Sialic acids and the metabolism of low density lipoprotein

Sialic acid-poor low density lipoprotein (LDL) is suggested to be atherogenic because it causes in vitro accumulation of cholesterol into epithelial cells and macrophages. We studied whether the whole-body catabolism of LDL varies according to its sialic acid content by analyzing the sialic acids in total (d 1.019-1.063 g/ml), light (d 1.019-1.036 g/ml), dense (d 1.037-1.055 g/ml), and very dense (d 1.056-1.063 g/ml) LDL, and the kinetics of total and dense LDL apolipoprotein (apo) B in 20 non-insulin-dependent diabetic and 10 non-diabetic men of similar age, both groups without and with coronary artery disease (CAD). The sialic acid/apoB ratio was significantly higher in the diabetics compared to the controls in every LDL fraction. Fractional catabolic rate (FCR) for LDL apoB was significantly faster in the diabetics than in the non-diabetics, and was positively associated with the sialic acid ratio in the total and dense LDL. In multiple linear regression analyses with FCR for total and dense LDL apoB as the dependent variable and the presence of diabetes, body mass index, LDL cholesterol, triglycerides, and sialic acid/apoB ratio as the independent variables, LDL cholesterol and serum triglycerides were the only variables entering significantly to these models. The sialic acid/apoB ratio of total and dense LDL was similar in subjects without and with CAD. These results suggest that in this population the sialic acid content of LDL was not associated with clinical signs of atherosclerosis, but the catabolic rate of dense LDL apoB was positively related to the sialic acid content of the respective lipoproteins.