Liquid crystalline phase formation by cholesterol in aqueous fatty acid salt solutions

The interaction of cholesterol with fatty acid salt solutions was investigated as a potential method for gallstone dissolution. In the presence of sodium oleate or laurate, crystalline cholesterol was rapidly converted into a lamellar liquid crystalline phase. Analysis of the mesophase showed that it contained approximately equimolar amounts of the lipid components, although water was the major constituent. The rate of conversion of cholesterol to mesophase was determined from a compressed disc immersed in a stirred solution, as if it were a simple dissolution process. The apparent rate of solubilization was independent of oleate concentration in the 2.5 to 10% range and was approximately 200 times faster than micellar dissolution of cholesterol in 5% sodium cholate. A mechanism is proposed in which the rate-limiting step in mesophase formation is dispersion of liquid crystalline fragments into the bulk medium.