Reperfusion Reduced Infarct Size Research Articles

β-hydroxybutyrate administered at reperfusion reduces infarct size and preserves cardiac function by improving mitochondrial function through autophagy in male mice

Ischemia/reperfusion (I/R) injury after revascularization contributes ∼50% of infarct size and causes heart failure, for which no established clinical treatment exists. β-hydroxybutyrate (β-OHB), which serves as both an energy source and a signaling molecule, has recently been reported to be cardioprotective when administered immediately before I/R and continuously after reperfusion. This study aims to determine whether administering β-OHB at the time of reperfusion with a single dose can alleviate I/R injury and, if so, to define the mechanisms involved. We found plasma β-OHB levels were elevated during ischemia in STEMI patients, albeit not to myocardial protection level, and decreased after revascularization. In mice, compared with normal saline, β-OHB administrated at reperfusion reduced infarct size (by 50%) and preserved cardiac function, as well as activated autophagy and preserved mtDNA levels in the border zone. Our treatment with one dose β-OHB reached a level achievable with fasting and strenuous physical activity. In neonatal rat ventricular myocytes (NRVMs) subjected to I/R, β-OHB at physiologic level reduced cell death, increased autophagy, preserved mitochondrial mass, function, and membrane potential, in addition to attenuating reactive oxygen species (ROS) levels. ATG7 knockdown/knockout abolished the protective effects of β-OHB observed both in vitro and in vivo. Mechanistically, β-OHB's cardioprotective effects were associated with inhibition of mTOR signaling. In conclusion, β-OHB, when administered at reperfusion, reduces infarct size and maintains mitochondrial homeostasis by increasing autophagic flux (potentially through mTOR inhibition). Since β-OHB has been safely tested in heart failure patients, it may be a viable therapeutic to reduce infarct size in STEMI patients.

Abstract 18622: The Role of MicroRNA-98 in the Context of Myocardial Ischemia-Reperfusion Injury During Late Pregnancy

BACKGROUND: We have shown that the late-pregnant (LP) rodent exhibits a higher susceptibility to myocardial ischemia-reperfusion injury (IRI) compared to non-pregnant (NP). The molecular mechanisms remain unclear. The dysregulation of multiple microRNAs (miRs) in IRI suggests their potential as promising targets for therapeutic interventions. Methods: Female Sprague-Dawley rats in both NP and LP states underwent occlusion of the left anterior descending coronary artery (LAD) for a duration of 45 minutes, followed by reperfusion for 3 hours or 24 hours. Expression of miR was assessed via fluorescent in situ hybridization. MicroRNA-microarray profiling was conducted on hearts of NP and LP rats subjected to IRI. Female H9c2 rat cardiomyoblast cells were transfected with miR mimics and inhibitors, and subjected to hypoxia/reoxygenation. Blood samples were obtained from NP, LP, and ischemic heart disease (IHD) patients. MiR98 inhibitor was administered at the initiation of reperfusion. Results: MicroRNA-microarray analysis revealed upregulation of microRNA-98-5p (miR-98) in LV of LP at baseline, and a further upregulation after IRI. The expression of Stat3 and Pgc-1α were decreased in LV of LP rats compared to NP rats upon IRI. Fluorescent in situ hybridization revealed expression of miR-98 in cardiomyocytes in NP rats, which was increased in LP rats. Overexpression of miR-98 in vitro in female H9c2 cells decreased Stat3 and Pgc-1α levels, and promoted apoptosis, oxidative stress, and inflammatory markers. MiR-98 inhibitor in LP rats at the onset of reperfusion reduced infarct size, apoptosis, oxidative stress, and inflammatory markers and was associated with upregulation of Stat3 and Pgc-1α. In humans, plasma miR-98 levels were significantly higher in healthy LP compared to healthy NP individuals and even higher in LP patients with IHD patients. CONCLUSIONS: We show the detrimental effects of miR-98 by promoting cardiomyocyte oxidative stress, inflammation, and apoptosis via its targets Stat3 and Pgc-1α in the context of late pregnancy. MiR-98 could be a novel cardio-protective strategy or biomarker in late pregnancy.

Using of supersaturated oxygen delivery (SSO2 therapy) in patients with acute myocardial ischemia

Oxygen is the main participant in redox reactions in the body and its deficiency can lead to organ dysfunction. Thus, a decrease in blood flow in a certain region of the myocardium in patients with coronary heart disease can cause a heart attack. According to experimental studies, early reperfusion reduces infarct size, and clinical studies have shown that early effective reperfusion of the affected artery and prevention of re-occlusion is the basis for minimizing infarct size and mortality.Timely performed percutaneous intervention in patients with acute myocardial infarction significantly reduced the mortality rate and the risk of heart failure. Despite the endovascular treatment effectiveness, there is still a need for additional methods of cardioprotection, reducing the area of myocardial infarction and preventing the development of heart failure and adverse left ventricular remodeling. Blood oxygen supersaturation (SSO2 therapy) is one of the adjuvant methods of cardioprotection in the treatment of patients with acute myocardial ischemia.This review describes possible mechanisms for implementing the cardioprotective effects of SSO2 therapy, technology and equipment necessary for the application of this technique. In addition, the results of experimental and clinical studies on SSO2 therapy are consecrated. Of note, only one multicentre prospective randomized controlled trial with uniform randomization was performed. Thus, the use of this technology is limited by the use a commercial equipment.

Transvalvular Unloading Mitigates Ventricular Injury Due to Venoarterial Extracorporeal Membrane Oxygenation in Acute Myocardial Infarction

Whether extracorporeal membrane oxygenation (ECMO) with Impella, known as EC-Pella, limits cardiac damage in acute myocardial infarction remains unknown. The authors now report that the combination of transvalvular unloading and ECMO (EC-Pella) initiated before reperfusion reduced infarct size compared with ECMO alone before reperfusion in a preclinical model of acute myocardial infarction. EC-Pella also reduced left ventricular pressure-volume area when transvalvular unloading was applied before, not after, activation of ECMO. The authors further observed that EC-Pella increased cardioprotective signaling but failed to rescue mitochondrial dysfunction compared with ECMO alone. These findings suggest that ECMO can increase infarct size in acute myocardial infarction and that EC-Pella can mitigate this effect but also suggest that left ventricular unloading and myocardial salvage may be uncoupled in the presence of ECMO in acute myocardial infarction. These observations implicate mechanisms beyond hemodynamic load as part of the injury cascade associated with ECMO in acute myocardial infarction.

Abstract P2076: β-hydroxybutyrate Administered At Reperfusion Alleviates Myocardial Ischemia-reperfusion Injury By Enhancing Autophagy And Mitochondrial Homeostasis

Introduction: ST-elevation myocardial infarction (STEMI) is the leading cause of heart failure. Ischemia/reperfusion (I/R) injury after revascularization contributes ~50% of infarct size, which we don’t have a clinical therapy. β-hydroxybutyrate (β-OHB) is a metabolite that increases during stress. In addition to providing energy, it serves as a signaling molecule (such as histone deacetylase inhibitor) to regulate many protective processes. Increasing the β-OHB level before I/R is cardiac protective. However, it has not been tested when administered at reperfusion. Hypothesis: The physiological concentration of β-OHB administered at the time of reperfusion reduces I/R injury by enhancing autophagy and mitochondrial homeostasis. Methods: C57BL6 wild-type mice were randomized into 2 groups and subjected to I/R surgery (I: 45 mins; R: 24 hrs). At reperfusion, normal saline or 10 mmol/kg of β-OHB (4-6 mM blood level) was given intraperitoneally. Echo was used to evaluate cardiac functions. We measured Infarct size, autophagic flux, and mitochondrial DNA levels in the heart. CAG-RFP-GFP-LC3 (RFLC3) mice were used to detect autophagic flux. Neonatal rat ventricular myocytes (NRVMs) were subjected to simulated I/R to test the effect of β-OHB in vitro . Small interfering RNA of ATG7 gene was used to assess the role of autophagy. Seahorse assay was performed to evaluate mitochondrial function after I/R. Results: β-OHB gave at reperfusion reduced infarct size by 50% (N=15 in control and N=11 in β-OHB group), and preserved systolic function in mice. In the border zone, the LC3II and the mtDNA level increased, and β-OHB increased autophagic flux in RFLC3 mice (N=5). In NRVMs subjected to I/R, β-OHB increased histone acetylation, cell viability, and maintained mitochondrial homeostasis (mitochondrial mass, membrane potential), and reduced ROS generation (N=4-6). Seahorse assay showed β-OHB enhanced ATP production after I/R. ATG7 knockdown blocked the protective effect of β-OHB in NRVMs. Conclusions: β-OHB administered at reperfusion reduces infarct size by increasing autophagic flux and maintaining mitochondrial homeostasis. Since β-OHB has been used in heart failure patients safely, it is a viable therapeutics to reduce infarct size in STEMI patients.

Percutaneous Intracoronary Delivery of Plasma Extracellular Vesicles Protects the Myocardium Against Ischemia-Reperfusion Injury in Canis.

[Figure: see text].

Activation of Autophagic Flux Blunts Cardiac Ischemia/Reperfusion Injury.

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Cardioprotection by post-conditioning with exogenous triiodothyronine in isolated perfused rat hearts and isolated adult rat cardiomyocytes

Ischemic post-conditioning (iPoCo) by coronary re-occlusion/reperfusion during immediate reperfusion after prolonged myocardial ischemia reduces infarct size. Mechanical manipulation of culprit lesions, however, carries the risk of coronary microembolization which may obscure iPoCo’s cardioprotection. Pharmacological post-conditioning with exogenous triiodothyronine (T3) could serve as an alternative conditioning strategy. Similar to iPoCo, T3 may activate cardioprotective prosurvival pathways. We aimed to study T3’s impact on infarct size and its underlying signal transduction. Hearts were isolated from male Lewis rats (200–380 g), buffer-perfused and subjected to 30 min/120 min global zero-flow ischemia/reperfusion (I/R). In additional hearts, either iPoCo (2 × 30 s/30 s I/R) was performed or T3 (100–500 µg/L) infused at reperfusion. Infarct size was demarcated with triphenyl tetrazolium chloride staining and calculated as percent of ventricular mass. Infarct size was reduced with iPoCo to 16 ± 7% vs. 36 ± 4% with I/R only. The maximum infarct size reduction was observed with 300 µg/L T3 (14 ± 2%). T3 increased the phosphorylation of protein kinase B and mitogen extracellular-regulated-kinase 1/2, both key enzymes of the reperfusion injury salvage kinase (RISK) pathway. Pharmacological RISK blockade (RISK-BL) during reperfusion abrogated T3’s cardioprotection (35 ± 10%). Adult ventricular cardiomyocytes were isolated from buffer-perfused rat hearts and exposed to 30 min/5 min hypoxia/reoxygenation (H/R); reoxygenation was initiated without or with T3, respectively, and without or with RISK-BL, respectively. Maximal preservation of viability was observed with 500 µg/L T3 after H/R (27 ± 4% of all cells vs. 5 ± 3% in time-matched controls). Again, RISK-BL abrogated protection (11 ± 3%). Mitochondria were isolated at early reperfusion from buffer-perfused rat hearts without or with iPoCo or 300 µg/L T3, respectively, at reperfusion. T3 improved mitochondrial function (i.e.: increased respiration, adenosine triphosphate production, calcium retention capacity, and decreased reactive oxygen species formation) to a similar extent as iPoCo. T3 at reperfusion reduces infarct size by activation of the RISK pathway. T3’s protection is a cardiomyocyte phenomenon and targets mitochondria.

Abstract 14412: Activation of Autophagic Flux Maintains Mitochondrial Homeostasis During Cardiac Ischemia/reperfusion Injury

Background and Hypothesis: Reperfusion injury accounts for ~50% of myocardial infarct size, and clinically efficacious therapies are lacking. Histone deacetylase (HDAC) inhibition enhances cardiomyocyte autophagic activity, mitochondria biogenesis, and blunts ischemia/reperfusion (I/R) injury when given at the time of reperfusion. However, as HDAC inhibition has pleiotropic effects, we will test whether augmentation of autophagic flux using a specific autophagy-inducing peptide, Tat-Beclin (TB), is cardioprotective. Methods: 8-12-week-old, wild-type, C57BL6 mice were randomized into three groups: vehicle control, Tat-Scrambled (TS) peptide, or Tat-Beclin (TB) peptide. Each group was subjected to I/R surgery (45min ischemia, 24h reperfusion). Infarct size, systolic function, and mitochondrial dynamics were assayed. Cultured neonatal rat ventricular myocytes (NRVMs) were used to test for cardiomyocyte specificity. Conditional cardiomyocyte ATG7 knockout (ATG7 KO) mice and ATG7 knockdown by siRNA in NRVMs were used to evaluate the role of autophagy. Results: TB treatment at reperfusion reduced infarct size by 20.1±6.3% (n=23, p<0.02) and improved systolic function. Increased autophagic flux and reduced reactive oxygen species (ROS) were observed in the infarct border zone. The cardioprotective effects of TB were abolished in ATG7 KO mice. TB increased mtDNA content in the border zone significantly. In NRVMs subjected to I/R, TB reduced cell death by 41±6% (n=12, p<0.001), decreased ROS, and increased mtDNA content significantly by ~50%. Moreover, TB promoted expression of PGC1α (a major driver of mitochondrial biogenesis) both in the infarct border zone and NRVMs subjected to I/R by ~40%, and increased levels of mitochondrial dynamics gene transcripts Drp1, Fis1, and MFN1 / 2. Conversely, ATG7 knockdown in NRVMs and cardiac ATG7 KO abolished the beneficial effects of TB on mitochondria DNA content. Conclusions: Autophagic flux is an essential process to mitigate myocardial reperfusion injury acting, at least in part, by inducing PGC1α-mediated mitochondrial biogenesis. Augmentation of autophagic flux may emerge as a viable clinical therapy to reduce reperfusion injury in myocardial infarction.

Abstract 13173: Unusual Fatigue and Failure to Utilize Emergency Medical Services Are Associated With Prolonged Prehospital Delay for Suspected Acute Coronary Syndrome

Introduction: Rapid reperfusion reduces infarct size and mortality for acute coronary syndrome (ACS) but efficacy is time dependent. Time to presentation in the Emergency Department (ED) remains excessive and patient-controlled prehospital delay may be a modifiable variable for intervention. The aim of the study was to determine if transportation factors and clinical presentation predicted prehospital delay for suspected ACS stratified by final diagnosis (ACS vs. no ACS). Hypothesis: Symptoms other than chest pain would contribute to longer prehospital delay that would vary by final diagnosis. Methods: Secondary analysis of data collected from a multi-center prospective study. A heterogeneous sample of ED patients with symptoms suggestive of ACS were enrolled at five sites in the US. Accelerated failure time (AFT) models were used to specify a direct relationship between delay time and variables to predict prehospital delay by final diagnosis. Results: The sample of 975 adults included 609 (62.5%) men and 366 (37.5%) women who were predominantly Caucasian (69.1%), had a mean age of 60.32 (±14.07) years, and had lower income levels (66.4% ≤$50,000 annually). Median delay time was 6.68 (1.91, 24.94) hours and only 26.2% had a prehospital delay of 2 hours or less. Patients with and without ACS presenting with unusual fatigue (TR=1.71, p=0.002; TR=1.54, p=0.003 , respectively) or self-transporting to the ED experienced significantly longer prehospital delay (TR 1.93, p<0.001; TR 1.71, p<0.001 , respectively). Predictors of shorter delay in patients with ACS were shoulder pain and lightheadedness (TR=0.65, p =0.013 and TR=0.67, p =0.022, respectively). Predictors of shorter delay for patients ruled-out for ACS were the presence of chest pain, sweating (TR=0.071, p =0.025 and TR=0.073, p =0.032, respectively). Conclusion: Patients self-transporting to the ED had prolonged prehospital delays. Encouraging the use of EMS is an important modifiable factor for patients with symptoms concerning for ACS. Calling 911 can be positively framed to at risk patients and the community as having advanced care come to them since EMS diagnostic capabilities include 12-lead ECG acquisition and possibly high sensitivity troponin assays.

Unusual Fatigue and Failure to Utilize EMS Are Associated With Prolonged Prehospital Delay for Suspected Acute Coronary Syndrome.

Rapid reperfusion reduces infarct size and mortality for acute coronary syndrome (ACS), but efficacy is time dependent. The aim of this study was to determine if transportation factors and clinical presentation predicted prehospital delay for suspected ACS, stratified by final diagnosis (ACS vs. no ACS). A heterogeneous sample of emergency department (ED) patients with symptoms suggestive of ACS was enrolled at 5 US sites. Accelerated failure time models were used to specify a direct relationship between delay time and variables to predict prehospital delay by final diagnosis. Enrolled were 609 (62.5%) men and 366 (37.5%) women, predominantly white (69.1%), with a mean age of 60.32 (±14.07) years. Median delay time was 6.68 (confidence interval 1.91, 24.94) hours; only 26.2% had a prehospital delay of 2 hours or less. Patients presenting with unusual fatigue [time ratio (TR) = 1.71, P = 0.002; TR = 1.54, P = 0.003, respectively) or self-transporting to the ED experienced significantly longer prehospital delay (TR = 1.93, P < 0.001; TR = 1.71, P < 0.001, respectively). Predictors of shorter delay in patients with ACS were shoulder pain and lightheadedness (TR = 0.65, P = 0.013 and TR = 0.67, P = 0.022, respectively). Predictors of shorter delay for patients ruled out for ACS were chest pain and sweating (TR = 0.071, P = 0.025 and TR = 0.073, P = 0.032, respectively). Patients self-transporting to the ED had prolonged prehospital delays. Encouraging the use of EMS is important for patients with possible ACS symptoms. Calling 911 can be positively framed to at-risk patients and the community as having advanced care come to them because EMS capabilities include 12-lead ECG acquisition and possibly high-sensitivity troponin assays.

Left Ventricular Unloading Increases the Coronary Collateral Flow Index Before Reperfusion and Reduces Infarct Size in a Swine Model of Acute Myocardial Infarction.

BackgroundUnloading the left ventricle and delaying reperfusion reduces infarct size in preclinical models of acute myocardial infarction. We hypothesized that a potential explanation for this effect is that left ventricular (LV) unloading before reperfusion increases collateral blood flow to ischemic myocardium.Methods and ResultsAcute myocardial infarction was induced by balloon occlusion of the left anterior descending artery for 120 minutes in adult swine, followed by reperfusion for 180 minutes. After 90 minutes of occlusion, animals were assigned to 30 minutes of continued occlusion (n=6) or to 30 minutes of support with either an Impella CP (n=4) or venoarterial extracorporeal membrane oxygenation (n=5) with persistent occlusion. The primary end point was measures of microcirculatory blood flow including the collateral flow index (CFI) during left anterior descending artery occlusion as (Pw−RA)/(Pa−RA), where Pa, Pw, and RA are aortic, coronary wedge, and right atrial pressure, respectively. Infarct size was quantified using triphenyltetrazolium chloride. Compared with continued occlusion, Impella, not venoarterial extracorporeal membrane oxygenation, reduced infarct size relative to the area at risk. Before reperfusion, Impella reduced LV stroke work by 25% and increased the CFI by 75%, but venoarterial extracorporeal membrane oxygenation did not. Among all groups, the change in CFI between 90 and 120 minutes correlated inversely with the change in LV stroke work (r 2=0.44, P=0.01) and infarct size (r 2=0.41, P=0.02).ConclusionsWe report for the first time that 30 minutes of LV unloading during coronary occlusion increases the CFI, which correlates inversely with LV stroke work and infarct size. Venoarterial extracorporeal membrane oxygenation failed to increase the CFI and did not reduce infarct size.

Abstract 887: Activation of Autophagic Flux Rescues Mitochondrial Homeostasis During Cardiac Ischemia/Reperfusion Injury

Objective: Reperfusion injury accounts for ~50% of myocardial infarct size, and meaningful clinical therapies targeting this do not exist. We have shown that HDAC inhibition-enhanced cardiomyocyte autophagy blunts ischemia/reperfusion (I/R) injury given at the time of reperfusion. However, as HDAC inhibition may have off-target effects, we set out to test whether augmentation of autophagy protects myocardium through maintenance of mitochondrial homeostasis and reduction of oxidative stress during reperfusion injury. Methods: 10-week-old, wild-type, C57BL6 mice were randomized into 3 groups: vehicle control, or exposed to a Tat-Scrambled (TS) peptide, or a Tat-Beclin (TB, autophagy-inducing molecule) peptide. Each group was subjected to I/R surgery (45min coronary ligation, 24h reperfusion). Infarct size, systolic function, and mitochondrial dynamics were assayed. Cultured neonatal rat ventricular myocytes (NRVMs) were exposed to TB during simulated ischemia/reperfusion injury. ATG7 knockout (ATG7 KO) mice and ATG7 knockdown by siRNA in NRVMs was used to evaluate the role of autophagy. Results: TB treatment at reperfusion reduced infarct size by 20.1% (n=23, p&lt;0.05) and improved systolic function (n=11, p&lt;0.05). Improvement correlated with increased autophagic flux in the border zone with less oxidative stress. ATG7 KO mice did not manifest TB-promoted cardioprotection during I/R. TB increased mtDNA content in the border zone (n=10, p&lt;0.05). In NRVMs subjected to I/R, TB reduced cell death by 41% (n=12, p&lt;0.001), reduced I/R-induced mtDNA damage, and increased mtDNA content by &gt;60% (n=3, p&lt;0.05). Moreover, TB promoted expression of the gene coding for PGC-1α, which controls mitochondrial biogenesis, in the border zone (n=10, p&lt;0.05) and in NRVMs subjected to I/R (n=3, p&lt;0.05), along with expression of the mitochondrial dynamics genes Drp1, Fis1 and MFN1 / 2 (n=9, p&lt;0.05). Conversely, ATG7 knockdown in NRVMs abolished these beneficent effects of TB on mitochondria. Conclusions: Autophagy is a sufficient and essential process to mitigate reperfusion injury through maintenance of mitochondrial homeostasis. Augmentation of autophagic flux may emerge as a viable clinical therapy to reduce reperfusion injury in myocardial infarction

A Noncanonical Role of Delta Protein Kinase C (δPKC) Phosphorylation of Troponin I in Cardiac Reperfusion Injury

Injury of the myocardium due to reperfusion following an ischemic period (ischemia/reperfusion injury; IR) is the consequence of an imbalance between the production of oxidants and the availability of endogenous antioxidants. Depriving the heart of oxygen and nutrients (ischemia) leads to impaired mitochondrial function, elevated mitochondrial fission, cardiac damage, and death. Paradoxically, restoring blood flow (reperfusion) to the heart following an ischemic event poses another type of insult in the form of increased mitochondrial dysfunction, apoptosis, and necrosis, resulting in cardiac failure. Our laboratory has found that δPKC mediates reperfusion injury; treatment with a selective inhibitor of δPKC, δV1‐1, at reperfusion reduces infarct size by 60% in a variety of animal models. One of several substrates of δPKC, cardiac troponin I (cTnI), undergoes partial proteolysis upon phosphorylation by δPKC during IR. Interestingly, using western blot and microscopy studies, we found that the N‐terminal fragment of cTnI co‐localizes with mitochondria following IR and that inhibition of δPKC by δV1‐1 inhibits this cleavage. To determine the role of phosphorylated cTnI, we rationally designed a highly selective inhibitor of cTnI phosphorylation by δPKC, ψTnI. ψTnI inhibits only cTnI phosphorylation and not the phosphorylation of pyruvate dehydrogenase kinase (PDK), myristoylated alanine rich C kinase substrate (MARCKS), signal transducers and activators of transcription (STAT), and glyceraldehyde 3‐phosphate dehydrogenase (GAPDH) – substrates of δPKC that are elevated during reperfusion injury to the myocardium. ψTnI also diminishes cTnI association with mitochondria following reperfusion. Importantly, ψTnI treatment alone was sufficient to obviate acute IR injury in a whole heart ischemic model, reducing infarct size by over 70% and improving mitochondrial respiration when given at reperfusion. Additionally, ψTnI treatment at reperfusion of H9c2 cardiomyocytes restored mitochondrial oxygen consumption, preserved mitochondrial morphology, and rescued mitochondrial membrane potential in a dose‐dependent manner. We will determine the effects of cTnI phosphorylation and fragment association with mitochondria using loss‐ and gain‐of‐function mutations, live‐imaging, and functional assays. Together, our study identified a non‐contractile role for cTnI; in addition to regulating cardiac contractility, we find that cTnI regulates mitochondrial function following reperfusion injury to the heart.Support or Funding InformationNIH grant R01‐HL052141 to DM‐R and AHA Postdoctoral Fellowship 19POST34380299 to AJLThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

100.25 Left Ventricular Unloading and Delayed Reperfusion Reduces Infarct Size in Large Anterior STEMI: A Substudy From the DTU-STEMI Safety and Feasibility Trial

For every 30-minute delay to reperfusion, myocardial infarct size should increase by 37%. However, extensive preclinical studies support that mechanically unloading the left ventricle (LV) and delaying reperfusion is cardioprotective and reduces infarct size (IS). The Door-To-Unload STEMI Pilot

100.32 Left Ventricular Unloading and Delayed Reperfusion Reduces Infarct Size to a Greater Extent in Women With Large Anterior STEMi. A Substudy From the DTU-STEMI Safety And Feasibility Trial

There is a growing interest in understanding the nuances of cardiac disease in women. Women suffering from STEMI wait longer to seek treatment, often receive different treatment, and have worse outcomes than men. The recently completed the STEMI Door-To-Unload Pilot Trial (DTU-STEMI) was the first

Unloading the Left Ventricle Before Reperfusion in Patients With Anterior ST-Segment-Elevation Myocardial Infarction.

In ST-segment-elevation myocardial infarction (STEMI), infarct size correlates directly with heart failure and mortality. Preclinical testing has shown that, in comparison with reperfusion alone, mechanically unloading the left ventricle (LV) before reperfusion reduces infarct size and that 30 minutes of unloading activates a cardioprotective program that limits reperfusion injury. The DTU-STEMI pilot trial (Door-To-Unload in STEMI Pilot Trial) represents the first exploratory study testing whether LV unloading and delayed reperfusion in patients with STEMI without cardiogenic shock is safe and feasible. In a multicenter, prospective, randomized exploratory safety and feasibility trial, we assigned 50 patients with anterior STEMI to LV unloading by using the Impella CP followed by immediate reperfusion (U-IR) versus delayed reperfusion after 30 minutes of unloading (U-DR). The primary safety outcome was a composite of major adverse cardiovascular and cerebrovascular events at 30 days. Efficacy parameters included the assessment of infarct size by using cardiac magnetic resonance imaging. All patients completed the U-IR (n=25) or U-DR (n=25) protocols with respective mean door-to-balloon times of 72 versus 97 minutes. Major adverse cardiovascular and cerebrovascular event rates were not statistically different between the U-IR versus U-DR groups (8% versus 12%, respectively, P=0.99). In comparison with the U-IR group, delaying reperfusion in the U-DR group did not affect 30-day mean infarct size measured as a percentage of LV mass (15±12% versus 13±11%, U-IR versus U-DR, P=0.53). We report that LV unloading using the Impella CP device with a 30-minute delay before reperfusion is feasible within a relatively short time period in anterior STEMI. The DTU-STEMI pilot trial did not identify prohibitive safety signals that would preclude proceeding to a larger pivotal study of LV unloading before reperfusion. An appropriately powered pivotal trial comparing LV unloading before reperfusion to the current standard of care is required. URL: https://www.clinicaltrials.gov . Unique identifier: NCT03000270.

Infarct size-limiting effect of epoxyeicosatrienoic acid analog EET-B is mediated by hypoxia-inducible factor-1α via downregulation of prolyl hydroxylase 3.

Epoxyeicosatrienoic acids (EETs) decrease cardiac ischemia-reperfusion injury; however, the mechanism of their protective effect remains elusive. Here, we investigated the cardioprotective action of a novel EET analog, EET-B, in reperfusion and the role of hypoxia-inducible factor (HIF)-1α in such action of EET-B. Adult male rats were subjected to 30 min of left coronary artery occlusion followed by 2 h of reperfusion. Administration of 14,15-EET (2.5 mg/kg) or EET-B (2.5 mg/kg) 5 min before reperfusion reduced infarct size expressed as a percentage of the area at risk from 64.3 ± 1.3% in control to 42.6 ± 1.9% and 46.0 ± 1.6%, respectively, and their coadministration did not provide any stronger effect. The 14,15-EET antagonist 14,15-epoxyeicosa-5( Z)-enoic acid (2.5 mg/kg) inhibited the infarct size-limiting effect of EET-B (62.5 ± 1.1%). Similarly, the HIF-1α inhibitors 2-methoxyestradiol (2.5 mg/kg) and acriflavine (2 mg/kg) completely abolished the cardioprotective effect of EET-B. In a separate set of experiments, the immunoreactivity of HIF-1α and its degrading enzyme prolyl hydroxylase domain protein 3 (PHD3) were analyzed in the ischemic areas and nonischemic septa. At the end of ischemia, the HIF-1α immunogenic signal markedly increased in the ischemic area compared with the septum (10.31 ± 0.78% vs. 0.34 ± 0.08%). After 20 min and 2 h of reperfusion, HIF-1α immunoreactivity decreased to 2.40 ± 0.48% and 1.85 ± 0.43%, respectively, in the controls. EET-B blunted the decrease of HIF-1α immunoreactivity (7.80 ± 0.69% and 6.44 ± 1.37%, respectively) and significantly reduced PHD3 immunogenic signal in ischemic tissue after reperfusion. In conclusion, EET-B provides an infarct size-limiting effect at reperfusion that is mediated by HIF-1α and downregulation of its degrading enzyme PHD3. NEW & NOTEWORTHY The present study shows that EET-B is an effective agonistic 14,15-epoxyeicosatrienoic acid analog, and its administration before reperfusion markedly reduced myocardial infarction in rats. Most importantly, we demonstrate that increased hypoxia-inducible factor-1α levels play a role in cardioprotection mediated by EET-B in reperfusion likely by mechanisms including downregulation of the hypoxia-inducible factor -1α-degrading enzyme prolyl hydroxylase domain protein 3.

Effect Of Membrane Sealing Copolymer Poloxamer188 On Cardiac Mitochondrial Subpopulations In A Porcine Model Of Acute Myocardial Infarction

Acute myocardial infarction (AMI) is characterized by the sudden loss of blood supply to the coronary arteries, leading to permanent cell death if left untreated. Every year, around 800,000 Americans are affected by AMI. Currently, the only successful treatment for AMI is the restoration of blood flow using angioplasty and fibrinolytic drugs. In spite of a higher success rate post treatment, AMI greatly increases the risk of future arrhythmia, stroke and cardiac arrest. Additionally, the abrupt reintroduction of oxygen to the ischemic tissue causes reperfusion injury (RI). In the mitochondria, RI leads to calcium overload, increased ROS production, opening of mitochondrial permeability transition pore (MPTP) and release of caspases, all contributing to cell death. Hence, mitochondria offer a promising target in reducing reperfusion injury post AMI. Previously, we showed that the administration of the membrane sealing copolymer Poloxamer188 (P188) post ST‐elevation myocardial infarction (STEMI) reperfusion reduced infarct size and improved cardiac myocardial and mixed mitochondrial function in pigs. In this current study, our aim was to identify the specific effects of P188 in improving the mitochondrial function post STEMI of the two cardiac mitochondrial subpopulations‐subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria. Female pigs that underwent 45 minutes of partial left anterior descending artery (LAD) occlusion were randomized to be reperfused with P188 (250 mg/kg, n=5) or saline(n=5). Each of these animals received an initial intracoronary bolus of either drug for 30 minutes, followed by an intravenous drip of the same dose for 3 hours. At 4 hours post reperfusion, the hearts were harvested and cardiac SSM and IFM were isolated from both the ischemic (LAD) and healthy circumflex (Circ) area through differential centrifugation. Their functions were assessed by measuring mitochondrial oxygen consumption and calcium buffering capacity. Initial results show that P188 likely improved complex 1 mediated mitochondrial oxygen consumption in the SSM (not significant) while there was no effect on IFM. P188 also improved the calcium buffering capacity of cardiac SSM and IFM (p=0.009 for SSM and p=0.03 for IFM) in the ischemic area. Together these results show a potential treatment benefit of P188 on cardiac SSM. Future studies include measurement of the levels of reactive oxygen species and total calcium content in the mitochondria, assessment of mitochondrial damage through electron microscopy as well as investigation of the mechanism of benefit conferred by P188 in the mitochondria. To our knowledge, this is the first study to investigate the effect of P188 in cardiac mitochondrial subpopulations. Results from this study will help in the development of better targeted compounds with greater accuracy for the treatment of heart disease.Support or Funding InformationSource of funding: National Institutes of Heath, RO1 HL122323‐01A1This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Does p53 Inhibition Suppress Myocardial Ischemia-Reperfusion Injury?

p53 is well known as a regulator of apoptosis and autophagy. In addition, a recent study showed that p53 is a modulator of the opening of the mitochondrial permeability transition pore (mPTP), a trigger event of necrosis, but the role of p53 in necrosis induced by myocardial ischemia-reperfusion (I/R) remains unclear. The aim of this study was to determine the role of p53 in acute myocardial I/R injury in perfused mouse hearts. In male C57BL6 mice between 12 and 15 weeks of age, 2 types of p53 inhibitors were used to suppress p53 function during I/R: pifithrin-α, an inhibitor of transcriptional functions of p53, and pifithrin-μ, an inhibitor of p53 translocation from the cytosol to mitochondria. Neither infusion of these inhibitors before ischemia nor infusion for the first 30-minute period of reperfusion reduced infarct size after 20-minute ischemia/120-minute reperfusion. Infarct sizes were similar in p53 heterozygous knockout mice (p53+/-) and wild-type mice (WT), but recovery of rate pressure product (RRP) 120 minutes after reperfusion was higher in p53+/- than in WT. The protein expression of p53 in WT was negligible under baseline conditions, during ischemia, and at 10 minutes after the start of reperfusion, but it became detectable at 120 minutes after reperfusion. In conclusion, upregulation of p53 during the late phase of reperfusion plays a significant role in contractile dysfunction after reperfusion, although p53 is not involved in cardiomyocyte necrosis during ischemia or in the early phase of reperfusion.