(516c) Structure-Function Study Of Bioartificial Islets Generated In A Stirred Suspension Bioreactor
Diabetes is characterized by insufficient pancreatic insulin production either due to autoimmune destruction of β-cells (type 1) or insulin resistance exhibited by the hormone-targeted tissues (type 2). Recent successes in islet transplantation have sparked hopes that a cure for diabetes may be feasible in the near future. Nonetheless, the scarcity of donor islets has severely limited the wide application of this therapeutic modality. To that end, bioprocesses aiming at large-scale production of pancreatic islet cell surrogates are highly desirable. Here, we investigated the generation of bioartificial islets in a stirred tank bioreactor. In addition, we examined the link between the three-dimensional structure of bioartificial islets and the function of β-cells, especially insulin secretion upon stimulation with glucose. Artificial islet-like structures were formed by culturing a pancreatic β-cell line in stirred suspension bioreactor vessels. These cells maintain the ability to secrete insulin comparable to native β-cells, and also organize into clusters or bioartificial islets when grown on low-adhesion substrata, or in a stirred suspension. Islet-like clusters were cultured in stirred reactors for up to eight days, reaching an average diameter of approximately 150 μm, while cell viability remained high (>90%). Secretory insulin-containing granules were detected in cells within the bioartificial islets similar to native pancreatic islets after analysis via transmission electron microscopy. Compared to dispersed cell monolayers, cells in bioartificial islets displayed elevated insulin response to glucose stimulation. The artificial islets demonstrated a 6-fold increase in insulin secretion when stimulated with 25 mM glucose compared to the basal level secretion at 2 mM glucose, while cells in monolayers reached only a 2-fold increase in released insulin under the same conditions. Beta-cell clusters were also responsive to known secretagogues. A 11-, 10- and 9-fold higher insulin release compared to baseline, was observed after incubation of β-cell islets with isobutylmethylxanthine, forskolin, and phorbol 12-myristate 13-acetate, respectively. In addition, cells cultured in the bioreactor were shown to modulate the expression of proteins known to contribute to β-cell regeneration. This suggests that bioartificial islets can be used as in vitro model to study pancreatic tissue morphogenesis, aspects of β-cell proliferation and islet function. The outcome of this study will contribute to the design and development of robust bioprocesses for the generation of islet surrogates. Such bioartificial islets can be used in the high-throughput screening of drug candidates for diabetes and in bioartificial pancreas devices.