Intracellular oxidative modification of low density lipoprotein by endothelial cells

We investigated intracellular oxidative modification of low density lipoprotein (IOM-LDL) by endothelial cells (ECs) and the role of ferritin in this process. IOM-LDL was examined by immunocytochemistry with an anti-oxidized phosphatidylcholine antibody and by lipid peroxidation assay. Incubation of LDL-treated ECs (human umbilical vein endothelial cells, passage 3) with ferritin produced cytoplasmic immunostain with the antibody, especially in large or giant ECs, and the formation of thiobarbituric acid-reactive substance (TBARS) in these cells. These observations suggest that ECs can perform IOM-LDL. Incubation with the iron chelator deferoxamine or pretreatment of LDL-treated ECs with deferoxamine suppressed ferritin-induced IOM-LDL by greater than 60%. Antioxidants dimethylsulphoxide and butylated hydroxytoluene markedly inhibited IOM-LDL, but mannitol did so only mildly. Catalase and superoxide dismutase had little or no effect on IOM-LDL. Apoferritin substituted for ferritin did not induce IOM-LDL. Our data suggest that IOM-LDL is mediated by intracellular hydroxyl radical formation, which is catalyzed mainly by free iron released from ferritin, and that ECs contribute to the development of atherosclerosis via IOM-LDL.