Microencapsulation to reduce mechanical loss of microspheres: implications in myocardial cell therapy.
ABSTRACT Previous regenerative studies have demonstrated massive cell losses after intramyocardial cellular delivery. Therefore, efforts at reducing mechanical losses may prove more successful in optimising cellular therapy. In this study, we hypothesized that escalating mesenchymal stem cells (MSCs) dose will not produce corresponding improvement in cardiac function due to washout of the small cells in microcirculation. Using microspheres similar in size to MSCs, that are encapsulated in alginate-poly-l-lysine-alginate (APA), we tested the hypothesis that size is an important factor in early losses.
In experiment I, five groups of rats (n=9 each) underwent coronary ligation; group I had no treatment; the other groups received escalating 0.5 × 10(6), 1.5 × 10(6), 3 × 10(6) and 5 × 10(6) of MSCs each. Echocardiogram was performed at baseline, 2 days and 7 weeks after surgery. In experiment II, cell-sized microspheres (10 μm) were encapsulated in APA microcapsules. In group I (n=16), rats received bare microspheres, group II (n=16) microspheres within 200 μm microcapsules and in group III (n=16), microspheres within 400 μm microcapsules. After 20 min, hearts were quantified for the amount retained.
Myocardial function did not improve further with escalating cell doses beyond an initial response at 1.5 × 10(6) cells. Encapsulated microspheres in 200 μm and 400 μm microcapsules demonstrated a fourfold increase in retention rate compared with 10 μm microspheres.
We concluded that suboptimal functional improvement in this animal model starts at 1.5 × 10(6) cells and does not respond to escalating cell doses. Improving mechanical retention is possible by increasing the size of the injectate. Microencapsulation could be used to encapsulate donor cells and facilitate functional improvement in cellular heart failure therapy.
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ABSTRACT: Transplantation of neonatal cardiomyocytes is a novel approach for the treatment of heart failure and myocardial infarction, but quantitative information on long-term cell survival and development is limited. Male donor cardiomyocytes were isolated from neonatal Fischer 344 rats (1-2 days), purified, and injected into the left ventricular wall of female syngeneic adult rats. One hour to 12 weeks later, genomic DNA was isolated from recipient hearts. The amount of male DNA per sample was determined by quantitative real-time TaqMan PCR of the male-specific Sry gene. Transplanted cell survival was 57 +/- 9% at 0-1 h, 24 +/- 6% at 24 h, 28 +/- 11% at 7 days, 27 +/- 3% at 14 days, 23 +/- 8% at 4 weeks and 15 +/- 3% at 12 weeks. The caspase inhibitor AcYVADcmk failed to improve transplanted cell survival at 24 h, suggesting that apoptosis did not play a major role in cell loss. Histology revealed that transplanted cells became more elongated over time, developed cross-striations, and that their nuclei increased in size. However, at 12 weeks, transplanted cells and their nuclei were still smaller than those of host myocardium. We established a quantitative survival profile for neonatal cardiomyocytes transplanted into normal adult myocardium. There was significant loss of cells within 24 h, but 15% of transplanted cells survived 12 weeks. Those cells that did survive underwent differentiation and developed visible sarcomeres, suggesting a potential contribution toward ventricular function.Journal of Molecular and Cellular Cardiology 03/2002; 34(2):107-16. · 5.15 Impact Factor
- Circulation 01/2004; 110. · 15.20 Impact Factor
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ABSTRACT: The functional benefit of cell transplantation after a myocardial infarction is diminished by early cell losses. IGF-1 enhances cell proliferation and survival. We hypothesized that IGF-1-transfected smooth muscle cells (SMCs) would enhance cell survival and improve engraftment after cell transplantation. The IGF-1 gene was transfected into male SMCs and compared with SMCs transfected with a plasmid vector (vector control) and nontransfected SMCs (cell control). IGF-1 mRNA (n=10/group) and protein levels (n=6/group) were higher (P <0.05 for all groups) at 3, 7, and 14 days compared with controls. VEGF was also increased in parallel to enhanced IGF-1 expression. IGF-1-transfected cells demonstrated greater cell proliferation, stimulated angiogenesis, and decreased caspase-3 activity after simulated ischemia and reperfusion (P <0.05 for all groups compared with vector or cell controls). A uniform left ventricular injury was produced in female rats using a cryoprobe. Three weeks later, 2 x 10(6) cells from three groups were implanted into the scar. One week later, IGF-1-transfected SMCs had increased myocardial IGF-1 and VEGF levels, increased Bcl2 expression, limited cell apoptosis, and enhanced vessel formation in the myocardial scar compared with the two control groups (P <0.05 for all groups). The proportion of SMCs surviving in the implanted region was greater (P <0.05) in the IGF-1-transfected group than in the vector or cell controls. Gene enhancement with IGF-1 improved donor cell proliferation, survival, and engraftment after cell transplantation, perhaps mediated by enhanced angiogenesis and reduced apoptosis.AJP Heart and Circulatory Physiology 12/2004; 287(6):H2840-9. · 3.63 Impact Factor