Very low density and low density lipoprotein subfractions in type III and type IV hyperlipoproteinemia Chemical and physical properties

Subfractions of VLDL (VLDL₁, Sf 100-400; VLDL₂V Sf 60-100; VLDL₃, Sf 20-60) and LDL (LDL₁, Sf 12-20; LDL₂, Sf 6-12; LDL₃, Sf 3-6) were isolated from the plasma of three normal, three type in and four type IV hyperlipoproteinemic subjects. In the type IV group, all VLDL subspecies Were of normal composition but were increased in concentration in the order VLDL₁ > VLDL₂ > VLDL₃. In the same subjects, although LDL₁ was lowered and LDL₃ increased, the total plasma LDL concentration Was normal. All VLDL subfractions were elevated in the type III group, but in this ease VLDL₃ predominated. These subfractions were enriched in cholesteryl esters and depleted in triglyceride. In the LDL density range there was a shift of mass towards the least dense fraction, LDL₁, which was of normal composition. EPR studies of the VLDL and LDL subfractions in a type IV subject demonstrated a decrease in fluidity with increasing density. The major change occurred between VLDL₃ and LDL, and was attributed to a substantial alteration in the cholesteryl ester: triglyceride ratio in the particle. A similar argument was used to explain the reduced fluidity of type III VLDL₃ with respect to that of the same subfraction in normal or type IV subjects. Particle diameters, determined by laser light-scattering speetroscopy were-in good agreement with the values obtained by electron microscopy. This study provides a baseline for the examination of the relationship' between the physical and metabolic properties of VLDL and LDL subtractions in type in and IV hyperlipoproteinemia.