Animal Models Of Liver Fibrosis Research Articles

Insulin-like growth factor binding protein 5 enhances survival of LX2 human hepatic stellate cells

BackgroundExpression of insulin-like growth factor binding protein 5 (IGFBP5) is strongly induced upon activation of hepatic stellate cells and their transdifferentiation into myofibroblasts in vitro. This was confirmed in vivo in an animal model of liver fibrosis. Since IGFBP5 has been shown to promote fibrosis in other tissues, the aim of this study was to investigate its role in the progression of liver fibrosis.MethodsThe effect of IGFBP5 was studied in LX2 cells, a model for partially activated hepatic stellate cells, and in human primary liver myofibroblasts. IGFBP5 signalling was modulated by the addition of recombinant protein, by lentiviral overexpression, and by siRNA mediated silencing. Furthermore, the addition of IGF1 and silencing of the IGF1R was used to investigate the role of the IGF-axis in IGFBP5 mediated effects.ResultsIGFBP5 enhanced the survival of LX2 cells and myofibroblasts via a >50% suppression of apoptosis. This effect of IGFBP5 was not modulated by the addition of IGF1, nor by silencing of the IGF1R. Additionally, IGFBP5 was able to enhance the expression of established pro-fibrotic markers, such as collagen Iα1, TIMP1 and MMP1.ConclusionIGFBP5 enhances the survival of (partially) activated hepatic stellate cells and myofibroblasts by lowering apoptosis via an IGF1-independent mechanism, and enhances the expression of profibrotic genes. Its lowered expression may, therefore, reduce the progression of liver fibrosis.

Alpha-lipoic acid inhibits hepatic PAI-1 expression and fibrosis by inhibiting the TGF-β signaling pathway

Accumulating evidence suggests that plasminogen activator inhibitor (PAI)-1 plays an important role in the development of hepatic fibrosis via its involvement in extracellular matrix remodeling. We previously reported that alpha-lipoic acid (ALA), a naturally occurring thiol antioxidant, prevents hepatic steatosis by inhibiting the expression of sterol regulatory element binding protein-1c. The aim of the present study was to determine whether ALA prevents hepatic PAI-1 expression and fibrosis through the inhibition of multiple TGF-β-mediated molecular mediators. We investigated whether ALA inhibited the development of hepatic fibrosis in mice following bile duct ligation (BDL), an established animal model of liver fibrosis. We found that ALA markedly inhibited BDL-induced hepatic fibrosis and PAI-1 expression. We also found that ALA attenuated TGF-β-stimulated PAI-1 mRNA expression, and inhibited PAI-1 promoter activity in liver cells; this effect was mediated by Smads and the JNK and ERK pathways. The results of the present study indicate that ALA inhibits hepatic PAI-1 expression through inhibition of TGF-β-mediated molecular mediators, including Smad3, AP1, and Sp1, and prevents the development of BDL-induced hepatic fibrosis. These findings suggest that ALA may have a clinical application in preventing the development and progression of hepatic fibrosis.

In vivo Quantification of Liver Stiffness in a Rat Model of Hepatic Fibrosis with Acoustic Radiation Force

Liver fibrosis is currently staged using needle biopsy, a highly invasive procedure with a number of disadvantages. Measurement of liver stiffness changes that accompany progression of the disease may provide a quantitative and noninvasive method to assess the health of the liver. The purpose of this study is to investigate the correlation between liver stiffness measured by radiation force induced shear waves and disease related changes in the liver. An additional aim is to present initial findings on the effects of liver viscosity on radiation force induced shear wave morphology. Liver fibrosis was induced in 10 rats using carbon tetrachloride (CCl 4), while five rats acted as controls. Liver stiffness was measured in vivo in all rats after a treatment period of 8 weeks using a modified Siemens SONOLINE Antares scanner (Siemens Medical Solutions USA, Ultrasound Division, Issaquah, WA, USA). The spatial coherence of radiation force induced shear waves propagating in the viscoelastic rat liver decreased significantly with propagation distance, compared with shear waves in an elastic phantom and a finite element model of a purely elastic medium. Animals were sacrificed after imaging and liver samples were taken for histopathologic analysis and collagen quantification using picrosirius red staining and hydroxyproline assay. At the end of the treatment period, five rats had healthy livers (stage F0), while six had severe fibrosis (F3) and the rest had light to moderate fibrosis (F1 and F2). The measured liver stiffness for the F0 group was 1.5 ± 0.1 kPa (mean ± 95% confidence interval) and for F3 livers was 1.8 ± 0.2kPa. In this study, liver stiffness was found to be linearly correlated with the amount of collagen in the liver measured by picrosirius red staining (r 2 = 0.43, p = 0.008). In addition, stiffness spatial heterogeneity was also linearly correlated with liver collagen content (r 2 = 0.58, p = 0.001) by picrosirius red staining. These results are consistent with those obtained by Salameh et al. (2007) and Yin et al. (2007b) using animal models of liver fibrosis and MR elastography. This suggests that stiffness measurement using acoustic radiation force can provide a quantitative assessment of the extent of fibrosis in the liver and can be potentially used for the diagnosis, management and study of liver fibrosis. (E-mail: michael.h.wang@duke.edu)

Targeted delivery of drugs for liver fibrosis

Liver fibrosis and its end stage disease cirrhosis are a major cause of mortality and morbidity around the world. There is no effective pharmaceutical intervention for liver fibrosis at present. Many drugs that show potent antifibrotic activities in vitro often show only minor effects in vivo because of insufficient concentrations of drugs accumulating around the target cell and their adverse effects as a result of affecting other non-target cells. Hepatic stellate cells (HSC) play a critical role in the fibrogenesis of liver, so they are the target cells of antifibrotic therapy. Several kinds of targeted delivery system that could target the receptors expressed on HSC have been designed, and have shown an attractive targeted potential in vivo. After being carried by these delivery systems, many agents showed a powerful antifibrotic effect in animal models of liver fibrosis. These targeted delivery systems provide a new pathway for the therapy of liver fibrosis. The characteristics of theses targeted carriers are reviewed in this paper.

Reduced liver fibrosis in hypoxia-inducible factor-1α-deficient mice

Liver fibrosis is characterized by excessive deposition of extracellular matrix in the liver during chronic injury. During early stages of this disease, cells begin to synthesize and secrete profibrotic proteins that stimulate matrix production and inhibit matrix degradation. Although it is clear that these proteins are important for development of fibrosis, what remains unknown is the mechanism by which chronic liver injury stimulates their production. In the present study, the hypothesis was tested that hypoxia-inducible factor-1alpha (HIF-1alpha) is activated in the liver during chronic injury and regulates expression of profibrotic proteins. To investigate this hypothesis, mice were subjected to bile duct ligation (BDL), an animal model of liver fibrosis. HIF-1alpha protein was increased in the livers of mice subjected to BDL by 3 days after surgery. To test the hypothesis that HIF-1alpha is required for the development of fibrosis, control and HIF-1alpha-deficient mice were subjected to BDL. Levels of type I collagen and alpha-smooth muscle actin mRNA and protein were increased in control mice by 14 days after BDL. These levels were significantly reduced in HIF-1alpha-deficient mice. Next, the levels of several profibrotic mediators were measured to elucidate the mechanism by which HIF-1alpha promotes liver fibrosis. Platelet-derived growth factor (PDGF)-A, PDGF-B, and plasminogen activator inhibitor-1 mRNA levels were increased to a greater extent in control mice subjected to BDL compared with HIF-1alpha-deficient mice at 7 and 14 days after BDL. Results from these studies suggest that HIF-1alpha is a critical regulator of profibrotic mediator production during the development of liver fibrosis.

Suppression of Carbon Tetrachloride-Induced Liver Fibrosis by Transplantation of a Clonal Mesenchymal Stem Cell Line Derived from Rat Bone Marrow

Transplantation of hepatocytes or bone marrow-derived cells has been shown to ameliorate liver fibrosis in animal models, but no direct comparison of relative efficiency has been made. The aim of this study was to compare the efficiency of a bone marrow-derived clonal mesenchymal stem cell line established by us (rBM25/S3) with that of its adipogenic or hepatogenic differentiation derivative for suppression of rat liver fibrosis. After induction of differentiation of rBM25/S3 cells into adipogenic or hepatogenic cells in culture, we intrasplenically transplanted the three types of cells into rats (3 x 10(7) cells/rat) before and 4 weeks after initiation of carbon tetrachloride treatment (1 ml/kg body weight twice a week for 8 weeks) to induce liver fibrosis. Undifferentiated rBM25/S3 cells were the most effective for suppression of liver fibrosis, followed by the adipogenic cells and hepatogenic cells. Expression levels of MMP-2 and MMP-9 were also highest in undifferentiated rBM25/S3 cells. These results indicate that bone marrow-derived clonal mesenchymal stem cell lines are useful for further mechanistic studies on cell-mediated suppression of liver fibrosis and that such cell lines will provide information on an appropriate cell source for transplantation therapy for cirrhosis.

What is the potential role of antifibrotic agents for the treatment of liver disease?

Liver fibrosis is characterized by the excessive deposition of extracellular matrix proteins, and results from chronic liver disease. The most important goal of antifibrotic therapy is to remove the fibrogenic stimulus by treating the underlying etiology of liver disease. The authors of this Viewpoint article discuss the promising targets for antifibrotic therapy that have been identified using animal models of liver fibrosis.

Spontaneous hepatic fibrosis in transgenic mice overexpressing PDGF-A

Platelet derived growth factor (PDGF) plays a central role in repair mechanisms after acute and chronic tissue damage. To further evaluate the role of PDGF-A in liver fibrogenesis in vivo, we generated transgenic mice with hepatocyte-specific overexpression of PDGF-A using the CRP-gene promoter. Transgenic but not wildtype mice showed expression of PDGF-A mRNA in the liver. Hepatic PDGF-A overexpression was accompanied by a significant increase in hepatic procollagen III mRNA expression as well as TGF-β1 expression. Liver histology showed increased deposition of extracellular matrix in transgenic but not in wildtype mice. PDGF-A-transgenic mice showed positive sinusoidal staining for α-SMA indicating an activation of hepatic stellate cells. Since the profibrogenic effect of PDGF-A was accompanied by increased TGF-β1 protein concentration in the liver of transgenic mice, it can be postulated that PDGF-A upregulates expression of TGF-β1 which is a strong activator of hepatic stellate cells. Thus, these results point towards a fibrosis induction by PDGF-A via the TGF-β1 signalling pathway. In conclusion, expression and functional analysis of PDGF-A in the liver of transgenic mice suggest a relevant profibrogenic role of PDGF-A via TGF-β1 induction. Counteracting PDGF-A may therefore be one of the effects of tyrosine kinase inhibitors which showed protective effects in animal models of liver fibrosis.

Hepatic Stellate Cells and Liver Fibrosis

Substantial evidence now exists to recognize hepatic stellate cells (HSCs) as the main matrix-producing cells in the process of liver fibrosis. Liver injury of any etiology will ultimately lead to activation of HSCs, which undergo transdifferentiation to fibrogenic myofibroblast-like cells. Quantitative analysis of HSC activation by immunohistochemistry has been shown to be useful in predicting the rate of progression of liver fibrosis in some clinical situations. In the activation process, transforming growth factor beta is thought to be the main mediator of fibrogenesis and platelet-derived growth factor is the major inducer of HSC proliferation. Different platelet-derived growth factor and transforming growth factor beta inhibitors have been shown to effectively prevent liver fibrosis in animal models and represent promising therapeutic agents for humans.

Establishment of an early liver fibrosis model by the hydrodynamics-based transfer of TGF-β1 gene

BackgroundLiver fibrosis represents a significant and severe health care problem and there are no efficient drugs for therapy so far. Preventing the progression of fibrogenesis and revival endogenous repair activities is an important strategy for both current and future therapies. Many studies of liver fibrosis consist of animal testing with various hepatotoxins. Although this method is often used, the model at which cirrhosis or extensive fibrosis becomes irreversible has not been well defined and is not representative of early-stage fibrogenesis. We here report the establishment of a transient and reversible liver fibrosis animal model which may better represent an early and natural fibrotic event. We used a high-speed intravenous injection of naked plasmid DNA of transforming growth factor-β1 (TGF-β1) gene which is under the control of a metallothionein-regulated gene in a pPK9A expression vector into the tail vein (the hydrodynamics-based transfer) and fed the mouse with zinc sulfate (ZnSO4)-containing water simultaneously.ResultsUsing our hydrodynamics-based gene transfer model we found that upon induction by ZnSO4, the serum TGF-β1 level in Balb/c mice and Sp1 transcription factor binding activity peaked at 48 h and declined thereafter to a normal level on the 5th day. In addition, mRNA and protein levels of TGF-β1 in the liver were also upregulated at 48 h. Furthermore, induction of TGF-β1 increased the α-smooth muscle actin (α-SMA), p-Smad2/3, hydroxyproline and collagen 1A2 (Col 1A2) levels in the liver, suggesting a significant liver fibrosis.ConclusionOur results show that TGF-β1 in pPK9a-transferred mice liver with ZnSO4 feeding can achieve a high expression level with significant fibrosis. However, since TGF-β1 induction is transient in our model, the fibrotic level does not reach a large scale (panlobular fibrosis) as seen in the CCl4-treated liver. Our model hence represents a dynamic and reversible liver fibrosis and could be a useful tool for studying early molecular mechanism of fibrogenesis or screening of antifibrotic drugs for clinical use.

Quantitative assessment of hepatic fibrosis in an animal model with magnetic resonance elastography

Chronic liver disease is a world-wide problem that causes progressive hepatic fibrosis as a hallmark of progressive injury. At present, the gold standard for diagnosing hepatic fibrosis is liver biopsy, which is an invasive method with many limitations, including questionable accuracy and risks of complications. MR elastography (MRE), a phase-contrast MRI technique for quantitatively assessing the mechanical properties of soft tissues, is a potential noninvasive diagnostic method to assess hepatic fibrosis. In this work, MRE was evaluated as a quantitative method to assess the in vivo mechanical properties of the liver tissues in a knockout animal model of liver fibrosis. This work demonstrates that the shear stiffness of liver tissue increases systematically with the extent of hepatic fibrosis, as measured by histology. A linear correlation between liver stiffness and fibrosis extent was well-defined in this animal model. An additional finding of the study was that fat infiltration, commonly present in chronic liver disease, does not significantly correlate with liver stiffness at each fibrosis stage and thus does not appear to interfere with the ability of MRE to assess fibrosis extent. In conclusion, MRE has the potential not only for assessing liver stiffness, but also for monitoring potential therapies for hepatic fibrosis.

Diagnosis and Measurement of Liver Fibrosis by MRI in Bile Duct Ligated Rats

The noninvasive evaluation of liver fibrosis is a major clinical goal in liver diseases. Our aim was to identify MRI parameters to quantify liver fibrosis in vivo in an animal model of liver fibrosis with slight inflammation. We evaluated serum hyaluronate, liver hydroxyproline, area of liver fibrosis (image analysis), and 1.5-T MRI in 10 sham rats and 24 bile duct ligated rats with different stages of liver fibrosis. Liver signal intensity (SI)/muscle SI ratio and liver relaxation times (rT) were measured on T1 and T2 weighted sequences at different echo (TE) or recovery (RT) times of MRI. Among the 66 MRI parameters tested, the highest correlation with the area of fibrosis was observed for rT2 (r=0.78, P < 0.01). The area of liver fibrosis was independently predicted by five MRI variables (adjusted R (2)=0.78, with R (2)=0.64 for rT2 and rT1). Diagnostic accuracy for liver fibrosis was 100% using two variables: liver/muscle SI ratio on T2 at 30-ms TE and liver/muscle SI ratio on T1 at 50-ms RT. We conclude that in this animal model, fibrosis could be diagnosed with an accuracy of 100% using two MRI parameters. The quantification of liver fibrosis was very accurate either with only one MRI parameter (r=0.78 for rT2) or with five parameters (r=0.90) in this cholestatic model.

Protective effect of verapamil on multiple hepatotoxic factors-induced liver fibrosis in rats

The purpose of the present work was to investigate the effect of verapamil on liver fibrosis induced by multiple hepatotoxic factors in rats. Male Wistar rats were divided into a normal control group, a liver fibrosis model control group, and verapamil groups with different dosages. Multiple hepatotoxic factors including carbon tetrachloride (CCl 4), ethanol and high cholesterol were used to make the animal model of liver fibrosis. The parameters of serum l-alanine aminotransferase (ALT), liver malondialdehyde and hydroxyproline contents were measured. Samples of the liver obtained by biopsy were subjected to histological and immunohistochemical studies for the expressions of α-smooth muscle actin (α-SMA) and transforming growth factor-β 1 (TGF-β 1). Results showed that verapamil induced a dose-dependent decrease of serum ALT, liver malondialdehyde and hydroxyproline compared with liver fibrosis model control. Verapamil reduced hepatocyte degeneration and necrosis, and delayed the formation of liver fibrosis. The levels of expression of α-SMA and TGF-β 1 in the hepatic tissue of three of the verapamil-treated groups were significantly less than those of the liver fibrosis model control group. The results showed that verapamil acts against the formation of liver fibrosis, the mechanism might be due to a protective effect for hepatocytes and through decreasing TGF-β 1 to block the activation of hepatic stellate cells (HSCs) and collagen gene expression.

Gene expression profile of quiescent and activated rat hepatic stellate cells implicates Wnt signaling pathway in activation

Liver fibrosis is characterized by accumulation of extracellular matrix proteins synthesized by activated hepatic stellate cells (HSCs). To understand molecular mechanisms of HSCs activation a comprehensive comparison of gene expression between quiescent and activated HSCs is needed. Using DNA microarrays we compared expression of 31,100 genes between quiescent rat HSCs and culture activated rat HSCs. Expression of the components of Wnt signaling was analyzed in HSCs and fibrotic livers by RT-PCR. Activation of beta-catenin was analyzed by Western blot. Nine hundred genes were upregulated more than 4.6-fold and 500 genes were downregulated more than 5.7-fold in activated HSCs. The upregulated genes included Wnt receptor frizzled 2, ligands Wnt4 and Wnt5, which was confirmed in fibrotic livers. Expression of the target genes of Wnt signaling was increased from 5- to 70-fold. Phosphorylation and nuclear translocation of beta-catenin were unchanged, indicating activation of the noncanonical Wnt pathway. Highly upregulated expression of Wnt5a and its receptor frizzled 2 implicates this pathway in differentiation of quiescent HSCs into myofibroblasts. Activation of Wnt signaling pathway in HSCs and in animal models of liver fibrosis has not been described previously, suggesting an important role of Wnt signaling in development of liver fibrosis.

Effect of Chinese medicine Qinggan Huoxuefang on inducing HSC apoptosis in alcoholic liver fibrosis rats

To investigate the effect of Qinggan Huoxuefang (QGHXF) on improvement of liver function and pathology in rats, and to analyze the mechanism. Wistar rats were divided into three groups at random: normal control group (12),micro-amount carbon tetrachloride group (CCl(4))(12) and model group A (60). The model group A was ingested with the mixture (500 mL/L alcohol, 8 mL/kg per day; corn oil, 2 mL/kg per day; pyrazole, 24 mg/kg per day) once a day and intraperitoneal injections of 0.25 mL/kg of a 250 mL/L solution of CCl(4) in olive oil twice a week for 12 wk. The CCl(4) group received intraperitoneal injections only. At the end of 8 wk the model group A (60) was divided into 5 subgroups: model group, Xiaochaihu Chongji (XCH) group, QGHXF high dose group, moderate dose group and low dose group, and were given the drugs respectively. At the end of 12 wk, all the rats were killed and blood samples collected, as well as liver tissue. Blood samples were used for evaluation of alanine transaminase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-glutamyltransferase (gamma-GT). Liver specimens were obtained for routine HE, apoptosis gene array and flow cytometry analysis. A liver fibrosis animal model was successfully established. Fibrosis was obviously reduced in QGHXF high dose group, and no fibrosis formed in CCl(4) group. Compared with model group the QGHXF group and XCH group could obviously decrease the level of ALT, AST, ALP, and GGT (P<0.05). QGHXF high dose group was better than XCH group in ALT (615+/-190 vs 867+/-115), and AST(1,972+/-366 vs 2,777+/-608). Moreover, QGHXF could reduce liver inflammation, fibrosis-induced hepatic stellate cell (HSC) apoptosis and regulate apoptosis gene expression. The HSC apoptosis rates of QGHXF groups were 22.4+/-3.13, 13.79+/-2.26 and 10.07+/-1.14, higher than model group, 6.58+/-1.04 (P<0.05). Compared to model group, 39 genes were up-regulated, 11 solely expressed and 17 down-regulated in high dose group. QGHXF can improve liver fibrosis and induce HSC apoptosis.

Effect of celecoxib on experimental liver fibrosis in rat

Cyclooxygenase-2 (COX-2), an inducible enzyme that catalyzes prostaglandin synthesis, has been implicated in a number of hepatic stellate cell (HSC) functions. In the current study, we assessed the in vivo effect of celecoxib, a COX-2-selective inhibitor, in experimental liver fibrosis in rats. Male Sprague-Dawley rats received experimental treatments for 5 weeks. Serum alanine transminase at the time of sacrifice was measured. Quantitative assessment of liver fibrosis was performed by computerized morphometry. Expression of COX-2, alpha smooth muscle actin and connective tissue growth factor (CTGF) was evaluated by immunohistochemistry. Real-time quantitative PCR was used to determine the expression of genes associated with fibrogenesis and extracellular matrix degradation. Liver fibrosis was significantly worse in rats that received both carbon tetrachloride (CCl4) and celecoxib, compared with rats that received CCl4 and gavage of water (P = 0.037). There was also more HSC activation, and upregulation of collagen alpha1(I), heat-shock protein 47, alphaB crystallin, matrix metalloproteinase (MMP)-2, MMP-9 and tissue inhibitor of MMP (TIMP)-2. The expression of TIMP-1 and CTGF was not significantly different between the two groups. The pro-fibrogenic effect of celecoxib in toxin-induced liver fibrosis in rats was further confirmed in thioacetamide model of liver injury. Celecoxib potentiates experimental liver fibrosis; further studies are warranted to investigate the potential pro-fibrogenic effect of celecoxib in other animal models of liver fibrosis and in patients with chronic hepatitis.

LIM-domain protein CRP2 is upregulated in activated hepatic stellate cells by TGFβ1

Background/Aim: Hepatic stellate cells (HSC) are prominent cellular effectors of liver fibrosis, which become activated during liver injury and transdifferentiate from quiescent, fat storing cells into a proliferative myofibroblast-like cell type (MFB) 1,2. This process is accompanied by modulations of gene expression. We examined the expression of the LIM-domain protein cysteine- and glycine-rich protein 2 (CRP2) during transdifferentiation, a protein which in smooth muscle cells is associated with the cell skeleton as well as located in the nucleus 3,4. Results: An increase of CRP2 was detectable by Western Blot in lysates from liver samples of bile duct ligated rats, an animal model of liver fibrosis. Analysis of different liver cell subpopulations revealed that activated HSC are the source of this upregulation. Cell culture experiments with primary rat HSC, which become activated by contact with uncoated plastic dishes, as well as CFSC, a rat cell line derived from MFB, and A10 cells, a rat smooth muscle cell line, demonstrated that CSRP2 (gene name of CRP2) is upregulated by TGFβ1. To localize promoter regions responsible for induction of gene expression, we generated luciferase constructs with different fragments of the rat CSRP2 promoter. Transfection experiments in CFSC and A10 cells showed that potential binding sites for Smad factors within the proximal 1100 nucleotides of the promoter are not relevant for TGFβ1 induction. Promoter region –1100 to –1600 basepairs was shown to be responsible for serum induction of reporter genes in A10 cells. Future experiments will be performed to identify promoter regions, which are necessary for response to TGFβ signals. Conclusion: Our data demonstrate that CRP2 is increased in activated HSC and that TGFβ1 is involved in upregulation of CSRP2 gene expression. These findings are similar to other known smooth muscle marker like α-smooth muscle actin or SM22α, which are upregulated in activated HSC and associated with the cell skeleton. In contrast, CRP2 is also found in the nucleus, thereby demonstrating an additional function in transition of HSC to MFB in liver fibrosis. Knowledge of CSRP2 regulation and function may help to extend our understanding of molecular mechanisms involved in hepatic fibrogenesis.

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.

Hepatic stellate cells as a target for TZD: Can we treat liver fibrosis and type II diabetes at the same time?

Background & Aims: The ligand-dependent transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) is expressed in hepatic stellate cells (HSC), and its transcriptional activity is reduced during cell transdifferentiation in culture. PPARgamma transcriptional activation decreases platelet-derived growth factor-induced proliferation and inhibits alpha-smooth muscle actin expression in cultured HSC. The aim of our study was to evaluate whether oral administration of synthetic PPARgamma ligands, thiazolidinediones (TZD), might affect collagen deposition in animal models of liver fibrosis. Methods: The effect of 2 TZD (pioglitazone or rosiglitazone) was tested on liver fibrosis induced in rats by either toxin administration (dimethylnitrosamine or carbon tetrachloride) or bile duct ligation. In vivo PPARgamma activation was evaluated by gel shift assay using nuclear extracts from HSC isolated from control and treated rats. Results: Oral administration of TZD reduced extracellular matrix deposition and HSC activation in both toxic and cholestatic models of liver fibrosis. PPARgamma-specific DNA binding was significantly impaired in nuclear extracts of HSC isolated from fibrotic rats compared with HSC from control rats. TZD administration restored PPARgamma DNA binding in HSC nuclei. In vitro, TZD-induced PPARgamma activation inhibited collagen and fibronectin synthesis induced by transforming growth factor (TGF)-betal in human HSC, as measured by enzyme-linked immunosorbent assay and Northen blotting. TZD also reduced the TGF-beta1-induced activity of a 3.5-kilobase procollagen type I promoter transfected in human HSC. conclusions: These findings indicate that PPARgamma activation in HSC retards fibrosis in vivo and suggest the use of TZD for the treatment of liver fibrosis.

Antidiabetic thiazolidinediones inhibit collagen synthesis and hepatic stellate cell activation in vivo and in vitro

Background & Aims: The ligand-dependent transcription factor peroxisome proliferator-activated receptor γ (PPARγ) is expressed in hepatic stellate cells (HSC), and its transcriptional activity is reduced during cell transdifferentiation in culture. PPARγ transcriptional activation decreases platelet-derived growth factor–induced proliferation and inhibits α-smooth muscle actin expression in cultured HSC. The aim of our study was to evaluate whether oral administration of synthetic PPARγ ligands, thiazolidinediones (TZD), might affect collagen deposition in animal models of liver fibrosis. Methods: The effect of 2 TZD (pioglitazone or rosiglitazone) was tested on liver fibrosis induced in rats by either toxin administration (dimethylnitrosamine or carbon tetrachloride) or bile duct ligation. In vivo PPARγ activation was evaluated by gel shift assay using nuclear extracts from HSC isolated from control and treated rats. Results: Oral administration of TZD reduced extracellular matrix deposition and HSC activation in both toxic and cholestatic models of liver fibrosis. PPARγ-specific DNA binding was significantly impaired in nuclear extracts of HSC isolated from fibrotic rats compared with HSC from control rats. TZD administration restored PPARγ DNA binding in HSC nuclei. In vitro, TZD-induced PPARγ activation inhibited collagen and fibronectin synthesis induced by transforming growth factor (TGF)-β1 in human HSC, as measured by enzyme-linked immunosorbent assay and Northen blotting. TZD also reduced the TGF-β1–induced activity of a 3.5-kilobase procollagen type I promoter transfected in human HSC. Conclusions: These findings indicate that PPARγ activation in HSC retards fibrosis in vivo and suggest the use of TZD for the treatment of liver fibrosis.GASTROENTEROLOGY 2002;122:1924-1940