Lipotoxicity and steatohepatitis in an overfed mouse model for non-alcoholic fatty liver disease

The major risk factors for non-alcoholic fatty liver disease (NAFLD) are obesity, insulin resistance and dyslipidemia. The cause for progression from the steatosis stage to the inflammatory condition (non-alcoholic steatohepatitis (NASH)) remains elusive at present. Aim of this study was to test whether the different stages of NAFLD as well as the associated metabolic abnormalities can be recreated in time in an overfed mouse model and study the mechanisms underlying the transition from steatosis to NASH.Male C57Bl/6J mice were subjected to continuous intragastric overfeeding with a high-fat liquid diet (HFLD) for different time periods. Mice fed a solid high-fat diet (HFD) ad libitum served as controls. Liver histology and metabolic characteristics of liver, white adipose tisue (WAT) and plasma were studied.Both HFD-fed and HFLD-overfed mice initially developed liver steatosis, but only the latter progressed in time to NASH. NASH coincided with obesity, hyperinsulinemia, loss of liver glycogen and hepatic endoplasmatic reticulum stress. Peroxisome proliferator-activated receptor γ (Pparγ), fibroblast growth factor 21 (Fgf21), fatty acid binding protein (Fabp) and fatty acid translocase (CD36) were induced exclusively in the livers of the HFLD-overfed mice. Inflammation, reduced adiponectin expression and altered expression of genes that influence adipogenic capacity were only observed in WAT of HFLD-overfed mice.In conclusion: this dietary mouse model displays the different stages and the metabolic settings often found in human NAFLD. Lipotoxicity due to compromised adipose tissue function is likely associated with the progression to NASH, but whether this is cause or consequence remains to be established.     

Lifestyle interventions for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a multi-factorial disease and the most common of chronic liver diseases worldwide. The four clinical-pathological entities which are usually followed by NAFLD course include non-alcoholic steatosis, non-alcoholic steatohepatitis, advanced fibrosis/cirrhosis, and hepatocellular carcinoma. The cornerstones of NAFLD management and treatment, however, are healthy lifestyles such as dietary modifications, regular physical activity, and gradual weight loss. At present, no drugs or pharmacological agents have been approved for long-term treatment of NAFLD. Therefore, lifestyle modification is considered the main clinical recommendation and an initial step for the management of NAFLD.     

New insights in the pathogenesis of non-alcoholic fatty liver disease

PURPOSE OF REVIEW: The hallmark of non-alcoholic fatty liver disease is hepatic steatosis. This is mostly a benign condition, but for largely unknown reasons it progresses to liver fibrosis, cirrhosis, and ultimately hepatocellular carcinoma in about 10% of patients. In this review we discuss recent progress in the understanding of the etiology of non-alcoholic fatty liver disease. RECENT FINDINGS: In the last few years many connections between carbohydrate and triglyceride homeostasis, as well as inflammation, have surfaced. These seemingly unrelated metabolic pathways are linked by the action of diverse nuclear receptors. Many intermediates in lipid metabolism were shown to be activating ligands of these receptors, explaining the dysregulation of intermediary metabolism and induction of insulin resistance by a lipid overload. In addition to invoking a derangement in nuclear receptor regulation, excessive hepatic lipid influx may have direct metabolic consequences, particularly on mitochondrial function. SUMMARY: Non-alcoholic fatty liver disease is a multifactorial disease. Many aspects of the disease and the links to inflammation can be understood when the multiple functions of the regulating nuclear receptors are taken into account. Many of these nuclear receptors seem attractive targets to develop therapy for non-alcoholic fatty liver disease and the closely related metabolic syndrome.     

Genetic modifiers of non-alcoholic fatty liver disease progression

Non-alcoholic fatty liver disease (NAFLD) is now recognised as the most common cause of liver dysfunction worldwide. However, whilst the majority of individuals who exhibit features of the metabolic syndrome including obesity and insulin resistance will develop steatosis, only a minority progress to steatohepatitis, fibrosis and cirrhosis. Subtle inter-patient genetic variations and environment interact to determine disease phenotype and influence progression. A decade after the sequencing of the human genome, the comprehensive study of genomic variation offers new insights into the modifier genes, pathogenic mechanisms and is beginning to suggest novel therapeutic targets. We review the current status of the field with particular focus on advances from recent genome-wide association studies.     

Characteristics of fecal microbiota in non-alcoholic fatty liver disease patients

This study was designed to investigate the gut microbiota of patients with non-alcoholic fatty liver disease. The inclusive and exclusive criteria for NAFLD patients and healthy subjects were formulated, and detailed clinical data were collected. The genomic DNA of stool samples were extracted for 16S rDNA sequencing, and the amplified V4-region was sequenced on the Illumina Miseq platform. Metastats analysis was performed to identify the differential taxa between the groups. Redundancy analysis was used to evaluate the association between gut microbial structure and clinical variables. Thirty NAFLD patients and 37 healthy controls were involved. The 16S rDNA sequencing showed that there was a dramatic variability of the fecal microbiota among all the individuals. Metastats analysis identified eight families and 12 genera with significant differences between the two groups. When some clinical parameters, such as waist-to-hip ratio (WHR) and homeostasis model assessment of insulin resistance (HOMA-IR), were enrolled in Redundancy analysis, the distribution of the two group of samples was obviously changed. The compositional shifts in fecal bacterial communities of NAFLD patients from the healthy controls were mainly at family or genus levels. According to our Redundancy analysis, insulin resistance and obesity might be closely related to both NAFLD phenotype and intestinal microecology.     

NHE1 deficiency in liver: Implications for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease NAFLD is closely associated with the dysregulation of lipid homeostasis. Diet-induced hepatic steatosis, which can initiate NAFLD progression, has been shown to be dramatically reduced in mice lacking the electroneutral Na⁺/H⁺ exchanger NHE1 (Slc9a1). In this study, we investigated if NHE1 deficiency had effects in liver that could contribute to the apparent protection against aberrant lipid accumulation. RT-PCR and immunoblot analyses of wild-type and NHE1-null livers revealed an expression profile that strongly suggested attenuation of both de novo lipogenesis and hepatic stellate cell activation, which is implicated in liver fibrosis. This included upregulation of the farnesoid X receptor FXR, peroxisome proliferator-activated receptor PPARγ, its co-activator PGC1α, and sestrin 2, an antioxidant protein involved in hepatic metabolic homeostasis. Furthermore, expression levels of the pro-lipogenic liver X receptor LXRα, and acetyl CoA carboxylases 1 and 2 were downregulated. These changes were associated with evidence of reduced cellular stress, which persisted even upon exposure to a high-fat diet, and the better preservation of insulin signaling, as evidenced by protein kinase B/Akt phosphorylation (Ser473). These results indicate that NHE1 deficiency may protect against NAFLD pathogenesis, which is significant given the availability of highly specific NHE1 inhibitors.     

Interleukin-15-mediated inflammation promotes non-alcoholic fatty liver disease

Interleukin-15 (IL-15) is essential for the homeostasis of lymphoid cells particularly memory CD8⁺ T cells and NK cells. These cells are abundant in the liver, and are implicated in obesity-associated pathogenic processes. Here we characterized obesity-associated metabolic and cellular changes in the liver of mice lacking IL-15 or IL-15Rα. High fat diet-induced accumulation of lipids was diminished in the livers of mice deficient for IL-15 or IL-15Rα. Expression of enzymes involved in the transport of lipids in the liver showed modest differences. More strikingly, the liver tissues of IL15-KO and IL15Rα-KO mice showed decreased expression of chemokines CCl2, CCL5 and CXCL10 and reduced infiltration of mononuclear cells. In vitro, IL-15 stimulation induced chemokine gene expression in wildtype hepatocytes, but not in IL15Rα-deficient hepatocytes. Our results show that IL-15 is implicated in the high fat diet-induced lipid accumulation and inflammation in the liver, leading to fatty liver disease.     

Mechanism of hepatic insulin resistance in non-alcoholic fatty liver disease

Short term high fat feeding in rats results specifically in hepatic fat accumulation and provides a model of non-alcoholic fatty liver disease in which to study the mechanism of hepatic insulin resistance. Short term fat feeding (FF) caused a approximately 3-fold increase in liver triglyceride and total fatty acyl-CoA content without any significant increase in visceral or skeletal muscle fat content. Suppression of endogenous glucose production (EGP) by insulin was diminished in the FF group, despite normal basal EGP and insulin-stimulated peripheral glucose disposal. Hepatic insulin resistance could be attributed to impaired insulin-stimulated IRS-1 and IRS-2 tyrosine phosphorylation. These changes were associated with activation of PKC-epsilon and JNK1. Ultimately, hepatic fat accumulation decreased insulin activation of glycogen synthase and increased gluconeogenesis. Treatment of the FF group with low dose 2,4-dinitrophenol to increase energy expenditure abrogated the development of fatty liver, hepatic insulin resistance, activation of PKC-epsilon and JNK1, and defects in insulin signaling. In conclusion, these data support the hypothesis hepatic steatosis leads to hepatic insulin resistance by stimulating gluconeogenesis and activating PKC-epsilon and JNK1, which may interfere with tyrosine phosphorylation of IRS-1 and IRS-2 and impair the ability of insulin to activate glycogen synthase.     

Biosynthesis and bioavailability of long-chain polyunsaturated fatty acids in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) has a high occurrence in most countries. Recent studies estimate its prevalence to be near 30% in United States, Italian and Japanese general adult populations. NAFLD commonly presents along with obesity and insulin resistance (IR), pathologies that share with NAFLD metabolic and inflammatory components. These conditions, particularly NAFLD, are associated with alterations in the bioavailability of long-chain polyunsaturated fatty acids (LCPUFAs). In the human population, the bioavailability of LCPUFAs depends both on endogenous biosynthesis and diet amount of preformed LCPUFAs. However, the lower liver LCPUFAs product/precursor ratio namely (20:5n?3 + 22:6n?3)/18:3n?3, 20:4n?6/18:2n?6 present in common Western diets, makes critical an adequate pathway activity to ensure minimum bioavailability of LCPUFAs in most Western populations. The key step of this biosynthesis involves Δ5 and Δ6-desaturases, whose activities are altered in NAFLD. During the disease, the presence of molecular activators of these two enzymes does not correlate with the scarce LCPUFAS biosynthesis observed. The key to this apparent contradiction, or at least part of it, could be explained on the basis of the possible sensitivity of the desaturases to oxidative stress; a metabolic condition strongly linked to inflammatory pathologies such as NAFLD, obesity and IR and that, according to latest research, not only would be consequence but also possibly a cause of these diseases. The present review is focused on the relationship between NAFLD and the bioavailability of LCPUFAs, with special reference to the role that oxidative stress could play in the modulation of the liver fatty acid desaturase activity.     

Oxysterols and redox signaling in the pathogenesis of non-alcoholic fatty liver disease

Abstract

Oxysterols are oxidized species of cholesterol coming from exogenous (e.g. dietary) and endogenous (in vivo) sources. They play critical roles in normal physiologic functions such as regulation of cellular cholesterol homeostasis. Most of biological effects are mediated by interaction with nuclear receptor LXRα, highly expressed in the liver as well as in many other tissues. Such interaction participates in the regulation of whole-body cholesterol metabolism, by acting as “lipid sensors”. Moreover, it seems that oxysterols are also suspected to play key roles in several pathologies, including cardiovascular and inflammatory disease, cancer, and neurodegeneration. Growing evidence suggests that oxysterols may contribute to liver injury in non-alcoholic fatty liver disease. The present review focuses on the current status of knowledge on oxysterols’ biological role, with an emphasis on LXR signaling and oxysterols’ physiopathological relevance in NAFLD, suggesting new pharmacological development that needs to be addressed in the near future.     

Probiotics: A possible specific liver drug for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is and will continue to be a major liver health issue worldwide in the coming decades. There are no leading drug candidates at this point, although there are several promising concepts in drug development. Recent studies have proposed a possible role of intestinal bacterial overgrowth in the development of non-alcoholic steatohepatitis, thus indicated probiotics maybe a potential specific liver drug for NAFLD in the future.     

Insulin resistance and oxidative stress interdependency in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is emerging as a major cause of chronic liver disease in association with the rising prevalence of obesity and type 2 diabetes in the population. Oxidative stress and insulin resistance (IR) are major contributors in the pathogenesis of NAFLD and in the progression from steatosis to steatohepatitis. Recently, Houstis and colleagues reported that reactive oxygen species have a causal role in multiple forms of IR, a phenomenon that can further promote exacerbation of oxidative stress. The improvement of the knowledge of these interrelationships should contribute to elucidate pathogenic pathways and design effective treatments for NAFLD.     

Breath biomarkers and non-alcoholic fatty liver disease: Preliminary observations

Breath biomarkers have the potential to offer information that is similar to conventional clinical tests or they are entirely unique. Preliminary data support the use of breath biomarkers in the study of liver disease, in particular non-alcoholic fatty liver disease (NAFLD). It was evaluated whether breath ethanol, ethane, sulfur compounds and acetone would be associated with hepatic histopathology amongst morbidly obese patients presenting for bariatric surgery. Breath samples were collected during a preoperative visit and compared with liver biopsies obtained during the surgery. A Student's two-tailed t-test was used to compare differences between the two groups. Linear regression was used to analyse associations between the concentrations of breath molecules and independent predictor variables. It was found that breath ethanol, ethane and acetone can be useful biomarkers in patients with NAFLD. In particular, breath ethanol can be associated with hepatic steatosis, and breath acetone can be associated with non-alcoholic steatohepatitis.     

The expanding role of fish models in understanding non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a condition in which excessive fat accumulates in the liver of an individual who has not consumed excessive alcohol. Non-alcoholic steatohepatitis (NASH), a severe form of NAFLD, can progress to hepatic cirrhosis and/or hepatocellular carcinoma (HCC). NAFLD is considered to be a hepatic manifestation of metabolic syndrome, and its incidence has risen worldwide in lockstep with the increased global prevalence of obesity. Over the last decade, rodent studies have yielded an impressive list of molecules associated with NAFLD and NASH pathogenesis. However, the identification of currently unknown metabolic factors using mammalian model organisms is inefficient and expensive compared with studies using fish models such as zebrafish (Danio rerio) and medaka (Oryzias latipes). Substantial advances in unraveling the molecular pathogenesis of NAFLD have recently been achieved through unbiased forward genetic screens using small fish models. Furthermore, these easily manipulated organisms have been used to great advantage to evaluate the therapeutic effectiveness of various chemical compounds for the treatment of NAFLD. In this Review, we summarize aspects of NAFLD (specifically focusing on NASH) pathogenesis that have been previously revealed by rodent models, and discuss how small fish are increasingly being used to uncover factors that contribute to normal hepatic lipid metabolism. We describe the various types of fish models in use for this purpose, including those generated by mutation, transgenesis, or dietary or chemical treatment, and contrast them with rodent models. The use of small fish in identifying novel potential therapeutic agents for the treatment of NAFLD and NASH is also addressed.     

Dysregulated RNA polyadenylation contributes to metabolic impairment in non-alcoholic fatty liver disease

Pre-mRNA processing is an essential mechanism for the generation of mature mRNA and the regulation of gene expression in eukaryotic cells. While defects in pre-mRNA processing have been implicated in a number of diseases their involvement in metabolic pathologies is still unclear. Here, we show that both alternative splicing and alternative polyadenylation, two major steps in pre-mRNA processing, are significantly altered in non-alcoholic fatty liver disease (NAFLD). Moreover, we find that Serine and Arginine Rich Splicing Factor 10 (SRSF10) binding is enriched adjacent to consensus polyadenylation motifs and its expression is significantly decreased in NAFLD, suggesting a role mediating pre-mRNA dysregulation in this condition. Consistently, inactivation of SRSF10 in mouse and human hepatocytes in vitro, and in mouse liver in vivo, was found to dysregulate polyadenylation of key metabolic genes such as peroxisome proliferator-activated receptor alpha (PPARA) and exacerbate diet-induced metabolic dysfunction. Collectively our work implicates dysregulated pre-mRNA polyadenylation in obesity-induced liver disease and uncovers a novel role for SRSF10 in this process.     

Therapeutic effect of oxyberberine on obese non-alcoholic fatty liver disease rats

BackgroundBerberine (BBR) has been widely used to treat non-alcoholic fatty liver disease (NAFLD). The metabolites of BBR were believed to contribute significantly to its pharmacological effects. Oxyberberine (OBB), a gut microbiota-mediated oxidative metabolite of BBR, has been firstly identified in our recent work.PurposeHere, we aimed to comparatively investigate the anti-NAFLD properties of OBB and BBR.MethodsThe anti-NAFLD effect was evaluated in high-fat diet-induced obese NAFLD rats with biochemical/ELISA tests and histological staining. The related gene and protein expressions were detected by qRT-PCR and Western blotting respectively. Molecular docking and dynamic simulation were also performed to provide further insight.ResultsResults indicated OBB remarkably and dose-dependently attenuated the clinical manifestations of NAFLD, which (100 mg/kg) achieved similar therapeutic effect to metformin (300 mg/kg) and was superior to BBR of the same dose. OBB significantly inhibited aberrant phosphorylation of IRS-1 and up-regulated the downstream protein expression and phosphorylation (PI3K, p-Akt/Akt and p-GSK-3β/GSK-3β) to improve hepatic insulin signal transduction. Meanwhile, OBB treatment remarkably alleviated inflammation via down-regulating the mRNA expression of MCP-1, Cd68, Nos2, Cd11c, while enhancing Arg1 mRNA expression in white adipose tissue. Moreover, OBB exhibited closer affinity with AMPK in silicon and superior hyperphosphorylation of AMPK in vivo, leading to increased ACC mRNA expression in liver and UCP-1 protein expression in adipose tissue.ConclusionTaken together, compared with BBR, OBB was more capable of maintaining lipid homeostasis between liver and WAT via attenuating hepatic insulin pathway and adipocyte inflammation, which was associated with its property of superior AMPK activator.     

Caffeine-stimulated muscle IL-6 mediates alleviation of non-alcoholic fatty liver disease

Caffeine intake is associated with a reduced risk developing non-alcoholic fatty liver disease (NAFLD), but the underlying molecular mechanisms remain to be fully elucidated. We report here that caffeine markedly improved high fat diet-induced NAFLD in mice resulting in a 10-fold increase in circulating IL-6 levels, leading to STAT3 activation in the liver. Interestingly, the expression of IL-6 mRNA was not increased in the liver, but increased substantially in the muscles of caffeine-treated mice. Caffeine was found to stimulate IL-6 production in cultured myotubes but not in hepatocytes, adipocytes, or macrophages. The inhibition of p38/MAPK abrogated caffeine-induced IL-6 production in muscle cells. Caffeine failed to improve NAFLD in IL-6 and hepatocyte-specific STAT3 knockout mice, indicating that the IL-6/STAT3 pathway is vital for the hepatoprotective effects of caffeine in NAFLD. The possibility that IL-6/STAT3-mediated hepatic autophagosome induction and hepatocytic oxygen consumption are involved in the anti-NAFLD effects of caffeine cannot be excluded, based on the findings presented here. Our results reveal that caffeine ameliorates NAFLD via crosstalk between muscle IL-6 production and liver STAT3 activation.     

肠道菌群与非酒精性脂肪肝病相关性研究进展

近年来关于肠道菌群与非酒精性脂肪肝疾病关系的研究越来越多。非酒精性脂肪肝是一种无过量饮酒史,肝内脂肪过量堆积的慢性疾病。生理解剖结构上的“肠-肝轴”表明肠道和肝脏有着密不可分的关系。肠道菌群一般情况下处于动态平衡,可以维持肠道正常生理功能。肠道菌群可通过改善肠道通透性、干预脂质代谢、产生内源性乙醇和产生短链脂肪酸等来影响非酒精性脂肪肝疾病的发生与发展。临床上对于治疗非酒精性脂肪肝没有确切的药物,增加有益肠道菌群的因素,如益生元、益生菌等能够调节肠道的微环境,这为非酒精性脂肪肝疾病的治疗开辟了新的方向。