Three-Step Test System for the Identification of Novel GABA_A Receptor Modulating Food Plants

Potentiation of γ-amino butyric acid (GABA)-induced GABA_A receptor (GABA_AR) activation is a common pathway to achieve sedative, sleep-enhancing, anxiolytic, and antidepressant effects. Presently, a three-component test system was established for the identification of novel GABA_AR modulating food plants. In the first step, potentiation of GABA-induced response of the GABA_AR was analysed by two-electrode voltage clamp (TEVC) for activity on human α1β2-GABA_AR expressed in Xenopus laevis oocytes. Positively tested food plants were then subjected to quantification of GABA content by high-performance liquid chromatography with fluorescence detection (HPLC-FLD) to exclude test foods, which evoke a TEVC-response by endogenous GABA. In the third step, specificity of GABA_A-modulating activity was assessed by TEVC analysis of Xenopus laevis oocytes expressing the homologous glycine receptor (GlyR). The three-component test was then applied to screen 10 aqueous extracts of food plants for their GABA_AR activity. Thus, hop cones (Humulus lupulus) and Sideritis sipylea were identified as the most potent specific GABA_AR modulators eliciting significant potentiation of the current by 182 ± 27 and 172 ± 19 %, respectively, at the lowest concentration of 0.5 μg/mL. The extracts can now be further evaluated by in vivo studies and by structural evaluation of the active components.