Adenine nucleotide levels in a closed enzymatic digestion system for porcine islet isolation

Obtaining viable islets is a crucial step for successful islet transplantation. Adenosine triphosphate (ATP) is a marker of cell viability. However, little is known about any changes in the energy status of the tissues that are being digested during the digestion phase. We herein examined whether the ATP content in serially digested pancreatic tissue samples could be specific objective parameters that signal the optimal point to stop the digestion process. We obtained partial pancreata (body to tail) from 4- to 5-year-old pigs from a slaughterhouse. The tissue samples were preserved in M-Kyoto solution for less than 3 h. They were digested using an automated enzymatic and mechanical dissociation system at 37°C for 90 min following intraductal injection of Liberase HI. Samples were collected from the digestive circuit every 5 or 10 min to determine the ATP level, total adenine nucleotide (TAN) level, islet count (count/g), and yield of islet equivalent (IEQ) in the serial digestive fluids. The ATP and TAN levels, IEQ and islet count were increased and then decreased during digestion process. The profile of these parameters differed from case to case. However, when ATP changing ratio (respective value/precedent value) was compared with IEQ changing ratio, a greater than threefold increase in the ATP changing ratio followed by an increase in the islet count changing ratio within 5 min was consistently observed, indicating the optimal time to stop the digestion. The ATP levels of the handpicked islets in the digested samples were lower in the overdigested phase in comparison to those in the earlier digested phase. These results indicate that the ATP level in digested fluid could be an effective indicator to estimate the viability of cells as well as determine the optimal time to terminate the digestion process in order to obtain viable islets.