Nrf2-dependent induction of NQO1 in mouse aortic endothelial cells overexpressing catalase

Methionine redox regulation of actin-interacting proteins primarily governs antioxidative signaling and response to the salvianolic acid B treatment in EA.hy926 cells

Actin-interacting proteins are important molecules for filament assembly and cytoskeletal signaling within vascular endothelium. Disruption in their interactions causes endothelial pathogenesis through redox imbalance. Actin filament redox regulation remains largely unexplored, in the context of pharmacological treatment. This work focused on the peptidyl methionine (M) redox regulation of actin-interacting proteins, aiming at elucidating its role on governing antioxidative signaling and response. Endothelial EA.hy926 cells were subjected to treatment with salvianolic acid B (Sal B) and tert-butyl-hydroperoxide (tBHP) stimulation. Mass spectrometry was employed to characterize redox status of proteins, including actin, myosin-9, kelch-like erythroid-derived cap-n-collar homology-associated protein 1 (Keap1), plastin-3, prelamin-A/C and vimentin. The protein redox landscape revealed distinct stoichiometric ratios or reaction site transitions mediated by M sulfoxide reductase and reactive oxygen species. In comparison with effects of tBHP stimulation, Sal B treatment prevented oxidation at actin M325, myosin-9 M1489/1565, Keap1 M120, plastin-3 M592, prelamin-A/C M187/371/540 and vimentin M344. For Keap1, reaction site was transitioned within its scaffolding region to the actin ring. These protein M oxidation regulations contributed to the Sal B cytoprotective effects on actin filament. Additionally, regarding the Keap1 homo-dimerization region, Sal B preventive roles against M120 oxidation acted as a primary signal driver to activate nuclear factor erythroid 2-related factor 2 (Nrf2). Transcriptional splicing of non-POU domain-containing octamer-binding protein was validated during the Sal B-mediated overexpression of NAD(P)H dehydrogenase [quinone] 1. This molecular redox regulation of actin-interacting proteins provided valuable insights into the phenolic structures of Sal B analogs, showing potential antioxidative effects on vascular endothelium.

Antioxidant enzymes immobilized on gold and silver nanoparticles enhance DNA repairing systems of rat skin after exposure to ultraviolet radiation

The aim of the study was to investigate in vivo whether the application of immobilized superoxide dismutase (SOD) and catalase (CAT) could enhance DNA repairing systems and reduce level of CPD (cyclobutane pyrimidine dimers) and 6-4PP ((6-4) pyrimidine-pyrimidone photoproducts), and whether the immobilization on gold (AuNPs) and silver (AgNPs) nanoparticles affects the outcome. The study presents secondary analysis of our previous research. Three-day application of SOD and CAT in all forms of solution decreased the levels of CPD and 6-4PP boosted by UV irradiation. The mRNA expression level of the nucleotide excision repair (NER) system genes (XPA, XPC, ERCC1, ERCC2, ERCC3, LIG1) increased after application of immobilized and free enzymes. Increased by UV irradiation, p53 mRNA expression level normalized with the enzyme application. In conclusion, application of free and immobilized antioxidant enzymes accelerates removal of harmful effects of UV radiation in the rat skin by increasing expression level of NER genes.

Gstm1/Gstt1 is essential for reducing cisplatin ototoxicity in CBA/CaJ mice

Cisplatin is a widely used chemotherapeutic agent. However, its clinical utility is limited because of cisplatin-induced ototoxicity. Glutathione S-transferase (GST) was found to play a vital role in reducing cisplatin ototoxicity in mice. Deletion polymorphisms of GSTM1 and GSTT1, members of the GST family, are common in humans and are presumed to be associated with cisplatin-induced hearing impairment. However, the specific roles of GSTM1 and GSTT1 in cisplatin ototoxicity are not completely clear. Here, under cisplatin treatment, simultaneous deletion of Gstm1 and Gstt1 lead to a more profound hearing loss in CBA/CaJ mice (Gstm1/Gstt1-DKO) than in wild-type mice. The Gstm1/Gstt1-DKO mice, in which phase II detoxification genes were upregulated, exhibited more severe oxidative stress and higher outer hair cell apoptosis in the cochleae than the control mice. Thus, our study revealed that Gstm1 and Gstt1 protect auditory hair cells from cisplatin-induced ototoxicity in the CBA/CaJ mice, and genetic screening for GSTM1 and GSTT1 polymorphisms could help determine a standard cisplatin dose for cancer patients undergoing chemotherapy.

Comparing the effects of an exposure to a polycyclic aromatic hydrocarbon mixture versus individual polycyclic aromatic hydrocarbons during monocyte to macrophage differentiation: Mixture exposure results in altered immune metrics

Polycyclic aromatic hydrocarbons (PAHs) are generated by the incomplete combustion of carbon. Exposures correlate with systemic immune dysfunction and overall immune suppression. Real-world exposures to PAHs are almost always encountered as mixtures; however, research overwhelmingly centers on isolated exposures to a single PAH, benzo[a]pyrene (B[a]P). Here, a human monocyte line (U937) was exposed to B[a]P, benz[a]anthracene (B[a]A), or a mixture of six PAHs (6-MIX) to assess the differential toxicity on monocytes. Further, monocytes were exposed to PAHs with and without CYP1A1 inhibitors during macrophage differentiation to delineate PAH exposure and PAH metabolism-driven alterations to the immune response. U937 monocytes exposed to B[a]P, B[a]A, or 6-MIX had higher levels of cellular health and growth not observed following equimolar exposures to other individual PAHs. PAH exposures during differentiation did not alter monocyte-derived macrophage (MDM) numbers; however, B[a]A and 6-MIX exposures significantly altered M1/M2 polarization in a CYP1A1-dependent manner. U937-MDM adherence was differentially suppressed by all three PAH treatments with 6-MIX exposed U937-MDM having significantly more adhesion than U937-MDM exposed to either individual PAH. Finally, 6-MIX exposures during differentiation reduced U937-MDM endocytic function significantly less than B[a]A exposed cells. Exposure to a unique PAH mixture during U937-MDM differentiation resulted in mixture-specific alterations of pro-inflammatory markers compared to individual PAH exposures. While subtle, these differences highlight the probability that using a model PAH, B[a]P, may not accurately reflect the effects of PAH mixture exposures. Therefore, future studies should include various PAH mixtures that encompass probable real-world PAH exposures for the endpoints under investigation.

Ginnalin A Binds to the Subpockets of Keap1 Kelch Domain To Activate the Nrf2-Regulated Antioxidant Defense System in SH-SY5Y Cells

Ginnalin A (GA), a polyphenol from the red maple, was reported to be a potential ROS scavenger or an activator of nuclear factor erythroid-2 related factor 2 (Nrf2) in cancer cells. However, whether GA could activate Nrf2 in neuronal cells and the exact mode of action are unknown. We performed molecular docking calculations, which revealed that GA fits well into the five subpockets of the Kelch-like ECH-associated protein1 (Keap1) Kelch domain via hydrogen bonding and hydrophobic interaction. Our cytotoxicity assays demonstrate that pretreating SH-SY5Y cells with 20 μM GA effectively prevents cells from oxidative assault by 6-hydroxydopamine (6-OHDA). Fluorescence imaging indicates that upon the GA pretreatment, Nrf2 dissociates from the Keap1-Nrf2 complex and translocates into nucleus to activate the cellular antixodant system. Real-time qPCR quantification and Western blotting verified that the GA pretreatment elevates NAD(P)H quinone oxidoreductase-1 (NQO1) by more than 4.6-fold, heme oxygenase (HO-1) by about 1.2-fold, and the glutamate-cysteine ligase catalytic (GCLC) subunit by 0.7-fold. The higher antixidant protein levels, along with increased glutathione concentration, decrease intracellular reactive oxygen species and alleviate the 6-OHDA-induced oxidative damage. Silence of Nrf2 abrogates the cytoprotection of the GA pretreatment, confirming that the Keap1/Nrf2-ARE (antioxidant response element) pathway is solely responsible for the GA's biological effects. GA is a promising natural compound for sensitizing neuronal cells' antioxidative defense system to offset oxidative stress, a condition closely linked to the pathogenesis of Parkinson's disease.

NADPH-quinone oxidoreductase-1 mediates Benzo-[a]-pyrene-1,6-quinone-induced cytotoxicity and reactive oxygen species production in human EA.hy926 endothelial cells

Numerous studies conducted in the past have reported deaths in the human population due to cardiovascular diseases (CVD) on exposure to air particulate matter (APM). BP-1,6-quinone (BP-1,6-Q) is one of the significant components of APM. However, the mechanism(s) by which it can exert its toxicity in endothelial cells is not yet completely understood. NAD(P)H: quinone oxidoreductase-1 (NQO1) is expressed highly in myocardium and vasculature tissues of the heart and plays a vital role in maintaining vascular homeostasis. This study, demonstrated that BP-1,6-Q diminishes NQO1 enzyme activity in a dose-dependent manner in human EA.hy926 endothelial cells. The decrease in the NQO1 enzyme causes potentiation in BP-1,6-Q-mediated toxicity in EA.hy926 endothelial cells. The enhancement of NQO1 in endothelial cells showed cytoprotection against BP-1,6-Q-induced cellular toxicity, lipid, and protein damage suggesting an essential role of NQO1 in cytoprotection against BP-1,6-Q toxicity. Using various biochemical assays and genetic approaches, results from this study further demonstrated that NQO1 also plays a crucial role in BP-1,6-Q-induced production of reactive oxygen species (ROS). These findings will contribute to elucidating BP-1,6-Q mediated toxicity and its role in the development of atherosclerosis.

CPUY192018, a potent inhibitor of the Keap1-Nrf2 protein-protein interaction, alleviates renal inflammation in mice by restricting oxidative stress and NF-κB activation

The Keap1-Nrf2-ARE pathway regulates the constitutive and inducible transcription of various genes that encode detoxification enzymes, antioxidant proteins and anti-inflammatory proteins and has pivotal roles in the defence against cellular oxidative stress. In this study, we investigated the therapeutic potential of CPUY192018, a potent small-molecule inhibitor of the Keap1-Nrf2 protein-protein interaction (PPI), in renal inflammation. In human proximal tubular epithelial HK-2 cells, CPUY192018 treatment significantly increased Nrf2 protein level and Nrf2 nuclear translocation, which enhanced Nrf2-ARE transcription capacity and the downstream protein content in a Nrf2 dependent manner. In lipopolysaccharide (LPS)-challenged human HK-2 cells, CPUY192018 exhibited cytoprotective effects by enhancing the Nrf2-ARE regulated antioxidant system and diminished the LPS-induced inflammatory response by hindering the ROS-mediated activation of the NF-κB pathway. In the LPS-induced mouse model of chronic renal inflammation, by activating Nrf2, CPUY192018 treatment balanced renal oxidative stress and suppressed inflammatory responses. Hence, administration of CPUY192018 reduced kidney damage and ameliorated pathological alterations of the glomerulus. Taken together, our study suggested that small-molecule Keap1-Nrf2 PPI inhibitors can activate the Nrf2-based cytoprotective system and protect the kidney from inflammatory injury, raising a potential application of Keap1-Nrf2 PPI inhibitors in the treatment of inflammatory kidney disorders.

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CPUY192018 activated Nrf2-ARE pathway to protect against LPS-induced renal inflammation both in cells and in vivo.

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CPUY192018 also inhibited NF-κB involved inflammatory response both in cells and kidney.

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The development of Keap1-Nrf2 PPI inhibitors may create treatment options for kidney diseases with reduced off-target effects.

Effects of simvastatin on nuclear receptors, drug metabolizing enzymes and transporters expression in Human Umbilical Vein Endothelial Cells

BACKGROUND

Vascular endothelial cells (EC) are constantly exposed to endo- and exogenous compounds, which may disturb EC function. One of the protecting mechanisms against chemicals consists of drug metabolizing enzymes and transporter proteins regulated by nuclear receptors and transcription factors. Therefore, the aim of the current study was to assess the regulation of nuclear receptors and their coordinated genes in Human Umbilical Vein Endothelial Cells (HUVEC).

METHODS

HUVEC were exposed to TCDD (10 nM), oltipraz (100 μM) and simvastatin (1 μM) for 24 h. Gene expressions were evaluated using quantitative real-time PCR. The protein expression levels were determined by Western blotting. Enzymatic activity of CYP1A1/CYP1B1 was assessed by luciferin-labelled CYPs substrate.

RESULTS

Our study confirmed that nuclear receptor AhR and nuclear factor Nrf2 are highly expressed in HUVECs. Treatment of HUVECs with TCDD (AhR inducer) resulted in a significant induction of AHR target genes CYP1A1, CYP1B1 and NQO1. Oltipraz (Nrf2 inducer) also markedly increased expression of NQO1 but did not affect Nrf2 mRNA nor protein levels. Under simvastatin stimulation PXR and NRF2 target transcripts were not altered, however AHR-regulated genes: CYP1A1, CYP1B1 and MDR1 were significantly induced. Western blot analysis confirmed CYP1B1 induction in TCDD-treated HUVECs, but not in the simvastatin group. Moreover, HUVEC exposure to TCDD resulted in induction of CYP1A1/CYP1B1 enzymatic activity.

CONCLUSIONS

This study revealed functional expression of AhR and Nrf2 in HUVECs. Moreover, it was defined that simvastatin induced AhR and its related genes.

Peanut sprout extract attenuates cisplatin-induced ototoxicity by induction of the Akt/Nrf2-mediated redox pathway

OBJECTIVE

Cisplatin is commonly used to treat solid tumors. However, permanent hearing loss is a major side effect of cisplatin chemotherapy and often results in dose reduction of the cisplatin chemotherapy. Peanut sprouts show cytoprotective properties owing to their antioxidant activities. This study was designed to investigate the effect of peanut sprout extract (PSE) on cisplatin-induced ototoxicity in an auditory cell line, HEI-OC1 cells.

METHODS

Cells were exposed to cisplatin for 24 h, with or without pre-treatment with PSE, cell viability was examined using the MTT assay. Apoptotic cells were identified by double staining with Hoechst 33258 and propidium iodide. Western blot analysis was performed to examine apoptotic proteins including C-PARP and C-caspase, anti-apoptotic protein Bcl-2, and Nrf2 redox system activation. Mitochondrial reactive oxygen species (ROS) were investigated to examine whether PSE could scavenge cisplatin-induced ROS. Real-time PCR analyses were performed to investigate the mRNA levels of antioxidant enzymes including NQO1, HO-1, GPx2, Gclc, and catalase.

RESULTS

The cisplatin-treated group showed reduced cell viability, increased apoptotic properties and markers, and increased ROS levels. PSE pre-treatment before cisplatin exposure significantly increased cell viability and reduced apoptotic properties and ROS production. These effects resulted from the up-regulation of antioxidant genes, including NQO1, HO-1, GPx2, Gclc, and catalase through Akt phosphorylation and Nrf2 activation.

CONCLUSION

Our results demonstrate that PSE protects from cisplatin-induced cytotoxicity by activating the antioxidant effects via the Akt/Nrf-2 pathway in this auditory cell line, and indicate that PSE may provide novel treatment to prevent cisplatin-induced ototoxicity.

The Nrf2-ARE pathway is associated with Schisandrin b attenuating benzo(a)pyrene-Induced HTR cells damages in vitro

As is ubiquitous in the environmental sources, benzo(a)pyrene (BaP) has been reported to induce reprotoxicity in previous studies. Toxicity to trophoblast cells may be one key factor, but evidences were absent. We speculated that BaP can induce cytotoxicity in human trophoblast HTR-8/SVneo (HTR) cells, and Schisandrin B (Sch B) as a potential protector can inhibit the cytotoxicity. MTS assay identified that BaP induced HTR cells death while Sch B played a cytoprotective role. And after Nrf2 interference, the ability of Sch B-induced cytoprotection was declined. Furthermore, PCR, western blot, ELISA, and SOD assays were found that Sch B significantly increased the mRNA and protein expression of Nrf2, HO1, NQO1, and SOD in the Nrf2-ARE pathway, and the extents of increase were declined after Nrf2 interference. These results demonstrated that the Nrf2-ARE pathway plays an important role in Sch B attenuating BaP-induced HTR cells damages in vitro. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1439-1449, 2016.

Overexpression of Catalase Enhances Benzo(a)pyrene Detoxification in Endothelial Microsomes

We previously reported that overexpression of catalase upregulated xenobiotic- metabolizing enzyme (XME) expression and diminished benzo(a)pyrene (BaP) intermediate accumulation in mouse aortic endothelial cells (MAECs). Endoplasmic reticulum (ER) is the most active organelle involved in BaP metabolism. To examine the involvement of ER in catalase-induced BaP detoxification, we compared the level and distribution of XMEs, and the profile of BaP intermediates in the microsomes of wild-type and catalase transgenic endothelial cells. Our data showed that endothelial microsomes were enriched in cytochrome P450 (CYP) 1A1, CYP1B1 and epoxide hydrolase 1 (EH1), and contained considerable levels of NAD(P)H: quinone oxidoreductase-1 (NQO1) and glutathione S-transferase-pi (GSTP). Treatment of wild-type MAECs with 1μM BaP for 2 h increased the expression of microsomal CYP1A1, 1B1 and NQO1 by ~300, 64 and 116%, respectively. However, the same treatment did not significantly alter the expression of EH1 and GSTP. Overexpression of catalase did not significantly increase EH1, but upregulated BaP-induced expression of microsomal CYP1A1, 1B1, NQO1 and GSTP in the following order: 1A1>NQO1>GSTP>1B1. Overexpression of catalase did not alter the distribution of each of these enzymes in the microsomes. In contrast to our previous report showing lower level of BaP phenols versus BaP diols/diones in the whole-cell, this report demonstrated that the sum of microsomal BaP phenolic metabolites were ~60% greater than that of the BaP diols/diones after exposure of microsomes to BaP. Overexpression of catalase reduced the concentrations of microsomal BaP phenols and diols/diones by ~45 and 95%, respectively. This process enhanced the ratio of BaP phenol versus diol/dione metabolites in a potent manner. Taken together, upregulation of phase II XMEs and CYP1 proteins, but not EH1 in the ER might be the mechanism by which overexpression of catalase reduces the levels of all the BaP metabolites, and enhances the ratio of BaP phenolic metabolites versus diol/diones in endothelial microsomes.

Short-Term and Sub-Chronic Dietary Exposure to Aspalathin-Enriched Green Rooibos (Aspalathus linearis) Extract Affects Rat Liver Function and Antioxidant Status

An aspalathin-enriched green rooibos (Aspalathus linearis) extract (GRE) was fed to male Fischer rats in two independent studies for 28 and 90 days. The average dietary total polyphenol (TP) intake was 75.6 and 62.7 mg Gallic acid equivalents (GAE)/kg body weight (bw)/day over 28 and 90 days, respectively, equaling human equivalent doses (HEDs) of 12.3 and 10.2 GAE mg/kg bw/day. Aspalathin intake of 29.5 mg/kg bw/day represents a HED of 4.8 mg/kg bw/day (90 day study). Consumption of GRE increased feed intake significantly (p < 0.05) compared to the control after 90 days, but no effect on body and organ weight parameters was observed. GRE significantly (p < 0.05) reduced serum total cholesterol and iron levels, whilst significantly (p < 0.05) increasing alkaline phosphatase enzyme activity after 90 days. Endogenous antioxidant enzyme activity in the liver, i.e., catalase and superoxide dismutase activity, was not adversely affected. Glutathione reductase activity significantly (p < 0.05) increased after 28 days, while glutathione (GSH) content was decreased after 90 days, suggesting an altered glutathione redox cycle. Quantitative Real Time polymerase chain reaction (PCR) analysis showed altered expression of certain antioxidant defense and oxidative stress related genes, indicative, among others, of an underlying oxidative stress related to changes in the GSH redox pathway and possible biliary dysfunction.

AHR promoter variant modulates its transcription and downstream effectors by allele-specific AHR-SP1 interaction functioning as a genetic marker for vitiligo

Vitiligo is an acquired depigmentation disorder largely caused by defective melanocyte- or autoimmunity-induced melanocyte destruction. The aryl hydrocarbon receptor (AHR) is essential for melanocyte homeostasis and immune process, and abnormal AHR was observed in vitiligo. We previously identified the T allele of AHR -129C > T variant as a protective factor against vitiligo. However, biological characterization underlying such effects is not fully certain, further validation by mechanistic research is warranted and was conducted in the present study. We showed that -129T allele promoted AHR transcriptional activity through facilitating its interaction with SP1 transcription factor (SP1) compared with -129C allele. We subsequently found reduced peripheral AHR and SP1 transcript expressions in vitiligo and a negative correlation of AHR level with disease duration. We also investigated AHR-related cytokines and observed increased serum TNF-α concentration and diminished serum levels of IL-10 and TGF-β1 in vitiligo. Further genetic analysis showed that -129T carriers possessed higher levels of AHR and IL-10 than -129C carriers. Therefore, our study indicates that the modulation of AHR transcription by a promoter variant has a profound influence on vitiligo, not only advancing our understanding on AHR function but also providing novel insight into the pathogenesis of degenerative or autoimmune diseases including vitiligo.

Estrogen Sulfotransferase Is an Oxidative Stress-responsive Gene That Gender-specifically Affects Liver Ischemia/Reperfusion Injury

Estrogen sulfotransferase (EST) regulates estrogen homeostasis by sulfonating and deactivating estrogens. Liver ischemia and reperfusion (I/R) involves both hypoxia during the ischemic phase and oxidative damage during the reperfusion phase. In this report, we showed that the expression of EST was markedly induced by I/R. Mechanistically, oxidative stress-induced activation of Nrf2 was responsible for the EST induction, which was abolished in Nrf2(-/-) mice. EST is a direct transcriptional target of Nrf2. In female mice, the I/R-responsive induction of EST compromised estrogen activity. EST ablation attenuated I/R injury as a result of decreased estrogen deprivation, whereas this benefit was abolished upon ovariectomy. The effect of EST ablation was sex-specific because the EST(-/-) males showed heightened I/R injury. Reciprocally, both estrogens and EST regulate the expression and activity of Nrf2. Estrogen deprivation by ovariectomy abolished the I/R-responsive Nrf2 accumulation, whereas the compromised estrogen deprivation in EST(-/-) mice was associated with increased Nrf2 accumulation. Our results suggested a novel I/R-responsive feedback mechanism to limit the activity of Nrf2 in which Nrf2 induces the expression of EST, which subsequently increases estrogen deactivation and limits the estrogen-responsive activation of Nrf2. Inhibition of EST, at least in females, may represent an effective approach to manage hepatic I/R injury.

Iron homeostasis and tumorigenesis: molecular mechanisms and therapeutic opportunities

Excess iron is tightly associated with tumorigenesis in multiple human cancer types through a variety of mechanisms including catalyzing the formation of mutagenic hydroxyl radicals, regulating DNA replication, repair and cell cycle progression, affecting signal transduction in cancer cells, and acting as an essential nutrient for proliferating tumor cells. Thus, multiple therapeutic strategies based on iron deprivation have been developed in cancer therapy. During the past few years, our understanding of genetic association and molecular mechanisms between iron and tumorigenesis has expanded enormously. In this review, we briefly summarize iron homeostasis in mammals, and discuss recent progresses in understanding the aberrant iron metabolism in numerous cancer types, with a focus on studies revealing altered signal transduction in cancer cells.

Acute exposure to 3-methylcholanthrene induces hepatic oxidative stress via activation of the Nrf2/ARE signaling pathway in mice

Polycyclic aromatic hydrocarbons (PAHs) are the most common contaminants in the environment. The primary focus on the toxicity of PAHs is their ability to activate the aryl hydrocarbon receptor (AhR)-mediated pathway and lead to carcinogenesis in different organisms. However, the influence of PAHs on the antioxidant system in mammalian systems has received only limited attention. In the present study, we observed that the intraperitoneal injection of 100 mg/kg 3-methylcholanthrene (3MC) into mice significantly increased reactive oxygen species (ROS) levels and malondialdehyde (MDA) contents and decreased glutathione (GSH) contents and the activity of total antioxidant capacity (T-AOC), indicating that serious oxidative stress had been induced in the liver of mice. Then, the oxidative stress signal activated the nuclear factor erythroid 2-related factor 2/antioxidant response element (Nrf2/ARE) pathway by enhancing the mRNA levels of Nrf2, p38, and Erk2. Moreover, the mRNA levels of Nrf2/ARE target genes, including glutathione peroxidase (Gpx), glutathione reductase (GR), glutathione synthetase (GS), NAD(P)H: quinone oxidoreductase 1 (Nqo1), superoxide dismutase 1 (Sod1), and Sod2, increased significantly after treatment with 3MC for 24 hours. The hepatic levels of NQO1 and the activities of GR and GS were also significantly enhanced at 24 hours after 3MC treatment. Because the expression of NQO1 is co-regulated by Nrf2/ARE and AhR/XRE in mammalian tissues, NQO1 may play an important role in protecting against the oxidative stress induced by 3MC. Taken together, our findings suggested that acute exposure to 3MC altered the cellular redox balance in hepatocytes to trigger Nrf2-regulated antioxidant responses, which may represent an adaptive cell defense mechanism against the oxidative stress induced by PAHs.

Pathway and time-resolved benzo[a]pyrene toxicity on Hepa1c1c7 cells at toxic and subtoxic exposure

Benzo[a]pyrene (B[a]P) is an environmental contaminant mainly studied for its toxic/carcinogenic effects. For a comprehensive and pathway orientated mechanistic understanding of the effects directly triggered by a toxic (5 μM) or a subtoxic (50 nM) concentration of B[a]P or indirectly by its metabolites, we conducted time series experiments for up to 24 h to study the effects in murine hepatocytes. These cells rapidly take up and actively metabolize B[a]P, which was followed by quantitative analysis of the concentration of intracellular B[a]P and seven representative degradation products. Exposure with 5 μM B[a]P led to a maximal intracellular concentration of 1604 pmol/5 × 10(4) cells, leveling at 55 pmol/5 × 10(4) cells by the end of the time course. Changes in the global proteome (>1000 protein profiles) and metabolome (163 metabolites) were assessed in combination with B[a]P degradation. Abundance profiles of 236 (both concentrations), 190 (only 5 μM), and 150 (only 50 nM) proteins were found to be regulated in response to B[a]P in a time-dependent manner. At the endogenous metabolite level amino acids, acylcarnitines and glycerophospholipids were particularly affected by B[a]P. The comprehensive chemical, proteome and metabolomic data enabled the identification of effects on the pathway level in a time-resolved manner. So in addition to known alterations, also protein synthesis, lipid metabolism, and membrane dysfunction were identified as B[a]P specific effects.

Polyhydroxylated fullerene attenuates oxidative stress-induced apoptosis via a fortifying Nrf2-regulated cellular antioxidant defence system

Polyhydroxylated derivatives of fullerene C60, named fullerenols (C60[OH]n), have stimulated great interest because of their potent antioxidant properties in various chemical and biological systems, which enable them to be used as a new promising pharmaceutical for the future treatment of oxidative stress-related diseases, but the details remain unknown. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a principal transcription factor that regulates expression of several antioxidant genes via binding to the antioxidant response element and plays a crucial role in cellular defence against oxidative stress. In this study we investigated whether activation of the Nrf2/antioxidant response element pathway contributes to the cytoprotective effects of C60(OH)24. Our results showed that C60(OH)24 enhanced nuclear translocation of Nrf2 and upregulated expression of phase II antioxidant enzymes, including heme oxygenase-1 (HO-1), NAD(P)H: quinine oxidoreductase 1, and γ-glutamate cysteine ligase in A549 cells. Treatment with C60(OH)24 resulted in phosphorylation of p38 mitogen-activated protein kinases (p38 MAPK), extracellular signal-regulated kinases, and c-Jun-N-terminal kinases. By using inhibitors of cellular kinases, we showed that pretreatment of A549 cells with SB203580, a specific inhibitor of p38 MAPK, abolished nuclear translocation of Nrf2 and induction of HO-1 protein induced by C60(OH)24, indicating an involvement of p38 MAPK in Nrf2/HO-1 activation by C 60(OH)24. Furthermore, pretreatment with C60(OH)24 attenuated hydrogen peroxide-induced apoptotic cell death in A549 cells, and knockdown of Nrf2 by small interfering ribonucleic acid diminished C60(OH)24-mediated cytoprotection. Taken together, these findings demonstrate that C60(OH)24 may attenuate oxidative stress-induced apoptosis via augmentation of Nrf2-regulated cellular antioxidant capacity, thus providing insights into the mechanisms of the antioxidant properties of C60(OH)24.

Sulindac compounds facilitate the cytotoxicity of β-lapachone by up-regulation of NAD(P)H quinone oxidoreductase in human lung cancer cells

β-lapachone, a major component in an ethanol extract of Tabebuia avellanedae bark, is a promising potential therapeutic drug for various tumors, including lung cancer, the leading cause of cancer-related deaths worldwide. In the first part of this study, we found that apoptotic cell death induced in lung cancer cells by high concentrations of β-lapachone was mediated by increased activation of the pro-apoptotic factor JNK and decreased activation of the cell survival/proliferation factors PI3K, AKT, and ERK. In addition, β-lapachone toxicity was positively correlated with the expression and activity of NAD(P)H quinone oxidoreductase 1 (NQO1) in the tumor cells. In the second part, we found that the FDA-approved non-steroidal anti-inflammatory drug sulindac and its metabolites, sulindac sulfide and sulindac sulfone, increased NQO1 expression and activity in the lung adenocarcinoma cell lines CL1-1 and CL1-5, which have lower NQO1 levels and lower sensitivity to β-lapachone treatment than the A549 cell lines, and that inhibition of NQO1 by either dicoumarol treatment or NQO1 siRNA knockdown inhibited this sulindac-induced increase in β-lapachone cytotoxicity. In conclusion, sulindac and its metabolites synergistically increase the anticancer effects of β-lapachone primarily by increasing NQO1 activity and expression, and these two drugs may provide a novel combination therapy for lung cancers.

Polyhydroxylated fullerene attenuates oxidative stress-induced apoptosis via a fortifying Nrf2-regulated cellular antioxidant defence system

Polyhydroxylated derivatives of fullerene C60, named fullerenols (C60[OH]n), have stimulated great interest because of their potent antioxidant properties in various chemical and biological systems, which enable them to be used as a new promising pharmaceutical for the future treatment of oxidative stress-related diseases, but the details remain unknown. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a principal transcription factor that regulates expression of several antioxidant genes via binding to the antioxidant response element and plays a crucial role in cellular defence against oxidative stress. In this study we investigated whether activation of the Nrf2/antioxidant response element pathway contributes to the cytoprotective effects of C60(OH)24. Our results showed that C60(OH)24 enhanced nuclear translocation of Nrf2 and upregulated expression of phase II antioxidant enzymes, including heme oxygenase-1 (HO-1), NAD(P)H: quinine oxidoreductase 1, and γ-glutamate cysteine ligase in A549 cells. Treatment with C60(OH)24 resulted in phosphorylation of p38 mitogen-activated protein kinases (p38 MAPK), extracellular signal-regulated kinases, and c-Jun-N-terminal kinases. By using inhibitors of cellular kinases, we showed that pretreatment of A549 cells with SB203580, a specific inhibitor of p38 MAPK, abolished nuclear translocation of Nrf2 and induction of HO-1 protein induced by C60(OH)24, indicating an involvement of p38 MAPK in Nrf2/HO-1 activation by C 60(OH)24. Furthermore, pretreatment with C60(OH)24 attenuated hydrogen peroxide-induced apoptotic cell death in A549 cells, and knockdown of Nrf2 by small interfering ribonucleic acid diminished C60(OH)24-mediated cytoprotection. Taken together, these findings demonstrate that C60(OH)24 may attenuate oxidative stress-induced apoptosis via augmentation of Nrf2-regulated cellular antioxidant capacity, thus providing insights into the mechanisms of the antioxidant properties of C60(OH)24.

Inhibition of endoplasmic reticulum stress and atherosclerosis by 2-aminopurine in apolipoprotein e-deficient mice

We previously reported that the apolipoprotein (apo) B48-carrying lipoproteins obtained from apoE knockout (apoE^−/−) mice, so called E⁻/B48 lipoproteins, transformed mouse macrophages into foam cells and enhanced the phosphorylation of eukaryotic translation initiation factor 2α (eIF-2α). Furthermore, the eIF-2α phosphorylation inhibitor, 2-aminopurine (2-AP), attenuated E⁻/B48 lipoprotein-induced foam cell formation. The present report studied the effect of 2-AP on atherosclerosis in apoE^−/− mice. Our results showed that the level of food intake, bodyweight, plasma cholesterol, and triglycerides was comparable in apoE^−/− mice treated with or without 2-AP. However, the mean size of atherosclerotic lesions in the aorta sinus as well as the surface area of the entire aorta of 2-AP-treated apoE^−/− mice were reduced by about 55% and 39%, respectively, compared to samples from untreated control apoE^−/− mice. In addition, the 2-AP-treated apoE^−/− mice showed a significant decrease in glucose-regulated protein 78 (GRP78) and phosphorylated eIF-2α in their aortic samples as compared to levels in untreated control apoE^−/− mice. These observations suggest that endoplasmic reticulum stress is a causal mechanism for the development of atherosclerosis in apoE^−/− mice and that therapeutic strategies can be developed for using eIF-2α phosphorylation inhibitors, such as 2-AP, to prevent or treat atherosclerosis.

Cholecystokinin elevates mouse plasma lipids

Cholecystokinin (CCK) is a peptide hormone that induces bile release into the intestinal lumen which in turn aids in fat digestion and absorption in the intestine. While excretion of bile acids and cholesterol into the feces eliminates cholesterol from the body, this report examined the effect of CCK on increasing plasma cholesterol and triglycerides in mice. Our data demonstrated that intravenous injection of [Thr28, Nle31]-CCK at a dose of 50 ng/kg significantly increased plasma triglyceride and cholesterol levels by 22 and 31%, respectively, in fasting low-density lipoprotein receptor knockout (LDLR^−/−) mice. The same dose of [Thr28, Nle31]-CCK induced 6 and 13% increases in plasma triglyceride and cholesterol, respectively, in wild-type mice. However, these particular before and after CCK treatment values did not achieve statistical significance. Oral feeding of olive oil further elevated plasma triglycerides, but did not alter plasma cholesterol levels in CCK-treated mice. The increased plasma cholesterol in CCK-treated mice was distributed in very-low, low and high density lipoproteins (VLDL, LDL and HDL) with less of an increase in HDL. Correspondingly, the plasma apolipoprotein (apo) B48, B100, apoE and apoAI levels were significantly higher in the CCK-treated mice than in untreated control mice. Ligation of the bile duct, blocking CCK receptors with proglumide or inhibition of Niemann-Pick C1 Like 1 transporter with ezetimibe reduced the hypercholesterolemic effect of [Thr28, Nle31]-CCK in LDLR^−/− mice. These findings suggest that CCK-increased plasma cholesterol and triglycerides as a result of the reabsorption of biliary lipids from the intestine.

Regulation of the activity and expression of aryl hydrocarbon receptor by ethanol in mouse hepatic stellate cells

BACKGROUND

During the course of alcohol-induced liver damage, hepatic stellate cells are transformed into proliferative, fibrogenic, and contractile myofibroblasts. Aryl hydrocarbon receptor (AhR) is a transcription factor that controls the expression of genes involved in the metabolism of xenobiotics, inflammation, cell proliferation, and death.

METHODS

Immortal mouse hepatic stellate cells (MHSCs) were isolated from transgenic mice that expressed a thermolabile SV40 tumor antigen. Quantitative real-time reverse transcription polymerase chain reaction assays, Western blot analysis, promoter activity assays, and chromatin immunoprecipitation analyses were performed for studying the effect of ethanol (EtOH) on AhR expression and transcriptional activity.

RESULTS

Treatment of MHSCs with 50 to 200 mM EtOH for 6 hours induced AhR nuclear translocation, enhanced the promoter activity of cytochrome P450 (CYP) 1A1, increased the amount of AhR bound to the promoter of CYP1A1 and 1B1, and up-regulated the mRNA expression of these AhR target genes in a dose-dependent manner. In contrast, EtOH exposure down-regulated AhR mRNA and protein expression. Similarly, benzo(a)pyrene (BaP) at 10 nM reduced AhR and increased CYP1A1 and 1B1 mRNAs. Pretreatment of MHSCs with 50 mM EtOH for 7 days diminished the capacity of MHSCs to express CYP1A1 and 1B1 induced by a 200 mM EtOH challenge, or by 10 nM BaP. However, the up-regulatory effect of EtOH on solute carrier family 16, member 6 (SLC16a6) was unaffected by EtOH pretreatment. Similar to EtOH, dimethyl sulfoxide (DMSO) at concentrations of 50 to 100 mM down-regulated AhR and up-regulated CYP1A1 mRNA expression in a dose-dependent manner.

CONCLUSIONS

These data, for the first time, demonstrate that EtOH activates MHSC AhR and down-regulates its expression. Chronic EtOH pretreatment lowers the availability of AhR, and specifically diminishes the inducibility of CYP genes. The effect on AhR appears to not be an EtOH-specific response, as DMSO alone (and possibly other organic solvents) was also able to activate AhR.

Up-regulation of ATP binding cassette transporter A1 expression by very low density lipoprotein receptor and apolipoprotein E receptor 2

Activation of very low density lipoprotein receptor (VLDLR) and apolipoprotein E receptor 2 (apoER2) results in either pro- or anti-atherogenic effects depending on the ligand. Using reelin and apoE as ligands, we studied the impact of VLDLR- and apoER2-mediated signaling on the expression of ATP binding cassette transporter A1 (ABCA1) and cholesterol efflux using RAW264.7 cells. Treatment of these mouse macrophages with reelin or human apoE3 significantly increased ABCA1 mRNA and protein levels, and apoAI-mediated cholesterol efflux. In addition, both reelin and apoE3 significantly increased phosphorylated disabled-1 (Dab1), phosphatidylinositol 3-kinase (PI3K), protein kinase Cζ (PKCζ), and specificity protein 1 (Sp1). This reelin- or apoER2-mediated up-regulation of ABCA1 expression was suppressed by 1) knockdown of Dab1, VLDLR, and apoER2 with small interfering RNAs (siRNAs), 2) inhibition of PI3K and PKC with kinase inhibitors, 3) overexpression of kinase-dead PKCζ, and 4) inhibition of Sp1 DNA binding with mithramycin A. Activation of the Dab1-PI3K signaling pathway has been implicated in VLDLR- and apoER2-mediated cellular functions, whereas the PI3K-PKCζ-Sp1 signaling cascade has been implicated in the regulation of ABCA1 expression induced by apoE/apoB-carrying lipoproteins. Taken together, these data support a model in which activation of VLDLR and apoER2 by reelin and apoE induces ABCA1 expression and cholesterol efflux via a Dab1-PI3K-PKCζ-Sp1 signaling cascade.

Identification of aryl hydrocarbon receptor binding targets in mouse hepatic tissue treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin

Genome-wide, promoter-focused ChIP-chip analysis of hepatic aryl hydrocarbon receptor (AHR) binding sites was conducted in 8-week old female C57BL/6 treated with 30 μg/kg/body weight 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for 2 h and 24 h. These studies identified 1642 and 508 AHR-bound regions at 2h and 24h, respectively. A total of 430 AHR-bound regions were common between the two time points, corresponding to 403 unique genes. Comparison with previous AHR ChIP-chip studies in mouse hepatoma cells revealed that only 62 of the putative target genes overlapped with the 2 h AHR-bound regions in vivo. Transcription factor binding site analysis revealed an over-representation of aryl hydrocarbon response elements (AHREs) in AHR-bound regions with 53% (2 h) and 68% (24 h) of them containing at least one AHRE. In addition to AHREs, E2f-Myc activator motifs previously implicated in AHR function, as well as a number of other motifs, including Sp1, nuclear receptor subfamily 2 factor, and early growth response factor motifs were also identified. Expression microarray studies identified 133 unique genes differentially regulated after 4 h treatment with TCDD. Of which, 39 were identified as AHR-bound genes at 2 h. Ingenuity Pathway Analysis on the 39 AHR-bound TCDD responsive genes identified potential perturbation in biological processes such as lipid metabolism, drug metabolism, and endocrine system development as a result of TCDD-mediated AHR activation. Our findings identify direct AHR target genes in vivo, highlight in vitro and in vivo differences in AHR signaling and show that AHR recruitment does not necessarily result in changes in target gene expression.