Oxysterol-induced activation of macrophage NADPH-oxidase enhances cell-mediated oxidation of LDL in the atherosclerotic apolipoprotein E deficient mouse: inhibitory role for vitamin E

In the present study we provide evidence, both direct and circumstantial. that macrophage oxysterols induce translocation of p47phox from the cytosol to the cell's plasma membrane, forming an active NADPH-oxidase complex which produces superoxide anion and facilitates cell-mediated oxidation of LDL. The study was performed on macrophages from atherosclerotic apolipoprotein E deficient (P) mice, which are under oxidative stress. The oxysterol content in peritoneal macrophages (MPM) from E-0 mice was significantly higher (by 50-80%) than that observed in MPM from control (C57BL6) mice. E-0 MPM release 2-fold more superoxide anions and oxidize LDL by 2.5-fold more than control MPM. Furthermore. macrophage protein kinase C (PKC) activity and arachidonic acid (AA) release (which are both involved in NADPH-oxidase activation) were elevated by 60 and 70% respectively, in E-0 MPM compared with control MPM. Dietary supplementation of vitamin E (40 mg/kg per day for 2 months) to E-0 mice resulted in a reduction in MPM total oxysterols content (- 27%) and this effect was associated with a reduction in PKC activity ( - 36%) AA release ( - 39%), cytosolic p47phox translocation to the plasma membrane ( - 30%), superoxide anion release ( - 25%) and MPM-mediated LDL oxidation ( - 28%,), compared with unsupplemented E-0 mice. Enrichment of MPM from control mice with the major oxysterols found in E-0 MPM (7-ketocholesterol, beta-epoxycholesterol and 7beta-hydroxycholesterol) resulted in a dose-dependent increase (60-80%) in PKC activity, AA release, p47phox translocation, superoxide anion release and cell-mediated oxidation of LDL. These data clearly demonstrate for the first time that under oxidative stress, cellular lipids are oxidized. and that macrophage enrichment with oxysterols (as exists in P mice) activates the NADPH-oxidase system and enhances cell-mediated oxidation of LDL, a key event during early atherogenesis. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.