Browsing by Subject "Carisoprodol"
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Item Carisoprodol's Pharmacological Properties at GABAA Receptors, In-vitro and In-silico Studies(2021-05) Claudio, Maria del Carmen; Sumien, Nathalie; Huang, Ren-Qi; Gonzales, Eric B.; Dillon, Glenn H.; Mathew, Porunelloor A.Carisoprodol (CSP) is a centrally-acting prescription muscle relaxant that can directly activate, allosterically modulate and inhibit GABAA receptors. The GABAA receptor is a pentameric chloride ion channel in the cys-loop receptor family. The mechanism of GABAA's inhibitory role in the central nervous system lies in the resulting hyperpolarized state of the cell following chloride ion influx upon ligand binding. GABAA receptors are the target of many different clinically prescribed compounds because of the role they play in regulating the central nervous system. We used pharmacological and computational approaches to investigate the underlying mechanism mediating carisoprodols effects at GABAA receptors, with the ultimate goal of generating a new subunit selective compound related to the structure of carisoprodol and gaining a more thorough understanding of the molecular interaction governing carisoprodol's pharmacoglogical effects. Our evaluation of novel compounds related to the structure of carisoprodol did not yield promising leads, though the potential still remains for development of a novel carisoprodol-related compound with a unique selectivity profile. Probe for a binding site mediating carisoprodols postive modulatory effects and evaluation of additional novel compounds was eventually hindered by time. Our investigaiton into carisoprodol's direct gating effects involved a previously reported single amino acid residue, L415, located at the top of the fourth transmembrane domain (TM4) in the ɑ1 subunit of the GABAA receptor that is critical to carisoprodol's direct gating. Whether the residue is involved in a carisoprodol binding site remained unsolved. In studies probing for a binding site for carisprodol's direct activation of GABAA receptors, promising computaitonal docking data was not able to be validated with elecrophysiology and site-directed mutatgenesis studies, indicating that the residues revealed in docking studies do not form a binding pocket for carisprodol's direct activation effect. Our site directed mutagenesis, electrophysiology and molecular dynamic simulation studies to investigate carisoprodol's inhibitory effects at GABAA receptors revealed a binding site at the Cl- channel pore, in a mechanism similar to picrotoxin, providing a mechanism of action for carisoprodol's inhibitory effects at GABAA receptors.Item Elucidation of the Mechanism of Action of Carisoprodol at GABAA Receptors(2009-05-01) Gonzalez, Lorie A.; Dillon, Glenn H.Carisoprodol is an increasingly abused, centrally-acting muscle relaxant. Its sedative effects, which contribute to its therapeutic and recreational use, are attributed to its metabolite, meprobamate, a controlled substance with barbiturate-like activity at GABAA receptors (GABAARs). GABAARs are ion channel-coupled protein complexes underlying the majority of fast synaptic inhibition in the central nervous system. Recent evidence suggests carisoprodol may act independently of meprobamate. Thus, we used behavioral and pharmacological approaches to investigate carisoprodol’s effects on GABAAR function with the ultimate goal of elucidating its mechanism of action at these receptors. In mice, the time course of locomotor depression was comparable for carisoprodol (intraperitoneal or oral) versus meprobamate (intraperitoneal). GABAergic ligands substituted for carisoprodol in drug discrimination studies using carisoprodol trained rats. As observed in vitro, carisoprodol’s effects were antagonized by bemegride, a barbiturate antagonist, but not by the benzodiazepine site antagonist flumazenil, suggesting carisoprodol produces barbiturate-like effects in vivo. Moreover, whole-cell patch clamp recordings were obtained from HEK293 cells expressing human α1β2 and αxβzγ2 (where x = 1-4 and z = 1-2) GABAARs. Each receptor configuration was directly activated and allosterically modulated by carisoprodol in a barbiturate-like manner. Carisoprodol efficacy, but not potency, was subunit-dependent with α and β isoforms contributing to carisoprodol site(s) of action. Notably, carisoprodol was more efficacious at α1-containing receptors, consistent with its sedative effects and abuse potential. Homomeric glycine α1 and GABA ρ1 receptors were carisoprodol-insensitive. Despite similarities between carisoprodol and barbiturates, their sites of action are likely not equivalent as barbiturate-sensitive ρ1W328M subunits were carisoprodol-insensitive. However, chimeric ρ1/α1 receptors gained sensitivity to modulation, but not direct activation by carisoprodol. Our findings indicate carisoprodol modulates GABAARs in a subunit- and receptor-dependent manner, contributing to its pharmacological profile and possibly its abuse potential. Furthermore, partial restoration of modulation, but not direct gating by carisoprodol suggests this drug may mediate its effects via multiple sites on GABAARs.