Microencapsulation to reduce mechanical loss of microspheres: implications in myocardial cell therapy §

Objective: 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. Methods: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 mm) were encapsulated in APA microcapsules. In group I (n = 16), rats received bare microspheres, group II (n = 16) microspheres within 200 mm microcapsules and in group III (n = 16), microspheres within 400 mm microcapsules. After 20 min, hearts were quantified for the amount retained. Results: Myocardial function did not improve further with escalatingcell dosesbeyondan initialresponse at1.5 � 10 6 cells.Encapsulatedmicrospheresin200 mm and 400 mm microcapsules demonstrated a fourfold increase in retention rate compared with 10 mm microspheres. Conclusion: 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. # 2010 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.