Pathogenesis of Nonalcoholic Steatohepatitis: Interactions between Liver Parenchymal and Nonparenchymal Cells

Overview of the Pathogenesis, Genetic, and Non-Invasive Clinical, Biochemical, and Scoring Methods in the Assessment of NAFLD

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease worldwide. It represents a range of disorders, including simple steatosis, nonalcoholic steatohepatitis (NASH), and liver cirrhosis, and its prevalence continues to rise. In some cases, hepatocellular carcinoma (HCC) may develop. The develop;ment of non-invasive diagnostic and screening tools is needed, in order to reduce the frequency of liver biopsies. The most promising methods are those able to exclude advanced fibrosis and quantify steatosis. In this study, new perspective markers for inflammation, oxidative stress, apoptosis, and fibrogenesis; emerging scoring models for detecting hepatic steatosis and fibrosis; and new genetic, epigenetic, and multiomic studies are discussed. As isolated biochemical parameters are not specific or sensitive enough to predict the presence of NASH and fibrosis, there is a tendency to use various markers and combine them into mathematical algorithms. Several predictive models and scoring systems have been developed. Current data suggests that panels of markers (NAFLD fibrosis score, Fib-4 score, BARD score, and others) are useful diagnostic modalities to minimize the number of liver biopsies. The review unveils pathophysiological aspects related to new trends in current non-invasive biochemical, genetic, and scoring methods, and provides insight into their diagnostic accuracies and suitability in clinical practice.

Free radicals, antioxidants, nuclear factor-E2-related factor-2 and liver damage

Oxidative/nitrosative stress is proposed to be a critical factor in various diseases, including liver pathologies. Antioxidants derived from medicinal plants have been studied extensively and are relevant to many illnesses, including liver diseases. Several hepatic disorders, such as viral hepatitis and alcoholic or nonalcoholic steatohepatitis, involve free radicals/oxidative stress as agents that cause or at least exacerbate liver injury, which can result in chronic liver diseases, such as liver fibrosis, cirrhosis and end-stage hepatocellular carcinoma. In this scenario, nuclear factor-E2-related factor-2 (Nrf2) appears to be an essential factor to counteract or attenuate oxidative or nitrosative stress in hepatic cells. In fact, a growing body of evidence indicates that Nrf2 plays complex and multicellular roles in hepatic inflammation, fibrosis, hepatocarcinogenesis and regeneration via the induction of its target genes. Inflammation is the most common feature of chronic liver diseases, triggering fibrosis, cirrhosis and hepatocellular carcinoma. Increasing evidence indicates that Nrf2 counteracts the proinflammatory process by modulating the recruitment of inflammatory cells and inducing the endogenous antioxidant response of the cell. In this review, the interactions between antioxidant and inflammatory molecular pathways are analyzed.

Health Benefits of Carotenoids: A Role of Carotenoids in the Prevention of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases with a prevalence of ~25% worldwide. NAFLD includes simple hepatic steatosis, non-alcoholic steatohepatitis, fibrosis, and cirrhosis, which can further progress to hepatocellular carcinoma. Therefore, effective strategies for the prevention of NAFLD are needed. The pathogenesis of NAFLD is complicated due to diverse injury insults, such as fat accumulation, oxidative stress, inflammation, lipotoxicity, and apoptosis, which may act synergistically. Studies have shown that carotenoids, a natural group of isoprenoid pigments, prevent the development of NAFLD by exerting antioxidant, lipid-lowering, anti-inflammatory, anti-fibrotic, and insulin-sensitizing properties. This review summarizes the protective action of carotenoids, with primary focuses on astaxanthin, lycopene, β-carotene, β-cryptoxanthin, lutein, fucoxanthin, and crocetin, against the development and progression of NAFLD.

Immunotherapy with oral administration of humanized anti-CD3 monoclonal antibody: a novel gut-immune system-based therapy for metaflammation and NASH

The immune system plays a role in the pathogenesis of non-alcoholic steatohepatitis (NASH) underlying hepatocyte injury and fibrosis progression at all disease stages. Oral administration of anti-CD3 monoclonal antibody (mAb) has been shown in preclinical studies to be an effective method for systemic immune modulation and alleviates immune-mediated disorders without T cell depletion. In the present review, we summarize the concept of the oral administration of humanized anti-CD3 mAb in patients with NASH and discuss the potential of this treatment to address the current requirements of treatments for NASH. Recently published preclinical and clinical data on oral administration of anti CD3 are discussed. Human trials have shown that the oral administration of anti-CD3 in healthy volunteers, patients with chronic hepatitis C virus (HCV) infection and patients with NASH and type 2 diabetes is safe and well tolerated, as well as biologically active. Oral anti-CD3 induces regulatory T cells, suppresses the chronic inflammatory state associated with NASH and exerts a beneficial effect on clinically relevant parameters. Foralumab is a fully human anti-CD3 mAb that has recently been shown to exert a potent anti-inflammatory effect in humanized mice. It is being developed for treatment of NASH and primary biliary cholangitis (PBC). Oral administration of anti CD3 may provide an effective therapy for patients with NASH.

Recent Insights into the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a burgeoning health problem worldwide and an important risk factor for both hepatic and cardiometabolic mortality. The rapidly increasing prevalence of this disease and of its aggressive form nonalcoholic steatohepatitis (NASH) will require novel therapeutic approaches based on a profound understanding of its pathogenesis to halt disease progression to advanced fibrosis or cirrhosis and cancer. The pathogenesis of NAFLD involves a complex interaction among environmental factors (i.e., Western diet), obesity, changes in microbiota, and predisposing genetic variants resulting in a disturbed lipid homeostasis and an excessive accumulation of triglycerides and other lipid species in hepatocytes. Insulin resistance is a central mechanism that leads to lipotoxicity, endoplasmic reticulum stress, disturbed autophagy, and, ultimately, hepatocyte injury and death that triggers hepatic inflammation, hepatic stellate cell activation, and progressive fibrogenesis, thus driving disease progression. In the present review, we summarize the currently available data on the pathogenesis of NAFLD, emphasizing the most recent advances. A better understanding of NAFLD/NASH pathogenesis is crucial for the design of new and efficient therapeutic interventions.

Folate receptor-beta expression as a diagnostic target in human & rodent nonalcoholic steatohepatitis

INTRODUCTION

Nonalcoholic steatohepatitis (NASH) afflicts 20-36% of individuals with nonalcoholic fatty liver disease (NAFLD). A lipotoxic hepatic environment, altered innate immune signaling and inflammation are defining features of progression to NASH. Activated resident liver macrophages express folate receptor beta (FR-β) which may be an indicator of progression from steatosis to NASH. The goals of this study were to characterize FR-β protein expression in human NAFLD and rodent models of NASH, and demonstrate liver targeting of an FR-β imaging agent to the liver of a rodent NASH model using FR-β.

METHODS

Rat liver lysates from methionine choline deficient (MCD) fed rats, high fat diet (HFD) and methionine choline sufficient (MC+) rat controls were analyzed for hepatic FR-β protein. The FR-β-targeted agent, Etarfolatide was injected into MCD and MC + -fed C57BL/6 mice for efficient FastSPECT hepatic imaging. Additionally, FR-β expression across the stages of human NAFLD from normal to NASH was assessed.

RESULTS

FastSPECT images show targeting of Etarfolatide to the liver of mice fed 8 weeks of MCD diet but not control-fed mice. The MCD rat model exhibited significantly increased protein expression of hepatic FR-β in contrast to HFD or normal samples. Similarly human liver samples categorized as NASH Fatty or NASH Not Fatty showed elevated FR-β protein when compared to normal liver. FR-β transcript expression levels were elevated across both NASH Fatty and NASH Not Fatty samples.

CONCLUSION

The findings in this study indicate that FR-β expression in NASH may be harnessed to target agents directly to the liver.

Regulatory Non-coding RNAs Network in Non-alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) spectrum comprises simple steatosis and non-alcoholic steatohepatitis (NASH) that can lead to fibrosis and cirrhosis. The patients usually have no history of excessive alcohol consumption and other etiologies that can cause fatty liver. Understanding of the pathophysiology of NAFLD has revealed that non-coding RNAs (ncRNAs) play significant roles in modulating the disease susceptibility, pathogenesis and progression. Currently, the ncRNAs are grouped according to their sizes and their regulatory or housekeeping functions. Each of these ncRNAs has a wide range of involvement in the regulation of the genes and biological pathways. Here, we briefly review the current literature the regulatory ncRNAs in NAFLD pathogenesis and progression, mainly the microRNAs, long non-coding RNAs and circular RNAs. We also discuss the co-regulatory functions and interactions between these ncRNAs in modulating the disease pathogenesis. Elucidation of ncRNAs in NAFLD may facilitate the identification of early diagnostic biomarkers and development of therapeutic strategies for NAFLD.

A Pathophysiological Model of Non-Alcoholic Fatty Liver Disease Using Precision-Cut Liver Slices

Non-alcoholic fatty liver disease (NAFLD) is a common liver disorder closely related to metabolic syndrome. NAFLD can progress to an inflammatory state called non-alcoholic steatohepatitis (NASH), which may result in the development of fibrosis and hepatocellular carcinoma. To develop therapeutic strategies against NAFLD, a better understanding of the molecular mechanism is needed. Current in vitro NAFLD models fail to capture the essential interactions between liver cell types and often do not reflect the pathophysiological status of patients. To overcome limitations of commonly used in vitro and in vivo models, precision-cut liver slices (PCLSs) were used in this study. PCLSs, prepared from liver tissue obtained from male Wistar rats, were cultured in supraphysiological concentrations of glucose, fructose, insulin, and palmitic acid to mimic metabolic syndrome. Accumulation of lipid droplets was visible and measurable after 24 h in PCLSs incubated with glucose, fructose, and insulin, both in the presence and absence of palmitic acid. Upregulation of acetyl-CoA carboxylase 1 and 2, and of sterol responsive element binding protein 1c, suggests increased de novo lipogenesis in PCLSs cultured under these conditions. Additionally, carnitine palmitoyltransferase 1 expression was reduced, which indicates impaired fatty acid transport and disrupted mitochondrial β-oxidation. Thus, steatosis was successfully induced in PCLSs with modified culture medium. This novel ex vivo NAFLD model could be used to investigate the multicellular and molecular mechanisms that drive NAFLD development and progression, and to study potential anti-steatotic drugs.

Role of Dietary Lipids in Modulating Inflammation through the Gut Microbiota

Inflammation and its resolution is a tenuous balance that is under constant contest. Though several regulatory mechanisms are employed to maintain homeostasis, disruptions in the regulation of inflammation can lead to detrimental effects for the host. Of note, the gut and microbial dysbiosis are implicated in the pathology of systemic chronic low-grade inflammation which has been linked to several metabolic diseases. What remains to be described is the extent to which dietary fat and concomitant changes in the gut microbiota contribute to, or arise from, the onset of metabolic disorders. The present review will highlight the role of microorganisms in host energy regulation and several mechanisms that contribute to inflammatory pathways. This review will also discuss the immunomodulatory effects of the endocannabinoid system and its link with the gut microbiota. Finally, a brief discussion arguing for improved taxonomic resolution (at the species and strain level) is needed to deepen our current knowledge of the microbiota and host inflammatory state.

Oxidative Stress and Nonalcoholic Fatty Liver Disease in Hemodialysis Patients

INTRODUCTION

Nonalcoholic fatty liver disease (NAFLD) is becoming more common around the world and it may progress to cirrhosis and liver failure, increasing mortality risk. In hemodialysis (HD) patients, NAFLD may be a novel risk factor for their high cardiovascular mortality. Heightened oxidative stress is highly prevalent in HD patients. However, the relationship between oxidative stress and NAFLD in HD patients is not well defined.

METHODS

We studied seventy-one stable nondiabetic HD patients. Nineteen patients had the diagnosis of NAFLD by ultrasonography. Blood levels of oxidative stress markers were measured in each patient, including thiobarbituric acid reactive substances (TBARS), free thiols, superoxide dismutase (SOD) activities, and glutathione peroxidase (GPx) activity. The copy numbers of mitochondrial DNA (mtDNA) in peripheral leukocytes were also determined. Demographic, biochemistry, and hemogram data were recorded. The two groups of patients were compared in order to determine the factors associated with NAFLD in HD patients.

FINDINGS

Compared to those without NAFLD, nondiabetic HD patients with NAFLD had significantly higher mtDNA copy number and GPx levels. The two groups did not differ significantly in dialysis adequacy, hemoglobin, serum calcium, phosphorus, albumin, liver function tests, or lipid profiles. Regression analysis confirmed mtDNA copy numbers and GPx levels as two independent factors associated with NAFLD. Compared to those with polysulfone, patients dialyzed with cellulose membrane have significantly higher levels of TBARS. However, patients with or without NAFLD did not differ in their use of either dialysis membrane.

DISCUSSION

Oxidative stress (represented by antioxidant defense, GPx) and mitochondrial DNA copy numbers are independently associated with fatty liver disease in nondiabetic HD patients. The diagnostic and therapeutic implications of this key observation warrant further exploration.

Saturated fatty acid combined with lipopolysaccharide stimulates a strong inflammatory response in hepatocytes in vivo and in vitro

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and consumption of high-fat diet (HFD) is a risk factor for NAFLD. The HFD not only increases intake of saturated fatty acid (SFA) but also induces metabolic endotoxemia, an HFD-associated increase in circulating lipopolysaccharide (LPS). Although it is known that SFA or LPS promote hepatic inflammation, a hallmark of NAFLD, it remains unclear how SFA in combination with LPS stimulates host inflammatory response in hepatocytes. In this study, we performed both in vivo and in vitro experiments to investigate the effect of SFA in combination with LPS on proinflammatory gene expression in hepatocytes. Our animal study showed that feeding low-density lipoprotein-deficient mice HFD enriched with SFA and injection of low-dose LPS cooperatively stimulated IL-6 expression in livers. To understand how SFA and LPS interact to promote IL-6 expression, our in vitro studies showed that palmitic acid (PA), a major SFA, and LPS exerted synergistic effect on the expression of IL-6 in hepatocytes. Furthermore, coculture of hepatocytes with macrophages resulted in a greater IL-6 expression than culture of hepatocytes without macrophages in response to the combination of PA and LPS. Finally, we observed that LPS and PA increased ceramide production by cooperatively stimulating ceramide de novo synthesis, which played an essential role in the synergistic stimulation of proinflammatory gene expression by LPS and PA. Taken together, this study showed that SFA in combination with LPS stimulated a strong inflammatory response in hepatocytes in vivo and in vitro.

Fecal microbiota transplantation: a promising strategy in preventing the progression of non-alcoholic steatohepatitis and improving the anti-cancer immune response

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) has the potential to progress to hepatocellular carcinoma (HCC). However, limited therapies are currently available for the treatment of advanced HCC, and one must strive to search for novel strategies.

AREAS COVERED

We provide insight on current knowledge related to gut microbiota and NAFLD, summarize the sequence linking obesity to HCC and highlight gut dysbiosis in obesity and its consequences on the liver. We detail the impact of the gut microbiota on immune checkpoint inhibitors, and speculate on the role of fecal microbiota transplantation (FMT) in NAFLD and in improving anti-neoplastic immune response.

EXPERT OPINION

Manipulation of the gut microbiota seems promising in the secondary prevention of NAFLD/NASH and/or in potentiating anti-cancer immune response, notably by a global 'resetting' using FMT. However, the composition of a 'harmful' gut microbiome in HCC still needs to be characterized, and the impact of FMT on HCC growth needs to be assessed.

Alcohol or Not: A Review Comparing Initial Mechanisms, Contributing Factors, and Liver Transplantation Outcomes Between Alcoholic and Nonalcoholic Steatohepatitis

Chronic liver diseases take many forms; alcohol-related liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD) are two common illnesses that potentially lead to cirrhosis, liver failure, and liver cancer. It is estimated that a quarter of heavy drinkers develop ALD and the same portion of people without heavy drinking habits have NAFLD. Alcohol intake is regularly used to differentiate NAFLD from ALD; however, diagnosis based on the discrimination threshold may be suboptimal when facing an obese patient with a high level of alcohol exposure. Therefore, understanding the common and/or different mechanism(s) driving each disease is extremely important. The ‘two-hit’ or ‘multi-hit’ hypothesis is used to explain the pathogenesis of both diseases. The ‘first hit’ refers to developing steatosis, the accumulation of fat components in the liver, and the ‘second hits’ are factors leading to oxidative stress, inflammation, and fibrosis, such as metabolic syndromes (e.g., morbid obesity, hyperglycaemia, hyperlipidaemia, disturbed circadian cycles, and altered intestinal microbiota) and environmental toxins (e.g., cigarette smoke and pollutants). Heritable factors also affect the probability and disease progression of both ALD and NAFLD. Whereas PNPLA3 and TM6SF2 variants are influential genetic risk factors for the diseases, epigenetic factors, such as DNA methylation, post-translational histone modifications, and small non-coding RNA, are of paramount importance. Moreover, considering that both ALD and NAFLD patients may eventually develop end-stage liver disease and require liver transplantation, the authors extensively investigated the worldwide outcomes from original literature for these two aetiologies, and the results showed no obvious differences in post-transplantation survival between them. Precise percentage determination of these two aetiologies contributing to steatohepatitis and its secondary injuries in the future would allow for better strategies for therapeutic and preventive intervention.

The Role of Long Non-Coding RNAs (lncRNAs) in the Development and Progression of Fibrosis Associated with Nonalcoholic Fatty Liver Disease (NAFLD)

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of conditions ranging from hepatic steatosis to inflammation (nonalcoholic steatohepatitis or NASH) with or without fibrosis, in the absence of significant alcohol consumption. The presence of fibrosis in NASH patients is associated with greater liver-related morbidity and mortality; however, the molecular mechanisms underlying the development of fibrosis and cirrhosis in NAFLD patients remain poorly understood. Long non-coding RNAs (lncRNAs) are emerging as key contributors to biological processes that are underpinning the initiation and progression of NAFLD fibrosis. This review summarizes the experimental findings that have been obtained to date in animal models of liver fibrosis and NAFLD patients with fibrosis. We also discuss the potential applicability of circulating lncRNAs to serve as biomarkers for the diagnosis and prognosis of NAFLD fibrosis. A better understanding of the role played by lncRNAs in NAFLD fibrosis is critical for the identification of novel therapeutic targets for drug development and improved, noninvasive methods for disease diagnosis.

Linking the gut and liver: crosstalk between regulatory T cells and mucosa-associated invariant T cells

The gut–liver axis is increasingly considered to play a vital part in the progression of chronic inflammatory gut and liver diseases. Hence, a detailed understanding of the local and systemic regulatory mechanisms is crucial to develop novel therapeutic approaches. In this review, we discuss in-depth the roles of regulatory T cells (Tregs) and mucosal-associated invariant T cells (MAITs) within the context of inflammatory bowel disease, primary sclerosing cholangitis, and non-alcoholic steatohepatitis. Tregs are crucial in maintaining peripheral tolerance and preventing autoimmunity. MAIT cells have a unique ability to rapidly recognize microbial metabolites and mount a local immune response and act as a ‘biliary firewall’ at the gut and biliary epithelial barrier. We also outline how current knowledge can be exploited to develop novel therapies to control the propagation of chronic gut- and liver-related inflammatory and autoimmune conditions. We specifically focus on the nature of the Tregs’ cell therapy product and outline an adjunctive role for low-dose IL-2. All in all, it is clear that translational immunology is at crucial crossroads. The success of ongoing clinical trials in cellular therapies for inflammatory gut and liver conditions could revolutionize the treatment of these conditions and the lives of our patients in the coming years.

Association between dietary total antioxidant capacity and hepatocellular ballooning in nonalcoholic steatohepatitis: a cross-sectional study

PURPOSE

Nonalcoholic steatohepatitis (NASH) is characterized by steatosis, lobular inflammation, ballooning, and in some cases, fibrosis, which can progress to cirrhosis and carcinoma. The progression of NASH is closely related to oxidative stress. Dietary intake of antioxidants has been suggested in protection against oxidative damage and related clinical complications. Thus, we evaluated the potential association of dietary total antioxidant capacity (TAC) with disease severity in NASH patients, as well as with anthropometric and body composition markers and biochemical parameters.

METHODS

Thirty-three outpatients with a mean age of 48.4 ± 1.9 years were evaluated. Dietary TAC was estimated from a quantitative food frequency questionnaire. NASH severity, determined by liver biopsy, lifestyle characteristics, occurrence of comorbidities, anthropometry, body composition, and biochemical parameters were assessed.

RESULTS

NASH patients who had a higher dietary TAC had fewer ballooned hepatocytes compared to those with a lower TAC (p = 0.024). The patients with the highest dietary TAC had a reduction of approximately 20% in the risk of having many ballooned hepatocytes (OR 0.791; 95% CI 0.643-0.974; p = 0.027). There was no association of steatosis, lobular inflammation, and fibrosis with dietary TAC. The same occurred for lifestyle characteristics, occurrence of comorbidities, anthropometry, body composition, and biochemical parameters.

CONCLUSION

Dietary TAC is higher in patients with lower hepatic injury (ballooning), suggesting a possible role of food intake naturally high in its antioxidant capacity in reducing free radical production and, consequently, oxidative stress.

Diabetes and hepatocellular carcinoma: A pathophysiological link and pharmacological management

Both diabetes mellitus (DM) and cancer are multifarious, dissimilar, and long-lasting, fatal diseases with a remarkable influence on health worldwide. DM is not only related to cardiovascular diseases, neuropathy, nephropathy, and retinopathy, but also related to a number of liver diseases such as nonalcoholic fatty liver disease, steatohepatitis, and liver cirrhosis. Recently, it is hypothesized that DM has a greater risk for many forms of cancer, such as breast, colorectal, endometrial, pancreatic, gallbladder, renal, and liver cancer including hepatocellular carcinoma (HCC). Both DM and cancer have many common risk factors, but the association between these two is poorly stated. Several epidemiologic studies have revealed the association between pathogenic and prognostic characteristics of DM and a higher incidence of HCC, thus representing DM as an independent risk factor for HCC development. The etiological and pathophysiological relationship between DM and HCC has been presented in this review by linking hyperglycemia, hyperinsulinemia, insulin resistance, and activation of insulin-like growth factor signaling pathways and pharmacological management of HCC associated with DM.

Triggering and resolution of inflammation in NASH

Nonalcoholic steatohepatitis (NASH) is considered the progressive form of nonalcoholic fatty liver disease (NAFLD) and is characterized by liver steatosis, inflammation, hepatocellular injury and different degrees of fibrosis. A central issue in this field relates to the identification of those factors that trigger inflammation, thus fuelling the transition from nonalcoholic fatty liver to NASH. These triggers of liver inflammation might have their origins outside the liver (such as in adipose tissue or the gut) as well as inside the organ (for instance, lipotoxicity, innate immune responses, cell death pathways, mitochondrial dysfunction and endoplasmic reticulum stress), both of which contribute to NASH development. In this Review, we summarize the currently available information on the key upstream triggers of inflammation in NASH. We further delineate the mechanisms by which liver inflammation is resolved and the implications of a defective pro-resolution process. A better knowledge of these mechanisms should help to design targeted therapies able to halt or reverse disease progression.

ILDR2 has a negligible role in hepatic steatosis

We have previously reported that Ildr2 knockdown via adenovirally-delivered shRNA causes hepatic steatosis in mice. In the present study we investigated hepatic biochemical and anatomic phenotypes of Cre-mediated Ildr2 knock-out mice. Liver-specific Ildr2 knock-out mice were generated in C57BL/6J mice segregating for a floxed (exon 1) allele of Ildr2, using congenital and acute (10-13-week-old male mice) Cre expression. In addition, Ildr2 shRNA was administered to Ildr2 knock-out mice to test the effects of Ildr2 shRNA, per se, in the absence of Ildr2 expression. RNA sequencing was performed on livers of these knockdown and knockout mice. Congenital and acute liver-specific and hepatocyte-specific knockout mice did not develop hepatic steatosis. However, administration of Ildr2 shRNA to Ildr2 knock-out mice did cause hepatic steatosis, indicating that the Ildr2 shRNA had apparent "off-target" effects on gene(s) other than Ildr2. RNA sequencing and BLAST sequence alignment revealed Dgka as a candidate gene mediating these "off-target" effects. Ildr2 shRNA is 63% homologous to the Dgka gene, and Dgka expression decreased only in mice displaying hepatic steatosis. Dgka encodes diacylglycerol kinase (DGK) alpha, one of a family of DGKs which convert diacylglycerides to phosphatidic acid for second messenger signaling. Dgka knockdown mice would be expected to accumulate diacylglyceride, contributing to the observed hepatic steatosis. We conclude that ILDR2 plays a negligible role in hepatic steatosis. Rather, hepatic steatosis observed previously in Ildr2 knockdown mice was likely due to shRNA targeting of Dgka and/or other "off-target" genes. We propose that the gene candidates identified in this follow-up study may lead to identification of novel regulators of hepatic lipid metabolism.

Membrane Remodeling as a Key Player of the Hepatotoxicity Induced by Co-Exposure to Benzo[a]pyrene and Ethanol of Obese Zebrafish Larvae

The rise in prevalence of non-alcoholic fatty liver disease (NAFLD) constitutes an important public health concern worldwide. Including obesity, numerous risk factors of NAFLD such as benzo[a]pyrene (B[a]P) and ethanol have been identified as modifying the physicochemical properties of the plasma membrane in vitro thus causing membrane remodeling—changes in membrane fluidity and lipid-raft characteristics. In this study, the possible involvement of membrane remodeling in the in vivo progression of steatosis to a steatohepatitis-like state upon co-exposure to B[a]P and ethanol was tested in obese zebrafish larvae. Larvae bearing steatosis as the result of a high-fat diet were exposed to ethanol and/or B[a]P for seven days at low concentrations coherent with human exposure in order to elicit hepatotoxicity. In this condition, the toxicant co-exposure raised global membrane order with higher lipid-raft clustering in the plasma membrane of liver cells, as evaluated by staining with the fluoroprobe di-4-ANEPPDHQ. Involvement of this membrane’s remodeling was finally explored by using the lipid-raft disruptor pravastatin that counteracted the effects of toxicant co-exposure both on membrane remodeling and toxicity. Overall, it can be concluded that B[a]P/ethanol co-exposure can induce in vivo hepatotoxicity via membrane remodeling which could be considered as a good target mechanism for developing combination therapy to deal with steatohepatitis.

Hepatocyte nuclear receptor SHP suppresses inflammation and fibrosis in a mouse model of nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is a burgeoning health problem worldwide, ranging from nonalcoholic fatty liver (NAFL, steatosis without hepatocellular injury) to the more aggressive nonalcoholic steatohepatitis (NASH, steatosis with ballooning, inflammation, or fibrosis). Although many studies have greatly contributed to the elucidation of NAFLD pathogenesis, the disease progression from NAFL to NASH remains incompletely understood. Nuclear receptor small heterodimer partner (Nr0b2, SHP) is a transcriptional regulator critical for the regulation of bile acid, glucose, and lipid metabolism. Here, we show that SHP levels are decreased in the livers of patients with NASH and in diet-induced mouse NASH. Exposing primary mouse hepatocytes to palmitic acid and lipopolysaccharide in vitro, we demonstrated that the suppression of Shp expression in hepatocytes is due to c-Jun N-terminal kinase (JNK) activation, which stimulates c-Jun-mediated transcriptional repression of Shp Interestingly, in vivo induction of hepatocyte-specific SHP in steatotic mouse liver ameliorated NASH progression by attenuating liver inflammation and fibrosis, but not steatosis. Moreover, a key mechanism linking the anti-inflammatory role of hepatocyte-specific SHP expression to inflammation involved SHP-induced suppression of NF-κB p65-mediated induction of chemokine (C-C motif) ligand 2 (CCL2), which activates macrophage proinflammatory polarization and migration. In summary, our results indicate that a JNK/SHP/NF-κB/CCL2 regulatory network controls communications between hepatocytes and macrophages and contributes to the disease progression from NAFL to NASH. Our findings may benefit the development of new management or prevention strategies for NASH.

MicroRNAs in the pathogenesis and treatment of progressive liver injury in NAFLD and liver fibrosis

Non-alcoholic fatty liver disease (NAFLD) increases the risk of various liver injuries, ranging from simple steatosis to non-alcoholic steatohepatitis (NASH), fibrosis and cirrhosis, and ultimately hepatocellular carcinoma (HCC). Ample evidence has suggested that aberrant expression of microRNAs (miRNAs) is functionally involved in the activation of cellular stress, inflammation and fibrogenesis in hepatic cells, including hepatocytes, Kupffer and hepatic stellate cells (HSCs), at different pathological stages of NAFLD and liver fibrosis. Here, we overview recent findings on the potential role of miRNAs in the pathogenesis of NAFLD, including lipotoxicity, oxidative stress, metabolic inflammation and fibrogenesis. We critically assess the literatures on both human subjects and animal models of NAFLD and liver fibrosis with miRNA dysregulation and their mechanisms of actions in liver damage. We further highlight the potential use of miRNA mimics or antimiRNAs as therapeutic approaches for the prevention and treatment of NAFLD and liver fibrosis.

Correlation between Serum Ferritin Level and Histopathological Disease Severity in Non-alcoholic Fatty Liver Disease

BACKGROUND Non-alcoholic fatty liver disease (NAFLD) is one of the most common causes of chronic liver disease worldwide. Recently several parameters, such as serum ferritin, have emerged as possible predictors for the severity of NAFLD and insulin sensitivity. We aimed to investigate the value of serum ferritin level as a useful biomarker for the prediction of histopathological disease severity in non-alcoholic steatohepatitis (NASH), the necro-inflammatory form of NAFLD. METHODS This was a prospective cross sectional study in which demographic, clinical, histological, laboratory, and anthropometric data of 30 adult patients with biopsy-proven NAFLD/NASH were analyzed. RESULTS In our patients population with mean age of 37.9 years and mean BMI of 26.5, statistical analysis did not show a significant difference between the three grades of steatosis in the mean ferritin levels (p = 0.559). It was also observed that ferritin level did not have a significant correlation with the stage of fibrosis (p = 0.228). The mean transferrin saturation did not show significant difference in different stages and grades of NASH (p = 0.260 and 0.944, respectively), either. CONCLUSION Serum ferritin level may not be useful as a single marker for the prediction of histopathological severity of disease in young patients with NASH who are not morbidly obese.

Prolonged cenicriviroc therapy reduces hepatic fibrosis despite steatohepatitis in a diet-induced mouse model of nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a progressive liver disease projected to become the leading cause of cirrhosis and liver transplantation in the next decade. Cenicriviroc (CVC), a dual chemokine receptor 2 and 5 antagonist, prevents macrophage trafficking and is under clinical investigation for the treatment of human NASH fibrosis. We assessed the efficacy and durability of short and prolonged CVC therapy in a diet‐induced mouse model of NASH, the choline deficient, L‐amino acid‐defined, high‐fat diet (CDAHFD) model. C57BL/6 mice received 4 or 14 weeks of standard chow or the CDAHFD. CVC (10 mg/kg/day and 30 mg/kg/day for 4 weeks and 20 mg/kg/day and 30 mg/kg/day for 14 weeks) was initiated simultaneously with the CDAHFD. At 4 and 14 weeks, livers were harvested for histology and flow cytometric analyses of intrahepatic immune cells. High‐dose CVC (30 mg/kg/day) therapy in CDAHFD mice for 4 or 14 weeks inhibited intrahepatic accumulation of Ly6C^high bone marrow‐derived macrophages. Prolonged CVC therapy (14 weeks) yielded no significant differences in the total intrahepatic macrophage populations among treatment groups but increased the frequency of intrahepatic anti‐inflammatory macrophages in the high‐dose CVC group. Despite ongoing steatohepatitis, there was significantly less fibrosis in CDAHFD mice receiving high‐dose CVC for 14 weeks based on histologic and molecular markers, mirroring observations in human NASH CVC trials. CVC also directly inhibited the profibrotic gene signature of transforming growth factor‐β‐stimulated primary mouse hepatic stellate cells in vitro. Conclusion: CVC is a novel therapeutic agent that is associated with reduced fibrosis despite ongoing steatohepatitis. Its ability to alter intrahepatic macrophage populations and inhibit profibrogenic genes in hepatic stellate cells in NASH livers may contribute to its observed antifibrotic effect. (Hepatology Communications 2018;2:529‐545)

Pathogenesis of Nonalcoholic Steatohepatitis and Hormone-Based Therapeutic Approaches

Non-alcoholic fatty liver disease (NAFLD) is an emerging global health problem and a potential risk factor for type 2 diabetes, cardiovascular disease, and chronic kidney disease. Nonalcoholic steatohepatitis (NASH), an advanced form of NAFLD, is a predisposing factor for development of cirrhosis and hepatocellular carcinoma. The increasing prevalence of NASH emphasizes the need for novel therapeutic approaches. Although therapeutic drugs against NASH are not yet available, fundamental insights into the pathogenesis of NASH have been made during the past few decades. Multiple therapeutic strategies have been developed and are currently being explored in clinical trials or preclinical testing. The pathogenesis of NASH involves multiple intracellular/extracellular events in various cell types in the liver or crosstalk events between the liver and other organs. Here, we review current findings and knowledge regarding the pathogenesis of NASH, focusing on the most recent advances. We also highlight hormone-based therapeutic approaches for treatment of NASH.

Non-alcoholic fatty liver disease (NAFLD) models in drug discovery

INTRODUCTION

The progressive disease spectrum of non-alcoholic fatty liver disease (NAFLD), which includes non-alcoholic steatohepatitis (NASH), is a rapidly emerging public health crisis with no approved therapy. The diversity of various therapies under development highlights the lack of consensus around the most effective target, underscoring the need for better translatable preclinical models to study the complex progressive disease and effective therapies. Areas covered: This article reviews published literature of various mouse models of NASH used in preclinical studies, as well as complex organotypic in vitro and ex vivo liver models being developed. It discusses translational challenges associated with both kinds of models, and describes some of the studies that validate their application in NAFLD. Expert opinion: Animal models offer advantages of understanding drug distribution and effects in a whole body context, but are limited by important species differences. Human organotypic in vitro and ex vivo models with physiological relevance and translatability need to be used in a tiered manner with simpler screens. Leveraging newer technologies, like metabolomics, proteomics, and transcriptomics, and the future development of validated disease biomarkers will allow us to fully utilize the value of these models to understand disease and evaluate novel drugs in isolation or combination.

Novel GLP-1 Analog Supaglutide Reduces HFD-Induced Obesity Associated with Increased Ucp-1 in White Adipose Tissue in Mice

GLP-1, an important incretin hormone plays an important role in the regulation of glucose homeostasis. However, the therapeutic use of native GLP-1 is limited due to its short half-life. We recently developed a novel GLP-1 mimetics (supaglutide) by genetically engineering recombinant fusion protein production techniques. We demonstrated that this formulation possessed long-lasting GLP-1 actions and was effective in glycemic control in both type 1 and type 2 diabetes rodent models. Here, we investigated the effects of supaglutide in regulating energy homeostasis in obese mice. Mice were fed with high-fat diet (HFD) for 6 months to induce obesity and then subjected to supaglutide treatment (300 μg/kg, bi-weekly for 4 weeks), and placebo as control. Metabolic conditions were monitored and energy expenditure was assessed by indirect calorimetry (CLAMS). Cold tolerance test was performed to evaluate brown-adipose tissue (BAT) activities in response to cold challenge. Glucose tolerance and insulin resistance were evaluated by intraperitoneal glucose tolerance test and insulin tolerance tests. Liver and adipose tissues were collected for histology analysis. Expression of uncoupling protein 1(Ucp1) in adipose tissues was evaluated by Western blotting. We found that supaglutide treatment reduced body weight, which was associated with reduced food intake. Compared to the placebo control, supaglutide treatment improved lipid profile, i.e., significantly decreased circulating total cholesterol levels, declined serum triglyceride, and free fatty acid levels. Importantly, the intervention significantly reduced fatty liver, decreased liver triglyceride content, and concomitantly ameliorated liver injury exemplified by declined hepatic alanine aminotransferase (ALT) and aspartic transaminase (AST) content. Remarkably, supaglutide reduced hepatic lipid accumulation and altered morphometry in favor of small adipocytes in fat. This is consistent with the observation that supaglutide increased tolerance of the mice to cold environment associated with up-regulation of Ucp1 in the inguinal fat. Furthermore, supaglutide improved glucose tolerance, and insulin sensitivity in the obese mice suggesting improved glucose and energy homeostasis. Our findings suggest that supaglutide exerts beneficial effect on established obesity through reducing energy intake and is associated with brown remodeling of white adipose tissue.

The role of bile acids in nonalcoholic fatty liver disease and nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease is growing in prevalence worldwide. It is marked by the presence of macrosteatosis on liver histology but is often clinically asymptomatic. However, it can progress into nonalcoholic steatohepatitis which is a more severe form of liver disease characterized by inflammation and fibrosis. Further progression leads to cirrhosis, which predisposes patients to hepatocellular carcinoma or liver failure. The mechanism by which simple steatosis progresses to steatohepatitis is not entirely clear. However, multiple pathways have been proposed. A common link amongst many of these pathways is disruption of the homeostasis of bile acids. Other than aiding in the absorption of lipids and lipid-soluble vitamins, bile acids act as ligands. For example, they bind to farnesoid X receptor, which is critically involved in many of the pathways responsible for maintaining bile acid, glucose, and lipid homeostasis. Alterations to these pathways can lead to dysregulation of energy balance and increased inflammation and fibrosis. Repeated insults over time may be the key to development of steatohepatitis. For this reason, current drug therapies target aspects of these pathways to try to reduce and halt inflammation and fibrosis. This review will focus on the role of bile acids in these various pathways and how changes in these pathways may result in steatohepatitis. While there is no approved pharmaceutical treatment for either hepatic steatosis or steatohepatitis, this review will also touch upon the multitude of potential therapies.

Role of FXR in Liver Inflammation during Nonalcoholic Steatohepatitis

PURPOSE OF REVIEW

About 15-25% of patients with simple steatosis of non-alcoholic fatty liver disease progresses to non-alcoholic steatohepatitis (NASH), and the underlying mechanism for this progression has not been elucidated. NASH ultimately could progress to cirrhosis, an irreversible condition.

RECENT FINDINGS

Farnesoid X receptor (FXR) has been studied for its role in modulating inflammation, and the expression of FXR is down-regulated during NASH development. FXR deficiency has shown to progress and exacerbate NASH development, and FXR activation has been protective against liver inflammation associated with NASH. The expression of factors in both the adaptive and innate immune response in the liver are regulated in a FXR-dependent and -independent manner.

SUMMARY

Therefore, understanding key signaling pathways of liver inflammation in NASH is important to determine essential components that predispose, progress, or exacerbate NASH. FXR has been identified as a therapeutic target for NASH to prevent liver inflammation.