MitoQ improves mitochondrial dysfunction in heart failure induced by pressure overload.

Heart failure remains a major public-health problem with an increase in the number of patients worsening from this disease. Despite current medical therapy, the condition still has a poor prognosis. Heart failure is complex but mitochondrial dysfunction seems to be an important target to improve cardiac function directly. Our goal was to analyze the effects of MitoQ (100 µM in drinking water) on the development and progression of heart failure induced by pressure overload after 14 weeks. The main findings are that pressure overload-induced heart failure in rats decreased cardiac function in vivo that was not altered by MitoQ. However, we observed a reduction in right ventricular hypertrophy and lung congestion in heart failure animals treated with MitoQ. Heart failure also decreased total mitochondrial protein content, mitochondrial membrane potential in the intermyofibrillar mitochondria. MitoQ restored membrane potential in IFM but did not restore mitochondrial protein content. These alterations are associated with the impairment of basal and stimulated mitochondrial respiration in IFM and SSM induced by heart failure. Moreover, MitoQ restored mitochondrial respiration in heart failure induced by pressure overload. We also detected higher levels of hydrogen peroxide production in heart failure and MitoQ restored the increase in ROS production. MitoQ was also able to improve mitochondrial calcium retention capacity, mainly in the SSM whereas in the IFM we observed a small alteration. In summary, MitoQ improves mitochondrial dysfunction in heart failure induced by pressure overload, by decreasing hydrogen peroxide formation, improving mitochondrial respiration and improving mPTP opening

Membrane Stabilizing Copolymer Poloxamer 188 in Preclinical Models of Acute Myocardial Infarction Reperfusion

University of Minnesota Ph.D. dissertation. November 2019. Major: Integrative Biology and Physiology. Advisor: Demetris Yannopoulos. 1 computer file (PDF); 161 pages.Coronary artery disease is the most common disease of the heart and number one cause of death worldwide, affecting millions annually. Acute myocardial infarction (AMI) is a classic manifestation of coronary artery disease and occurs when prolonged myocardial ischemia reaches a critical threshold, partially or completely occluding the coronary arteries, leading to necrosis of the adjacent tissue and subsequent scar formation. Despite recent advances in treatment strategies, risk of death by secondary cardiac events like hemorrhagic shock and cardiac arrest remain very high. Cellular injury after acute myocardial infarction occurs in two stages- ischemic injury, which occurs when there is a myocardial oxygen supply-demand mismatch, and reperfusion injury, which occurs with the sudden unrestrained return of blood to the oxygen deprived tissue. Some of the strategies to minimize reperfusion injury including ischemic pre-and post-conditioning, and therapeutic hypothermia have been successful in animal studies but have exhibited mixed results in clinical trials. Several cellular events that occur in ischemia including calcium overload and reactive oxygen species (ROS) generation, inflammation and myocardial contracture are further exacerbated during reperfusion injury. Mitochondria play a crucial role in augmenting the events of reperfusion injury by further increasing calcium overload, ROS induced ROS release and opening of the mitochondrial permeability transition pore, all of which triggers cell death pathways. Hence, there’s an urgent need for therapies that prevent mitochondrial dysfunction and mitigate reperfusion injury. Poloxamer 188 (P188) is the most studied member of the poloxamer family, comprised of non-ionic polymers made of a hydrophobic core, flanked by hydrophilic end chains. Due to its membrane stabilizing and anti-coagulant properties, P188 remains a favorable agent to prevent membrane damage in several disease models including sickle cell anemia, muscular dystrophy, cardiac arrest and acute myocardial infarction. The predominant theme of this dissertation revolves around understanding the events that occur at reperfusion after acute myocardial infarction and finding ways to combat this reperfusion injury with the use of P188. Here, we demonstrate for the first time the benefit of P188 administration in salvaging myocardial and mitochondrial function using a large animal model of AMI with current treatment procedures. We further investigate if this improvement in mitochondrial function transcends to the level of the two distinct mitochondrial subtypes in the heart. Finally, with the results from these studies, we examine if there’s a survival benefit with our model of AMI reperfusion. Results from this study will provide a better understanding of the events surrounding reperfusion injury within the distinctive subpopulations of mitochondria and underscore the immediate and long-lasting benefits of administering P188 promptly at reperfusion

Cardiac mitochondrial proteome dynamics with heavy water reveals stable rate of mitochondrial protein synthesis in heart failure despite decline in mitochondrial oxidative capacity

We recently developed a method to measure mitochondrial proteome dynamics with heavy water ((2)H(2)O)-based metabolic labeling and high resolution mass spectrometry. We reported the half-lives and synthesis rates of several proteins in the two cardiac mitochondrial subpopulations, subsarcolemmal and interfibrillar (SSM and IFM), in Sprague Dawley rats. In the present study, we tested the hypothesis that the mitochondrial protein synthesis rate is reduced in heart failure, with possible differential changes in SSM versus IFM. Six to seven week old male Sprague Dawley rats underwent transverse aortic constriction (TAC) and developed moderate heart failure after 22 weeks. Heart failure and sham rats of the same age received heavy water (5% in drinking water) for up to 80 days. Cardiac SSM and IFM were isolated from both groups and the proteins were separated by 1D gel electrophoresis. Heart failure reduced protein content and increased the turnover rate of several proteins involved in fatty acid oxidation, electron transport chain and ATP synthesis, while it decreased the turnover of other proteins, including pyruvate dehydrogenase subunit in IFM, but not in SSM. Because of these bidirectional changes, the average overall half-life of proteins was not altered by heart failure in both SSM and IFM. The kinetic measurements of individual mitochondrial proteins presented in this study may contribute to a better understanding of the mechanisms responsible for mitochondrial alterations in the failing heart

Intracoronary Poloxamer 188 Prevents Reperfusion Injury in a Porcine Model of ST-Segment Elevation Myocardial Infarction

Poloxamer 188 (P188) is a nonionic triblock copolymer believed to prevent cellular injury after ischemia and reperfusion. This study compared intracoronary (IC) infusion of P188 immediately after reperfusion with delayed infusion through a peripheral intravenous catheter in a porcine model of ST-segment elevation myocardial infarction (STEMI). STEMI was induced in 55 pigs using 45 min of endovascular coronary artery occlusion. Pigs were then randomized to 4 groups: control, immediate IC P188, delayed peripheral P188, and polyethylene glycol infusion. Heart tissue was collected after 4 h of reperfusion. Assessment of mitochondrial function or infarct size was performed. Mitochondrial yield improved significantly with IC P188 treatment compared with control animals (0.25% vs. 0.13%), suggesting improved mitochondrial morphology and survival. Mitochondrial respiration and calcium retention were also significantly improved with immediate IC P188 compared with control animals (complex I respiratory control index: 7.4 vs. 3.7; calcium retention: 1,152 nmol vs. 386 nmol). This benefit was only observed with activation of complex I of the mitochondrial respiratory chain, suggesting a specific effect from ischemia and reperfusion on this complex. Infarct size and serum troponin I were significantly reduced by immediate IC P188 infusion (infarct size: 13.9% vs. 41.1%; troponin I: 19.2 μg/l vs. 77.4 μg/l). Delayed P188 and polyethylene glycol infusion did not provide a significant benefit. These results demonstrate that intracoronary infusion of P188 immediately upon reperfusion significantly reduces cellular and mitochondrial injury after ischemia and reperfusion in this clinically relevant porcine model of STEMI. The timing and route of delivery were critical to achieve the benefit

Role of Epinephrine and Extracorporeal Membrane Oxygenation in the Management of Ischemic Refractory Ventricular Fibrillation

Summary: Extracorporeal membrane oxygenation (ECMO) is used in cardiopulmonary resuscitation (CPR) of refractory cardiac arrest. The authors used a 2 à 2 study design to compare ECMO versus CPR and epinephrine versus placebo in a porcine model of ischemic refractory ventricular fibrillation (VF). Pigs underwent 5 min of untreated VF and 10 min of CPR, and were randomized to receive epinephrine versus placebo for another 35 min. Animals were further randomized to left anterior descending artery (LAD) reperfusion at minute 45 with ongoing CPR versus venoarterial ECMO cannulation at minute 45 of CPR and subsequent LAD reperfusion. Four-hour survival was improved with ECMO whereas epinephrine showed no effect. Key Words: advanced cardiopulmonary life support, cardiac arrest, cardiopulmonary resuscitation, ECMO, extracorporeal membrane oxygenation, ischemic refractory ventricular fibrillation, ST-segment elevation myocardial infarction, ventricular fibrillatio