Pyrazole induced oxidative liver injury independent of CYP2E1/2A5 induction due to Nrf2 deficiency

Imidazole-4-N-acetamide Derivatives as a Novel Scaffold for Selective Targeting of Cyclin Dependent Kinases

The rational design of cyclin-dependent protein kinase (CDK) inhibitors presumes the development of approaches for accurate prediction of selectivity and the activity of small molecular weight anticancer drug candidates. Aiming at attenuation of general toxicity of low selectivity compounds, we herein explored the new chemotype of imidazole-4-N-acetamide substituted derivatives of the pan-CDK inhibitor PHA-793887. Newly synthesized compounds 1-4 containing an aliphatic methyl group or aromatic radicals at the periphery of the scaffold were analyzed for the prediction of relative free energies of binding to CDK1, -2, -5, and -9 using a protocol based on non-equilibrium (NEQ) thermodynamics. This methodology allows for the demonstration of a good correlation between the calculated parameters of interaction of 1-4 with individual targets and the values of inhibitory potencies in in vitro kinase assays. We provide evidence in support of NEQ thermodynamics as a time sparing, precise, and productive approach for generating chemical inhibitors of clinically relevant anticancer targets.

Uncovering the Fate and Risks of Intravenously Injected Prussian Blue Nanoparticles in mice by an Integrated Methodology of Toxicology, Pharmacokinetics, Proteomics, and Metabolomics

BACKGROUND

Prussian blue (PB) nanoparticles (NPs) have been intensively investigated for medical applications, but an in-depth toxicological investigation of PB NPs has not been implemented. In the present study, a comprehensive investigation of the fate and risks of PB NPs after intravenous administration was carried out by using a mouse model and an integrated methodology of pharmacokinetics, toxicology, proteomics, and metabolomics.

RESULTS

General toxicological studies demonstrated that intravenous administration of PB NPs at 5 or 10 mg/kg could not induce obvious toxicity in mice, while mice treated with a relatively high dose of PB NPs at 20 mg/kg exhibited loss of appetite and weight decrease in the first two days postinjection. Pharmacokinetic studies revealed that intravenously administered PB NPs (20 mg/kg) underwent fast clearance from blood, highly accumulated in the liver and lungs of mice, and finally cleared from tissues. By further integrated proteomics and metabolomics analysis, we found that protein expression and metabolite levels changed significantly in the liver and lungs of mice due to the high accumulation of PB NPs, leading to slight inflammatory responses and intracellular oxidative stress.

CONCLUSIONS

Collectively, our integrated experimental data imply that the high accumulation of PB NPs may cause potential risks to the liver and lungs of mice, which will provide detailed references and guidance for further clinical application of PB NPs in the future.

NRF2 Activation by Nitrogen Heterocycles: A Review

Several nitrogen heterocyclic analogues have been applied to clinical practice, and about 75% of drugs approved by the FDA contain at least a heterocyclic moiety. Thus, nitrogen heterocycles are beneficial scaffolds that occupy a central position in the development of new drugs. The fact that certain nitrogen heterocyclic compounds significantly activate the NRF2/ARE signaling pathway and upregulate the expression of NRF2-dependent genes, especially HO-1 and NQO1, underscores the need to study the roles and pharmacological effects of N-based heterocyclic moieties in NRF2 activation. Furthermore, nitrogen heterocycles exhibit significant antioxidant and anti-inflammatory activities. NRF2-activating molecules have been of tremendous research interest in recent times due to their therapeutic roles in neuroinflammation and oxidative stress-mediated diseases. A comprehensive review of the NRF2-inducing activities of N-based heterocycles and their derivatives will broaden their therapeutic prospects in a wide range of diseases. Thus, the present review, as the first of its kind, provides an overview of the roles and effects of nitrogen heterocyclic moieties in the activation of the NRF2 signaling pathway underpinning their antioxidant and anti-inflammatory actions in several diseases, their pharmacological properties and structural-activity relationship are also discussed with the aim of making new discoveries that will stimulate innovative research in this area.

Protective effect of lactobacillus plantarum on alcoholic liver injury and regulating of keap-Nrf2-ARE signaling pathway in zebrafish larvae

This research investigated the protective effect of lactobacillus plantarum against alcohol-induced liver injury and the regulatory mechanism of Keap-Nrf2-ARE signal pathway in zebrafish. Firstly, a zebrafish alcoholic liver injury model was established using1.0mM of ethanol concentration, then two forms of lactobacillus plantarum treatment were designed to perform repair, including a lactobacillus plantarum thallus suspension (LPS) and a lactobacillus plantarum thallus breaking solution (LPBS). After 24h of alcohol injury, lactobacillus plantarum concentrations of 0, 1.0×105, 1.0×106, 1.0×107 and 1.5×107 cfu/mL were added to protect zebrafish larvae. Then with the treatment of lactobacillus plantarum after 48h, activities of alanine transaminase (ALT), aspartate transaminase (AST), superoxide dismutase (SOD) and malondialdehyde (MDA) in zebrafish tissue homogenate were respectively determined. Keap-Nrf2-ARE signal pathway related gene expression conditions were also analyzed, including nuclear factor (erythroid-derived 2)-like 2(Nrf2), Kelch like ECH associated protein 1(Keap1), catalase(CAT), hemooxygenase1(HO1) and Glutathione S-Transferase Kappa 1(gstk1). Results showed that: in comparison with the control group, the LPBS with dosage of 1.0×107 cfu/mL remarkably improved the activities of SOD, CAT, HO1and gstk1 in zebrafish larvae liver (P<0.05), resulting in significant increase of the protein expression level of Nrf2 (225.78%) and suppression of Keap1 gene expression (73.67%)(P<0.01). As confirmed by the results, lactobacillus plantarum activated the Keap-Nrf2-ARE signal pathway from the level of transcription, the up-regulation of the expression quantity of Nrf2 protected the organism from oxidative stress and maximally reduced liver injury.

Insecticides induce the co-expression of glutathione S-transferases through ROS/CncC pathway in Spodoptera exigua

Glutathione S-transferases (GSTs) are a family of multifunctional enzymes that are involved in detoxification of electrophilic toxic compounds. Although the co-induced expression of GST genes by insecticides in insects has been documented in recent years, the underlying regulatory mechanisms are not understood. In this study, a total of thirty-one cytosolic S. exigua GSTs (SeGSTs) was cloned and identified. The bioinformatics and gene expression patterns were also analyzed. Out of them, SeGSTe9, SeGSTs6, SeGSTe1, SeGSTe6, SeGSTe8, SeGSTe14, and SeGSTd1 were significantly co-expressed following exposure to three insecticides (lambda-cyhalothrin, chlorpyrifos and chlorantraniliprole). The analysis of upstream sequences revealed that all of these seven SeGSTs harbored CncC/Maf binding site. The luciferase reporter assay showed that the pGL3-SeGST promoter construct exhibited a significant increase in luciferase activities after exposure to insecticides, and mutation of CncC/Maf binding site diminish the induction effect. These data indicate that CncC/Maf pathway regulates the co-expression of GST genes in response to different insecticides in S. exigua. Insecticides significantly enhanced the ROS content and treatment with the ROS inhibitor N-acetylcysteine (NAC) decreased the insecticide-induced luciferase activities of the PGL3-GSTe6 promoter construct, but not the CncC-mutated construct. These results indicate that ROS mediates GST gene expression after exposure to insecticides through CncC/Maf pathway. Overall, these data show that insecticides induce the co-expression of glutathione S-transferases through the ROS/CncC pathway in S. exigua.

Excessive alcohol consumption induces methane production in humans and rats

Various studies have established the possibility of non-bacterial methane (CH₄) generation in oxido-reductive stress conditions in plants and animals. Increased ethanol input is leading to oxido-reductive imbalance in eukaryotes, thus our aim was to provide evidence for the possibility of ethanol-induced methanogenesis in non-CH₄ producer humans, and to corroborate the in vivo relevance of this pathway in rodents. Healthy volunteers consumed 1.15 g/kg/day alcohol for 4 days and the amount of exhaled CH₄ was recorded by high sensitivity photoacoustic spectroscopy. Additionally, Sprague-Dawley rats were allocated into control, 1.15 g/kg/day and 2.7 g/kg/day ethanol-consuming groups to detect the whole-body CH₄ emissions and mitochondrial functions in liver and hippocampus samples with high-resolution respirometry. Mitochondria-targeted L-alpha-glycerylphosphorylcholine (GPC) can increase tolerance to liver injury, thus the effects of GPC supplementations were tested in further ethanol-fed groups. Alcohol consumption was accompanied by significant CH₄ emissions in both human and rat series of experiments. 2.7 g/kg/day ethanol feeding reduced the oxidative phosphorylation capacity of rat liver mitochondria, while GPC significantly decreased the alcohol-induced CH₄ formation and hepatic mitochondrial dysfunction as well. These data demonstrate a potential for ethanol to influence human methanogenesis, and suggest a biomarker role for exhaled CH₄ in association with mitochondrial dysfunction.

Interstrain differences in the expression and activity of Cyp2a5 in the mouse liver

Background

Cytochrome P450 2A5 (Cyp2a5), a mouse enzyme orthologous of human CYP2A6, catalyzes a number of toxicologically important reactions, including the metabolism of nicotine, aflatoxin B1, and several other xeno- and endobiotics. Cyp2a5 expression is complex and not yet fully understood. We investigated inter-strain differences in the activity and mRNA expression of hepatic Cyp2a5. Cyp1a1/2 and Cyp2b9/10 activities were evaluated for comparative purposes. Data on the interstrain differences in the expression and activity of Cyp2a5 are important to select a suitable mouse model for studying CYP2A6-mediated metabolism.

Results

Activity of Cyp2a5 (coumarin 7-hydroxylase) was highest in DBA-2 and DBA-1, intermediate in B6D2F1 (hybrid) and low in the remaining strains (C57BL/6, C57BL/10, CBA, BALB/cAn, SW). Contrasting with the activity, background levels of Cyp2a4/5 mRNA did not differ between high- and low-activity murine strains. Phenobarbital (PB, 80 mg/kg body weight/day × 3 days, i.p.) increased Cyp2a5, Cyp1a1/2 (ethoxyresorufin-O-deethylase) and Cyp2b9/10 (bezyloxyresorufin-O-debenzylase) activities while only Cyp2a5 was enhanced by pyrazole (PYR, 100 mg/kg body weight/day × 3 days, i.p.). Inductions of Cyp2a5 activity by PYR and PB were accompanied by increases of Cyp2a4/5 mRNA. PYR and PB did not upregulate heme oxygenase-1 (hmox-1) mRNA expression in any strain, a finding that is apparently at odds with the notion that Cyp2a5 and hmox-1 inductions are coordinated events.

Conclusions

Since background levels of Cyp2a4/5 gene transcripts of high-activity strains did not differ from those of low-activity mice, distinct constitutive activities did not result from different transcription rates and/or mRNA half-lives. Results therefore suggested that interstrain differences in constitutive activity of Cyp2a5 possibly arise from distinct translation efficiencies, protein half-lives and/or enzyme kinetics toward the substrate. Data from this study indicated that all tested strains are suitable models for studying toxicants that are substrates for human CYP2A6; DBA-2, DBA-1 and the hybrid B62DF1, however, have the advantage of presenting high constitutive activities of Cyp2a5.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-017-2435-x) contains supplementary material, which is available to authorized users.

Alcoholic Liver Disease: from CYP2E1 to CYP2A5

This article reviews recent studies on CYP2E1-mediated alcoholic liver injury, the induction of CYP2A5 by alcohol and the mechanism for this upregulation, especially the permissive role of CYP2E1 in the induction of CYP2A5 by alcohol and the CYP2E1-ROS-Nrf2 pathway, and protective effects of CYP2A5 against ethanol-induced oxidative liver injury. Ethanol can induce CYP2E1, an active generator of reactive oxygen species (ROS), and CYP2E1 is a contributing factor for alcoholinduced oxidative liver injury. CYP2A5, another isoform of cytochrome P450, can also be induced by ethanol. Chronic feeding of ethanol to wild type mice increased CYP2A5 catalytic activity, protein and mRNA levels as compared to pair-fed controls. This induction was blunted in CYP2E1 knockout (cyp2e1-/-) mice but was restored when human CYP2E1 was reintroduced and expressed in cyp2e1-/- mice. Ethanol-induced CYP2E1 co-localized with CYP2A5 and preceded the elevation of CYP2A5. The antioxidants N-acetyl cysteine and vitamin C lowered the alcohol elevation of ROS and blunted the alcohol induction of CYP2A5, but not CYP2E1, suggesting ROS play a novel role in the crosstalk between CYP2E1 and CYP2A5. The antioxidants blocked the activation of Nrf2, a transcription factor known to upregulate expression of CYP2A5. When alcohol-induced liver injury was enhanced in Nrf2 knockout (Nrf2-/-) mice, alcohol elevation of CYP2A5 but not CYP2E1 was also lower in Nrf2-/- mice. CYP2A5 knockout (cyp2a5-/-) mice exhibited an enhanced alcoholic liver injury compared with WT mice as indicated by serum ALT, steatosis and necroinflammation. Alcohol-induced hyperglycemia were observed in cyp2a5-/- mice but not in WT mice.

An improved in vitro method for screening toxin and medicine targeting CYP2E1

The cytochrome P450 enzyme 2E1 (CYP2E1) presents in both microsome and mitochondrion, which influences the metabolism of many xenobiotics. The mice active liver homogenate was prepared for the medicinal incubation and mitochondrion was extracted for chemical screening targeting CYP2E1 enzyme. Representative CYP2E1 inducers (ethanol and pyrazole) and inhibitors (diallyldisulfide and kaempferol) were applied to evaluate the effectiveness of homogenate-mitochondrial system. In parallel, the in-vitro microsomal method targeting CYP2E1 was also operated for comparison. The results showed that in homogenate-mitochondrial method, the protein level and activity of CYP2E1 were increased by ethanol and pyrazole; reduced by diallyldisulfide and kaempferol, and this homogenate-mitochondrial method is convenient with good repeatability and reproducibility in screening chemicals targeting CYP2E1, especially for the inducers. Thus, the homogenate-mitochondrial method might be effective in screening both CYP2E1 inhibitor and inducer.

The role of CYP2A5 in liver injury and fibrosis: chemical-specific difference

Liver injuries induced by carbon tetrachloride (CCL4) or thioacetamide (TAA) are dependent on cytochrome P450 2E1 (CYP2E1). CYP2A5 can be induced by TAA but not by CCL4. In this study, liver injury including fibrosis induced by CCL4 or TAA were investigated in wild-type (WT) mice and CYP2A5 knockout (cyp2a5 (-/-) ) mice as well as in CYP2E1 knockout (cyp2e1 (-/-) ) mice as a comparison. Acute and subchronic liver injuries including fibrosis were induced by CCL4 and TAA in WT mice but not in cyp2e1 (-/-) mice, confirming the indispensable role of CYP2E1 in CCL4 and TAA hepatotoxicity. WT mice and cyp2a5 (-/-) mice developed comparable acute liver injury induced by a single injection of CCL4 as well as subchronic liver injury including fibrosis induced by 1 month of repeated administration of CCL4, suggesting that CYP2A5 does not affect CCL4-induced liver injury and fibrosis. However, while 200 mg/kg TAA-induced acute liver injury was comparable in WT mice and cyp2a5 (-/-) mice, 75 and 100 mg/kg TAA-induced liver injury were more severe in cyp2a5 (-/-) mice than those found in WT mice. After multiple injections with 200 mg/kg TAA for 1 month, while subchronic liver injury as indicated by serum aminotransferases was comparable in WT mice and cyp2a5 (-/-) mice, liver fibrosis was more severe in cyp2a5 (-/-) mice than that found in WT mice. These results suggest that while both CCL4- and TAA-induced liver injuries and fibrosis are CYP2E1 dependent, under some conditions, CYP2A5 may protect against TAA-induced liver injury and fibrosis, but it does not affect CCL4 hepatotoxicity.

Intestinal NF-E2-related factor-2 expression and antioxidant activity changes in rats undergoing orthotopic liver autotransplantation

Liver transplantation is known to trigger intestinal injuries. Oxidative damage that is induced by reactive oxygen species (ROS) plays a crucial role in ischemia-reperfusion injuries. NF-E2-related factor-2 (Nrf2) and its modulated antioxidant enzymes form the critical endogenous antioxidant system to scavenge ROS. The present study investigated the dynamic changes of intestinal ROS levels, Nrf2 expression and antioxidant enzyme activity following orthotopic liver autotransplantation (OLAT). Sprague-Dawley rats were randomly divided into five groups consisting of one sham group and four groups with rats that underwent OLAT and were evaluated following 4, 8, 16 and 24 h, respectively. The intestinal specimens were collected for histopathological examination and the detection of hydrogen peroxide (H₂O₂), hydroxyl radical (^•OH), malondialdehyde (MDA), reduced glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT) levels and the expression of Nrf2. The present study demonstrated that OLAT resulted in severe intestinal injury, which manifested as a significant change in the intestine pathological scores as early as 4 h and peaking at 8 h post-treatment. Oxidative stress was also revealed by the increase of the H₂O₂, ^•OH and MDA levels. Significant decreases were observed in the activity of SOD and CAT and a dramatic decrease occurred in the levels of GSH at 4 and 8 h post-treatment. All the parameters were restored gradually at 16 and 24 h post-treatment. The expression of Nrf2 in the intestinal tissues increased significantly at 4, 16 and 24 h following OLAT. The present study shows that an imbalance between oxidants and antioxidants contributes to intestinal oxidative injury, and that the upregulation of Nrf2 is not sufficient to withstand intestinal oxidative injury following OLAT.

Experimental nonalcoholic fatty liver disease in mice leads to cytochrome p450 2a5 upregulation through nuclear factor erythroid 2-like 2 translocation

Mouse cytochrome P450 2A5 (CYP2A5) is upregulated in various liver diseases and a putative common feature for all of these conditions is altered cellular redox status. Nuclear factor erythroid 2-like 2 (Nrf2) is a transcription factor that is post-translationally regulated by oxidative stress and controls the transcription of protective target genes. In the present study, we have characterized the regulation of CYP2A5 by Nrf2 and evaluated gene expression, protein content and activity of anti-oxidant enzymes in the Nrf2^+/+ and Nrf2^−/− mice model of non-alcoholic fatty liver (NAFLD). After eight weeks of feeding on a high-fat diet, livers from Nrf2^−/− mice showed a substantial increase in macro and microvesicular steatosis and a massive increase in the number of neutrophil polymorphs, compared to livers from wild-type mice treated similarly. Livers of Nrf2^−/− mice on the high-fat diet exhibited more oxidative stress than their wild-type counterparts as assessed by a significant depletion of reduced glutathione that was coupled with increases in malondialdehyde. Furthermore, results in Nrf2-deficient mice showed that CYP2A5 expression was significantly attenuated in the absence of Nrf2, as was found with the conventional target genes of Nrf2. The treatment of wild-type mice with high-fat diet leaded to nuclear accumulation of Nrf2, and co-immunoprecipitation experiments showed that Nrf2 was bound to Cyp2a5. These findings suggest that the high-fat diet induced alteration in cellular redox status and induction of CYP2A5 was modulated through the redox-sensitive transcription Nrf2.

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CYP2A5 up-regulation in response to NAFLD was Nrf2 dependent.

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NAFLD induces oxidant stress.

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A protective role for Nrf2 against hepatic damage by NAFLD was demonstrated.

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NAFLD induces translocation of Nrf2 from the cytoplasm to the nucleus.

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Nrf2 binding to CYP2a5 was shown.

Nuclear erythroid 2-related factor 2: a novel potential therapeutic target for liver fibrosis

Hepatic stellate cells (HSC) are the key fibrogenic cells of the liver. HSC activation is a process of cellular transdifferentiation that occurs upon liver injury, but the mechanisms underlying liver fibrosis are unknown. Nuclear erythroid 2-related factor 2 (Nrf2) is an oxidative stress-mediated transcription factor with a variety of downstream targets aimed at cytoprotection. However, Nrf2 has recently been implicated as a new therapeutic target for the treatment of liver fibrosis. This review focuses on the transcriptional repressors that either control liver injury or regulate specific fibrogenic functions of liver fibrosis. We also show that Nrf2 may reveal significant gene expression changes, suggesting that Nrf2 activation may ameliorate liver fibrosis.

Whole grains, type 2 diabetes, coronary heart disease, and hypertension: links to the aleurone preferred over indigestible fiber

Higher whole grain cereal intakes are associated with substantially lower risks of type 2 diabetes, coronary heart disease, and hypertension. These reduced risks have been established in large prospective studies that now include millions of person-years of follow-up. We analyze the results of 11 major prospective studies to provide recommendations about whole grain consumption. The following review establishes the amount of whole grains that should ideally be consumed based on prospective evidence; defines the nature of whole grains; identifies that the whole grain evidence is robust and not due to confounding; and provides a detailed assessment of several potential mechanisms for the effect of whole grains on health. We draw the following conclusions. Firstly, to maintain health, 40 grams or more of whole grains should be consumed daily. This is about a bowl of whole grain breakfast cereal daily, but 80% of the population does not achieve this. Secondly, aleurone in bran is a critical grain component generally overlooked in favor of indigestible fiber. Live aleurone cells constitute 50% of millers' bran. They store minerals, protein, and the antioxidant ferulic acid, and are clearly more than just indigestible fiber. Finally, we suggest potential roles for magnesium, zinc, and ferulic acid in the development of chronic disease. If the results of prospective studies were applied to the life-style practices of modern societies there exists the potential for enormous personal health and public financial benefits.

Peroxiredoxin III and sulfiredoxin together protect mice from pyrazole-induced oxidative liver injury

AIMS

To define the mechanisms underlying pyrazole-induced oxidative stress and the protective role of peroxiredoxins (Prxs) and sulfiredoxin (Srx) against such stress.

RESULTS

Pyrazole increased Srx expression in the liver of mice in a nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent manner and induced Srx translocation from the cytosol to the endoplasmic reticulum (ER) and mitochondria. Pyrazole also induced the expression of CYP2E1, a primary reactive oxygen species (ROS) source for ethanol-induced liver injury, in ER and mitochondria. However, increased CYP2E1 levels only partially accounted for the pyrazole-mediated induction of Srx, prompting the investigation of CYP2E1-independent ROS generation downstream of pyrazole. Indeed, pyrazole increased ER stress, which is known to elevate mitochondrial ROS. In addition, pyrazole up-regulated CYP2E1 to a greater extent in mitochondria than in ER. Accordingly, among Prxs I to IV, PrxIII, which is localized to mitochondria, was preferentially hyperoxidized in the liver of pyrazole-treated mice. Pyrazole-induced oxidative damage to the liver was greater in PrxIII(-/-) mice than in wild-type mice. Such damage was also increased in Srx(-/-) mice treated with pyrazole, underscoring the role of Srx as the guardian of PrxIII.

INNOVATION

The roles of Prxs, Srx, and ER stress have not been previously studied in relation to pyrazole toxicity.

CONCLUSION

The concerted action of PrxIII and Srx is important for protection against pyrazole-induced oxidative stress arising from the convergent induction of CYP2E1-derived and ER stress-derived ROS in mitochondria.

Effect of copper overload on the survival of HepG2 and A-549 human-derived cells

We investigated the effect of copper (Cu) overload (20–160 µM/24 h) in two cell lines of human hepatic (HepG2) and pulmonary (A-549) origin by determining lipid and protein damage and the response of the antioxidant defence system. A-549 cells were more sensitive to Cu overload than HepG2 cells. A marked increase was observed in both the cell lines in the nitrate plus nitrite concentration, protein carbonyls and thiobarbituric acid reactive substances (TBARS). The TBARS increase was consistent with an increment in saturated fatty acids at the expense of polyunsaturated acids in a Cu concentration-dependent fashion. Antioxidant enzymes were stimulated by Cu overload. Superoxide dismutase activity increased significantly in both the cell lines, with greater increases in HepG2 than in A-549 cells. A marked increase in ceruloplasmin and metallothionein content in both the cell types was also observed. Dose-dependent decreases in α-tocopherol and ferric reducing ability were observed. Total glutathione content was lower in A-549 cells and higher in HepG2. Calpain and caspase-3 were differentially activated in a dose-dependent manner under copper-induced reactive oxygen species production. We conclude that Cu exposure of human lung- and liver-derived cells should be considered a reliable experimental system for detailed study of mechanism/mechanisms by which Cu overload exerts its deleterious effects.

Ethanol induction of CYP2A5: role of CYP2E1-ROS-Nrf2 pathway

Chronic ethanol consumption was previously shown to induce CYP2A5 in mice, and this induction of CYP2A5 by ethanol was CYP2E1 dependent. In this study, the mechanisms of CYP2E1-dependent ethanol induction of CYP2A5 were investigated. CYP2E1 was induced by chronic ethanol consumption to the same degree in wild-type (WT) mice and CYP2A5 knockout (Cyp2a5 (-/-)) mice, suggesting that unlike the CYP2E1-dependent ethanol induction of CYP2A5, ethanol induction of CYP2E1 is not CYP2A5 dependent. Microsomal ethanol oxidation was about 25% lower in Cyp2a5 (-/-) mice compared with that in WT mice, suggesting that CYP2A5 can oxidize ethanol although to a lesser extent than CYP2E1 does. CYP2A5 was induced by short-term ethanol consumption in human CYP2E1 transgenic knockin (Cyp2e1 (-/-) KI) mice but not in CYP2E1 knockout (Cyp2e1 (-/-)) mice. The redox-sensitive transcription factor nuclear factor-erythroid 2-related factor 2 (Nrf2) was also induced by acute ethanol in Cyp2e1 (-/-) KI mice but not in Cyp2e1 (-/-) mice. Ethanol induction of CYP2A5 in Nrf2 knockout (Nrf2 (-/-)) mice was lower compared with that in WT mice, whereas CYP2E1 induction by ethanol was comparable in WT and Nrf2 (-/-) mice. Antioxidants (N-acetyl-cysteine and vitamin C), which blocked oxidative stress induced by chronic ethanol in WT mice and acute ethanol in Cyp2e1 (-/-) KI mice, also blunted the induction of CYP2A5 and Nrf2 by ethanol but not the induction of CYP2E1 by ethanol. These results suggest that oxidative stress induced by ethanol via induction of CYP2E1 upregulates Nrf2 activity, which in turn regulates ethanol induction of CYP2A5. Results obtained from primary hepatocytes, mice gavaged with binge ethanol or fed chronic ethanol, show that Nrf2-regulated ethanol induction of CYP2A5 protects against ethanol-induced steatosis.

Alpha-lipoic acid attenuates methionine choline deficient diet-induced steatohepatitis in C57BL/6 mice

AIMS

Non-alcoholic steatohepatitis (NASH) is a liver disease that causes fat accumulation, inflammation and fibrosis. Increased oxidative stress contributes to hepatic inflammation and fibrosis by upregulation of Cytochrome P450 2E1 (CYP2E1), endoplasmic reticulum (ER) stress and mitogen-activated protein kinase (MAPK) activity. This study examined whether alpha-lipoic acid (ALA), a naturally occurring thiol antioxidant, prevents steatohepatitis through the inhibition of several pathways involved in hepatic inflammation and fibrosis.

MAIN METHODS

C57BL/6 mice were fed an MCD diet with or without ALA for 4weeks. Liver sections from mice on control or MCD diets with or without ALA were stained with hematoxylin-eosin, oil red O, and anti-4-HNE antibody. The effects of ALA on methionine-choline deficient MCD-diet induced plasma AST and ALT as well as tissue TBARS were measured. The effects of ALA on CYP2E1 expression, ER stress, MAPK levels, and NF-κB activity in MCD diet-fed mice liver were measured by northern and western blot analysis.

KEY FINDINGS

Dietary supplementation with ALA reduced MCD diet-induced hepatic lipid accumulation, hepatic inflammation, TBARS, 4-HNE, and plasma ALT and AST levels. These effects were associated with a reduced expression of CYP2E1 and reduced ER stress and MAPK and NF-κB activity.

SIGNIFICANCE

Taken together, the results of the present study indicate that ALA attenuates steatohepatitis through inhibition of several pathways, and provide the possibility that ALA can be used to prevent the development and progression of non-alcoholic fatty liver disease in patients who have strong risk factors for NASH.

The role of Nrf2 in migration and invasion of human glioma cell U251

OBJECTIVE

NF-E2-related factor 2 (Nrf2) is a transcription factor that is related to tumor cell multidrug resistance and proliferation. Here we studied the involvement of Nrf2 in the migration and invasion of human U251 glioma cells.

METHODS

Two kinds of plasmid, that is, pEGFP-Nrf2 and Si-Nrf2, were constructed and transfected to upregulate or downregulate the expression of Nrf2 in U251 glioma cell line. Blank vectors or random siRNA plasmid were used as negative control. Cells treated with lipofectamine only were set up as blank control. Protein and mRNA level of Nrf2 and matrix metalloproteinase 9 (MMP9) were investigated by reverse transcriptase-polymerase chain reaction and western blot after transfection. Wound healing assay and transwell assay were used to study migration and invasion of U251 after transfection. Gelatin zymography was performed to reveal the change of MMP9 activity after transfection.

RESULTS

The mRNA and protein level of Nrf2 was upregulated in U251-pEGFP-Nrf2 while downregulated in U251-Si-Nrf2 48 hours after transfection. In the wound healing assay, there were more cells in group pEGFP-Nrf2 crossing the scratch line than in group Si-Nrf2. Furthermore, in transwell migration and invasion assay, there were more cells in group pEGFP-Nrf2 penetrating the membranes than in group Si-Nrf2. Then we investigated the change of MMP9 activity, mRNA, and protein levels after transfection. The results suggested that upregulation of Nrf2 led to an increase in MMP9 expression and activity whereas downregulation of Nrf2 led to a decrease in MMP9 expression and activity.

CONCLUSION

Nrf2 is involved in migration and invasion of U251 cells, which may be related to MMP9.

The protective effect of ENA Actimineral resource A on CCl4-induced liver injury in rats

ENA Actimineral Resource A (ENA-A) is alkaline water that is composed of refined edible cuttlefish bone and two different species of seaweed, Phymatolithon calcareum and Lithothamnion corallioides. In the present study, ENA-A was investigated as an antioxidant to protect against CCl(4)-induced oxidative stress and hepatotoxicity in rats. Liver injury was induced by either subacute or chronic CCl(4) administration, and the rats had free access to tap water mixed with 0% (control group) or 10% (v/v) ENA-A for 5 or 8 weeks. The results of histological examination and measurement of antioxidant activity showed that the reactive oxygen species production, lipid peroxidation, induction of CYP2E1 were decreased and the antioxidant activity, including glutathione and catalase production, was increased in the ENA-A groups as compared with the control group. On 2-DE gel analysis of the proteomes, 13 differentially expressed proteins were obtained in the ENA-A groups as compared with the control group. Antioxidant proteins, including glutathione S-transferase, kelch-like ECH-associated protein 1, and peroxiredoxin 1, were increased with hepatocyte nuclear factor 3-beta and serum albumin precursor, and kininogen precursor decreased more in the ENA-A groups than compared to the control group. In conclusion, our results suggest that ENA-A does indeed have some protective capabilities against CCl(4)-induced liver injury through its antioxidant function.

Ethanol induction of CYP2A5: permissive role for CYP2E1

CYP2A5 metabolizes xenobiotics and activates hepatocarcinogens, and induction occurs in response to hepatic damage and cellular stress. We evaluated whether ethanol can elevate CYP2A5 and whether CYP2E1 plays a role in the ethanol induction of CYP2A5. Wild-type (WT), CYP2E1 knockout (KO), and CYP2E1 knockin (KI) mice were fed ethanol for 3 weeks. Ethanol increased CYP2E1 and CYP2A5 protein and activity in WT mice but not in the KO mice. Induction of CYP2A5 (and CYP2E1) was restored in the KI mice. Ethanol induction of CYP2A5 occurred only after CYP2E1 was first induced. Immunohistochemical staining revealed that CYP2E1 and CYP2A5 colocalize to the same zones in the liver. Ethanol also elevated CYP2A5 mRNA levels in WT and KI mice but not in KO mice. Induction of CYP2A5 by cadmium was partially decreased in KO mice compared with WT or KI mice. Ethanol elevated CYP2A4 mRNA levels in all mice although the extent of induction was lowest in the KO mice. In summary, ethanol elevated mouse hepatic CYP2A5 levels, which may be of toxicological significance because CYP2A5 metabolizes nicotine and other drugs and activates hepatocarcinogens. Induction of CYP2A5 by ethanol is potentiated by the induction of CYP2E1. We speculate that ethanol induction of CYP2E1 followed by increases in reactive oxygen species and activation of Nrf2 are important steps in the mechanism by which ethanol induces CYP2A5. The possibility that induction of CYP2E1 is permissive for the induction of CYP2A5 may reflect a new contribution by CYP2E1 to the actions of ethanol.

Cytochrome P450 2A5 constitutive expression and induction by heavy metals is dependent on redox-sensitive transcription factor Nrf2 in liver

Mouse cytochrome P450 2A5 (CYP2A5) is upregulated in various pathophysiological liver diseases and induced by structurally variable hepatotoxic chemicals. A putative common feature for all of these conditions is altered cellular redox status. Nuclear factor erythroid 2-like 2 (Nrf2) is a transcription factor that is post-translationally regulated by oxidative stress and controls the transcription of numerous protective target genes. In the present study, we have extensively characterized the regulation of Cyp2a5 by Nrf2 and compared it to a well-characterized target gene Hmox1. The treatment of mouse primary hepatocytes with lead chloride, methylmercury chloride, or phenethyl isothiocyanate all leads to nuclear accumulation of Nrf2. Both CYP2A5 and HMOX1 were induced by all three compounds; however, HMOX1 responded more rapidly and transiently as compared to CYP2A5. Experiments in Nrf2(-/-) primary hepatocytes showed that Nrf2 is crucial for CYP2A5 induction but not for elevation of HMOX1. Both CYP2A5 and HMOX1 were upregulated by Nrf2 overexpression and downregulated by Keap1 or Bach1 overexpression. However, in all cases, CYP2A5 responded much more potently. Results in Nrf2-deficient animals showed that CYP2A5 expression is significantly attenuated in the absence of Nrf2, while expression of HMOX1 was unaffected. Therefore, Cyp2a5 joins the group of genes constitutively regulated by Nrf2. Our current results unequivocally show that expression of CYP2A5 is tightly controlled by Nrf2 in liver. Nrf2 is needed for constitutive expression of CYP2A5, and CYP2A5 is also sensitively upregulated by an increased level of Nrf2 protein. Therefore, CYP2A5 upregulation could be a useful indicator for hepatic activation of the Nrf2 pathway.

Proteomic analysis of Nrf2 deficient transgenic mice reveals cellular defence and lipid metabolism as primary Nrf2-dependent pathways in the liver

The transcription factor Nrf2 regulates expression of multiple cellular defence proteins through the antioxidant response element (ARE). Nrf2-deficient mice (Nrf2(-/-)) are highly susceptible to xenobiotic-mediated toxicity, but the precise molecular basis of enhanced toxicity is unknown. Oligonucleotide array studies suggest that a wide range of gene products is altered constitutively, however no equivalent proteomics analyses have been conducted. To define the range of Nrf2-regulated proteins at the constitutive level, protein expression profiling of livers from Nrf2(-/-) and wild type mice was conducted using both stable isotope labelling (iTRAQ) and gel electrophoresis methods. To establish a robust reproducible list of Nrf2-dependent proteins, three independent groups of mice were analysed. Correlative network analysis (MetaCore) identified two predominant groups of Nrf2-regulated proteins. As expected, one group comprised proteins involved in phase II drug metabolism, which were down-regulated in the absence of Nrf2. Surprisingly, the most profound changes were observed amongst proteins involved in the synthesis and metabolism of fatty acids and other lipids. Importantly, we show here for the first time, that the enzyme ATP-citrate lyase, responsible for acetyl-CoA production, is negatively regulated by Nrf2. This latter finding suggests that Nrf2 is a major regulator of cellular lipid disposition in the liver.

Nrf2 the rescue: effects of the antioxidative/electrophilic response on the liver

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that positively regulates the basal and inducible expression of a large battery of cytoprotective genes. These gene products include proteins that catalyze reduction reactions (NAD(P)H:quinone oxidoreductase 1, Nqo1), conjugation reactions (glutathione-S-transferases, Gsts and UDP-glucuronosyltransferases, Ugts), as well as the efflux of potentially toxic xenobiotics and xenobiotic conjugates (multidrug resistance-associated proteins, Mrps). The significance of Nrf2 in the liver has been established, as livers of Nrf2-null mice are more susceptible to various oxidative/electrophilic stress-induced pathologies than wild-type mice. In contrast, both pharmacological and genetic models of hepatic Nrf2 activation are protective against oxidative/electrophilic stress. Furthermore, because certain Nrf2-target genes in the liver could affect the distribution, metabolism, and excretion of xenobiotics, the effects of Nrf2 on the kinetics of drugs and other xenobiotics should also be considered, with a special emphasis on metabolism and excretion. Therefore, this review highlights the research that has contributed to the understanding of the importance of Nrf2 in toxicodynamics and toxicokinetics, especially that which pertains to the liver.

Nrf2 and antioxidant defense against CYP2E1 toxicity

The transcription factor Nrf2 regulates the expression of important cytoprotective enzymes. Induction of CYP2E1 is one of the central pathways by which ethanol generates oxidative stress. CYP2E1 can be induced by ethanol and several low molecular mass chemicals such as pyrazole. This review discusses biochemical and toxicological effects of CYP2E1 and the effects of Nrf2 in modulating these actions of CYP2E1. Besides ethanol, CYP2E1 metabolizes and activates many other toxicologic important compounds. One approach to try to understand the basic effects and actions of CYP2E1 was to establish HepG2 cell lines that constitutively express human CYP2E1. Ethanol, polyunsaturated fatty acids and iron were toxic to the HepG2 cells, which express CYP2E1 (E47 cells) but not control C34HepG2 cells, which do not express CYP2E1. Toxicity was associated with enhanced oxidant stress and could be prevented by antioxidants and potentiated if glutathione was removed. The E47 cells had higher glutathione levels and a twofold increase in catalase, cytosolic and microsomal glutathione transferase, and heme oxygenase-1 than control HepG2 cells due to activation of their respective genes. These activations were prevented by antioxidants, suggesting that reactive oxygen species generated by CYP2E1 were responsible for the upregulation of these antioxidant genes. This upregulation may reflect an adaptive mechanism to remove CYP2E1-derived oxidants. Increases in Nrf2 protein and mRNA were observed in livers of chronic alcohol-fed mice or rats and of pyrzole-treated rats or mice, conditions known to elevate CYP2E1. E47 cells showed increased Nrf2 mRNA and protein expression compared with control HepG2 C34 cells. Upregulation of antioxidant genes in E47 cells is dependent on Nrf2 and is prevented by siRNA-Nrf2. Blocking Nrf2 by siRNA-Nrf2 decreases glutathione and increases reactive oxygen species and lipid peroxidation, resulting in decreased mitochondrial membrane potential and loss of cell viability of E47 cells, but not C34 cells. Nrf2 is activated and levels of Nrf2 protein and mRNA are increased when CYP2E1 is elevated. These results suggest that Nrf2 plays a key role in the adaptive response against increased oxidative stress caused by CYP2E1 in the HepG2 cells. However, it is not clear whether Nrf2 is protective against CYP2E1 toxicity in vivo as pyrazole which elevates CYP2E1 in wild-type mice did not elevate CYP2E1 in Nrf2 knockout mice, although pyrazole produced toxicity in the Nrf2 knockout mice.