Chemoprevention through the Keap1-Nrf2 signaling pathway by phase 2 enzyme inducers

Essential role of Nrf2 in protection against hydroquinone- and benzoquinone-induced cytotoxicity

Benzene is a well-established human carcinogen. Benzene metabolites hydroquinone (HQ) and benzoquinone (BQ) are highly reactive molecules capable of producing reactive oxygen species and causing oxidative stress. In this study, we investigated the role of the Nrf2, a key nuclear transcription factor that regulates antioxidant response element (ARE)-containing genes, in defense against HQ- and BQ-induced cytotoxicity in cultured human lung epithelial cells (Beas-2B). When the cells were exposed to HQ or BQ the activity of an ARE reporter was induced in a dose-dependent manner, meanwhile Nrf2 protein levels were elevated and accumulated in the nucleus. Increased expression of well-known Nrf2-dependent proteins including NQO1, GCLM, GSS and HMOX was also observed in the HQ/BQ-treated cells. Moreover, transient overexpression of Nrf2 conferred protection against HQ- and BQ-induced cell death, whereas knockdown of Nrf2 by small interfering RNA resulted in increased apoptosis. We also found that the increased susceptibility of Nrf2-knockdown cells to HQ and BQ was associated with reduced glutathione levels and loss of inducibility of ARE-driven genes, suggesting that deficiency of Nrf2 impairs cellular redox capacity to counteract oxidative damage. Altogether, these results suggest that Nrf2-ARE pathway is essential for protection against HQ- and BQ-induced toxicity.

Sulforaphane inhibits 4-aminobiphenyl-induced DNA damage in bladder cells and tissues

Sulforaphane (SF) is a well-known chemopreventive phytochemical and occurs in broccoli and to a lesser extent in other cruciferous vegetables, whereas 4-aminobiphenyl (ABP) is a major human bladder carcinogen and is present at significant levels in tobacco smoke. Here, we show that SF inhibits ABP-induced DNA damage in both human bladder cells in vitro and mouse bladder tissue in vivo, using dG-C8-ABP as a biomarker, which is the predominant ABP-DNA adduct formed in human bladder cells and tissues. SF activates NF-E2 related factor-2 (Nrf2), which is a well-recognized chemopreventive target and activates the Nrf2-regulated cytoprotective signaling pathway. Comparison between wild-type mice and mice without Nrf2 shows that Nrf2 activation is required by SF for inhibition of ABP-induced DNA damage. Moreover, Nrf2 activation by SF in the bladder occurs primarily in the epithelium, which is the principal site of bladder cancer development. These data, together with our recent observation that SF-enriched broccoli sprout extracts strongly inhibits N-butyl-N-(4-hydroxybutyl)nitrosamine-induced bladder cancer development, suggest that SF is a highly promising agent for bladder cancer prevention and provides a mechanistic insight into the repeated epidemiological observation that consumption of broccoli is inversely associated with bladder cancer risk and mortality.

Anti-cancer and potential chemopreventive actions of ginseng by activating Nrf2 (NFE2L2) anti-oxidative stress/anti-inflammatory pathways

This article reviews recent basic and clinical studies of ginseng, particularly the anti-cancer effects and the potential chemopreventive actions by activating the transcriptional factor, nuclear factor (erythroid-derived 2)-like 2 (Nrf2 or NFE2L2)-mediated anti-oxidative stress or anti-inflammatory pathways. Nrf2 is a novel target for cancer prevention as it regulates the antioxidant responsive element (ARE), a critical regulatory element in the promoter region of genes encoding cellular phase II detoxifying and anti-oxidative stress enzymes. The studies on the chemopreventive effects of ginseng or its components/products showed that Nrf2 could also be a target for ginseng's actions. A number of papers also demonstrated the anti-inflammatory effects of ginseng. Targeting Nrf2 pathway is a novel approach to the investigation of ginseng's cancer chemopreventive actions, including some oxidative stress and inflammatory conditions responsible for the initiation, promotion and progression of carcinogenesis.

Role of sulforaphane in the anti-initiating mechanism of lung carcinogenesis in vivo by modulating the metabolic activation and detoxification of benzo(a)pyrene

Biomarkers are central to the molecular epidemiology approach. Since scientific research progress within this standard, a more complete biological understanding of the specific events underlying the multistage carcinogenesis model is essential. Hence the present investigation was designed to assess the anti-initiating potential of Sulforaphane (SFN) against benzo(a)pyrene [B(a)P] induced lung carcinogenesis in female Swiss Albino Mice by evaluating the activities of xenobiotic markers, and the balance between phase I and phase II carcinogen/drug metabolizing enzymes. We sought to institute whether orally administered SFN reaches the lung tissue and increases functional capacity of detoxification enzymes in this tissue and compare the biochemical changes associated with the initiation of cancer. We demonstrated the inhibitory effects of orally administered sulforaphane on B[a]P-induced aryl hydrocarbon receptor (AHR) activation which subsequently resulted in decreased Phase-I enzyme activities in vivo. The study also highlights that treatment with sulforaphane enhanced the Nuclear factor erythroid 2-related factor 2 (Nrf2) transcription which reflects its nuclear accumulation and DNA binding in mice, together with the induction of phase II enzymes as evident from our results. These modulations by sulforaphane further result in decreased carcinogen-induced stress. By and large, the results suggest an anti-initiating role of sulforaphane in pre- and post-initiation phase of experimentally induced lung carcinogenesis in female Swiss albino mice.

Ablation of the Transcription Factor Nrf2 Promotes Ischemia-Induced Neovascularization by Enhancing the Inflammatory Response

Objective— To investigate the potential role of nuclear factor–erythroid 2–related factor 2 (Nrf2) in neovascularization with a murine surgical model of ischemia.

Methods and Results— The transcription factor Nrf2 protects against oxidative stress by increasing the transcription of genes, including those for several antioxidant enzymes that contain an antioxidant response element. Ischemia was induced by femoral artery ligation in Nrf2-deficient (Nrf2 −/− ) and wild-type mice. Ischemia-induced neovascularization was enhanced in Nrf2 −/− mice compared with that in wild-type mice. The expression of Nrf2 target genes for heme oxygenase 1 and thioredoxin 1 and the concentration of total glutathione in the ischemic hindlimb were reduced for Nrf2 −/− mice compared with wild-type mice. The infiltration of inflammatory cells and the abundance of adhesion molecule mRNA were greater in the ischemic hindlimb of Nrf2 −/− mice than in wild-type mice. The expression of monocyte chemoattractant protein-1, tumor necrosis factor-α, cyclooxygenase 2, and angiogenic factors in the ischemic hindlimb was also greater for Nrf2 −/− mice than for wild-type mice.

Conclusion— The ablation of Nrf2 promoted ischemia-induced neovascularization. This effect likely resulted from impaired antioxidant defense and increased accumulation of reactive oxygen species in endothelial cells; consequently, there was an enhanced inflammatory response.

Candidate dietary phytochemicals modulate expression of phase II enzymes GSTP1 and NQO1 in human lung cells

Many phytochemicals possess cancer-preventive properties, some putatively through phase II metabolism-mediated mutagen/oxidant quenching. We applied human lung cells in vitro to investigate the effects of several candidate phytopreventive agents, including green tea extracts (GTE), broccoli sprout extracts (BSE), epigallocatechin gallate (EGCG), sulforaphane (SFN), phenethyl isothiocyanate (PEITC), and benzyl isothiocyanate (BITC), on inducing phase II enzymes glutathione S-transferase P1 (GSTP1) and NAD(P)H:quinone oxidoreductase 1 (NQO1) at mRNA and protein levels. Primary normal human bronchial epithelial cells (NHBE), immortalized human bronchial epithelial cells (HBEC), and lung adenocarcinoma cells (A549) were exposed to diet-achievable levels of GTE and BSE (0.5, 1.0, 2.0 mg/L), or individual index components EGCG, SFN, PEITC, BITC (0.5, 1.0, 2.0 micromol/L) for 24 h, 48 h, and 6 d, respectively. mRNA assays employed RNA-specific quantitative RT-PCR and protein assays employed Western blotting. We found that in NHBE cells, while GSTP1 mRNA levels were slightly but significantly increased after exposure to GTE or BSE, NQO1 mRNA increased to 2- to 4-fold that of control when exposed to GTE, BSE, or SFN. Effects on NQO1 mRNA expression in HBEC cells were similar. NQO1 protein expression increased up to 11.8-fold in SFN-treated NHBE cells. Both GSTP1 and NQO1 protein expression in A549 cells were constitutively high but not induced under any condition. Our results suggest that NQO1 is more responsive to the studied chemopreventive agents than GSTP1 in human lung cells and there is discordance between single agent and complex mixture effects. We conclude that modulation of lung cell phase II metabolism by chemopreventive agents requires cell- and agent-specific discovery and testing.

Fermented wheat aleurone induces enzymes involved in detoxification of carcinogens and in antioxidative defence in human colon cells

Dietary fibre is fermented by the human gut flora resulting mainly in the formation of SCFA, for example, acetate, propionate and butyrate. SCFA, in particular butyrate, may be important for secondary cancer prevention by inducing apoptosis and inhibiting cell growth of cancer cells, thereby inhibiting the promotion and/or progression of cancer. Furthermore, SCFA could also act on primary cancer prevention by activation of detoxifying and antioxidative enzymes. We investigated the effects of fermented wheat aleurone on the expression of genes involved in stress response and toxicity, activity of drug-metabolising enzymes and anti-genotoxic potential. Aleurone was digested and fermented in vitro to obtain samples that reflect the content of the colon. HT29 cells and colon epithelial stripes were incubated with the resulting fermentation supernatant fractions (fs) and effects on mRNA expression of CAT, GSTP1 and SULT2B1 and enzyme activity of glutathione S-transferase (GST) and catalase (CAT) were measured. Fermented aleurone was also used to study the protection against H2O2-induced DNA damage in HT29 cells. The fs of aleurone significantly induced the mRNA expression of CAT, GSTP1 and SULT2B1 (HT29) and GSTP1 (epithelial stripes), respectively. The enzyme activities of GST (HT29) and CAT (HT29, epithelial stripes) were also unambiguously increased (1·4- to 3·7-fold) by the fs of aleurone. DNA damage induced by H2O2 was significantly reduced by the fs of aleurone after 48 h, whereupon no difference was observed compared with the faeces control. In conclusion, fermented aleurone is able to act on primary prevention by inducing mRNA expression and the activity of enzymes involved in detoxification of carcinogens and antioxidative defence.

Sulforaphane protects liver injury induced by intestinal ischemia reperfusion through Nrf2-ARE pathway

AIM: To investigate the effect of sulforaphane (SFN) on regulation of NF-E2-related factor-2 (Nrf2)-antioxidant response element (ARE) pathway in liver injury induced by intestinal ischemia/reperfusion (I/R).

METHODS: Rats were divided randomly into four experimental groups: control, SFN control, intestinal I/R and SFN pretreatment groups (n = 8 in each group). The intestinal I/R model was established by clamping the superior mesenteric artery for 1 h and 2 h reperfusion. In the SFN pretreatment group, surgery was performed as in the intestinal I/R group, with intraperitoneal administration of 3 mg/kg SFN 1 h before the operation. Intestine and liver histology was investigated. Serum levels of aspartate aminotransferase (AST), and alanine aminotransferase (ALT) were measured. Liver tissue superoxide dismutase (SOD), myeloperoxidase (MPO), glutathione (GSH) and glutathione peroxidase (GSH-Px) activity were assayed. The liver transcription factor Nrf2 and heme oxygenase-1 (HO-1) were determined by immunohistochemical analysis and Western blotting analysis.

RESULTS: Intestinal I/R induced intestinal and liver injury, characterized by histological changes as well as a significant increase in serum AST and ALT levels (AST: 260.13 ± 40.17 U/L vs 186.00 ± 24.21 U/L, P < 0.01; ALT: 139.63 ± 11.35 U/L vs 48.38 ± 10.73 U/L, P < 0.01), all of which were reduced by pretreatment with SFN, respectively (AST: 260.13 ± 40.17 U/L vs 216.63 ± 22.65 U/L, P < 0.05; ALT: 139.63 ± 11.35 U/L vs 97.63 ± 15.56 U/L, P < 0.01). The activity of SOD in the liver tissue decreased after intestinal I/R (P < 0.01), which was enhanced by SFN pretreatment (P < 0.05). In addition, compared with the control group, SFN markedly reduced liver tissue MPO activity (P < 0.05) and elevated liver tissue GSH and GSH-Px activity (P < 0.05, P < 0.05), which was in parallel with the increased level of liver Nrf2 and HO-1 expression.

CONCLUSION: SFN pretreatment attenuates liver injury induced by intestinal I/R in rats, attributable to the antioxidant effect through Nrf2-ARE pathway.

Glutathione S-transferase A4 is a positive marker for rat hepatic foci induced by clofibrate and genotoxic carcinogens

Peroxisome proliferators (PP), including clofibrate (CF), are non-genotoxic rodent carcinogens, and oxidative DNA damages are suggested as a causative event for carcinogenesis. Gene expression profiles differ between hepatic lesions induced by PP and genotoxic carcinogens. Our previous study revealed that expression of L-bifunctional enzyme (enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase, BE) was repressed in preneoplastic lesions induced by PP, whereas it was enhanced in the surrounding tissues. In the present study, we immunohistochemically examined expression of the specific glutathione S-transferase (GST) form, GST-A4, which detoxifies 4-hydroxy-alkenal, the end-product of lipid peroxides, and nuclear factor-erythroid 2-related factor 2 (Nrf2), a transcription factor for many genes encoding drug-metabolizing enzymes and defending enzymes against oxidative stress, during rat hepatocarcinogenesis induced by CF and genotoxic carcinogens. GST-A4 and Nrf2 were not expressed in BE-negative foci at 8 weeks of CF administration, but were expressed in the foci at 60 weeks. GST-A4-positive foci appeared at later stages than BE-negative foci, but its localization was coincidental with that of the latter foci. The areas of GST-A4-positive foci were larger than those of BE-negative foci without GST-A4 expression. Most GST-A4-positive foci were also positive for Nrf2. In rat livers induced by genotoxic carcinogens, GST-P-negative foci as well as GST-P-positive foci were demonstrated. GST-A4 and Nrf2 were expressed in GST-P-negative foci, whereas they were not expressed in most GST-P-positive foci. Thus, GST-A4-positive foci developed in rat livers by CF and genotoxic carcinogen administration, indicating that the enzyme is a positive marker for hepatic foci induced by these different carcinogens.

Oxidative stress in ALS: key role in motor neuron injury and therapeutic target

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder characterized by death of motor neurons leading to muscle wasting, paralysis, and death, usually within 2-3 years of symptom onset. The causes of ALS are not completely understood, and the neurodegenerative processes involved in disease progression are diverse and complex. There is substantial evidence implicating oxidative stress as a central mechanism by which motor neuron death occurs, including elevated markers of oxidative damage in ALS patient spinal cord and cerebrospinal fluid and mutations in the antioxidant enzyme superoxide dismutase 1 (SOD1) causing approximately 20% of familial ALS cases. However, the precise mechanism(s) by which mutant SOD1 leads to motor neuron degeneration has not been defined with certainty, and the ultimate trigger for increased oxidative stress in non-SOD1 cases remains unclear. Although some antioxidants have shown potential beneficial effects in animal models, human clinical trials of antioxidant therapies have so far been disappointing. Here, the evidence implicating oxidative stress in ALS pathogenesis is reviewed, along with how oxidative damage triggers or exacerbates other neurodegenerative processes, and we review the trials of a variety of antioxidants as potential therapies for ALS.

Oxidative stress generation by microcystins in aquatic animals: why and how

Microcystins (MICs) are potent toxins produced worldwide by cyanobacteria during bloom events. Phosphatases inhibition is a well recognized effect of this kind of toxins as well as oxidative stress. However, it is not fully understood why and how MICs exposure can lead to an excessive formation of reactive oxygen species (ROS) that culminate in oxidative damage. Some evidences suggest a close connection between cellular hyperphosphorylation state and oxidative stress generation induced by MICs exposure. It is shown, based on literature data, that MICs incorporation per se can be the first event that triggers glutathione depletion and the consequent increase in ROS concentration. Also, literature data suggest that hyperphosphorylated cellular environment induced by MICs exposure can modulate antioxidant enzymes, contributing to the generation of oxidative damage. This review summarizes information on MICs toxicity in aquatic animals, focusing on mechanistic aspects, and rise questions that in our opinion needs to be further investigated.

Does molecular docking reveal alternative chemopreventive mechanism of activation of oxidoreductase by sulforaphane isothiocyanates?

Isothiocyanates (ITC) are well-known chemopreventive agents extracted from vegetables. This activity results from the activation of human oxidoreductase. In this letter, the uncompetitive activatory mechanism of ITC was investigated using docking and molecular dynamics simulations. This indicates that NAD(P)H:quinone oxidoreductase can efficiently improve enzyme-substrate recognition within the catalytic site if the ITC activator supports the interaction in the uncompetitive binding site.

Dihydro-CDDO-trifluoroethyl amide (dh404), a novel Nrf2 activator, suppresses oxidative stress in cardiomyocytes

Targeting Nrf2 signaling appears to be an attractive approach for the treatment of maladaptive cardiac remodeling and dysfunction; however, pharmacological modulation of the Nrf2 pathway in the cardiovascular system remains to be established. Herein, we report that a novel synthetic triterpenoid derivative, dihydro-CDDO-trifluoroethyl amide (dh404), activates Nrf2 and suppresses oxidative stress in cardiomyocytes. Dh404 interrupted the Keap1-Cul3-Rbx1 E3 ligase complex-mediated Nrf2 ubiquitination and subsequent degradation saturating the binding capacity of Keap1 to Nrf2, thereby rendering more Nrf2 to be translocated into the nuclei to activate Nrf2-driven gene transcription. A mutant Keap1 protein containing a single cysteine-to-serine substitution at residue 151 within the BTB domain of Keap1 was resistant to dh404-induced stabilization of Nrf2 protein. In addition, dh404 did not dissociate the interaction of Nrf2 with the Keap1-Cul3-Rbx1 E3 ligase complex. Thus, it is likely that dh404 inhibits the ability of Keap1-Cul3-Rbx1 E3 ligase complex to target Nrf2 for ubiquitination and degradation via modifying Cys-151 of Keap1 to change the conformation of the complex. Moreover, dh404 was able to stabilize Nrf2 protein, to enhance Nrf2 nuclear translocation, to activate Nrf2-driven transcription, and to suppress angiotensin II (Ang II)-induced oxidative stress in cardiomyocytes. Knockdown of Nrf2 almost blocked the anti-oxidative effect of dh404. Dh404 activated Nrf2 signaling in the heart. Taken together, dh404 appears to be a novel Nrf2 activator with a therapeutic potential for cardiac diseases via suppressing oxidative stress.

Anti-inflammatory agents as cancer therapeutics

Cancer prevention sometimes referred to as tertiary prevention or chemoprevention makes use of specific xenobiotics or drugs to prevent, delay, or retard the development of cancer. Over the last two decades or so cancer prevention has made significant strides. For example, prevention of lung cancer through smoking cessation; cervical cancer prevention through regular Pap smear tests; colon cancer prevention through screening colonoscopy; and prostate cancer reductions by prostate-specific antigen measurements in conjunction with regular prostate examinations. The seminal epidemiological observation that nonsteroidal anti-inflammatory drugs (NSAIDs) prevent colon and other cancers has provided the impetus to develop novel chemoprevention approaches against cancer. To that end, a number of "designer drugs" have been synthesized that are in different stages of development, evaluation, and deployment. Some include the cyclooxygenase-2-specific inhibitors (coxibs), nitric oxide-releasing NSAIDs (NO-NSAIDs and NONO-NSAIDs), hydrogen sulfide-releasing NSAIDs, modulators of the lipoxygenase pathway, prostanoid receptor blockers, and chemokine receptor antagonists. In addition to these novel agents, there are also a host of naturally occurring compounds/micronutrients that have chemopreventive properties. This chapter reviews these classes of compounds, their utility and mechanism(s) of action against the background of mediators that link inflammation and cancer.

Inflammation compromises renal dopamine D1 receptor function in rats

We tested the effects of inflammation on renal dopamine D1 receptor signaling cascade, a key pathway that maintains sodium homeostasis and blood pressure during increased salt intake. Inflammation was produced by administering lipopolysaccharide (LPS; 4 mg/kg ip) to rats provided without (normal salt) and with 1% NaCl in drinking water for 2 wk (high salt). Control rats had saline injection and received tap water. We found that LPS increased the levels of inflammatory cytokines, interleukin-6, and tumor necrosis factor-alpha in the rats given either normal- or high-salt intake. Also, these rats had higher levels of oxidative stress markers, malondialdehyde and nitrotyrosine, and lower levels of antioxidant enzyme superoxide dismutase in the renal proximal tubules (RPTs). The nuclear levels of transcription factors NF-kappaB increased and Nrf2 decreased in the RPTs in response to LPS in rats given normal and high salt. Furthermore, D1 receptor numbers, D1 receptor proteins, and D1 receptor agonist (SKF38393)-mediated (35)S-GTPgammaS binding decreased in the RPTs in these rats. The basal activities of Na-K-ATPase in the RPTs were similar in control and LPS-treated rats given normal and high salt. SKF38393 caused inhibition of Na-K-ATPase activity in the primary cultures of RPTs treated with vehicle but not in the cultures treated with LPS. Furthermore, LPS caused an increase in blood pressure in the rats given high salt but not in the rats given normal salt. These results suggest that LPS differentially regulates NF-kappaB and Nrf2, produces inflammation, decreases antioxidant enzyme, increases oxidative stress, and causes D1 receptor dysfunction in the RPTs. The LPS-induced dysfunction of renal D1 receptors alters salt handling and causes hypertension in rats during salt overload.

LAS0811: from combinatorial chemistry to activation of antioxidant response element

The antioxidant response element (ARE) and its transcription factor, nuclear factor-erythroid 2 p45-related factor 2 (Nrf2), are potential targets for cancer chemoprevention. We sought to screen small molecules synthesized with combinatorial chemistry for activation of ARE. By high-throughput screening of 9400 small molecules from 10 combinatorial chemical libraries using HepG2 cells with an ARE-driven reporter, we have identified a novel small molecule, 1,2-dimethoxy-4,5-dinitrobenzene (LAS0811), as an activator of the ARE. LAS0811 upregulated the activity of NAD(P)H:quinone oxidoreductase 1 (NQO1), a representative antioxidative enzyme regulated by ARE. It enhanced production of an endogenous reducing agent, glutathione (GSH). In addition, LAS0811 induced expression of heme oxygenase 1 (HO1), which is an ARE-regulated enzyme with anti-inflammatory activity. Furthermore, LAS0811 reduced cell death due to the cytotoxic stress of a strong oxidant, t-butyl hydroperoxide (t-BOOH). Mechanistically, LAS0811 upregulated the expression of Nrf2 and promoted its translocation into the nuclei leading to subsequent ARE activation. Taken together, LAS0811 is a novel activator of the ARE and its associated detoxifying genes and, thus, a potential agent for cancer chemoprevention.

Targeting NRF2 signaling for cancer chemoprevention

Modulation of the metabolism and disposition of carcinogens through induction of cytoprotective enzymes is one of several promising strategies to prevent cancer. Chemopreventive efficacies of inducers such as dithiolethiones and sulforaphane have been extensively studied in animals as well as in humans. The KEAP1-NRF2 system is a key, but not unilateral, molecular target for these chemopreventive agents. The transcription factor NRF2 (NF-E2-related factor 2) is a master regulator of the expression of a subset of genes, which produce proteins responsible for the detoxication of electrophiles and reactive oxygen species as well as the removal or repair of some of their damage products. It is believed that chemopreventive enzyme inducers affect the interaction between KEAP1 and NRF2 through either mediating conformational changes of the KEAP1 protein or activating phosphorylation cascades targeting the KEAP1-NRF2 complex. These events in turn affect NRF2 stability and trafficking. Recent advances elucidating the underlying structural biology of KEAP1-NRF2 signaling and identification of the gene clusters under the transcriptional control of NRF2 are facilitating understanding of the potential pleiotropic effects of NRF2 activators and discovery of novel classes of potent chemopreventive agents such as the triterpenoids. Although there is appropriately a concern regarding a deleterious role of the KEAP1-NRF2 system in cancer cell biology, especially as the pathway affects cell survival and drug resistance, the development and the use of NRF2 activators as chemopreventive agents still holds a great promise for protection of normal cells from a diversity of environmental stresses that contribute to the burden of cancer and other chronic, degenerative diseases.

Targeting the Nrf2 pathway against cardiovascular disease

Nuclear factor E2-related factor 2 (Nrf2) is a transcription factor that controls the basal and inducible expression of a battery of antioxidant genes and other cytoprotective Phase II detoxifying enzymes. Nrf2 is ubiquitously expressed in the cardiovascular system. While several Nrf2 downstream genes have been implicated in protection against the pathogenesis of cardiovascular diseases, the precise role of Nrf2 in the cardiovascular system remains to be elucidated. Nevertheless, mounting evidence has revealed that Nrf2 is a critical regulator of cardiovascular homeostasis via the suppression of oxidative stress, a major causative factor for the development and progression of cardiovascular diseases. Therefore, Nrf2 promises to be an attractive therapeutic target for the treatment of cardiovascular disease. Herein, we review the current literature that suggests that Nrf2 is a valuable therapeutic target for cardiovascular disease, as well as experiments that illustrate the mechanisms of Nrf2 cardioprotection.

Involvement of Nrf2 activation in resistance to 5-fluorouracil in human colon cancer HT-29 cells

Acquisition of drug resistance by cancer cells is attributed to various factors including alterations in apoptotic pathways, enhanced expression of multidrug resistance-associated proteins, altered drug metabolism or uptake and/or overexpression of cytoprotective genes. Thus, potential induction of defence pathways by anticancer drugs might have a marked incidence on cancer cell resistance. 5-Fluorouracil (5-FU) remains the most commonly used anticancer drug for the treatment of colorectal cancer, although objective response rates are as low as 20%. The aim of our study was to investigate the effects of 5-FU on cytoprotective systems in human colon HT-29 cells. Our results demonstrate that 5-FU induced the expression of mRNAs encoding glutathione transferases and antioxidant enzymes. To further determine the mechanisms involved in 5-FU effects, we investigated whether it activates the Nrf2/antioxidant response element pathway which is implicated in the regulation of several genes involved in cytoprotection. Translocation of Nrf2 into the nucleus after 5-FU exposure was demonstrated by immunocytochemistry and western blotting. Using an ARE-driven reporter gene assay, activation of the luciferase activity by 5-FU was also evidenced. Moreover, transfection of HT-29 cells with siRNA directed against Nrf2 inhibited induction of Nrf2 target genes and increased 5-FU cytotoxicity. In conclusion, we demonstrate for the first time that 5-FU activates the Nrf2/ARE pathway which in turn induces cytoprotective genes and modulates chemosensitivity of HT-29 colon cancer cells. Therefore, we postulate that Nrf2 might represent a potential therapeutic target in 5-FU treatment of colon cancer.

The proximal promoter governs germ cell-specific expression of the mouse glutathione transferase mGstm5 gene

To explain the tissue-selective expression patterns of a distinct subclass of glutathione S-transferase (GST), transgenic mice expressing EGFP under control of a 2 kb promoter sequence in the 5'-flanking region of the mGstm5 gene were produced. The intent of the study was to establish whether the promoter itself or whether posttranscriptional mechanisms, particularly at the levels of mRNA translation and stability or protein targeting, based on unique properties of mGSTM5, determine the restricted expression pattern. Indeed, the transgene expression was limited to testis as the reporter was not detected in somatic tissues such as brain, kidney or liver, indicating that the mGstm5 proximal promoter is sufficient to target testis-specific expression of the gene. EGFP expression was also more restricted vis-a-vis the natural mGstm5 gene and exclusively found in germ but not in somatic cells. Real-time quantitative PCR (qPCR) data were consistent with alternate transcription start sites in which the promoter region of the natural mGstm5 gene in somatic cells is part of exon 1 of the germ cell transcript. Thus, the primary transcription start site for mGstm5 is upstream of a TATA box in testis and downstream of this motif in somatic cells. The 5' flanking sequence of the mGstm5 gene imparts germ cell-specific transcription.

Induction of antioxidant enzymes by curcumin and its analogues in human islets: implications in transplantation

OBJECTIVES

The survival of transplanted human islets is hampered by the quality of islets, which is affected by oxidative stress during isolation. The objective of this study was to determine if curcumin and its analogues could induce antioxidant enzymes in beta cells of human islets.

METHODS

The expression of antioxidant enzymes in isolated human islets exposed to curcuminoids was determined at the messenger RNA levels by real-time quantitative reverse transcription-polymerase chain reaction using Taqman probes and at the protein level by Western blot analysis. Double immunofluorescent staining of islets was carried out to determine the induction of antioxidant enzymes in beta cells.

RESULTS

Curcuminoids induced the expression of heme oxygenase 1; modulatory subunit of gamma-glutamyl-cysteine ligase; and NAD(P)H:quinone oxidoreductase 1 at the messenger RNA levels by 2- to 12-fold and at the protein levels by 2- to 6-fold in human islets. Increased expression of antioxidant enzymes was seen in beta cells of islets as shown by immunofluorescent staining. Curcuminoids also increased the islet content of glutathione (a product of the modulatory subunit of gamma-glutamyl-cysteine ligase) and the basal insulin secretion and protected them from oxidative stress.

CONCLUSIONS

Our observations suggest that curcumin or its analogues could be used to induce cellular defense against oxidative stress and improve islet transplantation outcomes.

Gamma-tocopherol-enriched mixed tocopherol diet inhibits prostate carcinogenesis in TRAMP mice

Gamma-tocopherol (gamma-T) alone or in combination with alpha-tocopherol has been shown to suppress biomarkers of oxidative stress in asthamatics and human subjects with metabolic syndrome. Oxidative stress has been implicated as a key event in prostate carcinogenesis. Hence, the purpose of this study was to examine the effects of gamma-tocopherol-enriched mixed tocopherol diet on prostate carcinogenesis in a murine prostate cancer model (TRAMP). 8 week old TRAMP males were fed 0.1% gamma-T-enriched mixed tocopherol diet that contained 20-fold higher levels of gamma-tocopherol, and roughly 3-fold higher levels of alpha-tocopherol. The effect of such diet on tumor and PIN development was observed. The expression of phase II detoxifying, antioxidant enzymes and Nrf2 mRNA and protein were determined by RT-PCR, immunohistochemistry and western blotting techniques. Treatment with gamma-T-enriched mixed tocopherols significantly suppressed the incidence of palpable tumor and Prostate Intraepithelial Neoplasia (PIN) development without affecting the expression of the transgene (SV-40). Tumor progression occurred with a significant suppression of antioxidant enzymes such as catalase, superoxide dismutase, glutathione peroxidase, heme-oxygenase-1 and phase II detoxifying enzymes. Treatment with gamma-T-enriched mixed tocopherol diet upregulated the expression of most detoxifying and antioxidant enzymes. Nrf2-a redox sensitive transcription factor known to mediate the expression of phase II detoxifying enzymes, was also significantly upregulated following treatment with gamma-T-enriched mixed tocopherol diet. Gamma-T-enriched mixed tocopherols significantly up-regulated the expression of Nrf2 and its related detoxifying and antioxidant enzymes thereby suppressing PIN and tumor development.

Dietary chemoprevention strategies for induction of phase II xenobiotic-metabolizing enzymes in lung carcinogenesis: A review

Lung cancer is the leading cause of cancer mortality for men and women in the United States and is a growing worldwide problem. Protection against lung cancer is associated with higher dietary intake of fruits and vegetables, according to recent large epidemiologic studies. One strategy for lung cancer chemoprevention focuses on the use of agents to modulate the metabolism and disposition of tobacco, environmental and endogenous carcinogens through upregulation of detoxifying phase II enzymes. We summarize the substantial evidence that suggests that induction of phase II enzymes, particularly the glutathione S-transferases, plays a direct role in chemoprotection against lung carcinogenesis. The engagement of the Keap1-Nrf2 complex regulating the antioxidant response element (ARE) signaling pathway has been identified as a key molecular target of chemopreventive phase II inducers in several systems. Monitoring of phase II enzyme induction has led to identification of novel chemopreventive agents such as the isothiocyanate sulforaphane, and the 1,2-dithiole-3-thiones. However, no agents have yet demonstrated clear benefit in human cell systems, or in clinical trials. Alternative strategies include: (a) using intermediate cancer biomarkers for the endpoint in human trials; (b) high-throughput small molecule discovery approaches for induced expression of human phase II genes; and (c) integrative approaches that consider pharmacogenetics, along with pharmacokinetics and pharmacodynamics in target lung tissue. These approaches may lead to a more effective strategy of tailored chemoprevention efforts using compounds with proven human activity.

Activation of the Nrf2-antioxidant system by a novel cyclooxygenase-2 inhibitor furan-2-yl-3-pyridin-2-yl-propenone: implication in anti-inflammatory function by Nrf2 activator

Furan-2-yl-3-pyridin-2-yl-propenone (FPP-3) is a novel synthetic compound and has demonstrated anti-inflammatory activity by inhibiting cyclooxygenase-2 (COX-2). It is widely accepted that reactive oxygen species (ROS) generated by activated inflammatory cells can exacerbate inflammation. In this study, the potential antioxidative efficacy of FPP-3 has been investigated in murine cells. FPP-3 increased the expression of multiple antioxidative enzymes, including NAD(P)H:quinone oxidoreductase 1 (Nqo1), gamma-glutamylcysteine ligase (GCL) and heme oxygenase-1 (HO-1), by facilitating the nuclear translocation of nuclear factor-erythroid 2-p45-related factor 2 (Nrf2). Inducibility of antioxidant proteins such as HO-1 were lost in nrf2-deficient murine fibroblasts. As a result of enhanced cellular antioxidative capacity, elevation of NF-kappaB-driven reporter gene expression by lipopolysaccharide was attenuated by FPP-3 treatment in murine fibroblasts. Furthermore, FPP-3 treatment inhibited UVA-mediated induction of COX-2 in murine keratinocytes. Our current study suggests that FPP-3, which has been developed as a novel COX-2 inhibitor, has antioxidative properties by activating the Nrf2-ARE pathway. The dual function of this compound may provide a better strategy to block/attenuate the inflammation process and to alleviate ROS-associated inflammatory complications.

The Antioxidant/electrophile Response Element Motif

Cells exposed to oxidative stress or electrophilic xenobiotics respond by transcriptionally up-regulating a battery of genes that contain a cis-acting element in their promoter region known as the antioxidant/electrophile response element (ARE). Mutational analysis of the promoter regions of ARE-containing genes led to the creation of two different models for the ARE; a core ARE (cARE: RTGACnnnGC) and an extended ARE (eARE: TMAnnRTGAYnnnGCAwwww). Using bioinformatic software we have aligned the promoter regions of several ARE-containing genes to produce two position-specific probability matrices that independently describe the cARE and eARE. These matrices can also be used to quantitatively assess putative AREs.

Inhibitory effects of methanol extract of plum (Prunus salicina L., cv. 'Soldam') fruits against benzo(alpha)pyrene-induced toxicity in mice

This study was carried out to investigate the chemopreventive effects of immature plum extracts. The methanol extract of immature plums (plum 1), that are picked at 20-40 days before final harvest, has remarkably inhibited the growth of hepatoma HepG2 cells. The effects of immature plum extracts on hepatotoxicity in benzo(alpha)pyrene (B(alpha)P, carcinogen)-treated mice were investigated. Male ICR mice were pretreated with immature plum extracts (2.5 or 5 g/kg bw/day, for 5 days, i.p.) before treatment with B(alpha)P(0.5 mg/kg bw, i.p., single dose). The activities of serum aminotransferase, cytochrome P450 (CYPs) and the hepatic content of lipid peroxide were increased on B(alpha)P-treatment group than control, but those levels were significantly decreased by the pretreatment of immature plum extracts. The primary CYPs involved in the metabolism and bioactivation of B(alpha)P are CYP1A1. The pretreatment of immature plum extracts inhibited the induction of CYP1A1 expression. The activities of glutathione peroxidase, superoxide dismutase and catalase were decreased by the pretreatment of immature plum extracts more than with B(alpha)P alone. Whereas, the hepatic content of glutathione and glutathione S-transferase activity depleted by B(alpha)P was significantly increased (p > 0.05). These results suggest that immature plum extracts may counteract toxic effects of carcinogens, such as B(alpha)P, and therefore possess the chemopreventive efficacy.

Gender divergent expression of Nqo1 in Sprague Dawley and August Copenhagen x Irish rats

In the mammalian liver, there is an abundance of enzymes that function to enable the safe and efficient elimination of potentially harmful xenobiotics that are encountered through environmental exposure. A variety of factors, including gender and genetic polymorphisms, contribute to the variation between an individual system's detoxification capacity and thus its ability to protect itself against oxidative stress, cellular damage, cell death, etc. NAD(P)H:quinone oxidoreducatase 1 (Nqo1) is an antioxidant enzyme that plays a major role in reducing reactive electrophiles, thereby protecting cells from free-radical damage and oxidative stress. The goal of this study was to determine the gender-specific expression and inducibility of Nqo1 in the Sprague Dawley (SD) and August Copenhagen x Irish (ACI) rat strains, two strains that are commonly used in drug metabolism and drug-induced enzyme induction, toxicity, and carcinogenesis studies. Nqo1 mRNA, protein, and activity levels were determined through 96 h in SD and ACI males and females following treatment with known Nqo1 inducers oltipraz and butylated hydroxyanisole. In the SD strain, gender dimorphic expression of Nqo1 was observed with female mRNA, protein, and activity levels being significantly higher than in males. In contrast, there were minimal differences in Nqo1 mRNA, protein, and activity levels between ACI males and females. The gender dimorphic expression of Nqo1 in the SD rats was maintained through the course of induction, with female-induced levels greater than male-induced levels indicating that SD females may have a greater capacity to protect against oxidative stress and thus a decreased susceptibility to carcinogens.

Renal protection by 3H-1,2-dithiole-3-thione against cisplatin through the Nrf2-antioxidant pathway

Cisplatin is commonly used for the treatment of several solid tumors. However, its clinical use is often limited by renal toxicity. The indirect antioxidant 3H-1,2-dithiole-3-thione (D3T) has been known to protect cells from oxidative damage by up-regulating the expression of antioxidative genes through the transcription factor NF-E2-related factor 2 (Nrf2) pathway. We hypothesized that D3T treatment may be protective against cisplatin-induced nephrotoxicity by enhancing the antioxidative capacity of renal cells. In cultured murine tubular epithelial cells, D3T facilitates the nuclear accumulation of Nrf2 and the subsequent expression of its target genes such as glutamate cysteine ligase (GCL). Increased GSH pool in D3T-treated renal cells appears to be associated with amelioration of cisplatin-mediated cell death. Protective effects of D3T were also observed in mice. Oral administration of D3T (0.25mmol/kg) increased the expression of GCL in mouse kidney, which resulted in suppression of cisplatin-mediated increases in blood urea nitrogen and serum creatinine. Histopathological changes representing cisplatin-induced acute renal failure were also effectively ameliorated by D3T treatment. Collectively, these results indicate that pharmacological activation of the Nrf2 pathway might have a beneficial effect on reducing chemotherapy-associated cytotoxic adverse effects.

Protein targets of reactive metabolites of thiobenzamide in rat liver in vivo

Thiobenzamide (TB) is a potent hepatotoxin in rats, causing dose-dependent hyperbilirubinemia, steatosis, and centrolobular necrosis. These effects arise subsequent to and appear to result from the covalent binding of the iminosulfinic acid metabolite of TB to cellular proteins and phosphatidylethanolamine lipids [ Ji et al. ( 2007) Chem. Res. Toxicol. 20, 701- 708 ]. To better understand the relationship between the protein covalent binding and the toxicity of TB, we investigated the chemistry of the adduction process and the identity of the target proteins. Cytosolic and microsomal proteins isolated from the livers of rats treated with a hepatotoxic dose of [ carboxyl- (14)C]TB contained high levels of covalently bound radioactivity (25.6 and 36.8 nmol equiv/mg protein, respectively). These proteins were fractionated by two-dimensional gel electrophoresis, and radioactive spots (154 cytosolic and 118 microsomal) were located by phosphorimaging. Corresponding spots from animals treated with a 1:1 mixture of TB and TB- d 5 were similarly separated, the spots were excised, and the proteins were digested in gel with trypsin. Peptide mass mapping identified 42 cytosolic and 24 microsomal proteins, many of which appeared in more than one spot on the gel; however, only a few spots contained more than one identifiable protein. Eighty-six peptides carrying either a benzoyl or a benzimidoyl adduct on a lysine side chain were clearly recognized by their d 0/ d 5 isotopic signature (sometimes both in the same digest). Because model studies showed that benzoyl adducts do not arise by hydrolysis of benzimidoyl adducts, it was proposed that TB undergoes S-oxidation twice to form iminosulfinic acid 4 [PhC(NH)SO 2H], which either benzimidoylates a lysine side chain or undergoes hydrolysis to 9 [PhC(O)SO 2H] and then benzoylates a lysine side chain. The proteins modified by TB metabolites serve a range of biological functions and form a set that overlaps partly with the sets of proteins known to be modified by several other metabolically activated hepatotoxins. The relationship of the adduction of these target proteins to the cytotoxicity of reactive metabolites is discussed in terms of three currently popular mechanisms of toxicity: inhibition of enzymes important to the maintenance of cellular energy and homeostasis, the unfolded protein response, and interference with kinase-based signaling pathways that affect cell survival.

The significance of Nrf2 pathway in (photo)-oxidative stress response in melanocytes and keratinocytes of the human epidermis

The expression of genes encoding antioxidant and/or phase 2 detoxifying enzymes can be enhanced in response to various environmental stresses. The main transcription factor involved in this response is nuclear factor erythroid 2-related factor 2 (Nrf2). Nrf2 activity is negatively regulated by the protein Kelch-like-Ech-associated-protein 1 (Keap1). While the roles of Nrf2 and phase 2 genes in chemoprevention of carcinogenesis have been well described; only few studies have dealt with their role in skin cancer. Normal human keratinocytes (NHK) and melanocytes (NHM) were treated by chemical inducers of the Nrf2 pathway or by small interfering RNAs (siRNA) used to knock down Keap1 mRNA. The above treatments resulted in significant stimulation of NQO-1 (NADPH-Quinone-Oxidoreductase 1) gene expression. GCL (gamma-Glutamyl-cysteinyl-ligase) gene was also induced but interestingly increased mRNA encoding the catalytic, heavy subunit GCLC was mainly stimulated in NHK, whereas the mRNA encoding the modifier, light subunit GCLM was mostly induced in NHM. HO-1 (Heme Oxygenase 1) gene induction was relatively strong in NHM, but generally absent in NHK, except when the cells were subjected to cytotoxic doses of the above chemicals. Exposure to solar UV (UVB + UVA, 300-400 nm) or to UVA alone (320-400 nm) confirmed this trend, but interestingly, at doses where cell growth reduction was comparable, UVA was generally more efficient than solar UV in inducing phase 2 genes. When siRNAs directed against Nrf2 were used, a strong down-regulation of NQO-1 expression was observed in both, NHM and NHK, whereas reduction of HO-1 expression was mainly detected in NHM. To our knowledge, this is the first study comparing phase 2 gene modulation in NHK and NHM. The results hereby presented should contribute to a better understanding of the molecular mechanisms involved in skin adaptation to environmental stress.

Protective interventions to prevent aflatoxin-induced carcinogenesis in developing countries

The public health impact of aflatoxin exposure is pervasive in economically developing countries; consequently, we need to design intervention strategies for prevention that are practicable for these high-risk populations. The adverse health consequences of aflatoxins in populations are quite varied, eliciting acute effects, such as rapid death, and chronic outcomes, such as hepatocellular carcinoma. Furthermore, a number of epidemiological studies describe a variety of general adverse health effects associated with aflatoxin, such as impaired growth in children. Thus, the magnitude of the problem is disseminated across the entire spectrum of age, gender, and health status in the population. The aflatoxins multiplicatively increase the risk of liver cancer in people chronically infected with hepatitis B virus (HBV), which illustrates the deleterious impact that even low toxin levels in the diet can pose for human health. Thus other aflatoxin interactions, which likely contribute to the disease burden, still remain to be identified. Therefore, many diverse and appropriate strategies for disease prevention are needed to decrease the incidence of aflatoxin carcinogenesis in developing countries.

The role of Nrf2 in increased reactive oxygen species and DNA damage in prostate tumorigenesis

The impact of oxidative stress in human cancer has been extensively studied. It is accepted that elevated reactive oxygen species (ROS) promote mutagenic DNA damage. Even with an extensive armament of cellular antioxidants and detoxification enzymes, alterations to DNA occur that initiate cellular transformation. Erythroid 2p45 (NF-E2)-related factor 2 (Nrf2) is a basic-region leucine zipper transcription factor that mediates the expression of key protective enzymes through the antioxidant-response element (ARE). By analysing 10 human prostate cancer microarray data sets, we have determined that Nrf2 and members of the glutathione-S-transferase (GST) mu family are extensively decreased in human prostate cancer. Using the TRAMP transgene and Rb and Nrf2 knockout murine models, we demonstrated that the loss of Nrf2 initiates a detrimental cascade of reduced GST expression, elevated ROS levels and ultimately DNA damage associated with tumorigenesis. Based on overwhelming data from clinical samples and the current functional analysis, we propose that the disruption of the Nrf2-antioxidant axis leads to increased oxidative stress and DNA damage in the initiation of cellular transformation in the prostate gland.

Phytochemical regulation of UDP-glucuronosyltransferases: implications for cancer prevention

Uridine 5'-diphospho-glucuronosyltransferases (UGTs) are Phase II biotransformation enzymes that metabolize endogenous and exogenous compounds, some of which have been associated with cancer risk. Many phytochemicals have been shown to induce UGTs in humans, rodents, and cell culture systems. Because UGTs maintain hormone balance and facilitate excretion of potentially carcinogenic compounds, regulation of their expression and activity may affect cancer risk. Phytochemicals regulate transcription factors such as the nuclear factor-erythroid 2-related factor 2 (Nrf2), aryl hydrocarbon, and pregnane X receptors as well as proteins in several signal transduction cascades that converge on Nrf2 to stimulate UGT expression. This induction can be modified by several factors, including phytochemical dose and bioavailability and interindividual variation in enzyme expression. In this review, we summarize the knowledge of dietary modulation of UGTs, particularly by phytochemicals, and discuss the potential mechanisms by which phytochemicals regulate UGT transcription.

Sulindac and its metabolites induce carcinogen metabolizing enzymes in human colon cancer cells

Sulindac is a nonsteroidal antiinflammatory drug that has been demonstrated to be a potent chemopreventive agent against colorectal cancer in both human and animal models. In vivo, sulindac may be reversibly reduced to the active antiinflammatory compound, sulindac sulfide, or irreversibly oxidized to sulindac sulfone. Sulindac has also been shown to inhibit polycyclic aromatic hydrocarbon (PAH)-induced cancer, but the molecular mechanisms of its antitumor effect remain unclear. In this study, we investigated the effects of sulindac and its metabolites on the expression of enzymes that metabolize and detoxify PAHs in 2 human colon cancer cell lines, LS180 and Caco-2. Sulindac and sulindac sulfide induced a sustained, concentration-dependent increase in CYP enzyme activity as well as an increase in the mRNA levels of CYP1A1, CYP1A2 and CYP1B1. Sulindac and sulindac sulfide induced the transcription of the CYP1A1 gene, as measured by the level of heterogeneous nuclear CYP1A1 RNA and verified by the use of actinomycin D as a transcription inhibitor. Chromatin immunoprecipitation assays demonstrated that sulindac and sulindac sulfide also increased the nuclear level of activated aryl hydrocarbon receptor, the transcription factor which mediates CYP expression. Additionally, sulindac and both metabolites increased the activity and mRNA expression of the carcinogen detoxification enzyme NAD(P)H:quinone oxidoreductase, as well as the expression of UDP-glucuronosyltransferase mRNA. These results show an overall upregulation of carcinogen metabolizing enzymes in colon cancer cells treated with sulindac, sulindac sulfide and sulindac sulfone that may contribute to the established chemoprotective effects of these compounds.

Resveratrol induces glutathione synthesis by activation of Nrf2 and protects against cigarette smoke-mediated oxidative stress in human lung epithelial cells

Nuclear erythroid-related factor 2 (Nrf2), a redox-sensitive transcription factor, is involved in transcriptional regulation of many antioxidant genes, including glutamate-cysteine ligase (GCL). Cigarette smoke (CS) is known to cause oxidative stress and deplete glutathione (GSH) levels in alveolar epithelial cells. We hypothesized that resveratrol, a polyphenolic phytoalexin, has antioxidant signaling properties by inducing GSH biosynthesis via the activation of Nrf2 and protects lung epithelial cells against CS-mediated oxidative stress. Treatment of human primary small airway epithelial and human alveolar epithelial (A549) cells with CS extract (CSE) dose dependently decreased GSH levels and GCL activity, effects that were associated with enhanced production of reactive oxygen species. Resveratrol restored CSE-depleted GSH levels by upregulation of GCL via activation of Nrf2 and also quenched CSE-induced release of reactive oxygen species. Interestingly, CSE failed to induce nuclear translocation of Nrf2 in A549 and small airway epithelial cells. On the contrary, Nrf2 was localized in the cytosol of alveolar and airway epithelial cells due to CSE-mediated posttranslational modifications such as aldehyde/carbonyl adduct formation and nitration. On the other hand, resveratrol attenuated CSE-mediated Nrf2 modifications, thereby inducing its nuclear translocation associated with GCL gene transcription, as demonstrated by GCL-promoter reporter and Nrf2 small interfering RNA approaches. Thus resveratrol attenuates CSE-mediated GSH depletion by inducing GSH synthesis and protects epithelial cells by reversing CSE-induced posttranslational modifications of Nrf2. These data may have implications in dietary modulation of antioxidants in treatment of chronic obstructive pulmonary disease.

Role of the Nrf2-antioxidant system in cytotoxicity mediated by anticancer cisplatin: implication to cancer cell resistance

The treatment of alkylating cytotoxic drug cisplatin is often limited by high incidence rate of resistance. In the present study, the potential involvement of the transcription factor Nrf2 in determination of cisplatin cytotoxicity has been investigated. Nrf2-deficient murine embryonic fibroblasts showed increased cell death, cytotoxicity, and apoptosis in response to cisplatin treatment compared to wild-type cells. Cisplatin-resistant human ovarian cancer SK-OV cells, which are retaining 25-fold higher levels of GSH than murine fibroblasts, could be sensitized by inhibition of Nrf2. Transfection with Nrf2 siRNA into SK-OV cells resulted in severe degree of GSH depletion and exacerbated cytotoxicity following cisplatin treatment compared to scrambled RNA control. In conclusion, we propose that the Nrf2 pathway, which plays a protective role in normal cells, can be a potential target to control cancer cell resistance to oxidants, cytotoxic chemicals, and radiation.

Structural modulation of reactivity/activity in design of improved benzothiophene selective estrogen receptor modulators: induction of chemopreventive mechanisms

The benzothiophene selective estrogen receptor modulators (SERM) raloxifene and arzoxifene are in clinical use and clinical trials for chemoprevention of breast cancer and other indications. These SERMs are "oxidatively labile" and therefore have potential to activate antioxidant responsive element (ARE) transcription of genes for cytoprotective phase II enzymes such as NAD(P)H-dependent quinone oxidoreductase 1 (NQO1). To study this possible mechanism of cancer chemoprevention, a family of benzothiophene SERMs was developed with modulated redox activity, including arzoxifene and its metabolite desmethylarzoxifene (DMA). The relative antioxidant activity of these SERMs was assayed and correlated with induction of NQO1 in murine and human liver cells. DMA was found to induce NQO1 and to activate ARE more strongly than other SERMs, including raloxifene and 4-hydroxytamoxifen. Livers from female, juvenile rats treated for 3 days with estradiol and/or with the benzothiophene SERMs arzoxifene, DMA, and F-DMA showed substantial induction of NQO1 by the benzothiophene SERMs. No persuasive evidence in this assay or in MCF-7 breast cancer cells was obtained of a major role for the estrogen receptor in induction of NQO1 by the benzothiophene SERMs. These results suggest that arzoxifene might provide chemopreventive benefits over raloxifene and other SERMs via metabolism to DMA and stimulation of ARE-mediated induction of phase II enzymes. The correlation of SERM structure with antioxidant activity and NQO1 induction also suggests that oxidative bioactivation of SERMs may be modulated to enhance chemopreventive activity.

Induction of Nrf2-regulated genes by 3H-1, 2-dithiole-3-thione through the ERK signaling pathway in murine keratinocytes

Electrophile and free radical detoxifying enzymes including NAD(P)H:quinine oxidoreductase 1 (Nqo1) play an important role in the defense system by enhancing cellular antioxidant capacity. Chemopreventive efficacy of 3H-1,2-dithiole-3-thione (D3T) is mediated through activation of the transcription factor Nrf2 and subsequent elevation of detoxifying enzymes. In the present study, we have investigated the potential role of extracellular signal-regulated kinase (ERK) in regulation of D3T-induced and Nrf2-dependent gene expression in murine keratinocytes. Expression levels of Nqo1 were highly inducible by D3T treatment and increased nuclear levels of Nrf2 were observed in these cells. Treatment with pharmacological inhibitor of ERK1/2 largely blocked nuclear accumulation of Nrf2, ARE-driven reporter gene expression, and induction of Nqo1, as well as other phase 2 genes. Activation of ERK1/2 has been demonstrated following treatment with D3T. While, inhibitors of p38, PKC and PI3K did not affect ARE-driven gene expression. Involvement of the ERK1/2 cascade in inducible ARE-transcription activities was also observed in cells treated with other types of inducers oltipraz, sulforaphane and hydrogen peroxide. Collectively, current study suggests that phosphorylation cascade via ERK1/2 is associated with the activation process of Nrf2 and subsequent transactivation of its target gene Nqo1 following treatment with dithiolethione in murine keratinocyte.

Induction of Apoptosis in HT-29 Cells by Extracts from Isothiocyanates-rich Varieties ofBrassica Oleracea

Among the vegetables with anti-carcinogenic properties, members of the genus Brassica are the most effective at reducing the risk of cancer. This property may be explained by their principle bioactive compounds, isothiocyanates (ITCs). The aim of this study was to measure the amounts of ITCs in extracts from vegetables of the Brasssica genus and assay them for potency of induction of apoptosis in a colorectal cancer cell line (HT-29). ITCs were determined by the cyclocondensation assay with 1,2-benzenedithiol and induction of apoptosis by assessment of cell viability, caspase-3 activity and DNA fragmentation. Purple cabbage extract showed the highest ITC concentration per gram, fresh weight, followed by black cabbage and Romanesco cauliflower. At ITC concentrations of 7.08 microg/mL these extracts decreased cell viability and induced caspase-3 and DNA fragmentation at 48h. Brussels sprouts showed the strongest effects on cell viability and caspase-3 activity. Varieties of Brassica Oleracea are rich sources of ITCs that potently inhibit the growth of colon cancer cells by inducting apoptosis. All the extracts showed anticancer activity at ITC concentrations of between 3.54 to 7.08 mug/mL, which are achievable in vivo. Our results showed that ITC concentration and the chemopreventive responses of plant extracts vary among the varieties of Brassica Oleracea studied and among their cultivars.

Histone acetyltransferase MOZ acts as a co-activator of Nrf2-MafK and induces tumour marker gene expression during hepatocarcinogenesis

HATs (histone acetyltransferases) contribute to the regulation of gene expression, and loss or dysregulation of these activities may link to tumorigenesis. Here, we demonstrate that expression levels of HATs, p300 and CBP [CREB (cAMP-response-element-binding protein)-binding protein] were decreased during chemical hepatocarcinogenesis, whereas expression of MOZ (monocytic leukaemia zinc-finger protein; MYST3)--a member of the MYST [MOZ, Ybf2/Sas3, Sas2 and TIP60 (Tat-interacting protein, 60 kDa)] acetyltransferase family--was induced. Although the MOZ gene frequently is rearranged in leukaemia, we were unable to detect MOZ rearrangement in livers with hyperplastic nodules. We examined the effect of MOZ on hepatocarcinogenic-specific gene expression. GSTP (glutathione S-transferase placental form) is a Phase II detoxification enzyme and a well-known tumour marker that is specifically elevated during hepatocarcinogenesis. GSTP gene activation is regulated mainly by the GPE1 (GSTP enhancer 1) enhancer element, which is recognized by the Nrf2 (nuclear factor-erythroid 2 p45 subunit-related factor 2)-MafK heterodimer. We found that MOZ enhances GSTP promoter activity through GPE1 and acts as a co-activator of the Nrf2-MafK heterodimer. Further, exogenous MOZ induced GSTP expression in rat hepatoma H4IIE cells. These results suggest that during early hepatocarcinogenesis, aberrantly expressed MOZ may induce GSTP expression through the Nrf2-mediated pathway.

Preclinical and clinical evaluation of sulforaphane for chemoprevention in the breast

Consumers of higher levels of Brassica vegetables, particularly those of the genus Brassica (broccoli, Brussels sprouts and cabbage), reduce their susceptibility to cancer at a variety of organ sites. Brassica vegetables contain high concentrations of glucosinolates that can be hydrolyzed by the plant enzyme, myrosinase, or intestinal microflora to isothiocyanates, potent inducers of cytoprotective enzymes and inhibitors of carcinogenesis. Oral administration of either the isothiocyanate, sulforaphane, or its glucosinolate precursor, glucoraphanin, inhibits mammary carcinogenesis in rats treated with 7,12-dimethylbenz[a]anthracene. In this study, we sought to determine whether sulforaphane exerts a direct chemopreventive action on animal and human mammary tissue. The pharmacokinetics and pharmacodynamics of a single 150 mumol oral dose of sulforaphane were evaluated in the rat mammary gland. We detected sulforaphane metabolites at concentrations known to alter gene expression in cell culture. Elevated cytoprotective NAD(P)H:quinone oxidoreductase (NQO1) and heme oxygenase-1 (HO-1) gene transcripts were measured using quantitative real-time polymerase chain reaction. An observed 3-fold increase in NQO1 enzymatic activity, as well as 4-fold elevated immunostaining of HO-1 in rat mammary epithelium, provides strong evidence of a pronounced pharmacodynamic action of sulforaphane. In a subsequent pilot study, eight healthy women undergoing reduction mammoplasty were given a single dose of a broccoli sprout preparation containing 200 mumol of sulforaphane. Following oral dosing, sulforaphane metabolites were readily measurable in human breast tissue enriched for epithelial cells. These findings provide a strong rationale for evaluating the protective effects of a broccoli sprout preparation in clinical trials of women at risk for breast cancer.

Application of genomic biomarkers to predict increased lung tumor incidence in 2-year rodent cancer bioassays

Rodent cancer bioassays are part of a legacy of safety testing that has not changed significantly over the past 30 years. The bioassays are expensive, time consuming, and use hundreds of animals. Fewer than 1500 chemicals have been tested in a rodent cancer bioassay compared to the thousands of environmental and industrial chemicals that remain untested for carcinogenic activity. In this study, we used existing data generated by the National Toxicology Program (NTP) to identify gene expression biomarkers that can predict results from a rodent cancer bioassay. A set of 13 diverse chemicals was selected from those tested by the NTP. Seven chemicals were positive for increased lung tumor incidence in female B6C3F1 mice and six were negative. Female mice were exposed subchronically to each of the 13 chemicals, and microarray analysis was performed on the lung. Statistical classification analysis using the gene expression profiles identified a set of eight probe sets corresponding to six genes whose expression correctly predicted the increase in lung tumor incidence with 93.9% accuracy. The sensitivity and specificity were 95.2 and 91.8%, respectively. Among the six genes in the predictive signature, most were enzymes involved in endogenous and xenobiotic metabolism, and one gene was a growth factor receptor involved in lung development. The results demonstrate that increases in chemically induced lung tumor incidence in female mice can be predicted using gene biomarkers from a subchronic exposure and may form the basis of a more efficient and economical approach for evaluating the carcinogenic activity of chemicals.