Sphingosine kinase-2 inhibition improves mitochondrial function and survival after hepatic ischemia-reperfusion

Background & Aims: The mitochondrial permeability transition (MPT) and inflammation play important roles in liver injury caused by ischemia-reperfusion (IR). This study investigated the roles of sphingosine kinase-2 (SK2) in mitochondrial dysfunction and inflammation after hepatic IR. Methods: Mice were gavaged with vehicle or ABC294640 (50 mg/kg), a selective inhibitor of SK2, 1 h before surgery and subjected to 1 h-warm ischemia to similar to 70% of the liver followed by reperfusion. Results: Following IR, hepatic SK2 mRNA and sphingosine-1-phosphate (S1P) levels increased similar to 25- and 3-fold, respectively. SK2 inhibition blunted S1P production and liver injury by 54-91%, and increased mouse survival from 28% to 100%. At 2 h after reperfusion, mitochondrial depolarization was observed in 74% of viable hepatocytes, and mitochondrial voids excluding calcein disappeared, indicating MPT onset in vivo. SK2 inhibition decreased mitochondrial depolarization and prevented MPT onset. Inducible nitric oxide synthase, phosphorylated NF kappa B-p65, TNF alpha mRNA, and neutrophil infiltration, all increased markedly after hepatic IR, and these increases were blunted by SK2 inhibition. In cultured hepatocytes, anoxia/re-oxygenation resulted in increases of SK2 mRNA, S1P levels, and cell death. SK2 siRNA and ABC294640 each substantially decreased S1P production and cell death in cultured hepatocytes. Conclusions: SK2 plays an important role in mitochondrial dysfunction, inflammation responses, hepatocyte death, and survival after hepatic IR and represents a new target for the treatment of IR injury. (C) 2011 European Association for the Study of the Liver. Published by Elsevier B. V. All rights reserved.