Involvement of the macrophage low density lipoprotein receptor-binding domains in the uptake of oxidized low density lipoprotein.

Abstract

Macrophages, unlike most other cells, possess both low density lipoprotein (LDL) and scavenger receptors. The scavenger receptor has been shown to mediate the uptake of oxidized LDL (ox-LDL), which ultimately leads to cholesterol loading of the macrophages. The present study was undertaken to define epitopes on ox-LDL that are important for lipoprotein binding to macrophages and to ascertain whether ox-LDL can bind to the LDL receptor. Monoclonal antibodies (Mabs) directed against several epitopes along the apolipoprotein B-100 (apo B-100) molecule were used. LDL (300 /tg/ml) was oxidized by incubation with 10 jtM CuSO, for 24 hours. Ox-LDL, as opposed to acetylated LDL (ac-LDL), reacted with Mabs directed against the LDL receptor-binding domains (Mabs B1B6 and B1B3). Similarly, uptake of ox-LDL but not ac-LDL by a murine J774 macrophage-like cell line was inhibited by as much as 40% after using Mab B1B6. The anti-LDL receptor antibody IgG-C7 also inhibited '"I-ox-LDL uptake by macrophages by 60%. Chromatography on heparin-Sepharose columns of LDL that was partially oxidized for only 3 hours resulted in two fractions: an unbound traction with characteristics similar to those of ox-LDL and a bound fraction similar to native LDL. Macrophage degradation of the unbound fraction was inhibited by Mab IgG-C7 and Mab B1B6, whkh are directed toward the LDL receptor and the LDL receptor-binding domains on apo B-100, respectively. When incubated with three types of macrophages, J774 macrophage cells, mouse peritoneal macrophages, and human monocyte-derived macrophages, excess amounts of unlabeled ox-LDL, like native LDL but unlike ac-LDL, substantially suppressed the uptake and degradation of l25 l-labekd LDL. Similar studies with fibroblasts, however, revealed that unlabeled LDL but not unlabeled ox-LDL or ac-LDL competed with ""I-LDL for cellular uptake and degradation. Mab directed against epitopes on the amino terminus domain of apo B-100 (C14) demonstrates a similar immunoreactivity with ox-LDL and native LDL but a much lower reactivity with ac-LDL. Mab C14 inhibited macrophage degradation of ox-LDL by 34% but had no inhibitory effect on the uptake of native LDL or ac-LDL. Thus, the ac-LDL and LDL receptor-binding domains as well as a unique epitope on the ammo terminus of apo B-100 may be involved in macrophage binding of ox-LDL. We conclude that 1) ox-LDL contains epitopes that are also present in native LDL, although considerable changes in these epitopes are suggested and 2) these epitopes are involved in the uptake of ox-LDL by macrophages. {Arteriosclerosis and Thrombosis 1992;12:484-493) KEY WORDS • oxidized low density lipoproteins • monoclonal antibodies • macrophages M acrophages, like those resident in the atherosclerotic lesion, poorly take up native low density lipoprotein (LDL), whereas several modified forms of LDL are taken up avidly by the macrophage scavenger receptor.

Minimally oxidized LDL inhibits macrophage selective cholesteryl ester uptake and native LDL-induced foam cell formation

“…1 ). Chemical or oxidative apoB modifi cation is known to alter binding of LDL to the LDL receptor (LDL-R) ( 27,28 ). Therefore, the possible contribution of LDL-R to selective CE uptake from LDL and oxLDL was investigated using BMMs from LDL-R Ϫ / Ϫ mice ( Fig.…”

Essential involvement of 12‐lipoxygenase in regiospecific andstereospecific oxidation of low density lipoprotein by macrophages

“…Oxidized LDL was prepared with the 12‐LOX‐expressing cells as described in HPLC analysis. The extent of LDL oxidation was determined by its ability to compete with J774A.1 cell‐mediated degradation of [ 125 I]‐oxidized LDL [23,41]. Namely, the J774A.1 (10 5 cells) were preincubated in 12‐well plates at 37 °C for 12 h followed by washing three times with NaCl/P i .…”

Pleiotrophe Effekte von Statinen (3-Hydroxy-3-Methylglutaryl-Coenzym A-Reduktasehemmer)

“…Des weiteren schwächen Statine die vasokonstriktorische Wirkung von Angiotensin II und Noradrenalin ab [25] und verstärken schon nach 4 Wochen den vasodilatatorischen Effekt von Acetylcholin [26]. endotheliale Monozytenadhäsion [29] und die Cholesterin-Aufnahme und Cholesterin-Anreicherung in Makrophagen reduziert wird [30,31]. Obwohl die Anzahl der LDL-Rezeptoren auf der Makrophagenoberfläche durch Statine erhöht wird, nimmt deren Affinität zum LDL ab [32].…”