Optimization of the concanavalin a self-regulating insulin delivery system

A self-regulating insulin delivery system based on the competitive binding of glycosylated insulin and glucose to Concanavalin A was developed. To avoid the leakage of Con A, Con A microspheres were prepared by a water in oil emulsion technique. The binding constants of the porous Con A microspheres to glucose and SAPG-insulin have been proven to be close to those of unmodified Con A molecules; 1.11 x 10[3] M-1 and 1.21 x 10[4] M-1, respectively. As an alternative approach for Con A modification, soluble Con A oligomer was synthesized by crosslinking Con A with glutaraldehyde. The size of filtered oligomer ranged from 870 A to 4070 A and molecular weight ranged from 6 x 10[5] to higher than 2 x 10[6] daltons. The binding constants of Con A oligomer were similar to those of Con A microspheres, while the binding capacity of Con A oligomer improved to be 85 to 90%. The Durapore ® membrane and the cellulose acetate hollow fiber were selected and were fabricated. Rapid glucose equilibrium between inside and outside device was achieved by both devices. With the aid of a mathematical model of the system, various in vitro experiments with two types of devices (the Durapore ® pouch-Con A microsphere system and the cellulose acetate hollow fiber-Con A oligomer system) were performed by varying the several involved parameters to optimize system. Both systems showed a stepwise SAPG-insulin release in response to the glucose challenge. The hollow fiber device was implanted into the diabetic dog and its function of the blood glucose regulation in response to food challenges with the refilling of fresh loading solution (SAPG-insulin and Con A oligomer) was evaluated. The blood glucose of pancreatectomized dog was maintained in the normal glycemic range with several food challenges until the inflammational tissue mass was covered around the implanted hollow fiber device. The hollow fiber device demonstrated the feasibility of self-regulating insulin delivery system for short term period, but it is necessary to develop the biocompatible membrane device for the long term insulin delivery system.