Formulation and in vitro absorption analysis of Rhizoma paridis steroidal saponins

Rhizoma paridis steroidal saponins (RPS) have been prepared and identified as the active compounds for antitumor activity in our previous study. However, the low oral bioavailability of the steroidal saponins restricted its using. In the present research, solid dispersion (SD) and phytosome (PHY) formulation of RPS were prepared, and the physicochemical parameters as well as the intestinal absorption in rat everted gut sac model were investigated. Seven agents were selected as the carriers of SD, and poloxamer 407 (P 407) was the most suitable one. SD reduced the particle size of saponins in the water solution, enhanced the solubility of the saponins by about 3.5 folds, and significantly improved the absorption transport of saponins from 48 to 104 μg in everted gut sac of the rat system. PHY significantly enhanced the hydrophilic of saponins but showed little effect on the absorption in small intestine. Jejunum and ileum part absorbed more absolute contents of total saponins than duodenum parts. Six saponins, the main contents of RPS, used as the index of comparing the three forms, were also further investigated in the physico-chemical properties and the absorption tests. n-Octanol/water partition coefficients of the six saponins ordered in RPS, SD and PHY were Chonglouoside H > Dioscin > Polyphyllin D > Gracillin > Paris-VII > Formosanin C. All the saponins possessed the higher absorptive characteristics in SD formulation. The absorption rate of diosgenyl saponins in intestine was more than the pennogenyl saponins.