Characterization of desialylated low-density lipoproteins which cause intracellular lipid accumulation

The properties of sialylated (sialic acid rich) and desialylated (sialic acid poor) fractions of low-density lipoproteins (LDL) isolated from blood plasma of healthy subjects and coronary atherosclerosis patients have been investigated. Sialylated (60-90% of total LDL) and desialylated (10-40%) LDL were separated by affinity chromatography on Ricinus communis agglutinin-agarose. Sialic acid contents in sialylated LDL fractions of healthy subjects and patients were found to be the same, and 1.5 to 3-fold higher than in desialylated LDL. Desialylated LDL had smaller sizes and greater electrophoretic mobility than sialylated, ones. Desialylated, but not sialylated, LDL induced 1.5 to 4-fold accumulation of neutral lipids in human aortic smooth-muscle cells. Desialylated LDL contained lower amounts of cholesteryl esters, free cholesterol and triglycerides as compared to sialylated LDL. On the other hand, the concentrations of di-, monoglycerides and free fatty acids in desialylated LDL were 2 to 3-fold higher than in sialylated lipoproteins. The desialylated LDL fraction was characterized by lower levels of phosphatidylcholine, sphingomyelin and phosphatidylethanolamine, but a higher content of lysophosphatidylcholine. Levels of thiobarbituric acid-reactive substances in freshly isolated desialylated and sialylated LDL were the same. Desialylated LDL had a higher level of oxysterols and lower amounts of vitamins A and E. The content of free amino groups of lysine in desialylated LDL of patients was 2-fold lower than in sialylated LDL. The results of this study demonstrate that multiple physico-chemical parameters of desialylated LDL differ from those of sialylated LDL.