Targeting Nrf2-Keap1 signaling for chemoprevention of skin carcinogenesis with bioactive phytochemicals

Essential oil from Citrus depressa peel exhibits antimicrobial, antioxidant and cancer chemopreventive effects

BACKGROUND

Many diseases may be caused by pathogens and oxidative stress resulting from carcinogens. Earlier studies have highlighted the antimicrobial and antioxidant effects of plant essential oils (EO). It is crucial to effectively utilize agricultural waste to achieve a sustainable agricultural economy and protect the environment. The present study aimed to evaluate the potential benefits of EO extracted from the discarded peels of Citrus depressa Hayata (CD) and Citrus microcarpa Bunge (CM), synonyms of Citrus deliciosa Ten and Citrus japonica Thunb, respectively.

RESULTS

Gas chromatography-mass spectrometry analysis revealed that the main compounds in CD-EO were (R)-(+)-limonene (38.97%), γ-terpinene (24.39%) and linalool (6.22%), whereas, in CM-EO, the main compounds were (R)-(+)-limonene (48.00%), β-pinene (13.60%) and γ-terpinene (12.07%). CD-EO exhibited inhibitory effects on the growth of common microorganisms, including Candida albicans, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. However, CM-EO showed only inhibitory effects on E. coli. Furthermore, CD-EO exhibited superior antioxidant potential, as demonstrated by its ability to eliminate 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azinobis-3-ethylbenzthiazoline-6-sulfonate free radicals. Furthermore, CD-EO at a concentration of 100 μg mL-1 significantly inhibited 12-O-tetradecanoylphorbol-13-acetate-induced cancer transformation in mouse epidermal JB6 P+ cells (P < 0.05), possibly by up-regulating protein expression of nuclear factor erythroid 2-related factor 2 and its downstream antioxidant enzymes, such as NAD(P)H:quinone oxidoreductase 1, heme oxygenase-1 and UGT1A.

CONCLUSION

These findings suggest that CD-EO exhibits inhibitory effects on pathogenic microorganisms, possesses antioxidant properties and has cancer chemopreventive potential. © 2024 Society of Chemical Industry.

Anti-cancer potential of zerumbone in cancer and glioma: current trends and future perspectives

Plant-derived immunomodulators and antitumor factors have appealed lots of attention from natural product scientists for their efficiency and safety and their important contribution to well-designed targeted drug action and delivery mechanisms. Zerumbone (ZER), the chief component of Zingiber zerumbet rhizomes, has been examined for its wide-spectrum in the treatment of multi-targeted diseases. The rhizomes have been used as food flavoring agents in numerous cuisines and in flora medication. Numerous in vivo and in vitro experiments have prepared confirmation of ZER as a potent immunomodulator as well as a potential anti-tumor agent. This review is an interesting compilation of all the important results of the research carried out to date to investigate the immunomodulatory and anticancer properties of ZER. The ultimate goal of this comprehensive review is to supply updated information and a crucial evaluation on ZER, including its chemistry and immunomodulating and antitumour properties, which may be of principal importance to supply a novel pathway for subsequent investigation to discover new agents to treat cancers and immune-related sickness. In addition, updated information on the toxicology of ZER has been summarized to support its safety profile.

Targeting oncogenic transcription factors in skin malignancies: An update on cancer stemness and therapeutic outcomes

The skin is the largest organ of the human body and prone to various diseases, including cancer; thus, provides the first line of defense against exogenous biological and non-biological agents. Skin cancer, a complex and heterogenic process, with steep incidence rate often metastasizes due to poor understanding of the underlying mechanisms of pathogenesis and clinical challenges. Indeed, accumulating evidence indicates that deregulation of transcription factors (TFs) due to genetic, epigenetic and signaling distortions plays essential role in the development of cutaneous malignancies and therapeutic challenges including cancer stemness features and reprogramming. This review highlights the recent developments exploring underlying mechanisms how deregulated TFs (e.g., NF-κB, AP-1, STAT etc.,) orchestrates cutaneous onco-pathogenesis, reprogramming, stemness and poor clinical outcomes. Along this line, bioactive drugs, and their derivatives from natural and or synthetic origin has gained attention due to their multitargeting potential, potentially safer and effective therapeutic outcome for human malignancies. We also discussed therapeutic importance of targeting aberrantly expressed TFs in skin cancers with bioactive natural products and or synthetic agents.

NRF2, a crucial modulator of skin cells protection against vitiligo, psoriasis, and cancer

The skin represents a physical barrier between the organism and the environment that has evolved to confer protection against biological, chemical, and physical insults. The inner layer, known as dermis, is constituted by connective tissue and different types of immune cells whereas the outer layer, the epidermis, is composed by different layers of keratinocytes and an abundant number of melanocytes, localized in the stratum basale of the epidermis. Oxidative stress is a common alteration of inflammatory skin disorders such as vitiligo, dermatitis, or psoriasis but can also play a causal role in skin carcinogenesis and tumor progression. Nuclear factor (erythroid-derived 2)-like 2 (NRF2) has emerged as a crucial regulator of cell defense mechanisms activating complex transcriptional programs that facilitate reactive oxygen species detoxification, repair oxidative damage and prevent xenobiotic-induced toxicity. Accumulating evidence suggests that the keratinocytes, melanocytes, and other skin cell types express high levels of NRF2, which is known to play a pivotal role in the skin homeostasis, differentiation, and metabolism during normal and pathologic conditions. In the present review, we summarize the current evidence linking NRF2 to skin pathophysiology and we discuss some recent modulators of NRF2 activity that have shown a therapeutic efficacy in skin protection against tumor initiation and common inflammatory skin conditions such as vitiligo or psoriasis, with a particular emphasis on natural compounds.

Camellia japonica Root Extract Increases Antioxidant Genes by Induction of NRF2 in HeLa Cells

Camellia japonica L. (Theaceae) has been used for medicinal and cosmetic purposes in East Asian countries. Most functional components were obtained from the upper parts of the tree, such as leaves, flowers, or seeds. Here, we report a functional effect of the 80% methanolic extract of C. japonica root (CJRE) on antioxidative stress in HeLa cells. The nuclear factor erythroid-derived 2-related factor 2 (NRF2) is a key transcription factor that triggers the induction of oxidative stress-relating genes and drug detoxification. As result, CJRE showed a strong anti-radical scavenging effect in a dose-dependent manner. In addition, the induction of antioxidant response elements (ARE)-luciferase activity was maximized at CJRE 200 µg/mL. Furthermore, CJRE induced the mRNA levels of HO-1 and NQO1 by the nuclear NRF2 accumulation. As a possible mechanism of Nrf2 activation, the phosphorylation of p38 and ERK1/2 signaling might fortify the NRF2 induction as well as its stability. However, the phosphorylation of AKT is rather decreased. Taken together, CJRE may potentiate the antioxidant effects by increasing the NRF2 signaling through MAP kinase signaling and the properties of its radical scavenging activity. Thus, CJRE could apply for other medicinal and cosmetic purposes.

The Potential Key Role of the NRF2/NQO1 Pathway in the Health Effects of Arsenic Pollution on SCC

Arsenic is widely present in nature and is a common environmental poison that seriously damages human health. Chronic exposure to arsenic is a major environmental poisoning factor that promotes cell proliferation and leads to malignant transformation. However, its molecular mechanism remains unclear. In this study, we found that arsenite can promote the transformation of immortalized human keratinocyte cells (HaCaT) from the G0/G1 phase to S phase and demonstrated malignant phenotypes. This phenomenon is accompanied by obviously elevated levels of NRF2, NQO1, Cyclin E, and Cyclin-dependent kinase 2 (CDK2). Silencing the NRF2 expression with small interfering RNA (siRNA) in arsenite-transformed (T-HaCaT) cells was shown to reverse the malignant phenotype. Furthermore, the siRNA silencing of NQO1 significantly decreased the levels of the cyclin E-CDK2 complex, inhibiting the G0/G1 to S phase cell cycle progression and transformation to the T-HaCaT phenotypes. Thus, we hypothesized that the NRF2/NQO1 pathway played a key role in the arsenite-induced malignancy of HaCaT cells. By increasing the expression of Cyclin E-CDK2, the NRF2/NQO1 pathway can affect cell cycle progression and cell proliferation. A new common health effect mechanism of arsenic carcinogenesis has been identified; thus, it would contribute to the development of novel treatments to prevent and treat skin cancer caused by arsenic.

The anti-tumor effect of proteasome inhibitor MG132 for human adenoid cystic carcinoma: correlate with the emerging role of Nrf2/Keap1 signaling pathway

BACKGROUND

Adenoid cystic carcinoma (ACC) is one of the most common malignant salivary gland tumors. Moreover, the unique biological characteristics and complex structures of ACC contribute to its poor survival rates. Recently, proteasome inhibitors have been shown to elicit satisfactory therapeutic effects in the treatment of certain solid tumors, but few studies have been implemented to investigate the effects of proteasome inhibitor therapy for ACC.

METHODS

In this present study, cell counting kit-8 assay and flow cytometry assay were performed to examine the effects of proteasome inhibitor (MG132) on cell viability and apoptosis. We applied western blot and immunofluorescence staining to explore the expression of the Nrf2/Keap1 signaling pathway and P62, additionally Nrf2 inhibitor (ML385) was utilized to evaluate the role of Nrf2/Keap1 signaling pathway in MG132-induced cell apoptosis.

RESULTS

Our data indicated that MG132 significantly suppressed the growth of ACC-83 cells(MG132 10µM P = 0.0046; 40µM P = 0.0033; 70µM P = 0.0007 versus control) and induced apoptosis (MG132 10µM P = 0.0458; 40µM P = 0.0018; 70µM P = 0.0087 versus control). The application of MG132 induced the up-regulation of Nrf2/Keap1 signaling pathway. Furthermore, inhibition of Nrf2 attenuated the therapeutic effects of MG132 for ACC (both ML385 + MG132 10µM P = 0.0013; 40µM P = 0.0057; 70µM P = 0.0003 versus MG132). P < 0.05 was considered statistically significant.

CONCLUSIONS

Our results revealed that proteasome inhibitors MG132 could inhibit the cell viability and induce the apoptosis of ACC through Nrf2/Keap1 signaling pathway.

Molecular biological mechanism of action in cancer therapies: Juglone and its derivatives, the future of development

Juglone (5 - hydroxy - 1, 4 - naphthalene diketone) is a kind of natural naphthoquinone, present in the roots, leaves, nut-hulls, bark and wood of walnut trees. Recent studies have found that Juglone has special significance in the treatment of cancer, which plays a significant role in the resistance of cancer cell proliferation, induction of cancer cell apoptosis, induction of autophagy, anti-angiogenesis and inhibition of cancer cell migration and invasion, etc. Additionally, its derivatives also play a tumor suppressive effect. In conclusion, Juglone and its derivatives have been identified as effective anticancer drugs. This paper reviews action mechanisms of Juglone and its derivatives in cancer treatment.

Medicarpin Increases Antioxidant Genes by Inducing NRF2 Transcriptional Level in HeLa Cells

The nuclear factor erythroid-derived 2-related factor 2 (NRF2) plays a pivotal role in the regulation of genes involved in oxidative stress and drug detoxification. Therefore, it is important to find NRF2 inducers to protect cells from excessive oxidative damage. Here, we investigated the effect of medicarpin isolated from the root of Robinia pseudoacacia L. on the activity of NRF2 in HeLa cells. Medicarpin significantly induced the antioxidant response elements (ARE)-luciferase activity in a concentration-dependent manner. Furthermore, medicarpin not only induced HO-1, GCLC, and NQO1 mRNA by translocating NRF2 to the nucleus but also induced the mRNA level of NRF2. To verify the NRF2 induction mechanism by medicarpin, ~2 kb of NRF2 promoter-luciferase assay was executed. As a result, medicarpin significantly induced NRF2-luciferase activity. Moreover, medicarpin strongly inhibited the ubiquitin-dependent proteasomal degradation of NRF2. Thus, medicarpin might protect cells by promoting the NRF2 transcriptional activity.

Acute exposition to Roundup Transorb® induces systemic oxidative stress and alterations in the expression of newly sequenced genes in silverside fish (Odontesthes humensis)

Roundup Transorb® (RDT) is a glyphosate-based herbicide commonly used in agricultural practices worldwide. This herbicide exerts negative effects on the aquatic ecosystem and affects bioenergetic and detoxification pathways, oxidative stress, and cell damage in marine organisms. These effects might also occur at the transcriptional level; however, the expression of genes associated with oxidative stress has not been studied well. Odontesthes humensis is a native Brazilian aquatic species naturally distributed in the habitats affected by pesticides, including Roundup Transorb® (RDT). This study evaluated the toxic effects of short-term exposure to RDT on O. humensis. Moreover, the genes related to oxidative stress were sequenced and characterized, and their expressions in the gills, hepatopancreas, kidneys, and brain of the fish were quantified by quantitative reverse transcription-polymerase chain reaction. The animals were exposed to two environmentally relevant concentrations of RDT (2.07 and 3.68 mg L^-1) for 24 h. Lipid peroxidation, reactive oxygen species (ROS), DNA damage, and apoptosis in erythrocytes were quantified by flow cytometry. The expression of the target genes was modulated in most tissues in the presence of the highest tested concentration of RDT. In erythrocytes, the levels of lipid peroxidation, ROS, and DNA damage were increased in the presence of both the concentrations of RDT, whereas cell apoptosis was increased in the group exposed to 3.68 mg L^-1 RDT. In conclusion, acute exposure to RDT caused oxidative stress in the fish, induced negative effects on cells, and modulated the expression of genes related to the enzymatic antioxidant system in O. humensis.

Role of chemopreventive phytochemicals in NRF2-mediated redox homeostasis in humans

While functioning as a second messenger in the intracellular signaling, ROS can cause oxidative stress when produced in excess or not neutralized/eliminated properly. Excessive ROS production is implicated in multi-stage carcinogenesis. Our body is equipped with a defense system to cope with constant oxidative stress caused by the external insults, including redox-cycling chemicals, radiation, and microbial infection as well as endogenously generated ROS. The transcription factor, nuclear transcription factor erythroid 2-related factor 2 (NRF2) is a master switch in the cellular antioxidant signaling and plays a vital role in adaptive survival response to ROS-induced oxidative stress. Although NRF2 is transiently activated when cellular redox balance is challenged, this can be overwhelmed by massive oxidative stress. Therefore, it is necessary to maintain the NRF2-mediated antioxidant defense capacity at an optimal level. This review summarizes the natural NRF2 inducers/activators, especially those present in the plant-based diet, in relation to their cancer chemopreventive potential in humans. The molecular mechanisms underlying their stabilization or activation of NRF2 are also discussed.

Effect of ultraviolet radiation on the Nrf2 signaling pathway in skin cells

PURPOSE

Excessive exposure of skin to solar radiation is associated with greatly increased production of reactive oxygen and nitrogen species (ROS, RNS) resulting in oxidative stress (OS), inflammation, immunosuppression, the production of matrix metalloproteinase, DNA damage and mutations. These events lead to increased incidence of various skin disorders including photoaing and both non-melanoma and melanoma skin cancers. The ultraviolet (UV) part of sunlight, in particular, is responsible for structural and cellular changes across the different layers of the skin. Among other effects, UV photons stimulate oxidative damage to biomolecules via the generation of unstable and highly reactive compounds. In response to oxidative damage, cytoprotective pathways are triggered. One of these is the pathway driven by the nuclear factor erythroid-2 related factor 2 (Nrf2). This transcription factor translocates to the nucleus and drives the expression of numerous genes, among them various detoxifying and antioxidant enzymes. Several studies concerning the effects of UV radiation on Nrf2 activation have been published, but different UV wavelengths, skin cells or tissues and incubation periods were used in the experiments that complicate the evaluation of UV radiation effects.

CONCLUSIONS

This review summarizes the effects of UVB (280-315 nm) and UVA (315-400 nm) radiation on the Nrf2 signaling pathway in dermal fibroblasts and epidermal keratinocytes and melanocytes. The effects of natural compounds (pure compounds or mixtures) on Nrf2 activation and level as well as on Nrf2-driven genes in UV irradiated human skin fibroblasts, keratinocytes and melanocytes are briefly mentioned as well.HighlightsUVB radiation is a rather poor activator of the Nrf2-driven pathway in fibroblastsUVA radiation stimulates Nrf2 activation in dermal fibroblastsEffects of UVA on the Nrf2 pathway in keratinocytes and melanocytes remain unclearLong-term Nrf2 activation in keratinocytes disturbs their normal differentiationPharmacological activation of Nrf2 in the skin needs to be performed carefully.

Covalent Modification of Proteins by Plant-Derived Natural Products: Proteomic Approaches and Biological Impacts

Plant-derived natural products (NPs) with electrophilic functional groups engage various subsets of the proteome via covalent modification of nucleophilic cysteine residues. This electrophile-nucleophile interaction can change protein conformation, alter protein function, and modulate their biological action. The biological significance of these covalent protein modifications in health and disease is increasingly recognized. One way to understand covalent NP-protein interactions is to utilize traditional proteomics and modern mass spectrometry (MS)-based proteomic strategies. These strategies have proven effective in uncovering specific NP protein targets and are critical first steps that allow for a much deeper understanding of the ability of NPs to modulate cellular processes. Here, plant-derived NPs that covalently modify proteins are reviewed, the biological significance of these covalent modifications, and the different proteomic strategies that have been employed to study these NP-protein interactions.

Protective effects of natural compounds against oxidative stress in ischemic diseases and cancers via activating the Nrf2 signaling pathway: A mini review

Oxidative stress, an imbalance between reactive oxygen species and antioxidants, has been seen in the pathological states of many disorders such as ischemic diseases and cancers. Many natural compounds (NCs) have long been recognized to ameliorate oxidative stress due to their inherent antioxidant activities. The modulation of oxidative stress by NCs via activating the Nrf2 signaling pathway is summarized in the review. Three NCs, ursolic acid, betulinic acid, and curcumin, and the mechanisms of their cytoprotective effects are investigated in myocardial ischemia, cerebral ischemia, skin cancer, and prostate cancer. To promote the therapeutic performance of NCs with poor water solubility, the formulation approach, such as the nano drug delivery system, is elaborated as well in this review.

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.

Activation of NRF2 by topical apocarotenoid treatment mitigates radiation-induced dermatitis

Radiation therapy is a frontline treatment option for cancer patients; however, the effects of radiotherapy on non-tumor tissue (e.g. radiation-induced dermatitis) often worsen patient quality of life. Previous studies have implicated the importance of redox balance in preventing dermatitis, specifically in reference to modulation of the nuclear factor (erythroid-derived 2)-like 2 (NRF2) signaling pathway. Due to the cytoprotective functions of transcriptional target genes of NRF2, we investigated how modulation of NRF2 expression could affect DNA damage, oxidative stress, and cell viability in response to radiotherapy. Specifically, it was noted that NRF2 knockdown sensitized human skin keratinocytes to ionizing radiation; likewise, genetic ablation of NRF2 in vivo increased radiosensitivity of murine epidermis. Oppositely, pharmacological induction of NRF2 via the apocarotenoid bixin lowered markers of DNA damage and oxidative stress, while preserving viability in irradiated keratinocytes. Mechanistic studies indicated that topical pretreatment using bixin as an NRF2 activator antagonized initial DNA damage by raising cellular glutathione levels. Additionally, topical application of bixin prevented radiation-induced dermatitis, epidermal thickening, and oxidative stress in the skin of SKH1 mice. Overall, these data indicate that NRF2 is critical for mitigating the harmful skin toxicities associated with ionizing radiation, and that topical upregulation of NRF2 via bixin could prevent radiation-induced dermatitis.

Four active monomers from Moutan Cortex exert inhibitory effects against oxidative stress by activating Nrf2/Keap1 signaling pathway

Paeonol, quercetin, β-sitosterol, and gallic acid extracted from Moutan Cortex had been reported to possess anti-oxidative, anti-inflammatory, and antitumor activities. This work aimed to illustrate the potential anti-oxidative mechanism of monomers in human liver hepatocellular carcinoma (HepG2) cells-induced by hydrogen peroxide (H2O2) and to evaluate whether the hepatoprotective effect of monomers was independence or synergy in mice stimulated by carbon tetrachloride (CCl4). Monomers protected against oxidative stress in HepG2 cells in a doseresponse manner by inhibiting the generation of reactive oxygen species, increasing total antioxidant capacity, catalase and superoxide dismutase (SOD) activities, and activating the antioxidative pathway of nuclear factor E2-related factor 2/Kelchlike ECH-associated protein 1 (Nrf2/Keap1) signaling pathway. We found that the in vitro antioxidant capacities of paeonol and quercetin were better than those of β-sitosterol and gallic acid. Furthermore, paeonol apparently diminished the levels of alanine transaminase and aspartate aminotransferase, augmented the contents of glutathione and SOD, promoted the expressions of Nrf2 and heme oxygenase-1 proteins in mice stimulated by CCl4. In HepG2 cells, paeonol, quercetin, β-sitosterol, and gallic acid play a defensive role against H2O2-induced oxidative stress through activating Nrf2/Keap1 pathway, indicating that these monomers have anti-oxidative properties. Totally, paeonol and quercetin exerted anti-oxidative and hepatoprotective effects, which is independent rather than synergy.

Effect of UVA radiation on the Nrf2 signalling pathway in human skin cells

The harmful effects of low energy UVA photons (315-400 nm) are associated with the massive production of reactive oxygen species resulting in oxidative stress. In response to oxidative damage, NF-E2-related factor 2 (Nrf2) is translocated to the nucleus and drives the expression of detoxication and antioxidant enzymes. UVA's effect on Nrf2 has been quite well characterised in dermal fibroblasts. However, there is a dearth of such information for keratinocytes. This study aimed to evaluate and compare the effect of UVA radiation on the Nrf2 pathway and oxidative stress related proteins in primary human dermal fibroblasts (NHDF), epidermal keratinocytes (NHEK) and human keratinocyte cell line HaCaT. NHDF were exposed to doses of 2.5-7.5 J/cm², NHEK and HaCaT to 10-20 J/cm² using a solar simulator. Effects on Nrf2 translocation were evaluated after 1, 3 and 6 h and Nrf2-controlled proteins (heme oxygenase 1 (HO-1), NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione reductase (GSR), glutathione-S-transferase (GST), interleukine-6 (IL-6), and matrix metalloproteinases (MMP-1, MMP-2)) after 3, 6 and 24 h. The results showed the fastest Nrf2 translocation was in UVA-irradiated HaCaT (1 h), persisting until the subsequent time interval (3 h), while in primary keratinocytes the effect of radiation was minimal. In NHDF, UVA-stimulated Nrf2 translocation was conspicuous 3 h after UVA treatment. In NHDF, most of the studied proteins (NQO1, HO-1, GSR, GSTM1 and MMP-1) showed the highest level 24 h after UVA exposure, except for MMP-2 and IL-6 which had their highest level at a shorter time incubation interval (3 h). In NHEK, NQO1, HO-1 and GST were increased 6 h after UVA exposure, GSR and MMP-2 level was slightly below or above the control level, and MMP-1 and IL-6 increased at shorter time intervals. When comparing NHEK and HaCaT, these cells displayed contrary responses in most of the Nrf2-controlled proteins. Thus, primary keratinocytes cannot be replaced with HaCaT when studying cell signalling such as the Nrf2 driven pathway and Nrf2-controlled proteins.

Emerging Perspective: Role of Increased ROS and Redox Imbalance in Skin Carcinogenesis

Strategies to battle malignant tumors have always been a dynamic research endeavour. Although various vehicles (e.g., chemotherapeutic therapy, radiotherapy, surgical resection, etc.) are used for skin cancer management, they mostly remain unsatisfactory due to the complex mechanism of carcinogenesis. Increasing evidence indicates that redox imbalance and aberrant reactive oxygen species (ROS) are closely implicated in the oncogenesis of skin cancer. When ROS production goes beyond their clearance, excessive or accumulated ROS could disrupt redox balance, induce oxidative stress, and activate the altered ROS signals. These would damage cellular DNA, proteins, and lipids, further leading to gene mutation, cell hyperproliferation, and fatal lesions in cells that contribute to carcinogenesis in the skin. It has been known that ROS-mediated skin carcinogenesis involves multiple ways, including modulating related signaling pathways, changing cell metabolism, and causing the instability of the genome and epigenome. Nevertheless, the exact role of ROS in skin cancer has not been thoroughly elucidated. In spite of ROS inducing skin carcinogenesis, toxic-dose ROS could trigger cell death/apoptosis and, therefore, may be an efficient therapeutic tool to battle skin cancer. Considering the dual role of ROS in the carcinogenesis and treatment of skin cancer, it would be essential to clarify the relationship between ROS and skin cancer. Thus, in this review, we get the related data together to seek the connection between ROS and skin carcinogenesis. Besides, strategies basing on ROS to fight skin cancer are discussed.

2-Methoxy-7-Acetonyljuglone Isolated from Reynoutria japonica Increases the Activity of Nuclear Factor Erythroid 2-Related Factor-2 through Inhibition of Ubiquitin Degradation in HeLa Cells

The nuclear factor erythroid-derived 2-related factor 2 (NRF2) is a key transcription factor for the activation of genes responsible for oxidative stress and drug detoxification. Thus, it is important to identify NRF2 activators, which can be used to protect the cells from oxidative damage. Here, we investigated the effect of juglone derivatives isolated from Reynoutria japonica on the activity of NRF2 in HeLa cells. We demonstrated that among the juglone derivatives, 2-methoxy-7-acetonyljuglone (MA) strongly stimulated the antioxidant response element (ARE)-luciferase activity in a dose-dependent manner. In addition, MA significantly increased the nuclear localization of NRF2 and, consequently, increased the expression of NRF2 target genes, including heme oxygenase-1(HO-1), NAD(P)H: quinine oxidoreductase-1 (NQO-1), and glutamate-cysteine ligase catalytic (GCLC). To gain insights into the NRF2 signaling mechanism by MA, we measured the activities of RAC-alpha serine/threonine-protein kinase (AKT) and mitogen-activated protein (MAP) kinase family proteins, including extracellular signal-regulated kinase (ERK) and p38. Our results showed that MA induced NRF2 activity through p38 and AKT signaling. Subsequently, we found that MA significantly enhanced NRF2 stability by inhibiting ubiquitin-dependent proteasomal degradation. Thus, MA might protect cells by enhancing the activity and stability of NRF2 through inhibition of the proteasomal degradation pathway.

SIRT1-Dependent Upregulation of Antiglycative Defense in HUVECs Is Essential for Resveratrol Protection against High Glucose Stress

Uncontrolled accumulation of methylglyoxal (MG) and reactive oxygen species (ROS) occurs in hyperglycemia-induced endothelial dysfunction associated with diabetes. Resveratrol (RSV) protects the endothelium upon high glucose (HG); however, the mechanisms underlying such protective effects are still debated. Here we identified key molecular players involved in the glycative/oxidative perturbations occurring in endothelial cells exposed to HG. In addition, we determined whether RSV essentially required SIRT1 to trigger adaptive responses in HG-challenged endothelial cells. We used primary human umbilical vein endothelial cells (HUVECs) undergoing a 24-h treatment with HG, with or without RSV and EX527 (i.e., SIRT1 inhibitor). We found that HG-induced glycative stress (GS) and oxidative stress (OS), by reducing SIRT1 activity, as well as by diminishing the efficiency of MG- and ROS-targeting protection. RSV totally abolished the HG-dependent cytotoxicity, and this was associated with SIRT1 upregulation, together with increased expression of GLO1, improved ROS-scavenging efficiency, and total suppression of HG-related GS and OS. Interestingly, RSV failed to induce effective response to HG cytotoxicity when EX527 was present, thus suggesting that the upregulation of SIRT1 is essential for RSV to activate the major antiglycative and antioxidative defense and avoid MG- and ROS-dependent molecular damages in HG environment.

Signaling Pathways, Chemical and Biological Modulators of Nucleotide Excision Repair: The Faithful Shield against UV Genotoxicity

The continuous exposure of the human body's cells to radiation and genotoxic stresses leads to the accumulation of DNA lesions. Fortunately, our body has several effective repair mechanisms, among which is nucleotide excision repair (NER), to counteract these lesions. NER includes both global genome repair (GG-NER) and transcription-coupled repair (TC-NER). Deficiencies in the NER pathway underlie the development of several DNA repair diseases, such as xeroderma pigmentosum (XP), Cockayne syndrome (CS), and trichothiodystrophy (TTD). Deficiencies in GG-NER and TC-NER render individuals to become prone to cancer and neurological disorders, respectively. Therefore, NER regulation is of interest in fine-tuning these risks. Distinct signaling cascades including the NFE2L2 (NRF2), AHR, PI3K/AKT1, MAPK, and CSNK2A1 pathways can modulate NER function. In addition, several chemical and biological compounds have proven success in regulating NER's activity. These modulators, particularly the positive ones, could therefore provide potential treatments for genetic DNA repair-based diseases. Negative modulators, nonetheless, can help sensitize cells to killing by genotoxic chemicals. In this review, we will summarize and discuss the major upstream signaling pathways and molecules that could modulate the NER's activity.

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.

LMP1 and 2A Induce the Expression of Nrf2 Through Akt Signaling Pathway in Epstein-Barr Virus-Transformed B Cells

The transcription factor Nrf2, which regulates the expression of antioxidant and cytoprotective enzymes, contributes to cell proliferation and resistance to chemotherapy. Nrf2 is also dysregulated in many cancers such as lung, head and neck, and breast cancers, but its role in Epstein-Barr virus (EBV)–transformed B cells is still not understood. Here, we investigated EBV infection-induced Nrf2 activation in B cells by analyzing translocation of Nrf2 from the cytosol to the nucleus. In addition, we confirmed expression of the target genes in response to increased Nrf2 activation in EBV-transformed B cells. We demonstrated that knockdown of LMP1 and 2A blocks the translocation of Nrf2 to the nucleus and reduces ROS production in EBV-transformed B cells. Further, we showed that inhibition of Akt prevents Nrf2 activation. Moreover, knockdown of Nrf2 induces apoptotic cell death in EBV-transformed B cells. In conclusion, our study demonstrates that Nrf2 promotes proliferation of EBV-transformed B cells through the EBV-related proteins LMP1 and 2A and Akt signaling, implicating Nrf2 as a potential molecular target for EBV-associated disease.

Drug–DNA interaction, a joint DFT-D3/MD study on safranal as an anticancer and DNA nanostructure model

In this research, using a combination of quantum mechanics and molecular dynamic (MD) simulations, the interaction of safranal (2,6,6-trimethylcyclohexa-1,3-dien-1-carboxaldehyde) as an anti-cancer drug and Dickerson B-DNA was studied. MD simulations were executed for 35 ns in water. Binding energy analysis in three definite parts of the B-DNA and comparison between different contributions of the binding energy shows that the van der Waals energy part of the interaction is impressive among the standard molecular mechanic energy terms. On the basis of Gibbs energies, it is confirmed that the most important interactions in the safranal complex are related to the A–T and C–G rich regions, which is in agreement with the experimental data. Quantum theory of atoms in molecules and natural bond orbital analyses were applied. A diminution in the electronic chemical potential of the safranal–DNA complex in comparison with the isolated DNA, 0.026 and 0.022 au for the S1 region and 0.012 and 0.017 au for the S2 region, was obtained in the gas phase and water, respectively, which increases the complex stability. An enhancement in the electrophilicity character, during the complexation process, shows the electron charge flux between the safranal and DNA, especially in water. The strengths of the CH⋯O bonds at the center of safranal–DNA interaction were also evaluated. A mean value of 0.06 au for the electron density of the bond critical point of the H⋯O in the complex confirms the H-bond formation during the complexation.

Nuclear Factor Erythroid 2-Related Factor 2 Activating Triterpenoid Saponins from Camellia japonica Roots

Oxidative stress due to the presence of excess reactive oxygen species may cause cancers, aging, and many other conditions. Nuclear factor erythroid 2-related factor 2 (Nrf2) may control abnormal oxidative stress as a transcription factor by inducing antioxidant-related genes via antioxidant response elements (AREs) in the gene promoters. The 11 triterpenoid saponins (1-11) isolated from Camellia japonica roots were tested for ARE-luciferase activity and Nrf2 accumulation in human keratinocytes (HaCaT cells). The ARE-luciferase activity was significantly increased by compounds 1-11 (25 μM) as a result of nuclear Nrf2 accumulation in the cells. Thus, these compounds may contribute to the induction of Nrf2 activity against oxidative damage in cells.

Aberration of Nrf2‑Bach1 pathway in colorectal carcinoma; role in carcinogenesis and tumor progression

Nrf2 and Bach1 are important transcriptional factors that protect against reactive oxygen species (ROS). Although aberration of these molecules was associated with malignant transformation and progression, their aberration pattern in colorectal carcinoma (CRC) is not yet fully studied. In this study, Nrf2 and Bach1 were immunohistochemically examined in 93 formalin-fixed paraffin-embedded blocks of colonic tumors (65 carcinoma with their corresponding surgical margins and 28 adenomas). Nrf2 expression was gradually increased in the apparently normal mucosa (57 ± 41)-adenoma (90 ± 36)-carcinoma (198 ± 78) direction and only showed significant higher mean of expression in CRC with brisk inflammatory peritumoral response. The mean of Bach1 expression was highest in apparently normal colonic mucosa (267 ± 16), lowest in adenoma (53 ± 31) and high in carcinoma tissues (194 ± 93). Significant higher mean of expression was detected in carcinoma with: LN metastasis (p = 0.04), lymphovascular invasion (p = 0.024); perineural invasion (p = 0.03) and advanced pathological stage (p < 0.001). Significant higher mean of expression of Nrf2 and Bach1 was detected in adenoma specimens with high grade dysplasia (p = 0.016 and p = 0.024) respectively. In conclusion, Nfr2 and Bach1 expression are altered in CRC but in different way. Nrf2 is gradually increasing from normal mucosa to adenoma and was highest in carcinoma but was not associated with features of tumor invasiveness. Bach1 was highest in normal mucosa; less in adenoma then increased in carcinoma and was associated with features of tumor invasiveness and metastasis. This may indicate a possible role of Nrf2 in CRC carcinogenesis and a role of Bach1 in CRC progression.

Activation of Nrf2 signaling by natural products-can it alleviate diabetes?

Type 2 diabetes mellitus (DM) has reached pandemic proportions and effective prevention strategies are wanted. Its onset is accompanied by cellular distress, the nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor boosting cytoprotective responses, and many phytochemicals activate Nrf2 signaling. Thus, Nrf2 activation by natural products could presumably alleviate DM. We summarize function, regulation and exogenous activation of Nrf2, as well as diabetes-linked and Nrf2-susceptible forms of cellular stress. The reported amelioration of insulin resistance, β-cell dysfunction and diabetic complications by activated Nrf2 as well as the status quo of Nrf2 in precision medicine for DM are reviewed.

Suppression of NRF2/ARE by convallatoxin sensitises A549 cells to 5-FU-mediated apoptosis

NF-E2-related factor 2 (NRF2) regulates transcription of phase II cytoprotective enzymes to protect normal cells against oxidative stress. However, a high level of NRF2 offers a growth advantage, chemoresistance, and radioresistance in cancer. In the present study, we have identified convallatoxin as a novel inhibitor of NRF2/ARE. Suppression of NRF2 by convallatoxin was not transcriptionally mediated, but regulated at the level of proteolysis. Convallatoxin activated GSK-3β and suppression of NRF2 by convallatoxin required the Neh6 domain. Convallatoxin sensitised A549 cells to 5-fluorouracil-mediated cell death by promoting apoptosis. Together, our results provide evidence that convallatoxin might be useful as a chemotherapeutic adjuvant due to its ability to suppress NRF2/ARE.

The Current Status of the Pharmaceutical Potential of Juniperus L. Metabolites

Background: Plants and their derived natural compounds possess various biological and therapeutic properties, which turns them into an increasing topic of interest and research. Juniperus genus is diverse in species, with several traditional medicines reported, and rich in natural compounds with potential for development of new drugs. Methods: The research for this review were based in the Scopus and Web of Science databases using terms combining Juniperus, secondary metabolites names, and biological activities. This is not an exhaustive review of Juniperus compounds with biological activities, but rather a critical selection taking into account the following criteria: (i) studies involving the most recent methodologies for quantitative evaluation of biological activities; and (ii) the compounds with the highest number of studies published in the last four years. Results: From Juniperus species, several diterpenes, flavonoids, and one lignan were emphasized taking into account their level of activity against several targets. Antitumor activity is by far the most studied, being followed by antibacterial and antiviral activities. Deoxypodophyllotoxin and one dehydroabietic acid derivative appears to be the most promising lead compounds. Conclusions: This review demonstrates the Juniperus species value as a source of secondary metabolites with relevant pharmaceutical potential.

Dithiolethiones: a privileged pharmacophore for anticancer therapy and chemoprevention

Dithiolethiones are five-membered sulfur-containing cyclic scaffolds that exhibit antioxidative, anti-inflammatory, antithrombic and chemotherapeutic activities. Dithiolethiones display the chemopreventive and cytoprotective effects by activating the antioxidant response element and mounting the transcription of cytoprotective phase II enzymatic machinery. In addition, several classes of dithiolethiones efficiently modulate the activities of proteins that play crucial roles in normal and cancer cells, including glutathione S-transferase, cyclooxygenases and master regulator NF-κB. The present paper summarizes synthetic aspects, pharmacological potentials and biological attributes of dithiolethiones and its derivatives. Additionally, this review concludes with a discussion on how the current state-of-the-art technologies may help in defining a structure–activity relationship of dithiolethiones, thereby facilitating the design and synthesis of potent drug candidates.

E-p-Methoxycinnamoyl-α-l-rhamnopyranosyl Ester, a Phenylpropanoid Isolated from Scrophularia buergeriana, Increases Nuclear Factor Erythroid-Derived 2-Related Factor 2 Stability by Inhibiting Ubiquitination in Human Keratinocytes

The nuclear factor erythroid-derived 2-related factor 2 (Nrf2) is a key regulator of gene expression during oxidative stress and drug detoxification. Thus, identifying Nrf2 activators to protect from possible cell damage is necessary. In this study, we investigated whether E-p-methoxycinnamoyl-α-l-rhamnopyranosyl ester (MCR), a phenylpropanoid isolated from Scrophularia buergeriana, can activate Nrf2 signaling in human keratinocytes (HaCaT). First, we determined the dose- and time-dependent effects of MCR on the expression and activity of Nrf2. The antioxidant response element-luciferase reporter assay and western blot analysis results showed that MCR markedly induced Nrf2 activity and its protein expression, respectively. Further, MCR increased both the mRNA and protein levels of heme-oxygenase-1, one of the Nrf2 target genes, in the cells. Interestingly, we found that Nrf2 stability was remarkably enhanced by MCR. Furthermore, ubiquitin-dependent proteasomal degradation of Nrf2 was significantly reduced by MCR. Thus, MCR might afford skin protection by enhancing Nrf2 stability or by blocking its proteasomal degradation.

Topical Bixin Confers NRF2-Dependent Protection Against Photodamage and Hair Graying in Mouse Skin

Environmental exposure to solar ultraviolet (UV) radiation causes acute photodamage, premature aging, and skin cancer, attributable to UV-induced genotoxic, oxidative, and inflammatory stress. The transcription factor NRF2 [nuclear factor erythroid 2 (E2)-related factor 2] is the master regulator of the cellular antioxidant response protecting skin against various environmental stressors including UV radiation and electrophilic pollutants. NRF2 in epidermal keratinocytes can be activated using natural chemopreventive compounds such as the apocarotenoid bixin, an FDA-approved food additive and cosmetic ingredient from the seeds of the achiote tree (Bixa orellana). Here, we tested the feasibility of topical use of bixin for NRF2-dependent skin photoprotection in two genetically modified mouse models [SKH1 and C57BL/6J (Nrf2^+/+ versus Nrf2^-/- )]. First, we observed that a bixin formulation optimized for topical NRF2 activation suppresses acute UV-induced photodamage in Nrf2^+/+ but not Nrf2^-/- SKH1 mice, a photoprotective effect indicated by reduced epidermal hyperproliferation and oxidative DNA damage. Secondly, it was demonstrated that topical bixin suppresses PUVA (psoralen + UVA)-induced hair graying in Nrf2^+/+ but not Nrf2^-/- C57BL/6J mice. Collectively, this research provides the first in vivo evidence that topical application of bixin can protect against UV-induced photodamage and PUVA-induced loss of hair pigmentation through NRF2 activation. Topical NRF2 activation using bixin may represent a novel strategy for human skin photoprotection, potentially complementing conventional sunscreen-based approaches.

Correction to: In Vitro-In Vivo Dose Response of Ursolic Acid, Sulforaphane, PEITC, and Curcumin in Cancer Prevention

The citation of the author name "Ah-Ng Tony Kong" in PubMed is not the author's preference. Instead of "Kong AT", the author prefers "Kong AN".

Trans-cinnamic acid attenuates UVA-induced photoaging through inhibition of AP-1 activation and induction of Nrf2-mediated antioxidant genes in human skin fibroblasts

BACKGROUND

UVA irradiation-induced skin damage/photoaging is associated with redox imbalance and collagen degradation.

OBJECTIVE

Dermato-protective efficacies of trans-cinnamic acid (t-CA), a naturally occurring aromatic compound have been investigated against UVA irradiation, and elucidated underlying molecular mechanism.

METHODS

Human foreskin fibroblast-derived (Hs68) cells and nude mice were treated with t-CA prior to UVA exposure, and assayed the anti-photoaging effects of t-CA.

RESULTS

We found t-CA (20-100 μM) pretreatment substantially ameliorated UVA (3 J/cm²)-induced cytotoxicity, and inhibited intracellular ROS production in Hs68 cells. UVA-induced profound upregulation of metalloproteinase (MMP)-1/-3 and degradation of type I procollagen in dermal fibroblasts were remarkably reversed by t-CA, possibly through inhibition of AP-1 (c-Fos, but not c-Jun) translocation. The t-CA-mediated anti-photoaging properties are associated with increased nuclear translocation of Nrf2. Activation of Nrf2 signaling is accompanied with induction of HO-1 and γ-GCLC expressions in t-CA-treated fibroblasts. Furthermore t-CA-induced Nrf2 translocation is mediated through PKC, AMPK, CKII or ROS signaling cascades. This phenomenon was confirmed with respective pharmacological inhibitors, GF109203X, Compound C, CKII inhibitor or NAC, which blockade t-CA-induced Nrf2 activation. Silencing of Nrf2 signaling with siRNA showed no anti-photoaging effects of t-CA against UVA-induced ROS production, loss of HO-1 and type I collagen degradation in fibroblasts. In vivo evidence on nude mice revealed that t-CA pretreatment (20 or 100 mM/day) significantly suppressed MMP-1/-3 activation and maintained sufficient type I procollagen levels in biopsied skin tissue against UVA irradiation (3 J/cm²/day for 10-day).

CONCLUSION

t-CA treatment diminished UVA-induced photoaging/collagen degradation, and protected structural integrity of the skin.

In Vitro-In Vivo Dose Response of Ursolic Acid, Sulforaphane, PEITC, and Curcumin in Cancer Prevention

According to the National Center of Health Statistics, cancer was the culprit of nearly 600,000 deaths in 2016 in the USA. It is by far one of the most heterogeneous diseases to treat. Treatment for metastasized cancers remains a challenge despite modern diagnostics and treatment regimens. For this reason, alternative approaches are needed. Chemoprevention using dietary phytochemicals such as triterpenoids, isothiocyanates, and curcumin in the prevention of initiation and/or progression of cancer poses a promising alternative strategy. However, significant challenges exist in the extrapolation of in vitro cell culture data to in vivo efficacy in animal models and to humans. In this review, the dose at which these phytochemicals elicit a response in vitro and in vivo of a multitude of cellular signaling pathways will be reviewed highlighting Nrf2-mediated antioxidative stress, anti-inflammation, epigenetics, cytoprotection, differentiation, and growth inhibition. The in vitro-in vivo dose response of phytochemicals can vary due, in part, to the cell line/animal model used, the assay system of the biomarker used for the readout, chemical structure of the functional analog of the phytochemical, and the source of compounds used for the treatment study. While the dose response varies across different experimental designs, the chemopreventive efficacy appears to remain and demonstrate the therapeutic potential of triterpenoids, isothiocyanates, and curcumin in cancer prevention and in health in general.

Targeting NRF2 for Improved Skin Barrier Function and Photoprotection: Focus on the Achiote-Derived Apocarotenoid Bixin

The transcription factor NRF2 (nuclear factor-E2-related factor 2) orchestrates major cellular defense mechanisms including phase-II detoxification, inflammatory signaling, DNA repair, and antioxidant response. Recent studies strongly suggest a protective role of NRF2-mediated gene expression in the suppression of cutaneous photodamage induced by solar UV (ultraviolet) radiation. The apocarotenoid bixin, a Food and Drug Administration (FDA)-approved natural food colorant (referred to as ‘annatto’) originates from the seeds of the achiote tree native to tropical America, consumed by humans since ancient times. Use of achiote preparations for skin protection against environmental insult and for enhanced wound healing has long been documented. We have recently reported that (i) bixin is a potent canonical activator of the NRF2-dependent cytoprotective response in human skin keratinocytes; that (ii) systemic administration of bixin activates NRF2 with protective effects against solar UV-induced skin damage; and that (iii) bixin-induced suppression of photodamage is observable in Nrf2^+/+ but not in Nrf2^−/− SKH-1 mice confirming the NRF2-dependence of bixin-induced antioxidant and anti-inflammatory effects. In addition, bixin displays molecular activities as sacrificial antioxidant, excited state quencher, PPAR (peroxisome proliferator-activated receptor) α/γ agonist, and TLR (Toll-like receptor) 4/NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells) antagonist, all of which might be relevant to the enhancement of skin barrier function and environmental stress protection. Potential skin photoprotection and photochemoprevention benefits provided by topical application or dietary consumption of this ethno-pharmacologically validated phytochemical originating from the Americas deserves further preclinical and clinical examination.

Ginger Oleoresin Alleviated γ-Ray Irradiation-Induced Reactive Oxygen Species via the Nrf2 Protective Response in Human Mesenchymal Stem Cells

Unplanned exposure to radiation can cause side effects on high-risk individuals; meanwhile, radiotherapies can also cause injury on normal cells and tissues surrounding the tumor. Besides the direct radiation damage, most of the ionizing radiation- (IR-) induced injuries were caused by generation of reactive oxygen species (ROS). Human mesenchymal stem cells (hMSCs), which possess self-renew and multilineage differentiation capabilities, are a critical population of cells to participate in the regeneration of IR-damaged tissues. Therefore, it is imperative to search effective radioprotectors for hMSCs. This study was to demonstrate whether natural source ginger oleoresin would mitigate IR-induced injuries in human mesenchymal stem cells (hMSCs). We demonstrated that ginger oleoresin could significantly reduce IR-induced cytotoxicity, ROS generation, and DNA strand breaks. In addition, the ROS-scavenging mechanism of ginger oleoresin was also investigated. The results showed that ginger oleoresin could induce the translocation of Nrf2 to cell nucleus and activate the expression of cytoprotective genes encoding for HO-1 and NQO-1. It suggests that ginger oleoresin has a potential role of being an effective antioxidant and radioprotective agent.

Keap1 knockdown in melanocytes induces cell proliferation and survival via HO-1-associated β-catenin signaling

BACKGROUND

Nrf2-Keap1 signaling pathway protects cells against photo-oxidative stress. Yet in recent works, its role in melanogenesis together with cell protection functions against oxidative stress has been gaining interest. However, its effect on melanogenesis still has contradictory results from different studies.

OBJECTIVE

The aims of our study were to investigate the effect of Keap1 silencing in melanocyte on melanogenesis and its associated mechanism.

METHODS

Primary human epidermal melanocytes and melan-a cell line were used for this experiment. RNA sequencing was done to identify genes involved in melanocyte biology using Keap1 knockdown through siRNA techniques. And melanogenesis and the expression of melanogenesis-associated molecules were evaluated in Keap1 silenced melanocyte to examine the effects of Keap1 on melanogenesis, melanocyte growth, and related pathways.

RESULTS

RNA-sequencing data revealed that Keap1 knockdown in primary human epidermal melanocytes (PHEMs) induced cell survival-related gene expression. Additionally, siRNA-mediated inhibition of Keap1 led to upregulation of MITF and melanogenesis-associated molecules along with Nrf2 activation in PHEMs. HO-1, a major gene that is upregulated in RNA-sequencing using Keap1-silenced PHEMs, protected melanocytes against H₂O₂-induced cell death and upregulated MITF and β-catenin expression. Further, increased expression of melanogenesis-associated molecules after Keap1 silencing was validated to occur through HO-1-associated β-catenin activation in a Keap1 and HO-1 double knockdown experiment.

CONCLUSION

This work suggests that Keap1 silencing in melanocytes induced melanogenesis and the expression of melanogenesis-associated molecules through HO-1-associated β-catenin activation. Keap1 downregulation in melanocytes is important for cell proliferation and survival.

Oxidative Stress

Oxidative stress is two sided: Whereas excessive oxidant challenge causes damage to biomolecules, maintenance of a physiological level of oxidant challenge, termed oxidative eustress, is essential for governing life processes through redox signaling. Recent interest has focused on the intricate ways by which redox signaling integrates these converse properties. Redox balance is maintained by prevention, interception, and repair, and concomitantly the regulatory potential of molecular thiol-driven master switches such as Nrf2/Keap1 or NF-κB/IκB is used for system-wide oxidative stress response. Nonradical species such as hydrogen peroxide (H₂O₂) or singlet molecular oxygen, rather than free-radical species, perform major second messenger functions. Chemokine-controlled NADPH oxidases and metabolically controlled mitochondrial sources of H₂O₂ as well as glutathione- and thioredoxin-related pathways, with powerful enzymatic back-up systems, are responsible for fine-tuning physiological redox signaling. This makes for a rich research field spanning from biochemistry and cell biology into nutritional sciences, environmental medicine, and molecular knowledge-based redox medicine.

The role of quercetin and vitamin C in Nrf2-dependent oxidative stress production in breast cancer cells

The balance between the production and elimination of reactive oxygen species (ROS) is essential in determining whether cells survive or undergo apoptosis. Nuclear factor erythroid 2-related factor 2 (Nrf2) may act as a sensor for electrophilic stress, thus regulating the intracellular antioxidant response. The present study investigated the role of vitamin C (VC) and quercetin (Q) in the induction of Nrf2-mediated oxidative stress in cancer cells. An MTT assay was conducted to examine the anti-proliferative effects of VC and Q. Reverse transcription-quantitative polymerase chain reaction and western blot analysis were performed to determine the messenger RNA (mRNA) and protein expression of Nrf2, respectively. The activity of nicotinamide adenine dinucleotide phosphate dehydrogenase quinone 1, heme oxygenase 1, glutathione peroxidase, glutathione reductase and reduced glutathione were measured by spectrophotometric analysis. Intracellular generation of ROS was determined using 2'-7'-dichlorodihydrofluorescein diacetate fluorescent probes. The results demonstrated that the cytotoxicity (50% inhibitory concentration) of VC and Q were 271.6-480.1 and 155.1-232.9 µM, respectively. Additionally, there was a significant decrease in the expression of Nrf2 mRNA and protein levels following the treatment of breast cancer cells with VC and Q (P=0.024). Following treatment with VC and Q, the nuclear/cytosolic Nrf2 ratio was reduced by 1.7-fold in MDA-MB 231 cells, 2-fold in MDA-MB 468 cells, 1.4-fold in MCF-7 cells and 1.2 fold in A549 cells. Sequential treatment with VC and Q decreased endogenous production of ROS in a dose-dependent manner (P=0.027). The results of the current study suggest that VC and Q treatment may be developed as an adjuvant for patients with cancer and overexpression of Nrf2.

Magnolia officinalis (Hou Po) bark extract stimulates the Nrf2-pathway in hepatocytes and protects against oxidative stress

ETHNOPHARMACOLOGICAL RELEVANCE

The highly aromatic bark of Magnolia officinalis Rehder and EH Wilson, (magnolia bark) has been widely used in traditional Chinese medicine where it is known as Hou Po. Historically the bark of the tree has been used for treating variety of disorders the most common use of magnolia bark in traditional prescription has been to treat stress and anxiety disorders. Till date it is not clear regarding the fundamental cellular pathway it modulates. NRF2 signaling has emerged as the central pathway that protects cells from variety of stressors this led us to hypothesize that basis for magnolia bark's effects could be via activating NRF2 pathway.

MATERIALS AND METHODS

We utilized variety of biochemical procedures like luciferase reporter assay, enzyme induction, gene expression to determine NRF2 inducing activity by magnolia bark extract and its significance. Further we identified the phytochemicals inducing this activity using bio-directed fractionation procedure.

RESULTS

In this study, we demonstrate that magnolia bark extract activates Nrf2-dependent gene expression and protects against hydrogen peroxide mediated oxidative stress in hepatocytes. We further identified through HPLC fractionation and mass spectroscopy that magnolol, 4-methoxy honokiol and honokiol are the active phytochemicals inducing the Nrf2-mediated activity. This could be the molecular basis for its numerous beneficial activity.

Prophylaxis of Diallyl Disulfide on Skin Carcinogenic Model via p21-dependent Nrf2 stabilization

Cancer prevention through intake of biologically active natural products appears to be an accessible way to reduce the risk of cancer. Diallyl disulfide (DADS), a major garlic derivative, has exhibited potential role in cancer therapy. The study is aimed to evaluate the prophylactic effect of DADS in chemically induced mouse skin carcinogenesis and investigate the molecular targets mediated by DADS. Two-stage chemically induced carcinogenesis model by cutaneous application of DMBA and subsequent TPA was established to study the prophylactic effect of DADS. As a result, we observed that DADS dose-dependently attenuated skin tumor incidence and multiplicity in the model mice, which was related to the up-regulation of a bunch of antioxidant enzymes activities and the nuclear accumulation of Nrf2. Furthermore, we developed skin carcinogenesis in Nrf2 knockout mice which could reverse the activity of DADS. Finally, we uncovered the underlying mechanism that DADS promoted the endogenous interaction between p21 and Nrf2, which was critical for impairing the Keap1-mediated degradation of Nrf2. Based on the results, we concluded that DADS was a promising cancer chemoprevention agent and suggested a garlic-rich diet might be beneficial to reduce the cancer risk in our daily life.

What has passed is prolog: new cellular and physiological roles of G6PD

G6PD deficiency has been the most pervasive inherited disorder in the world since having been discovered. G6PD has an antioxidant role by functioning as a major nicotinamide adenine dinucleotide phosphate (NADPH) provider to reduce excessive oxidative stress. NADPH can produce reactive oxygen species (ROS) and reactive nitrogen species (RNS) mediated by NADPH oxidase (NOX) and nitric oxide synthase (NOS), respectively. Hence, G6PD also has a pro-oxidant role. Research in the past has focused on the enhanced susceptibility of G6PD-deficient cells or individuals to oxidative challenge. The cytoregulatory role of G6PD has largely been overlooked. By using a metabolomic approach, it is noted that upon oxidant challenge, G6PD-deficient cells will reprogram the GSH metabolism from regeneration to synthesis with exhaustive energy consumption. Recently, new cellular/physiologic roles of G6PD have been discovered. By using a proteomic approach, it has been found that G6PD plays a regulatory role in xenobiotic metabolism possibly via NOX and the redox-sensitive Nrf2-signaling pathway to modulate the expression of xenobiotic-metabolizing enzymes. Since G6PD is a key regulator responsible for intracellular redox homeostasis, G6PD deficiency can alter redox balance leading to many abnormal cellular effects such as the cellular inflammatory and immune response against viral infection. G6PD may play an important role in embryogenesis as G6PD-knockdown mouse cannot produce offspring and G6PD-deficient C. elegans with defective egg production and hatching. This array of findings indicates that the cellular and physiologic roles of G6PD, other than the classical role as an antioxidant enzyme, deserve further attention.

Fraxetin Induces Heme Oxygenase-1 Expression by Activation of Akt/Nrf2 or AMP-activated Protein Kinase α/Nrf2 Pathway in HaCaT Cells

Background

Fraxetin (7,8-dihydroxy-6-methoxy coumarin), a coumarin derivative, has been reported to possess antioxidative, anti-inflammatory and neuroprotective effects. A number of recent observations suggest that the induction of heme oxygenase-1 (HO-1) inhibits inflammation and tumorigenesis. In the present study, we determined the effect of fraxetin on HO-1 expression in HaCaT human keratinocytes and investigated its underlying molecular mechanisms.

Methods

Reverse transcriptase-PCR and Western blot analysis were performed to detect HO-1 mRNA and protein expression, respectively. Cell viability was measured by the MTS test. The induction of intracellular reactive oxygen species (ROS) by fraxetin was evaluated by 2′,7′-dichlorofluorescin diacetate staining.

Results

Fraxetin upregulated mRNA and protein expression of HO-1. Incubation with fraxetin induced the localization of nuclear factor-erythroid-2-related factor-2 (Nrf2) in the nucleus and increased the antioxidant response element-reporter gene activity. Fraxetin also induced the phosphorylation of Akt and AMP-activated protein kinase (AMPK)α and diminished the expression of phosphatase and tensin homolog, a negative regulator of Akt. Pharmacological inhibition of Akt and AMPKα abrogated fraxetin-induced expression of HO-1 and nuclear localization of Nrf2. Furthermore, fraxetin generated ROS in a concentration-dependent manner.

Conclusions

Fraxetin induces HO-1 expression through activation of Akt/Nrf2 or AMPKα/Nrf2 pathway in HaCaT cells.

A newly synthesized macakurzin C-derivative attenuates acute and chronic skin inflammation: The Nrf2/heme oxygenase signaling as a potential target

Impaired immune responses in skin play a pivotal role in the development and progression of chemical-associated inflammatory skin disorders. In this study, we synthesized new flavonoid derivatives from macakurzin C, and identified in vitro and in vivo efficacy of a potent anti-inflammatory flavonoid, Compound 14 (CPD 14), with its underlying mechanisms. In lipopolysaccharide (LPS)-stimulated murine macrophages and IFN-γ/TNF-α-stimulated human keratinocytes, CPD 14 significantly inhibited the release of inflammatory mediators including nitric oxide (NO), prostaglandins, and cytokines (IC50 for NO inhibition in macrophages: 4.61μM). Attenuated NF-κB signaling and activated Nrf2/HO-1 pathway were responsible for the anti-inflammatory effects of CPD 14. The in vivo relevance was examined in phorbol 12-myristate 13-acetate (TPA)-induced acute skin inflammation and oxazolone-induced atopic dermatitis models. Topically applied CPD 14 significantly protected both irritation- and sensitization-associated skin inflammation by suppressing the expression of inflammatory mediators. In summary, we demonstrated that a newly synthesized flavonoid, CPD 14, has potent inhibitory effects on skin inflammation, suggesting it is a potential therapeutic candidate to treat skin disorders associated with excessive inflammation.