Myocardial Infarction Animals Research Articles

Injectable Self-Oxygenating Cardio-Protective and Tissue Adhesive Silk-Based Hydrogel for Alleviating Ischemia After Mi Injury.

Myocardial infarction (MI) is a significant cardiovascular disease that restricts blood flow, resulting in massive cell death and leading to stiff and noncontractile fibrotic scar tissue formation. Recently, sustained oxygen release in the MI area has shown regeneration ability; however, improving its therapeutic efficiency for regenerative medicine remains challenging. Here, a combinatorial strategy for cardiac repair by developing cardioprotective and oxygenating hybrid hydrogels that locally sustain the release of stromal cell-derived factor-1 alpha (SDF) and oxygen for simultaneous activation of neovascularization at the infarct area is presented. A sustained release of oxygen and SDF from injectable, mechanically robust, and tissue-adhesive silk-based hybrid hydrogels is achieved. Enhanced endothelialization under normoxia and anoxia is observed. Furthermore, there is a marked improvement in vascularization that leads to an increment in cardiomyocyte survival by ≈30% and a reduction of the fibrotic scar formation in an MI animal rodent model. Improved left ventricular systolic and diastolic functions by ≈10% and 20%, respectively, with a ≈25% higher ejection fraction on day 7 are also observed. Therefore, local delivery of therapeutic oxygenating and cardioprotective hydrogels demonstrates beneficial effects on cardiac functional recovery for reparative therapy.

17 β-Estradiol ameliorates cardiac parasympathetic dysfunction following myocardial infarction in male mice

Background: Vagal dysfunction after chronic myocardial infarction (MI) is associated with an increased risk of ventricular tachycardia (VT)/ventricular fibrillation (VF) and increased mortality in heart failure. The incidence and outcomes of VT/VF are influenced by sex, with women having a lower incidence of VT/VF associated with ischemic heart disease. However, the mechanisms behind these sex differences remain unclear and could be due to sex differences in autonomic remodeling post-MI that is mediated by estrogen. Hypotheses: We hypothesized that estrogen improves vagal function after MI by reducing oxidative stress in vagal sensory neurons and improving vagal afferent/efferent reflexes and function. Methods: Mice with expression of channelrhodopsin (ChR2) in specific sensory afferent neurons were created by crossing vesicular glutamate transporter 2 (VGlut2)-IRES-Cre mice with ChR2-EYFP mice, and their offspring (Vglut2-ChR2-EYFP) used for optogenetic stimulation studies. Sham surgery (n=6) or MI (n=6) was performed in two separate groups of male mice. A third group of male mice (n=8) underwent 17β-Estradiol (E2) pellet (0.5 milligrams/pellet) implantation followed by MI (E2+MI) after 2.5 weeks. Terminal studies were performed 2-3 weeks post-MI/sham procedures by placing a blue light (473 nm) laser probe over the left cervical vagus in vivo to stimulate vagal sensory neurons (20 Hz, 10 & 20 msec stimulations for 5 sec). Heart rate (HR) and blood pressure (BP) responses were measured in response to optogenetic stimulation. Plasma E2 and nodose ganglion 4-hydroxynaneol (4HNE) levels, a marker of lipid peroxidation, were evaluated. Results: In response to optogenetic vagal stimulation, MI had reduced reflex heart rate responses vs. sham animals, while E2+MI mice demonstrated significantly better responses vs. MI and similar responses to sham animals (20 Hz, 10 msec: sham -59 ± 3%, MI -24 ± 3%, E2+MI -58 ± 4%, MI vs. E2+MI, P < 0.001; 20 Hz, 20 msec: sham -59 ± 4%, MI -31 ± 3%, E2+MI -60 ± 3%, MI vs. E2+MI, P < 0.001). In addition, while BP responses post-MI were reduced vs. sham, E2+MI male mice also demonstrated greater BP responses to optogenetic stimulation (20 Hz, 10 msec: sham -28 ± 4%, MI -12 ± 1%, E2+MI -27± 1%, MI vs. E2+MI, P < 0.001; 20 Hz, 20 msec: sham -32 ± 4%, MI -13 ± 1%, E2+MI -27 ± 5%, MI vs. E2+MI, P < 0.001). 4HNE levels were increased in MI vs. sham animals, while E2+MI mice demonstrated significant reductions in 4HNE levels (Sham 0.17 ± 0.09 μg/protein, MI 0.77 ± 0.11 μg/protein, E2±MI 0.26 ± 0.06 μg/protein, MI vs. E2+MI, P < 0.001). Finally, plasma measurements confirmed higher levels of estrogen in E2-implanted mice (MI 48 ± 10 pg/mL, E2+MI 850 ± 170 pg/mL, MI vs. E2+MI, P < 0.001). Conclusions: MI causes pathological vagal remodeling that is reflected in decreased sensory vagal neurotransmission and increased oxidative stress in the vagal ganglia. Parasympathetic dysfunction and oxidative stress are mitigated by estrogen, suggesting that estrogen may be an important factor in mitigating the resulting pathological autonomic remodeling post-MI that predisposes to VT/VF. NIHR01HL148190. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Evaluation of Tyrosine Kinase Inhibitors Loaded Injectable Hydrogels for Improving Connexin43 Gap Junction Intercellular Communication.

Myocardial infarction (MI) is one of the leading causes of death in the developed world, and the loss of cardiomyocytes plays a critical role in the pathogenesis of heart failure. Implicated in this process is a decrease in gap junction intercellular communication due to remodeling of Connexin43 (Cx43). We previously identified that intraperitoneal injection of the Pyk2 inhibitor PF4618433 reduced infarct size, maintained Cx43 at the intercalated disc in left ventricle hypertrophic myocytes, and improved cardiac function in an MI animal model of heart failure. With the emergence of injectable hydrogels as a therapeutic toward the regeneration of cardiac tissue after MI, here, we provide proof of concept that the release of tyrosine kinase inhibitors from hydrogels could have beneficial effects on cardiomyocytes. We developed an injectable hydrogel consisting of thiolated hyaluronic acid and P123-maleimide micelles that can incorporate PF4618433 as well as the Src inhibitor Saracatinib and achieved sustained release (of note, Src activates Pyk2). Using neonatal rat ventricular myocytes in the presence of a phorbol ester, endothelin-1, or phenylephrine to stimulate cardiac hypertrophy, the release of PF4618433 from the hydrogel had the same ability to decrease Cx43 tyrosine phosphorylation and maintain Cx43 localization at the plasma membrane as when directly added to the growth media. Additional beneficial effects included decreases in apoptosis, the hypertrophic marker atrial natriuretic peptide (ANP), and serine kinases upregulated in hypertrophy. Finally, the presence of both PF4618433 and Saracatinib further decreased the level of ANP and apoptosis than each inhibitor alone, suggesting that a combinatorial approach may be most beneficial. These findings provide the groundwork to test if tyrosine kinase inhibitor release from hydrogels will have a beneficial effect in an animal model of MI-induced heart failure.

Adipose Stem Cell-Seeded Decellularized Porcine Pericardium: A Promising Functional Biomaterial to Synergistically Restore the Cardiac Functions Post-Myocardial Infarction.

Myocardial infarction (MI) is a serious cardiovascular disease as the leading cause of death globally. Hence, reconstruction of the cardiac tissue comes at the forefront of strategies adopted to restore heart functions following MI. In this investigation, we studied the capacity of rat adipose-derived mesenchymal stem cells (r-AdMSCs) and decellularized porcine pericardium (DPP) to restore heart functions in MI animals. MI was induced in four different groups, three of which were treated either using DPP (MI-DPP group), stem cells (MI-SC group), or both (MI-SC/DPP group). Cardiac functions of these groups and the Sham group were evaluated using echocardiography, the intraventricular pressure gradient (IVPG) on weeks 2 and 4, and intraventricular hemodynamics on week 4. On day 31, the animals were euthanized for histological analysis. Echocardiographic, IVPG and hemodynamic findings indicated that the three treatment strategies shared effectively in the regeneration process. However, the MI-SC/DPP group had a unique synergistic ability to restore heart functions superior to the other treatment protocols. Histology showed that the MI-SC/DPP group presented the lowest (p < 0.05) degeneration score and fibrosis % compared to the other groups. Conclusively, stem cell-seeded DPP is a promising platform for the delivery of stem cells and restoration of heart functions post-MI.

Abstract 17513: Decreased Sensory Neurotransmission Due to Neuronal Mitochondrial Dysfunction Mediates Sex Differences in Vagal Remodeling After Myocardial Infarction

Background: Vagal dysfunction after chronic myocardial infarction (MI) exacerbates heart failure and predisposes to ventricular tachyarrhythmias (VT/VF). VT/VF after MI is more common in males than females. The mechanisms behind these sex differences are unknown. Hypothesis: We hypothesized that differences in autonomic remodeling in the vagal ganglia, which in a healthy state, provide beat-to-beat sensory neurotransmission and modulate efferent cardiac vagal tone, may serve as the mechanisms behind the sex differences in the incidence of VT/VF. Methods: MI was created (left anterior descending artery ligation) in male and female mice expressing channel rhodopsin in glutamatergic vagal neurons (VGlut2-ChR2-EYFP mice). Sham animals underwent thoracotomy only. Two weeks post-MI, heart rate (HR) responses were assessed following in vivo vagal afferent nerve activation via optogenetic stimulation (5 sec duration, 20 Hz, 10 ms and 20 ms stimulations). Ventricular fibrosis was quantified. Mitochondrial oxygen consumption rates (OCR), glutamate levels, and the levels of oxidative stress marker, 4-hydroxy nonenal (4HNE), were measured in the vagal ganglia. Results: Male MI animals demonstrated significantly reduced HR responses to optogenetic stimulation than female MI animals. No sex differences in the degree of ventricular fibrosis was observed. A decrease in glutamate content accompanied by decreased mitochondrial OCR and increased 4HNE levels was observed in the vagal ganglia of male infarcted vs. female infarcted mice, figure. There were no differences in the HR responses, glutamate content, mitochondrial OCR, and 4HNE levels between sham males vs. sham females. Conclusion: This study demonstrates significant sex differences in vagal remodeling post-MI, with decreased efferent vagal tone in males mediated at least in part by reduced vagal afferent glutamatergic signaling associated with impaired neuronal mitochondrial function.

Abstract 16084: Impairment of Cardio-Spleno-Bone Marrow Axis Following Myocardial Infarction in Diabetes Mellitus

Introduction: Precise comprehension of the cardio-spleen-bone-marrow immune cells axis is crucial to understanding the changes occurring during diabetes (DM) pathogenesis. This study aims to investigate the alterations in immune cell kinetics in DM after myocardial infarction (MI). Methods: MI was induced in DM and healthy control using C57BL/N6 mice. Animals were sacrificed at D1, D3, D7, &amp; D28 post-MI to obtain their heart, peripheral blood (PB), spleen, and bone marrow (BM) and then each organ cell suspension was isolated, and analyzed by flow cytometry. EPC-colony-forming assay (EPC-CFA) was performed using BM, PB, and spleen-derived MNCs. Results: Findings demonstrated that despite the normal production of BM, CD45+ cells are decreased at D1-D3 in spleen and PB of DM’s. Further analysis depicted that total and pro-inflammatory neutrophil (N1) decreased at D1-D3 in PB and spleen at D3-D7 in DM mice, suggesting that DM causes spleen's neutrophil alterations that cannot compensate for PB and ischemia tissue demand. Infiltrated macrophages (total, M1, M2) decreased at D3 in DM-ischemic heart. Total and M1 (D1-D3) and M2 (D3-D7) notably decreased in DM-PB than control group, showing impaired macrophage recruitment/polarization in DM. Moreover, heart myeloid dendritic cells (mDCs) increased from D1-D7, the latter enhanced recruitment of CD8 cells increase from D1 to D28 in DM-infarcted-myocardium. The total CD4 cells decreased at D1-D3 in DM-PB, indicating a delayed adaptive immune response to MI. The B-cells diminished at D1-D3 in PB, at D3 in myocardium, and D7 in spleen, indicating impaired mobilization of those cells from bone marrow to compensate. EPC-CFA demonstrated dramatically decrease of definitive EPC colonies in spleen and BM from D1-D28 in DM mice vs control in vitro , indicating that DM significantly impairs EPC colony-forming bioactivity by limiting EPCs' differentiation from primitive to definitive. Conclusion: Our study highlights significant alterations of cardio-spleno-bone-marrow immune cells axis following MI in DM animals, revealing delayed innate/adaptive immune responses and impaired differentiation of EPCs.

Animal Models and Methods of Myocardial Infarction Induction and the Role of Tissue Engineering in the Regeneration of Damaged Myocardium.

The introduction of an experimental animal model for myocardial infarction (MI) has particular importance. Research done on large animals provides valuable information for the researchers because of the similar characteristics of their hearts compared to humans, but the cost of purchasing and maintaining them is high. In comparison, using small animals has advantages, such as they are easy to work with and have low purchase and maintenance costs. However, in some of these animals, due to less similarity of the heart to humans, they cannot simulate the natural pathogenesis of human MI. Moreover, there are different methods for the induction of MI in animals; each has its own advantages and disadvantages. However, a method must be chosen to simulate the natural pathogenesis of MI with minimal complication. Currently, attempts are being made for myocardial regeneration after MI using the direct transplantation of stem cells or an engineered scaffold. The scaffold creates a 3D ambiance for the cultured cells. The task of tissue engineering is to optimize the scaffold with appropriate systems for the separation, proliferation, and differentiation of the desired cells until they are capable of promoting the threedimensional and appropriate growth of the tissue. The purpose of tissue engineering in cardiac is the use of scaffolds and cells in the damaged area, followed by the improvement of the heart function through automatic pulsation, communication with the host vessels, and electrical coupling with the myocardium, eventually creating a force to increase the heart function.

Modified mRNA as a Treatment for Myocardial Infarction

Myocardial infarction (MI) is a severe disease with high mortality worldwide. However, regenerative approaches remain limited and with poor efficacy. The major difficulty during MI is the substantial loss of cardiomyocytes (CMs) with limited capacity to regenerate. As a result, for decades, researchers have been engaged in developing useful therapies for myocardial regeneration. Gene therapy is an emerging approach for promoting myocardial regeneration. Modified mRNA (modRNA) is a highly potential delivery vector for gene transfer with its properties of efficiency, non-immunogenicity, transiency, and relative safety. Here, we discuss the optimization of modRNA-based therapy, including gene modification and delivery vectors of modRNA. Moreover, the effective of modRNA in animal MI treatment is also discussed. We conclude that modRNA-based therapy with appropriate therapeutical genes can potentially treat MI by directly promoting proliferation and differentiation, inhibiting apoptosis of CMs, as well as enhancing paracrine effects in terms of promoting angiogenesis and inhibiting fibrosis in heart milieu. Finally, we summarize the current challenges of modRNA-based cardiac treatment and look forward to the future direction of such treatment for MI. Further advanced clinical trials incorporating more MI patients should be conducted in order for modRNA therapy to become practical and feasible in real-world treatment.

Treatment for Myocardial Infarction: In Vivo Evaluation of Curcumin-Loaded PEGylated-GQD Nanoparticles.

Curcumin (Cur) has been suggested as a complementary treatment for cardiovascular diseases. Its efficiency, however, is modest due to poor biocompatibility. This study examined the effects of curcumin loaded on polyethylene glycol-graphene quantum dots (Cur-PEG-GQDs) on hemodynamic and cardiac function in rats with myocardial infarction (MI). The study groups included control, MI, MI+Cur-3, MI + Cur-7, MI + Cur-15, MI + PEG-GQDs-5, MI + PEG-GQDs-10, MI + Cur-PEG-GQDs-5, and MI + Cur-PEG-GQDs-10. MI was established by left anterior descending artery ligation. Two weeks after intraperitoneal administration of vehicle, Cur, PEG-GQDs, and Cur-PEG-GQDs, blood pressure and heart contractility indices were measured. Triphenyl tetrazolium chloride, colorimetry, and clinical laboratory methods were used to measure the infarct size, the oxidant and antioxidant content, and the kidney and liver function parameters, respectively. In the MI animals, Cur-7, PEG-GQDs-10, Cur-PEG-GQDs-5, and Cur-PEG-GQDs-10 recovered systolic blood pressure, diastolic blood pressure, left ventricular systolic pressure, and ±dp/dt max disturbances and reduced myocardial infarct size, fibrosis, and left ventricular end-diastolic pressure. Curcumin lowered antioxidant markers and elevated 1 oxidant marker in the heart in a dose-dependent manner. Although Cur-PEG-GQDs-5 and Cur-PEG-GQDs-10 reduced curcumin's oxidative stress effects, the superoxide dismutase, glutathione peroxidase, and total antioxidant capacity levels were significantly lower in Cur-PEG-GQDs-5 and Cur-PEG-GQDs-10 groups compared with the MI group. Malondialdehyde levels were lower in Cur-PEG-GQDs-5 and -10 groups compared with the Cur-3, Cur-7, and Cur-15 groups. The glutathione/glutathione disulfide ratio improved in the groups treated by Cur-7, PEG-GQDs-10, Cur-PEG-GQDs-5, and Cur-PEG-GQDs-10. The findings indicated that Cur-PEG-GQDs mitigated MI-induced cardiac dysfunction. However, because of the increase in oxidative stress in the heart, nonclassic mechanisms may be involved in the beneficial effect of Cur-PEG-GQDs on MI-induced cardiac dysfunction.

Idebenone attenuates ferroptosis by inhibiting excessive autophagy via the ROS-AMPK-mTOR pathway to preserve cardiac function after myocardial infarction

Cardiovascular diseases (CVDs) are the leading causes of mortality worldwide. As a type of CVDs, myocardial infarction (MI) induces ischemia hypoxia, which leads to excessive reactive oxygen species (ROS), resulting in multiple cell deaths and contributing to the subsequent development of heart failure or premature death. Recent evidence indicates that ROS-induced lipid peroxidation promotes autophagy and ferroptosis, leading to the loss of healthy myocardium and resulting in the dysfunction of cardiac tissue. Theoretically, cardiac function would be preserved after MI by inhibiting autophagy and ferroptosis. As an analog of coenzyme Q10 (CoQ10) and a clinically approved drug, idebenone would be used to inhibit ferroptosis and preserve cardiac function due to its capacity to improve mitochondrial physiology with antioxidant and anti-inflammatory properties. Here, we confirmed that the addition of idebenone inhibited H2O2-induced and RSL3-induced ferroptosis. Furthermore, the ROS-AMPK-mTOR pathway axis was identified as the signaling pathway that idebenone stimulated to prevent excessive autophagy and consequent ferroptosis. In the MI animal model, idebenone demonstrated a cardioprotective role by regulating ROS-dependent autophagy and inhibiting ferroptosis, which paves the way for the future clinical translation of idebenone in MI management.

Uric acid promotes myocardial infarction injury via activating pyrin domain-containing 3 inflammasome and reactive oxygen species/transient receptor potential melastatin 2/Ca2+pathway

Cardiomyocytes injury has been considered as a key contributor for myocardial infarction (MI). Uric acid (UA) can induce cardiomyocytes injury, which is closely related to NLRP3 activation and inflammatory factor generation. However, the mechanism how UA modulates cardiomyocytes remains elusive. Western blotting and qRT-PCR were applied for measuring protein and mRNA expression, respectively. ROS production and Ca2+ influx were measured by flow cytometry. Patch clamp technique was used for measuring transient receptor potential melastatin 2 (TRPM2) channel. Ligation of left anterior descending for 2 h was performed to induce MI animal model. The rats were treated by different concentration of uric acid. The artery tissues were stained by HE and collected for measurement of NLRP3 and inflammatory factors. Supplementation of UA significantly promoted apoptosis, and augmented the expression of intercellular adhesion molecule-1, chemoattractant protein-1, vascular cell adhesion molecule-1, and NLRP3 inflammasome. Knockdown of NLRP3 reversed the influence of UA on MI by decreasing collagen deposition, fibrotic area, apoptosis. The expression of NLRP3 inflammasome increased markedly after treatment of UA. UA activated ROS/TRPM2/Ca2+ pathway through targeting NLRP3. UA activated NLRP3 inflammasome and augments inflammatory factor production, which in turn exacerbates cardiomyocytes injury. Knockdown of NLRP3 reversed the influence of UA on apoptosis and cell cycle. UA may promote cardiomyocytes injury through activating NLRP3 inflammasome and ROS/TRPM2 channel/Ca2+ pathway.

The derivative of tissue activation as a marker of arrhythmogenic myocardium

Mapping techniques to identify diseased myocardial substrate during ventricular tachycardia ablation procedures remain limited. We hypothesized that tissue derivative of the voltage with respect to time (dV/dt), the slope of the unipolar ventricular electrogram registered by local ventricular activation, represents a unique parameter for identifying potential arrhythmogenic tissue in the ischemic scar border zone. Using high-resolution electrical mapping, we examined dV/dt characteristics in the border zone of animals after chronic myocardial infarction (MI). Minimum dV/dt (dV/dtmin) in MI animals was less than that in control animals (-344.7 ± 68.7 in controls vs -174.2 ± 104.5 in MI; P < .001) and related to ventricular fibrosis. In MI animals, dV/dtmin values were divided into high (≤-200 μV/ms) and low (>-200 μV/ms) dV/dtmin. Low dV/dtmin regions harbored arrhythmogenic substrates that were characterized by (1) high responsiveness to sympathetic stimulation, (2) presence of late potentials, and (3) lower unipolar and bipolar voltage amplitudes. Our data indicate that dV/dtmin is a unique parameter for identifying arrhythmogenic myocardium and may add a useful metric to conventional mapping strategies.

Analysis of Anti-Arrhythmic Impacts of Crocin through Estimation of Expression of Cx43 in Myocardial Infarction Using a Rat Animal Model.

Arrhythmia is an important cause of death after myocardial infarction (MI). Different substances have been evaluated for their anti-arrhythmic effect in MI. This study was performed to evaluate the anti-arrhythmic impacts of crocin in an MI animal model (rat) by estimation of the expression of connexin 43 (Cx43). Fifty male Sprague–Dawley rats were grouped into 5 groups, each composed of 10 rats. The first group was regarded as the normal control group and the second one was considered as the MI group, which was caused by ligation of the left anterior descending artery. The other three groups received crocin 50 or 10 mg/kg/day or metoprolol 100 mg/kg/day for 1 week, following ligation of the left anterior descending artery. Evaluated outcomes were cardiac Cx43 expression, arrhythmia incidence, histological findings, and myocyte resting potential. Crocin-treated MI groups showed a significantly lower arrhythmia score than the non-treated MI group, 10 mg/kg/day (1.85 ± 0.55, p < 0.01) and 50 mg/kg/day (1.70 ± 0.33, p < 0.01). Groups that received crocin 10 mg/kg/day (66.30 ± 2.59, p < 0.01), crocin 50 mg/kg/day (68.10 ± 2.43, p < 0.01), and metoprolol 100 mg/kg/day (−63.54 ± 0.63 mV, p < 0.01) significantly prevented depolarization in comparison with the non-treated MI group. Expression of Cx43 mRNA in crocin 10 mg/kg/day (1.54 ± 0.24, p < 0.01), crocin 50 mg/kg/day (1.73 ± 0.09, p < 0.01), and metoprolol 100 mg/kg/day (1.75 ± 0.14, p < 0.01) treatment groups was significantly higher in comparison with the non-treated MI group. Crocin showed a preventive effect on the arrhythmogenic impact of MI in an experimental model of ischemic injury through an increase in expression of Cx43.

Protective Effect of CXCR4 Antagonist DBPR807 against Ischemia-Reperfusion Injury in a Rat and Porcine Model of Myocardial Infarction: Potential Adjunctive Therapy for Percutaneous Coronary Intervention.

CXCR4 antagonists have been claimed to reduce mortality after myocardial infarction in myocardial infarction (MI) animals, presumably due to suppressing inflammatory responses caused by myocardial ischemia-reperfusion injury, thus, subsequently facilitating tissue repair and cardiac function recovery. This study aims to determine whether a newly designed CXCR4 antagonist DBPR807 could exert better vascular-protective effects than other clinical counterparts (e.g., AMD3100) to alleviate cardiac damage further exacerbated by reperfusion. Consequently, we find that instead of traditional continuous treatment or multiple-dose treatment at different intervals of time, a single-dose treatment of DBPR807 before reperfusion in MI animals could attenuate inflammation via protecting oxidative stress damage and preserve vascular/capillary density and integrity via mobilizing endothelial progenitor cells, leading to a desirable fibrosis reduction and recovery of cardiac function, as evaluated with the LVEF (left ventricular ejection fraction) in infarcted hearts in rats and mini-pigs, respectively. Thus, it is highly suggested that CXCR4 antagonists should be given at a single high dose prior to reperfusion to provide the maximal cardiac functional improvement. Based on its favorable efficacy and safety profiles indicated in tested animals, DBPR807 has a great potential to serve as an adjunctive medicine for percutaneous coronary intervention (PCI) therapies in acute MI patients.

Vagally-mediated heart block after myocardial infarction associated with plasticity of epicardial neurons controlling the atrioventricular node.

Imbalances in the opposing actions of sympathetic and parasympathetic nerves controlling the heart enhance risk for arrhythmia and sudden cardiac death after myocardial infarction (MI). Plasticity in peripheral neuron function may underlie the observed changes in cardiomotor nerve activity. We studied vagal control of the heart in pigs after chronic infarction of the left ventricle. Stimulation of the cervical vagus nerve produced greater bradycardic responses 8-weeks after MI. Recordings of epicardial electrocardiograms demonstrate increased severity and duration of atrioventricular (AV) block in MI-pigs during 20 Hz vagal stimulation. Intracellular voltage recordings from isolated neurons of the inferior vena cava-inferior left atrium (IVC-ILA) ganglionated plexus, a cluster of epicardial neurons receiving innervation from the vagus known to regulate the AV node, were used to assess plasticity of membrane and synaptic physiology of intrinsic cardiac neurons (ICNs) after MI. Changes to both passive and active membrane properties were observed, including more negative resting membrane potentials and greater input resistances in MI-pig ICNs, concomitant with a depression of neuronal excitability. Immunoreactivity to pituitary adenylate cyclase-activating polypeptide (PACAP), a cardiotropic peptide known to modulate cardiac neuron excitability, was localized to perineuronal varicosities surrounding pig IVC-ILA neurons. Exogenous application of PACAP increased excitability of control but not MI-ICNs. Stimulation (20 Hz) of interganglionic nerves in the ex vivo whole-mount preparations elicited slow excitatory postsynaptic potentials (sEPSPs) which persisted in hexamethonium (500 μM), but were blocked by atropine (1 μM), indicating muscarinic receptor-mediated inhibition of M-current. Extracellular application of 1 mM BaCl2 to inhibit M-current increased neuronal excitability. The muscarine-sensitive sEPSPs were observed more frequently and were of larger amplitude in IVC-ILA neurons from MI animals. In conclusion, we suggest the increased probability of muscarinic sEPSPs play a role in the potentiation of the vagus nerve mediated-slowing of AV nodal conduction following chronic MI. We identify both a novel role of a muscarinic sensitive current in the regulation of synaptic strength at ICNs projecting to the AV node, and demonstrate changes to both intrinsic plasticity and synaptic plasticity of IVC-ILA neurons which may contribute to greater risk for heart block and sudden cardiac death after MI.

Effects of Cyproheptadine on Mitral Valve Remodeling and Regurgitation After Myocardial Infarction

BackgroundIschemic mitral regurgitation (MR) is primarily caused by left ventricle deformation, but leaflet thickening with fibrotic changes are also observed in the valve. Increased levels of 5-hydroxytryptamine (5-HT; ie, serotonin) are described after myocardial infarction (MI); 5-HT can induce valve fibrosis through the 5-HT type 2B receptor (5-HT2BR). ObjectivesThis study aims to test the hypothesis that post-MI treatment with cyproheptadine (5-HT2BR antagonist) can prevent ischemic MR by reducing the effect of serotonin on mitral biology. MethodsThirty-six sheep were divided into 2 groups: inferior MI and inferior MI treated with cyproheptadine (0.5 mg/kg/d). Animals were followed for 90 days. Blood 5-HT, infarct size, left ventricular volume and function, MR fraction and mitral leaflet size were assessed. In a complementary in vitro study, valvular interstitial cells were exposed to pre-MI and post-MI serum collected from the experimental animals. ResultsIncreased 5-HT levels were observed after MI in nontreated animals, but not in the group treated with cyproheptadine. Infarct size was similar in both groups (11 ± 3 g vs 9 ± 5 g; P = 0.414). At 90 days, MR fraction was 16% ± 7% in the MI group vs 2% ± 6% in the cyproheptadine group (P = 0.0001). The increase in leaflet size following MI was larger in the cyproheptadine group (+40% ± 9% vs +22% ± 12%; P = 0.001). Mitral interstitial cells overexpressed extracellular matrix genes when treated with post-MI serum, but not when exposed to post-MI serum collected from treated animals. ConclusionsCyproheptadine given after inferior MI reduces post-MI 5-HT levels, prevents valvular fibrotic remodeling, is associated with larger increase in mitral valve size and less MR.

Chronic Vagal Nerve Stimulation Rescues Sympathetic Control of the Heart following Myocardial Infarction

Cardiac injury, such as myocardial infarction (MI), leads to neurohormonal activation and autonomic remodeling, resulting in reflexive sympathoexcitation and parasympathetic dysfunction, which further contribute to progression of disease. The purpose of this study was to determine whether chronic cervical vagal nerve stimulation (VNS) influences MI‐associated changes in cardiac sympathetic function. Yucatan minipigs were divided into control (n=6), chronic MI (n=7), and chronic MI + chronic VNS (n=8) groups. VNS therapy was delivered to the right cervical vagus nerve and systematically titrated to an optimal intensity based on heart rate dynamics (5Hz, 2.1±0.3mA, 250μs, 17.5% duty cycle) using telemetry in the conscious state. Chronic MI was created using percutaneous embolization of the left anterior descending coronary artery with polystyrene beads under fluoroscopy (Figure 1A). VNS therapy was started 2 days following MI, and the animals maintained for 6‐8 weeks. At terminal study, we evaluated hemodynamic responses to graded bilateral sympathetic chain stimulation (BSS). Left ventricular (LV) strips encompassing regions of scar, border zone, and normal myocardium were fixed in 10% formalin, embedded in paraffin, sectioned, and studied using Masson's trichrome stain (Figure 1B‐C). Structural changes at the peri‐infarct area were scored (0‐3) for myocyte morphology and presence of hypertrophy or myocytolysis. Animals with MI alone exhibited spontaneous ventricular arrhythmias, including two that experienced sudden cardiac death (Figure 1D). At terminal study, there were no significant differences in baseline systolic function among groups. Moderate (4Hz) and high (10Hz) intensity BSS increased LV contractility (dp/dtmax) in all groups (Figure 2A‐B); however, evoked changes were significantly reduced in the chronic MI compared to control or MI + VNS groups. While control animals displayed evidence of contractile reserve at 10Hz vs 4Hz (1297±266 mmHg/s, p=0.03), chronic MI animals did not (631.9±264 mmHg/s, p=0.11), which was improved with chronic VNS therapy (1027±160.6 mmHg/s, p&lt;0.01, Figure 2C). Chronic VNS therapy also significantly reduced MI‐associated structural remodeling in the peri‐infarct area, including the degree of myocytolysis and dysmorphic myocytes (structural abnormality index 0.6±0.2 vs 1.8±0.2, p&lt;0.01). Our findings suggest that chronic VNS ameliorates sympathetic functional remodeling following myocardial infarction and improves cardiac mechanical performance in response to simulated stress. Furthermore, chronic VNS reduces pathologic myocardial remodeling at the peri‐infarct zone, potentially stabilizing the resultant ventricular scar.

Hypoglycosylated Follistatin‐Like 1 Attenuates the Loss of Coronary and Cerebral Vascular Functional Capacity in Ossabaw Swine with Cardiometabolic Heart Failure with Reduced Ejection Fraction

Ischemic heart disease is a leading cause of death, often resulting from heart failure caused by myocardial infarction. Diabetic cardiomyopathy is increasingly problematic clinically, with the combination of metabolic syndrome and chronic inflammation greatly increasing the risk for both coronary and cerebral vascular disease. Follistatin‐like 1 (FSTL1) is a protein that, when non‐glycosylated, displays regenerative properties including pro‐angiogenic effects and prevention of abnormal vascular remodeling. Thus, the objective of the current study was to assess the therapeutic benefit of human recombinant non‐glycosylated FSTL1 protein on both coronary and cerebral vascular function in a pre‐clinical Ossabaw swine model of myocardial infarction (MI). We hypothesized FSTL1 would attenuate the development of coronary and cerebral vascular dysfunction in an experimental setting of cardiometabolic heart failure with reduced ejection fraction (HFrEF). Intact female Ossabaw swine (2 months old) were fed a Western Diet for 4 months to develop metabolic syndrome. At 6 months of age, animals were subjected to 90 minutes ischemia followed by reperfusion (I/R) to induce MI. One month post‐MI, ALZET osmotic pumps were implanted and either vehicle (MI group) or FSTL1 (MI+FSTL1 group) was delivered over two weeks, with terminal vascular experiments performed 2 months post‐MI. In vitroassessment of isolated coronary (n=5‐6 for infarct, border, and remote regions of the left ventricle; 139.5 ± 4.9 μm diameter) and cerebral (n=2‐6 for middle cerebral artery second order pial; 385.3 ± 18.7 μm diameter) arteriole function was examined using pressure myography. Dose response curves for: 1) U46619 (thromboxane A2 agonist); and 2) NS‐1619 (large‐conductance calcium‐activated potassium channel activator; BKCa) were conducted. A 2x2 ANOVA (Group X Dose) was used to determine significance at the p &lt; 0.05 level. Cardiometabolic HFrEF was indicated by a combined ejection fraction of 38 ± 2% and a fasting HOMA‐IR of 3.8 ± 0.4 (vs. 0.6 ± 0.1 historical control). In coronary arterioles, the NS‐1619 induced vasodilatory capacity was increased ~18‐fold in MI+FSTL1 animals relative to MI (100 ± 13% vs. 1832 ± 3% in MI and MI+FSTL1, respectively) in the remote region of the heart (interaction effect), but not the infarct nor border regions. In cerebral arterioles, the vasoconstrictor capacity in response to U46619 was increased ~2‐fold in MI+FSTL1 relative to MI animals (100 ± 19% vs. 213 ± 25% in MI and MI+FSTL1, respectively; interaction effect). In conclusion, FSTL1 partially attenuates the loss of functional capacity in both coronary and cerebral arterioles, demonstrating its potential to improve vascular function in an experimental setting of cardiometabolic HFrEF.

Synthetic Analogs of 6-Bromohypaphorine, a Natural Agonist of Nicotinic Acetylcholine Receptors, Reduce Cardiac Reperfusion Injury in a Rat Model of Myocardial Ischemia

The data available to date indicate that the activation of nicotinic acetylcholine receptors (nAChR) of α7 type can reduce heart damage resulting from ischemia and subsequent reperfusion. We have studied two new synthetic D-analogs of 6-bromohypaphorine, which are selective agonists of α7 nAChR, in a rat model of myocardial ischemia. Acute myocardial infarction in animals was induced by occlusion of the left coronary artery with its subsequent reperfusion under mechanical lung ventilation. It was found that one of the analogs was more active, and treatment with it at the onset of reperfusion statistically reduced infarct size. This analog also prevented changes in the concentration of potassium and sodium ions in the blood, occurring during occlusion/reperfusion injury. The data obtained indicate that hypaphorine analogs are promising for the development of drugs that reduce the adverse effects of myocardial infarction.

Intraventricular pressure gradient: a promising tool to predict the post-infarction chronic congestive heart failure in rats

Abstract Funding Acknowledgements Type of funding sources: None. Background/Introduction: Congestive heart failure (CHF), the main reason for morbidity and mortality, is considered a serious consequence of myocardial infarction (MI). The use of left ventricular end-diastolic pressure (LVEDP) as a chief indicator of CHF becomes limited because of the possible impairment of cardiac function and induced aortic valve damage during its recording. Echocardiography is the gold standard approach to diagnose structural myocardial dysfunction. However, its ability to predict chronic CHF following MI is still limited. Recently, intraventricular pressure gradient (IVPG) was presented as a non-invasive, highly sensitive preload-independent diastolic function parameter to assess cardiac function, especially during cardiomyopathy. However, there have not been any investigations demonstrating the feasibility of IVPG in the evaluation of post-infarction chronic CHF. Purpose This study aimed to investigate the utility of IVPG to assess the heart function in a rat model with chronic CHF following MI with evaluating its capacity to predict these changes. Methods Fifty male rats were included. MI was induced via ligation of the left anterior descending artery (LAD) at the level of the atrioventricular junction (MI animals, n = 35). Sham animals were subjected to the same left thoracotomy procedure without LAD ligation (Sham animals, n = 15). Transthoracic conventional echocardiography and colour M-mode echocardiography (CMME) for IVPG were performed in all animals 6 months post-surgery. The next day, animals were anesthetized, ventilated, and euthanized after the recording of hemodynamics. The heart weight, and lung and liver wet-to-dry weight ratios were recorded. J-tree cluster-analysis was performed based on ten echocardiographic variables indicative of CHF. Results Based on the cluster analysis, animals were joined into two clusters; CHF+ (n = 22) and named MI/HF+, and CHF- (n = 28) that was joined from sham (n = 15), and MI/HF- (n = 13). MI/HF+ presented the most severe anatomical and echocardiographic changes indicative of CHF with significant reduction of all IVPG indices and impairment of the hemodynamics. The IVPG indices were significantly (P&amp;lt; 0.0001) correlated with the anatomical and echocardiographic findings, LVDP, LVEDP, HR, -dP/dtmin, and Tau. Meanwhile, LVSP was only significantly correlated with apical IVPG (R = 0.677, P = 0.022). dP/dtmax was significantly correlated with total IVPG, basal IVPG, and apical IVPG (R = 0.797, P = 0.017, R = 0.724, P = 0.003, and R = 0.652, P = 0.026 ; respectively). Moreover, total, basal, mid-to-apical, mid-, and apical IVPG were significant (P&amp;lt; 0.0001) predictors of chronic CHF following MI. Conclusion Compared to the structural, and functional indices of conventional echocardiography, IVPG derived from CMME could provide a substantial non-invasive tool to diagnose and predict CHF after long-term MI.