Acetaldehyde selectively stimulates collagen production in cultured rat liver fat-storing cells but not in hepatocytes

Role of medium-chain triglycerides in the alcohol-mediated cytochrome P450 2E1 induction of mitochondria

BACKGROUND

Chronic alcohol consumption is known to induce cytochrome P450 2E1 (CYP2E1) leading to lipid peroxidation, mitochondrial dysfunction and hepatotoxicity. We showed that replacement of dietary long-chain triglycerides (LCT) by medium-chain triglycerides (MCT) could be protective. We now wondered whether the induction of mitochondrial CYP2E1 plays a role and whether liver injury could be avoided through mitochondrial intervention.

METHODS

Rats were fed 4 different isocaloric liquid diets. The control group received our standard dextrin-maltose diet with intake limited to the average consumption of the 3 alcohol groups fed ad libitum the alcohol containing Lieber-DeCarli liquid diet. The fat was either 32% of calories as LCT (alcohol), or 16% as LCT + 16% as MCT (alcohol-MCT 16%), or 32% as MCT only (alcohol-MCT 32%).

RESULTS

After 21 days, compared to the controls, the alcohol and both alcohol-MCT groups had a significant increase in mitochondrial CYP2E1 (p < 0.05 for both). As shown before, the same was found for the microsomal CYP2E1. When MCT replaced all the fat, like in the alcohol-MCT 32% group, CYP2E1 was significantly reduced by 40% in mitochondria (p < 0.05) and 30% in microsomes (p < 0.01). In mitochondria, 4-hydroxynonenal (4-HNE), a parameter of oxidative stress, paralleled CYP2E1. Compared to controls, alcohol and alcohol-MCT 16% significantly raised mitochondrial 4-HNE (p < 0.001), whereas the alcohol-MCT 32% diet brought it down to control levels (p < 0.001). Mitochondrial reduced glutathione (GSH) was also significantly lowered by alcohol consumption (p < 0.05), and it increased to almost normal levels with alcohol-MCT 32% (p = 0.006). These changes in the mitochondria reflected the reduction observed in total liver in which alcohol-MCT 32% decreased the alcohol-induced steatosis with a diminution of triglycerides (p < 0.001) and of the pro-inflammatory cytokine tumor necrosis factor-alpha (p < 0.001).

CONCLUSION

Mitochondria participate in the induction of CYP2E1 by alcohol and contribute to lipid peroxidation and GSH depletion. Thus, lipid composition of the diet is an important determinant for the beneficial effect of MCT, with a diet containing a mixture of LCT/MCT being ineffective.

Human and rat bile acid-CoA:amino acid N-acyltransferase are liver-specific peroxisomal enzymes: implications for intracellular bile salt transport

Bile acid-coenzyme A:amino acid N-acyltransferase (BAAT) is the sole enzyme responsible for conjugation of primary and secondary bile acids to taurine and glycine. Previous studies indicate a peroxisomal location of BAAT in peroxisomes with variable amounts up to 95% detected in cytosolic fractions. The absence or presence of a cytosolic pool of BAAT has important implications for the intracellular transport of unconjugated/deconjugated bile salts. We used immunofluorescence microscopy and digitonin permeabilization assays to determine the subcellular location of endogenous BAAT in primary human and rat hepatocytes. In addition, green fluorescent protein (GFP)-tagged rat Baat (rBaat) and human BAAT (hBAAT) were transiently expressed in primary rat hepatocytes and human fibroblasts. Catalase and recombinant GFP-SKL and DsRed-SKL were used as peroxisomal markers. Endogenous hBAAT and rBaat were found to specifically localize to peroxisomes in human and rat hepatocytes, respectively. No significant cytosolic fraction was detected for either protein. GFP-tagged hBAAT and rBaat were efficiently sorted to peroxisomes of primary rat hepatocytes. Significant amounts of GFP-tagged hBAAT or rBaat were detected in the cytosol only when coexpressed with DsRed-SKL, suggesting that hBAAT/rBaat and DsRed-SKL compete for the same peroxisomal import machinery. When expressed in fibroblasts, GFP-tagged hBAAT localized to the cytosol, confirming earlier observations.

CONCLUSION

hBAAT and rBaat are peroxisomal enzymes present in undetectable amounts in the cytosol. Unconjugated or deconjugated bile salts returning to the liver need to shuttle through the peroxisome before reentering the enterohepatic circulation.

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.

Vitamin A metabolic aspects and alcoholic liver disease

The liver is a strategic organ in the metabolism of macro and micronutrients; when its functioning is compromised, it may cause some change in the nutritional status of vitamin A. The purpose of this article is to review scientific evidence in literature on the liver metabolism of vitamin A, the role of ethanol and retinol interactions on hepatic morphology, besides the alterations in the metabolism of this vitamin in alcoholic liver disease. Data were collected from Medline database. The liver is the main organ responsible for the storage, metabolism and distribution of vitamin A to peripheral tissues. This organ uses retinol for its normal functioning such as cell proliferation and differentiation. This way, vitamin A deficiency seems to alter liver morphology. Patients with alcoholic liver disease have been found to have low hepatic levels of retinol in all stages of their disease. In alcoholic liver disease, vitamin A deficiency may result from decreased ingestion or absorption, reduction in retinoic acid synthesis or increased degradation. Long-term alcohol intake results in reduced levels of retinoic acid, which may promote the development of liver tumor. So, in chronic alcoholic subjects, vitamin A status needs to be closely monitored to avoid its deficiency and clinical effects, however its supplementation must be done with caution since the usual dose may be toxic for those who consume ethanol.

Effects of ethanol and acetaldehyde on reactive oxygen species production in rat hepatic stellate cells

BACKGROUND

Alcoholism is a common cause of cirrhosis. Hepatic stellate cells are the main source of collagen that ultimately leads to hepatic fibrosis and cirrhosis. Reactive oxygen species (ROS) enhance stellate cell activation and stimulate fibrogenesis. In this study, the acute effects of ethanol (ET) and acetaldehyde (AC) were determined on the production of ROS in isolated rat hepatic stellate cells.

METHODS

Rat stellate cells were isolated in situ by perfusion of the portal vein and cultured. Hydrogen peroxide (H(2)O(2)) was determined by luminol-derived chemiluminescence (CL), while superoxide anion (O(2*-)) production was assessed by the fluorescent probe hydroethidine.

RESULTS

AC increased the formation of H(2)O(2) and O(2*-), and these effects were first detectable at AC concentrations of 5 and 10 microM, respectively, reaching a maximum at 50 to 75 microM. Reduction of glutathione (GSH) synthesis by 1-buthionine sulfoximide (BSO) or by GSH conjugation with dimethylmaleate (DEM) further enhanced the effects of AC on H(2)O(2) and O(2*-) formation, while N-acetylcysteine (NAC) decreased H(2)O(2) and eliminated the enhanced generation of O(2*-) caused by AC. Raloxifene, which inhibits O(2*-) production by NAD(P)H oxidase, reduced the effects of AC on H(2)O(2) and O(2*-) production. ET increased H(2)O(2) or O(2*-) only in the presence of BSO or DEM.

CONCLUSION

This study shows that concentrations of AC, which occur in vivo after the ingestion of alcoholic beverages, result in the formation of ROS in rat hepatic stellate cells. The increases in ROS are known to activate stellate cells promoting fibrogenesis.

Curcumin blocks activation of pancreatic stellate cells

Activated pancreatic stellate cells (PSCs) play a pivotal role in the pathogenesis of pancreatic fibrosis and inflammation. Inhibition of activation and cell functions of PSCs is a potential target for the treatment of pancreatic fibrosis and inflammation. The polyphenol compound curcumin is the yellow pigment in curry, and has anti-inflammatory and anti-fibrotic properties. We here evaluated the effects of curcumin on the activation and cell functions of PSCs. PSCs were isolated from rat pancreas tissue and used in their culture-activated, myofibroblast-like phenotype unless otherwise stated. The effects of curcumin on proliferation, alpha-smooth muscle actin gene expression, monocyte chemoattractant protein (MCP)-1 production, and collagen expression were examined. The effect of curcumin on the activation of freshly isolated cells in culture was also assessed. Curcumin inhibited platelet-derived growth factor (PDGF)-induced proliferation, alpha-smooth muscle actin gene expression, interleukin-1beta- and tumor necrosis factor (TNF)-alpha-induced MCP-1 production, type I collagen production, and expression of type I and type III collagen genes. Curcumin inhibited PDGF-BB-induced cyclin D1 expression and activation of extracellular signal-regulated kinase (ERK). Curcumin inhibited interleukin-1beta- and TNF-alpha-induced activation of activator protein-1 (AP-1) and mitogen-activated protein (MAP) kinases (ERK, c-Jun N-terminal kinase (JNK), and p38 MAP kinase), but not of nuclear factor-kappaB (NF-kappaB). In addition, curcumin inhibited transformation of freshly isolated cells to myofibroblast-like phenotype. In conclusion, curcumin inhibited key cell functions and activation of PSCs.

Superoxide anions and hydrogen peroxide induce hepatocyte death by different mechanisms: involvement of JNK and ERK MAP kinases

BACKGROUND/AIMS

In liver diseases, reactive oxygen species (ROS) are involved in cell death and liver injury, but the mechanisms are not completely elucidated. To elucidate the mechanisms of hepatocyte cell death induced by the ROS superoxide anions and hydrogen peroxide, primary cultures of hepatocytes were exposed to the superoxide anion donor menadione (10-50 micromol/L) or H2O2 (1-5 mmol/L). Hepatocytes were also treated with caspases and MAPKs inhibitors, superoxide dismutase (PEG-SOD) and SNAP, a nitric oxide donor. Apoptosis was determined by measuring caspase-9, -6, -3 activation and cleaved PARP, and necrotic cell death by Sytox Green staining.

RESULTS

(1) Menadione (50 micromol/L) induces JNK phosphorylation, caspase-9, -6, -3 activation, PARP cleavage and apoptosis. Superoxide anions-induced apoptosis is dependent on JNK activity. Menadione (50 micromol/L) induces the phosphorylation of ERK1/2 and this attenuates cell death. (2) H2O2 increases necrotic cell death at high concentration or when H2O2 detoxification is impaired. H2O2 does not activate MAPKs signalling. (3) PEG-SOD prevents ERK1/2-, JNK- phosphorylation, caspase activation and apoptosis induced by menadione. Glutathione depletion increases menadione-induced apoptosis. (4) SNAP abolishes menadione-induced apoptosis but increases necrotic cell death.

CONCLUSIONS

In normal hepatocytes, superoxide anions-induced caspase activation and apoptosis is dependent on JNK activity and totally abolished by superoxide scavengers.

Peroxisome proliferator-activated receptor alpha mediates the effects of high-fat diet on hepatic gene expression

Peroxisome proliferator-activated receptors (PPARs) are transcription factors involved in the regulation of numerous metabolic processes. The PPARalpha isotype is abundant in liver and activated by fasting. However, it is not very clear what other nutritional conditions activate PPARalpha. To examine whether PPARalpha mediates the effects of chronic high-fat feeding, wild-type and PPARalpha null mice were fed a low-fat diet (LFD) or high-fat diet (HFD) for 26 wk. HFD and PPARalpha deletion independently increased liver triglycerides. Furthermore, in wild-type mice HFD was associated with a significant increase in hepatic PPARalpha mRNA and plasma free fatty acids, leading to a PPARalpha-dependent increase in expression of PPARalpha marker genes CYP4A10 and CYP4A14. Microarray analysis revealed that HFD increased hepatic expression of characteristic PPARalpha target genes involved in fatty acid oxidation in a PPARalpha-dependent manner, although to a lesser extent than fasting or Wy14643. Microarray analysis also indicated functional compensation for PPARalpha in PPARalpha null mice. Remarkably, in PPARalpha null mice on HFD, PPARgamma mRNA was 20-fold elevated compared with wild-type mice fed a LFD, reaching expression levels of PPARalpha in normal mice. Adenoviral overexpression of PPARgamma in liver indicated that PPARgamma can up-regulate genes involved in lipo/adipogenesis but also characteristic PPARalpha targets involved in fatty acid oxidation. It is concluded that 1) PPARalpha and PPARalpha-signaling are activated in liver by chronic high-fat feeding; and 2) PPARgamma may compensate for PPARalpha in PPARalpha null mice on HFD.

The G0/G1 switch gene 2 is a novel PPAR target gene

PPARs (peroxisome-proliferator-activated receptors) alpha, beta/delta and gamma are a group of transcription factors that are involved in numerous processes, including lipid metabolism and adipogenesis. By comparing liver mRNAs of wild-type and PPARalpha-null mice using microarrays, a novel putative target gene of PPARalpha, G0S2 (G0/G1 switch gene 2), was identified. Hepatic expression of G0S2 was up-regulated by fasting and by the PPARalpha agonist Wy14643 in a PPARalpha-dependent manner. Surprisingly, the G0S2 mRNA level was highest in brown and white adipose tissue and was greatly up-regulated during mouse 3T3-L1 and human SGBS (Simpson-Golabi-Behmel syndrome) adipogenesis. Transactivation, gel shift and chromatin immunoprecipitation assays indicated that G0S2 is a direct PPARgamma and probable PPARalpha target gene with a functional PPRE (PPAR-responsive element) in its promoter. Up-regulation of G0S2 mRNA seemed to be specific for adipogenesis, and was not observed during osteogenesis or myogenesis. In 3T3-L1 fibroblasts, expression of G0S2 was associated with growth arrest, which is required for 3T3-L1 adipogenesis. Together, these data indicate that G0S2 is a novel target gene of PPARs that may be involved in adipocyte differentiation.

Molecular pathogenesis of alcohol-induced hepatic fibrosis

Alcohol abuse is a main cause of liver fibrosis and cirrhosis in the western world. Although the major mechanisms of fibrogenesis are independent of the origin of liver injury, alcoholic liver fibrosis features distinctive characteristics, including the pronounced inflammatory response of immune cells due to elevated gut-derived endotoxin plasma levels, increased formation of reactive oxygen species (ROS), ethanol-induced pericentral hepatic hypoxia or formation of cell-toxic and pro-fibrogenic ethanol metabolites (e.g., acetaldehyde or lipid oxidation products). These factors are together responsible for increased hepatocellular cell death and activation of hepatic stellate cells (HSCs), the key cell type of liver fibrogenesis. To date, removing the causative agent is the most effective intervention to prevent the manifestation of liver cirrhosis. A novel experimental approach in fibrosis therapy is the selective induction of cell death in HSCs. Substances such as gliotoxin, anandamide or antibody against tissue inhibitor of metalloproteinase (TIMP)-1 can selectively induce cell death in activated HSCs. These new results in basic science are encouraging for the search of new antifibrotic treatment.

Expression pattern of matrix metalloproteinases in alcohol- and thermally oxidized sunflower oil-induced toxicity: protective role of an aminothiazole derivative

The matrix metalloproteinases (MMPs) are a family of secreted and membrane-bound zinc endopeptidases. Collectively, these enzymes can degrade all of the components of the extracellular matrix including collagen, fibronectin, laminin, and basement membrane glycoproteins. Regulation in expression and activation of proteinases is one of the most important mechanisms in organ morphogenesis. Fibrosis is a dynamic pathological process with a net accumulation of extracellular matrix proteins. In the present communication, we have investigated the changes that occur in the activity of liver MMPs in normal and in pathological conditions. The activity of MMPs was increased in thermally oxidized sunflower oiland alcohol-treated groups, whereas the activity was decreased in the thermally oxidized oil + alcohol-fed group when compared with the normal control group. The activity was positively modulated when dendrodoine analogue [4-amino-5-benzoyl- 2(4-methoxyphenylamino)thiazole] was administered along with ethanol and thermally oxidized oil, which indicates the protective effect of this drug.

Current research of hepatic cirrhosis in China

Hepatic cirrhosis is a common disease that poses a serious threat to public health, and is characterized by chronic, progressive and diffuse hepatic lesions preceded by hepatic fibrosis regardless of the exact etiologies. In recent years, considerable achievements have been made in China in research of the etiopathogenesis, diagnosis and especially the treatment of hepatic fibrosis, resulting in much improved prognosis of hepatic fibrosis and cirrhosis. In this paper, the authors review the current status of research in hepatic fibrosis, cirrhosis and their major complications.

Molecular mechanisms of alcohol-induced hepatic fibrosis

Alcohol abuse is a major cause of liver fibrosis and cirrhosis in developed countries. Before alcoholic liver fibrosis becomes evident, the liver undergoes several stages of alcoholic liver disease including steatosis and steatohepatitis. Although the main mechanisms of fibrogenesis are independent of the etiology of liver injury, alcoholic liver fibrosis is distinctively characterized by a pronounced inflammatory response due to elevated gut-derived endotoxin plasma levels, an augmented generation of oxidative stress with pericentral hepatic hypoxia and the formation of cell-toxic and profibrogenic ethanol metabolites (e.g. acetaldehyde or lipid oxidation products). These factors, based on a complex network of cytokine actions, together result in increased hepatocellular damage and activation of hepatic stellate cells, the key cell type of liver fibrogenesis. Although to date removal of the causative agent, i.e. alcohol, still represents the most effective intervention to prevent the manifestation of alcoholic liver disease, sophisticated molecular approaches are underway, aiming to specifically blunt profibrogenic signaling pathways in liver cells or specifically induce cell death in activated hepatic stellate cells to decrease the scarring of the liver.

4-hydroxy-2, 3-nonenal activates activator protein-1 and mitogen-activated protein kinases in rat pancreatic stellate cells

AIM: Activated pancreatic stellate cells (PSCs) are implicated in the pathogenesis of pancreatic inflammation and fibrosis, where oxidative stress is thought to play a key role. 4-hydroxy-2,3-nonenal (HNE) is generated endogenously during the process of lipid peroxidation, and has been accepted as a mediator of oxidative stress. The aim of this study was to clarify the effects of HNE on the activation of signal transduction pathways and cellular functions in PSCs.

METHODS: PSCs were isolated from the pancreas of male Wistar rats after perfusion with collagenase P, and used in their culture-activated, myofibroblast-like phenotype unless otherwise stated. PSCs were treated with physiologically relevant and non-cytotoxic concentrations (up to 5 μmol/L) of HNE. Activation of transcription factors was examined by electrophoretic mobility shift assay and luciferase assay. Activation of mitogen-activated protein (MAP) kinases was assessed by Western blotting using anti-phosphospecific antibodies. Cell proliferation was assessed by measuring the incorporation of 5-bromo-2’-deoxyuridine. Production of type I collagen and monocyte chemoattractant protein-1 was determined by enzyme-linked immunosorbent assay. The effect of HNE on the transformation of freshly isolated PSCs in culture was also assessed.

RESULTS: HNE activated activator protein-1, but not nuclear factor κB. In addition, HNE activated three classes of MAP kinases: extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 MAP kinase. HNE increased type I collagen production through the activation of p38 MAP kinase and c-Jun N-terminal kinase. HNE did not alter the proliferation, or monocyte chemoattractant protein-1 production. HNE did not initiate the transformation of freshly isolated PSCs to myofibroblast-like phenotype.

CONCLUSION: Specific activation of these signal transduction pathways and altered cell functions such as collagen production by HNE may play a role in the pathogenesis of pancreatic disorders.

Increased risk of hepatocellular carcinoma and liver cirrhosis in vinyl chloride workers: synergistic effect of occupational exposure with alcohol intake

Hepatocellular carcinoma (HCC) and liver cirrhosis (LC) are not well-established vinyl chloride monomer (VCM)-induced diseases. Our aim was to appraise the role of VCM, alcohol intake, and viral hepatitis infection, and their interactions, in the etiology of HCC and LC. Thirteen cases of HCC and 40 cases of LC were separately compared with 139 referents without chronic liver diseases or cancer in a case-referent study nested in a cohort of 1,658 VCM workers. The odds ratios (ORs) and the 95% confidence intervals (CIs) were estimated by common methods and by fitting models of logistic regression. We used Rothman's synergy index (S) to evaluate interactions. By holding the confounding factors constant at logistic regression analysis, each extra increase of 1,000 ppm times years of VCM cumulative exposure was found to increase the risk of HCC by 71% (OR = 1.71; 95% CI, 1.28-2.44) and the risk of LC by 37% (OR = 1.37; 95% CI, 1.13-1.69). The joint effect of VCM exposure above 2,500 ppm times years and alcohol intake above 60 g/day resulted in ORs of 409 (95% CI, 19.6-8,553) for HCC and 752 (95% CI, 55.3-10,248) for LC; both S indexes suggested a synergistic effect. The joint effect of VCM exposure above 2,500 ppm times years and viral hepatitis infection was 210 (95% CI, 7.13-6,203) for HCC and 80.5 (95% CI, 3.67-1,763) for LC; both S indexes suggested an additive effect. In conclusion, according to our findings, VCM exposure appears to be an independent risk factor for HCC and LC interacting synergistically with alcohol consumption and additively with viral hepatitis infection.

Alcoholic fatty liver: its pathogenesis and mechanism of progression to inflammation and fibrosis

Liver disease in the alcoholic is due not only to malnutrition but also to ethanol's hepatotoxicity linked to its metabolism by means of the alcohol dehydrogenase and cytochrome P450 2E1 (CYP2E1) pathways and the resulting production of toxic acetaldehyde. In addition, alcohol dehydrogenase-mediated ethanol metabolism generates the reduced form of nicotinamide adenine dinucleotide (NADH), which promotes steatosis by stimulating the synthesis of fatty acids and opposing their oxidation. Steatosis is also promoted by excess dietary lipids and can be attenuated by their replacement with medium-chain triglycerides. Through reduction of pyruvate, elevated NADH also increases lactate, which stimulates collagen synthesis in myofibroblasts. Furthermore, CYP2E1 activity is inducible by its substrates, not only ethanol but also fatty acids. Their excess and metabolism by means of this pathway generate release of free radicals, which cause oxidative stress, with peroxidation of lipids and membrane damage, including altered enzyme activities. Products of lipid peroxidation such as 4-hydroxynonenal stimulate collagen generation and fibrosis, which are further increased through diminished feedback inhibition of collagen synthesis because acetaldehyde forms adducts with the carboxyl-terminal propeptide of procollagen in hepatic stellate cells. Acetaldehyde is also toxic to the mitochondria, and it aggravates their oxidative stress by binding to reduced glutathione and promoting its leakage. Oxidative stress and associated cellular injury promote inflammation, which is aggravated by increased production of the proinflammatory cytokine tumor necrosis factor-alpha in the Kupffer cells. These are activated by induction of their CYP2E1 as well as by endotoxin. The endotoxin-stimulated tumor necrosis factor-alpha release is decreased by dilinoleoylphosphatidylcholine, the active phosphatidylcholine (PC) species of polyenylphosphatidylcholine (PPC). Moreover, defense mechanisms provided by peroxisome proliferator-activated receptor alpha and omega fatty acid oxidation are readily overwhelmed, particularly in female rats and also in women who have low hepatic induction of fatty acid-binding protein (L-FABPc). Accordingly, the intracellular concentration of free fatty acids may become high enough to injure membranes, thereby contributing to necrosis, inflammation, and progression to fibrosis and cirrhosis. Eventually, hepatic S-adenosylmethionine and PCs become depleted in the alcoholic, with impairment of their multiple cellular functions, which can be restored by PC replenishment. Thus, prevention and therapy opposing the development of steatosis and its progression to more severe injury can be achieved by a multifactorial approach: control of alcohol consumption, avoidance of obesity and of excess dietary long-chain fatty acids, or their replacement with medium-chain fatty acids, and replenishment of S-adenosylmethionine and PCs by using PPC. Progress in the understanding of the pathogenesis of alcoholic fatty liver and its progression to inflammation and fibrosis has resulted in prospects for their better prevention and treatment.

Leptin deficiency prevents the activation of the murine α2(I) collagen promoter by acetaldehyde

Leptin enhances hepatic fibrosis induced experimentally by various agents. The influence of leptin deficiency on murine alpha 2(I) collagen promoter activation by acetaldehyde and by TGF beta 1 was investigated. Acetaldehyde failed to activate the promoter in ob/ob stellate cells as compared to its activating effect in wild-type cells. By contrast, TGF beta 1 increased the activity of the promoter in the ob/ob and wild-type cells. Total cell TGF beta 1 and secretion of total and free TGF beta 1 were lower in cultured stellate cells from ob/ob mice than wild-type mice. Acetaldehyde increased free cell TGF beta1 and secretion of total and free TGF beta 1 in wild-type, but not in ob/ob cells. The lack of activation of the alpha 2(I) collagen promoter by acetaldehyde in association with a lack of increase in TGF beta 1 in response to acetaldehyde in ob/ob stellate cells provides further evidence for a mediating role of TGF beta 1 in the actions of acetaldehyde on collagen transcription.

Tauroursodeoxycholic acid protects rat hepatocytes from bile acid-induced apoptosis via activation of survival pathways

Ursodeoxycholic acid (UDCA) is used in the treatment of cholestatic liver diseases, but its mechanism of action is not yet well defined. The aim of this study was to explore the protective mechanisms of the taurine-conjugate of UDCA (tauroursodeoxycholic acid [TUDCA]) against glycochenodeoxycholic acid (GCDCA)-induced apoptosis in primary cultures of rat hepatocytes. Hepatocytes were exposed to GCDCA, TUDCA, the glyco-conjugate of UDCA (GUDCA), and TCDCA. The phosphatidylinositol-3 kinase pathway (PI3K) and nuclear factor-kappaB were inhibited using LY 294002 and adenoviral overexpression of dominant-negative IkappaB, respectively. The role of p38 and extracellular signal-regulated protein kinase mitogen-activated protein kinase (MAPK) pathways were investigated using the inhibitors SB 203580 and U0 126 and Western blot analysis. Transcription was blocked by actinomycin-D. Apoptosis was determined by measuring caspase-3, -9, and -8 activity using fluorimetric enzyme detection, Western blot analysis, immunocytochemistry, and nuclear morphological analysis. Our results demonstrated that uptake of GCDCA is needed for apoptosis induction. TUDCA, but not TCDCA and GUDCA, rapidly inhibited, but did not delay, apoptosis at all time points tested. However, the protective effect of TUDCA was independent of its inhibition of caspase-8. Up to 6 hours of preincubation with TUDCA before addition of GCDCA clearly decreased GCDCA-induced apoptosis. At up to 1.5 hours after exposure with GCDCA, the addition of TUDCA was still protective. This protection was dependent on activation of p38, ERK MAPK, and PI3K pathways, but independent of competition on the cell membrane, NF-kappaB activation, and transcription. In conclusion, TUDCA contributes to the protection against GCDCA-induced mitochondria-controlled apoptosis by activating survival pathways.

A c-Jun NH2-Terminal Kinase Inhibitor SP600125 (Anthra[1,9-cd]pyrazole-6 (2H)-one) Blocks Activation of Pancreatic Stellate Cells

In response to pancreatic injury and in cell culture, pancreatic stellate cells (PSCs) are transformed ("activated") into highly proliferative myofibroblast-like cells that express alpha-smooth muscle actin and produce extracellular matrix components. Activated PSCs are implicated in the pathogenesis of pancreatic fibrosis and inflammation. We here evaluated the effects of SP600125 (anthra[1,9-cd]pyrazole-6 (2H)-one), an inhibitor of c-Jun NH(2)-terminal kinase (JNK), on the activation of PSCs. PSCs were isolated from rat pancreas tissue and used in their culture-activated, myofibroblast-like phenotype unless otherwise stated. Activation of JNK was determined by Western blotting using anti-phosphospecific JNK and c-Jun antibodies. Activation of transcription factors was determined by electrophoretic mobility shift assay. The effects of SP600125 on the key parameters of activation (chemokine production, collagen production, and proliferation) were examined. The effect of SP600125 on the activation of freshly isolated PSCs in culture also was examined. Interleukin-1beta activated both 46- and 54-kDa JNK, whereas platelet-derived growth factor-BB activated only 46-kDa JNK. SP600125 inhibited interleukin-1beta-induced JNK activity and activator protein-1 activation, but it did not affect the activation of extracellular-regulated kinase, p38 mitogen-activated protein kinase, and nuclear factor-kappaB. SP600125 inhibited platelet-derived growth factor-induced proliferation, inducible monocyte chemoattractant protein-1 production, and serum-induced type I collagen production. Although SP600125 did not inhibit the transformation, it attenuated the proliferation of freshly isolated PSCs in culture. Collectively, our results suggest a role of JNK in the activation of PSCs, and a potential application of JNK inhibitors for the treatment of pancreatic fibrosis and inflammation.

Acarbose attenuates experimental non-alcoholic steatohepatitis

The alpha-glucosidase inhibitor acarbose is beneficial in the prevention of type 2 diabetes. To determine whether it attenuates the commonly associated non-alcoholic steatohepatitis (NASH), we used an experimental NASH model. Rats were fed ad libitum a nutritionally adequate high fat diet (71% of calories as fat) with or without acarbose (200 mg/1000 calories) for 3 weeks. All rats given the high fat diet only developed typical NASH whereas acarbose attenuated several of the characteristic hepatic alterations of NASH: there was less steatosis and inflammation, with a significant reduction in the mRNA of the hepatic inflammatory cytokine TNF-alpha and of its protein. There was also a decrease in the CYP2E1 mRNA and in collagen, with similar trends for CYP2E1 protein and procollagen mRNA. Because acarbose attenuates many of the hepatic alterations associated with experimental NASH, it is now indicated to determine whether it exerts similar beneficial effects in patients afflicted by this disease.

New concepts of the pathogenesis of alcoholic liver disease lead to novel treatments

Activation of methionine to S-adenosylmethionine is depressed in alcoholics. Its repletion opposes alcoholic liver cirrhosis in baboons, decreases mortality in cirrhotic patients, and opposes oxidative stress resulting from cytochrome P4502E1 (CYP2E1) induction by alcohol, ketones, and fatty acids. Their excess causes alcoholic and nonalcoholic steatohepatitis. CYP2E1 is also induced in Kupffer cells, promoting their activation and release of inflammatory cytokines, including tumor necrosis factor (TNF)-alpha. The TNF-alpha inhibitor pentoxifylline decreased mortality from alcoholic hepatitis. Polyenylphosphatidylcholine (PPC), an antioxidant phosphatidylcholine mixture extracted from soybeans, 50% of which consists of the highly bioavailable dilinoleoylphosphatidylcholine, restores phospholipids of the damaged membranes and reactivates their enzymes, including phosphatidylethanolamine methyltransferase, needed for phospholipid regeneration. In baboons, PPC prevented cirrhosis by stimulating collagenase and by opposing lipid peroxidation, which produces the fibrogenic hydroxynonenal. PPC was beneficial in patients with alcoholic hepatitis, and it opposed fibrosis in heavy drinkers and decreased aminotransferases in patients with hepatitis C. The antioxidant silymarin also successfully opposed alcoholic cirrhosis in baboons and in some but not all clinical trials; this effect also pertains to a-tocopherol. The anti-inflammatory corticosteroids and colchicine yielded mixed results. Finally, replacing long-chain with medium-chain triglycerides opposed the fatty liver experimentally and clinically.

Model of nonalcoholic steatohepatitis

BACKGROUND

Obesity and diabetes are frequently associated with nonalcoholic steatohepatitis (NASH), but studies have been hampered by the absence of a suitable experimental model.

OBJECTIVE

Our objective was to create a rat model of NASH.

DESIGN

Sprague-Dawley rats were fed a high-fat, liquid diet (71% of energy from fat, 11% from carbohydrates, 18% from protein) or the standard Lieber-DeCarli diet (35% of energy from fat, 47% from carbohydrates, 18% from protein). The diets were given ad libitum or as two-thirds of the amount consumed ad libitum.

RESULTS

Rats fed the high-fat diet ad libitum for 3 wk developed panlobular steatosis, whereas those fed the standard diet had few fat droplets. Accordingly, total lipid concentrations with the high-fat and standard diets were 129.9 +/- 9.1 ( +/- SEM) and 66.7 +/- 4.6 mg/g liver, respectively (P < 0.001). The high-fat diet caused abnormal mitochondria and mononuclear inflammation, which were accompanied by increased hepatic tumor necrosis factor alpha (TNF-alpha; P < 0.001), TNF-alpha messenger RNA (mRNA) (P < 0.001), collagen type 1, and alpha1(I) procollagen mRNA (P < 0.001). In addition, these rats had increased cytochrome P4502E1 (CYP2E1) mRNA (P < 0.001), which was accompanied by CYP2E1 induction (P < 0.001) and oxidative stress with increased 4-hydroxynonenal (P < 0.001). Plasma insulin was elevated, which reflected insulin resistance, a NASH pathogenic factor. Rats fed a restricted high-fat diet developed only mild steatosis with attenuated biochemical changes, whereas those given a restricted standard diet had normal livers.

CONCLUSION

This rat model reproduces the key features of human NASH and provides a realistic experimental model for elucidating its treatment.

Nonoxidative ethanol metabolites alter extracellular matrix protein content in rat pancreas

BACKGROUND & AIMS

The mechanisms involved in ethanol-induced pancreas fibrosis are poorly understood. Here we show that fatty acid ethyl esters (FAEEs), nonoxidative ethanol metabolites, increase extracellular matrix (ECM) protein levels in pancreas.

METHODS

Rat pancreatic acini were incubated for 1-4 hours with FAEEs or acetaldehyde. In another set of experiments, rats received an intravenous infusion of FAEEs for 6 hours. Collagens were assessed by a hydroxyproline assay. Laminin and fibronectin were analyzed by Western blotting. Gene expression of ECM proteins was measured by conventional and real-time reverse-transcription polymerase chain reaction (RT-PCR). Matrix metalloproteinase (MMP), plasmin, and urokinase-type plasminogen activator (uPA) activities were determined by zymography and fluorogenic assays.

RESULTS

FAEEs increased collagen, laminin, and fibronectin levels in pancreatic acini without affecting messenger RNA (mRNA) expression for these proteins. Actinomycin D, a transcriptional inhibitor, did not block the increase in ECM proteins induced by FAEEs. FAEEs reduced the activity of the serine protease, plasmin, and that of the uPA. Consistent with these results, the serine protease inhibitor aprotinin reproduced the effects of FAEEs and prevented the further increase in ECM proteins induced by FAEEs. In vivo administration of FAEEs reduced plasmin and uPA activities and increased ECM protein levels in pancreas. Acetaldehyde had minor effects on ECM protein levels and did not affect plasmin activity.

CONCLUSIONS

FAEEs increase ECM protein levels in pancreas. The results suggest that this effect is caused primarily by an inhibition in ECM degradation via serine proteases including the plasminogen system.

Rho kinase inhibitors block activation of pancreatic stellate cells

1. In response to pancreatic injury and in cell culture, pancreatic stellate cells (PSCs) are transformed ('activated') into highly proliferative myofibroblast-like cells, which express alpha-smooth muscle actin (alpha-SMA), and produce type I collagen and other extracellular matrix components. There is accumulating evidence that activated PSCs play important roles in pancreatic fibrosis and inflammation. 2. The small GTP-binding protein Rho has emerged as an important regulator of the actin cytoskeleton and cell morphology through the downstream effector Rho kinase (ROCK). But, the roles of Rho-ROCK pathway in PSCs are unknown. Here, we examined the effects of (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide (Y-27632) and HA-1077 (fasudil), specific inhibitors of ROCK, on the activation of PSCs. 3. PSCs were isolated from the pancreas of male Wistar rats after perfusion with collagenase P. The actin cytoskeleton was analyzed by phalloidin staining. Expression of RhoA and ROCK was examined by immunostaining and Western blotting. Effects of Y-27632 and HA-1077 on alpha-SMA expression, platelet-derived growth factor-induced proliferation and chemotaxis, and collagen production were assessed. 4. Culture-activated PSCs developed a well-spread cell shape, with extended stress fiber formation. PSCs expressed RhoA, ROCK-1, and ROCK-2. 5. Y-27632 caused disassembly of stress fibers. Y-27632 and HA-1077 inhibited alpha-SMA expression, proliferation, chemotaxis, and type I collagen production in culture-activated PSCs. 6. In addition, Y-27632 and HA-1077 inhibited spontaneous activation of freshly isolated PSCs in culture on plastic. 7. These findings suggest a role of Rho-ROCK pathway in the activation process of PSCs by regulating the actin cytoskeleton, and a potential application of Rho-ROCK pathway inhibitors for the treatment of pancreatic inflammation and fibrosis.

Silymarin retards the progression of alcohol-induced hepatic fibrosis in baboons

GOAL/BACKGROUND: Hepatoprotective effects of silymarin in patients with alcoholic liver disease are controversial. For strict control, this was assessed in non-human primates. STUDY Twelve baboons were fed alcohol with or without silymarin for 3 years with a nutritionally adequate diet.

RESULTS

Silymarin opposed the alcohol-induced oxidative stress (assessed by plasma 4-hydroxynonenal) and the rise in liver lipids and circulating ALT. Alcohol also increased hepatic collagen type I by 50% over the 3 years with a significant rise in mRNA for alpha1 (I) procollagen, both prevented by silymarin. There were corresponding morphologic changes: at 36 months, 2 of 6 animals fed alcohol had cirrhosis and 2 septal fibrosis, with perivenular fibrosis in 2, whereas with alcohol + silymarin, there was only 1 cirrhosis and 1 septal fibrosis, with perivenular fibrosis in 2, and virtually no lesions in the remaining 2.

CONCLUSIONS

Silymarin retards the development of alcohol-induced hepatic fibrosis in baboons, consistent with several positive clinical trials. The negative outcome observed in other trials possibly reflects poor compliance resulting in irregular or low silymarin intake. Thus, in view of the innocuity of silymarin, it might be advisable in future clinical studies to insure the controlled administration of sufficient amounts of silymarin.

Inhibition of markers of hepatic stellate cell activation by the hormone relaxin

Hepatic fibrosis results from excess extracellular matrix produced primarily by hepatic stellate cells (HSC). In response to injury, HSC differentiate to a myofibroblastic phenotype expressing smooth muscle actin and fibrillar collagens. Relaxin is a polypeptide hormone shown to have antifibrotic effects in fibrosis models. In this study, activated HSC from rat liver were treated with relaxin to determine if relaxin can reverse markers of HSC activation. Relaxin treatment resulted in a decrease in the expression of smooth muscle actin, but had no effect on cell proliferation rate. The levels of total collagen and type I collagen were reduced, while the synthesis of new collagen was inhibited. Furthermore, relaxin caused an increase in the expression and secretion of rodent interstitial collagenase (MMP-13), but there was no effect on the gelatinases MMP-2 or MMP-9. Relaxin also increased secretion of TIMP-1 and TIMP-2. The effective concentration of relaxin to induce these effects was consistent with action through the relaxin receptor. In conclusion, relaxin reversed markers of the activated phenotype of HSC including the production of fibrillar collagen. At the same time, the activity of a fibrillar collagenase was increased. These data suggest that relaxin not only inhibits HSC properties that contribute to the progression of hepatic fibrosis, but also promotes the clearance of fibrillar collagen. Therefore, relaxin may be a useful approach in the treatment of hepatic fibrosis.

Vitamin A and infancy. Biochemical, functional, and clinical aspects

Vitamin A is a very intriguing natural compound. The molecule not only has a complex array of physiological functions, but also represents the precursor of promising and powerful new pharmacological agents. Although several aspects of human retinol metabolism, including absorption and tissue delivery, have been clarified, the type and amounts of vitamin A derivatives that are intracellularly produced remain quite elusive. In addition, their precise function and targets still need to be identified. Retinoic acids, undoubtedly, play a major role in explaining activities of retinol, but, recently, a large number of physiological functions have been attributed to different retinoids and to vitamin A itself. One of the primary roles this vitamin plays is in embryogenesis. Almost all steps in organogenesis are controlled by retinoic acids, thus suggesting that retinol is necessary for proper development of embryonic tissues. These considerations point to the dramatic importance of a sufficient intake of vitamin A and explain the consequences if intake of retinol is deficient. However, hypervitaminosis A also has a number of remarkable negative consequences, which, in same cases, could be fatal. Thus, the use of large doses of retinol in the treatment of some human diseases and the use of megavitamin therapy for certain chronic disorders as well as the growing tendency toward vitamin faddism should alert physicians to the possibility of vitamin overdose.

Resistance of rat hepatocytes against bile acid-induced apoptosis in cholestatic liver injury is due to nuclear factor-kappa B activation

BACKGROUND/AIMS

To examine the extent and mechanisms of apoptosis in cholestatic liver injury and to explore the role of the transcription factor nuclear factor-kappa B in protection against bile acid-induced apoptosis.

METHODS

Cholestatic liver injury was induced by bile duct ligation in Wistar rats. Furthermore, primary cultures of rat hepatocytes were exposed to glycochenodeoxycholic acid (GCDCA), tauroursodeoxycholic acid (TUDCA), taurochenodeoxycholic acid (TCDCA) and to cytokines. Apoptosis was determined by TUNEL-staining, active caspase-3 staining, activation of caspase-8, -9 and -3.

RESULTS

Limited hepatocyte apoptosis and an increased expression of NF-kappaB-regulated anti-apoptotic genes A1 and cIAP2 were detected in cholestatic rat livers. Bcl-2 expression was restricted to bile duct epithelium. In contrast to TCDCA and TUDCA, GCDCA induced apoptosis in a Fas-associated protein with death domain (FADD)-independent pathway in hepatocytes. Although bile acids do not activate NF-kappaB, NF-kappaB activation by cytokines (induced during cholestasis) protected against GCDCA-induced apoptosis in vitro by upregulating A1 and cIAP2.

CONCLUSIONS

GCDCA induces apoptosis in a mitochondria-controlled pathway in which caspase-8 is activated in a FADD-independent manner. However, bile acid-induced apoptosis in cholestasis is limited. This could be explained by cytokine-induced activation of NF-kappaB-regulated anti-apoptotic genes like A1 and cIAP2.

Ethanol induces transforming growth factor-alpha expression in hepatocytes, leading to stimulation of collagen synthesis by hepatic stellate cells

BACKGROUND

Liver fibrosis often develops in alcoholic liver diseases without accompanying inflammation; however, the underlying mechanism is unclear. Using ethanol-exposed human HepG2 hepatoblastoma cells as a model for alcoholic liver diseases, we previously found that ethanol exposure causes HepG2 cells to secrete an approximately 6,000 Da nonheparin-binding polypeptide that stimulates collagen synthesis in human IMR-90 fibroblasts. The aim of the current study was to characterize and identify this factor.

METHODS

Concentration of type I procollagen peptide and transforming growth factor (TGF)-alpha was assessed by enzyme-linked immunosorbent assay. TGF-alpha protein expression was examined by Western blot. Type I collagen messenger RNA expression in rat hepatic stellate cells was assessed by reverse transcription-polymerase chain reaction.

RESULTS

The collagen-stimulating activity in conditioned media from ethanol-exposed HepG2 cells to stimulate type I procollagen peptide synthesis of IMR-90 cells was specifically inhibited by addition of anti-TGF-alpha antibodies. Western blot analysis showed increased TGF-alpha protein expression in ethanol-treated HepG2 cells. TGF-alpha in conditioned medium from ethanol-exposed HepG2 cells stimulated type-I collagen messenger RNA expression in rat hepatic stellate cells.

CONCLUSIONS

These results suggest that TGF-alpha derived from ethanol-exposed hepatocytes may contribute to the development of hepatic fibrosis in alcoholic liver diseases.

Dilinoleoylphosphatidylcholine decreases acetaldehyde-induced TNF-alpha generation in Kupffer cells of ethanol-fed rats

We previously reported that dilinoleoylphosphatidylcholine (DLPC) decreases lipopolysaccharide-induced TNF-alpha generation by Kupffer cells of ethanol-fed rats by blocking p38, ERK1/2, and NF-kappaB activation. Here we show that DLPC also decreases TNF-alpha induction by acetaldehyde, a toxic metabolite released by ethanol oxidation. Acetaldehyde induces TNF-alpha generation with a maximal effect at 200 microM and activates p38 and ERK1/2; the latter in turn activates NF-kappaB. This effect is augmented in Kupffer cells of ethanol-fed rats, with upregulation of cytochrome P4502E1 by ethanol. DLPC decreases TNF-alpha generation by blocking p38, ERK1/2, and NF-kappaB activation. Likewise, SB203580, which abolishes p38 activation, and PD098059, which abrogates ERK1/2 and NF-kappaB activation, diminish TNF-alpha generation. Since increased TNF-alpha generation plays a pathogenic role in alcoholic liver disease, the DLPC action on Kupffer cells may explain, in part, its beneficial effects on liver cell injury after ethanol consumption.

DLPC decreases TGF-beta1-induced collagen mRNA by inhibiting p38 MAPK in hepatic stellate cells

Dilinoleoylphosphatidylcholine (DLPC), the active component of polyenylphosphatidylcholine extracted from soybeans, decreases collagen accumulation induced by TGF-beta1 in cultured hepatic stellate cells (HSCs). Because DLPC exerts antioxidant effects and TGF-beta1 generates oxidative stress, we evaluated whether the antifibrogenic effect of DLPC is linked to its antioxidant action. In passage 1 culture of rat HSCs, TGF-beta1 induced a concentration-dependent increase in procollagen-alpha(1)(I) mRNA levels and enhanced intracellular H(2)O(2) and superoxide anion formation and lipid peroxidation but decreased GSH levels. These changes were prevented by DLPC. Upregulation of collagen mRNA by TGF-beta1 was likewise inhibited by catalase and p38 MAPK inhibitor SB-203580, suggesting involvement of H(2)O(2) and p38 MAPK signaling in this process. TGF-beta1 or addition of H(2)O(2) to HSCs activated p38 MAPK with a rise in procollagen mRNA level; these changes were blocked by catalase and SB-203580 and likewise by DLPC. alpha-Smooth muscle actin abundance in HSCs was not altered by TGF-beta1 treatment (with or without DLPC), indicating that downregulation of procollagen mRNA by DLPC was not due to alteration in HSC activation. These results demonstrate that DLPC prevents TGF-beta1-induced increase in collagen mRNA by inhibiting generation of oxidative stress and associated H(2)O(2)-dependent p38 MAPK activation, which explains its antifibrogenic effect. DLPC, an innocuous phospholipid, may be considered for prevention and treatment of liver fibrosis.

Cytokine regulation of pro- and anti-apoptotic genes in rat hepatocytes: NF-kappaB-regulated inhibitor of apoptosis protein 2 (cIAP2) prevents apoptosis

BACKGROUND/AIMS

In acute liver failure, hepatocytes are exposed to various cytokines that activate both cell survival and apoptotic pathways. NF-kappaB is a central transcription factor in these responses. Recent studies indicate that blocking NF-kappaB causes apoptosis, indicating the existence of NF-kappaB-regulated anti-apoptotic genes. In the present study the relationship between NF-kappaB activation and apoptosis has been investigated in hepatocytes.

METHODS

Primary rat hepatocytes were exposed to a cytokine mixture of tumor necrosis factor alpha, interleukin-1beta, interferon-gamma and lipopolysaccharide. Modulation of signalling pathways was performed by using dominant negative adenoviral constructs. Apoptosis and NF-kappaB activation were determined by caspase-3 activity, Hoechst staining and electrophoretic mobility shift assay, respectively. Furthermore, expression and regulation of apoptosis-related genes were investigated.

RESULTS

(1) Inhibition of NF-kappaB activation results in apoptosis. (2) Inhibitor of apoptosis protein (IAP) family members, inhibitor of apoptosis protein1 (cIAP1), and X-chromosome-linked IAP, are expressed in rat hepatocytes. cIAP2 is induced by cytokines in an NF-kappaB-dependent manner and overexpression of cIAP2 inhibits apoptosis. (3) The anti-apoptotic Bcl-2 family member A1/Bfl-1 and the pro-apoptotic members Bak and Bid are induced by cytokines and NF-kappaB-dependent. (4) Nitric oxide inhibits caspase-3 activity in hepatocytes.

CONCLUSIONS

In inflammatory conditions, hepatocyte survival is dependent on NF-kappaB activation and cIAP2 contributes significantly to this protection.

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.

Alcoholic liver injury: pathogenesis and therapy in 2001

Much progress has been made in the understanding of the pathogenesis of alcoholic liver disease, resulting in improvement of prevention and promising prospects for even more effective treatments. It continues to be important to replenish nutritional deficiencies when present but it is crucial to recognize that, because of the alcohol-induced disease process, some of the nutritional requirements change. For instance, methionine, one of the essential amino acids for humans, must be activated to SAMe but, in severe liver disease, the activity of the corresponding enzyme is depressed. Therefore, the resulting deficiencies and associated pathology can be attenuated by the administration of SAMe, but not by methionine. Similarly, phosphatidylethanolamine methyltransferase (PEMT) activity, which is important for hepatic phosphatidylcholine (PC) synthesis, is also depressed in alcoholic liver disease, therefore calling for administration of the products of the reaction. It might also be beneficial to add other compounds to such therapeutic regiment. Since free radical generation by the ethanol-induced CYP2E1 plays a key role in the oxidative stress, inhibitors of this enzyme have great promise. Several have been investigated experimentally and PPC is particularly interesting because of its innocuity. In view of the striking negative interaction between alcoholic liver injury and hepatitis C, an antiviral agent is eagerly awaited that, unlike Interferon, is not contraindicated in the alcoholic. Anti-inflammatory agents are also required. In addition to down-regulators of cytokines and end toxic are being considered. Finally, since excess drinking is the crux of the issue, anticraving agents should be incorporated in any contemplated therapeutic cocktail, in view of the recent promising results obtained with some of these agents such as naltrexone and acamprosate.

Metadoxine prevents damage produced by ethanol and acetaldehyde in hepatocyte and hepatic stellate cells in culture

Metadoxine (pyridoxine-pyrrolidone carboxylate) has been reported to improve liver function tests in alcoholic patients. In the present work we have investigated the effect of metadoxine on some parameters of cellular damage in hepatocytes and hepatic stellate cells in culture treated with ethanol and acetaldehyde. HepG2 and CFSC-2G cells were treated with 50 mM ethanol or 175 microM acetaldehyde as initial concentration in the presence or absence of 10 microg ml(-1) of metadoxine. Twenty-four hours later reduced and oxidized glutathione content, lipid peroxidation damage, collagen secretion and IL-6, IL-8 and TNF- alpha secretion were determined. Our results suggest that metadoxine prevents glutathione depletion and the increase in lipid peroxidation damage caused by ethanol and acetaldehyde in HepG2 cells. In hepatic stellate cells, metadoxine prevents the increase in collagen and attenuated TNF- alpha secretion caused by acetaldehyde. Thus, metadoxine could be useful in preventing the damage produced in early stages of alcoholic liver disease as it prevents the redox imbalance of the hepatocytes and prevents TNF- alpha induction, one of the earliest events in hepatic damage.

Identification of new sites of binding and activation of the murine alpha1(I) collagen promoter by CCAAT/enhancer binding protein beta

The CCAAT/enhancer binding protein beta (C/EBPbeta) was previously shown to bind to the alpha(1)(I) collagen promoter at -365 to -335 (site 1) and to activate it. Acetaldehyde also activates the promoter, and this effect is mediated by an increase in stellate-cell C/EBPbeta protein and C/EBPbeta binding. The present study identified two additional distal sites (sites 2 and 3) of binding of C/EBPbeta, in the nuclear extracts of stellate cells, at -399 to -370 and -623 to -592 in the alpha(1)(I) collagen promoter. The C/EBPbeta protein activates the promoter at all three sites. Acetaldehyde increases C/EBPbeta binding to all three sites. Activation by acetaldehyde is abrogated in the transfected promoter mutated at either site 1 or site 3 but is not affected by mutation at site 2. Binding of the 20-kDa C/EBPbeta isoform (p20C/EBPbeta), which is eliminated by mutation at the distal site 3 of C/EBP binding, is necessary for the activation by acetaldehyde of the alpha(1)(I) collagen promoter.

Aldehydes potentiate alpha(2)(I) collagen gene activity by JNK in hepatic stellate cells

Hepatic stellate cells (HSCs) are responsible for type I collagen deposition in liver fibrosis that leads to cirrhosis. The purpose of this study was to examine potential molecular signals that lead to increased alpha(2)(I) collagen gene expression by acetaldehyde, the primary metabolite of alcohol and malondialdehyde (MDA), a lipid peroxidation product known to be associated with chronic liver injury. MDA and the combination of MDA and acetaldehyde were employed to determine the effect on alpha(2)(I) collagen gene expression as assessed by transient transfection analysis and reverse transcriptase polymerase chain reaction (RT-PCR). Immunoblot and subsequent immunoprecipitation analysis examined stress-activated protein kinase (SAPK) activity. Cotransfection with a dominant negative mutant for c-jun nuclear kinase (dnJNK1) was also employed with the alpha(2)(I) collagen promoter. MDA increased alpha(2)(I) collagen gene expression nearly 2.5- to 3-fold, however there was no synergistic effect of the combination of acetaldehyde and MDA on alpha(2)(I) collagen gene activation and expression. Acetaldehyde, MDA, or both significantly increased JNK activity when compared to untreated stellate cells. The dnJNK1 expression vector abrogated alpha(2)(I) collagen transgene activity. In conclusion, JNK activation appears to be critical in the signaling cascade of oxidative metabolites of chronic alcohol-related liver injury and collagen gene activation.

Hepatic, metabolic, and nutritional disorders of alcoholism: from pathogenesis to therapy

Much progress has been made in the understanding of the pathogenesis of alcoholic liver disease, resulting in an improvement in treatment. Nutritional deficiencies should be corrected when present but, because of the alcohol-induced disease process, some of the nutritional requirements change. For instance, methionine, one of the essential amino acids for humans, must be activated to S-adenosylmethionine (SAMe), but, in severe liver disease, the activity of the corresponding enzyme is depressed. Therefore, the resulting deficiencies and associated pathology can be attenuated by the administration of SAMe, but not by methionine. Similarly, phosphatidylethanolamine methyltransferase (PEMT) activity, which is important for hepatic phosphatidylcholine (PC) synthesis, is also depressed in alcoholic liver disease, therefore calling for the administration of the products of the reaction. Inasmuch as free radical generation by the ethanol-induced CYP2E1 plays a key role in the oxidative stress, inhibitors of this enzyme have great promise and PPC, which is presently being evaluated clinically, is particularly interesting because of its innocuity. In view of the striking negative interaction between alcoholic liver injury and hepatitis C, an antiviral agent is eagerly awaited that, unlike Interferon, is not contraindicated in the alcoholic. Antiinflamatory agents may also be useful. In addition to steroids, down-regulators of cytokines and endotoxin are being considered. Finally, anticraving agents such as naltrexone or acamprosate should be incorporated into any contemplated therapeutic cocktail.

Covalent adducts of proteins with acetaldehyde in the liver as a result of acetaldehyde administration in drinking water

BACKGROUND/AIMS

Acetaldehyde, the first metabolic product of ethanol, has been suggested to be responsible for several adverse effects of ethanol through its ability to form covalent adducts with proteins and cellular constituents. It has recently been suggested that acetaldehyde derived from microbial ethanol oxidation in the gut could also contribute to the effects of ethanol in the liver. The present work aimed to examine whether modification of proteins by acetaldehyde occurs in rat liver as a result of acetaldehyde administration in drinking water.

METHODS

Rats were fed with either 0.7% acetaldehyde (n=10) or water (n=10) for 11 weeks. At the end of the feeding period, liver specimens were processed for immunohistochemistry for protein adducts with acetaldehyde and for hepatic cell type-specific protein markers.

RESULTS

Mild fatty change was found in the liver of the acetaldehyde-treated animals but not in the control animals. Immunohistochemical stainings for acetaldehyde adducts revealed intensive positive staining for acetaldehyde adducts in eight (80%) of the animals fed with acetaldehyde. The adducts were predominantly perivenular, although positive staining also occurred along the sinusoids and in the periportal area. Double immunofluorescence staining experiments revealed that hepatocytes were the primary targets of acetaldehyde adduct deposition, although stellate cells and Kupffer cells also showed weak positive reactions.

CONCLUSIONS

The present data indicate that acetaldehyde-protein adducts are formed in the liver of animals following acetaldehyde administration in drinking water, which may contribute to the hepatotoxicity of extrahepatic acetaldehyde. These findings should be implicated in studies on the extrahepatic pathways of ethanol oxidation.

Liver fibrosis

Knowledge on the development and progression of liver fibrosis has grown exponentially in the past decade. At present, liver fibrogenesis is referred to as a dynamic process involving complex cellular and molecular mechanisms, resulting from the chronic activation of the tissue repair mechanisms that follows reiterated liver tissue injury. The identification and characterization of the cell types and of the different mediators involved in this process has allowed a "re-visitation" of several issues related to liver cirrhosis and its immediate consequences. Among these, evaluation of the relationships occurring between fibrogenesis and portal hypertension, cholestasis and the development of hepatocellular carcinoma, represent some of the hottest areas of research in this field of hepatology. The elucidation of many of the cellular and molecular mechanisms responsible for the progression of liver fibrosis has provided a sound basis for the development of pharmacological strategies able to modulate this important pathophysiological process.

Acute and chronic effect of alcohol on Ca2+ channels in hepatic stellate cells

BACKGROUND

Hepatic stellate cells have been reported to play important roles in the regulation of hepatic microcirculation via cell contraction. Increase in intracellular calcium concentration is required to induce cell contraction. We have already reported the existence of L-type voltage-operated Ca2+ channels (VOCC), such as smooth muscle cells. On the other hand, alcohol has been known to disturb hepatic microcirculation. In this study, we evaluated the effect of acute and chronic treatment of alcohol on VOCC in rat hepatic stellate cells.

METHODS

Stellate cells isolated from rats were cultured with or without 100 mM ethanol for up to 14 days. VOCC were detected by the patch clamp technique. Cells cultured for 14 days without ethanol were exposed to ethanol to investigate calcium current during membrane depolarization. alpha-Smooth muscle actin (alpha-SMA) was stained by indirect immunofluorescence.

RESULTS

In the control model, VOCC were recognized in cells cultured for more than 7 days. Detection of VOCC increased from 9% on day 7 to 55% on day 14. On the other hand, VOCC in cells treated chronically with 100 mM ethanol appeared earlier than in the control and the incidences were significantly higher than those of the control accompanied with an early activation of cells. In contrast, simultaneous exposure to ethanol during the membrane depolarization inhibited Ca2+ current.

CONCLUSIONS

The expression of Ca2+ channels in stellate cells were up-regulated by the chronic treatment of alcohol accompanied with the transformation to myofibroblast-like phenotype. However, alcohol itself inhibited Ca2+ current.

CCAAT/enhancer binding protein beta mediates the activation of the murine alpha1(I) collagen promoter by acetaldehyde

Acetaldehyde was previously shown to activate the alpha1(I) and alpha2(I) collagen promoters and to increase collagen production in activated stellate cells. Also, CCAAT/enhancer binding protein beta (C/EBPbeta) binds and activates the mouse alpha1(I) collagen promoter. This study investigates the role of C/EBPbeta in mediating the activation of the alpha1(I) collagen promoter by acetaldehyde. Nuclear extracts isolated from cultured activated rat hepatic stellate cells formed four protein-DNA complexes on electrophoretic mobility shift assay with an oligonucleotide including the C/EBP binding site between -365 and -335 in the alpha1(I) collagen promoter. The four complexes were identified to represent C/EBPbeta binding to the oligonucleotide by supershift with C/EBPbeta antibody. The principal C/EBP isoform found in the nuclear extracts from stellate cells was C/EBPbeta, with very low amounts of C/EBPalpha detected. Acetaldehyde (200 microM) increased C/EBPbeta protein in stellate nuclear extracts, increased its binding to the promoter, and activated the alpha1(I) collagen promoter in transfected stellate cells. Mutation of the C/EBPbeta binding site markedly decreased nuclear protein binding. A transfected promoter, mutated at the C/EBP binding site, had decreased basal activity, was not activated by acetaldehyde, and was not activated when cotransfected with a C/EBPbeta expression vector. This study shows that C/EBPbeta is the predominant C/EBP isoform found in activated stellate cells and that increased C/EBPbeta protein and C/EBPbeta binding to a proximal C/EBP binding site in the promoter mediates the activating effect of acetaldehyde.

A p160ROCK-specific inhibitor, Y-27632, attenuates rat hepatic stellate cell growth

BACKGROUND/AIMS

p160ROCK, a serine/threonine protein kinase, is a direct RhoA target mediating RhoA-induced assembly of focal adhesions and stress fibers. Recently, Rho signaling pathways were reported to play an important role in the activation of rat hepatic stellate cells (HSC). The aim of this study was to investigate the mechanism of action of a p160ROCK-specific inhibitor, Y-27632, on cultured rat HSC.

METHODS

HSC were isolated from normal rat livers and cultured on fibronectin-coated dishes. The cell morphology and actin cytoskeleton were studied with phase contrast and fluorescence microscopy, respectively. Immunoblot analysis was used to examine phosphorylation of focal adhesion kinase and extracellular signal-regulated kinase, and the expression of cell cycle-associated proteins. HSC proliferation was measured by quantitating the percentage of cells that exhibited nuclear incorporation of 5-bromodeoxyuridine. Type I collagen gene expression and accumulation in HSC culture media were evaluated by Northern blot and enzyme-linked immunosorbent assay, respectively.

RESULTS

Y-27632 consistently blocked cell spreading and suppressed RhoA-induced formation of stress fibers in HSC. In addition, Y-27632 inhibited phosphorylation of focal adhesion kinase and extracellular signal-regulated kinase. Cells treated with Y-27632 failed to proliferate, in contrast to untreated spread cells. This shape-dependent block in cell proliferation correlated with a failure to increase cyclin D1 protein level and to down-regulate the cell cycle inhibitor p27. Y-27632 decreased type I collagen gene expression and accumulation in HSC culture media.

CONCLUSIONS

Our findings indicate that p160ROCK-mediated actin stress fiber assembly is involved in the pathophysiology of hepatic fibrogenesis and suggest that inhibitors of the RhoA-ROCK pathway might be useful therapeutically in liver fibrogenesis.

Does alcohol directly stimulate pancreatic fibrogenesis? Studies with rat pancreatic stellate cells

BACKGROUND & AIMS

Activated pancreatic stellate cells have recently been implicated in pancreatic fibrogenesis. This study examined the role of pancreatic stellate cells in alcoholic pancreatic fibrosis by determining whether these cells are activated by ethanol itself and, if so, whether such activation is caused by the metabolism of ethanol to acetaldehyde and/or the generation of oxidant stress within the cells.

METHODS

Cultured rat pancreatic stellate cells were incubated with ethanol or acetaldehyde. Activation was assessed by cell proliferation, alpha-smooth muscle actin expression, and collagen synthesis. Alcohol dehydrogenase (ADH) activity in stellate cells and the influence of the ADH inhibitor 4-methylpyrazole (4MP) on the response of these cells to ethanol was assessed. Malondialdehyde levels were determined as an indicator of lipid peroxidation. The effect of the antioxidant vitamin E on the response of stellate cells to ethanol or acetaldehyde was also examined.

RESULTS

Exposure to ethanol or acetaldehyde led to cell activation and intracellular lipid peroxidation. These changes were prevented by the antioxidant vitamin E. Stellate cells exhibited ethanol-inducible ADH activity. Inhibition of ADH by 4MP prevented ethanol-induced cell activation.

CONCLUSIONS

Pancreatic stellate cells are activated on exposure to ethanol. This effect of ethanol is most likely mediated by its metabolism (via ADH) to acetaldehyde and the generation of oxidant stress within the cells.

Effect of retinoic acid on the enhancing effect of acetaldehyde on mouse type I collagen expression

Acetaldehyde alone and retinoic acid alone have been shown to increase and decrease, respectively, collagen production by stellate cells in culture. In this study the effects of retinoic acid on alpha(1)(I) and alpha(2)(I) collagen expression and its influence on the enhancing effects of acetaldehyde were determined. Retinoic acid decreased the activation of the alpha(2)(I) collagen promoter and decreased the message of alpha(2)(I) collagen in cultured stellate cells, but had no effect on either the activation of the alpha(1)(I) collagen promoter or on the alpha(1)(I) collagen message. This depressant effect of retinoic acid was also evident in the transfected alpha(2)(I) collagen promoter mutated at the retinoic acid response element (RARE). The activation of the alpha(2)(I) collagen promoter by acetaldehyde was not decreased significantly by retinoic acid, but was suppressed by the retinoic acid receptor (RAR) selective retinoid SRI-6751-84. Retinoic acid, however, decreased the acetaldehyde-induced enhancement of the alpha(1)(I) and alpha(2)(I) collagen messages. Acetaldehyde also resulted in a decrease in RAR beta message and RARbeta protein. This study shows that retinoic acid depresses alpha(2)(I) collagen gene expression but that this effect is less pronounced when the expression of this collagen is enhanced by acetaldehyde, which also decreases RARbeta message and protein. Furthermore, the action of retinoic acid in inhibiting alpha(2)(I) collagen gene expression occurs at sites other than the RARE site.

Hydrogen peroxide: a link between acetaldehyde-elicited alpha1(I) collagen gene up-regulation and oxidative stress in mouse hepatic stellate cells

Ethanol induces liver fibrosis by several means that include, among others, the direct fibrogenic actions of acetaldehyde and the induction of an oxidative stress response. However, the mechanisms responsible for these activities, and the possible connections between oxidative stress and acetaldehyde-induced fibrosis are not well understood. In this communication we investigated the molecular mechanisms whereby acetaldehyde induces mouse alpha1(I) procollagen (col1a1) gene expression in cultured hepatic stellate cells. Transfection assays using reporter plasmids driven by different segments of the col1a1 promoter localized an acetaldehyde-responsive element (AcRE) between nucleotides -370 and -345. We also show that acetaldehyde enhances binding of a CCAAT/enhancer binding protein-beta (C/EBPbeta)-containing complex to this element, and that this effect is due, at least in part, to an increase in the concentration of nuclear p35C/EBPbeta protein. Although this element overlaps to a previously described transforming growth factor beta1 (TGF-beta1)-responsive element, the stimulatory effect of acetaldehyde is not mediated through this cytokine, because addition of neutralizing anti-TGF-beta1 antibodies does not prevent acetaldehyde-elicited col1a1 up-regulation. On the other hand, this effect is blocked by the addition of catalase, an H(2)O(2) scavenger. Moreover, this ethanol metabolite stimulates production of H(2)O(2) in stellate cells. Thus, these results suggest that acetaldehyde-induced col1a1 up-regulation is mediated, at least in part, through H(2)O(2). Altogether, these data suggest that the -370 to -344 region of the col1a1 gene is a point of convergence of the action of numerous extracellular stimuli that ultimately leads to col1a1 up-regulation. In addition, we have established a direct connection between oxidative stress and enhanced col1a1 expression induced by acetaldehyde.

Acetaldehyde increases the activity and gene expression of urokinase type plasminogen activator in a hepatic stellate cell line

The aim of this study was to investigate the effect of acetaldehyde on the activity and expression of urokinase type plasminogen activator gene in a clone of hepatic stellate cells. CFSC-2G cells showed typical morphological changes of the stellate cell activation, which were accompanied by an increase in the amount of collagen with all doses of acetaldehyde used. The treatment of the cells with doses of 100 and 175 micromol/l acetaldehyde, produced an increase in the urokinase type plasminogen activator activity not only in the cell extract, but also in conditioned medium. However, the use of higher doses of acetaldehyde (250 and 350 micromol/l) produced an inhibitory effect on the urokinase type plasminogen activator activity. In contrast, the higher urokinase type plasminogen activator gene expression was observed with doses of 175, 250, and 350 micromol/l. Our results shown that acetaldehyde induced changes in synthesis, release, and expression of urokinase type plasminogen activator in CFSC-2G cells. Those findings suggest that the alterations in the synthesis and expression of the urokinase type plasminogen activator might be another event associated to the activation of hepatic stellate cell after exposure to hepatotoxic agents like-acetaldehyde. The role of urokinase type plasminogen activator in fibrogenesis was analyzed.