Isoflurane Protects Human Kidney Proximal Tubule Cells against Necrosis via Sphingosine Kinase and Sphingosine-1-Phosphate Generation

Abstract

Background/Aims: We previously showed that the inhalational anesthetic isoflurane protects against renal ischemia reperfusion injury in part via sphingosine kinase (SK)-mediated synthesis of sphingosine-1-phosphate (S1P). In this study, we tested the hypothesis that isoflurane directly targets renal proximal tubule cells via SK activation, S1P synthesis and activation of S1P receptors to initiate cytoprotective signaling. Methods and Results: Isoflurane-mediated phosphorylation of extracellular signal-regulated kinase (ERK) and Akt and induction of HSP70 in human kidney proximal tubule (HK-2) cells were inhibited by dimethylsphingosine (DMS), an SK inhibitor, and VPC23019, an S1P_1/3 receptor selective antagonist, in HK-2 cells. A selective S1P₁ receptor agonist, SEW2781, mimicked isoflurane-induced phosphorylation of ERK and Akt and induction of HSP70. Moreover, isoflurane-mediated protection against H₂O₂-induced necrosis of HK-2 cells was significantly attenuated by an S1P_1/3 receptor antagonist, VPC23019, and by SK inhibitors DMS or 4-[[4- (4-chlorophenyl)-2-thiazolyl]amino]phenol. Finally, overexpression of the SK1 enzyme in HK-2 cells protected against H₂O₂-induced necrosis. Conclusions: Collectively, our study demonstrates that S1P released via isoflurane-mediated SK1 stimulation produces direct anti-necrotic effects probably via S1P₁ receptor-mediated cytoprotective signaling (ERK/Akt phosphorylation and HSP70 induction) in HK-2 cells. Our findings may help to unravel the cellular signaling pathways of volatile anesthetic-mediated renal protection and lead to new therapeutic applications of volatile anesthetics during the perioperative period.