A comparison of some immunological characteristics of very low density lipoproteins of normal and hypercholesterolemic rat sera

The immunological characteristics of very low density lipoproteins (VLDL) from normal and hypercholesterolemic rat sera were compared using polyspecific antisera to VLDL and high density lipoproteins (HDL) and monospecific antisera to apo-B, apo-C, apo-A-I, and apo-E. Ultracentrifugally isolated VLDL from normal serum were studied by immunodiffusion and found to contain both discrete and associated (with apo-B) apo-C and apo-E, probably in the form of lipid-containing lipoproteins. However, immunoelectrophoresis of whole serum revealed only an associated form of the lipoprotein having pre-β mobility (i.e., VLDL), suggesting that the presence of discrete lipoproteins in isolated VLDL, each containing a single apoprotein family, may represent ultracentrifugal artifacts. Ultracentrifugally isolated VLDL from diet-induced hypercholesterolemic rat serum contained only trace amounts of apo-C and large quantities of apo-E, both of which were totally associated with apo-B. VLDL isolated by ultracentrifugation from perfusate of normal and hypercholesterolemic livers contained only associated lipoprotein complexes made up of apo-B, apo-C, and apo-E in the former but only apo-B and apo-E in the latter. These data suggest that normal VLDL are secreted as lipoprotein complexes containing apo-B, apo-C, and apo-E which may become destabilized in the circulation. However, VLDL from hypercholesterolemic serum show a marked diminution in the quantity of apo-C as indicated by the relative incorporation of [³H]leucine in vivo and by polyacrylamide gel electrophoresis of apo-VLDL.