The bidesmosidic triterpene saponins hederacoside C and ginsenoside Rb1 exhibit low affinity to cholesterol in liposomal membranes

Abstract

Abstract The formation of nanoparticulate structures in the presence of liposomal components has recently been demonstrated for a few saponins, with cholesterol being the essential component. As a follow-up from previous studies, we have studied the interaction of two bidesmosidic triterpene saponins (ginsenoside Rb1, hederacoside C) with liposomal components (cholesterol, DPPC (dipalmitoylphosphatidylcholine)) using the Langmuir film balance technique. In addition, we examined the influence of saponins in aqueous pseudo-binary (saponin:cholesterol/DPPC) and pseudo-ternary systems (saponin:cholesterol:DPPC) regarding particle formation utilizing transmission electron microscopy (TEM). Saponin formulations with liposomal components were prepared by the lipid film method. Langmuir monolayer studies showed a weak affinity of both saponins to cholesterol. Saponin molecules from the subphase migrated into the cholesterol monolayer only at low surface pressure. Further compression of the monolayer led to an exclusion of the saponin molecules back into the subphase. In mixed monolayers (cholesterol, DPPC) as well as in a pure DPPC monolayer, the saponins remained completely in the subphase independent of the pressure applied. TEM images of aqueous pseudo-ternary systems showed no colloidal associations along with the weak affinity for cholesterol. These results emphasize the correlation between the affinity for cholesterol and the formation of nanoparticular structures with liposomal components.