Studies on regression of atherosclerosis--role of lipid containers

The appearance of the aortic wall of rabbits fed a lanolin containing diet was examined by scanning (SEM) and transmission electron microscopy (TEM) in order to clarify the mechanism of removal of lipids deposited in the aorta. SEM study showed that circulating leukocytes penetrated into the arterial wall in the early phase of the experimental atherosclerosis. In some specimens, spherical bodies with a diameter of 10-30 mu were observed along the cleavage of the marginal folds between the endothelial cells. TEM demonstrated that these bodies contained many lipid particles, and numerous active microvilli were seen on the body surface. In the deeper subendothelial space, villi of each body interdigitated. From these results, it is postulated that the circulating leukocytes penetrate under the endothelium and take up the deposited lipids. Then, they return to the blood stream, containing lipid rich particles. The deposited lipids in the atherosclerotic lesion would be removed by this process. We named this phenomenon as "exo-tissuesis with lipid containers". While lipids are believed to be removed from the atherosclerotic lesion by HDL, lecithin cholesterol acyltransferase and others at the molecular level, we suggest that lipid containers play important roles in the regression and prevention of atherosclerosis on a major scale-cellular and tissue level.