Determination of human apolipoprotein e by electroimmunoassay

Abstract

1. 1.|Apolipoprotein E (“arginine-rich” polypeptide) was isolated from delipidized human very low density lipoproteins by agarose column chromatography in the presence of 6 M guanidine · hydrochloride. 2. 2.|An electroimmunoassay (“rocket” electrophoresis) is described for quantitative determination of human serum apolipoprotein E. Purified apolipoprotein E was used for the preparation of monospecific antisera and standardization of assay. This sensitive, specific, rapid (time required for the completion of the assay is 5 h) and precise (the within- and between-assay coefficients of variation are 5 and 8%, respectively) assay is applicable to measurment of apolipoprotein E in whole serum and density classes. The results correlated well with those obtained by radial immunodiffusion ( r = 0.85). 3. 3.|Serum apolipoprotein E levels of normal subjects and hyperlipoproteinemic phenotypes IIa, IIb and IV were the same (10 to 16 mg/100 ml). In contrast, patients with type III and V hyperlipoproteinemias had markedly elevated serum apolipoprotein E levels (27 and 25 mg/100 ml, respectively). The apolipoprotein E in serum of normolipidemic subjects was equally distributed among three major lipoprotein density classes: d < 1.030 g/ml (27%), d 1.030−1.063 g/ml (36%) and d 1.063−1.21 g/ml (37%).