(347c) The Effect of Nanothin Biofunctional PEG Coating of Pancreatic Islets On Insulin Secretion Capability

Covalent attachment of polymers to cells and tissues could be used to solve a variety of problems associated with cellular therapies. Insulin dependent diabetes mellitus is a disease resulting from the auto-immune destruction of the beta cells of the islets of langerhans in the pancreas. Transplantation of islets into diabetic patients would be an attractive form of treatment, provided that the islets could be protected from the host's immune system in order to prevent graft rejection, and fewer number of islets transplanted in small volumes could be sufficient to reverse diabetes. Therefore, a need exists to develop islet encapsulation strategies that minimize transplant volume. In this study, we demonstrate the formation of nanothin, PEG rich conformal coatings on individual islets via layer-by-layer assembly of amine reactive N-hydroxysuccinimide-poly(ethylene glycol)-biotin (biotin-PEG-NHS), streptavidin, and biotin-PEG-peptide. The surface of the islets is modified with biotin-PEG-NHS, and the islets are further covered by streptavidin and biotin-PEG-peptide conjugates using layer-by-layer method. Glucagon-like-peptide (GLP-1) (7-37) is used for conjugation to biotin-PEG-NHS. GLP-1 (7-37) is a type of incretin hormone that binds and activates the pancreatic GLP-1 receptor (GLP-1R) to promote insulin secretion in a glucose dependent manner. In this study, the insulinotropic effect of GLP-1(7-37) is investigated through layer-by-layer encapsulation of islets using biotin-PEG-GLP-1(7-37) conjugate. The effect of islet surface modification using biotin-PEG-GLP-1(7-37) conjugate on insulin secretion in response to glucose is compared via static incubation assay and dynamic perifusion assay. The results show that islets that are coated with functional PEG conjugate are capable of secreting more insulin in response to high glucose levels compared to control islets. Finally, the presence of streptavidin is confirmed by indirect fluorescent staining with streptavidin-Cy3, and the presence of PEG-peptide on the surface of the islets after treatment with biotin-PEG-GLP-1 is confirmed by indirect fluorescent staining with biotin-PEG-FITC. This work has a potential to demonstrate the feasibility of treating pancreatic islets with reactive polymeric segments and provide the foundation of the novel means of potential immunoisolation. Finally, with this technique, it may be possible to encapsulate and/or modify islets prior to portal vein transplantation and reduce transplantation volume due to the presence of insulinotropic peptides on islet surface. All told, layer-by-layer self assembly of PEG-peptide offers a unique approach to resurfacing the biochemical landscape of living cell and tissue interfaces with broad applications in tissue targeted chemistry, biosensing, in-situ tissue engineering, and targeted cell delivery.