Presence of a modified low density lipoprotein in humans

Low density lipoproteins (LDL) collected from 18 fasting humans were subjected to ion exchange chromatography on DEAE Sepharose. By this procedure, a LDL subfraction was isolated with an electric charge more negative than the LDL bulk. This LDL appeared to be mainly characterized by low phospholipid content, high free cholesterol and protein content, low esterified/free cholesterol ratio, and a high content of conjugated dienes, particularly of cholesterol esters. This subfraction, in an amount ranging from 5% to 20% of total LDL, was characterized by the presence of apo B-100 and protein aggregates that were reactive to anti-apo B monoclonal antibodies. Electron microscopy showed the more electronegative LDL to be heterogeneous in size with a tendency to aggregate. This LDL had low binding capacity with high affinity receptors of fibroblasts and low immunoreactivity with the monoclonal antibodies that recognize the receptor binding domain of apo B. Finally, the incubation of this LDL subfraction with cultured macrophages led to a higher increase in cellular cholesterol in spite of a lower rate of uptake as compared to the LDL bulk and to acetyl-LDL. The more electronegative LDL subfraction that we isolated for chemico-physical behavior and conjugated diene content may represent the peroxidized aliquot of human LDL.