Microencapsulating pancreatic islets is a strategy being explored as a treatment for type 1 diabetes which may overcome the immune-mediated rejection of the graft without toxic immunosuppression. Allo- and xeno- transplantation studies with microencapsulated islets have shown considerable promise but long term graft survival was limited and varied considerably. Microencapsulated cells are often injected free-floating into the peritoneal cavity, so the position of the grafts remains elusive after transplantation. The aim of this study was to assess magnetic resonance imaging (MRI) as a non-invasive means to track microencapsulated insulin-producing cells following transplantation.
Murine insulin-producing cells (MIN6) and human islets were labelled with fluorescent superparamagnetic iron oxide (SPIO) nanoparticles and encapsulated within barium alginate microcapsules. Viability and insulin secretion of encapsulated SPIO-labelled MIN6 and human islets were assessed. In vitro imaging of encapsulated SPIO-labelled cells was carried out using a clinical grade 3 T MRI. Encapsulated SPIO-labelled MIN6 were transplanted into the peritoneal cavity of immunocompetent (C57BL/6) mice and tracked non-invasively using both 3 T and 11.7 T MRI.
Fluorescent imaging demonstrated the uptake of SPIO nanoparticles by both MIN6 and human islets with no evident changes in cell morphology. SPIO-labelling affected neither the viability of encapsulated MIN6 and islets over 7 days in culture, nor their capacity to secrete insulin in response to glucose. Normalization of blood glucose levels was achieved when encapsulated SPIO-labelled MIN6 were transplanted into the peritoneal cavity of diabetic C57BL/6 mice. In vitro imaging demonstrated that clusters as well as single capsules of encapsulated SPIO-labelled MIN6 and islets could be visualised using the 3 T MRI (Figure 1). In vivo encapsulated SPIO-labelled MIN6 cells could be visualised within the peritoneal cavity as discrete hypointensities using the high power 11.7 T but not the clinical grade 3 T MRI (Figure 2).