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Keywords:

  • catalase;
  • endocytosis;
  • lysosomes;
  • oxidized high-density lipoprotein;
  • peroxisomes;
  • phosphatidyl choline;
  • retroendocytosis

ABSTRACT—Aims/Background: The metabolism of rat apo E-free high-density lipoproteins (HDL) was contrasted with oxidatively modified apo E-free high-density lipoproteins (OX-HDL) in the rat hepatoma cell, Fu5AH. Results: When 10–100 μg/ml [125I]-HDL or [125I]-OX-HDL were incubated with cells for 4 h at 37°C, cellular uptake of oxidized lipoproteins was twice control. In contrast, protein degradation was equal. [125I]-HDL or [125I]-OX-HDL were incubated with the cells for 4 h followed by a 4 h chase with unlabeled HDL and OX-HDL, respectively. In these experiments, 80% of [125I]-HDL was resecreted from the cell within 30 min while 50% of [125I]-OX-HDL was retained by the cell after 2 h. Electron microscopy was used to determine if the OX-HDL was retained in lysosomes. Cells were incubated with gold-labeled OX-HDL, and lysosomes were stained with acid phosphatase. Gold-labeled OX-HDL was abundant in intracellular vesicles that were not reactive to acid phosphatase. However, vesicles with a high content of OX-HDL frequently stained positively for 3,3′-diaminobenzidine, a stain that reacts with catalase and is used to detect peroxisomes. Conclusions: The present evidence indicates that the cellular metabolism of OX-HDL is different from that of unmodified HDL.