Evaluation of a system for normothermic and subnormothermic ex vivo machine perfusion of isolated rat livers

Background: Poor patient outcome of extended criteria donor (ECD) liver grafts after static cold storage calls for new methods of ex vivo organ preservation in light of the exhausted donor organ pool. In recent years, ex vivo machine perfusion at different temperatures, ranging from hypothermic (4 °C), subnormothermic (21 °C) to normothermic (37 °C), reemerged as possible alternative to static cold storage. Our aim was to establish and evaluate an ex vivo perfusion system for rat livers that mimics the clinical conditions of machine-perfusion. Methods: We investigated perfusion conditions at both subnormothermic and normothermic temperatures with varying setups. The perfusion system consists of a pressure-controlled roller pump, an oxygenator, and a custom-made perfusion chamber. Male Wistar rat livers were perfused via the portal vein for 12 hours using solely oxygenated culture medium or oxygenated culture medium (DMEM) supplemented with rat erythrocytes. A final perfusion setup using erythrocyte supplemented culture medium and an added circuit connected via a dialysis membrane for plasma expansion was established. Results: Potassium, Glucose and Urea concentractions soon reached high levels with solely oxygenated and erythrocyte-supplemented medium. The addition of the dialysis circuit led to almost physiological electrolyte concentrations in the perfusate with lower transaminase secretion during perfusion. Normothermic perfusion showed a greater Transaminase release compared to subnormothermic perfusion but also increased bile and Urea production, indicating a more active metabolism. Histological analysis, using HE and TUNEL-stains, of perfused rat livers showed no differences between both temperatures and showed an intact vascular system and lobular structure. Conclusion: As observed in normothermic human liver machine perfusion, plasma expansion was key for maintaining physiological perfusion conditions during perfusion. Our system might be suitable for small animal studies of machine perfusion of the liver at both temperatures.