Ethanol induces the expression of alpha 1(I) procollagen mRNA in a co-culture system containing a liver stellate cell-line and freshly isolated hepatocytes

Nutritional and microbiota-based therapeutic interventions for alcohol-associated liver disease: From pathogenesis to therapeutic insights

Alcohol-associated liver disease (ALD) manifests as a consequence of prolonged and excessive alcohol consumption. This disease is closely associated with the interplay between gut health and liver function, which can lead to complex pathophysiological changes in the body. This review offers a comprehensive exploration of ALD's multifaceted nature, with a keen focus on its pathogenesis and the potential of nutritional and microbiota-based therapies. Insights derived from diverse case studies are utilized to shed light on how interventions can rebalance the gut microbiome and enhance liver function in ALD patients. Furthermore, the feasibility of liver transplantation and stem cell therapy as ultimate measures for ALD has been discussed, with acknowledgment of the inherent risks and challenges accompanying them. ALD's complexity underscores the necessity for a thorough understanding of its etiology and progression to devise effective treatments that mitigate its profound impact on an individual's health.

Insights of mitochondrial involvement in alcoholic fatty liver disease

Alcoholic liver disease (ALD) is a global concern affecting most of the population and leading to the development of end-stage liver disease. Metabolic alterations due to increased alcohol consumption surge the hepatic accumulation of lipids and develop into a severe form of alcoholic steatohepatitis (ASH), depending on age and the consumption rate. The mitochondria in the hepatocyte actively regulate metabolic homeostasis and are disrupted in ALD pathogenesis. The increased NADH upon ethanol metabolism inhibits the mitochondrial oxidation of fatty acids, alters oxidative phosphorylation, and favors de novo lipogenesis. The higher mitochondrial respiration in early ALD increases free radical generation, whereas mitochondrial respiration is uncoupled in chronic ALD, affecting the cellular energy status. The defective glutathione importer due to excessive cholesterol loading and low adenosine triphosphate accounts for additional oxidative stress leading to hepatocyte apoptosis. The defective mitochondrial transcription machinery and sirtuins function in ALD affect mitochondrial function and biogenesis. The metabolites of ethanol metabolism epigenetically alter the gene expression profile of hepatic cell populations by modulating the promoters and sirtuins, aiding hepatic fibrosis and inflammation. The defect in mitophagy increases the accumulation of megamitochondria in hepatocytes and attracts immune cells by releasing mitochondrial damage-associated molecular patterns to initiate hepatic inflammation and ASH progression. Thus, maintaining mitochondrial lipid homeostasis and antioxidant capacity pharmacologically could provide a better outcome for ALD management.

cAMP Signaling in Pathobiology of Alcohol Associated Liver Disease

The importance of cyclic adenosine monophosphate (cAMP) in cellular responses to extracellular signals is well established. Many years after discovery, our understanding of the intricacy of cAMP signaling has improved dramatically. Multiple layers of regulation exist to ensure the specificity of cellular cAMP signaling. Hence, disturbances in cAMP homeostasis could arise at multiple levels, from changes in G protein coupled receptors and production of cAMP to the rate of degradation by phosphodiesterases. cAMP signaling plays critical roles in metabolism, inflammation and development of fibrosis in several tissues. Alcohol-associated liver disease (ALD) is a multifactorial condition ranging from a simple steatosis to steatohepatitis and fibrosis and ultimately cirrhosis, which might lead to hepatocellular cancer. To date, there is no FDA-approved therapy for ALD. Hence, identifying the targets for the treatment of ALD is an important undertaking. Several human studies have reported the changes in cAMP homeostasis in relation to alcohol use disorders. cAMP signaling has also been extensively studied in in vitro and in vivo models of ALD. This review focuses on the role of cAMP in the pathobiology of ALD with emphasis on the therapeutic potential of targeting cAMP signaling for the treatment of various stages of ALD.

SWI/SNF complex subunit BAF60a represses hepatic ureagenesis through a crosstalk between YB-1 and PGC-1α

Objective

Ureagenesis predominantly occurs in the liver and functions to remove ammonia, and the dysregulation of ureagenesis leads to the development of hyperammonemia. Recent studies have shown that ureagenesis is under the control of nutrient signals, but the mechanism remains elusive. Therefore, intensive investigation of the molecular mechanism underlying ureagenesis will shed some light on the pathology of metabolic diseases related to ammonia imbalance.

Methods

Mice were fasted for 24 h or fed a high-fat diet (HFD) for 16 weeks. For human evaluation, we obtained a public data set including 41 obese patients with and without hepatic steatosis. We analyzed the expression levels of hepatic BAF60a under different nutrient status. The impact of BAF60a on ureagenesis and hyperammonemia was assessed by using gain- and loss-of-function strategies. The molecular chaperons mediating the effects of BAF60a on ureagenesis were validated by molecular biological strategies.

Results

BAF60a was induced in the liver of both fasted and HFD-fed mice and was positively correlated with body mass index in obese patients. Liver-specific overexpression of BAF60a inhibited hepatic ureagenesis, leading to the increase of serum ammonia levels. Mechanistically, BAF60a repressed the transcription of Cps1, a rate-limiting enzyme, through interaction with Y-box protein 1 (YB-1) and by switching the chromatin structure of Cps1 promoter into an inhibitory state. More importantly, in response to different nutrient status, PGC-1α (as a transcriptional coactivator) and YB-1 competitively bound to BAF60a, thus selectively regulating hepatic fatty acid β-oxidation and ureagenesis.

Conclusion

The BAF60a-YB-1 axis represses hepatic ureagenesis, thereby contributing to hyperammonemia under overnutrient status. Therefore, hepatic BAF60a may be a novel therapeutic target for the treatment of overnutrient-induced urea cycle disorders and their associated diseases.

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HFD-feeding increases hepatic BAF60a expression, while inhibits ureagenesis genes.

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BAF60a represses Cps1 transcription and ureagenesis, causing ammonia accumulation.

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YB-1 binds to BAF60a and mediates the inhibitory effects of BAF60a on ureagenesis.

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BAF60a mediates crosstalk between hepatic ureagenesis and fatty acid oxidation.

Silencing of α-complex protein-2 reverses alcohol- and cytokine-induced fibrogenesis in hepatic stellate cells

BACKGROUND AND AIM

α-complex protein-2 (αCP2) encoded by the poly (rC) binding protein 2(PCBP2) gene is responsible for the accumulation of type I collagen in fibrotic livers. In this study, we silenced the PCBP2 gene using a small interfering RNA (siRNA) to reverse alcohol-and cytokine-induced profibrogenic effects on hepatic stellate cells (HSCs).

METHODS

Primary rat HSCs and the HSC-T6 cell line were used as fibrogenic models to mimic the initiation and perpetuation stages of fibrogenesis, respectively. We previously found that a PCBP2 siRNA, which efficiently silences expression of αCP2, reduces the stability of type I collagen mRNA. We investigated the effects of the PCBP2 siRNA on cell proliferation and migration. Expression of type I collagen in HSCs was analyzed by quantitative real-time PCR and western blotting. In addition, we evaluated the effects of the PCBP2 siRNA on apoptosis and the cell cycle.

RESULTS

PCBP2 siRNA reversed multiple alcohol- and cytokine-induced profibrogenic effects on primary rat HSCs and HSC-T6 cells. The PCBP2 siRNA also reversed alcohol- and cytokine-induced accumulation of type I collagen as well as cell proliferation and migration. Moreover, the combination of LY2109761, a transforming growth factor-β1 inhibitor, and the PCBP2 siRNA exerted a synergistic inhibitive effect on the accumulation of type I collagen in HSCs.

CONCLUSIONS

Silencing of PCBP2 using siRNA could be a potential therapeutic strategy for alcoholic liver fibrosis.

The importance of the interaction between hepatocyte and hepatic stellate cells in fibrogenesis induced by fatty accumulation

BACKGROUND & AIMS

Non-alcoholic fatty liver disease is characterized by an initial accumulation of triglycerides that can progress to non-alcoholic steatohepatitis, which can ultimately evolve to cirrhosis and hepatocellular carcinoma. Hepatic stellate cells play a key role in liver fibrogenesis by an increased activation and an altered profile of genes involved in the turnover of extracellular matrix components. To reproduce in-vitro the functional cell connections observed in vivo it is essential to consider cell-to-cell proximity and interaction. The aim of this study was to determine the response to free fatty acids in a simultaneous co-culture model of hepatocytes and hepatic stellate cells.

METHODS

Simultaneous co-culture model and monoculture of each cell type (control) were exposed to FFA for 24 up to 144 h. Quantification of steatosis; stellate cell activation; assessment of fibrogenic response; expression and activity of metalloproteinases as well as collagen biosynthesis were evaluated.

RESULTS

Free fatty acids induced comparable steatosis in simultaneous co-culture and monoculture. However, the activation of the stellate cells assessed by alpha-smooth muscle actin expression is greater when cells were in close contact. Furthermore, a time-dependent increment of tissue inhibitor metalloproteinase-2 protein was observed, which was inversely correlated with protein expression and activity of matrix-metalloproteinases, suggesting enhanced collagen biosynthesis. This behavior was absent in cell monoculture.

CONCLUSIONS

These data indicate that cell-to-cell proximity between hepatocytes and stellate cells is necessary for the initiation of the fibrotic process.

Non-invasive markers for hepatic fibrosis

With great advancements in the therapeutic modalities used for the treatment of chronic liver diseases, the accurate assessment of liver fibrosis is a vital need for successful individualized management of disease activity in patients. The lack of accurate, reproducible and easily applied methods for fibrosis assessment has been the major limitation in both the clinical management and for research in liver diseases. However, the problem of the development of biomarkers capable of non-invasive staging of fibrosis in the liver is difficult due to the fact that the process of fibrogenesis is a component of the normal healing response to injury, invasion by pathogens, and many other etiologic factors. Current non-invasive methods range from serum biomarker assays to advanced imaging techniques such as transient elastography and magnetic resonance imaging (MRI). Among non-invasive methods that gain strongest clinical foothold are FibroScan elastometry and serum-based APRI and FibroTest. There are many other tests that are not yet widely validated, but are none the less, promising. The rate of adoption of non-invasive diagnostic tests for liver fibrosis differs from country to country, but remains limited. At the present time, use of non-invasive procedures could be recommended as pre-screening that may allow physicians to narrow down the patients' population before definitive testing of liver fibrosis by biopsy of the liver. This review provides a systematic overview of these techniques, as well as both direct and indirect biomarkers based approaches used to stage fibrosis and covers recent developments in this rapidly advancing area.

PCBP2 siRNA reverses the alcohol-induced pro-fibrogenic effects in hepatic stellate cells

PURPOSE

Type I collagen accumulates during liver fibrosis primarily because α-complex protein-2 (αCP(2)), encoded by the poly(rC) binding protein 2 (PCBP2) gene, binds to the 3' end of the collagen mRNA and increases its half-life. This study aimed to reverse the pro-fibrogenic effect of alcohol on hepatic stellate cells (HSCs) by silencing the PCBP2 gene with siRNA.

METHODS

The silencing effects of a series of predesigned PCBP2 siRNAs were evaluated in the rat hepatic stellate cell line, HSC-T6. The pro-fibrogenic effects of alcohol on the expression levels of PCBP2 and type-I collagen were examined by several methods. The effect of PCBP2 siRNA on the stability of type I collagen α1(I) mRNA was investigated by an in vitro mRNA decay assay.

RESULTS

We identified one potent PCBP2 siRNA that reversed the alcohol-induced expression of PCBP2 in HSCs. The decay rate of the collagen α1(I) mRNA increased significantly in HSCs treated with the PCBP2 siRNA.

CONCLUSION

This study provides the first evidence that alcohol up-regulates the expression of PCBP2, which subsequently increases the half-life of collagen α1(I) mRNA. Silencing of PCBP2 using siRNA may provide a promising strategy to reverse the alcohol-induced pro-fibrogenic effects in HSCs.

Oxidative stress and hepatic stellate cell activation are key events in arsenic induced liver fibrosis in mice

Arsenic is an environmental toxicant and carcinogen. Exposure to arsenic is associated with development of liver fibrosis and portal hypertension through ill defined mechanisms. We evaluated hepatic fibrogenesis after long term arsenic exposure in a murine model. BALB/c mice were exposed to arsenic by daily gavages of 6 μg/gm body weight for 1 year and were evaluated for markers of hepatic oxidative stress and fibrosis, as well as pro-inflammatory, pro-apoptotic and pro-fibrogenic factors at 9 and 12 months. Hepatic NADPH oxidase activity progressively increased in arsenic exposure with concomitant development of hepatic oxidative stress. Hepatic steatosis with occasional collection of mononuclear inflammatory cells and mild portal fibrosis were the predominant liver lesion observed after 9 months of arsenic exposure, while at 12 months, the changes included mild hepatic steatosis, inflammation, necrosis and significant fibrosis in periportal areas. The pathologic changes in the liver were associated with markers of hepatic stellate cells (HSCs) activation, matrix reorganization and fibrosis including α-smooth muscle actin, transforming growth factor-β1, PDGF-Rβ, pro-inflammatory cytokines and enhanced expression of tissue inhibitor of metalloproteinase-1 and pro(α) collagen type I. Moreover, pro-apoptotic protein Bax was dominantly expressed and Bcl-2 was down-regulated along with increased number of TUNEL positive hepatocytes in liver of arsenic exposed mice. Furthermore, HSCs activation due to increased hepatic oxidative stress observed after in vivo arsenic exposure was recapitulated in co-culture model of isolated HSCs and hepatocytes exposed to arsenic. These findings have implications not only for the understanding of the pathology of arsenic related liver fibrosis but also for the design of preventive strategies in chronic arsenicosis.

Alcohol induced hepatic fibrosis: role of acetaldehyde

Alcohol abuse is one of the major causes of liver fibrosis worldwide. Although the pathogenesis of liver fibrosis is a very complex phenomenon involving different molecular and biological mechanisms, several lines of evidence established that the first ethanol metabolite, acetaldehyde, plays a key role in the onset and maintenance of the fibrogenetic process. This review briefly summarizes the molecular mechanisms underlying acetaldehyde pro-fibrogenic effects. Liver fibrosis represents a general wound-healing response to a variety of insults. Although mortality due to alcohol abuse has been constantly decreasing in the past 20 years in Southern Europe and North America, in several Eastern-European countries and Great Britain Alcoholic Liver Disease (ALD) shows a sharply increasing trend [Bosetti, C., Levi, F., Lucchini, F., Zatonski, W.A., Negri, E., La, V.C., 2007. Worldwide mortality from cirrhosis: an update to 2002. J. Hepatol. 46, 827-839]. ALD has a complex pathogenesis, in which acetaldehyde (AcCHO), the major ethanol metabolite, plays a central role. Ethanol is mainly metabolized in the liver by two oxidative pathways. In the first one ethanol is oxidized to acetaldehyde by the cytoplasmic alcohol dehydrogenase enzyme (ADH), acetaldehyde is then oxidized to acetic acid by the mitochondrial acetaldehyde dehydrogenase (ALDH). The second pathway is inducible and involves the microsomal ethanol-oxidizing system (MEOS), in which the oxidation of ethanol to acetaldehyde and acetic acid also leads to generation of reactive oxygen species (ROS). Chronic ethanol consumption significantly inhibits mitochondrial ALDH activity while the rate of ethanol oxidation to acetaldehyde is even enhanced, resulting in a striking increase of tissue and plasma acetaldehyde levels [Lieber, C.S., 1997. Ethanol metabolism, cirrhosis and alcoholism. Clin. Chim. Acta 257, 59-84]. This review will focus on the molecular mechanisms by which acetaldehyde promote liver fibrosis.

Ethanol and fish oil induce NFkappaB transactivation of the collagen alpha2(I) promoter through lipid peroxidation-driven activation of the PKC-PI3K-Akt pathway

To analyze whether fish oil, as a source of polyunsaturated fatty acids from the n-3 series, could synergize with ethanol to promote collagen I upregulation in vivo, collagen alpha2(I) promoter-betaGal (COL1A2-betaGal) transgenic mice were fed a diet enriched in fish oil in the presence of ethanol (ethanol group) or dextrose (control group). Ethanol-fed mice showed mild steatosis, increased alanine aminotransferase (ALT), aspartate aminotransferase (AST), nonsterified fatty acids, and plasma alcohol levels along with elevated cytochrome P450 2E1 activity, lipid peroxidation end products, and low glutathione (GSH) levels, which suggested enhanced oxidant stress and liver injury. Increased transactivation of the COL1A2 promoter assessed by betaGal activity was shown in vivo and by transfection with deletion constructs for the collagen alpha1(I) promoter (COL1A1) and COL1A2 promoters in vitro. Transcriptional regulation of both COL1A1 and COL1A2 promoters was validated by nuclear in vitro transcription run-on, northern blot analysis, and quantitative polymerase chain reaction, which was followed by the subsequent upregulation of collagen I protein with no changes in matrix metalloproteinase 13 (MMP 13). To further analyze the potential mechanism for collagen I upregulation, an in vitro coculture model was designed with primary stellate cells seeded on the bottom plate of a Boyden chamber and the rest of the liver cells plated on a cell culture insert, and fish oil or fish oil plus ethanol were added. The combination of fish oil plus ethanol increased nuclear factor kappaB binding to the COL1A2 promoter both in vivo and in the cocultures and also resulted in increased phosphorylation of protein kinase C, activation of PI3 kinase, and phosphorylation of Akt. The in vitro addition of vitamin E prevented such activation and collagen I increase. Furthermore, inhibitors of all 3 kinases blocked the increase in collagen I and NFkappaB binding to the COL1A2 promoter; the latter was also prevented by vitamin E.

CONCLUSION

These results suggest that fish oil (mainly n-3 polyunsaturated fatty acids [PUFAs]) can synergize with ethanol to induce collagen I, transactivating the COL1A2 promoter through a lipid peroxidation-PKC-PI3K-Akt-NFkappaB-driven mechanism in the absence of overt steatosis and inflammation.

Liver fibrosis in vitro: Cell culture models and precision-cut liver slices

Chronic liver injury of various etiologies can cause liver fibrosis, which is characterized by the progressive accumulation of connective tissue in the liver. As no effective treatment for liver fibrosis is available yet, extensive research is ongoing to further study the mechanisms underlying the development of disease- or toxicity-induced liver fibrosis and to identify potential pro- or anti-fibrotic properties of compounds. This review gives an overview of the in vitro methods that are currently available for this purpose. The first focus is on cell culture models, since the majority of in vitro research uses these systems. Both primary cells and cell lines as well as the use of different culture matrices and co-culture models are discussed. Second, the use of precision-cut liver slices, which recently came into attention as in vitro model for the study of fibrosis, is discussed. The overview clearly shows that continuous optimization and adaptation have extended the potential of in vitro models for liver fibrosis during the past years. By combining the use of the different cell and tissue culture models, the mechanisms underlying multicellular fibrosis development can be studied in vitro and potential pro- or anti-fibrotic properties of compounds can be identified both on single liver cell types and in human liver tissue.

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.

Early response of alpha2(I) collagen to acetaldehyde in human hepatic stellate cells is TGF-beta independent

Acetaldehyde is fibrogenic and induces the expression of type I collagen genes in hepatic stellate cells. Some of these acetaldehyde-dependent events are mediated by H(2)O(2) and thus establish a direct connection between oxidative stress and collagen upregulation. We localized to the -378 to -183 region of the alpha2(I) collagen (COL1A2) promoter an acetaldehyde-responsive element (AcRE) functional in human hepatic stellate cells (HHSCs) and investigated molecular mechanisms whereby acetaldehyde stimulates and modulates its transcriptional activity. Because the AcRE co-localized with a previously described transforming growth factor beta (TGF-beta)1-responsive element, and both acetaldehyde and this cytokine induce their effects through H(2)O(2), we investigated whether all fibrogenic actions of acetaldehyde were mediated by this cytokine. Here we show that acetaldehyde-induced COL1A2 upregulation in HHSCs recognizes two distinct but overlapping early and late stages that last from 1 to 6 hours and from 6 to 24 hours, respectively. We present several lines of evidence to show that early acetaldehyde-mediated events are independent of TGF-beta1. These include significant time-course differences in the expression of COL1A2 and TGF-beta1 mRNAs and inability of neutralizing antibodies to TGF-beta1 to inhibit acetaldehyde-dependent collagen gene transcription and Smad 3 phosphorylation. We also show that although acetaldehyde-dependent upregulation of collagen was PI3K dependent, that of TGF-beta1 was PI3K independent. In conclusion, acetaldehyde-dependent mechanisms involved in COL1A2 upregulation are similar, but not identical, to those of TGF-beta1. We suggest that early acetaldehyde-dependent events induce the late expression of TGF-beta1 and create an H(2)O(2)-dependent autocrine loop that may sustain and amplify the fibrogenic response of this alcohol metabolite.

Ethanol stimulates the expression of fibronectin in lung fibroblasts via kinase-dependent signals that activate CREB

Ethanol renders the lung susceptible to acute lung injury in the setting of insults such as sepsis. The mechanisms mediating this effect are unknown, but activation of tissue remodeling is considered key to this process. We found that chronic ethanol ingestion in rats increased the expression of fibronectin, a matrix glycoprotein implicated in acute lung injury. In cultured NIH/3T3 cells and in primary rat and mouse lung fibroblasts, ethanol induced fibronectin mRNA and protein expression in a dose- and time-dependent fashion. The effect of ethanol was prevented by inhibitors of protein kinase C and mitogen-activated protein kinases and was associated with the phosphorylation and increased DNA binding of the transcription factor cAMP response element binding protein, followed by increased transcription of the fibronectin gene. Fibroblasts were found to express alpha(7) nicotinic acetylcholine receptor (nAChR), and ethanol induction of fibronectin was abolished by alpha-bungarotoxin and methyllcaconitine, inhibitors of alpha(7) nAChRs. However, ethanol was able to induce fibronectin mRNA and protein in primary lung fibroblasts isolated from alpha(7) nAChR knockout mice. The ethanol-induced fibronectin response was dependent on ethanol metabolism since 4-methylpyrazole, an inhibitor of alcohol dehydrogenase, abolished the effect and acetaldehyde induced it. These observations suggest that ethanol or ethanol metabolites stimulate lung fibroblasts to produce fibronectin by inducing specific signals transmitted via nAChRs independent of the alpha(7-)subunit, and this might represent a mechanism by which ethanol renders the lung susceptible to acute lung injury.

Reciprocal modulation of matrix metalloproteinase-13 and type I collagen genes in rat hepatic stellate cells

Collagen degradation by matrix metalloproteinases is the limiting step in reversing liver fibrosis. Although collagen production in cirrhotic livers is increased, the expression and/or activity of matrix metalloproteinases could be normal, increased in early fibrosis, or decreased during advanced liver cirrhosis. Hepatic stellate cells are the main producers of collagens and matrix metalloproteinases in the liver. Therefore, we sought to investigate whether they simultaneously produce alpha1(I) collagen and matrix metalloproteinase-13 mRNAs. In this communication we show that expression of matrix metalloproteinase-13 mRNA is reciprocally modulated by tumor necrosis factor-alpha and transforming growth factor-beta1. When hepatic stellate cells are co-cultured with hepatocytes, matrix metalloproteinase-13 mRNA is up-regulated and alpha1(I) collagen is down-regulated. Injuring hepatocytes with galactosamine further increased matrix metalloproteinase-13 mRNA production. Confocal microscopy and differential centrifugation of co-cultured cells revealed that matrix metalloproteinase-13 is localized mainly within hepatic stellate cells. Studies performed with various hepatic stellate cell lines revealed that they are heterogeneous regarding expression of matrix metalloproteinase-13. Those with myofibroblastic phenotypes produce more type I collagen whereas those resembling freshly isolated hepatic stellate cells express matrix metalloproteinase-13. Overall, these findings strongly support the notion that alpha1(I) collagen and matrix metalloproteinase-13 mRNAs are reciprocally modulated.

Chronic ethanol ingestion increases susceptibility to acute lung injury: role of oxidative stress and tissue remodeling

Clinical studies have demonstrated that chronic alcohol abuse is an independent outcome variable in acute lung injury. The Emory Center for the Study of Acute Lung Injury is determining the mechanisms by which ethanol increases susceptibility to acute lung injury. We developed a rat model of chronic ethanol ingestion and demonstrated that ethanol predisposes rats to edematous lung injury elicited by endotoxemia or sepsis. Chronic ethanol ingestion in rats led to decreased levels of glutathione, an important antioxidant in the lung, and this defect was associated with alterations in epithelial cell permeability, decreased alveolar liquid clearance, decreased cell viability, and decreased surfactant production. Chronic ethanol ingestion also led to the activation of lung tissue remodeling as demonstrated by the increased expression of profibrotic growth factors, matrix components, and metalloproteases. In cultured fibroblasts, the induction of the matrix glycoprotein fibronectin by ethanol was mediated via nicotinic acetylcholine receptor-dependent signal transduction. We speculate that these alterations render the host susceptible to acute lung injury by diminishing the protective mechanisms of the lung and promoting exaggerated inflammatory and tissue repair responses elicited against injurious agents.

Cytochrome P450 2E1-derived reactive oxygen species mediate paracrine stimulation of collagen I protein synthesis by hepatic stellate cells

To evaluate possible fibrogenic effects of CYP2E1-dependent generation of reactive oxygen species, a model was developed using co-cultures of HepG2 cells, which do (E47 cells) or do not (C34 cells) express cytochrome P450 2E1 (CYP2E1) with stellate cells. There was an increase in intra- and extracellular H(2)O(2), lipid peroxidation, and collagen type I protein in stellate cells co-cultured with E47 cells compared with stellate cells alone or co-cultured with C34 cells. The increase in collagen was prevented by antioxidants and a CYP2E1 inhibitor. CYP3A4 did not mimic the stimulatory effects found with CYP2E1. Collagen mRNA levels remained unchanged, and pulse-chase analysis indicated similar half-lives of collagen I protein between both co-cultures. However, collagen protein synthesis was increased in E47 co-culture. Hepatocytes from pyrazole-treated rats (with high levels of CYP2E1) induced collagen protein in primary stellate cells, and antioxidants and CYP2E1 inhibitors blocked this effect. These results suggest that increased translation of collagen mRNA by CYP2E1-derived reactive oxygen species is responsible for the increase in collagen protein produced by the E47 co-culture. These co-culture models may be useful for understanding the impact of CYP2E1-derived ROS on stellate cell function and activation.

Cadmium induces alpha(1)collagen (I) and metallothionein II gene and alters the antioxidant system in rat hepatic stellate cells

The mechanism of cadmium-mediated hepatotoxicity has been the subject of numerous investigations, principally in hepatocytes. Although, some uncertainties persist, sufficient evidence has emerged to provide a reasonable account of the toxic process in parenchymal cells. However, there is no information about the effect of cadmium in other hepatic cell types, such as stellate cells (fat storing cells, Ito cells, perisinusoidal cells, parasinusoidal cells, lipocytes). Hepatic stellate cells (HSC) express a quiescent phenotype in a healthy liver and acquire an activated phenotype in liver injury. These cells play an important role in the fibrogenic process. The objective of this study was to investigate the effect of a 24 h treatment of low Cd concentrations in glutathione content, lipid peroxidation damage, cytosolic free Ca, antioxidant enzyme activities: glutathione peroxidase, glutathione reductase, superoxide dismutase and catalase along with the capacity of this heavy metal to induce metallothionein II and alpha(1)collagen (I) in an hepatic stellate cell line (CFSC-2G). Cd-treated cells increased lipid peroxidation and the content of cytosolic free calcium, decreased glutathione content and superoxide dismutase, glutathione peroxidase and catalase activity. Cd was able to induce the expression of the metallothionein II and alpha(1)collagen (I) gene, that was not described in this cell type. Cadmium may act as a pro-fibrogenic agent in the liver probably by inducing oxidative damage by enhancing lipid peroxidation and altering the antioxidant system of the cells. Although, the exact role metallothionein induction plays in this process is unknown, it probably, provides a cytosolic pool of potential binding sites to sequester ionic Cd, thereby decreasing its toxicity.

Stimulation and proliferation of primary rat hepatic stellate cells by cytochrome P450 2E1-derived reactive oxygen species

The alcohol-inducible cytochrome P450 2E1 (CYP2E1) is expressed mainly in hepatocytes and generates reactive oxygen species (ROS). To better understand how hepatic stellate cells (HSC) become activated in the presence of oxidative stress and evaluate whether CYP2E1-derived ROS activate stellate cells, we coincubated primary stellate cells with HepG2 cells, which do (E47 cells) or do not (C34 cells) express CYP2E1. Morphologic changes and loss of lipid droplets were more apparent in the stellate cells cocultured with E47 cells. There was a more pronounced increase in alpha-smooth muscle actin (alpha-sma), intracellular and secreted collagen type I protein, and intra- and extracellular H(2)O(2) and lipid peroxidation products in stellate cells coincubated with E47 cells. Expression of collagen in stellate cells did not change when cocultured with HepG2 cells expressing a different P450, CYP3A4. Stellate cells cultured on Matrigel expressed increased alpha-sma and collagen when incubated with E47 cells. The increase in collagen production by coculture with E47 cells was prevented by antioxidants, by CYP2E1 inhibitors, and by transfected antisense CYP2E1. The addition of arachidonic acid plus ferric nitrilotriacetate (Fe-NTA), agents that potentiate oxidative stress, further induced collagen protein in the E47 coculture. Stellate cell proliferation was greater in the E47 coculture, and this was partially abrogated by catalase and vitamin E. These results show that hepatocytes containing CYP2E1 release diffusible mediators including ROS, which can activate HSC. Thus, besides perturbing the homeostasis of hepatocytes, CYP2E1-derived diffusible oxidants may also interact with stellate cells and contribute to hepatic fibrosis.

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.

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-mediated collagen regulation in hepatic stellate cells

Alcohol-induced liver cirrhosis is one of the major causes of death worldwide. Strong evidence has established that ethanol's first metabolite, acetaldehyde, is highly fibrogenic and enhances the deposition of many extracellular matrix components by hepatic stellate cells. This article reviews our current knowledge of the molecular mechanisms whereby acetaldehyde induces these activities, with particular emphasis on those related to the upregulation of type I collagen.