Journal of Lipid Research, Vol 30, 189-197, Copyright © 1989 by Lipid Research, Inc.
Triglyceride and cholesteryl ester hydrolysis in a cell culture model of smooth muscle foam cells
LK Minor, GH Rothblat and JM Glick
Department of Physiology and Biochemistry, Medical College of Pennsylvania, Philadelphia 19129.
Cultured rabbit aortic smooth muscle cells were converted to foam cells by
exposure to sonicated lipid droplets of defined composition using an
inverted culture technique. Uptake of the lipid droplets by the cells was
shown to be dependent on the time of exposure to the droplets and on the
mass of droplets presented to the cells. A comparison of the hydrolysis of
triolein and cholesteryl oleate by cells that had been exposed to isotropic
lipid droplets containing equimolar amounts of the two lipids revealed that
the rate of hydrolysis of triglyceride was 3 to 4 times faster than that
for cholesteryl ester. The hydrolysis of cholesteryl oleate from cells
loaded with the isotropic droplets was approximately 1.5 times as fast as
that from cells loaded with anisotropic droplets containing only
cholesteryl oleate. A comparison of the hydrolysis of cholesteryl ester in
the presence and absence of Sandoz compound 58-035, an inhibitor of acyl
CoA:cholesterol acyl transferase, by cells loaded with isotropic droplets
showed that about 30% of the free cholesterol liberated by hydrolysis was
reesterified regardless of the mass of free cholesterol. We conclude that
cultured smooth muscle cells have a greater capacity to hydrolyze
triglyceride than cholesteryl ester, and that the rate of hydrolysis of
cholesteryl ester appears to be related to the physical state of the
droplet in which the cholesteryl ester is stored. In addition, it appears
that the smooth muscle cells have a cholesteryl ester cycle that is
inefficient in the reesterification of excess free cholesterol.