Cryopreservation of hamster pancreatic islets using a rapid cooling rate

Abstract

To clarify the possibility of developing a rapid cooling rate for islet cryopreservation, we used a cooling rate of 25 degrees C/min for hamster pancreatic islet cryopreservation using 15 per cent dimethylsulfoxide as a cryoprotectant. After preservation, these islets were examined for their morphology and function by assaying the insulin release after glucose stimulation and the contents of the insulin and DNA in 10 islets. In addition, islet cell replicatory activity was investigated by an autoradiographic technique. The effects of transplantation of the islets upon isogeneic and xenogeneic transplantation were also examined. Freezing using a rapid cooling rate of 25 degrees C/min was found to be as effective as a slow cooling rate of 1 degree C/min for hamster islet cryopreservation. Morphologically, the cryopreserved islets appeared to be similar to the non-frozen cultured islets. The glucose-stimulated insulin release and cell replicatory activities in vitro also remained unchanged, whereas the number of cells per islet decreased slightly after cryopreservation. The grafting of cryopreserved islets normalized streptozotocin induced hyperglycemia following isogeneic transplantation. On the other hand, no prolongation of graft survivals in the case of the xenogeneic transplantation of hamster islets to rats was observed. The isogeneically transplanted islets exhibited the same cell replicatory activities in vivo, which was even higher compared that of normal hamster pancreatic islets in situ. In conclusion, the present findings indicate that hamster pancreatic islets can be successfully cryopreserved using a rapid cooling rate, however, it does not appear that this treatment reduces islet vulnerability to xenogeneic graft rejection.