Bone marrow transplantation for the heart: fact or fiction?

Tissue Engineering of the Microvasculature

The ability to generate new microvessels in desired numbers and at desired locations has been a long-sought goal in vascular medicine, engineering, and biology. Historically, the need to revascularize ischemic tissues nonsurgically (so-called therapeutic vascularization) served as the main driving force for the development of new methods of vascular growth. More recently, vascularization of engineered tissues and the generation of vascularized microphysiological systems have provided additional targets for these methods, and have required adaptation of therapeutic vascularization to biomaterial scaffolds and to microscale devices. Three complementary strategies have been investigated to engineer microvasculature: angiogenesis (the sprouting of existing vessels), vasculogenesis (the coalescence of adult or progenitor cells into vessels), and microfluidics (the vascularization of scaffolds that possess the open geometry of microvascular networks). Over the past several decades, vascularization techniques have grown tremendously in sophistication, from the crude implantation of arteries into myocardial tunnels by Vineberg in the 1940s, to the current use of micropatterning techniques to control the exact shape and placement of vessels within a scaffold. This review provides a broad historical view of methods to engineer the microvasculature, and offers a common framework for organizing and analyzing the numerous studies in this area of tissue engineering and regenerative medicine. © 2019 American Physiological Society. Compr Physiol 9:1155-1212, 2019.

Angiogenesis: Bench to Bedside, Have We Learned Anything?

End-stage ischemic cardiomyopathy patients are an ever-increasing group of coronary artery disease patients, often with no options in our current treatment armamentarium. Angiogenesis therapy pre-clinical and phase I clinical trials showed great promise, however, the benefits of single growth factor treatments have not been borne out in the larger phase II randomized trials. The complexity of angiogenesis process and the challenges in creating animal models to replicate and study this process in ischemic adult human myocardium have been major limitations to progress in this field. In addition failure to control for the powerful placebo effect in the clinical trials and inadequate methods of outcomes measures assessment have created difficult to overcome road blocks in establishing the efficacy of angiogenic strategies. Herein we review the challenges of angiogenesis research and development of treatment strategies. We also propose a structured model for further investigations of angiogenic therapies. The adherence to such a regimented approach as proposed here is, in our opinion, the only way to achieve success in angiogenesis approach development to treatment of patients with end-stage cardiac ischemia refractory to other established therapies.

Are purified or expanded cord blood-derived CD133+ cells better at improving cardiac function?

Endothelial progenitor cells (EPCs), which express the CD133 marker, can differentiate into mature endothelial cells (ECs) and create new blood vessels. Normal angiogenesis is unable to repair the injured tissues that result from myocardial infarction (MI). Patients who have high cardiovascular risks have fewer EPCs and their EPCs exhibit greater in vitro senescence. Human umbilical cord blood (HUCB)-derived EPCs could be an alternative to rescue impaired stem cell function in the sick and elderly. The aim of this study was to purify HUCB-derived CD133(+) cells, expand them in vitro and evaluate the efficacy of the purified and expanded cells in treating MI in rats. CD133(+) cells were selected for using CD133-coupled magnetic microbeads. Purified cells stained positive for EPC markers. The cells were expanded and differentiated in media supplemented with fetal calf serum and basic fibroblast growth factor, insulin-like growth factor-I and vascular endothelial growth factor (VEGF). Differentiation was confirmed by lack of staining for EPC markers. These expanded cells exhibited increased expression of mature EC markers and formed tubule-like structures in vitro. Only the expanded cells expressed VEGF mRNA. Cells were expanded up to 70-fold during 60 days of culture, and they retained their functional activity. Finally, we evaluated the therapeutic potential of purified and expanded CD133(+) cells in treating MI by intramyocardially injecting them into a rat model of MI. Rats were divided into three groups: A (purified CD133(+) cells-injected); B (expanded CD133(+) cells-injected) and C (saline buffer-injected). We observed a significant improvement in left ventricular ejection fraction for groups A and B. In summary, CD133(+) cells can be purified from HUCB, expanded in vitro without loosing their biological activity, and both purified and expanded cells show promising results for use in cellular cardiomyoplasty. However, further pre-clinical testing should be performed to determine whether expanded CD133(+) cells have any clinical advantages over purified CD133(+) cells.

Nuclear imaging in the evaluation of clinical restorative cardiac therapies

Gene- and cell-based therapeutic procedures have entered the cardiovascular field. Many of these novel interventions aim at cardiac regeneration and the initial experimental groundwork has been promising. But early clinical experience did not always confirm the experimental findings and it is felt that the full potential of cardiac gene and cell therapy has, by far, not been exploited. Conflicting clinical results emphasise the need for powerful non-invasive tools to monitor the success of therapy and identify most suitable candidates. As reviewed here, established clinical cardiac imaging tools, together with novel molecular-targeted approaches, are expected to advance the field of myocardial regeneration and to expedite progress and clinical translation.

The possible use of stem cells in regenerative medicine: dream or reality?

Stem cells are one of the most fascinating areas in regenerative medicine today. They play a crucial role in the development and regeneration of human life and are defined as cells that continuously reproduce themselves while maintaining the ability to differentiate into various cell types. Stem cells are found at all developmental stages, from embryonic stem cells that differentiate into all cell types found in the human body to adult stem cells that are responsible for tissue regeneration. The general opinion postulates that clinical therapies based on the properties of stem cells may have the potential to change the treatment of degenerative diseases or important traumatic injuries in the "near" future. We here briefly review the literature in particularly for the liver, heart, kidney, cartilage, and bone regeneration.

Skin-derived microorgan autotransplantation as a novel approach for therapeutic angiogenesis

Despite promising preclinical results, transient single-factor-based therapeutic angiogenesis has shown no definitive benefits in clinical trials. The use of skin-derived microorgans (SMOs), capable of sustained expression of angiogenic factors and sustained viability with their cellular and extracellular elements, constitutes an attractive alternative. We sought to evaluate the efficacy of SMO implantation in a porcine model of chronic myocardial ischemia. Eighteen pigs underwent placement of an ameroid constrictor on the proximal circumflex artery. Three weeks later, split-thickness skin biopsies were harvested and pigs were randomized to lateral wall implantation of either 8 or 16 SMOs or blank injections. The procedure was safe and resulted in no adverse events. Three weeks after treatment, SMO implantation resulted in significant improvement of lateral wall perfusion during pacing, assessed by isotope-labeled microspheres [post- vs. pretreatment ratios of lateral/anterior wall blood flow were 1.31 ± 0.09 (SMOs) and 1.04 ± 0.06 (controls); P = 0.03]. No significant difference in angiographic scores was observed. Microvascular relaxation in response to VEGF was impaired in the ischemic territory of the control group but returned to normal after SMO implantation, indicating restoration of endothelial function. Molecular studies showed significant increases in VEGF and CD31 expression in the ischemic area of treated animals. Morphometric analysis showed increased neovascularization with SMO treatment. Autotransplantation of SMOs constitutes a novel approach for safe and effective therapeutic angiogenesis with improvement in perfusion, normalization of microvascular reactivity, and increased expression of VEGF and CD31.

Enhanced wound-healing quality with bone marrow mesenchymal stem cells autografting after skin injury

Adult stem cells exist in various tissues and organs and have the potential to differentiate into different cell lineages, including bone, cartilage, fat, tendon, muscle, and epithelial cells of the gastrointestinal tract. Here, we report that the in vitro expanded and purified bone marrow mesenchymal stem cells (MSCs) might take on phenotypes with characteristics of vascular endothelial cells (7% on day 3 and 15% on day 1) or epidermal cells (3% on day 3 and 13% on day 1) after being cultured under different lineage-specific culture conditions. Also, in vivo grafting experiments showed that 5-bromodeoxyuridine-labeled MSCs could convert into the phenotypes of vascular endothelial cells (3.43, 3.46, and 2.94% on days 7, 14, and 28, respectively) in granulation tissues, sebaceous duct cells, and epidermal cells (0-1.49%) in regenerated skin, implying that these grafted MSCs might have transdifferentiated into the above three cell types. Animal autografting experiments with MSCs further confirmed that indices pertaining to wound healing quality, such as the speed of reepithelialization, the number of epidermal ridges and thickness of the regenerated epidermis, the morphology and the number and arrangement of microvasculature, fibroblasts and collagen, were much enhanced. Our results indicate that locally delivered bone marrow MSCs can enhance wound healing quality, and may generate de novo intact skin, resulting in perfect skin regeneration after full-thickness injury.

Granulocyte colony-stimulating factor-induced blood stem cell mobilisation in patients with chronic heart failure--Feasibility, safety and effects on exercise tolerance and cardiac function

Bone marrow-derived stem cells may contribute to the regeneration of non-haematopoietic organs. In order to test whether an increase in circulating stem cell numbers improves impaired myocardial function we treated 16 male patients with chronic heart failure due to dilated (DCM; n = 7) or ischaemic cardiomyopathy (ICM; n = 9) with the stem cell mobilising cytokine granulocyte colony-stimulating factor (G-CSF; four 10-day treatment periods interrupted by treatment-free intervals of equal length). Safety and efficacy analyses were performed at regular intervals. Peak CD34+ cell counts remained constant from cycle to cycle. Cardiac side effects in ICM patients included occasional episodes of dyspnea or angina and one episode of fatal ventricular fibrillation. Nine (4 DCM, 5 ICM) of 12 patients receiving four full G-CSF cycles experienced an improvement by one New York Heart Association (NYHA) class and a statistically significant increase in six-minute walking distance. By contrast, none of 8 ICM historical controls had a change in NYHA class during a similar time period. Statistically significant changes in echocardiographic parameters were not recorded. Sequential administration of G-CSF is feasible and possibly effective in improving physical performance in patients with chronic heart failure. Patients with ICM may be at risk of increased angina and arrhythmias.

Transplantation of Autologous Bone Marrow-Derived Cells into the Myocardium of Patients Undergoing Coronary Bypass

BACKGROUND

Animal studies suggest that cell transplantation, including bone marrow-derived cells, can ameliorate left ventricular remodeling following myocardial ischemia. Clinical evaluation of the potential benefits of this approach is limited by the lack of safety and feasibility studies. We have assessed the safety and feasibility of intramyocardial transplantation of autologous bone marrow-derived cells in patients undergoing coronary artery bypass graft (CABG) surgery.

METHODS AND RESULTS

Between December 2001 and May 2002 7 patients, scheduled for CABG, consented to the trial. All had CABG using hypothermic cardiopulmonary bypass (CPB) and cold cardioplegic arrest. An average of 21 10(6) (8.6 10(6) to 35.1 10(6)) nucleated cells, and 4.2 10(4) (2.5 10(4) to 8.1 10(4)) CD34+ cells were injected into the anterior-lateral wall of the left ventricle, after discontinuation of cardiopulmonary bypass. The end points to assess safety included death, massive bleeding, electrocardiographic or biochemical evidence of myocardial infarction, ventricular dysrhythmia, myocardial perfusion, ventricular function, and the patients' functional status. All patients recovered well without ventricular arrhythmia, bleeding, or other major peri-operative complications. The average intensive care unit (ICU) and hospital stay was 1 and 7 days, respectively. Repeat Technetium-99m myocardial perfusion stress imaging and echocardiography 6 weeks after surgery showed improvement in tissue perfusion, and an average improvement of left ventricular function of 13.5% +/- 11.54% (the mean pre- and post-operative left ventricular EF were 32.5% +/- 15.46% and 46% +/- 18.55%, respectively). Twenty-four hours Holter monitoring showed no significant arrhythmia, 3 months post-operatively. All patients with narrow QRS complex showed no evidence of late potential, on signal-averaged electrocardiogram. At 4 to 9 months after surgery patients were in NYHA functional class "I".

CONCLUSIONS

This early clinical experience shows that autologous bone marrow-derived cell transplantation into myocardium is feasible and relatively safe. Further clinical trials to assess the role of cell transplantation for myocardial repair are required.

A Cell-Based Multifactorial Approach to Angiogenesis

We here propose an alternative cell therapy approach to induce angiogenesis. We prepared small organ fragments whose geometry allows preservation of the natural epithelial/mesenchymal interactions and ensures appropriate diffusion of nutrients and gases to all cells. Fragments derived from lung are shown to behave as fairly independent units, to undergo a marked upregulation of angiogenic factors and to continue to function for several weeks in vitro in serum-free media. When implanted into hosts, they transcribe a similar array of angiogenic factors that specifically induce the formation of a potent vascular network. The angiogenic induction capacity of these fragments was also tested in a mouse and rat model of limb ischemia. We report that such fragments, when implanted in the vicinity of the ischaemic area, induce an angiogenic response which can rescue the ischaemia-induced damage. The approach presented differs from single factor application, gene therapy and other cell therapy methods in that it exploits the complex behaviour of autologous cells in their near to normal environment in order to achieve secretion of a whole range of angiogenic stimuli continuously and in an apparently coordinated fashion.

Therapeutic Angiogenesis in Peripheral Arterial Disease: Can Biotechnology Produce an Effective Collateral Circulation?

The physiological processes of angiogenesis, vasculogenesis and arteriogenesis contribute to the growth of collateral vessels in response to obstructive arterial disease causing lower limb or myocardial ischaemia, but in clinical practice the endogenous angiogenic response is often suboptimal or impaired, e.g. by factors such as ageing, diabetes or drug therapies. Therapeutic angiogenesis is an application of biotechnology to stimulate new vessel formation via local administration of pro-angiogenic growth factors in the form of recombinant protein or gene therapy, or by implantation of endothelial progenitor cells that will synthesize multiple angiogenic cytokines. Numerous experimental and clinical studies have sought to establish 'proof of concept' for therapeutic angiogenesis in PAD and myocardial ischaemia using different treatment modalities, but the results have been inconsistent. This review summarises the mechanisms of angiogenesis and the results of recent trials evaluating the efficacy and safety of different gene therapy, recombinant protein and cellular-based treatment approaches to enhance collateral vessel formation.

Bone Marrow Cells and Myocardial Regeneration

Hematopoietic stem cell (HSC) plasticity and its clinical application have been studied profoundly in the past few years. Recent investigations indicate that HSC and other bone marrow stem cells can develop into other tissues. Because of the high morbidity and mortality of myocardial infarction and other heart disorders, myocardial regeneration is a good example of the clinical application of HSC plasticity in regenerative medicine. Preclinical studies in animals suggest that the use of this kind of treatment can reconstruct heart blood vessels, muscle, and function. Some clinical study results have been reported in the past 2 years. In 2003, reports of myocardial regeneration treatment increased significantly. Other studies include observations on the cell surface markers of transplanted cells and treatment efficacy. Some investigations, such as HSC testing, have focused on clinical applications using HSC plasticity and bone marrow transplantation to treat different types of disorders. In this review, we focus on the clinical application of bone marrow cells for myocardial regeneration.