Stem Cells For Myocardial Repair Research Articles

Conductive single-wall carbon nanotubes/extracellular matrix hybrid hydrogels promote the lineage-specific development of seeding cells for tissue repair through reconstructing an integrin-dependent niche

BackgroundThe niche of tissue development in vivo involves the growth matrix, biophysical cues and cell-cell interactions. Although natural extracellular matrixes may provide good supporting for seeding cells in vitro, it is evitable to destroy biophysical cues during decellularization. Reconstructing the bioactivities of extracellular matrix-based scaffolds is essential for their usage in tissue repair.ResultsIn the study, a hybrid hydrogel was developed by incorporating single-wall carbon nanotubes (SWCNTs) into heart-derived extracellular matrixes. Interestingly, insoluble SWCNTs were well dispersed in hybrid hydrogel solution via the interaction with extracellular matrix proteins. Importantly, an augmented integrin-dependent niche was reconstructed in the hybrid hydrogel, which could work like biophysical cues to activate integrin-related pathway of seeding cells. As supporting scaffolds in vitro, the hybrid hydrogels were observed to significantly promote seeding cell adhesion, differentiation, as well as structural and functional development towards mature cardiac tissues. As injectable carrier scaffolds in vivo, the hybrid hydrogels were then used to delivery stem cells for myocardial repair in rats. Similarly, significantly enhanced cardiac differentiation and maturation(12.5 ± 2.3% VS 32.8 ± 5%) of stem cells were detected in vivo, resulting in improved myocardial regeneration and repair.ConclusionsThe study represented a simple and powerful approach for exploring bioactive scaffold to promote stem cell-based tissue repair.Graphic abstract

NGF nanoparticles enhance the potency of transplanted human umbilical cord mesenchymal stem cells for myocardial repair.

In this study, we investigated whether human umbilical cord mesenchymal stem cell (hUCMSC) fibrin patches loaded with nerve growth factor (NGF) poly(lactic-co-glycolic acid) (PLGA) nanoparticles could enhance the therapeutic potency of hUCMSCs for myocardial infarction (MI). In vitro, NGF significantly improved the proliferation of hUCMSCs and mitigated cytotoxicity and apoptosis under hypoxic injury. NGF also promoted the paracrine effects of hUCMSCs on angiogenesis and cardiomyocyte protection. The tyrosine kinase A (TrkA) and phosphoinositide 3-kinase (PI3K)-serine/threonine protein kinase (Akt) signaling pathways in hUCMSCs were involved in the NGF-induced protection. NGF PLGA nanoparticles continued to release NGF for at least 1 mo and also exerted a protective effect on hUCMSCs, the same with free NGF. In vivo, we treated MI mice with nothing (MI group), a cell-free fibrin patch with blank PLGA nanoparticles (MI + OP group), a cell-free fibrin patch with NGF nanoparticles (MI + NGF group), and hUCMSC fibrin patches with blank PLGA nanoparticles (MI + MSC group) or NGF PLGA nanoparticles (MSC + NGF group). Among these groups, the MSC + NGF group exhibited the best cardiac contractile function, the smallest infarct size, and the thickest ventricular wall. The application of NGF PLGA nanoparticles significantly improved the retention of transplanted hUCMSCs and enhanced their ability to reduce myocardial apoptosis and promote angiogenesis in the mouse heart after MI. These findings demonstrate the promising therapeutic potential of hUCMSC fibrin cardiac patches loaded with NGF PLGA nanoparticles.NEW & NOTEWORTHY NGF PLGA nanoparticles can exert a protective effect on hUCMSCs and promote the paracrine effects of hUCMSCs on angiogenesis and cardiomyocyte protection through TrkA-PI3K/Akt signaling pathway, the same with free NGF. The application of NGF PLGA nanoparticles in the hUCMSC fibrin cardiac patches can significantly improve the retention of transplanted hUCMSCs and enhance their ability to reduce myocardial apoptosis and promote angiogenesis in the mouse heart after MI.

The pivotal roles of exosomes derived from endogenous immune cells and exogenous stem cells in myocardial repair after acute myocardial infarction.

Acute myocardial infarction (AMI) is one of the leading causes of mortality around the world, and the inflammatory response plays a pivotal role in the progress of myocardial necrosis and ventricular remodeling, dysfunction and heart failure after AMI. Therapies aimed at modulating immune response after AMI on a molecular and cellular basis are urgently needed. Exosomes are a type of extracellular vesicles which contain a large amount of biologically active substances, like lipids, nucleic acids, proteins and so on. Emerging evidence suggests key roles of exosomes in immune regulation post AMI. A variety of immune cells participate in the immunomodulation after AMI, working together to clean up necrotic tissue and repair damaged myocardium. Stem cell therapy for myocardial infarction has long been a research hotspot during the last two decades and exosomes secreted by stem cells are important active substances and have similar therapeutic effects of immunomodulation, anti-apoptosis, anti-fibrotic and angiogenesis to those of stem cells themselves. Therefore, in this review, we focus on the characteristics and roles of exosomes produced by both of endogenous immune cells and exogenous stem cells in myocardial repair through immunomodulation after AMI.

Engineered cell-degradable poly(2-alkyl-2-oxazoline) hydrogel for epicardial placement of mesenchymal stem cells for myocardial repair

Epicardial placement of mesenchymal stromal cells (MSCs) is a promising strategy for cardiac repair post-myocardial infarction, but requires the design of biomaterials to maximise the retention of donor cells on the heart surface and control their phenotype. To this end, we propose the use of a poly(2-alkyl-2-oxazoline) (POx) derivative, based on 2-ethyl-2-oxazoline and 2-butenyl-2-oxazoline. This POx polymer can be cured rapidly (less than 2 min) via photo-irradiation due to the use of di-cysteine cell degradable peptides. We report that the cell-degradable properties of the resulting POx hydrogels enables the regulation of cell protrusion in corresponding 3D matrices and that this, in turn, regulates the secretory phenotype of MSCs. In particular, the expression of pro-angiogenic genes was upregulated in partially cell-degradable POx hydrogels. Improved angiogenesis was confirmed in an in vitro microfluidic assay. Finally, we confirmed that, owing to the excellent tissue adhesive properties of thiol-ene crosslinked hydrogels, the epicardial placement of MSC-loaded POx hydrogels promoted the recovery of cardiac function and structure with reduced interstitial fibrosis and improved neovascular formation in a rat myocardial infarction model. This report demonstrates that engineered synthetic hydrogels displaying controlled mechanical, cell degradable and bioactive properties are particularly attractive candidates for the epicardial placement of stem cells to promote cardiac repair post myocardial infarction.

Abstract 16726: N-Cadherin Overexpression Improves the Reparative Potency of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes in Infarcted Mouse Hearts

Background: Stem-cell-based therapy is a promising approach for the treatment of myocardial infarction (MI); however, the effectiveness of the treatment is believed to be limited by the poor survival and functional integration of transplanted cells. Within the heart, the adhesion between cardiomyocytes (CMs) is mediated by N-cadherin (CDH2), and CDH2 expression is well correlated with the efficacy of mesenchymal stem cells for myocardial repair. Thus, we determined whether the electrical connectivity, engraftment, and reparative potency of human induced-pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs) can be improved via CDH2 overexpression. Materials and methods: Conduction velocities were measured in cultured CDH2-overexpressing hiPSC-CMs (CDH2-CMs) and wild-type hiPSC-CMs (WT-CMs) via optical mapping. MI was induced in SCID mice via coronary artery ligation; then, the mice were treated with CDH2-CMs or WT-CMs (310 5 cells/mouse) (i.e., the MI+WT-CM and MI+WT-CM groups, respectively), or with neither experimental treatment (the MI group). The cells were injected directly into the infarcted region of the heart, cardiac function and infarct size were evaluated via post mortem examination, and the engraftment rate was evaluated histologically. Results: In-vitro conduction velocities were significantly greater (p<0.05) in CDH2-overexpressing hiPSC-CMs than in wild-type hiPSC-CMs, while in-vivo measurements of cardiac function (left-ventricular ejection fraction and fractional shortening), infarct size, and the hiPSC-CM engraftment/survival rate at week 4 after MI were significantly better in the MI+CDH2-CM group than in MI+WT-CM animals and in both cell-treatment groups than in MI animals . Conclusion: N-cadherin overexpression improves the electrical connectivity of cultured hiPSC-CMs, as well as the engraftment/survival and reparative potency of transplanted hiPSC-CMs in infarcted mouse hearts. Key words: N-cadherin, Myocardial Infarction, human induced pluripotent stem cells.

A Large-Scale Investigation of Hypoxia-Preconditioned Allogeneic Mesenchymal Stem Cells for Myocardial Repair in Nonhuman Primates: Paracrine Activity Without Remuscularization.

The effectiveness of transplanted bone marrow mesenchymal stem cells (MSCs) for cardiac repair has been limited; thus, strategies for optimizing stem-cell-based myocardial therapy are needed. The present study was designed to test our central hypothesis that hypoxia-preconditioned MSCs (HP-MSCs) are more effective than MSCs cultured under ambient oxygen levels for the treatment of myocardial injury in a large-scale (N=49), long-term (9 months), nonhuman primate (Cynomolgous monkeys) investigation. MSCs were engineered to express green fluorescent protein, cultured under ambient oxygen or 0.5% oxygen (HP-MSCs) for 24 hours and then tested in the infarcted hearts of Cynomolgus monkeys (1×10(7) cells per heart). Hypoxia preconditioning increased the expression of several prosurvival/proangiogenic factors in cultured MSCs, and measurements of infarct size and left-ventricular function at day 90 after myocardial infarction were significantly more improved in monkeys treated with HP-MSCs than in monkeys treated with the control vehicle; functional improvements in normal cultured bone marrow mesenchymal stem cells-treated monkeys were not significant. HP-MSCs transplantation was also associated with increases in cardiomyocyte proliferation, vascular density, myocardial glucose uptake, and engraftment of the transplanted cells and with declines in endogenous cell apoptosis, but did not increase the occurrence of arrhythmogenic complications. Hypoxia preconditioning improved the effectiveness of MSCs transplantation for the treatment of myocardial infarction in nonhuman primates without increasing the occurrence of arrhythmogenic complications, which suggests that future clinical trials of HP-MSCs transplantation are warranted.

Possibilities and limitations for co-transplantation of cardiac atrial appendage stem cells and mesenchymal stem cells for myocardial repair

[Fanton, Yanick; Rummens, Jean-Luc; Daniels, Annick; Windmolders, Severina; Willems, Leen; Declercq, Jeroen; Hensen, Karen; Koninckx, Remco] Jessa Hosp, Lab Expt Hematol, Hasselt, Belgium. [Fanton, Yanick; Robic, Boris; Rummens, Jean-Luc; Windmolders, Severina; Willems, Leen; Notelaers, Kristof; Paesen, Rik; Ameloot, Marcel; Bito, Virginie; Declercq, Jeroen; Hensen, Karen; Koninckx, Remco; Hendrikx, Marc] Hasselt Univ, Fac Med & Life Sci, Hasselt, Belgium. [Robic, Boris; Mees, Urbain; Hendrikx, Marc] Jessa Hosp, Dept Cardiothorac Surg, Hasselt, Belgium. [Jamaer, Luc; Dubois, Jasperina] Jessa Hosp, Dept Cardiac Anesthesia, Hasselt, Belgium. [Bijnens, Eric; Heuts, Nic] Jessa Hosp, Dept Radiol, MRI Unit, Hasselt, Belgium. [Notelaers, Kristof; Paesen, Rik; Ameloot, Marcel; Bito, Virginie] Hasselt Univ, Biomed Res Inst, Hasselt, Belgium.

Recent developments in cardiovascular stem cells.

Heart failure, a common consequence of ischemic heart disease, is a major cause of morbidity and mortality in the world.1–3 Pharmacological treatment with β-blockers and inhibitors of the renin–angiotensin–aldosterone system has improved the clinical outcomes in patients with heart failure.4–7 Likewise, mechanical unloading with left ventricular assist devices and resynchronization therapy have led to partial reversal of cardiac structural and molecular remodeling and symptomatic improvement.8–10 Despite these remarkable advances, however, mortality and morbidity of patients with heart failure, with or without reduced ejection fraction remains high.1,2 Moreover, heart transplantation, while an effective option, is available only for a selected number of patients and is not without considerable negative consequences.11 Furthermore, gene therapy still remains in early investigational stages and not yet ready for clinical applications.12 The high residual mortality and morbidity of patients with heart failure might be inherent to the shortcomings of the current therapeutic approaches, as none directly targets the underlying causal problem in heart failure, that is, loss of or intrinsically dysfunctional myocytes. Consequently, novel therapeutic approaches are necessary to further improve the clinical outcomes in patients with heart failure. The heart is considered, by and large, a terminally differentiated organ with a limited intrinsic regenerative capacity that alone is insufficient to compensate for the pathological loss of cardiac myocytes during the postnatal period.13–15 The discovery of cardiac progenitor cells (CPCs) in the heart more than a decade ago along with the recent data showing that the existing myocytes undergo a gradual turnover have raised the potentials for regenerative cardiac repair.16,17 Likewise, the discovery of mesenchymal stem cells (MSCs), which was thought to have the potential to differentiate to cardiac myocytes, but yet to proven, or enhance …

Thymosin β4 Increases the Potency of Transplanted Mesenchymal Stem Cells for Myocardial Repair

Thymosin β4 (Tβ4) has been shown to enhance the survival of cultured cardiomyocytes. Here, we investigated whether the cytoprotective effects of Tβ4 can increase the effectiveness of transplanted swine mesenchymal stem cells (sMSCs) for cardiac repair in a rat model of myocardial infarction (MI). Under hypoxic conditions, cellular damage (lactate dehydrogenase leakage), apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labelingc cells), and caspase-8 activity were significantly lower, whereas B-cell lymphoma-extra large protein expression was significantly higher, in sMSCs cultured with Tβ4 (1 μg/mL) than in sMSCs cultured without Tβ4, and Tβ4 also increased sMSC proliferation. For in vivo experiments, animals were treated with basal medium (MI: n=6), a fibrin patch (Patch: n=6), a patch containing sMSCs (sMSC: n=9), or a patch containing sMSCs and Tβ4 (sMSC/Tβ4: n=11); Tβ4 was encapsulated in gelatin microspheres to extend Tβ4 delivery. Four weeks after treatment, echocardiographic assessments of left-ventricular ejection fraction and fractional shortening were significantly better (P<0.05) in sMSC/Tβ4 animals (left-ventricular ejection fraction=51.7 ± 1.1%; fractional shortening=26.7 ± 0.7%) than in animals from MI (39 ± 3%; 19.5 ± 1.7%) and Patch (43 ± 1.4%; 21.6 ± 0.9%) groups. Histological assessment of infarct wall thickness was significantly higher (P<0.05) in sMSC/Tβ4 animals (50%, [45%, 80%]) than in animals from MI (25%, [20%, 25%]) group. Measurements in sMSC (left-ventricular ejection fraction=45 ± 2.6%; fractional shortening=22.9 ± 1.6%; TH = 43% [25%, 45%]), Patch, and MI animals were similar. Tβ4 administration also significantly increased vascular growth, the retention/survival of the transplanted sMSCs, and the recruitment of endogenous c-Kit(+) progenitor cells to the infarcted region. Extended-release Tβ4 administration improves the retention, survival, and regenerative potency of transplanted sMSCs after myocardial injury.

Risk Factors in Heart Disease: Therapeutic Interventions

Antioxidants & Redox SignalingVol. 15, No. 7 Forum EditorialHeart Diseases (N. Maulik, Ed.)Risk Factors in Heart Disease: Therapeutic InterventionsNilanjana Maulik and Juan A. SanchezNilanjana MaulikMolecular Cardiology and Angiogenesis Laboratory, Department of Surgery, University of Connecticut School of Medicine, Farmington, Connecticut.Search for more papers by this author and Juan A. SanchezMolecular Cardiology and Angiogenesis Laboratory, Department of Surgery, University of Connecticut School of Medicine, Farmington, Connecticut.Department of Surgery, Saint Mary's Hospital, Waterbury, Connecticut.Search for more papers by this authorPublished Online:21 Aug 2011https://doi.org/10.1089/ars.2011.3981AboutSectionsView articleView Full TextPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View articleFiguresReferencesRelatedDetails Volume 15Issue 7Oct 2011 InformationCopyright 2011, Mary Ann Liebert, Inc.To cite this article:Nilanjana Maulik and Juan A. Sanchez.Risk Factors in Heart Disease: Therapeutic Interventions.Antioxidants & Redox Signaling.Oct 2011.1765-1767.http://doi.org/10.1089/ars.2011.3981Published in Volume: 15 Issue 7: August 21, 2011Online Ahead of Print:June 8, 2011Online Ahead of Editing: March 14, 2011PDF download

Aesthetic cardiology: adipose-derived stem cells for myocardial repair.

Stem cell biology has increasingly gained scientific and public interest in recent years. In particular, the use of stem cells for treatment of heart disease has been strongly pursued within the scientific and medical communities. Significant effort has gone into the use of adult tissue-derived stem cells for cardiac repair including bone marrow, blood, and cardiac-derived cell populations. Significant interest in this area has been balanced by the difficulties of understanding stem cells, cardiac injury, and the amalgamation of these areas of investigation in translational medicine. Recent studies have emerged on adipose-derived stem cells which show the potential for cardiac lineage development in vitro and may have application in cell-mediated in vivo therapy for the diseased heart. This review provides a summary of current findings within the field of adipose-derived stem cell biology regarding their cardiac differentiation potential.

Translational potential of human embryonic and induced pluripotent stem cells for myocardial repair: Insights from experimental models

Heart diseases have been a major cause of death worldwide, including developed countries. Indeed, loss of non-regenerative, terminally differentiated cardiomyocytes (CMs) due to aging or diseases is irreversible. Current therapeutic regimes are palliative in nature, and in the case of end-stage heart failure, transplantation remains the last resort. However, this option is significantly hampered by a severe shortage of donor cells and organs. Human embryonic stem cells (hESCs) can self-renew while maintaining their pluripotency to differentiate into all cell types. More recently, direct reprogramming of adult somatic cells to become pluripotent hES-like cells (a.k.a. induced pluripotent stem cells or iPSCs) has been achieved. The availability of hESCs and iPSCs, and their successful differentiation into genuine human heart cells have enabled researchers to gain novel insights into the early development of the human heart as well as to pursue the revolutionary paradigm of heart regeneration. Here we review our current knowledge of hESC-/iPSC-derived CMs in the context of two fundamental operating principles of CMs (i.e. electrophysiology and Ca2+-handling), the resultant limitations and potential solutions in relation to their translation into clinical (bioartificial pacemaker, myocardial repair) and other applications (e.g. as models for human heart disease and cardiotoxicity screening).

Stem cells for myocardial repair

There is a growing interest in the clinical application for stem cell as a novel therapy for treatment of acute myocardial infarction and chronic myocardial ischaemia. The initial premise is the transplanted exogenous stem cells can engraft and integrate with host myocardium for cardiac regeneration. However, recent experimental studies suggest that multiple mechanisms, including remodelling of extracellular matrix, enhancement of neovascularisation and recruitment of endogenous stem cells are more likely to contribute to the beneficial effects of stem cell therapy that direct trans-differentiation of stem cells into functional myocardium. Among different potential cell sources, bone marrow-derived cells and skeletal myoblasts have been tested in pilot clinical trials. Phase I/II randomised controlled clinical trials suggest that intracoronary or intramyocardial injection of bone marrow-derived cells may be safe and feasible strategies for treatment of acute myocardial infarction as well as chronic myocardial ischaemia. In addition, these studies show a modest, but significant improvement in left ventricular ejection fraction and clinical status of patients after cell transplantation. Nevertheless, most of these studies included a relatively small sample size (<200) and short duration of follow-up (<6 months), and the clinical efficacy of stem cell therapy need to be confirmed by future clinical trials. Furthermore, the optimal timing, cell types and mode of delivery need to be addressed, and strategies to improve cell survival and engraftment should also be developed to overcome the potential hurdles related to cell-based therapy.

Bioengineered cardiac patch constructed from multilayered mesenchymal stem cells for myocardial repair

Growing three-dimensional scaffolds that contain more than a few layers of seeded cells is crucial for the creation of thick and viable cardiac tissues. To achieve this goal, a bioengineered cardiac patch (the MSC patch) composed of a sliced porous biological scaffold inserted with multilayered mesenchymal stem cells (MSCs) was developed for myocardial repair in a syngeneic rat model. After culture, sliced layers of the scaffold were stuck together and seeded MSCs were redistributed throughout the scaffold. Immunofluorescence analyses indicated that cells were viable and tightly adhered to a robust fibronectin meshwork within the scaffold. Results of echocardiography and heart catheterization revealed that the MSC-patch group had a superior heart function to the infarct group. Cells together with neo-muscle fibers and neo-microvessels were clearly observed in the entire MSC patch to fill its original pores, indicating that the implanted patch became well integrated into the host. The thickness of the retrieved MSC patch increased significantly as compared to that before implantation. When compared with the infarct group, expressions of angiogenic cytokines (bFGF, vWF and PDGF-B) and cardioprotective factors (IGF-1 and HGF) were significantly increased in the MSC-patch group. The aforementioned results indicated that transplantation of the MSC patch could restore the dilated LV and preserve cardiac functions after infarction.

Skeletal Muscle Derived Stem Cells for Myocardial Repair

Treatment of patients with heart failure secondary to myocardial infarction remains a therapeutic challenge. Extensive myocyte death in the heart and post-ischemic remodeling accentuate progressive expansion of the scar area and compromise left ventricular contractile function. The scarcity of resident stem cells in the heart and limited proliferative capacity of adult cardiomyocytes warrant novel strategies of outside intervention to supplement the inept intrinsic repair mechanism. Heart cell therapy using patient's own skeletal muscle derived myoblasts (SkMs) provides a relatively simple and inexpensive therapeutic option. Phase-I and II clinical trials supported by plethora of pre-clinical studies have shown the safety and effectiveness of SkMs engraftment in the treatment of infarcted heart. However, before widespread application of this approach in the clinical settings, there remain some fundamental issues including extensive donor cell death during acute phase after SkMs engraftment, failure of SkMs to adopt cardiac phenotype and transient ventricular arrhythmias subsequent to SkMs transplantation which require serious considerations. This review will provide profound analysis of merits and limitations of SkMs as the choice cells for heart cell therapy and will summarize the potential of genetic and pharmacological manipulation SkMs to enhance their therapeutic efficacy for myocardial repair. Present article also includes recent patent review coverage on this topic.

Stem cells for myocardial repair

The adult human heart has limited regenerative capacity and therefore any significant myocardial damage results in progressive deterioration in its function. Cell-based cardiac repair represents an exciting approach for rebuilding the injured heart. Consequentially, during the last decade, significant efforts have been made to assess the potential role of skeletal myoblasts, foetal cardiomyocytes, bone marrow stem cells, endothelial progenitors, resident cardiac progenitor cells, and embryonic stem cells (ESC) to restore the myocardial performance. Clinical translation of these basic studies has progressed rapidly with several Phase I and II clinical trials, utilizing autologous bone marrow cells and skeletal myoblasts, being well underway. In this review, we will describe these basic and clinical efforts. A specific emphasis will be placed on the potential role of human ESC for myocardial repair. These unique pluripotent cell lines can be propagated in the undifferentiated state in culture and coaxed to differentiate into cell derivatives of all three germ layers, including cardiomyocytes. The potential applications of this unique differentiating system in the emerging field of cardiovascular regenerative medicine will be discussed with special emphasis on the steps required to fully harness their unique potential.

Reply to Letter from Drs. Haider and Ashraf

Dear Editor, It was proposed by Haider and Ashraf1 that cytokine and growth factor mediated mobilization of endogenous mesenchymal stem cells from their bone marrow niches for homing into the infarcted myocardium could be a better therapeutic strategy than the explantation and subsequent injection of these cells (either autologous or from a donated allogenic source) directly into the damaged heart.2 Besides being less invasive to the patient, it was argued that this approach would obviate the need for ex vivo processing of the putative stem cells, which could in turn reduce the risk of nonspecific differentiation into undesired lineages at the transplantation site.3–5 Nevertheless, such an approach could be severely hampered by the age related decline in the regenerative capacity of the putative mesenchymal stem cell population within the bone marrow, as has been demonstrated by a number of studies.6,7 It must be remembered that the overwhelming majority of myocardial infarct cases occur in the older segment of the population.8 Quarto and colleagues6 demonstrated in a rat model that there was an age associated decline in the ability of marrow stromal cells to repair bone, which could be the underlying cause of age related osteodegenerative diseases. Subsequently, D’Ippolito and colleagues7 reported a similar finding with the human model. This would be expected because, with increasing age, the putative mesenchymal stem cell population within the bone marrow would have gone through more rounds of cell division, in addition to having been exposed to free radicals and metabolic toxins over a longer lifespan. Hence it is no surprise that there is a gradual decline in their regenerative capacity with increasing age. Although there have been no studies to date that have conclusively demonstrated an age associated decline in the capacity of bone marrow cells to repair the infarcted heart, we could make such a conjecture based upon extrapolation from the bone repair model.6,7 The obvious solution to overcome this age related decline in regenerative capacity would be to look at donated allogenic sources of stem cells for myocardial repair. In this regard, human embryonic stem (hES) cells or their differentiated progenies would hold much promise because these potentially represent an abundant and readily available source of transplantable cells. Recently, Zandstra and colleagues9 successfully developed a scalable, robust, and reproducible process for obtaining purified cardiomyocytes from hES cells. Nevertheless, the immunologic barrier10 probably represents the most formidable challenge to the allogenic transplantation of hES cells or their differentiated progenies into the infarcted myocardium. It is hoped that this could somehow be overcome in the near future. Boon Chin Heng* Eugene Kwang-Wei Sim† Tong Cao* *Stem Cell Laboratory, Faculty of Dentistry, †Department of Surgery, Faculty of Medicine National University of Singapore.

Combined transplantation of skeletal myoblasts and bone marrow stem cells for myocardial repair in rats.

To prove whether intramyocardial transplantation of combined skeletal myoblasts (SM) and mononuclear bone marrow stem cells is superior to the isolated transplantation of these cell types after myocardial infarction in rats. In 67 male Fischer rats myocardial infarction was induced by direct ligature of the LAD. Seven days postinfarction baseline echocardiography and intramyocardial cell transplantation were performed. Via lateral thoracotomy 200 microl containing either 10(7) SMs or 10(7) bone marrow-derived mononuclear cells (BM-MNC) or a combination of 5x10(6) of both cell types (MB) were injected in 10-15 sites in and around the infarct zone. In controls (C) 200 microl of cell-free medium were injected in the same manner. Before injection both cell types were stained using a fluorescent cell linker kit (PKH, Sigma). In addition, SMs were transfected with green fluorescent protein. Nine weeks postinfarction follow-up echocardiography was performed and animals were sacrificed for further analysis. At baseline echocardiography there was no difference in left ventricular ejection fraction (LVEF; C, SM, BM-MNC, MB: 60.1+/-3.2, 53.3+/-10.2, 53.1+/-8.7, 49+/-9.0%) and left ventricular end diastolic diameter (LVEDD; C, SM, BM-MNC, MB: 6.5+/-0.8, 5.17+/-0.8, 5.77+/-1.4, 6.25+/-0.8 mm) between the different therapeutic groups. Eight weeks after cell transplantation LVEDD was significantly increased in all animals except those that received a combination of myoblasts and bone marrow stem cells (MB; C, SM, BM-MNC, MB: 7.7+/-0.6 mm, P=0.001; 7.7+/-1.5 mm, P<0.001; 7.7+/-1.1 mm, P=0.005; 6.6+/-1.7 mm, P=0.397. At the same time LVEF decreased significantly in the control group (C), stayed unchanged in animals that received bone marrow stem cells (BM-MNC) and increased in animals that received myoblasts (SM) and a combination of both cell types (MB; C, SM, BM-MNC, MB: 45.3+/-7.0%, P=0.05; 63.9+/-15.4%, P=0.044; 54.3+/-6.3%, P=0.607; 63.0+/-11.5%, P=0.039). The present data show that the concept of combining SMs with bone marrow-derived stem cells may be of clinical relevance by merging the beneficial effects of each cell line and potentially reducing the required cell quantity. Further studies are required to identify the exact mechanisms underlying this synergy and to allow full exploitation of its therapeutic potential.