Regeneration of the Infarcted Heart With Stem Cells Derived by Nuclear Transplantation

A Review on the Applications of Natural Biodegradable Nano Polymers in Cardiac Tissue Engineering

As cardiac diseases, which mostly result in heart failure, are increasing rapidly worldwide, heart transplantation seems the only solution for saving lives. However, this practice is not always possible due to several reasons, such as scarcity of donors, rejection of organs from recipient bodies, or costly medical procedures. In the framework of nanotechnology, nanomaterials greatly contribute to the development of these cardiovascular scaffolds as they provide an easy regeneration of the tissues. Currently, functional nanofibers can be used in the production of stem cells and in the regeneration of cells and tissues. The small size of nanomaterials, however, leads to changes in their chemical and physical characteristics that could alter their interaction and exposure to stem cells with cells and tissues. This article aims to review the naturally occurring biodegradable nanomaterials that are used in cardiovascular tissue engineering for the development of cardiac patches, vessels, and tissues. Moreover, this article also provides an overview of cell sources used for cardiac tissue engineering, explains the anatomy and physiology of the human heart, and explores the regeneration of cardiac cells and the nanofabrication approaches used in cardiac tissue engineering as well as scaffolds.

First Evidence of Cardiac Stem Cells From the Left Ventricular Apical Tip in Patients With Left Ventricular Assist Device Implantation

BACKGROUND

Recent studies have challenged the dogma that the adult heart is a postmitotic organ and raise the possibility of the existence of resident cardiac stem cells (CSCs). Our study aimed to explore if these CSCs are present in the "ventricular tip" obtained during left ventricular assist device (LVAD) implantation from patients with end-stage heart failure (HF) and the relationship with LV dysfunctional area extent.

METHODS

Four consecutive patients with ischemic cardiomyopathy and end-stage HF submitted to LVAD implantation were studied. The explanted "ventricular tip" was used as a sample of apical myocardial tissue for the pathological examination. Patients underwent clinical and echocardiographic examination, both standard transthoracic echocardiography (TTE) and speckle tracking echocardiography (STE), before LVAD implantation.

RESULTS

All patients presented severe apical dysfunction, with apical akinesis/diskinesis and very low levels of apical longitudinal strain (-3.5 ± 2.9%). Despite this, the presence of CSCs was demonstrated in pathological myocardial samples of "ventricular tip" in all 4 of the patients. It was found to be a mean of 6 c-kit cells in 10 fields magnification 40×.

CONCLUSIONS

Cardiac stem cells can be identified in the LV apical segment of patients who have undergone LVAD implantation despite LV apical fibrosis.

Current Science of Regenerative Medicine with Stem Cells

Regenerative medicine with stem cells holds great hope for the treatment of degenerative disease. The medical potential of embryonic stem cells remains relatively untapped at this point, and significant scientific hurdles remain to be overcome before these cells might be considered safe and effective for uses in patients. Meanwhile, adult stem cells have begun to show significant capabilities of their own in repair of damaged tissues, in both animal models and early patient trials.

Stem cell therapy for heart failure

The last decade has witnessed the publication of a large number of clinical trials, primarily using bone marrow-derived stem cells as the injected cell. Much has been learned through these "first-generation" clinical trials. The considerable advances in our understanding include (1) cell therapy is safe, (2) cell therapy has been modestly effective, (3) the recognition that in humans bone marrow-derived stem cells do not transdifferentiate into cardiomyocytes or new blood vessels (or at least in sufficient numbers to have any effect). The primary mechanism of action for cell therapy is now believed to be through paracrine effects that include the release of cytokines, chemokines, and growth factors that inhibit apoptosis and fibrosis, enhance contractility, and activate endogenous regenerative mechanisms through endogenous circulating or site-specific stem cells. The new direction for clinical trials includes the use of stem cells capable of cardiac lineage, such as endogenous cardiac stem cells.

Hematopoietic stem cells: an overview

Considerable efforts have been made in recent years in understanding the mechanisms that govern hematopoietic stem cell (HSC) origin, development, differentiation, self-renewal, aging, trafficking, plasticity and transdifferentiation. Hematopoiesis occurs in sequential waves in distinct anatomical locations during development and these shifts in location are accompanied by changes in the functional status of the stem cells and reflect the changing needs of the developing organism. HSCs make a choice of either self-renewal or committing to differentiation. The balance between self-renewal and differentiation is considered to be critical to the maintenance of stem cell numbers. It is still under debate if HSC can rejuvenate infinitely or if they do not possess ''true" self-renewal and undergo replicative senescence such as any other somatic cell. Gene therapy applications that target HSCs offer a great potential for the treatment of hematologic and immunologic diseases. However, the clinical success has been limited by many factors. This review is intended to summarize the recent advances made in the human HSC field, and will review the hematopoietic stem cell from definition through development to clinical applications.

Regenerative therapy and tissue engineering for the treatment of end-stage cardiac failure: new developments and challenges

Regeneration of myocardium through regenerative therapy and tissue engineering is appearing as a prospective treatment modality for patients with end-stage heart failure. Focusing on this area, this review highlights the new developments and challenges in the regeneration of myocardial tissue. The role of various cell sources, calcium ion and cytokine on the functional performance of regenerative therapy is discussed. The evolution of tissue engineering and the role of tissue matrix/scaffold, cell adhesion and vascularisation on tissue engineering of cardiac tissue implant are also discussed.

Renovation of the injured heart with myocardial tissue engineering

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

Hydrogel based injectable scaffolds for cardiac tissue regeneration

Tissue engineering promises to be an effective strategy that can overcome the lacuna existing in the current pharmacological and interventional therapies and heart transplantation. Heart failure continues to be a major contributor to the morbidity and mortality across the globe. This may be attributed to the limited regeneration capacity after the adult cardiomyocytes are terminally differentiated or injured. Various strategies involving acellular scaffolds, stem cells, and combinations of stem cells, scaffolds and growth factors have been investigated for effective cardiac tissue regeneration. Recently, injectable hydrogels have emerged as a potential candidate among various categories of biomaterials for cardiac tissue regeneration due to improved patient compliance and facile administration via minimal invasive mode that treats complex infarction. This review discusses in detail on the advances made in the field of injectable materials for cardiac tissue engineering highlighting their merits over their preformed counterparts.

Stem cell therapy for heart failure

The last decade has witnessed the publication of a large number of clinical trials primarily using bone marrow-derived stem cells as the injected cell. These "first-generation" clinical trials have advanced our understanding and shown us that (1) cell therapy is safe, (2) cell therapy has been modestly effective, and (3) in humans, bone marrow-derived stem cells do not transdifferentiate into cardiomyocytes or new blood vessels (or at least in sufficient numbers to have any effect). The primary mechanism of action for cell therapy is now believed to be through paracrine effects that include the release of cytokines, chemokines, and growth factors that inhibit apoptosis and fibrosis, enhance contractility, and activate endogenous regenerative mechanisms through endogenous circulating or site-specific stem cells. The new direction for clinical trials includes the use of stem cells capable of cardiac lineage, such as endogenous cardiac stem cells.

What does it take to make a heart?

Ever increasing advances are being made in our quest to understand what it takes to direct pluripotent precursor cells to adopt a specific developmental fate. Eventually, the obvious goal is that targeted manipulation of these precursor cells will result in an efficient and reliable production of tissue-specific cells, which can be safely employed for therapeutic purposes. We have gained an incredible insight as to which molecular pathways are involved in governing neural, skeletal and cardiac muscle fate decisions. However, we still face the challenge of how to direct, for example, a cardiac fate in stem cells in the amounts needed to be employed for regenerative means. Equally importantly, we need to resolve critical questions such as: can the in vitro generated cardiomyocytes actually functionally replace damaged heart tissue? Here I will provide an overview of the molecules and signalling pathways that have first been demonstrated in embryological studies to function in cardiogenesis, and summarize how this knowledge is being applied to differentiate mouse and human embryonic stem cells into cardiomyocytes.

Biomaterial strategies for alleviation of myocardial infarction

World Health Organization estimated that heart failure initiated by coronary artery disease and myocardial infarction (MI) leads to 29 per cent of deaths worldwide. Heart failure is one of the leading causes of death in industrialized countries and is expected to become a global epidemic within the twenty-first century. MI, the main cause of heart failure, leads to a loss of cardiac tissue impairment of left ventricular function. The damaged left ventricle undergoes progressive ‘remodelling’ and chamber dilation, with myocyte slippage and fibroblast proliferation. Repair of diseased myocardium with in vitro-engineered cardiac muscle patch/injectable biopolymers with cells may become a viable option for heart failure patients. These events reflect an apparent lack of effective intrinsic mechanism for myocardial repair and regeneration. Motivated by the desire to develop minimally invasive procedures, the last 10 years observed growing efforts to develop injectable biomaterials with and without cells to treat cardiac failure. Biomaterials evaluated include alginate, fibrin, collagen, chitosan, self-assembling peptides, biopolymers and a range of synthetic hydrogels. The ultimate goal in therapeutic cardiac tissue engineering is to generate biocompatible, non-immunogenic heart muscle with morphological and functional properties similar to natural myocardium to repair MI. This review summarizes the properties of biomaterial substrates having sufficient mechanical stability, which stimulates the native collagen fibril structure for differentiating pluripotent stem cells and mesenchymal stem cells into cardiomyocytes for cardiac tissue engineering.

Production of cloned and transgenic embryos using buffalo (Bubalus bubalis) embryonic stem cell-like cells isolated from in vitro fertilized and cloned blastocysts

Here, we report the isolation and characterization of embryonic stem (ES) cell-like cells from cloned blastocysts, generated using fibroblasts derived from an adult buffalo (BAF). These nuclear transfer embryonic stem cell-like cells (NT-ES) grew in well-defined and dome-shaped colonies. The expression pattern of pluripotency marker genes was similar in both NT-ES and in vitro fertilization (IVF) embryo-derived embryonic stem cell-like cells (F-ES). Upon spontaneous differentiation via embryoid body formation, cells of different morphology were observed, among which predominant were endodermal-like and epithelial-like cell types. The ES cell-like cells could be passaged only mechanically and did not form colonies when plated as single cell suspension at different concentrations. When F-ES cell-like, NT-ES cell-like, and BAF cells of same genotype were used for hand-made cloning (HMC), no significant difference (p > 0.05) was observed in cleavage and blastocyst rate. Following transfer of HMC embryos to synchronized recipients, pregnancies were established only with F-ES cell-like and BAF cell-derived embryos, and one live calf was born from F-ES cell-like cells. Further, when transfected NT-ES cell-like cells and BAF were used for HMC, no significant difference (p > 0.05) was observed between cleavage and blastocyst rate. In conclusion, here we report for the first time the derivation of ES cell-like cells from an adult buffalo, and its genetic modification. We also report the birth of a live cloned calf from buffalo ES cell-like cells.

Human cardiac and bone marrow stromal cells exhibit distinctive properties related to their origin

AIMS

Bone marrow mesenchymal stromal cell (BMStC) transplantation into the infarcted heart improves left ventricular function and cardiac remodelling. However, it has been suggested that tissue-specific cells may be better for cardiac repair than cells from other sources. The objective of the present work has been the comparison of in vitro and in vivo properties of adult human cardiac stromal cells (CStC) to those of syngeneic BMStC.

METHODS AND RESULTS

Although CStC and BMStC exhibited a similar immunophenotype, their gene, microRNA, and protein expression profiles were remarkably different. Biologically, CStC, compared with BMStC, were less competent in acquiring the adipogenic and osteogenic phenotype but more efficiently expressed cardiovascular markers. When injected into the heart, in rat a model of chronic myocardial infarction, CStC persisted longer within the tissue, migrated into the scar, and differentiated into adult cardiomyocytes better than BMStC.

CONCLUSION

Our findings demonstrate that although CStC and BMStC share a common stromal phenotype, CStC present cardiovascular-associated features and may represent an important cell source for more efficient cardiac repair.

Aquaporin-1 expression and angiogenesis in rabbit chronic myocardial ischemia is decreased by acetazolamide

Aquaporin-1 (AQP1) is a water channel protein expressed in endothelial and epithelial cells of many tissues, including the vasculature, where it serves to increase water permeability of the cell membrane. Prior studies have also reported that AQP1 plays a central role in tumor angiogenesis by promoting endothelial cell migration. To investigate whether AQP1 might also influence vascular angiogenesis in ischemic myocardium, the expression level of AQP1 for 21 days post myocardial infarction in rabbit hearts was observed. Aquaporin-1 mRNA and protein levels in day 3, and peaked on day 7 post surgery. This correlated well with the pattern of neovascularization and increased water content of infarct border tissue, and suggested that AQP1 may be involved in myocardial angiogenesis in response to ischemia injury. These AQP1-induced changes were tempered by acetazolamide, a carbonic anhydrase inhibitor, which acted by downregulating AQP1 expression. Acetazolamide treatment did not significantly affect the expression of vascular endothelial growth factor in the tissues studied. Our findings indicate a novel role for AQP1 in postnatal angiogenesis, which has implications in diverse pathophysiological conditions including wound healing, tumor metastasis, and organ regeneration.

Repair of senescent myocardium by mesenchymal stem cells is dependent on the age of donor mice

Myocardial infarction is one of the leading causes of mortality in aged people. Whether age of donors of mesenchymal stem cells (MSCs) affects its ability to repair the senescent heart tissue is unknown. In the present study, MSCs from young (2 months) and aged (18 months) green fluorescent protein expressing C57BL/6 mice were characterized with p16(INK4a) and β-gal associated senescence. Myocardial infarction was produced in 18-month-old wild-type C57BL/6 mice transplanted with MSCs from young and aged animals in the border of the infarct region. Expression of p16(INK4a) in MSCs from aged animals was significantly higher (21.5%± 1.2, P < 0.05) as compared to those from young animals (9.2%± 2.8). A decline in the tube-forming ability on Matrigel was also observed in aged MSCs as well as down-regulation of insulin-like growth factor-1, fibroblast growth factor (FGF-2), vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) compared to young cells. Mice transplanted with young MSCs exhibited significant improvement in their left ventricle (LV) systolic and diastolic function as demonstrated by dp/dt(max) , dp/dt(min) , P(max) . Reduction in the LV fibrotic area was concomitant with neovascularization as demonstrated by CD31 and smooth muscle actin (SMA) expression. Real-time RT-PCR analysis for VEGF, stromal cell derived factor (SDF-1α) and GATA binding factor 4 (GATA-4) genes further confirmed the effect of age on MSC differentiation towards cardiac lineages and enhanced angiogenesis. These studies lead to the conclusion that repair potential of MSCs is dependent on the age of donors and the repair of senescent infarcted myocardium requires young healthy MSCs.

Characterization of canine embryonic stem cell lines derived from different niche microenvironments

Embryo-derived stem cells hold enormous potential for producing cell-based transplantation therapies, allowing high-throughput drug screening and delineating early embryonic development. However, potential clinical applications must first be tested for safety and efficacy in preclinical animal models. Due to physiological and genetic parity to humans, the domestic dog is widely used as a clinically relevant animal model for cardiovascular, neurodegenerative, orthopedic, and oncologic diseases. Therefore, we established numerous putative canine embryonic stem cell (cESC) lines by immunodissection of the inner cell mass (ICM), which we termed OVC.ID.1-23, and by explant outgrowths from whole canine blastocysts, named OVC.EX.1-16. All characterized lines were immunopositive for OCT4, SOX2, NANOG, SSEA-3, and SSEA-4; displayed high telomerase and alkaline phosphatase (ALP) activities; and were maintained in this state up to 37 passages ( approximately 160 days). Colonies from OVC.EX lines showed classic domed hESC-like morphology surrounded by a ring of fibroblast-like cells, whereas all OVC.ID lines exhibited a mixed cell colony of tightly packed cESCs surrounded by a GATA6+/CDX2- hypoblast-derived support layer. Spontaneous serum-only differentiation without feeder layers demonstrated a strong lineage selection associated with the colony niche type, and not the isolation method. Upon differentiation, cESC lines formed embryoid bodies (EB) comprised of cells representative of all germinal layers, and differentiated into cell types of each layer. Canine ESC lines such as these have the potential to identify differences between embryonic stem cell line derivations, and to develop or to test cell-based transplantation therapies in the dog before attempting human clinical trials.

Embryonic stem cells attenuate myocardial dysfunction and inflammation after surgical global ischemia via paracrine actions

Stem cell treatment may positively influence recovery and inflammation after shock by multiple mechanisms, including the paracrine release of protective growth factors. Embryonic stem cells (ESCs) are understudied and may have greater protective power than adult bone marrow stem cells (BMSCs). We hypothesized that ESC paracrine protective mechanisms in the heart (decreased injury by enhanced growth factor-mediated reduction of proinflammatory cytokines) would be superior to the paracrine protective mechanisms of the adult stem cell population in a model of surgically induced global ischemia. Adult Sprague-Dawley rat hearts were isolated and perfused via Langendorff model. Hearts were subjected to 25 min of warm global ischemia and 40 min of reperfusion and were randomly assigned into one of four groups: 1) vehicle treated; 2) BMSC or ESC preischemic treatment; 3) BMSC or ESC postischemic treatment; and 4) BMSC- or ESC-conditioned media treatment. Myocardial function was recorded, and hearts were analyzed for expression of tissue cytokines and growth factors (ELISA). Additionally, ESCs and BMSCs in culture were assessed for growth factor production (ELISA). ESC-treated hearts demonstrated significantly greater postischemic recovery of function (left ventricular developed pressure, end-diastolic pressure, and maximal positive and negative values of the first derivative of pressure) than BMSC-treated hearts or controls at end reperfusion. ESC-conditioned media (without cells) also conferred cardioprotection at end reperfusion. ESC-infused hearts demonstrated increased VEGF and IL-10 production compared with BMSC hearts. ESC hearts also exhibited decreased proinflammatory cytokine expression compared with MSC hearts. Moreover, ESCs in cell culture demonstrated greater pluripotency than MSCs. ESC paracrine protective mechanisms in surgical ischemia are superior to those of adult stem cells.

Engineered cardiac organoid chambers: toward a functional biological model ventricle

A growing area in the field of tissue engineering is the development of tissue equivalents as model systems for in vitro experimentation and high-throughput screening applications. Although a variety of strategies have been developed to enhance the structure and function of engineered cardiac tissues, an inherent limitation with traditional myocardial patches is that they do not permit evaluation of the fundamental relationships between pressure and volume that characterize global contractile function of the heart. Therefore, in the following study we introduce fully biological, living engineered cardiac organoids, or simplified heart chambers, that beat spontaneously, develop pressure, eject fluid, contain residual stress, exhibit a functional Frank-Starling mechanism, and generate positive stroke work. We also demonstrate regional variations in pump function following local cryoinjury, yielding a novel engineered tissue model of myocardial infarction. With the unique ability to directly evaluate relevant pressure-volume characteristics and regulate wall stress, this organoid chamber culture system provides a flexible platform for developing a controllable biomimetic cardiac niche environment that can be adapted for a variety of high-throughput and long-term investigations of cardiac pump function.

Stem cells and nuclear reprogramming

Derivation of human embryonic stem (ES) cells from preimplantation embryos ten years ago raised great hopes that they may be an excellent source of cells for cell replacement therapy. However, serious ethical concerns and the risk of immune rejection of allotransplanted cells have hindered the translation of ES cell-based therapies into the clinic. In an attempt to circumvent these barriers, a number of methods have been developed for converting adult somatic cells into a pluripotent state from which ethically acceptable patient-specific mature cells of interest could be derived. These efforts, backed by advances in elucidating the molecular basis of pluripotency, have culminated in successful reprogramming of fibroblasts into ES cell-like cells, termed induced pluripotent stem (iPS) cells, by ectopic expression of only a handful of "stemness" factors. iPS cells possess morphological, molecular and developmental features of conventional blastocyst-derived ES cells and have the potential to serve as a source of therapeutic cells for customized tissue repair, gene therapy, drug discovery, toxicological testing and for studying the molecular basis of human disease. The goal of this review is to provide the current state-of-the-art in this very exciting and dynamic field and to discuss barriers that remain to be removed before the therapeutic potential of iPS cells can be fully realized.

The problem of deception in embryonic stem cell research

The field of embryonic stem cell research has been plagued by exaggeration and misrepresentation, as three major journals have had to retract significant claims about progress in this field. This problem is exacerbated by the politicized climate in which the research is conducted and defended; it may also lie deeper, in a utilitarian ethic that in principle could justify unethical actions for admittedly worthwhile long-term goals. Such an ethic risks undermining the credibility of science, which must show a commitment to the facts that is independent of social and political goals.

Stem cells and cardiac repair: a critical analysis

Utilizing stem cells to repair the damaged heart has seen an intense amount of activity over the last 5 years or so. There are currently multiple clinical studies in progress to test the efficacy of various different cell therapy approaches for the repair of damaged myocardium that were only just beginning to be tested in preclinical animal studies a few years earlier. This rapid transition from preclinical to clinical testing is striking and is not typical of the customary timeframe for the progress of a therapy from bench-to-bedside. Doubtless, there will be many more trials to follow in the upcoming years. With the plethora of trials and cell alternatives, there has come not only great enthusiasm for the potential of the therapy, but also great confusion about what has been achieved. Cell therapy has the potential to do what no drug can: regenerate and replace damaged tissue with healthy tissue. Drugs may be effective at slowing the progression of heart failure, but none can stop or reverse the process. However, tissue repair is not a simple process, although the idea on its surface is quite simple. Understanding cells, the signals that they respond to, and the keys to appropriate survival and tissue formation are orders of magnitude more complicated than understanding the pathways targeted by most drugs. Drugs and their metabolites can be monitored, quantified, and their effects correlated to circulating levels in the body. Not so for most cell therapies. It is quite difficult to measure cell survival except through ex vivo techniques like histological analysis of the target organ. This makes the emphasis on preclinical research all the more important because it is only in the animal studies that research has the opportunity to readily harvest the target tissues and perform the detailed analyses of what has happened with the cells. This need for detailed and usually time-intensive research in animal studies stands in contrast to the rapidity with which therapies have progressed to the clinic. It is now becoming clear through a number of notable examples that progress to the clinic may have occurred too quickly, before adequate testing and independent verification of results could be completed (Check, Nature 446:485-486, 2007; Chien, J Clin Investig 116:1838-1840, 2006; Giles, Nature 442:344-347, 2006). Broad reproducibility and transfer of results from one lab to another has been and always will be essential for the successful application of any cell therapy. So, what is the prognosis for cell therapy to repair heart damage? Will there be an approved cell therapy, or multiple ones, or will it require combinations of more than one cell type to be successful? These are questions often asked. The answers are difficult to know and even more difficult to predict because there are so many variables associated with cell-based therapies. There is much about the biology of cell systems that we still do not understand. Much of the pluripotency or transdifferentiation phenomena (see below) being observed go against accepted and well-tested principles for cell development and fate choice, and has caused a reevaluation of long-accepted theories. Clearly, new pathways for tissue repair and regeneration have been uncovered, but will these new pathways be sufficient to effect significant tissue repair and regeneration? Despite the false starts so far, there is the strong likelihood one or possibly multiple cell therapies will succeed. Clearly, important information has been gained, which should better guide the field to achieving success. When there is the successful verification in patients of a cell therapy, there will be an explosion of technological advances around the approach(es) that succeed. Whatever cells get approved accompanying them will be: more effective delivery methods; growth and storage methods; combination therapies, mixes of cells or cells + gene therapies; combinations with biomaterials and technologies for immune protection, allowing allografting. There are many parallel paths of technology development waiting to be brought together once there is an effective cellular approach. The coming years will no doubt bring some exciting developments.

Improvement of kidney failure with fetal kidney precursor cell transplantation

BACKGROUND

Current therapies for end-stage renal disease have severe limitations. Dialysis is only a temporary treatment and does not restore kidney function. Transplantation is limited by donor organ shortage and immune-related problems. Here, we show that the transplantation of fetal kidney precursor cells reconstitutes kidney tissues, reduces uremic symptoms, and provides life-saving metabolic support in kidney failure animal models.

METHODS

Kidney failure was surgically induced by resecting kidneys, leaving approximately 1/6 of the total kidney mass (5/6 nephrectomy). Fetal kidney precursor cells were isolated from metanephroi of E17.5 rat fetuses using collagenase/dispase digestion. Five weeks after the nephrectomy procedure, isolated fetal kidney precursor cells were transplanted under the kidney capsule of rats using fibrin gel matrix. Six and ten weeks after transplantation, animals were analyzed biochemically and the grafts were retrieved for histological analyses.

RESULTS

Five weeks after the nephrectomy, glomerular hypertrophy, and increased blood urea nitrogen and serum creatinine levels were observed. The cell transplantation into the kidneys of kidney failure-induced rats resulted in kidney tissue reconstitution and the transplanted cells were observed in the reconstitution region of the kidneys as evidenced by the presence of fluorescently labeled cells. In addition, biochemical parameters from serum and urine samples showed improved kidney functions compared with non-treated group without severe immune response after ten weeks.

CONCLUSION

Transplanting fetal kidney precursor cells showed the potential for the partial augmentation of kidney structure and function in the treatment of kidney failure.

The future of cell therapy for myocardial regeneration

There are a number of promising cell therapy products under development for the treatment of heart failure, whether due to myocardial infarction or cardiomyopathy. Looking forward beyond current products in development, there are a multitude of possibilities that hold significant promise; however, cell-based therapies present challenges that are unique to this platform. Results from transplant studies can often be misleading and need to be interpreted in the context of fundamental biologic properties of cells and development. Provided here is a summary of the current and future developments in the field of cell therapy for cardiac regeneration along with some critical insights to interpret the multitude of studies recently undertaken. Summarized are both clinical and preclinical studies that should serve as a useful entrée into this exciting new field of therapeutic development.

Cellular cardiomyoplasty by catheter-based infusion of stem cells in clinical settings

Myocardial infarction is the leading cause of congestive heart failure and death in the industrialized world. However, the intrinsic repair mechanism of the heart is inadequate. Current therapy is limited in preventing ventricular remodeling, but can not regenerate the lost cardiomyocytes. Recent interests have been focused on cellular cardiomyoplasty which is an outside intervention to support the reparative process in the heart through transplantation of stem/progenitor cells or cardiac cells. Cellular cardiomyoplasty with stem cells is a possible option to reverse the adverse hemodynamic and neurohormonal imbalance after myocardial infarction. Experimental studies and clinical trials suggest that cellular cardiomyoplasty may benefit tissue perfusion and contractile performance of the injured heart. Although the mechanisms are still intensively debated, cellular cardiomyoplasty with stem cells has already been introduced into the clinical settings. However, it is an important challenge how stem cells are delivered to targeted area. In early studies on animals, intramyocardial injection of stem cells after thoracotomy is the predominant transplantation route which is not suitable for most patients in clinical settings. Then the catheter-based infusion of stem cells is clinically introduced and rapidly developed in patients because of the safety, convenience and mini-invasion. We mainly review the progress in catheter-based transplantation with stem cells in order to fully understand the application of various intervention-based approaches to stem cells transplantation in clinical settings.

Beraprost sodium enhances neovascularization in ischemic myocardium by mobilizing bone marrow cells in rats

Beraprost sodium, an orally active prostacyclin analogue, has vasoprotective effects such as vasodilation and antiplatelet activities. We investigated the therapeutic potential of beraprost for myocardial ischemia. Immediately after coronary ligation of Sprague-Dawley rats, beraprost (200 microg/kg/day) or saline was subcutaneously administered for 28 days. Four weeks after coronary ligation, administration of beraprost increased capillary density in ischemic myocardium, decreased infarct size, and improved cardiac function in rats with myocardial infarction. Beraprost markedly increased the number of CD34-positive cells and c-kit-positive cells in plasma. Also, four weeks after coronary ligation of chimeric rats with GFP-expressing bone marrow, bone marrow-derived cells were incorporated into the infarcted region and its border zone. Treatment with beraprost increased the number of GFP/von Willebrand factor-double-positive cells in the ischemic myocardium. These results suggest that beraprost has beneficial effects on ischemic myocardium partly by its ability to enhance neovascularization in ischemic myocardium by mobilizing bone marrow cells.

Stem cells for repair of the heart

PURPOSE OF REVIEW

Stem cell therapy for treatment of cardiac disease has shown therapeutic potential.

RECENT FINDINGS

A number of stem and progenitor populations have been identified for potential use in cardiac repair. Each possesses a unique potency that justifies consideration for use. Autologous, unfractionated bone marrow cells or skeletal myoblasts were used in early clinical trails to evaluate reparative effects on recent or record infarcts. In each case, evidence of limited improvement in cardiac function was obtained. Myoblast grafts were unexpectedly correlated with arrhythmias, thereby identifying a safety issue. The small number of patients and the lack of randomized control groups preclude conclusions regarding efficacy. Randomized controlled, intermediate-sized, double-blind clinical trials must be undertaken to this end.

SUMMARY

Cellular therapy may be useful in the treatment of cardiac disease in adults. Appropriate adaptations to meet unique requirements for treatment of pediatric cardiovascular disease may be required. Bone marrow and skeletal myoblasts do not promote true tissue regeneration in spite of observed functional improvement. Trials using cells possessing true potential for (trans)differentiation may elucidate the potential and value of this therapy as a reparative modality. Development of optimal strategies for targeted delivery consistent with pathobiology is of exception clinical relevance.

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.

Myocardial regeneration by embryonic stem cell transplantation: present and future trends

Embryonic stem cells are a promising source for myocardial regeneration due to their pluripotency and plasticity. In theory, embryonic stem cells are capable of self-renewal in an unlimited fashion, and can differentiate into any cell type required for cell-based therapy, including cardiac myocytes. In recent years, embryonic stem cells have been transplanted for cardiac regeneration in animal models, and the results are encouraging. However, there are still many hurdles to be overcome for the clinical application of embryonic stem cells.

In vivo MR imaging of magnetically labeled human embryonic stem cells

INTRODUCTION

Human embryonic stem cells (hES) have emerged as a potentially new therapeutic approach for treatment of heart and other diseases applying the concept of regenerative medicine. A method for in vivo visualization and tracking of transplanted hES would increase our understanding of in vivo hES behavior in both experimental and clinical settings. The aim of this study was to evaluate the feasibility of magnetic labeling and visualization of hES with magnetic resonance imaging (MRI).

METHODS

hES were established and expanded according to standard procedures. After expansion, the cells were cultured under feeder free conditions and magnetically labeled by addition of dextran-coated Ferrum-oxide particles (Endorem) to the medium. Accumulation of small particles of iron-oxide (SPIO) in hES was assessed by Prussian blue staining and electron microscopy. For in vitro MRI, the labeled and unlabeled hES were examined in cell solution and after transplantation into explanted mouse heart ( approximately 100,000 cells) on a Bruker Avance DMX 500 vertical magnet at 11.75 T. A multi-slice, multi spin-echo T(2)-weighted images were obtained. For in vivo imaging, the experiments were performed on male Sprague-Dawley using Bruker Biospec 2.35 T magnet. The hES were directly injected ( approximately 500,000 cells) after surgical procedure (thoracotomy) into anterior left ventricular (LV) wall. Multi-slice T(2)-weighted gradient echo images were obtained using cardiac gating.

RESULTS

hES appeared to be unaffected by magnetic labeling and maintained their ability to proliferate and differentiate. No additive agent for membrane permeabilisation was needed for facilitation of intracellular SPIO accumulation. Prussian blue and electron microscopy have revealed numerous iron particles in the cytoplasm of hES. On T(2)-weighted images, the labeled cells have shown well-defined hyopintense areas at the site of injection in anterior LV wall both in vitro and in vivo.

CONCLUSIONS

It is feasible to magnetically label and visualize hES both in vitro and in vivo. MR visualization of magnetically labeled hES may be a valuable tool for in vivo tracking of hES.

Mammalian stem cells

Stem cells are quickly coming into focus of much biomedical research eventually aiming at the therapeutic applications for various disorders and trauma. It is important, however, to keep in mind the difference between the embryonic stem cells, somatic stem cells and somatic precursor cells when considering potential clinical applications. Here we provide the review of the current status of stem cell field and discuss the potential of therapeutic applications for blood and Immune system disorders, multiple sclerosis, hypoxic-ischemic brain injury and brain tumors. For the complimentary information about various stem cells and their properties we recommend consulting the National Institutes of Health stem cell resources (http://stemcells.nih.gov/info/basics).

The new face of bispecific antibodies: targeting cancer and much more

The term magic bullet was first coined by bacteriologist Paul Ehrlich in the late 1800s to describe a chemical with the ability to specifically target microorganisms while sparing normal host cells. His concept was later expanded to include treatments for cancer, but it is only in recent decades, with development and improvements in monoclonal antibody (mAb) technology, that the full therapeutic implications of "magic bullet" strategies have been realized. Expanding on the success of mAb-targeting, linking the specificity of two mAbs into a single agent, called a bispecific antibody (BiAb), allows for targeting of a therapeutic biological agent or cell to specific tissue antigens. Classically, BiAbs have been used for several decades to redirect cytotoxic T cells or other effector cells to kill tumor cells. Here, we review preclinical models and ongoing phase I clinical trials in which arming polyclonally activated T cells with BiAbs may provide anti-tumor activity without dose-limiting toxicities. Additionally, we review findings from this novel strategy that merges magic bullet technology with hematopoietic stem cells to repair injured myocardium. Arming stem cells with BiAbs directed at injury-associated antigens enhances specific homing and engraftment to myocardial infarctions and may significantly improve cardiac function, strongly suggesting new paradigms for BiAb-targeting applications in tissue repair.

Stem cell factor receptor induces progenitor and natural killer cell-mediated cardiac survival and repair after myocardial infarction

Inappropriate cardiac remodeling and repair after myocardial infarction (MI) predisposes to heart failure. Studies have reported on the potential for lineage negative, steel factor positive (c-kit+) bone marrow-derived hematopoetic stem/progenitor cells (HSPCs) to repair damaged myocardium through neovascularization and myogenesis. However, the precise contribution of the c-kit signaling pathway to the cardiac repair process has yet to be determined. In this study, we sought to directly elucidate the mechanistic contributions of c-kit+ bone marrow-derived hematopoetic stem/progenitor cells in the maintenance and repair of damaged myocardium after MI. Using c-kit-deficient mice, we demonstrate the importance of c-kit signaling in preventing ventricular dilation and hypertrophy, and the maintenance of cardiac function after MI in c-kit-deficient mice. Furthermore, we show phenotypic rescue of cardiac repair after MI of c-kit-deficient mice by bone marrow transplantation of wild-type HSPCs. The transplanted group also had reduced apoptosis and collagen deposition, along with an increase in neovascularization. To better understand the mechanisms underlying this phenotypic rescue, we investigated the gene expression pattern within the infarcted region by using microarray analysis. This analysis suggested activation of inflammatory pathways, specifically natural killer (NK) cell-mediated mobilization after MI in rescued hearts. This finding was confirmed by immunohistology and by using an NK blocker. Thus, our investigation revealed a previously uncharacterized role for c-kit signaling after infarction by mediating bone marrow-derived NK and angiogenic cell mobilization, which contributes to improved remodeling and cardiac function after MI.

Human umbilical cord blood cells: a new alternative for myocardial repair?

Cell therapy for myocardial disease is a rapidly progressive field. However, present strategies of cell transplantation into the infarcted myocardium have limitations from practical points of view. One of the biggest challenges is to achieve a sufficient number of suitable cells. Umbilical cord blood (UCB), an unlimited source of stem/progenitor cells that could be used for transplantation into the injured heart, is readily available. The aim of our review is to describe the potential and prospect of UCB as a new supplier of cells for myocardial repair. The use of UCB stem cells might be of importance to elderly and sick people in whom the availability of autologous stem cells is limited.

The area composita of adhering junctions connecting heart muscle cells of vertebrates. I. Molecular definition in intercalated disks of cardiomyocytes by immunoelectron microscopy of desmosomal proteins

Among sarcomeric muscles the cardiac muscle cells are unique by, inter alia, a systemic and extended cell-cell contact structure, the intercalated disk (ID), comprising frequent and closely spaced arrays of plaque-coated cell-cell adhering junctions (AJs). As some of these junctions may look somewhat like desmosomes and others like fasciae adhaerentes, the dogma has emerged in the literature that IDs contain - like epithelial cells - both kinds of AJs formed by - for the most - mutually exclusive molecular ensembles. This, however, is not the case. In comprehensive immunoelectron microscopic studies of mammalian (human, bovine, rat, mouse) and non-mammalian (chicken, amphibia, fishes) heart muscle tissues, we have localized major constituents of the desmosomal plaques of polar epithelia, desmoplakin, plakophilin-2 and plakoglobin, as well as the desmosomal cadherins, desmoglein Dsg2 and desmocollin Dsc2, in both kinds of ID AJs, independent of the specific morphological appearance. The desmosomal molecules are not restricted to the desmosome-like-looking junctions but can also be detected in junctions appearing similar to the zonula or fascia adhaerens structures. These AJs of cardiac ID are therefore subsumed under the collective term area composita. We discuss our results with respect to the importance of ID junction molecules for the formation, maintenance and function of the heart, particularly in relation to recent findings that deletions of - or mutations in - genes encoding such proteins can cause severe, sometimes lethal damages.

Engineering myocardial tissue

To create an artificial heart is one of the most ambitious dreams of the young field of tissue engineering, a dream that, when publicly announced in 1999 (LIFE initiative around M. Sefton), provoked as much compassion as scepticism in the scientific and lay press. Today, it is fair to state that the field is still far away from having built the "bioartificial heart." Nevertheless, substantial progress has been made over the past 10 years, and a realistic perspective exists to create 3-dimensional heart muscle equivalents that may not only serve as experimental models but could also be useful for cardiac regeneration.

Stem cell transplantation for the treatment of myocardial infarction

Stem cell transplantation provides a potential regenerative therapy for the heart damaged by myocardial infarction. Numerous scientific studies have been undertaken in animals and humans to analyze the safety and efficacy of this new approach. However, at the present time, the results have been mixed and inconclusive, and the mechanism of stem cell transplantation therapy remains unclear. This review discusses the controversies and problems that need to be addressed in future investigations.

Epigenetic modification is central to genome reprogramming in somatic cell nuclear transfer

The recent high-profile reports of the derivation of human embryonic stem cells (ESCs) from human blastocysts produced by somatic cell nuclear transfer (SCNT) have highlighted the possibility of making autologous cell lines specific to individual patients. Cell replacement therapies have much potential for the treatment of diverse conditions, and differentiation of ESCs is highly desirable as a means of producing the ranges of cell types required. However, given the range of immunophenotypes of ESC lines currently available, rejection of the differentiated cells by the host is a potentially serious problem. SCNT offers a means of circumventing this by producing ESCs of the same genotype as the donor. However, this technique is not without problems because it requires resetting of the gene expression program of a somatic cell to a state consistent with embryonic development. Some remodeling of parental DNA does occur within the fertilized oocyte, but the somatic genome presented in a radically different format to those of the gametes. Hence, it is perhaps unsurprising that many genes are expressed aberrantly within "cloned" embryos and the ESCs derived from them. Epigenetic modification of the genome through DNA methylation and covalent modification of the histones that form the nucleosome is the key to the maintenance of the differentiated state of the cell, and it is this that must be reset during SCNT. This review focuses on the mechanisms by which this is achieved and how this may account for its partial failure in the "cloning" process. We also highlight the potential dangers this may introduce into ESCs produced by this technology.

The egg-sharing model for human therapeutic cloning research: managing donor selection criteria, the proportion of shared oocytes allocated to research, and amount of financial subsidy given to the donor

Recent advances in human therapeutic cloning made by Hwang and colleagues have opened up new avenues of therapy for various human diseases. However, the major bottleneck of this new technology is the severe shortage of human donor oocytes. Egg-sharing in return for subsidized fertility treatment has been suggested as an ethically justifiable and practical solution to overcome the shortage of donor oocytes for therapeutic cloning. Because the utilization of shared oocytes in therapeutic cloning research does not result in any therapeutic benefit to a second party, this would necessitate a different management strategy compared to their use for the assisted conception of infertile women who are unable to produce any oocytes of their own. It is proposed that the pool of prospective egg-sharers in therapeutic cloning research be limited only to younger women (below 30 years of age) with indications for either male partner sub-fertility or tubal blockage. With regards to the proportion of the shared gametes being allocated to research, a threshold number of retrieved oocytes should be set that if not exceeded, would result in the patient being automatically removed from the egg-sharing scheme. Any excess supernumerary oocyte above this threshold number can be contributed to science, and allocation should be done in a randomized manner. Perhaps, a total of 10 retrieved oocytes from the patient may be considered a suitable threshold, since the chances of conception are unlikely to be impaired. With regards to the amount of subsidy being given to the patient, it is suggested that the proportion of financial subsidy should be equal to the proportion of the patient's oocytes being allocated to research. No doubt, the promise of future therapeutic benefit may be offered to the patient instead of financial subsidy. However, this is ethically controversial because therapeutic cloning has not yet been demonstrated to be a viable model of clinical therapy and any promises made to the patient might turn out to be illusionary. Hence, it is proposed that a tangible financial subsidy on the medical fees might be the better option for the patient's welfare.