Immune activation during liver machine perfusion is shaped by perfusate composition and is independent of the ischemic injury

Background Ischemia–reperfusion injury remains a major challenge in liver transplantation and plays a major role in pathophysiology leading to graft failure. Machine perfusion (MP) is a promising approach to restitute marginal donor livers. However, the impact of MP on innate immunity remains insufficiently defined. We hypothesized that MP activates the innate inflammatory response. Thus, we investigated whether the ischemic injury and perfusate composition [plasma-rich perfusate (PRP) versus plasma-poor perfusate (PPP)] modulate the inflammatory response, identified by complement activation and cytokine release. Methods Thirty porcine livers were subjected to ex situ MP. The first 24 porcine livers were subject to induced biliary ischemic injury (BileINJ, n = 8), global ischemic injury (GlobalINJ, n = 8), or no induced ischemic injury (CTRL, n = 8) using PRP during MP. The subsequent six porcine livers were subjected to the same ex situ MP protocol using PPP ( n = 6) with no induced ischemic injury. MP was conducted in three phases: 1 h hypothermic, 1 h controlled rewarming, and 4 h normothermic perfusion. Results Except for interleukin-1β (IL-1β) in bile tissue in the BileINJ group and tumor necrosis factor (TNF) in plasma in the GlobalINJ group, all mediators assessed whether in perfusate, liver, or bile tissue did not differ significantly between ischemic injury groups and CTRL. Data were therefore combined into a common PRP group for further comparisons. In PRP perfusate, MP induced robust complement activation (sC5b-9: median fold change (FC) 4 [2–6 interquartile range]) and cytokine release (IL-1β: FC 88 [51–165], IL-6: FC 1,549 [587–3,053], IL-8: FC 389 [120–1,259], IL-10: FC 404 [222–656], all p < 0.001). This pattern persisted in PPP group perfusate, liver, and bile tissue, though the concentrations were significantly lower compared to PRP (sC5b-9, IL-10, IL-6, IL-1β, and IL-8, all p < 0.05). Conclusions Liver MP reliably induced innate immune-driven inflammation regardless of prior ischemic injury. The magnitude of the inflammatory response was substantially lower in the PPP group compared to the PRP group. Future therapeutic trials targeting innate immunity during ex situ MP are warranted to improve the preservation of liver grafts.