Abstract
Cryopreservation of islets adds great flexibility to clinical islet transplant programs. Methods of islet cryopreservation have traditionally utilized permeating cryoprotectants contained within isotonic solutions without specifically addressing issues of ionic balances, buffering capacity, or oxygen free radicals that occur during hypothermic stresses. These factors may become significant issues during low-temperature storage and during the freezing and thawing process. Since its development in the early 1980s, the University of Wisconsin (UW) organ preservation solution has become the standard vascular flush and preservation solution. Recently, Hypothermosol preservation solution (HTS) was developed as a hypothermic blood substitute. The unique characteristics and composition of these preservation solutions may be important when developing solutions specific for the cryopreservation of cells and tissues. It was the aim of this study to evaluate these two hypothermic preservation solutions as the media used in cryopreservation of islets. Groups of canine islets [5000 islet equivalents (IE)/group] were cryopreserved using the standard protocol of stepwise addition of dimethyl sulfoxide (DMSO) to 2 M, controlled nucleation, slow cooling (0.25°C/min), and rapid thawing (200°C/min). The cryopreservation solutions were made with 1) UW solution, 2) HTS solution, or 3) Medium 199 solution with 10% fetal calf serum (FCS). Additional control groups included islets cryopreserved using 4) HTS, 5) UW solution, and 6) Medium 199 alone, without DMSO. Recovery of islets immediately following thawing was equivalent between the groups with the exception of the islets cryopreserved without DMSO (groups 4–6, p < 0.05). After 48 h of postcryopreservation tissue culture, islet recovery was highest in the groups frozen with UW and HTS (mean ± SEM) (79.8 ± 1.9% and 82.5 ± 1.5%, p < 0.05 vs. group 3, 69.1 ± 3.3%, p < 0.05, ANOVA). Less than 15% of the islets were recovered when they were cryopreserved without the cryoprotectant DMSO (groups 4–6). Functional viability was assessed by measuring the glucose-stimulated insulin secretion during static incubation after 48-h culture. The stimulation indexes were 4.6 ± 1.0, 4.2 ± 0.8, 3.6 ± 1.2, 0.6 ± 0.5, and 0.4 ± 0.2 for islets in groups 1–5, respectively. This study demonstrates that postcryopreservation survival can be improved using intracellular-based preservation solutions, including UW or HTS, in conjunction with DMSO.