Apolipoprotein E-enriched lipoprotein subclasses in normolipidemic subjects.

This study was undertaken to objectively define the lipoprotein association of apoE without ultracentrifugation and represents a description of three distinct apoE-containing lipoprotein (LP) subclasses in normal human plasma. The lipoproteins of whole plasma were fractionated in a continuous manner by molecular sieve chromatography using 4% agarose and the elution profile of apoE was compared to that of apoB, apoA-I, cholesterol, and triglyceride. The data show that all apoE in normal subjects is LP-associated and is confined to three discrete LP subfractions of characteristic size. The largest (fraction I), appears to be a subclass of very low density lipoproteins (VLDL). The other two, however, are distinct in size from the major cholesterol-carrying LP; fraction II is intermediate in size between VLDL and the major apoB-containing lipoprotein, LDL; and fraction III is larger than the major apoA-I-containing lipoproteins, HDL, but smaller than LDL. Parallel chromatography of supernatant and infranatant fractions obtained after ultracentrifugation of serum at each of three different densities, 1.006, 1.019, and 1.063 g/ml confirmed that fraction I is of density less than 1.006 g/ml, but that fractions II and III overlap the conventional density intervals.