Comparative study of effects of various sterols and triterpenoids on permeability of model lipid membranes

Using permeability to labeled glucose as a criterion of stability for liposomal membranes, a comparative study on stabilizing properties of different sterols and triterpenes in phospholipid bilayer has been carried out as well as on structural peculiarities of sterols responsible for membranolytic properties of cucumarioside G(1) from the cucumaria Eupentacta fraudatris. Stabilizing action of the studied sterols and triterpenoides incorporated in the bilayer decreases in the following order: cholesterol sulfate > cholesterol > Delta(5)-sterols > beta-sitosterol > ergosterols > Delta(7)-sterols > epicholesterol > pregnane > androstane > coprosterol > 14alpha-methylcholest-9(11)-en-3beta-ol > 4alpha,14alpha-dimethylcholest-9(11)-en-3beta-ol > holothurinogenin A(1) > glucoside of cholesterol > beta-xylosidase of Delta(7)-sterols > betulin > protopanaxatriol > phosphatidylcholine liposomes without sterol > protopanaxadiol > oleanolic acid. Sterol-dependent membranolytic cucumarioside G(1) practically loses its ability to increase permeability of phospholipid membranes containing sterols obtained from this holothuria as well as coprosterol, epicholestrol, sulfated and glycosylated forms of sterols. The obtained results confirm the "sterol" hypothesis of the mechanism of membranotropic action of holothuria glycosides and of resistance to them of holothutia cell membranes.