N-Acetylcysteine alleviates high fat diet-induced hepatic steatosis and liver injury via regulating the intestinal microecology in mice.

N-Acetylcysteine (NAC), a well-accepted antioxidant, has been shown to protect against high fat diet (HFD)-induced obesity-associated non-alcoholic fatty liver disease (NAFLD) in mice. However, the underlying mechanism(s) of the beneficial role of NAC is still not fully understood. Our study aimed to evaluate the protective effect of NAC against NAFLD in terms of gut microbiota homeostasis. Thirty-two C57BL/6 mice were divided into four groups, including chow diet (CHOW), high-fat diet (HFD), CHOW + NAC (2 g L-1 in the drinking water), and HFD + NAC groups, and fed for 12 weeks. NAC supplementation significantly improved HFD-induced obesity, dyslipidemia, and liver dysfunction in mice. NAC also rescued HFD-caused disorder of the gut microbiota. Intriguingly, removing intestinal microorganisms by antibiotics (ABX) obviously abolished NAC supplementation-rescued hepatic steatosis and liver injury, indicating the involvement of the gut microbiota in the beneficial role of NAC. The profiles of 1145 expressed hepatic mRNAs were analyzed by whole transcriptome sequencing. Among those, 5 up-expressed mRNAs induced by a HFD, including Cidea, CD36, Acnat2, Mogat1, and GPAT3, were reversed by NAC treatment, which was further verified by a quantitative real-time polymerase chain reaction (qRT-PCR). Meanwhile, those 5 mRNAs exhibited a significant (negative or positive) association with bacterial phyla or genera, including phyla Firmicutes and Bacteroidetes and genera norank_f_Erysipelotrichaceae and Lachnoclostridium, by Spearman's correlation analysis. These results suggested that the homeostasis of the gut microbiota plays an important role in NAC-improved NAFLD by affecting the enterohepatic axis.

Cynaroside prevents macrophage polarization into pro-inflammatory phenotype and alleviates cecal ligation and puncture-induced liver injury by targeting PKM2/HIF-1α axis.

The treatment of sepsis is still challenging and the liver is an important target of sepsis-related injury. Macrophages are important innate immune cells in liver, and modulation of macrophages M1/M2 polarization may be a promising strategy for septic liver injury treatment. Macrophage polarization and inflammation of liver tissue has been shown regulated by pyruvate kinase M2 (PKM2)-mediated aerobic glycolysis and immune inflammatory pathways. Therefore, modulating PKM2-mediated immunometabolic reprogramming presents a novel strategy for inflammation-associated diseases. In this study, cynaroside, a flavonoid compound, promoted macrophage phenotypic transition from pro-inflammatory M1 to anti-inflammatory M2, and mitigated sepsis-associated liver inflammatory damage. We established that cynaroside reduced binding of PKM2 to hypoxia-inducible factor-1α (HIF-1α) by abolishing translocation of PKM2 to the nucleus and promoting PKM2 tetramer formation, as well as suppressing phosphorylation of PKM2 at Y105 in vivo and in vitro. Moreover, cynaroside restored pyruvate kinase activity, inhibited glycolysis-related proteins including PFKFB3, HK2 and HIF-1α, and inhibited glycolysis-related hyperacetylation of HMGB1 in septic liver. Therefore, this study reports a novel function of cynaroside in hepatic macrophage polarization, and cecum ligation and puncture-induced liver injury in septic mice. The findings provide crucial information with regard to therapeutic efficacy of cynaroside in the treatment of sepsis.