Improved cryopreservation yield of pancreatic islets using combination of lower dose permeable cryoprotective agents.

Islet transplantation has been shown to restore normoglycemia in animal models and for type 1 diabetic patients in clinical trials. One method of storing islets intended for transplantation is via cryobanking at very low temperatures (-196 °C). Cryobanking islets without the use of cryoprotecting agents (CPAs) contributes to cellular shear stress and cell death. Although current CPA protocols vary, high concentrations of these agents are toxic to islets cells. This study tested the effects of the permeating CPA dimethyl sulfoxide (MeSO) with the addition of ethylene glycol (EG), both at reduced concentrations, on rat and human islet cell yield, viability, and glucose stimulated insulin release (GSIR). To test this, islets were treated using three combinations of CPAs (2M MESO, 1M MESO + 1M EG, and 1M MESO + 0.5M EG). Next, fresh islets, 2M MESO islets, and 1M MESO + 0.5M EG isolated rat islets were transplanted into streptozotocin-induced (STZ) diabetic mice. Our data showed that cryopreservation with a reduced concentration of MESO (1M MESO + multimolar EG) achieved a higher percent yield and viability when compared to the current standard 2M MESO treatment for both rat and human islets. Furthermore, STZ-induced diabetic mice achieved normoglycemia after transplantation with 1000 islet equivalents (IE), an average 12 days sooner, with islets cryopreserved with reduced-concentration (MESO + 0.5M EG), compared to islets preserved with 2M MESO. In conclusion, reduced concentration of penetrating CPAs during islet cryopreservation increases islet yield and viability in vitro and reduces delay before normoglycemia in diabetic mice.