Contribution of sinusoidal endothelial liver cells to liver fibrosis: expression of transforming growth factor-beta 1 receptors and modulation of plasmin-generating enzymes by transforming growth factor-beta 1

Epigallocatechin 3-gallate ameliorates bile duct ligation induced liver injury in mice by modulation of mitochondrial oxidative stress and inflammation

Cholestatic liver fibrosis was achieved by bile duct ligation (BDL) in mice. Liver injury associated with BDL for 15 days included significant reactive oxygen/nitrogen species generation, liver inflammation, cell death and fibrosis. Administration of Epigallocatechin 3-Gallate (EGCG) in animals reduced liver fibrosis involving parenchymal cells in BDL model. EGCG attenuated BDL-induced gene expression of pro-fibrotic markers (Collagen, Fibronectin, alpha 2 smooth muscle actin or SMA and connective tissue growth factor or CTGF), mitochondrial oxidative stress, cell death marker (DNA fragmentation and PARP activity), NFκB activity and pro-inflammatory cytokines (TNFα, MIP1α, IL1β, and MIP2). EGCG also improved BDL induced damages of mitochondrial electron transport chain complexes and antioxidant defense enzymes such as glutathione peroxidase and manganese superoxide dismutase. EGCG also attenuated hydrogen peroxide induced cell death in hepatocytes in vitro and alleviate stellate cells mediated fibrosis through TIMP1, SMA, Collagen 1 and Fibronectin in vitro. In conclusion, the reactive oxygen/nitrogen species generated from mitochondria plays critical pathogenetic role in the progression of liver inflammation and fibrosis and this study indicate that EGCG might be beneficial for reducing liver inflammation and fibrosis.

Liver fibrogenesis and metabolic factors

Mechanisms of liver fibrosis are complex and varied. Among them, metabolic factors are particularly important in the development of fibrosis associated with nonalcoholic steatohepatitis (NASH). These factors are some of the "multiple parallel hits" responsible for liver damage during NASH. Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome. Major profibrogenic protagonists, such as hepatic stellate cells and Kupffer cells, are activated by insulin resistance, apoptosis and local inflammation. Relations between steatosis, insulin resistance and fibrosis are complex. Initially, simple steatosis may be a way to store deleterious free fatty acid in neutral triglycerides. If the lipid storage threshold is exceeded, steatosis may become associated with lipotoxicity. Similarly, interindividual variations of adipose tissue expandability might explain various phenotypes, ranging from "metabolically obese patients with normal weight" to "metabolically normal morbidly obese patients". The metabolic abnormalities in subcutaneous and visceral adipose tissue are insulin resistance and low-grade inflammation, which are associated with increased release of free fatty acid flux and changes in adipocytokines production such as leptin, adiponectin and interleukin 6. The nuclear transcription factor peroxisome proliferator-activated receptor gamma (PPARγ) and the endocannabinoid system might have important roles in liver fibrogenesis and are potential therapeutic targets. Finally, with the development of new molecular tools, gut microbiota has been recently identified for its pleiotropic functions, including metabolism regulation. Better knowledge of these mechanisms should lead to new strategies for the treatment of metabolic factors that play a key role in liver injuries.

Inhibition of VEGF- and NO-dependent angiogenesis does not impair liver regeneration

Angiogenesis occurs through a convergence of diverse signaling mechanisms with prominent pathways that include autocrine effects of endothelial nitric oxide (NO) synthase (eNOS)-derived NO and vascular endothelial growth factor (VEGF). However, the redundant and distinct roles of NO and VEGF in angiogenesis remain incompletely defined. Here, we use the partial hepatectomy model in mice genetically deficient in eNOS to ascertain the influence of eNOS-derived NO on the angiogenesis that accompanies liver regeneration. While sinusoidal endothelial cell (SEC) eNOS promotes angiogenesis in vitro, surprisingly the absence of eNOS did not influence the angiogenesis that occurs after partial hepatectomy in vivo. While this observation could not be attributed to induction of alternate NOS isoforms, it was associated with induction of VEGF signaling as evidenced by enhanced levels of VEGF ligand in regenerating livers from mice genetically deficient in eNOS. However, surprisingly, mice that were genetically heterozygous for deficiency in the VEGF receptor, fetal liver kinase-1, also maintained unimpaired capacity for liver regeneration. In summary, inhibition of VEGF- and NO-dependent angiogenesis does not impair liver regeneration, indicating signaling redundancies that allow liver regeneration to continue in the absence of this canonical vascular pathway.

Bioimaging for targeted delivery of hyaluronic Acid derivatives to the livers in cirrhotic mice using quantum dots

Liver fibrosis or cirrhosis is one of the representative liver diseases with a high morbidity and mortality worldwide. Over the past decades, many kinds of antifibrotic compounds have been investigated in vitro and in vivo for the treatment of liver cirrhosis. In this work, real-time bioimaging of hyaluronic acid (HA) derivatives was carried out using quantum dots (QDots) to assess the possibility of HA derivatives as target-specific drug delivery carriers for the treatment of liver diseases. HA-QDot conjugates with an HA modification degree of about 22 mol % was synthesized by amide bond formation between carboxyl groups of QDots and amine groups of adipic acid dihydrazide modified HA (HA-ADH). According to in vitro cell culture tests, HA-QDot conjugates were taken up more to the cells causing chronic liver diseases such as hepatic stellate cells (HSC-T6) and hepatoma cells (HepG2) than normal hepatocytes (FL83B). After tail-vein injection, HA-QDot conjugates were target-specific, being delivered to the cirrhotic liver with a slow clearance longer than 8 days. Furthermore, immunofluorescence and flow cytometric analyses of dissected liver tissues revealed the target-specific delivery of HA derivatives to liver sinusoidal endothelial cells (LSEC) and HSC. The results were thought to reflect the feasibility of HA derivatives as novel drug delivery carriers for the treatment of various chronic liver diseases including hepatitis, liver cirrhosis, and liver cancer.

Relationship between transforming growth factor β1 and chronic hepatitis B

Transforming growth factor-β (TGF-β) is a family of related proteins that regulate many cellular processes including growth, differentiation, extracellular matrix formation and breaking down and immunosuppression. TGF-β1 is considered to play a pivotal role in hepatic stellate cell activation and a confirmed role in liver fibrosis, and its antiproliferative, proapoptotic, and immunosuppressive activities can play important roles in the pathogenesis of viral hepatitis. There is a marked correlation between the concentration and gene polymorphisms of TGF-β1 and chronic hepatitis B.

Role of ethanol in the regulation of hepatic stellate cell Function

Evidence has accumulated to suggest an important role of ethanol and/or its metabolites in the pathogenesis of alcohol-related liver disease. In this review, the fibrogenic effects of ethanol and its metabolites on hepatic stellate cells (HSCs) are discussed. In brief, ethanol interferes with retinoid metabolism and its signaling, induces the release of fibrogenic cytokines such as transforming growth factor β-1 (TGFβ-1) from HSCs, up-regulates the gene expression of collagen I and enhances type I collagen protein production by HSCs. Ethanol further perpetuates an activated HSC phenotype through extracellular matrix remodeling. The underlying pathophysiologic mechanisms by which ethanol exerts these pro-fibrogenic effects on HSCs are reviewed.

Direct hepatotoxic effect of KC chemokine in the liver without infiltration of neutrophils

KC is a mouse homolog of human chemokine gro-alpha (CXCL1), expression of which is increased in liver diseases. We show that activated, but not quiescent, hepatic stellate cells (HSCs) express KC. Hepatic stellate cells constitutively express the KC receptor, CXCR2. Addition of recombinant KC to HSCs undergoing activation in culture increases secretion and processing of Type I collagen. Overexpression of endogenous KC in the mouse liver could be achieved by an intraperitoneal injection of CCl(4), followed after 24 hrs by an injection of recombinant KC into circulation. This protocol resulted in about a 14-fold increase in concentration of KC protein in the liver. Overexpression of KC was associated with upregulation of the mRNA for CXCR2 and MIP-2 and with necrosis and increased synthesis of Type I collagen. This suggests that KC has a direct hepatotoxic effect, which led to a massive liver necrosis after 48 hrs. No accumulation of neutrophils was seen in the livers as judged by histology and reverse transcriptase-polymerase chain reaction analysis of myeloperoxidase mRNA. Autostimulation of KC and CXCR2 expression by recombinant KC protein in the mice with preexisting liver injury indicates a positive feedback regulation. Such regulation and direct hepatotoxicity of KC with increased collagen synthesis represent novel findings about the role of KC/ gro-alpha in liver pathology.

Co-administration of cyclosporine A alleviates thioacetamide-induced liver injury

AIM: To investigate the effects of cyclosporine A (CsA) on thioacetamide (TAA)-induced liver injury.

METHODS: CsA was co-administrated (7.5 μg/kg body weight per day, i.p.) into rat to investigate the role of CsA on TAA-(200 mg/kg body weight per 3 d for 30 d, i.p.)induced liver injury.

RESULTS: The data show that TAA caused liver fibrosis in rat after 30 d of treatment. CsA alleviates the morphological changes of TAA-induced fibrosis in rat liver. The blood glutamyl oxaloacetic transaminase (GOT)/glutamyl pyruvic transaminase (GPT) in the TAA-injury group is elevated compared to that of the normal rat. Compared with the TAA-injury group, the blood GOT/GPT and TGFβ1 (by RT-PCR analysis) are reduced in the CsA plus TAA-treated rat. The level of the transforming growth factor receptor I (TGFβ-R1) in the CsA plus TAA-treated group shows higher than that in the TAA only group, but shows a lower level of the fibroblast growth factor receptor 4 (FGFR4) in the CsA plus TAA-treated group, when using the Western blot analysis. After immunostaining of the frozen section, TGFβ-R1 and FGFR4 are more concentrated in rat liver after CsA plus TAA injury.

CONCLUSION: This result suggests that CsA has an alleviated effect on TAA-induced liver injury by increasing the multidrug resistance P-glycoprotein and could be through the regulation of TGFβ-R1 and FGFR4.

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Hepatitis B virus X antigen promotes transforming growth factor-beta1 (TGF-beta1) activity by up-regulation of TGF-beta1 and down-regulation of alpha2-macroglobulin

Hepatitis B virus (HBV) X antigen (HBxAg) may contribute to the development of hepatocellular carcinoma (HCC) by activation of signalling pathways such as NF-kappaB. To identify NF-kappaB target genes differentially expressed in HBxAg-positive compared to -negative cells, HepG2 cells consistently expressing HBxAg (HepG2X cells) were stably transfected with pZeoSV2 or pZeoSV2-IkappaBalpha. mRNA from each culture was isolated and compared by PCR select cDNA subtraction. The results showed lower levels of alpha(2)-macroglobulin (alpha(2)-M) in HepG2X-pZeoSV2 compared to HepG2X-pZeoSV2-IkappaBalpha cells. This was confirmed by Northern and Western blotting, and by measurement of extracellular alpha(2)-M levels. Elevated transforming growth factor-beta1 (TGF-beta1) levels were also seen in HepG2X compared to control cells. Serum-free conditioned medium (SFCM) from HepG2X cells suppressed DNA synthesis in a TGF-beta-sensitive cell line, Mv1Lu. The latter was reversed when the SFCM was pretreated with exogenous, activated alpha(2)-M or with anti-TGF-beta. Since elevated TGF-beta1 promotes the development of many tumour types, these observations suggest that the HBxAg-mediated alteration in TGF-beta1 and alpha(2)-M production may contribute importantly to the pathogenesis of HCC.

Leptin receptor-deficient Zucker (fa/fa) rat retards the development of pig serum-induced liver fibrosis with Kupffer cell dysfunction

The aim of this study was to investigate the role of leptin in the development of liver fibrosis with Kupffer cell function using leptin receptor deficient rats. Male Zucker (fa/fa) and control (fa/-) rats received pig serum for 8 weeks. Animals were sacrificed to estimate the degree of liver fibrosis and stellate cell activation with the expression of alpha smooth muscle actin (alphaSMA). Microarray analysis was performed. Isolated Kuppfer cells of Zucker and control rats were treated with LPS. LPS uptake and TNF-alpha production were examined. Stellate cells were also isolated from Zucker and control rats. The expression of procollagen type I mRNAs was examined. Control rats developed liver fibrosis 8 weeks after injection of pig serum and showed an increased liver hydroxyproline content of 348 +/- 34 microg/g (n = 10) compared with Zucker rats (225 +/- 13, n = 10, P < 0.01). The procollagen type I mRNA level and alphaSMA expression of Zucker rats were also significantly reduced. Microarray analysis indicated significantly reduced expression of TNF-alpha, LPS-binding protein, urokinase-type plasminogen activator (uPA), IGF, IGF-binding protein (IGFBP)-3,5, and increased expression of apolipoprotein IV. Isolated Kupffer cells of Zucker rats showed significantly reduced LPS uptake as well as TNF-alpha production compared with control rats. However, no significant change was observed in procollagen type I mRNA levels of isolated stellate cells after 4 days of culture on plastic dishes. These results suggest that leptin receptor deficiency retards the development of liver fibrosis due to the dysfunction of Kuppfer cells.

The pharmacokinetic and biological activity profile of dexamethasone targeted to sinusoidal endothelial and Kupffer cells

Dexamethasone (Dexa) was coupled to human serum albumin (Dexa10-HSA) for the targeting of this anti-inflammatory drug to Kupffer cells (KC) and sinusoidal endothelial cells (SEC) in the liver: key players in the pathogenesis of acute and chronic inflammatory liver diseases like fibrosis. Cell-specific delivery of Dexa may increase its efficacy and prevent side effects. We, therefore, studied the pharmacokinetic profile, efficacy, and toxicity of Dexa10-HSA in bile duct ligation (BDL)-induced fibrosis in rats.

RESULTS

Dexa10-HSA was taken up by scavenger receptors on KC and SEC and was rapidly cleared from the blood stream, with no differences in kinetic parameters between normal and fibrotic rats. KC isolated from livers of rats treated wi th Dexa10-HSA were unresponsive to lipopolysaccharide in contrast to controls. A dose of 0.1 mg kg(-1) three times a week reduced intrahepatic reactive oxygen species production strongly as compared to untreated BDL rats. This dose, however, also stimulated the depositions of collagens I and III. Overdosing of Dexa10-HSA (10 mgkg(-1)) led to a lethal reduction of body and spleen weight.

CONCLUSIONS

Dexa10-HSA has potent anti-inflammatory effects during BDL at extremely low doses, demonstrating the cell-specific targeting. However, the fibrotic process was not favourably affected. These results indicate a dual role for Dexa; besides blocking the release of pro-inflammatory cytokines it also reduces the release of antifibrotic mediators by SEC and KC.

Mechanisms controlling early development of the liver

Over the last decade significant advances have been made in our understanding of the molecular mechanisms that control early aspects of mammalian liver development. Studies using tissue explant cultures and molecular biology techniques as well as the analysis of transgenic and knockout mice have identified signaling molecules and transcription factors that are necessary for the onset of hepatogenesis. This review presents an overview of these studies and discusses the role of individual factors during hepatic development.

Leptin receptor-mediated signaling regulates hepatic fibrogenesis and remodeling of extracellular matrix in the rat

BACKGROUND & AIMS

In this study, we investigated the role of leptin and its receptors (Ob-R) in profibrogenic responses in the liver using Zucker (fa/fa) rats, a natural occurring Ob-R-deficient animal.

METHODS

Male Zucker (fa/fa) rats and their lean (+/?) littermates were given intraperitoneal injections of thioacetamide (TAA) (200 mg/kg body wt, 3 times/wk) for 4-8 weeks, and progression of hepatic fibrosis was evaluated. In vitro transactivation of hepatic stellate cells (HSCs) isolated from Zucker rats was evaluated by Western blotting and immunocytochemistry for alpha-smooth muscle actin and type I collagen. Further, a long-form Ob-R (Ob-Rb) in sinusoidal endothelial cells (SECs) and Kupffer cells was identified by reverse-transcription polymerase chain reaction. Moreover, transforming growth factor (TGF)-beta1 messenger RNA in LSE cells, a human SEC-derived cell line, was measured by Northern blotting.

RESULTS

Although the normal liver does not produce leptin, activated HSCs produced leptin in vivo during fibrogenesis caused by TAA. In Zucker rats, TAA-induced hepatic fibrosis was prevented almost completely, whereas induction of TGF-beta1 and activation of HSCs were abolished. It is less likely, however, that leptin plays an essential role in the activation of HSCs as a strong autocrine regulator, because HSCs isolated from Zucker rats undergo normal transactivation process in vitro. In contrast, SECs and Kupffer cells contain Ob-Rb, through which leptin up-regulates the expression of matrix remodeling genes including TGF-beta1.

CONCLUSIONS

Collectively, these findings indicated that leptin and its functional receptors (Ob-Rb) play a pivotal role in profibrogenic responses in the liver.

Effect of malondialdehyde-acetaldehyde-protein adducts on the protein kinase C-dependent secretion of urokinase-type plasminogen activator in hepatic stellate cells

Previous studies from our laboratory have shown that malondialdehyde-acetaldehyde-protein adducts (MAA adducts) are formed in hepatocytes of ethanol-fed rats and directly influence the hepatic stellate cells (HSCs) to induce their secretion of chemokines and to up-regulate their expression of adhesion molecules. Since protein kinase C (PKC) is known to play a major role in many diverse intracellular signal transduction processes, we investigated whether MAA adducts influence the function of HSCs via a PKC-dependent pathway. HSCs in culture were exposed to MAA adducts, and PKC activity was determined. We observed a time- and concentration-dependent activation of PKC when cultures were exposed to BSA-MAA as compared with unmodified BSA. Using PKC isoform-specific inhibitors, we also showed that BSA-MAA induces the activation of a specific isoform of PKC, PKC-alpha, in HSCs. No activation of PKC was observed when HSCs were exposed to other aldehyde adducts such as BSA-acetaldehyde or BSA-malondialdehyde, indicating that the effects of MAA adducts on HSCs were somewhat specific. We further examined whether the observed increase in PKC activation induced by MAA adducts in HSCs, in turn, causes a functional effect. We observed that BSA-MAA induces the increased secretion of urokinase-type plasminogen activator, a key component of the plasmin-generating system, and that PKC activation is necessary for this enhanced urokinase-type plasminogen activator secretion. These results indicate that MAA adducts via a PKC-mediated pathway may regulate plasmin-mediated matrix degradation in the liver, thereby contributing to the progression of hepatic fibrosis.

Induction of type 1 plasminogen activator inhibitor in human liver ischemia and reperfusion

BACKGROUND/AIMS

The detailed role of type 1 plasminogen activator inhibitor (PAI-1) in liver with ischemia reperfusion injury remains unclear. The aim of the present study was to examine this mechanism, focusing on inflammatory cytokines.

METHODS

Eighteen patients who underwent partial hepatectomy (PH) for metastatic liver tumors using only Pringle's maneuver were enrolled in the study. Peripheral blood was taken perioperatively and PAI-1, tissue type plasminogen activator (tPA), plasma aspartate aminotransferase (AST) and cytokine levels were measured. Two liver specimens were taken from each patient, one before ischemia and the other after PH, for detection of mRNA of PAI-1, tPA, tumor growth factor (TGF)-beta1, interleukin-1beta and tumor necrosis factor-a. Immunohistochemistry and Western blotting were performed to detect PAI-1 protein in the liver.

RESULTS

The average plasma PAI-1 antigen level reached a maximum after the final clamp (121.6+/-5.9 ng/ml). The average PAI-1 level in hepatic veins (140.4+/-6.3 ng/ml) after the last Pringle's maneuver was higher than that in peripheral veins (p<0.0001). A correlation was observed between the ratio of the corrected fluorescent activity of PAI-1 before and after ischemia and TGF-beta1 mRNA levels in the liver after PH (p=0.003). PAI-1 protein could be detected in parenchymal and non-parenchymal cells of the liver obtained after ischemia reperfusion injury.

CONCLUSIONS

PAI-1 was produced in human livers after ischemia reperfusion injury provoked by Pringle's maneuver, giving valuable information regarding the degree of warm ischemic damage.

In vivo inhibition of rat stellate cell activation by soluble transforming growth factor beta type II receptor: a potential new therapy for hepatic fibrosis

Transforming growth factor beta (TGF-beta) is a well characterized cytokine that appears to play a major role in directing the cellular response to injury, driving fibrogenesis, and, thus, potentially underlying the progression of chronic injury to fibrosis. In this study, we report the use of a novel TGF-beta receptor antagonist to block fibrogenesis induced by ligation of the common bile duct in rats. The antagonist consisted of a chimeric IgG containing the extracellular portion of the TGF-beta type II receptor. This "soluble receptor" was infused at the time of injury; in some experiments it was given at 4 days after injury, as a test of its ability to reverse fibrogenesis. The latter was assessed by expression of collagen, both as the mRNA in stellate cells isolated from control or injured liver and also by quantitative histochemistry of tissue sections. When the soluble receptor was administered at the time of injury, collagen I mRNA in stellate cells from the injured liver was 26% of that from animals receiving control IgG (P < 0.0002); when soluble receptor was given after injury induction, collagen I expression was 35% of that in control stellate cells (P < 0.0001). By quantitative histochemistry, hepatic fibrosis in treated animals was 55% of that in controls. We conclude that soluble TGF-beta receptor is an effective inhibitor of experimental fibrogenesis in vivo and merits clinical evaluation as a novel agent for controlling hepatic fibrosis in chronic liver injury.

Increased expression of plasminogen activator and plasminogen activator inhibitor during liver fibrogenesis of rats: role of stellate cells

BACKGROUND/AIMS

Plasminogen activators and plasminogen activator inhibitors are important regulators of the balance between the proteolytic and antiproteolytic activities that determine extracellular matrix turnover. We examined the expression of plasminogen activator-plasmin system components in experimental liver fibrosis of rats.

METHODS

Liver fibrosis was produced in rats by injecting carbon tetrachloride for 6 to 12 weeks. Gene expression for plasminogen activator inhibitor-1 (PAI-1), urokinase and tissue plasminogen activators (uPA and tPA), urokinase plasminogen activator receptor (uPAR), and transforming growth factor-beta1 (TGF-beta1) was examined by Northern analysis. Western analysis was performed to detect protein expression of PAI-1, uPA and uPAR. An immunohistochemical study was performed to detect the localization of PAI-1. Additionally, primary cultured liver cells were examined by Northern and Western analyses for this protein with or without prior incubation with TGF-beta1.

RESULTS

At 6 weeks, when fibrosis had occurred, uPA and uPAR mRNAs had increased 2.8-fold and 1.8-fold, respectively; PAI-1 and tPA mRNA levels were unchanged. At the cirrhotic stage (9 to 12 weeks), mRNA levels for PAI-1, uPA, uPAR and tPA were all increased. Western analysis also showed increased uPA and uPAR expressions in fibrotic liver, and increased PAI-1, uPA and uPAR expressions in cirrhotic liver. PAI-1 protein was also demonstrated immunohistochemically along sinusoids, vessels, and bile duct cells of normal and fibrotic liver. In liver cell cultures, Kupffer cells, hepatocytes, and especially stellate cells, expressed PAI-1. Expression was enhanced in stellate cells cultured from fibrotic or cirrhotic liver or stimulated in vitro with TGF-beta1.

CONCLUSION

Though increased uPA and uPAR may act on matrix degradation in fibrotic liver, increased PAI-1 together with uPA, uPAR and tPA are associated with overall inhibition of matrix degradation in cirrhotic liver. Hepatic stellate cells are an important source of PAI-1 during liver fibrosis.

Transforming growth factor-beta1 stimulates the synthesis of basement membrane proteins laminin, collagen type IV and entactin in rat liver sinusoidal endothelial cells

BACKGROUND/AIMS

It is suggested that during fibrogenesis as well as during carcinogenesis of the liver, the hepatic microvascular phenotype is transformed from sinusoids - which lack a basement membrane--into continuous capillaries which rest on a basement membrane. As transforming growth factor (TGF)-beta1 seems to be the most effective mediator in the stimulation of matrix protein synthesis, we were interested in the modulation of basement membrane proteins collagen type IV, laminin, and entactin expression by TGF-beta1 in liver sinusoidal endothelial cells (SECs), especially since a stimulation of the synthesis of collagen type IV but not of entactin and laminin by TGF-beta1 has been demonstrated in a fibrosarcoma cell line.

METHODS

The synthesis of the basement membrane (BM) proteins entactin, laminin, and collagen type IV and of the extracellular matrix (ECM) proteins tenascin and fibronectin with or without TGF-beta1--stimulation was analyzed by immunostaining, immunoprecipitation of endogenously labeled proteins and Northern blot analysis of total RNA extracted from freshly isolated or cultured SECs from rat or guinea pig livers. Furthermore, SECs were isolated from acutely and chronically CCl4-damaged rat livers and were analyzed for matrix protein expression.

RESULTS

SECs were adherent 24 h after isolation and formed confluent monolayers on day 4 of primary culture. Specific immunoprecipitates and specific transcripts for the BM proteins entactin, laminin, and collagen type IV and for ECM proteins tenascin and fibronectin were detectable in freshly isolated or cultured SECs. The synthesis of all tested BM proteins and ECM proteins was stimulated at least 3-fold by TGF-beta1. In SECs isolated after CCl4-induced acute and chronic liver damage, increased levels of matrix protein transcripts were detectable.

CONCLUSIONS

The stimulation of the synthesis of all BM-proteins by TGF-beta1 in vitro and the accumulation of ECM transcripts in SECs isolated from CCl4-treated livers, suggests that SECs are involved in the formation of a basement membrane during the "capillarization" of the sinusoids during liver disease.

Alpha2-macroglobulin reduces paracrine- and autocrine-stimulated matrix synthesis of cultured rat hepatic stellate cells

BACKGROUND

Transforming growth factor beta1 (TGF-beta1) is considered to represent a major fibrogenic mediator in the liver. The aim of the present study was to investigate whether alpha2-macroglobulin (alpha2M) might reduce paracrine- and autocrine-stimulated matrix synthesis of cultured rat hepatic stellate cells (HSCs) by scavenging TGF-beta.

METHODS AND RESULTS

Using native agarose electrophoresis, we demonstrated that alpha2M binds [125I]-TGF-beta1 within minutes. Preincubation of transiently acidified supernatants of cultured Kupffer cells, secondary cultured (activated) HSC and platelet lysate with, respectively, 500 and 2000 microg mL-1 alpha2M significantly reduced the concentration of active TGF-beta1 in these media. As a consequence of TGF-beta scavenging by alpha2M, paracrine-stimulated proteoglycan synthesis of primary cultured HSCs was reduced significantly. Furthermore, addition of 200 microg mL-1 alpha2M to passaged (activated) HSCs resulted in (a) a reduction in autocrine-stimulated extracellular matrix synthesis (proteoglycan -52%, fibronectin -55%) and (b) increased cell proliferation. A similar reduction in matrix synthesis was observed after the addition of 5 micromol L-1 TGF-beta1 antisense oligonucleotide to activated HSCs.

CONCLUSION

We conclude that alpha2M reduces paracrine-and autocrine-stimulated extracellular matrix synthesis of cultured HSCs by scavenging TGF-beta. These mechanisms might restrict liver fibrogenesis.

Targeting of naproxen covalently linked to HSA to sinusoidal cell types of the liver

The kinetic behaviour of a naproxen human serum albumin conjugate (Nap23-HSA) was investigated in rats and in isolated perfused rat livers (IPRL), as compared to its active metabolite naproxen-lysine (Nap-lysine) and free naproxen. Through covalently linking the anti-inflammatory drug naproxen to HSA, this drug can be selectively delivered to non parenchymal cells of the liver. Liver endothelial and Kupffer cells play an important role in the pathogenesis of inflammatory liver diseases. Targeting naproxen to these cells might increase its efficacy and reduce the side effects. The altered kinetic properties of Nap23-HSA, after i.v. injection of 22 mg x kg(-1), as compared to an equimolar amount of the uncoupled drug, were demonstrated in vivo by a decrease in the steady state volume of distribution (41 +/- 5 vs. 134 +/- 19 ml x kg(-1)), a decrease in its clearance (0.48 +/- 0.05 vs. 0.63 +/- 0.1 ml x min(-1) x kg(-1)), a shorter plasma half life (60 +/- 11 vs. 152 +/- 44 min) and a sustained biliary excretion. Liver targeting of Nap23-HSA was clearly demonstrated: drug content of the liver 180 min after injection was about 30 times higher for Nap23-HSA as compared to naproxen itself. The IPRL experiments showed that the Vmax of hepatic removal of the conjugate was 40 microg x min(-1) x g liver(-1). With doses below receptor saturation a rapid removal of the conjugate (t1/2 = 6 min) from the perfusion medium was found. In conclusion, this study demonstrates the saturable uptake of Nap23-HSA and its lysosomal degradation in both in vivo and IPRL experiments. Covalently linked naproxen is released as Nap-lysine. This active metabolite accumulates in Kupffer and endothelial cells in which it reaches therapeutic concentrations. Release from these cells leads to rapid uptake by hepatocytes and carrier mediated excretion into bile. Levels of Nap-lysine in bile and plasma reflect the slowest step in its generation: the proteolytic release in endothelial and Kupffer cells.

The significance of colocalization of plasminogen activator inhibitor-1 and vitronectin in hepatic fibrosis

BACKGROUND

We examined the relationships among vitronectin (VN), plasminogen activator inhibitor-1 (PAI-1), and transforming growth factor beta 1 (TGF-beta 1) in liver diseases to evaluate the presence of plasmin cascade in human hepatic fibrosis.

METHODS

Blood and liver tissues were obtained from 57 patients with liver disease. Plasma VN, PAI-1 antigen, and PAI-1 activity levels were evaluated. Biopsied liver specimens were observed by light and electron microscopy after immunohistochemical staining. Morphometric analysis was performed on these specimens.

RESULTS

Plasma VN and PAI-1 activity levels decreased significantly with the progression of hepatic fibrosis and were particularly marked in the liver cirrhosis group. Plasma PAI-1 antigen level increased significantly. The immunolocalization of the active form of TGF-beta became more intense with the progression of hepatic fibrosis, whereas that of the dual-stained positive areas of PAI-1 and VN (PAI-1.VN) decreased. There was a positive correlation between TGF-beta and PAI-1, whereas there was a negative correlation between TGF-beta and PAI-1.VN. Immunoelectron microscopy showed the localization of PAI-1-VN in the extracellular space around the sinusoidal cells or surface of aggregating platelets, TGF-beta mainly in Ito cells, and VN in hepatocytes near the focal necrotic area or fibrous septa.

CONCLUSIONS

These findings suggest that VN and PAI-1 are related to the active form of TGF-beta and that it is possible that the plasmin cascade is present in the human liver.

Cytokines and the hepatic acute phase response

The acute phase response is an orchestrated response to tissue injury, infection or inflammation. A prominent feature of this response is the induction of acute phase proteins, which are involved in the restoration of homeostasis. Cytokines are important mediators of the acute phase response. Uncontrolled and prolonged action of cytokines is potentially harmful, therefore mechanisms exist which limit the activity of cytokines; these include soluble cytokine receptors and receptor antagonists. The cytokine signal is transmitted into the cell via membrane-bound receptors. Different intracellular signalling pathways are activated by different cytokine-receptor interactions. Eventually, cytokine-inducible transcription factors interact with their response elements in the promotor region of acute phase genes and transcription is induced. Systemic inflammation results in a systemic acute phase response. However, local inflammatory or injurious processes in the liver may also induce an acute phase response, for example after partial hepatectomy and during hepatic fibrosis. The acute phase proteins induced in these conditions probably act to limit proteolytic and/or fibrogenic activity and tissue damage. The possible function of the acute phase protein alpha 2-macroglobulin in hepatic fibrosis is discussed in some detail.

Cytokine gene expression in cirrhotic and non-cirrhotic human liver

BACKGROUND/AIMS

In order to explore the role of cytokines in the pathogenesis of liver cirrhosis, we analyzed their gene expression in hepatic biopsies from patients with alcoholic liver cirrhosis, post-hepatitis C liver cirrhosis, and with idiopathic portal hypertension without cirrhosis.

METHODS

We assessed the gene expression of interleukins 1 beta, 2, 6, 8, and 10, as well as of tumor necrosis factor-alpha, transforming growth factor-beta and interferon-gamma by a quantitative polymerase chain reaction.

RESULTS

We found high levels of transforming growth factor-beta in post-hepatitis C liver cirrhosis, high to moderate in alcoholic liver cirrhosis and low in non-cirrhotic specimens. Expression of interleukin-10, tumor necrosis factor-alpha, and interferon-gamma genes was detected in most post-hepatitis C liver cirrhosis, but not in idiopathic portal hypertension or alcoholic liver cirrhosis biopsies. The interleukin1-beta, 6 and 8 gene expression was significantly lower in alcoholic liver cirrhosis compared to post-hepatitis C liver cirrhosis, but higher compared to idiopathic portal hypertension specimens. Thus, post-hepatitis C liver cirrhosis samples showed a high degree of cytokine gene expression, whereas in alcoholic liver cirrhosis it tended to be moderate, and restricted to some cytokines (transforming growth factor-beta, interleukin-1, 6 and 8, but not interleukin-10, tumor necrosis factor-alpha or interferon-gamma). In contrast, most non-cirrhotic specimens showed a restricted and low cytokine gene expression.

CONCLUSIONS

These data suggest that transforming growth factor-beta may have an important role in liver fibrosis and inflammation. Interleukin-1 beta, 6, 8, tumor necrosis factor-alpha and interferon-gamma, appear to participate in the pathogenesis of the mild to severe inflammatory phenomena seen in alcoholic and post-hepatitis C liver cirrhosis, respectively. Our data suggest that tumor necrosis factor-alpha does not participate in the hepatocellular damage of alcoholic liver cirrhosis, and indicate that neither interferon-gamma nor interleukin-10, at least at the levels observed in post-hepatitis C liver cirrhosis, are able to counteract the fibrotic/inflammatory process seen in this condition.

Transforming growth factor-beta in GI neoplasia, wound healing and immune response

The last decade has been marked by tremendous advances in the biochemical and functional characterization of TGF-betas and their receptors in normal and transformed cells. TGF-betas have been shown to modulate proliferation, differentiation and motility of different cell types in a number of in vitro model systems and in some cases with some intriguing results. It is obvious that there is no simple pattern that explains the TGF-betas biological activity in vitro and their effects on cell behaviour need to be assessed in the context of an appropriate physiological cellular environment. Cell-cell and cell-matrix interactions, the differentiating status of the cell together with the functional activity of other soluble growth factors can influence how TGF-betas modulate cell behaviour. However, the overwhelming interest in this field shown by clinicians and basic scientists is rapidly increasing our understanding of how growth factors such as TGF-betas regulate the homeostasis of the GI mucosa and their role in gastrointestinal carcinogenesis.

Enhancement of plasma fibrinolysis in vitro by jararhagin, the main haemorrhagic metalloproteinase in Bothrops jararaca venom

Jararhagin, a haemorrhagic metalloproteinase from Bothrops jararaca venom, plays an important role in systemic as well as local haemorrhage. In this study, the effect of jararhagin on the fibrinolytic system was investigated. The fibrinolytic activity of various kinds of animal plasmas was measured by the fibrin plate method. No activity was detected in plasma alone. However, after mixing plasma with jararhagin, strong fibrinolytic activity was recorded in guinea-pig, horse, dog, rabbit and human plasmas. The mechanism of the increase of firbinolytic activity by jararhagin was studied further in guinea-pig plasma. Fibrin-zymographic studies indicated that jararhagin increased tissue-type plasminogen activator (tPA) activity by the dissociation of a complex of tPA with type 1 plasminogen activator inhibitor (PAI-1). alpha 2-Plasmin inhibitor (alpha 2-PI) activity in the plasma was measured using a synthetic chromogenic substrate method after incubation with jararhagin. The alpha 2-PI activity in the plasma decreased in both time-dependent and dose-dependent manners. These in vitro results suggest that, in some animal plasmas, jararhagin increases plasma fibrinolytic activity by causing dissociation of the tPA/PAI-1 complex and by the inactivation of alpha 2-PI. It is possible that this direct action of jararhagin on the enhancement of plasma fibrinolytic activity may contribute to the aetiology of systemic haemorrhage frequently observed in human victims of B. jararaca envenoming.

Role of Ito cells in the degradation of matrix in liver

Liver fibrosis is a dynamic process caused by changes in not only the synthesis of matrix proteins but also their degradation. Current evidence indicates that Ito cells, when activated to a myofibroblastic phenotype, play a very active role in regulating matrix degradation in liver. This is mediated via their ability to synthesize and release several members of the matrix metalloproteinase family, a class of enzymes which are responsible for degradation of matrix proteins in the extracellular space. Activated Ito cells have been demonstrated to release prostromelysin, progelatinase A and the pro-enzyme form of interstitial collagenase. In addition, these cells can express appropriate systems for cleaving pro-metalloproteinases to active forms (e.g. the plasminogen activator system, urokinase) as well as specific tissue inhibitors of the activated metalloproteinases (TIMP). In the early phases of liver injury, enzymes with the ability to degrade components of normal liver matrix are expressed (stromelysin and gelatinase A). In contrast, in the fibrotic phase of liver injury, during which fibrillar collagens accumulate, there is little (if any) expression of interstitial collagenase but marked expression of TIMP. These findings suggest that metalloproteinase and their inhibitors play a significant role in liver injury and fibrosis.

Cell-specific expression of transforming growth factor-beta in rat liver. Evidence for autocrine regulation of hepatocyte proliferation

Expression of the group of cytokines known as transforming growth factor-beta (TGF-beta 1, -beta 2 and -beta 3) is increased during liver regeneration induced by a 70% partial hepatectomy. The origin of these changes was examined in purified isolates of hepatocytes, sinusoidal endothelial cells, Kupffer cells (liver macrophages), and lipocytes (Ito or stellate cells) from normal and regenerating liver. In normal liver, TGF-beta 1 and -beta 2 levels were relatively high in sinusoidal endothelial cells and Kupffer cells. After partial hepatectomy, an early peak of TGF-beta 2 and -beta 3 was present in all four cell types, followed by a sustained increase in mRNA for TGF-beta 1, -beta 2, and -beta 3 primarily in the hepatocyte population. The specificity of these changes was established by examining a mechanistically different injury model, fibrosis induced by ligation of the biliary duct. In this model, TGF beta mRNA was increased only in lipocytes and the increase was progressive over a 7-d period of observation. Secretion of TGF beta protein was examined in cell isolates placed in short-term primary culture and generally reflected the corresponding mRNA level. The TGF beta released by hepatocytes was entirely in the latent form, whereas the individual nonparenchymal cell isolates released 50-90% active TGF beta. Hepatocyte-conditioned culture medium, after treatment to activate latent TGF beta, inhibited hepatocellular DNA synthesis as did the authentic factor. The data indicate that after injury TGF beta increases selectively in the cells that are the target of the factor, i.e., in hepatocytes after partial hepatectomy and in lipocytes in inflammation and fibrosis. We conclude that the effects of TGF beta in liver regeneration and fibrogenesis are predominantly, if not exclusively, autocrine.