Epigenetic DNA methylation of antioxidative stress regulator NRF2 in human prostate cancer

Pterostilbene Reverses Epigenetic Silencing of Nrf2 and Enhances Antioxidant Response in Endothelial Cells in Hyperglycemic Microenvironment

The epigenetic regulation of nuclear factor erythroid 2-related factor 2 (Nrf2), a pivotal redox transcription factor, plays a crucial role in maintaining cellular homeostasis. Recent research has underscored the significance of epigenetic modifications of Nrf2 in the pathogenesis of diabetic foot ulcers (DFUs). This study investigates the epigenetic reversal of Nrf2 by pterostilbene (PTS) in human endothelial cells in a hyperglycemic microenvironment (HGM). The activation potential of PTS on Nrf2 was evaluated through ARE-Luciferase reporter assays and nuclear translocation studies. Following 72 h of exposure to an HGM, mRNA expression and protein levels of Nrf2 and its downstream targets NAD(P)H quinone oxidoreductase 1 (NQO1), heme-oxygenase 1(HO-1), superoxide dismutase (SOD), and catalase (CAT) exhibited a decrease, which was mitigated in PTS-pretreated endothelial cells. Epigenetic markers, including histone deacetylases (HDACs class I-IV) and DNA methyltransferases (DNMTs 1/3A and 3B), were found to be downregulated under diabetic conditions. Specifically, Nrf2-associated HDACs, including HDAC1, HDAC2, HDAC3, and HDAC4, were upregulated in HGM-induced endothelial cells. This upregulation was reversed in PTS-pretreated cells, except for HDAC2, which exhibited elevated expression in endothelial cells treated with PTS in a hyperglycemic microenvironment. Additionally, PTS was observed to reverse the activity of the methyltransferase enzyme DNMT. Furthermore, CpG islands in the Nrf2 promoter were hypermethylated in cells exposed to an HGM, a phenomenon potentially counteracted by PTS pretreatment, as shown by methyl-sensitive restriction enzyme PCR (MSRE-qPCR) analysis. Collectively, our findings highlight the ability of PTS to epigenetically regulate Nrf2 expression under hyperglycemic conditions, suggesting its therapeutic potential in managing diabetic complications.

Synthetic augmentation of bilirubin metabolism in human pluripotent stem cell-derived liver organoids

UGT1A1 (UDP glucuronosyltransferase family 1 member A1) is the primary enzyme required for bilirubin conjugation, which is essential for preventing hyperbilirubinemia. Animal models lack key human organic anion transporting polypeptides with distinct epigenetic control over bilirubin metabolism, necessitating a human model to interrogate the regulatory mechanism behind UGT1A1 function. Here, we use induced pluripotent stem cells to develop human liver organoids that can emulate conjugation failure phenotype. Bilirubin conjugation assays, chromatin immunoprecipitation, and transcriptome analysis elucidated the role of glucocorticoid antagonism in UGT1A1 activation. This antagonism prevents the binding of transcriptional repressor MECP2 at the expense of NRF2 with associated off-target effects. Therefore, we introduced functional GULO (L-gulonolactone oxidase) in human organoids to augment intracellular ascorbate for NRF2 reactivation. This engineered organoid conjugated more bilirubin and protected against hyperbilirubinemia when transplanted in immunosuppressed Crigler-Najjar syndrome rat model. Collectively, we demonstrate that our organoid system serves as a manipulatable model for interrogating hyperbilirubinemia and potential therapeutic development.

Effects and Mechanisms of Non-Thermal Plasma-Mediated ROS and Its Applications in Animal Husbandry and Biomedicine

Non-thermal plasma (NTP) is an ionized gas composed of neutral and charged reactive species, electric fields, and ultraviolet radiation. NTP presents a relatively low discharge temperature because it is characterized by the fact that the temperature values of ions and neutral particles are much lower than that of electrons. Reactive species (atoms, radicals, ions, electrons) are produced in NTP and delivered to biological objects induce a set of biochemical processes in cells or tissues. NTP can mediate reactive oxygen species (ROS) levels in an intensity- and time-dependent manner. ROS homeostasis plays an important role in animal health. Relatively low or physiological levels of ROS mediated by NTP promote cell proliferation and differentiation, while high or excessive levels of ROS mediated by NTP cause oxidative stress damage and even cell death. NTP treatment under appropriate conditions not only produces moderate levels of exogenous ROS directly and stimulates intracellular ROS generation, but also can regulate intracellular ROS levels indirectly, which affect the redox state in different cells and tissues of animals. However, the treatment condition of NTP need to be optimized and the potential mechanism of NTP-mediated ROS in different biological targets is still unclear. Over the past ten decades, interest in the application of NTP technology in biology and medical sciences has been rapidly growing. There is significant optimism that NTP can be developed for a wide range of applications such as wound healing, oral treatment, cancer therapy, and biomedical materials because of its safety, non-toxicity, and high efficiency. Moreover, the combined application of NTP with other methods is currently a hot research topic because of more effective effects on sterilization and anti-cancer abilities. Interestingly, NTP technology has presented great application potential in the animal husbandry field in recent years. However, the wide applications of NTP are related to different and complicated mechanisms, and whether NTP-mediated ROS play a critical role in its application need to be clarified. Therefore, this review mainly summarizes the effects of ROS on animal health, the mechanisms of NTP-mediated ROS levels through antioxidant clearance and ROS generation, and the potential applications of NTP-mediated ROS in animal growth and breeding, animal health, animal-derived food safety, and biomedical fields including would healing, oral treatment, cancer therapy, and biomaterials. This will provide a theoretical basis for promoting the healthy development of animal husbandry and the prevention and treatment of diseases in both animals and human beings.

The untapped potential of targeting NRF2 in neurodegenerative disease

Since its initial discovery almost three decades ago, the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) has been shown to regulate a host of downstream transcriptional responses and play a critical role in preventing or promoting disease progression depending on the context. Critically, while the importance of proper nuclear factor erythroid 2-related factor 2 function has been demonstrated across a variety of pathological settings, the ability to progress NRF2-targeted therapeutics to clinic has remained frustratingly elusive. This is particularly true in the case of age-related pathologies, where nuclear factor erythroid 2-related factor 2 is a well-established mitigator of many of the observed pathogenic effects, yet options to target this pathway remain limited. Along these lines, loss of nuclear factor erythroid 2-related factor 2 function has clearly been shown to enhance neuropathological outcomes, with enhancing nuclear factor erythroid 2-related factor 2 pathway activation to prevent neurodegenerative/neurological disease progression continuing to be an active area of interest. One critical obstacle in generating successful therapeutics for brain-related pathologies is the ability of the compound to cross the blood brain barrier (BBB), which has also hampered the implementation of several promising nuclear factor erythroid 2-related factor 2 inducers. Another limitation is that many nuclear factor erythroid 2-related factor 2 activators have undesirable off-target effects due to their electrophilic nature. Despite these constraints, the field has continued to evolve, and several viable means of targeting nuclear factor erythroid 2-related factor 2 in a neuropathological context have emerged. In this perspective, we will briefly discuss the key findings and promising therapeutic options that have been discovered to date, as well as highlight emerging areas of NRF2-neurodegeneration research that provide hope for successfully targeting this pathway in the future.

Dietary Polyphenols Remodel DNA Methylation Patterns of NRF2 in Chronic Disease

The nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor crucial in regulating cellular homeostasis and apoptosis. The NRF2 gene has been implicated in various biological activities, including antioxidant, anti-inflammatory, and anticancer properties. NRF2 can be regulated genetically and epigenetically at the transcriptional, post-transcriptional, and translational levels. Although DNA methylation is one of the critical biological processes vital for gene expression, sometimes, anomalous methylation patterns result in the dysregulation of genes and consequent diseases and disorders. Several studies have reported promoter hypermethylation downregulated NRF2 expression and its downstream targets. In contrast to the unalterable nature of genetic patterns, epigenetic changes can be reversed, opening up new possibilities in developing therapies for various metabolic disorders and diseases. This review discusses the current state of the NRF2-mediated antioxidative and chemopreventive activities of several natural phytochemicals, including sulforaphane, resveratrol, curcumin, luteolin, corosolic acid, apigenin, and most other compounds that have been found to activate NRF2. This epigenetic reversal of hypermethylated NRF2 states provides new opportunities for research into dietary phytochemistry that affects the human epigenome and the possibility for cutting-edge approaches to target NRF2-mediated signaling to prevent chronic disorders.

The mechanistic insights of the antioxidant Keap1-Nrf2 pathway in oncogenesis: a deadly scenario

The Nuclear factor erythroid 2-related factor 2 (Nrf2) protein has garnered significant interest due to its crucial function in safeguarding cells and tissues. The Nrf2 protein is crucial in preserving tissue integrity by safeguarding cells against metabolic, xenobiotic and oxidative stress. Due to its various functions, Nrf2 is a potential pharmacological target for reducing the incidence of diseases such as cancer. However, mutations in Keap1-Nrf2 are not consistently favored in all types of cancer. Instead, they seem to interact with specific driver mutations of tumors and their respective tissue origins. The Kelch-like ECH-associated protein 1 (Keap1)-Nrf2 pathway mutations are a powerful cancer adaptation that utilizes inherent cytoprotective pathways, encompassing nutrient metabolism and ROS regulation. The augmentation of Nrf2 activity elicits significant alterations in the characteristics of neoplastic cells, such as resistance to radiotherapy and chemotherapy, safeguarding against apoptosis, heightened invasiveness, hindered senescence, impaired autophagy and increased angiogenesis. The altered activity of Nrf2 can arise from diverse genetic and epigenetic modifications that instantly impact Nrf2 regulation. The present study aims to showcase the correlation between the Keap1-Nrf2 pathway and the progression of cancers, emphasizing genetic mutations, metabolic processes, immune regulation, and potential therapeutic strategies. This article delves into the intricacies of Nrf2 pathway anomalies in cancer, the potential ramifications of uncontrolled Nrf2 activity, and therapeutic interventions to modulate the Keap1-Nrf2 pathway.

Uncovering the Secrets of Prostate Cancer's Radiotherapy Resistance: Advances in Mechanism Research

Prostate cancer (PCa) is a critical global public health issue with its incidence on the rise. Radiation therapy holds a primary role in PCa treatment; however, radiation resistance has become increasingly challenging as we uncover more about PCa's pathogenesis. Our review aims to investigate the multifaceted mechanisms underlying radiation therapy resistance in PCa. Specifically, we will examine how various factors, such as cell cycle regulation, DNA damage repair, hypoxic conditions, oxidative stress, testosterone levels, epithelial-mesenchymal transition, and tumor stem cells, contribute to radiation therapy resistance. By exploring these mechanisms, we hope to offer new insights and directions towards overcoming the challenges of radiation therapy resistance in PCa. This can also provide a theoretical basis for the clinical application of novel ultra-high-dose-rate (FLASH) radiotherapy in the era of PCa.

Epigenetic effects of herbal medicine

Epigenetic memory is essential for life that governs the predefined functional features of cells. Recent evidence has indicated that the epigenetic modification provides a potential link to gene expression changes that may be involved in the development of various chronic diseases, and targeting the epigenome becomes a plausible method for treating diseases. Traditional herbal medicine has gradually entered the vision of researchers due to its low toxicity and its effectiveness in treating diseases. As a matter of fact, researchers found that the possessed epigenetic modification capacity of herbal medicine had the ability to combat the progression of the disease, such as various types of cancer, diabetes, inflammation, amnesia, liver fibrosis, asthma, and hypertension-induced renal injury. Studies on the epigenetic effects of herbal medicine will provide valuable insights into the molecular mechanisms of human diseases, which may lead to new therapeutic approaches and diagnoses. Thus, this review summarized the impact of herbal medicine and its bioactive components on disease epigenome as examples of how utilization of epigenetic plasticity could be useful as the basis for the future development of targeted therapies in chronic diseases.

Activation of Nrf2 pathway as a protective mechanism against oxidative stress-induced diseases: Potential of astaxanthin

Astaxanthin, a red-orange liposoluble carotenoid, has been the centre of considerable attention in recent years for its numerous biological activities, notably its potent antioxidant activity. It is reported that astaxanthin elicits these biological activities via a number of cellular pathways. The Nrf2/Keap1 pathway is a major regulator of the antioxidant defence system of cells; it modulates the expression of a plethora of genes related to redox homeostasis as well as cellular detoxification. The pathway has received lots of attention as a prospective therapeutic target for diseases related to oxidative stress and aging. Several reports have shown that the pathway is inducible by many natural compounds. This present work reviews the Nrf2/Keap1 pathway, its regulation and involvement in diseases, provides a brief overview of naturally occurring compounds as activators of the pathway as well as discusses the effect of astaxanthin on the pathway.

NRF2 modulation in TRAMP mice: an in vivo model of prostate cancer

BACKGROUND

Prostate cancer (PCa) is one of the most common cancers worldwide and oxidative stress is involved in its occurrence, development and progression. In fact, in transgenic adenocarcinoma of mouse prostate (TRAMP) mice, prostate cancer onset is associated with the methylation of the first five CpG in the nuclear factor erythroid 2-related factor 2 (NRF2) promoter, a key regulator of oxidative stress response, leading to its downregulation and accumulation of reactive oxygen species (ROS). It has been demonstrated that both natural and synthetic compounds can reactivate NRF2 expression inhibiting the methylation status of its promoter by downregulation of DNA methyltransferases (DNMTs) and histone deacetylases (HDACs). Interestingly, NRF2 re-expression significantly reduced prostate cancer onset in TRAMP mice highlighting an important role of NRF2 in prostate tumorigenesis.

METHODS AND RESULTS

We analysed the current literature regarding the role of natural and synthetic compounds in modulating NRF2 pathway in TRAMP mice, an in vivo model of prostate cancer, to give an overview on prostate carcinogenesis and its possible prevention.

CONCLUSION

We can conclude that specific natural and synthetic compounds can downregulate DNMTs and/or HDACs inhibiting the methylation status of NRF2 promoter, then reactivating the expression of NRF2 protecting normal prostatic cells from ROS damage and tumorigenesis.

Histone lysine methyltransferase SETDB2 suppresses NRF2 to restrict tumor progression and modulates chemotherapy sensitivity in lung adenocarcinoma

OBJECTIVE

Aberrant epigenetic remodeling represents a molecular hallmark in lung adenocarcinoma (LUAD). We aim to investigate the biological roles of SETDB2 and its underlying associations with oxidative stress, providing therapeutic targets for individualized treatment of LUAD.

METHODS

Differential analysis was conducted via Limma package, and Kaplan-Meier analysis was performed with survival package. CCK-8, cell proliferation assay, transwell assay, and in vivo assays were conducted to assess the function of SETDB2. Western blot assay, RT-qPCR, and immunohistochemistry (IHC) were conducted to assess the expression levels of SETDB2/NRF2. Chromatin immunoprecipitation (ChIP) assay and ChIP-qPCR were conducted to assess the epigenetic roles of SETDB2.

RESULTS

We found that SETDB2 expression is decreased in tumor samples versus normal tissues in TCGA-LUAD cohort, LUAD-EAS cohort, GSE72094 dataset, and independent Soochow-LUAD dataset. Patients with low SETDB2 levels had a worse prognosis relative to those with high SETDB2. SETDB2 inhibition could significantly promote cell growth, migration ability, and stemness maintenance. Gene set enrichment analysis (GSEA) suggested that SETDB2 correlated with oxidative stress crosstalk and regulated NRF2 mRNA levels. ChIP assay suggested that SETDB2 mainly recruited the H3K9me3 enrichment at the NRF2 promoter region to suppress the mRNA levels of NRF2. Downregulated SETDB2 could activate NRF2 transcription and expression, thereby promoting its downstream targets, like NQO1, FTH1, and ME1. Functional experiments demonstrated that low SETDB2 allowed NRF2 to drive malignant processes of LUAD. SETDB2 overexpression attenuated the ability of NRF2 signaling to neutralize cellular reactive oxygen species (ROS) levels, leading to enhanced cell apoptosis. Overexpressed SETDB2 could inhibit tumor progression in vivo and further render LUAD cells sensitive to chemotherapy.

CONCLUSIONS

In conclusion, these findings uncovered the suppressive role of SETDB2 in LUAD. SETDB2 negatively regulates NRF2 signaling to modulate tumor progression, which creates a therapeutic vulnerability in LUAD.

Targeting NRF2-KEAP1 axis by Omega-3 fatty acids and their derivatives: Emerging opportunities against aging and diseases

The transcription factor NRF2 and its endogenous inhibitor KEAP1 play a crucial role in the maintenance of cellular redox homeostasis by regulating the gene expression of diverse networks of antioxidant, anti-inflammatory, and detoxification enzymes. Therefore, activation of NRF2 provides cytoprotection against numerous pathologies, including age-related diseases. An age-associated loss of NRF2 function may be a key driving force behind the aging phenotype. Recently, numerous NRF2 inducers have been identified and some of them are promising candidates to restore NRF2 transcriptional activity during aging. Emerging evidence indicates that omega-3 (n-3) polyunsaturated fatty acids (PUFAs) and their electrophilic derivatives may trigger a protective response via NRF2 activation, rescuing or maintaining cellular redox homeostasis. In this review, we provide an overview of the NRF2-KEAP1 system and its dysregulation in aging cells. We also summarize current studies on the modulatory role of n-3 PUFAs as potential agents to prevent multiple chronic diseases and restore the age-related impairment of NRF2 function.

NRF2: A crucial regulator for mitochondrial metabolic shift and prostate cancer progression

Metabolic alterations are a common survival mechanism for prostate cancer progression and therapy resistance. Oxidative stress in the cellular and tumor microenvironment dictates metabolic switching in the cancer cells to adopt, prosper and escape therapeutic stress. Therefore, regulation of oxidative stress in tumor cells and in the tumor-microenvironment may enhance the action of conventional anticancer therapies. NRF2 is the master regulator for oxidative stress management. However, the overall oxidative stress varies with PCa clinical stage, metabolic state and therapy used for the cancer. In agreement, the blanket use of NRF2 inducers or inhibitors along with anticancer therapies cause adverse effects in some preclinical cancer models. In this review, we have summarized the levels of oxidative stress, metabolic preferences and NRF2 activity in the different stages of prostate cancer. We also propose condition specific ways to use NRF2 inducers or inhibitors along with conventional prostate cancer therapies. The significance of this review is not only to provide a detailed understanding of the mechanism of action of NRF2 to regulate oxidative stress-mediated metabolic switching by prostate cancer cells to escape the radiation, chemo, or hormonal therapies, and to grow aggressively, but also to provide a potential therapeutic method to control aggressive prostate cancer growth by stage specific proper use of NRF2 regulators.

Novel epigenetic therapeutic strategies and targets in cancer

The critical role of dysregulated epigenetic pathways in cancer genesis, development, and therapy has typically been established as a result of scientific and technical innovations in next generation sequencing. RNA interference, histone modification, DNA methylation and chromatin remodelling are epigenetic processes that control gene expression without causing mutations in the DNA. Although epigenetic abnormalities are thought to be a symptom of cell tumorigenesis and malignant events that impact tumor growth and drug resistance, physicians believe that related processes might be a key therapeutic target for cancer treatment and prevention due to the reversible nature of these processes. A plethora of novel strategies for addressing epigenetics in cancer therapy for immuno-oncological complications are currently available - ranging from basic treatment to epigenetic editing. - and they will be the subject of this comprehensive review. In this review, we cover most of the advancements made in the field of targeting epigenetics with special emphasis on microbiology, plasma science, biophysics, pharmacology, molecular biology, phytochemistry, and nanoscience.

Oxidative Stress and Cancer Heterogeneity Orchestrate NRF2 Roles Relevant for Therapy Response

Oxidative stress and its end-products, such as 4-hydroxynonenal (HNE), initiate activation of the Nuclear Factor Erythroid 2-Related Factor 2 (NRF2)/Kelch Like ECH Associated Protein 1 (KEAP1) signaling pathway that plays a crucial role in the maintenance of cellular redox homeostasis. However, an involvement of 4-HNE and NRF2 in processes associated with the initiation of cancer, its progression, and response to therapy includes numerous, highly complex events. They occur through interactions between cancer and stromal cells. These events are dependent on many cell-type specific features. They start with the extent of NRF2 binding to its cytoplasmic repressor, KEAP1, and extend to the permissiveness of chromatin for transcription of Antioxidant Response Element (ARE)-containing genes that are NRF2 targets. This review will explore epigenetic molecular mechanisms of NRF2 transcription through the specific molecular anatomy of its promoter. It will explain the role of NRF2 in cancer stem cells, with respect to cancer therapy resistance. Additionally, it also discusses NRF2 involvement at the cross-roads of communication between tumor associated inflammatory and stromal cells, which is also an important factor involved in the response to therapy.

Nrf2 activation does not affect adenoma development in a mouse model of colorectal cancer

Transcription factor nuclear factor erythroid 2 p45-related factor 2 (Nrf2) and its main negative regulator, Kelch-like ECH associated protein 1 (Keap1), are at the interface between redox and intermediary metabolism. Nrf2 activation is protective in models of human disease and has benefits in clinical trials. Consequently, the Keap1/Nrf2 protein complex is a drug target. However, in cancer Nrf2 plays a dual role, raising concerns that Nrf2 activators may promote growth of early neoplasms. To address this concern, we examined the role of Nrf2 in development of colorectal adenomas by employing genetic, pharmacological, and metabolomic approaches. We found that colorectal adenomas that form in Gstp-/-: ApcMin/+ mice are characterized by altered one-carbon metabolism and that genetic activation, but not disruption of Nrf2, enhances these metabolic alterations. However, this enhancement is modest compared to the magnitude of metabolic differences between tumor and peri-tumoral tissues, suggesting that the metabolic changes conferred by Nrf2 activation may have little contribution to the early stages of carcinogenesis. Indeed, neither genetic (by Keap1 knockdown) nor pharmacological Nrf2 activation, nor its disruption, affected colorectal adenoma formation in this model. We conclude that pharmacological Nrf2 activation is unlikely to impact the early stages of development of colorectal cancer.

DNA methylome, transcriptome, and prostate cancer prevention by phenethyl isothiocyanate in TRAMP mice

Epigenetics/epigenomics has been shown to be involved in carcinogenesis. However, how the epigenome would be altered in the transgenic adenocarcinoma of the mouse prostate (TRAMP) cancer model and the effect of cancer chemopreventive phytochemical phenethyl isothiocyanate (PEITC) on the epigenome in TRAMP mice are not known. PEITC has been reported to reduce the risk of many cancers including prostate cancer (PCa). In this study, male TRAMP mice were fed a control diet or diet containing 0.05% PEITC from 8 weeks to 16 weeks. The tumor incidence was reduced in the PEITC diet (0/6) as compared with the control diet (6/7). RNA-sequencing (RNA-seq) analyses on nontumor and tumor prostatic tissues revealed several pathways like cell cycle/Cdc42 signaling, inflammation, and cancer-related signaling, were activated in prostate tissues of TRAMP mice but were reversed or attenuated in TRAMP mice fed with PEITC diet. DNA CpG methyl-seq analyses showed that global methylation patterns of prostate samples from TRAMP mice were hugely different from those of wild-type mice. Dietary PEITC partially reversed the global methylation changes during prostatic carcinogenesis. Integration of RNA-seq and DNA methyl-seq analyses identified a list of genes, including Adgrb1 and Ebf4, with an inverse regulatory relationship between their RNA expression and CpG methylation. In summary, our current study demonstrates that alteration of the global epigenome in TRAMP prostate tumor and PEITC administration suppresses PCa carcinogenesis, impacts global CpG epigenome and transcriptome, and attenuates carcinogenic pathways like cell cycle arrest and inflammation. These results may provide insights and epigenetic markers/targets for PCa prevention and treatment in human PCa patients.

Neferine improves oxidative stress and apoptosis in benign prostate hyperplasia via Nrf2-ARE pathway

BACKGROUND

Progression of Benign Prostate hyperplasia (BPH) is vulnerable to oxidative stress (OS) and prostatic enlargement among the aging males through apoptosis deregulation. Our present study aimed to investigate the effect of neferine (NF) in the regulation of oxidative stress and apoptosis in human BPH-1 cells.

METHODS

BPH epithelial cell line BPH-1 was treated with NF for 24 and 48 h. To measure oxidative stress (OS) we investigated MDA, SOD, and GST expression along with Nrf2 and its downstream gene and protein expression. Cell proliferation and apoptosis regulation was assayed with respective methods.

RESULTS

Investigation revealed NF remarkably activate Nrf2 and its downstream proteins HO-1 and NQO1 at 48 h more substantially. Nrf2/Keap1 relative gene and protein expression indicated that NF might trigger Nrf2 upregulation by decreasing Keap1 expression. Both NF concentrations (3 µM and 9 µM) were able to deplete ROS and lipid peroxidation, concurrently, up-regulated SOD and GST. NF reduced cell proliferation significantly along with the regulation of apoptotic proteins Bax, Bcl2, Cyt-C, Caspase 9, and Caspase 3 at the same time (48 h).

CONCLUSION

This study is the first to manifest that NF may potentially regulate BPH by counterbalancing between OS and apoptosis through the activation of Nrf2-ARE pathway.

Nuclear Factor Erythroid 2-Related Factor 2 in Regulating Cancer Metabolism

Significance: Nuclear factor erythroid 2 (NFE2)-related factor 2 (NFE2L2, or NRF2) is a transcription factor predominantly affecting the expression of antioxidant genes. NRF2 plays a significant role in the control of redox balance, which is crucial in cancer cells. NRF2 activation regulates numerous cancer hallmarks, including metabolism, cancer stem cell characteristics, tumor aggressiveness, invasion, and metastasis formation. We review the molecular characteristics of the NRF2 pathway and discuss its interactions with the cancer hallmarks previously listed. Recent Advances: The noncanonical activation of NRF2 was recently discovered, and members of this pathway are involved in carcinogenesis. Further, cancer-related changes (e.g., metabolic flexibility) that support cancer progression were found to be redox- and NRF2 dependent. Critical Issues: NRF2 undergoes Janus-faced behavior in cancers. The pro- or antineoplastic effects of NRF2 are context dependent and essentially based on the specific molecular characteristics of the cancer in question. Therefore, systematic investigation of NRF2 signaling is necessary to clarify its role in cancer etiology. The biggest challenge in the NRF2 field is to determine which cancers can be targeted for better clinical outcomes. Further, large-scale genomic and transcriptomic studies are missing to correlate the clinical outcome with the activity of the NRF2 system. Future Directions: To exploit NRF2 in a clinical setting in the future, the druggable members of the NRF2 pathway should be identified. In addition, it will be important to study how the modulation of the NRF2 system interferes with cytostatic drugs and their combinations.

Roles of Nrf2 in Liver Diseases: Molecular, Pharmacological, and Epigenetic Aspects

Liver diseases represent a critical health problem with 2 million deaths worldwide per year, mainly due to cirrhosis and its complications. Oxidative stress plays an important role in the development of liver diseases. In order to maintain an adequate homeostasis, there must be a balance between free radicals and antioxidant mediators. Nuclear factor erythroid 2-related factor (Nrf2) and its negative regulator Kelch-like ECH-associated protein 1 (Keap1) comprise a defense mechanism against oxidative stress damage, and growing evidence considers this signaling pathway as a key pharmacological target for the treatment of liver diseases. In this review, we provide detailed and updated evidence regarding Nrf2 and its involvement in the development of the main liver diseases such as alcoholic liver damage, viral hepatitis, steatosis, steatohepatitis, cholestatic damage, and liver cancer. The molecular and cellular mechanisms of Nrf2 cellular signaling are elaborated, along with key and relevant antioxidant drugs, and mechanisms on how Keap1/Nrf2 modulation can positively affect the therapeutic response are described. Finally, exciting recent findings about epigenetic modifications and their link with regulation of Keap1/Nrf2 signaling are outlined.

Epigenetic Regulation of NRF2/KEAP1 by Phytochemicals

Epigenetics has provided a new dimension to our understanding of nuclear factor erythroid 2–related factor 2/Kelch-like ECH-associated protein 1 (human NRF2/KEAP1 and murine Nrf2/Keap1) signaling. Unlike the genetic changes affecting DNA sequence, the reversible nature of epigenetic alterations provides an attractive avenue for cancer interception. Thus, targeting epigenetic mechanisms in the corresponding signaling networks represents an enticing strategy for therapeutic intervention with dietary phytochemicals acting at transcriptional, post-transcriptional, and post-translational levels. This regulation involves the interplay of histone modifications and DNA methylation states in the human NFE2L2/KEAP1 and murine Nfe2l2/Keap1 genes, acetylation of lysine residues in NRF2 and Nrf2, interaction with bromodomain and extraterminal domain (BET) acetyl “reader” proteins, and non-coding RNAs such as microRNA (miRNA) and long non-coding RNA (lncRNA). Phytochemicals documented to modulate NRF2 signaling act by reversing hypermethylated states in the CpG islands of NFE2L2 or Nfe2l2, via the inhibition of DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), through the induction of ten-eleven translocation (TET) enzymes, or by inducing miRNA to target the 3′-UTR of the corresponding mRNA transcripts. To date, fewer than twenty phytochemicals have been reported as NRF2 epigenetic modifiers, including curcumin, sulforaphane, resveratrol, reserpine, and ursolic acid. This opens avenues for exploring additional dietary phytochemicals that regulate the human epigenome, and the potential for novel strategies to target NRF2 signaling with a view to beneficial interception of cancer and other chronic diseases.

Demethylation of the NRF2 Promoter Protects Against Carcinogenesis Induced by Nano-SiO2

Nano silicon dioxide (Nano-SiO₂) has been widely used in industries such as the field of biomedical engineering. Despite the existing evidence that Nano-SiO₂ exposure could induce oxidative stress and inflammatory responses in multiple organ systems, the carcinogenicity of Nano-SiO₂ exposure has rarely been investigated. Thus in this study, two types of human bronchial epithelial cell lines (16HBE and BEAS-2B) were selected as in vitro models to investigate the carcinogenicity of Nano-SiO₂. Our results revealed that Nano-SiO₂ induces a malignant cellular transformation in human bronchial epithelial cells according to the soft agar colony formation assay. The carcinogenesis induced by Nano-SiO₂ was also confirmed in nude mice. By using immunofluorescence assay and high-performance capillary electrophoresis (HPCE), we observed a genome-wide DNA hypomethylation induced by Nano-SiO₂. Besides the reduced enzyme activity of total DNMTs upon Nano-SiO₂ treatment, altered expression of DNMTs and methyl-CpG binding proteins were observed. Besides, we found that the expression of NRF2 was activated by demethylation of CpG islands within the NRF2 promoter region and the overexpression of NRF2 could alleviate the carcinogenesis induced by Nano-SiO₂. Taken together, our results suggested that Nano-SiO₂ induces malignant cellular transformation with a global DNA hypomethylation, and the demethylation of NRF2 promoter activates the expression of NRF2, which plays an important role in protecting against the carcinogenesis induced by Nano-SiO₂.

Oxidative stress in alcohol-related liver disease

Alcohol consumption is one of the leading causes of the global burden of disease and results in high healthcare and economic costs. Heavy alcohol misuse leads to alcohol-related liver disease, which is responsible for a significant proportion of alcohol-attributable deaths globally. Other than reducing alcohol consumption, there are currently no effective treatments for alcohol-related liver disease. Oxidative stress refers to an imbalance in the production and elimination of reactive oxygen species and antioxidants. It plays important roles in several aspects of alcohol-related liver disease pathogenesis. Here, we review how chronic alcohol use results in oxidative stress through increased metabolism via the cytochrome P450 2E1 system producing reactive oxygen species, acetaldehyde and protein and DNA adducts. These trigger inflammatory signaling pathways within the liver leading to expression of pro-inflammatory mediators causing hepatocyte apoptosis and necrosis. Reactive oxygen species exposure also results in mitochondrial stress within hepatocytes causing structural and functional dysregulation of mitochondria and upregulating apoptotic signaling. There is also evidence that oxidative stress as well as the direct effect of alcohol influences epigenetic regulation. Increased global histone methylation and acetylation and specific histone acetylation inhibits antioxidant responses and promotes expression of key pro-inflammatory genes. This review highlights aspects of the role of oxidative stress in disease pathogenesis that warrant further study including mitochondrial stress and epigenetic regulation. Improved understanding of these processes may identify novel targets for therapy.

The role of natural products in revealing NRF2 function

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

PTEN deletion drives aberrations of DNA methylome and transcriptome in different stages of prostate cancer

Phosphatase and tensin homolog located on chromosome 10 (PTEN) is a tumor suppressor gene and one of the most frequently mutated/deleted genes in human prostate cancer (PCa). However, how PTEN deletion would impact the epigenome and transcriptome alterations remain unknown. This hypothesis was tested in a prostate-specific PTEN-/- (KO) mouse prostatic adenocarcinoma model through DNA methyl-Seq and RNA-Seq analyses. Examination of cancer genomic datasets revealed that PTEN is expressed at lower levels in PTEN-deleted tumor samples than in normal solid tissue samples. Methylome and transcriptome profiling identified several inflammatory responses and immune response signaling pathways, including NF-kB signaling, IL-6 signaling, LPS/IL-1-mediated inhibition of RXR Function, PI3K in B lymphocytes, iCOS-iCOSL in T helper cells, and the role of NFAT in regulating the immune response, were affected by PTEN deletion. Importantly, a small subset of genes that showed DNA hypermethylation or hypomethylation was correlated with decreased or increased gene expression including CXCL1. quantitative polymerase chain reaction analyses of representative genes validated the RNA-Seq results. Histopathological examinations showed that the severity of prostatic intraepithelial neoplasia and inflammation development gradually increased as PTEN null mice aged. Collectively, these findings suggest that loss of PTEN drives global changes in DNA CpG methylation and transcriptomic gene expression and highly associated with several inflammatory and immune molecular pathways during PCa development. These biomarkers could be valuable molecular targets for cancer drug discovery and development against PCa.

The Role of Nrf2 Activity in Cancer Development and Progression

Nrf2 is a transcription factor that stimulates the expression of genes which have antioxidant response element-like sequences in their promoter. Nrf2 is a cellular protector, and this principle applies to both normal cells and malignant cells. While healthy cells are protected from DNA damage induced by reactive oxygen species, malignant cells are defended against chemo- or radiotherapy. Through our literature search, we found that Nrf2 activates several oncogenes unrelated to the antioxidant activity, such as Matrix metallopeptidase 9 (MMP-9), B-cell lymphoma 2 (BCL-2), B-cell lymphoma-extra large (BCL-xL), Tumour Necrosis Factor α (TNF-α), and Vascular endothelial growth factor A (VEGF-A). We also did a brief analysis of The Cancer Genome Atlas (TCGA) data of lung adenocarcinoma concerning the effects of radiation therapy and found that the therapy-induced Nrf2 activation is not universal. For instance, in the case of recurrent disease and radiotherapy, we observed that, for the majority of Nrf2-targeted genes, there is no change in expression level. This proves that the universal, axiomatic rationale that Nrf2 is activated as a response to chemo- and radiation therapy is wrong, and that each scenario should be carefully evaluated with the help of Nrf2-targeted genes. Moreover, there were nine genes involved in lipid peroxidation, which showed underexpression in the case of new radiation therapy: ADH1A, ALDH3A1, ALDH3A2, ADH1B, GPX2, ADH1C, ALDH6A1, AKR1C3, and NQO1. This may relate to the fact that, while some studies reported the co-activation of Nrf2 and other oncogenic signaling pathways such as Phosphoinositide 3-kinases (PI3K), mitogen-activated protein kinase (MAPK), and Notch1, other reported the inverse correlation between Nrf2 and the tumor-promoter Transcription Factor (TF), Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Lastly, Nrf2 establishes its activity through interactions at multiple levels with various microRNAs. MiR-155, miR-144, miR-28, miR-365-1, miR-93, miR-153, miR-27a, miR-142, miR-29-b1, miR-340, and miR-34a, either through direct repression of Nrf2 messenger RNA (mRNA) in a Kelch-like ECH-associated protein 1 (Keap1)-independent manner or by enhancing the Keap1 cellular level, inhibit the Nrf2 activity. Keap1–Nrf2 interaction leads to the repression of miR-181c, which is involved in the Nuclear factor kappa light chain enhancer of activated B cells (NF-κB) signaling pathway. Nrf2’s role in cancer prevention, diagnosis, prognosis, and therapy is still in its infancy, and the future strategic planning of Nrf2-based oncological approaches should also consider the complex interaction between Nrf2 and its various activators and inhibitors.

Anthocyanin Delphinidin Prevents Neoplastic Transformation of Mouse Skin JB6 P+ Cells: Epigenetic Re-activation of Nrf2-ARE Pathway

Redox imbalance is a major contributor to the pathogenesis of melanoma and nonmelanoma skin cancer. Activation of the nuclear factor E2-related factor 2 (Nrf2) antioxidant responsive element (ARE) pathway is an intrinsic defense mechanism against oxidative stress. Flavonoids such as anthocyanidins, which are found abundantly in fruits and vegetables, have been shown to activate Nrf2. However, the epigenetic and genetic mechanisms by which anthocyanidins modulate the Nrf2-ARE pathway remain poorly understood in the context of skin cancer. In this study, delphinidin, one of the most potent and abundant anthocyanidins in berries, significantly inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced neoplastic cell transformation in mouse epidermal JB6 P+ cells by 69.4 to 99.4%. The mechanism was elucidated based on observations of increased ARE-driven luciferase activity and elevated mRNA and protein expression of Nrf2 downstream genes, such as heme oxygenase-1 (Ho-1), in JB6 P+ cells. Activation of the Nrf2-ARE pathway was correlated with demethylation of 15 CpG sites in the mouse Nrf2 promoter region between nt - 1226 and - 863 from the transcription start site. The reduced CpG methylation ratio in the Nrf2 promoter region was consistent with observed decreases in the protein expression of DNA methyltransferases 1 (DNMT1), DNMT3a, and class I/II histone deacetylases (HDACs). Overall, our results suggest that delphinidin, an epigenetic demethylating agent of the Nrf2 promoter, can activate the Nrf2-ARE pathway, which can be applied as a potential skin cancer chemopreventive agent.

Potential Applications of NRF2 Inhibitors in Cancer Therapy

The NRF2/KEAP1 pathway represents one of the most important cell defense mechanisms against exogenous or endogenous stressors. Indeed, by increasing the expression of several cytoprotective genes, the transcription factor NRF2 can shelter cells and tissues from multiple sources of damage including xenobiotic, electrophilic, metabolic, and oxidative stress. Importantly, the aberrant activation or accumulation of NRF2, a common event in many tumors, confers a selective advantage to cancer cells and is associated to malignant progression, therapy resistance, and poor prognosis. Hence, in the last years, NRF2 has emerged as a promising target in cancer treatment and many efforts have been made to identify therapeutic strategies aimed at disrupting its prooncogenic role. By summarizing the results from past and recent studies, in this review, we provide an overview concerning the NRF2/KEAP1 pathway, its biological impact in solid and hematologic malignancies, and the molecular mechanisms causing NRF2 hyperactivation in cancer cells. Finally, we also describe some of the most promising therapeutic approaches that have been successfully employed to counteract NRF2 activity in tumors, with a particular emphasis on the development of natural compounds and the adoption of drug repurposing strategies.

Redox regulation by NRF2 in aging and disease

NRF2, a transcription factor that has been deemed the master regulator of cellular redox homeostasis, declines with age. NRF2 transcriptionally upregulates genes that combat oxidative stress; therefore, loss of NRF2 allows oxidative stress to go unmitigated and drive the aging phenotype. Oxidative stress is a common theme among the key features associated with the aging process, collectively referred to as the "Hallmarks of Aging", as it disrupts proteostasis, alters genomic stability, and leads to cell death. In this review, we outline the role that oxidative stress and the reduction of NRF2 play in each of the Hallmarks of Aging, including how they contribute to the onset of neurodegenerative disorders, cancer, and other age-related pathologies.

Effects of sulforaphane in the central nervous system

Sulforaphane (SFN) is an active component extracted from vegetables like cauliflower and broccoli. Activation of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling is a common mechanism for the anti-oxidative and anti-inflammatory activity of some herb-derived compounds, such as icariin and berberine. However, due to its peculiar ability in Nrf2 activation, SFN is recognized as an activator of Nrf2 and recommended as a supplementation for prevention and/or treatment of disorders like neoplasm and heart failure. In the central nervous system (CNS), the prophylactic and/or therapeutic effects of SFN have been revealed in recent years. For example, it has been reported to prevent the progression of Alzheimer's disease, Parkinson's disease, cerebral ischemia, Huntington's disease, multiple sclerosis, epilepsy, and psychiatric disorders via promotion of neurogenesis or inhibition of oxidative stress and neuroinflammation. SFN is also implicated in reversing cognition, learning, and memory impairment in rodents induced by scopolamine, lipopolysaccharide, okadaic acid, and diabetes. In models of neurotoxicity, SFN has been shown to suppress neurotoxicity induced by a wide range of toxic factors, such as hydrogen peroxide, prion protein, hyperammonemia, and methamphetamine. To date, no consolidated source of knowledge about the pharmacological effects of SFN in the CNS has been presented in the literature. In this review, we summarize and discuss the pharmacological effects of SFN as well as their possible mechanisms in prevention and/or therapy of disorders afflicting the CNS, aiming to get a further insight into how SFN affects the pathophysiological process of CNS disorders.

Modulating NRF2 in Disease: Timing Is Everything

The transcription factor nuclear factor erythroid 2 (NF-E2)-related factor 2 (NRF2) is a central regulator of redox, metabolic, and protein homeostasis that intersects with many other signaling cascades. Although the understanding of the complex nature of NRF2 signaling continues to grow, there is only one therapeutic targeting NRF2 for clinical use, dimethyl fumarate, used for the treatment of multiple sclerosis. The discovery of new therapies is confounded by the fact that NRF2 levels vary significantly depending on physiological and pathological context. Thus, properly timed and targeted manipulation of the NRF2 pathway is critical in creating effective therapeutic regimens. In this review, we summarize the regulation and downstream targets of NRF2. Furthermore, we discuss the role of NRF2 in cancer, neurodegeneration, and diabetes as well as cardiovascular, kidney, and liver disease, with a special emphasis on NRF2-based therapeutics, including those that have made it into clinical trials.

Nrf2: Molecular and epigenetic regulation during aging

Increase in life-span is commonly related with age-related diseases and with gradual loss of genomic, proteomic and metabolic integrity. Nrf2 (Nuclear factor-erythroid 2-p45 derived factor 2) controls the expression of genes whose products include antioxidant proteins, detoxifying enzymes, drug transporters and numerous cytoprotective proteins. Several experimental approaches have evaluated the potential regulation of the transcription factor Nrf2 to enhance the expression of genes that contend against accumulative oxidative stress and promote healthy aging. Negative regulators of Nrf2 that act preventing it´s binding to DNA-responsive elements, have been identified in young and adult animal models. However, it is not clearly established if Nrf2 decreased activity in several models of aging results from disruption of that regulation. In this review, we present a compilation of evidences showing that changes in the levels or activity of Keap1 (Kelch-like ECH associated protein 1), GSK-3β (glycogen synthase kinase-3), Bach1, p53, Hrd1 (E3 ubiquitin ligase) and miRNAs might impact on Nrf2 activity during elderly. We conclude that understanding Nrf2 regulatory mechanisms is essential to develop a rational strategy to prevent the loss of cellular protection response during aging.

Importance of the Keap1-Nrf2 pathway in NSCLC: Is it a possible biomarker?

Worldwide, lung cancer remains the most common cause of cancer-related mortality, with non-small cell lung cancer (NSCLC) accounting for 85% of all diagnosed lung cancer cases. Chemotherapy is considered the standard of care for patients with advanced NSCLC; however, the tumors can develop mechanisms that inactivate these drugs. Comparative genomic analyses have revealed that disruptions in the kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid-2-related factor-2 (Nrf2) pathway are frequent in NSCLC, although Nrf2 mutations occur less frequently than Keap1 mutations. As the Keap1-Nrf2 pathway appears to be a primary regulator of key cellular processes that aid to resist the action of chemotherapy drugs, the clinical implementation of Nrf2 inhibitors in patients with advanced NSCLC may be a useful therapeutic approach for patients harboring KEAP1-NRF2 mutations. The aim of the present review was to highlight findings of how constitutive Nrf2 activation may be a specific biomarker for predicting patients most likely to benefit from classical chemotherapy drugs, overall improving patient survival rate.

The dietary flavone luteolin epigenetically activates the Nrf2 pathway and blocks cell transformation in human colorectal cancer HCT116 cells

Colorectal cancer remains a leading malignancy in humans. The importance of epigenetic modification in the development of this disease is now being recognized. The reversible and dynamic nature of epigenetic modifications provides a promising strategy in colorectal cancer chemoprevention and treatment. Luteolin (LUT), a flavone dietary phytochemical, can modulate various signaling pathways involved in carcinogenesis. Many studies have demonstrated that LUT inhibits colorectal carcinogenesis by activating the Nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant-responsive element (ARE) pathway. However, the potential epigenetic mechanism underlying Nrf2/ARE pathway activation remains unclear. In this study, we aimed to explore the anticancer potential of LUT in human colon cancer cells and the epigenetic regulation of the Nrf2/ARE pathway. Specifically, our data showed that LUT suppressed cell proliferation and cellular transformation of HCT116 and HT29 cells in a dose-dependent manner. Additionally, quantitative real-time polymerase chain reaction and Western blot analysis were performed to determine the mRNA and protein expression of Nrf2 and its downstream genes after LUT treatment. Bisulfite genomic sequencing revealed that methylation of the Nrf2 promoter region was decreased by LUT, corresponding with the increased mRNA expression of Nrf2. Decreased protein levels and enzyme activities of epigenetic modifying enzymes, such as DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), were also observed in LUT-treated HCT116 cells. In summary, our findings suggest that LUT may exert its antitumor activity in part via epigenetic modifications of the Nrf2 gene with subsequent induction of its downstream antioxidative stress pathway.

Anti-Inflammatory and Antioxidant Effects of Kelong-Capsule on Testosterone-Induced Benign Prostatic Hyperplasia in Rats

Benign prostatic hyperplasia (BPH) is a common disease in the current ageing male population. This research aims to study the effects of Kelong-Capsules (KLC) on testosterone-induced BPH. Thirty rats were randomly divided into normal group, model group, and three treatment groups. Three treatment groups were given KLC (3.6 g/kg), KLC (7.2 g/kg), and finasteride (0.9 mg/kg), respectively, for 28 days after establishing the animal model. The BPH rat models were evaluated by Traditional Chinese Medicine (TCM) symptoms and prostate index (PI). Results indicated that three treatment groups all alleviated the pathological changes of prostate and kidney at different levels. Compared with the model group, the PI of the groups treated with KLC (7.2 g/kg) and finasteride decreased significantly. The expressions of NF-E2 related factor 2 (Nrf-2) and quinine oxidoreductase (NQO1) in the group treated with KLC (3.6 g/kg) increased markedly (p < 0.01). The cyclooxygenase-2 (COX-2) protein expression of the group treated with KLC (7.2 g/kg) was increased (p < 0.01). In conclusion, KLC could obviously inhibit the growth of prostate, and KLC (3.6 g/kg) could promote the expressions of Nrf2 and NQO1.

Anticancer Activity of Sulforaphane: The Epigenetic Mechanisms and the Nrf2 Signaling Pathway

Sulforaphane (SFN), a compound derived from cruciferous vegetables that has been shown to be safe and nontoxic, with minimal/no side effects, has been extensively studied due to its numerous bioactivities, such as anticancer and antioxidant activities. SFN exerts its anticancer effects by modulating key signaling pathways and genes involved in the induction of apoptosis, cell cycle arrest, and inhibition of angiogenesis. SFN also upregulates a series of cytoprotective genes by activating nuclear factor erythroid-2- (NF-E2-) related factor 2 (Nrf2), a critical transcription factor activated in response to oxidative stress; Nrf2 activation is also involved in the cancer-preventive effects of SFN. Accumulating evidence supports that epigenetic modification is an important factor in carcinogenesis and cancer progression, as epigenetic alterations often contribute to the inhibition of tumor-suppressor genes and the activation of oncogenes, which enables cells to acquire cancer-promoting properties. Studies on the mechanisms underlying the anticancer effects of SFN have shown that SFN can reverse such epigenetic alterations in cancers by targeting DNA methyltransferases (DNMTs), histone deacetyltransferases (HDACs), and noncoding RNAs. Therefore, in this review, we will discuss the anticancer activities of SFN and its mechanisms, with a particular emphasis on epigenetic modifications, including epigenetic reactivation of Nrf2.

Epigenetic versus Genetic Deregulation of the KEAP1/NRF2 Axis in Solid Tumors: Focus on Methylation and Noncoding RNAs

Oxidative and electrophilic changes in cells are mainly coordinated by the KEAP1/NRF2 (Kelch-like erythroid-derived cap-n-collar homology- (ECH-) associated protein-1/nuclear factor (erythroid-derived 2)-like 2) axis. The physical interaction between these two proteins promotes the expression of several antioxidant defense genes in response to exogenous and endogenous insults. Recent studies demonstrated that KEAP1/NRF2 axis dysfunction is also strongly related to tumor progression and chemo- and radiotherapy resistance of cancer cells. In solid tumors, the KEAP1/NRF2 system is constitutively activated by the loss of KEAP1 or gain of NFE2L2 functions that leads to its nuclear accumulation and enhances the transcription of many cytoprotective genes. In addition to point mutations, epigenetic abnormalities, as aberrant promoter methylation, and microRNA (miRNA) and long noncoding RNA (lncRNA) deregulation were reported as emerging mechanisms of KEAP1/NRF2 axis modulation. This review will summarize the current knowledge about the epigenetic mechanisms that deregulate the KEAP1/NRF2 cascade in solid tumors and their potential usefulness as prognostic and predictive molecular markers.

Epigenetic modulation of Nrf2 and Ogg1 gene expression in testicular germ cells by methyl parathion exposure

Methyl parathion (Me-Pa) is an oxidizing organophosphate (OP) pesticide that generates reactive oxygen species (ROS) through its biotransformation. Some studies have also suggested that OP pesticides have the capacity to alkylate biomolecules, including DNA. In general, DNA methylation in gene promoters represses transcription. NRF2 is a key transcription factor that regulates the expression of antioxidant, metabolic and detoxifying genes through the antioxidant response element (ARE) situated in promoters of regulated genes. Furthermore, DNA repair genes, including 8-oxoguanine DNA glycosidase (OGG1), have been proposed as NRF2 target genes. Me-Pa exposure produces poor semen quality, genetic and oxidative damage in sperm cells, and reduced fertility. However, the Me-Pa effects on the methylation status and the expression of antioxidant (Nrf2) or DNA repair (Ogg1) genes in male germ cells have not been investigated. Therefore, mice were exposed to Me-Pa to evaluate the global (%5-mC) and specific methylation of Nrf2 and Ogg1 genes using pyrosequencing, gene expression, and total protein carbonylation in male germ cells. The results showed that Me-Pa significantly decreased the global DNA methylation pattern and significantly increased the methylation of two CpG sites within Ogg1 promoter and one CpG site within Nrf2 promoter. In addition, Ogg1 or Nrf2 expression did not change after Me-Pa exposure despite the oxidative damage produced. Altogether, our data suggest that Me-Pa toxicity alters Ogg1 and Nrf2 promoter methylation in male germ cells that may be modulating their gene expression.

A novel mechanism of action of HER2 targeted immunotherapy is explained by inhibition of NRF2 function in ovarian cancer cells

Nuclear erythroid related factor-2 (NRF2) is known to promote cancer therapeutic detoxification and crosstalk with growth promoting pathways. HER2 receptor tyrosine kinase is frequently overexpressed in cancers leading to uncontrolled receptor activation and signaling. A combination of HER2 targeting monoclonal antibodies shows greater anticancer efficacy than the single targeting antibodies, however, its mechanism of action is largely unclear. Here we report novel actions of anti-HER2 drugs, Trastuzumab and Pertuzumab, involving NRF2.

HER2 targeting by antibodies inhibited growth in association with persistent generation of reactive oxygen species (ROS), glutathione (GSH) depletion, reduction in NRF2 levels and inhibition of NRF2 function in ovarian cancer cell lines. The combination of antibodies produced more potent effects than single antibody alone; downregulated NRF2 substrates by repressing the Antioxidant Response (AR) pathway with concomitant transcriptional inhibition of NRF2. We showed the antibody combination produced increased methylation at the NRF2 promoter consistent with repression of NRF2 antioxidant function, as HDAC and methylation inhibitors reversed such produced transcriptional effects. These findings demonstrate a novel mechanism and role for NRF2 in mediating the response of cancer cells to the combination of Trastuzumab and Pertuzumab and reinforce the importance of NRF2 in drug resistance and as a key anticancer target.

Fucoxanthin Elicits Epigenetic Modifications, Nrf2 Activation and Blocking Transformation in Mouse Skin JB6 P+ Cells

Nuclear factor erythroid-2-related factor-2 (Nrf2 or NFE2L2) is a master regulator of the anti-oxidative stress response, which is involved in the defense against many oxidative stress/inflammation-mediated diseases, including anticancer effects elicited by an increasing number of natural products. Our previous studies showed that the epigenetic modification of the Nrf2 gene plays a key role in restoring the expression of Nrf2. In this study, we aimed to investigate the epigenetic regulation of Nrf2 by astaxanthin (AST) and fucoxanthin (FX), carotenoids which are abundant in microalgae and seaweeds, in mouse skin epidermal JB6 P+ cells. FX induced the anti-oxidant response element (ARE)-luciferase and upregulated the mRNA and protein levels of Nrf2 and Nrf2 downstream genes in HepG2-C8 cells overexpressing the ARE-luciferase reporter. Both FX and AST decreased colony formation in 12-Otetradecanoylphorbol-13-acetate (TPA)-induced transformation of JB6 P+ cells. FX decreased the methylation of the Nrf2 promoter region in the JB6 P+ cells by the bisulfite conversion and pyrosequencing. Both FX and AST significantly reduced DNA methyltransferase (DNMT) activity but did not affect histone deacetylase (HDAC) activity in JB6 P+ cells. In summary, our results show that FX activates the Nrf2 signaling pathway, induces the epigenetic demethylation of CpG sites in Nrf2 and blocks the TPA-induced transformation of JB6 P+ cells, indicating the potential health-promoting effects of FX in skin cancer prevention.

Epigenetic modification of Nrf2 by sulforaphane increases the antioxidative and anti-inflammatory capacity in a cellular model of Alzheimer's disease

Sulforaphane was reported to exert neuroprotective effects via upregulating expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and has received increasing attention as an alternative candidate for treatment of Alzheimer's disease (AD). However, the mechanism to account for Nrf2 upregulation by sulforaphane in AD remains unknown. Herein, we found that sulforaphane upregulated Nrf2 expression and promoted Nrf2 nuclear translocation via decreasing DNA methylation levels of the Nrf2 promoter in mouse neuroblastoma N2a cells stably expressing human Swedish mutant amyloid precursor protein (N2a/APPswe cells), a cellular model of AD. Furthermore, sulforaphane (1.25 and 2.5 μM) decreased the levels of amyloid β 1-40 (Aβ_1-40) (21.7% and 33.4% decrease for intracellular Aβ_1-40; 22.0% and 30.2% decrease in culture medium), Aβ_1-42 (26.4% and 42.9% decrease for intracellular Aβ_1-42; 25.8% and 43.8% decrease in culture medium), reactive oxygen species (15.0% and 28.5% decrease), and malondialdehyde (MDA) (34.4% and 39.2% decrease) and increased superoxide dismutase (SOD) (60.0% and 89.3% increase) activity in N2a/APPswe cells. Sulforaphane also decreased the levels of pro-inflammatory cytokines interleukin 1β (IL-1β) (16.5% and 33.6% decrease) and IL-6 (15.6% and 26.1% decrease) and reduced phosphorylated nuclear factor-κB (NF-κB) p65 (19.2% and 32.2% decrease), cyclooxygenase-2 (COX-2) (20.5% and 28.6% decrease), and iNOS protein (40.2% and 54.7% decrease) expression levels in N2a/APPswe cells. Our study suggested that sulforaphane upregulated the expression of Nrf2 and promoted the nuclear translocation of Nrf2 by decreasing DNA demethylation levels of the Nrf2 promoter, thus leading to antioxidative and anti-inflammatory effects in a cellular model of AD.

Role of histone acetylation in activation of nuclear factor erythroid 2-related factor 2/heme oxygenase 1 pathway by manganese chloride

Manganese neurotoxicity is characterized by Parkinson-like symptoms with degeneration of dopaminergic neurons in the basal ganglia as the principal pathological feature. Manganese neurotoxicity studies may contribute to a good understanding of the mechanism of Parkinson's disease (PD). In this study, we first confirmed that MnCl₂ can promote the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) protein in the nucleus or cytoplasm while increasing the binding activity of Nrf2 and antioxidant response elements, further promoting the expression of downstream target gene heme oxygenase 1 (HO-1) and leading to increase levels of reactive oxygen species (ROS) and reduce the levels of reduced glutathione (GSH). Second, we investigated the role of histone acetylation in the activation of Nrf2/HO-1 pathway by manganese chloride in rat adrenal pheochromocytoma (PC12) cells. Histone acetyltransferase inhibitor (anacardic acid) and histone deacetylase inhibitor (trichostatin A, TSA) were used as pretreatment reagents to adjust the level of histone acetylation. Here, we show that downregulation of histone acetylation can inhibit Mn-induced Nrf2 nuclear translocation and further inhibits the Mn-activated Nrf2/HO-1 pathway. This downregulation also promotes manganese-induced increase of ROS and decrease of GSH in neurons. These results suggest that the downregulation of histone acetylation may play an important role in the neurotoxicity caused by manganese and that TSA may provide new ideas and targets in treating manganese-induced Parkinson's syndrome and PD.

Nrf2: a potential therapeutic target for naturally occurring anticancer drugs?

INTRODUCTION

Nuclear factor (erythroid-derived-2)-like 2 is one of the most efficient cytoprotective rheostats against exogenous or endogenous oxidative insults. At present, the modulation of the Nrf2 pathway represents an interesting and highly explored strategy in the oncological area. Area covered: In this review, we present and discuss the different modulation of the Nrf2 pathway by some natural compounds with a well demonstrated anticancer activity, and critically analyze the challenges associated with the development of an Nrf2-based anticancer strategy. Expert opinion: Many natural compounds with a well-defined anticancer activity are able to modulate this pathway. Both Nrf2 inducers and inhibitors can be useful as anticancer strategy. However, since Nrf2 modulates many networks potentially involved in the detoxification process of anticancer drugs, its activation in cancer cells could lead to chemoresistance. The switch between a beneficial or detrimental role of Nrf2 in cancer cells essentially depends on the tight control of its activity, the specific conditions of tumor microenvironment, and cell type. In line with the paucity of clear data related to the mechanisms underpinning the role of Nrf2 in cancer development and chemoresistance, discovery and development of Nrf2-based strategies is one of the most critical and challenging assignments for fighting cancers.

Protection against oxidative stress mediated by the Nrf2/Keap1 axis is impaired in Primary Biliary Cholangitis

In response to oxidative stress, nuclear factor (erythroid-derived 2)-like2 (Nrf2) induces expression of cytoprotective genes. The Nrf2 pathway is controlled by microRNAs and Kelch-like ECH-associated protein1 (Keap1). Nrf2 is stabilized when Keap1 is degraded through the autophagy pathway in a p62-dependent manner. The inhibition of autophagy causes protein accumulation, and Keap1 is inactivated by binding to p62. We investigated the role of the Nrf2/Keap1 axis in the amelioration of oxidative stress in primary biliary cholangitis (PBC). Liver specimens from patients with PBC, with (n = 24) or without cirrhosis (n = 14), and from controls (n = 16) were used for molecular analyses. We found that Nrf2 protein levels were elevated in PBC compared to controls, but Nrf2 gene expression was significantly reduced in cirrhotic PBC. Nrf2 target gene products, HO-1 and GCLC proteins, were reduced compared to controls and reduction of Nrf2 gene expression was associated with elevated levels of microRNA-132 and microRNA-34a. Both Keap1 and p62 protein levels were substantially increased in PBC compared to controls. PBC was associated with reduced Nrf2 expression and autophagy deterioration and these impairments were more advanced in patients with cirrhosis. Aberrant Nrf2/Keap1 system integrity may affect self-defence mechanisms against oxidative stress in PBC.

Oxidative stress indicated by elevated expression of Nrf2 and 8-OHdG promotes hepatocellular carcinoma progression

Reactive oxygen species (ROS) is excessively generated in tumors creating an oxidative stress in tumor microenvironment. We investigated hepatic expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and 8-hydroxydeoxyguanosine (8-OHdG) in hepatocellular carcinoma (HCC) patients, and asked if ROS epigenetically upregulated Nrf2 and enhanced aggressiveness in HCC cells. Expression of Nrf2 (n = 100) and 8-OHdG (n = 53) was remarkably increased in HCC tissues compared with the noncancerous hepatic tissues. Elevated expression of 8-OHdG was associated with poor survival in HCC patients. H₂O₂, as ROS representative, provoked oxidative stress in HepG2 cells, indicated by increased protein carbonyl content and decreased total antioxidant capacity. Nrf2 expression and 8-OHdG formation were markedly increased in the H₂O₂-treated cells compared with the untreated control. Co-treatment with antioxidants, tocopheryl acetate (TA) and S-adenosylmethionine (SAM) effectively attenuated expression of Nrf2 and 8-OHdG in H₂O₂-treated cells. HepG2 cells treated with H₂O₂ had significantly higher migration and invasion capabilities than the untreated control cells, and this aggressiveness was significantly inhibited by TA and SAM. Bisulfite sequencing revealed that CpG dinucleotides in Nrf2 promoter were unmethylated in the H₂O₂-treated cells similar to the untreated control. In conclusion, robust histological evidence of increased antioxidative response and oxidative DNA damage in human HCC tissues was demonstrated. Elevated oxidative DNA lesion 8-OHdG was associated with shorter survival. Experimentally, ROS enhanced Nrf2 expression, 8-OHdG formation and tumor progression in HCC cells. These effects were inhibited by antioxidants. Therefore, oxidative stress-reducing regimens might be beneficial to diminish the ROS-induced HCC progression.

The Keap1-Nrf2 pathway: promising therapeutic target to counteract ROS-mediated damage in cancers and neurodegenerative diseases

The overproduction of reactive oxygen species (ROS) generates oxidative stress in cells. Oxidative stress results in various pathophysiological conditions, especially cancers and neurodegenerative diseases (NDD). The Keap1-Nrf2 [Kelch-like ECH-associated protein 1-nuclear factor (erythroid-derived 2)-like 2] regulatory pathway plays a central role in protecting cells against oxidative and xenobiotic stresses. The Nrf2 transcription factor activates the transcription of several cytoprotective genes that have been implicated in protection from cancer and NDD. The Keap1-Nrf2 system acts as a double-edged sword: Nrf2 activity protects cells and makes the cell resistant to oxidative and electrophilic stresses, whereas elevated Nrf2 activity helps in cancer cell survival and proliferation. Several groups in the recent past, from both academics and industry, have reported the potential role of Nrf2-mediated transcription to protect from cancer and NDD, resulting from mechanisms involving xenobiotic and oxidative stress. It suggests that the Keap1-Nrf2 system is a potential therapeutic target to combat cancer and NDD by designing and developing modulators (inhibitors/activators) for Nrf2 activation. Herein, we review and discuss the recent advancement in the regulation of the Keap1-Nrf2 system, its role under physiological and pathophysiological conditions including cancer and NDD, and modulators design strategies for Nrf2 activation.