Effects of bacteriohopane-32-ol on the stability of various kinds of liposomal membranes.

The effects of bacteriohopane-32-ol (Monol) on the stability of various kinds of liposomal membranes composed of phosphatidylcholine (PC) were examined by measuring the release of calcein entrapped in the liposomes; these effects were then compared with those of cholesterol (Chol). Incorporation of Chol enhanced the stability of both small unilamellar vesicles (SUV) and reverse-phase evaporation vesicles (REV) by increasing their content. However, the incorporation of Monol into PC membranes produced different effects on liposome stability due to the difference in vesicle size, fatty acyl chains of phospholipids and Monol contents. At a low Monol content of dipalmitoylphosphatidylcholine (DPPC) in SUV, incorporation of Monol exerted relatively major stabilizing effect at temperatures above Tm compared with those below Tm. Furthermore, the incorporation of Monol into REV of DPPC at about 12 mol% lowered the stability of REV below Tm of DPPC while at other concentrations this was increased. This peculiar effect was not observed in SUV membranes of DPPC and membranes composed of dimyristoylphosphatidylcholine (DMPC). These results are discussed with reference to the interaction between Monol and phospholipid molecules.