Oxidized LDL induces an oxidative stress and activates the tumor suppressor p53 in MRC5 human fibroblasts

It is now well established that oxidized LDL (OxLDL) is involved in the pro gression of the atheromatous plaque via several mechanisms, including its c ytotoxicity toward the arterial wall. Our study demonstrates that a 4-h inc ubation of cultured human fibroblasts with 25-75 mu g/ml OxLDL induced a do se-dependent increase in the intracellular levels of reactive oxygen specie s (ROS) and lipid peroxidation end products (TBARS). This effect was marked ly prevented by the antioxidant vitamin E. The lipid extract of OxLDL parti ally reproduced the action of the LDL particle itself. Concomitantly, OxLDL enhanced the DNA binding activity of p53 measured by electrophoretic mobil ity shift assay, and the intracellular protein level of p53 determined by i mmunoblot analysis. Cycloheximide prevented the OxLDL-induced aug mentation in both p53 binding activity and intracellular level. Again, the lipid ext ract of OxLDL reproduced the effect of OxLDL on p53 binding activity, where as vitamin E prevented it. These results indicate that OxLDL initiates an i ntracellular oxidative stress by means of its lipid peroxidation products, leading to the activation of the tumour suppressor p53 by enhancement of p5 3 protein synthesis. This effect might be related to the cytotoxic effect o f OxLDL since the activation of p53 is known to lead to cell cycle arrest, necrosis apoptosis. (C) 2000 Academic Press.