Prolonging effects of Valeriana fauriei root extract on pentobarbital-induced sleep in caffeine-induced insomnia model mice and the pharmacokinetics of its active ingredients under conditions of glycerol fatty acid ester as emulsifiers

Abstract

Ethnopharmacological relevance: Valeriana plant roots have traditionally been used to treat central nervous system-related disorders in European countries. Among this genus, the Japanese Pharmacopoeia registers the dried roots of V. fauriei Briq. (VF). However, insufficient pharmacological data are available for this species.

Aim of the study: We investigated the sedative effects of VF extract in a murine caffeine-induced insomnia model as well as the active ingredients and their pharmacokinetics to determine its basic pharmacological action mechanisms under conditions glycerol fatty acid ester is used as emulsifiers.

Materials and methods: A murine insomnia model was created by caffeine. Samples derived from the ethanol extract of VF were administered per oral (p.o.), and caffeine was injected intraperitoneally (i.p.). Pentobarbital was injected i.p. and the sleep latency and duration were measured. To confirm the mechanism of action of VF, flumazenil, a specific γ-aminobutyric acid receptor type A (GABA_A receptor) antagonist, was administered (i.p.) immediately prior to the sample administration. We examined the pharmacokinetic profiles of the active ingredients in the plasma, brain, urine, and feces of mice after the administration (p.o and intravenous (i.v.)) of VF samples.

Results: VF extract (5 g as VF/kg, p.o.) significantly shorten sleep latency and prolonged pentobarbital-induced sleep in caffeine-induced insomnia mice, partially mediated via the GABAergic nervous system, although a higher dose (10 g as VF/kg, p.o.) was required to exhibit the significant effects in normal mice. Kessyl glycol diacetate (KGD), the main constitutive compound in VF, did not shorten sleep latency but exhibited the same sleep prolonged effect at a dose related to VF extract. The concentration of kessyl glycol 8-acetate (KG8) in the plasma was higher than that of KGD in mice treated (p.o.) with VF extract. The profiles of brain concentrations of KGD and KG8 were similar to those in the plasma, and approximately 20% of those in the plasma were distributed throughout the brain. The excretions of KGD and KG8 in urine and feces was slightly detected, and an unknown large peak related to KG8 was detected in the urine of mice administered with VF extract by HPLC-MS/MS analysis.

Conclusions: VF exhibits more sedative effects under stressed conditions, such as insomnia, and the major active ingredients are KGD and its metabolite KG8, which are distributed from the blood circulation into the brain by simple diffusion. KG8 is further metabolized into other metabolites that are easily excreted in the urine.

Keywords: Capsaicin; Diazepam; Distribution; Kessyl glycol; Kessyl glycol 2-acetate; Kessyl glycol 8-acetate; Kessyl glycol diacetate; Sedative; Umbelliferone; Valeriana fauriei root; γ-aminobutyric acid receptor type a.