The transcriptional activation of the human copper/zinc superoxide dismutase gene by 2,3,7,8-tetrachlorodibenzo-p-dioxin through two different regulator sites, the antioxidant responsive element and xenobiotic responsive element

Omeprazole attenuates hyperoxic injury in H441 cells via the aryl hydrocarbon receptor

Hyperoxia contributes to the development of bronchopulmonary dysplasia in premature infants. Earlier we observed that aryl hydrocarbon receptor (AhR)-deficient mice are more susceptible to hyperoxic lung injury than AhR-sufficient mice, and this phenomenon was associated with a lack of expression of cytochrome P450 1A enzymes. Omeprazole, a proton pump inhibitor used in humans with gastric acid-related disorders, activates AhR in hepatocytes in vitro. However, the effects of omeprazole on AhR activation in the lungs and its impact on hyperoxia-induced reactive oxygen species (ROS) generation and inflammation are unknown. In this study, we tested the hypothesis that omeprazole attenuates hyperoxia-induced cytotoxicity, ROS generation, and expression of monocyte chemoattractant protein-1 (MCP-1) in human lung-derived H441 cells via AhR activation. Experimental groups included cells transfected with AhR small interfering RNA (siRNA). Hyperoxia resulted in significant increases in cytotoxicity, ROS generation, and MCP-1 production, which were significantly attenuated with the functional activation of AhR by omeprazole. The protective effects of omeprazole on cytotoxicity, ROS production, and MCP-1 production were lost in H441 cells whose AhR gene was silenced by AhR siRNA. These findings support the hypothesis that omeprazole protects against hyperoxic injury in vitro via AhR activation that is associated with decreased ROS generation and expression of MCP-1.

Omeprazole attenuates hyperoxic lung injury in mice via aryl hydrocarbon receptor activation and is associated with increased expression of cytochrome P4501A enzymes

Hyperoxia contributes to lung injury in experimental animals and bronchopulmonary dysplasia (BPD) in preterm infants. Cytochrome P4501A (CYP1A) enzymes, which are regulated by the aryl hydrocarbon receptor (AhR), have been shown to attenuate hyperoxic lung injury in rodents. Omeprazole, a proton pump inhibitor, used in humans to treat gastric acid-related disorders, induces hepatic CYP1A in vitro. However, the mechanism by which omeprazole induces CYP1A and its impact on CYP1A expression in vivo and hyperoxic lung injury are unknown. Therefore, we tested the hypothesis that omeprazole attenuates hyperoxic lung injury in adult wild-type (WT) C57BL/6J mice by an AhR-mediated induction of pulmonary and hepatic CYP1A enzymes. Accordingly, we determined the effects of omeprazole on pulmonary and hepatic CYP1A expression and hyperoxic lung injury in adult WT and AhR dysfunctional (AhRd) mice. We found that omeprazole attenuated lung injury in WT mice. Attenuation of lung injury by omeprazole paralleled enhanced pulmonary CYP1A1 and hepatic CYP1A2 expression in the omeprazole-treated mice. On the other hand, omeprazole failed to enhance pulmonary CYP1A1 and hepatic CYP1A2 expression and protect against hyperoxic lung injury in AhRd mice. In conclusion, our results suggest that omeprazole attenuates hyperoxic lung injury in mice by AhR-mediated mechanisms, and this phenomenon is associated with induction of CYP1A enzymes. These studies have important implications for the prevention and/or treatment of hyperoxia-induced disorders such as BPD in infants and acute respiratory distress syndrome in older children and adults.

In vitro oxidative metabolism of xenobiotics in the lancet fluke (Dicrocoelium dendriticum) and the effects of albendazole and albendazole sulphoxide ex vivo

Dicrocoeliosis, a parasitic infection caused by Dicrocoelium dendriticum (lancet fluke), is often treated by the anthelmintic drug albendazole (ABZ). In the lancet fluke, ABZ metabolism via enzymatic sulphoxidation was found, but no information about ABZ oxidases has been available. The aim of our project was to find out which enzyme of the lancet fluke is responsible for ABZ sulphoxidation, as well as to assay the activities of oxidation enzymes. We also studied whether ex vivo 24-h exposures of flukes to ABZ or its sulphoxide (ABZ.SO) would alter ABZ sulphoxidation rate and the activities of tested enzymes. In subcellular fractions from flukes, marked activities of peroxidase (Px), glutathione Px (GPx), catalase (CAT), superoxide dismutase, and thioredoxin glutathione reductase were found. Using specific inhibitors, the participation of flavine monooxygenases in ABZ-oxidation was found. The ex vivo exposition of flukes to ABZ or ABZ.SO did not change the rate of ABZ sulphoxidation in vitro, but the ex vivo exposure of flukes to anthelmintics increased Px, CAT, and GPx activity. The modulation of these enzyme activities after ABZ or ABZ.SO exposition may be characteristic of the parasite’s protective mechanism against oxidative stress caused by drug treatment.

SOD1 Transcriptional and Posttranscriptional Regulation and Its Potential Implications in ALS

Copper-zinc superoxide dismutase (SOD1) is a detoxifying enzyme localized in the cytosol, nucleus, peroxisomes, and mitochondria. The discovery that mutations in SOD1 gene cause a subset of familial amyotrophic lateral sclerosis (FALS) has attracted great attention, and studies to date have been mainly focused on discovering mutations in the coding region and investigation at protein level. Considering that changes in SOD1 mRNA levels have been associated with sporadic ALS (SALS), a molecular understanding of the processes involved in the regulation of SOD1 gene expression could not only unravel novel regulatory pathways that may govern cellular phenotypes and changes in diseases but also might reveal therapeutic targets and treatments. This review seeks to provide an overview of SOD1 gene structure and of the processes through which SOD1 transcription is controlled. Furthermore, we emphasize the importance to focus future researches on investigating posttranscriptional mechanisms and their relevance to ALS.

Chemical Library Screening Identifies a Small Molecule That Downregulates SOD1 Transcription for Drugs to Treat Amyotrophic Lateral Sclerosis

Familial amyotrophic lateral sclerosis (fALS) accounts for 10% of ALS cases, and about 25% of fALS cases are due to mutations in superoxide dismutase 1 (SOD1). Mutant SOD1-mediated ALS is caused by a gain of toxic function of the mutant protein, and the SOD1 level in nonneuronal neighbors, including astrocytes, determines the progression of ALS (non-cell-autonomous toxicity). Therefore, the authors hypothesized that small molecules that reduce SOD1 protein levels in astrocytes might slow the progression of mutant SOD1-mediated ALS. They developed and optimized a cell-based, high-throughput assay to identify low molecular weight compounds that decrease SOD1 expression transcriptionally in human astrocyte-derived cells. Screening of a chemical library of 9600 compounds with the assay identified two hit compounds that selectively and partially downregulate SOD1 expression in a dose-dependent manner, without any detectable cellular toxicity. Western blot analysis showed that one hit compound significantly decreased the level of endogenous SOD1 protein in H4 cells, with no reduction in expression of β-actin. The assay developed here provides a powerful strategy for discovering novel lead molecules for treating familial SOD1-mediated ALS.

Superoxide dismutase type 1 in monocytes of chronic kidney disease patients

We analyzed proteomic profiles in monocytes of chronic kidney disease (CKD) patients and healthy control subjects. Two-dimensional electrophoresis (2-DE) and silver staining indicated differences in protein pattern. Among the analyzed proteins, superoxide dismutase type 1 (SOD1), which was identified both by MS/MS mass-spectrometry and immunoblotting, was reduced in kidney disease. We characterized SOD1 protein amount, using quantitative in-cell Western assay and immunostaining of 2-DE gel blots, and SOD1 gene expression, using quantitative real-time polymerase chain reaction (PCR), in 98 chronic hemodialysis (HD) and 211 CKD patients, and 34 control subjects. Furthermore, we showed that different SOD1 protein species exist in human monocytes. SOD1 protein amount was significantly lower in HD (normalized SOD1 protein, 27.2 ± 2.8) compared to CKD patients (34.3 ± 2.8), or control subjects (48.0 ± 8.6; mean ± SEM; P < 0.05). Analysis of SOD1 immunostaining showed significantly more SOD1 protein in control subjects compared to patients with CKD or HD (P < 0.0001, analysis of main immunoreactive protein spot). SOD1 gene expression was significantly higher in HD (normalized SOD1 gene expression, 17.8 ± 2.3) compared to CKD patients (9.0 ± 0.7), or control subjects (5.5 ± 1.0; P < 0.0001). An increased SOD1 gene expression may indicate increased protein degradation in patients with CKD and compensatory increase of SOD1 gene expression. Taken together, we show reduced SOD1 protein amount in monocytes of CKD, most pronounced in HD patients, accompanied by increased SOD1 gene expression.

Melatonin prevents the decreased activity of antioxidant enzymes and activates nuclear erythroid 2-related factor 2 signaling in an animal model of fulminant hepatic failure of viral origin

This work was undertaken to investigate whether treatment with melatonin prevents oxidative stress and changes in the expression and activity of factor erythroid 2-related factor 2 (Nrf2)-mediated antioxidant enzymes in an animal model of fulminant hepatic failure of viral origin. Rabbits were experimentally infected with 2 x 10(4) hemagglutination units of a rabbit hemorrhagic disease virus (RHDV) isolate and received melatonin at two concentrations of 10 mg/kg and 20 mg/kg at 0, 12 and 24 hr postinfection. Blood transaminases, blood lactate dehydrogenase, liver concentration of thiobarbituric reactive acid substances and the liver oxidized to reduced glutathione ratio significantly increased at 36 hr postinfection in infected animals. Significant decreases were found in the mRNA levels and in the liver activities of Mn-superoxide dismutase, glutathione peroxidase and glutathione-S-transferase in infected rabbits. These effects were prevented by melatonin administration in a concentration-dependent manner. Melatonin treatment was not accompanied by changes in protein levels of Kelch-like ECH-associating protein 1 (Keap1) but resulted in an increased protein expression of Nrf2 in the cytoplasm and the nucleus, which was confirmed by the results of Nrf2 immunostaining. Nuclear extracts from livers of melatonin-treated rats displayed an enhanced antioxidant responsive element (ARE)-binding activity of Nrf2. Our results suggest a potential hepatoprotective role of melatonin in fulminant hepatic failure, partially mediated through the abrogation of oxidative stress and the prevention of the decreased activity of antioxidant enzymes via the Nrf2 pathways.

Transcriptional up-regulation of SOD1 by CEBPD: a potential target for cisplatin resistant human urothelial carcinoma cells

Bladder cancer is the fourth most common type of cancer in men (ninth in women) in the United States. Cisplatin is an effective agent against the most common subtype, urothelial carcinoma. However, the development of chemotherapy resistance is a severe clinical problem for the successful treatment of this and other cancers. A better understanding of the cellular and molecular events in response to cisplatin treatment and the development of resistance are critical to improve the therapeutic options for patients. Here, we report that expression of the CCAAT/enhancer binding protein delta (CEBPD, C/EBPdelta, NF-IL6beta) is induced by cisplatin in the human bladder urothelial carcinoma NTUB1 cell line and is specifically elevated in a cisplatin resistant subline. Expression of CEBPD reduced cisplatin-induced reactive oxygen species (ROS) and apoptosis in NTUB1 cells by inducing the expression of Cu/Zn-superoxide dismutase (SOD1) via direct promoter transactivation. Several reports have implicated CEBPD as a tumor suppressor gene. This study reveals a novel role for CEBPD in conferring drug resistance, suggesting that it can also be pro-oncogenic. Furthermore, our data suggest that SOD inhibitors, which are already used as anti-angiogenic agents, may be suitable for combinatorial chemotherapy to prevent or treat cisplatin resistance in bladder and possibly other cancers.

Effects of atmospheric pollutants on the Nrf2 survival pathway

BACKGROUND, AIM, AND SCOPE

Atmospheric pollution is a worldwide problem. Exposure to atmospheric pollutants causes toxic cellular effects. One of the mechanisms of toxicity by these pollutants is the promotion of oxidative stress. Several signaling pathways control cellular redox homeostasis. In this respect, nuclear factor erythroid 2-related factor 2 (Nrf2) is a crucial transcription factor in the cell's response to oxidative stress.

MAIN FEATURES

In cellular animal models, exposure to atmospheric pollutants activates Nrf2, attenuating its toxic and even its carcinogenic effects. Therefore, we have reviewed the scientific literature in order to indicate that air pollutants, such as particulate matter, polycyclic aromatic hydrocarbons, and gaseous matter, are Nrf2 pathway inductors, triggering self-defense through the establishment of proinflammatory and antioxidant responses.

RESULTS AND DISCUSSION

Exposure to reactive molecules as atmospheric pollutants causes the activation of Nrf2 and the subsequent regulation of the expression of cytoprotective and detoxifying enzymes, as well as antioxidants. Moreover, induction of Nrf2 prior to exposure reduces the harmful effects of pollutants. The present article discusses the protective role of the Nrf2 pathway against different atmospheric pollutant insults.

CONCLUSIONS

Nrf2 regulates the expression of numerous cytoprotective genes that function to detoxify reactive species produced during atmospheric pollutant metabolic reactions. From the papers highlighted in this review, we conclude that Nrf2 has an important role in the defense against atmospheric pollutant-induced toxicity.

PERSPECTIVES

Further studies are needed to understand the signaling events that turn on the system in response to atmospheric pollutant stress. This could allow for the possibility of targeting the pathway for prevention benefits in the near future.

The keap1-nrf2 cellular defense pathway: mechanisms of regulation and role in protection against drug-induced toxicity

Adverse drug reactions pose a significant public health problem. In some cases, the process of drug metabolism can contribute to the onset of toxicity through the bioactivation of a parent molecule to a chemically reactive intermediate. In order to maintain a favorable balance between bioactivation and detoxification, mammalian cells have evolved an inducible cell defense system known as the antioxidant response pathway. The activity of this cytoprotective pathway is largely regulated by the transcription factor Nrf2, which governs the expression of many phase II detoxification and antioxidant enzymes. In turn, the activity of Nrf2 is regulated by the cysteine-rich cytosolic inhibitor Keap1, which acts as a "sensor" for chemical/oxidative stress. This article summarizes our current understanding of the molecular mechanisms that regulate the function of the Keap1-Nrf2 pathway and highlights the importance of Nrf2 in the protection against drug-induced toxicity.

Clair DK. Regulation of superoxide dismutase genes: implications in disease

Numerous short-lived and highly reactive oxygen species (ROS) such as superoxide (O2(.-)), hydroxyl radical, and hydrogen peroxide are continuously generated in vivo. Depending upon concentration, location, and intracellular conditions, ROS can cause toxicity or act as signaling molecules. The cellular levels of ROS are controlled by antioxidant enzymes and small-molecule antioxidants. As major antioxidant enzymes, superoxide dismutases (SODs), including copper-zinc superoxide dismutase (Cu/ZnSOD), manganese superoxide dismutase, and extracellular superoxide dismutase, play a crucial role in scavenging O2(.-). This review focuses on the regulation of the sod genes coding for these enzymes, with an emphasis on the human genes. Current knowledge about sod structure and regulation is summarized and depicted as diagrams. Studies to date on genes coding for Cu/ZnSOD (sod1) are mostly focused on alterations in the coding region and their associations with amyotrophic lateral sclerosis. Evaluation of nucleotide sequences reveals that regulatory elements of the sod2 gene reside in both the noncoding and the coding region. Changes associated with sod2 lead to alterations in expression levels as well as protein function. We also discuss the structural basis for the changes in SOD expression associated with pathological conditions and where more work is needed to establish the relationship between SODs and diseases.

Protection of vascular cells from oxidative stress by proteasome inhibition depends on Nrf2

AIMS

Increased levels of reactive oxygen species cause oxidative stress and severely damage lipids, proteins, and DNA. We have previously shown that partial proteasome inhibition induces an antioxidative gene pattern in endothelial cells. Here, we elucidate the mechanisms of proteasome inhibitor-mediated upregulation of antioxidative enzymes and cytoprotection.

METHODS AND RESULTS

Non-toxic proteasome inhibition upregulated mRNA and protein expression of superoxide dismutase 1 (SOD1) and haem oxygenase 1 (HO1) in several human endothelial and vascular smooth muscle cell types. Transcriptional activation of these enzymes was shown by inhibition of RNA polymerase II and nuclear run-on assays. Transfection of endothelial cells with luciferase reporter constructs revealed that upregulation can be largely confined to an antioxidant response element (ARE), which proved to be sufficient for transcriptional activation of SOD1 and HO1. Co-transfection studies and bandshift analyses confirmed binding of the antioxidative transcription factor NF-E2-related factor 2 (Nrf2)-which was stabilized by proteasome inhibition as shown by immunoblots-to the ARE site of HO1. Experiments with aortic endothelial and smooth muscle cells from Nrf2 wild-type and knockout mice revealed an essential role of Nrf2: in wild-type cells, proteasome inhibitor-mediated induction of SOD1 and HO1 was accompanied by protection of vascular cells against oxidative stress as determined by lactate dehydrogenase release assays. In contrast, proteasome inhibitor-mediated induction of antioxidative enzymes and cytoprotection were completely lost in cells from Nrf2 knockout mice.

CONCLUSION

Nrf2-dependent transcriptional activation of antioxidative enzymes is crucial for proteasome inhibitor-mediated protection of vascular cells against oxidative stress.

Gene structure and expression of metallothionein during metal exposures in Hemibarbus mylodon

Metallothionein gene was characterized in Hemibarbus mylodon, an endangered fish species. H. mylodon MT shared a high homology with other vertebrate MTs, including (1) tripartite exon/intron structure, (2) typical regulatory elements such as MREs and GC boxes in the 5'-flanking region, and (3) high proportion of Cysteines (33.3%) in its amino acid sequence. MT mRNA was ubiquitously detected in various tissues. Basal level of MT mRNA was the highest in ovary while the lowest in heart. Transcription of MT was highly inducible by exposures to waterborne cadmium (0.1-10 microM), copper (2-10 microM) or zinc (2-10 microM), based on real-time RT-PCR. Cadmium was more potent for the stimulation of MT transcripts than copper and zinc. Liver was more responsive to heavy metals than kidney and gill. In overall, the transcriptional activation of MT gene by metal exposures followed a dose- and/or time-dependent fashion.

Network inference algorithms elucidate Nrf2 regulation of mouse lung oxidative stress

A variety of cardiovascular, neurological, and neoplastic conditions have been associated with oxidative stress, i.e., conditions under which levels of reactive oxygen species (ROS) are elevated over significant periods. Nuclear factor erythroid 2-related factor (Nrf2) regulates the transcription of several gene products involved in the protective response to oxidative stress. The transcriptional regulatory and signaling relationships linking gene products involved in the response to oxidative stress are, currently, only partially resolved. Microarray data constitute RNA abundance measures representing gene expression patterns. In some cases, these patterns can identify the molecular interactions of gene products. They can be, in effect, proxies for protein-protein and protein-DNA interactions. Traditional techniques used for clustering coregulated genes on high-throughput gene arrays are rarely capable of distinguishing between direct transcriptional regulatory interactions and indirect ones. In this study, newly developed information-theoretic algorithms that employ the concept of mutual information were used: the Algorithm for the Reconstruction of Accurate Cellular Networks (ARACNE), and Context Likelihood of Relatedness (CLR). These algorithms captured dependencies in the gene expression profiles of the mouse lung, allowing the regulatory effect of Nrf2 in response to oxidative stress to be determined more precisely. In addition, a characterization of promoter sequences of Nrf2 regulatory targets was conducted using a Support Vector Machine classification algorithm to corroborate ARACNE and CLR predictions. Inferred networks were analyzed, compared, and integrated using the Collective Analysis of Biological Interaction Networks (CABIN) plug-in of Cytoscape. Using the two network inference algorithms and one machine learning algorithm, a number of both previously known and novel targets of Nrf2 transcriptional activation were identified. Genes predicted as novel Nrf2 targets include Atf1, Srxn1, Prnp, Sod2, Als2, Nfkbib, and Ppp1r15b. Furthermore, microarray and quantitative RT-PCR experiments following cigarette-smoke-induced oxidative stress in Nrf2(+/+) and Nrf2(-/-) mouse lung affirmed many of the predictions made. Several new potential feed-forward regulatory loops involving Nrf2, Nqo1, Srxn1, Prdx1, Als2, Atf1, Sod1, and Park7 were predicted. This work shows the promise of network inference algorithms operating on high-throughput gene expression data in identifying transcriptional regulatory and other signaling relationships implicated in mammalian disease.

Expression of Nrf2 and its downstream gene targets in hibernating 13-lined ground squirrels, Spermophilus tridecemlineatus

Mammalian hibernation is associated with wide variation in heart rate, blood flow, and oxygen delivery to tissues and is used as a model of natural ischemia/reperfusion. In non-hibernators, ischemia/reperfusion is typically associated with oxidative stress but hibernators seem to deal with potential oxidative damage by enhancing antioxidant defenses in an anticipatory manner. The present study assesses the role of the Nrf2 transcription factor in the regulation of antioxidant defenses during hibernation. Nrf2 mRNA and protein expression were enhanced in selected organs of 13-lined ground squirrels, Spermophilus tridecemlineatus during hibernation. Furthermore, Nrf2 protein in heart was elevated by 1.4-1.5 fold at multiple stages over a torpor-arousal bout including during entry, long term torpor, and early arousal. Levels returned to euthermic values when squirrels were fully aroused in interbout. Protein levels of selected downstream target genes under Nrf2 control were also measured via immunoblotting over the torpor-arousal cycle in heart. Cu/Zn superoxide dismutase and aflatoxin aldehyde reductase levels increased significantly during entry into torpor and then gradually declined falling to control levels or below in fully aroused animals. Heme oxygenase-1 also showed the same trend. This suggests a role for Nrf2 in regulating the antioxidant defenses needed for hibernation success. Heart nrf2 was amplified by PCR and sequenced. The deduced amino acid sequence showed high identity with the sequence from other mammals but with selected unique substitutions (e.g., proline residues at positions 111 and 230) that might be important for conformational stability of the protein at near 0 degrees C body temperatures in the torpid state.

The Nrf2-Keap1 defence pathway: role in protection against drug-induced toxicity

The metabolic biotransformation of xenobiotics to chemically reactive metabolites can, in some instances, underlie the pathogenesis of certain adverse drug reactions, due to the development of chemical or oxidative stress. In order to guard against such stresses, mammalian cells have evolved multi-faceted, highly-regulated defence systems, one of the most important being that which is regulated by the transcription factor Nrf2. Through regulating the expression of numerous cytoprotective genes, Nrf2 serves as a critical determinant of a cell's capacity to survive, or succumb, to a toxic insult. The aim of this review is to summarise our current understanding of the biochemistry that underlies the Nrf2 defence pathway, and highlight the important role of this transcription factor in the protection against drug-induced toxicity, primarily through the examination of recent investigations that have demonstrated an increased vulnerability to various toxins in animals lacking Nrf2.

Lipid peroxidation and antioxidant status in workers exposed to PCDD/Fs of metal recovery plants

Secondary copper smelters, which primarily utilize the waste materials that contain organic impurities, and the zinc recovery plant, which handles mostly fly ash and slag from the iron and steel industry, are major emission sources of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in Taiwan. In this study, we compared the levels of erythrocyte glutathione (GSH), erythrocyte superoxide dismutase (SOD) and plasma malondialdehyde (MDA) in workers at a secondary copper smelting plant and a zinc recovery plant who may have been exposed to PCDD/Fs. Though the PCDD/F levels were higher in workers of zinc recovery plant than those of secondary copper smelting plant, no significant difference was found for serum PCDD/F levels between the two kinds of plants. We observed a significant difference in plasma MDA levels between workers at the zinc recovery plant (2.54 microM) and those at the copper smelting plant (1.79 microM). There was and a significant positive correlation between plasma MDA levels and the PCDD/Fs levels. In addition, we observed that the MDA levels were not affected by smoking and exercise status. Therefore, the data suggest that the MDA levels of the metal recovery workers are influenced by their PCDD/F exposure. The erythrocyte SOD activity in workers from the zinc recovery plant was marginally higher than that from the secondary copper plant (196 vs. 146 units/ml, p<0.06). In both plants, large variations in the MDA and SOD levels were found, especially in the high-PCDD/Fs-exposure group, which may be attributed, at least partially, to the differences in smoking status and the number of cigarettes smoked. Overall, our results indicate a higher oxidative stress in workers of the zinc recovery plant than in workers of the secondary copper smelting plant in Taiwan.

Active defense under oxidative stress. The antioxidant responsive element

This review considers the mechanisms and factors that stimulate transcription of genes regulated by the antioxidant responsive element (ARE). The latter is important for cell defense under conditions of oxidative stress and also for detoxification of electrophilic xenobiotics. There are differences in regulation of intracellular homeostasis involving Nrf2-mediated activation of ARE and other redox-sensitive factors (NF-kappaB and AP-1).

Methoxychlor Inhibits Growth and Induces Atresia of Antral Follicles through an Oxidative Stress Pathway

The mammalian ovary contains antral follicles, which are responsible for the synthesis and secretion of hormones that regulate estrous cyclicity and fertility. The organochlorine pesticide methoxychlor (MXC) causes atresia (follicle death via apoptosis) of antral follicles, but little is known about the mechanisms by which MXC does so. Oxidative stress is known to cause apoptosis in nonreproductive and reproductive tissues. Thus, we tested the hypothesis that MXC inhibits growth and induces atresia of antral follicles through an oxidative stress pathway. To test this hypothesis, antral follicles isolated from 39-day-old CD-1 mice were cultured with vehicle control (dimethylsulfoxide [DMSO]), MXC (1-100 microg/ml), or MXC + the antioxidant N-acetyl cysteine (NAC) (0.1-10 mM). During culture, growth was monitored daily. At the end of culture, follicles were processed for quantitative real-time polymerase chain reaction of Cu/Zn superoxide dismutase (SOD1), glutathione peroxidase (GPX), and catalase (CAT) mRNA expression or for histological evaluation of atresia. The results indicate that exposure to MXC (1-100 microg/ml) inhibited growth of follicles compared to DMSO controls and that NAC (1-10 mM) blocked the ability of MXC to inhibit growth. MXC induced follicular atresia, whereas NAC (1-10 mM) blocked the ability of MXC to induce atresia. In addition, MXC reduced the expression of SOD1, GPX, and CAT, whereas NAC reduced the effects of MXC on their expression. Collectively, these data indicate MXC causes slow growth and increased atresia by inducing oxidative stress.

CYP1A in TCDD toxicity and in physiology-with particular reference to CYP dependent arachidonic acid metabolism and other endogenous substrates

Toxicologic and physiologic roles of CYP1A enzyme induction, the major biochemical effect of aryl hydrocarbon receptor activation by TCDD and other receptor ligands, are unknown. Evidence is presented that CYP1A exerts biologic effects via metabolism of endogenous substrates (i.e., arachidonic acid, other eicosanoids, estrogens, bilirubin, and melatonin), production of reactive oxygen, and effects on K(+) and Ca(2+) channels. These interrelated pathways may connect CYP1A induction to TCDD toxicities, including cardiotoxicity, vascular dysfunction, and wasting. They may also underlie homeostatic roles for CYP1A, especially when transiently induced by common chemical exposures and environmental conditions (i.e., tryptophan photoproducts, dietary indoles, and changes in oxygen tension).

Selenium Supplementation Restores the Antioxidative Capacity and Prevents Cell Damage in Bone Marrow Stromal Cells In Vitro

Bone marrow stromal cells (BMSCs) and other cell populations derived from mesenchymal precursors are developed for cell-based therapeutic strategies and undergo cellular stress during ex vivo procedures. Reactive oxygen species (ROS) of cellular and environmental origin are involved in redox signaling, cumulative cell damage, senescence, and tumor development. Selenium-dependent (glutathione peroxidases [GPxs] and thioredoxin reductases [TrxRs]) and selenium-independent (superoxide dismutases [SODs] and catalase [CAT]) enzyme systems regulate cellular ROS steady state levels. SODs process superoxide anion to hydrogen peroxide, which is subsequently neutralized by GPx and CAT; TrxR neutralizes other ROS, such as peroxinitrite. Primary BMSCs and telomerase-immortalized human mesenchymal stem cells (hMSC-TERT) express GPx1-3, TrxR1, TrxR2, SOD1, SOD2, and CAT. We show here that in standard cell cultures (5%-10% fetal calf serum, 5-10 nM selenite), the activity of antioxidative selenoenzymes is impaired in hMSC-TERT and BMSCs. Under these conditions, the superoxide anion processing enzyme SOD1 is not sufficiently stimulated by an ROS load. Resulting oxidative stress favors generation of micronuclei in BMSCs. Supplementation of selenite (100 nM) restores basal GPx and TrxR activity, rescues basal and ROS-stimulated SOD1 mRNA expression and activity, and reduces ROS accumulation in hMSC-TERT and micronuclei generation in BMSCs. In conclusion, BMSCs in routine cell culture have low antioxidative capacity and are subjected to oxidative stress, as indicated by the generation of micronuclei. Selenite supplementation of BMSC cultures appears to be an important countermeasure to restore their antioxidative capacity and to reduce cell damage in the context of tissue engineering and transplantation procedures.

Expression of the fetal Alz-50 clone 1 protein induces apoptotic cell death

The fetal Alz-50 clone 1 (FAC1) protein exhibits altered expression patterns in neurodegenerative disease. Though it has been shown to bind DNA in a site-specific, phosphorylation-dependent manner, its cellular function remains unknown. Here, we demonstrate that overexpression of FAC1 in PT67 fibroblasts induces nuclear condensation and cleavage of caspase 3 to its active form indicating induction of apoptosis. The amino-terminal domain of FAC1 is necessary and sufficient to induce both nuclear condensation and activation of caspase 3. Disruption of FAC1 interaction with a known binding partner, kelch-like ECH-associated protein 1 (Keap1), enhances activation of caspase 3. Keap1 is known to block activation of the antioxidant response gene products by direct interaction with the transcriptional activator, Nrf2. Disruption of the Keap1:Nrf2 interaction enhances FAC1 induction of apoptosis. These findings suggest a role for FAC1 in apoptosis following release of Nrf2 from Keap1 in response to oxidative stress.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) alters the mRNA expression of critical genes associated with cholesterol metabolism, bile acid biosynthesis, and bile transport in rat liver: a microarray study

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent hepatotoxin that exerts its toxicity through binding to the aryl hydrocarbon receptor (AhR) and the subsequent induction or repression of gene transcription. In order to further identify novel genes and pathways that may be associated with TCDD-induced hepatotoxicity, we investigated gene changes in rat liver following exposure to single oral doses of TCDD. Male Sprague-Dawley rats were administered single doses of 0.4 microg/kg bw or 40 microg/kg bw TCDD and killed at 6 h, 24 h, or 7 days, for global analyses of gene expression. In general, low-dose TCDD exposure resulted in greater than 2-fold induction of genes coding for a battery of phase I and phase II metabolizing enzymes including CYP1A1, CYP1A2, NADPH quinone oxidoreductase, UGT1A6/7, and metallothionein 1. However, 0.4 microg/kg bw TCDD also altered the expression of Gadd45a and Cyclin D1, suggesting that even low-dose TCDD exposure can alter the expression of genes indicative of cellular stress or DNA damage and associated with cell cycle control. At the high-dose, widespread changes were observed for genes encoding cellular signaling proteins, cellular adhesion, cytoskeletal and membrane transport proteins as well as transcripts coding for lipid, carbohydrate and nitrogen metabolism. In addition, decreased expression of cytochrome P450 7A1, short heterodimer partner (SHP; gene designation nr0b2), farnesyl X receptor (FXR), Ntcp, and Slc21a5 (oatp2) were observed and confirmed by RT-PCR analyses in independent rat liver samples. Altered expression of these genes implies major deregulation of cholesterol metabolism and bile acid synthesis and transport. We suggest that these early and novel changes have the potential to contribute significantly to TCDD induced hepatotoxicity and hypercholesterolemia.

Quercetin protects human hepatoma HepG2 against oxidative stress induced by tert-butyl hydroperoxide

Flavonols such as quercetin, have been reported to exhibit a wide range of biological activities related to their antioxidant capacity. The objective of the present study was to investigate the protective effect of quercetin on cell viability and redox status of cultured HepG2 cells submitted to oxidative stress induced by tert-butyl hydroperoxide. Concentrations of reduced glutathione and malondialdehyde, generation of reactive oxygen species and activity and gene expression of antioxidant enzymes were used as markers of cellular oxidative status. Pretreatment of HepG2 with 10 microM quercetin completely prevented lactate dehydrogenase leakage from the cells. Pretreatment for 2 or 20 h with all doses of quercetin (0.1-10 microM) prevented the decrease of reduced glutathione and the increase of malondialdehyde evoked by tert-butyl hydroperoxide in HepG2 cells. Reactive oxygen species generation induced by tert-butyl hydroperoxide was significantly reduced when cells were pretreated for 2 or 20 h with 10 microM and for 20 h with 5 microM quercetin. Finally, some of the quercetin treatments prevented the significant increase of glutathione peroxidase, superoxide dismutase, glutathione reductase and catalase activities induced by tert-butyl hydroperoxide. Gene expression of antioxidant enzymes was also affected by the treatment with the polyphenol. The results of the biomarkers analyzed clearly show that treatment of HepG2 cells in culture with the natural dietary antioxidant quercetin strongly protects the cells against an oxidative insult.

Glutathione transferases

This review describes the three mammalian glutathione transferase (GST) families, namely cytosolic, mitochondrial, and microsomal GST, the latter now designated MAPEG. Besides detoxifying electrophilic xenobiotics, such as chemical carcinogens, environmental pollutants, and antitumor agents, these transferases inactivate endogenous alpha,beta-unsaturated aldehydes, quinones, epoxides, and hydroperoxides formed as secondary metabolites during oxidative stress. These enzymes are also intimately involved in the biosynthesis of leukotrienes, prostaglandins, testosterone, and progesterone, as well as the degradation of tyrosine. Among their substrates, GSTs conjugate the signaling molecules 15-deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ2) and 4-hydroxynonenal with glutathione, and consequently they antagonize expression of genes trans-activated by the peroxisome proliferator-activated receptor gamma (PPARgamma) and nuclear factor-erythroid 2 p45-related factor 2 (Nrf2). Through metabolism of 15d-PGJ2, GST may enhance gene expression driven by nuclear factor-kappaB (NF-kappaB). Cytosolic human GST exhibit genetic polymorphisms and this variation can increase susceptibility to carcinogenesis and inflammatory disease. Polymorphisms in human MAPEG are associated with alterations in lung function and increased risk of myocardial infarction and stroke. Targeted disruption of murine genes has demonstrated that cytosolic GST isoenzymes are broadly cytoprotective, whereas MAPEG proteins have proinflammatory activities. Furthermore, knockout of mouse GSTA4 and GSTZ1 leads to overexpression of transferases in the Alpha, Mu, and Pi classes, an observation suggesting they are part of an adaptive mechanism that responds to endogenous chemical cues such as 4-hydroxynonenal and tyrosine degradation products. Consistent with this hypothesis, the promoters of cytosolic GST and MAPEG genes contain antioxidant response elements through which they are transcriptionally activated during exposure to Michael reaction acceptors and oxidative stress.

Response of the antioxidant defense system totert-butyl hydroperoxide and hydrogen peroxide in a human hepatoma cell line (HepG2)

The aim of this work was to investigate the response of the antioxidant defense system to two oxidative stressors, hydrogen peroxide and tert-butyl hydroperoxide, in HepG2 cells in culture. The parameters evaluated included enzyme activity and gene expression of superoxide dismutase, catalase, glutathione peroxidase, and activity of glutathione reductase. Besides, markers of the cell damage and oxidative stress evoked by the stressors such as cell viability, intracellular reactive oxygen species generation, malondialdehyde levels, and reduced glutathione concentration were evaluated. Both stressors, hydrogen peroxide and tert-butyl hydroperoxide, enhanced cell damage and reactive oxygen species generation at doses above 50 microM. The concentration of reduced glutathione decreased, and levels of malondialdehyde and activity of the antioxidant enzymes consistently increased only when HepG2 cells were treated with tert-butyl hydroperoxide but not when hydrogen peroxide was used. A slight increase in the gene expression of Cu/Zn superoxide dismutase and catalase with 500 microM tert-butyl hydroperoxide and of catalase with 200 microM hydrogen peroxide was observed. The response of the components of the antioxidant defense system evaluated in this study indicates that tert-butyl hydroperoxide evokes a consistent cellular stress in HepG2.

Influence of quercetin and rutin on growth and antioxidant defense system of a human hepatoma cell line (HepG2)

BACKGROUND

Dietary polyphenols like quercetin and rutin are considered beneficial because of their potential protective role in the pathogenesis of multiple diseases associated to oxidative stress such as cancer, coronary heart disease and atherosclerosis. However, many of these effects may depend on the concentration of the polyphenol utilized since high doses of some phenolic compounds may be prooxidant and negatively affect cell growth and viability.

AIM OF THE STUDY

To test the potential chemoprotective effects of quercetin and rutin, two flavonols with high antioxidant capacity, on cell growth, viability and the response of the antioxidant defense system of a human hepatoma cell line (HepG2).

METHODS

Cell growth was measured by diaminobenzoic acid and bromodeoxyuridine assays, cell toxicity by lactate dehydrogenase leakage assay, reduced glutathione was quantified by a fluorimetric assay, cellular malondialdehyde was analyzed by high-performance liquid chromatography, reactive oxygen species were quantified by the dichlorofluorescein assay, antioxidant enzyme activities were determined by spectrophotometric analysis and their gene expression by northern blot.

RESULTS

Short-term exposure (4 h) to these flavonols had no antiproliferative nor cytotoxic effect. High doses of quercetin (50-100 microM) increased glutathione concentration and gene expression of Cu/Zn superoxide dismutase and catalase inhibiting the activity of the latter enzyme, whereas lower doses (0.1-1 microM) decreased gene expression of Cu/Zn superoxide dismutase and increased that of glutathione peroxidase. All doses of quercetin and rutin diminished reactive oxygen species and high doses (10-100 microM) decreased malondialdehyde concentration.

CONCLUSION

The results indicate that both natural antioxidants induce favorable changes in the antioxidant defense system of cultured HepG2 that prevent or delay conditions which favor cellular oxidative stress.

Antioxidative and Cardioprotective Effects of Phyllanthus urinaria L. on Doxorubicin-Induced Cardiotoxicity

Cardiac toxicity is a major adverse effect caused by doxorubicin (DOX) therapy. Many recent studies have shown that DOX toxicity involves generation of reactive oxygen species (ROS). Although protection or alleviation of DOX toxicity can be achieved by administration of antioxidant vitamins such as ascorbic acid and vitamin E, their cardioprotective effect remains controversial. Thus alternative naturally occurring antioxidants may potentially be candidates for antioxidant therapy. In this study, we investigated the antioxidative and cytoprotective effects of Phyllanthus urinaria (PU) against DOX toxicity using H9c2 cardiac myoblasts. The total antioxidant capacity of PU (1 mg/ml) was 5306.75+/-461.62 FRAP value (microM). DOX IC50 values were used to evaluate the cytoprotective effects of PU ethanolic extract (1 or 10 microg/ml) in comparison with those of ascorbic acid (VIT C, 100 microM) and N-acetylcysteine (NAC, 100 microM). PU treatments (1 or 10 microg/ml) dose dependently caused rightward DOX IC50 shifts of 2.8- and 8.5-fold, respectively while treatments with VIT C and NAC increased DOX IC50 by 3.3- and 4.2-fold, respectively. Additionally, lipid peroxidation and caspase-3 activity were parameters used to evaluate cytoprotective effect. All antioxidants completely inhibited cellular lipid peroxidation and caspase-3 activation induced by DOX (1 microM). Endogenous antioxidant defense such as total glutathione (tGSH), catalase and superoxide dismutase (SOD) activity was also modulated by the antioxidants. PU treatment alone dose dependently increased tGSH, and this effect was retained in the presence of DOX. Similar effect was observed in the assessment of catalase and SOD enzyme activity. The nuclear factor kappaB (NFkappaB) transcription factor assay demonstrated that all antioxidants significantly inhibited DOX-induced NFkappaB activation. Our results suggest that PU protection against DOX cardiotoxicity was mediated through multiple pathways and this plant may serve as an alternative source of antioxidants for prevention of DOX cardiotoxicity.

Regulation of Cu/Zn-superoxide dismutase expression via the phosphatidylinositol 3 kinase/Akt pathway and nuclear factor-kappaB

Aerobic cells adjust the expression of antioxidant enzymes to maintain reactive oxygen species within tolerable levels. In addition, phosphatidylinositol 3 kinase (PI3K) and its downstream protein kinase effector Akt adapt cells to survive in the presence of oxidative stress. Here we provide evidence for an association between these two defense systems via transcriptional regulation of Cu/Zn-superoxide dismutase (Cu/Zn-SOD). PC12 pheochromocytoma cells expressing active Akt1 exhibit lower ROS levels in response to hydrogen peroxide, as determined with the superoxide-sensitive probe hydroethidine. Transfection of constitutive or 4-hydroxytamoxifen-inducible versions of Akt1 results in higher messenger RNA and protein levels of Cu/Zn-SOD. Luciferase reporter constructs, carrying different length fragments of the human sod1 gene promoter, have identified a region between -552 and -355 that is targeted by PI3K and Akt and that contains a putative site of regulation by nuclear factor-kappaB (NF-kappaB). Nerve growth factor (NGF) and Akt augment the transactivating activity and produce higher nuclear levels of p65-NF-kappaB. Electrophoretic mobility shift assays indicate that the putative NF-kappaB regulatory sequence binds p65-NF-kappaB more efficiently in nuclear extracts from these cells. A dominant-negative mutant of IkappaBalpha further demonstrates that the PI3K/Akt axis targets the sod1 promoter at the level of the newly characterized NF-kappaB site. These results illustrate a new mechanism by which the PI3K/Akt pathway protects cells against oxidative stress, involving the upregulation of Cu/Zn-SOD gene expression, and the results identify NF-kappaB as a key mediator in the regulation of this gene.

Disruption of the Ah receptor gene alters the susceptibility of mice to oxygen-mediated regulation of pulmonary and hepatic cytochromes P4501A expression and exacerbates hyperoxic lung injury

Administration of supplemental oxygen is frequently encountered in infants suffering from pulmonary insufficiency and in adults with acute respiratory distress syndrome. However, hyperoxia causes acute lung damage in experimental animals. In the present study, we investigated the roles of the Ah receptor (AHR) in the modulation of cytochrome P4501A (CYP1A) enzymes and in the development of lung injury by hyperoxia. Adult male wild-type [AHR (+/+)] mice and AHR-deficient animals [AHR (-/-)] were maintained in room air or exposed to hyperoxia (>95% oxygen) for 24 to 72 h, and pulmonary and hepatic expression of CYP1A and lung injury were studied. Hyperoxia caused significant increases in pulmonary and hepatic CYP1A1 activities (ethoxyresorufin O-deethylase) and mRNA levels in wild-type (C57BL/6J) AHR (+/+), but not AHR (-/-) mice, suggesting that AHR-dependent mechanisms contributed to CYP1A1 induction. On the other hand, hyperoxia augmented hepatic CYP1A2 expression in both wild-type and AHR (-/-) animals, suggesting that AHR-independent mechanisms contributed to the CYP1A2 regulation by hyperoxia. AHR (-/-) mice exposed to hyperoxia were more susceptible than wild-type mice to lung injury and inflammation, as indicated by significantly higher lung weight/body weight ratios, increased pulmonary edema, and enhanced neutrophil recruitment into the lungs. In conclusion, our results support the hypothesis that the hyperoxia induces CYP1A1, but not CYP1A2, expression in vivo by AHR-dependent mechanisms, a phenomenon that may mechanistically contribute to the beneficial effects of the AHR in hyperoxic lung injury.

Scrapie-like prion protein is translocated to the nuclei of infected cells independently of proteasome inhibition and interacts with chromatin

Prion diseases are fatal transmissible neurodegenerative disorders characterized by the accumulation of an abnormally folded isoform of the cellular prion protein (PrPC) denoted PrPSc. Recently, wild-type and pathogenic PrP mutants have been shown to be degraded by the endoplasmic reticulum-associated degradation proteasome pathway after translocation into the cytosol. We show here that a protease resistant form of PrP accumulated in the nuclei of prion-infected cells independently of proteasome activity, and that this nuclear translocation required an intact microtubule network. Moreover, our results show for the first time that nuclear PrP interacts with chromatin in vivo, which may have physiopathological consequences in prion diseases