Long-term machine perfusion of human split livers: a new model for regenerative and translational research

Abstract

Recent advances in machine perfusion have revolutionised the field of transplantation by prolonging preservation, permitting evaluation of viability prior to implant and rescue of discarded organs. Long-term perfusion for days-to-weeks provides time to modify these organs prior to transplantation. By using long-term normothermic machine perfusion to facilitate liver splitting and subsequent perfusion of both partial organs, possibilities even outside the clinical arena become possible. This model remains in its infancy but in the future, could allow for detailed study of liver injury and regeneration, and ex-situ treatment strategies such as defatting, genetic modulation and stem-cell therapies. Here we provide insight into this new model for research and highlight its great potential and current limitations.

Fig. 1. Schematic summary of model for long-term perfusion of human split livers using normothermic machine perfusion.

After back table dissection, whole livers are resuscitated using normothermic machine perfusion for 12–24 hours. The liver is then surgically split without interruption to perfusion, and the two partial grafts are transferred to separate perfusion machines. The partial grafts are then perfused in the long-term, which allows for a number of experimental models, including testing therapeutics and the study of liver injury and liver regeneration. Surgery icon created by Yoyon Pujiono, https://thenounproject.com/icon/surgery-3681231/. Licensed under: https://creativecommons.org/licenses/by/3.0/”.

Fig. 2. Potential ex-situ treatment strategies using long-term normothermic machine perfusion.

The machine perfusion system offers a uniquely controllable environment that potentially allows for the introduction of therapeutic agents without interference from the host immune system. The peak of cellular injury occurs 24–48 hours after reperfusion. The process of repair and regeneration occurs in the following days to weeks. Long-term perfusion provides an adequate time frame for these agents to be effective. Defatting cocktails, genetic modulation, stem cell therapy and agents for liver regeneration are under investigation.

Fig. 3. Potential targets for liver regeneration.

Liver splitting and long-term perfusion provide the opportunity to induce liver regeneration and potentially improve partial organs prior to transplant. Multiple pathways have shown potential as mechanisms for liver regeneration, including phosphatase and tensin homologue (PTEN) inhibition, Hippo/Yap and Wnt-pathway activation, stem cell treatments, and modulation of cellular membrane potentials. An ex situ model of long-term perfusion of split livers allows a detailed study of liver regeneration and testing of these potential targets.