Genetic versus chemoprotective activation of Nrf2 signaling: overlapping yet distinct gene expression profiles between Keap1 knockout and triterpenoid-treated mice

NRF-2 and nonalcoholic fatty liver disease

Currently, chronic liver diseases have conditioned morbidity and mortality, many of these with a metabolic, toxicologic, immunologic, viral, or other etiology. Thus, a transcription factor that has been of huge importance for biomedical research is NRF-2. The latter is considered a principal component of the antioxidant mechanism, and it has been acknowledged that it impairs the function of NRF-2 in many liver diseases and that it forms an essential part of the pathologic changes that occur in the liver to contain inflammation and damage. Within the investigations and experiments carried out, there are isolated drugs, many of them related to plants and natural extracts that possess antioxidant properties through the NRF-2 signaling pathway, or even involving the stimulation of the transcription target proteins of NRF-2. Notwithstanding all of these experimental findings, to date there is not sufficient clinical evidence to justify the use of NRF-2 in medical practice.

Butein inhibits lipogenesis in Caenorhabditis elegans

Butein, a flavonoid found in annatto seeds and lacquer trees, may be used for many health benefits, including the prevention of obesity. However, its anti-obesity effects are not completely understood; in particular, the effects of butein on the regulation of lipid metabolism have not been explained. Thus, the goal of the current study was to determine the effects of butein on lipid metabolism in Caenorhabditis elegans, which is a multi-organ nematode used as an animal model in obesity research. Butein at 70 μM reduced triglyceride content by 27% compared to the control without altering food intake and energy expenditure. The reduced triglyceride content by butein was associated with the downregulation of sbp-1, fasn-1, and fat-7, the lipogenesis-related homologs of sterol regulatory element-binding proteins, fatty acid synthase and stearoyl-CoA desaturase, respectively. Furthermore, fat-7 and skn-1, a homolog of nuclear respiratory factors, were identified as genetic requirements for butein's effects on triglyceride content in C. elegans. The effects of butein on sbp-1 and fasn-1 were dependent on skn-1, but the downregulation of fat-7 was independent of skn-1. These results suggest that the inhibitory effects of butein on lipogenesis are via SKN-1- and FAT-7-dependent pathways in C. elegans.

Current Landscape of NRF2 Biomarkers in Clinical Trials

The transcription factor NF-E2 p45-related factor 2 (NRF2; encoded by NFE2L2) plays a critical role in the maintenance of cellular redox and metabolic homeostasis, as well as the regulation of inflammation and cellular detoxication pathways. The contribution of the NRF2 pathway to organismal homeostasis is seen in many studies using cell lines and animal models, raising intense attention towards targeting its clinical promise. Over the last three decades, an expanding number of clinical studies have examined NRF2 inducers targeting an ever-widening range of diseases. Full understanding of the pharmacokinetic and pharmacodynamic properties of drug candidates rely partly on the identification, validation, and use of biomarkers to optimize clinical applications. This review focuses on results from clinical trials with four agents known to target NRF2 signaling in preclinical studies (dimethyl fumarate, bardoxolone methyl, oltipraz, and sulforaphane), and evaluates the successes and limitations of biomarkers focused on expression of NRF2 target genes and others, inflammation and oxidative stress biomarkers, carcinogen metabolism and adduct biomarkers in unavoidably exposed populations, and targeted and untargeted metabolomics. While no biomarkers excel at defining pharmacodynamic actions in this setting, it is clear that these four lead clinical compounds do touch the NRF2 pathway in humans.

Ameliorative effects and molecular mechanisms of vine tea on western diet-induced NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a disease that is prevalent worldwide, and its prevention by dietary administration has recently been considered as an important strategy. In this study, we administered mice with vine tea polyphenol (VTP) extracted from Ampelopsis grossedentata, a Chinese herb, to investigate the preventive effect on western diet (WD)-induced NAFLD. Male C57BL/6N mice were fed either a normal diet (ND) or WD with or without VTP for 12 weeks. The results revealed that VTP supplementation decreased the serum levels of cholesterol and triglycerides, and reduced the accumulation of hepatic lipid droplets caused by WD. Molecular data revealed that VTP enhanced fatty acid oxidation by reactivating the WD-suppressed phosphorylation of AMP-activated protein kinaseα (AMPKα) and the expressions of peroxisome proliferator-activated receptor alpha (PPARα), carnitine palmitoyl transferase IA (CPT1A) and cytochrome P450, family 4, subfamily a1 (CYP4A1). VTP inhibited hepatic lipogenesis by reducing the WD-enhanced level of mature sterol regulatory element-binding protein 1 (SREBP1) and fatty acid synthase (FAS). Moreover, VTP activated nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated expressions of hemeoxygenase-1 (HO-1) and quinone oxidoreductase (NQO1), and reduced hepatic TBARS levels to prevent hepatic oxidative stress. On the other hand, VTP also increased intestinal zonula occludens-1 (ZO-1) expression and the relative abundance of gut Akkermansia, and reduced the ratio of Firmicutes/Bacteroidetes. Thus, VTP might prevent WD-induced NAFLD by balancing fatty acid oxidation and lipogenesis, hepatic oxidative stress, and gut microbiome, at least. These results suggest that vine tea, containing a high content of the bioactive compound dihydromyricetin, is a potential food resource for preventing NAFLD.

Hepatoprotective Effect of Pericarpium zanthoxyli Extract Is Mediated via Antagonism of Oxidative Stress

Pericarpium zanthoxyli has been extensively used in traditional Oriental medicine to treat gastric disorders and has anti-inflammatory and antioxidative activities. Therefore, the present study examined a possible hepatoprotective effect of a P. zanthoxyli extract (PZE) and investigated the underlying molecular mechanisms. We employed an in vitro model of arachidonic acid (AA) + iron-induced hepatocyte damage and an in vivo model of CCl₄-induced liver injury to assess the effects of PZE and evaluated the relevant molecular targets using biochemical assays, flow cytometry analysis, Western blot, and histopathological analysis. The PZE inhibited AA + iron-induced hepatotoxicity in HepG2 cells, improved mitochondrial dysfunction, and reversed an increase in the cellular H₂O₂ production and a decrease in the reduced GSH levels induced by AA + iron. Treatment with either 30 or 100 μg/ml PZE significantly increased the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) protein, and the latter dose also increased the antioxidant response element- (ARE-) driven luciferase activity and enhanced the protein expressions of glutamate-cysteine ligase catalytic subunit and NAD(P)H:quinone oxidoreductase 1. In addition, treatment with 100 μg/ml PZE for 3 or 6 h increased the phosphorylation rates of Nrf2 and the extracellular signal-regulated kinase. In the in vivo experiment, oral treatment with both 100 and 300 mg/kg PZE inhibited the plasma aspartate aminotransferase activity, and the latter also inhibited the plasma alanine aminotransferase activity. In addition, both doses of PZE ameliorated the parenchymal degeneration and necrosis in the liver induced by CCl₄ administration, which was associated with reduced expressions of cleaved caspase-3, cleaved poly (ADP-ribose) polymerase, nitrotyrosine, and 4-hydroxynonenal by PZE. These findings suggest that PZE has protective effects against hepatotoxicity both in vitro and in vivo, which are mainly mediated via its antioxidant activity.

Molecular Study on the Potential Protective Effects of Bee Venom against Fructose-Induced Nonalcoholic Steatohepatitis in Rats

BACKGROUND

There is a causative relation between the increased hepatic steatohepatitis prevalence and sweeteners intake, fructose in particular. Despite an increasing understanding of the mechanisms of nonalcoholic steatohepatitis (NASH) pathogenesis, there are no drugs approved for it.

OBJECTIVES

Evaluate the effect of bee venom (BV) treatment on the fructose-induced NASH in rats and demonstrate its possible molecular mechanisms.

METHODS

NASH was induced in rats by 10% fructose in drinking water for 8 weeks. BV was administered (0.1 mg/kg, i.p.) 3 times per week during the last 2 weeks of the experiment. Sera were used for the determination of lipids, cholesterol, glucose, insulin, and liver enzymes. Hepatic gene expressions of farnesoid X receptor (FXR)α and the liver X receptor (LXR) were determined. Hepatic sterol regulatory element-binding protein (SREBP)1/2, oxidative stress, and inflammation parameters were measured. Liver parts were used for histopathological examination. Small intestine was removed for the determination of tight junction proteins.

RESULTS

Fructose caused overt histological damage in the liver, and this was associated with parallel changes in all parameters measured. BV effectively prevented these changes, presumably through amelioration of hepatic SREBP1/2, LXR, and FXRα expression as well as intestinal tight junction proteins.

CONCLUSION

These findings support the therapeutic usefulness of BV, a remedy with a favorable safety profile, in the prevention of fructose-induced NASH.

NRF2, a Transcription Factor for Stress Response and Beyond

Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that regulates the cellular defense against toxic and oxidative insults through the expression of genes involved in oxidative stress response and drug detoxification. NRF2 activation renders cells resistant to chemical carcinogens and inflammatory challenges. In addition to antioxidant responses, NRF2 is involved in many other cellular processes, including metabolism and inflammation, and its functions are beyond the originally envisioned. NRF2 activity is tightly regulated through a complex transcriptional and post-translational network that enables it to orchestrate the cell’s response and adaptation to various pathological stressors for the homeostasis maintenance. Elevated or decreased NRF2 activity by pharmacological and genetic manipulations of NRF2 activation is associated with many metabolism- or inflammation-related diseases. Emerging evidence shows that NRF2 lies at the center of a complex regulatory network and establishes NRF2 as a truly pleiotropic transcription factor. Here we summarize the complex regulatory network of NRF2 activity and its roles in metabolic reprogramming, unfolded protein response, proteostasis, autophagy, mitochondrial biogenesis, inflammation, and immunity.

The Molecular Mechanisms Regulating the KEAP1-NRF2 Pathway

The KEAP1-NRF2 pathway is the principal protective response to oxidative and electrophilic stresses. Under homeostatic conditions, KEAP1 forms part of an E3 ubiquitin ligase, which tightly regulates the activity of the transcription factor NRF2 by targeting it for ubiquitination and proteasome-dependent degradation. In response to stress, an intricate molecular mechanism facilitated by sensor cysteines within KEAP1 allows NRF2 to escape ubiquitination, accumulate within the cell, and translocate to the nucleus, where it can promote its antioxidant transcription program. Recent advances have revealed that KEAP1 contains multiple stress sensors and inactivation modalities, which together allow diverse cellular inputs, from oxidative stress and cellular metabolites to dysregulated autophagy, to regulate NRF2 activity. This integration of the KEAP1-NRF2 system into multiple cellular signaling and metabolic pathways places NRF2 activation as a critical regulatory node in many disease phenotypes and suggests that the pharmaceutical modulation of NRF2's cytoprotective activity will be beneficial for human health in a broad range of noncommunicable diseases.

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.

The NRF2/KEAP1 Axis in the Regulation of Tumor Metabolism: Mechanisms and Therapeutic Perspectives

The NRF2/KEAP1 pathway is a fundamental signaling cascade that controls multiple cytoprotective responses through the induction of a complex transcriptional program that ultimately renders cancer cells resistant to oxidative, metabolic and therapeutic stress. Interestingly, accumulating evidence in recent years has indicated that metabolic reprogramming is closely interrelated with the regulation of redox homeostasis, suggesting that the disruption of NRF2 signaling might represent a valid therapeutic strategy against a variety of solid and hematologic cancers. These aspects will be the focus of the present review.

Epigenetics/epigenomics of triterpenoids in cancer prevention and in health

Triterpenoids are a powerful group of phytochemicals derived from plant foods and herbs. Many reports have shown that they possess chemopreventive and chemotherapeutic effects not only in cell lines and animal models but also in clinical trials. Because epigenetic changes could potentially occur in the early stages of carcinogenesis preceding genetic mutations, epigenetics are considered promising targets in early interventions against cancer using epigenetic bioactive substances. The biological properties of triterpenoids in cancer prevention and in health have multiple mechanisms, including antioxidant and anti-inflammatory activities, cell cycle regulation, as well as epigenetic/epigenomic regulation. In this review, we will discuss and summarize the latest advances in the study of the pharmacological effects of triterpenoids in cancer chemoprevention and in health, including the epigenetic machinery.

Small molecular Nrf2 inhibitors as chemosensitizers for cancer therapy

The basic leucine zipper transcription factor Nrf2 is the primary regulator of cellular oxidative stress. Activation of Nrf2 is regarded as a potential preventive and therapeutic strategy. However, aberrant hyperactivation of Nrf2 is found in a variety of cancers and promotes cancer progression and metastasis. Moreover, constitutive activation of Nrf2 confers cancer cells resistance to chemo- and radio-therapy. Thus, inhibiting Nrf2 could be a new therapeutic strategy for cancer. With the aim of accelerating the discovery and development of novel Nrf2 inhibitors, we summarize the biological and pathological functions of Nrf2 in cancer. Furthermore, the recent studies of small molecular Nrf2 inhibitors and potential Nrf2 inhibitory mechanisms are also summarized in this review.

Inhibiting miR-27a and miR-142-5p attenuate nonalcoholic fatty liver disease by regulating Nrf2 signaling pathway

The gene Nrf2 (nuclear factor-erythroid 2-related factor 2) is the most important regulator of the cellular antioxidant system and its dysregulation has a role in the etiology of nonalcoholic fatty liver disease (NAFLD). The aim of this study was to investigate the association between Nrf2 targeted miRNAs (miR-27a, miR-142-5p, miR-153, and miR-128) with lipid accumulation in vitro and in vivo models of NAFLD. We used two in vivo and in vitro models of NAFLD. The expression of the genes and miRNAs was assessed by real-time PCR and the protein level was evaluated using western blot. To investigate the potential role of miRNAs in NAFLD, the inhibitors or mimics of the miR-27a and miR-142-5p were transfected into HepG2 cells. The mRNA and protein levels of Nrf2 were significantly decreased in the liver of high fat diet-fed mice as well as in HepG2 cells treated with high glucose (HG). Reduced expression of Nrf2 was associated with increased expression levels of miR-27a and miR-142-5p in both models of NAFLD. HG-induced triglyceride accumulation was attenuated by inhibition of miR-27a or miR-142-5p in HepG2 cells. Overexpression of miR-27a or miR-142-5p suppressed the expression of Nrf2 and its downstream antioxidant genes and increased production of reactive oxygen species, whereas inhibition of miR-27a or miR-142-5p reversed these effects. In conclusion, the data of this study may suggest that miR-27a and miR-142-5p are increased in NAFLD, where they suppress Nrf2 expression and contribute to the accumulation of lipids in the hepatocytes.

Nrf2 Activation Ameliorates Hepatotoxicity Induced by a Heme Synthesis Inhibitor

Transcription factor Nrf2 protects hepatocytes against various toxicants by upregulating cytoprotective genes. The heme synthesis inhibitor 3, 5-diethoxycarbonyl-1, 4-dihydrocollidine (DDC) leads to liver injury around the portal vein, unlike other groups of toxicants that cause hemorrhage and necrosis in the centrilobular area. To examine whether and how Nrf2 protects livers from the injury, we fed DDC to Nrf2 knockout (Nrf2KO), wild-type (WT), Keap1flox/flox (Keap1-knockdown; Keap1KD), and liver-specific Keap1 knockout (Keap1-Alb) mice, as these lines of mice exhibit stepwise increases in Nrf2 protein expression levels. Liver-specific Keap1::Nrf2 double-knockout (Keap1::Nrf2-Alb) mice were also exploited to examine the contribution of Nrf2. Two weeks after DDC feeding, Keap1-Alb mice were fully recovered from body weight loss, but the WT and Nrf2KO mice were not. The liver-to-body-weight ratio of Keap1-Alb mice was significantly larger than that of WT and Nrf2KO mice. Two indicators of hepatotoxicity, alanine aminotransferase and bilirubin in plasma, were both elevated in WT mice, but downregulated in Keap1-Alb mice after the DDC-feeding. DDC-induced porphyrin accumulation was reduced in the livers of Keap1-Alb and Keap1KD mice compared with that of WT mice. When assessed by the Nqo1 level, Nrf2 expression was further enhanced by DDC in Keap1-Alb mice, suggesting that DDC may have a Keap1 independent potential to activate Nrf2. Genetic activation of Nrf2 in Keap1-Alb mice increased the extracellular excretion of porphyrins, but contrary to our expectation, hepatic damages in Nrf2KO mice appeared to be similar to that of WT mice. Based on these observations, we conclude that Nrf2 activation protects livers against DDC-elicited hepatotoxicity.

Chemical Activation of the Constitutive Androstane Receptor Leads to Activation of Oxidant-Induced Nrf2

Exposure to environmentally relevant chemicals that activate the xenobiotic receptors aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), and peroxisome proliferator-activated receptor alpha (PPARα) in rodent test systems often leads to increases in oxidative stress (OS) that contributes to liver cancer induction. We hypothesized that activation of the oxidant-induced transcription factor Nrf2 could be used as a surrogate endpoint for increases in OS. We examined the relationships between activation of xenobiotic receptors and Nrf2 using previously characterized gene expression biomarkers that accurately predict modulation. Using a correlation approach (Running Fisher Test), the biomarkers were compared with microarray profiles in a mouse liver gene expression compendium. Out of the 163 chemicals examined, 47% from 53 studies activated Nrf2. We found consistent coupling between CAR and Nrf2 activation. Out of the 41 chemicals from 32 studies that activated CAR, 90% also activated Nrf2. CAR was activated earlier and at lower doses than Nrf2, indicating CAR activation preceded Nrf2 activation. Nrf2 activation by 2 CAR activators was abolished in CAR-null mice. We hypothesized that Nrf2 is activated by reactive oxygen species from the increased activity of enzymes encoded by Cyp2b family members. However, Nrf2 was similarly activated in the livers of both TCPOBOP-treated wild-type and Cyp2b9/10/13-null mice. This study provides evidence that Nrf2 activation (1) often occurs after exposure to xenobiotic chemicals, (2) is tightly linked to activation of CAR, and (3) does not require induction of 3 Cyp2b genes secondary to CAR activation.

Resveratrol alleviates non-alcoholic fatty liver disease through epigenetic modification of the Nrf2 signaling pathway

Recent findings have demonstrated the aberrant DNA methylation of the Nrf2-Keap1 genes in human cancers; however, the epigenetic control of this pathway in non-alcoholic fatty liver disease (NAFLD) is unknown. Resveratrol can modify epigenetic mechanisms. Our objectives in this study were to explore the correlation between promoter methylation of the Nrf2-Keap1 genes and NAFLD, and that investigate the effect of resveratrol on the epigenetic regulation Nrf2-Keap1 in vitro and in vivo models of NAFLD. Resveratrol attenuated high fat-diet (HFD)-induced methylation of the Nrf2 promoter in the liver of mice, and this effect was correlated with reduction in triglyceride level and decrease in the expression of lipogenesis-related genes such as FAS and SREBP-1c. In addition, treatment of HepG2 cells with high glucose (HG) enhanced methylation level of the Nrf2 promoter, whereas resveratrol reversed this effect. Treatment of the cells with resveratrol or 5-aza, a demethylating agent, could prevent HG-induced reactive oxygen species production and expression of Nrf2-controlled antioxidant genes. Moreover, resveratrol or 5-aza could significantly attenuate HG-induced triglyceride accumulation in HepG2 cells. These findings indicate that resveratrol attenuates NAFLD through the epigenetic modification the Nrf2 signaling.

Nrf2 in liver toxicology

Liver plays essential roles in the metabolism of many endogenous chemicals and exogenous toxicants. Mechanistic studies in liver have been at the forefront of efforts to probe the roles of bioactivation and detoxication of environmental toxins and toxicants in hepatotoxicity. Moreover, idiosyncratic hepatoxicity remains a key barrier in the clinical development of drugs. The now vast Nrf2 field emerged in part from biochemical and molecular studies on chemical inducers of hepatic detoxication enzymes and subsequent characterization of the modulation of drug/toxicant induced hepatotoxicities in mice through disruption of either Nrf2 or Keap1 genes. In general, loss of Nrf2 increases the sensitivity to such toxic chemicals, highlighting a central role of this transcription factor and its downstream target genes as a modifier to chemical stress. In this review, we summarize the impact of Nrf2 on the toxicology of multiple hepatotoxicants, and discuss efforts to utilize the Nrf2 response in predictive toxicology.

Hypoxia preconditioning promotes endurance exercise capacity of mice by activating skeletal muscle Nrf2

Elite endurance athletes are used to train under hypoxic/high-altitude conditions, which can elicit certain stress responses in skeletal muscle and helps to improve their physical performance. Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates cellular redox homeostasis and metabolism in skeletal muscle, playing important roles in adaptation to various stresses. In this study, Nrf2 knockout (KO) and wild-type (WT) mice were preconditioned to 48 h of hypoxia exposure (11.2% oxygen), and the effects of hypoxia preconditioning (HP) on exercise capacity and exercise-induced changes of antioxidant status, energetic metabolism, and mitochondrial adaptation in skeletal muscle were evaluated. Nrf2 knockout (KO) and wild-type (WT) mice were exposed to normoxia or hypoxia for 48 h before taking incremental treadmill exercise to exhaustion under hypoxia. The skeletal muscles were collected immediately after the incremental treadmill exercise to evaluate the impacts of HP and Nrf2 on the exercise-induced changes. The results indicate the absence of Nrf2 did not affect exercise capacity, although the mRNA expression of certain muscular genes involved in antioxidant, glycogen and fatty acid catabolism was decreased in Nrf2 KO mice. However, 48-h HP enhanced exercise capacity in WT mice but not in Nrf2 KO mice, and the exercise capacity of WT mice was significantly higher than that of Nrf2 KO mice. These findings suggest HP promotes exercise capacity of mice with the participation of the Nrf2 signal in skeletal muscle.

NEW & NOTEWORTHY Hypoxia preconditioning (HP) activated the nuclear factor erythroid 2-related factor 2 (Nrf2) signal, which was involved in HP-elicited adaptation responses to hypoxia, oxidative, and metabolic stresses in skeletal muscle. On the other hand, Nrf2 deficiency abolished the enhanced exercise capacity after the 48-h HP. Our results indicate that Nrf2 plays an essential role in the exercise capacity-enhancing effect of HP, possibly by modulating muscular antioxidative responses, the mRNA expression of muscular genes involved in glycogen and fatty acid metabolism, as well as mitochondrial biogenesis, and through the cross talk with AMPK and hypoxia-inducible factor-1α signaling.

Sulforaphane: Its "Coming of Age" as a Clinically Relevant Nutraceutical in the Prevention and Treatment of Chronic Disease

A growing awareness of the mechanisms by which phytochemicals can influence upstream endogenous cellular defence processes has led to intensified research into their potential relevance in the prevention and treatment of disease. Pharmaceutical medicine has historically looked to plants as sources of the starting materials for drug development; however, the focus of nutraceutical medicine is to retain the plant bioactive in as close to its native state as possible. As a consequence, the potency of a nutraceutical concentrate or an extract may be lower than required for significant gene expression. The molecular structure of bioactive phytochemicals to a large extent determines the molecule's bioavailability. Polyphenols are abundant in dietary phytochemicals, and extensive in vitro research has established many of the signalling mechanisms involved in favourably modulating human biochemical pathways. Such pathways are associated with core processes such as redox modulation and immune modulation for infection control and for downregulating the synthesis of inflammatory cytokines. Although the relationship between oxidative stress and chronic disease continues to be affirmed, direct-acting antioxidants such as vitamins A, C, and E, beta-carotene, and others have not yielded the expected preventive or therapeutic responses, even though several large meta-analyses have sought to evaluate the potential benefit of such supplements. Because polyphenols exhibit poor bioavailability, few of their impressive in vitro findings have been replicated in vivo. SFN, an aliphatic isothiocyanate, emerges as a phytochemical with comparatively high bioavailability. A number of clinical trials have demonstrated its ability to produce favourable outcomes in conditions for which there are few satisfactory pharmaceutical solutions, foreshadowing the potential for SFN as a clinically relevant nutraceutical. Although myrosinase-inert broccoli sprout extracts are widely available, there now exist myrosinase-active broccoli sprout supplements that yield sufficient SFN to match the doses used in clinical trials.

Free radicals, antioxidants, nuclear factor-E2-related factor-2 and liver damage

Oxidative/nitrosative stress is proposed to be a critical factor in various diseases, including liver pathologies. Antioxidants derived from medicinal plants have been studied extensively and are relevant to many illnesses, including liver diseases. Several hepatic disorders, such as viral hepatitis and alcoholic or nonalcoholic steatohepatitis, involve free radicals/oxidative stress as agents that cause or at least exacerbate liver injury, which can result in chronic liver diseases, such as liver fibrosis, cirrhosis and end-stage hepatocellular carcinoma. In this scenario, nuclear factor-E2-related factor-2 (Nrf2) appears to be an essential factor to counteract or attenuate oxidative or nitrosative stress in hepatic cells. In fact, a growing body of evidence indicates that Nrf2 plays complex and multicellular roles in hepatic inflammation, fibrosis, hepatocarcinogenesis and regeneration via the induction of its target genes. Inflammation is the most common feature of chronic liver diseases, triggering fibrosis, cirrhosis and hepatocellular carcinoma. Increasing evidence indicates that Nrf2 counteracts the proinflammatory process by modulating the recruitment of inflammatory cells and inducing the endogenous antioxidant response of the cell. In this review, the interactions between antioxidant and inflammatory molecular pathways are analyzed.

Phenethyl isothiocyanate stimulates glucose uptake through the Akt pathway in C2C12 myotubes

Phenethyl isothiocyanate (PEITC) is an aromatic isothiocyanate present in cruciferous vegetables. Several studies have shown that isothiocyanates regulate various intracellular signaling pathways, and thereby show anti-inflammatory and detoxifying activities. However, little is known about the effects of PEITC on glucose metabolism. In this study, we examined whether PEITC promotes glucose utilization in mouse skeletal muscle cells, C2C12 myotubes. PEITC induced glucose uptake, glucose transporter 4 (Glut4) translocation to the plasma membrane, and activation of Akt and ERK in C2C12 cells. Inhibition of Akt suppressed PEITC-induced Glut4 translocation and glucose uptake, whereas ERK inhibition did not. Furthermore, PEITC increased phosphorylation of ErbB2 and ErbB3. Treatment with a pan-ErbB inhibitor reduced Akt activation and the subsequent glucose uptake induced by PEITC. These results indicate that PEITC promotes glucose utilization through the ErbB/Akt pathway in C2C12 myotubes. PEITC may therefore serve as a dietary constituent with beneficial effects on the carbohydrate metabolism.

Abbreviations: PEITC: phenethyl isothiocyanate; Glut4: glucose transporter 4; PI3K: phosphatidylinositide 3-kinase; Nrf2: erythroid−2-related factor; ARE: antioxidant response element; HO−1: heme oxygenase−1; NRG: neuregulin

TrxR1, Gsr, and oxidative stress determine hepatocellular carcinoma malignancy

Thioredoxin reductase-1 (TrxR1)-, glutathione reductase (Gsr)-, and Nrf2 transcription factor-driven antioxidant systems form an integrated network that combats potentially carcinogenic oxidative damage yet also protects cancer cells from oxidative death. Here we show that although unchallenged wild-type (WT), TrxR1-null, or Gsr-null mouse livers exhibited similarly low DNA damage indices, these were 100-fold higher in unchallenged TrxR1/Gsr-double-null livers. Notwithstanding, spontaneous cancer rates remained surprisingly low in TrxR1/Gsr-null livers. All genotypes, including TrxR1/Gsr-null, were susceptible to N-diethylnitrosamine (DEN)-induced liver cancer, indicating that loss of these antioxidant systems did not prevent cancer cell survival. Interestingly, however, following DEN treatment, TrxR1-null livers developed threefold fewer tumors compared with WT livers. Disruption of TrxR1 in a marked subset of DEN-initiated cancer cells had no effect on their subsequent contributions to tumors, suggesting that TrxR1-disruption does not affect cancer progression under normal care, but does decrease the frequency of DEN-induced cancer initiation. Consistent with this idea, TrxR1-null livers showed altered basal and DEN-exposed metabolomic profiles compared with WT livers. To examine how oxidative stress influenced cancer progression, we compared DEN-induced cancer malignancy under chronically low oxidative stress (TrxR1-null, standard care) vs. elevated oxidative stress (TrxR1/Gsr-null livers, standard care or phenobarbital-exposed TrxR1-null livers). In both cases, elevated oxidative stress was correlated with significantly increased malignancy. Finally, although TrxR1-null and TrxR1/Gsr-null livers showed strong Nrf2 activity in noncancerous hepatocytes, there was no correlation between malignancy and Nrf2 expression within tumors across genotypes. We conclude that TrxR1, Gsr, Nrf2, and oxidative stress are major determinants of liver cancer but in a complex, context-dependent manner.

Phytochemical Combination PB125 Activates the Nrf2 Pathway and Induces Cellular Protection against Oxidative Injury

Bioactive phytochemicals in Rosmarinus officinalis, Withania somnifera, and Sophora japonica have a long history of human use to promote health. In this study we examined the cellular effects of a combination of extracts from these plant sources based on specified levels of their carnosol/carnosic acid, withaferin A, and luteolin levels, respectively. Individually, these bioactive compounds have previously been shown to activate the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor, which binds to the antioxidant response element (ARE) and regulates the expression of a wide variety of cytoprotective genes. We found that combinations of these three plant extracts act synergistically to activate the Nrf2 pathway, and we identified an optimized combination of the three agents which we named PB125 for use as a dietary supplement. Using microarray, quantitative reverse transcription-PCR, and RNA-seq technologies, we examined the gene expression induced by PB125 in HepG2 (hepatocellular carcinoma) cells, including canonical Nrf2-regulated genes, noncanonical Nrf2-regulated genes, and genes which appear to be regulated by non-Nrf2 mechanisms. Ingenuity Pathway Analysis identified Nrf2 as the primary pathway for gene expression changes by PB125. Pretreatment with PB125 protected cultured HepG2 cells against an oxidative stress challenge caused by cumene hydroperoxide exposure, by both cell viability and cell injury measurements. In summary, PB125 is a phytochemical dietary supplement comprised of extracts of three ingredients, Rosmarinus officinalis, Withania somnifera, and Sophora japonica, with specified levels of carnosol/carnosic acid, withaferin A, and luteolin, respectively. Each ingredient contributes to the activation of the Nrf2 pathway in unique ways, which leads to upregulation of cytoprotective genes and protection of cells against oxidative stress and supports the use of PB125 as a dietary supplement to promote healthy aging.

Therapeutic targeting of the NRF2 and KEAP1 partnership in chronic diseases

The transcription factor NF-E2 p45-related factor 2 (NRF2; encoded by NFE2L2) and its principal negative regulator, the E3 ligase adaptor Kelch-like ECH-associated protein 1 (KEAP1), are critical in the maintenance of redox, metabolic and protein homeostasis, as well as the regulation of inflammation. Thus, NRF2 activation provides cytoprotection against numerous pathologies including chronic diseases of the lung and liver; autoimmune, neurodegenerative and metabolic disorders; and cancer initiation. One NRF2 activator has received clinical approval and several electrophilic modifiers of the cysteine-based sensor KEAP1 and inhibitors of its interaction with NRF2 are now in clinical development. However, challenges regarding target specificity, pharmacodynamic properties, efficacy and safety remain.

Critical Role of Nrf2 in Experimental Ischemic Stroke

Ischemic stroke is one of the leading causes of death and long-term disability worldwide; however, effective clinical approaches are still limited. The transcriptional factor Nrf2 is a master regulator in cellular and organismal defense against endogenous and exogenous stressors by coordinating basal and stress-inducible activation of multiple cytoprotective genes. The Nrf2 network not only tightly controls redox homeostasis but also regulates multiple intermediary metabolic processes. Therefore, targeting Nrf2 has emerged as an attractive therapeutic strategy for the prevention and treatment of CNS diseases including stroke. Here, the current understanding of the Nrf2 regulatory network is critically examined to present evidence for the contribution of Nrf2 pathway in rodent ischemic stroke models. This review outlines the literature for Nrf2 studies in preclinical stroke and focuses on the in vivo evidence for the role of Nrf2 in primary and secondary brain injuries. The dynamic change and functional importance of Nrf2 signaling, as well as Nrf2 targeted intervention, are revealed in permanent, transient, and global cerebral ischemia models. In addition, key considerations, pitfalls, and future potentials for Nrf2 studies in preclinical stroke investigation are discussed.

Prostate cancer chemoprevention by sulforaphane in a preclinical mouse model is associated with inhibition of fatty acid metabolism

Increased de novo synthesis of fatty acids is a rather unique and targetable mechanism of human prostate cancer. We have shown previously that oral administration of sulforaphane (SFN) significantly inhibits the incidence and/or burden of prostatic intraepithelial neoplasia and well-differentiated adenocarcinoma in TRansgenic Adenocarcinoma of Mouse Prostate (TRAMP) mice. The present study used cellular models of prostate cancer and archived plasma/adenocarcinoma tissues and sections from the TRAMP study to demonstrate inhibition of fatty acid synthesis by SFN treatment in vitro and in vivo. Treatment of androgen-responsive (LNCaP) and castration-resistant (22Rv1) human prostate cancer cells with SFN (5 and 10 μM) resulted in downregulation of protein and mRNA levels of acetyl-CoA carboxylase 1 (ACC1) and fatty acid synthase (FASN), but not ATP citrate lyase. Protein and mRNA levels of carnitine palmitoyltransferase 1A (CPT1A), which facilitates fatty acid uptake by mitochondria for β-oxidation, were also decreased following SFN treatment in both cell lines. Immunohistochemistry revealed a significant decrease in expression of FASN and ACC1 proteins in prostate adenocarcinoma sections of SFN-treated TRAMP mice when compared with controls. SFN administration to TRAMP mice resulted in a significant decrease in plasma and/or prostate adenocarcinoma levels of total free fatty acids, total phospholipids, acetyl-CoA and ATP. Consistent with these results, number of neutral lipid droplets was lower in the prostate adenocarcinoma sections of SFN-treated TRAMP mice than in control tumors. Collectively, these observations indicate that prostate cancer chemoprevention by SFN in TRAMP mice is associated with inhibition of fatty acid metabolism.

Berberine attenuates hepatic oxidative stress in rats with non-alcoholic fatty liver disease via the Nrf2/ARE signalling pathway

The present study investigated the effects of berberine (BBR) on hepatic oxidative stress and the nuclear factor erythroid 2-related factor 2/antioxidant response element (Nrf2/ARE) signalling pathway in rats in which non-alcoholic fatty liver disease (NAFLD) was induced by a high-fat diet. Rats were randomly divided into three groups: The normal control (NC), high-fat diet (HFD) and BBR groups. The NC group received a normal diet, while the other two groups were fed a high-fat diet. The rats in the BBR group were also fed BBR (100 mg/kg body weight) daily. A total of 8 weeks later, serum and liver lipid levels were measured. Hepatic histopathological changes were observed with haematoxylin and eosin and Oil Red O staining. Transmission electron microscopy was performed to observe the ultrastructural changes of the liver. The levels of superoxide dismutase (SOD), glutathione (GSH) and malondialdehyde (MDA) in the liver were measured. Quantitative polymerase chain reaction and western blotting were performed to investigate the expression of genes in the Nrf2/ARE signalling pathway in the liver. Histopathological results demonstrated that rats fed a high-fat diet for 8 weeks developed NAFLD, characterized by hepatic steatosis. BBR significantly decreased the body weight and liver weight. BBR markedly reduced hepatic steatosis, and the serum and liver lipid levels. Hepatic SOD and GSH levels were increased, while MDA levels were decreased by BBR co-administered with a high-fat diet. Additionally, the Nrf2/ARE signalling pathway was revealed to be involved in the protective effect of BBR on rats fed a high-fat diet. In conclusion, BBR may alleviate hepatic oxidative stress in rats with NAFLD, which may be partly attributed to the activation of the Nrf2/ARE signalling pathway.

Dysregulation of Nrf2/Keap1 Redox Pathway in Diabetes Affects Multipotency of Stromal Cells

The molecular and cellular level reaches of the metabolic dysregulations that characterize diabetes are yet to be fully discovered. As mechanisms underlying management of reactive oxygen species (ROS) gain interest as crucial factors in cell integrity, questions arise about the role of redox cues in the regulation and maintenance of bone marrow-derived multipotent stromal cells (BMSCs) that contribute to wound healing, particularly in diabetes. Through comparison of BMSCs from wild-type and diabetic mice, with a known redox and metabolic disorder, we found that the cytoprotective nuclear factor erythroid-related factor 2 (Nrf2)/kelch-like erythroid cell-derived protein 1 (Keap1) pathway is dysregulated and functionally insufficient in diabetic BMSCs (dBMSCs). Nrf2 is basally active, but in chronic ROS, we found irregular inhibition of Nrf2 by Keap1, altered metabolism, and limited BMSC multipotency. Forced upregulation of Nrf2-directed transcription, through knockdown of Keap1, restores redox homeostasis. Normalized Nrf2/Keap1 signaling restores multipotent cell properties in dBMSCs through Sox2 expression. These restored BMSCs can resume their role in regenerative tissue repair and promote healing of diabetic wounds. Knowledge of diabetes and hyperglycemia-induced deficits in BMSC regulation, and strategies to reverse them, offers translational promise. Our study establishes Nrf2/Keap1 as a cytoprotective pathway, as well as a metabolic rheostat, that affects cell maintenance and differentiation switches in BMSCs.

Transcriptional Regulation by Nrf2

SIGNIFICANCE

Nuclear factor E2-related factor 2 (Nrf2) is a transcription factor that coordinates the basal and stress-inducible activation of a vast array of cytoprotective genes. Understanding the regulation of Nrf2 activity and downstream pathways has major implications for human health. Recent Advances: Nrf2 regulates the transcription of components of the glutathione and thioredoxin antioxidant systems, as well as enzymes involved in phase I and phase II detoxification of exogenous and endogenous products, NADPH regeneration, and heme metabolism. It therefore represents a crucial regulator of the cellular defense mechanisms against xenobiotic and oxidative stress. In addition to antioxidant responses, Nrf2 is involved in other cellular processes, such as autophagy, intermediary metabolism, stem cell quiescence, and unfolded protein response. Given the wide range of processes that Nrf2 controls, its activity is tightly regulated at multiple levels. Here, we review the different modes of regulation of Nrf2 activity and the current knowledge of Nrf2-mediated transcriptional control.

CRITICAL ISSUES

It is now clear that Nrf2 lies at the center of a complex regulatory network. A full comprehension of the Nrf2 program will require an integrated consideration of all the different factors determining Nrf2 activity.

FUTURE DIRECTIONS

Additional computational and experimental studies are needed to obtain a more dynamic global view of Nrf2-mediated gene regulation. In particular, studies comparing how the Nrf2-dependent network changes from a physiological to a pathological condition can provide insight into mechanisms of disease and instruct new treatment strategies.

Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) Inhibition: An Emerging Strategy in Cancer Therapy

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a pleiotropic transcription factor, especially for its complex and dual effects in cancer. With the continuous growing research, new regulatory modes and new functions of Nrf2 and tumor-promoting effects of Nrf2 in malignant transformed tumors have become increasingly clear. Accumulating evidence has established that Nrf2 contributes to the whole process of pathogenesis, progression, metastasis, and prognosis of cancer, and Nrf2 could be a promising target in cancer therapy. However, the development of Nrf2 inhibitor is still limited. In this perspective, we will briefly describe the biological function and modulating network of Nrf2, stress its oncogenic role, and point out possible ways to inhibit Nrf2, as well as summarize the reported Nrf2 inhibitors.

Quercetin‑3‑O‑α‑L‑rhamnopyranoside derived from the leaves of Lindera aggregata (Sims) Kosterm. evokes the autophagy‑induced nuclear factor erythroid 2‑related factor 2 antioxidant pathway in human umbilical vein endothelial cells

Quercetin‑3‑O‑α‑L‑rhamnopyranoside (QI) is derived from the leaves of Lindera aggregata (Sims) Kosterm. And exhibits multiple biological activities, including an antioxidant activity. However, the detailed molecular mechanism of its antioxidant activity remains unknown. The aim of the present study was to investigate the antioxidant activity of QI and the underlying molecular mechanism in human umbilical vein endothelial cells (HUVECs). An oxidative stress model was established in HUVECs using H2O2, and cells were then treated with different concentrations of QI. The results revealed that the exposure of HUVECs to QI protected these cells from H2O2‑induced damage. QI treatment also increased the activities of the antioxidant enzymes superoxide dismutase (SOD) and glutathione (GSH) in the cell culture medium. In addition, QI inhibited H2O2‑induced apoptosis by decreasing the expression levels of cleaved Caspase‑9 and poly(ADP‑ribose) polymerase. QI also inhibited the production of DNA fragments and reactive oxygen species induced by H2O2. Furthermore, QI decreased the oxidative stress by promoting the nuclear transfer of nuclear factor erythroid 2‑related factor 2 (Nrf2) and heme oxygenase‑1 by activating autophagy, and inhibited the competition of Bach1 from Nrf2. Finally, QI significantly improved the activities of T‑SOD and GSH, and decreased the content of malondialdehyde in the serum and heart tissue of aging rats. These data support the use of QI as a health supplement to alleviate oxidative stress or further development of this compound as an antioxidant drug.

RPA1 binding to NRF2 switches ARE-dependent transcriptional activation to ARE-NRE-dependent repression

NRF2 regulates cellular redox homeostasis, metabolic balance, and proteostasis by forming a dimer with small musculoaponeurotic fibrosarcoma proteins (sMAFs) and binding to antioxidant response elements (AREs) to activate target gene transcription. In contrast, NRF2-ARE-dependent transcriptional repression is unreported. Here, we describe NRF2-mediated gene repression via a specific seven-nucleotide sequence flanking the ARE, which we term the NRF2-replication protein A1 (RPA1) element (NRE). Mechanistically, RPA1 competes with sMAF for NRF2 binding, followed by interaction of NRF2-RPA1 with the ARE-NRE and eduction of promoter activity. Genome-wide in silico and RNA-seq analyses revealed this NRF2-RPA1-ARE-NRE complex mediates negative regulation of many genes with diverse functions, indicating that this mechanism is a fundamental cellular process. Notably, repression of MYLK, which encodes the nonmuscle myosin light chain kinase, by the NRF2-RPA1-ARE-NRE complex disrupts vascular integrity in preclinical inflammatory lung injury models, illustrating the translational significance of NRF2-mediated transcriptional repression. Our findings reveal a gene-suppressive function of NRF2 and a subset of negatively regulated NRF2 target genes, underscoring the broad impact of NRF2 in physiological and pathological settings.

CB1 receptor blockade ameliorates hepatic fat infiltration and inflammation and increases Nrf2-AMPK pathway in a rat model of severely uncontrolled diabetes

Previous studies have shown that the CB1 receptor antagonist reverses steatohepatitis and its related features of metabolic syndrome, such as obesity and type 2 diabetes. However, the beneficial effects of CB1 receptor blockade on hepatic steatosis and inflammation have not been investigated independently of its effects on body weight and glycemic control. At 32 weeks of age, OLETF rats were administered with rimonabant (10 mg·kg⁻¹·day⁻¹) by oral gavage for 6 weeks. No significant changes in body weight, OGTT, and serum glucose were observed in spite of rimonabant-decreased food intake. Moreover, there was a significant difference between initial and final body weight, regardless of rimonabant administration, indicating that OLETF rats were severely diabetic rats. Rimonabant administration significantly decreased serum liver enzyme levels such as ALT and AST, hepatic fat accumulation, lipid peroxidation, and cell death as demonstrated by the number of TUNEL-positive cells in severely uncontrolled diabetic OLETF rats. Significant decreases in hepatic gene expression of proinflammatory cytokines (CD11b, F4/80, MCP1, and TNFα), negative inflammatory mediators (SOCS1 and SOCS3), and fibrosis-related proteins (TGFβ, collagen 1, and TIMP1) were found in rimonabant-treated OLETF rats. Six-week administration of rimonabant significantly upregulated mRNA levels of CPT1α and PPARα related to β-oxidation. Moreover, significant increases in Nrf2 gene expression and its downstream genes, NQO1, GSAT, HO-1, and TXNRD1 along with increased AMPK phosphorylation were noted in uncontrolled diabetic rats treated with rimonabant. The observed potent inhibitory effects of CB1 receptor blockade on hepatic fat infiltration and cellular death in severely uncontrolled diabetic rats indicate that CB1 receptor is a possible therapeutic target. Increased Nrf2 and AMPK phosphorylation may play a role in the mechanism of rimonabant action.

Phenethyl Isothiocyanate, a Dual Activator of Transcription Factors NRF2 and HSF1

Cruciferous vegetables are rich sources of glucosinolates which are the biogenic precursor molecules of isothiocyanates (ITCs). The relationship between the consumption of cruciferous vegetables and chemoprotection has been widely documented in epidemiological studies. Phenethyl isothiocyanate (PEITC) occurs as its glucosinolate precursor gluconasturtiin in the cruciferous vegetable watercress (Nasturtium officinale). PEITC has multiple biological effects, including activation of cytoprotective pathways, such as those mediated by the transcription factor nuclear factor erythroid 2 p45-related factor 2 (NRF2) and the transcription factor heat shock factor 1 (HSF1), and can cause changes in the epigenome. However, at high concentrations, PEITC leads to accumulation of reactive oxygen species and cytoskeletal changes, resulting in cytotoxicity. Underlying these activities is the sulfhydryl reactivity of PEITC with cysteine residues in its protein targets. This chemical reactivity highlights the critical importance of the dose of PEITC for achieving on-target selectivity, which should be carefully considered in the design of future clinical trials.

Activation of Nrf2 in the liver is associated with stress resistance mediated by suppression of the growth hormone-regulated STAT5b transcription factor

The transcription factor Nrf2 (encoded by Nfe2l2) induces expression of numerous detoxifying and antioxidant genes in response to oxidative stress. The cytoplasmic protein Keap1 interacts with and represses Nrf2 function. Computational approaches were developed to identify factors that modulate Nrf2 in a mouse liver gene expression compendium. Forty-eight Nrf2 biomarker genes were identified using profiles from the livers of mice in which Nrf2 was activated genetically in Keap1-null mice or chemically by a potent activator of Nrf2 signaling. The rank-based Running Fisher statistical test was used to determine the correlation between the Nrf2 biomarker genes and a test set of 81 profiles with known Nrf2 activation status demonstrating a balanced accuracy of 96%. For a large number of factors examined in the compendium, we found consistent relationships between activation of Nrf2 and feminization of the liver transcriptome through suppression of the male-specific growth hormone (GH)-regulated transcription factor STAT5b. The livers of female mice exhibited higher Nrf2 activation than male mice in untreated or chemical-treated conditions. In male mice, Nrf2 was activated by treatment with ethinyl estradiol, whereas in female mice, Nrf2 was suppressed by treatment with testosterone. Nrf2 was activated in 5 models of disrupted GH signaling containing mutations in Pit1, Prop1, Ghrh, Ghrhr, and Ghr. Out of 59 chemical treatments that activated Nrf2, 36 exhibited STAT5b suppression in the male liver. The Nrf2-STAT5b coupling was absent in in vitro comparisons of chemical treatments. Treatment of male and female mice with 11 chemicals that induce oxidative stress led to activation of Nrf2 to greater extents in females than males. The enhanced basal and inducible levels of Nrf2 activation in females relative to males provides a molecular explanation for the greater resistance often seen in females vs. males to age-dependent diseases and chemical-induced toxicity.

NRF2 and the Hallmarks of Cancer

The transcription factor NRF2 is the master regulator of the cellular antioxidant response. Though recognized originally as a target of chemopreventive compounds that help prevent cancer and other maladies, accumulating evidence has established the NRF2 pathway as a driver of cancer progression, metastasis, and resistance to therapy. Recent studies have identified new functions for NRF2 in the regulation of metabolism and other essential cellular functions, establishing NRF2 as a truly pleiotropic transcription factor. In this review, we explore the roles of NRF2 in the hallmarks of cancer, indicating both tumor suppressive and tumor-promoting effects.

The therapeutic effects of bee venom on some metabolic and antioxidant parameters associated with HFD-induced non-alcoholic fatty liver in rats

The present study was designed to investigate the therapeutic effects of bee venom (BV) on high-fat diet (HFD)-induced non-alcoholic fatty liver (NAFL) in rats at different levels. Histological manifestations, hepatic lipid content, liver function tests, glucose homeostasis, lipid abnormalities, adipocytokines, lipid peroxidation, disturbed glutathione and antioxidant enzymes systems and dysregulation of Nrf2 transcription factor were assessed. In the present study, the NAFL rats were subcutaneously treated with BV with different doses (0.01, 0.05, 0.1 mg/kg). The results indicated that BV treatment completely normalized the lipid profile values of NAFL rats. Fasting blood sugar, insulin level and homeostatic model assessment of insulin resistance significantly decreased. BV treated rats showed a significantly lower level of all liver enzymes and bilirubin. Moreover, BV treatment significantly increased the levels of active nuclear erythroid factor 2 like 2, glutathione (GSH) (total and reduced), GSH/glutathione disulphide ratio and activities of glutathione reductase, glutathione-S-transferase and glutathione peroxidase (total and Se-dependent). The level of tumor necrosis factor-α was reduced. Treatment showed correction of adiponectin level, and significant downregulation of hepatic triglycerides and cholesterol. At the histological level, BV improved the architecture of liver cells showing normal sinusoids. It may be concluded that BV may represent an interesting therapeutic alternative for the treatment of NAFL disease.

Nrf2-mediated anti-oxidant effects contribute to suppression of non-alcoholic steatohepatitis-associated hepatocellular carcinoma in murine model

The exact mechanisms of hepatocellular carcinoma development in non-alcoholic steatohepatitis remain unclear. In this study, we used a new class of high-fat diet, which could induce hepatocellular carcinoma development without the use of general chemical carcinogens or knockout mice. We investigated the correlation between hepatocellular carcinoma and oxidative stress/anti-oxidant effects after depletion of the gut microbiota by treatment with antibiotics. Mice fed with the steatohepatitis-inducing high-fat diet (STHD-01) for 41 weeks developed hepatocellular carcinoma. Antibiotic-treatment in mice fed with STHD-01 significantly depleted the gut microbiota and significantly ameliorated liver injury/histology. The tumor numbers of hepatocellular carcinoma were dramatically decreased by the antibiotics-treatment. We analyzed the factors involved in oxidative stress and anti-oxidant effects. Oxidative stress was elevated in mice fed with STHD-01, whereas some anti-oxidant factors were significantly elevated after antibiotics treatment. These results suggest that the gut microbiota is a key factor in improving oxidative stress induced by STHD-01 feeding.

Pharmacogenomics of Chemically Distinct Classes of Keap1-Nrf2 Activators Identify Common and Unique Gene, Protein, and Pathway Responses In Vivo

The Kelch-like erythroid-associated protein 1 (Keap1)-NF-E2-related factor 2 (Nrf2) signaling pathway is the subject of several clinical trials evaluating the effects of Nrf2 activation on the prevention of cancer and diabetes and the treatment of chronic kidney disease and multiple sclerosis. 3H-1,2-dithiole-3-thione (D3T) and 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im) are representative members of two distinct series of Nrf2 chemical activators. Previous reports have described activator-specific effects on Nrf2-dependent gene regulation and physiologic outcomes. Here we used a robust chemical genomics approach to characterize expression profiles between D3T and CDDO-Im in livers from wild-type and Nrf2-null mice. At equally efficacious doses in wild-type mice, 406 genes show common RNA responses to both treatments. These genes enriched the Nrf2-regulated pathways of antioxidant defense and xenobiotic metabolism. In addition, 197 and 745 genes were regulated uniquely in response to either D3T or CDDO-Im, respectively. Functional analysis of the D3T-regulated set showed a significant enrichment of Nrf2-regulated enzymes involved in cholesterol biosynthesis. This result was supported by Nrf2-dependent increases in lanosterol synthase and CYP51 protein expression. CDDO-Im had no effect on cholesterol biosynthesis regardless of the dose tested. However, unlike D3T, CDDO-Im resulted in Nrf2-dependent elevation of peroxisome proliferator α and Kruppel-like factor 13, as well as the coactivator peroxisome proliferator γ coactivator 1β, together indicating regulation of β-oxidation and lipid metabolic pathways. These findings provide novel insights into the pharmacodynamic action of these two activators of Keap1-Nrf2 signaling. Although both compounds modify Keap1 to affect canonical cytoprotective gene expression, additional unique sets of Nrf2-dependent genes were regulated by each agent with enrichment of selective metabolic pathways.

Nitrolipids in kidney physiology and disease

The kidneys are vital organs responsible for maintaining body fluid homeostasis within proper physiologic ranges. Kidney disease is an epidemic clinical problem causing significant morbidity and mortality, and current treatments are limited to renin-angiotensin system blockade or renal replacement therapy for the majority of affected individuals. There is a critical, unmet need for novel pharmacological agents to improve the outcome of patients with kidney disease. Nitro-oleic acid (NO2-OA) is an endogenously generated electrophilic compound with the capacity to modify thiols in proteins, altering their function. The most important targets appear to be the Keap1/Nrf2 and NF-κB pathways, which have widespread effects on antioxidant, detoxifying, and inflammatory responses in cells and tissues. Through these and potentially additional protective actions, NO2-OA may be capable of preserving or enhancing kidney function in acute and chronic kidney diseases.

NRF2 regulates core and stabilizing circadian clock loops, coupling redox and timekeeping in Mus musculus

Diurnal oscillation of intracellular redox potential is known to couple metabolism with the circadian clock, yet the responsible mechanisms are not well understood. We show here that chemical activation of NRF2 modifies circadian gene expression and rhythmicity, with phenotypes similar to genetic NRF2 activation. Loss of Nrf2 function in mouse fibroblasts, hepatocytes and liver also altered circadian rhythms, suggesting that NRF2 stoichiometry and/or timing of expression are important to timekeeping in some cells. Consistent with this concept, activation of NRF2 at a circadian time corresponding to the peak generation of endogenous oxidative signals resulted in NRF2-dependent reinforcement of circadian amplitude. In hepatocytes, activated NRF2 bound specific enhancer regions of the core clock repressor gene Cry2, increased Cry2 expression and repressed CLOCK/BMAL1-regulated E-box transcription. Together these data indicate that NRF2 and clock comprise an interlocking loop that integrates cellular redox signals into tissue-specific circadian timekeeping.

Inducers of Senescence, Toxic Compounds, and Senolytics: The Multiple Faces of Nrf2-Activating Phytochemicals in Cancer Adjuvant Therapy

The reactivation of senescence in cancer and the subsequent clearance of senescent cells are suggested as therapeutic intervention in the eradication of cancer. Several natural compounds that activate Nrf2 (nuclear factor erythroid-derived 2-related factor 2) pathway, which is involved in complex cytoprotective responses, have been paradoxically shown to induce cell death or senescence in cancer. Promoting the cytoprotective Nrf2 pathway may be desirable for chemoprevention, but it might be detrimental in later stages and advanced cancers. However, senolytic activity shown by some Nrf2-activating compounds could be used to target senescent cancer cells (particularly in aged immune-depressed organisms) that escape immunosurveillance. We herein describe in vitro and in vivo effects of fifteen Nrf2-interacting natural compounds (tocotrienols, curcumin, epigallocatechin gallate, quercetin, genistein, resveratrol, silybin, phenethyl isothiocyanate, sulforaphane, triptolide, allicin, berberine, piperlongumine, fisetin, and phloretin) on cellular senescence and discuss their use in adjuvant cancer therapy. In light of available literature, it can be concluded that the meaning and the potential of adjuvant therapy with natural compounds in humans remain unclear, also taking into account the existence of few clinical trials mostly characterized by uncertain results. Further studies are needed to investigate the therapeutic potential of those compounds that display senolytic activity.

Regulation of redox balance in cancer and T cells

Reactive oxygen species (ROS) mediate redox signaling necessary for numerous cellular functions. Yet, high levels of ROS in cells and tissues can cause damage and cell death. Therefore, regulation of redox homeostasis is essential for ROS-dependent signaling that does not incur cellular damage. Cells achieve this optimal balance by coordinating ROS production and elimination. In this Minireview, we discuss the mechanisms by which proliferating cancer and T cells maintain a carefully controlled redox balance. Greater insight into such redox biology may enable precisely targeted manipulation of ROS for effective medical therapies against cancer or immunological disorders.