Abstract
Pancreatic islet cryopreservation is necessary to facilitate organizational aspects of transplantation, including islet banking, tissue matching, organ sharing, immunomanipulation of islets, and multiple-donor transplantation. It may not be ideal, however, to use a general protocol in which the same cryopreservation strategy is applied to islets isolated from different species. The present study presents a theoretical discussion, based on the use of experimentally measured, species-specific parameters, to propose optimized cryopreservation protocols specific for canine pancreatic islets. This study builds upon previously determined canine islet osmotic and permeability data by measuring hydraulic conductivity and ethylene glycol (EG) permeability at below ambient temperature, allowing calculation of activation energies for hydraulic conductivity and cryoprotectant solute permeability, which were found to be 9.6 and 17.3 kcal/mol, respectively. These data were then used, in conjunction with water/NaCl/EG phase diagram data and a mathematical model, to theoretically predict optimum initial EG concentration, cooling rate, and terminal temperature for controlled-rate cooling prior to plunging into liquid nitrogen. The results predicted 2.57 M initial EG concentration, 0.24°C/min cooling rate, and plunging at - 42°C would result in the highest survival. These data were used to develop a new cryopreservation method presented in a flow diagram that may be superior to the empirically based protocol. Verification of this optimized protocol will be established with ongoing future experiments.
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