Myocardial tissue engineering with autologous myoblast implantation.

OBJECTIVE: Implanting myoblasts derived from autologous skeletal muscle, that is, satellite cells, for myocardial replacement has many advantages when compared with implanting either fetal cardiac myocytes (ethical and donor availability issues) or established cell lines (oncogenicity). Furthermore, autologous myoblasts do not require immunosuppression. The feasibility of satellite cell differentiation into muscle fibers, after implantation into the myocardium, was confirmed by means of a unique cell-labeling technique. METHODS: Myoblasts (satellite cells) isolated from the skeletal muscle of adult rats are labeled with 4',6-diamidino-2-phenylindone, which binds to DNA and to the protein tubulin to form a fluorescent complex, and implanted into the left ventricular wall of isogenic rats. The specimens are harvested 1 to 4 weeks after myoblast implantation. Histologic sections are examined under a fluorescent microscope. RESULTS: The labeling efficiency of satellite cells with 4',6-diamidino-2-phenylindole is nearly 100%. In 4 specimens, the progressive differentiation of implanted myoblasts into fully developed striated muscle fibers can be observed. CONCLUSION: Our earlier studies of autologous myoblast implantation into the cryoinjured myocardium of dogs suggested that these cells could differentiate into cardiac myocytes. However, it had been difficult to firmly establish these findings with the use of cell markers, thereby proving that the neomyocardium had indeed been derived from the implanted myoblasts. In this study, using 4',6-diamidino-2-phenylindole as a satellite cell marker, we were able to demonstrate that the implanted satellite cells did in fact differentiate into fully developed, labeled muscle fibers. Because of the obvious advantages of using autologous donor myoblasts, the clinical application of this approach may provide a novel strategy for the future management of heart failure.

Cellular cardiomyoplasty: myocardial regeneration with satellite cell implantation.

BACKGROUND: Damaged skeletal muscle is able to regenerate because of the presence of satellite cells, which are undifferentiated myoblasts. In contrast, destruction of cardiac myocytes is associated with an irreversible loss of myocardium and replacement with scar tissue, because it lacks stem cells. We tested the hypothesis that skeletal muscle satellite cells implanted into injured myocardium can differentiate into cardiac muscle fibers and thus repair damaged heart muscle. METHODS: Two series of canine studies were performed. In the first series (n = 26), satellite cells were isolated from skeletal muscle, cultured, and labeled with tritiated thymidine. The cells were implanted into acutely cryoinjured myocardium and the specimens harvested 4 to 18 weeks later. In the second series (n = 20), satellite cells in culture were labeled with lacZ reporter gene, which encodes production of Escherichia coli beta-galactosidase. Four to 6 weeks later, beta-galactosidase activity was studied using X-Gal stain. RESULTS: New striated muscles were found in the first series of experiments at the site of implantation, within a dense scar created by cryoinjury. These muscles showed histologic evidence of intercalated discs and centrally located nuclei, similar to those seen in cardiac muscle fibers. Tritiated thymidine radioactivity was not identified clearly, presumably due to dilutional effect as the stem cells replicated repeatedly. In the second series, histochemical studies of reporter gene-labeled and implanted satellite cells revealed the presence of beta-galactosidase within the cells at the implant site, which confirmed the survival of implanted cells. CONCLUSIONS: Our data are consistent with the hypothesis of milieu-influenced differentiation of satellite cells into cardiac-like muscle cells. Confirmation of these findings and its functional capabilities could have important clinical implications.

Hybrid biomechanical assist for acute biventricular failure.

It is now clear dynamic cardiomyoplasty alone will not be able to support patients in severe cardiogenic shock. On the other hand, implantable univentricular electromechanically driven devices for permanent circulatory support are undergoing early clinical trials. Because of the potential for existing or subsequent biventricular failure and to avoid the need to implant two space-occupying mechanical devices, hybrid biomechanical assist devices could have certain advantages. To evaluate the feasibility of supporting profound biventricular failure, utilizing the combination of dynamic cardiomyoplasty and mechanical ventricular assistance, six dogs underwent simultaneous right latissimus dorsi cardiomyoplasty and left heart bypass. Microspheres were embolized into the pulmonary artery resulting in pulmonary hypertension and acutely impairing the right ventricle. The left ventricle was unloaded via a centrifugal Biomedicus pump. To create severe biventricular failure, the aorta was cross-clamped and potassium cardioplegia was infused into the aortic root to achieve a flaccid diastolic arrest of the heart. Infusion of microspheres into the pulmonary artery resulted in a dose-dependent increase in pulmonary artery pressure. Stimulation of the cardiomyoplasty under these conditions showed a 25.9 +/- 7.9% (S.E.M.) (p less than 0.05, paired t-test) increase in mean pulmonary artery flow. There was a corresponding increase of 6.75 +/- 10.6% in the centrifugal pump flow. Following diastolic arrest, the mean pulmonary artery and centrifugal pump flows increased 90.8 +/- 11.5% (p less than 0.001) and 16.4 +/- 12.1%, respectively. These preliminary results suggest this approach could be a useful alternative to patients who require long-term biventricular support.

Pulmonary artery counterpulsation with a skeletal muscle power source.

We evaluated the feasibility of using skeletal muscle (SM) to provide pulmonary artery (PA) counterpulsation in an acute pulmonary hypertension (PHT) model. PA counterpulsation was achieved in six dogs with a dual chambered pump powered by the latissimus dorsi muscle. A rate-responsive stimulator was used to make the muscle contract in counterpulsation. Graded PHT was induced by infusing 150 microns glass beads into the PA, while RV and PA pressures were monitored. With PA pressures ranging from 19/10 to 115/62 mmHg, effective counterpulsation was observed. The degree of counterpulsation was influenced by the extent of PHT induced, with the amount of RV tension-time index (TTI) unloading correlated with the level of PA systole (r = 0.92). Therefore, results were divided into two groups (Group 1: PA systole less than or equal to 40 mmHg, and Group 2: PA systole greater than 40 mmHg). In Group 1, RV TTI decreased from 11.29 +/- 0.76 to 9.99 +/- 0.72 mmHg.sec, PA diastole increased from 20 +/- 2.3 to 31 +/- 3.0 mmHg, and PA mean increased from 24 +/- 2.2 to 2.9 +/- 2.2 mmHg (all p less than 0.05). In Group 2, RV TT1 decreased from 15.12 +/- 1.83 to 10.99 +/- 0.90 mmHg.sec, PA diastole increased from 41 +/- 3.5 to 64 +/- 6.2 mmHg, and PA mean increased from 49 +/- 4.8 to 55 +/- 5.7 mmHg (all p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)