Preferential uptake of intermediate-density lipoproteins from nephrotic patients by human mesangial and liver cells

Hyperlipidemia of nephrotic origin could potentially cause glomerular injury as well as increase the risk of atherosclerosis. The precise interaction of human lipoproteins abnormal in lipid and protein composition, with lipoprotein receptors has not been clearly defined. This study examines receptor-mediated uptake and intracellular cholesterol metabolism of apolipoprotein (apo)B,E containing intermediate-density lipoprotein (IDL) and apoB-100 containing low-density lipoprotein (LDL), isolated from patients with the nephrotic syndrome (N = 6), in human glomerular mesangial and HepG2 cells. In the patients, serum IDL and LDL cholesterol levels were significantly increased as compared with those of healthy subjects. The IDL of nephrotic patients contained 80% more cholesterol than the IDL of healthy controls. No differences in lipid/protein composition were found in the LDL density range. Therefore, nephrotic and control LDL showed identical affinities for receptor-mediated uptake. In contrast, the IDL of nephrotic patients was taken up by mesangial cells and HepG2 with higher affinity than the LDL. Intracellular sterol synthesis was suppressed more effectively and cholesterol esterification rate was enhanced 2.2-fold by nephrotic IDL as compared with control IDL. These data indicate that hypercholesterolemia of nephrotic origin cannot be explained by reduced ligand binding for LDL. ApoE-containing IDL of patients with the nephrotic syndrome were avidly taken up by glomerular mesangial cells and could therefore play the predominant role in the development of glomerulosclerosis and atherosclerosis associated with this disorder.