OPTIMIZATION OF THE MICROENCAPSULATED ISLET FOR TRANSPLANTATION

Background. Microencapsulation of isolated islets is a good method for providing protection against immunologic reactions to the cells in bo th allogeneic and xenogenic grafts. Current methods of microencapsulat ion require chelation of the alginate-calcium core, which solubilizes the structural support of the capsules and may adversely affect durabi lity. The purpose of the present study was to determine the in vitro r esponse to glucose stimulation, of microencapsulated islets that have not been subjected to chelation. Materials and methods. Using an air-j et-syringe-pump droplet generator, islets isolated from male Sprague-D awley rats were encapsulated in alginate, followed by washes with poly -l-lysine, saline, and a second coat of alginate. Different groups of the microencapsulated islets were then tested for response to high glu cose perifusion, before or after chelation, and the responses were com pared with those of unencapsulated islets. Results. Chelated microenca psulated islets showed a normal biphasic insulin response to stimulati on with 16.7 mM (300 mg%). Thus, insulin secretion increased from a me an +/- SEM basal rate of 3005 +/- 645 to a stimulated rate of 5165 +/- 1030 pg/min (P < 0.05, n = 6) in the first phase, comparable to resul ts obtained with the unencapsulated islets. In contrast, unchelated mi croencapsulated islets did not respond to stimulation with 16.7 mM glu cose. However, after a 24-h culture of these unchelated microcapsules, a small but significant response was observed. Conclusions. Although culturing unchelated microcapsules of islets may enhance their functio n, chelation of the microcapsular core is essential for optimal functi on of the enclosed islets. (C) 1998 Academic Press.