The involvement of p62-Keap1-Nrf2 antioxidative signaling pathway and JNK in the protection of natural flavonoid quercetin against hepatotoxicity

Protective effect of Pinot noir pomace extract against the cytotoxicity induced by polycyclic aromatic hydrocarbons on endothelial cells

Polycyclic Aromatic Hydrocarbons (PAHs) are pollutants found in the air generated mainly by the combustion of coal or biomass burning. Exposure to Polycyclic Aromatic Hydrocarbons is positively correlated with cardiovascular diseases. Phenolic compounds are widely found in the plant kingdom, and their availability from agri-food processing waste has led to an increased interest in their recovery. The production of large amounts of organic waste created by the wine industry has emphasized the valuation of these wastes to generate high-added-value by-products. The objective of this work was to investigate the protective effect of Pinot noir pomace extract on human endothelial cells against PAHs found in the polluted air of Temuco, Chile. The pomace extract was characterized by spectrophotometric analysis and high-performance liquid chromatography (HPLC). Results revealed the presence of 5 glycosylated anthocyanins and 9 low molecular weight polyphenols. Molecular docking indicated that cyanidin-3-glucoside (-9.2 kcal/mol) and quercetin (-9.6 kcal/mol) had the highest affinities for the Nrf2 binding site in the Keap1 protein, suggesting a possible competition with this transcription factor. Endothelial cells from the human umbilical vein were exposed to increasing concentrations of Phenanthrene, Fluoranthene, and Pyrene diluted in DMSO in a ratio of 3:1:1 (10 μM-200 μM). Viability through the MTS assay showed that 150 μM of PAHs was sufficient to reduce viability by 75% (p ˂ 0.0001). When the cells were pre-treated with 400 μg/ml of the extract, 150 μM of PAHs did not exert cell death (80% viability). Our preliminary results show that polyphenolic components found in Pinot noir pomace might have a beneficial effect as a protective agent.

Exploiting Anti-Inflammation Effects of Flavonoids in Chronic Inflammatory Diseases

BACKGROUND

Inflammation is a complex response of the host defense system to different internal and external stimuli. It is believed that persistent inflammation may lead to chronic inflammatory diseases such as, inflammatory bowel disease, neurological and cardiovascular diseases. Oxidative stress is the main factor responsible for the augmentation of inflammation via various molecular pathways. Therefore, alleviating oxidative stress is effective a therapeutic option against chronic inflammatory diseases.

METHODS

This review article extends the knowledge of the regulatory mechanisms of flavonoids targeting inflammatory pathways in chronic diseases, which would be the best approach for the development of suitable therapeutic agents against chronic diseases.

RESULTS

Since the inflammatory response is initiated by numerous signaling molecules like NF-κB, MAPK, and Arachidonic acid pathways, their encountering function can be evaluated with the activation of Nrf2 pathway, a promising approach to inhibit/prevent chronic inflammatory diseases by flavonoids. Over the last few decades, flavonoids drew much attention as a potent alternative therapeutic agent. Recent clinical evidence has shown significant impacts of flavonoids on chronic diseases in different in-vivo and in-vitro models.

CONCLUSION

Flavonoid compounds can interact with chronic inflammatory diseases at the cellular level and modulate the response of protein pathways. A promising approach is needed to overlook suitable alternative compounds providing more therapeutic efficacy and exerting fewer side effects than commercially available antiinflammatory drugs.

Quercetin supports bovine preimplantation embryo development under oxidative stress condition via activation of the Nrf2 signalling pathway

Nrf2 is a master regulator for antioxidant machinery against oxidative stress in bovine preimplantation embryos. The endogenous or exogenous modulation of Nrf2-KEAP1 system in bovine embryos may contribute to the understanding of the mechanisms behind the response of embryos to stress conditions. Therefore, here we aimed to investigate the protective effect of quercetin on bovine preimplantation embryos exposed to higher atmospheric oxygen concentration. For that, blastocysts, which were developed from zygotes cultured in media supplemented with or without quercetin under high oxygen level (20%), were subjected intracellular ROS level and mitochondrial analysis, and determining blastocyst formation rate and total cell number. Moreover, mRNA and protein expression level of Nrf2 and selected downstream antioxidant genes were investigated in the resulting blastocysts. Quercetin supplementation in vitro culture did not affect cleavage and blastocyst rate until day 7. However, quercetin supplementation resulted in higher blastocyst total cell number and reduction of intracellular ROS level accompanied by increasing mitochondrial activity compared with control group in both day 7 and day 8 blastocysts. Moreover, quercetin supplementation induced mRNA and protein of Nrf2 with subsequent increase in the expression of downstream antioxidants namely: NQO1, PRDX1, CAT and SOD1 antioxidants. In conclusion, quercetin protects preimplantation embryos against oxidative stress and improves embryo viability through modulation of the Nrf2 signalling pathway.

Role of Nrf2 in cell senescence regulation

Nuclear factor-E2-related factor 2 (Nrf2) is a key transcription factor known to be involved in maintaining cell redox balance and signal transduction and plays central role in reducing intracellular oxidative stress damage, delaying cell senescence and preventing age-related diseases. However, it has been shown that the level of Nrf2 decreases with age and that the silencing of the Nrf2 gene is associated with the induction of premature senescence. Therefore, a plethora of researchers have focused on elucidating the regulatory mechanism of Nrf2 in the prevention of cell senescence. This complex regulatory mechanism of Nrf2 in the cell senescence process involves coordinated regulation of multiple signaling molecules. After summarizing the function of Nrf2 and its relationship with cell senescence pathway, this review focuses on the recent advances and progress made in elucidating the regulatory mechanism of Nrf2 in the cell senescence process. Additionally, the information collected here may provide insights for further research on Nrf2, in particular, on its regulatory mechanism in the cell senescence process.

Toosendanin-induced apoptosis in colorectal cancer cells is associated with the κ-opioid receptor/β-catenin signaling axis

Developing new drugs for killing colorectal cancer (CRC) cells is urgently needed. Here, we explored the antitumor effects of toosendanin (TSN) in CRC, as well as explored its antitumor mechanisms and direct targets. Cell proliferation and apoptosis were analyzed by CCK8, colony formation, real-time cell impedance and flow cytometry. The signaling pathway and Wnt activity were analyzed by Wnt luciferase activity assay, quantitative real-time PCR and western blot. The interaction between TSN and the κ-opioid receptor was analyzed by a molecular docking simulation. BALB/c nude mice were used to detect the effects of TSN on tumor growth in vivo. We found that TSN inhibited proliferation, induced G1 phase arrest and caused caspase-dependent apoptosis in both 5-FU-sensitive and 5-FU-resistant CRC cells. Moreover, TSN effectively inhibited CRC growth in vivo. In terms of the mechanism, TSN inhibited Wnt/β-catenin signaling in CRC cells, and the molecular docking results showed that TSN could bind to κ-opioid receptors directly. Additionally, TSN-induced apoptosis and β-catenin decline were both reversed by the selective κ-opioid receptor agonist U50,488H. Our data demonstrate that TSN-induced apoptosis in CRC cells is associated with the κ-opioid receptor/β-catenin signaling axis, and TSN has promising potential as an antitumor agent for CRC treatment.

Protective and therapeutic effects of nanoliposomal quercetin on acute liver injury in rats

BACKGROUND

Quercetin, a pigment (flavonoid) found in many plants and foods, has good effects on protecting liver function but poor solubility and bioavailability in vivo. A drug delivery system can improve the accumulation and bioavailability of quercetin in liver. In this study, we used liposomal nanoparticles to entrap quercetin and evaluated its protective and therapeutic effects on drug-induced liver injury in rats.

METHODS

The nanoliposomal quercetin was prepared by a thin film evaporation-high pressure homogenization method and characterized by morphology, particle size and drug content. Acute liver injury was induced in rats by composite factors, including carbon tetrachloride injection, high-fat corn powder intake and ethanol drinking. After pure quercetin or nanoliposomal quercetin treatment, liver function was evaluated by detecting serum levels of glutamic-pyruvic transaminase (GPT), glutamic-oxal acetic transaminase (GOT) and direct bilirubin (DBIL). Histology of injured liver tissues was evaluated by hematoxylin and eosin staining.

RESULTS

On histology, liposomal nanoparticles loading quercetin were evenly distributed spherical particles. The nanoliposomal quercetin showed high bioactivity and bioavailability in rat liver and markedly attenuated the liver index and pathologic changes in injured liver tissue. With nanoliposomal quercetin treatment, the serum levels of GPT, GOT and DBIL were significantly better than treated with pure quercetin. Using liposomal nanoparticles to entrap quercetin might be an effective strategy to reduce hepatic injury and protect hepatocytes against damage.

CONCLUSION

Liposomal nanoparticles may improve the solubility and bioavailability of quercetin in liver. Furthermore, nanoliposomal quercetin could effectively protect rats against acute liver injury and may be a new hepatoprotective and therapeutic agent for patients with liver diseases.

Guavinoside B from Psidium guajava alleviates acetaminophen-induced liver injury via regulating the Nrf2 and JNK signaling pathways

GUB, a main phenolic compound present in guava fruits, could alleviate APAP-induced liver injury in vitro and in vivo by activating the Nrf2 signaling pathway and inhibiting the JNK signaling pathway.

Theoretical Study of the Antioxidant Activity of Quercetin Oxidation Products

It was recently shown that, when tested in cellular systems, quercetin oxidized products (Qox) have significantly better antioxidant activity than quercetin (Q) itself. The main Qox identified in the experiments are either 2,5,7,3',4'-pentahydroxy-3,4-flavandione (Fl) or its tautomer, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (Bf). We have now performed a theoretical evaluation of different physicochemical properties using density functional theory (DFT) calculations on Q and its main Qox species. The most stable structures (for Q and Qox) were identified after a structural search on their potential energy surface. Since proton affinities (PAs) are much lower than the bond dissociation enthalpies (BDEs) of phenolic hydrogens, we consider that direct antioxidant activity in these species is mainly due to the sequential proton loss electron transfer (SPLET) mechanism. Moreover, our kinetic studies, according to transition state theory, show that Q is more favored by this mechanism. However, Qox have lower PAs than Q, suggesting that antioxidant activity by the SPLET mechanism should be a result of a balance between proclivity to transfer protons (which favors Qox) and the reaction kinetics of the conjugated base in the sequential electron transfer mechanism (which favors Q). Therefore, our results support the idea that Q is a better direct antioxidant than its oxidized derivatives due to its kinetically favored SPLET reactions. Moreover, our molecular docking calculations indicate a stabilizing interaction between either Q or Qox and the kelch-like ECH-associated protein-1 (Keap1), in the nuclear factor erythroid 2-related factor 2 (Nrf2)-binding site. This should favor the release of the Nrf2 factor, the master regulator of anti-oxidative responses, promoting the expression of the antioxidant responsive element (ARE)-dependent genes. Interestingly, the computed Keap1-metabolite interaction energy is most favored for the Bf compound, which in turn is the most stable oxidized tautomer, according to their computed energies. These results provide further support for the hypothesis that Qox species may be better indirect antioxidants than Q, reducing reactive oxygen species in animal cells by activating endogenous antioxidants.

Phytochemical composition, isolation and hepatoprotective activity of active fraction from Veronica ciliata against acetaminophen-induced acute liver injury via p62-Keap1-Nrf2 signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Veronica ciliata Fisch, a traditional Tibetan medicine, used to cure hepatitis and existed in lots of Tibetan medicine prescriptions owing to its hepatoprotective activity.

AIMS OF THIS STUDY

In this study, we are aimed to systematically analysis and isolate the chemical constituents of the ethyl acetate fraction from V. ciliata (EAFVC), and test the hepatoprotective effect and mechanism of EAFVC and its compounds on attenuating the liver injury induced by acetaminophen (APAP) in vivo and vitro.

MATERIALS AND METHODS

UPLC-PDA-ESI-MS method was established for the analysis of the components in EAFVC, which was further separated using multiple chromatographic techniques. The MS, ¹H and ¹³C NMR were applied to elucidate their structures. UPLC-PDA method was applied for the simultaneous quantification of major compounds of EAFVC. Furthermore, the protective effect of the EAFVC was determined using APAP-induced acute hepatotoxicity in mice and BRL-3A cells model, respectively. In addition, the hepatoprotective activity of two main compounds in EAFVC on relieving APAP-induced liver injury was further evaluated. Finally, we have some concerns about the protective mechanism of EAFVC via enzyme-linked immunosorbent assay (ELISA), reactive oxygen species (ROS) detection, quantitative real-time PCR (qPCR), western blot analysis and molecular docking.

RESULTS

Thirteen compounds were successfully identified using UPLC-PDA-ESI-MS for the first time. Meanwhile, other twelve compounds were separated from EAFVC. Eventually, twenty-five compounds were successfully identified from the EAFVC. Among these compounds, fourteen compounds (3, 8, 10, 14-17, 19-25) were separated from V.ciliata for the first time. In addition, UPLC-PDA analysis method was first to establish for simultaneous determination of the main compounds (1, 2, 4, 5, 7, 9, 12). Further assay indicated that the liver injury in mice induced by APAP showed a significant reversal by EAFVC, as evidenced by reducing the activities of liver function enzymes, suppressing the lipid peroxidation as well as increasing the serum total antioxidant capacity (T-AOC) and the activities of antioxidant enzymes. Pathological sections showed that the liver in the high dose has significant improvement in mice. In vitro experiment also showed that EAFVC elevate the viability, inhibiting the activities of liver function enzymes as well as the generation of ROS of BRL-3A cells. In addition, Catalposide and verproside could reverse the low cell viability of BRL-3A cells induced by APAP. The mechanism research in vitro demonstrated that EAFVC could promote the mRNA and protein expression of heme oxygenase-1 (HO-1), NAD(P) H dehydrogenase quinone 1 (NQO-1) and catalytic or modify subunit of glutamate-cysteine ligase (GCLC/GCLCM) via enhancing nuclear factor-E2-related factor 2 (Nrf2) and p62/SQSTM1 (p62) expression in protein level. Molecular docking results demonstrated that catalposide and verproside have strong affinity to the kelch-like ECH-associated protein-1(Keap1) Kelch domain.

CONCLUSION

This research is the first to clarify the substance basis of the hepatoprotective activity of the EAFVC and provide the further scientific data for the traditional use of this Tibetan Medicine. EAFVC is valuable to be further investigated as active preparations for application in liver protection via activating p62- Keap1-Nrf2 pathway.

Crosstalk between mitochondrial metabolism and oxidoreductive homeostasis: a new perspective for understanding the effects of bioactive dietary compounds

Mitochondria play an important role in a number of fundamental cellular processes, including energy production, biosynthetic pathways and cellular oxidoreductive homeostasis (redox status), and their dysfunction can lead to numerous pathophysiological consequences. As the biochemical mechanisms orchestrating mitochondrial metabolism and redox homeostasis are functionally linked, mitochondria have been identified as a potential therapeutic target. Consequently, considerable effort has been made to evaluate the efficacy of natural compounds that modulate mitochondrial function. Molecules produced by plants (for example, polyphenols and isothiocyanates) have been shown to modulate mitochondrial metabolism/biogenesis and redox status; however, despite the existence of a functional link, few studies have considered the combined efficacy of these mitochondrial functions. The present review provides a complete overview of the molecular pathways involved in modulating mitochondrial metabolism/biogenesis and redox status. Crosstalk between these critical mechanisms is also discussed, whilst major data from the literature regarding their antioxidant abilities are described and critically analysed. We also provide a summary of recent evidence regarding the ability of several plant-derived compounds to target these mitochondrial functions. An in-depth understanding of the functional link between mitochondrial metabolism/biogenesis and redox status could facilitate the analysis of the biological effects of natural compounds as well as the development of new therapeutic approaches.

Recent Advances of Natural Polyphenols Activators for Keap1-Nrf2 Signaling Pathway

The Keap1-Nrf2/ARE signaling pathway is an important defense system against exogenous and endogenous oxidative stress injury. The dysregulation of the signaling pathway is associated with many diseases, such as cancer, diabetes, and respiratory diseases. Over the years, a wide range of natural products has provided sufficient resources for the discovery of potential therapeutic drugs. Among them, polyphenols possess Nrf2 activation, not only inhibit the production of ROS, inhibit Keap1-Nrf2 protein-protein interaction, but also degrade Keap1 and regulate the Nrf2 related pathway. In fact, with the continuous improvement of natural polyphenols separation and purification technology and further studies on the Keap1-Nrf2 molecular mechanism, more and more natural polyphenols monomer components of Nrf2 activators have been gradually discovered. In this view, we summarize the research status of natural polyphenols that have been found with apparent Nrf2 activation and their action modes. On the whole, this review may guide the design of novel Keap1-Nrf2 activator.

Discovery of Keap1-Nrf2 small-molecule inhibitors from phytochemicals based on molecular docking

Various phytochemicals have been reported to protect against oxidative stress. However, the mechanism underlying has not been systematically evaluated, which limited their application in disease treatment. Nuclear factor erythroid 2−related factor 2 (Nrf2), a central transcription factor in oxidative stress response related to numerous diseases, is activated after dissociating from the cytoskeleton−anchored Kelch−like ECH−associated protein 1 (Keap1). The Keap1–Nrf2 protein–protein interaction has become an important drug target. This study was designed to clarify whether antioxidantive phytochemicals inhibit the Keap1–Nrf2 protein–protein interaction and activate the Nrf2-ARE signaling pathway efficiently. Molecular docking and 3D−QSAR were applied to evaluate the interaction effects between 178 antioxidant phytochemicals and the Nrf2 binding site in Keap1. The Nrf2 activation effect was tested on a H₂O₂−induced oxidative−injured cell model. Results showed that the 178 phytochemicals could be divided into high−, medium−, and low−total−score groups depending on their binding affinity with Keap1, and the high−total−score group consisted of 24 compounds with abundant oxygen or glycosides. Meanwhile, these compounds could bind with key amino acids in the structure of the Keap1−Nrf2 interface. Compounds from high−total−score group show effective activation effects on Nrf2. In conclusion, phytochemicals showed high binding affinity with Keap1 are promising new Nrf2 activators.

•

178 phytochemicals were collected and the Keap1-binding-affinity was estimated.

•

24 compounds with high Keap1-binding-affinity was obtained.

•

Compounds with high Keap1-binding-affinity effectively activated Nrf2.

Isoflavone biochanin A, a novel nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element activator, protects against oxidative damage in HepG2 cells

Isoflavones are one group of the major flavonoids and possess multiple biological activities due to their antioxidant properties. However, a clear antioxidant mechanism of dietary isoflavones is still remained to be answered. In this study, the effects of isoflavones on the nuclear factor E2-related factor 2 (Nrf2)-antioxidant response element (ARE) signaling pathway and the underlying molecular mechanisms were investigated. Results showed that isoflavones are potential Nrf2-ARE activators while their activities were structure dependent. Biochanin A (BCA), an O-methylated isoflavone with low direct antioxidant activity, can effectively protect HepG2 cells against tert-butyl hydroperoxide (t-BHP)-induced oxidative damage via activation of the Nrf2 signaling, and thereby the induction of downstream cytoprotective enzymes including NAD(P)H quinone oxidoreductase-1, heme oxygenasae-1, and glutamate-cysteine ligase catalytic subunit. A molecular docking study revealed that BCA could directly bind into the pocket of Kelch-like erythroid cell-derived protein with CNC homology (ECH)-associated protein 1 (Keap1), a cytoplasmic suppressor of Nrf2, to facilitate Nrf2 activation. The upstream mitogen-activated protein kinase (MAPK) pathways were also involved in the activation of Nrf2 signaling. These findings indicate that the protective actions of dietary isoflavones against oxidative damage may be at least partly due to their ability to enhance the intracellular antioxidant response system by modulating the Nrf2-ARE signaling pathway.

Induction of Nrf2 pathway by Dendrobium nobile Lindl. alkaloids protects against carbon tetrachloride induced acute liver injury

Dendrobium nobile Lindl. alkaloids (DNLA), the active ingredients of Dendrobium, has been shown to possess anti-oxidative effects. The nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant signaling pathway plays a critical role in the cellular response to oxidative stress. Oxidative damage has been implicated in the mechanism of various hepatotoxins induced liver injury. The present study aimed to examine the protective effects of DNLA on CCl₄-induced acute liver injury, and to explore the role of the Nrf2 pathway in the protective action of DNLA. Wild-type (WT) and Nrf2-knockout (Nrf2^-/-) mice were administrated with DNLA (20 mg/kg/day, ig) for 7 days, and then challenged with CCl₄ (20 μL/kg, ip). In WT mice, DNLA reduced CCl₄ induced liver injury, as evidenced by the reduction in the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), attenuation of malondialdehyde (MDA) production, and improved ultrastructural morphology in hepatocytes. However, the protective effect was diminished in Nrf2^-/- mice, indicating an essential role of Nrf2 in DNLA-mediated protection over CCl₄ liver injury. Furthermore, it was found that DNLA enhanced Nrf2 expression and nuclear accumulation and increased the expression of Nrf2 regulated downstream proteins. These results demonstrate that DNLA protects mice from CCl₄ induced liver injury, probably through the activation of the Nrf2 signaling pathway.

Chrysanthemum extract attenuates hepatotoxicity via inhibiting oxidative stress in vivo and in vitro

Background

‘Bianliang ziyu’, a famous chrysanthemum variety commonly planted in Kaifeng, China, is often consumed by local residents. However, the hepatoprotective effects of Bianliang ziyu and their underlying mechanisms are not clear.

Objective

In this study, we investigated the hepatoprotective and antioxidative effects of Bianliang ziyu extract (BZE) on liver injury and explored its molecular mechanisms.

Design

Sprague-Dawley rats were administered BZE by intragastric administration for 8–9 days, and then alcohol or carbon tetrachloride (CCl₄) was administered by gavage to induce acute liver injury. The activities of serum alanine aminotransferase, aspartate aminotransferase, superoxide dismutase, and malondialdehyde in the rats were measured, and the liver of each rat was examined for histopathological changes. In vitro, HL-7702 cells were pretreated with BZE for 24 h and then exposed to 30 mmol•L⁻¹ acetaminophen (APAP) for 12 h. The survival rate of the cells and the alanine aminotransferase and aspartate aminotransferase activities were determined. Then, we investigated the effects of BZE on oxidative stress, apoptosis, and the activation of nuclear factor erythroid-2-related factor 2 (Nrf2) signaling in HL-7702 cells induced by APAP.

Results

The results showed that BZE prevented alcohol-, CCl₄-, and APAP-induced liver injury and suppressed hepatic oxidative stress in vitro and in vivo. BZE was also observed to significantly inhibit the reduction of mitochondrial membrane potential and regulate the expression of Bcl-2, Bax and Caspase-3 in APAP-induced HL-7702 cells. In addition, BZE significantly promoted nuclear translocation and the expression of Nrf2 as well as its downstream gene hemeoxygenase-1 (HO-1) in vitro. Furthermore, the findings showed that Nrf2 siRNA reversed the effects of BZE on cell survival and apoptosis-related protein expression in APAP-induced HL-7702 cells.

Conclusions

BZE plays an important role in preventing hepatotoxicity by inhibiting oxidative stress and apoptosis through activation of Nrf2 signaling. BZE could be developed as an effective functional food for protecting the liver.

Endogenous and Exogenous Modulation of Nrf2 Mediated Oxidative Stress Response in Bovine Granulosa Cells: Potential Implication for Ovarian Function

Nrf2 is a redox sensitive transcription factor regulating the expression of antioxidant genes as defense mechanism against various stressors. The aim of this study is to investigate the potential role of noncoding miRNAs as endogenous and quercetin as exogenous regulators of Nrf2 pathway in bovine granulosa cells. For this cultured granulosa cells were used for modulation of miRNAs (miR-28, 153 and miR-708) targeting the bovine Nrf2 and supplementation of quercentin to investigate the regulatory mechanisms of the Nrf2 antioxidant system. Moreover, cultured cells were treated with hydrogen peroxide to induce oxidative stress in those cells. Our results showed that, oxidative stress activated the expression of Nrf2 as a defense mechanism, while suppressing the expression of those miRNAs. Overexpression of those miRNAs resulted in downregulation of Nrf2 expression resulted in higher ROS accumulation, reduced mitochondrial activity and cellular proliferation. Quercetin supplementation showed its protective role against oxidative stress induced by H₂O₂ by inducing the expression of antioxidant enzymes. In conclusion, this study highlighted the involvement of miR-153, miR-28 and miR-708 in regulatory network of Nrf2 mediated antioxidant system in bovine granulosa cells function. Furthermore, quercetin at a low dose played a protective role in bovine granulosa cells against oxidative stress damage.

Antioxidant Activities of Quercetin and Its Complexes for Medicinal Application

Quercetin is a bioactive compound that is widely used in botanical medicine and traditional Chinese medicine due to its potent antioxidant activity. In recent years, antioxidant activities of quercetin have been studied extensively, including its effects on glutathione (GSH), enzymatic activity, signal transduction pathways, and reactive oxygen species (ROS) caused by environmental and toxicological factors. Chemical studies on quercetin have mainly focused on the antioxidant activity of its metal ion complexes and complex ions. In this review, we highlight the recent advances in the antioxidant activities, chemical research, and medicinal application of quercetin.

(-)-Epicatechin attenuates hepatic sinusoidal obstruction syndrome by inhibiting liver oxidative and inflammatory injury

Hepatic sinusoidal obstruction syndrome (HSOS) is a rare liver disease with considerable morbidity and mortality. (-)-Epicatechin (EPI) is a natural flavonol. This study aims to investigate the protection of EPI against monocrotaline (MCT)-induced HSOS and its engaged mechanism. Results of serum alanine/aspartate aminotransferases (ALT/AST) activities, total bilirubin (TBil) and bile acids (TBA) amounts, liver histological evaluation, scanning electron microscope observation and hepatic metalloproteinase-9 (MMP-9) expression all demonstrated the protection by EPI against MCT-induced HSOS in rats. EPI attenuated liver oxidative injury induced by MCT. EPI enhanced the nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) and increased the expression of its downstream antioxidant genes in rats. Molecular docking results implied the potential interaction of EPI with the Nrf2 binding site in kelch-like ECH-associated protein-1 (Keap1). The EPI-provided protection against MCT-induced HSOS was diminished in Nrf2 knock-out mice when mice were treated with MCT for 24 h but not for 48 h. However, EPI reduced the increased liver myeloperoxidase (MPO) activity, hepatic infiltration of immune cells, pro-inflammatory cytokines expression and nuclear factor κB (NFκB) activation in both wild-type and Nrf2 knock-out mice when mice were treated with MCT for 48 h. EPI reduced the elevated serum heat shock protein 60 (HSP60) content, and reversed the decreased mitochondria expression of HSP60 and Lon in livers from MCT-treated rats. Furthermore, the MCT-induced HSOS was markedly alleviated in mice treated with anti-HSP60 antibody. Taken together, this study demonstrates that EPI attenuates MCT-induced HSOS by reducing liver oxidative injury via activating Nrf2 antioxidant pathway and inhibiting liver inflammatory injury through abrogating NFκB signaling pathway initiated by HSP60.

•

EPI attenuates MCT-induced HSOS in rats.

•

EPI inhibits MCT induced liver oxidative injury in rats.

•

Nrf2 is important for the EPI-provided protection against MCT-induced HSOS.

•

EPI also abrogates MCT-induced liver inflammatory injury.

•

EPI reduced the release of HSP60.

Contribution of Nrf2 Modulation to the Mechanism of Action of Analgesic and Anti-inflammatory Drugs in Pre-clinical and Clinical Stages

Despite the progress that has occurred in recent years in the development of therapies to treat painful and inflammatory diseases, there is still a need for effective and potent analgesics and anti-inflammatory drugs. It has long been known that several types of antioxidants also possess analgesic and anti-inflammatory properties, indicating a strong relationship between inflammation and oxidative stress. Understanding the underlying mechanisms of action of anti-inflammatory and analgesic drugs, as well as essential targets in disease physiopathology, is essential to the development of novel therapeutic strategies. The Nuclear factor-2 erythroid related factor-2 (Nrf2) is a transcription factor that regulates cellular redox status through endogenous antioxidant systems with simultaneous anti-inflammatory activity. This review summarizes the molecular mechanisms and pharmacological actions screened that link analgesic, anti-inflammatory, natural products, and other therapies to Nrf2 as a regulatory system based on emerging evidences from experimental disease models and new clinical trial data.

Quercetin attenuates toosendanin-induced hepatotoxicity through inducing the Nrf2/GCL/GSH antioxidant signaling pathway

Toosendanin (TSN) is the main active compound in Toosendan Fructus and Meliae Cortex, two commonly used traditional Chinese medicines. TSN has been reported to induce hepatotoxicity, but its mechanism remains unclear. In this study, we demonstrated the critical role of nuclear factor erythroid 2-related factor 2 (Nrf2) in protecting against TSN-induced hepatotoxicity in mice and human normal liver L-02 cells. In mice, administration of TSN (10 mg/kg)-induced acute liver injury evidenced by increased serum alanine/aspartate aminotransferase (ALT/AST) and alkaline phosphatase (ALP) activities, and total bilirubin (TBiL) content as well as the histological changes. Furthermore, TSN markedly increased liver reactive oxygen species (ROS) and malondialdehyde (MDA) levels, and decreased liver glutathione (GSH) content and Nrf2 expression. In L-02 cells, TSN (2 μM) time-dependently reduced glutamate-cysteine ligase (GCL) activity and cellular expression of the catalytic/modify subunit of GCL (GCLC/GCLM). Moreover, TSN reduced cellular GSH content and the increased ROS formation, and time-dependently decreased Nrf2 expression and increased the expression of the Nrf2 inhibitor protein kelch-like ECH-associated protein-1 (Keap1). Pre-administration of quercetin (40, 80 mg/kg) effectively inhibited TSN-induced liver oxidative injury and reversed the decreased expression of Nrf2 and GCLC/GCLM in vivo and in vitro. In addition, the quercetin-provided protection against TSN-induced hepatotoxicity was diminished in Nrf2 knock-out mice. In conclusion, TSN decreases cellular GSH content by reducing Nrf2-mediated GCLC/GCLM expression via decreasing Nrf2 expression. Quercetin attenuates TSN-induced hepatotoxicity by inducing the Nrf2/GCL/GSH antioxidant signaling pathway. This study implies that inducing Nrf2 activation may be an effective strategy to prevent TSN-induced hepatotoxicity.

Andrographolide simultaneously augments Nrf2 antioxidant defense and facilitates autophagic flux blockade in cigarette smoke-exposed human bronchial epithelial cells

Cigarette smoking is the leading cause of chronic obstructive pulmonary disease (COPD). Cigarette smoke heightens oxidative stress and impairs autophagy, advancing COPD progression. Andrographolide is a bioactive diterpenoid lactone isolated from the plant Andrographis paniculata which has been a traditional medicinal herb for respiratory diseases. As airway epithelial cells form the first interface to be exposed to cigarette smoke, this study aimed to explore the modulatory effects of andrographolide on oxidative stress and autophagy in human bronchial epithelial BEAS-2B cells exposed to cigarette smoke extract (CSE). CSE (2%) exposure increased autophagic markers p62 and LC3B-II levels in BEAS-2B cells. Andrographolide alone increased p62 and p-p62 (S349) but not LC3B-II in BEAS-2B cells. However, in the presence of CSE, andrographolide was able to simultaneously increase LC3B-II level and enhance antioxidant defense by decreasing oxidative stress and increasing total antioxidant capacity, through upregulation of nuclear Nrf2 via the p62-Nrf2 positive feedback loop. Using RFP-GFP-LC3B transfected BEAS-2B cells exposed to CSE, andrographolide was found to impair autophagosome fusion with lysosome, which may account for the moderate increase in activated caspase 3/7 and annexin V levels. Our findings revealed for the first time that andrographolide simultaneously upregulated antioxidant defense through the p62-Nrf2 loop and moderately induced apoptosis through impairment of autophagic flux in CSE-exposed bronchial epithelium. Andrographolide facilitated cigarette smoke-induced apoptosis may be a potential toxicological outcome or may protect against chronic inflammation and aberrant DNA repair. Validation of these in-vitro findings in an experimental COPD model by andrographolide is warranted.

Quercetin preserves redox status and stimulates mitochondrial function in metabolically-stressed HepG2 cells

Hyperglycemia augments formation of intracellular reactive oxygen species (ROS) with associated mitochondrial damage and increased risk of insulin resistance in type 2 diabetes. We examined whether quercetin could reverse chronic high glucose-induced oxidative stress and mitochondrial dysfunction. Following long-term high glucose treatment, complex I activity was significantly decreased in isolated mitochondria from HepG2 cells. Quercetin dose-dependently recovered complex I activity and lowered cellular ROS generation under both high and normal glucose conditions. Respirometry studies showed that quercetin could counteract the detrimental increase in inner mitochondrial membrane proton leakage resulting from high glucose while it increased oxidative respiration, despite a decrease in electron transfer system (ETS) capacity, and lower non-ETS oxygen consumption. A quercetin-stimulated increase in cellular NAD⁺/NADH was evident within 2 h and a two-fold increase in PGC-1α mRNA within 6 h, in both normal and high glucose conditions. A similar pattern was also found for the mRNA expression of the repulsive guidance molecule b (RGMB) and its long non-coding RNA (lncRNA) RGMB-AS1 with quercetin, indicating a potential change of the glycolytic phenotype and suppression of aberrant cellular growth which is characteristic of the HepG2 cells. Direct effects of quercetin on PGC-1α activity were minimal, as quercetin only weakly enhanced PGC-1α binding to PPARα in vitro at higher concentrations. Our results suggest that quercetin may protect mitochondrial function from high glucose-induced stress by increasing cellular NAD⁺/NADH and activation of PGC-1α-mediated pathways. Lower ROS in combination with improved complex I activity and ETS coupling efficiency under conditions of amplified oxidative stress could reinforce mitochondrial integrity and improve redox status, beneficial in certain metabolic diseases.

Therapeutic Potential of Plants and Plant Derived Phytochemicals against Acetaminophen-Induced Liver Injury

Acetaminophen (APAP), which is also known as paracetamol or N-acetyl-p-aminophenol is a safe and potent drug for fever, pain and inflammation when used at its normal therapeutic doses. It is available as over-the-counter drug and used by all the age groups. The overdose results in acute liver failure that often requires liver transplantation. Current clinical therapy for APAP-induced liver toxicity is the administration of N-acetyl-cysteine (NAC), a sulphydryl compound an approved drug which acts by replenishing cellular glutathione (GSH) stores in the liver. Over the past five decades, several studies indicate that the safety and efficacy of herbal extracts or plant derived compounds that are used either as monotherapy or as an adjunct therapy along with conventional medicines for hepatotoxicity have shown favorable responses. Phytochemicals mitigate necrotic cell death and protect against APAP-induced liver toxicityby restoring cellular antioxidant defense system, limiting oxidative stress and subsequently protecting mitochondrial dysfunction and inflammation. Recent experimental evidences indicat that these phytochemicals also regulate differential gene expression to modulate various cellular pathways that are implicated in cellular protection. Therefore, in this review, we highlight the role of the phytochemicals, which are shown to be efficacious in clinically relevant APAP-induced hepatotoxicity experimental models. In this review, we have made comprehensive attempt to delineate the molecular mechanism and the cellular targets that are modulated by the phytochemicals to mediate the cytoprotective effect against APAP-induced hepatotoxicity. In this review, we have also defined the challenges and scope of phytochemicals to be developed as drugs to target APAP-induced hepatotoxicity.

DC32, a Dihydroartemisinin Derivative, Ameliorates Collagen-Induced Arthritis Through an Nrf2-p62-Keap1 Feedback Loop

Artemisinins have been reported to have diverse functions, such as antimalaria, anticancer, anti-inflammation, and immunoregulation activities. DC32 [(9α,12α-dihydroartemisinyl) bis(2′-chlorocinnmate)], a dihydroartemisinin derivative possessing potent immunosuppressive properties, was synthesized in our previous study. Collagen-induced arthritis (CIA) in DBA/1 mice and inflammatory model in NIH-3T3 cells were established to evaluate the effect of DC32 on RA and discover the underlying mechanisms. The results showed that DC32 could markedly alleviate footpad inflammation, reduce cartilage degradation, activate the Nrf2/HO-1 signaling pathway, and increase the transcription of p62 in DBA/1 mice with CIA. Further mechanistic exploration with NIH-3T3 cells indicated that DC32 could increase the transcription, expression, and nuclear translocation of Nrf2. In addition, DC32 promoted degradation of Keap1 protein and upregulated HO-1 and p62 expression. Furthermore, the effect of DC32 on Keap1 degradation could be prevented by p62 knockdown using siRNA. Administration of DC32 could inhibit the activation of Akt/mTOR and ERK, and pretreatment of NIH-3T3 cells with the autophagy inhibitor 3-methyladenine (3-MA) attenuated the degradation of Keap1 induced by DC32. These results suggest that DC32 inhibits the degradation of Nrf2 by promoting p62-mediated selective autophagy and that p62 upregulation contributed to a positive feedback loop for persistent activation of Nrf2. In summary, our present study demonstrated that DC32 significantly suppressed rheumatoid arthritis (RA) via the Nrf2-p62-Keap1 feedback loop by increasing the mRNA and protein levels of Nrf2 and inducing p62 expression. These findings provide new mechanisms for artemisinins in RA treatment and a potential strategy for discovering antirheumatic drugs.

Protective effects of Coptis chinensis inflorescence extract and linarin against carbon tetrachloride-induced damage in HepG2 cells through the MAPK/Keap1-Nrf2 pathway

Coptis chinensis inflorescence is traditionally used as tea and has been popular in the local market. C. chinensis inflorescence extract (CE) exhibits protective effects against carbon tetrachloride (CCl4)-induced damage, but the underlying mechanism remains unclear. The main chemicals of CE were detected, purified, and identified in this study. CE and linarin could reverse changes in cell viability, decrease alanine aminotransferase and aspartate transaminase levels, and reduce reactive oxygen species (ROS) generation induced by CCl4 in HepG2 cells. CE and linarin could also phosphorylate mitogen-activated protein kinases (MAPKs) and up-regulate Kelth-like ECH-associated protein (Keap1). The pathways of MAPKs and Keap1 lead to the separation of Keap1 and nuclear factor (erythroid-derived 2)-like 2 (Nrf2). Free Nrf2 transferred to the nucleus and enhanced the expression of phase II detoxification enzymes. This study provides a scientific basis for the use of C. chinensis inflorescence, which exhibits a hepatoprotective function, as a supplement in the food industry.

Discovery of natural flavonoids as activators of Nrf2-mediated defense system: Structure-activity relationship and inhibition of intracellular oxidative insults

Continuous overproduction of reactive oxygen species (ROS), termed as oxidative stress, plays a crucial role in the onset and progression of many human diseases. Activation of nuclear transcription factor erythroid 2-related factor (Nrf2) by small molecules could eliminate ROS, and thus block the pathogenesis of oxidative stress-induced diseases. In this study, a natural flavonoid library was established and tested for their potential Nrf2 inducing effects. Based on QR inducing effect of flavonoids, their structure-activity relationship (SAR) on Nrf2 induction was summarized, and twenty flavonoids were firstly identified to be potential activators of Nrf2-mediated defensive response. Then, 7-O-methylbiochanin A (7-MBA) was further investigated for its capability on the Nrf2 activation and prevention against oxidative insults in human lung epithelial cells. Further studies indicated that 7-MBA activated Nrf2 signaling pathway and protected human lung epithelial Beas-2B cells against sodium arsenite [As(III)]-induced cytotoxicity in an Nrf2-dependent manner. Activation of Nrf2 by 7-MBA upregulated intracellular antioxidant capacity, which was produced by enhancement of Nrf2 stabilization, blockage of Nrf2 ubiquitination, as well as Nrf2 phosphorylation by mitogen-activated protein kinase (MAPK), protein kinase C (PKC), protein kinase R-like endoplasmic reticulum kinase (PERK), and phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K). Taken together, 7-MBA is a novel isoflavone-type Nrf2 activator displaying potential preventive effect against oxidative damages in human lung epithelial cells.

Targeting Nrf-2 is a promising intervention approach for the prevention of ethanol-induced liver disease

Alcoholic liver disease (ALD) remains to be a worldwide health problem. It is generally accepted that oxidative stress plays critical roles in the pathogenesis of ALD, and antioxidant therapy represents a logical strategy for the prevention and treatment of ALD. Nuclear factor erythroid-derived 2-like 2 (NFE2L2 or Nrf-2) is essential for the antioxidant responsive element (ARE)-mediated induction of endogenous antioxidant enzymes such as heme oxygenase 1 (HO-1) and glutamate-cysteine ligase [GCL, the rate-limiting enzyme in the synthesis of glutathione (GSH)]. Activation of Nrf-2 pathway by genetic manipulation or pharmacological agents has been demonstrated to provide protection against ALD, which suggests that targeting Nrf-2 may be a promising approach for the prevention and treatment of ALD. Herein, we review the relevant literature about the potential hepatoprotective roles of Nrf-2 activation against ALD.

Effects of Quercetin on Proliferation and H₂O₂-Induced Apoptosis of Intestinal Porcine Enterocyte Cells

Weanling stress and toxicosis, which are harmful to the health of pigs' intestines, are associated with oxidative stress. Quercetin (Que) is a polyphenolic compound that shows good anti-cancer, anti-inflammation and anti-oxidation effects. This study aimed to elaborate whether or not Que promotes IPEC-J2 (intestinal porcine enterocyte cells) proliferation and protects IPEC-J2 from oxidative damage. Thus, we examined the effects of Que on proliferation and H₂O₂-induced apoptosis in IPEC-J2. The results showed that Que increased IPEC-J2 viabililty, propelled cells from G1 phase into S phase and down-regulated gene levels of P27 and P21, respectively. Besides, H₂O₂-induced cell damage was alleviated by Que after different exposure times, and Que depressed apoptosis rate, reactive oxygen species (ROS) level and percentage of G1 phase cells and elevated the percentage of cells in G2 phase and S phase and mitochondrial membrane potential (Δψm) after IPEC-J2 exposure to H₂O₂. Meanwhile, Que reduced the value of Bax/Bcl-2 in H₂O₂ exposed cells. In low-degree oxidative damage cells, lipid peroxidation product malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were increased. In turn, Que could reverse the change of MDA content and SOD activity in low-degree damage cells. Nevertheless, catalase (CAT) activity was not changed in IPEC-J2 incubated with Que under low-degree damage conditions. Interestingly, relative expressive levels of the proteins claudin-1 and occludin were not altered under low-degree damage conditions, but Que could improve claudin-1 and occludin levels, slightly. This research indicates that Que can be greatly beneficial for intestinal porcine enterocyte cell proliferation and it protects intestinal porcine enterocyte cells from oxidation-induced apoptosis, and could be used as a potential feed additive for porcine intestinal health against pathogenic factor-induced oxidative damages and apoptosis.

Antioxidants from Plants Protect against Skin Photoaging

Exposure to UV light triggers the rapid generation and accumulation of reactive oxygen species (ROS) in skin cells, with consequent increase in oxidative stress and thus in photoaging. Exogenous supplementation with dietary antioxidants and/or skin pretreatment with antioxidant-based lotions before sun exposure might be a winning strategy against age-related skin pathologies. In this context, plants produce many secondary metabolites to protect themselves from UV radiations and these compounds can also protect the skin from photoaging. Phenolic compounds, ascorbic acid and carotenoids, derived from different plant species, are able to protect the skin by preventing UV penetration, reducing inflammation and oxidative stress, and influencing several survival signalling pathways. In this review, we focus our attention on the double role of oxidants in cell metabolism and on environmental and xenobiotic agents involved in skin photoaging. Moreover, we discuss the protective role of dietary antioxidants from fruits and vegetables and report their antiaging properties related to the reduction of oxidative stress pathways.

Attenuation of tert-Butyl Hydroperoxide ( t-BHP)-Induced Oxidative Damage in HepG2 Cells by Tangeretin: Relevance of the Nrf2-ARE and MAPK Signaling Pathways

The current study evaluates the protective effects of tangeretin, a representative polymethoxyflavone (PMF) mainly isolated from the peels of citrus fruits, against tert-butyl hydroperoxide ( t-BHP)-induced oxidative damage in HepG2 cells and the potential mechanisms of this protection. Tangeretin suppressed t-BHP-induced oxidative damage, as evaluated by cell viability, reactive-oxygen-species (ROS) levels, lactate dehydrogenase (LDH) leakage and glutathione (GSH) levels. Further mechanistic studies showed that tangeretin up-regulated the expression of heme oxygenase 1 (HO-1) and NAD(P)H quinone oxidoreductase 1 (NQO1). Moreover, tangeretin induced antioxidant-responsive-element (ARE)-dependent luciferase activation, nuclear factor (erythroid-derived 2)-like 2 (Nrf2) nuclear translocation, and mitogen-activated-protein-kinase (MAPK) phosphorylation. Results in the study indicate that the protective effects of tangeretin may be at least partly due to its capacity to up-regulate the antioxidant enzymes NQO1 and HO-1 via the MAPK-Nrf2-ARE signaling pathway. Tangeretin may play an effective protective role in liver injury.

Mitochondria-Targeting Small Molecules Effectively Prevent Cardiotoxicity Induced by Doxorubicin

Doxorubicin (Dox) is a chemotherapeutic agent widely used for the treatment of numerous cancers. However, the clinical use of Dox is limited by its unwanted cardiotoxicity. Mitochondrial dysfunction has been associated with Dox-induced cardiotoxicity. To mitigate Dox-related cardiotoxicity, considerable successful examples of a variety of small molecules that target mitochondria to modulate Dox-induced cardiotoxicity have appeared in recent years. Here, we review the related literatures and discuss the evidence showing that mitochondria-targeting small molecules are promising cardioprotective agents against Dox-induced cardiac events.

Activation of p62/SQSTM1-Keap1-Nuclear Factor Erythroid 2-Related Factor 2 Pathway in Cancer

Autophagy and the Keap1–Nrf2 system are major cellular defense mechanisms against metabolic and oxidative stress. These two systems are linked via phosphorylation of the ubiquitin binding autophagy receptor protein p62/SQSTM1 in the p62–Keap1–Nrf2 pathway. The p62–Keap1–Nrf2 pathway plays a protective role in normal cells; however, recent studies indicate that this pathway induces tumorigenesis of pre-malignant cells, and promotes the growth and drug resistance of tumor cells via metabolic reprogramming mediated by Nrf2 activation. These findings suggest that impairment of autophagy is involved in the acquisition of malignancy and maintenance of tumors, and furthermore, that p62/SQSTM1 could be a potential target for chemotherapy in cancers that harbor excess p62.

Ingredients from Litsea garrettii as Potential Preventive Agents against Oxidative Insult and Inflammatory Response

Oxidative stress and inflammation undoubtedly contribute to the pathogenesis of many human diseases. The nuclear transcription factor erythroid 2-related factor (Nrf2) and the nuclear factor κB (NF-κB) play central roles in regulation of oxidative stress and inflammation and thus are targets for developing agents against oxidative stress- and inflammation-related diseases. Our previous study indicated that the EtOH extract of Litsea garrettii protected human bronchial epithelial cells against oxidative insult via the activation of Nrf2. In the present study, a systemic phytochemical investigation of L. garrettii led to the isolation of twenty-one chemical ingredients, which were further evaluated for their inhibitions on oxidative stress and inflammation using NAD(P)H:quinone reductase (QR) assay and nitric oxide (NO) production assay. Of these ingredients, 3-methoxy-5-pentyl-phenol (MPP, 5) was identified as an Nrf2 activator and an NF-κB inhibitor. Further studies demonstrated the following: (i) MPP upregulated the protein levels of Nrf2, NAD(P)H:quinone oxidoreductase 1 (NQO1), and glutamate-cysteine ligase regulatory subunit (GCLM); enhanced the nuclear translocation and stabilization of Nrf2; and inhibited arsenic [As(III)]-induced oxidative insult in normal human lung epithelial Beas-2B cells. And (ii) MPP suppressed the nuclear translocation of NF-κB p65 subunit; inhibited the lipopolysaccharide- (LPS-) stimulated increases of NF-κB p65 subunit, COX-2, iNOS, TNF-α, and IL-1β; and blocked the LPS-induced biodegrade of IκB-α in RAW 264.7 murine macrophages. Taken together, MPP displayed potential preventive effects against inflammation- and oxidative stress-related diseases.

Chrysin suppresses proliferation, migration, and invasion in glioblastoma cell lines via mediating the ERK/Nrf2 signaling pathway

Background

Chrysin, an active natural bioflavonoid, has been proven to protect against carcinogenesis. However, the role of chrysin in glioblastoma and the potential molecular mechanisms remain to be elucidated. In our previous study, we found that nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) is highly expressed in a variety of glioblastoma cell lines associated with the mitogen-activated protein kinase (MAPK) pathway. The aim of this study was to evaluate the antitumor effects of chrysin in glioblastoma cells and how chrysin is related to the MAPK/Nrf2 signaling pathway.

Methods

A Cell Counting Kit-8 assay and a plate colony formation assay were performed to evaluate cell proliferation. Cell migration ability was tested by a wound-healing assay. Transwell migration and Matrigel invasion assay were used to test the migration and invasion potential of cells. Nrf2 was knocked down by shRNA transfection. Protein expression was determined by Western blotting and immunofluorescence staining. The in vivo anticancer effect was measured using tumor xenografts in nude mice.

Results

Chrysin inhibited the proliferation, migration, and invasion capacity of glioblastoma cells in dose- and time-dependent manners. Mechanistically, chrysin deactivated the Nrf2 signaling pathway by decreasing the translocation of Nrf2 into the nucleus and suppressing the expression of hemeoxygenase-1 (HO-1) and NAD(P)H quinine oxidoreductase-1, meanwhile, Nrf2 shRNA attenuated the anticancer activity of chrysin. Furthermore, chrysin downregulated the protein expression of p-extracellular signal-regulated kinase 1 and 2 (ERK1/2), but did not significantly affect p-JNK and p-P38 expression levels. However, the downregulated level of Nrf2 and the antitumor effect of chrysin in glioblastoma cell lines were partially abrogated by the ERK1/2 signaling inhibitor (U0126). Finally, chrysin inhibited tumor growth in U87 xenografts.

Conclusion

Our results show that chrysin exerts anticancer activity in glioblastoma cell lines possibly via the ERK/Nrf2 signaling pathway and indicate the potential application of chrysin as a natural sensitizer in chemotherapy.

Black rice (Oryza sativa L.) extract modulates ultraviolet-induced expression of matrix metalloproteinases and procollagen in a skin cell model

Exposure of the skin to ultraviolet (UV) radiation causes extracellular matrix (ECM) collapse in the dermis, owing to an increase in matrix metalloproteinase (MMP) production in both the epidermis and dermis, and a decrease in type I collagen expression in the dermis. Recently, black rice (Oryza sativa L.) was reported to have a wide range of pharmacological effects in various settings. However, the effects of black rice extract (BRE) on UV‑irradiated skin cells have not yet been characterized. BRE treatment did not affect cell morphology and viability of HaCaT and human dermal fibroblasts (HDF). We demonstrated that BRE downregulated basal and UV‑induced MMP‑1 expression in HaCaT cells. Furthermore, BRE significantly increased type I procollagen expression, and decreased MMP‑1 and MMP‑3 expression in UV‑irradiated HDF. The underlying mechanisms of these results involve a decrease in p38 and c‑Jun N‑terminal kinase activity, and suppression of UV‑induced activation of activator protein‑1 (AP‑1). BRE reduced UV‑induced reactive oxygen species production in HaCaT cells in a dose‑dependent manner. Indeed, mass spectrometry revealed that BRE contained antioxidative flavonoid components such as cyanidin‑3‑O‑β‑D‑glycoside and taxifolin‑7‑O‑glucoside. These findings suggest that BRE attenuates UV‑induced ECM damage by modulating mitogen‑activated protein kinase and AP‑1 signaling, and could be used as an active ingredient for preventing photoaging of the skin.

Sesamin inhibits IL-1β-stimulated inflammatory response in human osteoarthritis chondrocytes by activating Nrf2 signaling pathway

Sesamin, a bioactive component extracted from sesame, has been reported to exert anti-inflammatory and anti-oxidant effects. In this study, we evaluated the anti-inflammatory effects of sesamin on IL-1β-stimulated human osteoarthritis chondrocytes and investigated the possible mechanism. Results demonstrated that sesamin treatment significantly inhibited PGE2 and NO production induced by IL-1β. Sesamin inhibited MMP1, MMP3, and MMP13 production in IL-1β-stimulated chondrocytes. Sesamin also inhibited IL-1β-induced phosphorylation of NF-κB p65 and IκBa. Meanwhile, sesamin was found to up-regulate the expression of Nrf2 and HO-1. However, Nrf2 siRNA reversed the anti-inflammatory effects of sesamin. In conclusion, our results suggested that sesamin showed anti-inflammatory effects in IL-1β-stimulated chondrocytes by activating Nrf2 signaling pathway.

Antioxidant and Cytoprotective Activities of Enzymatic Extracts from Rhizoid of Laminaria japonica

Rhizoid of Laminaria japonica was hydrolyzed with proteases and carbohydrases to obtain antioxidant materials. Oxygen radical absorbance capacity (ORAC) of the enzymatic extracts was evaluated and the Protamex extract (PE) exhibited the highest ORAC value. PE also potently scavenged 2,2-diphenyl-1-picrylhydrazyl radical, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic) acid cation radical, and hydrogen peroxide (H₂O₂) and had good reducing power. PE inhibited hydroxyl radical-induced DNA scission by measuring the conversion of supercoiled pBR322 plasmid DNA to the open circular form. The cytoprotective effect of PE against H₂O₂-induced hepatic cell damage was also investigated. PE showed a dose-dependent cytoprotective effect in cultured hepatocytes by inhibiting intracellular reactive oxygen species scavenging activity. In addition, PE up-regulated the expression of heme oxygenase-1, which is a cytoprotective enzyme, by activating translocation of nuclear factor-erythroid 2-related factor 2. Taken together, the enzymatic extract of rhizoid of L. japonica, particularly PE, may be useful for antioxidant additives.

Huangqi Decoction Alleviates Alpha-Naphthylisothiocyanate Induced Intrahepatic Cholestasis by Reversing Disordered Bile Acid and Glutathione Homeostasis in Mice

Intrahepatic cholestasis is a serious symptom of liver disorders with limited therapies. In this study, we investigated the efficacy of Huangqi decoction (HQD), a two-herb classic traditional Chinese medicine (TCM), in the treatment of alpha-naphthylisothiocyanate (ANIT)-induced intrahepatic cholestasis in mice. HQD treatment ameliorated impaired hepatic function and tissue damage. A metabolomics study revealed that the endogenous metabolites significantly affected by HQD were related to bile acid (BA) biosynthesis and glutathione metabolism pathways. HQD treatment decreased the intrahepatic accumulation of cytotoxic BAs, normalized serum BA levels, and increased biliary and urinary BA excretion. Additionally, HQD restored the hepatic glutathione content and suppressed reactive oxygen species (ROS) in cholestatic mice. Protein and gene analysis revealed that HQD increased the expression of the hepatic metabolizing enzymes cytochrome P450 (CYP) 2B10 and UDP glucuronosyltransferase family 1 member A1 (UGT1A1), as well as multidrug resistance-associated protein 2 (Mrp2), Mrp3, and Mrp4, which play crucial roles in BA homeostasis. Further, HQD increased the protein expression of glutamate-cysteine ligase, which is involved in the synthesis of glutathione. Importantly, HQD increased the nuclear expression of nuclear factor-E2-related factor-2 (Nrf2). In conclusion, HQD protects against intrahepatic cholestasis by reversing the disordered homeostasis of BAs and glutathione.

A composition of medicinal plants with an enhanced ability to suppress microsomal lipid peroxidation and a protective activity against carbon tetrachloride-induced hepatotoxicity

Treatment of liver injury induced by various toxicants represents a serious clinical challenge. Here, we utilized the ability of natural agents to inhibit microsomal lipid peroxidation (LPO) as the in-vitro screening paradigm for selecting efficacious tissue-protective combinations of cooperatively acting medicinal plants. Based on screening of 70 water-ethanol extracts obtained from different parts of 65 plants we prepared a highly active phytocomposition (PC-1) containing oregano (Origanum vulgare), wild thyme (Thymus serpyllum) and coltsfoot (Tussilago farfara) aerial parts, valerian (Valeriana officinalis) leaves and little-leaf linden (Tilia cordata) flowers. PC-1 extract exhibited the strongest anti-PLO and antihemolytic effects in vitro compared to those of the individual plants and other compositions tested. Using luciferase reporter assay and Western blotting in HepG2 human hepatocellular carcinoma cells, we found that PC-1 extract activated the Nrf2/antioxidant response element signaling pathway more effectively than the extracts of other phytocompositions. Importantly, oral administration of PC-1 extract (100-200 mg/kg) markedly ameliorated liver injury in rats acutely or chronically intoxicated by carbon tetrachloride. This was evidenced by improved liver histology, blood chemistry parameters, and microsomal LPO status and superoxide dismutase activity. In addition, treatment with PC-1 extract salvaged the osmotic resistance of erythrocytes in carbon tetrachloride-intoxicated rats. Collectively, these data support the strategy of in-vitro plant selection for developing efficacious tissue-protective phytocompositions.

Gallic acid, a natural polyphenol, protects against tert-butyl hydroperoxide- induced hepatotoxicity by activating ERK-Nrf2-Keap1-mediated antioxidative response

Gallic acid (GA), a natural polyphenol, has been shown to exert a variety of heath promoting effects. We herein investigated the critical role of nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated antioxidant response in the protection of GA against tert-butyl hydroperoxide (t-BHP)-induced hepatotoxicity in L02 cells. Pretreatment of GA prevented the hepatocytotoxicity induced by t-BHP, as evidenced by the facts that GA suppressed t-BHP-induced cytotoxicity and reactive oxygen species (ROS) generation. GA induced nuclear translocation of Nrf2 along with expression of target proteins, including heme oxygenase-1 (HO-1) and glutamate cysteine ligase catalytic modify subunit (GCLC), and increased intracellular glutathione (GSH) content. Additionally, GA induced phosphorylated activation of extracellular regulated kinase (ERK), and ERK inhibitor PD98059 partially decreased GA-induced hepatoprotection, and downregulated the increased protein expressions of Nrf2, GCLC and HO-1 induced by GA. Interestingly, we found that GA could enhance the thermal stability of Keap1, which indicated the potential interaction between GA and Keap1. Furthermore, molecular docking indicated that GA possibly competed with Nrf2 for binding to Keap1. Collectively, GA effectively protects against t-BHP-induced hepatotoxicity via inducing ERK/Nrf2-mediated antioxidative signaling pathway. Meanwhile, GA disturbs protein-protein interaction between Keap1 and Nrf2 which might also contribute to nuclear translocation of Nrf2.