Long-term effects of chronic statin treatment in the post-ischemic brain

Abstract

Pretreatment with statins, inhibitors of HMG-CoA reductase, augments cerebral blood flow during cerebral ischemia, resulting in neuroprotection via mechanisms related to the upregulation of endothelial nitric oxide synthase (eNOS). Endothelium-derived NO is also known to be essential for the growth of new vessels, and statins increase neovascularization through NO-dependent pathways. In addition, it has recently been demonstrated that statins mobilize bone marrow-derived endothelial progenitor cells, which are dependent on eNOS. Here, we investigated the long-term effects of the HMG-CoA reductase inhibitor rosuvastatin in a model of mild ischemic stroke. SV129 mice were treated by daily subcutaneous injections with rosuvastatin (2 mg/kg body weight). Treatment started two weeks before 30 minutes of filamentous left middle cerebral artery occlusion (MCAo) and reperfusion and was continued for 4 additional weeks. Ischemic lesion size, functional outcome and eNOS regulation in the vasculature were determined in animals following sacrifice. Additionally, we measured absolute cerebral blood flow with the Iodo-C14-antipyrine-technique, counted capillary density via Evans blue perfusion signal and detected engraftment of bone marrow-derived progenitor cells and newly-generated endothelial cells within the ischemic lesion. We demonstrated that chronic continuous administration of rosuvastatin conferred long-term histologic and functional protection six weeks after cerebral ischemia. Upregulation of eNOS expression in the aorta was sustained until 6 weeks after onset of treatment, but neuroprotection was completely abolished when the NOS inhibitor L-NAME was co-adminstered. This shows that eNOS plays a role in the effect of rosuvastatin on tissue recovery. In addition, rosuvastatin augmented disc neovascularization, enhanced the engraftment of bone marrow-derived progenitor cells and the number of von-Willebrand-factor/bromodeoxyuridine double-positive cells in the lesion, indicating an angiogenic stimulus. The density of perfused vessels in the post-ischemic brain was not increased in rosuvastatin-treated animals while large increases in average caliber were observed four weeks after MCAo. Moreover, areas of enlarged vessels were associated with lower blood flow levels. In conclusion, stroke protection by chronic rosuvastatin treatment extends until weeks after the ischemic insult. While the protection is mediated by eNOS upregulation and accompanied by an angiogenic response, vessel density and absolute cerebral blood flow levels were not increased by chronic rosuvastatin treatment in the post-ischemic brain.