Stability of SUV liposomes in the presence of cholate salts and pancreaticlipases: effect of lipid composition

The effect of bile salts (sodium cholate and sodium taurocholate), and panc reatic lipases on the structural integrity of SW liposomes of different lip id compositions was studied. Liposomal membrane integrity was judged by bil e salt or pancreatin-induced release of vesicle encapsulated 5,6-carboxyflu orescein, and vesicle size distribution before and after incubations. Bile salt concentration was 10 mM, while a saturated solution of pancreatin (mix ed with equal volume of liposomes) was utilized. Results agree with earlier studies, demonstrating the instability of liposomes composed of lipids wit h low transition temperatures (PC and DMPC) in presence of cholates. Additi on of cholesterol (1:1 lipid:chol molar ratio) does not substantially incre ase the encapsulated molecule retention. Nevertheless, liposomes composed o f lipids with high transition temperatures (DPPC, DSPC and SM), retain sign ificantly higher amounts of encapsulated material, under all conditions stu died. Furthermore, the vesicles formed by mixing cholesterol with these lip ids will possibly be sufficiently stable in the gastrointestinal tract for long periods of time. Sizing results reveal that in most cases release of e ncapsulated molecules is mainly caused by their leakage through holes forme d on the Lipid bilayer. However, in stearylamine containing DPPC and DSPC v esicles, the cholate-induced drastic decrease in vesicle size suggests tota l liposome disruption as the possible mechanism of encapsulated material im mediate release. (C) 2000 Elsevier Science B.V. All rights reserved.