Cryopreservation of pancreatic islets prior to transplantation: a comparison between UW solution and RPMI culture medium.

Effective cryopreservation of pancreatic islets would be valuable in several contexts: for the assessment of islet cell viability, the measurement of beta-cell function, and the maintenance of viability and sterility prior to islet transplantation. In this study, isolated rat islets were cryopreserved or not following overnight culture and the most suitable preservation solution for transportation between centers was sought. Unfrozen and frozen-and-thawed islets were allocated to each of four different groups: untreated controls; cultured overnight in RPMI at 37 degrees C; cold stored at 4 degrees C in RPMI for 18-24 h; and stored at 4 degrees C in University of Wisconsin (UW) solution for 18-24 h. The greatest cell viability, as assessed by ethidium bromide/acridine orange staining and image analysis, was observed when postthawed islets were cultured in RPMI, whereas the least viable samples were those that were stored in UW solution. Measurement of insulin content and secretion in static incubation assays using 2.8 and 16.7 mM glucose showed that all treated groups exhibited a significant insulin secretory response to glucose stimulation whereas the untreated frozen-thawed islets failed to show any response. The cryopreserved islets in each group were equally successful in reversing hyperglycemia in streptozotocin-treated allogeneic rats when grafted intraportally in sufficient numbers (2000-2500). The groups also showed a similar mean graft survival time of 6-7 days before rejection. However, the best experimental group (the postthaw cultured islets) failed to cure diabetic rats when grafted in a smaller numbers (<2000). These data demonstrate prompt and sustained function in cryopreserved islets when they were maintained by any of the methods studied if they were grafted in sufficient numbers. We conclude that cold storage of thawed cryopreserved islets using either RPMI or UW solution is an effective method for their transportation and/or storage, but does not reduce their immunogenicity before transplantation.