Approaches for treatment of liver fibrosis in chronic hepatitis C

Progress in evaluating the status of hepatitis C infection based on the functional changes of hepatic stellate cells (Review)

Hepatitis C virus (HCV) infection is a global public health problem. Cirrhosis and hepatocellular carcinoma are the main causes of death in patients with chronic hepatitis C (CHC) infection. Liver fibrosis is an important cause of cirrhosis and end‑stage liver disease after CHC infection. Along with the course of infection, liver fibrosis exhibits a progressive exacerbation. Hepatic stellate cells (HSCs) are involved in both physiological and pathological processes of the liver. During the chronic liver injury process, the activated HSCs transform into myofibroblasts, which are important cells in the development of liver fibrosis. At present, HCV infection still lacks specific markers for the accurate detection of the disease condition and progression. Therefore, the present review focused on HSCs, which are closely related to HCV‑infected liver fibrosis, and analyzed the changes in the HSCs, including their surface‑specific markers, cytokine production, activation, cell function and morphological structure. The present review aimed to propose novel diagnostic markers, at both the cellular and molecular level, which would be of great significance for the timely diagnosis of the disease. According to this aim, the characteristic changes of HSCs during HCV infection were reviewed in the present article.

Proteomic profiling of hepatic stellate cells in alcohol liver fibrosis reveals proteins involved in collagen production

BACKGROUND

Hepatic stellate cell (HSC) activation has central functions in alcohol-induced liver fibrosis. Proteins of HSCs in alcoholic liver fibrosis (ALF) are still not completely understood. Here, we performed a proteomic study to discover proteins related to ALF using HSCs isolated from a rat model.

METHODS

Sprague-Dawley rats were fed with ethanol for 2 or 6 weeks. Liver histology was assessed using Sirius red and Oil red O staining. HSCs were enriched by using Percoll density gradient centrifugation, and analyzed using flow cytometry. Proteins extracted from HSCs were separated using two-dimensional electrophoresis (2DE). Differentially expressed proteins were identified using liquid chromatography-mass spectrometry (LC-MS). The characteristics of the differentially expressed proteins were analyzed using the UniProtKB database and STRING software. The mRNA levels of two differentially expressed proteins were analyzed using real-time RT-PCR, of which NADH dehydrogenase (ubiquinone) flavoprotein 2, mitochondrial (Ndufv2) was further investigated using Western blot (WB) and immunohistochemical analysis in the ALF model and human liver tissues. The relationship between Ndufv2 and alcohol stimulation was evaluated using WB. Next, Ndufv2 was knocked-down by shRNA in the HSC-T6 cell line. Three genes (encoding collagen, metalloproteinase inhibitor 1 [TIMP-1], and α-smooth muscle actin [a-SMA]) related to HSC activation were detected.

RESULTS

An ALF model was successfully established, with a liver fibrosis score of 1-2 (S1-2), and some big fat vacuoles development. Twenty-one non-abundant proteins with more than a 2-fold difference were identified using mass spectrometry, including 7 upregulated and 14 downregulated proteins. These differential proteins are a response to antigen presentation, mitochondrial metabolism, ethanol, and collagen degradation. Among them, two upregulated proteins (Ndufv2 and ATP synthase subunit alpha, mitochondrial [ATP5a1]) were involved in mitochondrial metabolism in ALF, and showed concurrent changes in mRNA and protein levels. Ndufv2 was upregulated in HSCs, as shown by WB, in non-parenchymal cells (NPCs) in the rat model and human liver tissues, and detected using immunohistochemistry. Ndufv2 was also upregulated after alcohol stimulation. Following Ndufv2 knockdown, collagen, TIMP-1, and α-SMA were downregulated compared with that in the controls.

CONCLUSIONS

A proteomic study was performed to discover proteins related to ALF in HSCs isolated from a rat model. Twenty-one differentially expressed proteins were identified, including proteins involved in mitochondrial metabolism and antigen presentation. Ndufv2, an upregulated protein in ALF, might be involved in ALF through regulating the production of fibrosis factors.

Blockade of YAP alleviates hepatic fibrosis through accelerating apoptosis and reversion of activated hepatic stellate cells

Yes-associated protein (YAP) is a significant downstream protein in the Hippo signaling pathway with important functions in cell proliferation, apoptosis, invasion and migration. YAP also plays a role in the progression and development of various liver diseases. In hepatic fibrosis development and reversion, the proliferation and apoptosis of activated hepatic stellate cells (HSCs) play a critical role. However, the contribution of YAP to hepatic fibrosis progression and reversion and the underlying mechanism have not been investigated. Here we investigated the expression and function of YAP in the proliferation and apoptosis of activated HSCs. We found that YAP expression was increased in liver fibrosis tissues from CCl₄-induced model mice and restored to normal level after stopping CCl₄ injection and 6 weeks of spontaneously recovery. YAP expression was elevated in HSC-T6 cells treated with TGF-β1 and recovered after MDI treatment. Silencing of YAP inhibited the activation and proliferation of HSC-T6 cells stimulated by TGF-β1. In addition, the apoptosis of activated HSC-T6 cells silenced for YAP was slightly enhanced. Furthermore, over-expression of YAP repressed the reversion of activated HSC-T6 cells mediated by MDI reversal. We found that HSC-T6 cells activated by TGF-β1 showed higher levels of nuclear YAP compared with MDI-treated cells, indicating that YAP was activated in HSC-T6 cells treated by TGF-β1. We also found that loss of YAP attenuated Wnt/β-catenin pathway activity in activated HSC-T6 cells. Treatment of VP, an inhibitor of the YAP-TEAD complex, reduced both activation and proliferation of HSC-T6 cells and increased apoptosis. Together these results indicated that reduced expression of YAP contributes to acquisition of the quiescent phenotype in HSCs. Our results suggest that YAP may be a useful target in HSCs activation and reversion.

Modulation of hepatic stellate cells and reversibility of hepatic fibrosis

Hepatic fibrosis (HF) is the pathological component of a variety of chronic liver diseases. Hepatic stellate cells (HSC) are the main collagen-producing cells in the liver and their activation promotes HF. If HSC activation and proliferation can be inhibited, HF occurrence and development can theoretically be reduced and even reversed. Over the past ten years, a number of studies have addressed this process, and here we present a review of HSC modulation and HF reversal.

Expression of Septin4 in human hepatic stellate cells LX-2 stimulated by LPS

Septin4, a member of polymerizing GTP-binding proteins family, is reported to be involved in cytoskeletal organization in mitosis, apoptosis, fibrosis, and other cellular processes. Since various Septin4 expression patterns were reported in different diseases, this study aimed to investigate Septin4 expression in human LX-2 cell line stimulated by lipopolysaccharides (LPS) and attempted to clarify the relationship between Septin4 and hepatic inflammatory injury and fibrosis. In this subject, human stellate cell line LX-2 was stimulated by LPS. The expression of Septin4 was analyzed by Western blot and quantitative real-time PCR. To observe the relationship among Toll-like receptor 4 (TLR4), TGF-β, and Septin4, proteins from the anti-TLR4 antibody blocked cells, as well as the TGF-β-induced cells, were analyzed by the method of Western blot. As the results, LPS could induce the alteration of α-smooth muscle actin and Septin4 expression in LX-2 cells. Septin4 expression was regulated by LPS stimulation through TLR4 and TGF-β pathway. These results therefore suggest that Septin4 may be involved in the process of activation of hepatic stellate cells by LPS stimulation. Further work would focus on the function of Septin4 in hepatic inflammatory injury and fibrosis.

Oxidative stress and glutathione in TGF-beta-mediated fibrogenesis

Transforming growth factor beta (TGF-beta) is the most potent and ubiquitous profibrogenic cytokine, and its expression is increased in almost all the fibrotic diseases and in experimental fibrosis models. TGF-beta increases reactive oxygen species production and decreases the concentration of glutathione (GSH), the most abundant intracellular free thiol and an important antioxidant, which mediates many of the fibrogenic effects of TGF-beta in various types of cells. A decreased GSH concentration is also observed in human fibrotic diseases and in experimental fibrosis models. Although the biological significance of GSH depletion in the development of fibrosis remains obscure, GSH and N-acetylcysteine, a precursor of GSH, have been used in clinics for the treatment of fibrotic diseases. This review summarizes recent findings in the field to address the potential mechanism whereby oxidative stress mediates fibrogenesis induced by TGF-beta and the potential therapeutic value of antioxidant treatment in fibrotic diseases.

Activity and expression of ecto-nucleotide pyrophosphate/phosphodiesterases in a hepatic stellate cell line

Nucleotides and nucleosides represent an important and ubiquitous class of molecules that interact with specific receptors, regulate a variety of activities within the liver, and play a role in the pathogenesis of hepatic fibrosis. Ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPPs) are ecto-enzymes that are located on the cell surface. NPP1, NPP2, and NPP3 (abbreviated as NPP1-3 hereafter) have been implicated in the hydrolysis of nucleotides; together with other ecto-nucleotidases, they control the events induced by extracellular nucleotides. We have identified and compared the expression of E-NPP family members in two different phenotypes of the mouse hepatic stellate cell line (GRX). In quiescent-like hepatic stellate cells (HSCs), E-NPP activity was significantly higher, NPP2 mRNA expression decreased and NPP3 mRNA increased. The differential NPP activity and expression in two phenotypes of GRX cells suggests that they are involved in the regulation of extracellular nucleotide metabolism in HSCs. However, the role of E-NPPs in the liver remains to be clarified.

Oxidative stress, plasminogen activator inhibitor 1, and lung fibrosis

Fibrosis is characterized by excessive accumulation of extracellular matrix (ECM) in basement membranes and interstitial tissues, resulting from increased synthesis or decreased degradation of ECM or both. The plasminogen activator/plasmin system plays an important role in ECM degradation, whereas the plasminogen activator inhibitor 1 (PAI-1) is a physiologic inhibitor of plasminogen activators. PAI-1 expression is increased in the lung fibrotic diseases and in experimental fibrosis models. The deletion of the PAI-1 gene reduces, whereas the overexpression of PAI-1 enhances, the susceptibility of animals to lung fibrosis induced by different stimuli, indicating an important role of PAI-1 in the development of lung fibrosis. Many growth factors, including transforming growth factor beta (TGF-beta) and tumor necrosis factor alpha (TNF-alpha), as well as other chemicals/agents, induce PAI-1 expression in cultured cells and in vivo. Reactive oxygen and nitrogen species (ROS/RNS) have been shown to mediate the induction of PAI-1 by many of these stimuli. This review summarizes some recent findings that help us to understand the role of PAI-1 in the development of lung fibrosis and ROS/RNS in the regulation of PAI-1 expression during fibrogenesis.

Activity and expression of ecto-5'-nucleotidase/CD73 are increased during phenotype conversion of a hepatic stellate cell line

Hepatic stellate cells (HSC) play a crucial role in the development of liver fibrosis and are important targets in liver disease therapy. Adenosine acts as an extracellular signaling molecule in various tissues and in liver this nucleoside exerts protective effects. Ecto-5'-nucleotidase/CD73 is a marker for the plasma membrane and is considered to be a key enzyme in the generation of adenosine in the extracellular medium, by transforming AMP into adenosine. In addition, adenosine production from AMP is also catalyzed by alkaline phosphatase. We compared the extracellular metabolism of AMP and transcriptional levels of the ecto-5'-nucleotidase/CD73 and tissue non-specific alkaline phosphatase (TNALP) in activated and quiescent HSC of the mouse hepatic stellate cell line GRX. This cell line expresses a myofibroblast phenotype in basal medium and both retinol and indomethacin treatment induced a phenotypic change of GRX cells to quiescent HSC. Ecto-5'-nucleotidase activity and its mRNA expression were found to be higher in quiescent HSC than in activated HSC. During phenotype conversion, mediated by retinol, the AMP decay was accelerated with adenosine accumulation in extracellular medium, likely due to the decrease in adenosine deaminase activity also observed in quiescent HSC. The treatment with retinol also involves transcriptional activation of TNALP. Taken together, these data suggest that ecto-5'-nucleotidase-dependent adenosine generation may play a role in the regulation of quiescent HSC functions.

Histamine dihydrochloride: actions and efficacy in the treatment of chronic hepatitis C infection

The host immune response, in addition to viral factors, is the critical determinant of the pathological consequences of hepatitis C virus infection. Current therapies for genotype 1 are unsuccessful in a substantial number of patients. Histamine dihydrochloride by virtue of its histamine H2 agonistic activity, has the potential to prevent damage induced by oxidative stress in tissues and can protect T and natural killer lymphocytes from oxygen radical-induced functional inhibition and apoptosis, thereby, potentiating interferon-alpha-induced activation of these cells. Coadministration of histamine dihydrochloride and interferon therapy for chronic hepatitis C virus infection was tested in several clinical trials. However, conflicting data and the relatively small numbers of patients enrolled, suggest that this combination should be the focus of further investigation.

Enhanced Hepatic Uptake and Bioactivity of Type α1(I) Collagen Gene Promoter-Specific Triplex-Forming Oligonucleotides after Conjugation with Cholesterol

A triplex-forming oligonucleotide (TFO) specific for type alpha1(I) collagen promoter is a promising candidate for treating liver fibrosis. Earlier, we determined the pharmacokinetics and biodistribution of TFO after systemic administration into normal and fibrotic rats. In this study, we conjugated cholesterol to the 3' end of the TFO via a disulfide bond and determined its cellular and nuclear uptake and bioactivity using HSC-T6 cell lines in vitro, followed by biodistribution at whole-body, organ (liver), and subcellular levels. Conjugation with cholesterol had little effect on the triplex-forming ability of the TFO with target duplex DNA, and the cellular uptake of (33)P-TFO-cholesterol (Chol) increased by 2- to approximately 4-fold. Real-time reverse transcriptase-polymerase chain reaction analysis after transfection of HSC-T6 cells with TFO-Chol or TFO indicated that TFO-Chol had higher inhibition on type alpha1(I) collagen primary transcript than naked TFO at low concentration (200 nM) but showed similar inhibition at higher concentration (500 and 1000 nM). There was increase in the inhibition on primary transcript with transfection time. The hepatic uptake of (33)P-TFO-Chol after systemic administration was 72.22% of the dose compared with 45.8% of (33)P-TFO. There was significant increase in the uptake of (33)P-TFO-Chol by hepatic stellate cells and hepatocytes. More importantly, the nuclear uptake of TFO-Chol was higher than TFO in cell culture system and in vivo studies. In conclusion, TFO-Chol is a potential antifibrotic agent.

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Changes of ECM and CAM gene expression profile in the cirrhotic liver after HCV infection: Analysis by cDNA expression array

AIM: We aimed to observe the expression of extracellular matrix (ECM) and cellular adhesion molecules (CAM) in cirrhotic liver tissues after hepatitis C virus (HCV) infection.

METHODS: Twelve patients with post HCV inflammatory liver cirrhosis were selected to evaluate their liver function and other virological, pathological parameters. Then three specimens of cirrhotic patients whose health assessment results and laboratory data were similar and three normal liver specimens explanted from liver grafts prepared for liver transplantation were chosen for investigating gene expression of ECM and CAM using cDNA expression array.

RESULTS: The cDNA array assay revealed 36.7% (36/96) of genes with changes, in which 26.3% (26/96) was up-regulated and 10.1% (10/96) was down-regulated. Integrin (ITGA), collagen (COL), ADAMTS were identified as the characteristic changes of ECM and CAM gene expression levels. ITGA were demonstrated β1 and β2 sub-section changed in liver cirrhosis.

CONCLUSION: ECM and CAM play an important role in the progression of liver cirrhosis after HCV infection. The capital mechanism is related to the inflammatory cells infiltration, the activation and transformation of ECM producing cells and the imbalance between production and elimination of ECM.

Pathophysiology of hepatitis C virus infection and related liver disease

Hepatitis C virus (HCV) infects over 170 million people worldwide. Chronic infection occurs in 50-80% of cases and eventually leads to cirrhosis and hepatocellular carcinoma. The HCV lifecycle is only partly understood owing to the lack of a productive cell culture system. Several molecules have been implicated in the receptor complex at the surface of target cells, but the mode of HCV entry remains unknown. Persistent infection appears to be due to weak CD4+and CD8+ T-cell responses during acute infection, which fail to control viral replication. When chronic infection is established, HCV does not appear to be cytopathic. Liver lesions appear to result from locally driven immune responses, which are mainly non-specific. Local inflammation triggers fibrogenesis, in which hepatic stellate cells play a major role. Cirrhosis is facilitated by external factors, such as chronic alcohol consumption and viral co-infections. Patients with cirrhosis are at high risk of developing hepatocellular carcinoma. The role of HCV proteins in hepatocarcinogenesis is unknown. Further progress in our understanding of HCV infection and pathogenesis awaits the advent of new model systems and technologies.

Liver extracellular matrix in health and disease

Liver fibrosis is the hallmark of every chronic liver disease. It is also the major factor of morbidity and mortality due to the development of cirrhosis and its complications including hepatocellular carcinoma. But even at the beginning of the process of liver fibrosis and due to the strategic position of the extracellular matrix at the interface between blood flow and epithelial compartment, any quantitative or qualitative modification of extracellular matrix will rapidly affect structure and function of the liver. The development of several animal models of liver fibrosis as well as isolation and cultivation of hepatic stellate cells, the major fibrogenic cell type in the liver, led to the gathering of recent knowledge on the mechanism of liver fibrosis. Activation of hepatic stellate cells is a key event in this process and many details on this finely tuned mechanism are now available. In addition to these experimental data, experience from chronic hepatitis C now allows the development of new concepts and perspectives such as liver fibrosis regression and antifibrotic therapies.