Simultaneous Determination of Seven Anthraquinone Aglycones of Crude and Processed Semen Cassiae Extracts in Rat Plasma by UPLC–MS/MS and Its Application to a Comparative Pharmacokinetic Study

Semen cassiae is the ripe seed of Cassia obtusifolia L. or Cassia tora L. of the family Leguminosae. In traditional Chinese medicine, the two forms of Semen cassiae are raw Semen cassiae (R-SC) and parched Semen cassiae (P-SC). To clarify the processing mechanism of Semen cassiae, the pharmacokinetics of R-SC and P-SC extracts were examined. A simple, rapid, sensitive ultra-high-performance liquid chromatography–tandem mass spectroscopy (UPLC-MS/MS) method was developed and validated for the simultaneous determination of seven anthraquinone aglycones of Semen cassiae (aurantio-obtusin, obtusifolin, questin, 2-hydroxyemodin-1-methyl-ether, rhein, emodin, 1,2,7-trimethoxyl-6,8-dihydroxy-3-methylanthraquinone) to compare the pharmacokinetics of raw and parched Semen cassiae in rat plasma. Compared with the R-SC group, Cmax and AUC0-12 tended to be higher in the P-SC group. In particular, Cmax values for aurantio-obtusin, obtusifolin, questin, 2-hydroxyemodin-1-methyl-ether and rhein were significantly higher in the P-SC group (p < 0.05). Meanwhile, Tmax and MRT0-12 tended to be lower in the P-SC group. Specifically, Tmax for aurantio-obtusin and 2-hydroxyemodin-1-methyl-ether and MRT0-12 for obtusifolin and rhein were significantly higher in the P-SC group (p < 0.05).