Vascularization of purified pancreatic islet-like cell aggregates (pseudoislets) after syngeneic transplantation

Abstract

To clarify whether avascular purified endocrine cell aggregates derived from islets of Langerhans (pseudoislets) revascularize similarly to what is known for intact pancreatic islet grafts, we studied the process of angiogenesis and revascularization of syngeneically transplanted pseudoislets using intravital fluorescence microscopy. Pseudoislets were composed of pure beta-cells (B) or non-beta-cells (NB), as well as of mixed beta- and non-beta-cells (B/NB; 70/30%) or nonsorted-cells (NC), and were transplanted into the dorsal skinfold of Syrian golden hamsters. Intact islet grafts served as controls. At day 6 after transplantation, microvascularization of all types of pseudoislets was found to be less than in controls, as indicated by a reduced number of transplants that contained newly formed microvessels (take-rate: B, 38.8; NB, 38.7; B/NB, 43.8; and NC, 40.3% vs. intact islet grafts, 71.9%; P < 0.01). Moreover, those pseudoislets that had developed a microvascular network revealed a significantly lower functional capillary density (145.8+/-49.5 to 241.0+/-47.5 cm(-1) vs. intact islet grafts: 459.8+/-65.6 cm(-1); P < 0.05). After 20 days, the take-rate of pseudoislets was still lower (B, 67.4; NB, 45.3; B/NB, 48.4; and NC, 64.2%) when compared with intact islet grafts (88%; P < 0.05); however, islet-like aggregates with vascularization now showed an islet-specific glomerulus-like network of capillaries with a functional capillary density (498.5+/-49.1 to 601.4+/-124.0 cm[-1]) similar to that of intact islet grafts (644.3+/-26.8 cm[-1]). We conclude that the dissociation of pancreatic islets, followed by reaggregation of the purified endocrine cells to islet-like clusters (pseudoislets), delays the process of angiogenesis and revascularization after free transplantation; however, this does not influence the capacity to form an intact islet-specific microvasculature (angio-architecture), which appears to be independent from the cellular composition of pseudoislets.