Isolation of Apolipoprotein E-Rich Very-Low-Density Lipoprotein from Human Plasma with Anti-Apolipoprotein B-100 Monoclonal Antibodies

It is well known that apolipoprotein E (apo E) has a significant role in the metabolism of plasma cholesterol through receptor-mediated endocytosis of lipoproteins containing apo B-100. Recently E. Campos et al. reported that the human very-lowdensity lipoprotein (VLDL) that does not bind to an immunoaffinity gel of anti-apolipoprotein (apo) B-100 monoclonal antibody (anti-apo B-100) contains several molecules of apo E on the particle. We also reported that the content of apo E in VLDL, which had been incubated with purified apo E (VLDL-E), was 2-to 3-fold greater than that in unmodified VLDL as determined by radioimmunoassay and as visualized in SDS polyacrylamide gel electrophoretograms.In the present study, VLDL-E was used in the anti-apo B-100 immunoaffiinity chromatography to isolate apo E lipoproteins in the unbound fraction. We found that the unbound fraction of VLDL-E was very rich in apo E, with 5-to 10-fold levels as compared with VLDL. In agarose gel electrophoresis, the particles in the unbound fraction migrated to the area between the α and pre-β positions, whereas particle sizes of VLDL and VLDL-E were similar on gel filtration chromatography. The lipid composition of the VLDL-E unbound fraction was not significantly different from the original VLDL.These results indicated that the size and lipid composition of the VLDL-E unbound fraction were quite similar to those of VLDL besides its electrophoretic mobility and content of apo E. Anti-apo B-100 monoclonal affinity chromatography is useful to obtain apo E-rich VLDL and to study the metabolic significance of apo E-rich VLDL.