Transcriptional regulation of NF-E2 p45-related factor (NRF2) expression by the aryl hydrocarbon receptor-xenobiotic response element signaling pathway: direct cross-talk between phase I and II drug-metabolizing enzymes

The role of nuclear factor erythroid 2-related factor 2 (NRF2) in arsenic toxicity

Arsenic, a naturally occurring toxic element, manifests in various chemical forms and is widespread in the environment. Exposure to arsenic is a well-established risk factor for an elevated incidence of various cancers and chronic diseases. The crux of arsenic-mediated toxicity lies in its ability to induce oxidative stress, characterized by an unsettling imbalance between oxidants and antioxidants, accompanied by the rampant generation of reactive oxygen species and free radicals. In response to this oxidative turmoil, cells deploy their defense mechanisms, prominently featuring the redox-sensitive transcription factor known as nuclear factor erythroid 2-related factor 2 (NRF2). NRF2 stands as a primary guardian against the oxidative harm wrought by arsenic. When oxidative stress activates NRF2, it orchestrates a symphony of downstream antioxidant genes, leading to the activation of pivotal antioxidant enzymes like glutathione-S-transferase, heme oxygenase-1, and NAD(P)H: quinone oxidoreductase 1. This comprehensive review embarks on the intricate and diverse ways by which various arsenicals influence the NRF2 antioxidant pathway and its downstream targets, shedding light on their roles in defending against arsenic exposure toxic effects. It offers valuable insights into targeting NRF2 as a strategy for safeguarding against or treating the harmful and carcinogenic consequences of arsenic exposure.

Arsenic Trioxide (ATOIII) Induces NAD(P)H Quinone Oxidoreductase 1 (NQO1) Expression in Hepatic and Extrahepatic Tissues of C57BL/6 Mice

Arsenic trioxide (ATOIII) has emerged as a potent therapeutic agent for acute promyelocytic leukemia (APL), yet its clinical application is often limited by significant adverse effects. This study investigates the molecular mechanisms underlying ATOIII's impact on cellular detoxification pathways, focusing on the regulation of NAD(P)H/quinone oxidoreductase (NQO1), a crucial enzyme in maintaining cellular homeostasis and cancer prevention. We explored ATOIII's effects on NQO1 expression in C57BL/6 mice and Hepa-1c1c7 cells, both independently and in combination with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a known NQO1 inducer. Our findings revealed that ATOIII significantly increased NQO1 expression in hepatic and extrahepatic tissues, as well as in Hepa-1c1c7 cells, at mRNA, protein, and activity levels. This upregulation occurred both in the presence and absence of TCDD. Mechanistically, we demonstrated that ATOIII promotes the nuclear translocation of both nuclear factor erythroid 2-related factor-2 (NRF2) and aryl hydrocarbon receptor (AHR) transcription factors. Furthermore, ATOIII exposure increased antioxidant response element (ARE)-driven reporter gene activity, indicating a transcriptional mechanism of NQO1 induction. Notably, gene silencing experiments confirmed the critical roles of both NRF2 and AHR in mediating ATOIII-induced NQO1 expression. In conclusion, ATOIII exposure is found to upregulate the NQO1 enzyme through a transcriptional mechanism via AHR- and NRF2- dependent mechanisms, offering valuable insights into its therapeutic mechanisms.

PRDM16 suppresses ferroptosis to protect against sepsis-associated acute kidney injury by targeting the NRF2/GPX4 axis

Acute kidney injury (AKI) constitutes a significant public health issue. Sepsis accounts for over 50 % of AKI cases in the ICU. Recent findings from our research indicated that the PRD1-BF1-RIZ1 homeodomain protein 16 (PRDM16) inhibited the progression of diabetic kidney disease (DKD). However, its precise role and regulatory mechanism in sepsis-induced AKI remain obscure. This study reveals that lipopolysaccharide (LPS) and cecum ligation and puncture (CLP) instigated PRDM16 expression in Boston University mouse proximal tubule (BUMPT) cells and mouse kidneys, respectively. Functionally, PRDM16 curtailed LPS-induced ferroptosis. Mechanistically, PRDM16 associates with the promoter regions of nuclear factor-erythroid 2-related factor-2 (NRF2) and augments its expression, subsequently enhancing glutathione peroxidase 4 (GPX4) expression. Additionally, PRDM16 directly engages with the promoter regions of GPX4, stimulating its expression. Notably, these observations were corroborated in human renal tubular epithelial (HK-2) cells. Furthermore, the ablation of PRDM16 from kidney proximal tubules in mice inhibited NRF2 and GPX4 expression, leading to decreased glutathione (GSH)/oxidized glutathione (GSSG) ratio, increased Fe2+ and reactive oxygen species (ROS) production, exacerbated ferroptosis, and AKI progression. Conversely, PRDM16 knock-in exhibited the opposite effects. Ultimately, adenovirus (ADV)-PRDM16 plasmid or poly (lactide-glycolide acid) (PLGA)-encapsulated formononetin not only mitigated sepsis-induced AKI but also alleviated liver, cardiac, and lung injury. In summary, PRDM16 inhibits ferroptosis via the NRF2/GPX4 axis or GPX4 to prevent sepsis-induced multi-organ injury, including AKI. PLGA-encapsulated formononetin presents a promising therapeutic approach.

Benzo(a)pyrene exposure during pregnancy leads to germ cell apoptosis in male mice offspring via affecting histone modifications and oxidative stress levels

Infertility has gradually become a global health concern, and evidence suggests that exposure to environmental endocrine-disrupting chemicals (EDCs) represent one of the key causes of infertility. Benzo(a)pyrene (BaP) is a typical EDC that is widespread in the environment. Previous studies have detected BaP in human urine, semen, cervical mucus, oocytes and follicular fluid, resulting in reduced fertility and irreversible reproductive damage. However, the mechanisms underlying the effects of gestational BaP exposure on offspring fertility in male mice have not been fully explored. In this study, pregnant mice were administered BaP at doses of 0, 5, 10 and 20 mg/kg/day via gavage from Days 7.5 to 12.5 of gestation. The results revealed that BaP exposure during pregnancy disrupted the structural integrity of testicular tissue, causing a disorganized arrangement of spermatogenic cells, compromised sperm quality, elevated levels of histone modifications and increased apoptosis in the testicular tissue of F1 male mice. Furthermore, oxidative stress was also increased in the testicular tissue of F1 male mice. BaP activated the AhR/ERα signaling pathway, affected H3K4me3 expression and induced apoptosis in testicular tissue. AhR and Cyp1a1 were overexpressed, and the expression of key molecules in the antioxidant pathway, including Keap1 and Nrf2, was reduced. The combined effects of these molecules led to apoptosis in testicular tissues, damaging and compromising sperm quality. This impairment in testicular cells further contributed to compromised testicular tissues, ultimately impacting the reproductive health of F1 male mice.

Role of microbiota in the GUT-SKIN AXIS responses to outdoor stressors

Beside the respiratory tract, the skin and the gut represent the first defensive lines of our body against the external insults displaying many important biochemical features able to maintain the epithelial barrier integrity and to regulate the tissue immune responses. The human microbiome is essential in maintaining the tissue homeostasis and its dysregulation may lead to tissue conditions including inflammatory pathologies. Among all external insults, air pollutants have been shown to cause oxidative stress damage within the target tissues via an OxInflammatory response. Dysregulation of the gut microbiome (dysbiosis) by outdoor stressors, including air pollutants, may promote the exacerbation of the skin tissue damage via the interplay between the gut-skin axis. The intent of this review is to highlight the ability of exogenous stressors to modulate the human gut-skin axis via a redox regulated mechanism affecting the microbiome and therefore contributing to the development and aggravation of gut and skin conditions.

Aryl-hydrocarbon receptor in smooth muscle cells protect against dioxin induced adverse remodeling of atherosclerosis

Introduction

Environmental exposure to dioxin has been linked to increased myocardial infarction. Smooth muscle cells (SMC) in the coronary vasculature play a critical role in atherosclerotic plaque remodeling due to their phenotypic plasticity, however, the detailed mechanism linking dioxin exposure to adverse SMC modulation is not well understood.

Methods

Single-cell RNA and ATAC sequencing and histological analyses were performed on the aorta from mouse models of atherosclerosis exposed to 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) or control. Primary human coronary artery SMC (HCASMC) treated in culture with TCDD were used to perform RNA-Seq, ATAC-Seq, and functional phenotypic assays. ChIP-Seq was performed with antibodies against Aryl-hydrocarbon receptor (AHR) and TCF21, two of known SMC modulating transcription factors.

Results

Modulated SMC were the most transcriptionally responsive cell type to dioxin in the atherosclerotic aorta. Dioxin accelerated disease phenotype by promoting a modulated SMC phenotype early, resulting in increased lesion size, migration of SMC, and macrophage recruitment to the lesion. We found C3 expressing modulated SMCs to be likely contributing to the increased macrophage recruitment and inflammation. Analysis of the RNA-Seq data from HCASMC treated with TCDD showed differential enrichment of biological pathways related to cell migration, localization, and inflammation. Furthermore, ATAC-Seq data showed a significant activation for pathways regulating vascular development, cell migration, inflammation, and apoptosis. With TCDD treatment, there was also enrichment of AHR ChIP-Seq peaks, while the TCF21 enrichment decreased significantly. The SMC-specific Ahr knockout resulted in increased oxidative stress in SMC, increased lesion size and macrophage content, and loss of SMC lineage cells in the lesion cap when exposed to TCDD, consistent with a more vulnerable plaque phenotype.

Conclusion

Dioxin adversely remodels atherosclerotic plaque by accelerating the SMC- phenotypic modulation, and increasing inflammation and oxidative stress resulting in increased macrophage recruitment and lesion size. Dioxin may adversely affect the SMC phenotype and disease state by affecting the TCF21 occupancy in the open chromatin regions. Furthermore, we observed that SMC-specific deletion of Ahr in mice resulted in worsening of dioxin mediated SMC modulation and atherosclerosis, suggesting that Ahr in SMC confers protection against dioxin by promoting a stable plaque phenotype and reducing dioxin induced oxidative stress.

Summary

Exposure to dioxin, an environmental pollutant present in tobacco smoke and air pollution, accelerates smooth muscle cell modulation, and atherosclerosis.Dioxin exposure leads to inflammatory smooth muscle cell phenotype characterized by complement pathway activation and increased macrophage recruitment to plaqueAryl-hydrocarbon receptor in SMC protects against oxidative stress, and promotes a stable plaque phenotype.

Aryl hydrocarbon receptor restricts axon regeneration of DRG neurons in response to injury

Injured neurons sense environmental cues to balance neural protection and axon regeneration, but the mechanisms are unclear. Here, we unveil aryl hydrocarbon receptor (AhR), a ligand-activated bHLH-PAS transcription factor, as a molecular sensor and key regulator of acute stress response at the expense of axon regeneration. We demonstrate responsiveness of DRG sensory neurons to AhR signaling, which functions to inhibit axon regeneration. Conditional Ahr deletion in neurons accelerates axon regeneration after sciatic nerve injury. Ahr deletion partially mimics the conditioning lesion in priming DRG to initiate axonogenesis gene programs; upon peripheral axotomy, Ahr ablation suppresses inflammation and stress signaling while augmenting pro-growth pathways. Moreover, comparative transcriptomics revealed signaling interactions between AhR and HIF-1α, two structurally related bHLH-PAS α units that share the dimerization partner Arnt/HIF-1β. Functional assays showed that the growth advantage of AhR-deficient DRG neurons requires HIF-1α; but in the absence of Arnt, DRG neurons can still mount a regenerative response. We further unveil a link between bHLH-PAS transcription factors and DNA hydroxymethylation in response to peripheral axotomy, while RNA-seq of DRG neurons and neuronal single cell RNA-seq analysis revealed a link of AhR regulon to RNA regulation and integrated stress response (ISR). Altogether, AhR activation favors stress coping and inflammation at the expense of axon regeneration; targeting AhR has the potential to enhance nerve repair.

PIP-seq identifies novel heterogeneous lung innate lymphocyte population activation after combustion product exposure

Innate lymphoid cells (ILCs) are a heterogeneous population that play diverse roles in airway inflammation after exposure to allergens and infections. However, how ILCs respond after exposure to environmental toxins is not well understood. Here we show a novel method for studying the heterogeneity of rare lung ILC populations by magnetic enrichment for lung ILCs followed by particle-templated instant partition sequencing (PIP-seq). Using this method, we were able to identify novel group 1 and group 2 ILC subsets that exist after exposure to both fungal allergen and burn pit-related constituents (BPC) that include dioxin, aromatic hydrocarbon, and particulate matter. Toxin exposure in combination with fungal allergen induced activation of specific ILC1/NK and ILC2 populations as well as promoted neutrophilic lung inflammation. Oxidative stress pathways and downregulation of specific ribosomal protein genes (Rpl41 and Rps19) implicated in anti-inflammatory responses were present after BPC exposure. Increased IFNγ expression and other pro-neutrophilic mediator transcripts were increased in BPC-stimulated lung innate lymphoid cells. Further, the addition of BPC induced Hspa8 (encodes HSC70) and aryl hydrocarbon transcription factor activity across multiple lung ILC subsets. Overall, using an airway disease model that develops after occupational and environmental exposures, we demonstrate an effective method to better understand heterogenous ILC subset activation.

Para-Hydroxycinnamic Acid Mitigates Senescence and Inflammaging in Human Skin Models

Para-hydroxycinnamic acid (pHCA) is one of the most abundant naturally occurring hydroxycinnamic acids, a class of chemistries known for their antioxidant properties. In this study, we evaluated the impact of pHCA on different parameters of skin aging in in vitro skin models after H2O2 and UV exposure. These parameters include keratinocyte senescence and differentiation, inflammation, and energy metabolism, as well as the underlying molecular mechanisms. Here we demonstrate that pHCA prevents oxidative stress-induced premature senescence of human primary keratinocytes in both 2D and 3D skin models, while improving clonogenicity in 2D. As aging is linked to inflammation, referred to as inflammaging, we analyzed the release of IL-6, IL-8, and PGE2, known to be associated with senescence. All of them were downregulated by pHCA in both normal and oxidative stress conditions. Mechanistically, DNA damage induced by oxidative stress is prevented by pHCA, while pHCA also exerts a positive effect on the mitochondrial and glycolytic functions under stress. Altogether, these results highlight the protective effects of pHCA against inflammaging, and importantly, help to elucidate its potential mechanisms of action.

Benzo[a]pyrene evokes epithelial-mesenchymal transition and pulmonary fibrosis through AhR-mediated Nrf2-p62 signaling

Benzo[a]pyrene (BaP) and its metabolic end product benzo(a)pyren-7,8-dihydrodiol-9,10-epoxide (BPDE), are known toxic environmental pollutants. This study aimed to analyze whether sub-chronic BPDE exposure initiated pulmonary fibrosis and the potential mechanisms. In this work, male C57BL6/J mice were exposed to BPDE by dynamic inhalation exposure for 8 weeks. Our results indicated that sub-chronic BPDE exposure evoked pulmonary fibrosis and epithelial-mesenchymal transition (EMT) in mice. Both in vivo and in vitro, BPDE exposure promoted nuclear translocation of Snail. Further experiments indicated that nuclear factor erythroid 2-related factor 2 (Nrf2) and p62 were upregulated in BPDE-exposed alveolar epithelial cells. Moreover, Nrf2 siRNA transfection evidently attenuated BPDE-induced p62 upregulation. Besides, p62 shRNA inhibited BPDE-incurred Snail nuclear translocation and EMT. Mechanically, BPDE facilitated physical interaction between p62 and Snail in the nucleus, then repressed Snail protein degradation by p62-dependent autophagy-lysosome pathway, and finally upregulated transcriptional activity of Snail. Additionally, aryl hydrocarbon receptor (AhR) was activated in BPDE-treated alveolar epithelial cells. Dual-luciferase assay indicated activating AhR could bind to Nrf2 gene promoter. Moreover, pretreatment with CH223191 or α-naphthoflavone (α-NF), AhR antagonists, inhibited BPDE-activated Nrf2-p62 signaling, and alleviated BPDE-induced EMT and pulmonary fibrosis in mice. Taken together, AhR-mediated Nrf2-p62 signaling contributes to BaP-induced EMT and pulmonary fibrosis.

Kynurenic Acid/AhR Signaling at the Junction of Inflammation and Cardiovascular Diseases

Persistent systemic chronic inflammatory conditions are linked with many pathologies, including cardiovascular diseases (CVDs), a leading cause of death across the globe. Among various risk factors, one of the new possible contributors to CVDs is the metabolism of essential amino acid tryptophan. Proinflammatory signals promote tryptophan metabolism via the kynurenine (KYN) pathway (KP), thereby resulting in the biosynthesis of several immunomodulatory metabolites whose biological effects are associated with the development of symptoms and progression of various inflammatory diseases. Some participants in the KP are agonists of aryl hydrocarbon receptor (AhR), a central player in a signaling pathway that, along with a regulatory influence on the metabolism of environmental xenobiotics, performs a key immunomodulatory function by triggering various cellular mechanisms with the participation of endogenous ligands to alleviate inflammation. An AhR ligand with moderate affinity is the central metabolite of the KP: KYN; one of the subsequent metabolites of KYN-kynurenic acid (KYNA)-is a more potent ligand of AhR. Understanding the role of AhR pathway-related metabolites of the KP that regulate inflammatory factors in cells of the cardiovascular system is interesting and important for achieving effective treatment of CVDs. The purpose of this review was to summarize the results of studies about the participation of the KP metabolite-KYNA-and of the AhR signaling pathway in the regulation of inflammation in pathological conditions of the heart and blood vessels and about the possible interaction of KYNA with AhR signaling in some CVDs.

Malignant Melanoma: An Overview, New Perspectives, and Vitamin D Signaling

Melanoma, originating through malignant transformation of melanin-producing melanocytes, is a formidable malignancy, characterized by local invasiveness, recurrence, early metastasis, resistance to therapy, and a high mortality rate. This review discusses etiologic and risk factors for melanoma, diagnostic and prognostic tools, including recent advances in molecular biology, omics, and bioinformatics, and provides an overview of its therapy. Since the incidence of melanoma is rising and mortality remains unacceptably high, we discuss its inherent properties, including melanogenesis, that make this disease resilient to treatment and propose to use AI to solve the above complex and multidimensional problems. We provide an overview on vitamin D and its anticancerogenic properties, and report recent advances in this field that can provide solutions for the prevention and/or therapy of melanoma. Experimental papers and clinicopathological studies on the role of vitamin D status and signaling pathways initiated by its active metabolites in melanoma prognosis and therapy are reviewed. We conclude that vitamin D signaling, defined by specific nuclear receptors and selective activation by specific vitamin D hydroxyderivatives, can provide a benefit for new or existing therapeutic approaches. We propose to target vitamin D signaling with the use of computational biology and AI tools to provide a solution to the melanoma problem.

MLL1 histone methyltransferase and UTX histone demethylase functionally cooperate to regulate the expression of NRF2 in response to ROS-induced oxidative stress

The transcription factor NRF2 plays a pivotal role in maintaining redox and metabolic homeostasis by orchestrating oxidative stress-dependent transcription programs. Despite growing evidence implicating various cellular components in the regulation of NRF2 activity at the posttranslational stage, relatively less is known about the factors dictating the transcriptional activation of NRF2 in response to oxidative stress. In this study, we report the crucial roles of MLL1, an H3K4-specific methyltransferase, and UTX, an H3K27-specific histone demethylase, in the NRF2-dependent transcription program under oxidative stress. We find that the depletion of MLL1 or UTX results in increased susceptibility to oxidative stress, accompanied by higher intracellular ROS and the failed activation of antioxidant genes, including NRF2. In addition, MLL1 and UTX selectively target the NRF2 promoter, and exogenous FLAG-NRF2 expression increases the viability of MLL1-or UTX-depleted cells upon exposure to hydrogen peroxide. RNA-seq analysis demonstrates that depletion of MLL1 or UTX affects the changes in NRF2-dependent transcriptome in response to oxidative stress. Furthermore, ChIP and ChIP-seq analyses find that MLL1 and UTX functionally cooperate to establish a chromatin environment that favors active transcription at the H3K4me3/H3K27me3 bivalent NRF2 promoter in response to ROS-induced oxidative stress. Collectively, these findings provide a molecular mechanism underlying the cellular response to oxidative stress and highlight the importance of the chromatin structure and function in maintaining redox homeostasis.

Lipid Peroxidation-Related Redox Signaling in Osteosarcoma

Oxidative stress and lipid peroxidation play important roles in numerous physiological and pathological processes, while the bioactive products of lipid peroxidation, lipid hydroperoxides and reactive aldehydes, act as important mediators of redox signaling in normal and malignant cells. Many types of cancer, including osteosarcoma, express altered redox signaling pathways. Such redox signaling pathways protect cancer cells from the cytotoxic effects of oxidative stress, thus supporting malignant transformation, and eventually from cytotoxic anticancer therapies associated with oxidative stress. In this review, we aim to explore the status of lipid peroxidation in osteosarcoma and highlight the involvement of lipid peroxidation products in redox signaling pathways, including the involvement of lipid peroxidation in osteosarcoma therapies.

PPARγ alleviates preeclampsia development by regulating lipid metabolism and ferroptosis

The study aims to explore the effect of PPARγ signaling on ferroptosis and preeclampsia (PE) development. Serum and placental tissue are collected from healthy subjects and PE patients. The PPARγ and Nrf2 decreases in the PE. Rosiglitazone intervention reverses hypoxia-induced trophoblast ferroptosis and decreases lipid synthesis by regulating Nfr2 and SREBP1. Compared to the Hypoxia group, the migratory and invasive abilities enhance after rosiglitazone and ferr1 treatment. Rosiglitazone reduces the effect of hypoxia and erastin. The si-Nrf2 treatment attenuats the effects of rosiglitazone on proliferation, migration, and invasion. The si-Nrf2 does not affect SREBP1 expression. PPARγ agonists alleviates ferroptosis in the placenta of the PE rats. The study confirms that PPARγ signaling and ferroptosis-related indicators were dysregulated in PE. PPARγ/Nrf2 signaling affects ferroptosis by regulating lipid oxidation rather than SREBP1-mediated lipid synthesis. In conclusion, our study find that PPARγ can alleviate PE development by regulating lipid oxidation and ferroptosis.

The Antioxidant Drug Edaravone Binds to the Aryl Hydrocarbon Receptor (AHR) and Promotes the Downstream Signaling Pathway Activation

A considerable effort has been spent in the past decades to develop targeted therapies for the treatment of demyelinating diseases, such as multiple sclerosis (MS). Among drugs with free radical scavenging activity and oligodendrocyte protecting effects, Edaravone (Radicava) has recently received increasing attention because of being able to enhance remyelination in experimental in vitro and in vivo disease models. While its beneficial effects are greatly supported by experimental evidence, there is a current paucity of information regarding its mechanism of action and main molecular targets. By using high-throughput RNA-seq and biochemical experiments in murine oligodendrocyte progenitors and SH-SY5Y neuroblastoma cells combined with molecular docking and molecular dynamics simulation, we here provide evidence that Edaravone triggers the activation of aryl hydrocarbon receptor (AHR) signaling by eliciting AHR nuclear translocation and the transcriptional-mediated induction of key cytoprotective gene expression. We also show that an Edaravone-dependent AHR signaling transduction occurs in the zebrafish experimental model, associated with a downstream upregulation of the NRF2 signaling pathway. We finally demonstrate that its rapid cytoprotective and antioxidant actions boost increased expression of the promyelinating Olig2 protein as well as of an Olig2:GFP transgene in vivo. We therefore shed light on a still undescribed potential mechanism of action for this drug, providing further support to its therapeutic potential in the context of debilitating demyelinating conditions.

Keap1-Nrf2 pathway: a key mechanism in the occurrence and development of cancer

The Keap1-Nrf2 signaling pathway is a major regulator of the cytoprotective response, participating in endogenous and exogenous stress caused by ROS (reactive oxygen species). Nrf2 is the core of this pathway. We summarized the literature on Keap1-Nrf2 signaling pathway and summarized the following three aspects: structure, function pathway, and cancer and clinical application status. This signaling pathway is similar to a double-edged sword: on the one hand, Nrf2 activity can protect cells from oxidative and electrophilic stress; on the other hand, increasing Nrf2 activity can enhance the survival and proliferation of cancer cells. Notably, oxidative stress is also considered a marker of cancer in humans. Keap1-Nrf2 signaling pathway, as a typical antioxidant stress pathway, is abnormal in a variety of human malignant tumor diseases (such as lung cancer, liver cancer, and thyroid cancer). In recent years, research on the Keap1-Nrf2 signaling pathway has become increasingly in-depth and detailed. Therefore, it is of great significance for cancer prevention and treatment to explore the molecular mechanism of the occurrence and development of this pathway.

The crucial role of NRF2 in erythropoiesis and anemia: Mechanisms and therapeutic opportunities

The nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor crucial in cellular defense against oxidative and electrophilic stresses. Recent research has highlighted the significance of NRF2 in normal erythropoiesis and anemia. NRF2 regulates genes involved in vital aspects of erythroid development, including hemoglobin catabolism, inflammation, and iron homeostasis in erythrocytes. Disrupted NRF2 activity has been implicated in various pathologies involving abnormal erythropoiesis. In this review, we summarize the progress made in understanding the mechanisms of NRF2 activation in erythropoiesis and explore the roles of NRF2 in various types of anemia. This review also discusses the potential of targeting NRF2 as a new therapeutic approach to treat anemia.

Uremic toxins mediate kidney diseases: the role of aryl hydrocarbon receptor

Aryl hydrocarbon receptor (AhR) was originally identified as an environmental sensor that responds to pollutants. Subsequent research has revealed that AhR recognizes multiple exogenous and endogenous molecules, including uremic toxins retained in the body due to the decline in renal function. Therefore, AhR is also considered to be a uremic toxin receptor. As a ligand-activated transcriptional factor, the activation of AhR is involved in cell differentiation and senescence, lipid metabolism and fibrogenesis. The accumulation of uremic toxins in the body is hazardous to all tissues and organs. The identification of the endogenous uremic toxin receptor opens the door to investigating the precise role and molecular mechanism of tissue and organ damage induced by uremic toxins. This review focuses on summarizing recent findings on the role of AhR activation induced by uremic toxins in chronic kidney disease, diabetic nephropathy and acute kidney injury. Furthermore, potential clinical approaches to mitigate the effects of uremic toxins are explored herein, such as enhancing uremic toxin clearance through dialysis, reducing uremic toxin production through dietary interventions or microbial manipulation, and manipulating metabolic pathways induced by uremic toxins through controlling AhR signaling. This information may also shed light on the mechanism of uremic toxin-induced injury to other organs, and provide insights into clinical approaches to manipulate the accumulated uremic toxins.

Allyl isothiocyanate regulates oxidative stress, inflammation, cell proliferation, cell cycle arrest, apoptosis, angiogenesis, invasion and metastasis via interaction with multiple cell signaling pathways

Cancer growth is a molecular mechanism initiated by genetic and epigenetic modifications that are involved in cell proliferation, differentiation, apoptosis, and senescence pathways. Chemoprevention is an important strategy for cancer treatment that leads to blocking, reversing, or impeding the multistep process of tumorigenesis, including the blockage of its vital morphogenetic milestones viz. normal, preneoplasia, neoplasia, and metastasis. Naturally occurring phytochemicals are becoming ever more popular compared to synthetic drugs for many reasons, including safety, bioavailability, efficacy, and easy availability. Allyl isothiocyanate (AITC) is a natural compound present in all plants of the Cruciferae family, such as Brussels sprouts, cauliflower, mustard, cabbage, kale, horseradish, and wasabi. In vitro and in vivo studies carried out over the decades have revealed that AITC inhibits tumorigenesis without any toxicity and undesirable side effects. The bioavailability of AITC is exceedingly high, as it was reported that nearly 90% of orally administered AITC is absorbed. AITC exhibits multiple pharmacological properties among which its anticancer activity is the most significant for cancer treatment. Its anticancer activity is exerted via selective modulation of multiple cell signaling pathways related to oxidative stress, inflammation, cell proliferation, cell cycle arrest, apoptosis, angiogenesis, invasion, and metastasis. This review highlights the current knowledge on molecular targets that are involved in the anticancer effect of AITC associated with (i) inhibition of carcinogenic activation and induction of antioxidants, (ii) suppression of pro-inflammatory and cell proliferative signals, (iii) induction of cell cycle arrest and apoptosis, and (iv) inhibition of angiogenic and invasive signals related to metastasis.

Heavy metals, oxidative stress, and the role of AhR signaling

The Aryl Hydrocarbon Receptor (AhR) is a ligand-activated transcriptional factor pivotal in responding to environmental stress and maintaining cellular homeostasis. Exposure to specific xenobiotics or industrial compounds in the environment activates AhR and its subsequent signaling, inducing oxidative stress and related toxicity. Past research has also identified and characterized several classes of endogenous ligands, particularly some tryptophan (Trp) metabolic/catabolic products, that act as AhR agonists, influencing a variety of physiological and pathological states, including the modulation of immune responses and cell death. Heavy metals, being non-essential elements in the human body, are generally perceived as toxic and hazardous, originating either naturally or from industrial activities. Emerging evidence indicates that heavy metals significantly influence AhR activation and its downstream signaling. This review consolidates current knowledge on the modulation of the AhR signaling pathway by heavy metals, explores the consequences of co-exposure to AhR ligands and heavy metals, and investigates the interplay between oxidative stress and AhR activation, focusing on the regulation of immune responses and ferroptosis.

Exploring the multifaceted role of NRF2 in brain physiology and cancer: A comprehensive review

Chronic oxidative stress plays a critical role in the development of brain malignancies due to the high rate of brain oxygen utilization and concomitant production of reactive oxygen species. The nuclear factor-erythroid-2-related factor 2 (NRF2), a master regulator of antioxidant signaling, is a key factor in regulating brain physiology and the development of age-related neurodegenerative diseases. Also, NRF2 is known to exert a protective antioxidant effect against the onset of oxidative stress-induced diseases, including cancer, along with its pro-oncogenic activities through regulating various signaling pathways and downstream target genes. In glioblastoma (GB), grade 4 glioma, tumor resistance, and recurrence are caused by the glioblastoma stem cell population constituting a small bulk of the tumor core. The persistence and self-renewal capacity of these cell populations is enhanced by NRF2 expression in GB tissues. This review outlines NRF2's dual involvement in cancer and highlights its regulatory role in human brain physiology and diseases, in addition to the development of primary brain tumors and therapeutic potential, with a focus on GB.

Transcription Factor NRF2 in Shaping Myeloid Cell Differentiation and Function

NFE2-related factor 2 (NRF2) is a master transcription factor (TF) that coordinates key cellular homeostatic processes including antioxidative responses, autophagy, proteostasis, and metabolism. The emerging evidence underscores its significant role in modulating inflammatory and immune processes. This chapter delves into the role of NRF2 in myeloid cell differentiation and function and its implication in myeloid cell-driven diseases. In macrophages, NRF2 modulates cytokine production, phagocytosis, pathogen clearance, and metabolic adaptations. In dendritic cells (DCs), it affects maturation, cytokine production, and antigen presentation capabilities, while in neutrophils, NRF2 is involved in activation, migration, cytokine production, and NETosis. The discussion extends to how NRF2's regulatory actions pertain to a wide array of diseases, such as sepsis, various infectious diseases, cancer, wound healing, atherosclerosis, hemolytic conditions, pulmonary disorders, hemorrhagic events, and autoimmune diseases. The activation of NRF2 typically reduces inflammation, thereby modifying disease outcomes. This highlights the therapeutic potential of NRF2 modulation in treating myeloid cell-driven pathologies.

Antioxidant effect of lactic acid bacteria in human bronchial epithelial cells exposed to cigarette smoke

AIMS

Chronic lung diseases are a major and increasing global health problem, commonly caused by cigarette smoke. We aimed to explore the antioxidant effects of lactic acid bacteria (LAB) against cigarette smoke in bronchial epithelial cells.

METHODS AND RESULTS

The antioxidant effects of 21 heat-killed (HK) LAB strains were tested in cigarette smoke-stimulated BEAS-2B cells and 3-D bronchospheres organoids. We showed that HK Lactiplantibacillus plantarum BGPKM22 possesses antioxidant activity against cigarette smoke, resistance to hydrogen peroxide, and free radical neutralizing activity. We demonstrated that HK BGPKM22 inhibited cigarette smoke-induced expression of the Aryl hydrocarbon receptor (AhR) and Nuclear factor erythroid 2 related factor 2 (Nrf2) genes. The cell-free supernatant (SN) of BGPKM22 fully confirmed the effects of HK BGPKM22.

CONCLUSIONS

For the first time, we revealed that HK and SN of Lactip. plantarum BGPKM22 possess antioxidant activity and modulate AhR and Nrf2 gene expression in bronchial epithelial cells exposed to cigarette smoke.

Persistent organic pollutants (POPs) in marine crustaceans: Bioaccumulation, physiological and cellular responses

Persistent organic pollutants (POPs) are ubiquitous in marine ecosystems. These compounds can be accumulated in water, sediments and organisms, persist in time, and have toxic effects in human and wildlife. POPs can be uptaken and bioaccumulated by crustaceans, affecting different physiological processes, including energy metabolism, immunity, osmoregulation, excretion, growth, and reproduction. Nonetheless, animals have evolved sub-cellular mechanisms for detoxification and protection from chemical stress. POPs induce the activity of enzymes involved in xenobiotic metabolism and antioxidant systems, that in vertebrates are importantly regulated at gene expression (transcriptional) level. However, the activation and control of these enzyme systems upon the exposure to POPs have been scarcely studied in invertebrate species, including crustaceans. Herein, we summarize various aspects of the bioaccumulation of POPs in marine crustaceans and their physiological effects. We specially focus on the regulation of xenobiotics metabolism and antioxidant enzymes as key sub-cellular mechanisms for detoxification and protection from chemical stress.

The effects of environmental aryl hydrocarbon receptor ligands on signaling and cell metabolism in cancer

Dioxin and dioxin-like compounds are chlorinated organic pollutants formed during the manufacturing of other chemicals. Dioxins are ligands of the aryl hydrocarbon receptor (AHR), that induce AHR-mediated biochemical and toxic responses and are persistent in the environment. 2,3,7,8- tetrachlorodibenzo para dioxin (TCDD) is the prototypical AHR ligand and its effects represent dioxins. TCDD induces toxicity, immunosuppression and is a suspected tumor promoter. The role of TCDD in cancer however is debated and context-dependent. Environmental particulate matter, polycyclic aromatic hydrocarbons, perfluorooctane sulfonamide, endogenous AHR ligands, and cAMP signaling activate AHR through TCDD-independent pathways. The effect of activated AHR in cancer is context-dependent. The ability of FDA-approved drugs to modulate AHR activity has sparked interest in their repurposing for cancer therapy. TCDD by interfering with endogenous pathways, and overstimulating other endogenous pathways influences all stages of cancer. Herein we review signaling mechanisms that activate AHR and mechanisms by which activated AHR modulates signaling in cancer including affected metabolic pathways.

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.

Methylmercury (MeHg) transcriptionally regulates NAD(P)H:quinone oxidoreductase 1 (NQO1) in Hepa-1c1c7 cells

The detoxification of quinones through NAD(P)H:quinone oxidoreductase (NQO1) is a crucial mechanism to maintain cellular homeostasis. The exposure to heavy metals, specifically methylmercury (MeHg), induces several antioxidant enzymes, including NQO1. The nuclear factor erythroid 2-related factor-2 (NRF2) is known to regulate the expression of Nqo1 gene and also the aryl hydrocarbon receptor (AHR) is another Nqo1 gene regulator. This co-regulation prompted us to investigate which transcription factor (NRF2 or AHR) orchestrates the regulation of NQO1 expression upon MeHg exposure. Therefore, we investigated how MeHg can modulate the level of NQO1 expression by exposing Hepa-1c1c7 cells to several concentrations of MeHg with and without the addition of NQO1 inducers, DL-sulforaphane (SUL) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We found that the mRNA expression of Nqo1 is up-regulated by MeHg in time- as well as dose-dependent fashions. Additionally, MeHg increased the NQO1 at all expression levels with and without the presence of its inducers, SUL or TCDD. Furthermore, the MeHg-mediated increase of NQO1 expression was in parallel with a concurrent increase in the nuclear localization of NRF2 protein, but not that of AHR. Mechanistically, the antioxidant response element-driven reporter gene activity was induced by 215% upon MeHg exposure. Also, transfecting Hepa-1c1c7 with Nrf2 siRNA reduced the MeHg-induced NQO1 protein expression by 60%. In conclusion, our findings provide evidence supporting the hypothesis that MeHg upregulates the Nqo1 gene through a transcriptional mechanism at least in part via a NRF2-dependent mechanism.

NRF2, a Superstar of Ferroptosis

Ferroptosis is an iron-dependent and lipid peroxidation-driven cell death cascade, occurring when there is an imbalance of redox homeostasis in the cell. Nuclear factor erythroid 2-related factor 2 (NFE2L2, also known as NRF2) is key for cellular antioxidant responses, which promotes downstream genes transcription by binding to their antioxidant response elements (AREs). Numerous studies suggest that NRF2 assumes an extremely important role in the regulation of ferroptosis, for its various functions in iron, lipid, and amino acid metabolism, and so on. Many pathological states are relevant to ferroptosis. Abnormal suppression of ferroptosis is found in many cases of cancer, promoting their progression and metastasis. While during tissue damages, ferroptosis is recurrently promoted, resulting in a large number of cell deaths and even dysfunctions of the corresponding organs. Therefore, targeting NRF2-related signaling pathways, to induce or inhibit ferroptosis, has become a great potential therapy for combating cancers, as well as preventing neurodegenerative and ischemic diseases. In this review, a brief overview of the research process of ferroptosis over the past decade will be presented. In particular, the mechanisms of ferroptosis and a focus on the regulation of ferroptosis by NRF2 will be discussed. Finally, the review will briefly list some clinical applications of targeting the NRF2 signaling pathway in the treatment of diseases.

Ferroptosis in the colon epithelial cells as a therapeutic target for ulcerative colitis

BACKGROUND

Ferroptosis, a type of programmed cell death triggered by oxidative stress, was suspected to play a role in ulcerative colitis. Indigo naturalis is highly effective against ulcerative colitis, but its mechanism is unclear. This study found that indigo naturalis treatment suppressed ferroptosis.

METHODS

We analyzed 770 mRNA expressions of patients with ulcerative colitis. Suppression of ferroptosis by indigo naturalis treatment was shown using a cell death assay. Malondialdehyde levels and reactive oxygen species were analyzed in CaCo-2 cells treated with indigo naturalis. Glutathione metabolism was shown by metabolomic analysis. Extraction of the ingredients indigo naturalis from the rectal mucosa was performed using liquid chromatograph-mass spectrometry.

RESULTS

Gene expression profiling showed that indigo naturalis treatment increased antioxidant genes in the mucosa of patients with ulcerative colitis. In vitro analysis showed that nuclear factor erythroid-2-related factor 2-related antioxidant gene expression was upregulated by indigo naturalis. Indigo naturalis treatment rendered cells resistant to ferroptosis. Metabolomic analysis suggested that an increase in reduced glutathione by indigo naturalis. The protein expression of CYP1A1 and GPX4 was increased in the rectum by treatment with indigo naturalis. The main ingredients of indigo naturalis, indirubin and indigo inhibited ferroptosis. Indirubin was detected in the rectal mucosa of patients with ulcerative colitis who were treated with indigo naturalis.

CONCLUSIONS

Suppression of ferroptosis by indigo naturalis in the intestinal epithelium could be therapeutic target for ulcerative colitis. The main active ingredient of indigo naturalis may be indirubin.

Jdp2 is a spatiotemporal transcriptional activator of the AhR via the Nrf2 gene battery

BACKGROUND

Crosstalk between the aryl hydrocarbon receptor (AhR) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling is called the "AhR-Nrf2 gene battery", which works synergistically in detoxification to support cell survival. Nrf2-dependent phase II gene promoters are controlled by coordinated recruitment of the AhR to adjacent dioxin responsive element (DRE) and Nrf2 recruitment to the antioxidative response element (ARE). The molecular interaction between AhR and Nrf2 members, and the regulation of each target, including phase I and II gene complexes, and their mediators are poorly understood.

METHODS

Knockdown and forced expression of AhR-Nrf2 battery members were used to examine the molecular interactions between the AhR-Nrf2 axis and AhR promoter activation. Sequential immunoprecipitation, chromatin immunoprecipitation, and histology were used to identify each protein complex recruited to their respective cis-elements in the AhR promoter. Actin fiber distribution, cell spreading, and invasion were examined to identify functional differences in the AhR-Jdp2 axis between wild-type and Jdp2 knockout cells. The possible tumorigenic role of Jdp2 in the AhR-Nrf2 axis was examined in mutant Kras-Trp53-driven pancreatic tumors.

RESULTS

Crosstalk between AhR and Nrf2 was evident at the transcriptional level. The AhR promoter was activated by phase I ligands such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) through the AhR-Jdp2-Nrf2 axis in a time- and spatial transcription-dependent manner. Jdp2 was a bifunctional activator of DRE- and ARE-mediated transcription in response to TCDD. After TCDD exposure, Jdp2 activated the AhR promoter at the DRE and then moved to the ARE where it activated the promoter to increase reactive oxygen species (ROS)-mediated functions such as cell spreading and invasion in normal cells, and cancer regression in mutant Kras-Trp53-driven pancreatic tumor cells.

CONCLUSIONS

Jdp2 plays a critical role in AhR promoter activation through the AhR-Jdp2-Nrf2 axis in a spatiotemporal manner. The AhR functions to maintain ROS balance and cell spreading, invasion, and cancer regression in a mouse model of mutant Kras-Trp53 pancreatic cancer. These findings provide new insights into the roles of Jdp2 in the homeostatic regulation of oxidative stress and in the antioxidation response in detoxification, inflammation, and cancer progression.

Interferon Gamma Enhances Cytoprotective Pathways via Nrf2 and MnSOD Induction in Friedreich's Ataxia Cells

Friedreich's ataxia (FRDA) is a rare monogenic disease characterized by multisystem, slowly progressive degeneration. Because of the genetic defect in a non-coding region of FXN gene, FRDA cells exhibit severe deficit of frataxin protein levels. Hence, FRDA pathophysiology is characterized by a plethora of metabolic disruptions related to iron metabolism, mitochondrial homeostasis and oxidative stress. Importantly, an impairment of the antioxidant defences exacerbates the oxidative damage. This appears closely associated with the disablement of key antioxidant proteins, such as the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and the mitochondrial superoxide dismutase (MnSOD). The cytokine interferon gamma (IFN-γ) has been shown to increase frataxin expression in FRDA cells and to improve functional deficits in FRDA mice. Currently, IFN-γ represents a potential therapy under clinical evaluation in FRDA patients. Here, we show that IFN-γ induces a rapid expression of Nrf2 and MnSOD in different cell types, including FRDA patient-derived fibroblasts. Our data indicate that IFN-γ signals two separate pathways to enhance Nrf2 and MnSOD levels in FRDA fibroblasts. MnSOD expression increased through an early transcriptional regulation, whereas the levels of Nrf2 are induced by a post-transcriptional mechanism. We demonstrate that the treatment of FRDA fibroblasts with IFN-γ stimulates a non-canonical Nrf2 activation pathway through p21 and potentiates antioxidant responses under exposure to hydrogen peroxide. Moreover, IFN-γ significantly reduced the sensitivity to hydrogen peroxide-induced cell death in FRDA fibroblasts. Collectively, these results indicate the presence of multiple pathways triggered by IFN-γ with therapeutic relevance to FRDA.

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.

Fenofibrate attenuates the cytotoxic effect of cisplatin on lung cancer cells by enhancing the antioxidant defense system in vitro

Fenofibrate (FF) is a peroxisome proliferator- activated receptor (PPAR)-α agonist that is widely used for the treatment of hyperlipidemia. It has been shown to have pleiotropic actions beyond its hypolipidemic effect. FF has been shown to exert a cytotoxic effect on some cancer cells when used at higher than clinically relevant concentrations; on the other hand, its cytoprotective effect on normal cells has also been reported. The present study assessed the effect of FF on cisplatin (CDDP) cytotoxicity to lung cancer cells in vitro. The results demonstrated that the effect of FF on lung cancer cells depends on its concentration. FF at ≤50 µM, which is a clinically achievable blood concentration, attenuated CDDP cytotoxicity to lung cancer cells, whereas FF at ≥100 µM, albeit clinically unachievable, had an anticancer effect. The mechanism of FF attenuation of CDDP cytotoxicity involved PPAR-α-dependent aryl hydrocarbon receptor (AhR) expression, which in turn stimulated nuclear factor erythroid 2-related factor 2 (Nrf2) expression and antioxidant production, resulting in lung cancer cell protection from CDDP-evoked oxidative damage. In conclusion, the present study revealed that FF, at clinically relevant concentrations, attenuated CDDP cytotoxicity to lung cancer cells by enhancing the antioxidant defense system through activation of a pathway that involves the PPAR-α-PPAR response element-AhR xenobiotic response element-Nrf2-antioxidant response element. These findings suggested that concomitant use of FF with CDDP may compromise the efficacy of chemotherapy. Although the anticancer property of FF has recently attracted much attention, concentrations that exceed clinically relevant concentrations are required.

Aryl hydrocarbon receptor (AHR): towards understanding intestinal microbial ligands including vitamin B12 and folic acid as natural antagonists

AHR has been identified as ligand-modulated transcription factor and environmental sensor. However, explanation of its multiple agonistic and antagonistic ligands is far from complete. Studies of AHR's role in host-microbiome interaction are currently a fruitful area of research. Microbial products and virulence factors have been identified as AHR agonists. In steady state they are involved in safeguarding intestinal barrier integrity. When virulence factors from pathogenic bacteria are identified by AHR of intestinal immune cells, anti-microbial defense mechanisms are activated by generating reactive oxygen species (ROS) in intestinal epithelial cells and recruited immune cells. ROS production has to be strictly controlled, and anti-inflammatory responses have to be initiated timely in the resolution phase of inflammation to avoid tissue damage and chronic inflammatory responses. Surprisingly, bacteria-generated vitamin B12/cobalamin and vitamin B9/folic acid have been identified as natural AHR antagonists, stimulating the interest of biochemists. Hints for AHR-cobalamin antagonism are pointing to cobalamin-dependent enzymes leading to alterations of TCA cycle intermediates, and TCDD-mediated loss of serum cobalamin. Although we are still at the beginning to understand mechanisms, it is likely that scientific efforts are on a rewarding path to understand novel AHR functions.

Development, scrutiny, and modulation of transient reporter gene assays of the xenobiotic metabolism pathway in zebrafish hepatocytes

The "toxicology in the twenty-first century" paradigm shift demands the development of alternative in vitro test systems. Especially in the field of ecotoxicology, coverage of aquatic species-specific assays is relatively scarce. Transient reporter gene assays could be a quick, economical, and reliable bridging technology. However, the user should be aware of potential pitfalls that are influenced by reporter vector geometry. Here, we report the development of an AhR-responsive transient reporter-gene assay in the permanent zebrafish hepatocytes cell line (ZFL). Additionally, we disclose how viral, constitutive promoters within reporter-gene assay cassettes induce squelching of the primary signal. To counter this, we designed a novel normalization vector, bearing an endogenous zebrafish-derived genomic promoter (zfEF1aPro), which rescues the squelching-delimited system, thus, giving new insights into the modulation of transient reporter systems under xenobiotic stress. Finally, we uncovered how the ubiquitously used ligand BNF promiscuously activates multiple toxicity pathways of the xenobiotic metabolism and cellular stress response in an orchestral manner, presumably leading to a concentration-related inhibition of the AhR/ARNT/XRE-toxicity pathway and non-monotonous concentration-response curves. We named such a multi-level inhibitory mechanism that might mask effects as "maisonette squelching." A transient reporter gene assay in zebrafish cell lines utilizing endogenous regulatory gene elements shows increased in vitro toxicity testing performance. Synthetic and constitutive promotors interfere with signal transduction ("squelching") and might increase cellular stress (cytotoxicity). The squelching phenomenon might occur on multiple levels (toxicity pathway crosstalk and normalization vector), leading to a complete silencing of the reporter signal.

Tryptophan depletion sensitizes the AHR pathway by increasing AHR expression and GCN2/LAT1-mediated kynurenine uptake, and potentiates induction of regulatory T lymphocytes

BACKGROUND

Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan-dioxygenase (TDO) are enzymes catabolizing the essential amino acid tryptophan into kynurenine. Expression of these enzymes is frequently observed in advanced-stage cancers and is associated with poor disease prognosis and immune suppression. Mechanistically, the respective roles of tryptophan shortage and kynurenine production in suppressing immunity remain unclear. Kynurenine was proposed as an endogenous ligand for the aryl hydrocarbon receptor (AHR), which can regulate inflammation and immunity. However, controversy remains regarding the role of AHR in IDO1/TDO-mediated immune suppression, as well as the involvement of kynurenine. In this study, we aimed to clarify the link between IDO1/TDO expression, AHR pathway activation and immune suppression.

METHODS

AHR expression and activation was analyzed by RT-qPCR and western blot analysis in cells engineered to express IDO1/TDO, or cultured in medium mimicking tryptophan catabolism by IDO1/TDO. In vitro differentiation of naïve CD4⁺ T cells into regulatory T cells (Tregs) was compared in T cells isolated from mice bearing different Ahr alleles or a knockout of Ahr, and cultured in medium with or without tryptophan and kynurenine.

RESULTS

We confirmed that IDO1/TDO expression activated AHR in HEK-293-E cells, as measured by the induction of AHR target genes. Unexpectedly, AHR was also overexpressed on IDO1/TDO expression. AHR overexpression did not depend on kynurenine but was triggered by tryptophan deprivation. Multiple human tumor cell lines overexpressed AHR on tryptophan deprivation. AHR overexpression was not dependent on general control non-derepressible 2 (GCN2), and strongly sensitized the AHR pathway. As a result, kynurenine and other tryptophan catabolites, which are weak AHR agonists in normal conditions, strongly induced AHR target genes in tryptophan-depleted conditions. Tryptophan depletion also increased kynurenine uptake by increasing SLC7A5 (LAT1) expression in a GCN2-dependent manner. Tryptophan deprivation potentiated Treg differentiation from naïve CD4⁺ T cells isolated from mice bearing an AHR allele of weak affinity similar to the human AHR.

CONCLUSIONS

Tryptophan deprivation sensitizes the AHR pathway by inducing AHR overexpression and increasing cellular kynurenine uptake. As a result, tryptophan catabolites such as kynurenine more potently activate AHR, and Treg differentiation is promoted. Our results propose a molecular explanation for the combined roles of tryptophan deprivation and kynurenine production in mediating IDO1/TDO-induced immune suppression.

Variation in pentose phosphate pathway-associated metabolism dictates cytotoxicity outcomes determined by tetrazolium reduction assays

Tetrazolium reduction and resazurin assays are the mainstay of routine in vitro toxicity batteries. However, potentially erroneous characterization of cytotoxicity and cell proliferation can arise if verification of baseline interaction of test article with method employed is neglected. The current investigation aimed to demonstrate how interpretation of results from several standard cytotoxicity and proliferation assays vary in dependence on contributions from the pentose phosphate pathway (PPP). Non-tumorigenic Beas-2B cells were treated with graded concentrations of benzo[a]pyrene (B[a]P) for 24 and 48 h prior to cytotoxicity and proliferation assessment with commonly used MTT, MTS, WST1, and Alamar Blue assays. B[a]P caused enhanced metabolism of each dye assessed despite reductions in mitochondrial membrane potential and was reversed by 6-aminonicotinamide (6AN)-a glucose-6-phosphate dehydrogenase inhibitor. These results demonstrate differential sensitivity of standard cytotoxicity assessments on the PPP, thus (1) decoupling "mitochondrial activity" as an interpretation of cellular formazan and Alamar Blue metabolism, and (2) demonstrating the implicit requirement for investigators to sufficiently verify interaction of these methods in routine cytotoxicity and proliferation characterization. The nuances of method-specific extramitochondrial metabolism must be scrutinized to properly qualify specific endpoints employed, particularly under the circumstances of metabolic reprogramming.

Targeting the aryl hydrocarbon receptor by gut phenolic metabolites: A strategy towards gut inflammation

The Aryl Hydrocarbon Receptor (AHR) is a ligand-dependent transcription factor able to control complex transcriptional processes in several cell types, which has been correlated with various diseases, including inflammatory bowel diseases (IBD). Numerous studies have described different compounds as ligands of this receptor, like xenobiotics, natural compounds, and several host-derived metabolites. Dietary (poly)phenols have been studied regarding their pleiotropic activities (e.g., neuroprotective and anti-inflammatory), but their AHR modulatory capabilities have also been considered. However, dietary (poly)phenols are submitted to extensive metabolism in the gut (e.g., gut microbiota). Thus, the resulting gut phenolic metabolites could be key players modulating AHR since they are the ones that reach the cells and may exert effects on the AHR throughout the gut and other organs. This review aims at a comprehensive search for the most abundant gut phenolic metabolites detected and quantified in humans to understand how many have been described as AHR modulators and what could be their impact on inflammatory gut processes. Even though several phenolic compounds have been studied regarding their anti-inflammatory capacities, only 1 gut phenolic metabolite, described as AHR modulator, has been evaluated on intestinal inflammatory models. Searching for AHR ligands could be a novel strategy against IBD.

Antioxidants attenuate mitochondrial oxidative damage through the Nrf2 pathway: A promising therapeutic strategy for stroke

Stroke represents one of the leading causes of disability and death worldwide. Reactive oxygen species overproduction-induced oxidative stress in mitochondria results in mitochondrial DNA damage, mitochondrial autophagy (mitophagy), inflammation, and apoptosis during the pathologic progression of stroke. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulator that induces the transcription of a wide range of antioxidant genes to attenuate mitochondrial oxidative stress. Different antioxidative compounds, including polyphenols, mitochondrial antioxidants, triterpenoids, and others, have been shown to be able to activate Nrf2 and, thus, exert neuroprotective effects on stroke by ameliorating mitochondrial oxidative damage. In this review, we briefly discussed the role of mitochondrial oxidative stress in the pathophysiology of stroke and focused on the protective effects of antioxidative compounds through attenuating mitochondrial oxidative damage by activating Nrf2 in stroke. In conclusion, these antioxidants may represent novel therapeutic strategies against stroke.

The inhibitory effect of vitamin D on myocardial homocysteine levels involves activation of Nrf2-mediated methionine synthase

BACKGROUND

Homocysteine (Hcy) is a synthetic amino acid containing sulfhydryl group, which is an intermediate product of the deep metabolic pathway of methionine and cysteine. The abnormal increase in fasting plasma total Hcy concentration caused by various factors is called hyperhomocysteine (HHcy). HHcy is closely relevant to the occurrence and progression of diverse cardiovascular and cerebrovascular diseases, such as coronary heart disease, hypertension and diabetes, etc. Vitamin D/vitamin D receptor (VDR) pathway is pointed out that prevent cardiovascular disease by reducing serum homocysteine levels. Our research is designed to explore the potential mechanism of vitamin D in the prevention and treatment of HHcy.

METHODS AND RESULTS

The Hcy and 25(OH)D₃ levels in mouse myocardial tissue, serum or myocardial cells were detected using ELISA kits. The expression levels of VDR, Nrf2 and methionine synthase (MTR) were observed using Western blotting, immunohistochemistry and real time polymerase chain reaction (PCR). General information of the mice, including diet, water intake and body weight, was recorded. Vitamin D up-regulated the mRNA and protein expression of Nrf2 and MTR in mouse myocardial tissue and cells. CHIP assay determined that the combination of Nrf2 binding to the S1 site of the MTR promoter in cardiomyocytes using traditional PCR and real time PCR. Dual Luciferase Assay was applied to detect the transcriptional control of Nrf2 on MTR. The up-regulation effect of Nrf2 on MTR was verified by Nrf2 knockout and overexpression in cardiomyocytes. The role of Nrf2 in vitamin D inhibition of Hcy was revealed using Nrf2-knockdown HL-1 cells and Nrf2 heterozygous mice. Western blotting, real time PCR, IHC staining and ELISA showed that Nrf2 deficiency could restrain the increase in MTR expression and the decrease in Hcy level induced by vitamin D. The transcriptional activities of Nrf2/MTR were activated by vitamin D/VDR with a decrease in Hcy.

CONCLUSION

Vitamin D/VDR upregulates MTR in an Nrf2-dependent manner, thereby reducing the risk of HHcy.

2,3',4,4',5-Pentachlorobiphenyl induces mitochondria-dependent apoptosis mediated by AhR/Cyp1a1 in mouse germ cells

Polychlorinated biphenyls (PCBs) are environmental organic pollutants widely used in industry that can bioaccumulate and affect the reproductive systems of male animals of different species. 2,3',4,4',5-Pentachlorobiphenyl (PCB118) is a representative of the 209 toxic PCB congeners. In this study, male mice were exposed to PCB118 at 0, 50, and 500 μg/kg/day for 35 days beginning 3-4 weeks after birth. The results of the study showed that PCB118 exposure during puberty reduced testicular quality, caused tissue damage, decreased sperm motility and sperm count, and increased malformation and testicular cell apoptosis in mice. Moreover, PCB118 increased the oxidative stress levels in sperm and testicular tissue and the expression of aryl hydrocarbon receptor (AhR) and Cyp1a1 and siginificantly decreased the level of nuclear factor-erythroid 2-related factor 2 (Nrf2). The results indicate that PCB118 can activate the AhR/Cyp1a1 pathway and inhibit Nrf2 expression to aggravate testicular oxidative stress and induce cell apoptosis, resulting in testicular and sperm quality damage.

Reprotoxic Effect of Tris(2,3-Dibromopropyl) Isocyanurate (TBC) on Spermatogenic Cells In Vitro

Tris(2,3-dibromopropyl) isocyanurate (TBC) belongs to the class of novel brominated flame retardants (NFBRs) that are widely used in industry. It has commonly been found in the environment, and its presence has been discovered in living organisms as well. TBC is also described as an endocrine disruptor that is able to affect male reproductive processes through the estrogen receptors (ERs) engaged in the male reproductive processes. With the worsening problem of male infertility in humans, a mechanism is being sought to explain such reproductive difficulties. However, so far, little is known about the mechanism of action of TBC in male reproductive models in vitro. Therefore, the aim of the study was to evaluate the effect of TBC alone and in cotreatment with BHPI (estrogen receptor antagonist), 17β-estradiol (E₂), and letrozole on the basic metabolic parameters in mouse spermatogenic cells (GC-1 spg) in vitro, as well as the effect of TBC on mRNA expression (Ki67, p53, Pparγ, Ahr, and Esr1). The presented results show the cytotoxic and apoptotic effects of high micromolar concentrations of TBC on mouse spermatogenic cells. Moreover, an increase in Pparγ mRNA levels and a decrease in Ahr and Esr1 gene expression were observed in GS-1spg cells cotreated with E₂. These results suggest the significant involvement of TBC in the dysregulation of the steroid-based pathway in the male reproductive cell models in vitro and may be the cause of the currently observed deterioration of male fertility. However, more research is needed to reveal the full mechanism of TBC engagement in this phenomenon.

Cellular Stress Response (Hormesis) in Response to Bioactive Nutraceuticals with Relevance to Alzheimer Disease

Significance: Alzheimer's disease (AD) is the most common form of dementia associated with aging. As the large Baby Boomer population ages, risk of developing AD increases significantly, and this portion of the population will increase significantly over the next several decades. Recent Advances: Research suggests that a delay in the age of onset by 5 years can dramatically decrease both the incidence and cost of AD. In this review, the role of nuclear factor erythroid 2-related factor 2 (Nrf2) in AD is examined in the context of heme oxygenase-1 (HO-1) and biliverdin reductase-A (BVR-A) and the beneficial potential of selected bioactive nutraceuticals. Critical Issues: Nrf2, a transcription factor that binds to enhancer sequences in antioxidant response elements (ARE) of DNA, is significantly decreased in AD brain. Downstream targets of Nrf2 include, among other proteins, HO-1. BVR-A is activated when biliverdin is produced. Both HO-1 and BVR-A also are oxidatively or nitrosatively modified in AD brain and in its earlier stage, amnestic mild cognitive impairment (MCI), contributing to the oxidative stress, altered insulin signaling, and cellular damage observed in the pathogenesis and progression of AD. Bioactive nutraceuticals exhibit anti-inflammatory, antioxidant, and neuroprotective properties and are potential topics of future clinical research. Specifically, ferulic acid ethyl ester, sulforaphane, epigallocatechin-3-gallate, and resveratrol target Nrf2 and have shown potential to delay the progression of AD in animal models and in some studies involving MCI patients. Future Directions: Understanding the regulation of Nrf2 and its downstream targets can potentially elucidate therapeutic options for delaying the progression of AD. Antioxid. Redox Signal. 38, 643-669.

Coupling Environmental Whole Mixture Toxicity Screening with Unbiased RNA-Seq Reveals Site-Specific Biological Responses in Zebrafish

Passive sampling device (PSD) extracts paired with developmental toxicity assays in Danio Rerio (zebrafish) are excellent sensors for whole mixture toxicity associated with the bioavailable non-polar organics at environmental sites. We expand this concept by incorporating RNA-Seq in 48-h post fertilization zebrafish statically exposed to PSD extracts from two Portland Harbor Superfund Site locations: river mile 6.5W (RM 6.5W) and river mile 7W (RM 7W). RM 6.5W contained higher concentrations of polycyclic aromatic hydrocarbons (PAHs), but the diagnostic ratios of both extracts indicated similar PAH sourcing and composition. Developmental screens determined RM 6.5W to be more toxic with the most sensitive endpoint being a "wavy" notochord malformation. Differential gene expression from exposure to both extracts was largely parallel, although more pronounced for RM 6.5W. When compared to the gene expression associated with individual chemical exposures, PSD extracts produced some gene signatures parallel to PAHs but were more closely matched by oxygenated-PAHs. Additionally, differential expression, reminiscent of the wavy notochord phenotype, was not accounted for by either class of chemical, indicating the potential of other contaminants driving mixture toxicity. These techniques offer a compelling method for non-targeted hazard characterization of whole mixtures in an in vivo vertebrate system without requiring complete chemical characterization.

Pharmacological Modulations of Nrf2 and Therapeutic Implications in Aneurysmal Subarachnoid Hemorrhage

An aneurysmal subarachnoid hemorrhage (aSAH) is a subtype of stroke with high morbidity and mortality. The main causes of a poor prognosis include early brain injury (EBI) and delayed vasospasm, both of which play a significant role in the pathophysiological process. As an important mechanism of EBI and delayed vasospasm, oxidative stress plays an important role in the pathogenesis of aSAH by producing reactive oxygen species (ROS) through the mitochondria, hemoglobin, or enzymatic pathways in the early stages of aSAH. As a result, antioxidant therapy, which primarily targets the Nrf2-related pathway, can be employed as a potential strategy for treating aSAH. In the early stages of aSAH development, increasing the expression of antioxidant enzymes and detoxifying enzymes can relieve oxidative stress, reduce brain damage, and improve prognosis. Herein, the regulatory mechanisms of Nrf2 and related pharmacological compounds are reviewed, and Nrf2-targeted drugs are proposed as potential treatments for aSAH.

Functions of the aryl hydrocarbon receptor (AHR) beyond the canonical AHR/ARNT signaling pathway

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor regulating adaptive and maladaptive responses toward exogenous and endogenous signals. Research from various biomedical disciplines has provided compelling evidence that the AHR is critically involved in the pathogenesis of a variety of diseases and disorders, including autoimmunity, inflammatory diseases, endocrine disruption, premature aging and cancer. Accordingly, AHR is considered an attractive target for the development of novel preventive and therapeutic measures. However, the ligand-based targeting of AHR is considerably complicated by the fact that the receptor does not always follow the beaten track, i.e. the canonical AHR/ARNT signaling pathway. Instead, AHR might team up with other transcription factors and signaling molecules to shape gene expression patterns and associated physiological or pathophysiological functions in a ligand-, cell- and micromilieu-dependent manner. Herein, we provide an overview about some of the most important non-canonical functions of AHR, including crosstalk with major signaling pathways involved in controlling cell fate and function, immune responses, adaptation to low oxygen levels and oxidative stress, ubiquitination and proteasomal degradation. Further research on these diverse and exciting yet often ambivalent facets of AHR biology is urgently needed in order to exploit the full potential of AHR modulation for disease prevention and treatment.

Bifidobacterium bifidum Ameliorates DSS-Induced Colitis in Mice by Regulating AHR/NRF2/NLRP3 Inflammasome Pathways through Indole-3-lactic Acid Production

In this study, the effectors and mechanisms of Bifidobacterium bifidum FL-276.1 and B. bifidum FL-228.1 in alleviating dextran sulfate sodium (DSS)-induced colitis were investigated. Both FL-276.1 and FL-228.1 significantly alleviated DSS-induced colitis, whether they were supplemented from the beginning of the experiment (whole course intervention) or after the DSS induction started (partial intervention). Aryl hydrocarbon receptor (AHR) and the nuclear factor erythroid 2-related factor 2 (NRF2) pathways were activated in mice colons, while the NLR family pyrin domain containing 3 (NLRP3) was downregulated under the whole course intervention modes. Indole-3-lactic acid, an AHR ligand produced by FL-276.1 and FL-228.1, could regulate the AHR/NRF2/NLRP3 pathway in Caco-2 monolayers, thus upregulating the tight junction proteins and protecting the integrity of the epithelial barrier. These results are conducive to promoting clinical trials and product development of probiotics for alleviating colitis.

Health Benefits of Coffee Consumption for Cancer and Other Diseases and Mechanisms of Action

Coffee is one of the most widely consumed beverages worldwide, and epidemiology studies associate higher coffee consumption with decreased rates of mortality and decreased rates of neurological and metabolic diseases, including Parkinson's disease and type 2 diabetes. In addition, there is also evidence that higher coffee consumption is associated with lower rates of colon and rectal cancer, as well as breast, endometrial, and other cancers, although for some of these cancers, the results are conflicting. These studies reflect the chemopreventive effects of coffee; there is also evidence that coffee consumption may be therapeutic for some forms of breast and colon cancer, and this needs to be further investigated. The mechanisms associated with the chemopreventive or chemotherapeutic effects of over 1000 individual compounds in roasted coffee are complex and may vary with different diseases. Some of these mechanisms may be related to nuclear factor erythroid 2 (Nrf2)-regulated pathways that target oxidative stress or pathways that induce reactive oxygen species to kill diseased cells (primarily therapeutic). There is evidence for the involvement of receptors which include the aryl hydrocarbon receptor (AhR) and orphan nuclear receptor 4A1 (NR4A1), as well as contributions from epigenetic pathways and the gut microbiome. Further elucidation of the mechanisms will facilitate the potential future clinical applications of coffee extracts for treating cancer and other inflammatory diseases.