Rationale Ventricular arrhythmias remain the leading cause of death in patients suffering myocardial ischemia. Myeloperoxidase (MPO), a heme-enzyme released by polymorphonuclear neutrophils, accumulates within ischemic myocardium and has been linked to adverse left ventricular remodeling. Objective To reveal the role of MPO for the development of ventricular arrhythmias. Methods and Results In different murine models of myocardial ischemia MPO deficiency profoundly decreased vulnerability for ventricular tachycardia (VT) upon programmed right ventricular and burst stimulation and spontaneously as assessed by ECG telemetry following isoproterenol injection. Experiments employing CD11b/CD18-integrin-deficient (CD11b-/-) mice and intravenous MPO infusion revealed that neutrophil infiltration is a prerequisite for myocardial MPO accumulation. Ventricles from MPO-deficient (Mpo-/-) mice showed less pronounced slowing and decreased heterogeneity of electrical conduction in the periinfarct zone than WT mice. Expression of the redox sensitive gap-junctional protein connexin43 (Cx43) was reduced in the periinfarct area of WT compared to Mpo-/- mice. In isolated WT cardiomyocytes, Cx43 protein content decreased upon MPO/H2O2-incubation. Mapping of induced pluripotent stem-cell-derived cardiomyocyte (iPSCM) networks and in vivo investigations linked Cx43 breakdown to MPO-dependent activation of matrix-metalloproteinase 7. Moreover, Mpo-/- mice showed decreased ventricular postischemic fibrosis reflecting reduced accumulation of myofibroblasts. Ex vivo, MPO was demonstrated to induce fibroblast-to-myofibroblast transdifferentiation by activation of p38 mitogen-activated protein kinases (MAPK) resulting in upregulated collagen generation. In support of our experimental findings, baseline MPO plasma levels were independently associated with a history of ventricular arrhythmias, sudden cardiac death, or implantable cardioverter defibrillator implantation in a cohort of 2622 stable patients with an ejection fraction above 35% undergoing elective diagnostic cardiac evaluation. Conclusions MPO emerges as a crucial mediator of post-ischemic myocardial remodeling, and may evolve as a novel pharmacological target for secondary disease prevention following myocardial ischemia.

Pulmonary arterial hypertension (PAH) is characterized by adverse remodeling of pulmonary arteries. Although the origin of the disease and its underlying pathophysiology remain incompletely understood, inflammation has been identified as a central mediator of disease progression. Oxidative inflammatory conditions support the formation of electrophilic fatty acid nitroalkene derivatives, which exert potent anti-inflammatory effects. The current study investigated the role of 10-nitro-oleic acid (OA-NO 2 ) in modulating the pathophysiology of PAH in mice. Mice were kept for 28 days under normoxic or hypoxic conditions, and OA-NO 2 was infused subcutaneously. Right ventricular systolic pressure (RVPsys) was determined, and right ventricular and lung tissue was analyzed. The effect of OA-NO 2 on cultured pulmonary artery smooth muscle cells (PASMCs) and macrophages was also investigated. Changes in RVPsys revealed increased pulmonary hypertension in mice on hypoxia, which was significantly decreased by OA-NO 2 administration. Right ventricular hypertrophy and fibrosis were also attenuated by OA-NO 2 treatment. The infiltration of macrophages and the generation of reactive oxygen species were elevated in lung tissue of mice on hypoxia and were diminished by OA-NO 2 treatment. Moreover, OA-NO 2 decreased superoxide production of activated macrophages and PASMCs in vitro. Vascular structural remodeling was also limited by OA-NO 2 . In support of these findings, proliferation and activation of extracellular signal-regulated kinases 1/2 in cultured PASMCs was less pronounced on application of OA-NO 2 . Our results show that the oleic acid nitroalkene derivative OA-NO 2 attenuates hypoxia-induced pulmonary hypertension in mice. Thus, OA-NO 2 represents a potential therapeutic agent for the treatment of PAH.Keywords: pulmonary arterial hypertension; nitro-fatty acids; inflammation; hypoxia Clinical RelevancePulmonary hypertension is a severe disease whose pathophysiology is incompletely understood and for which therapeutic options are limited. The present study enforces the hypothesis that inflammatory and oxidative mechanisms play an important role in the development of pulmonary hypertension. Electrophilic nitro-fatty acids decreased hypoxia-induced pulmonary hypertension not only by antiinflammatory and antioxidant mechanisms but also by reducing smooth muscle cell proliferation via attenuation of extracellular signal-regulated kinases 1 and 2 activation. These findings suggest that nitro-fatty acids may serve as a new multimodal therapeutic approach in this disease.

Inflammation is an immune response triggered by microbial invasion and/or tissue injury. While acute inflammation is directed toward invading pathogens and injured cells, thus enabling tissue regeneration, chronic inflammation can lead to severe pathologies and tissue dysfunction. These processes are linked with macrophage polarization into specific inflammatory “M1-like” or regulatory “M2-like” subsets. Nitro-fatty acids (NO2-FAs), produced endogenously as byproducts of metabolism and oxidative inflammatory conditions, may be useful for treating diseases associated with dysregulated immune homeostasis. The goal of this study was to characterize the role of nitro-oleic acid (OA-NO2) in regulating the functional specialization of macrophages induced by bacterial lipopolysaccharide or interleukin-4, and to reveal specific signaling mechanisms which can account for OA-NO2-dependent modulation of inflammation and fibrotic responses. Our results show that OA-NO2 inhibits lipopolysaccharide-stimulated production of both pro-inflammatory and immunoregulatory cytokines (including transforming growth factor-β) and inhibits nitric oxide and superoxide anion production. OA-NO2 also decreases interleukin-4-induced macrophage responses by inhibiting arginase-I expression and transforming growth factor-β production. These effects are mediated via downregulation of signal transducers and activators of transcription, mitogen-activated protein kinase and nuclear factor-κB signaling responses. Finally, OA-NO2 inhibits fibrotic processes in an in vivo model of angiotensin II-induced myocardial fibrosis by attenuating expression of α-smooth muscle actin, systemic transforming growth factor-β levels and infiltration of both “M1-“ and “M2-like” macrophage subsets into afflicted tissue. Overall, the electrophilic fatty acid derivative OA-NO2 modulates a broad range of “M1-” and “M2-like” macrophage functions and represents a potential therapeutic approach to target diseases associated with dysregulated macrophage subsets.

OA-NO2 potently inhibits atrial fibrosis and subsequent AF. Nitro-fatty acids and possibly other lipid electrophiles thus emerge as potential therapeutic agents for AF, either by increasing endogenous levels through dietary modulation or by administration as synthetic drugs.