Small molecule modulators of antioxidant response pathway

The Role of NRF2 in Trinucleotide Repeat Expansion Disorders

Trinucleotide repeat expansion disorders, a diverse group of neurodegenerative diseases, are caused by abnormal expansions within specific genes. These expansions trigger a cascade of cellular damage, including protein aggregation and abnormal RNA binding. A key contributor to this damage is oxidative stress, an imbalance of reactive oxygen species that harms cellular components. This review explores the interplay between oxidative stress and the NRF2 pathway in these disorders. NRF2 acts as the master regulator of the cellular antioxidant response, orchestrating the expression of enzymes that combat oxidative stress. Trinucleotide repeat expansion disorders often exhibit impaired NRF2 signaling, resulting in inadequate responses to excessive ROS production. NRF2 activation has been shown to upregulate antioxidative gene expression, effectively alleviating oxidative stress damage. NRF2 activators, such as omaveloxolone, vatiquinone, curcumin, sulforaphane, dimethyl fumarate, and resveratrol, demonstrate neuroprotective effects by reducing oxidative stress in experimental cell and animal models of these diseases. However, translating these findings into successful clinical applications requires further research. In this article, we review the literature supporting the role of NRF2 in the pathogenesis of these diseases and the potential therapeutics of NRF2 activators.

Indole-3-carbinol ameliorates ovarian damage in female old mice through Nrf2/HO-1 pathway activation

Ovarian aging leads to infertility and birth defects. We aimed to clarify the role of Indole-3-carbinol (I3C) in resistance to oxidative stress, apoptosis, and fibrosis in ovarian aging. I3C was administered via intraperitoneal injection for 3 weeks in young or old mice. Immunohistochemistry; Masson, Sirius red, and TUNEL staining; follicle counting; estrous cycle analysis; and Western blotting were used for validating the protective effect of I3C against ovarian senescence. Human granulosa-like tumor cell line and primary granulosa cells were used for in vitro assay. The results indicated that I3C inhibited ovarian fibrosis and apoptosis while increasing the number of primordial follicles. Mechanistic studies have shown that I3C promoted the nuclear translocation of nuclear factor-erythroid 2-related factor (Nrf2) and upregulated the expression of heme oxygenase 1 (HO-1). Additionally, I3C increased cell viability and decreased lactate dehydrogenase, malondialdehyde, reactive oxygen species and JC-1 levels. Furthermore, the antioxidant effect of I3C was found to be dependent on the activation of Nrf2 and HO-1, as demonstrated by the disappearance of the effect upon inhibition of Nrf2 expression. In conclusion, I3C can alleviate the ovarian damage caused by aging and may be a protective agent to delay ovarian aging.

Age-Dependent Changes in Nrf2/Keap1 and Target Antioxidant Protein Expression Correlate to Lipoxidative Adducts, and Are Modulated by Dietary N-3 LCPUFA in the Hippocampus of Mice

The brain has a high metabolism rate that may generate reactive oxygen and nitrogen species. Consequently, nerve cells require highly efficient antioxidant defenses in order to prevent a condition of deleterious oxidative stress. This is particularly relevant in the hippocampus, a highly complex cerebral area involved in processing superior cognitive functions. Most current evidence points to hippocampal oxidative damage as a causal effect for neurodegenerative disorders, especially Alzheimer's disease. Nuclear factor erythroid-2-related factor 2/Kelch-like ECH-associated protein 1 (Nrf2/Keap1) is a master key for the transcriptional regulation of antioxidant and detoxifying systems. It is ubiquitously expressed in brain areas, mainly supporting glial cells. In the present study, we have analyzed the relationships between Nrf2 and Keap1 isoforms in hippocampal tissue in response to aging and dietary long-chain polyunsaturated fatty acids (LCPUFA) supplementation. The possible involvement of lipoxidative and nitrosative by-products in the dynamics of the Nrf2/Keap1 complex was examined though determination of protein adducts, namely malondialdehyde (MDA), 4-hydroxynonenal (HNE), and 3-nitro-tyrosine (NTyr) under basal conditions. The results were correlated to the expression of target proteins heme-oxygenase-1 (HO-1) and glutathione peroxidase 4 (GPx4), whose expressions are known to be regulated by Nrf2/Keap1 signaling activation. All variables in this study were obtained simultaneously from the same preparations, allowing multivariate approaches. The results demonstrate a complex modification of the protein expression patterns together with the formation of adducts in response to aging and diet supplementation. Both parameters exhibited a strong interaction. Noticeably, LCPUFA supplementation to aged animals restored the Nrf2/Keap1/target protein patterns to the status observed in young animals, therefore driving a "rejuvenation" of hippocampal antioxidant defense.

Structural modification of C2-substituents on 1,4-bis(arylsulfonamido)benzene or naphthalene-N,N'-diacetic acid derivatives as potent inhibitors of the Keap1-Nrf2 protein-protein interaction

The Keap1-Nrf2-ARE signaling pathway is an attractive therapeutic target for the prevention and treatment of oxidative stress-associated diseases by activating the cellular expression of cytoprotective enzymes and proteins. Small molecule inhibitors can directly disrupt the Keap1-Nrf2 protein-protein interaction (PPI), resulting in elevated levels of Nrf2 protein and subsequent stimulation of related antioxidant responses. Previously, we found that 1,4-bis(arylsulfonamido)benzene or naphthalene-N,N'-diacetic acid derivatives with an ether type C2-substituent on the benzene or naphthalene core exhibited potent inhibitory activities with IC50's in the submicromolar or nanomolar range. We here describe a more detailed structure-activity relationship study around the C2 substituents containing various polar linkers shedding new insight on their binding interactions with the Keap1 Kelch domain. The key observation from our findings is that the substituents at the C2-position of the benzene or naphthalene scaffold impact their inhibitory potencies in biochemical assays as well as activities in cell culture. The biochemical FP and TR-FRET assays revealed that the naphthalene derivatives 17b and 18 with an additional carboxylate at the C2 were the most active inhibitors against Keap1-Nrf2 PPI. In the cell-based assay, the two compounds were shown to be potent Nrf2 activators of the transcription of the Nrf2-dependent genes, such as HMOX2, GSTM3, and NQO1.

Nrf2 differentially regulates osteoclast and osteoblast differentiation for bone homeostasis

Nuclear factor erythroid-derived factor 2-related factor 2 (Nrf2) is a master regulator of antioxidant response and protects cells from excessive oxidative stress. Nrf2 emerges as a prospective therapeutic target for metabolic bone disorders, in which the balance between osteoblastic bone formation and osteoclastic bone resorption is disrupted. However, the molecular mechanism through which Nrf2 modulates bone homeostasis remains unclear. In this study, we compared the differences in Nrf2-mediated antioxidant response and ROS regulation in osteoblasts and osteoclasts, both in vitro and in vivo. Findings indicated a close connection between the Nrf2 expression and its related antioxidant response with osteoclasts than osteoblasts. We next pharmacologically manipulated the Nrf2-mediated antioxidant response during osteoclast or osteoblast differentiation. Nrf2 inhibition enhanced osteoclastogenesis, while its activation suppressed it. In contrast, osteogenesis decreased irrespective of whether Nrf2 was inhibited or activated. These findings highlight the distinct ways in which the Nrf2-mediated antioxidant response regulates osteoclast and osteoblast differentiation, thereby contributing to the development of Nrf2 targeted therapies for metabolic bone diseases.

Dietary Polyphenols Remodel DNA Methylation Patterns of NRF2 in Chronic Disease

The nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor crucial in regulating cellular homeostasis and apoptosis. The NRF2 gene has been implicated in various biological activities, including antioxidant, anti-inflammatory, and anticancer properties. NRF2 can be regulated genetically and epigenetically at the transcriptional, post-transcriptional, and translational levels. Although DNA methylation is one of the critical biological processes vital for gene expression, sometimes, anomalous methylation patterns result in the dysregulation of genes and consequent diseases and disorders. Several studies have reported promoter hypermethylation downregulated NRF2 expression and its downstream targets. In contrast to the unalterable nature of genetic patterns, epigenetic changes can be reversed, opening up new possibilities in developing therapies for various metabolic disorders and diseases. This review discusses the current state of the NRF2-mediated antioxidative and chemopreventive activities of several natural phytochemicals, including sulforaphane, resveratrol, curcumin, luteolin, corosolic acid, apigenin, and most other compounds that have been found to activate NRF2. This epigenetic reversal of hypermethylated NRF2 states provides new opportunities for research into dietary phytochemistry that affects the human epigenome and the possibility for cutting-edge approaches to target NRF2-mediated signaling to prevent chronic disorders.

Nrf2: a dark horse in doxorubicin-induced cardiotoxicity

Being a broad-spectrum anticancer drug, doxorubicin is indispensable for clinical treatment. Unexpectedly, its cardiotoxic side effects have proven to be a formidable obstacle. Numerous studies are currently devoted to elucidating the pathological mechanisms underlying doxorubicin-induced cardiotoxicity. Nrf2 has always played a crucial role in oxidative stress, but numerous studies have demonstrated that it also plays a vital part in pathological mechanisms like cell death and inflammation. Numerous studies on the pathological mechanisms associated with doxorubicin-induced cardiotoxicity demonstrate this. Several clinical drugs, natural and synthetic compounds, as well as small molecule RNAs have been demonstrated to prevent doxorubicin-induced cardiotoxicity by activating Nrf2. Consequently, this study emphasizes the introduction of Nrf2, discusses the role of Nrf2 in doxorubicin-induced cardiotoxicity, and concludes with a summary of the therapeutic modalities targeting Nrf2 to ameliorate doxorubicin-induced cardiotoxicity, highlighting the potential value of Nrf2 in doxorubicin-induced cardiotoxicity.

Optimization of 3-aminotetrahydrothiophene 1,1-dioxides with improved potency and efficacy as non-electrophilic antioxidant response element (ARE) activators

Activating NRF2-driven transcription with non-electrophilic small molecules represents an attractive strategy to therapeutically target disease states associated with oxidative stress and inflammation. In this study, we describe a campaign to optimize the potency and efficacy of a previously identified bis-sulfone based non-electrophilic ARE activator 2. This work identifies the efficacious analog 17, a compound with a non-cytotoxic profile in IMR32 cells, as well as ARE activators 18 and 22, analogs with improved cellular potency. In silico drug-likeness prediction suggested the optimized bis-sulfones 17, 18, and 22 will likely be of pharmacological utility.

Humulus lupulus L. extract and its active constituent xanthohumol attenuate oxidative stress and nerve injury induced by iron overload via activating AKT/GSK3β and Nrf2/NQO1 pathways

Hops, the dried female clusters from Humulus lupulus L., have traditionally been used as folk medicines for treating insomnia, neuralgia, and menopausal disorders. However, its pharmacological action on iron overload induced nerve damage has not been investigated. This study aims to evaluate the protective effects of hops extract (HLE) and its active constituent xanthohumol (XAN) on nerve injury induced by iron overload in vivo and in vitro, and to explore its underlying mechanism. The results showed that HLE and XAN significantly improved the memory impairment of iron overload mice, mainly manifested as shortened latency time, increased crossing platform times and spontaneous alternation ratio, and increased the expression of related proteins. Additionally, HLE and XAN significantly increased superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) activities, and remarkably decreased malondialdehyde (MDA) level in hippocampus. Also, HLE and XAN apparently reduced reactive oxygen species (ROS) content of PC12 cells induced by iron dextran (ID), and improved the oxidative stress level. Moreover, HLE and XAN significantly upregulated the expression of nuclear factor E2-related factor (Nrf2), NAD(P)H quinone oxidoreductase (NQO1), heme oxygenase-1 (HO-1), SOD, phosphorylated AKT (p-AKT), and phosphorylated GSK3β (p-GSK3β) both in hippocampus and PC12 cells. These findings demonstrated the protective effect of HLE and XAN against iron-induced memory impairment, which is attributed to its antioxidant profile by activation of AKT/GSK3β and Nrf2/NQO1 pathways. Also, it was suggested that hops could be a potential candidate for iron overload-related neurological diseases treatment.

Role of Nrf2 in aging, Alzheimer's and other neurodegenerative diseases

Nuclear Factor-Erythroid Factor 2 (Nrf2) is an important transcription factor that regulates the expression of large number of genes in healthy and disease states. Nrf2 is made up of 605 amino acids and contains 7 conserved regions known as Nrf2-ECH homology domains. Nrf2 regulates the expression of several key components of oxidative stress, mitochondrial biogenesis, mitophagy, autophagy and mitochondrial function in all organs of the human body, in the peripheral and central nervous systems. Mounting evidence also suggests that altered expression of Nrf2 is largely involved in aging, neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's diseases, Amyotrophic lateral sclerosis, Stroke, Multiple sclerosis and others. The purpose of this article is to detail the essential role of Nrf2 in oxidative stress, antioxidative defense, detoxification, inflammatory responses, transcription factors, proteasomal and autophagic/mitophagic degradation, and metabolism in aging and neurodegenerative diseases. This article also highlights the Nrf2 structural and functional activities in healthy and disease states, and also discusses the current status of Nrf2 research and therapeutic strategies to treat aging and neurodegenerative diseases.

Design, synthesis and evaluation of novel small molecules acting as Keap1-Nrf2 protein-protein interaction inhibitors

Direct interference with Kelch-like ECH-associated protein 1 (Keap1)-Nrf2 protein-protein interaction (PPI) has recently been introduced as an attractive approach to control life-threatening diseases like myocarditis. The present study aimed to investigate the potential application in myocarditis of a series of novel non-naphthalene derivatives as potential Keap1-Nrf2 PPI inhibitors. Our results indicated that the optimal compound K22 displayed the highest metabolic stability and showed notable Keap1-Nrf2 PPI inhibitory activities in vitro. K22 effectively triggered Nrf2 activation and increased the protein and mRNA expression of Nrf2-regulated genes in H9c2 cells. Moreover, pre-treatment with K22 was shown to mitigate LPS-induced damage to H9c2 cells, causing a marked decrease in the levels of inflammatory factors as well as reactive oxygen species (ROS). Furthermore, K22 was also shown to be non-mutagenic in the Ames test. Overall, our findings suggest that K22 may be a promising drug lead as a Keap1-Nrf2 PPI inhibitor for myocarditis treatment.

Exploring the target scope of KEAP1 E3 ligase-based PROTACs

Targeted protein degradation (TPD) uses small molecules to recruit E3 ubiquitin ligases into the proximity of proteins of interest, inducing ubiquitination-dependent degradation. A major bottleneck in the TPD field is the lack of accessible E3 ligase ligands for developing degraders. To expand the E3 ligase toolbox, we sought to convert the Kelch-like ECH-associated protein 1 (KEAP1) inhibitor KI696 into a recruitment handle for several targets. While we were able to generate KEAP1-recruiting degraders of BET family and murine focal adhesion kinase (FAK), we discovered that the target scope of KEAP1 was narrow, as targets easily degraded using a cereblon (CRBN)-recruiting degrader were refractory to KEAP1-mediated degradation. Linking the KEAP1-binding ligand to a CRBN-binding ligand resulted in a molecule that induced degradation of KEAP1 but not CRBN. In sum, we characterize tool compounds to explore KEAP1-mediated ubiquitination and delineate the challenges of exploiting new E3 ligases for generating bivalent degraders.

Roles of NRF2 in Fibrotic Diseases: From Mechanisms to Therapeutic Approaches

Fibrosis is a persistent inflammatory response that causes scarring and tissue sclerosis by stimulating myofibroblasts to create significant quantities of extracellular matrix protein deposits in the tissue. Oxidative stress has also been linked to the development of fibrosis in several studies. The nuclear erythroid 2-related factor 2 (NRF2) transcription factor controls the expression of several detoxification and antioxidant genes. By binding to antioxidant response elements, NRF2 is activated by oxidative or electrophilic stress and promotes its target genes, resulting in a protective effect on cells. NRF2 is essential for cell survival under oxidative stress conditions. This review describes Kelch-like epichlorohydrin-associated protein 1 (KEAP1)/NRF2 signaling mechanisms and presents recent research advances regarding NRF2 and its involvement in primary fibrotic lesions such as pulmonary fibrosis, hepatic fibrosis, myocardial fibrosis, and renal fibrosis. The related antioxidant substances and drugs are described, along with the mechanisms by which KEAP1/NRF2 regulation positively affects the therapeutic response. Finally, the therapeutic prospects and potential value of NRF2 in fibrosis are summarized. Further studies on NRF2 may provide novel therapeutic approaches for fibrosis.

Dimethyl Fumarate Ameliorates Doxorubicin-Induced Cardiotoxicity By Activating the Nrf2 Pathway

Doxorubicin (DOX) is limited in clinical application because of its cardiotoxicity. Oxidative stress and apoptosis are crucial in DOX-induced cardiac injury. Dimethyl fumarate (DMF) is an FDA-approved oral drug with powerful effects to reduce oxidative stress and apoptosis through the Nrf2 pathway. This study was aimed to determine whether DMF can protect against DOX-induced cardiac injury. We used both neonatal rat cardiomyocytes (NRCMs) in vitro and DOX-induced cardiac toxicity in vivo to explore the effects of DMF. The results showed that DMF significantly improved cell viability and morphology in NRCMs. In addition, DMF alleviated DOX-induced cardiac injury in rats, as evidenced by decreased CK-MB, LDH levels, improved survival rates, cardiac function, and pathological changes. Moreover, DMF significantly inhibited cardiac oxidative stress by reducing MDA levels and increasing GSH, SOD, and GSH-px levels. And DMF also inhibited DOX-induced cardiac apoptosis by modulating Bax, Bcl-2 and cleaved caspase-3 expression. Moreover, DMF exerted its protective effects against DOX by promoting Nrf2 nuclear translocation, which activated its downstream antioxidant gene Hmox1. Silencing of Nrf2 attenuated the protective effects of DMF in NRCMs as manifested by increased intracellular oxidative stress, elevated apoptosis levels, and decreased cell viability. In addition, DMF showed no protective effects on the viability of DOX-treated tumor cells, which suggested that DMF does not interfere with the antitumor effect of DOX in vitro. In conclusion, our data confirmed that DMF alleviated DOX-induced cardiotoxicity by regulating oxidative stress and apoptosis through the Nrf2 pathway. DMF may serve as a new candidate to alleviate DOX-related cardiotoxicity in the future.

Pectolinarigenin Induces Antioxidant Enzymes through Nrf2/ARE Pathway in HepG2 Cells

Pectolinarigenin (PG) and its glycoside pectolinarin (PN) were reported to have various health beneficial functions such as anti-inflammatory and anti-carcinogenic activities. It has also been reported that PG and PN have radical scavenging ability as direct antioxidant activity. However, the indirect antioxidant activity of PG and PN by inducing antioxidant enzymes in hepatocytes is not fully understood yet. In this study, we investigated whether PG and PN increase expression of antioxidant enzymes through the nuclear factor-erythroid-2-related factor 2 (Nrf2)-mediated pathway in human hepatoma HepG2 cells and the liver of male ICR mice. PG, but not PN, induced antioxidant enzymes, namely heme oxigenase-1, NAD(P)H:quinone oxidoreductase 1, and aldo-keto reductase family 1 member B10, in HepG2 cells. As for the induction mechanism of these enzymes, PG-induced nuclear accumulation of Nrf2 increased antioxidant response element (ARE)-mediated transcriptional activity and suppressed degradation of Nrf2 through modification of Kelch-like EXH-associated protein 1. Oral administration of PG also induced nuclear accumulation Nrf2 and expression of antioxidant enzymes in the liver of mice. Therefore, PG, but not PN, exhibits the indirect antioxidant activity by inducing antioxidant enzymes through the Nrf2/ARE pathway and may protect liver from oxidative stress.

Integrative Metabolomics, Proteomics and Transcriptomics Analysis Reveals Liver Toxicity of Mesoporous Silica Nanoparticles

As pharmaceutical excipients, mesoporous silica nanoparticles (MSNs) have attracted considerable concern based on potential risks to the public. The impact of MSNs on biochemical metabolism is poorly understood, and few studies have compared the effects of MSNs administered via different routes. To evaluate the hepatotoxicity of MSNs, metabolomics, proteomics and transcriptomic analyses were performed in mice after intravenous (20 mg/kg/d) or oral ad-ministration (200 mg/kg/d) of MSNs for 10 days. Intravenous injection induced significant hepatic injury based on pathological inspection and increased the levels of AST/ALT and the inflammatory factors IL-6, IL-1β and TNF-a. Omics data suggested intravenous administration of MSNs perturbed the following metabolites: succinate, hypoxanthine, GSSG, NADP+, NADPH and 6-phosphogluconic acid. In addition, increases in GPX, SOD3, G6PD, HK, and PFK at proteomic and transcriptomic levels suggested elevation of glycolysis and pentose phosphate pathway, synthesis of glutathione and nucleotides, and antioxidative pathway activity, whereas oxidative phosphorylation, TCA and mitochondrial energy metabolism were reduced. On the other hand, oral administration of MSNs disturbed inflammatory factors and metabolites of ribose-5-phosphate, 6-phosphogluconate, GSSG, and NADP+ associated with the pentose phosphate pathway, glutathione synthesis and oxidative stress albeit to a lesser extent than intravenous injection despite the administration of a ten-fold greater dose. Overall, systematic biological data suggested that intravenous injection of nanoparticles of pharmaceutical excipients substantially affected hepatic metabolism function and induced oxidative stress and inflammation, whereas oral administration exhibited milder effects compared with intravenous injection.

Nrf2/Keap1/ARE signaling: Towards specific regulation

The Nrf2 transcription factor governs the expression of hundreds genes involved in cell defense against oxidative stress, the hallmark of numerous diseases such as neurodegenerative, cardiovascular, some viral pathologies, diabetes and others. The main route for Nrf2 activity regulation is via interactions with the Keap1 protein. Under the normoxia the Keap1 binds the Nrf2 and targets it to the proteasomal degradation, while the Keap1 is regenerated. Upon oxidative stress the interactions between Nrf2 and Keap1 are interrupted and the Nrf2 activates the transcription of the protective genes. Currently, the Nrf2 system activation is considered as a powerful cytoprotective strategy for treatment of different pathologies, which pathogenesis relies on oxidative stress including viral diseases of pivotal importance such as COVID-19. The implementation of this strategy is accomplished mainly through the inactivation of the Keap1 "guardian" function. Two approaches are now developing: the Keap1 modification via electrophilic agents, which leads to the Nrf2 release, and direct interruption of the Nrf2:Keap1 protein-protein interactions (PPI). Because of theirs chemical structure, the Nrf2 electrophilic inducers could non-specifically interact with others cellular proteins leading to undesired effects. Whereas the non-electrophilic inhibitors of the Nrf2:Keap1 PPI could be more specific, thereby widening the therapeutic window.

Quercetin Hybrids—Synthesis, Spectral Characterization and Radical Scavenging Potential

New quercetin-based derivatives are synthesized in an easily accessible one-pot manner. The method is based on the reaction of quercetin with in situ formed electrophilic N-alkoxycarbonylazolium ions. The position of the newly formed C-C bond and structure were spectrally characterized by 1D, 2D 1H, 13C-NMR, IR, and MS analysis. Thus, in all cases, good regioselectivity in the C-8 position for the obtained products was demonstrated. The obtained compounds were evaluated for their DPPH and ABTS free radical scavenging activity and compared to natural compounds—quercetin and rutin.

Antioxidant response to severe hypoxia in Brandt's vole Lasiopodomys brandtii

The antioxidant defense system is essential for animals to cope with homeostasis disruption and overcome oxidative stress caused by adverse environmental conditions such as hypoxia. However, our understanding of how this system works in subterranean rodents remains limited. In this study, Brandt's vole Lasiopodomys brandtii was exposed to normoxia (21% O₂ ) or hypoxia (mild or severe hypoxia: 10% or 5% O₂ ) for 6 h. Changes in key enzymes of the classic enzymatic antioxidant system at both mRNA and enzyme activity levels, and tissue antioxidant levels of the low-molecular-weight antioxidant system were determined in brain, liver, and kidney. Transcript levels of the upstream regulator NF-E2-related factor 2 (Nrf2) were also measured. We found that the mRNA expression of Nrf2 and its downstream antioxidant enzyme genes in L. brandtii were relatively conserved in response to hypoxia in most tissues and genes tested, except in the liver. Hepatic Nrf2, Cu/Zn SOD, GPx1, and GPx3 levels were significantly upregulated in response to mild hypoxia, whereas Mn SOD level decreased significantly in severe hypoxia. Unmatched with changes at the RNA level, constitutively high and relatively stable antioxidant enzyme activities were maintained throughout. For the low-molecular-weight antioxidant system, an abrupt increase of cerebral ascorbic acid (AA) levels in hypoxia indicated a tissue-specific antioxidant response. Although hypoxia did not cause significant oxidative damage in most tissues tested, the significant decrease in antioxidant enzyme activities (GPX and GR) and increase in lipid peroxidation in the kidney suggest that prolonged hypoxia may pose a critical threat to this species.

Impaired antioxidant KEAP1-NRF2 system in amyotrophic lateral sclerosis: NRF2 activation as a potential therapeutic strategy

BACKGROUND

Oxidative stress (OS) is an imbalance between oxidant and antioxidant species and, together with other numerous pathological mechanisms, leads to the degeneration and death of motor neurons (MNs) in amyotrophic lateral sclerosis (ALS).

MAIN BODY

Two of the main players in the molecular and cellular response to OS are NRF2, the transcription nuclear factor erythroid 2-related factor 2, and its principal negative regulator, KEAP1, Kelch-like ECH (erythroid cell-derived protein with CNC homology)-associated protein 1. Here we first provide an overview of the structural organization, regulation, and critical role of the KEAP1-NRF2 system in counteracting OS, with a focus on its alteration in ALS. We then examine several compounds capable of promoting NRF2 activity thereby inducing cytoprotective effects, and which are currently in different stages of clinical development for many pathologies, including neurodegenerative diseases.

CONCLUSIONS

Although challenges associated with some of these compounds remain, important advances have been made in the development of safer and more effective drugs that could actually represent a breakthrough for fatal degenerative diseases such as ALS.

Novel Chalcone BDD-39 Mitigated Diabetic Nephropathy through the Activation of Nrf2/ARE Signaling

BACKGROUND

In this study, we investigated the Nrf2/ARE signaling pathway activating capacity of Biphenyl Diester Derivative-39 (BDD-39) in diabetic nephropathy in order to elucidate the mechanism surrounding its antidiabetic potential.

OBJECTIVES

Protein expressions of Nrf2, HO-1, NQO-1 and biomarkers of kidney fibrosis were executed after which mRNA levels of Nrf2, HO-1 and NQO-1 were estimated after creating the models following BBD-39 treatment.

METHODS

Type 2 diabetes model was established in mice with high-fat diet feeding combined with streptozocin intraperitoneal administration. The diabetic mice were then treated with BDD-39 (15, 45mg· kg-1· d-1, ig) or a positive control drug resveratrol (45mg· kg-1·d-1, ig) for 8 weeks. Staining techniques were used to investigate collagen deposition in the glomerulus of the renal cortex and also to investigate the expression and localization of Nrf2 and extracellular matrix (ECM) proteins (collagen IV and laminin) in vitro and in vivo. Furthermore, we studied the mechanism of action of BDD-39 using RNA-mediated Nrf2 silencing technique in mouse SV40 glomerular mesangial cells (SV40 GM cells).

RESULTS

We found that BDD-39 activates Nrf2/ARE signaling pathway, promotes Nrf2 nuclear translocation (Nrf2nuc/Nrf2cyt) and modulate prominent biomarkers of kidney fibrosis at the protein level. However, BDD-39 could not activate Nrf2/ARE signaling in RNA-mediated Nrf2-silenced HG-cultured SV40 GM cells.

CONCLUSION

Taken together, this study demonstrates for the first time that BDD-39 ameliorates experimental DN through attenuation of renal fibrosis progression and modulation of Nrf2/ARE signaling pathway.

A bioactive ligand-conjugated iridium(III) metal-based complex as a Keap1-Nrf2 protein-protein interaction inhibitor against acetaminophen-induced acute liver injury

Hepatotoxicity caused by an overdose of acetaminophen (APAP) is the leading reason for acute drug-related liver failure. Nuclear factor erythroid-2-related factor 2 (Nrf2) is a protein that helps to regulate redox homeostasis and coordinate stress responses via binding to the Kelch-like ECH-associated protein 1 (Keap1). Targeting the Keap1-Nrf2 interaction has recently emerged as a potential strategy to alleviate liver injury caused by APAP. Here, we designed and synthesized a number of iridium (III) and rhodium (III) complexes bearing ligands with reported activity against oxidative stress, which is associated with Nrf2 transcriptional activation. The iridium (III) complex 1 bearing a bioactive ligand 2,9-dimethyl-1,10-phenanthroline and 4-chloro-2-phenylquinoline, a derivative of the bioactive ligand 2-phenylquinoline, was identified as a direct small-molecule inhibitor of the Keap1–Nrf2 protein-protein interaction. 1 could stabilize Keap1 protein, upregulate HO-1 and NQO1, and promote Nrf2 nuclear translocation in normal liver cells. Moreover, 1 reversed APAP-induced liver damage by disrupting Keap1–Nrf2 interaction and without inducing organ damage and immunotoxicity in mice. Our study demonstrates the identification of a selective and efficacious antagonist of Keap1–Nrf2 interaction possessed good cellular permeability in cellulo and ideal pharmacokinetic parameters in vivo, and, more importantly, validates the feasibility of conjugating metal complexes with bioactive ligands to generate metal-based drug leads as non-toxic Keap1–Nrf2 interaction inhibitors for treating APAP-induced acute liver injury.

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1 reversed APAP-induced liver damage by disrupting Keap1–Nrf2 interaction without inducing organ damage or immunotoxicity.

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Complex 1 possessed good cellular permeability in cellulo and ideal pharmacokinetic parameters in vivo.

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Conjugating metal complexes with bioactive ligands opens a novel avenue for the treatment of APAP-induced liver damage.

Therapeutic effect of Keap1-Nrf2-ARE pathway-related drugs on age-related eye diseases through anti-oxidative stress

Age-related eye diseases, including cataract, glaucoma, diabetic retinopathy (DR), and age-related macular degeneration (AMD), are the leading causes of vision loss in the world. Several studies have shown that the occurrence and development of these diseases have an important relationship with oxidative stress in the eye. The Keap1-Nrf2-ARE pathway is a classical pathway that resists oxidative stress and inflammation in the body. This pathway is also active in the development of age-related eye diseases. A variety of drugs have been shown to treat age-related eye diseases through the Keap1-Nrf2-ARE (Kelch-like ECH-Associating protein 1- nuclear factor erythroid 2 related factor 2-antioxidant response element) pathway. This review describes the role of oxidative stress in the development of age-related eye diseases, the function and regulation of the Keap1-Nrf2-ARE pathway, and the therapeutic effects of drugs associated with this pathway on age-related eye diseases.

Harnessing the cardiovascular benefits of exercise: are Nrf2 activators useful?

The ability of physical activity to ameliorate cardiovascular disease and improve cardiovascular health is well accepted, but many aspects of the molecular mechanisms underlying these benefits are incompletely understood. Exercise increases the levels of reactive oxygen species (ROS) through various mechanisms. This triggers the activation of Nrf2, a redox-sensitive transcription factor activated by increases in oxidative stress. Activation of Nrf2 mitigates oxidative stress by increasing the nuclear transcription of many antioxidant genes while also mediating additional beneficial effects through the cytoprotective nature of Nrf2 signaling. Understanding the transcriptional patterns of Nrf2 caused by exercise can help in the design of pharmacological mimicry of the process in patients who are unable to exercise for various reasons.

Oxidative stress and redox signaling in CRPC progression: therapeutic potential of clinically-tested Nrf2-activators

Androgen deprivation therapy (ADT) is the mainstay regimen in patients with androgen-dependent prostate cancer (PCa). However, the selection of androgen-independent cancer cells leads to castrate resistant prostate cancer (CRPC). The aggressive phenotype of CRPC cells underscores the need to elucidate mechanisms and therapeutic strategies to suppress CRPC outgrowth. Despite ADT, the activation of androgen receptor (AR) transcription factor continues via crosstalk with parallel signaling pathways. Understanding of how these signaling cascades are initiated and amplified post-ADT is lacking. Hormone deprivation can increase oxidative stress and the resultant reactive oxygen species (ROS) may activate both AR and non-AR signaling. Moreover, ROS-induced inflammatory cytokines may further amplify these redox signaling pathways to augment AR function. However, clinical trials using ROS quenching small molecule antioxidants have not suppressed CRPC progression, suggesting that more potent and persistent suppression of redox signaling in CRPC cells will be needed. The transcription factor Nrf2 increases the expression of numerous antioxidant enzymes and downregulates the function of inflammatory transcription factors, e.g., nuclear factor kappa B. We documented that Nrf2 overexpression can suppress AR-mediated transcription in CRPC cell lines. Furthermore, two Nrf2 activating agents, sulforaphane (a phytochemical) and bardoxolone-methyl (a drug in clinical trial) suppress AR levels and sensitize CRPC cells to anti-androgens. These observations implicate the benefits of potent Nrf2-activators to suppress the lethal signaling cascades that lead to CRPC outgrowth. This review article will address the redox signaling networks that augment AR signaling during PCa progression to CRPC, and the possible utility of Nrf2-activating agents as an adjunct to ADT.

Discovery and SAR studies of 3-amino-4-(phenylsulfonyl)tetrahydrothiophene 1,1-dioxides as non-electrophilic antioxidant response element (ARE) activators

The transcription factor NRF2 controls resistance to oxidative insult and is thus a key therapeutic target for treating a number of disease states associated with oxidative stress and aging. We previously reported CBR-470-1, a bis-sulfone which activates NRF2 by increasing the levels of methylglyoxal, a metabolite that covalently modifies NRF2 repressor KEAP1. Here, we report the design, synthesis, and structure activity relationship of a series of bis-sulfones derived from this unexplored chemical template. We identify analogs with sub-micromolar potencies, 7f and 7g, as well as establish that efficacious NRF2 activation can be achieved by non-toxic analogs 7c, 7e, and 9, a key limitation with CBR-470-1. Further efforts to identify non-covalent NRF2 activators of this kind will likely provide new insight into revealing the role of central metabolism in cellular signaling.

Generation of potent Nrf2 activators via tuning the electrophilicity and steric hindrance of vinyl sulfones for neuroprotection

Oxidative stress is constantly involved in the etiopathogenesis of an ever-widening range of neurodegenerative diseases. As a consequence, effective repression of cellular oxidative stress to a redox homeostatic condition is a promising and feasible strategy to treat, or at least retard the progression of, such disorders. Nrf2, a primary orchestrator of cellular antioxidant response machine, is responsible for detoxifying and compensating for deleterious oxidative stress via transcriptional activation of a diverse array of antioxidant biomolecules. In the framework of our persistent interest in disclosing small molecules that interfere with cellular redox-regulating machinery, we report herein the synthesis, optimization, and biological assessment of 47 vinyl sulfone scaffold-bearing small molecules, most of which exhibit robust neuroprotective effect against H₂O₂-mediated lesions to PC12 cells. After initial screening, the most potent neuroprotective compounds 9b and 9c with marginal cytotoxicity were selected for the follow-up studies. Our results demonstrate that their neuroprotective effects are attributed to the up-regulation of a panel of antioxidant genes and corresponding gene products. Further mechanistic studies indicate that Nrf2 is indispensable for the cellular performances of 9b and 9c, arising from the fact that silence of Nrf2 gene drastically nullifies their protective action. Taken together, 9b and 9c discovered in this work merit further development as neuroprotective candidates for the treatment of oxidative stress-mediated pathological conditions.

Exposure of Rats to Multiple Oral Doses of Dichloroacetate Results in Upregulation of Hepatic Glutathione Transferases and NAD(P)H Dehydrogenase [Quinone] 1

Dichloroacetate (DCA) is an investigational drug that is used in the treatment of various congenital and acquired disorders of energy metabolism. Although DCA is generally well tolerated, some patients experience peripheral neuropathy, a side effect more common in adults than children. Repetitive DCA dosing causes downregulation of its metabolizing enzyme, glutathione transferase zeta 1 (GSTZ1), which is also critical in the detoxification of maleylacetoacetate and maleylacetone. GSTZ1 (-/-) knockout mice show upregulation of glutathione transferases (GSTs) and antioxidant enzymes as well as an increase in the ratio of oxidized glutathione (GSSG) to reduced glutathione (GSH), suggesting GSTZ1 deficiency causes oxidative stress. We hypothesized that DCA-mediated depletion of GSTZ1 causes oxidative stress and used the rat to examine induction of GSTs and antioxidant enzymes after repeated DCA exposure. We determined the expression of alpha, mu, pi, and omega class GSTs, NAD(P)H dehydrogenase [quinone] 1 (NQO1), gamma-glutamylcysteine ligase complex (GCLC), and glutathione synthetase (GSS). GSH and GSSG levels were measured by liquid chromatography-tandem mass spectrometry. Enzyme activity was measured in hepatic cytosol using 1-chloro-2,4-dinitrobenzene, 1,2-dichloro-4-nitrobenzene, and 2,6-dichloroindophenol as substrates. In comparison with acetate-treated controls, DCA dosing increased the relative expression of GSTA1/A2 irrespective of rodent age, whereas only adults displayed higher levels of GSTM1 and GSTO1. NQO1 expression and activity were higher in juveniles after DCA dosing. GSH concentrations were increased by DCA in adults, but the GSH:GSSG ratio was not changed. Levels of GCLC and GSS were higher and lower, respectively, in adults treated with DCA. We conclude that DCA-mediated depletion of GSTZ1 causes oxidative stress and promotes the induction of antioxidant enzymes that may vary between age groups. SIGNIFICANCE STATEMENT: Treatment with the investigational drug, dichloroacetate (DCA), results in loss of glutathione transferase zeta 1 (GSTZ1) and subsequent increases in body burden of the electrophilic tyrosine metabolites, maleylacetoacetate and maleylacetone. Loss of GSTZ1 in genetically modified mice is associated with induction of glutathione transferases and alteration of the ratio of oxidized to reduced glutathione. Therefore, we determined whether pharmacological depletion of GSTZ1 through repeat administration of DCA produced similar changes in the liver, which could affect responses to other drugs and toxicants.

Primary Amine Modified Gold Nanodots Regulate Macrophage Function and Antioxidant Response: Potential Therapeutics Targeting of Nrf2

BACKGROUND

Gold nanoparticles with high biocompatibility and immunomodulatory properties have potential applications in the development of new diagnostic and therapeutic strategies for nanomedicine. Nanoparticles targeting macrophages can manipulate or control immunological diseases. This study assessed the activity of dendrimer-encapsulated gold nanodots (AuNDs) with three surface modifications [ie, outfacing groups with primary amine (AuNDs-NH2), hydroxyl (AuNDs-OH), and quaternary ammonium ions (AuNDs-CH3)] regulated macrophage function and antioxidant response through Nrf2-dependent pathway.

METHODS

AuNDs were prepared and characterized. Intracellular distribution of AuNDs in human macrophages was observed through confocal microscopy. The activity of AuNDs was evaluated using macrophage functions and antioxidant response in the human macrophage cell line THP-1.

RESULTS

AuNDs-NH2 and AuNDs-CH3, but not AuNDs-OH, drove the obvious Nrf2-antioxidant response element pathway in THP-1 cells. Of the three, AuNDs-NH2 considerably increased mRNA levels and antioxidant activities of heme oxygenase 1 and NAD(P)H quinone dehydrogenase 1 in THP-1 cells. IL-6 mRNA and protein expression was mediated through Nrf2 activation in AuNDs-NH2-treated macrophages. Furthermore, Nrf2 activation by AuNDs-NH2 increased the phagocytic ability of THP-1 macrophages.

CONCLUSION

AuNDs-NH2 had immunomodulatory activities in macrophages. The findings of the present work suggested that AuNDs have potential effects against chronic inflammatory diseases via the Nrf2 pathway.

Predicting oxidative stress induced by organic chemicals by using quantitative Structure-Activity relationship methods

Cellular exposure to xenobiotic human-made products will lead to oxidative stress that gives rise to DNA damage, as well as chemical or mechanical damage. Distinguishing the chemicals that will induce oxidative stress and predicting their toxicity is necessary. In the present study, 4270 compounds in the ARE-bla assay were investigated to predict active and inactive compounds by using simple algorithms, namely, recursive partitioning (RP) and binomial logistic regression, and to develop the quantitative structure-activity relationship (QSAR) models of chemicals that activate the ARE pathway to induce oxidative stress and exert toxic effects on cells. A decision tree based on scaffold-based fragments obtained through RP analysis showed the best identification accuracy. However, the overall identification accuracy of this model for active compounds was unsatisfactory due to limited fragments. Furthermore, a binomial logistic regression model was developed from 638 active compounds and 3632 inactive chemicals. The model with a cutoff of 0.15 could predict chemicals that were active or inactive with the prediction accuracy of 69.1%. Its area under the receiver operating characteristic (ROC) curve metric (AUROC) was 0.762, which indicated the acceptable predictive ability of this model. The parameters nBM (number of multiple bonds) and H% (percentage of H atom) played dominant roles in the prediction of the activity (inactive or active) of chemicals. A global QSAR model was developed to predict the toxicity of active chemicals. However, the model displayed an unsatisfactory result with R² = 0.316 and R²_ext = 0.090. Active chemicals were then classified on the basis of structure. A total of 79 compounds with carbon chains could be predicted with acceptable performance by using a QSAR model with six descriptors (R² = 0.722, R²_ext = 0.798, Q²_Loo = 0.654, Q²_Boot = 0.755, Q²_ext = 0.721). The simple models established here contribute to efforts on identification compounds inducing oxidative stress and provide the scientific basis for risk assessment to organisms in the environment.

CDDO-imidazolide Targets Multiple Amino Acid Residues on the Nrf2 Adaptor, Keap1

Synthetic triterpenoids including CDDO, its methyl ester (CDDO-Me, bardoxolone methyl), and its imidazolide (CDDO-Im) enhance Nrf2-mediated antioxidant and anti-inflammatory activity in many diseases by reacting with thiols on the adaptor protein, Keap1. Unlike monofunctional CDDO-Me, the bifunctional analog, CDDO-Im, has a second reactive site (imidazolide) and can covalently bind to amino acids other than cysteine on target proteins such as glutathione S-transferase pi (GSTP), serum albumin, or Keap1. Here we show for the first time that bifunctional CDDO-Im (in contrast to CDDO-Me), as low as 50 nM, can covalently transacylate arginine and serine residues in GSTP and cross-link them to adjacent cysteine residues. Moreover, we show that CDDO-Im binds covalently to Keap1 by forming permanent Michael adducts with eight different cysteines, and acyl adducts with lysine and several tyrosine residues. Modeling studies suggest that the Tyr 85 adduct stabilizes the Keap1-Cul3 complex, thereby enhancing the potency of CDDO-Im.

Recent progress in Keap1-Nrf2 protein-protein interaction inhibitors

Therapeutic targeting the protein-protein interaction (PPI) of Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and its main regulator, Kelch-like ECH-Associating protein 1 (Keap1) has been emerged as a feasible way to combat oxidative stress related diseases, due to the key role of Nrf2 in oxidative stress regulation. In recent years, many efforts have been made to develop potent Keap1-Nrf2 inhibitors with new chemical structures. Various molecules with diverse chemical structures have been reported and some compounds exhibit high potency. This review summarizes peptide and small molecule Keap1-Nrf2 inhibitors reported recently. We also highlight the pharmacological effects and discuss the possible therapeutic application of Keap1-Nrf2 inhibitors.

NRF2 Regulation Processes as a Source of Potential Drug Targets against Neurodegenerative Diseases

NRF2 acts by controlling gene expression, being the master regulator of the Phase II antioxidant response, and also being key to the control of neuroinflammation. NRF2 activity is regulated at several levels, including protein degradation by the proteasome, transcription, and post-transcription. The purpose of this review is to offer a concise and critical overview of the main mechanisms of NRF2 regulation and their actual or potential use as targets for the treatment of neurodegenerative diseases.

Medicinal Chemistry of Inhibiting RING-Type E3 Ubiquitin Ligases

The ubiquitin proteasome system (UPS) presents many opportunities for pharmacological intervention. Key players in the UPS are E3 ubiquitin ligases, responsible for conjugation of ubiquitin to specific cognate substrates. Numbering more than 600 members, these ligases represent the most selective way to intervene within this physiologically important system. This Perspective highlights some of the dedicated medicinal chemistry efforts directed at inhibiting the function of specific single-protein and multicomponent RING-type E3 ubiquitin ligases. We present opportunities and challenges associated with targeting this important class of enzymes.

Recent progress in the development of small molecule Nrf2 activators: a patent review (2017-present)

Introduction: The transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) is the first line of defense against a plethora of environmental or endogenous deviations in redox metabolism, proteostasis, inflammation, etc. Therefore, pharmacological activation of Nrf2 is a potential therapeutic approach for several diseases related to oxidative stress and inflammation, such as cancer, cardiovascular, and neurodegenerative diseases.Areas covered: The authors first describe the biological function of Nrf2 and the molecular regulatory mechanism of Keap1-Nrf2-ARE ((Kelch-like ECH-Associating protein 1)-Nrf2-(antioxidant response element)). Then, they review recent progress of covalent activators and non-covalent Keap1-Nrf2 protein-protein interaction (PPI) inhibitors from patents and publications in 2017-present, consisting of new chemical molecules, structure optimization of reported activators and progress in preclinical or clinical trials.Expert opinion: Despite significant achievements in the development of Nrf2 activators, the selectivity is the primary consideration. Due to reacting with redox-sensitive cysteines in proteins except for Keap1, electrophilic activators often exhibit off-target effects. For Keap1-Nrf2 PPI inhibitors, how to enhance in vivo efficacy and/or penetrate blood-brain barrier (BBB) to reach central nervous system (CNS) is also challenging. Fragment-based drug discovery (FBDD), carboxylic acid bioisosteric replacement and prodrug approach might be used to circumvent this challenge. Moreover, the possibility of cancer risk caused by Nrf2 activation needs to be considered carefully.

Stress Resistance Screen in a Human Primary Cell Line Identifies Small Molecules That Affect Aging Pathways and Extend Caenorhabditis elegans' Lifespan

Increased resistance to environmental stress at the cellular level is correlated with the longevity of long-lived mutants and wild-animal species. Moreover, in experimental organisms, screens for increased stress resistance have yielded mutants that are long-lived. To find entry points for small molecules that might extend healthy longevity in humans, we screened ∼100,000 small molecules in a human primary-fibroblast cell line and identified a set that increased oxidative-stress resistance. Some of the hits fell into structurally related chemical groups, suggesting that they may act on common targets. Two small molecules increased C. elegans’ stress resistance, and at least 9 extended their lifespan by ∼10–50%. We further evaluated a chalcone that produced relatively large effects on lifespan and were able to implicate the activity of two, stress-response regulators, NRF2/skn-1 and SESN/sesn-1, in its mechanism of action. Our findings suggest that screening for increased stress resistance in human cells can enrich for compounds with promising pro-longevity effects. Further characterization of these compounds may reveal new ways to extend healthy human lifespan.

Glutamate and aspartate alleviate testicular/epididymal oxidative stress by supporting antioxidant enzymes and immune defense systems in boars

Several potential oxidative agents have damaging effects on mammalian reproductive systems. This study was conducted to investigate the effects of glutamate (Glu) and aspartate (Asp) supplementation on antioxidant enzymes and immune defense systems in the outer scrotum of boars injected with H₂O₂. A total of 24 healthy boars were randomly divided into 4 treatment groups: control (basal diet, saline-treated), H₂O₂ (basal diet, H₂O₂-challenged outer scrotum (1 mL kg^-1 BW)), Glu (basal diet +2% Glu, H₂O₂-challenged), and Asp (basal diet+2% Asp, H₂O₂-challenged). Our results showed that both Glu and Asp supplementation improved testicular morphology and decreased the genital index in the H₂O₂-treated boars. Glu and Asp administration increased the antioxidant enzyme activities and affected the testicular inflammatory cytokine secretion but had no effect on sex hormone levels. Furthermore, the mRNA expression of CAT, CuZnSOD, and GPx4 was altered in the testes and epididymis of boars treated with Asp and Glu. Glu and Asp supplementation also modulated the expression of TGF-β1, IL-10, TNF-α, IL-6 and IL-1β in the testis and epididymis. These results indicate that dietary Glu and Asp supplementation might enhance antioxidant capacity and regulate the secretion and expression of inflammatory cytokines to protect the testes and epididymis of boars against oxidative stress.

Fabrication and characterization of solid lipid nano-formulation of astraxanthin against DMBA-induced breast cancer via Nrf-2-Keap1 and NF-kB and mTOR/Maf-1/PTEN pathway

In the current experimental study, we scrutinized the chemoprotective effect of astraxanthin against the 7,12-dimethylbenz(a)anthracene (DMBA)-induced breast cancer via Nrf-2-Keap1 and NF-kB and mTOR/Maf-1/PTEN pathway. The double emulsion solvent displacement method was used for the preparation of astraxanthin solid lipid nanoparticles (SLN). SLNs were appraised for entrapment, potential, size, drug-release performance, and gastric stability. DMBA (8 mg/kg) was used for the induction of breast cancer. Tumor weight, body weight, and tumor incidence were estimated at a regular interval. Different biochemical parameters such as Na+/K+, Ca2+, and Mg2+ activity, antioxidant, lipid, glycoprotein, phase I and II biotransformation enzymes, mitochondrial TCA cycle, and carbohydrate metabolizing enzymes were estimated. Keap1-Nrf-2, associated HO-1, and NF-kB expressions were estimated. Moreover, it estimated the mRNA expression of LXR (α,β), HMG-CoAR, PTEN, Maf1, PI3K, mTOR, Akt, FASN, and ACC1. AX-SLN reduced the tumor incidence, tumor weight, and increased the body weight. AX-SLN exhibited the protective effect against the LPO, enzymic (SOD, CuZnSOD, MnSOD, GPx, and CAT), and nonenzymic (GSH) in the serum, mammary gland, renal, and hepatic tissues. AX-SLN reduced the p-AKT which is accountable for the reduction in the NF-kB expression and also reduced the expression of Keap1 and NF-kB along with increasing the expression of HO-1 and Nrf-2. Further, AX-SLN significantly altered the mRNA of LXR (α,β), HMG-CoAR, PTEN, Maf1, PI3K, mTOR, Akt, FASN, and ACC1. On the basis of the results, we can conclude that AX-SLN inhibits the mammary gland carcinogenesis via Nrf-2-Keap1, NF-kB, and mTOR/Maf-1/PTEN pathway.

Reasonably activating Nrf2: A long-term, effective and controllable strategy for neurodegenerative diseases

Neurodegenerative diseases are a variety of debilitating and fatal disorder in central nervous system (CNS). Besides targeting neuronal activity by influencing neurotransmitters or their corresponding receptors, modulating the underlying processes that lead to cell death, such as oxidative stress and mitochondrial dysfunction, should also be emphasized as an assistant strategy for neurodegeneration therapy. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) has been closely verified to be related to anti-inflammation and oxidative stress, rationally regulating its belonging pathway and activating Nrf2 is emphasized to be a potential treatment approach. There have existed multiple Nrf2 activators with different mechanisms and diverse structures, but those applied for neuro-disorders are still limited. On the basis of research arrangement and compound summary, we put forward the limitations of existing Nrf2 activators for neurodegenerative diseases and their future developing directions in enhancing the blood-brain barrier permeability to make Nrf2 activators function in CNS and designing Nrf2-based multi-target-directed ligands to affect multiple nodes in pathology of neurodegenerative diseases.

Effects of Resistance Exercise on Cerebral Redox Regulation and Cognition: An Interplay Between Muscle and Brain

This review highlighted resistance training as an important training type for the brain. Most studies that use physical exercise for the prevention or treatment of neurodegenerative diseases have focused on aerobic physical exercise, revealing different behavioral, biochemical, and molecular effects. However, recent studies have shown that resistance training can also significantly contribute to the prevention of neurodegenerative diseases as well as to the maintenance, development, and recovery of brain activities through specific neurochemical adaptations induced by the training. In this scenario we observed the results of several studies published in different journals in the last 20 years, focusing on the effects of resistance training on three main neurological aspects: Neuroprotective mechanisms, oxidative stress, and cognition. Systematic database searches of PubMed, Web of Science, Scopus, and Medline were performed to identify peer-reviewed studies from the 2000s. Combinations of keywords related to brain disease, aerobic/resistance, or strength physical exercise were used. Other variables were not addressed in this review but should be considered for a complete understanding of the effects of training in the brain.

Post-transcriptional regulation of Nrf2-mRNA by the mRNA-binding proteins HuR and AUF1

The nuclear factor erythroid 2-related factor 2 (Nrf2) signaling axis is a target of covalent drugs and bioactive native electrophiles. However, much of our understanding of Nrf2 regulation has been focused at the protein level. Here we report a post-transcriptional modality to directly regulate Nrf2-mRNA. Our initial studies focused on the effects of the key mRNA-binding protein (mRBP) HuR on global transcriptomic changes incurred upon oxidant or electrophile stimulation. These RNA-sequencing data and subsequent mechanistic analyses led us to discover a novel role of HuR in regulating Nrf2 activity, and in the process, we further identified the related mRBP AUF1 as an additional novel Nrf2 regulator. Both mRBPs regulate Nrf2 activity by direct interaction with the Nrf2 transcript. Our data showed that HuR enhances Nrf2-mRNA maturation and promotes its nuclear export, whereas AUF1 stabilizes Nrf2-mRNA. Both mRBPs target the 3'-UTR of Nrf2-mRNA. Using a Nrf2 activity-reporter zebrafish strain, we document that this post-transcriptional control of Nrf2 activity is conserved at the whole-vertebrate level.-Poganik, J. R., Long, M. J. C., Disare, M. T., Liu, X., Chang, S.-H., Hla, T., Aye, Y. Post-transcriptional regulation of Nrf2-mRNA by the mRNA-binding proteins HuR and AUF1.

Tamoxifen promotes white matter recovery and cognitive functions in male mice after chronic hypoperfusion

Cerebral white matter lesions (WMLs) induced by chronic cerebral hypoperfusion are one of the major components of stroke pathology and closely associated with cognitive impairment. However, the repair and related pathophysiology of white matter after brain injury remains relatively elusive and underexplored. Successful neuroregeneration is a method for the potential treatment of central nervous system (CNS) disorders. A non-steroidal estrogen receptor modulator, Tamoxifen, is an effective inhibitor of cell-swelling-activated anion channels and can mimic neuroprotective effects of estrogen in experimental ischemic stroke. However, its remains unclear whether Tamoxifen has beneficial effects in the pathological process after WMLs. In the present study, we investigated the efficacy of Tamoxifen on multiple elements of oligovascular niche of the male C57BL/6 mice brain after bilateral carotid artery stenosis (BCAS) - induced WMLs. Tamoxifen was injected intraperitoneally once daily from 1 day after BCAS until 1 day before sacrificed. Following chronic hypoperfusion, BCAS mice presented white matter demyelination, loss of axon-glia integrity, activated inflammatory response, and cognitive impairments. Tamoxifen treatment significantly facilitated functional restoration of working memory impairment in mice after white matter injury, thus indicating a translational potential for this estrogen receptor modulator given its clinical safety and applicability for WMLs, which lack of currently available treatments. Furthermore, Tamoxifen treatment reduced microglia activation and inflammatory response, favored microglial polarization toward to the M2 phenotype, enhanced oligodendrocyte precursor cells proliferation and differentiation, and promoted remyelination after chronic hypoperfusion. Together, our data indicate that Tamoxifen could alleviate white matter injury and play multiple targets protective effects following chronic hypoperfusion, which is a promising candidate for the therapeutic target for ischemic WMLs and other demyelination diseases associated cognitive impairment.

Resveratrol, an Nrf2 activator, ameliorates aging-related progressive renal injury

Background. Two important issues in the aging kidney are mitochondrial dysfunction and oxidative stress. An Nrf2 activator, resveratrol, is known to have various effects. Resveratrol may prevent inflammation and oxidative stress by activating Nrf2 and SIRT1 signaling. We examined whether resveratrol could potentially ameliorate the cellular condition, such as renal injury due to cellular oxidative stress and mitochondrial dysfunction caused by aging.

Methods. Male 18-month-old C57BL/6 mice were used. Resveratrol (40 mg/kg) was administered to aged mice for 6 months. We compared histological changes, oxidative stress, and aging-related protein expression in the kidney between the resveratrol-treated group (RSV) and the control group (cont). We performed experiments using small-interfering RNAs (siRNAs) for Nrf2 and SIRT1 in cultured HK2 cells.

Results. Resveratrol improved renal function, proteinuria, histological changes and inflammation in aging mice. Also, expression of Nrf2-HO-1-NOQ-1 signaling and SIRT1-AMPK-PGC-1α signaling was increased in the RSV group. Transfection with Nrf2 and SIRT1 siRNA prevented resveratrol-induced anti-oxidative effect in HK2 cells in media treated with H₂O₂.

Conclusions. Activation of the Nrf2 and SIRT1 signaling pathways ameliorated oxidative stress and mitochondrial dysfunction. Pharmacological targeting of Nrf2 signaling molecules may reduce the pathologic changes of aging in the kidney.

Novel diterpenoid-type activators of the Keap1/Nrf2/ARE signaling pathway and their regulation of redox homeostasis

Oxidative stress is involved in the onset and progression of many human diseases. Activators of the Keap1/Nrf2/ARE pathway effectively inhibit the progression of oxidative stress-induced diseases. Herein, a small library of diterpenoids was established by means of phytochemical isolation, and chemical modification on naturally occurring molecules. The diterpenoids were subjected to a NAD(P)H: quinone reductase (QR) assay to evaluate its potential inhibition against oxidative stress. Sixteen diterpenoids were found to be novel potential activators of Nrf2-mediated defensive response. Of which, an isopimarane-type diterpenoid, sphaeropsidin A (SA), was identified as a potent activator of the Keap1/Nrf2/ARE pathway, and displayed approximately 5-folds potency than that of sulforaphane (SF). SA activated Nrf2 and its downstream cytoprotective genes through enhancing the stabilization of Nrf2 in a process involving PI3K, PKC, and PERK, as well as potentially interrupting Nrf2-Keap1 protein-protein interaction. In addition, SA conferred protection against sodium arsenite [As(III)]- and cigarette smoke extract (CSE)-induced redox imbalance and cytotoxicity in human lung epithelial cells, as wells as inhibited metronidazole (MTZ)-induced oxidative insult in Tg (krt4: NTR-hKikGR)^cy17 transgenic zebrafish and lipopolysaccharide (LPS)-induced oxidative damage in wild-type AB zebrafish. These results imply that SA is a lead compound for therapeutic agent against oxidative stress-induced diseases, and diterpenoid is a good resource for discovering drug candidates and leads of antioxidant therapy.

Activators and Inhibitors of NRF2: A Review of Their Potential for Clinical Development

The transcription factor NRF2 (nuclear factor erythroid 2-related factor 2) triggers the first line of homeostatic responses against a plethora of environmental or endogenous deviations in redox metabolism, proteostasis, inflammation, etc. Therefore, pharmacological activation of NRF2 is a promising therapeutic approach for several chronic diseases that are underlined by oxidative stress and inflammation, such as neurodegenerative, cardiovascular, and metabolic diseases. A particular case is cancer, where NRF2 confers a survival advantage to constituted tumors, and therefore, NRF2 inhibition is desired. This review describes the electrophilic and nonelectrophilic NRF2 activators with clinical projection in various chronic diseases. We also analyze the status of NRF2 inhibitors, which at this time provide proof of concept for blocking NRF2 activity in cancer therapy.

Isolation of Myricitrin and 3,5-di-O-Methyl Gossypetin from Syzygium samarangense and Evaluation of their Involvement in Protecting Keratinocytes against Oxidative Stress via Activation of the Nrf-2 Pathway

The wax apple (Syzygium samarangense) is traditionally employed as an antibacterial and immunostimulant drug in traditional medicine. This plant is rich in different flavonoids and tannins. In this study, we isolated two compounds from S. samarangense leaves: myricitrin and 3,5-di-O-methyl gossypetin. Then, we investigated the mechanisms of action of the two compounds against oxidative stress (induced by sodium arsenite) and inflammation (induced by UV light) on human keratinocytes. We could clearly demonstrate that the pre-treatment of cells with both compounds was able to mitigate the negative effects induced by oxidative stress, as no alteration in reactive oxygen species (ROS) production, glutathione (GSH) level, or protein oxidation was observed. Additionally, both compounds were able to modulate mitogen-activated protein kinase (MAPK) signaling pathways to counteract oxidative stress activation. Finally, we showed that 3,5-di-O-methyl gossypetin exerted its antioxidant activity through the nuclear transcription factor-2 (Nrf-2) pathway, stimulating the expression of antioxidant proteins, such as HO-1 and Mn-SOD-3.

Identification of compounds that inhibit the binding of Keap1a/Keap1b Kelch DGR domain with Nrf2 ETGE/DLG motifs in zebrafish

The Keap1-Nrf2-ARE system serves as a premier defence mechanism to curb oxidative stress, which remains as one of the major causes of ageing and pathogenesis in various diseases. Nrf2 is the principal master regulator of the cellular defence system, and its activation remains the prospective therapeutic approach against chronic diseases. One of the recent strategies is to disrupt Keap1-Nrf2 protein-protein interaction (PPI) that alters the docking of Keap1 with Nrf2 by compounds occupying a position in the Keap1 blocking the interface with Nrf2. In this study, we made an attempt to identify the compounds with anticancer, antioxidant and anti-inflammatory properties to disrupt Keap1a/b-Nrf2 PPI through in silico molecular docking in zebrafish. The phylogenetic analysis of Keap1 proteins revealed the existence of orthologous Keap1-Nrf2-ARE system in lower vertebrates that includes zebrafish. The DGR domains of zebrafish Keap1a and Keap1b were modelled with Modeller 9.19 using Keap1 of Mus musculus (PDB ID:5CGJ) as template. Based on the docking calculations, top hit compounds were identified to disrupt both Keap1a and Keap1b interaction with Nrf2 which include quercetin 3,4'-diglucoside, flavin adenine dinucleotide disodium salt hydrate, salvianolic acid A, tunicamycin and esculin. The LC₅₀ of esculin in 3 dpf zebrafish larvae is 5 mmol/L, and the qRT-PCR results showed that esculin significantly increased the transcription of Nrf2 target genes-Gstpi, Nqo1, Hmox1a and Prdx1 in 3 dpf zebrafish larvae. These potential hits could serve as safer Nrf2 activators due to their non-covalent disruption of Keap1-Nrf2 PPI and be developed into efficacious preventive/therapeutic agents for various diseases.

Lights and shadows of electrophile signaling: focus on the Nrf2-Keap1 pathway

Targeted covalent modification is assuming consolidated importance in drug discovery. In this context, the electrophilic tuning of redox-dependent cell signaling is attracting major interest, as it opens prospect for treating numerous pathologic conditions. Herein, we discuss the rationale and the issues of electrophile-based approaches, focusing on the transcriptional Nrf2-Keap1 pathway as a test case. We also highlight relevant medicinal chemistry strategies researchers have devised to meet the ambitious goal, dwelling on the investigational and therapeutic potential of modulating redox-signaling networks through regulatory cysteine switches.

Nonanimal Models for Acute Toxicity Evaluations: Applying Data-Driven Profiling and Read-Across

BACKGROUND

Low-cost, high-throughput in vitro bioassays have potential as alternatives to animal models for toxicity testing. However, incorporating in vitro bioassays into chemical toxicity evaluations such as read-across requires significant data curation and analysis based on knowledge of relevant toxicity mechanisms, lowering the enthusiasm of using the massive amount of unstructured public data.

OBJECTIVE

We aimed to develop a computational method to automatically extract useful bioassay data from a public repository (i.e., PubChem) and assess its ability to predict animal toxicity using a novel bioprofile-based read-across approach.

METHODS

A training database containing 7,385 compounds with diverse rat acute oral toxicity data was searched against PubChem to establish in vitro bioprofiles. Using a novel subspace clustering algorithm, bioassay groups that may inform on relevant toxicity mechanisms underlying acute oral toxicity were identified. These bioassays groups were used to predict animal acute oral toxicity using read-across through a cross-validation process. Finally, an external test set of over 600 new compounds was used to validate the resulting model predictivity.

RESULTS

Several bioassay clusters showed high predictivity for acute oral toxicity (positive prediction rates range from 62-100%) through cross-validation. After incorporating individual clusters into an ensemble model, chemical toxicants in the external test set were evaluated for putative acute toxicity (positive prediction rate equal to 76%). Additionally, chemical fragment -in vitro-in vivo relationships were identified to illustrate new animal toxicity mechanisms.

CONCLUSIONS

The in vitro bioassay data-driven profiling strategy developed in this study meets the urgent needs of computational toxicology in the current big data era and can be extended to develop predictive models for other complex toxicity end points. https://doi.org/10.1289/EHP3614.