Covalent Modification at Cys151 Dissociates the Electrophile Sensor Keap1 from the Ubiquitin Ligase CUL3

Synthesis and evaluation of novel ethyl ferulate derivatives as potent Keap1 inhibitors to activate the Nrf2/ARE pathway in Parkinson's disease

The Kelch-like ECH-associated protein 1/Nuclear factor erythroid 2 related factor 2/Antioxidant Response Elements (Keap1/Nrf2/ARE) pathway is essential for neuronal resilience against the complex pathogenesis of Parkinson's disease (PD). Activating this pathway by covalently modifying Keap1 cysteine residues is a promising strategy for regulating neuroprotective gene expression. Our study aimed to identify phytochemicals that could irreversibly inhibit Keap1. A preliminary docking analysis revealed that ethyl ferulate could covalently bind with Cys151 of Keap1 by Michael's addition reaction. Further, we designed several ethyl ferulate derivatives with improved lipophilicity and assessed their binding affinity with Keap1. The molecules with good binding scores were synthesized and structures were confirmed through 1H NMR, 13C NMR, FT-IR, and mass spectroscopy. Neuroprotection screening was conducted in all-trans retinoic acid differentiated SH-SY5Y cells using rotenone as a disease-inducing agent. Pre-treatment with compounds C2 and C4 significantly mitigated rotenone toxicity. Additionally, C2 and C4 decreased rotenone-induced ROS production and mitochondrial membrane potential loss. C2 and C4 also induced Nrf2 nuclear translocation in SH-SY5Y cells and increased mRNA expression of heme oxygenase-1, an Nrf2-regulated antioxidant response element. In vivo, pretreatment with C2 (50, 100 mg/kg, p.o.) and C4 (50, 100 mg/kg, p.o.) protected against neurodegenerative phenotypes associated with rotenone (1.5 mg/kg, s.c.) induction in Wistar rats. Results indicate, C2 and C4 dose-dependently improved muscle rigidity, catalepsy, and cognitive deficits in rotenone-induced Wistar rats, and mitigated dopaminergic neurodegeneration in the substantia nigra. These findings highlight the potential of ethyl ferulate derivatives in modulating oxidative stress and neurodegeneration in PD via activation of Nrf2.

Unlocking peak performance: The role of Nrf2 in enhancing exercise outcomes and training adaptation in humans

Since the discovery of the nuclear factor erythroid-derived 2-like 2 (Nrf2) transcription factor thirty years ago, it has been shown that it regulates more than 250 genes involved in a multitude of biological processes, including redox balance, mitochondrial biogenesis, metabolism, detoxification, cytoprotection, inflammation, immunity, autophagy, cell differentiation, and xenobiotic metabolism. In skeletal muscle, Nrf2 signalling is primarily activated in response to perturbation of redox balance by reactive oxygen species or electrophiles. Initial investigations into human skeletal muscle Nrf2 responses to exercise, dating back roughly a decade, have consistently indicated that exercise-induced ROS production stimulates Nrf2 signalling. Notably, recent studies employing Nrf2 knockout mice have revealed impaired skeletal muscle contractile function characterised by reduced force output and increased fatigue susceptibility compared to wild-type counterparts. These deficiencies partially stem from diminished basal mitochondrial respiratory capacity and an impaired capacity to upregulate specific mitochondrial proteins in response to training, findings corroborated by inducible muscle-specific Nrf2 knockout models. In humans, baseline Nrf2 expression in skeletal muscle correlates with maximal oxygen uptake and high-intensity exercise performance. This manuscript delves into the mechanisms underpinning Nrf2 signalling in response to acute exercise in human skeletal muscle, highlighting the involvement of ROS, antioxidants and Keap1/Nrf2 signalling in exercise performance. Furthermore, it explores Nrf2's role in mediating adaptations to chronic exercise and its impact on overall exercise performance. Additionally, the influence of diet and certain supplements on basal Nrf2 expression and its role in modulating acute and chronic exercise responses are briefly addressed.

A potential therapeutic strategy based on acute oxidative stress induction for wild-type NRF2/KEAP1 lung squamous cell carcinoma

Extensive efforts have been conducted in the search for new targetable drivers of lung squamous cell carcinoma (LUSC); to date, however, candidates remain mostly unsuccessful. One of the oncogenic pathways frequently found to be active in LUSC is NFE2L2 (NRF2 transcription factor), the levels of which are regulated by KEAP1. Mutations in NFE2L2 or KEAP1 trigger NRF2 activation, an essential protector against reactive oxygen species (ROS). We hypothesized that the frequency of NRF2 activation in LUSC (∼35 %) may reflect a sensitivity of LUSC to ROS. Results from this study reveal that whereas tumors containing active forms of NRF2 were protected, ROS induction in wild-type NFE2L2/KEAP1 LUSC cells triggered ferroptosis. The mechanism of ROS action in normal-NRF2 LUSC cells involved transient NRF2 activation, miR-126-3p/miR-126-5p upregulation, and reduction of p85β and SETD5 levels. SETD5 levels reduction triggered pentose pathway gene levels increase to toxic values. Simultaneous depletion of p85βPI3K and SETD5 triggered LUSC cell death, while p85βPI3K and SETD5 overexpression rescued survival of ROS-treated normal-NRF2 LUSC cells. This shows that the cascade involving NRF2 > miR-126-3p, miR-126-5p > p85βPI3K and SETD5 is responsible for ROS-induced cell death in normal-NRF2 LUSC. Transient ROS-induced cell death is shown in 3D spheroids, patient-derived organoids, and in xenografts of wild-type NFE2L2/KEAP1 LUSC cells, supporting the potential of acute local ROS induction as a therapeutic strategy for LUSC patients with normal-NRF2.

Sesamin Exerts an Antioxidative Effect by Activating the Nrf2 Transcription Factor in the Glial Cells of the Central Nervous System in Drosophila Larvae

Sesame seeds are abundant in sesamin, which exerts health-promoting effects such as extending the lifespan of adult Drosophila and suppressing oxidative stress by activating the Nrf2 transcription factor. Here, we investigated whether sesamin activated Nrf2 in larval tissues and induced the expression of Nrf2 target genes. In the sesamin-fed larvae, Nrf2 was activated in the central nervous system (CNS), gut, and salivary glands. The ectopic expression of Keap1 in glial cells inhibited sesamin-induced Nrf2 activation in the whole CNS more than in the neurons, indicating that sesamin activates Nrf2 in glia efficiently. We labeled the astrocytes as well as cortex and surface glia with fluorescence to identify the glial cell types in which Nrf2 was activated; we observed their activation in both cell types. These data suggest that sesamin may stimulate the expression of antioxidative genes in glial cells. Among the 17 candidate Nrf2 targets, the mRNA levels of Cyp6a2 and Cyp6g1 in cytochrome P450 were elevated in the CNS, gut, and salivary glands of the sesamin-fed larvae. However, this elevation did not lead to resistance against imidacloprid, which is detoxified by these enzymes. Our results suggest that sesamin may exert similar health-promoting effects on the human CNS and digestive tissues.

Tweaking the NRF2 signaling cascade in human myelogenous leukemia cells by artificial nano-organelles

NRF2 (nuclear factor erythroid-2-related factor 2) is a key regulator of genes involved in the cell's protective response to oxidative stress. Upon activation by disturbed redox homeostasis, NRF2 promotes the expression of metabolic enzymes to eliminate reactive oxygen species (ROS). Cell internalization of peroxisome-like artificial organelles that harbor redox-regulating enzymes was previously shown to reduce ROS-induced stress and thus cell death. However, if and to which extent ROS degradation by such nanocompartments interferes with redox signaling pathways is largely unknown. Here, we advance the design of H2O2-degrading artificial nano-organelles (AnOs) that exposed surface-attached cell penetrating peptides (CPP) for enhanced uptake and were equipped with a fluorescent moiety for rapid visualization within cells. To investigate how such AnOs integrate in cellular redox signaling, we engineered leukemic K562 cells that report on NRF2 activation by increased mCherry expression. Once internalized, ROS-metabolizing AnOs dampen intracellular NRF2 signaling upon oxidative injury by degrading H2O2. Moreover, intracellular AnOs conferred protection against ROSinduced cell death in conditions when endogenous ROS-protection mechanisms have been compromised by depletion of glutathione or knockdown of NRF2. We demonstrate CPP-facilitated AnO uptake and AnO-mediated protection against ROS insults also in the T lymphocyte population of primary peripheral blood mononuclear cells from healthy donors. Overall, our data suggest that intracellular AnOs alleviated cellular stress by the on-site reduction of ROS.

Anti-Inflammatory Therapeutic Mechanisms of Isothiocyanates: Insights from Sulforaphane

Isothiocyanates (ITCs) belong to a group of natural products that possess a highly reactive electrophilic -N=C=S functional group. They are stored in plants as precursor molecules, glucosinolates, which are processed by the tyrosinase enzyme upon plant tissue damage to release ITCs, along with other products. Isolated from broccoli, sulforaphane is by far the most studied antioxidant ITC, acting primarily through the induction of a transcription factor, the nuclear factor erythroid 2-related factor 2 (Nrf2), which upregulates downstream antioxidant genes/proteins. Paradoxically, sulforaphane, as a pro-oxidant compound, can also increase the levels of reactive oxygen species, a mechanism which is attributed to its anticancer effect. Beyond highlighting the common pro-oxidant and antioxidant effects of sulforaphane, the present paper was designed to assess the diverse anti-inflammatory mechanisms reported to date using a variety of in vitro and in vivo experimental models. Sulforaphane downregulates the expression of pro-inflammatory cytokines, chemokines, adhesion molecules, cycloxyhenase-2, and inducible nitric oxide synthase. The signalling pathways of nuclear factor κB, activator protein 1, sirtuins 1, silent information regulator sirtuin 1 and 3, and microRNAs are among those affected by sulforaphane. These anti-inflammatory actions are sometimes due to direct action via interaction with the sulfhydryl structural moiety of cysteine residues in enzymes/proteins. The following are among the topics discussed in this paper: paradoxical signalling pathways such as the immunosuppressant or immunostimulant mechanisms; crosstalk between the oxidative and inflammatory pathways; and effects dependent on health and disease states.

Small molecule deoxynyboquinone triggers alkylation and ubiquitination of Keap1 at Cys489 on Kelch domain for Nrf2 activation and inflammatory therapy

Activation of nuclear factor erythroid 2-related factor 2 (Nrf2) by Kelch-like ECH-associated protein 1 (Keap1) alkylation plays a central role in anti-inflammatory therapy. However, activators of Nrf2 through alkylation of Keap1-Kelch domain have not been identified. Deoxynyboquinone (DNQ) is a natural small molecule discovered from marine actinomycetes. The current study was designed to investigate the anti-inflammatory effects and molecular mechanisms of DNQ via alkylation of Keap1. DNQ exhibited significant anti-inflammatory properties both in vitro and in vivo. The pharmacophore responsible for the anti-inflammatory properties of DNQ was determined to be the α, β-unsaturated amides moieties by a chemical reaction between DNQ and N-acetylcysteine. DNQ exerted anti-inflammatory effects through activation of Nrf2/ARE pathway. Keap1 was demonstrated to be the direct target of DNQ and bound with DNQ through conjugate addition reaction involving alkylation. The specific alkylation site of DNQ on Keap1 for Nrf2 activation was elucidated with a synthesized probe in conjunction with liquid chromatography-tandem mass spectrometry. DNQ triggered the ubiquitination and subsequent degradation of Keap1 by alkylation of the cysteine residue 489 (Cys489) on Keap1-Kelch domain, ultimately enabling the activation of Nrf2. Our findings revealed that DNQ exhibited potent anti-inflammatory capacity through α, β-unsaturated amides moieties active group which specifically activated Nrf2 signal pathway via alkylation/ubiquitination of Keap1-Kelch domain, suggesting the potential values of targeting Cys489 on Keap1-Kelch domain by DNQ-like small molecules in inflammatory therapies.

The ubiquitin codes in cellular stress responses

Ubiquitination/ubiquitylation, one of the most fundamental post-translational modifications, regulates almost every critical cellular process in eukaryotes. Emerging evidence has shown that essential components of numerous biological processes undergo ubiquitination in mammalian cells upon exposure to diverse stresses, from exogenous factors to cellular reactions, causing a dazzling variety of functional consequences. Various forms of ubiquitin signals generated by ubiquitylation events in specific milieus, known as ubiquitin codes, constitute an intrinsic part of myriad cellular stress responses. These ubiquitination events, leading to proteolytic turnover of the substrates or just switch in functionality, initiate, regulate, or supervise multiple cellular stress-associated responses, supporting adaptation, homeostasis recovery, and survival of the stressed cells. In this review, we attempted to summarize the crucial roles of ubiquitination in response to different environmental and intracellular stresses, while discussing how stresses modulate the ubiquitin system. This review also updates the most recent advances in understanding ubiquitination machinery as well as different stress responses and discusses some important questions that may warrant future investigation.

Advances in Nrf2 Signaling Pathway by Targeted Nanostructured-Based Drug Delivery Systems

Nanotechnology has gained significant interest in various applications, including sensors and therapeutic agents for targeted disease sites. Several pathological consequences, including cancer, Alzheimer's disease, autoimmune diseases, and many others, are mostly driven by inflammation and Nrf2, and its negative regulator, the E3 ligase adaptor Kelch-like ECH-associated protein 1 (Keap1), plays a crucial role in maintaining redox status, the expression of antioxidant genes, and the inflammatory response. Interestingly, tuning the Nrf2/antioxidant response element (ARE) system can affect immune-metabolic mechanisms. Although many phytochemicals and synthetic drugs exhibited potential therapeutic activities, poor aqueous solubility, low bioavailability, poor tissue penetration, and, consequently, poor specific drug targeting, limit their practical use in clinical applications. Also, the therapeutic use of Nrf2 modulators is hampered in clinical applications by the absence of efficient formulation techniques. Therefore, we should explore the engineering of nanotechnology to modulate the inflammatory response via the Nrf2 signaling pathway. This review will initially examine the role of the Nrf2 signaling pathway in inflammation and oxidative stress-related pathologies. Subsequently, we will also review how custom-designed nanoscale materials encapsulating the Nrf2 activators can interact with biological systems and how this interaction can impact the Nrf2 signaling pathway and its potential outcomes, emphasizing inflammation.

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.

Involvement of Nrf2 Signaling in Lead-induced Toxicity

Nuclear factor erythroid 2-related factor 2 (Nrf2) is used as one of the main protective factors against various pathological processes, as it regulates cells resistant to oxidation. Several studies have extensively explored the relationship between environmental exposure to heavy metals, particularly lead (Pb), and the development of various human diseases. These metals have been reported to be able to, directly and indirectly, induce the production of reactive oxygen species (ROS) and cause oxidative stress in various organs. Since Nrf2 signaling is important in maintaining redox status, it has a dual role depending on the specific biological context. On the one hand, Nrf2 provides a protective mechanism against metal-induced toxicity; on the other hand, it can induce metalinduced carcinogenesis upon prolonged exposure and activation. Therefore, the aim of this review was to summarize the latest knowledge on the functional interrelation between toxic metals, such as Pb and Nrf2 signaling.

4-Octyl Itaconate Alleviates Airway Eosinophilic Inflammation by Suppressing Chemokines and Eosinophil Development

4-Octyl itaconate (4-OI) is a derivative of the Krebs cycle-derived metabolite itaconate and displays an array of antimicrobial and anti-inflammatory properties through modifying cysteine residues within protein targets. We have found that 4-OI significantly reduces the production of eosinophil-targeted chemokines in a variety of cell types, including M1 and M2 macrophages, Th2 cells, and A549 respiratory epithelial cells. Notably, the suppression of these chemokines in M1 macrophages was found to be NRF2-dependent. In addition, 4-OI can interfere with IL-5 signaling and directly affect eosinophil differentiation. In a model of eosinophilic airway inflammation in BALB/c mice, 4-OI alleviated airway resistance and reduced eosinophil recruitment to the lungs. Our findings suggest that itaconate derivatives could be promising therapeutic agents for the treatment of eosinophilic asthma.

Aberrations in Energetic Metabolism and Stress-Related Pathways Contribute to Pathophysiology in the Neb Conditional Knockout Mouse Model of Nemaline Myopathy

Nemaline myopathy (NM) is a genetically and clinically heterogeneous disease that is diagnosed on the basis of the presence of nemaline rods on skeletal muscle biopsy. Although NM has typically been classified by causative genes, disease severity or prognosis cannot be predicted. The common pathologic end point of nemaline rods (despite diverse genetic causes) and an unexplained range of muscle weakness suggest that shared secondary processes contribute to the pathogenesis of NM. We speculated that these processes could be identified through a proteome-wide interrogation using a mouse model of severe NM in combination with pathway validation and structural/functional analyses. A proteomic analysis was performed using skeletal muscle tissue from the Neb conditional knockout mouse model compared with its wild-type counterpart to identify pathophysiologically relevant biological processes that might impact disease severity or provide new treatment targets. A differential expression analysis and Ingenuity Pathway Core Analysis predicted perturbations in several cellular processes, including mitochondrial dysfunction and changes in energetic metabolism and stress-related pathways. Subsequent structural and functional studies demonstrated abnormal mitochondrial distribution, decreased mitochondrial respiratory function, an increase in mitochondrial transmembrane potential, and extremely low ATP content in Neb conditional knockout muscles relative to wild type. Overall, the findings of these studies support a role for severe mitochondrial dysfunction as a novel contributor to muscle weakness in NM.

Structural and biochemical characterization establishes a detailed understanding of KEAP1-CUL3 complex assembly

KEAP1 promotes the ubiquitin-dependent degradation of NRF2 by assembling into a CUL3-dependent ubiquitin ligase complex. Oxidative and electrophilic stress inhibit KEAP1 allowing NRF2 to accumulate for the transactivation of stress response genes. To date there are no structures of the KEAP1-CUL3 interaction nor binding data to show the contributions of different domains to their binding affinity. We determined a crystal structure of the BTB and 3-box domains of human KEAP1 in complex with the CUL3 N-terminal domain that showed a heterotetrameric assembly with 2:2 stoichiometry. To support the structural data, we developed a versatile TR-FRET-based assay system to profile the binding of BTB-domain-containing proteins to CUL3 and determine the contribution of distinct protein features, revealing the importance of the CUL3 N-terminal extension for high affinity binding. We further provide direct evidence that the investigational drug CDDO does not disrupt the KEAP1-CUL3 interaction, even at high concentrations, but reduces the affinity of KEAP1-CUL3 binding. The TR-FRET-based assay system offers a generalizable platform for profiling this protein class and may form a suitable screening platform for ligands that disrupt these interactions by targeting the BTB or 3-box domains to block E3 ligase function.

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.

The Effects of Antioxidant Nutraceuticals on Cellular Sulfur Metabolism and Signaling

Significance: Nutraceuticals are ingested for health benefits, in addition to their general nutritional value. These dietary supplements have become increasingly popular since the late 20th century and they are a rapidly expanding global industry approaching a half-trillion U.S. dollars annually. Many nutraceuticals are promulgated as potent antioxidants. Recent Advances: Experimental support for the efficacy of nutraceuticals has lagged behind anecdotal exuberance. However, accumulating epidemiological evidence and recent, well-controlled clinical trials are beginning to support earlier animal and in vitro studies. Although still somewhat limited, encouraging results have been suggested in essentially all organ systems and against a wide range of pathophysiological conditions. Critical Issues: Health benefits of "antioxidant" nutraceuticals are largely attributed to their ability to scavenge oxidants. This has been criticized based on several factors, including limited bioavailability, short tissue retention time, and the preponderance of endogenous antioxidants. Recent attention has turned to nutraceutical activation of downstream antioxidant systems, especially the Keap1/Nrf2 (Kelch like ECH associated protein 1/nuclear factor erythroid 2-related factor 2) axis. The question now becomes, how do nutraceuticals activate this axis? Future Directions: Reactive sulfur species (RSS), including hydrogen sulfide (H2S) and its metabolites, are potent activators of the Keap1/Nrf2 axis and avid scavengers of reactive oxygen species. Evidence is beginning to accumulate that a variety of nutraceuticals increase cellular RSS by directly providing RSS in the diet, or through a number of catalytic mechanisms that increase endogenous RSS production. We propose that nutraceutical-specific targeting of RSS metabolism will lead to the design and development of even more efficacious antioxidant therapeutic strategies. Antioxid. Redox Signal. 38, 68-94.

KEAP1-NRF2 protein-protein interaction inhibitors: Design, pharmacological properties and therapeutic potential

The transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) is considered the master regulator of the phase II antioxidant response. It controls a plethora of cytoprotective genes related to oxidative stress, inflammation, and protein homeostasis, among other processes. Activation of these pathways has been described in numerous pathologies including cancer, cardiovascular, respiratory, renal, digestive, metabolic, autoimmune, and neurodegenerative diseases. Considering the increasing interest of discovering novel NRF2 activators due to its clinical application, initial efforts were devoted to the development of electrophilic drugs able to induce NRF2 nuclear accumulation by targeting its natural repressor protein Kelch-like ECH-associated protein 1 (KEAP1) through covalent modifications on cysteine residues. However, off-target effects of these drugs prompted the development of an innovative strategy, the search of KEAP1-NRF2 protein-protein interaction (PPI) inhibitors. These innovative activators are proposed to target NRF2 in a more selective way, leading to potentially improved drugs with the application for a variety of diseases that are currently under investigation. In this review, we summarize known KEAP1-NRF2 PPI inhibitors to date and the bases of their design highlighting the most important features of their respective interactions. We also discuss the preclinical pharmacological properties described for the most promising compounds.

The molecular biology and therapeutic potential of Nrf2 in leukemia

NF-E2-related factor 2 (Nrf2) transcription factor has contradictory roles in cancer, which can act as a tumor suppressor or a proto-oncogene in different cell conditions (depending on the cell type and the conditions of the cell environment). Nrf2 pathway regulates several cellular processes, including signaling, energy metabolism, autophagy, inflammation, redox homeostasis, and antioxidant regulation. As a result, it plays a crucial role in cell survival. Conversely, Nrf2 protects cancerous cells from apoptosis and increases proliferation, angiogenesis, and metastasis. It promotes resistance to chemotherapy and radiotherapy in various solid tumors and hematological malignancies, so we want to elucidate the role of Nrf2 in cancer and the positive point of its targeting. Also, in the past few years, many studies have shown that Nrf2 protects cancer cells, especially leukemic cells, from the effects of chemotherapeutic drugs. The present paper summarizes these studies to scrutinize whether targeting Nrf2 combined with chemotherapy would be a therapeutic approach for leukemia treatment. Also, we discussed how Nrf2 and NF-κB work together to control the cellular redox pathway. The role of these two factors in inflammation (antagonistic) and leukemia (synergistic) is also summarized.

Structure-activity relationships of 1,4-bis(arylsulfonamido)-benzene or naphthalene-N,N'-diacetic acids with varying C2-substituents as inhibitors of Keap1-Nrf2 protein-protein interaction

The Keap1-Nrf2-ARE pathway plays an important role in responding to oxidative stress and maintaining the redox homeostasis. Small molecule inhibitors targeting directly the Keap1-Nrf2 protein-protein interaction (PPI) can potentially be developed into effective preventive and therapeutic agents for numerous chronic inflammatory diseases. To improve the drug-like properties and inhibitory potency of these inhibitors, a series of 1,4-bis(arylsulfonamido)benzene or naphthalene-N,N'-diacetic acids with varying substituents at C-2 position of the benzene or naphthalene core were designed and synthesized. Among them, compound 12d with 2-(4-fluorobenzyloxy) group was the most potent direct inhibitor of Keap1-Nrf2 PPI with an IC₅₀ of 64.5 nM in the fluorescent polarization (FP) assay and 14.2 nM in a time-resolved fluorescence resonance energy transfer (TR-FRET) assay. Moreover, cell-based biological assay showed that 12d significantly increased the mRNA levels of Nrf2 downstream genes, GSTM3, HMOX2 and NQO1, through Nrf2 activation. The discovery of the new scaffolds possessing diverse O-linked fragments at the C2 position offers opportunities to further modify the chemical structures of Keap1-Nrf2 PPI inhibitors to improve their pharmacokinetic, efficacy and safety profiles.

Counting Degrons: Lessons From Multivalent Substrates for Targeted Protein Degradation

E3s comprise a structurally diverse group of at least 800 members, most of which target multiple substrates through specific and regulated protein-protein interactions. These interactions typically rely on short linear motifs (SLiMs), called "degrons", in an intrinsically disordered region (IDR) of the substrate, with variable rules of engagement governing different E3-docking events. These rules of engagement are of importance to the field of targeted protein degradation (TPD), where substrate ubiquitination and destruction require tools to effectively harness ubiquitin ligases (E3s). Substrates are often found to contain multiple degrons, or multiple copies of a degron, contributing to the affinity and selectivity of the substrate for its E3. One important paradigm for E3-substrate docking is presented by the Anaphase-Promoting Complex/Cyclosome (APC/C), a multi-subunit E3 ligase that targets hundreds of proteins for destruction during mitotic exit. APC/C substrate targeting takes place in an ordered manner thought to depend on tightly regulated interactions of substrates, with docking sites provided by the substoichiometric APC/C substrate adaptors and coactivators, Cdc20 or Cdh1/FZR1. Both structural and functional studies of individual APC/C substrates indicate that productive ubiquitination usually requires more than one degron, and that degrons are of different types docking to distinct sites on the coactivators. However, the dynamic nature of APC/C substrate recruitment, and the influence of multiple degrons, remains poorly understood. Here we review the significance of multiple degrons in a number of E3-substrate interactions that have been studied in detail, illustrating distinct kinetic effects of multivalency and allovalency, before addressing the role of multiple degrons in APC/C substrates, key to understanding ordered substrate destruction by APC/C. Lastly, we consider how lessons learnt from these studies can be applied in the design of TPD tools.

Recent Advances in the Role of Nuclear Factor Erythroid-2-Related Factor 2 in Spinal Cord Injury: Regulatory Mechanisms and Therapeutic Options

Nuclear factor erythroid-2-related factor 2 (Nrf2) is a pleiotropic transcription factor, and it has been documented that it can induce defense mechanisms both oxidative stress and inflammatory injury. At present, more and more evidences show that the Nrf2 signaling pathway is a key pharmacological target for the treatment of spinal cord injury (SCI), and activating the Nrf2 signaling pathway can effectively treat the inflammatory injury and oxidative stress after SCI. This article firstly introduces the biological studies of the Nrf2 pathway. Meanwhile, it is more powerful to explain that activating the Nrf2 signaling pathway can effectively treat SCI by deeply exploring the relationship between Nrf2 and oxidative stress, inflammatory injury, and SCI. In addition, several potential drugs for the treatment of SCI by promoting Nrf2 activation and Nrf2-dependent gene expression are reviewed. And some other treatment strategies of SCI by modulating the Nrf2 pathway are also summarized. It will provide new ideas and directions for the treatment of SCI.

A Perspective on Nrf2 Signaling Pathway for Neuroinflammation: A Potential Therapeutic Target in Alzheimer's and Parkinson's Diseases

Neuroinflammation plays a pivotal role in Alzheimer's disease (AD) and Parkinson's disease (PD), the leading causes of dementia. These neurological disorders are characterized by the accumulation of misfolded proteins such as amyloid-ß (Aß), tau protein and α-synuclein, contributing to mitochondrial fragmentation, oxidative stress, and neuroinflammation. Misfolded proteins activate microglia, which induces neuroinflammation, expression of pro-inflammatory cytokines and subsequently facilitates synaptic damage and neuronal loss. So far, all the proposed drugs were based on the inhibition of protein aggregation and were failed in clinical trials. Therefore, the treatment options of dementia are still a challenging issue. Thus, it is worthwhile to study alternative therapeutic strategies. In this context, there is increasing data on the pivotal role of transcription factor NF- E2 p45-related factor 2 (Nrf2) on the redox homeostasis and anti-inflammatory functions in neurodegenerative disorders. Interestingly, Nrf2 signaling pathway has shown upregulation of antioxidant genes, inhibition of microglia-mediated inflammation, and improved mitochondrial function in neurodegenerative diseases, suggesting Nrf2 activation could be a novel therapeutic approach to target pathogenesis. The present review will examine the correlation between Nrf2 signaling with neuroinflammation in AD and PD.

Potential Therapeutic Use of the Rosemary Diterpene Carnosic Acid for Alzheimer's Disease, Parkinson's Disease, and Long-COVID through NRF2 Activation to Counteract the NLRP3 Inflammasome

Rosemary (Rosmarinus officinalis [family Lamiaceae]), an herb of economic and gustatory repute, is employed in traditional medicines in many countries. Rosemary contains carnosic acid (CA) and carnosol (CS), abietane-type phenolic diterpenes, which account for most of its biological and pharmacological actions, although claims have also been made for contributions of another constituent, rosmarinic acid. This review focuses on the potential applications of CA and CS for Alzheimer's disease (AD), Parkinson's disease (PD), and coronavirus disease 2019 (COVID-19), in part via inhibition of the NLRP3 inflammasome. CA exerts antioxidant, anti-inflammatory, and neuroprotective effects via phase 2 enzyme induction initiated by activation of the KEAP1/NRF2 transcriptional pathway, which in turn attenuates NLRP3 activation. In addition, we propose that CA-related compounds may serve as therapeutics against the brain-related after-effects of SARS-CoV-2 infection, termed "long-COVID." One factor that contributes to COVID-19 is cytokine storm emanating from macrophages as a result of unregulated inflammation in and around lung epithelial and endovascular cells. Additionally, neurological aftereffects such as anxiety and "brain fog" are becoming a major issue for both the pandemic and post-pandemic period. Many reports hold that unregulated NLRP3 inflammasome activation may potentially contribute to the severity of COVID-19 and its aftermath. It is therefore possible that suppression of NLRP3 inflammasome activity may prove efficacious against both acute lung disease and chronic neurological after-effects. Because CA has been shown to not only act systemically but also to penetrate the blood-brain barrier and reach the brain parenchyma to exert neuroprotective effects, we discuss the evidence that CA or rosemary extracts containing CA may represent an effective countermeasure against both acute and chronic pathological events initiated by SARS-CoV-2 infection as well as other chronic neurodegenerative diseases including AD and PD.

Iso-seco-tanapartholide activates Nrf2 signaling pathway through Keap1 modification and oligomerization to exert anti-inflammatory effects

Covalent modification of Keap1 results in reducing ubiquitination and the accumulation of Nrf2, which subsequently initiates the transcription of cellular anti-oxidant and anti-inflammatory genes. Iso-seco-tanapartholide (IST), a sesquiterpene isolated from the traditional Chinese medicine Artemisia argyi, had been reported to possess NF-κB inhibitory activity. However, its deep anti-inflammatory effects and direct target have never been reported. Here we show that IST activated Nrf2 and increased its target gene expression. In particular, LPS-caused inflammation in vitro and in vivo was mitigated by IST-induced Nrf2 activation but aggravated by Nrf2 inhibition. Mechanically, IST targeted Keap1 proteins via alkylating its cysteine residues 151, 273, 288, and so on. Subsequently, the modifying agent IST was displaced by intermolecular sulfhydryl disulfide interchange to lead to a disulfide dimer of Keap1. The resulting conformational change of Keap1 liberated Nrf2 from sequestration and allowed it translocation to the nucleus to activate the transcriptional program. Further studies demonstrated that Keap1 dimer formation contributed to the anti-inflammatory effects of IST. Taken together, our findings reveal a new mechanism for Nrf2 activation and provide a potential lead compound to treat inflammatory diseases through targeting Keap1.

4-Octyl-Itaconate and Dimethyl Fumarate Inhibit COX2 Expression and Prostaglandin Production in Macrophages

Prostaglandins (PGs) are important proinflammatory lipid mediators, the significance of which is highlighted by the widespread and efficacious use of non-steroidal anti-inflammatory drugs (NSAIDs) in the treatment of inflammation. 4-Octyl itaconate (4-OI), a derivative of the Krebs cycle-derived metabolite itaconate, has recently garnered much interest as an anti-inflammatory agent. Here we show that 4-OI limits PG production in macrophages stimulated with the Toll-like receptor 1/2 (TLR1/2) ligand Pam3CSK4. This decrease in PG secretion is due to a robust suppression of COX2 expression by 4-OI, with both mRNA and protein levels decreased. Dimethyl fumarate (DMF), a fumarate derivative used in the treatment of multiple sclerosis (MS), with properties similar to itaconate, replicated the phenotype observed with 4-OI. We also demonstrate that the decrease in COX2 expression and inhibition of downstream prostaglandin production occurs in an NRF2-independent manner. Our findings provide a new insight into the potential of 4-OI as an anti-inflammatory agent and also identifies a novel anti-inflammatory function of DMF.

Protein abundance and folding rather than the redox state of Kelch13 determine the artemisinin susceptibility of Plasmodium falciparum

Decreased susceptibilities of the human malaria parasite Plasmodium falciparum towards the endoperoxide antimalarial artemisinin are linked to mutations of residue C580 of PfKelch13, a homologue of the redox sensor Keap1 and other vertebrate BTB-Kelch proteins. Here, we addressed whether mutations alter the artemisinin susceptibility by modifying the redox properties of PfKelch13 or by compromising its native fold or abundance. Using selection-linked integration and the glmS ribozyme, efficient down-regulation of PfKelch13 resulted in ring-stage survival rates around 40%. While the loss of the thiol group of C469 or of the potential disulfide bond between residues C580 and C532 had no effect on the artemisinin susceptibility, the thiol group of C473 could not be replaced. Furthermore, we detected two different forms of PfKelch13 with distinct electrophoretic mobilities around 85 and 95 kDa, suggesting an unidentified post-translational modification. We also established a protocol for the production of recombinant PfKelch13 and produced an antibody against the protein. Recombinant PfKelch13 adopted alternative oligomeric states and only two of its seven cysteine residues, C469 and C473, reacted with Ellman's reagent. While common field mutations resulted in misfolded and completely insoluble recombinant PfKelch13, cysteine-to-serine replacements had no effect on the solubility except for residue C473. In summary, in contrast to residues C469, C532, and C580, the surface-exposed thiol group of residue C473 appears to be essential. However, not the redox properties but impaired folding of PfKelch13, resulting in a decreased PfKelch13 abundance, alters the artemisinin susceptibility and is the central parameter for mutant selection.

Anticancer Targets and Signaling Pathways Activated by Britannin and Related Pseudoguaianolide Sesquiterpene Lactones

Sesquiterpene lactones (SLs) are abundant in plants and display a large spectrum of bioactivities. The compound britannin (BRT), found in different Inula species, is a pseudoguaianolide-type SL equipped with a typical and highly reactive α-methylene-γ-lactone moiety. The bioproperties of BRT and related pseudoguaianolide SLs, including helenalin, gaillardin, bigelovin and others, have been reviewed. Marked anticancer activities of BRT have been evidenced in vitro and in vivo with different tumor models. Three main mechanisms are implicated: (i) interference with the NFκB/ROS pathway, a mechanism common to many other SL monomers and dimers; (ii) blockade of the Keap1-Nrf2 pathway, with a covalent binding to a cysteine residue of Keap1 via the reactive α-methylene unit of BRT; (iii) a modulation of the c-Myc/HIF-1α signaling axis leading to a downregulation of the PD-1/PD-L1 immune checkpoint and activation of cytotoxic T lymphocytes. The non-specific reactivity of the α-methylene-γ-lactone moiety with the sulfhydryl groups of proteins is discussed. Options to reduce or abolish this reactivity have been proposed. Emphasis is placed on the capacity of BRT to modulate the tumor microenvironment and the immune-modulatory action of the natural product. The present review recapitulates the anticancer effects of BRT, some central concerns with SLs and discusses the implication of the PD1/PD-L1 checkpoint in its antitumor action.

Protein Carbonylation: Emerging Roles in Plant Redox Biology and Future Prospects

Plants are sessile in nature and they perceive and react to environmental stresses such as abiotic and biotic factors. These induce a change in the cellular homeostasis of reactive oxygen species (ROS). ROS are known to react with cellular components, including DNA, lipids, and proteins, and to interfere with hormone signaling via several post-translational modifications (PTMs). Protein carbonylation (PC) is a non-enzymatic and irreversible PTM induced by ROS. The non-enzymatic feature of the carbonylation reaction has slowed the efforts to identify functions regulated by PC in plants. Yet, in prokaryotic and animal cells, studies have shown the relevance of protein carbonylation as a signal transduction mechanism in physiological processes including hydrogen peroxide sensing, cell proliferation and survival, ferroptosis, and antioxidant response. In this review, we provide a detailed update on the most recent findings pertaining to the role of PC and its implications in various physiological processes in plants. By leveraging the progress made in bacteria and animals, we highlight the main challenges in studying the impacts of carbonylation on protein functions in vivo and the knowledge gap in plants. Inspired by the success stories in animal sciences, we then suggest a few approaches that could be undertaken to overcome these challenges in plant research. Overall, this review describes the state of protein carbonylation research in plants and proposes new research avenues on the link between protein carbonylation and plant redox biology.

Nrf2 as a potential target for Parkinson's disease therapy

Parkinson's disease (PD) is a complex neurodegenerative disorder featuring both motor and nonmotor symptoms associated with a progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Conventionally, PD treatment options have focused on dopamine replacement and provide only symptomatic relief. However, disease-modifying therapies are still unavailable. Mechanistically, genetic and environmental factors can produce oxidative stress which has been implicated as a core contributor to the initiation and progression of PD through the degeneration of dopaminergic neurons. Importantly, nuclear factor erythroid 2-related factor 2 (Nrf2) is essential for maintaining redox homeostasis by binding to the antioxidant response element which exists in the promoter regions of most genes coding for antioxidant enzymes. Furthermore, protein kinase C, mitogen-activated protein kinases, and phosphotidylinositol 3-kinase have been implicated in the regulation of Nrf2 activity during PD. Here, we review the evidence supporting the regulation of Nrf2 through Keap1-dependent and Keap1-independent mechanisms. We also address that targeting Nrf2 may provide a therapeutic option to mitigate oxidative stress-associated PD. Finally, we discuss currently known classes of small molecule activators of Nrf2, including Nrf2-activating compounds in PD.

Role of Polyphenols as Antioxidant Supplementation in Ischemic Stroke

Stroke is the second most common cause of death globally and the leading cause of death in China. The pathogenesis of cerebral ischemia injury is complex, and oxidative stress plays an important role in the fundamental pathologic progression of cerebral damage in ischemic stroke. Previous studies have preliminarily confirmed that oxidative stress should be a potential therapeutic target and antioxidant as a treatment strategy for ischemic stroke. Emerging experimental studies have demonstrated that polyphenols exert the antioxidant potential to play the neuroprotection role after ischemic stroke. This comprehensive review summarizes antioxidant effects of some polyphenols, which have the most inhibition effects on reactive oxygen species generation and oxidative stress after ischemic stroke.

Targeting NRF2 to treat cancer

NRF2 is a basic leucine zipper (bZip) transcription factor that is the master regulator of redox homeostasis. Under basal conditions, the cellular level of NRF2 is low due to a posttranslational regulation by the ubiquitin proteasome system (UPS). But, when an organism is challenged with oxidative or xenobiotic stress, the NRF2 pathway is activated by inhibition of the E3 ubiquitin ligase complex that normally marks NRF2 for destruction. For several decades, researchers have searched for molecules that can intentionally activate NRF2, as this was shown to be a means to prevent certain diseases, at least in animal models. In the present era, there are many compounds known to activate the NRF2 pathway including natural products and synthetic compounds, covalent and non-covalent compounds, and others. However, it was also revealed that like many protective pathways, the NRF2 pathway has a dark side. Just as NRF2 can protect normal cells from damage, it can protect malignant cells from damage. As cells transform, they are exposed to many stressors and aberrant upregulation of NRF2 can facilitate transformation and it can help cancer cells to grow, to spread, and to resist treatment. For this reason, researchers are also interested in the discovery and development of NRF2 inhibitors. In the present review, we will begin with a general discussion of NRF2 structure and function, we will discuss the latest in NRF2 non-covalent activators, and we will discuss the current state of NRF2 inhibitors.

Potential Cancer- and Alzheimer's Disease-Targeting Phosphodiesterase Inhibitors from Uvaria alba: Insights from In Vitro and Consensus Virtual Screening

Inhibition of the major cyclic adenosine monophosphate-metabolizing enzyme PDE4 has shown potential for the discovery of drugs for cancer, inflammation, and neurodegenerative disorders such as Alzheimer's disease. As a springboard to explore new anti-cancer and anti-Alzheimer's chemical prototypes from rare Annonaceae species, the present study evaluated anti-PDE4B along with antiproliferative and anti-cholinesterase activities of the extracts of the Philippine endemic species Uvaria alba using in vitro assays and framed the resulting biological significance through computational binding and reactivity-based experiments. Thus, the PDE4 B2B-inhibiting dichloromethane sub-extract (UaD) of U. alba elicited antiproliferative activity against chronic myelogenous leukemia (K-562) and cytostatic effects against human cervical cancer (HeLa). The extract also profoundly inhibited acetylcholinesterase (AChE), an enzyme involved in the progression of neurodegenerative diseases. Chemical profiling analysis of the bioactive extract identified 18 putative secondary metabolites. Molecular docking and molecular dynamics simulations showed strong free energy binding mechanisms and dynamic stability at 50-ns simulations in the catalytic domains of PDE4 B2B, ubiquitin-specific peptidase 14, and Kelch-like ECH-associated protein 1 (KEAP-1 Kelch domain) for the benzylated dihydroflavone dichamanetin (16), and of an AChE and KEAP-1 BTB domain for 3-(3,4-dihydroxybenzyl)-3',4',6-trihydroxy-2,4-dimethoxychalcone (8) and grandifloracin (15), respectively. Density functional theory calculations to demonstrate Michael addition reaction of the most electrophilic metabolite and kinetically stable grandifloracin (15) with Cys151 of the KEAP-1 BTB domain illustrated favorable formation of a β-addition adduct. The top-ranked compounds also conferred favorable in silico pharmacokinetic properties.

SUMO-Modification of Human Nrf2 at K110 and K533 Regulates Its Nucleocytoplasmic Localization, Stability and Transcriptional Activity

BACKGROUND/AIMS

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that binds to the antioxidant response element(s) (ARE) in target gene promoters, enabling oxidatively stressed cells to respond in order to restore redox homeostasis. Post-translational modifications (PTMs) that mediate activation of Nrf2, in the cytosol and its release from Keap1, have been extensively studied but PTMs that impact its biology after activation are beginning to emerge. In this regard, PTMs like acetylation, phosphorylation, ubiquitination and sumoylation contribute towards the Nrf2 subcellular localization, and its transactivation function. We previously demonstrated that Nrf2 traffics to the promyelocytic leukemia-nuclear bodies (PML-NB), where it is a target for modification by small ubiquitin-like modifier (SUMO) proteins (sumoylation), but the site(s) for SUMO conjugation have not been determined. In this study, we aim to identify SUMO-2 conjugation site(s) and explore the impact, sumoylation of the site(s) have on Nrf2 stability, nuclear localization and transcriptional activation of its target gene expression upon oxidative stress.

METHODS

The putative SUMO-binding sites in Nrf2 for human isoform1 (NP_006155.2) and mouse homolog (NP_035032.1) were identified using a computer-based SUMO-predictive software (SUMOplot™). Site-directed mutagenesis, immunoblot analysis, and ARE-mediated reporter gene assays were used to assess the impact of sumoylation on these site(s) in vitro. Effect of mutation of these sumoylation sites of Nrf2 on expression of Heme Oxygenase1 (HO-1) was determined in HEK293T cell.

RESULTS


Eight putative sumoylation sites were identified by SUMOplot™ analysis. Out of the eight predicted sites only one 532LKDE535 of human (h) and its homologous 524LKDE527 of mouse (m) Nrf2, exactly matches the SUMO-binding consensus motif. The other high probability SUMO-acceptor site identified was residue K110, in the motifs 109PKSD112 and 109PKQD112 of human and mouse Nrf2, respectively. Mutational analysis of putative sumoylation sites (human (h)/mouse (m)
K110, hK533 and mK525) showed that these residues are needed for SUMO-2 conjugation, nuclear localization and ARE driven transcription of reporter genes and the endogenous HO-1 expression by Nrf2. These residues also stabilized Nrf2, as evident from shorter half-lives of the mutant protein compared to wild-type Nrf2.

CONCLUSION

Our findings indicate that SUMO-2
mediated sumoylation of K110 and K533 in human Nrf2 regulates in part its transcriptional activity by enhancing its stabilization and nuclear localization.

PERK Pathway and Neurodegenerative Disease: To Inhibit or to Activate?

With the extension of life span in recent decades, there is an increasing burden of late-onset neurodegenerative diseases, for which effective treatments are lacking. Neurodegenerative diseases include the widespread Alzheimer’s disease (AD) and Parkinson’s disease (PD), the less frequent Huntington’s disease (HD) and Amyotrophic Lateral Sclerosis (ALS) and also rare early-onset diseases linked to mutations that cause protein aggregation or loss of function in genes that maintain protein homeostasis. The difficulties in applying gene therapy approaches to tackle these diseases is drawing increasing attention to strategies that aim to inhibit cellular toxicity and restore homeostasis by intervening in cellular pathways. These include the unfolded protein response (UPR), activated in response to endoplasmic reticulum (ER) stress, a cellular affliction that is shared by these diseases. Special focus is turned to the PKR-like ER kinase (PERK) pathway of the UPR as a target for intervention. However, the complexity of the pathway and its ability to promote cell survival or death, depending on ER stress resolution, has led to some confusion in conflicting studies. Both inhibition and activation of the PERK pathway have been reported to be beneficial in disease models, although there are also some reports where they are counterproductive. Although with the current knowledge a definitive answer cannot be given on whether it is better to activate or to inhibit the pathway, the most encouraging strategies appear to rely on boosting some steps without compromising downstream recovery.

Modulating Nrf2 transcription factor activity: Revealing the regulatory mechanisms of antioxidant defenses during hibernation in 13-lined ground squirrels

Mammalian hibernators undergo major behavioural, physiological and biochemical changes to survive hypothermia, ischaemia-reperfusion and finite fuel reserves during days or weeks of continuous torpor. During hibernation, the 13-lined ground squirrel (Ictidomys tridecemlineatus) undergoes a global suppression of energetically expensive processes such as transcription and translation, while selectively upregulating certain genes/proteins to mitigate torpor-related damage. Antioxidant defenses are critical for preventing damage caused by reactive oxygen species (ROS) during torpor and arousal, and Nrf2 is a critical regulator of these antioxidant genes. This study analysed the relative protein expression levels of Nrf2, KEAP1, small Mafs (MafF, MafK and MafG) and catalase and the regulation of Nrf2 transcription factors by post-translational modifications (PTMs) and protein-protein interactions with a negative regulator (KEAP1) during hibernation. It was found that a significant increase in MafK during late torpor predicated an increase in relative Nrf2 and catalase levels seen in arousal. Additionally, Nrf2-KEAP1 protein-protein interactions and Nrf2 PTMs, including serine phosphorylation and lysine acetylation, were responsive to cycles of torpor-arousal with peak responses occurring during arousal. These peaks seen during arousal correspond to a surge in oxygen consumption, which causes increased ROS production. Thus, these regulatory mechanisms could be important during hibernation because they provide mechanisms for mitigating the deleterious effects of oxidative stress by modifying Nrf2 expression and function in an energetically inexpensive manner.

Interdependence of Anti-Inflammatory and Antioxidant Properties of Squalene-Implication for Cardiovascular Health

Cardiovascular diseases (CVD) have been recognized as the leading cause of mortality worldwide, accounting for 31% of global mortality. Among the risk factors of CVD, hyperlipidemia has been established as the most potent risk factor. Statins, a class of drug that reduces lower-density lipoprotein cholesterol (LDL-C), are the preferred medical treatment. However, due to the development of statin-associated muscle symptoms, statins are associated with patients' discontinuation and nonadherence. Other statin-induced side effects, such as hepatotoxicity and gastrointestinal upset, all contribute to patients choosing alternative medicines. Squalene (SQ), an unsaturated hydrocarbon naturally synthesized in plants and animals, could become the alternative treatment or supplementary agent for cardiovascular health. SQ has been shown to exert cardioprotective effect via its antioxidant activity. Oxidative stress and inflammatory responses are closely related to each other, which proposes an interdependence relation between antioxidant and anti-inflammatory. Therefore, this review explores the interdependence between the antioxidant and anti-inflammatory effects of SQ implicated on cardiovascular health.

Covalent modification of Keap1 at Cys77 and Cys434 by pubescenoside a suppresses oxidative stress-induced NLRP3 inflammasome activation in myocardial ischemia-reperfusion injury

Background and Purpose: Kelch ECH-associating protein 1 (Keap1) is a crucial chaperonin for E3 ubiquitin ligases. Modification of the key reactive cysteine residues in Keap1 affects the interaction between Keap1 and its substrate nuclear factor erythroid 2-related factor 2 (Nrf2), subsequently regulating oxidative stress and NLPR3 inflammasome activation, which are important factors for myocardial ischemia-reperfusion injury (MI/RI). Pubescenoside A (PBA), an active compound from Ilex pubescens, has antithrombotic and anti-inflammatory effects. However, the effect of PBA on MI/RI is still unknown. In the present study, we aimed to determine whether PBA can protect the heart against MI/RI and clarify the direct target and the underlying mechanism of PBA.

Methods: The left anterior descending artery (LAD) ligation-induced MI/RI mice model or oxygen and glucose deprivation/reperfusion (OGD/R) were used to evaluate the cardioprotective effect of PBA. Pull-down assays, co-immunoprecipitation (Co-IP) assays, LC/MS/MS, isothermal calorimetry (ITC) experiments and covalent docking were used to identify the target of PBA.

Results: PBA protected cardiomyocytes against OGD/R in vitro and LAD-induced MI/RI in vivo. PBA suppressed NLRP3 inflammation activation and induced the Nrf2 signaling pathway. Interestingly, PBA targeted Keap1 by selectively covalently binding to conserved cysteine residues, cysteine 77 (Cys77) in the BTB domain and cysteine 434 (Cys434) in the Kelch domain of Keap1, subsequently inhibiting ubiquitination of Nrf2 and activating antioxidant enzymes. Additionally, the cysteines of Keap1 has different degree of activation by PBA as follows: Cys77 > Cys434 > Cys23 > Cys38 > Cys226 > Cys273, which further elucidates the cysteine sensitivity of Keap1.

Conclusions: Our results indicated that PBA might be a new Nrf2 activator that covalently binds to two critical domains of Keap1, and shows cardioprotective activities against ischemia-reperfusion injury.

Development of a Homogeneous Time-Resolved Fluorescence Resonance Energy Transfer (TR-FRET) Assay for the Inhibition of Keap1-Nrf2 Protein-Protein Interaction

The transcription factor, nuclear factor erythroid 2-related factor 2 (Nrf2), plays a major role in regulating the antioxidant defense system through the Kelch-like ECH-associated protein 1-Nrf2-antioxidant response element (Keap1-Nrf2-ARE) pathway. Small-molecule inhibitors targeting Keap1-Nrf2 protein-protein interaction (PPI) decrease the rate of Nrf2 degradation by the 26S proteasome and thus increase the intracellular level of Nrf2, which translocates into the nucleus, leading to upregulated expression of cytoprotective and antioxidant enzymes. Such inhibitors can be developed into potential preventive and therapeutic agents of diseases caused by oxidative damage. To more effectively identify promising Nrf2 activators through the inhibition of Keap1-Nrf2 PPI, a homogeneous time-resolved fluorescence resonance energy transfer (TR-FRET) assay was developed in this work by indirectly labeling the Keap1 Kelch domain protein with Tb-anti-His antibody as the donor and using, as the acceptor, fluorescein isothiocyanate (FITC)-labeled 9mer Nrf2 peptide amide, the same fluorescent probe that was used in an earlier fluorescence polarization (FP) assay. Assay conditions, including concentrations of the various components, buffer type, and incubation time, were optimized in the TR-FRET competition assay with known small-molecule inhibitors of Keap1-Nrf2 PPI. Under the optimized conditions, the Keap1-Nrf2 TR-FRET assay exhibited great sensitivity with a high dynamic range and considerable stability for as long as 5 h. The Z' factor was determined to be 0.82, suggesting that the assay is suitable for high-throughput screening and lead optimization of inhibitors of Keap1-Nrf2 PPI. Furthermore, the TR-FRET assay is capable of differentiating potent inhibitors of Keap1-Nrf2 PPI down to the subnanomolar inhibition constant (Ki) range.

Clinical Implications of KEAP1-NFE2L2 Mutations in NSCLC

The KEAP1-NFE2L2 pathway is an important modulator of cell homeostasis. Mutations in this pathway are common in NSCLC and have been associated with enhanced tumor growth and aggressiveness. In addition, tumors with mutations in the KEAP1-NFE2L2 pathway have been reported in preclinical and clinical studies to convey refractoriness to cancer-directed therapy such as radiation, chemotherapy, and targeted therapy. The role of immunotherapy in this patient population is less clear, and there are conflicting studies on the efficacy of immune checkpoint inhibitors in KEAP1-NFE2L2-mutant NSCLC. Here, we review the current clinical evidence on several classes of anticancer therapeutics in KEAP1-NFE2L2-mutant tumors. Furthermore, we provide an overview of the landscape of the current clinical trials in this patient population, highlighting the work being done with mTORC1, mTORC2, and glutaminase inhibition.

An Overview of Nrf2 Signaling Pathway and Its Role in Inflammation

Inflammation is a key driver in many pathological conditions such as allergy, cancer, Alzheimer’s disease, and many others, and the current state of available drugs prompted researchers to explore new therapeutic targets. In this context, accumulating evidence indicates that the transcription factor Nrf2 plays a pivotal role controlling the expression of antioxidant genes that ultimately exert anti-inflammatory functions. Nrf2 and its principal negative regulator, the E3 ligase adaptor Kelch-like ECH- associated protein 1 (Keap1), play a central role in the maintenance of intracellular redox homeostasis and regulation of inflammation. Interestingly, Nrf2 is proved to contribute to the regulation of the heme oxygenase-1 (HO-1) axis, which is a potent anti-inflammatory target. Recent studies showed a connection between the Nrf2/antioxidant response element (ARE) system and the expression of inflammatory mediators, NF-κB pathway and macrophage metabolism. This suggests a new strategy for designing chemical agents as modulators of Nrf2 dependent pathways to target the immune response. Therefore, the present review will examine the relationship between Nrf2 signaling and the inflammation as well as possible approaches for the therapeutic modulation of this pathway.

Redox Post-translational Modifications of Protein Thiols in Brain Aging and Neurodegenerative Conditions-Focus on S-Nitrosation

Reactive oxygen species and reactive nitrogen species (RONS) are by-products of aerobic metabolism. RONS trigger a signaling cascade that can be transduced through oxidation-reduction (redox)-based post-translational modifications (redox PTMs) of protein thiols. This redox signaling is essential for normal cellular physiology and coordinately regulates the function of redox-sensitive proteins. It plays a particularly important role in the brain, which is a major producer of RONS. Aberrant redox PTMs of protein thiols can impair protein function and are associated with several diseases. This mini review article aims to evaluate the role of redox PTMs of protein thiols, in particular S-nitrosation, in brain aging, and in neurodegenerative diseases. It also discusses the potential of using redox-based therapeutic approaches for neurodegenerative conditions.

Molecular Mechanism of Cellular Oxidative Stress Sensing by Keap1

The Keap1-Nrf2 system plays a central role in the oxidative stress response; however, the identity of the reactive oxygen species sensor within Keap1 remains poorly understood. Here, we show that a Keap1 mutant lacking 11 cysteine residues retains the ability to target Nrf2 for degradation, but it is unable to respond to cysteine-reactive Nrf2 inducers. Of the 11 mutated cysteine residues, we find that 4 (Cys226/613/622/624) are important for sensing hydrogen peroxide. Our analyses of multiple mutant mice lines, complemented by MEFs expressing a series of Keap1 mutants, reveal that Keap1 uses the cysteine residues redundantly to set up an elaborate fail-safe mechanism in which specific combinations of these four cysteine residues can form a disulfide bond to sense hydrogen peroxide. This sensing mechanism is distinct from that used for electrophilic Nrf2 inducers, demonstrating that Keap1 is equipped with multiple cysteine-based sensors to detect various endogenous and exogenous stresses.

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.

Role of thiocyanate in the modulation of myeloperoxidase-derived oxidant induced damage to macrophages

Myeloperoxidase (MPO) is a vital component of the innate immune system, which produces the potent oxidant hypochlorous acid (HOCl) to kill invading pathogens. However, an overproduction of HOCl during chronic inflammatory conditions causes damage to host cells, which promotes disease, including atherosclerosis. As such, there is increasing interest in the use of thiocyanate (SCN^-) therapeutically to decrease inflammatory disease, as SCN^- is the favoured substrate for MPO, and a potent competitive inhibitor of HOCl formation. Use of SCN^- by MPO forms hypothiocyanous acid (HOSCN), which can be less damaging to mammalian cells. In this study, we examined the ability of SCN^- to modulate damage to macrophages induced by HOCl, which is relevant to lesion formation in atherosclerosis. Addition of SCN^- prevented HOCl-mediated cell death, altered the extent and nature of thiol oxidation and the phosphorylation of mitogen activated protein kinases. These changes were dependent on the concentration of SCN^- and were observed in some cases, at a sub-stoichiometric ratio of SCN^-: HOCl. Co-treatment with SCN^- also modulated HOCl-induced perturbations in the expression of various antioxidant and inflammatory genes. In general, the data reflect the conversion of HOCl to HOSCN, which can induce reversible modifications that are repairable by cells. However, our data also highlight the ability of HOSCN to increase pro-inflammatory gene expression and cytokine/chemokine release, which may be relevant to the use of SCN^- therapeutically in atherosclerosis. Overall, this study provides further insight into the cellular pathways by which SCN^- could exert protective effects on supplementation to decrease the development of chronic inflammatory diseases, such as atherosclerosis.

The Molecular Mechanisms Regulating the KEAP1-NRF2 Pathway

The KEAP1-NRF2 pathway is the principal protective response to oxidative and electrophilic stresses. Under homeostatic conditions, KEAP1 forms part of an E3 ubiquitin ligase, which tightly regulates the activity of the transcription factor NRF2 by targeting it for ubiquitination and proteasome-dependent degradation. In response to stress, an intricate molecular mechanism facilitated by sensor cysteines within KEAP1 allows NRF2 to escape ubiquitination, accumulate within the cell, and translocate to the nucleus, where it can promote its antioxidant transcription program. Recent advances have revealed that KEAP1 contains multiple stress sensors and inactivation modalities, which together allow diverse cellular inputs, from oxidative stress and cellular metabolites to dysregulated autophagy, to regulate NRF2 activity. This integration of the KEAP1-NRF2 system into multiple cellular signaling and metabolic pathways places NRF2 activation as a critical regulatory node in many disease phenotypes and suggests that the pharmaceutical modulation of NRF2's cytoprotective activity will be beneficial for human health in a broad range of noncommunicable diseases.

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.

The role of natural products in revealing NRF2 function

Covering: up to 2020The transcription factor NRF2 is one of the body's major defense mechanisms, driving transcription of >300 antioxidant response element (ARE)-regulated genes that are involved in many critical cellular processes including redox regulation, proteostasis, xenobiotic detoxification, and primary metabolism. The transcription factor NRF2 and natural products have an intimately entwined history, as the discovery of NRF2 and much of its rich biology were revealed using natural products both intentionally and unintentionally. In addition, in the last decade a more sinister aspect of NRF2 biology has been revealed. NRF2 is normally present at very low cellular levels and only activated when needed, however, it has been recently revealed that chronic, high levels of NRF2 can lead to diseases such as diabetes and cancer, and may play a role in other diseases. Again, this "dark side" of NRF2 was revealed and studied largely using a natural product, the quassinoid, brusatol. In the present review, we provide an overview of NRF2 structure and function to orient the general reader, we will discuss the history of NRF2 and NRF2-activating compounds and the biology these have revealed, and we will delve into the dark side of NRF2 and contemporary issues related to the dark side biology and the role of natural products in dissecting this biology.

TBHQ Attenuates Neurotoxicity Induced by Methamphetamine in the VTA through the Nrf2/HO-1 and PI3K/AKT Signaling Pathways

Methamphetamine (METH) leads to nervous system toxicity. Long-term exposure to METH results in damage to dopamine neurons in the ventral tegmental area (VTA), and depression-like behavior is a clinical symptom of this toxicity. The current study was designed to investigate whether the antioxidant tertiary butylhydroquinone (TBHQ) can alleviate neurotoxicity through both antioxidative stress and antiapoptotic signaling pathways in the VTA. Rats were randomly divided into a control group, a METH-treated group (METH group), and a METH+TBHQ-treated group (METH+TBHQ group). Intraperitoneal injections of METH at a dose of 10 mg/kg were administered to the rats in the METH and METH+TBHQ groups for one week, and METH was then administered at a dose that increased by 1 mg/kg per week until the sixth week, when the daily dosage reached 15 mg/kg. The rats in the METH+TBHQ group received 12.5 mg/kg TBHQ intragastrically. Chronic exposure to METH resulted in increased immobility times in the forced swimming test (FST) and tail suspension test (TST) and led to depression-like behavior. The production of reactive oxygen species (ROS) and apoptosis levels were increased in the VTA of animals in the METH-treated group. METH downregulated Nrf2, HO-1, PI3K, and AKT, key factors of oxidative stress, and the apoptosis signaling pathway. Moreover, METH increased the caspase-3 immunocontent. These changes were reversed by treatment with the antioxidant TBHQ. The results indicate that TBHQ can enhance Nrf2-induced antioxidative stress and PI3K-induced antiapoptotic effects, which can alleviate METH-induced ROS and apoptosis, and that the crosstalk between Nrf2 and PI3K/AKT is likely the key factor involved in the protective effect of TBHQ against METH-induced chronic nervous system toxicity.

Nrf2 activation through the inhibition of Keap1-Nrf2 protein-protein interaction

Activation of the transcription factor Nrf2 via the Keap1-Nrf2-ARE signaling system regulates the transcription and subsequent expression of cellular cytoprotective proteins and plays a crucial role in preventing pathological conditions exacerbated by the overproduction of oxidative stress. In addition to electrophilic modulators, direct non-covalent inhibitors that interrupt the Keap1-Nrf2 protein-protein interaction (PPI) leading to Nrf2 activation have attracted a great deal of attention as potential preventive and therapeutic agents for oxidative stress-related diseases. Structural studies of Keap1-binding ligands, development of biochemical and cellular assays, and new structure-based design approaches have facilitated the discovery of small molecule PPI inhibitors. This perspective reviews the Keap1-Nrf2-ARE system, its physiological functions, and the recent progress in the discovery and the potential applications of direct inhibitors of Keap1-Nrf2 PPI.

Structural and mechanistic insights into the Keap1-Nrf2 system as a route to drug discovery

The proteins Keap1 and Nrf2 together act as a cytoprotective mechanism that enables cells to overcome electrophilic and oxidative stress. Research has shown that manipulating this system by modulating the Keap1-Nrf2 interaction either through inhibition at the binding interface or via the covalent modification of Keap1 could provide a powerful therapeutic strategy for a range of diseases. However, despite intensive investigation of the system and significant progress in the development of inhibitory small molecules, there is still much to learn about the pathways associated with the Keap1-Nrf2 system and the structural details underpinning its mechanism of action. In this review, we discuss how a deeper understanding could prove revolutionary in the development of new inhibitors and activators as well as guiding how to best harness Keap1 for targeted protein degradation.