Monitoring of dissolved oxygen and cellular bioenergetics within a pancreatic substitute

This work investigated the use of nuclear magnetic resonance (NMR) spectroscopy in combination with a mathematical model of an encapsulated cell system as a method for rapidly assessing the status of a pancreatic substitute. To validate this method, an in vitro experiment was performed in which the encapsulated cells were perfused in an NMR-compatible system and the dissolved oxygen (DO) concentration of the perfusing medium was lowered from 0.20 to 0.05 mM, then returned to 0.20 mM in a stepwise fashion. The cellular metabolic activity and bioenergetics were evaluated by measuring the oxygen consumption rate (via DO sensors) and nucleotide triphosphate levels (via (31)P NMR). By incorporating a perfluorocarbon emulsion into the alginate beads, the cellular oxygenation state was monitored by measuring the average intrabead DO (AIDO) concentration by (19)F NMR. The in vitro measurements were then compared with model predictions based on the measured external DO concentration and time. Model-predicted cell growth and AIDO closely matched the experimentally acquired data. As the DO concentrations both external to and within the pancreatic substitute are needed to apply this methodology in vivo, the feasibility of measuring the DO concentration from two distinct bead populations implanted in the peritoneal cavity of mice was established. It is concluded that PFC incorporation and (19)F NMR measurements, in combination with a mechanistic model of the encapsulated system, allow the tracking of the state of a pancreatic substitute in vitro and potentially in vivo.