Acute Response of Hepatocyte MRP2 Internalization as an Indicator of Ischemia-reperfusion Injury in Liver Transplantation

BACKGROUND: The introduction of normothermic machine perfusion (NMP) offers new opportunities to evaluate liver graft viability before liver transplantation (LT). Under ischemic stress, multidrug resistance-associated protein 2 (MRP2) translocates from the hepatocyte membrane to the cytoplasm, resulting in loss of function. METHODS: We measured the cytoplasmic proportion of MRP2 (MRP2 internalization index, MII) by immunofluorescence colocalization analysis using CD13 as a canalicular membrane marker. RESULTS: The data showed that MII significantly correlated with ischemia time in both in situ ischemia-reperfusion injury and NMP rat models (R 2 = 0.331, P < 0.0001; R 2 = 0.632, P < 0.0001, respectively). Perfusate levels of liver injury markers at the end of NMP showed a significant positive correlation with MII for aspartate aminotransferase (R² = 0.444, P = 0.0013) and arginase 1 (R² = 0.637, P < 0.0001). Conversely, bile production exhibited a significant inverse correlation with MII (R² = 0.618, P < 0.0001). The maximum transport rate of MRP2 ( Vmax,MRP2 ), derived from kinetic modeling of sodium fluorescein biliary excretion, showed a significant inverse correlation with ischemia time (R 2 = 0.326, P = 0.0086) and MII (R 2 = 0.554, P = 0.0002). In human LT, MII values from donor liver biopsies preLT correlated significantly with peak postLT serum aminotransferase levels (R 2 = 0.398, P = 0.0007). CONCLUSIONS: MRP2 is a putative biomarker for the assessment of hepatic ischemia-reperfusion injury. The biliary excretion kinetics of sodium fluorescein reflects MRP2-mediated transport activity, providing a novel diagnostic method for predicting liver graft viability after LT.