Liraglutide Attenuates Preestablished Atherosclerosis in Apolipoprotein E-Deficient Mice via Regulation of Immune Cell Phenotypes and Proinflammatory Mediators

We have shown that the glucagon-like peptide-1 receptor agonist (GLP-1RA) liraglutide (Lir) inhibits development of early atherosclerosis in vivo by modulating immune cell function. We hypothesized that Lir could attenuate pre-established disease by modulating monocyte or macrophage phenotype to induce atheroprotective responses. Human atherosclerotic plaques obtained postendarterectomy and human peripheral blood macrophages were treated ex vivo with Lir. In parallel, apolipoprotein E-deficient (ApoE^-/-) mice received a high-fat, high-cholesterol diet to induce atherosclerosis for 8 weeks, after which ApoE^-/- mice received 300 μg/kg of Lir daily or vehicle control for a further 4 weeks to investigate the attenuation of atherosclerosis. Lir inhibited proinflammatory monocyte chemoattractant protein-1 secretion from human endarterectomy samples and monocyte chemoattractant protein-1, tumor necrosis factor-α, and interleukin (IL)-1β secretion from human macrophages after ex vivo treatment. An increase in CD206 mRNA and IL-10 secretion was also detected, which implies resolution of inflammation. Importantly, Lir significantly attenuated pre-established atherosclerosis in ApoE^-/- mice in the whole aorta and aortic root. Proteomic analysis of ApoE^-/- bone marrow cells showed that Lir upregulated the proinflammatory cathepsin protein family, which was abolished in differentiated macrophages. In addition, flow cytometry analysis of bone marrow cells induced a shift toward reduced proinflammatory and increased anti-inflammatory macrophages. We concluded that Lir attenuates pre-established atherosclerosis in vivo by altering proinflammatory mediators. This is the first study to describe a mechanism through which Lir attenuates atherosclerosis by increasing bone marrow proinflammatory protein expression, which is lost in differentiated bone marrow-derived macrophages. This study contributes to our understanding of the anti-inflammatory and cardioprotective role of GLP-1RAs. SIGNIFICANCE STATEMENT: It is critical to understand the mechanisms through which liraglutide (Lir) mediates a cardioprotective effect as many type 2 diabetic medications increase the risk of myocardial infarction and stroke. We have identified that Lir reduces proinflammatory immune cell populations and mediators from plaque-burdened murine aortas in vivo and augments proresolving bone marrow-derived macrophages in attenuation of atherosclerotic disease, which provides further insight into the atheroprotective effect of Lir.