Stem cells for cardiac repair in acute myocardial infarction

Despite recent advances in medical therapy, reperfusion strategies, implantable cardioverter-defibrillators and cardiac assist devices, ischemic heart disease is a frequent cause of morbidity and mortality worldwide. Cell therapy has been introduced as a new treatment modality to regenerate lost cardiomyocytes. At present, several cell types seem to improve left ventricular function in animal models as well as in humans, but evidence for true generation of new myocardium is confined to the experimental models. In the clinical perspective, myocardial regeneration has been replaced by myocardial repair, as other mechanisms seem to be involved. Clinical studies on adult stem cells suggest, at best, moderate beneficial effects on surrogate end points, but some applications may qualify for evaluation in larger trials. Complete regeneration of the myocardium by cell therapy after a large myocardial infarction is still visionary, but pluripotent stem cells and tissue engineering are important tools to solve the puzzle.     

Cell‐based therapies for cardiac disease: a cellular therapist's perspective

Cell‐based therapy is an exciting, promising, and a developing new treatment for cardiac diseases. Stem cell–based therapies have the potential to fundamentally transform the treatment of ischemic cardiac injury and heart failure by achieving what would have been unthinkable only a few years ago—the Holy Grail of myocardial regeneration. Recent therapeutic approaches involve bone marrow (BM)‐derived mononuclear cells and their subsets such as mesenchymal stem/stromal cells (MSCs), endothelial progenitor cells as well as adipose tissue–derived MSCs, cardiac tissue–derived stem cells, and cell combinations. Clinical trials employing these cells have demonstrated that cellular therapy is feasible and safe. Regarding delivery methods, the safety of catheter‐based, transendocardial and ‐epicardial stem cell injection has been established. However, the results, while variable, suggest rather modest clinical efficacy overall in both heart failure and ischemic heart disease, such as in acute myocardial infarction. Future studies will focus on determining the most efficacious cell type(s) and/or cell combinations and the most reasonable indications and optimal timing of transplantation, as well as the mechanisms underlying their therapeutic effects. We will review and summarize the clinical trial results to date. In addition, we discuss challenges and operational issues in cell processing for cardiac applications.     

Materials Science and Tissue Engineering: Repairing the Heart

Heart failure after a myocardial infarction continues to be a leading killer in the Western world. Currently, there are no therapies that effectively prevent or reverse the cardiac damage and negative left ventricular remodeling process that follows a myocardial infarction. Because the heart has limited regenerative capacity, there has been considerable effort to develop new therapies that could repair and regenerate the myocardium. Although cell transplantation alone was initially studied, more recently, tissue engineering strategies using biomaterial scaffolds have been explored. In this review, we cover the different approaches to engineering the myocardium, including cardiac patches, which are in vitro–engineered constructs of functional myocardium, and injectable scaffolds, which can either encourage endogenous repair and regeneration or act as vehicles to support the delivery of cells and other therapeutics.     

Gene therapy for myocardial regeneration

Most of cardiac myocytes have lost their ability to proliferate and differentiate into new myocytes. Therefore, myocyte regeneration and replacement in adult myocardium was thought to be impossible by medical community. However, recent findings in cardiovascular researches provide the possibility that gene therapy and stem cell therapy could have supportive effects on myocyte regeneration and myocardial revascularization in damaged heart. Here, we presented recent progress, especially, in gene therapy for myocardial regeneration under ischemic heart disease and heart failure.     

Cellular cardiac regenerative therapy in which patients?

Cell-based myocardial regenerative therapy is undergoing experimental and clinical trials in order to limit the consequences of decreased contractile function and compliance of damaged ventricles owing to ischemic and nonischemic myocardial diseases. A variety of myogenic and angiogenic cell types have been proposed, such as skeletal myoblasts, mononuclear and mesenchymal bone marrow cells, circulating blood-derived progenitors, adipose-derived stromal cells, induced pluripotent stem cells, umbilical cord cells, endometrial mesenchymal stem cells, adult testis pluripotent stem cells and embryonic cells. Current indications for stem cell therapy concern patients who have had a left- or right-ventricular infarction or idiopathic dilated cardiomyopathies. Other indications and potential applications include patients with diabetic cardiomyopathy, Chagas heart disease (American trypanosomiasis), ischemic mitral regurgitation, left ventricular noncompacted myocardium and pediatric cardiomyopathy. Suitable sources of cells for cardiac implant will depend on the types of diseases to be treated. For acute myocardial infarction, a cell that reduces myocardial necrosis and augments vascular blood flow will be desirable. For heart failure, cells that replace or promote myogenesis, reverse apoptopic mechanisms and reactivate dormant cell processes will be useful. It is important to note that stem cells are not an alternative to heart transplantation; selected patients should be in an early stage of heart failure as the goal of this regenerative approach is to avoid or delay organ transplantation. Since the cell niche provides crucial support needed for stem cell maintenance, the most interesting and realistic perspectives include the association of intramyocardial cell transplantation with tissue-engineered scaffolds and multisite cardiac pacing in order to transform a passive regenerative approach into a ‘dynamic cellular support’, a promising method for the creation of ‘bioartificial myocardium’.     

Cellular Antioxidant Levels Influence Muscle Stem Cell Therapy

Although cellular transplantation has been shown to promote improvements in cardiac function following injury, poor cell survival following transplantation continues to limit the efficacy of this therapy. We have previously observed that transplantation of muscle-derived stem cells (MDSCs) improves cardiac function in an acute murine model of myocardial infarction to a greater extent than myoblasts. This improved regenerative capacity of MDSCs is linked to their increased level of antioxidants such as glutathione (GSH) and superoxide dismutase. In the current study, we demonstrated the pivotal role of antioxidant levels on MDSCs survival and cardiac functional recovery by either reducing the antioxidant levels with diethyl maleate or increasing antioxidant levels with N-acetylcysteine (NAC). Both the anti- and pro-oxidant treatments dramatically influenced the survival of the MDSCs in vitro. When NAC-treated MDSCs were transplanted into infarcted myocardium, we observed significantly improved cardiac function, decreased scar tissue formation, and increased numbers of CD31⁺ endothelial cell structures, compared to the injection of untreated and diethyl maleate–treated cells. These results indicate that elevating the levels of antioxidants in MDSCs with NAC can significantly influence their tissue regeneration capacity.     

SDF-1α as a therapeutic stem cell homing factor in myocardial infarction

Myocardial infarction is associated with persistent muscle damage, scar formation and depressed cardiac performance. Recent studies have demonstrated the clinical significance of stem cell-based therapies after myocardial infarction with the aim to improve cardiac remodeling and function by inducing the reconstitution of functional myocardium and formation of new blood vessels. Stem cell homing signals play an important role in stem cell mobilization from the bone marrow to the ischemic cardiac environment and are therefore crucial for myocardial repair. To date, the most prominent stem cell homing factor is the chemokine SDF-1α/CXCL12. This protein was shown to be significantly upregulated in many experimental models of myocardial infarction and in patients suffering from ischemic cardiac diseases, suggesting the involvement in the pathophysiology of these disorders. A number of studies focused on manipulating SDF-1α and its receptor CXCR4 as central regulators of the stem cell mobilization process. Targeted expression of SDF-1α after myocardial infarction was shown to result in increased engraftment of bone marrow-derived stem cells into infarcted myocardium. This was accompanied by beneficial effects on cardiomyocyte survival, neovascularization and cardiac function. Thus, the SDF-1/CXCR4 axis seems to be a promising novel therapeutic approach to improve post-infarction therapy by attracting circulating stem cells to remain, survive and possibly differentiate in the infarct area. This review will summarize clinical trials of stem cell therapy in patients with myocardial infarction. We further discuss the basic findings about SDF-1α in stem cell recruitment and its therapeutic implications in experimental myocardial infarction.     

在心肌组织工程构建中的心肌干细胞：认识现状与预测未来

背景：长期以来,人们认为成年哺乳动物的心肌是终末分化的组织,没有再生能力。心肌细胞一旦受损将由纤维结缔组织取代。目的：重新认识心肌细胞,对心肌干细胞的相关研究做一综述,以明确心肌干细胞的存在。方法：计算机检索中国期刊网全文数据库以及PubMed数据库2003至2014年期间有关心肌干细胞的文章。检索词分别为“心肌干细胞,干细胞,心脏再生”和“cardiac stem cel s,stem cel s,cardiac regeneration ”。初检得到82篇文献,最终纳入文章40篇。结果与结论：心脏中存在具有再生潜能的心肌干细胞,现已研究出一些心肌干细胞的表面标记物。心肌干细胞的研究为临床治疗某些心肌细胞损伤性疾病开辟了崭新的思路,但心肌干细胞的数量较少,如何分离纯化、培养鉴定,并扩增为满足再生医学和组织工程需要的心肌细胞还有待于进一步研究,心肌干细胞的研究将为心肌组织工程研究开辟崭新的途径。     

Cells, scaffolds, and molecules for myocardial tissue engineering

Unlike heart valves or blood vessels, heart muscle has no replacement alternatives. The most challenging goal in the field of cardiovascular tissue engineering is the creation/ regeneration of an engineered heart muscle. Recent advances in methods of stem cell isolation, culture in bioreactors, and the synthesis of bioactive materials promise to create engineered cardiac tissue ex vivo. At the same time, new approaches are conceived that explore ways to induce tissue regeneration after injury. The purpose of our review is to describe the principles, status, and challenges of myocardial tissue engineering with emphasize on the concept of in situ cardiac tissue engineering and regeneration.     

Creating the bioartificial myocardium for cardiac repair: challenges and clinical targets

The association of stem cells with tissue-engineered scaffolds constitutes an attractive approach for the repair of myocardial tissue with positive effects to avoid ventricular chamber dilatation, which changes from a natural elliptical to spherical shape in heart failure patients. Biohybrid scaffolds using nanomaterials combined with stem cells emerge as new therapeutic tool for the creation of ‘bioartificial myocardium’ and ‘cardiac wrap bioprostheses’ for myocardial regeneration and ventricular support. Biohybrids are created introducing stem cells and self-assembling peptide nanofibers inside a porous elastomeric membrane, forming cell niches. Our studies lead to the creation of semi-degradable ‘ventricular support bioprostheses’ for adaptative LV and/or RV wrapping, designed with the concept of ‘helical myocardial bands’. The goal is to restore LV elliptical shape, and contribute to systolic contraction and diastolic filling (suction mechanism). Cardiac wrapping with ventricular bioprostheses may reduce the risk of heart failure progression and the indication for heart transplantation.     

High-resolution X-ray microtomography for three-dimensional imaging of cardiac progenitor cell homing in infarcted rat hearts

The recent introduction of stem cells in cardiology provides new tools in understanding the regenerative processes of the normal and pathological heart and has opened a search for new therapeutic strategies. Recent published reports have contributed to identifying possible cellular therapy approaches to generate new myocardium, involving transcoronary and intramyocardial injection of progenitor cells. However, one of the limiting factors in the overall interpretation of clinical results obtained by cell therapy is represented by the lack of three-dimensional (3D) high-resolution methods for the visualization of the injected cells and their fate within the myocardium. This work shows that X-ray computed microtomography may offer the unique possibility of detecting, with high definition and resolution and in ex vivo conditions, the 3D spatial distribution of rat cardiac progenitor cells, labelled with iron oxide nanoparticles, inside the infarcted rat heart early after injection. The obtained 3D images represent a very innovative progress as compared to experimental two-dimensional (2D) histological analysis, which requires time-consuming energies for image reconstruction in order to provide the overall distribution of rat clonogenic cells within the heart. Through microtomography, we were able to observe in 3D the presence of these cells within damaged cardiac tissue, with important structural details that are difficult to visualize by conventional bidimensional imaging techniques. This new 3D-imaging approach appears to be an important way to investigate the cellular events involved in cardiac regeneration and represents a promising tool for future clinical applications.     

Cardiac imaging

Congestive heart failure is a state of inadequate cardiac function under various etiologies. Cardiac imaging plays an important role for accurate detection of heart failure, assessment of severity of LV function, and precise analysis of tissue function in vivo. Recently, multislice CT(MSCT), magnetic resonance imaging (MRI), and positron emission tomography(PET) have been rapidly developed for clinical use for assessing patients with congestive heart failure. MSCT has been used for accurate assessment of LV function. Due to high spatial resolution, MSCT permits assessment of coronary stenosis without cardiac catheterization. MRI permits assessment of LV function and also tissue function. Particularly, infarcted myocardium is accurately delineated as an area of delayed enhancement by contrast enhancement MRI study. PET has been used for accurate assessment of myocardial viability based on the persistence of myocardial glucose metabolism. In addition, a various new PET tracers permit molecular and cellular function, such as neurotransmission and receptor function in vivo. These new imaging technique has a potential role for assessing risk stratification and providing appropriate treatment strategy.     

Myocardial repair: from salvage to tissue reconstruction

Cardiac tissue reconstruction following myocardial infarction represents a major challenge in cardiovascular therapy, as current clinical approaches are limited in their ability to regenerate or replace damaged myocardium. Thus, different novel treatments have been introduced aimed at myocardial salvage and repair. Here, we present a review of recent advancements in cardiac cell, gene-based and tissue engineering therapies. Selected strategies in cell therapy and new tools for myocardial gene transfer are summarized. Finally, we consider novel approaches to myocardial tissue engineering as a platform for the integration of various modalities in an attempt to rejuvenate infarcted tissue in vivo.     

Endothelial and cardiac progenitors: boosting, conditioning and (re)programming for cardiovascular repair

Preclinical studies performed in cell culture and animal systems have shown the outstanding ability of stem cells to repair ischemic heart and lower limbs by promoting the formation of new blood vessels and new myocytes. In contrast, clinical studies of stem cell administration in patients with myocardial ischemia have revealed only modest, although promising, results. Basic investigations have shown the feasibility of adult cells reprogramming into pluripotent cells by defined factors, thus opening the way to the devise of protocols to ex vivo derive virtually unexhausted cellular pools. In contrast, cellular and molecular studies have indicated that risk factors limit adult-derived stem cell survival, proliferation and engraftment in ischemic tissues. The use of fully reprogrammed cells raises safety concerns; therefore, adult cells remain a primary option for clinicians interested in therapeutic cardiovascular repair. Pharmacologic approaches have been devised to restore the cardiovascular repair ability of failing progenitors from patients at risk. In the present contribution, the most advanced pharmacologic approaches to (re)program, boost, and condition endothelial and cardiac progenitor cells to enhance cardiovascular regeneration are discussed.     

Myocardial localization and isoforms of neural cell adhesion molecule (N-CAM) in the developing and transplanted human heart.

Neural cell adhesion molecule (N-CAM) has been implicated in cellular interactions involved in cardiac morphogenesis and innervation. Immunohistochemical techniques and Western blot analysis were used to determine the localization and isoforms of N-CAM in the developing and extrinsically denervated human heart. Myocardial and conducting cells in the fetal heart (7-24 wk gestation) exhibited sarcolemmal immunoreactivity, the major desialo N-CAM isoforms being 150, 145, 120, 115, and 110 kD. N-CAM expression appeared to be downregulated in the myocardium during adult life, with relatively little sarcolemmal immunoreactivity being detected in normal donor tissues. In contrast to the temporal changes observed in the myocardium, both the developing and mature cardiac innervation displayed N-CAM immunofluorescence staining, localized to neuronal cell bodies, nerve fascicles and fibres. Extrinsically denervated cardiac allografts, obtained 2 d to 91 mo after transplantation, showed extensive sarcolemmal and intercalated disc immunostaining and expression of 125-, 120-, and 115-kD isoforms. Tissues from explanted recipient hearts and atrial appendage samples obtained during coronary bypass graft operations were also examined and displayed varying amounts of N-CAM immunoreactivity. We conclude that the expression of N-CAM immunoreactivity and isoforms in the human heart is developmentally regulated and may be modulated by factors such as cardiac innervation and myocardial hypertrophy.     

肝素缓释支架置入联合心肌钻孔对急性心肌梗死猪心肌细胞再生的影响

背景:课题组前期发明了一种新的心肌再血管化的方法,即肝素缓释支架置入联合心肌钻孔,可明显改善心肌灌注.目的:观察肝素缓释支架置入联合心肌钻孔在猪急性心肌梗死后心肌细胞再生中的作用.方法:通过结扎冠状动脉前降支制作猪急性心肌梗死模型,随机分为模型对照组、支架置入组,6只,组.支架置入组于心肌梗死区采用自制高速钻孔器由心外膜打2个直径为3.5 mm透壁孔道,每个孔道内置入1枚肝素缓释支架.置入后静脉注射BrdU用以标记DNA复制.观察治疗前后基质细胞衍生因子1 mRNA表达及心肌灌注、新生心肌、心功能等变化.结果与结论:与模型对照组比较,置入6周后支架置入组基质细胞衍生因子1的表达明显增强(P<0.001),灌注质量缺损百分率的差值明显降低(P<0.001),左室射血分数明显提高(P<0.05),新生心肌明显增加(P<0.001),缺血区存活心肌明显增多(P<0.001).证实心肌钻孔与肝素缓释支架置入可以通过提高基质细胞衍生因子1表达和增加缺血区灌注,增强心肌梗死区损伤心肌细胞的修复,改善心功能.     

脐血干细胞移植治疗心肌梗死的作用与机制

背景：多项基础和临床研究表明,干细胞移植可以改善心肌梗死后心力衰竭患者的心脏功能。目的：总结脐血干细胞移植治疗心肌梗死的的作用与机制。方法：由第一作者检索2000/2009 PubMed数据库及CNKI、万方数据库有关脐血干细胞移植治疗心肌梗死基础研究方面的文献。结果与结论：干细胞移植在治疗急性心肌梗死方面已表现出传统治疗方法无法比拟的优势,而目前一系列基础研究证实人脐血干细胞有望成为更为理想的细胞源,但因其尚处于探索性研究阶段,仍有许多问题有待解决,诸如人脐血干细胞的体外分离、培养,最适宜的移植治疗时间,最有利的移植途径,最佳的移植数量,移植细胞的存活率如何,移植后能否分化为心肌细胞,分化程度如何以及其疗效和安全性等。     

Myocardial repair: from salvage to tissue reconstruction

Cardiac tissue reconstruction following myocardial infarction represents a major challenge in cardiovascular therapy, as current clinical approaches are limited in their ability to regenerate or replace damaged myocardium. Thus, different novel treatments have been introduced aimed at myocardial salvage and repair. Here, we present a review of recent advancements in cardiac cell, gene-based and tissue engineering therapies. Selected strategies in cell therapy and new tools for myocardial gene transfer are summarized. Finally, we consider novel approaches to myocardial tissue engineering as a platform for the integration of various modalities in an attempt to rejuvenate infarcted tissue in vivo.     

Robust Cardiac Regeneration: Fulfilling the Promise of Cardiac Cell Therapy

PurposeWe review the history of cardiac cell therapy, highlighting lessons learned from initial adult stem cell (ASC) clinical trials. We present pluripotent stem cell–derived cardiomyocytes (PSC-CMs) as a leading candidate for robust regeneration of infarcted myocardium but identify several issues that must be addressed before successful clinical translation.MethodsWe conducted an unstructured literature review of PubMed-listed articles, selecting the most comprehensive and relevant research articles, review articles, clinical trials, and basic or translation articles in the field of cardiac cell therapy. Articles were identified using the search terms adult stem cells, pluripotent stem cells, cardiac stem cell, and cardiac regeneration or from references of relevant articles, Articles were prioritized and selected based on their impact, originality, or potential clinical applicability.FindingsSince its inception, the ASC therapy field has been troubled by conflicting preclinical data, academic controversies, and inconsistent trial designs. These issues have damaged perceptions of cardiac cell therapy among investors, the academic community, health care professionals, and, importantly, patients. In hindsight, the key issue underpinning these problems was the inability of these cell types to differentiate directly into genuine cardiomyocytes, rendering them unable to replace damaged myocardium. Despite this, beneficial effects through indirect paracrine or immunomodulatory effects remain possible and continue to be investigated. However, in preclinical models, PSC-CMs have robustly remuscularized infarcted myocardium with functional, force-generating cardiomyocytes. Hence, PSC-CMs have now emerged as a leading candidate for cardiac regeneration, and unpublished reports of first-in-human delivery of these cells have recently surfaced. However, the cardiac cell therapy field's history should serve as a cautionary tale, and we identify several translational hurdles that still remain. Preclinical solutions to issues such as arrhythmogenicity, immunogenicity, and poor engraftment rates are needed, and next-generation clinical trials must draw on robust knowledge of mechanistic principles of the therapy.ImplicationsThe clinical transplantation of functional stem cell–derived heart tissue with seamless integration into native myocardium is a lofty goal. However, considerable advances have been made during the past 2 decades. Currently, PSC-CMs appear to be the best prospect to reach this goal, but several hurdles remain. The history of adult stem cell trials has taught us that shortcuts cannot be taken without dire consequences, and it is essential that progress not be hurried and that a worldwide, cross-disciplinary approach be used to ensure safe and effective clinical translation.