Myocardial Infarction and Functional Outcome Assessment in Pigs

Introduction of newly discovered cardiovascular therapeutics into first-in-man trials depends on a strictly regulated ethical and legal roadmap. One important prerequisite is a good understanding of all safety and efficacy aspects obtained in a large animal model that validly reflect the human scenario of myocardial infarction (MI). Pigs are widely used in this regard since their cardiac size, hemodynamics, and coronary anatomy are close to that of humans. Here, we present an effective protocol for using the porcine MI model using a closed-chest coronary balloon occlusion of the left anterior descending artery (LAD), followed by reperfusion. This approach is based on 90 min of myocardial ischemia, inducing large left ventricle infarction of the anterior, septal and inferoseptal walls. Furthermore, we present protocols for various measures of outcome that provide a wide range of information on the heart, such as cardiac systolic and diastolic function, hemodynamics, coronary flow velocity, microvascular resistance, and infarct size. This protocol can be easily tailored to meet study specific requirements for the validation of novel cardioregenerative biologics at different stages (i.e. directly after the acute ischemic insult, in the subacute setting or even in the chronic MI once scar formation has been completed). This model therefore provides a useful translational tool to study MI, subsequent adverse remodeling, and the potential of novel cardioregenerative agents.     

A Plant-Derived Remedy for Repair of Infarcted Heart

Background

Myocardial infarction (MI) due to coronary artery disease remains one of the leading causes of premature death. Replacement of infarcted heart tissue with regenerating myocardium from endogenous progenitor pools or exogenously introduced stem cells remains a therapeutic ideal. Their impracticality mainly lies in their low efficiency in cardiogenic differentiation (CD). Our recent studies with an acute MI animal model have already demonstrated the therapeutic effect of the MeOH extract of Geum japonicum (EGJ), providing clear evidence of myocardial regeneration.

Methods and Findings

The present study further isolated the active component contained in EGJ using bioassay-guided isolation and investigated its efficacy in the treatment of infarcted heart in animal MI models. We demonstrated that substantial repair of infarcted heart in animal MI models by EGJ can be mimicked by the isolated candidate compound (cardiogenin) in MI animal models. Clear evidence of newly regenerated endogenous mesenchymal stem cells (MSCs) derived cardiomyocytes was observed throughout the infarct zone, accompanied by significantly improved functional performance of the heart. Transplantation of MSCs pretreated with EGJ or cardiogenin into a MI animal model also resulted in substantial regeneration of functional myocardium, implying that the activated MSCs carry all the necessary blueprints for myocardial regeneration. Signaling pathways specific to cell survival, CD identified in embryonic heart induction and angiogenesis were activated in both cardiogenin-treated MSCs and cardiogenin-induced regenerating myocardium.

Conclusions

This study has demonstrated the therapeutic effects of cardiogenin in infarcted heart repair, and identified the associated signalling pathways for effective cardiogenic differentiation of MSCs, cell survival and angiogenesis. These findings should enable new treatment strategies for MI to be developed immediately.     

A rodent model of myocardial infarction for testing the efficacy of cells and polymers for myocardial reconstruction

We have developed a robust rat model of myocardial infarction (MI). Here we describe the step-by-step protocol for creating an ischemia-reperfusion rat model of MI. We also describe how to deliver therapeutic injections of mesenchymal stem cells (MSCs) together with fibrin, to show an application of this model. In addition, to confirm the presence of fibrin and cells in the infarct, visualization of MSCs and fibrin by histological techniques are also described. The ischemia-reperfusion MI model can be modified and generalized for use with various injectable polymers, cell types, drugs, DNA and combinations thereof. The model can be created in 7 days or less, depending on the timing of therapeutic intervention.     

The effect of hydrogel injection on cardiac function and myocardial mechanics in a computational post-infarction model

An emerging therapy to limit adverse heart remodelling following myocardial infarction (MI) is the injection of polymers into the infarcted left ventricle (LV). In the few numerical studies carried out in this field, the definition and distribution of the hydrogel in the infarcted myocardium were simplified. In this computational study, a more realistic biomaterial distribution was simulated after which the effect on cardiac function and mechanics was studied. A validated finite element heart model was used in which an antero-apical infarct was defined. Four infarct models were created representing different temporal phases in the progression of a MI. Hydrogel layers were simulated in the infarcted myocardium in each model. Biomechanical and functional improvement of the LV was found after hydrogel inclusion in the ischaemic models representing the early phases of MI. In contrast, only functional but no mechanical restitution was shown in the scar model due to hydrogel presence.     

Cloning and expression pattern of dog SDF-1 and the implications of altered expression of SDF-1 in ischemic myocardium

Stromal cell derived factor-1 (SDF-1) plays a pivotal role in the mobilization and homing of stem cells, indicative of its potential in myocardial regeneration after heart damage. The use of large animal models in cardiac surgery research plays an essential role in the translation of results from basic studies into clinical trials. Considering the aforesaid two reasons, for the first time, we cloned dog SDF-1 cDNA and characterized the constitutive expression pattern of SDF-1 gene in normal dog tissues and the dynamic expression pattern in a dog model of myocardial infarction (MI) by means of ELISA test, real-time RT-PCR, and Western blotting. In a dog model of MI, We also examined and compared the differentially expressed pattern of SDF-1 between infarct area and border zone of myocardium in order to explore the implication of differentially distribution of SDF-1 in the mobilization and homing of stem cells to the damaged heart. Our results provide insights into expression pattern and pathophysiologic significance of dog SDF-1 in normal and heart-damaged dogs.     

Adipose stromal vascular fraction cell construct sustains coronary microvascular function after acute myocardial infarction

A three-dimensional tissue construct was created using adipose-derived stromal vascular fraction (SVF) cells and evaluated as a microvascular protection treatment in a myocardial infarction (MI) model. This study evaluated coronary blood flow (BF) and global left ventricular function after MI with and without the SVF construct. Fischer-344 rats were separated into four groups: sham operation (sham), MI, MI Vicryl patch (no cells), and MI SVF construct (MI SVF). SVF cells were labeled with green fluorescent protein (GFP). Immediately postinfarct, constructs were implanted onto the epicardium at the site of ischemia. Four weeks postsurgery, the coronary BF reserve was significantly decreased by 67% in the MI group and 75% in the MI Vicryl group compared with the sham group. The coronary BF reserve of the sham and MI SVF groups in the area at risk was not significantly different (sham group: 83 ± 22% and MI SVF group: 57 ± 22%). Griffonia simplicifolia I and GFP-positive SVF immunostaining revealed engrafted SVF cells around microvessels in the infarct region 4 wk postimplant. Overall heart function, specifically ejection fraction, was significantly greater in MI SVF hearts compared with MI and MI Vicryl hearts (MI SVF: 66 ± 4%, MI: 37 ± 8%, and MI Vicryl: 29 ± 6%). In conclusion, adipose-derived SVF cells can be used to construct a novel therapeutic modality for treating microvascular instability and ischemia through implantation on the epicardial surface of the heart. The SVF construct implanted immediately after MI not only maintains heart function but also sustains microvascular perfusion and function in the infarct area by sustaining the coronary BF reserve.     

In vivo models of arterial thrombosis and thrombolysis

This year approximately 1.5 million Americans will undergo a myocardial infarction (MI). Of those who make it to the hospital (approximately 1.2 million), only about 20% will receive thrombolytic therapy. Multiple factors contribute to this dismaying figure, but most of them are risk/benefit-related. Moreover, of those receiving lytic therapy, the coronary arteries of as many as one-third may not reopen, and of those that do undergo coronary thrombolysis, an unacceptable fraction will experience reocclusion acutely. Thus, despite significant progress, major challenges for antithrombotic and thrombolytic therapy remain. Promising results with aspirin provide some hope that the figures above can be altered favorably. Efforts are under way in industry and academia to develop drugs to accomplish one or more of the following: lower the incidence of MI, prevent the development of unstable angina or retard its progression to frank MI, increase the inclusion window for lytic therapy, raise the percentage of patients undergoing successful thrombolysis, and maintain coronary patency. During the period that thrombolytic agents have come into vogue important advances have been made in our understanding of platelet function, coagulation, and the endogenous fibrinolytic system. These have spurred the development of novel drugs, such as platelet fibrinogen receptor antagonists, plasminogen activators, and inhibitors of factor IIa (thrombin) and XIIIa. Evaluation of these agents for their antithrombotic or profibrinolytic activity requires relevant animal models of thrombosis. Despite appropriate concerns about their clinical relevance, these models bridge the wide gap between test tube assays of aggregation or coagulation and humans.     

Optical mapping of late myocardial infarction in rats

Late myocardial infarction (MI) is associated with ventricular arrhythmias and sudden cardiac death. The exact mechanistic relationship between abnormal cellular electrophysiology, conduction abnormalities, and arrhythmogenesis associated with late MI is not completely understood. We report a novel, rapid dye superfusion technique to enable whole heart, high-resolution optical mapping of late MI. Optical mapping of action potentials was performed in normal rats and rats with anterior MI 7 days after left anterior descending artery ligation. Hearts from normal rats exhibited normal action potentials and impulse conduction. With the use of programmed stimulation to assess arrhythmia inducibility, 29% of hearts with late MI had inducible sustained ventricular tachycardia, compared with 0% in normal rats. A causal relationship between the site of infarction, abnormal action potential conduction (i.e., block and slow conduction), and arrhythmogenesis was observed. Optical mapping techniques can be used to measure high-resolution action potentials in a whole heart model of late MI. This experimental model reproduces many of the electrophysiological characteristics (i.e., conduction slowing, block, and ventricular tachycardia) associated with MI in patients. Importantly, the results of this study can enhance our ability to understand the interplay between cellular heterogeneity, conduction abnormalities, and arrhythmogenesis associated with MI.     

Cardioprotection through autophagy: Ready for clinical trial?

Interventions that reduce infarct size in animal models have largely failed to improve outcome in patients suffering acute myocardial infarction (MI), or 'heart attack'. Our group recently reported a reduction of infarct size by chloramphenicol treatment in a porcine in vivo model of acute MI, through a mechanism involving the induction of autophagy. Since 2005 several studies have implicated autophagy as a target for cardioprotection.     

Cardioprotection through autophagy

Interventions that reduce infarct size in animal models have largely failed to improve outcome in patients suffering acute myocardial infarction (MI), or ‘heart attack’. Our group recently reported a reduction of infarct size by chloramphenicol treatment in a porcine in vivo model of acute MI, through a mechanism involving the induction of autophagy. Since 2005 several studies have implicated autophagy as a target for cardioprotection.     

Mesenchymal stem cell therapy: A promising cell‐based therapy for treatment of myocardial infarction

For decades, mesenchymal stem (MSCs) cells have been used for cardiovascular diseases as regenerative therapy. This review is an attempt to summarize the types of MSCs involved in myocardial infarction (MI) therapy, as well as its possible mechanisms effects, especially the paracrine one in MI focusing on the studies (human and animal) conducted within the last 10 years. Recently, reports showed that MSC therapy could have infarct‐limiting effects after MI in both experimental and clinical trials. In this context, various types of MSCs can help cardiac regeneration by either revitalizing the cardiac stem cells or revascularizing the arteries and veins of the heart. Furthermore, MSCs could produce paracrine growth factors that increase the survival of nearby cardiomyocytes, as well as increase angiogenesis through recruitment of stem cell from bone marrow or inducing vessel growth from existing capillaries. Recent research suggests that the paracrine effects of MSCs could be mediated by extracellular vesicles including exosomes. Exosomal microRNAs (miRNAs) released by MSCs are promising therapeutic hotspot target for MI. This could be attributed to the role of miRNA in cardiac biology, including cardiac regeneration, stem cell differentiation, apoptosis, neovascularization, cardiac contractility and cardiac remodeling. Furthermore, gene‐modified MSCs could be a recent promising therapy for MI to enhance the paracrine effects of MSCs, including better homing and effective cell targeted tissue regeneration. Although MSC therapy has achieved considerable attention and progress, there are critical challenges that remains to be overcome to achieve the most effective successful cell‐based therapy in MI.     

A Murine Model of Myocardial Ischemia-reperfusion Injury through Ligation of the Left Anterior Descending Artery

Acute or chronic myocardial infarction (MI) are cardiovascular events resulting in high morbidity and mortality. Establishing the pathological mechanisms at work during MI and developing effective therapeutic approaches requires methodology to reproducibly simulate the clinical incidence and reflect the pathophysiological changes associated with MI. Here, we describe a surgical method to induce MI in mouse models that can be used for short-term ischemia-reperfusion (I/R) injury as well as permanent ligation. The major advantage of this method is to facilitate location of the left anterior descending artery (LAD) to allow for accurate ligation of this artery to induce ischemia in the left ventricle of the mouse heart. Accurate positioning of the ligature on the LAD increases reproducibility of infarct size and thus produces more reliable results. Greater precision in placement of the ligature will improve the standard surgical approaches to simulate MI in mice, thus reducing the number of experimental animals necessary for statistically relevant studies and improving our understanding of the mechanisms producing cardiac dysfunction following MI. This mouse model of MI is also useful for the preclinical testing of treatments targeting myocardial damage following MI.     

Psychological consequences of myocardial infarction: a self-regulation perspective on health-related quality of life and cardiac rehabilitation

The aim of this review was to gain insight into prevalence of and interventions targeted specifically at psychological distress and health-related quality of life (HRQL) after a myocardial infarction (MI). For this purpose, self-regulation theory was introduced as frame of reference. Psychological distress and a reduction in HRQL after an MI are prevalent and can, for some patients, be persistent. This can negatively influence secondary prevention efforts, adherence, return to work and progression of the underlying coronary heart disease. At the same time, the effectiveness of cardiac rehabilitation programmes in improving HRQL is inconclusive. By starting off from a theoretical framework, effective strategies can be either identified or developed. Self-regulation theory is concerned with the process of goal setting and goal attainment and offers a model for explaining well-being and quality of life. The usefulness of this theory is supported by empirical evidence. Psychological factors derived from this theoretical framework (e.g. higher order goal disturbance) are associated with psychological distress and HRQL in the short and medium term after an MI and should thus be the target of cardiac rehabilitation programmes.     

Stem cell therapy: A novel approach for myocardial infarction

Myocardial infarction (MI) is a major cause of morbidity and mortality worldwide. Until recently, it was thought that myocardium was not able to repair itself, but studies have now shown that resident cardiac stem cells have regenerative capacity, and stem cell therapy may be a novel approach for cardiac muscle repair and regeneration. Stem cell-derived paracrine factors have been shown to regulate ventricular remodeling, inflammation, apoptosis, cardiomyocytes regeneration, and neovascularization in regions of infarcted cardiac tissue. In this review, we summarize the evidence from cellular, animal, and clinical studies supporting the potential clinical significance of stem cell therapy as a novel therapeutic approach for the treatment of MI.     

Establishment of a Reperfusion Model in Rabbits with Acute Myocardial Infarction

Clinically effective cardioprotection under acute myocardial infarction (AMI) can only be achieved by establishing the mechanisms of reperfusion-induced cardiac cell death. In spite of the numerous earlier studies on the prevention of ischemia–reperfusion injury of myocardium, the problem of cardiac cell death upon reperfusion is not yet resolved. Even though animal models provide an immense opportunity in the understanding of the mechanisms of ischemia–reperfusion injury, clinically relevant animal models through which translation of this knowledge into clinic are lacking. In this work, we have established a reperfusion model in rabbits with induced AMI by obstructing and releasing the left anterior ventricular branch of left circumflex coronary artery, which is clinically more relevant. This was achieved by cutting the two left ribs of the rabbit followed by obstructing and releasing the artery unlike the traditional approach, which involves incision through sternum and blocking the anterior descending coronary artery. This animal model of ischemia–reperfusion more closely mimics the physiological condition and also the trauma the animal suffers is much smaller with higher survival rate and thus is a potentially better model for studying the pathology related to ischemia–reperfusion injury.     

Evaluating the role of autologous mesenchymal stem cell seeded on decellularized pericardium in the treatment of myocardial infarction: an animal study

Inappropriate left ventricular remodeling following myocardial infarction (MI) can result in subsequent severe dysfunction. In this study, we tested the hypothesis that decellularized pericardium (DP) or seeded pericardial patch with autologous adipose-derived mesenchymal stem cells (ADMSCs) could be safely used in a MI scar and could improve heart function. Twelve rabbits were randomly divided into three equal groups. Four weeks after MI induction by ligation of the left anterior descending artery in 12 rabbits, animals of G1 (n = 4) received DP patch with labeled ADMSCs. DP patch was implanted in animals of G2 (n = 4). Rabbits of G3 (n = 4) remained without any intervention after MI induction (control group). Serial examinations including echocardiography, electrocardiography (ECG), scanning electron microscopy, histology and immunohistochemistry (IHC) were performed to evaluate the efficacy of the implanted scaffolds on recovery of the infracted myocardium. The results demonstrated that left ventricular contractile function and myocardial pathological changes were significantly improved in rabbits implanted with either DP or ADMSC-seeded pericardium. However, the seeded pericardium was more effective in scar repairing 2 months after the operation, IHC staining with Desmin and CD34 and positive immunofluorescence staining verified the differentiation of ADMSCs to functional cardiomyocytes. This approach may involve the application of autologous ADMSCs seeded on pericardial patch in an attempt to regenerate a contractible myocardium in an animal model of MI.     

Reviewing the role of cardiac exosomes in myocardial repair at a glance

Exosome-based therapy is an emerging novel approach for myocardial infarction (MI) treatment. Exosomes are identified as extracellular vesicles that are produced within multivesicular bodies in the cells' cytosols and then are secreted from the cells. Exosomes are 30–100 nm in diameter that are released from viable cells and are different from other secreted vesicles such as apoptotic bodies and microvesicles in their origin and contents such as RNAs, proteins, and nucleic acid. The recent advances in exosome research have demonstrated the role of these bionanovesicles in the physiological, pathological, and molecular aspects of the heart. The results of in vitro and preclinical models have shown that exosomes from different cardiac cells can improve cardiac function following MI. For example, mesenchymal stem cells (MSCs) and cardiac progenitor cells (CPCs) containing exosomes can affect the proliferation, survival, and differentiation of cardiac fibroblasts and cardiomyocytes. Moreover, MSCs- and CPCs-derived exosomes can enhance the migration of endothelial cells. Exosome-based therapy approaches augment the cardiac function by multiple means, such as reducing fibrosis, stimulation of vascular angiogenesis, and proliferation of cardiomyocytes that result in replacing damaged heart tissue with newly generated functional myocytes. This review article aims to briefly discuss the recent advancements in the role of secreted exosomes in myocardial repair by focusing on cardiac cells-derived exosomes.     

C-type natriuretic peptide: A new cardiac mediator

Natriuretic peptides are endogenous hormones released by the heart in response to myocardial stretch and overload. While atrial and brain natriuretic peptides (ANP, BNP) were immediately considered cardiac hormones and their role was well-characterized and defined in predicting risk in cardiovascular disease, evidence indicating the role of C-type natriuretic peptide (CNP) in cardiovascular regulation was slow to emerge until about 8 years ago. Since then, considerable literature on CNP and the cardiovascular system has been published; the aim of this review is to examine current literature relating to CNP and cardiovascular disease, in particular its role in heart failure (HF) and myocardial infarction (MI). This review retraces the fundamental steps in research that led understanding the role of CNP in HF and MI; from increased CNP mRNA expression and plasmatic concentrations in humans and in animal models, to detection of CNP expression in cardiomyocytes, to its evaluation in human leukocytes. The traditional view of CNP as an endothelial peptide has been surpassed by the results of many studies published in recent years, and while its physiological role is still under investigation, information is now available regarding its contribution to cardiovascular function. Taken together, these observations suggest that CNP and its specific receptor, NPR-B, can play a very important role in regulating cardiac hypertrophy and remodeling, indicating NPR-B as a new potential drug target for the treatment of cardiovascular disease.     

国际前沿

高伟坚博士,英籍华人,1986年出生于英国。18岁以全优成绩考取曼彻斯特大学生命科学院。2008年以优等生荣誉毕业,获学士学位。2012年,获得该校博士学位。2004～2012年,先后获得“默沙东杰出学术成就奖”、英联邦帕金森氏病学会的“杰出研究和展示奖”、“曼彻斯特领袖项目”金奖、双重博士奖学金。他从小热爱生物医学,经过系统求学过程及严格的科研训练,在科研课题设计和科技论文撰写方面,表现出不菲的成绩。毕业后仅仅两年,便发表有影响的科技论文4篇。并参与Springer 组织的‘L-DOPA-induced dyskinesia in Parkinson ’ s disease ’一书的编撰工作。同时,还组织申请国际合作课题两项,参研课题四项。高博士现供职于法国波尔多第二大学,在华开展联合研发工作期间,多次表达了“自己作为华人,愿意为祖国生物医学发展贡献自己力量的想法”。也深知华人科学家因为语言障碍,而在科技论文发表和科研课题申请上遇到的重重困难。经我刊编委推荐及编辑部与部分专家讨论商议,特聘请高博士为两刊特约通讯员,开设专栏,希望高博士从信息获取、论文撰写、课题设计等方面开展工作,并定期向我刊介绍业内国际前沿动态,为我刊读者扩大视角。 本期推出神经科学研究中的动物选择和模型制作,欢迎读者就相关内容展开互动。