538 In vivo and in vitro characterization of 1.5 mm Ba2+-alginate macro-encapsulated cynomolgus monkey islets
Tuesday November 17, 2015 from 15:30 to 16:30
Room 110

Matthew A Bochenek, United States

Graduate Research Assistant

Transplant Surgery/Bioengineering

University of Illinois at Chicago


In vivo and in vitro characterization of 1.5 mm Ba2+-alginate macro-encapsulated cynomolgus monkey islets

Matthew A Bochenek1,2, James J McGarrigle1, Joshua Mendoza-Elias1,2, Enza Marchese1, Mohammad Nourmohammadzadeh1,2, Yong Wang1,2, Arshad Khan1, Mustafa Omami1, Chun-Chieh Yeh1, Igor Lacik3, Berit Strand4, Jose Oberholzer1,2.

1Division of Transplant Surgery, University of Illinois at Chicago, Chicago, IL, United States; 2Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, United States; 3Department for Biomaterials Research, Polymer Institute of the Slovak Academy of Sciences, Bratislava, Slovakia (Slovak Republic); 4Department of Biotechnology, Norwegian University of Science and Technology (NTNU), Trondheim, Norway

Introduction: Micro-encapsulation of islets for the treatment of Type I diabetes has shown limited efficacy in small-scale clinical trials. There are numerous variables that may attribute to the lack of success of this technology including the transplantation site, encapsulation material, and formation of pericapsular fibrotic overgrowth. Our collaborators have recently shown that rat islets encapsulated in large diameter (1.5 mm) alginate beads are better at curing streptozotocin (STZ) induced diabetic C57b/6 mice when compared to medium (0.5 mm) beads, largely due to decreased fibrosis of large beads.  This trend was also evident for large spheres made of various materials[1]. In this study, we investigated the ability of large alginate encapsulated cynomolgus monkey islets to cure STZ induced diabetic mice in immune incompetent and competent models, and explore islet functionality within large Ba2+-alginate beads. 
Methods: Cyno islets were encapsulated in large 1.5 mm ultra-pure low viscosity high guluronic (UPLVG) alginate gelled with 20 mM Ba2+. These were transplanted into various STZ induced diabetic mice models using the same marginal amount of islets (1,500 islets/1 ml beads/mouse). Blood glucose levels were measured three times per week, followed by an oral glucose tolerance test (OGTT). Naked and encapsulated islets were also compared for in vitro functionality. This included a glucose stimulated insulin secretion (GSIS) assay. For the GSIS assay, 10 islets were picked and cultured in cell culture inserts. The inserts were then incubated with Kreb’s Ringer solution containing low and high glucose for 1 hr each, and insulin secretion quantified. This was repeated on day 1, 14 and 28 for both naked and macro-encapsulated islets to evaluate how they functioned over time using mostly paired measurements. Graphs depict insulin secretion (mean ± SEM) under low and high glucose at each day.
Results/Conclusion: Using a marginal mass transplant model, macro-encapsulated islets cured STZ nude mice (n=9) similarly to kidney capsule transplanted islets (n=5) (30 day cure rate: 77% vs. 75%). Furthermore, macro-encapsulated cyno islets cured 81% of STZ C57b/6 mice (n=8) for at least 4 months (time of submission). Interestingly, Ba2+ macro-encapsulated islets tended to have increased glucose stimulated insulin secretion (GSIS) after 14 days of culture with no significant decline at day 28 (p < 0.01). These results contrasted with naked islets, which predictably tended to decrease insulin secretion when cultured 28 days (p < 0.01). Surprisingly, preliminary day 1 insulin secretion of naked islets was substantially higher compared to encapsulated islets (p < 0.0001); however, insulin secretion became comparatively insignificant at later time points (p = 0.61; 0.83). Since encapsulated islets seemed to show improved function after culture for 14 days, we wanted to see if this would translate in vivo. Macro-encapsulated islets were aliquotted and then transplanted into STZ induced diabetic nude mice on day 1 and 14 post-encapsulation (n=8 per group). Culture time did not impact the islet graft function in vivo (30 day cure rate: 88% vs. 86%); (OGTT, p = 0.43). This contradiction between in vitro and in vivo results is perplexing; however, showing that short-term culture is not detrimental to function may prove beneficial for patients to ensure time for proper quality control assessments or if pooling islets from multiple donors is required.


[1] Veiseh et al, Nature Materials 2015

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