Influence of Intrinsic Aerobic Exercise Capacity and Sex on Cardiac Injury Following Acute Myocardial Ischemia and Reperfusion

Purpose: Previous reports have suggested that active exercise aside, intrinsic aerobic running capacity (Low = LCR, high = HCR) in otherwise sedentary animals may influence several cardiovascular health-related indicators. Relative to the HCR phenotype, the LCR phenotype is characterized by decreased endothelial reactivity, increased susceptibility to reperfusion-induced arrhythmias following short, non-infarction ischemia, and increased diet-induced insulin resistance. More broadly, the LCR phenotype has come to be characterized as a “disease prone” model, with the HCRs as “disease resistant.” Whether these effects extend to injury outcomes in an overt infarction or whether the effects are gender specific is not known. This study was designed to determine whether HCR/LCR phenotypic differences would be evident in injury responses to acute myocardial ischemia-reperfusion injury (AIR), measured as infarct size and to determine whether sex differences in infarction size were preserved with phenotypic selection.Methods: Regional myocardial AIR was induced in vivo by either 15 or 30 min ligation of the left anterior descending coronary artery, followed by 2 h of reperfusion. Global ischemia was induced in isolated hearts ex vivo using a Langendorff perfusion system and cessation of perfusion for either 15 or 30 min followed by 2 h of reperfusion. Infarct size was determined using 2, 3, 5–triphenyltetrazolium chloride (TTC) staining, and normalized to area at risk in the regional model, or whole heart in the global model. Portions of the tissue were paraffin embedded for H&E staining and histology analysis.Results: Phenotype dependent differences in infarct size were seen with 15 min occlusion/2 h reperfusion (LCR > HCR, p < 0.05) in both regional and global models. In both models, longer occlusion times (30 min/2 h) produced significantly larger infarctions in both phenotypes, but phenotypic differences were no longer present (LCR vs. HCR, p = n.s.). Sex differences in infarct size were present in each phenotype (LCR male > LCR female, p < 0.05; HCR male > HCR female, p < 0.05 regardless of length of occlusion, or ischemia model.Conclusions: There is cardioprotection afforded by high intrinsic aerobic capacity, but it is not infinite/continuous, and may be overcome with sufficient injury burden. Phenotypic selection based on endurance running capacity preserved sex differences in response to both short and longer term coronary occlusive challenges. Outcomes could not be associated with differences in system characteristics such as circulating inflammatory mediators or autonomic nervous system influences, as similar phenotypic injury patterns were seen in vivo, and in isolated crystalloid perfused heart ex vivo.

Activation of Nrf2 by Lithospermic Acid Ameliorates Myocardial Ischemia and Reperfusion Injury by Promoting Phosphorylation of AMP-Activated Protein Kinase α (AMPKα)

Background: As a plant-derived polycyclic phenolic carboxylic acid isolated from Salvia miltiorrhiza, lithospermic acid (LA) has been identified as the pharmacological management for neuroprotection and hepatoprotection. However, the role and mechanism of lithospermic acid in the pathological process of myocardial ischemia-reperfusion injury are not fully revealed.Methods: C57BL/6 mice were subjected to myocardial ischemia and reperfusion (MI/R) surgery and pretreated by LA (50 mg/kg, oral gavage) for six consecutive days before operation. The in vitro model of hypoxia reoxygenation (HR) was induced by hypoxia for 24 h and reoxygenation for 6 h in H9C2 cells, which were subsequently administrated with lithospermic acid (100 μM). Nrf2 siRNA and dorsomorphin (DM), an inhibitor of AMPKα, were used to explore the function of AMPKα/Nrf2 in LA-mediated effects.Results: LA pretreatment attenuates infarct area and decreases levels of TnT and CK-MB in plasm following MI/R surgery in mice. Echocardiography and hemodynamics indicate that LA suppresses MI/R-induced cardiac dysfunction. Moreover, LA ameliorates oxidative stress and cardiomyocytes apoptosis following MI/R operation or HR in vivo and in vitro. In terms of mechanism, LA selectively activates eNOS, simultaneously increases nuclear translocation and phosphorylation of Nrf2 and promotes Nrf2/HO-1 pathway in vivo and in vitro, while cardioprotection of LA is abolished by pharmacological inhibitor of AMPK or Nrf2 siRNA in H9C2 cells.Conclusion: LA protects against MI/R-induced cardiac injury by promoting eNOS and Nrf2/HO-1 signaling via phosphorylation of AMPKα.

Mitochondrial redox regulation and myocardial ischemia-reperfusion injury

Mitochondrial reactive oxygen species (ROS) have emerged as an important mechanism of disease and redox signaling in the cellular system. Under basal or pathological conditions, electron leakage for ROS production is primarily mediated by complexes I and III of the electron transport chain (ETC) and by the proton motive force (PMF), consisting of a membrane potential (ΔΨ) and a proton gradient (ΔpH). Several factors control redox status in mitochondria, including ROS, the PMF, oxidative post-translational modification (OPTM) of the ETC, SOD2, and HCCS (cytochrome c heme lyase). In the mitochondrial PMF, increased ΔpH-supported back-pressure due to diminishing electron transport and chemiosmosis promotes a more reductive mitochondrial physiological setting. OPTM by protein cysteine sulfonation in complex I and complex III has been shown to affect enzymatic catalysis, the proton gradient, redox status, and enzyme-mediated ROS production. Pathological conditions associated with oxidative or nitrosative stress, such as myocardial ischemia and reperfusion (I/R), increase mitochondrial ROS production and redox dysfunction via oxidative injury to complexes I and III, intensely enhancing protein cysteine sulfonation and impairing heme integrity. The physiological conditions of reductive stress induced by gains in SOD2 function normalizes I/R-mediated redox dysfunction. Further insight into the cellular mechanisms by which HCCS, biogenesis of c-type cytochrome, and OPTM regulate PMF and ROS production in mitochondria will enrich our understanding of redox signal transduction and identify new therapeutic targets for cardiovascular diseases in which oxidative stress perturbs normal redox signaling.

Empagliflozin protects the heart against ischemia/reperfusion-induced sudden cardiac death

Background Empagliflozin is a selective sodium–glucose cotransporter 2 (SGLT2) inhibitor used to lower blood sugar in adults with type 2 diabetes. Empagliflozin also exerts cardioprotective effects independent from glucose control, but its benefits on arrhythmogenesis and sudden cardiac death are not known. The purpose of this study was to examine the effect of empagliflozin on myocardial ischemia/reperfusion-provoked cardiac arrhythmia and sudden cardiac death in vivo. Methods Male Sprague Dawley rats were randomly assigned to sham-operated, control or empagliflozin groups. All except for the sham-operated rats were subjected to 5-min left main coronary artery ligation followed by 20-min reperfusion. A standard limb lead II electrocardiogram was continuously measured throughout the experiment. Coronary artery reperfusion-induced ventricular arrhythmogenesis and empagliflozin therapy were evaluated. The hearts were used for protein phosphorylation analysis and immunohistological assessment. Results Empagliflozin did not alter baseline cardiac normal conduction activity. However, empagliflozin eliminated myocardial vulnerability to sudden cardiac death (from 69.2% mortality rate in the control group to 0% in the empagliflozin group) and reduced the susceptibility to reperfusion-induced arrhythmias post I/R injury. Empagliflozin increased phosphorylation of cardiac ERK1/2 after reperfusion injury. Furthermore, inhibition of ERK1/2 using U0126 abolished the anti-arrhythmic action of empagliflozin and ERK1/2 phosphorylation. Conclusions Pretreatment with empagliflozin protects the heart from subsequent severe lethal ventricular arrhythmia induced by myocardial ischemia and reperfusion injury. These protective benefits may occur as a consequence of activation of the ERK1/2-dependent cell-survival signaling pathway in a glucose-independent manner.

Remote Ischemic Perconditioning Ameliorates Myocardial Ischemia and Reperfusion-Induced Coronary Endothelial Dysfunction and Aortic Stiffness in Rats

Background: Vascular stiffness and endothelial dysfunction are accelerated by acute myocardial infarction (AMI) and subsequently increase the risk for recurrent coronary events. Aim: To explore whether remote ischemic perconditioning (RIPerc) protects against coronary and aorta endothelial dysfunction as well as aortic stiffness following AMI. Methods: Male OFA-1 rats were subjected to 30 min of occlusion of the left anterior descending artery (LAD) followed by reperfusion either 3 or 28 days with or without RIPerc. Three groups: (1) sham operated (Sham, without LAD occlusion); (2) myocardial ischemia and reperfusion (MIR) and (3) MIR + RIPerc group with 3 cycles of 5 minutes of IR on hindlimb performed during myocardial ischemia were used. Assessment of vascular reactivity in isolated septal coronary arteries (non-occluded) and aortic rings as well as aortic stiffness was assessed by wire myography either 3 or 28 days after AMI, respectively. Markers of pro-inflammatory cytokines, adhesion molecules were assessed by RT-qPCR and ELISA. Results: MIR promotes impaired endothelial-dependent relaxation in septal coronary artery segments, increased aortic stiffness and adverse left ventricular remodeling. These changes were markedly attenuated in rats treated with RIPerc and associated with a significant decline in P-selectin, IL-6 and TNF-α expression either in infarcted or non-infarcted myocardial tissue samples. Conclusions: Our study for the first time demonstrated that RIPerc alleviates MIR-induced coronary artery endothelial dysfunction in non-occluded artery segments and attenuates aortic stiffness in rats. The vascular protective effects of RIPerc are associated with ameliorated inflammation and might therefore be caused by reduced inflammatory signaling.

Erythrocyte membrane coated nanoparticle-based control releasing hydrogen sulfide system protects ischemic myocardium

Aim: To construct a long circulatory and sustained releasing H2S system and explore its protective effects on myocardial ischemia and reperfusion (I/R) injury. Materials & methods: Red blood cell (RBC) membrane-coated, diallyl trisulfide (DATS)-carrying mesoporous iron oxide nanoparticles (MIONs) (RBC-DATS-MIONs) were prepared and characterized. Cytotoxicity and cellular uptake were studied in vitro, followed by in vivo assessment of safety, distribution and effect on cardiac function following I/R injury. Results: RBC-DATS-MIONs exhibited excellent biocompatibility, extended circulatory time and controlled-release of H2S in plasma and myocardium. They exhibited superior therapeutic effects on in vitro hypoxia/reoxygenation models and in vivo myocardial I/R models, which involved various mechanisms, including anti-apoptosis, anti-inflammatory and antioxidant activities. Conclusion: This work provides a new potential platform for best utilizing the protective effects of H2S by prolonging its releasing process.