CHOLESTEROL-INDEPENDENT MEMBRANE DISRUPTION CAUSED BY TRITERPENOID SAPONINS

The membrane-disrupting activity of 15 triterpenoid saponins, obtained from Chinese plants oi the genus Aralia, was investigated using phosp hatidylcholine liposomes with and without cholesterol. The permeabilit y of the membrane was examined by monitoring the induced fluorescent d ye release from the liposome. On the basis of the obtained results, th e structure-activity relationship among glucuronides of oleanolic acid was discussed. This takes into account particularly the variation in the carboxyl function. Namely, the saponins could induce a permeabilit y change on liposomal membrane without cholesterol when they are glyco sylated at both C-3 and C-28 of the oleanolic acid. There also exists a great similarity in the time-course curves for dye-release within su ch saponins, reflecting their similar action with the lipid bilayer me mbrane. The saponins glycosylated only at C-3 could also exhibit the s ame activity with somewhat different action profiles when the glucuron ic acid is esterified, while those with the free glucuronic acid requi red cholesterol in the liposomes to induce permeability change thereof .