Monocyte chemotactic protein-1 as a chemoattractant for human hepatic stellate cells

Functional linkage of cirrhosis-predictive single nucleotide polymorphisms of Toll-like receptor 4 to hepatic stellate cell responses

In a recent study, a single nucleotide polymorphism (SNP) of the Toll-like receptor 4 (TLR4) gene (c.1196C>T [rs4986791, p.T399I]) emerged as conferring protection from fibrosis progression compared to a major, wild-type (WT) CC allele (p.T399). The present study examined the functional linkage of this SNP, along with another common, highly cosegregated TLR4 SNP (c.896A>G [rs4986790, p.D299G]), to hepatic stellate cell (HSC) responses. Both HSCs from TLR4(-/-) mice and a human HSC line (LX-2) reconstituted with either TLR4 D299G and/or T399I complementary DNAs were hyporesponsive to lipopolysaccharide (LPS) stimulation compared to those expressing WT TLR4, as assessed by the expression and secretion of LPS-induced inflammatory and chemotactic cytokines (i.e., monocyte chemoattractant protein-1, interleukin-6), down-regulation of bone morphogenic protein and the activin membrane-bound inhibitor expression (an inhibitory transforming growth factor beta pseudoreceptor), and activation of a nuclear factor kappaB (NF-kappaB)-responsive luciferase reporter. In addition, spontaneous apoptosis, as well as apoptosis induced by pathway inhibitors of NF-kappaB, extracellular signal-regulated kinase (ERK), and phosphatidylinositol 3-kinase were greatly increased in HSCs from either TLR4(-/-) or myeloid differentiation factor 88(-/-) (a TLR adaptor protein) mice, as well as in murine HSCs expressing D299G and/or T399I SNPs; increased apoptosis in these lines was accompanied by decreased phospho-ERK and Bcl-2.

CONCLUSION

TLR4 D299G and T399I SNPs that are associated with protection from hepatic fibrosis reduce TLR4-mediated inflammatory and fibrogenic signaling and lower the apoptotic threshold of activated HSCs. These findings provide a mechanistic link that explains how specific TLR4 SNPs may regulate the risk of fibrosis progression.

Chemokines in the immunopathogenesis of hepatitis C infection

Chronic infection with the hepatitis C virus, a noncytopathic hepatotropic RNA virus, affects over 170 million people worldwide. In the majority of cases, neither the early innate immune response nor the later adaptive immune response succeeds in clearing the virus, and the infection becomes chronic. Furthermore, in many patients, the ineffective inflammatory response drives fibrogenesis and the development of cirrhosis. It is critical to understand this immune pathology if preventative and curative therapies are to be developed. Chemokines are a superfamily of small proteins that promote leukocyte migration and orchestrate the immune response to viruses, including hepatitis C virus. Chemokines are crucial for viral elimination, but inappropriate persistence of expression in chronic hepatitis C infection can drive tissue damage and inflammation. Here we review the role of chemokines and their receptors in hepatitis C virus infection.

Fibrogenesis in pediatric cholestatic liver disease: role of taurocholate and hepatocyte-derived monocyte chemotaxis protein-1 in hepatic stellate cell recruitment

Cholestatic liver diseases, such as cystic fibrosis (CF) liver disease and biliary atresia, predominate as causes of childhood cirrhosis. Despite diverse etiologies, the stereotypic final pathway involves fibrogenesis where hepatic stellate cells (HSCs) are recruited, producing excess collagen which initiates biliary fibrosis. A possible molecular determinant of this recruitment, monocyte chemotaxis protein-1 (MCP-1), an HSC-responsive chemokine, was investigated in CF liver disease and biliary atresia. The bile-duct-ligated rat and in vitro coculture models of cholestatic liver injury were used to further explore the role of MCP-1 in HSC recruitment and proposed mechanism of induction via bile acids. In both CF liver disease and biliary atresia, elevated hepatic MCP-1 expression predominated in scar margin hepatocytes, closely associated with activated HSCs, and was also expressed in cholangiocytes. Serum MCP-1 was elevated during early fibrogenesis. Similar observations were made in bile-duct-ligated rat liver and serum. Hepatocytes isolated from cholestatic rats secreted increased MCP-1 which avidly recruited HSCs in coculture. This HSC chemotaxis was markedly inhibited in interventional studies using anti-MCP-1 neutralizing antibody. In CF liver disease, biliary MCP-1 was increased, positively correlating with levels of the hydrophobic bile acid, taurocholate. In cholestatic rats, increased MCP-1 positively correlated with taurocholate in serum and liver, and negatively correlated in bile. In normal human and rat hepatocytes, taurocholate induced MCP-1 expression.

CONCLUSION

These observations support the hypothesis that up-regulation of hepatocyte-derived MCP-1, induced by bile acids, results in HSC recruitment in diverse causes of cholestatic liver injury, and is a key early event in liver fibrogenesis in these conditions. Therapies aimed at neutralizing MCP-1 or bile acids may help reduce fibro-obliterative liver injury in childhood cholestatic diseases.

Paraoxonase-1 is related to inflammation, fibrosis and PPAR delta in experimental liver disease

BACKGROUND

Paraoxonase-1 (PON1) is an antioxidant enzyme synthesized by the liver. It protects against liver impairment and attenuates the production of the pro-inflammatory monocyte chemoattractant protein-1 (MCP-1). We investigated the relationships between hepatic PON1 and MCP-1 expression in rats with liver disease and explored the possible molecular mechanisms involved.

METHODS

CCl4 was administered for up to 12 weeks to induce liver damage. Serum and hepatic levels of PON1 and MCP-1, their gene and protein expression, nuclear transcription factors, and histological and biochemical markers of liver impairment were measured.

RESULTS

High levels of PON1 and MCP-1 expression were observed at 12th week in the hepatocytes surrounding the fibrous septa and inflammatory areas. CCl4-administered rats had an increased hepatic PON1 concentration that was related to decreased gene transcription and inhibited protein degradation. Decreased PON1 gene transcription was associated with PPARdelta expression. These changes were accompanied by increased hepatic MCP-1 concentration and gene expression. There were significant direct relationships between hepatic PON1 and MCP-1 concentrations (P = 0.005) and between PON1 and the amount of activated stellate cells (P = 0.001).

CONCLUSION

Our results from this experimental model suggest a hepato-protective role for PON1 against inflammation, fibrosis and liver disease mediated by MCP-1.

Paraoxonase-1 is related to inflammation, fibrosis and PPAR delta in experimental liver disease

BACKGROUND

Paraoxonase-1 (PON1) is an antioxidant enzyme synthesized by the liver. It protects against liver impairment and attenuates the production of the pro-inflammatory monocyte chemoattractant protein-1 (MCP-1). We investigated the relationships between hepatic PON1 and MCP-1 expression in rats with liver disease and explored the possible molecular mechanisms involved.

METHODS

CCl4 was administered for up to 12 weeks to induce liver damage. Serum and hepatic levels of PON1 and MCP-1, their gene and protein expression, nuclear transcription factors, and histological and biochemical markers of liver impairment were measured.

RESULTS

High levels of PON1 and MCP-1 expression were observed at 12th week in the hepatocytes surrounding the fibrous septa and inflammatory areas. CCl4-administered rats had an increased hepatic PON1 concentration that was related to decreased gene transcription and inhibited protein degradation. Decreased PON1 gene transcription was associated with PPARdelta expression. These changes were accompanied by increased hepatic MCP-1 concentration and gene expression. There were significant direct relationships between hepatic PON1 and MCP-1 concentrations (P = 0.005) and between PON1 and the amount of activated stellate cells (P = 0.001).

CONCLUSION

Our results from this experimental model suggest a hepato-protective role for PON1 against inflammation, fibrosis and liver disease mediated by MCP-1.

Intracellular calcium signals regulate growth of hepatic stellate cells via specific effects on cell cycle progression

Hepatic stellate cells (HSC) are important mediators of liver fibrosis. Hormones linked to downstream intracellular Ca(2+) signals upregulate HSC proliferation, but the mechanisms by which this occurs are unknown. Nuclear and cytosolic Ca(2+) signals may have distinct effects on cell proliferation, so we expressed plasmid and adenoviral constructs containing the Ca(2+) chelator parvalbumin (PV) linked to either a nuclear localization sequence (NLS) or a nuclear export sequence (NES) to block Ca(2+) signals in distinct compartments within LX-2 immortalized human HSC and primary rat HSC. PV-NLS and PV-NES constructs each targeted to the appropriate intracellular compartment and blocked Ca(2+) signals only within that compartment. PV-NLS and PV-NES constructs inhibited HSC growth. Furthermore, blockade of nuclear or cytosolic Ca(2+) signals arrested growth at the G2/mitosis (G2/M) cell-cycle interface and prevented the onset of mitosis. Blockade of nuclear or cytosolic Ca(2+) signals downregulated phosphorylation of the G2/M checkpoint phosphatase Cdc25C. Inhibition of calmodulin kinase II (CaMK II) had identical effects on LX-2 growth and Cdc25C phosphorylation. We propose that nuclear and cytosolic Ca(2+) are critical signals that regulate HSC growth at the G2/M checkpoint via CaMK II-mediated regulation of Cdc25C phosphorylation. These data provide a new logical target for pharmacological therapy directed against progression of liver fibrosis.

MCP-1-induced migration of NT2 neuroprogenitor cells involving APP signaling

Neuroprogenitor cells are an important resource because of their great potential to replace damaged cells in the brain caused by trauma and disease. Studies have shown that when neuroprogenitor cells are transplanted into the brain they migrate towards damaged areas, suggesting that these areas express factors that recruit migrating cells. Generally, after neuronal injury, there is a neuroinflammatory response that results in increased chemokine production. In this present study, we demonstrate that monocyte chemoattractant protein-1 (MCP-1) significantly induces the migration of NT2 neuroprogenitor cells. Activation of intracellular cyclic adenosine monophosphate or protein kinase C with forskolin and phorbol 12-myristate 13-acetate, respectively, was able to completely abolish the MCP-1-induced migration. Contrarily, neither extracellular signal-regulated kinase nor p38 mitogen-activated protein kinase was required for NT2 cells to respond to MCP-1. Previously, we showed that amyloid precursor protein (APP) activity increases MCP-1 expression in NT2 cells. We now demonstrate that NT2 cells expressing APP can induce migration of other neuroprogenitor cells. Utilizing a MCP-1 neutralizing antibody, we discovered that APP-induced migration was not caused solely by increased MCP-1 production. Interestingly, APP-increased expression of several C-C chemokines: MCP-1, regulated upon activation, normal T-cell expressed, and secreted (RANTES), and macrophage inflammatory protein alpha (MIP-1 alpha). This demonstrates the unique role APP has in regulating chemokine production, which directly affects cell migration. Taken together, these data provides greater detail of the chemotactic factors and intracellular signaling that direct neuroprogenitor cell migration, allowing for better understanding of cell migration during transplantation.

Induction of matrix metalloproteinase-1 gene transcription by tumour necrosis factor alpha via the p50/p50 homodimer of nuclear factor-kappa B in activated human hepatic stellate cells

BACKGROUND/AIMS

Liver injury results in the activation of hepatic stellate cells (HSCs), which in turn produce matrix metalloproteinase (MMP) in response to pro-inflammatory cytokines for tissue remodelling. This study explored the transcriptional induction of the MMP-1 gene by tumour necrosis factor-alpha (TNF-alpha) in HSCs.

METHODS

The LI90 human HSC line was used in the present study. Gelatin zymography, enzyme-linked immunosorbent assay, Northern blotting and gene promoter-reporter assays were used to analyse the induction of MMP-1 protein, mRNA expression and gene transcription respectively. Deletional or site-directed mutations were introduced into the promoter region and transiently transfected into LI90 cells to determine the cis-acting elements necessary for TNF-alpha inducibility. Gel shift mobility assays were used to determine the transcriptional factors involved in the TNF-alpha responsiveness.

RESULTS

TNF-alpha upregulated MMP-1 protein and mRNA expression in a dose-dependent manner. A time-course experiment revealed a rapid induction of MMP-1 mRNA expression after TNF-alpha treatment. Mutation in a putative nuclear factor (NF)-kappaB-binding site at -2541 bp almost completely abolished the TNF-alpha response to MMP-1 gene-promoter activity, suggesting transcriptional regulation of MMP-1 expression by TNF-alpha via this site. Electrophoretic mobility shift assay and supershift assays indicated that this transcriptional regulation was regulated via the p50/p50 homodimer of NF-kappaB.

CONCLUSIONS

MMP-1 gene expression might be induced by TNF-alpha via the p50/p50 homodimer of NF-kappaB in activated human HSCs.

Advances in antifibrotic therapy

Sustained progress in defining the molecular pathophysiology of hepatic fibrosis has led to a comprehensive framework for developing antifibrotic therapies. Indeed, the single greatest limitation in bringing new drugs to the clinical setting is a lack of clarity regarding clinical trial and treatment end points, not a lack of promising agents. A range of treatments, including those developed for other indications, as well as those specifically developed for hepatic fibrosis, are nearing or in clinical trials. Most are focused on attacking features of either hepatic injury and/or activated stellate cells and myofibroblasts, which are the primary sources of extracellular matrix (scar) proteins. Thus, features of injury and stellate cell activation provide a useful template for classifying these emerging agents and point to a new class of therapies for patients with fibrosing liver disease.

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.

Cytokines and renin-angiotensin system signaling in hepatic fibrosis

Hepatic fibrosis is the result of a complex interplay between resident hepatic cells, infiltrating inflammatory cells, and a number of locally acting peptides called cytokines. Key mediators include transforming growth factor b1, vasoactive substances, adipokines, inflammatory cytokines and chemokines. Angiotensin II, the main effector of the renin-angiotensin system, is a true cytokine that plays a major role in liver fibrosis. Angiotensin II is locally synthesized in the injured liver and induces profibrogenic actions in hepatic stellate cells. Drugs blocking the renin-angiotensin system are promising antifibrotic agents. There are multiple signal transduction pathways involved in cytokine signaling. Drugs interfering intracellular pathways involved in increased collagen production are potential therapies for liver fibrosis.

Recognition of genetic factors influencing the progression of hepatitis C : potential for personalized therapy

Infection with hepatitis C virus (HCV) is a major cause of chronic liver disease. Hepatic fibrosis may develop in subjects with chronic HCV infection, culminating in cirrhosis and an increased risk of hepatocellular carcinoma. The rate of development of fibrosis varies substantially between individuals; while it is influenced by a number of demographic and environmental factors, these account for only a small proportion of the variability. There are no clinical markers or tests that predict the rate of fibrosis progression in an individual subject. Thus, there has been increasing interest in the influence of host genetic factors on the rate of disease progression, and whether a genetic signature can be developed to reliably identify individuals at risk of severe disease. Numerous case-control, candidate gene, allele-association studies have examined the relationship between host single nucleotide polymorphisms or other genetic mutations and fibrosis in patients with chronic HCV infection. However, these studies have generally been irreproducible and disappointing. As seen with genetic studies for other diseases, small study cohorts and poor study design have contributed to limited meaningful findings. The successful determination of genetic signatures for fibrosis progression in chronic HCV will require multicenter collaborations using genome-wide association studies, with large, phenotypically well-defined sample sets. While these studies will require a significant financial commitment, a successful outcome offers the potential for personalized therapy and better patient management.

Redox mechanisms in hepatic chronic wound healing and fibrogenesis

Reactive oxygen species (ROS) generated within cells or, more generally, in a tissue environment, may easily turn into a source of cell and tissue injury. Aerobic organisms have developed evolutionarily conserved mechanisms and strategies to carefully control the generation of ROS and other oxidative stress-related radical or non-radical reactive intermediates (that is, to maintain redox homeostasis), as well as to 'make use' of these molecules under physiological conditions as tools to modulate signal transduction, gene expression and cellular functional responses (that is, redox signalling). However, a derangement in redox homeostasis, resulting in sustained levels of oxidative stress and related mediators, can play a significant role in the pathogenesis of major human diseases characterized by chronic inflammation, chronic activation of wound healing and tissue fibrogenesis. This review has been designed to first offer a critical introduction to current knowledge in the field of redox research in order to introduce readers to the complexity of redox signalling and redox homeostasis. This will include ready-to-use key information and concepts on ROS, free radicals and oxidative stress-related reactive intermediates and reactions, sources of ROS in mammalian cells and tissues, antioxidant defences, redox sensors and, more generally, the major principles of redox signalling and redox-dependent transcriptional regulation of mammalian cells. This information will serve as a basis of knowledge to introduce the role of ROS and other oxidative stress-related intermediates in contributing to essential events, such as the induction of cell death, the perpetuation of chronic inflammatory responses, fibrogenesis and much more, with a major focus on hepatic chronic wound healing and liver fibrogenesis.

Monocyte chemoattractant protein-1 secreted by adipose tissue induces direct lipid accumulation in hepatocytes

For many years, adipose tissue has been mainly considered as an inert reservoir for storing triglycerides. Since the discovery that adipocytes may secrete a variety of bioactive molecules (hormones, chemokines, and cytokines), an endocrine and paracrine role for white adipose tissue (WAT) in the regulation of energy balance and other physiological processes has been established, particularly with regard to brain and muscle. In contrast, little is known about the interactions of WAT with liver. Hence, we examined the effect of the secretory products of WAT on hepatocytes. Conditioned medium of human WAT explants induced significant steatosis in hepatocyte cell lines. Factor(s) responsible for the conditioned medium-induced steatosis were screened by a battery of blocking antibodies against different cytokines/chemokines shown to be secreted by WAT. In contrast to interleukin-8 and interleukin-6, the monocyte chemoattractant protein-1 was capable of inducing steatosis in hepatocytes in a time-dependent manner at concentrations similar to those found in conditioned medium. Incubation of conditioned medium with antimonocyte chemoattractant protein-1 antibodies prevented triglyceride accumulation. Investigation of the mechanism leading to the triglyceride accumulation showed that both a diminution of apolipoprotein B secretion and an increase in phosphoenolpyruvate carboxykinase messenger RNA may be involved.

CONCLUSION

The monocyte chemoattractant protein-1 secreted by adipose tissue may induce steatosis not only recruiting macrophages but also acting directly on hepatocytes.

Advanced glycation end products enhance the proliferation and activation of hepatic stellate cells

BACKGROUND

Advanced glycation end products (AGEs), final reaction products of protein with sugars, are known to contribute to diabetes-related complications. We have recently demonstrated high levels of serum AGEs in patients with nonalcoholic steatohepatitis (NASH). However, direct evidence for the participation of AGEs in hepatic inflammation and fibrosis has not been shown. To explore the pathogenesis of NASH, we examined the biological infl uence of AGEs on hepatic stellate cells (HSCs) in vitro.

METHODS

An established human HSC line, LI90, was exposed to a glyceraldehyde-derived-AGE (glycer-AGE), and the phenotypical changes of the LI90 cells were investigated. Intracellular formation of reactive oxygen species (ROS) was measured using a fl uorescent probe. Cell proliferation was examined by MTS assay. Fibrogenic marker gene expression was analyzed by quantitative real-time polymerase chain reaction. The production of monocyte chemoattractant protein 1 (MCP-1) was assessed by enzyme-linked immunosorbent assay.

RESULTS

The expression of AGE receptor was confirmed in LI90 cells at the mRNA and protein levels. In addition to increasing intracellular ROS generation, glycer-AGE upregulated fibrogenic genes such as those encoding for alpha-smooth muscle actin, transforming growth factor-beta1, and collagen type Ialpha2. The expression of MCP-1 mRNA in LI90 cells as well as its secretion into the culture medium was significantly increased in response to AGEs. These changes were attenuated by treatment with the antioxidant N-acetylcysteine.

CONCLUSIONS

These data indicate that AGEs induce ROS generation and intensify the proliferation and activation of HSCs, supporting the possibility that antioxidants may represent a promising treatment for prevention of the development of hepatic fibrosis in NASH.

Hepatic fibrosis -- overview

The study of hepatic fibrosis, or scarring in response to chronic liver injury, has witnessed tremendous progress in the past two decades. Clarification of the cellular sources of scar, and emergence of hepatic stellate cells not only as a fibrogenic cell type, but also as a critical immunomodulatory and homeostatic regulator are among the most salient advances. Activation of hepatic stellate cells remains a central event in fibrosis, complemented by evidence of additional sources of matrix-producing cells including bone marrow, portal fibroblasts, and epithelial-mesenchymal transition from both hepatocytes and cholangiocytes. A growing range of cytokines and their receptors and inflammatory cell subsets have further expanded our knowledge about this dynamic process. Collectively, these findings have laid the foundation for continued elucidation of underlying mechanisms, and more importantly for the implementation of rationally based approaches to limit fibrosis, accelerate repair and enhance liver regeneration in patients with chronic liver disease.

The role of adipokines in liver fibrosis

Liver fibrosis is a dynamic process consisting of the chronic activation of the wound healing reaction in response to reiterated liver damage, leading to the excessive deposition of fibrillar extracellular matrix into the liver and eventually, if the cause of injury is not removed, to liver cirrhosis. The term "adipokines" identifies a group of polypeptide molecules secreted primarily by adipose tissue, which exert local, peripheral and/or central actions. Additionally to their well-established role in controlling adipose tissue physiology, adipokines have been shown to be involved in different obesity-related diseases, such as hypertension, atherosclerosis and type 2 diabetes. Accumulating data demonstrate that obesity and insulin resistance are associated with a more severe and faster progression of the fibrogenic process in different chronic liver diseases. Therefore, numerous recent studies have analyzed the role played by adipokines in the hepatic wound healing process, identifying novel roles as modulators of liver pathophysiology. This review summarizes the more significant and recent findings concerning the role played by adipocyte-derived molecules, such as leptin, adiponectin and resistin, in the liver fibrogenic process. The actions of different adipokines on the biology of liver resident cells, as well as their effects in different animal models of liver injury are discussed. The variations in the circulating levels and in the intrahepatic expression of these molecules occurring in patients with different chronic liver diseases will be also analyzed.

Mechanisms of hepatic fibrogenesis

Substantial improvements in the treatment of chronic liver disease have accelerated interest in uncovering the mechanisms underlying hepatic fibrosis and its resolution. Activation of resident hepatic stellate cells into proliferative, contractile, and fibrogenic cells in liver injury remains a dominant theme driving the field. However, several new areas of rapid progress in the past 5-10 years also have taken root, including: (1) identification of different fibrogenic populations apart from resident stellate cells, for example, portal fibroblasts, fibrocytes, and bone-marrow-derived cells, as well as cells derived from epithelial mesenchymal transition; (2) emergence of stellate cells as finely regulated determinants of hepatic inflammation and immunity; (3) elucidation of multiple pathways controlling gene expression during stellate cell activation including transcriptional, post-transcriptional, and epigenetic mechanisms; (4) recognition of disease-specific pathways of fibrogenesis; (5) re-emergence of hepatic macrophages as determinants of matrix degradation in fibrosis resolution and the importance of matrix cross-linking and scar maturation in determining reversibility; and (6) hints that hepatic stellate cells may contribute to hepatic stem cell behavior, cancer, and regeneration. Clinical and translational implications of these advances have become clear, and have begun to impact significantly on the management and outlook of patients with chronic liver disease.

Wound healing and local neuroendocrine regulation in the injured liver

The hepatic wound-healing response is a complex process involving many different cell types and factors. It leads to the formation of excessive matrix and a fibrotic scar, which ultimately disrupts proper functioning of the liver and establishes cirrhosis. Activated hepatic myofibroblasts, which are derived from cells such as hepatic stellate cells (HSCs), play a key role in this process. Upon chronic liver injury, there is an upregulation in the local neuroendocrine system and it has recently been demonstrated that activated HSCs express specific receptors and respond to different components of this system. Neuroendocrine factors and their receptors participate in a complex network that modulates liver inflammation and wound healing, and controls the development and progression of liver fibrosis. The first part of this review provides an overview of the molecular mechanisms governing hepatic wound healing. In the second section, we explore important components of the hepatic neuroendocrine system and their recently highlighted roles in HSC biology and hepatic fibrogenesis. We discuss the therapeutic interventions that are being developed for use in antifibrotic therapy.

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.

Environmental and genetic modifiers of the progression to fibrosis and cirrhosis in hemochromatosis

Hereditary hemochromatosis is a genetic disorder of iron metabolism leading to inappropriate iron absorption and iron loading in various organs especially the liver. Despite the genetic mutation being relatively common in those of Anglo Celtic descent, cirrhosis of the liver occurs in only a small proportion of affected individuals. The risk of hepatic fibrosis and cirrhosis relates to the degree of iron loading with threshold hepatic iron concentrations being identified from population studies. However, other environmental and possibly genetic factors appear to modify this risk. Excess alcohol consumption appears to be one of the most important cofactors with steatosis and coexistent viral infection also implicated. Genetic polymorphisms in genes associated with fibrogenesis, antioxidant activity, and inflammation have been investigated in several different forms of chronic liver disease. The variability in the expression of these genes that predispose patients with hemochromatosis to increased risk of severe liver disease is the subject of ongoing investigations. Clearly the progression of iron loading to cirrhosis marks a crucial stage in the natural history of a patient's disease and therefore therapy and prognosis. This review explores recent developments in knowledge of environmental and genetic modifiers of this process.

Glycosaminoglycans and their synthetic mimetics inhibit RANTES-induced migration and invasion of human hepatoma cells

The CC-chemokine regulated on activation, normal T-cell expressed, and presumably secreted (RANTES)/CCL5 mediates its biological activities through activation of G protein-coupled receptors, CCR1, CCR3, or CCR5, and binds to glycosaminoglycans. This study was undertaken to investigate whether this chemokine is involved in hepatoma cell migration or invasion and to modulate these effects in vitro by the use of glycosaminoglycan mimetics. We show that the human hepatoma Huh7 and Hep3B cells express RANTES/CCL5 G protein-coupled receptor CCR1 but not CCR3 nor CCR5. RANTES/CCL5 binding to these cells depends on CCR1 and glycosaminoglycans. Moreover, RANTES/CCL5 strongly stimulates the migration and the invasion of Huh7 cells and to a lesser extent that of Hep3B cells. RANTES/CCL5 also stimulates the tyrosine phosphorylation of focal adhesion kinase and activates matrix metalloproteinase-9 in Huh7 hepatoma cells, resulting in increased invasion of these cells. The fact that RANTES/CCL5-induced migration and invasion of Huh7 cells are both strongly inhibited by anti-CCR1 antibodies and heparin, as well as by beta-d-xyloside treatment of the cells, suggests that CCR1 and glycosaminoglycans are involved in these events. We then show by surface plasmon resonance that synthetic glycosaminoglycan mimetics, OTR4120 or OTR4131, directly bind to RANTES/CCL5. The preincubation of the chemokine with each of these mimetics strongly inhibited RANTES-induced migration and invasion of Huh7 cells. Therefore, targeting the RANTES-glycosaminoglycan interaction could be a new therapeutic approach for human hepatocellular carcinoma.

Chemokine system polymorphisms, survival and hepatocellular carcinoma occurrence in patients with hepatitis C virus-related cirrhosis

AIM: To explore the influence of polymorphisms in genes encoding for the chemokines Stromal cell-Derived Factor-1 (SDF-1)/CXCL12 and Monocyte Chemotactic Protein-1 (MCP-1)/CCL2, or for the chemokine receptor CCR5 on the risks of liver-related death and hepatocellular carcinoma (HCC) occurrence in hepatitis C virus (HCV)-infected patients.

METHODS: SDF-1 3’A, MCP-1 (-2518) and CCR5-Δ32 polymorphisms, SDF-1α, Regulated upon Activation Normal T cells Expressed and Secreted (RANTES)/CCL5 and MCP-1 serum levels were determined in 120 HCV-infected patients, included at time of cirrhosis diagnosis and prospectively followed-up.

RESULTS: During follow-up, 23/120 (19.1%) patients died and 47/120 (39.1%) developed HCC. Carriers and noncarriers of each genetic marker had similar baseline characteristics estimating the severity of liver disease. The occurrence of death or HCC during follow-up was similar among carriers and noncarriers of each polymorphism. There was no association between the carriage of mutated alleles and chemokine serum levels and the latter were not associated with the risks of death or HCC.

CONCLUSION: This study suggests the lack of association of SDF-1 3’A, MCP-1 (-2518), CCR5-Δ32 polymorphisms with death and HCC occurrence in cirrhotic HCV-infected patients.

The fractalkine receptor CX3CR1 is involved in liver fibrosis due to chronic hepatitis C infection

BACKGROUND/AIMS

The chemokine receptor CX3CR1 and its specific ligand fractalkine (CX3CL1) are known to modulate inflammatory and fibroproliferative diseases. Here we investigate the role of CX3CR1/fractalkine in HCV-induced liver fibrosis.

METHODS

A genotype analysis of CX3CR1 variants was performed in 211 HCV-infected patients. Hepatic expression of CX3CR1 was studied in HCV-infected livers and isolated liver cell populations by RT-PCR and immunohistochemistry. The effects of fractalkine on mRNA expression of profibrogenic genes were determined in isolated hepatic stellate cells (HSC) and CX3CR1 genotypes were related to intrahepatic TIMP-1 mRNA levels.

RESULTS

The intrahepatic mRNA expression of CX3CR1 correlates with the stage of HCV-induced liver fibrosis (P=0.03). The CX3CR1 coding variant V249I is associated with advanced liver fibrosis, independent of the T280M variant (P=0.009). CX3CR1 is present on primary HSC and fractalkine leads to a suppression of tissue inhibitor of metalloproteinase (TIMP)-1 mRNA in HSC (P=0.03). Furthermore, CX3CR1 genotypes are associated with TIMP-1 mRNA expression in HCV-infected liver (P=0.03).

CONCLUSIONS

The results identify the fractalkine receptor CX3CR1 as susceptibility a gene for hepatic fibrosis in HCV infection. The modulation of TIMP-1 expression by fractalkine and CX3CR1 genotypes provides functional support for the observed genotype-phenotype association.

Coculture of human liver macrophages and cholangiocytes leads to CD40-dependent apoptosis and cytokine secretion

In the vanishing bile duct syndromes (VBDS), primary biliary cirrhosis and chronic allograft rejection, cholangiocyte apoptosis is associated with sustained macrophage infiltration of the liver, suggesting that these cells may mediate tissue damage and contribute to bile duct destruction. We have previously reported that activation of CD40 on cholangiocytes with either soluble CD154 or cross-linking monoclonal antibody to CD40 induces apoptosis in vitro. We have now developed a novel primary human cell coculture model and used it to investigate (1) how macrophages kill cholangiocytes; (2) how paracrine cell interactions can shape the local cytokine milieu within the liver. We report that lipopolysaccharide (LPS) and interferon (IFN) induce sustained expression of CD154 on liver-derived macrophages (LDM) in vitro. Coculture of activated LDM expressing high levels of CD154 (CD40 ligand) with human cholangiocytes resulted in (1) CD40-dependent secretion of proinflammatory cytokines; (2) apoptosis of cholangiocytes that was abolished by antagonistic antibodies directed against human CD40 or human CD154.

CONCLUSION

Macrophages are important effector cells in bile duct destruction in VBDS, and this role is dependent on CD40-mediated mechanisms. Thus activation of CD40 on cholangiocytes by activated macrophages provides a molecular mechanism to amplify chronic inflammation and bile duct destruction in liver disease. These data suggest that effective targeting strategies to antagonize CD40/CD154 may have beneficial effects in patients suffering from the VBDS.

Intrahepatic mRNA expression in hepatitis C virus and HIV/hepatitis C virus co-infection: infiltrating cells, cytokines, and influence of HAART

OBJECTIVE

Liver disease is more progressive in HIV/hepatitis C virus (HCV) co-infection than in HCV infection alone. This accelerated pathogenesis is probably influenced by differences in the composition of infiltrating inflammatory cells and the local release of inflammatory and profibrogenic cytokines.

METHODS

Using quantitative real-time reverse transcriptase-polymerase chain reaction (qRT-PCR) we studied intrahepatic messenger RNA levels of cytokines and cellular markers defining distinct subsets of inflammatory cells in liver biopsies from 33 HCV-mono-infected and 40 HIV/HCV-co-infected patients.

RESULTS

Despite their well preserved peripheral blood CD4 cell counts (median 598 cells/microl), HIV/HCV-co-infected patients displayed significantly lower CD4 mRNA levels than HCV-mono-infected patients, whereas increased mRNA levels of CD3epsilon, TCRalpha, CD8alpha and CD8beta suggested intrahepatic enrichment of CD8 T cells in HIV co-infection. Intrahepatic mRNA levels of the inflammatory cytokines interferon gamma (IFN-gamma), regulated upon activation, normal T-cell expressed and secreted (RANTES, CCL5), macrophage inflammatory protein 1 alpha (CCL3) and interferon-inducible protein 10 (CXCL10) were significantly higher in HIV-positive than in HIV-negative patients, whereas mRNA levels of the profibrogenic cytokines macrophage chemoattractant protein 1 (CCL2), secondary lymphochemokine (CCL21) and stroma-derived factor 1 (CXCL12) did not differ between the two groups. All changes were less pronounced in the subgroup of HIV-positive patients receiving antiretroviral treatment (HAART) than in untreated HIV-positive patients.

CONCLUSION

The accelerated liver disease observed in HIV/HCV-co-infected patients might reflect enhanced intrahepatic inflammatory responses rather than increased local transcription of directly profibrogenic cytokines.

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

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

Focal adhesion disassembly is an essential early event in hepatic stellate cell chemotaxis

Chemotaxis (i.e., directed migration) of hepatic stellate cells to areas of inflammation is a requisite event in the liver's response to injury. Previous studies of signaling pathways that regulate stellate cell migration suggest a key role for focal adhesions, but the exact function of these protein complexes in motility remains unclear. Focal adhesions attach a cell to its substrate and therefore must be regulated in a highly coordinated manner during migration. To test the hypothesis that focal adhesion turnover is an essential early event for chemotaxis in stellate cells, we employed a live-cell imaging technique in which chemotaxis was induced by locally stimulating the tips of rat stellate cell protrusions with platelet-derived growth factor-BB (PDGF). Focal adhesions were visualized with an antibody directed against vinculin, a structural component of the focal adhesion complex. PDGF triggered rapid disassembly of adhesions within 6.25 min, subsequent reassembly by 12.5 min, and continued adhesion assembly in concert with the spreading protrusion until the completion of chemotaxis. Blockade of adhesion disassembly by growing cells on fibronectin or treatment with nocodazole prevented a chemotactic response to PDGF. Augmentation of adhesion disassembly with ML-7 enhanced the chemotactic response to PDGF. These data suggest that focal adhesion disassembly is an essential early event in stellate cell chemotaxis in response to PDGF.

Comparative protection against liver inflammation and fibrosis by a selective cyclooxygenase-2 inhibitor and a nonredox-type 5-lipoxygenase inhibitor

In this study, we examined the relative contribution of cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LO), two major proinflammatory pathways up-regulated in liver disease, to the progression of hepatic inflammation and fibrosis. Separate administration of 4-[5-(4-chlorophenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide (SC-236), a selective COX-2 inhibitor, and CJ-13,610, a 5-LO inhibitor, to carbon tetrachloride-treated mice significantly reduced fibrosis as revealed by the analysis of Sirius Red-stained liver sections without affecting necroinflammation. Conversely, combined administration of SC-236 and 4-[3-[4-(2-methylimidazol-1-yl)-phenylthio]]phenyl-3,4,5,6-tetrahydro-2H-pyran-4-carboxamide (CJ-13,610) reduced both necroinflammation and fibrosis. These findings were confirmed in 5-LO-deficient mice receiving SC-236, which also showed reduced hepatic monocyte chemoattractant protein 1 expression. Interestingly, SC-236 and CJ-13,610 significantly increased the number of nonparenchymal liver cells with apoptotic nuclei (terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive). Additional pharmacological profiling of SC-236 and CJ-13,610 was performed in macrophages, the primary hepatic inflammatory cell type. In these cells, SC-236 inhibited prostaglandin (PG) E2 formation in a concentration-dependent manner, whereas CJ-13,610 blocked leukotriene B4 biosynthesis. Of note, the simultaneous addition of SC-236 and CJ-13,610 resulted in a higher inhibitory profile on PGE2 biosynthesis than the dual COX/5-LO inhibitor licofelone. These drugs differentially regulated interleukin-6 mRNA expression in macrophages. Taken together, these findings indicate that both COX-2 and 5-LO pathways are contributing factors to hepatic inflammation and fibrosis and that these two pathways of the arachidonic acid cascade represent potential targets for therapy.

Chemokines in hepatitis C virus infection: Pathogenesis, prognosis and therapeutics

Hepatitis C virus infection and its associated liver inflammatory disease is a major global health problem affecting over 170 million people worldwide. Following viral infection, multiple pro-inflammatory mediators contribute to recruitment of immune cells to the liver and to the generation of an anti-viral immune response. However, when this vigorous immune response fails to eliminate the virus, chronic infection is established. This in turn, results in an ongoing process of inflammation, regeneration and fibrosis that in many cases leads to the development of cirrhosis and of hepatocellular carcinoma. Multiple recent publications mark chemokines and their receptors as key players in leukocyte recirculation through the inflamed liver. Furthermore, chemokines may also be involved in liver regeneration, fibrosis, and in malignant transformation, which is induced by the persistence of inflammation. Accumulating data indicates that distinct chemokines and chemokine receptors may be associated with different stages of the chronic hepatitis C virus infection-associated liver disease. Multiple small molecules and peptide antagonizing chemokines and their receptors are in advanced phase 3 and phase 2 clinical trials. In the near future, such drugs are expected to enter clinical use raising the question whether they may be applicable for the treatment of chronic viral infection-associated liver disease. In this review, recent advances in understanding the role of chemokines and their receptors in the pathogenesis of chronic viral infection-associated liver disease are presented. Furthermore, the clinical implications of these novel findings, which mark chemokines as prognostic markers and therapeutic targets for immune-modulation during chronic liver viral infection, are documented.

Thrombin inhibits migration of human hepatic myofibroblasts

Several lines of data recently pointed out a role of the serine proteinase thrombin in liver fibrogenesis, but its mechanism of action is unknown. The aim of this study was to evaluate the effect of thrombin on the migration of human liver myofibroblasts. We show here that thrombin inhibits both basal migration and platelet-derived growth factor (PDGF)-BB-induced migration of myofibroblasts. By using a thrombin antagonist, a protease-activated receptor (PAR)-1 mimetic peptide, and a PAR-1 antibody, we show that this effect is dependent on the catalytic activity of thrombin and on PAR-1 activation. Thrombin's effect on basal migration was dependent on cyclooxygenase 2 (COX-2) activation because it was blocked by the COX-2 inhibitors NS-398 and nimesulide, and pharmacological studies showed that it was relayed through prostaglandin E(2) and its EP(2) receptor. On the other hand, thrombin-induced inhibition of PDGF-BB-induced migration was not dependent on COX-2. We show that thrombin inhibits PDGF-induced Akt-1 phosphorylation. This effect was consecutive to inhibition of PDGF-beta receptor activation through active dephosphorylation. Thus thrombin, through two distinct mechanisms, inhibits both basal- and PDGF-BB-induced migration of human hepatic liver myofibroblasts. The fine tuning of myofibroblast migration may be one of the mechanisms used by thrombin to regulate liver fibrogenesis.

RANTES, MCP-1, CCR2, CCR5, CXCR1 and CXCR4 gene polymorphisms are not associated with the outcome of hepatitis B virus infection: results from a large scale single ethnic population

Recovery from hepatitis B virus (HBV) infection depends on the cellular immune responses. Chemokines and their receptors play significant roles in immune defense. This study was undertaken to investigate the association between HBV infection and single nucleotide polymorphisms (SNPs) of genes for the chemokines and their receptors. Between March 2002 and February 2004, a total of 957 single ethnic Korean patients were enrolled into two different groups; "HBV clearance group" (n=350), who have recovered from HBV infection, and "HBV persistence group" (n=607), who were repeatedly HBsAg-positive. The HBV persistence group was subdivided into "inactive carrier" and "HBV progression group (chronic hepatitis and cirrhosis)". We assessed polymorphisms in regulated and normal T-cell expressed and secreted (RANTES) at position -403, monocyte chemoattractant protein-1 (MCP-1) at position -2518, CCR2 V64I, CCR5 -2459, CXCR1 S276T and CXCR4 I138I using single primer extension assay. Genotype distributions of the "HBV clearance versus persistence group" and "inactive carrier versus HBV progression group" were compared. On the basis of unconditional logistic regression analysis with adjustment for age and sex, no statistically significant association with susceptibility to persistent HBV infection was observed with RANTES -403, MCP-1 -2518, CCR2 V64I, CCR5 -2459, CXCR1 S276T, and CXCR4 I138I polymorphisms. In addition, no association of analyzed SNPs with HBV disease progression was found.

Hepatic stellate cell protrusions couple platelet-derived growth factor-BB to chemotaxis

Hepatic stellate cells play an essential role in the liver's injury response. Although stellate cells are defined by the presence of cytoplasmic protrusions, the function of these characteristic structures has been obscure. We hypothesized that stellate cell protrusions act by coupling injury-associated stimuli to chemotaxis. To test this hypothesis, we developed an assay for directly visualizing the response of living stellate cells in early primary culture to local stimulation of the tips of protrusions with platelet-derived growth factor-BB (PDGF). Stellate cells exhibited elongate protrusions containing actin, myosin, and tubulin. PDGF, but not cytochrome C, localized at a protrusion tip induced a coordinated series of morphological events--cell spreading at the tip, movement of the cell body toward the PDGF, and retraction of trailing protrusions--that resulted in chemotaxis. Soluble PDGF and AG 1296, a receptor tyrosine kinase inhibitor, both reduced stellate cell chemotaxis. PDGF-induced chemotaxis was associated with an early and transient increase in myosin phosphorylation within the spreading lamella. We observed that blebbistatin, a myosin II inhibitor, completely and reversibly blocked protrusion-mediated lamella formation and chemotaxis. Moreover, blockade of MRLC phosphorylation with the myosin light chain kinase inhibitor, ML-7, or the rho kinase inhibitor, Y-27632, blocked lamella formation, myosin phosphorylation within the protrusion, and chemotaxis.

CONCLUSION

These results support a model in which protrusions permit stellate cells to promptly detect PDGF distant from their cell bodies and transduce this signal into mechanical forces that propel the cell toward the site of injury.

Pharmacological inhibition of the vitronectin receptor abrogates PDGF-BB-induced hepatic stellate cell migration and activation in vitro

BACKGROUND/AIMS

Activated hepatic stellate cells (HSC) play a central role in the development of liver fibrosis. Platelet-derived growth factor (PDGF)-BB and the integrin alphavbeta3 mediate mesenchymal cell migration and proliferation. However, their contribution and interaction during fibrogenic activation of HSC remains unclear. To this aim we investigated if PDFGF-BB and alphavbeta3 interact, and how far small molecular inhibitors of alphavbeta3 modulate PDGF-BB and serum-induced migration, proliferation and fibrogenic activation of HSC.

METHODS

Rat and human HSC were subjected to migration and proliferation assays in the presence or absence of a peptide or a nonpeptide alphavbeta3 inhibitor. Activation of mitogen-activated protein kinases (ERK1/2, p38), Akt, focal adhesion kinase (FAK), paxillin and beta3 integrin was evaluated by phospho-specific Western blotting. Fibrosis related transcripts were determined by quantitative real-time PCR.

RESULTS

PDGF-BB-stimulated HSC migration which was blocked dose-dependently by the alphavbeta3 antagonists, with complete inhibition at 10(-6)M. alphavbeta3 blockage did not affect cell viability or proliferation, while it decreased phosphorylation of FAK, paxillin, beta3 integrin and p38, but not of ERK1/2 or Akt. alphavbeta3 inhibition led to downregulation of certain profibrogenic transcripts, while it upregulated fibrolytic MMP-13 mRNA.

CONCLUSIONS

Inhibition of integrin alphavbeta3 leads to abrogation of migration of HSC stimulated with PDGF-BB and to an antifibrogenic gene expression pattern.

Lack of association of some chemokine system polymorphisms with the risks of death and hepatocellular carcinoma occurrence in patients with alcoholic cirrhosis: a prospective study

BACKGROUND

Polymorphisms in genes encoding for the chemokines stromal cell-derived factor-1 (SDF-1)/CXCL12, monocyte chemotactic protein-1 (MCP-1)/CCL2, or for the chemokine receptors, CC chemokine receptor 5 (CCR5) or CC chemokine receptor 2 (CCR2) have been associated with the progression of hepatitis C virus-related liver injury and with various cancer development. Their influence on the prognosis of alcoholic liver disease is unknown.

PATIENTS AND METHODS

SDF-1 3'A, MCP-1(-2518), CCR5-Delta32 and CCR2-64I polymorphisms, SDF-1alpha, regulated upon activation normal T cells expressed and secreted (RANTES)/CCL5 and MCP-1 sera levels were determined in 222 alcoholic patients, included at the time of cirrhosis diagnosis and prospectively followed up.

RESULTS

Carriers and noncarriers of each genetic marker had similar baseline characteristics estimating the severity of liver disease. Mean time of follow-up of the cohort was 62.9+/-43.2 months. One hundred and forty-seven out of 222 (66.3%) patients were alive at the end of the study. The occurrence of death (75/222; 33.7%) or hepatocellular carcinoma (67/222; 30.1%) during follow-up was similar among carriers and noncarriers of each polymorphism. No association between the carriage of mutated alleles and chemokine sera levels was found: CCR5-Delta32/RANTES, SDF-1 3'A/SDF-1alpha and CCR2-64I or MCP-1(-2518)/MCP-1. Baseline RANTES, SDF-1alpha and MCP-1 sera levels were associated neither with the risk of death nor with the risk of hepatocellular carcinoma.

CONCLUSIONS

The present study suggests the lack of association of SDF-1 3'A, MCP-1(-2518), CCR5-Delta32 and CCR2-64I polymorphisms with death and hepatocellular carcinoma occurrence in cirrhotic alcoholic patients.

Stromal cell-derived factor-1/chemokine (C-X-C motif) ligand 12 stimulates human hepatoma cell growth, migration, and invasion

In addition to their physiologic effects in inflammation and angiogenesis, chemokines are involved in cancer pathology. The aim of this study was to determine whether the chemokine stromal cell-derived factor 1 (SDF-1) induces the growth, migration, and invasion of human hepatoma cells. We show that SDF-1 G protein-coupled receptor, chemokine (C-X-C motif) receptor 4 (CXCR4), and SDF-1 mRNA are expressed in human hepatoma Huh7 cells, which secrete and bind SDF-1. This binding depends on CXCR4 and glycosaminoglycans. SDF-1 associates with CXCR4, and syndecan-4 (SDC-4), a heparan sulfate proteoglycan at the plasma membrane of Huh7 cells, induces the growth of Huh7 cells by promoting their entry into the cell cycle, and inhibits the tumor necrosis factor-alpha-mediated apoptosis of the cells. SDF-1 also reorganizes Huh7 cytoskeleton and induces tyrosine phosphorylation of focal adhesion kinase. Finally, SDF-1 activates matrix metalloproteinase-9, resulting in increased migration and invasion of Huh7 cells. These biological effects of SDF-1 were strongly inhibited by the CXCR4 antagonist AMD3100, by a glycosaminoglycan, heparin, as well as by beta-D-xyloside treatment of the cells, or by c-jun NH(2)-terminal kinase/stress-activated protein kinase inhibitor. Therefore, the CXCR4, glycosaminoglycans, and the mitogen-activated protein kinase signaling pathways are involved in these events. The fact that reducing SDC-4 expression by RNA interference decreased SDF-1-induced Huh7 hepatoma cell migration and invasion strongly indicates that SDC-4 may be an auxiliary receptor for SDF-1. Finally, the fact that CXCR4 is expressed in hepatocellular carcinoma cells from liver biopsies indicates that the in vitro results reported here could be extended to in vivo conditions.

Prevention of severe toxic liver injury and oxidative stress in MCP-1-deficient mice

BACKGROUND/AIMS

Administration of carbon tetrachloride determines liver injury, inflammation and oxidative stress, but the molecular mechanisms of damage are only partially understood. In this study, we investigated the development of acute toxic damage in mice lacking monocyte chemoattractant protein-1 (MCP-1), a chemokine which recruits monocytes and activated lymphocytes.

METHODS

Mice with targeted deletion of the MCP-1 gene and wild type controls were administered a single intragastric dose of carbon tetrachloride. Serum liver enzymes, histology, expression of different chemokines and cytokines, and intrahepatic levels of oxidative stress-related products were evaluated.

RESULTS

Compared to wild type mice, peak aminotransferase levels were significantly lower in MCP-1-deficient animals. This was paralleled by a delayed appearance of necrosis at histology. In addition, MCP-1-deficient mice showed a shift in the pattern of infiltrating inflammatory cells, with a predominance of polymorphonuclear leukocytes. Lack of MCP-1 was also accompanied by reduced intrahepatic expression of cytokines regulating inflammation and tissue repair. The increase in tissue levels of reactive oxygen species and 4-hydroxy-nonenal following administration of the hepatotoxin was also significantly lower in animals lacking MCP-1.

CONCLUSIONS

Lack of MCP-1 affords protection from damage and development of oxidative stress in a toxic model of severe acute liver injury.

Longitudinal analysis of murine steatohepatitis model induced by chronic exposure to high-fat diet

Several lines of epidemiological evidence have suggested that non-alcoholic steatohepatitis (NASH) is closely associated with obesity in humans. However, the precise mechanisms of the progression of NASH and its key metabolic abnormalities remain to be elucidated. We found that long-term high-fat diet (HFD) exposure induces NASH, with excess body weight, hyperinsulinemia and hypercholesteremia in mice. Longitudinal analysis of the model showed that steatohepatitis was induced after onset of metabolic abnormalities. In addition, we found that expression of MCP-1 mRNA was induced in the liver before induction of TNFalpha and type I collagen alpha1 mRNAs, and prior to onset of steatohepatitis. We confirmed that hepatic MCP-1 contents were increased in mice fed HFD for 50 weeks, although the precise role of MCP-1 in the development of NASH remains to be addressed. The mouse model was also characterized by moderate reductions in catalase activity and glutathione content, as well as by overexpression of fatty acid synthase, acetyl-CoA carboxylase 1 and FAT/CD36 mRNAs in the liver. The murine NASH model apparently mimics clinical aspects of the condition and provides insight into NASH.

Loss of TGF-beta dependent growth control during HSC transdifferentiation

Liver injury induces activation of hepatic stellate cells (HSCs) comprising expression of receptors, proliferation, and extracellular matrix synthesis triggered by a network of cytokines provided by damaged hepatocytes, activated Kupffer cells and HSCs. While 6 days after bile duct ligation in rats TGF-beta inhibited DNA synthesis in HSCs, it was enhanced after 14 days, indicating a switch from suppression to DNA synthesis stimulation during fibrogenesis. To delineate mechanisms modulating TGF-beta function, we analyzed crosstalk with signaling pathways initiated by cytokines in damaged liver. Lipopolysaccharide and tumor necrosis factor-alpha enhanced proliferation inhibition of TGF-beta, whereas interleukin-6, oncostatin M, interleukin-1alpha, and interleukin-1beta did not. Hepatocyte growth factor (HGF) counteracted TGF-beta dependent inhibition of DNA synthesis in quiescent HSCs. Since expression of c-met is induced during activation of HSCs and HGF is overrepresented in damaged liver, crosstalk of HGF and TGF-beta contributes to loss of TGF-beta dependent inhibition of DNA synthesis in HSCs.

Role of Kupffer cells in the pathogenesis of liver disease

Kupffer cells, the resident liver macrophages have long been considered as mostly scavenger cells responsible for removing particulate material from the portal circulation. However, evidence derived mostly from animal models, indicates that Kupffer cells may be implicated in the pathogenesis of various liver diseases including viral hepatitis, steatohepatitis, alcoholic liver disease, intrahepatic cholestasis, activation or rejection of the liver during liver transplantation and liver fibrosis. There is accumulating evidence, reviewed in this paper, suggesting that Kupffer cells may act both as effector cells in the destruction of hepatocytes by producing harmful soluble mediators as well as antigen presenting cells during viral infections of the liver. Moreover they may represent a significant source of chemoattractant molecules for cytotoxic CD8 and regulatory T cells. Their role in fibrosis is well established as they are one of the main sources of TGFβ1 production, which leads to the transformation of stellate cells into myofibroblasts. Whether all these variable functions in the liver are mediated by different Kupffer cell subpopulations remains to be evaluated. In this review we propose a model that demonstrates the role of Kupffer cells in the pathogenesis of liver disease.

Green tea polyphenol epigallocatechin-3-gallate suppresses rat hepatic stellate cell invasion by inhibition of MMP-2 expression and its activation

AIM

Epigallocatechin-3-gallate (EGCG) is the major component of green tea polyphenols, whose wide range of biological properties includes anti-fibrogenic activity. Matrix metalloproteinases (MMP) that participate in extracellular matrix degradation are involved in the development of hepatic fibrosis. The present study investigates whether EGCG inhibits activation of the major gelatinase matrix metalloproteinase-2 (MMP-2) in rat hepatic stellate cells (HSC).

METHODS

The expression of MMP-2, tissue inhibitors of metalloproteinases-2 (TIMP-2), and membrane-type 1-MMP (MT1-MMP) was assessed by RT-PCR and Western blot analyses. MMP-2 activity was evaluated by zymography and MT1-MMP activity was assessed by an enzymatic assay. HSC migration was measured by a wound healing assay and cell invasion was performed using Transwell cell culture chambers.

RESULTS

The expression of MMP-2 mRNA and protein in HSC was substantially reduced by EGCG treatment. EGCG treatment also reduced concanavalin A (ConA)-induced activation of secreted MMP-2 and reduced MT1-MMP activity in a dose-dependent manner. In addition, EGCG inhibited either HSC migration or invasion.

CONCLUSION

The abilities of EGCG to suppress MMP-2 activation and HSC invasiveness suggest that EGCG may be useful in the treatment and prevention of hepatic fibrosis.

The role of monocyte chemoattractant protein-1 in biliary atresia

BACKGROUND

The aim of this study was to explain the role of monocyte chemoattractant protein-1 (MCP-1) in biliary atresia (BA).

METHODS

Concentrations of serum MCP-1 and collagen type IV were measured in 38 patients with BA by using commercially available kits. MCP-1 was also assessed in liver biopsy specimens by using immunohistochemistry. Subjects were classified into groups. Group 1 comprised BA patients with normal liver function (n = 13), group II comprised BA patients with moderate liver dysfunction (n = 18), group III comprised BA patients older than 20 years awaiting liver transplantation (n = 7), and the control group comprised age-matched patients without evidence of liver disease (n = 23).

RESULTS

Serum MCP-1 levels were significantly increased in group II compared with group I (P < .0001) and the control group (P < .0001). Serum MCP-1 levels in group III were lower than in the control group (P < .0001). There was a significant linear correlation between serum MCP-1 levels and type IV collagen levels in group II. Group II subjects with portal hypertension (PH) had higher MCP-1 levels than those without PH (P = .0009). Biopsy specimens showed MCP-1 was expressed mainly on biliary epithelial cells, vascular endothelial cells, and hepatocytes in group II.

CONCLUSIONS

These findings suggest that MCP-1 probably plays a significant role in the development of progressive liver fibrosis in BA.

Simvastatin inhibits the migration and adhesion of monocytic cells and disorganizes the cytoskeleton of activated endothelial cells

Statins are powerful agents for lowering plasma cholesterol levels, which act by inhibition of the 3-hydroxy-3-methylglutaryl-CoA reductase. Evidence suggests that some of the beneficial effects may depend on their anti-inflammatory properties, due to their ability to suppress the synthesis of isoprenoids. The present study analyzes the effects of short-term simvastatin exposure on monocyte migration, cell adhesion, and endothelial cytoskeleton. We demonstrate that simvastatin completely inhibited the migration of THP-1 monocytic cells after 24 h of incubation, being prevented by coincubation with mevalonate (MVA) and geranylgeranylpyrophosphate (GGPP), but not by farnesylpyrophosphate (FPP). Simvastatin decreased chemotaxis to 70% after one hour of incubation; surprisingly neither MVA, GGPP nor FPP were able to restore the effects of the drug. Simvastatin also significantly reduced the adhesion of monocytes to interleukin-1beta (IL-1beta)-activated endothelium to 80% after preincubation for 24 h. This effect was completely reversed by coincubation with MVA and GGPP, and partially with FPP. Unexpectedly, simvastatin increased adhesion molecules expression VCAM-1 and ICAM-1 on cytokine-stimulated endothelial cells. Examination of the actin cytoskeleton on IL-1beta-activated endothelial cells showed that both 4 and 24 h of incubation with simvastatin produced a complete disappearance of F-actin, being completely restored by MVA and partially by GGPP and FPP after 24 h of coincubation. We suggest that cytoskeleton disorganization in endothelial cells is important for inhibiting monocyte adhesion, altering the adhesion molecules function. Taken together, these results strongly support the beneficial anti-inflammatory properties of statins, contributing to the overall clinical effects.

Hepatic fibrosis, stellate cells, and portal hypertension

Hepatic fibrogenesis is the common result of injury to the liver. It is believed to be a critical factor that leads to hepatic dysfunction and may be important in portal hypertension. The fibrogenic response is a complex process in which accumulation of extracellular matrix proteins, tissue contraction, and alteration in blood flow are prominent. A critical event in fibrogenesis is activation of resident perisinusoidal cells that are termed "hepatic stellate cells". Stellate cell activation is characterized by many important phenotypes, including enhanced extracellular matrix synthesis and prominent contractility. Given the central role of stellate cell activation in hepatic fibrogenesis (and portal hypertension), effective therapy for hepatic fibrogenesis is most likely will be directed at this event.

Fas ligand is responsible for CXCR3 chemokine induction in CD4+ T cell-dependent liver damage

Immune-mediated hepatic damage has been demonstrated in the pathogenesis of hepatitis C virus (HCV) and other hepatotrophic infections. Fas/Fas ligand (FasL) interaction plays a critical role in immune-mediated hepatic damage. To understand the molecular mechanism(s) of FasL-mediated liver inflammation, we examined the effect of CD4(+) T cells expressing high levels of FasL on the initiation of hepatic damage through analysis of chemokine and chemokine receptor expression in HCV core x TCR (DO11.10) double-transgenic mice. In vivo antigenic stimulation triggers a marked influx of core-expressing Ag-specific CD4(+) T cells into the liver of the immunized core(+) TCR mice but not their core(-) TCR littermates. Strikingly, the inflammatory process in the liver of core(+) TCR mice was accompanied by a dramatic increase in IFN-inducible protein 10 and monokine induced by IFN-gamma production. The intrahepatic lymphocytes were primarily CXCR3-positive and anti-CXCR3 Ab treatment abrogates migration of CXCR3(+) lymphocytes into the liver and hepatic damage. Importantly, the blockade of Fas/FasL interaction reduces the expression of IFN-inducible protein 10 and monokine induced by IFN-gamma and cellular infiltration into the liver. These findings suggest that activated CD4(+) T cells with elevated FasL expression are involved in promoting liver inflammation and hepatic damage through the induction of chemokines.

Secretion of MCP-1/CCL2 by bile duct epithelia induces myofibroblastic transdifferentiation of portal fibroblasts

Portal fibroblasts (PF) are fibrogenic liver cells distinct from hepatic stellate cells (HSC). Recent evidence suggests that PF may be important mediators of biliary fibrosis and cirrhosis. The cytokine monocyte chemoattractant protein-1 (MCP-1)/CCL2 is upregulated in biliary fibrosis by bile duct epithelia (BDE) and induces functional responses in HSC. Thus we hypothesized that release of MCP-1 may mediate biliary fibrosis. We report that PF express functional receptors for MCP-1 that are distinct from the receptor CCR2. MCP-1 induces proliferation, increase and redistribution of alpha-smooth muscle (alpha-SMA) expression, loss of the ectonucleotidase NTPDase2, and upregulation of alpha(1)-procollagen production in PF. BDE secretions induce alpha-SMA levels in PF, and this is inhibited by MCP-1 blocking antibody. Together, these data suggest that BDE regulate PF proliferation and myofibroblastic transdifferentiation in a paracrine fashion via release of MCP-1.

Effects of bile acids on biliary epithelial cell proliferation and portal fibroblast activation using rat liver slices

During cholestasis, bile acids accumulate in the liver, and induce cellular alterations. Cholestasis is a major cause of liver fibrosis. We have used precision-cut liver slices (PCLS) in culture to investigate the effects of bile acids on hepatic cells. Rat PCLS were placed on an insert in a vial containing culture medium, and gently agitated on a roller platform. PCLS were treated with 100 microM taurolithocholate (TLC), taurodeoxycholate (TDC) or taurocholate (TC) for 24 or 48 h. PCLS viability was measured, and immunohistochemistry was performed with antibodies against active caspase 3, platelet-derived growth factor (PDGF) receptor-beta and ED-A fibronectin. TDC and TLC, two hydrophobic bile acids, induced hepatocyte necrosis and apoptosis, whereas TC, an hydrophilic bile acid, improved slice viability as compared with controls. Both TDC and TC induced biliary epithelial cell proliferation, together with portal fibroblast proliferation and activation, as shown by PDGF receptor-beta and ED-A fibronectin expression. TLC induced biliary epithelial cell apoptosis. Our results indicate that individual bile acids induce cell type-specific effects in a complex liver microenvironment. The fact that PCLS support biliary epithelial cell and portal fibroblast proliferation will make this model very useful for the study of the mechanisms involved in portal fibrosis.

Effect of celecoxib on experimental liver fibrosis in rat

BACKGROUND/AIM

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Attenuated liver tumor formation in the absence of CCR2 with a concomitant reduction in the accumulation of hepatic stellate cells, macrophages and neovascularization

The liver parenchyma is populated by hepatocytes and several nonparenchymal cell types, including Kupffer cells and hepatic stellate cells. Both Kupffer cells and hepatic stellate cells are responsive to the chemokine CCL2, but the precise roles of CCL2 and these cells in liver tumor formation remain undefined. Hence, we investigated the effects of the lack of the major CCL2 receptor, CCR2, on liver tumor formation induced by intraportal injection of the murine colon adenocarcinoma cell line, colon 26. Wild-type mice showed macroscopic tumor foci in the liver 10 days after injection of colon 26 cells. After 10 days, CCL2 proteins were detected predominantly in tumor cells, coincident with increased intratumoral macrophage and hepatic stellate cell numbers. Although tumor formation occurred at similar rates in wild-type and CCR2-deficient mice up to 10 days after tumor cell injection, the number and size of tumor foci were significantly attenuated in CCR2-deficient mice relative to wild-type mice thereafter. Moreover, neovascularization and matrix metalloproteinase 2 expression were diminished in CCR2-deficient mice with a concomitant reduction in the accumulation of macrophages and hepatic stellate cells. Furthermore, matrix metalloproteinase 2 was detected predominantly in hepatic stellate cells but not in macrophages. We provided the first definitive evidence that the absence of CCR2-mediated signals can reduce the trafficking of hepatic stellate cells, a main source of matrix metalloproteinase 2, and consequently can diminish neovascularization during liver tumor formation.