Donor cell-type specific paracrine effects of cell transplantation for post-infarction heart failure

Growth factors: avenues for the treatment of myocardial infarction and potential delivery strategies

Acute myocardial infarction (AMI) is one of the leading causes of death worldwide. Despite recent advances in clinical management, reoccurence of heart failure after AMI remains high, in part because of the limited capacity of cardiac tissue to repair after AMI-induced cell death. Growth factor-based therapy has emerged as an alternative AMI treatment strategy. Understanding the underlying mechanisms of growth factor cardioprotective and regenerative actions is important. This review focuses on the function of different growth factors at each stage of the cardiac repair process. Recent evidence for growth factor therapy in preclinical and clinical trials is included. Finally, different delivery strategies are reviewed with a view to providing workable strategies for clinical translation.

Delivering More of an Injectable Human Recombinant Collagen III Hydrogel Does Not Improve Its Therapeutic Efficacy for Treating Myocardial Infarction

Injectable hydrogels are a promising method to enhance repair in the heart after myocardial infarction (MI). However, few studies have compared different strategies for the application of biomaterial treatments. In this study, we use a clinically relevant mouse MI model to assess the therapeutic efficacy of different treatment protocols for intramyocardial injection of a recombinant human collagen III (rHCIII) thermoresponsive hydrogel. Comparing a single hydrogel injection at an early time point (3 h) versus injections at multiple time points (3 h, 1 week, and 2 weeks) post-MI revealed that the single injection group led to superior cardiac function, reduced scar size and inflammation, and increased vascularization. Omitting the 3 h time point and delivering the hydrogel at 1 and 2 weeks post-MI led to poorer cardiac function. The positive effects of the single time point injection (3 h) on scar size and vascular density were lost when the hydrogel's collagen concentration was increased from 1% to 2%, and it did not confer any additional functional improvement. This study shows that early treatment with a rHCIII hydrogel can improve cardiac function post-MI but that injecting more rHCIII (by increased concentration or more over time) can reduce its efficacy, thus highlighting the importance of investigating optimal treatment strategies of biomaterial therapy for MI.

On-site fabrication of Bi-layered adhesive mesenchymal stromal cell-dressings for the treatment of heart failure

Mesenchymal stromal/stem cell (MSC)-based therapy is a promising approach for the treatment of heart failure. However, current MSC-delivery methods result in poor donor cell engraftment, limiting the therapeutic efficacy. To address this issue, we introduce here a novel technique, epicardial placement of bi-layered, adhesive dressings incorporating MSCs (MSC-dressing), which can be easily fabricated from a fibrin sealant film and MSC suspension at the site of treatment. The inner layer of the MSC dressing, an MSC-fibrin complex, promptly and firmly adheres to the heart surface without sutures or extra glues. We revealed that fibrin improves the potential of integrated MSCs through amplifying their tissue-repair abilities and activating the Akt/PI3K self-protection pathway. Outer collagen-sheets protect the MSC-fibrin complex from abrasion by surrounding tissues and also facilitates easy handling. As such, the MSC-dressing technique not only improves initial retention and subsequent maintenance of donor MSCs but also augment MSC's reparative functions. As a result, this technique results in enhanced cardiac function recovery with improved myocardial tissue repair in a rat ischemic cardiomyopathy model, compared to the current method. Dose-dependent therapeutic effects by this therapy is also exhibited. This user-friendly, highly-effective bioengineering technique will contribute to future success of MSC-based therapy.

Long-Term Engraftment (16 Years) of Myoblasts in a Human Infarcted Heart

We report the case of a patient who had undergone injections of myoblasts in an infarct area 16 years before being referred for heart transplantation. The pathological examination of the explanted heart found persisting myotubes embedded in fibrosis. This finding supports the ability of myoblasts to survive in harsh environments, which can make them appealing candidates for transplantation in diseases requiring supply of new myogenic cells. Stem Cells Translational Medicine2018;7:705–708

The CardiAMP Heart Failure trial: A randomized controlled pivotal trial of high-dose autologous bone marrow mononuclear cells using the CardiAMP cell therapy system in patients with post-myocardial infarction heart failure: Trial rationale and study design

BACKGROUND

Heart failure following myocardial infarction is a common, disabling, and deadly condition. Direct injection of autologous bone marrow mononuclear cells into the myocardium may result in improved functional recovery, relieve symptoms, and improve other cardiovascular outcomes.

METHODS

CardiAMP-HF is a randomized, double-blind, sham-controlled, pivotal trial designed to investigate the safety and efficacy of autologous bone marrow mononuclear cells treatment for patients with medically refractory and symptomatic ischemic cardiomyopathy. The primary end point is change in 6-minute walk distance adjusted for major adverse cardiovascular events at 12 months following treatment. Particularly novel aspects of this trial include a cell potency assay to screen subjects who have bone marrow cell characteristics that suggest a favorable response to treatment, a point-of-care treatment method, a high target dose of 200 million cells, and an efficient transcatheter intramyocardial delivery method that is associated with high cell retention.

CONCLUSIONS

This novel approach may lead to a new treatment for those with ischemic heart disease suffering from medically refractory heart failure.

Concise Review: Is Cardiac Cell Therapy Dead? Embarrassing Trial Outcomes and New Directions for the Future

Stem cell therapy is a promising strategy for tissue regeneration. The therapeutic benefits of cell therapy are mediated by both direct and indirect mechanisms. However, the application of stem cell therapy in the clinic is hampered by several limitations. This concise review provides a brief introduction into stem cell therapies for ischemic heart disease. It summarizes cell‐based and cell‐free paradigms, their limitations, and the benefits of using them to target disease. stemcellstranslationalmedicine2018;7:354–359

Possible Muscle Repair in the Human Cardiovascular System

The regenerative potential of tissues and organs could promote survival, extended lifespan and healthy life in multicellular organisms. Niches of adult stemness are widely distributed and lead to the anatomical and functional regeneration of the damaged organ. Conversely, muscular regeneration in mammals, and humans in particular, is very limited and not a single piece of muscle can fully regrow after a severe injury. Therefore, muscle repair after myocardial infarction is still a chimera. Recently, it has been recognized that epigenetics could play a role in tissue regrowth since it guarantees the maintenance of cellular identity in differentiated cells and, therefore, the stability of organs and tissues. The removal of these locks can shift a specific cell identity back to the stem-like one. Given the gradual loss of tissue renewal potential in the course of evolution, in the last few years many different attempts to retrieve such potential by means of cell therapy approaches have been performed in experimental models. Here we review pathways and mechanisms involved in the in vivo repair of cardiovascular muscle tissues in humans. Moreover, we address the ongoing research on mammalian cardiac muscle repair based on adult stem cell transplantation and pro-regenerative factor delivery. This latter issue, involving genetic manipulations of adult cells, paves the way for developing possible therapeutic strategies in the field of cardiovascular muscle repair.

Cellular Therapy for Heart Failure

The pathogenesis of cardiomyopathy and heart failure (HF) is underpinned by complex changes at subcellular, cellular and extracellular levels in the ventricular myocardium. For all of the gains that conventional treatments for HF have brought to mortality and morbidity, they do not adequately address the loss of cardiomyocyte numbers in the remodeling ventricle. Originally conceived to address this problem, cellular transplantation for HF has already gone through several stages of evolution over the past two decades. Various cell types and delivery routes have been implemented to positive effect in preclinical models of ischemic and nonischemic cardiomyopathy, with pleiotropic benefits observed in terms of myocardial remodeling, systolic and diastolic performance, perfusion, fibrosis, inflammation, metabolism and electrophysiology. To a large extent, these salubrious effects are now attributed to the indirect, paracrine capacity of transplanted stem cells to facilitate endogenous cardiac repair processes. Promising results have also followed in early phase human studies, although these have been relatively modest and somewhat inconsistent. This review details the preclinical and clinical evidence currently available regarding the use of pluripotent stem cells and adult-derived progenitor cells for cardiomyopathy and HF. It outlines the important lessons that have been learned to this point in time, and balances the promise of this exciting field against the key challenges and questions that still need to be addressed at all levels of research, to ensure that cell therapy realizes its full potential by adding to the armamentarium of HF management.

Striated muscle function, regeneration, and repair

As the only striated muscle tissues in the body, skeletal and cardiac muscle share numerous structural and functional characteristics, while exhibiting vastly different size and regenerative potential. Healthy skeletal muscle harbors a robust regenerative response that becomes inadequate after large muscle loss or in degenerative pathologies and aging. In contrast, the mammalian heart loses its regenerative capacity shortly after birth, leaving it susceptible to permanent damage by acute injury or chronic disease. In this review, we compare and contrast the physiology and regenerative potential of native skeletal and cardiac muscles, mechanisms underlying striated muscle dysfunction, and bioengineering strategies to treat muscle disorders. We focus on different sources for cellular therapy, biomaterials to augment the endogenous regenerative response, and progress in engineering and application of mature striated muscle tissues in vitro and in vivo. Finally, we discuss the challenges and perspectives in translating muscle bioengineering strategies to clinical practice.

Infarcted cardiac microenvironment may hinder cardiac lineage differentiation of human embryonic stem cells

Microenvironment regulates cell fate and function. In this study, we investigated the effects of the infarcted cardiac microenvironment on cardiac differentiation of human embryonic stem cells (hESCs). hESCs were intramyocardially transplanted into infarcted or uninjured rat hearts. After 4 weeks, mesodermal and cardiac lineage markers were detected by immunofluorescence. Cardiac function was assessed by echocardiography. hESCs were differentiated in vitro under hypoxic (5% O₂ ), low-nutrient (5% FBS), or control condition. The numbers of beating clusters, proportions of cardiac troponin T (cTnT)-positive cells, and relative levels of cardiac-specific markers were determined. Results showed that in both uninjured and infarcted hearts, hESCs survived, underwent development, and formed intracardiac grafts, with a higher proportion in the uninjured hearts. However, cells that were double positive for human fetal liver kinase 1 (Flk1), a marker of cardiac progenitors, and human β-tubulin, a marker for labeling human cells, were found in the uninjured hearts but not in the infarcted hearts. hESC transplantation did not restore the cardiac function of acutely infarcted rats. In vitro, low FBS treatment was associated with fewer beating clusters, a lower proportion of cTnT-positive cells and lower levels of cardiac troponin I (cTnI) and α-myosin heavy chain (α-MHC) expression than those in the control. Conversely, hypoxia treatment was associated with a higher proportion of cTnT-positive cells and higher levels of cTnI expression. In conclusion, transplanted hESCs differentiate toward Flk1-positive cardiac progenitors in the uninjured but not infarcted hearts. The infarcted cardiac microenvironment recapitulated is unsuitable for cardiac differentiation of hESCs, likely due to nutrient deprivation.

Stem cell death and survival in heart regeneration and repair

Cardiovascular diseases are major causes of mortality and morbidity. Cardiomyocyte apoptosis disrupts cardiac function and leads to cardiac decompensation and terminal heart failure. Delineating the regulatory signaling pathways that orchestrate cell survival in the heart has significant therapeutic implications. Cardiac tissue has limited capacity to regenerate and repair. Stem cell therapy is a successful approach for repairing and regenerating ischemic cardiac tissue; however, transplanted cells display very high death percentage, a problem that affects success of tissue regeneration. Stem cells display multipotency or pluripotency and undergo self-renewal, however these events are negatively influenced by upregulation of cell death machinery that induces the significant decrease in survival and differentiation signals upon cardiovascular injury. While efforts to identify cell types and molecular pathways that promote cardiac tissue regeneration have been productive, studies that focus on blocking the extensive cell death after transplantation are limited. The control of cell death includes multiple networks rather than one crucial pathway, which underlies the challenge of identifying the interaction between various cellular and biochemical components. This review is aimed at exploiting the molecular mechanisms by which stem cells resist death signals to develop into mature and healthy cardiac cells. Specifically, we focus on a number of factors that control death and survival of stem cells upon transplantation and ultimately affect cardiac regeneration. We also discuss potential survival enhancing strategies and how they could be meaningful in the design of targeted therapies that improve cardiac function.

Generating patient-specific induced pluripotent stem cells-derived cardiomyocytes for the treatment of cardiac diseases

INTRODUCTION

Induced pluripotent stem cells (iPSC) represent an appealing cell source to develop disease-modeling assays, drug testing assays and cell-based replacement therapies especially for cardiac disorders.

AREAS COVERED

The development of efficient protocols to generate pure populations of cardiac myocytes is a prerequisite to provide reproducible, robust and valid assays. Different techniques have been recently proposed that allow production of high-yield high-quality cardiomyocytes. In addition, the newly developed genome-editing techniques offer multiple opportunities to manipulate the genome of patient-specific iPSC thus generating syngeneic iPSC lines. Genome-editing techniques will also allow engineering of iPSC to make them suitable for replacement therapies.

EXPERT OPINION

Since their discovery, iPSCs have shown promise to revolutionize the way human diseases are studied. During the last years, different protocols have been developed to achieve reproducible and efficient differentiation of iPSCs including in cardiac and vascular cells. The recent introduction of the genome-editing techniques now allow targeted manipulation of the genome of patient-specific and control iPSCs lines. This approach would help to address a couple of current limitations, including the generation of isogenic lines for disease modeling and of clinical-grade lines for replacement therapy.

The Paracrine Effect of Skeletal Myoblasts Is Cardioprotective Against Oxidative Stress and Involves EGFR-ErbB4 Signaling, Cystathionase, and the Unfolded Protein Response

Therapeutic effects of skeletal myoblast transplantation into the myocardium are mediated via paracrine factors. We investigated the ability of myoblast-derived soluble mediators to protect cardiomyocytes from oxidative stress. Fetal rat cardiac cells were treated with conditioned medium from cultures of myoblasts or cardiac fibroblasts, and oxidative stress was induced with H2O2. Myoblast-derived factors effectively prevented oxidative stress-induced cardiac cell death and loss of mitochondrial membrane potential. This protective effect was mediated via epidermal growth factor (EGF) receptor and c-Met signaling, and mimicked by neuregulin 1 but not EGF. Microarray analysis of cardiac cells treated with myoblast versus cardiac fibroblast-derived mediators revealed differential regulation of genes associated with antioxidative effects: cystathionine-γ-lyase (cst), xanthine oxidase, and thioredoxin-interacting protein as well as tribbles homolog 3 (trib3). Cardiac cell pretreatment with tunicamycin, an inducer of trib3, also protected them against H2O2-induced cell death. Epicardial transplantation of myoblast sheets in a rat model of acute myocardial infarction was used to evaluate the expression of CST and trib3 as markers of myoblasts' paracrine effect in vivo. Myoblast sheets induced expression of the CST as well as trib3 in infarcted myocardium. CST localized around blood vessels, suggesting smooth muscle cell localization. Our results provide a deeper molecular insight into the therapeutic mechanisms of myoblast-derived paracrine signaling in cardiac cells and suggest that myoblast transplantation therapy may prevent oxidative stress-induced cardiac deterioration and progression of heart failure.

Programming and reprogramming a human heart cell

The latest discoveries and advanced knowledge in the fields of stem cell biology and developmental cardiology hold great promise for cardiac regenerative medicine, enabling researchers to design novel therapeutic tools and approaches to regenerate cardiac muscle for diseased hearts. However, progress in this arena has been hampered by a lack of reproducible and convincing evidence, which at best has yielded modest outcomes and is still far from clinical practice. To address current controversies and move cardiac regenerative therapeutics forward, it is crucial to gain a deeper understanding of the key cellular and molecular programs involved in human cardiogenesis and cardiac regeneration. In this review, we consider the fundamental principles that govern the "programming" and "reprogramming" of a human heart cell and discuss updated therapeutic strategies to regenerate a damaged heart.

Stem cell therapy and breast cancer treatment: review of stem cell research and potential therapeutic impact against cardiotoxicities due to breast cancer treatment

A new problem has emerged with the ever-increasing number of breast cancer survivors. While early screening and advances in treatment have allowed these patients to overcome their cancer, these treatments often have adverse cardiovascular side effects that can produce abnormal cardiovascular function. Chemotherapeutic and radiation therapy have both been linked to cardiotoxicity; these therapeutics can cause a loss of cardiac muscle and deterioration of vascular structure that can eventually lead to heart failure (HF). This cardiomyocyte toxicity can leave the breast cancer survivor with a probable diagnosis of dilated or restrictive cardiomyopathy (DCM or RCM). While current HF standard of care can alleviate symptoms, other than heart transplantation, there is no therapy that replaces cardiac myocytes that are killed during cancer therapies. There is a need to develop novel therapeutics that can either prevent or reverse the cardiac injury caused by cancer therapeutics. These new therapeutics should promote the regeneration of lost or deteriorating myocardium. Over the last several decades, the therapeutic potential of cell-based therapy has been investigated for HF patients. In this review, we discuss the progress of pre-clinical and clinical stem cell research for the diseased heart and discuss the possibility of utilizing these novel therapies to combat cardiotoxicity observed in breast cancer survivors.

Three-dimensional extracellular matrix scaffolds by microfluidic fabrication for long-term spontaneously contracted cardiomyocyte culture

To repair damaged cardiac tissue, the important principle of in vitro cell culture is to mimic the in vivo cell growth environment. Thus, micro-sized cells are more suitably cultured in three-dimensional (3D) than in two-dimensional (2D) microenvironments (ex: culture dish). With the matching dimensions of works produced by microfluidic technology, chemical engineering and biochemistry applications have used this technology extensively in cellular works. The 3D scaffolds produced in our investigation has essential properties, such has high mass transfer efficiency, and variable pore sizes, to adapt to various needs of different cell types. In addition to the malleability of these innovative scaffolds, fabrication procedure was effortless and fast. Primary neonatal mice cardiomyocytes were successfully harvested and cultured in 3D scaffolds made of gelatin and collagen. Gelatin and gelatin-collagen scaffold were produced by the formation of microbubbles through a microfluidic device, and the mechanical properties of gelatin scaffold and gelatin-collagen scaffold were measured. Cellular properties in the microbubbles were also monitored. Fluorescence staining results assured that cardiomyocytes could maintain in vivo morphology in 3D gelatin scaffold. In addition, it was found that 3D scaffold could prolong the contraction behavior of cardiomyocytes compared with a conventional 2D culture dish. Spontaneously contracted behavior was maintained for the longest (about 1 month) in the 3D gelatin scaffold, about 19 days in the 3D gelatin-collagen scaffold. To sum up, this 3D platform for cell culture has promising potential for myocardial tissue engineering.

Cardiac regeneration using pluripotent stem cells--progression to large animal models

Pluripotent stem cells (PSCs) have indisputable cardiomyogenic potential and therefore have been intensively investigated as a potential cardiac regenerative therapy. Current directed differentiation protocols are able to produce high yields of cardiomyocytes from PSCs and studies in small animal models of cardiovascular disease have proven sustained engraftment and functional efficacy. Therefore, the time is ripe for cardiac regenerative therapies using PSC derivatives to be tested in large animal models that more closely resemble the hearts of humans. In this review, we discuss the results of our recent study using human embryonic stem cell derived cardiomyocytes (hESC-CM) in a non-human primate model of ischemic cardiac injury. Large scale remuscularization, electromechanical coupling and short-term arrhythmias demonstrated by our hESC-CM grafts are discussed in the context of other studies using adult stem cells for cardiac regeneration.

Cell therapy for heart failure: a comprehensive overview of experimental and clinical studies, current challenges, and future directions

Despite significant therapeutic advances, the prognosis of patients with heart failure (HF) remains poor, and current therapeutic approaches are palliative in the sense that they do not address the underlying problem of the loss of cardiac tissue. Stem cell-based therapies have the potential to fundamentally transform the treatment of HF by achieving what would have been unthinkable only a few years ago-myocardial regeneration. For the first time since cardiac transplantation, a therapy is being developed to eliminate the underlying cause of HF, not just to achieve damage control. Since the initial report of cell therapy (skeletal myoblasts) in HF in 1998, research has proceeded at lightning speed, and numerous preclinical and clinical studies have been performed that support the ability of various stem cell populations to improve cardiac function and reduce infarct size in both ischemic and nonischemic cardiomyopathy. Nevertheless, we are still at the dawn of this therapeutic revolution. Many important issues (eg, mechanism(s) of action of stem cells, long-term engraftment, optimal cell type(s), and dose, route, and frequency of cell administration) remain to be resolved, and no cell therapy has been conclusively shown to be effective. The purpose of this article is to critically review the large body of work performed with respect to the use of stem/progenitor cells in HF, both at the experimental and clinical levels, and to discuss current controversies, unresolved issues, challenges, and future directions. The review focuses specifically on chronic HF; other settings (eg, acute myocardial infarction, refractory angina) are not discussed.

The use of scaffold-free cell sheet technique to refine mesenchymal stromal cell-based therapy for heart failure

Transplantation of bone marrow-derived mesenchymal stromal cells (MSCs) is an emerging treatment for heart failure based on their secretion-mediated "paracrine effects". Feasibility of the scaffoldless cell sheet technique to enhance the outcome of cell transplantation has been reported using other cell types, though the mechanism underpinning the enhancement remains uncertain. We here investigated the role of this innovative technique to amplify the effects of MSC transplantation with a focus on the underlying factors. After coronary artery ligation in rats, syngeneic MSCs were grafted by either epicardial placement of MSC sheets generated using temperature-responsive dishes or intramyocardial (IM) injection. Markedly increased initial retention boosted the presence of donor MSCs persistently after MSC sheet placement although the donor survival was not improved. Most of the MSCs grafted by the cell sheet technique remained resided on the epicardial surface, but the epicardium quickly regressed and new vessels sprouted into the sheets, assuring the permeation of paracrine mediators from MSCs into the host myocardium. In fact, there was augmented upregulation of various paracrine effect-related genes and signaling pathways in the early phase after MSC sheet therapy. Correspondingly, more extensive paracrine effects and resultant cardiac function recovery were achieved by MSC sheet therapy. Further development of this approach towards clinical application is encouraged.

Mechanisms of greater cardiomyocyte functions on conductive nanoengineered composites for cardiovascular application

Background

Recent advances in nanotechnology (materials with at least one dimension between 1 nm and 100 nm) have led to the use of nanomaterials in numerous medical device applications. Recently, nanomaterials have been used to create innovative biomaterials for cardiovascular applications. Specifically, carbon nanofibers (CNF) embedded in poly(lactic-co-glycolic-acid) (PLGA) have been shown to promote cardiomyocyte growth compared with conventional polymer substrates, but the mechanisms involved in such events remain unknown. The aim of this study was to determine the basic mechanism of cell growth on these novel nanocomposites.

Methods

CNF were added to biodegradable PLGA (50:50 PGA:PLA weight ratio) to increase the conductivity, mechanical and cytocompatibility properties of pure PLGA. For this reason, different PLGA to CNF ratios (100:0, 75:25, 50:50, 25:75, and 0:100 wt%) with different PLGA densities (0.1, 0.05, 0.025, and 0.0125 g/mL) were used, and their compatibility with cardiomyocytes was assessed.

Results

Throughout all the cytocompatibility experiments, cardiomyocytes were viable and expressed important biomarkers, including cardiac troponin T, connexin-43, and alpha-sarcomeric actin (α-SCA). Adhesion and proliferation experiments indicated that a PLGA density of 0.025 g/mL with a PLGA to CNF ratio of 75:25 and 50:50 (wt%) promoted the best overall cell growth, ie, a 55% increase in cardiomyocyte density after 120 hours compared with pure PLGA and a 75% increase compared with the control at the same time point for 50:50 (wt%). The PLGA:CNF materials were conductive, and their conductivity increased as greater amounts of CNF were added to pure PLGA, from 0 S · m⁻¹ for pure PLGA (100:0 wt%) to 5.5 × 10⁻³ S · m⁻¹ for pure CNF (0:100 wt%), as compared with natural heart tissue (ranging from 0.16 S · m⁻¹ longitudinally to 0.005 S · m⁻¹ transversely). Tensile tests showed that the addition of CNF increased the tensile strength to mimic that of natural heart tissue, ie, 0.15 MPa for 100% PLGA to 5.41 MPa for the 50:50 (PLGA to CNF [wt%:wt%]) ratio at 0.025 g/mL. Atomic force microscopy indicated that the addition of CNF to PLGA increased the material surface area from 10% (100:0 [PLGA to carbon nanofiber (wt%:wt%)]) to over 60% (50:50 [PLGA to carbon nanofibers (wt%:wt%)]). Lastly, the adsorption of specific proteins (fibronectin and vitronectin) showed significantly more adsorption for the 50:50 PLGA to CNF (wt%:wt%) ratio at 0.025 g/mL PLGA compared with pure PLGA, which may be why cardiomyocyte function increased on CNF-enriched composites.

Conclusion

This study demonstrates that cardiomyocyte function was enhanced on 50:50 PLGA to CNF (wt%:wt%) composite ratios at 0.025 g/mL PLGA densities because they mimicked native heart tissue tensile strength/conductivity and increased the adsorption of proteins known to promote cardiomyocyte function.

The use of cell-sheet technique eliminates arrhythmogenicity of skeletal myoblast-based therapy to the heart with enhanced therapeutic effects

BACKGROUND

Clinical application of skeletal myoblast transplantation has been curtailed due to arrhythmogenicity and inconsistent therapeutic benefits observed in previous studies. However, these issues may be solved by the use of a new cell-delivery mode. It is now possible to generate "cell-sheets" using temperature-responsive dishes without artificial scaffolds. This study aimed to validate the safety and efficacy of epicardial placement of myoblast-sheets (myoblast-sheet therapy) in treating heart failure.

METHODS AND RESULTS

After coronary artery ligation in rats, the same numbers of syngeneic myoblasts were transplanted by intramyocardial injection or cell-sheet placement. Continuous radio-telemetry monitoring detected increased ventricular arrhythmias, including ventricular tachycardia, after intramyocardial injection compared to the sham-control, while these were abolished in myoblast-sheet therapy. This effect was conjunct with avoidance of islet-like cell-cluster formation that disrupts electrical conduction, and with prevention of increased arrhythmogenic substrates due to exaggerated inflammation. Persistent ectopic donor cells were found in the lung only after intramyocardial injection, strengthening the improved safety of myoblast-sheet therapy. In addition, myoblast-sheet therapy enhanced cardiac function, corresponding to a 9.2-fold increase in donor cell survival, compared to intramyocardial injection. Both methods achieved reduced infarct size, decreased fibrosis, attenuated cardiomyocyte hypertrophy, and increased neovascular formation, in association with myocardial upregulation of a group of relevant molecules. The pattern of these beneficial changes was similar between two methods, but the degree was more substantial after myoblast-sheet therapy.

CONCLUSION

The cell-sheet technique enhanced safety and therapeutic efficacy of myoblast-based therapy, compared to the current method, thereby paving the way for clinical application.

Increased angiogenesis and improved left ventricular function after transplantation of myoblasts lacking the MyoD gene into infarcted myocardium

Skeletal myoblast transplantation has therapeutic potential for repairing damaged heart. However, the optimal conditions for this transplantation are still unclear. Recently, we demonstrated that satellite cell-derived myoblasts lacking the MyoD gene (MyoD(-/-)), a master transcription factor for skeletal muscle myogenesis, display increased survival and engraftment compared to wild-type controls following transplantation into murine skeletal muscle. In this study, we compare cell survival between wild-type and MyoD(-/-) myoblasts after transplantation into infarcted heart. We demonstrate that MyoD(-/-) myoblasts display greater resistance to hypoxia, engraft with higher efficacy, and show a larger improvement in ejection fraction than wild-type controls. Following transplantation, the majority of MyoD(-/-) and wild-type myoblasts form skeletal muscle fibers while cardiomyocytes do not. Importantly, the transplantation of MyoD(-/-) myoblasts induces a high degree of angiogenesis in the area of injury. DNA microarray data demonstrate that paracrine angiogenic factors, such as stromal cell-derived factor-1 (SDF-1) and placental growth factor (PlGF), are up-regulated in MyoD(-/-) myoblasts. In addition, over-expression and gene knockdown experiments demonstrate that MyoD negatively regulates gene expression of these angiogenic factors. These results indicate that MyoD(-/-) myoblasts impart beneficial effects after transplantation into an infarcted heart, potentially due to the secretion of paracrine angiogenic factors and enhanced angiogenesis in the area of injury. Therefore, our data provide evidence that a genetically engineered myoblast cell type with suppressed MyoD function is useful for therapeutic stem cell transplantation.

Bioengineered myocardium derived from induced pluripotent stem cells improves cardiac function and attenuates cardiac remodeling following chronic myocardial infarction in rats

Cell-based therapies are promising strategies for myocardial repair following myocardial infarction. Induced pluripotent stem (iPS) cells have the potential to generate many cardiomyocytes, and they hold significant promise for the application of regenerative medicine to heart failure. Here, we developed cardiac tissue sheets, termed bioengineered myocardium (BM), from mouse iPS cells and measured cardiac performance following BM implantation in a rat chronic myocardial infarction model. Immunostaining analyses revealed that the α-actinin(+) cell population was isolated with more than 99% purity under specific culture conditions. To evaluate the contribution of BM to the improvements in cardiac performance, we induced myocardial infarction in 30 F344/NJcl-rnu/rnu rats by left anterior descending coronary ligation. The rats were randomly divided into two groups, 2 weeks after ligation: a BM implantation group (n = 15) and a sham group (n = 15). Echocardiography and catheter examination showed that the BM implantation significantly improved cardiac function and attenuated cardiac remodeling compared with the sham group. Histological analyses demonstrated that the implanted BM survived at the epicardial implantation site 4 weeks after implantation. The implanted BM survived and attenuated left ventricular remodeling in the rat chronic myocardial infarction model. Thus, BM derived from iPS cells might be a promising new treatment for heart failure.

Injection of human bone marrow and mononuclear cell extract into infarcted mouse hearts results in functional improvement

BACKGROUND

We have previously shown that mouse whole bone marrow cell (BMC) extract results in improvement of cardiac function and decreases scar size in a mouse model of myocardial infarction (MI), in the absence of intact cells. It is not clear if these results are translatable to extracts from human BMC (hBMC) or mononuclear cells (hMNC), which would have significant clinical implications.

METHODS

Male C57BL/6J (10-12 weeks old) mice were included in this study. MI was created by permanent ligation of the left anterior descending artery. Animals were randomized into three groups to receive ultrasound-guided myocardial injections with either hBMCs extract (n=6), hMNCs extract (n=8) or control with 0.5% bovine serum albumin (BSA) (n=7). Cardiac function was assessed by echocardiography at baseline, 2 and 28 days post-MI. Infarct size and vascularity was assessed at 28 days post-MI.

RESULTS

hBMC and hMNC extract preserve cardiac function and result in smaller scar size post-MI when compared with the control group.

CONCLUSIONS

The current study for the first time reports that hBMC and hMNC extracts improve cardiac function post-MI in a mouse MI model. Further studies are necessary to fully address the potential clinical benefits of these therapies.

Cardiosphere-derived cells improve function in the infarcted rat heart for at least 16 weeks--an MRI study

Aims

Endogenous cardiac progenitor cells, expanded from explants via cardiosphere formation, present a promising cell source to prevent heart failure following myocardial infarction. Here we used cine-magnetic resonance imaging (MRI) to track administered cardiosphere-derived cells (CDCs) and to measure changes in cardiac function over four months in the infarcted rat heart.

Methods and Results

CDCs, cultured from neonatal rat heart, comprised a heterogeneous population including cells expressing the mesenchymal markers CD90 and CD105, the stem cell marker c-kit and the pluripotency markers Sox2, Oct3/4 and Klf-4. CDCs (2×10⁶) expressing green fluorescent protein (GFP+) were labelled with fluorescent micron-sized particles of iron oxide (MPIO). Labelled cells were administered to the infarcted rat hearts (n = 7) by intramyocardial injection immediately following reperfusion, then by systemic infusion (4×10⁶) 2 days later. A control group (n = 7) was administered cell medium. MR hypointensities caused by the MPIOs were detected at all times and GFP+ cells containing MPIO particles were identified in tissue slices at 16 weeks. At two days after infarction, cardiac function was similar between groups. By 6 weeks, ejection fractions in control hearts had significantly decreased (47±2%), but this was not evident in CDC-treated hearts (56±3%). The significantly higher ejection fractions in the CDC-treated group were maintained for a further 10 weeks. In addition, CDC-treated rat hearts had significantly increased capillary density in the peri-infarct region and lower infarct sizes. MPIO-labelled cells also expressed cardiac troponin I, von Willebrand factor and smooth muscle actin, suggesting their differentiation along the cardiomyocyte lineage and the formation of new blood vessels.

Conclusions

CDCs were retained in the infarcted rat heart for 16 weeks and improved cardiac function.

Sensing the cardiac environment: exploiting cues for regeneration

Recent pre-clinical and clinical studies indicate that certain exogenous stem cells and biomaterials can preserve cardiac tissue after myocardial infarction. Regarding stem cells, a growing body of data suggests that the short-term positive outcomes are mainly attributed to paracrine signaling mechanisms. The release of such factors is due to the cell's ability to sense cardiac environmentally derived cues, though the exact feedback loops are still poorly understood. However, given the limited engraftment and survival of transplanted cells in the ischemic environment, the long-term clinical benefits of these therapies have not yet been realized. To overcome this, the long-term controlled delivery of bioactive factors using biomaterials is a promising approach. A major challenge has been the ability to develop timely and spatially controlled gradients of different cues, pivotal for the development and regeneration of tissues. In addition, given the complexity of the remodeling process after myocardial infarction, multiple factors may be required at distinct disease stages to maximize therapeutic outcomes. Therefore, novel smart materials that can sense the surrounding environment and generate cues through on demand mechanisms will be of major importance in the translation of these promising advanced therapies. This article reviews how the cardiac environment can mediate the release profiles of bioactive cues from cells and biomaterials and how the controlled delivery impacts heart regeneration.

In vitro and in vivo cardiomyogenic differentiation of amniotic fluid stem cells

Cell therapy has developed as a complementary treatment for myocardial regeneration. While both autologous and allogeneic uses have been advocated, the ideal candidate has not been identified yet. Amniotic fluid-derived stem (AFS) cells are potentially a promising resource for cell therapy and tissue engineering of myocardial injuries. However, no information is available regarding their use in an allogeneic context. c-kit-sorted, GFP-positive rat AFS (GFP-rAFS) cells and neonatal rat cardiomyocytes (rCMs) were characterized by cytocentrifugation and flow cytometry for the expression of mesenchymal, embryonic and cell lineage-specific antigens. The activation of the myocardial gene program in GFP-rAFS cells was induced by co-culture with rCMs. The stem cell differentiation was evaluated using immunofluorescence, RT-PCR and single cell electrophysiology. The in vivo potential of Endorem-labeled GFP-rAFS cells for myocardial repair was studied by transplantation in the heart of animals with ischemia/reperfusion injury (I/R), monitored by magnetic resonance imaging (MRI). Three weeks after injection a small number of GFP-rAFS cells acquired an endothelial or smooth muscle phenotype and to a lesser extent CMs. Despite the low GFP-rAFS cells count in the heart, there was still an improvement of ejection fraction as measured by MRI. rAFS cells have the in vitro propensity to acquire a cardiomyogenic phenotype and to preserve cardiac function, even if their potential may be limited by poor survival in an allogeneic setting.

RETRACTED: Poly(lactic-co-glycolic acid): carbon nanofiber composites for myocardial tissue engineering applications

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Coordinating Editor and the Editor-in-Chief. An author-provided and previously published corrigendum updated Figures 9A and C and 10A and B. The authors had also provided a justification and an explanation for concerns raised in regards to Figure 3A. It was determined at that time that the conclusions of the publication remained the same. However, it has since been identified that parts of Figures 3, 9 and 10 are falsified and/or fabricated. The original data reported in this manuscript were not retained by the authors and the reliability of the reported results could not be confirmed. The editors regret any negative consequences that may have arisen from this matter within the scientific community.

Scaffold-based transplantation of akt1-overexpressing skeletal myoblasts: functional regeneration is associated with angiogenesis and reduced infarction size

Myoblast-based therapy can improve cardiac function after infarction and is conventionally performed by direct injection. A scaffold-based transfer could overcome injection-associated problems. In upgrading this approach we transplanted skeletal myoblasts (SkM) overexpressing the prosurvival gene Akt1. SkM were transfected with pcDNA3-huda-Akt1 and seeded on polyurethane scaffolds. These scaffolds were transplanted in rats 2 weeks after myocardial infarction. Hemodynamics were analyzed before therapy and 6 weeks later. Infarction size and capillary density were performed thereafter. Additional groups received injections of Akt1-transfected or untransfected myoblasts, scaffolds seeded with untransfected myoblasts, or sham operation. Deterioration of global systolic left ventricular function could be inhibited by all therapeutic approaches. In addition, transplantation of Akt1-transfected cells, either scaffold-based or injected, was superior with regard to systolic properties of the left ventricular wall. This effect was accompanied by smaller infarction sizes and angiogenesis. Scaffolds with untransfected myoblasts yielded also smaller infarctions than injections of untransfected myoblasts. Both Akt groups profited with regard to dP/dt(min). In contrast, other diastolic parameters pointed at impaired relaxation and stiffer myocardium especially in the Akt1-scaffold group. In conclusion, SkM overexpressing Akt1 can maintain myocardial function after infarction, reduce infarction size, and induce neovascularization. Scaffold-based cell transfer does not augment this reverse remodeling capacity.

[Stem cells in the amniotic fluid: the new chance of regenerative medicine]

Amniotic fluid has been used in prenatal diagnosis for more than decades. It yields a simple and reliable screening and diagnostic tool for a variety of congenital malformations and genetic diseases such as chromosomal aberrations, neural tube defects or storage diseases. Nowadays the widening knowledge provides evidence that amniotic fluid is not only a screening and diagnostic tool, but it may be also the source of the effective therapy of several congenital and adult disorders. A subset of cells, the so-called stem cells were found in the amniotic fluid as well as the placenta, and they proved to be capable of maintaining prolonged undifferentiated proliferation. Stem cells are able to differentiate into multiple tissue types, originating from the three germ layers. In the near future stem cells isolated from amniotic fluid or placenta and stored by cryopreservation may play a significant role in regenerative medicine. Congenital malformations as well as certain diseases in adults might be treated by tissues coming from progenitor cells of amniotic fluid stem cell origin. This study gives a summary of the main characteristics of amniotic fluid stem cells and it also presents important examples of their possible clinical application.

Human embryonic stem cell-derived cardiomyocytes engraft but do not alter cardiac remodeling after chronic infarction in rats

Previous studies indicated that, in an acute myocardial infarction model, human embryonic stem cell-derived cardiomyocytes (hESC-CM) injected with a pro-survival cocktail (PSC) can preserve contractile function. Because patients with established heart failure may also benefit from cell transplantation, we evaluated the physiological effects of hESC-CM transplanted into a chronic model of myocardial infarction. Intramyocardial injection of hESC-CM with PSC was performed in nude rats at 1 month following ischemia-reperfusion. The left ventricular function of hESC-CM injected rats was evaluated at 1, 2 and 3 months after the cell injection procedure and was compared to 3 control groups (rats injected with serum-free media, PSC only, or non-cardiac human cells in PSC). Histology at 3 months revealed that human cardiomyocytes survive, develop increased sarcomere organization and are still proliferating. Despite successful engraftment, both echocardiography and MRI analyses showed no significant difference in left ventricular structure or function between these 4 groups at any time point of the study, suggesting that human cardiomyocytes do not affect cardiac remodeling in a rat model of chronic myocardial infarction. When injected into a chronic infarct model, hESC-CM can engraft, survive and form grafts with striated cardiomyocytes at least as well as was previously observed in an acute myocardial infarction model. However, although hESC-CM transplantation can attenuate the progression of heart failure in an acute model, the same hESC-CM injection protocol is insufficient to restore heart function or to alter adverse remodeling of a chronic myocardial infarction model.

Stem cell therapy for chronic myocardial infarction

Although recent advances for the treatment of myocardial infarction have dramatically increased the rate of survival after the ischemic event, this has also led to a rise in the number of chronic patients, making the finding of a suitable therapy a compulsory subject for modern medicine. Over the last decade, stem cells have been a promise for the cure of several diseases not only due to their plasticity but also to their capacity to act in a paracrine manner and influence the affected tissue, prompting the launching of several clinical trials. In spite of the knowledge already acquired, stem cell application to chronically infarcted hearts has been much less approached than its acute counterpart. Through this review, we will focus in stem cell therapy in animal models of chronic myocardial infarction: cell types employed, functional results, mechanisms analyzed, and questions raised.