title: Novel approaches to cryopreservation of human pancreatic islets.
abstract: BACKGROUND
  Optimized conditions for survival and function of human islets must be defined if sufficient islets are to be recovered from a single human donor pancreas to reverse type-1 diabetes after isolation, cryopreservation, and transplantation. The objective of this study was to compare the cryoprotective effect of ethylene glycol (EG) with the standard cryoprotectant, dimethyl sulfoxide (DMSO), on isolated human islet survival and function. Furthermore, the effect of different addition protocols and equilibrium concentrations of the cryoprotectants were studied.
  
  
  METHODS
  Islets were isolated from human pancreata by using standard techniques of collagenase digestion and discontinuous Ficoll gradient purification. Aliquots of freshly isolated human islets were cryopreserved in six groups by using DMSO or EG. Cryoprotectants were added stepwise to produce a final concentration of 1.5 or 2.0 M, or added in a single step to a concentration of 1.5 M. Islets were cryopreserved by using established protocols and cultured for 48 hr at 37 degrees C before assessment of percentage of recovery and in vitro viability.
  
  
  RESULTS
  After cryopreservation, percentage of recovery of islets was significantly higher in the group treated with 1.5 M of DMSO added in a stepwise protocol (74+/-3%, mean+/-SEM) compared with the standard 2.0 M of DMSO (62+/-4%) (P<0.05, unpaired t test, n=6). There was no difference between the recovery of islets cryopreserved with either 1.5 M of DMSO stepwise (74+/-3%) or 1.5 M of DMSO one-step (69+/-3%). Islet recovery was higher in groups treated with DMSO compared with EG, regardless of concentration of cryoprotectant or addition protocol, although the difference was significant only when comparing DMSO and EG 1.5 M one-step. Furthermore, islets treated with 1.5 M of DMSO, added either stepwise (6.0+/-0.4) or in one-step (6.5+/-0.8), had significantly higher stimulation indices compared with islets treated with the standard cryoprotectant for human islets, 2.0 M of DMSO (4.5+/-0.5) (P<0.05).
  
  
  CONCLUSIONS
  These results demonstrate that a lower concentration of DMSO (1.5 M) allows for the cryopreservation of human islets with superior survival and preservation of function post-culture compared with 2.0 M of DMSO and various concentrations of EG.
authors.affiliation: Surgical-Medical Research Institute, 1074 Dentistry/Pharmacy Centre, University of Alberta, Edmonton, Alberta, T6G 2N8 Canada. jonathan.lakey@ualberta.ca
authors.forename: J R
authors.initials: JR
authors.lastname: Lakey
authors.forename: T J
authors.initials: TJ
authors.lastname: Anderson
authors.forename: R V
authors.initials: RV
authors.lastname: Rajotte
mesh_terms: D015925:Cryopreservation / Q000379:methods*; D003451:Cryoprotective Agents / Q000494:pharmacology* / Q000592:standards*; D004121:Dimethyl Sulfoxide / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D019855:Ethylene Glycol / Q000494:pharmacology*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D009994:Osmolar Concentration; D014022:Tissue Survival / Q000187:drug effects
chemical_list: D003451:Cryoprotective Agents; D007328:Insulin; D019855:Ethylene Glycol; D004121:Dimethyl Sulfoxide