Comprehensive study of the interplay between immunological and metabolic factors in hepatic steatosis

The pathophysiology of hepatic steatosis is thoroughly reviewed in this comprehensive report, with particular attention to the complex interactions between inflammatory pathways, insulin resistance, lipid metabolism, metabolic dysregulation, and immunological responses in the liver including non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and hepatocellular carcinoma (HCC). The study highlights the role of immune cell regulation in disease progression and explores the potential of immune cell-specific treatments for treating hepatic disorders. The development of liver disorders is significantly influenced by immune cells, including dendritic cells, T cells, and natural killer cells. Clinical investigations show that immune cell-specific treatments can effectively reduce liver fibrosis and inflammation. Future research should focus on finding new immunological targets for therapeutic interventions, as well as addressing the management challenges associated with NAFLD/NASH. Hepatic immune microorganisms also impact liver homeostasis and disorders. Improvements in immune cell regulation and liver transplantation methods give patients hope for better prognoses. Important phases include optimizing the selection of donors for malignancy of the liver, using machine perfusion for organ preservation, and fine-tuning immunosuppressive strategies. For focused treatments in hepatic steatosis, it is imperative to understand the intricate interactions between immune and metabolic variables. Understanding the liver's heterogeneous immune profile, encompassing a range of immune cell subpopulations, is crucial for formulating focused therapeutic interventions. To improve patient care and outcomes in hepatic illnesses, there is an urgent need for further research and innovation. Therefore, to effectively treat hepatic steatosis, it is important to enhance therapeutic techniques and maximize liver transplantation strategies.

Monocyte bioenergetics: An immunometabolic perspective in metabolic dysfunction-associated steatohepatitis

Monocytes (Mos) are crucial in the evolution of metabolic dysfunction-associated steatotic liver disease (MASLD) to metabolic dysfunction-associated steatohepatitis (MASH), and immunometabolism studies have recently suggested targeting leukocyte bioenergetics in inflammatory diseases. Here, we reveal a peculiar bioenergetic phenotype in circulating Mos of patients with MASH, characterized by high levels of glycolysis and mitochondrial (mt) respiration. The enhancement of mt respiratory chain activity, especially complex II (succinate dehydrogenase [SDH]), is unbalanced toward the production of reactive oxygen species (ROS) and is sustained at the transcriptional level with the involvement of the AMPK-mTOR-PGC-1α axis. The modulation of mt activity with dimethyl malonate (DMM), an SDH inhibitor, restores the metabolic profile and almost abrogates cytokine production. Analysis of a public single-cell RNA sequencing (scRNA-seq) dataset confirms that in murine models of MASH, liver Mo-derived macrophages exhibit an upregulation of mt and glycolytic energy pathways. Accordingly, the DMM injection in MASH mice contrasts Mo infiltration and macrophagic enrichment, suggesting immunometabolism as a potential target in MASH.

Innate Immunity and MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) has emerged as the most common liver disease worldwide in recent years. MASLD commonly presents as simple hepatic steatosis, but ~25% of patients develop liver inflammation, progressive fibrosis, liver cirrhosis and related hepatocellular carcinoma. Liver inflammation and the degree of fibrosis are key determinants of the prognosis. The pathophysiology of liver inflammation is incompletely understood and involves diverse factors and specifically innate and adaptive immune responses. More specifically, diverse mediators of innate immunity such as proinflammatory cytokines, adipokines, inflammasomes and various cell types like mononuclear cells, macrophages and natural killer cells are involved in directing the inflammatory process in MASLD. The activation of innate immunity is driven by various factors including excess lipids and lipotoxicity, insulin resistance and molecular patterns derived from gut commensals. Targeting pathways of innate immunity might therefore appear as an attractive therapeutic strategy in the future management of MASLD and possibly its complications.

The role of dendritic cells in MASH: friends or foes?

Dendritic cells (DCs) are major antigen-presenting cells that connect innate and adaptive immunity. Hepatic DCs are less activated and contribute to maintain the tolerogenic environment of the liver under steady state. Several studies indicated DCs in metabolic dysfunction-associated steatohepatitis (MASH), representing a substantial burden on healthcare systems due to its association with liver-related morbidity and mortality. Studies highlighted the potential disease-promoting role of liver DCs in the development of MASH while other experimental systems suggested their protective role. This review discusses this controversy and the current understanding of how DCs affect the pathogenesis of MASH.

Steatosis, Steatohepatitis and Cancer Immunotherapy: An Intricate Story

Immune checkpoint inhibitors represent one of the most significant recent advances in clinical oncology, since they dramatically improved the prognosis of deadly cancers such as melanomas and lung cancer. Treatment with these drugs may be complicated by the occurrence of clinically-relevant adverse drug reactions, most of which are immune-mediated, such as pneumonitis, colitis, endocrinopathies, nephritis, Stevens Johnson syndrome and toxic epidermal necrolysis. Drug-induced steatosis and steatohepatitis are not included among the typical forms of cancer immunotherapy-induced liver toxicity, which, instead, usually occurs as a panlobular hepatitis with prominent lymphocytic infiltrates. Nonetheless, non-alcoholic fatty liver disease is a risk factor for immunotherapy-induced hepatitis, and steatosis and steatohepatitis are frequently observed in this condition. In the present review we discuss how these pathology findings could be explained in the context of current models suggesting immune-mediated pathogenesis for steatohepatitis. We also review evidence suggesting that in patients with hepatocellular carcinoma, the presence of steatosis or steatohepatitis could predict a poor therapeutic response to these agents. How these findings could fit with immune-mediated mechanisms of these liver diseases will also be discussed.

Single-cell profiling reveals distinct immune phenotypes that contribute to ischaemia-reperfusion injury after steatotic liver transplantation

OBJECTIVES

The discrepancy between supply and demand of organ has led to an increased utilization of steatotic liver for liver transplantation (LT). Hepatic steatosis, however, is a major risk factor for graft failure due to increased susceptibility to ischaemia-reperfusion (I/R) injury during transplantation.

MATERIALS AND METHODS

To assess the plasticity and phenotype of immune cells within the microenvironment of steatotic liver graft at single-cell level, single-cell RNA-sequencing (scRNA-Seq) was carried out on 23 675 cells from transplanted rat livers. Bioinformatic analyses and multiplex immunohistochemistry were performed to assess the functional properties, transcriptional regulation, phenotypic switching and cell-cell interactions of different cell subtypes.

RESULTS

We have identified 11 different cell types in transplanted livers and found that the highly complex ecosystem was shaped by myeloid-derived cell subsets that transit between different states and interact mutually. Notably, a pro-inflammatory phenotype of Kupffer cells (KCs) with high expression of colony-stimulating factor 3 (CSF3) that was enriched in transplanted steatotic livers was potentially participated in fatty graft injury. We have also detected a subset of dendritic cells (DCs) with highly expressing XCR1 that was correlated with CD8+ T cells, mediating the severer steatotic liver damage by I/R injury.

CONCLUSIONS

The findings of our study provide new insight into the mechanisms by which steatosis exacerbates liver damage from I/R injury. Interventions based on these observations create opportunities in attenuating fatty liver graft injury and expanding the donor pool.

Moderate Exercise Inhibits Age-Related Inflammation, Liver Steatosis, Senescence, and Tumorigenesis

Age-related chronic inflammation promotes cellular senescence, chronic disease, cancer, and reduced lifespan. In this study, we wanted to explore the effects of a moderate exercise regimen on inflammatory liver disease and tumorigenesis. We used an established model of spontaneous inflammaging, steatosis, and cancer (nfkb1-/- mouse) to demonstrate whether 3 mo of moderate aerobic exercise was sufficient to suppress liver disease and cancer development. Interventional exercise when applied at a relatively late disease stage was effective at reducing tissue inflammation (liver, lung, and stomach), oxidative damage, and cellular senescence, and it reversed hepatic steatosis and prevented tumor development. Underlying these benefits were transcriptional changes in enzymes driving the conversion of tryptophan to NAD+, this leading to increased hepatic NAD+ and elevated activity of the NAD+-dependent deacetylase sirtuin. Increased SIRT activity was correlated with enhanced deacetylation of key transcriptional regulators of inflammation and metabolism, NF-κB (p65), and PGC-1α. We propose that moderate exercise can effectively reprogram pre-established inflammatory and metabolic pathologies in aging with the benefit of prevention of disease.

Macrophages and scavenger receptors in obesity-associated non-alcoholic liver fatty disease (NAFLD)

With an increase in sedentary lifestyle and dietary over nutrition, obesity has become one of the major public health problems worldwide and is a prevalent predisposing risk factor to non-alcoholic fatty liver disease (NAFLD), the most common chronic liver disease in Western developed countries. NAFLD represents a series of diseased states ranging from non-alcoholic fatty liver (NAFL) to steatohepatitis (NASH), which can lead to fibrosis and eventually to cirrhosis and hepatocellular carcinoma. Currently, the only effective treatment to cure end-stage liver disease is liver transplantation. Macrophages have been reported to play a crucial role in the progression of NAFLD, thereby are a potential target for therapy. In this review, we discuss the current knowledge on the role of macrophages and inflammatory signalling pathways associated with obesity and chronic liver inflammation, and their contribution to NAFLD development and progression.

Molecular Mechanisms: Connections between Nonalcoholic Fatty Liver Disease, Steatohepatitis and Hepatocellular Carcinoma

Nonalcoholic fatty liver disease (NAFLD), including nonalcoholic steatohepatitis (NASH), causes hepatic fibrosis, cirrhosis and hepatocellular carcinoma (HCC). The patatin-like phospholipase-3 (PNPLA3) I148M sequence variant is one of the strongest genetic determinants of NAFLD/NASH. PNPLA3 is an independent risk factor for HCC among patients with NASH. The obesity epidemic is closely associated with the rising prevalence and severity of NAFLD/NASH. Furthermore, metabolic syndrome exacerbates the course of NAFLD/NASH. These factors are able to induce apoptosis and activate immune and inflammatory pathways, resulting in the development of hepatic fibrosis and NASH, leading to progression toward HCC. Small intestinal bacterial overgrowth (SIBO), destruction of the intestinal mucosa barrier function and a high-fat diet all seem to exacerbate the development of hepatic fibrosis and NASH, leading to HCC in patients with NAFLD/NASH. Thus, the intestinal microbiota may play a role in the development of NAFLD/NASH. In this review, we describe recent advances in our knowledge of the molecular mechanisms contributing to the development of hepatic fibrosis and HCC in patients with NAFLD/NASH.

Fpr2 Deficiency Alleviates Diet-Induced Insulin Resistance Through Reducing Body Weight Gain and Inhibiting Inflammation Mediated by Macrophage Chemotaxis and M1 Polarization

Obesity and related inflammation are critical for the pathogenesis of insulin resistance, but the underlying mechanisms are not fully understood. Formyl peptide receptor 2 (FPR2) plays important roles in host immune responses and inflammation-related diseases. We found that Fpr2 expression was elevated in the white adipose tissue of high-fat diet (HFD)-induced obese mice and db/db mice. The systemic deletion of Fpr2 alleviated HFD-induced obesity, insulin resistance, hyperglycemia, hyperlipidemia, and hepatic steatosis. Furthermore, Fpr2 deletion in HFD-fed mice elevated body temperature, reduced fat mass, and inhibited inflammation by reducing macrophage infiltration and M1 polarization in metabolic tissues. Bone marrow transplantations between wild-type and Fpr2^-/- mice and myeloid-specific Fpr2 deletion demonstrated that Fpr2-expressing myeloid cells exacerbated HFD-induced obesity, insulin resistance, glucose/lipid metabolic disturbances, and inflammation. Mechanistic studies revealed that Fpr2 deletion in HFD-fed mice enhanced energy expenditure probably through increasing thermogenesis in skeletal muscle; serum amyloid A3 and other factors secreted by adipocytes induced macrophage chemotaxis via Fpr2; and Fpr2 deletion suppressed macrophage chemotaxis and lipopolysaccharide-, palmitate-, and interferon-γ-induced macrophage M1 polarization through blocking their signals. Altogether, our studies demonstrate that myeloid Fpr2 plays critical roles in obesity and related metabolic disorders via regulating muscle energy expenditure, macrophage chemotaxis, and M1 polarization.

Myeloid-specific deletion of Zfp36 protects against insulin resistance and fatty liver in diet-induced obese mice

Obesity is associated with adipose tissue inflammation that contributes to insulin resistance. Zinc finger protein 36 (Zfp36) is an mRNA-binding protein that reduces inflammation by binding to cytokine transcripts and promoting their degradation. We hypothesized that myeloid-specific deficiency of Zfp36 would lead to increased adipose tissue inflammation and reduced insulin sensitivity in diet-induced obese mice. As expected, wild-type (Control) mice became obese and diabetic on a high-fat diet, and obese mice with myeloid-specific loss of Zfp36 [knockout (KO)] demonstrated increased adipose tissue and liver cytokine mRNA expression compared with Control mice. Unexpectedly, in glucose tolerance testing and hyperinsulinemic-euglycemic clamp studies, myeloid Zfp36 KO mice demonstrated improved insulin sensitivity compared with Control mice. Obese KO and Control mice had similar macrophage infiltration of the adipose depots and similar peripheral cytokine levels, but lean and obese KO mice demonstrated increased Kupffer cell (KC; the hepatic macrophage)-expressed Mac2 compared with lean Control mice. Insulin resistance in obese Control mice was associated with enhanced Zfp36 expression in KCs. Compared with Control mice, KO mice demonstrated increased hepatic mRNA expression of a multitude of classical (M1) inflammatory cytokines/chemokines, and this M1-inflammatory hepatic milieu was associated with enhanced nuclear localization of IKKβ and the p65 subunit of NF-κB. Our data confirm the important role of innate immune cells in regulating hepatic insulin sensitivity and lipid metabolism, challenge-prevailing models in which M1 inflammatory responses predict insulin resistance, and indicate that myeloid-expressed Zfp36 modulates the response to insulin in mice.

Complement Activation in Liver Transplantation: Role of Donor Macrosteatosis and Implications in Delayed Graft Function

The complement system anchors the innate inflammatory response by triggering both cell-mediated and antibody-mediated immune responses against pathogens. The complement system also plays a critical role in sterile tissue injury by responding to damage-associated molecular patterns. The degree and duration of complement activation may be a critical variable controlling the balance between regenerative and destructive inflammation following sterile injury. Recent studies in kidney transplantation suggest that aberrant complement activation may play a significant role in delayed graft function following transplantation, confirming results obtained from rodent models of renal ischemia/reperfusion (I/R) injury. Deactivating the complement cascade through targeting anaphylatoxins (C3a/C5a) might be an effective clinical strategy to dampen reperfusion injury and reduce delayed graft function in liver transplantation. Targeting the complement cascade may be critical in donor livers with mild to moderate steatosis, where elevated lipid burden amplifies stress responses and increases hepatocyte turnover. Steatosis-driven complement activation in the donor liver may also have implications in rejection and thrombolytic complications following transplantation. This review focuses on the roles of complement activation in liver I/R injury, strategies to target complement activation in liver I/R, and potential opportunities to translate these strategies to transplanting donor livers with mild to moderate steatosis.

Dysregulation of Kupffer Cells/Macrophages and Natural Killer T Cells in Steatohepatitis in LXRα Knockout Male Mice

Liver X receptor (LXR) α expression is mainly localized to metabolic tissues, such as the liver, whereas LXRβ is ubiquitously expressed. LXRα is activated by oxysterols and plays an important role in the regulation of lipid metabolism in metabolic tissues. In macrophages, LXRs stimulate reverse cholesterol transport and regulate immune responses. Although a high-cholesterol diet induces severe steatohepatitis in LXRα-knockout (KO) mice, the underlying mechanisms linking lipid metabolism and immune responses remain largely unknown. In this study, we investigated the role of LXRα in the pathogenesis of steatohepatitis by assessing the effects of a high-fat and high-cholesterol diet (HFCD) on hepatic immune cell proportion and function as well as lipid metabolism in wild-type (WT) and LXRα-KO mice. HFCD feeding induced severe steatohepatitis in LXRα-KO mice compared with WT mice. These mice had higher cholesterol levels in the plasma and the liver and dysregulated expression of LXR target and proinflammatory genes in both whole liver samples and isolated hepatic mononuclear cells. Flow cytometry showed an increase in CD68+CD11b+ Kupffer cells/macrophages and a decrease in invariant natural killer T cells in the liver of HFCD-fed LXRα-KO mice. These mice were more susceptible to lipopolysaccharide-induced liver injury and resistant to inflammatory responses against α-galactosylceramide or concanavalin-A treatment. The findings provide evidence for activation of bone marrow-derived Kupffer cells/macrophages and dysfunction of invariant natural killer T cells in LXRα-KO mouse liver. These findings indicate that LXRα regulates hepatic immune function along with lipid metabolism and protects against the pathogenesis of nonalcoholic steatohepatitis.

Markers of intestinal permeability are already altered in early stages of non-alcoholic fatty liver disease: Studies in children

Background & aims

Recent studies have shown that patients with manifest non-alcoholic fatty liver disease (NAFLD), e.g. steatosis grade 3 or steatohepatitis with or without beginning fibrosis frequently show altered fecal microbiota composition and elevated bacterial endotoxin levels. However, if these alterations are signs of a progressing disease or are already found in initial disease stages has not yet been clarified.

Methods

Twenty children with simple steatosis (grade 1) diagnosed by ultrasound and 29 normal weight healthy control children (age <10 years) were included in the study (mean age 7.6 ± 1.1 years). Metabolic parameters, markers of intestinal barrier function and inflammation were determined.

Results

Activity of alanine aminotransferase, concentrations of some markers of inflammation and insulin resistance were significantly higher in plasma of NAFLD children than in controls. When compared to controls, plasma bacterial endotoxin and lipopolysaccharide-binding protein (LBP) levels were significantly higher in NAFLD children (+50% and +24%, respectively), while soluble CD14 serum and D-lactate plasma levels as well as the prevalence of small intestinal bacterial overgrowth did not differ between groups. Plasma endotoxin and LBP levels were positive associated with proinflammatory markers like plasminogen activator inhibitor-1, c-reactive protein, interleukin-6 and leptin while no associations with markers of insulin resistance were found.

Conclusions

Taken together, our results indicate that even in juvenile patients with early stages of NAFLD e.g. simple steatosis grade 1, plasma endotoxin concentrations are already elevated further suggesting that intestinal barrier dysfunction might be present already in the initial phases of the disease.

Pigment epithelium-derived factor improves TNFα-induced hepatic steatosis in grass carp (Ctenopharyngodon idella)

Pro-inflammatory cytokines, such as tumor necrosis factor alpha (TNFα), may contribute to hepatic steatosis in the situation of excess lipid accumulation in farmed fish. Pigment epithelium-derived factor (PEDF) is an endogenous anti-inflammatory factor and promotes lipolysis. Accordingly, we isolated PEDF from grass carp and investigated its role in TNFα-induced hepatic steatosis. Sequence analysis showed that PEDF gene, which possesses 8 exons and 7 introns, encodes a protein with 409 amino acids. PEDF was a critical determinant of the transcriptional response to nutrient availability in grass carp. Endogenous PEDF was an intracellular protein with cytoplasmic distribution and directly interacts with adipose triglyceride lipase (ATGL), which might mediate PEDF-induced lipolysis. TNFα significantly promoted lipid accumulation in vivo and in vitro, accompanied with a decrease in mRNA levels of PEDF and peroxisome proliferator-activated receptor alpha (PPARα). Recombinant PEDF and PPARα agonist diminished the TNFα-induced hepatic steatosis. Meanwhile, PPARα agonist caused an increase in PEDF expression, suggesting that TNFα antagonizes the actions of PEDF possibly in a PPARα-dependent manner. These findings suggest that PEDF is an important protective factor against hepatic steatosis induced by TNFα, which provided a new therapeutic target for inflammation-associated hepatic steatosis.

Interleukin-13 Activates Distinct Cellular Pathways Leading to Ductular Reaction, Steatosis, and Fibrosis

Fibroproliferative diseases are driven by dysregulated tissue repair responses and are a major cause of morbidity and mortality because they affect nearly every organ system. Type 2 cytokine responses are critically involved in tissue repair; however, the mechanisms that regulate beneficial regeneration versus pathological fibrosis are not well understood. Here, we have shown that the type 2 effector cytokine interleukin-13 simultaneously, yet independently, directed hepatic fibrosis and the compensatory proliferation of hepatocytes and biliary cells in progressive models of liver disease induced by interleukin-13 overexpression or after infection with Schistosoma mansoni. Using transgenic mice with interleukin-13 signaling genetically disrupted in hepatocytes, cholangiocytes, or resident tissue fibroblasts, we have revealed direct and distinct roles for interleukin-13 in fibrosis, steatosis, cholestasis, and ductular reaction. Together, these studies show that these mechanisms are simultaneously controlled but distinctly regulated by interleukin-13 signaling. Thus, it may be possible to promote interleukin-13-dependent hepatobiliary expansion without generating pathological fibrosis. VIDEO ABSTRACT.

IL-25 or IL-17E Protects against High-Fat Diet-Induced Hepatic Steatosis in Mice Dependent upon IL-13 Activation of STAT6

IL-25 or IL-17E is a member of IL-17 cytokine family and has immune-modulating activities. The role of IL-25 in maintaining lipid metabolic homeostasis remains unknown. We investigated the effects of exogenous IL-25 or deficiency of IL-25 on hepatic lipid accumulation. IL-25 expression was examined in paraffin-embedded tissue sections of liver from patients or in the livers from mice. Mouse model of steatosis was induced by feeding a high-fat diet (HFD). Extent of steatosis as well as expression of cytokines, key enzymes for lipid metabolic pathways, markers for Kupffer cells/macrophages, and lipid droplet (LD) proteins, were analyzed. Our results show that hepatic steatosis in mice was accompanied by increased LD proteins, but decreased IL-25 in the liver. Decreased hepatic IL-25 was also observed in patients with fatty liver. Administration of IL-25 to HFD-fed wild-type mice led to a significant improvement in hepatic steatosis. This effect was associated with increased expression of IL-13, development of alternatively activated Kupffer cells/macrophages, and decreased expression of LD proteins in the liver. In contrast, administration of IL-25 to HFD-fed mice deficient in STAT6 or IL-13 had no effects. In addition, stimulation of primary hepatocytes with IL-13, but not IL-25, resulted in downregulation of LD proteins. Finally, mice deficient in IL-25 had exacerbated hepatic lipid accumulation when fed the HFD. These data demonstrate that dysregulated IL-25 expression contributes to lipid accumulation, whereas exogenous IL-25 protects against hepatic steatosis through IL-13 activation of STAT6. IL-25 and IL-13 are potential therapeutic agents for hepatic steatosis and associated pathologies.

Myeloid cell TRAF3 promotes metabolic inflammation, insulin resistance, and hepatic steatosis in obesity

Myeloid cells, particularly macrophages, mediate metabolic inflammation, thus promoting insulin resistance and metabolic disease progression in obesity. Numerous cytokines, toxic metabolites, damage-associated molecular patterns, and pathogen-associated molecular patterns are involved in activating macrophages via their cognate receptors in obesity. TRAF3 (TNF receptor-associated factor 3) is a common signaling molecule for these ligands/receptors and negatively regulates the proinflammatory NF-κB and MAPK pathways, but its metabolic activity is unknown. We here show that myeloid cell TRAF3 is required for metabolic inflammation and metabolic disease progression in obesity. Myeloid cell-specific deletion of TRAF3 significantly attenuated insulin resistance, hyperglycemia, hyperinsulinemia, glucose intolerance, and hepatic steatosis in mice with either genetic (ob/ob) or high-fat diet (HFD)-induced obesity. Myeloid cell-specific deletion of TRAF3 had the opposite effects on metabolic inflammation between obese and lean mice. It decreased the expression of proinflammatory cytokines in the liver and adipose tissue of obese mice and largely prevented HFD-induced inflammation in these metabolic tissues; by contrast, in lean mice, it increased the expression of proinflammatory cytokines in the liver and adipose tissue. These data suggest that, in obesity progression, myeloid TRAF3 functionally switches its activity from anti-inflammatory to proinflammatory modes, thereby coupling overnutrition to metabolic inflammation, insulin resistance, and metabolic disease.

Anti-CD44 antibody treatment lowers hyperglycemia and improves insulin resistance, adipose inflammation, and hepatic steatosis in diet-induced obese mice

Type 2 diabetes (T2D) is a metabolic disease affecting >370 million people worldwide. It is characterized by obesity-induced insulin resistance, and growing evidence has indicated that this causative link between obesity and insulin resistance is associated with visceral adipose tissue inflammation. However, using anti-inflammatory drugs to treat insulin resistance and T2D is not a common practice. We recently applied a bioinformatics methodology to open public data and found that CD44 plays a critical role in the development of adipose tissue inflammation and insulin resistance. In this report, we examined the role of CD44 in T2D by administering daily injections of anti-CD44 monoclonal antibody (mAb) in a high-fat-diet mouse model. Four weeks of therapy with CD44 mAb suppressed visceral adipose tissue inflammation compared with controls and reduced fasting blood glucose levels, weight gain, liver steatosis, and insulin resistance to levels comparable to or better than therapy with the drugs metformin and pioglitazone. These findings suggest that CD44 mAb may be useful as a prototype drug for therapy of T2D by breaking the links between obesity and insulin resistance.

Association of peripheral total and differential leukocyte counts with obesity-related complications in young adults

OBJECTIVE

Obesity has been demonstrated to be associated with elevated leukocytes in adults and children. This study assessed the associations between peripheral total and differential leukocyte counts and obesity-related complications in young adults.

METHODS

12 obese (median age 21.5 (range 19-28) years, median BMI 35.7 (range 32.0-44.9) kg/m(2)) and 11 normal (median age 23 (range 18-27) years, median BMI 19.5 (range 18.1-21.7) kg/m(2)) adults were enrolled. Complete blood count and serum levels of liver enzymes, fasting blood glucose, insulin and lipids were measured, and the homeostasis model assessment of insulin resistance was calculated. Fat mass was calculated using a bioimpedance analysis device, and ultrasonography was performed to measure fat thickness and to detect fatty change of the liver.

RESULTS

Total leukocyte and monocyte counts were significantly increased in obese young adults. Total leukocyte count was associated with liver enzyme levels, insulin resistance as well as visceral and subcutaneous fat thickness. Neutrophil count was associated with insulin resistance. Lymphocyte count was associated with serum liver enzymes, insulin resistance, and dyslipidemia. Monocyte count was associated with serum liver enzyme, insulin resistance, visceral and subcutaneous fat thickness, body fat mass, and percentage body fat.

CONCLUSION

The results of this study suggest that chronic low-grade systemic inflammation is associated with obesity-related complications such as nonalcoholic fatty liver disease, insulin resistance, and dyslipidemia in young adults.

Macrophage migration inhibitory factor deficiency ameliorates high-fat diet induced insulin resistance in mice with reduced adipose inflammation and hepatic steatosis

Macrophage infiltration is a critical determinant of high-fat diet induced adipose tissue inflammation and insulin resistance. The precise mechanisms underpinning the initiation of macrophage recruitment and activation are unclear. Macrophage migration inhibitory factor (MIF), a pro-inflammatory cytokine, displays chemokine-like properties. Circulating MIF levels are elevated during obesity however its role in high-fat diet induced adipose inflammation and insulin resistance remains elusive. Wildtype and MIF-/- C57Bl\6J mice were fed chow or high-fat diet. Body weight and food intake was assessed. Glucose homeostasis was monitored by glucose and insulin tolerance tests. Adipose tissue macrophage recruitment and adipose tissue insulin sensitivity was evaluated. Cytokine secretion from stromal vascular fraction, adipose explants and bone marrow macrophages was measured. Inflammatory signature and insulin sensitivity of 3T3-L1-adipocytes co-cultured with wildtype and MIF-/- macrophage was quantified. Hepatic triacylglyceride levels were assessed. MIF-/- exhibited reduced weight gain. Age and weight-matched obese MIF-/- mice exhibited improved glucose homeostasis coincident with reduced adipose tissue M1 macrophage infiltration. Obese MIF-/- stromal vascular fraction secreted less TNFα and greater IL-10 compared to wildtype. Activation of JNK was impaired in obese MIF-/-adipose, concomitant with pAKT expression. 3T3-L1-adipocytes cultured with MIF-/- macrophages had reduced pro-inflammatory cytokine secretion and improved insulin sensitivity, effects which were also attained with MIF inhibitor ISO-1. MIF-/- liver exhibited reduced hepatic triacyglyceride accumulation, enhanced pAKT expression and reduced NFκB activation. MIF deficiency partially protects from high-fat diet induced insulin resistance by attenuating macrophage infiltration, ameliorating adipose inflammation, which improved adipocyte insulin resistance ex vivo. MIF represents a potential therapeutic target for treatment of high-fat diet induced insulin resistance.

Metabolic activation of intrahepatic CD8+ T cells and NKT cells causes nonalcoholic steatohepatitis and liver cancer via cross-talk with hepatocytes

Hepatocellular carcinoma (HCC), the fastest rising cancer in the United States and increasing in Europe, often occurs with nonalcoholic steatohepatitis (NASH). Mechanisms underlying NASH and NASH-induced HCC are largely unknown. We developed a mouse model recapitulating key features of human metabolic syndrome, NASH, and HCC by long-term feeding of a choline-deficient high-fat diet. This induced activated intrahepatic CD8(+) T cells, NKT cells, and inflammatory cytokines, similar to NASH patients. CD8(+) T cells and NKT cells but not myeloid cells promote NASH and HCC through interactions with hepatocytes. NKT cells primarily cause steatosis via secreted LIGHT, while CD8(+) and NKT cells cooperatively induce liver damage. Hepatocellular LTβR and canonical NF-κB signaling facilitate NASH-to-HCC transition, demonstrating that distinct molecular mechanisms determine NASH and HCC development.

Association of inflammatory response and oxidative injury in the pathogenesis of liver steatosis and insulin resistance following subchronic exposure to malathion in rats

Insulin resistance and risk of type 2 diabetes are the most important complications following exposure to organophosphorous (OPs) pesticides. Regarding the importance of liver on metabolic pathways regulation, in particular blood glucose homeostasis, we focused on liver inflammation and oxidative damages in a subchronic model of toxicity by malathion. Adult male Wistar rats of body weight 200-250g were used for the study. Malathion (200mg/kg b.w./day) was administered to rats by oral intubation for 28 days. Glycemic and insulin resistance indices, markers of liver injury, markers of inflammation and oxidative stress were assessed. Malathion-treated rats showed increased glycemia, insulinemia and glycated hemoglobin level, HOMA-IR and HOMA-β indices, plasma activities of hepatocellular enzymes, lipid peroxidation index, CD3(+)/CD4(+) and CD3(+)/CD4(+) and pro-inflammatory cytokines when decreased antioxidant status in liver was noted. Most of our study indicates that malathion promotes insulin resistance, inflammation and Hepatosteatosis in subchronic model of exposure. On the basis of biochemical and molecular findings, it is concluded that insulin resistance induced by malathion occurs through oxidative stress and related pro-inflammatory markers in a way to result in a reduced function of insulin in liver cells.

Immunologic, metabolic and genetic factors in hepatitis C virus infection

The mechanisms that regulate disease progression during hepatitis C virus (HCV) infection and the response to treatment are not clearly identified. Numerous studies have demonstrated that a strong host immune response against HCV favors HCV clearance. In addition, genetic factors and metabolic machinery, particularly cholesterol modulation, are involved in HCV infection. It is likely that the interplay between all of these factors contributes to the outcome of HCV infection. In recent years, the world has experienced its largest epidemic of obesity. Mexico and the United States are the leading sufferers from this epidemic at the global level. Obesity is associated with the development of numerous pathologies including hypercholesterolemia which is one of the eight most important risk factors for mortality in Mexico. This may be related to the course of HCV infection in this population. Here, we focus on the urgent need to study the progression of HCV infection in relation to ethnic characteristics. Discoveries are discussed that hold promise in identifying immune, metabolic and genetic factors that, in conjunction, could be therapeutic targets or predictors of the progression of HCV infection.

Chrysin attenuates inflammation by regulating M1/M2 status via activating PPARγ

Chrysin (5,7-di-OH-flavone), a widely distributed natural flavonoid, has been well documented for involving in various biological activities, especially in regulation of peroxisome proliferator activated receptor γ (PPARγ) activity as a modest modulator. However, the exact molecular mechanism is still unrevealed. In the current study, for the first time, we discovered that, chrysin not only significantly attenuated inflammation in high-fat feeding mice, but also alleviated high fat diet-induced hepatic, muscular steatosis in obese mice without altering the body weight. Chrysin decreases the infiltration of macrophages into adipose tissue in obese mice. In addition, chrysin was also found to induce an anti-inflammatory M2 phenotype and decreases M1 phenotype, both in peritoneal macrophages of obese mice and cultured macrophages in vitro, and thereby, chrysin changed the M1/M2 status. Our data further showed that chrysin regulated the phenotype of macrophages through enhancing the transcriptional activation of PPARγ and the expression of its target genes. Taken together, we conclude that chrysin may serve as an effective modulator of PPARγ during the pathogenesis of inflammation, thereby our findings shed light on the potential therapeutic feature of chrysin in recovering inflammatory diseases via regulating M1/M2 status.

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.

Splanchnic-aortic inflammatory axis in experimental portal hypertension

Splanchnic and systemic low-grade inflammation has been proposed to be a consequence of long-term prehepatic portal hypertension. This experimental model causes minimal alternations in the liver, thus making a more selective study possible for the pathological changes characteristic of prehepatic portal hypertension. Low-grade splanchnic inflammation after long-term triple partial portal vein ligation could be associated with liver steatosis and portal hypertensive intestinal vasculopathy. In fact, we have previously shown that prehepatic portal hypertension in the rat induces liver steatosis and changes in lipid and carbohydrate metabolism similar to those produced in chronic inflammatory conditions described in metabolic syndrome in humans. Dysbiosis and bacterial translocation in this experimental model suggest the existence of a portal hypertensive intestinal microbiome implicated in both the splanchnic and systemic alterations related to prehepatic portal hypertension. Among the systemic impairments, aortopathy characterized by oxidative stress, increased levels of proinflammatory cytokines and profibrogenic mediators stand out. In this experimental model of long-term triple portal vein ligated-rats, the abdominal aortic proinflammatory response could be attributed to oxidative stress. Thus, the increased aortic reduced-nicotinamide-adenine dinucleotide phosphate [NAD(P)H] oxidase activity could be associated with reactive oxygen species production and promote aortic inflammation. Also, oxidative stress mediated by NAD(P)H oxidase has been associated with risk factors for inflammation and atherosclerosis. The splanchnic and systemic pathology that is produced in the long term after triple partial portal vein ligation in the rat reinforces the validity of this experimental model to study the chronic low-grade inflammatory response induced by prehepatic portal hypertension.

Immunological mechanisms in the pathophysiology of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is characterized by the presence of steatosis, inflammation and hepatocyte injury and constitutes hepatic manifestation of the metabolic syndrome. The pathogenesis of NASH is complex and implicates cross-talk between different metabolically active sites, such as liver and adipose tissue. Obesity is considered a chronic low-grade inflammatory state and the liver has been recognized as being an "immunological organ". The complex role of the immune system in the pathogenesis of NASH is currently raising great interest, also in view of the possible therapeutic potential of immunotherapy in NASH. This review focuses on the disturbances of the cells constituting the innate and adaptive immune system in the liver and in adipose tissue.

[Activation of Kupffer cell and related signal pathway proteins in the liver of high fat and high fructose diet induced NAFLD mice]

OBJECTIVE

To investigate the expression of F4/80, NF-kappaB, p-AKT, AKT in the liver of nonalcoholic fatty liver disease (NAFLD) mice. To determine the role of Kupffer cells (KCs) in the development of NASH (non-alcoholic steatohepatitis), and understand the pathogenic mechanism of NASH.

METHODS

Five C3H/HeN mice fed with normal diet were served as controls, while fifteen fed with high fat, high fructose, high fat combined fructose diet respectively for 16 weeks were as NAFLD mice models. The liver inflammation and hepatic damage were examined, and the expression of F4/80, NF-Kb, p-AKT, AKT and the content of lipid in the liver were also detected.

RESULTS

Chronic intake of high fat and 30% fructose solution caused a significant increase in hepatic steatosis in animals in comparison to water controls. Liver F4/80 and NF-kappaB were significantly higher in high fat and high fat combined fructose diet fed mice than that in controls (P < 0.01, P < 0.01), F4/80 protein were higher in high fat diet treated mice than those in fructose and high fat combined fructose groups (P < 0.01, P < 0.01). Markers of insulin resistance (e. g, hepatic phospho-AKT, AKT) were only altered in fructose-fed or high fat combined fructose animals (P < 0.01, P < 0.01).

CONCLUSION

High fat and fructose diet may induce NAFLD in C3H/HeN mice. Kupffer cells and signal pathway proteins were activated, and they may play key roles in the initiation and progression of NASH.

Effects of indoleamine 2,3-dioxygenase deficiency on high-fat diet-induced hepatic inflammation

Hepatic immune regulation is associated with the progression from simple steatosis to non-alcoholic steatohepatitis, a severe condition of inflamed fatty liver. Indoleamine 2,3-dioxygenase (IDO), an intracellular enzyme that mediates the catabolism of L-tryptophan to L-kynurenine, plays an important role in hepatic immune regulation. In the present study, we examined the effects of IDO gene silencing on high-fat diet (HFD)-induced liver inflammation and fibrosis in mice. After being fed a HFD for 26 weeks, the IDO-knockout (KO) mice showed a marked infiltration of inflammatory cells, especially macrophages and T lymphocytes, in the liver. The expression levels of F4/80, IFNγ, IL-1β, and IL-6 mRNA in the liver and the expression levels of F4/80 and TNF-α mRNA in the white adipose tissue were significantly increased in IDO-KO mice, although hepatic steatosis, the accumulation of intrahepatic triglycerides, and the amount of oxidative stress were lower than those in IDO-wild-type mice. IDO-KO mice also developed marked pericellular fibrosis in the liver, accumulated hepatic hydroxyproline, and exhibited increased expression levels of hepatic TGF-β1 mRNA. These findings suggest that IDO-KO renders the mice more susceptible to HFD-induced hepatic inflammation and fibrosis. Therefore, IDO may have a protective effect against hepatic fibrosis, at least in this HFD-induced liver injury model.

What does irritable bowel syndrome share with non-alcoholic fatty liver disease?

Non-alcoholic fatty liver disease (NAFLD) and irritable bowel syndrome (IBS) are two very common diseases in the general population. To date, there are no studies that highlight a direct link between NAFLD and IBS, but some recent reports have found an interesting correlation between obesity and IBS. A systematic PubMed database search was conducted highlighting that common mechanisms are involved in many of the local and systemic manifestations of NAFLD, leading to an increased cardiovascular risk, and IBS, leading to microbial dysbiosis, impaired intestinal barrier and altered intestinal motility. It is not known when considering local and systemic inflammation/immune system activation, which one has greater importance in NAFLD and IBS pathogenesis. Also, the nervous system is implicated. In fact, inflammation participates in the development of mood disorders, such as anxiety and depression, characteristics of obesity and consequently of NAFLD and, on the other hand, in intestinal hypersensitivity and dysmotility.

Non-viral causes of liver cancer: does obesity led inflammation play a role?

Liver cancer is the fifth most common cancer worldwide and the third most common cause of cancer mortality. Hepatocellular carcinoma (HCC) accounts for around 90% of primary liver cancers. Chronic infection with hepatitis B and hepatitis C viruses are two of most common causes of liver cancer. However, there are non-viral factors that are associated with liver cancer development. Numerous population studies have revealed strong links between obesity and the development of liver cancer. Obesity can alter hepatic pathology, metabolism and promote inflammation, leading to nonalcoholic fatty liver disease (NAFLD) and the progression to the more severe form, non-alcoholic steatohepatitis (NASH). NASH is characterised by prominent steatosis and inflammation, and can lead to HCC. Here, we discuss the role of obesity in inflammation and the principal signalling mechanisms involved in HCC formation.

Inflammation as a potential link between nonalcoholic fatty liver disease and insulin resistance

Nonalcoholic fatty liver disease (NAFLD) has become a major health problem in developed countries. It has affected more than 30% of the general population and is commonly associated with insulin resistance, which is a major risk factor for the development of type 2 diabetes and a central feature of the metabolic syndrome. Furthermore, accumulating evidences reveal that NAFLD as well as insulin resistance is strongly related to inflammation. Cytokines and adipokines play a pivotal role in inflammatory processes. In addition, these inflammatory mediators regulate various functions including metabolic energy balance, inflammation, and immune response. However, their role in modulating ectopic lipids involved in the development of insulin resistance, such as diacylglycerols and ceramides, remains unknown. The aim of this review is first to describe the pathophysiology of insulin resistance in NAFLD. In particular, we discuss the role of ectopic lipid accumulation in the liver. Secondly, we also summarize recent findings emphasizing the role of main inflammatory markers in both NAFLD and insulin resistance and their potential role in modulating hepatic fat content in NAFLD and associated hepatic insulin resistance.

Bile acid receptors in non-alcoholic fatty liver disease

Accumulating data have shown that bile acids are important cell signaling molecules, which may activate several signaling pathways to regulate biological processes. Bile acids are endogenous ligands for the farnesoid X receptor (FXR) and TGR5, a G-protein coupled receptor. Gain- and loss-of-function studies have demonstrated that both FXR and TGR5 play important roles in regulating lipid and carbohydrate metabolism and inflammatory responses. Importantly, activation of FXR or TGR5 lowers hepatic triglyceride levels and inhibits inflammation. Such properties of FXR or TGR5 have indicated that these two bile acid receptors are ideal targets for treatment of non-alcoholic fatty liver disease, one of the major health concerns worldwide. In this article, we will focus on recent advances on the role of both FXR and TGR5 in regulating hepatic triglyceride metabolism and inflammatory responses under normal and disease conditions.

Interferon regulatory factor 7 deficiency prevents diet-induced obesity and insulin resistance

Obesity-related inflammation has been implicated in the pathogenesis of insulin resistance and type 2 diabetes. In this study, we addressed the potential role of interferon regulatory factor 7 (IRF7), a master regulator of type I interferon-dependent immune responses, in the regulation of energy metabolism. The expression levels of IRF7 were increased in white adipose tissue, liver tissue, and gastrocnemius muscle of both diet-induced obese mice and ob/ob mice compared with their lean counterparts. After feeding a high-fat diet (HFD) for 24 wk, IRF7 knockout (KO) mice showed less weight gain and adiposity than wild-type controls. KO of IRF7 improved glucose and lipid homeostasis and insulin sensitivity. Additionally, KO of IRF7 ameliorated diet-induced hepatic steatosis. Next, we assessed the inflammatory state of the IRF7 KO mice on the HFD. These mice showed less macrophage infiltration into multiple organs and were protected from local and systemic inflammation. This study demonstrates a role for IRF7 in diet-induced alterations in energy metabolism and insulin sensitivity. Our results also suggest that IRF7 is involved in the etiology of metabolic abnormalities, which suggests a new strategy for treating obesity and type 2 diabetes.

MLK3 promotes metabolic dysfunction induced by saturated fatty acid-enriched diet

Saturated fatty acids activate the c-Jun NH₂-terminal kinase (JNK) pathway, resulting in chronic low-grade inflammation and the development of insulin resistance. Mixed-lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase (MAP3K) that mediates JNK activation in response to saturated fatty acids in vitro; however, the exact mechanism for diet-induced JNK activation in vivo is not known. Here, we have used MLK3-deficient mice to examine the role of MLK3 in a saturated-fat diet model of obesity. MLK3-KO mice fed a high-fat diet enriched in medium-chain saturated fatty acids for 16 wk had decreased body fat compared with wild-type (WT) mice due to increased energy expenditure independently of food consumption and physical activity. Moreover, MLK3 deficiency attenuated palmitate-induced JNK activation and M1 polarization in bone marrow-derived macrophages in vitro, and obesity induced JNK activation, macrophage infiltration into adipose tissue, and expression of proinflammatory cytokines in vivo. In addition, loss of MLK3 improved insulin resistance and decreased hepatic steatosis. Together, these data demonstrate that MLK3 promotes saturated fatty acid-induced JNK activation in vivo and diet-induced metabolic dysfunction.

Garcinia Cambogia attenuates diet-induced adiposity but exacerbates hepatic collagen accumulation and inflammation

AIM: To investigate long-term effects of Garcinia Cambogia (GC), weight-loss supplement, on adiposity and non-alcoholic fatty liver disease in obese mice.

METHODS: Obesity-prone C57BL/6J mice were fed a high-fat diet (HFD, 45 kcal% fat) with or without GC (1%, w/w) for 16 wk. The HFD contained 45 kcal% fat, 20 kcal% protein and 35 kcal% carbohydrate. They were given free access to food and distilled water, and food consumption and body weight were measured daily and weekly, respectively. Data were expressed as the mean ± SE. Statistical analyses were performed using the statistical package for the social science software program. Student’s t test was used to assess the differences between the groups. Statistical significance was considered at P < 0.05.

RESULTS: There were no significant changes in body weight and food intake between the groups. However, the supplementation of GC significantly lowered visceral fat accumulation and adipocyte size via inhibition of fatty acid synthase activity and its mRNA expression in visceral adipose tissue, along with enhanced enzymatic activity and gene expression involved in adipose fatty acid β-oxidation. Moreover, GC supplementation resulted in significant reductions in glucose intolerance and the plasma resistin level in the HFD-fed mice. However, we first demonstrated that it increased hepatic collagen accumulation, lipid peroxidation and mRNA levels of genes related to oxidative stress (superoxide dismutase and glutathione peroxidase) and inflammatory responses (tumor necrosis factor-α and monocyte chemoattractant protein-1) as well as plasma alanine transaminase and aspartate transaminase levels, although HFD-induced hepatic steatosis was not altered.

CONCLUSION: GC protects against HFD-induced obesity by modulating adipose fatty acid synthesis and β-oxidation but induces hepatic fibrosis, inflammation and oxidative stress.

Differences in innate immune signaling between alcoholic and non-alcoholic steatohepatitis

The similar histopathological characteristics of alcoholic steatohepatitis (ASH) and non-alcoholic steatohepatitis (NASH), and the crucial role of the innate immune response in both conditions may lead to the assumption that ASH and NASH represent the same pathophysiological entities caused by different risk factors. In this review paper, we elaborate on the pathophysiological differences between these two entities and highlight the disease-specific involvement of signaling molecules downstream of the Toll-like receptor 4, and the differential mechanism by which the inflammasome contributes to ASH versus NASH. Our findings emphasize that ASH and NASH have disease-specific mechanisms and therefore represent distinct biological entities. Further studies are needed to dissect the emerging differences in pathogenesis of these two conditions.

Toll-like receptors in alcoholic liver disease, non-alcoholic steatohepatitis and carcinogenesis

Activation of innate immune systems including Toll-like receptor (TLR) signaling is a key in chronic liver disease. Recent studies suggest that gut microflora-derived bacterial products (i.e. lipopolysaccharide [LPS], bacterial DNA) and endogenous substances (i.e. high-mobility group protein B1 [HMGB1], free fatty acids) released from damaged cells activate hepatic TLRs that contribute to the development of alcoholic (ASH) and non-alcoholic steatohepatitis (NASH) and liver fibrosis. The crucial role of TLR4, a receptor for LPS, has been implicated in the development of ASH, NASH, liver fibrosis, and hepatocellular carcinoma. However, the role of other TLRs, such as TLR2 and TLR9 in chronic liver disease remains less clear. In this review, we will discuss the role of TLR2, 4, and 9 in Kupffer cells and hepatic stellate cells in the development of ASH, NASH, and hepatocarcinogenesis.

Vismodegib suppresses TRAIL-mediated liver injury in a mouse model of nonalcoholic steatohepatitis

Hedgehog signaling pathway activation has been implicated in the pathogenesis of NASH. Despite this concept, hedgehog pathway inhibitors have not been explored. Thus, we examined the effect of vismodegib, a hedgehog signaling pathway inhibitor, in a diet-induced model of NASH. C57BL/6 mice were placed on 3-month chow or FFC (high saturated fats, fructose, and cholesterol) diet. One week prior to sacrifice, mice were treated with vismodegib or vehicle. Mice fed the FFC diet developed significant steatosis, which was unchanged by vismodegib therapy. In contrast, vismodegib significantly attenuated FFC-induced liver injury as manifested by reduced serum ALT and hepatic TUNEL-positive cells. In line with the decreased apoptosis, vismodegib prevented FFC-induced strong upregulation of death receptor DR5 and its ligand TRAIL. In addition, FFC-fed mice, but not chow-fed animals, underwent significant liver injury and apoptosis following treatment with a DR5 agonist; however, this injury was prevented by pre-treatment with vismodegib. Consistent with a reduction in liver injury, vismodegib normalized FFC-induced markers of inflammation including mRNA for TNF-α, IL-1β, IL-6, monocyte chemotactic protein-1 and a variety of macrophage markers. Furthermore, vismodegib in FFC-fed mice abrogated indices of hepatic fibrogenesis. In conclusion, inhibition of hedgehog signaling with vismodegib appears to reduce TRAIL-mediated liver injury in a nutrient excess model of NASH, thereby attenuating hepatic inflammation and fibrosis. We speculate that hedgehog signaling inhibition may be salutary in human NASH.

Maternal obesity programs offspring nonalcoholic fatty liver disease by innate immune dysfunction in mice

The global prevalence of obesity-induced liver disease (nonalcoholic fatty liver disease; NAFLD) is rising. Suggested causes include a role for in utero influences of maternal obesity compounded by the availability of energy-dense foods throughout postnatal life. Using a physiologically relevant model, we investigated the role of the innate immune system in liver injury induced by maternal obesity followed by a postnatal obesogenic diet. Female C57BL/6J mice were fed a standard or obesogenic diet before and throughout pregnancy and during lactation. Female offspring were weaned onto a standard or obesogenic diet at 3 weeks postpartum. Biochemical and histological indicators of dysmetabolism, NAFLD and fibrosis, analysis of profibrotic pathways, liver innate immune cells, and reactive oxygen species (ROS) were investigated at 3, 6, and 12 months. Female offspring exposed to a postweaning obesogenic diet (OffCon-OD) demonstrated evidence of liver injury, which was exacerbated by previous exposure to maternal obesity (OffOb-OD), as demonstrated by raised alanine aminotransferase, hepatic triglycerides, and hepatic expression of interleukin (IL)-6, tumor necrosis factor alpha, transforming growth factor beta, alpha smooth muscle actin, and collagen (P < 0.01). Histological evidence of hepatosteatosis and a more-robust NAFLD phenotype with hepatic fibrosis was observed at 12 months in OffOb-OD. A role for the innate immune system was indicated by increased Kupffer cell numbers with impaired phagocytic function and raised ROS synthesis (P < 0.01), together with reduced natural killer T cells and raised interleukin (IL)-12 and IL-18.

CONCLUSION

Maternal obesity in the context of a postnatal hypercalorific obesogenic diet aggressively programs offspring NAFLD associated with innate immune dysfunction, resulting in a comprehensive phenotype that accurately reflects the human disease.

Liver-spleen axis: Intersection between immunity, infections and metabolism

Spleen has been considered a neglected organ so far, even though is strictly linked to liver. The spleen plays an important role in the modulation of the immune system and in the maintenance of peripheral tolerance via the clearance of circulating apoptotic cells, the differentiation and activation of T and B cells and production of antibodies in the white pulp. Moreover, splenic macrophages are able to remove bacteria from the blood and protect from sepsis during systemic infections. We review the spleen function and its assessment in humans starting from the description of spleen diseases, ranging from the congenital asplenia to secondary hyposplenism. From the literature data it is clear that obesity in humans affects different compartments of immune system, even thought there are still few data available on the implicated mechamisms. The intent is to enable clinicians to evaluate the newly recognized role of metabolic and endocrine functions of the spleen with special emphasis to obesity and nonalcoholic fatty liver disease in the context of the available literature. Moreover, understanding the spleen function could be important to develop appropriate prevention strategies in order to counteract the pandemia of obesity. In this direction, we suggest spleen longitudinal diameter at ultrasonography, as simple, cheap and largely available tool, be used as new marker for assessing splenic function, in the context of the so-called liver-spleen axis.

Rutin suppresses palmitic acids-triggered inflammation in macrophages and blocks high fat diet-induced obesity and fatty liver in mice

PURPOSE

To elucidate the mechanism of rutin in blocking macrophage-mediated inflammation and high fat diet-induced obesity and fatty liver.

METHODS

Both in vitro and in vivo approaches were taken in evaluating the effects of rutin on palmitic acids-triggered inflammation in cultured macrophages, and on weight gain and development of fatty liver of mice fed a high fat diet.

RESULTS

Palmitic acids increase mRNA levels of pro-inflammatory cytokines, and elevate the production of TNFα in cultured macrophages. Pre-exposure of rutin to cells greatly suppressed these elevations. The suppressed inflammation by rutin was correlated with a decrease in transcription of genes responsible for ER stress and production of reactive oxygen species. In vivo, rutin protects mice from high fat diet-induced obesity, fatty liver and insulin resistance. The protective effects were associated with lack of hypertrophy and crown-like structures in the white adipose tissue, decreased mRNA levels of marker genes for macrophages including F4/80, Cd11c and Cd68, and repressed transcription of genes involved in chronic inflammation such as Mcp1 and Tnfα in white adipose tissue. In addition, rutin increases the expression of genes responsible for energy expenditure in brown adipose tissue including Pgc1α and Dio2. Furthermore, rutin suppresses transcription of Srebp1c and Cd36 in the liver, leading to a blockade of fatty liver development.

CONCLUSION

These results suggest that supplementation of rutin is a promising strategy for blocking macrophage-mediated inflammation and inflammation-induced obesity and its associated complications.

Inhibition of Glutaminyl Cyclases alleviates CCL2-mediated inflammation of non-alcoholic fatty liver disease in mice

Inflammation is an integral part of non-alcoholic fatty liver disease (NAFLD), the most prevalent form of hepatic pathology found in the general population. In this context, recently we have examined the potential role of Glutaminyl Cyclases (QC and isoQC), and their inhibitors, in the maturation of chemokines, for example, monocyte chemoattractant protein 1 (MCP-1, CCL2), to generate their bioactive conformation. Catalysis by isoQC leads to the formation of an N-terminal pyroglutamate residue protecting CCL2 against degradation by aminopeptidases. This is of importance because truncated forms possess a reduced potential to attract immune cells. Since liver inflammation is characterized by the up-regulation of different chemokine pathways, and within this CCL2 is known to be a prominent example, we hypothesised that application of QC/isoQC inhibitors may alleviate liver inflammation by destabilizing CCL2. Therefore, we investigated the role of QC/isoQC inhibition, in comparison with the angiotensin receptor blocker Telmisartan, during development of pathology in a mouse model of non-alcoholic fatty liver disease. Application of a QC/isoQC inhibitor led to a significant reduction in circulating alanine aminotransferase and NAFLD activity score accompanied by an inhibitory effect on hepatocyte ballooning. Further analysis revealed a specific reduction of inflammation by decreasing the number of F4/80-positive macrophages, which is in agreement with the proposed CCL2-related mechanism of action of QC/isoQC inhibitors. Finally, QC/isoQC inhibitor application attenuated liver fibrosis as characterized by reduced collagen deposition in the liver parenchyma. Thus in conclusion, QC/isoQC inhibitors are a promising novel class of anti-non-alcoholic steatohepatitis drugs which have a comparable disease-modifying effect to that of Telmisartan, which is probably mediated via specific interference with a comparable monocyte/macrophage infiltration that occurs under inflammatory conditions.

Genetic association of interleukin-6 polymorphism (-174 G/C) with chronic liver diseases and hepatocellular carcinoma

Interleukin-6 (IL-6) is a pleiotropic cytokine which is expressed in many inflammatory cells in response to different types of stimuli, regulating a number of biological processes. The IL-6 gene is polymorphic in both the 5’ and 3’ flanking regions and more than 150 single nucleotide polymorphisms have been identified so far. Genetic polymorphisms of IL-6 may affect the outcomes of several diseases, where the presence of high levels of circulating IL-6 have been correlated to the stage and/or the progression of the disease itself. The -174 G/C polymorphism is a frequent polymorphism, that is located in the upstream regulatory region of the IL-6 gene and affects IL-6 production. However, the data in the literature on the genetic association between the -174 G/C polymorphism and some specific liver diseases characterized by different etiologies are still controversial. In particular, most of the studies are quite unanimous in describing a correlation between the presence of the high-producer genotype and a worse evolution of the chronic liver disease. This is valid for patients with hepatitis C virus (HCV)-related chronic hepatitis and liver cirrhosis and hepatocellular carcinoma (HCC) whatever the etiology. Studies in hepatitis B virus-related chronic liver diseases are not conclusive, while specific populations like non alcoholic fatty liver disease/non-alcoholic steatohepatitis, autoimmune and human immunodeficiency virus/HCV co-infected patients show a higher prevalence of the low-producer genotype, probably due to the complexity of these clinical pictures. In this direction, a systematic revision of these data should shed more light on the role of this polymorphism in chronic liver diseases and HCC.

[Effect of probiotics on proinflammatory cytokines level in patients with type 2 diabetes and nonalcoholic fatty liver disease]

We examined 72 patients with T2D and NAFLD. All patients divided by us on the way of therapy into 2 groups. The main group (n = 45) received oral antidiabetic therapy and multiprobiotic "Symbiter" within 30 days. Patients of comparison group (n = 27) received only hypoglycemic drugs. Also in each group we identified patients with normal and elevated level of transaminases. We observed 1.5-2 times increasing of cytokines in patients with NAFLD and elevated transaminase levels compared to patients with normal transaminase levels. We noted statistically significant reduction of proinflammatory cytokines in plasma, after 30 days of therapy, in patients with elevated levels of transaminases. In particular, the level of IL-6 decreased on 30.9% (P < 0.001), IL-8 - 19.9% (P = 0.001), TNF-alpha - 13.4% (P < 0.001), IL-1beta - 17.9% (P < 0.001) and IFN-gamma on 18.7% (P < 0.001) respectively. In patients with normal levels transaminases and NAFLD were significantly decreased only TNF-alpha on 15.1% (P = 0.003) and IL-8 on 15.2% (P = 0.017). Significant changes in cytokines levels in patients of comparative group we don't observed. Probiotics can be recommended for use in patients with different stages of NAFLD and T2D as an adjunct to standard treatment regimens because it decreases manifestations of low-grade systemic inflammatory response.

The changing epidemiology of liver disease in HIV patients

Liver disease continues to be one of the leading causes of hospitalization and death in HIV-infected individuals. Important etiologies include both alcoholic and non-alcoholic steatohepatitis, and coinfection with hepatitis viruses B and C. While non-alcoholic fatty liver disease is increasingly diagnosed in this population, most cases of chronic hepatitis B can be well controlled with tenofovir-based regimens, and hepatitis C has entered a revolutionary era in which most patients may be cured with direct-acting antivirals. However, important gaps remain unaddressed. Hepatitis delta is a neglected disease, despite 15 million people being infected worldwide, and represents the most severe form of viral hepatitis. Hepatitis E is largely unrecognized, despite being the major cause of acute viral hepatitis worldwide and occasionally leading to chronicity in immunosuppressed individuals.

Molecular pathways involved in the improvement of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis are components of the metabolic syndrome. Serum leptin levels are elevated in obesity, but the role of leptin in the pathophysiology of the liver involvement is still unclear. To identify the effects and mechanisms by which leptin influences the pathogenesis of NAFLD, we performed epididymal white adipose tissue (eWAT) transplantation from congenic wild-type mice into the subcutaneous dorsal area of Lep(ob/ob) recipient mice and compared the results with those of the Lep(ob/ob) sham-operated mice. The mice were followed for 102-216 days. During killing, the transplanted mice had significantly lost body weight and exhibited significantly higher leptin levels, improved glucose tolerance, and lower liver injury scores than the sham-operated mice. Liver microarray analysis showed that novel pathways related to GA-binding protein (GABP) transcription factor targets, pheromone binding, and olfactory signaling were differentially expressed in the transplanted mice. Our data also replicate pathways known to be involved in NAFLD, such as those involved in the regulation of microRNAs, lipid, glucose, and glutathione metabolism, peroxisome proliferator-activated receptor signaling, cellular regulation, carboxylic acid processes, iron, heme, and tetrapyrrole binding, immunity and inflammation, insulin signaling, cytochrome P450 function, and cancer.

CONCLUSION

wild-type eWAT transplantation into Lep(ob/ob) mice led to improvements in metabolism, body weight, and liver injury, possibly attributed to the production of leptin by the transplanted eWAT. These improvements were accompanied by the differential expression of novel pathways. The causal relationship between GABP downregulation and NAFLD improvement remains to be determined.

Toll-like receptor 4 deficiency promotes the alternative activation of adipose tissue macrophages

Obesity is characterized by adipose tissue (AT) macrophage (ATM) accumulation, which promotes AT inflammation and dysfunction. Toll-like receptor 4 (TLR4) deficiency attenuates AT inflammation in obesity but does not impede the accumulation of ATMs. The purpose of the current study was to determine whether TLR4 deficiency alters ATM polarization. TLR4(-/-) and wild-type mice were fed a low-fat, high-monounsaturated fat (HF(MUFA)), or a high-saturated fat (HF(SFA)) diet for 16 weeks. Further, we used a bone marrow transplant model to determine the influence of hematopoietic cell TLR4 signaling. The metabolic and inflammatory responses to high-fat feeding and ATM phenotype were assessed. Global and hematopoietic cell TLR4 deficiency, irrespective of recipient genotype, produced a shift in ATM phenotype toward an alternatively activated state, which was accompanied by reduced AT inflammation. Despite the observed shift in ATM phenotype, neither global nor hematopoietic cell TLR4 deficiency influenced systemic insulin sensitivity after high-fat feeding. Results of the current study suggest that TLR4 directly influences ATM polarization but question the relevance of TLR4 signaling to systemic glucose homeostasis in obesity.