INrf2 (Keap1) targets Bcl-2 degradation and controls cellular apoptosis

Targeting kelch-like (KLHL) proteins: achievements, challenges and perspectives

Kelch-like proteins (KLHLs) are a large family of BTB-containing proteins. KLHLs function as the substrate adaptor of Cullin 3-RING ligases (CRL3) to recognize substrates. KLHLs play pivotal roles in regulating various physiological and pathological processes by modulating the ubiquitination of their respective substrates. Mounting evidence indicates that mutations or abnormal expression of KLHLs are associated with various human diseases. Targeting KLHLs is a viable strategy for deciphering the KLHLs-related pathways and devising therapies for associated diseases. Here, we comprehensively review the known KLHLs inhibitors to date and the brilliant ideas underlying their development.

The roles of KLHL family members in human cancers

The Kelch-like (KLHL) family members consist of three domains: bric-a-brac, tramtrack, broad complex/poxvirus and zinc finger domain, BACK domain and Kelch domain, which combine and interact with Cullin3 to form an E3 ubiquitin ligase. Research has indicated that KLHL family members ubiquitinate target substrates to regulate physiological and pathological processes, including tumorigenesis and progression. KLHL19, a member of the KLHL family, is associated with tumorigenesis and drug resistance. However, the regulation and cross talks of other KLHL family members, which also play roles in cancer, are still unclear. Our review mainly explores studies concerning the roles of other KLHL family members in tumor-related regulation to provide novel insights into KLHL family members.

Protective effect and mechanism of cannabidiol on myocardial injury in exhaustive exercise training mice

Cannabinoid diphenol (CBD) is a non-toxic main component extracted from cannabis, which has the effects of anti-inflammatory, anti-apoptosis and anti-oxidative stress. In recent years, exercise-induced myocardial injury has become a research hotspot in the field of sports medicine and sports physiology. Exercise-induced myocardial injury is closely related to oxidative stress, inflammatory response and apoptosis. However, there is no clear evidence of the relationship between CBD and exercise-induced myocardial injury. In this study, by establishing an animal model of exhaustive exercise training in mice, the protective effect of CBD on myocardial injury in mice was elaborated, and the possible molecular mechanism was discussed. After CBD intervention, the arrangement and rupture of myocardial fiber tissue and the degree of inflammatory cell infiltration were reduced, the deposition of collagen fibers in myocardial tissue decreased. CBD can also significantly inhibit cardiac hypertrophy. Meanwhile, the expression of IL-6, IL-10, TNF-α, Bax, Caspase-3, Bcl-2, MDA-5, IRE-1α, NOX-2, SOD-1, Keap1, Nrf2, HO-1, NF-κB and COX-2 was recovered to normal. In addition, after CBD intervention, the protein expression of Keap1 was down-regulated, the translocation of Nrf2 from the cytoplasm to the nucleus was significantly increased, then the transcriptional activity was increased, and the expression of the downstream HO-1 antioxidant protein was increased, indicating that CBD may improve the cardiac function of exhaustive exercise training mice by activating Keap1/Nrf2/HO-1 signaling pathway. Molecular docking results also confirmed that CBD had a good binding effect with Keap1/Nrf2/HO-1 signaling pathway proteins. In conclusion, the protective mechanism of CBD on myocardial injury in exhaustive exercise training mice may be to activate Keap1/Nrf2/HO-1 signaling pathway, and then exert anti-inflammatory, anti-apoptosis and inhibition of oxidative stress.

Nrf2/Keap1/ARE signaling: Towards specific regulation

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

Bioactive Peptide F2d Isolated from Rice Residue Exerts Antioxidant Effects via Nrf2 Signaling Pathway

Studies have shown that the peroxidation caused by oxygen free radicals is an important reason of vascular endothelial dysfunction and multiple diseases. In this study, active peptides (F2ds) were isolated from the fermentation product of rice dregs and its antioxidant effects were approved. Human umbilical vein endothelial cells (HUVECs) stimulated by H2O2 were used to evaluate the antioxidation effect and its molecular mechanism in the oxidative stress model. F2d protected H2O2-induced damage in HUVECs in a dosage-dependent manner. F2d can reduce the expression of Keap1, promote the expression of Nrf2, and activate the downstream target HO-1, NQO1, etc. It means F2d can modulate the Nrf2 signaling pathway. Using Nrf2 inhibitor ML385 to block the Nrf2 activation, the protective function of F2d is partially lost in the damage model. Our results indicated that F2d isolated from rice exerts antioxidant effects via the Nrf2 signaling pathway in H2O2-induced damage, and the work will benefit to develop functional foods.

Evaluation of Nrf2, Keap1 and Apoptotic Pathway Genes Expression in Acute Myeloid Leukemia Patients

The aim of this study was to evaluate the expression Nrf2 (Nuclear factor-erythroid 2-p45 derived factor 2) and Keap1 (Kelch-like ECH-associated protein 1) genes and Bcl-2 (B-cell lymphoma 2), Bcl-XL (B-cell lymphoma-extra large), Bax (Bcl2-associated X protein) apoptotic pathway genes in acute myeloid leukemia patients. In this case-control study, the expression of genes encoding Nrf2, Keap1, Bcl2, Bcl- XL and Bax in 40 acute myeloid leukemia (AML) patients were compared with 40 normal individuals in the Iranian population. We evaluated the mRNA expression of genes by using the real-time quantitative polymerase chain reaction. The expression of Nrf2, Bcl2 and Bcl- XL genes in new AML patients were increased (p < 0.05). The patients treated with chemotherapy had a significantly more than four times higher expression level of Nrf2 than new case patients (P < 0.05), while there was a decrease in the expression level of Bcl2 and Bcl-XL, which was not statistically significant. In other hands in relapsed patients, the expressions of Nrf2, Bcl2 and Bcl- XL were higher level than new case patients (p < 0.05) but this was less than patients treated with chemotherapy (p > 0.05). The high levels of mentioned genes may be associated with poor treatment response, chemoresistance and disease recurrence. Because of hyperactivation and overexpression of Nrf2 in leukemia, suggest that Nrf2 inhibitors could be used as a pharmacological target in combination with classical chemotherapeutic agents to increase the efficacy of anticancer therapy.

Evaluation of chemo-preventive efficacy of Ficus religiosa latex extract by flow cytometry analysis and gene expression studies performed by RT-PCR in various cell lines

Background

An extract of Ficus religiosa latex has been previously found to possess potent pharmacological activity with high antioxidant content phytochemical. The present research was conducted to investigate the chemo-preventive efficacy of latex extract on human breast adenocarcinoma MDA MB 231, human neroblastoma IMR 32, and human colorectal HCT 116 cell lines.

Results

The results showed that the latex crude extract induced cytotoxicity in all the selected cell lines with IC50 value 4.8 ± 1.13 μg/ml against the IMR 32 cell line. The cell cycle analysis results indicated the arrest and accumulation of cells at G1 phase in case of MDA MB 231 cells and HCT 116 cells whereas in the case of IMR 32 cells the arrest was in G2/M phase. The clear bands of fragments observed in DNA ladder experiments showed that apoptosis is induced by extracts in the cell lines. This could be correlated with the gene level expression studies on selected pro-apoptotic (p53 and caspase-3) and anti-apoptotic (Bcl-2, AKT) genes, which got upregulated and downregulated, respectively.

Conclusion

Based on the experimental evidence, Ficus religiosa contains phytochemicals with potent antitumor activities.

A multi-scale systems pharmacology approach uncovers the anti-cancer molecular mechanism of Ixabepilone

It has been realized that FDA approved drugs may have more molecular targets than is commonly thought. Thus, to find the exact drug-target interactions (DTIs) is of great significance for exploring the new molecular mechanism of drugs. Here, we developed a multi-scale system pharmacology (MSSP) method for the large-scale prediction of DTIs. We used MSSP to integrate drug-related and target-related data from multiple levels, the network structural data formed by known drug-target relationships for predicting likely unknown DTIs. Prediction results revealed that Ixabepilone, an epothilone B analog for treating breast cancer patients, may target Bcl-2, an oncogene that contributes to tumor progression and therapy resistance by inhibiting apoptosis. Furthermore, we demonstrated that Ixabepilone could bind with Bcl-2 and decrease its protein expression in breast cancer cells. The down-regulation of Bcl-2 by Ixabepilone is resulted from promoting its degradation by affecting p-Bcl-2. We further found that Ixabepilone could induce autophagy by releasing Beclin1 from Beclin1/Bcl-2 complex. Inhibition of autophagy by knockdown of Beclin1 or pharmacological inhibitor augmented apoptosis, thus enhancing the antitumor efficacy of Ixabepilone against breast cancer cells in vitro and in vivo. In addition, Ixabepilone also decreases Bcl-2 protein expression and induces cytoprotective autophagy in human hepatic carcinoma and glioma cells. In conclusion, this study not only provides a feasible and alternative way exploring new molecular mechanisms of drugs by combing computation DTI prediction, but also reveals an effective strategy to reinforce the antitumor efficacy of Ixabepilone.

Non-esterified Fatty Acid Induce Dairy Cow Hepatocytes Apoptosis via the Mitochondria-Mediated ROS-JNK/ERK Signaling Pathway

Elevated plasma non-esterified fatty acid (NEFA) levels and hepatocytes damage are characteristics of ketosis in dairy cows. Oxidative stress is associated with the pathogenesis of NEFA-induced liver damage. However, the exact mechanism by which oxidative stress mediates NEFA-induced hepatocytes apoptosis and liver injury remains poorly understood. The results of the present study demonstrated that NEFA contribute to reactive oxygen species (ROS) generation, resulting in an imbalance between oxidative and antioxidant species, transcriptional activation of p53, transcriptional inhibition of nuclear factor E2-related factor 2 (Nrf2), loss of mitochondria membrane potential (MMP) and release of apoptosis-inducing factor (AIF) and cytochrome c (cyt c) into the cytosol, leading to hepatocytes apoptosis. Besides, NEFA triggered apoptosis in dairy cow hepatocytes via the regulation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), Bcl-2-associated X protein (Bax), B-cell lymphoma gene 2 (Bcl-2), caspase 9 and poly (ADP-ribose) polymerase (PARP). Pretreatment with the inhibitor SP600125 or PD98059 or the antioxidant N-acetylcysteine (NAC) revealed that NEFA-ROS-JNK/ERK-mediated mitochondrial signaling pathway plays a crucial role in NEFA-induced hepatocytes apoptosis. Moreover, the results suggested that the transcription factors p53 and Nrf2 function downstream of this NEFA-ROS-JNK/ERK pathway and are involved in NEFA-induced hepatocytes apoptosis. In conclusion, these findings indicate that the NEFA-ROS-JNK/ERK-mediated mitochondrial pathway plays an important role in NEFA-induced dairy cow hepatocytes apoptosis and strongly suggests that the inhibitors SP600125 and PD98059 and the antioxidant NAC may be developed as therapeutics to prevent hyperlipidemia-induced apoptotic damage in ketotic dairy cows.

FGF10 Enhances Peripheral Nerve Regeneration via the Preactivation of the PI3K/Akt Signaling-Mediated Antioxidant Response

The process of axonal regeneration after peripheral nerve injury (PNI) is slow and mostly incomplete. Previous studies have investigated the neuroprotective effects of fibroblast growth factor 10 (FGF10) against spinal cord injury and cerebral ischemia brain injury. However, the role of FGF10 in peripheral nerve regeneration remains unknown. In this study, we aimed to investigate the underlying therapeutic effects of FGF10 on nerve regeneration and functional recovery after PNI and to explore the associated mechanism. Our results showed that FGF10 administration promoted axonal regeneration and functional recovery after nerve damage. Moreover, exogenous FGF10 treatment also prevented SCs from excessive oxidative stress-induced apoptosis, which was probably related to the activation of phosphatidylinositol-3 kinase/protein kinase B (PI3K/Akt) signaling. The inhibition of the PI3K/Akt pathway by the specific inhibitor LY294002 partially reversed the therapeutic effects of FGF10 both in vivo and in vitro. Thus, from our perspective, FGF10 may be a promising therapeutic drug for repairing sciatic nerve damage through countering excessive oxidative stress-induced SC apoptosis.

Downregulation of Keap1 contributes to poor prognosis and Axitinib resistance of renal cell carcinoma via upregulation of Nrf2 expression

Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) signaling has a protective effect on normal cells. A number of previous studies demonstrated that Keap1/Nrf2 signaling is associated with drug resistance in numerous tumors. The aim of the present study was to investigate the roles of Keap1 in renal cell carcinoma (RCC) and its effect on sensitivity to chemotherapy. Reverse transcription-quantitative polymerase chain reaction was used to detect the mRNA expression of Keap1 in 45 cases of RCC tumors and adjacent normal tissues. A total of five randomly selected patients with RCC, five RCC cell lines and normal renal tubular cells were examined to detect the protein and mRNA expressions of Keap1. The 5-year survival rate was analyzed by Kaplan-Meier analysis. The cell viability was assessed by a Cell Counting kit-8 assay. The cell apoptosis and reactive oxygen species (ROS) were determined by flow cytometry. The expressions of associated proteins were determined by western blot analysis. It was identified that in RCC tissues and RCC cell lines, the expression of Keap1 was downregulated, which was considered to be associated with poor prognosis. In total, 1 µM Axitinib significantly decreased cell viability, promoted ROS release and induced cell apoptosis in ACHN cells. Silencing Keap1 was able to reverse the inhibitory effect of Axitinib and enhance the protein expressions of Nrf2, NAD(P)H dehydrogenase [quinone] 1 and heme oxygenase 1. However, silencing Nrf2 increased the cell sensitivity to Axitinib. Under Axitinib condition, overexpressing Nrf2 was able to increase cell viability; however, overexpressing Keap1 resulted in an opposite effect. Keap1 serves as a tumor suppressor; its low expression was associated with poor prognosis and a decreased sensitivity of RCC cells to Axitinib. A possible mechanism underlying Axitinib resistance may involve Nrf2 overexpression.

Beneficial Role of Some Natural Products to Attenuate the Diabetic Cardiomyopathy Through Nrf2 Pathway in Cell Culture and Animal Models

Diabetic cardiomyopathy, as one of the main cardiac complications in diabetic patients, is identified to connect with oxidative stress that is due to interruption in balance between reactive oxygen species or/and reactive nitrogen species generation and their clearance by antioxidant protection systems. Transcription factor the nuclear factor erythroid 2-related factor 2 (Nrf2) plays a significant role in maintaining the oxidative homeostasis by regulating multiple downstream antioxidants. The Nrf2 plays a significant role in ARE-mediated basal and inducible expression of more than 200 genes that can be grouped into numerous categories as well as antioxidant genes and phase II detoxifying enzymes. On the other hand, activation of Nrf2 by natural and synthetic therapeutics or antioxidants has been revealed effective for the prevention and treatment of toxicities and diseases connected with oxidative stress. Hence, recently focus has been shifted toward plants and plant-based medicines in curing such chronic diseases, as they are supposed to be less toxic. In this review, we focused on the role of some natural products on diabetic cardiomyopathy through Nrf2 pathway.

Decursin induces apoptosis in glioblastoma cells, but not in glial cells via a mitochondria-related caspase pathway

Decursin is a major biological active component of Angelica gigas Nakai and is known to induce apoptosis of metastatic prostatic cancer cells. Recently, other reports have been commissioned to examine the anticancer activities of this plant. In this study, we evaluated the inhibitory activity and related mechanism of action of decursin against glioblastoma cell line. Decursin demonstrated cytotoxic effects on U87 and C6 glioma cells in a dose-dependent manner but not in primary glial cells. Additionally, decursin increased apoptotic bodies and phosphorylated JNK and p38 in U87 cells. Decursin also down-regulated Bcl-2 as well as cell cycle dependent proteins, CDK-4 and cyclin D1. Furthermore, decursin-induced apoptosis was dependent on the caspase activation in U87 cells. Taken together, our data provide the evidence that decursin induces apoptosis in glioblastoma cells, making it a potential candidate as a chemotherapeutic drug against brain tumor.

p62-Dependent Phase Separation of Patient-Derived KEAP1 Mutations and NRF2

Cancer-derived loss-of-function mutations in the KEAP1 tumor suppressor gene stabilize the NRF2 transcription factor, resulting in a prosurvival gene expression program that alters cellular metabolism and neutralizes oxidative stress. In a recent genotype-phenotype study, we classified 40% of KEAP1 mutations as ANCHOR mutants. By immunoprecipitation, these mutants bind more NRF2 than wild-type KEAP1 and ubiquitylate NRF2, but they are incapable of promoting NRF2 degradation. BioID-based protein interaction studies confirmed increased abundance of NRF2 within the KEAP1 ANCHOR mutant complexes, with no other statistically significant changes to the complexes. Discrete molecular dynamic simulation modeling and limited proteolysis suggest that the ANCHOR mutations stabilize residues in KEAP1 that contact NRF2. The modeling supports an intramolecular salt bridge between the R470C ANCHOR mutation and E493; mutation of the E493 residue confirmed the model, resulting in the ANCHOR phenotype. In live cells, the KEAP1 R320Q and R470C ANCHOR mutants colocalize with NRF2, p62/SQSTM1, and polyubiquitin in structured spherical droplets that rapidly fuse and dissolve. Transmission electron microscopy coupled with confocal fluorescent imaging revealed membraneless phase-separated biomolecular condensates. We present a model wherein ANCHOR mutations form p62-dependent biomolecular condensates that may represent a transitional state between impaired proteasomal degradation and autophagy.

Hydrogen-rich saline protects rat from oxygen glucose deprivation and reperusion-induced apoptosis through VDAC1 via Bcl-2

BACKGROUND

Hydrogen is received as an inert gas that thought to be non-functional in vivo previously. Recently, emerging evidences showed that in ischemia/reperfusion (IR) condition, hydrogen reduced cellular reactive oxygen species (ROS) production and ameliorated cell apoptosis. However, the underlying mechanism of hydrogen on IR-induced apoptosis remains elusive. Here we tried to unravel the mode of action of hydrogen with rat adrenal medulla cell line PC-12 in vitro.

METHODS

The mitochondrial functions before and after oxygen glucose deprivation and reperfusion (OGD/RP) were determined with corresponding dyes. The expression of Bcl-2, Bax, VDAC1, cytochrome c and caspase 9 was detected using qRT-PCR and Western Blotting method. Then Bcl-2 inhibitor, AB-199, was applied to investigate the role of Bcl-2 in OGD/RP-induced cell apoptosis. Finally, we manipulated the expression of VDAC1 with plasmids transfection to understand the effects of VDAC1 on Bcl-2-mediated anti-apoptosis in OGD/RP.

RESULTS

In this study, we demonstrated that hydrogen-rich saline (HRS) reduced OGD/RP-mediated neuronal loss by stimulating the expression of Bcl-2, which suppressed the activity of VDAC1. Consequently, HRS maintained the mitochondrial functions, restrained the release of cytochrome c and caspase 9 activation, resulting in ameliorated cell viability.

CONCLUSIONS

HRS ameliorated OGD/RP-induced PC-12 cell apoptosis and provided a novel treatment option for ischemia.

Hepatoprotective effect of rhein against methotrexate-induced liver toxicity

The purpose of this study was to investigate the protective effect of rhein, a major metabolite of diacerein, on methotrexate (MTX)-induced hepatotoxicity and clarify the pharmacological mechanism. Rhein significantly reduced the elevation of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) caused by MTX in rat serum and improved liver morphological damage induced by MTX. Moreover, rhein increased the cell survival rate and reduced the number of apoptosis cells in MTX-treated normal human hepatocyte (L02 cells). Rhein treatment in rats up-regulated nuclear factor erythroid 2-related factor 2 (Nrf2), B-cell lymphoma-2 (Bcl-2), heme oxygenase 1 (HO-1) and glutamate-cysteine ligase catalytic subunit (GCLC), and down-regulated Bcl-2 associated x (Bax) in mRNA and protein levels. Furthermore, rhein treatment further decreased protein expression of nuclear factor-kappa B (NF-κB), tumor necrosis factor alpha (TNF-α) and cysteine aspartic acid specific protease 3 (Caspase-3), increased protein expression of B-cell lymphoma-extra large (Bcl-xl), and reduced mRNA expression of Bcl-2 homologous antagonist/killer (Bak) in MTX-treated rat liver in vivo. However, the protein expression changes of Nrf2, HO-1, GCLC, Bcl-2, Bcl-xl and Bax could be abrogated by Nrf2 antagonist brusatol. In addition, protective effect of rhein against MTX-mediated liver damage could also be suppressed by Nrf2 siRNA in L02 cells. Taken together, these findings suggested that rhein ameliorated liver damage mediated by MTX through acting on Nrf2-HO-1 pathway. NF-κB, TNF-α, Caspase-3 and Bcl-2 family were also participated in the protection. As effectively hepatoprotective ability of rhein, it would raise an important issue for patients orally receiving MTX treatment together with diacerein/rhein.

p62 as a therapeutic target for inhibition of autophagy in prostate cancer

BACKGROUND

To test the hypothesis that p62 is an optimal target for autophagy inhibition and Verteporfin, a clinically available drug approved by FDA to treat macular degeneration that inhibits autophagy by targeting p62 protein, can be developed clinically to improve therapy for advanced prostate cancer.

METHODS

Forced expression of p62 in PC-3 cells and normal prostate epithelial cells, RWPE-1 and PZ-HPV7, were carried out by transfection of these cells with pcDNA3.1/p62 or p62 shRNA plasmid. Autophagosomes and autophagic flux were measured by transfection of tandem fluorescence protein mCherry-GFP-LC3 construct. Apoptosis was measured by Annexin V/PI staining. Tumorigenesis was measured by a xenograft tumor growth model.

RESULTS

Verteporfin inhibited cell growth and colony formation in PC-3 cells. Verteporfin generated crosslinked p62 oligomers, resulting in inhibition of autophagy and constitutive activation of Nrf2 as well as its target genes, Bcl-2 and TNF-α. In normal prostate epithelial cells, forced expression of p62 caused constitutive Nrf2 activation, development of apoptosis resistance, and Verteporfin treatment exhibited inhibitory effects. Verteporfin treatment also inhibited starvation-induced autophagic flux of these cells. Verteporfin inhibited tumorigenesis of both normal prostate epithelial cells with p62 expression and prostate cancer cells and decreased p62, constitutive Nrf2, and Bcl-xL in xenograft tumor tissues, indicating that p62 can be developed as a drug target against prostate cancer.

CONCLUSIONS

p62 has a high potential to be developed as a therapeutic target. Verteporfin represents a prototypical agent with therapeutic potential against prostate cancer through inhibition of autophagy by a novel mechanism of p62 inhibition.

Dual Roles of Oxidative Stress in Metal Carcinogenesis

It has been well established that environmental and occupational exposure to heavy metal causes cancer in several organs. Although the exact mechanism of heavy metal carcinogenesis remains elusive, metal-generated reactive oxygen species (ROS) are essential. ROS can play two roles in metal carcinogenesis; two stages in the process of metal carcinogenesis differ in the amounts of ROS activating a dual redox-mediated mechanism. In the early stage of metal carcinogenesis, ROS acts in an oncogenic role. However, in the late stage of metal carcinogenesis, ROS plays an antioncogenic role. Similarly, NF-E2-related factor 2 (Nrf2) also has two different roles, which makes it a key molecule for separating metal carcinogenesis into two different stages. In the early stage, inducible Nrf2 fights against elevated ROS to decrease cell transformation by its antioxidant protection property. In the late stage, constitutively activated Nrf2 manipulates reduced ROS to perform a comfortable environment for apoptosis resistance through an oncogenic role. Interestingly, a cunning carcinogenic mechanism takes advantage of the dual role of Nrf2 to implement the dual role of ROS through a series of redox adaption mechanisms. In this review, we discuss the paradox in the rationales behind the two opposite ROS roles and focus on their potential pharmacological application. The dual role of ROS represents a 'double-edged sword' with many possible novel ROS-mediated strategies in cancer therapy in metal carcinogenesis.

Pterostilbene attenuates myocardial ischemia-reperfusion injury via the phosphatidylinositol 3'-kinase-protein kinase B signaling pathway

The current study aimed to evaluate the cardioprotective effects of pterostilbene (PTB) on myocardial ischemia-reperfusion (I/R) injury in rats and identify its possible underlying mechanisms of action. A rat I/R model was established by ligating the left anterior descending coronary artery for 30 min and releasing the ligature to induce reperfusion for 120 min. Serum creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) levels were measured using CK-MB and LDH assay kits and myeloperoxidase (MPO) activity in the myocardium was evaluated using an MPO assay kit. Tumor necrosis factor-α, interleukin (IL)-6 and IL-8 levels were assayed using ELISA kits. Cardiomyocyte apoptosis was measured using terminal deoxynucleotidyl transferase dUTP nick end labeling staining. Levels of protein kinase B (Akt) and phosphorylated Akt (p-Akt) were measured using western blotting. The results demonstrated that treatment with PTB significantly reduced cardiomyocyte apoptosis, significantly increased Bcl-2 and p-Akt levels and decreased Bax expression in the hearts of rats subjected to I/R injury. However, the protective effects induced by PTB were attenuated by LY294002, which inhibits Akt activation. The results of the current study suggest that PTB treatment may reduce the I/R injury-induced apoptosis of cardiomyocytes, which is mediated by the phosphoinositide 3-kinase/Akt signaling pathway.

4-Hydroxynonenal metabolites and adducts in pre-carcinogenic conditions and cancer

4-hydroxy-2-nonenal (HNE) is an amazing reactive compound, originating from lipid peroxidation within cells but also in food and considered as a "second messenger" of oxidative stress. Due to its chemical features, HNE is able to make covalent links with DNA, proteins and lipids. The aim of this review is to give a comprehensive summary of the chemical properties of HNE and of the consequences of its reactivity in relation to cancer development. The formation of exocyclic etheno-and propano-adducts and genotoxic effects are addressed. The adduction to cellular proteins and the repercussions on the regulation of cell signaling pathways involved in cancer development are reviewed, notably on the Nrf2/Keap1/ARE pathway. The metabolic pathways leading to the inactivation/elimination or, on the contrary, to the bioactivation of HNE are considered. A special focus is given on the link between HNE and colorectal cancer development, due to its occurrence in foodstuffs and in the digestive lumen, during digestion.

Mitochondrial phosphatase PGAM5 regulates Keap1-mediated Bcl-xL degradation and controls cardiomyocyte apoptosis driven by myocardial ischemia/reperfusion injury

Phosphoglycerate mutase 5 (PGAM5) is a mitochondrial membrane protein that plays crucial roles in necroptosis and apoptosis. Though PGAM5 is known to be required for inducing intrinsic apoptosis through interacting with BCL2 associated X protein (Bax) and dynamin-related protein 1 (Drp1), the expression and role of PGAM5 in cardiomyocyte apoptosis driven by myocardial ischemia/reperfusion injury(MIRI) has not been studied. The present study shows that PGAM5 expression decreased after MIRI in vivo, positively correlated with Bcl-xL expression, negatively correlated with Kelch-ECH associating protein 1 (Keap1) expression. Furthermore, PGAM5 expression also decreased in cardiomyocytes after hypoxia/reoxygenation (H/R) treatment in vitro. PGAM5 silence promoted cardiomyocyte apoptosis and inhibited Bcl-xL expression, but with no effect on Keap1 expression. Accordingly, Keap1 overexpression further inhibited Bcl-xL and PGAM5 expression. Additionally, PGAM5-Bcl-xL-Keap1 interaction was identified, suggesting that PGAM5 might participate in the degradation of Bcl-xL mediated by Keap1. In summary, PGAM5 controls cardiomyocyte apoptosis induced by MIRI through regulating Keap1-mediated Bcl-xL degradation, which may supply a novel molecular target for acute myocardial infarction (AMI) therapy. Graphical abstract ᅟ.

Lentivirus-mediated angiopoietin-2 gene silencing decreases TNF-α induced apoptosis of alveolar epithelium cells

OBJECTIVE

To investigate the role of angiopoietin-2 (Ang-2) in tumor necrosis factor-α (TNF-α) induced apoptosis of alveolar epithelium cells (AECs).

METHODS

TNF-α was used to induce human alveolar epithelial HPAEpiC cells, and Ang-2 siRNA vector was transfected to the HPAEpiC cells. RT-PCR and Western blot were used. TUNEL staining was applied to observe apoptosis, and annexin V-FITC-PI staining was used to calculate apoptosis rate.

RESULTS

mRNA and protein expressions of Ang-2, activated Bax, and cleaved caspase-3 in HPAEpiC cells were up-regulated, but the expression level of Bcl-2 decreased (P < 0.05). After transfection of Ang-2 siRNA, mRNA and protein expressions of Ang-2, activated Bax, and cleaved caspase-3 in HPAEpiC cells were down-regulated, but the expression level of Bcl-2 increased (P < 0.05). The number of apoptotic cells increased after TNF-α treatment; however, the number decreased after Ang-2 siRNA transfection. Annexin V-FITC-PI staining verified that the total number of apoptotic cells was elevated with TNF-α treatment, but declined after transfection of Ang-2 siRNA.

CONCLUSIONS

The expression level of Ang-2 increased during TNF-α-induced apoptosis. Inhibiting Ang-2 expression may suppress the early stages of cell apoptosis and the degree of TNF-α-induced apoptosis.

Targeting Bcl-2 stability to sensitize cells harboring oncogenic ras

The pro-survival factor Bcl-2 and its family members are critical determinants of the threshold of the susceptibility of cells to apoptosis. Studies are shown that cells harboring an oncogenic ras were extremely sensitive to the inhibition of protein kinase C (PKC) and Bcl-2 could antagonize this apoptotic process. However, it remains unrevealed how Bcl-2 is being regulated in this apoptotic process. In this study, we investigate the role of Bcl-2 stability in sensitizing the cells harboring oncogenic K-ras to apoptosis triggered by PKC inhibitor GO6976. We demonstrated that Bcl-2 in Swiss3T3 cells ectopically expressing or murine lung cancer LKR cells harboring K-ras rapidly underwent ubiquitin-dependent proteasome pathway after the treatment of GO6976, accompanied with induction of apoptosis. In this process, Bcl-2 formed the complex with Keap-1 and Cul3. The mutation of serine-17 and deletion of BH-2 or 4 was required for Bcl-2 ubiquitination and degradation, which elevate the signal threshold for the induction of apoptosis in the cells following PKC inhibition. Thus, Bcl-2 appears an attractive target for the induction of apoptosis by PKC inhibition in cancer cells expressing oncogenic K-ras.

Nuclear factor erythroid 2-related factor 2 antibody attenuates thermal hyperalgesia in the dorsal root ganglion: Neurochemical changes and behavioral studies after sciatic nerve-pinch injury

Oxidative stress is generated in several peripheral nerve injury models.Nuclear factor erythroid 2-related factor 2 (Nrf2) is activated to have a role in antioxidant effect. After nerve injury, the severely painful behavior is also performed. However, little has been explored regarding the function of Nrf2 in this painful process. Therefore, in this study, we compared the effects of Nrf2 antibody administration following sciatic nerve-pinch injury on painful behavior induced in young mice and neurochemical changes in dorsal root ganglion neurons. After pinch nerve injury, we found that the magnitude of the thermal allodynia was significantly decreased after application of Nrf2 antibody (5ul, 1mg/ml) in such injured animals and phosphorylated ERK(p-ERK) as well as the apoptotic protein (i.e., Bcl-6) in DRG neurons were also down-regulated in the anti-Nrf2-treated injured groups compared to the saline-treated groups. Taken collectively, these data suggested that the Nrf2 antibody reduced thermal hyperalgesia via ERK pathway and the down regulation of Bcl-6 protein from the apoptosis pathway might be protecting against the protein deletions caused by anti-Nrf2 effect and suggested the new therapeutic strategy with Nrf2 inhibitor following nerve injury.

Paeoniflorin protects Schwann cells against high glucose induced oxidative injury by activating Nrf2/ARE pathway and inhibiting apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Paeoniflorin (PF) is the principal bioactive component of Paeonia lactiflora Pall., which an included in Tang Luo Ning recipe, a traditional Chinese herbal medicine based on Huangqi Guizhi Wuwu decoction. PF is also widely used in Traditional Chinese Medicine for the treatment of blood-arthralgia disease including diabetic peripheral neuropathy (DPN), but its underlying molecular mechanism of neuroprotective effects is not yet well understood. Diabetic hyperglycemia induced oxidative stress in Schwann cells, an important component of the peripheral nervous system, has been proposed as a unifying mechanism for DPN. The objective of this study is to determine the effects of PF on Schwann cells oxidative stress and apoptosis induced by high glucose.

MATERIALS AND METHODS

RSC96 cells, a Schwann cell line, were treated with high glucose (150mM) and PF (1, 10 and 100μM). Subsequently, MTT assay was performed. The level of apoptosis was examined by flow cytometry and the oxidative stress was reflected by reactive oxygen species (ROS), malondialdehyde (MDA), glutathione S-transferases (GST) and glutathione peroxidase (GPX) levels. The mRNA expressions of Nuclear factor-E2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) were detected by qRT-PCR. The levels of Kelch-like ECH-associating protein 1 (Keap1), Nrf2, HO-1, γ-glutamylcysteine synthetase (γGCS), B-cell CLL/lymphoma 2 (Bcl-2), Bax and Caspase 3 were detected by High content analysis and/or Western blot.

RESULTS

The role of PF markedly suppressed high glucose induced Schwann cells oxidative stress by decreasing ROS and MDA levels and increasing GST and GPX activity. Western blot analysis showed that PF induced nuclear translocation of Nrf2. High content analysis showed that PF promoted Nrf2 dissociation from Keap1 and upregulating the Nrf2/ antioxidant response element (ARE) pathway. Furthermore, PF reduced Schwann cells apoptosis by increasing Bcl-2 and inhibiting Bax and Caspase-3 expressions.

CONCLUSIONS

PF in the management of Schwann cells oxidative stress induced by high glucose may be associated with activation of Nrf2/ARE pathway and Bcl-2-related apoptotic pathway.

Tert-butylhydroquinone attenuates the ethanol-induced apoptosis of and activates the Nrf2 antioxidant defense pathway in H9c2 cardiomyocytes

Tert-butylhydroquinone (tBHQ), an inducer of nuclear factor erythroid 2-related factor 2 (Nrf2), has been demonstrated to attenuate oxidative stress-induced injury and the apoptosis of human neural stem cells and other cell types. However, whether tBHQ is able to exert a protective effect against oxidative stress and the apoptosis of cardiomyocytes has not yet been determined. Thus, the objective of the present study was to determine whether tBHQ protects H9c2 cardiomyocytes against ethanol-induced apoptosis. For this purpose, four sets of experiments were performed under standard culture conditions as follows: i) untreated control cells; ii) cell treatment with 200 mM ethanol; iii) cell treatment with 5 µM tBHQ; and iv) cell pre-treatment with 5 µM tBHQ for 24 h, followed by medium change and co-culture with 200 mM ethanol containing 5 µM tBHQ for a further 24 h. The viability of the cardiomyocytes was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The levels of intracellular reactive oxygen species (ROS) and apoptosis were assessed by flow cytometry. Protein expression was measured by western blot analysis, and Nrf2 nuclear localization was observed by immunofluorescence. Exposure to ethanol led to a decrease in the protein expression of Nrf2 and its downstream antioxidant enzymes, accompanied by an increase in ROS generation and in the apoptosis of H9c2 cells. Pre-treatment with tBHQ significantly prevented the H9c2 cells from undergoing ethanol-induced apoptosis. tBHQ also increased the expression of B-cell lymphoma-2 (Bcl-2), whereas Bcl-2-associated X protein (Bax) expression was decreased. tBHQ promoted Nrf2 nuclear localization and increased the expression of Nrf2, superoxide dismutase (SOD), catalase (CAT) and heme oxygenase-1 (HO-1), and simultaneously inhibited the ethanol-induced overproduction of intracellular ROS. Therefore, tBHQ confers protection against the ethanol-induced apoptosis of and activates the Nrf2 antioxidant pathway in H9c2 cardiomyocytes.

The Keap1-Nrf2-ARE Pathway As a Potential Preventive and Therapeutic Target: An Update

The Keap1-Nrf2-ARE ((Kelch-like ECH-Associating protein 1) nuclear factor erythroid 2 related factor 2-antioxidant response element) pathway is one of the most important defense mechanisms against oxidative and/or electrophilic stresses, and it is closely associated with inflammatory diseases, including cancer, neurodegenerative diseases, cardiovascular diseases, and aging. In recent years, progress has been made in strategies aimed at modulating the Keap1-Nrf2-ARE pathway. The Nrf2 activator DMF (Dimethylfumarates) has been approved by the FDA as a new first-line oral drug to treat patients with relapsing forms of multiple sclerosis, while a phase 3 study of another promising candidate, CDDO-Me, was terminated for safety reasons. Directly inhibiting Keap1-Nrf2 protein-protein interactions as a novel Nrf2-modulating strategy has many advantages over using electrophilic Nrf2 activators. The development of Keap1-Nrf2 protein-protein interaction inhibitors has become a topic of intense research, and potent inhibitors of this target have been identified. In addition, inhibiting Nrf2 activity has attracted an increasing amount of attention because it may provide an alternative cancer therapy. This review summarizes the molecular mechanisms and biological functions of the Keap1-Nrf2-ARE system. The main focus of this review is on recent progress in studies of agents that target the Keap1-Nrf2-ARE pathway and the therapeutic applications of such agents.

Antioxidant tert-butylhydroquinone ameliorates arsenic-induced intracellular damages and apoptosis through induction of Nrf2-dependent antioxidant responses as well as stabilization of anti-apoptotic factor Bcl-2 in human keratinocytes

Human skin is a known target site of inorganic arsenic with effects ranging from hyperkeratosis to dermal malignancies. Tert-butylhydroquinone (tBHQ), approved food-grade phenolic antioxidant, is demonstrated to induce remarkable antioxidant activity in a variety of cells and tissues. The present study aimed at the protective effects of tBHQ on arsenic-induced cytotoxicity and apoptosis in human keratinocytes. Our results demonstrated that tBHQ antagonized arsenic-induced decrease of cell viability, generation of reactive oxygen species (ROS) and lipid peroxidation, as well as reduction of antioxidative enzymes superoxide dismutase (SOD) and catalase (CAT) activities. We also found that tBHQ relieved the G2/M phase arrest by arsenic exposure, which was associated with altering the expression of cell cycle regulators cyclin D1 and CDK4. tBHQ treatment further reduced the numbers of arsenic-induced mitochondrial-mediated apoptotic cells, which occurred concomitantly with the effective recovery of mitochondrial membrane potential (ΔΨm) depolarization, the release of cytochrome c releasing from the mitochondrial as well as the survival signal related factor caspase 3 activation. Our experiments then confirmed that tBHQ activated nuclear factor E2-related factor 2 (NRF2) pathway by increasing NRF2 protein in both nucleus and cytoplasm and upregulating NRF2 downstream targets

NAD(P)H

quinine oxidoreductase 1 (NQO1) and heme oxygenase-1 (HO-1). More interestingly, arsenic-induced decrease of anti-apoptotic factor B-cell lymphoma-2 (Bcl-2) and increase of pro-apoptotic factor Bcl-2-associated X protein (Bax) could all be reversed by tBHQ pretreatment. These results suggested together that tBHQ could ameliorate arsenic-induced cytotoxicity and apoptosis, which might be linked with the induction of Nrf2-dependent antioxidant responses as well as stabilization of anti-apoptotic factor Bcl-2 in human keratinocytes.

Progress and prospects of reactive oxygen species in metal carcinogenesis

Carcinogenesis induced by environmental metal exposure is a major public health concern. The exact mechanisms underlying metal carcinogenesis remain elusive. In the past few decades, the relationship between metal induced generation of reactive oxygen species (ROS) and the mechanism of metal carcinogenesis has been established. The carcinogenic process is a very complex one. In the early stage of metal carcinogenesis or cell transformation high levels of ROS are oncogenic by causing DNA damage, genetic instability, epigenetic alteration, and metabolic reprogramming, leading to malignant transformation. In the second stage of metal carcinogenesis or the cancer development of metal-transformed cells, low levels of ROS are carcinogenic by promoting apoptosis resistance. The metal-transformed cells have the property of autophagy deficiency, resulting in accumulation of p62 and constitutive activation of Nrf2, and leading to higher levels of antioxidants, decreased levels of ROS, apoptosis resistance, inflammation, and angiogenesis. This review summarizes the most recent development in the field of metal carcinogenesis with emphasis on the difference in cellular events between early (cell transformation) and late (after cell transformation) stages of metal carcinogenesis.

Pharmacology and Clinical Drug Candidates in Redox Medicine

SIGNIFICANCE

Oxidative stress is suggested to be a disease mechanism common to a wide range of disorders affecting human health. However, so far, the pharmacotherapeutic exploitation of this, for example, based on chemical scavenging of pro-oxidant molecules, has been unsuccessful.

RECENT ADVANCES

An alternative emerging approach is to target the enzymatic sources of disease-relevant oxidative stress. Several such enzymes and isoforms have been identified and linked to different pathologies. For some targets, the respective pharmacology is quite advanced, that is, up to late-stage clinical development or even on the market; for others, drugs are already in clinical use, although not for indications based on oxidative stress, and repurposing seems to be a viable option.

CRITICAL ISSUES

For all other targets, reliable preclinical validation and drug ability are key factors for any translation into the clinic. In this study, specific pharmacological agents with optimal pharmacokinetic profiles are still lacking. Moreover, these enzymes also serve largely unknown physiological functions and their inhibition may lead to unwanted side effects.

FUTURE DIRECTIONS

The current promising data based on new targets, drugs, and drug repurposing are mainly a result of academic efforts. With the availability of optimized compounds and coordinated efforts from academia and industry scientists, unambiguous validation and translation into proof-of-principle studies seem achievable in the very near future, possibly leading towards a new era of redox medicine.

Atorvastatin attenuates inflammation and oxidative stress induced by ischemia/reperfusion in rat heart via the Nrf2 transcription factor

The role of atorvastatin in inflammation and oxidative stress induced by ischemia/reperfusion is currently not well understood. The aim of this study was toinvestigate whether atorvastatin modulates neutrophil accumulation, TNF-α induction and oxidative stress and to examine the possible role of the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway in an ischemia/reperfusion injured rat heart model. Rats were randomly assigned into tosham operation group, myocardial ischemia/reperfusion (MI/R) group, MI/R + atorvastatin group. Myocardial infarct area, myeloperoxidase (MPO), serum creatinine kinase (CK) and lactate dehydrogenase (LDH) levels were monitored. The results indicate that compared to MI/R, atorvastatin reduced myocardial infarction area, MPO level, serum CK and LDH levels, and both serum and myocardial TNF-αproduction. In addition, atorvastatin increased SOD and GSH-PX activity and decreased MDA content. Atorvastatin also enhanced levels of Nrf2 and heme oxygenase-1. In summary, our data suggests that atorvastatin exerts significant cardioprotective effects following myocardial ischemia, possibly through the activation of the Nrf2/ARE signaling pathway.

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

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

Ginsenoside Rd mitigates myocardial ischemia-reperfusion injury via Nrf2/HO-1 signaling pathway

Ginsenoside Rd (GsRd) reportedly protects the heart against ischemia-reperfusion (I/R) injury. Nrf2/HO-1 signaling plays a key role in attenuating oxidative stress. However, it remains unclear whether GsRd protects against myocardial I/R injury via Nrf2/HO-1 signaling. This study aimed to investigate the role of Nrf2/HO-1 signaling in the cardioprotective effect of GsRd. Rats received 30 min ischemia followed by 2 h reperfusion. Cardiac function, infarct size and serum CK, LDH, cTnI levels were detected. The expression of Nrf2 and HO-1 was detected by western blot. The results suggested that GsRd attenuated myocardial I/R injury as evidenced by improved cardiac function, decreased infarct size and decreased levels of serum CK, LDH and cTnI. In addition, GsRd administration enhanced the expression of Nrf2 and HO-1. In conclusion, the present study shows that GsRd protects against myocardial I/R injury via Nrf2/HO-1 signaling.

Resveratrol attenuates inflammation and oxidative stress induced by myocardial ischemia-reperfusion injury: role of Nrf2/ARE pathway

The protective role of resveratrol in myocardial ischemia/reperfusion is not well understood. The aim of this study was to investigate whether resveratrol modulates inflammation and oxidative stress and the possible role of nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway in an ischemia/reperfusion injured rat heart model. Rats were randomly exposed to sham operation, myocardial ischemia/reperfusion (MI/R) alone, and MI/R + resveratrol. The results demonstrated that compared to MI/R, resveratrol improved cardiac function, reduced myocardial infarction area, myocardial myeloperoxidase (MPO) levels, serum creatinine kinase (CK) and lactate dehydrogenase (LDH) levels. Resveratrol also markedly enhanced the activities of antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX), and reduced the level of malondialdehyde (MDA) in MI/R rats. Resveratrol also enhanced levels of Nrf2 and heme oxygenase-1. In summary, these results demonstrated that resveratrol exerted significant antioxidant and cardioprotective effects following myocardial ischemia, possibly through the activation of the Nrf2/ARE signaling pathway.

RTA 408, A Novel Synthetic Triterpenoid with Broad Anticancer and Anti-Inflammatory Activity

Semi-synthetic triterpenoids are antioxidant inflammation modulator (AIM) compounds that inhibit tumor cell growth and metastasis. Compounds in the AIM class bind to Keap1 and attenuate Nrf2 degradation. In the nucleus, Nrf2 increases antioxidant gene expression and reduces pro-inflammatory gene expression. By increasing Nrf2 activity, AIMs reduce reactive oxygen species and inflammation in the tumor microenvironment, which reverses tumor-mediated immune evasion and inhibits tumor growth and metastasis. AIMs also directly inhibit tumor cell growth by modulating oncogenic signaling pathways, such as IKKβ/NF-κB. Here, we characterized the in vitro antioxidant, anti-inflammatory, and anticancer activities of RTA 408, a novel AIM that is currently being evaluated in patients with advanced malignancies. At low concentrations (≤ 25 nM), RTA 408 activated Nrf2 and suppressed nitric oxide and pro-inflammatory cytokine levels in interferon-γ-stimulated RAW 264.7 macrophage cells. At higher concentrations, RTA 408 inhibited tumor cell growth (GI₅₀ = 260 ± 74 nM) and increased caspase activity in tumor cell lines, but not in normal primary human cells. Consistent with the direct effect of AIMs on IKKβ, RTA 408 inhibited NF-κB signaling and decreased cyclin D1 levels at the same concentrations that inhibited cell growth and induced apoptosis. RTA 408 also increased CDKN1A (p21) levels and JNK phosphorylation. The in vitro activity profile of RTA 408 is similar to that of bardoxolone methyl, which was well-tolerated by patients at doses that demonstrated target engagement. Taken together, these data support clinical evaluation of RTA 408 for cancer treatment.

Emerging functional cross-talk between the Keap1-Nrf2 system and mitochondria

Nuclear factor erythroid-derived 2-related factor 2 (Nrf2) was originally identified as a positive regulator of drug detoxifying enzyme gene expression during exposure to environmental electrophiles. Currently, Nrf2 is known to regulate the expression of hundreds of cytoprotective genes to counteract endogenously or exogenously generated oxidative stress. Furthermore, when activated in human tumors by somatic mutations, Nrf2 confers growth advantages and chemoresistance by regulating genes involved in various processes such as the pentose phosphate pathway and nucleotide synthesis in addition to antioxidant proteins. Interestingly, increasing evidence shows that Nrf2 is associated with mitochondrial biogenesis during environmental stresses in certain tissues such as the heart. Furthermore, SKN-1, a functional homolog of Nrf2 in C. elegans, is activated by mitochondrial reactive oxygen species and extends life span by promoting mitochondrial homeostasis (i.e., mitohormesis). Similarly, Nrf2 activation was recently observed in the heart of surfeit locus protein 1 (Surf1) -/- mice in which cellular respiration was decreased due to cytochrome c oxidase defects. In this review, we critically examine the relationship between Nrf2 and mitochondria and argue that the Nrf2 stress pathway intimately communicates with mitochondria to maintain cellular homeostasis during oxidative stress.

The role of transcription factor Nrf2 in skin cells metabolism

Skin, which is a protective layer of the body, is in constant contact with physical and chemical environmental factors. Exposure of the skin to highly adverse conditions often leads to oxidative stress. Moreover, it has been observed that skin cells are also exposed to reactive oxygen species generated during cell metabolism particularly in relation to the synthesis of melanin or the metabolism in immune system cells. However, skin cells have special features that protect them against oxidative modifications including transcription factor Nrf2, which is responsible for the transcription of the antioxidant protein genes such as antioxidant enzymes, small molecular antioxidant proteins or interleukins, and multidrug response protein. In the present study, the mechanisms of Nrf2 activation have been compared in the cells forming the various layers of the skin: keratinocytes, melanocytes, and fibroblasts. The primary mechanism of control of Nrf2 activity is its binding by cytoplasmic inhibitor Keap1, while cells have also other controlling mechanisms, such as phosphorylation of Nrf2 and modifications of its activators (e.g., Maf, IKKβ) or inhibitors (e.g., Bach1, caveolae, TGF-β). Moreover, there are a number of drugs (e.g., ketoconazole) used in the pharmacotherapy of skin diseases based on the activation of Nrf2, but they may also induce oxidative stress. Therefore, it is important to look for compounds that cause a selective activation of Nrf2 particularly natural substances such as curcumin, sulforaphane, or extracts from the broccoli leaves without side effects. These findings could be helpful in the searching for new drugs for people with vitiligo or even melanoma.

Inhibitory effects of Saururus chinensis and its components on stomach cancer cells

Saururus chinensis (SC) Baill. (Saururaceae), a perennial herb commonly called Chinese lizard's tail or Sam-baekcho in Korea, has been used in the treatment of edema, gonorrhea, jaundice, and inflammatory diseases. Recently, several reports have been commissioned to examine the anti-cancer activities of this plant. In this study, we evaluated the inhibitory activity and mechanism of action on SC and its components against stomach cancer cells. SC extracts displayed cytotoxic effects on AGS cells in a dose-dependent manner. Moreover, SC increased the number of annexin V-positive apoptotic bodies and phosphorylated JNK and p38 in AGS cells. SC also down-regulated anti-apoptotic (Bcl-2) genes and up-regulated apoptotic (Bax) genes in AGS cells. We further confirmed that caspase activation plays an important role in SC-induced apoptosis in AGS cells. Furthermore, we examined erythro-Austrobailignan-6 and meso-dihydroguaiaretic acid, major active constituents of SC, which induced apoptosis in both the AGS and NCI-N87 stomach cancer cell lines. Taken together, our data provide the evidence that SC and its components induce apoptosis in stomach cancer cells, making it a potential candidate as a chemotherapeutic drug.

The Keap1-Nrf2-antioxidant response element pathway: a review of its regulation by melatonin and the proteasome

Both melatonin and proteasome inhibitors upregulate antioxidant enzymes including superoxide dismutase (SOD), glutathione peroxidase (GP), hemoxygenase 1 (HO-1), and NADPH:quinone oxidoreductase (NQO1). Recent evidence suggests that the antioxidant action of both melatonin and proteasome inhibitors involves the Keap1-ARE (Keap1 antioxidant response element) pathway via the upregulation of Nrf2. Melatonin and proteasome inhibitors suppress the degradation of Nrf2 and also enhance its nuclear translocation. In the nucleus Nrf2, together with a cofactor, stimulates the transcription of antioxidant enzymes and detoxifying enzymes. The ligase (E3) complex (Keap1-Cul3-Rbx1) responsible for ubiquitinating Nrf2, prior to proteasomal degradation, also ubiquitinates IkB kinase and the antiapoptotic factor Bcl-2, and possibly additional proteins. In various systems, NF-κB, which is inhibited by IkBα, is downregulated by proteasome inhibitors as well as by melatonin. Similarly in leukemic cells, Bcl-2 is down-regulated by the proteasome inhibitor, bortezomib, and also by melatonin. Thus melatonin administration modulates the activity of three separate substrates of the Keap1-Cul3-Rbx1 ubiquitin ligase. These facts could be accounted for by the hypothesis that melatonin interacts with the ubiquitin ligase complex or, more likely, by the hypothesis that melatonin acts as a proteasome inhibitor. A recent study documented that melatonin acts as a proteasome inhibitor in cancer cells as well as inhibiting chymotrypsin-like activity in cell-free systems of these cells. Further studies, however, are needed to clarify the interaction of melatonin and the ubiquitin-proteasome system as they relate to oxidative stress.

Novel curcumin analogue 14p protects against myocardial ischemia reperfusion injury through Nrf2-activating anti-oxidative activity

BACKGROUND

Alleviating the oxidant stress associated with myocardial ischemia reperfusion has been demonstrated as a potential therapeutic approach to limit ischemia reperfusion (I/R)-induced cardiac damage. Curcumin, a natural compound with anti-oxidative activity, exerts beneficial effect against cardiac I/R injury, but poor chemical and metabolic stability. Previously, we have designed and synthesized a series of mono-carbonyl analogues of curcumin (MACs) with high stability. This study aims to find new anti-oxidant MACs and to demonstrate their effects and mechanisms against I/R-induced heart injury.

METHODS

H9c2 cells challenged with H2O2 or TBHP were used for in vitro bio-screening and mechanistic studies. The MDA, H2O2 and SOD levels in H9C2 cells were determined, and the cell viability was assessed by MTT assay. Myocardial I/R mouse models administrated with or without the compound were used for in vivo studies.

RESULTS

The in vitro cell-based screening showed that curcumin analogues 8d and 14p exhibited strong anti-oxidative effects. Pre-treatment of H9c2 cells with 14p activated Nrf2 signaling pathway, attenuated H2O2-increased MDA and SOD level, followed by the inhibition of TBHP-induced cell death and Bax/Bcl-2-caspase-3 pathway activation. Silencing Nrf2 significantly reversed the protective effects of 14p. In in vivo animal model of myocardial I/R, administration of low dose 14p (10mg/kg) reduced infarct size and myocardial apoptosis to the same extent as the high dose curcumin (100mg/kg).

CONCLUSION

These data support the novel curcumin analogue 14p as a promising antioxidant to decrease oxidative stress and limit myocardial ischemia reperfusion injury via activating Nrf2.

Targeting nrf2 signaling to combat chemoresistance

Nuclear factor E2-related factor 2 (Nrf2) is a transcription factor that upregulates expression of a battery of genes to combat oxidative and electrophilic stress. Modification of Kelch-like ECH-associated protein 1 (Keap1) by reactive oxygen species stabilizes Nrf2 by escaping from degradation. Nrf2 then binds to antioxidant response elements (AREs) on the promoter region of various genes. Activation of the Keap1-Nrf2-ARE pathway plays critical roles in the chemopreventive effect of various phytochemicals. However, Nrf2 can protect cancer cells from oxidative stress and promote cell proliferation. Moreover, recent studies reveal that activation of the Nrf2 pathway is critical for resistance to chemotherapeutic agents. The aim of this review is to provide a molecular basis for the use of Nrf2 inhibitors in overcoming chemoresistance.

Investigation of the intermolecular recognition mechanism between the E3 ubiquitin ligase Keap1 and substrate based on multiple substrates analysis

E3 ubiquitin ligases are attractive drug targets due to their specificity to the ubiquitin machinery. However, the development of E3 ligase inhibitors has proven challenging for the fact that they must disrupt protein-protein interactions (PPIs). The E3 ligase involved in interactome provide new hope for the discovery of the E3 ligase inhibitors. These currently known natural binding partners of the E3 ligase can benefit the discovery of other unknown substrates and also the E3 ligase inhibitors. Herein, we present a novel strategy that using multiple substrates to elucidate the molecular recognition mechanism of E3 ubiquitin ligase. Molecular dynamics simulation, molecular mechanics-generalized born surface area (MM-GBSA) binding energy calculation and energy decomposition scheme were incorporated to evaluate the quantitative contributions of sub-pocket and per-residue to binding. In this case, Kelch-like ECH-associated protein-1 (Keap1), a substrate adaptor component of the Cullin-RING ubiquitin ligases complex, is applied for the investigation of how it recognize its substrates, especially Nrf2, a master regulator of the antioxidant response. By analyzing multiple substrates binding determinants, we found that both the polar sub-pockets (P1 and P2) and the nonpolar sub-pockets (P4 and P5) of Keap1 can make remarkable contributions to intermolecular interactions. This finding stresses the requirement for substrates to interact with the polar and nonpolar sub-pockets simultaneously. The results discussed in this paper not only show the binding determinants of the Keap1 substrates but also provide valuable implications for both Keap1 substrate discovery and PPI inhibitor design.

Involvement of Nrf2 in development of anxiety-like behavior by linking Bcl2 to oxidative phosphorylation: estimation in rat hippocampus, amygdala, and prefrontal cortex

Anxiety-related disorders are complex illnesses that underlying molecular mechanisms of these complicated emotional disorders are poorly understood. Nuclear factor erythroid 2-related factor 2 (Nrf2) is the most important regulator of the antioxidant defense system. Its protective actions are not only limited to antioxidative transactivation, but also plays important roles in encountering various physiological and pathological stresses. In this study, we evaluated whether silencing of Nrf2 plays a role in development of anxiety-related behavior. In this regard, we exerted small interfering RNA (siRNA) targeting Nrf2 in dorsal third ventricle and subsequently examined the effect of this silencing on anxiety-related behavior along with supposed molecular mechanisms. Therefore, we evaluated apoptotic markers and mitochondrial electron transport chain (ETC) activity in three brain regions: hippocampus, amygdala, and prefrontal cortex. Based on our result, Nrf2-silenced rats exhibited greater anxiety-like behavior compared to control group. Furthermore, Nrf2 silencing increased activity of ETC complexes. Also, Bax/Bcl2 ratio of all mentioned areas of the brain and cleavage of caspase-3 in hippocampus increased in Nrf2 silenced group, however, with a distinct pattern.

Targeting the NF-E2-related factor 2 pathway: a novel strategy for glioblastoma (review)

Glioblastoma is the most common and malignant subtype among all brain tumors. Nuclear factor erythroid 2-related factor 2 (Nrf2) is an essential component of cellular defense against a variety of endogenous and exogenous stresses. A marked increase in research over the past few decades focusing on Nrf2 and its role in regulating glioblastoma has revealed the potential value of Nrf2 in the treatment of glioblastoma. In the present review, we discuss a novel framework of Nrf2 in the regulation of glioblastoma and the mechanisms regarding the downregulation of Nrf2 in treating glioblastoma. The candidate mechanisms include direct and indirect means. Direct mechanisms target tumor molecular pathways in order to overcome resistance to chemotherapy and radiotherapy, to inhibit proliferation, to block invasion and migration, to induce apoptosis, to promote differentiation, to enhance autophagy and to target glioblastoma stem cells. Indirect mechanisms target the reaction between glioblastoma cells and the surrounding microenvironment. Overall, the value of the Nrf2 pathway in glioblastoma provides a promising opportunity for new approaches by which to treat glioblastoma.

Modulation of NRF2 signaling pathway by nuclear receptors: implications for cancer

Nuclear factor-erythroid 2 p45-related factor 2 (NRF2, also known as Nfe2l2) plays a critical role in regulating cellular defense against electrophilic and oxidative stress by activating the expression of an array of antioxidant response element-dependent genes. On one hand, NRF2 activators have been used in clinical trials for cancer prevention and the treatment of diseases associated with oxidative stress; on the other hand, constitutive activation of NRF2 in many types of tumors contributes to the survival and growth of cancer cells, as well as resistance to anticancer therapy. In this review, we provide an overview of the NRF2 signaling pathway and discuss its role in carcinogenesis. We also introduce the inhibition of NRF2 by nuclear receptors. Further, we address the biological significance of regulation of the NRF2 signaling pathway by nuclear receptors in health and disease. Finally, we discuss the possible impact of NRF2 inhibition by nuclear receptors on cancer therapy.

Degradation of Keap1 activates BH3-only proteins Bim and PUMA during hepatocyte lipoapoptosis

Non-alcoholic steatohepatitis is characterized by hepatic steatosis, elevated levels of circulating free fatty acids (FFA) and hepatocyte lipoapoptosis. This lipoapoptosis requires increased JNK phosphorylation and activation of the pro-apoptotic BH3-only proteins Bim and PUMA. Kelch-like ECH-associated protein (Keap)-1 is a BTB/Kelch protein that can regulate the expression of Bcl-2 protein and control apoptotic cell death. Yet, the role of Keap1 in hepatocyte lipotoxicity is unclear. Here we demonstrate that Keap1 protein was rapidly degraded in hepatocytes, through autophagy in a p62-dependent manner, in response to the toxic saturated FFA palmitate, but not following incubation with the non-toxic FFA oleic acid. Stable knockdown of Keap1 expression, using shRNA technology, in hepatocarcinoma cell lines induced spontaneous cell toxicity that was associated with JNK1-dependent upregulation of Bim and PUMA protein levels. Also, Keap1 knockdown further sensitized hepatocytes to lipoapoptosis by palmitate. Likewise, primary hepatocytes isolated from liver-specific Keap1(-/-) mice displayed higher Bim and PUMA protein levels and demonstrated increased sensitivity to palmitate-induced apoptosis than wild-type mouse hepatocytes. Finally, stable knockdown of Bim or PUMA expression prevented cell toxicity induced by loss of Keap1. These results implicate p62-dependent autophagic degradation of Keap1 by palmitate as a mechanism contributing to hepatocyte lipoapoptosis.