Pharmacokinetics and tissue distribution of Aucubin, Ajugol and Catalpol in rats using a validated simultaneous LC-ESI-MS/MS assay

To enable an investigation of pharmacokinetics and tissue distribution of Aucubin, Ajugol and Catalpol in rats, a high-performance liquid chromatography-electro spray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) method was developed for the simultaneous quantitative determination of the three compounds. Biological samples were prepared by a simple protein precipitation with methanol (containing 0.05% formic acid). The analytes were separated by a C₁₈ reversed phase column and detected with a triple quadrupole tandem mass spectrometer in the multiple-reaction monitoring (MRM) mode to monitor the precursor-to-product ion transitions of m/z 364.3→149.0 for Aucubin, m/z 366.5→151.1 for Ajugol, m/z 380.0→183.3 for Catalpol and m/z 530.3→183.1 for Picroside-II (IS) in positive ionization. Good linearity of each calibration curve was produced over the concentration range of 1-1000ng/mL. The lower limit of quantification (LLOQ) was 1ng/mL for the three analytes. This method was successfully applied to the pharmacokinetic and tissue distribution studies of Aucubin, Ajugol and Catalpol in rat. The current results revealed pharmacokinetic behaviors of the herb compound and provided novel evidence of the presence of Aucubin and Catalpol in rat brain. The acquired data would be helpful for the clinical application and further studies of Traditional Chinese Medicines (TCM) with active ingredients of Iridoid Glycosides.