Lipoprotein Models: Ultrasonicated Emulsions of Phosphatidylcholine, Cholesterol and Triolein.

Abstract

A method for preparation of stable triolein-phosphatidylcholine and triolein-phosphatidylcholine-cholesterol emulsions is presented. The resulting emulsion particles are apparently good models for structural and enzymatic studies of serum lipoproteins. The maximal emulsifying effect was obtained at a wt/wt ratio of 2.2:1 between triolein and phosphatidylcholine, either with or without cholesterol. Emulsions constituted in this ratio were fairly homogeneous both in respect of particle size and lipid ratio. The cholesterol solubilizing capacity of the 2.2:1 triolein/phosphatidylcholine emulsion was a cholesterol/phosphatidylcholine molar ratio of 2:1. EM pictures gave mean values for the particle diameters of 300 .ANG. for a triolein-phosphatidylcholine and 340 .ANG. for a triolein-phosphatidylcholine-cholesterol emulsion. Light-scattering measurements gave corresponding aggregate weights of 0.8 .times. 107 and 1.3 .times. 107, respectively. Cholesterol had a condensing effect on egg phosphatidylcholine and removed the gel-liquid crystal transition of dipalmitoyl phosphatidylcholine when added to 2.2:1 triolein/phosphatidylcholine emulsions in a 1:1 molar ratio with the phosphatidylcholine. The results are discussed with respect to the structural arrangement of the lipid molecules; they are consistent with a particle with a nucleus of triolein and an interfacial region consisting of phosphatidylcholine and cholesterol.