Treatment of rat pancreatic islets with reactive PEG

Covalent attachment of polymers to cells and tissues could be used to solve a variety of problems associated with cellular therapies. Insulin-dependen t diabetes mellitus is a disease resulting from the autoimmune destruction of the beta cells of the islets of Langerhans in the pancreas. Transplantat ion of islets into diabetic patients would be an attractive form of treatme nt, provided that the islets could be protected from the host's immune syst em in order to prevent graft rejection. If reaction of polyethylene glycol (PEG) segments with the islet surface did not damage function, the immunoge nicity and cell binding characteristics of the islet could be altered. To d etermine if this process damages islets, rat islets have been isolated and treated with protein-reactive PEG-isocyanate (MW 5000) under mild reaction conditions. An assessment of cell viability using a colorimetric mitochrond rial activity assay showed that treatment of the islets with PEG-isocyanate did not reduce cell viability. Insulin release in response to secretagogue challenge was used to evaluate islet function after treatment with the pol ymer. The insulin response of the PEG-treated islets was not significantly different than untreated islets in a static incubation secretagogue challen ge. In addition, PEG-isocyanate-treated islets responded in the same manner as untreated islets in a glucose perifusion assay. Finally, the presence o f PEG on the surface of the islets after treatment with the amine-reactive N-hydroxysuccinimide-PEG-biotin (not PEG-isocyanate) was confirmed by indir ect fluorescence staining. These results demonstrate the feasibility of tre ating pancreatic islets with reactive polymeric segments and provide the fo undation for further investigation of this novel means of potential immunoi solation. (C) 2000 Elsevier Science Ltd. All rights reserved.