Assessment of Tissue-Engineered Islet Graft Viability by Fluorine Magnetic Resonance Spectroscopy

IntroductionDespite significant progress in the last decade, islet transplantation remains an experimental therapy for a limited number of patients with type 1 diabetes. Tissue-engineered approaches may provide promising alternatives to the current clinical protocol and would benefit greatly from concurrent development of graft quality assessment techniques. This study was designed to evaluate whether viability of tissue-engineered islet grafts can be assessed using fluorine magnetic resonance spectroscopy (19F-MRS), by the noninvasive measurement of oxygen partial pressure (pO2) and the subsequent calculation of islet oxygen consumption rate (OCR).MethodsScaffolds composed of porcine plasma were seeded with human islets and perfluorodecalin. Each graft was covered with the same volume of culture media in a Petri dish. Four scaffolds were seeded with various numbers (0–8000) of islet equivalents (IE) aliquoted from the same preparation. After randomizing run order, grafts were examined by 19F-MRS at 37°C using a 5T spectrometer and a single-loop surface coil placed underneath. A standard inversion recovery sequence was used to obtain characteristic 19F spin-lattice relaxation times (T1), which were converted to steady-state average pO2 estimates using a previously determined linear calibration (R2 = 1.000). Each condition was assessed using replicate 19F-MRS measurements (n = 6–8).ResultsGrafts exhibited IE dose-dependent increases in T1 and decreases in pO2 estimates. From the difference between scaffold pO2 estimates and ambient pO2, the islet preparation OCR was calculated to be 95 ± 12 (mean ± standard error of the mean) nmol/(min · mg DNA) using theoretical modeling. This value compared well with OCR values measured using established methods for human islet preparations.Conclusions19F-MRS can be used for noninvasive pre- and possibly posttransplant assessment of tissue-engineered islet graft viability by estimating the amount of viable, oxygen-consuming tissue in a scaffold.