Adaptive immune responses triggered by oxidative stress contribute to hepatic inflammation in NASH

Crucial role of T cells in NAFLD-related disease: A review and prospect

Nonalcoholic fatty liver disease (NAFLD) includes a series of hepatic manifestations, starting with liver steatosis and potentially evolving towards nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis or even hepatocellular carcinoma (HCC). Its incidence is increasing worldwide. Several factors including metabolic dysfunction, oxidative stress, lipotoxicity contribute to the liver inflammation. Several immune cell-mediated inflammatory processes are involved in NAFLD in which T cells play a crucial part in the progression of the disease. In this review, we focus on the role of different subsets of both conventional and unconventional T cells in pathogenesis of NAFLD. Factors regarding inflammation and potential therapeutic approaches targeting immune cells in NASH are also discussed.

Immune cell profile and immune-related gene expression of obese peripheral blood and liver tissue

Obesity is associated with changes in immune cell subpopulations. However, tissue and blood obesity-responsive immune phenotypic pathways have not been contrasted. Here, the local niche immune cell population and gene expression in fatty liver is compared to peripheral blood of obese individuals. The Cibersort algorithm enumerated increased fractions of memory CD4+ T lymphocytes and reductions in natural killer and memory B cells in obese liver tissue and obese blood, with similar reductions found in nonalcoholic fatty liver disease tissue. Gene expression analysis identified inflammatory immune signatures of regulatory CD4+ T cells with inferred Th1, Th17, Th2, or Treg phenotypes that differed between liver and blood. Our study suggests that the local tissue-specific immune phenotype in the liver differs from the obese peripheral circulation, with the latter reflective of multisystemic persistent inflammation that is characteristic of obesity.

Damage associated molecular patterns in necrotic femoral head inhibit osteogenesis and promote fibrogenesis of mesenchymal stem cells

In Legg-Calvé-Perthes disease (LCPD), a loss of blood supply to the juvenile femoral head leads to extensive cell death and release of damage-associated molecular patterns (DAMPs). Over time chronic inflammatory repair process is observed with impaired bone regeneration. Increased fibrous tissue and adipose tissue are seen in the marrow space with decreased osteogenesis in a piglet model of LCPD, suggesting inhibition of osteoblastic differentiation and stimulation of fibroblastic and adipogenic differentiation of mesenchymal stem cell (MSC) during the healing process. Little is known about the DAMPs present in the necrotic femoral head and their effects on MSC differentiation. The purpose of this study was to characterize the DAMPs present in the femoral head following ischemic osteonecrosis and to determine their effects on MSC differentiation. Necrotic femoral heads were flushed with saline at 48 h, 2 weeks and 4 weeks following the induction of ischemic osteonecrosis in piglets to obtain necrotic bone fluid (NBF). Western blot analysis of the NBF revealed the presence of prototypic DAMP, high mobility group box 1 (HMGB1), and other previously described DAMPs: biglycan, 4-hydroxynonenal (4-HNE), and receptor activator of NF-κB ligand (RANKL). ELISA of the NBF revealed increasing levels of inflammatory cytokines IL1β, IL6 and TNFα with the temporal progression of osteonecrosis. To determine the effects of NBF on MSC differentiation, we cultured primary porcine MSCs with NBF obtained by in vivo necrotic bone flushing method. NBF inhibited osteoblastic differentiation of MSCs with significantly decreased OSX expression (p = 0.008) and Von Kossa/Alizarin Red staining for mineralization. NBF also significantly increased the expression of proliferation markers Ki67 (p = 0.03) and PCNA (p < 0.0001), and fibrogenic markers Vimentin (p = 0.02) and Fibronectin (p = 0.04). Additionally, NBF treated MSC cells showed significantly elevated RANKL/OPG secretion ratio (p = 0.003) and increased expression of inflammatory cytokines IL1β (p = 0.006) and IL6 (p < 0.0001). To specifically assess the role of DAMPs in promoting the fibrogenesis, we treated porcine fibroblasts with artificial NBF produced by bone freeze-thaw method. We found increased fibroblastic cell proliferation in an NBF dose-dependent manner. Lastly, we studied the effect of HMGB1, a prototypic DAMP, and found that HMGB1 partially contributes to MSC proliferation and fibrogenesis. In summary, our findings show that DAMPs and the inflammatory cytokines present in the necrotic femoral head inhibit osteogenesis and promote fibrogenesis of MSCs, potentially contributing to impaired bone regeneration following ischemic osteonecrosis as observed in LCPD.

Differential iNKT and T Cells Activation in Non-Alcoholic Fatty Liver Disease and Drug-Induced Liver Injury

Background: Non-alcoholic fatty liver disease (NAFLD) and idiosyncratic drug-induced liver injury (DILI) could share molecular mechanisms involving the immune system. We aimed to identify activation immunological biomarkers in invariant natural killer T (iNKT) and CD4/CD8+ T cells in NAFLD and DILI. Methods: We analyzed the activation profile (CD69, CD25, and HLA-DR) and natural killer group 2 member D (NKG2D) on iNKT cells, and CD4/CD8 T cells in peripheral blood mononuclear cells from NAFLD, with or without significant liver fibrosis, and DILI patients. Results: There was an increase in iNKT cells in NAFLD patients compared to DILI or control subjects. Regarding the cellular activation profile, NAFLD with significant liver fibrosis (F ≥ 2) displayed higher levels of CD69+iNKT cells compared to NAFLD with none or mild liver fibrosis (F ≤ 1) and control patients. CD69+iNKT positively correlated with insulin resistance, aspartate aminotransferase (AST) level, liver fibrosis-4 index (FIB4) and AST to Platelet Ratio Index (APRI). DILI patients showed an increase in CD69+ and HLA-DR+ in both CD4+ and CD8+ T cells, detecting the most relevant difference in the case of CD69+CD8+ T cells. Conclusions: CD69+iNKT may be a biomarker to assess liver fibrosis progression in NAFLD. CD69+CD8+ T cells were identified as a potential distinctive biomarker for distinguishing DILI from NAFLD.

Inflammation and Fibrogenesis in MAFLD: Role of the Hepatic Immune System

Metabolic (dysfunction)-associated fatty liver disease (MAFLD) is the definition recently proposed to better circumscribe the spectrum of conditions long known as non-alcoholic fatty liver disease (NAFLD) that range from simple steatosis without inflammation to more advanced liver diseases. The progression of MAFLD, as well as other chronic liver diseases, toward cirrhosis, is driven by hepatic inflammation and fibrogenesis. The latter, result of a "chronic wound healing reaction," is a dynamic process, and the understanding of its underlying pathophysiological events has increased in recent years. Fibrosis progresses in a microenvironment where it takes part an interplay between fibrogenic cells and many other elements, including some cells of the immune system with an underexplored or still unclear role in liver diseases. Some therapeutic approaches, also acting on the immune system, have been probed over time to evaluate their ability to improve inflammation and fibrosis in NAFLD, but to date no drug has been approved to treat this condition. In this review, we will focus on the contribution of the liver immune system in the progression of NAFLD, and on therapies under study that aim to counter the immune substrate of the disease.

CC chemokine ligand 3 deficiency ameliorates diet-induced steatohepatitis by regulating liver macrophage recruitment and M1/M2 status in mice

BACKGROUND AND AIMS

The global prevalence of nonalcoholic fatty liver disease (NAFLD) is increasing. Chemokines and their receptors have potential as therapeutic targets of NAFLD. We investigated the role of CC chemokine ligand 3 (CCL3) in the development of murine and human NAFLD.

METHODS

CCL3-knockout mice (CCL3^-/-) and littermate CCL3 wild-type control mice (WT) were fed a high-cholesterol and high-fat (CL) diet for 16 weeks to induce NAFLD. We investigated the impact of CCL3 gene deletion in bone marrow cells and leptin-deficient ob/ob mice on CL diet-induced steatohepatitis. We assayed the serum CCL3 levels in 36 patients with biopsy-proven NAFLD and nine healthy control subjects.

RESULTS

Compared with normal chow (NC), the CL diet induced steatohepatitis and hepatic fibrosis and elevated the plasma CCL3 level. In the liver, CCL3 protein colocalized with F4/80⁺ macrophages, especially CD11c⁺ M1-like macrophages, rather than other cell types. CCL3^-/- attenuated CL diet-induced steatohepatitis and fibrosis associated with M2-dominant liver macrophages compared with the WT. The reconstitution of bone marrow (BM) cells from CCL3^-/- attenuated steatohepatitis in WT mice fed a CL diet. Furthermore, crossing CCL3^-/- onto the ob/ob background prevented CL diet-induced NAFLD in ob/ob mice, which was associated with a lesser inflammatory phenotype of liver macrophages. Also, the serum and hepatic levels of CCL3 were significantly increased in patients with non-alcoholic steatohepatitis (NASH) compared to those with simple fatty liver (NAFL) and healthy subjects.

CONCLUSION

Our data indicate that CCL3 facilitates macrophage infiltration into the liver and M1 polarization in the progression of steatohepatitis and highlight the need for further studies to determine the effect of CCL3-CCR1 and -CCR5 signaling blockade on the treatment of NAFLD.

Immunoglobulin G in non-alcoholic steatohepatitis predicts clinical outcome: A prospective multi-centre cohort study

BACKGROUND

Autoimmune markers including plasma cells (PC), anti-smooth-muscle antibody (ASMA), anti-nuclear antibody (ANA), and raised immunoglobulin G (IgG) are commonly observed in non-alcoholic steatohepatitis (NASH), however their clinical significance is unknown.

AIM

To determine if autoimmune markers in NASH patients are independently associated with poorer clinical outcomes.

METHODS

Consecutive patients with biopsy proven NASH from Christchurch Hospital, New Zealand and Singapore General Hospital (SGH) were included between 2005 to 2016 in a prospective multi-centre cohort study. Patients with other causes of chronic liver disease were excluded. IgG > 14 g/L or globulin fraction > 50%, ANA ≥ 1:40, SMA ≥ 1:40 were considered positive. Multivariate analysis was performed to assess which markers were independently associated with mortality and hepatic decompensation.

RESULTS

Total 261 patients were included of which 201 were from SGH. The median age was 53 and 51.9% were male. Advanced fibrosis was present in 31.4% at diagnosis. PC, ASMA, ANA and raised IgG were observed in 13.1%, 4.9%, 27.8% and 30.1% of patients respectively. After multivariate analysis, elevated IgG [Hazard Ratio (HR) 6.79, 95%CI: 2.93-17.15] and fibrosis stage (HR 1.37, 95%CI: 1.03-1.87) were found to be independently associated with increased risk of liver decompensation. Age (HR 1.06, 95%CI: 1.02-1.10) and elevated IgG (HR 3.79, 95%CI: 1.90-7.68) were independent factors associated with higher mortality risk.

CONCLUSION

Elevated IgG, rather than ANA, ASMA or plasma cells, is independently associated with increased risk of hepatic decompensation and mortality in NASH. It could hence be important for prognostication.

Danshensu derivative ADTM ameliorates CCl4‑induced acute liver injury in mice through inhibiting oxidative stress and apoptosis

Previous studies reported a novel danshensu derivative (R)-(3,5,6-Trimethylpyrazinyl) methyl-2-acetoxy-3-(3,4-diacetoxyphenyl) propanoate (ADTM), which conferred cardioprotective, neuroprotective and anti-thrombotic effects. Here we aim to investigate the hepatoprotective effect of ADTM on acute liver injury caused by carbon tetrachloride (CCl₄) and the underlying molecular mechanisms. ADTM (30 and 60 mg/kg) was given to mice by gavage for two weeks. At the last day mice were injected with 0.3% CCl₄, 10 mL/kg, ip for 24 h. Clinical and histological chemistry assays were performed to assess liver injury. Moreover, hepatic oxidative stress and apoptosis related markers were determined by western blotting. As a result, ADTM significantly protected against CCl₄-induced liver injury by the decrease of elevated serum transaminases and liver index, and the attenuation of histopathological changes in mice. In addition, ADTM remarkably alleviated hepatic oxidative stress (MDA contents and SOD activity) and apoptosis. Further studies revealed that ADTM significantly inhibited the CCl₄-induced upregulation of Bax/Bcl-2, increased the CCl₄-induced decrease of AKT phosphorylation and inhibited the expression level of NF-κB p65 in CCl₄-intoxicated mice. These findings suggest that ADTM possesses the potential protective effects against CCl₄-induced liver injury in mice by exerting antioxidative stress and antiapoptosis.

The Emerging Role of B Cells in the Pathogenesis of NAFLD

NAFLD is one of the leading causes of abnormal liver function worldwide. NAFLD refers to a group of liver conditions ranging from nonalcoholic fatty liver to NASH, which involves inflammation, hepatocellular damage, and fibrosis. Triggering of inflammation in NASH is a key event in the progression of the disease, and identifying the factors that initiate or dysregulate this process is needed to develop strategies for its prevention or treatment. B cells have been implicated in several autoimmune and inflammatory diseases. However, their role in the pathogenesis of NAFLD and NASH is less clear. This review discusses the emerging evidence implicating intrahepatic B cells in the progression of NAFLD. We highlight the potential mechanisms of B-cell activation during NAFLD, such as increased hepatic expression of B-cell-activating factor, augmented oxidative stress, and translocation of gut-derived microbial products. We discuss the possible effector functions by which B cells promote NAFLD, including the production of proinflammatory cytokines and regulation of intrahepatic T cells and macrophages. Finally, we highlight the role of regulatory and IgA⁺ B cells in the pathogenesis of NASH-associated HCC. In this review, we make the case that future research is needed to investigate the potential of B-cell-targeting strategies for the treatment of NAFLD.

Are Serum Levels of Nuclear Factor Kappa B and Forkhead Box Protein P3 in Patients with Non-Alcoholic Fatty Liver Disease Related to Severity of Fibrosis?

BACKGROUND Inflammation has a significant impact on the development and progression of fatty liver diseases.In this study, we aimed to investigate the relation between serum levels of nuclear factor kappa B (NFkB) and Forkhead box protein P3 (FOXP3)with fibrosis severity among patients with non-alcoholic fatty liver disease(NAFLD). METHODS In a prospective study, the patients suspicios of havingfatty liver were enrolled. The exclusion criteria lack of viral hepatitis, autoimmune hepatitis, Wilson's or other known liver diseases,history of liver or biliary surgery,bariatric surgery, and medications that influence liver metabolism. The participantsunderwent liver fibroscan. According to liver fibrosis, the patients weredivided into two groups; 1)fibrosis less than 7.2 KP,2)advanced NAFLD, fibrosis ≥7.3 KP. A10 cc fasting blood sample was taken from each patient for laboratory assessments.The variables between the two groups were compared using Chi-square or Fisher's exact test.The independence of cytokines was assessed by a logistic regression test. RESULTS Totally 90 patients were enrolled.The mean age was 42.21 ± 11 years. Of them, 50 and 47 participants were allocated to groups 1 and 2, respectively. In the univariate analysis, we revealed asignificant difference between age, body mass index (BMI), fasting blood glucose, liver enzymes, total cholesterol, andtriglyceride levels. Also, there was a significant difference betweenthe levels of NFKB and FOXP3 in group one compared with group two of the participants,as FOXP3(9.17 ± 10.0 vs. 18.63 ± 12.9; p < 0.001) and NFKB (1.70 ± 1.70; p < 0.01). After excluding the confounding factors, we observed a significant association between fibrosis level and cytokine levels in logistic regression. CONCLUSION Serum levels of NFKB and FOXP3 increased by advancing liver fibrosis in patients with NAFLD.This is an independent association. The identification of intermediary regulatory factors would be necessary.

Zinc and Selenium in Inflammatory Bowel Disease: Trace Elements with Key Roles?

Inflammatory bowel disease (IBD) is a chronic inflammatory condition that may emerge at a young age and often lasts for life. It often goes through phases of recurrence and remission and has a devastating effect on quality of life. The exact etiology of the disease is still unclear, but it appears that an inappropriate immune response to intestinal flora bacteria in people with a genetic predisposition may cause the disease. Managing inflammatory bowel disease is still a serious challenge. Oxidative stress and free radicals appear to be involved in the pathogenesis of this disease, and a number of studies have suggested the use of antioxidants as a therapeutic approach. The antioxidant and anti-inflammatory properties of some trace elements have led some of the research to focus on studying these trace elements in inflammatory bowel disease. Zinc and selenium are among the most important trace elements that have significant anti-inflammatory and antioxidant properties. Some studies have shown the importance of these trace elements in inflammatory bowel disease. In this review, we have attempted to provide a comprehensive overview of the findings of these studies and to gather current knowledge about the association of these trace elements with the inflammatory process and inflammatory bowel disease.

The immunological and metabolic landscape in primary and metastatic liver cancer

The liver is the sixth most common site of primary cancer in humans, and generally arises in a background of cirrhosis and inflammation. Moreover, the liver is frequently colonized by metastases from cancers of other organs (particularly the colon) because of its anatomical location and organization, as well as its unique metabolic and immunosuppressive environment. In this Review, we discuss how the hepatic microenvironment adapts to pathologies characterized by chronic inflammation and metabolic alterations. We illustrate how these immunological or metabolic changes alter immunosurveillance and thus hinder or promote the development of primary liver cancer. In addition, we describe how inflammatory and metabolic niches affect the spreading of cancer metastases into or within the liver. Finally, we review the current therapeutic options in this context and the resulting challenges that must be surmounted.

Pathophysiological communication between hepatocytes and non-parenchymal cells in liver injury from NAFLD to liver fibrosis

Non-alcoholic fatty liver disease (NAFLD) is a multifactorial disease that encompasses a spectrum of pathological conditions, ranging from simple steatosis (NAFL), nonalcoholic steatohepatitis (NASH), fibrosis/cirrhosis which can further progress to hepatocellular carcinoma and liver failure. The progression of NAFL to NASH and liver fibrosis is closely associated with a series of liver injury resulting from lipotoxicity, oxidative stress, redox imbalance (excessive nitric oxide), ER stress, inflammation and apoptosis that occur sequentially in different liver cells which ultimately leads to the activation of liver regeneration and fibrogenesis, augmenting collagen and extracellular matrix deposition and promoting liver fibrosis and cirrhosis. Type 2 diabetes is a significant risk factor in NAFLD development by accelerating liver damage. Here, we overview recent findings from human study and animal models on the pathophysiological communication among hepatocytes (HCs), Kupffer cells (KCs), hepatic stellate cells (HSCs) and liver sinusoidal endothelial cells (LSECs) during the disease development. The mechanisms of crucial signaling pathways, including Toll-like receptor, TGFβ and hedgehog mediated hepatic injury are also discussed. We further highlight the potentials of precisely targeting hepatic individual cell-type using nanotechnology as therapeutic strategy for the treatment of NASH and liver fibrosis.

Functional heterogeneity of CD4+ T cells in liver inflammation

CD4⁺ T cells play an essential role in orchestrating adequate immunity, but their overactivity has been associated with the development of immune-mediated inflammatory diseases, including liver inflammatory diseases. These cells can be subclassified according to their maturation stage, cytokine profile, and pro or anti-inflammatory functions, i.e., functional heterogeneity. In this review, we summarize what has been discovered so far regarding the role of the different CD4⁺ T cell polarization states in the progression of two prominent and still different liver inflammatory diseases: non-alcoholic steatohepatitis (NASH) and autoimmune hepatitis (AIH). Finally, the potential of CD4⁺ T cells as a therapeutic target in both NASH and AIH is discussed.

Long Non-Coding RNAs Involved in Progression of Non-Alcoholic Fatty Liver Disease to Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease and is characterized by different stages varying from benign fat accumulation to non-alcoholic steatohepatitis (NASH) that may progress to cirrhosis and liver cancer. In recent years, a regulatory role of long non-coding RNAs (lncRNAs) in NAFLD has emerged. Therefore, we aimed to characterize the still poorly understood lncRNA contribution to disease progression. Transcriptome analysis in 60 human liver samples with various degrees of NAFLD/NASH was combined with a functional genomics experiment in an in vitro model where we exposed HepG2 cells to free fatty acids (FFA) to induce steatosis, then stimulated them with tumor necrosis factor alpha (TNFα) to mimic inflammation. Bioinformatics analyses provided a functional prediction of novel lncRNAs. We further functionally characterized the involvement of one novel lncRNA in the nuclear-factor-kappa B (NF-κB) signaling pathway by its silencing in Hepatoma G2 (HepG2) cells. We identified 730 protein-coding genes and 18 lncRNAs that responded to FFA/TNFα and associated with human NASH phenotypes with consistent effect direction, with most being linked to inflammation. One novel intergenic lncRNA, designated lncTNF, was 20-fold up-regulated upon TNFα stimulation in HepG2 cells and positively correlated with lobular inflammation in human liver samples. Silencing lncTNF in HepG2 cells reduced NF-κB activity and suppressed expression of the NF-κB target genes A20 and NFKBIA. The lncTNF we identified in the NF-κB signaling pathway may represent a novel target for controlling liver inflammation.

Exposure to Plasma From Non-alcoholic Fatty Liver Disease Patients Affects Hepatocyte Viability, Generates Mitochondrial Dysfunction, and Modulates Pathways Involved in Fat Accumulation and Inflammation

Changes of lipidic storage, oxidative stress and mitochondrial dysfunction may be involved in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Although the knowledge of intracellular pathways has vastly expanded in recent years, the role and mechanisms of circulating triggering factor(s) are debated. Thus, we tested the hypothesis that factors circulating in the blood of NAFLD patients may influence processes underlying the disease. Huh7.5 cells/primary human hepatocytes were exposed to plasma from 12 NAFLD patients and 12 healthy subjects and specific assays were performed to examine viability, H₂O₂ and mitochondrial reactive oxygen species (ROS) release, mitochondrial membrane potential and triglycerides content. The involvement of NLRP3 inflammasome and of signaling related to peroxisome-proliferator-activating-ligand-receptor-γ (PPARγ), sterol-regulatory-element-binding-protein-1c (SREBP-1c), nuclear-factor-kappa-light-chain-enhancer of activated B cells (NF-kB), and NADPH oxidase 2 (NOX2) was evaluated by repeating the experiments in the presence of NLRP3 inflammasome blocker, MCC950, and through Western blot. The results obtained shown that plasma of NAFLD patients was able to reduce cell viability and mitochondrial membrane potential by about 48 and 24% (p < 0.05), and to increase H₂O₂, mitochondrial ROS, and triglycerides content by about 42, 19, and 16% (p < 0.05), respectively. An increased expression of SREBP-1c, PPARγ, NF-kB and NOX2 of about 51, 121, 63, and 46%, respectively, was observed (p < 0.05), as well. Those effects were reduced by the use of MCC950. Thus, in hepatocytes, exposure to plasma from NAFLD patients induces a NAFLD-like phenotype by interference with NLRP3-inflammasome pathways and the activation of intracellular signaling related to SREBP-1c, PPARγ, NF-kB and NOX2.

The Role of Oxidative Stress in NAFLD-NASH-HCC Transition-Focus on NADPH Oxidases

A peculiar role for oxidative stress in non-alcoholic fatty liver disease (NAFLD) and its transition to the inflammatory complication non-alcoholic steatohepatitis (NASH), as well as in its threatening evolution to hepatocellular carcinoma (HCC), is supported by numerous experimental and clinical studies. NADPH oxidases (NOXs) are enzymes producing reactive oxygen species (ROS), whose abundance in liver cells is closely related to inflammation and immune responses. Here, we reviewed recent findings regarding this topic, focusing on the role of NOXs in the different stages of fatty liver disease and describing the current knowledge about their mechanisms of action. We conclude that, although there is a consensus that NOX-produced ROS are toxic in non-neoplastic conditions due to their role in the inflammatory vicious cycle sustaining the transition of NAFLD to NASH, their effect is controversial in the neoplastic transition towards HCC. In this regard, there are indications of a differential effect of NOX isoforms, since NOX1 and NOX2 play a detrimental role, whereas increased NOX4 expression appears to be correlated with better HCC prognosis in some studies. Further studies are needed to fully unravel the mechanisms of action of NOXs and their relationships with the signaling pathways modulating steatosis and liver cancer development.

Nutrigenomics and Nutrigenetics in Metabolic- (Dysfunction) Associated Fatty Liver Disease: Novel Insights and Future Perspectives

Metabolic- (dysfunction) associated fatty liver disease (MAFLD) represents the predominant hepatopathy and one of the most important systemic, metabolic-related disorders all over the world associated with severe medical and socio-economic repercussions due to its growing prevalence, clinical course (steatohepatitis and/or hepatocellular-carcinoma), and related extra-hepatic comorbidities. To date, no specific medications for the treatment of this condition exist, and the most valid recommendation for patients remains lifestyle change. MAFLD has been associated with metabolic syndrome; its development and progression are widely influenced by the interplay between genetic, environmental, and nutritional factors. Nutrigenetics and nutrigenomics findings suggest nutrition’s capability, by acting on the individual genetic background and modifying the specific epigenetic expression as well, to influence patients’ clinical outcome. Besides, immunity response is emerging as pivotal in this multifactorial scenario, suggesting the interaction between diet, genetics, and immunity as another tangled network that needs to be explored. The present review describes the genetic background contribution to MAFLD onset and worsening, its possibility to be influenced by nutritional habits, and the interplay between nutrients and immunity as one of the most promising research fields of the future in this context.

The Impact of the NLRP3 Pathway in the Pathogenesis of Non-Alcoholic Fatty Liver Disease and Alcohol-Related Liver Disease

The presence of hepatic steatosis and inflammation is increasingly associated with both metabolic and alcohol-related liver conditions. Both are on the increase globally and, apart from liver transplantation, there are no licensed therapies that target the full complement of disease features. The presence of some shared pathogenic mechanisms and histological features in NAFLD and ALD suggests that it may be possible to develop markers for prognostication or staging, or indeed new therapeutic tools to treat both conditions. One such example of an approach exists in the form of the NACHT-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome pathway. Activation of the NLRP3 inflammasome results in hepatocyte pyroptosis, persistence, and amplification of liver inflammation and activation of profibrogenic signaling cascades. Thus, targeting elements of the pathway in NAFLD and ALD may provide a tractable route to pharmacological therapy. In this review, we summarize the contribution of this inflammasome to disease and review the current options for therapy.

Lingonberry Improves Non-Alcoholic Fatty Liver Disease by Reducing Hepatic Lipid Accumulation, Oxidative Stress and Inflammatory Response

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease globally and there is a pressing need for effective treatment. Lipotoxicity and oxidative stress are the important mediators in NAFLD pathogenesis. Lingonberry (Vaccinium vitis-idaea L.) is rich in anthocyanins that have antioxidant and anti-inflammatory properties. The present study investigated the effect of lingonberry supplementation on liver injury in C57BL/6J male mice fed a high-fat diet (HFD) for 12 weeks. Mice fed HFD displayed liver injury with steatosis, increased lipid peroxidation and inflammatory cytokine expression in the liver as compared to mice fed a control diet. Lingonberry supplementation for 12 weeks alleviated HFD-induced liver injury, attenuated hepatic lipid accumulation, and inflammatory cytokine expression. Lingonberry supplementation inhibited the expression of sterol regulatory element-binding protein-1c (SREBP-1c) and acetyl-CoA carboxylase-1 (AAC-1) as well as activated AMP-activated protein kinase (AMPK) in the liver. It also decreased HFD-induced hepatic oxidative stress and aggregation of inflammatory foci. This was associated with a restoration of nuclear factor erythroid 2-related factor 2 (Nrf2) and glutathione level in the liver. These results suggest that lingonberry supplementation can protect against HFD-induced liver injury partly through attenuation of hepatic lipid accumulation, oxidative stress, and inflammatory response.

Systemic and adipose tissue inflammation in NASH: correlations with histopathological aspects

INTRODUCTION

Non-alcoholic steatohepatitis (NASH) is a progressive form of liver steatosis that involves a risk of progression towards fibrosis, cirrhosis, and end-stage liver disease. Low-grade inflammation is recognized to be involved in non-alcoholic fatty liver disease (NAFLD) pathogeny. Additionally, adipose tissue dysfunction plays an important role in the development of metabolic diseases.

PATIENTS, MATERIALS AND METHODS

We conducted a study on 68 patients with liver steatosis confirmed through liver biopsy during the surgery. In all the patients, we recorded anthropometric parameters and we performed blood tests for systemic inflammation [high-sensitivity C-reactive protein (hs-CRP), fibrinogen] and serum adipokines related to adipose tissue inflammation (leptin, adiponectin). Additional to histopathological examination, we also performed the immunohistochemical study of inflammatory mononuclear cells.

RESULTS

The 68 patients had a mean age of 56.57±4.94 years old, had a mean value of hs-CRP of 2.30±0.91 mg∕L, a mean value of leptin of 14.02±17.02 ng∕mL and a mean value of adiponectin of 7.54±0.38 mg∕L. In all the cases studied by liver biopsy, the steatosis exceeded 5% of hepatocytes, but the frequency of NASH was 26.47%. Cluster of differentiation (CD)45-positive, CD4-positive, and CD8-positive T-lymphocytes predominated in the studied cases. We obtained a statistically significant high association between definite NASH and the values of hs-CRP, serum adiponectin and leptin∕adiponectin ratio (p<0.0001).

CONCLUSIONS

Systemic and adipose tissue inflammation was statistically significant associated with histological lesions of steatosis and NASH, suggesting that the determination of hs-CRP and serum adipokines in dynamics in patients with NAFLD is predictive for the progression of the disease.

Innate and Adaptive Immunity Alterations in Metabolic Associated Fatty Liver Disease and Its Implication in COVID-19 Severity

The coronavirus infectious disease 2019 (COVID-19) pandemic has hit the world, affecting health, medical care, economies and our society as a whole. Furthermore, COVID-19 pandemic joins the increasing prevalence of metabolic syndrome in western countries. Patients suffering from obesity, type II diabetes mellitus, cardiac involvement and metabolic associated fatty liver disease (MAFLD) have enhanced risk of suffering severe COVID-19 and mortality. Importantly, up to 25% of the population in western countries is susceptible of suffering from both MAFLD and COVID-19, while none approved treatment is currently available for any of them. Moreover, it is well known that exacerbated innate immune responses are key in the development of the most severe stages of MAFLD and COVID-19. In this review, we focus on the role of the immune system in the establishment and progression of MAFLD and discuss its potential implication in the development of severe COVID-19 in MAFLD patients. As a result, we hope to clarify their common pathology, but also uncover new potential therapeutic targets and prognostic biomarkers for further research.

Prolyl endopeptidase disruption reduces hepatic inflammation and oxidative stress in methionine-choline-deficient diet-induced steatohepatitis

AIMS

Prolyl endopeptidase (PREP) is a serine endopeptidase widely distributed in the body, and accumulated evidence suggests that PREP participates in inflammation and oxidative stress. Here, we explored the effect of PREP gene disruption on hepatic inflammation and oxidative stress status in a methionine-choline-deficient (MCD)-induced nonalcoholic steatohepatitis (NASH) model.

MAIN METHODS

PREP gene disruption (PREP^gt) mice and wild-type (WT) littermates were placed on a control or an MCD diet for 4 weeks, respectively. The liver histopathological analysis and the number of inflammatory cells were determined by hematoxylin-eosin (HE) and immunohistochemical staining. Inflammation-associated genes and cytokine levels in liver tissue were evaluated by quantitative PCR and ELISA. The levels of P53, Sesn2, Nrf2, HO-1, and oxidative stress indicators in mice and the palmitic acid (PA)-treated human hepatocellular carcinoma cells (HepG2) were examined by immunoblotting and commercially available kits, respectively.

KEY FINDINGS

We found that PREP expression was upregulated in the MCD-induced NASH model. In addition, PREP disruption alleviated MCD-induced hepatic inflammation accompanied by diminished infiltration of inflammatory cells and secretion of inflammatory mediators. More importantly, the results of this study indicate that targeting PREP can improve oxidative stress status in the liver of MCD-diet mice and PA-exposed HepG2 cells. The effect is most likely mediated by the activation of P53 and its downstream signaling pathways (Sesn2/Nrf2/HO-1).

SIGNIFICANCE

Our results showed that PREP disruption (or inhibition) could decrease oxidative stress and inflammation and improve liver function, indicating that targeting PREP might be a new potential therapeutic option for NAFLD/NASH.

Macrophages as a source of fibrosis biomarkers for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease/steatohepatitis (NAFLD/NASH) are becoming major liver diseases worldwide. Liver fibrosis and cirrhosis are among the most significant risk factors of hepatocellular carcinoma (HCC) and associated with the long-term prognosis of NAFLD patients. To stratify the risk of HCC in NAFLD patients clinically, the discovery of non-invasive fibrosis markers is needed urgently. Liver macrophages play critical roles in the regulation of inflammation and fibrosis by interacting with hepatic stellate cells (HSCs) and other immune cells. Thus, it is rational to explore feasible biomarkers for liver fibrosis by focusing on macrophage-related factors. We examined serum factors comprehensively in multiple cohorts of NAFLD/NASH patients to determine whether they were correlated with the biopsy-proven fibrosis stage. We found that the serum levels of interleukin (IL)-34, YKL-40 and soluble Siglec-7 (sSiglec7) were closely associated with liver fibrosis and served as diagnostic biomarkers in patients with NAFLD/NASH. In the NAFLD liver, IL-34 was produced by activated fibroblasts, and YKL-40 and sSiglec-7 were secreted from macrophages. The sensitivity and specificity of these markers to detect advanced liver fibrosis varied, supporting the notion that the combination of these markers with other modalities is an option for clinical application.

Aloin protects mice from diet-induced non-alcoholic steatohepatitis via activation of Nrf2/HO-1 signaling

Aloin, a naturally occurring anthraquinone glycoside derived from the Aloe species, has antioxidant and anti-inflammatory activities, but its role in non-alcoholic steatohepatitis (NASH) remains unknown. This study was designed to investigate the anti-inflammatory, antioxidant, and anti-apoptotic effects of aloin and the underlying mechanisms during NASH. Wild-type or nuclear erythroid 2-related factor 2 (Nrf2) knock-out (KO) mice were fed a choline-deficient, l-amino acid-defined, high-fat (CDAAH) diet and treated with aloin (10, 20 or 40 mg per kg bw per day) by gavage for twelve weeks. Liver and blood samples were collected to evaluate liver function, protein abundance, and histopathological status. Supplementing aloin at 20 mg kg^-1 was optimal for mitigating liver damage during NASH, as evidenced by reduced alanine transaminase and aspartate aminotransferase activity in serum. Supplementation with aloin significantly reduced serum concentration or liver protein abundance of malondialdehyde, tumor necrosis factor alpha, Interleukin (IL)-1β and IL-6. Aloin treatment enhanced hepatic superoxide dismutase activity, glutathione and serum IL-10 levels in mice with NASH. Furthermore, supplementation with aloin inhibited hepatocyte apoptosis caused by Bcl-2 up-regulation and cleaved caspase-3 and Bax down-regulation. Mechanistically, by using Nrf2 KO mice, the protective effects of aloin were associated with enhanced antioxidant, anti-inflammatory and anti-apoptotic activity, all of which were mediated by Nrf2/heme oxygenase-1 (HO-1) signaling activation. Data suggested that aloin activates the Nrf2/HO-1 pathway and has protective potential against liver injury during NASH. Therefore, aloin supplementation might contribute to the prevention and treatment of NASH via activation of the Nrf2/HO-1 pathway.

Immunity as Cornerstone of Non-Alcoholic Fatty Liver Disease: The Contribution of Oxidative Stress in the Disease Progression

Non-alcoholic fatty liver disease (NAFLD) is considered the hepatic manifestation of metabolic syndrome and has become the major cause of chronic liver disease, especially in western countries. NAFLD encompasses a wide spectrum of hepatic histological alterations, from simple steatosis to steatohepatitis and cirrhosis with a potential development of hepatocellular carcinoma. Non-alcoholic steatohepatitis (NASH) is characterized by lobular inflammation and fibrosis. Several studies reported that insulin resistance, redox unbalance, inflammation, and lipid metabolism dysregulation are involved in NAFLD progression. However, the mechanisms beyond the evolution of simple steatosis to NASH are not clearly understood yet. Recent findings suggest that different oxidized products, such as lipids, cholesterol, aldehydes and other macromolecules could drive the inflammation onset. On the other hand, new evidence indicates innate and adaptive immunity activation as the driving force in establishing liver inflammation and fibrosis. In this review, we discuss how immunity, triggered by oxidative products and promoting in turn oxidative stress in a vicious cycle, fuels NAFLD progression. Furthermore, we explored the emerging importance of immune cell metabolism in determining inflammation, describing the potential application of trained immune discoveries in the NASH pathological context.

A Mineralocorticoid Receptor Deficiency in Myeloid Cells Reduces Liver Steatosis by Impairing Activation of CD8+ T Cells in a Nonalcoholic Steatohepatitis Mouse Model

Background and Aims

The mineralocorticoid receptor (MR) and renin-angiotensin-aldosterone system (RAAS) are implicated in non-alcoholic liver fatty disease (NALFD). However, inflammatory mechanisms linking MR and RAAS with disease pathology remain unclear. Here we aimed to evaluate the contribution of myeloid MR to the inflammatory response in an animal model of non-alcoholic steatohepatitis (NASH), induced with a methionine-choline deficient diet (MCD).

Methods

Mice with a conditional deficiency of MR in myeloid cells (MyMRKO) and their counterpart floxed control mice (FC) were fed for 18 days with MCD or chow diet, respectively. Serum levels of aminotransferases and aldosterone levels were measured and hepatic steatosis, inflammation and fibrosis scored histologically. Hepatic triglyceride content (HTC) and hepatic mRNA levels of pro-inflammatory pro-fibrotic-associated genes were also assessed. Deep flow cytometric analysis was used to dissect the immune response during NASH development.

Results

MyMRKO mice fed with an MCD diet exhibited reduced hepatic inflammation and lower HTC than controls. Absolute number and percentage of liver inflammatory infiltrate cells (except for CD8⁺ T lymphocytes) were similar in both MyMRKO and control mice fed with an MCD diet but expression of the costimulatory molecule CD86 by dendritic cells and the CD25 activation marker in CD8⁺ T cells were significantly reduced in MyMRKO.

Conclusions

Proinflammatory cells are functionally suppressed in the absence of MR. We hypothesized that loss of MR in myeloid cells reduces lipid accumulation in the liver, in part through modulating the adaptive immune response, which is pivotal for the development of steatosis.

Fructose, Omega 3 Fatty Acids, and Vitamin E: Involvement in Pediatric Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is currently the most common form of liver disease in both adults and children, becoming the leading cause for liver transplant in many countries. Its prevalence has increased considerably in recent years, mainly due to the explosive increase in pediatric obesity rates. NAFLD is strongly associated with central obesity, diabetes, dyslipidemia and insulin resistance, and it has been considered as the hepatic manifestation of the metabolic syndrome. Its complex pathophysiology involves a series of metabolic, inflammatory and oxidative stress processes, among others. Given the sharp increase in the prevalence of NAFLD and the lack of an appropriate pharmacological approach, it is crucial to consider the prevention/management of the disease based on lifestyle modifications such as the adoption of a healthy nutrition pattern. Herein, we review the literature and discuss the role of three key nutrients involved in pediatric NAFLD: fructose and its participation in metabolism, Omega-3 fatty acids and its anti-inflammatory effects and vitamin E and its action on oxidative stress.

Innate lymphocytes: pathogenesis and therapeutic targets of liver diseases and cancer

The liver is a lymphoid organ with unique immunological properties, particularly, its predominant innate immune system. The balance between immune tolerance and immune activity is critical to liver physiological functions and is responsible for the sensitivity of this organ to numerous diseases, including hepatotropic virus infection, alcoholic liver disease, nonalcoholic fatty liver disease, autoimmune liver disease, and liver cancer, which are major health problems globally. In the past decade, with the discovery of liver-resident natural killer cells, the importance of innate lymphocytes with tissue residency has gradually become the focus of research. In this review, we address the current knowledge regarding hepatic innate lymphocytes with unique characteristics, including NK cells, ILC1/2/3s, NKT cells, γδ T cells, and MAIT cells, and their potential roles in liver homeostasis maintenance and the progression of liver diseases and cancer. A better understanding of the immunopathogenesis of hepatic innate lymphocytes will be helpful for proposing effective treatments for liver diseases and cancer.

Innate-adaptive immunity interplay and redox regulation in immune response

Innate and adaptive immune cell activation and infiltration is the key characteristic of tissue inflammation. The innate immune system is the front line of host defense in which innate immune cells are activated by danger signals, including pathogen- and danger-associated molecular pattern, and metabolite-associated danger signal. Innate immunity activation can directly contribute to tissue inflammation or immune resolution by phagocytosis and secretion of biologically active molecules, or indirectly via antigen-presenting cell (APC) activation-mediated adaptive immune responses. This review article describes the cellular and molecular interplay of innate-adaptive immune systems. Three major mechanisms are emphasized in this article for their role in facilitating innate-adaptive immunity interplay. 1) APC can be formed from classical and conditional innate immune cells to bridge innate-adaptive immune response. 2) Immune checkpoint molecular pairs connect innate and adaptive immune cells to direct one-way and two-way immune checkpoint reactions. 3) Metabolic reprogramming during immune responses leads to excessive cytosolic and mitochondrial reactive oxygen species (ROS) production. Increased NADPH oxidase-derived extracellular and intracellular ROS are mostly responsible for oxidative stress, which contributes to functional changes in immune cells. Further understanding of innate-adaptive immunity interplay and its underlying molecular basis would lead to the identification of therapeutic targets for immunological and inflammatory disease.

Nonalcoholic fatty liver disease and colorectal cancer: Correlation and missing links

Nonalcoholic fatty liver disease (NAFLD) is one of the major metabolic diseases that occur in almost one in every four global population, while colorectal cancer (CRC) is one of the leading causes of cancer related deaths in the world. Individuals with pre-existing NAFLD show a higher rate of developing CRC and liver metastasis, suggesting a causal relationship. Interestingly, both of these diseases are strongly associated with obesity, which is also a growing global health concern. In this current review, we will explore scientific findings that demonstrate the relationship between NAFLD, CRC and obesity, as well as the underlying mechanisms. We will also indicate the missing links and knowledge gaps that require more in-depth investigation.

Danger signals in liver injury and restoration of homeostasis

Damage-associated molecular patterns are signalling molecules involved in inflammatory responses and restoration of homeostasis. Chronic release of these molecules can also promote inflammation in the context of liver disease. Herein, we provide a comprehensive summary of the role of damage-associated molecular patterns as danger signals in liver injury. We consider the role of reactive oxygen species and reactive nitrogen species as inducers of damage-associated molecular patterns, as well as how specific damage-associated molecular patterns participate in the pathogenesis of chronic liver diseases such as alcohol-related liver disease, non-alcoholic steatohepatitis, liver fibrosis and liver cancer. In addition, we discuss the role of damage-associated molecular patterns in ischaemia reperfusion injury and liver transplantation and highlight current studies in which blockade of specific damage-associated molecular patterns has proven beneficial in humans and mice.

Interplay and roles of oxidative stress, toll-like receptor 4 and Nrf2 in trichloroethene-mediated autoimmunity

Previous studies in MRL+/+ mice suggest involvement of oxidative stress (OS) in trichloroethene (TCE)-mediated autoimmunity. However, molecular mechanisms underlying the autoimmunity remain to be fully elucidated. Even though toll-like receptors (TLRs) and Nuclear factor (erythroid-derived 2)-like2 (Nrf2) pathways are implicated in autoimmune diseases (ADs), interplay of OS, TLR and Nrf2 in TCE-mediated autoimmune response remains unexplored. This study was, therefore, undertaken to clearly establish a link among OS, TLR4 and Nrf2 pathways in TCE-induced autoimmunity. Groups of female MRL+/+ mice were treated with TCE, sulforaphane (SFN, an antioxidant) or TCE + SFN (TCE, 10 mmol/kg, i.p., every 4th day; SFN, 8 mg/kg, i.p., every other day) for 6 weeks. TCE exposure led to greater formation of serum 4-hydroxynonenal (HNE)-protein adducts, HNE-specific circulating immune complexes (CICs) and protein carbonyls which were associated with significant increases in serum antinuclear antibodies (ANAs). Moreover, incubation of splenocytes from TCE-treated mice with HNE-modified proteins resulted in enhanced splenocyte proliferation and cytokine release evidenced by increased expression of cyclin D3, Cyclin-dependent kinase 6 (CDK6) and phospho-pRb as well as increased release of IL-6, TNF-α and INF-γ. More importantly, TCE exposure resulted in increased expression of TLR4, MyD88, IRAK4, NF-kB and reduced expression of Nrf2 and HO-1 in the spleen. Remarkably, SFN supplementation not only attenuated TCE-induced OS, upregulation in TLR4 and NF-kB signaling and downregulation of Nrf2, but also ANA levels. These results, in addition to providing further support to a role of OS, also suggest that an interplay among OS, TLR4 and Nrf2 pathways contributes to TCE-mediated autoimmune response. Attenuation of TCE-mediated autoimmunity by SFN provides an avenue for preventive and/or therapeutic strategies for ADs involving OS.

CD4+ T Cells Mediate the Development of Liver Fibrosis in High Fat Diet-Induced NAFLD in Humanized Mice

Non-alcoholic fatty liver disease (NAFLD) has been on a global rise. While animal models have rendered valuable insights to the pathogenesis of NAFLD, discrepancy with patient data still exists. Since non-alcoholic steatohepatitis (NASH) involves chronic inflammation, and CD4⁺ T cell infiltration of the liver is characteristic of NASH patients, we established and characterized a humanized mouse model to identify human-specific immune response(s) associated with NAFLD progression. Immunodeficient mice engrafted with human immune cells (HIL mice) were fed with high fat and high calorie (HFHC) or chow diet for 20 weeks. Liver histology and immune profile of HIL mice were analyzed and compared with patient data. HIL mice on HFHC diet developed steatosis, inflammation and fibrosis of the liver. Human CD4⁺ central and effector memory T cells increased within the liver and in the peripheral blood of our HIL mice, accompanied by marked up-regulation of pro-inflammatory cytokines (IL-17A and IFNγ). In vivo depletion of human CD4⁺ T cells in HIL mice reduced liver inflammation and fibrosis, but not steatosis. Our results highlight CD4⁺ memory T cell subsets as important drivers of NAFLD progression from steatosis to fibrosis and provides a humanized mouse model for pre-clinical evaluation of potential therapeutics.

The role of neutrophils in innate immunity-driven nonalcoholic steatohepatitis: lessons learned and future promise

The enrichment of innate immune cells and the enhanced inflammation represent the hallmark of non-alcoholic steatohepatitis (NASH), the advanced subtype with a significantly increased risk of progression to end-stage liver diseases within the spectrum of non-alcoholic fatty liver disease. Neutrophils are traditionally recognized as key components in the innate immune system to defend against pathogens. Recently, a growing body of evidence supports neutrophils as emerging key player in mediating the transition from steatosis to NASH, which is largely inspired by the histological findings in human liver biopsy indicating the enhanced infiltration of neutrophils as one of the key histological features of NASH. In this review, we discuss data regarding histological perspectives of hepatic infiltration of neutrophils in NASH. We also highlight the pathophysiological role of neutrophils in promoting metabolic inflammation in the liver through the release of a vast array of granule proteins, the interaction with other pro-inflammatory immune cells, and the formation of neutrophil extracellular traps. Neutrophil granule proteins possess pleiotropic effects on regulating neutrophil biology and functions. A variety of granule proteins (including lipocalin-2, myeloperoxidase, proteinase 3, neutrophil elastase, etc.) produced by neutrophils enhance liver metabolic inflammation, thereby promoting NASH progression by mediating neutrophil-macrophage interaction. Therapeutically, pharmacological inhibitors targeting neutrophil granule proteins hold promise to combat NASH. In addition, this article also summarizes potentials of neutrophils and its derived various granule proteins for the accurate, even non-invasive diagnosis of NASH.

Immunological distinctions between nonalcoholic steatohepatitis and hepatocellular carcinoma

Nonalcoholic fatty liver disease (NAFLD), the most common cause of chronic liver disease, ranges from simple hepatic steatosis to nonalcoholic steatohepatitis (NASH), which is a more aggressive form characterized by hepatocyte injury, inflammation, and fibrosis. Increasing evidence suggests that NASH is a risk factor for hepatocellular carcinoma (HCC), which is the fifth most common cancer worldwide and the second most common cause of cancer-related death. Recent studies support a strong mechanistic link between the NASH microenvironment and HCC development. The liver has a large capacity to remove circulating pathogens and gut-derived microbial compounds. Thus, the liver is a central player in immunoregulation. Altered immune responses are tightly associated with the development of NASH and HCC. The objective of this study was to differentiate the roles of specific immune cell subsets in NASH and HCC pathogenesis.

Clarifying the role of specific cells in the immune system in the transition from non-alcoholic fatty liver disease (NAFLD) to liver cancer will help to understand disease progression and may open avenues towards new preventive and therapeutic strategies. NAFLD is the most common chronic liver disease. Growing evidence suggests that its most aggressive form, non-alcoholic steatohepatitis (NASH), can promote the development of liver cancer, the second most common cause of cancer deaths worldwide. Chang-Woo Lee and colleagues at Sungkyunkwan University, Suwon, South Korea review the immunological distinction between NASH and liver cancer, focusing on the levels and activities of six key types of immune system cells. Chronic inflammation mediated by the immune system can create conditions for NAFLD, NASH and liver cancer to develop and worsen.

Apoptosis-inducing factor deficient mice fail to develop hepatic steatosis under high fat high fructose diet or bile duct ligation

Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein involved in redox signalling and programmed cell death. The role of AIF has been well recognized in diabetes and obesity. However, the aspect of AIF deficiency in the development of hepatic steatosis and liver injury is unknown. Therefore, in the current study, Harlequin (Hq mutant) mouse with markedly reduced content of AIF was investigated to explore the role of AIF on the initiation of liver injury. The wild type (WT) developed physiological and pathological features of non-alcoholic fatty liver disease (NAFLD) that were not seen in the Hq mice with AIF deficiency, when fed on high fat high fructose (HFHF) diet. Following bile duct ligation (BDL), the liver associated pathological changes were less conspicuous in Hq mice as compared to WT mice. The expression of AIF protein and apoptosis was markedly lesser as compared to their respective control in Hq mice on HFHF diet. Furthermore, the genes involved in fatty acid metabolism were also altered in the group of treated Hq mice. In conclusion, Hq mice failed to develop diet induced hepatic steatosis, suggestive of a role of AIF mediated pathway in the initiation and progression of liver inflammation. Thus, partial loss of AIF appears to be hepatoprotective. SIGNIFICANCE OF THE STUDY: AIF deficiency has multiple roles in altered pathology processes and cellular metabolism, thereby compromising the cellular homeostasis. Considering the molecular functions of AIF in other organ pathology little is known about its role in diet induced liver injury. Hence, the aim of the current study was to investigate the role of AIF deficiency in liver injury and diseases with focus on NAFLD. The study will help to deliniate the mechanisms of NAFLD using Harliquin Mice.

Protective Effects of MitoTEMPO on Nonalcoholic Fatty Liver Disease via Regulating Myeloid-Derived Suppressor Cells and Inflammation in Mice

MitoTEMPO, a mitochondrial antioxidant, has protective effects on liver-related diseases. However, the role of MitoTEMPO on nonalcoholic fatty liver disease (NAFLD) and its possible mechanisms are largely unknown. Here, we investigated the effects of MitoTEMPO on NAFLD using high fat diet- (HFD-) induced obese mice as animal models. MitoTEMPO was intraperitoneally injected into HFD mice. Liver morphological changes were observed by H&E and Oil Red O staining, and the frequency of MDSCs in peripheral blood was analyzed by flow cytometry. Moreover, real-time quantitative PCR, western blot, and immunohistochemistry were conducted to detect the mRNA and protein expressions in the liver tissues. The results showed that the hepatic steatosis in liver tissues of HFD mice injected with MitoTEMPO was significantly ameliorated. Additionally, MitoTEMPO reduced the frequency of CD11b⁺Gr-1⁺ MDSCs in peripheral circulation and decreased Gr-1⁺ cell accumulation in the livers. Further studies demonstrated that MitoTEMPO administration suppressed the mRNA and protein expressions of MDSC-associated proinflammatory mediators, such as monocyte chemoattractant protein-1 (MCP-1), S100 calcium-binding protein A8 (S100A8), and S100 calcium-binding protein A9 (S100A9). Our results suggest that MitoTEMPO appears to be a potential chemical compound affecting certain immune cells and further ameliorates inflammation in obese-associated NAFLD.

Roles of Hepatic Innate and Innate-Like Lymphocytes in Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH), a progressive form of nonalcoholic fatty liver disease (NAFLD), is accompanied by steatosis, hepatocyte injury and liver inflammation, which has been a health problem in the world as one of the major high risk factors of cirrhosis and hepatocellular carcinoma (HCC). Complex immune responses involving T cells, B cells, Kupffer cells, monocytes, neutrophils, DCs and other innate lymphocytes account for the pathogenesis of NASH; however, the underlying mechanisms have not been clearly elucidated in detail. In the liver, innate and innate-like lymphocytes account for more than two-thirds of total lymphocytes and play an important role in maintaining the immune homeostasis. Therefore, their roles in the progression of NASH deserves investigation. In this review, we summarized murine NASH models for immunological studies, including the diet-induced NASH, chemical-induced NASH and genetic-induced NASH. The role of innate and innate-like lymphocytes including NK cells, ILCs, NKT, γδT and MAIT cells in the progression of NASH were elucidated. Further, the metabolic regulation of the innate immune response was addressed in consideration to explain the molecular mechanisms. Based on the findings of the reviewed studies, strategies of immune intervention are proposed to control the progression of NASH.

Fatty acid-driven modifications in T-cell profiles in non-alcoholic fatty liver disease patients

BACKGROUND

The interaction between T-cells/fatty acids involved in non-alcoholic fatty liver disease (NAFLD) and liver fibrosis progression is poorly understood. In this study, we conducted a comprehensive analysis of T-cell profiles of NAFLD patients to better understand their relationship with fatty acids and relevance to liver fibrosis.

METHODS

We analyzed the differences in T-cell profiles of peripheral blood mononuclear cells (PBMCs) between 40 NAFLD patients and 5 healthy volunteers (HVs), and their relationship with liver fibrosis stage or progression. Moreover, we analyzed the relationship between T-cell profiles and fatty acid compositions in vivo, and changes in T-cell profiles after treatment with fatty acids in vitro.

RESULTS

T-cell profiles of NAFLD patients were different from those of HVs. The CD25⁺CD45⁺CD4⁺ T-cell frequency was increased in NAFLD patients with high liver fibrosis stage and progression, and this indicated immune activation. Despite such a state of immune activation, the PD1⁺CD4⁺ T-cell frequency was decreased in the same patients group. The PD1⁺CD4⁺ T-cell frequency had a significantly negative correlation with the serum fatty acid composition ratio C16:1n7/C16:0. Moreover, the PD1⁺CD4⁺ T-cell frequency was significantly decreased by in vitro treatment with fatty acids. In addition, its rate of frequency change was significantly different between C16:0 and C16:1n7 and decreased by artificially increasing the C16:1n7/C16:0 ratio.

CONCLUSIONS

The analysis of PBMCs in NAFLD patients showed that T-cell profiles were different from those of HVs. And, it suggested that fatty acids modified T-cell profiles and were involved in liver fibrosis in NAFLD patients.

The visceral adiposity index is a predictor of incident nonalcoholic fatty liver disease: A population-based longitudinal study

BACKGROUND AND AIMS

Visceral adiposity index (VAI), calculated with body mass index, high-density lipoprotein cholesterol, triglyceride and waist circumference, has been proposed as a marker of visceral fat accumulation and dysfunction.

METHODS

The impact of VAI on incident nonalcoholic fatty liver disease (NAFLD) in a historical cohort study of 8399 (3773 men and 4626 women) participants. NAFLD was defined as having fatty liver diagnosed by abdominal ultrasonography. We divided the participants into two groups according to sex and into quartiles according to VAI (Q1-4). We calculated VAI using the formulas. Men: VAI = [waist circumference (WC)/39.68 + (1.88 × body mass index [BMI])] × [triglycerides (TG)/1.03] × [1.31/high-density lipoprotein cholesterol (HDL)]; women: VAI = [WC/36.58 + (1.89 × BMI)] × (TG/0.81) × (1.52/HDL). We performed Cox proportional hazard models, adjusting for age, alanine aminotransferase, fasting plasma glucose, systolic blood pressure, alcohol consumption, smoking status and exercise.

RESULTS

During the median 4.5-year follow-up for men and 4.9-year follow-up for women, 1078 participants (737 men and 341 women) developed NAFLD. The 4000 days cumulative incidence rate of NAFLD for men and women were 7.5% and 2.2% in Q1, 14.5% and 4.0% in Q2, 22.3% and 6.7% in Q3 and 33.8% and 16.7% in Q4. The hazard ratios of incident NAFLD in Q4 (VAI: men, > 1.13; women, > 0.83) were 3.69 (95% confidence interval 2.84-4.86, P < 0.001) in men and 4.93 (3.28-7.73, P < 0.001) in women, compared to Q1 (VAI: men, < 0.44; women, < 0.36).

CONCLUSIONS

The visceral adiposity index can be a predictor of incident NAFLD.

Processes exacerbating apoptosis in non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is a significant public health concern, owing to its high prevalence, progressive nature and lack of effective medical therapies. NAFLD is a complex and multifactorial disease involving the progressive and concerted action of factors that contribute to the development of liver inflammation and eventually fibrosis. Here, we summarize fundamental molecular mechanisms underlying the pathogenesis of non-alcoholic steatohepatitis (NASH), how they are interrelated and possible translation to clinical applications. We focus on processes triggering and exacerbating apoptotic signalling in the liver of NAFLD patients and their metabolic and pathological implications. Indeed, liver injury and inflammation are cardinal histopathological features of NASH, a duo in which derailment of apoptosis is of paramount importance. In turn, the liver houses a very high number of mitochondria, crucial metabolic unifiers of both extrinsic and intrinsic signals that converge in apoptosis activation. The role of lifestyle options is also dissected, highlighting the management of modifiable risk factors, such as obesity and harmful alcohol consumption, influencing apoptosis signalling in the liver and ultimately NAFLD progression. Integrating NAFLD-associated pathologic mechanisms in the cell death context could provide clues for a more profound understating of the disease and pave the way for novel rational therapies.

Lycopene prevents the progression of lipotoxicity-induced nonalcoholic steatohepatitis by decreasing oxidative stress in mice

Excessive fatty acid uptake-induced oxidative stress causes liver injury and the consecutive recruitment of inflammatory immune cells, thereby promoting the progression of simple steatosis to nonalcoholic steatohepatitis (NASH). Lycopene, the most effective singlet oxygen scavenger of the antioxidant carotenoids, has anti-inflammatory activity. Here, we investigated the preventive and therapeutic effects of lycopene in a lipotoxic model of NASH: mice fed a high-cholesterol and high-fat diet. Lycopene alleviated excessive hepatic lipid accumulation and enhanced lipolysis, decreased the proportion of M1-type macrophages/Kupffer cells, and activated stellate cells to improve hepatic inflammation and fibrosis, and subsequently reduced the recruitment of CD4⁺ and CD8⁺ T cells in the liver. Importantly, lycopene reversed insulin resistance, as well as hepatic inflammation and fibrosis, in pre-existing NASH. In parallel, lycopene decreased LPS-/IFN-γ-/TNFα-induced M1 marker mRNA levels in peritoneal macrophages, as well as TGF-β1-induced expression of fibrogenic genes in a stellate cell line, in a dose-dependent manner. These results were associated with decreased oxidative stress in cells, which might be mediated by the expression of NADPH oxidase subunits. In summary, lycopene prevented and reversed lipotoxicity-induced inflammation and fibrosis in NASH mice by reducing oxidative stress. Therefore, it might be a novel and promising treatment for NASH.

Cellular Interactions in the Human Fatty Liver

Non-alcoholic steatohepatitis morbidity and mortality is on the rise due to the obesity pandemic. Its pathophysiology is not well understood and implies complex interactions between local hepatic cells populations, adipocytes, immune effectors that lead to hepatic lipid excess, lipotoxicity, cellular stress and inflammation, as well as programmed cell death. A better understanding of these pathogenic interactions would allow better identification of therapeutic targets in a disease that has no known pharmacological therapy until now.

Hepatic NK cells attenuate fibrosis progression of non-alcoholic steatohepatitis in dependent of CXCL10-mediated recruitment

BACKGROUND & AIMS

Non-alcoholic steatohepatitis (NASH) is a major cause of chronic liver disease. The precise role of NK cells in the progression of NASH has yet to be elucidated.

METHODS

Using methionine- and choline-deficient diets (MCD)-induced NASH model, the role of NK cells was identified in WT mice compared with conventional NK cell-deficient Nfil3^-/- mice.

RESULTS

After 8 weeks of MCD treatment, NASH was induced as shown by the significant macrovesicular steatosis, necro-inflammation and fibrosis in the liver of WT B6 mice. In MCD-treated WT B6 mice, the number of NK cells was markedly increased in the liver, but decreased in the spleen. Intrahepatic NK cells exhibited high levels of activation, as evidenced by the expression of CD107a and cytokine production of IFN-γ, TGF-β and IL-10. Lower expression levels of Ki67 indicated a reduction in the proliferation of intrahepatic NK cells after MCD treatment. Increased expression of CXCL10 in the liver early after MCD treatment led to the increased recruitment of CXCR3⁺ NK cells into the liver. The MCD-treated Nfil3^-/- mice showed similar levels of TG and macrovesicular steatosis, thus more inflammatory infiltration and increased collagen deposition in the liver. Furthermore, the depletion of NK cells during MCD-induced NASH caused a significant increase in the infiltration of monocyte-derived macrophages (MoMFs) particularly Ly6C^lo subsets towards M2.

CONCLUSIONS

Intrahepatic NK cells, recruited through CXCL10-CXCR3 interaction, play a protective role against the fibrosis progression in NASH, which provide us with a better understanding of the immunopathogenesis of NASH.

Adaptive immunity: an emerging player in the progression of NAFLD

In the past decade, nonalcoholic fatty liver disease (NAFLD) has become a leading cause of chronic liver disease and cirrhosis, as well as an important risk factor for hepatocellular carcinoma (HCC). NAFLD encompasses a spectrum of liver lesions, including simple steatosis, steatohepatitis and fibrosis. Although steatosis is often harmless, the lobular inflammation that characterizes nonalcoholic steatohepatitis (NASH) is considered a driving force in the progression of NAFLD. The current view is that innate immune mechanisms represent a key element in supporting hepatic inflammation in NASH. However, increasing evidence points to the role of adaptive immunity as an additional factor promoting liver inflammation. This Review discusses data regarding the role of B cells and T cells in sustaining the progression of NASH to fibrosis and HCC, along with the findings that antigens originating from oxidative stress act as a trigger for immune responses. We also highlight the mechanisms affecting liver immune tolerance in the setting of steatohepatitis that favour lymphocyte activation. Finally, we analyse emerging evidence concerning the possible application of immune modulating treatments in NASH therapy.

Inflammation and fibrosis in chronic liver diseases including non-alcoholic fatty liver disease and hepatitis C

At present chronic liver disease (CLD), the third commonest cause of premature death in the United Kingdom is detected late, when interventions are ineffective, resulting in considerable morbidity and mortality. Injury to the liver, the largest solid organ in the body, leads to a cascade of inflammatory events. Chronic inflammation leads to the activation of hepatic stellate cells that undergo trans-differentiation to become myofibroblasts, the main extra-cellular matrix producing cells in the liver; over time increased extra-cellular matrix production results in the formation of liver fibrosis. Although fibrogenesis may be viewed as having evolved as a “wound healing” process that preserves tissue integrity, sustained chronic fibrosis can become pathogenic culminating in CLD, cirrhosis and its associated complications. As the reference standard for detecting liver fibrosis, liver biopsy, is invasive and has an associated morbidity, the diagnostic assessment of CLD by non-invasive testing is attractive. Accordingly, in this review the mechanisms by which liver inflammation and fibrosis develop in chronic liver diseases are explored to identify appropriate and meaningful diagnostic targets for clinical practice. Due to differing disease prevalence and treatment efficacy, disease specific diagnostic targets are required to optimally manage individual CLDs such as non-alcoholic fatty liver disease and chronic hepatitis C infection. To facilitate this, a review of the pathogenesis of both conditions is also conducted. Finally, the evidence for hepatic fibrosis regression and the mechanisms by which this occurs are discussed, including the current use of antifibrotic therapy.