Function and viability of human islets encapsulated in alginate sheets: in vitro and in vivo culture

Abstract

Islet encapsulation offers an immune system barrier for islet transplantation, and encapsulation within an alginate sheetlike structure offers the ability to be retrievable after transplanted. This study aims to show that human islets encapsulated into islet sheets remain functional and viable after 8 weeks in culture or when transplanted into the subcutaneous space of rats. Human islets were isolated from cadaveric organs. Dissociation and purification were done using enzymatic digestion and a continuous Ficoll-UWD gradient. Purified human islets were encapsulated in alginate sheets. Human Islet sheets were either kept in culture, at 37°C and 5% CO(2), or transplanted subcutaneously into Lewis rats. After 1, 2, 4, and 8 weeks, the human islet sheets were retrieved from the rats and assessed. The viability of the sheets was measured using fluorescein diacetate (FDA)/propidium iodide (PI), and function was measured through glucose-stimulated insulin release, in which the sheets were incubated for an hour in low-glucose concentration (2.8 mmol/L) and then high (28 mmol/L), then high (28 mmol/L) plus 3-isobutyl-1-methylxanthine (50 μm). Human islet sheets remained both viable, above 70%, and functional, with a stimulation index (insulin secretion in high glucose divided by insulin secretion in low glucose) above 1.5, over 8 weeks of culture or subcutaneous transplantation. Islet transplantation continues to make advances in the treatment of type 1 diabetes. These preliminary results suggest that encapsulated islets sheets can survive and maintain islet viability and function in vivo, within the subcutaneous region.