Improving the function of microencapsulated islets using co-encapsulation with pancreatic duct cells

Islet transplantation has normalized the blood glucose levels in patients with type 1 diabetes. However, this treatment requires the use of potentially harmful immunosuppressive drugs. An alternative to immunosuppression is the use of semi-permeable microcapsules that allow the diffusion of glucose, nutrients and oxygen but protect the transplanted cells against immune reaction. Another important problem is the limited survival of encapsulated and free islet cells. Pancreatic duct cells have been shown to play an important role in pancreas morphogenesis. The co-incubation of pancreatic duct cells and islets has decreased cell apoptosis and necrosis in the immediate post-isolation period. We have previously shown that incubating islets with IGF-II, the principal peptide that is secreted by duct cells, diminishes apoptosis and necrosis of encapsulated islets and allows the restoration of euglycaemia in diabetic mice using fewer islets. The objective of this study is to investigate the effect of co-encapsulating islets with pancreatic duct cells on islet cell survival. Pancreatic duct cells were isolated from C57BL/6 mice and their identity was confirmed by immunohistochemistry using antibodies against cytokeratin 7 (CK7) and IGF-II. The presence of known contaminants (fibroblasts and mesenchymals cells) was investigated by flow cytometry using their common marker: vimentin. Islets encapsulated alone or co-encapsulated with two different concentrations of duct cells (20 or 100 cells per capsule) were maintained in culture and evaluated at days 1, 7, 14 and 27 postencapsulation. Islet viability was evaluated using fluorescent dyes (acridine orange and propidium iodide), the percentage of necrotic islets by inverted-microscope analysis and their function by an MTS test. Duct cells expressed IGF-II and CK7. The cell preparation was pure at >85%. Islets cell viability was between 60-80% for islets encapsulated alone or with duct cells with no significant difference. This coencapsulation did not have a significant impact on the islets necrosis which remained consistently between 30-40%. Co-encapsulating islets with 100 duct cells had a significant impact on islet function (vs. islets encapsulated alone). This was demonstrated by the MTS test, which showed an absorbance at 492 nm of 0.32 ± 0.06 for co-encapsulated islets (vs 0.09 ± 0.01; p<0.005) at day 1 and 0.38 ± 0.12 (vs 0.10 ± 0.02; p<0.05) at day 27. The present study demonstrated that co-encapsulation with duct cells had a moderate effect on islet function, but failed to show a positive effect on islet cell survival. Considering the concordant results of previous studies, the present results were unexpected. Further studies are needed to explain these results and will involve in vivo transplantation in diabetic animals.