Effect of tauroursodeoxycholic and ursodeoxycholic acid on ethanol-induced cell injuries in the human Hep G2 cell line

Inhibition of Abelson Tyrosine-Protein Kinase 2 Suppresses the Development of Alcohol-Associated Liver Disease by Decreasing PPARgamma Expression

BACKGROUND & AIMS

Alcohol-associated liver disease (ALD) represents a spectrum of alcohol use-related liver diseases. Outside of alcohol abstinence, there are currently no Food and Drug Administration-approved treatments for advanced ALD, necessitating a greater understanding of ALD pathogenesis and potential molecular targets for therapeutic intervention. The ABL-family proteins, including ABL1 and ABL2, are non-receptor tyrosine kinases that participate in a diverse set of cellular functions. We investigated the role of the ABL kinases in alcohol-associated liver disease.

METHODS

We used samples from patients with ALD compared with healthy controls to elucidate a clinical phenotype. We established strains of liver-specific Abl1 and Abl2 knockout mice and subjected them to the National Institute on Alcohol Abuse and Alcoholism acute-on-chronic alcohol feeding regimen. Murine samples were subjected to RNA sequencing, AST, Oil Red O staining, H&E staining, Western blotting, and quantitative polymerase chain reaction to assess phenotypic changes after alcohol feeding. In vitro modeling in HepG2 cells as well as primary hepatocytes from C57BL6/J mice was used to establish this mechanistic link of ALD pathogenesis.

RESULTS

We demonstrate that the ABL kinases are highly activated in ALD patient liver samples as well as in liver tissues from mice subjected to an alcohol feeding regimen. We found that the liver-specific knockout of Abl2, but not Abl1, attenuated alcohol-induced steatosis, liver injury, and inflammation. Subsequent RNA sequencing and gene set enrichment analyses of mouse liver tissues revealed that relative to wild-type alcohol-fed mice, Abl2 knockout alcohol-fed mice exhibited numerous pathway changes, including significantly decreased peroxisome proliferator activated receptor (PPAR) signaling. Further examination revealed that PPARγ, a previously identified regulator of ALD pathogenesis, was induced upon alcohol feeding in wild-type mice, but not in Abl2 knockout mice. In vitro analyses revealed that shRNA-mediated knockdown of ABL2 abolished the alcohol-induced accumulation of PPARγ as well as subsequent lipid accumulation. Conversely, forced overexpression of ABL2 resulted in increased PPARγ protein expression. Furthermore, we demonstrated that the regulation of hypoxia inducible factor 1 subunit alpha (HIF1α) by ABL2 is required for alcohol-induced PPARγ expression. Furthermore, treatment with ABL kinase inhibitors attenuated alcohol-induced PPARγ expression, lipid droplet formation, and liver injury.

CONCLUSIONS

On the basis of our current evidence, we propose that alcohol-induced ABL2 activation promotes ALD through increasing HIF1α and the subsequent PPARγ expression, and ABL2 inhibition may serve as a promising target for the treatment of ALD.

Sirtuin 6 ameliorates alcohol-induced liver injury by reducing endoplasmic reticulum stress in mice

Alcoholic liver disease (ALD) occurs as a result of chronic and excessive alcohol consumption. It encompasses a wide spectrum of chronic liver abnormalities that range from steatosis to alcoholic hepatitis, progressive fibrosis and cirrhosis. Endoplasmic reticulum (ER) stress induced by ethanol metabolism in hepatocytes has been established as an important contributor to the pathogenesis of ALD. However, whether SIRT6 exerts regulatory effects on ethanol-induced ER stress and contributes to the pathogenesis of ALD is unclear. In this study, we developed and characterized Sirt6 hepatocyte-specific knockout and transgenic mouse models that were treated with chronic-plus-binge ethanol feeding. We observed that hepatic Sirt6 deficiency led to exacerbated ethanol-induced liver injury and aggravated hepatic ER stress. Tauroursodeoxycholic acid (TUDCA) treatment remarkably attenuated ethanol-induced ER stress and ameliorated ALD pathologies caused by Sirt6 ablation. Reciprocally, SIRT6 hepatocyte-specific transgenic mice exhibited reduced ER stress and ameliorated liver injury caused by ethanol exposure. Consistently, knockdown of Sirt6 elevated the expression of ER stress related genes in primary hepatocytes treated with ethanol, whereas overexpression of SIRT6 reduced their expression, indicating SIRT6 regulates ethanol-induced hepatic ER stress in a cell autonomous manner. Collectively, our results suggest that SIRT6 is a positive regulator of ethanol-induced ER stress in the liver and protects against ALD by relieving ER stress.

BiP Inducer X: An ER Stress Inhibitor for Enhancing Recombinant Antibody Production in CHO Cell Culture

Prolonged endoplasmic reticulum (ER) stress reduces protein synthesis and induces apoptosis in mammalian cells. When dimethyl sulfoxide (DMSO), a specific monoclonal antibody productivity (q_mAb )-enhancing reagent, is added to recombinant Chinese hamster ovary (rCHO) cell cultures (GSR cell line), it induces ER stress and apoptosis in a dose-dependent manner. To determine an effective ER stress inhibitor, three ER stress inhibitors (BiP inducer X [BIX], tauroursodeoxycholic acid, and carbazole) are examined and BIX shows the best production performance. Coaddition of BIX (50 μm) with DMSO extends the culture longevity and enhances q_mAb . As a result, the maximum mAb concentration is significantly increased with improved galactosylation. Coaddition of BIX significantly increases the expression level of binding immunoglobulin protein (BiP) followed by increased expression of chaperones (calnexin and GRP94) and galactosyltransferase. Furthermore, the expression levels of CHOP, a well-known ER stress marker, and cleaved caspase-3 are significantly reduced, suggesting that BIX addition reduces ER stress-induced cell death by relieving ER stress. The beneficial effect of BIX on mAb production is also demonstrated with another q_mAb -enhancing reagent (sodium butyrate) and a different rCHO cell line (CS13-1.00). Taken together, BIX is an effective ER stress inhibitor that can be used to increase mAb production in rCHO cells.

Biomarkers of Drug-Induced Liver Toxicity

Drug-induced liver injury (DILI) is a comprehensive phenomenon. The injury to the liver may occur as an unexpected and undesired reaction to a therapeutic dose of a drug (idiosyncratic reaction) or as an expected therapeutic effect of the direct (intrinsic) toxicity of a drug taken in a large enough dose to cause liver injury. The direct toxicity (type A) reactions represent an extension of the drug's therapeutic effect; they occur relatively frequently and are typically dose-related and frequency-of-exposure-related. By contrast, idiosyncratic reactions, or type B reactions, are unpredictable, occurring only in susceptible individuals, and are unrelated to the dose or frequency of exposure. DILI encompasses both acute and/or chronic hepatic lesions. The liver injury may be the only clinical manifestation of the adverse drug effect. Otherwise, it may be accompanied by injury to other organs, or by systemic manifestations. The liver injury may be observed in 1-8 days from taking the drug. DILI cases may result in the disapproval of a new drug or in the removal of a useful drug from the market by regulatory agencies. The purpose of this review is to provide guidance to facilitate the detection and assessment of hepatotoxicity induced by therapeutics that received market authorization. This review supports the safe and effective use of drugs by patients and guides laboratory medicine professional in determining the possible drug-induced liver damage.

Role of farnesoid X receptor and bile acids in alcoholic liver disease

Alcoholic liver disease (ALD) is one of the major causes of liver morbidity and mortality worldwide. Chronic alcohol consumption leads to development of liver pathogenesis encompassing steatosis, inflammation, fibrosis, cirrhosis, and in extreme cases, hepatocellular carcinoma. Moreover, ALD may also associate with cholestasis. Emerging evidence now suggests that farnesoid X receptor (FXR) and bile acids also play important roles in ALD. In this review, we discuss the effects of alcohol consumption on FXR, bile acids and gut microbiome as well as their impacts on ALD. Moreover, we summarize the findings on FXR, FoxO3a (forkhead box-containing protein class O3a) and PPARα (peroxisome proliferator-activated receptor alpha) in regulation of autophagy-related gene transcription program and liver injury in response to alcohol exposure.

Neuropathy- and myopathy-associated mutations in human small heat shock proteins: Characteristics and evolutionary history of the mutation sites

Mutations in four of the ten human small heat shock proteins (sHSP) are associated with various forms of motor neuropathies and myopathies. In HspB1, HspB3, and HspB8 all known mutations cause motor neuropathies, whereas in HspB5 they cause myopathies. Several features are common to the majority of these mutations: (i) they are missense mutations, (ii) most associated disease phenotypes exhibit a dominant inheritance pattern and late disease onset, (iii) in the primary protein sequences, the sites of most mutations are located in the conserved α-crystallin domain and the variable C-terminal extensions, and (iv) most human mutation sites are highly conserved among the vertebrate orthologs and have been historically exposed to significant purifying selection. In contrast, a minor fraction of these mutations deviate from these rules: they are (i) frame shifting, nonsense, or elongation mutations, (ii) associated with recessive or early onset disease phenotypes, (iii) positioned in the N-terminal domain of the proteins, and (iv) less conserved among the vertebrates and were historically not subject to a strong selective pressure. In several vertebrate sHSPs (including primate sHSPs), homologous sites differ from the human sequence and occasionally even encode the same amino acid residues that cause the disease in humans. Apparently, a number of these mutations sites are not crucial for the protein function in single species or entire taxa, and single species even seem to have adopted mechanisms that compensate for potentially adverse effects of 'mutant-like' sHSPs. The disease-associated dominant sHSP missense mutations have a number of cellular consequences that are consistent with gain-of-function mechanisms of genetic dominance: dominant-negative effects, the formation of cytotoxic amyloid protein oligomers and precipitates, disruption of cytoskeletal networks, and increased downstream enzymatic activities. Future therapeutic concepts should aim for reducing these adverse effects of mutant sHSPs in patients. Indeed, initial experimental results are encouraging.

InterfERing with endoplasmic reticulum stress

Stress to the endoplasmic reticulum (ER) is a recognized factor in Alzheimer's and Parkinson's diseases, diabetes, heart disease, liver disorders and cancer. Thus, drugs that interfere with ER stress have wide therapeutic potential. Here we review the effects of drugs on three arms of ER stress: the protein kinase RNA-activated (PKR)-like ER kinase (PERK) arm, the activated transcription factor 6 (ATF6) arm and the inositol-requiring enzyme 1 (IRE1) arm. Drugs fall into five groups: (i) compounds directly binding to ER stress molecules; (ii) chemical chaperones; (iii) inhibitors of protein degradation; (iv) antioxidants; (v) drugs affecting calcium signaling. Treatments are generally inhibitory and lead to increased viability, except when applied to cancer cells. A focus on interfering with the ATF6 arm is required, and more in vivo testing of these compounds concurrently across all three arms is needed if the full importance of ER stress to human disease is to be realized.

Alcohol disrupts endoplasmic reticulum function and protein secretion in hepatocytes

BACKGROUND

Many alcoholic patients have serum protein deficiency that contributes to their systemic problems. The unfolded protein response (UPR) is induced in response to disequilibrium in the protein folding capability of the endoplasmic reticulum (ER) and is implicated in hepatocyte lipid accumulation and apoptosis, which are associated with alcoholic liver disease (ALD). We investigated whether alcohol affects ER structure, function, and UPR activation in hepatocytes in vitro and in vivo.

METHODS

HepG2 cells expressing human cytochrome P450 2E1 and mouse alcohol dehydrogenase (VL-17A) were treated for up to 48 hours with 50 and 100 mM ethanol. Zebrafish larvae at 4 days postfertilization were exposed to 350 mM ethanol for 32 hours. ER morphology was visualized by fluorescence in cells and transmission electron microscopy in zebrafish. UPR target gene activation was assessed using quantitative PCR, in situ hybridization, and Western blotting. Mobility of the major ER chaperone, BIP, was monitored in cells by fluorescence recovery after photobleaching (FRAP).

RESULTS

VL-17A cells metabolized alcohol yet only had slight activation of some UPR target genes following ethanol treatment. However, ER fragmentation, crowding, and accumulation of unfolded proteins as detected by immunofluorescence and FRAP demonstrate that alcohol induced some ER dysfunction despite the lack of UPR activation. Zebrafish treated with alcohol, however, showed modest ER dilation, and several UPR targets were significantly induced.

CONCLUSIONS

Ethanol metabolism directly impairs ER structure and function in hepatocytes. Zebrafish are a novel in vivo system for studying ALD.

The mechanism of elevated toxicity in HepG2 cells due to combined exposure to ethanol and ionizing radiation

Ethanol and ionizing radiation exposure are independently known to cause tissue damage through various mechanisms. The non-enzymatic and enzymatic metabolism of ethanol, the latter via the cytochrome P(450) 2E1-dependent pathway produces free radicals, which deplete cellular glutathione (GSH). Ionizing radiation exposure has been shown to induce lipid peroxidation, DNA damage, protein oxidation and GSH depletion. It was postulated that cells sensitized by ethanol will be susceptible to additional insult, such as by radiation through increased oxidative stress. In this investigation, cultured liver cells (HepG2, human hepatocellular liver carcinoma) were exposed to ethanol, followed by ionizing radiation. The antioxidant status of the cells was evaluated by an array of techniques. Levels of glutathione, cysteine (CYS), and malondialdehyde (MDA) were measured by HPLC. Activities of antioxidant enzymes, catalase and glutathione reductase (GR) were determined enzymatically. Apoptosis was evaluated by the caspases-3 assay and fluorescence microscopy. The data showed that combined treatment with ethanol and radiation resulted in the lowest levels of GSH, and highest MDA level compared with the control. The catalase activity was lower in the combined exposure groups, when compared with the single agent exposure groups, and the glutathione reductase activity was the highest in the combined exposure groups and lowest in the control. These findings suggest that a combination of ethanol and ionizing radiation results in greater toxicity in vitro through elevated oxidative stress.

Senecio latifolius induces in vitro hepatocytotoxicity in a human cell lineThis article is one of a selection of papers published in this special issue (part 2 of 2) on the Safety and Efficacy of Natural Health Products

The objectives of this study were twofold: (i) to determine the mechanism(s) of Senecio -induced toxicity in human hepatoblastoma cells (HepG2) in vitro and whether such toxicity could be prevented using N-acetyl-cysteine (NAC), and (ii) to evaluate whether caspases are involved in Senecio-induced apoptosis. Cells were treated with aqueous extracts of Senecio (10 mg·mL–1) with and without NAC. Cytotoxicity was determined by using the MTT assay. Total glutathione (GSH) was measured by using the Tietze assay. Cells were also treated with aqueous extracts of Senecio in the presence or absence of 50 μmol/L caspase-3 inhibitor (IDN) for 24 h. Apoptosis was determined by transmission electron microscopy, and DNA fragmentation was determined by ELISA and terminal dUTP nick-end labelling (TUNEL). Senecio produced cytotoxicity and depleted GSH in a concentration- and time-dependent manner. A significant depletion in GSH was observed after 15 min (p < 0.001 vs. control), whereas significant cytotoxicity was only observed after 3 h (p < 0.001 vs. control). Treatment with NAC prevented Senecio-induced GSH depletion and resulted in a significant decrease in Senecio-induced cytotoxicity (p < 0.001 vs. NAC-untreated cells). Treatment with Senecio for 24 h resulted in 22% ± 2.5% (p < 0.001) apoptosis (vs. control). Pretreatment with 50 μmol caspase inhibitor reduced Senecio-induced apoptosis significantly (vs. non-exposed to IDN) (12% ± 1.5%; p < 0.05). Our results suggest the mechanism of Senecio-induced cytotoxicity in HepG2 cells in vitro involves depletion of cellular GSH. Cytotoxicity is reduced by supplementation with NAC, which thus prevents GSH depletion. Caspase activation is involved in Senecio-induced apoptosis.

Dosage effects of ginkgolide B on ethanol-induced cell death in human hepatoma G2 cells

Ginkgolide B is a major active component of Ginkgo biloba extracts, which has been shown to confer anticancer effects by inducing apoptosis or inhibiting oxidative stress generation. Ethanol induces a wide range of cellular toxicities, many of which have been linked to free radical generation. To further elucidate the cellular effects of ginkgolide B, we examined the dose-response effect of ginkgolide B on ethanol-induced toxicity in human Hep G2 cells. TUNEL and MTT assays revealed that ethanol (50-400 mM) induced apoptotic cell death in human Hep G2 cells, and that this effect was inhibited by low (5-25 microM) doses of ginkgolide B, but enhanced by high (50-100 microM) doses of ginkgolide B. Additional experiments revealed that ethanol treatment directly increased intracellular oxidative stress; this effect was enhanced by high doses of ginkgolide B but decreased following treatment with low concentrations of ginkgolide B. The dose-response effects of ginkgolide B on reactive oxygen species (ROS) generation were directly correlated with cell apoptotic biochemical changes including c-Jun N-terminal kinase (JNK) activation, caspase-3 activation, and DNA fragmentation. These results indicate that treatment dosage may determine the effect of ginkgolide B on ethanol-induced ROS generation and cell apoptosis, and support the notion that an appropriate dosage of ginkgolide B may aid in decreasing the toxic effects of ethanol.

Protective effect of ursodeoxycholic acid on liver mitochondrial function in rats with alloxan-induced diabetes: link with oxidative stress

We investigated the effects of ursodeoxycholic acid (UDCA) on mitochondrial functions and oxidative stress and evaluated their relationships in the livers of rats with alloxan-induced diabetes. Diabetes was induced in male Wistar rats by a single alloxan injection (150 mg kg(-1) b.w., i.p.). UDCA (40 mg kg(-1) b.w., i.g., 30 days) was administered from the 5th day after the alloxan treatment. Mitochondrial functions were evaluated by oxygen consumption with Clark oxygen electrode using succinate, pyruvate+malate or palmitoyl carnitine as substrates and by determination of succinate dehydrogenase and NADH dehydrogenase activities. Liver mitochondria were used to measure chemiluminiscence enhanced by luminol and lucigenin, reduced liver glutathione and the end-products of lipid peroxidation. The activities of both NADH dehydrogenase and succinate dehydrogenase as well as the respiratory control (RC) value with all the substrates and the ADP/O ratio with pyruvate+malate and succinate as substrates were significantly decreased in diabetic rats. UDCA developed the beneficial effect on the mitochondrial respiration and oxidative phosphorylation parameters in alloxan-treated rats, whereas the activities of mitochondrial enzymes were increased insignificantly after the administration of UDCA. The contents of polar carbonyls and MDA as well as the chemiluminescence with luminol were elevated in liver mitochondria of diabetic rats. The treatment with UDCA normalized all the above parameters measured except the MDA content. UDCA administration prevents mitochondrial dysfunction in rats treated with alloxan and this process is closely connected with inhibition of oxidative stress by this compound.

Capillary electrophoresis with electrochemiluminescence detection for measurement of aspartate aminotransferase and alanine aminotransferase activities in biofluids

A new sensitive assay for aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities in biofluids was developed, based on the separation and detection of alanine, glutamate, and aspartate using capillary electrophoresis (CE) with electrochemiluminescence (ECL) detection. The three amino acids were separated in 5 mM phosphate of pH 2.1 as background electrolyte, and detected on a 500 microm platinum disk electrode at 1.2V (versus Ag/AgCl) in the presence of 10 mM tris(2,2'-bipyridyl)ruthenium(II) dissolved in 80 mM phosphate of pH 10.5. A mass detection limit of 37.3 fmol (or 81.5 fmol) for glutamate, corresponding to the product in the enzyme reaction catalyzed by 1.24 x 10(-9)U AST (or 2.72 x 10(-9)U ALT) in a 30 min reaction period, was achieved. This assay was applied to investigate the cytotoxicity effect of ethanol on HepG2 cells and differentiating nonalcoholic steatohepatitis (NASH) from alcoholic liver disease, indicating that the technique is promising for the application in the cell biological and clinical fields.

Metabolic basis of ethanol-induced cytotoxicity in recombinant HepG2 cells: role of nonoxidative metabolism

Chronic alcohol abuse, a major health problem, causes liver and pancreatic diseases and is known to impair hepatic alcohol dehydrogenase (ADH). Hepatic ADH-catalyzed oxidation of ethanol is a major pathway for the ethanol disposition in the body. Hepatic microsomal cytochrome P450 (CYP2E1), induced in chronic alcohol abuse, is also reported to oxidize ethanol. However, impaired hepatic ADH activity in a rat model is known to facilitate a nonoxidative metabolism resulting in formation of nonoxidative metabolites of ethanol such as fatty acid ethyl esters (FAEEs) via a nonoxidative pathway catalyzed by FAEE synthase. Therefore, the metabolic basis of ethanol-induced cytotoxicity was determined in HepG2 cells and recombinant HepG2 cells transfected with ADH (VA-13), CYP2E1 (E47) or ADH + CYP2E1 (VL-17A). Western blot analysis shows ADH deficiency in HepG2 and E47 cells, compared to ADH-overexpressed VA-13 and VL-17A cells. Attached HepG2 cells and the recombinant cells were incubated with ethanol, and nonoxidative metabolism of ethanol was determined by measuring the formation of FAEEs. Significantly higher levels of FAEEs were synthesized in HepG2 and E47 cells than in VA-13 and VL-17A cells at all concentrations of ethanol (100-800 mg%) incubated for 6 h (optimal time for the synthesis of FAEEs) in cell culture. These results suggest that ADH-catalyzed oxidative metabolism of ethanol is the major mechanism of its disposition, regardless of CYP2E1 overexpression. On the other hand, diminished ADH activity facilitates nonoxidative metabolism of ethanol to FAEEs as found in E47 cells, regardless of CYP2E1 overexpression. Therefore, CYP2E1-mediated oxidation of ethanol could be a minor mechanism of ethanol disposition. Further studies conducted only in HepG2 and VA-13 cells showed lower ethanol disposition and ATP concentration and higher accumulation of neutral lipids and cytotoxicity (apoptosis) in HepG2 cells than in VA-13 cells. The apoptosis observed in HepG2 vs. VA-13 cells incubated with ethanol appears to be mediated by release of mitochondrial cytochrome c via activation of caspase-9 and caspase-3. These results strongly support our hypothesis that diminished hepatic ADH activity facilitates nonoxidative metabolism of ethanol and the products of ethanol nonoxidative metabolism cause apoptosis in HepG2 cells via intrinsic pathway.

Dosage effects of resveratrol on ethanol-induced cell death in the human K562 cell line

Previous studies have established that ethanol induces cell apoptosis and necrosis. However, the precise molecular mechanisms are currently unclear. Here, we show that higher concentrations of ethanol (250-400 mM) induced a shift from apoptotic to necrotic cell death in human K562 cells, and that resveratrol, a grape-derived phytoalexin with known antioxidant and anti-inflammatory properties, inhibited or enhanced ethanol-induced apoptosis/necrosis depending on the treatment dosage. Using the cell permeable dye 2',7'-dichlorofluorescin diacetate (DCF-DA) as an indicator of reactive oxygen species (ROS) generation, we showed that ethanol treatment directly increased intracellular oxidative stress. This intracellular oxidative stress increased in response to high concentrations (100-200 microM) of resveratrol, but remained unchanged following treatment with low concentrations (10-25 microM) of resveratrol. Further studies showed that resveratrol could attenuate or enhance ethanol-induced intracellular oxidative stress generation-dependent on treatment dosage, and that this effect could be correlated with cell apoptosis or necrosis. Importantly, ethanol-induced changes in intracellular ATP levels were also correlated with resveratrol dosage. Taken together, these results indicate that the treatment dosage may determine the effect of resveratrol on ethanol-induced ROS generation, intracellular ATP levels, and cell apoptosis or necrosis. Thus our findings support the possibility that appropriate dosage of resveratrol aids in decreasing the toxic effect of ethanol.

Role for membrane fluidity in ethanol-induced oxidative stress of primary rat hepatocytes

The relationship between bulk membrane fluidizing effect of ethanol and its toxicity due to oxidative stress is still unknown. To elucidate this issue, membrane fluidity of primary rat hepatocytes was studied by measuring order parameter after inhibition of ethanol-induced oxidative stress. We showed that pretreating cells with either 4-methyl-pyrazole (to inhibit ethanol metabolism), thiourea [a reactive oxygen species (ROS) scavenger], or vitamin E (a free radical chain-breaking antioxidant) prevented the ethanol-induced increase in membrane fluidity, thus suggesting that ethanol metabolism and ROS formation were involved in this elevation. The effects of membrane stabilizing agents (ursodeoxycholic acid or ganglioside GM1), shown to prevent fluidification, next pointed to a role for this increase in membrane fluidity in the development of ethanol-induced oxidative stress. Indeed, ROS production, lipid peroxidation, and cell death were all inhibited by these agents. In contrast, the fluidizing compounds Tween 20 or 2-(2-methoxyethoxy) ethyl 8-(cis-2-n-octylcyclopropyl) octanoate, which increased the membrane fluidizing effect of ethanol, enhanced the related oxidative stress. Using electron paramagnetic resonance to determine low molecular weight iron, we finally demonstrated that membrane fluidity influence proceeded through an increase in low molecular weight iron to enhance oxidative stress. In conclusion, the present findings clearly highlight the pivotal role of membrane fluidity in ethanol-induced oxidative stress and the potential therapeutic effect of membrane stabilizing compounds.

Immunomodulating and anti-apoptotic action of ursodeoxycholic acid: where are we and where should we go?

Ursodeoxycholic acid (UDCA) is currently used in clinical practice worldwide not only for the dissolution of cholesterol gallstones, but also, mainly, to treat patients with chronic cholestatic liver diseases. However, the mechanisms of action of UDCA at the hepatocyte and cholangiolyte levels are still not completely understood. Much progress has been made from the first concept that the only mechanism of action of this bile acid was its choleretic action. One of the most fascinating mechanisms of action that was evoked for UDCA is its immunomodulating and anti-apoptotic action, which could, in part, be explained by its interaction with the glucocorticoid nuclear receptor at the hepatocyte level. Glucocorticoids, whose prototype is dexamethasone, are the major ligands of the glucocorticoid receptor. The biological effects of glucocorticoids are driven by a multiple-step reaction including binding of the steroid to the glucocorticoid receptor, DNA binding, receptor transformation, nuclear translocation and either positive or negative gene transactivation. In this issue of the journal, Weitzel and co-workers clearly demonstrated that the binding of UDCA to the glucocorticoid receptor is unspecific. Therefore, the anti-inflammatory, cytoprotective and anti-apoptotic actions of UDCA should be due not only to the mild interaction with the glucocorticoid receptor, but also to transactivation or transrepression of different cytoplasmic proteins that are involved in the survival pathway.

Toxicity of ethanol and acetaldehyde in hepatocytes treated with ursodeoxycholic or tauroursodeoxycholic acid

In hepatocytes ethanol (EtOH) is metabolized to acetaldehyde and to acetate. Ursodeoxycholic acid (UDCA) and tauroursodeoxycholic acid (TUDCA) are said to protect the liver against alcohol. We investigated the influence of ethanol and acetaldehyde on alcohol dehydrogenase (ADH)-containing human hepatoma cells (SK-Hep-1) and the protective effects of UDCA and TUDCA (0.01 and 0.1 mM). Cells were incubated with 100 and 200 mM ethanol, concentrations in a heavy drinker, or acetaldehyde. Treatment with acetaldehyde or ethanol resulted in a decrease of metabolic activity and viability of hepatocytes and an increase of cell membrane permeability. During simultaneous incubation with bile acids, the metabolic activity was better preserved by UDCA than by TUDCA. Due to its more polar character, acetaldehyde mostly damaged the superficial, more polar domain of the membrane. TUDCA reduced this effect, UDCA was less effective. Damage caused by ethanol was smaller and predominantly at the more apolar site of the cell membrane. In contrast, preincubation with TUDCA or UDCA strongly decreased metabolic activity and cell viability and led to an appreciable increase of membrane permeability. TUDCA and UDCA only in rather high concentrations reduce ethanol and acetaldehyde-induced toxicity in a different way, when incubated simultaneously with hepatocytes. In contrast, preincubation with bile acids intensified cell damage. Therefore, the protective effect of UDCA or TUDCA in alcohol- or acetaldehyde-treated SK-Hep-1 cells remains dubious.

Ursodeoxycholic acid (UDCA) can inhibit deoxycholic acid (DCA)-induced apoptosis via modulation of EGFR/Raf-1/ERK signaling in human colon cancer cells

Ursodeoxycholic acid (UDCA), a hydrophilic bile acid, is known as a cytoprotective agent. UDCA prevents apoptosis induced by a variety of stress stimuli including cytotoxic bile acids such as deoxycholic acid (DCA). Here we examined the molecular mechanism by which UDCA can antagonize DCA-induced apoptosis in human colon cancer cells. UDCA pretreatment decreases the number of apoptotic cells caused by exposure to DCA and UDCA. Further studies of the signaling pathway showed that UDCA pretreatment suppressed DNA binding activity of activator protein-1 and this was accompanied by downregulation of both extracellular signal-regulated kinase (ERK) and Raf-1 kinase activities stimulated by exposure to DCA. DCA was also found to activate epidermal growth factor receptor (EGFR) activity and UDCA inhibited this. Collectively, these findings suggest that the inhibitory effect of UDCA in DCA-induced apoptosis is partly mediated by modulation of EGFR/Raf-1/ERK signaling.

Effect of ethanol on cell growth and cholesterol metabolism in cultured Hep G2 cells

The Hep G2 human hepatoma cell line has been recognized as an excellent in vitro human model system. For this reason, this line was used to study the effect of ethanol on HMG-CoA reductase activity concerning cell growth and cholesterol metabolism. Cells were incubated in ethanol-containing medium (0–400 mmol/L) for up to 102 h. Ethanol caused an inhibition in the growth rate and in HMG-CoA reductase activity that could be reverted by the removal of ethanol from the culture medium, indicating no cellular damage. These changes cannot be ascribed to the regulatory effect of cholesterol levels, since its content was not modified either in the cells or in the medium. The addition of mevalonate to the culture medium could not revert the growth rate inhibition evoked by ethanol. Moreover, ethanol produced an increment in the cholesterol efflux in [3H]cholesterol-prelabeled cells. We conclude that the decrease in HMG-CoA reductase activity evoked by ethanol treatment on Hep G2 cells would not be the cause but the consequence of the impairment in cellular growth, since this impairment could not be reverted by the addition of mevalonate to the culture medium.Key words: ethanol, cholesterol, HMG-CoA reductase, hepatoma cells, lipid metabolism.

Inhibitory effect of Artemisia capillaris on ethanol-induced cytokines (TNF-alpha, IL-1alpha) secretion in Hep G2 cells

A human hepatoma cell line, Hep G2 cell, is reliable for the study of alcohol-induced hepatotoxicity. In this study, we investigated the effect of an aqueous extract of Artemisia capillaris Thunb (Compositae) plant (AC) on ethanol (EtOH)-induced cytotoxicity in Hep G2 cells. AC (0.5-5 microg/mL) inhibited the secretion of EtOH-induced interluekin-1alpha (IL-1alpha) and tumor necrosis factor-alpha (TNF-alpha). AC also inhibited the EtOH-, IL-1alpha-, and TNF-alpha-induced cytotoxicity. Furthermore, we found that AC inhibited the EtOH-induced apoptosis of Hep G2 cells. These results suggest that AC may prevent the EtOH-induced cytotoxicity through inhibition of the apoptosis of Hep G2 cells.

Synergetic signaling for apoptosis in vitro by ethanol and acetaminophen

In vitro, ethanol in combination with acetaminophen induces hepatocyte apoptosis resembling immune-mediated fulminant hepatic failure in human beings. Intracellular pathways originating at the mitochondria are linked to apoptosis. I studied ethanol-induced apoptosis and hepatocytotoxicity after using an in vitro model of normal human primary hepatocytes that were exposed to 5 or 10 mM acetaminophen, 40 or 100 mM ethanol, 40 mM ethanol + 5 mM acetaminophen, or 40 mM ethanol + 10 mM acetaminophen, or nonexposed (control; plain medium). Transmission electron microscopy was performed at different time points after exposure to the various treatments. Apoptosis, as assessed by transmission electron microscopy, was increased in a time-dependent manner after exposure to ethanol + acetaminophen. In the ethanol + acetaminophen model, mitochondrial injury was associated with apoptosis of hepatocytes. Ultrastructural damage and induction of apoptosis were seen in response to N-acetyl-benzoquinone-imine plus ethanol, supporting the suggestion that the damage was due to the active metabolite of acetaminophen. The modulation of mitochondrial damage in vitro may have implications for the development of new therapeutic strategies to prevent apoptosis.

Ethanol-induced apoptosis in hepatoma cells proceeds via intracellular Ca(2+) elevation, activation of TLCK-sensitive proteases, and cytochrome c release

Ethanol is known to induce apoptosis in hepatocytes. However, intracellular signaling events of ethanol-induced death are still only partially understood. We studied such processes in ethanol-induced apoptosis in HepG2 cells as a model system for human liver cells. We determined the incidence of apoptosis by DNA fragmentation and tested the effects of various known inhibitors. Ethanol induces apoptosis in HepG2 cells in a dose- and time-dependent manner as well as in rat primary hepatocytes. This effect was not mediated through the death receptor CD95 and the tumor necrosis factor receptors. It was efficiently inhibited by the caspase inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone (zVAD-fmk), the Ca(2+) chelator EGTA, and the serine protease inhibitor N-p-tosyl-l-lysine chloromethyl ketone (TLCK). Upon ethanol treatment, the intracellular calcium ion concentration was increased and cytochrome c was released from the mitochondria, and caspases were activated. EGTA and TLCK could inhibit cytochrome c release from the mitochondria. Furthermore, overexpression of Bcl-x(L) saved cells from ethanol-induced apoptosis. These data suggest that ethanol-induced apoptosis in liver cells is initiated by the intracellular Ca(2+) elevation in the cytoplasm and activation of TLCK-sensitive serine proteases. Our data provide new insight into ethanol-induced apoptosis in liver cells and may lead to therapeutic strategies to prevent liver damage.

Effect of ursodeoxycholic acid on prostaglandin metabolism and microsomal membranes in alcoholic fatty liver

The aim of the present study was to evaluate the effect of ursodeoxycholic acid (UDCA) on prostaglandin and fatty acid metabolism and the possible relation of these substances to the development of alcoholic fatty liver in rats. The effects of UDCA (40 mg/kg/day, 30 days) were studied in rats pair-fed a high-fat diet (52% of calories as fat) with daily ethanol (4 g/kg/day, 30 days) intragastric intubation. The livers of ethanol-treated animals were characterized by fatty dystrophy. Liver triglyceride and cholesterol ester contents and the activities of serum marker enzymes, alanine aminotransferase and gamma-glutamyltransferase, were significantly increased. Ethanol enhanced phosphoinositol and sphingomyelin content in liver microsomes and lowered prostaglandin E(2) (PGE(2)) concentration in the liver. An increase in the percentage of monoenoic fatty acids and a decrease in the n-6 acid family in liver phospholipids, linoleoyl-CoA desaturase, and PGE(2) synthase activities in liver microsomes were observed in ethanol-treated rats. Treatment with UDCA improved liver morphologic characteristics, decreased triglyceride and cholesterol ester contents, increased the PGE(2) level, and normalized linoleoyl-CoA desaturase and PGE(2) synthase activities, as well as phospholipid and fatty acid patterns in the liver. The activities of the serum marker enzymes were decreased in the ethanol- and UDCA-treated group. Ursodeoxycholic acid lowered the viscosity of the microsomal membrane, as assessed by both fluorescence probe techniques and the saturated/unsaturated fatty acid ratio. We propose that the hepatoprotective effect of UDCA in alcoholic fatty liver is related to the stabilization of microsomal membranes, the prevention of a decrease in essential fatty acids and PGE(2) in the liver, and, probably, an improvement in biochemical processes controlled by PGE(2).

Apoptosis in diseases of the liver

Apoptosis, or programmed cell death, and the elimination of apoptotic cells are crucial factors in the maintenance of liver health Apoptosis allows hepatocytes to die without provoking a potentially harmful inflammatory response In contrast to necrosis, apoptosis is tightly controlled and regulated via several mechanisms, including Fas/Fas ligand interactions, the effects of cytokines such as tumor necrosis factor alpha (TNF-alpha) and transforming growth factor beta (TGF-beta), and the influence of pro- and antiapoptotic mitochondria-associated proteins of the B-cell lymphoma-2 (Bcl-2) family. Efficient elimination of apoptotic cells in the liver relies on Kupffer cells and endothelial cells and is thought to be regulated by the expression of certain cell surface receptors. Liver disease is often associated with enhanced hepatocyte apoptosis, which is the case in viral and autoimmune hepatitis, cholestatic diseases, and metabolic disorders. Disruption of apoptosis is responsible for other diseases, for example, hepatocellular carcinoma. Use and abuse of certain drugs, especially alcohol, chemotherapeutic agents, and acetaminophen, have been associated with increased apoptosis and liver damage. Apoptosis also plays a role in transplantation-associated liver damage, both in ischemia/reperfusion injury and graft rejection. The role of apoptosis in various liver diseases and the mechanisms by which apoptosis occurs in the liver may provide insight into these diseases and suggest possible treatments.

The effect of drugs and toxins on the process of apoptosis

In this review we examine the modifying effect of specific drugs on apoptosis. Apoptosis is a type of cell death prevalent during many physiological and pathological conditions, consisting of several steps, namely, initiating stimuli, transduction pathways, effector mechanisms, nuclear fragmentation, and phagocytosis. Pharmacological substances such as glucocorticoids can either induce or inhibit the process of apoptosis in various cells depending on the type of drug and its concentration. Understanding the mechanisms of interaction of drugs with cells undergoing apoptosis could encourage novel therapeutic approaches to human diseases in which apoptosis has a critical role.

Ursodeoxycholic acid 'mechanisms of action and clinical use in hepatobiliary disorders'

UDCA exerts its beneficial effect in liver diseases through a diverse, probably, complementary array of mechanisms. The clinical use and efficacy of UDCA in PBC have been evident. UDCA may also have a place in the management of PSC, ICP, cystic fibrosis, PFIC and GVHD involving the liver, although, more studies are needed to further determine its therapeutic potential in these diseases and in other hepatobiliary disorders such as liver allograft rejection, drug and TPN-induced cholestasis, NASH, and alcoholic liver disease.

Signaling for ethanol-induced apoptosis and repair in vitro

OBJECTIVES

To evaluate whether caspases are involved in ethanol (EtOH)-induced apoptosis and if polyenylphosphatidylcholine (PPC) affects apoptosis, in vitro in Hep G2 cells.

METHODS

Cells were treated with 100 mmol/L EtOH for 24 h and with 2 doses of 100 mmol/L EtOH (1/24 h) in the presence of absence of 20 mmol/L of PPC or 50 micromol/L caspase 3 inhibitor (IDN). Cells were analyzed for apoptosis by transmission electron microscopy (TEM) 6000 cells/treatment, DNA fragmentation by ELISA and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (T dt-mediated d-UTP) nick-end-labeling, TUNEL.

RESULTS

100 mmol/L dose of EtOH resulted in 22 +/- 2.5% (p < 0.001) apoptosis (vs. control). Two consecutive doses of 100 mmol/L EtOH for 24 h each caused 36 +/- 3.0% (p < 0.001 vs. control and p < 0.05 vs. one dose). PPC significantly reduced apoptosis (vs. non exposed to PPC): 100 mmol/L -12 +/- 1.5% (p < 0.05) and 2 x 10(-)(0) mmol/L -20 +/- 2.0% (p < 0.001). Pretreatment with 50 micromol caspase inhibitor reduced EtOH-induced apoptosis in a similar proportion.

CONCLUSIONS

PPC downregulates EtOH-apoptosis by a mechanism similar to caspase inhibition.

CYP2E1-mediated modulation of valproic acid-induced hepatocytotoxicity

OBJECTIVES

To determine the cytotoxicity of valproic acid (VPA) and its metabolite, 4-ene-valproic acid (4-ene-VPA) in human hepatoblastoma cells (Hep G2), and to study the modulatory effect of cytochrome P450 2E1 induction in this model.

METHODS

Cells were exposed to VPA or 4-ene-VPA in the presence of either ethanol (EtOH), or EtOH combined with disulphiram (DS). Some cells were exposed to alpha-fluoro-VPA or to alpha-fluoro-4-ene-VPA in the absence of CYP2E1 inducers. Apoptosis and necrosis were measured by analyzing 6000 cells per sample using transmission electron microscopy, while cytokine release and apoptosis were quantitated by ELISA.

RESULTS

VPA + EtOH increased VPA cytotoxicity. 4-ene-VPA + EtOH significantly increased toxicity, while DS + EtOH significantly reduced this toxicity. Alpha-fluorinated analogues reduced cytotoxicity compared to the corresponding VPA compounds. Neither VPA nor alpha-fluorinated VPA increased the release of IL-6 or TNF-alpha in media. A significant increase in the release of TNF-alpha was observed in cells exposed to 4-ene-VPA that further increased with EtOH exposure.

CONCLUSIONS

Cells exposed to 4-ene-VPA experience greater cytotoxicity than those treated with VPA. Cytochrome P450 2E1 inducers enhance toxicity in VPA-exposed cells, while alpha-fluorination of VPA diminishes cytotoxicity by directly interfering with the beta-oxidation of the 4-ene-VPA metabolite.

Effects of bile salts on cholestan-3beta,5alpha,6beta-triol-induced apoptosis in dog gallbladder epithelial cells

Oxysterols are cytotoxic agents. The gallbladder epithelium is exposed to high concentrations of oxysterols, and so elucidating the mechanisms of cytotoxicity in this organ may enhance our understanding of the pathogenesis of biliary tract disorders. We investigated the cytotoxic effects of the oxysterol cholestan-3beta,5alpha,6beta-triol (TriolC) on dog gallbladder epithelial cells. Apoptosis was the major form of cytotoxicity, as determined by analysis of nuclear morphologic changes and by multiparameter flow cytometry. Hydrophobic bile salts are known to have cytotoxic effects, whereas hydrophilic bile salts have cytoprotective effects. We therefore examined whether the hydrophobic bile acid taurodeoxycholic acid (TDC) and the hydrophilic bile acid tauroursodeoxycholic acid (TUDC) had modifying effects on oxysterol-induced cytotoxicity. TriolC caused an increase in the number of apoptotic cells from 14+/-11% (control) to 48+/-12% of total cells (P<0.01). After combining TriolC with TDC, cell apoptosis increased to 63+/-16% (P<0.05), whereas after addition of TUDC, the number of apoptotic cells decreased to 31+/-12% (P<0.05) of total cells. In summary, oxysterols such as TriolC induce apoptosis. Hydrophobic bile salts enhance TriolC-induced apoptosis, whereas hydrophilic bile salts diminish TriolC-induced apoptosis. These results suggest that interactions between oxysterols and bile salts play a role in the pathophysiology of biliary tract disorders.

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.

Inhibition of tumor necrosis factor-alpha-induced apoptosis by Asparagus cochinchinensis in Hep G2 cells

A human hepatoma cell line, Hep G2 cells, is a reliable system for the study of alcohol-induced hepatotoxicity. In this study, we investigated the effect of an aqueous extract of Asparagus cochinchinensis(MERRIL) (Liliaceae) roots (ACAE) on ethanol (EtOH)-induced cytotoxicity in Hep G2 cells. ACAE (1-100 microg/ml) dose-dependently inhibited the EtOH-induced tumor necrosis factor-alpha (TNF-alpha) secretion. ACAE (1-100 microg/ml) also inhibited the EtOH and TNF-alpha-induced cytotoxicity. Furthermore, we found that ACAE inhibited the TNF-alpha-induced apoptosis of Hep G2 cells. These results suggest that ACAE may prevent the EtOH-induced cytotoxicity through inhibition of the apoptosis of Hep G2 cells.

A novel lymphocyte toxicity assay to assess drug hypersensitivity syndromes

OBJECTIVES

To validate the novel lymphocyte toxicity assay (LTA) based on the mitochondrial succinate dehydrogenase (SDH) activity vs. the LTA by using trypan blue exclusion and to determine the utility of the assay to confirm drug hypersensitivity syndrome (DHS) to sulphonamides (SMX) and aromatic anticonvulsants.

METHODS

Incubation of patient lymphocytes, with or without murine hepatic microsomes with anticonvulsants or SMX. The viability of lymphocytes was based on SDH activity that can be measured spectrophotometrically. The percentage of cells displaying cytotoxicity compared to controls (cells treated only with drug) was calculated. Seventy-two immunocompetent and 16 immunocompromised (HIV) patients with DHS to SMX were sampled. The results were validated vs. 26 controls that had not experienced DHS to SMX. Sixty-two patients who had DHS to anticonvulsants were compared with 24 controls that did not have any DHS to the same anticonvulsants.

RESULTS

The results showed a very good percentage of sensitivity 98 and specificity 96 with a kappa-score of 0.96. LTA higher than 13.5% was considered positive for the immunocompetent population and LTA higher than 22% was positive for the immunocompromised population. In two of the 26 controls, LTA was positive.

CONCLUSION

The high quantitative kappa-value 0.96 emphasizes that the novel LTA is at least as good as the trypan blue assay. The latter is labor intensive, time consuming, and prone to human error. The new assay is objective, faster, and has been reproducible in assessing cytotoxicity.

Inhibitory effect of interleukin-1alpha-induced apoptosis by Polygala tenuifolia in Hep G2 cells

A human hepatoma cell line, Hep G2 cells are reliable for the study of alcohol-induced hepatotoxicity. In this study, we investigated the effect of an aqueous extract of Polygala tenuifolia WILLDENOW (Polygalaceae) roots (PTAE) on ethanol (EtOH)-induced cytotoxicity in Hep G2 cells. PTAE (0.01-1 microg/ml) dose-dependently inhibited the EtOH-induced interleukin-1alpha (IL-1alpha) secretion. PTAE (0.01-1 microg/ml) also inhibited the EtOH- and IL-1alpha-induced cytotoxicity. Furthermore, we found that PTAE inhibited the IL-1alpha-induced apoptosis of Hep G2 cells. These results suggest that PTAE may prevent the EtOH-induced cytotoxicity through inhibition of the apoptosis of Hep G2 cells.

Risk factors for alcoholic liver disease

Abstract Alcoholic liver disease (ALD) is still a frequent disorder, even though its incidence appears to be decreasing. In spite of intense investigation, the precise mechanisms leading to ALD are still imprecisely known. This is due in part to the lack of a reliable animal model; in part to the difficulty of obtaining clinical data of adequate sample size and derived from unblased populations and finally from the lack of uniformity of the criteria used to define ALD. This paper will review what is known of the various pieces of this puzzle, with particular emphasis not only on the total amount of alcohol consumed, but also on drinking patterns and type of alcoholic beverage ingested. The other potential factors such as age, gender, genetic background, nutritional status, occupational hazards and viral diseases (especially HCV infection) will be touched upon.

Ethanol-induced apoptosis in vitro

OBJECTIVES

The aim is to study the apoptotic process in a human hepatocyte model for ethanol (EtOH)-induced apoptosis.

DESIGN AND METHODS

Normal human primary hepatocytes (HPH) and Hep G2 cells were exposed to increasing EtOH. 6000 cells/ sample were analyzed by transmission electron microscopy.

RESULTS

Apoptotic cells were observed (mmol/L EtOH): 40: 6 +/-0.5%, 60:13 +/- 2% (p < 0.05), 80: 26 +/- 1% (p < 0.001) (vs. control). Two consecutive doses of 80 mmol/L for 24 h each additionally increased apoptosis 55 +/- 3% (p < 0.0001 vs. control and p < 0.001 vs. single dose). In response to this exposure, there is a stronger apoptotic activity in HPH when compared to Hep G2 (p < 0.05).

CONCLUSIONS

In vitro, EtOH-induced apoptosis is regulated by dose level and the frequency of exposure.

Inducers of cytochrome P450 2E1 enhance methotrexate-induced hepatocytoxicity

OBJECTIVES

To study the effect of cytochrome P450 2E1-inducers on methotrexate (MTX)-induced cytotoxicity in human hepatocytes, and investigate the role of silymarin in preventing this toxicity.

DESIGN AND METHODS

Cells were exposed to MTX in the presence of either ethanol (EtOH) or acetaminophen (APAP), or either combined with silymarin (S). Apoptosis and necrosis were measured by analyzing 6000 cells/sample using transmission electron microscopy, while cytokine release and apoptosis were quantitated by ELISA. Cytokine expression was measured by RT-PCR. Gluthatione (GSH) content was determined in cytosolic (c) and mitochondrial (m) fractions.

RESULTS

MTX+EtOH and MTX+APAP increased MTX cytotoxicity 2.9-fold and 1.9-fold, respectively. S abolished this toxicity. MTX + EtOH increased the release of IL 6, IL 8 and TNF alpha by 1.0, 1.2, and 1.1 times, respectively. Cytokine expression was upregulated versus control for IL 6 (22%), IL 8 (38%), and TNF alpha (29%). Addition of 0.5 mmol/L S downregulated TNF alpha expression and reduced cytokine release. TNF alpha increased cytotoxicity by 22%, while anti-TNFalpha antibody eradicated it. MTX+EtOH depleted 45% mGSH (0 < 0.001) while S replenished it to 87% (p < 0.001), when both were compared to control levels.

CONCLUSIONS

Cytochrome P450 2E1-inducers contribute to increase oxidative stress in MTX-exposed cells by increasing TNF alpha and depleting both cGSH and mGSH. This enhances MTX-cytotoxicity and promotes apoptosis.

Novel morphologic findings in alcoholic liver disease

OBJECTIVES

To study light and electron microscopic changes in alcohol-liver disease (ALD) patients, and characterize the expression pattern of Kupffer and stellate cells, correlating changes with serum cytokine levels.

DESIGN AND METHODS

Liver biopsies studied in 35 ALD patients were compared to 51 normal histology patients. Quantitation was done using immunochemistry for Kupffer cells and morphometry, electron microscopy for stellate cells. ELISA was used to measure serum cytokines in 80 controls and ALD patients.

RESULTS

Biopsies of ALD patients confirmed increased number of perisinusoidal, multivesicular, and stellate cells compared to controls. There was a significant increase in the number and activity of multivesicular stellate cells in ALD patients (p < 0.001). These changes were associated with significant increase in the degree of perisinusoidal collagenisation (p < 0.001). The number of Kupffer cells, serum tumor necrosis factor (TNFalpha), interleukins-6 (IL-6) and IL-12 levels, were also significantly higher in ALD patients than controls.

CONCLUSIONS

In non-cirrhotic ALD, stellate cells may be involved in lipid transport and a cytokine network may influence liver inflammation.

CYP2E1 and CYP3A1/2 gene expression is not associated with the ursodeoxycholate effect on ethanol-induced lipoperoxidation

Ethanol is a well-known hepatotoxicant inducing steatosis and membrane lipoperoxidation. The aim of the present study was to investigate in rats, whether the protective effect of UDC on ethanol-induced lipid peroxidation may be related with CYP2E1 and CYP3A1/2 gene expression. We showed that UDC treatment in ethanol-fed rats induced a significant decrease in liver triglyceride concentration which was closely correlated with a reduction in malondialdehyde and hydroxyalkenal levels. In chronically ethanol-fed rats, CYP2E1 and CYP3A1/2 gene expressions were increased by a post-transcriptional mechanism. These inductions, mainly of CYP2E1, could take part in alcohol-induced hepatic lipoperoxidation. UDC modified neither the specific activity, nor the protein level, nor the mRNA level of CYP2E1 when compared with control. UDC supplementation to alcohol diet did not prevent the increase in CYP2E1 expression of ethanol-fed rats. Furthermore, CYP3A1/2 protein levels were similarly increased by ethanol and ethanol plus UDC treatment. Therefore, UDC protective effect against ethanol-induced lipoperoxidation was not associated with a modification of CYP2E1 and CYP3A1/2 expression.

Cholestasis and alcoholic liver disease

Histologic cholestasis and clinical jaundice may be seen in all stages of alcoholic liver disease. In rare cases, isolated cholestasis without significant steatosis, hepatitis, or cirrhosis is identified in an alcoholic patient. The mechanisms of ethanol-induced cholestasis are not well studied but may involve compression of intrahepatic biliary radicals or interference with basolateral uptake and intracellular transport of bile acids. In the evaluation of the jaundiced alcoholic patient, clinical, biochemical, and radiologic data are usually sufficient to distinguish alcohol-induced liver disease from extrahepatic biliary obstruction. In cases where the diagnosis is not readily apparent, more invasive studies such as liver biopsy or ERCP may be necessary. The risk of these invasive studies is directly related to the degree of underlying hepatic dysfunction.

Review article: mechanisms of action and therapeutic applications of ursodeoxycholic acid in chronic liver diseases

Ursodeoxycholic acid (ursodiol) is a non-toxic, hydrophilic bile acid used to treat predominantly cholestatic liver disorders. Better understanding of the cellular and molecular mechanisms of action of ursodeoxycholic acid has helped to elucidate its cytoprotective, anti-apoptotic, immunomodulatory and choleretic effects. Ursodeoxycholic acid prolongs survival in primary biliary cirrhosis and it improves biochemical parameters of cholestasis in various other cholestatic disorders including primary sclerosing cholangitis, intrahepatic cholestasis of pregnancy, cystic fibrosis and total parenteral nutrition-induced cholestasis. However, a positive effect on survival remains to be established in these diseases. Ursodeoxycholic acid is of unproven efficacy in non-cholestatic disorders such as acute rejection after liver transplantation, non-alcoholic steatohepatitis, alcoholic liver disease and chronic viral hepatitis. This review outlines the present knowledge of the modes of action of ursodeoxycholic acid, and presents data from clinical trials on its use in chronic liver diseases.

Ursodeoxycholate alleviates alcoholic fatty liver damage in rats

The hydrophilic bile salt ursodeoxycholate (UDC) improves cholestasis in several liver diseases and is in vitro an efficient membrane stabilizer. However, its action on chronic ethanol-induced liver damage is not established. We thus sought to determine the effect of UDC on chronic ethanol-induced steatosis and on liver plasma membrane fluidity in rats. Male rats were pair-fed liquid diets containing 36% of calories as ethanol (alcohol diet) or an isocaloric maltose-dextrin mixture (control diet). Four groups of 10 animals received, respectively, during 30 days: the control diet, the control diet + UDC (90 mg/kg/day), the alcohol diet, and the alcohol diet + UDC. Bile was collected for assessment of bile flow, biliary lipids, and individual bile salts. Liver lipid contents and lipid peroxidation were determined. Plasma membrane fluidity was assessed by fluorescence polarization of various probes. Alcohol treatment caused a 4-fold increase in liver triacylglycerol and cholesterol ester levels. UDC supplementation significantly reduced these increases by 50% and 40%, respectively. UDC intake was associated with a marked decrease in alcohol-induced lipid peroxidation. Bile flow, bile salt, and phospholipid secretion were slightly increased by alcohol intake. The addition of UDC-enriched bile with tauroursodeoxycholate (38%) without significantly affecting the biliary parameters. Lastly, UDC treatment almost totally prevented the 20% increase in liver plasma membrane fluidity due to chronic alcohol intake. This study shows that UDC intake, concomitant with alcohol diet, exerts a clear-cut membrane protective effect that might alleviate ethanol-induced lipid disorders.

Ursodeoxycholate protects against ethanol-induced liver mitochondrial injury

The purpose of this work was to examine whether ursodeoxycholate (UDC), a hydrophilic bile salt, could reduce mitochondrial liver injury from chronic ethanol consumption in rats. Animals were pair-fed liquid diets containing 36% of calories as ethanol or isocaloric carbohydrates. They were randomly assigned into 4 groups of 7 rats each and received a specific treatment for 5 weeks: control diet, ethanol diet, control diet + UDC, and ethanol diet + UDC. Respiratory rates of isolated liver mitochondria were measured using a Clark oxygen electrode with sodium succinate as substrate. Mitochondria from rats chronically fed ethanol demonstrated an impaired ability to produce energy. At the fatty liver stage, the ADP-stimulated respiration (V3) was depressed by 33%, the respiratory control ratio (RC) by 25% and the P/O ratio by 15%. In ethanol-fed rats supplemented with UDC, both the rate and efficiency of ATP synthesis via the oxidative phosphorylation were improved: V3 was increased by 35%, P/O by 8%. All the respiratory parameters were similar in control group and control + UDC group. On the other hand, the number and size of mitochondria were assessed by electron microscopy and computer-assisted quantitative analysis. The number of mitochondria from ethanol-treated rats was decreased by 29%, and they were enlarged by 74%. Both parameters were normalized to control values by UDC treatment. These studies demonstrate that UDC has a protective effect against ethanol-induced mitochondrial injury by improving ATP synthesis and preserving liver mitochondrial morphology. These UDC positive effects may contribute to the observed decrease in fat accumulation and may delay the progression of alcoholic injury to more advanced stages.