Abstract TP282: The Role of Metformin in Ischemic Stroke: AMPKalpha, eNOS, and mTOR Signaling Pathways

Background and purpose: Metformin is an important metabolic regulator for type 2 diabetes mellitus and cerebrovascular diseases including stroke. We investigate the mechanisms of metformin effects via catalytic alpha subunit of the AMP-activated protein kinase (AMPKalpha)-, endothelial nitric oxide synthase (eNOS)-, and mammalian target of rapamycin (mTOR)-signaling pathways in photothrombotic and ischemic stroke. Methods: We used a 1 h middle cerebral artery occlusion (MCAO)/23 h reperfusion stroke injury model with and without metformin. Metformin (30, 100, and 300 mg/kg) was orally administered via oral gavage in wild-type (C57Black6, WT) and eNOS deficient (eNOS-/-) mice. Infarction volume measured by MCID image-analysis software after TTC staining and Neurological deficit score (NDS) were determined at 23 h of reperefusion. We cultured the HUVEC and bEnd.3 cells with and without oxygen-glucose deprivation (OGD) condition. The AMPKalpha, eNOS, and mTOR expressions were measured in both OGD condition in cells and brain lysates in cerebral cortex at 23 h of reperfusion by a Western blot. Results: Treatment with metformin significantly increased rCBF, improved NDS, and reduced infarction volume in WT mice. eNOS-/- mice showed decreased rCBF and larger infarction volume in ischemic areas. In contradistinction, metformin increased rCBF, improved NDS, regulated blood glucose levels, and reduced infarction volume. Based on western blotting analysis of brain lysates in ischemic stroke, the expressions of AMPKalpha, eNOS, and mTOR were significantly increased by metformin compared to those of control. AMPKalpha, eNOS, and mTOR signaling pathways were activated and nitric oxide was increased by metformin in both HUVEC and bEnd.3 cells with and without OGD. Regulation of glucose and blood gases by metformin was related to reduced infarction in a dose-dependent manner. Conclusions: These findings indicate that the neuroprotective effect of metformin is mediated by AMPKalpha, eNOS, and mTOR signaling pathways and suggest that upregulation of AMPKalpha, eNOS, and mTOR activation is a potentially important therapeutic target for stroke.