NAD(P)H: quinone oxidoreductase 1 expression in kidney podocytes.

NAD(P)H:quinone oxidoreductase 1 (NQO1; DT-diaphorase; DTD) is a cytosolic two-electron reductase, and compounds of the quinone family such as mitomycin C are efficiently bioactivated by this enzyme. The observation that DT-diaphorase is highly expressed in many cancerous tissues compared to normal tissues has provided us with a potentially selective target that can be exploited in the design of novel anticancer agents. Because of the relative lack of information about the cell-specific expression of DT-diaphorase, the purpose of this study was to map the distribution of this enzyme in normal human tissues. Fifteen tissue samples from normal human kidney were analyzed for expression of DT-diaphorase by immunohistochemistry (two-step indirect method). We found a specific high expression of DT-diaphorase in glomerular visceral epithelial cells (podocytes). These results suggest that a high expression of DT-diaphorase in podocytes could play a major role in the pathogenesis of renal toxicity and mitomycin C-induced hemolytic uremic syndrome, in which injury to the glomerular filtration mechanism is the primary damage, leading to a cascade of deleterious events including microangiopathic hemolytic anemia and thrombocytopenia. This observation has potential therapeutic implications because the DT-diaphorase metabolic pathway is influenced by many agents, including drugs, diet, and environmental cell factors such as pH and oxygen tension.     

Regulation of MUC5AC expression by NAD(P)H:quinone oxidoreductase 1

Neutrophil elastase (NE), a potent neutrophil inflammatory mediator, increases MUC5AC mucin gene expression through undefined pathways involving reactive oxygen species. To determine the source of NE-generated reactive oxygen species, we used pharmacologic inhibitors of oxidoreductases to test whether they blocked NE-regulated MUC5AC mRNA expression. We found that dicumarol, an inhibitor of the NADP(H):quinone oxidoreductase 1 (NQO1), inhibited MUC5AC mRNA expression in A549 lung adenocarcinoma cells and primary normal human bronchial epithelial cells. We further tested the role of NQO1 in mediating NE-induced MUC5AC expression by inhibiting NQO1 expression using short interfering RNA (siRNA). Transfection with siRNA specific for NQO1 suppressed NQO1 expression and significantly abrogated MUC5AC mRNA expression. NE treatment caused lipid peroxidation in A549 cells; this effect was inhibited by pretreatment with dicumarol, suggesting that NQO1 also regulates oxidant stress in A549 cells after NE exposure. NE exposure increased NQO1 protein and activity levels; NQO1 expression and activity were limited to the cytosol and did not translocate to the plasma membrane. Our results indicate that NQO1 has an important role as a key mediator of NE-regulated oxidant stress and MUC5AC mucin gene expression.     

Regeneration of lipophilic antioxidants by NAD(P)H:quinone oxidoreductase 1

Summary.  The aim of this work was to study the activity of NAD(P)H:(quinone acceptor) oxidoreductase 1 (EC 1.6.99.2) in the regeneration of lipophilic antioxidants, alpha-tocopherol, and reduced-coenzyme Q analogs. First, we tested whether or not two isoforms of the NAD(P)H:(quinone acceptor) oxidoreductase 1 designated as “hydrophilic” and “hydrophobic” (H. J. Prochaska and P. Talalay, Journal of Biological Chemistry 261: 1372–1378, 1986) show differential enzyme activities towards hydrophilic or hydrophobic ubiquinone homologs. By chromatography on phenyl Sepharose, we purified the two isoforms from pig liver cytosol and measured their reduction of several ubiquinone homologs of different side chain length. We also studied by electron paramagnetic resonance the effect of NAD(P)H:(quinone acceptor) oxidoreductase 1 on steady-state levels of chromanoxyl radicals generated by linoleic acid and lipooxygenase and confirmed the enzyme's ability to protect alpha-tocopherol against oxidation induced with H₂O₂-Fe²⁺. Our results demonstrated that the different hydrophobicities of the isoforms do not reflect different reactivities towards ubiquinones of different side chain length. In addition, electron paramagnetic resonance studies showed that in systems containing the reductase plus NADH, levels of chromanoxyl radicals were dramatically reduced. Morever, in the presence of oxidants, alpha-tocopherol was preserved by NAD(P)H:(quinone acceptor) oxidoreductase 1, supporting our hypothesis that regeneration of alpha-tocopherol may be one of the physiologic functions of this enzyme. Received May 20, 2002; accepted September 20, 2002; published online May 21, 2003 RID="*" ID="*" Correspondence and reprints: Departamento de Biología Celular, Fisiología e Inmunología, Facultad de Ciencias, Edificio Severo Ochoa, Campus de Rabanales, Universidad de Córdoba, 14014 Córdoba, Spain.     

Immunodetection of NAD(P)H:quinone oxidoreductase 1 (NQO1) in human tissues

Despite the extensive interest in NADPH:quinone oxidoreductase (NQO1, DT-diaphorase), there is little immunohistochemical information regarding its distribution in either normal human tissues or in human tumors. Using immunohistochemistry (IHC), we have examined cell-specific expression of NQO1 in many normal tissues and tumors as a step toward defining the distribution of NQO1 in humans. NQO1 was detected by IHC in respiratory, breast duct, thyroid follicle, and colonic epithelium, as well as in the corneal and lens epithelium of the eye. NQO1 was also detected by IHC in vascular endothelium in all tissues examined. NQO1 could also readily be detected in the endothelial lining of the aorta but was not detected using immunoblot analysis in the myocardium. Adipocytes stained positive for NQO1, and the enzyme was also detected by both IHC and immunoblot analysis in parasympathetic ganglia in the small intestine and in the optic nerve and nerve fibers. NQO1 was not highly expressed in five different human liver samples using immunoblot analysis, whereas studies using IHC demonstrated only trace NQO1 staining in isolated bile duct epithelium. NQO1 expresion was also examined by IHC in a variety of solid tumors. Marked NQO1 staining was detected in solid tumors from thyroid, adrenal, breast, ovarian, colon, and cornea and in non-small cell lung cancers. The NQO1 content of many solid tumors supports the use of NQO1-directed anticancer agents for therapeutic purposes, but the distribution of NQO1 in normal tissues suggests that potential adverse effects of such agents need to be carefully monitored in preclinical studies.     

NAD(P)H:quinone oxidoreductase 1 protects lungs from oxidant-induced emphysema in mice

Emphysema is currently a leading cause of mortality with no known effective therapy to attenuate progressive loss of lung function. Previous work supports that activation of nuclear factor erythroid 2-related factor 2 (Nrf2) is protective to the lung through induction of hundreds of antioxidant genes. In models of lung injury, the expression of NAD(P)H:quinone oxidoreductase 1 (NQO1) is upregulated in a manner dependent on Nrf2 and human emphysema is associated with reduced levels of NQO1. However, the functional role of NQO1 in emphysema remains unknown. In this study, we demonstrate the protective role of NQO1 in the development of emphysema using mouse models. NQO1-deficient animals demonstrated premature age-related emphysema and were more susceptible to both elastase and inhaled lipopolysaccharide models of emphysema. The absence of NQO1 was associated with enhanced markers of oxidant stress. Treatment of NQO1-deficient animals with the antioxidant N-acetylcysteine reversed the NQO1-dependent emphysematous changes. In vitro studies utilizing either inhibition or induction of NQO1 demonstrated a potent antioxidant role of NQO1 in macrophages, suggesting a role for macrophage-derived oxidants in the pathogenesis of emphysema. These novel findings support a functional role for NQO1 in protecting the lung from development of emphysema.     

NAD(P)H quinone oxidoreductase 1 regulates neutrophil elastase-induced mucous cell metaplasia

Mucous cell metaplasia (MCM) and neutrophil-predominant airway inflammation are pathological features of chronic inflammatory airway diseases. A signature feature of MCM is increased expression of a major respiratory tract mucin, MUC5AC. Neutrophil elastase (NE) upregulates MUC5AC in primary airway epithelial cells by generating reactive oxygen species, and this response is due in part to upregulation of NADPH quinone oxidoreductase 1 (NQO1) activity. Delivery of NE directly to the airway triggers inflammation and MCM and increases synthesis and secretion of MUC5AC protein from airway epithelial cells. We hypothesized that NE-induced MCM is mediated in vivo by NQO1. Male wild-type and Nqo1-null mice (C57BL/6 background) were exposed to human NE (50 μg) or vehicle via oropharyngeal aspiration on days 1, 4, and 7. On days 8 and 11, lung tissues and bronchoalveolar lavage (BAL) samples were obtained and evaluated for MCM, inflammation, and oxidative stress. MCM, inflammation, and production of specific cytokines, granulocyte-macrophage colony-stimulating factor, macrophage inflammatory protein-2, interleukin-4, and interleukin-5 were diminished in NE-treated Nqo1-null mice compared with NE-treated wild-type mice. However, in contrast to the role of NQO1 in vitro, we demonstrate that NE-treated Nqo1-null mice had greater levels of BAL and lung tissue lipid carbonyls and greater BAL iron on day 11, all consistent with increased oxidative stress. NQO1 is required for NE-induced inflammation and MCM. This model system demonstrates that NE-induced MCM directly correlates with inflammation, but not with oxidative stress.     

Overexpression of NAD(P)H:quinone oxidoreductase 1 in human reproductive system.

NAD(P)H:quinone oxidoreductase 1 (NQO1; DT-diaphorase; DTD) is a two-electron reductase that efficiently bioactivates compounds of the quinone family, such as mitomycin C. The observation that DTD is overexpressed in many cancerous tissues compared to normal tissues has provided us with a potentially selective target that can be exploited in the design of novel anticancer agents. Because of the relative lack of information on the cell-specific expression of DTD, the purpose of this study was to perform a body mapping of its normal distribution. Tissue samples from various components of the human reproductive system were analyzed by immunohistochemistry. We found strong expression of this enzyme in testicular stromal cells (Leydig cells) and in the epithelium of epididymis, ductuli efferentes, and Fallopian tube. These results suggest that DTD-bioactivated quinones could be responsible for a selective toxicity on these components of the reproductive system and cause clinical problems due to testosterone deficiency and infertility. This observation needs to be investigated in preclinical evaluation of new anticancer quinones and in patients treated with these compounds. (J Histochem Cytochem 49:1187-1188, 2001)     

NAD(P)H: quinone oxidoreductase 1 inducer activity of novel 4-aminoquinazoline derivatives

Fourteen novel 4-aminoquinazoline derivatives 2–15 were designed and synthesized. The structure of the newly synthesized compounds was established on the basis of elemental analyses, IR, ¹H-NMR, ¹³C-NMR, and mass spectral data. The compounds were evaluated for their potential cytoprotective activity in murine Hepa1c1c7 cells. All of the synthesized compounds showed concentration-dependent ability to induce the cytoprotective enzyme NAD(P)H: quinone oxidoreductase (NQO1) with potencies in the low- to sub-micromolar range. This approach offers an encouraging framework which may lead to the discovery of potent cytoprotective agents.     

Molecular characterization of NAD(P)H:quinone oxidoreductase of tobacco leaves

Summary The NAD(P)H:quinone oxidoreductase activity of tobacco leaves is catalyzed by a soluble flavoprotein [NAD(P)H-QR] and membrane-bound forms of the same enzyme. In particular, the activity associated with the plasma membrane cannot be released by hypoosmotic and salt washing of the vesicles, suggesting a specific binding. The products of the plasma-membrane-bound quinone reductase activity are fully reduced hydroquinones rather than semi-quinone radicals. This peculiar kinetic property is common with soluble NAD(P)H-QR, plasma-membrane-bound NAD(P)H:quinone reductase purified from onion roots, and animal DT-diaphorase. These and previous results demonstrate that soluble and plasma-membrane-bound NAD(P)H:quinone reductases are strictly related flavo-dehydrogenases which seem to replace DT-diaphorase in plant tissues. Following purification to homogeneity, the soluble NAD(P)H-QR from tobacco leaves was digested. Nine peptides were sequenced, accounting for about 50% of NAD(P)H-QR amino acid sequence. Although one peptide was found homologous to animal DT-diaphorase and another one to plant monodehydroascorbate reductase, native NAD(P)H-QR does not seem to be structurally similar to any known flavoprotein.Abbreviations MDAR monodehydroascorbate reductase - PM plasma membrane - NAD(P)H-QR NAD(P)H:quinone oxidoreductase - DPI diphenylene iodonium - DQ duroquinone - CoQ₂ coenzyme Q₂     

Human NAD(P)H:quinone oxidoreductase inhibition by flavonoids in living cells

Procedures for assessing enzyme inhibition in living cells are an important tool in the study of the relevance of enzyme-catalyzed reactions and interactions in the human body. This paper presents the effects of flavonoids on NAD(P)H:quinone oxidoreductase 1 (NQO1) activity, by a newly developed method to measure NQO1 inhibition in intact cells. The principle of this method is based on the resorufin reductase activity of NQO1. The change in fluorescence in time was used to determine NQO1 activity in intact Chinese hamster ovary (CHO) cells genetically engineered to overexpress human NQO1. Applying this method to determine the inhibitory effects of reported in vitro NQO1 inhibitors (dicoumarol, 7,8-dihydroxyflavone, chrysin) showed that for all inhibitors tested, the IC50 in intact cells was at least 3 orders of magnitude higher than the IC50 in cell lysates. This result demonstrates that in vitro studies with purified NQO1 or with extracts from disrupted tissues are of limited value for obtaining insight into the situation in living cells. Possible factors underlying this discrepancy are being discussed. For the first time, we determined NQO1 inhibition by flavonoids in cells without disruption of the cells or addition of cofactors, enabling the assessment of enzymatic activity and the interaction of modulators of enzymatic activity in an intracellular situation.     

NAD(P)H:quinone oxidoreductase 1 activity reduces hypertrophy in 3T3-L1 adipocytes

The nuclear factor E2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap1) pathway responds to oxidative stress via control of several antioxidant defense gene expressions. Recent efforts demonstrate that Nrf2 modulates development of adiposity and adipogenesis. One of the major Nrf2-regulated proteins, NAD(P)H:quinone oxidoreductase 1 (NQO1), is implicated in the development of adipose tissue and obesity. However, little is known about in situ disposition of Nrf2, Keap1, and NQO1 during adipogenesis in isolated adipocytes. Based on literature data, we hypothesized that adipocyte differentiation would increase expression of the Nrf2/Keap1 pathway and NQO1. Using murine 3T3-L1 preadipocytes, we mapped an increase in NQO1 protein at limited clonal expansion and postmitotic growth arrest (Days 1-3) stages and a decrease in terminally differentiated (Day 8) adipocytes that lasted for several days afterward. Conversely, NQO1, Nrf2, and Keap1 mRNA expressions were all increased in differentiated adipocytes (Days 11-14), indicating a discrepancy between steady-state mRNA levels and resulting protein. Treatment of differentiated 3T3-L1 adipocytes with glycogen synthase kinase-3β (GSK-3β) inhibitor, LiCl, led to 1.9-fold increase in NQO1 protein. Sulforaphane enhanced NQO1 protein (10.5-fold) and blunted triglyceride and FABP4 accumulation. The decrement in triglyceride content was partially reversed when NQO1 activity was pharmacologically inhibited. These data demonstrate a biphasic response of Nrf2 and NQO1 during adipocyte differentiation that is regulated by Keap1- and GSK-3β-dependent mechanisms, and that hypertrophy is negatively regulated by NQO1 activity.     

Novel quinolinequinone antitumor agents: structure-metabolism studies with NAD(P)H:quinone oxidoreductase (NQO1)

A series of quinolinequinones bearing various substituents has been synthesized, and the effects of substituents on the metabolism of the quinones by recombinant human NAD(P)H:quinone oxidoreductase (hNQO1) was studied. A range of quinolinequinones were selected for study, and were specifically designed to probe the effects of aryl substituents at C-2. A range of 28 quinolinequinones 2-29 was prepared using three general strategies: the palladium(0) catalyzed coupling of 2-chloroquinolines, the classical Friedl?nder synthesis and the double-Vilsmeier reaction of acetanilides. One example of an isoquinolinequinone 30 was also prepared, and the reduction potentials of the quinones were measured by cyclic voltammetry. For simple substituents R(2) at the quinoline 2-position, the rates of quinone metabolism by hNQO1 decrease for R(2)=Cl>H approximately Me>Ph. For aromatic substituents, the rate of reduction decreases dramatically for R(2)=Ph>1-naphthyl>2-naphthyl>4-biphenyl. Compounds containing a pyridine substituent are the best substrates, and the rates decrease as R(2)=4-pyridyl>3-pyridyl>2-pyridyl>4-methyl-2-pyridyl>5-methyl-2-pyridyl. The toxicity toward human colon carcinoma cells with either no detectable activity (H596 or BE-WT) or high NQO1 activity (H460 or BE-NQ) was also studied in representative quinones. Quinones that are good substrates for hNQO1 are more toxic to the NQO1 containing or expressing cell lines (H460 and BE-NQ) than the NQO1 deficient cell lines (H596 and BE-WT).     

Novel quinolinequinone antitumor agents: structure-metabolism studies with NAD(P)H:quinone oxidoreductase (NQO1).

The effects of functional group changes on the metabolism of novel quinolinequinones by recombinant human NAD(P)H:quinone oxidoreductase (NQO1) are described. Overall, the quinolinequinones were much better substrates for NQO1 than analogous indolequinones, with compounds containing heterocyclic substituents at C-2 being among the best substrates.     

Protection of NAD(P)H:quinone oxidoreductase 1 against renal ischemia/reperfusion injury in mice

Ischemia/reperfusion (I/R) is the most common cause of acute renal injury. I/R-induced reactive oxygen species (ROS) are thought to be a major factor in the development of acute renal injury by promoting the initial tubular damage. NAD(P)H:quinone oxidoreductase 1 (NQO1) is a well-known antioxidant protein that regulates ROS generation. The purpose of this study was to investigate whether NQO1 modulates the renal I/R injury (IRI) associated with NADPH oxidase (NOX)-derived ROS production in an animal model. We analyzed renal function, oxidative stress, and tubular apoptosis after IRI. NQO1^−/− mice showed increased blood urea nitrogen and creatinine levels, tubular damage, oxidative stress, and apoptosis. In the kidneys of NQO1^−/− mice, the cellular NADPH/NADP⁺ ratio was significantly higher and NOX activity was markedly higher than in those of NQO1^+/+ mice. The activation of NQO1 by β-lapachone (βL) significantly improved renal dysfunction and reduced tubular cell damage, oxidative stress, and apoptosis by renal I/R. Moreover, the βL treatment significantly lowered the cellular NADPH/NADP⁺ ratio and dramatically reduced NOX activity in the kidneys after IRI. From these results, it was concluded that NQO1 has a protective role against renal injury induced by I/R and that this effect appears to be mediated by decreased NOX activity via cellular NADPH/NADP⁺ modulation. These results provide convincing evidence that NQO1 activation might be beneficial for ameliorating renal injury induced by I/R.     

L-Dopa stimulates expression of the antioxidant enzyme NAD(P)H:quinone oxidoreductase (NQO) in cultured astroglial cells

The autooxidation of L-Dopa, a catecholamine used in the symptomatic treatment of Parkinson's disease, generally yields reactive oxygen species and neurotoxic quinones. NAD(P)H:quinone oxidoreductase (NQO) is a flavoenzyme that is implicated in the detoxication of quinones, including those formed during L-Dopa autooxidation. Through the action of this enzyme, deleterious redox-labile quinones are turned into less toxic and more stable hydroquinones that are amenable to further detoxication and/or cellular excretion. In the present study, using primary rat astrocytes and C6 astroglioma as a model to evaluate the neuroprotective response of astroglial cells upon exposure to L-Dopa, we demonstrate that this compound, or more correctly its quinone (auto)oxidation products, up-regulates astroglial NQO in a time- and concentration-dependent way as assessed at the level of mRNA expression, protein level, and enzymatic activity. Moreover, under similar conditions cellular glutathione content was enhanced. It is concluded that, similar to glutathione, the oxidative stress limiting NQO is likely to contribute to the capacity of astroglial cells to protect dopaminergic neurons against L-Dopa, and, hence, may be considered as a potential target for the development of neuroprotective strategies for Parkinson's disease.     

Genetic evidence for NAD(P)H:quinone oxidoreductase 1-catalyzed quinone reduction on passage through the mouse pulmonary circulation

The quinones duroquinone (DQ) and coenzyme Q(1) (CoQ(1)) and quinone reductase inhibitors have been used to identify reductases involved in quinone reduction on passage through the pulmonary circulation. In perfused rat lung, NAD(P)H:quinone oxidoreductase 1 (NQO1) was identified as the predominant DQ reductase and NQO1 and mitochondrial complex I as the CoQ(1) reductases. Since inhibitors have nonspecific effects, the goal was to use Nqo1-null (NQO1(-)/(-)) mice to evaluate DQ as an NQO1 probe in the lung. Lung homogenate cytosol NQO1 activities were 97 ± 11, 54 ± 6, and 5 ± 1 (SE) nmol dichlorophenolindophenol reduced·min(-1)·mg protein(-1) for NQO1(+/+), NQO1(+/-), and NQO1(-/-) lungs, respectively. Intact lung quinone reduction was evaluated by infusion of DQ (50 μM) or CoQ(1) (60 μM) into the pulmonary arterial inflow of the isolated perfused lung and measurement of pulmonary venous effluent hydroquinone (DQH(2) or CoQ(1)H(2)). DQH(2) efflux rates for NQO1(+/+), NQO1(+/-), and NQO1(-/-) lungs were 0.65 ± 0.08, 0.45 ± 0.04, and 0.13 ± 0.05 (SE) μmol·min(-1)·g dry lung(-1), respectively. DQ reduction in NQO1(+/+) lungs was inhibited by 90 ± 4% with dicumarol; there was no inhibition in NQO1(-/-) lungs. There was no significant difference in CoQ(1)H(2) efflux rates for NQO1(+/+) and NQO1(-/-) lungs. Differences in DQ reduction were not due to differences in lung dry weights, wet-to-dry weight ratios, perfusion pressures, perfused surface areas, or total DQ recoveries. The data provide genetic evidence implicating DQ as a specific NQO1 probe in the perfused rodent lung.