Liver fibrosis: searching for cell model answers

Predictive toxicological effects of Artemisia absinthium essential oil on hepatic stellate cells

Medicinal plants are important worldwide, considering their properties for treating diseases; however, few studies have evaluated their toxicological potential. Among them, Artemisia absinthium is frequently used to treat liver diseases, because its essential oil has several popular therapeutic properties. Based on this information, in the present study, we investigated molecular connectors of physiological effects of the Artemisia absinthium essential oil on human hepatic stellate cell line, LX-2, to explore the potential toxicity of the plant on liver cells. LX-2 is a cellular model to investigate mechanisms of liver fibrosis; then, to analyze the essential oil effects LX-2 was cultured under different conditions, treated or not with the essential oil at 0.4 μg/μL for 24 h. Next, fluorescence microscopy analyses, gene expression measurements, and biochemical approaches revealed that the essential oil reduced pro-fibrogenic markers; however, disrupt lipid metabolism, and cause cellular stress, by the activation of cellular detoxification and pro-inflammatory processes. In conclusion, the hepatic stellate cells incubated with the essential oil present an antifibrotic potential, supporting its popular use; however, the combined results suggest that the essential oil of Artemisia absinthium should be used with caution.

Identification and mechanistic investigation of ellagitannins from Osbeckia octandra that attenuate liver fibrosis via the TGF-β/SMAD signaling pathway

Fibrosis is a major problem in chronic liver disease with limited treatment options due to its complex nature. Herbal medicines are often used as an alternative. The aim of this study was to investigate the therapeutic potential of Osbeckia octandra and to identify its active compounds and regulatory pathways. The effects of crude leaf suspension and boiled leaf extract were investigated in an animal model, and the extract was found to be the more effective treatment. Three major bioactive compounds, pedunculagin, casuarinin, and gallic acid, were isolated from the extract using the hepatic stellate cell line, LX-2-based antifibrotic effect evaluation system. The results showed that all these compounds ameliorated LX-2 in fibrotic state. This inhibitory mechanism was confirmed through the TGF-β/SMAD signaling pathway. Collectively, the presence of these compounds in O. octandra suggests its potential as a treatment for liver fibrosis.

Generation of functionally competent hepatic stellate cells from human stem cells to model liver fibrosis in vitro

The detailed understanding of fibrogenesis has been hampered by a lack of important functional quiescence characteristics and an in vitro model to recapitulate hepatic stellate cell (HSC) activation. In our study, we establish robust endoderm- and mesoderm-sourced quiescent-like induced HSCs (iHSCs) derived from human pluripotent stem cells. Notably, iHSCs present features of mature HSCs, including accumulation of vitamin A in the lipid droplets and maintained quiescent features. In addition, iHSCs display a fibrogenic response and secrete collagen I in response to hepatoxicity caused by thioacetamide, acetaminophen, and hepatitis B and C virus infection. Antiviral therapy attenuated virally induced iHSC activation. Interestingly, endoderm- and mesoderm-derived iHSCs showed similar iHSC phenotypes. Therefore, we provide a novel and robust method to efficiently generate functional iHSCs from hESC and iPSC differentiation, which could be used as a model for hepatocyte toxicity prediction, anti-liver-fibrosis drug screening, and viral hepatitis-induced liver fibrosis.

•

Generation of endoderm- and mesoderm-derived quiescent hepatic stellate cells (qHSCs)

•

Induced qHSC-like cells can be activated into myofibroblasts in vitro

•

Induced qHSC-like cells can respond to hepatoxicity from thioacetamide treatment

•

Hepatitis B and C virus infection can convert qHSC-like cells into activated HSCs

Targeting the Wnt Signaling Pathway in Liver Fibrosis for Drug Options: An Update

Liver fibrosis is a life-threatening disease, with challenging morbidity and mortality for healthcare systems worldwide. It imparts an enormous economic burden to societies, making continuous research and informational updates about its pathogenesis and treatment crucial. This review's focus is on the current knowledge about the Wnt signaling pathway, serving as an important pathway in liver fibrosis development and activation of hepatic stellate cells (HSCs). Two types of Wnt pathways are distinguished, namely the ß-catenin-dependent canonical and non-canonical Ca²⁺ or planar cell polarity (PCP)-dependent pathway. The dynamic balance of physiologically healthy liver and hepatocytes is disturbed by repeated liver injuries. Activation of the ß-catenin Wnt pathway prevents the regeneration of hepatocytes by the replacement of extracellular matrix (ECM), leading to the appearance of scar tissue and the formation of regenerated nodular hepatocytes, lacking the original function of healthy hepatocytes. Therefore, liver function is reduced due to the severely advanced disease. Selective inhibition of ß-catenin inhibits inflammatory processes (since chemokines and pro-inflammatory cytokines are produced during Wnt activation), reduces growth of activated HSCs and reduces collagen synthesis and angiogenesis, thereby reducing the progression of liver fibrosis in vivo. While the canonical Wnt pathway is usually inactive in a physiologically healthy liver, it shows activity during cell regeneration or renewal and in certain pathophysiological conditions, such as liver diseases and cancer. Targeted blocking of some of the basic components of the Wnt pathway is a therapeutic approach. These include the frizzled transmembrane receptor (Fz) receptors using the secreted frizzled-related protein family (sFRP), Fz-coreceptors low-density LRP 5/6 through dickkopf-related protein 1 (DKK1) or niclosamide, glycogen kinase-3 beta (GSK-3β) using SB-216763, cyclic-AMP response element-binding protein (CBP) using PRI-724 and ICG-001, the lymphoid enhancer binding factor (LEF)/T cell-specific transcription factor (TCF) system as well as Wnt inhibitory factor 1 (WIF1) and miR-17-5p using pinostilbene hydrate (PSH). Significant progress has been made in inhibiting Wnt and thus stopping the progression of liver fibrosis by diminishing key components for its action. Comprehending the role of the Wnt signaling pathway in liver fibrosis may lead to discovery of novel targets in liver fibrosis therapeutic strategies' development.

Hepatic stellate cells - from past till present: morphology, human markers, human cell lines, behavior in normal and liver pathology

Hepatic stellate cell (HSC), initially analyzed by von Kupffer, in 1876, revealed to be an extraordinary mesenchymal cell, essential for both hepatocellular function and lesions, being the hallmark of hepatic fibrogenesis and carcinogenesis. Apart from their implications in hepatic injury, HSCs play a vital role in liver development and regeneration, xenobiotic response, intermediate metabolism, and regulation of immune response. In this review, we discuss the current state of knowledge regarding HSCs morphology, human HSCs markers and human HSC cell lines. We also summarize the latest findings concerning their roles in normal and liver pathology, focusing on their impact in fibrogenesis, chronic viral hepatitis and liver tumors.

Effect of hepato-toxins in the acceleration of hepatic fibrosis in hepatitis B mice

Chronic liver diseases such as hepatitis B viral (HBV) infection and liver fibrosis have been a major health problem worldwide. However, less research has been conducted owing to the lack of animal models. The key purpose of this study was to determine the effects of different hepatotoxins in HBV-affected liver. In this study, we successfully generated a combined liver fibrosis model by administering HBV 1.2 plasmid and thioacetamide/ethanol (TAA/EtOH). To our knowledge, this is the first study in which an increase in the liver fibrosis level is observed by the intraperitoneal administration of TAA and EtOH in drinking water after the hydrodynamic transfection of the HBV 1.2 plasmid in C3H/HeN mice. The HBV+TAA/EtOH group exhibited higher level of hepatic fibrosis than that of the control groups. The hepatic stellate cell activation in the TAA- and EtOH-administered groups was demonstrated by the elevation in the level of fibrotic markers. In addition, high levels of collagen content and histopathological results were also used to confirm the prominent fibrotic levels. We established a novel HBV mice model by hydrodynamic injection-based HBV transfection in C3H/HeN mice. C3H/HeN mice were reported to have a higher HBV persistence level than that of the C57BL/6 mouse model. All the results showed an increased fibrosis level in the HBV mice treated with TAA and EtOH; hence, this model would be useful to understand the effect of hepatotoxins on the high risk of fibrosis after HBV infection. The acceleration of liver fibrosis can occur with prolonged administration as well as the high dosage of hepatotoxins in mice.

PBI-4050 Reduces Stellate Cell Activation and Liver Fibrosis through Modulation of Intracellular ATP Levels and the Liver Kinase B1/AMP-Activated Protein Kinase/Mammalian Target of Rapamycin Pathway

Hepatic fibrosis is a major cause of morbidity and mortality for which there is currently no effective therapy. We previously showed that 2-(3-pentylphenyl)acetic acid (PBI-4050) is a dual G protein-coupled receptor GPR40 agonist/GPR84 antagonist that exerts antifibrotic, anti-inflammatory, and antiproliferative action. We evaluated PBI-4050 for the treatment of liver fibrosis in vivo and elucidated its mechanism of action on human hepatic stellate cells (HSCs). The antifibrotic effect of PBI-4050 was evaluated in carbon tetrachloride (CCl₄)- and bile duct ligation-induced liver fibrosis rodent models. Treatment with PBI-4050 suppressed CCl₄-induced serum aspartate aminotransferase levels, inflammatory marker nitric oxide synthase, epithelial to mesenchymal transition transcription factor Snail, and multiple profibrotic factors. PBI-4050 also decreased GPR84 mRNA expression in CCl₄-induced injury, while restoring peroxisome proliferator-activated receptor γ (PPARγ) to the control level. Collagen deposition and α-smooth muscle actin (α-SMA) protein levels were also attenuated by PBI-4050 treatment in the bile duct ligation rat model. Transforming growth factor-β-activated primary HSCs were used to examine the effect of PBI-4050 and its mechanism of action in vitro. PBI-4050 inhibited HSC proliferation by arresting cells in the G0/G1 cycle phase. Subsequent analysis demonstrated that PBI-4050 signals through a reduction of intracellular ATP levels, activation of liver kinase B1 (LKB1) and AMP-activated protein kinase (AMPK), and blockade of mammalian target of rapamycin (mTOR), resulting in reduced protein and mRNA levels of α-SMA and connective tissue growth factor and restored PPARγ mRNA expression. Our findings suggest that PBI-4050 may exert antifibrotic activity in the liver through a novel mechanism of action involving modulation of intracellular ATP levels and the LKB1/AMPK/mTOR pathway in stellate cells, and PBI-4050 may be a promising agent for treating liver fibrosis.

Di (2-Ethylhexyl) Phthalate and Its Role in Developing Cholestasis: An In Vitro Study on Different Liver Cell Types

OBJECTIVES

Di(2-ethylhexyl) phthalate (DEHP) is a plasticizer used in many polyvinylchloride medical devices and is washed out easily. Thereby critically ill infants can become exposed to DEHP concentrations significantly exceeding the recommended threshold. We suspect DEHP to play an important role in the development of intestinal failure-associated liver disease. The aim of this study was therefore to determine the direct influence of DEHP on different liver cell types.

METHODS

HepG2, human upcyte hepatocytes, primary murine hepatocytes, LX-2, human upcyte hepatic stellate cells, and liver organoids were cultured with DEHP (0.5-500 μmol/L) and parameters including cytotoxicity, cell-cell interactions, and expression of metabolizing enzymes were investigated.

RESULTS

DEHP modulated the expression of xenobiotic metabolizing enzymes, reduced the formation of bile canaliculi and cell polarity, and inhibited Cyp-activity in hepatocytes. DEHP had a toxic effect on LX-2 and induced the fibrogenic activation of hepatic stellate cells. The mode of action of DEHP was different in monolayer cultures compared to 3D-liver organoids, which were more sensitive to DEHP.

CONCLUSIONS

This study suggests that DEHP modulates expression and activity of drug-detoxifying liver enzymes in humans at a clinically relevant concentration. Furthermore, it may contribute to the development of cholestasis and fibrosis. These findings strongly support the opinion, that there is a significant potential for serious adverse effects of DEHP derived from medical devices on human health, especially in very young infants with immature livers.

Human hepatic stellate cell isolation and characterization

The hepatic stellate cells (HSCs) localize at the space of Disse in the liver and have multiple functions. They are identified as the major contributor to hepatic fibrosis. Significant understanding of HSCs has been achieved using rodent models and isolated murine HSCs; as well as investigating human liver tissues and human HSCs. There is growing interest and need of translating rodent study findings to human HSCs and human liver diseases. However, species-related differences impose challenges on the translational research. In this review, we focus on the current information on human HSCs isolation methods, human HSCs markers, and established human HSC cell lines.

A comparative study on the anti-schistosomal and hepatoprotective effects of vinpocetine and isosorbide-5-mononitrate on Schistosoma mansoni-infected mice

Schistosomiasis is a remarkable public health problem in developing countries. Presently, praziquantel is the optional drug for all human schistosomiasis. Owing to the increased praziquantel resistance, there is an urgent need to develop new alternatives. This study aims at determining the anti-schistosomal and/or the hepatoprotective effects of the anti-inflammatory drug; vinpocetine, and the vasodilator and the nitric oxide donor; isosorbide-5-mononitrate, in comparison to praziquantel. In the present research, the therapeutic efficacies of these drugs were assessed in Swiss albino female mice (CD-I strain) experimentally infected with an Egyptian strain of Schistosoma mansoni, using some general, parasitological, and histopathological parameters. In this work, praziquantel significantly reduced worm burden and hepatic egg load, increased the percentage of dead eggs in the small intestine and decreased granuloma count, but did not reduce granuloma diameter. While, either vinpocetine or isosorbide-5-mononitrate monotherapy did not induce significant reduction in the worm count, hepatic egg load or shift in the oogram pattern, but significantly reduced granuloma count and diameter. Moreover, isosorbide-5-mononitrate significantly reduced hepatic inflammation and necrosis. The best results were obtained in the mice groups treated with isosorbide-5-mononitrate combined with praziquantel or vinpocetine. Our results point to vinpocetine and isosorbide-5-mononitrate as a convenient and promising adjuvant to praziquantel for ameliorating schistosomal liver pathology. Further studies are recommended to reveal the actual pathways responsible for the different activities of vinpocetine and isosorbide-5-mononitrate.

Quercetin prevents hepatic fibrosis by inhibiting hepatic stellate cell activation and reducing autophagy via the TGF-β1/Smads and PI3K/Akt pathways

The aim of this study was to investigate the effect of quercetin on hepatic fibrosis, a characteristic response to acute or chronic liver injury. Mice were randomized to bile duct ligation (BDL) or carbon tetrachloride (CCl₄) cirrhosis models. Quercetin (100 mg/kg or 200 mg/kg daily) was administered by gavage for 2 or 4 weeks. Liver tissue and blood samples were collected for histological and molecular analysis. The results of our experiments showed that quercetin reduced BDL or CCl₄ liver fibrosis, inhibited extracellular matrix formation, and regulated matrix metallopeptidase (MMP)-9 and tissue inhibitor of metalloproteinase (TIMP)-1. Quercetin attenuated liver damage by suppressing the TGF-β1/Smads signaling pathway and activating the PI3K/Akt signaling pathway to inhibit autophagy in BDL- or CCl₄- induced liver fibrosis. Quercetin prevented hepatic fibrosis by attenuating hepatic stellate cell activation and reducing autophagy through regulating crosstalk between the TGF-β1/Smads and PI3K/Akt pathways.

Sodium valproate, a histone deacetylase inhibitor, with praziquantel ameliorates Schistosoma mansoni-induced liver fibrosis in mice

AIMS

This study explores the potential antifibrotic effect of sodium valproate (SV), an inhibitor of class I histone deacetylase (HDAC) enzymes, and/or praziquantel (PZQ) on Schistosoma mansoni (S. mansoni)-induced liver fibrosis in mice.

MAIN METHODS

Male Swiss albino mice were divided into nine groups: group I- normal control (NC); group II- uninfected gum mucilage (GM) treated; group III- uninfected PZQ- treated; group IV- uninfected SV-treated; group V- control S. mansoni infected mice; group VI- infected GM-treated; group VII- infected PZQ-treated; group VIII- infected SV-treated; group IX- infected PZQ+SV treated. All SV administrations were 300mg/kg/day orally and administered for five weeks beginning on the 5th week post infection (WPI). All PZQ administrations were 500mg/kg/day orally and administered for 2 consecutive days beginning on the 7th WPI. Serum transforming growth factor-beta 1 (TGF-β1), tumor necrosis factor-alpha (TNF-α), hepatic hydroxyproline (Hyp) content, and liver function tests (AST and ALT) were determined. Specimens of the hepatic tissues were examined histologically.

KEY FINDINGS

Treatment of S. mansoni-infected mice with SV significantly decreased the serum levels of ALT, TGF-β1 and TNF-α, and the liver tissue hydroxyproline content compared with the S. mansoni infected untreated groups. Histologically, treatment with SV revealed regression of the granulomatous inflammatory reaction. Combined treatment with PZQ and SV produces more favorable biochemical results, and aborted granulomatous reaction compared with either drug alone.

SIGNIFICANCE

Sodium valproate is a promising anti-fibrotic agent. It demonstrated an anti-fibrotic effect in early stages of S. mansoni infection through downregulation of profibrogenic cytokines, and collagen deposition.

Hepatic fibrogenesis and transforming growth factor/Smad signaling activation in rats chronically exposed to low doses of lead

Lead is an important heavy metal pollutant in the environment. The nervous system, kidney and liver are the most susceptible organs to lead deposition, showing that this pollutant has no single target system. To examine the cellular and molecular mechanisms involved in their pathobiology of chronic lead at low-dose exposure in the liver, male Wistar rats were exposed to 0.06% lead acetate in drinking water every day for 4 months. At the end of the study, hepatic metal accumulation, morphology and function were examined. Immunochemical staining and Western blot analysis were performed to detect extracellular matrix proteins, α-smooth muscle actin and transforming growth factor (TGF)β1/Smad pathway expression. Results showed increased laminin, collagen IV and fibronectin, located at the perisinusoidal space. Phenotypic transformation of hepatic stellate cells into myofibroblast-like cells was evidenced at the ultrastructural level and a significant expression of α-smooth muscle actin in Disse’s space was observed. These findings were associated with a marked increase in TGFβ1/Smad2/3 signaling. Our data suggest that, chronically, exposure to low levels of lead could trigger the onset of a hepatic fibrogenic process through upregulated TGFβ1/Smad signaling.

Adenoviral overexpression of Lhx2 attenuates cell viability but does not preserve the stem cell like phenotype of hepatic stellate cells

Hepatic stellate cells (HSC) are well known initiators of hepatic fibrosis. After liver cell damage, HSC transdifferentiate into proliferative myofibroblasts, representing the major source of extracellular matrix in the fibrotic organ. Recent studies also demonstrate a role of HSC as progenitor or stem cell like cells in liver regeneration. Lhx2 is described as stem cell maintaining factor in different organs and as an inhibitory transcription factor in HSC activation. Here we examined whether a continuous expression of Lhx2 in HSC could attenuate their activation and whether Lhx2 could serve as a potential target for antifibrotic gene therapy. Therefore, we evaluated an adenoviral mediated overexpression of Lhx2 in primary HSC and investigated mRNA expression patterns by qRT-PCR as well as the activation status by different in vitro assays. HSC revealed a marked increase in activation markers like smooth muscle actin alpha (αSMA) and collagen 1α independent from adenoviral transduction. Lhx2 overexpression resulted in attenuated cell viability as shown by a slightly hampered migratory and contractile phenotype of HSC. Expression of stem cell factors or signaling components was also unaffected by Lhx2. Summarizing these results, we found no antifibrotic or stem cell maintaining effect of Lhx2 overexpression in primary HSC.

The use of pentoxifylline as adjuvant therapy with praziquantel downregulates profibrogenic cytokines, collagen deposition and oxidative stress in experimental schistosomiasis mansoni

This study investigates the possible use of pentoxifylline (PTX), with antifibrotic and anti-inflammatory properties, as adjuvant in treatment of schistosomal liver fibrosis through determination of some profibrogenic cytokines, oxidative stress and collagen deposition. Animals were classified into seven groups: normal control (i), Schistosoma mansoni-infected untreated (ii), infected treated with praziquantel (PZQ) curative, 1000mg/kg (iii) or sub curative, 200mg/kg dose (iv), infected treated with PTX alone (10mg/kg/day; 5days/wk) for 8weeks starting from the 2nd to the 10th week post infection (v), or in addition to curative (vi) or sub curative dose of PZQ (vii). Serum transforming growth factor-β1 (TGF-β1), tumor necrosis factor-α (TNF-α), matrix metalloproteinases-2 (MMP-2) and hepatic hydroxyproline (Hyp) content, glutathione related antioxidant enzymes and malondialdehyde (MDA) were determined. Results showed that S. mansoni infection produced remarkable elevations in the serum levels of TGF-β1, TNF-α, MMP-2 and the hepatic contents of Hyp, glutathione reductase (GR), MDA with significant reduction in reduced glutathione (GSH), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and superoxide dismutase (SOD) when compared with their corresponding normal controls. Treatment of infected mice with PTX in addition to PZQ curative rather than its sub curative dose produced the best results evidenced by complete normalization in the previously mentioned serum and hepatic parameters.

CONCLUSION

PTX could attenuate liver fibrosis in early stages of S. mansoni infection through downregulation of profibrogenic cytokines, oxidative stress and collagen deposition.

Dimethylnitrosamine-induced liver fibrosis and recovery in NOD/SCID mice

There is a need for a new liver fibrosis model of immunodeficient mice to study the effects of cell therapy on liver disease because there are not many animal models available to study the effects of cell therapy. In this study, we induced liver fibrosis using dimethylnitrosamine (DMN) in NOD/SCID mice to create an animal model for liver disease. DMN (5 mg/kg, i.p.) was injected intraperitoneally for three consecutive days per week for 6 or 8 weeks, and the mice were sacrificed at weeks 0, 4 and 8 after the last DMN injection. The 6-week DMN-treated group gradually recovered from serum biochemical changes, histopathological toxic effects and lesions in the liver at weeks 4 and 8 after the last DMN injection. However, the progression of liver fibrosis and toxic levels were maintained in the 8-week DMN-treated group at week 4 after the last DMN injection. The increases in iron and extracellular matrix (collagen) in the DMN-treated group were confirmed by Prussian blue (PB) and Masson's trichrome (MT) staining, respectively. Additionally, activation of hepatic stellate cells was observed by alpha smooth muscle actin (α-SMA) immunostaining and western blot. In conclusion, treatment of NOD/SCID mice with 5 mg/kg of DMN for 8 weeks can be used to induce an appropriate animal model of disease for liver fibrosis. This model may be useful for evaluation of the efficacy and safety of cell therapies such as human mesenchymal stem cell therapy.

Accelerated liver fibrosis in hepatitis B virus transgenic mice: involvement of natural killer T cells

The immunopathogenic process from hepatitis B virus (HBV) infection to liver fibrosis is incompletely understood because it lacks an animal model. In this study we observed the development of liver fibrosis in HBV transgenic (HBV-tg) mice and found the roles of natural killer T (NKT) cells in HBV-related liver fibrosis. We found liver fibrosis spontaneously developed in HBV-tg mice with the elevated transcription of col1a1, matrix metalloproteinase (MMP)2, and tissue inhibitor of metalloproteinase (TIMP)1. Mice were then injected with repetitive hepatotoxin carbon tetrachloride (CCl(4) ) to induce prominent liver fibrosis. After chronic CCl(4) treatment, the serum alanine aminotransferase (ALT) was higher, the liver regenerative nodules became more and bigger, and the fibrosis area was remarkably increased in HBV-tg mice than in C57BL/6 mice. Moreover, the increase in col1a1 and MMP2 transcription was greater, with a sustaining high level of TIMP1 and a greater activation of hepatic stellate cells (HSCs) in the livers of CCl(4) -treated HBV-tg mice. Our data also showed that there were more liver mononuclear cells (MNCs) in HBV-tg mice after CCl(4) injection, and Rag1(-/-) mice adoptive transferred lymphocytes from HBV-tg mice displayed increased collagen deposition. Further study demonstrated the number of liver NKT cells increased after CCl(4) treatment and NKT cells were overactivated in HBV-tg mice in the long term. It was further confirmed that NKT cells were critical for HSCs activation by depletion of NKT cells of HBV-tg mice and adoptive transfer of purified NKT cells from HBV-tg mice into recipient Rag1(-/-) mice. The inflammatory cytokines IL-4 and IL-13 produced by NKT cells played a pivotal role in HSCs activation in an in vitro coculture experiment.

CONCLUSION

These data suggest that NKT cells from HBV-tg mice induce the HSC activation in liver fibrogenesis.

Roles of liver innate immune cells in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become the most common liver disease in the United States and other developed countries and is expected to increase in the next few years. Emerging data suggest that some patients with NAFLD may progress to nonalcoholic steatohepatitis (NASH), cirrhosis and even hepatocellular carcinoma. NAFLD can also promote the development and progression of disease in other organ systems, such as the cardiovascular and endocrine (i.e. diabetes) systems. Thus, understanding the pathogenesis of NAFLD is of great clinical importance and is critical for the prevention and treatment of the disease. Although the “two-hit hypothesis” is generally accepted, the exact pathogenesis of NAFLD has not been clearly established. The liver is an important innate immune organ with large numbers of innate immune cells, including Kupffer cells (KCs), natural killer T (NKT) cells and natural killer (NK) cells. Recent data show that an imbalance in liver cytokines may be implicated in the development of fatty liver disease. For example, Th1 cytokine excess may be a common pathogenic mechanism for hepatic insulin resistance and NASH. Innate immune cells in the liver play important roles in the excessive production of hepatic Th1 cytokines in NAFLD. In addition, liver innate immune cells participate in the pathogenesis of NAFLD in other ways. For example, activated KCs can generate reactive oxygen species, which induce liver injury. This review will focus primarily on the possible effect and mechanism of KCs, NKT cells and NK cells in the development of NAFLD.

Bcl-2 overexpression in hepatic stellate cell line CFSC-2G, induces a pro-fibrotic state

BACKGROUND AND AIM

Development of hepatic fibrosis is a complex process that involves oxidative stress (OS) and an altered balance between pro- and anti-apoptotic molecules. Since Bcl-2 overexpression preserves viability against OS, our objective was to address the effect of Bcl-2 overexpression in the hepatic stellate cells (HSC) cell-line CFSC-2G under acetaldehyde and H(2)O(2) challenge, and explore if it protects these cells against OS, induces replicative senescence and/or modify extracellular matrix (ECM) remodeling potential.

METHODS

To induce Bcl-2 overexpression, HSC cell line CFSC-2G was transfected by lipofection technique. Green fluorescent protein-only CFSC-2G cells were used as a control. Cell survival after H(2)O(2) treatment and total protein oxidation were assessed. To determine cell cycle arrest, proliferation-rate, DNA synthesis and senescence were assessed. Matrix metalloproteinases (MMP), tissue-inhibitor of MMP (TIMP), transglutaminases (TG) and smooth muscle a-actin (alpha-SMA) were evaluated by western blot in response to acetaldehyde treatment as markers of ECM remodeling capacity in addition to transforming growth factor-beta (TGF-beta) mRNA.

RESULTS

Cells overexpressing Bcl-2 survived approximately 20% more than control cells when exposed to H(2)O(2) and approximately 35% proteins were protected from oxidation, but Bcl-2 did not slow proliferation or induced senescence. Bcl-2 overexpression did not change alpha-SMA levels, but it increased TIMP-1 (55%), tissue transglutaminases (tTG) (25%) and TGF-beta mRNA (49%), when exposed to acetaldehyde, while MMP-13 content decreased (47%).

CONCLUSIONS

Bcl-2 overexpression protected HSC against oxidative stress but it did not induce replicative senescence. It increased TIMP-1, tTG and TGF-beta mRNA levels and decreased MMP-13 content, suggesting that Bcl-2 overexpression may play a key role in the progression of fibrosis in chronic liver diseases.

Changes in the expression of methionine adenosyltransferase genes and S-adenosylmethionine homeostasis during hepatic stellate cell activation

Hepatic stellate cell (HSC) activation is an essential event during liver fibrogenesis. Methionine adenosyltransferase (MAT) catalyzes biosynthesis of S-adenosylmethionine (SAMe), the principle methyl donor. SAMe metabolism generates two methylation inhibitors, methylthioadenosine (MTA) and S-adenosylhomocysteine (SAH). Liver cell proliferation is associated with induction of two nonliver-specific MATs: MAT2A, which encodes the catalytic subunit alpha2, and MAT2beta, which encodes a regulatory subunit beta that modulates the activity of the MAT2A-encoded isoenzyme MATII. We reported that MAT2A and MAT2beta genes are required for liver cancer cell growth that is induced by the profibrogenic factor leptin. Also, MAT2beta regulates leptin signaling. The strong association of MAT genes with proliferation and leptin signaling in liver cells led us to examine the role of these genes during HSC activation. MAT2A and MAT2beta are induced in culture-activated primary rat HSCs and HSCs from 10-day bile duct ligated (BDL) rat livers. HSC activation led to a decline in intracellular SAMe and MTA levels, a drop in the SAMe/SAH ratio, and global DNA hypomethylation. The decrease in SAMe levels was associated with lower MATII activity during activation. MAT2A silencing in primary HSCs and MAT2A or MAT2beta silencing in the human stellate cell line LX-2 resulted in decreased collagen and alpha-smooth muscle actin (alpha-SMA) expression and cell growth and increased apoptosis. MAT2A knockdown decreased intracellular SAMe levels in LX-2 cells. Activation of extracellular signal-regulated kinase and phosphatidylinositol-3-kinase signaling in LX-2 cells required the expression of MAT2beta but not that of MAT2A.

CONCLUSION

MAT2A and MAT2beta genes are induced during HSC activation and are essential for this process. The SAMe level falls, resulting in global DNA hypomethylation.

Chronic administration of valproic acid inhibits activation of mouse hepatic stellate cells in vitro and in vivo

Hepatic stellate cell (HSC) activation is a pivotal step in the pathogenesis of liver fibrosis. The clarification of this transdifferentiation process is therefore important for the development of effective therapies for fibrosis. We analyzed the effect of a histone deacetylase inhibitor, valproic acid (VPA), on mouse HSC transdifferentiation in vitro and in vivo. The exposure of freshly isolated mouse HSCs to 2.5 mM VPA led to increased histone H4 acetylation and inhibited cell proliferation. Expression of stellate cell activation markers analyzed by quantitative polymerase chain reaction and western blotting revealed that treatment with VPA inhibited the induction of activation markers such as Acta2, Lox, Spp1, and Myh11. Treatment of mice with VPA decreased collagen deposition and in vivo activation of stellate cells in the livers of CCl(4)-treated mice. Class I histone deacetylase silencing through RNA interference in mouse HSCs only partially mimicked treatment with VPA.

CONCLUSION

Chronic administration of VPA results in a marked decrease in stellate cell activation both in vitro and in vivo. We hypothesize that the VPA effect results partially from class I histone deacetylase inhibition, but that also non-histone deacetylase class I VPA targets are involved in the stellate cell activation process.

Ameliorative effects of Moringa oleifera Lam seed extract on liver fibrosis in rats

This study was carried out to evaluate the effect of Moringa oleifera Lam (Moringa) seed extract on liver fibrosis. Liver fibrosis was induced by the oral administration of 20% carbon tetrachloride (CCl(4)), twice weekly and for 8 weeks. Simultaneously, M.oleifera Lam seed extract (1g/kg) was orally administered daily. The biochemical and histological results showed that Moringa reduced liver damage as well as symptoms of liver fibrosis. The administration of Moringa seed extract decreased the CCl(4)-induced elevation of serum aminotransferase activities and globulin level. The elevations of hepatic hydroxyproline content and myeloperoxidase activity were also reduced by Moringa treatment. Furthermore, the immunohistochemical study showed that Moringa markedly reduced the numbers of smooth muscle alpha-actin-positive cells and the accumulation of collagens I and III in liver. Moringa seed extract showed significant inhibitory effect on 1,1-diphenyl-2-picrylhydrazyl free radical, as well as strong reducing antioxidant power. The activity of superoxide dismutase as well as the content of both malondialdehyde and protein carbonyl, which are oxidative stress markers, were reversed after treatment with Moringa. Finally, these results suggested that Moringa seed extract can act against CCl(4)-induced liver injury and fibrosis in rats by a mechanism related to its antioxidant properties, anti-inflammatory effect and its ability to attenuate the hepatic stellate cells activation.

Optimum concentration of hydrocamptothecin for inhibiting proliferation of rat hepatic stellate cells

AIM: To evaluate the effects of hydrocamptothecin (HCPT) on proliferation of rat hepatic stellate cells (HSC) in vitro, and meanwhile, to investigate the cytotoxicity of HCPT on rat hepatocytes, then to determine the optimum concentration of HCPT for inhibiting proliferation of rat HSC.

METHODS: Rat HSC line (HSC-T6) and rat hepatocyte line (BRL-3A) were incubated with different concentrations of HCPT (0.008, 0.016, 0.031, 0.125, 0.25, 0.5, 1, 2, 4, 8, 16, 32 mg/L respectively) or without HCPT for 24, 48, 72 hours, respectively. The proliferation rates of the HSC-T6 and BRL-3A were determined by MTT assay. The optimum concentration of HCPT with highest inhibitory action on proliferation of HSC-T6 was examined. The morphological changes of the HSC-T6 were observed with light microscopy.

RESULTS: MTT assay indicated that the proliferation rates of HSC-T6 induced with different concentrations of HCPT were significantly reduced compared with the control group incubated in vitro for 24, 48, 72 h (t = 6.07-46.98, 10.98-63.97, 20.76-107.68, all P < 0.01). HCPT significantly inhibited the proliferation of HSC-T6 in a dose-dependent and time-dependent manner. On the other hand, HCPT also inhibited the proliferation of BRL-3A in a dose-dependent and time-dependent manner. When the concentration was higher than 0.5 mg/L, the cytotoxicity of HCPT on the BRL-3A had a significant raise (all P < 0.05). After stimulation of HSC-T6 by HCPT with the concentrations of 0.25, 0.5, 1 mg/L for 24 hours, light microscopy showed the morphological changes of HSC-T6, including cells shrinkage, karyorrhexis and karyopycnosis, and the changes were more significant as the concentration increased.

CONCLUSION: HCPT could significantly inhibit the proliferation of HSC-T6 in a dose-dependent and time-dependent manner; 0.5 mg/L is the optimum concentration of HCPT for inhibiting the proliferation of HSC-T6.

Protective effects of total flavonoids of Bidens bipinnata L. against carbon tetrachloride-induced liver fibrosis in rats

Bidens bipinnata L. is well known in China as a traditional Chinese medicine and has been used to treat hepatitis in clinics for many years. In a previous study we found that total flavonoids of Bidens bipinnata L. (TFB) had a protective effect against carbon tetrachloride (CCl4)-induced acute liver injury in mice. Now this study was designed to investigate its therapeutic effect against CCl4-induced liver fibrosis in rats and to determine, in part, its mechanism of action. The liver fibrosis model was established by subcutaneous injection of 50% CCl4 twice a week for 18 weeks. TFB (40, 80 and 160 mg kg(-1)) was administered by gastrogavage daily from the 9th week. The results showed that TFB (80 and 160 mg kg(-1)) treatment for 10 weeks significantly reduced the elevated liver index (liver weight/body weight) and spleen index (spleen weight/body weight), elevated levels of serum transaminases (alanine aminotransferase and aspartate aminotransferase), hyaluronic acid, type III procollagen and hepatic hydroxyproline. In addition, TFB markedly inhibited CCl4-induced lipid peroxidation and enhanced the activity of the antioxidant enzymes superoxide dismutase and glutathione peroxidase. Moreover, TFB (80 and 160 mg kg(-1)) treatment improved the morphologic changes of hepatic fibrosis induced by CCl4 and suppressed nuclear factor (NF)-kappaB, alpha-smooth muscle actin (SMA) protein expression and transforming growth factor (TGF)-beta1 gene expression in the liver of liver fibrosis of rats. In conclusion, TFB was able to ameliorate liver injury and protect rats from CCl4-induced liver fibrosis by suppressing oxidative stress. This process may be related to inhibiting the induction of NF-kappaB on hepatic stellate cell activation and the expression of TGF-beta1.

Phosphatidylinositol 3-kinase/Akt pathway regulates hepatic stellate cell apoptosis

AIM: To investigate the role of phosphatidylinositol 3-kinase (PI 3-K)/Akt signaling pathway in the balance of HSC activation and apoptosis in rat hepatic stellate cells (HSC).

METHODS: An activated HSC cell line was used in this study. LY 294002, the PI 3-K/Akt signal pathway blocker was used to investigate the molecular events on apoptosis in HSC and to interpret the role of this pathway in HSC apoptosis. Immunocytochemistry, Western blot and reverse transcription polymerase chain reaction (RT-PCR) analysis were applied to detect the expression of PI 3-K, and simultaneously phosphorylated-Akt (p-Akt) and total-Akt were determined by Western blot. The HSC apoptosis was examined by annexin-V/propidium iodide double-labelled flow cytometry and transmission electron microscopy.

RESULTS: The apoptosis rates in LY 294002 (30.82% ± 2.90%) and LY 294002 + PDGF-BB (28.16% ± 2.58%) groups were significantly increased compared with those of control (9.02% ± 1.81%) and PDGF-BB (4.35% ± 1.18%). PDGF-BB augmented PI 3-K and p-Akt expression. LY 294002 significantly reduced the contents of PI 3-K and p-Akt. mRNA transcription evaluated by RT-PCR showed similar tendencies as protein expression.

CONCLUSION: Inhibition of PI 3-K/Akt signaling pathway induces apoptosis in HSC.

Changing the pathogenetic roadmap of liver fibrosis? Where did it start; where will it go?

The pathophysiology of liver injury has attracted the interest of experimentalists and clinicians over many centuries. With the discovery of liver-specific pericytes - formerly called fat-storing cells, Ito-cells, lipocytes, and currently designated as hepatic stellate cells (HSC) - the insight into the cellular and molecular pathobiology of liver fibrosis has evolved and the pivotal role of HSC as a precursor cell-type for extracellular matrix-producing myofibroblasts has been established. Although activation and transdifferentiation of HSC to myofibroblasts is still regarded as the pathogenetic key mechanism of fibrogenesis, recent studies point to a prominent heterogeneity of the origin of myofibroblasts. Currently, the generation of matrix-synthesizing fibroblasts by epithelial-mesenchymal transition, by influx of bone marrow-derived fibrocytes into damaged liver tissue, and by differentiation of circulating monocytes to fibroblasts after homing in the injured liver are discussed as important complementary mechanisms to enlarge the pool of (myo-)fibroblasts in the fibrosing liver. Among the molecular mediators, transforming growth factor-beta (TGF-beta) plays a central role, which is controlled by the bone-morphogenetic protein (BMP)-7, an important antagonist of TGF-beta action. The newly discovered pathways supplement the linear concept of HSC activation to myofibroblasts, point to fibrosis as a systemic response involving extrahepatic organs and reactions, add further evidence to a more or less uniform concept of organ fibrosis in general (e.g. liver, lung, kidney), and offer innovative approaches for the development of non-invasive biomarkers and antifibrotic trials.

Rosiglitazone prevents murine hepatic fibrosis induced by Schistosoma japonicum

AIM: To evaluate the effect of rosiglitazone in a murine model of liver fibrosis induced by Schistosoma japonicum infection.

METHODS: A total of 50 mice were randomly and averagely divided into groups A, B, C, D and E. The mice in group A served as normal controls, while those in the other four groups were infected with Schistosoma japonicum to induce the model of liver fibrosis. Besides, the mice in groups C, D and E were treated with praziquantel, rosiglitazone and praziquantel plus rosiglitazone, respectively. NF-κB binding activity and expression of PPARγ-mRNA were determined by Western blot assay and real-time quantitative PCR. Radioimmunoassay technique was used to detect the serum content changes of TNF-α and IL-6. Histological specimens were stained with HE. Expression of TGF-β1, a-smooth muscle actin and type I and type III collagen was detected by immunohistochemistry and multimedia color pathographic analysis system.

RESULTS: Inflammation and fibrosis in the rosiglitazone plus praziquantel treatment group (group E) were lightest among the mice infected with Schistosoma (P < 0.05). To further explore the mechanism of rosiglitazone action, we found that rosiglitazone can significantly increase the expression of PPARγ [E: -18.212 ± (-3.909) vs B: -27.315 ± (-6.348) and C: -25.647 ± (-5.694), P < 0.05], reduce the NF-κB binding activity (E: 88.89 ± 19.34 vs B: 141.11 ± 15.37, C: 112.89 ± 20.17 and D: 108.89 ± 20.47, P < 0.05), and lower the serum level of TNF-α (E: 1.613 ± 0.420 ng/mL vs B: 2.892 ± 0.587 ng/mL, C: 2.346 ± 0.371 ng/mL and D: 2.160 ± 0.395 ng/mL, P < 0.05) and IL-6 (E: 0.106 ± 0.021 ng/mL vs B: 0.140 ± 0.031 ng/mL and C: 0.137 ± 0.027 ng/mL, P < 0.05) in mice with liver fibrosis. Rosiglitazone can also substantially reduce the hepatic expression of TGF-β1, α-SMA type I and type III collagen in mice with liver fibrosis.

CONCLUSION: The activation of PPARγ by its ligand can retard liver fibrosis and suggest the use of rosiglitazone for the treatment of liver fibrosis due to Schistosoma japonicum infection.

Resveratrol inhibits cell growth by inducing cell cycle arrest in activated hepatic stellate cells

Resveratrol (RSV) exerts anti-proliferative and pro-apoptotic actions in different cell lines. Hepatic stellate cells (HSCs) are major fibrogenic cell types that contribute to collagen accumulation during chronic liver disease. In the present study, the inhibitory effects of RSV on cell proliferation, cell cycle, and apoptosis were evaluated in the mouse hepatic stellate cell line GRX. Cells treated with 1 nM-1 muM of RSV demonstrated a decrease in cell growth of about 35% after 5 days. GRX cells, treated with RSV (100 nM or 1 muM), were analyzed by flow cytometry; RSV induced an increase in the number of GRX cells in the S- and sub-G1 phases. The increase in sub-G1 phase cells and the nuclear condensation and fragmentation shown by DAPI staining identified a possible pro-apoptotic effect of RSV on GRX cells. Furthermore, the RSV anti-proliferative effects could be explained by an S-phase accumulation caused by a decrease in the progression through the cell cycle or an inhibition of S or G2 phase transition. It is notable that these RSV actions are mediated at nanomolar levels, compatible with the concentrations of free RSV in biological fluids after ingestion of polyphenol-rich foods, suggesting a possible effect of these foods as an adjuvant treatment in chronic liver diseases.

Proteomics in liver fibrosis is more than meets the eye

Liver fibrosis is a serious health issue for many liver patients and is currently diagnosed using liver biopsy. The erroneous nature of this technique urges the search for better, noninvasive alternatives. In this regard, proteomics has been described as a useful biomarker discovery tool and has become increasingly applied in the study of liver fibrosis. Experimental and clinical studies have already provided deeper insights in the molecular pathways of liver fibrosis and even confirmed previous findings. Recent advances in proteomic strategies and tools enable multiple fractionation, multiple protein identifications and parallel analyses of multiple samples. Despite its increasing popularity, proteomics still faces certain pitfalls concerning preanalytical variability, protein coverage and statistic reliability. Proteomics is still evolving, but will undoubtedly contribute to a better understanding of the basics of the pathology and certainly offer opportunities in liver fibrosis diagnostics and therapeutics.

Gene therapy for hepatic fibrosis

Hepatic fibrosis is a common pathological process of chronic liver diseases, characterized by increased synthesis and relatively low degradation of extracellular matrix (ECM) resulting from their dynamic imbalance. Recent progress in molecular biology techniques has made it possible to treat hepatic fibrosis with gene therapy. At present, the commonly used method is to induce the expression of exogenous genes by transducing enough therapeutic genes into injured liver to delay or cure liver fibrosis.

Bone marrow cell transplant does not prevent or reverse murine liver cirrhosis

We tested the effect of bone marrow cell (BMC) transplantation in either preventing or reversing cirrhosis on an experimental model of chronic liver disease. Female Wistar rats were fed a liquid alcohol diet and received intraperitoneal injections of carbon tetrachloride (CCl4) over 15 weeks. Ten animals (cell-treated group) received five injections of BMCs during the cirrhosis induction protocol (on the 4th, 6th, 8th, 10th, and 12th weeks) and four animals received the cells after liver injury was established through tail vein. Nine animals (nontreated group) were submitted to the previously described protocols; however, they received vehicle injections. Analyses were performed to verify whether the infusion of cells was effective in preventing the development of cirrhosis in our model of induction, and if the cells could reverse cirrhosis once it was established. Hepatic architecture and fibrotic septa were analyzed in liver slices stained with hematoxilin & eosin and Sirius red, respectively. Fibrosis quantification was measured by Sirius red histomorphometry. Indirect immunofluorescence was performed to detect the amount of tissue transglutaminase 2. Blood analyses were performed to assess liver injury and function by the assessment of alanine aminotransferase and albumin. Ultrasound was performed to analyze the portal vein caliber and presence of ascitis. Cirrhosis features (regenerative nodules and fibrous septa) were observed in histopathology after 15 weeks of continuous hepatic injury in nontreated and cell-treated groups. Collagen content, immunofluorescence analysis, and biochemical and ultrasound parameters were similar in nontreated and cell-treated groups; however, both groups showed significant differences compared to a normal control group. Cell infusions with bone marrow-derived cells seem to be ineffective in improving morphofunctional parameters of the liver when applied to chronic cases either during or after establishment of the hepatic lesion.

Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver

The hepatic stellate cell has surprised and engaged physiologists, pathologists, and hepatologists for over 130 years, yet clear evidence of its role in hepatic injury and fibrosis only emerged following the refinement of methods for its isolation and characterization. The paradigm in liver injury of activation of quiescent vitamin A-rich stellate cells into proliferative, contractile, and fibrogenic myofibroblasts has launched an era of astonishing progress in understanding the mechanistic basis of hepatic fibrosis progression and regression. But this simple paradigm has now yielded to a remarkably broad appreciation of the cell's functions not only in liver injury, but also in hepatic development, regeneration, xenobiotic responses, intermediary metabolism, and immunoregulation. Among the most exciting prospects is that stellate cells are essential for hepatic progenitor cell amplification and differentiation. Equally intriguing is the remarkable plasticity of stellate cells, not only in their variable intermediate filament phenotype, but also in their functions. Stellate cells can be viewed as the nexus in a complex sinusoidal milieu that requires tightly regulated autocrine and paracrine cross-talk, rapid responses to evolving extracellular matrix content, and exquisite responsiveness to the metabolic needs imposed by liver growth and repair. Moreover, roles vital to systemic homeostasis include their storage and mobilization of retinoids, their emerging capacity for antigen presentation and induction of tolerance, as well as their emerging relationship to bone marrow-derived cells. As interest in this cell type intensifies, more surprises and mysteries are sure to unfold that will ultimately benefit our understanding of liver physiology and the diagnosis and treatment of liver disease.