| Diseases of the cardiovascular system remain a leading cause of morbidity and mortality worldwide. Congestive heart failure is the only cardiovascular disorder increasing in prevalence. Quantitative deficiency of cardiomyocytes and progressive ventricular remodeling characterize the final pathway of heart failure caused by various etiologies,especially myocardial infarction. We generally accepted twin notions that (l)in the adult heart all myocytes are terminally differentiated and,therefore,cannot be recalled into the cell cycle,and that (2) the myocardium lacks a stem cell population able to generate new myocytes. Cellular cardiomyoplasty (CCM), in which one delivers appropriate donor cells into the injured myocardium,targets the basic pathophysiology of heart failure and represents a novel means of augmenting the myocyte number and the contractile function of a failing heart. Data derived from animal models have demonstrated the feasibility of this approach, but the optimal choice of donor cell source remains controversial.Bone marrow stromal cells (MSCs), which are mesenchymal stem cells,have been shown to have the potential of differentiating into cardiomyocytes in vitro when treated with 5-azacytidine (5-aza). Since autologous MSCs can be obtained from patients by simple routine bone marrow aspiration, and their use as donor cells does not require fetal tissue or immunosuppression, this approach appears to be highly advantageous for clinical use.In this study,we want to induce cultured rabbit MSCs into myogenic cells which express cardiac muscle cell markers, actin, troponin I,and myosin heavy chain; simultaneously have cell to cell connecting markers, desmin and connexin 43. The induced cells were autotransplanted into infarted myocardial tissue by ligation of the left anterior decending artery. We tested the hypotheis that the induced cells can improve cardiac function in postinfarcted rabbits. We also assessed whether this benefit is still manifested in the clinically relevant setting of a treatment by angiotensin-converting enzyme inhibitors (ACEI).New Zealand white rabbits were used as tested animals. In vitro studies: Isolation and primary culture of MSCs from the femoral bones of donor rabbits were performed according to Wakitani's method. Then MSCs were cultured in cell culture medium with 5-aza (8 umol/L) for 24 hours. MSCs cultured with 5-aza formed myotubules which immunohisto-chemically stained positive for actin, troponin I,desmin,and connexin 43. The induced cells had expression of myosin heavy chain. Transmission electron microscopy revealed a cardiomyocyte-like ultrastructure, including myofilaments, a centrally positioned nucleus, and rich glycogen granules.In vivo studies:A myocardial infarction was created in 50 rabbits by coronary ligation. They were divided into 5 groups. At 2 weeks after injury, one group was autologously transplanted into scar with cultured MSCs (MSCs,n=6). Two groups did not receive any drug and were intra-myocardially injected 2 weeks after the infarct with either free-serum culture medium alone (control rabbits, n=7) or autologous 5-aza-induced MSCs previously expanded ex vivo for 4 weeks (5-aza-MSCs,n=7). Two other groups receive the ACEI ramipril (1 mg/kg/d), started the day of the infarct and continued uninterruptedlythereafter, and underwent time-matched procedures, that is, they were intramyocardially injected at 2 weeks after infarction with either free-serum culture medium alone (ACEI, n=8), or autologous 5-aza-induced MSCs (ACEI+5-aza-MSCs,n=7). Implanted MSCs were labeled with 4', 6-diamidino-2-phenylindole (DAPI) and then injected into the autologous myocardium. Left ventricular function was assessed by echocardiography at 6 weeks after implantation. A fluid-filled catheter was introduced into the carotid and left ventricular end-diastolic pressure (LVEDP) were analyzed. Specimens of ischemic myocardium were taken 6 weeks after MSCs implantation. Histologic sections were examined under common light microscope and fluorescent micro...
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