Type 1 diabetes is a devastating disease with increasing incidence and prevalence. Insulin therapy, while life-saving, does not prevent severe complications that substantially increase both morbidity and mortality. Whole pancreas and pancreatic islet transplantation are treatments for diabetes, but favorable long-term outcomes are inconsistent and the procedures are restricted to a small group of patients due to a variety of limitations. These impediments include the current demand for donor pancreata far exceeding supply, allotransplantation requiring a lifetime of immunosuppression, and premature graft failure. Macroencapsulated tissue-engineered grafts (TEGs) may mitigate or eliminate these limitations by allowing the use of alternative cell sources (such as porcine or stem-cell-derived islets), providing immunoisolation, and encourage graft survival through therapeutic interventions. TEGs possess great potential, but require significant development to fulfill their promise of a safe, effective, and definitive cure for type 1 diabetes. To enable and expedite TEG development, novel techniques to assess oxygen status (pO₂) and viability were developed, validated, and applied. Hypoxia is currently the most significant obstruction preventing widespread utilization of TEGs, rendering measurements of TEG pO₂ critically necessary. Fluorine-19 magnetic resonance spectroscopy (¹⁹F-MRS) was adapted for in vivo pO₂ measurement in TEGs and validated with a well-established technique. It was found that ¹⁹F-MRS can be a robust, accurate, and noninvasive technique to monitor TEG pO₂ for long durations post-implantation. This technique was applied to the murine model and demonstrated that TEGs implanted subcutaneously experience hypoxia unconducive to supporting islet viability and function. Therefore, a method for the delivery of supplemental oxygen (DSO) to increase in vivo pO₂ was developed and its efficacy was evaluated with ¹⁹F-MRS. It was found that DSO can successfully increase the pO₂ of macroencapsulated TEGs and enhance islet survival. While providing crucial information, measuring pO₂ does not necessarily correlate to islet viability, necessitating the development of additional techniques. Islet viability was first assessed by measuring pO₂ with ¹⁹F-MRS and calculating the oxygen consumption rate (OCR) using a mathematical model. Finally, to facilitate in vivo viability assessment and increase measurement accuracy, oxygen-17 MRS was developed to directly measure and noninvasively quantify the OCR of TEGs.
University of Minnesota Ph.D. dissertation. June 2016. Major: Biophysical Sciences and Medical Physics. Advisors: Michael Garwood, Klearchos Papas. 1 computer file (PDF); xiv, 196 pages.
Development and Validation of a Multinuclear Magnetic Resonance Spectroscopy Toolkit for Bioartificial Pancreas Assessment.
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