Objective: To clarify the possibility that midband Lp in LDL fractions might act as an atherogenic lipoprotein in their interaction with macrophages.
Design and methods: Low density lipoproteins (LDL) isolated by zonal ultracentrifugation from midband lipoprotein-positive serum in type lib hyperlipidemics were subjected to polyacrylamide gel disc electrophoresis.
Results: A part of midband lipoprotein was observed between pre beta-and beta-band, in addition to the main beta-band. We named this midband lipoprotein "slow beta-migrating Lp (slow beta-Lp)." The larger LDL subfraction from midband-lipoprotein positive serum on Sepharose 2B column chromatography contained much slow beta-Lp, named slow beta-Lp-rich LDL. The smaller LDL subfraction contained a little slow beta-Lp, named slow beta-Lp-poor LDL. Slow beta-Lp-rich LDL had similar composition to the control LDL except for apolipoprotein E. The uptake of [3H]cholesteryl linoleate-labeled slow beta-Lp-rich LDL by J774 macrophages was higher than that of control LDL. The cholesterol ester content of J774 macrophages incubated with slow beta-Lp-rich LDL increased significantly compared with slow beta-Lp-poor LDL, beta-VLDL, and control LDL.
Conclusion: These results suggest that slow beta-Lp in type llb might generate foam cells from macrophages in atherosclerotic lesions.