Cytokine regulation of hepatic stellate cells in liver fibrosis

Dilinoleoylphosphatidylcholine prevents transforming growth factor-beta1-mediated collagen accumulation in cultured rat hepatic stellate cells

Polyenylphosphatidylcholine (PPC), a mixture of polyunsaturated phosphatidylcholines, protects against alcoholic and nonalcoholic liver fibrosis in baboons and rats, respectively. In this study, we assessed the antifibrogenic action of dilinoleoylphosphatidylcholine (DLPC), the main phosphatidylcholine species of PPC, against transforming growth factor-beta1-mediated expression of alpha1(I) procollagen, tissue inhibitor of metallopreoteinase-1 (TIMP-1) and matrix metalloproteinase-13 (MMP-13) in cultured rat hepatic stellate cells (HSCs). In primary culture-activated HSCs, TGF-beta1 up-regulated the alpha1(I) procollagen mRNA level with a concomitant increase in type I collagen accumulation in culture media. Whereas TIMP-1 mRNA levels and TIMP-1 accumulation in media were also increased by TGF-beta1, MMP-13 mRNA expression and MMP-13 concentration in media were not altered. DLPC fully blocked TGF-beta1-induced increase in alpha1(I) procollagen mRNA expression and decreased collagen accumulation in media. Whereas TIMP-1 mRNA level and TIMP-1 accumulation in media were decreased by DLPC, MMP-13 mRNA expression and MMP-13 concentration in media were not changed by this treatment. Palmitoyl-linoleoylphosphatidylcholine (PLPC), the second most abundant component of PPC, had no effect on the concentrations of collagen, TIMP-1, and MMP-13 in HSC culture. We conclude that DLPC prevents TGF-beta1-mediated HSC fibrogenesis through down-regulation of alpha1(I) procollagen and TIMP-1 mRNA expression. The latter effect leads to a decreased accumulation of TIMP-1 that, in the presence of unchanged MMP-13 mRNA expression and MMP-13 concentration, results in a larger ratio of MMP-13/TIMP-1 concentrations in the culture media, favoring collagen degradation and lesser collagen accumulation. This effect of DLPC may explain, at least in part, the antifibrogenic action of PPC against alcoholic and other fibrotic disorders of the liver.

Iron regulation of hepatic macrophage TNFalpha expression

Sustained TNFalpha induction is central to the pathogenesis of chronic liver disease including alcoholic liver disease (ALD). However, molecular understanding of this abnormality at the cellular level remains elusive. Redox regulation of NF-kappaB is critical in the transcriptional control of TNFalpha expression. Evidence supports that increased iron storage in hepatic macrophages (HM) is causally associated with accentuated and sustained NF-kappaB activation in these cells in ALD. Treatment of cultured HM with a lipophilic iron chelator (deferiprone) abrogates LPS-induced NF-kappaB activation. HM from an animal model of ALD have increased nonheme iron content accompanied by increased generation of EPR-detected radicals, NF-kappaB activation, and TNFalpha induction, all of which are normalized by ex vivo treatment of the cells with deferiprone. A moderate increase in the nonheme iron content in HM by erythrophagocytosis, promotes subsequent LPS-stimulated NF-kappaB activation in a hemeoxygenase-dependent manner. Recent evidence also suggests a role of intracellular low molecular weight iron in the early signal transduction for LPS-mediated NF-kappaB activation.

Effect of endotoxin pretreatment on hepatic stellate cell response to ethanol and acetaldehyde

BACKGROUND AND AIM

The role of endotoxin in alcohol-induced liver damage is well recognized. How pre-exposure to endotoxin might affect alcohol injury is not known. We herein studied the effect of endotoxin pretreatment on hepatic stellate cell (HSC) response to ethanol and acetaldehyde.

METHODS

Rat HSC (CFSC-2G) were exposed to media supplemented with 1 microg/mL lipopolysaccharide (LPS). This was followed by a 24 h exposure to media containing LPS plus 50 mmol/L ethanol or 175 micromol/L acetaldehyde. Lipid peroxidation, collagen, and tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6 and transforming growth factor (TGF)-beta1 secretion were determined at the end of both periods of exposure.

RESULTS

Lipopolysaccharide pretreatment did not modify lipid peroxidation induced by ethanol or acetaldehyde alone. Glutathione (GSH) content decreased to 4.2 +/- 0.5 and 16.3 +/- 0.8 nmol protein after exposure to ethanol or acetaldehyde alone, and decreased further with LPS pretreatment (2.4 +/- 0.2 and 2.7 +/- 0.3 nmol/mg protein, respectively). Oxidized GSH (GSSG) content increased in ethanol and acetaldehyde LPS-pretreated cells only. Collagen secretion increased to 988 +/- 82 and 1169 +/- 91 microg/10(6) cells after exposure to acetaldehyde or LPS alone. Lipopolysaccharide pretreatment enhanced collagen secretion significantly in both ethanol- and acetaldehyde-treated cells (969 +/- 56 and 1360 +/- 72 microg/10(6) cells, respectively). Interleukin-6 production increased to 288 +/- 48, 1195 +/- 86 and 247 +/- 35 pg/mL per 10(6) cells after ethanol, acetaldehyde and LPS exposure, and increased further with LPS pretreatment in ethanol-exposed cells (680 +/- 23 pg/mL 10(6) cells).

CONCLUSION

Lipopolysaccharide pretreatment of HSC adds to the damage produced by ethanol and acetaldehyde by diminishing GSH content and increasing GSSG content, collagen and IL-6 secretion.

Intrasplenic transplantation of IL-18 gene-modified hepatocytes: an effective approach to reverse hepatic fibrosis in schistosomiasis through induction of dominant Th1 response

Hepatic fibrosis is a common outcome of chronic liver diseases. In schistosomiasis, chronic parasite egg-induced granuloma formation can lead to fibrosis, which is immunologically characterized by the dominant Th2 response. Recently, it has been shown that gene therapy is an attractive approach for the treatment of hepatic fibrosis. To investigate the antifibrotic effects of IL-18 gene transfer, a normal murine liver cell line BNL.CL2 was transfected with recombinant adenovirus encoding mouse IL-18, and then intrasplenically transplanted into mice infected with Schistosoma japonicum (S. japonicum). Our data show that IL-18 gene-modified hepatocytes intrasplenically transplanted into mice can effectively express IL-18 in the liver and in peripheral blood. Intrasplenic transplantation of IL-18 gene-modified hepatocytes into S. japonicum-infected mice could result in a significantly increased IFN-gamma and IL-2 but decreased IL-4 and IL-10 concentration both in the liver and in the serum, suggesting that the dominant Th2 response in mice with schistosomiasis could be reversed by this intervention. Consistent with the changes in Th1 and Th2 cytokine production, mice intrasplenically transplanted with IL-18 gene-modified hepatocytes developed much less hepatic fibrosis at 20 weeks after infection, which was evaluated by liver content of hydroxyproline, collagens, and hepatic mRNA expression of procollagens. These data indicate that intrasplenic transplantation of IL-18 gene-modified hepatocytes can be a candidate for therapeutic intervention in hepatic fibrosis through induction of a dominant Th1 response.

Pirfenidone inhibits dimethylnitrosamine-induced hepatic fibrosis in rats

1. In the present study, we investigated the preventive effects of pirfenidone (PFD), an antifibrotic agent, on experimental hepatic fibrosis induced by dimethylnitrosamine (DMN) in rats. 2. Treatment with DMN caused a significant decrease in bodyweight and liver weight. Oral PFD (500 mg/kg daily for 4 weeks) essentially prevented this DMN-induced loss in bodyweight and tended to suppress the loss in liver weight. There were no significant differences in liver weight and serum L-alanine aminotransferase levels between PFD-treated and -untreated groups. Pirfenidone has no major side effects in vivo. 3. Pirfenidone suppressed the induction of hepatic fibrosis determined by histological evaluation and reduced hepatic hydroxyproline levels. Expression of mRNA for type I collagen and transforming growth factor-beta in the liver was also suppressed by PFD treatment. 4. Because hepatic stellate cells (HSC) are the major cellular source of extracellular matrix in hepatic fibrosis, we examined the effects of PFD on type I collagen production in vitro using rat primary HSC cultures. Pirfenidone inhibited collagen production in HSC culture in a dose-dependent manner. 5. These results demonstrate that the inhibitory effects of PFD against hepatic fibrosis may be due, at least in part, to blockade of collagen production by HSC and suggest that PFD may be potentially useful in the prevention of the development of hepatic fibrosis.

JunD regulates transcription of the tissue inhibitor of metalloproteinases-1 and interleukin-6 genes in activated hepatic stellate cells

Activation of hepatic stellate cells (HSCs) to a myofibroblast-like phenotype is the pivotal event in hepatic wound healing and fibrosis. Rat HSCs activated in vitro express JunD, Fra2, and FosB as the predominant AP-1 DNA-binding proteins, and all three associate with an AP-1 sequence that is essential for activity of the tissue inhibitor of metalloproteinases-1 (TIMP-1) promoter. In this study, we used expression vectors for wild-type, dominant-negative, and forced homodimeric (Jun/eb1 chimeric factors) forms of JunD and other Fos and Jun proteins to determine the requirement for JunD in the transcriptional regulation of the TIMP-1 and interleukin-6 (IL-6) genes. JunD activity was required for TIMP-1 gene promoter activity, whereas overexpression of Fra2 or FosB caused a repression of promoter activity. The ability of homodimeric JunD/eb1 to elevate TIMP-1 promoter activity supports a role for JunD homodimers as the major AP-1-dependent transactivators of the TIMP-1 gene. IL-6 promoter activity was induced upon activation of HSCs and also required JunD activity; however, expression of JunD/eb1 homodimers resulted in transcriptional repression. Mutagenesis of the IL-6 promoter showed that an AP-1 DNA-binding site previously reported to be an activator of transcription in fibroblasts functions as a suppressor of promoter activity in HSCs. We conclude that JunD activates IL-6 gene transcription as a heterodimer and operates at an alternative DNA-binding site in the promoter. The relevance of these findings to events occurring in the injured liver was addressed by showing that AP-1 DNA-binding complexes are induced during HSC activation and contain JunD as the predominant Jun family protein. JunD is therefore an important transcriptional regulator of genes responsive to Jun homo- and heterodimers in activated HSCs.

Expression of tumor necrosis factor-alpha, interleukin-6, and interferon-gamma in spontaneous chronic pancreatitis in the WBN/Kob rat

To clarify the pathophysiological significance of cytokines in chronic pancreatitis (CP), we analyzed tissue expressions of various cytokines in the onset and progression of spontaneous CP in the WBN/Kob rat. Four-week-old male WBN/Kob rats were fed a special pellet diet (MB-3) for 20 weeks, and 6 rats were killed every 4 weeks. Pathologically, CP occurred at 12 weeks and progressed thereafter. The inflammation and fibrosis peaked at 12 and 16 weeks, respectively. By semiquantitative reverse transcription-polymerase chain reaction, the expression of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and interferon (IFN)-gamma mRNAs peaked at 8, 12, and 16 weeks, respectively. Immunohistochemistry showed IL-6 expression in infiltrating inflammatory cells and vascular endothelial cells, whereas TNF-alpha was expressed in both acinar and infiltrating cells. IFN-gamma was localized to acinar, infiltrating and ductal cells, and its expression intensity showed significant correlation with those of fibrosis, type III collagen and alpha-smooth muscle actin. The in situ hybridization results were consistent with the RT-PCR data. These results suggest that tissue expressions of TNF-alpha and IL-6 are involved in the onset of pancreatitis and that IFN-gamma expression is related to the progression of CP.

A selective ROCK inhibitor, Y27632, prevents dimethylnitrosamine-induced hepatic fibrosis in rats

BACKGROUND

p160ROCK is a direct Rho target which mediates Rho-induced assembly of focal adhesions and stress fibers. We previously reported that Rho signaling pathways are involved in the activation of hepatic stellate cells (HSC) in vitro. The aim of the present study was to test the hypothesis that an inhibitor specific for p160ROCK (Y27632) could prevent experimental hepatic fibrosis induced by dimethylnitrosamine (DMN) in rats.

METHODS

Y27632 was given orally at 30 mg/kg daily for 4 weeks after the first injection of DMN. The degree of fibrosis was evaluated by image analysis and also by measurements of collagen and hydroxyproline content in the liver. The expression of alpha-smooth muscle actin (alpha-SMA) in the liver and in the primary cultured HSC was also evaluated. Semi-quantitative RT-PCR was performed to evaluate the expression of type I collagen mRNA in the liver.

RESULTS

Y27632 treatment significantly decreased the occurrence of DMN-induced hepatic fibrosis and reduced the collagen and hydroxyproline content and alpha-SMA expression in the liver. The expression of alpha-SMA in HSC was also suppressed in vitro.

CONCLUSIONS

These findings indicate that inhibitors of the Rho-ROCK pathway might be useful therapeutically in hepatic fibrosis.

5'-Methylthioadenosine administration prevents lipid peroxidation and fibrogenesis induced in rat liver by carbon-tetrachloride intoxication

BACKGROUND

5'-Methylthioadenosine (MTA), a product of S-adenosylmethionine (SAM) catabolism, could undergo oxidation by mono-oxygenases and auto-oxidation. MTA and SAM effects on oxidative liver injury were evaluated in CCl4-treated rats.

METHODS

Male Wistar rats were killed 1-48 h after poisoning with a single intraperitoneal CCl4 dose (0.15 ml/100 g) or with the same dose twice a week for 14 weeks. Daily doses of MTA or SAM (384 micromol/kg), started 1 week before acute CCl4 administration or with chronic treatment, were continued up to the time of sacrifice.

RESULTS

Acute and chronic CCl4 intoxication decreased MTA and, to a lesser extent, SAM and reduced glutathione (GSH) liver levels. MTA administration increased liver MTA without affecting SAM and GSH. SAM treatment caused complete/partial recovery of these compounds. MTA and, to a lesser extent, SAM prevented an increase in liver phospholipid hydroperoxides in acutely and chronically intoxicated rats and in prolyl hydroxylase activity and trichrome-positive areas in chronically treated rats. MTA prevented upregulation of Tgf-beta1, Collagen-alpha1 (I) and Tgf-alpha genes in liver of chronically intoxicated rats, and TGF-beta1-induced transdifferentiation to myofibroblasts and growth stimulation by platelet-derived growth factor-b of stellate cells in vitro.

CONCLUSIONS

MTA and SAM protect against oxidative liver injury through partially different mechanisms.

Peroxisome proliferator-activated receptors and hepatic stellate cell activation

The present study examined the roles of peroxisome proliferator-activated receptors (PPAR) in activation of hepatic stellate cells (HSC), a pivotal event in liver fibrogenesis. RNase protection assay detected mRNA for PPARgamma1 but not that for the adipocyte-specific gamma2 isoform in HSC isolated from sham-operated rats, whereas the transcripts for neither isoforms were detectable in HSC from cholestatic liver fibrosis induced by bile duct ligation (BDL). Semi-quantitative reverse transcriptase-polymerase chain reaction confirmed a 70% reduction in PPARgamma mRNA level in HSC from BDL. Nuclear extracts from BDL cells showed an expected diminution of binding to PPAR-responsive element, whereas NF-kappaB and AP-1 binding were increased. Treatment of cultured-activated HSC with ligands for PPARgamma (10 microm 15-deoxy-Delta(12,14)-PGJ(2) (15dPGJ(2)); 0.1 approximately 10 microm BRL49653) inhibited DNA and collagen synthesis without affecting the cell viability. Suppression of HSC collagen by 15dPGJ(2) was abrogated 70% by the concomitant treatment with a PPARgamma antagonist (GW9662). HSC DNA and collagen synthesis were inhibited by WY14643 at the concentrations known to activate both PPARalpha and gamma (>100 microm) but not at those that only activate PPARalpha (<10 microm) or by a synthetic PPARalpha-selective agonist (GW9578). 15dPGJ(2) reduced alpha1(I) procollagen, smooth muscle alpha-actin, and monocyte chemotactic protein-1 mRNA levels while inducing matrix metalloproteinase-3 and CD36. 15dPGJ(2) and BRL49653 inhibited alpha1(I) procollagen promoter activity. Tumor necrosis factor alpha (10 ng/ml) reduced PPARgamma mRNA, and this effect was prevented by the treatment with 15dPGJ(2). These results demonstrate that HSC activation is associated with the reductions in PPARgamma expression and PPAR-responsive element binding in vivo and is reversed by the treatment with PPARgamma ligands in vitro. These findings implicate diminished PPARgamma signaling in molecular mechanisms underlying activation of HSC in liver fibrogenesis and the potential therapeutic value of PPARgamma ligands for liver fibrosis.

Fibrosis and angiogenesis

Research during the past few years has contributed vastly to a better understanding of fibrosis and angiogenesis. Although studies to understand the molecular processes associated with fibrosis and angiogenesis were performed independently of each other, some common parallels have emerged. Translation of these observations into potential therapeutic possibilities needs further exploration.

Alcoholic liver disease

Important mechanisms responsible for alcohol-induced liver injury include mitochondrial damage and loss of ATP, formation of acetaldehyde-and other aldehyde-protein adducts, release of reactive oxygen species (ROS) from mitochondrial electron transfer chain, CYP2E1 , and activated Kupffer cells (KCs); weakening of antioxidant defense systems; and increased intestinal permeability with endotoxemia. Endotoxin interacts with ethanol and/or acetaldehyde, and such interaction leads to a complex cascade of autocrine and paracrine pathways that involve the release of cytokines (proinflammatory, anti-inflammatory, and mutagenic), chemokines, and eicosanoids. These pathways are mediated by activation of KCs, induction of proliferation, and other phenotype changes in hepatic stellate cells (HSCs) leading to transformation to myofibroblasts (the latter is responsible for fibrogenesis, chemotaxis, and contractility, therefore contributing to portal hypertension, angiogenic response, and release of additional cytokines), and stimulation of sinusoidal cells (SECs) to release adhesive molecules and cytokines. Recent data implicate a likely role of apoptosis as a mechanism of hepatocyte cell death in alcoholic liver disease.