Glutathione Depletion in CYP2E1-Expressing Liver Cells Induces Toxicity Due to the Activation of p38 Mitogen-Activated Protein Kinase and Reduction of Nuclear Factor-κB DNA Binding Activity

Formation of potentially toxic metabolites of drugs in reactions catalyzed by human drug-metabolizing enzymes

Data are presented on the formation of potentially toxic metabolites of drugs that are substrates of human drug metabolizing enzymes. The tabular data lists the formation of potentially toxic/reactive products. The data were obtained from in vitro experiments and showed that the oxidative reactions predominate (with 96% of the total potential toxication reactions). Reductive reactions (e.g., reduction of nitro to amino group and reductive dehalogenation) participate to the extent of 4%. Of the enzymes, cytochrome P450 (P450, CYP) enzymes catalyzed 72% of the reactions, myeloperoxidase (MPO) 7%, flavin-containing monooxygenase (FMO) 3%, aldehyde oxidase (AOX) 4%, sulfotransferase (SULT) 5%, and a group of minor participating enzymes to the extent of 9%. Within the P450 Superfamily, P450 Subfamily 3A (P450 3A4 and 3A5) participates to the extent of 27% and the Subfamily 2C (P450 2C9 and P450 2C19) to the extent of 16%, together catalyzing 43% of the reactions, followed by P450 Subfamily 1A (P450 1A1 and P450 1A2) with 15%. The P450 2D6 enzyme participated in an extent of 8%, P450 2E1 in 10%, and P450 2B6 in 6% of the reactions. All other enzymes participate to the extent of 14%. The data show that, of the human enzymes analyzed, P450 enzymes were dominant in catalyzing potential toxication reactions of drugs and their metabolites, with the major role assigned to the P450 Subfamily 3A and significant participation of the P450 Subfamilies 2C and 1A, plus the 2D6, 2E1 and 2B6 enzymes contributing. Selected examples of drugs that are activated or proposed to form toxic species are discussed.

Aqueous extract of Laurus nobilis leaf accelerates the alcohol metabolism and prevents liver damage in single-ethanol binge rats

BACKGROUND/OBJECTIVES

Excessive alcohol consumption has harmful health effects, including alcohol hangovers and alcohol-related liver disease. Therefore, methods to accelerate the alcohol metabolism are needed. Laurus nobilis is a spice, flavoring agent, and traditional herbal medicine against various diseases. This study examined whether the standardized aqueous extract of L. nobilis leaves (LN) accelerates the alcohol metabolism and protects against liver damage in single-ethanol binge Sprague-Dawley (SD) rats.

MATERIALS/METHODS

LN was administered orally to SD rats 1 h before ethanol administration (3 g/kg body weight [BW]) at 100 and 300 mg/kg BW. Blood samples were collected 0.5, 1, 2, and 4 h after ethanol administration. The livers were excised 1 h after ethanol administration to determine the hepatic enzyme activity. The alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities in the liver tissue were measured.

RESULTS

LN decreased the serum ethanol and acetaldehyde levels in ethanol-administered rats. LN increased the hepatic ADH and ALDH activities but decreased the alanine aminotransferase, aspartate aminotransferase, and gamma-glutamyl transferase activities in the ethanol-administered rats. In addition, LN inhibited lipid peroxidation and increased the activities of SOD and GPx.

CONCLUSIONS

LN modulates the mediators of various etiological effects of excessive alcohol consumption and enhances the alcohol metabolism and antioxidant activity, making it a potential candidate for hangover treatments.

Autophagy, Oxidative Stress, and Alcoholic Liver Disease: A Systematic Review and Potential Clinical Applications

Ethanol consumption triggers oxidative stress by generating reactive oxygen species (ROS) through its metabolites. This process leads to steatosis and liver inflammation, which are critical for the development of alcoholic liver disease (ALD). Autophagy is a regulated dynamic process that sequesters damaged and excess cytoplasmic organelles for lysosomal degradation and may counteract the harmful effects of ROS-induced oxidative stress. These effects include hepatotoxicity, mitochondrial damage, steatosis, endoplasmic reticulum stress, inflammation, and iron overload. In liver diseases, particularly ALD, macroautophagy has been implicated as a protective mechanism in hepatocytes, although it does not appear to play the same role in stellate cells. Beyond the liver, autophagy may also mitigate the harmful effects of alcohol on other organs, thereby providing an additional layer of protection against ALD. This protective potential is further supported by studies showing that drugs that interact with autophagy, such as rapamycin, can prevent ALD development in animal models. This systematic review presents a comprehensive analysis of the literature, focusing on the role of autophagy in oxidative stress regulation, its involvement in organ-organ crosstalk relevant to ALD, and the potential of autophagy-targeting therapeutic strategies.

SUMO-triggered ubiquitination of NR4A1 controls macrophage cell death

Nuclear receptor NR4A1 has been implicated as a key regulator in a wide range of pathophysiological responses. As an immediate early response gene, NR4A1 can be rapidly and potently induced by a variety of stimuli. Its induction is followed by its rapid degradation, but the mechanism by which NR4A1 is degraded remains poorly understood. Here we show that nuclear receptor NR4A1 is sumoylated by SUMO2/3. Upon poly-SUMO modification, NR4A1 can be targeted by the SUMO-dependent E3 ubiquitin ligase RNF4 for polyubiquitination and subsequent degradation. The SUMO E3 ligase PIAS3 promotes SUMOylation and polyubiquitination of NR4A1, while the SUMO protease SENP1 acts to de-conjugate SUMO. We demonstrate that this pathway is important for rapid degradation of NR4A1 after induced by stress. Moreover, we identify two SUMO modification sites in NR4A1 that are critical for maintaining low levels of NR4A1 expression. Mutation of these two NR4A1 SUMO modification sites enhances the stability of NR4A1. Importantly, we show that SUMOylation is critical in controlling NR4A1 function in inflammatory cytokine signaling and controlling macrophage cell death. SUMOylation and subsequent ubiquitination on NR4A1 mitigates its inhibition of innate immune signaling, such as TNF-α- and IL-1β-induced NF-κB activation. This mechanism of sequential SUMOylation and ubiquitination, which together control the degradation of NR4A1, could be exploited for the therapeutic treatment of diseases with NR4A1 involvement.

Alcohol, microbiome, life style influence alcohol and non-alcoholic organ damage

This paper is based upon the "8th Charles Lieber's Satellite Symposium" organized by Manuela G. Neuman at the Research Society on Alcoholism Annual Meeting, on June 25, 2016 at New Orleans, Louisiana, USA. The integrative symposium investigated different aspects of alcohol-induced liver disease (ALD) as well as non-alcohol-induced liver disease (NAFLD) and possible repair. We revealed the basic aspects of alcohol metabolism that may be responsible for the development of liver disease as well as the factors that determine the amount, frequency and which type of alcohol misuse leads to liver and gastrointestinal diseases. We aimed to (1) describe the immuno-pathology of ALD, (2) examine the role of genetics in the development of alcoholic hepatitis (ASH) and NAFLD, (3) propose diagnostic markers of ASH and non-alcoholic steatohepatitis (NASH), (4) examine age and ethnic differences as well as analyze the validity of some models, (5) develop common research tools and biomarkers to study alcohol-induced effects, 6) examine the role of alcohol in oral health and colon and gastrointestinal cancer and (7) focus on factors that aggravate the severity of organ-damage. The present review includes pre-clinical, translational and clinical research that characterizes ALD and NAFLD. Strong clinical and experimental evidence lead to recognition of the key toxic role of alcohol in the pathogenesis of ALD with simple fatty infiltrations and chronic alcoholic hepatitis with hepatic fibrosis or cirrhosis. These latter stages may also be associated with a number of cellular and histological changes, including the presence of Mallory's hyaline, megamitochondria, or perivenular and perisinusoidal fibrosis. Genetic polymorphisms of ethanol metabolizing enzymes and cytochrome p450 (CYP) 2E1 activation may change the severity of ASH and NASH. Other risk factors such as its co-morbidities with chronic viral hepatitis in the presence or absence of human deficiency virus were discussed. Dysregulation of metabolism, as a result of ethanol exposure, in the intestine leads to colon carcinogenesis. The hepatotoxic effects of ethanol undermine the contribution of malnutrition to the liver injury. Dietary interventions such as micro and macronutrients, as well as changes to the microbiota have been suggested. The clinical aspects of NASH, as part of the metabolic syndrome in the aging population, have been presented. The symposium addressed mechanisms and biomarkers of alcohol induced damage to different organs, as well as the role of the microbiome in this dialog. The microbiota regulates and acts as a key element in harmonizing immune responses at intestinal mucosal surfaces. It is known that microbiota is an inducer of proinflammatory T helper 17 cells and regulatory T cells in the intestine. The signals at the sites of inflammation mediate recruitment and differentiation in order to remove inflammatory inducers and promote tissue homeostasis restoration. The change in the intestinal microbiota also influences the change in obesity and regresses the liver steatosis. Evidence on the positive role of moderate alcohol consumption on heart and metabolic diseases as well on reducing steatosis have been looked up. Moreover nutrition as a therapeutic intervention in alcoholic liver disease has been discussed. In addition to the original data, we searched the literature (2008-2016) for the latest publication on the described subjects. In order to obtain the updated data we used the usual engines (Pub Med and Google Scholar). The intention of the eighth symposia was to advance the international profile of the biological research on alcoholism. We also wish to further our mission of leading the forum to progress the science and practice of translational research in alcoholism.

Hepatic Deficiency of Augmenter of Liver Regeneration Exacerbates Alcohol-Induced Liver Injury and Promotes Fibrosis in Mice

Why only a subpopulation (about 15%) of humans develops liver cirrhosis due to alcohol is a critical as yet unanswered question. Liver-specific depletion of augmenter of liver regeneration (ALR) protein in mice causes robust steatosis and hepatocyte apoptosis by 2 weeks; these pathologies regress subsequently with return of ALR expression even at lower than control levels, but the mice develop modest steatohepatitis by 8 weeks. We aimed to investigate whether chronic alcohol ingestion promotes excessive hepatic fibrosis in these ALR-deficient mice. Liver-specific ALR-deficient and wild type (WT) female mice (8–10 weeks old) were placed on 4% alcohol-supplemented or isocaloric diet for 4 weeks. Liver sections were examined for histopathology, and parameters of steatosis and fibrosis were quantified. The mRNA expression of alcohol dehydrogenase-1, acetaldehyde dehydrogenase-1 and cytochrome P450-2E1 increased in WT mice but decreased in ALR-deficient mice upon alcohol ingestion. While alcohol induced steatosis and mild inflammation in WT mice, ALR-deficient mice showed minimal steatosis, strong hepatocellular injury and inflammation, prominent ductular proliferation, and robust fibrosis. Compared to the WT mice, alcohol feeding of ALR-deficient mice resulted in significantly greater increase in hepatic TNFα and TGFβ, and oxidative stress; there was also hepatic iron accumulation, robust lipid peroxidation and mitochondrial DNA damage. Importantly, similar to ALR-deficient mice, lower hepatic ALR levels in human alcoholic liver cirrhosis were associated with increased iron content, reduced expression of alcohol dehydrogenase and acetaldehyde dehydrogenase, and elevated fibrogenic markers. We conclude that ALR deficiency or anomaly can play a critical role in alcohol-induced hepatic fibrosis/cirrhosis, mechanisms of which may involve dysregulation of alcohol metabolism and iron homeostasis, mitochondrial damage and oxidative injury.

Cannabidiol protects liver from binge alcohol-induced steatosis by mechanisms including inhibition of oxidative stress and increase in autophagy

Acute alcohol drinking induces steatosis, and effective prevention of steatosis can protect liver from progressive damage caused by alcohol. Increased oxidative stress has been reported as one mechanism underlying alcohol-induced steatosis. We evaluated whether cannabidiol, which has been reported to function as an antioxidant, can protect the liver from alcohol-generated oxidative stress-induced steatosis. Cannabidiol can prevent acute alcohol-induced liver steatosis in mice, possibly by preventing the increase in oxidative stress and the activation of the JNK MAPK pathway. Cannabidiol per se can increase autophagy both in CYP2E1-expressing HepG2 cells and in mouse liver. Importantly, cannabidiol can prevent the decrease in autophagy induced by alcohol. In conclusion, these results show that cannabidiol protects mouse liver from acute alcohol-induced steatosis through multiple mechanisms including attenuation of alcohol-mediated oxidative stress, prevention of JNK MAPK activation, and increasing autophagy.

Inhibition of autophagy promotes CYP2E1-dependent toxicity in HepG2 cells via elevated oxidative stress, mitochondria dysfunction and activation of p38 and JNK MAPK

Autophagy has been shown to be protective against drug and alcohol-induced liver injury. CYP2E1 plays a role in the toxicity of ethanol, carcinogens and certain drugs. Inhibition of autophagy increased ethanol-toxicity and accumulation of fat in wild type and CYP2E1 knockin mice but not in CYP2E1 knockout mice as well as in HepG2 cells expressing CYP2E1 (E47 cells) but not HepG2 cells lacking CYP2E1 (C34 cells). The goal of the current study was to evaluate whether modulation of autophagy can affect CYP2E1-dependent cytotoxicity in the E47 cells. The agents used to promote CYP2E1 -dependent toxicity were a polyunsaturated fatty acid, arachidonic acid (AA), buthionine sulfoximine (BSO), which depletes GSH, and CCl4, which is metabolized to the CCl3 radical. These three agents produced a decrease in E47 cell viability which was enhanced upon inhibition of autophagy by 3-methyladenine (3-MA) or Atg 7 siRNA. Toxicity was lowered by rapamycin which increased autophagy and was much lower to the C34 cells which do not express CYP2E1. Toxicity was mainly necrotic and was associated with an increase in reactive oxygen production and oxidative stress; 3-MA increased while rapamycin blunted the oxidative stress. The enhanced toxicity and ROS formation produced when autophagy was inhibited was prevented by the antioxidant N-Acetyl cysteine. AA, BSO and CCl4 produced mitochondrial dysfunction, lowered cellular ATP levels and elevated mitochondrial production of ROS. This mitochondrial dysfunction was enhanced by inhibition of autophagy with 3-MA but decreased when autophagy was increased by rapamycin. The mitogen activated protein kinases p38 MAPK and JNK were activated by AA especially when autophagy was inhibited and chemical inhibitors of p38 MAPK and JNK lowered the elevated toxicity of AA produced by 3-MA. These results show that autophagy was protective against the toxicity produced by several agents known to be activated by CYP2E1. Since CYP2E1 plays an important role in the toxicity of ethanol, drugs and carcinogens and is activated under various pathophysiological conditions such as diabetes, NASH and obesity, attempts to stimulate autophagy may be beneficial in preventing/lowering CYP2E1/ethanol liver injury.

Immunomodulatory and immunotoxic effects of bilirubin: molecular mechanisms

The immunomodulatory and immunotoxic effects of purified UCB have not been evaluated previously at clinically relevant UCB concentrations and UCB:BSA ratios. To delineate the molecular mechanism of UCB-induced immunomodulation, immune cells were exposed to clinically relevant concentrations of UCB. It inhibited LPS-induced B cell proliferation and cytokine production from splenic macrophages. UCB (≥25 μM) was toxic to unfractionated splenocytes, splenic T cells, B cells, macrophages, LPS-stimulated CD19(+) B cells, human PBMCs, and RBCs. Purified UCB also was found to be toxic to splenocytes and human PBMCs. UCB induced necrosis and apoptosis in splenocytes. UCB activated the extrinsic and intrinsic pathways of apoptosis, as reflected by the markers, such as CD95, caspase-8, Bax, MMP, cytoplasmic Ca(+2), caspase-3, and DNA fragmentation. UCB depleted GSH and activated p38MAPK. NAC, caspase inhibitors, and p38MAPK inhibitor attenuated the UCB-induced apoptosis. In vivo administration of ≥25 mg/kbw UCB induced atrophy of spleen, depletion of bone marrow cells, and leukopenia and decreased lymphocyte count and the T and B cell response to mitogens. UCB administration to mice led to induction of oxidative stress, activation of p38MAPK, and cell death in splenocytes. These parameters were attenuated by the injection of NAC and the p38MAPK inhibitor. Our results demonstrate for the first time that clinically relevant concentrations of UCB induce apoptosis and necrosis in immune cells by depleting cellular GSH. These findings should prove useful in understanding the immunosuppression associated with hyperbilirubinemia.

Depletion of cytosolic or mitochondrial thioredoxin increases CYP2E1-induced oxidative stress via an ASK-1-JNK1 pathway in HepG2 cells

Thioredoxin is an important reducing molecule in biological systems. Increasing CYP2E1 activity induces oxidative stress and cell toxicity. However, whether thioredoxin protects cells against CYP2E1-induced oxidative stress and toxicity is unknown. SiRNA were used to knockdown either cytosolic (TRX-1) or mitochondrial thioredoxin (TRX-2) in HepG2 cells expressing CYP2E1 (E47 cells) or without expressing CYP2E1 (C34 cells). Cell viability decreased 40-60% in E47 but not C34 cells with 80-90% knockdown of either TRX-1 or TRX-2. Depletion of either thioredoxin also potentiated the toxicity produced either by a glutathione synthesis inhibitor or by TNFα in E47 cells. Generation of reactive oxygen species and 4-HNE protein adducts increased in E47 but not C34 cells with either thioredoxin knockdown. GSH was decreased and adding GSH completely blocked E47 cell death induced by either thioredoxin knockdown. Lowering TRX-1 or TRX-2 in E47 cells caused an early activation of ASK-1, followed by phosphorylation of JNK1 after 48 h of siRNA treatment. A JNK inhibitor caused a partial recovery of E47 cell viability after thioredoxin knockdown. In conclusion, knockdown of TRX-1 or TRX-2 sensitizes cells to CYP2E1-induced oxidant stress partially via ASK-1 and JNK1 signaling pathways. Both TRX-1 and TRX-2 are important for defense against CYP2E1-induced oxidative stress.

Nitric oxide and DOPAC-induced cell death: from GSH depletion to mitochondrial energy crisis

The molecular mechanisms inherent to cell death associated with Parkinson's disease are not clearly understood. Diverse pathways, sequence of events and models have been explored in several studies. Recently, we have proposed an integrative mechanism, encompassing the interaction of nitric oxide (•NO) and a major dopamine metabolite, dihydroxyphenylacetic (DOPAC), leading to a synergistic mitochondrial dysfunction and cell death that may be operative in PD. In this study, we have studied the sequence of events underlying the mechanisms of cell death in PC12 cells exposed to •NO and DOPAC in terms of: a) free radical production; b) modulation by glutathione (GSH); c) energetic status and d) outer membrane mitochondria permeability. Using Electron Paramagnetic Resonance (EPR) it is shown the early production of oxygen free radicals followed by a depletion of GSH reflected by an increase of GSSG/GSH ratio in the cells treated with the mixture of •NO/DOPAC, as compared with the cells individually exposed to each of the stimulus. Glutathione ethyl ester (GSH-EE) and N-acetylcysteine (NAC) may rescue cells from death, increasing GSH content and preventing ATP loss in cells treated with the mixture DOPAC/•NO but failed to exert similar effects in the cells challenged only with •NO. The depletion of GSH is accompanied by a decreased activity of mitochondrial complex I. At a later stage, the concerted action of DOPAC and •NO include a rise in the ratio Bax/Bcl-2, an observation not evident when cells were exposed only to •NO. The results support a free radical-induced pathway leading to cell death involving the concerted action of DOPAC and •NO and the critical role of GSH in maintaining a functional mitochondria.

Rat strain differences in susceptibility to alcohol-induced chronic liver injury and hepatic insulin resistance

The finding of more severe steatohepatitis in alcohol fed Long Evans (LE) compared with Sprague Dawley (SD) and Fisher 344 (FS) rats prompted us to determine whether host factors related to alcohol metabolism, inflammation, and insulin/IGF signaling predict proneness to alcohol-mediated liver injury. Adult FS, SD, and LE rats were fed liquid diets containing 0% or 37% (calories) ethanol for 8 weeks. Among controls, LE rats had significantly higher ALT and reduced GAPDH relative to SD and FS rats. Among ethanol-fed rats, despite similar blood alcohol levels, LE rats had more pronounced steatohepatitis and fibrosis, higher levels of ALT, DNA damage, pro-inflammatory cytokines, ADH, ALDH, catalase, GFAP, desmin, and collagen expression, and reduced insulin receptor binding relative to FS rats. Ethanol-exposed SD rats had intermediate degrees of steatohepatitis, increased ALT, ADH and profibrogenesis gene expression, and suppressed insulin receptor binding and GAPDH expression, while pro-inflammatory cytokines were similarly increased as in LE rats. Ethanol feeding in FS rats only reduced IL-6, ALDH1-3, CYP2E1, and GAPDH expression in liver. In conclusion, susceptibility to chronic steatohepatitis may be driven by factors related to efficiency of ethanol metabolism and degree to which ethanol exposure causes hepatic insulin resistance and cytokine activation.

Hypothesis: a unifying mechanism for nutrition and chemicals as lifelong modulators of DNA hypomethylation

BACKGROUND

Although both nutrition and chemicals are important environmental factors modulating epigenetic changes, they are commonly studied separately by researchers in different fields. However, these two environmental factors cannot be separated from each other in the real world because a number of chemical agents contaminate food chains.

OBJECTIVE

We propose a unifying mechanism that can link epigenetic alterations in relation to DNA hypomethylation due to chemical agents and to nutrient deficiency or imbalance, emphasizing the importance of an integrative approach in the field of environmental epidemiology.

DISCUSSION

Methyl groups from S-adenosylmethionine (SAM) are needed for DNA methylation. Diets low in sources of methyl groups can lead to global DNA hypomethylation by impairing synthesis of SAM. However, even without nutritional deficiency, enhanced need to synthesize glutathi-one (GSH) can impair synthesis of SAM and perturb DNA methylation, because the methylation cycle and the GSH synthesis pathways are biochemically linked. Exposure to environmental chemicals is a common situation in which the need for GSH synthesis is enhanced, because GSH is consumed to conjugate diverse chemicals. Given that GSH conjugation happens at any chemical dose, this hypothesis is relevant even at exposures below the high doses that cause toxicologic responses.

CONCLUSION

At present, general populations are exposed to a large number of chemicals, each at a very low dose. Thus, DNA hypomethylation due to chemical exposure may be common in modern societies and can synergistically interact with nutrition-induced DNA hypomethylation.

Inhibition of Na+/H+ exchanger enhances low pH-induced L-selectin shedding and beta2-integrin surface expression in human neutrophils

Ischemia-reperfusion injury is a common pathological occurrence causing tissue damage in heart attack and stroke. Entrapment of neutrophils in the vasculature during ischemic events has been implicated in this process. In this study, we examine the effects that lactacidosis and consequent reductions in intracellular pH (pH(i)) have on surface expression of adhesion molecules on neutrophils. When human neutrophils were exposed to pH 6 lactate, there was a marked decrease in surface L-selectin (CD62L) levels, and the decrease was significantly enhanced by inclusion of Na(+)/H(+) exchanger (NHE) inhibitor 5-(N,N-hexamethylene)amiloride (HMA). Similar effects were observed when pH(i) was reduced while maintaining normal extracellular pH, by using an NH(4)Cl prepulse followed by washes and incubation in pH 7.4 buffer containing NHE inhibitors [HMA, cariporide, or 5-(N,N-dimethyl)amiloride (DMA)]. The amount of L-selectin shedding induced by different concentrations of NH(4)Cl in the prepulse correlated with the level of intracellular acidification with an apparent pK of 6.3. In contrast, beta(2)-integrin (CD11b and CD18) was only slightly upregulated in the low-pH(i) condition and was enhanced by NHE inhibition to a much lesser extent. L-selectin shedding was prevented by treating human neutrophils with inhibitors of extracellular metalloproteases (RO-31-9790 and KD-IX-73-4) or with inhibitors of intracellular signaling via p38 MAP kinase (SB-203580 and SB-239063), implying a transmembrane effect of pH(i). Taken together, these data suggest that the ability of NHE inhibitors such as HMA to reduce ischemia-reperfusion injury may be related to the nearly complete removal of L-selectin from the neutrophil surface.

Cytochrome P4502E1 sensitizes to tumor necrosis factor alpha-induced liver injury through activation of mitogen-activated protein kinases in mice

The goal of this study was to evaluate the role of mitogen-activated protein kinase (MAPK) in cytochrome P4502E1 (CYP2E1) potentiation of lipopolysaccharide or tumor necrosis factor alpha (TNF-alpha)-induced liver injury. Treatment of C57/BL/6 mice with pyrazole (PY) plus lipopolysaccharide (LPS) induced liver injury compared with mice treated with PY or LPS alone. The c-Jun N-terminal kinase (JNK) inhibitor SP600125 or p38 MAPK inhibitor SB203580 prevented this liver injury. PY plus LPS treatment activated p38 MAPK and JNK but not extracellular signal-regulated kinase (ERK). PY plus LPS treatment triggered oxidative stress in the liver with increases in lipid peroxidation, decrease of glutathione (GSH) levels, and increased production of 3-nitrotyrosine adducts and protein carbonyl formation. This oxidative stress was blocked by SP600125 or SB203580. PY plus LPS treatment elevated TNF-alpha production, and this was blocked by SP600125 or SB203580. Neither SP600125 nor SB203580 affected CYP2E1 activity or protein levels. Treating C57/BL/6 mice with PY plus TNF-alpha also induced liver injury and increased lipid peroxidation and decreased GSH levels. Prolonged activation of JNK and p38 MAPK was observed. All of these effects were blocked by SP600125 or SB203580. In contrast to wild-type SV 129 mice, treating CYP2E1 knockout mice with PY plus TNF-alpha did not induce liver injury, thus validating the role of CYP21E1 in this potentiated liver injury. Liver mitochondria from PY plus LPS or PY plus TNF-alpha treated mice underwent calcium-dependent, cyclosporine A-sensitive swelling, which was prevented by SB203580 or SP600125.

CONCLUSION

These results show that CYP2E1 sensitizes liver hepatocytes to LPS or TNF-alpha and that the CYP2E1-enhanced LPS or TNF-alpha injury, oxidant stress, and mitochondrial injury is JNK or p38 MAPK dependent.

Specificity proteins Sp1 and Sp3 interact with the rat GTP cyclohydrolase I proximal promoter to regulate transcription

The role of the proximal promoter GC-box in regulating basal and cAMP-dependent GTP Cyclohydrolase I gene transcription was investigated using a variety of cell lines and techniques. These studies show that the GC-box is composed of a triad of cis-elements that in vitro bind specificity proteins Sp1 and Sp3. Sp1 and Sp3 were found associated with the native proximal promoter in PC12 cells but were not recruited to the promoter during cAMP-dependent transcription. Studies using Drosophila SL2 cells showed that Sp3 occupies two sites within the GC-box and enhances transcription when acting alone and synergistically when combined with nuclear factor-Y (NF-Y) and CCAAT/Enhancer-Binding Protein (C/EBP)beta, cognate binding proteins for the adjacent cAMP response element (CRE) and CCAAT-box cAMP response elements. In contrast, Sp1 bound only one site within the GC-box and did not enhance transcription unless combined with NF-Y and C/EBPbeta. Studies in SL2 cells also showed that Sp1 and Sp3 do not co-occupy the GC-box, and accordingly Sp1 competes for Sp3 binding to repress Sp3-dependent transcription. In PC12 cells, complete mutation of the GC-box reduced basal but not cAMP-dependent transcription, resulting in an overall increase in the cAMP response and demonstrating that formation of this enhanceosome does not require Sp1 or Sp3. Experiments in which the GC-box was replaced with a Gal4 element and the promoter challenged with Gal4 fusion proteins support this conclusion and a role for Sp3 in maintaining high levels of basal transcription in PC12 cells. Equivalent amounts of Sp1 and Sp3 were found associated with the native proximal promoter in PC12 and Rat2 cells, which differ 10-fold in basal transcription. Similar levels of methylation of CpG dinucleotides located within the GC-box were also observed in these two cells lines. These results suggest that Sp1 and Sp3 bound to the GC-box might help to preserve an open chromatin configuration at the proximal promoter in cells which constitutively express low levels of GTP Cyclohydrolase I.

Patulin influences the expression of Th1/Th2 cytokines by activated peripheral blood mononuclear cells and T cells through depletion of intracellular glutathione

Patulin is a mold toxin secreted mainly by fungi of the Penicillium species. Exposure generally results from consumption of moldy fruits and fruit products. Since recent studies identified mold exposure as a risk factor for allergic diseases, we examined the effects of patulin on human peripheral blood mononuclear cells (PBMC) prepared from buffy coats of healthy donors. Cells were stimulated with CD3- and CD28-specific antibodies in the presence or absence of patulin. Effects of patulin on PBMCs were evaluated by proliferation, viability assays, and cytokine ELISAs. The presence of 50 ng/mL patulin strongly decreased the amounts of several cytokines in the supernatant of stimulated PBMCs. This decrease in cytokine secretion was not due to cytotoxic effects of patulin. Moreover, the extent of the reduction of cytokine amounts was cytokine specific, affecting some (IL-4, IL-13, IFNgamma, and IL-10), but not others (IL-8, IL-5). We show that all effects could be abolished by adding thiol containing compounds. A depletion of intracellular GSH could be measured after incubation of cells with patulin. Taken together, our data indicate that patulin modulates the functional activation of PBMCs with respect to proliferation and cytokine secretion patterns by depletion of intracellular GSH. The depletion of intracellular glutathione may influence the balance between Th1 and Th2 cells and have implications for allergic diseases.

Crosstalk between the SUMO and ubiquitin pathways

Several ways in which the SUMO and ubiquitin pathways can intersect and communicate have recently been discovered. This review discusses the principles of crosstalk between SUMOylation and ubiquitination, focusing on the RNF4 family of RING finger E3 ubiquitin ligases, which specifically recognize SUMOylated proteins via their SUMO moiety for ubiquitination.

Glutathione depletion activates mitogen-activated protein kinase (MAPK) pathways that display organ-specific responses and brain protection in mice

Because mitogen-activated protein kinases (MAPK) are downstream effectors of antioxidant responses, changes in GSH levels in an organism might induce organ-specific responses. To test our hypothesis, mice were treated intraperitoneally with L-buthionine-S-R-sulfoximine (BSO) to inhibit GSH synthesis. A time-related GSH depletion in the liver and kidney correlated with p38(MAPK) phosphorylation and induction of thioredoxin 1 (Tx-1) transcription. This positive regulation was associated with nuclear translocation of NF-kappaB and ATF-2 and c-Jun phosphorylation in the liver, but only c-Jun phosphorylation in the kidney. Increased levels of GSH were observed in the brain together with extracellular regulated kinase 2 (ERK2) activation, Nrf2 nuclear accumulation, and increases in transcription of Nrf2, xCT, gamma-glutamylcysteine synthetase (gammaGCSr), and Tx-1. Pretreatment with MAPK inhibitors SB203580 and U0126, or addition of the exogenous thiol N-acetylcysteine, abrogated both p38(MAPK) and ERK2 activation as well as downstream effects on gene expression. No effect on gammaGCSr was observed. These results indicate that in mice, GSH depletion is associated with p38(MAPK) phosphorylation in the liver and kidney and with ERK2 activation in the brain, in what could be considered part of the brain's protective response to thiol depletion.

Synergistic toxicity induced by prolonged glutathione depletion and inhibition of nuclear factor-kappaB signaling in liver cells

TNF-alpha, GSH depletion and CYP2E1 are factors that play an important role in alcoholic liver disease. Activation of NF-kappaB prevents hepatocyte damage caused by TNF-alpha. This work describes the effect of NF-kappaB inhibition on toxicities caused by GSH depletion or arachidonic acid (AA) treatment in liver cells, and evaluates the possible influence of CYP2E1 overexpression. Cells were exposed to the NF-kappaB inhibitor BAY11-7082, in the absence or presence of l-buthionine sulfoximine (BSO) to block GSH synthesis. BSO toxicity was higher in CYP2E1-expressing E47 HepG2 cells compared to control cells; the incubation with BAY11-7082 potentiated BSO toxicity in both cell lines comparably. Several other agents which suppress activation of NF-kappaB increased BSO toxicity in E47 cells. NF-kappaB inhibition, however, did not sensitize E47 cells to AA toxicity. Suppressing activity of NF-kappaB also potentiated BSO, but not AA toxicity, in isolated rat hepatocytes. BAY11-7082 plus BSO induced a greater p38 MAPK activation as compared to BAY11-7082 or BSO alone, and a p38 MAPK inhibitor protected against the synergistic toxicity. In summary, inhibition of NF-kappaB sensitizes liver cells to toxicity linked to GSH depletion, probably accelerating the processes of thiol homeostasis deregulation and induction of apoptosis through a mechanism mediated by p38 MAPK.

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.

Induction of DNA strand breaks and oxidative stress in HeLa cells by ethanol is dependent on CYP2E1 expression

Induction of cytochrome P4502E1 (CYP2E1) is considered to be an important mechanism by which ethanol can cause toxicity related to oxidative stress both in vivo and in vitro. In the current study, we used HeLa cells with doxycycline-regulated CYP2E1 expression to test the hypothesis that induction of CYP2E1 could lead to secondary DNA oxidation that could potentially contribute to the carcinogenicity of ethanol in vivo. Overexpression of CYP2E1 protein was not associated with oxidative stress per se as assessed by markers of lipid peroxidation (cis-parinaric acid oxidation), glutathione depletion and elevation of intracellular reactive oxygen species (dichlorofluoroscin oxidation) in the presence or absence of ethanol substrate (10 mM, 24 h). Furthermore, there was no evidence of elevation of frequency of DNA strand breaks as assessed by the comet assay. In contrast, however, after pre-incubation of cells with L-buthionine-(S,R)-sulphoximine (BSO, 10 microM) which caused a 75% reduction in intracellular reduced glutathione (GSH) levels, CYP2E1 expression resulted in oxidative stress as assessed by all of these markers and DNA strand breaks but only in the presence of ethanol (10 mM). No effect was observed under these conditions in control cells not expressing CYP2E1. Furthermore, these effects could be attenuated by co-incubation with 1-aminobenzotriazole (0.5 mM), a suicide inhibitor of P450 activity. In conclusion, in this in vitro model CYP2E1-mediated interaction with ethanol results in the intracellular oxidative stress and the formation of DNA strand breaks which are detectable in cells pre-sensitized by depletion of intracellular levels of GSH.

Curcumin-induced GADD153 upregulation: Modulation by glutathione

As we reported previously, GADD153 is upregulated in colon cancer cells exposed to curcumin. In the present study, we ascertained the involvement of glutathione and certain sulfhydryl enzymes associated with signal transduction in mediating the effect of curcumin on GADD153. Curcumin-induced GADD153 gene upregulation was attenuated by reduced glutathione (GSH) or N-acetylcysteine (NAC) and potentiated by the glutathione synthesis inhibitor, L-buthionine-(S,R)-sulfoximine (BSO). Additionally, GSH and NAC decreased the intracellular content of curcumin. Conversely, curcumin decreased intracellular glutathione and also increased the formation of reactive oxygen species (ROS) in cells, but either GSH or NAC prevented both of these effects of curcumin. In affecting the thiol redox status, curcumin caused activation of certain sulfhydryl enzymes involved in signal transduction linked to GADD153 expression. Curcumin increased the expression of the phosphorylated forms of PTK, PDK1, and PKC-delta, which was attenuated by either GSH or NAC and potentiated by BSO. Furthermore, selective inhibitors of PI3K and PKC-delta attenuated curcumin-induced GADD153 upregulation. Collectively, these findings suggest that a regulatory thiol redox-sensitive signaling cascade exists in the molecular pathway leading to induction of GADD153 expression as caused by curcumin.

Nitric oxide donors prevent while the nitric oxide synthase inhibitor l-NAME increases arachidonic acid plus CYP2E1-dependent toxicity

Polyunsaturated fatty acids such as arachidonic acid (AA) play an important role in alcohol-induced liver injury. AA promotes toxicity in rat hepatocytes with high levels of cytochrome P4502E1 and in HepG2 E47 cells which express CYP2E1. Nitric oxide (NO) participates in the regulation of various cell activities as well as in cytotoxic events. NO may act as a protectant against cytotoxic stress or may enhance cytotoxicity when produced at elevated concentrations. The goal of the current study was to evaluate the effect of endogenously or exogenously produced NO on AA toxicity in liver cells with high expression of CYP2E1 and assess possible mechanisms for its actions. Pyrazole-induced rat hepatocytes or HepG2 cells expressing CYP2E1 were treated with AA in the presence or absence of an inhibitor of nitric oxide synthase L-N(G)-Nitroarginine Methylester (L-NAME) or the NO donors S-nitroso-N-acetylpenicillamine (SNAP), and (Z)-1-[-(2-aminoethyl)-N-(2-aminoethyl)]diazen-1-ium-1,2-diolate (DETA-NONO). AA decreased cell viability from 100% to 48+/-6% after treatment for 48 h. In the presence of L-NAME, viability was further lowered to 23+/-5%, while, SNAP or DETA-NONO increased viability to 66+/-8 or 71+/-6%. The L-NAME potentiated toxicity was primarily necrotic in nature. L-NAME did not affect CYP2E1 activity or CYP2E1 content. SNAP significantly lowered CYP2E1 activity but not protein. AA treatment increased lipid peroxidation and lowered GSH levels. L-NAME potentiated while SNAP prevented these changes. Thus, L-NAME increased, while NO donors decreased AA-induced oxidative stress. Antioxidants prevented the L-NAME potentiation of AA toxicity. Damage to mitochondria by AA was shown by a decline in the mitochondrial membrane potential (MMP). L-NAME potentiated this decline in MMP in association with its increase in AA-induced oxidative stress and toxicity. NO donors decreased this decline in MMP in association with their decrease in AA-induced oxidative stress and toxicity. These results indicate that NO can be hepatoprotective against CYP2E1-dependent toxicity, preventing AA-induced oxidative stress.

Antitumor quinols: Role of glutathione in modulating quinol-induced apoptosis and identification of putative cellular protein targets

Novel heteroaromatic quinols 4-(benzothiazol-2-yl)-4-hydroxycyclohexa-2,5-dienone (1) and 4-(1-benzenesulfonyl-1H-indol-2-yl)-4-hydroxycyclohexa-2,5-dienone (2) are promising novel anticancer agents. They exhibit in vitro antiproliferative activity against colon, renal, and breast carcinoma cell lines as well as in vivo antitumor activity in colon, renal, and breast tumor xenografts. Elucidation of the mechanism of antitumor action of these compounds is of great importance. We show in this study that the compounds induced apoptosis as demonstrated by caspase 3 and PARP cleavage at doses causing G(2)/M cell cycle arrest. Glutathione was found to play an important role in modulating quinol-mediated cytotoxicity. In HCT 116 cells, treatment with 1 and 2 caused a 2- to 3-fold increase in the total glutathione content, suggestive of a glutathione-mediated antioxidant response. Indeed, buthionine sulfoximine (BSO)-induced glutathione depleted cells were 6-10 times more sensitive to 1 and 2, while glutathione monoethyl ester supplementation decreased the antitumor potencies by 2-3 times. In further studies we determined other cellular proteins which bind to an immobilized quinol analog, and identified several proteins including beta-tubulin, heat shock protein 60, and peroxiredoxin 1 as potential molecular targets of quinols that may contribute to their proapoptotic and antiproliferative effects.

Opposite action of S-adenosyl methionine and its metabolites on CYP2E1-mediated toxicity in pyrazole-induced rat hepatocytes and HepG2 E47 cells

S-adenosyl-L-methionine (SAMe) is protective against a variety of hepatotoxins, including ethanol. The ability of SAMe to protect against cytochrome P-450 2E1 (CYP2E1)-dependent toxicity was studied in hepatocytes from pyrazole-treated rats and HepG2 E47 cells, both of which actively express CYP2E1. Toxicity was initiated by the addition of arachidonic acid (AA) or by depletion of glutathione after treatment with L-buthionine sulfoximine (BSO). In pyrazole hepatocytes, SAMe (0.25-1 mM) protected against AA but not BSO toxicity. SAMe elevated GSH levels, thus preventing the decline in GSH caused by AA, and SAMe prevented AA-induced lipid peroxidation. SAMe analogs such as methionine or S-adenosyl homocysteine, which elevate GSH, also protected against AA toxicity. 5'-Methylthioadenosine (MTA), which cannot produce GSH, did not protect. The toxicity of BSO was not prevented by SAMe and the analogs because GSH cannot be synthesized. In contrast, in E47 cells, SAMe and MTA but not methionine or S-adenosyl homocysteine potentiated AA and BSO toxicity. Antioxidants such as trolox or N-acetyl cysteine prevented this synergistic toxicity of SAMe plus AA or SAMe plus BSO, respectively. In pyrazole hepatocytes, SAMe prevented the decline in mitochondrial membrane potential produced by AA, whereas in E47 cells, SAMe potentiated the decline in mitochondrial membrane potential. In E47 cells, but not pyrazole hepatocytes, the combination of SAMe plus BSO lowered levels of the antioxidant transcription factor Nrf2. Because SAMe can be metabolized enzymatically or spontaneously to MTA, MTA may play a role in the potentiation of AA and BSO toxicity by SAMe, but the exact mechanisms require further investigation. In conclusion, contrasting effects of SAMe on CYP2E1 toxicity were observed in pyrazole hepatocytes and E47 cells. In hepatocytes, SAMe protects against CYP2E1 toxicity by a mechanism involving maintaining or elevating GSH levels.

Nrf2 is increased by CYP2E1 in rodent liver and HepG2 cells and protects against oxidative stress caused by CYP2E1

Induction of CYP2E1 by ethanol is one pathway through which ethanol generates oxidative stress. Nrf2 is a transcription factor that regulates important antioxidant and phase II detoxification genes. Nrf2 induction by CYP2E1 and its importance in the adaptive response to increased oxidative stress caused by CYP2E1 was studied. Increases in Nrf2 protein and mRNA were observed in livers or hepatocytes of chronic alcohol-fed mice or rats and of pyrazole-treated rats or mice, conditions known to elevate CYP2E1. HepG2 cells expressing CYP2E1 (E47 cells) showed increased Nrf2 mRNA and protein expression compared with control HepG2 C34 cells. Nrf2 is activated in E47 cells as shown by an increase in nuclear Nrf2 levels and Nrf2-antioxidant-responsive element binding activity, and upregulation of Nrf2-regultated genes, glutamate cysteine ligase catalytic subunit (GCLC), and heme oxygenase 1 (HO-1). Increases in Nrf2 protein and mRNA are blocked by inhibitors of CYP2E1 activity and a reactive oxygen species (ROS) scavenger, N-acetylcysteine, which decrease ROS levels as well as Nrf2 mRNA induction. Upregulation of GCLC and HO-1 in E47 cells is dependent on Nrf2 and is prevented by siRNA-Nrf2. Blocking Nrf2 by siRNA-Nrf2 decreases glutathione and increases ROS and lipid peroxidation, resulting in decreased mitochondrial membrane potential and loss of cell viability of E47 cells but not C34 cells. These results suggest that Nrf2 is activated and that levels of protein and mRNA are increased when CYP2E1 is elevated. In conclusion, Nrf2 plays a key role in the adaptive response against increased oxidative stress caused by CYP2E1.

Alcohol increases tumor necrosis factor alpha and decreases nuclear factor-kappab to activate hepatic apoptosis in genetically obese mice

Both obesity and alcohol can cause oxidative stress, cytokine induction, and steatohepatitis. To determine the consequences of their combination, we compared the hepatic effects of moderate ethanol binges in lean and obese ob/ob mice. Mice received water or ethanol (2.5 g/kg) by gastric intubation daily for 4 days, and were killed 2 hours after the last administration. Some obese mice also received pentoxifylline, an inhibitor of tumor necrosis factor-alpha (TNF-alpha) production, before each ethanol administration. In lean mice, these moderate ethanol doses did not increase plasma TNF-alpha and hepatic caspase-3 activity, but triggered some apoptotic hepatocytes. Naive ob/ob mice had a few necrotic and apoptotic hepatocytes, but exhibited little oxidative stress, possibly because of adaptive increases in manganese superoxide dismutase, heat shock protein 70 (Hsp70), mitochondrial cytochrome c, and mitochondrial DNA. Alcohol administration to ob/ob mice did not increase oxidative stress despite increased CYP2E1, but increased plasma TNF-alpha, further increased Hsp70, and profoundly decreased p65 nuclear factor kappaB (NF-kappaB) protein and DNA-binding activity in nuclear extracts. Caspase-3 was activated, and more apoptotic hepatocytes were found in intoxicated obese mice than naive obese mice. In intoxicated obese mice, pentoxifylline fully prevented the increase in plasma TNF-alpha the decrease in nuclear NF-kappaB activity, and the increase in hepatic caspase-3, and it also decreased hepatic triglycerides. In conclusion, obese mice develop adaptations that may limit oxidative stress. Moderate ethanol intoxication does not increase oxidative stress in obese mice, but increases TNF-alpha and also decreases nuclear NF-kappaB activity, thus unleashing the apoptotic effects of TNF-alpha.

Ethanol metabolism alters interferon gamma signaling in recombinant HepG2 cells

We previously showed that IFNgamma signal transduction was suppressed by ethanol in recombinant HepG2 cells (VL-17A cells), which express alcohol dehydrogenase (ADH) and CYP2E1. We examined the mechanisms by which STAT1 phosphorylation is blocked by ethanol treatment in VL-17A cells. Cells were exposed to 0 or 100 mmol/L ethanol for 72 hours. STAT1 phosphorylation was determined by Western blot after 1 hour IFNgamma exposure. Reduction of STAT1 phosphorylation by ethanol was prevented in the presence of 4MP, DAS, or uric acid, indicating that the oxidative products from ethanol metabolism were partly responsible for suppression of STAT1 phosphorylation. Ethanol exposure decreased STAT1 tyrosine phosphorylation, whereas serine phosphorylation on the protein was unchanged. These effects of ethanol were mimicked by the peroxynitrite (PN) donor, SIN-1, which also blocked tyrosine, but not serine phosphorylation, on STAT1. When cells expressing either ADH (VA-13 cells) or CYP2E1 (E-47 cells) were exposed to ethanol, both ADH- and CYP2E1-generated products reduced STAT1 phosphorylation. In addition, SOCS1, a negative regulator of IFNgamma signaling and which is degraded by the proteasome, was stabilized by ethanol treatment, presumably because of inhibited proteasome activity. Furthermore, SIN-1 treatment elevated SOCS1 levels in VL-17A cells, indicating that PN has a role in SOCS1 elevation. In conclusion, under conditions of ethanol-elicited oxidative stress, PN prevents STAT1 phosphorylation by stabilization of SOCS1, and possibly by nitration of tyrosine residues in STAT1 protein.

Role of intracellular glutathione in cell sensitivity to the apoptosis induced by tumor necrosis factor {alpha}-related apoptosis-inducing ligand/anticancer drug combinations

PURPOSE

We have recently shown that combination of tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL) with anticancer drugs induced an apoptotic cell death pathway involving both caspases and mitochondria. The present work further explores the role of intracellular reduced glutathione (GSH) level in cell sensitivity to this cell death pathway.

EXPERIMENTAL DESIGN

Intracellular GSH level was measured by high-performance liquid chromatography. Cell death was detected by immunofluorescence after Hoechst 33342/propidium iodide staining. Reactive oxygen species production was evaluated by flow cytometry after dihydroethidium probe labeling. Western blot analysis was done to study stress-activated protein kinase/c-jun NH(2)-terminal kinase (SAPK/JNK) phosphorylation. The Student's t test was used to determine significance of the results. Three to six experiments were done.

RESULTS

GSH depletion enhanced apoptosis induced by TRAIL/cisplatin (CDDP) or TRAIL/5-fluorouracil (5-FU) combinations in both human HT29 colon carcinoma and HepG2 hepatocarcinoma cells, whereas it enhanced cytotoxicity induced only by TRAIL/CDDP in human primary hepatocytes. Our results further suggested that GSH depletion enhanced SAPK/JNK phosphorylation upon TRAIL/5-FU exposure and likely reduced the detoxification mechanisms of CDDP in HT29 cells. Resistance of Bcl-2-expressing HT29 and HepG2 cells to combined treatment was not overcome by GSH depletion, thus indicating that Bcl-2-mediated antiapoptotic effect occurs independently of intracellular GSH level.

CONCLUSION

GSH depletion could be useful to increase the therapeutic efficacy of cancer treatment by TRAIL/anticancer drug combinations. Furthermore, TRAIL/5-FU combination might be a potential anticancer treatment of human tumors, being ineffective on human primary hepatocytes and thus could be of interest in clinical cancer treatment. Nevertheless, Bcl-2 expression remains an important resistance factor.

Lipopolysaccharide-induced liver injury in rats treated with the CYP2E1 inducer pyrazole

Elevated LPS and elevated cytochrome P-450 2E1 (CYP2E1) in liver are two major independent risk factors in alcoholic liver disease. We investigated possible synergistic effects of the two risk factors in causing oxidative stress and liver injury. Sprague-Dawley rats were injected intraperitoneally with pyrazole (inducer of CYP2E1) for 2 days, and then LPS was injected via tail vein. Other rats were treated with pyrazole alone or LPS alone or saline. Eight hours later, blood was collected and livers were excised. Pathological evaluation showed severe inflammatory responses and necroses only in liver sections from rats in the pyrazole plus LPS group; blood transaminase levels were significantly elevated only in the combination group. Activities of caspase-3 and -9 and positive terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining were highest in the LPS alone and the LPS plus pyrazole group, with no significant difference between the two groups. Lipid peroxidation and protein carbonyls in liver homogenate as well as in situ superoxide production were maximally elevated in the LPS plus pyrazole group. Levels of nitrite plus nitrate and inducible nitric oxide (NO) synthase (iNOS) content were comparably elevated in LPS alone and the LPS plus pyrazole group; however, 3-nitrotyrosine adducts were elevated in the combined group but not the LPS group. It is likely that LPS induction of iNOS, which produces NO, coupled to pyrazole induction of CYP2E1 which produces superoxide, sets up conditions for maximal peroxynitrite formation and production of 3-nitrotyrosine adducts. CYP2E1 activity and content were elevated in the pyrazole and the LPS plus pyrazole groups. Immunohistochemical staining indicated that distribution of CYP2E1 was in agreement with that of necrosis and production of superoxide. These results show that pyrazole treatment enhanced LPS-induced necrosis, not apoptosis. The enhanced liver necrosis appears to involve an increase in oxidative and nitrosative stress generated by the combination of LPS plus elevated CYP2E1 levels.

Chronic ethanol feeding and folate deficiency activate hepatic endoplasmic reticulum stress pathway in micropigs

Previously, we showed that feeding micropigs ethanol with a folate-deficient diet promoted the development of hepatic injury while increasing hepatic levels of homocysteine and S-adenosylhomocysteine (SAH) and reducing the level of S-adenosylmethionine (SAM) and the SAM-to-SAH ratio. Our present goals were to evaluate mechanisms for hepatic injury using liver specimens from the same micropigs. The effects of ethanol feeding or folate-deficient diets, singly or in combination, on cytochrome P-450 2E1 (CYP2E1) and signal pathways for apoptosis and steatosis were analyzed using microarray, real-time PCR, and immunoblotting techniques. Apoptosis was increased maximally by the combination of ethanol feeding and folate deficiency and was correlated positively to liver homocysteine and SAH. Liver CYP2E1 and the endoplasmic reticulum stress signals glucose-regulated protein 78 (GRP78), caspase 12, and sterol regulatory element binding protein-1c (SREBP-1c) were each activated in pigs fed folate-deficient or ethanol diets singly or in combination. Liver mRNA levels of CYP2E1, GRP78, and SREBP-1c, and protein levels of CYP2E1, GRP78, nuclear SREBP, and activated caspase 12 each correlated positively to liver levels of SAH and/or homocysteine and negatively to the SAM-to-SAH ratio. The transcripts of the lipogenic enzymes fatty acid synthase, acetyl-CoA carboxylase, and stearoyl-CoA desaturase were elevated in the ethanol-fed groups, and each was positively correlated to liver homocysteine levels. The induction of abnormal hepatic methionine metabolism through the combination of ethanol feeding with folate deficiency is associated with the activation of CYP2E1 and enhances endoplasmic reticulum stress signals that promote steatosis and apoptosis.

Glutathione depletion inhibits lipopolysaccharide-induced intercellular adhesion molecule 1 synthesis

Cellular redox status is known to regulate a number of biological processes, including the activation of inflammatory genes. Our previous studies demonstrated that thiol depletion using diethyl maleate (DEM) reduced neutrophil sequestration in animal models of inflammation, an effect primarily mediated by impaired upregulation of the adhesion molecule, ICAM-1. The present studies were performed to discern the mechanism whereby DEM prevents LPS-induced ICAM-1 expression in human umbilical vein endothelial cells. DEM caused a time- and concentration-dependent inhibition of ICAM-1 expression in LPS-stimulated HUVEC by blocking induction of gene transcription. Interestingly, DEM had little effect on the degradation of the inhibitory protein IkappaB-alpha, but rather appeared to prevent translocation of the transcription factor NF-kappaB into the nucleus. Readdition of glutathione following DEM treatment restored the ability of LPS to induce NF-kappaB translocation and ICAM-1 synthesis. DEM plus LPS caused synergistic induction of heme oxygenase-1 (HO-1), suggesting its role in the inhibitory effects of DEM. However, HO-1 was shown to be neither sufficient nor necessary for the anti-inflammatory effects of glutathione depletion. These studies illustrate that thiol depletion may represent a potential therapy for inflammation, exerting its effects via a distinct mechanism on cell signaling pathways.