Apolipoprotein E-/- Mice Lacking Hemopexin Develop Increased Atherosclerosis via Mechanisms That Include Oxidative Stress and Altered Macrophage Function.

OBJECTIVE: We previously reported that hemopexin (Hx), a heme scavenger, is significantly increased and associated with proinflammatory high-density lipoprotein under atherogenic conditions. Although it is established that Hx together with macrophages plays a role in mitigating oxidative damage, the role of Hx in the development of atherosclerosis is unknown.

APPROACH AND RESULTS: We used Hx and apoE double-knockout mice (HxE(-/-)) to determine the role of Hx in the development of atherosclerosis. HxE(-/-) mice had significantly more free heme, reactive oxygen species, and proinflammatory high-density lipoprotein in their circulation, when compared with control apoE(-/-) mice. Atherosclerotic plaque area (apoE(-/-)=9.72±2.5×10(4) μm(2) and HxE(-/-)=27.23±3.6×10(4) μm(2)) and macrophage infiltration (apoE(-/-)=38.8±5.8×10(3) μm(2) and HxE(-/-)=103.4±17.8×10(3) μm(2)) in the aortic sinus were significantly higher in the HxE(-/-) mice. Atherosclerotic lesions in the aortas were significantly higher in the HxE(-/-) mice compared with apoE(-/-) mice. Analysis of polarization revealed that macrophages from HxE(-/-) mice were more M1-like. Ex vivo studies demonstrated that HxE(-/-) macrophage cholesterol efflux capacity was significantly reduced when compared with apoE(-/-) mice. Injection of human Hx into HxE(-/-) mice reduced circulating heme levels and human Hx pretreatment of naive bone marrow cells ex vivo resulted in a shift from M1- to M2-like macrophages.

CONCLUSIONS: We conclude that Hx plays a novel protective role in alleviating heme-induced oxidative stress, improving inflammatory properties of high-density lipoprotein, macrophage phenotype and function, and inhibiting the development of atherosclerosis in apoE(-/-) mice.