Encapsulation of Porcine Insulin in Rabbit Erythrocytes and Its Disposition in the Circulation System in Normal and Diabetic Rabbits

Abstract

The application and usefulness of resealed erythrocytes as a cell carrier of porcine insulin were studied in rabbits. The insulin was loaded in rabbit erythrocytes by a dialysis method followed by isotonic resealing of the erythrocytes at 25 and 37 °C. The amounts of insulin entrapped in the erythrocytes at these temperatures were 6.23±1.05 and 5.89±1.33 IU/ml of packed cell, with efficiency of encapsulation being 6.0±1.2 and 5.8±2.0%, respectively. When the insulin loaded erythrocytes were incubated in phosphate buffered saline at 37 °C, the insulin levels in the resealed cells declined according to a biexponential function. The in vitro stability of the cells resealed at 25 °C was superior to that at 37 °C. After subcutaneous (s.c.) administration of free insulin, the absorption rate constants in diabetic rabbits were larger than those of normal rabbits. The in vivo decline of insulin released from the loaded erythrocytes indicated a biexponential kinetics. Although the pharmacokinetic behavior of plasma insulin between normal and diabetic rabbits was similar, the hypoglycemic effect was very different between them. These insulin dosings, be they intravenous (i.v.) dosing of insulin or loaded cells or s.c. dosing of insulin, maintained the hypoglycemic effect in diabetic rabbits about twice as long as in a normal animal. Moreover, the effective period of insulin-loaded erythrocytes was longer than that of free insulin dosings. These results suggest that the insulin-loaded erythrocytes may be useful as a dosage form for treatment of patients with diabetes mellitus. © 1989, The Pharmaceutical Society of Japan. All rights reserved.