Favored T helper 1 response in a mouse model of hepatosteatosis is associated with enhanced T cell-mediated hepatitis

The Role of CD4+T Cells in Nonalcoholic Steatohepatitis and Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) has become the fourth leading cause of cancer-related deaths worldwide; annually, approximately 830,000 deaths related to liver cancer are diagnosed globally. Since early-stage HCC is clinically asymptomatic, traditional treatment modalities, including surgical ablation, are usually not applicable or result in recurrence. Immunotherapy, particularly immune checkpoint blockade (ICB), provides new hope for cancer therapy; however, immune evasion mechanisms counteract its efficiency. In addition to viral exposure and alcohol addiction, nonalcoholic steatohepatitis (NASH) has become a major cause of HCC. Owing to NASH-related aberrant T cell activation causing tissue damage that leads to impaired immune surveillance, NASH-associated HCC patients respond much less efficiently to ICB treatment than do patients with other etiologies. In addition, abnormal inflammation contributes to NASH progression and NASH-HCC transition, as well as to HCC immune evasion. Therefore, uncovering the detailed mechanism governing how NASH-associated immune cells contribute to NASH progression would benefit HCC prevention and improve HCC immunotherapy efficiency. In the following review, we focused our attention on summarizing the current knowledge of the role of CD4+T cells in NASH and HCC progression, and discuss potential therapeutic strategies involving the targeting of CD4+T cells for the treatment of NASH and HCC.

The double roles of T cell-mediated immune response in the progression of MASLD

Metabolic dysfunction-associated steatotic liver disease(MASLD), formerly known as non-alcoholic fatty liver disease(NAFLD), has become a major cause of chronic liver disease and a significant risk factor for hepatocellular carcinoma, which poses a huge burden on global public health and economy. MASLD includes steatotic liver disease, steatohepatitis, and cirrhosis, and the latter two cause great harm to human health and life, even complicated with liver cancer. Immunologic mechanism plays a major role in promoting its development into hepatitis and cirrhosis. Now more and more evidences show that T cells play an important role in the progression of MASLD. In this review, we discuss the double roles of T cells in MASLD from the perspective of T cell response pathways, as well as new evidences regarding the possible application of immunomodulatory therapy in MASH.

Transcriptomic screening of novel targets of sericin in human hepatocellular carcinoma cells

Sericin, a natural protein derived from Bombyx mori, is known to ameliorate liver tissue damage; however, its molecular mechanism remains unclear. Herein, we aimed to identify the possible novel targets of sericin in hepatocytes and related cellular pathways. RNA sequencing analysis indicated that a low dose of sericin resulted in 18 differentially expressed genes (DEGs) being upregulated and 68 DEGs being downregulated, while 61 DEGs were upregulated and 265 DEGs were downregulated in response to a high dose of sericin (FDR ≤ 0.05, fold change > 1.50). Functional analysis revealed that a low dose of sericin regulated pathways associated with the complement and coagulation cascade, metallothionine, and histone demethylate (HDMs), whereas a high dose of sericin was associated with pathways involved in lipid metabolism, mitogen-activated protein kinase (MAPK) signaling and autophagy. The gene network analysis highlighted twelve genes, A2M, SERPINA5, MT2A, MT1G, MT1E, ARID5B, POU2F1, APOB, TRAF6, HSPA8, FGFR1, and OGT, as novel targets of sericin. Network analysis of transcription factor activity revealed that sericin affects NFE2L2, TFAP2C, STAT1, GATA3, CREB1 and CEBPA. Additionally, the protective effects of sericin depended on the counterregulation of APOB, POU2F1, OGT, TRAF6, and HSPA5. These findings suggest that sericin exerts hepatoprotective effects through diverse pathways at different doses, providing novel potential targets for the treatment of liver diseases.

The bidirectional immune crosstalk in metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is an unabated risk factor for end-stage liver diseases with no available therapies. Dysregulated immune responses are critical culprits of MASLD pathogenesis. Independent contributions from either the innate or adaptive arms of the immune system or their unidirectional interplay are commonly studied in MASLD. However, the bidirectional communication between innate and adaptive immune systems and its impact on MASLD remain insufficiently understood. Given that both innate and adaptive immune cells are indispensable for the development and progression of inflammation in MASLD, elucidating pathogenic contributions stemming from the bidirectional interplay between these two arms holds potential for development of novel therapeutics for MASLD. Here, we review the immune cell types and bidirectional pathways that influence the pathogenesis of MASLD and highlight potential pharmacologic approaches to combat MASLD based on current knowledge of this bidirectional crosstalk.

CD73 mediates the therapeutic effects of endometrial regenerative cells in concanavalin A-induced hepatitis by regulating CD4+ T cells

BACKGROUND

As a kind of mesenchymal-like stromal cells, endometrial regenerative cells (ERCs) have been demonstrated effective in the treatment of Concanavalin A (Con A)-induced hepatitis. However, the therapeutic mechanism of ERCs is not fully understood. Ecto-5`-nucleotidase (CD73), an enzyme that could convert immune-stimulative adenosine monophosphate (AMP) to immune-suppressive adenosine (ADO), was identified highly expressed on ERCs. The present study was conducted to investigate whether the expression of CD73 on ERCs is critical for its therapeutic effects in Con A-induced hepatitis.

METHODS

ERCs knocking out CD73 were generated with lentivirus-mediated CRISPR-Cas9 technology and identified by flow cytometry, western blot and AMPase activity assay. CD73-mediated immunomodulatory effects of ERCs were investigated by CD4+ T cell co-culture assay in vitro. Besides, Con A-induced hepatitis mice were randomly assigned to the phosphate-buffered saline treated (untreated), ERC-treated, negative lentiviral control ERC (NC-ERC)-treated, and CD73-knockout-ERC (CD73-KO-ERC)-treated groups, and used to assess the CD73-mediated therapeutic efficiency of ERCs. Hepatic histopathological analysis, serum transaminase concentrations, and the proportion of CD4+ T cell subsets in the liver and spleen were performed to assess the progression degree of hepatitis.

RESULTS

Expression of CD73 on ERCs could effectively metabolize AMP to ADO, thereby inhibiting the activation and function of conventional CD4+ T cells was identified in vitro. In addition, ERCs could markedly reduce levels of serum and liver transaminase and attenuate liver damage, while the deletion of CD73 on ERCs dampens these effects. Furthermore, ERC-based treatment achieved less infiltration of CD4+ T and Th1 cells in the liver and reduced the population of systemic Th1 and Th17 cells and the levels of pro-inflammatory cytokines such as IFN-γ and TNF-α, while promoting the generation of Tregs in the liver and spleen, while deletion of CD73 on ERCs significantly impaired their immunomodulatory effects locally and systemically.

CONCLUSION

Taken together, it is concluded that CD73 is critical for the therapeutic efficiency of ERCs in the treatment of Con A-induced hepatitis.

Decoding the role of immune T cells: A new territory for improvement of metabolic-associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) is a new emerging concept and is associated with metabolic dysfunction, generally replacing the name of nonalcoholic fatty liver disease (NAFLD) due to heterogeneous liver condition and inaccuracies in definition. The prevalence of MAFLD is rising by year due to dietary changes, metabolic disorders, and no approved therapy, affecting a quarter of the global population and representing a major economic problem that burdens healthcare systems. Currently, in addition to the common causative factors like insulin resistance, oxidative stress, and lipotoxicity, the role of immune cells, especially T cells, played in MAFLD is increasingly being emphasized by global scholars. Based on the diverse classification and pathophysiological effects of immune T cells, we comprehensively analyzed their bidirectional regulatory effects on the hepatic inflammatory microenvironment and MAFLD progression. This interaction between MAFLD and T cells was also associated with hepatic-intestinal immune crosstalk and gut microbiota homeostasis. Moreover, we pointed out several T-cell-based therapeutic approaches including but not limited to adoptive transfer of T cells, fecal microbiota transplantation, and drug therapy, especially for natural products and Chinese herbal prescriptions. Overall, this study contributes to a better understanding of the important role of T cells played in MAFLD progression and corresponding therapeutic options and provides a potential reference for further drug development.

Pattern recognition receptor CD14 gene polymorphisms in alcohol use disorder patients and its Influence on liver disease susceptibility

Background

Alcohol use disorders (AUDs) leading to liver disease is major concern over other spectrum of disorder. Excessive alcohol consumption resulting in leaky gut syndrome is attributed to alcohol-induced liver injury through portal translocation of bacterial endotoxin. Susceptibility to alcoholic liver disease (ALD) in AUD patients could be dependent upon genes responsible for inflammation and alcohol metabolism. The pattern recognition receptor CD14 gene is a major player in endotoxin-mediated inflammation and susceptibility to ALD. This study investigated the genetic association of CD14 polymorphisms and other mechanisms relevant to altered inflammatory responses leading to ALD.

Methods

Patients with alcohol use disorder with ALD (n = 128) and without liver disease (ALC, n = 184) and controls without alcohol use disorder (NALC, n = 152) from North India were enrolled. The CD4 gene polymorphisms in the North Indian population were evaluated by RFLP and sequencing. Secretory CD14 (sCD14), LBP, TLR4, MD2, TNFα, IL1b, IFNγ, IL6, IL10, and IL4 levels in serum were measured by ELISA among groups. The influence of polymorphisms on CD14 gene promoter activity and circulatory bacterial DNA level was determined.

Results

The CD14 gene promoter and exonic region SNPs were found to be monomorphic, except for SNP rs2569190 for the North Indian population. The genetic association of SNP rs2569190(C/T) with the risk of developing ALD was found significant for TT genotype [OR_TT, 95% CI = 2.19, 1.16–4.13 for ALD vs. ALC and OR, 2.09, 1.18–3.72 for ALD vs. NALC]. An increased sCD14 level was observed in AUD patients compared to NALC control. Increased levels of LBP, TLR4, TNFα, IL1β, IFNγ, and IL6 and reduced levels of MD2, IL10, and IL4 were observed among the ALD patients compared to the other two control groups. Elevated levels of pro-inflammatory and reduced levels of anti-inflammatory cytokines were observed in the risk genotype TT groups of ALD patients and the ALC group compared to NALC. Promoter activity was observed in the intronic region flanking SNPs and risk genotype can influence reporter activity, indicating CD14 gene expression.

Conclusion

Enhanced CD14 expression associated with inflammatory responses increases susceptibility to ALD in the TT genotype of AUD patients.

CD4+ T cell activation and inflammation in NASH-related fibrosis

Liver fibrosis is a common pathological feature of end stage liver failure, a severe life-threatening disease worldwide. Nonalcoholic fatty liver disease (NAFLD), especially its more severe form with steatohepatitis (NASH), results from obesity, type 2 diabetes and metabolic syndrome and becomes a leading cause of liver fibrosis. Genetic factor, lipid overload/toxicity, oxidative stress and inflammation have all been implicated in the development and progression of NASH. Both innate immune response and adaptive immunity contribute to NASH-associated inflammation. Innate immunity may cause inflammation and subsequently fibrosis via danger-associated molecular patterns. Increasing evidence indicates that T cell-mediated adaptive immunity also provokes inflammation and fibrosis in NASH via cytotoxicity, cytokines and other proinflammatory and profibrotic mediators. Recently, the single-cell transcriptome profiling has revealed that the populations of CD4+ T cells, CD8+ T cells, γδ T cells, and TEMs are expanded in the liver with NASH. The activation of T cells requires antigen presentation from professional antigen-presenting cells (APCs), including macrophages, dendritic cells, and B-cells. However, since hepatocytes express MHCII molecules and costimulators, they may also act as an atypical APC to promote T cell activation. Additionally, the phenotypic switch of hepatocytes to proinflammatory cells in NASH contributes to the development of inflammation. In this review, we focus on T cells and in particular CD4+ T cells and discuss the role of different subsets of CD4+ T cells including Th1, Th2, Th17, Th22, and Treg in NASH-related liver inflammation and fibrosis.

Liver damage promotes pro-inflammatory T-cell responses against apolipoprotein B-100

OBJECTIVES

Liver-derived apolipoprotein B-100 (ApoB100) is an autoantigen that is recognized by atherogenic CD4⁺ T cells in cardiovascular disease (CVD). CVD is a major mortality risk for patients with chronic inflammatory liver diseases. However, the impact of liver damage for ApoB100-specific T-cell responses is unknown.

METHODS

We identified ApoB100-specific T cells in blood from healthy controls, nonalcoholic fatty liver disease (NAFLD) patients, and CVD patients by activation-induced marker expression and analyzed their differentiation pattern in correlation to the lipid profile and liver damage parameters in a cross-sectional study. To assess the induction of extrahepatic ApoB100-specific T cells upon transient liver damage in vivo, we performed hydrodynamic tail vein injections with diphtheria toxin A (DTA)-encoding plasmid in human ApoB100-transgenic mice.

RESULTS

Utilizing immunodominant ApoB100-derived peptides, we found increased ApoB100-specific T-cell populations in NAFLD and CVD patients compared to healthy controls. In a peptide-specific manner, ApoB100 reactivity in healthy controls was accompanied by expression of the regulatory T (Treg)-cell transcription factor FOXP3. In contrast, FOXP3 expression decreased, whereas expression of pro-inflammatory cytokine interleukin (IL)-17A increased in ApoB100-specific T cells from NAFLD and CVD patients. Dyslipidemia and liver damage parameters in blood correlated with reduced FOXP3 expression and elevated IL-17A production in ApoB100-specific T-cell populations, respectively. Moreover, DTA-mediated transient liver damage in human ApoB100-transgenic mice accumulated IL-17a-expressing ApoB100-specific T cells in the periphery.

CONCLUSION

Our results show that liver damage promotes pro-inflammatory ApoB100-specific T-cell populations, thereby providing a cellular mechanism for the increased CVD risk in liver disease patients.

The National Consensus statement on the management of adult patients with non-alcoholic fatty liver disease and main comorbidities

The National Consensus was prepared with the participation of the National Medical Association for the Study of the Multimorbidity, Russian Scientific Liver Society, Russian Association of Endocrinologists, Russian Association of Gerontologists and Geriatricians, National Society for Preventive Cardiology, Professional Foundation for the Promotion of Medicine Fund PROFMEDFORUM. The aim of the multidisciplinary consensus is a detailed analysis of the course of non-alcoholic fatty liver disease (NAFLD) and the main associated conditions. The definition of NAFLD is given, its prevalence is described, methods for diagnosing its components such as steatosis, inflammation and fibrosis are described. The association of NAFLD with a number of cardio-metabolic diseases (arterial hypertension, atherosclerosis, thrombotic complications, type 2 diabetes mellitus (T2DM), obesity, dyslipidemia, etc.), chronic kidney disease (CKD) and the risk of developing hepatocellular cancer (HCC) were analyzed. The review of non-drug methods of treatment of NAFLD and modern opportunities of pharmacotherapy are presented. The possibilities of new molecules in the treatment of NAFLD are considered: agonists of nuclear receptors, antagonists of pro-inflammatory molecules, etc. The positive properties and disadvantages of currently used drugs (vitamin E, thiazolidinediones, etc.) are described. Special attention is paid to the multi-target ursodeoxycholic acid (UDCA) molecule in the complex treatment of NAFLD as a multifactorial disease. Its anti-inflammatory, anti-oxidant and cytoprotective properties, the ability to reduce steatosis an independent risk factor for the development of cardiovascular pathology, reduce inflammation and hepatic fibrosis through the modulation of autophagy are considered. The ability of UDCA to influence glucose and lipid homeostasis and to have an anticarcinogenic effect has been demonstrated. The Consensus statement has advanced provisions for practitioners to optimize the diagnosis and treatment of NAFLD and related common pathogenetic links of cardio-metabolic diseases.

Spred2 controls the severity of Concanavalin A-induced liver damage by limiting interferon-gamma production by CD4+ and CD8+ T cells

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Spred2^-/- mice developed exacerbated Con A-induced liver damage with increased IFNγ production.

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MEK/ERK inhibitor U0126 markedly inhibited the damage and reduced IFNγ production.

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Neutralization of IFNγ abolished the damage with down-regulated hepatic STAT1 activation.

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Depletion of CD4⁺/CD8⁺ T cells improved the damage with decreased IFNγ production.

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Transplantation of CD4⁺/CD8⁺ T cells into RAG1^-/- mice reproduced severe liver damage.

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Liver damage and IFNγ production were significantly lower in Spred2 transgenic mice.

Introduction

Mitogen-activated protein kinases (MAPKs) are involved in T cell-mediated liver damage. However, the inhibitory mechanism(s) that controls T cell-mediated liver damage remains unknown.

Objectives

We investigated whether Spred2 (Sprouty-related, EVH1 domain-containing protein 2) that negatively regulates ERK-MAPK pathway has a biological impact on T cell-mediated liver damage by using a murine model.

Methods

We induced hepatotoxicity in genetically engineered mice by intravenously injecting Concanavalin A (Con A) and analyzed the mechanisms using serum chemistry, histology, ELISA, qRT-PCR, Western blotting and flow cytometry.

Results

Spred2-deficient mice (Spred2^-/-) developed more sever liver damage than wild-type (WT) mice with increased interferon-γ (IFNγ) production. Hepatic ERK phosphorylation was enhanced in Spred2^-/- mice, and pretreatment of Spred2^-/- mice with the MAPK/ERK inhibitor U0126 markedly inhibited the liver damage and reduced IFNγ production. Neutralization of IFNγ abolished the damage with decreased hepatic Stat1 activation in Spred2^-/- mice. IFNγ was mainly produced from CD4⁺ and CD8⁺ T cells, and their depletion decreased liver damage and IFNγ production. Transplantation of CD4⁺ and/or CD8⁺ T cells from Spred2^-/- mice into RAG1^-/- mice deficient in both T and B cells caused more severe liver damage than those from WT mice. Hepatic expression of T cell attractants, CXCL9 and CXCL10, was augmented in Spred2^-/- mice as compared to WT mice. Conversely, liver damage, IFNγ production and the recruitment of CD4⁺ and CD8⁺ T cells in livers after Con A challenge were lower in Spred2 transgenic mice, and Spred2-overexpressing CD4⁺ and CD8⁺ T cells produced lower levels of IFNγ than WT cells upon stimulation with Con A in vitro.

Conclusion

We demonstrated, for the first time, that Spred2 functions as an endogenous regulator of T cell IFNγ production and Spred2-mediated inhibition of ERK-MAPK pathway may be an effective remedy for T cell-dependent liver damage.

Protective Property of Scutellarin Against Liver Injury Induced by Carbon Tetrachloride in Mice

Liver injury is a clinical disorder caused by toxins, drugs, and alcohol stimulation without effective therapeutic approaches thus far. Scutellarin (SCU), isolated from the edible herb Erigeron breviscapus (Vant.) Hand. -Mazz. showed potential hepatoprotective effects, but the mechanisms remain unknown. In this study, transcriptomics combined with nontargeted metabolomics and 16S rRNA amplicon sequencing were performed to elucidate the functional mechanisms of SCU in carbon tetrachloride (CCl₄)–induced liver injury in mice. The results showed that SCU exerted potential hepatoprotective effects against CCl₄-induced liver injury by repressing CYP2E1 and IκBα/NF-κB signaling pathways, modulating the gut microbiota (especially enriching Lactobacillus), and regulating the endogenous metabolites involved in lipid metabolism and bile acid homeostasis. SCU originates from a functional food that appears to be a promising agent to guard against liver injury.

The Role of Leaky Gut in Nonalcoholic Fatty Liver Disease: A Novel Therapeutic Target

The liver directly accepts blood from the gut and is, therefore, exposed to intestinal bacteria. Recent studies have demonstrated a relationship between gut bacteria and nonalcoholic fatty liver disease (NAFLD). Approximately 10–20% of NAFLD patients develop nonalcoholic steatohepatitis (NASH), and endotoxins produced by Gram-negative bacilli may be involved in NAFLD pathogenesis. NAFLD hyperendotoxicemia has intestinal and hepatic factors. The intestinal factors include impaired intestinal barrier function (leaky gut syndrome) and dysbiosis due to increased abundance of ethanol-producing bacteria, which can change endogenous alcohol concentrations. The hepatic factors include hyperleptinemia, which is associated with an excessive response to endotoxins, leading to intrahepatic inflammation and fibrosis. Clinically, the relationship between gut bacteria and NAFLD has been targeted in some randomized controlled trials of probiotics and other agents, but the results have been inconsistent. A recent randomized, placebo-controlled study explored the utility of lubiprostone, a treatment for constipation, in restoring intestinal barrier function and improving the outcomes of NAFLD patients, marking a new phase in the development of novel therapies targeting the intestinal barrier. This review summarizes recent data from studies in animal models and randomized clinical trials on the role of the gut–liver axis in NAFLD pathogenesis and progression.

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.

Relationship between NAFLD and Periodontal Disease from the View of Clinical and Basic Research, and Immunological Response

Periodontal disease is an inflammatory disease caused by pathogenic oral microorganisms that leads to the destruction of alveolar bone and connective tissues around the teeth. Although many studies have shown that periodontal disease is a risk factor for systemic diseases, such as type 2 diabetes and cardiovascular diseases, the relationship between nonalcoholic fatty liver disease (NAFLD) and periodontal disease has not yet been clarified. Thus, the purpose of this review was to reveal the relationship between NAFLD and periodontal disease based on epidemiological studies, basic research, and immunology. Many cross-sectional and prospective epidemiological studies have indicated that periodontal disease is a risk factor for NAFLD. An in vivo animal model revealed that infection with periodontopathic bacteria accelerates the progression of NAFLD accompanied by enhanced steatosis. Moreover, the detection of periodontopathic bacteria in the liver may demonstrate that the bacteria have a direct impact on NAFLD. Furthermore, Porphyromonas gingivalis lipopolysaccharide induces inflammation and accumulation of intracellular lipids in hepatocytes. Th17 may be a key molecule for explaining the relationship between periodontal disease and NAFLD. In this review, we attempted to establish that oral health is essential for systemic health, especially in patients with NAFLD.

Stress kinases in the development of liver steatosis and hepatocellular carcinoma

Non-alcoholic fatty liver disease (NAFLD) is an important component of metabolic syndrome and one of the most prevalent liver diseases worldwide. This disorder is closely linked to hepatic insulin resistance, lipotoxicity, and inflammation. Although the mechanisms that cause steatosis and chronic liver injury in NAFLD remain unclear, a key component of this process is the activation of stress-activated kinases (SAPKs), including p38 and JNK in the liver and immune system. This review summarizes findings which indicate that the dysregulation of stress kinases plays a fundamental role in the development of steatosis and are important players in inducing liver fibrosis. To avoid the development of steatohepatitis and liver cancer, SAPK activity must be tightly regulated not only in the hepatocytes but also in other tissues, including cells of the immune system. Possible cellular mechanisms of SAPK actions are discussed.

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Hepatic JNK triggers steatosis and insulin resistance, decreasing lipid oxidation and ketogenesis in HFD-fed mice.

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Decreased liver expression of p38α/β in HFD increases lipogenesis.

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Hepatic p38γ/δ drive insulin resistance and inhibit autophagy, which may lead to steatosis.

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Macrophage p38α/β promote cytokine production and M1 polarization, leading to lipid accumulation in hepatocytes.

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Myeloid p38γ/δ contribute to cytokine production and neutrophil migration, protecting against steatosis, diabetes and NAFLD.

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JNK1 and p38γ induce HCC while p38α blocks it. However, deletion of hepatic JNK1/2 induces cholangiocarcinoma.

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SAPK are potential therapeutic target for metabolic disorders, steatohepatitis and liver cancer.

Can Walnut Serve as a Magic Bullet for the Management of Non-Alcoholic Fatty Liver Disease?

Walnut contains many nutrients and bioactive components such as essential fatty acids, polyphenols, fiber, ɤ-tocopherol, folate, minerals, and vegetable protein, and has therefore been regarded as a natural functional food. Walnut-enriched diets have been demonstrated to be useful for heart health, cancer prevention, and metabolic disorders owing to their anti-oxidative and anti-inflammatory properties as well as for the maintenance of a healthy metabolism and immune function. Walnut extracts, either phenolic or lipid, also demonstrated the health effects in animal and cultured cell studies. More recently, the beneficial effects of walnut consumption on non-alcoholic fatty liver disease, which is a hepatic manifestation of obesity, hyperlipidemia, type 2 diabetes mellitus, and metabolic syndrome with substantial hepatic accumulation of triglyceride, have been proposed because walnut and a walnut-containing diet can modulate the etiologic mechanism such as ameliorating systemic and hepatic dyslipidemia, reducing lipotoxicity and inflammation, enhancing immune function, and maintaining gut microbiota balance. Through the extensive literature review we discuss the preventive roles of walnut in the development and progression of non-alcoholic fatty liver disease (NAFLD) and provide mechanistic insights into these effects.

Pathophysiological mechanisms underlying MAFLD

BACKGROUND AND AIMS

The pathophysiology underlying metabolic associated fatty liver disease (MAFLD) involves a multitude of interlinked processes, including insulin resistance (IR) underlying the metabolic syndrome, lipotoxicity attributable to the accumulation of toxic lipid species, infiltration of proinflammatory cells causing hepatic injury and ultimately leading to hepatic stellate cell (HSC) activation and fibrogenesis. The proximal processes, such as IR, lipid overload and lipotoxicity are relatively well established, but the downstream molecular mechanisms, such as inflammatory processes, hepatocyte lipoapoptosis, and fibrogenesis are incompletely understood.

METHODS

A literature search was performed with Medline (PubMed), Scopus and Google Scholar electronic databases till June 2020, using relevant keywords (nonalcoholic fatty liver disease; metabolic associated fatty liver disease; nonalcoholic steatohepatitis; NASH pathogenesis) to extract relevant studies describing pathogenesis of MAFLD/MASH.

RESULTS

Several studies have reported new concepts underlying pathophysiology of MAFLD. Activation of HSCs is the common final pathway for diverse signals from damaged hepatocytes and proinflammatory cells. Activated HSCs then secrete excess extracellular matrix (ECM) which accumulates and impairs structure and function of the liver. TAZ (a transcriptional regulator), hedgehog (HH) ligands, transforming growth factor-β (TGF-β), bone morphogenetic protein 8B (BMP8B) and osteopontin play important roles in activating these HSCs. Dysfunctional gut microbiome, dysregulated bile acid metabolism, endogenous alcohol production, and intestinal fructose handling, modify individual susceptibility to MASH.

CONCLUSIONS

Newer concepts of pathophysiology underlying MASH, such as TAZ/Ihh pathway, extracellular vesicles, microRNA, dysfunctional gut microbiome and intestinal fructose handling present promising targets for the development of therapeutic agents.

Diet Reversal and Immune Modulation Show Key Role for Liver and Adipose Tissue T Cells in Murine Nonalcoholic Steatohepatitis

BACKGROUND & AIMS

Nonalcoholic steatohepatitis (NASH) is a multisystem condition, implicating liver and adipose tissue. Although the general involvement of the innate and adaptive immune system has been established, we aimed to define the exact role of the functionally diverse T-cell subsets in NASH pathogenesis through diet reversal and immunologic modulation.

METHODS

Multiple experimental set-ups were used in 8-week-old C57BL/6J mice, including prolonged high-fat high-fructose diet (HFHFD) feeding, diet reversal from HFHFD to control diet, and administration of anti-CD8a and anti-interleukin 17A antibodies. Plasma alanine aminotransferase, glucose, and lipid levels were determined. Liver and adipose tissue were assessed histologically. Cytotoxic T (Tc), regulatory T, T helper (Th) 1, and Th17 cells were characterized in liver and visceral adipose tissue (VAT) via flow cytometry and RNA analysis.

RESULTS

HFHFD feeding induced the metabolic syndrome and NASH, which coincided with an increase in hepatic Th17, VAT Tc, and VAT Th17 cells, and a decrease in VAT regulatory T cells. Although diet reversal induced a phenotypical metabolic and hepatic normalization, the observed T-cell disruptions persisted. Treatment with anti-CD8a antibodies decreased Tc cell numbers in all investigated tissues and induced a biochemical and histologic attenuation of the HFHFD-induced NASH. Conversely, anti-interleukin 17A antibodies decreased hepatic inflammation without affecting other features of NASH or the metabolic syndrome.

CONCLUSIONS

HFHFD feeding induces important immune disruptions in multiple hepatic and VAT T-cell subsets, refractory to diet reversal. In particular, VAT Tc cells are critically involved in NASH pathogenesis, linking adipose tissue inflammation to liver disease.

Pathogenesis of Nonalcoholic Steatohepatitis: An Overview

Nonalcoholic fatty liver disease (NAFLD) is a heterogeneous group of liver diseases characterized by the accumulation of fat in the liver. The heterogeneity of NAFLD is reflected in a clinical and histologic spectrum where some patients develop isolated steatosis of the liver, termed nonalcoholic fatty liver, whereas others develop hepatocyte injury, ballooning, inflammation, and consequent fibrosis, termed nonalcoholic steatohepatitis (NASH). Systemic insulin resistance is a major driver of hepatic steatosis in NAFLD. Lipotoxicity of accumulated lipids along with activation of the innate immune system are major drivers of NASH. Lipid‐induced sublethal and lethal stress culminates in the activation of inflammatory processes, such as the release of proinflammatory extracellular vesicles and cell death. Innate and adaptive immune mechanisms involving macrophages, dendritic cells, and lymphocytes are central drivers of inflammation that recognize damage‐ and pathogen‐associated molecular patterns and contribute to the progression of the inflammatory cascade. While the activation of the innate immune system and the recruitment of proinflammatory monocytes into the liver in NASH are well known, the exact signals that lead to this remain less well defined. Further, the contribution of other immune cell types, such as neutrophils and B cells, is an area of intense research. Many host factors, such as the microbiome and gut–liver axis, modify individual susceptibility to NASH. In this review, we discuss lipotoxicity, inflammation, and the contribution of interorgan crosstalk in NASH pathogenesis.

Metabolic Triggers of Invariant Natural Killer T-Cell Activation during Sterile Autoinflammatory Disease

Ample evidence exists for activation of invariant natural killer T (iNKT) cells in a sterile manner by endogenous ligands or microbial antigens from the commensal flora, indicating that iNKT cells are not truly self-tolerant. Their controlled autoreactivity state is disturbed in many types of sterile inflammatory disease, resulting in their central role in modulating autoimmune responses. This review focuses on sterile iNKT-cell responses that are initiated by metabolic triggers, such as obesity-associated inflammation and fatty liver disease, as a manifestation of metabolic disease and dyslipidemia, as well as ischemia reperfusion injuries and sickle cell disease, characterized by acute lack of oxygen and oxidative stress response on reperfusion. In the intestine, inflammation and iNKT-cell response type are shaped by the microbiome as an extended "self". Disease- and organ-specific differences in iNKT-cell response type are summarized and help to define common pathways that shape iNKT-cell responses in the absence of exogenous antigen.

Tissue Immune Cells Fuel Obesity-Associated Inflammation in Adipose Tissue and Beyond

Obesity-associated inflammation stems from a combination of cell-intrinsic changes of individual immune cell subsets and the dynamic crosstalk amongst a broad array of immune cells. Although much of the focus of immune cell contributions to metabolic disease has focused on adipose tissue-associated cells, these potent sources of inflammation inhabit other metabolic regulatory tissues, including liver and gut, and recirculate to promote systemic inflammation and thus obesity comorbidities. Tissue-associated immune cells, especially T cell subpopulations, have become a hotspot of inquiry based on their contributions to obesity, type 2 diabetes, non-alcoholic fatty liver diseases and certain types of cancers. The cell-cell interactions that take place under the stress of obesity are mediated by intracellular contact and cytokine production, and constitute a complicated network that drives the phenotypic alterations of immune cells and perpetuates a feed-forward loop of metabolic decline. Herein we discuss immune cell functions in various tissues and obesity-associated cancers from the viewpoint of inflammation. We also emphasize recent advances in the understanding of crosstalk amongst immune cell subsets under obese conditions, and suggest future directions for focused investigations with clinical relevance.

The Differential Roles of T Cells in Non-alcoholic Fatty Liver Disease and Obesity

Non-alcoholic fatty liver disease (NAFLD) constitutes a spectrum of disease states characterized by hepatic steatosis and is closely associated to obesity and the metabolic syndrome. In non-alcoholic steatohepatitis (NASH), additionally, inflammatory changes and hepatocellular damage are present, representing a more severe condition, for which the treatment is an unmet medical need. Pathophysiologically, the immune system is one of the main drivers of NAFLD progression and other obesity-related comorbidities, and both the innate and adaptive immune system are involved. T cells form the cellular component of the adaptive immune system and consist of multiple differentially active subsets, i.e., T helper (Th) cells, regulatory T (Treg) cells, and cytotoxic T (Tc) cells, as well as several innate T-cell subsets. This review focuses on the role of these T-cell subsets in the pathogenesis of NAFLD, as well as the association with obesity and type 2 diabetes mellitus, reviewing the available evidence from both animal and human studies. Briefly, Th1, Th2, Th17, and Th22 cells seem to have an attenuating effect on adiposity. Th2, Th22, and Treg cells seem to decrease insulin resistance, whereas Th1, Th17, and Tc cells have an aggravating effect. Concerning NAFLD, both Th22 and Treg cells appear to have an overall tempering effect, whereas Th17 and Tc cells seem to induce more liver damage and fibrosis progression. The evidence regarding the role of the innate T-cell subsets is more controversial and warrants further exploration.

Expression of Natural Killer Cell Inhibitory Receptors is Associated with Significant Liver Injury in Chronic Hepatitis C in Children

INTRODUCTION AND AIM

Natural Killer (NK) cells play an important role in innate immune response to viral infections and their high proportion is situated in the liver. The aim of this study was to analyze possible relation between the expression of NK cell receptors and varied intensity of liver lesions in chronic hepatitis C (CHC) in children.

MATERIAL AND METHODS

Study included 105 children with CHC - 54 boys and 51 girls, age 13.62 ± 3.48 years. Blood specimens were taken at the day of the liver biopsy. Histological evaluation was performed according to METAVIR scoring system. Circulating NK cells were evaluated by flow cytometry. The results were shown as a proportion of cells expressing evaluated receptor and its' mean fluorescent intensity (MFI).

RESULTS

In 58 children with CHC (55.2%) significant liver fibrosis was observed ( ≥F2). Higher proportion of cells expressing CD158e inhibitory receptors was observed in the group of children with ALT > 2UNL (21.11 ± 14.60 vs. 12.22 ± 8.99%; p = 0.037). While higher proportion of cells expressing inhibitory CD158b receptor was observed in children with significant fibrosis (F ≥ 2) compared to minimal fibrosis (F < 2) - (34.14 ± 12.44 vs. 27.48 ± 8.71%; p = 0.049). Children with advanced fibrosis (F ≥ 3) had higher MFI of NK cell CD 158b receptor than children with fibrosis scored F < 3 - (5344.20 ± 3407.49 vs. 2979.67 ± 1190.64; p = 0.049). Proportion of NK cells expressing CD158b was found a predictor of significant fibrosis in univariate analysis - [OR 1.065; 95%CI (1.07-1.15); p = 0.046].

CONCLUSIONS

Higher proportion of NK cells expressing inhibitory CD158b and CD158e receptors is associated with significant liver injury.

Impaired T cell-mediated hepatitis in peroxisome proliferator activated receptor alpha (PPARα)-deficient mice

Background

Peroxisome proliferator activated receptor alpha (PPARα), a regulator of enzymes involved in β oxidation, has been reported to influence lymphocyte activation. The purpose of this study was to determine whether PPARα plays a role in T cell-mediated hepatitis induced by Concanavalin A (ConA).

Methods

Wild type (wt) or PPARα-deficient (PPARα^−/−) mice were treated with ConA (15 mg/kg) by intravenous injection 0, 10 or 24 h prior to sacrifice and serum and tissue collection for analysis of tissue injury, cytokine response, T cell activation and characterization.

Results

Ten and 24 h following ConA administration, wt mice had significant liver injury as demonstrated by serum transaminase levels, inflammatory cell infiltrate, hepatocyte apoptosis, and expression of several cytokines including interleukin 4 (IL4) and interferon gamma (IFNγ). In contrast, PPARα^−/− mice were protected from ConA-induced liver injury with significant reductions in serum enzyme release, greatly reduced inflammatory cell infiltrate, hepatocellular apoptosis, and IFNγ expression, despite having similar levels of hepatic T cell activation and IL4 expression. This resistance to liver injury was correlated with reduced numbers of hepatic natural killer T (NKT) cells and their in vivo responsiveness to alpha-galactosylceramide. Interestingly, adoptive transfer of either wt or PPARα^−/− splenocytes reconstituted ConA liver injury and cytokine production in lymphocyte-deficient, severe combined immunodeficient mice implicating PPARα within the liver, possibly through support of IL15 expression and/or suppression of IL12 production and not the lymphocyte as the key regulator of T cell activity and ConA-induced liver injury.

Conclusion

Taken together, these data suggest that PPARα within the liver plays an important role in ConA-mediated liver injury through regulation of NKT cell recruitment and/or survival.

IL-33 treatment attenuated diet-induced hepatic steatosis but aggravated hepatic fibrosis

The aim of our work was to investigate the role of interleukin-33 (IL-33) and its receptor ST2 in the progression of diet-induced nonalcoholic steatohepatitis (NASH) in mice, and the characteristic expression in livers of patients with NASH. Mice were fed with high-fat diet (HFD) or methionine-choline 4-deficient diet (MCD) and injected intraperitoneally with IL-33. Both mRNA and protein expression levels of IL-33 and ST2 were up-regulated in the livers of mice fed with HFD or MCD. Treatment with IL-33 attenuated diet-induced hepatic steatosis and reduced activities of ALT in serum, as well as ameliorated HFD-induced systemic insulin resistance and glucose intolerance, while aggravated hepatic fibrosis in diet-induced NASH. Furthermore, treatment with IL-33 can also promote Th2 response and M2 macrophage activation and beneficial modulation on expression profiles of fatty acid metabolism genes in livers. ST2 deficiency did not affect hepatic steatosis and fibrosis when fed with controlling diet. IL-33 did not affect diet-induced hepatic steatosis and fibrosis in ST2 knockout mice. Meanwhile, in the livers of patients with NASH, IL-33 was mainly located in hepatic sinusoid, endothelial cells, and hepatic stellate cells. The mRNA expression level of IL-33 and ST2 was elevated with the progression of NASH. In conclusion, treatment with IL-33 attenuated diet-induced hepatic steatosis, but aggravated hepatic fibrosis, in a ST2-dependent manner.

Mechanisms of the prevention and inhibition of the progression and development of non-alcoholic steatohepatitis by genetic and pharmacological decoy receptor 3 supplementation

AIMS

Treatment of non-alcoholic steatohepatitis (NASH) is difficult due to the absence of a proven treatment and its comprehensive mechanisms. In the NASH animal model, upregulated hepatic inflammation and oxidative stress, with the resultant M1 polarization of macrophages as well as imbalanced adipocytokines, all accelerate NASH progression. As a member of the tumor necrosis factor receptor superfamily, decoy receptor 3 (DcR3) not only neutralizes the death ligands, but also performs immune modulations. In this study, we aimed to investigate the possible non-decoy effects of DcR3 on diet-induced NASH mice.

METHODS

Methionine- and choline-deficient (MCD) diet feeding for 9 weeks was applied to induce NASH in BALB/c mice. Decoy receptor 3 heterozygous transgenesis or pharmacological pretreatment with DcR3a for 1 month were designed as interventions. Intrahepatic inflammatory status as well as macrophage polarization, oxidative stress, and steatosis as well as lipogenic gene expression and fibrotic status were analyzed. Additionally, acute effects of DcR3a on HepG2 cells, Hep3B cells, and primary mouse hepatocytes in various MCD medium-stimulated changes were also evaluated.

RESULTS

Both DcR3 genetic and pharmacologic supplement significantly reduced MCD diet-induced hepatic M1 polarization. In addition, DcR3 supplement attenuated MCD diet-increased hepatic inflammation, oxidative stress, adipocytokine imbalance, steatosis, and fibrogenesis. Moreover, acute DcR3a incubation in HepG2 cells, Hep3B cells, and mouse hepatocytes could normalize the expression of genes related to lipid oxidation along with inflammation and oxidative stress.

CONCLUSION

The ability of DcR3 to attenuate hepatic steatosis and inflammation through its non-decoy effects of immune modulation and oxidative stress attenuation makes it a potential treatment for NASH.

Clostridium butyricum B1 alleviates high-fat diet-induced steatohepatitis in mice via enterohepatic immunoregulation

BACKGROUND AND AIM

Enterohepatic immunologic derangement is associated with non-alcoholic steatohepatitis. Here, we investigated whether Clostridium butyricum B1 (CB) would be an effective immune-targeted substance to attenuate steatohepatitis in mice.

METHODS

Thirty mice were randomized into a control group fed with common forage, a high-fat diet (HFD) group fed an HFD for 16 weeks, and an HFD + CB group treated with CB for the latter 8 weeks. Inflammation-associated or metabolism-associated genes in the liver or epididymal fat tissue were quantified; intrahepatic and intestinal immune factors were detected. Further short-chain fatty acids in the cecal contents or liver were measured, and differentiations of T cells in vitro were analyzed.

RESULTS

Characteristics of non-alcoholic steatohepatitis in the HFD group were obvious and were significantly attenuated in the HFD + CB group. The messenger RNA levels of monocyte chemotactic protein-1 and tumor necrosis factor-α in the liver and epididymal fat tissue were increased in the HFD group compared with the control group and were downregulated in the HFD + CB group. Intrahepatic and intestinal interferon-γ and interleukin (IL)-17 were significantly increased, whereas forkhead box P3, IL-4, and IL-22 were significantly decreased in the HFD group compared with the control group. However, these intrahepatic or intestinal immune changes were reversed after CB intervention. Furthermore, butyrate in the cecal content and liver of the HFD + CB group was significantly elevated. An in vitro investigation showed that sodium butyrate promoted CD4⁺ T cell differentiation into Th2, Th22, or Treg, whereas it inhibited CD4⁺ T cell differentiation into Th1 or Th17 under a cytokine milieu, which was mimicked by Trichostatin A.

CONCLUSION

Clostridium butyricum B1 could attenuate HFD-induced steatohepatitis in mice partially through butyrate-induced enterohepatic immunoregulation.

Progression from Nonalcoholic Fatty Liver to Nonalcoholic Steatohepatitis Is Marked by a Higher Frequency of Th17 Cells in the Liver and an Increased Th17/Resting Regulatory T Cell Ratio in Peripheral Blood and in the Liver

Nonalcoholic fatty liver disease is increasing in prevalence. It can be subdivided into nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH). Five to twenty percent of cases progress from NAFL to NASH. Increased hepatic Th17 cells and IL-17 expression were observed in NASH mice and patients, respectively. We analyzed CD4(+) effector T cells and regulatory T cells (Tregs) from peripheral blood and livers of NAFL and NASH patients. A total of 51 NAFL patients, 30 NASH patients, 31 nonalcoholic fatty liver disease patients (without histology), and 43 healthy controls were included. FACS analysis was performed on PBMCs and intrahepatic lymphocytes. Compared with healthy controls, a lower frequency of resting Tregs (rTregs; CD4(+)CD45RA(+)CD25(++)) and higher frequencies of IFN-γ(+) and/or IL-4(+) cells were detected among CD4(+) T cells of peripheral blood in NASH, and to a lesser degree in NAFL. In hepatic tissue, NAFL to NASH progression was marked by an increase in IL-17(+) cells among intrahepatic CD4(+) T cells. To define immunological parameters in peripheral blood to distinguish NAFL from NASH, we calculated different ratios. Th17/rTreg and Th2/rTreg ratios were significantly increased in NASH versus NAFL. The relevance of our findings for NASH pathogenesis was highlighted by the normalization of all of the changes 1 y after bariatric surgery. In conclusion, our data indicate that NAFL patients show changes in their immune cell profile compared with healthy controls. NAFL to NASH progression is marked by an increased frequency of IL-17(+) cells among intrahepatic CD4(+) T cells and higher Th17/rTreg and Th2/rTreg ratios in peripheral blood.

Fatty acid-binding protein 5 limits the anti-inflammatory response in murine macrophages

The beginning stages of liver damage induced by various etiologies (i.e. high fat diet, alcohol consumption, toxin exposure) are characterized by abnormal accumulation of lipid in liver. Alterations in intracellular lipid transport, storage, and metabolism accompanied by cellular insult within the liver play an important role in the pathogenesis of liver disease, often involving a sustained inflammatory response. The intracellular lipid transporter, fatty acid binding protein 5 (FABP5), is highly expressed in macrophages and may play an important role in the hepatic inflammatory response after endotoxin exposure in mice. This study tested the hypothesis that FABP5 regulates macrophage response to LPS in male C57bl/6 (wild type) and FABP5 knockout mice, both in vitro and in vivo. Treatment with LPS revealed that loss of FABP5 enhances the number of hepatic F4/80(+) macrophages in the liver despite limited liver injury. Conversely, FABP5 knock out mice display higher mRNA levels of anti-inflammatory cytokines IL-10, arginase, YM-1, and Fizz-1 in liver compared to wild type mice. Bone marrow derived macrophages stimulated with inflammatory (LPS and IFN-γ) or anti-inflammatory (IL-4) mediators also showed significantly higher expression of anti-inflammatory/regulatory factors. These findings reveal a regulatory role of FABP5 in the acute inflammatory response to LPS-induced liver injury, which is consistent with the principle finding that FABP5 is a regulator of macrophage phenotype. Specifically, these findings demonstrate that loss of FABP5 promotes a more anti-inflammatory response.

Smad3 signaling in the regenerating liver: implications for the regulation of IL-6 expression

Liver regeneration is vital for graft survival and adequate organ function. Smad activation regulates hepatocyte proliferation and macrophage function. The aim of the current study was to evaluate the impact of Smad3 signaling during liver regeneration in the mouse. Male C57Bl/6 wild-type (wt) mice or mice deficient in Smad3 (Smad3(-/-) ) were subjected to a 70% partial hepatectomy (pHx) or sham surgery and sacrificed 24, 42, or 48 h later. Tissue was analyzed for TGF-β signaling, the mitogenic cytokine response [i.e., tumor necrosis factor alpha, TNF-α; interleukin (IL)-6], and liver regeneration. Partial hepatectomy stimulated a strong regenerative response measured by proliferating cell nuclear antigen-positive hepatocytes 42 and 48 h post-pHx in conjunction with an increased expression of IL-6, TNF-α, and Smad2/3 phosphorylation 24 h post-pHx in both hepatocytes and nonparenchymal cells. Surprisingly, Smad3 deficiency led to reduced hepatocyte proliferation 42 h post-pHx which recovered by 48 h, a process that correlated with and was preceded by significant reductions in IL-6 expression and signal transducer and activator of transcription 3 phosphorylation, and cyclin D1 induction 24 h post-pHx. Loss of Smad3 signaling suppresses the expression of key mitogenic cytokines and delays hepatocellular regeneration. Therapies directed at finely regulating Smad3 activation early within the regenerating liver may prove useful in promoting liver cell proliferation and restoration of liver mass.

Alterations in NK cell phenotype in relation to liver steatosis in children with chronic hepatitis C

NK cells were found to play an important role in liver fibrosis, a process commonly seen in a chronic liver disease such as chronic hepatitis C (CHC). The aim of this study was to evaluate potential differences in relation to coexisting liver steatosis in children with chronic hepatitis C. The study group consisted of 31 children with chronic hepatitis, aged 7–18 years (mean = 15 ± 2 years). Blood samples were taken prior to liver biopsy. The METAVIR scale was used for histological evaluation. Peripheral lymphocytes were subjected to monoclonal antibodies to CD56 antigen, KIRs and NKG2D antigens. Cells were assayed by flow cytometry for the ratio of positive cells and mean fluorescence intensity (MFI). Results were evaluated regarding the presence of liver steatosis. Significantly higher mean AST activity as well as higher AST-to-platelets ratio index (APRI) was observed in a group of children with coexisting liver steatosis. These children had significantly higher MFI for CD158e and lower MFI for NKG2D. All CHC patients had significantly higher MFI for NKG2D than the controls. The proportion of cells with expression of CD158i, KIR2D and APRI was found independent predictors of liver steatosis in univariate analysis and body mass index in logistic regression. The expression of NK cell receptors is altered in coexisting steatosis that may influence long-term prognosis in CHC.

Microbiota and nonalcoholic steatohepatitis

The recent rise in obesity-related diseases, such as nonalcoholic fatty liver disease and its strong association with microbiota, has elicited interest in the underlying mechanisms of these pathologies. Experimental models have highlighted several mechanisms connecting microbiota to the development of liver dysfunction in nonalcoholic steatohepatitis (NASH) such as increased energy harvesting from the diet, small intestine bacterial overgrowth, modulation of the intestinal barrier by glucagon-like peptide-2 secretions, activation of innate immunity through the lipopolysaccharide-CD14 axis caused by obesity-induced leptin, periodontitis, and sterile inflammation. The manipulation of microbiota through probiotics, prebiotics, antibiotics, and periodontitis treatment yields encouraging results for the treatment of obesity, diabetes, and NASH, but data in humans is scarce.

Pro-inflammatory activated Kupffer cells by lipids induce hepatic NKT cells deficiency through activation-induced cell death

Background

Dietary lipids play an important role in the progression of non-alcoholic fatty liver disease (NAFLD) through alternation of liver innate immune response.

Aims

The present study was to investigate the effect of lipid on Kupffer cells phenotype and function invivo and invitro. And further to investigate the impact of lipid on ability of Kupffer cell lipid antigen presentation to activate NKT cells.

Methods

Wild type male C57BL/6 mice were fed either normal or high-fat diet. Hepatic steatosis, Kupffer cell abundance, NKT cell number and cytokine gene expression were evaluated. Antigen presentation assay was performed with Kupffer cells treated with certain fatty acids invitro and co-cultured with NKT cells.

Results

High-fat diet induced hepatosteatosis, significantly increased Kupffer cells and decreased hepatic NKT cells. Lipid treatment invivo or invitro induced increase of pro-inflammatory cytokines gene expression and toll-like receptor 4 (TLR4) expression in Kupffer cells. Kupffer cells expressed high levels of CD1d on cell surface and only presented exogenous lipid antigen to activate NKT cells. Ability of Kupffer cells to present antigen and activate NKT cells was enhanced after lipid treatment. In addition, pro-inflammatory activated Kupffer cells by lipid treatment induced hepatic NKT cells activation-induced apoptosis and necrosis.

Conclusion

High-fat diet increase Kupffer cells number and induce their pro-inflammatory status. Pro-inflammatory activated Kupfffer cells by lipid promote hepatic NKT cell over-activation and cell death, which lead to further hepatic NKT cell deficiency in the development of NAFLD.

IFN-γ deficiency attenuates hepatic inflammation and fibrosis in a steatohepatitis model induced by a methionine- and choline-deficient high-fat diet

Cytokines play important roles in all stages of steatohepatitis, including hepatocyte injury, the inflammatory response, and the altered function of sinusoidal cells. This study examined the involvement of a major inflammatory cytokine, interferon-γ (IFN-γ), in the progression of steatohepatitis. In a steatohepatitis model by feeding a methionine- and choline-deficient high-fat (MCDHF) diet to both wild-type and IFN-γ-deficient mice, the liver histology, expression of genes encoding inflammatory cytokines, and fibrosis-related markers were examined. To analyze the effects of IFN-γ on Kupffer cells in vitro, we examined the tumor necrosis factor-α (TNF-α) production by a mouse macrophage cell line. Forty two days of MCDHF diet resulted in weight loss, elevated aminotransferases, liver steatosis, and inflammation in wild-type mice. However, the IFN-γ-deficient mice exhibited less extensive changes. RT-PCR revealed that the expression of tumor necrosis factor-α (TNF-α), transforming growth factor-β, inducible nitric oxide synthase, interleukin-4 and osteopontin were increased in wild-type mice, although they were suppressed in IFN-γ-deficient mice. Seventy days of MCDHF diet induced much more liver fibrosis in wild-type mice than in IFN-γ-deficient mice. The expression levels of fibrosis-related genes, α-smooth muscle actin, type I collagen, tissue inhibitor of matrix metalloproteinase-1, and matrix metalloproteinase-2, were dramatically increased in wild-type mice, whereas they were significantly suppressed in IFN-γ-deficient mice. Moreover, in vitro experiments showed that, when RAW 264.7 macrophages were treated with IFN-γ, they produced TNF-α in a dose-dependent manner. The present study showed that IFN-γ deficiency might inhibit the inflammatory response of macrophages cells and subsequently suppress stellate cell activation and liver fibrosis. These findings highlight the critical role of IFN-γ in the progression of steatohepatitis.

Immunohistochemical phenotyping of the inflammatory infiltrate in de novo autoimmune hepatitis after liver transplantation in children

We have investigated the inflammatory infiltrate in post-transplant dn-AIH, a form of late insidious graft rejection, focusing on transcription factors defining effector and T-regs, using an antigen retrieval immunohistochemical method on archived liver tissue, and compared it with ACR and classical AIH. Paraffin-embedded liver biopsies from pediatric patients with dn-AIH (n = 10), ACR (n = 10), and AIH (n = 13) were selected randomly and stained using antibodies directed to CD4, CD8, T-bet (marker of Th1 polarization), GATA-3 (marker of Th2 polarization), FOXP3 (marker for T regulatory cells), IL-17, CD56 (NK cells), and perforin. Portal and lobular lymphocytic infiltrate was assessed semi-quantitatively. Prominent CD4, CD8, and T-bet positivity were present in both the lobular and portal infiltrate of all three conditions. Overall T-bet score of lobular inflammation in the dn-AIH group was lower than in the ACR and AIH groups (p = 0.02). In contrast, most samples showed absent or minimal GATA-3 positivity. FOXP3, CD56, IL-17, and perforin staining of mild to moderate severity were present in all three groups in both the portal and lobular infiltrate. A Th1 polarization of the inflammatory infiltrate characterizes dn-AIH, but also ACR and AIH.

Bias in macrophage activation pattern influences non-alcoholic steatohepatitis (NASH) in mice

In humans, there is large inter-individual variability in the evolution of NAFLD (non-alcoholic fatty liver disease) to NASH (non-alcoholic steatohepatitis). To investigate this issue, NASH was induced with an MCD (methionine-choline-deficient) diet in C57BL/6 and Balb/c mice that are characterized by different biases in Th1/Th2 and macrophage (M1/M2) responses. Following 4 weeks on the MCD diet, steatosis and lobular inflammation were prevalent in C57BL/6 (Th1, M1 oriented) than in Balb/c (Th2, M2 oriented) mice. Consistently, hepatic TNFα (tumour necrosis factor α) mRNA expression and circulating TNFα levels were higher in MCD-fed C57BL/6 than in MCD-fed Balb/c mice. The Th1/Th2 bias did not account for the increased NASH severity, as in both strains MCD feeding did not significantly modify the liver mRNA expression of the Th1 markers IFNγ (interferon γ) and T-bet or that of the Th2 markers IL-4 (interleukin 4) and GATA-3. Conversely, MCD-fed C57BL/6 mice displayed higher liver mRNAs for the macrophage M1 activation markers iNOS (inducible NO synthase), IL-12p40 and CXCL10 (CXC chemokine ligand 10) than similarly treated Balb/c mice, without effects on the M2 polarization markers IL-10 and MGL-1 (macrophage galactose-type C-type lectin-1). Circulating IL-12 was also higher in MCD-fed C57BL/6 than in MCD-fed Balb/c mice. The analysis of macrophages isolated from the livers of MCD-fed animals confirmed an enhanced expression of M1 markers in C57BL/6 mice. Among all of the MCD-treated mice, liver iNOS, IL-12p40 and CXCL10 mRNA levels positively correlated with the frequency of hepatic necro-inflammatory foci. We concluded that the macrophage M1 bias in C57BL/6 mice may account for the increased severity of NASH in this strain, suggesting macrophage responses as important contributors to NAFLD progression.

Role of NKT Cells in the Pathogenesis of NAFLD

Nonalcoholic fatty liver disease (NAFLD) is the most frequent chronic liver disease and shows various inflammatory changes in the liver. Among those inflammatory cells, natural killer T (NKT) cells are found to have a critical role during the disease progression. NKT cells may have a protective role at the early stage with simple steatosis through modification of insulin resistance, whereas they act as a progression factor at the advanced stage with fibrosis. Those processes are thought to depend on interaction between NKT cells and CD1d molecule in the liver.

Interleukin-17 exacerbates hepatic steatosis and inflammation in non-alcoholic fatty liver disease

Mechanisms associated with the progression of simple steatosis to non-alcoholic fatty liver disease (NAFLD) remain undefined. Regulatory T cells (T(regs)) play a critical role in regulating inflammatory processes in non-alcoholic steatohepatitis (NASH) and because T helper type 17 (Th17) functionally oppose T(reg)-mediated responses, this study focused on characterizing the role of Th17 cells using a NAFLD mouse model. C57BL/6 mice were fed either a normal diet (ND) or high fat (HF) diet for 8 weeks. Mice in the HF group had a significantly higher frequency of liver Th17 cells compared to ND-fed mice. Neutralization of interleukin (IL)-17 in HF mice ameliorated lipopolysaccharide (LPS)-induced liver injury reflected by decreased serum alanine aminotransferase (ALT) levels and reduced inflammatory cell infiltrates in the liver. In vitro, HepG2 cells cultured in the presence of free fatty acids (FFA; oleic acid and palmitic acid) for 24 h and IL-17 developed steatosis via insulin-signalling pathway interference. IL-17 and FFAs synergized to induce IL-6 production by HepG2 cells and murine primary hepatocytes which, in combination with transforming growth factor (TGF-β), expanded Th17 cells. It is likely that a similar process occurs in NASH patients, as there were significant levels of IL-17(+) cell infiltrates in NASH patient livers. The hepatic expression of Th17 cell-related genes [retinoid-related orphan receptor gamma (ROR)γt, IL-17, IL-21 and IL-23] was also increased significantly in NASH patients compared to healthy controls. Th17 cells and IL-17 were associated with hepatic steatosis and proinflammatory response in NAFLD and facilitated the transition from simple steatosis to steatohepatitis. Strategies designed to alter the balance between Th17 cells and T(regs) should be explored as a means of preventing progression to NASH and advanced liver diseases in NAFLD patients.

The split personality of NKT cells in malignancy, autoimmune and allergic disorders

NKT cells are a heterogeneous subset of specialized, self-reactive T cells, with innate and adaptive immune properties, which allow them to bridge innate and adaptive immunity and profoundly influence autoimmune and malignant disease outcomes. NKT cells mediate these activities through their ability to rapidly express pro- and anti-inflammatory cytokines that influence the type and magnitude of the immune response. Not only do NKT cells regulate the functions of other cell types, but experimental evidence has found NKT cell subsets can modulate the functions of other NKT subsets. Depending on underlying mechanisms, NKT cells can inhibit or exacerbate autoimmunity and malignancy, making them potential targets for disease intervention. NKT cells can respond to foreign and endogenous antigenic glycolipid signals that are expressed during pathogenic invasion or ongoing inflammation, respectively, allowing them to rapidly react to and influence a broad array of diseases. In this article we review the unique development and activation pathways of NKT cells and focus on how these attributes augment or exacerbate autoimmune disorders and malignancy. We also examine the growing evidence that NKT cells are involved in liver inflammatory conditions that can contribute to the development of malignancy.

Cafeteria diet is a robust model of human metabolic syndrome with liver and adipose inflammation: comparison to high-fat diet

Obesity has reached epidemic proportions worldwide and reports estimate that American children consume up to 25% of calories from snacks. Several animal models of obesity exist, but studies are lacking that compare high-fat diets (HFD) traditionally used in rodent models of diet-induced obesity (DIO) to diets consisting of food regularly consumed by humans, including high-salt, high-fat, low-fiber, energy dense foods such as cookies, chips, and processed meats. To investigate the obesogenic and inflammatory consequences of a cafeteria diet (CAF) compared to a lard-based 45% HFD in rodent models, male Wistar rats were fed HFD, CAF or chow control diets for 15 weeks. Body weight increased dramatically and remained significantly elevated in CAF-fed rats compared to all other diets. Glucose- and insulin-tolerance tests revealed that hyperinsulinemia, hyperglycemia, and glucose intolerance were exaggerated in the CAF-fed rats compared to controls and HFD-fed rats. It is well-established that macrophages infiltrate metabolic tissues at the onset of weight gain and directly contribute to inflammation, insulin resistance, and obesity. Although both high fat diets resulted in increased adiposity and hepatosteatosis, CAF-fed rats displayed remarkable inflammation in white fat, brown fat and liver compared to HFD and controls. In sum, the CAF provided a robust model of human metabolic syndrome compared to traditional lard-based HFD, creating a phenotype of exaggerated obesity with glucose intolerance and inflammation. This model provides a unique platform to study the biochemical, genomic and physiological mechanisms of obesity and obesity-related disease states that are pandemic in western civilization today.

Inflammatory links between obesity and metabolic disease

The obesity epidemic has forced us to evaluate the role of inflammation in the health complications of obesity. This has led to a convergence of the fields of immunology and nutrient physiology and the understanding that they are inextricably linked. The reframing of obesity as an inflammatory condition has had a wide impact on our conceptualization of obesity-associated diseases. In this Review, we highlight the cellular and molecular mechanisms at play in the generation of obesity-induced inflammation. We also emphasize how defining the immune regulation in metabolic tissues has broadened the understanding of the diversity of inflammatory responses.

Rhein ameliorates fatty liver disease through negative energy balance, hepatic lipogenic regulation, and immunomodulation in diet-induced obese mice

Nonalcoholic fatty liver disease (NAFLD) is associated with obesity, insulin resistance, and inflammatory disorders. In this study, we tested the effect of rhein, a lipophilic anthraquinone derived from a traditional Chinese herbal medicine Rheum palmatum L., on NAFLD-associated hepatic steatosis, insulin resistance, and the T helper (Th)1/Th2 cytokine imbalance in high-fat diet-induced obese (DIO) mice. We found that oral administration of rhein for 40 days significantly increased energy expenditure, reduced body weight, particularly body fat content, improved insulin resistance, and lowered circulating cholesterol levels in DIO mice without affecting food intake. Rhein treatment also reduced liver triglyceride levels, reversed hepatic steatosis, and normalized alanine aminotransferase (ALT) levels in these mice. Gene analysis and Western blot showed that rhein markedly suppressed the expression of the lipogenic enzyme sterol regulatory element-binding protein-1c (SREBP-1c) and its target genes in the liver. Luciferase reporter assay revealed that rhein suppressed the transcriptional activity of SREBP-1c through its upstream regulator, liver X receptor (LXR). This suggests that rhein exerts its effects by targeting LXR, which is also supported by its inability to reduce body weight in LXR knockout mice. Moreover, multiplex ELISA displayed a downregulated Th1 response after rhein treatment. Rhein shifted the Th1/Th2 responses by inhibiting T-box expressed in T-cells (T-bet) expression and enhancing GATA-binding protein-3 (GATA-3) expression through increased signal transducer and activator of transcription 6 (STAT6) phosphorylation. These data indicate that rhein ameliorated NAFLD and associated disorders through LXR-mediated negative energy balance, metabolic regulatory pathways, and immunomodulatory activities involved in hepatic steatosis. The combined effects of rhein to target hepatic metabolic and immune pathways may be beneficial for complex metabolic diseases such as NAFLD.

Preventive effects of 1,25-(OH)2VD3 against ConA-induced mouse hepatitis through promoting vitamin D receptor gene expression

AIM

To investigate the immunosuppressive effects of 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)VD(3)) on concanavalin A (ConA)-induced hepatitis and elucidate the action mechanism.

METHODS

Female BALB/C mice were intravenously administered ConA (20 mg/kg) to induce acute immunological liver injury. Liver damage was evaluated in respect to serum alanine transaminase (ALT) level and liver histological changes. The proliferation of splenocytes was measured by using [(3)H]-thymidine incorporation. The cytokine level in the cultured splenocyte supernatant was determined by using enzyme-linked immunosorbent assays (ELISAs). The percentage of different splenic T cell subtypes was analyzed by using flow cytometry. The expression of splenic vitamin D receptor (VDR) mRNA and protein was detected by using real-time qRT-PCR and Western blot, respectively.

RESULTS

1,25-(OH)(2)VD(3) (2.5 microg/kg, ip) significantly decreased the serum ALT levels and markedly attenuated the histological liver damage. The beneficial effect of 1,25-(OH)(2)VD(3) was associated with: (i) inhibition of CD4(+) T cell activation; (ii) reduction of interferon-gamma (IFN-gamma) and elevation of both IL-4 and IL-5 in supernatants of cultured splenocytes; and (iii) elimination of activated T cells by increasing VDR mRNA and protein expression in the spleen.

CONCLUSION

1,25-(OH)(2)VD(3) had a significant protective effect against ConA-induced hepatitis, and its mechanism of action was associated with down-regulation of T cell-mediated immunity and up-regulation of VDR gene expression.

Inflammatory mediators and insulin resistance in obesity: role of nuclear receptor signaling in macrophages

Visceral obesity is coupled to a general low-grade chronic inflammatory state characterized by macrophage activation and inflammatory cytokine production, leading to insulin resistance (IR). The balance between proinflammatory M1 and antiinflammatory M2 macrophage phenotypes within visceral adipose tissue appears to be crucially involved in the development of obesity-associated IR and consequent metabolic abnormalities. The ligand-dependent transcription factors peroxisome proliferator activated receptors (PPARs) have recently been implicated in the determination of the M1/M2 phenotype. Liver X receptors (LXRs), which form another subgroup of the nuclear receptor superfamily, are also important regulators of proinflammatory cytokine production in macrophages. Disregulation of macrophage-mediated inflammation by PPARs and LXRs therefore underlies the development of IR. This review summarizes the role of PPAR and LXR signaling in macrophages and current knowledge about the impact of these actions in the manifestation of IR and obesity comorbidities such as liver steatosis and diabetic osteopenia.

Heme oxygenase-1 protects against steatohepatitis in both cultured hepatocytes and mice

BACKGROUND & AIMS

Heme oxygenase-1 (HO-1), an antioxidant defense enzyme, has been shown to protect against oxidant-induced tissue injury. We investigated the role of HO-1 in nutritional steatohepatitis in vitro and in vivo.

METHODS

AML-12 hepatocytes were cultured in methionine- and choline-deficient (MCD) medium. Cells were transfected with an adenovirus vector that expressed HO-1 (Ad-HO-1) or incubated with the HO-1 inducer hemin or the HO-1 inhibitor stannic mesoporphyrin for 24 hours. C57BL6 mice and db/db mice were fed MCD or control diets, with or without hemin, for up to 4 weeks.

RESULTS

AML-12 cells exposed to MCD medium developed significant steatosis, increased release of alanine aminotransferase, and showed signs of oxidative injury. Incubation with hemin induced HO-1 protein, suppressed steatosis, and reduced levels of alanine aminotransferase and lipid peroxidation. A comparable effect was observed in cells transfected with Ad-HO-1, whereas incubation of these cells with stannic mesoporphyrin completely abolished the Ad-HO-1- or hemin-mediated protection of hepatocytes. Mice injected with hemin significantly attenuated MCD-induced steatohepatitis and increased HO-1 protein and activity. This effect was associated with up-regulation of antioxidant chaperones and enzymes, down-regulation of proinflammatory cytokines, and up-regulation of the anti-inflammatory interleukin-22. Moreover, the reduction in steatosis caused by hemin was affected by up-regulation of peroxisome proliferator-activated receptor-alpha and by down-regulation of sterol regulatory element binding protein-1c.

CONCLUSIONS

HO-1 can interrupt progression of nutritional steatohepatitis by inducing an antioxidant pathway, suppressing production of cytokines, and modifying fatty acid turnover. Induction of HO-1 might provide a new approach for treatment of steatohepatitis.

Co-appearance of autoantibody-producing B220(low) B cells with NKT cells in the course of hepatic injury

Severe hepatic injury is induced by Concanavalin A (Con A) administration in mice, the major effector cells being CD4(+) T cells, NKT cells and macrophages. Since autologous lymphocyte subsets are associated with tissue damage, Con A-induced hepatic injury is considered to be autoimmune hepatitis. However, it has remained to be investigated how autoantibodies and B-1 cells are responsible for this phenomenon. In this study, it was demonstrated that autoantibodies which were detected using Hep-2 cells in immunofluorescence tests and using double-strand (ds) DNA in the ELISA method, appeared after Con A administration (a peak at day 14). Moreover, autoantibody-producing B220(low) cells (i.e., B-1 cells) also appeared at this time. Purified B220(low) cells were found to have a potential to produce autoantibodies. These results suggest that Con A-induced hepatic injury indeed includes the mechanism of autoimmune hepatitis.

Kupffer cell and interleukin-12-dependent loss of natural killer T cells in hepatosteatosis

Hepatosteatosis is associated with increased expression of tumor necrosis factor alpha (TNF-alpha) and interleukin (IL)-12, major T helper (Th) 1 cytokines, and reduced hepatic natural killer T (NKT) cell numbers. The relationship between lipid accumulation, cytokine expression, and hepatic NKT cells is not known. This study was conducted to assess the role of IL-12 in the development of hepatic steatosis and its potential impact on liver NKT cells. Male C57Bl/6 wildtype (WT) and IL-12-deficient (IL-12(-/-)) mice were fed a choline-deficient diet (CDD) for 0, 10, or 20 weeks. CDD led to marked hepatosteatosis, reduced hepatic but not splenic NKT cell numbers and function, and increased hepatic expression of the T(h)1-type cytokines IL-12, interferon gamma (IFN-gamma), and TNF-alpha in WT mice. The absence of IL-12 resulted in similar CDD-induced hepatosteatosis, but preserved hepatic NKT cells and significantly reduced hepatic IFN-gamma and TNF-alpha expression. Treatment of CDD-fed mice with lipopolysaccharide led to a significant increase in hepatic IL-12 expression, and Kupffer cell (KC) depletion reduced liver IL-12 expression and restored NKT cells in CDD-induced fatty liver. Interestingly, KCs from CDD-fed mice failed to produce increased quantities of IL-12 upon activation in vitro when compared to similarly treated KCs from control fed mice, suggesting that secondary factors in vivo promote heightened IL-12 production. Finally, human livers with severe steatosis showed a substantial decrease in NKT cells.

CONCLUSION

Hepatosteatosis reduces the numbers of hepatic NKT cells in a KC-and IL-12-dependent manner. Our results suggest a pivotal and multifunctional role of KC-derived IL-12 in the altered immune response in steatotic liver, a process that is likely active within human nonalcoholic fatty liver disease.

Retinol supplements antiviral action of interferon in patients with chronic hepatitis C: a prospective pilot study

Sustained virologic response with peg-interferon and ribavirin combination therapy for 48 weeks is still inadequate. Our study examined whether short-term administration of retinol clinically influences the anti-viral activity of interferon early during interferon and ribavirin combination therapy. The control group received 6 MIU of interferon α-2b every day for two weeks and then 3 times a week for 22 weeks intramuscularly plus 600 mg or 800 mg per day of ribavirin orally for 24 weeks. The retinol group, in addition to above treatment, received retinol 30,000 units per day orally for 3 weeks from one week before the start of interferon α-2b plus ribavirin combination therapy. The hepatitis C virus (HCV) RNA negativity rate at 1 week after the end of interferon α-2b and ribavirin combination therapy was 46.7% (28/60) for the retinol group and 31.7% (19/60) for the control group, which was significantly higher for the retinol group. The level of serum HCV RNA in the retinol group was significantly lower at 1 week after beginning treatment as compared to the control group (p<0.01). Furthermore, serum 2,5'AS protein at 1 week after beginning treatment was significantly higher in the retinol group (p = 0.0002). The results suggest that retinol supplement increases the antiviral effect of interferon α-2b plus ribavirin only during the administration of IFN α-2b, ribavirin and retinol in patients with chronic hepatitis C.