Electron microscopic features of lipoprotein-glycosaminoglycan complexes from human atherosclerotic plaques

Lipoprotein-glycosaminoglycan (GAG) complexes were isolated from fibrous plaque lesions of human aortas and examined by electron microscopy. After fractionation by gel chromatography and ultracentrifugation, both very low density lopoprotein-GAG and low density lopoprotein-GAG complexes showed particles which were mainly 1,000 to 2,000 A in diameter. Occasional large aggregations 3,000 to 10,000 A in diameter were seen after gel filtration and in the very low density lipoprotein fraction of complexes. In general, the complexes were larger than serum very low density lipoprotein and low density lipoprotein, although serum very low density lipoprotein particles ranged from 250 to 2,000 A. In vitro low density lipoprotein-heparin complexes consisted of spherical particles generally 1,000 to 2,000 A in diameter formed by the aggregation and coalescing of smaller low density liproprotein particles in the presence of heparin and Ca2+. These observations support a concept that GAG of the aortic intimal "ground substance" sequester certain serum lipoproteins in a manner similar to in vitro complexing of lipoproteins and GAG in the presence of Ca2+.