Quantitation Assay for Absorption and First-Pass Metabolism of Emodin in Isolated Rat Small Intestine Using Liquid Chromatography-Tandem Mass Spectrometry

Emodin has numerous biochemical and pharmacological activities, though information about its intestinal absorption and first-pass metabolism is scarce. The purpose of this study was to evaluate intestinal absorption and metabolism of luminally administered emodin in an isolated rat small intestine using the method of LC/MS/MS. About 22.55% of the administered emodin appeared at the vascular side, chiefly as free emodin (12.01%), but some emodin glucuronide (8.69%) and sulfate (1.84%) were also detected. Free glucuronide (5.23%) and sulfate (1.08%) moieties were found in the luminal perfusate. This model serves as a valuable tool for understanding intestinal handling of emodin, and our results confirm absorption and first-pass metabolism of emodin in the rat small intestine. Phase II metabolic enzymes such as glucuronyl transferase or sulfate transferase may also play an important role in the first-pass metabolism of emodin in the small intestine, which may ultimately reduce the bioavailability (and thus the efficacy) of orally administered emodin.