The coronary delivery of marrow stromal cells for myocardial regeneration: pathophysiologic and therapeutic implications

Intracoronary delivery of bone marrow cells to the acutely infarcted myocardium. Optimization of the delivery technique

OBJECTIVES

Intracoronary cell transplantation during catheter balloon inflations may be associated with adverse events. We studied the effectiveness of an alternative transplantation technique--intracoronary cell infusion.

METHODS

Fourteen pigs, which had survived acute myocardial infarction, were randomized into 2 treatment groups and 2 controls. Three days after infarction, 12 pigs underwent allogeneic intracoronary mononuclear bone marrow cell transplantation using either the standard technique (short-term cell injections during repeat balloon inflations, technique A, n = 6) or continuous intracoronary cell infusion without balloon inflations (technique B, n = 6). Implanted cells were stained with fluorescent dye. After transplantation, the pigs were euthanized and myocardial samples were analyzed by fluorescent microscopy.

RESULTS

The mean numbers of fluorescently labeled bone marrow cells in the infarction border zone, in the infarction mid-area and in the center of myocardial infarction were 84, 72 and 55 using technique A, and 29, 57 and 46 using technique B, respectively. The mean cell retention in the infarction border zone of 84 cells for technique A and 29 cells for technique B differed significantly (p = 0.034, two-tailed t test).

CONCLUSION

The continuous intracoronary cell infusion technique is a less efficient cell delivery technique as compared with the standard technique using repeat intracoronary balloon inflations.

Mesenchymal stem cells and cardiac repair: principles and practice

Mesenchymal stem cells (MSCs) are cluster of differentiation 34 (CD34)-CD45-negative nonhematopoietic progenitors derived typically from the stromal fraction of the bone marrow. These stem cells display multipotent properties with a demonstrable differentiation capacity along multiple mesodermal lineages. In the setting of myocardial injury, preclinical studies indicate benefit of both autologous and allogeneic transplantation in line with a recognized immunotolerant profile. Initial clinical experience supports the value of mesenchymal stem-cell-based therapy in ischemic cardiomyopathy. Experience is however limited to naïve mesenchymal stem cells, with efforts underway to identify optimal means of enhancing the cardiogenic potential of transplanted cells through guided cardiopoiesis with the ultimate aim of achieving standardized therapy of the ischemic myocardium.

Stem cell therapy for heart failure: the science and current progress

Cell therapy, particularly with stem cells, has created great interest as a solution to the fact that there are limited treatments for postischemic heart disease and none that can regenerate damaged heart cells to strengthen cardiac performance. From the first efforts with myoblasts to recent clinical trials with bone marrow-derived stem cells, early reports of cell therapy suggest improvement in cardiac performance as well as other clinical end points. Based on these exciting but tentative results, other stem cell types are being explored for their particular advantages as a source of adult stem cells. Autologous adipose-derived stem cells are multilinear and can be obtained relatively easily in large quantities from patients; cardiac-derived stem cells are highly appropriate for engraftment in their natural niche, the heart. Human umbilical cord blood cells are potentially forever young and allogenic adult mesenchymal stem cells appear not to evoke the graft versus host reaction. Human embryonic stem cells are effective and can be scaled up for supply purposes. The recent discovery of induced pluripotentcy in human adult stem cells, with only three transcription factor genes, opens a whole new approach to making autologous human pluripotent stem cells from skin or other available tissues. Despite the excitement, stem cells may have to be genetically modified with heme oxygenase, Akt or other genes to survive transplantation in a hypoxic environment. Homing factors and hormones secreted from transplanted stem cells may be more important than cells if they provide the necessary stimulus to trigger cardiac regrowth to replace scar tissue. As we await results from larger and more prolonged clinical trials, the science of stem cell therapy in cardiac disease keeps progressing.

Bone marrow-derived mesenchymal stem cells for treatment of heart failure: is it all paracrine actions and immunomodulation?

Despite significant advances in medical and surgical management of heart failure, mostly of ischaemic origin, the mortality and morbidity associated with it continue to be high. Pluripotent stem cells are being evaluated for treatment of heart failure. Bone marrow-derived mesenchymal stem cells (MSCs) have been extensively studied. Emerging evidence suggests that locally delivered MSCs can lead to an improvement in ventricular function, but the cellular and molecular mechanisms involved remain unclear. Myocardial regeneration, as proposed by many researchers as the underlying mechanism, has failed to convince the scientific community. Recently some authors have ascribed improvement in ventricular function to paracrine actions of MSCs.A lot has been written about the host immune response triggered by embryonic stem cells and the consequent need for immunosuppression. Not enough work has been done on immune interactions involving allogeneic bone marrow cells. Full potential of stem cell therapy can be realised only when we are able to use allogeneic cells. The potential use of MSCs in cellular therapy has recently prompted researchers to look into their interaction with the host immune response. MSCs have immunomodulatory properties. They cause suppression of proliferation of alloreactive T cells in a dose-dependent manner.Tissue injury causes inflammation and release of several chemokines, cytokines and growth factors. They can cause recruitment of bone marrow-derived MSCs to the injured area. We review the literature on paracrine actions and immune interactions of allogeneic MSCs.

The therapeutic potential of stem cells in heart disease

Coronary heart disease and chronic heart failure are common and have an increasing frequency. Although interventional and conventional drug therapy may delay ventricular remodelling, there is no basic therapeutic regime available for preventing or even reversing this process. Chronic coronary artery disease and heart failure impairs quality of life and are associated with subsequent worsening of the cardiac pump function. Numerous studies within the past few years have been demonstrated, that the intracoronary stem cell therapy has to be considered as a safe therapeutic procedure in heart disease, when destroyed and/or compromised heart muscle must be regenerated. This kind of cell therapy with autologous bone marrow cells is completely justified ethically, except for the small numbers of patients with direct or indirect bone marrow disease (e.g. myeloma, leukaemic infiltration) in whom there would be lesions of mononuclear cells. Several preclinical as well as clinical trials have shown that transplantation of autologous bone marrow cells or precursor cells improved cardiac function after myocardial infarction and in chronic coronary heart disease. The age of infarction seems to be irrelevant to regenerative potency of stem cells, since stem cells therapy in old infarctions (many years old) is almost equally effective in comparison to previous infarcts. Further indications are non-ischemic cardiomyopathy (dilative cardiomyopathy) and heart failure due to hypertensive heart disease.

Therapeutic potentials of human embryonic stem cells in Parkinson's disease

The loss of dopaminergic neurons of the substantia nigra is the pathological hallmark characteristic of Parkinson's disease (PD). The strategy of replacing these degenerating neurons with other cells that produce dopamine has been the main approach in the cell transplantation field for PD research. The isolation, differentiation, and long-term cultivation of human embryonic stem cells and the therapeutic research discovery made in relation to the beneficial properties of neurotrophic and neural growth factors has advanced the transplantation field beyond dopamine-producing cells. The present review addresses recent advances in human embryonic stem cell experimentation in relation to treating PD, as well as cell transplantation techniques in conjunction with alternative therapeutics.

In vitro secreting profile of human mesenchymal stem cells

In addition to their multilineage potential, mesenchymal stem cells (MSCs) also have a wide range of functionality. Not only can MSCs reconstruct a tissue, but they also have the ability to control or cure other cells and can reconstruct a coordinating function. The opportunity to control other cells depends on MSCs being able to secrete factors like cytokines and chemokines. Therefore, we focused on asking, Which factors can be secreted by human MSCs? To answer this question, we analyzed the secreting profile of in vitro-expanded MSCs by using cytokine arrays. The media concentrations of 44 of the 120 analyzed cytokines were significantly increased by MSCs. Conversely, concentrations of 40 cytokines given with the sera were significantly decreased. The data presented here provide an overview about a large range of factors that were secreted by MSCs under cell culture conditions. These data indicate that MSCs demonstrate all previously described functions in cellular interactions without an external stimulus. The MSCs secreted angiogenic, immunosuppressive, anti-apoptotic, and proliferation-stimulating factors.

Lysophosphatidic acid protects mesenchymal stem cells against hypoxia and serum deprivation-induced apoptosis

Bone marrow-derived mesenchymal stem cells (MSCs) have shown great promise for cardiac repair. However, poor viability of transplanted MSCs within the ischemic heart has limited their therapeutic potential. Our previous studies have documented that hypoxia and serum deprivation (hypoxia/SD), induced MSCs apoptosis through the mitochondrial apoptotic pathway. Since serum lysophosphatidic acid (LPA) levels are known to be significantly elevated after acute myocardial infarction and that LPA enhanced survival of other cell systems, we embarked on determining whether LPA protects MSCs against hypoxia/SD-induced apoptosis. We have also investigated the potential mechanism(s) that may mediate such actions of LPA. All experiments were carried out on rat bone marrow MSCs. Apoptosis was induced by exposure of cells to hypoxia/SD in a sealed GENbox hypoxic chamber. Effects of LPA were investigated in the absence and presence of inhibitors that target either G(i)proteins, the mitogen activated protein kinases ERK1/2, or phosphoinositide 3-kinase (PI3K). The data obtained showed that hypoxia/SD-induced apoptosis was significantly attenuated by LPA through Gi-coupled LPA(1) receptors linked to the downstream ERK1/2 and PI3K/Akt signaling pathways that function in parallel. Additional studies have demonstrated that hypoxia/SD-induced activation of mitochondrial dysfunction was virtually abolished by LPA treatment and that inhibition of the LPA(1) receptor, Gi proteins, the PI3K/Akt pathway, or ERKs effectively reversed this protective action of LPA. Taken together, our findings indicate that LPA is a novel, potent survival factor for MSCs and this may prove to be of considerable therapeutic significance in terms of exploiting MSC-based therapy in the infracted myocardium.

Therapeutic applications of mesenchymal stromal cells

Mesenchymal stromal cells (MSC) are multipotent cells that can be derived from many different organs and tissues. They have been demonstrated to play a role in tissue repair and regeneration in both preclinical and clinical studies. They also have remarkable immunosuppressive properties. We describe their application in settings that include the cardiovascular, central nervous, gastrointestinal, renal, orthopaedic and haematopoietic systems. Manufacturing of MSC for clinical trials is also discussed. Since tissue matching between MSC donor and recipient does not appear to be required, MSC may be the first cell type able to be used as an "off-the-shelf" therapeutic product.

Bringing cardiac cell therapy with bone marrow stem cells to the clinic: where are we now?

Stem cell therapy is emerging as a potential therapeutic option for cell death-related heart diseases. Preclinical as well as early-phase human studies have demonstrated the ability for cell therapy to augment perfusion and increase myocardial contractility. In addition, recent intermediate-size randomized trials suggested the potential of bone marrow stem cells to augment left ventricular recovery after a recent myocardial infarction. In general, the effects are modest and often similar despite differences in the study design, cell number or type. Therefore, a number of issues should be addressed before stem cell therapy will become standard clinical practice. They are related to the selection of the optimal cell type, standardization of the cell processing and release criteria. Other issues include timing of the cells injections and cell homing and retention. Further research is needed to understand the mechanisms underlying observed functional and beneficial effects including optimization of myocardial biological effects. Finally, despite overall enthusiasm, safety of the cardiac stem cell therapy should remain under scrutiny. The safety profile needs to be established in the large clinical trials and in a close interaction between translational and clinical research to address conceptual or procedural issues.

The bone marrow--cardiac axis of myocardial regeneration

Congestive heart failure remains the leading cause of morbidity and mortality in the developed world. Current therapies do not address the underlying pathophysiology of this disease, namely, the progressive loss of functional cardiomyocytes. The notion of repairing or regenerating lost myocardium via cell-based therapies remains highly appealing. The recent identification of adult stem cells, including both cardiac stem/progenitor cells and bone marrow stem cells, has triggered an explosive interest in using these cells for physiologically relevant cardiomyogenesis. Enthusiasm for cardiac regeneration via cell therapy has further been fueled by the many encouraging reports in both animals and human studies. Further intensive research in basic science and clinical arenas are needed to make this next great frontier in cardiovascular regenerative medicine a reality. In this review, we focus on the role of bone marrow-derived stem cells and cardiac stem/progenitor cells in cardiomyocyte homeostasis and myocardial repair and regeneration, as well as provide a brief overview of current clinical trials using cell-based therapeutic approaches in patients with heart disease.

Skeletal myoblasts transplanted in the ischemic myocardium enhance in situ oxygenation and recovery of contractile function

It is unclear whether oxygen plays a role in stem cell therapy. Hence, the determination of local oxygenation (Po(2)) in the infarct heart and at the site of transplantation may be critical to study the efficacy of cell therapy. To demonstrate this, we have developed an oxygen-sensing paramagnetic spin probes (OxySpin) to monitor oxygenation in the region of cell transplantation using electron paramagnetic resonance (EPR) spectroscopy. Skeletal myoblast (SM) cells isolated from thigh muscle biopsies of mice were labeled with OxySpin by coculturing the cells with submicron-sized (270 +/- 120 nm) particulates of the probe. Myocardial infarction was created by left coronary artery ligation in mice. Immediately after ligation, labeled SM cells were transplanted in the ischemic region of the heart. The engraftment of the transplanted cells and in situ Po(2) in the heart were monitored weekly for 4 wk. EPR measurements revealed the retention of cells in the infarcted tissue. The myocardial Po(2) at the site of SM cell therapy was significantly higher compared with the untreated group throughout the 4-wk period. Histological studies revealed differentiation and engraftment of SM cells into myotubes and increased incidence of neovascularization in the infarct region. The infarct size in the treated group was significantly decreased, whereas echocardiography showed an overall improvement in cardiac function when compared with untreated hearts. To our knowledge, this the first report detailing changes in in situ oxygenation in cell therapy. The increased myocardial Po(2) positively correlated with neoangiogenesis and cardiac function.

Cellular therapy in Chagas' disease: potential applications in patients with chronic cardiomyopathy

Nearly a century after its discovery, Chagas' disease, caused by the protozoan Trypanosoma cruzi, remains a major health problem in Latin America. Although efforts in transmission control have contributed to a decrease in the number of new cases, approximately a third of chronic Chagasic individuals have or will develop the symptomatic forms of the disease, mainly cardiomyopathy. Chagas' disease is a progressively debilitating disease, which, at the final stages, there are no currently available treatments other than heart transplantation. In this scenario, cellular therapy is being tested as an alternative for millions of patients with heart dysfunction due to Chagas' disease. In this article, we review the studies of cellular therapy in animal models and in patients with Chagasic cardiomyopathy and the possible mechanisms by which cellular therapy may act in this disease.

Stem Cell Therapy for the Heart

Cellular cardiomyoplasty is an expanding field of research that involves numerous types of immature cells administered via several modes of delivery. The purpose of this review is to investigate the benefits of different types of cells used in stem cell research as well as the most efficient mode of delivery. The authors also present data showing that stem cells isolated from bone marrow are present at both 2 weeks and 3 months after engraftment in a myocardial infarction. These cells express muscle markers at both time points, which suggests that they have begun to differentiate into cardiomyocytes. Several questions must be answered, however, before stem cells can be used routinely in the clinic. Once these questions have been addressed, the use of stem cells in clinical practice can be realized.

Feasibility of bone marrow stromal cells autologous transplantation for dilated cardiomyopathy

The feasibility of bone marrow stromal cells autologous transplantation for rabbit model of dilated cardiomyopathy induced by adriamycin was studied. Twenty rabbits received 2 mg/kg of adriamycin intravenously once a week for 8 weeks (total dose, 16 mg/kg) to induce the cardiomyopathy model with the monitoring of cardiac function by transthoracic echocardiography. Marrow stromal cells were isolated from cell-transplanted group rabbits and were culture-expanded on the 8th week. On the 10th week, cells were labeled with 4,6-diamidino-2-phenylindole (DAPI), and then injected into the myocardium of the same rabbits. The results showed that viable cells labeled with DAPI could be identified in myocardium at 2nd week after transplantation. Histological findings showed the injury of the myocardium around the injection site was relieved with less apoptosis and more expression of bcl-2. The echocardiography found the improvement of local tissue movement from (2.12+/-0.51) cm/s to (3.81+/-0.47) cm/s (P<0.05) around the inject site, but no improvement of heart function as whole. It was concluded bone marrow stromal cells transplantation for dilated cardiomyopathy was feasibe. The management of cells in vitro, the quantity and the pattern of the cells transplantation and the action mechanism still need further research.

Donor cell transplantation for myocardial disease: does it complement current pharmacological therapies?This paper is one of a selection of papers published in this Special Issue, entitled Young Investigators' Forum

Heart failure secondary to ischemic heart disease, hypertension, and myocardial infarction is a common cause of death in developed countries. Although pharmacological therapies are very effective, poor prognosis and shorter life expectancy of heart disease patients clearly indicate the need for alternative interventions to complement the present therapies. Since the progression of heart disease is associated with the loss of myocardial cells, the concept of donor cell transplantation into host myocardium is emerging as an attractive strategy to repopulate the damaged tissue. To this end, a number of donor cell types have been tested for their ability to increase the systolic function of diseased hearts in both experimental and clinical settings. Although initial clinical trials with bone marrow stem cells are encouraging, long-term consequences of such interventions are yet to be rigorously examined. While additional laboratory studies are required to address several issues in this field, there is also a clear need for further characterization of drug interactions with donor cells in these interventions. Here, we provide a brief summary of current pharmacological and cell-based therapies for heart disease. Further, we discuss the potential of various donor cell types in myocardial repair, mechanisms underlying functional improvement in cell-based therapies, as well as potential interactions between pharmacological and cell-based therapies.

Limited plasticity of mesenchymal stem cells cocultured with adult cardiomyocytes

In order to assess, in a controlled in vitro model, the differentiation potential of adult bone marrow derived stem cells we have developed a coculture procedure using adult rat cardiomyocytes and mesenchymal stem cells (MSCs) from transgenic GFP positive rats. We investigated in the cocultured MSCs the time course of cellular processes that are difficult to monitor in in vivo experiments. Adult rat cardiomyocytes and adult rat MSCs were cocultured for up to 7 days and analyzed by confocal microscopy. Several markers were studied by immunofluorescence technique. The fluorescent ST-BODIPY-Dihydropyridine was used to label calcium channels in living cells. Intracellular calcium was monitored with the fluorescent probe X-Rhod-1. Immunofluorescence experiments showed the presence of connexin-43 between cardiomyocytes and MSCs and between MSCs, while no sarcomeric structures were observed at any time of the coculture. We looked at the expression of calcium channels and development of voltage-dependent calcium signaling in cocultured MSCs. MSCs showed a time-dependent increase of labeling of ST-BODIPY-Dihydropyridine, reaching a relatively strong level after 72 h of coculture. The treatment with a non-fluorescent DHP, Nifedipine, completely abolished ST-BODIPY labeling. We investigated whether depolarization could modulate intracellular calcium. Depolarization-induced calcium transients increased in MSCs in relation to the coculture time. We conclude that MSCs cocultured with adult cardiomyocytes present preliminary evidence of voltage-dependent calcium modulation uncoupled with the development of nascent or adult myofibrils, thus showing a limited lineage specification and a low plasticity to differentiate in a full cardiomyocyte-like phenotype.

Cardiac repair--fact or fancy?

Patients with ischemic cardiomyopathy have a poor prognosis despite all pharmacological, interventional and surgical treatment modalities currently applied. Heart transplantation remains the ideal treatment for this group of patients but the scarcity of donors hinders its widespread application. The autologous transplantation of stem cells (SCs) for cardiac repair is emerging as a new therapy for patients with myocardial dysfunction early after an acute infarction or ischemic cardiomyopathy. The rationale of this novel method is the enhancement of the repair mechanisms achieved by tissue-specific and circulating stem/progenitor cells. SCs assist naturally occurring myocardial repair by contributing to increased myocardial perfusion and contractile performance especially in the setting of acute myocardial infarction (AMI), but also in patients with chronic ischemic heart failure and advanced, diffuse coronary artery disease. The exact mechanism of their action has not been fully elucidated. Few studies continue to suggest a formation of few new contractile tissue. The majority if investigators believe that these cells do not persist long in the myocardium but that they secrete vascular growth and other cardioprotective factors.

Labeling of skeletal myoblasts with a novel oxygen-sensing spin probe for noninvasive monitoring of in situ oxygenation and cell therapy in heart

We report the labeling (internalization) of skeletal myoblasts (SMs) with a novel class of oxygen-sensing paramagnetic spin probe for noninvasive tracking and in situ monitoring of oxygenation in stem cell therapy using electron paramagnetic resonance (EPR) spectroscopy. SM cells were isolated from thigh muscle biopsies of mice and propagated in culture. Labeling of SM cells with the probe was achieved by coincubating the cells with submicron-sized (270 +/- 120 nm) particulates of the probe in culture for 48 h. The labeling had no significant effect on the viability or proliferation of the cells. The SM cells labeled with the probe were transplanted in the infarcted region of mouse hearts. The engraftment of the transplanted cells in the infarct region was verified by using MY-32 staining for skeletal myocytes. The in situ Po(2) in the heart was determined noninvasively and repeatedly for 4 wk after transplantation. The results showed significant enhancement of myocardial oxygenation at the site of cell transplant compared with untreated control. In conclusion, labeling of SM cells with the oxygen-sensing spin probe offers a unique opportunity for the noninvasive monitoring of transplanted cells as well as in situ tissue Po(2) in infarcted mouse hearts.

Surgery Insight: surgical methods to reverse left ventricular remodeling

The management of patients with congestive heart failure (CHF) is challenging and the mortality with medical therapy alone is high. Left ventricular dilatation represents one of the strongest predictors of mortality in CHF, and a variety of surgical interventions have been proposed over the years to reverse ventricular remodeling. The most common surgical methods currently used are myocardial revascularization, left ventricular restoration, mitral valve repair, surgical ablation of atrial fibrillation, and employment of diastolic support and ventricular assist devices. In many patients a combination of these procedures is required to address the multiple pathophysiologic components of CHF. As techniques are refined and more data become available, the results of surgical treatment of heart failure are likely to improve. In addition, advances in innovations such as gene therapy, cell therapy and engineered artificial myocardial tissue will hopefully bring additional benefits to this problematic therapy over the next few years. In this review we discuss the characteristics of the most common surgical techniques for reversing left ventricular remodeling.

Regenerative medicine for cardiovascular disorders-new milestones: adult stem cells

Cardiovascular disorders are the leading causes of mortality and morbidity in the developed world. Cell-based modalities have received considerable scientific attention over the last decade for their potential use in this clinical arena. This review was intended as a brief overview on the subject of therapeutic potential of adult stem cells in cardiovascular medicine with basic science findings and the current status of clinical applications. The historical perspective and basic concepts are reviewed and a description of current applications and potential adverse effects in cardiovascular medicine is given. Future improvements on cell-based therapies will likely provide remarkable improvement in survival and quality of life for millions of patients with cardiovascular disorders.

Potential Hazards and Technical Considerations Associated With Myocardial Cell Transplantation Protocols for Ischemic Myocardial Syndrome

Cell transplantation has recently emerged as a promising therapeutic approach to ischemic cardiomyopathy syndromes. Clinical studies suggest important benefits, including improved myocardial perfusion and function. The safety profile so far seems to be high overall, although the technique may harbor several adverse effects, such as ventricular arrhythmia, acceleration of atherosclerosis or restenosis, and induction of ischemic events. Multiple factors may affect the safety of cell infusion into the diseased heart, including the mode of delivery, the type of cells injected, compound characterization, and the heart status, function, and arrhythmogenic potential. Also, any adjunctive treatment used to enhance cellular homing and/or transdifferentiation increases the likelihood of unexpected local or systemic toxicity or side effects. In the present review, we discuss the potential hazards of this novel treatment and its relationship to technical considerations.

Basic fibroblast growth factor controls migration in human mesenchymal stem cells

Little is known about the migration of mesenchymal stem cells (MSCs). Some therapeutic approaches had demonstrated that MSCs were able to regenerate injured tissues when applied from different sites of application. This implies that MSCs are not only able to migrate but also that the direction of migration is controlled. Factors that are involved in the control of the migration of MSCs are widely unknown. The migratory ability of isolated MSCs was tested in different conditions. The migratory capability was examined using Boyden chamber assay in the presence or absence of basic fibroblast growth factor (bFGF), erythropoietin, interleukin-6, stromal cell-derived factor-beta, and vascular endothelial growth factor. bFGF in particular was able to increase the migratory activity of MSCs through activation of the Akt/protein kinase B (PKB) pathway. The results were supported by analyzing the orientation of the cytoskeleton. In the presence of a bFGF gradient, the actin filaments developed a parallelized pattern that was strongly related to the gradient. Surprisingly, the influence of bFGF was not only an attraction but also routing of MSCs. The bFGF gradient experiment showed that low concentrations of bFGF lead to an attraction of the cells, whereas higher concentrations resulted in repulsion. This ambivalent effect of bFGF provides the possibility to a purposeful routing of MSCs.

Effect of intracoronary transplantation of autologous bone marrow-derived mononuclear cells on outcomes of patients with refractory chronic heart failure secondary to ischemic cardiomyopathy

Recent studies have indicated that stem cell implantation increases cardiac function by repairing damaged myocardium. We investigated whether intracoronary transplantation of autologous bone marrow-derived mononuclear cells (BMMCs) confers beneficial effects in patients with refractory chronic heart failure. Twenty-eight patients received standard heart failure medication and BMMC transplantation (BMMC treatment) or standard medication only (controls). BMMCs were harvested from each patient. Clinical manifestations, biochemical assays, rhythm studies, echocardiograms, and positron emission tomograms were recorded. Fourteen patients with cell grafting had symptomatic relief of heart failure within 3 days. Left ventricular ejection fraction increased by 9.2% and 10.5% at 1 week and 3 months after the procedure, respectively, versus baseline (p < 0.01 for the 2 comparisons). Left ventricular end-systolic volume decreased by 30.7% after 3 months (p < 0.01). Brain natriuretic peptide levels at days 3 and 7 after cell infusion significantly decreased by 69.2% and 70.4%, respectively, whereas atrial natriuretic peptide levels increased by 30.1% at day 7. Positron emission tomographic analysis showed a significant increase in cell viability of 10.3% in the infarcted zone. No patient died in the BMMC-treated group at 6-month follow-up. In contrast, heart failure did not improve in any control patient. Left ventricular ejection fraction decreased by 7.2% after 3 months. Two control patients died from heart failure within 6 months. In conclusion, this is the first demonstration in humans that intracoronary BMMC transplantation is a feasible and safe therapeutic strategy to decrease symptoms, increase cardiac function, and possibly prolong life in patients with end-stage heart failure refractory to standard medical therapy.

Paracrine action enhances the effects of autologous mesenchymal stem cell transplantation on vascular regeneration in rat model of myocardial infarction

BACKGROUND

There are several reports that engrafted mesenchymal stem cells (MSCs) stimulate angiogenesis in the ischemic heart, but the mechanism remains controversial. We hypothesize that transplantation of MSCs enhances vascular regeneration through a paracrine action.

METHODS

A transmural myocardial infarction was created by ligation of the left anterior descending coronary artery in rats. Those with an ejection fraction less than 0.70 1 week after myocardial infarction were included. Autologous MSCs (1 x 10(7); 0.2 mL) or culture medium (0.2 mL) was injected intramyocardially into the periinfarct zone (50 microL/injection at four sites; n = 20/group). At 2 weeks after transplantation, Western blot analysis was used to assay the paracrine factors and proapoptotic proteins. Echocardiography to assess heart function was performed on additional groups at 8 weeks after implantation.

RESULTS

The angiogenic factors basic fibroblast growth factor, vascular endothelial growth factor, and stem cell homing factor (stromal cell-derived factor -1alpha) increased in the MSC-treated hearts compared with medium-treated hearts. This was accompanied by a downregulation of proapoptotic protein Bax in ischemic myocardium. Similarly, capillary density increased about 40% in MSC-treated hearts compared with medium-treated hearts (p = 0.001). Left ventricular contractility, indicated by fractional shortening, improved in MSC-treated hearts at 2 months after implantation (MSCs: 48.6% +/- 19.9%; medium: 18.7% +/- 6.4%; p = 0.004).

CONCLUSIONS

Autologous MSC transplantation attenuates left ventricular remodeling and improves cardiac performance. The major mechanism appears to be paracrine action of the engrafted cells, increasing angiogenesis and cytoprotection.

Safety of intramyocardial injection of autologous bone marrow cells to treat myocardial ischemia in pigs

OBJECTIVE

The purpose of this study is to determine the potential adverse consequences of intracardiac injections of bone marrow mononuclear cells (BMCs) to facilitate the revascularization of ischemic myocardium.

BACKGROUND

Bone marrow mononuclear cells are used to treat heart failure, though there are few studies that evaluated the safety of BMC transplantation for chronic myocardial ischemia.

METHODS

The pigs received coronary ameroid constrictors to induce chronic myocardial ischemia and left ventricular dysfunction. At 4 weeks, autologous BMCs were injected intramyocardially by Boston Scientific Stiletto catheter with low-dose (10(7) cells) or high-dose BMC (10(8)). Control animals received saline. Blood samples were collected for hematological and chemical indices, including cardiac enzyme levels at regular time intervals postinfarction. At 7 weeks, animals underwent electrophysiological study to evaluate the arrhythmic potential of transplanted BMC, followed by necropsy and histopathology.

RESULTS

No mortalities were associated with intramyocardial delivery of BMC or saline. At Day 0, the total creatine phosphokinase (CPK) was in the normal range in all groups. All groups had significant elevations in CPK after ameroid placement, with no significant differences between groups. At 7 weeks, CPK in all groups had returned to pretreatment levels. Electrophysiological assessment revealed that one control animal had an inducible arrhythmia. No arrhythmias were induced in low- or high-dose BMC-treated pigs. There were no histopathological changes associated with BMC injection.

CONCLUSION

This study showed, in a clinically relevant large-animal model, that catheter-based intramyocardial injection of autologous BMC into ischemic myocardium is safe.

Characterization and clinical application of human CD34+ stem/progenitor cell populations mobilized into the blood by granulocyte colony-stimulating factor

A phase I study was performed to determine the safety and tolerability of injecting autologous CD34(+) cells into five patients with liver insufficiency. The study was based on the hypothesis that the CD34(+) cell population in granulocyte colony-stimulating factor (G-CSF)-mobilized blood contains a subpopulation of cells with the potential for regenerating damaged tissue. We separated a candidate CD34(+) stem cell population from the majority of the CD34(+) cells (99%) by adherence to tissue culture plastic. The adherent and nonadherent CD34(+) cells were distinct in morphology, immunophenotype, and gene expression profile. Reverse transcription-polymerase chain reaction-based gene expression analysis indicated that the adherent CD34(+) cells had the potential to express determinants consistent with liver, pancreas, heart, muscle, and nerve cell differentiation as well as hematopoiesis. Overall, the characteristics of the adherent CD34(+) cells identify them as a separate putative stem/progenitor cell population. In culture, they produced a population of cells exhibiting diverse morphologies and expressing genes corresponding to multiple tissue types. Encouraged by this evidence that the CD34(+) cell population contains cells with the potential to form hepatocyte-like cells, we gave G-CSF to five patients with liver insufficiency to mobilize their stem cells for collection by leukapheresis. Between 1 x 10(6) and 2 x 10(8) CD34(+) cells were injected into the portal vein (three patients) or hepatic artery (two patients). No complications or specific side effects related to the procedure were observed. Three of the five patients showed improvement in serum bilirubin and four of five in serum albumin. These observations warrant further clinical trials.

Human adipose tissue-derived mesenchymal stem cells improve postnatal neovascularization in a mouse model of hindlimb ischemia

BACKGROUND/AIM

It has been reported that adipose tissue contain progenitor cells with angiogenic potential and that therapy based on adipose tissue-derived progenitor cells administration may constitute a promising cell therapy in patients with ischemic disease. In this study we evaluated the effect of culture-expanded mesenchymal stem cells (MSC) derived from adipose tissue on neovascularization and blood flow in an animal model of limb ischemia in immunodeficient mice.

METHODS

MSC were cultured from human adipose tissue by collagenase digestion. Hindlimb ischemia was created by ligating the proximal femoral artery of male nude mice. Human adipose tissue stromal cells (hADSC) were transplanted one day or 7 days after ligation.

RESULTS

During culture expansion of hADSC CD34 expression was downregulated. The laser Doppler perfusion index was significantly higher in the CD34(-), Flk-1(-), CD31(-) ADSC-transplanted group than in the control group, even when cells were transplanted 7 days after hindlimb ischemia. Histological examination showed that hADSC transplantation recovered muscle injury and increased vascular density, compared with the control group. The effect of hADSC was correlated with the number of transplanted cells, but not with the ratio of CD34 expression. In vitro, hADSC can form vessel-like structure and express von Willibrand Factor. Conditioned media from hADSC increased proliferation and inhibited apoptotic cell death in of human aortic endothelial cells.

CONCLUSION

This study showed that hADSC can be an ideal source for therapeutic angiogenesis in ischemic disease.

Stem cell therapy in ischemic heart disease

Coronary artery disease (CAD) remains the leading cause of death in the Western world. The high impact of its main sequelae, acute myocardial infarction and congestive heart failure (CHF), on the quality of life of patients and the cost of health care drives the search for new therapies. The recent finding that stem cells contribute to neovascularization and possibly improve cardiac function after myocardial infarction makes stem cell therapy the most highly active research area in cardiology. Although the concept of stem cell therapy may revolutionize heart failure treatment, several obstacles need to be addressed. To name a few: 1) Which patient population should be considered for stem cell therapy? 2) What type of stem cell should be used? 3) What is the best route for cell delivery? 4) What is the optimum number of cells that should be used to achieve functional effects? 5) Is stem cell therapy safer and more effective than conventional therapies? The published studies vary significantly in design, making it difficult to draw conclusions on the efficacy of this treatment. For example, different models of ischemia, species of donors and recipients, techniques of cell delivery, cell types, cell numbers and timing of the experiments have been used. However, these studies highlight the landmark concept that stem cell therapy may play a major role in treating cardiovascular diseases in the near future. It should be noted that stem cell therapy is not limited to the treatment of ischemic cardiac disease. Non-ischemic cardiomyopathy, peripheral vascular disease, and aging may be treated by stem cells. Stem cells could be used as vehicle for gene therapy and eliminate the use of viral vectors. Finally, stem cell therapy may be combined with pharmacological, surgical, and interventional therapy to improve outcome. Here we attempt a systematic overview of the science of stem cells and their effects when transplanted into ischemic myocardium.

Homing of intravenously infused embryonic stem cell-derived cells to injured hearts after myocardial infarction

OBJECTIVE

The present study was designed to test whether intravenously infused embryonic stem cell-derived cells could translocate to injured myocardium after myocardial infarction and improve cardiac function.

METHODS

Cultured embryonic stem cell-derived cells were transfected with green fluorescent protein. Embryonic stem cell-derived cells were administered through the tail vein (approximately 10(7) cells in 1 mL of medium for each rat) every other day for 6 days in 45 rats after myocardial infarction. Six weeks after myocardial infarction and cell infusion, cardiac function, blood flow, and the numeric density of arterioles were measured to test the benefits of cell therapy. An in vitro Transwell assay was performed to evaluate the embryonic stem cell migration.

RESULTS

Ventricular function, regional blood flow, and arteriole density were significantly increased in rats receiving intravenously infused embryonic stem cell-derived cells compared with control rats after myocardial infarction. Histologic analysis demonstrated that infused embryonic stem cell-derived cells formed green fluorescent protein-positive grafts in infarcted myocardium. Additionally, positive immunostaining for cardiac troponin I was found in hearts after myocardial infarction receiving embryonic stem cell-derived cell infusion that corresponded to the green fluorescent protein-positive staining. The Transwell migration assay indicated that cultured neonatal rat cardiomyocytes with overexpression of tumor necrosis factor alpha induced greater migration of embryonic stem cells compared with cardiomyocytes without tumor necrosis factor alpha expression.

CONCLUSIONS

Our data demonstrate that intravenously infused embryonic stem cell-derived cells homed to the infarcted heart, improved cardiac function, and enhanced regional blood flow at 6 weeks after myocardial infarction. The in vitro migration assay suggested that such a homing mechanism could be associated with locally released cytokines, such as tumor necrosis factor alpha, that are upregulated in the setting of acute myocardial infarction and heart failure.

Autologous bone marrow cell transplantation improves left ventricular function in rabbit hearts with cardiomyopathy via myocardial regeneration-unrelated mechanisms

Recent studies suggest transplanted bone marrow cells (BMCs) can be used to reconstitute coronary vessels and myocardium following acute myocardial infarction, thereby improving cardiac function. We sought to investigate the therapeutic potential of BMC transplantation in the treatment of nonischemic cardiomyopathy. Experimental cardiomyopathy was produced by treating rabbits for 8 weeks with doxorubicin (2 mg/kg per week). Two weeks after the treatment was finished, freshly aspirated BMCs or an equivalent volume of phosphate-buffered saline was injected directly into the left ventricular free wall. Four weeks later, heart function was examined during perfusion on a Langendorff apparatus. Left ventricular developed pressure and +/-dp/dt were significantly better in the transplantation group, among which echocardiography also showed significantly better ejection fractions. In addition, left ventricular weights as a fraction of body weight and left ventricular wall thicknesses were both lower in rabbits transplanted with BMCs than in controls. Immunohistochemical analyses carried out 2 weeks after transplantation showed no new myocardium and a very small number of endothelial cells originating from BMCs. On the other hand, immunoblotting revealed upregulated expression of transforming growth factor-beta1 and downregulated expression of matrix metalloproteinase-1 and tumor necrosis factor-alpha following BMC transplantation. In conclusion, autologous BMC transplantation into cardiomyopathic rabbit hearts ameliorates the decline in ventricular function without regenerating cardiomyocytes, most likely by altering expression of various cytokines.

Evidence supporting paracrine hypothesis for Akt-modified mesenchymal stem cell-mediated cardiac protection and functional improvement

We previously reported that intramyocardial injection of bone marrow-derived mesenchymal stem cells overexpressing Akt (Akt-MSCs) inhibits ventricular remodeling and restores cardiac function measured 2 wk after myocardial infarction. Here, we report that the functional improvement occurs in < 72 h. This early remarkable effect cannot be readily attributed to myocardial regeneration from the donor cells. Thus, we hypothesized that paracrine actions exerted by the cells through the release of soluble factors might be important mechanisms of tissue repair and functional improvement after injection of the Akt-MSCs. Indeed, in the current study we demonstrate that conditioned medium from hypoxic Akt-MSCs markedly inhibits hypoxia-induced apoptosis and triggers vigorous spontaneous contraction of adult rat cardiomyocytes in vitro. When injected into infarcted hearts, the Akt-MSC conditioned medium significantly limits infarct size and improves ventricular function relative to controls. Support to the paracrine hypothesis is provided by data showing that several genes, coding for factors (VEGF, FGF-2, HGF, IGF-I, and TB4) that are potential mediators of the effects exerted by the Akt-MSC conditioned medium, are significantly up-regulated in the Akt-MSCs, particularly in response to hypoxia. Taken together, our data support Akt-MSC-mediated paracrine mechanisms of myocardial protection and functional improvement.

Intramyocardial injection of allogenic bone marrow-derived mesenchymal stem cells without immunosuppression preserves cardiac function in a porcine model of myocardial infarction

BACKGROUND

We investigated the efficacy of directly injected allogenic bone marrow-derived mesenchymal stem cells in improving left ventricular function in a porcine model of myocardial infarction.

METHODS

Left ventricular infarction was created in 16 adult Yorkshire pigs by coil embolization and thrombotic occlusion distal to the second diagonal artery. One month after myocardial infarction was induced, the animals were randomized to either direct injection of allogenic mesenchymal stem cells or sham treatment (culture medium). Allogenic bromodeoxyuridine-labeled mesenchymal stem cells (2 +/- 0.1 x 10(8)) were directly injected into the infarct and peri-infarct areas during an open chest procedure. No immunosuppressive therapy was used. The left ventricular function was measured using serial biplane left ventricular angiography at baseline, 30, 60, and 90 days before sacrifice. Mesenchymal stem cells were localized using bromodeoxyuridine, and differentiation of mesenchymal stem cells was assessed by confocal microscopic colocalization of bromodeoxyuridine with immunofluorescent antibodies specific for cardiomyocytes (troponin I and MF-20) and endothelial cells (von Willebrand factor).

RESULTS

Mesenchymal stem cells labeled with bromodeoxyuridine engrafted the peri-infarct zone and colocalized with both cardiomyocyte-specific and endothelial cell-specific immunofluorescence. No intramyocardial bromodeoxyuridine was observed in sham-treated animals. At the time of the mesenchymal stem cell injection 30 days after myocardial infarction, the left ventricular ejection fraction (LVEF) was 58% +/- 3% in mesenchymal stem cell-treated pigs and 56% +/- 2% in sham-treated pigs (P = NS). LVEF deteriorated progressively thereafter in untreated pigs (8.5% and 10.5% decline at 60 days and 90 days after myocardial infarction, respectively), but was preserved in mesenchymal stem cell-treated pigs (2.1% increase and -2.0% decline at 60 and 90 days post-MI respectively) (P < .05).

CONCLUSIONS

Direct intramyocardial injection of mesenchymal stem cells results in successful intramyocardial engraftment and differentiation into cardiomyocytes and endothelial cells and preserves left ventricular function after myocardial infarction in pigs.

Extracardiac progenitor cells repopulate most major cell types in the transplanted human heart

BACKGROUND

Extracardiac progenitor cells are capable of repopulating cardiomyocytes at very low levels in the human heart after injury. Here, we explored the extent of endothelial, smooth muscle, and Schwann cell chimerism in patients with sex-mismatched (female-to-male) heart transplants.

METHODS AND RESULTS

Autopsy specimens from 5 patients and endomyocardial biopsies from 7 patients were used for this study. Endothelial, vascular smooth muscle, and Schwann cells were stained with antibodies against CD31 or Ulex europaeus lectin, smooth muscle alpha-actin, and S-100, respectively, and the Y chromosome was identified with in situ hybridization. Biopsy specimens from 1, 4, 6, and 12 months and 5 and 10 years after heart transplantation were evaluated. Y-positive cells were counted by conventional bright-field microscopy and confirmed by confocal microscopy. Endothelial cells showed the highest degree of chimerism, averaging 24.3+/-8.2% from extracardiac sources. Schwann cells showed the next highest chimerism, averaging 11.2+/-2.1%; vascular smooth muscle cells averaged 3.4+/-1.8%. All 3 cell types showed substantially higher chimerism than we previously observed for cardiomyocytes (0.04+/-0.05%). Endothelial chimerism was much higher in the microcirculation than in larger vessels. Analysis of serial endomyocardial biopsies revealed that high levels of endothelial chimerism occurred as early as 1 month after transplantation (22+/-6.6%) with no significant increases even up to 10 years after cardiac transplantation.

CONCLUSIONS

Extracardiac progenitor cells are capable of repopulating most major cell types in the heart, but they do so with varying frequency. The signals for endothelial progenitor recruitment occur early and could relate to injury during allograft harvest or transplantation. The high degree of endothelial chimerism may have immune implications such as for myocardial rejection or graft vasculopathy.

Resident progenitors and bone marrow stem cells in myocardial renewal and repair

Although cardiac transplantation is still the treatment of choice for end-stage heart disease, the side effects derived from the use of immunosuppressants and the limited availability of donors have prompted the search for alternative therapeutic strategies. Among other possibilities, cell transplantation approaches have recently emerged as new alternatives to stimulate myocardial regeneration. These approaches are mainly based on the increasing number of reports documenting the plasticity of stem cells of various origins, particularly the ability of several types of embryonic and adult stem cells to give rise to cardiomyocytes. Unprecedented in the field of 'translational research' and based on the urgent need for alternative therapies, the promising results obtained with animal models have been quickly transferred to the clinical arena, where numerous small pilot studies using different cell types are already ongoing and/or have reported promising results. Nevertheless, the lack of randomization, the variability and small size of the treated cohorts and the use of mixed populations of cells have often clouded the significance and prevented a mechanistic interpretation of the results. Here, we briefly review the use of bone-marrow-derived and cardiac-derived stem/progenitor cells in myocardial regeneration studies and discuss their significance for the future of the field of myocardial regeneration.

Potential application for mesenchymal stem cells in the treatment of cardiovascular diseases

Stem cells isolated from various sources have been shown to vary in their differentiation capacity or pluripotentiality. Two groups of stem cells, embryonic and adult stem cells, may be capable of differentiating into any desired tissue or cell type, which offers hope for the development of therapeutic applications for a large number of disorders. However, major limitations with the use of embryonic stem cells for human disease have led researchers to focus on adult stem cells as therapeutic agents. Investigators have begun to examine postnatal sources of pluripotent stem cells, such as bone marrow stroma or adipose tissue, as sources of mesenchymal stem cells. The following review focuses on recent research on the use of stem cells for the treatment of cardiovascular and pulmonary diseases and the future application of mesenchymal stem cells for the treatment of a variety of cardiovascular disorders.

Persistence of marrow stromal cells implanted into acutely infarcted myocardium: observations in a xenotransplant model

OBJECTIVE

It has been reported that unmatched adult bone marrow stromal cells could be tolerated by immune-competent allotransplant or xenotransplant recipients under various conditions. This study examined whether xenogeneic bone marrow stromal cells implanted immediately after myocardial infarction can survive and differentiate, attenuating deterioration in left ventricular function.

METHODS

In groups I and II (n = 34), myocardial infarctions were created in immunocompetent adult Lewis rats by proximal left coronary artery ligation. In group I, 3 x 10(6)lacZ-labeled mouse bone marrow stromal cells were immediately injected into the peri-infarct area of the left ventricle, whereas in group II, only culture medium was injected. There were 10 early and 4 late deaths. At 4 weeks after injection, hearts were stained for beta-galactosidase and troponin IC. In groups IIIA and IIIB, lacZ-labeled mouse skin fibroblasts were implanted into rat myocardium (n = 10 each) with and without left coronary artery ligation, respectively, and the rats were killed serially. In group IV, animals underwent sham surgery (n = 5, no deaths). At 4 weeks, surviving rats in groups I, II, and IV (n = 10, n = 10, and n = 5, respectively) underwent blinded transthoracic echocardiography for ventricular function studies.

RESULTS

In group I, labeled mouse-derived bone marrow stromal cells were found within rat myocardium that stained positively for troponin IC 4 weeks after implantation. Functionally, mean left ventricular ejection fraction (P = .007), stroke volume (P = .03), and fractional shortening (P = .02) were all significantly higher in group I than in group II. In groups IIIA and IIIB, mouse fibroblasts induced cellular infiltration with rapid loss of donor cells. No labeled cells were found after 4 days. In group IV, there was no change in cardiac function.

CONCLUSION

Xenogeneic bone marrow stromal cells implanted into acutely ischemic myocardium induced by coronary artery ligation were immunologically tolerated, survived and differentiated, resulting in a cardiac chimera which improved left ventricular function. This unique immunologic tolerance may suggest the feasibility of using bone marrow stromal cells as universal donor cells.

Characterization of multipotent mesenchymal stem cells from the bone marrow of rhesus macaques

The isolation and characterization of embryonic and adult stem cells from higher-order mammalian species will enhance the understanding of the biology and therapeutic application of stem cells. The aim of this study was to purify rhesus mesenchymal stem cells (MSCs) from adult bone marrow and to characterize functionally their abilities to differentiate along diverse lineages. Adherent cells from adult rhesus macaque bone marrow were characterized for their growth characteristics, lineage differentiation, cell-surface antigen expression, telomere length, chromosome content, and transcription factor gene expression. Rhesus bone marrow MSCs (BMSCs) are very heterogeneous, composed of primarily long, thin cells and some smaller, round cells. The cells are capable of differentiating along osteogenic, chondrogenic, and adipogenic lineages in vitro. The cell morphology and multipotential differentiation capabilities are maintained throughout extended culture. They express CD59, CD90 (Thy-1), CD105, and HLA-1 and were negative for hematopoietic markers such as CD3, CD4, CD8, CD11b, CD13, CD34, and platelet endothelial cell adhesion molecule-1 (CD31). BMSCs were also demonstrated to express the mRNA for important stem cell-related transcription factors such as Oct-4, Sox-2, Rex-1, and Nanog. Rhesus BMSCs have a normal chromosome content, and the shortening of telomeres is minimal during early passages. These data demonstrate that BMSCs isolated from rhesus macaques have a high degree of commonality with MSCs isolated from other species. Therefore, isolation of these cells provides an effective and convenient method for rapid expansion of pluripotent rhesus MSCs.

Cellular and molecular therapeutic modalities for arterial obstructive syndromes

Arterial obstructive syndromes result in heart disease, stroke and limb loss, disability, and mortality. Currently available therapeutics for patients with these conditions are inadequate or fail in a significant number of patients. The development of novel therapies for severe coronary arterial disease (CAD), peripheral arterial disease (PAD), and cerebral vascular disease (CVD) is a major goal for modern medicine. Molecular and cell-based therapies for arterial obstructive syndromes have the potential to become clinically useful in the near future. Molecular therapy employs angiogenic proteins and genes in order to initiate the development of new blood vessels that by-pass an arterial occlusion. The induction of a collateral artery system is termed therapeutic angiogenesis or neovascularization. Proteins have been delivered either directly into the ischemic area or via a vector encoding an angiogenic gene. Both protein and gene therapies have been associated with promising preclinical and early phase human trial results in patients with PAD as well as CAD. However, to date, efficacy has not been demonstrated in placebo-controlled, large trails. Today's cell-based therapy is focused on stem cells (SCs) for the treatment of patients after acute myocardial infarction (AMI) or for patients with severe left ventricular dysfunction. Stem cells have shown to increase cardiac performance in uncontrolled, early phase human studies. This improvement is believed to have its origin in myogenesis and neovascularization. In the following review, we will cover current state of molecular- and cellular-based treatments for PAD and CAD that have reached the clinical arena.

Cell Transplantation Improves Ventricular Function After a Myocardial Infarction

Background— Cell transplantation offers the promise in the restoration of ventricular function after an extensive myocardial infarction, but the optimal cell type remains controversial. Human unrestricted somatic stem cells (USSCs) isolated from umbilical cord blood have great potential to differentiate into myogenic cells and induce angiogenesis. The present study evaluated the effect of USSCs on myocardial regeneration and improvement of heart function after myocardial infarction in a porcine model.

Method and Results— The distal left anterior descending artery of Yorkshire pigs (30 to 35 kg) was occluded by endovascular implantation of a coil. Four weeks after infarction, single-photon emission computed tomography technetium 99m sestamibi scans (MIBI) and echocardiography were performed. USSCs (100×10 6 ) or culture media were then directly injected into the infarcted region (n=8 per group). Pigs were immunosuppressed by daily administration of cyclosporin A. At 4 weeks after transplantation, MIBI and echocardiography were repeated and heart function was also assessed with a pressure-volume catheter. The infarcted myocardium and implanted cells were studied histologically. MIBI showed improved regional perfusion ( P <0.05) and wall motion ( P <0.05) of the infarct region in the transplant group compared with the control. Ejection fraction evaluated by both MIBI and echocardiography decreased in the control group but increased in the transplant group ( P <0.01). Scar thickness of the transplant group was higher than the control. The grafted cells were detected 4 weeks after transplantation by both immunohistochemistry and in situ hybridization.

Conclusion— Engrafted USSCs were detected in the infarct region 4 weeks after cell transplantation, and the implanted cells improved regional and global function of the porcine heart after a myocardial infarction. This study suggests that the USSC implantation will be efficacious for cellular cardiomyoplasty.

Possible Advantages of Stem Cell Transfusion into the Peripheral Circulation, As Opposed to Localized Transplantation In Situ

Studies to date have overlooked the possible limitations of transplanting stem cells locally (in situ), directly at the site of tissue or organ damage. This approach is contrary to the intrinsic physiological process of tissue and organ regeneration in vivo, which is thought to involve the activation of stem cells resident within the transplanted tissues or their mobilization from ectopic sites, in particular the bone marrow. Signaling pathways and other molecular processes within stem cells transplanted in situ may not be primed to achieve optimal tissue regeneration and may even be confused by the sudden rapid transition in the cellular microenvironment encountered during transplantation. Moreover, there is a risk of the transplanted cells giving rise to undesired lineages at the transplantation site. A novel alternative would be to transfuse stem cells into the peripheral blood circulation, followed by induced homing to the site of tissue damage. This could better replicate the natural physiological process of tissue repair in vivo. Transfusion into the peripheral blood circulation could be a strategy to augment the inadequate mobilization of endogenous adult stem cells from ectopic sites for tissue repair, which may be the case for older patients. The transfused stem cells can then be induced to home in on a damaged tissue or organ, via the controlled release of specific cytokines or chemokines (i.e., stromal cell derived factor-1) emanating from that particular tissue or organ. The gradient of released cytokines/ chemokines within the peripheral blood circulation would then direct the chemotactic migration and homing of the transfused stem cells to the target tissue or organ.