Successful long-term cryopreservation of highly purified canine islets

This study evaluated the ability of cryopreservation to store large quantities of canine islets for transplantation studies. Islets were isolated by automated screen methods and purified by Euro-Ficoll gradients. After overnight 37 degrees C incubation, islets were equilibrated with 2 M dimethylsulfoxide, cryopreserved at a cooling rate of 0.25 degree C/min and subjected to long-term storage in liquid nitrogen. Six months later, some islets were thawed at a rate of 180 degrees C/min. The viability of cryothawed islets was determined in vitro by comparing islet count, total insulin content, morphology and perifusion studies in both control and cryothawed islets, and in vivo by transplantation into diabetic nude mice. The percentages of recovery of both islet count and total insulin content were 74.17 +/- 4.46 and 70.66 +/- 14.08, respectively. Islet morphology after cryothaw by light and electron microscopy revealed structurally intact islets with varying degrees of granulation. The results of perifusion indicated that there was no significant difference (p > 0.1) in both total stimulated insulin secretion and stimulation index response to high-dose glucose plus 3-isobutyl-1-methylxanthine and carbachol of isolated islets as compared to those of cryothawed islets. Transplantation into nude mice proved that grafted islets can successfully reverse diabetes. In conclusion, these findings indicate that the majority of purified canine islets can survive the frozen-thawed insult while maintaining their secretory function and permitting mass storage of canine islets for further transplant studies.