Biopharmaceutics and Pharmacokinetics of Timosaponin A-III by a Sensitive HPLC-MS/MS Method: Low Bioavailability Resulting from Poor Permeability and Solubility

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 mg/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 C max of 120.90 ± 24.97 ng/mL at 8 h, and the t 1/2 was 9.94 h. The absolute oral bioavailability of timosaponin A-III was 9.18%. The permeability coefficients of timosaponin A-III in four intestinal segments ranged from 4.98 to 5.42 × 10 -7 cm/s, indicating a difficult absorption. A strikingly high efflux transport of timosaponin A-III was found, P appBA 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 t 1/2 of over 12 h. In addition, the solubility test showed a low solubility in PBS solution, i.e. 30.58 μg/mL. Conclusion: Timosaponin A-III exhibited low oral bioavailability by oral and intravenous administration, which was probably caused by its low permeability and solubility. This study may provide a reference for its rational clinical use and further study on the pharmacology or toxicology of timosaponin A-III.