A significant obstacle in islet transplantation is the high rate of primary nonfunction and early islet destruction, which has been observed after intraportal islet infusion, both in animal models and in clinical trials. Substantial evidence now suggests that an acute blood mediated inflammatory injury is largely responsible for the observed functional stunning or destruction of islets and may well amplify subsequent immune reactions. In this proposal, we hypothesize that physiologically relevant anti-coagulant/anti-inflammatory processes establish an important paradigm for the design of a conformal islet encapsulation barrier that is """"""""actively"""""""" anti-inflammatory. Specifically, we plan to fabricate an ultrathin film on the islet surface by a strategy of layer-by-layer (LbL) polymer assembly. Maladaptive inflammatory responses will be modulated by incorporating into the thin film, thrombomodulin (TM) and heparin, as inhibitors of thrombin dependent responses and CD39 as an inhibitor of purinergic mediated (i.e. ATP/ADP) procoagulant/pro-inflammatory pathways. In this manner, the islet cell mass required to achieve euglycemia will be reduced and long-term graft survival enhanced. Specifically, we intend to: (1) Fabricate a biocompatible conformal islet encapsulation barrier of deemed permeability by a strategy of layer-by-layer (LbL) polymer assembly. Porcine and mouse islets will be conformally coated with a polymer film and their short-term function and viability characterized. The ability of a conformal coating to prevent activation of the coagulation cascade and enhance islet engraftment will be defined using established allograft (B 10.BR -> C57/BL6) and xenograft (Porcine -> C57/BL6) models. (2) Determine the complementary effects of surface-bound heparin and thrombomodulin as interactive anti-inflammatory strategies designed to optimize islet engraftment and long-term islet survival. The ability of a TM and heparin containing conformal coating to prevent activation of the pro-inflammatory responses will be determined in vitro and in vivo and the capacity to enhance islet engraftment and long-term survival characterized. (3) Define the capacity of CD39 to abrogate prothrombotic and proinflammatory pathways that contribute to primary islet non-function and late islet destruction. CD39 will be incorporated onto conformally coated islets, either alone or as a component of TM and heparin containing films. The capacity of CD39 to potentiate the anticoagulant/anti-inflammatory properties of a protein C activating polymer coating will be determined. Enhancement of islet engraftment and long-term survival will be investigated.
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