Liver inflammatory cells, apoptosis, regeneration and stellate cell activation in non-alcoholic steatohepatitis

Molecular pathways of nonalcoholic fatty liver disease development and progression

Nonalcoholic fatty liver disease (NAFLD) is a main hepatic manifestation of metabolic syndrome. It represents a wide spectrum of histopathological abnormalities ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) with or without fibrosis and, eventually, cirrhosis and hepatocellular carcinoma. While hepatic simple steatosis seems to be a rather benign manifestation of hepatic triglyceride accumulation, the buildup of highly toxic free fatty acids associated with insulin resistance-induced massive free fatty acid mobilization from adipose tissue and the increased de novo hepatic fatty acid synthesis from glucose acts as the "first hit" for NAFLD development. NAFLD progression seems to involve the occurrence of "parallel, multiple-hit" injuries, such as oxidative stress-induced mitochondrial dysfunction, endoplasmic reticulum stress, endotoxin-induced, TLR4-dependent release of inflammatory cytokines, and iron overload, among many others. These deleterious factors are responsible for the triggering of a number of signaling cascades leading to inflammation, cell death, and fibrosis, the hallmarks of NASH. This review is aimed at integrating the overwhelming progress made in the characterization of the physiopathological mechanisms of NAFLD at a molecular level, to better understand the factor influencing the initiation and progression of the disease.

Review article: drug-induced liver injury in the context of nonalcoholic fatty liver disease - a physiopathological and clinical integrated view

BACKGROUND

Nonalcoholic fatty disease (NAFLD) is the most common liver disease, since it is strongly associated with obesity and metabolic syndrome pandemics. NAFLD may affect drug disposal and has common pathophysiological mechanisms with drug-induced liver injury (DILI); this may predispose to hepatoxicity induced by certain drugs that share these pathophysiological mechanisms. In addition, drugs may trigger fatty liver and inflammation per se by mimicking NAFLD pathophysiological mechanisms.

AIMS

To provide a comprehensive update on (a) potential mechanisms whereby certain drugs can be more hepatotoxic in NAFLD patients, (b) the steatogenic effects of drugs, and (c) the mechanism involved in drug-induced steatohepatitis (DISH).

METHODS

A language- and date-unrestricted Medline literature search was conducted to identify pertinent basic and clinical studies on the topic.

RESULTS

Drugs can induce macrovesicular steatosis by mimicking NAFLD pathogenic factors, including insulin resistance and imbalance between fat gain and loss. Other forms of hepatic fat accumulation exist, such as microvesicular steatosis and phospholipidosis, and are mostly associated with acute mitochondrial dysfunction and defective lipophagy, respectively. Drug-induced mitochondrial dysfunction is also commonly involved in DISH. Patients with pre-existing NAFLD may be at higher risk of DILI induced by certain drugs, and polypharmacy in obese individuals to treat their comorbidities may be a contributing factor.

CONCLUSIONS

The relationship between DILI and NAFLD may be reciprocal: drugs can cause NAFLD by acting as steatogenic factors, and pre-existing NAFLD could be a predisposing condition for certain drugs to cause DILI. Polypharmacy associated with obesity might potentiate the association between this condition and DILI.

The Selective SGLT2 Inhibitor Ipragliflozin Has a Therapeutic Effect on Nonalcoholic Steatohepatitis in Mice

Background & Aims

In recent years, nonalcoholic steatohepatitis (NASH) has become a considerable healthcare burden worldwide. Pathogenesis of NASH is associated with type 2 diabetes mellitus (T2DM) and insulin resistance. However, a specific drug to treat NASH is lacking. We investigated the effect of the selective sodium glucose cotransporter 2 inhibitor (SGLT2I) ipragliflozin on NASH in mice.

Methods

We used the Amylin liver NASH model (AMLN), which is a diet-induced model of NASH that results in obesity and T2DM. AMLN mice were fed an AMLN diet for 20 weeks. SGLT2I mice were fed an AMLN diet for 12 weeks and an AMLN diet with 40 mg ipragliflozin/kg for 8 weeks.

Results

AMLN mice showed steatosis, inflammation, and fibrosis in the liver as well as obesity and insulin resistance, features that are recognized in human NASH. Ipragliflozin improved insulin resistance and liver injury. Ipragliflozin decreased serum levels of free fatty acids, hepatic lipid content, the number of apoptotic cells, and areas of fibrosis; it also increased lipid outflow from the liver.

Conclusions

Ipragliflozin improved the pathogenesis of NASH by reducing insulin resistance and lipotoxicity in NASH-model mice. Our results suggest that ipragliflozin has a therapeutic effect on NASH with T2DM.

Free fatty acids shift insulin-induced hepatocyte proliferation towards CD95-dependent apoptosis

Insulin is known to induce hepatocyte swelling, which triggers via integrins and c-Src kinase an activation of the epidermal growth factor receptor (EGFR) and subsequent cell proliferation (1). Free fatty acids (FFAs) are known to induce lipoapoptosis in liver cells in a c-Jun-NH2-terminal kinase (JNK)-dependent, but death receptor-independent way (2). As non-alcoholic steatohepatitis (NASH) is associated with hyperinsulinemia and increased FFA-blood levels, the interplay between insulin and FFA was studied with regard to hepatocyte proliferation and apoptosis in isolated rat and mouse hepatocytes. Saturated long chain FFAs induced apoptosis and JNK activation in primary rat hepatocytes, but did not activate the CD95 (Fas, APO-1) system, whereas insulin triggered EGFR activation and hepatocyte proliferation. Coadministration of insulin and FFAs, however, abolished hepatocyte proliferation and triggered CD95-dependent apoptosis due to a JNK-dependent association of the activated EGFR with CD95, subsequent CD95 tyrosine phosphorylation and formation of the death-inducing signaling complex (DISC). JNK inhibition restored the proliferative insulin effect in presence of FFAs and prevented EGFR/CD95 association, CD95 tyrosine phosphorylation and DISC formation. Likewise, in presence of FFAs insulin increased apoptosis in hepatocytes from wild type but not from Alb-Cre-FAS(fl/fl) mice, which lack functional CD95. It is concluded that FFAs can shift insulin-induced hepatocyte proliferation toward hepatocyte apoptosis by triggering a JNK signal, which allows activated EGFR to associate with CD95 and to trigger CD95-dependent apoptosis. Such phenomena may contribute to the pathogenesis of NASH.

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

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

Adipose tissue-derived stem cells as a regenerative therapy for a mouse steatohepatitis-induced cirrhosis model

Cirrhosis is a chronic liver disease that impairs hepatic function and causes advanced fibrosis. Mesenchymal stem cells have gained recent popularity as a regenerative therapy since they possess immunomodulatory functions. We found that injected adipose tissue-derived stem cells (ADSCs) reside in the liver. Injection of ADSCs also restores albumin expression in hepatic parenchymal cells and ameliorates fibrosis in a nonalcoholic steatohepatitis model of cirrhosis in mice. Gene expression analysis of the liver identifies up- and down-regulation of genes, indicating regeneration/repair and anti-inflammatory processes following ADSC injection. ADSC treatment also decreases the number of intrahepatic infiltrating CD11b(+) and Gr-1(+) cells and reduces the ratio of CD8(+) /CD4(+) cells in hepatic inflammatory cells. This is consistent with down-regulation of genes in hepatic inflammatory cells related to antigen presentation and helper T-cell activation.

CONCLUSION

These results suggest that ADSC therapy is beneficial in cirrhosis, as it can repair and restore the function of the impaired liver.

Protective effects of matrine against progression of high-fructose diet-induced steatohepatitis by enhancing antioxidant and anti-inflammatory defences involving Nrf2 translocation

The present study was aimed to investigate the hepatoprotective effects of matrine against nonalcoholic steatohepatitis induced by a high-fructose diet. After being fed a high-fructose diet (HFD) for 4weeks, male Wistar rats were orally administered matrine in three different doses (40, 80, or 160mg/kg) once daily. Serum and liver samples were collected after treatment with matrine for 4weeks. Lipid droplets within hepatocytes, infiltration of inflammatory cells, and necrotic foci in the liver were morphologically alleviated by matrine in a dose-dependent manner compared with the HFD group. ALT and AST in the blood and the triglyceride content in the liver also decreased. The increased malondialdehyde and depleted glutathione by HFD were ameliorated in a dose-related manner with matrine. Matrine promoted Nrf2 translocation to the nucleus with subsequently up-regulated antioxidative enzyme protein expression, and it enhanced antioxidant activities compared with the HFD group (p<0.05). The increased activity of nuclear factor-kappa B in the liver and the tumour necrosis factor-alpha levels in plasma induced by HFD were inhibited by matrine as well (p<0.05). In this study, we also found that matrine ameliorated HFD-induced hyperglycaemia and insulin resistance. Taken together, our findings demonstrate that matrine is effective in preventing conversion of high-fructose diet-induced hepatic steatosis into nonalcoholic steatohepatitis in rats.

Molecular mechanisms of lipotoxicity in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is characterized by insulin resistance, which results in elevated serum concentration of free fatty acids (FFAs). Circulating FFAs provide the substrate for triacylglycerol formation in the liver, and may also be directly cytotoxic. Hepatocyte apoptosis is a key histologic feature of NAFLD, and correlates with progressive inflammation and fibrosis. The molecular pathways leading to hepatocyte apoptosis are not fully defined; however, recent studies suggest that FFA-induced apoptosis contributes to the pathogenesis of nonalcoholic steatohepatitis. FFAs directly engage the core apoptotic machinery by activating the proapoptotic protein Bax, in a c-jun N-terminal kinase-dependent manner. FFAs also activate the lysosomal pathway of cell death and regulate death receptor gene expression. The role of ER stress and oxidative stress in the pathogenesis of nonalcoholic steatohepatitis has also been described. Understanding the molecular mediators of liver injury should promote development of mechanism-based therapeutic interventions.

Effects of a high-fiber diet on hepatocyte apoptosis and liver regeneration after partial hepatectomy in rats with fatty liver

BACKGROUND

The morbidity and mortality that accompany fatty liver may occur as a result of increased apoptosis of hepatocytes and decreased liver regeneration. We determined the effects of a high-fiber diet on hepatocyte apoptosis and liver regeneration after partial hepatectomy in rats with fatty liver.

METHODS

Fatty liver was induced in male Wistar rats weighing around 200 g through feeding of a high-fat diet for 4 weeks. The rats were then randomly assigned to 3 groups that received a high-fat diet, a normal diet, or a high-fiber diet for another 4 weeks. Partial hepatectomy (around 70%) was performed, and rats were killed 6, 24, 48, or 72 hours after hepatectomy. We then measured (1) the ratio of remnant liver weight to body weight and assessed the histology of the remnant liver as indicators of fatty liver, (2) caspase-3 activity and in situ cell death detection of DNA fragmentation as indicators of apoptosis, and (3) 5-bromo-2-deoxyuridine (BrdU) activity and (4) ornithine decarboxylase (ODC) contents in remnant livers as markers of regeneration.

RESULTS

We found that (1) a high-fat diet for 4 weeks can markedly induce fatty liver, (2) apoptosis of hepatocytes is greater in fatty liver than in normal liver (98 +/- 19 vs 36 +/- 7) at 6 hours after partial hepatectomy (p < .05), (3) the capacity of liver regeneration decreases significantly (BrdU index: 30 +/- 5 vs 12 +/- 3, and ODC contents: 604 +/- 48 vs 390 +/- 42 mg/dL) in fatty liver 24 hours after partial hepatectomy (p < .05), (4) a normal diet can partially reverse the effects of fatty liver; (5) a high-fiber diet can significantly reverse the effects of fatty liver (p < .05).

CONCLUSIONS

A high-fiber diet can reverse the negative effects of fatty liver on apoptosis and regenerative capacity after partial hepatectomy.

Apoptosis and Bcl-2 expression in the livers of patients with steatohepatitis

OBJECTIVES

Apoptosis may play a role in the pathogenesis of alcoholic (ASH) and non-alcoholic steatohepatitis (NASH). In this study, we investigated the modulation of apoptosis-related liver proteins in steatohepatitis.

METHODS

Hepatocyte apoptosis was evaluated by the TUNEL assay in liver tissue of 12 patients with NASH, 12 with ASH and in histologically normal controls. In addition, caspase-3 processing was evaluated by immunoblot analysis. Expression of death receptors, Bcl-2 family members, and NF-kappaB inhibitor (IkappaB) were determined by western blot. Liver biopsies were also graded for inflammation and fibrosis.

RESULTS

Apoptotic hepatocytes were markedly increased in NASH (P<0.05) and ASH (P<0.001) as compared to controls. Active caspase-3 was also elevated in steatohepatitis (P<0.01), coinciding with upregulation of pro-apoptotic Bax (P<0.001). Further, production of tumour necrosis factor-receptor 1 was increased up to 4-fold (P<0.05). Degradation of IkappaB increased >70% in steatohepatitis (P<0.001). Notably, Bcl-2 was also strongly expressed (>100-fold; P<0.001). These data were significantly correlated with relative degrees of portal and lobular inflammation.

CONCLUSION

The results show that liver injury in NASH and ASH is associated with apoptosis and NF-kappaB activation. Anti-apoptotic Bcl-2 is strongly expressed, probably reflecting an adaptive response to obesity or alcohol-related stress.

HCV core protein localizes in the nuclei of nonparenchymal liver cells from chronically HCV-infected patients

Understanding the mechanism of hepatitis C virus (HCV) pathogenesis is an important part of HCV research. Recent experimental evidence suggests that the HCV core protein (HCcAg) has numerous functional activities. These properties suggest that HCcAg, in concert with cellular factors, may contribute to pathogenesis during persistent HCV infection. HCV is capable of infecting cells other than hepatocytes. Although the extrahepatic cellular tropism of HCV may play a role in the pathophysiology of this infection, the precise biological significance of the presence of HCV components in different liver cell types presently remains to be established. In this study, HCcAg was detected in nonparenchymal liver cells of six patients out of eight positive for serum HCV RNA. Immunostaining with anti-HCcAg mAbs revealed the presence of this protein in different liver cell types such as lymphocytes, Kupffer, polymorphonuclear, pit, endothelial, stellate, and fibroblast-like cells. Interestingly, HCcAg was immunolabeled not only in the cytoplasm but also in the nucleus of these cells. Remarkably, HCcAg co-localized with large lipid droplets present in stellate cells and with collagen fibers in the extracellular matrix. Moreover, HCcAg was immunolabeled in bile canaliculus suggesting the involvement of the biliary system in the pathobiology of HCV. Data suggest that nonparenchymal liver cells may constitute a reservoir for HCV replication. Besides, HCcAg may contribute to modulate immune function and fibrosis in the liver as well as steatosis.

Hodgkin' s disease with fulminant non-alcoholic steatohepatitis

We report a woman with daily febrile episodes who developed fulminant hepatic failure. A percutaneous liver biopsy demonstrated non-alcoholic steatohepatitis, with no evidence of neoplastic infiltration. Post-mortem examination revealed stage IV Hodgkin's disease with trivial liver involvement. Rapidly progressive steatohepatitis causing acute liver failure may be a paraneoplastic presentation of Hodgkin's disease, possibly mediated by cytokines.

Hepatocyte apoptosis, expression of death receptors, and activation of NF-kappaB in the liver of nonalcoholic and alcoholic steatohepatitis patients

OBJECTIVES

The increasing incidence of nonalcoholic (NASH) and alcoholic steatohepatitis (ASH), associated with lack of effective treatment, has prompted intensive studies on disease pathogenesis. Apoptosis is recognized as common in liver injury and may also contribute to tissue inflammation, fibrogenesis, and development of cirrhosis. In this study, we identified mechanisms of apoptosis induction in human steatohepatitis, and evaluated potential associations between apoptosis, liver pathology, and clinical presentation in NASH and ASH.

METHODS

Hepatocyte apoptosis was evaluated by the TUNEL assay in 20 patients with NASH (all ambulatory), 40 with ASH (20 ambulatory, 20 hospitalized), and 20 controls. Liver biopsies were also graded for inflammation and fibrosis. Immunohistochemistry was performed for death receptors (Fas and TNF-R1), activated caspase-3, NF-kappaB p65, antiapoptotic Bcl-2 protein, and uncoupling protein 2 (UCP-2).

RESULTS

TUNEL-positive hepatocytes were markedly increased in NASH (p < 0.05) and ASH (p < 0.01). Similar results were obtained for activated caspase-3, confirming the occurrence of apoptosis. The Fas receptor was upregulated in ASH, especially in hospitalized patients (p < 0.01), whereas TNF-R1 was expressed both in NASH and ASH (p < 0.01). In addition, patients with ASH showed a remarkable expression of active NF-kappaB, as compared to NASH and controls (p < 0.01). Degrees of inflammation and fibrosis correlated with NF-kappaB p65 expression, which in turn coincided with apoptosis albeit Bcl-2 and UCP-2 expression.

CONCLUSIONS

Liver injury in NASH and ASH is associated with increased hepatocyte apoptosis mediated by death receptors. Further, apoptosis correlates with active NF-kappaB expression, and disease severity. This potential mechanistic link might provide multiple interesting targets for therapeutic intervention.

Non-alcoholic steatohepatitis: review of a growing medical problem

Non-alcoholic steatohepatitis (NASH) is a metabolic liver disorder that is seen in 2-6% of the general population. It manifests itself by elevated liver enzymes, frequently without symptoms. The histological findings include steatosis, inflammation, fibrosis, and cirrhosis. Three case reports are presented to illustrate features of NASH. A two-hit model has been proposed in the pathogenesis of NASH. The first hit is hepatic steatosis. A hypercaloric diet with high levels of carbohydrates and saturated fatty acids results in elevated plasma free fatty acids (FFA) and expands the adipose tissue. Insulin resistance develops and augments steatosis. Oxidation of FFA yields toxic free radicals, resulting in lipid peroxidation. They cause the second hits: increased oxidative stress on hepatocytes and induction of pro-inflammatory cytokines. When the antioxidant capacities of the liver are insufficient, mitochondrial dysfunction and tumor necrosis factor alpha (TNF-alpha) cause inflammation and fibrosis. Treatment consists of life style modifications, particularly weight loss and exercise. Many drugs have been tried in the treatment of NASH. The insulin-sensitizing drugs metformin, rosiglitazone, and pioglitazone, and the antioxidant vitamin E show promising results. Further investigation of therapeutic options is needed to direct the choice of therapy in the future.