Modified phosphatidylethanolamine as the active component of oxidized low density lipoprotein promoting platelet prothrombinase activity

We analyzed the influence of the atherogenic oxidized low density lipoprote ins (LDL) on the activity of the platelet prothrombinase complex, a major c ontributor to overall thrombin formation in vivo, Platelet dependent thromb in generation was found to be strongly stimulated by in vitro oxidized LDL. The enhancement was additive to that observed with the platelet agonist th rombin. Oxidized LDL increased the platelet binding of annexin-V, suggestin g that the augmented surface exposure of aminophospholipids promoted the pr othrombinase activity, All of the stimulatory activity of the oxidized LDL could be recovered in the microemulsions prepared hom the Lipid portion of the modified particles. Phospholipid vesicles were prepared containing the total lipids of the oxidized LDL but lacking specifically in one lipid comp onent. Following the selective removal of the ethanolamine phospholipids (P E) from the LDL lipids, the platelet-dependent thrombin formation was marke dly reduced. Vesicles enriched with the isolated PE fraction alone enhanced the thrombin generation. Analyses with autoxidized phospholipids indicated that oxidation products of unsaturated diacyl-PE Fc-ere mainly responsible for the increased prothrombinase activity. Oxidized LDL and its PE fractio n lost their stimulatory activity after treatment with NaCNBH3, a chemical reductant of Schiff base adducts. Phospholipid vesicles supplemented with s ynthetic aldehyde-PE adducts largely reproduced the stimulation of the thro mbin generation. Ne conclude that the oxidized LDL particles elicit a prono unced prothrombotic response by increasing the activity of the platelet pro thrombinase complex, Specific oxidative modifications of the EDL associated ethanolamine phospholipids are mainly responsible for this stimulation.