Cell TherapySafety of intramyocardial injection of autologous bone marrow cells to treat myocardial ischemia in pigs☆
Introduction
Cardiovascular disease accounted for 40% of all deaths or 1 in every 2.5 deaths in the United States in 2000 [1]. Ischemic heart disease accounts for nearly half of all cardiovascular deaths and is the leading cause of congestive heart failure. Chronic myocardial ischemia results in cardiac contractile dysfunction. If the ischemic episode is limited in severity or duration, then cardiomyocytes survive and are protected from further ischemic insult through several preconditioning mechanisms. However, with prolonged severe periods of ischemia, cardiomyocyte death occurs [2]. Adult human cardiomyocytes lack the capability to regenerate, and over time, damaged myocardial cells are replaced by connective scar tissue [3] along with a compensatory hypertrophy of the remaining viable cardiomyocytes. This replacement of infarct by scar tissue leads to a loss of functional myocardium within the ischemic area, a progressive remodeling of the nonischemic area, or border zone, and an overall reduction in cardiac performance.
It has been demonstrated that bone marrow mononuclear cells (BMCs) can differentiate into cardiomyocytes [4], [5], [6]. In one study, transplanted isogenic bone marrow cells were introduced into damaged rat hearts by coronary perfusion. Surviving cells were formed in the majority of animals with distribution throughout the myocardium [6]. This study also revealed that the BMCs that infiltrated the myocardial scar were fibroblast-like, whereas BMCs within the surrounding tissue expressed cardiomyocyte markers. Other studies have shown that BMCs transplanted into the damaged myocardium of mice survive, express cardiomyocyte-specific genes, and may participate in neovascularization [4], [5]. We and others have conducted studies demonstrating improvements in myocardial blood flow and cardiac function following intramyocardial injection of bone marrow or bone marrow-derived cells [7], [8]. Additionally, clinical studies have documented the feasibility of harvesting and transplanting circulating endothelial progenitor cells or BMCs in patients suffering from ischemic heart disease.
Because of the compelling preclinical data illustrating the ability of BMCs to improve cardiac function, clinical trials were initiated. These trials are currently being performed as single-center studies using BMCs or skeletal myoblasts. Safety and feasibility have initially been favorable in trials utilizing human adult bone marrow stem cells, but unresolved issues remain regarding the initial arrhythmogenic potential of myoblasts [9]. In the published reports of human stem cell trials thus far, the use of BMCs delivered in patients with previous myocardial infarction was shown to improve function and perfusion in a small number of patients [10]. It appears therefore that stem cells, whether derived from bone marrow or isolated from the blood circulation, can help improve cardiac dysfunction and repair damaged cardiac tissue. However, there are few studies [11] that systematically evaluated the safety of bone marrow-derived cell transplantation for chronic ischemic conditions of the myocardium. The purpose of this study is to evaluate the safety of autologous stem cell transplantation into chronically ischemic myocardium as a potential therapy for the repair of cardiac tissue. By demonstrating that catheter-based BMC injection was safe, we provided a basis for developing, evaluating, and improving the therapeutic potential of bone marrow-derived cells.
Section snippets
Chronic ischemia surgical procedure (ameroid constrictor based)
Animal care and handling conformed to the National Institutes of Health and American Heart Association guidelines and were approved by the Institutional Animal Care and Use Committee of the American Cardiovascular Research Institute. Adult Yucatan miniswines (30–60 kg) were sedated with intramuscular injection of Telazol (2–4 mg/kg), intubated, and anesthetized. While under anesthesia and using mechanical ventilatory support, a thoracotomy was performed, the pericardium was opened, and an
Mortalities
Of the 14 animals enrolled, 2 animals died (14% mortality rate). Both mortalities occurred prior to treatment: one on the surgical table after ameroid placement and the other 3 days after ameroid placement surgery. No casualties occurred during or immediately after intracardiac BMC or saline injections.
Bone marrow cell characterization
The majority of BMCs were positive for the common leukocyte marker CD45 (63±6%) (Fig. 1, Fig. 2). The percentage of T cells (CD3+ cells) isolated from the BMC injectate was 29.97±1.4%. T-helper
Discussion
This study is the first to report the safety of intramyocardial bone marrow cell injection with full characterization of the bone marrow cell injectate. Injection of autologous bone marrow cells into ischemic myocardium was not associated with any serious side effects; specifically, there were no casualties due to cell implantation, arrhythmias were unable to be induced even during electrophysiological stimulation, there was no evidence of local infection as assessed by histopathological
Conclusions
In conclusion, intramyocardial injection of freshly isolated bone marrow cells is safe and feasible for the clinical setting. Many other groups, including our own, have previously shown the efficacy of the cellular therapy by the ability of these cells to induce angiogenesis and improve cardiac function. This study shows, in a clinically relevant large-animal model, that catheter-based intramyocardial injection of autologous bone marrow cells into chronically ischemic myocardium is safe.
Acknowledgments
We would like to thank Dr. Roger Broderson, DVM, MS, PhD, for his help during the necropsy procedures and Mr. Todd Dennis for acquiring the echocardiographic images. We would like to thank Dr. Alka Redkar for providing laboratory space and equipment for the cell characterization studies. We would also like to thank Mr. Jesse Rios, Ms. Melissa Fowlkes, RVT, and Mr. David Robinson for their support during the procedures and Ms. Molly Jones for all her administrative assistance.
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Funding for this project was provided by AC Therapeutics, 3155 Northwoods Place, Norcross, GA 30071, USA.
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These authors contributed equally to this manuscript.