C-peptide Responses After Meal Challenge in Mice Transplanted with Microencapsulated Rat Islets

Aims/hypothesis: This study aimed to assess a response of microencapsulated rat islets to a meal challenge after being transplanted intraperitoneally into diabetic mice.

Methods: Microencapsulated rat islets or control naked syngeneic mouse islets were transplanted intraperitoneally into mice with streptozotocin-induced diabetes. Meal challenges were done 3, 6 and 9 weeks after transplantation. Glucose-induced insulin secretion from microencapsulated islets before and after transplantation was assessed in vitro.

Results: Within the first week, all animals transplanted with either microencapsulated rat islets or with syngeneic murine islets became normoglycaemic (< 11 mmol/l). At 4 and 6 weeks, body weight was less than normal in the non-diabetic control mice. Mice with the encapsulated rat islets had lower fasting glucose concentrations and more rapid glucose clearance after a meal challenge than the control mice. The group of mice with transplanted syngeneic islets had similar glucose profiles to control mice, except for slightly accelerated glucose clearance. The C peptide responses of mice with either microencapsulated or naked islets were clearly lower than the controls. An increase of C peptide appeared as early as 20 min in the plasma of the group with encapsulated islets, but this was considerably slower than in the other two groups. Microencapsulated rat islets retrieved 9 weeks after transplantation did not lose their ability to respond to glucose, but their output was less than half of the pretransplant control islets.

Conclusion/interpretation: The delivery of C peptide and presumably the accompanying insulin are delayed by restrictions of the capsules and the peritoneal location. However, this delay in reaching peripheral target organs does not prevent microencapsulated grafts from efficiently clearing glucose after a meal.