Simvastatin pretreatment enhances ischemia-induced neovascularization and blood flow recovery in streptozotocin-treated mice

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Abstract

Objective:

In contrast to statins, ezetimibe belongs to a new class of cholesterol-lowering agent not known to mediate pleiotropic effects. Here we investigate whether ezetimibe or simvastatin can help recover blood flow and reduce tissue damage after hindlimb ischemia surgery in diabetic mice.

Methods:

Diabetic mice were created by intraperitoneal streptozotocin injection in male FVB/NJ mice. All diabetic mice were subsequently divided into three groups: diabetic control, diabetic with simvastatin (0.2 mg/kg), and diabetic with ezetimibe (0.1 mg/kg). All experimental mice received hindlimb ischemia surgery after 2 weeks of drug treatment. Circulating endothelial progenitor cell number was determined by flow cytometry (Sca-1+/C-kit+/Flk-1+) in peripheral blood.

Results:

In comparison to the mice in the diabetic control group (n = 6), wild-type mice (n = 6) and diabetic mice that received simvastatin (n = 6) had significantly increased ischemic/nonischemic limb blood perfusion ratio, higher capillary density (P< .05, respectively), and reduced ischemic limb damage (diabetic control, 80%; diabetic with simvastatin, 40%; diabetic with ezetimibe, 80%). However, these proangiogenic effects were not observed in diabetic mice that had been treated with ezetimibe. In addition, the number of ischemia-triggered endothelial progenitor cells in peripheral blood was significantly enhanced in the wild-type mice and in the diabetic mice being treated with simvastatin, but not in those being treated with ezetimibe, after ischemic surgery. Endothelial nitric oxide synthase activity as determined by acetylcholine-stimulated vasorelaxation recovered notably in diabetic mice that were treated with simvastatin but was not improved by ezetimibe (n = 6, each group). Moreover, simvastatin led to a significant upregulation of endothelial nitric oxide synthase phosphorylation; vascular endothelial growth factor protein levels in ischemic tissues were also increased. By contrast, administration of ezetimibe did not produce these effects.

Conclusions:

Simvastatin helped recover blood flow and reduce tissue damage in ischemic hindlimbs and also promoted new vessel formation in streptozotocin-treated mice, whereas ezetimibe did not. These results may help explain why statins and ezetimibe decrease cholesterol levels, whereas their pleiotropic effects on vasoprotective functions independent of low-density lipoprotein cholesterol lowering are different.

Clinical Relevance:

Compared with statins (3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors), ezetimibe belongs to a new class of cholesterol-lowering drugs that is not known to mediate pleiotropic effects. This study has shown that simvastatin improves blood flow recovery and increases new vessel formation by improvement of endothelial function and enhancement of endothelial progenitor cell mobilization after tissue ischemia in streptozotocin-treated mice. However, these effects were not observed in streptozotocin-induced diabetic mice treated with ezetimibe, implying that both statins and ezetimibe decrease cholesterol levels, but they may have different effects on vasoprotective functions, independent of changes in plasma lipids.

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