Differential expression of monocyte chemotactic protein-1 (MCP-1) in transforming rat hepatic stellate cells

Non-alcoholic Fatty Liver Disease and Alcohol-Related Liver Disease: Two Intertwined Entities

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide, with a prevalence of 25-30%. Since its first description in 1980, NAFLD has been conceived as a different entity from alcohol-related fatty liver disease (ALD), despite that, both diseases have an overlap in the pathophysiology, share genetic-epigenetic factors, and frequently coexist. Both entities are characterized by a broad spectrum of histological features ranging from isolated steatosis to steatohepatitis and cirrhosis. Distinction between NAFLD and ALD is based on the amount of consumed alcohol, which has been arbitrarily established. In this context, a proposal of positive criteria for NAFLD diagnosis not considering exclusion of alcohol consumption as a prerequisite criterion for diagnosis had emerged, recognizing the possibility of a dual etiology of fatty liver in some individuals. The impact of moderate alcohol use on the severity of NAFLD is ill-defined. Some studies suggest protective effects in moderate doses, but current evidence shows that there is no safe threshold for alcohol consumption for NAFLD. In fact, given the synergistic effect between alcohol consumption, obesity, and metabolic dysfunction, it is likely that alcohol use serves as a significant risk factor for the progression of liver disease in NAFLD and metabolic syndrome. This also affects the incidence of hepatocellular carcinoma. In this review, we summarize the overlapping pathophysiology of NAFLD and ALD, the current data on alcohol consumption in patients with NAFLD, and the effects of metabolic dysfunction and overweight in ALD.

Pro- and Anti-fibrogenic Functions of Gram-Negative Bacterial Lipopolysaccharide in the Liver

Extensive research performed over several decades has identified cells participating in the initiation and progression of fibrosis, and the numerous underlying inter- and intra-cellular signaling pathways. However, liver fibrosis continues to be a major clinical challenge as the precise targets of treatment are still elusive. Activation of physiologically quiescent perisinusoidal hepatic stellate cells (HSCs) to a myofibroblastic proliferating, contractile and fibrogenic phenotype is a critical event in the pathogenesis of chronic liver disease. Thus, elucidation of the mechanisms of the reversal to quiescence or inhibition of activated HSCs, and/or their elimination via apoptosis has been the focus of intense investigation. Lipopolysaccharide (LPS), a gut-resident Gram-negative bacterial endotoxin, is a powerful pro-inflammatory molecule implicated in hepatic injury, inflammation and fibrosis. In both acute and chronic liver injury, portal venous levels of LPS are elevated due to increased intestinal permeability. LPS, via CD14 and Toll-like receptor 4 (TLR4) and its adapter molecules, stimulates macrophages, neutrophils and several other cell types to produce inflammatory mediators as well as factors that can activate HSCs and stimulate their fibrogenic activity. LPS also stimulates synthesis of pro- and anti-inflammatory cytokines/chemokines, growth mediators and molecules of immune regulation by HSCs. However, LPS was found to arrest proliferation of activated HSCs and to convert them into non-fibrogenic phenotype. Interestingly, LPS can elicit responses in HSCs independent of CD14 and TLR4. Identifying and/or developing non-inflammatory but anti-fibrogenic mimetics of LPS could be relevant for treating liver fibrosis.

Intestinally derived bacterial products stimulate development of nonalcoholic steatohepatitis

Fatty livers are susceptible to factors that cause inflammation and fibrosis, but fat deposition and the inflammatory response can be dissociated. While nonalcoholic fatty liver disease (NAFLD), caused by pathologic fat accumulation inside the liver, can remain stable for several years, in other cases NAFLD progresses to nonalcoholic steatohepatitis (NASH), which is characterized by fat accumulation and inflammation and is not a benign condition. In this review, we discuss the NASH host cells and microbial mechanisms that stimulate inflammation and predispose the liver to hepatocyte injury and fibrotic stages via increased lipid deposition. We highlight the interactions between intestine-derived bacterial products, such as lipopolysaccharide, and nutritional models of NAFLD and/or obese individuals. The results of modulating enteric microbiota suggest that gut-derived endotoxins may be essential determinants of fibrotic progression and regression in NASH.

Natural Compound Oridonin Inhibits Endotoxin-Induced Inflammatory Response of Activated Hepatic Stellate Cells

Hepatic stellate cells (HSCs) play an important role in hepatic fibrogenesis and inflammatory modulation. Endotoxin is dramatically increased in portal venous blood after serious injury and can contribute to liver damage. However, the mechanism underlying endotoxin's effects on HSCs remains largely unknown. Oridonin is a bioactive diterpenoid isolated from Rabdosia rubescens that exhibits anti-inflammatory properties in different tissues. In the present study, we determined the effects of oridonin on endotoxin-induced inflammatory response and signaling pathways in vitro. The production of proinflammatory cytokines in activated human HSCs line LX-2 was measured by ELISA and Western blots. Immunofluorescence and nuclear fractionation assay were used to determine NF-κB activity. Oridonin treatment significantly inhibited LPS-induced proinflammatory cytokines IL-1β, IL-6, and MCP-1 production as well as cell adhesion molecules ICAM-1 and VCAM-1. Additionally, oridonin blocked LPS-induced NF-κB p65 nuclear translocation and DNA binding activity. Oridonin prevented LPS-stimulated NF-κB regulator IKKα/β and IκBα phosphorylation and IκBα degradation. Combined treatment of oridonin and an Hsp70 substrate binding inhibitor synergistically suppressed LPS-stimulated proinflammatory cytokines and NF-κB pathway activation. Therefore, oridonin inhibits LPS-stimulated proinflammatory mediators through IKK/IκBα/NF-κB pathway. Oridonin could be a promising agent for a hepatic anti-inflammatory.

Therapeutic opportunities for alcoholic steatohepatitis and nonalcoholic steatohepatitis: exploiting similarities and differences in pathogenesis

Alcoholic steatohepatitis (ASH) and nonalcoholic steatohepatitis (NASH) are among the most frequent causes of chronic liver disease in the United States. Although the two entities are triggered by different etiologies - chronic alcohol consumption (ASH) and obesity-associated lipotoxicity (NASH) - they share overlapping histological and clinical features owing to common pathogenic mechanisms. These pathogenic processes include altered hepatocyte lipid metabolism, organelle dysfunction (i.e., ER stress), hepatocyte apoptosis, innate immune system activation, and hepatic stellate cell activation. Nonetheless, there are several disease-specific molecular signaling pathways, such as differential pathway activation downstream of TLR4 (MyD88-dependence in NASH versus MyD88-independence in ASH), inflammasome activation and IL-1β signaling in ASH, insulin resistance and lipotoxicity in NASH, and dysregulation of different microRNAs, which clearly highlight that ASH and NASH are two distinct biological entities. Both pathogenic similarities and differences have therapeutic implications. In this Review, we discuss these pathogenic mechanisms and their therapeutic implications for each disease, focusing on both shared and distinct targets.

Functional Immune Anatomy of the Liver-As an Allograft

The liver is an immunoregulatory organ in which a tolerogenic microenvironment mitigates the relative "strength" of local immune responses. Paradoxically, necro-inflammatory diseases create the need for most liver transplants. Treatment of hepatitis B virus, hepatitis C virus, and acute T cell-mediated rejection have redirected focus on long-term allograft structural integrity. Understanding of insults should enable decades of morbidity-free survival after liver replacement because of these tolerogenic properties. Studies of long-term survivors show low-grade chronic inflammatory, fibrotic, and microvascular lesions, likely related to some combination of environment insults (i.e. abnormal physiology), donor-specific antibodies, and T cell-mediated immunity. The resultant conundrum is familiar in transplantation: adequate immunosuppression produces chronic toxicities, while lightened immunosuppression leads to sensitization, immunological injury, and structural deterioration. The "balance" is more favorable for liver than other solid organ allografts. This occurs because of unique hepatic immune physiology and provides unintended benefits for allografts by modulating various afferent and efferent limbs of allogenic immune responses. This review is intended to provide a better understanding of liver immune microanatomy and physiology and thereby (a) the potential structural consequences of low-level, including allo-antibody-mediated injury; and (b) how liver allografts modulate immune reactions. Special attention is given to the microvasculature and hepatic mononuclear phagocytic system.

Kupffer cell-monocyte communication is essential for initiating murine liver progenitor cell-mediated liver regeneration

Liver progenitor cells (LPCs) are necessary for repair in chronic liver disease because the remaining hepatocytes cannot replicate. However, LPC numbers also correlate with disease severity and hepatocellular carcinoma risk. Thus, the progenitor cell response in diseased liver may be regulated to optimize liver regeneration and minimize the likelihood of tumorigenesis. How this is achieved is currently unknown. Human and mouse diseased liver contain two subpopulations of macrophages with different ontogenetic origins: prenatal yolk sac-derived Kupffer cells and peripheral blood monocyte-derived macrophages. We examined the individual role(s) of Kupffer cells and monocyte-derived macrophages in the induction of LPC proliferation using clodronate liposome deletion of Kupffer cells and adoptive transfer of monocytes, respectively, in the choline-deficient, ethionine-supplemented diet model of liver injury and regeneration. Clodronate liposome treatment reduced initial liver monocyte numbers together with the induction of injury and LPC proliferation. Adoptive transfer of monocytes increased the induction of liver injury, LPC proliferation, and tumor necrosis factor-α production.

CONCLUSION

Kupffer cells control the initial accumulation of monocyte-derived macrophages. These infiltrating monocytes are in turn responsible for the induction of liver injury, the increase in tumor necrosis factor-α, and the subsequent proliferation of LPCs.

Hepatic stellate cells and liver fibrosis

Hepatic stellate cells are resident perisinusoidal cells distributed throughout the liver, with a remarkable range of functions in normal and injured liver. Derived embryologically from septum transversum mesenchyme, their precursors include submesothelial cells that invade the liver parenchyma from the hepatic capsule. In normal adult liver, their most characteristic feature is the presence of cytoplasmic perinuclear droplets that are laden with retinyl (vitamin A) esters. Normal stellate cells display several patterns of intermediate filaments expression (e.g., desmin, vimentin, and/or glial fibrillary acidic protein) suggesting that there are subpopulations within this parental cell type. In the normal liver, stellate cells participate in retinoid storage, vasoregulation through endothelial cell interactions, extracellular matrix homeostasis, drug detoxification, immunotolerance, and possibly the preservation of hepatocyte mass through secretion of mitogens including hepatocyte growth factor. During liver injury, stellate cells activate into alpha smooth muscle actin-expressing contractile myofibroblasts, which contribute to vascular distortion and increased vascular resistance, thereby promoting portal hypertension. Other features of stellate cell activation include mitogen-mediated proliferation, increased fibrogenesis driven by connective tissue growth factor, and transforming growth factor beta 1, amplified inflammation and immunoregulation, and altered matrix degradation. Evolving areas of interest in stellate cell biology seek to understand mechanisms of their clearance during fibrosis resolution by either apoptosis, senescence, or reversion, and their contribution to hepatic stem cell amplification, regeneration, and hepatocellular cancer.

Next generation sequencing of the Ago2 interacting transcriptome identified chemokine family members as novel targets of neuronal microRNAs in hepatic stellate cells

BACKGROUND & AIMS

After myofibroblastic transdifferentiation, hepatic stellate cells (HSC), mainly involved in liver fibrosis by extracellular matrix production, exhibit an altered growth factor profile including increased expression of neuronal mediators. Here, we analyzed putative targets of neuronal microRNAs miR-9, miR-125b, and miR-128 by deep sequencing of the transcript population, interacting with the miRNA/Argonaute 2 (Ago2) complex in myofibroblastic HSC.

METHODS

MicroRNA expression was quantified by real-time PCR in primary HSC, isolated from the rat or human liver. Myofibroblastic HSC were transfected either with mimics or inhibitors of miR-9, miR-125b, and miR-128. RNA from immunoprecipitated Ago2-miRNA/transcript complexes was purified and used for next generation sequencing. Additionally, gene expression was investigated in quiescent and activated primary HSC, treated with the miR-128 mimic or inhibitor, by microarray analysis.

RESULTS

During myofibroblastic transdifferentiation of HSC, miR-9, miR-125b, and miR-128 expression was markedly increased. Transcriptome analysis of Ago2 bound mRNA by deep sequencing identified a broad spectrum of transcripts that interact with neuronal miRNAs in myofibroblastic HSC. In particular, in HSC overexpressing miR-128, many members of the chemokine family were bound to the Ago2 repression complex. Furthermore, a comprehensive profiling of gene expression demonstrates the high impact of neuronal miRNAs on the chemokine network.

CONCLUSIONS

Ago2 immunoprecipitation followed by deep sequencing is a useful tool to identify novel miRNA targets. Upregulation of neuronal miR-9, miR-125b, and miR-128 during myofibroblastic transition and the identified interaction with a wide range of chemokines and chemokine receptors suggest a prominent role of neuronal miRNAs in the inflammatory response of HSC during fibrosis.

Monocyte chemoattractant protein-1 deficiency does not affect steatosis or inflammation in livers of mice fed a methionine-choline-deficient diet

Monocyte chemoattractant protein-1 (MCP-1, Ccl2) expression is increased in livers of patients with nonalcoholic steatohepatitis and in murine models of steatohepatitis. Several studies in rodents indicate that MCP-1 contributes to liver steatosis induced by feeding a high-fat diet. However, the extent of MCP-1 involvement in the widely utilized methionine-choline-deficient (MCD) diet model of steatohepatitis has not been determined. We tested the hypothesis that MCP-1 contributes to steatohepatitis in mice fed the MCD diet. MCP-1-deficient mice on a C57Bl/6J background and age-matched C57Bl/6J mice were fed either MCD diet or control diet for 4 weeks. MCP-1 deficiency did not affect steatohepatitis, as indicated by liver histopathology, nor did it affect serum alanine aminotransferase activity, hepatic triglyceride levels, hepatic inflammatory gene induction, or macrophage accumulation in mice fed the MCD diet. MCP-1 deficiency reduced the expression of the profibrogenic genes, pro-collagen 1a1, connective tissue growth factor, and transforming growth factor-β, in mice fed the MCD diet. MCP-1 deficiency significantly reduced collagen deposition and α-smooth muscle actin protein levels in the livers of mice fed the MCD diet. The results indicate that MCP-1 does not contribute to liver steatosis or inflammation in the MCD diet model of steatohepatitis. Rather, the data suggest that MCP-1 contributes to fibrosis in mice fed the MCD diet, independent of effects on steatosis and inflammation.

Thyroid hormones induce activation of rat hepatic stellate cells through increased expression of p75 neurotrophin receptor and direct activation of Rho

We have previously shown that hyperthyroidism is detrimental for liver fibrosis and in this study we have investigated the mechanisms regulating triiodothyronine (T3) and L-thyroxine (T4) activation of hepatic stellate cells (HSC). Expression of alpha-smooth muscle actin (alphaSMA) and p75 neurotrophin receptor (p75NTR) was determined by western blot analyses and transient transfection of the promoters. Rho activation was assayed using a pull-down assay and by ELISA. Expression of thyroid hormone receptor alpha1 decreases, whereas T4 receptor integrin alphaVbeta3 increases, with transdifferentiation of HSC to myofibroblasts. T3 and T4 enhance HSC activation, without affecting proliferation or phosphorylation of mitogen-activated protein kinase, signal transducer and activator of transcription 3 or Akt. Addition of 10(-7) M T3 or T4 to thyroid hormone-depleted serum induces a twofold increase in activation marker alphaSMA, as well as upregulation of p75NTR protein levels. Both hormones enhance transcription of alphaSMA and p75NTR. We report a novel signaling pathway for thyroid hormones, activation of Rho. T4 induces activation of Rho acting through alphavbeta3 integrin, and the activation is abolished by the T4 antagonist, tetraiodothyroacetic acid, by peptide RGD and by a function-blocking antibody to integrin beta3. T3 and T4 increase phosphorylation of non-muscle myosin light chain II, a downstream signal to Rho/Rho-kinase activation. T3 also induces expression of tumor necrosis factor-alpha. In vivo, administration of T3 or T4 together with thioacetamide (TAA) enhances fibrosis after 3 weeks, compared with the TAA-treated group, accompanied by increased alphaSMA in T3- and T4-treated groups, and of p75NTR in T4-treated rats. Thyroid hormones enhance activation of HSC through increased p75NTR and alphaSMA expression and activation of Rho, therefore accelerating development of liver fibrosis.

Hepatic tumor-stroma crosstalk guides epithelial to mesenchymal transition at the tumor edge

The tumor-stroma crosstalk is a dynamic process fundamental in tumor development. In hepatocellular carcinoma (HCC), the progression of malignant hepatocytes frequently depends on transforming growth factor (TGF)-beta provided by stromal cells. TGF-beta induces an epithelial to mesenchymal transition (EMT) of oncogenic Ras-transformed hepatocytes and an upregulation of platelet-derived growth factor (PDGF) signaling. To analyse the influence of the hepatic tumor-stroma crosstalk onto tumor growth and progression, we co-injected malignant hepatocytes and myofibroblasts (MFBs). For this, we either used in vitro-activated p19(ARF) MFBs or in vivo-activated MFBs derived from physiologically inflamed livers of Mdr2/p19(ARF) double-null mice. We show that co-transplantation of MFBs with Ras-transformed hepatocytes strongly enhances tumor growth. Genetic interference with the PDGF signaling decreases tumor cell growth and maintains plasma membrane-located E-cadherin and beta-catenin at the tumor-host border, indicating a blockade of hepatocellular EMT. We further generated a collagen gel-based three dimensional HCC model in vitro to monitor the MFB-induced invasion of micro-organoid HCC spheroids. This invasion was diminished after inhibition of TGF-beta or PDGF signaling. These data suggest that the TGF-beta/PDGF axis is crucial during hepatic tumor-stroma crosstalk, regulating both tumor growth and cancer progression.

A TLR4/MD2 fusion protein inhibits LPS-induced pro-inflammatory signaling in hepatic stellate cells

Activated hepatic stellate cells (HSCs) play a key role in hepatic fibrogenesis. In injured liver they are the main extracellular matrix protein producing cell type and further perpetuate hepatic injury by secretion of pro-inflammatory mediators. Since LPS-mediated signaling through toll-like receptor 4 (TLR4) has been identified as key fibrogenic signal in HSCs we aimed to test TLR4 as potential target of therapy via ligand-binding soluble receptors. Incubation of human HSCs with a fusion protein between the extracellular domain of TLR4 and MD2 which binds LPS inhibited LPS-induced NFkappaB and JNK activation. TLR4/MD2 abolished LPS-induced secretion of IL-6, IL-8, MCP1, and RANTES in HSCs. In addition, TLR4/MD2 fused to human IgG-Fc neutralized LPS activity. Since TLR4 mutant mice are resistant to liver fibrosis, the TLR4/MD2 soluble receptor might represent a new therapeutic molecule for liver fibrogenesis in vivo.

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.

Protective effects of Ginkgo biloba, Panax ginseng, and Schizandra chinensis extract on liver injury in rats

This study investigated the effects of the combined extracts of Ginkgo biloba, Panax ginseng, and Schizandra chinensis at different doses on hepatic antioxidant status and fibrosis in rats with carbon tetrachloride (CCl4)-induced liver injury. Male Sprague-Dawley rats (n = 8-12 per group) were divided into the control, CCl4, CCl4 + silymarin (0.35%), CCl4 + low-dose herbal extract (0.24% of Ginkgo biloba, Panax ginseng, and Schizandra chinensis extract at 1:1:1; LE), and CCl4 + high-dose herbal extract (1.20% of the same herbal extract; HE) groups. Silymarin or herbal extract was orally given to rats a week before chronic intraperitoneal injection with CCl4 for 6 weeks. The pathological results showed that herbal extract suppressed hepatic bile duct proliferation, and low-dose herbal extract inhibited liver fibrosis. Hepatic superoxide dismutase (SOD) activity was lower in the CCl4 group, but there was no difference in the silymarin or herbal extract treated groups compared to the control group. Hepatic catalase activity and the ratio of reduced to oxidized glutathione were significantly higher (p < 0.05) in the HE group than those in the CCl4 group. Silymarin and herbal extract reversed the impaired hepatic total antioxidant status (p < 0.05). Herbal extract partially reduced the elevated hepatic lipid peroxides. Hepatic transforming growth factor-beta1 (TGF-beta1) level decreased significantly (p < 0.05) in the LE group. Therefore, high-dose herbal extract improved hepatic antioxidant capacity through enhancing catalase activity and glutathione redox status, whereas low-dose herbal extract inhibited liver fibrosis through decreasing hepatic TGF-beta1 level in rats with CCl4-induced liver injury.

Addressing liver fibrosis with liposomes targeted to hepatic stellate cells

Liver fibrosis is a chronic disease that results from hepatitis B and C infections, alcohol abuse or metabolic and genetic disorders. Ultimately, progression of fibrosis leads to cirrhosis, a stage of the disease characterized by failure of the normal liver functions. Currently, the treatment of liver fibrosis is mainly based on the removal of the underlying cause of the disease and liver transplantation, which is the only treatment for patients with advanced fibrosis. Hepatic stellate cells (HSC) are considered to be key players in the development of liver fibrosis. Chronically activated HSC produces large amounts of extracellular matrix and enhance fibrosis by secreting a broad spectrum of cytokines that exert pro-fibrotic actions in other cells, and in an autocrine manner perpetuate their own activation. Therefore, therapeutic interventions that inhibit activation of HSC and its pro-fibrotic activities are currently under investigation worldwide. In the present study we applied targeted liposomes as drug carriers to HSC in the fibrotic liver and explored the potential of these liposomes in antifibrotic therapies. Moreover, we investigated effects of bioactive compounds delivered by these liposomes on the progression of liver fibrosis. To our knowledge, this is the first study demonstrating that lipid-based drug carriers can be selectively delivered to HSC in the fibrotic liver. By incorporating the bioactive lipid DLPC, these liposomes can modulate different processes such as inflammation and fibrogenesis in the fibrotic liver. This dual functionality of liposomes as a drug carrier system with intrinsic biological effects may be exploited in new approaches to treat liver fibrosis.

Effects of a new bioactive lipid-based drug carrier on cultured hepatic stellate cells and liver fibrosis in bile duct-ligated rats

In the fibrotic liver, hepatic stellate cells (HSC) produce large amounts of collagen and secrete variety of mediators that promote development of fibrosis in this organ. Therefore, these cells are considered an attractive target for antifibrotic therapies. We incorporated the bioactive lipid dilinoleoylphosphatidylcholine (DLPC) into the membrane of liposomes, and then we evaluated its effect on hepatic stellate cell activation and liver fibrosis. To target DLPC-liposomes to HSC, human serum albumin modified with mannose 6-phosphate (M6P-HSA) was coupled to the surface of these liposomes. In vitro, the effects of the carrier were determined in primary cultures of HSC, Kupffer cells, and liver endothelial cells using real-time reverse transcription-polymerase chain reaction. In vivo DLPC-liposomes were tested in bile duct-ligated rats. Targeted M6P-HSA-DLPC-liposomes and DLPC-liposomes significantly reduced gene expression levels for collagen 1alpha1, alpha-smooth muscle actin (alpha-SMA), and transforming growth factor-beta (TGF-beta) in cultured HSC. In fibrotic livers, DLPC-liposomes decreased gene expression for TGF-beta and collagen 1alpha1 as well as alpha-SMA and collagen protein expression. In contrast, M6P-HSA-DLPC-liposomes enhanced expression of profibrotic and proinflammatory genes in vivo. In cultured Kupffer and endothelial cells M6P-HSA liposomes influenced the expression of proinflammatory genes. Both types of liposomes increased hepatocyte glycogen content in fibrotic livers, indicating improved functionality of the hepatocytes. We conclude that DLPC-containing liposomes attenuate activation of cultured HSC. In fibrotic livers, M6P-HSA-mediated activation of Kupffer and endothelial cells probably counteracts this beneficial effect of DLPC-liposomes. Therefore, these bioactive drug carriers modulate the activity of all liver cells during liver fibrosis.

Exposure to bacterial cell wall products triggers an inflammatory phenotype in hepatic stellate cells

Activated hepatic stellate cells (HSCs) secrete extracellular matrix components during hepatic fibrosis, but recent studies have shown that HSCs can also release a variety of proinflammatory cytokines. Moreover, bacterial endotoxemia is not only associated with systemic complications in the late stages of liver failure but is also a direct cause of liver damage, activating resident inflammatory cells. In this study, we investigated whether HSCs can respond directly to bacterial cell wall products acquiring a new phenotype. RT-PCR and immunocytochemistry assays were used to show that murine HSCs expressed specific mRNA transcripts and proteins for LPS and lipoteichoic acid (LTA) receptor systems and peptidoglycan recognition proteins. Exposing HSCs to bacterial endotoxins led to phosphorylation of mitogen-activated protein kinase ERK1 and the development of a proinflammatory phenotype. After exposure to LPS, LTA, or N-acetyl muramyl peptide, transforming growth factor-beta1, IL-6, and monocyte chemoattractant protein-1 (MCP-1) mRNA specific transcripts and proteins increased significantly in HSCs, as assayed by quantitative real-time RT-PCR and ELISA. These LPS-mediated effects in HSCs were receptor dependent, because LPS-induced ERK1 phosphorylation, IL-6, and MCP-1 mRNA and protein level upregulation were significantly less pronounced in HSCs isolated from C3H/HeJ mice lacking Toll-like receptor 4. In conclusion, our results show that murine HSCs express functional receptors for bacterial endotoxins, and HSCs exposed to bacterial products develop a strong proinflammatory phenotype. We speculate that high levels of bacterial endotoxins in the portal vein may directly induce a proinflammatory phenotype in HSCs that contributes to liver damage.

Normal rat hepatic stellate cells respond to endotoxin in LBP-independent manner to produce inhibitor(s) of DNA synthesis in hepatocytes

Endotoxin is implicated in the pathology of acute liver failure. The mechanisms of its actions on quiescent hepatic stellate cells (qHSCs) and their implications in hepatocyte injury are incompletely understood. We investigated effects of endotoxin (bacterial lipopolysaccharide; LPS) on qHSCs and subsequently on hepatocytes. After overnight culture following their isolation, qHSCs were incubated with or without endotoxin for 24 h. The cells and the culture supernatant were analyzed for cytokines and nitric oxide (NO) synthesis. The effects of qHSC-conditioned media on hepatocytes were then determined. LPS increased inducible NO synthase expression, stimulated NO synthesis, and inhibited DNA synthesis in qHSCs. qHSC-conditioned medium inhibited DNA synthesis in hepatocytes without affecting NO synthesis, while LPS (1-1,000 ng/ml)-conditioned qHSC medium stimulated NO synthesis and caused further inhibition of DNA synthesis and apoptosis. These effects of LPS were more pronounced when qHSCs were incubated with serum, but not with LPS-binding protein (LBP) although CD14 (a receptor for LPS-LBP complex) was found in qHSCs. LPS stimulated the synthesis of TNF-alpha, interleukin (IL)-6, and IL-1beta but not of TGF-beta in qHSCs. Individually or together, L-N(G)-monomethylarginine and antibodies to IL-1beta, IL-6, and TNF-alpha only partly reversed qHSC + LPS-conditioned medium-induced inhibition of DNA synthesis in hepatocytes. These results suggest that the effects of LPS on qHSCs are novel, occurring without the aid of LBP/CD14. They also indicate that other factors, in addition to NO, TGF-beta, TNF-alpha, IL-1beta, and IL-6 are involved in the mechanisms of the growth inhibitory effects of qHSCs on hepatocytes.

LPS-mediated NFκB activation varies between activated human hepatic stellate cells from different donors

The activation of hepatic stellate cells (HSC) is recognized as the key event of hepatic fibrosis [Virchows Arch. 430 (1997) 195; Semin. Liver Dis. 21 (2001) 437; Front. Biosci. 7 (2002) d808]. NFkappaB has been associated with the development of the activated phenotype, the expression of proinflammatory genes, and with promoting survival of activated HSC. High levels of circulating endotoxin are observed in liver fibrosis and several lines of evidence indicate that LPS plays an important role in chronic liver disease. Here, we investigated the LPS-induced NFkappaB activation in activated HSC from different human donors. HSC were isolated from liver specimens obtained during surgical liver resection and were activated by culturing on plastic. LPS-induced NFkappaB activity and IL-8 expression revealed a significant correlation but differed significantly comparing HSC from individual donors. These variations seen in LPS mediated NFkappaB activation and chemokine secretion between HSC from different donors in vitro may contribute to differences seen in vivo between patients in the progression of fibrosis and the degree of inflammation during chronic liver disease.

Limited role for CXC chemokines in the pathogenesis of alpha-naphthylisothiocyanate-induced liver injury

Alpha-naphthylisothiocyanate (ANIT) is a hepatotoxin that causes severe neutrophilic inflammation around portal tracts and bile ducts. The chemotactic signals that provoke this inflammatory response are unknown. In this study, we addressed the possibility that ANIT upregulates CXC chemokines in the liver and that these compounds mediate hepatic inflammation and tissue injury after ANIT treatment. Mice treated with a single dose of ANIT (50 mg/kg) exhibited rapid hepatic induction of the CXC chemokine macrophage inflammatory protein-2 (MIP-2). MIP-2 derived primarily from hepatocytes, with no apparent contribution by biliary cells. In ANIT-treated mice, the induction of MIP-2 coincided with an influx of neutrophils to portal zones; this hepatic neutrophil recruitment was suppressed by 50% in mice that lack the receptor for MIP-2 (CXCR2(-/-)). Interestingly, despite their markedly reduced degree of hepatic inflammation, CXCR2(-/-) mice displayed just as much hepatocellular injury and cholestasis after ANIT treatment as wild-type mice. Moreover, after long-term exposure, ANIT CXCR2(-/-) mice developed liver fibrosis that was indistinguishable from that in wild-type mice. In summary, our data show that CXC chemokines are responsible for some of the hepatic inflammation that occurs in response to ANIT but that these compounds are not essential to the pathogenesis of either acute or chronic ANIT hepatotoxicity.

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Impaired hepatic granuloma formation in mice deficient in C-C chemokine receptor 2

Granulomas are characterized histologically by a nodular collection of macrophages with occasional admixture of epithelioid cells, multinucleate giant cells, and other immunocompetent cells. Chemokines are considered to play an important role in the recruitment of these constituent cells of granulomas. The present study has examined the effect of a deficiency of C-C chemokine receptor-2 (CCR2) on hepatic granuloma formation induced by a single injection of Zymosan A. In CCR2+/+ mice, the number and the size of granulomas gradually increased until they reached peak values at 10 days after the injection. In contrast, both the number and the size of granulomas were smaller in CCR2-/- mice than in CCR2+/+ mice from days 5 to 21. They showed low peaks at day 5, after which the number and the size of the granulomas gradually decreased. Immunohistochemical analysis of the constituent granuloma cells using cell type-specific monoclonal antibodies revealed rapid accumulation of blood monocytes, with subsequent differentiation to macrophages, in CCR2+/+ mice during days 2-10. This process was greatly impaired in CCR2-/- mice and granulomas remained small. At all time points, the percentage of polymorphonuclear cells in granulomas was higher in CCR2-/- mice than in CCR2+/+ mice. Interestingly, multinucleate giant cells were frequently observed in granulomas in CCR2-/- mice, whereas they rarely appeared in CCR2+/+ mice. Profiles of liver cytokine RNA levels as well as serum cytokine levels revealed reduced expression of the Th1 cytokine IFN-gamma in CCR2-/- mice. These data clearly indicate that signalling through CCR2 has many effects on the normal growth and development of hepatic granulomas.

Toll-like receptor 4 mediates inflammatory signaling by bacterial lipopolysaccharide in human hepatic stellate cells

Bacterial lipopolysaccharide (LPS) stimulates Kupffer cells and participates in the pathogenesis of alcohol-induced liver injury. However, it is unknown whether LPS directly affects hepatic stellate cells (HSCs), the main fibrogenic cell type in the injured liver. This study characterizes LPS-induced signal transduction and proinflammatory gene expression in activated human HSCs. Culture-activated HSCs and HSCs isolated from patients with hepatitis C virus-induced cirrhosis express LPS-associated signaling molecules, including CD14, toll-like receptor (TLR) 4, and MD2. Stimulation of culture-activated HSCs with LPS results in a rapid and marked activation of NF-kappaB, as assessed by in vitro kinase assays for IkappaB kinase (IKK), IkappaBalpha steady-state levels, p65 nuclear translocation, NF-kappaB-dependent luciferase reporter gene assays, and electrophoretic mobility shift assays. Lipid A induces NF-kappaB activation in a similar manner. Both LPS- and lipid A-induced NF-kappaB activation is blocked by preincubation with either anti-TLR4 blocking antibody (HTA125) or Polymyxin B. Lipid A induces NF-kappaB activation in HSCs from TLR4-sufficient (C3H/OuJ) mice but not from TLR4-deficient (C3H/HeJ) mice. LPS also activates c-Jun N-terminal kinase (JNK), as assessed by in vitro kinase assays. LPS up-regulates IL-8 and MCP-1 gene expression and secretion. LPS-induced IL-8 secretion is completely inhibited by the IkappaB super repressor (Ad5IkappaB) and partially inhibited by a specific JNK inhibitor, SP600125. LPS also up-regulates cell surface expression of ICAM-1 and VCAM-1. In conclusion, human activated HSCs utilize components of TLR4 signal transduction cascade to stimulate NF-kappaB and JNK and up-regulate chemokines and adhesion molecules. Thus, HSCs are a potential mediator of LPS-induced liver injury.

ADAM12 in human liver cancers: TGF-beta-regulated expression in stellate cells is associated with matrix remodeling

"A disintegrin and metalloproteinases" (ADAMs) form a family of cell-surface glycoproteins with potential protease and cell-adhesion activities. We have investigated ADAM expression in human liver cancers and their regulation by several cytokines involved in liver injury. Using degenerative RT-PCR, cDNA encoding sequences for ADAM9 and ADAM12 were identified in human activated hepatic stellate cells (HSCs). Northern blot analyses showed that HSCs, but not hepatocytes, expressed transcripts for ADAM9 messenger RNA (mRNA) and both the long and short forms of ADAM12. This expression was associated with the transition from quiescent to activated state of rat HSCs and markedly increased in human livers with cirrhosis. ADAM12 but not ADAM9 expression was up-regulated by transforming growth factor beta (TGF-beta) in human activated HSCs. The PI3K inhibitor LY294002 and the mitogen-activated protein kinase kinase (MEK) inhibitor UO126 prevented ADAM12 induction by TGF-beta, suggesting the involvement of PI3K and MEK activities. In vivo, the steady-state of both ADAM9 and ADAM12 mRNA levels was nearly undetectable in both normal livers and benign tumors and increased in hepatocellular carcinomas (up to 3- and 6-fold, respectively) and liver metastases from colonic carcinomas (up to 40- and 60-fold, respectively). The up-regulation of both ADAM9 and ADAM12 was correlated with an increase in matrix metalloproteinase 2 expression and activity. In conclusion, in liver cancers ADAM9 and ADAM12 expression is associated with tumor aggressiveness and progression.

Emergence of different macrophage populations in hepatic fibrosis following thioacetamide-induced acute hepatocyte injury in rats

Macrophages may play a role in fibrogenesis. The kinetics and distribution of different macrophage populations were investigated immunohistochemically in hepatic lesions following acute hepatocyte injury induced in F344 rats by a single injection of thioacetamide (TAA) (300 mg/kg body weight, intraperitoneally). Hepatocyte degeneration or necrosis induced by TAA occurred mainly in the perivenular areas of hepatic lobules as early as post-injection (PI) days 1 and 3; fibrotic lesion development began in the damaged areas on day 1, and peaked on day 5; thereafter (PI days 7 and 10), the fibrotic areas decreased and were replaced by regenerated hepatocytes on PI days 15 and 20, indicating a remodelling process. In this rat model, the number of macrophages reacting with ED1 antibody (specific for exudate macrophages), ED2 (recognizing cell membrane antigens of resident macrophages, including Kupffer cells) and OX6 (recognizing MHC class II antigens expressed in antigen-presenting macrophages and dendritic cells) began to increase on PI day 1, peaking on PI day 3. The numbers gradually decreased on PI days 5 and 7; however, the statistically significant increase was maintained in respect of ED1-positive cells up to PI day 20, whereas no significant increase in ED2- and OX6-positive cells remained from PI day 10 onwards. Interestingly, of the ED1-, ED2- and OX6-positive cells, the OX6-positive cells were the least numerous. ED1- and OX6-positive cells appeared exclusively in the injured perivenular areas, whereas ED2-positive cells were present mainly in the mid-zonal areas and in smaller numbers in the perivenular areas. These findings indicated differences in kinetics and distribution between macrophage populations appearing in hepatic fibrosis. In addition, RT-PCR revealed that mRNA expression of osteopontin, a factor for induction and maintenance of macrophages in inflammation, was markedly increased on PI days 5, 7 and 10, suggesting a role in the pathogenesis of hepatic fibrosis.

Malondialdehyde-acetaldehyde-protein adducts increase secretion of chemokines by rat hepatic stellate cells

Findings obtained from our recent studies have demonstrated that malondialdehyde, a product of lipid peroxidation, and acetaldehyde can react together with proteins in a synergistic manner and form hybrid protein conjugates, which have been designated as malondialdehyde-acetaldehyde (MAA)-protein adducts. These adducts have been detected in livers of ethanol-fed rats and are immunogenic because significant increases in circulating antibody titers against MAA-adducted proteins have been observed in ethanol-fed rats and more recently in human alcoholics. Although immunological factors may tend to perpetuate liver injury, little is known about the direct functional consequences of MAA-adducted proteins on the different cellular populations of the liver. Hepatic stellate cells (HSCs) have been shown to be pivotal in the pathogenesis of fibrosis and in the amplification and self-perpetuation of the inflammatory process. The present study was conducted to determine the effects of MAA-adducted proteins on the function of HSCs. Rat HSCs were exposed to various amounts of MAA-protein adducts and their unmodified controls, and the secretion of two chemokines, monocyte chemoattractant protein (MCP)-1 and macrophage inflammatory protein (MIP)-2, that are involved in the chemotaxis of monocytes/macrophages and neutrophils, respectively, was determined. We observed that bovine serum albumin-MAA induced a dose- and time-dependent increase in the secretion of both of these chemokines. These findings indicate that MAA-adducted proteins may play a role in the modulation of the hepatic inflammatory response and could contribute to the pathogenesis of alcoholic liver disease.

The lymphoid liver: considerations on pathways to autoimmune injury

Immunologic injury in the liver involves immigrant T and B lymphocytes and a resident lymphoid population that comprises distinct lymphocytic cells and accessory cells. The forerunner to autoimmunity is breaching of natural self-tolerance and hence the disruption of a fundamental property of the immune system. Such breaching occurs by processes that include inflammatory activation of immunocytes and macrophages, spillage of intracellular constituents, and epitope mimicry by constituents of microorganisms, with these acting on a genetically conditional phenotype; compounding factors include aberrations of apoptosis, whether insufficient or excess. The downstream end requires specifically directed inflammatory leukocyte traffic as an essential component of autoimmune expressions in the liver. The culmination is an orchestrated attack on hepatocytes or biliary epithelial cells by multiple effector pathways. Progress in type 1 autoimmune hepatitis still requires knowledge of a disease-specific autoantigen(s) involved in T-cell reactivity, although such knowledge in type 2 autoimmune hepatitis, in which the known autoantigen is cytochrome P4502D6, has not yet been integrated into a clearly defined scheme of pathogenesis. For PBC there has been a very promising amalgamation of molecular knowledge of the mitochondrial autoantigens. Future insights require deeper analysis of molecular, genetic, macroenvironmental, and microenvironmental elements in predisposition.

Semi-quantification of human C-C chemokine mRNAs with reverse transcription/real-time PCR using multi-specific standards

A reverse transcription/real-time polymerase chain reaction (PCR) assay was established to semi-quantify the mRNA levels of the human C-C chemokines RANTES, MIP-1beta and MCP-1 relative to the housekeeping gene beta-actin. The assay showed a high sensitivity (below 60 cDNA molecules/10 microl reaction) and dynamic range (8 log units); both within-assay and inter-assay variability were below 0.06 log units and the accuracy was +/-0.06 log units for all four chemokines. Moreover, it is demonstrated that a multi-specific DNA fragment, which had previously been constructed for competitive PCR, can be used as a reliable external standard. This allows a direct semi-quantitative comparison of different chemokine mRNA levels and is a convenient alternative to the use of different sets of homologous external standards. The method was successfully applied to the semi-quantification of chemokines in human liver specimens and should be useful in further studies on steady state mRNA levels of C-C chemokines from low cell numbers or small tissue specimens.

Impact of alcohol on the ability of Kupffer cells to produce chemokines and its role in alcoholic liver disease

Chemokines are implicated in the pathogenesis of alcoholic liver disease in humans and in experimental models of alcohol intoxication. The major sources of these chemokines are Kupffer cells which represent more than 80% of tissue macrophages in the body. Kupffer cells are highly responsive to the effects of ethanol, endotoxin and human immunodeficiency virus (HIV)-1 glycoprotein120. These agents, either independently or in combination, may exacerbate the production of chemokines. Chemokines are agents that are highly chemotactic to mononuclear cells and granulocytes. The levels of these chemokines in sera and tissue are elevated in patients with alcoholic hepatitis, alcoholic cirrhosis, diseased livers, viral hepatitis, and in experimental models of chronic alcohol intoxication. Alcohol-induced influx of endotoxin from the gut into the portal circulation is suggested to play an important role in the activation of Kupffer cells which leads to enhanced chemokine release. The up-regulation of chemokines during alcohol consumption is selective. During the early phase of alcoholic liver disease, C-X-C or alpha-chemokines predominate. This is also associated with neutrophilic infiltration of the liver. In the later stage, up-regulation of C-C or beta-chemokine production and migration of mononuclear cells into the liver are observed, and this may lead to liver cirrhosis. Selective up-regulation of chemokine synthesis and release may involve differential modulation of the transcription factors required for chemokine gene expression. Increased cytokine release following alcohol consumption may also regulate chemokine secretion in Kupffer cells via paracrine and autocrine mechanisms and vice versa. In addition, infection with HIV-1 may further compromise the liver to more damage. During HIV-1 infection, a pre-existing liver disease superimposed on chronic alcohol consumption may also exacerbate HIV-1 replication and lymphocytic infiltration in the liver, because of the ability of HIV-1 gp120 to stimulate chemokine production by Kupffer cells and stimulate migration of inflammatory leucocytes in the liver.

Exaggerated hepatic injury due to acetaminophen challenge in mice lacking C-C chemokine receptor 2

Monocyte chemoattractant protein-1 is one of the major C-C chemokines that has been implicated in liver injury. The C-C chemokine receptor, CCR2, has been identified as the primary receptor that mediates monocyte chemoattractant protein-1 (MCP-1) responses in the mouse. Accordingly, the present study addressed the role of CCR2 in mice acutely challenged with acetaminophen (APAP). Mice genetically deficient in CCR2 (CCR2(-/-)) and their wild-type counterparts (CCR2(+/+)) were fasted for 10 hours before receiving an intraperitoneal injection of APAP (300 mg/kg). Liver and serum samples were removed from both groups of mice before and at 24 and 48 hours post APAP. Significantly elevated levels of MCP-1 were detected in liver samples from CCR2(+/+) and CCR2(-/-) mice at 24 hours post-APAP. Although CCR2(+/+) mice exhibited no liver injury at any time after receiving APAP, CCR2(-/-) mice exhibited marked evidence of necrotic and TUNEL-positive cells in the liver, particularly at 24 hours post-APAP. Enzyme-linked immunosorbent assay analysis of liver homogenates from both groups of mice at the 24 hours time point revealed that liver tissue from CCR2(-/-) mice contained significantly greater amounts of immunoreactive IFN-gamma and TNF-alpha. The in vivo immunoneutralization of IFN-gamma or TNF-alpha significantly attenuated APAP-induced liver injury in CCR2(-/-) mice and increased hepatic IL-13 levels. Taken together, these findings demonstrate that CCR2 expression in the liver provides a hepatoprotective effect through its regulation of cytokine generation during APAP challenge.

Acute alcohol intoxication and gadolinium chloride attenuate endotoxin-induced release of CC chemokines in the rat

This work tests the hypotheses that Kupffer cells are a major source of CC-chemokines (MIP-1alpha, MCP-1, RANTES) during acute endotoxemia and that acute ethanol intoxication modulates Escherichia coli lipopolysaccharide (LPS, 1 mg/Kg, i.v.)-induced chemokine release in the rat. LPS stimulated the release of CC-chemokines into the circulation, hepatic sequestration of leukocytes and liver injury. LPS-induced serum chemokines peaked at 1-3 h and could not be detected at 24-h posttreatment. Splenectomy significantly suppressed LPS-induced RANTES release, but not MIP-1alpha and MCP-1. Kupffer cell depletion by gadolinium chloride or acute ethanol intoxication significantly attenuated LPS-induced CC-chemokine release and hepatic injury. Hepatic sequestration of leukocytes during endotoxemia was also suppressed by acute ethanol. LPS downregulated the expression of MIP-1alpha and MCP-1 mRNAs and upregulated RANTES mRNA in Kupffer cells at 3-h post endotoxin. The expression of mRNAs was further suppressed in ethanol plus the LPS-treated group. Ethanol also suppressed the LPS-mediated priming of Kupffer cells for enhanced CC-chemokine release in vitro. Ethanol alone significantly upregulated the expression of CC-chemokine mRNA, and primed the Kupffer cells for enhanced RANTES release. CC-chemokine release and mRNA expression in hepatic sinusoidal endothelial cells were not significantly altered by ethanol, except for MCP-1 release. These data show that acute ethanol may be beneficial in tissue injury during acute endotoxemia.