Therapeutic angiogenesis by transplantation of human embryonic stem cell-derived CD133+ endothelial progenitor cells for cardiac repair.

OBJECTIVE: This study aim to enhance endothelial differentiation of human embryonic stem cells (hESCs) by transduction of an adenovirus (Ad) vector expressing hVEGF(165) gene (Ad-hVEGF(165) ). Purified hESC-derived CD133(+) endothelial progenitors were transplanted into a rat myocardial infarct model to assess their ability to contribute to heart regeneration. METHODS: Optimal transduction efficiency with high cell viability was achieved by exposing differentiating hESCs to viral particles at a ratio of 1:500 for 4 h on three consecutive days. RESULTS: Reverse transcription-PCR analysis showed positive upregulation of VEGF, Ang-1, Flt-1, Tie-2, CD34, CD31, CD133 and Flk-1 gene expression in Ad-hVEGF(165) -transduced cells. Additionally, flow cytometric analysis of CD133, a cell surface marker, revealed an approximately fivefold increase of CD133 marker expression in Ad-hVEGF(165)-transduced cells compared with the nontransduced control. Within a rat myocardial infarct model, transplanted CD133(+) endothelial progenitor cells survived and participated, both actively and passively, in the regeneration of the infarcted myocardium, as seen by an approximately threefold increase in mature blood vessel density (13.62 +/- 1.56 vs 5.11 +/- 1.23; p < 0.01), as well as significantly reduced infarct size (28% +/- 8.2% vs 76% +/- 5.6%; p < 0.01) in the transplanted group compared with the culture medium-injected control. There was significant improvement in heart function 6 weeks post-transplantation, as confirmed by regional blood-flow analysis (1.72 +/- 0.612 ml/min/g vs 0.8 +/- 0.256 ml/min/g; p < 0.05), as well as echocardiography assessment of left ventricular ejection fraction (60.855% +/- 7.7% vs 38.22 +/- 8.6%; p < 0.05) and fractional shortening (38.63% +/- 9.3% vs 25.2% +/- 7.11%; p < 0.05). CONCLUSION: hESC-derived CD133(+) endothelial progenitor cells can be utilized to regenerate the infarcted heart.

Tracking transplanted cells in live animal using upconversion fluorescent nanoparticles.

With the emergence of cell transplant as an attractive treatment modality for various diseases, there is a parallel need to track the fate of these cells to assess their therapeutic effectiveness. Here, we report the use of upconversion fluorescent nanoparticles, silica/NaYF(4):Yb,Er, to dynamically track live myoblast cells in vitro and in a living mouse model of cryoinjured hind limb. Nanoparticles loaded into cells were confirmed for its intracellular uptake by confocal imaging, spectrophotometry and inductively coupled plasma analysis. Loaded nanoparticles demonstrated absolute resistance to photobleaching and were applied for dynamic imaging to real time track in vitro cell migratory activity for a continuous 5 h duration using a time-lapse confocal microscope. Direct observation on the direction, speed and cell-cell interaction of migrating cells was clearly visualized. In vivo confocal imaging of nanoparticle-loaded cells intravenously injected into a mouse tail vein showed them flowing in the ear blood vessels. Nanoparticle-loaded cells were also unambiguously identified with superior contrast against a negligible background at least 1300 microm deep in a fully vascularized living tissue upon intramuscular injection. Spatiotemporal migratory activity of the transplanted cells within the three-dimensional living tissue was captured for at least 7 days post-delivery. Direct in vivo visualization of cell dynamics in the native tissue was unobtrusively followed over a 4 h time course and revealed subtle migratory activity of the transplanted cells. With these unique optical properties, we present silica/NaYF(4):Yb,Er nanoparticles as a new fluorescent live cell tracker probe for superior in vitro and in vivo dynamic imaging.

Directing endothelial differentiation of human embryonic stem cells via transduction with an adenoviral vector expressing the VEGF(165) gene.

Endothelial progenitors derived from human embryonic stem cells (hESCs) hold much promise in clinical therapy. Conventionally, lineage-specific differentiation of hESCs is achieved through supplementation of various cytokines and chemical factors within the culture milieu. Nevertheless, this is a highly inefficient approach that is often limited by poor replicability. An alternative is through genetic modulation with recombinant DNA. Hence, this study investigated whether transduction of hESCs with an adenoviral vector expressing the human VEGF(165) gene (Ad-hVEGF(165)) can enhance endothelial-lineage differentiation. The hESCs were induced to form embryoid bodies (EBs) by culturing them within low-attachment plates for 7 days, and were subsequently trypsinized into single cells, prior to transduction with Ad-hVEGF(165). Optimal transduction efficiency with high cell viability was achieved by 4-h exposure of the differentiating hESCs to viral particles at a ratio of 1 : 500 for three consecutive days. ELISA results showed that Ad-hVEGF(165)-transduced cells secreted human vascular endothelial growth factor (hVEGF) for more than 30 days post-transduction, peaking on day 8, and the conditioned medium from the transduced cells stimulated extensive proliferation of HUVEC. Real-time PCR analysis showed positive upregulation of VEGF, Ang-1, Flt-1, Tie-2, CD34, CD31, CD133 and Flk-1 gene expression in Ad-hVEGF(165)-transduced cells. Additionally, flow cytometric analysis of CD133 cell surface marker revealed an approximately 5-fold increase in CD133 marker expression in Ad-hVEGF(165)-transduced cells compared to the non-transduced control. Hence, this study demonstrated that transduction of differentiating hESCs with Ad-hVEGF(165) facilitated expression of the VEGF transgene, which in turn significantly enhanced endothelial differentiation of hESCs.

Application of inverted J-shaped partial sternotomy in intracardiac operations.

OBJECTIVE: To report our experience of intracardiac surgery with an inverted J-shaped partial sternotomy (IJPS) and describe the technical details of this approach. METHODS: From January to December 2002, 31 patients underwent intracardiac operations using the IJPS instead of a standard conventional full-length median sternotomy (FLMS). Twenty-one patients had mitral valve replacements (MVR), with combined tricuspid valvuloplasty in three, six had closure of secundum atrial septal defects, three had closure of ventricular septal defects and one had repair of cor triatriatum. Data from 26 randomly selected patients who had undergone MVR through a conventional FLMS were included for comparison. RESULTS: There were no perioperative or in-hospital deaths in either group. There was a significant difference between the two MVR groups in incision length, mediastinal drainage and blood transfusion volume, but not in cardiopulmonary bypass time, aortic cross-clamp time, duration of operation and duration of ventilatory support. There were no conversions from IJPS to FLMS, indicating that access was satisfactory for all the procedures. All patients were discharged without any significant postoperative complications. CONCLUSION: The IJPS is aesthetically pleasing with regard to cosmesis and does not affect safety and exposure. Furthermore, the smaller incision resulted in a significant reduction in blood loss and blood requirements.

Reprogramming autologous skeletal myoblasts to express cardiomyogenic function. Challenges and possible approaches.

Cell transplantation therapy is emerging as a promising mode of treatment following myocardial infarction. Of the various cell types that can potentially be used for transplantation, autologous skeletal myoblasts appear particularly attractive, because this would avoid issues of immunogenicity, tumorigenesis, ethics and donor availability. Additionally, skeletal myoblasts display much higher levels of ischemic tolerance and graft survival compared to other cell types. There is some evidence for improvement in heart function with skeletal myoblast transplantation. However, histological analysis revealed that transplanted myoblasts do not transdifferentiate into functional cardiomyocytes in situ. This is evident by the lack of expression of cardiac-specific antigens, and the absence of intercalated disc formation. Instead, there is differentiation into myotubes that are not electromechanically coupled to neighboring cardiomyocytes. This could in turn limit the clinical efficacy of treatment. This review would therefore examine the various challenges faced in attempting to reprogram autologous skeletal myoblast to express cardiomyogenic function, together with the various possible strategies that could be employed to achieve this objective.

Comments about possible use of human embryonic stem cell-derived cardiomyocytes to direct autologous adult stem cells into the cardiomyogenic lineage.

Several studies have shown that cell-transplantation therapy following myocardial infarction has some efficacy in aiding myocardial repair and subsequent recovery of heart function. Large-scale production of human embryonic stem cell-derived cardiomyocytes can potentially provide an abundant supply of donor cells for myocardial transplantation. There are, however, immunological barriers to their use in human clinical therapy.A novel approach would be to look at utilizing human embryonic stem cell-derived cardiomyocytes to reprogram autologous adult stem cells to express cardiomyogenic function, instead of using these directly for transplantation. This could be achieved through a number of novel techniques. Enucleated cytoplasts generated from human embryonic stem cell-derived cardiomyocytes could be fused with autologous adult stem cells to generate cytoplasmic hybrids or cybrids. Adult stem cells could also be temporarily permeabilized and exposed to cytoplasmic extracts derived from these cardiomyocytes. Alternatively, intact cells or enucleated cytoplasts from human embryonic stem cell-derived cardiomyocytes could be co-cultured with adult stem cells in vitro, to provide the cellular contacts and electrical coupling that might enable some degree of trans-differentiation to take place. This review would therefore examine the potential advantages and disadvantages of such a novel approach, in comparison to other more conventional techniques such as the use of exogenous cytokines/growth factors or the use of genetic modulation.

Strategies for directing the differentiation of stem cells into the cardiomyogenic lineage in vitro.

Most studies on stem cell transplantation therapy on myocardially infarcted animal models and phase-I human clinical trials have focused on the use of undifferentiated stem cells. There is a strong possibility that some degree of cardiomyogenic differentiation of stem cells in vitro prior to transplantation would result in higher engraftment efficiency, as well as enhanced myocardial regeneration and recovery of heart function. Additionally, this may also alleviate the probability of spontaneous differentiation of stem cells into undesired lineages and reduces the risk of teratoma formation, in the case of embryonic stem cells. The development of efficient protocols for directing the cardiomyogenic differentiation of stem cells in vitro will also provide a useful model for molecular studies and genetic manipulation. This review therefore critically examines the various techniques that could possibly be used to direct and control the cardiomyogenic differentiation of stem cells in vitro.

An overview and synopsis of techniques for directing stem cell differentiation in vitro.

The majority of studies on stem cell differentiation have so far been based in vivo, on live animal models. The usefulness of such models is limited, since it is much more technically challenging to conduct molecular studies and genetic manipulation on live animal models compared to in vitro cell culture. Hence, it is imperative that efficient protocols for directing stem cell differentiation into well-defined lineages in vitro are developed. The development of such protocols would also be useful for clinical therapy, since it is likely that the transplantation of differentiated stem cells would result in higher engraftment efficiency and enhanced clinical efficacy, compared to the transplantation of undifferentiated stem cells. The in vitro differentiation of stem cells, prior to transplantation in vivo, would also avoid spontaneous differentiation into undesired lineages at the transplantation site, as well as reduce the risk of teratoma formation, in the case of embryonic stem cells. Hence, this review critically examines the various strategies that could be employed to direct and control stem cell differentiation in vitro.

Transformation of adult mesenchymal stem cells isolated from the fatty tissue into cardiomyocytes.

BACKGROUND: Myocardial infarction results in the death of cardiomyocytes, which are replaced by scar tissue. Cardiomyocytes cannot regenerate because they are terminally differentiated. Mesenchymal cells are pluripotent cells, which have the potential to differentiate to specialized tissues under appropriate stimuli. The aim of this study was to direct differentiation of the adult mesenchymal stem cells isolated from fatty tissue into cardiomyocytes using 5-azacytidine. METHODS: Adult mesenchymal stem cells were isolated from the fatty tissue of New Zealand White rabbits and cultured in RPMI medium. Second-passaged mesenchymal cells were treated with various concentrations of 5-azacytidine and incubated for different intervals of time. The cells were plated in six-well dishes at 500, 5,000, and 50,000 cells/well. These cells were treated with 1-, 3-, 6-, 9-, and 12-micromol/L concentrations of 5-azacytidine and incubated for 12, 24, 48, and 72 hours. Later, the medium was replaced with fresh medium and incubated in a CO2 incubator. The medium was changed once at 3 to 4 days. At 2 months, the cells were fixed with 0.4% glutaraldehyde for 2 hours and later washed with phosphate-buffered saline. The transformed cells were subjected to immunostaining for the myosin heavy chain, alpha actinin, and troponin-I. RESULTS: After treatment with 5-azacytidine, the adult mesenchymal stem cells were transformed into cardiomyocytes. At 1 week, some cells showed binucleation and extended cytoplasmic processes with adjacent cells. At 2 weeks, 20% to 30% of the cells increased in size and formed a ball-like appearance. At 3 weeks, these cells began to beat spontaneously in culture when observed under phase contrast microscope. Immunostaining of the transformed cells for myosin heavy chain, alpha actinin, and troponin-I was positive. The differentiated cells maintained the phenotype and did not dedifferentiate up to 2 months after treatment with 5-azacytidine. CONCLUSIONS: These observations confirm that adult mesenchymal stem cells isolated from fatty tissue can be chemically transformed into cardiomyocytes. This can potentially be a source of autologous cells for myocardial repair.