Characteristics of Lipid Inclusions in Early Arteriosclerotic Lesions of Human Aorta

Fatty streaks of human aortas, studied by electron microscopy, showed lipid inclusions to be inside foam cells. Solid, ring and vacuolar inclusions were most frequent. Others were of reticular, laminar and lysosome-like appearance or showed a central core with a clear zone around. Intermediate forms were frequent. The differences in morphological appearance may be due to differences in lipid composition or may reflect some interference of the processing of the tissue.Isolated lipid inclusions, examined by polarizing microscopy, were found to be present as a mixture of anisotropic and isotropic inclusions (84% and 16%, respectively, at 22°C). With increasing temperature, more anisotropic inclusions became isotropic. Anisotropic forms were more frequent in younger individuals and early lesions, thus possibly representing the initial form.Lipid inclusions accounted for approximately 50% of the lipid in the lesion. In contrast to the lesion residue, they consisted by 95% of cholesterol ester with minor amounts of free cholesterol, phospholipids and triglycerides. Major fatty acids esterified with cholesterol were oleic and linoleic acids (50% and 15%, respectively). Since the lipid composition of the lesion residue was identical with that of normal, undiseased intima, the results did not contradict with the possibility that fatty streaks could undergo complete regression.