Oral absorption and antitussive activity of tuberostemonine alkaloids from the roots of Stemona tuberosa

The intestinal absorption of four stereoisomers of tuberostemonine-type Alkaloids, neotuberostemonine (1), tuberostemonine (2), tuberostemonine H (3), and tuberostemonine J (4), isolated from the antitussive Chinese medicinal herb Radix Stemonae, and the IN VIVO antitussive activity of Alkaloids 1, 2 and 3 were investigated in the current study. All three Alkaloids exhibited dose-dependent inhibitory effects on citric acid-induced cough in guinea pigs after intraperitoneal administration. Alkaloid 2 had the same potency via both oral and intraperitoneal dosing, 1 exhibited significantly lower oral activity than that following intraperitoneal application, while 3 did not show oral activity. Alkaloid 4 demonstrated a moderate permeability in Caco-2 monolayer cells while Alkaloids 1, 2 and 3 exhibited relatively higher intestinal permeabilities, indicating that all four Alkaloids tested had reasonable oral absorption.