Neovascularization and cardiac repair by bone marrow-derived stem cells

Postinfarction congestive heart failure with impaired systolic left ventricular function is a loss of cardiomyocyte disease. Adult stem or progenitor cells from the bone marrow and the peripheral blood have been experimentally shown to differentiate towards endothelial cells and cardiomyocytes under the appropriate conditions. The use of autologous adult stem cells for neovascularization and cardiac regeneration is a promising concept and has shown benefit in pilot clinical trails enrolling postinfarction patients with coronary artery disease. Cell therapy may act through differentiation into and thus replacement of cardiomyocytes and/or neovascularization, the formation of new vessels in the adult organism. Moreover, the release of factors acting in a paracrine manner may contribute to neovascularization and scar remodelling. In this review, the experimental data regarding neovascularization and cardiomyocyte formation from adult stem/progenitor cells are discussed.     

Stem cell therapy for the treatment of myocardial infarction

Despite timely reperfusion and subsequent optimal postinfarct pharmacotherapy and device-based treatment, the outcome in patients with severe myocardial infarction remains unfavourable. Myocardial salvage is incomplete, resulting in adverse left ventricular remodeling with concomitant morbidity and mortality. The combined risk of recurrent myocardial infarction, death or readmission for heart failure amounts to 25 % within the first year, highlighting the need for additional treatment strategies. Recent and rapidly evolving insights in cardiac biology, recognizing endogenous repair capabilities of the adult human heart, paved the path towards progenitor or stem cell based cardiac protection and repair strategies following ischemic injury. We critically report on the major randomized controlled clinical trials published so far concerning intracoronary transfer of autologous bone marrow cells in the setting of acute myocardial infarction. Moreover, underlying mechanisms, practical aspects, remaining questions and future challenges are highlighted. Taken together, these trials confirm the safety and feasibility of intracoronary progenitor cell transfer in the setting of myocardial infarction. Efficacy data suggests its potential to improve left ventricular function recovery beyond current state of the art therapy, but results are mixed, modest at best and do not support true cardiomyogenesis. Hence, due to its complexity, costs and remaining uncertainties, it is still too early to implement progenitor cell therapy in its current form in standard treatment strategies for ischemic heart disease. Future studies on strategies for cardiomyocyte regeneration in combination with myocardial protection are needed.     

Resident cardiac stem cells

The introduction of stem cells in cardiology provides new tools in understanding the regenerative processes of the normal and pathologic heart and opens new options for the treatment of cardiovascular diseases. The feasibility of adult bone marrow autologous and allogenic cell therapy of ischemic cardiomyopathies has been demonstrated in humans. However, many unresolved questions remain to link experimental with clinical observations. The demonstration that the heart is a self-renewing organ and that its cell turnover is regulated by myocardial progenitor cells offers novel pathogenetic mechanisms underlying cardiac diseases and raises the possibility to regenerate the damaged heart. Indeed, cardiac stem progenitor cells (CSPCs) have recently been isolated from the human heart by several laboratories although differences in methodology and phenotypic profile have been described. The present review points to the potential role of CSPCs in the onset and development of congestive heart failure and its reversal by regenerative approaches aimed at the preservation and expansion of the resident pool of progenitors.     

Do adult stem cells ameliorate the damaged myocardium? Human cord blood as a potential source of stem cells

The heart does not mend itself after infarction. However, stem cells may revolutionize heart disease treatment. A vast and growing body of evidence indicates that cell-based strategies have promising therapeutic potential. Recent clinical and pre-clinical studies demonstrate varying degrees of improvement in cardiac function using different adult stem cell types such as bone marrow (BM)-derived progenitor cells and skeletal myoblasts. However, the efficacy of cell therapy after myocardial infarction (MI) is inconclusive and the cellular source with the highest potential for regeneration is unclear. Clinically, BM and skeletal muscle are the most commonly used sources of autologous stem cells. One major pitfall of using autologous stem cells is that the number of functional cells is generally depleted in the elderly and chronically ill. Therefore, there is an urgent need for a new source of adult stem cells. Human umbilical cord blood (CB) is a candidate and appears to have several key advantages. CB is a viable and practical source of progenitor cells. The cells are na?ve and what's more, CB contains a higher number of immature stem/progenitor cells than BM. We review recent clinical experience with adult stem cells and explore the potential of CB as a source of cells for cardiac repair following MI. We conclude that there is a conspicuous absence of clinical studies utilizing CB-derived cells and there is a pressing need for large randomized double-blinded clinical trials to assess the overall efficacy of cell-based therapy.     

Stem cell implantation for myocardial disorders

Cell therapy is currently attracting growing interest as a potential new means of improving the prognosis of patients with heart failure. For practical reasons, autologous skeletal myoblasts have been the first to be tested in clinical trials, but recently cardiovascular researchers has explored many other cell types, including bone marrow cells, endothelial progenitor cells, mesenchymal stem cells, embryonic stem cells, and resident cardiac stem cells. While recent experimental studies and early-phase clinical trials seem to support the concept that cell therapy may enhance cardiac repair, many challenges remain before achieving this goal. Further studies should focus on finding the optimal donor cells for transplantation, the mechanism by which engrafted cells improve cardiac function, controlling the survival and proliferation of transplanted cells, and the development of more efficient cell delivery techniques.     

The role of chemokines, cytokines and adhesion molecules in stem cell trafficking and homing

Although definition and mechanistic understanding of pro-angiogenic progenitor cells remains unsatisfactory, general agreement highlights their role in regenerative process following tissue injury and ischemia. Furthermore, stem-cell based therapy represents a hot topic of cardiovascular medicine. Recent studies provide new insights on the signalling pathways that modulate stem/progenitor cell mobilization from bone marrow, homing to ischemic area and participation in vascular remodelling and tissue healing. This review focuses on current knowledge and emerging concepts on stem cell/progenitor cell trafficking in relation to changes in surrounding environment and epigenetic modifications caused by risk factors and comorbidities.     

Cytokines in haemopoietic progenitor mobilisation for peripheral blood stem cell transplantation

Haemopoietic progenitors mobilised into peripheral blood are now almost universally used in autologous haemopoietic stem cell transplantation in the treatment of a range of malignant and some nonmalignant disease. Although chemotherapy alone was initially used, all modern protocols now involve the use of cytokines, with or without chemotherapy. Important developments have included an in understanding of the importance of prior cancer therapy on progenitor yield, knowledge of the kinetics of mobilisation and development of necessary skills to collect and cryopreserve progenitors. More accurate measurement of haemopoietic progenitors and definitions of target cell yields for optimal haemopoietic recovery after high-dose therapy have also contributed to more predictable outcomes and provide a reference point for newer mobilisation approaches. Although G-CSF based regimens are usually successful, some patients either fail to mobilise sufficient progenitors or require an excessive number of collections. Clinical studies with the early acting cytokine, stem cell factor, in combination with G-CSF have demonstrated increased progenitor yields in a range of patients which may translate to clinical benefit in selected situations. In animal models and to a lesser extent in humans, other cytokines such as thrombopoietin and Flt-3 ligand or a number of engineered small molecules with single or dual agonist activity for cytokine receptors (IL-3, Flt-3L, TPO, G-CSF), have also been found to be promising mobilising agents. Further research into the relative importance of cell proliferation, cellular adhesion and the role of accessory cells and other signalling events is leading to an improved understanding of the underlying mechanisms of haemopoietic progenitor mobilisation. Administration of appropriate high-dose chemotherapy followed by re-infusion of haemopoietic progenitor cells capable of long-term reconstitution has long had a place in the treatment of a number of malignant (largely haematological) and non-malignant diseases. For many years these progenitor cells were obtained by direct aspiration of bone marrow under general anaesthetic, hence the term bone marrow transplantation. However, it has also been recognized that haemopoietic stem cells may be recovered from peripheral blood, albeit in low numbers, and also from umbilical cord blood. Further empirical observations showed that the number of haemopoietic progenitors circulating in the blood could be transiently augmented after chemotherapy and/or administration of one or more of a number of cytokines. Refinements to the clinical practice of progenitor mobilisation, collection and enumeration have proved very successful such that in many cases peripheral blood stem cells (PBSC) have largely replaced bone marrow as the preferred source.     

Mobilization of bone marrow-derived progenitors

Bone marrow (BM) is a source of various stem and progenitor cells in the adult, and it is able to regenerate a variety of tissues following transplantation. In the 1970s the first BM stem cells identified were hematopoietic stem cells (HSCs). HSCs have the potential to differentiate into all myeloid (including erythroid) and lymphoid cell lineages in vitro and reconstitute the entire hematopoietic and immune systems following transplantation in vivo. More recently, nonhematopoietic stem and progenitor cells have been identified that can differentiate into other cell types such as endothelial progenitor cells (EPCs), contributing to the neovascularization of tumors as well as ischemic tissues, and mesenchymal stem cells (MSCs), which are able to differentiate into many cells of ectodermal, endodermal, and mesodermal origins in vitro as well as in vivo. Following adequate stimulation, stem and progenitor cells can be forced out of the BM to circulate into the peripheral blood, a phenomenon called "mobilization." This chapter reviews the molecular mechanisms behind mobilization and how these have led to the various strategies employed to mobilize BM-derived stem and progenitor cells in experimental and clinical settings. Mobilization of HSCs will be reviewed first, as it has been best-explored--being used extensively in clinics to transplant large numbers of HSCs to rescue cancer patients requiring hematopoietic reconstitution--and provides a paradigm that can be generalized to the mobilization of other types of BM-derived stem and progenitor cells in order to repair other tissues.     

Using cytokines to stimulate neoangiogenesis and cardiac regeneration

Data published on the use of cytokines for the stimulation of neoangiogenesis and cardiac regeneration have been systematized. There is evidence that insulin-like growth factor (IGF1) can stimulate proliferation of cardiomyocytes; hepatocyte growth factor (HGF) does not influence the mitosis of cardiac cells, but prevents post-infarction remodeling of heart; vascular endothelial growth factor (VEGF) stimulates proliferation of endothelial cells in vitro and neovasculogenesis in the ischemic heart in vivo for both animals and humans; fibroblast growth factor (FGF) can also induce neovasculogenesis in the ischemic heart; granulocyte-colony-stimulating factor (G-CSF) can mobilize stem cells and endothelial progenitor cells in bone marrow, which are involved in neoangiogenesis and cardiac regeneration; erythropoietin can mobilize endothelial progenitor cells from bone marrow and induce neovascularization of ischemic tissue in vivo. It is suggested that VEGF, G-CSF and erythropoietin are the most promising compounds for the stimulation of neoangiogenesis and cardiac regeneration in patients with myocardial infarction.     

青蒿琥酯对小鼠骨髓造血干/祖细胞分化的抑制与毒性作用

目的:观察青蒿琥酯(artesunate,AS)对小鼠骨髓造血干/祖细胞分化的影响。方法:取小鼠骨髓干细胞进行体外液体或半固体定向培养并加入不同浓度的AS,光镜下计数半固体培养的红系集落形成单位(CFU-E)与红系爆式集落形成单位(BFU-E)数量,流式细胞术检测液体定向培养的细胞凋亡和线粒体膜电位变化,同时进行DNAladder凝胶电泳实验。结果:AS可显著抑制CFU-E与BFU-E集落的生成(P<0.05)并具有一定的量效关系;DNAladder凝胶电泳结果显示0.01～1.30mmol/L的AS可明显诱导细胞凋亡,流式细胞仪检测细胞晚期凋亡/死亡率具有统计学意义(P<0.05);线粒体膜电位的下降程度也与AS浓度正相关(r=0.546,P=0.018)。结论:AS对小鼠骨髓造血干/祖细胞的增殖和分化具有明显抑制作用,小剂量AS可诱导小鼠骨髓造血干/祖细胞发生凋亡,大剂量可直接引起细胞坏死。     

Heart regeneration: what cells to use and how?

Coronary artery disease (CAD) is the leading cause of death in modern societies. Recent achievements in the treatment of CAD including statins, ACE inhibitors, beta blockers, and interventional procedure improved the outcome of patients with CAD, but this conventional approach failed to control cardiovascular mortality. Nowadays, cells (stem cells) and their potential role in managing patients with heart disease is a field of intensive research. Various types of cells have been used for transplantation targeting heart regeneration, including bone marrow cells (BMCs), cardiac stem cells (CSCs), endothelial progenitor cells (EPCs), skeletal myoblasts (SMs), adipose stroma tissue cells (ATSCs), mesenchymal cells (MCs), and embryonic stem cells (ESCs). Several routes have been used to deliver these cells to human myocardium or to the coronary circulation such as, intracoronary injection, intravenous infusion, direct injection into the ventricular wall, or transepicardial/transendocardial infusions. Although the results of the recent clinical trials in this area are rather conflicting, these therapeutic approaches seem to be promising for the treatment of ischemic heart disease.     

Demonstration of residual bone marrow effect in mice exposed to ethylene glycol monomethyl ether

Ethylene glycol monomethyl ether (EGMME) has been reported to cause hematopoietic abnormalities in man. We have shown that mice exposed to EGMME post-natally have suppressed bone marrow cellularity and progenitor cells 8 weeks post-exposure which returns to normal values by 16 weeks. Studies were designed to determine whether EGMME exposed mice that recovered had evidence of residual marrow stem cell injury. B6C3F1 mice were injected subcutaneously with EGMME on days 1-5 after birth at doses of 0, 100, 200 and 400 mg/kg per day, allowed to recover, and stressed with 200 rads whole body irradiation at 15 and 21 weeks post-exposure. Bone marrow functions were examined during the recovery period. Mice that had been exposed to EGMME were more sensitive to irradiation and recovery of marrow cellularity and progenitor cell numbers occurred more slowly than in unexposed controls. This indicates that EGMME can cause persistent residual damage of bone marrow progenitor cells in mice, an effect that would not be apparent with routine hematological techniques.     

Therapeutic use of stem and endothelial progenitor cells in acute renal injury: ça ira

Acute renal failure (ARF) seriously worsens prognosis of hospitalized patients. The dysfunction and apoptosis/necrosis of tubular epithelial cells is of key importance for the pathophysiological consequences of the syndrome. ARF also affects the structure and function of the renal endothelium because these cells undergo an early swelling with narrowing of the vascular lumen, resulting in prolonged renal hypoperfusion. The dysfunctional renal epithelium and endothelium have remarkable capacity to recover. With the growing knowledge in the field of stem cell research, these regenerative mechanisms become more and more elucidated. Recent data suggest that bone marrow derived mesenchymal stem cells can ameliorate ARF through both paracrine effects and repair of injured microvasculature by providing endothelial progenitor cells. Evidence for resident adult renal stem cells is also now emerging.     

Stem cell therapy (Aastrom Biosciences Inc)

The expansion of human stem cells and their genetic manipulation represent areas of increasing interest in the field of stem cell transplantation. Previously, stem cell transplantation has been accomplished by using cellular products obtained by large volume bone marrow or peripheral blood harvest. Difficulties with this approach include inadequate cell numbers and tumor cell contamination. Furthermore, for gene transfer modalities requiring proliferating progenitor cells, low gene expression would be expected in these products. To address these difficulties, the AastromReplicell System has been developed as a fully closed and automated system for expanding hematopoietic cells. Investigators at Aastrom have evaluated the conditions needed for optimal growth including the need for unpurified bone marrow or cord blood mononuclear cells, high cell densities, serum-containing medium and certain types of plastic surfaces. Studies have now been initiated to demonstrate the feasibility of generating enough cells to fully reconstitute hematopoiesis from small volumes of cellular progenitors. It has also been demonstrated that tumor cell contamination passively decreases during the culture period. It now remains to be shown in a direct comparison that this approach yields greater efficacy and a lower cost than transplantation with unmanipulated large volume marrow or peripheral blood stem cell products.     

Mesenchymal progenitor cells differentiate into an endothelial phenotype, enhance vascular density and improve heart function in a rat cellular cardiomyoplasty model

AIM: Cellular cardiomyoplasty is promising for improving postinfarcted cardiac function. Over the past decade, a variety of cell types have been proposed including mononuclear bone marrow cells. The latter contains different lineages including mesenchymal stem cells (MSCs). The aim of this study was to analyse the differentiation pathways of engrafted syngenic mesenchymal progenitor cells (MPCs) obtained in culture from bone marrow     

Angiotensin-(1–7) administration benefits cardiac,renal and progenitor cell function in db/db mice

Background and Purpose

Diabetic patients are at an increased risk of cardiovascular disease, in part due to inflammation and oxidative stress. These two pathological mechanisms also affect other organs and cells including the kidneys and progenitor cells. Angiotensin-(1–7) [Ang-(1–7)] has previously been shown to counterbalance pathological effects of angiotensin II, including inflammation and oxidative stress. The aim of this study was to investigate the effects of short-term (2 weeks) Ang-(1–7) treatment on cardiovascular and renal function in a mouse model of type 2 diabetes (db/db).

Experimental Approach

Eight- to nine-week-old db/db mice were administered either vehicle, Ang-(1–7) alone, or Ang-(1–7) combined with an inhibitor (losartan, PD123319, A-779, L-NAME or icatibant) daily for 14 days.

Key Results

An improvement in physiological heart function was observed in Ang-(1–7)-treated mice. Ang-(1–7) also reduced cardiomyocyte hypertrophy, fibrosis and inflammatory cell infiltration of the heart tissue and increased blood vessel number. These changes were blocked by antagonists of the MAS1, AT₂ and bradykinin receptors and inhibition of NO formation. Treatment with Ang-(1–7) reduced glomerular damage and oxidative stress in kidney tissue. Bone marrow and circulating endothelial progenitors, as well as bone marrow mesenchymal stem cells, were increased in mice treated with Ang-(1–7).

Conclusions and Implications

Short-term Ang-(1–7) treatment of young db/db mice improved heart function and reduced kidney damage. Treatment also improved bone marrow and circulating levels of endothelial and mesenchymal stem cells. All of this may contribute to improved cardiovascular and renal function.