Journal of Lipid Research, Vol 18, 203-210, Copyright © 1977 by Lipid Research, Inc.
Effect of an aqueous phase on the solubility of cholesterol in an oil phase
RJ Jandacek, MR Webb and FH Mattson
In the absence of water, the solubility of cholesterol in triolein at 21
degrees C was 2.8%. When water was added to the system, the solubility of
cholesterol in the oil phase decreased to 1.9%, and cholesterol monohydrate
precipitated. The precipitation of the sterol evidently resulted from the
excess concentration of the surface-active cholesterol at the interface,
allowing the rapid interaction of water with cholesterol and the resulting
formation of cholesterol monohydrate with its attendant lower energy and
less soluble crystalline lattice. The ternary phase diagram for the system
cholesterol--triolein--water, modified to include cholesterol monohydrate
formation with the consequent decrease in sterol solubility; differs from
the previously reported phase diagram. Other cholesterol--oil--aqueous
systems related to biologically important lipids were studied. Cholesteryl
oleate was more soluble than cholesterol in triolein (23% at 21 degrees C),
and this value did not decrease when water was present. Water caused
cholesterol to precipitate from cholesteryl linoleate at 37 degrees C. Thus
crystalline cholesterol may be present in lipids found in atherosclerotic
plaques at a lower concentration of free cholesterol than had been
predicted previously. In another experiment, a micellar taurocholate
solution precipitated cholesterol from triolein and from corn oil. These
effects of aqueous systems suggest the possibility of cholesterol
precipitation from dietary fat when it becomes mixed with water in the diet
or stomach, or with the micellar phase in the intestine. Plant sterols were
precipitated also from oil solutions by an aqueous phase. Water-induced
sterol precipitation is a phenomenon that could occur in a variety of
biological systems, and may be applicable to sterols in general.