An LC–MS method for simultaneous determination of five iridoids from Zhi-zi-chi Decoction in rat brain microdialysates and tissue homogenates: Towards an in depth study for its antidepressive activity

• LC–MS method was developed for simultaneous determination of five iridoids in brain.
• Microdialysis coupled with brain tissue homogenate method was applied to the brain study.
• The observations could contribute to the study of antidepressant.

Zhi-zi-chi Decoction has been clinically utilized for the treatment of depression for more than thousand years. In order to investigate the possible bioactive components that could pass through the blood brain barrier (BBB) and the mechanism of antidepressant, a sensitive LC–MS method was developed to detect the ingredients (geniposide, scandoside methyl ester, gardenoside, deacetyl asperulosidic acid methyl ester and genipin-1-β-gentiobioside) in rat brain microdialysates and tissue homogenates samples (hippocampus, hypothalamus, premotor cortex, striatum, oblongata and cerebellum). Method development and validation are described in terms of calibration curves, extraction yield, lower limit of quantification (LLOQ), precision, accuracy, intra- and inter-day variability, which are in accordance with the requirements. Microdialysis in hippocampus demonstrated that the five iridoids possessed complete pharmacokinetic process while brain tissue homogenate method testified the distribution regularity in brain. The work clarified that the five iridoids, as antidepressant ingredients, could pass through the BBB, distribute targeted and possess complete pharmacokinetics in brain. These observations, along with the large database of rat brain microdialysates and tissue homogenates data, could enable future efforts aimed to improve our understanding of the relationship between bioactive ingredients and clinical therapy of depression.