A therosclerosis is a chronic inflammatory disease causing progressive lesion formation and luminal narrowing of arteries. The underlying pathology is initiated by endothelial dysfunction and structural alterations after an imbalanced lipid metabolism and trapping of low-density lipoprotein (LDL) particles in the intima of arteries.1,2 Subsequently, intimal lipid accumulation triggers the release of various chemokines by activated endothelial cells, inducing a multiphase cascade of leukocyte infiltration and inflammatory responses in the arterial walls. As the knowledge of these inflammatory pathways has been growing during the past years, it has also uncovered new druggable targets that could complement the current treatment options, which do not directly interfere with the central inflammatory mechanisms driving atheroprogression. One endogenous pathway that has gained increasing attention for its wide-ranging and potent actions in suppressing maladaptive inflammatory responses is the melanocortin system consisting of melanocortin peptides and their cellular receptors. 3,4 However, the role of melanocortin signaling and its promise as a therapeutic target in atherosclerosis remain fully unexplored.Melanocortins are a family of peptides that are proteolytically cleaved from the common precursor molecule pro-opiomelanocortin. These peptides include melanocyte-stimulating hormones (α-, β-, and γ-MSH) and adrenocorticotropic hormone. They regulate important physiological functions by acting via G-protein-coupled melanocortin receptors (MC-Rs), named from MC1-R to MC5-R. 5,6 Our recent findings indicate that α-MSH serves as a protective regulator in the vasculature by enhancing endothelium-dependent control of blood vessel tone. 7 Mechanistically, α-MSH was shown to augment vascular nitric oxide (NO) availability by activating MC1-R in the endothelium. Besides promoting endothelial function, mounting evidence indicates that α-MSH, through the activation of © 2014 American Heart Association, Inc. Objective-Melanocortin peptides have been shown to elicit anti-inflammatory actions and to promote vascular endothelial function by activating type 1 and 3 melanocortin receptors. Here, we addressed whether these favorable properties of melanocortins could reduce atherosclerotic plaque inflammation and improve vasoreactivity in atherosclerotic mice. Approach and Results-Low-density lipoprotein receptor-deficient mice expressing only apolipoprotein B100 were fed a high-fat diet for 8 or 16 weeks and treated with either vehicle or a stable melanocortin analog, melanotan II (MT-II, 0.3 mg/kg per day, 4 weeks). We determined plaque uptake of fluorine-18-labeled fluorodeoxyglucose as a surrogate marker for atherosclerotic plaque inflammation and vascular function of the aorta by ex vivo analyses. MT-II had no effect on body weight or composition, or plasma cholesterol levels in atherosclerotic mice. Without attenuating atherosclerotic lesion size or lesional macrophage accumulation, MT-II treatment reduced fluorine-18-labeled...