Application of microdialysis for elucidating the existing form of hyperoside in rat brain: comparison between intragastric and intraperitoneal administration.

Hypericum perforatum (St. John's wort) is an important anti-depressant herb used in clinic and commonly prescribed for mild depression. Hyperoside is one of the major components of H. perforatum and is also detected in many plant species such as Abelmoschus manihot, Black Currant, Rosa agrestis, Apocynum venetum and Nelumbo nucifera. As the hyperoside showed CNS (central nervous system) protective activity (e.g. anti-depressant-like effect), the possibility of hyperoside or its metabolites to reach CNS should be investigated. Moreover, the pharmacokinetics profile of hyperoside or its metabolites in rat brain should be studied for further elucidating the mechanism of hyperoside action on CNS. A simple method for simultaneous determination of unbound hyperoside and its metabolite 3'-O-methyl-hyperoside in rat brain was developed by using ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) and microdialysis technique. This method was applied for pharmacokinetics study of hyperoside and 3'-O-methyl-hyperoside in rat brain after intragastric (i.g.) and intraperitoneally (i.p.) administration of hyperoside in vivo. Results showed that neither hyperoside nor its metabolites were detected in rat brain after i.g. administration but both compounds could be detected after i.p. administration. Considering the activity of hyperoside through both i.g. and i.p. administration, our results imply that the active components of hyperoside in vivo might be different. Therefore, further studies are needed to identify the active components of hyperoside in vivo through these two different routes. Moreover, non-oral administration route (e.g., i.p.) should be further investigated and be explored to obtain higher bioavailability and better activity for hyperoside. Our results also showed that the real existing form of hyperoside in rat brain were hyperoside and its methylated metabolite with maximum concentration to be 63.78 ng/mL and 24.66 ng/mL after 20mg/kg i.p. administration, respectively. Therefore, a more reasonable concentration of hyperoside should be considered in in vitro assay to reflect the real situation of hyperoside concentration in vivo. Due to the wide use of herbal remedies containing hyperoside, our investigation will contribute to further clarifying the action of this substance. Moreover, this method will be applied for clinical pharmacokinetics study of hyperoside and its metabolite as well as herbs that contain hyperoside.