Saponin-lipid interplay in model membranes: The case of the diosgenyl saponins

Dioscorea species have been consumed for the treatment of illnesses such as rheumatoid arthritis, bronchitis and also used for pain reduction and poor blood circulation. The diosgenyl saponins diosin (DSN) and trillin (TRL), and diosgenin (Dios), their common aglycone, are known to be the main bioactive components (Fig. 1). Dios, DSN and TRL have distinct biological activities when studied individually. With their wide spectrum of pharmacological and biological activities, the diosgenyl saponins have been considered as potential drug leads in the development of treatment strategies.This study investigates the membrane behavior towards Cho-incorporated membrane lipids. Dios, which is the sapogenin or aglycone of TRL and DSN, was also studied to correlate the steroidal backbone effect of the saponins as well as compare the saponin activities in the presence of Cho. Using different biophysical techniques, this study revealed that the diosgenyl saponins have a distinct membrane activity. For majority of the saponins, the key factor for their membranolytic activity is Cho; but the diosgenyl saponins exert their bioactivities owing to their inherently strong affinity for the phospholipidsThe flat, rigid steroid core which is shared by both Cho and Dios appears to have important consequences in the ordering and structure of the bilayer. Results of the experiments suggest the notable influence of the tetracyclic core in terms of the lipid ordering. Dios differs from Cho by having a fixed spirostanol posterior. But this distinction does not seem to largely affect the membrane behavior of Dios in relation to Cho. Our findings confirmed the results of the MD simulation which revealed that modifications of the acyl side chain of Cho has very minimal difference in condensing effect compared to normal Cho. The aliphatic side chain of Cho is a so relatively rigid and that the spirostanol ring of Dios may have spatial Iikeness to the aliphatic side chain of Cho in membranes.