Epoxyisoprostane E2-containing phospholipids in oxidized low density lipoprotein and atherosclerotic lesions

The initial event in the development of the atherosclerotic lesion is adhesion and transmigration of monocytes into the artery wall. We have previously reported that lipid mediators derived from the oxidation of arachidonic acid-containing phospholipids were present in mildly oxidized-low density lipoprotein (MM-LDL) and atherosclerotic lesions. These mediators induced the adhesion and transmigration of monocytes to endothelial cells in vitro. Using liquid chromatography combined with electrospray ionization-mass spectrometry (LC-ESI-MS) we have unambiguously identified two of these oxidized phospholipids as 1-palmitoyl-2-(5)oxovaleroyl-phosphatidylcholine (POVPC) and 1-palmitoyl-2-glutaroyl-phosphatidylcholine (PGPC). In addition, we have characterized a third biologically active oxidized phospholipid present in MM-LDL and atherosclerotic lesions with an eicosanioid-like moiety in the sn-2 position. This phospholipid had a mass [M + H⁺] of 828.5381 (C₄₄H₇₉NO₁₁P = 828.5391) by high resolution fast atom bombardment mass spectrometry. Combining normal and reversed phase LC-ESI-MS we isolated six major isomers of the eicosanophospholipid which were individually tested for their ability to induce monocyte-endothelial interactions. One of the six isomers was biologically active and have determined the molecular structure of that isomer by ESI-MS/MS (with and without chemical derivatization), ultraviolet and infrared spectroscopy, and nuclear magnetic resonance spectroscopy. These data support the presence of a novel 5,6-epoxyisoprostane-containing phospholipid in MM-LDL and atherosclerotic lesions which may contribute to atherogenesis.