Abstract-Clinical studies have reported that the widely used antihyperglycemic drug metformin significantly reduces cardiac risk factors and improves clinical outcomes in patients with heart failure. The mechanisms by which metformin exerts these cardioprotective effects remain unclear and may be independent of antihyperglycemic effects. We tested the hypothesis that chronic activation of AMP-activated protein kinase (AMPK) with low-dose metformin exerts beneficial effects on cardiac function and survival in in vivo murine models of heart failure. Mice were subjected to permanent left coronary artery occlusion or to 60 minutes left coronary artery occlusion followed by reperfusion for 4 weeks. High-resolution, 2D echocardiography was performed at baseline and 4 weeks after myocardial infarction to assess left ventricular dimensions and function. Metformin (125 g/kg) administered to mice at ischemia and then daily improved survival by 47% (PϽ0.05 versus vehicle) at 4 weeks following permanent left coronary artery occlusion. Additionally, metformin given at reperfusion and then daily preserved left ventricular dimensions and left ventricular ejection fraction (PϽ0.01 versus vehicle) at 4 weeks. The improvement in cardiac structure and function was associated with increases in AMPK and endothelial nitric oxide synthase (eNOS) phosphorylation, as well as increased peroxisome proliferatoractivated receptor-␥ coactivator (PGC)-1␣ expression in cardiac myocytes. Furthermore, metformin significantly improved myocardial cell mitochondrial respiration and ATP synthesis compared to vehicle. The cardioprotective effects of metformin were ablated in mice lacking functional AMPK or eNOS. This study demonstrates that metformin significantly improves left ventricular function and survival via activation of AMPK and its downstream mediators, eNOS and PGC-1␣, in a murine model of heart failure. Key Words: myocardial ischemia Ⅲ heart failure Ⅲ metformin Ⅲ nitric oxide H eart failure (HF) is the inability of the heart to meet hemodynamic demands and represents the end stage of various forms of cardiac disease. In the industrialized nations, HF represents a major health problem that has been increasing in prevalence and incidence. In the United States, HF affects more than 5 million people, with 500 000 new cases reported every year. It is responsible for almost 1 million hospital admissions and 40 000 deaths annually. 1 The most important cause of HF is coronary artery disease and acute myocardial infarction, leading to loss of functioning myocytes, development of myocardial fibrosis, and subsequent left ventricular (LV) remodeling, all of which contribute toward the development of LV dysfunction.Metformin is an orally administered biguanide drug that is widely used to lower blood glucose concentrations in patients with diabetes mellitus. Metformin decreases blood glucose by mechanisms different from those of sulfonylureas or insulin and exerts its actions by enhancing insulin sensitivity, inducing greater peripheral uptake of glu...

Nitrite has emerged as an endogenous signaling molecule with potential therapeutic implications for cardiovascular disease. Steadystate levels of nitrite are derived in part from dietary sources; therefore, we investigated the effects of dietary nitrite and nitrate supplementation and deficiency on NO homeostasis and on the severity of myocardial ischemia-reperfusion (MI/R) injury. Mice fed a standard diet with supplementation of nitrite (50 mg/liter) in their drinking water for 7 days exhibited significantly higher plasma levels of nitrite, exhibited significantly higher myocardial levels of nitrite, nitroso, and nitrosyl-heme, and displayed a 48% reduction in infarct size (Inf) after MI/R. Supplemental nitrate (1 g/liter) in the drinking water for 7 days also increased blood and tissue NO products and significantly reduced Inf. A time course of ischemia-reperfusion revealed that nitrite was consumed during the ischemic phase, with an increase in nitroso/nitrosyl products in the heart. Mice fed a diet deficient in nitrite and nitrate for 7 days exhibited significantly diminished plasma and heart levels of nitrite and NO metabolites and a 59% increase in Inf after MI/R. Supplementation of nitrite in the drinking water for 7 days reversed the effects of nitrite deficiency. These data demonstrate the significant influence of dietary nitrite and nitrate intake on the maintenance of steady-state tissue nitrite/nitroso levels and illustrate the consequences of nitrite deficiency on the pathophysiology of MI/R injury. Therefore, nitrite and nitrate may serve as essential nutrients for optimal cardiovascular health and may provide a treatment modality for cardiovascular disease.dietary supplementation ͉ myocardial infarction ͉ nitric oxide T he loss of nitric oxide (NO) generation as a result of a dysfunctional vascular endothelium is an often cited correlate of heart disease (1). Continuous generation of NO is essential for the integrity of the cardiovascular system, and a decreased production and/or bioavailability of NO is central to the development of cardiovascular disorders (2, 3). NO is a highly reactive and diffusible gas formed by three NO synthase (NOS) isoforms: neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). NO has been extensively studied in the setting of ischemiareperfusion (I/R) injury. Previous studies clearly demonstrate that the deficiency of eNOS exacerbates myocardial I/R (MI/R) injury (4), whereas the overexpression of eNOS (5, 6), NO donor (7, 8), or inhaled NO gas (9) therapy significantly protect the myocardium (10). NO possesses a number of physiological properties that make it a potent cardioprotective-signaling molecule. These include vasodilation and the inhibition of oxidative stress, platelet aggregation, leukocyte chemotaxis, and apoptosis (11-13). NO synthesis is influenced critically by various cofactors, such as tetrahydrobiopterin, flavin mononucleotide, and flavin adenine dinucleotide, as well as the presence of reduced thiols, the endogenous NOS inhibitor asy...

Objective Humanin, an endogenous anti-apoptotic peptide, has previously been shown to protect against Alzheimer’s disease and a variety of cellular insults. We evaluated the effects of a potent analog of humanin, HNG, in an in vivo murine model of myocardial ischemia and reperfusion (MI-R). Methods Male C57BL6/J mice (8–10 week old) were subjected to 45 min of left coronary artery occlusion followed by 24 hr reperfusion. HNG or vehicle was administered intra-peritoneally one hour prior or at the time of reperfusion. The extent of myocardial infarction per area-at-risk was evaluated at 24 hrs using Evans Blue dye and 2,3,5 triphenyltetrazolium chloride (TTC) staining. Left ventricular (LV) function was evaluated at one week post ischemia using high-resolution, 2- D echocardiography (VisualSonics Vevo 770). Myocardial cell signaling pathways and apoptotic markers were assessed at various time points (0–24 hrs) following reperfusion. Cardiomyocyte survival and apoptosis in response to HNG were assessed in vitro. Results HNG reduced infarct size relative to the area-at-risk in a dose dependent fashion, with a maximal reduction at the dose of 2 mg/kg. HNG therapy enhanced LV ejection fraction and preserved post-ischemic LV dimensions (end-diastolic and end-systolic), resulting in improved cardiac function. Treatment with HNG significantly increased the expression of pAMPK and p-eNOS in the heart and attenuated Bax and Bcl-2 levels following MI-R. HNG improved cardiomyocyte survival and decreased apoptosis in response to daunorubicin in vitro. Conclusions These data show that HNG provides cardioprotection in a mouse model of MI-R potentially through activation of AMPK-eNOS mediated signaling and regulation of apoptotic factors. HNG may represent a novel agent for the treatment of acute myocardial infarction.