Identification of the kinase cascades mediating oxidised low density lipoprotein-induced intracellular oxidative stress.

The oxidation of low density lipoprotein (LDL) to form cytotoxic oxidised LDL (oxLDL) is a central atherogenic process. Exposure to oxLDL triggers an oxidative stress response in various immune and vascular cell types and thus may play a critical role in cell death within the necrotic core region of atherosclerotic plaque. This study confirmed that exposure to oxLDL in U937 monocyte-like cells causes a concentration dependent increase in intracellular oxidant production leading to necrotic cell death, while native LDL (nLDL) has no significant effect. Pretreatment with the macrophage antioxidant 7,8-dihydroneopterin returns oxLDL-induced U937 intracellular oxidant production to near basal levels over a 12-hour period. A primary intracellular oxidant source is the NADPH oxidase (NOX) multimeric enzyme complex, which generates the superoxide anion radical (O2 -). Phosphorylation of the p47phox subunit by protein kinases is a key event in NOX activation and induces assembly of the active complex. In this study, the roles of three signal transduction cascades in oxLDL-cytotoxicity were investigated: p38 mitogen activated kinase (p38 MAPK), extracellular signal-regulated kinase 1/2 (ERK1/2) and protein kinase C (PKC). Inhibition of the p38 MAPK cascade by SB202190 reduced oxLDL-induced intracellular oxidant production, glutathione loss and cell death. Likewise, ERK1/2 cascade inhibition by PD98059 reduced oxLDL-induced oxidant production and cell death. PKC inhibition by Go6983 had no significant effect on oxLDL cytotoxicity, however these results were inconclusive. These findings suggest that both the p38 MAPK and ERK1/2 cascades act as key mediators of oxLDLinduced intracellular oxidative stress, possibly via NOX activation