Ethyl Pyruvate Directly Attenuates Active Secretion of HMGB1 in Proximal Tubular Cells via Induction of Heme Oxygenase-1.

Renal ischemia reperfusion (IR) is a main cause of acute kidney injury leading to high morbidity and mortality during postoperative periods. This study investigated whether ethyl pyruvate (EP) protects the kidney against renal IR injury. Male C57BL/6 mice were treated with vehicle or EP (40 mg/kg) 1 h before ischemia and the plasma creatinine (Cr) levels and tubular damage were evaluated after reperfusion. EP attenuated the IR-induced plasma Cr levels, renal inflammation and apoptotic cell death, but the effect of EP was abolished by pretreating Zinc protoporphyrin (ZnPP), a heme oxygenase (HO)-1 inhibitor. HO-1 is a stress-induced protein and protects the kidney against IR injury. EP increased significantly HO-1 expression in the proximal tubular cells in vivo and HK-2 cells in vitro. Inhibition of PI3K/Akt pathway and knockdown of Nrf2 blocked HO-1 induction by EP. High mobility group box 1 (HMGB1) secretion was assessed as an early mediator of IR injury; plasma HMGB1 were significantly elevated as early as 2 h to 24 h after reperfusion and these were attenuated by EP, but the effect of EP was abolished by ZnPP. EP also reduced HMGB1 secretion stimulated by TNF-α in HK-2 cells, and the inhibition of PI3K/Akt and knockdown of HO-1 blocked the effect of EP. Conclusively, EP inhibits the active secretion of HMGB1 from proximal tubular cells during IR injury by inducing HO-1 via activation of PI3K/Akt and Nrf2 pathway.

Honokiol activates the LKB1-AMPK signaling pathway and attenuates the lipid accumulation in hepatocytes.

Honokiol is a bioactive neolignan compound isolated from the species of Magnolia. This study was designed to elucidate the cellular mechanism by which honokiol alleviates the development of non-alcoholic steatosis. HepG2 cells were treated with honokiol for 1h, and then exposed to 1mM free fatty acid (FFA) for 24h to simulate non-alcoholic steatosis in vitro. C57BL/6 mice were fed with a high-fat diet for 28days, and honokiol (10mg/kg/day) was daily treated. Honokiol concentration-dependently attenuated intracellular fat overloading and triglyceride (TG) accumulation in FFA-exposed HepG2 cells. These effects were blocked by pretreatment with an AMP-activated protein kinase (AMPK) inhibitor. Honokiol significantly inhibited sterol regulatory element-binding protein-1c (SREBP-1c) maturation and the induction of lipogenic proteins, stearoyl-CoA desaturase-1 (SCD-1) and fatty acid synthase (FAS) in FFA-exposed HepG2 cells, but these effects were blocked by pretreatment of an AMPK inhibitor. Honokiol induced AMPK phosphorylation and subsequent acetyl-CoA carboxylase (ACC) phosphorylation, which were inhibited by genetic deletion of liver kinase B1 (LKB1). Honokiol stimulated LKB1 phosphorylation, and genetic deletion of LKB1 blocked the effect of honokiol on SREBP-1c maturation and the induction of SCD-1 and FAS proteins in FFA-exposed HepG2 cells. Honokiol attenuated the increases in hepatic TG and lipogenic protein levels and fat accumulation in the mice fed with high-fat diet, while significantly induced LKB1 and AMPK phosphorylation. Taken together, our findings suggest that honokiol has an anti-lipogenic effect in hepatocytes, and this effect may be mediated by the LKB1-AMPK signaling pathway, which induces ACC phosphorylation and inhibits SREBP-1c maturation in hepatocytes.

Magnolia officinalis attenuates free fatty acid-induced lipogenesis via AMPK phosphorylation in hepatocytes.

ETHNOPHARMACOLOGICAL RELEVANCE: Magnolia officinalis (MO) is a traditional Chinese herbal medicine that has been used in clinical practice to treat liver disease. The aim of this study is to examine the effects of MO on the development of nonalcoholic fatty liver in hepatocytes. MATERIALS AND METHODS: Human hepatoma-derived HepG2 cells and mouse normal FL83B hepatocytes were exposed to 0.5mM free fatty acids (FFAs; oleate:palmitate, 2:1) for 24h to simulate conditions of nonalcoholic fatty liver in vitro. The cells were treated with a standardized MO extract 1h prior to FFA exposure. RESULTS: MO pretreatment attenuated the increases in intracellular lipid accumulation and triglyceride content in FFA-exposed hepatocytes in a dose-dependent manner. MO pretreatment significantly inhibited both sterol regulatory element-binding protein (SREBP)-1c activation and increases in fatty acid translocase, fatty acid synthase, and stearoyl CoA desaturase-1 protein expression in FFA-exposed hepatocytes in a dose-dependent manner. MO pretreatment markedly induced adenosine monophosphate-activated protein kinase (AMPK) phosphorylation in hepatocytes. Compound C, an AMPK inhibitor, blocked the inhibitory effect of MO on the increases in intracellular lipid accumulation and triglyceride content induced by FFAs. In hepatocytes pretreated with compound C, MO failed to inhibit SREBP-1c activation and the increases in fatty acid translocase, fatty acid synthase, and stearoyl-CoA desaturase-1 protein expression induced by FFAs. CONCLUSIONS: Our results indicate that MO attenuates triglyceride biosynthesis and accumulation induced by FFAs in hepatocytes, suggesting its pharmacological potential for the prevention of nonalcoholic fatty liver disease. These effects may be mediated by the inhibition of SREBP-1c via AMPK phosphorylation.