Precipitation of apo E-containing lipoproteins by precipitation reagents for apolipoprotein B.

We measured the solubility of apolipoprotein E (apo E) after precipitation, with heparin-Mn2+ or dextran sulfate-Mg2+, of lipoproteins containing apo B. Data from 46 randomly selected subjects suggest that apo E is readily precipitated by dextran sulfate-Mg2+, but that heparin-Mn2+ preferentially precipitates apo E associated with apo B-containing lipoproteins while leaving the apo E-containing fraction of high-density lipoproteins (HDL) in solution. In a more detailed analysis of three subjects, we measured the lipoprotein association of apo E by column chromatography on agarose beads, before and after its precipitation from plasma. This study confirmed the preferential solubility of apo E associated with HDL lipoproteins. Using plasma from two normolipidemic subjects, we maintained the heparin concentration at 1.30 g/L and varied the manganese concentration from 9.2 to 184 mmol/L. A 46 mmol/L concentration best separated apo E-containing HDL from apo B-containing lipoproteins. Thus, at these final concentrations, heparin-Mn2+ appears to precipitate the apo E associated with apo B-containing lipoproteins, leaving soluble most of the apo E associated with lipoproteins of HDL size.