NRH:quinone oxidoreductase2 (NQO2)

The regulation and function of Nrf2 signaling in ferroptosis-activated cancer therapy

Ferroptosis is an iron-dependent programmed cell death process that involves lipid oxidation via the Fenton reaction to produce lipid peroxides, causing disruption of the lipid bilayer, which is essential for cellular survival. Ferroptosis has been implicated in the occurrence and treatment response of various types of cancer, and targeting ferroptosis has emerged as a promising strategy for cancer therapy. However, cancer cells can escape cellular ferroptosis by activating or remodeling various signaling pathways, including oxidative stress pathways, thereby limiting the efficacy of ferroptosis-activating targeted therapy. The key anti-oxidative transcription factor, nuclear factor E2 related factor 2 (Nrf2 or NFE2L2), plays a dominant role in defense machinery by reprogramming the iron, intermediate, and glutathione peroxidase 4 (GPX4)-related network and the antioxidant system to attenuate ferroptosis. In this review, we summarize the recent advances in the regulation and function of Nrf2 signaling in ferroptosis-activated cancer therapy and explore the prospect of combining Nrf2 inhibitors and ferroptosis inducers as a promising cancer treatment strategy.

Bridging population pharmacokinetic and semimechanistic absorption modeling of APX3330

APX3330 ((2E)-2-[(4,5-dimethoxy-2-methyl-3,6-dioxo-1,4-cyclohexadien-1-yl)methylene]-undecanoic acid), a selective inhibitor of APE1/Ref-1, has been investigated in treatment of hepatitis, cancer, diabetic retinopathy, and macular edema. APX3330 is administered orally as a quinone but is rapidly converted to the hydroquinone form. This study describes the pharmacokinetics of APX3330 and explores effect of food on absorption. Total plasma quinone concentrations of APX3330 were obtained following oral administration from studies in healthy Japanese male subjects (single dose-escalation; multiple-dose; food-effect) and patients with cancer patients. Nonlinear mixed effects modeling was performed using Monolix to estimate pharmacokinetic parameters and assess covariate effects. To further evaluate the effect of food on absorption, a semi-physiologic pharmacokinetic model was developed in Gastroplus to delineate effects of food on dissolution and absorption. A two-compartment, first order absorption model with lag time best described plasma concentration-time profiles from 49 healthy Japanese males. Weight was positively correlated with apparent clearance (CL/F) and volume. Administration with food led to an 80% higher lag time. CL/F was 41% higher in the cancer population. The semi-physiologic model indicates a switch from dissolution-rate control of absorption in the fasted-state to gastric emptying rate determining absorption rate in the fed-state. Oral clearance of APX3330 is higher in patients with cancer than healthy Japanese males, possibly due to reduced serum albumin in patients with cancer. Delayed APX3330 absorption with food may be related to higher conversion to the more soluble but less permeable hydroquinone form in the gastrointestinal tract. Future work should address pharmacokinetic differences between APX3330 quinone and hydroquinone forms.

Afzelin induces immunogenic cell death against lung cancer by targeting NQO2

BACKGROUND

Lung cancer is one of the most common malignant cancers worldwide. Previous studies have shown that Afzelin, a flavonoid, possesses anticancer activity. The aim of this study was to explore Afzelin's effect on lung cancer cells and delineate potential anti-cancer mechanism.

METHODS

The effect of Afzelin on cell viability, proliferation, and apoptosis of lung cancer cells i.e., A549 and H1299 cells, was studied. The targets for Afzelin in lung cancer were predicted using SwissTargetPrediction, Next, the GO analysis and pathway enrichment were analyzed using String. For in vitro studies, the overexpression plasmid of NQO2, the identified target of Afzelin, was transfected into Afzelin-treated cells to verify the regulatory role of Afzelin on its target and signaling pathway.

RESULTS

In in vitro studies, Afzelin markedly inhibited cell viability, proliferation, and raised apoptotic rate of A549 and H1299 cells. In addition, Afzelin activated endoplasmic reticulum (ER) stress and increased ATP, HMGB1, and CRT levels in lung cancer cells, indicating that Afzelin induced immunogenic cell death (ICD). SwissTargetPrediction identified NQO2 as a target of Afzelin. Further, Afzelin markedly inhibited NQO2 protein expression and in turn, overexpression of NQO2 attenuated the effect of Afzelin on A549 and H1299 cells.

CONCLUSION

Afzelin inhibits lung cancer progression by targeting NQO2, in turn, activating ER stress and inducing ICD.

Large-scale across species transcriptomic analysis identifies genetic selection signatures associated with longevity in mammals

Lifespan varies significantly among mammals, with more than 100-fold difference between the shortest and longest living species. This natural difference may uncover the evolutionary forces and molecular features that define longevity. To understand the relationship between gene expression variation and longevity, we conducted a comparative transcriptomics analysis of liver, kidney, and brain tissues of 103 mammalian species. We found that few genes exhibit common expression patterns with longevity in the three organs analyzed. However, pathways related to translation fidelity, such as nonsense-mediated decay and eukaryotic translation elongation, correlated with longevity across mammals. Analyses of selection pressure found that selection intensity related to the direction of longevity-correlated genes is inconsistent across organs. Furthermore, expression of methionine restriction-related genes correlated with longevity and was under strong selection in long-lived mammals, suggesting that a common strategy is utilized by natural selection and artificial intervention to control lifespan. Our results indicate that lifespan regulation via gene expression is driven through polygenic and indirect natural selection.

Modeling Cardiotoxicity in Pediatric Oncology Patients Using Patient-Specific iPSC-Derived Cardiomyocytes Reveals Downregulation of Cardioprotective microRNAs

Anthracyclines are widely used in the treatment of many solid cancers, but their efficacy is limited by cardiotoxicity. As the number of pediatric cancer survivors continues to rise, there has been a concomitant increase in people living with anthracycline-induced cardiotoxicity. Accordingly, there is an ongoing need for new models to better understand the pathophysiological mechanisms of anthracycline-induced cardiac damage. Here we generated induced pluripotent stem cells (iPSCs) from two pediatric oncology patients with acute cardiotoxicity induced by anthracyclines and differentiated them to ventricular cardiomyocytes (hiPSC-CMs). Comparative analysis of these cells (CTX hiPSC-CMs) and control hiPSC-CMs revealed that the former were significantly more sensitive to cell injury and death from the anthracycline doxorubicin (DOX), as measured by viability analysis, cleaved caspase 3 expression, oxidative stress, genomic and mitochondrial damage and sarcomeric disorganization. The expression of several mRNAs involved in structural integrity and inflammatory response were also differentially affected by DOX. Functionally, optical mapping analysis revealed higher arrythmia complexity after DOX treatment in CTX iPSC-CMs. Finally, using a panel of previously identified microRNAs associated with cardioprotection, we identified lower levels of miR-22-3p, miR-30b-5p, miR-90b-3p and miR-4732-3p in CTX iPSC-CMs under basal conditions. Our study provides valuable phenotype information for cellular models of cardiotoxicity and highlights the significance of using patient-derived cardiomyocytes for studying the associated pathogenic mechanisms.

The influence of NQO2 on the dysfunctional autophagy and oxidative stress induced in the hippocampus of rats and in SH-SY5Y cells by fluoride

INTRODUCTION

For investigating the mechanism of brain injury caused by chronic fluorosis, this study was designed to determine whether NRH:quinone oxidoreductase 2 (NQO2) can influence autophagic disruption and oxidative stress induced in the central nervous system exposed to a high level of fluoride.

METHODS

Sprague-Dawley rats drank tap water containing different concentrations of fluoride for 3 or 6 months. SH-SY5Y cells were either transfected with NQO2 RNA interference or treated with NQO2 inhibitor or activator and at the same time exposed to fluoride. The enrichment of gene signaling pathways related to autophagy was evaluated by Gene Set Enrichment Analysis; expressions of NQO2 and autophagy-related protein 5 (ATG5), LC3-II and p62, and mammalian target of rapamycin (mTOR) were quantified by Western-blotting or fluorescent staining; and the levels of malondialdehyde (MDA) and superoxide dismutase (SOD) assayed biochemically and reactive oxygen species (ROS) detected by flow cytometry.

RESULTS

In the hippocampal CA3 region of rats exposed to high fluoride, the morphological characteristics of neurons were altered; the numbers of autophagosomes in the cytoplasm and the levels of NQO2 increased; the level of p-mTOR was decreased, and the levels of ATG5, LC3-II and p62 were elevated; and genes related to autophagy enriched. In vitro, in addition to similar changes in NQO2, p-mTOR, ATG5, LC3 II, and p62, exposure of SH-SY5Y cells to fluoride enhanced MDA and ROS contents and reduced SOD activity. Inhibition of NQO2 with RNAi or an inhibitor attenuated the disturbance of the autophagic flux and enhanced oxidative stress in these cells exposed to high fluoride.

CONCLUSION

Our findings indicate that NQO2 may be involved in regulating autophagy and oxidative stress and thereby exerts an impact on brain injury caused by chronic fluorosis.

Emerging Role of Nicotinamide Riboside in Health and Diseases

Among all the NAD⁺ precursors, nicotinamide riboside (NR) has gained the most attention as a potent NAD⁺-enhancement agent. This recently discovered vitamin, B3, has demonstrated excellent safety and efficacy profiles and is orally bioavailable in humans. Boosting intracellular NAD⁺ concentrations using NR has been shown to provide protective effects against a broad spectrum of pathological conditions, such as neurodegenerative diseases, diabetes, and hearing loss. In this review, an integrated overview of NR research will be presented. The role NR plays in the NAD⁺ biosynthetic pathway will be introduced, followed by a discussion on the synthesis of NR using chemical and enzymatic approaches. NR’s effects on regulating normal physiology and pathophysiology will also be presented, focusing on the studies published in the last five years.

An Axis between the Long Non-Coding RNA HOXA11-AS and NQOs Enhances Metastatic Ability in Oral Squamous Cell Carcinoma

Long non-coding RNAs (lncRNAs) play critical roles in human cancers. HOXA11 anti-sense RNA (HOXA11-AS) is an lncRNA belonging to the homeobox (HOX) gene cluster that promotes liver metastasis in human colon cancer. However, its role and mechanism of action in human oral squamous cell carcinoma (OSCC) are unclear. In this study, we investigated HOXA11-AS expression and function in human OSCC tissues and cell lines, as well as a mouse model of OSCC. Our analyses showed that HOXA11-AS expression in human OSCC cases correlates with lymph node metastasis, nicotinamide adenine dinucleotide (NAD)(P)H: quinone oxidoreductase 1 (NQO1) upregulation, and dihydronicotinamide riboside (NRH): quinone oxidoreductase 2 (NQO2) downregulation. Using the human OSCC cell lines HSC3 and HSC4, we demonstrate that HOXA11-AS promotes NQO1 expression by sponging microRNA-494. In contrast, HOXA11-AS recruits zeste homolog 2 (EZH2) to the NQO2 promoter to suppress its expression via the trimethylation of H3K27. The upregulation of NQO1 enzymatic activity by HOXA11-AS results in the consumption of flavin adenine dinucleotide (FAD), which reduces FAD-requiring glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity and suppresses glycolysis. However, our analyses show that lactic acid fermentation levels are preserved by glutaminolysis due to increased malic enzyme-1 expression, promoting enhanced proliferation, invasion, survival, and drug resistance. In contrast, suppression of NQO2 expression reduces the consumption of NRH via NQO2 enzymatic activity and increases NAD levels, which promotes enhanced stemness and metastatic potential. In mouse tumor models, knockdown of HOXA11-AS markedly suppressed tumor growth and lung metastasis. From these findings, targeting HOXA11-AS may strongly suppress high-grade OSCC by regulating both NQO1 and NQO2.

Targets preliminary screening for the fresh natural drug molecule based on Cosine-correlation and similarity-comparison of local network

Background

Chinese herbal medicine is made up of hundreds of natural drug molecules and has played a major role in traditional Chinese medicine (TCM) for several thousand years. Therefore, it is of great significance to study the target of natural drug molecules for exploring the mechanism of treating diseases with TCM. However, it is very difficult to determine the targets of a fresh natural drug molecule due to the complexity of the interaction between drug molecules and targets. Compared with traditional biological experiments, the computational method has the advantages of less time and low cost for targets screening, but it remains many great challenges, especially for the molecules without social ties.

Methods

This study proposed a novel method based on the Cosine-correlation and Similarity-comparison of Local Network (CSLN) to perform the preliminary screening of targets for the fresh natural drug molecules and assign weights to them through a trained parameter.

Results

The performance of CSLN is superior to the popular drug-target-interaction (DTI) prediction model GRGMF on the gold standard data in the condition that is drug molecules are the objects for training and testing. Moreover, CSLN showed excellent ability in checking the targets screening performance for a fresh-natural-drug-molecule (scenario simulation) on the TCMSP (13 positive samples in top20), meanwhile, Western-Blot also further verified the accuracy of CSLN.

Conclusions

In summary, the results suggest that CSLN can be used as an alternative strategy for screening targets of fresh natural drug molecules.

Association of NQO1 levels and its genetic polymorphism with susceptibility to methamphetamine dependence

BACKGROUND

The quinone oxidoreductase 1 (NQO1) gene was involved in the pathophysiological process of illicit drugs abuse, and its polymorphisms might be associated with methamphetamine (METH) dependence susceptibility. The purpose of this study was to examine the NQO1 mRNA and protein levels and to analyze the 609C/T polymorphism (rs1800566) between METH-dependent patients and controls.

METHODS

A total of 392 METH-dependent patients (cases) and 669 healthy controls (controls) were enrolled in the study. The quantitative real-time polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) were used to detect the relative expressions of NQO1 mRNA in PBMCs and protein levels in plasma, respectively. PCR-restriction fragment length polymorphism (RFLP-PCR) and direct-sequencing genotyping were used to detect the alleles and genotypes of NQO1 609C/T polymorphism.

RESULTS

The levels of NQO1 mRNA in cases (3.2650 ± 2.2943) was significantly higher than in controls (1.0125 ± 0.7959) (p < 0.001), the plasma protein in cases (0.2368 ± 0.1486) was significantly lower than in controls (0.5844 ± 0.1742) (p < 0.001). The T allele of the 609C/T polymorphism significantly increased the risk of METH dependence (p = 0.032, OR = 1.214, 95%CI = 1.017-1.450). The TC and TC/TT genotypes of 609C/T were observed significantly more frequently in cases than in controls, respectively (TC vs CC: p = 0.012, OR = 1.457, 95% CI = 1.087-1.952; TC/TT vs CC: p = 0.008, OR = 1.460, 95% CI = 1.102-1.935). Similar results were obtained after adjusting for age and sex. We failed to find that any genotype of 609C/T polymorphism affected the mRNA or plasma protein levels in controls, respectively (p > 0.05).

CONCLUSION

The findings suggested that NQO1 might play an important role in the pathophysiological process of METH dependence, and the 609C/T polymorphism might contribute to the susceptibility to METH dependence in a Chinese Han population.

Interactions of the antioxidant enzymes NAD(P)H: Quinone oxidoreductase 1 (NQO1) and NRH: Quinone oxidoreductase 2 (NQO2) with pharmacological agents, endogenous biochemicals and environmental contaminants

NAD(P)H

Quinone Oxidoreductase 1 (NQO1) is an antioxidant enzyme that catalyzes the two-electron reduction of several different classes of quinone-like compounds (quinones, quinone imines, nitroaromatics, and azo dyes). One-electron reduction of quinone or quinone-like metabolites is considered to generate semiquinones to initiate redox cycling that is responsible for the generation of reactive oxygen species and oxidative stress and may contribute to the initiation of adverse drug reactions and adverse health effects. On the other hand, the two-electron reduction of quinoid compounds appears important for drug activation (bioreductive activation) via chemical rearrangement or autoxidation. Two-electron reduction decreases quinone levels and opportunities for the generation of reactive species that can deplete intracellular thiol pools. Also, studies have shown that induction or depletion (knockout) of NQO1 were associated with decreased or increased susceptibilities to oxidative stress, respectively. Moreover, another member of the quinone reductase family, NRH: Quinone Oxidoreductase 2 (NQO2), has a significant functional and structural similarity with NQO1. The activity of both antioxidant enzymes, NQO1 and NQO2, becomes critically important when other detoxification pathways are exhausted. Therefore, this article summarizes the interactions of NQO1 and NQO2 with different pharmacological agents, endogenous biochemicals, and environmental contaminants that would be useful in the development of therapeutic approaches to reduce the adverse drug reactions as well as protection against quinone-induced oxidative damage. Also, future directions and areas of further study for NQO1 and NQO2 are discussed.

Advances in NAD-Lowering Agents for Cancer Treatment

Nicotinamide adenine dinucleotide (NAD) is an essential redox cofactor, but it also acts as a substrate for NAD-consuming enzymes, regulating cellular events such as DNA repair and gene expression. Since such processes are fundamental to support cancer cell survival and proliferation, sustained NAD production is a hallmark of many types of neoplasms. Depleting intratumor NAD levels, mainly through interference with the NAD-biosynthetic machinery, has emerged as a promising anti-cancer strategy. NAD can be generated from tryptophan or nicotinic acid. In addition, the "salvage pathway" of NAD production, which uses nicotinamide, a byproduct of NAD degradation, as a substrate, is also widely active in mammalian cells and appears to be highly exploited by a subset of human cancers. In fact, research has mainly focused on inhibiting the key enzyme of the latter NAD production route, nicotinamide phosphoribosyltransferase (NAMPT), leading to the identification of numerous inhibitors, including FK866 and CHS-828. Unfortunately, the clinical activity of these agents proved limited, suggesting that the approaches for targeting NAD production in tumors need to be refined. In this contribution, we highlight the recent advancements in this field, including an overview of the NAD-lowering compounds that have been reported so far and the related in vitro and in vivo studies. We also describe the key NAD-producing pathways and their regulation in cancer cells. Finally, we summarize the approaches that have been explored to optimize the therapeutic response to NAMPT inhibitors in cancer.

Coenzyme Q10 Analogues: Benefits and Challenges for Therapeutics

Coenzyme Q₁₀ (CoQ₁₀ or ubiquinone) is a mobile proton and electron carrier of the mitochondrial respiratory chain with antioxidant properties widely used as an antiaging health supplement and to relieve the symptoms of many pathological conditions associated with mitochondrial dysfunction. Even though the hegemony of CoQ₁₀ in the context of antioxidant-based treatments is undeniable, the future primacy of this quinone is hindered by the promising features of its numerous analogues. Despite the unimpeachable performance of CoQ₁₀ therapies, problems associated with their administration and intraorganismal delivery has led clinicians and scientists to search for alternative derivative molecules. Over the past few years, a wide variety of CoQ₁₀ analogues with improved properties have been developed. These analogues conserve the antioxidant features of CoQ₁₀ but present upgraded characteristics such as water solubility or enhanced mitochondrial accumulation. Moreover, recent studies have proven that some of these analogues might even outperform CoQ₁₀ in the treatment of certain specific diseases. The aim of this review is to provide detailed information about these Coenzyme Q₁₀ analogues, as well as their functionality and medical applications.

Molecular Pharmacology of NRH:Quinone Oxidoreductase 2: A Detoxifying Enzyme Acting as an Undercover Toxifying Enzyme

N-ribosyldihydronicotinamide:quinone oxidoreductase 2 (NQO2/QR2, Enzyme Commission number 1.10.99.2) is a cytosolic enzyme, abundant in the liver and variably expressed in mammalian tissues. Cloned 30 years ago, it was characterized as a flavoenzyme catalyzing the reduction of quinones and pseudoquinones. To do so, it uses exclusively N-alkyl nicotinamide derivatives, without being able to recognize NADH, the reference hydrure donor compound, in contrast to its next of a kind, NAD(P)H:quinone oxidoreductase 1 (NQO1). For a long time both enzymes have been considered as key detoxifying enzymes in quinone metabolism, but more recent findings point to a more toxifying function of NQO2, particularly with respect to ortho-quinones. In fact, during the reduction of substrates, NQO2 generates fairly unstable intermediates that reoxidize immediately back to the original quinone, creating a futile cycle, the byproducts of which are deleterious reactive oxygen species. Beside this peculiarity, it is a target for numerous drugs and natural compounds such as melatonin, chloroquine, imiquimod, resveratrol, piceatannol, quercetin, and other flavonoids. Most of these enzyme-ligand interactions have been documented by numerous crystallographic studies, and now NQO2 is one of the best represented proteins in the structural biology database. Despite evidence for a causative role in several important diseases, the functional role of NQO2 remains poorly explored. In the present review, we aimed at detailing the main characteristics of NQO2 from a molecular pharmacology perspective. By drawing a clear border between facts and speculations, we hope to stimulate the future research toward a better understanding of this intriguing drug target. SIGNIFICANCE STATEMENT: Evidence is reviewed on the prevalent toxifying function of N-ribosyldihydronicotinamide:quinone oxidoreductase 2 while catalyzing the reduction of ortho-quinones such as dopamine quinone. The product of this reaction is unstable and generates a futile but harmful cycle (substrate/product/substrate) associated with reactive oxygen species generation.

Acute sources of mitochondrial NAD+ during respiratory chain dysfunction

It is a textbook definition that in the absence of oxygen or inhibition of the mitochondrial respiratory chain by pharmacologic or genetic means, hyper-reduction of the matrix pyridine nucleotide pool ensues due to impairment of complex I oxidizing NADH, leading to reductive stress. However, even under these conditions, the ketoglutarate dehydrogenase complex (KGDHC) is known to provide succinyl-CoA to succinyl-CoA ligase, thus supporting mitochondrial substrate-level phosphorylation (mSLP). Mindful that KGDHC is dependent on provision of NAD⁺, hereby sources of acute NADH oxidation are reviewed, namely i) mitochondrial diaphorases, ii) reversal of mitochondrial malate dehydrogenase, iii) reversal of the mitochondrial isocitrate dehydrogenase as it occurs under acidic conditions, iv) residual complex I activity and v) reverse operation of the malate-aspartate shuttle. The concept of NAD⁺ import through the inner mitochondrial membrane as well as artificial means of manipulating matrix NAD⁺/NADH are also discussed. Understanding the above mechanisms providing NAD⁺ to KGDHC thus supporting mSLP may assist in dampening mitochondrial dysfunction underlying neurological disorders encompassing impairment of the electron transport chain.

Transcriptomic analysis of Anabas testudineus and its defensive mechanisms in response to persistent organic pollutants exposure

The freshwater climbing perch (Anabas testudineus) can tolerate water environments contaminated with persistent organic pollutants (POPs). The mechanisms underlying this tolerance are unknown. We used de novo transcriptomic analysis to investigate the defensive mechanisms of A. testudineus against POPs based on its genetic features and biological responses to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure. Our results revealed a specific expansion of cytochrome P450 (CYP) 3A subfamily, which may be involved in the elimination of certain POPs. In xenobiotic responses, the aryl-hydrocarbon receptor (AhR) pathway represents a critical signaling mechanism, and we characterized four AhR and two AhR nuclear translocator homologs and one AhR repressor (AhRR) gene in A. testudineus. TCDD-induced AhRR and CYP1A mRNA upregulation suggests that negative-feedback regulation of AhR signaling through AhRR helps avoid excessive xenobiotic responses. Furthermore, liver and gill transcriptomic profiles were markedly altered after TCDD exposure, with some of the altered genes being related to common defensive responses reported in other species. Based on the newly identified TCDD-altered genes, several A. testudineus-specific responses are proposed, such as enhanced fatty acid β-oxidation. The genetic features of CYP3A subfamily and AhR pathway and the TCDD-induced defensive biological processes elucidated here enhance our understanding of A. testudineus defensive responses against POPs.

NAD(P)H-dependent quinone oxidoreductase 1 (NQO1) and cytochrome P450 oxidoreductase (CYP450OR) differentially regulate menadione-mediated alterations in redox status, survival and metabolism in pancreatic β-cells

NQO1 (NAD(P)H-quinone oxidoreductase 1) reduces quinones and xenobiotics to less-reactive compounds via 2-electron reduction, one feature responsible for the role of NQO1 in antioxidant defense in several tissues. In contrast, NADPH cytochrome P450 oxidoreductase (CYP450OR), catalyzes the 1-electron reduction of quinones and xenobiotics, resulting in enhanced superoxide formation. However, to date, the roles of NQO1 and CYP450OR in pancreatic β-cell metabolism under basal conditions and oxidant challenge have not been characterized. Using NQO1 inhibition, over-expression and knock out, we have demonstrated that, in addition to protection of β-cells from toxic concentrations of the redox cycling quinone menadione, NQO1 also regulates the basal level of reduced-to-oxidized nucleotides, suggesting other role(s) beside that of an antioxidant enzyme. In contrast, over-expression of NADPH cytochrome P450 oxidoreductase (CYP450OR) resulted in enhanced redox cycling activity and decreased cellular viability, consistent with the enhanced generation of superoxide and H₂O₂. Basal expression of NQO1 and CYP450OR was comparable in isolated islets and liver. However, NQO1, but not CYP450OR, was strongly induced in β-cells exposed to menadione. NQO1 and CYP450OR exhibited a reciprocal preference for reducing equivalents in β-cells: while CYP450OR preferentially utilized NADPH, NQO1 primarily utilized NADH. Together, these results demonstrate that NQO1 and CYP450OR reciprocally regulate oxidant metabolism in pancreatic β-cells.

Reactive oxygen species in development and infection processes

Reactive oxygen species (ROS) are important signaling molecules that affect vegetative and pathogenic processes in pathogenic fungi. There is growing evidence that ROS are not only secreted during the interaction of host and pathogen but also involved in tightly controlled intracellular processes. The major ROS producing enzymes are NADPH oxidases (Nox). Recent investigations in fungi revealed that Nox-activity is responsible for the formation of infection structures, cytoskeleton architecture as well as interhyphal communication. However, information about the localization and site of action of the Nox complexes in fungi is limited and signaling pathways and intracellular processes affected by ROS have not been fully elucidated. This review focuses on the role of ROS as signaling molecules in fungal "model" organisms: it examines the role of ROS in vegetative and pathogenic processes and gives special attention to Nox complexes and their function as important signaling hubs.

Overview of Nrf2 as Therapeutic Target in Epilepsy

Oxidative stress is a biochemical state of imbalance in the production of reactive oxygen and nitrogen species and antioxidant defenses. It is involved in the physiopathology of degenerative and chronic neuronal disorders, such as epilepsy. Experimental evidence in humans and animals support the involvement of oxidative stress before and after seizures. In the past few years, research has increasingly focused on the molecular pathways of this process, such as that involving transcription factor nuclear factor E2-related factor 2 (Nrf2), which plays a central role in the regulation of antioxidant response elements (ARE) and modulates cellular redox status. The aim of this review is to present experimental evidence on the role of Nrf2 in this neurological disorder and to further determine the therapeutic impact of Nrf2 in epilepsy.

Reductive metabolism of the sanguinarine iminium bond by rat liver preparations

BACKGROUND

Sanguinarine (SA) is a quaternary benzo[c]phenanthridine alkaloid that is mainly present in the Papaveraceae family. SA has been extensively studied because of its antimicrobial, anti-inflammatory, antitumor, antihypertensive, antiproliferative and antiplatelet activities. Metabolic studies demonstrated that SA bioavailability is apparently low, and the main pathway of SA metabolism is iminium bond reduction resulting in dihydrosanguinarine (DHSA) formation. Nevertheless, the metabolic enzymes involved in SA reduction are still not known in detail. Thus, the aim of this study was to investigate the rat liver microsomes and cytosol-induced SA iminium bond reduction, and to examine the effects of cytosol reductase inhibitors on the reductive activity.

METHODS

DHSA formation was quantified by HPLC. The possible enzymes responsible for DHSA formation were examined using selective individual metabolic enzyme inhibitors.

RESULTS

When SA was incubated with liver microsomes and cytosol in the absence of NAD(P)H, DHSA, the iminium bond reductive metabolite was formed. The reductase activity of the liver microsomes and cytosol was also enhanced significantly in the presence of NADH. The amount of DHSA formed in the liver cytosol was 4.6-fold higher than in the liver microsomes in the presence of NADH. The reductase activity in the liver cytosol was inhibited by the addition of flavin mononucleotide and/or riboflavin. Inhibition studies indicated that menadione, dicoumarol, quercetin and 7-hydroxycoumarin inhibited rat liver cytosol-mediated DHSA formation in the absence of NADH. However, only menadione and quercetin inhibited rat liver cytosol-mediated DHSA formation in the presence of NADH.

CONCLUSIONS

These results suggest that the SA iminium bond reduction proceeds via two routes in the liver cytosol. One route is direct non-enzymatic reduction by NAD(P)H, and the other is enzymatic reduction by possible carbonyl and/or quinone reductases in the liver cytosol.

The Saccharomyces cerevisiae quinone oxidoreductase Lot6p: stability, inhibition and cooperativity

Lot6p (EC 1.5.1.39; Ylr011wp) is the sole quinone oxidoreductase in the budding yeast, Saccharomyces cerevisiae. Using hexahistidine tagged, recombinant Lot6p, we determined the steady-state enzyme kinetic parameters with both NADH and NADPH as electron donors; no cooperativity was observed with these substrates. The NQO1 inhibitor curcumin, the NQO2 inhibitor resveratrol, the bacterial nitroreductase inhibitor nicotinamide and the phosphate mimic vanadate all stabilise the enzyme towards thermal denaturation as judged by differential scanning fluorimetry. All except vanadate have no observable effect on the chemical cross-linking of the two subunits of the Lot6p dimer. These compounds all inhibit Lot6p's oxidoreductase activity, and all except nicotinamide exhibit negative cooperativity. Molecular modelling suggests that curcumin, resveratrol and nicotinamide all bind over the isoalloxazine ring of the FMN cofactor in Lot6p. Resveratrol was predicted to contact an α-helix that links the two active sites. Mutation of Gly-142 (which forms part of this helix) to serine does not greatly affect the thermal stability of the enzyme. However, this variant shows less cooperativity towards resveratrol than the wild type. This suggests a plausible hypothesis for the transmission of information between the subunits and, thus, the molecular mechanism of negative cooperativity in Lot6p.

The two common polymorphic forms of human NRH-quinone oxidoreductase 2 (NQO2) have different biochemical properties

There are two common forms of NRH-quinone oxidoreductase 2 (NQO2) in the human population resulting from SNP rs1143684. One has phenylalanine at position 47 (NQO2-F47) and the other leucine (NQO2-L47). Using recombinant proteins, we show that these variants have similar steady state kinetic parameters, although NQO2-L47 has a slightly lower specificity constant. NQO2-L47 is less stable towards proteolytic digestion and thermal denaturation than NQO2-F47. Both forms are inhibited by resveratrol, but NQO2-F47 shows negative cooperativity with this inhibitor. Thus these data demonstrate, for the first time, clear biochemical differences between the variants which help explain previous biomedical and epidemiological findings.

Mitochondrial diaphorases as NAD⁺ donors to segments of the citric acid cycle that support substrate-level phosphorylation yielding ATP during respiratory inhibition

Substrate-level phosphorylation mediated by succinyl-CoA ligase in the mitochondrial matrix produces high-energy phosphates in the absence of oxidative phosphorylation. Furthermore, when the electron transport chain is dysfunctional, provision of succinyl-CoA by the α-ketoglutarate dehydrogenase complex (KGDHC) is crucial for maintaining the function of succinyl-CoA ligase yielding ATP, preventing the adenine nucleotide translocase from reversing. We addressed the source of the NAD(+) supply for KGDHC under anoxic conditions and inhibition of complex I. Using pharmacologic tools and specific substrates and by examining tissues from pigeon liver exhibiting no diaphorase activity, we showed that mitochondrial diaphorases in the mouse liver contribute up to 81% to the NAD(+) pool during respiratory inhibition. Under these conditions, KGDHC's function, essential for the provision of succinyl-CoA to succinyl-CoA ligase, is supported by NAD(+) derived from diaphorases. Through this process, diaphorases contribute to the maintenance of substrate-level phosphorylation during respiratory inhibition, which is manifested in the forward operation of adenine nucleotide translocase. Finally, we show that reoxidation of the reducible substrates for the diaphorases is mediated by complex III of the respiratory chain.

NQO1 involves in the imine bond reduction of sanguinarine and recombinant adeno-associated virus mediated NQO1 overexpression decreases sanguinarine-induced cytotoxicity in rat BRL cells

Although sanguinarine (SANG) can be transformed to dihydrosanguinarine (DHSA) in human and animals, the enzyme involved in the imine bond reduction of SANG is still unknown. In this study, we found that rat

NAD(P)H

quinone oxidoreductase 1 expressed by prokaryotic system can transform SANG to DHSA in an NADPH dependent manner. We also found out that there was more DHSA in rAAV-NQO1 infected than rAAV-CYP1A1 and rAAV-control infected BRL cells. SANG decreased rat BRL cell proliferation and augmented cell apoptosis in a time and dose dependent manner. However, the influence of DHSA to BRL cells is not significant difference than SANG. SANG-induced apoptosis was correlated with the up-regulation of Bax/Bcl2 ratio and the down-regulation of Bcl2. SANG can also dose dependently down regulate NQO1 expression, but CYP1A1 expression was a little up regulated. Since CYP1A1 involving in SANG oxidative reactions and NQO1 involving in the transform of SANG to DHSA, we hypothesized that up regulation of NQO1 could reduce SANG cytotoxicity and up regulation of CYP1A1 could increase SANG cytotoxitity. Our further study showed that recombinant adeno-associated virus (rAAV) mediated overexpression of NQO1 significantly increased cell proliferation and decreased Bax/Bcl2 ratio, apoptosis, and cytotoxicity, whereas rAAV mediated CYP1A1 overexpression had opposite effects. These data illustrated that NQO1 involved in the imine bond reduction of sanguinarine and this was a less toxic metabolizing pathway than CYP1A1-metabolizing pathway.

Evidence for NQO1 and NQO2 catalyzed reduction of ortho- and para-quinone methides

NAD(P)H

quinone oxidoreductase (NQO1) and NRH:quinone oxidoreductase 2 (NQO2) catalyze the two-electron reduction of quinones and thereby prevent generation of toxic radicals. Quinone methides (QMs) covalently react with cellular macromolecules to form DNA adducts and/or protein conjugates resulting in toxicity and carcinogenesis. Based on similar structural features of quinones and QMs, it is logical to assume that NQO1 and/or NQO2 could also catalyze the two-electron reduction of QMs. However, hitherto the reduction of QMs, as both endogenous and/or exogenous biological substrates, by either NQO1/NQO2 has never been demonstrated. Here we show for the first time that both NQO1 and NQO2 can catalyze the reduction of electrophilic ortho-/para-QMs. The involvement of the enzyme in the reduction of p-cresol quinone methide (PCQM) and o-cresol quinone methide (OCQM) was demonstrated by reappearance of NQO1/NQO2-FAD peak at 450 nm after addition of the QMs to the assay mixture. Further reduction of methides by NQO1/NQO2 was confirmed by analyzing the assay mixture by tandem mass spectrometry. Preliminary kinetic studies show that NQO2 is faster in reducing QMs than its homolog NQO1, and moreover, ortho-QMs are reduced faster than para-QMs. Enzyme-substrate docking studies showed results consistent with enzyme catalysis. Thus, NQO1/NQO2 can play a significant role in deactivation of QMs.

Karyotype-phenotype correlation in partial trisomies of the short arm of chromosome 6: a family case report and review of the literature

The first child (proband) of nonconsanguineous Caucasian parents underwent genetic investigation because she was affected with congenital choanal atresia, heart defects and kidney hyposplasia with mild transient renal insufficiency. The direct DNA sequencing after PCR of the CHD7 gene, which is thought to be responsible for approximately 60-70% of the cases of CHARGE syndrome/association, found no mutations. The cytogenetic analysis (standard GTG banding karyotype) revealed the presence of extrachromosomal material on 10q. The chromosome analysis was completed with array CGH (30 kb resolution), MLPA and FISH, which allowed the identification of three 6p regions (6p.25.3p23 × 3): 2 of these regions are normally located on chromosome 6, and the third region is translocated to the long arm of chromosome 10. The same chromosomal rearrangement was subsequently found in the father, who was affected with congenital ptosis and progressive hearing loss, and in the proband's sister, the second child, who presented at birth with choanal atresia and congenital heart defects. The mutated karyotypes, which were directly inherited, are thought to be responsible for a variable phenotype, including craniofacial dysmorphisms, choanal atresia, congenital ptosis, sensorineural hearing loss, heart defects, developmental delay, and renal dysfunction. Nevertheless, to achieve a complete audiological assessment of the father, he underwent further investigation that revealed an increased level of the coagulation factor XIII (300% increased activity), fluctuating levels of fibrin D-dimer degradation products (from 296 to 1,587 ng/ml) and a homoplasmic mitochondrial DNA mutation: T961G in the MTRNR1 (12S rRNA) gene. He was made a candidate for cochlear implantation. Preoperative high-resolution computed tomography and magnetic resonance imaging of the temporal bone revealed the presence of an Arnold-Chiari malformation type I. To the best of our knowledge, this study is the second report on partial 6p trisomy that involves the 10q terminal region. Furthermore, we report the first case of documented Arnold-Chiari malformation type I and increased factor XIII activity associated with 6p trisomy. We present a comprehensive report of the familial cases and an exhaustive literature review.

Disturbed balance between phase I and II metabolizing enzymes in ovarian endometriosis: a source of excessive hydroxy-estrogens and ROS?

Oxidative metabolism of estrogens was studied in 31 ovarian endometriosis and 29 normal endometrium samples, by qPCR. Expression was monitored for genes encoding five estrogen hydroxylating, five hydroxy (OH)-estrogen conjugating, and three estrogen quinone detoxifying enzymes. CYP1B1, COMT, NQO1, and GSTP1 protein levels were determined using Western blotting and immunohistochemistry staining. Increased expression of CYP1A1, CYP3A7 and COMT, and higher levels of MB-COMT were seen in endometriosis, as compared to normal endometrium. Expression of CYP1B1, CYP3A5, SULT1A1 and NQO2 was unchanged, with comparable CYP1B1 protein levels. Expression of SULT1E1, SULT2B1, UGT2B7, NQO1, and GSTP1 was decreased. Three NQO1 isoforms were detected; NQO1c appears to be endometriosis-specific. Our data indicate a disturbed balance between phase I and II metabolizing enzymes in endometriosis, potentially leading to excessive OH-estrogen and altered ROS formation, and stimulation of proliferation of ectopic endometrium. This is the first report on disturbed expression of estrogen oxidative metabolism genes in ovarian endometriosis.

Features of idebenone and related short-chain quinones that rescue ATP levels under conditions of impaired mitochondrial complex I

Short-chain quinones have been investigated as therapeutic molecules due to their ability to modulate cellular redox reactions, mitochondrial electron transfer and oxidative stress, which are pathologically altered in many mitochondrial and neuromuscular disorders. Recently, we and others described that certain short-chain quinones are able to bypass a deficiency in complex I by shuttling electrons directly from the cytoplasm to complex III of the mitochondrial respiratory chain to produce ATP. Although this energy rescue activity is highly interesting for the therapy of disorders associated with complex I dysfunction, no structure-activity-relationship has been reported for short-chain quinones so far. Using a panel of 70 quinones, we observed that the capacity for this cellular energy rescue as well as their effect on lipid peroxidation was influenced more by the physicochemical properties (in particular logD) of the whole molecule than the quinone moiety itself. Thus, the observed correlations allow us to explain the differential biological activities and therapeutic potential of short-chain quinones for the therapy of disorders associated with mitochondrial complex I dysfunction and/or oxidative stress.

Maternal intake of quercetin during gestation alters ex vivo benzo[a]pyrene metabolism and DNA adduct formation in adult offspring

Variation in xenobiotic metabolism cannot entirely be explained by genetic diversity in metabolic enzymes. We suggest that maternal diet during gestation can contribute to variation in metabolism by creating an in utero environment that shapes the offspring's defence against chemical carcinogens. Therefore, pregnant mice were supplemented with the natural aryl hydrocarbon receptor (AhR) agonist quercetin (1 mmol quercetin/kg feed) until delivery. Next, it was investigated whether the adult offspring at the age of 12 weeks had altered biotransformation of the environmental pollutant benzo[a]pyrene (B[a]P). In utero quercetin exposure resulted in significantly enhanced gene expression of Cyp1a1, Cyp1b1, Nqo1 and Ugt1a6 in liver of foetuses at Day 14.5 of gestation. Despite cessation of supplementation after delivery, altered gene expression persisted into adulthood, but in a tissue- and gender-dependent manner. Expression of Phase I enzymes (Cyp1a1 and Cyp1b1) was up-regulated in the liver of adult female mice in utero exposed to quercetin, whereas expression of Phase II enzymes (Gstp1, Nqo1 and Ugt1a6) was predominantly enhanced in the lung tissue of female mice. Epigenetic mechanisms may contribute to this adapted gene expression, as the repetitive elements (SINEB1) were hypomethylated in liver of female mice prenatally exposed to quercetin. Studies on ex vivo metabolism of B[a]P by lung and liver microsomes showed that the amount of B[a]P-9,10-dehydrodiol, B[a]P-7,8-dihydrodiol and 3-hydroxy-B[a]P did not change, but the amount of unmetabolised B[a]P was significantly lower after incubation with lung microsomes from offspring that received quercetin during gestation. Moreover, ex vivo B[a]P-induced DNA adduct formation was significantly lower for liver microsomes of offspring that were exposed to quercetin during gestation. These results suggest that prenatal diet leads to persistent alterations in Phase I and II enzymes of adult mice and may affect cancer risk.

Control of stability of cyclin D1 by quinone reductase 2 in CWR22Rv1 prostate cancer cells

Aberrant expression of cyclin D1, frequently observed in human malignant disorders, has been linked to the control of G(1)→S cell cycle phase transition and development and progression in carcinogenesis. Cyclin D1 level changes are partially controlled by GSK-3β-dependent phosphorylation at threonine-286 (Thr286), which targets cyclin D1 for ubiquitination and proteolytic degradation. In our continuing studies on the mechanism of prostate cancer prevention by resveratrol, focusing on the role of its recently discovered target protein, quinone reductase 2 (NQO2), we generated NQO2 knockdown CWR22Rv1 using short hairpin RNA (shRNA)-mediated gene silencing approach. We found that, compared with cells expressing NQO2 (shRNA08), NQO2 knockdown cells (shRNA25) displayed slower proliferation and G(1) phase cell accumulation. Immunoblot analyses revealed a significant decrease in phosphorylation of retinoblastoma Rb and cyclin D1 in shRNA25 compared with shRNA08. Moreover, shRNA25 cells showed a 37% decrease in chymotrypsin-like proteasome activity. An increase in AKT activity was also observed in shRNA25, supported by a ∼1.5-fold elevation in phosphorylation and ∼50% reduction/deactivation of GSK-3α/β at Ser21/9, which were accompanied by a decrease in phosphorylation of cyclin D1 at T286. NQO2 knockdown cells also showed attenuation of resveratrol-induced downregulation of cyclin D1. Our results indicate a hitherto unreported role of NQO2 in the control of AKT/GSK-3β/cyclin D1 and highlight the involvement of NQO2 in degradation of cyclin D1, as part of mechanism of chemoprevention by resveratrol.

Stress-induced NQO1 controls stability of C/EBPα against 20S proteasomal degradation to regulate p63 expression with implications in protection against chemical-induced skin cancer

Previously, we have shown a role of cytosolic NAD(P)H:quinone oxidoreductase 1 (NQO1) in stabilization of p63 against 20S proteasomal degradation resulting in thinning of epithelium and chemical-induced skin cancer [Oncogene (2011) 30,1098–1107]. Current studies demonstrate that NQO1 control of C/EBPα against20S proteasomal degradation also contributes to the up regulation of p63 expression and protection. Western and immunohistochemistry analysis revealed that disruption of NQO1 gene in mice and mouse keratinocytes led todegradation of C/EBPα and loss of p63 gene expression. p63 promoter mutagenesis, transfection and ChIP assays identified C/EBPα binding site between nucleotide position −185 to −174 that bound to C/EBPα and up regulated p63 gene expression. Coimmunoprecipitation and immunoblot analysis demonstrated that 20S proteasomes directly interacted and degraded C/EBPα. NQO1 direct interaction with C/EBPα led to stabilization of C/EBPα against 20S proteasomal degradation. NQO1 protection of C/EBPα required binding of NADH with NQO1. Exposure of skin and keratinocytes to chemical stress agent benzo(a)pyrene led to induction of NQO1 and stabilization of C/EBPα protein resulting in an increase in p63 RNA and protein in wild type but not in NQO1−/− mice. Collectively, the current data combined with previous suggest that stress-induction of NQO1 through both stabilization of C/EBPα and increase in p63 and direct stabilization of p63 controls keratinocyte differentiation leading to protection against chemical-induced skin carcinogenesis. The studies are significant since 2–4% human individuals are homozygous and 23% are heterozygous for NQO1P187S mutation and might be susceptible to stress-induced skin diseases.

X-ray structural studies of quinone reductase 2 nanomolar range inhibitors

Quinone reductase 2 (QR2) is one of two members comprising the mammalian quinone reductase family of enzymes responsible for performing FAD mediated reductions of quinone substrates. In contrast to quinone reductase 1 (QR1) which uses NAD(P)H as its co-substrate, QR2 utilizes a rare group of hydride donors, N-methyl or N-ribosyl nicotinamide. Several studies have linked QR2 to the generation of quinone free radicals, several neuronal degenerative diseases, and cancer. QR2 has been also identified as the third melatonin receptor (MT3) through in cellulo and in vitro inhibition of QR2 by traditional MT3 ligands, and through recent X-ray structures of human QR2 (hQR2) in complex with melatonin and 2-iodomelatonin. Several MT3 specific ligands have been developed that exhibit both potent in cellulo inhibition of hQR2 nanomolar, affinity for MT3. The potency of these ligands suggest their use as molecular probes for hQR2. However, no definitive correlation between traditionally obtained MT3 ligand affinity and hQR2 inhibition exists limiting our understanding of how these ligands are accommodated in the hQR2 active site. To obtain a clearer relationship between the structures of developed MT3 ligands and their inhibitory properties, in cellulo and in vitro IC₅₀ values were determined for a representative set of MT3 ligands (MCA-NAT, 2-I-MCANAT, prazosin, S26695, S32797, and S29434). Furthermore, X-ray structures for each of these ligands in complex with hQR2 were determined allowing for a structural evaluation of the binding modes of these ligands in relation to the potency of MT3 ligands.

The human carcinogen aristolochic acid i is activated to form DNA adducts by human NAD(P)H:quinone oxidoreductase without the contribution of acetyltransferases or sulfotransferases

Ingestion of aristolochic acid (AA) is associated with development of urothelial tumors linked with AA nephropathy and is implicated in the development of Balkan endemic nephropathy-associated urothelial tumors. We investigated the efficiency of human NAD(P)H:quinone oxidoreductase (NQO1) to activate aristolochic acid I (AAI) and used in silico docking, using soft-soft (flexible) docking procedure, to study the interactions of AAI with the active site of human NQO1. AAI binds to the active site of NQO1 indicating that the binding orientation allows for direct hydride transfer (i.e., two electron reductions) to the nitro group of AAI. NQO1 activated AAI, generating DNA adduct patterns reproducing those found in urothelial tissues from humans exposed to AA. Because reduced aromatic nitro-compounds are often further activated by sulfotransferases (SULTs) or N,O-acetlytransferases (NATs), their roles in AAI activation were investigated. Our results indicate that phase II reactions do not play a major role in AAI bioactivation; neither native enzymes present in human hepatic or renal cytosols nor human SULT1A1, -1A2, -1A3, -1E, or -2A nor NAT1 or NAT2 further enhanced DNA adduct formation by AAI. Instead under the in vitro conditions used, DNA adducts arise by enzymatic reduction of AAI through the formation of a cyclic hydroxamic acid (N-hydroxyaristolactam I) favored by the carboxy group in peri position to the nitro group without additional conjugation. These results emphasize the major importance of NQO1 in the metabolic activation of AAI and provide the first evidence that initial nitroreduction is the rate limiting step in AAI activation.

NQO1-dependent redox cycling of idebenone: effects on cellular redox potential and energy levels

Short-chain quinones are described as potent antioxidants and in the case of idebenone have already been under clinical investigation for the treatment of neuromuscular disorders. Due to their analogy to coenzyme Q10 (CoQ10), a long-chain quinone, they are widely regarded as a substitute for CoQ10. However, apart from their antioxidant function, this provides no clear rationale for their use in disorders with normal CoQ10 levels. Using recombinant NAD(P)H:quinone oxidoreductase (NQO) enzymes, we observed that contrary to CoQ10 short-chain quinones such as idebenone are good substrates for both NQO1 and NQO2. Furthermore, the reduction of short-chain quinones by NQOs enabled an antimycin A-sensitive transfer of electrons from cytosolic NAD(P)H to the mitochondrial respiratory chain in both human hepatoma cells (HepG2) and freshly isolated mouse hepatocytes. Consistent with the substrate selectivity of NQOs, both idebenone and CoQ1, but not CoQ10, partially restored cellular ATP levels under conditions of impaired complex I function. The observed cytosolic-mitochondrial shuttling of idebenone and CoQ1 was also associated with reduced lactate production by cybrid cells from mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) patients. Thus, the observed activities separate the effectiveness of short-chain quinones from the related long-chain CoQ10 and provide the rationale for the use of short-chain quinones such as idebenone for the treatment of mitochondrial disorders.

Screening natural products for inhibitors of quinone reductase-2 using ultrafiltration LC-MS

Inhibitors of quinone reductase-2 (NQO2; QR-2) can have antimalarial activity and antitumor activities or can function as chemoprevention agents by preventing the metabolic activation of toxic quinones such as menadione. To expedite the search for new natural product inhibitors of QR-2, we developed a screening assay based on ultrafiltration liquid chromatography-mass spectrometry that is compatible with complex samples such as bacterial or botanical extracts. Human QR-2 was prepared recombinantly, and the known QR-2 inhibitor, resveratrol, was used as a positive control and as a competitive ligand to eliminate false positives. Ultrafiltration LC-MS screening of extracts of marine sediment bacteria resulted in the discovery of tetrangulol methyl ether as an inhibitor of QR-2. When applied to the screening of hop extracts from the botanical, Humulus lupulus L., xanthohumol and xanthohumol D were identified as ligands of QR-2. Inhibition of QR-2 by these ligands was confirmed using a functional enzyme assay. Furthermore, binding of xanthohumol and xanthohumol D to the active site of QR-2 was confirmed using X-ray crystallography. Ultrafiltration LC-MS was shown to be a useful assay for the discovery of inhibitors of QR-2 in complex matrixes such as extracts of bacteria and botanicals.

In silico identification and biochemical evaluation of novel inhibitors of NRH:quinone oxidoreductase 2 (NQO2)

The NCI chemical database has been screened using in silico docking to identify novel inhibitors of NRH:quinone oxidoreductase 2 (NQO2). Compounds identified from the screen exhibit a diverse range of scaffolds and inhibitory potencies are generally in the micromolar range. Some of the compounds also have the ability to inhibit NQO1. The modes of binding of the different compounds to the two enzymes are illustrated and discussed.

Resveratrol: Biological and pharmaceutical properties as anticancer molecule

There is ample evidence that shows an inverse relationship between consumption of fruit/vegetable-rich diets and the risk of cancer at various anatomical sites. In this review, we will assess and summarize recent advances on cancer prevention by resveratrol, a natural stilbenoid present in red grapes, peanuts, some common drinks, and dietary supplements. We will focus on data published within the past few years on in vivo model tumor animal studies that reinforce the chemopreventive efficacy of resveratrol against a multitude of cancers, as well as on its sensitization/enhancing activities against tumor cells when used in combination with established chemotherapeutic and pharmaceutical agents. In addition, we will review examples resveratrol-target proteins, denoted RTPs, including the 24-kDa cytosolic protein quinone reductase 2 (NQO2) discovered in our laboratory that may confer resveratrol responsiveness to cancer cells. We will discuss the possible role of NQO2 in mediating cancer prevention by resveratrol. Our analysis of published data strengthen support that resveratrol displays novel roles in various cellular processes, and help to establish an expanded molecular framework for cancer prevention by resveratrol in vivo.

Triazoloacridin-6-ones as novel inhibitors of the quinone oxidoreductases NQO1 and NQO2

A range of triazoloacridin-6-ones functionalized at C5 and C8 have been synthesized and evaluated for ability to inhibit NQO1 and NQO2. The compounds were computationally docked into the active site of NQO1 and NQO2, and calculated binding affinities were compared with IC(50) values for enzyme inhibition. Excellent correlation coefficients were demonstrated suggesting a predictive QSAR model for this series of structurally similar analogues. From this we have identified some of these triazoloacridin-6-ones to be the most potent NQO2 inhibitors so far reported.

Functional polymorphisms, altered gene expression and genetic association link NRH:quinone oxidoreductase 2 to breast cancer with wild-type p53

We hypothesized that NRH:quinone oxidoreductase 2 (NQO2) is a candidate susceptibility gene for breast cancer because of its known enzymatic activity on estrogen-derived quinones and its ability to stabilize p53. We performed case-control studies to investigate the contributions of genetic variants/haplotypes of the NQO2 gene to breast cancer risk. In the first hospital-based study (n = 1604), we observed significant associations between the incidence of breast cancer and a 29 bp-insertion/deletion polymorphism (29 bp-I/D) and the rs2071002 (+237A>C) polymorphism, both of which are located within the NQO2 promoter region. Decreased risk was associated with the D-allele of 29 bp-I/D [odds ratio (OR), 0.76; P = 0.0027] and the +237C-allele of rs2071002 (OR, 0.80; P = 0.0031). Specifically, the susceptibility variants within NQO2 were notably associated with breast carcinomas with wild-type p53 (the most significant P-value: 3.3 x 10(-6)). The associations were successfully replicated in an independent population set (familial/early-onset breast cancer cases and community-based controls, n = 1442). The combined P-values of the two studies (n = 3046) are 3.8 x 10(-7) for 29 bp-I/D and 2.3 x 10(-6) for rs2071002. Furthermore, we revealed potential mechanisms of pathogenesis of the two susceptibility polymorphisms. Previous work has demonstrated that the risk-allele I-29 of 29 bp-I/D introduces transcriptional-repressor Sp3 binding sites. Using promoter reporter-gene assays and electrophoretic-mobility-shift assays, our present work demonstrated that the other risk-allele, +237A-allele of rs2071002, abolishes a transcriptional-activator Sp1 binding site. Furthermore, an ex vivo study showed that normal breast tissues harboring protective genotypes expressed significantly higher levels of NQO2 mRNA than those in normal breast tissues harboring risk genotypes. Taken together, the data presented here strongly suggest that NQO2 is a susceptibility gene for breast carcinogenesis.

Evidence for NQO2-mediated reduction of the carcinogenic estrogen ortho-quinones

The physiological function of NAD(P)H:quinone oxidoreductase (NQO1, DT-diaphorase) is to detoxify potentially reactive quinones by direct transfer of two electrons. A similar detoxification role has not been established for its homologue NRH:quinone oxidoreductase 2 (NQO2). Estrogen quinones, including estradiol(E(2))-3,4-Q, generated by estrogen metabolism, are thought to be responsible for estrogen-initiated carcinogenesis. In this investigation, we have shown for the first time that NQO2 catalyzes the reduction of electrophilic estrogen quinones and thereby may act as a detoxification enzyme. ESI and MALDI mass spectrometric binding studies involving E(2)-3,4-Q with NQO2 clearly support the formation of an enzyme-substrate physical complex. The problem of spontaneous reduction of substrate by cofactor, benzyldihydronicotinamide riboside (BNAH), was successfully overcome by taking advantage of the ping-pong mechanism of NQO2 catalysis. The involvement of the enzyme in the reduction of E(2)-3,4-Q was further supported by addition of the inhibitor quercetin to the assay mixture. NQO2 is a newly discovered binding site (MT3) of melatonin. However, addition of melatonin to the assay mixture did not affect the catalytic activity of NQO2. Preliminary kinetic studies show that NQO2 is faster in reducing estrogen quinones than its homologue NQO1. Both UV and liquid chromatography-tandem mass spectrometry assays unequivocally corroborate the reduction of estrogen ortho-quinones by NQO2, indicating that it could be a novel target for prevention of breast cancer initiation.

Nrf2-induced antioxidant protection: a promising target to counteract ROS-mediated damage in neurodegenerative disease?

Neurodegenerative diseases share various pathological features, such as accumulation of aberrant protein aggregates, microglial activation, and mitochondrial dysfunction. These pathological processes are associated with generation of reactive oxygen species (ROS), which cause oxidative stress and subsequent damage to essential molecules, such as lipids, proteins, and DNA. Hence, enhanced ROS production and oxidative injury play a cardinal role in the onset and progression of neurodegenerative disorders. To maintain a proper redox balance, the central nervous system is endowed with an antioxidant defense mechanism consisting of endogenous antioxidant enzymes. Expression of most antioxidant enzymes is tightly controlled by the antioxidant response element (ARE) and is activated by nuclear factor E2-related factor 2 (Nrf2). In past years reports have highlighted the protective effects of Nrf2 activation in reducing oxidative stress in both in vitro and in vivo models of neurodegenerative disorders. Here we provide an overview of the involvement of ROS-induced oxidative damage in Alzheimer's disease, Parkinson's disease, and Huntington's disease and we discuss the potential therapeutic effects of antioxidant enzymes and compounds that activate the Nrf2-ARE pathway.

Negative regulation of quinone reductase 2 by resveratrol in cultured vascular smooth muscle cells

1. Resveratrol, a polyphenol in red wine, has a cardioprotective effect. Resveratrol-targeting protein (RTP) has been purified using a resveratrol affinity column (RAC) and has been identified as quinone reductase type 2 (NQO2). We hypothesize that NQO2 is the target protein of resveratrol in vascular smooth muscle cells (VSMC) and that resveratrol inhibits proliferation of VSMC through its action on NQO2. In the present study, we investigated the correlation between NQO2 regulation and cell proliferation in VSMC in response to resveratrol treatment. 2. The RTP was purified using RAC and was detected with a NQO2 polyclonal antibody. The VSMC were incubated with resveratrol (1, 10 and 50 micromol/L) for 24, 48 and 72 h. Cell proliferation was detected by cell counting and bromodeoxyuridine (BrdU) assay. A lentiviral vector incorporating NQO2 short interference (si) RNA of short hairpin design was constructed and transduced into VSMC. Real-time quantitative polymerase chain reaction was used to measure NQO2 mRNA levels; NQO2 expression was determined by western blot analysis. 3. Using RAC, we extracted a 26 kDa protein from aortic smooth muscle, which was referred to as RTP-26. Proliferation of VSMC was inhibited by resveratrol in a concentration- and time-dependent manner. The mRNA and protein expression of NQO2 was also repressed by resveratrol in a concentration- and time-dependent manner. A similar pattern of inhibition was observed for cells treated with resveratrol (25 micromol/L) as for cells transduced with a lentiviral vector containing siRNA sequences against NQO2. 4. Collectively, these data indicate that the suppression of VSMC proliferation mediated by resveratrol correlates with NQO2 downregulation.

Metabolic activation of carcinogenic aristolochic acid, a risk factor for Balkan endemic nephropathy

Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, is associated with tumor development in patients suffering from Chinese herbs nephropathy (now termed aristolochic acid nephropathy, AAN) and may also be a cause for the development of a similar type of nephropathy, the Balkan endemic nephropathy (BEN). Major DNA adducts [7-(deoxyadenosin-N6-yl)-aristolactam and 7-(deoxyguanosin-N2-yl)aristolactam] formed from AA after reductive metabolic activation were found in renal tissues of patients with both diseases. Understanding which human enzymes are involved in AA activation and/or detoxication is important in the assessment of an individual's susceptibility to this plant carcinogen. This paper reviews major hepatic and renal enzymes responsible for AA-DNA adduct formation in humans. Phase I biotransformation enzymes play a crucial role in the metabolic activation of AA to species forming DNA adducts, while a role of phase II enzymes in this process is questionable. Most of the activation of AA in human hepatic microsomes is mediated by cytochrome P450 (CYP) 1A2 and, to a lower extent, by CYP1A1; NADPH:CYP reductase plays a minor role. In human renal microsomes NADPH:CYP reductase is more effective in AA activation. Prostaglandin H synthase (cyclooxygenase, COX) is another enzyme activating AA in human renal microsomes. Among the cytosolic reductases, NAD(P)H:quinone oxidoreductase (NQO1) is the most efficient in the activation of AA in human liver and kidney. Studies with purified enzymes confirmed the importance of CYPs, NADPH:CYP reductase, COX and NQO1 in the AA activation. The orientation of AA in the active sites of human CYP1A1, -1A2 and NQO1 was predicted from molecular modeling and explains the strong reductive potential of these enzymes for AA detected experimentally. We hypothesized that inter-individual variations in expressions and activities of enzymes activating AA may be one of the causes responsible for the different susceptibilities to this carcinogen reflected in the development of AA-induced nephropathies and associated urothelial cancer.

Deficiency of NRH:quinone oxidoreductase 2 differentially regulates TNF signaling in keratinocytes: up-regulation of apoptosis correlates with down-regulation of cell survival kinases

NRH:quinone oxidoreductase 2 (NQO2) is a cytosolic flavoprotein that catalyzes the two-electron reduction of quinones and quinoid compounds to hydroquinones. Although the role of a homologue, NAD(P)H:quinone oxidoreductase 1 (NQO1), is well defined in oxidative stress, neoplasia, and carcinogenesis, little is known about the mechanism of actions of NQO2 in these cellular responses. Whether NQO2 has any role in tumor necrosis factor (TNF) signaling was investigated using keratinocytes derived from wild-type and NQO2 knockout (NQO2-/-) mice. Although exposure of wild-type cells to TNF led to activation of nuclear factor-kappaB (NF-kappaB) and IkappaBalpha kinase, IkappaBalpha degradation, p65 phosphorylation, and p65 nuclear translocation, this cytokine had no effect on NQO2-/- cells. Deletion of NQO2 also abolished TNF-induced c-Jun NH2-terminal kinase, Akt, p38, and p44/p42 mitogen-activated protein kinase activation. The induction of various antiapoptotic gene products (MMP-9, cyclin D1, COX-2, IAP1, IAP2, Bcl-2, cFLIP, and XIAP) by TNF was also abolished in NQO2-/- cells. This correlated with potentiation of TNF-induced apoptosis as indicated by cell viability, Annexin V staining, and caspase activation. In agreement with this, we also found that TNF activated NQO2, and NQO2-specific small interfering RNA abrogated the TNF-induced NQO2 activity and NF-kappaB activation. Overall, our results indicate that deletion of NQO2 plays a differential role in TNF signaling pathway: by suppressing cell survival signals and potentiating TNF-induced apoptosis.

Therapeutic potential and biological role of endogenous antioxidant enzymes in multiple sclerosis pathology

Reactive oxygen species contribute to the formation and persistence of multiple sclerosis (MS) lesions by acting on distinct pathological processes. To counteract the detrimental effects of ROS the central nervous system is endowed with a protective mechanism consisting of enzymatic and non-enzymatic antioxidants. Expression of most antioxidant enzymes is regulated through the transcription factor nuclear factor-E2-related factor (Nrf2) and antioxidant response elements (ARE) in the genes encoding enzymatic antioxidants and is induced by oxidative stress. In brain tissue of MS patients, enhanced expression of Nrf2/ARE-regulated antioxidants is suggestive of the occurrence of oxidative stress in these lesions. Antioxidant therapy may therefore represent an attractive treatment of MS. Several studies have shown that antioxidant therapy is beneficial in vitro and in vivo in animal models for MS. However, the use of exogenous antioxidants for MS treatment has drawbacks, as large amounts of antioxidants are required to achieve functional antioxidant levels in the central nervous system. Therefore, the induction of endogenous antioxidant enzymes by activators of the Nrf2/ARE pathway may be an interesting approach to obtain sufficient levels of antioxidants to interfere with pathological processes underlying MS lesion formation. In this review we summarize and discuss the biological role, regulation and potential therapeutic effects of endogenous antioxidant enzymes in MS. We propose that antioxidants may inhibit the development and progression of MS lesions and may therefore represent an attractive therapeutic target for the treatment of MS and other oxidative stress-related neurological diseases.