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Macrophage oxidation of low density lipoprotein generates a modified form recognized by the scavenger receptor
Abstract:
Incubation of low density lipoprotein (LDL) with endothelial cells or smooth muscle cells overnight has resulted in an oxidative modification of LDL that results in its recognition by macrophages by way of the acetyl LDL receptor. In the present study, we examined whether macrophages themselves can oxidize and modify LDL in a manner similar to that of endothelial cells. Incubation of 125I-labeled LDL with resident or thioglycollate-elicited macrophages for 24 hours in Ham's F-10 medium resulted in the appearance of thiobarbituric acid (TBA) reactive materials and trichloroacetic acid (TCA) soluble radioactivity in the medium. The LDL harvested from these incubations showed increased electrophoretic mobility and was degraded rapidly when added to fresh macrophages as compared to LDL previously incubated in the absence of cells. These macrophage-induced modifications could be prevented if the first incubation was carried out in the presence of the antioxidant butylated hydroxytoluene (BHT) or in Dulbecco's modified Eagle's medium (DMEM). The degradation of 125I-labeled macrophage-modified LDL by macrophages was competitively inhibited by unlabeled acetyl LDL or unlabeled endothelial cell-modified LDL but not by native LDL, indicating that the degradation was mediated by the acetyl LDL receptor.
Insights
Macrophages can oxidize low-density lipoprotein (LDL), modifying it for uptake via the acetyl LDL receptor. This process, similar to endothelial cell modification, can be blocked by antioxidants.
Area of Science:
- Biochemistry
- Cell Biology
- Immunology
Background:
- Oxidative modification of low-density lipoprotein (LDL) by endothelial cells leads to its recognition by macrophages via the acetyl LDL receptor.
- This study investigates whether macrophages themselves can induce similar oxidative modifications in LDL.
Purpose of the Study:
- To determine if macrophages can oxidize and modify LDL.
- To characterize the modifications induced by macrophages and their mechanism of uptake.
Main Methods:
- Incubation of 125I-labeled LDL with macrophages.
- Measurement of thiobarbituric acid (TBA) reactive materials and trichloroacetic acid (TCA) soluble radioactivity.
- Assessment of LDL electrophoretic mobility and degradation by fresh macrophages.
- Inhibition studies using antioxidants (BHT) and different media (DMEM).
- Competitive inhibition assays with acetyl LDL, endothelial cell-modified LDL, and native LDL.
Main Results:
- Macrophages induced LDL modifications, evidenced by TBA reactive materials and TCA soluble radioactivity.
- Macrophage-modified LDL exhibited increased electrophoretic mobility and was rapidly degraded by fresh macrophages.
- These modifications were prevented by butylated hydroxytoluene (BHT) and Dulbecco's modified Eagle's medium (DMEM).
- Degradation of modified LDL by macrophages was mediated by the acetyl LDL receptor, as shown by competitive inhibition.
Conclusions:
- Macrophages possess the capability to oxidatively modify LDL.
- Macrophage-induced LDL modification is similar to that induced by endothelial cells and involves the acetyl LDL receptor for uptake.
- Antioxidants and specific cell culture media can prevent these modifications.