LAUSR

BACKGROUND Timosaponin A-III is one of the most promising active saponins from Anemarrhena asphodeloides Bge. As an oral chemotherapeutic agent, there is an urgent need to clarify its biopharmaceutics and pharmacokinetics to improve its development potential. OBJECTIVE This research explores the bioavailability of timosaponin A-III and clarifies its absorption and metabolism mechanisms by a sensitive and specific HPLC-MS/MS method. METHODS Pharmacokinetics and bioavailability studies of timosaponin A-III were performed in Sprague-Dawley rats by oral (20 g/kg) and intravenous administration (2 mg/kg). Control group was given the same volume of normal saline. The absorption of timosaponin A-III was investigated in a rat intestinal perfusion model in situ and a Caco-2 cell transport model in vitro. The metabolic rate of timosaponin A-III was determined in a rat liver microsome incubation system. RESULTS After the oral administration, timosaponin A-III reached Cmax of 120.90 ± 24.97 ng/mL at 8 h, and the t1/2 was 9.94 h. The absolute oral bioavailability of timosaponin A-III is 9.18%. The permeability coefficients of timosaponin A-III in four intestinal segments ranged from 4.98 to 5.42 cm/s, indicating a difficult absorption. A strikingly high transport of timosaponin A-III was found, PappBA 3.27 ± 0.64 × 10-6 cm/s, which was abolished by a P-gp inhibitor. Rat liver microsome incubation studies showed that timosaponin A-III could hardly be metabolized, with a t1/2 of over 12 h. In addition, the solubility test showed a low solubility in PBS solution, 30.58 μg/mL. CONCLUSION Timosaponin A-III exhibited low oral bioavailability by oral and intravenous admiConclusion: nistration, which was probably caused by its low permeability and solubility. This study may provide a reference for the rational clinical use and further study on the pharmacology or toxicology of timosaponin A-III.