Progression of non-alcoholic steatosis to steatohepatitis and fibrosis parallels cumulative accumulation of danger signals that promote inflammation and liver tumors in a high fat-cholesterol-sugar diet model in mice

Therapeutic Benefits of Spleen Tyrosine Kinase Inhibitor Administration on Binge Drinking-Induced Alcoholic Liver Injury, Steatosis, and Inflammation in Mice

BACKGROUND

Binge drinking is increasingly recognized as an important cause of liver disease with limited therapeutic options for patients. Binge alcohol use, similar to chronic alcohol consumption, induces numerous deregulated signaling events that drive liver damage, steatosis, and inflammation. In this article, we evaluated the role of spleen tyrosine kinase (SYK), which modulates numerous signaling events previously identified linked in the development alcohol-induced liver pathology.

METHODS

A 3-day alcohol binge was administered to C57BL/6 female mice, and features of alcoholic liver disease were assessed. Some mice were treated daily with intraperitoneal injections of a SYK inhibitor (R406; 5 to 10 mg/kg body weight) or drug vehicle control. Liver and serum samples were collected and were assessed by Western blotting, biochemical, ELISA, electrophoretic mobility shift assays, real-time quantitative polymerase chain reaction, and histopathological analysis.

RESULTS

We found that binge drinking induced significant SYK activation (SYK(Y525/526) ) with no change in total SYK expression in the liver. Functional inhibition of SYK activation using a potent SYK inhibitor, R406, was associated with a significant decrease in alcohol-induced hepatic inflammation as demonstrated by decreased phospho-nuclear factor kappa beta (NF-κB) p65, NF-κB nuclear binding, tumor necrosis factor-alpha, and monocyte chemoattractant protein-1 mRNA in the liver. Compared to vehicle controls, SYK inhibitor treatment decreased alcohol binge-induced hepatocyte injury indicated by histology and serum alanine aminotransferase. Strikingly, SYK inhibitor treatment also resulted in a significant reduction in alcohol-induced liver steatosis.

CONCLUSIONS

Our novel observations demonstrate the role of SYK, activation in the pathomechanism of binge drinking-induced liver disease highlighting SYK a potential multifaceted therapeutic target.

Impact of dietary fat on the development of non-alcoholic fatty liver disease in Ldlr-/- mice

The prevalence of non-alcoholic fatty liver disease (NAFLD) has increased in parallel with central obesity and is now the most common chronic liver disease in developed countries. NAFLD is defined as excessive accumulation of lipid in the liver, i.e. hepatosteatosis. The severity of NAFLD ranges from simple fatty liver (steatosis) to non-alcoholic steatohepatitis (NASH). Simple steatosis is relatively benign until it progresses to NASH, which is characterised by hepatic injury, inflammation, oxidative stress and fibrosis. Hepatic fibrosis is a risk factor for cirrhosis and primary hepatocellular carcinoma. Our studies have focused on the impact of diet on the onset and progression of NASH. We developed a mouse model of NASH by feeding Ldlr-/- mice a western diet (WD), a diet moderately high in saturated and trans-fat, sucrose and cholesterol. The WD induced a NASH phenotype in Ldlr-/- mice that recapitulates many of the clinical features of human NASH. We also assessed the capacity of the dietary n-3 PUFA, i.e. EPA (20 : 5,n-3) and DHA (22 : 6,n-3), to prevent WD-induced NASH in Ldlr-/- mice. Histologic, transcriptomic, lipidomic and metabolomic analyses established that DHA was equal or superior to EPA at attenuating WD-induced dyslipidemia and hepatic injury, inflammation, oxidative stress and fibrosis. Dietary n-3 PUFA, however, had no significant effect on WD-induced changes in body weight, body fat or blood glucose. These studies provide a molecular and metabolic basis for understanding the strengths and weaknesses of using dietary n-3 PUFA to prevent NASH in human subjects.

Iron overload results in hepatic oxidative stress, immune cell activation, and hepatocellular ballooning injury, leading to nonalcoholic steatohepatitis in genetically obese mice

The aim of this study was to determine the effect of iron overload in the development of nonalcoholic steatohepatitis (NASH) in a genetically obese mouse model (Lepr(db/db)). Leptin receptor-deficient mice were fed a normal or an iron-supplemented chow for 8 wk and switched to normal chow for 8 wk. All dietary iron (DI)-fed mice developed hepatic iron overload predominantly in the reticuloendothelial system. Hepatocellular ballooning injury was observed in the livers of 85% of DI mice, relative to 20% of chow-fed Lepr(db/db). Hepatic malonyldialdehyde levels and mRNA levels of antioxidant genes (Nrf2, Gpx1, and Hmox1) were significantly increased in the DI mice. Hepatic mRNA levels of mitochondrial biogenesis regulators Pgc1α, Tfam, Cox4, and Nrf1 were diminished in the DI mice. In addition, gene expression levels of cytokines (Il6, Tnfα) and several innate and adaptive immune cell markers such as Tlr4, Inos, CD11c, CD4, CD8, and Ifnγ were significantly increased in livers of the DI group. Strikingly, Nlrp3, a component of the inflammasome and Il18, a cytokine elicited by inflammasome activation, were significantly upregulated in the livers of DI mice. In addition, RAW 264.7 macrophages loaded with exogenous iron showed significantly higher levels of inflammatory markers (Inos, Tnfα, Mcp1, Tlr4). Thus dietary iron excess leads to hepatic oxidative stress, inflammasome activation, induction of inflammatory and immune mediators, hepatocellular ballooning injury, and therefore NASH in this model. Taken together, these studies indicate a multifactorial role for iron overload in the pathogenesis of NASH in the setting of obesity and metabolic syndrome.

An Overview of Murine High Fat Diet as a Model for Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a worldwide epidemic, which by all predictions will only increase. To help in combating the devastating array of phenotypes associated with T2DM a highly reproducible and human disease-similar mouse model is required for researchers. The current options are genetic manipulations to cause T2DM symptoms or diet induced obesity and T2DM symptoms. These methods to model human T2DM have their benefits and their detractions. As far as modeling the majority of T2DM cases, HFD establishes the proper etiological, pathological, and treatment options. A limitation of HFD is that it requires months of feeding to achieve the full spectrum of T2DM symptoms and no standard protocol has been established. This paper will attempt to rectify the last limitation and argue for a standard group of HFD protocols and standard analysis procedures.

Inhibition of HMGB1 release via salvianolic acid B-mediated SIRT1 up-regulation protects rats against non-alcoholic fatty liver disease

The inflammatory mediator high-mobility group box 1 (HMGB1) plays a critical role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). However, the regulation of HMGB1 in NAFLD, particularly through sirtuin 1 (SIRT1), remains unclear. In this study, we investigated the role of SIRT1-mediated inhibition of HMGB1 release in NAFLD and the effect of salvianolic acid B (SalB), which is a water-soluble phenolic acid extracted from Radix Salvia miltiorrhiza, on NAFLD through SIRT1/HMGB1 signaling. In vivo, SalB treatment significantly attenuated high-fat diet (HFD)-induced liver damage, hepatic steatosis, and inflammation. Importantly, SalB significantly inhibited HMGB1 nuclear translocation and release, accompanied by SIRT1 elevation. In HepG2 cells, palmitic acid (PA)-induced pro-inflammatory cytokines release were blocked by HMGB1 small interfering RNA (siRNA) transfection. Moreover, pharmacological SIRT1 inhibition by Ex527 induced HMGB1 translocation and release, whereas SIRT1 activation by resveratrol or SalB reversed this trend. SIRT1 siRNA abrogated the SalB-mediated inhibition of HMGB1 acetylation and release, suggesting that SalB-mediated protection occurs by SIRT1 targeting HMGB1 for deacetylation. We are the first to demonstrate that the SIRT1/HMGB1 pathway is a key therapeutic target for controlling NAFLD inflammation and that SalB confers protection against HFD- and PA-induced hepatic steatosis and inflammation through SIRT1-mediated HMGB1 deacetylation.

The Role of HMGB1 Signaling Pathway in the Development and Progression of Hepatocellular Carcinoma: A Review

The story of high mobility group protein B1 (HMGB1) in cancer is complicated and the function of HMGB1 in different cancers is uncertain. This review aims to retrieve literature regarding HMGB1 from English electronic resources, analyze and summarize the role of the HMGB1 signaling pathway in hepatocellular carcinoma (HCC), and provide useful information for carcinogenesis and progression of HCC. Results showed that HMGB1 could induce cell proliferation, differentiation, cell death, angiogenesis, metastasis, inflammation, and enhance immunofunction in in vitro and in vivo HCC models. HMGB1 and its downstream receptors RAGE, TLRs and TREM-1 may be potential anticancer targets. In conclusion, HMGB1 plays an important role in oncogenesis and represents a novel therapeutic target, which deserves further study.

Inflammasome activation in the liver: Focus on alcoholic and non-alcoholic steatohepatitis

Upregulation of the inflammatory cascade is a major element both in the progression of steatohepatitis to severe alcoholic hepatitis as well as in the progression of NASH to advanced NASH with fibrosis. The mechanisms underpinning these changes are only partially understood. Activation of the inflammatory cascade requires multiple stimuli and in this report, we discuss the role of inflammasomes that activate IL-1β as well as the sterile and pathogen-derived danger signals that results in inflammasome activation and inflammation in alcoholic and non-alcoholic steatohepatitis. The dynamics of inflammasome activation, the cell types involved and the trigger signals appear to be somewhat different between ASH and NASH. Further studies are needed to dissect the pathology-related differences between these two major forms of steatohepatitis. Clinical and therapeutic implications of inflammasome activation in steatohepatitis are also discussed.