Plasma cathepsin D correlates with histological classifications of fatty liver disease in adults and responds to intervention

Non-alcoholic steatohepatitis (NASH) is characterized by liver lipid accumulation and inflammation. The mechanisms that trigger hepatic inflammation are poorly understood and subsequently, no specific non-invasive markers exist. We previously demonstrated a reduction in the plasma lysosomal enzyme, cathepsin D (CatD), in children with NASH compared to children without NASH. Recent studies have raised the concept that non-alcoholic fatty liver disease (NAFLD) in adults is distinct from children due to a different histological pattern in the liver. Yet, the link between plasma CatD to adult NASH was not examined. In the current manuscript, we investigated whether plasma CatD in adults correlates with NASH development and regression. Biopsies were histologically evaluated for inflammation and NAFLD in three complementary cohorts of adults (total n = 248). CatD and alanine aminotransferase (ALT) were measured in plasma. Opposite to our previous observations with childhood NASH, we observed increased levels of plasma CatD in patients with NASH compared to adults without hepatic inflammation. Furthermore, after surgical intervention, we found a reduction of plasma CatD compared to baseline. Our observations highlight a distinct pathophysiology between NASH in children and adults. The observation that plasma CatD correlated with NASH development and regression is promising for NASH diagnosis.

CX3CR1 is a gatekeeper for intestinal barrier integrity in mice: Limiting steatohepatitis by maintaining intestinal homeostasis

Nonalcoholic fatty liver disease is seen as the hepatic manifestation of the metabolic syndrome and represents the most common liver disease in Western societies. The G protein-coupled chemokine receptor CX3CR1 plays a central role in several metabolic syndrome-related disease manifestations and is involved in maintaining intestinal homeostasis. Because diet-induced intestinal dysbiosis is a driver for nonalcoholic fatty liver disease, we hypothesized that CX3CR1 may influence the development of steatohepatitis. In two independent models of diet-induced steatohepatitis (high-fat diet and methionine/choline-deficient diet), CX3CR1 protected mice from excessive hepatic steatosis and inflammation, as well as systemic glucose intolerance. Lack of Cx3cr1 expression was associated with significantly altered intestinal microbiota composition, which was linked to an impaired intestinal barrier. Concomitantly, endotoxin levels in portal serum and inflammatory macrophages in liver were increased in Cx3cr1-/- mice, indicating an increased inflammatory response. Depletion of intestinal microbiota by administration of broad-spectrum antibiotics suppressed the number of infiltrating macrophages and promoted macrophage polarization in liver. Consequently, antibiotic-treated mice demonstrated a marked improvement of steatohepatitis.

CONCLUSION

Microbiota-mediated activation of the innate immune responses through CX3CR1 is crucial for controlling steatohepatitis progression, which recognizes CX3CR1 as an essential gatekeeper in this scenario.

Hematopoietic overexpression of Cyp27a1 reduces hepatic inflammation independently of 27-hydroxycholesterol levels in Ldlr(-/-) mice

BACKGROUND & AIMS

Non-alcoholic steatohepatitis (NASH) is characterized by hepatic lipid accumulation and inflammation. Currently, the underlying mechanisms, leading to hepatic inflammation, are still unknown. The breakdown of free cholesterol inside Kupffer cells (KCs) by the mitochondrial enzyme CYP27A1 produces 27-hydroxycholesterol (27HC). We recently demonstrated that administration of 27HC to hyperlipidemic mice reduced hepatic inflammation. In line, hematopoietic deletion of Cyp27a1 resulted in increased hepatic inflammation. In the current manuscript, the effect of hematopoietic overexpression of Cyp27a1 on the development of NASH and cholesterol trafficking was investigated. We hypothesized that Cyp27a1 overexpression in KCs will lead to reduced hepatic inflammation.

METHODS

Irradiated Ldlr(-/-) mice were transplanted (tp) with bone marrow from mice overexpressing Cyp27a1 (Cyp27a1(over)) and wild type (Wt) mice and fed either chow or a high-fat, high-cholesterol (HFC) diet for 3 months. Additionally, gene expression was assessed in bone marrow-derived macrophages (BMDM) from Cyp27a1(over) and Wt mice.

RESULTS

In line with our hypothesis, hepatic inflammation in HFC-fed Cyp27a1(over)-tp mice was reduced and KCs were less foamy compared to Wt-tp mice. Remarkably, these changes occurred even though plasma and liver levels of 27HC did not differ between both groups. BMDM from Cyp27a1(over) mice revealed reduced inflammatory gene expression and increased expression of cholesterol transporters compared to Wt BMDM after lipopolysaccharide (LPS) stimulation.

CONCLUSIONS

Our data suggest that overexpression of Cyp27a1 in KCs reduces hepatic inflammation independently of 27HC levels in plasma and liver, further pointing towards KCs as specific target for improving the therapy of NASH.

Innate immune signaling and gut-liver interactions in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome and covers a disease spectrum ranging from steatosis to inflammation, fibrosis, cirrhosis and hepatocellular carcinoma (HCC). The innate immune response in the liver plays an important role during NAFLD progression. In addition, changes in the intestinal microbial balance and bacterial translocation can further affect disease progression. Immune cells in the liver recognize cell damage or pathogen invasion with intracellular or surface-expressed pattern recognition receptors (PRRs), subsequently initiating signaling cascades that trigger the release of factors promoting the inflammatory response during NAFLD progression. Therefore, mechanisms by which cells of the immune system are activated and recruited into the liver and how these cells cause injury and stress are important for understanding the inflammatory response during NAFLD.

Protective role of plant sterol and stanol esters in liver inflammation: insights from mice and humans

The inflammatory component of non-alcoholic steatohepatitis (NASH) can lead to irreversible liver damage. Therefore there is an urgent need to identify novel interventions to combat hepatic inflammation. In mice, omitting cholesterol from the diet reduced hepatic inflammation. Considering the effects of plant sterol/stanol esters on cholesterol metabolism, we hypothesized that plant sterol/stanol esters reduces hepatic inflammation. Indeed, adding plant sterol/stanol esters to a high-fat-diet reduced hepatic inflammation as indicated by immunohistochemical stainings and gene expression for inflammatory markers. Finally, adding sterol/stanol esters lowered hepatic concentrations of cholesterol precursors lathosterol and desmosterol in mice, which were highly elevated in the HFD group similarly as observed in severely obese patients with NASH. In vitro, in isolated LPS stimulated bone marrow derived macrophages desmosterol activated cholesterol efflux whereas sitostanol reduced inflammation. This highly interesting observation that plant sterol/stanol ester consumption leads to complete inhibition of HFD-induced liver inflammation opens new venues in the treatment and prevention of hepatic inflammation.

Exendin-4 decreases liver inflammation and atherosclerosis development simultaneously by reducing macrophage infiltration

BACKGROUND AND PURPOSE

The aetiology of inflammation in the liver and vessel wall, leading to non-alcoholic steatohepatitis (NASH) and atherosclerosis, respectively, shares common mechanisms including macrophage infiltration. To treat both disorders simultaneously, it is highly important to tackle the inflammatory status. Exendin-4, a glucagon-like peptide-1 (GLP-1) receptor agonist, reduces hepatic steatosis and has been suggested to reduce atherosclerosis; however, its effects on liver inflammation are underexplored. Here, we tested the hypothesis that exendin-4 reduces inflammation in both the liver and vessel wall, and investigated the common underlying mechanism.

EXPERIMENTAL APPROACH

Female APOE*3-Leiden.CETP mice, a model with human-like lipoprotein metabolism, were fed a cholesterol-containing Western-type diet for 5 weeks to induce atherosclerosis and subsequently treated for 4 weeks with exendin-4.

KEY RESULTS

Exendin-4 modestly improved dyslipidaemia, but markedly decreased atherosclerotic lesion severity and area (-33%), accompanied by a reduction in monocyte adhesion to the vessel wall (-42%) and macrophage content in the plaque (-44%). Furthermore, exendin-4 reduced hepatic lipid content and inflammation as well as hepatic CD68⁺ (-18%) and F4/80⁺ (-25%) macrophage content. This was accompanied by less monocyte recruitment from the circulation as the Mac-1⁺ macrophage content was decreased (-36%). Finally, exendin-4 reduced hepatic chemokine expression in vivo and suppressed oxidized low-density lipoprotein accumulation in peritoneal macrophages in vitro, effects dependent on the GLP-1 receptor.

CONCLUSIONS AND IMPLICATIONS

Exendin-4 reduces inflammation in both the liver and vessel wall by reducing macrophage recruitment and activation. These data suggest that exendin-4 could be a valuable strategy to treat NASH and atherosclerosis simultaneously.

Macrophage specific caspase-1/11 deficiency protects against cholesterol crystallization and hepatic inflammation in hyperlipidemic mice

Background & Aims

While non-alcoholic steatohepatitis (NASH) is characterized by hepatic steatosis combined with inflammation, the mechanisms triggering hepatic inflammation are unknown. In Ldlr^-/- mice, we have previously shown that lysosomal cholesterol accumulation in Kupffer cells (KCs) correlates with hepatic inflammation and cholesterol crystallization. Previously, cholesterol crystals have been shown to induce the activation of inflammasomes. Inflammasomes are protein complexes that induce the processing and release of pro-inflammatory cytokines IL-1b and IL-18 via caspase-1 activation. Whereas caspase-1 activation is independent of caspase-11 in the canonical pathway of inflammasome activation, caspase-11 was found to trigger caspase-1-dependent IL-1b and IL-18 in response to non-canonical inflammasome activators. So far, it has not been investigated whether inflammasome activation stimulates the formation of cholesterol crystals. We hypothesized that inflammasome activation in KCs stimulates cholesterol crystallization, thereby leading to hepatic inflammation.

Methods

Ldlr^-/- mice were transplanted (tp) with wild-type (Wt) or caspase-1/11^-/- (dKO) bone marrow and fed either regular chow or a high-fat, high-cholesterol (HFC) diet for 12 weeks. Invitro, bone marrow derived macrophages (BMDM) from wt or caspase-1/11^-/- mice were incubated with oxLDL for 24h and autophagy was assessed.

Results

In line with our hypothesis, caspase-1/11^-/--tp mice had less severe hepatic inflammation than Wt-tp animals, as evident from liver histology and gene expression analysis in isolated KCs. Mechanistically, KCs from caspase-1/11^-/--tp mice showed less cholesterol crystals, enhanced cholesterol efflux and increased autophagy. In wt BMDM, oxLDL incubation led to disturbed autophagy activity whereas BMDM from caspase-1/11^-/- mice had normal autophagy activity.

Conclusion

Altogether, these data suggest a vicious cycle whereby disturbed autophagy and decreased cholesterol efflux leads to newly formed cholesterol crystals and thereby maintain hepatic inflammation during NASH by further activating the inflammasome.

Trapping of oxidized LDL in lysosomes of Kupffer cells is a trigger for hepatic inflammation

BACKGROUND & AIMS

Non-alcoholic steatohepatitis (NASH) is characterized by steatosis and inflammation. The transition from steatosis towards NASH represents a key step in pathogenesis, as it will set the stage for further severe liver damage. Under normal conditions, lipoproteins that are endocytosed by Kupffer cells (KCs) are easily transferred from the lysosomes into the cytoplasm. Oxidized LDL (oxLDL) that is taken up by the macrophages in vitro is trapped within the lysosomes, while acetylated LDL (acLDL) is leading to normal lysosomal hydrolysis, resulting in cytoplasmic storage. We have recently demonstrated that hepatic inflammation is correlated with lysosomal trapping of lipids. So far, a link between lysosomal trapping of oxLDL and inflammation was not established. We hypothesized that lysosomal trapping of oxLDL in KCs will lead to hepatic inflammation.

METHODS

Ldlr(-/-) mice were injected with LDL, acLDL and oxLDL and sacrificed after 2, 6 and 24 h.

RESULTS

Electron microscopy of KCs demonstrated that after oxLDL injection, small lipid inclusions were present inside the lysosomes after all time points and were mostly pronounced after 6 and 24 h. In contrast, no lipid inclusions were present inside KCs after LDL or acLDL injection. Hepatic expression of several inflammatory genes and scavenger receptors was higher after oxLDL injections compared with LDL or acLDL.

CONCLUSIONS

These data suggest that trapping of oxLDL inside lysosomes of KCs in vivo is causally linked to increased hepatic inflammatory gene expression. Our novel observations provide new bases for prevention and treatment of NASH.

The innate immune response during liver inflammation and metabolic disease

The role of the inflammatory response is to combat tissue injury and infection. Innate immune cells recognize cell damage or pathogen invasion with intracellular or surface-expressed pattern recognition receptors (PRRs). Activated PRRs subsequently initiate signaling cascades that trigger the release of factors promoting the inflammatory response. Because the liver is a site where foreign antigens from the gastrointestinal tract encounter the immune system, it is particularly enriched with innate immune cells. These cells can modify and disrupt critical processes implicated in metabolic disease. As such, metabolic stress initiates a feedforward cycle of inflammatory responses, resulting in a state of unresolved chronic inflammation in the liver. Accordingly, the crosstalk between these innate immune cells and the resident parenchymal cells plays an important role in the development of acute and chronic liver 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 cholesterol derivative 27-hydroxycholesterol reduces steatohepatitis in mice

BACKGROUND & AIMS

Non-alcoholic steatohepatitis is characterized by hepatic steatosis with inflammation. Although steatosis is benign and reversible, inflammation can increase liver damage. Hepatic inflammation has been associated with accumulation of cholesterol in lysosomes of Kupffer cells. 27-Hydroxycholesterol (27HC), a derivative of cholesterol formed by CYP27A1, can mobilize cholesterol from the lysosomes to the cytoplasm. We investigated whether 27HC can change the intracellular distribution cholesterol and reduce hepatic inflammation in mice.

METHODS

We transplanted bone marrow from irradiated wild-type or Cyp27a1(-/-) mice to mice that do not express the low density lipoprotein receptor (Ldlr(-/-)), which are hyperlipidemic; 9 weeks later, mice were fed either regular chow or a high-fat, high-cholesterol (HFC) diet for 3 months. In a separate experiment, Ldlr(-/-) mice were given subcutaneous injections of 27HC and placed on regular chow or HFC diets for 3 weeks. Blood and liver tissues samples were collected and analyzed for intracellular cholesterol distribution and inflammation.

RESULTS

In Ldlr(-/-) mice that received bone marrow transplants from Cyp27a1(-/-) mice, lysosomes of Kupfer cells had a greater accumulation of cholesterol than those of mice that received bone marrow from wild-type mice, after the HFC diet. Liver histology and gene expression analyses showed increased inflammation and liver damage in mice given bone marrow transplants from Cyp27a1(-/-) mice and placed on the HFC diet. Administration of 27HC to Ldlr(-/-) mice, following the HFC diet, reduced the accumulation of lysosomal cholesterol and hepatic inflammation, compared with mice that were not given 27HC.

CONCLUSIONS

Accumulation of cholesterol in lysosomes of Kupfer cells promotes hepatic inflammation in mice. The cholesterol derivative 27HC reduces accumulation of cholesterol in lysosomes and might be used to treat non-alcoholic steatohepatitis.

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.

Internalization of modified lipids by CD36 and SR-A leads to hepatic inflammation and lysosomal cholesterol storage in Kupffer cells

Background & Aims

Non-alcoholic steatohepatitis (NASH) is characterized by steatosis and inflammation, which can further progress into fibrosis and cirrhosis. Recently, we demonstrated that combined deletion of the two main scavenger receptors, CD36 and macrophage scavenger receptor 1 (MSR1), which are important for modified cholesterol-rich lipoprotein uptake, reduced NASH. The individual contributions of these receptors to NASH and the intracellular mechanisms by which they contribute to inflammation have not been established. We hypothesize that CD36 and MSR1 contribute independently to the onset of inflammation in NASH, by affecting intracellular cholesterol distribution inside Kupffer cells (KCs).

Methods & Results

Ldlr^−/− mice were transplanted with wild-type (Wt), Cd36^−/− or Msr1^−/− bone marrow and fed a Western diet for 3months. Cd36^−/−- and Msr1^−/−- transplanted (tp) mice showed a similar reduction in hepatic inflammation compared to Wt-tp mice. While the total amount of cholesterol inside KCs was similar in all groups, KCs of Cd36^−/−- and Msr1^−/−-tp mice showed increased cytoplasmic cholesterol accumulation, while Wt-tp mice showed increased lysosomal cholesterol accumulation.

Conclusion

CD36 and MSR1 contribute similarly and independently to the progression of inflammation in NASH. One possible explanation for the inflammatory response related to expression of these receptors could be abnormal cholesterol trafficking in KCs. These data provide a new basis for prevention and treatment of NASH.

Chorioamnionitis induced hepatic inflammation and disturbed lipid metabolism in fetal sheep

Chorioamnionitis frequently induces a fetal inflammatory response syndrome (FIRS), characterized by an elevation of proinflammatory mediators and systemic inflammation. Although there is increasing evidence that inflammation and lipid metabolism influence each other, the effects of chorioamnionitis-induced FIRS on fetal lipid homeostasis are currently not known. Accordingly, we hypothesize that chorioamnionitis induces an inflammatory response in the fetal liver, consequently leading to metabolic disturbances. Chorioamnionitis was induced by intra-amniotic injection of 10 mg endotoxin (control) for 2 d or 2 wk before delivery. Saline injections were given to controls. The effect of chorioamnionitis on hepatic inflammation and metabolic parameters was analyzed in ovine fetuses at the GA of 125 d (normal GA = 150 d). We found that 2 d after the endotoxin injections, inflammatory markers were significantly higher compared with controls. In addition, lipid and glucose metabolism were disturbed in response to endotoxin. Moreover, the antioxidant state capacity was reduced, and hepatic damage was apparent. Two weeks after the endotoxin injections, the fetal livers were still inflamed and had higher glucose concentrations in the blood. In addition, the levels of markers for hepatic damage (alanine aminotransferase and aspartate aminotransferase) were increased. In conclusion, chorioamnionitis induces liver inflammation leading to metabolic disturbances in the fetus.

Intrahepatic cholesterol influences progression, inhibition and reversal of non-alcoholic steatohepatitis in hyperlipidemic mice

Hepatic inflammation is the key factor in non-alcoholic steatohepatitis (NASH) and promotes progression to liver damage. We recently identified dietary cholesterol as the cause of hepatic inflammation in hyperlipidemic mice. We now show that hepatic transcriptome responses are strongly dependent on cholesterol metabolism during diet-induced NASH and its inhibition by fenofibrate. Furthermore, we show that, despite doubling hepatic steatosis, pharmacological LXR activation reverses hepatic inflammation, in parallel with reversing hepatic cholesterol levels. Together, the results indicate a prominent role of cholesterol during the development, inhibition and reversal of hepatic inflammation in NASH and reveal potential new therapeutic strategies against NASH.

Intrahepatic cholesterol influences progression, inhibition and reversal of non-alcoholic steatohepatitis in hyperlipidemic mice

Hepatic inflammation is the key factor in non-alcoholic steatohepatitis (NASH) and promotes progression to liver damage. We recently identified dietary cholesterol as the cause of hepatic inflammation in hyperlipidemic mice. We now show that hepatic transcriptome responses are strongly dependent on cholesterol metabolism during diet-induced NASH and its inhibition by fenofibrate. Furthermore, we show that, despite doubling hepatic steatosis, pharmacological LXR activation reverses hepatic inflammation, in parallel with reversing hepatic cholesterol levels. Together, the results indicate a prominent role of cholesterol during the development, inhibition and reversal of hepatic inflammation in NASH and reveal potential new therapeutic strategies against NASH.

Increased hepatic myeloperoxidase activity in obese subjects with nonalcoholic steatohepatitis

Inflammation and oxidative stress are considered critical factors in the progression of nonalcoholic fatty liver disease. Myeloperoxidase (MPO) is an important neutrophil enzyme that can generate aggressive oxidants; therefore, we studied the association between MPO and nonalcoholic fatty liver disease. The distribution of inflammatory cells containing MPO in liver biopsies of 40 severely obese subjects with either nonalcoholic steatohepatitis (NASH) (n = 22) or simple steatosis (n = 18) was investigated by immunohistochemistry. MPO-derived oxidative protein modifications were identified by immunohistochemistry and correlated to hepatic gene expression of CXC chemokines and M1/M2 macrophage markers as determined by quantitative PCR. MPO plasma levels were determined by ELISA. The number of hepatic neutrophils and MPO-positive Kupffer cells was increased in NASH and was accompanied by accumulation of hypochlorite-modified and nitrated proteins, which can be generated by the MPO-H2O2 system. Liver CXC chemokine expression was higher in patients with accumulation of MPO-mediated oxidation products and correlated with hepatic neutrophil sequestration. Plasma MPO levels were elevated in NASH patients. Interestingly, neutrophils frequently surrounded steatotic hepatocytes, resembling the crown-like structures found in obese adipose tissue. Furthermore, hepatic M2 macrophage marker gene expression was increased in NASH. Our data indicate that accumulation of MPO-mediated oxidation products, partly derived from Kupffer cell MPO, is associated with induction of CXC chemokines and hepatic neutrophil infiltration and may contribute to the development of NASH.

Dietary cholesterol, rather than liver steatosis, leads to hepatic inflammation in hyperlipidemic mouse models of nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) involves liver lipid accumulation (steatosis) combined with hepatic inflammation. The transition towards hepatic inflammation represents a key step in pathogenesis, because it will set the stage for further liver damage, culminating in hepatic fibrosis, cirrhosis, and liver cancer. The actual risk factors that drive hepatic inflammation during the progression to NASH remain largely unknown. The role of steatosis and dietary cholesterol in the etiology of diet-induced NASH was investigated using hyperlipidemic mouse models fed a Western diet. Livers of male and female hyperlipidemic (low-density lipoprotein receptor-deficient [ldlr(-/-)] and apolipoprotein E2 knock-in [APOE2ki]) mouse models were compared with livers of normolipidemic wild-type (WT) C57BL/6J mice after short-term feeding with a high-fat diet with cholesterol (HFC) and without cholesterol. Whereas WT mice displayed only steatosis after a short-term HFC diet, female ldlr(-/-) and APOE2ki mice showed steatosis with severe inflammation characterized by infiltration of macrophages and increased nuclear factor kappaB (NF-kappaB) signaling. Remarkably, male ldlr(-/-) and APOE2ki mice developed severe hepatic inflammation in the absence of steatosis after 7 days on an HFC diet compared with WT animals. An HFC diet induced bloated, "foamy" Kupffer cells in male and female ldlr(-/-) and APOE2ki mice. Hepatic inflammation was found to be linked to increased plasma very low-density lipoprotein (VLDL) cholesterol levels. Omitting cholesterol from the HFC diet lowered plasma VLDL cholesterol and prevented the development of inflammation and hepatic foam cells.

CONCLUSION

These findings indicate that dietary cholesterol, possibly in the form of modified plasma lipoproteins, is an important risk factor for the progression to hepatic inflammation in diet-induced NASH.