Are the binding and degradation of low density lipoprotein altered in Type 2 (non-insulin-dependent) diabetes mellitus?

Abstract

Studies in vitro have shown that glycosylation of low density lipoprotein (LDL) will decrease its ability to bind to its receptor. We have evaluated the possibility that such an event might occur in vivo in diabetes by comparing the binding and degradation by normal fibroblasts and mouse peritoneal macrophages of LDL obtained from normal control subjects and patients with Type 2 (non-insulin-dependent) diabetes mellitus. When compared with control subjects, Type 2 diabetic patients had elevated fasting glucose (increased by 160%), haemoglobin AIc (increased by 75%), triglyceride (increased by 550%), and cholesterol (increased by 48%) levels. LDL from Type 2 diabetic patients displayed populations of particles with more heterogeneous hydrated densities than LDL from control subjects, with enrichment in the triglyceride content of the lighter population. 125I-LDL from normal and Type 2 diabetic subjects bound to fibroblasts with similar binding affinities and binding capacities. The kinetics of degradation of LDL from normal and Type 2 diabetic subjects by fibroblasts were also similar. Furthermore, all populations of LDL particles from Type 2 diabetic patients were bound and degraded by normal fibroblasts in identical fashions. In addition, 125I-LDL from normal and Type 2 diabetic subjects were not bound or degraded by mouse peritoneal macrophages. It is concluded that the LDL of patients with Type 2 diabetes with moderate hyperglycaemia are not modified sufficiently to alter their normal binding and degradation by human fibroblasts or to cause their uptake by mouse peritoneal macrophages.