*Purpose: Realizing the liver’s unique ability to regenerate, this ongoing study examines Normothermic Machine Perfusion (NMP) as a promising platform for evaluating & potentially simulating regeneration of liver segments in an ex-vivo environment.

*Methods: 16 rat liver grafts were perfused for 12 hours at mean temperature of 37°C. Following the first 1.5 hours of perfusion, 8 livers underwent a 2/3 partial hepatectomy (PHx) & were subsequently perfused for the total duration of 12h. Perfusion was performed using an oxygenated, William’s E based medium flowing continuously through a closed circuit. Parameters of biochemical & synthetic liver function, as well as molecular & immunohistochemical parameters of early liver regeneration were analyzed pre & post hepatectomy. Ki-67 was used as an immunohistochemistry target, Proliferating Cell Nuclear Antigen (PCNA) & p27 – a cyclin dependent kinase inhibitor in quiescent cells – were targeted in western blot analyses. Ki-67, PCNA & p27 levels were correlated to a control group of livers that underwent in-vivo 2/3 PHx.

*Results: Perfused livers showed positive Ki-67 staining, comparable but lower than the amount observed in vivo after PHx. Notably, the staining was predominantly in the hepatocyte nuclei. Moreover, the number of stained cells increase with time similar to the in vivo case. In parallel p27 – a key inhibitor protein of cells which needs to be reduced for cells to undergo proliferation – displayed a significant decrease over 12 hours in perfused livers (p<0.05) similar to in vivo PHx. This decrease was common in both perfused groups, although it appears to be faster in PHx perfused livers compared to whole perfused livers. On comparing hemodynamic performance of whole & partial livers during NMP, both groups behaved similarly during the first 1.5 hours of perfusion. After PHx there was a significant & sudden increase in portal vein flow resistance (p<0.05), which later gradually dropped by time. Lactate clearance trends were similar in both groups, although partial livers showed a slower rate of clearance (p<0.05) that corresponded with levels of bile production. Glucose demonstrated a similar pattern, with lower levels following PHx.

*Conclusions: Our preliminary data revealed a strong & reproducible molecular signal indicating increased mitotic activity in normothermic perfused livers. This work paves the way for better characterization & optimization of regeneration oriented NMP systems.

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