Prediction of the effects of Volatile Anesthetics on GABAA receptor in complex with GABA by Molecular Modelling

Anesthesia, the reversible pharmacological suspension of conscious brain activity, is a cornerstone of modern surgery and has been one of the main drivers of its progress, as it allows patients to undergo procedures without feeling pain (analgesia) or anxiety (due to unconsciousness), nor having memory of the surgical procedure (amnesia). Despite these considerations, the molecular mechanism by which anesthetics exert their action is still not fully understood and remains an active subject of study: over the years, several hypotheses have been proposed by the scientific community. Initially, the so-called “lipid theory” had a substantial support, according to which anesthetics, being lipophilic drugs, would exert their action by penetrating biological membranes and thereby altering its physical-chemical characteristics and permeability. Most recently, the currently widely accepted hypothesis is the ion channel and protein theory, which suggests that the mechanism by which anesthetics act is related to their interaction with ion channels on the membrane of nerve cells as well as their interaction with receptors, that allosterically influence ion channels. Supporting this hypothesis, it has been demonstrated that some drugs interact with increased affinity with the gamma-aminobutyric acid type A receptor (GABAA receptor). The latter is an ion channel that adopts an open conformation when activated by its agonist (gamma-aminobutyric acid, or GABA), allowing chloride ions to enter the neuron and causing hyperpolarization, resulting in an inhibitory effect. Indeed, GABA is the most important inhibitory neurotransmitter in the central nervous system. General anesthetics have been found to be positive allosteric modulators of GABAAR and alter its conformation, thereby increasing the probability that GABA will bind to the receptor, enhancing its inhibitory effects. The present thesis investigated the molecular-level behaviour of inhalation anesthetics, in particular Isoflurane, Sevoflurane, and Desflurane, in their interaction with the GABAA ion channel in complex with its ligand, GABA. To this end, molecular models of the Human GABAA receptor alpha1-beta2-gamma2 subtype, in complex with GABA, have been created and subsequently simulated together with the phospholipid bilayer through molecular dynamics (MD) simulations. Simulations have been performed in the absence and in the presence of volatile anesthetics, using a flood MD approach. Simulations shed light on the permeation dynamics of anesthetics and allowed to map the binding hotspots of VAs on the receptor, and to study its conformational behaviour. This study lays the groundwork for an improved understanding of how pharmacologically and chemically diverse and clinically essential drugs synergically act to enhance inhibitory signalling in the brain.