A newly discovered apolipoprotein B-containing high-density lipoprotein produced by human hepatoma cells

Apolipoprotein B-containing high-density lipoprotein was detected in the high-density lipoprotein fraction of the concentrated conditioned medium of human hepatoma HuH-7 cells (Apo-B-containing HDLHuH-7). Electrophoretically, the Apo-B-containing HDLHuH-7 migrated more slowly and broadly than beta-lipoprotein on agarose gel. The Apo-B-containing HDLHuH-7 was not precipitated by heparin-Mn2+ treatment. High-performance gel filtration chromatography indicated that the peak of Apo-B-containing HDLHuH-7 was eluted faster than that of plasma LDL and electron microscopic analysis demonstrated that the particles of Apo-B-containing HDLHuH-7 ranged from 140 A to about 450 A, indicating the heterogeneity of Apo-B-containing HDLHuH-7. The protein/lipid ratio of HDLHuH-7 (1.35) is higher than that of plasma HDL3 (1.2). The lipids of HDLHuH-7 are composed of phospholipids (170 micrograms/mg protein), free cholesterol (410 micrograms/mg protein), cholesterol ester (20 micrograms/mg protein) and triacylglycerols (140 micrograms/mg protein). The results described above indicated that Apo-B-containing HDLHuH-7 was a novel lipoprotein discovered for the first time.