Effect of triterpene and steroid saponins on lecithin bilayers

We describe the effect of four triterpene (alpha-hederin, hederacoside C, ammonium glycyrrhizate, Quillaja bark saponins (QBS)) and one steroid (digitonin) saponins on lecithin and lecithin-cholesterol (4:1 mol/mol) model bilayers. For this purpose the Giant Unilamellar Vesicles (GUV), Large Unilamellar Vesicles (LUV) and Supported Lipid Bilayers (SLB) were probed with fluorescence microscopy, dynamic light scattering and neutron reflectivity, respectively. In most cases the results provided from the three techniques were consistent. In cholesterol-free systems, only alpha-hederin was able to penetrate SLB and induce macroscopic changes in LUV and GUV. Digitonin can adsorb to a small extent on the surface of cholesterol-free SLB, but does not affect macroscopically the LUV and GUV. In the presence of cholesterol, not only alpha-hederin but also QBS and digitonin affect the liposomes both microscopically and macroscopically. The present data clearly confirm that cholesterol significantly enhances the effect of membrane-active saponins on bilayers and that the effect on model bilayers correlates well with the membrane-activity of the saponins. (C) 2016 Elsevier B.V. All rights reserved.