Long-Term Cell Survival and Hemodynamic Improvements after Neonatal Cardiomyocyte and Satellite Cell Transplantation into Healed Myocardial Cryoinfarcted Lesions in Rats

Bisphosphonate of Zoledronate Has Antiapoptotic Effect on Hypoxia/Reoxygenation Injury in Human Embryonic Stem Cell-Derived Cardiomyocytes Through Trk Signaling Pathway

In this work, we investigated the in vitro and in vivo functions of bisphosphonate of zoledronate (Zd) in hypoxia/reoxygenation (H/R) injured human embryonic stem cell-derived cardiomyocytes (hES-CMs). In the in vitro setting, the effects of Zd on hES-CM survival and differentiation were examined. We found that low and medium concentrations (<2 µm) of Zd did not induce cell death of hES-CMs. 0.5 µm Zd protected H/R-induced hES-CM apoptosis but did not affect key differentiation proteins, including hcTnl, PECM-1 Cnx43 and Pan-Cadherin. In addition, Zd-induced TrkA/B phosphorylation and promoted VEGF to counter the apoptotic effect of H/R injury. In the in vivo animal model of myocardial infarction, Zd treatment promoted the survival of hES-CMs by inducing PECAM1 and hcTnl. Thus, we concluded that Zd protected H/R-induced hES-CM apoptosis in vitro and promoted hES-CM survival in vivo. These data may facilitate the development of human embryonic stem cells into clinical applications for patients with ischemic heart disease.

Plasticized poly(vinylalcohol) and poly(vinylpyrrolidone) based patches with tunable mechanical properties for cardiac tissue engineering applications

Polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) are the two most investigated biopolymers for various tissue engineering applications. However, their poor tensile strength renders them unsuitable for cardiac tissue engineering (CTE). In this study, we developed and evaluated PVA-PVP-based patches, plasticized with glycerol or propylene glycol (0.1%-0.4%; v:v), for their application in CTE. The cardiac patches were evaluated for their physico-chemical (weight, thickness, folding endurance, FT-IR, and swelling behavior) and mechanical properties. The optimized patches were characterized for their ability to support in vitro attachment, viability, proliferation, and beating behavior of neonatal mouse cardiomyocytes (CMs). In vivo evaluation of the cardiac patches was done under the subcutaneous skin pouch and heart of rat models. Results showed that the optimized molar ratio of PVA:PVP with plasticizers (0.3%; v-v) resulted in cardiac patches, which were dry at room temperature and had desirable folding endurance of at least 300, a tensile strength of 6-23 MPa and, percentage elongation at break of more than 250%. Upon contact with phosphate-buffered saline, these PVA-PVP patches formed hydrogel patches having the tensile strength of 1.3-3.0 MPa. The patches supported the attachment, viability, and proliferation of primary neonatal mouse CMs and were nonirritant and noncorrosive to cardiac cells. In vivo transplantation of cardiac patches into a subcutaneous pouch and on the heart of rat models revealed them to be biodegradable, biocompatible, and safe for use in CTE applications.

Allogenic Myocytes and Mesenchymal Stem Cells Partially Improve Fatty Rotator Cuff Degeneration in a Rat Model

PURPOSE

Rotator cuff (RC) tears result not only in functional impairment but also in RC muscle atrophy, muscle fattening and eventually to muscle fibrosis. We hypothesized that allogenic bone marrow derived mesenchymal stem cells (MSC) and myocytes can be utilized to improve the rotator cuff muscle fattening and increase the atrophied muscle mass in a rat model.

METHODS

The right supraspinatus (SSP) tendons of 105 inbred rats were detached and muscle fattening was provoked over 4 weeks; the left side remained untouched (control group). The animals (n = 25) of the output group were euthanized after 4 weeks for reference purposes. The SSP-tendon of one group (n = 16) was left unoperated to heal spontaneously. The SSP-tendons of the remaining 64 rats (4 groups with n = 16) were repaired with transosseous sutures. One group received a saline solution injection in the SSP muscle belly, two other groups received 5 × 10⁶ allogenic myocytes and 5 × 10⁶ allogenic MSC injections from donor rats, respectively, and one group received no additional treatment. After 4 weeks of healing, the supraspinatus muscle mass was compared quantitatively and histologically to all the treated groups and to the untreated contralateral side.

RESULTS

In the end of the experiments at week 8, the myocyte and MCS treated groups showed a significantly higher muscle mass with 0.2322 g and 0.2257 g, respectively, in comparison to the output group (0.1911 g) at week 4 with p < 0.05. There was no statistical difference between the repaired, treated, or spontaneous healing groups at week 8. Supraspinatus muscle mass of all experimental groups of the right side was significantly lower compared to the untreated contralateral muscle mass.

CONCLUSION

This defect model shows that the injection of allogenic mycocytes and MSC in fatty infiltrated SSP muscles is better than no treatment and can partially improve the SSP muscle belly fattening. Nevertheless, a full restoration of the degenerated and fattened rotator cuff muscle to its original condition is not possible using myocytes and MSC in this model.

Cell-Based Therapies for Cardiac Regeneration: A Comprehensive Review of Past and Ongoing Strategies

Despite considerable improvements in the treatment of cardiovascular diseases, heart failure (HF) still represents one of the leading causes of death worldwide. Poor prognosis is mostly due to the limited regenerative capacity of the adult human heart, which ultimately leads to left ventricular dysfunction. As a consequence, heart transplantation is virtually the only alternative for many patients. Therefore, novel regenerative approaches are extremely needed, and several attempts have been performed to improve HF patients’ clinical conditions by promoting the replacement of the lost cardiomyocytes and by activating cardiac repair. In particular, cell-based therapies have been shown to possess a great potential for cardiac regeneration. Different cell types have been extensively tested in clinical trials, demonstrating consistent safety results. However, heterogeneous efficacy data have been reported, probably because precise end-points still need to be clearly defined. Moreover, the principal mechanism responsible for these beneficial effects seems to be the paracrine release of antiapoptotic and immunomodulatory molecules from the injected cells. This review covers past and state-of-the-art strategies in cell-based heart regeneration, highlighting the advantages, challenges, and limitations of each approach.

The Heart and Great Vessels

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

Stem cells in the management of heart failure: what have we learned from clinical trials?

Research shows that various types of stem cells (SCs) have the ability to rebuild damaged heart tissue. The TIME and Late TIME human trials shed light on the optimum timing of SC therapy administration after myocardial damage. The FOCUS study failed to show a substantial positive effect of bone marrow-derived mononuclear cells in patients suffering from ischemic heart failure; however, some completed human trials do show promise, with improvement in cardiac function. Recent clinical trials have identified a subset of marrow cells that was able to stimulate endogenous adult cardiac SCs where cardiac SCs administration showed promise in the SCIPIO trial. This review addresses some of the lessons learned from clinical trials with SC therapy in ischemic heart failure.

Thin filament incorporation of an engineered cardiac troponin C variant (L48Q) enhances contractility in intact cardiomyocytes from healthy and infarcted hearts

Many current pharmaceutical therapies for systolic heart failure target intracellular [Ca(2+)] ([Ca(2+)]i) metabolism, or cardiac troponin C (cTnC) on thin filaments, and can have significant side-effects, including arrhythmias or adverse effects on diastolic function. In this study, we tested the feasibility of directly increasing the Ca(2+) binding properties of cTnC to enhance contraction independent of [Ca(2+)]i in intact cardiomyocytes from healthy and myocardial infarcted (MI) hearts. Specifically, cardiac thin filament activation was enhanced through adenovirus-mediated over-expression of a cardiac troponin C (cTnC) variant designed to have increased Ca(2+) binding affinity conferred by single amino acid substitution (L48Q). In skinned cardiac trabeculae and myofibrils we and others have shown that substitution of L48Q cTnC for native cTnC increases Ca(2+) sensitivity of force and the maximal rate of force development. Here we introduced L48Q cTnC into myofilaments of intact cardiomyocytes via adeno-viral transduction to deliver cDNA for the mutant or wild type (WT) cTnC protein. Using video-microscopy to monitor cell contraction, relaxation, and intracellular Ca(2+) transients (Fura-2), we report that incorporation of L48Q cTnC significantly increased contractility of cardiomyocytes from healthy and MI hearts without adversely affecting Ca(2+) transient properties or relaxation. The improvements in contractility from L48Q cTnC expression are likely the result of enhanced contractile efficiency, as intracellular Ca(2+) transient amplitudes were not affected. Expression and incorporation of L48Q cTnC into myofilaments was confirmed by Western blot analysis of myofibrils from transduced cardiomyocytes, which indicated replacement of 18±2% of native cTnC with L48Q cTnC. These experiments demonstrate the feasibility of directly targeting cardiac thin filament proteins to enhance cardiomyocyte contractility that is impaired following MI.

Transcatheter based electromechanical mapping guided intramyocardial transplantation and in vivo tracking of human stem cell based three dimensional microtissues in the porcine heart

Stem cells have been repeatedly suggested for cardiac regeneration after myocardial infarction (MI). However, the low retention rate of single cell suspensions limits the efficacy of current therapy concepts so far. Taking advantage of three dimensional (3D) cellular self-assembly prior to transplantation may be beneficial to overcome these limitations. In this pilot study we investigate the principal feasibility of intramyocardial delivery of in-vitro generated stem cell-based 3D microtissues (3D-MTs) in a porcine model. 3D-MTs were generated from iron-oxide (MPIO) labeled human adipose-tissue derived mesenchymal stem cells (ATMSCs) using a modified hanging-drop method. Nine pigs (33 ± 2 kg) comprising seven healthy ones and two with chronic MI in the left ventricle (LV) anterior wall were included. The pigs underwent intramyocardial transplantation of 16 × 10(3) 3D-MTs (1250 cells/MT; accounting for 2 × 10(7) single ATMSCs) into the anterior wall of the healthy pigs (n = 7)/the MI border zone of the infarcted (n = 2) of the LV using a 3D NOGA electromechanical mapping guided, transcatheter based approach. Clinical follow-up (FU) was performed for up to five weeks and in-vivo cell-tracking was performed using serial magnet resonance imaging (MRI). Thereafter, the hearts were harvested and assessed by PCR and immunohistochemistry. Intramyocardial transplantation of human ATMSC based 3D-MTs was successful in eight animals (88.8%) while one pig (without MI) died during the electromechanical mapping due to sudden cardiac-arrest. During FU, no arrhythmogenic, embolic or neurological events occurred in the treated pigs. Serial MRI confirmed the intramyocardial presence of the 3D-MTs by detection of the intracellular iron-oxide MPIOs during FU. Intramyocardial retention of 3D-MTs was confirmed by PCR analysis and was further verified on histology and immunohistochemical analysis. The 3D-MTs appeared to be viable, integrated and showed an intact micro architecture. We demonstrate the principal feasibility and safety of intramyocardial transplantation of in-vitro generated stem cell-based 3D-MTs. Multimodal cell-tracking strategies comprising advanced imaging and in-vitro tools allow for in-vivo monitoring and post-mortem analysis of transplanted 3D-MTs. The concept of 3D cellular self-assembly represents a promising application format as a next generation technology for cell-based myocardial regeneration.

Label-free enrichment of functional cardiomyocytes using microfluidic deterministic lateral flow displacement

Progress in cardiac cell replacement therapies and tissue engineering critically depends on our ability to isolate functional cardiomyocytes (CMs) from heterogeneous cell mixtures. Label-free enrichment of cardiomyocytes is desirable for future clinical application of cell based products. Taking advantage of the physical properties of CMs, a microfluidic system was designed to separate CMs from neonatal rat heart tissue digest based on size using the principles of deterministic lateral displacement (DLD). For the first time, we demonstrate enrichment of functional CMs up to 91±2.4% directly from the digested heart tissue without any pre-treatment or labeling. Enriched cardiomyocytes remained viable after sorting and formed contractile cardiac patches in 3-dimensional culture. The broad significance of this work lies in demonstrating functional cell enrichment from the primary tissue digest leading directly to the creation of the engineered tissue.

Age-Dependent Availability and Functionality of Bone Marrow Stem Cells in an Experimental Model of Acute and Chronic Myocardial Infarction

The aim of this study was to investigate the effect of aging and timing of left ventricular ischemic injury on the availability and functionality of stem cells. We studied young and aged male inbred Lewis rats that were used as donors of bone marrow mononuclear cells (BM-MNCs), divided in four experimental groups: controls, sham operated, 48 h post-myocardial infarction (MI), and 28 days post-MI. In vitro studies included flow cytometry analysis, hematopoietic colony-forming capacity, and invasion assays of migration capacity. BM-MNCs from these groups were transplanted in female rats after MI induction. Late engraftment was evaluated by real-time PCR of the SRY chromosome. Percentage of CD34+/CD45+low cells was similar among different experimental groups in young rats, but was significantly higher in aged animals ( p < 0.001), particularly 28 days post-MI. KDR+/CD34+ cells were increased 48 h after MI and decreased 28 days post-MI in young animals, while they were profoundly reduced in the aged group ( p < 0.001). Triple staining for CD44+/CD29+/CD71+ cells was similar in different groups of aged rats, but we observed an intense increase 48 h post-MI in young animals. Colony-forming units and cytokine-induced migration were significantly attenuated 28 days after the MI. Late engraftment in infarcted transplanted female hearts was present, but considerably heterogeneous. Finally, recovery of left ventricular systolic function in transplanted female recipients was significantly influenced by donors' BM-MNCs groups ( p < 0.01). We have demonstrated that aging and timing of myocardial injury are factors that may act synergistically in determining stem cell availability and function. Such interaction should be considered when planning new cell therapy strategies for acute and chronic ischemic heart disease in the clinical arena.

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

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

Photocrosslinkable chitosan modified with angiopoietin-1 peptide, QHREDGS, promotes survival of neonatal rat heart cells

Myocardial infarction (MI) results in the death of cardiomyocytes (CM), which causes scar formation and pathological remodeling of the heart. The delivery of healthy myocytes or bone marrow cells reduces pathological remodeling after MI, however, current cell injection methods have low cell survival rates and high cell loss. The main objective of this work was to develop a novel hydrogel that can promote survival of CMs. Photocrosslinkable azidobenzoic acid modified chitosan (Az-chitosan) was conjugated with the angiopoietin-1-derived peptide, QHREDGS. This novel peptide is thought to mediate attachment and survival responses of CM to angiopoietin-1 via integrin binding. Thin layers of Az-chitosan, Az-chitosan-QHREDGS, and Az-chitosan-DGQESHR (scrambled peptide control) were spin coated on glass slides and photocrosslinked with application of UV light (365 nm). Neonatal rat heart cells cultured up to 5 days, demonstrated significantly higher attachment and viability on Az-chitosan-QHREDGS compared to cells on other hydrogel controls. Surfaces were also stained for the CM-specific marker troponin I, demonstrating significantly higher percentage of CMs on Az-chitosan-QHREDGS compared to Az-chitosan. The cells cultivated on Az-chitosan-QHREDGS demonstrated significantly lower levels of caspase 3/7 activation after taxol treatment in comparison to cells cultivated on the control hydrogels, glass substrate, or Az-chitosan linked to RGD, an established integrin binding peptide that did not protect against apoptosis. Thus, Az-chitosan-QHREDGS supports attachment and survival of neonatal rat heart cells.

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

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

Cell therapy enhances function of remote non-infarcted myocardium

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

The real estate of myoblast cardiac transplantation: negative remodeling is associated with location

BACKGROUND

Skeletal myoblast transplantation has been proposed as a therapy for ischemic cardiomyopathy owing to its possible role in myogenesis. The relative safety and efficacy based on location within scar is not known. We hypothesized that skeletal myoblasts transplanted into peripheral scar (compared with central scar) would more effectively attenuate negative left ventricular (LV) remodeling but at the risk of arrhythmia.

METHODS

New Zealand White rabbits (n = 34) underwent mid-left anterior descending artery (LAD) ligation to produce a transmural LV infarction. One month after LAD ligation, skeletal myoblasts were injected either in the scar center (n = 13) or scar periphery (n = 10) and compared with saline injection (n = 11). Holter monitoring and magnetic resonance imaging (MRI) was performed pre-injection; Holter monitoring was continued until 2 weeks after injection, with follow-up MRI at 1 month.

RESULTS

The centrally treated animals demonstrated increased LV end-systolic volume, end-diastolic volume, and mass that correlated with the number of injected cells. There was a trend toward attenuation of negative LV remodeling in peripherally treated animals compared with vehicle. Significant late ectopy was seen in several centrally injected animals, with no late ectopy seen in peripherally injected animals.

CONCLUSIONS

We noted untoward effects with respect to negative LV remodeling after central injection, suggesting that transplanted cell location with respect to scar may be a key factor in the safety and efficacy of skeletal myoblast cardiac transplantation. Administration of skeletal myoblasts into peripheral scar appears safe, with a trend toward improved function in comparison with sham injection.

Tissue-Transplant Fusion and Vascularization of Myocardial Microtissues and Macrotissues Implanted into Chicken Embryos and Rats

Cell-based therapies and tissue engineering initiatives are gathering clinical momentum for next-generation treatment of tissue deficiencies. By using gravity-enforced self-assembly of monodispersed primary cells, we have produced adult and neonatal rat cardiomyocyte-based myocardial microtissues that could optionally be vascularized following coating with human umbilical vein endothelial cells (HUVECs). Within myocardial microtissues, individual cardiomyocytes showed native-like cell shape and structure, and established electrochemical coupling via intercalated disks. This resulted in the coordinated beating of microtissues, which was recorded by means of a multi-electrode complementary metal-oxide-semiconductor microchip. Myocardial microtissues (microm3 scale), coated with HUVECs and cast in a custom-shaped agarose mold, assembled to coherent macrotissues (mm3 scale), characterized by an extensive capillary network with typical vessel ultrastructures. Following implantation into chicken embryos, myocardial microtissues recruited the embryo's capillaries to functionally vascularize the rat-derived tissue implant. Similarly, transplantation of rat myocardial microtissues into the pericardium of adult rats resulted in time-dependent integration of myocardial microtissues and co-alignment of implanted and host cardiomyocytes within 7 days. Myocardial microtissues and custom-shaped macrotissues produced by cellular self-assembly exemplify the potential of artificial tissue implants for regenerative medicine.

Haematopoietic stem cells and repair of the ischaemic heart

HSCs (haematopoietic stem cells) are multipotent stem cells that give rise to all cells of the blood cell lineage. In recent years, it has been proposed that bone marrow serves as a reservoir for cardiomyogenic precursors and that, following cardiac injury, these stem cells circulate to the site of injury where they contribute to myocardial repair and regeneration. This concept of stem cell plasticity has been controversial and, in fact, several key studies on the cardiomyogenic potential of HSCs have not been reproducible in the hands of independent investigators. Despite this controversy, the clinical community has pushed forward with clinical trials of bone marrow transplantation for the treatment of ischaemic heart disease. The following review summarizes the mechanistic underpinnings of bone marrow transplantation into ischaemic myocardium, focusing on the basic science that forms the foundation of this field, and highlights the controversies and new avenues for research that have emerged. It also describes the current state of the art in clinical trials of bone marrow transplantation for heart failure.

Reduction of Myocardial Scar Size after Implantation of Mesenchymal Stem Cells in Rats: What Is the Mechanism?

The use of a cellular therapy offers a promising approach for the treatment of heart disease. Besides other precursor cells, bone marrow (BM)-derived stem cells were discovered that migrate into ischemic myocardium and participate in myogenesis as well as angiogenesis. A subpopulation of those are the mesenchymal stem cells (MSC), which may be potential candidates for repairing ischemic heart tissue. MSC are easy to prepare and can be used in an autologous strategy. Here we demonstrate the effect of transplanted MSC in our autologous rat model of myocardial injury. BM was isolated from tibiae and femurs of Wistar rats. After 24 h, the adhering MSC were separated, expanded, retrovirally transduced using green fluorescent protein (GFP), and cloned. A cryo-infarct was generated in the rat hearts, and immediately after this the cells were injected into the border zone of the lesion. After a 10-week follow up, the hearts were excised and the myocardial scar areas were measured using computer-guided morphometry. When comparing transplanted rats (n = 8) with control animals (n = 5) treated rats demonstrated a significant reduction in the width (p < 0.05) of the myocardial scar area. The depth of the scars of the cell therapy rats was less extended (p > 0.05) and the myocardium of these animals was thicker than in the controls (p > 0.05). Immunohistochemical analyses revealed neither evidence of MSC transdifferentiation into cardiomyocytes, nor could an increased neovascularization be found. In conclusion, MSC are responsible for a remarkable reduction of the myocardial scar size in the treated animals. But, whether this strategy is directly transferable to the patient suffering from heart disease has to be determined. In addition, the mechanism by which MSC act in the ischemic heart remains to be determined.

Healing a broken heart with stem cells

We discuss here the rapid progress of stem cell therapy in myocardial infarction. In particular, we focus on the issue of transdifferentiation as a "hallmark" of the stem cell's potential to replace damaged cells of the heart. A study by Henning and colleagues in this issue of Cell Transplantation supports the alternative notion of a nontransdifferentiation-mediated protection of the heart as an equally robust mechanism underlying the therapeutic potential of stem cells.

Human umbilical cord blood mononuclear cells for the treatment of acute myocardial infarction

Cell transplantation is a new treatment to improve cardiac function in hearts that have been damaged by myocardial infarction. We have investigated the use of human umbilical cord blood mononuclear progenitor cells (HUCBC) for the treatment of acute myocardial infarction. The control group consisted of 24 normal rats with no interventions. The infarct + vehicle group consisted of 33 rats that underwent left anterior descending coronary artery (LAD) ligation and after 1 h were given Isolyte in the border of the infarction. The infarct + HUCBC group consisted of 38 rats that underwent LAD ligation and after 1 h were given 10(6) HUCBC in Isolyte directly into the infarct border. Immunosuppression was not given to any rat. Measurements of left ventricular (LV) ejection fraction, LV pressure, dP/dt, and infarct size were determined at baseline and 1, 2, 3, and 4 months. The ejection fraction in the controls decreased from 88+/-3% to 78+/-4% at 4 months (p = 0.03) as a result of normal aging. Following infarction in the infarct + vehicle group, the ejection fraction decreased from 87+/-4% to 51+/-3% between 1 and 4 months (p < 0.01). In contrast, the ejection fraction of the infarcted + HUCBC-treated rat hearts decreased from 87+/-4% to 63+/-3% at 1 month, but progressively increased to 69+/-6% at 3 and 4 months, which was different from infarct + vehicle group rats (p < 0.02) but similar to the controls. At 4 months, anteroseptal wall thickening in infarct + HUCBC group was 57.9+/-11.6%, which was nearly identical to the control anteroseptal thickening of 59.2+/-8.9%, but was significantly greater than the infarct + vehicle group, which was 27.8+/-7% (p < 0.02). dP/dt(max) increased by 130% in controls with 5.0 microg of phenylephrine (PE)/min (p < 0.001). In the infarct + vehicle group, dP/dt(max) increased by 91% with PE (p = 0.01). In contrast, in the infarct + HUCBC group, dP/dt(max) increased with PE by 182% (p < 0.001), which was significantly greater than the increase in dP/dt(max) in the infarct + vehicle group (p = 0.03) and similar to the increase in the controls. Infarct sizes in the infarct + HUCBC group were smaller than the infarct + vehicle group and averaged 3.0+/-2.8% for the infarct + HUCBC group versus 22.1+/-5.6% for infarct + vehicle group at 3 months (p < 0.01); at 4 months they averaged 9.2+/-2.0% for infarct + HUCBC group versus 40.0+/-9.2% for the infarct + vehicle group (p < 0.001). The present experiments demonstrate that HUCBC substantially reduce infarction size in rats without requirements for immunosuppression. As a consequence, LV function measurements, determined by LV ejection fraction, wall thickening, and dP/dt, are significantly greater than the same measurements in rats with untreated infarctions.

[Cell transplantation in heart failure management]

Heart failure is becoming a major issue for public health in western countries and the effect of currently available therapies is limited. Therefore cell transplantation was developed as an alternative strategy to improve cardiac structure and function. This review describes the multiple cell types and clinical trials considered for use in this indication. Most studies have been developed in models of post-ischemic heart failure. The transplantation of fetal or neonatal cardiomyocytes has proven to be functionally successful, but ethical as well as immunological and technical reasons make their clinical use limited. Recent reports, however, suggested that adult autologous cardiomyocytes could be prepared from stem cells present in various tissues (bone marrow, vessels, adult heart itself, adipose tissue). Alternatively, endothelial progenitors originating from bone marrow or peripheral blood could promote the neoangiogenesis within the scar tissue. Hematopietic stem cells prepared from bone marrow or peripheral blood have been proposed but their differentiation ability seems limited. Finally, the transplantation of skeletal muscle cells (myoblasts) in the infarcted area improved myocardial function, in correlation with the development of skeletal muscle tissue in various animal models. The latter results paved the way for the development of a first phase I clinical trial of myoblast transplantation in patients with severe post-ischemic heart failure. It required the scale-up of human cell production according to good manufacturing procedures, started in june 2000 in Paris and was terminated in november 2001, and was followed by several others. The results were encouraging and prompted the onset of a blinded, multicentric phase II clinical trial for skeletal muscle cells transplantation. Meanwhile, phase I clinical trials also evaluate the safeness and efficacy of various cell types originating from the bone marrow or the peripheral blood. However, potential side effects related to the biological properties of the cells or the delivery procedures are being reported. High quality clinical trials supported by strong pre-clinical data will help to evaluate the role of cell therapy as a potential treatment for heart failure.

Natriuretic peptides in ectopic myocardial tissues originating from mouse embryonic stem cells

In a previous report we described the survival and contractile function of mouse embryonic stem cell-derived cardiomyocytes in the host retroperitoneum. To further understand the nature of embryonic stem cell-derived cardiomyocytes, the study assessed the synthesis of natriuretic peptides in ectopic myocardial tissues of embryonic stem cell origin. Cardiomyocytes formed in embryoid body outgrowths were transplanted into the retroperitoneum of adult nude mice, and the myocardial tissues that developed were characterized by RT-PCR and immunohistochemistry concerning atrial and brain natriuretic peptides (ANP, BNP). In the outgrowths of embryoid bodies in vitro, gene expression of ANP and BNP was detected by RT-PCR and granules positive for the peptides were identified in a few cardiomyocytes by light and electron microscopic immunocytochemistry. Seven days after transplantation the transplants exhibited multidifferentiated teratoma tissues. Developing chamber myocardial tissues positive for cardiac troponin I, cadherin, and connexin 43 were evident in the transplants, which contained ANP-positive cardiomyocytes. Transplants with beating bundles were observed 30 days after transplantation, in which gene expression of both natriuretic peptides was detected. Myocardial tissues with abundant ANP-immunoreactivity, as well as with BNP-immunoreactivity to a lesser extent, were evident in the transplants. Also, myocardial tissues without immunoreactivity for natriuretic peptides were observed. Immunoelectron microscopy showed discernible secretory granules containing ANP and/or BNP in the cardiomyocytes. These results showed that part of the cardiomyocytes in embryonic stem cell-derived ectopic myocardial tissues are capable of producing natriuretic peptides, which suggests that they may be used as an endocrine source for cardiac hormones.

Establishment of Vessel-Like Structures in Long-Term Three-Dimensional Tissue Culture of Myocardium: An Electron Microscopy Study

To assess whether long-term three-dimensional (3D) tissue culture of myocardium enables the in vitro establishment of vessel-like structures, myocardial tissue from newborn mice was incubated under conditions of 3D culture for at least 3 weeks, and studied by phase-contrast microscopy, conventional histology, immunohistochemistry, and electron microscopy. During 3 weeks of culture, a mean 24.35 +/- 3.74% of all aggregates contracted spontaneously. The contracting aggregates displayed a tissue-like architecture with small basal and apical zones, and a large central zone. The basal and apical zone consisted of immature mesenchymal cells. The underlying shell of the aggregate contained many cardiomyocytes. Vessel-like structures were found concentrated within the aggregates. Immunohistochemistry showed that up to 15% of the cells in the central zone of the aggregate were positive for the endothelial-specific BS-I lectin. Vessel-like structures were formed by cells, which often showed intracytoplasmatic lumena. Surrounding the neocapillaries, structures of a rudimentary basal membrane could be detected. A 3D culture of myocardial tissue permits the establishment of a rudimentary capillary network within the tissue aggregates, which presumably guarantees a sufficient tissue perfusion up to a maximum aggregate diameter of approximately 900 microm.