Naturally Occurring Modified Low Density Lipoproteins Are Similar if Not Identical: More Electronegative and Desialylated Lipoprotein Subfractions
Previous studies demonstrated that more electronegative low density lipoprotein (LDL) isolated from human blood by ion exchange chromatography has a chemical composition and physical properties similar to desialylated LDL obtained by lectin chromatography (Avogaro et al., 1988; Orekhov et al., 1989). In this study, sialic acid content and percentage of desialylated LDL in the electronegative LDL (LDL - ) subfraction have been investigated. The sialic acid content of the LDL - was 2- to 6-fold lower than that of native LDL and close to that of desialylated LDL. In the native LDL subfraction, 83% of lipoprotein particles did not bind to the Ricinus communis agglutinin, indicating lack of terminal galactose, presumably appearing as a result of desialylation of LDL carbohydrate chains. By contrast, a major proportion of human LDL - (81%) was bound to the lectin. It was also found that the desialylated LDL subfraction consists of 88% LDL - . Native LDL did not affect the contents of free and esterified cholesterol in intimal cells cultured from grossly normal human aorta, while LDL - and desialylated LDL induced a 1.5- to 3-fold increase in the intracellular content of cholesteryl esters. Thus, LDL- is desialylated LDL which induces lipid accumulation in intimal cells. Our finding suggest that the LDL - particle is similar if not identical to the desialylated LDL particle.