Recovery of regional but not global contractile function by the direct intramyocardial autologous bone marrow transplantation: results from a randomized controlled clinical trial

Large animal models of heart failure: a critical link in the translation of basic science to clinical practice

Congestive heart failure (HF) is a clinical syndrome, with hallmarks of fatigue and dyspnea, that continues to be highly prevalent and morbid. Because of the growing burden of HF as the population ages, the need to develop new pharmacological treatments and therapeutic interventions is of paramount importance. Common pathophysiologic features of HF include changes in left ventricle structure, function, and neurohormonal activation. The recapitulation of the HF phenotype in large animal models can allow for the translation of basic science discoveries into clinical therapies. Models of myocardial infarction/ischemia, ischemic cardiomyopathy, ventricular pressure and volume overload, and pacing-induced dilated cardiomyopathy have been created in dogs, pigs, and sheep for the investigation of HF and potential therapies. Large animal models recapitulating the clinical HF phenotype and translating basic science to clinical applications have successfully traveled the journey from bench to bedside. Undoubtedly, large animal models of HF will continue to play a crucial role in the elucidation of biological pathways involved in HF and the development and refinement of HF therapies.

Mesenchymal cell transplantation and myocardial remodeling after myocardial infarction

BACKGROUND

Targeted delivery of mesenchymal precursor cells (MPCs) can modify left ventricular (LV) cellular and extracellular remodeling after myocardial infarction (MI). However, whether and to what degree LV remodeling may be affected by MPC injection post-MI, and whether these effects are concentration-dependent, remain unknown.

METHODS AND RESULTS

Allogeneic MPCs were expanded from sheep bone marrow, and direct intramyocardial injection was performed within the borderzone region 1 hour after MI induction (coronary ligation) in sheep at the following concentrations: 25x10(6) (25 M, n=7), 75x10(6) (75 M, n=7), 225x10(6) (225 M, n=10), 450x10(6) (450 M, n=8), and MPC free media only (MI Only, n=14). LV end diastolic volume increased in all groups but was attenuated in the 25 and 75 M groups. Collagen content within the borderzone region was increased in the MI Only, 225, and 450 M groups, whereas plasma ICTP, an index of collagen degradation, was highest in the 25 M group. Within the borderzone region matrix metalloproteinases (MMPs) and MMP tissue inhibitors (TIMPs) also changed in a MPC concentration-dependent manner. For example, borderzone levels of MMP-9 were highest in the 25 M group when compared to the MI Only and other MPC treatment group values.

CONCLUSIONS

MPC injection altered collagen dynamics, MMP, and TIMP levels in a concentration-dependent manner, and thereby influenced indices of post-MI LV remodeling. However, the greatest effects with respect to post-MI remodeling were identified at lower MPC concentrations, thus suggesting a therapeutic threshold exists for this particular cell therapy.

Stem cell therapy for heart failure

Heart failure (HF) is a chronic disease and a significant global public health concern. Current medical treatment for HF can reduce symptoms but does little to decrease mortality and the need for cardiac transplantation. Novel therapies are needed to further decrease mortality and limit or eliminate the need for cardiac transplantation. Recently, several basic science and clinical trials have suggested that enhancing endogenous regeneration (repair) and exogenous cell therapy might be an approach to improve the function of the failing heart. This article reviews cell therapy clinical trials in patients with chronic HF. The three major subgroups of cells being studied in phase 1 and beginning phase 2 trials are skeletal myoblasts, bone marrow-derived mononuclear cells, and enriched subpopulations of bone marrow and cardiac stem cells. Techniques for stimulating upregulation of endogenous bone marrow progenitor cells in the circulating blood have raised serious safety issues and need to be carefully evaluated. Intracoronary infusion and both transepicardial and transendocardial direct injection of stem cells have been tested clinically and shown to be safe. Skeletal myoblast implantation has led to improved cardiac function, but studies show formation of skeletal muscle in the heart and a lack of electrical integration with surrounding myocardium, a cause for concern. Bone marrow-derived mononuclear cells and enriched subpopulations of cardiac and bone marrow stem cells have been studied extensively in animals and in recent clinical trials, with both controversy and success. There is still much room for improvement, but animal and human studies of enriched subpopulations of cardiac and bone marrow stem cells have shown that these cells are safe, have significant capability for cardiac repair, and offer the best chance for legitimate medical therapy for patients with chronic HF.

Microencapsulated stem cells for tissue repairing: implications in cell-based myocardial therapy

Stem cells have the unique properties of self-renewal, pluripotency and a high proliferative capability, which contributes to a large biomass potential. Hence, these cells act as a useful source for acquiring renewable adult cell lines. This, in turn, acts as a potent therapeutic tool to treat various diseases related to the heart, liver and kidney, as well as neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease. However, a major problem that must be overcome before it can be effectively implemented into the clinical setting is a suitable delivery system that can retain an optimal quantity of the cells at the targeted site for a maximal clinical benefit; a system that will give a mechanical as well as an immune protection to the foreign cells, while at the same time enhancing the yields of differentiated cells, maintaining cell microenvironments and sustaining the differentiated cell functions. To address this issue we opted for a novel delivery system, termed the ‘artificial cells’, which are semipermeable microcapsules with strong and thin multilayer membrane components with specific mass transport properties. Here, we briefly introduce the concept of artificial cells for encapsulation of stem cells and investigate the application of microencapsulation technology as an ideal tool for all stem transplantations and relate their role to the emerging field of cellular cardiomyoplasty.

Intracoronary blood- or bone marrow-derived cell transplantation in patients with ischemic heart disease

Soon after the first experimental scientific investigations of cell transplantation in various animal models of myocardial infarction and left ventricular dysfunction, a growing number of clinical trials evaluated the effects of intracoronary injection of peripheral blood- or bone marrow-derived cells in patients with myocardial infarction or chronic ischemic heart disease. In most of these trials, changes in parameters of left ventricular remodeling over time, such as left ventricular volumes, ejection fraction or infarct size, were used as trial end points, whereas information on mortality and morbidity after cell transplantation is sparse. Several meta-analyses, each including various sets of studies, estimated that intracoronary cell therapy was associated with small reductions in left ventricular end-systolic volumes and a moderate increase in left ventricular ejection fraction of 2.9–6.1% over time compared with control patients. As most of the clinical trials included a limited number of patients, results vary substantially between different studies. When evaluating whether effects of intracoronary cell transplantation on parameters of left ventricular remodeling may be transferable to meaningful consequences in terms of clinical outcome, the following aspects appear to be imperative. Robust data on mortality and clinical events based on a sufficient number of patients are required. Furthermore, effects of cell therapy must be compared with established therapeutic concepts for the treatment of myocardial infarction, such as reperfusion therapy or pharmacological interventions aiming at favorably influencing the remodeling process. Moreover, the potential effects of cell therapy must be evaluated as treatment options additive to established therapeutic strategies.

Route of delivery and baseline left ventricular ejection fraction, key factors of bone-marrow-derived cell therapy for ischaemic heart disease

AIMS

Previous evaluation of autologous bone-marrow stem-cell (BMSC) therapy following acute myocardial infarction (AMI) suggests that cell dose and timing of stem-cell administration post-MI are important factors in the efficacy of cellular therapy. This study aimed to assess whether route of delivery and baseline left ventricular ejection fraction (LVEF) of the participants may also affect the outcome of BMSC treatment in patients with AMI and ischaemic heart disease (IHD).

METHODS AND RESULTS

Randomized controlled trials of BMSCs as treatment for AMI and IHD were identified by searching MEDLINE, EMBASE, the Cochrane Library, and the Current Controlled Trials Register through to November 2008. Twenty-one trials (25 comparisons) with a total of 1091 participants were eligible. Data were analysed using a random-effects model. Improvement in LVEF in favour of the control was observed when BMSC were administered by intracoronary infusion [-0.19% (95% CI, -0.24 to -0.14; P < 0.00001)] in IHD patients. However, the effect on LVEF was statistically significant and in favour of BMSC when cells were delivered by intra-myocardial injection [5.85% (95% CI, 2.50-9.19; P = 0.0006)]. The significant improvement in LVEF observed in AMI patients was independent from the baseline LVEF of the participants. However, in patients suffering from chronic IHD, increase in LVEF was significant only in the group with lower LVEF at baseline [4.42% (CI, 1.87-6.96; P = 0.0007)].

CONCLUSION

Clinical evidence suggests that route of delivery and baseline LVEF influence the effect of BMSC therapy in treating AMI and chronic IHD.

Remodeling of the ischemia-reperfused murine heart: 11.7-T cardiac magnetic resonance imaging of contrast-enhanced infarct patches and transmurality

Our laboratory has published the first evidence obtained from fast low-angle-shot cine magnetic resonance imaging (11.7 T) studies demonstrating secondary myocyte death after ischemia/reperfusion (IR) of the murine heart. This work provides the first evidence from 11.7-T magnet-assisted pixel-level analysis of the post-IR murine myocardial infarct patches. Changes in function of the remodeling heart were examined in tandem. IR compromised cardiac function and induced LV hypertrophy. During recovery, the IR-induced increase in LV mass was partly offset. IR-induced wall thinning was noted in the anterior aspect of LV and at the diametrically opposite end. Infarct size was observed to be largest on post-IR days 3 and 7. With time (day 28), however, the infarct size was significantly reduced. IR-induced absolute signal-intensity enhancement was highest on post-IR days 3 and 7. As a function of post-IR time, signal-intensity enhancement was attenuated. The threshold of hyperenhanced tissue resulted in delineation of contours that identified necrotic (bona fide infarct) and reversibly injured infarct patches. The study of infarct transmurality indicated that whereas the permanently injured tissue volume remained unchanged, part of the reversibly injured infarct patch recovered in 4 weeks after IR. The approach validated in the current study is powerful in noninvasively monitoring remodeling of the post-IR beating murine myocardium.

Cardiac repair with adult bone marrow-derived cells: the clinical evidence

On the basis of strong evidence from animal studies, numerous clinical trials of cardiac repair with adult bone marrow-derived cells (BMC) have been completed. These relatively smaller studies employed different BMC types with highly variable numbers, routes, and timings of transplantation, and included patients with acute myocardial infarction (MI), chronic ischemic heart disease (IHD), as well as ischemic cardiomyopathy. Although the outcomes have been predictably disparate, analysis of pooled data indicates that BMC therapy in patients with acute MI and chronic IHD results in modest improvements in left ventricular function and infarct scar size without any increase in untoward effects. However, the precise mechanisms underlying these benefits remain to be ascertained, and the specific advantages of one BMC type over another remain to be determined. The long-term benefit and safety issues with different BMC types are currently being evaluated critically in larger randomized controlled trials with a view to applying this novel therapeutic strategy to broader patient populations. The purpose of this review is to summarize the available clinical evidence regarding the efficacy and safety of therapeutic cardiac repair with different types of adult BMCs, and to discuss the key variables that need optimization to further enhance the benefits of BMC therapy.

Cardiac repair and regeneration: the Rubik's cube of cell therapy for heart disease

Acute ischemic injury and chronic cardiomyopathies damage healthy heart tissue. Dead cells are gradually replaced by a fibrotic scar, which disrupts the normal electromechanical continuum of the ventricular muscle and compromises its pumping capacity. Recent studies in animal models of ischemic cardiomyopathy suggest that transplantation of various stem cell preparations can improve heart recovery after injury. The first clinical trials in patients produced some encouraging results, showing modest benefits. Most of the positive effects are probably because of a favorable paracrine influence of stem cells on the disease microenvironment. Stem cell therapy attenuates inflammation, reduces apoptosis of surrounding cells, induces angiogenesis, and lessens the extent of fibrosis. However, little new heart tissue is formed. The current challenge is to find ways to improve the engraftment, long-term survival and appropriate differentiation of transplanted stem cells within the cardiovascular tissue. Hence, there has been a surge of interest in pluripotent stem cells with robust cardiogenic potential, as well as in the inherent repair and regenerative mechanisms of the heart. Recent discoveries on the biology of adult stem cells could have relevance for cardiac regeneration. Here, we discuss current developments in the field of cardiac repair and regeneration, and present our ideas about the future of stem cell therapy.

The relative potency and safety of endothelial progenitor cells and unselected mononuclear cells for recovery from myocardial infarction and ischemia

Endothelial progenitor cells (EPCs) are a subset of the total mononuclear cell population (tMNCs) that possess an enhanced potential for differentiation within the endothelial-cell lineage. Typically, EPCs are selected from tMNCs via the expression of both hematopoietic stem-cell markers and endothelial-cell markers, such as CD34, or by culturing tMNCs in media selective for endothelial cells. Both EPCs and tMNCs participate in vascular growth and regeneration, and their potential use for treatment of myocardial injury or disease has been evaluated in early-phase clinical studies. Direct comparisons between EPCs and tMNCs are rare, but the available evidence appears to favor EPCs, particularly CD34+ cells, and the potency of EPCs may be increased as much as 30-fold through genetic modification. However, these observations must be interpreted with caution because clinical investigations of EPC therapy are ongoing. We anticipate that with continued development, EPC therapy will become a safe and effective treatment option for patients with acute myocardial infarction or chronic ischemic disease.

Cell-based therapy for heart disease: a clinically oriented perspective

Over the past decade, cell therapy has emerged as a potential new treatment of a variety of cardiac diseases, including acute myocardial infarction, refractory angina, and chronic heart failure. A myriad of cell types have been tested experimentally, each of them being usually credited by its advocates of a high "regeneration" potential. This has led to a flurry of clinical trials entailing the use of skeletal myoblasts or bone marrow-derived cells either unfractionated or enriched in progenitor subpopulations. As often in medicine, the hype generated by the early uncontrolled and small-sized studies has been dampened by the marginally successful outcomes of the subsequent, more rigorously conducted randomized trials. Although they may have failed to achieve their primary end points, these trials have been positive in the sense that they have allowed to identify some key issues and it is reasonable to speculate that if these issues can now be addressed by appropriately focused benchwork, the outcomes of the second generation of cell-transplantation studies would likely be upgraded. It, thus, appears that not "one cell fits all" but that the selection of the cell type should be tailored to the primary clinical indication. On the one hand, it does not make sense to develop an "ideal" cell in a culture dish, if we remain unable to deliver it appropriately and to keep it alive, at least for a while, which requires to improve on the delivery techniques and to provide cells along with the vascular and extracellular matrix type of support necessary for their survival and patterning. On the other hand, the persisting mechanistic uncertainties about cell therapy should not preclude continuing clinical trials, which often provide the unique opportunity of identifying issues missed by our suboptimal preclinical models. Finally, regardless of whether cells are expected to act paracrinally or by physically replacing lost cardiomyocytes and, thus, effecting a true myocardial regeneration, safety remains a primary concern. It is, thus, important that clinical development programs be shaped in a way that allows the final cell-therapy product to be manufactured from fully traceable materials, phenotypically well characterized, consistent, scalable, sterile, and genetically stable as these characteristics are those that will be required by the ultimate gatekeeper, i.e., the regulator, and are thus unbypassable prerequisites for an effective and streamlined leap from bench to bedside.

In vivo magnetic resonance imaging of injected mesenchymal stem cells in rat myocardial infarction; simultaneous cell tracking and left ventricular function measurement

To determine whether magnetic resonance imaging (MRI) can enable magnetically labeled mesenchymal stem cell (MSC) tracking and simultaneous in vivo functional data acquisition in rat models of myocardial infarction. Superparamagnetic iron oxide-laden human MSCs were injected into rat myocardium infarcted by cryoinjury 3 weeks after myocardial infarction. The control group received cell-free media injection. Before injection and for 3 months after, in vivo serial MRI was performed. Electrocardiography-gated gradient echo sequence MRI and cine MRI were performed for in vivo cell tracking and assessing cardiac function using left ventricular ejection fraction (LVEF), respectively. MRI revealed a persistent signal-void representing iron-laden MSCs until ten post-injection weeks. Serial follow-up MRI revealed that LVEF was significantly higher in the MSC injection group than in the control group. We conclude that MRI enables in vivo tracking of injected cells and evaluation of the long-term therapeutic potential of MSCs for myocardial infarction.

Human peripheral blood endothelial progenitor cells synthesize and express functionally active tissue factor

INTRODUCTION

Endothelial progenitor cells are circulating cells able to home to sites of vascular damage and to contribute to the revascularization of ischemic areas. We evaluated whether endothelial progenitor cells synthesize tissue factor, a procoagulant protein also involved in angiogenesis.

MATERIALS AND METHODS

Endothelial progenitor cells were obtained from the peripheral blood mononuclear fraction of normal donors and cultured in endothelial medium supplemented with specific growth factors. The procoagulant activity expressed by cells disrupted by freeze-thaw cycles was assessed by a one stage clotting assay. Tissue factor mRNA expression was evaluated by RT-PCR.

RESULTS

Endothelial progenitor cells do not express procoagulant activity in baseline conditions. However, lipopolysaccharide induces the expression of procoagulant activity. The effect is dose-dependent and reaches statistical significance at 100 ng/mL lipopolysaccharide. Inhibition with an anti-tissue factor antibody and amplification of cDNA with primers based on the tissue factor sequence confirm the identity of this activity with tissue factor. The kinetics of tissue factor expression by endothelial progenitor cells is identical to that of human umbilical vein endothelial cells showing maximal activity within 4 hours, and then decreasing; in contrast, tissue factor expression by mononuclear cells lasts for longer times. Both 5,6-dichloro-beta D-ribofuranosyl-benzimidazole and cycloheximide prevented the expression of procoagulant activity. Stimulation of endothelial progenitor cells with tumor necrosis factor-alpha did not elicit any detectable procoagulant activity.

CONCLUSIONS

Endothelial progenitor cells can be stimulated by lipopolysaccharide to synthesize tissue factor. This protein might be involved in thrombotic phenomena and might contribute to endothelial progenitor cells related neovascularization.

Endothelial progenitor cells in neovascularization of infarcted myocardium

Historically, revascularization of ischemic tissue was believed to occur through the migration and proliferation of endothelial cells in nearby tissues; however, evidence accumulated in recent years indicates that a subpopulation of adult, peripheral-blood cells, collectively referred to as endothelial progenitor cells (EPCs), can differentiate into mature endothelial cells. After ischemic insult, EPCs are believed to home to sites of neovascularization, where they contribute to vascular regeneration by forming a structural component of capillaries and by secreting angiogenic factors; new evidence indicates that EPCs can also differentiate into cardiomyocytes and smooth-muscle cells. These insights into the molecular and cellular processes of tissue formation suggest that cardiac function may be preserved after myocardial infarction by transplanting EPCs into ischemic heart tissue, thereby enhancing vascular and myocardial recovery. This therapeutic strategy has been effective in animal models of ischemic disorders, and results from randomized clinical trials suggest that cell-based strategies may be safe and feasible for treatment of myocardial infarction in humans and have provided early evidence of efficacy. However, the scarcity of EPCs in the peripheral blood and evidence that several disease states reduce EPC number and/or function have prompted the development of several strategies to overcome these limitations, such as the administration of genetically modified EPCs that overexpress angiogenic growth factors. To optimize therapeutic outcomes, researchers must continue to refine methods of EPC purification, expansion, and administration, and to develop techniques that overcome the intrinsic scarcity and phenotypic deficiencies of EPCs.

Randomized, controlled trial of intramuscular or intracoronary injection of autologous bone marrow cells into scarred myocardium during CABG versus CABG alone

BACKGROUND

Studies of the transplantation of autologous bone marrow cells (BMCs) in patients with chronic ischemic heart disease have assessed effects on viable, peri-infarct tissue. We conducted a single-blinded, randomized, controlled study to investigate whether intramuscular or intracoronary administration of BMCs into nonviable scarred myocardium during CABG improves contractile function of scar segments compared with CABG alone.

METHODS

Elective CABG patients (n = 63), with established myocardial scars diagnosed as akinetic or dyskinetic segments by dobutamine stress echocardiography and confirmed at surgery, were randomly assigned CABG alone (control) or CABG with intramuscular or intracoronary administration of BMCs. The BMCs, which were obtained at the time of surgery, were injected into the mid-depth of the scar in the intramuscular group or via the graft conduit supplying the scar in the intracoronary group. Contractile function was assessed in scar segments by dobutamine stress echocardiography before and 6 months after treatment.

RESULTS

The proportion of patients showing improved wall motion in at least one scar segment after BMC treatment was not different to that observed in the control group (P = 0.092). Quantitatively, systolic fractional thickening in scar segments did not improve with BMC administration. Furthermore, BMCs did not improve scar transmurality, infarct volume, left ventricular volume, or ejection fraction.

CONCLUSION

Injection of autologous BMCs directly into the scar or into the artery supplying the scar is safe but does not improve contractility of nonviable scarred myocardium, reduce scar size, or improve left ventricular function more than CABG alone.

Stem cell therapy: MRI guidance and monitoring

With the recent advances in magnetic resonance (MR) labeling of cellular therapeutics, it is natural that interventional MRI techniques for targeting would be developed. This review provides an overview of the current methods of stem cell labeling and the challenges that are created with respect to interventional MRI administration. In particular, stem cell therapies will require specialized, MR-compatible devices as well as integration of graphical user interfaces with pulse sequences designed for interactive, real-time delivery in many organs. Specific applications that are being developed will be reviewed as well as strategies for future translation to the clinical realm.

Cellular replacement therapy for arrhythmia treatment: early clinical experience

Clinical and experimental studies have demonstrated the proarrhythmic potential of skeletal myoblast transplantation for repair of infarcted myocardium. The evidence on proarrhythmia following bone marrow-derived stem cells, and particular msenchymal stem cells, transplantation is inconclusive. There are experimental and preliminary clinical data supporting the possibility that mesenchymal stem cell transplantation might exert an anti-arrhythmic action by intervening with myocardial scar remodeling. However, clinical experience is limited.

Contrast-enhanced magnetic resonance imaging in the assessment of myocardial infarction and viability

Contrast-enhanced magnetic resonance imaging (MRI) can be used to visualize the transmural extent of myocardial infarction with high spatial resolution. The aim of this review is to provide an overview of the use of contrast-enhanced MRI for characterization of ischemic myocardial injury in comparison to other imaging methods and its relevance in clinical syndromes related to coronary artery disease. Infarcted myocardium appears hyperenhanced compared with normal myocardium when imaged by a delayed-enhancement MRI technique with the use of an inversion-prepared T(1)-weighted sequence after injection of gadolinium chelates, such as gadolinium-diethylenetriamine pentaacetic acid. Experimental and clinical studies indicate that the extent of delayed enhancement is reproducible and closely correlates with the size of myocardial necrosis or infarct scar as determined by established in vitro and in vivo methods. Furthermore, MRI appears to be more sensitive than other imaging methods in detecting small subendocardial infarctions. The transmural extent of delayed enhancement potentially predicts functional outcome after revascularization in acute myocardial infarction and chronic ischemic heart disease, indicating that it can accurately discriminate between infarction and dysfunctional but viable myocardium. Further experience from clinical trials is needed to understand the association of delayed enhancement with clinical outcomes.

Therapeutic myocardial angiogenesis

Armed with an improved understanding of the mediators of angiogenesis, physicians and scientists have made significant efforts at harnessing this naturally occurring process in order to treat patients with a variety of peripheral vascular and coronary ischemic syndromes. There is a growing population of patients with end-stage coronary artery disease (CAD) who are no longer candidates for mechanical revascularization, yet suffer from chronic myocardial ischemia who may benefit from regeneration of the depleted microvasculature.

Bone marrow cell-mediated cardiovascular repair: potential of combined therapies

Recent evidence indicates that bone-marrow cells (BMCs) can contribute to the healing process of the injured cardiovascular system via the chemokine receptor CXCR4/SDF-1, thymosin beta(4) and integrin alpha(4)beta(1) molecular pathways. During tissue ischemia overwhelming numbers of detrimental oxygen radicals are generated, and therefore treatment with antioxidants and L-arginine, the precursor of nitric oxide (NO), could induce beneficial effects beyond those achieved by BMC transplantation alone. Recent studies have reported that BMCs have enhanced neovascularization capacity in cotreatment with alpha-tocopherol (vitamin E), ascorbic acid (vitamin C) and L-arginine. Moreover, BMC therapy can be combined with gene therapy. Clinical trials employing BMCs in the treatment of cardiovascular diseases have been completed with mixed or positive results, and several trials are ongoing. Here, we discuss the clinical potential of BMC transplantation alone and in combined therapy that aims to restore organ vascularization and function. We also consider the mechanisms of mobilization, differentiation and incorporation of BMCs.