Large- and Medium-sized Arteries Remaining in Transmural Scar Distal to Permanent Coronary Ligation Undergo Neointimal Hyperplasia and Inward Remodeling

This study aimed to investigate the structural integrity and dynamic changes in chronically occluded residual arteries found in post–myocardial infarction (MI) scar. A transmural MI was induced in middle-aged, male Sprague-Dawley rats by left coronary artery ligation. The rats were euthanized 3 days and 1, 2, 4, 8, and 12 weeks after MI, and their hearts were processed into paraffin for histology, immunohistochemistry, and quantitative morphometry. It has been found that large- and medium-sized arteries were able to survive inside the transmural scars for 12 post-MI weeks. Furthermore, most residual arteries preserved their structural integrity for up to 2 weeks post-MI, but gradually all disused vessels had undergone neointimal hyperplasia and inward remodeling at later time periods. In addition, the replacement of vascular smooth muscle cells in the wall of residual arteries by extracellular matrix components led to a disruption of the vessel integrity and progressive obliteration of their lumen between 4 and 12 post-MI weeks. Taken together, this study demonstrate that residual arteries in post-infarcted region were capable of maintaining their structural integrity, including the patent lumen, during two post-MI weeks, suggesting that during this period they can be used as potential conduits for conceivable reflow of arterial blood within the scarred region of the heart

Coronary blood flow influences tolerance to environmental extremes in fish

Approximately half of all fishes have, in addition to the luminal venous O2 supply, a coronary circulation supplying the heart with fully oxygenated blood. Yet, it is not fully understood how coronary O2 delivery affects tolerance to environmental extremes such as warming and hypoxia. Hypoxia reduces arterial oxygenation, while warming increases overall tissue O2 demand. Thus, as both stressors are associated with reduced venous O2 supply to the heart, we hypothesised that coronary flow benefits hypoxia and warming tolerance. To test this hypothesis, we blocked coronary blood flow (via surgical coronary ligation) in rainbow trout (Oncorhynchus mykiss), and assessed how in vivo cardiorespiratory performance and whole-animal tolerance to acute hypoxia and warming was affected. While coronary ligation reduced routine stroke volume relative to trout with intact coronaries, cardiac output was maintained by increases in heart rate. However, in hypoxia, coronary ligated trout were unable to increase stroke volume to maintain cardiac output when bradycardia developed, which was associated with a slightly reduced hypoxia tolerance. Moreover, during acute warming coronary ligation caused cardiac function to collapse at lower temperatures, and reduced overall heat tolerance relative to trout with intact coronaries. We also found a positive relationship between individual hypoxia and heat tolerance across treatment groups, and tolerance to both environmental stressors was positively correlated with cardiac performance. Collectively, our findings show that coronary perfusion improves cardiac O2 supply, and therefore, cardiovascular function at environmental extremes, which benefits tolerance to natural and anthropogenically induced environmental perturbations.

Abstract 13306: Impella Combined With Extracorporeal Membrane Oxygenation Synergistically Unloads the Left Ventricle and Reduces Infarct Size in a Model of Myocardial Infarction With Cardiogenic Shock

Introduction: Extracorporeal membrane oxygenation (ECMO) supports hemodynamics in cardiogenic shock (CS) at the expense of left ventricular (LV) overload. LV assist device (LVAD) also supports hemodynamics, whereas LVAD unloads LV. Therefore, the combination of ECMO and LVAD would augment hemodynamic support and unload LV. We hypothesized that the combination therapy in acute myocardial infarct (AMI) in CS could synergistically improve hemodynamics and unload LV, which, in turn, reduces infarct size. Methods: In protocol 1, we ligated coronary arteries and created AMI with CS in 5 mongrel dogs (15.1±0.3 kg). We transvascularly introduced Impella CP into LV. We kept the ECMO flow constant at 1.8L/min. We compared hemodynamics and the LV pressure-volume area (PVA, an index of LV oxygen consumption) under 3 conditions; Control, ECMO, and ECMO+Impella (ECPELLA) in each dog. In protocol 2 (n=15), we ligated coronary arteries for 180 min and then reperfused. We activated Impella CP and/or ECMO from 60 min after the coronary ligation to the end of the experiment. We allocated dogs into 3 groups, no support (Control), ECMO, and ECPELLA and compared infarct size at 180 min after reperfusion among 3 groups. Results: In protocol 1, both ECMO and ECPELLA increased arterial pressure compared to Control (Control: 63±9, ECMO: 88±10 and ECPELLA: 97±18 mmHg, p < 0.05), and resolved the CS status. ECPELLA strikingly reduced PVA by 83% relative to Control (1500±326, 2038±357 and 258±182 mmHg*ml, p<0.001). In protocol 2, ECPELLA markedly reduced the infarct size (15±8%) compared to Control (53±7%, p<0.05) and ECMO (39±10%, p<0.05). Conclusions: ECPELLA before reperfusion markedly improved hemodynamics, reduced PVA, and limited infarct size in a dog model of MI with CS. ECPELLA could prevent ECMO-induced LV overload and synergistically exert powerful anti-infarct effects in AMI with CS.

Transcatheter occlusion of an anomalous origin of left coronary artery from pulmonary artery in an adult as an alternative to surgery

Anomalous origin of the left coronary artery from the pulmonary artery causes heart failure and death in infancy. In rare adult survivors with well-developed collaterals, surgical left coronary ligation to arrest steal is often combined with bypass grafting. Transcatheter left coronary artery closure in a symptomatic adult as an alternative to surgical ligation resulted in complete resolution of inducible ischaemia on myocardial perfusion imaging.

Targeting Cardiac Myocyte Na + -K + Pump Function With β3 Adrenergic Agonist in Rabbit Model of Severe Congestive Heart Failure

Background: Abnormally high cytosolic Na + concentrations in advanced heart failure impair myocardial contractility. Stimulation of the membrane Na + -K + pump should lower Na + concentrations, and the β3 adrenoceptor (β3 AR) mediates pump stimulation in myocytes. We examined if β3 AR-selective agonists given in vivo increase myocyte Na + -K + pump activity and reverse organ congestion in severe heart failure (HF). Methods: Indices for HF were lung-, heart-, and liver: body weight ratios and ascites after circumflex coronary artery ligation in rabbits. Na + -K + pump current, I p , was measured in voltage-clamped myocytes from noninfarct myocardium. Rabbits were treated with the β3 AR agonists CL316,243 or ASP9531, starting 2 weeks after coronary ligation. Results: Coronary ligation caused ascites in most rabbits, significantly increased lung-, heart-, and liver: body weight ratios, and decreased I p relative to that for 10 sham-operated rabbits. Treatment with CL316,243 for 3 days significantly reduced lung-, heart-, and liver: body weight ratios and prevalence of ascites in 8 rabbits with HF relative to indices for 13 untreated rabbits with HF. It also increased I p significantly to levels of myocytes from sham-operated rabbits. Treatment with ASP9531 for 14 days significantly reduced indices of organ congestion in 6 rabbits with HF relative to indices of 6 untreated rabbits, and it eliminated ascites. β3 AR agonists did not significantly change heart rates or blood pressures. Conclusions: Parallel β3 AR agonists-induced reversal of Na + -K + pump inhibition and indices of congestion suggest pump inhibition is a useful target for treatment with β3 AR agonists in congestive HF.

Abstract 393: S-nitrosylation of Atg7 by Thioredoxin-1 (trx1) Protects the Heart Against Myocardial Ischemia via Autophagy Regulation

Thioredoxin 1 (Trx1) is an oxidoreductase that reduces proteins with disulfide bonds. Trx1 also functions as a transnitrosylase, but this occurs only when Trx1 is oxidized at Cys32 and Cys35. In cultured cardiomyocytes (CMs), glucose deprivation (GD) induces oxidation of Trx1 and Trx1 is transnitrosylated. Thus, we hypothesized that Trx1 promotes GD-induced autophagy through its function as a transnitrosylase rather than as an oxidoreductase. GD-induced autophagy, evaluated by counting GFP-LC3 puncta, was inhibited in the presence of the transnitrosylation-defective Trx1C73S mutant (GFP-LC3 puncta per cell under GD; control: 38; Trx1 knockdown: 2*; Trx1C73S: 17*; p<0.05 vs. control), suggesting that Cys73 in Trx1 plays an important role in mediating GD-induced autophagy. Mass spectrometric analyses and biochemical assays showed that Atg7, an essential autophagy regulator, is a Trx1 target and that Trx1 binds to Atg7 via Cys454 and Cys458 in Atg7, thereby transnitrosylating Atg7 at Cys294 and Cys402. Trx1C73S knock-in (Trx1C73S-KI) promoted coronary ligation (CL)-induced myocardial infarction (MI) (MI size/area at risk (AAR) (%); Wild type (WT): 21; Trx1C73S-KI: 42*; p<0.05 vs. WT), in association with reduced S-nitrosylation of Atg7. To test the role of S-nitrosylation of Atg7 in mediating autophagy, we transduced an S-nitrosylation defective Atg7 mutant (Atg7CC294/402SS) into adult cardiomyocytes isolated from cardiac-specific Atg7 knockout mice. Compared to intact Atg7, Atg7CC294/402SS was less able to induce autophagy, as evidenced by reduced LC-3II formation (relative LC3-II; intact Atg7: 1.0; Atg7CC294/402SS: 0.81*; p<0.05). Atg7C402S, but not Atg7C294S, knock-in exacerbated CL-induced MI (MI size/AAR (%); WT: 32; Atg7C402-KI: 42*; p<0.05 vs. WT). These results suggest that Trx1 protects the heart against MI by mediating autophagy via S-nitrosylation of Atg7 at Cys402.

XPO1 Gene Therapy Attenuates Cardiac Dysfunction in Rats with Chronic Induced Myocardial Infarction

Transcriptomic signature of XPO1 was highly expressed and inversely related to left ventricular function in ischemic cardiomyopathy patients. We hypothesized that treatment with AAV9-shXPO1 attenuates left ventricular dysfunction and remodeling in a myocardial infarction rat model. We induced myocardial infarction by coronary ligation in Sprague-Dawley rats (n = 10), which received AAV9-shXPO1 (n = 5) or placebo AAV9-scramble (n = 5) treatment. Serial echocardiographic assessment was performed throughout the study. After myocardial infarction, AAV9-shXPO1-treated rats showed partial recovery of left ventricular fractional shortening (16.8 ± 2.8 vs 24.6 ± 4.1%, P < 0.05) and a maintained left ventricular dimension (6.17 ± 0.95 vs 4.70 ± 0.93 mm, P < 0.05), which was not observed in non-treated rats. Furthermore, lower levels of EXP-1 (P < 0.05) and lower collagen fibers and fibrosis in cardiac tissue were observed. However, no differences were found in the IL-6 or TNFR1 plasma levels of the myocardium of AAV9-shXPO1 rats. AAV9-shXPO1 administration attenuates cardiac dysfunction and remodeling in rats after myocardial infarction, producing the gene silencing of XPO1.

Targeting cardiac myocyte Na+-K+ pump function with β3 adrenergic agonist in rabbits and patients with severe congestive heart failure

BackgroundReported one- and two-year mortality for patients with advanced heart failure (HF) treated medically are ~75% and nearly 100%. In such patients, reversible cellular abnormalities are potential treatment targets and a raised cytosolic Na+ concentration that impairs their myocardial contractility is one potential target. β3 adrenoceptor (β3 AR) agonists stimulate the myocyte Na+-K+ pump.MethodsWe induced severe HF in rabbits by coronary ligation and measured indices of organ congestion after treatment with β3 AR agonists. Na+-K+ pump current was measured in voltage-clamped myocytes isolated from non-infarct myocardium. To assess if β3 ARs might add benefit to optimised guideline-directed medical treatment we report outcomes of giving the β3 AR agonist mirabegron to patients hospitalized with advanced, treatment-refractory stage D HF.ResultsTreatment of rabbits after coronary ligation with β3 AR agonist reversed a decreased myocyte Na+-K+ pump current and significantly reduced organ congestion and prevalence of ascites. Oral treatment with mirabegron rapidly improved signs and symptoms of 9 patients with advanced HF and improvement of ≥1 NYHA Class was maintained early post-discharge with continued treatment. One patient died from HF at 16 months, 4 died from other causes at 2 – 30 months and 4 remain alive at 38 ± 4 months with NYHA Class II symptoms.ConclusionsParallel β3 AR agonist-induced reversal of Na+-K+ pump inhibition and severe HF in rabbits identify pump inhibition as a treatment target, and changed in-hospital clinical trajectory and post-discharge course more favorable than expected suggest efficacy of mirabegron in advanced human HF.

Expression of Leukocytes Following Myocardial Infarction in Rats is Modulated by Moderate White Wine Consumption

How moderate white wine consumption modulates inflammatory cells infiltration of the ischemic myocardium following permanent coronary ligation was the key question addressed in this study. Male Sprague–Dawley rats were given either a combination of different white wines or water only for 28 days. Three peri-infarct/border zones and a control/nonischemic zone were analysed to determine the expression of myeloperoxidase (MPO) and cluster of differentiation 68 (CD68). Smaller expressions for both MPO and CD68 were found in all three peri-infarct zones of wine drinking animals (p < 0.001). There was no difference in the expression of leukocyte markers between animals drinking standard and polyphenol-rich white wine, although for CD68, a nonsignificant attenuation was noticed. In sham animals, a subepicardial MPO/CD68 immunoreactive “inflammatory ring” is described. Standard white wine consumption caused attenuation of the expression of MPO but not of CD68 in these animals. We conclude that white wine consumption positively modulates peri-infarct inflammatory infiltration.

Human Neonatal Thymus Mesenchymal Stem Cells Promote Neovascularization and Cardiac Regeneration

Newborns with critical congenital heart disease are at significant risk of developing heart failure later in life. Because treatment options for end-stage heart disease in children are limited, regenerative therapies for these patients would be of significant benefit. During neonatal cardiac surgery, a portion of the thymus is removed and discarded. This discarded thymus tissue is a good source of MSCs that we have previously shown to be proangiogenic and to promote cardiac function in an in vitro model of heart tissue. The purpose of this study was to further evaluate the cardiac regenerative and protective properties of neonatal thymus (nt) MSCs. We found that ntMSCs expressed and secreted the proangiogenic and cardiac regenerative morphogen sonic hedgehog (Shh) in vitro more than patient-matched bone-derived MSCs. We also found that organoid culture of ntMSCs stimulated Shh expression. We then determined that ntMSCs were cytoprotective of neonatal rat cardiomyocytes exposed to H2O2. Finally, in a rat left coronary ligation model, we found that scaffoldless cell sheet made of ntMSCs applied to the LV epicardium immediately after left coronary ligation improved LV function, increased vascular density, decreased scar size, and decreased cardiomyocyte death four weeks after infarction. We conclude that ntMSCs have cardiac regenerative properties and warrant further consideration as a cell therapy for congenital heart disease patients with heart failure.