[Membranotropic effect of some triterpene glycosides possessing immunostimulating properties]

The peculiarities of the interaction between cell membrane lipids and triterpene glycosides from holothurians Apostichopus japonicus S. and Cucumaria japonica (holotoxin A1 and cucumarioside A2-2, respectively) were studied in comparison with plant saponins from Quillaja saponaria, known as hemolytic, adjuvant, and structure-forming components of immunostimulating complexes. Similar to Quillaja saponins, the sea glycosides, holotoxin A1 and cucumarioside A2-2 were shown to possess a high hemolytic activity (2.6 and 3 microg/ml, respectively) and sterol-depending membranotropic effect mediated by the formation of nonbilayer sterol-lipid-glycoside complexes. At the same time, cucumarioside A2-2 bound exogenic cholesterol only in the presence of membrane lipids, such as phosphatidylcholine or monogalactosyldiacylglycerol, in contrast to Quillaja saponins and holotoxin A1, which bound cholesterol in the molar ratios 1:2 and 1:8, respectively. Moreover, in all cases, tree-component complexes containing cholesterol, lipid, and glycoside exhibited a lower hemolytic activity compared with two-component sterol-glycoside complexes. It was concluded that the hydrophobic medium of cell membranes performs a potentiative role in the effective interaction between triterpene glycosides and "sterol receptors". A method for decreasing the toxicity of membranotropic holothurian glycosides possessing the immunomodulating properties was suggested.