Increased hepatic myeloperoxidase activity in obese subjects with nonalcoholic steatohepatitis

Myeloperoxidase-Hepatocyte-Stellate Cell Cross Talk Promotes Hepatocyte Injury and Fibrosis in Experimental Nonalcoholic Steatohepatitis

AIMS

Myeloperoxidase (MPO), a highly oxidative enzyme secreted by leukocytes has been implicated in human and experimental nonalcoholic steatohepatitis (NASH), but the underlying mechanisms remain unknown. In this study, we investigated how MPO contributes to progression from steatosis to NASH.

RESULTS

In C57Bl/6J mice fed a diet deficient in methionine and choline to induce NASH, neutrophils and to a lesser extent inflammatory monocytes are markedly increased compared with sham mice and secrete abundant amounts of MPO. Through generation of HOCl, MPO directly causes hepatocyte death in vivo. In vitro experiments demonstrate mitochondrial permeability transition pore induction via activation of SAPK/JNK and PARP. MPO also contributes to activation of hepatic stellate cells (HSCs), the most important source of collagen in the liver. In vitro MPO-activated HSCs have an activation signature (MAPK and PI3K-AKT phosphorylation) and upregulate COL1A1, α-SMA, and CXCL1. MPO-derived oxidative stress also activates transforming growth factor β (TGF-β) in vitro, and TGF-β signaling inhibition with SB-431542 decreased steatosis and fibrosis in vivo. Conversely, congenital absence of MPO results in reduced hepatocyte injury, decreased levels of TGF-β, fewer activated HSCs, and less severe fibrosis in vivo.

INNOVATION AND CONCLUSION

Cumulatively, these findings demonstrate important cross talk between inflammatory myeloid cells, hepatocytes, and HSCs via MPO and establish MPO as part of a proapoptotic and profibrotic pathway of progression in NASH, as well as a potential therapeutic target to ameliorate this disease.

S100A8 Production in CXCR2-Expressing CD11b+Gr-1high Cells Aggravates Hepatitis in Mice Fed a High-Fat and High-Cholesterol Diet

Nonalcoholic fatty liver disease (NAFLD) is a common chronic liver disease with a spectrum of presentations. S100A8 has been suggested to play a pivotal role as an endogenous immune-activator in inflammatory diseases. In this study, we investigated the involvement of S100A8 in the development of NAFLD. We used a diet model of NAFLD, in which mice were fed either a high-fat and high-cholesterol diet (HFHCD) or a normal diet (ND) as a control. We also assessed liver tissues from patients with NAFLD, including patients with nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH). HFHCD-fed mice, but not ND-fed mice, developed steatohepatitis. S100A8 expression was significantly elevated in the livers of HFHCD-fed mice compared with the controls. S100A8 was exclusively expressed in CXCR2-expressing CD11b(+)Gr-1(high) cells, which significantly increased in the livers of HFHCD-fed mice. These cells were F4/80 negative and did not possess a suppressor function. TNF-α expression was enhanced by S100A8 in primary liver leukocytes or a hepatocyte cell line and significantly elevated in the livers of HFHCD-fed mice. TNF-α was primarily produced from CD11b(+)F4/80(+) cells in liver leukocytes in response to S100A8. TNF-α deficiency attenuated hepatitis in HFHCD-fed mice. S100A8 was significantly more expressed in the liver tissues of patients with NASH than in those of patients with NAFL. In conclusion, these results suggest that S100A8 is primarily produced from CXCR2-expressing CD11b(+)Gr-1(high) cells, and it upregulates TNF-α production in CD11b(+)F4/80(+) cells through cellular cross-talk, which is an important mechanism in the development of NAFLD.

Niacin inhibits fat accumulation, oxidative stress, and inflammatory cytokine IL-8 in cultured hepatocytes: Impact on non-alcoholic fatty liver disease

OBJECTIVE

Non-alcoholic fatty liver disease (NAFLD) is a common disorder characterized by excessive hepatic fat accumulation, production of reactive oxygen species (ROS), inflammation and potentially resulting in non-alcoholic steatohepatitis (NASH), cirrhosis and end-stage liver disease. Recently, we have shown that niacin significantly prevented hepatic steatosis and regressed pre-existing steatosis in high-fat fed rat model of NAFLD. To gain further insight into the cellular mechanisms, this study investigated the effect of niacin on human hepatocyte fat accumulation, ROS production, and inflammatory mediator IL-8 secretion.

MATERIALS AND METHODS

Human hepatoblastoma cell line HepG2 or human primary hepatocytes were first stimulated with palmitic acid followed by treatment with niacin or control for 24 h.

RESULTS

The data indicated that niacin (at 0.25 and 0.5 mmol/L doses) significantly inhibited palmitic acid-induced fat accumulation in human hepatocytes by 45-62%. This effect was associated with inhibition of diacylglycerol acyltransferase 2 (DGAT2) mRNA expression without affecting the mRNA expression of fatty acid synthase (FAS) and carnitine palmitoyltransferase 1 (CPT1). Niacin attenuated hepatocyte ROS production and it also inhibited NADPH oxidase activity. Niacin reduced palmitic acid-induced IL-8 levels.

CONCLUSIONS

These findings suggest that niacin, through inhibiting hepatocyte DGAT2 and NADPH oxidase activity, attenuates hepatic fat accumulation and ROS production respectively. Decreased ROS production, at least in part, may have contributed to the inhibition of pro-inflammatory IL-8 levels. These mechanistic studies may be useful for the clinical development of niacin and niacin-related compounds for the treatment of NAFLD/NASH and its complications.

Fat-laden macrophages modulate lobular inflammation in nonalcoholic steatohepatitis (NASH)

Nonalcoholic steatohepatitis (NASH) is characterized by extensive hepatic monocyte infiltration and monocyte-derived macrophages have an important role in regulating the disease evolution. However, little is known about the functional changes occurring in liver macrophages during NASH progression. In this study, we investigated phenotypic and functional modifications of hepatic macrophages in experimental NASH induced by feeding C57BL/6 mice with a methionine-choline deficient (MCD) diet up to 8weeks. In mice with steatohepatitis liver F4/80-positive macrophages increased in parallel with the disease progression and formed small clusters of enlarged and vacuolated cells. At immunofluorescence these cells contained lipid vesicles positive for the apoptotic cell marker Annexin V suggesting the phagocytosis of apoptotic bodies derived from dead fat-laden hepatocytes. Flow cytometry revealed that these enlarged macrophages expressed inflammatory monocyte (CD11b, Ly6C, TNF-α) markers. However, as compared to regular size macrophages the enlarged sub-set was characterized by an enhanced production of arginase-1 and of the anti-inflammatory mediators IL-10 and annexin A1. Similar vacuolated macrophages producing annexin A1 were also evident in liver biopsies of NASH patients. In mice with NASH, the accumulation of enlarged F4/80(+) cells paralleled with a decline in the expression of the macrophage M1 activation markers iNOS, IL-12 and CXCL10, while the levels of M2 polarization markers arginase-1 and MGL-1 were unchanged. Interestingly, the lowering of IL-12 expression mainly involved the macrophage sub-set with regular size. We conclude that during the progression of NASH fat accumulation within liver macrophages promotes the production of anti-inflammatory mediators that influence hepatic inflammatory responses.

Soluble urokinase plasminogen activator receptor levels are associated with severity of fibrosis in nonalcoholic fatty liver disease

The identification of individuals with severe liver fibrosis among patients with chronic liver disease is of major importance when evaluating prognosis, potential risk for complications, and when deciding treatment strategies. Although percutaneous liver biopsy is still considered a "gold standard" for staging of liver fibrosis, attempts to find reliable noninvasive markers of liver fibrosis are frequent. Inflammation is essential for the progression of fibrosis. The urokinase plasminogen activator and its receptor have been associated with hepatic inflammation and fibrosis in mice. High serum concentrations of soluble urokinase plasminogen activator receptor (suPAR) are suggested to be involved in inflammation, tissue remodeling, and cancer metastasis. Here, we evaluated serum suPAR as a noninvasive test to detect liver fibrosis in 82 well-characterized patients with nonalcoholic fatty liver disease (NAFLD), and in 38 untreated patients with chronic hepatitis C virus (HCV) infection at the time of their first liver biopsy. suPAR levels were increased in chronic liver disease compared with blood donors (P < 0.001). Patients with HCV had higher suPAR concentrations than patients with NAFLD (P < 0.002). suPAR levels were associated with the severity of fibrosis, particularly in NAFLD, but did not correlate with inflammation. Regarding the performance in predicting severity of fibrosis, suPAR was essentially as good as other commonly used noninvasive fibrosis scoring systems. The results in HCV confirm previous observations. However, this is the first study to investigate suPAR as a biomarker in NAFLD, and the results indicate that suPAR may constitute a severity marker related to fibrosis and prognosis rather than reflecting inflammation.

Management and diagnosis of fatty liver disease

Nonalcoholic fatty liver disease is a common cause of chronic liver disease and has been an increasingly studied topic of research as the obesity epidemic has been growing. There is a significant morbidity and mortality with uncontrolled steatohepatitis, which can progress to fibrosis, cirrhosis and hepatocellular carcinoma. The prevalence of this disease has been estimated to be roughly one-third of the western population, thought to be largely due to diet and sedentary lifestyle. Several treatments have been studied including vitamin E, insulin-sensitizing agents and ursodeoxycholic acid; however, the only treatment shown to improve the histologic changes of nonalcoholic fatty liver disease is weight loss. Given the proven benefit of weight loss, there may be reason to screen at-risk populations; however, limited availability of other disease-modifying treatments may limit the cost-benefit ratios. A better understanding of the diagnosis and management of this condition is required to alter the course of this modifiable disease.

A CONSORT-compliant, randomized, double-blind, placebo-controlled pilot trial of purified anthocyanin in patients with nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a common liver disease that can progress to cirrhosis and liver failure. Anthocyanin, a member of the flavonoid family, has been shown to ameliorate NAFLD-associated pathologies in rodents.The aim of this CONSORT-compliant pilot study is to evaluate the effects of anthocyanin supplementation on insulin resistance and liver injury biomarkers in patients with NAFLD.A total of 74 subjects with NAFLD were divided into 2 groups in this double-blind, randomized study. Patients received either purified anthocyanin (320 mg/d) derived from bilberry and black currant or placebo for 12 weeks. Diet, physical activity, anthropometric parameters, glucose tolerance, and a set of biomarkers related to NAFLD were evaluated before and after intervention.No significant differences were observed in nutrient intake, physical activity, anthropometric parameters, or plasma lipid profile between patients receiving anthocyanin or placebo. Compared to controls, the anthocyanin group exhibited significant decreases (P < 0.05, all comparisons) in plasma alanine aminotransferase (-19.1% vs 3.1%), cytokeratin-18 M30 fragment (-8.8% vs 5.6%) and myeloperoxidase (-75.0% vs -44.8%). Significant decreases from baseline in fasting blood glucose and homeostasis model assessment for insulin resistance were observed in the anthocyanin group; however, these differences were not significant relative to placebo controls. In addition, the oral glucose tolerance test indicated that anthocyanin supplementation significantly decreased the 2-hour loading glucose level compared to control (-18.7% vs -3.8%, P = 0.02).A 12-week supplement of purified anthocyanin improved insulin resistance, indicators of liver injury, and clinical evolution in NAFLD patients. Further studies are warranted to determine the clinical applications of anthocyanin in NAFLD.This trial was registered at clinicaltrials.gov as NCT01940263.

Non-alcoholic fatty liver disease: The diagnosis and management

Non-alcoholic fatty liver disease (NAFLD) is now the most frequent chronic liver disease that occurs across all age groups and is recognized to occur in 14%-30% of the general population, representing a serious and growing clinical problem due to the growing prevalence of obesity and overweight. Histologically, it resembles alcoholic liver injury but occurs in patients who deny significant alcohol consumption. NAFLD encompasses a spectrum of conditions, ranging from benign hepatocellular steatosis to inflammatory nonalcoholic steatohepatitis, fibrosis, and cirrhosis. The majority of hepatocellular lipids are stored as triglycerides, but other lipid metabolites, such as free fatty acids, cholesterol, and phospholipids, may also be present and play a role in disease progression. NAFLD is associated with obesity and insulin resistance and is considered the hepatic manifestation of the metabolic syndrome, a combination of medical conditions including type 2 diabetes mellitus, hypertension, hyperlipidemia, and visceral adiposity. Confirmation of the diagnosis of NAFLD can usually be achieved by imaging studies; however, staging the disease requires a liver biopsy. Current treatment relies on weight loss and exercise, although various insulin-sensitizing agents, antioxidants and medications appear promising. The aim of this review is to highlight the current information regarding epidemiology, diagnosis, and management of NAFLD as well as new information about pathogenesis, diagnosis and management of this disease.

Hypochlorous acid via peroxynitrite activates protein kinase Cθ and insulin resistance in adipocytes

We recently reported that genetic deletion of myeloperoxidase (MPO) alleviates obesity-related insulin resistance in mice in vivo. How MPO impairs insulin sensitivity in adipocytes is poorly characterized. As hypochlorous acid (HOCl) is a principal oxidant product generated by MPO, we evaluated the effects of HOCl on insulin signaling in adipocytes differentiated from 3T3-L1 cells. Exposure of 3T3-L1 adipocytes to exogenous HOCl (200 μmol/l) attenuated insulin-stimulated 2-deoxyglucose uptake, GLUT4 translocation, and insulin signals, including tyrosine phosphorylation of insulin receptor substrate 1 (IRS1) and phosphorylation of Akt. Furthermore, treatment with HOCl induced phosphorylation of IRS1 at serine 307, inhibitor κB kinase (IKK), c-Jun NH2-terminal kinase (JNK), and phosphorylation of PKCθ (PKCθ). In addition, genetic and pharmacological inhibition of IKK and JNK abolished serine phosphorylation of IRS1 and impairment of insulin signaling by HOCl. Furthermore, knockdown of PKCθ using siRNA transfection suppressed phosphorylation of IKK and JNK and consequently attenuated the HOCl-impaired insulin signaling pathway. Moreover, activation of PKCθ by peroxynitrite was accompanied by increased phosphorylation of IKK, JNK, and IRS1-serine 307. In contrast, ONOO(-) inhibitors abolished HOCl-induced phosphorylation of PKCθ, IKK, JNK, and IRS1-serine 307, as well as insulin resistance. Finally, high-fat diet (HFD)-induced insulin resistance was associated with enhanced phosphorylation of PKCθ, IKK, JNK, and IRS1 at serine 307 in white adipose tissues from WT mice, all of which were not found in Mpo knockout mice fed HFDs. We conclude that HOCl impairs insulin signaling pathway by increasing ONOO(-) mediated phosphorylation of PKCθ, resulting in phosphorylation of IKK/JNK and consequent serine phosphorylation of IRS1 in adipocytes.

Cardiovascular dysfunction in patients with liver cirrhosis

Hyperdynamic syndrome is a well-known clinical condition found in patients with cirrhosis and portal hypertension, characterized by increased heart rate and cardiac output, and reduced systemic vascular resistance and arterial blood pressure. The leading cause of hyperdynamic circulation in cirrhotic patients is peripheral and splanchnic vasodilatation, due to an increased production/activity of vasodilator factors and decreased vascular reactivity to vasoconstrictors. The term "cirrhotic cardiomyopathy" describes impaired contractile responsiveness to stress, diastolic dysfunction and electrophysiological abnormalities in patients with cirrhosis without known cardiac disease. Underlying circulatory and cardiac dysfunctions are the main determinant in the development of hepatorenal syndrome in advanced cirrhosis. Moreover, the clinical consequences of cirrhosis-related cardiovascular dysfunction are evident during and after liver transplantation, and after transjugular intrahepatic portosystemic shunt insertion. Cardiovascular complications following these procedures are common, with pulmonary edema being the most common complication. Other complications include overt heart failure, arrhythmia, pulmonary hypertension, pericardial effusion, and cardiac thrombus formation. This review discusses the circulatory and cardiovascular dysfunctions in cirrhosis, examining the pathophysiologic and clinical implications in light of the most recent published literature.

Complement alternative pathway activation in human nonalcoholic steatohepatitis

The innate immune system plays a major role in the pathogenesis of nonalcoholic steatohepatitis (NASH). Recently we reported complement activation in human NASH. However, it remained unclear whether the alternative pathway of complement, which amplifies C3 activation and which is frequently associated with pathological complement activation leading to disease, was involved. Here, alternative pathway components were investigated in liver biopsies of obese subjects with healthy livers (n = 10) or with NASH (n = 12) using quantitative PCR, Western blotting, and immunofluorescence staining. Properdin accumulated in areas where neutrophils surrounded steatotic hepatocytes, and colocalized with the C3 activation product C3c. C3 activation status as expressed by the C3c/native C3 ratio was 2.6-fold higher (p<0.01) in subjects with NASH despite reduced native C3 concentrations (0.94±0.12 vs. 0.57±0.09; p<0.01). Hepatic properdin levels positively correlated with levels of C3c (r_s = 0.69; p<0.05) and C3c/C3 activation ratio (r_s = 0.59; p<0.05). C3c, C3 activation status (C3c/C3 ratio) and properdin levels increased with higher lobular inflammation scores as determined according to the Kleiner classification (C3c: p<0.01, C3c/C3 ratio: p<0.05, properdin: p<0.05). Hepatic mRNA expression of factor B and factor D did not differ between subjects with healthy livers and subjects with NASH (factor B: 1.00±0.19 vs. 0.71±0.07, p = 0.26; factor D: 1.00±0.21 vs. 0.66±0.14, p = 0.29;). Hepatic mRNA and protein levels of Decay Accelerating Factor tended to be increased in subjects with NASH (mRNA: 1.00±0.14 vs. 2.37±0.72; p = 0.22; protein: 0.51±0.11 vs. 1.97±0.67; p = 0.28). In contrast, factor H mRNA was downregulated in patients with NASH (1.00±0.09 vs. 0.71±0.06; p<0.05) and a similar trend was observed with hepatic protein levels (1.12±0.16 vs. 0.78±0.07; p = 0.08). Collectively, these data suggest a role for alternative pathway activation in driving hepatic inflammation in NASH. Therefore, alternative pathway factors may be considered attractive targets for treating NASH by inhibiting complement activation.

Association of obesity with leukocyte count in obese individuals without metabolic syndrome

AIMS

Inflammation in obesity is associated to insulin resistance (IR), hyperglycemia, hypertension and hyperlipidemia. Leukocytes play an important role in obesity associated inflammation. The initial factors that generate the inflammatory events in the obesity remain unclear. Therefore, the aim of this study was to determine the association of circulating leukocytes with clinical and biochemical parameters in obese individuals with clinical and biochemical parameters in normal range and with or without IR.

METHODS

Nineteen obese non-diabetic and 9 lean subjects were studied for serum levels of insulin, lipids, glycated hemoglobin, glycemia, for clinical parameters as HOMA-IR, arterial pressure and anthropometric parameters, and for leukocyte counts. Neutrophil/lymphocyte ratio (N/L) was calculated using the loge of leukocyte counts. Association between leukocytes and studied parameters was determined by Pearson's correlation.

RESULTS

Two groups of obese individuals were observed: with high levels of insulin (with IR) and with normal levels (without IR). Positive correlations were observed between leukocyte and lymphocyte counts with body mass index and HOMA-IR and negative correlation with decreased HDL levels. Lymphocytes correlated with increased levels of insulin. Leukocytes and neutrophils correlated positively with increased visceral fat and liver steatosis. These associations were absent in the obese group without IR. N/L ratio did not show correlations with studied parameters. The leukocyte associations were mainly observed in obese individuals with IR.

CONCLUSIONS

These data may represent initial leukocyte associations with morbidity features and define two different obese individuals that may evolve to the chronic inflammation observed in the obesity.

Reactive oxygen and nitrogen species in steatotic hepatocytes: a molecular perspective on the pathophysiology of ischemia-reperfusion injury in the fatty liver

SIGNIFICANCE

Hepatic ischemia-reperfusion (IR) injury results from the temporary deprivation of hepatic blood supply and is a common side effect of major liver surgery (i.e., transplantation or resection). IR injury, which in most severe cases culminates in acute liver failure, is particularly pronounced in livers that are affected by non-alcoholic fatty liver disease (NAFLD). In NAFLD, fat-laden hepatocytes are damaged by chronic oxidative/nitrosative stress (ONS), a state that is acutely exacerbated during IR, leading to extensive parenchymal damage.

RECENT ADVANCES

NAFLD triggers ONS via increased (extra)mitochondrial fatty acid oxidation and activation of the unfolded protein response. ONS is associated with widespread protein and lipid (per)oxidation, which reduces the hepatic antioxidative capacity and shifts the intracellular redox status toward an oxidized state. Moreover, activation of the transcription factor peroxisome proliferator-activated receptor α induces expression of mitochondrial uncoupling protein 2, resulting in depletion of cellular energy (ATP) reserves. The reduction in intracellular antioxidants and ATP in fatty livers consequently gives rise to severe ONS and necrotic cell death during IR.

CRITICAL ISSUES

Despite the fact that ONS mediates both NAFLD and IR injury, the interplay between the two conditions has never been described in detail. An integrative overview of the pathophysiology of NAFLD that renders steatotic hepatocytes more vulnerable to IR injury is therefore presented in the context of ONS.

FUTURE DIRECTIONS

Effective methods should be devised to alleviate ONS and the consequences thereof in NAFLD before surgery in order to improve resilience of fatty livers to IR injury.

Nonalcoholic fatty liver disease: A main driver of insulin resistance or a dangerous liaison?

Insulin resistance is one of the key components of the metabolic syndrome and it eventually leads to the development of type 2 diabetes, making it one of the biggest medical problems of modern society. Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are tightly associated with insulin resistance. While it is fairly clear that insulin resistance causes hepatic steatosis, it is not known if NAFLD causes insulin resistance. Hepatic inflammation and lipid accumulation are believed to be the main drivers of hepatic insulin resistance in NAFLD. Here we give an overview of the evidence linking hepatic lipid accumulation to the development of insulin resistance, including the accumulation of triacylglycerol and lipid metabolites, such as diacylglycerol and ceramides. In particular, we discuss the role of obesity in this relation by reviewing the current evidence in terms of the reported changes in body weight and/or adipose tissue mass. We further discuss whether the activation or inhibition of inflammatory pathways, Kupffer cells and other immune cells influences the development of insulin resistance. We show that, in contrast to what is commonly believed, neither hepatic steatosis nor hepatic inflammation is sufficient to cause insulin resistance. Many studies show that obesity cannot be ignored as an underlying factor in this relationship and NAFLD is therefore less likely to be one of the main drivers of insulin resistance.

Susceptibility of Nrf2-null mice to steatohepatitis and cirrhosis upon consumption of a high-fat diet is associated with oxidative stress, perturbation of the unfolded protein response, and disturbance in the expression of metabolic enzymes but not with insulin resistance

Mice lacking the transcription factor NF-E2 p45-related factor 2 (Nrf2) develop more severe nonalcoholic steatohepatitis (NASH), with cirrhosis, than wild-type (Nrf2^+/+) mice when fed a high-fat (HF) diet for 24 weeks. Although NASH is usually associated with insulin resistance, HF-fed Nrf2^−/− mice exhibited better insulin sensitivity than HF-fed Nrf2^+/+ mice. In livers of HF-fed mice, loss of Nrf2 resulted in greater induction of lipogenic genes, lower expression of β-oxidation genes, greater reduction in AMP-activated protein kinase (AMPK) levels, and diminished acetyl coenzyme A (CoA) carboxylase phosphorylation than in the wild-type livers, which is consistent with greater fatty acid (FA) synthesis in Nrf2^−/− livers. Moreover, primary Nrf2^−/− hepatocytes displayed lower glucose and FA oxidation than Nrf2^+/+ hepatocytes, with FA oxidation partially rescued by treatment with AMPK activators. The unfolded protein response (UPR) was perturbed in control regular-chow (RC)-fed Nrf2^−/− mouse livers, and this was associated with constitutive activation of NF-κB and JNK, along with upregulation of inflammatory genes. The HF diet elicited an antioxidant response in Nrf2^+/+ livers, and as this was compromised in Nrf2^−/− livers, they suffered oxidative stress. Therefore, Nrf2 protects against NASH by suppressing lipogenesis, supporting mitochondrial function, increasing the threshold for the UPR and inflammation, and enabling adaptation to HF-diet-induced oxidative stress.

Reversal of high-fat diet-induced hepatic steatosis by n-3 LCPUFA: role of PPAR-α and SREBP-1c

Nonalcoholic fatty liver disease is characterized by an abnormal accumulation of triacylglycerides in the liver in absence of significant alcohol consumption. Under these conditions, it has been observed an impaired bioavailability of hepatic n-3 long-chain polyunsaturated fatty acids (LCPUFAs). The aim of this study was to test the reversion of the prosteatotic and proinflammatory effects of high-fat diet (HFD) in the mouse liver by changing to normocaloric diet and n-3 LCPUFA supplementation. Male C57BL/6J mice were given either control diet (CD) or HFD for 12 weeks. Control and HFD groups were divided into subgroups that continue with CD or subjected to CD plus n-3 LCPUFA for 8 additional weeks. After this time, blood and liver samples were taken and metabolic, morphologic, oxidative stress, inflammatory and signaling parameters were analyzed. The dietary change from HFD to a normocaloric diet with n-3 LCPUFA supplementation significantly reduced insulin resistance and liver steatosis when compared to switching HFD to normocaloric diet alone. In addition, HFD-induced increases in adiposity, adipocyte enlargement and liver oxidative stress and inflammatory cytokine expression were suppressed by n-3 LCPUFA to control values. Importantly, n-3 LCPUFA supplementation abolish HFD-induced enhancement in hepatic SREBP-1c/PPAR-α ratios, suggesting a change in the metabolic status of the liver from a lipogenic condition to one favoring fatty acid oxidation and steatosis attenuation. These findings may provide the rational basis for the use of normocaloric diets supplemented with n-3 LCPUFA in patients with liver steatosis.

Comparative reactivity of myeloperoxidase-derived oxidants with mammalian cells

Myeloperoxidase is an important heme enzyme released by activated leukocytes that catalyzes the reaction of hydrogen peroxide with halide and pseudo-halide ions to form various hypohalous acids. Hypohalous acids are chemical oxidants that have potent antibacterial, antiviral, and antifungal properties and, as such, play key roles in the human immune system. However, increasing evidence supports an alternative role for myeloperoxidase-derived oxidants in the development of disease. Excessive production of hypohalous acids, particularly during chronic inflammation, leads to the initiation and accumulation of cellular damage that has been implicated in many human pathologies including atherosclerosis, neurodegenerative disease, lung disease, arthritis, inflammatory cancers, and kidney disease. This has sparked a significant interest in developing a greater understanding of the mechanisms involved in myeloperoxidase-derived oxidant-induced mammalian cell damage. This article reviews recent developments in our understanding of the cellular reactivity of hypochlorous acid, hypobromous acid, and hypothiocyanous acid, the major oxidants produced by myeloperoxidase under physiological conditions.

Metabolically induced liver inflammation leads to NASH and differs from LPS- or IL-1β-induced chronic inflammation

The nature of the chronic inflammatory component that drives the development of non-alcoholic steatohepatitis (NASH) is unclear and possible inflammatory triggers have not been investigated systematically. We examined the effect of non-metabolic triggers (lipopolysaccharide (LPS), interleukin-1β (IL-1β), administered by slow-release minipumps) and metabolic dietary triggers (carbohydrate, cholesterol) of inflammation on the progression of bland liver steatosis (BS) to NASH. Transgenic APOE3*Leiden.huCETP (APOE3L.CETP) mice fed a high-fat diet (HFD) developed BS after 10 weeks. Then, inflammatory triggers were superimposed or not (control) for six more weeks. Mouse livers were analyzed with particular emphasis on hallmarks of inflammation which were defined in human liver biopsies with and without NASH. Livers of HFD-treated control mice remained steatotic and did not progress to NASH. All four inflammatory triggers activated hepatic nuclear factor-κB (NF-κB) significantly and comparably (≥5-fold). However, HFD+LPS or HFD+IL-1β did not induce a NASH-like phenotype and caused intrahepatic accumulation of almost exclusively mononuclear cells. By contrast, mice treated with metabolic triggers developed NASH, characterized by enhanced steatosis, hepatocellular hypertrophy, and formation of mixed-type inflammatory foci containing myeloperoxidase-positive granulocytes (neutrophils) as well as mononuclear cells, essentially as observed in human NASH. Specific for the metabolic inducers was an activation of the proinflammatory transcription factor activator protein-1 (AP-1), neutrophil infiltration, and induction of risk factors associated with human NASH, that is, dyslipidemia (by cholesterol) and insulin resistance (by carbohydrate). In conclusion, HFD feeding followed by NF-κB activation per se (LPS, IL-1β) does not promote the transition from BS to NASH. HFD feeding followed by metabolically evoked inflammation induces additional inflammatory components (neutrophils, AP-1 pathway) and causes NASH.

IL-17 signaling accelerates the progression of nonalcoholic fatty liver disease in mice

Inflammation plays a central pathogenic role in the pernicious metabolic and end-organ sequelae of obesity. Among these sequelae, nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease in the developed world. The twinned observations that obesity is associated with increased activation of the interleukin (IL)-17 axis and that this axis can regulate liver damage in diverse contexts prompted us to address the role of IL-17RA signaling in the progression of NAFLD. We further examined whether microbe-driven IL-17A regulated NAFLD development and progression. We show here that IL-17RA(-/-) mice respond to high-fat diet stress with significantly greater weight gain, visceral adiposity, and hepatic steatosis than wild-type controls. However, obesity-driven lipid accumulation was uncoupled from its end-organ consequences in IL-17RA(-/-) mice, which exhibited decreased steatohepatitis, nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase enzyme expression, and hepatocellular damage. Neutralization of IL-17A significantly reduced obesity-driven hepatocellular damage in wild-type mice. Further, colonization of mice with segmented filamentous bacteria (SFB), a commensal that induces IL-17A production, exacerbated obesity-induced hepatocellular damage. In contrast, SFB depletion protected from obesity-induced hepatocellular damage.

CONCLUSION

These data indicate that obesity-driven activation of the IL-17 axis is central to the development and progression of NAFLD to steatohepatitis and identify the IL-17 pathway as a novel therapeutic target in this condition.

Systematic review with meta-analysis: non-invasive assessment of non-alcoholic fatty liver disease--the role of transient elastography and plasma cytokeratin-18 fragments

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) affects 15-40% of the general population. Some patients have non-alcoholic steatohepatitis (NASH) and progressive fibrosis, and would be candidates for monitoring and treatment.

AIM

To review current literature on the use of non-invasive tests to assess the severity of NAFLD.

METHODS

Systematic literature searching identified studies evaluating non-invasive tests of NASH and fibrosis using liver biopsy as the reference standard. Meta-analysis was performed for areas with adequate number of publications.

RESULTS

Serum tests and physical measurements like transient elastography (TE) have high negative predictive value (NPV) in excluding advanced fibrosis in NAFLD patients. The NAFLD fibrosis score comprises of six routine clinical parameters and has been endorsed by current American guidelines as a screening test to exclude low-risk individuals. The pooled sensitivities and specificities for TE to diagnose F ≥ 2, F ≥ 3 and F4 disease were 79% and 75%, 85% and 85%, and 92% and 92% respectively. Liver stiffness measurement often fails in obese patients, but the success rate can be improved with the use of the XL probe. A number of biomarkers have been developed for the diagnosis of NASH, but few were independently validated. Serum/plasma cytokeratin-18 fragments have been most extensively evaluated and have a pooled sensitivity of 66% and specificity of 82% in diagnosing NASH.

CONCLUSIONS

Current non-invasive tests are accurate in excluding advanced fibrosis in NAFLD patients, and may be used for initial assessment. Further development and evaluation of NASH biomarkers are needed.

Hepatic crown-like structure: a unique histological feature in non-alcoholic steatohepatitis in mice and humans

Although macrophages are thought to be crucial for the pathogenesis of chronic inflammatory diseases, how they are involved in disease progression from simple steatosis to non-alcoholic steatohepatitis (NASH) is poorly understood. Here we report the unique histological structure termed "hepatic crown-like structures (hCLS)" in the mouse model of human NASH; melanocortin-4 receptor deficient mice fed a Western diet. In hCLS, CD11c-positive macrophages aggregate to surround hepatocytes with large lipid droplets, which is similar to those described in obese adipose tissue. Histological analysis revealed that hCLS is closely associated with activated fibroblasts and collagen deposition. When treatment with clodronate liposomes effectively depletes macrophages scattered in the liver, with those in hCLS intact, hepatic expression of inflammatory and fibrogenic genes is unaffected, suggesting that hCLS is an important source of inflammation and fibrosis during the progression of NASH. Notably, the number of hCLS is positively correlated with the extent of liver fibrosis. We also observed increased number of hCLS in the liver of non-alcoholic fatty liver disease/NASH patients. Collectively, our data provide evidence that hCLS is involved in the development of hepatic inflammation and fibrosis, thereby suggesting its pathophysiologic role in disease progression from simple steatosis to NASH.

Transgenic expression of human neutrophil peptide-1 enhances hepatic fibrosis in mice fed a choline-deficient, L-amino acid-defined diet

BACKGROUND

Neutrophils infiltrate the livers of patients with nonalcoholic steatohepatitis (NASH). Human neutrophil peptides (HNPs) induce cytokine and chemokine production under inflammatory conditions, which may contribute to the progression of NASH. In this study, we focused on the effects of HNP-1 on hepatic steatosis and fibrosis in a mouse model of NASH induced by a choline-deficient, L-amino acid-defined (CDAA) diet.

MATERIALS & METHODS

We generated transgenic mice expressing HNP-1 under the control of a β-actin-based promoter. HNP-1 transgenic and wild-type C57BL/6N mice were fed a CDAA diet for 16 weeks to induce hepatic steatosis and fibrosis. Serological and histological features were examined, and the effects of HNP-1 on hepatic stellate cell lines were assessed.

RESULTS

HNP-1 transgenic and wild-type mice fed the CDAA diet showed no significant differences in serum alanine aminotransferase levels or the degree of hepatic steatosis based on Oil red O staining and hepatic triglyceride content. In contrast, Sirius Red and Azan staining showed significantly more severe hepatic fibrosis in HNP-1 transgenic mice compared with wild-type mice. In addition, significantly more α-smooth muscle actin-positive hepatic stellate cells were observed in the transgenic mice than in the wild-type mice. Finally, the proliferation of the LI90 hepatic stellate cell line increased in response to HNP-1.

CONCLUSION

Our data indicate that HNP-1 enhances hepatic fibrosis in fatty liver by inducing hepatic stellate cell proliferation. Thus, neutrophil-derived HNP-1 may contribute to the progression of NASH.

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.

Immune and inflammatory pathways in NASH

Immune and inflammatory pathways have a central role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Both the innate and adaptive immune systems contribute to the development of NAFLD. Pathogen-associated molecular patterns and danger-associated molecular patterns are known to activate a variety of pattern-recognition receptors that result in inflammation. The key features of the immune system and inflammatory pathways in the development of NAFLD are discussed in this review.

Dendritic cells limit fibroinflammatory injury in nonalcoholic steatohepatitis in mice

Nonalcoholic steatohepatitis (NASH) is the most common etiology of chronic liver dysfunction in the United States and can progress to cirrhosis and liver failure. Inflammatory insult resulting from fatty infiltration of the liver is central to disease pathogenesis. Dendritic cells (DCs) are antigen-presenting cells with an emerging role in hepatic inflammation. We postulated that DCs are important in the progression of NASH. We found that intrahepatic DCs expand and mature in NASH liver and assume an activated immune phenotype. However, rather than mitigating the severity of NASH, DC depletion markedly exacerbated intrahepatic fibroinflammation. Our mechanistic studies support a regulatory role for DCs in NASH by limiting sterile inflammation through their role in the clearance of apoptotic cells and necrotic debris. We found that DCs limit CD8(+) T-cell expansion and restrict Toll-like receptor expression and cytokine production in innate immune effector cells in NASH, including Kupffer cells, neutrophils, and inflammatory monocytes. Consistent with their regulatory role in NASH, during the recovery phase of disease, ablation of DC populations results in delayed resolution of intrahepatic inflammation and fibroplasia.

CONCLUSION

Our findings support a role for DCs in modulating NASH. Targeting DC functional properties may hold promise for therapeutic intervention in NASH.

Low-density lipoprotein modified by myeloperoxidase in inflammatory pathways and clinical studies

Oxidation of low-density lipoprotein (LDL) has a key role in atherogenesis. Among the different models of oxidation that have been studied, the one using myeloperoxidase (MPO) is thought to be more physiopathologically relevant. Apolipoprotein B-100 is the unique protein of LDL and is the major target of MPO. Furthermore, MPO rapidly adsorbs at the surface of LDL, promoting oxidation of amino acid residues and formation of oxidized lipoproteins that are commonly named Mox-LDL. The latter is not recognized by the LDL receptor and is accumulated by macrophages. In the context of atherogenesis, Mox-LDL accumulates in macrophages leading to foam cell formation. Furthermore, Mox-LDL seems to have specific effects and triggers inflammation. Indeed, those oxidized lipoproteins activate endothelial cells and monocytes/macrophages and induce proinflammatory molecules such as TNFα and IL-8. Mox-LDL may also inhibit fibrinolysis mediated via endothelial cells and consecutively increase the risk of thrombus formation. Finally, Mox-LDL has been involved in the physiopathology of several diseases linked to atherosclerosis such as kidney failure and consequent hemodialysis therapy, erectile dysfunction, and sleep restriction. All these issues show that the investigations of MPO-dependent LDL oxidation are of importance to better understand the inflammatory context of atherosclerosis.

Diverse novel functions of neutrophils in immunity, inflammation, and beyond

Neutrophils have long been considered simple suicide killers at the bottom of the hierarchy of the immune response. That view began to change 10-20 yr ago, when the sophisticated mechanisms behind how neutrophils locate and eliminate pathogens and regulate immunity and inflammation were discovered. The last few years witnessed a new wave of discoveries about additional novel and unexpected functions of these cells. Neutrophils have been proposed to participate in protection against intracellular pathogens such as viruses and mycobacteria. They have been shown to intimately shape the adaptive immune response at various levels, including marginal zone B cells, plasmacytoid dendritic cells and T cell populations, and even to control NK cell homeostasis. Neutrophils have been shown to mediate an alternative pathway of systemic anaphylaxis and to participate in allergic skin reactions. Finally, neutrophils were found to be involved in physiological and pathological processes beyond the immune system, such as diabetes, atherosclerosis, and thrombus formation. Many of those functions appear to be related to their unique ability to release neutrophil extracellular traps even in the absence of pathogens. This review summarizes those novel findings on versatile functions of neutrophils and how they change our view of neutrophil biology in health and disease.

Liver manipulation during liver surgery in humans is associated with hepatocellular damage and hepatic inflammation

BACKGROUND

Manipulation of the liver during liver surgery results in profound hepatocellular damage. Experimental data show that mobilization-induced hepatocellular damage is related to hepatic inflammation. To date, information on this link in humans is lacking. As it is possible to modulate inflammation, it is clinically relevant to unravel this relationship.

AIM

This observational study aimed to establish the association between liver mobilization and hepatic inflammation in humans.

METHODS

Consecutive patients requiring mobilization of the right hemi-liver during liver surgery were studied. Plasma samples and liver biopsies were collected prior to and directly after mobilization and after transection of the liver. Hepatocellular damage was assayed by liver fatty acid-binding protein (L-FABP) and aminotransferase levels. Hepatic inflammation was determined by (a) immunohistochemical identification of myeloperoxidase (MPO) and CD68- positive cells and (b) hepatic gene expression of inflammatory and cell adhesion molecules (IL-1β, IL-6, IL-8, VCAM-1 and ICAM-1).

RESULTS

A total of 25 patients were included. L-FABP levels increased significantly during mobilization (301 ± 94 ng/ml to 1599 ± 362 ng/ml, P = 0.008), as did ALAT levels (36 ± 5 IU/L to 167 ± 21 IU/L, P < 0.001). A significant increase in MPO (P = 0.001) and CD68 (P = 0.002) positive cells was noticed in the liver after mobilization. The number of MPO-positive cells correlated with the duration of mobilization (Pearson correlation=0.505, P = 0.033). Hepatic gene expression of pro-inflammatory cytokines IL-1β and IL-6, chemo-attractant IL-8 and adhesion molecule ICAM-1 increased significantly during liver manipulation.

CONCLUSIONS

Liver mobilization is associated with hepatocellular damage and liver inflammation, as shown by infiltration of inflammatory cells and upregulation of genes involved in acute inflammation.

Non-alcoholic steatohepatitis: the role of oxidized low-density lipoproteins

Non-alcoholic steatohepatitis (NASH) is hallmarked by lipid accumulation in the liver (steatosis) along with inflammation (hepatitis). The transition from simple steatosis towards NASH represents a key step in pathogenesis, as it will set the stage for further severe liver damage. Yet, the pathogenesis behind hepatic inflammation is still poorly understood. It is of relevance to better understand the underlying mechanisms involved in NASH in order to apply new knowledge to potential novel therapeutic approaches. In the current review, we propose oxidized cholesterol as a novel risk factor for NASH. Here, we summarize mouse and human studies that provide possible mechanisms for the involvement of oxidized low-density lipoproteins in NASH and consequent potential novel diagnostic tools and treatment strategies for hepatic inflammation.

The protective effects of different-time-ischemic preconditioning on the reperfusion injury in fatty livers in rats

BACKGROUND

The present study was aimed to investigate the protective effects of different-time-ischemic preconditioning on the reperfusion injury in fatty livers in rats, and to elucidate the mechanisms underlying the protective effects and the optimal safe ischemic preconditioning time on the hepatic IR injury in steatotic livers.

METHODOLOGY/PRINCIPAL FINDINGS

A rat fatty liver model was established by high-fat diet feeding. We investigated the changes in the concentration of AST, ALT, LDH and NO in the serum, and of MDA, SOD, and MPO in the liver samples in response to different ischemic preconditioning times and ischemia-reperfusion injury. Histological analysis was performed to evaluate the results of the hepatic fatty infiltration. 1) At 24 h after 15 min ischemic preconditioning with 10 min reperfusion (15 min +10 min IP), the extent and area of the necrosis was markedly higher in the fatty liver samples with respect to IR, compared to the normal liver samples. 2) In response to the treatment of 5/8 min +10 min IP, the fatty liver group showed lower levels of serological indicators and liver MDA and MPO compared to the other groups, while the SOD activity of the fatty liver group was significantly higher than the other groups (p<0.05). Compared to the corresponding IR group, all IP groups showed a significantly higher serum NO concentration (p<0.05). Among the fatty liver groups, the 5/8 min+10 min IP group showed the highest NO concentration (p<0.05).

CONCLUSIONS/SIGNIFICANCE

Fat infiltration could aggravate the ischemia-reperfusion injury in the rat liver. Furthermore, ischemic preconditioning could increase the tolerance of the fatty liver, which was induced by the high-fat diet, to hepatic ischemia-reperfusion injury in rats. The protocol of 5/8 min +10 min IP was the optimal regimen for the treatment of moderate and severe fatty livers.

The microcirculation in adipose tissue inflammation

In most humans, obesity is associated with a chronic low-grade inflammatory reaction occurring in several organ tissues, including the adipose tissue. Infiltration of bone marrow derived leukocytes (granulocytes, monocytes, lymphocytes) into expanding adipose depots appears to be an integral component of inflammation in obesity. Circulating leukocytes invade organ tissues mainly through post-capillary venules in the microcirculation. The endothelium of the post-capillary venules acts as a gatekeeper to leukocyte adhesion and extravasation by displacing on its luminal surface adhesion molecules that bind the adhesive receptors expressed on circulating leukocytes. Several studies investigating the impact of obesity on the microcirculation have demonstrated the occurrence of microvascular dysfunction in experimental animal model of obesity, as well as in obese humans. To date though, working hypotheses and study designs have favored the view that microvascular alterations are secondary to adipose tissue dysfunction. Indeed, a significant amount of data exists in the scientific literature to support the concept that microvascular dysfunction may precede and cause adipose tissue inflammation in obesity. Through review of key published data, this article prospectively presents the concept that in response to nutrients overload the vascular endothelium of the microcirculation acutely activates inflammatory pathways that initiate infiltration of leukocytes in visceral adipose tissue, well before weight gain and overt obesity. The anatomical and physiological heterogeneity of different microcirculations is also discussed toward the understanding of how obesity induces different inflammatory phenotypes in visceral and subcutaneous fat depots.

Roles of chemokine ligand-2 (CXCL2) and neutrophils in influencing endothelial cell function and inflammation of human adipose tissue

The hypertrophied white adipose tissue (WAT) during human obesity produces inflammatory mediators, including cytokines (IL-6 and TNFα) and chemokines ([C-C motif] chemokine ligand 2 and IL-8). These inflammatory factors are preferentially produced by the nonadipose cells, particularly the adipose tissue infiltrating macrophages. We identified the chemokine (C-X-C motif) ligand 2 (CXCL2) by a transcriptomic approach. Because CXCL2 could represent a WAT-produced chemokine, we explored its role in obesity-associated inflammation. CXCL2 levels in serum and mRNA in WAT were higher in obese subjects compared with lean ones. CXCL2 secretions were higher in sc and visceral (vis) WAT from obese compared with lean subjects. In vis WAT, CXCL2 mRNA expression was higher in macrophages compared with other WAT cells and positively correlated with the inflammatory macrophage markers TNFα and IL-6. CXCL2 triggered the in vitro adhesion of the neutrophils, its selective cell targets, to endothelial cells (ECs) of vis WAT (vis WAT-ECs). Immunohistological analysis indicated that activated neutrophils were adherent to the endothelium of vis WAT from human obese subjects. Blood neutrophils from obese subjects released high levels of proinflammatory mediators (IL-8, chemokine motif ligand 2 [CCL2], matrix metalloproteinase [MMP] 9, and myeloperoxidase [MPO]). Visceral WAT-ECs, treated by neutrophil-conditioned media prepared from obese subjects, displayed an increase of the expression of inflammatory molecules associated with senescence and angiogenic capacities. To conclude, CXCL2, a WAT-produced chemokine being up-regulated in obesity, stimulates neutrophil adhesion to vis WAT-ECs. Activated neutrophils in obesity may influence vis WAT-ECs functions and contribute to WAT inflammation.

Neutrophil-derived myeloperoxidase aggravates non-alcoholic steatohepatitis in low-density lipoprotein receptor-deficient mice

Background

Chronic inflammation and oxidative stress play fundamental roles in the pathogenesis of non-alcoholic steatohepatitis (NASH). Previously, we reported that myeloperoxidase (MPO), an aggressive oxidant-generating neutrophil enzyme, is associated with NASH severity in man. We now investigated the hypothesis that MPO contributes to the development and progression of NASH.

Methodology

Low-density lipoprotein receptor-deficient mice with an MPO-deficient hematopoietic system (LDLR^−/−/MPO^−/−tp mice) were generated and compared with LDLR^−/−/MPO^+/+tp mice after induction of NASH by high-fat feeding.

Results

High-fat feeding caused a ∼4-fold induction of liver MPO in LDLR^−/−/MPO^+/+ mice which was associated with hepatic sequestration of MPO-positive neutrophils and high levels of nitrotyrosine, a marker of MPO activity. Importantly, LDLR^−/−/MPO^−/−tp mice displayed markedly reduced hepatic neutrophil and T-lymphocyte infiltration (p<0.05), and strong down regulation of pro-inflammatory genes such as TNF-α and IL-6 (p<0.05, p<0.01) in comparison with LDLR^−/−/MPO^+/+tp mice. Next to the generalized reduction of inflammation, liver cholesterol accumulation was significantly diminished in LDLR^−/−/MPO^−/−tp mice (p = 0.01). Moreover, MPO deficiency appeared to attenuate the development of hepatic fibrosis as evident from reduced hydroxyproline levels (p<0.01). Interestingly, visceral adipose tissue inflammation was markedly reduced in LDLR^−/−/MPO^−/−tp mice, with a complete lack of macrophage crown-like structures. In conclusion, MPO deficiency attenuates the development of NASH and diminishes adipose tissue inflammation in response to a high fat diet, supporting an important role for neutrophils in the pathogenesis of metabolic disease.

Specific immunization strategies against oxidized low-density lipoprotein: a novel way to reduce nonalcoholic steatohepatitis in mice

Nonalcoholic steatohepatitis (NASH) is characterized by hepatic lipid accumulation combined with inflammation, which can ultimately progress into cirrhosis. Recently, we demonstrated that deletion of scavenger receptors (SRs) CD36 and SR-A in hematopoietic cells reduced hepatic inflammation. In addition to uptake of modified lipoproteins, CD36 and SR-A are also involved in other functions that can activate the inflammatory response. Therefore, the actual trigger for SR activation during NASH is unclear. Here, we hypothesized that hepatic inflammation is triggered by recognition of oxidized LDL (oxLDL) by Kupffer cells (KCs). To inhibit recognition of oxLDL by KCs, low-density lipoprotein receptor (Ldlr(-/-) ) mice were immunized with heat-inactivated pneumococci, which were shown to induce the production of anti-oxLDL immunoglobulin M (IgM) antibodies, due to molecular mimicry with oxLDL. The mice received a high-fat, high-cholesterol diet during the last 3 weeks to induce NASH. Immunization with pneumococci increased anti-oxLDL IgM levels and led to a reduction in hepatic inflammation, as shown by reduced macrophage, neutrophil, and T cell infiltration, and reduced gene expression of tumor necrosis factor (Tnf), interleukin-6 (Il-6), interleukin-1β (Il-1b), monocyte chemoattractant protein 1 (Mcp1), and fibrosis-related genes. In immunized mice, KCs were smaller and showed fewer cholesterol crystals compared with nonimmunized mice.

CONCLUSION

Antibodies to oxLDL play an important role in the pathogenesis of NASH. Therefore, the potential of phosphorylcholine-based vaccination strategies as a novel tool for the prevention and therapy of NASH should be tested in the future.

The utility of immunohistochemistry for the identification of hematopoietic and lymphoid cells in normal tissues and interpretation of proliferative and inflammatory lesions of mice and rats

Expression of antigens in cells and tissues can be readily studied immunohistochemically with the use of antibodies. A panel of antibodies to cell-specific markers can be used to diagnose lesions, including tumors, in the hematopoietic and lymphoid systems. This review discusses the use of readily available antibodies and procedures to identify antigens expressed in normal tissues and in proliferative and inflammatory lesions in formalin-fixed, paraffin-embedded (FFPE) murine specimens.

Decreased nucleotide excision repair in steatotic livers associates with myeloperoxidase-immunoreactivity

Chronic inflammation is characterized by the influx of neutrophils and is associated with an increased production of reactive oxygen species that can damage DNA. Oxidative DNA damage is generally thought to be involved in the increased risk of cancer in inflamed tissues. We previously demonstrated that activated neutrophil mediated oxidative stress results in a reduction in nucleotide excision repair (NER) capacity, which could further enhance mutagenesis. Inflammation and oxidative stress are critical factors in the progression of nonalcoholic fatty liver disease that is linked with enhanced liver cancer risk. In this report, we therefore evaluated the role of neutrophils and the associated oxidative stress in damage recognition and DNA repair in steatotic livers of 35 severely obese subjects with either nonalcoholic steatohepatitis (NASH) (n=17) or steatosis alone (n=18). The neutrophilic influx in liver was assessed by myeloperoxidase (MPO) staining and the amount of oxidative DNA damage by measuring M(1)dG adducts. No differences in M(1)dG adduct levels were observed between patients with or without NASH and also not between individuals with high or low MPO immunoreactivity. However, we found that high expression of MPO in the liver, irrespective of disease status, reduced the damage recognition capacity as determined by staining for histone 2AX phosphorylation (γH2AX). This reduction in γH2AX formation in individuals with high MPO immunoreactivity was paralleled by a significant decrease in NER capacity as assessed by a functional repair assay, and was not related to cell proliferation. Thus, the observed reduction in NER capacity upon hepatic inflammation is associated with and may be a consequence of reduced damage recognition. These findings suggest a novel mechanism of liver cancer development in patients with nonalcoholic fatty liver disease.

Therapeutic administration of the direct thrombin inhibitor argatroban reduces hepatic inflammation in mice with established fatty liver disease

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.

Recent progress in histochemistry and cell biology

Studies published in Histochemistry and Cell Biology in the year 2011 represent once more a manifest of established and newly sophisticated techniques being exploited to put tissue- and cell type-specific molecules into a functional context. The review is therefore the Histochemistry and Cell Biology's yearly intention to provide interested readers appropriate summaries of investigations touching the areas of tissue biology, developmental biology, the biology of the immune system, stem cell research, the biology of subcellular compartments, in order to put the message of such studies into natural scientific-/human- and also pathological-relevant correlations.

Endogenous formation of Nε-(carboxymethyl)lysine is increased in fatty livers and induces inflammatory markers in an in vitro model of hepatic steatosis

BACKGROUND & AIMS

Increased lipid peroxidation and inflammation are major factors in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). A lipoxidation product that could play a role in the induction of hepatic inflammation is N(ε)-(carboxymethyl)lysine (CML). The aim of the present study was to investigate the relationship between steatosis and CML and to study the role of CML in hepatic inflammation.

METHODS

We included 74 obese individuals, which were categorized into 3 groups according to the grade of hepatic steatosis. CML accumulation in liver biopsies was assessed by immunohistochemistry and plasma CML levels were measured by mass spectrometry. Plasma CML levels were also determined in the hepatic artery, portal, and hepatic vein of 22 individuals, and CML fluxes across the liver were calculated. Hepatocyte cell lines were used to study CML formation during intracellular lipid accumulation and the effect of CML on pro-inflammatory cytokine expression. Gene expression levels of the inflammatory markers were determined in liver biopsies of the obese individuals.

RESULTS

CML accumulation was significantly associated with the grade of hepatic steatosis, the grade of hepatic inflammation, and gene expression levels of inflammatory markers PAI-1, IL-8, and CRP. Analysis of CML fluxes showed no release/uptake of CML by the liver. Lipid accumulation in hepatocytes, induced by incubation with fatty acids, was associated with increased CML formation and expression of the receptor for advanced glycation endproducts (RAGE), PAI-1, IL-8, IL-6, and CRP. Pyridoxamine and aminoguanidine inhibited the endogenous CML formation and the increased RAGE, PAI-1, IL-8, IL-6, and CRP expression. Incubation of hepatocytes with CML-albumin increased the expression of RAGE, PAI-1, and IL-6, which was inhibited by an antibody against RAGE.

CONCLUSIONS

Accumulation of CML and a CML-upregulated RAGE-dependent inflammatory response in steatotic livers may play an important role in hepatic steatosis and in the pathogenesis of NAFLD.

The role of innate cells is coupled to a Th1-polarized immune response in pediatric nonalcoholic steatohepatitis

BACKGROUND

Nonalcoholic steatohepatitis (NASH) is a chronic inflammatory liver disease influenced by risk factors for the metabolic syndrome. In adult patients, NASH is associated with an altered phenotype and functionality of peripheral immune cells, the recruitment of leukocytes and intrahepatic activation, and an exacerbated production of reactive oxygen species (ROS) and cytokines. It remains unclear if the previously described differences between pediatric and adult nonalcoholic fatty liver diseases also reflect differences in their pathogenesis.

AIMS

We aimed to investigate the phenotype and functionality of circulating immune cells and the potential contribution of liver infiltrating leukocytes to the immunological imbalance in pediatric NASH.

RESULTS

By a real-time PCR-based analysis of cytokines and immunohistochemical staining of liver biopsies, we demonstrated that the hepatic microenvironment is dominated by interferon-gamma (IFN-γ) but not interleukin-4 and is infiltrated by a higher number of CD8(+) cells in pediatric NASH. The number of infiltrating neutrophils positively correlated with ROS generation by peripheral polymorphonuclear cells. By a flow cytometric analysis of peripheral blood lymphocytes, a distinctive increase in CD8(+) CD45RO and CD8(+) CD45RA subpopulations and an increased production of IFN-γ by CD4(+) and CD8(+) cells were shown. The production of ROS following PMA stimulation was augmented in circulating neutrophils but not in monocytes.

CONCLUSION

In sum, the distinctive phenotype and functionality of infiltrating and circulating cells suggest that the role of innate cells is coupled to a Th1-polarized immune response in pediatric NASH.

Neutrophil-cytokine interactions in a rat model of sulindac-induced idiosyncratic liver injury

Previous studies indicated that lipopolysaccharide (LPS) interacts with the nonsteroidal anti-inflammatory drug sulindac (SLD) to produce liver injury in rats. In the present study, the mechanism of SLD/LPS-induced liver injury was further investigated. Accumulation of polymorphonuclear neutrophils (PMNs) in the liver was greater in SLD/LPS-cotreated rats compared to those treated with SLD or LPS alone. In addition, PMN activation occurred specifically in livers of rats cotreated with SLD/LPS. The hypothesis that PMNs and proteases released from them play critical roles in the hepatotoxicity was tested. SLD/LPS-induced liver injury was attenuated by prior depletion of PMNs or by treatment with the PMN protease inhibitor, eglin C. Previous studies suggested that tumor necrosis factor-α (TNF) and the hemostatic system play critical roles in the pathogenesis of liver injury induced by SLD/LPS. TNF and plasminogen activator inhibitor-1 (PAI-1) can contribute to hepatotoxicity by affecting PMN activation and fibrin deposition. Therefore, the role of TNF and PAI-1 in PMN activation and fibrin deposition in the SLD/LPS-induced liver injury model was tested. Neutralization of TNF or inhibition of PAI-1 attenuated PMN activation. TNF had no effect on PAI-1 production or fibrin deposition. In contrast, PAI-1 contributed to fibrin deposition in livers of rats treated with SLD/LPS. In summary, PMNs, TNF and PAI-1 contribute to the liver injury induced by SLD/LPS cotreatment. TNF and PAI-1 independently contributed to PMN activation, which is critical to the pathogenesis of liver injury. Moreover, PAI-1 contributed to liver injury by promoting fibrin deposition.

Redox balance in the pathogenesis of nonalcoholic fatty liver disease: mechanisms and therapeutic opportunities

Nonalcoholic fatty liver disease (NAFLD) is currently the most common liver disease in the world. It encompasses a histological spectrum, ranging from simple, nonprogressive steatosis to nonalcoholic steatohepatitis (NASH), which may progress to cirrhosis and hepatocellular carcinoma. While liver-related complications are confined to NASH, emerging evidence suggests both simple steatosis and NASH predispose to type 2 diabetes and cardiovascular disease. The pathogenesis of NAFLD is currently unknown, but accumulating data suggest that oxidative stress and altered redox balance play a crucial role in the pathogenesis of steatosis, steatohepatitis, and fibrosis. We will examine intracellular mechanisms, including mitochondrial dysfunction and impaired oxidative free fatty acid metabolism, leading to reactive oxygen species generation; additionally, the potential pathogenetic role of extracellular sources of reactive oxygen species in NAFLD, including increased myeloperoxidase activity and oxidized low density lipoprotein accumulation, will be reviewed. We will discuss how these mechanisms converge to determine the whole pathophysiological spectrum of NAFLD, including hepatocyte triglyceride accumulation, hepatocyte apoptosis, hepatic inflammation, hepatic stellate cell activation, and fibrogenesis. Finally, available animal and human data on treatment opportunities with older and newer antioxidant will be presented.

Mitochondria and redox signaling in steatohepatitis

Alcoholic and nonalcoholic fatty liver diseases are potentially pathological conditions that can progress to steatohepatitis, fibrosis, and cirrhosis. These conditions affect millions of people throughout the world in part through poor lifestyle choices of excess alcohol consumption, overnutrition, and lack of regular physical activity. Abnormal mitochondrial and cellular redox homeostasis has been documented in steatohepatitis and results in alterations of multiple redox-sensitive signaling cascades. Ultimately, these changes in signaling lead to altered enzyme function and transcriptional activities of proteins critical to mitochondrial and cellular function. In this article, we review the current hypotheses linking mitochondrial redox state to the overall pathophysiology of alcoholic and nonalcoholic steatohepatitis and briefly discuss the current therapeutic options under investigation.

Green tea extract protects against nonalcoholic steatohepatitis in ob/ob mice by decreasing oxidative and nitrative stress responses induced by proinflammatory enzymes

Oxidative and nitrative stress responses resulting from inflammation exacerbate liver injury associated with nonalcoholic steatohepatitis (NASH) by inducing lipid peroxidation and protein nitration. The objective of this study was to investigate whether the anti-inflammatory properties of green tea extract (GTE) would protect against NASH by suppressing oxidative and nitrative damage mediated by proinflammatory enzymes. Obese mice (ob/ob) and their 5-week-old C57BL6 lean littermates were fed 0%, 0.5% or 1% GTE for 6 weeks (n=12-13 mice/group). In obese mice, hepatic lipid accumulation, inflammatory infiltrates and serum alanine aminotransferase activity were markedly increased, whereas these markers of hepatic steatosis, inflammation and injury were significantly reduced among obese mice fed GTE. GTE also normalized hepatic 4-hydroxynonenal and 3-nitro-tyrosine (N-Tyr) concentrations to those observed in lean controls. These oxidative and nitrative damage markers were correlated with alanine aminotransferase (P<.05; r=0.410-0.471). Improvements in oxidative and nitrative damage by GTE were also associated with lower hepatic nicotinamide adenine dinucleotide phosphate oxidase activity. Likewise, GTE reduced protein expression levels of hepatic myeloperoxidase and inducible nitric oxide synthase and decreased the concentrations of nitric oxide metabolites. Correlative relationships between nicotinamide adenine dinucleotide phosphate oxidase and hepatic 4-hydroxynonenal (r=0.364) as well as nitric oxide metabolites and N-Tyr (r=0.598) suggest that GTE mitigates lipid peroxidation and protein nitration by suppressing the generation of reactive oxygen and nitrogen species. Further study is warranted to determine whether GTE can be recommended as an effective dietary strategy to reduce the risk of obesity-triggered NASH.