Massachusetts Institute of Technology
Enhanced oxygen supply to islets encapsulated at high density leads to long-term normoglycenia in diabetic rats and facilitates development of smaller devices
Clark Colton1, Y. Evron2, B. Ludwig3, G. C. Weir4, B. Zimmerman2, S. Maimon2, T. Neufield2, N. Shalev2, T. Goldman2, A. Leon2, K. Yavriyants2, N. Shabtay2, T. Rozenshtein2, A. R. DiIenno1, A. Stefan3, P. Vardi5, K. Bloch5, P. de Vos6, S. R. Bornstein3, U. Barkai1, A. Rotem1.
1Department of Chemical Engineering, , Massachusetts Institute of Technology, Cambridge, MA, United States; 2Beta-O2 Technologies, Rosh-Ha'ain, Israel; 3Department of Medicine III, University Hospital Carl Gustav Carus, Dresden Technical University, Dresden, Germany; 44Section of islet Trasnplantation and Cell Biology, Research Division, Joslin Diabetes Center, Boston, MA, United States; 5Feisenstein Medical research center, Sackler School of Medicine, Tel Aviv University, Petah Tikva, Israel; 6Department of Pathology and Laboratory Medicine, University Medical Center Groningen, Groningen, Netherlands
Introduction. Islet encapsulation may cure diabetes without immunosuppression, but O2 supply limitation can cause failure. Our solution: supply exogenous O2 to islets encapsulated in a device. Here, we investigate if islet surface density can be increased without harming islets by increasing gas pO2.
Methods. Rat islets were embedded in an alginate slab reinforced on each side with a metal grid. The outer face was a microporous membrane containing alginate, the interior face an O2-permeable polymeric membrane. The slab and gas chamber were contained in a disc-shaped housing implanted subcutaneously and connected to remote ports. The gas chamber was flushed daily with a mixture at specified p02. Roughly 2,400 IEQ were encapsulated in slabs at different densities. Using a stirred vessel containing an oxygen electrode, O2 consumption rate (OCR) was measured preimplantation with islets in a coin-shaped slab and postexplantation with the slab removed from the device. O2 profiles were measured in slabs of different densities in the device without the microporous membrane and top metal grid. The slab top was overlain with medium exposed to a p02 of 40 mmHg. Initial chamber p02 was varied, and slab pO2 was measured by aoxygen electrode attached to a micromanipulator.
Results. At each islet density, the minimum chamber p02 leading to a p02 about 50 mmHg at the slab-microporous membrane interface (to maintain all IEQ viable and functional) was determined, as was initial value to account for subsequent 02 depletion from 02 consumption and escape via diffusion through alginate. Ambient air was used for 1,000 IEQ/cm2. The minimum mixture p02 was 304, 456, and 570 mmHg at 2,400, 3,600, and 4,800 IEQ/cm2, respectively. Devices were implantated in 106 rats. The total time period during which animals remained normoglycemic was grouped: (1) 0 (never normoglycemic), (2) 0-4 wk, (3) 4-8 wk, and (4) > 8 week or until explantation (up to 34 wk). Normoglycemic time was independent of islet density but increased with IEQ and OCR of the encapsulated islets. For implants with >2400 IEQ and OCR >7,400 pmol/min, 100% of animals (n=33) were in groups 3/4. Conversely, with IEQ <2,000 or OCR <5,500 pmol/min, only 32% (n=22) were in groups 3/4. When expressed as IEQ/wt and OCR/DNA, data from this study were consistent with previous results for rat islets in mice. In group 4, OCR of the islet alginate slab after explantation of devices (n=17) averaged 88% of the preimplantation value. Thus, little or no viable tissue was lost after implantations as long as 34 wk before elective explantation. IVGTT in normoglycemic animals (40 days) were near normal and were not affected by islet density.
Conclusions. With increased pO2 in the replenishment gas mixture, islets were successfully maintained at densities up to 4,800 IEQ/cm2. Islets encapsualted at high density in alginate slabs within devices that met minimum IEQ and OCR requirements had little loss of viability and function after long implantation times. Use of high islet densities will reduce device size required for human implantation.
15:30 - 16:30
|Zeroing in on the Perfect Encapsulation and Immunoisolation Device||Enhanced oxygen supply to islets encapsulated at high density leads to long-term normoglycenia in diabetic rats and facilitates development of smaller devices||Room 110|