Hepatic monocyte chemoattractant protein-1 is upregulated by dietary cholesterol and contributes to liver steatosis

CCL2-CCR2 signaling axis in obesity and metabolic diseases

Obesity and metabolic diseases, such as insulin resistance, type 2 diabetes, nonalcoholic fatty liver disease, and cardiovascular ailments, represent formidable global health challenges, bearing considerable implications for both morbidity and mortality rates. It has become increasingly evident that chronic, low-grade inflammation plays a pivotal role in the genesis and advancement of these conditions. The involvement of C-C chemokine ligand 2 (CCL2) and its corresponding receptor, C-C chemokine receptor 2 (CCR2), has been extensively documented in numerous inflammatory maladies. Recent evidence indicates that the CCL2/CCR2 pathway extends beyond immune cell recruitment and inflammation, exerting a notable influence on the genesis and progression of metabolic syndrome. The present review seeks to furnish a comprehensive exposition of the CCL2-CCR2 signaling axis within the context of obesity and metabolic disorders, elucidating its molecular mechanisms, functional roles, and therapeutic implications.

Bombesin-like receptor 3 expression induced by bisphenol A is likely associated with reduced cell proliferation by inhibiting DNA synthesis and inducing inflammation in liver cells

BACKGROUND

Bisphenol A (BPA) is an exogenous endocrine disruptor mimicking hormones closely associated with health complications, such as cancer progression. BPA is also related to an increase in the prevalence of obesity-related diseases due to its obesogenic action. Bombesin-like receptor 3 (BRS3) is an important factor that should be considered in the adipogenic gene network, as depletion of this gene alters adiposity.

METHODS

Therefore, the present study aimed to investigate the messenger ribonucleic acid (mRNA) expression of BRS3 in human liver THLE-2 cells post-BPA treatment by real-time polymerase chain reaction. The effects of BPA on the levels of pro-inflammatory proteins, interleukin 6 (IL6) and CC motif chemokine ligand 2 (CCL2), in conditioned media of BPA-treated THLE-2 cells and deoxyribonucleic acid (DNA) synthesis in replicating BPA-treated THLE-2 cells during the cell cycle were also examined by enzyme-linked immunosorbent assay (ELISA) and flow cytometry, respectively.

RESULTS

The study found that the mRNA expression of BRS3 was increased in THLE-2 cells treated with BPA. The study also showed that the expression levels of IL6 and CCL2 reached an optimum level in the conditioned media of BPA-treated THLE-2 cells after 48 h of treatment. Subsequently, the DNA synthesis analysis showed that bromodeoxyuridine/propidium iodide (BrdU/PI) stained positive cells were decreased in BPA-treated THLE-2 cells at 72 h of treatment.

CONCLUSION

The study demonstrates that BRS3 expression induced by BPA is likely associated with reduced cell proliferation by inhibiting DNA synthesis and inducing cellular inflammation in liver cells.

Daraesoon (shoot of hardy kiwi) mitigates hyperglycemia in db/db mice by alleviating insulin resistance and inflammation

BACKGROUND/OBJECTIVES

Mitigating insulin resistance and hyperglycemia is associated with a decreased risk of diabetic complications. The effect of Daraesoon (shoot of hardy kiwi, Actinidia arguta) on hyperglycemia was investigated using a type 2 diabetes animal model.

MATERIALS/METHODS

Seven-week-old db/db mice were fed either an AIN-93G diet or a diet containing 0.4% of a 70% ethanol extract of Daraesoon, whereas db/+ mice were fed the AIN-93G diet for 7 weeks.

RESULTS

Consumption of Daraesoon significantly reduced serum glucose and blood glycated hemoglobin levels, along with homeostasis model assessment for insulin resistance in db/db mice. Conversely, Daraesoon elevated the serum adiponectin levels compared to the db/db control group. Furthermore, Daraesoon significantly decreased both serum and hepatic triglyceride levels, as well as serum total cholesterol levels. Additionally, consumption of Daraesoon resulted in decreased hepatic tumor necrosis factor-α and monocyte chemoattractant protein-1 expression.

CONCLUSIONS

These results suggest that hypoglycemic effect of Daraesoon is mediated through the improvement of insulin resistance and the downregulation of pro-inflammatory cytokine expression in db/db mice.

Multidimensional Biomarker Analysis Including Mitochondrial Stress Indicators for Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is accompanied by a complex and multifactorial pathogenesis with sequential progressions from inflammation to fibrosis and then to cancer. This heterogeneity interferes with the development of precise diagnostic and prognostic strategies for NAFLD. The current approach for the diagnosis of simple steatosis, steatohepatitis, and cirrhosis mainly consists of ultrasonography, magnetic resonance imaging, elastography, and various serological analyses. However, individual dry and wet biomarkers have limitations demanding an integrative approach for the assessment of disease progression. Here, we review diagnostic strategies for simple steatosis, steatohepatitis and hepatic fibrosis, followed by potential biomarkers associated with fat accumulation and mitochondrial stress. For mitochondrial stress indicators, we focused on fibroblast growth factor 21 (FGF21), growth differentiation factor 15 (GDF15), angiopoietin-related growth factor and mitochondrial-derived peptides. Each biomarker may not strongly indicate the severity of steatosis or steatohepatitis. Instead, multidimensional analysis of different groups of biomarkers based on pathogenic mechanisms may provide decisive diagnostic/prognostic information to develop a therapeutic plan for patients with NAFLD. For this purpose, mitochondrial stress indicators, such as FGF21 or GDF15, could be an important component in the multiplexed and contextual interpretation of NAFLD. Further validation of the integrative evaluation of mitochondrial stress indicators combined with other biomarkers is needed in the diagnosis/prognosis of NAFLD.

Novel Combinatorial Regimen of Garcinol and Curcuminoids for Non-alcoholic Steatohepatitis (NASH) in Mice

Non-alcoholic steatohepatitis (NASH) is a progressive form of Non-alcoholic fatty liver disease (NAFLD), a chronic liver disease with a significant unmet clinical need. In this study, we examined the protective effects of Garcinia indica extract standardized to contain 20% w/w of Garcinol (GIE) and 95% Curcuminoids w/w from Curcuma longa (Curcuminoids) in a Stelic animal model (STAM) of NASH. The STAM mice developed steatosis, hepatocyte ballooning, and inflammation, which were significantly reduced by the combination of GIE and Curcuminoids, resulting in a lower NAFLD activity score. The treatment reduced fibrosis as observed by Sirius red staining, liver hydroxyproline content and mRNA levels of TGF- β and collagen in the liver. Immunostaining with alpha-smooth muscle actin (α SMA) revealed a significant reduction in hepatic stellate cells. Intriguingly, the combination regimen markedly decreased the mRNA levels of MCP1 and CRP and both mRNA and protein levels of TNF-α. NF-kB, reduced the hepatic and circulating FGF21 levels and altered the nonenzymatic (glutathione) and enzymatic antioxidant markers (Glutathione peroxidase, and superoxide dismutase). Our results suggest that the combination of GIE and Curcuminoids can reduce the severity of NASH by reducing steatosis, fibrosis, oxidative stress, and inflammation. The results suggest that the combinatorial regimen could be an effective supplement to prevent the progression of liver steatosis to inflammation and fibrosis in NASH.

Chemokine (C-C motif) ligand 2 gene ablation protects low-density lipoprotein and paraoxonase-1 double deficient mice from liver injury, oxidative stress and inflammation

The risk of non-alcoholic fatty liver disease increases with obesity. Vulnerability to oxidative stress and/or inflammation represents a crucial step in non-alcoholic fatty liver disease progression through abnormal metabolic responses. In this study, we investigated the role of CCL2 gene ablation in mice that were double deficient in low density lipoprotein receptor and in paraoxonase-1. Mass spectrometry methods were used to assess the liver metabolic response in mice fed either regular chow or a high-fat diet. Dietary fat caused liver steatosis, oxidative stress and the accumulation of pro-inflammatory macrophages in the livers of double deficient mice. We observed alterations in energy metabolism-related pathways and in metabolites associated with the methionine cycle and the glutathione reduction pathway. This metabolic response was associated with impaired autophagy. Conversely, when we established CCL2 deficiency, histologic features of fatty liver disease were abrogated, hepatic liver oxidative stress decreased, and anti-inflammatory macrophage marker expression levels increased. These changes were associated with the normalization of metabolic disturbances and increased lysosome-associated membrane protein 2, expression, which suggests enhanced chaperone-mediated autophagy. This study demonstrates that CCL2 is a key molecule for the development of metabolic and histological alterations in the liver of mice sensitive to the development of hyperlipidemia and hepatic steatosis, a finding with potential to identify new therapeutic targets in liver diseases.

Chemokines and Chemokine Receptors in the Development of NAFLD

Chemokines are chemo-attractants for leukocyte trafficking, growth, and activation in injured and inflammatory tissues. The chemokine system is comprised of 50 chemokine ligands and 20 cognate chemokine receptors. In the context of liver diseases, leukocytes, hepatocytes, hepatic stellate cells, endothelial cells, and vascular smooth muscle cells are capable of producing chemokines. Chemokine receptors are typically expressed in various leukocyte subsets. Given that inflammation is a critical factor for the transition from simple steatosis to non-alcoholic steatohepatitis (NASH), and fibrosis, the chemokine system may play a prominent role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Indeed, accumulating evidence shows elevated expression of chemokines and their receptors in the livers of obese patients with advanced steatosis and NASH. This chapter will discuss the underlying molecular mechanisms and the therapeutic potential of the chemokine systems in the pathogenesis of NAFLD. Among chemokines, we will highlight CCL2, CCL5, CXCL8-10, CX3CL1, and CXCL16 as pivotal mediators in the development of steatosis, NASH, and fibrosis.

C-X-C motif chemokine 10 in non-alcoholic steatohepatitis: role as a pro-inflammatory factor and clinical implication

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease. Non-alcoholic steatohepatitis (NASH) is a more severe form of NAFLD and causes subsequent pathological changes including cirrhosis and hepatocellular carcinoma. Inflammation is the key pathological change in NASH and involves a series of cytokines and chemokines. The C-X-C motif chemokine 10 (CXCL10), which is known as a pro-inflammation chemokine, was recently proven to play a pivotal role in the pathogenesis of NASH. Hepatic CXCL10 is mainly secreted by hepatocytes and liver sinusoidal endothelium. By binding to its specific receptor CXCR3, CXCL10 recruits activated CXCR3+ T lymphocytes and macrophages to parenchyma and promotes inflammation, apoptosis and fibrosis. The circulating CXCL10 level correlates with the severity of lobular inflammation and is an independent risk factor for NASH patients. Thus, CXCL10 may be both a potential prognostic tool and a therapeutic target for the treatment of patients with NASH. The aim of this review is to highlight the growing advances in basic knowledge and clinical interest of CXCL10 in NASH to propagate new insights into novel pharmacotherapeutic avenues.

Epigenetics and nutrition-related epidemics of metabolic diseases: Current perspectives and challenges

We live in a world fascinated by the relationship between disease and nutritional disequilibrium. The subtle and slow effects of chronic nutrient toxicity are a major public health concern. Since food is potentially important for the development of "metabolic memory", there is a need for more information on the type of nutrients causing adverse or toxic effects. We now know that metabolic alterations produced by excessive intake of some nutrients, drugs and chemicals directly impact epigenetic regulation. We envision that understanding how metabolic pathways are coordinated by environmental and genetic factors will provide novel insights for the treatment of metabolic diseases. New methods will enable the assembly and analysis of large sets of complex molecular and clinical data for understanding how inflammation and mitochondria affect bioenergetics, epigenetics and health. Collectively, the observations we highlight indicate that energy utilization and disease are intimately connected by epigenetics. The challenge is to incorporate metabolo-epigenetic data in better interpretations of disease, to expedite therapeutic targeting of key pathways linking nutritional toxicity and metabolism. An additional concern is that changes in the parental phenotype are detectable in the methylome of subsequent offspring. The effect might create a menace to future generations and preconceptional considerations.

Liver fat deposition and mitochondrial dysfunction in morbid obesity: An approach combining metabolomics with liver imaging and histology

AIM: To explore the usefulness of magnetic resonance imaging (MRI) and spectroscopy (MRS) for assessment of non-alcoholic fat liver disease (NAFLD) as compared with liver histological and metabolomics findings.

METHODS: Patients undergoing bariatric surgery following procedures involved in laparoscopic sleeve gastrectomy were recruited as a model of obesity-induced NAFLD in an observational, prospective, single-site, cross-sectional study with a pre-set duration of 1 year. Relevant data were obtained prospectively and surrogates for inflammation, oxidative stress and lipid and glucose metabolism were obtained through standard laboratory measurements. To provide reliable data from MRI and MRS, novel procedures were designed to limit sampling variability and other sources of error using a 1.5T Signa HDx scanner and protocols acquired from the 3D or 2D Fat SAT FIESTA prescription manager. We used our previously described ¹H NMR-based metabolomics assays. Data were obtained immediately before surgery and after a 12-mo period including histology of the liver and measurement of metabolites. Values from ¹H NMR spectra obtained after surgery were omitted due to technical limitations.

RESULTS: MRI data showed excellent correlation with the concentration of liver triglycerides, other hepatic lipid components and the histological assessment, which excluded the presence of non-alcoholic steatohepatitis (NASH). MRI was sufficient to follow up NAFLD in obese patients undergoing bariatric surgery and data suggest usefulness in other clinical situations. The information provided by MRS replicated that obtained by MRI using the -CH3 peak (0.9 ppm), the -CH2- peak (1.3 ppm, mostly triglyceride) and the

-CH=CH- peak (2.2 ppm). No patient depicted NASH. After surgery all patients significantly decreased their body weight and steatosis was virtually absent even in patients with previous severe disease. Improvement was also observed in the serum concentrations of selected variables. The most relevant findings using metabolomics indicate increased levels of triglyceride and monounsaturated fatty acids in severe steatosis but those results were accompanied by a significant depletion of diglycerides, polyunsaturated fatty acids, glucose-6-phosphate and the ATP/AMP ratio. Combined data indicated the coordinated action on mitochondrial fat oxidation and glucose transport activity and may support the consideration of NAFLD as a likely mitochondrial disease. This concept may help to explain the dissociation between excess lipid storage in adipose tissue and NAFLD and may direct the search for plasma biomarkers and novel therapeutic strategies. A limitation of our study is that data were obtained in a relatively low number of patients.

CONCLUSION: MRI is sufficient to stage NAFLD in obese patients and to assess the improvement after bariatric surgery. Other data were superfluous for this purpose.

Chemokine ligand 2 and paraoxonase-1 in non-alcoholic fatty liver disease: The search for alternative causative factors

The incidence and prevalence of non-alcoholic fatty liver disease (NAFLD) is constantly increasing. Despite this is apparently associated with the growing increase in obesity, insulin resistance and obesity-related metabolic disturbances their presence is not a necessary or sufficient condition to explain the accumulation of fat in the liver. Conversely, NAFLD is a predictor of other metabolic risks. NAFLD is currently the most frequent chronic liver disease but should not be considered benign or anecdotic because a considerable proportion of patients with NAFLD progress to cirrhosis and end-stage liver disease. Consequently, the search for alternative molecular mechanisms with therapeutic implications in NAFLD and associated disorders deserves a careful consideration. Mitochondria are possible targets as these organelles generate energy from nutrient oxidation. Some findings, generated in patients with extreme obesity and in murine models, support the notion that NAFLD could be a mitochondrial disease. This is plausible because mitochondrial dysfunction affects the accumulation of lipids in hepatocytes and promotes lipid peroxidation, the production of reactive oxygen species, the release of cytokines causing inflammation and cell death. Here we discuss basic research and mechanistic studies targeting the role of chemokine ligand 2 in liver inflammation and that of the paraoxonases in the oxidative stress. Their combination and association with mitochondrial dysfunction may uncover mechanisms underlying the progression of NAFLD and may help to identify novel therapeutic targets.

Paraoxonases and chemokine (C-C motif) ligand-2 in noncommunicable diseases

Oxidative stress and inflammation underpin most diseases; their mechanisms are inextricably linked. Chronic inflammation is associated with oxidation, anti-inflammatory cascades are linked to decreased oxidation, increased oxidative stress triggers inflammation, and redox balance inhibits the inflammatory cellular response. Whether or not oxidative stress and inflammation represent the cause or consequence of cellular pathology, they contribute significantly to the pathogenesis of noncommunicable diseases (NCD). The incidence of obesity and other related metabolic disturbances are increasing, as are age-related diseases due to a progressively aging population. Relationships between oxidative stress, inflammatory signaling, and metabolism are, in the broad sense of energy transformation, being increasingly recognized as part of the problem in NCD. In this chapter, we summarize the pathologic consequences of an imbalance between circulating and cellular paraoxonases, the system for scavenging excessive reactive oxygen species and circulating chemokines. They act as inducers of migration and infiltration of immune cells in target tissues as well as in the pathogenesis of disease that perturbs normal metabolic function. This disruption involves pathways controlling lipid and glucose homeostasis as well as metabolically driven chronic inflammatory states that encompass several response pathways. Dysfunction in the endoplasmic reticulum and/or mitochondria represents an important feature of chronic disease linked to oxidation and inflammation seen as self-reinforcing in NCD. Therefore, correct management requires a thorough understanding of these relationships and precise interpretation of laboratory test results.

Aerobic exercise and not a diet supplemented with jussara açaí (Euterpe edulis Martius) alters hepatic oxidative and inflammatory biomarkers in ApoE-deficient mice

The pulp of jussara açaí (Euterpe edulis Martius) fruit is rich in anthocyanins that exert antioxidant and anti-inflammatory effects similar to those exerted by aerobic exercise. In the present study, we investigated the effects of jussara açaí fruit pulp consumption, either alone or in combination with aerobic exercise, on the hepatic oxidative and inflammatory status of ApoE-deficient (ApoE - / - ) mice. Male mice were divided into four groups (control (C), control plus açaí, exercise plus açaí (EXA) and exercise (EX)) and fed the AIN-93M diet or the AIN-93M diet formulated to contain 2 % freeze-dried açaí pulp. Mice in the EX and EXA groups were subjected to a progressive running programme (5 d/week, 60 min/d, 16 m/min) for 12 weeks. Mice that were made to exercise exhibited reduced (40·85 %; P< 0·05) hepatic superoxide dismutase activity when compared with the C mice, independent of the açaí diet. Mice in the EX group exhibited a lower (42 %; P< 0·05) mRNA expression of monocyte chemotactic protein-1 in the liver compared with the C mice. Mice in the EXA and EX groups had lower percentages of hepatic lipid droplets (70 % and 56 %, respectively; P< 0·05) when compared with the C mice. Mice in the EX group had smaller (58 %; P< 0·05) area of lesions in the aorta when compared with the C mice. Serum lipid profile was not affected (P>0·05). In conclusion, aerobic exercise training rather than açaí fruit pulp consumption or a combination of both enhances the hepatic oxidative and inflammatory status of ApoE - / - mice.

Ubiquitous transgenic overexpression of C-C chemokine ligand 2: a model to assess the combined effect of high energy intake and continuous low-grade inflammation. Mediators Inflamm. 2013;2013:953841. [PMID: 24453432 PMCID: PMC3876923 DOI: 10.1155/2013/953841]

Excessive energy management leads to low-grade, chronic inflammation, which is a significant factor predicting noncommunicable diseases. In turn, inflammation, oxidation, and metabolism are associated with the course of these diseases; mitochondrial dysfunction seems to be at the crossroads of mutual relationships. The migration of immune cells during inflammation is governed by the interaction between chemokines and chemokine receptors. Chemokines, especially C-C-chemokine ligand 2 (CCL2), have a variety of additional functions that are involved in the maintenance of normal metabolism. It is our hypothesis that a ubiquitous and continuous secretion of CCL2 may represent an animal model of low-grade chronic inflammation that, in the presence of an energy surplus, could help to ascertain the afore-mentioned relationships and/or to search for specific therapeutic approaches. Here, we present preliminary data on a mouse model created by using targeted gene knock-in technology to integrate an additional copy of the CCl2 gene in the Gt(ROSA)26Sor locus of the mouse genome via homologous recombination in embryonic stem cells. Short-term dietary manipulations were assessed and the findings include metabolic disturbances, premature death, and the manipulation of macrophage plasticity and autophagy. These results raise a number of mechanistic questions for future study.

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.

Choline's role in maintaining liver function: new evidence for epigenetic mechanisms

PURPOSE OF REVIEW

Humans eating diets low in choline develop fatty liver and liver damage. Rodents fed choline-methionine-deficient diets not only develop fatty liver, but also progress to develop fibrosis and hepatocarcinoma. This review focuses on the role of choline in liver function, with special emphasis on the epigenetic mechanisms of action.

RECENT FINDINGS

Dietary intake of methyl donors like choline influences the methylation of DNA and histones, thereby altering the epigenetic regulation of gene expression. The liver is the major organ within which methylation reactions occur, and many of the hepatic genes involved in pathways for the development of fatty liver, hepatic fibrosis, and hepatocarcinomas are epigenetically regulated.

SUMMARY

Dietary intake of choline varies over a three-fold range and many humans have genetic polymorphisms that increase their demand for choline. Choline is an important methyl donor needed for the generation of S-adenosylmethionine. Dietary choline intake is an important modifier of epigenetic marks on DNA and histones, and thereby modulates the gene expression in many of the pathways involved in liver function and dysfunction.

Exploring PPAR modulation in experimental mice

The main concern in exploring modulation of PPARs in experimental animals is probably the choice of the model. Although mechanistic studies may be well designed using knockout and transgenic animals, the interpretation of results with respect to inferred results of PPAR activation into humans should be performed cautiously. This is even more important in this field considering that undesired and unexpected effects have been already described in human epidemiologic studies. Taken together, these observations suggest that a global approach using omic technologies, although expensive, is probably the most suitable to obtain useful data. Also, in this approach, we propose all tissues should be explored, not only those obviously relevant to metabolism, or stored in proper conditions if further assessment is required.

Paraoxonase-1 deficiency is associated with severe liver steatosis in mice fed a high-fat high-cholesterol diet: a metabolomic approach

Oxidative stress is a determinant of liver steatosis and the progression to more severe forms of disease. The present study investigated the effect of paraoxonase-1 (PON1) deficiency on histological alterations and hepatic metabolism in mice fed a high-fat high-cholesterol diet. We performed nontargeted metabolomics on liver tissues from 8 male PON1-deficient mice and 8 wild-type animals fed a high-fat, high-cholesterol diet for 22 weeks. We also measured 8-oxo-20-deoxyguanosine, reduced and oxidized glutathione, malondialdehyde, 8-isoprostanes and protein carbonyl concentrations. Results indicated lipid droplets in 14.5% of the hepatocytes of wild-type mice and in 83.3% of the PON1-deficient animals (P < 0.001). The metabolomic assay included 322 biochemical compounds, 169 of which were significantly decreased and 16 increased in PON1-deficient mice. There were significant increases in lipid peroxide concentrations and oxidative stress markers. We also found decreased glycolysis and the Krebs cycle. The urea cycle was decreased, and the pyrimidine cycle had a significant increase in orotate. The pathways of triglyceride and phospholipid synthesis were significantly increased. We conclude that PON1 deficiency is associated with oxidative stress and metabolic alterations leading to steatosis in the livers of mice receiving a high-fat high-cholesterol diet.

Kuppfer cells trigger nonalcoholic steatohepatitis development in diet-induced mouse model through tumor necrosis factor-α production

BACKGROUND

The mechanisms triggering nonalcoholic steatohepatitis (NASH) remain poorly defined.

RESULTS

Kupffer cells are the first responding cells to hepatocyte injuries, leading to TNFα production, chemokine induction, and monocyte recruitment. The silencing of TNFα in myeloid cells reduces NASH progression.

CONCLUSION

Increase of TNFα-producing Kupffer cells is crucial for triggering NASH via monocyte recruitment.

SIGNIFICANCE

Myeloid cells-targeted silencing of TNFα might be a tenable therapeutic approach. Nonalcoholic steatohepatitis (NASH), characterized by lipid deposits within hepatocytes (steatosis), is associated with hepatic injury and inflammation and leads to the development of fibrosis, cirrhosis, and hepatocarcinoma. However, the pathogenic mechanism of NASH is not well understood. To determine the role of distinct innate myeloid subsets in the development of NASH, we examined the contribution of liver resident macrophages (i.e. Kupffer cells) and blood-derived monocytes in triggering liver inflammation and hepatic damage. Employing a murine model of NASH, we discovered a previously unappreciated role for TNFα and Kupffer cells in the initiation and progression of NASH. Sequential depletion of Kupffer cells reduced the incidence of liver injury, steatosis, and proinflammatory monocyte infiltration. Furthermore, our data show a differential contribution of Kupffer cells and blood monocytes during the development of NASH; Kupffer cells increased their production of TNFα, followed by infiltration of CD11b(int)Ly6C(hi) monocytes, 2 and 10 days, respectively, after starting the methionine/choline-deficient (MCD) diet. Importantly, targeted knockdown of TNFα expression in myeloid cells decreased the incidence of NASH development by decreasing steatosis, liver damage, monocyte infiltration, and the production of inflammatory chemokines. Our findings suggest that the increase of TNFα-producing Kupffer cells in the liver is crucial for the early phase of NASH development by promoting blood monocyte infiltration through the production of IP-10 and MCP-1.

Kuppfer cells trigger nonalcoholic steatohepatitis development in diet-induced mouse model through tumor necrosis factor-α production

BACKGROUND

The mechanisms triggering nonalcoholic steatohepatitis (NASH) remain poorly defined.

RESULTS

Kupffer cells are the first responding cells to hepatocyte injuries, leading to TNFα production, chemokine induction, and monocyte recruitment. The silencing of TNFα in myeloid cells reduces NASH progression.

CONCLUSION

Increase of TNFα-producing Kupffer cells is crucial for triggering NASH via monocyte recruitment.

SIGNIFICANCE

Myeloid cells-targeted silencing of TNFα might be a tenable therapeutic approach. Nonalcoholic steatohepatitis (NASH), characterized by lipid deposits within hepatocytes (steatosis), is associated with hepatic injury and inflammation and leads to the development of fibrosis, cirrhosis, and hepatocarcinoma. However, the pathogenic mechanism of NASH is not well understood. To determine the role of distinct innate myeloid subsets in the development of NASH, we examined the contribution of liver resident macrophages (i.e. Kupffer cells) and blood-derived monocytes in triggering liver inflammation and hepatic damage. Employing a murine model of NASH, we discovered a previously unappreciated role for TNFα and Kupffer cells in the initiation and progression of NASH. Sequential depletion of Kupffer cells reduced the incidence of liver injury, steatosis, and proinflammatory monocyte infiltration. Furthermore, our data show a differential contribution of Kupffer cells and blood monocytes during the development of NASH; Kupffer cells increased their production of TNFα, followed by infiltration of CD11b(int)Ly6C(hi) monocytes, 2 and 10 days, respectively, after starting the methionine/choline-deficient (MCD) diet. Importantly, targeted knockdown of TNFα expression in myeloid cells decreased the incidence of NASH development by decreasing steatosis, liver damage, monocyte infiltration, and the production of inflammatory chemokines. Our findings suggest that the increase of TNFα-producing Kupffer cells in the liver is crucial for the early phase of NASH development by promoting blood monocyte infiltration through the production of IP-10 and MCP-1.

Correction of liver steatosis by a hydrophobic iminosugar modulating glycosphingolipids metabolism

The iminosugar N-(5′-adamantane-1′-yl-methoxy)-pentyl-1-deoxynoijirimycin (AMP-DNM), an inhibitor of glycosphingolipid (GSL) biosynthesis is known to ameliorate diabetes, insulin sensitivity and to prevent liver steatosis in ob/ob mice. Thus far the effect of GSL synthesis inhibition on pre-existing NASH has not yet been assessed. To investigate it, LDLR(−/−) mice were kept on a western-type diet for 12 weeks to induce NASH. Next, the diet was continued for 6 weeks in presence or not of AMP-DNM in the diet. AMP-DNM treated mice showed less liver steatosis, inflammation and fibrosis. Induction of fatty acid beta-oxydation was observed, as well as a reduction of plasma lipids. Our study demonstrates that AMP-DNM treatment is able to significantly correct pre-existing NASH, suggesting that inhibiting GSL synthesis may represent a novel strategy for the treatment of this pathology.

Therapeutic administration of the direct thrombin inhibitor argatroban reduces hepatic inflammation in mice with established fatty liver disease. Am J Pathol. 2012;181:1287-1295. [PMID: 22841818 DOI: 10.1016/j.ajpath.2012.06.011]

Thrombin generation is increased in patients with nonalcoholic fatty liver disease (NAFLD) and in mouse models of diet-induced obesity. Deficiency in the thrombin receptor protease activated receptor-1 reduces hepatic inflammation and steatosis in mice fed a Western diet. However, it is currently unclear whether thrombin inhibitors can modify the pathogenesis of established NAFLD. We tested the hypothesis that thrombin inhibition could reverse hepatic steatosis and inflammation in mice with established diet-induced NAFLD. Low-density lipoprotein receptor-deficient LDLr(-/-) mice were fed a control diet or a Western diet for 19 weeks. Mice were given the direct thrombin inhibitor argatroban ∼15 mg/kg/day or its vehicle via a miniosmotic pump for the final 4 weeks of the study. Argatroban administration significantly reduced hepatic proinflammatory cytokine expression and reduced macrophage and neutrophil accumulation in livers of mice fed a Western diet. Argatroban did not significantly impact hepatic steatosis, as indicated by histopathology, Oil Red O staining, and hepatic triglyceride levels. Argatroban reduced serum triglyceride and cholesterol levels in mice fed a Western diet. Argatroban reduced both α-smooth muscle actin expression and Type 1 collagen mRNA levels in livers of mice fed a Western diet, indicating reduced activation of hepatic stellate cells. This study indicates that therapeutic intervention with a thrombin inhibitor attenuates hepatic inflammation and several profibrogenic changes in mice fed a Western diet.

Notch ligand delta-like 4 blockade attenuates atherosclerosis and metabolic disorders

Atherosclerosis and insulin resistance are major components of the cardiometabolic syndrome, a global health threat associated with a systemic inflammatory state. Notch signaling regulates tissue development and participates in innate and adaptive immunity in adults. The role of Notch signaling in cardiometabolic inflammation, however, remains obscure. We noted that a high-fat, high-cholesterol diet increased expression of the Notch ligand Delta-like 4 (Dll4) in atheromata and fat tissue in LDL-receptor-deficient mice. Blockade of Dll4-Notch signaling using neutralizing anti-Dll4 antibody attenuated the development of atherosclerosis, diminished plaque calcification, improved insulin resistance, and decreased fat accumulation. These changes were accompanied by decreased macrophage accumulation, diminished expression of monocyte chemoattractant protein-1 (MCP-1), and lower levels of nuclear factor-κB (NF-κB) activation. In vitro cell culture experiments revealed that Dll4-mediated Notch signaling increases MCP-1 expression via NF-κB, providing a possible mechanism for in vivo effects. Furthermore, Dll4 skewed macrophages toward a proinflammatory phenotype ("M1"). These results suggest that Dll4-Notch signaling plays a central role in the shared mechanism for the pathogenesis of cardiometabolic disorders.

Plant-derived polyphenols regulate expression of miRNA paralogs miR-103/107 and miR-122 and prevent diet-induced fatty liver disease in hyperlipidemic mice

BACKGROUND

MicroRNAs have the potential for clinical application. Probable modulation by plant-derived polyphenols might open preventive measures using simple dietary recommendations.

METHODS

We assessed the ability of continuous administration of high-dose polyphenols to modulate hepatic metabolism and microRNA expression in diet-induced fatty liver disease in commercially available hyperlipidemic mice using well-established and accepted procedures that included the development of new antibodies against modified quercetin.

RESULTS

Weight gain, liver steatosis, changes in the composition of liver tissue, and insulin resistance were all attenuated by the continuous administration of polyphenols. We also demonstrated that metabolites of polyphenols accumulate in immune cells and at the surface of hepatic lipid droplets indicating not only bioavailability but a direct likely action on liver cells. The addition of polyphenols also resulted in changes in the expression of miR-103, miR-107 and miR-122.

CONCLUSIONS

Polyphenols prevent fatty liver disease under these conditions. The differential expression of mRNAs and miRNAs was also associated with changes in lipid and glucose metabolism and with the activation of 5'-adenosine monophosphate-activated protein kinase, effects that are not necessarily connected. miRNAs function via different mechanisms and miRNA-mRNA interactions are difficult to ascertain with current knowledge. Further, cell models usually elicit contradictory results with those obtained in animal models.

GENERAL SIGNIFICANCE

Our data indicate that plant-derived polyphenols should be tested in humans as preventive rather than therapeutic agents in the regulation of hepatic fatty acid utilization. A multi-faceted mechanism of action is likely and the regulation of liver miRNA expression blaze new trails in further research.

Effect of quercetin on inflammatory gene expression in mice liver in vivo - role of redox factor 1, miRNA-122 and miRNA-125b

The anti-inflammatory properties of the flavonol quercetin have been intensively investigated using in vitro cell systems and are to a great extent reflected by changes in the expression of inflammatory markers. However, information relating to the degree at which quercetin affects inflammatory gene expression in vivo is limited. Recently, micro RNAs (miRNAs) have been identified as powerful post-transcriptional gene regulators. The effect of quercetin on miRNA regulation in vivo is largely unknown. Laboratory mice were fed for six weeks with control or quercetin enriched high fat diets and biomarkers of inflammation as well as hepatic levels of miRNAs previously involved in inflammation (miR-125b) and lipid metabolism (miR-122) were determined. We found lower mRNA steady state levels of the inflammatory genes interleukin 6, C-reactive protein, monocyte chemoattractant protein 1, and acyloxyacyl hydrolase in quercetin fed mice. In addition we found evidence for an involvement of redox factor 1, a modulator of nuclear factor κB signalling, on the attenuation of inflammatory gene expression mediated by dietary quercetin. Furthermore, the results demonstrate that hepatic miR-122 and miR-125b concentrations were increased by dietary quercetin supplementation and may therefore contribute to the gene-regulatory activity of quercetin in vivo.

Role of cytokines and chemokines in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) includes a variety of histological conditions (ranging from liver steatosis and steatohepatitis, to fibrosis and hepatocarcinoma) that are characterized by an increased fat content within the liver. The accumulation/deposition of fat within the liver is essential for diagnosis of NAFLD and might be associated with alterations in the hepatic and systemic inflammatory state. Although it is still unclear if each histological entity represents a different disease or rather steps of the same disease, inflammatory processes in NAFLD might influence its pathophysiology and prognosis. In particular, non-alcoholic steatohepatitis (the most inflamed condition in NAFLDs, which more frequently evolves towards chronic and serious liver diseases) is characterized by a marked activation of inflammatory cells and the upregulation of several soluble inflammatory mediators. Among several mediators, cytokines and chemokines might play a pivotal active role in NAFLD and are considered as potential therapeutic targets. In this review, we will update evidence from both basic research and clinical studies on the potential role of cytokines and chemokines in the pathophysiology of NAFLD.

Apolipoprotein CIII overexpressing mice are predisposed to diet-induced hepatic steatosis and hepatic insulin resistance

Nonalcoholic fatty liver disease (NAFLD) and insulin resistance have recently been found to be associated with increased plasma concentrations of apolipoprotein CIII (APOC3) in humans carrying single nucleotide polymorphisms within the insulin response element of the APOC3 gene. To examine whether increased expression of APOC3 would predispose mice to NAFLD and hepatic insulin resistance, human APOC3 overexpressing (ApoC3Tg) mice were metabolically phenotyped following either a regular chow or high-fat diet (HFD). After HFD feeding, ApoC3Tg mice had increased hepatic triglyceride accumulation, which was associated with cellular ballooning and inflammatory changes. ApoC3Tg mice also manifested severe hepatic insulin resistance assessed by a hyperinsulinemic-euglycemic clamp, which could mostly be attributed to increased hepatic diacylglycerol content, protein kinase C-ϵ activation, and decreased insulin-stimulated Akt2 activity. Increased hepatic triglyceride content in the HFD-fed ApoC3Tg mice could be attributed to a ≈ 70% increase in hepatic triglyceride uptake and ≈ 50% reduction hepatic triglyceride secretion.

CONCLUSION

These data demonstrate that increase plasma APOC3 concentrations predispose mice to diet-induced NAFLD and hepatic insulin resistance.

Protease-activated receptor 1 and hematopoietic cell tissue factor are required for hepatic steatosis in mice fed a Western diet

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of obesity and metabolic syndrome and contributes to increased risk of cardiovascular disease and liver-related morbidity and mortality. Indeed, obese patients with metabolic syndrome generate greater amounts of thrombin, an indication of coagulation cascade activation. However, the role of the coagulation cascade in Western diet-induced NAFLD has not been investigated. Using an established mouse model of Western diet-induced NAFLD, we tested whether the thrombin receptor protease-activated receptor 1 (PAR-1) and hematopoietic cell-derived tissue factor (TF) contribute to hepatic steatosis. In association with hepatic steatosis, plasma thrombin-antithrombin levels and hepatic fibrin deposition increased significantly in C57Bl/6J mice fed a Western diet for 3 months. PAR-1 deficiency reduced hepatic inflammation, particularly monocyte chemoattractant protein-1 expression and macrophage accumulation. In addition, PAR-1 deficiency was associated with reduced steatosis in mice fed a Western diet, including reduced liver triglyceride accumulation and CD36 expression. Similar to PAR-1 deficiency, hematopoietic cell TF deficiency was associated with reduced inflammation and reduced steatosis in livers of low-density lipoprotein receptor-deficient mice fed a Western diet. Moreover, hematopoietic cell TF deficiency reduced hepatic fibrin deposition. These studies indicate that PAR-1 and hematopoietic cell TF are required for liver inflammation and steatosis in mice fed a Western diet.

Dietary cholesterol and egg yolks: not for patients at risk of vascular disease

A widespread misconception has been developing among the Canadian public and among physicians. It is increasingly believed that consumption of dietary cholesterol and egg yolks is harmless. There are good reasons for long- standing recommendations that dietary cholesterol should be limited to less than 200 mg/day; a single large egg yolk contains approximately 275 mg of cholesterol (more than a day's worth of cholesterol). Although some studies showed no harm from consumption of eggs in healthy people, this outcome may have been due to lack of power to detect clinically relevant increases in a low-risk population. Moreover, the same studies showed that among participants who became diabetic during observation, consumption of one egg a day doubled their risk compared with less than one egg a week. Diet is not just about fasting cholesterol; it is mainly about the postprandial effects of cholesterol, saturated fats, oxidative stress and inflammation. A misplaced focus on fasting lipids obscures three key issues. Dietary cholesterol increases the susceptibility of low-density lipoprotein to oxidation, increases postprandial lipemia and potentiates the adverse effects of dietary saturated fat. Dietary cholesterol, including egg yolks, is harmful to the arteries. Patients at risk of cardiovascular disease should limit their intake of cholesterol. Stopping the consumption of egg yolks after a stroke or myocardial infarction would be like quitting smoking after a diagnosis of lung cancer: a necessary action, but late. The evidence presented in the current review suggests that the widespread perception among the public and health care professionals that dietary cholesterol is benign is misplaced, and that improved education is needed to correct this misconception.

Monocyte chemoattractant protein-1 deficiency does not affect steatosis or inflammation in livers of mice fed a methionine-choline-deficient diet

Monocyte chemoattractant protein-1 (MCP-1, Ccl2) expression is increased in livers of patients with nonalcoholic steatohepatitis and in murine models of steatohepatitis. Several studies in rodents indicate that MCP-1 contributes to liver steatosis induced by feeding a high-fat diet. However, the extent of MCP-1 involvement in the widely utilized methionine-choline-deficient (MCD) diet model of steatohepatitis has not been determined. We tested the hypothesis that MCP-1 contributes to steatohepatitis in mice fed the MCD diet. MCP-1-deficient mice on a C57Bl/6J background and age-matched C57Bl/6J mice were fed either MCD diet or control diet for 4 weeks. MCP-1 deficiency did not affect steatohepatitis, as indicated by liver histopathology, nor did it affect serum alanine aminotransferase activity, hepatic triglyceride levels, hepatic inflammatory gene induction, or macrophage accumulation in mice fed the MCD diet. MCP-1 deficiency reduced the expression of the profibrogenic genes, pro-collagen 1a1, connective tissue growth factor, and transforming growth factor-β, in mice fed the MCD diet. MCP-1 deficiency significantly reduced collagen deposition and α-smooth muscle actin protein levels in the livers of mice fed the MCD diet. The results indicate that MCP-1 does not contribute to liver steatosis or inflammation in the MCD diet model of steatohepatitis. Rather, the data suggest that MCP-1 contributes to fibrosis in mice fed the MCD diet, independent of effects on steatosis and inflammation.

Insulin resistance, inflammation, and obesity: role of monocyte chemoattractant protein-1 (or CCL2) in the regulation of metabolism. Mediators Inflamm. 2010;2010. [PMID: 20936118 PMCID: PMC2948922 DOI: 10.1155/2010/326580]

To maintain homeostasis under diverse metabolic conditions, it is necessary to coordinate nutrient-sensing pathways with the immune response. This coordination requires a complex relationship between cells, hormones, and cytokines in which inflammatory and metabolic pathways are convergent at multiple levels. Recruitment of macrophages to metabolically compromised tissue is a primary event in which chemokines play a crucial role. However, chemokines may also transmit cell signals that generate multiple responses, most unrelated to chemotaxis, that are involved in different biological processes. We have reviewed the evidence showing that monocyte chemoattractant protein-1 (MCP-1 or CCL2) may have a systemic role in the regulation of metabolism that sometimes is not necessarily linked to the traffic of inflammatory cells to susceptible tissues. Main topics cover the relationship between MCP-1/CCL2, insulin resistance, inflammation, obesity, and related metabolic disturbances.

Transcriptional profiles of leukocyte populations provide a tool for interpreting gene expression patterns associated with high fat diet in mice

Background

Microarray experiments in mice have shown that high fat diet can lead to elevated expression of genes that are disproportionately associated with immune functions. These effects of high fat (atherogenic) diet may be due to infiltration of tissues by leukocytes in coordination with inflammatory processes.

Methodology/Principal Findings

The Novartis strain-diet-sex microarray database (GSE10493) was used to evaluate the hepatic effects of high fat diet (4 weeks) in 12 mouse strains and both genders. We develop and apply an algorithm that identifies “signature transcripts” for many different leukocyte populations (e.g., T cells, B cells, macrophages) and uses this information to derive an in silico “inflammation profile”. Inflammation profiles highlighted monocytes, macrophages and dendritic cells as key drivers of gene expression patterns associated with high fat diet in liver. In some strains (e.g., NZB/BINJ, B6), we estimate that 50–60% of transcripts elevated by high fat diet might be due to hepatic infiltration by these cell types. Interestingly, DBA mice appeared to exhibit resistance to localized hepatic inflammation associated with atherogenic diet. A common characteristic of infiltrating cell populations was elevated expression of genes encoding components of the toll-like receptor signaling pathway (e.g., Irf5 and Myd88).

Conclusions/Significance

High fat diet promotes infiltration of hepatic tissue by leukocytes, leading to elevated expression of immune-associated transcripts. The intensity of this effect is genetically controlled and sensitive to both strain and gender. The algorithm developed in this paper provides a framework for computational analysis of tissue remodeling processes and can be usefully applied to any in vivo setting in which inflammatory processes play a prominent role.

Differential response of two models of genetically modified mice fed with high fat and cholesterol diets: relationship to the study of non-alcoholic steatohepatitis

Research on the molecular basis of the hepatic alterations associated to obesity is dependent on the availability of suitable animal models. Apolipoprotein E deficient mice (ApoE(-/-)) and LDL-receptor deficient mice (LDLr(-/-)) develop steatosis and steatohepatitis when given pro-atherogenic diets. However, previous data suggest that these two models are not completely interchangeable, and that their metabolic phenotype may partially differ in response to nutrient stimuli. The present study further investigates this question, by comparing changes in hepatic inflammation, lipoprotein metabolism, and their related gene expressions. LDLr(-/-) mice were more susceptible to the development of obesity and hepatic steatosis, while the ApoE(-/-) model increased the amount of macrophages and inflammatory nodules in the liver. These changes were accompanied by a differential expression of selected members of the MAPK family and PPARs in the liver.

Expression of cytokine genes in the aorta is altered by the deficiency in MCP-1: effect of a high-fat, high-cholesterol diet

BACKGROUND

Monocyte chemoattractant protein-1 (MCP-1) facilitates the recruitment of monocytes/macrophages into vascular intima, and it is probably involved in the regulation of other signaling pathways relevant to the pathogenesis of arteriosclerosis and metabolic disturbances. However, chemokines are redundant. Consequently, the protective effect of MCP-1 deficiency may be mediated by changes in other cytokine signals.

METHODS AND RESULTS

Changes in the pattern of gene expression in the aorta were evaluated in LDLr(-/-) and MCP-1(-/-) LDLr(-/-) mice fed either chow or Western-style diet. Functional analyses were used to characterize the pathways affected and to identify biological processes in which MCP-1 may play an additional role. Some data also suggest that MCP-5 may act as a surrogate for MCP-1 deletion. Arteriosclerosis lesion and plaque composition are associated with enrichment in the cytokine-cytokine receptor interaction pathway.

CONCLUSIONS

There is a complex network of interactions linking MCP-1 and other cytokines. The lack of MCP-1 limits the aortic response to atherogenic stimuli, but does not completely protect against neointima formation. Activation of alternative inflammatory pathways in the vascular wall in response to MCP-1 deficiency should be considered to fully understand the actual role of this chemokine.