Slowβ-migrating Lipoprotein: An Atherogenic Subclass of Low Density Lipoproteins

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 IIb hyperlipidemics were subjected to polyacrylamide gel disc electrophoresis. Results: A part of midband lipoprotein was observed between preβ- and β-band, in addition to the main β-band. We named this midband lipoprotein “slowβ-migrating Lp (slowβ-Lp).” The larger LDL subfraction from midband-lipoprotein positive serum on Sepharose 2B column chromatography contained much slowβ-Lp, named slowβ-Lp-rich LDL. The smaller LDL subfraction contained a little slowβ-Lp, named slowβ-Lp-poor LDL. Slowβ-Lp-rich LDL had similar composition to the control LDL except for apolipoprotein E. The uptake of [3H]cholesteryl linoleate-labeled slowβ-Lp-rich LDL by J774 macrophages was higher than that of control LDL. The cholesterol ester content of J774 macrophages incubated with slowβ-Lp-rich LDL increased significantly compared with slowβ-Lp-poor LDL, β-VLDL, and control LDL. Conclusion: These results suggest that slowβ-Lp in type IIb might generate foam cells from macrophages in atherosclerotic lesions.