][55][56][57] . Although the 19′ arginine is highly conserved, this conformational change is unique to the β subunit and is observed only at the β/α TMD binding pocket.…”

The Toxicity and Therapeutic Efficacy of Mefenamic Acid and its Hydroxyethyl Ester in Mice: In Vivo Comparative Study: A promising Drug Derivative

“…However, a line of molecular research revealed that MFA is capable to interact with GABAergic function in a dose-dependent manner. (33,34). In this regard, the ability of HEMA to prevent CNS toxicity is assumed to be attributable to pharmacokinetic changes or a change in drug release profile that reduce the risk of GABAergic disruption.…”

Etomidate Depresses Spontaneous Complex Spikes Activity of Cerebellar Purkinje Cells via Cannabinoid 1 Receptor in vivo in Mice

“…Etomidate is an ultrashort-acting nonbarbiturate intravenous anesthetic, which is used for the induction of general anesthesia in clinic. Pharmacological studies reveal that etomidate produces sedation by activation of γ-aminobutyric acid type A (GABA A ) receptors [6][7][8][9][10][11]. Electrophysiological studies demonstrate that etomidate enhances the GABA-mediated Clcurrents and increases GABAergic inhibitory synaptic transmission [6][7][8][9][10][11].…”

“…Pharmacological studies reveal that etomidate produces sedation by activation of γ-aminobutyric acid type A (GABA A ) receptors [6][7][8][9][10][11]. Electrophysiological studies demonstrate that etomidate enhances the GABA-mediated Clcurrents and increases GABAergic inhibitory synaptic transmission [6][7][8][9][10][11]. Application of etomidate at a clinically relevant concentration potentiates GABA A receptor-mediated currents by increasing open probability, membrane conductance, and the open time of single Clchannel in isolated hippocampal neurons [12,13].…”