A selective and sensitive UFLC-MS/MS method for the simultaneous determination of five alkaloids from Piper longum L. and its application in the pharmacokinetic study of 6-OHDA-induced Parkinson's disease rats
The alkaloids from Piper longum L. (PLA) mainly contain piperine (PPR), piperlongumine (PPL), Δα,β-dihydropiperlonguminine (DPPL), piperanine (PPRA) and pellitorine (PLTR), which have neuroprotective effects on a 6-OHDA-induced rat model of Parkinson's disease (PD). To elucidate the pharmacokinetic profiles of these main compounds in PD rats, we developed a rapid, selective and sensitive ultra-fast liquid chromatography-electronic spray ionization-tandem mass spectrometry (UFLC-ESI-MS/MS) method which was validated for the simultaneous determination of the 5 absorbed compounds in the plasma of 6-OHDA-induced PD rats. The plasma samples were pretreated using a protein precipitation method with methanol/acetonitrile (1 : 1, v/v). The analytes and internal standard (IS) were separated on a Phenomenex Gemini C18 column using gradient elution with a mobile phase consisting of acetonitrile and a 0.1% formic acid aqueous solution at a flow rate of 0.5 mL min−1. The total chromatographic running time was 4.5 min. The detection was performed with positive electrospray ionization (ESI) using the multiple reaction monitoring (MRM) mode of transitions at m/z 286.2 → 201.2, m/z 274.2 → 201.2, m/z 276.2 → 135.1, m/z 288.2 → 135.1, m/z 224.1 → 168.2, and m/z 472.1 → 436.1 for PPR, PPL, DPPL, PPRA, PLTR and IS, respectively. All five analytes showed excellent linearity (R > 0.995) within the concentration range of 0.20–5000 ng mL−1. The established method was then applied to investigate the pharmacokinetics of multi-components (PPR, PPL, DPPL, PPRA and PLTR) in PD rats after oral administration of PLA. The results showed that no obvious differences were observed in the pharmacokinetic parameters of PPR, PPL, DPPL, PPRA and PLTR in PD rats compared with those in sham rats after oral administration of PLA except for MRTs for PPR, PPL and PLTR. Additionally, the activities of superoxide dismutase (SOD) were related to the concentrations of the multi-components in plasma.