br Transparency document br Introduction During major liver
Introduction During major liver resection, the induction of liver ischemia by surgical clamping of the afferent hepatic vasculature is used to counter the risks of excessive blood loss. This surgical technique is known as vascular inflow occlusion (VIO) or the Pringle maneuver . When employed within predefined time limits and in selected patients, this maneuver is considered safe. However, the transient lack of organ perfusion and oxygenation also inadvertently causes ischemia/reperfusion (I/R) injury [, , ]. The severity of hepatic I/R injury impacts the recovery of patients after major liver surgery. Activation of sterile inflammation is a key feature of hepatic I/R injury. During ischemia, the lack of oxygen halts oxidative phosphorylation and leads to the build-up of citric Cefepime cycle metabolites such as succinate [5,6]. Once the oxygen supply is restored, the consumption of accumulated succinate during the first minutes of reperfusion fuels a burst of reactive oxygen species (ROS) production by the mitochondrial electron transport chain [5,6]. The consequent wave of ROS-induced cell death triggers the release of damage-associated molecular patterns (DAMPs) by hepatocytes. DAMPs are innocuous intracellular constituents that become potent triggers of the innate immune system once released into the circulation [2,7]. Effector cells of the innate immune system such as neutrophils in turn confer the bulk of hepatic tissue injury. Based on this sequence of events, DAMPs occupy a crucial role in the onset of I/R injury as signal transducers and amplifiers of the sterile immune response. Several DAMPs, including histones , DNA , and high-mobility group box 1 (HMGB1)  have been causally linked to hepatic I/R injury in animal studies. DAMP release has also been measured in clinical studies on sterile liver injury [11,12]. However, the link between mitochondrial oxidative stress and DAMP release has not been clinically elaborated in the context of hepatic I/R injury to date, and was therefore investigated in this study. To that end, DAMP release was studied in patients undergoing liver resection with or without being subjected to I/R during surgery. It is shown that patients who underwent major liver surgery rapidly exhibit DAMP release after resection. Of the tested DAMPs, only HMGB1 levels increased specifically in I/R-subjected patients and not in the control group operated without I/R. HMGB1 release correlated positively with ischemia time and postoperative hepatocellular injury markers. The results were back-translated to a validated mouse model  to allow experimental confirmation and further elaboration. Decreasing mitochondrial oxidative damage during early reperfusion with the mitochondria-targeted antioxidant MitoQ in mice prevented HMGB1 release and attenuated the I/R immune response. Decreasing mitochondrial oxidative damage therefore may potentially improve outcomes in patients undergoing major liver surgery with prolonged ischemia times.
Materials and methods
Discussion Major liver resection remains associated with considerable mortality, exceeding 10% in patients with high-risk tumors . The ramifications of liver ischemia therefore still influence surgical practice on a daily basis. Part of the challenge is that supportive care is the only current treatment for hepatic I/R injury, and in that respect, several observations can be made based on the current work. It is the first report that shows DAMP release directly after major liver resection, and additionally identifies HMGB1 as the DAMP most pertinent to clinical I/R injury. Liver I/R in patients was characterized by an early rise in HMGB1 levels 1 h after surgery, whereas HMGB1 returned to baseline 6 h after surgery. The early release of HMGB1 fits previous reports showing that HMGB1 from hepatocytes is already propagated by ischemia, and persists throughout the reperfusion phase in mice subjected to I/R . It is also consistent with the finding that HMGB1 is found in the caval effluent immediately after liver transplantation . The notion that HMGB1 levels correlated to transaminase release and the duration of ischemia indicates that HMGB1 may hold prognostic or even therapeutic value, as HMGB1 is an active mediator of immune activation that could serve as an interventional target. Small-molecule inhibitors of the HMGB1 receptor RAGE are being clinically evaluated for ancillary indications , whereas inhibition of TLR receptors has been proposed to treat inflammatory disorders . Direct HMGB1 inhibition has also shown promise in treating drug-induced liver injury in mice . This starkly contrasts the liver injury markers such as ALT or bilirubin, which are ‘passive’ markers for hepatocellular injury that do not modulate immune responses. The latter also applies to other hepatic I/R biomarkers such as keratin 18 . DAMP-targeted interventions could for instance be used on an on-demand basis to control I/R injury in patients with anticipated (or unexpected) extensive ischemia times. A similar rationale has driven the introduction of in situ liver cooling techniques [37,38].