Metabolic profiles of neotuberostemonine and tuberostemonine in rats by high performance liquid chromatography/quadrupole time-of-flight mass spectrometry.

Neotuberostemonine (NS) and tuberostemonine (TS), a pair of stereoisomers, are the active components contained in Stemona tuberosa, an antitussive herbal medicine in China. Two isomers have different pharmacological efficacies, which will be related with their in vivo disposition. However, the metabolic fates of NS and TS remain unknown. A method of high performance liquid chromatography/quadrupole time-of-flight mass spectrometry coupled with mass detect filter technique was established to investigate the metabolites in rat plasma, bile, urine, and feces after oral administration of the equal doses of NS and TS. The results showed that NS produced 48 phase I metabolites, including NS, 3 hydrolyzed, 14 hydroxylated, 20 monohydrolyzed+hydroxylated and 10 dihydrolyzed+hydroxylated metabolites. The number of detected NS metabolites was 11, 39, 22 and 30 in plasma, bile, urine and feces. TS yielded 23 phase I metabolites, including TS, 3 hydrolyzed, 7 hydroxylated, 9 monohydrolyzed+hydroxylated and 3 dihydrolyzed+hydroxylated metabolites. Besides, TS yielded 9 phase II metabolites, including 1 glucuronic acid and 2 glutathione conjugates, and the later further degraded and modified into cysteine-glycine, cysteine and N-acetylcysteine conjugates. The number of detected TS metabolites was 9, 24, 24 and 15 in plasma, bile, urine and feces. Different metabolic patterns may be one of the main reasons leading to different pharmacological effects of NS and TS.