Signal transduction in hepatic stellate cells

Endogenous alpha-calcitonin gene-related peptide mitigates liver fibrosis in chronic hepatitis induced by repeated administration of concanavalin A

BACKGROUND

Alpha-calcitonin gene-related peptide (alphaCGRP) is a 37-amino acid pleiotropic peptide that we previously showed to exert a hepatoprotective effect during concanavalin A (Con A)-induced acute hepatitis. In the present study, we used alphaCGRP(-/-) mice to further investigate the antifibrogenic and hepatoprotective effects of endogenous alphaCGRP in Con A-induced chronic hepatitis.

METHODS

Chronic hepatitis was induced in alphaCGRP(-/-) and wild-type mice by repeated administration of Con A. Serum transaminases were measured to assess hepatic injury. The severity of fibrosis and the activation of hepatic stellate cells (HSCs) were analysed by Masson trichrome staining and immunohistochemical staining of alpha-smooth muscle actin (alpha-SMA) respectively. Altered expression of fibrosis- and inflammation-related genes was evaluated using a quantitative real-time polymerase chain reaction. Activation and proliferation of HSCs were analysed using both primary cultured HSCs from the mice and the LI90 HSC cell line.

RESULTS

alphaCGRP(-/-) mice showed more severe liver fibrosis than wild-type mice in a Con A-induced chronic hepatitis model. In histological and gene expression analyses, alphaCGRP(-/-) mice showed greater inflammatory and fibrotic changes, greater HSC activation and a higher incidence of apoptosis among nonparenchymal cells than wild-type mice.

CONCLUSIONS

Endogenous alphaCGRP mitigates liver fibrosis in chronic hepatitis induced by repeated administration of Con A. alphaCGRP could be a useful therapeutic target for the treatment of chronic hepatitis.

[The role of activated hepatic stellate cells in liver fibrosis, portal hypertension and cancer angiogenesis]

Although hepatic stellate cells, which are liver specific pericytes, have been recognized within the vasculature of the sinusoid for more than one hundred years, the biology and function of these cells is unclear. Recent studies have highlighted the key role of stellate cells in a number of fundamental processes that include wound healing/fibrosis, vasoregulation, and vascular remodeling/angiogenesis. In the liver, these processes are particularly important in the development of cirrhosis, portal hypertension and cancer. This article highlights the recent advances in our understanding of the biology of hepatic stellate cells and discusses some of the recently-ascribed functions that are relevant to liver fibrosis, portal hypertension and cancer angiogenesis.

Curcumin prevents and reverses cirrhosis induced by bile duct obstruction or CCl4 in rats: role of TGF-beta modulation and oxidative stress

Curcumin is a phytophenolic compound, which is highly efficacious for treating several inflammatory diseases. The aim of this study was to evaluate the efficacy of curcumin in preventing or reversing liver cirrhosis. A 4-week bile duct ligation (BDL) rat model was used to test the ability of curcumin (100 mg/kg, p.o., daily) to prevent cirrhosis. To reverse cirrhosis, CCl(4) was administered chronically for 3 months, and then it was withdrawn and curcumin administered for 2 months. Alanine aminotransferase, gamma-glutamyl transpeptidase, liver histopathology, bilirubin, glycogen, reduced and oxidized glutathione, and TGF-beta (mRNA and protein) levels were assessed. Curcumin preserved normal values of markers of liver damage in BDL rats. Fibrosis, assessed by measuring hydroxyproline levels and histopathology, increased nearly fivefold after BDL and this effect was partially but significantly prevented by curcumin. BDL increased transforming growth factor-beta (TGF-beta) levels (mRNA and proteins), while curcumin partially suppressed this mediator of fibrosis. Curcumin also partially reversed the fibrosis induced by CCl(4). Curcumin was effective in preventing and reversing cirrhosis, probably by its ability of reducing TGF-beta expression. These data suggest that curcumin might be an effective antifibrotic and fibrolitic drug in the treatment of chronic hepatic diseases.

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.

Immune interactions in hepatic fibrosis

Liver cirrhosis is caused by iterative cycles of tissue injury, inflammation, and repair. Although most causes of acute hepatitis resolve without scarring, chronic hepatitis is associated with persistent inflammation and matrix remodeling, which leads to fibrosis and, eventually, cirrhosis. The mechanisms that govern wound healing involve interactions between the innate and adaptive immune systems and stromal cells within a microenvironment composed of cytokines, growth factors, and modified matricellular proteins. The immune system plays a central role in the regulation of fibrosis, tissue repair, and recovery that is vital for the maintenance of tissue homeostasis. Chronic inflammation and fibrosis are inextricably linked and the cellular interactions between immune effector cells, local fibroblasts, and tissue macrophages at sites of scar formation determine the outcome of liver injury and the development of scarring.

Impact of the L-arginine-Nitric Oxide Pathway and Oxidative Stress on the Pathogenesis of the Metabolic Syndrome

The discovery of the physiological roles of nitric oxide has revolutionized the understanding of regulation of vascular tone, platelet adhesion and aggregation, and immune activation. Perhaps the most intriguing aspect of nitric oxide (NO) is that it is a gas that, in the absence of receptors, can regulate both normal physiological events and mediate cytotoxicity under pathological conditions. NO is produced from L-arginine by NO synthases (NOS), yielding L-citrulline and NO. The regulation of L-arginine pathway activity occurs at the level of NO production. The metabolic syndrome is a cluster of insulin resistance, elevated blood pressure, and atherogenic dyslipidemia, a common basis of cardiovascular disease. It occurs in genetically susceptible individuals with environmental influences and has serious economic and social consequences. Pharmacological and non-pharmacological therapies should be individualized and targeted to normalize its alterations of blood pressure, HDL cholesterol, triglycerides and glucose values. Despite the increasing prevalence of the metabolic syndrome in the last decades, there has been little progress in the understanding of the precise mechanisms involved in the pathogenesis of this syndrome and its complications. Emerging evidence is available that NO, inflammation and oxidative stress play important roles in the physiopathology of this syndrome. This review summarizes and evaluates the participation of the L-arginine-NO pathway and oxidative stress in the physiopathology of the metabolic syndrome and cardiovascular events at the systemic level, as well as the effects of exercise on this syndrome.

Severe liver steatosis correlates with nitrosative and oxidative stress in rats

BACKGROUND

Little is known about nitric oxide (NO) metabolism and redox changes with hepatocyte adipocytic transformation. The aims of this study were to investigate the changes occurring in plasma and hepatic NO metabolites and redox balance in a rat experimental model of simple fatty liver, and to relate plasma with hepatic and mitochondrial changes at different degrees of steatosis.

MATERIALS AND METHODS

Circulating and hepatic redox active and nitrogen regulating molecules thioredoxin, glutathione, protein thiols (PSH), mixed disulfides (PSSG), NO metabolites nitrosothiols, nitrite plus nitrate (NOx), and lipid peroxides (TBARs) were measured in rats fed a choline deprived (CD) diet for 30 days.

RESULTS

At histology, the CD diet resulted in hepatocellular steatosis (75% of liver weight at day 30) with no signs of necro-inflammation. In plasma, thioredoxin, nitrosothiols and NOx were unchanged, while TBARs levels increased significantly and were positively related with hepatic TBARs (r = 0.87, P < 0.001) and lipid content (r = 0.90, P < 0.001). In the liver, glutathione initially increased (day 3) and then decreased. From day 14, PSH decreased and NO derivatives increased. Thioredoxin 1 had initially increased (days 7-14) and then decreased. In the mitochondria, on day 14, nitrosothiols were inversely related to thioredoxin 2 (r = 0.988, P < 0.05); on day 30, PSH were decreased by 70%, PSSG were doubled and related with nitrosothiols levels (r = 0.925, P < 0.001).

CONCLUSION

Adipocytic transformation of hepatocytes is accompanied by major interrelated modifications of redox parameters and NO metabolism especially at mitochondrial level, suggesting an early adaptive protective response but also an increased predisposition towards pro-oxidant insults.

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-beta1 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 alpha-SMA indicating an activation of hepatic stellate cells. Since the profibrogenic effect of PDGF-A was accompanied by increased TGF-beta1 protein concentration in the liver of transgenic mice, it can be postulated that PDGF-A upregulates expression of TGF-beta1 which is a strong activator of hepatic stellate cells. Thus, these results point towards a fibrosis induction by PDGF-A via the TGF-beta1 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-beta1 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.

Beneficial drugs for liver diseases

Liver diseases are a major problem of worldwide proportions. However, the number of drugs actually used successfully in humans is very small. In this review some of the most promising/studied drugs utilized for liver diseases were chosen and analysed critically from the basic to the clinical point of view. Antiviral agents are not discussed because excellent reviews have appeared on this topic. The compounds/preparations described herein are, alphabetically: colchicine, corticosteroids, curcumin, glycyrrhizin, interferons (for their antifibrotic properties), Liv 52, nitric oxide, resveratrol, silymarin, sulfoadenosylmethionine, and thalidomide. Colchicine and corticosteroids have been studied extensively in animals and humans; most clinical studies suggest that these compounds are not useful in the treatment of liver diseases. Glycyrrhizin is an herbal medicine with several components that has interesting hepatoprotective properties in patients with subacute liver failure but deserves more prospective controlled trials. Interferon has shown interesting antifibrotic properties in animals and humans; prospective studies on their antifibrotic/fibrolytic activity are required. Curcumin, resveratrol and thalidomide are very attractive newly discovered protective and curative compounds on experimental hepatic diseases. Their mechanism of action is associated with the ability to down-regulate NF-kappaB and to decrease pronecrotic and profibrotic cytokines. Unfortunately, clinical studies are lacking. Sulfoadenosylmethionine and silymarin are also promising drugs utilized mainly in cholestasis but the benefits can be expanded if more controlled trials are performed. The future is to carry out controlled prospective double-blind multicenter studies with the newly discovered drugs with proven beneficial effects on animals. Fundamental hepatobiology should also be encouraged.

The effect of Ras inhibition on the proliferation, apoptosis and matrix metalloproteases activity in rat hepatic stellate cells

In vivo inhibition of Ras by its antagonist farnesylthiosalicylic acid (FTS) prevents and reverses liver fibrosis in a rat model. In this study we showed the in vitro effects of Ras inhibition in a rat hepatic stellate cell line, HSC-T6. The IC(50) of FTS that inhibited PDGF-induced proliferation was 15 microM. FTS, by itself or in combination with PDGF, induced a three- to fivefold increase in the number of apoptotic stellate cells but did not induce apoptosis in cells cultured with TGFbeta1. We observed increased activity of MMP-9 and MMP-2 induced by FTS in combination with PDGF or TGFbeta. FTS, alone or in the presence of PDGF and TGFbeta, reduced collagen I mRNA expression. In conclusion, the in vivo amelioration of liver fibrosis by FTS may be explained by its ability to inhibit hepatic stellate cell proliferation, induce apoptosis and MMP-2 and MMP-9 activity, and decrease collagen I expression.

Pressure loading and ethanol exposure differentially modulate rat hepatic stellate cell activation

Ethanol may cause an increase in sinusoidal pressure accompanied by portal hypertension. Hepatic stellate cells (HSCs) located in hepatic sinusoids may therefore be frequently exposed to dual stimulations of mechanical pressure and ethanol exposure in alcoholic liver injury. In this study, the effects of pressure loading and ethanol exposure on activation of rat cultured HSCs were investigated using an in vitro pressure-inducing apparatus. HSCs were cultured in media containing ethanol (0-100 mM) under different pressures (1-40 mmHg). Morphological changes and migration index were determined. We also determined the expression levels of alpha-smooth muscle actin (alpha-SMA) and mitogen-activated protein kinases (MAPKs) by Western blot analysis and the level of collagen IV and transforming growth factor beta1 (TGF-beta1) by ELISA. Pressure loading alone induced up-regulation of alpha-SMA via the extracellular signal-regulated kinases 1 and 2 (ERK1/2) and c-jun N-terminal kinase (JNK) signaling pathways, prolonged extension of marginal length, and increased production of collagen IV. In contrast, ethanol exposure alone increased only extension of marginal length and cell migration. Dual stimulations of pressure loading and ethanol exposure enhanced the production of TGF-beta1 and migration index. The TGF-beta1-dependent p38 MAPK pathway may operate for production of extracellular matrix (ECM) or enhanced migration in the case of dual stimulations. In conclusion, static pressure loading is an important factor directly accelerating the activation of HSCs. Although increased sinusoidal pressure and ethanol exposure might differentially modulate HSC activation, both stimuli are involved in an additive manner in some situations.

Suppressive effect of leflunomide on rat hepatic stellate cell proliferation involves on PDGF-BB-elicited activation of three mitogen-activated protein kinases

In this manuscript, we demonstrated that following stimulus by Kupffer cell-conditioned medium (KCM) and PDGF-BB, hepatic stellate cells (HSCs) showed significant increases in DNA synthesis and PDGFR-beta expression. Furthermore, phosphorylation of PDGFR-beta and three major members of the mitogen-activated protein kinase (MAPK) family were also significantly increased. Studies with respective neutralizing antibodies against released cytokines in conditioned medium demonstrated that PDGF-BB played an essential role in this complex activation process. Administration of A771726, leflunomide's metabolite, markedly blunted these effects. However, the combination of A771726 with any of the three MAPK inhibitors potentiated this inhibitory effect and showed completely blockage on PDGFR-beta expression and phosphorylation. Collectively, these data demonstrate that leflunomide inhibits KCM-mediated HSC proliferation via PDGFR-beta phosphorylation and the subsequent activation of the MAPK pathway. Accordingly, targeted intervention against the PDGF-BB isoform may also offer a promising therapeutic approach to liver fibrosis.

Bioconjugation of oligonucleotides for treating liver fibrosis

Liver fibrosis results from chronic liver injury due to hepatitis B and C, excessive alcohol ingestion, and metal ion overload. Fibrosis culminates in cirrhosis and results in liver failure. Therefore, a potent antifibrotic therapy is urgently needed to reverse scarring and eliminate progression to cirrhosis. Although activated hepatic stellate cells (HSCs) remain the principle cell type responsible for liver fibrosis, perivascular fibroblasts of portal and central veins as well as periductular fibroblasts are other sources of fibrogenic cells. This review will critically discuss various treatment strategies for liver fibrosis, including prevention of liver injury, reduction of inflammation, inhibition of HSC activation, degradation of scar matrix, and inhibition of aberrant collagen synthesis. Oligonucleotides (ODNs) are short, single-stranded nucleic acids, which disrupt expression of target protein by binding to complementary mRNA or forming triplex with genomic DNA. Triplex forming oligonucleotides (TFOs) provide an attractive strategy for treating liver fibrosis. A series of TFOs have been developed for inhibiting the transcription of alpha1(I) collagen gene, which opens a new area for antifibrotic drugs. There will be in-depth discussion on the use of TFOs and how different bioconjugation strategies can be utilized for their site-specific delivery to HSCs or hepatocytes for enhanced antifibrotic activities. Various insights developed in individual strategy and the need for multipronged approaches will also be discussed.

Homeobox Gene Prx1 Is Expressed in Activated Hepatic Stellate Cells and Transactivates Collagen α1(I) Promoter

Hepatic stellate cells (HSCs) are mesenchymal cells of the liver, which are normally in quiescent state and synthesize tracing amounts of extracellular matrix proteins. Upon fibrogenic stimulus, HSCs become activated and increase synthesis of type I collagen 50–100 fold. Prx1 and Prx2 are two homeobox transcription factors which are required for mesenchymal tissue formation during embryogenesis. The present study shows that Prx1 mRNA is expressed in in vivo and in vitro activated HSCs, but not in quiescent HSCs. Prx1 is also expressed in fibrotic livers, while it is undetectable in normal livers. Overexpression of Prx1a in quiescent HSCs cultured in vitro induced collagen α1(I) mRNA and TGFβ3 mRNA expression. Prx1 transactivated TGFβ3 promoter 3 fold in transient transfection experiments. In the whole liver, Prx1a induced expression of collagen α1(I), α2(I), α1(III) and α-smooth muscle mRNAs, which are the markers of activation of HSCs. Prx1 also increased expression of collagen α1(I) mRNA after acute liver injury. This suggests that Prx1a promotes activation of HSCs and expression of type I collagen. Several regions in the collagen α1(I) promoter were identified which mediate transcriptional induction by Prx1. The regions are scattered throughout the promoter and individually have modest effects; however, the cumulative effect of all sequences is >50 fold. This is the first description of the effects of Prx1 in HSCs and in the liver, and identification of the two Prx1 target genes, which play a pivotal role in development of liver fibrosis, is a novel finding for liver pathophysiology.

Liver cirrhosis and hepatic stellate cells

The cirrhosis represents the final stage of several chronic hepatic diseases and it is characterized by the presence of fibrosis and morphologic conversion from the normal hepatic architecture into structurally abnormal nodules. In the evolution of the disease there is loss of the normal vascular relationship and portal hypertension. There are also regenerative hepatocellular alterations that become more prominent with the progression of the disease. The liver transplantation continues to be the only therapeutic option in cases of disease in terminal phase. The hepatic stellate cells (HSC) are perisinusoidal cells that store vitamin A and produce growth factors, citocins, prostaglandins and other bioactive substances. They can suffer an activation process that convert them to cells with a phenotype similar to myofibroblasts. When activated, they present increased capacity of proliferation, mobility, contractility and synthesis of collagen and other components of extracellular matrix. They possess cytoplasmic processes adhered to sinusoids and can affect the sinusoidal blood flow. HSC are important in pathogenesis of fibrosis and portal hypertension.

Oxidative stress-induced risk factors associated with the metabolic syndrome: a unifying hypothesis

Although the biochemical steps linking insulin resistance with the metabolic syndrome have not been completely clarified, mounting experimental and clinical evidence indicate oxidative stress as an attractive candidate for a central pathogenic role since it potentially explains the appearance of all risk factors and supports the clinical manifestations. In fact, metabolic syndrome patients exhibit activation of biochemical pathways leading to increased delivery of reactive oxygen species, decreased antioxidant protection and increased lipid peroxidation. The described associations between increased abdominal fat storage, liver steatosis and systemic oxidative stress, the diminished concentration of nitric oxide derivatives and antioxidant vitamins and the endothelial oxidative damages observed in subjects with the metabolic syndrome definitively support oxidative stress as the common second-level event in a unifying pathogenic view. Moreover, it has been observed that oxidative stress regulates the expression of genes governing lipid and glucose metabolism through activation or inhibition of intracellular sensors. Diet constituents can modulate redox reactions and the oxidative stress extent, thus also acting on nuclear gene expression. As a consequence of the food-gene interaction, metabolic syndrome patients may express different disease features and extents according to the different pathways activated by oxidative stress-modulated effectors. This view could also explain family differences and interethnic variations in determining risk factor appearance. This review mechanistically focused on oxidative stress events leading to individual disease factor appearance in metabolic syndrome patients and their setting for a more helpful clinical approach.

Molecular mechanisms of hepatic fibrogenesis

Liver fibrosis, a wound-healing response to a variety of chronic stimuli, is characterized by excessive deposition of extracellular matrix (ECM) proteins, of which type I collagen predominates. This alters the structure of the liver leading to organ dysfunction. The activated hepatic stellate cell (HSC) is primarily responsible for excess collagen deposition during liver fibrosis. Two important aspects are involved in mediating the fibrogenic response: first the HSC becomes directly fibrogenic by synthesizing ECM proteins; second, the activated HSC proliferates, effectively amplifying the fibrogenic response. Although the precise mechanisms responsible for HSC activation remain elusive, substantial insight is being gained into the molecular mechanisms responsible for ECM production and cell proliferation in the HSC. The activated HSC becomes responsive to both proliferative (platelet-derived growth factor) and fibrogenic (transforming growth factor-beta[TGF-beta]) cytokines. It is becoming clear that these cytokines activate both mitogen-activated protein kinase (MAPK) signaling, involving p38, and focal adhesion kinase-phosphatidylinositol 3-kinase-Akt-p70 S6 kinase (FAK-PI3K-Akt-p70(S6K)) signaling cascades. Together, these regulate the proliferative response, activating cell cycle progression as well as collagen gene expression. In addition, signaling by both TGF-beta, mediated by Smad proteins, and p38 MAPK influence collagen gene expression. Smad and p38 MAPK signaling have been found to independently and additively regulate alpha1(I) collagen gene expression by transcriptional activation while p38 MAPK, but not Smad signaling, increases alpha1(I) collagen mRNA stability, leading to increased synthesis and deposition of type I collagen. It is anticipated that by understanding the molecular mechanisms responsible for HSC proliferation and excess ECM production new therapeutic targets will be identified for the treatment of liver fibrosis.

Signal transduction and activation of hepatic stellate cells

Liver fibrosis, which leads to cirrhosis, occurs as a result of various injurious processes and it is the common pathologic basis of all the chronic hepatic diseases. At present, a good many researches demonstrate that the activation of hepatic stellate cells play a critical role in fibrogenesis. Prolonged liver injury results in hepatocyte damages and secretion of many fibrogenic cytokines such as transforming growth factor-beta 1, angiotensin, and leptin, which triggers the activation of hepatic stellate cells through different intracellular signal transduction pathways. In this article, we reviewed the research advancement in the signal transduction pathway of nuclear receptor and membrane receptor during the activation of hepatic stellate cells.

Resistin as an intrahepatic cytokine: overexpression during chronic injury and induction of proinflammatory actions in hepatic stellate cells

Obesity and insulin resistance accelerate the progression of fibrosis during chronic liver disease. Resistin antagonizes insulin action in rodents, but its role in humans is still controversial. The aims of this study were to investigate resistin expression in human liver and to evaluate whether resistin may affect the biology of activated human hepatic stellate cells (HSCs), key modulators of hepatic fibrogenesis. Resistin gene expression was low in normal human liver but was increased in conditions of severe fibrosis. Up-regulation of resistin during chronic liver damage was confirmed by immunohistochemistry. In a group of patients with alcoholic hepatitis, resistin expression correlated with inflammation and fibrosis, suggesting a possible action on HSCs. Exposure of cultured HSCs to recombinant resistin resulted in increased expression of the proinflammatory chemokines monocyte chemoattractant protein-1 and interleukin-8, through activation of nuclear factor (NF)-kappaB. Resistin induced a rapid increase in intracellular calcium concentration, mainly through calcium release from intracellular inositol triphosphate-sensitive pools. The intracellular calcium chelator BAPTA-AM blocked resistin-induced NF-kappaB activation and monocyte chemoattractant protein-1 expression. In conclusion, this study shows a role for resistin as an intrahepatic cytokine exerting proinflammatory actions in HSCs, via a Ca2+/NF-kappaB-dependent pathway and suggests involvement of this adipokine in the pathophysiology of liver fibrosis.

Resistin as an intrahepatic cytokine: overexpression during chronic injury and induction of proinflammatory actions in hepatic stellate cells

Obesity and insulin resistance accelerate the progression of fibrosis during chronic liver disease. Resistin antagonizes insulin action in rodents, but its role in humans is still controversial. The aims of this study were to investigate resistin expression in human liver and to evaluate whether resistin may affect the biology of activated human hepatic stellate cells (HSCs), key modulators of hepatic fibrogenesis. Resistin gene expression was low in normal human liver but was increased in conditions of severe fibrosis. Up-regulation of resistin during chronic liver damage was confirmed by immunohistochemistry. In a group of patients with alcoholic hepatitis, resistin expression correlated with inflammation and fibrosis, suggesting a possible action on HSCs. Exposure of cultured HSCs to recombinant resistin resulted in increased expression of the proinflammatory chemokines monocyte chemoattractant protein-1 and interleukin-8, through activation of nuclear factor (NF)-kappaB. Resistin induced a rapid increase in intracellular calcium concentration, mainly through calcium release from intracellular inositol triphosphate-sensitive pools. The intracellular calcium chelator BAPTA-AM blocked resistin-induced NF-kappaB activation and monocyte chemoattractant protein-1 expression. In conclusion, this study shows a role for resistin as an intrahepatic cytokine exerting proinflammatory actions in HSCs, via a Ca2+/NF-kappaB-dependent pathway and suggests involvement of this adipokine in the pathophysiology of liver fibrosis.

Dynamic expression of extracellular signal-regulated kinase in rat liver tissue during hepatic fibrogenesis

AIM: To investigate whether extracellular signal-regulated kinase 1 (ERK₁) is activated and associated with hepatic stellate cell (HSC) proliferation in fibrotic rat liver tissue.

METHODS: Rat hepatic fibrosis was induced by bile duct ligation (BDL). Histopathological changes were evaluated by hematoxylin and eosin staining, and Masson’s trichrome method. ERK₁ mRNA in rat liver tissue was determined by reverse transcription-polymerase chain reaction, while the distribution of ERK₁ was assessed by immunohistochemistry. ERK₁ protein was detected by Western blotting analysis. The number of activated HSCs was quantified after alpha smooth muscle actin (α-SMA) staining.

RESULTS: With the development of hepatic fibrosis, the positive staining cells of α-SMA increased obviously, and mainly resided in the portal ducts. Fiber septa and perisinuses were accompanied with proliferating bile ducts. The positive staining areas of the rat livers in model groups 1-4 wk after ligation of common bile duct (12.88% ± 2.63%, 22.65% ± 2.16%, 27.45% ± 1.86%, 35.25% ± 2.34%, respectively) were significantly larger than those in the control group (5.88% ± 1.46%, P < 0.01). With the development of hepatic fibrosis, the positive cells of ERK₁ increased a lot, and were mainly distributed in portal ducts, fiber septa around the bile ducts, vascular endothelial cells and perisinusoidal cells. Western blotting analysis displayed that the expression of ERK₁ and ERK₂ protein was up-regulated during the model course, and its level was the highest 4 wk after operation, being 3.9-fold and 7.2-fold higher in fibrotic rat liver than in controls. ERK₁ mRNA was expressed in normal rat livers as well, which was up-regulated two days after BDL and reached the highest 4 wk after BDL. The expression of ERK₁ was positively correlated with α-SMA expression (r = 0.958，P < 0.05).

CONCLUSION: The expression of ERK₁ protein and mRNA is greatly increased in fibrotic rat liver tissues, which may play a key role in HSC proliferation and hepatic fibrogenesis.

Inhibition of TGFβ1-mediated PAI-1 induction by oltipraz through selective interruption of Smad 3 activation

Transforming growth factor-beta1 (TGFbeta1) induces plasminogen activator inhibitor-1 (PAI-1) as a major target protein. PAI-1 is associated with fibrosis, thrombosis, and metabolic disorders. TGFbeta1 induces PAI-1 via phosphorylation and nuclear translocation of Smads. Oltipraz inhibits TGFbeta1 expression and also regenerates cirrhotic liver. Nevertheless, whether oltipraz modulates TGFbeta1-mediated cell signaling is unclear. First, this study examined the effect of oltipraz on PAI-1 expression in cirrhotic rat liver. The cells immunochemically stained with anti-PAI-1 antibody accumulated around and within fibrous nodules in cirrhotic liver, which was notably decreased by oltipraz treatment. Next, whether oltipraz inhibits TGFbeta1-mediated Smads activation or Smad-mediated PAI-1 induction was determined in L929 fibroblasts. Oltipraz inhibited the ability of TGFbeta1 to induce PAI-1, as indicated by repression of TGFbeta1-mediated luciferase induction from the plasmid comprising the human PAI-1 promoter and of TGFbeta1-induced Smad-DNA-binding activity. TGFbeta1 induced nuclear transport of receptor-regulated Smad 2 and Smad 3, of which oltipraz selectively inhibited the transport and phosphorylation of Smad 3, thereby reducing formation of Smad 3/4 complex in the nucleus. In summary, oltipraz inhibits PAI-1 induction via a decrease in the formation of Smad 3/4 complex due to selective interruption of Smad 3 activation, indicating that oltipraz regulates the cellular responses downstream of ligand-activated TGFbeta1 receptor.

Therapeutic effects and molecular mechanisms of Ginkgo biloba extract on liver fibrosis in rats

Oxidative stress can be implicated as a cause of liver fibrosis. In this sense, Ginkgo Biloba Extract (EGB), an antioxidant, may be beneficial in restraining liver fibrosis. The aim of this study was to evaluate the effects of EGB on experimental liver fibrosis. Rat liver fibrosis was induced by intraperitoneal injection of carbon tetrachloride (CCl4) twice a week for 8 weeks. Three groups of rats received EGB (0.25, 0.5 and 1.0 g/kg, respectively) by stomach everyday. CCl4 administration induced liver fibrosis, which was inhibited by EGB in a dose-dependent manner. The histopathologic score of fibrosis, liver function and the levels of plasma hyaluronic acid (HA) and laminin (LN) were significantly improved in rats treated with CCl4 + EGB, compared with those treated with CCl4 only (p < 0.01 or p < 0.05). The activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were notably elevated, while malondialdehyde (MDA) content was significantly decreased in the rats treated with CCl4 + EGB (p < 0.01 or p < 0.05). Inhibition of hepatic stellate cell (HSC) activation and nuclear factor kappaBP65 (NF-kappaBP65) expression was demonstrated in the livers of EGB-treated rats. The activation of NF-kappaB was significantly suppressed in EGB-treated rats determined by electrophoretic mobility shift assay (EMSA). Furthermore, EGB reduced expressions of transforming growth factor-beta1 (TGF-beta1) and collagen I mRNA. In conclusion, EGB is able to ameliorate liver injury and prevent rats from CCl4-induced liver fibrosis by suppressing oxidative stress. This process may be related to inhibiting the induction of NF-kappaB on HSC activation and the expression of TGF-beta1.

Relationship between transforming growth factor β1 and anti-fibrotic effect of interleukin-10

AIM: To study the effect of interleukin-10 (IL-10) on the expression of transforming growth factor β1 (TGF-β1) in hepatic fibrosis rats and the anti-fibrotic role of exo-genous IL-10.

METHODS: Hepatic fibrosis was induced by carbon tetrachloride administered (CCl₄) intraperitoneally. The experiment was performed in two stages. In the first stage, 60 SD rats were divided randomly into normal control group 1(GN₁, n = 8), hepatic fibrosis group(GC, n = 28)and IL-10 intervened group(GI, n = 24). At the beginning of the 7^th and 11^th wk, hepatic stellate cells (HSCs) were isolated, reverse transcription-polymerase chain reation (RT-PCR) and immunocytochemistry were performed to detect the expression of TGF-β1 in HSCs. Histological examination was used to determine the degree of hepatic fibrosis. In the second stage, 47 SD rats were divided randomly into normal control group 2(GN₂, n = 6)and CCl₄ group(GZ, n = 41). At the end of the 9th week, rats in GZ group were allocated randomly into model group(GM, n = 9), IL-10 treatment group(GT, n = 9)and recovered group(GR, n = 9). At the end of the 12^th week, all rats were sacrificed. RT-PCR and immunohistochemistry were performed to detect the expression of TGF-β1 in liver tissue. ELISA was used to assay serum TGF-β1 levels.

RESULTS: Hepatic fibrosis developed in rats with the increase of the injection frequency of CCl₄. In the first stage, hepatic fibrosis developed and HSCs were isolated successfully. At the 7^th and 11^th week, TGF-β1 mRNA in GC group increased significantly compared with that in GN₁(P = 0.001/0.042)and GI groups(P = 0.001/0.007), whereas there was no significant difference between the two groups. The levels of TGF-β1 at the beginning of the 7^th wk was higher than that of the 11^th wk(P = 0.049). Immunocytochemistry results of TGF-β1 were consistent with the above findings. In the second stage, TGF-β1 increased significantly in GM group compared to GN₂. After treatment with IL-10, TGF-β1 declined obviously. The expression of TGF-β1 decreased in GR group but was still higher than that in GT group.

CONCLUSION: The levels of TGF-β1 are increased in hepatic fibrosis rats and decreased after treatment with exogenous IL-10. IL-10 may play an anti-fibrotic role by suppressing TGF-β1 expression.

Collagen binding alpha2beta1 and alpha1beta1 integrins play contrasting roles in regulation of Ets-1 expression in human liver myofibroblasts

Activation of hepatic stellate cells from quiescence to myofibroblast-like cells (MFBs) is a pivotal event in hepatic fibrogenesis. Plastic-cultured stellate cells (an established in vitro model of the activated phenotype) recultured on Matrigel revert to quiescence. In the present study we analyzed the molecular mechanism underlying this process, focusing on the effect of collagen receptors alpha(2)beta(1) and alpha(1)beta(1) integrin signaling on the expression of Ets-1 transcription factor and its target gene MMP1 in cultured human MFBs. Cells grown in 3-dimensional (3D) substrates (Matrigel) or collagen type I gel) markedly upregulated Ets-1 and MMP1 messages, in comparison to cells cultured on plastic. A similar effect but less intense was mimicked by stimulation of alpha(2)beta(1) or blocking of alpha(1)beta(1) integrin in cells grown on plastic. We observed increased expression of MMP1 transcripts with parallel changes in MMP1 promoter activity, and in mRNA and protein levels of upstream transcription factors Ets-1 and c-Jun. Interference with alpha(2)beta(1) and alpha(1)beta(1) integrin function in cells cultured in a 3D collagen substrate resulted in an even greater effect. Morphologically, stimulation of alpha(2)beta(1) integrin resulted in formation of multicellular networks, probably by facilitation of cell migration. Thus, we report the novel observation that in cultured human MFBs reverting to quiescence, the expression of transcription factor Ets-1 and its downstream target MMP1 can be modulated by changes in the microenvironment, which are mediated, at least in part, by the balance between collagen receptor integrin alpha(2)beta(1) and alpha(1)beta(1) activities.

[Hepatic stellate cells: it's role in normal and pathological conditions]

Hepatic fibrosis is a dynamic and sophisticatedly regulated wound healing response to chronic hepatocellular injury. This fibrotic process results from the accumulation of extracellular matrix (ECM) including collagen, proteoglycan, and adhesive glycoproteins which are principally produced by hepatic stellate cells (HSC), a mesenchymal cell type located between parenchymal cell plates and sinusoidal endothelial cells in the space of Disse. In physiological conditions, quiescent HSCs play important roles in the regulation of retinoid homeostasis and ECM remodeling by producing ECM components as well as metalloproteases and its inhibitor. However during hepatic fibrogenesis, HSCs are known to be activated or "transdifferentiated" to myofibroblast-like cells which play a pivotal role in ECM remodeling and hepatic blood flow regulation. Activation of HSC is now well established as the key process involved in the development of hepatic fibrosis. Both basic morphology and functions of HSCs in normal conditions and its role in pathological fibrosis will be discussed in this review.

Expression and location of Smad2, 4 mRNAs during and after liver fibrogenesis of rats

AIM: To investigate the location alteration of Smad2 and Smad4 mRNAs in the liver during and after fibrogenesis in rats.

METHODS: Eighty male Wistar rats weighing approximately 200 g each were used. The rat models of experimental hepatic fibrosis were established by injection with carbon tetrachloride (CCl₄), normal rats and rats were injected with olive oil and served as control groups. In situ hybridization(ISH) was used to detect the Smad2 and Smad4 mRNA in liver.

RESULTS: In situ hybridization showed Smad2 and Smad4 mRNA expressions in the cytoplasm of hepatic stellate cells (HSC), fibroblasts and myofibroblasts around the central vein and hepatic sinus during and after fibrogenesis. Expression of Smad2, 4 mRNA was higher than that in normal and control rats.

CONCLUSION: In the process of and after hepatic fibrosis formation, HSC, fibroblasts and myofibroblasts are the major cells that express Smad2 and Smad4. The more serious the hepatic fibrosis is in the injured liver, the higher the level of Smad2 and Smad4 gene expression is during and after fibrogenesis respectively.

Halofuginone induces matrix metalloproteinases in rat hepatic stellate cells via activation of p38 and NFkappaB

The semisynthetic plant alkaloid halofuginone (HAL) was reported to prevent and partly reverse experimental liver fibrosis. However, its mechanisms of action are poorly understood. We therefore aimed to determine the antifibrotic potential of HAL and to characterize involved signal transduction pathways in hepatic stellate cells (HSCs). Results were compared with its in vivo effects in a rat model of reversal of established liver fibrosis induced by thioacetamide. In vitro HAL inhibited HSC proliferation and migration dose dependently at submicromolar concentrations. HAL (200 nm) up-regulated matrix metalloproteinase (MMP)-3 and MMP-13 expression between 10- and 50-fold, resulting in a 2- to 3-fold increase of interstitial collagenase activity. Procollagen alpha1(I) and MMP-2 transcript levels were suppressed 2- to 3-fold, whereas expression of other profibrogenic mRNAs remained unaffected. p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor kappaB(NFkappaB) pathways were activated by HAL, and specific inhibitors of p38 MAPK and NFkappaB dose dependently inhibited MMP-13 induction. Treatment with HAL did not affect HSC viability, and observed effects were reversible after its removal. In vivo HAL up-regulated MMP-3 and -13 mRNA expression 1.5- and 2-fold, respectively, in cirrhotic rats, whereas tissue inhibitor of metalloproteinase-1 was suppressed by 50%. In conclusion, submicromolar concentrations of HAL inhibit HSC proliferation and migration and up-regulate their expression of fibrolytic MMP-3 and -13 via activation of p38 MAPK and NFkappaB. The remarkable induction of MMP-3 and -13 makes HAL a promising agent for antifibrotic combination therapies.

Involvement of phosphatidylinositol 3-kinase and extracellular-regulated kinase in hepatic stellate cell antioxidant response and myofibroblastic transdifferentiation

Liver fibrogenesis is dependent upon transdifferentiation of hepatic stellate cells to a profibrogenic phenotype. Prooxidant stress purportedly stimulates both an antioxidant response and myofibroblastic transdifferentiation with fibrogenic gene expression; however, mechanisms by which oxidative stress mediates stellate cell activation remain unclear. To this end, stellate cells were treated with tert-butylhydroquinone (tBHQ), a known inducer of antioxidant response genes. As anticipated, tBHQ induced expression of antioxidant response element (ARE)-regulated genes via the transcription factor Nrf2. Further, tBHQ promoted transdifferentiation of quiescent stellate cells cultured on Engelbreth-Holm-Swarm extracellular matrix. Pretreatment of cultured stellate cells with a phosphatidylinositol 3-kinase (PI3K) inhibitor blocked tBHQ-mediated ARE-dependent gene induction as well as stellate cell transdifferentiation. In contrast, extracellular signal-regulated kinase, which was demonstrated to be prominently phosphorylated following tBHQ treatment, was not found to affect either induction of the antioxidant response nor stellate cell transdifferentiation. These data implicate involvement of PI3K pathways in tBHQ-mediated stellate cell activation and demonstrate a requirement for PI3K in the antioxidant response of hepatic stellate cells.

Relaxin receptor expression in hepatic stellate cells and in cirrhotic rat liver tissue

Relaxin has antifibrotic effects on the hepatic stellate cells (HSCs) responsible for collagen deposition in cirrhosis. The expression of relaxin receptors LGR7 and LGR8 in HSCs and liver disease was examined. Activated and quiescent HSCs expressed LGR7, whereas only activated HSCs expressed LGR8. Relaxin, relaxin-3, or InsL3 treatment increased cAMP, suggesting activation of both receptors. LGR8 and LGR7 were present in cirrhotic rat liver, but were undetectable in normal liver. In conclusion, both LGR7 and LGR8 are expressed in activated HSCs and cirrhotic liver, suggesting that relaxin, InsL3, or relaxin-3 may be useful in the treatment of hepatic fibrosis.

Mechanisms of liver fibrosis

Liver fibrosis represents a significant health problem worldwide of which no acceptable therapy exists. The most characteristic feature of liver fibrosis is excess deposition of type I collagen. A great deal of research has been performed to understand the molecular mechanisms responsible for the development of liver fibrosis. The activated hepatic stellate cell (HSC) is the primary cell type responsible for the excess production of collagen. Following a fibrogenic stimulus, HSCs change from a quiescent to an activated, collagen-producing cell. Numerous changes in gene expression are associated with HSC activation including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses in understanding the molecular basis of collagen gene regulation have revealed a complex process offering the opportunity for multiple potential therapeutic strategies. However, further research is still needed to gain a better understanding of HSC activation and how this cell maintains its fibrogenic nature. In this review we describe many of the molecular events that occur following HSC activation and collagen gene regulation that contribute to the fibrogenic nature of these cells and provide a review of therapeutic strategies to treat this disease.

Liver fibrogenesis: a new role for the renin-angiotensin system

Liver fibrosis is the consequence of chronic liver injury of any etiology. When advanced, fibrosis causes portal hypertension and liver insufficiency, and is a risk factor for developing hepatocellular carcinoma. In the last decade, there have been major advances in the knowledge of the pathogenesis of hepatic fibrosis. Hepatic stellate cells (HSCs) are recognized as the main collagen-producing cells in the injured liver, and key fibrogenic factors have been identified. Among these factors, the renin-angiotensin system (RAS) appears to play a major role. Angiotensin II (Ang II) mediates key biological actions involved in hepatic tissue repair, including myofibroblast proliferation, infiltration of inflammatory cells, and collagen synthesis. Activated HSCs secrete Ang II, which induces fibrogenic actions through the activation of NADPH oxidase. Importantly, the blockade of the RAS attenuates fibrosis development in different experimental models of chronic liver injury. Based on these studies, it has been proposed that the blockade of the RAS could be effective in preventing fibrosis progression in chronic liver diseases. Although no prospective studies have evaluated the antifibrotic effect of RAS inhibitors in patients with chronic liver diseases, controlled clinical trials are under way.

Effect of IL-10 on the expression of HSC growth factors in hepatic fibrosis rat

AIM: To study the effect of IL-10 on the expression of growth factors - transforming growth factor-β1 (TGF-β1), epidermal growth factor (EGF), hepatocyte growth factor (HGF)and platelet-derived growth factor (PDGF) of hepatic stellate cells (HSCs) of hepatic fibrosis rat and the anti-fibrogenic role of exogenous IL-10.

METHODS: Hepatic fibrosis was induced by CCl4 administration intra-peritoneally. Sixty clean male Sprague-Dawley (SD) rats were randomly divided into three groups: normal control group (GN, 8 rats), hepatic fibrosis model group (GC, 28 rats) and IL-10 treated group (GI, 24 rats). At the beginning of the 7^th and 11^th wk, rats in each group were routinely perfused with pronase E and type IV collag-enase through a portal vein catheter and the suspension obtained from the liver was spun by centrifugation with 11% Nycodenz density gradient to isolate HSCs. Histological examination was used to determine the degree of hepatic fibrosis. RT-PCR was employed to analyze mRNA expression from freshly isolated cells. Immunocytochemistry was performed to detect protein expression in primary cultured HSCs.

RESULTS: Rat hepatic fibrosis was developed with the increase of injection frequency of CCl4, and HSCs were successfully isolated. At the 7^th and 11^th wk, TGF-β1, EGF, and HGF mRNA in GC increased obviously compared with GN (P = 0.001/0.042, 0.001/0.001, 0.001/0.001) and GI (P = 0.001/0.007, 0.002/0.001, 0.001/0.001). For TGF-β1, no difference was observed between GI and GN. For EGF, mRNA level in GI increased compared with GN during the 7^th wk (P = 0.005) and 11^th wk (P = 0.049). For HGF, mRNA level in GI decreased compared with GN at the 7^th wk (P = 0.001) and 11^th wk (P = 0.021). Between these two time points, TGF-β1 expression at the 7^th wk was higher than that of the 11^th wk (P = 0.049), but for EGF, the former was lower than the latter (P = 0.022). As for PDGF mRNA, there was no significant difference between these groups, but difference seemed to exist in protein levels. Results by immunocytochemistry of TGF-β1 and EGF were paralleled with the above findings.

CONCLUSION: The expression of TGF-β1, EGF and HGF increased in HSC of hepatic fibrosis rat and decreased after treatment with IL-10. IL-10 plays an anti-fibrogenic role by suppressing growth factors expression.

Effect of ligand of peroxisome proliferator-activated receptor gamma on the biological characters of hepatic stellate cells

AIM

To study the effect of rosiglitazone, which is a ligand of peroxisome proliferator-activated receptor gamma (PPARgamma), on the expression of PPARgamma in hepatic stellate cells (HSCs) and on the biological characteristics of HSCs.

METHODS

The activated HSCs were divided into three groups: control group, 3 micromol/L rosiglitazone group, and 10 micromol/L rosiglitazone group. The expression of PPARgamma, alpha-smooth muscle actin (alpha-SMA), and type I and III collagen was detected by RT-PCR, Western blot and immunocytochemical staining, respectively. Cell proliferation was determined with methylthiazolyltetrazolium (MTT) colorimetric assay. Cell apoptosis was demonstrated with flow cytometry.

RESULTS

The expression of PPARgamma at mRNA and protein level markedly increased in HSCs of 10 micromol/L rosiglitazone group (t value was 10.870 and 4.627 respectively, P<0.01 in both). The proliferation of HSCs in 10 micromol/L rosiglitazone group decreased significantly (t = 5.542, P<0.01), alpha-SMA expression level and type I collagen synthesis ability were also reduced vs controls (t value = 10.256 and 14.627 respectively, P<0.01 in both). The apoptotic rate of HSCs significantly increased in 10 micromol/L rosiglitazone group vs control (chi(2) = 16.682, P<0.01).

CONCLUSION

By increasing expression of PPARgamma in activated HSCs, rosiglitazone, an agonist of PPARgamma, decreases alpha-SMA expression and type I collagen synthesis, inhibits cell proliferation, and induces cell apoptosis.

Persistence of liver cirrhosis in association with proliferation of nonparenchymal cells and altered location of alpha-smooth muscle actin-positive cells

This study was carried out to achieve pathological understanding for the persistence of cirrhosis induced by thioacetamide (TAA). Forty-five, male,21-day-old, F344 rats were randomly allocated to group I and received drinking water as a control, and groups 2 and 3 given 0.015% or 0.03%TAA, respectively for 12 weeks. Two-third of animals per group were sacrificed, and remainder were maintained for a further 4 weeks without TAA treatment. Liver cirrhosis was induced in all animals in group 3 at week 12, with obvious increase of collagen content, and this persisted after cessation of TAA. Proliferating cell nuclear antigen (PCNA) positive labeling indices of nonparenchymal cells were increased significantly after cessation in groups 2 and 3 (p < 0.01). RT-RCR analysis of a-smooth muscle actin (alpha-SMA) showed significant increase in group 3 compared to that of control at both time points (p < 0.05). Immunohistochemical staining of it demonstrated positive cells to mainly be located around regenerating hepatic nodules at week 12, however, they were focused into enlarged portal areas consisting of fibrous tissues and pseudo-bile ductular cells after the cessation. Taken together, we conclude persistence of liver cirrhosis could be associated with the proliferation of nonparenchymal cells and altered location of alpha-SMA positive cells.

Effects of adrenomedullin gene overexpression on biological behavior of hepatic stellate cells

AIM: To investigate the effects of adrenomedullin (AM) gene overexpression on the biological characteristics of human hepatic stellate cells (hHSCs) by stable transfection.

METHODS: hHSCs which express low basal levels of AM were stably transfected with an expression construct containing rat AM gene or with an empty expression vector. Expression of AM in hHSCs was determined by reverse transcription (RT)-polymerase chain reaction (PCR) and radioimmunoassay (RIA). Cell proliferation was evaluated by 5-bromo-2’-deoxyuridine (BrdU) incorporation and immunocytochemistry. RT-PCR and Western blot were used to test the expression of procollagen types I and III. Protein expressions of interstitial collagenase (MMP-1), gelatinase (MMP-2) and tissue inhibitors of matrix metalloproteinases-2 (TIMP-2) were assessed by Western blot.

RESULTS: Two cell clones (A-2, A-8) transfected with the AM gene expressed higher levels of AM mRNA (non-transfected group: 0.86±0.11, empty vector group: 1.01±0.11, A-2 clone group: 1.44±0.08 and A-8 clone group: 1.36±0.05) and protein (12.31±0.17, 12.35±0.12, 12.56±0.06 and 12.62±0.07) (P<0.05). AM gene overexpression had inhibitory effects on cell proliferation of hHSCs (29.6%, 30.9%, 18.9% and 21.8%, respectively. P<0.05) and expression of procollagen type I (0.58±0.1, 0.48±0.11, 0.3±0.06 and 0.31±0.07 at mRNA level) (0.27±0.07, 0.3±0.06, 0.14±0.05 and 0.13±0.05 at protein level) (P<0.05) and procollagen type III (0.17±0.04, 0.15±0.03, 0.1±0.02 and 0.09±0.02 at mRNA level) (0.22±0.04, 0.2±0.03, 0.11±0.04 and 0.13±0.03 at protein level) (P<0.05). Compared with cells non-transfected (TIMP2: 2.77±0.03, MMP-2: 0.5±0.04, MMP-1: 0.49±0.07) and transfected with empty vector (TIMP2: 2.79±0.04, MMP-2: 0.48±0.03, MMP-1: 0.45±0.09), these two clones had lower expression levels of TIMP2(A-2 clone group: 2.7±0.02 and A-8 clone group: 2.71±0.02) (P<0.05) and MMP-2(A-2 clone group: 0.15±0.05 and A-8 clone group: 0.13±0.04) (P<0.05) but displayed a higher expression level of MMP-1(A-2 clone group: 0.68±0.06 and A-8 clone group: 0.81±0.09) (P<0.05).

CONCLUSION: AM gene exerts negative influence to some extent on hHSCs by inhibiting proliferation and production of extracellular matrix (ECM) in addition to inducing MMP-1 expression.

NAD(P)H oxidase plays a crucial role in PDGF-induced proliferation of hepatic stellate cells

The proliferation of hepatic stellate cells (HSCs) is a critical step in hepatic fibrogenesis. Platelet-derived growth factor (PDGF) is the most potent mitogen for HSCs. We investigated the role of nonphagocytic NAD(P)H oxidase-derived reactive oxygen species (ROS) in PDGF-induced HSC proliferation. The human HSC line, LI-90 cells, murine primary-cultured HSCs, and PDGF-BB were used in this study. We examined the mechanism of PDGF-BB-induced HSC proliferation in relation to the role of a ROS scavenger and diphenylene iodonium, an inhibitor of NAD(P)H oxidase. We also measured ROS production with the aid of chemiluminescence. We showed that PDGF-BB induced proliferation of HSCs through the intracellular production of ROS. We also demonstrated that HSCs expressed key components of nonphagocytic NAD(P)H oxidase (p22phox, gp91phox, p47phox, and p67phox) at both the messenger RNA and protein levels. Diphenylene iodonium suppressed PDGF-BB-induced ROS production and HSC proliferation. Coincubation of H2O2 and PDGF-BB restored the proliferation of HSCs that was inhibited by diphenylene iodonium pretreatment. Phosphorylation of the mitogen-activated protein kinase (MAPK) family constitutes a signal transduction pathway of cell proliferation. Our data demonstrate that NAD(P)H oxidase-derived ROS induce HSC proliferation mainly through the phosphorylation of p38 MAPK. Moreover, an in vivo hepatic fibrosis model also supported the critical role of NAD(P)H oxidase in the activation and proliferation of HSCs. In conclusion, NAD(P)H oxidase is expressed in HSCs and produces ROS via activation of NAD(P)H oxidase in response to PDGF-BB. ROS further induce HSC proliferation through the phosphorylation of p38 MAPK.

Efficacy of Chinese medicine Yi-gan-kang granule in prophylaxis and treatment of liver fibrosis in rats

AIM

To investigate the efficacy of a Chinese medicine, Yi-gan-kang granule (granules for benefiting the liver), in prophylaxis and treatment of liver fibrosis in rats and its possible mechanism.

METHODS

One hundred and forty Sprague-Dawley rats were randomly divided into seven groups (20 each): group 1, blank control group without any interference during the study; group 2, CCl4-induced liver fibrosis group; group 3, pig serum-induced liver fibrosis group; group 4, prophylaxis group of CCl4-induced liver fibrosis by Yi-gan-kang; group 5, prophylaxis group of pig serum-induced liver fibrosis by Yi-gan-kang; group 6, treatment group of CCl4-induced liver fibrosis by Yi-gan-kang; group 7, treatment group of CCl4-induced liver fibrosis by Yi-gan-kang. At wk 6, 10, 14 and 20 (baseline for CCl4 or big serum induction), five rats in each group were anesthetized and their livers were removed for pathological studies including immunohistochemical studies for alpha-SMA, type I collagen and in situ hybridization of tissue inhibitor of metalloproteinase-1 (TIMP-1) mRNA of hepatic stellate cells (HSCs). Anti-lipid peroxidation in isolated mitochondria and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay for proliferation and terminal deoxynucleotidyl transferase-medicated dUTP-biotin nick end-labeling (TUNEL), flow cytometry and electron microscopy for apoptosis in isolated HSCs were also studied.

RESULTS

The mean number of pseudolobuli at wk 10, 14 and 20 in the prophylaxis group was significantly less than that in the control group (P<0.05 or 0.01). The effect of prophylaxis at wk 14 in CCl4 rats and at wk 10 in pig serum-induced rats was much better than that of treatment group (P<0.01). The thickness (in microm) of fibers both in pig serum-induced prophylaxis and in treatment groups at wk 14 and 20 was significantly less than that in control group (P<0.05). The number of fibers both in prophylaxis and in treatment groups from wk 10 or 14 to 20 was significantly less than that in control group (P<0.05 or P<0.01). The tissue HSC positive rates of type I collagen, alpha-SMA and TIMP-1 mRNA, which represented the active phenotype of HSCs in tissues, remained very high from wk 6 to the end of model making in control group. While in prophylaxis group, they were at a relatively low level. In treatment group, there was a gradual decreasing trend. Time- and dose-dependent effects of anti-lipid peroxidation on isolated mitochondria, cell proliferation and apoptosis in cultured HSCs were also observed during the study.

CONCLUSION

Yi-gan-kang can effectively inhibit or inverse the course of liver fibrogenesis in CCl4- and pig serum-induced rat models.

Imatinib mesylate (STI-571) attenuates liver fibrosis development in rats

It is widely recognized that activated hepatic stellate cells (HSC) play a pivotal role in development of liver fibrosis. A platelet-derived growth factor (PDGF) is the most potent mitogen for HSC. The aim of this study was to examine the effect of imatinib mesylate (STI-571, Gleevec), a clinically used PDGF receptor (PDGFR) tyrosine kinase inhibitor, on development of experimental liver fibrosis. The rat model of pig serum-induced hepatic fibrosis was used to assess the effect of daily oral administration of STI-571 on the indexes of fibrosis. STI-571 markedly attenuated development of liver fibrosis and hepatic hydroxyproline and serum fibrosis markers. The number of alpha-smooth muscle actin-positive cells and mRNA expression of alpha2-(I)-procollagen, tissue inhibitor of metalloproteinases-1, and transforming growth factor-beta were also significantly suppressed by STI-571. Our in vitro study showed that STI-571 markedly attenuated PDGF-BB-induced proliferation and migration and alpha-SMA and alpha2-(I)-procollagen mRNA of activated HSC in a dose-dependent manner. STI-571 also significantly attenuated PDGF-BB-induced phosphorylation of PDGFR-beta, MEK1/2, and Akt in activated HSC. Because STI-571 is widely used in clinical practice, it may provide an effective new strategy for antifibrosis therapy.

Inhibitory effect of dicationic diphenylfurans on production of type I collagen by human fibroblasts and activated hepatic stellate cells

Excessive production of extracellular matrix is responsible for clinical manifestations of fibroproliferative disorders and drugs which can inhibit excessive synthesis of type I collagen are needed for the therapy. Several dicationic diphenylfurans were synthesized and were found to bind RNA. Two of these type compounds were able to reduce synthesis of type I collagen by human fibroblasts and human activated hepatic stellate cells (HSCs). Activated HSCs are responsible for collagen production in liver fibrosis. When added at 40 microM compound 588 reduced intracellular level and secretion of procollagen alpha1(I) by 50%, while compound 654 reduced these parameters by more than 80% at 20 microM. 654 also significantly reduced secretion of fibronectin. Toxic effects were observed at 80 microM for 588 and 40 microM for 654. 654 reduced expression of a reporter gene with collagen signal peptide, while expression of the same gene without signal peptide was unaffected. Also, expression of intracellular proteins tubulin and calnexin was unchanged. 654 accumulated inside the cell in the cytoplasm and did not change the steady-state level of collagen mRNAs. Treatment of cells with proteosome inhibitor MG132 did not change the inhibitory effect of 654, suggesting that 654 acts as suppressor of translation of proteins containing a signal peptide. Most secreted proteins of fibroblasts and activated HSCs are components of extracellular matrix. Therefore inhibition of their production, as shown here for procollagen alpha1(I) and fibronectin, may be a useful property of some of diphenylfurans, making these compounds a basis for development of antifibrotic drugs.

Effects of drug serum of anti-fibrosis I herbal compound on calcium in hepatic stellate cell and its molecular mechanism

AIM: To investigate the effects of anti-fibrosis I herbal compound on intracellular Ca²⁺ in activated hepatic stellate cell (HSC) and to try to survey its molecular mechanism in treatment and prevention of hepatic fibrosis and portal hypertension.

METHODS: The activated HSC line was plated on small glass cover slips in 24 wells culture dishes at a density of 5×10⁶ /mL, and incubated in RPMI-1640 media for 24 h. After the cells were loaded with Fluo-3/AM, intracellular Ca²⁺ was measured with laser scanning confocal microscopy (LSCM). The dynamic changes of intracellular Ca²⁺, stimulated by carbon tetrachloride, TGF-β₁ antibody and the drug serum of anti-fibrosis I herbal compound and under orthogonal design were determined by LSCM. The effect of anti-fibrosis I herbal compound on intracellular Ca²⁺ was observed before and after the addition of TGF-β₁ antibody.

RESULTS: The intracellular Ca²⁺ were significantly different in different dosage of carbon tetrachloride anti-fibrosis I formula drug serum, TGF-β₁ antibody and different turn of these substance, but their interval time between CCl₄ and TGF-β₁ antibody, CCl₄ and anti-fibrosis I drug serum had no influence on intracellular Ca²⁺. The result showed intracellular Ca²⁺ wasn’t significantly different between rat serum without anti-fibrosis I and untreated group. After carbon tetrachloride stimulation, intracellular Ca²⁺ of activated HSC increased significantly when the dosage of CCl₄ from 5 to 15 mmol/L, however, decreased significantly after stimulation by 5-20 μg/mL TGF-β₁ antibody or 5-20 mL/L drug serum. Moreover, before and after the addition of TGF-β₁ antibody, intracellular Ca²⁺ was significantly different. These results suggested that the molecular mechanism was independent of blocking TGF-β₁ effects.

CONCLUSION: Anti-fibrosis I herbal compound may treat hepatic fibrosis and decrease portal hypertension by inhibiting activated HSC contractility through decrease of intracellular Ca²⁺.

Zedoariae rhizoma and curcumin inhibits platelet-derived growth factor-induced proliferation of human hepatic myofibroblasts

During the course of liver fibrogenesis, hepatic myofibroblast cells (hMF), mostly derived from hepatic stellate cells (HSC), proliferate and synthesize excessive amounts of extracellular matrix (ECM) components. To evaluate the antiproliferative effect of a traditional herbal medicine, Zedoariae rhizoma water extracts (ZR) was examined on the growth inhibition of human hMF since proliferation of hMF is known to be central for the development of fibrosis during liver injury, and factors that may limit their growth are potential antifibrotic agents. The aim of this study was to test the effects of ZR on the proliferation and to clarify the molecular mechanisms of ZR inhibition of HSC proliferation in cultured human hMF. The cells were stimulated by platelet-derived growth factor (PDGF)-BB in the presence or absence of ZR. Proliferation was determined by bromodeoxy-uridine (BrdU) incorporation. The mRNA expressions of collagen alpha1(I) and (IV) were evaluated by a quantitative reverse transcription-polymerase chain reaction (RT-PCR). PDGF-receptor tyrosine phosphorylation was detected using anti-phosphotyrosine antibody. PDGF-receptor radioligand binding assay was performed by [125I]PDGF-BB. ZR inhibited the PDGF-BB-induced cell-proliferation and collagen alpha1(I) and (IV) mRNA expressions. ZR reduced the autophosphorylation of the PDGF-receptor. ZR blocked PDGF-BB binding to its receptor in a non-competitive manner. Furthermore, the 80% aqueous acetone extract of ZR was also found to show a decreasing effect against the proportion of S phase cells after PDGF stimulation. To clarify the active compounds, the principal constituents of seven sesquiterpenes (curdione, dehydrocurdione, germacrone, curcumenol, isocurcumenol, zedoarondiol and curcumenone) and a diarylheptanoid (curcumin) were examined. Among them, curcumin was found to decrease the proportion of S phase cells after PDGF stimulation at a dose of 30-50 microM. Potent antiproliferative and antifibrogenic effects of ZR toward hMF indicated that ZR might have therapeutic implications in chronic liver disease, indicating a novel role for ZR as a growth inhibitory mediator and pointing out its potential involvement in the negative regulation of liver fibrogenesis. In conclusion, ZR has an inhibitory effect on PDGF-induced proliferation of hMF and the blocking of PDGF-BB binding to its receptor may be the mechanism behind this effect.

Platelet-derived growth factor C induces liver fibrosis, steatosis, and hepatocellular carcinoma

Members of the platelet-derived growth factor (PDGF) ligand family are known to play important roles in wound healing and fibrotic disease. We show that both transient and stable expression of PDGF-C results in the development of liver fibrosis consisting of the deposition of collagen in a pericellular and perivenular pattern that resembles human alcoholic and nonalcoholic fatty liver disease. Fibrosis in PDGF-C transgenic mice, as demonstrated by staining and hydroxyproline content, is preceded by activation and proliferation of hepatic stellate cells, as shown by collagen, alpha-smooth muscle actin and glial fibrillary acidic protein staining and between 8 and 12 months of age is followed by the development of liver adenomas and hepatocellular carcinomas. The hepatic expression of a number of known profibrotic genes, including type beta1 TGF, PDGF receptors alpha and beta, and tissue inhibitors of matrix metalloproteinases-1 and -2, increased by 4 weeks of age. Increased PDGF receptor alpha and beta protein levels were associated with activation of extracellular regulated kinase-1 and -2 and protein kinase B. At 9 months of age, PDGF-C transgenic mice had enlarged livers associated with increased fibrosis, steatosis, cell dysplasia, and hepatocellular carcinomas. These studies indicate that hepatic expression of PDGF-C induces a number of profibrotic pathways, suggesting that this growth factor may act as an initiator of fibrosis. Moreover, PDGF-C transgenic mice represent a unique model for the study of hepatic fibrosis progressing to tumorigenesis.

Effects of c-myb antisense RNA on TGF-β1 and α1-I collagen expression in cultured hepatic stellate cells

AIM: To investigate the effects of c-myb antisense RNA on cell proliferation and the expression of c-myb, TGF-β1 and α1-I collagen in cultured hepatic stellate cells (HSC) from rats.

METHODS: Recombinant retroviral vector of c-myb antisense gene (pDOR-myb) was constructed, and then transfected into retroviral package cell line PA317 by means of DOTAP. The pseudoviruses produced from the resistant PA317 cells were selected with G418 to infect HSCs isolated from rat livers. The cell proliferation was measured by 3-[4, 5-Dimethylthiazolzyl]-2, 5-diphenyl tetrazo-dium bromide (MTT) method.The expression of c-myb, α1-I collagen and TGF-β1 mRNA, and c-myb protein in HSCs was detected with semi-quantitive reverse transeription-polymerase chain reaction (RT-PCR) and Western-blot respectively.

RESULTS: HSCs from rats were isolated successfully with the viability > 98%. In the pDOR-myb infected HSCs, the c-myb protein expression, cell proliferation,and α1-I collagen and TGF-β1 mRNA expression were repressed significantly compared with their corresponding control groups (P < 0.01).

CONCLUSION: c-myb plays a key role in activation and proliferation of HSC. c-myb antisense RNA can inhibit cell proliferation, α1-I collagen and TGF-β1 mRNA expression, suggesting that inhibition of c-myb gene expression might be a potential way for the treatment of liver fibrosis.

Hydrodynamic-based in vivo transfection of retinoic X receptor-alpha gene can enhance vitamin A-induced attenuation of liver fibrosis in mice

BACKGROUND/AIM

In hepatic stellate cells isolated from rat fibrotic livers, the amount of retinoid X receptor-alpha (RXR-alpha) mRNA is greatly reduced. However, the effectiveness of retinoids in the treatment of liver fibrosis is controversial. We hypothesized that increasing the expression levels of RXR-alpha in livers will improve the response of liver fibrosis to retinoids treatment.

METHODS

pTracer-CMV2 vector harboring both green fluorescent protein and RXR-alpha genes was given to mice with carbon tetrachloride (CCl(4))-induced liver fibrosis, by hydrodynamic-based in vivo transfection. Vitamin A was simultaneously administered to the mice. Sirius red staining and measurement of hydroxyproline content were performed to evaluate liver fibrosis. The incorporation of 5-bromo-2-deoxyribouridine (BrdU) was carried out to determine liver cell proliferation.

RESULTS

Successful transfection and expression of exogenous RXR-alpha gene in the liver was determined by observance of green fluorescence under a confocal microscope, and detection of RXR-alpha protein by immunohistochemistry. Hepatic fibrosis, evaluated by both Sirius red staining with image analysis and quantity of hydroxyproline in livers of RXR-alpha-transfected group, tapered off remarkably. The hydroxyproline content and Sirius red-positive staining area on liver sections from RXR-alpha-transfected mice decreased by 34.3% and 54.63%, respectively, compared with the control group receiving empty vector. The labeling index of BrdU in non-parenchymal cells was much lower in livers from the RXR-alpha-transfected group than that of empty vector-transfected group.

CONCLUSIONS

Hydrodynamic-based in vivo transfection of the RXR-alpha gene can enhance the vitamin A-induced attenuation of liver fibrosis in mice. One of the possible mechanisms of action for this gene treatment is inhibition of non-parenchymal cell proliferation mainly composed of hepatic stellate cells in fibrotic livers.

Antifibrotic effects of a tissue inhibitor of metalloproteinase-1 antibody on established liver fibrosis in rats

Liver fibrosis is characterized by increased synthesis, and decreased degradation, of extracellular matrix (ECM) within the injured tissue. Decreased ECM degradation results, in part, from increased expression of tissue inhibitor of metalloproteinase-1 (TIMP-1), which blocks matrix metalloproteinase (MMP) activity. TIMP-1 is also involved in promoting survival of activated hepatic stellate cells (HSCs), a major source of ECM. This study examined the effects of blocking TIMP-1 activity in a clinically relevant model of established liver fibrosis. Rats were treated with carbon tetrachloride (CCl(4)), or olive oil control, for 6 weeks; 24 days into the treatment, the rats were administered a neutralizing anti-TIMP-1 antibody derived from a fully human combinatorial antibody library (HuCAL), PBS, or an isotype control antibody. Livers from CCl(4)-treated rats exhibited substantial damage, including bridging fibrosis, inflammation, and extensive expression of smooth muscle alpha-actin (alpha-SMA). Compared to controls, rats administered anti-TIMP-1 showed a reduction in collagen accumulation by histological examination and hydroxyproline content. Administration of anti-TIMP-1 resulted in a marked decrease in alpha-SMA staining. Zymography analysis showed antibody treatment decreased the activity of MMP-2. In conclusion, administration of a TIMP-1 antibody attenuated CCl(4)-induced liver fibrosis and decreased HSC activation and MMP-2 activity.

Relationship between focal adhesion kinase and hepatic stellate cell proliferation during rat hepatic fibrogenesis

AIM: To investigate the dynamic expression of focal adhesion kinase (FAK) protein and FAK mRNA in fibrotic rat liver tissue, and the relationship between FAK and hepatic stellate cell (HSC) proliferation.

METHODS: Rat hepatic fibrosis was induced by bile duct ligation (BDL). Histopathological changes were evaluated by hematoxylin and eosin staining, and by Masson’s trichrome method. FAK mRNA in the rat livers was determined by reverse transcription-polymerase chain reaction (RT-PCR), and the distributions of FAK were assessed immunohistochemistrically. The number of activated HSCs was quantified after alpha smooth muscle actin (α -SMA) staining.

RESULTS: With the development of hepatic fibrosis, the positively stained cells of α -SMA increased obviously, which were mainly resided in the portal ducts, fiber septa and perisinuses accompanied with proliferating bile ducts. The positively stained areas of the rat livers in model groups 1 to 4 wk after ligation of common bile duct (12.88 ± 2.63%, 22.65 ± 2.16%, 27.45 ± 1.86%, 35.25 ± 2.34%, respectively) were significantly larger than those in the control group (5.88 ± 1.46%) (P < 0.01). The positive staining for FAK significantly increased, which was mainly situated in portal ducts, fiber septa and around the bile ducts, vascular endothelial cells and perisinusoidal cells. The expression of FAK was positively correlated with α -SMA expression (r = 0.963, P < 0.05). FAK mRNA expression was obviously up-regulated in the model groups compared to the control group.

CONCLUSION: These data suggest that expressions of FAK protein and mRNA are greatly increased in fibrotic rat livers, which may play an important role in HSC proliferation and hepatic fibrogenesis.