Structural Identification of a Novel Pro-inflammatory Epoxyisoprostane Phospholipid in Mildly Oxidized Low Density Lipoprotein

Abstract

One of the earliest steps in the development of the atherosclerotic lesion is the accumulation of monocyte/ macrophages within the vessel wall. Oxidized lipids present in minimally modified-low density lipoproteins (MM-LDL) contribute to this process by activating endothelial cells to express monocyte-specific adhesion molecules and chemoattractant factors. A major focus of our group has been the isolation and characterization of the biologically active oxidized lipids in MM-LDL. We have previously characterized three oxidized phospholipids present in MM-LDL, atherosclerotic lesions of fat fed rabbits, and autoxidized 1-palmitoyl-2-arachidonoyl-snglycero-3-phosphocholine (Ox-PAPC) that induced human aortic endothelial cells to adhere human monocytes in vitro. We have used sequential normal and reverse phase-high performance liquid chromatography to isolate various isomers of an oxidized phospholipid from autoxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine. The fatty acid in the sn-2 position of this biologically active isomer and its dehydration product was released by phospholipase A 2 and characterized. Hydrogenation with platinum(IV) oxide/hydrogen suggested a cyclic moiety, and reduction with sodium borohydride suggested two reducible oxygencontaining groups in the molecule. The fragmentation pattern produced by electrospray ionization-collision induced dissociation-tandem mass spectrometry was consistent with a molecule resembling an E-ring prostaglandin with an epoxide at the 5,6 position. The structure of this lipid was confirmed by proton nuclear magnetic resonance spectroscopy analysis of the free fatty acid isolated from the dehydration product of m/z 828.5. Based on these studies, we arrived at the structure of the biologically active oxidized phospholipids as 1-palmitoyl-2-(5,6-epoxyisoprostane E 2 )-sn-glycero-3-phosphocholine. The identification of this molecule adds epoxyisoprostanes to the growing list of biologically active isoprostanes.

Transdifferentiation of mouse aortic smooth muscle cells to a macrophage-like state after cholesterol loading

“…Another possible explanation for these results is that cholesterol accumulation per se is not an inflammatory stimulus or that it is, but that induction of inflammatory molecules occurs at a later time. Support for the former possibility comes from the above-cited study (10), in which activation of SMCs was accomplished by delivery of cholesterol in the form of modified LDL [which contains the inflammatory factors (31,32)], and from studies by Lawn and colleagues (33), which have shown that loading of macrophage cell lines with oxidized LDL leads to increased expression of inflammatory genes and greater responsiveness of these genes to lipopolysaccharide stimulation (34).…”

Combined Serum Paraoxonase Knockout/Apolipoprotein E Knockout Mice Exhibit Increased Lipoprotein Oxidation and Atherosclerosis

“…In recent years, PON1 has also been shown to inhibit LDL oxidation in vitro (24,25). Among the oxidized lipids that PON1 can destroy are 1-palmitoyl-2-(5)oxovaleroyl-sn-glycero-3-phosphorylcholine (POVPC), 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphorylcholine (PGPC) (34), 2 1-palmitoyl-2-(5,6-epoxyisoprostane E 2 )-sn-glycero-3-phosphorylcholine (PEIPC) (35), 2 and cholesteryl linoleate hydroperoxides (36). PON1 can also destroy hydrogen peroxide (H 2 O 2 ), a major reactive oxygen species produced under oxidative stress during atherogenesis (36), suggesting that it has peroxidase activity as well.…”

Oxidized Low-Density Lipoprotein Promotes Mature Dendritic Cell Transition from Differentiating Monocyte

“…Paraoxonase (PON1) and platelet-activating factor acetylhydrolase (PAF-AH) are two enzymes complexed with lipoproteins that prevent the accumulation of oxLDL (19 -21). PON1 can inhibit LDL oxidation and destroy various bioactive oxidized phospholipids as well as hydrogen peroxide (22)(23)(24). In the model proposed by Watson et al (20), oxidized phospholipids are first substrate for PON1 in HDL.…”