Autologous mesenchymal stem cells mobilize cKit+ and CD133+ bone marrow progenitor cells and improve regional function in hibernating myocardium

Cellular and molecular mechanisms driving cardiac tissue fibrosis: On the precipice of personalized and precision medicine

Cardiac fibrosis is a significant contributor to heart failure, a condition that continues to affect a growing number of patients worldwide. Various cardiovascular comorbidities can exacerbate cardiac fibrosis. While fibroblasts are believed to be the primary cell type underlying fibrosis, recent and emerging data suggest that other cell types can also potentiate or expedite fibrotic processes. Over the past few decades, clinicians have developed therapeutics that can blunt the development and progression of cardiac fibrosis. While these strategies have yielded positive results, overall clinical outcomes for patients suffering from heart failure continue to be dire. Herein, we overview the molecular and cellular mechanisms underlying cardiac tissue fibrosis. To do so, we establish the known mechanisms that drive fibrosis in the heart, outline the diagnostic tools available, and summarize the treatment options used in contemporary clinical practice. Finally, we underscore the critical role the immune microenvironment plays in the pathogenesis of cardiac fibrosis.

MSC Pretreatment for Improved Transplantation Viability Results in Improved Ventricular Function in Infarcted Hearts

Many clinical studies utilizing MSCs (mesenchymal stem cells, mesenchymal stromal cells, or multipotential stromal cells) are underway in multiple clinical settings; however, the ideal approach to prepare these cells in vitro and to deliver them to injury sites in vivo with maximal effectiveness remains a challenge. Here, pretreating MSCs with agents that block the apoptotic pathways were compared with untreated MSCs. The treatment effects were evaluated in the myocardial infarct setting following direct injection, and physiological parameters were examined at 4 weeks post-infarct in a rat permanent ligation model. The prosurvival treated MSCs were detected in the hearts in greater abundance at 1 week and 4 weeks than the untreated MSCs. The untreated MSCs improved ejection fraction in infarcted hearts from 61% to 77% and the prosurvival treated MSCs further improved ejection fraction to 83% of normal. The untreated MSCs improved fractional shortening in the infarcted heart from 52% to 68%, and the prosurvival treated MSCs further improved fractional shortening to 77% of normal. Further improvements in survival of the MSC dose seems possible. Thus, pretreating MSCs for improved in vivo survival has implications for MSC-based cardiac therapies and in other indications where improved cell survival may improve effectiveness.

Non-coding RNAs in cardiac regeneration: Mechanism of action and therapeutic potential

In the past two decades, thousands of non-coding RNAs (ncRNAs) have been discovered, annotated, and characterized in nearly every tissue under both physiological and pathological conditions. Here, we will focus on the role of ncRNAs, including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) in ischemic heart disease (IHD), which remains the leading cause of morbidity and mortality in humans-resulting in 8.9 million deaths annually. Cardiomyocyte (CM) proliferation, differentiation, and survival in addition to neovascularization of injured tissues and the prevention of fibrosis are commonly regarded as critically important for the recovery of the heart following myocardial infarction (MI). An abundance of evidence has been accumulated to show ncRNAs participate in cardiac recovery after MI. Because miRNAs are important regulators of cardiac regeneration, the therapeutic potential of at least five of these molecules has been assessed in large animal models of human IHD. In particular, miRNA-based interventions based on miR-132 and miR-92a inhibition in related diseases have displayed favorable outcomes that have provided the impetus for miRNA-based clinical trials for IHD. At the same time, the functional roles of lncRNAs and circRNAs in cardiac regeneration are also being explored. In the present review, we will summarize the latest ncRNA studies aimed at reversing damage to the ischemic heart and discuss the therapeutic potential of targeting miRNAs, lncRNAs, and circRNAs to stimulate cardiac regeneration.

Mesenchymal stem cell-derived extracellular vesicles in the failing heart: past, present, and future

Cardiovascular disease (CVD) is the leading cause of death globally. Current treatment options include lifestyle changes, medication, and surgical intervention. However, many patients are unsuitable candidates for surgeries due to comorbidities, diffuse coronary artery disease, or advanced stages of heart failure. The search for new treatment options has recently transitioned from cell-based therapies to stem-cell-derived extracellular vesicles (EVs). A number of challenges remain in the EV field, including the effect of comorbidities, characterization, and delivery. However, recent revolutionary developments and insight into the potential of personalizing EV contents by bioengineering methods to alter specific signaling pathways in the ischemic myocardium hold promise. Here, we discuss the past limitations of cell-based therapies and recent EV studies involving in vivo, in vitro, and omics, and future challenges and opportunities in EV-based treatments in CVD.

Clinical Application of Novel Therapies for Coronary Angiogenesis: Overview, Challenges, and Prospects

Cardiovascular diseases continue to be the leading cause of death worldwide, with ischemic heart disease as the most significant contributor. Pharmacological and surgical interventions have improved clinical outcomes, but are unable to ameliorate advanced stages of end-heart failure. Successful preclinical studies of new therapeutic modalities aimed at revascularization have shown short lasting to no effects in the clinical practice. This lack of success may be attributed to current challenges in patient selection, endpoint measurements, comorbidities, and delivery systems. Although challenges remain, the field of therapeutic angiogenesis is evolving, as novel strategies and bioengineering approaches emerge to optimize delivery and efficacy. Here, we describe the structure, vascularization, and regulation of the vascular system with particular attention to the endothelium. We proceed to discuss preclinical and clinical findings and present challenges and future prospects in the field.

Production of Cardiomyocyte-Like Cells by Fibroblast Reprogramming with Defined Factors

Over the last decade, great achievements have been made in the field of direct epigenetic reprogramming, which converts one type of adult somatic cells into another type of differentiated cells, such as direct reprogramming of fibroblasts into cardiomyocytes, without passage through an undifferentiated pluripotent stage. Discovery of direct cardiac reprogramming offers a promising therapeutic strategy to prevent/attenuate cardiac fibrotic remodeling in a diseased heart. Furthermore, in vitro reprogramming of fibroblasts into cardiomyocyte-like cells provides new avenues to conduct basic mechanistic studies, to test drugs, and to model cardiac diseases in a dish. Here, we describe a detailed step-by-step protocol for in vitro production of induced cardiomyocyte-like cells (iCMs) from fibroblasts. The related procedures include high-quality fibroblast isolation of different origins (neonatal cardiac, tail-tip, and adult cardiac fibroblasts), retroviral preparation of reprogramming factors, and iCM generation by fibroblast reprogramming via retroviral transduction of Gata4, Mef2c, and Tbx5. A detailed written protocol will help many other laboratories, inexperienced in this area, to use and further improve this technology in their studies of cardiac regenerative medicine.

Application of Mesenchymal Stem Cells in Inflammatory and Fibrotic Diseases

Mesenchymal stem cells (MSCs) are multipotent stem cells that can be isolated from various tissues in the adult body. MSCs should be characterized by three criteria for regenerative medicine. MSCs must (1) adhere to plastic surfaces, (2) express specific surface antigens, and (3) differentiate into mesodermal lineages, including chondrocytes, osteoblasts, and adipocytes, in vitro. Interestingly, MSCs have immunomodulatory features and secrete trophic factors and immune receptors that regulate the microenvironment in host tissue. These specific and unique therapeutic properties make MSCs ideal as therapeutic agents in vivo. Specifically, pre-clinical and clinical investigators generated inflammatory and fibrotic diseases models, and then transplantation of MSCs into diseases models for therapeutic effects investigation. In this review, we characterize MSCs from various tissues and describe their applications for treating various inflammation and fibrotic diseases.

Arrhythmogenic risks of stem cell replacement therapy for cardiovascular diseases

Ischemic heart disease and congestive heart failure are major contributors to high morbidity and mortality. Approximately 1.5 million cases of myocardial infarction occur annually in the United States; the yearly incidence rate is approximately 600 cases per 100,000 people. Although significant progress to improve the survival rate has been made by medications and implantable medical devices, damaged cardiomyocytes are unable to be recovered by current treatment strategies. After almost two decades of research, stem cell therapy has become a very promising approach to generate new cardiomyocytes and enhance the function of the heart. Along with clinical trials with stem cells conducted in cardiac regeneration, concerns regarding safety and potential risks have emerged. One of the contentious issues is the electrical dysfunctions of cardiomyocytes and cardiac arrhythmia after stem cell therapy. In this review, we focus on the cell sources currently used for stem cell therapy and discuss related arrhythmogenic risk.

Recovery of hibernating myocardium using stem cell patch with coronary bypass surgery

OBJECTIVE

This study aims to investigate the utility of mesenchymal stem cells (MSCs) applied as an epicardial patch during coronary artery bypass graft (CABG) to target hibernating myocardium; that is, tissue with persistently decreased myocardial function, in a large animal model.

METHODS

Hibernating myocardium was induced in juvenile swine (n = 12) using a surgically placed constrictor on the left anterior descending artery, causing stenosis without infarction. After 12 weeks, single-vessel CABG was performed using left internal thoracic artery to left anterior descending artery graft. During CABG, an epicardial patch was applied to the hibernating myocardium region consisting either of MSCs grown onto a polyglactin mesh (n = 6), or sham polyglactin mesh without MSCs (n = 6). Four weeks after CABG and patch placement, cardiac magnetic resonance imaging was performed and cardiac tissue was examined by gross inspection, including coronary dilators for vessel stenosis and patency, electron microscopy, protein assays, and proteomic analysis.

RESULTS

CABG + MSC myocardium showed improvement in contractile function (78.24% ± 19.6%) compared with sham patch (39.17% ± 5.57%) during inotropic stimulation (P < .05). Compared with sham patch control, electron microscopy of CABG + MSC myocardium showed improvement in mitochondrial size, number, and morphology; protein analysis similarly showed increases in expression of the mitochondrial biogenesis marker peroxisome proliferator-activated receptor gamma coactivator 1-alpha (0.0022 ± 0.0009 vs 0.023 ± 0.009) (P < .01) along with key components of the electron transport chain, including succinate dehydrogenase (complex II) (0.06 ± 0.02 vs 0.14 ± 0.03) (P < .05) and adenosine triphosphate synthase (complex V) (2.7 ± 0.4 vs 4.2 ± 0.26) (P < .05).

CONCLUSIONS

In hibernating myocardium, placement of a stem cell patch during CABG shows promise in improving myocardial function by improving mitochondrial morphology and function.

Troponin Release and Reversible Left Ventricular Dysfunction After Transient Pressure Overload

BACKGROUND

The authors previously demonstrated that brief ischemia elicits cardiac troponin I (cTnI) release and myocyte apoptosis in the absence of necrosis. It remains uncertain whether other pathophysiological stresses can produce apoptosis and transient cTnI release without ischemia.

OBJECTIVES

This study sought to determine whether a transient increase in left ventricular (LV) preload elicits cTnI release in the absence of ischemia.

METHODS

Propofol-anesthetized swine (N = 13) received intravenous phenylephrine (PE) (300 μg/min) for 1 h to increase left ventricular end-diastolic pressure (LVEDP) to ∼30 mm Hg. Serial cTnI and echocardiographic function were assessed for 24 h, and myocardial tissue was analyzed for apoptosis and necrosis.

RESULTS

PE infusion increased systolic blood pressure from 137 ± 14 mm Hg to 192 ± 11 mm Hg (mean ± SD; p < 0.001) and increased LVEDP from 17 ± 2 mm Hg to 30 ± 5 mm Hg (p < 0.001). Myocardial flow measurements demonstrated no evidence of ischemia. Hemodynamics normalized rapidly after PE, but LV ejection fraction remained depressed (32 ± 21% vs. 58 ± 7%; p < 0.01) with normalization after 24 h (51 ± 16%; p = 0.31). Baseline transcoronary cTnI release was low (16 ± 20 ng/l) but increased to 856 ± 956 ng/l (p = 0.01) 1 h after LVEDP elevation. Circulating cTnI rose above the 99th percentile within 30 min and remained elevated at 24 h (1,462 ± 1,691 ng/l). Pathological analysis demonstrated myocyte apoptosis at 3 h (31.3 ± 11.9 myocytes/cm² vs. 4.6 ± 3.7 myocytes/cm²; p < 0.01), that normalized after 24 h (6.2 ± 5.6 myocytes/cm²; p = 0.46) without histological necrosis.

CONCLUSIONS

Transient elevations of LVEDP lead to cTnI release, apoptosis, and reversible stretch-induced stunning in the absence of ischemia. Thus, preload-induced myocyte injury may explain many cTnI elevations seen in the absence of clinical signs or symptoms of myocardial ischemia.

A Small Peptide Ac-SDKP Inhibits Radiation-Induced Cardiomyopathy

BACKGROUND

Advances in radiotherapy for thoracic cancers have resulted in improvement of survival. However, radiation exposure to the heart can induce cardiotoxicity. No therapy is currently available to inhibit these untoward effects. We examined whether a small tetrapeptide, N-acetyl-Ser-Asp-Lys-Pro (Ac-SDKP), can counteract radiation-induced cardiotoxicity by inhibiting macrophage-dependent inflammatory and fibrotic pathways.

METHODS AND RESULTS

After characterizing a rat model of cardiac irradiation with magnetic resonance imaging protocols, we examined the effects of Ac-SDKP in radiation-induced cardiomyopathy. We treated rats with Ac-SDKP for 18 weeks. We then compared myocardial contractile function and extracellular matrix by cardiac magnetic resonance imaging and the extent of inflammation, fibrosis, and Mac-2 (galectin-3) release by tissue analyses. Because Mac-2 is a crucial macrophage-derived mediator of fibrosis, we performed studies to determine Mac-2 synthesis by macrophages in response to radiation, and change in profibrotic responses by Mac-2 gene depleted cardiac fibroblasts after radiation. Cardiac irradiation diminished myocardial contractile velocities and enhanced extracellular matrix deposition. This was accompanied by macrophage infiltration, fibrosis, cardiomyocyte apoptosis, and cardiac Mac-2 expression. Ac-SDKP strongly inhibited these detrimental effects. Ac-SDKP migrated into the perinuclear cytoplasm of the macrophages and inhibited radiation-induced Mac-2 release. Cardiac fibroblasts lacking the Mac-2 gene showed reduced transforming growth factor β1, collagen I, and collagen III expression after radiation exposure.

CONCLUSIONS

Our study identifies novel cardioprotective effects of Ac-SDKP in a model of cardiac irradiation. These protective effects are exerted by inhibiting inflammation, fibrosis, and reducing macrophage activation. This study shows a therapeutic potential of this endogenously released peptide to counteract radiation-induced cardiomyopathy.

Ameliorating the Fibrotic Remodeling of the Heart through Direct Cardiac Reprogramming

Coronary artery disease is the most common form of cardiovascular diseases, resulting in the loss of cardiomyocytes (CM) at the site of ischemic injury. To compensate for the loss of CMs, cardiac fibroblasts quickly respond to injury and initiate cardiac remodeling in an injured heart. In the remodeling process, cardiac fibroblasts proliferate and differentiate into myofibroblasts, which secrete extracellular matrix to support the intact structure of the heart, and eventually differentiate into matrifibrocytes to form chronic scar tissue. Discovery of direct cardiac reprogramming offers a promising therapeutic strategy to prevent/attenuate this pathologic remodeling and replace the cardiac fibrotic scar with myocardium in situ. Since the first discovery in 2010, many progresses have been made to improve the efficiency and efficacy of reprogramming by understanding the mechanisms and signaling pathways that are activated during direct cardiac reprogramming. Here, we overview the development and recent progresses of direct cardiac reprogramming and discuss future directions in order to translate this promising technology into an effective therapeutic paradigm to reverse cardiac pathological remodeling in an injured heart.

Nonocclusive multivessel intracoronary infusion of allogeneic cardiosphere-derived cells early after reperfusion prevents remote zone myocyte loss and improves global left ventricular function in swine with myocardial infarction

Intracoronary cardiosphere-derived cells (icCDCs) infused into the infarct-related artery reduce scar volume but do not improve left ventricular (LV) ejection fraction (LVEF). We tested the hypothesis that this reflects the inability of regional delivery to prevent myocyte death or promote myocyte proliferation in viable myocardium remote from the infarct. Swine (n = 23) pretreated with oral cyclosporine (200 mg/day) underwent a 1-h left anterior descending coronary artery (LAD) occlusion, which reduced LVEF from 61.6 ± 1.0 to 45.3 ± 1.5% 30 min after reperfusion. At that time, animals received global infusion of allogeneic icCDCs (n = 8), regional infusion of icCDCs restricted to the LAD using the stop-flow technique (n = 8), or vehicle (n = 7). After 1 mo, global icCDCs increased LVEF from 44.8 ± 1.9 to 60.8 ± 3.8% (P < 0.05) with no significant change after LAD stop-flow icCDCs (44.8 ± 3.6 to 50.9 ± 3.1%) or vehicle (46.5 ± 2.5 to 47.7 ± 2.6%). In contrast, global icCDCs did not alter infarct volume (%LV mass) assessed at 2 days (11.2 ± 2.3 vs. 12.6 ± 2.3%), whereas it was reduced after LAD stop-flow icCDCs (7.1 ± 1.1%, P < 0.05). Histopathological analysis of remote myocardium after global icCDCs demonstrated a significant increase in myocyte proliferation (147 ± 32 vs. 14 ± 10 nuclei/10⁶ myocytes, P < 0.05) and a reduction in myocyte apoptosis (15 ± 9 vs. 46 ± 10 nuclei/10⁶ myocytes, P < 0.05) that increased myocyte nuclear density (1,264 ± 39 vs. 1,157 ± 33 nuclei/mm², P < 0.05) and decreased myocyte diameter (13.2 ± 0.2 vs. 14.5 ± 0.3 μm, P < 0.05) compared with vehicle-treated controls. In contrast, remote zone changes after regional LAD icCDCs were no different from vehicle. These data indicate that changes in global LVEF after icCDCs are dependent upon preventing myocyte loss and hypertrophy in myocardium remote from the infarct. These arise from stimulating myocyte proliferation and reducing myocyte apoptosis indicating the importance of directing cell therapy to viable remote regions.NEW & NOTEWORTHY Administration of allogeneic cardiosphere-derived cells to the entire heart via global intracoronary infusion shortly after myocardial infarction favorably influenced left ventricular ejection fraction by preventing myocyte death and promoting myocyte proliferation in remote, noninfarcted myocardium in swine. In contrast, regional intracoronary cell infusion did not significantly affect remote zone myocyte remodeling. Global cell administration targeting viable myocardium remote from the infarct may be an effective approach to prevent adverse ventricular remodeling after myocardial infarction.

The Effects of Periostin in a Rat Model of Isoproterenol: Mediated Cardiotoxicity

Periostin is an extracellular matrix protein from fasciclin family, and it plays an important role in the cell adhesion, migration, and growth of the organism. Periostin prevents apoptosis while stimulating cardiomyocytes. The present study was designed to investigate cardioprotective effects of the recombinant murine periostin peptide administration in a rat model of isoproterenol (ISO)-induced myocardial injury. The experiment was performed on 84 adult male Sprague Dawley rats in 4 groups (n = 21): control group (1), periostin-treated group (2), ISO-treated group (3), and ISO + periostin-treated group (4). The groups were further divided into three subgroups based on the duration of the experiment in which rats were killed on days 1, 7, and 28 (n = 7). Growth factors (VEGF, ANGPT, FGF-2, TGFβ), mitosis and apoptosis (Bcl-2, Bax, PCNA, Ki-67, phospho-histone H3), cell cycle activators and inhibitors (cyclin D1, D2, A2, Cdc2), the origin of regenerating cells (cKit and CD45) mRNA were detected using quantitative real-time polymerase chain reaction (PCR) and PCR array. Immunohistochemistry staining was used to directly detect protein level and distribution in the heart tissues. Administration of periostin following ISO-induced cardiotoxicity revealed that periostin alleviated deleterious effects of ISO through several pathways: (1) periostin induced mitotic activity of endothelial/fibroblastic cells, (2) periostin drives cardiomyocytes into S and M phases, thus promoting proliferation of cardiomyocytes, (3) periostin contributed to collagen degradation, tissue remodeling, and reduced cardiac fibrosis during the healing process following myocardial damage while preserving tissue matrix, (4) periostin stimulated angiogenesis by upregulating THBS1, TGFB2, and HGF genes, (5) periostin regulated cell growth and proliferation while maintaining cell shape and cellular muscle contractions (ACTB) and functioned as chemoattractant factor (CCL2) at the beginning of myocardial damage.

KIT as a therapeutic target for non-oncological diseases

KIT is a receptor tyrosine kinase that after binding to its ligand stem cell factor activates signaling cascades linked to biological processes such as proliferation, differentiation, migration and cell survival. Based on studies performed on SCF and/or KIT mutant animals that presented anemia, sterility, and/or pigmentation disorders, KIT signaling was mainly considered to be involved in the regulation of hematopoiesis, gametogenesis, and melanogenesis. More recently, novel animal models and ameliorated cellular and molecular techniques have led to the discovery of a widen repertoire of tissue compartments and functions that are being modulated by KIT. This is the case for the lung, heart, nervous system, gastrointestinal tract, pancreas, kidney, liver, and bone. For this reason, the tyrosine kinase inhibitors that were originally developed for the treatment of hemato-oncological diseases are being currently investigated for the treatment of non-oncological disorders such as asthma, rheumatoid arthritis, and alzheimer's disease, among others. The beneficial effects of some of these tyrosine kinase inhibitors have been proven to depend on KIT inhibition. This review will focus on KIT expression and regulation in healthy and pathologic conditions other than cancer. Moreover, advances in the development of anti-KIT therapies, including tyrosine kinase inhibitors, and their application will be discussed.

miR-10a rejuvenates aged human mesenchymal stem cells and improves heart function after myocardial infarction through KLF4

Background

Aging is one of the key factors that regulate the function of human bone marrow mesenchymal stem cells (hBM-MSCs) and related changes in microRNA (miRNA) expression. However, data reported on aging-related miRNA changes in hBM-MSCs are limited.

Methods

We demonstrated previously that miR-10a is significantly decreased in aged hBM-MSCs and restoration of the miR-10a level attenuated cell senescence and increased the differentiation capacity of aged hBM-MSCs by repressing Krüpple-like factor 4 (KLF4). In the present study, miR-10a was overexpressed or KLF4 was downregulated in old hBM-MSCs by lentiviral transduction. The hypoxia-induced apoptosis, cell survival, and cell paracrine function of aged hBM-MSCs were investigated in vitro. In vivo, miR-10a-overexpressed or KLF4-downregulated old hBM-MSCs were implanted into infarcted mouse hearts after myocardial infarction (MI). The mouse cardiac function of cardiac angiogenesis was measured and cell survival of aged hBM-MSCs was investigated.

Results

Through lentivirus-mediated upregulation of miR-10a and downregulation of KLF4 in aged hBM-MSCs in vitro, we revealed that miR-10a decreased hypoxia-induced cell apoptosis and increased cell survival of aged hBM-MSCs by repressing the KLF4–BAX/BCL2 pathway. In vivo, transplantation of miR-10a-overexpressed aged hBM-MSCs promoted implanted stem cell survival and improved cardiac function after MI. Mechanistic studies revealed that overexpression of miR-10a in aged hBM-MSCs activated Akt and stimulated the expression of angiogenic factors, thus increasing angiogenesis in ischemic mouse hearts.

Conclusions

miR-10a rejuvenated aged hBM-MSCs which improved angiogenesis and cardiac function in injured mouse hearts.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0895-0) contains supplementary material, which is available to authorized users.

Mesenchymal Stem Cell-Based Therapy for Cardiovascular Disease: Progress and Challenges

Administration of mesenchymal stem cells (MSCs) to diseased hearts improves cardiac function and reduces scar size. These effects occur via the stimulation of endogenous repair mechanisms, including regulation of immune responses, tissue perfusion, inhibition of fibrosis, and proliferation of resident cardiac cells, although rare events of transdifferentiation into cardiomyocytes and vascular components are also described in animal models. While these improvements demonstrate the potential of stem cell therapy, the goal of full cardiac recovery has yet to be realized in either preclinical or clinical studies. To reach this goal, novel cell-based therapeutic approaches are needed. Ongoing studies include cell combinations, incorporation of MSCs into biomaterials, or pre-conditioning or genetic manipulation of MSCs to boost their release of paracrine factors, such as exosomes, growth factors, microRNAs, etc. All of these approaches can augment therapeutic efficacy. Further study of the optimal route of administration, the correct dose, the best cell population(s), and timing for treatment are parameters that still need to be addressed in order to achieve the goal of complete cardiac regeneration. Despite significant progress, many challenges remain.

Stem Cell Therapies in Cardiovascular Disease

Despite considerable advances in medicine, cardiovascular disease is still rising, with ischemic heart disease being the leading cause of death and disability worldwide. Thus extensive efforts are continuing to establish effective therapeutic modalities that would improve both quality of life and survival in this patient population. Novel therapies are being investigated not only to protect the myocardium against ischemia-reperfusion injury but also to regenerate the heart. Stem cell therapy, such as potential use of human mesenchymal stem cells and induced pluripotent stem cells and their exosomes, will make it possible not only to address molecular mechanisms of cardiac conditioning, but also to develop new therapies for ischemic heart disease. Despite the studies and progress made over the last 15 years on the use of stem cell therapy for cardiovascular disease, the efforts are still in their infancy. Even though the expectations have been high, the findings indicate that most of the clinical trials generally have been small and the results inconclusive. Because of many negative findings, there is certain pessimism that cardiac cell therapy is likely to yield any meaningful results over the next decade or so. Similar to other new technologies, early failures are not unusual and they may be followed by impressive success. Nevertheless, there has been considerable attention to safety by the clinical investigators because the adverse events of stem cell therapy have been impressively rare. In summary, although regenerative biology might not help the cardiovascular patient in the near term, it is destined to do so over the next several decades.

Cardiac Stem Cells for Myocardial Regeneration: They Are Not Alone

Heart failure is the number one killer worldwide with ~50% of patients dying within 5 years of prognosis. The discovery of stem cells, which are capable of repairing the damaged portion of the heart, has created a field of cardiac regenerative medicine, which explores various types of stem cells, either autologous or endogenous, in the hope of finding the “holy grail” stem cell candidate to slow down and reverse the disease progression. However, there are many challenges that need to be overcome in the search of such a cell candidate. The ideal cells have to survive the harsh infarcted environment, retain their phenotype upon administration, and engraft and be activated to initiate repair and regeneration in vivo. Early bench and bedside experiments mostly focused on bone marrow-derived cells; however, heart regeneration requires multiple coordinations and interactions between various cell types and the extracellular matrix to form new cardiomyocytes and vasculature. There is an observed trend that when more than one cell is coadministered and cotransplanted into infarcted animal models the degree of regeneration is enhanced, when compared to single-cell administration. This review focuses on stem cell candidates, which have also been tested in human trials, and summarizes findings that explore the interactions between various stem cells in heart regenerative therapy.

Intramyocardial fate and effect of iron nanoparticles co-injected with MACS® purified stem cell products

BACKGROUND

Magnetic activated cell sorting (MACS^®) is routinely used to isolate stem cell subpopulations intended for the treatment of cardiovascular diseases. In strong contrast, studies examining the amount, effect and intramyocardial distribution of iron nanoparticles used for magnetic cell labelling are missing, although iron excess can cause functional disorders in the heart.

METHODS AND RESULTS

CD133⁺ haematopoietic and CD271⁺ mesenchymal stem cells were purified from bone marrow using automatically and manually MACS^® based systems. Flow cytometric measurements demonstrated a rapid loss of MACS^® MicroBeads from cells under culture conditions, while storage under hypothermic conditions decelerated their detachment. Moreover, an average loading of ∼11 fg iron/cell caused by magnetic labelling was determined in magnetic particle spectroscopy. Importantly, hemodynamic measurements as well as histological examinations using a myocardial ischemia/reperfusion mouse model showed no influence of MACS^® MicroBeads on cardiac regeneration, while the transplantation of stem cells caused a significant improvement. Furthermore, immunostainings demonstrated the clearance of co-injected iron nanoparticles from stem cells and the surrounding heart tissue within 48 h post transplantation.

CONCLUSIONS

Our results indicate that iron amounts typically co-injected with MACS^® purified stem cells do not harm cardiac functions and are cleared from heart tissue within a few hours. Therefore, we conclude that MACS^® MicroBeads exhibit a good compatibility in the cardiac environment.

Therapeutic Application of Adult Stem Cells in the Heart

Cell therapies have been explored as a potential treatment avenue to treat heart diseases, such as myocardial infarction, doxorubicin-induced cardiomyopathy, and heart failure. Embryonic and adult stem cells (ASCs) have been examined in animal and clinical settings. Unlike embryonic and induced pluripotent stem cells, ASCs do not pose a threat to form teratomas, nor do they have immune system concerns, making them ideal for therapeutic use in humans. In this review, we will investigate different characteristics and sources of adult stem cells and progenitor cells, as well as determine their efficacy in cell transplantation in experimental and clinical trials. In addition, we will propose other research avenues that may promote further understanding and use of ASCs in therapeutic designs.

Heart-Derived Stem Cells in Miniature Swine with Coronary Microembolization: Novel Ischemic Cardiomyopathy Model to Assess the Efficacy of Cell-Based Therapy

A major problem in translating stem cell therapeutics is the difficulty of producing stable, long-term severe left ventricular (LV) dysfunction in a large animal model. For that purpose, extensive infarction was created in sinclair miniswine by injecting microspheres (1.5 × 10⁶ microspheres, 45 μm diameter) in LAD. At 2 months after embolization, animals (n = 11) were randomized to receive allogeneic cardiosphere-derived cells derived from atrium (CDCs: 20 × 10⁶, n = 5) or saline (untreated, n = 6). Four weeks after therapy myocardial function, myocyte proliferation (Ki67), mitosis (phosphor-Histone H3; pHH3), apoptosis, infarct size (TTC), myocyte nuclear density, and cell size were evaluated. CDCs injected into infarcted and remodeled remote myocardium (global infusion) increased regional function and global function contrasting no change in untreated animals. CDCs reduced infarct volume and stimulated Ki67 and pHH3 positive myocytes in infarct and remote regions. As a result, myocyte number (nuclear density) increased and myocyte cell diameter decreased in both infarct and remote regions. Coronary microembolization produces stable long-term ischemic cardiomyopathy. Global infusion of CDCs stimulates myocyte regeneration and improves left ventricular ejection fraction. Thus, global infusion of CDCs could become a new therapy to reverse LV dysfunction in patients with asymptomatic heart failure.

Stimulatory Effects of Mesenchymal Stem Cells on cKit+ Cardiac Stem Cells Are Mediated by SDF1/CXCR4 and SCF/cKit Signaling Pathways

RATIONALE

Culture-expanded cells originating from cardiac tissue that express the cell surface receptor cKit are undergoing clinical testing as a cell source for heart failure and congenital heart disease. Although accumulating data support that mesenchymal stem cells (MSCs) enhance the efficacy of cardiac cKit(+) cells (CSCs), the underlying mechanism for this synergistic effect remains incompletely understood.

OBJECTIVE

To test the hypothesis that MSCs stimulate endogenous CSCs to proliferate, migrate, and differentiate via the SDF1/CXCR4 and stem cell factor/cKit pathways.

METHODS AND RESULTS

Using genetic lineage-tracing approaches, we show that in the postnatal murine heart, cKit(+) cells proliferate, migrate, and form cardiomyocytes, but not endothelial cells. CSCs exhibit marked chemotactic and proliferative responses when cocultured with MSCs but not with cardiac stromal cells. Antagonism of the CXCR4 pathway with AMD3100 (an SDF1/CXCR4 antagonist) inhibited MSC-induced CSC chemotaxis but stimulated CSC cardiomyogenesis (P<0.0001). Furthermore, MSCs enhanced CSC proliferation via the stem cell factor/cKit and SDF1/CXCR4 pathways (P<0.0001).

CONCLUSIONS

Together these findings show that MSCs exhibit profound, yet differential, effects on CSC migration, proliferation, and differentiation and suggest a mechanism underlying the improved cardiac regeneration associated with combination therapy using CSCs and MSCs. These findings have important therapeutic implications for cell-based therapy strategies that use mixtures of CSCs and MSCs.

Rebuilding the Damaged Heart: Mesenchymal Stem Cells, Cell-Based Therapy, and Engineered Heart Tissue

Mesenchymal stem cells (MSCs) are broadly distributed cells that retain postnatal capacity for self-renewal and multilineage differentiation. MSCs evade immune detection, secrete an array of anti-inflammatory and anti-fibrotic mediators, and very importantly activate resident precursors. These properties form the basis for the strategy of clinical application of cell-based therapeutics for inflammatory and fibrotic conditions. In cardiovascular medicine, administration of autologous or allogeneic MSCs in patients with ischemic and nonischemic cardiomyopathy holds significant promise. Numerous preclinical studies of ischemic and nonischemic cardiomyopathy employing MSC-based therapy have demonstrated that the properties of reducing fibrosis, stimulating angiogenesis, and cardiomyogenesis have led to improvements in the structure and function of remodeled ventricles. Further attempts have been made to augment MSCs' effects through genetic modification and cell preconditioning. Progression of MSC therapy to early clinical trials has supported their role in improving cardiac structure and function, functional capacity, and patient quality of life. Emerging data have supported larger clinical trials that have been either completed or are currently underway. Mechanistically, MSC therapy is thought to benefit the heart by stimulating innate anti-fibrotic and regenerative responses. The mechanisms of action involve paracrine signaling, cell-cell interactions, and fusion with resident cells. Trans-differentiation of MSCs to bona fide cardiomyocytes and coronary vessels is also thought to occur, although at a nonphysiological level. Recently, MSC-based tissue engineering for cardiovascular disease has been examined with quite encouraging results. This review discusses MSCs from their basic biological characteristics to their role as a promising therapeutic strategy for clinical cardiovascular disease.

Murine Models Demonstrate Distinct Vasculogenic and Cardiomyogenic cKit+ Lineages in the Heart

After 2 recent genetic studies in mice addressing the developmental origins and regenerative activity of cardiac cKit+ cells, 2 additional reports by Sultana et al and Liu et al provide further information on the expression of cKit in the embryonic and adult hearts. Here, we synthesize the findings from the 4 distinct cKit models to gain insights into the biology of this important cell type.

Enhanced cell survival and paracrine effects of mesenchymal stem cells overexpressing hepatocyte growth factor promote cardioprotection in myocardial infarction

Poor cell survival post transplantation compromises the therapeutic benefits of mesenchymal stem cells (MSCs) in myocardial infarction (MI). Hepatocyte growth factor (HGF) is an important cytokine for angiogenesis, anti-inflammation and anti-apoptosis. This study aimed to evaluate the cardioprotective effects of MSCs overexpressing HGF in a mouse model of MI. The apoptosis of umbilical cord-derived MSCs (UC-MSCs) and HGF-UC-MSCs under normoxic and hypoxic conditions was detected. The conditioned medium (CdM) of UC-MSCs and HGF-UC-MSCs under a hypoxic condition was harvested and its protective effect on neonatal cardiomyocytes (NCMs) exposed to a hypoxic challenge was examined. UC-MSCs and HGF-UC-MSCs were transplanted into the peri-infarct region in mice following MI and heart function assessed 4 weeks post transplantation. The apoptosis of HGF-UC-MSCs under hypoxic conditions was markedly decreased compared with that of UC-MSCs. NCMs treated with HGF-UC-MSC hypoxic CdM (HGF-UC-MSCs-hy-CdM) exhibited less cell apoptosis in response to hypoxic challenge than those treated with UC-MSC hypoxic CdM (UC-MSCs-hy-CdM). HGF-UC-MSCs-hy-CdM released the inhibited p-Akt and lowered the enhanced ratio of Bax/Bcl-2 induced by hypoxia in the NCMs. HGF-UC-MSCs-hy-CdM expressed higher levels of HGF, EGF, bFGF and VEGF than UC-MSCs-hy-CdM. Transplantation of HGF-UC-MSCs or UC-MSCs greatly improved heart function in the mouse model of MI. Compared with UC-MSCs, transplantation of HGF-UC-MSCs was associated with less cardiomyocyte apoptosis, enhanced angiogenesis and increased proliferation of cardiomyocytes. This study may provide a novel therapeutic strategy for MSC-based therapy in cardiovascular disease.

Intracoronary delivery of self-assembling heart-derived microtissues (cardiospheres) for prevention of adverse remodeling in a pig model of convalescent myocardial infarction

BACKGROUND

Preclinical studies in rodents and pigs indicate that the self-assembling microtissues known as cardiospheres may be more effective than dispersed cardiosphere-derived cells. However, the more desirable intracoronary route has been assumed to be unsafe for cardiosphere delivery: Cardiospheres are large (30-150 μm), raising concerns about likely microembolization. We questioned these negative assumptions by evaluating the safety and efficacy of optimized intracoronary delivery of cardiospheres in a porcine model of convalescent myocardial infarction.

METHODS AND RESULTS

First, we standardized the size of cardiospheres by modifying culture conditions. Then, dosage was determined by infusing escalating doses of cardiospheres in the left anterior descending artery of naive pigs, looking for acute adverse effects. Finally, in a randomized efficacy study, 14 minipigs received allogeneic cardiospheres (1.3 × 10(6)) or vehicle 1 month after myocardial infarction. Animals underwent magnetic resonance imaging before infusion and 1 month later to assess left ventricular ejection fraction, scar mass, and viable mass. In the dosing study, we did not observe any evidence of microembolization after cardiosphere infusion. In the post-myocardial infarction study, cardiospheres preserved LV function, reduced scar mass and increased viable mass, whereas placebo did not. Moreover, cardiosphere decreased collagen content, and increased vessel densities and myocardial perfusion. Importantly, intracoronary cardiospheres decreased left ventricular end-diastolic pressure and increased cardiac output.

CONCLUSIONS

Intracoronary delivery of cardiospheres is safe. Intracoronary cardiospheres are also remarkably effective in decreasing scar, halting adverse remodeling, increasing myocardial perfusion, and improving hemodynamic status after myocardial infarction in pigs. Thus, cardiospheres may be viable therapeutic candidates for intracoronary infusion in selected myocardial disorders.

Lung Regeneration: Endogenous and Exogenous Stem Cell Mediated Therapeutic Approaches

The tissue turnover of unperturbed adult lung is remarkably slow. However, after injury or insult, a specialised group of facultative lung progenitors become activated to replenish damaged tissue through a reparative process called regeneration. Disruption in this process results in healing by fibrosis causing aberrant lung remodelling and organ dysfunction. Post-insult failure of regeneration leads to various incurable lung diseases including chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis. Therefore, identification of true endogenous lung progenitors/stem cells, and their regenerative pathway are crucial for next-generation therapeutic development. Recent studies provide exciting and novel insights into postnatal lung development and post-injury lung regeneration by native lung progenitors. Furthermore, exogenous application of bone marrow stem cells, embryonic stem cells and inducible pluripotent stem cells (iPSC) show evidences of their regenerative capacity in the repair of injured and diseased lungs. With the advent of modern tissue engineering techniques, whole lung regeneration in the lab using de-cellularised tissue scaffold and stem cells is now becoming reality. In this review, we will highlight the advancement of our understanding in lung regeneration and development of stem cell mediated therapeutic strategies in combating incurable lung diseases.

Translational research of adult stem cell therapy

Congestive heart failure (CHF) secondary to chronic coronary artery disease is a major cause of morbidity and mortality world-wide. Its prevalence is increasing despite advances in medical and device therapies. Cell based therapies generating new cardiomyocytes and vessels have emerged as a promising treatment to reverse functional deterioration and prevent the progression to CHF. Functional efficacy of progenitor cells isolated from the bone marrow and the heart have been evaluated in preclinical large animal models. Furthermore, several clinical trials using autologous and allogeneic stem cells and progenitor cells have demonstrated their safety in humans yet their clinical relevance is inconclusive. This review will discuss the clinical therapeutic applications of three specific adult stem cells that have shown particularly promising regenerative effects in preclinical studies, bone marrow derived mesenchymal stem cell, heart derived cardiosphere-derived cell and cardiac stem cell. We will also discuss future therapeutic approaches.

Myocardial infarction: stem cell transplantation for cardiac regeneration

It is estimated that by 2030, almost 23.6 million people will perish from cardiovascular disease, according to the WHO. The review discusses advances in stem cell therapy for myocardial infarction, including cell sources, methods of differentiation, expansion selection and their route of delivery. Skeletal muscle cells, hematopoietic cells and mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs)-derived cardiomyocytes have advanced to the clinical stage, while induced pluripotent cells (iPSCs) are yet to be considered clinically. Delivery of cells to the sites of injury and their subsequent retention is a major issue. The development of supportive scaffold matrices to facilitate stem cell retention and differentiation are analyzed. The review outlines clinical translation of conjugate stem cell-based cellular therapeutics post-myocardial infarction.

Cell surface glycoengineering improves selectin-mediated adhesion of mesenchymal stem cells (MSCs) and cardiosphere-derived cells (CDCs): Pilot validation in porcine ischemia-reperfusion model

Promising results are emerging in clinical trials focused on stem cell therapy for cardiology applications. However, the low homing and engraftment of the injected cells to target tissue continues to be a problem. Cellular glycoengineering can address this limitation by enabling the targeting of stem cells to sites of vascular injury/inflammation. Two such glycoengineering methods are presented here: i. The non-covalent incorporation of a P-selectin glycoprotein ligand-1 (PSGL-1) mimetic 19Fc[FUT7(+)] via lipid-protein G fusion intermediates that intercalate onto the cell surface, and ii. Over-expression of the α(1,3)fucosyltransferse FUT7 in cells. Results demonstrate the efficient coupling of 19Fc[FUT7(+)] onto both cardiosphere-derived cells (CDCs) and mesenchymal stem cells (MSCs), with coupling being more efficient when using protein G fused to single-tailed palmitic acid rather than double-tailed DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine). This non-covalent cellular modification was mild since cell proliferation and stem-cell marker expression was unaltered. Whereas coupling using 19Fc[FUT7(+)] enhanced cell capture on recombinant P-selectin or CHO-P cell surfaces, α(1,3)fucosylation was necessary for robust binding to E-selectin and inflamed endothelial cells under shear. Pilot studies confirm the safety and homing efficacy of the modified stem cells to sites of ischemia-reperfusion in the porcine heart. Overall, glycoengineering with physiological selectin-ligands may enhance stem cell engraftment.

Comparative Efficacy of Intracoronary Allogeneic Mesenchymal Stem Cells and Cardiosphere-Derived Cells in Swine with Hibernating Myocardium

RATIONALE

Allogeneic bone marrow-derived mesenchymal stem cells (MSCs) and cardiosphere-derived cells (CDCs) have each entered clinical trials, but a direct comparison of these cell types has not been performed in a large animal model of hibernating myocardium.

OBJECTIVE

Using completely blinded methodology, we compared the efficacy of global intracoronary allogeneic MSCs (icMSCs, ≈35×10(6)) and CDCs (icCDCs, ≈35×10(6)) versus vehicle in cyclosporine-immunosuppressed swine with a chronic left anterior descending coronary artery stenosis (n=26).

METHODS AND RESULTS

Studies began 3 months after instrumentation when wall thickening was reduced (left anterior descending coronary artery % wall thickening [mean±SD], 38±11% versus 83±26% in remote; P<0.01) and similar among groups. Four weeks after treatment, left anterior descending coronary artery % wall thickening increased similarly after icCDCs and icMSCs, whereas it remained depressed in vehicle-treated controls (icMSCs, 51±13%; icCDCs, 51±17%; vehicle, 34±3%, treatments P<0.05 versus vehicle). There was no change in myocardial perfusion. Both icMSCs and icCDCs increased left anterior descending coronary artery myocyte nuclear density (icMSCs, 1601±279 nuclei/mm(2); icCDCs, 1569±294 nuclei/mm(2); vehicle, 973±181 nuclei/mm(2); treatments P<0.05 versus vehicle) and reduced myocyte diameter (icMSCs, 16.4±1.5 μm; icCDCs, 16.8±1.2 μm; vehicle, 20.2±3.7 μm; treatments P<0.05 versus vehicle) to the same extent. Similar changes in myocyte nuclear density and diameter were observed in the remote region of cell-treated animals. Cell fate analysis using Y-chromosome fluorescent in situ hybridization demonstrated rare cells from sex-mismatched donors.

CONCLUSIONS

Allogeneic icMSCs and icCDCs exhibit comparable therapeutic efficacy in a large animal model of hibernating myocardium. Both cell types produced equivalent increases in regional function and stimulated myocyte regeneration in ischemic and remote myocardium. The activation of endogenous myocyte proliferation and regression of myocyte cellular hypertrophy support a common mechanism of cardiac repair.

Use of mesenchymal stem cells for therapy of cardiac disease

Despite substantial clinical advances over the past 65 years, cardiovascular disease remains the leading cause of death in America. The past 15 years has witnessed major basic and translational interest in the use of stem and precursor cells as a therapeutic agent for chronically injured organs. Among the cell types under investigation, adult mesenchymal stem cells are widely studied, and in early stage, clinical studies show promise for repair and regeneration of cardiac tissues. The ability of mesenchymal stem cells to differentiate into mesoderm- and nonmesoderm-derived tissues, their immunomodulatory effects, their availability, and their key role in maintaining and replenishing endogenous stem cell niches have rendered them one of the most heavily investigated and clinically tested type of stem cell. Accumulating data from preclinical and early phase clinical trials document their safety when delivered as either autologous or allogeneic forms in a range of cardiovascular diseases, but also importantly define parameters of clinical efficacy that justify further investigation in larger clinical trials. Here, we review the biology of mesenchymal stem cells, their interaction with endogenous molecular and cellular pathways, and their modulation of immune responses. Additionally, we discuss factors that enhance their proliferative and regenerative ability and factors that may hinder their effectiveness in the clinical setting.

High density lipoprotein promotes proliferation of adipose-derived stem cells via S1P1 receptor and Akt, ERK1/2 signal pathways

INTRODUCTION

Adipose-derived stem cells (ADSC) are non-hematopoietic mesenchymal stem cells that have shown great promise in their ability to differentiate into multiple cell lineages. Their ubiquitous nature and the ease of harvesting have attracted the attention of many researchers, and they pose as an ideal candidate for applications in regenerative medicine. Several reports have demonstrated that transplanting ADSC can promote repair of injured tissue and angiogenesis in animal models. Survival of these cells after transplant remains a key limiting factor for the success of ADSC transplantation. Circulating factors like High Density Lipoprotein (HDL) has been known to promote survival of other stems cells like bone marrow derived stem cells and endothelial progenitor cells, both by proliferation and by inhibiting cell apoptosis. The effect of HDL on transplanted adipose-derived stem cells in vivo is largely unknown.

METHODS

This study focused on exploring the effects of plasma HDL on ADSC and delineating the mechanisms involved in their proliferation after entering the bloodstream. Using the MTT and BrdU assays, we tested the effects of HDL on ADSC proliferation. We probed the downstream intracellular Akt and ERK1/2 signaling pathways and expression of cyclin proteins in ADSC using western blot.

RESULTS

Our study found that HDL promotes proliferation of ADSC, by binding to sphingosine-1- phosphate receptor-1(S1P1) on the cell membrane. This interaction led to activation of intracellular Akt and ERK1/2 signaling pathways, resulting in increased expression of cyclin D1 and cyclin E, and simultaneous reduction in expression of cyclin-dependent kinase inhibitors p21 and p27, therefore promoting cell cycle progression and cell proliferation.

CONCLUSIONS

These studies raise the possibility that HDL may be a physiologic regulator of stem cells and increasing HDL concentrations may be valuable strategy to promote ADSC transplantation.

c-Kit+ progenitors generate vascular cells for tissue-engineered grafts through modulation of the Wnt/Klf4 pathway

The development of decellularised scaffolds for small diameter vascular grafts is hampered by their limited patency, due to the lack of luminal cell coverage by endothelial cells (EC) and to the low tone of the vessel due to absence of a contractile smooth muscle cells (SMC). In this study, we identify a population of vascular progenitor c-Kit+/Sca-1- cells available in large numbers and derived from immuno-privileged embryonic stem cells (ESCs). We also define an efficient and controlled differentiation protocol yielding fully to differentiated ECs and SMCs in sufficient numbers to allow the repopulation of a tissue engineered vascular graft. When seeded ex vivo on a decellularised vessel, c-Kit+/Sca-1-derived cells recapitulated the native vessel structure and upon in vivo implantation in the mouse, markedly reduced neointima formation and mortality, restoring functional vascularisation. We showed that Krüppel-like transcription factor 4 (Klf4) regulates the choice of differentiation pathway of these cells through β-catenin activation and was itself regulated by the canonical Wnt pathway activator lithium chloride. Our data show that ESC-derived c-Kit+/Sca-1-cells can be differentiated through a Klf4/β-catenin dependent pathway and are a suitable source of vascular progenitors for the creation of superior tissue-engineered vessels from decellularised scaffolds.

Safety of intracoronary infusion of 20 million C-kit positive human cardiac stem cells in pigs

Background

There is mounting interest in using c-kit positive human cardiac stem cells (c-kit^pos hCSCs) to repair infarcted myocardium in patients with ischemic cardiomyopathy. A recent phase I clinical trial (SCIPIO) has shown that intracoronary infusion of 1 million hCSCs is safe. Higher doses of CSCs may provide superior reparative ability; however, it is unknown if doses >1 million cells are safe. To address this issue, we examined the effects of 20 million hCSCs in pigs.

Methods

Right atrial appendage samples were obtained from patients undergoing cardiac surgery. The tissue was processed by an established protocol with eventual immunomagnetic sorting to obtain in vitro expanded hCSCs. A cumulative dose of 20 million cells was given intracoronarily to pigs without stop flow. Safety was assessed by measurement of serial biomarkers (cardiac: troponin I and CK-MB, renal: creatinine and BUN, and hepatic: AST, ALT, and alkaline phosphatase) and echocardiography pre- and post-infusion. hCSC retention 30 days after infusion was quantified by PCR for human genomic DNA. All personnel were blinded as to group assignment.

Results

Compared with vehicle-treated controls (n=5), pigs that received 20 million hCSCs (n=9) showed no significant change in cardiac function or end organ damage (assessed by organ specific biomarkers) that could be attributed to hCSCs (P>0.05 in all cases). No hCSCs could be detected in left ventricular samples 30 days after infusion.

Conclusions

Intracoronary infusion of 20 million c-kit positive hCSCs in pigs (equivalent to ~40 million hCSCs in humans) does not cause acute cardiac injury, impairment of cardiac function, or liver and renal injury. These results have immediate translational value and lay the groundwork for using doses of CSCs >1 million in future clinical trials. Further studies are needed to ascertain whether administration of >1 million hCSCs is associated with greater efficacy in patients with ischemic cardiomyopathy.

Revascularization of chronic hibernating myocardium stimulates myocyte proliferation and partially reverses chronic adaptations to ischemia

BACKGROUND

The time course and extent of recovery after revascularization of viable dysfunctional myocardium are variable. Although fibrosis is a major determinant, myocyte structural and molecular remodeling may also play important roles.

OBJECTIVES

This study sought to determine whether persistent myocyte loss and/or irreversibility of protein changes that develop in hibernating myocardium have an impact on functional recovery in the absence of infarction.

METHODS

Swine implanted with a chronic left anterior descending artery (LAD) stenosis to produce hibernating myocardium underwent percutaneous revascularization, with serial functional recovery evaluated for 1 month (n = 12). Myocardial tissue was evaluated to assess myocyte size, nuclear density, and proliferation indexes in comparison with those of normal animals and nonrevascularized controls. Proteomic analysis by 2-dimensional differential in-gel electrophoresis was used to determine the reversibility of molecular adaptations of hibernating myocytes.

RESULTS

At 3 months, physiological features of hibernating myocardium were confirmed, with depressed LAD wall thickening and no significant infarction. Revascularization normalized LAD flow reserve, with no immediate change in LAD wall thickening. Regional LAD wall thickening slowly improved but remained depressed 1 month post-percutaneous coronary intervention. Surprisingly, revascularization was associated with histological evidence of myocytes re-entering the growth phase of the cell cycle and increases in the number of c-Kit(+) cells. Myocyte nuclear density returned to normal, whereas regional myocyte hypertrophy regressed. Proteomic analysis demonstrated heterogeneous effects of revascularization. Up-regulated stress and cytoskeletal proteins normalized, whereas reduced contractile and metabolic proteins persisted.

CONCLUSIONS

Delayed recovery of hibernating myocardium in the absence of scar may reflect persistent reductions in the amounts of contractile and metabolic proteins. Although revascularization appeared to stimulate myocyte proliferation, the persistence of small immature myocytes may have contributed to delayed functional recovery.

Allogeneic cardiospheres delivered via percutaneous transendocardial injection increase viable myocardium, decrease scar size, and attenuate cardiac dilatation in porcine ischemic cardiomyopathy

BACKGROUND

Epicardial injection of heart-derived cell products is safe and effective post-myocardial infarction (MI), but clinically-translatable transendocardial injection has never been evaluated. We sought to assess the feasibility, safety and efficacy of percutaneous transendocardial injection of heart-derived cells in porcine chronic ischemic cardiomyopathy.

METHODS AND RESULTS

We studied a total of 89 minipigs; 63 completed the specified protocols. After NOGA-guided transendocardial injection, we quantified engraftment of escalating doses of allogeneic cardiospheres or cardiosphere-derived cells in minipigs (n = 22) post-MI. Next, a dose-ranging, blinded, randomized, placebo-controlled ("dose optimization") study of transendocardial injection of the better-engrafting product was performed in infarcted minipigs (n = 16). Finally, the superior product and dose (150 million cardiospheres) were tested in a blinded, randomized, placebo-controlled ("pivotal") study (n = 22). Contrast-enhanced cardiac MRI revealed that all cardiosphere doses preserved systolic function and attenuated remodeling. The maximum feasible dose (150 million cells) was most effective in reducing scar size, increasing viable myocardium and improving ejection fraction. In the pivotal study, eight weeks post-injection, histopathology demonstrated no excess inflammation, and no myocyte hypertrophy, in treated minipigs versus controls. No alloreactive donor-specific antibodies developed over time. MRI showed reduced scar size, increased viable mass, and attenuation of cardiac dilatation with no effect on ejection fraction in the treated group compared to placebo.

CONCLUSIONS

Dose-optimized injection of allogeneic cardiospheres is safe, decreases scar size, increases viable myocardium, and attenuates cardiac dilatation in porcine chronic ischemic cardiomyopathy. The decreases in scar size, mirrored by increases in viable myocardium, are consistent with therapeutic regeneration.

Global intracoronary infusion of allogeneic cardiosphere-derived cells improves ventricular function and stimulates endogenous myocyte regeneration throughout the heart in swine with hibernating myocardium

Background

Cardiosphere-derived cells (CDCs) improve ventricular function and reduce fibrotic volume when administered via an infarct-related artery using the “stop-flow” technique. Unfortunately, myocyte loss and dysfunction occur globally in many patients with ischemic and non-ischemic cardiomyopathy, necessitating an approach to distribute CDCs throughout the entire heart. We therefore determined whether global intracoronary infusion of CDCs under continuous flow improves contractile function and stimulates new myocyte formation.

Methods and Results

Swine with hibernating myocardium from a chronic LAD occlusion were studied 3-months after instrumentation (n = 25). CDCs isolated from myocardial biopsies were infused into each major coronary artery (∼33×10⁶ icCDCs). Global icCDC infusion was safe and while ∼3% of injected CDCs were retained, they did not affect ventricular function or myocyte proliferation in normal animals. In contrast, four-weeks after icCDCs were administered to animals with hibernating myocardium, %LADWT increased from 23±6 to 51±5% (p<0.01). In diseased hearts, myocyte proliferation (phospho-histone-H3) increased in hibernating and remote regions with a concomitant increase in myocyte nuclear density. These effects were accompanied by reductions in myocyte diameter consistent with new myocyte formation. Only rare myocytes arose from sex-mismatched donor CDCs.

Conclusions

Global icCDC infusion under continuous flow is feasible and improves contractile function, regresses myocyte cellular hypertrophy and increases myocyte proliferation in diseased but not normal hearts. New myocytes arising via differentiation of injected cells are rare, implicating stimulation of endogenous myocyte regeneration as the primary mechanism of repair.

Intracoronary infusion of encapsulated glucagon-like peptide-1-eluting mesenchymal stem cells preserves left ventricular function in a porcine model of acute myocardial infarction

BACKGROUND

Engraftment and survival of stem cells in the infarcted myocardium remain problematic in cell-based therapy for cardiovascular disease. To overcome these issues, encapsulated mesenchymal stem cells (eMSCs) were developed that were transfected to produce glucagon-like peptide-1, an incretin hormone with known cardioprotective effects, alongside MSC endogenous paracrine factors. This study was designed to investigate the efficacy of different doses of intracoronary infusion of eMSC in a porcine model of acute myocardial infarction (AMI).

METHODS AND RESULTS

One hundred pigs were subjected to a moderate AMI (posterolateral AMI; n=50) or a severe AMI (anterior AMI; n=50), whereupon surviving animals (n=36 moderate, n=33 severe) were randomized to receive either intracoronary infusion of 3 incremental doses of eMSC or Ringers' lactate control. Cardiac function was assessed using invasive hemodynamics, echocardiography, and histological analysis. A trend was observed in the moderate AMI model, whereas in the severe AMI model, left ventricular ejection fraction improved by +9.3% (P=0.004) in the best responding eMSC group, because of a preservation of left ventricular end-systolic volume. Arteriolar density increased 3-fold in the infarct area (8.4±0.9/mm(2) in controls versus 22.2±2.6/mm(2) in eMSC group; P<0.001). Although not statistically significant, capillary density was 30% higher in the border zone (908.1±99.7/mm(2) in control versus 1209.0±64.6/mm(2) in eMSC group; P=ns).

CONCLUSIONS

eMSCs enable sustained local delivery of cardioprotective proteins to the heart, thereby enhancing angiogenesis and preserving contractile function in an animal AMI model.

Complement component 3 is necessary to preserve myocardium and myocardial function in chronic myocardial infarction

Activation of the complement cascade (CC) with myocardial infarction (MI) acutely initiates immune cell infiltration, membrane attack complex formation on injured myocytes, and exacerbates myocardial injury. Recent studies implicate the CC in mobilization of stem/progenitor cells and tissue regeneration. Its role in chronic MI is unknown. Here, we consider complement component C3, in the chronic response to MI. C3 knockout (KO) mice were studied after permanent coronary artery ligation. C3 deficiency exacerbated myocardial dysfunction 28 days after MI compared to WT with further impaired systolic function and LV dilation despite similar infarct size 24 hours post-MI. Morphometric analysis 28 days post-MI showed C3 KO mice had more scar tissue with less viable myocardium within the infarct zone which correlated with decreased c-kit(pos) cardiac stem/progenitor cells (CPSC), decreased proliferating Ki67(pos) CSPCs and decreased formation of new BrdU(pos) /α-sarcomeric actin(pos) myocytes, and increased apoptosis compared to WT. Decreased CSPCs and increased apoptosis were evident 7 days post-MI in C3 KO hearts. The inflammatory response with MI was attenuated in the C3 KO and was accompanied by attenuated hematopoietic, pluripotent, and cardiac stem/progenitor cell mobilization into the peripheral blood 72 hours post-MI. These results are the first to demonstrate that CC, through C3, contributes to myocardial preservation and regeneration in response to chronic MI. Responses in the C3 KO infer that C3 activation in response to MI expands the resident CSPC population, increases new myocyte formation, increases and preserves myocardium, inflammatory response, and bone marrow stem/progenitor cell mobilization to preserve myocardial function.

Enhancing the efficacy of mesenchymal stem cell therapy

Mesenchymal stem cell (MSC) therapy is entering a challenging phase after completion of many preclinical and clinical trials. Among the major hurdles encountered in MSC therapy are inconsistent stem cell potency, poor cell engraftment and survival, and age/disease-related host tissue impairment. The recognition that MSCs primarily mediate therapeutic benefits through paracrine mechanisms independent of cell differentiation provides a promising framework for enhancing stem cell potency and therapeutic benefits. Several MSC priming approaches are highlighted, which will likely allow us to harness the full potential of adult stem cells for their future routine clinical use.