Transcription factor Nrf2 regulates promoter activity of mouse aldose reductase (AKR1B3) gene

Irisin protects against doxorubicin-induced cardiotoxicity by improving AMPK-Nrf2 dependent mitochondrial fusion and strengthening endogenous anti-oxidant defense mechanisms

Irisin, a new exercise-mediated myokine, plays an important role in cardiovascular diseases by regulating cell energy metabolism. The induction of mitochondrial dysfunction and oxidative stress are the crucial mechanisms involved in doxorubicin-induced cardiomyocyte damage and cardiac dysfunction, but the mitochondria-dependent protective mechanisms of irisin in DOX-impaired cardiomyocytes are poorly understood. In this study, we exposed mouse-FNDC5 (irisin-precursor)-knockout, FNDC5 transgenic mice and their WT littermates, as well as cultured neonatal rat cardiomyocytes to DOX at a dosage of 4 mg/kg (once a week for 4 weeks) in vivo and 2 μM in vitro, respectively, then investigated how irisin alleviated DOX-induced oxidative stress and myocardial injury. Irisin knockout worsened, while irisin overexpression attenuated DOX-induced mortality, body weight loss, myocardial atrophy, damage and oxidative stress, cardiac remodeling and dysfunction in mice. Exogenous irisin supplementation (20 nM) also relieved these DOX-induced damage in cardiomyocytes. Intriguingly, irisin activated AMPK-Nrf2 signaling axis, and then up-regulated the transcription and protein expression of the downstream target genes of Nrf2, including mitochondrial fusion-related genes (mitofusin 1/2 and Optic Atrophy Type 1) and endogenous anti-oxidant genes, to promote mitochondrial fusion, improve mitochondrial dynamics and mitochondrial function, and reduced oxidative stress damage in DOX-induced cardiomyocytes. These results suggest that irisin protects the hearts from DOX-induced cardiotoxicity by improving mitochondrial dynamics and strengthening the endogenous anti-oxidant system through an AMPK-Nrf2 axis dependent manner, thus reducing DOX-induced oxidative stress injury in cardiomyocytes.

Aldo-keto reductase inhibitors increase the anticancer effects of tyrosine kinase inhibitors in chronic myelogenous leukemia

Tyrosine kinase inhibitors (TKIs) are widely utilized in clinical practice to treat carcinomas, but secondary tumor resistance during chronic treatment can be problematic. AKR1B1 and AKR1B10 of the aldo-keto reductase (AKR) superfamily are highly expressed in cancer cells and are believed to be involved in drug resistance. The aim of this study was to understand how TKI treatment of chronic myelogenous leukemia (CML) cells changes their glucose metabolism and if inhibition of AKRs can sensitize CML cells to TKIs. K562 cells were treated with the TKIs imatinib, nilotinib, or bosutinib, and the effects on glucose metabolism, cell death, glutathione levels, and AKR levels were assessed. To assess glucose dependence, cells were cultured in normal and low-glucose media. Pretreatment with AKR inhibitors, including epalrestat, were used to determine AKR-dependence. Treatment with TKIs increased intracellular glucose, AKR1B1/10 levels, glutathione oxidation, and nuclear translocation of nuclear factor erythroid 2-related factor 2, but with minimal cell death. These effects were dependent on intracellular glucose accumulation. Pretreatment with epalrestat, or a selective inhibitor of AKR1B10, exacerbated TKI-induced cell death, suggesting that especially AKR1B10 was involved in protection against TKIs. Thus, by disrupting cell protective mechanisms, AKR inhibitors may render CML more susceptible to TKI treatments.

Age-related alteration in HNE elimination enzymes

4-hydroxynonenal (HNE, 4-hydroxy-2-nonenal) is a primary α,β-unsaturated aldehyde product of lipid peroxidation. The accumulation of HNE increases with aging and the mechanisms are mainly attributable to increased oxidative stress and decreased capacity of HNE elimination. In this review article, we summarize the studies on age-related change of HNE concentration and alteration of HNE metabolizing enzymes (GCL, GST, ALDHs, aldose reductase, and 20S-proteasome), and discuss potential mechanism of age-related decrease in HNE-elimination capacity by focusing on Nrf2 redox signaling.

Mitochondrial biology in airway pathogenesis and the role of NRF2

A constant improvement in understanding of mitochondrial biology has provided new insights into mitochondrial dysfunction in human disease pathogenesis. Impaired mitochondrial dynamics caused by various stressors are characterized by structural abnormalities and leakage, compromised turnover, and reactive oxygen species overproduction in mitochondria as well as increased mitochondrial DNA mutation frequency, which leads to modified energy production and mitochondria-derived cell signaling. The mitochondrial dysfunction in airway epithelial, smooth muscle, and endothelial cells has been implicated in diseases including chronic obstructive lung diseases and acute lung injury. Increasing evidence indicates that the NRF2-antioxidant response element (ARE) pathway not only enhances redox defense but also facilitates mitochondrial homeostasis and bioenergetics. Identification of functional or potential AREs further supports the role for Nrf2 in mitochondrial dysfunction-associated airway disorders. While clinical reports indicate mixed efficacy, NRF2 agonists acting on respiratory mitochondrial dynamics are potentially beneficial. In lung cancer, growth advantage provided by sustained NRF2 activation is suggested to be through increased cellular antioxidant defense as well as mitochondria reinforcement and metabolic reprogramming to the preferred pathways to meet the increased energy demands of uncontrolled cell proliferation. Further studies are warranted to better understand NRF2 regulation of mitochondrial functions as therapeutic targets in airway disorders.

Antioxidant response elements: Discovery, classes, regulation and potential applications

Exposure to antioxidants and xenobiotics triggers the expression of a myriad of genes encoding antioxidant proteins, detoxifying enzymes, and xenobiotic transporters to offer protection against oxidative stress. This articulated universal mechanism is regulated through the cis-acting elements in an array of Nrf2 target genes called antioxidant response elements (AREs), which play a critical role in redox homeostasis. Though the Keap1/Nrf2/ARE system involves many players, AREs hold the key in transcriptional regulation of cytoprotective genes. ARE-mediated reporter constructs have been widely used, including xenobiotics profiling and Nrf2 activator screening. The complexity of AREs is brought by the presence of other regulatory elements within the AREs. The diversity in the ARE sequences not only bring regulatory selectivity of diverse transcription factors, but also confer functional complexity in the Keap1/Nrf2/ARE pathway. The different transcription factors either homodimerize or heterodimerize to bind the AREs. Depending on the nature of partners, they may activate or suppress the transcription. Attention is required for deeper mechanistic understanding of ARE-mediated gene regulation. The computational methods of identification and analysis of AREs are still in their infancy. Investigations are required to know whether epigenetics mechanism plays a role in the regulation of genes mediated through AREs. The polymorphisms in the AREs leading to oxidative stress related diseases are warranted. A thorough understanding of AREs will pave the way for the development of therapeutic agents against cancer, neurodegenerative, cardiovascular, metabolic and other diseases with oxidative stress.

Chemical toxicology of reactive species in the atmosphere: two decades of progress in an electron acceptor and an electrophile

Air pollutants such as diesel exhaust particles (DEP) are thought to cause pulmonary diseases such as asthma as a result of oxidative stress. While DEP contain a large number of polycyclic aromatic hydrocarbons, we have focused on 9,10-phenanthrenequinone (9,10-PQ) and 1,2-naphthoquinone (1,2-NQ) because of their chemical properties based on their oxidative and chemical modification capabilities. We have found that 9,10-PQ interacts with electron donors such as NADPH (in the presence of enzymes) and dithiols, resulting in generation of excess reactive oxygen species (ROS) through redox cycling. We have also shown that 1,2-NQ is able to modify protein thiols, leading to protein adducts associated with activation of redox signal transduction pathways at lower concentrations and toxicity at higher concentrations. In this review, we briefly introduce our findings from the last two decades.

Subcritical water-hydrolyzed fish collagen ameliorates survival of endotoxemic mice by inhibiting HMGB1 release in a HO-1-dependent manner

To investigate potential mechanisms underlying the bioactivity of hydrolyzed fish collagen, we examined the anti-inflammatory actions of subcritical water-hydrolyzed fish collagen (SWFC) in lipopolysaccharide (LPS)-triggered inflammation and endotoxemia. SWFC markedly inhibited LPS-stimulated release of high mobility group box 1 (HMGB1) in murine RAW264.7 macrophages, along with decreased cytosolic translocation of HMGB1. Both the protein and mRNA levels of heme oxygenase-1 (HO-1) were significantly upregulated in SWFC-treated RAW 264.7 cells in an Nrf2-dependent manner. In line with these effects of SWFC, both HO-1 siRNA and ZnPPIX (zinc protoporphyrin IX) actually attenuated the effects of SWFC on HMGB1 release stimulated by LPS, indicating a possible mechanism by which SWFC modulates HMGB1 release through HO-1 signaling. Notably, administration of SWFC improved the survival rates of LPS-injected endotoxemic mice, in which the serum level of HMGB1 was significantly reduced. Taken together, these results indicate that the anti-inflammatory activities of SWFC are achieved by inhibiting HMGB1 release induced by LPS in a HO-1-sensitive manner.

Identification and characterization of functional antioxidant response elements in the promoter of the aldo-keto reductase AKR1B10 gene

AKR1B10 is a human-type aldo-keto reductase. The up-regulation of AKR1B10 has been associated with various cancers including non-small cell lung carcinoma, viral and bacterial infections, and skin diseases. However, the mechanisms underlying AKR1B10 gene regulation are not fully understood. We previously indicated the involvement of the transcription factor Nrf2 in AKR1B10 gene regulation. There are at least five potential Nrf2-responsive consensus sequences, so-called antioxidant response elements (AREs), and several ARE-like sequences in the 5'-flanking region up to -3282 bp of the AKR1B10 gene. In the present study, we attempted to identify functional AREs by luciferase reporter analyses using various mutants for each ARE. And we found that only those between -530 and -520 bp (ARE-A), which is the closest location to the translation start site, were functional among the five ARE consensus sites examined. Furthermore, ARE-A functioned co-operatively with the neighboring AP-1 site. Since the AP-1 site resembles ARE, the tandem arrangement of these two elements may be essential for augmented responsiveness to Nrf2 and plays an important role in AKR1B10 gene regulation by various Nrf2-mediating stimuli.

Dicarbonyls and glyoxalase in disease mechanisms and clinical therapeutics

The reactive dicarbonyl metabolite methylglyoxal (MG) is the precursor of the major quantitative advanced glycation endproducts (AGEs) in physiological systems - arginine-derived hydroimidazolones and deoxyguanosine-derived imidazopurinones. The glyoxalase system in the cytoplasm of cells provides the primary defence against dicarbonyl glycation by catalysing the metabolism of MG and related reactive dicarbonyls. Dicarbonyl stress is the abnormal accumulation of dicarbonyl metabolites leading to increased protein and DNA modification contributing to cell and tissue dysfunction in ageing and disease. It is produced endogenously by increased formation and/or decreased metabolism of dicarbonyl metabolites. Dicarbonyl stress contributes to ageing, disease and activity of cytotoxic chemotherapeutic agents. It contributes to ageing through age-related decline in glyoxalase 1 (Glo-1) activity. Glo-1 has a dual role in cancer as a tumour suppressor protein prior to tumour development and mediator of multi-drug resistance in cancer treatment, implicating dicarbonyl glycation of DNA in carcinogenesis and dicarbonyl-driven cytotoxicity in mechanism of action of anticancer drugs. Glo-1 is a driver of cardiovascular disease, likely through dicarbonyl stress-driven dyslipidemia and vascular cell dysfunction. Dicarbonyl stress is also a contributing mediator of obesity and vascular complications of diabetes. There are also emerging roles in neurological disorders. Glo-1 responds to dicarbonyl stress to enhance cytoprotection at the transcriptional level through stress-responsive increase of Glo-1 expression. Small molecule Glo-1 inducers are in clinical development for improved metabolic, vascular and renal health and Glo-1 inhibitors in preclinical development for multidrug resistant cancer chemotherapy.

Epalrestat Upregulates Heme Oxygenase-1, Superoxide Dismutase, and Catalase in Cells of the Nervous System

Heme oxygenase (HO)-1 has potent antioxidant and anti-inflammatory functions. Recent studies have shown that the upregulation of HO-1 is beneficial to counteract neuroinflammation, making HO-1 a new therapeutic target for neurological diseases. We have reported that epalrestat (EPS), which is currently used for the treatment of diabetic neuropathy, increases HO-1 levels through the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) in bovine aortic endothelial cells. In this study, we tested the hypothesis that EPS upregulates HO-1 via Nrf2 activation in the component cells of the nervous system, by using rat Schwann cells and human SH-SY5Y cells. Treatment of Schwann cells with EPS at near-plasma concentration led to a dramatic increase in HO-1 levels. Nrf2 knockdown by small interfering RNA (siRNA) suppressed the EPS-induced HO-1 expression. EPS did not promote the intracellular accumulation of free ferrous ion and reactive oxygen species, by increasing ferritin via Nrf2 during HO-1 induction. Moreover, EPS stimulated the expression of superoxide dismutase 1 and catalase, which also are Nrf2 target gene products. It also markedly increased HO-1 levels in SH-SY5Y cells through the activation of Nrf2. We demonstrated for the first time that EPS upregulates HO-1, superoxide dismutase, and catalase by activating Nrf2. We suggest that EPS has the potential to prevent several neurological diseases.

Paternal Psychological Stress Reprograms Hepatic Gluconeogenesis in Offspring

Both epidemiologic and experimental animal studies demonstrate that chronic psychological stress exerts adverse effects on the initiation and/or progression of many diseases. However, intergenerational effects of this environmental information remains poorly understood. Here, using a C57BL/6 mouse model of restraint stress, we show that offspring of stressed fathers exhibit hyperglycemia due to enhanced hepatic gluconeogenesis and elevated expression of PEPCK. Mechanistically, we identify an epigenetic alteration at the promoter region of the Sfmbt2 gene, a maternally imprinted polycomb gene, leading to a downregulation of intronic microRNA-466b-3p, which post-transcriptionally inhibits PEPCK expression. Importantly, hyperglycemia in F1 mice is reversed by RU486 treatment in fathers, and dexamethasone administration in F0 mice phenocopies the roles of restraint stress. Thus, we provide evidence showing the effects of paternal psychological stress on the regulation of glucose metabolism in offspring, which may have profound implications for our understanding of health and disease risk inherited from fathers.

Lipoxin A4 attenuates LPS-induced mouse acute lung injury via Nrf2-mediated E-cadherin expression in airway epithelial cells

A fundamental element of acute lung injury (ALI) is the inflammation that is part of the body's immune response to a variety of local or systemic stimuli. Lipoxins (LXs) are important endogenous lipids that mediate resolution of inflammation. Previously, we demonstrated that LXA4 reduced the LPS inhalation-induced pulmonary edema, neutrophil infiltration and TNF-α production in mice. With the same model, the current investigation focused on the role of the airway epithelium, a first-line barrier and a prime target of inhaled toxicants. We report that LXA4 strongly inhibited LPS-induced ALI in mice, in part by protecting the airway epithelium and preserving the E-cadherin expression and airway permeability. Using a cryo-imaging assay and fluorescence detection, LXA4 was shown to block LPS-induced ROS generation and preserve mitochondrial redox status both in vivo and in vitro. To further assess whether and how NF-E2-related factor 2 (Nrf2) was involved in the protective effect of LXA4, fluorescence resonance energy transfer (FRET) analysis was employed in human epithelial cell line (16HBE), to determine the relative distance between Nrf2 and its negative regulator or cytosolic inhibitor, Kelch-like ECH-associated protein 1 (Keap1). It provided us the evidence that LXA4 further promoted the dissociation of Nrf2 and Keap1 in LPS-treated 16HBE cells. The results also showed that LXA4 activates Nrf2 by phosphorylating it on Ser40 and triggering its nuclear translocation. Moreover, when the plasmid expression dominant negative mutation of Nrf2 was transfected as an inhibitor of wild-type Nrf2, the protective effect of LXA4 on E-cadherin expression was almost completely blocked. These results provide a new mechanism by which LXA4 inhibits LPS-induced ALI through Nrf2-mediated E-cadherin expression.

Identification of a functional antioxidant responsive element in the promoter of the Chinese hamster carbonyl reductase 3 (Chcr3) gene

CHCR3, a member of the short-chain dehydrogenase/reductase superfamily, is a carbonyl reductase 3 enzyme in Chinese hamsters. Carbonyl reductase 3 in humans has been believed to involve the metabolism and/or pharmacokinetics of anthracycline drugs, and the mechanism underlying the gene regulation has been investigated. In this study, the nucleotide sequence of the Chcr3 promoter was originally determined, and its promoter activity was characterised. The proximal promoter region is TATA-less and GC-rich, similar to the promoter region of human carbonyl reductase 3. Cobalt stimulated the transcriptional activity of the Chcr3 gene. The results of a luciferase gene reporter assay demonstrated that cobalt-induced stimulation required an antioxidant responsive element. Forced expression of Nrf2, the transcription factor that binds to antioxidant responsive elements, enhanced the transcriptional activity of the Chcr3 gene. These results suggest that cobalt induces the expression of the Chcr3 gene via the Nrf2-antioxidant responsive element pathway.

CO Induces Nrf2-Dependent Heme Oxygenase-1 Transcription by Cooperating with Sp1 and c-Jun in Rat Brain Astrocytes

Upregulation of heme oxygenase 1 (HO-1) by carbon monoxide (CO) delivered by CO-releasing molecules (CORMs) may be utilized as a therapeutic intervention for neurodegenerative diseases. This study was to delineate the two putative anti-oxidant response elements (AREs) in modulating HO-1 gene by participating with its promoter elements in rat brain astrocytes (RBA-1). CORM-2-induced HO-1 expression was mediated through superoxide, p38 mitogen-activated protein kinase(MAPK), extracellular signal-regulated protein kinases 1 and 2 (Erk1/2), protein tyrosine kinase 2 (Pyk2), platelet-derived growth factor receptor (PDGFR), and phosphatidylinositol 3'-kinase (PI3K/Akt), revealed by the pharmacological inhibitors or knockdown of these signaling molecules. CORM-2-enhanced HO-1 promoter activity was inhibited by co-transfection with small interfering RNA (siRNA) of c-Jun, specificity protein 1 (Sp1), or nuclear factor-erythroid 2-related factor 2 (Nrf2). Immunoprecipitation assay showed that CORM-2 increased the association of nuclear Nrf2 with Sp1 and c-Jun. Furthermore, chromatin immunoprecipitation (ChIP) assay confirmed that Nrf2, Sp1, and c-Jun are associated with the proximal ARE binding site on HO-1 promoter, suggesting that Nrf2/Sp1/c-Jun cooperations are key transcription factors modulating HO-1 expression. Mechanistically, CORM-2-induced ARE promoter activity was reduced by the inhibitors of reactive oxygen species (ROS), p38 MAPK, Pyk2, MAPK/ERK kinases 1 and 2 (MEK1/2), PDGFR, and PI3K/Akt or the siRNAs of c-Jun, SP1, and Nrf2. These findings suggested that CORM-2 increases formation of c-Jun, Sp1, and Nrf2 complex and binding with ARE1 binding site, which is mediated through both ROS/p38 MAPK and Pyk2-dependent PDGFR/PI3K/Akt/Erk1/2 pathways, resulting in HO-1 expression in RBA-1 cells.

Aldose reductase regulates miR-200a-3p/141-3p to coordinate Keap1-Nrf2, Tgfβ1/2, and Zeb1/2 signaling in renal mesangial cells and the renal cortex of diabetic mice

Aberrant regulation in oxidative stress, fibrogenesis, and the epithelial-mesenchymal transition (EMT) in renal cells under hyperglycemic conditions contributes significantly to the onset and progression of diabetic nephropathy. The mechanisms underlying these hyperglycemia-induced dysregulations, however, have not been clearly elucidated. Herein, we report that aldose reductase is capable of regulating the expression of miR-200a-3p/141-3p negatively in renal mesangial cells. MiR-200a-3p/141-3p, in turn, act to target Keap1, Tgfβ2, fibronectin, and Zeb2 directly and regulate Tgfβ1 and Nrf2 indirectly under high-glucose conditions, resulting in profound dysregulations in Keap1-Nrf2, Tgfβ1/2, and Zeb1/2 signaling. In vivo in streptozotocin-induced diabetic mice, we found that aldose reductase deficiency caused significant elevations in miR-200a-3p/141-3p in the renal cortex, which were accompanied by a significant downregulation of Keap1, Tgfβ1/2, and fibronectin but significant upregulation of Nrf2. Moreover, in vivo administration of inhibitors of miR-200a-3p in diabetic animals significantly exacerbated cortical and glomerular fibrogenesis and increased urinary albumin excretion, tightly linking dysregulated miR-200a-3p with the development of diabetic nephropathy. Collectively, our results reveal a novel mechanism whereby hyperglycemia induces aldose reductase to regulate renal expression of miR-200a-3p/141-3p to coordinately control hyperglycemia-induced renal oxidative stress, fibrogenesis, and the EMT. Our novel findings also suggest that inhibition of aldose reductase and in vivo renal cortical restoration of miR-200a-3p/141-3p or their combination are very promising avenues for the development of therapeutic strategies or drugs against diabetic nephropathy.

Biochemical basis of the antidiabetic activity of oleanolic acid and related pentacyclic triterpenes

Oleanolic acid (OA), a natural component of many plant food and medicinal herbs, is endowed with a wide range of pharmacological properties whose therapeutic potential has only partly been exploited until now. Throughout complex and multifactorial mechanisms, OA exerts beneficial effects against diabetes and metabolic syndrome. It improves insulin response, preserves functionality and survival of β-cells, and protects against diabetes complications. OA may directly modulate enzymes connected to insulin biosynthesis, secretion, and signaling. However, its major contributions appear to be derived from the interaction with important transduction pathways, and many of its effects are consistently related to activation of the transcription factor Nrf2. Doing that, OA induces the expression of antioxidant enzymes and phase II response genes, blocks NF-κB, and represses the polyol pathway, AGEs production, and hyperlipidemia. The management of type 2 diabetes requires an integrated approach, which includes the early intervention to prevent or delay the disease progression, and the use of therapies to control glycemia and lipidemia in its late stages. In this sense, the use of functional foods or drugs containing OA is, undoubtedly, an interesting path.

Regulation of human carbonyl reductase 1 (CBR1, SDR21C1) gene by transcription factor Nrf2

Monomeric carbonyl reductase 1 (CBR1, SDR21C1) is a member of the short-chain dehydrogenase/reductase superfamily and is involved in the metabolism of anthracycline anti-cancer drugs, prostaglandins, and isatin, which is an endogenous inhibitor of monoamine oxidases. Additionally, cancer progression may be partly regulated by CBR1. In the present study, we screened more than 10 drugs for the induction of the human CBR1 gene to investigate its regulation. Of the drugs, butylated hydroxyanisole (BHA) was found to be an inducer. BHA induced the mRNA and protein expression of CBR1 in hepatoma HepG2 cells. In a luciferase reporter gene assay, the promoter region between -2062 bp and the transcription start site of CBR1 was also activated by BHA. The transcription factor Nrf2 is known to be activated by BHA. There are 2 anti-oxidant responsive elements (ARE) that are bound by Nrf2 in this region. Mutation analyses revealed that one of the AREs participates in the gene regulation of CBR1 by Nrf2. Electrophoretic mobility shift assay revealed that Nrf2 binds the site. Moreover, to determine whether the functional ARE of CBR1 is conserved with the promoter region of homologues in other species, the nucleotide sequences of the functional AREs of the Chcr1 and Chcr2 genes, which are the Chinese hamster homologues of CBR1, were determined. The region has 2 AREs, and these genes were also induced by the forced expression of Nrf2 (cotransfection of pNrf2) in the luciferase reporter gene assay. In conclusion, Nrf2 is a novel transcriptional regulator of CBR1 genes in humans and the Chinese hamster. Because the regulation of CBR1 appears to be important for diseases, the induction of CBR1 by Nrf2 may be a therapeutic target.

Aldo-keto reductases mediate constitutive and inducible protection against aldehyde toxicity in human neuroblastoma SH-SY5Y cells

Reactive aldehydes including methyl glyoxal, acrolein and 4-hydroxy-2-nonenal (4-HNE) have been implicated in the progression of neurodegenerative diseases. The reduction of aldehydes to alcohols by the aldo-keto reductase (AKR) family of enzymes may represent an important detoxication route within neuronal cells. In this study, the ability of AKR enzymes to protect human neuroblastoma SH-SY5Y cells against reactive aldehydes was assessed. Using gene-specific RNA interference (RNAi), we report that AKR7A2 makes a significant contribution to the reduction of methyl glyoxal in SH-SY5Y cells, with its knockdown altering the IC(50) from 410 to 25.8μM, and that AKR1C3 contributes to 4-HNE reduction, with its knockdown lowering the IC(50) from 1.25 to 0.58μM. In addition, we have shown that pretreatment of cells with sub-lethal concentrations of 4-HNE or methyl glyoxal leads to a significant increase in IC(50) when cells are exposed to higher concentrations of the toxic aldehyde. The IC(50) for methyl glyoxal increased from 410μM to 1.9mM, and the IC(50) for 4-HNE increased from 120 to 690nM. To investigate this protection, we show that pretreatment of cells with the AKR inhibitor sorbinil lead to decreased resistance to aldehydes. We show that AKR1C can be induced 8-fold in SH-SY5Y cells by treatment with sub-lethal concentrations of methyl glyoxal, and 5-fold by 4-HNE treatment. AKR1B is not induced by methyl glyoxal but is induced 10-fold by 4-HNE treatment. Furthermore, we have shown that this adaptive response can also be induced using the chemoprotective agent tert-butyl hydroquinone (t-BHQ), and that this also evokes an increase in the expression and activity of AKR1B and AKR1C. These findings highlight the potential for the interventional upregulation of AKR via non-toxic derivatives or natural compounds as a novel therapeutic approach towards the detoxication of aldehydes, with the aim of halting the progression of aldehyde-dependent neurodegenerative diseases.

Regulation of transforming growth factor β1-dependent aldose reductase expression by the Nrf2 signal pathway in human mesangial cells

Aldose reductase (AR) is a key enzyme in the alternative glucose metabolism pathway, the polyol pathway. To date, AR is known to be involved in several secondary complications of diabetes and various kidney diseases. The goal of this study was to elucidate how the Nrf2-anti-oxidant response element (ARE) signal pathway plays a role in TGFβ1's regulation of AR expression in human renal mesangial cells (HRMCs). As an in vitro model system, HRMCs were used to investigate AR mRNA by qPCR, protein by Western blot and enzymatic activity by spectrophotometric assay. The ability of TGFβ1 to induce reactive oxygen species (ROS) in cells was measured by electron-spin resonance (ESR) trapping method. Reporter assays were used to test the activity of the AR promoter region, and ChIP was employed to test the direct binding of Nrf2 with the endogenous AR promoter. Treatment of HRMCs with TGFβ1 up-regulated the expression of AR mRNA, protein, and activity level. Additionally, TGFβ1 rapidly increased cellular ROS levels, which in turn activated the Nrf2-ARE pathway. Either inhibition of ROS production or knockdown of Nrf2 in HRMCs decreased the TGFβ1-induction of AR expression. Nrf2 regulated AR luciferase activity specifically via two AREs within the AR promoter, and bound directly to the endogenous AR promoter. Furthermore, the TGFβ1-mediated expression of AR required Nrf2 and was significantly abrogated in Nrf2-/- cells. These data show the regulation of AR by TGFβ1 is induced by TGFβ1 stimulation of ROS, which activates the Nrf2-ARE pathway allowing Nrf2 to directly increase AR expression in HRMCs.

Aldo-Keto Reductases 1B in Endocrinology and Metabolism

The aldose reductase (AR; human AKR1B1/mouse Akr1b3) has been the focus of many research because of its role in diabetic complications. The starting point of these alterations is the massive entry of glucose in polyol pathway where it is converted into sorbitol by this enzyme. However, the issue of AR function in non-diabetic condition remains unresolved. AR-like enzymes (AKR1B10, Akr1b7, and Akr1b8) are highly related isoforms often co-expressed with bona fide AR, making functional analysis of one or the other isoform a challenging task. AKR1B/Akr1b members share at least 65% protein identity and the general ability to reduce many redundant substrates such as aldehydes provided from lipid peroxidation, steroids and their by-products, and xenobiotics in vitro. Based on these properties, AKR1B/Akr1b are generally considered as detoxifying enzymes. Considering that divergences should be more informative than similarities to help understanding their physiological functions, we chose to review specific hallmarks of each human/mouse isoforms by focusing on tissue distribution and specific mechanisms of gene regulation. Indeed, although the AR shows ubiquitous expression, AR-like proteins exhibit tissue-specific patterns of expression. We focused on three organs where certain isoforms are enriched, the adrenal gland, enterohepatic, and adipose tissues and tried to connect recent enzymatic and regulation data with endocrine and metabolic functions of these organs. We presented recent mouse models showing unsuspected physiological functions in the regulation of glucido-lipidic metabolism and adipose tissue homeostasis. Beyond the widely accepted idea that AKR1B/Akr1b are detoxification enzymes, these recent reports provide growing evidences that they are able to modify or generate signal molecules. This conceptually shifts this class of enzymes from unenviable status of scavenger to upper class of messengers.

Effect of graded Nrf2 activation on phase-I and -II drug metabolizing enzymes and transporters in mouse liver

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that induces a battery of cytoprotective genes in response to oxidative/electrophilic stress. Kelch-like ECH associating protein 1 (Keap1) sequesters Nrf2 in the cytosol. The purpose of this study was to investigate the role of Nrf2 in regulating the mRNA of genes encoding drug metabolizing enzymes and xenobiotic transporters. Microarray analysis was performed in livers of Nrf2-null, wild-type, Keap1-knockdown mice with increased Nrf2 activation, and Keap1-hepatocyte knockout mice with maximum Nrf2 activation. In general, Nrf2 did not have a marked effect on uptake transporters, but the mRNAs of organic anion transporting polypeptide 1a1, sodium taurocholate cotransporting polypeptide, and organic anion transporter 2 were decreased with Nrf2 activation. The effect of Nrf2 on cytochrome P450 (Cyp) genes was minimal, with only Cyp2a5, Cyp2c50, Cyp2c54, and Cyp2g1 increased, and Cyp2u1 decreased with enhanced Nrf2 activation. However, Nrf2 increased mRNA of many other phase-I enzymes, such as aldo-keto reductases, carbonyl reductases, and aldehyde dehydrogenase 1. Many genes involved in phase-II drug metabolism were induced by Nrf2, including glutathione S-transferases, UDP- glucuronosyltransferases, and UDP-glucuronic acid synthesis enzymes. Efflux transporters, such as multidrug resistance-associated proteins, breast cancer resistant protein, as well as ATP-binding cassette g5 and g8 were induced by Nrf2. In conclusion, Nrf2 markedly alters hepatic mRNA of a large number of drug metabolizing enzymes and xenobiotic transporters, and thus Nrf2 plays a central role in xenobiotic metabolism and detoxification.

The Prostaglandin F Synthase Activity of the Human Aldose Reductase AKR1B1 Brings New Lenses to Look at Pathologic Conditions

Prostaglandins are important regulators of female reproductive functions to which aldose reductases exhibiting hydroxysteroid dehydrogenase activity also contribute. Our work on the regulation of reproductive function by prostaglandins (PGs), lead us to the discovery that AKR1B5 and later AKR1B1were highly efficient and physiologically relevant PGF synthases. PGE2 and PGF2α are the main prostanoids produced in the human endometrium and proper balance in their relative production is important for normal menstruation and optimal fertility. Recent evidence suggests that PGE2/EP2 and PGF2α/FP may constitute a functional dyad with physiological relevance comparable to the prostacyclin-thromboxane dyad in the vascular system. We have recently reported that AKR1B1 was expressed and modulated in association with PGF2α production in response to IL-1β in the human endometrium. In the present study, we show that the human AKR1B1 (gene ID: 231) also known as ALDR1 or ALR2 is a functional PGF2α synthase in different models of living cells and tissues. Using human endometrial cells, prostate, and vascular smooth muscle cells, cardiomyocytes and endothelial cells we demonstrate that IL-1β is able to up regulate COX-2 and AKR1B1 proteins as well as PGF2α production under normal glucose concentrations. We show that the promoter activity of AKR1B1 gene is increased by IL-1β particularly around the multiple stress response region containing two putative antioxidant response elements adjacent to TonE and AP1. We also show that AKR1B1 is able to regulate PGE2 production through PGF2α acting on its FP receptor and that aldose reductase inhibitors like alrestatin, Statil (ponalrestat), and EBPC exhibit distinct and characteristic inhibition of PGF2α production in different cell models. The PGF synthase activity of AKR1B1 represents a new and important target to regulate ischemic and inflammatory responses associated with several human pathologies.

Nuclear factor of activated T cells 5 deficiency increases the severity of neuronal cell death in ischemic injury

Nuclear factor of activated T cells 5 (NFAT5) has been implicated in regulating several genes that are thought to be neuroprotective in ischemic injury. Because of the embryonic lethality of NFAT5 knockout (NFAT5(-/-)) mice, the heterozygous (NFAT5(+/-)) mice were used to study the in vivo role of NFAT5 in hypoxia/ischemia (H/I) condition. The NFAT5(+/-) mice exhibited more severe neurological deficits, larger infarct area and edema formation associated with increased aquaporin 4 expressions in the brain. Under in vitro H/I condition, increased apoptotic cell death was found in NFAT5(-/-) neurons. Moreover, SMIT, a downstream to NFAT5, was upregulated in NFAT5(+/+) neurons, while the SMIT level could not be upregulated in NFAT5(-/-) neurons under H/I condition. The elevation of reactive oxygen species generation in NFAT5(-/-) neurons under H/I condition further confirmed that NFAT5(-/-) neurons were more susceptible to oxidative stress. The present study demonstrated that activation of NFAT5 and its downstream SMIT induction is important in protecting neurons from ischemia-induced oxidative stress.

Sp3 transcription factor is crucial for transcriptional activation of the human NOX4 gene

NOX is the catalytic subunit of NADPH oxidase, the superoxide-generating enzyme. Among several isoforms of NOX, NOX4 is abundantly expressed in various tissues. To clarify the mechanisms of constitutive and ubiquitous expression of NOX4, the promoter activities of the human NOX4 gene were analyzed by reporter assays. The 5'-flanking and non-coding regions of the human NOX4 gene are known to contain multiple GC bases. Among them, three GC-boxes containing putative Sp/Klf-binding sites, which were not found in rodent genes, were suggested to be essential for the basal expression of the NOX4 gene in SH-SY5Y and HEK293 cells. Electrophoresis mobility shift assays demonstrated that Sp1 and Sp3 could bind to GC-boxes at positions -239/-227 and +69/+81 in these cells. Chromatin immunoprecipitation assays showed that Sp1 and Sp3 could also bind to GC-boxes at positions -239/-227 and +69/+81 in vivo. The promoter activity of the NOX4 gene was reduced in SH-SY5Y and HEK293 cells by transfection of an anti-Sp3 short hairpin RNA-expression plasmid. Taken together, these results suggest that Sp3 plays a key role in the expression of NOX4 in various cell lineages in humans.

Impaired redox signaling and antioxidant gene expression in endothelial cells in diabetes: a role for mitochondria and the nuclear factor-E2-related factor 2-Kelch-like ECH-associated protein 1 defense pathway

Type 2 diabetes is an age-related disease associated with vascular pathologies, including severe blindness, renal failure, atherosclerosis, and stroke. Reactive oxygen species (ROS), especially mitochondrial ROS, play a key role in regulating the cellular redox status, and an overproduction of ROS may in part underlie the pathogenesis of diabetes and other age-related diseases. Cells have evolved endogenous defense mechanisms against sustained oxidative stress such as the redox-sensitive transcription factor nuclear factor E2-related factor 2 (Nrf2), which regulates antioxidant response element (ARE/electrophile response element)-mediated expression of detoxifying and antioxidant enzymes and the cystine/glutamate transporter involved in glutathione biosynthesis. We hypothesize that diminished Nrf2/ARE activity contributes to increased oxidative stress and mitochondrial dysfunction in the vasculature leading to endothelial dysfunction, insulin resistance, and abnormal angiogenesis observed in diabetes. Sustained hyperglycemia further exacerbates redox dysregulation, thereby providing a positive feedback loop for severe diabetic complications. This review focuses on the role that Nrf2/ARE-linked gene expression plays in regulating endothelial redox homeostasis in health and type 2 diabetes, highlighting recent evidence that Nrf2 may provide a therapeutic target for countering oxidative stress associated with vascular disease and aging.

Regulation of aldo-keto reductase AKR1B10 gene expression: involvement of transcription factor Nrf2

Aldo-keto reductase 1B10 (AKR1B10) is an aldose reductase-like oxidoreductase of human origin. The expression of AKR1B10 is highly induced in the cells of various cancers such as lung non-small-cell carcinoma and hepatocellular carcinoma. Since the enzyme exhibits broad substrate specificities toward various xenobiotics such as anti-tumor drugs or various endogenous compounds such as retinaldehyde, AKR1B10 may play an important role in tumor progression or drug resistance. However, very little is known about its gene regulation. In this study, we investigated the regulation of AKR1B10 expression. A -3282bp of the 5'-flanking fragment of AKR1B10 gene was isolated from A549 lung carcinoma cells. This region contains several putative regulatory motifs such as AP-1, NF-κB and antioxidant response element. In addition, a complex polymorphic microsatellite with repetitive sequences enriched with C and T was found. However, luciferase reporter assay revealed that the microsatellite polymorphism did not influence the basal promoter activity. We found that an antioxidant ethoxyquin induced the AKR1B10 expression based on RT-PCR analysis and luciferase reporter assay. Since ethoxyquin is known to activate the gene expression mediated through transcription factor Nrf2, the involvement of Nrf2 was examined. Forced expression of dominant-negative Nrf2 mutant suppressed the ethoxyquin-induced AKR1B10 expression, and co-introduction of Nrf2 expression plasmid into the cells significantly augmented the luciferase reporter activity. Deletion analysis revealed that Nrf2-regulating cis-element(s) lay within -539bp of the 5'-flanking region. These results suggest that Nrf2 is one of the major factors involved in the AKR1B10 gene regulation.

Cancer chemoprevention mechanisms mediated through the Keap1-Nrf2 pathway

The cap'n'collar (CNC) bZIP transcription factor Nrf2 controls expression of genes for antioxidant enzymes, metal-binding proteins, drug-metabolising enzymes, drug transporters, and molecular chaperones. Many chemicals that protect against carcinogenesis induce Nrf2-target genes. These compounds are all thiol-reactive and stimulate an adaptive response to redox stress in cells. Such agents induce the expression of genes that posses an antioxidant response element (ARE) in their regulatory regions. Under normal homeostatic conditions, Nrf2 activity is restricted through a Keap1-dependent ubiquitylation by Cul3-Rbx1, which targets the CNC-bZIP transcription factor for proteasomal degradation. However, as the substrate adaptor function of Keap1 is redox-sensitive, Nrf2 protein evades ubiquitylation by Cul3-Rbx1 when cells are treated with chemopreventive agents. As a consequence, Nrf2 accumulates in the nucleus where it heterodimerizes with small Maf proteins and transactivates genes regulated through an ARE. In this review, we describe synthetic compounds and phytochemicals from edible plants that induce Nrf2-target genes. We also discuss evidence for the existence of different classes of ARE (a 16-bp 5'-TMAnnRTGABnnnGCR-3' versus an 11-bp 5'-RTGABnnnGCR-3', with or without the embedded activator protein 1-binding site 5'-TGASTCA-3'), species differences in the ARE-gene battery, and the identity of critical Cys residues in Keap1 required for de-repression of Nrf2 by chemopreventive agents.

Regulation of human carbonyl reductase 3 (CBR3; SDR21C2) expression by Nrf2 in cultured cancer cells

Carbonyl reduction is a central metabolic process that controls the level of key regulatory molecules as well as xenobiotics. Carbonyl reductase 3 (CBR3; SDR21C2), a member of the short-chain dehydrogenase/reductase (SDR) superfamily, has been poorly characterized so far, and the regulation of its expression is a complete mystery. Here, we show that CBR3 expression is regulated via Nrf2, a key regulator in response to oxidative stress. In human cancer cell lines, CBR3 mRNA was expressed differentially, ranging from very high (A549, lung) to very low (HT-29, colon; HepG2, liver) levels. CBR3 protein was highly expressed in SW-480 (colon) cells but was absent in HCT116 (colon) and HepG2 cells. CBR3 mRNA could be induced in HT-29 cells by Nrf2 agonists [sulforaphane (SUL, 7-fold) and diethyl maleate (DEM, 4-fold)] or hormone receptor ligand Z-guggulsterone (5-fold). Aryl hydrocarbon receptor agonist B[k]F failed to induce CBR3 mRNA after incubation for 8 h but elevated CBR3 levels after 24 h, most likely mediated by B[k]F metabolites that can activate Nrf2 signaling. Inhibition of Nrf2-activating upstream kinase MEK/ERK by PD98059 weakened DEM-mediated induction of CBR3 mRNA. Proteasome inhibitors MG-132 (5 μM) and bortezomib (50 nM) dramatically increased the level of CBR3 mRNA, obviously because of the increase in the level of Nrf2 protein. While siRNA-mediated knockdown of Nrf2 led to a decrease in the level of CBR3 mRNA in A549 cells (30% of control), Keap1 knockdown increased the level of CBR3 mRNA expression in HepG2 (9.3-fold) and HT-29 (2.7-fold) cells. Here, we provide for the first time evidence that human CBR3 is a new member of the Nrf2 gene battery.

Protective effects of magnesium lithospermate B against diabetic atherosclerosis via Nrf2-ARE-NQO1 transcriptional pathway

Hyperglycemia-induced oxidative stress is known to play an important role in the development of several diabetic complications, including atherosclerosis. Although a number of antioxidants are available, none have been found to be suitable for regulating the oxidative stress response and enhancing antioxidative defense mechanisms. In this study, we evaluated the effects of magnesium lithospermate B (LAB) against oxidative stress. We also endeavored to identify the target molecule of LAB in vascular smooth muscle cells (VSMCs) and the underlying biochemical pathways related to diabetic atherosclerosis. Modified MTT and transwell assays showed that the increased proliferation and migration of rat aortic VSMCs in culture with high glucose was significantly inhibited by LAB. LAB also attenuated neointimal hyperplasia after balloon catheter injury in diabetic rat carotid arteries. To determine molecular targets of LAB, we studied the effects of LAB on aldose reductase (AR) activity, O-GlcNAcylation, and protein kinase C (PKC) activity in VSMCs under normoglycemic or hyperglycemic conditions and showed the improvement of major biochemical pathways by LAB. Potential involvement of the nuclear factor erythroid 2-related factor-2 (Nrf2)--antioxidant responsive element (ARE)-NAD(P)H: quinone oxidoreductase-1 (NQO1) pathway was assessed using siRNA methods. We found that LAB activates the NQO1 via the Nrf2-ARE pathway, which plays an important role in inhibition of the major molecular mechanisms that lead to vascular damage and the proliferation and migration of VSMCs. Together, these findings demonstrate that the induction of the Nrf2-ARE-NQO1 pathway by LAB could be a new therapeutic strategy to prevent diabetic atherosclerosis.

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

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

Aldose reductase protects against early atherosclerotic lesion formation in apolipoprotein E-null mice

RATIONALE

Atherosclerotic lesion formation is associated with the accumulation of oxidized lipids. Products of lipid oxidation, particularly aldehydes, stimulate cytokine production and enhance monocyte adhesion; however, their contribution to atherosclerotic lesion formation remains unclear.

OBJECTIVE

To test the hypothesis that inhibition of aldehyde removal by aldose reductase (AR), which metabolizes both free and phospholipid aldehydes, exacerbates atherosclerotic lesion formation.

METHODS AND RESULTS

In atherosclerotic lesions of apolipoprotein (apo)E-null mice, AR protein was located in macrophage-rich regions and its abundance increased with lesion progression. Treatment of apoE-null mice with AR inhibitors sorbinil or tolrestat increased early lesion formation but did not affect the formation of advanced lesions. Early lesions of AR(-/-)/apoE(-/-) mice maintained on high-fat diet were significantly larger when compared with age-matched AR(+/+)/apoE(-/-) mice. The increase in lesion area attributable to deletion of the AR gene was seen in both male and female mice. Pharmacological inhibition or genetic ablation of AR also increased the lesion formation in male mice made diabetic by streptozotocin treatment. Lesions in AR(-/-)/apoE(-/-) mice exhibited increased collagen and macrophage content and a decrease in smooth muscle cells. AR(-/-)/apoE(-/-) mice displayed a greater accumulation of the AR substrate 4-hydroxy trans-2-nonenal (HNE) in the plasma and protein-HNE adducts in arterial lesions than AR(+/+)/apoE(-/-) mice.

CONCLUSIONS

These observations indicate that AR is upregulated in atherosclerotic lesions and it protects against early stages of atherogenesis by removing toxic aldehydes generated in oxidized lipids.

Activation of antioxidant defense during dehydration stress in the African clawed frog

The glutathione S-transferase (GST) and aldo-keto reductase (AKR) families of proteins are major groups of detoxifying enzymes that are known to be regulated by the NF-E2 related factor 2 (Nrf2) transcription factor via the antioxidant response element that is present in the promoter regions of GST and AKR genes. Expression of Nrf2, GST and AKR proteins was analyzed in the African clawed frog, Xenopus laevis, focusing on their responses to dehydration stress. Dehydration/rehydration cycles can generate oxidative stress and this could be ameliorated by enhancing antioxidant defenses. Dehydration to 28% of total body water lost triggered organ-specific changes in nrf2 mRNA expression (a 2-fold increase in liver), total Nrf2 protein (2-4-fold elevation in lung, heart, skin and liver), and a 4.3-fold increase in the content of Nrf2 in the nucleus in muscle. Protein levels of six GST and three AKR family members were assessed and showed organ-specific patterns of expression during dehydration. In particular, GSTP1 was strongly induced in liver, heart and skin, levels rising by 9-, 2.6- and 1.7-fold, respectively, whereas GSTM1 and M3 rose in skeletal muscle, kidney and skin. Selective expression of GSTK1, A3 and T1 also occurred. Dehydration also stimulated organ-specific increases in the levels of AKR family members (AKR1B4, AKR1A3, AFAR1) by 1.5-2-fold. The results show that metabolic responses to dehydration include activation of the Nrf2 transcription factor and selective up-regulation of genes under Nrf2 control.

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.

Liver gene expression analysis reveals endoplasmic reticulum stress and metabolic dysfunction in SCD1-deficient mice fed a very low-fat diet

We previously reported that mice deficient in stearoyl-CoA desaturase-1 ( Scd1) and maintained on a very low-fat (VLF) diet for 10 days developed severe loss of body weight, hypoglycemia, hypercholesterolemia, and many cholestasis-like phenotypes. To better understand the metabolic changes associated with these phenotypes, we performed microarray analysis of hepatic gene expression in chow- and VLF-fed female Scd1+/+ and Scd1−/− mice. We identified an extraordinary number of differentially expressed genes (>4,000 probe sets) in the VLF Scd1−/− relative to both VLF Scd1+/+ and chow Scd1−/− mice. Transcript levels were reduced for genes involved in detoxification and several facets of fatty acid metabolism including biosynthesis, elongation, desaturation, oxidation, transport, and ketogenesis. This pattern is attributable to the decreased mRNA abundance of several genes encoding key transcription factors, including LXRα, RXRα, FXR, PPARα, PGC-1β, SREBP1c, ChREBP, CAR, DBP, TEF, and HLF. A robust induction of endoplasmic reticulum (ER) stress is indicated by enhanced splicing of XBP1, increased expression of the stress-induced transcription factors CHOP and ATF3, and elevated expression of several genes involved in the integrated stress and unfolded protein response pathways. The gene expression profile is also consistent with induction of an acute inflammatory response and macrophage recruitment. These results highlight the importance of monounsaturated fatty acid synthesis for maintaining metabolic homeostasis in the absence of sufficient dietary unsaturated fat and point to a novel cellular nutrient-sensing mechanism linking fatty acid availability and/or composition to the ER stress response.

Transcription factor AP-1 regulates TGF-beta(1)-induced expression of aldose reductase in cultured human mesangial cells

AIM

The previous studies demonstrated that transforming growth factor-beta(1) (TGF-beta(1)) could upregulate the expression of aldose reductase (AR). The aim of this study is to clarify (investigate) the mechanism of TGF-beta(1)-induced AR expression.

METHODS

Real-time polymerase chain reaction and western blot were used to analyse the AR expression in mRNA and protein levels in human mesangial cells, and reporter assay was used to analyse the function of various sites within 5'-flanking region of AR gene in AR expression.

RESULTS

TGF-beta(1) (4 ng/mL) stimulation could upregulate AR expression. The cells pretreated with pharmacological inhibitors, U0126 and PD98059 for blocking extracellular signal-related kinase (ERK) signalling pathway or SP6000125 for blocking c-Jun N-terminal kinase (JNK) signalling pathway, respectively, showed reduced expression of AR after TGF-beta(1) stimulation. Similarly, the cells transiently transfected with pCMVTAM67, which is an expression plasmid for DN-c-Jun showed decreasing AR expression. Reporter assay revealed that the 5'-promoter region of AR consisting of an AP-1 site and two putative antioxidant response elements (ARE) was responsible for TGF-beta(1) stimulation. Mutation of either ARE did not affect the promoter activity in the reporter assay while mutation of AP-1 site caused a significant decrease in the responsiveness to TGF-beta(1).

CONCLUSION

TGF-beta(1) upregulate AR expression in both mRNA and protein levels. The results demonstrated that ERK and JNK are involved in the downstream signalling pathways and transcription factor AP-1 plays an important role in the regulation of TGF-beta(1)-induced AR expression in mesangial cells.

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

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

Myocyte enhancer factor 2B is involved in the inducible expression of NOX1/NADPH oxidase, a vascular superoxide-producing enzyme

NADPH oxidase is a major source of the superoxide produced in cardiovascular tissues. Expression of NOX1, a catalytic subunit of NADPH oxidase, is induced by various vasoactive factors, including angiotensin II, prostaglandin (PG) F(2alpha) and platelet-derived growth factor (PDGF). To clarify the molecular basis of this transcriptional activation, we delineated the promoter region of the NOX1 gene. RT-PCR and 5'-rapid amplification of cDNA ends-based analyses revealed a novel 5'-terminal exon of the rat NOX1 gene located approximately 28 kb upstream of the exon containing the start codon. Both PGF(2alpha) and PDGF enhanced the transcriptional activity of the - 3.6 kb 5'-flanking region of the NOX1 gene in A7r5 cells, a rat vascular smooth muscle cell line. A PGF(2alpha)-response element was located between -146 and -125 in the 5'-flanking region containing a consensus binding site for myocyte enhancer factor 2 (MEF2), to which binding of MEF2 was augmented by PGF(2alpha). Gene silencing of MEF2B by RNA interference significantly suppressed the expression of NOX1, while silencing of activating transcription factor (ATF)-1, previously implicated in up-regulation of NOX1, abolished the PGF(2alpha)- or PDGF-induced expression of MEF2B. These results indicate that superoxide production in vascular smooth muscle cells is regulated by the ATF-1-MEF2B cascade by induction of the expression of the NOX1 gene.

The antitumor agent imexon activates antioxidant gene expression: evidence for an oxidative stress response

PURPOSE

The aim of this study was to identify biomarkers that may be predictive for the clinical activity of the redox-active antitumor agent imexon.

EXPERIMENTAL DESIGN

cDNA microarray and quantitative real-time PCR were used to identify global changes in gene expression in peripheral blood mononuclear cells (PBMC) collected from patients treated with imexon during a phase I trial. Electrophoretic mobility shift assays and Western blot analysis were done using the RPMI8226 myeloma cell line grown in vitro and PBMCs treated ex vivo to investigate the molecular mechanism responsible for these gene changes.

RESULTS

Both cDNA microarray and quantitative real-time PCR showed the up-regulation of many antioxidant genes, including thioredoxin reductase-1, glutaredoxin-2, and peroxiredoxin-3 in PBMCs collected from patients treated with imexon. Studies in PBMCs treated ex vivo and RPMI8226 myeloma cells showed that imexon increased binding to the activator protein-1 consensus sequence measured by electrophoretic mobility shift assay. Supershift analysis showed that the majority of the activator protein-1 DNA binding activity was c-Jun, with minor contribution of Jun-D. Nuclear translocation of the nuclear factor (erythroid-derived 1)-like 2 transcription factor and its binding to the antioxidant response element was also increased after imexon treatment, which correlated with an increase in the message levels for nuclear factor (erythroid-derived 1)-like 2/antioxidant response element-regulated antioxidant genes.

CONCLUSIONS

Together, these results show that a predominant biological effect of imexon is a change in redox state that can be detected in surrogate normal tissues as increased redox-sensitive transcription factor binding and increased antioxidant gene expression.

Up-regulation of aldose reductase expression mediated by phosphatidylinositol 3-kinase/Akt and Nrf2 is involved in the protective effect of curcumin against oxidative damage

Up-regulation of aldose reductase (AR) by reactive oxygen species (ROS) and aldehyde derivatives has been observed in vascular smooth muscle cells. However, the pathophysiological consequences of the induction of AR in vascular tissues are not fully elucidated. Herein we report that an herb-derived polyphenolic compound, curcumin, elicited a dose- and time-dependent increase in AR expression. Inhibition of phosphatidylinositol 3-kinase (PI3K) and p38 mitogen-activated protein kinase (MAPK) significantly suppressed the curcumin-augmented mRNA levels and promoter activity of the AR gene. Luciferase reporter assays indicated that an osmotic response element in the promoter was essential for the responsiveness to curcumin. Curcumin accelerated the nuclear translocation of nuclear factor-erythroid 2-related factor 2 (Nrf2), and overexpression of Nrf2, but not the dominant negative Nrf2, enhanced the promoter activity of the AR gene. Cells preincubated with curcumin demonstrated resistance to ROS-induced apoptotic death. These effects were significantly attenuated in the presence of AR inhibitors or small interfering RNAs, indicating a protective role for AR against ROS-induced cell damage. Taken together, the activation of PI3K and p38 MAPK by curcumin augmented the expression of the AR gene via Nrf2, and increased AR activity may be an important cellular response against oxidative stress.

Reactive carbonyls and oxidative stress: potential for therapeutic intervention

Reactive aldehydes and ketones are produced as a result of oxidative stress in several disease processes. Considerable evidence is now accumulating that these reactive carbonyl products are also involved in the progression of diseases, including neurodegenerative disorders, diabetes, atherosclerosis, diabetic complications, reperfusion after ischemic injury, hypertension, and inflammation. To counter carbonyl stress, cells possess enzymes that can decrease aldehyde load. These enzymes include aldehyde dehydrogenases (ALDH), aldo-keto reductases (AKR), carbonyl reductase (CBR), and glutathione S-transferases (GST). Some of these enzymes are inducible by chemoprotective compounds via Nrf2/ARE- or AhR/XRE-dependent mechanisms. This review describes the metabolism of reactive carbonyls and discusses the potential for manipulating levels of carbonyl-metabolizing enzymes through chemical intervention.

Aldo-keto reductases and bioactivation/detoxication

Aldo-keto reductases (AKRs) are soluble NAD(P)(H) oxidoreductases that primarily reduce aldehydes and ketones to primary and secondary alcohols, respectively. The ten known human AKR enzymes can turnover a vast range of substrates, including drugs, carcinogens, and reactive aldehydes. They play central roles in the metabolism of these agents, and this can lead to either their bioactivation or detoxication. AKRs are Phase I drug metabolizing enzymes for a variety of carbonyl-containing drugs and are implicated in cancer chemotherapeutic drug resistance. They are involved in tobacco-carcinogenesis because they activate polycyclic aromatic trans-dihydrodiols to yield reactive and redox active o-quinones, but they also catalyze the detoxication of nicotine derived nitrosamino ketones. They also detoxify reactive aldehydes formed from exogenous toxicants, e.g., aflatoxin, endogenous toxicants, and those formed from the breakdown of lipid peroxides. AKRs are stress-regulated genes and play a central role in the cellular response to osmotic, electrophilic, and oxidative stress.

Curcumin activates human glutathione S-transferase P1 expression through antioxidant response element

Curcumin is a plant-derived diferuloylmethane compound extracted from Curcuma longa, possessing antioxidative and anticarcinogenic properties. Antioxidants and oxidative stress are known to induce the expression of certain classes of detoxification enzymes. Since the upregulation of detoxifying enzymes affects the drug metabolism and cell defense system, it is important to understand the gene regulation by such agents. In this study, we demonstrated that curcumin could induce the expression of human glutathione S-transferase P1 (GSTP1). In HepG2 cells treated with 20muM curcumin, the level of GSTP1 mRNA was significantly increased. In luciferase reporter assays, curcumin augmented the promoter activity of a reporter construct carrying 336bp upstream of the 5'-flanking region of the GSTP1 gene. Mutation analyses revealed that the region including antioxidant response element (ARE), which overlaps AP1 in sequence, was essential to the response to curcumin. While the introduction of a wild-type Nrf2 expression construct augmented the promoter activity of the GSTP1 gene, co-expression of a dominant-negative Nrf2 abolished the responsiveness to curcumin. In addition, curcumin activated the expression of the luciferase gene from a reporter construct carrying multiple ARE consensus sequences but not one with multiple AP1 sites. In a gel mobility shift assay with an oligonucleotide with GSTP1 ARE, an increase in the amount of the binding complex was observed in the nuclear extracts of curcumin-treated HepG2 cells. These results suggested that ARE is the primary sequence for the curcumin-induced transactivation of the GSTP1 gene. The induction of GSTP1 may be one of the mechanisms underlying the multiple actions of curcumin.

The Activity of Aldose Reductase Is Elevated in Diabetic Mouse Heart

The importance of aldose reductase (AR) has been implicated in the pathogenesis of diabetic complications, although the alterations in the expression and activity of AR during hyperglycemia in the heart have not been well characterized. We investigated the expression and enzyme activity of AR in a murine diabetic model. Three weeks after the induction of hyperglycemia with streptozotocin, the level of AR mRNA was significantly reduced in the cardiac ventricles of BDF-1 mice. In contrast, the activity of AR was significantly elevated in the heart without any significant change in the protein level. In these mice, the level of cardiac thiobarbituric acid-reactive substances was unaltered, whereas the level of reduced glutathione (GSH) was significantly increased. Daily administration of insulin for 3 weeks completely normalized the level of AR mRNA and the enzyme activity. On the other hand, daily administration of an antioxidant, N-acetylcysteine significantly reduced the level of AR mRNA in the heart with a concomitant elevation in the enzyme activity. These results suggest that the activity of AR in the heart is affected by GSH dynamics. Augmented AR activity at the early stage of hyperglycemia may perturb glycolysis and affect cardiac performance.