Sensitive and robust UPLC–MS/MS method to determine the gender-dependent pharmacokinetics in rats of emodin and its glucuronide

In this study, a sensitive and robust ultraperformance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method was developed, validated, and applied to determine gender-dependent pharmacokinetics of total emodin (aglycone + glucuronide) in male and female Sprague–Dawley rats. The lower limit of quantification for emodin and emodin glucuronide in rat plasma was 39 and 78 ng/ml, with signal-to-noise ratio of ≥10. Precision and accuracy studies showed emodin and emodin glucuronide plasma concentrations well within the 10% range in all studies. Plasma recovery of emodin and emodin glucuronide was always above 86% for low (emodin: 39 ng/ml; glucuronide: 78 ng/ml), 92% for medium (625 ng/ml), and 97% for high (10 000 ng/ml) concentrations. Furthermore, emodin showed more than 95% plasma stability under short-term and long-term storage conditions, as well as after three freeze–thaw cycles in the experiments. The developed and validated analytical method was successfully applied to study the gender-dependent 10-fold higher oral bioavailability of total emodin in male than female rats. The oral bioavailability of emodin and emodin glucuronide was also measured separately and showed a statistically significant gender difference in oral bioavailability of emodin and emodin glucuronide in rats.