6,2′-Dihydroxyflavone, a subtype-selective partial inverse agonist of GABAA receptor benzodiazepine site

Neuroactivity of a number of flavonoids is mediated by modulation of type A γ-aminobutyric acid (GABAA) receptor function via benzodiazepine sites, mostly as partial agonists. In the present study, 6,2′-dihydroxyflavone (DHF) was characterized for potential inverse agonistic activity, and its mechanism of action was explored for receptor subtype selectivity. In whole-cell patch clamp studies on neuroblastoma IMR-32 cells expressing native GABAA receptors, DHF decreased GABA-induced currents, to an extent similar to that induced by the partial inverse agonist FG-7142, which could be blocked by flumazenil, a BZ site antagonist. In mouse behavioral models, DHF elicited significant anxiogenic-like effects in the elevated plus-maze test, and enhanced cognitive performance in the step-through passive avoidance test, as expected for an inverse agonist. However, DHF did not exhibit any proconvulsant effects, a typical action of inverse agonists. In electrophysiological studies on subtypes of recombinant GABAA receptors expressed in HEK 293T cells, DHF decreased GABA-induced currents in α1β3γ2, α2β3γ2, or α5β3γ2, but not α3β3γ2 receptors. The results demonstrated DHF as a partial inverse agonist-like modulator of GABAA receptors with selectivity in receptor subtypes as well as behavioral effects. The DHF subtype-selectivity suggested that α3-containing subtypes could be a mediator of the convulsion activities of GABAA receptor inverse agonists. Moreover, the pharmacological profile displayed in mouse behavioral models supported DHF as a useful lead compound for the development of cognition-enhancing agents devoid of convulsion side effects.