Flavan-3-ol derivatives are positive modulators of GABAA receptors with higher efficacy for the α2 subtype and anxiolytic action in mice

Recent genetic and pharmacological studies have demonstrated that α2-containing GABAA receptors mediate the anxiolytic effects of benzodiazepines, setting a new strategy in developing novel, non-sedative anxiolytic agents. In this study we show that stereoisomers of 3-acetoxy-4′-methoxyflavan are positive modulators of recombinant α1,2,3,5β2γ2L and α1β2 GABAA receptors expressed in Xenopus laevis oocytes. GABAC receptors are insensitive to modulation by these compounds. In each case, the enhancement was evident at low micromolar concentrations and occurred independently of the classical high affinity benzodiazepine site, as it could not be blocked by the antagonist flumazenil. Importantly, the compound Fa131 was significantly more efficacious at enhancing GABA-induced currents (EC5) at α2β2γ2L receptors compared to α1β2γ2L, α3β2γ2L and α5β2γ2L receptors (Emax = 21.0 ± 1.7 times, compared to 8.5 ± 0.7 times at α1-, 9.5 ± 0.6 times at α3- and 5.2 ± 0.4 times at α5-contaning GABAA receptors), suggesting a potential use as an anxiolytic. In mice, this agent (1–30 mg/kg i.p.) induced anxiolytic-like action in two unconditioned models of anxiety: the elevated plus maze and the light/dark paradigms. No sedative or myorelaxant effects were detected using the hole board, actimeter and horizontal wire tests, and only weak barbiturate-potentiating effects on the loss of righting reflex test. Fa131 demonstrated improved segregation of anxiolytic and sedative doses when compared to the non-selective agonist diazepam. Finally, flavan derivatives highlight the potential of targeting non-benzodiazepine allosteric sites in the search for new anxioselective drugs.