Influence of embryonic cardiomyocyte transplantation on the progression of heart failure in a rat model of extensive myocardial infarction

Human pluripotent stem cell-based cardiac repair: Lessons learned and challenges ahead

The transplantation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) and hPSC-derived cardiac progenitors (hPSC-CPs) represents a promising strategy for regenerating hearts damaged by myocardial infarction (MI). After nearly two decades of experience testing these cell populations in various small- and large-animal MI models, multiple clinical trials have recently been initiated. In this review, we consider the principal lessons learned from preclinical experience with hPSC-CMs and -CPs, focusing on three conclusions that have been supported by the majority of reported transplantation studies. First, hPSC-CMs and -CPs stably engraft in injured hearts and partially remuscularize the infarct scar, but more progress is needed to improve graft cell retention and survival. Second, the transplantation of hPSC-CMs and -CPs has been found to improve contractile function in infarcted hearts, but the mechanistic basis for these effects remains incompletely elucidated. Third, the graft tissue formed by these cells can integrate and activate synchronously with host myocardium, but this capacity for electromechanical integration has been associated with an elevated risk of graft-related arrhythmias. Here, we summarize the preclinical evidence supporting these three observations, identify the relevant gaps and barriers to translation, and summarize ongoing efforts to improve the safety and efficacy of hPSC-CM- and -CP-based regenerative therapies.

An Alginate/Gelatin Injectable Hydrogel Containing Au Nanoparticles for Transplantation of Embryonic Mouse Cardiomyocytes in Myocardial Repair

In advancing cardiac tissue engineering (CTE), the development of injectable hydrogels mirroring myocardial properties is pivotal. The designed hydrogels must not only support cardiac cell growth but also have to be conductive to properly promote the functionalities of cardiac cells. Here, a facile approach is developed to incorporate gold nanoparticles (AuNPs) into an injectable hydrogel composed of Alginate (Alg) and Gelatin (Gel). The resultant nanocomposite hydrogel boasts a porous interconnected network and superior conductivity (2.04 × 10-4 S cm-1) compared to the base Alg/Gel hydrogel. Hydrogel hydration and in vitro degradation profiles affirm their suitability as carriers for cardiac cells. Importantly, Alg/Gel+AuNPs hydrogels exhibit no toxicity to mouse Embryonic Cardiac Cells (mECCs) over 7 days, elevating connexin 43 (Cx43) and cardiac troponin T (CTnT) gene expression compared to controls. Then, the Alg/Gel+AuNPs hydrogel is used as a carrier for intramyocardial delivery of mECCs in rats with myocardial infarction. The significant increase in α-Smooth Muscle Actin (α-SMA) and cardiac troponin T (CTnT) expression along with the increase in ejection fraction (EF), smaller infarction size, less fibrosis area confirmed that the hydrogel efficiently promoted the transmission of mechanical and electrical signals between transplanted cells and surrounding tissue.

A review on experimental surgical models and anesthetic protocols of heart failure in rats

Heart failure (HF) is a serious health and economic burden worldwide, and its prevalence is continuously increasing. Current medications effectively moderate the progression of symptoms, and there is a need for novel preventative and reparative treatments. The development of novel HF treatments requires the testing of potential therapeutic procedures in appropriate animal models of HF. During the past decades, murine models have been extensively used in fundamental and translational research studies to better understand the pathophysiological mechanisms of HF and develop more effective methods to prevent and control congestive HF. Proper surgical approaches and anesthetic protocols are the first steps in creating these models, and each successful approach requires a proper anesthetic protocol that maintains good recovery and high survival rates after surgery. However, each protocol may have shortcomings that limit the study's outcomes. In addition, the ethical regulations of animal welfare in certain countries prohibit the use of specific anesthetic agents, which are widely used to establish animal models. This review summarizes the most common and recent surgical models of HF and the anesthetic protocols used in rat models. We will highlight the surgical approach of each model, the use of anesthesia, and the limitations of the model in the study of the pathophysiology and therapeutic basis of common cardiovascular diseases.

An overview of the myocardial regeneration potential of cardiac c-Kit+ progenitor cells via PI3K and MAPK signaling pathways

In recent years, several studies have investigated cell transplantation as an innovative strategy to restore cardiac function following heart failure. Previous studies have also shown cardiac progenitor cells as suitable candidates for cardiac cell therapy compared with other stem cells. Cellular kit (c-kit) plays an important role in the survival and migration of cardiac progenitor cells. Like other types of cells, in the heart, cellular responses to various stimuli are mediated via coordinated pathways. Activation of c-kit⁺ cells leads to subsequent activation of several downstream mediators such as PI3K and the MAPK pathways. This review aims to outline current research findings on the role of PI3K/AKT and the MAPK pathways in myocardial regeneration potential of c-kit⁺.

Cardiac tissue engineering therapeutic products to enhance myocardial contractility

Researchers continue to develop therapeutic products for the repair and replacement of myocardial tissue that demonstrates contractility equivalent to normal physiologic states. As clinical trials focused on pure adult stem cell populations undergo meta-analysis for preclinical through clinical design, the field of tissue engineering is emerging as a new clinical frontier to repair the myocardium and improve cardiac output. This review will first discuss the three primary tissue engineering product themes that are advancing in preclinical to clinical models: (1) cell-free scaffolds, (2) scaffold-free cellular, and (3) hybrid cell and scaffold products. The review will then focus on the products that have advanced from preclinical models to clinical trials. In advancing the cardiac regenerative medicine field, long-term gains towards discovering an optimal product to generate functional myocardial tissue and eliminate heart failure may be achieved.

Deformation imaging to assess global and regional effects of cardiac regenerative therapy in ischaemic heart disease: A systematic review

Currently, left ventricular ejection fraction (LVEF) is the most common endpoint in cardiovascular stem cell therapy research. However, this global measure of cardiac function might not be suitable to detect the regional effects sorted by this therapy and is hampered by high operator variability and loading dependency. Deformation imaging might be more accurate in detecting potential regional functional improvements by cardiac regenerative therapy. The aim of this systematic review is to provide a comprehensive overview of current literature on the value of deformation imaging in cardiac regenerative therapy. A systematic review of current literature available on PubMed, Embase, and Cochrane databases was performed regarding both animal and patient studies in which deformation imaging was used to study cardiac cell therapy. After critical appraisal, outcomes regarding study design, type of cell therapy, procedural characteristics, outcome measure, method for measuring strain, and efficacy on both LVEF and deformation parameters were depicted. A total of 30 studies, 15 preclinical and 15 clinical, were included for analysis. Deformation outcomes improved significantly in 14 out of 15 preclinical studies and in 10 out of 15 clinical studies, whereas LVEF improved in 12 and 4 articles, respectively. Study designs and used deformation outcomes varied significantly among the included papers. Six studies found a positive effect on deformation outcomes without LVEF improvement. Hence, deformation imaging seems at least equal, and perhaps superior, to LVEF measurement in the assessment of cardiac regenerative therapy. However, strategies varied substantially and call for a standardized approach.

The Heart and Great Vessels

Cardiovascular disease is the leading cause of mortality worldwide. We have made large strides over the past few decades in management, but definitive therapeutic options to address this health-care burden are still limited. Given the ever-increasing need, much effort has been spent creating engineered tissue to replaced diseased tissue. This article gives a general overview of this work as it pertains to the development of great vessels, myocardium, and heart valves. In each area, we focus on currently studied methods, limitations, and areas for future study.

Embryonic Stem Cells Attenuate Viral Myocarditis in Murine Model

We used mice to test our hypothesis that in response to viral invasion, stem cells may migrate into the heart and attenuate the effect of viral myocarditis. Male BALB/c mice were divided into three groups: mouse embryonic stem (ES) cell control, encephalomyocarditis virus (EMCV), and EMCV + ES cells. After administration of ES cells via tail vein, mice were immediately inoculated with EMCV. Mice were sacrificed at different days after EMCV inoculation. Mortality was recorded. Inflammatory cell infiltration and necrosis (major pathological changes of viral myocarditis) were evaluated by hematoxylin-eosin staining. ES cell migration and differentiation were identified by immunofluorescence. The survival rate in the EMCV + ES cell group (80%) was significantly increased (p < 0.05) over the EMCV-alone group (64%). Also, the incidence of inflammatory cell infiltration and myocardial lesions was lower in the EMCV + ES cell mice. Furthermore, the result of green fluorescent protein (GFP) and a-actinin analysis indicated that ES cells migrated into the heart and differentiated into myocytes after virus inoculation. In conclusion, ES cells significantly increased the survival of viral myocarditis mice and also decreased the necrosis and infiltration of inflammatory cells. These results demonstrated the ability of stem cells to mitigate the effects of viral infection on the heart and illustrated their potential therapeutic application to other mammalian species, including humans.

Intramyocardially Transplanted Neonatal Cardiomyocytes (NCMs) Show Structural and Electrophysiological Maturation and Integration and Dose-Dependently Stabilize Function of Infarcted Rat Hearts

Cardiac cell replacement therapy is a promising therapy to improve cardiac function in heart failure. Persistence, structural and functional maturation, and integration of transplanted cardiomyocytes into recipients' hearts are crucial for a safe and efficient replacement of lost cells. We studied histology, electrophysiology, and quantity of intramyocardially transplanted rat neonatal cardiomyocytes (NCMs) and performed a detailed functional study with repeated invasive (pressure-volume catheter) and noninvasive (echocardiography) analyses of infarcted female rat hearts including pharmacological stress before and 3 weeks after intramyocardial injection of 5 × 106 (low NCM) or 25 × 106 (high NCM) syngeneic male NCMs or medium as placebo (Ctrl). Quantitative real-time polymerase chain reaction (PCR) for Y-chromosome confirmed a fivefold higher persisting male cell number in high NCM versus low NCM after 3 weeks. Sharp electrode measurements within viable slices of recipient hearts demonstrated that transplanted NCMs integrate into host myocardium and mature to an almost adult phenotype, which might be facilitated through gap junctions between host myocardium and transplanted NCMs as indicated by connexin43 in histology. Ejection fraction of recipient hearts was severely impaired after ligation of left anterior descending (LAD; pressure-volume catheter: 39.2 ± 3.6%, echocardiography: 39.9 ± 1.4%). Repeated analyses revealed a significant further decline within 3 weeks in Ctrl and a dose-dependent stabilization in cell-treated groups. Consistently, stabilized cardiac function/morphology in cell-treated groups was seen in stroke volume, cardiac output, ventricle length, and wall thickness. Our findings confirm that cardiac cell replacement is a promising therapy for ischemic heart disease since immature cardiomyocytes persist, integrate, and mature after intramyocardial transplantation, and they dose-dependently stabilize cardiac function after myocardial infarction.

On the existence of cardiomesenchymal stem cells

The most efficient cells for cardiac regeneration are myocardium-resident cardiac stem cells. However, the limited availability of these cells restricts their utility for cardiac cellular therapy. Mesenchymal stem cells can differentiate into a wide variety of tissues, but it is not simple to accurately direct cell differentiation into a specific lineage, such as cardiac tissue; this renders a low efficiency for cardiac regeneration therapy. Given the heterogeneity of mesenchymal stem cells, it may be possible to find specific stem cell subpopulations with a definite differentiation capacity toward cardiac lineage. A parameter to assess cardiac differentiation specificity could be surface marker expression; a population with an immunophenotype similar to cardiac stem cells may have a superior therapeutic value than unsorted mesenchymal stem cells. We hypothesize the existence of a cell line that combines the expression of cardiac stem cell surface markers with those of mesenchymal stem cells, a suitable name for this population is cardiomesenchymal stem cells (CMSC); such cells would be ideal for cardiac regeneration.

Tissue engineering: construction of a multicellular 3D scaffold for the delivery of layered cell sheets

Many tissues, such as the adult human hearts, are unable to adequately regenerate after damage.(2,3) Strategies in tissue engineering propose innovations to assist the body in recovery and repair. For example, TE approaches may be able to attenuate heart remodeling after myocardial infarction (MI) and possibly increase total heart function to a near normal pre-MI level.(4) As with any functional tissue, successful regeneration of cardiac tissue involves the proper delivery of multiple cell types with environmental cues favoring integration and survival of the implanted cell/tissue graft. Engineered tissues should address multiple parameters including: soluble signals, cell-to-cell interactions, and matrix materials evaluated as delivery vehicles, their effects on cell survival, material strength, and facilitation of cell-to-tissue organization. Studies employing the direct injection of graft cells only ignore these essential elements.(2,5,6) A tissue design combining these ingredients has yet to be developed. Here, we present an example of integrated designs using layering of patterned cell sheets with two distinct types of biological-derived materials containing the target organ cell type and endothelial cells for enhancing new vessels formation in the "tissue". Although these studies focus on the generation of heart-like tissue, this tissue design can be applied to many organs other than heart with minimal design and material changes, and is meant to be an off-the-shelf product for regenerative therapies. The protocol contains five detailed steps. A temperature sensitive Poly(N-isopropylacrylamide) (pNIPAAM) is used to coat tissue culture dishes. Then, tissue specific cells are cultured on the surface of the coated plates/micropattern surfaces to form cell sheets with strong lateral adhesions. Thirdly, a base matrix is created for the tissue by combining porous matrix with neovascular permissive hydrogels and endothelial cells. Finally, the cell sheets are lifted from the pNIPAAM coated dishes and transferred to the base element, making the complete construct.

Expression of microRNA-1, microRNA-133a and Hand2 protein in cultured embryonic rat cardiomyocytes

In this study, we investigated the expression of the pathway, SRF-microRNA-1/microRNA-133a-Hand2, in the Wistar rat embryonic ventricular cardiomyocytes under conventional monolayer culture. The morphological observation of the cultured cardiomyocytes and the mRNA expression levels of three vital constituent proteins, MLC-2v, N-cadherin, and connexin43, demonstrated the immaturity of these cultured cells, which was featured by less myofibril density, immature sarcomeric structure, and significantly lower mRNA expression of the three constituent proteins than those in neonatal ventricular samples. More importantly, results in this study suggest that the change of SRF-microRNA-1/microRNA-133a-Hand2 pathway results into the attenuation of the Hand2 repression in cultured cardiomyocytes. These outcomes are valuable to understand the cellular state as embryonic cardiomyocytes to be in vitro model and might be useful for the assessment of engineered cardiac tissue and cardiac differentiation of stem cells.

Renovation of the injured heart with myocardial tissue engineering

Tissue engineering aims to create, repair and/or replace tissues and organs by using cells, scaffolds, biologically active molecules and physiologic signals. It is an interdisciplinary field that integrates aspects of engineering, chemistry, biology and medicine. One of the most challenging goals in the field of cardiovascular tissue engineering is the creation of a heart muscle patch. This review describes the principles, achievements and challenges of achieving this ambitious goal of creating contractile heart muscle. In addition, the new strategy of in situ and injectable tissue engineering for myocardial repair and regeneration is presented.

Update: Innovation in cardiology (IV). Cardiac tissue engineering and the bioartificial heart

Heart failure is the end-stage of many cardiovascular diseases-such as acute myocardial infarction-and remains one of the most appealing challenges for regenerative medicine because of its high incidence and prevalence. Over the last 20 years, cardiomyoplasty, based on the isolated administration of cells with regenerative capacity, has been the focal point of most studies aimed at regenerating the heart. Although this therapy has proved feasible in the clinical setting, the degree of infarcted myocardium regenerated and of improved cardiac function are at best modest. Hence, tissue engineering has emerged as a novel technology using cells with regenerative capacity, biological and/or synthetic materials, growth, proangiogenic and differentiation factors, and online registry systems, to induce the regeneration of whole organs or locally damaged tissue. The next step, seen recently in pioneering animal studies, is de novo generation of bioartificial hearts by decellularization and preservation of supporting structures for their subsequent repopulation with new contractile, vascular muscle tissue. Ultimately, this new approach would entail transplantation of the "rebuilt" heart, reestablishing cardiac function in the recipient.

Minimally invasive cell-seeded biomaterial systems for injectable/epicardial implantation in ischemic heart disease

Myocardial infarction (MI) is characterized by heart-wall thinning, myocyte slippage, and ventricular dilation. The injury to the heart-wall muscle after MI is permanent, as after an abundant cell loss the myocardial tissue lacks the intrinsic capability to regenerate. New therapeutics are required for functional improvement and regeneration of the infarcted myocardium, to overcome harmful diagnosis of patients with heart failure, and to overcome the shortage of heart donors. In the past few years, myocardial tissue engineering has emerged as a new and ambitious approach for treating MI. Several left ventricular assist devices and epicardial patches have been developed for MI. These devices and acellular/cellular cardiac patches are employed surgically and sutured to the epicardial surface of the heart, limiting the region of therapeutic benefit. An injectable system offers the potential benefit of minimally invasive release into the myocardium either to restore the injured extracellular matrix or to act as a scaffold for cell delivery. Furthermore, intramyocardial injection of biomaterials and cells has opened new opportunities to explore and also to augment the potentials of this technique to ease morbidity and mortality rates owing to heart failure. This review summarizes the growing body of literature in the field of myocardial tissue engineering, where biomaterial injection, with or without simultaneous cellular delivery, has been pursued to enhance functional and structural outcomes following MI. Additionally, this review also provides a complete outlook on the tissue-engineering therapies presently being used for myocardial regeneration, as well as some perceptivity into the possible issues that may hinder its progress in the future.

Dental pulp stem cells differentiation reveals new insights in Oct4A dynamics

Although the role played by the core transcription factor network, which includes c-Myc, Klf4, Nanog, and Oct4, in the maintenance of embryonic stem cell (ES) pluripotency and in the reprogramming of adult cells is well established, its persistence and function in adult stem cells are still debated. To verify its persistence and clarify the role played by these molecules in adult stem cell function, we investigated the expression pattern of embryonic and adult stem cell markers in undifferentiated and fully differentiated dental pulp stem cells (DPSC). A particular attention was devoted to the expression pattern and intracellular localization of the stemness-associated isoform A of Oct4 (Oct4A). Our data demonstrate that: Oct4, Nanog, Klf4 and c-Myc are expressed in adult stem cells and, with the exception of c-Myc, they are significantly down-regulated following differentiation. Cell differentiation was also associated with a significant reduction in the fraction of DPSC expressing the stem cell markers CD10, CD29 and CD117. Moreover, a nuclear to cytoplasm shuttling of Oct4A was identified in differentiated cells, which was associated with Oct4A phosphorylation. The present study would highlight the importance of the post-translational modifications in DPSC stemness maintenance, by which stem cells balance self-renewal versus differentiation. Understanding and controlling these mechanisms may be of great importance for stemness maintenance and stem cells clinical use, as well as for cancer research.

Experience from experimental cell transplantation therapy of myocardial infarction: what have we learned?

During the past 15 years, our research group has transplanted fetal/neonatal cardiomyocytes, mesenchymal stem cells, and embryonic stem cell-derived cardiomyocytes into infarcted myocardium in a rat myocardial infarction model. Our experimental data demonstrated that cell transplantation therapy provides a potential approach for the treatment of injured myocardium after myocardial infarction based on the reported positive effects upon histological appearance and left ventricular function. However, the underlying mechanisms of the benefits from cell transplantation therapy remain unclear and may involve replacement of scar tissue by transplanted cells, induced neoangiogenesis and paracrine effects of factors released by the transplanted cells. In this review, we summarize our experiences from experimental cell transplantation therapy in a rat myocardial infarction model and discuss the controversies and questions that need to be addressed in future studies.

Combinatorial polymer electrospun matrices promote physiologically-relevant cardiomyogenic stem cell differentiation

Myocardial infarction results in extensive cardiomyocyte death which can lead to fatal arrhythmias or congestive heart failure. Delivery of stem cells to repopulate damaged cardiac tissue may be an attractive and innovative solution for repairing the damaged heart. Instructive polymer scaffolds with a wide range of properties have been used extensively to direct the differentiation of stem cells. In this study, we have optimized the chemical and mechanical properties of an electrospun polymer mesh for directed differentiation of embryonic stem cells (ESCs) towards a cardiomyogenic lineage. A combinatorial polymer library was prepared by copolymerizing three distinct subunits at varying molar ratios to tune the physicochemical properties of the resulting polymer: hydrophilic polyethylene glycol (PEG), hydrophobic poly(ε-caprolactone) (PCL), and negatively-charged, carboxylated PCL (CPCL). Murine ESCs were cultured on electrospun polymeric scaffolds and their differentiation to cardiomyocytes was assessed through measurements of viability, intracellular reactive oxygen species (ROS), α-myosin heavy chain expression (α-MHC), and intracellular Ca(2+) signaling dynamics. Interestingly, ESCs on the most compliant substrate, 4%PEG-86%PCL-10%CPCL, exhibited the highest α-MHC expression as well as the most mature Ca(2+) signaling dynamics. To investigate the role of scaffold modulus in ESC differentiation, the scaffold fiber density was reduced by altering the electrospinning parameters. The reduced modulus was found to enhance α-MHC gene expression, and promote maturation of myocyte Ca(2+) handling. These data indicate that ESC-derived cardiomyocyte differentiation and maturation can be promoted by tuning the mechanical and chemical properties of polymer scaffold via copolymerization and electrospinning techniques.

Cardiac regeneration therapy: connections to cardiac physiology

Without heart transplantation, a large number of patients with failing hearts worldwide face poor outcomes. By means of cardiomyocyte regeneration, cardiac regeneration therapy is emerging with great promise as a means for restoring loss of cardiac function. However, the limited success of clinical trials using bone marrow-derived cells and myoblasts with heterogeneous constituents, transplanted at a wide range of cell doses, has led to disagreement on the efficacy of cell therapy. It is therefore essential to reevaluate the evidence for the efficacy of cell-based cardiac regeneration therapy, focusing on targets, materials, and methodologies. Meanwhile, the revolutionary innovation of cardiac regeneration therapy is sorely needed to help the millions of people who suffer heart failure from acquired loss of cardiomyocytes. Cardiac regeneration has been used only in limited species or as a developing process in the rodent heart; now, the possibility of cardiomyocyte turnover in the human heart is being revisited. In the pursuit of this concept, the use of cardiac stem/progenitor stem cells in the cardiac niche must be focused to usher in a second era of cardiac regeneration therapy for the severely injured heart. In addition, tissue engineering and cellular reprogramming will advance the next era of treatment that will enable current cell-based therapy to progress to "real" cardiac regeneration therapy. Although many barriers remain, the prevention of refractory heart failure through cardiac regeneration is now becoming a realistic possibility.

Terminal differentiation is not a major determinant for the success of stem cell therapy - cross-talk between muscle-derived stem cells and host cells

We have found that when muscle-derived stem cells (MDSCs) are implanted into a variety of tissues only a small fraction of the donor cells can be found within the regenerated tissues and the vast majority of cells are host derived. This observation has also been documented by other investigators using a variety of different stem cell types. It is speculated that the transplanted stem cells release factors that modulate repair indirectly by mobilizing the host's cells and attracting them to the injury site in a paracrine manner. This process is loosely called a 'paracrine mechanism', but its effects are not necessarily restricted to the injury site. In support of this speculation, it has been reported that increasing angiogenesis leads to an improvement of cardiac function, while inhibiting angiogenesis reduces the regeneration capacity of the stem cells in the injured vascularized tissues. This observation supports the finding that most of the cells that contribute to the repair process are indeed chemo-attracted to the injury site, potentially through host neo-angiogenesis. Since it has recently been observed that cells residing within the walls of blood vessels (endothelial cells and pericytes) appear to represent an origin for post-natal stem cells, it is tempting to hypothesize that the promotion of tissue repair, via neo-angiogenesis, involves these blood vessel-derived stem cells. For non-vascularized tissues, such as articular cartilage, the regenerative property of the injected stem cells still promotes a paracrine, or bystander, effect, which involves the resident cells found within the injured microenvironment, albeit not through the promotion of angiogenesis. In this paper, we review the current knowledge of post-natal stem cell therapy and demonstrate the influence that implanted stem cells have on the tissue regeneration and repair process. We argue that the terminal differentiation capacity of implanted stem cells is not the major determinant of the cells regenerative potential and that the paracrine effect imparted by the transplanted cells plays a greater role in the regeneration process.

The promotion of myocardial repair by the sequential delivery of IGF-1 and HGF from an injectable alginate biomaterial in a model of acute myocardial infarction

Proper spatio-temporal delivery of multiple therapeutic proteins represents a major challenge in therapy strategies aimed at inducing myocardial regeneration after myocardial infarction (MI). We hypothesized that the dual delivery of insulin-like growth factor-1 (IGF-1) and hepatocyte growth factor (HGF) by injectable affinity-binding alginate biomaterial would maximize their therapeutic effects, leading to a more favorable course of tissue restoration after acute MI. A sequential release of IGF-1 followed by HGF was attained from affinity-binding alginate biomaterial, which also protected the proteins from proteolysis (shown by mass spectroscopy). The released factors retained bioactivity, as judged by their capability to activate their respective signaling pathways and to prevent cardiomyocyte apoptosis in vitro. In a rat model of acute MI, an intramyocardial injection of the dual IGF-1/HGF affinity-bound alginate biomaterial preserved scar thickness, attenuated infarct expansion and reduced scar fibrosis after 4 weeks, concomitantly with increased angiogenesis and mature blood vessel formation at the infarct. Furthermore, this treatment prevented cell apoptosis, induced cardiomyocyte cell cycle re-entry and increased the incidence of GATA-4-positive cell clusters. The dual delivery of IGF-1 and HGF from affinity-binding alginate biomaterial represents a useful strategy to treat MI. It showed a marked therapeutic efficacy at various tissue levels, as well as potential to induce endogenous regeneration of cardiac muscle.

Engineered heart tissue enables study of residual undifferentiated embryonic stem cell activity in a cardiac environment

Embryonic stem cell (ESC) derivatives are a promising cell source for cardiac cell therapy. Mechanistic studies upon cell injection in conventional animal models are limited by inefficient delivery and poor cell survival. As an alternative, we have used an engineered heart tissue (EHT) based on neonatal rat cardiomyocytes (CMs) cultivated with electrical field stimulation as an in vitro model to study cell injection. We injected (0.001, 0.01, and 0.1 million) and tracked (by qPCR and histology) undifferentiated yellow-fluorescent protein transgenic mouse ESCs and Flk1 + /PDGFRα+ cardiac progenitor (CPs) cells, to investigate the effect of the cardiac environment on cell differentiation, as well as to test whether our in vitro model system could recapitulate the formation of teratoma-like structures commonly observed upon in vivo ESC injection. By 8 days post-injection, ESCs were spatially segregated from the cardiac cell population; however, ESC injection increased survival of CMs. The presence of ESCs blocked electrical conduction through the tissue, resulting in a 46% increase in the excitation threshold. Expression of mouse cardiac troponin I, was markedly increased in CP injected constructs compared to ESC injected constructs at all time points and cell doses tested. As early as 2 weeks, epithelial and ganglion-like structures were observed in ESC injected constructs. By 4 weeks of ESC injection, teratoma-like structures containing neural, epithelial, and connective tissue were observed in the constructs. Non-cardiac structures were observed in the CP injected constructs only after extended culture (4 weeks) and only at high cell doses, suggesting that these cells require further enrichment or differentiation prior to transplantation. Our data indicate that the cardiac environment of host tissue and electrical field stimulation did not preferentially guide the differentiation of ESCs towards the cardiac lineage. In the same environment, injection of CP resulted in a more robust cardiac differentiation than injection of ESC. Our data demonstrate that the model-system developed herein can be used to study the functional effects of candidate stem cells on the host myocardium, as well as to measure the residual activity of undifferentiated cells present in the mixture.

Blood supply of the graft after cellular cardiomyoplasty

Cellular cardiomyoplasty is under extensive investigation as a potential therapeutic strategy after myocardial infarction, in congestive heart failure and chronic ischemic heart disease. Various cell sources and techniques for transplantation have been studied in animal models of cardiac disease. The initial goal of replacing myocardial scar tissue by vital myocardial cells, integrated into the host, simultaneously beating and contributing to systolic force, has not yet been accomplished. However, most experimental models provided evidence for enhanced vascularization after cell transplantation. In some investigations, neovascularization was also shown to be accompanied by increased myocardial perfusion. Mechanisms by which vascularization occurs have not been fully elucidated: either the transplanted cells provide an angiogenic stimulus, involving various paracrine or hormone-like factors, which induces the formation of a new vasculature or, depending on the source of transplanted cells, the cells incorporate into the vascular network after proliferation and differentiation. This review summarizes research that specifically studied the occurrence, magnitude and mechanisms of enhanced myocardial blood supply after cellular cardiomyoplasty.

Are purified or expanded cord blood-derived CD133+ cells better at improving cardiac function?

Endothelial progenitor cells (EPCs), which express the CD133 marker, can differentiate into mature endothelial cells (ECs) and create new blood vessels. Normal angiogenesis is unable to repair the injured tissues that result from myocardial infarction (MI). Patients who have high cardiovascular risks have fewer EPCs and their EPCs exhibit greater in vitro senescence. Human umbilical cord blood (HUCB)-derived EPCs could be an alternative to rescue impaired stem cell function in the sick and elderly. The aim of this study was to purify HUCB-derived CD133(+) cells, expand them in vitro and evaluate the efficacy of the purified and expanded cells in treating MI in rats. CD133(+) cells were selected for using CD133-coupled magnetic microbeads. Purified cells stained positive for EPC markers. The cells were expanded and differentiated in media supplemented with fetal calf serum and basic fibroblast growth factor, insulin-like growth factor-I and vascular endothelial growth factor (VEGF). Differentiation was confirmed by lack of staining for EPC markers. These expanded cells exhibited increased expression of mature EC markers and formed tubule-like structures in vitro. Only the expanded cells expressed VEGF mRNA. Cells were expanded up to 70-fold during 60 days of culture, and they retained their functional activity. Finally, we evaluated the therapeutic potential of purified and expanded CD133(+) cells in treating MI by intramyocardially injecting them into a rat model of MI. Rats were divided into three groups: A (purified CD133(+) cells-injected); B (expanded CD133(+) cells-injected) and C (saline buffer-injected). We observed a significant improvement in left ventricular ejection fraction for groups A and B. In summary, CD133(+) cells can be purified from HUCB, expanded in vitro without loosing their biological activity, and both purified and expanded cells show promising results for use in cellular cardiomyoplasty. However, further pre-clinical testing should be performed to determine whether expanded CD133(+) cells have any clinical advantages over purified CD133(+) cells.

The effects of controlled HGF delivery from an affinity-binding alginate biomaterial on angiogenesis and blood perfusion in a hindlimb ischemia model

Enhancing tissue self-repair through the use of active acellular biomaterials is one of the main goals of regenerative medicine. We now describe the features of an injectable alginate biomaterial designed to affinity-bind heparin-binding proteins and release them at a rate reflected by their association constant to alginate-sulfate. The interactions of hepatocyte growth factor (HGF) with alginate-sulfate resulted in factor protection from proteolysis, as shown by mass spectroscopy analysis after trypsin digestion. When the HGF/alginate-sulfate bioconjugate was incorporated into alginate hydrogel, HGF release was sustained by a factor of 3, as compared to the release rate from non-modified hydrogel. The released factor retained activity, as shown by its induction of ERK1/2 activation and affording cytoprotection in rat neonatal cardiomyocyte cultures. In vivo, an injectable form of the affinity-binding alginate system extended by 10-fold, as compared to a saline-treated group, retention of HGF in myocardial tissue when delivered immediately after myocardial infarction. In a severe murine hindlimb ischemia model, HGF delivery from the affinity-binding system improved tissue blood perfusion and induced mature blood vessel network formation. The therapeutic efficacy of the affinity-binding system, as well as its ease of delivery by injection, provides a proof-of-concept for the potential use of this bioactive biomaterial strategy in cardiovascular repair.

Making stem cells infarct avid

A major factor limiting the engraftment of transplanted stem cells after myocardial infarction is the low rate of retention in the infarcted site. Our long-term objective is to improve engraftment by enabling stem cells to recognize and bind infarcted tissue. To this end, we proposed to modify the surface of embryonic stem cells (ESCs) with the C2A domain of synaptotagmin I; this allows the engineered stem cells to bind to dead and dying cardiac cells by recognizing phosphatidylserine (PS). The latter is a molecular marker for apoptotic and necrotic cells. The C2A domain of synaptotagmin I, which binds PS with high affinity and specificity, was attached to the surface of mouse ESCs using the biotin-avidin coupling mechanism. Binding of C2A-ESCs to dead and dying cardiomyocytes was tested in vitro. After the surface modification, cellular physiology was examined for viability, pluripotency, and differentiation potential. C2A covalently attached to the ESC surface at an average of about 1 million C2A molecules per cell under mild conjugation reaction conditions. C2A-ESCs avidly bound to dying, but not viable, cardiomyocytes in culture. The normal physiology of C2A-modified ESCs was maintained. The binding of C2A-ESCs to moribund cardiomyocytes demonstrates that the retention of transplanted cells may be improved by conferring these cells with the ability to bind infarcted tissue. Once established, this novel approach may be applicable to other types of transplanted therapeutic cells.

Multimodality evaluation of the viability of stem cells delivered into different zones of myocardial infarction

BACKGROUND

We tested the hypothesis that multimodality imaging of mouse embryonic stem cells (mESCs) provides accurate assessment of cellular location, viability, and restorative potential after transplantation into different zones of myocardial infarction.

METHODS AND RESULTS

Mice underwent left anterior descending artery ligation followed by transplantation of dual-labeled mESCs with superparamagnetic iron oxide and luciferase via direct injection into 3 different zones of myocardial infarction: intra-infarction, peri-infarction, and normal (remote). One day after transplantation, magnetic resonance imaging enabled assessment of the precise anatomic locations of mESCs. Bioluminescence imaging allowed longitudinal analysis of cell viability through detection of luciferase activity. Subsequent evaluation of myocardial regeneration and functional restoration was performed by echocardiography and pressure-volume loop analysis. Using 16-segment analysis, we demonstrated precise localization of dual-labeled mESCs. A strong correlation between histology and magnetic resonance imaging was established (r=0.962, P=0.002). Bioluminescent imaging data demonstrated that cell viability in the remote group was significantly higher than in other groups. Echocardiography and pressure-volume loop analysis revealed improved functional restoration in animals treated with mESCs, although myocardial regeneration was not observed.

CONCLUSIONS

Multimodality evaluation of mESC engraftment in the heterogeneous tissue of myocardial infarction is possible. Magnetic resonance imaging demonstrated accurate anatomic localization of dual-labeled mESCs. Bioluminescent imaging enabled assessment of variable viability of mESCs transplanted into the infarcted myocardium. Echocardiography and pressure-volume loop analysis validated the restorative potential of mESCs. Although mESCs transplanted into the remote zone demonstrated the highest viability, precise delivery of mESCs into the peri-infarction region might be equally critical in restoring the injured myocardium.

Functional improvement of infarcted heart by co-injection of embryonic stem cells with temperature-responsive chitosan hydrogel

Transplantation of embryonic stem cells (ESCs) can improve cardiac function in treatment of myocardial infarction. The low rate of cell retention and survival within the ischemic tissues makes the application of cell transplantation techniques difficult. In this study, we used a temperature-responsive chitosan hydrogel (as scaffold) combined with ESCs to maintain viable cells in the infarcted tissue. Temperature-responsive chitosan hydrogel was prepared and injected into the infarcted heart wall of rat infarction models alone or together with mouse ESCs. The result showed that the 24-h cell retention and 4 week graft size of both groups was significantly greater than with a phosphate buffered saline control. After 4 weeks of implantation, heart function, wall thickness, and microvessel densities within the infarct area improved in the chitosan + ESC, chitosan, and ESC group more than the PBS control. Of the three groups, the chitosan + ESC performed best. Results of this study indicate that temperature-responsive chitosan hydrogel is an injectable scaffold that can be used to deliver stem cells to infarcted myocardium. It can also increase cell retention and graft size. Cardiac function is well preserved, too.

Cell therapy enhances function of remote non-infarcted myocardium

Cell transplantation improves cardiac function after myocardial infarction; however, the underlying mechanisms are not well-understood. Therefore, the goals of this study were to determine if neonatal rat cardiomyocytes transplanted into adult rat hearts 1 week after infarction would, after 8-10 weeks: 1) improve global myocardial function, 2) contract in a Ca2+ dependent manner, 3) influence mechanical properties of remote uninjured myocardium and 4) alter passive mechanical properties of infarct regions. The cardiomyocytes formed small grafts of ultrastructurally maturing myocardium that enhanced fractional shortening compared to non-treated infarcted hearts. Chemically demembranated tissue strips of cardiomyocyte grafts produced force when activated by Ca2+, whereas scar tissue did not. Furthermore, the Ca2+ sensitivity of force was greater in cardiomyocyte grafts compared to control myocardium. Surprisingly, cardiomyocytes grafts isolated in the infarct zone increased Ca2+ sensitivity of remote uninjured myocardium to levels greater than either remote myocardium from non-treated infarcted hearts or sham-operated controls. Enhanced calcium sensitivity was associated with decreased phosphorylation of cTnT, tropomyosin and MLC2, but not changes in myosin or troponin isoforms. Passive compliance of grafts resembled normal myocardium, while infarct tissue distant from grafts had compliance typical of scar. Thus, cardiomyocyte grafts are contractile, improve local tissue compliance and enhance calcium sensitivity of remote myocardium. Because the volume of remote myocardium greatly exceeds that of the grafts, this enhanced calcium sensitivity may be a major contributor to global improvements in ventricular function after cell transplantation.

Cell therapy with bone marrow cells for myocardial regeneration

Cell therapy has tremendous potential for the damaged heart, which has limited self-renewing capability. Bone marrow (BM) cells are attractive for cell therapy, as they contain diverse stem and progenitor cell populations that can give rise to various cell types, including cardiomyocytes, endothelial cells, and smooth muscle cells. Studies have shown BM cells to be safe and efficacious in the treatment of myocardial infarction. Possible therapeutic mechanisms mediated by both host and transplanted cells include cardiomyogenesis, neovascularization, and attenuation of adverse remodeling. In this review, different stem and progenitor cells in the bone marrow and their application in cell therapy are reviewed, and evidence for their therapeutic mechanisms is discussed.

Hepatocyte growth factor and granulocyte colony-stimulating factor form a combined neovasculogenic therapy for ischemic cardiomyopathy

BACKGROUND

Myocardial infarction (MI) is a significant cause of heart failure. Current therapies are limited and, therefore, the development of novel revascularization methods is potentially important. We investigated whether hepatocyte growth factor (HGF), expressed by genetically modified mesenchymal stromal cells (MSC), in combination with granulocyte colony-stimulating factor (G-CSF), exhibited a synergistic therapeutic benefit, as measured 8 weeks after MI induction in a rat model.

METHODS

Four weeks after MI, rats were randomly divided into a control group (n=11), HGF group (Adenovirus vector carrying human HGF (Ad-HGF)-transfected MSC transplanted into the infarct zone; n=11), G-CSF group (intraperitoneal injection with G-CSF; n=11), and HGF + G-CSF group (Ad-HGF-transfected MSC transplanted into the infarct zone and intraperitoneal injection with G-CSF; n=11). Four weeks later, hearts were analyzed for endothelial cell density and angiogenesis, ventricular geometry, myocardial function and levels of VCAM-1 and MMP-9 protein.

RESULTS

The HGF + G-CSF group exhibited improved left ventricular systolic and diastolic function and experienced less adverse ventricular remodeling, as manifested by decreased left ventricular dilatation and increased border zone wall thickness. Angiogenesis was significantly enhanced in HGF + G-CSF rats by inducing the proliferation of endothelial cells. Furthermore, HGF induced expression of VCAM-1, and HGF treatment together with G-CSF synergistically stimulated MMP-9 expression in ischemic hearts.

DISCUSSION

The combination of G-CSF and HGF exhibited a significant synergistic effect and enhanced myocardial endothelial density, angiogenesis, geometric preservation and heart function in an ischemic cardiomyopathy model.

Evaluation of a peritoneal-generated cardiac patch in a rat model of heterotopic heart transplantation

Tissue engineering holds the promise of providing new solutions for heart transplant shortages and pediatric heart transplantation. The aim of this study was to evaluate the ability of a peritoneal-generated, tissue-engineered cardiac patch to replace damaged myocardium in a heterotopic heart transplant model. Fetal cardiac cells (1 x 10(6)/scaffold) from syngeneic Lewis rats were seeded into highly porous alginate scaffolds. The cell constructs were cultured in vitro for 4 days and then they were implanted into the rat peritoneal cavity for 1 week. During this time the peritoneal-implanted patches were vascularized and populated with myofibroblasts. They were harvested and their performance in an infrarenal heterotopic abdominal heart transplantation model was examined (n = 15). After transplantation and before reperfusion of the donor heart, a 5-mm left (n = 6) or right (n = 9) ventriculotomy was performed and the patch was sutured onto the donor heart to repair the defect. Echocardiographical studies carried out 1-2 weeks after transplantation showed normal LV function in seven of the eight hearts studied. After 1 month, visual examination of the grafted patch revealed no aneurysmal dilatation. Microscopic examination revealed, in most of the cardiac patches, a complete disappearance of the scaffold and its replacement by a consistent tissue composed of myofibroblasts embedded in collagen bundles. The cardiac patch was enriched with a relatively large number of infiltrating blood vessels. In conclusion, cardiac patches generated in the peritoneum were developed into consistent tissue patches with properties to seal and correct myocardial defects. Our study also offers a viable rat model for screening and evaluating new concepts in cardiac reconstruction and engineering.

Injection of bone marrow cell extract into infarcted hearts results in functional improvement comparable to intact cell therapy

We compared therapeutic benefits of intramyocardial injection of unfractionated bone marrow cells (BMCs) versus BMC extract as treatments for myocardial infarction (MI), using closed-chest ultrasound-guided injection at a clinically relevant time post-MI. MI was induced in mice and the animals treated at day 3 with either: (i) BMCs from green fluorescent protein (GFP)-expressing mice (n = 14), (ii) BMC extract (n = 14), or (iii) saline control (n = 14). Six animals per group were used for histology at day 6 and the rest followed to day 28 for functional analysis. Ejection fraction was similarly improved in the BMC and extract groups versus control (40.6 +/- 3.4 and 39.1 +/- 2.9% versus 33.2 +/- 5.0%, P < 0.05) with smaller scar sizes. At day 6 but not day 28, both therapies led to significantly higher capillary area and number of arterioles versus control. At day 6, BMCs increased the number of cycling cardiomyocytes (CMs) versus control whereas extract therapy resulted in significant reduction in the number of apoptotic CMs at the border zone (BZ) versus control. Intracellular components within BMCs can enhance vascularity, reduce infarct size, improve cardiac function, and influence CM apoptosis and cycling early after therapy following MI. Intact cells are not necessary and death of implanted cells may be a major component of the benefit.

Embryonic stem cell transplantation: promise and progress in the treatment of heart disease

Cardiovascular diseases remain the leading cause of death worldwide, and the burden is equally shared between men and women around the globe. Cardiomyocytes that die in response to disease processes or aging are replaced by scar tissue instead of new muscle cells. Although recent reports suggest an intrinsic capacity for the mammalian myocardium to regenerate via endogenous stem/progenitor cells, the magnitude of such a response appears to be minimal and has yet to be realized fully in cardiovascular patients. Despite the advances in pharmacotherapy and new biomedical technologies, the prognosis for patients diagnosed with end-stage heart failure appears to be grave. While heart transplantation is a viable option, this life-saving intervention suffers from an acute shortage of cardiac organ donors. In view of these existing issues, donor cell transplantation is emerging as a promising strategy to regenerate diseased myocardium. Studies from multiple laboratories have shown that transplantation of donor cells (e.g. fetal cardiomyocytes, skeletal myoblasts, smooth muscle cells, and adult stem cells) can improve the function of diseased hearts over a short period of time (1-4 weeks). While long-term follow-up studies are warranted, it is generally perceived that the beneficial effects of transplanted cells are mainly due to increased angiogenesis or favorable scar remodeling in the engrafted myocardium. Although skeletal myoblasts and bone marrow stem cells hold the highest potential for implementation of autologous therapies, initial results from phase I trials are not promising. In contrast, transplantation of fetal cardiomyocytes has been shown to confer protection against the induction of ventricular tachycardia in experimental myocardial injury models. Furthermore, results from multiple laboratories suggest that fetal cardiomyocytes can couple functionally with host myocytes, stimulate formation of new blood vessels, and improve myocardial function. While it is neither practical nor ethical to test the potential of fetal cardiomyocytes in clinical trials, embryonic stem (ES) cells serve as a novel source for generation of unlimited quantities of cardiomyocytes for myocardial repair. The initial success in the application of ES cells to partially repair and improve myocardial function in experimental models of heart disease has been quite promising. However, multiple hurdles need to be crossed before the potential benefits of ES cells can be translated to the clinic. In this review, we summarize the current knowledge of cardiomyocyte derivation and enrichment from ES-cell cultures and provide a brief survey of factors increasing cardiomyogenic induction in both mouse and human ES cultures. Subsequently, we summarize the current state of research using mouse and human ES cells for the treatment of heart disease in various experimental models. Furthermore, we discuss the challenges that need to be overcome prior to the successful clinical utilization of ES-derived cardiomyocytes for the treatment of end-stage heart disease. While we are optimistic that the researchers in this field will sail across the hurdles, we also suggest that a more cautious approach to the validation of ES cardiomyocytes in experimental models would certainly prevent future disappointments, as seen with skeletal myoblast studies.

Human embryonic stem cells and cardiac repair

The muscle lost after a myocardial infarction is replaced with noncontractile scar tissue, often initiating heart failure. Whole-organ cardiac transplantation is the only currently available clinical means of replacing the lost muscle, but this option is limited by the inadequate supply of donor hearts. Thus, cell-based cardiac repair has attracted considerable interest as an alternative means of ameliorating cardiac injury. Because of their tremendous capacity for expansion and unquestioned cardiac potential, pluripotent human embryonic stem cells (hESCs) represent an attractive candidate cell source for obtaining cardiomyocytes and other useful mesenchymal cell types for such therapies. Human embryonic stem cell-derived cardiomyocytes exhibit a committed cardiac phenotype and robust proliferative capacity, and recent testing in rodent infarct models indicates that they can partially remuscularize injured hearts and improve contractile function. Although the latter successes give good reason for optimism, considerable challenges remain in the successful application of hESCs to cardiac repair, including the need for preparations of high cardiac purity, improved methods of delivery, and approaches to overcome immune rejection and other causes of graft cell death. This review will describe the phenotype of hESC-derived cardiomyocytes and preclinical experience with these cells and will consider strategies to overcoming the aforementioned challenges.

Transplantation of genetically engineered cardiac fibroblasts producing recombinant human erythropoietin to repair the infarcted myocardium

Background

Erythropoietin possesses cellular protection properties. The aim of the present study was to test the hypothesis that in situ expression of recombinant human erythropoietin (rhEPO) would improve tissue repair in rat after myocardial infarction (MI).

Methods and results

RhEPO-producing cardiac fibroblasts were generated ex vivo by transduction with retroviral vector. The anti-apoptotic effect of rhEPO-producing fibroblasts was evaluated by co-culture with rat neonatal cardiomyocytes exposed to H₂O₂-induced oxidative stress. Annexin V/PI assay and DAPI staining showed that compared with control, rhEPO forced expression markedly attenuated apoptosis and improved survival of cultured cardiomyocytes. To test the effect of rhEPO on the infarcted myocardium, Sprague-Dawley rats were subjected to permanent coronary artery occlusion, and rhEPO-producing fibroblasts, non-transduced fibroblasts, or saline, were injected into the scar tissue seven days after infarction. One month later, immunostaining identified rhEPO expression in the implanted engineered cells but not in controls. Compared with non-transduced fibroblasts or saline injection, implanted rhEPO-producing fibroblasts promoted vascularization in the scar, and prevented cell apoptosis. By two-dimensional echocardiography and postmortem morphometry, transplanted EPO-engineered fibroblasts did not prevent left ventricular (LV) dysfunction and adverse LV remodeling 5 and 9 weeks after MI.

Conclusion

In situ expression of rhEPO enhances vascularization and reduces cell apoptosis in the infarcted myocardium. However, local EPO therapy is insufficient for functional improvement after MI in rat.

Notch inhibition promotes human embryonic stem cell-derived cardiac mesoderm differentiation

The roles of Notch signaling in cardiac differentiation from murine embryonic stem cells have been well documented. We investigated whether Notch signaling plays a similar role in human embryonic stem cells (hESCs). Although, as previously reported, blocking Notch signaling via the addition of gamma-secretase inhibitor (GSI) alone failed to affect hESC differentiation, we found that GSI plus reduced-volume culture medium (GSI/RVCM) accelerated mesodermal differentiation. GSI/RVCM conditions simultaneously suppressed commitment toward neuroectodermal lineages. Furthermore, sustained inhibition of Notch signaling further enhanced differentiation into cardiac mesoderm. Spontaneous beating activity was typically observed from 12 days after initiation of GSI treatment in RVCM. Moreover, hESC-derived cardiomyocytes expressed connexin 43 and possessed spontaneous calcium oscillations and cardiomyocyte beats coupled to neonatal rat cardiomyocytes when cocultured. These findings strongly suggest a distinct role for Notch signaling in the induction and specification of hESC-derived cardiac mesoderm in vitro. Disclosure of potential conflicts of interest is found at the end of this article.

The effects of peptide-based modification of alginate on left ventricular remodeling and function after myocardial infarction

Adverse cardiac remodeling and dysfunction after myocardial infarction (MI) is associated with (BioLineRx, BL-1040 myocardial implant) excessive damage to the extracellular matrix. Biomaterials, such as the in situ-forming alginate hydrogel, provide temporary support and attenuate these processes. Here, we tested the effects of decorating alginate biomaterial with cell adhesion peptides, containing the sequences RGD and YIGSR, or a non-specific peptide (RGE), in terms of therapeutic outcome soon after MI. The biomaterial (i.e., both unmodified and peptide-modified alginate) solutions retained the ability to flow after cross-linking with calcium ions, and could be injected into 7-day infarcts, where they underwent phase transition into hydrogels. Serial echocardiography studies performed before and 60 days after treatment showed that alginate modification with the peptides reduced the therapeutical effects of the hydrogel, as revealed by the extent of scar thickness, left ventricle dilatation and function. Histology and immunohistochemistry revealed no significant differences in blood vessel density, scar thickness, myofibroblast or macrophage infiltration or cell proliferation between the experimental groups BioLineRx BL-1040 myocardial implant. Our studies thus reveal that the chemical and physical traits of the biomaterial can affect its therapeutical efficacy in attenuating left ventricle remodeling and function, post-MI.

Systems approaches to preventing transplanted cell death in cardiac repair

Stem cell transplantation may repair the injured heart, but tissue regeneration is limited by death of transplanted cells. Most cell death occurs in the first few days post-transplantation, likely from a combination of ischemia, anoikis and inflammation. Interventions known to enhance transplanted cell survival include heat shock, over-expressing anti-apoptotic proteins, free radical scavengers, anti-inflammatory therapy and co-delivery of extracellular matrix molecules. Combinatorial use of such interventions markedly enhances graft cell survival, but death still remains a significant problem. We review these challenges to cardiac cell transplantation and present an approach to systematically address them. Most anti-death studies use histology to assess engraftment, which is time- and labor-intensive. To increase throughput, we developed two biochemical approaches to follow graft viability in the mouse heart. The first relies on LacZ enzymatic activity to track genetically modified cells, and the second quantifies human genomic DNA content using repetitive Alu sequences. Both show linear relationships between input cell number and biochemical signal, but require correction for the time lag between cell death and loss of signal. Once optimized, they permit detection of as few as 1 graft cell in 40,000 host cells. Pro-survival effects measured biochemically at three days predict long-term histological engraftment benefits. These methods permitted identification of carbamylated erythropoietin (CEPO) as a pro-survival factor for human embryonic stem cell-derived cardiomyocyte grafts. CEPO's effects were additive to heat shock, implying independent survival pathways. This system should permit combinatorial approaches to enhance graft viability in a fraction of the time required for conventional histology.

Cell-based therapy for myocardial ischemia and infarction: pathophysiological mechanisms

Cell-based cardiac repair has emerged as an attractive approach to preventing or reversing heart failure resulting from myocyte dysfunction-e.g., due to infarction-and to enhancing the development of collaterals in patients with symptoms of myocardial ischemia. These two problems involve both overlapping and differing mechanisms, and these differences must be considered in cell-based therapies. In terms of myocardial dysfunction due to infarction, only committed cardiomyocytes have been shown to form new myocardium that is electrically coupled with the host heart. Despite this, multiple cell populations appear to improve function of the infarcted heart, including many that are clearly nonmyogenic. In terms of myocardial ischemia, although cell-based strategies improve ischemia in animal models, clinical trials to date have not shown robustly beneficial results. We review the evidence for potential mechanisms underlying the benefits of cell transplantation in the heart and discuss the clinical contexts in which they may be relevant.

Regional expression of the hypoxia-inducible factor (HIF) system and association with cardiomyocyte cell cycle re-entry after myocardial infarction in rats

Hypoxia-inducible factor (HIF)-1alpha and-2alpha have diverse actions on the myocardium, but the importance of direct effects on cardiac myocytes is unclear. To define their regional accumulation and association with cardiomyocyte cell cycle change after myocardial infarction (MI), a rat MI model was established by occluding the coronary arteries. To further prove a causative relationship between HIF and cell cycle regulation, cultured cardiomyocytes were transfected with adenoviral vectors carrying HIF-1alpha and HIF-2alpha. Two weeks after MI, both HIF-1alpha and HIF-2alpha mRNA were moderately increased in the infarcted left ventricle and noninfarcted left ventricle; HIF-2alpha amplification was also detected in areas of the interventricular septum and the right ventricle. In concordance with the changes in mRNA levels, immunohistochemistry signals of HIF-1alpha and HIF-2alpha were characterized by different regional distributions. In the myocardium adjacent to the infarcted tissue, a significant correlation between HIF-1alpha or HIF-2alpha and Ki-67 labeling index was observed (P < 0.001). Immunohistochemical double staining showed that HIF positive cardiomyocytes underwent DNA synthesis. Cardiomyocytes treated with HIF-1alpha or -2alpha expressed Ki-67, phosphohistone H3, and bromodeoxyuridine effectively in vitro. In conclusion, HIF-1alpha and HIF-2alpha had a distinct spatial expression pattern in a rat model of ischemic heart disease. Both HIF subunits might be potent stimuli for cardiomyocytes to re-enter the cell cycle and initiate DNA synthesis.

Locally overexpressing hepatocyte growth factor prevents post-ischemic heart failure by inhibition of apoptosis via calcineurin-mediated pathway and angiogenesis

BACKGROUND

Myocardial infarction is a significant cause of heart failure. Currently, therapies are limited and novel revascularization methods may play a role. We investigated the effects of hepatocyte growth factor (HGF) expressed by bone marrow-derived mesenchymal stem cells (MSCs) on post-ischemic heart failure.

METHODS

Four weeks after myocardial infarction (MI), Sprague Dawley rats were randomly divided into saline control group, MSC-GFP group, MSC-HGF group, and MSC-HGF+CsA group. After another 4 weeks, hearts were analyzed for ventricular geometry, myocardial function, angiogenesis and endothelial cell density, apoptosis and the expression of calcineurin, Akt, and Bcl-2 protein.

RESULTS

In MSC-HGF group, rats exhibited better LV systolic and diastolic function compared with other groups after 8 weeks of MI. Angiogenesis was significantly enhanced by HGF through inducing proliferation of endothelial cells. The effects of HGF on apoptosis were associated with the expression level of calcineurin protein.

CONCLUSIONS

Our findings suggest that overexpression of HGF improved ischemic cardiac function through angiogenesis and reduction of apoptosis partly mediated by upregulation of calcineurin.

Effect of injectable alginate implant on cardiac remodeling and function after recent and old infarcts in rat

BACKGROUND

Adverse cardiac remodeling and progression of heart failure after myocardial infarction are associated with excessive and continuous damage to the extracellular matrix. We hypothesized that injection of in situ-forming alginate hydrogel into recent and old infarcts would provide a temporary scaffold and attenuate adverse cardiac remodeling and dysfunction.

METHODS AND RESULTS

We developed a novel absorbable biomaterial composed of calcium-crosslinked alginate solution, which displays low viscosity and, after injection into the infarct, undergoes phase transition into hydrogel. To determine the outcome of the biomaterial after injection, calcium-crosslinked biotin-labeled alginate was injected into the infarct 7 days after anterior myocardial infarction in rat. Serial histology studies showed in situ formation of alginate hydrogel implant, which occupied up to 50% of the scar area. The biomaterial was replaced by connective tissue within 6 weeks. Serial echocardiography studies before and 60 days after injection showed that injection of alginate biomaterial into recent (7 days) infarct increased scar thickness and attenuated left ventricular systolic and diastolic dilatation and dysfunction. These beneficial effects were comparable and sometimes superior to those achieved by neonatal cardiomyocyte transplantation. Moreover, injection of alginate biomaterial into old myocardial infarction (60 days) increased scar thickness and improved systolic and diastolic dysfunction.

CONCLUSIONS

We show for the first time that injection of in situ-forming, bioabsorbable alginate hydrogel is an effective acellular strategy that prevents adverse cardiac remodeling and dysfunction in recent and old myocardial infarctions in rat.