title: A cycloartane glycoside derived from Actaea racemosa L. modulates GABAA receptors and induces pronounced sedation in mice.
abstract: 23-O-Acetylshengmanol 3-O-β-D-xylopyranoside (Ac-SM) isolated from Actaea racemosa L.-an herbal remedy for the treatment of mild menopausal disorders-has been recently identified as a novel efficacious modulator of GABAA receptors composed of α1-, β2-, and γ2S-subunits. In the present study, we analyzed a potential subunit-selective modulation of GABA-induced chloride currents (IGABA) at GABA concentrations eliciting 3-8% of the maximal GABA response (EC3-8) through nine GABAA receptor isoforms expressed in Xenopus laevis oocytes by Ac-SM with two-microelectrode voltage clamp and behavioral effects 30 minutes after intraperitoneal application in a mouse model. Efficacy of IGABA enhancement by Ac-SM displayed a mild α-subunit dependence with α2β2γ2S (maximal IGABA potentiation [Emax] = 1454 ± 97%) and α5β2γ2S (Emax = 1408 ± 87%) receptors being most efficaciously modulated, followed by slightly weaker IGABA enhancement through α1β2γ2S (Emax = 1187 ± 166%), α3β2γ2S (Emax = 1174 ± 218%), and α6β2γ2S (Emax = 1171 ± 274%) receptors and less pronounced effects on receptors composed of α4β2γ2S (Emax = 752 ± 53%) subunits, whereas potency was not affected by the subunit composition (EC50 values ranging from α1β2γ2S = 35.4 ± 12.3 µM to α5β2γ2S = 50.9 ± 11.8 µM). Replacing β2- with β1- or β3-subunits as well as omitting the γ2S-subunit affected neither efficacy nor potency of IGABA enhancement by Ac-SM. Ac-SM shifted the GABA concentration-response curve toward higher GABA sensitivity (about 3-fold) and significantly increased the maximal GABA response by 44 ± 13%, indicating a pharmacological profile distinct from a pure allosteric GABAA receptor modulator. In mice, Ac-SM significantly reduced anxiety-related behavior in the elevated plus maze test at a dose of 0.6 mg/kg, total ambulation in the open field test at doses ≥6 mg/kg, stress-induced hyperthermia at doses ≥0.6 mg/kg, and significantly elevated seizure threshold at doses ≥20 mg/kg body weight. High efficacy and long biologic half-life of Ac-SM suggest that potential cumulative sedative side effects upon repetitive intake of A. racemosa L. preparations might not be negligible.
authors.affiliation: Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria (B.S., S.K., S.H.); Department of Pharmacology, Medical University Innsbruck, Innsbruck, Austria (I.K., C.S.); and Institute of Pharmacy/Pharmacognosy, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria (S.S.C., H.S.).
authors.forename: Barbara
authors.initials: B
authors.lastname: Strommer
authors.affiliation: Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria (B.S., S.K., S.H.); Department of Pharmacology, Medical University Innsbruck, Innsbruck, Austria (I.K., C.S.); and Institute of Pharmacy/Pharmacognosy, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria (S.S.C., H.S.).
authors.forename: Sophia
authors.initials: S
authors.lastname: Khom
authors.affiliation: Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria (B.S., S.K., S.H.); Department of Pharmacology, Medical University Innsbruck, Innsbruck, Austria (I.K., C.S.); and Institute of Pharmacy/Pharmacognosy, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria (S.S.C., H.S.).
authors.forename: Iris
authors.initials: I
authors.lastname: Kastenberger
authors.affiliation: Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria (B.S., S.K., S.H.); Department of Pharmacology, Medical University Innsbruck, Innsbruck, Austria (I.K., C.S.); and Institute of Pharmacy/Pharmacognosy, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria (S.S.C., H.S.).
authors.forename: Serhat Sezai
authors.initials: SS
authors.lastname: Cicek
authors.affiliation: Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria (B.S., S.K., S.H.); Department of Pharmacology, Medical University Innsbruck, Innsbruck, Austria (I.K., C.S.); and Institute of Pharmacy/Pharmacognosy, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria (S.S.C., H.S.).
authors.forename: Hermann
authors.initials: H
authors.lastname: Stuppner
authors.affiliation: Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria (B.S., S.K., S.H.); Department of Pharmacology, Medical University Innsbruck, Innsbruck, Austria (I.K., C.S.); and Institute of Pharmacy/Pharmacognosy, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria (S.S.C., H.S.) schwarzer.christoph@i-med.ac.at.
authors.forename: Christoph
authors.initials: C
authors.lastname: Schwarzer
authors.affiliation: Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria (B.S., S.K., S.H.); Department of Pharmacology, Medical University Innsbruck, Innsbruck, Austria (I.K., C.S.); and Institute of Pharmacy/Pharmacognosy, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria (S.S.C., H.S.).
authors.forename: Steffen
authors.initials: S
authors.lastname: Hering
mesh_terms: D000818:Animals; D002712:Chlorides / Q000378:metabolism; D031885:Cimicifuga / Q000737:chemistry*; D006027:Glycosides / Q000494:pharmacology*; D006207:Half-Life; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009043:Motor Activity / Q000187:drug effects; D009865:Oocytes / Q000378:metabolism; D011963:Receptors, GABA-A / Q000378:metabolism*; D014315:Triterpenes / Q000494:pharmacology*; D014982:Xenopus laevis / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D002712:Chlorides; D006027:Glycosides; D006993:Hypnotics and Sedatives; D011963:Receptors, GABA-A; D014315:Triterpenes; C085352:cycloartane; D005680:gamma-Aminobutyric Acid