Nanoparticle-Mediated Delivery of Antioxidants for Improving the Survival of Beta Cell Implants for Treating Type 1 Diabetes

Abstract

Type 1 diabetes mellitus, an autoimmune disorder that destroys insulin-producing beta cells of the pancreas, poses a substantial monetary and clinical burden. A promising curative, noninvasive treatment of type I diabetes is pancreatic islet transplantation from a healthy donor to the afflicted recipient. However, transplantation stressors in the immediate post-isolation period, especially hypoxic stress, contribute to more than half of islet cell death within hours to days, limiting therapeutic restoration of normoglycemia. Recent studies on the cytoprotective effects of antioxidant-laden nanoparticles for survival and preservation of insulin secretion in pancreatic beta cells have demonstrated that two candidate antioxidants, bilirubin and quercetin, can significantly increase beta cell viability under hypoxic stress, as quercetin stimulates the heme oxygenase-1 pathways and stabilizes bilirubin levels. Therefore, this study aims to formulate PLGA-PF-127 polymeric nanoparticles surface-coated with chitosan for encapsulation and delivery of both bilirubin and quercetin to beta cells to increase cell survival under hypoxic stress, under the hypothesis that bilirubin and quercetin nanoparticles potentiate greater beta cell survival and protection of insulin secretion than either nanoparticle alone in a synergistic effect. Nanoparticles were formulated by a single emulsion method and subject to characterization. Cellular uptake of nanoparticle-encapsulated bilirubin was compared to free bilirubin in an insulinoma cell line (TC-6) model using confocal fluorescence microscopy. Finally, the model TC-6 cells were treated with concentrations of 0 to 40 μM of bilirubin and/or quercetin in nanoparticles or free drug form prior to incubation in hypoxic conditions, after which cell viability was assessed. Both types of nanoparticles presented an encapsulation efficiency of approximately 25% with a diameter of ~200 nm and less than 0.1 polydispersity. Confocal fluorescence imaging showed greater uptake of nanoparticle bilirubin into the TC-6 cells compared to free drug. The combination of nanoparticle bilirubin and quercetin at the dose of 40 μM increased the viability (40.7 ± 12.8% of control; p = 0.11) of TC-6 cells challenged by hypoxic stress, compared to untreated control cells. Thus, co-delivery of bilirubin and quercetin polymeric nanoparticles improves uptake compared to free drug and has the potential to increase islet survival under hypoxia.