Identification of a novel small-molecule Keap1-Nrf2 PPI inhibitor with cytoprotective effects on LPS-induced cardiomyopathy

Icariin ameliorates osteoporosis in ovariectomized rats by targeting Cullin 3/Nrf2/OH pathway for osteoclast inhibition

Osteoporosis, characterized by low bone mass and bone microarchitecture breakdown, has become a growing public health problem. The increase in oxidative stress could lead to an imbalance between osteoblasts-mediated osteogenesis and osteoclast-mediated bone resorption, which gives rise to osteoporosis. Nrf2 is a master transcription factor that regulates oxidative stress and has recently been reported to take part in the development of osteoporosis. Icariin, a leading active flavonoid in herbal Epimedium pubescens, has significant antioxidant activity in and is widely applied for treating bone diseases. In this study, we aimed to explore the effect of icariin on osteoclastogenesis and its potential mechanism from the perspective of oxidative stress inhibition, using ovariectomized (OVX) rats and RANKL-induced RAW264.7 cells. Our results demonstrated that icariin-treated OVX rats exhibited higher bone density, fewer tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts, and lower ROS levels in bone tissues than vehicle-treated OVX rats. Also, icariin suppressed osteoclast differentiation and inhibited the expression of osteoclastogenesis-related genes, such as NFATc1, Ctsk, Trap, and c-Fos, in RANKL-induced RAW264.7 cells. Icariin also reduced intracellular ROS levels by increasing the expression of nuclear Nrf2 and HO-1. Further mechanistic studies showed icariin inhibited Cullin 3 expression and could delay Nrf2 degradation by reducing the ubiquitination of endogenous Nrf2 in RANKL-stimulated RAW264.7 cells, and these effects were markedly reversed by cullin three overexpression. These findings suggest icariin alleviated osteoporosis by suppressing osteoclastogenesis via targeting the Cullin 3/Nrf2/OH signaling pathway. Our study implied that icariin may be a potential candidate to treat osteoporosis.

Ferroptosis mechanisms and regulations in cardiovascular diseases in the past, present, and future

Cardiovascular diseases (CVDs) are the main diseases that endanger human health, and their risk factors contribute to high morbidity and a high rate of hospitalization. Cell death is the most important pathophysiology in CVDs. As one of the cell death mechanisms, ferroptosis is a new form of regulated cell death (RCD) that broadly participates in CVDs (such as myocardial infarction, heart transplantation, atherosclerosis, heart failure, ischaemia/reperfusion (I/R) injury, atrial fibrillation, cardiomyopathy (radiation-induced cardiomyopathy, diabetes cardiomyopathy, sepsis-induced cardiac injury, doxorubicin-induced cardiac injury, iron overload cardiomyopathy, and hypertrophic cardiomyopathy), and pulmonary arterial hypertension), involving in iron regulation, metabolic mechanism and lipid peroxidation. This article reviews recent research on the mechanism and regulation of ferroptosis and its relationship with the occurrence and treatment of CVDs, aiming to provide new ideas and treatment targets for the clinical diagnosis and treatment of CVDs by clarifying the latest progress in CVDs research.

Discovery of anti-inflammatory agents from 3, 4-dihydronaphthalene-1(2H)-one derivatives by inhibiting NLRP3 inflammasome activation

NLRP3 inflammatory vesicles are a polymer of cellular innate immunity composed of a pair of proteins. The continuous activation of NOD-like receptor pyrin domain-containing protein 3 (NLRP3) inflammatory vesicles induces the occurrence and enhancement of inflammatory response. In this study, a series of 3, 4-dihydronaphthalene-1(2H)-one derivatives (DHNs, 6a-u, 7a-e, 8a-n) were synthesized and characterized by NMR and HRMS. We evaluated the cytotoxicity and anti-inflammatory activity of all compounds in vitro, and selected 7a substituted by 7-Br in A-ring and 2-pyridylaldehyde in C-ring as effective lead compounds. Specifically, 7a can block the assembly and activation of NLRP3 inflammasome by down-regulating the expression of NLPR3 and apoptosis-associated speck-like protein containing a CARD (ASC), and inhibiting the production of reactive oxygen species (ROS) and other inflammatory mediators. In addition, 7a inhibits the phosphorylation of inhibitor kappa B alpha (IκBα) and NF-κB/p65 and the nuclear translocation of p65, thereby inhibiting nuclear factor kappa-B (NF-κB) signaling. Molecular docking analysis confirmed that 7a could reasonably bind the active sites of NLRP3, ASC and p65 proteins. Therefore, 7a is predicted as a potential NLRP3 inflammatory vesicle inhibitor and deserves further research and development.

Rhizoma Paridis saponins attenuate Gram-negative bacteria-induced inflammatory acne by binding to KEAP1 and modulating Nrf2 and MAPK pathways

Acne vulgaris represents a chronic inflammatory condition, the pathogenesis of which is closely associated with the altered skin microbiome. Recent studies have implicated a profound role of Gram-negative bacteria in acne development, but there is a lack of antiacne agents targeting these bacteria. Polyphyllins are major components of Rhizoma Paridis with great anti-inflammatory potential. In this study, we aimed to evaluate the antiacne effects and the underlying mechanisms of PPH and a PPH-enriched Rhizoma Paridis extract (RPE) in treating the Gram-negative bacteria-induced acne. PPH and RPE treatments significantly suppressed the mRNA and protein expressions of interleukin (IL)-1β and IL-6 in lipopolysaccharide (LPS)-induced RAW 264.7 and HaCaT cells, along with the intracellular reactive oxygen species (ROS) generation. Furthermore, PPH and RPE inhibited the nuclear translocation of nuclear factor kappa-B (NF-κB) P65 in LPS-induced RAW 264.7 cells. Based on molecular docking, PPH could bind to kelch-like ECH-associated protein 1 (KEAP1) protein. PPH and RPE treatments could activate nuclear factor erythroid 2-related factor 2 (NRF2) and upregulate haem oxygenase-1 (HO-1). Moreover, RPE suppressed the mitogen-activated protein kinase (MAPK) pathway. Therefore, PPH-enriched RPE showed anti-inflammatory and antioxidative effects in vitro, which is promising for alternative antiacne therapeutic.

Discovery of marine phidianidine-based Nrf2 activators and their potential against oxLDL- and HG-induced injury in HUVECs

One effective strategy for treating atherosclerosis is to inhibit the injury of vascular endothelial cells (VECs) induced by oxidized low-density lipoprotein (oxLDL) and high glucose (HG). This study synthesized and evaluated a series of novel Nrf2 activators derived from the marine natural product phidianidine for their ability to protect human umbilical VECs against oxLDL- and HG-induced injury. The results of in vitro bioassays demonstrated that compound D-36 was the most promising Nrf2 activator, effectively inhibiting the apoptosis of HUVECs induced by oxLDL and HG. Furthermore, Nrf2 knockdown experiments confirmed that compound D-36 protected against oxLDL- and HG-induced apoptosis in HUVECs by activating the Nrf2 pathway. These findings provide important insights into a new chemotype of marine-derived Nrf2 activators that could potentially be optimized to develop effective anti-atherosclerosis agents.

Ginsenoside CK targeting KEAP1-DGR/Kelch domain disrupts the binding between KEAP1 and NRF2-DLG motif to ameliorate oxidative stress damage

BACKGROUND

Panax ginseng and Panax notoginseng as traditional Chinese medicines, are widely used in the treatment of qi deficiency, viral or bacterial infection, inflammation and cancer. Ginsenoside CK, an active metabolite of protopanoxadiol among the ginseng saponins, has been shown in previous studies to improve the organism's oxidative balance by regulating the KEAP1-NRF2/ARE pathway, thus slowing the progression of diseases. However, the specific targets and mechanisms of CK in improving oxidative stress remain unclear.

PURPOSE

The aim of this study was to determine the potential therapeutic targets and molecular mechanisms of CK in improving oxidative stress injury both in vitro and in vivo.

METHODS

LPS was used to induce oxidative damage in RAW 264.7 cells to evaluate the regulatory effects of CK on the KEAP1-NRF2/ARE pathway. Drug affinity responsive target stability technology (DARTS) combined with proteomics was employed to identify CK's potential target proteins. CK functional probe were designed to analyze the target protein using click chemistry. Furthermore, small molecule and protein interaction technologies were used to verify the mechanism, and computer dynamic simulation technology was used to analyze the interaction sites between CK and the target protein. The pharmacological effects and mechanism of CK in improving oxidative damage were verified in vivo by LPS-induced acute injury in mice and physical mechanical injury in rat soft tissues.

RESULTS

KEAP1 was identified as the target protein that CK regulates to improve oxidative damage through the KEAP1-NRF2/ARE pathway. CK competitively binds to the DGR/Kelch domain of KEAP1, disrupting the binding between DLG peptide in NRF2 and KEAP1, thereby inhibiting the occurrence of oxidative damage induced by LPS or physical mechanical stress.

CONCLUSIONS

CK functions as a natural KEAP1-NRF2 inhibitor, disrupting the binding between KEAP1 and NRF2-DLG motifs by targeting the DGR/Kelch domain of KEAP1, activating the antioxidant transcriptional program of NRF2, and reducing oxidative stress damage.

Allicin protects against LPS-induced cardiomyocyte injury by activating Nrf2-HO-1 and inhibiting NLRP3 pathways

BACKGROUND

Allicin is a bioactive compound with potent antioxidative activity and plays a protective effect in myocardial damage and fibrosis. The role and mechanism of Allicin in septic cardiomyopathy are unclear. In this study, we investigated the effects and underlying mechanisms of Allicin on lipopolysaccharide (LPS) induced injury in H9c2 cardiomyocytes.

METHODS

H9c2 cardiomyocyte cells were pretreated with Allicin (0, 25, 50, and 100 µM) for 2 h, followed by incubation with LPS (10 µg/mL) for 24 h at 37 °C. Cell viability (cell counting kit-8 [CCK-8]), apoptosis (TUNEL staining), oxidative stress (malondialdehyde [MDA] and superoxide dismutase [SOD]), and cytokines release (Interleukin beta [IL-β], Interleukin 6 [IL-6], and tumor necrosis factor-alpha [TNF-α]) were determined. The mRNA and protein expression of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and NLR family pyrin domain containing 3 (NLRP3) signaling pathway molecules were quantified by real-time quantitative PCR (RT-qPCR) and western blot, respectively.

RESULTS

Allicin had no effect on H9c2 cell viability but attenuated LPS-induced injury, with increased cell viability, reduction in inflammatory cytokines release, apoptosis, reduced MDA, and increased SOD (P < 0.05). Additionally, Allicin increased Nrf2 and cellular HO-1 expressions in LPS-treated H9c2 cells. Moreover, Allicin modulated the NLRP3 inflammasome, increased the cleaved caspase-1 (p10) protein, and attenuated the LPS-induced increase in NLRP3, pro-IL-1β, and IL-1β proteins. Silencing of Nrf2 by siRNA (siNrf2) significantly attenuated Allicin-induced increase in cell viability and HO-1 and decrease in NLRP3 protein in LPS-stimulated H9c2 cells.

CONCLUSIONS

Allicin protects cardiomyocytes against LPS‑induced injury through activation of Nrf2/HO-1 and inhibition of NLRP3 signaling pathways.

Regulated cell death pathways in cardiomyopathy

Heart disease is a worldwide health menace. Both intractable primary and secondary cardiomyopathies contribute to malignant cardiac dysfunction and mortality. One of the key cellular processes associated with cardiomyopathy is cardiomyocyte death. Cardiomyocytes are terminally differentiated cells with very limited regenerative capacity. Various insults can lead to irreversible damage of cardiomyocytes, contributing to progression of cardiac dysfunction. Accumulating evidence indicates that majority of cardiomyocyte death is executed by regulating molecular pathways, including apoptosis, ferroptosis, autophagy, pyroptosis, and necroptosis. Importantly, these forms of regulated cell death (RCD) are cardinal features in the pathogenesis of various cardiomyopathies, including dilated cardiomyopathy, diabetic cardiomyopathy, sepsis-induced cardiomyopathy, and drug-induced cardiomyopathy. The relevance between abnormity of RCD with adverse outcome of cardiomyopathy has been unequivocally evident. Therefore, there is an urgent need to uncover the molecular and cellular mechanisms for RCD in order to better understand the pathogenesis of cardiomyopathies. In this review, we summarize the latest progress from studies on RCD pathways in cardiomyocytes in context of the pathogenesis of cardiomyopathies, with particular emphasis on apoptosis, necroptosis, ferroptosis, autophagy, and pyroptosis. We also elaborate the crosstalk among various forms of RCD in pathologically stressed myocardium and the prospects of therapeutic applications targeted to various cell death pathways.

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.

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.

Evaluation of Proanthocyanidins from Kiwi Leaves (Actinidia chinensis) against Caco-2 Cells Oxidative Stress through Nrf2-ARE Signaling Pathway

Proanthocyanidins (PAs) are considered to be effective natural byproduct and bioactive antioxidants. However, few studies have focused on their mode of action pathways. In this study, reactive oxygen species (ROS), oxidative stress indices, real-time PCR, Western blotting, confocal microscopy, and molecular docking were used to investigate the protective effect of purified kiwi leaves PAs (PKLPs) on Caco-2 cells’ oxidative stress mechanisms. The results confirmed that pre-treatment with PKLPs significantly reduced H2O2-induced oxidative damage, accompanied by declining ROS levels and malondialdehyde (MDA) accumulation in the Caco-2 cells. The PKLPs upregulated the expression of antioxidative enzymes (GSH-px, CAT, T-SOD) and the relative mRNA (Nrf, HO-1, SOD-1, CAT) of the nuclear factor erythroid 2-related factor (Nrf2) signaling pathway. The protein-expressing level of the Nrf2 and its relative protein (NQO-1, HO-1, SOD-1) were significantly increased (p < 0.05) in the PKLPs pre-treatment group compared to the model group. In conclusion, the novelty of this study is that it explains how PKLPs’ efficacy on the Nrf2-ARE signaling pathway, in protecting vital cells from oxidative stress, could be used for cleaner production.

Crystallography-Guided Optimizations of the Keap1-Nrf2 Inhibitors on the Solvent Exposed Region: From Symmetric to Asymmetric Naphthalenesulfonamides

Directly inhibiting the Keap1-Nrf2 protein-protein interaction has been investigated as a promising strategy to activate Nrf2 for anti-inflammation. We previously reported a naphthalensulfonamide Keap1-Nrf2 inhibitor NXPZ-2, but have not determined the exact binding mode with Keap1. This symmetric naphthalenesulfonamide compound has relatively low solubility. Herein, we first determined a crystal complex (resolution: 2.3 Å) of human Keap1 Kelch domain with NXPZ-2. Further optimizations on the solvent exposed region obtained asymmetric naphthalenesulfonamides and three crystal structures of Keap1 in complex with designed compounds. Among them, the asymmetric piperazinyl-naphthalenesulfonamide 6k with better aqueous solubility showed the best K_D2 value of 0.21 μM to block the interaction. The productions of ROS and NO and the expression of TNF-α were inhibited by 6k in the in vitro model. This compound could relieve inflammations by significantly increasing the Nrf2 nuclear translocation in the LPS-induced ALI model with promising pharmacokinetic properties.

Ferroptosis and its role in cardiomyopathy

Heart disease is the leading cause of death worldwide. Cardiomyopathy is a disease characterized by the heart muscle damage, resulting heart in a structurally and functionally change, as well as heart failure and sudden cardiac death. The key pathogenic factor of cardiomyopathy is the loss of cardiomyocytes, but the related molecular mechanisms remain unclear. Ferroptosis is a newly discovered regulated form of cell death, characterized by iron accumulation and lipid peroxidation during cell death. Recent studies have shown that ferroptosis plays an important regulatory roles in the occurrence and development of many heart diseases such as myocardial ischemia/reperfusion injury, cardiomyopathy and heart failure. However, the systemic association of ferroptosis and cardiomyopathy remains largely unknown and needs to be elucidated. In this review, we provide an overview of the molecular mechanisms of ferroptosis and its role in individual cardiomyopathies, highlight that targeting ferroptosis maybe a potential therapeutic strategy for cardiomyopathy therapy in the future.

Protecting Effect of Bacillus coagulans T242 on HT-29 Cells Against AAPH-Induced Oxidative Damage

The aim of the present study was to investigate the in vitro antioxidant potential of Bacillus coagulans T242. B. coagulans T242 showed better antioxidant activities, including the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radical scavenging ability, lipid peroxidation inhibiting ability and reducing ability, than those exerted by Lactobacillus rhamnosus GG (LGG). B. coagulans T242 positively regulated the expression of the nuclear factor erythroid 2-relatedfactor 2/Kelch-like ECH-associated protein-1 (Nrf2/Keap1) pathway-related proteins (Nrf2, Keap1, heine oxygenase-1 (HO-1)); increased antioxidant enzymes (glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD)); reduced the content of malondialdehyde (MDA) level; decreased the expression of inflammatory-related cytokines interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor-α (TNF-α); and thus increased the survival rate in 2,2'-azobis (2-methylpropionamidine) dihydrochloride (AAPH)-damaged HT-29 cells. This study proved that B. coagulans T242 exerted antioxidative effects by quenching oxygen free radicals and activating the Nrf2 signaling pathway in HT-29 cells.

Importance of Binding Site Hydration and Flexibility Revealed When Optimizing a Macrocyclic Inhibitor of the Keap1-Nrf2 Protein-Protein Interaction

Upregulation of the transcription factor Nrf2 by inhibition of the interaction with its negative regulator Keap1 constitutes an opportunity for the treatment of disease caused by oxidative stress. We report a structurally unique series of nanomolar Keap1 inhibitors obtained from a natural product-derived macrocyclic lead. Initial exploration of the structure-activity relationship of the lead, followed by structure-guided optimization, resulted in a 100-fold improvement in inhibitory potency. The macrocyclic core of the nanomolar inhibitors positions three pharmacophore units for productive interactions with key residues of Keap1, including R415, R483, and Y572. Ligand optimization resulted in the displacement of a coordinated water molecule from the Keap1 binding site and a significantly altered thermodynamic profile. In addition, minor reorganizations of R415 and R483 were accompanied by major differences in affinity between ligands. This study therefore indicates the importance of accounting both for the hydration and flexibility of the Keap1 binding site when designing high-affinity ligands.

Honeysuckle extract (Lonicera pallasii L.) exerts antioxidant properties and extends the lifespan and healthspan of Drosophila melanogaster

Honeysuckle Lonicera pallasii (Lonicera caerulea L.) is an excellent source of anthocyanins which have a number of health-promoting properties mainly associated with antioxidant and anti-inflammatory activities. Cyanidin-3-O-glucoside (C3G) is one of the most common anthocyanins naturally found in honeysuckle. The goal of the present study was to investigate antioxidant and anti-aging properties of Lonicera pallasii (Lonicera caerulea L.) extract (LE) and C3G using red blood cells (RBC) and Drosophila melanogaster models. LE and C3G treatment at a concentration of 100 μM induced enhancement of median and maximum lifespan up to 8%. LE and C3G supplementation at a concentration of 100 μM increased stress resistance up to 10%. The locomotor activity decreased during LE and C3G treatment in 4 and 6 weeks up to 52% in females. The integrity of the intestinal barrier was increased by 4% after LE treatment. These effects were accompanied by increased expression of Hif1 (pro-longevity gene) in response to C3G treatment and decreased expression of Keap1 (anti-longevity gene) after C3G and LE supplementation. RNA interference-mediated knockdown of Sirt6 completely abolished the positive effect obtained of LE and C3G supplementation in males which indicates that lifespan-extending effect is associated with Sirt6 activation. The experiments on the various in-vitro models (including radical scavenging activity and oxidative hemolysis of RBC demonstrated antioxidant and membrane-protective activities of LE and C3G. The present study indicates that Lonicera extract can prolong the lifespan and improve the healthspan of Drosophila model through biological and antioxidant activities.

The isoquinoline PRL-295 increases the thermostability of Keap1 and disrupts its interaction with Nrf2

Transcription factor Nrf2 and its negative regulator Keap1 orchestrate a cytoprotective response against oxidative, metabolic, and inflammatory stress. Keap1 is a drug target, with several small molecules in drug development. Here, we show that the isoquinoline PRL-295 increased Keap1 thermostability in lysates from cells expressing fluorescently tagged Keap1. The thermostability of endogenous Keap1 also increased in intact cells and murine liver following PRL-295 treatment. Fluorescence Lifetime Imaging-Förster Resonance Energy Transfer (FLIM-FRET) experiments in cells co-expressing sfGFP-Nrf2 and Keap1-mCherry further showed that PRL-295 prolonged the donor fluorescence lifetime, indicating disruption of the Keap1-Nrf2 protein complex. Orally administered PRL-295 to mice activated the Nrf2transcriptional target NAD(P)H:quinone oxidoreductase 1 (NQO1) in liver and decreased the levels of plasma alanine aminotransferase and aspartate aminotransferase upon acetaminophen-induced hepatic injury. Thus, PRL-295 engages the Keap1 protein target in cells and in vivo, disrupting its interaction with Nrf2, leading to activation of Nrf2-dependent transcription and hepatocellular protection.

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.

Dibenzocyclooctadiene lignans from Kadsura coccinea alleviate APAP-induced hepatotoxicity via oxidative stress inhibition and activating the Nrf2 pathway in vitro

Phytochemical investigation on the roots of Kadsura coccinea led to the isolation five previously unknown dibenzocyclooctadiene lignans, named heilaohusuins A-E (1-5). Their structures determined by NMR spectroscopy, HR-ESI-MS, and ECD spectra. Hepatoprotection effects of a series of dibenzocyclooctadiene derivatives (1-68) were investigated against acetaminophen (APAP) induced HepG2 cells. Compounds 2, 10, 13, 21, 32, 41, 46, and 49 showed remarkable protective effects, increasing the viabilities to > 52.2% (bicyclol, 52.1 ± 1.3%) at 10 μM. The structure-activity relationships (SAR) for hepatoprotective activity were summarized, according to the activity results of dibenzocyclooctadiene derivatives. Furthermore, we found that one new dibenzocyclooctadiene lignan heilaohusuin B attenuates hepatotoxicity, the mechanism might be closely correlated with oxidative stress inhibition via activating the Nrf2 pathway.

Trifluoromethyl-substituted 3,5-bis(arylidene)-4-piperidones as potential anti-hepatoma and anti-inflammation agents by inhibiting NF-кB activation

Some methoxy-, hydroxyl-, pyridyl-, or fluoro-substituted 3,5-bis(arylidene)-4-piperidones (BAPs) could reduce inflammation and promote hepatoma cell apoptosis by inhibiting activation of NF-κB, especially after introduction of trifluoromethyl. Herein, a series of trifluoromethyl-substituted BAPs (4-30) were synthesised and the biological activities were evaluated. We successfully found the most potential 16, which contains three trifluoromethyl substituents and exhibits the best anti-tumour and anti-inflammatory activities. Preliminary mechanism research revealed that 16 could promote HepG2 cell apoptosis in a dose-dependent manner by down-regulating the expression of Bcl-2 and up-regulating the expression of Bax, C-caspase-3. Meanwhile, 16 inhibited activation of NF-κB by directly inhibiting the phosphorylation of p65 and IκBα induced by LPS, together with indirectly inhibiting MAPK pathway, thereby exhibiting both anti-hepatoma and anti-inflammatory activities. Molecular docking confirmed that 16 could bind to the active sites of Bcl-2, p65, and p38 reasonably. The above results suggested that 16 has enormous potential to be developed as a multifunctional agent for the clinical treatment of liver cancers and inflammatory diseases.

The piperine derivative HJ105 inhibits Aβ1-42-induced neuroinflammation and oxidative damage via the Keap1-Nrf2-TXNIP axis

BACKGROUND

Piperine is a great lead compound, as a phytopharmaceutical with reported neuroprotective effects in neurodegenerative diseases. HJ105, a piperine derivative with high affinity to Keap1 receptor, attracts increasing attention in Alzheimer's disease (AD) treatment.

PURPOSE

This work mainly aimed to study HJ105's therapeutic effects on Aβ_1-42-associated AD and the underpinning mechanisms.

METHODS

In the in vivo part, a rat model of AD was established by bilateral intra-hippocampal administration of aggregated Aβ_1-42, followed by a month of intragastric HJ105 or donepezil administration. Spatial and learning memories were detected by the Morris water maze assay, passive avoidance learning as well as Y-maze test. The morphology of hippocampal neurons was assessed by hematoxylin-eosin (H&E) staining. In addition, the amounts of the IL-1β and TNF-α were obtained with specific ELISA kits. More importantly, apoptosis-related proteins and factors involved in Nrf2/TXNIP/NLPR3 pathways were detected by Western blot, while the interaction between Keap1 and Nrf2 was assessed by co-immunoprecipitation. In the in vitro part, human neuroblastoma (SH-SY5Y) cells were applied to evaluate the role of HJ105 on Aβ_1-42-induced neuronal damage.

RESULTS

Treatment of HJ105 not only reversed memory impairment, but also protected neurons in the hippocampus by inhibiting Bax/Bcl2 ratio increase. HJ105 decreased TXNIP expression, suppressing NLRP3 inflammasome activation in the hippocampus, which in turn counteracted the upregulation of IL-1β and TNF-α. Notably, HJ105 exerted an inhibitory effect on Keap1-Nrf2 interaction and upregulated nuclear Nrf2, which conversely increased the expression levels of superoxide dismutase, catalase and glutathione peroxidase and downregulated malondialdehyde. Additionally, neurotoxicity induced by Aβ_1-42 in SH-SY5Y cells was alleviated by HJ105.

CONCLUSION

Overall, HJ105 exerts neuroprotective effects in SH-SY5Y cells induced by Aβ_1-42 as well as in experimental rats with AD by decreasing apoptosis, oxidative stress and neuroinflammation, partly via suppression of Keap1-Nrf2 complex generation. HJ105 might represent a promising compound for AD treatment.

Structure-based molecular hybridization design of Keap1-Nrf2 inhibitors as novel protective agents of acute lung injury

Blocking the Kelch-like epichlorohydrin-related protein 1 (Keap1)-nuclear factor-erythroid 2 related factor 2 (Nrf2) pathway represents as a promising strategy to reduce oxidative stress and related-inflammation, including acute lung injury (ALI). NXPZ-2, a naphthalensulfonamide derivative, was previously reported to effectively inhibit the Keap1-Nrf2 protein-protein interaction (PPI) by our group. In the present work, a series of novel isothiocyanate-containing naphthalensulfonamides with the thioether, sulfoxide and sulfone moieties were designed by a structure-based molecular hybridization strategy using NXPZ-2 and the Nrf2 activator sulforaphane. They possessed good Keap1-Nrf2 PPI inhibitory activity and low cytotoxicity. The molecular docking study was performed to further explain the different activity of the thioether-, sulfoxide- and sulfone-containing naphthalensulfonamides. Among these new derivatives, 2-((N-(4-((N-(2-amino-2-oxoethyl)-4-((3-isothiocyanatopropyl)sulfinyl)phenyl)sulfonamido) naphthalen-1-yl)-4-methoxyphenyl)sulfonamido)acetamide (SCN-16) showed a good K_D2 value of 0.455 μM to disrupt the PPI. In an LPS-induced peritoneal macrophage cell model, this compound could cause a significant increase in the nuclear Nrf2 protein, decrease in the cytosolic Nrf2 protein, and further elevate the downstream protective enzymes HO-1 and NQO-1, which were better than the lead compound NXPZ-2 and sulforaphane. What's more, the production of ROS and NO and the expression of pro-inflammatory cytokine TNF-α were also suppressed. In the LPS-induced ALI model, SCN-16 could significantly reduce LPS-induced inflammations and alleviate lung injuries by triggering Nrf2 nuclear translocation. Collectively, our results suggested that SCN-16 could be a novel lead compound targeting Keap1-Nrf2 protective pathway for clinical treatment of ALI.

Potential anti-neuroinflammatory NF-кB inhibitors based on 3,4-dihydronaphthalen-1(2H)-one derivatives

Nuclear factor kappa B (NF-кB) inhibition represents a new therapeutic strategy for the treatment of neuroinflammatory diseases. In this study, a series of 3,4-dihydronaphthalen-1(2H)-one (DHN; 6a-n, 7a-c) derivatives were synthesised and characterised by NMR and HRMS. We assessed the toxicity and anti-neuroinflammatory properties of these compounds and found that 6m showed the greatest anti-neuroinflammatory properties, with relatively low toxicity. Specifically, 6m significantly reduced reactive oxygen species production, down-regulated the expression of NOD-like receptor pyrin domain-containing protein 3 (NLRP3), apoptosis-associated speck-like protein containing a CARD (ASC), and caspase-1 and prevented lipopolysaccharide-stimulated BV2 microglia cells polarisation towards an M1 phenotype. Furthermore, 6m significantly decreased IκBα and NF-кB p65 phosphorylation, thus inhibiting the NF-кB signalling pathway. This suggests that 6m may be explored as a functional anti-neuroinflammatory agent for the treatment of inflammatory diseases in the central nervous system, such as multiple sclerosis, traumatic brain injury, stroke and spinal cord injury.

E3 Ligase Ligands for PROTACs: How They Were Found and How to Discover New Ones

Bifunctional degrader molecules, also called proteolysis-targeting chimeras (PROTACs), are a new modality of chemical tools and potential therapeutics to understand and treat human disease. A required PROTAC component is a ligand binding to an E3 ubiquitin ligase, which is then joined to another ligand binding to a protein to be degraded via the ubiquitin-proteasome system. The advent of nonpeptidic small-molecule E3 ligase ligands, notably for von Hippel-Lindau (VHL) and cereblon (CRBN), revolutionized the field and ushered in the design of drug-like PROTACs with potent and selective degradation activity. A first wave of PROTAC drugs are now undergoing clinical development in cancer, and the field is seeking to extend the repertoire of chemistries that allow hijacking new E3 ligases to improve the scope of targeted protein degradation.Here, we briefly review how traditional E3 ligase ligands were discovered, and then outline approaches and ligands that have been recently used to discover new E3 ligases for PROTACs. We will then take an outlook at current and future strategies undertaken that invoke either target-based screening or phenotypic-based approaches, including the use of DNA-encoded libraries (DELs), display technologies and cyclic peptides, smaller molecular glue degraders, and covalent warhead ligands. These approaches are ripe for expanding the chemical space of PROTACs and usher in the advent of other emerging bifunctional modalities of proximity-based pharmacology.

Mining Natural Products for Macrocycles to Drug Difficult Targets

Lead generation for difficult-to-drug targets that have large, featureless, and highly lipophilic or highly polar and/or flexible binding sites is highly challenging. Here, we describe how cores of macrocyclic natural products can serve as a high-quality in silico screening library that provides leads for difficult-to-drug targets. Two iterative rounds of docking of a carefully selected set of natural-product-derived cores led to the discovery of an uncharged macrocyclic inhibitor of the Keap1-Nrf2 protein–protein interaction, a particularly challenging target due to its highly polar binding site. The inhibitor displays cellular efficacy and is well-positioned for further optimization based on the structure of its complex with Keap1 and synthetic access. We believe that our work will spur interest in using macrocyclic cores for in silico-based lead generation and also inspire the design of future macrocycle screening collections.

Recent advances in the development of protein-protein interactions modulators: mechanisms and clinical trials

Protein-protein interactions (PPIs) have pivotal roles in life processes. The studies showed that aberrant PPIs are associated with various diseases, including cancer, infectious diseases, and neurodegenerative diseases. Therefore, targeting PPIs is a direction in treating diseases and an essential strategy for the development of new drugs. In the past few decades, the modulation of PPIs has been recognized as one of the most challenging drug discovery tasks. In recent years, some PPIs modulators have entered clinical studies, some of which been approved for marketing, indicating that the modulators targeting PPIs have broad prospects. Here, we summarize the recent advances in PPIs modulators, including small molecules, peptides, and antibodies, hoping to provide some guidance to the design of novel drugs targeting PPIs in the future.

Nrf2 mitigates prolonged PM2.5 exposure-triggered liver inflammation by positively regulating SIKE activity: Protection by Juglanin

Air pollution containing particulate matter (PM) less than 2.5 μm (PM2.5) plays an essential role in regulating hepatic disease. However, its molecular mechanism is not yet clear, lacking effective therapeutic strategies. In this study, we attempted to investigate the effects and mechanisms of PM2.5 exposure on hepatic injury by the in vitro and in vivo experiments. At first, we found that PM2.5 incubation led to a significant reduction of nuclear factor erythroid-derived 2-related factor 2 (Nrf2), along with markedly reduced expression of different anti-oxidants. Notably, suppressor of IKKε (SIKE), known as a negative regulator of the interferon pathway, was decreased in PM2.5-incubated cells, accompanied with increased activation of TANK-binding kinase 1 (TBK1) and nuclear factor-κB (NF-κB). The in vitro studies showed that Nrf2 positively regulated SIKE expression under the conditions with or without PM2.5. After PM2.5 treatment, Nrf2 knockdown further accelerated SIEK decrease and TBK1/NF-κB activation, and opposite results were observed in cells with Nrf2 over-expression. Subsequently, the gene loss- and gain-function analysis demonstrated that SIKE deficiency further aggravated inflammation and TBK1/NF-κB activation caused by PM2.5, which could be abrogated by SIKE over-expression. Importantly, SIKE-alleviated inflammation was mainly dependent on TBK1 activation. The in vivo studies confirmed that SIKE- and Nrf2-knockout mice showed significantly accelerated hepatic injury after long-term PM2.5 exposure through reducing inflammatory response and oxidative stress. Juglanin (Jug), mainly isolated from Polygonum aviculare, exhibits anti-inflammatory and anti-oxidant effects. We found that Jug could increase Nrf2 activation, and then up-regulated SIKE in cells and liver tissues, mitigating PM2.5-induced liver injury. Together, all these data demonstrated that Nrf2 might positively meditate SIKE to inhibit inflammatory and oxidative damage, ameliorating PM2.5-induced liver injury. Jug could be considered as an effective therapeutic strategy against this disease by improving Nrf2/SIKE signaling pathway.

Natural phenylethanoid glycosides isolated from Callicarpa kwangtungensis suppressed lipopolysaccharide-mediated inflammatory response via activating Keap1/Nrf2/HO-1 pathway in RAW 264.7 macrophages cell

ETHNOPHARMACOLOGICAL RELEVANCE

Callicarpa kwangtungensis, as a characteristic traditional herb in China, has been widely used as indigenous medicine for thousands of years in the treatment of upper respiratory tract infection, tonsillitis, pneumonia and traumatic bleeding in China. Phenylethanoid glycosides (PhGs), as natural polyphenols, are especially abundant in this herb and can be regarded as the representative active ingredients in C. kwangtungensis.

AIM OF THIS STUDY

This study was performed to investigate the anti-inflammatory pharmacodynamic basis of six PhGs (acteoside, forsythoside B, poliumoside, alyssonoside, parvifloroside A, and syringalide A 3'-α-L-rhanmnopyranoside) isolated from C. kwangtungensis from the perspective of antioxidation.

MATERIALS AND METHODS

Six PhGs were isolated from the anti-inflammatory extracts of C. kwangtungensis by various chromatographic techniques and their anti-inflammatory activity on RAW 264.7 murine macrophages induced by LPS was investigated by measuring the release of tumor necrosis factor (TNF-α), the colonic interleukin-6 (IL-6), nitric oxide (NO) and reactive oxygen species (ROS). Further, the underlying anti-inflammatory mechanism of two PhGs (forsythoside B and alyssonoside) was explored by determining the expression of Kelch-like ECH-association protein 1 (Keap1), nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (OH-1) and quinone oxidoreductase 1 (NQO1). Besides, molecular simulation was also employed to evaluate the binding capacity of two PhGs with Keap1.

RESULTS

Compared with the model group, six PhGs revealed obviously inhibitory effects on TNF-α, IL-6, NO and the generation of ROS in RAW 264.7 macrophages. Moreover, forsythoside B and alyssonoside could act as the inhibitors of Keap1-Nrf2 interaction, then activated the nuclear translocation of Nrf2 and promoted the upregulated protein expression of HO-1 and NQO1, finally suppressed LPS-induced inflammatory response in RAW 264.7 macrophages. Molecular modeling exhibited hydrogen bonds played a crucial role for the binding of PhGs with the Nrf2 binding site in Keap1 protein.

CONCLUSIONS

Natural PhGs-induced protection against LPS-induced inflammatory response via activating Keap1/Nrf2/HO-1 signaling pathway in RAW 264.7 macrophages were confirmed, which provided experimental and theoretical basis for the deeper use of C. Kwangtungensis in the treatment and prevention of diseases related to inflammation and oxidative stress.

Discovery of novel NF-кB inhibitor based on scaffold hopping: 1,4,5,6,7,8-hexahydropyrido[4,3-d]pyrimidine

NF-κB is a key signaling pathway molecule linking hepatoma and chronic inflammation. Inhibition of NF-κB activation can alleviate inflammation, and promote hepatoma cell apoptosis. In this study, a series of fluoro-substituted 1,4,5,6,7,8-hexahydropyrido[4,3-d]pyrimidines (PPMs, 31-57) were synthesized from 3,5-bis(arylidene)-4-piperidones (BAPs, 4-30) based on scaffold hopping. We successfully discovered the most potent 43 substituted by electron-withdrawing substitutes (3-F and 4-CF₃) exhibited less toxicity and higher anti-inflammatory activity. Preliminary mechanistic studies revealed that 43 induced dose-dependent cell apoptosis at cell and protein level, while inhibited NF-κB activation by suppressing LPS-induced phosphorylation levels of p65, IκBα and Akt, and by indirectly suppressing MAPK signaling, and by inhibiting the nuclear translocation of NF-κB induced by TNF-α or LPS. Docking analysis verified simulated 43 could reasonably bind to the active site of Bcl-2, p65 and p38 proteins. This compound, as a novel NF-κB inhibitor, also demonstrated both anti-inflammatory and anti-hepatoma activities, warranting its further development as a potential multifunctional agent for the clinical treatment of liver cancers and inflammatory diseases.

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.

HJ22, a Novel derivative of piperine, Attenuates ibotenic acid-induced cognitive impairment, oxidativestress, apoptosis and inflammation via inhibiting the protein-protein interaction of Keap1-Nrf2

Kelch-like ECH-associated protein (Keap1)-nuclear factor erythroid-2-related factor 2 (Nrf2) protein-protein interaction has become an important drug target for the treatment of Alzheimer's disease. In this study, we found a novel piperine derivative (HJ22) synthesized by our group with great ability to bind to Keap-1 and activate Keap1-Nrf2-ARE signaling pathway in vitro, driving us to investigate the beneficial effects of HJ22 on ibotenic acid (IBO)-induced neurological disorders in rats and underlying mechanisms. Interestingly, HJ22 significantly ameliorated IBO-induced cognitive impairment in Morris water maze, Y-maze and passive avoidance tests. Moreover, HJ22 significantly attenuated cholinergic dysfunction and neuronal morphological changes via inhibiting apoptotic cell death induced by IBO. Notably, HJ22 inhibited the interaction between Keap1 and Nrf2, and subsequently up-regulated nuclear Nrf2 expression, thereby inhibiting oxidative stress and Thioredoxin-interacting protein (TXNIP)-mediated Nod-like receptor protein 3 (NLRP3) inflammasome activation. These findings demonstrated that HJ22 exhibited potent therapeutic effects against IBO-induced cognitive impairment by alleviating cholinergic damage, oxidative stress, apoptosis and neuroinflammation, which might be partly attributed to its inhibitory activity on Keap1-Nrf2 protein-protein interaction.

ZJ01, a Small Molecule Inhibitor of the Kelch-Like ECH-Associated Protein 1-Nuclear Factor Erythroid 2-Related Factor 2 (Keap1-Nrf2) Protein-Protein Interaction, Reduces Hyperoxic Acute Lung Injury in a Mouse Model

Background

Hyperoxic acute lung injury (ALI) is a complication of ventilation in patients with respiratory failure. Nuclear factor erythroid-2-related factor 2 (Nrf2) has an important role in ALI. Kelch-like ECH-associated protein 1 (Keap1) binds to Nrf2. ZJ01 is a small molecule inhibitor of Keap1-Nrf2 protein-protein interaction (PPI) that can reduce Keap1-induced inhibition of Nrf2. This study aimed to investigate the effects of ZJ01 and the heme oxygenase-1 (HO-1) inhibitor, zinc protoporphyrin IX (ZnPP IX), in a mouse model of hyperoxic ALI.

Material/Methods

C57BL/6J mice included five study groups: the room air+vehicle-treated group; the room air+ZJ01 group; the hyperoxia+vehicle-treated group; the hyperoxia+ZJ01 group; and the hyperoxia+ZJ01+ZnPP IX group. ZJ01, ZnPP IX, or vehicle were given 1 h after the hyperoxia challenge. The lungs from the mice were harvested at 72 h following the hyperoxia challenge.

Results

Hyperoxia exposure for 72 h increased the activity of myeloperoxidase, the lung water content, the levels of tumor necrosis factor-α (TNF-α), and matrix metalloprotease-9 (MMP-9) in the vehicle-treated mice. ZJ01 treatment reduced hyperoxia-induced inflammation and increased the activation of Nrf2 and HO-1 compared with the vehicle-treated mice. Histology of the lungs showed that ZJ01 treatment reduced the changes of hyperoxia-induced ALI. Pretreatment with ZnPP IX reversed the beneficial effect of ZJ01.

Conclusions

ZJ01, a Keap1-Nrf2 PPI inhibitor, reduced hyperoxic ALI in a mouse model through the Nrf2/HO-1 pathway.

In silico and In vivo Evaluation of Oxidative Stress Inhibitors Against Parkinson's Disease using the C. elegans Model

BACKGROUND

Parkinson's disease ranks second, after Alzheimer's as the major neurodegenerative disorder, for which no cure or disease-modifying therapies exist. Ample evidence indicate that PD manifests as a result of impaired anti-oxidative machinery leading to neuronal death wherein Cullin-3 has ascended as a potential therapeutic target for diseases involving damaged anti-oxidative machinery.

OBJECTIVE

The design of target specific inhibitors for the Cullin-3 protein might be a promising strategy to increase the Nrf2 levels and to decrease the possibility of "off-target" toxic properties.

METHODS

In the present study, an integrated computational and wet lab approach was adopted to identify small molecule inhibitors for Cullin-3. The rational drug designing process comprised homology modeling and derivation of the pharmacophore for Cullin-3, virtual screening of Zinc natural compound database, molecular docking and Molecular dynamics based screening of ligand molecules. In vivo validations of an identified lead compound were conducted in the PD model of C. elegans.

RESULTS AND DISCUSSION

Our strategy yielded a potential inhibitor; (Glide score = -12.31), which was evaluated for its neuroprotective efficacy in the PD model of C. elegans. The inhibitor was able to efficiently defend against neuronal death in PD model of C. elegans and the neuroprotective effects were attributed to its anti-oxidant activities, supported by the increase in superoxide dismutase, catalase and the diminution of acetylcholinesterase and reactive oxygen species levels. In addition, the Cullin-3 inhibitor significantly restored the behavioral deficits in the transgenic C. elegans.

CONCLUSION

Taken together, these findings highlight the potential utility of Cullin-3 inhibition to block the persistent neuronal death in PD. Further studies focusing on Cullin-3 and its mechanism of action would be interesting.

A hydrogen peroxide responsive prodrug of Keap1-Nrf2 inhibitor for improving oral absorption and selective activation in inflammatory conditions

Transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2) and its negative regulator, the E3 ligase adaptor Kelch-like ECH-associated protein 1 (Keap1), control the redox and metabolic homeostasis and oxidative stress. Inhibitors of Keap1-Nrf2 interaction are promising in oxidative stress related inflammatory diseases but now hit hurdles. By utilizing thiazolidinone moiety to shield the key carboxyl pharmacophore in Keap1-Nrf2 inhibitor, a hydrogen peroxide (H₂O₂)-responsive prodrug pro2 was developed. The prodrug modification improved the physicochemical properties and cell membrane permeability of the parent drug. Pro2 was stable and stayed inactive under various physiological conditions, while became active by stimulation of H₂O₂ or inflammation derived reactive oxygen species. Moreover, pro2 exhibited proper pharmacokinetic profile suitable for oral administration and enhanced anti-inflammatory efficiency in vivo. Thus, this novel prodrug approach may not only provide an important advance in the therapy of chronic inflammatory diseases with high level of H₂O₂, but also offer a fresh solution to improve the drug-like and selectivity issues of Keap1-Nrf2 inhibitors.

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Pro2 was developed by utilizing H₂O₂-responsive thiazolidinone moiety to shield carboxyl group in Keap1-Nrf2 inhibitor.

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Pro2 was stable and inactive under various physiological conditions, while became active under inflammatory conditions.

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Pro2 exhibited proper pharmacokinetic profile for oral administration and enhanced anti-inflammatory efficiency in vivo.

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.

Evaluation and Exploration of Potentially Bioactive Peptides in Casein Hydrolysates against Liver Oxidative Damage in STZ/HFD-Induced Diabetic Rats

Hyperglycemia-induced oxidative stress can cause liver damage in diabetes, and protein hydrolysates with antidiabetic and antioxidant properties are emerging as a potential therapy. In this study, protective effects of casein hydrolysates against live oxidative damage in streptozotocin/high-fat-induced diabetic rats were studied and potentially bioactive peptides were explored by an integrated approach of differential peptide and in silico analysis. Results showed that different casein hydrolysates significantly alleviated liver oxidative damage (p < 0.05) via different mechanisms. Particularly, casein hydrolyzed by a papain-flavourzyme combination (P-FCH) treatment significantly improved liver antioxidant enzyme activities by enhancing nuclear factor erythroid 2-related factor 2 (Nrf2) transcription (p < 0.05). Furthermore, 18 peptides were screened as potential bioactive peptides by analyzing differential peptides among different hydrolysates combined with in silico prediction. Among them, the dipeptide WM might directly inhibit the Kelch-like ECH-associated protein 1 (Keap1)-Nrf2 interaction as potential Nrf2 activators. These results suggested that P-FCH might be an alternative way to treat liver damage in diabetes.

Discovery of disubstituted xylylene derivatives as small molecule direct inhibitors of Keap1-Nrf2 protein-protein interaction

The Keap1-Nrf2-ARE system represents a crucial antioxidant defense mechanism that protects cells against reactive oxygen species. Targeting Keap1-Nrf2 protein-protein interaction (PPI) has become a promising drug target for several oxidative stress-related and inflammatory diseases including pulmonary fibrosis, chronic obstructive pulmonary disorder (COPD) and cancer chemoprevention. For the development of a potential therapeutic agent, drug-like properties and potency are important considerations. In this work, we focused on the modification of 4 as a lead through a molecular dissection strategy in an effort to improve its metabolic stability, leading to the discovery of a series of new disubstituted xylylene derivatives. The preliminary SAR of 9a indicated that compound 21a containing S-methylated acetate moieties exhibited comparable potency to the lead compound 4 in a fluorescent polarization assay but with improved metabolic stability in the presence of human liver microsomes.

Keap1/Nrf2/ARE signaling unfolds therapeutic targets for redox imbalanced-mediated diseases and diabetic nephropathy

Hyperglycemia/oxidative stress has been implicated in the initiation and progression of diabetic complications while the components of Keap1/Nrf2/ARE signaling are being exploited as therapeutic targets for the treatment/management of these pathologies. Antioxidant agents like drugs, nutraceuticals and pure compounds that target the proteins of this pathway and their downstream genes hold the therapeutic strength to put the progression of this disease at bay. Here, we elucidate how the modulation of Keap1/Nrf2/ARE had been exploited for the treatment/management of end-stage diabetic kidney complication (diabetic nephropathy) by looking into (1) Nrf2 nuclear translocation and phosphorylation by some protein kinases at specific amino acid sequences and (2) Keap1 downregulation/Keap1-Nrf2 protein-protein inhibition (PPI) as potential therapeutic mechanisms exploited by Nrf2 activators for the modulation of diabetic nephropathy biomarkers (Collagen IV, Laminin, TGF-β1 and Fibronectin) that ultimately lead to the amelioration of this disease progression. Furthermore, we brought to limelight the relationship between diabetic nephropathy and Keap1/Nrf2/ARE and finally elucidate how the modulation of this signaling pathway could be further explored to create novel therapeutic milestones.

Emerging Screening Approaches in the Development of Nrf2-Keap1 Protein-Protein Interaction Inhibitors

Due to role of the Keap1–Nrf2 protein–protein interaction (PPI) in protecting cells from oxidative stress, the development of small molecule inhibitors that inhibit this interaction has arisen as a viable approach to combat maladies caused by oxidative stress, such as cancers, neurodegenerative disease and diabetes. To obtain specific and genuine Keap1–Nrf2 inhibitors, many efforts have been made towards developing new screening approaches. However, there is no inhibitor for this target entering the clinic for the treatment of human diseases. New strategies to identify novel bioactive compounds from large molecular databases and accelerate the developmental process of the clinical application of Keap1–Nrf2 protein–protein interaction inhibitors are greatly needed. In this review, we have summarized virtual screening and other methods for discovering new lead compounds against the Keap1–Nrf2 protein–protein interaction. We also discuss the advantages and limitations of different strategies, and the potential of this PPI as a drug target in disease therapy.

<Omega>-3 PUFA Attenuates LPS-Induced Neuro-Injury of Neonatal Rats through the PI3K/AKT Pathway

Inflammation may result in periventricular leukomalacia, which is the leading cause of preterm brain encephalopathy. Moreover, <omega>-3 polyunsaturated fatty acids (<omega>-3 PUFAs) play a pivotal role against central nervous system injury, which is likely related to its anti-inflammatory effect. However, the mechanism regarding the remedial effects of <omega>-3 PUFA for LPS-induced neuro-injury has remained unclear. In this study, newborn SD rats were intraperitoneally injected with LPS or < omega>-3 PUFA, and the proliferation and apoptosis of neurocytes in the hippocampus were measured by TUNEL and BrdU. Quantitative real-time PCR (qPCR) and Western blot assay were used to analyze the mRNA and protein levels of PI3K, AKT and β-catenin in vitro and in vivo. We found that <omega>-3 PUFA promoted the proliferation and migration of neurocytes in vitro and in vivo and inhibited apoptosis. Furthermore, we confirmed that <omega>-3 PUFA through the PI3K/AKT signaling pathway positively regulated the expression of PI3K and further caused the phosphorylation of AKT activation, followed by the upregulation of β-catenin expression. Interestingly, this phenomenon became more noticeable with the combined application of <omega>-3 PUFA and a PI3K/AKT agonist. In conclusion, we confirm that <omega>-3 PUFA plays an important role in neuroprotection by activating the PI3K/AKT/β-catenin pathway. It may be a promising strategy against brain injury.

CPUY192018, a potent inhibitor of the Keap1-Nrf2 protein-protein interaction, alleviates renal inflammation in mice by restricting oxidative stress and NF-κB activation

The Keap1-Nrf2-ARE pathway regulates the constitutive and inducible transcription of various genes that encode detoxification enzymes, antioxidant proteins and anti-inflammatory proteins and has pivotal roles in the defence against cellular oxidative stress. In this study, we investigated the therapeutic potential of CPUY192018, a potent small-molecule inhibitor of the Keap1-Nrf2 protein-protein interaction (PPI), in renal inflammation. In human proximal tubular epithelial HK-2 cells, CPUY192018 treatment significantly increased Nrf2 protein level and Nrf2 nuclear translocation, which enhanced Nrf2-ARE transcription capacity and the downstream protein content in a Nrf2 dependent manner. In lipopolysaccharide (LPS)-challenged human HK-2 cells, CPUY192018 exhibited cytoprotective effects by enhancing the Nrf2-ARE regulated antioxidant system and diminished the LPS-induced inflammatory response by hindering the ROS-mediated activation of the NF-κB pathway. In the LPS-induced mouse model of chronic renal inflammation, by activating Nrf2, CPUY192018 treatment balanced renal oxidative stress and suppressed inflammatory responses. Hence, administration of CPUY192018 reduced kidney damage and ameliorated pathological alterations of the glomerulus. Taken together, our study suggested that small-molecule Keap1-Nrf2 PPI inhibitors can activate the Nrf2-based cytoprotective system and protect the kidney from inflammatory injury, raising a potential application of Keap1-Nrf2 PPI inhibitors in the treatment of inflammatory kidney disorders.

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CPUY192018 activated Nrf2-ARE pathway to protect against LPS-induced renal inflammation both in cells and in vivo.

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CPUY192018 also inhibited NF-κB involved inflammatory response both in cells and kidney.

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The development of Keap1-Nrf2 PPI inhibitors may create treatment options for kidney diseases with reduced off-target effects.

Alpha lipoic acid inhibits oxidative stress-induced apoptosis by modulating of Nrf2 signalling pathway after traumatic brain injury

Alpha lipoic acid (ALA) is a powerful antioxidant which has been widely used in the treatment of different system diseases, such as cardiovascular and cerebrovascular diseases. But, there are few studies that refer to protective effects and potential mechanisms on traumatic brain injury (TBI). This study was carried out to investigate the neuroprotective effect following TBI and illuminate the underlying mechanism. Weight drop‐injured model in rats was induced by weight‐drop. ALA was administrated via intraperitoneal injection after TBI. Neurologic scores were examined following several tests. Neurological score was performed to measure behavioural outcomes. Nissl staining and TUNEL were performed to evaluate the neuronal apoptosis. Western blotting was engaged to analyse the protein content of the Nuclear factor erythroid 2‐related factor 2 (Nrf2) and its downstream protein factors, including hemeoxygenase‐1 (HO‐1) and quinine oxidoreductase‐1 (NQO1). ALA treatment alleviated TBI‐induced neuron cell apoptosis and improved neurobehavioural function by up‐regulation of Nrf2 expression and its downstream protein factors after TBI. This study presents new perspective of the mechanisms responsible for the neuronal apoptosis of ALA, with possible involvement of Nrf2 pathway.