Cryopreservation of mouse pancreatic islets: effects of human serum on islet survival

The aim of this study was to compare the survival of cryopreserved mouse pancreatic islets frozen in the presence of either a simple salt solution (Hanks' balanced salt solution) or a complete tissue culture medium (RPMI 1640). Moreover, the addition of 10% human serum to the freezing solutions was evaluated. Collagenase isolated islets were kept in culture for three days, before being cooled at a rate of 5 degrees C/min or 25 degrees C/min to -70 degrees C, at which temperature the islets were transferred to liquid nitrogen. All freezing media were supplemented with 2 M dimethylsulphoxide as cryoprotectant. The islets were rapidly thawed at 37 degrees C and subsequently cultured for another three days. The recovery of islets was higher when the more rapid cooling rate was used and the addition of serum further improved the recovery. Compared to non-frozen cultured islets there was a loss of cells in all groups of cryopreserved islets, as measured by their DNA content, and this was accompanied by a lowered insulin content. All groups of frozen-thawed islets responded to a high glucose stimulus in vitro with a 5-9 fold increase in insulin secretion. There was no obvious advantage of using a complete tissue culture medium for islet cryopreservation, but the addition of serum had some beneficial effects. Data obtained from non-frozen control islets suggest that human serum slightly impairs the function of mouse pancreatic B-cells.