Neuroprotective effect of Nrf2/ARE activators, CDDO ethylamide and CDDO trifluoroethylamide, in a mouse model of amyotrophic lateral sclerosis

Comparative Analysis of VOCs in Exhaled Breath of Amyotrophic Lateral Sclerosis and Cervical Spondylotic Myelopathy Patients

Amyotrophic lateral sclerosis (ALS) is an incurable neurological degenerative disease. It can cause irreversible neurological damage to motor neurons; typical symptoms include muscle weakness and atrophy, bulbar paralysis and pyramidal tract signs. The ALS-mimicking disease cervical spondylotic myelopathy (CSM) presents similar symptoms, but analysis of breath volatile organic compounds (VOCs) can potentially be used to distinguish ALS from CSM. In this study, breath samples were collected from 28 ALS and 13 CSM patients. Subsequently, gas chromatography/mass spectrometry (GCMS) was used to analyze breath VOCs. Principal component analysis (PCA) and orthogonal partial least-squares discriminant analysis (OPLSDA) were the statistical methods used to process the final data. We identified 4 compounds with significantly decreased levels in ALS patients compared with CSM controls: (1) carbamic acid, monoammonium salt; (2) 1-alanine ethylamide, (S)-; (3) guanidine, N,N-dimethyl-; and (4) phosphonic acid, (p-hydroxyphenyl)-. Currently, the metabolic origin of the VOCs remains unclear; however, several pathways might explain the decreasing trends observed. The results of this study demonstrate that there are specific VOC profiles associated with ALS and CSM patients that can be used to differentiate between the two. In addition, these metabolites could contribute to a better understanding of the underlying pathophysiological mechanisms of ALS.

Advances in the Development of Disease-Modifying Treatments for Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive adult-onset, neurodegenerative disease characterized by the degeneration of upper and lower motor neurons. Over recent years, numerous genes ha ve been identified that promote disease pathology, including SOD1, TARDBP, and the expanded hexanucleotide repeat (GGGGCC) within C9ORF72. However, despite these major advances in identifying genes contributing to ALS pathogenesis, there remains only one currently approved therapeutic: the glutamate antagonist, riluzole. Seminal breakthroughs in the pathomechanisms and genetic factors associated with ALS have heavily relied on the use of rodent models that recapitulate the ALS phenotype; however, while many therapeutics have proved to be significant in animal models by prolonging life and rescuing motor deficits, they have failed in human clinical trials. This may be due to fundamental differences between rodent models and human disease, the fact that animal models are based on overexpression of mutated genes, and confounding issues such as difficulties mimicking the dosing schedules and regimens implemented in mouse models to humans. Here, we review the major pathways associated with the pathology of ALS, the rodent models engineered to test efficacy of candidate drugs, the advancements being made in stem cell therapy for ALS, and what strategies may be important to circumvent the lack of successful translational studies in the clinic.

UPS Activation in the Battle Against Aging and Aggregation-Related Diseases: An Extended Review

Aging is a biological process accompanied by gradual increase of damage in all cellular macromolecules, i.e., nucleic acids, lipids, and proteins. When the proteostasis network (chaperones and proteolytic systems) cannot reverse the damage load due to its excess as compared to cellular repair/regeneration capacity, failure of homeostasis is established. This failure is a major hallmark of aging and/or aggregation-related diseases. Dysfunction of the major cellular proteolytic machineries, namely the proteasome and the lysosome, has been reported during the progression of aging and aggregation-prone diseases. Therefore, activation of these pathways is considered as a possible preventive or therapeutic approach against the progression of these processes. This chapter focuses on UPS activation studies in cellular and organismal models and the effects of such activation on aging, longevity and disease prevention or reversal.

CDDO and Its Role in Chronic Diseases

There has been a continued interest in translational research focused on both natural products and manipulation of functional groups on these compounds to create novel derivatives with higher desired activities. Oleanolic acid, a component of traditional Chinese medicine used in hepatitis therapy, was modified by chemical processes to form 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO). This modification increased anti-inflammatory activity significantly and additional functional groups on the CDDO backbone have shown promise in treating conditions ranging from kidney disease to obesity to diabetes. CDDO's therapeutic effect is due to its upregulation of the master antioxidant transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2) through conformational change of Nrf2-repressing, Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1 (Keap1) and multiple animal and human studies have verified subsequent activation of Nrf2-controlled antioxidant genes via upstream Antioxidant Response Element (ARE) regions. At the present time, positive results have been obtained in the laboratory and clinical trials with CDDO derivatives treating conditions such as lung injury, inflammation and chronic kidney disease. However, clinical trials for cancer and cardiovascular disease have not shown equally positive results and further exploration of CDDO and its derivatives is needed to put these shortcomings into context for the purpose of future therapeutic modalities.

Nrf2--a therapeutic target for the treatment of neurodegenerative diseases

The brain is very sensitive to changes in redox status; thus maintaining redox homeostasis in the brain is critical for the prevention of accumulating oxidative damage. Aging is the primary risk factor for developing neurodegenerative diseases. In addition to age, genetic and environmental risk factors have also been associated with disease development. The primary reactive insults associated with the aging process are a result of oxidative stress (OS) and nitrosative stress (NS). Markers of increased oxidative stress, protein and DNA modification, inflammation, and dysfunctional proteostasis have all been implicated in contributing to the progression of neurodegeneration. The ability of the cell to combat OS/NS and maintain a clearance mechanism for misfolded aggregating proteins determines whether or not it will survive. A critical pathway in this regard is the Nrf2 (nuclear factor erythroid 2-related factor 2)- antioxidant response element (ARE) pathway. Nrf2 activation has been shown to mitigate a number of pathologic mechanisms associated with Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and multiple sclerosis. This review will focus on the role of Nrf2 in these diseases and the potential for Nrf2 activation to attenuate disease progression.

Radiation promotes colorectal cancer initiation and progression by inducing senescence-associated inflammatory responses

Proton radiotherapy is becoming more common since protons induce more precise DNA damage at the tumor site with reduced side effects to adjacent normal tissues. However, the long-term biological effects of proton irradiation in cancer initiation compared to conventional photon irradiation are poorly characterized. In this study, using a human familial adenomatous polyposis syndrome susceptible mouse model, we show that whole body irradiation with protons are more effective in inducing senescence-associated inflammatory responses (SIR) which are involved in colon cancer initiation and progression. After proton irradiation, a subset of SIR genes (Troy, Sox17, Opg, Faim2, Lpo, Tlr2 and Ptges) and a gene known to be involved in invasiveness (Plat), along with the senescence associated gene (P19Arf) are markedly increased. Following these changes loss of Casein kinase Iα (CKIα) and induction of chronic DNA damage and TP53 mutations are increased compared to x-ray irradiation. Proton irradiation also increases the number of colonic polyps, carcinomas and invasive adenocarcinomas. Pretreatment with the non-steroidal anti-inflammatory drug, CDDO-EA, reduces proton irradiation associated SIR and tumorigenesis. Thus, exposure to proton irradiation elicits significant changes in colorectal cancer initiation and progression that can be mitigated using CDDO-EA.

A review on mitochondrial restorative mechanism of antioxidants in Alzheimer's disease and other neurological conditions

Neurodegenerative diseases are intricate in nature because of the involvement of the multiple pathophysiological events including mitochondrial dysfunction, neuroinflammation and oxidative stress. Alzheimer’s disease (AD) is a neurodegenerative disease explained by extracellular amyloid β deposits, intracellular neurofibrillary tangles and mitochondrial dysfunction. Increasing evidence has indicated that mitochondrial dysfunction displays significant role in the pathophysiological processes of AD. Mitochondrial dysfunction involves alterations in mitochondrial respiratory enzyme complex activities, oxidative stress, opening of permeability transition pore, and enhanced apoptosis. Various bioenergetics and antioxidants have been tried or under different investigational phase against AD and other neurodegenerative disorders (Parkinson’s disease, Huntington’s disease, and Amyotrophic lateral sclerosis) because of their complex and multiple site of action. These mitochondrial-targeting bioenergetics and antioxidant compounds such as coenzyme Q10, idebenone, creatine, mitoQ, mitovitE, MitoTEMPOL, latrepirdine, methylene blue, triterpenoids, SS peptides, curcumin, Ginkgo biloba, and omega-3 polyunsaturated fatty acids with potential efficacy in AD have been identified. Present review is intent to discuss mitochondrial restorative mechanisms of these bioenergetics and antioxidants as a potential alternative drug strategy for effective management of AD.

Proteasome activation: An innovative promising approach for delaying aging and retarding age-related diseases

Aging is a natural process accompanied by a progressive accumulation of damage in all constituent macromolecules (nucleic acids, lipids and proteins). Accumulation of damage in proteins leads to failure of proteostasis (or vice versa) due to increased levels of unfolded, misfolded or aggregated proteins and, in turn, to aging and/or age-related diseases. The major cellular proteolytic machineries, namely the proteasome and the lysosome, have been shown to dysfunction during aging and age-related diseases. Regarding the proteasome, it is well established that it can be activated either through genetic manipulation or through treatment with natural or chemical compounds that eventually result to extension of lifespan or deceleration of the progression of age-related diseases. This review article focuses on proteasome activation studies in several species and cellular models and their effects on aging and longevity. Moreover, it summarizes findings regarding proteasome activation in the major age-related diseases as well as in progeroid syndromes.

A retrospective review of the progress in amyotrophic lateral sclerosis drug discovery over the last decade and a look at the latest strategies

INTRODUCTION

Drug discovery for amyotrophic lateral sclerosis (ALS) has experienced a surge in clinical studies and remarkable preclinical milestones utilizing a variety of mutant superoxide dismutase 1 model systems. Of the drugs that were tested and showed positive preclinical effects, none demonstrated therapeutic benefits to ALS patients in clinical settings.

AREAS COVERED

This review discusses the advances made in drug discovery for ALS and highlights why drug development is proving to be so difficult. It also discusses how a closer look at both preclinical and clinical studies could uncover the reasons why these preclinical successes have yet to result in the availability of an effective drug for clinical use.

EXPERT OPINION

Valuable lessons from the numerous preclinical and clinical studies supply the biggest advantage in the monumental task of finding a cure for ALS. Obviously, a single design type for ALS clinical trials has not yielded success. The authors suggest a two-pronged approach that may prove essential to achieve clinical efficacy in the identification of novel targets and preclinical testing in multiple models to identify biomarkers that can function in diagnostic, predictive and prognostic roles, and changes to clinical trial design and patient recruitment criteria. The advancement of technology and invention of more powerful tools will further enhance the above. This will give rise to more sophisticated clinical trials with consideration of a range of criteria from: optimum dose, route of delivery, specific biomarkers, pharmacokinetics, pharmacodynamics and toxicology to biomarkers, timing for trial and patients' clinical status.

Cancer Cell Growth Is Differentially Affected by Constitutive Activation of NRF2 by KEAP1 Deletion and Pharmacological Activation of NRF2 by the Synthetic Triterpenoid, RTA 405

Synthetic triterpenoids are antioxidant inflammation modulators (AIMs) that exhibit broad anticancer activity. AIMs bind to KEAP1 and inhibit its ability to promote NRF2 degradation. As a result, NRF2 increases transcription of genes that restore redox balance and reduce inflammation. AIMs inhibit tumor growth and metastasis by increasing NRF2 activity in the tumor microenvironment and by modulating the activity of oncogenic signaling pathways, including NF-κB, in tumor cells. Accumulating evidence suggests that KEAP1 loss or mutation--which results in high levels of sustained NRF2 activity--may promote cancer growth and increase chemoresistance. Loss of KEAP1 also increases the levels of other oncogenic proteins, including IKKβ and BCL2. The apparent survival advantage provided to some tumor cells by loss of functional KEAP1 raises the question of whether pharmacological inhibition of KEAP1 could promote tumor growth. To address this issue, we characterized the basal levels of KEAP1 and NRF2 in a panel of human tumor cell lines and profiled the activity of an AIM, RTA 405. We found that in tumor cell lines with low or mutant KEAP1, and in Keap1-/- murine embryonic fibroblasts, multiple KEAP1 targets including NRF2, IKKβ, and BCL2 were elevated. Keap1-/- murine embryonic fibroblasts also had higher rates of proliferation and colony formation than their wild-type counterparts. In cells with functional KEAP1, RTA 405 increased NRF2 levels, but not IKKβ or BCL2 levels, and did not increase cell proliferation or survival. Moreover, RTA 405 inhibited growth at similar concentrations in cells with different basal NRF2 activity levels and in cells with wild-type or mutant KRAS. Finally, pre-treatment with RTA 405 did not protect tumor cells from doxorubicin- or cisplatin-mediated growth inhibition. Collectively, these data demonstrate that pharmacological activation of NRF2 by AIMs is distinct from genetic activation and does not provide a growth or survival advantage to tumor cells.

Dissecting molecular cross-talk between Nrf2 and NF-κB response pathways

In most tissues, cells are exposed to frequent changes in levels of oxidative stress and inflammation. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and nuclear factor-κB (NF-κB) are the two key transcription factors that regulate cellular responses to oxidative stress and inflammation respectively. Pharmacological and genetic studies suggest that there is functional cross-talk between these two important pathways. The absence of Nrf2 can exacerbate NF-κB activity leading to increased cytokine production, whereas NF-κB can modulate Nrf2 transcription and activity, having both positive and negative effects on the target gene expression. This review focuses on the potentially complex molecular mechanisms that link the Nrf2 and NF-κB pathways and the importance of designing more effective therapeutic strategies to prevent or treat a broad range of neurological disorders.

Autophagy of mitochondria: a promising therapeutic target for neurodegenerative disease

The autophagic process is the only known mechanism for mitochondrial turnover and it has been speculated that dysfunction of autophagy may result in mitochondrial error and cellular stress. Emerging investigations have provided new understanding of how autophagy of mitochondria (also known as mitophagy) is associated with cellular oxidative stress and its impact on neurodegeneration. This impaired autophagic function may be considered as a possible mechanism in the pathogenesis of several neurodegenerative disorders including Parkinson's disease, Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, and Huntington disease. It can be suggested that autophagy dysfunction along with oxidative stress is considered main events in neurodegenerative disorders. New therapeutic approaches have now begun to target mitochondria as a potential drug target. This review discusses evidence supporting the notion that oxidative stress and autophagy are intimately associated with neurodegenerative disease pathogenesis. This review also explores new approaches that can prevent mitochondrial dysfunction, improve neurodegenerative etiology, and also offer possible cures to the aforementioned neurodegenerative diseases.

State of the field: An informatics-based systematic review of the SOD1-G93A amyotrophic lateral sclerosis transgenic mouse model

Numerous sub-cellular through system-level disturbances have been identified in over 1300 articles examining the superoxide dismutase-1 guanine 93 to alanine (SOD1-G93A) transgenic mouse amyotrophic lateral sclerosis (ALS) pathophysiology. Manual assessment of such a broad literature base is daunting. We performed a comprehensive informatics-based systematic review or 'field analysis' to agnostically compute and map the current state of the field. Text mining of recaptured articles was used to quantify published data topic breadth and frequency. We constructed a nine-category pathophysiological function-based ontology to systematically organize and quantify the field's primary data. Results demonstrated that the distribution of primary research belonging to each category is: systemic measures an motor function, 59%; inflammation, 46%; cellular energetics, 37%; proteomics, 31%; neural excitability, 22%; apoptosis, 20%; oxidative stress, 18%; aberrant cellular chemistry, 14%; axonal transport, 10%. We constructed a SOD1-G93A field map that visually illustrates and categorizes the 85% most frequently assessed sub-topics. Finally, we present the literature-cited significance of frequently published terms and uncover thinly investigated areas. In conclusion, most articles individually examine at least two categories, which is indicative of the numerous underlying pathophysiological interrelationships. An essential future path is examination of cross-category pathophysiological interrelationships and their co-correspondence to homeostatic regulation and disease progression.

Nrf2 inducer and cncC overexpression attenuates neurodegeneration due to α-synuclein in Drosophila

The study of the genes that are related to the pathogenesis of Parkinson's disease (PD) will improve our understanding of the mechanisms that underlie the development of PD. α-Synuclein is a major protein component of Lewy bodies, which are characteristic structures of PD pathology. Mutations in α-synuclein are closely related to the early onset of autosomal dominant PD. Transgenic flies with mutant α-synuclein (A53T) display neurodegenerative changes that include movement dysfunctions and a loss of dopaminergic neurons in the brain. In the present study, we measured reactive oxygen species (ROS) levels in α-synuclein transgenic flies by monitoring the fluorescence levels of redox-sensitive indicators based on GFP (roGFP) in flies co-expressing roGFP and mutant α-synuclein. We found that the ROS levels were significantly increased in the mutant α-synuclein flies. The elevations in ROS levels were also proportionate to the behavioral disorders and the losses of dopaminergic neurons. We also found that CDDO-Me inhibited the increases in ROS levels in the A53T flies and improved the neurodegenerative changes by activating the Nrf2/antioxidant response element signaling pathway. Selective expression of the Nrf2 homologous gene cncC in the dopaminergic neurons effectively protected against the neurodegenerative phenotype of the A53T α-synuclein flies, compared to the flies that expressed cncC in all neurons. These results indicate that the reductions in oxidative stress that are mediated by the activation of the antioxidant signaling pathway can effectively attenuate the neurotoxicity caused by mutations in α-synuclein.

A chemical chaperone-based drug candidate is effective in a mouse model of amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the selective death of motor neurons and skeletal muscle atrophy. The majority of ALS cases are acquired spontaneously, with inherited disease accounting for only 10 % of all cases. Recent studies provide compelling evidence that aggregates of misfolded proteins underlie both types of ALS. Small molecules such as artificial chaperones can prevent or even reverse the aggregation of proteins associated with various human diseases. However, their very high active concentration (micromolar range) severely limits their utility as drugs. We synthesized several ester and amide derivatives of chemical chaperones. The lead compound 14, 3-((5-((4,6-dimethylpyridin-2-yl)methoxy)-5-oxopentanoyl)oxy)-N,N-dimethylpropan-1-amine oxide shows, in the micromolar concentration range, both neuronal and astrocyte protective effects in vitro; at daily doses of 10 mg kg(-1) 14 improved the neurological functions and delayed body weight loss in ALS mice. Members of this new chemical chaperone derivative class are strong candidates for the development of new drugs for ALS patients.

Potential compounds for the treatment of mitochondrial disease

INTRODUCTION

Mitochondrial diseases are a group of heterogeneous disorders for which no curative therapy is currently available. Several drugs are currently being pursued as candidates to correct the underlying biochemistry that causes mitochondrial dysfunction.

SOURCES OF DATA

A systematic review of pharmacological therapeutics tested using in vitro, in vivo models and clinical trials. Results presented from database searches undertaken to ascertain compounds currently being pioneered to treat mitochondrial disease.

AREAS OF AGREEMENT

Previous clinical research has been hindered by poorly designed trials that have shown some evidence in enhancing mitochondrial function but without significant results.

AREAS OF CONTROVERSY

Several compounds under investigation display poor pharmacokinetic profiles or numerous off target effects.

GROWING POINTS

Drug development teams should continue to screen existing and novel compound libraries for therapeutics that can enhance mitochondrial function. Therapies for mitochondrial disorders could hold potential cures for a myriad of other ailments associated with mitochondrial dysfunction such as neurodegenerative diseases.

Oleanolic Acid enhances the beneficial effects of preconditioning on PC12 cells

Preconditioning triggers endogenous protection against subsequent exposure to higher concentrations of a neurotoxin. In this study, we investigated whether exposure to oleanolic acid (OA) enhances the protective effects of preconditioning on PC12 cells exposed to 6-hydroxydopamine (6-OHDA). A concentration response curve was constructed using 6-OHDA (50, 150, 300, and 600 μM). The experiment consisted of 6 groups: untreated, OA only, Group 1: cells treated with 6-OHDA (50 μM) for 1 hour, Group 2: cells treated with 6-OHDA (150 μM) for 1 hour, Group 3: cells treated with 6-OHDA (50 μM) for 30 minutes followed 6 hours later by treatment with 6-OHDA (150 μM) for 30 minutes, and Group 4: cells treated as in group 3 but also received OA immediately after the second 6-OHDA treatment. Cell viability and apoptotic ratio were assessed using the MTT and Annexin V staining tests, respectively. In preconditioned cells, we found that cell viability remained high following exposure to 6-OHDA (150 μM). OA treatment enhanced the protective effects of preconditioning. Similarly, with the annexin V apoptosis test, preconditioning protected the cell and this was enhanced by OA. Therefore, preexposure of PC12 cells to low 6-OHDA concentration can protect against subsequent toxic insults of 6-OHDA and OA enhances this protection.

H63D HFE genotype accelerates disease progression in animal models of amyotrophic lateral sclerosis

H63D HFE is associated with iron dyshomeostasis and oxidative stress; each of which plays an important role in amyotrophic lateral sclerosis (ALS) pathogenesis. To examine the role of H63D HFE in ALS, we generated a double transgenic mouse line (SOD1/H67D) carrying the H67D HFE (homologue of human H63D) and SOD1(G93A) mutations. We found double transgenic mice have shorter survival and accelerated disease progression. We examined parameters in the lumbar spinal cord of double transgenic mice at 90days (presymptomatic), 110days (symptomatic) and end-stage. Transferrin receptor and L-ferritin expression, both indicators of iron status, were altered in double transgenic and SOD1 mice starting at 90days, indicating loss of iron homeostasis in these mice. However, double transgenic mice had higher L-ferritin expression than SOD1 mice. Double transgenic mice exhibited increased Iba-1 immunoreactivity and caspase-3 levels, indicating increased microglial activation which would be consistent with the higher L-ferritin levels. Although both SOD1 and double transgenic mice had increased GFAP expression, the magnitude of the increase was higher in double transgenic mice at 110days, suggesting increased gliosis in these mice. Increased hemeoxygenase-1 and decreased nuclear factor E2-related factor 2 levels in double transgenic mice strongly suggest the accelerated disease process could be associated with increased oxidative stress. There was no evidence of TAR-DNA-binding protein 43 mislocalization to the cytoplasm in double transgenic mice; however, there was evidence suggesting neurofilament disruption, which has been reported in ALS. Our findings indicate H63D HFE modifies ALS pathophysiology via pathways involving oxidative stress, gliosis and disruption of cellular functions.

Dynamic changes in the distribution and time course of blood-brain barrier-permeative nitroxides in the mouse head with EPR imaging: visualization of blood flow in a mouse model of ischemia

Electron paramagnetic resonance (EPR) imaging using nitroxides as redox-sensitive probes is a powerful, noninvasive method that can be used under various physiological conditions to visualize changes in redox status that result from oxidative damage. Two blood-brain barrier-permeative nitroxides, 3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (HMP) and 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-yloxy (MCP), have been widely used as redox-sensitive probes in the brains of small animals, but their in vivo distribution and properties have not yet been analyzed in detail. In this study, a custom-made continuous-wave three-dimensional (3D) EPR imager was used to obtain 3D EPR images of mouse heads using MCP or HMP. This EPR imager made it possible to take 3D EPR images reconstructed from data from 181 projections acquired every 60s. Using this improved EPR imager and magnetic resonance imaging, the distribution and reduction time courses of HMP and MCP were examined in mouse heads. EPR images of living mice revealed that HMP and MCP have different distributions and different time courses for entering the brain. Based on the pharmacokinetics of the reduction reactions of HMP and MCP in the mouse head, the half-lives of HMP and MCP were clearly and accurately mapped pixel by pixel. An ischemic mouse model was prepared, and the half-life of MCP was mapped in the mouse head. Compared to the half-life in control mice, the half-life of MCP in the ischemic model mouse brain was significantly increased, suggesting a shift in the redox balance. This in vivo EPR imaging method using BBB-permeative MCP is a useful noninvasive method for assessing changes in the redox status in mouse brains under oxidative stress.

Targeting nrf2-mediated gene transcription by triterpenoids and their derivatives

Chemoprevention represents a strategy designed to protect cells or tissues against various carcinogens and carcinogenic metabolites derived from exogenous or endogenous sources. Recent studies indicate that plant-derived triterpenoids, like oleanolic acid, may exert cytoprotective functions via regulation of the activity of different transcription factors. The chemopreventive effects may be mediated through induction of the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor. Activation of Nrf2 by triterpenoids induces the expression of phase 2 detoxifying and antioxidant enzymes such as NAD(P)H quinone oxidoreductase 1 (NQO1) and heme oxygenase-1 (HO-1) - proteins which can protect cells or tissues against various toxic metabolites. On the other hand, inhibition of other transcription factors, like NF-κB leads to the decrease in the pro-inflammatory gene expression. Moreover, the modulation of microRNAs activity may constitute a new mechanism responsible for valuable effects of triterpenoids. Recently, based on the structure of naturally occurring triterpenoids and with involvement of bioinformatics and computational chemistry, many synthetic analogs with improved biological properties have been obtained. Data from in vitro and in vivo experiments strongly suggest synthetic derivatives as promising candidates in the chemopreventive and chemotherapeutic strategies.

Effect of the human SOD1-G93A gene on the Nrf2/ARE signaling pathway in NSC-34 cells

Dominant mutations in superoxide dismutase 1 (SOD1) are a frequent cause of the lethal neurodegenerative disease amyotrophic lateral sclerosis (ALS). The nuclear factor erythroid 2‑related factor 2 (Nrf2)/antioxidant response element (ARE) signaling pathway is the major cellular defense mechanism against oxidative stress, however, its role in ALS remains to be fully elucidated. Therefore, the present study aimed to investigate whether the human SOD1-G93A gene affected the Nrf2/ARE signaling pathway in an ALS cell model. The soma became round and the number of neurites decreased in the NSC-34 cells transfected with the hSOD1-G93A gene, and the neurites were shorter and oxidative stress was increased compared with the normal NSC-34 cells. Furthermore, the mRNA and protein expression of Nrf2, heme oxygenase-1 and

NAD(P)H

quinone oxidoreductase 1 was significantly decreased in the NSC-34 cells transfected with the human SOD1-G93A gene. The present study indicated that human SOD1-G93A damaged the Nrf2/ARE signaling pathway in the ALS cell model and reduced the ability of cells to protect against oxidative injury.

Methylene blue upregulates Nrf2/ARE genes and prevents tau-related neurotoxicity

Methylene blue (MB, methylthioninium chloride) is a phenothiazine that crosses the blood brain barrier and acts as a redox cycler. Among its beneficial properties are its abilities to act as an antioxidant, to reduce tau protein aggregation and to improve energy metabolism. These actions are of particular interest for the treatment of neurodegenerative diseases with tau protein aggregates known as tauopathies. The present study examined the effects of MB in the P301S mouse model of tauopathy. Both 4 mg/kg MB (low dose) and 40 mg/kg MB (high dose) were administered in the diet ad libitum from 1 to 10 months of age. We assessed behavior, tau pathology, oxidative damage, inflammation and numbers of mitochondria. MB improved the behavioral abnormalities and reduced tau pathology, inflammation and oxidative damage in the P301S mice. These beneficial effects were associated with increased expression of genes regulated by NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE), which play an important role in antioxidant defenses, preventing protein aggregation, and reducing inflammation. The activation of Nrf2/ARE genes is neuroprotective in other transgenic mouse models of neurodegenerative diseases and it appears to be an important mediator of the neuroprotective effects of MB in P301S mice. Moreover, we used Nrf2 knock out fibroblasts to show that the upregulation of Nrf2/ARE genes by MB is Nrf2 dependent and not due to secondary effects of the compound. These findings provide further evidence that MB has important neuroprotective effects that may be beneficial in the treatment of human neurodegenerative diseases with tau pathology.

Lack of association between nuclear factor erythroid-derived 2-like 2 promoter gene polymorphisms and oxidative stress biomarkers in amyotrophic lateral sclerosis patients

Oxidative stress involvement has been strongly hypothesized among the possible pathogenic mechanisms of motor neuron degeneration in amyotrophic lateral sclerosis (ALS). The intracellular redox balance is finely modulated by numerous complex mechanisms critical for cellular functions, among which the nuclear factor erythroid-derived 2-like 2 (NFE2L2/Nrf2) pathways. We genotyped, in a cohort of ALS patients (n = 145) and healthy controls (n = 168), three SNPs in Nrf2 gene promoter: −653 A/G, −651 G/A, and −617 C/A and evaluated, in a subset (n = 73) of patients, advanced oxidation protein products (AOPP), iron-reducing ability of plasma (FRAP), and plasma thiols (-SH) as oxidative damage peripheral biomarkers. Nrf2 polymorphisms were not different among patients and controls. Increased levels of AOPP (P < 0.05) and decreased levels of FRAP (P < 0.001) have been observed in ALS patients compared with controls, but no difference in -SH values was found. Furthermore, no association was found between biochemical markers of redox balance and Nrf2 polymorphisms. These data confirm an altered redox balance in ALS and indicate that, while being abnormally modified compared to controls, the oxidative stress biomarkers assessed in this study are independent from the −653 A/G, −651 G/A, and −617 C/A Nrf2 SNPs in ALS patients.

Oxidative stress and autophagic alteration in brainstem of SOD1-G93A mouse model of ALS

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease involving both upper and lower motor neurons. The mechanism of motor neuron degeneration is still unknown. Although many studies have been performed on spinal motor neurons, few have been reported on brainstem and its motor nuclei. The aim of this study was to investigate oxidative stress and autophagic changes in the brainstem and representative motor nuclei of superoxide dismutase 1 (SOD1)-G93A mouse model of ALS. The expression levels of cluster of differentiation molecule 11b (CD11b), glial fibrillary acidic protein, glutamate-cysteine ligase catalytic subunit, heme oxygenase-1, NAD(P)H: quinone oxidoreductase 1, voltage-dependent anion-selective channel protein 1, Sequestosome 1/p62 (p62), microtubule-associated protein 1 light chain 3B (LC3), and SOD1 proteins in brainstem were examined by Western blot analysis. Immunohistochemistry and immunofluorescence were performed to identify the cellular localization of SOD1, p62, and LC3B, respectively. The results showed that there were progressive asctrocytic proliferation and microglial activation, induction of antioxidant proteins, and increased p62 and LC3II expression in brainstem of SOD1-G93A mice. Additionally, SOD1 and p62 accumulated in hypoglossal, facial, and red nuclei, but not in oculomotor nucleus. Furthermore, electron microscope showed increased autophagic vacuoles in affected brainstem motor nuclei. Our results indicate that brainstem share similar gliosis, oxidative stress, and autophagic changes as the spinal cord in SOD1-G93A mice. Thus, SOD1 accumulation in astrocytes and neurons, oxidative stress, and altered autophagy are involved in motor neuron degeneration in the brainstem, similar to the motor neurons in spinal cord. Therefore, therapeutic trials in the SOD1G93A mice need to target the brainstem in addition to the spinal cord.

Nrf2 and Nrf1 signaling and ER stress crosstalk: implication for proteasomal degradation and autophagy

The endoplasmic reticulum (ER) lumen is chemically complex and crowded with polypeptides in different stages of assembly. ER quality control monitors chaperone-assisted protein folding, stochastic errors and off-pathway intermediates. In acute conditions, potentially toxic polypeptides overflow the capacity of the chaperone system and lead to ER stress. Activation of the unfolded protein response (UPR) following ER stress buys time for non-native polypeptides to refold or be eliminated; otherwise cell death occurs. The clearance routes for deleterious proteins are endoplasmic reticulum-associated degradation (ERAD) and ER stress-activated autophagy. The ERAD pathway is a chaperone and proteasome-mediated polypeptide degradation, while autophagy applies to wider range of substances. ER stress signal transduction recruits diverse molecules and pathways upon UPR induction to compensate stress condition. NF-E2-related factor 1 (Nrf1) and Nrf2 are two transcription factors mostly known by their induction through an antioxidant response; they can also be activated by UPR machinery. Discovery of diverse molecules downstream of Nrf1 and Nrf2 has expanded our understanding of the biological impacts of these transcription factors beyond classic antioxidant activation. In this review, we summarize our current understanding of mutual relationships between Nrf1, Nrf2, and ER stress clearance mechanisms and highlight the crosstalk of specific molecules mediating these correlations.

Mitochondrial diseases of the brain

Neurodegenerative disorders are debilitating diseases of the brain, characterized by behavioral, motor and cognitive impairments. Ample evidence underpins mitochondrial dysfunction as a central causal factor in the pathogenesis of neurodegenerative disorders including Parkinson's disease, Huntington's disease, Alzheimer's disease, Amyotrophic lateral sclerosis, Friedreich's ataxia and Charcot-Marie-Tooth disease. In this review, we discuss the role of mitochondrial dysfunction such as bioenergetics defects, mitochondrial DNA mutations, gene mutations, altered mitochondrial dynamics (mitochondrial fusion/fission, morphology, size, transport/trafficking, and movement), impaired transcription and the association of mutated proteins with mitochondria in these diseases. We highlight the therapeutic role of mitochondrial bioenergetic agents in toxin and in cellular and genetic animal models of neurodegenerative disorders. We also discuss clinical trials of bioenergetics agents in neurodegenerative disorders. Lastly, we shed light on PGC-1α, TORC-1, AMP kinase, Nrf2-ARE, and Sirtuins as novel therapeutic targets for neurodegenerative disorders.

Human stem cell-derived astrocytes and their application to studying Nrf2-mediated neuroprotective pathways and therapeutics in neurodegeneration

Glia, including astrocytes, are increasingly at the forefront of neurodegenerative research for their role in the modulation of neuronal function and survival. Improved understanding of underlying disease mechanisms, including the role of the cellular environment in neurodegeneration, is central to therapeutic development for these currently untreatable diseases. In these endeavours, experimental models that more closely reproduce the human condition have the potential to facilitate the transition between experimental studies in model organisms and patient trials. In this review we discuss the growing role of astrocytes in neurodegenerative diseases, and how astrocytes generated from human pluripotent stem cells represent a useful tool for analyzing astrocytic signalling and influence on neuronal function.

Rodent models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterised by the degeneration of upper and lower motor neurons. Recent advances in our understanding of some of the genetic causes of ALS, such as mutations in SOD1, TARDBP, FUS and VCP have led to the generation of rodent models of the disease, as a strategy to help our understanding of the pathophysiology of ALS and to assist in the development of therapeutic strategies. This review provides detailed descriptions of TDP-43, FUS and VCP models of ALS, and summarises potential therapeutics which have been recently trialled in rodent models of the disease. This article is part of a Special Issue entitled: Animal Models of Disease.

Dual-energy precursor and nuclear erythroid-related factor 2 activator treatment additively improve redox glutathione levels and neuron survival in aging and Alzheimer mouse neurons upstream of reactive oxygen species

To determine whether glutathione (GSH) loss or increased reactive oxygen species (ROS) are more important to neuron loss, aging, and Alzheimer's disease (AD), we stressed or boosted GSH levels in neurons isolated from aging 3xTg-AD neurons compared with those from age-matched nontransgenic (non-Tg) neurons. Here, using titrating with buthionine sulfoximine, an inhibitor of γ-glutamyl cysteine synthetase (GCL), we observed that GSH depletion increased neuronal death of 3xTg-AD cultured neurons at increasing rates across the age span, whereas non-Tg neurons were resistant to GSH depletion until old age. Remarkably, the rate of neuron loss with ROS did not increase in old age and was the same for both genotypes, which indicates that cognitive deficits in the AD model were not caused by ROS. Therefore, we targeted for neuroprotection activation of the redox sensitive transcription factor, nuclear erythroid-related factor 2 (Nrf2) by 18 alpha glycyrrhetinic acid to stimulate GSH synthesis through GCL. This balanced stimulation of a number of redox enzymes restored the lower levels of Nrf2 and GCL seen in 3xTg-AD neurons compared with those of non-Tg neurons and promoted translocation of Nrf2 to the nucleus. By combining the Nrf2 activator together with the NADH precursor, nicotinamide, we increased neuron survival against amyloid beta stress in an additive manner. These stress tests and neuroprotective treatments suggest that the redox environment is more important for neuron survival than ROS. The dual neuroprotective treatment with nicotinamide and an Nrf2 inducer indicates that these age-related and AD-related changes are reversible.

S[+] Apomorphine is a CNS penetrating activator of the Nrf2-ARE pathway with activity in mouse and patient fibroblast models of amyotrophic lateral sclerosis

Compelling evidence indicates that oxidative stress contributes to motor neuron injury in amyotrophic lateral sclerosis (ALS), but antioxidant therapies have not yet achieved therapeutic benefit in the clinic. The nuclear erythroid 2-related-factor 2 (Nrf2) transcription factor is a key regulator of an important neuroprotective response by driving the expression of multiple cytoprotective genes via its interaction with the antioxidant response element (ARE). Dysregulation of the Nrf2-ARE system has been identified in ALS models and human disease. Taking the Nrf2-ARE pathway as an attractive therapeutic target for neuroprotection in ALS, we aimed to identify CNS penetrating, small molecule activators of Nrf2-mediated transcription in a library of 2000 drugs and natural products. Compounds were screened extensively for Nrf2 activation, and antioxidant and neuroprotective properties in vitro. S[+]-Apomorphine, a receptor-inactive enantiomer of the clinically approved dopamine-receptor agonist (R[-]-apomorphine), was identified as a nontoxic Nrf2 activating molecule. In vivo S[+]-apomorphine demonstrated CNS penetrance, Nrf2 induction, and significant attenuation of motor dysfunction in the SOD1(G93A) transgenic mouse model of ALS. S[+]-apomorphine also reduced pathological oxidative stress and improved survival following an oxidative insult in fibroblasts from ALS patients. This molecule emerges as a promising candidate for evaluation as a potential neuroprotective agent in ALS patients in the clinic.

SOD1 and DJ-1 converge at Nrf2 pathway: a clue for antioxidant therapeutic potential in neurodegeneration

Neurodegenerative diseases share diverse pathological features and among these oxidative stress (OS) plays a leading role. Impaired activity and reduced expression of antioxidant proteins have been reported as common events in several aging-associated disorders. In this review paper, we first provide an overview of the involvement of reactive oxygen species- (ROS-) induced oxidative damage in Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). Subsequently, we focus on DJ-1 and SOD1 proteins, which are involved in PD and ALS and also exert a prominent role in the interaction between redox homeostasis and neurodegeneration. Interestingly, recent studies demonstrated that DJ-1 and SOD1 are both tightly connected with Nrf2 protein, a transcriptional factor and master regulator of the expression of many antioxidant/detoxification genes. Nrf2 is emerging as a key neuroprotective protein in neurodegenerative diseases, since it helps neuronal cells to cope with toxic insults and OS. We herein summarize the recent literature providing a detailed picture of the promising therapeutic efficacy of Nrf2 natural and synthetic inducers as disease-modifying molecules for the treatment of neurodegenerative diseases.

The modest impact of transcription factor Nrf2 on the course of disease in an ALS animal model

Oxidative stress is associated with the pathogenesis of amyotrophic lateral sclerosis (ALS). Nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway is one of the major cellular defense mechanisms against oxidative stress. However, the role of Nrf2-mediated neuroprotection (antioxidant defense) in the disease development of ALS remains unclear. To further investigate the role of Nrf2 in ALS, we genetically eliminate the Nrf2 gene from SOD1-G93A mice, a commonly used ALS mouse model, by generating a double mutant (Nrf2-/- SOD1-G93A mice). We found that it only had a modest impact on the course of disease by knocking out Nrf2 gene in these mice. Further studies demonstrated that, among previously known Nrf2-regulated phase II enzymes, only NAD(P)H: quinone oxidoreductase 1 induction was significantly affected by the elimination of Nrf2 gene in SOD1-G93A mice. Taken together, our data suggested that Nrf2 is not the sole mediator for the induction of antioxidant genes in SOD1-G93A mice, and Nrf2-mediated neuroprotection is not the key protective mechanism against neurodegeneration in those mice.

Recent progress in the discovery of small molecules for the treatment of amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder with few therapeutic options. While several gene mutations have been implicated in ALS, the exact cause of neuronal dysfunction is unknown and motor neurons of affected individuals display numerous cellular abnormalities. Ongoing efforts to develop novel ALS treatments involve the identification of small molecules targeting specific mechanisms of neuronal pathology, including glutamate excitotoxicity, mutant protein aggregation, endoplasmic reticulum (ER) stress, loss of trophic factors, oxidative stress, or neuroinflammation. Herein, we review recent advances in the discovery and preclinical characterization of lead compounds that may ultimately provide novel drugs to treat patients suffering from ALS.

The Nrf2-ARE pathway: a valuable therapeutic target for the treatment of neurodegenerative diseases

Modulation of NF-E2 related factor 2 (Nrf2) has been shown in several neurodegenerative disorders. The overexpression of Nrf2 has become a potential therapeutic avenue for various neurodegenerative disorders such as Parkinson, Amyotrophic lateral sclerosis, and Alzheimer's disease. The expression of phase II detoxification enzymes is governed by the cis-acting regulatory element known as antioxidant response element (ARE). The transcription factor Nrf2 binds to ARE thereby transcribing multitude of antioxidant genes. Keap1, a culin 3-based E3 ligase that targets Nrf2 for degradation, sequesters Nrf2 in cytoplasm. Disruption of Keap1-Nrf2 interaction or genetic overexpression of Nrf2 can increase the endogenous antioxidant capacity of the brain thereby rendering protection against oxidative stress in neurodegenerative disorders. This review primarily focuses on recent patents that target Nrf2 overexpression as a promising therapeutic strategy for the treatment of neurodegenerative disorders.

Targeting Nrf2-mediated gene transcription by extremely potent synthetic triterpenoids attenuate dopaminergic neurotoxicity in the MPTP mouse model of Parkinson's disease

Although the etiology of Parkinson's disease (PD) remains unclear, ample empirical evidence suggests that oxidative stress is a major player in the development of PD and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity. Nuclear factor E2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that upregulates a battery of antioxidant response element (ARE)-driven antioxidative and cytoprotective genes that defend against oxidative stress.

AIMS

We evaluated whether the strategy of activation of Nrf2 and its downstream network of cytoprotective genes with small molecule synthetic triterpenoids (TP) attenuate MPTP-induced PD in mice.

RESULTS

We show that synthetic TP are thus far the most potent and direct activators of the Nrf2 pathway using a novel Neh2-luciferase reporter. They upregulate several cytoprotective genes, including those involved in glutathione biosynthesis in vitro. Oral administration of TP that were structurally modified to penetrate the brain-induced messenger RNA and protein levels for a battery of Nrf2-dependent cytoprotective genes reduced MPTP-induced oxidative stress and inflammation, and ameliorated dopaminergic neurotoxicity in mice. The neuroprotective effect of these TP against MPTP neurotoxicity was dependent on Nrf2, since treatment with TP in Nrf2 knockout mice failed to block against MPTP neurotoxicity and induce Nrf2-dependent cytoprotective genes.

INNOVATION

Extremely potent synthetic TP that are direct activators of the Nrf2 pathway block dopaminergic neurodegeneration in the MPTP mouse model of PD.

CONCLUSION

Our results indicate that activation of Nrf2/antioxidant response element (ARE) signaling by synthetic TP is directly associated with their neuroprotective effects against MPTP neurotoxicity and suggest that targeting the Nrf2/ARE pathway is a promising approach for therapeutic intervention in PD.

Effects of major ozonated autohemotherapy in the treatment of dry age related macular degeneration: a randomized controlled clinical study

AIM

To evaluate the effect of systemic ozonated major autohaemotherapy (O(3)-AHT) in patients affected by dry age related macular degeneration (AMD).

METHODS

This study was a randomized, controlled clinical study. One hundred and forty patients with the diagnosis of AMD in both eyes, with the study eye presenting dry AMD and soft drusen, were randomly assigned in a 1:1 ratio to either receive 27 major ozonated autohemotherapy treatments during 12-month period, or a standardized multi-vitamin therapy. Primary outcome was the change in best corrected visual acuity (mean logMar change) between the baseline and 6 and 12 months, end point of the study. In addition, to investigate the safety of prolonged ozonated autohaemotherapy, we measured the routine haematochemical parameters and biochemical oxidative stress values at baseline and after 12 months treatment time.

RESULTS

The mean baseline best corrected visual acuity in study eyes was 0.36 in the treatment group and 0.38 in the control group (difference not statistically significant). At the primary endpoint, 6 months post-baseline, the mean logMAR change in the treated group improved by 0.1 and the values of the control group at the same time impaired by 0.2 respect to the baseline. Four percent and twenty-five percent of eyes in the group treated with O(3)-AHT gained 1 or more lines after 6 and 12 months respectively compared to 0% in the eyes which received no treatment (P<0.05 at 12 months). None of the treated patients experienced a loss in visual acuity in their study eye at 6 and 12 months, compared to 16% and 40 % of patients in the control group who lost 2 lines or more at 6 months and 12 months respectively (P<0.05 treated vs control group)). Major ozonated autohemotherapy was shown to be safe and well- tolerated by the patients. Moreover, the haematochemical parameters showed a decrease in the Reactive Oxygen Metabolites (300±10.1 UCARR at 12 months compared to a baseline value of 380±10.4 UCARR, P<0.05) and an increase in Biological Antioxidant Potential plasma values (2100±34.8 micromoles/ C vitamin after 12 months compared to the baseline value of 1610±36.2, P<0.05) in the treated patients when compared to the control group. This data suggests that major ozonated autohaemotherapy may exert a role in reducing oxidative stress by endogenously stimulating the production of antioxidant molecules.

CONCLUSION

The results of this study suggests that major ozonated autohaemotherapy could be a safe and effective therapeutic option for high-risk patients with dry AMD, and that a series of such treatments could improve the natural course of AMD.

Impaired hypoxic sensor Siah-1, PHD3, and FIH system in spinal motor neurons of an amyotrophic lateral sclerosis mouse model

We recently reported spinal blood flow-metabolism uncoupling in the Cu/Zn-superoxide dismutase 1 (SOD1)-transgenic (Tg) mouse model of amyotrophic lateral sclerosis (ALS), suggesting relative hypoxia in the spinal cord. However, the hypoxic stress sensor pathway in ALS has not been well studied. In the present work, we examined the temporal and spatial changes of hypoxic stress sensor proteins (Siah-1, PHD3, and FIH) following motor neuron (MN) degeneration in the spinal cord of normoxic ALS mice. The expression of Siah-1 and PHD3 proteins progressively increased in the surrounding glial cells of presymptomatic Tg mice (10 weeks, 10 weeks) compared with the large MN of the anterior horn. In contrast, a significant reduction in Siah-1 and PHD3 protein expression was evident in end-stage ALS mice (18 weeks, 18 weeks). Double-immunofluorescence analysis revealed PHD3 plus Siah-1 double-positive cells in the surrounding glia of symptomatic Tg mice (14-18 weeks), with no change in the large MNs. In contrast, FIH protein expression decreased in the surrounding glial cells of Tg mice at end-stage ALS (18 weeks). The present study suggests a partial loss in the neuroprotective response of spinal MNs in ALS results from a relative hypoxia through the Siah-1, PHD3, and FIH system under normoxic conditions. This response could be an important mechanism of neurodegeneration in ALS.

Discovery of inhibitors of microglial neurotoxicity acting through multiple mechanisms using a stem-cell-based phenotypic assay

Stem cells, through their ability to both self-renew and differentiate, can produce a virtually limitless supply of specialized cells that behave comparably to primary cells. We took advantage of this property to develop an assay for small-molecule-based neuroprotection using stem-cell-derived motor neurons and astrocytes, together with activated microglia as a stress paradigm. Here, we report on the discovery of hit compounds from a screen of more than 10,000 small molecules. These compounds act through diverse pathways, including the inhibition of nitric oxide production by microglia, activation of the Nrf2 pathway in microglia and astrocytes, and direct protection of neurons from nitric-oxide-induced degeneration. We confirm the activity of these compounds using human neurons. Because microglial cells are activated in many neurological disorders, our hit compounds could be ideal starting points for the development of new drugs to treat various neurodegenerative and neurological diseases.

Targeting of Nrf2 induces DNA damage signaling and protects colonic epithelial cells from ionizing radiation

Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a key transcriptional regulator for antioxidant and anti-inflammation enzymes that binds to its endogenous inhibitor protein, Kelch-like ECH (erythroid cell-derived protein with CNC homology)-associated protein 1, in the cytoplasm under normal conditions. Various endogenous or environmental oxidative stresses, such as ionizing radiation (IR), can disrupt the Nrf2-Kelch-like ECH-associated protein 1 complex. This allows Nrf2 to translocate from the cytoplasm into the nucleus to induce transcription of heme oxygenase-1 and other cytoprotective enzymes through binding to antioxidant responsive elements. However, how Nrf2 protects cells from IR-induced damage remains unclear. Here, we report that Nrf2 activation by the synthetic triterpenoids, bardoxolone methyl (BARD) and 2-cyano-3,12-dioxooleana-1,9 (11)-dien-28-oic acid-ethyl amide, protects colonic epithelial cells against IR-induced damage, in part, by enhancing signaling of the DNA damage response. Pretreatment with BARD reduced the frequency of both G1 and S/G2 chromosome aberrations and enhanced the disappearance of repairosomes (C-terminal binding protein interacting protein, Rad51, and p53 binding protein-1 foci) after IR. BARD protected cells from IR toxicity in a Nrf2-dependent manner. The p53 binding protein-1 promoter contains three antioxidant responsive elements in which Nrf2 directly binds following BARD treatment. In addition, 2-cyano-3,12-dioxooleana-1,9 (11)-dien-28-oic acid-ethyl amide provided before exposure to a lethal dose of whole-body irradiation protected WT mice from DNA damage and acute gastrointestinal toxicity, which resulted in improved overall survival. These results demonstrate that Nrf2 activation by synthetic triterpenoids is a promising candidate target to protect the gastrointestinal tract against acute IR in vitro and in vivo.

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.

Nrf2/ARE Signaling Pathway: Key Mediator in Oxidative Stress and Potential Therapeutic Target in ALS

Nrf2 (nuclear erythroid 2-related factor 2) is a basic region leucine-zipper transcription factor which binds to the antioxidant response element (ARE) and thereby regulates the expression of a large battery of genes involved in the cellular antioxidant and anti-inflammatory defence as well as mitochondrial protection. As oxidative stress, inflammation and mitochondrial dysfunctions have been identified as important pathomechanisms in amyotrophic lateral sclerosis (ALS), this signaling cascade has gained interest both with respect to ALS pathogenesis and therapy. Nrf2 and Keap1 expressions are reduced in motor neurons in postmortem ALS tissue. Nrf2-activating compounds have shown therapeutic efficacy in the ALS mouse model and other neurodegenerative disease models. Alterations in Nrf2 and Keap1 expression and dysregulation of the Nrf2/ARE signalling program could contribute to the chronic motor neuron degeneration in ALS and other neurodegenerative diseases. Therefore, Nrf2 emerges as a key neuroprotective molecule in neurodegenerative diseases. Our recent studies strongly support that the Nrf2/ARE signalling pathway is an important mediator of neuroprotection and therefore represents a promising target for development of novel therapies against ALS, Parkinson's disease (PD), Huntington's disease (HD), and Alzheimer's disease (AD).

Synthetic oleanane triterpenoids: multifunctional drugs with a broad range of applications for prevention and treatment of chronic disease

We review the rationale for the use of synthetic oleanane triterpenoids (SOs) for prevention and treatment of disease, as well as extensive biological data on this topic resulting from both cell culture and in vivo studies. Emphasis is placed on understanding mechanisms of action. SOs are noncytotoxic drugs with an excellent safety profile. Several hundred SOs have now been synthesized and in vitro have been shown to: 1) suppress inflammation and oxidative stress and therefore be cytoprotective, especially at low nanomolar doses, 2) induce differentiation, and 3) block cell proliferation and induce apoptosis at higher micromolar doses. Animal data on the use of SOs in neurodegenerative diseases and in diseases of the eye, lung, cardiovascular system, liver, gastrointestinal tract, and kidney, as well as in cancer and in metabolic and inflammatory/autoimmune disorders, are reviewed. The importance of the cytoprotective Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1/nuclear factor (erythroid-derived 2)-like 2/antioxidant response element (Keap1/Nrf2/ARE) pathway as a mechanism of action is explained, but interactions with peroxisome proliferator-activated receptor γ (PARPγ), inhibitor of nuclear factor-κB kinase complex (IKK), janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT), human epidermal growth factor receptor 2 (HER2)/ErbB2/neu, phosphatase and tensin homolog (PTEN), the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway, mammalian target of rapamycin (mTOR), and the thiol proteome are also described. In these interactions, Michael addition of SOs to reactive cysteine residues in specific molecular targets triggers biological activity. Ultimately, SOs are multifunctional drugs that regulate the activity of entire networks. Recent progress in the earliest clinical trials with 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) methyl ester (bardoxolone methyl) is also summarized.

Impaired response of hypoxic sensor protein HIF-1α and its downstream proteins in the spinal motor neurons of ALS model mice

We have recently reported spinal blood flow-metabolism uncoupling in an amyotrophic lateral sclerosis (ALS) animal model using Cu/Zn-superoxide dismutase 1 (SOD1)-transgenic (Tg) mice, suggesting a relative hypoxia in the spinal cord. However, the hypoxic stress sensor pathway has not been well studied in ALS. Here, we examined temporal and spatial changes of the hypoxic stress sensor proteins HIF-1α and its downstream proteins (VEGF, HO-1, and EPO) during the normoxiccourse of motor neuron (MN) degeneration in the spinal cord of these ALS model mice. We found that HIF-1α protein expression progressively increased both in the anterior large MNs and the surrounding glial cells in Tg mice from early symptomatic 14 week (W) and end stage 18 W. Double immunofluorescence analysis revealed that HIF-1α, plus GFAP and Iba-1 double-positive surrounding glial cells, progressively increased from 14 W to 18 W, although the immunohistochemistry in large MNs did not change. Expression levels of VEGF and HO-1 also showed a progressive increase but were significant only in the surrounding glial cells at 18 W. In contrast, EPO protein expression was decreased in the surrounding glial cells of Tg mice at 18 W. Because HIF1-α serves as an important mediator of the hypoxic response, these findings indicate that MNs lack the neuroprotective response to hypoxic stress through the HIF-1α system, which could be an important mechanism of neurodegeneration in ALS.

NRF2 and cancer: the good, the bad and the importance of context

Many studies of chemopreventive drugs have suggested that their beneficial effects on suppression of carcinogenesis and many other chronic diseases are mediated through activation of the transcription factor NFE2-related factor 2 (NRF2). More recently, genetic analyses of human tumours have indicated that NRF2 may conversely be oncogenic and cause resistance to chemotherapy. It is therefore controversial whether the activation, or alternatively the inhibition, of NRF2 is a useful strategy for the prevention or treatment of cancer. This Opinion article aims to rationalize these conflicting perspectives by critiquing the context dependence of NRF2 functions and the experimental methods behind these conflicting data.