IntroductionIslet transplantation is an attractive solution for type I diabetes, but the results are at the present discouraging. Collagenase, the enzyme used to obtain islets for transplantation, presents interbatch variability and endotoxin contamination that induces inflammatory cytokine production. Liberase (Roche, Basel, Switzerland), a new mixture of purified enzymes, has the same composition in all batches and is endotoxin-free.AimsTo compare the engraftment of islets obtained using either enzyme in streptozotocin-induced diabetic rats.MethodologyCollagenase- or Liberase-isolated islets were transplanted under the kidney capsule of diabetic rats. Collagenase islets restored glycemia and insulinemia in all animals at 24 hours, and both parameters were maintained in 45% of rats over 90 days; however, Liberase islets failed to reverse diabetes in all subjects.ResultsIn vitro experiments showed that Liberase islets did not maintain active insulin secretion. Cytotoxicity assays showed toxicity of Liberase to islets; both enzymes induced inflammatory cytokine production by macrophages.ConclusionIn summary, in our model, Liberase is not a good substitute for collagenase as an islet-isolating reagent. A major effort and investment in developing enzymes for tissue dispersion is needed to improve the outcome of islet transplantation.