Liposome interactions with hydroxyapatite crystals: a possible mechanism in the calcification of atherosclerotic plaques.

Some stages in the calcification of atherosclerotic plaques may involve associations between lipids and hydroxyapatite (HA) by surface interactions. Liposomes, artificial membranous lipid vesicles, have been used in this study as model structures for biological calcification processes. Liposome (containing cholesterol and phosphatidylcholine in most cases) suspensions were prepared by sonication, after which HA seed crystals were added to the suspensions and stirred at 37 degrees C. Aliquots of the liposome suspensions were analyzed for particle size distribution and by transmission electron microscopy and electron diffraction. The results showed that HA induced aggregation of liposomes and modifications of the microscopic shapes of the liposomes in the aggregates. These data can be explained by the electron diffraction pattern where superimposition of liposome reflection and crystal reflection exists and may suggest organic-inorganic interaction. The potential of HA crystals to induce formation of liposome aggregates may be seen as a step in atherosclerotic plaques calcification.