Propofol postconditioning confers hepatic protection via activating nrf2 in the early minutes of reperfusion which requires adiponectin in mice

Abstract

INTRODUCTION: Propofol, an anaesthetic agent, given during early reperfusion (propofol postconditioning, PPC) attenuates hepatic ischemia reperfusion (HIR) injury. However, the underlying mechanism of PPC hepatic protection is unclear. We and others showed that nuclear factor-like 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway activation1,2 and the accumulation of adiponectin (APN, a molecule with cytoprotection)3 in response to HIR injury are cytoprotective against HIR. The aims of this study were to examine whether the activation of Nrf2 in the early minutes of reperfusion is critical in PPC hepatic protection, and whether this activation of Nrf2/HO-1 in PPC is mediated by APN. METHODS: Wild-type(WT) or APN knock-out(KO) mice were subjected to seventy percent partial hepatic warm ischemia for 60 min followed by various durations (0, 0.5, 1, 2, 4, 24hr) of reperfusion in the absence or presence of PPC achieved by intravenously injection of propofol (30 mg/kg body weight per hour) for 30 min at the onset of reperfusion. Some of the WT mice were treated with selective Nrf2 inhibitor, luetolin (20μM), 5 minutes before inducing HIR. Cultured mouse hepatocytes (AML12) were subjected to 12 hours hypoxia and 6 hours reoxygenation (H/R) without or with PPC, some of the sub-groups were infected with Nrf2 or APN siRNAs to knock down Nrf2 or APN gene, respectively. RESULTS: HIR significantly increased hepatic injury manifested as evaluated serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and evaluated suzike’s injury score that were associated with increased hepatic 15-F2t-isoprostane and reduced superoxide dismutase(SOD) from 4hr to 24hr after the induction of reperfusion (Rep) in WT mice (P<0.05 vs. Shamoperatived control). And these changes were further aggravated in APN KO mice (P<0.05 vs. WT). HIR-induced Nrf2 activation ( translocation into the nucleus) was detected from 1 hour after Rep while HO-1 expression was increased from 4 hours after Rep in WT but not in KO mice (P<0.05 vs. sham-operatived control). PPC significantly enhanced Nrf2 activation as early as 0.5 hours and increased HO-1 protein expression at 2 hours after Rep, which was accompanied with reduced AST, ALT, 15-F2t-isoprostane and elevated SOD. All these protective effects of PPC were cancelled in WT mice treated with leotulin or in KO mice. Similarly, PPC significantly reduced post-hypoxic lactate dehydrogenase release and apoptotic cells, accompanied with increased Nrf2 activation and HO-1 protein expression in cultured AML12 cells, where these cellular protection of PPC were cancelled by either Nrf2 or APN gene knock-down. CONCLUSIONS: PPC confers hepatic protective effects against HIR by reducing oxidative stress via activating Nrf2 in the early minutes of reperfusion, and subsequently enhanced HO-1 induction, and this process is mediated by APN.