Endothelial-targeted Nitroxides Inhibit MPO-mediated Endothelial Dysfunction

Abstract

During inflammatory cardiovascular disease myeloperoxidase (MPO) is released by circulating leukocytes and transported into the sub-endothelial matrix of diseased arteries. At this site, MPO catalyzes oxidative reactions that promote endothelial dysfunction. Accordingly, there is interest in developing MPO inhibitor drugs that can effectively access and target endothelial-localized MPO. Here we studied a series of newly developed piperidine nitroxides conjugated to different polyamine moieties as a novel class of endothelial-targeted MPO inhibitors. Electron paramagnetic resonance (EPR) analysis showed that polyamine-conjugated nitroxides were efficiently internalized into endothelial cells and isolated rat aorta in a manner inhibited by heparin. These novel nitroxides inhibited several oxidative reactions catalyzed by purified MPO and endothelial-localized MPO including the production of hypochlorous acid (HOCl) and the nitrogen dioxide radical, as well as the catalytic-consumption of nitric oxide (NO), with their efficacy of action dependent on nitroxide and conjugated-polyamine structure. Piperidine nitroxides were also effective at inhibiting MPO-mediated impairment of endothelial-dependent relaxation of isolated aorta containing endothelial-sequestered MPO and exposed to hydrogen peroxide (H2O2). These studies show for the first time that polyamine-conjugated piperidine-based nitroxides can efficiently inhibit oxidative reactions catalyzed by endothelial-localized MPO. They also provided important structure-function information useful for the further development of endothelial-targeted nitroxides, which represent a promising and versatile class of therapeutics available to inhibit endothelial dysfunction during cardiovascular disease.