Distribution and concentration of apolipoprotein E in high and low density lipoproteins

An electroimmunoassay of apolipoprotein E (Apo E) in total human plasma and in the supernatant following precipitation with sodium phosphotungstate in the presence of MgCl2 of the apolipoprotein B (Apo B)-containing lipoproteins is described. The assay is specific and sensitive enough to record also low levels of Apo E found in isolated lipoprotein fractions. In 30 normal male subjects, the method gave a total plasma Apo E concentration of 6.67 +/- 1.92 mg/dl and a HDL Apo E concentration of 2.58 +/- 0.91 mg/dl. Total Apo E is positively correlated with total plasma triglycerides. The values of Apo E in the lipoproteins obtained by ultracentrifugation were lower than the corresponding values obtained by a precipitation procedure, with a mean Apo E loss of 12.1% in the low density lipoproteins (VLDL + LDL) and of 34.3% in HDL. After ultracentrifugation, a substantial amount of Apo E was detected in the d greater than 1.210 g/ml fraction. The proposed method allows to study the Apo E concentration and distribution between low and high density lipoproteins in large samples, avoiding the problems connected with high salt concentrations and centrifugal forces.