Isolevuglandins, a novel class of isoprostenoid derivatives, function as integrated sensors of oxidant stress and are generated by myeloperoxidase in vivo

Abstract

Isolevuglandins (isoLGs) are a family of reactive gamma-ketoaldehydes generated by free radical oxidation of arachidonate-containing lipids through the isoprostane pathway. Elevated plasma levels of isoLG protein adducts are observed in subjects with atherosclerosis compared with age/gender-matched controls. However, mechanisms for the generation of isoLGs in vivo are not established. Here we show that free radical-induced peroxidation promoted by the myeloperoxidase (MPO)/H2O2 system of leukocytes serves as one mechanism for the generation of isoLGs in vivo. Using a Candida sepsis model of inflammation, we demonstrate 3.5- and 2.7-fold increases in iso[4]LGE2 and isoLGE2 adducts of plasma proteins after pathogen exposure in wild-type mice. Plasma levels of F2 isoprostanes were not significantly increased after pathogen challenge in this model. MPO knockout mice demonstrated significant reductions (34%, P=0.003) in plasma levels of iso[4]LGE2 protein adducts after pathogen challenge compared with wild-type mice. Mass spectrometry and immunochemical methods demonstrate MPO-dependent formation of iso[4]LGE2 and isoLGE2 phospholipids and their corresponding isoLG protein adducts in model systems. The present studies thus identify MPO as one pathway for generation of isoLGs in vivo. They also suggest that long-lived protein isoLG adducts may serve as an alternative integrated sensor of oxidant stress in vivo.

Thematic review series: The Pathogenesis of Atherosclerosis The oxidation hypothesis of atherogenesis: the role of oxidized phospholipids and HDL

“…Berliner and colleagues (20)(21)(22)(23)(24)(25)(26) reported that mildly oxidized LDL, which was still recognized by the LDL receptor, stimulated human aortic endothelial cells to bind monocytes but not neutrophils and caused artery wall cells to produce the potent monocyte chemoattractant monocyte chemoattractant protein-1 and the differentiation factor monocyte colony stimulating factory. Subsequently, it was found that the biological activity of this minimally modified LDL (MM-LDL) was attributable to the oxidation of LDL phospholipids, which contain arachidonic acid in the sn -2 position (27)(28)(29)(30)(31)(32)(33)(34). Direct measurement of these oxidized phospholipids in atherosclerotic lesions in animals suggested that they exist at concentrations that would be biologically active in vivo (29).…”

“…Myeloperoxidase reaction products have been found in human atherosclerotic lesions (52), and there is increasing evidence that the myeloperoxidase pathway can generate proinflammatory oxidized lipids (32,(53)(54)(55)(56)(57)(58)). Another pathway that may be a potential source of reactive oxygen species for the generation of proinflammatory oxidized lipids is the NADPH oxidase pathway (59,60).…”

“…As indicated in the title of this paper, this review is focused on oxidized phospholipids and HDL. For a more broadly focused perspective, the reader is referred to a number of excellent recent reviews (32,33,42,57,61,62).…”

Eosinophil Peroxidase Catalyzed Protein Carbamylation Participates in Asthma

“…However, the reactive species EPO and MPO form can also oxidatively modify host tissues. Under physiological conditions, both EPO and MPO use hydrogen peroxide (H 2 O 2 ) as one substrate and an assortment of co-substrates to generate an array of reactive oxidant species that can damage both proteins and lipids at sites of inflammation (7)(8)(9)(10)(11)(12)13). For example, we have shown that eosinophils use EPOgenerated oxidants to promote modification of lung and airway proteins during allergen challenge in mild asthma, and in severe asthma (9, 14 -16).…”

Isoketals form cytotoxic phosphatidylethanolamine adducts in cells

“…In the presence of oxygen, these pyrrole adducts convert over time into highly stable lactam adducts, as well as hydroxylactam adducts ( 5,7 ). Increased concentrations of IsoK protein adducts have been observed in vivo during a wide variety of conditions associated with infl ammation and oxidative stress, including atherosclerosis, end stage kidney disease, myocardial infarction, Alzheimer's Disease, glaucoma, hyperoxia, allergic infl ammation, and experimental sepsis (8)(9)(10)(11)(12)(13)(14).…”