Coordinate regulation of NAD(P)H:Quinone oxidoreductase and glutathione-S-transferases in primary cultures of rat neurons and glia: Role of the antioxidant/electrophile responsive element

NAD(P)H-quinone oxidoreductase 1 induces complicated effects on mitochondrial dysfunction and ferroptosis in an expression level-dependent manner

NAD(P)H-quinone oxidoreductase 1 (NQO1) is an essential redox enzyme responsible for redox balance and energy metabolism. Despite of its importance, the brain contains high capacity of polyunsaturated fatty acids and maintains low levels of NQO1 expression. In this study, we examined how levels of NQO1 expression affects cell survival in response to toxic insults causing mitochondrial dysfunction and ferroptosis, and whether NQO1 has a potential as a biomarker in different stressed conditions. Following treatment with rotenone, overexpressed NQO1 in SH-SY5Y cells improved cell survival by reducing mitochondrial reductive stress via increased NAD+ supply without mitochondrial biogenesis. However, NQO1 overexpression boosted lipid peroxidation following treatment with RSL3 and erastin. A lipid droplet staining assay showed increased lipid droplets in cells overexpressing NQO1. In contrast, NQO1 knockdown protected cells against ferroptosis by increasing GPX4, xCT, and the GSH/GSSG system. Also, NQO1 knockdown showed lower iron contents and lipid droplets than non-transfectants and cells overexpressing NQO1, even though it could not attenuate cell death when exposed to rotenone. In summary, our study suggests that different NQO1 levels may have advantages and disadvantages depending on the surrounding environments. Thus, regulating NQO1 expression could be a potential supplementary tool when treating neuronal diseases.

Alleviation of microcystin-leucine arginine -induced hepatotoxicity: An updated overview

OBJECTIVES

Contamination of surface waters is a major health threat for all living creatures. Some types of blue-green algae that naturally occur in fresh water, are able to produce various toxins, like Microcystins (MCs). Microcystin-leucine arginine (MC-LR) produced by Microcystis aeruginosa is the most toxic and abundant isoforms of MCs, and it causes hepatotoxicity. The present article reviews preclinical experiments examined different treatments, including herbal derivatives, dietary supplements and drugs against MC-LR hepatotoxicity.

METHODS

We searched scientific databases Web of Science, Embase, Medline (PubMed), Scopus, and Google Scholar using relevant keywords to find suitable studies until November 2023.

RESULTS

MC-LR through Organic anion transporting polypeptide superfamily transporters (OATPs) penetrates and accumulates in hepatocytes, and it inhibits protein phosphatases (PP1 and PP2A). Consequently, MC-LR disturbs many signaling pathways and induces oxidative stress thus damages cellular macromolecules. Some protective agents, especially plants rich in flavonoids, and natural supplements, as well as chemoprotectants were shown to diminish MC-LR hepatotoxicity.

CONCLUSION

The reviewed agents through blocking the OATP transporters (nontoxic nostocyclopeptide-M1, captopril, and naringin), then inhibition of MC-LR uptake (naringin, rifampin, cyclosporin-A, silymarin and captopril), and finally at restoration of PPAse activity (silybin, quercetin, morin, naringin, rifampin, captopril, azo dyes) exert hepatoprotective effect against MC-LR.

Exploring the multifaceted role of NRF2 in brain physiology and cancer: A comprehensive review

Chronic oxidative stress plays a critical role in the development of brain malignancies due to the high rate of brain oxygen utilization and concomitant production of reactive oxygen species. The nuclear factor-erythroid-2-related factor 2 (NRF2), a master regulator of antioxidant signaling, is a key factor in regulating brain physiology and the development of age-related neurodegenerative diseases. Also, NRF2 is known to exert a protective antioxidant effect against the onset of oxidative stress-induced diseases, including cancer, along with its pro-oncogenic activities through regulating various signaling pathways and downstream target genes. In glioblastoma (GB), grade 4 glioma, tumor resistance, and recurrence are caused by the glioblastoma stem cell population constituting a small bulk of the tumor core. The persistence and self-renewal capacity of these cell populations is enhanced by NRF2 expression in GB tissues. This review outlines NRF2's dual involvement in cancer and highlights its regulatory role in human brain physiology and diseases, in addition to the development of primary brain tumors and therapeutic potential, with a focus on GB.

Limited expression of Nrf2 in neurons across the central nervous system

Nrf2, encoded by the gene Nfe2l2, is a broadly expressed transcription factor that regulates gene expression in response to reactive oxygen species (ROS) and oxidative stress. It is commonly referred to as a ubiquitous pathway, but this generalization overlooks work indicating that Nrf2 is essentially unexpressed in some neuronal populations. To explore whether this pattern extends throughout the central nervous system (CNS), we quantified Nfe2l2 expression and chromatin accessibility at the Nfe2l2 locus across multiple single cell datasets. In both the mouse and human CNS, Nfe2l2 was repressed in almost all mature neurons, but highly expressed in non-neuronal support cells, and this pattern was robust across multiple human CNS diseases. A subset of key Nrf2 target genes, like Slc7a11, also remained low in neurons. Thus, these data suggest that while most cells express Nfe2l2, with activity determined by ROS levels, neurons actively avoid Nrf2 activity by keeping Nfe2l2 expression low.

Limited Expression of Nrf2 in Neurons Across the Central Nervous System

Nrf2 is a broadly expressed transcription factor that regulates gene expression in response to reactive oxygen species (ROS) and oxidative stress. It is commonly referred to as a ubiquitous pathway, but this generalization overlooks work indicating that Nrf2 is essentially unexpressed in some neuronal populations. To explore whether this pattern extends throughout the central nervous system (CNS), we quantified Nrf2 expression and chromatin accessibility at the Nrf2 locus across multiple single cell datasets. In both the mouse and human CNS, Nrf2 was repressed in almost all mature neurons, but highly expressed in non-neuronal support cells, and this pattern was robust across multiple human CNS diseases. A subset of key Nrf2 target genes, like Slc7a11 , also remained low in neurons. Thus, these data suggest that while most cells express Nrf2, with activity determined by ROS levels, neurons actively avoid Nrf2 activity by keeping Nrf2 expression low.

The Interplay between Intracellular Iron Homeostasis and Neuroinflammation in Neurodegenerative Diseases

Iron is essential for life. Many enzymes require iron for appropriate function. However, dysregulation of intracellular iron homeostasis produces excessive reactive oxygen species (ROS) via the Fenton reaction and causes devastating effects on cells, leading to ferroptosis, an iron-dependent cell death. In order to protect against harmful effects, the intracellular system regulates cellular iron levels through iron regulatory mechanisms, including hepcidin-ferroportin, divalent metal transporter 1 (DMT1)-transferrin, and ferritin-nuclear receptor coactivator 4 (NCOA4). During iron deficiency, DMT1-transferrin and ferritin-NCOA4 systems increase intracellular iron levels via endosomes and ferritinophagy, respectively. In contrast, repleting extracellular iron promotes cellular iron absorption through the hepcidin-ferroportin axis. These processes are regulated by the iron-regulatory protein (IRP)/iron-responsive element (IRE) system and nuclear factor erythroid 2-related factor 2 (Nrf2). Meanwhile, excessive ROS also promotes neuroinflammation by activating the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). NF-κB forms inflammasomes, inhibits silent information regulator 2-related enzyme 1 (SIRT1), and induces pro-inflammatory cytokines (IL-6, TNF-α, and IL-1β). Furthermore, 4-hydroxy-2,3-trans-nonenal (4-HNE), the end-product of ferroptosis, promotes the inflammatory response by producing amyloid-beta (Aβ) fibrils and neurofibrillary tangles in Alzheimer's disease, and alpha-synuclein aggregation in Parkinson's disease. This interplay shows that intracellular iron homeostasis is vital to maintain inflammatory homeostasis. Here, we review the role of iron homeostasis in inflammation based on recent findings.

The NRF2-Dependent Transcriptional Regulation of Antioxidant Defense Pathways: Relevance for Cell Type-Specific Vulnerability to Neurodegeneration and Therapeutic Intervention

Oxidative stress has been implicated in the etiology and pathobiology of various neurodegenerative diseases. At baseline, the cells of the nervous system have the capability to regulate the genes for antioxidant defenses by engaging nuclear factor erythroid 2 (NFE2/NRF)-dependent transcriptional mechanisms, and a number of strategies have been proposed to activate these pathways to promote neuroprotection. Here, we briefly review the biology of the transcription factors of the NFE2/NRF family in the brain and provide evidence for the differential cellular localization of NFE2/NRF family members in the cells of the nervous system. We then discuss these findings in the context of the oxidative stress observed in two neurodegenerative diseases, Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), and present current strategies for activating NFE2/NRF-dependent transcription. Based on the expression of the NFE2/NRF family members in restricted populations of neurons and glia, we propose that, when designing strategies to engage these pathways for neuroprotection, the relative contributions of neuronal and non-neuronal cell types to the overall oxidative state of tissue should be considered, as well as the cell types which have the greatest intrinsic capacity for producing antioxidant enzymes.

Glutathione: An Old and Small Molecule with Great Functions and New Applications in the Brain and in Alzheimer's Disease

Significance: Glutathione (GSH) represents the most abundant and the main antioxidant in the body with important functions in the brain related to Alzheimer's disease (AD). Recent Advances: Oxidative stress is one of the central mechanisms in AD. We and others have demonstrated the alteration of GSH levels in the AD brain, its important role in the detoxification of advanced glycation end-products and of acrolein, a by-product of lipid peroxidation. Recent in vivo studies found a decrease of GSH in several areas of the brain from control, mild cognitive impairment, and AD subjects, which are correlated with cognitive decline. Critical Issues: Several strategies were developed to restore its intracellular level with the l-cysteine prodrugs or the oral administration of γ-glutamylcysteine to prevent alterations observed in AD. To date, no benefit on GSH level or on oxidative biomarkers has been reported in clinical trials. Thus, it remains uncertain if GSH could be considered a potential preventive or therapeutic approach or a biomarker for AD. Future Directions: We address how GSH-coupled nanocarriers represent a promising approach for the functionalization of nanocarriers to overcome the blood/brain barrier (BBB) for the brain delivery of GSH while avoiding cellular toxicity. It is also important to address the presence of GSH in exosomes for its potential intercellular transfer or its shuttle across the BBB under certain conditions. Antioxid. Redox Signal. 35, 270-292.

Molecular Mechanisms and Genetics of Oxidative Stress in Alzheimer's Disease

Alzheimer’s disease is the most common neurodegenerative disorder that can cause dementia in elderly over 60 years of age. One of the disease hallmarks is oxidative stress which interconnects with other processes such as amyloid-β deposition, tau hyperphosphorylation, and tangle formation. This review discusses current thoughts on molecular mechanisms that may relate oxidative stress to Alzheimer’s disease and identifies genetic factors observed from in vitro, in vivo, and clinical studies that may be associated with Alzheimer’s disease-related oxidative stress.

TBHQ-Overview of Multiple Mechanisms against Oxidative Stress for Attenuating Methamphetamine-Induced Neurotoxicity

Methamphetamine is a derivative of amphetamines, a highly addictive central stimulant with multiple systemic toxicity including the brain, heart, liver, lung, and spleen. It has adverse effects such as apoptosis and breakdown of the blood-brain barrier. Methamphetamine is a fatal and toxic chemical substance, and its lethal mechanism has been widely studied in recent years. The possible mechanism is that methamphetamine can cause cardiotoxicity and neurotoxicity mainly by inducing oxidative stress so as to generate heat, eliminate people's hunger and thirst, and maintain a state of excitement so that people can continue to exercise. According to many research, there is no doubt that methamphetamine triggers neurotoxicity by inducing reactive oxygen species (ROS) production and redox imbalance. This review summarized the mechanisms of methamphetamine-induced neurotoxicity including apoptosis and blood-brain barrier breakdown through oxidative stress and analyzed several possible antioxidative mechanisms of tert-butylhydroquinone (TBHQ) which is a kind of food additive with antioxidative effects. As a nuclear factor E2-related factor 2 (Nrf2) agonist, TBHQ may inhibit neurotoxicity caused by oxidative stress through the following three mechanisms: the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system, the astrocytes activation, and the glutathione pathway. The mechanism about methamphetamine's toxic effects and its antioxidative therapeutic drugs would become a research hotspot in this field and has very important research significance.

Jdp2-deficient granule cell progenitors in the cerebellum are resistant to ROS-mediated apoptosis through xCT/Slc7a11 activation

The Jun dimerization protein 2 (Jdp2) is expressed predominantly in granule cell progenitors (GCPs) in the cerebellum, as was shown in Jdp2-promoter-Cre transgenic mice. Cerebellum of Jdp2-knockout (KO) mice contains lower number of Atoh-1 positive GCPs than WT. Primary cultures of GCPs from Jdp2-KO mice at postnatal day 5 were more resistant to apoptosis than GCPs from wild-type mice. In Jdp2-KO GCPs, the levels of both the glutamate‒cystine exchanger Sc7a11 and glutathione were increased; by contrast, the activity of reactive oxygen species (ROS) was decreased; these changes confer resistance to ROS-mediated apoptosis. In the absence of Jdp2, a complex of the cyclin-dependent kinase inhibitor 1 (p21^Cip1) and Nrf2 bound to antioxidant response elements of the Slc7a11 promoter and provide redox control to block ROS-mediated apoptosis. These findings suggest that an interplay between Jdp2, Nrf2, and p21^Cip1 regulates the GCP apoptosis, which is one of critical events for normal development of the cerebellum.

The role of astrocytes in oxidative stress of central nervous system: A mixed blessing

Central nervous system (CNS) maintains a high level of metabolism, which leads to the generation of large amounts of free radicals, and it is also one of the most vulnerable organs to oxidative stress. Emerging evidences have shown that, as the key homeostatic cells in CNS, astrocytes are deeply involved in multiple aspects of CNS function including oxidative stress regulation. Besides, the redox level in CNS can in turn affect astrocytes in morphology and function. The complex and multiple roles of astrocytes indicate that their correct performance is crucial for the normal functioning of the CNS, and its dysfunction may result in the occurrence and progression of various neurological disorders. To date, the influence of astrocytes in CNS oxidative stress is rarely reviewed. Therefore, in this review we sum up the roles of astrocytes in redox regulation and the corresponding mechanisms under both normal and different pathological conditions.

Attenuation of diabetic retinopathy and neuropathy by resveratrol: Review on its molecular mechanisms of action

Resveratrol is an important phenolic phytochemical from the therapeutic perspective. It has therapeutic impacts over wide range of diseases, especially the ones related to oxidative stress. Resveratrol, being primarily a potent anti-oxidant phytochemical, has significant impact against major diseases as inflammatory disorders, diabetes, and cancer. In the current review article, we intend to highlight the molecular aspects of the mechanism of action of resveratrol against major diabetic implications, namely, retinopathy and neuropathy. Both these diabetic implications are among the first fallouts of chronic hyperglycaemia. Resveratrol, via multiple molecular pathways, tend to attenuate and reverse these deformity and other disease-causing implications.

Regulation of neuronal development and function by ROS

Reactive oxygen species (ROS) have long been studied as destructive agents in the context of nervous system ageing, disease and degeneration. Their roles as signalling molecules under normal physiological conditions is less well understood. Recent studies have provided ample evidence of ROS-regulating neuronal development and function, from the establishment of neuronal polarity to growth cone pathfinding; from the regulation of connectivity and synaptic transmission to the tuning of neuronal networks. Appreciation of the varied processes that are subject to regulation by ROS might help us understand how changes in ROS metabolism and buffering could progressively impact on neuronal networks with age and disease.

Adaptive regulation of the brain's antioxidant defences by neurons and astrocytes

The human brain generally remains structurally and functionally sound for many decades, despite the post-mitotic and non-regenerative nature of neurons. This is testament to the brain's profound capacity for homeostasis: both neurons and glia have in-built mechanisms that enable them to mount adaptive or protective responses to potentially challenging situations, ensuring that cellular viability and functionality is maintained. The high and variable metabolic and mitochondrial activity of neurons places several demands on the brain, including the task of neutralizing the associated reactive oxygen species (ROS) produced, to limit the accumulation of oxidative damage. Astrocytes play a key role in providing antioxidant support to nearby neurons, and redox regulation of the astrocytic Nrf2 pathway represents a powerful homeostatic regulator of the large cohort of Nrf2-regulated antioxidant genes that they express. In contrast, the Nrf2 pathway is weak in neurons, robbing them of this particular homeostatic device. However, many neuronal antioxidant genes are controlled by synaptic activity, enabling activity-dependent increases in ROS production to be offset by enhanced antioxidant capacity of both glutathione and thioredoxin-peroxiredoxin systems. These distinct homeostatic mechanisms in neurons and astrocytes together combine to promote neuronal resistance to oxidative insults. Future investigations into signaling between distinct cell types within the neuro-glial unit are likely to uncover further mechanisms underlying redox homeostasis in the brain.

Role of the Keap1/Nrf2 pathway in neurodegenerative diseases

As the elderly population increases, a growing number of individuals suffer from age-associated neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). Oxidative stress is considered to play a crucial role in the pathogenesis of age-related diseases. The transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) is activated by oxidative stress and regulates the expression of a variety of antioxidant enzymes and proteins that exert cytoprotective effects against oxidative stress. Numerous studies have addressed the role of Nrf2 in age-related diseases, including neurodegenerative diseases, using animal or in vitro cell culture models. Here, we introduce the role of oxidative stress in the pathogenesis of neurodegenerative diseases and critically examine the recent findings concerning the role for Nrf2 in the amelioration of AD and PD. Nrf2 not only regulates antioxidant proteins but also regulates the genes associated with autophagy and nerve growth factor signaling. Current research unequivocally demonstrates that the activation of the Nrf2 pathway is a promising novel strategy for the prevention and modification of neurodegenerative diseases.

Idebenone and neuroprotection: antioxidant, pro-oxidant, or electron carrier?

Ubiquinone, commonly called coenzyme Q10 (CoQ), is a lipophilic electron carrier and endogenous antioxidant found in all cellular membranes. In the mitochondrial inner membrane it transfers electrons to complex III of the electron transport chain. The short chain CoQ analogue idebenone is in clinical trials for a number of diseases that exhibit a mitochondrial etiology. Nevertheless, evidence that idebenone ameliorates neurological symptoms in human disease is inconsistent. Although championed as an antioxidant, idebenone can also act as a pro-oxidant by forming an unstable semiquinone at complex I. The antioxidant function of idebenone is critically dependent on two-electron reduction to idebenol without the creation of unstable intermediates. Recently, cytoplasmic

NAD(P)H

quinone oxidoreductase 1 (NQO1) was identified as a major enzyme catalyzing idebenone reduction. While reduction allows idebenone to act as an antioxidant, evidence also suggests that NQO1 enables idebenone to shuttle reducing equivalents from cytoplasmic NAD(P)H to mitochondrial complex III, bypassing any upstream damage to the electron transport chain. In this mini-review we discuss how idebenone can influence mitochondrial function within the context of cytoprotection. Importantly, in the brain NQO1 is expressed primarily by glia rather than neurons. As NQO1 is an inducible enzyme regulated by oxidative stress and the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway, optimizing NQO1 expression in appropriate cell types within a specific disease context may be key to delivering on idebenone's therapeutic potential.

Effects of rutaecarpine on hydrogen peroxide-induced apoptosis in murine hepa-1c1c7 cells

The aim of this study was to investigate the inhibitory effects of rutaecarpine on DNA strand breaks and apoptosis induced by hydrogen peroxide (H2O2) in murine Hepa-1c1c7 cells. Oxidative DNA damage was estimated by nuclear condensation assessment, fluorescence-activated cell sorting analysis, and Comet assay. Rutaecarpine inhibited cell death induced by 500 μM H2O2, as assessed by 4',6-diamidino-2-phenylindole (DAPI) staining. Treatment with rutaecarpine reduced the number of DNA strand breaks induced by H2O2, as assessed by DAPI staining and Comet assay, and increased quinone reductase, phosphatidylinositol 3-kinase, and pAkt protein levels, as assessed by western blotting.

Emerging roles of Nrf2 and phase II antioxidant enzymes in neuroprotection

Phase II metabolic enzymes are a battery of critical proteins that detoxify xenobiotics by increasing their hydrophilicity and enhancing their disposal. These enzymes have long been studied for their preventative and protective effects against mutagens and carcinogens and for their regulation via the Keap1 (Kelch-like ECH associated protein 1)/Nrf2 (Nuclear factor erythroid 2 related factor 2)/ARE (antioxidant response elements) pathway. Recently, a series of studies have reported the altered expression of phase II genes in postmortem tissue of patients with various neurological diseases. These observations hint at a role for phase II enzymes in the evolution of such conditions. Furthermore, promising findings reveal that overexpression of phase II genes, either by genetic or chemical approaches, confers neuroprotection in vitro and in vivo. Therefore, there is a need to summarize the current literature on phase II genes in the central nervous system (CNS). This should help guide future studies on phase II genes as therapeutic targets in neurological diseases. In this review, we first briefly introduce the concept of phase I, II and III enzymes, with a special focus on phase II enzymes. We then discuss their expression regulation, their inducers and executors. Following this background, we expand our discussion to the neuroprotective effects of phase II enzymes and the potential application of Nrf2 inducers to the treatment of neurological diseases.

Brain-derived neurotrophic factor and its receptors in Bergmann glia cells

Brain-derived neurotrophic factor is an abundant and widely distributed neurotrophin expressed in the Central Nervous System. It is critically involved in neuronal differentiation and survival. The expression of brain-derived neurotrophic factor and that of its catalytic active cognate receptor (TrkB) has been extensively studied in neuronal cells but their expression and function in glial cells is still controversial. Despite of this fact, brain-derived neurotrophic factor is released from astrocytes upon glutamate stimulation. A suitable model to study glia/neuronal interactions, in the context of glutamatergic synapses, is the well-characterized culture of chick cerebellar Bergmann glia cells. Using, this system, we show here that BDNF and its functional receptor are present in Bergmann glia and that BDNF stimulation is linked to the activation of the phosphatidyl-inositol 3 kinase/protein kinase C/mitogen-activated protein kinase/Activator Protein-1 signaling pathway. Accordingly, reverse transcription-polymerase chain reaction (RT-PCR) experiments predicted the expression of full-length and truncated TrkB isoforms. Our results suggest that Bergmann glia cells are able to express and respond to BDNF stimulation favoring the notion of their pivotal role in neuroprotection.

Induction of the Nrf2-driven antioxidant response by tert-butylhydroquinone prevents ethanol-induced apoptosis in cranial neural crest cells

Previous studies have shown that ethanol exposure causes apoptosis in cranial neural crest cells (NCCs), an ethanol-sensitive cell population implicated in Fetal Alcohol Spectrum Disorders (FASD). Additionally, induction of endogenous antioxidants through activation of nuclear factor-erythroid 2-related factor 2 (Nrf2) has been shown to prevent oxidative stress and apoptosis in ethanol-exposed mouse embryos. The objective of this study was to test whether tert-butylhydroquinone (tBHQ), an Nrf2 inducer, can protect NCCs against ethanol-induced apoptosis. Ethanol exposure was shown to cause a moderate increase in the protein expression of Nrf2 and its downstream antioxidants in the NCCs. Treatment of NCCs with tBHQ alone significantly increased the protein expression of Nrf2 and its downstream antioxidants and also significantly increased the activities of the antioxidant enzymes. In NCCs exposed to ethanol, the tBHQ-mediated antioxidant response prevented oxidative stress and apoptosis. These results clearly demonstrate that the activation of Nrf2 signaling confers protection against ethanol-induced apoptosis in NCCs.

C-Myc is a Nrf2-interacting protein that negatively regulates phase II genes through their electrophile responsive elements

c-Myc is a transcription factor that is implicated in many cellular processes including proliferation, apoptosis and cancers. Recently, c-Myc was shown to be involved in regulation of glutamate cysteine ligase through E-box sequences. This investigation examined whether c-Myc also regulates phase II genes through interaction with the electrophile response element (EpRE). Experiments were conducted in human bronchial epithelial cells using si-RNA to knock down c-Myc. RT-PCR and reporter assays were used to measure transcription and promoter activity. c-Myc downregulated transcription and promoter activity of phase II genes. Chromatin immunoprecipitation verified binding of c-Myc to EpRE while coimmunoprecipitation demonstrated interaction of c-Myc with Nrf2. c-Myc also forms a ternary complex with Nrf2 and p-c-Jun. Finally, c-Myc decreased Nrf2 stability. Thus, our results suggest regulation of the EpRE/Nrf2 signaling pathway by c-Myc through both interaction with the EpRE binding complex and increased degradation of Nrf2.

Expression of stress-response ATF3 is mediated by Nrf2 in astrocytes

Activating Transcription Factor 3 (ATF3), a member of the ATF/CREB family, is induced rapidly by various stresses. Its induction mechanism and role in response to changes in cellular redox status, however, have not been elucidated. Here, we found that NF-E2-related factor 2 (Nrf2), a transcription factor known to bind to antioxidant response element (ARE) in promoters, transcriptionally upregulated ATF3 expression in astrocytes. Treatment with Nrf2 activators and oxidants provoked ATF3 induction in astrocytes, whereas its expression was reduced in Nrf2-depleted cells. We further demonstrated that the consensus ARE in the ATF3 promoter is critical for Nrf2-mediation by promoter analyses using an ATF3 promoter-driven luciferase construct and a chromatin immunoprecipitation assay. In addition, we found that Nrf2-dependent ATF3 induction contributed to the antioxidative and cytoprotective functions of Nrf2 in astrocytes. Taken together, our findings suggest that ATF3 is a new target for Nrf2 and has a cytoprotective function in astrocytes.

Effects of the 1-alkyl-3-methylimidazolium bromide ionic liquids on the antioxidant defense system of Daphnia magna

This study examined the antioxidant responses of Daphnia magna following exposure to different concentrations of the ionic liquid (IL) 1-octyl-3-methylimidazolium bromide and the 50% LC(50) concentrations of methylimidazolium bromide ILs with different alkyl-chain lengths. Activities of antioxidant defense enzymes (superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase) and levels of the antioxidant glutathione and the lipid peroxidation by-product malondialdehyde were measured using traditional methods or commercial kits. The concentration and the alkyl-chain length of ILs were found to strongly influence the antioxidant system of D. magna following IL exposure, and exposure to higher IL concentrations and to ILs with longer alkyl chains generally increased the enzyme activities and biomarker levels examined. Therefore, the present study suggests that oxidative stress is involved in the mechanism of IL-induced toxicity in D. magna.

Antioxidant therapy in multiple sclerosis

Reactive oxygen species (ROS) play an important role in various events underlying multiple sclerosis pathology. In the initial phase of lesion formation, ROS are known to mediate the transendothelial migration of monocytes and induce a dysfunction in the blood-brain barrier. Although the pathogenesis of MS is not completely understood, various studies suggest that reactive oxygen species contribute to the formation and persistence of multiple sclerosis lesions by acting on distinct pathological processes. The detrimental effects of ROS in the central nervous system are endowed with a protective mechanism consisting of enzymatic and non-enzymatic antioxidant. 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. Since oxidative damage has been known to be involved in inflammatory and autoimmune-mediated tissue destruction in which, modulation of oxygen free radical production represents a new approach to the treatment of inflammatory and autoimmune diseases. Several experimental studies have been performed to see whether dietary intake of several antioxidants can prevent and or reduce the progression of EAE or not. Although a few antioxidants showed some efficacy in these studies, little information is available on the effect of treatments with such compounds in patients with MS. In this review, our aim is to clarify the therapeutic efficacy of antioxidants in MS disease.

Sensory neurons and schwann cells respond to oxidative stress by increasing antioxidant defense mechanisms

Elevated blood glucose is a key initiator of mechanisms leading to diabetic neuropathy. Increases in glucose induce acute mitochondrial oxidative stress in dorsal root ganglion (DRG) neurons, the sensory neurons normally affected in diabetic neuropathy, whereas Schwann cells are largely unaffected. We propose that activation of an antioxidant response in DRG neurons would prevent glucose-induced injury. In this study, mild oxidative stress (1 microM H2O2) leads to the activation of the transcription factor Nrf2 and expression of antioxidant (phase II) enzymes. DRG neurons are thus protected from subsequent hyperglycemia-induced injury, as determined by activation of caspase 3 and the TUNEL assay. Schwann cells display high basal antioxidant enzyme expression and respond to hyperglycemia and mild oxidative stress via further increases in these enzymes. The botanical compounds resveratrol and sulforaphane activate the antioxidant response in DRG neurons. Other drugs that protect DRG neurons and block mitochondrial superoxide, identified in a compound screen, have differential ability to activate the antioxidant response. Multiple cellular targets exist for the prevention of hyperglycemic oxidative stress in DRG neurons, and these form the basis for new therapeutic strategies against diabetic neuropathy.

Severe oxidative damage in multiple sclerosis lesions coincides with enhanced antioxidant enzyme expression

Reactive oxygen species (ROS) and subsequent oxidative damage may contribute to the formation and persistence of multiple sclerosis (MS) lesions by acting on distinct pathological processes. ROS initiate lesion formation by inducing blood-brain barrier disruption, enhance leukocyte migration and myelin phagocytosis, and contribute to lesion persistence by mediating cellular damage to essential biological macromolecules of vulnerable CNS cells. Relatively little is known about which CNS cell types are affected by oxidative injury in MS lesions. Here, we show the presence of extensive oxidative damage to proteins, lipids, and nucleotides occurring in active demyelinating MS lesions, predominantly in reactive astrocytes and myelin-laden macrophages. Oxidative stress can be counteracted by endogenous antioxidant enzymes that confer protection against oxidative damage. Here, we show that antioxidant enzymes, including superoxide dismutase 1 and 2, catalase, and heme oxygenase 1, are markedly upregulated in active demyelinating MS lesions compared to normal-appearing white matter and white matter tissue from nonneurological control brains. Particularly, hypertrophic astrocytes and myelin-laden macrophages expressed an array of antioxidant enzymes. Enhanced antioxidant enzyme production in inflammatory MS lesions may reflect an adaptive defense mechanism to reduce ROS-induced cellular damage.

Acute effects of 1-octyl-3-methylimidazolium bromide ionic liquid on the antioxidant enzyme system of mouse liver

The effects of acute exposure of intraperitoneal injection of aqueous 1-octyl-3-methylimidazolium bromide on the antioxidant enzymes and lipid peroxidation of the treated mouse liver were investigated in the present paper. Thirty mice were treated with 17.9 (0.5 median lethal dose, LD(50)) and 35.7 mg/kg (1 LD(50)) of the ionic liquid or saline solution by intraperitoneal injection for 10h. Significant increase in hepatosomatic index and decrease in liver protein content were found in 1 LD(50) group. No statistically significant change was observed in the activity of superoxide dismutase in both treated groups compared to the control group. In the case of catalase activity, the decrease was recorded only at dose of 1 LD(50). As for the activity of glutathione peroxidase, increase in 0.5 LD(50) group while significant decrease at dose of 1 LD(50) was noted. There was an increase in the activity of glutathione-S-transferase in these two treated groups in comparison to the control. However, no effect on the level of lipid peroxidation was found in the treated groups. These results showed that the acute exposure of aqueous ionic liquid could cause damage to mouse, leading to antioxidant responses in livers of the treated mice.

Dietary flavonoid (-)epicatechin stimulates phosphatidylinositol 3-kinase-dependent anti-oxidant response element activity and up-regulates glutathione in cortical astrocytes

Flavonoids are plant-derived polyphenolic compounds with neuroprotective properties. Recent work suggests that, in addition to acting as hydrogen donors, they activate protective signalling pathways. The anti-oxidant response element (ARE) promotes the expression of protective proteins including those required for glutathione synthesis (xCT cystine antiporter, gamma-glutamylcysteine synthetase and glutathione synthase). The use of a luciferase reporter (ARE-luc) assay showed that the dietary flavan-3-ol (-)epicatechin activates this pathway in primary cortical astrocytes but not neurones. We also examined the distribution of NF-E2-related factor-2 (Nrf2), a key transcription factor in ARE-mediated gene expression. We found, using immunocytochemistry, that Nrf2 accumulated in the nuclei of astrocytes following exposure to tert-butylhydroquinone (100 microM) and (-)epicatechin (100 nM). (-)Epicatechin signalling via Nrf2 was inhibited by wortmannin implicating a phosphatidylinositol 3-kinase-dependent pathway. Finally, (-)epicatechin increased glutathione levels in astrocytes consistent with an up-regulation of ARE-mediated gene expression. Together, this suggests that flavonoids may be cytoprotective by increasing anti-oxidant gene expression.

Carnosic acid, a catechol-type electrophilic compound, protects neurons both in vitro and in vivo through activation of the Keap1/Nrf2 pathway via S-alkylation of targeted cysteines on Keap1

Electrophilic compounds are a newly recognized class of redox-active neuroprotective compounds with electron deficient, electrophilic carbon centers that react with specific cysteine residues on targeted proteins via thiol (S-)alkylation. Although plants produce a variety of physiologically active electrophilic compounds, the detailed mechanism of action of these compounds remains unknown. Catechol ring-containing compounds have attracted attention because they become electrophilic quinones upon oxidation, although they are not themselves electrophilic. In this study, we focused on the neuroprotective effects of one such compound, carnosic acid (CA), found in the herb rosemary obtained from Rosmarinus officinalis. We found that CA activates the Keap1/Nrf2 transcriptional pathway by binding to specific Keap1 cysteine residues, thus protecting neurons from oxidative stress and excitotoxicity. In cerebrocortical cultures, CA-biotin accumulates in non-neuronal cells at low concentrations and in neurons at higher concentrations. We present evidence that both the neuronal and non-neuronal distribution of CA may contribute to its neuroprotective effect. Furthermore, CA translocates into the brain, increases the level of reduced glutathione in vivo, and protects the brain against middle cerebral artery ischemia/reperfusion, suggesting that CA may represent a new type of neuroprotective electrophilic compound.

Emerging role of Nrf2 in protecting against hepatic and gastrointestinal disease

Transcription factor NF-E2-related factor 2 (Nrf2) belongs to the basic region-leucine zipper family and is activated in response to electrophiles and reactive oxygen species. Nrf2 coordinately regulates the constitutive and inducible transcription of a wide array of genes involved in drug metabolism, detoxification, and antioxidant defenses. During periods of oxidative stress, Nrf2 is released from sequestration in the cytoplasm and translocates to the nucleus. Nrf2 binds antioxidant response elements (AREs) in the regulatory regions of target genes and activates transcription. Genetically modified mice lacking Nrf2 serve as a useful tool for identifying new ARE-regulated genes and assessing the ability of Nrf2 to confer protection against a variety of pathologies in numerous organs including the liver, intestine, lung, skin, and nervous system. With regards to the liver and gastrointestinal tract, Nrf2 knockout mice are more susceptible to acetaminophen-induced hepatocellular injury, benzo[a]pyrene-induced tumor formation and Fas- and TNFalpha -mediated hepatocellular apoptosis. The higher sensitivity of Nrf2 knockout mice to chemical toxicity is due in part to reduced basal and inducible expression of detoxification enzymes. Nrf2 may also be important in protecting against liver fibrosis, gallstone development, and formation of aberrant crypt foci. Research of Nrf2 has opened up new opportunities in understanding how antioxidant defense pathways are regulated, how oxidative stress contributes to disease progression and may serve as a novel target for designing therapies to prevent and treat diseases in which oxidative stress is implicated.

An international case-control study of glutathione transferase and functionally related polymorphisms and risk of primary adult brain tumors

BACKGROUND

Glutathione transferases (GST) detoxify environmental and endogenous compounds and levels of two polymorphic GST proteins, GSTM3 and GSTP1, are high in the brain. Previous studies of GSTM3 and GSTP1 polymorphisms and adult brain tumor risk have produced inconsistent results, whereas the GSTM3 -63 variant is newly identified and, therefore, has not yet been studied in this context. We therefore examined associations between GSTM3 -63, GSTM3 *A/*B, GSTP1 105, and GSTP1 114 variants and adult brain tumor risk and the interaction of the effects of these same polymorphisms with cigarette smoking. In addition, the enzymes NQO1 and CYP1A1 alter susceptibility to oxidative brain damage. Because there is less previous evidence for a role of NQO1, CYP1A1, GSTM1, and GSTT1 variants, we restricted analysis of these variants to a small preliminary study.

METHODS

We genotyped DNA collected for an international population-based case-control study of 725 glioma cases, 329 of which were glioblastoma cases, 546 meningioma cases and 1,612 controls. Study participants were residents of Sweden, southeast England, Denmark, and Finland.

RESULTS

We found no associations between the GSTM3, GSTP1, NQO1, CYP1A1, GSTM1, or GSTT1 polymorphisms and adult brain tumor risk with the possible exception of a weak association between the G-C (Val-Ala) GSTP1 105/114 haplotype and glioma [odds ratio (OR), 0.73; 95% confidence interval (95% CI), 0.54, 0.99], nor was there an interaction between the effects of the GSTM3 or GSTP1 polymorphisms and cigarette smoking.

CONCLUSIONS

Overall, we observed no strong evidence for an association between GST or related enzyme polymorphisms and adult brain tumor risk.

Dopamine activates Nrf2-regulated neuroprotective pathways in astrocytes and meningeal cells

The transcription factor Nrf2 controls inducible expression of multiple antioxidant/detoxification genes. We previously found that Nrf2-/- mice have increased sensitivity to in vivo mitochondrial stress and ischemia. Although Nrf2 regulated these forms of neuronal toxicity, it was unclear which injury-triggered signal(s) led to Nrf2 activation in vivo. In this study, we use primary cultures to test the hypothesis that excessive dopamine release can act as an endogenous Nrf2-inducing signal. We cultured two cell types that show increased Nrf2 activity during ischemia in vivo, astrocytes and meningeal cells. Cultures were infected with an adenovirus reporter of Nrf2 transcriptional activity. Dopamine-induced Nrf2 activity in both cell types by generating oxidative stressors, H2O2 and dopamine-quinones. Nrf2 activation in meningeal cells was significantly higher than astrocytes. The effect of dopamine was blocked by antioxidants, and by over-expression of either dominant-negative Nrf2 or Keap1. Nrf2 induction was specific to oxidative stress caused by catecholaminergic neurotransmitters as epinephrine also induced Nrf2, but the monoamine serotonin had no significant effect. These in vitro results suggest Nrf2 activity in astrocytes and meningeal cells link the neurotoxic actions of dopamine to neuroprotective pathways that may potentially modulate ischemic injury and neurodegeneration.

NAD(P)H:quinone oxidoreductase 1 expression in multiple sclerosis lesions

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS), marked by infiltration of monocyte-derived macrophages in the brain parenchyma. Macrophages contribute to disease pathology by secretion of inflammatory mediators, such as reactive oxygen species (ROS). ROS are involved in various processes underlying MS pathology, including monocyte migration across the blood-brain barrier, phagocytosis and degradation of myelin, axonal degeneration, and oligodendrocyte damage. High concentrations of ROS cause oxidative stress, which induces transcriptional activation of phase II detoxification enzymes, such as the antioxidant protein NAD(P)H:quinone oxidoreductase 1 (NQO1). Since NQO1 expression may act as an indicator of oxidative stress and knowledge about the cellular distribution pattern of NQO1 in MS brains is lacking, we examined the expression of NQO1 in various well-characterized MS lesions. Here, we show for the first time that NQO1 is highly upregulated in active and chronic active MS lesions, particularly in hypertrophic astrocytes and myelin-laden macrophages. We hypothesize that increased NQO1 expression may reflect an endogenous defense response against ROS-mediated cellular toxicity. Compounds that induce the production of endogenous antioxidant enzymes, such as NQO1, may be potential targets for future treatment strategies in MS.

Newly constructed stable reporter cell lines for mechanistic studies on electrophile-responsive element-mediated gene expression reveal a role for flavonoid planarity

The electrophile-responsive element (EpRE) is a transcriptional enhancer involved in cancer-chemoprotective gene expression modulation by certain food components. Two stably transfected luciferase reporter cell lines were developed, EpRE(hNQO1)-LUX and EpRE(mGST-Ya)-LUX, based on EpRE sequences from the human NAD(P)H:quinone oxidoreductase (hNQO1) and the mouse glutathione-S-transferase Ya (mGST-Ya) gene, containing one and two tandem EpRE core sequences, respectively. The standard inducer tert-butylhydroquinone (tBHQ), the electrophile benzyl isothiocyanate (BITC), and the antioxidant flavonoid quercetin were found to induce luciferase expression, thereby validating these newly developed reporter cell lines. For tBHQ and BITC, but not for quercetin, higher maximum luciferase induction was found under control of the mGST-Ya EpRE as compared to the hNQO1 EpRE, pointing at different induction mechanisms. Furthermore, we investigated the structure-activity relationship for induction of luciferase expression by flavonoids in EpRE(mGST-Ya)-LUX cells, and also the relation between luciferase induction and flavonoid antioxidant potency. Five different flavonoids with a planar molecular structure were found to induce various levels of luciferase activity, whereas taxifolin, a non-planar flavonoid, did not induce luciferase activity. This suggests that a stereospecific molecular interaction may be important for EpRE-mediated gene activation, possibly with Keap1, a regulator of EpRE-controlled transcription, or with another effector or receptor protein. No consistent relation between luciferase induction level and flavonoid antioxidant potential was observed. Altogether, these results point to differences in induction mechanism between the various chemoprotective compounds tested. The newly developed stably transfected reporter cell lines provide a validated tool for future screening and mechanistic studies of EpRE-mediated gene transcription.

Glia cell number modulates sensitivity to MPTP in mice

Free radical damage has been shown to play a significant role in the pathogenesis of a number of neurodegenerative diseases including Parkinson's disease. One model of experimental parkinsonism is the loss of substantia nigra cells following administration of MPTP. Previously, it has been shown that a number of inbred strains of mice have differential responses to this toxin, and this difference is dependent on glial cells. In this study, the number of glial cells in the substantia nigra pars compacta of C57Bl/6J (MPTP-sensitive) and Swiss Webster (MPTP-resistant) strains of mice was examined. The C57Bl/6J mice have an approximately 50% lower number of GFAP+ and S-100beta glial cells than the Swiss Webster mice. C57Bl/6J mice have a 25% increased number of resident nonactivated microglial cells. To determine whether this difference in cell number has functional significance, we used an in vitro SN culture system that allowed us to manipulate the number of glial cells. When C57Bl/6 neurons were grown on a glial mat plated with twice the number of cells, we were able to rescue the MPTP-sensitive neurons from toxin-induced cell death. This suggests that the number of glial cells in the SNpc may be an important factor in the survival of dopaminergic neurons following exposure to xenobiotics.

Biological response of human diploid keratinocytes to quinone-producing compounds: role of NAD(P)H:quinone oxidoreductase 1

Reactive oxygen species (ROS) and quinones are known to determine redox balance alteration, oxidative stress and carcinogenicity. Keratinocytes of the human epidermis, a tissue particularly exposed to oxidant stimuli, possess a wide range of antioxidant and detoxifying mechanisms aimed to avoid oxidative damage of the tissue. In the present study, we evaluate the response of diploid and transformed human keratinocytes to exposure to L-dopa and tetrahydropapaveroline (THP), catechol compounds susceptible to undergo oxidation to form quinones with concomitant production of reactive oxygen species. We demonstrated that these compounds elicit up-regulation of intracellular antioxidant enzymes, in a different degree in normal cells with respect to transformed ones. Normal diploid keratinocytes adequately scavenge toxic substances through the activation of several, concurrent pathways. Conversely, in transformed cells, the whole oxidative burden must be detoxified by the limited set of conserved pathways that, accordingly, have to be highly activated. The biological response to catechol toxicity appears to rely on the pathway of NAD(P)H:quinone oxidoreductase 1 (NQO1). In conclusion, NAD(P)H:quinone oxidoreductase 1 confirms its antioxidant and detoxifying role contributing to the capacity of keratinocytes to protect epidermis against oxidative stress. Being retained in almost any cell, it represents a mechanism of general relevance in cell physiology.

Induction of the Nrf2-driven antioxidant response confers neuroprotection during mitochondrial stress in vivo

NF-E2 related factor (Nrf2) controls a pleiotropic cellular defense, where multiple antioxidant/detoxification pathways are up-regulated in unison. Although small molecule inducers of Nrf2 activity have been reported to protect neurons in vitro, whether similar pathways can be accessed in vivo is not known. We have investigated whether in vivo toxicity of the mitochondrial complex II inhibitor 3-nitropropionic acid (3-NP) can be attenuated by constitutive and inducible Nrf2 activity. The absence of Nrf2 function in Nrf2(-/-) mice resulted in 3-NP hypersensitivity that became apparent with time and increasing dose, causing motor deficits and striatal lesions on a more rapid time scale than identically treated Nrf2(+/+) and Nrf2(+/-) controls. Striatal succinate dehydrogenase activity, the target of 3-NP, was inhibited to the same extent in all genotypes by a single acute dose of 3-NP, suggesting that brain concentrations of 3-NP were similar. Dietary supplementation with the Nrf2 inducer tert-butylhydroquinone attenuated 3-NP toxicity in Nrf2(+/-) mice, but not Nrf2(-/-), confirming the Nrf2-specific action of the inducer in vivo. Increased Nrf2 activity alone was sufficient to protect animals from 3-NP toxicity because intrastriatal adenovirus-mediated Nrf2 overexpression significantly reduced lesion size compared with green fluorescent protein overexpressing controls. In cultured astrocytes, 3-NP was found to increase Nrf2 activity leading to antioxidant response element-dependent gene expression providing a potential mechanism for the increased sensitivity of Nrf2(-/-) animals to 3-NP toxicity in vivo. We conclude that Nrf2 may underlie a feedback system limiting oxidative load during chronic metabolic stress.

Expression of NAD(P)H:quinone oxidoreductase in the normal and Parkinsonian substantia nigra

Dopamine (DA) autooxidation, and consequent formation of neurotoxic DA-derived quinones and reactive oxygen species, has been implicated in dopaminergic cell death and, hence, in the pathogenesis of Parkinson's disease (PD). Stimulation of pathways involved in the detoxication of DA-quinones in the brain is hypothesized to be an effective means to limit oxidative stress and to confer neuroprotection in PD. In this respect, the inducible flavoprotein NAD(P)H:quinone oxidoreductase (NQO1) is of particular interest as it is directly implicated in the detoxication of DA-quinones and, in addition, has broad spectrum anti-oxidant properties. To study the potential pathophysiological role of NQO1 in PD, the cellular expression of NQO1 was examined in the mesencephalon of PD patients and age-matched controls. In the substantia nigra pars compacta (SNpc), NQO1 was found to be expressed in astroglial and endothelial cells and, albeit less frequently, also in dopaminergic neurons. Moreover, while overt NQO1 immunoreactivity was absent in the surrounding nervous tissue, in the Parkinsonian SNpc a marked increase in the astroglial and neuronal expression of NQO1 was consistently observed.

Presence and induction of the enzyme NAD(P)H: quinone oxidoreductase 1 in the central nervous system

NAD(P)H:quinone oxidoreductase 1 (NQO1) catalyzes a reductive detoxification that is thought to protect cells against the adverse effects of quinones and related compounds. NQO1 activity is present in all tissues. Absence of the enzyme produces abnormalities in the redox state and seizures, suggesting an important role of the protein in the central nervous system. Immunohistochemical analysis showed that the protein was found throughout the brain of the adult rat and mouse, with complete absence of the protein in brains from NQO1-/- mice. NQO1 was not seen in any neuronal population, but was localized to Bergmann glial in the cerebellum and a subset of the oligodendrocytes throughout the brain. Prolonged seizures induced in adult rats with kainic acid resulted in an increase in activity of the enzyme throughout the brain, most prominently in the cerebellum, but immunoreactivity did not appear in neurons. Comparison of the axons in the corpus callosum from a wild-type mouse to a knockout mouse showed that myelin is produced in the absence of NQO1, but there appears to be more small-diameter axons in the knockout animal. These results suggest that NQO1 has a role in myelination in the central nervous system or in the insulating/wrapping function of glial cells.

An investigation into the detoxification of microcystin-LR by the glutathione pathway in Balb/c mice

Toxin-producing cyanobacteria pose a world-wide health threat to humans and animals due to their increasing presence in both drinking and recreational waters. The predominant cyanotoxin, microcystin-LR (MCLR), targets the liver and its toxicity depends on the uptake and removal rates in the liver. The role of the glutathione detoxification pathway in protecting the liver from the effects of MCLR was investigated. Mice exposed to a single 75% LD(50) dose of pure MCLR were sacrificed at 8, 16, 24 and 32 h post-exposure (pe). Toxin induced liver damage was observed 8 and 16 h pe as evidenced by raised serum ALT and LDH levels, reduced glycogen levels and liver histology. A significant increase in lipid peroxidation was seen at 16 h pe that decreased after 24 and 32 h pe, the time-points which showed significant increases in GPX activity. An increase in soluble GST activity was noted between 8 and 16 h pe, levels of total GSH increased at 24 h while oxidised glutathione increased throughout the investigation. The increase in activity of both GPX and GST corresponded with increased transcription of these enzymes, as well as the rate-limiting enzyme in GSH synthesis, gamma-glutamyl transferase. In conclusion, this study confirms that an increase in GST activity is critical for the detoxification of MCLR, that this is regulated at the transcriptional level, and that exposure to MCLR induces the de novo synthesis of GSH. Finally, we report the involvement of GPX in the removal of MCLR-induced lipid hydroperoxides.

Propylthiouracil alters the expression and activity of glutathione-dependent enzymes in the mouse olfactory mucosa

Propylthiouracil (PTU) is an anti-thyroid drug that reportedly can impair olfactory function in humans and mice. In the mouse, PTU treatment disrupts survival and differentiation of olfactory precursor neurons. While the mechanism responsible for this effect is not understood, it is suspected that these changes are consequent to localized toxicity due to PTU metabolism. In vitro and in vivo studies in other biological systems demonstrate that PTU can significantly alter glutathione S-transferase (GST) enzyme expression and activity. The localization of GST biotransformation enzymes in basal cells, sustentacular cells and Bowman's glands of the olfactory mucosa suggests that these cells play a significant role in olfactory physiology. This study investigated the effects of PTU treatment, T(4) replacement therapy and thyroidectomy on GST expression, GST and glutathione peroxidase (GSH-PX) activity in mouse olfactory tissue. One month treatment with PTU revealed a significant decrease in expression of GST alpha (37%) as identified by Western blot analysis. In contrast, no change in GST mu expression was observed after 1 month of treatment. Concomitant treatment with T(4) caused a significant induction of GST alpha, and mu isozymes. GST enzyme activity significantly decreased after 1 month of PTU treatment (53%) and remained suppressed, despite the presence of exogenous T(4). GSH-PX activity significantly decreased after 1 month of PTU treatment (30%) and remained at control levels with T(4) supplementation. Thyroidectomy caused a 25% reduction in olfactory GST alpha expression. Total GST and GSH-PX activity were not altered in these animals. Supplementation with T(4) in thyroidectomized animals prevented the suppression of GST alpha expression. These results suggest that the combined action of localized PTU toxicity and altered levels of circulating thyroid hormone contribute to PTU-mediated abnormalities in the olfactory system.

Role of NAD(P)H:quinone oxidoreductase in the progression of neuronal cell death in vitro and following cerebral ischaemia in vivo

A direct involvement of the antioxidant enzyme NAD(P)H:quinone oxidoreductase (NQO1) in neuroprotection has not yet been shown. The aim of this study was to examine changes, localization and role of NQO1 after different neuronal injury paradigms. In primary cultures of rat cortex the activity of NQO1 was measured after treatment with ethylcholine aziridinium (AF64A; 40 micro m), inducing mainly apoptotic cell death, or oxygen-glucose deprivation (OGD; 120 min), which combines features of apoptotic and necrotic cell death. After treatment with AF64A a significant NQO1 activation started after 24 h. Sixty minutes after OGD a significant early induction of the enzyme was observed, followed by a second increase 24 h later. Enzyme activity was preferentially localized in glial cells in control and injured cultures, however, expression also occurred in injured neuronal cells. Inhibition of the NQO1 activity by dicoumarol, cibacron blue or chrysin (1-100 nM) protected the cells both after exposure to AF64A or OGD as assessed by the decreased release of lactate dehydrogenase. Comparable results were obtained in vivo using a mouse model of focal cerebral ischaemia. Dicoumarol treatment (30 nmol intracerebroventricular) reduced the infarct volume by 29% (p = 0.005) 48 h after the insult. After chemical induction of NQO1 activity by t-butylhydroquinone in vitro neuronal damage was exaggerated. Our data suggest that the activity of NQO1 is a deteriorating rather than a protective factor in neuronal cell death.

Activation of the antioxidant response element in primary cortical neuronal cultures derived from transgenic reporter mice

Many phase II protective genes contain a cis -acting enhancer region known as the antioxidant response element (ARE). Increased expression of these genes contributes to the protection of cells from oxidative stress. Transgenic reporter mice were created that carry in their genome the core ARE coupled to the human placental alkaline phosphatase (hPAP) reporter gene. Primary cortical cultures derived from these mice were treated with tBHQ resulting in a dose-dependent increase in hPAP activity. Histochemical staining for hPAP activity was observed in both glia and neurons from tBHQ-treated cultures. The tBHQ-mediated increase in hPAP was not affected by the antioxidant glutathione monoethyl ester (GSHEE), whereas the increase in hPAP following DEM treatment was completely blocked by GSHEE. Pre-treatment of cultures with the PI3-kinase inhibitor LY 294002 demonstrated a dose-dependent decrease in tBHQ-induced hPAP activity. In addition, the tBHQ-mediated expression of ARE-driven genes in primary cortical cultures was blocked by LY 294002. Interestingly, basal expression of Nrf2 was also inhibited by LY 294002. We theorize that increased levels of genes controlled by the ARE are important for cellular protection against oxidative stress. These ARE-hPAP transgenic mice will be an important in vivo model for testing our hypothesis.

Induction of glutathione-S-transferase mRNA levels by chemopreventive selenocysteine Se-conjugates

Several selenocysteine Se-conjugates (SeCys-conjugates) prevent against chemically induced carcinogenesis. Bioactivation to selenols (RSeH) by beta-lyases is thought to be critical, but the mechanism of tumor suppression remains unclear. Induction of phase II biotransformation enzymes is a possible mechanism of chemoprevention. In this study, we evaluated the isoform-selective induction of glutathione-S-transferase (GST) at the mRNA level using a quantitative reverse transcriptase polymerase chain reaction assay. In cultured primary rat hepatocytes and H35 Reuber rat hepatoma cells, SeCys-conjugates time-dependently increased mRNA levels of GST Alpha isoforms and GST Pi, but not of GST Mu isoforms. Se-allyl-L-selenocysteine, the most potent chemopreventive SeCys-conjugate so far known, was also the most active GST inducer. After exposure for 24hr, it elevated GSTA2, GSTA3, GSTA5, and GSTP mRNA levels in primary hepatocytes 3.2+/-0.4-, 1.9+/-0.1-, 4.3+/-0.3-, and 2.9+/-0.3-fold, respectively. Se-allyl-D-selenocysteine was significantly less active, suggesting that stereoselective conversion of SeCys-conjugates to selenols is involved in GST induction. In H35 Reuber hepatoma cells, where conversion of SeCys-conjugates to selenols was 2-6-fold lower than in primary hepatocytes, GST induction was also much lower than in primary hepatocytes. SeCys-conjugates did not induce cytochrome P450 1A1, 2B1/2, or 3A1. This indicates that SeCys-conjugates are monofunctional inducers of phase II biotransformation enzymes. The present results suggest that induction of GST expression contributes to the chemopreventive activity of SeCys-conjugates.