On the lipoprotein abnormality in type III hyperlipoproteinemia

Two lipoprotein species were isolated by starch block electrophoresis from the very low density lipoproteins (VLDL) (S(f) 20-400) of patients with type III hyperlipoproteinemia. One of these, alpha(2)-VLDL, had a content of lipid and protein and physical characteristics similar to VLDL from normal subjects or patients with other forms of hyperglyceridemia. The other species, beta-VLDL, contained more cholesterol and less triglyceride in relation to the protein, than normal VLDL. Only the apoprotein of low density lipoprotein was immunochemically detectable in the beta-VLDL; the proteins in the alpha(2)-VLDL reacted with antisera specific for low density lipoprotein and high density lipoprotein. The electrophoretic mobility of beta-VLDL was similar to that of low density lipoprotein and significantly less than that of alpha(2)-VLDL. Isolated beta-VLDL had a lesser mean flotation rate than alpha(2)-VLDL, but both alpha(2)- and beta-VLDL were found throughout the S(f) 20-400 flotation range.The relative quantities of alpha(2)- and beta-VLDL could be varied by changing the diet or by heparin administration. Most of the VLDL from type III patients on a high carbohydrate diet was in the alpha(2)-VLDL form. During fasting, alpha(2)-VLDL fell and beta-VLDL increased becoming the predominant species of VLDL. Heparin-induced acceleration of triglyceride clearance also increased beta-VLDL and decreased alpha(2)-VLDL. These findings suggest a precursor-product relationship between the alpha(2)- and beta-forms of VLDL.