Bioactive Polymers of Effective Islet Delivery System

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This proposal is for competing renewal application of R01 DK56884 supported for 4 years. Bioactive polymers have been designed and tested for improved oxygen transport to the encapsulated islets by hemoglobin crosslinked with poly(ethylene glycol) (Hb-C) and for islet stimulation by water-soluble polymer conjugates of sulfonylurea (SU) and glucagon-like peptide-1 (GLP-1). The experimental results demonstrated that the polymers are effective in promoting the functioning and prolonging the life-span of encapsulated islets. In this proposal, the stabilization and expansion of the functionality of the bioactive polymers derived from Hb and GLP-1 intended for a longer duration will be pursued. Tetrameric Hb is prone to oxidation (metHb production), dissociation and denaturation. GLP-1 is also subject to destabilization and denaturation in physiological environment. The central research theme in this aspect will be placed on the stabilization of Hb and GLP-1 based bioactive polymers. For Hb-C, by using intramolecularly crosslinked and/or pyridoxalated Hb and introducing antioxidant enzymes to Hb-C, the stability of Hb-C could be promoted. In addition, the oxygen binding property will be optimized for improved oxygen supply to islets with a detailed mechanistic study of facilitated oxygen transport by directly measuring the profile of oxygen partial _ressure and Hb-C diffusivity in islet capsules. For GLP-1 conjugate, zinc-induced crystallization or precipitation approach will be employed. The precipitate will then be allowed to equilibrate with bioactive soluble GLP-1 conjugates and will be the source of continuous supply of GLP-1 conjugate in islet capsules. A new subject in this research is centered on the construction of effective polymeric gene carriers to pancreatic islets for the transfer of anti-apoptotic Bcl-2 gene. The protection of encapsulated islets from early cytokine assault when transplanted by Bcl-2 expression is an additional critical factor for determining islet survival. This challenge relies on our observation that SU-conjugate was actively internalized into the cells (islets and insulinoma cell line) that express SU receptors. Because the bioactive polymers designed were based on different mechanisms for the same goals of improved islet functionality and prolonged life-span, the combined effects of the bioactive polymers will be evaluated to verify if there is synergistic, summing up or one-component dominant effect.