Genetic disruption of NRF2 promotes the development of necroinflammation and liver fibrosis in a mouse model of HFE-hereditary hemochromatosis

Macrophage Perspectives in Liver Diseases: Programmed Death, Related Biomarkers, and Targeted Therapy

Macrophages, as important immune cells of the organism, are involved in maintaining intrahepatic microenvironmental homeostasis and can undergo rapid phenotypic changes in the injured or recovering liver. In recent years, the crucial role of macrophage-programmed cell death in the development and regression of liver diseases has become a research hotspot. Moreover, macrophage-targeted therapeutic strategies are emerging in both preclinical and clinical studies. Given the macrophages' vital role in complex organismal environments, there is tremendous academic interest in developing novel therapeutic strategies that target these cells. This review provides an overview of the characteristics and interactions between macrophage polarization, programmed cell death, related biomarkers, and macrophage-targeted therapies. It aims to deepen the understanding of macrophage immunomodulation and molecular mechanisms and to provide a basis for the treatment of macrophage-associated liver diseases.

Mechanisms controlling cellular and systemic iron homeostasis

In mammals, hundreds of proteins use iron in a multitude of cellular functions, including vital processes such as mitochondrial respiration, gene regulation and DNA synthesis or repair. Highly orchestrated regulatory systems control cellular and systemic iron fluxes ensuring sufficient iron delivery to target proteins is maintained, while limiting its potentially deleterious effects in iron-mediated oxidative cell damage and ferroptosis. In this Review, we discuss how cells acquire, traffick and export iron and how stored iron is mobilized for iron-sulfur cluster and haem biogenesis. Furthermore, we describe how these cellular processes are fine-tuned by the combination of various sensory and regulatory systems, such as the iron-regulatory protein (IRP)-iron-responsive element (IRE) network, the nuclear receptor co-activator 4 (NCOA4)-mediated ferritinophagy pathway, the prolyl hydroxylase domain (PHD)-hypoxia-inducible factor (HIF) axis or the nuclear factor erythroid 2-related factor 2 (NRF2) regulatory hub. We further describe how these pathways interact with systemic iron homeostasis control through the hepcidin-ferroportin axis to ensure appropriate iron fluxes. This knowledge is key for the identification of novel therapeutic opportunities to prevent diseases of cellular and/or systemic iron mismanagement.

Iron overload induces dysplastic erythropoiesis and features of myelodysplasia in Nrf2-deficient mice

Iron overload (IOL) is hypothesized to contribute to dysplastic erythropoiesis. Several conditions, including myelodysplastic syndrome, thalassemia and sickle cell anemia, are characterized by ineffective erythropoiesis and IOL. Iron is pro-oxidant and may participate in the pathophysiology of these conditions by increasing genomic instability and altering the microenvironment. There is, however, lack of in vivo evidence demonstrating a role of IOL and oxidative damage in dysplastic erythropoiesis. NRF2 transcription factor is the master regulator of antioxidant defenses, playing a crucial role in the cellular response to IOL in the liver. Here, we crossed Nrf2-/- with hemochromatosis (Hfe-/-) or hepcidin-null (Hamp1-/-) mice. Double-knockout mice developed features of ineffective erythropoiesis and myelodysplasia including macrocytic anemia, splenomegaly, and accumulation of immature dysplastic bone marrow (BM) cells. BM cells from Nrf2/Hamp1-/- mice showed increased in vitro clonogenic potential and, upon serial transplantation, recipients disclosed cytopenias, despite normal engraftment, suggesting defective differentiation. Unstimulated karyotype analysis showed increased chromosome instability and aneuploidy in Nrf2/Hamp1-/- BM cells. In HFE-related hemochromatosis patients, NRF2 promoter SNP rs35652124 genotype TT (predicted to decrease NRF2 expression) associated with increased MCV, consistent with erythroid dysplasia. Our results suggest that IOL induces ineffective erythropoiesis and dysplastic hematologic features through oxidative damage in Nrf2-deficient cells.

Haemochromatosis

Haemochromatosis is one of the most common genetic diseases affecting patients of northern European ancestry. It is overdiagnosed in patients without iron overload and is underdiagnosed in many patients. Early diagnosis by genetic testing and therapy by periodic phlebotomy can prevent the most serious complications, which include liver cirrhosis, liver cancer, and death. This Seminar includes an update on the origins of haemochromatosis; and an overview pathophysiology, genetics, natural history, signs and symptoms, differential diagnoses, treatment with phlebotomy, outcomes, and future directions.

SARS-CoV-2 induced liver injury: Incidence, risk factors, impact on COVID-19 severity and prognosis in different population groups

Liver is unlikely the key organ driving mortality in coronavirus disease 2019 (COVID-19) however, liver function tests (LFTs) abnormalities are widely observed mostly in moderate and severe cases. According to this review, the overall prevalence of abnormal LFTs in COVID-19 patients ranges from 2.5% to 96.8% worldwide. The geographical variability in the prevalence of underlying diseases is the determinant for the observed discrepancies between East and West. Multifactorial mechanisms are implicated in COVID-19-induced liver injury. Among them, hypercytokinemia with "bystander hepatitis", cytokine storm syndrome with subsequent oxidative stress and endotheliopathy, hypercoagulable state and immuno-thromboinflammation are the most determinant mechanisms leading to tissue injury. Liver hypoxia may also contribute under specific conditions, while direct hepatocyte injury is an emerging mechanism. Except for initially observed severe acute respiratory distress syndrome corona virus-2 (SARS-CoV-2) tropism for cholangiocytes, more recent cumulative data show SARS-CoV-2 virions within hepatocytes and sinusoidal endothelial cells using electron microscopy (EM). The best evidence for hepatocellular invasion by the virus is the identification of replicating SARS-CoV-2 RNA, S protein RNA and viral nucleocapsid protein within hepatocytes using in-situ hybridization and immunostaining with observed intrahepatic presence of SARS-CoV-2 by EM and by in-situ hybridization. New data mostly derived from imaging findings indicate possible long-term sequelae for the liver months after recovery, suggesting a post-COVID-19 persistent live injury.

Protein Susceptibility to Peroxidation by 4-Hydroxynonenal in Hereditary Hemochromatosis

Iron overload caused by hereditary hemochromatosis (HH) increases free reactive oxygen species that, in turn, induce lipid peroxidation. Its 4-hydroxynonenal (HNE) by-product is a well-established marker of lipid peroxidation since it reacts with accessible proteins with deleterious consequences. Indeed, elevated levels of HNE are often detected in a wide variety of human diseases related to oxidative stress. Here, we evaluated HNE-modified proteins in the membrane of erythrocytes from HH patients and in organs of Hfe^-/- male and female mice, a mouse model of HH. For this purpose, we used one- and two-dimensional gel electrophoresis, immunoblotting and MALDI-TOF/TOF analysis. We identified cytoskeletal membrane proteins and membrane receptors of erythrocytes bound to HNE exclusively in HH patients. Furthermore, kidney and brain of Hfe^-/- mice contained more HNE-adducted protein than healthy controls. Our results identified main HNE-modified proteins suggesting that HH favours preferred protein targets for oxidation by HNE.

Nrf2 Signaling Pathway Mediates the Protective Effects of Daphnetin Against D-Galactose Induced-Premature Ovarian Failure

Oxidative damage can lead to severe ovarian dysfunctions and even premature ovarian failure. Nrf2, a significant transcription factor that regulates the oxidative stress response of cells, declines with age. Daphnetin, as a kind of natural Chinese herbal medicine, can activate Nrf2 and further promote the antioxidant defense of cells. However, whether Daphnetin treatment can protect ovary from premature ovarian failure and the specific mechanism involved are not understood. This study aimed to investigate the protective function of Daphnetin against the ovarian aging induced by D-galactose in wild-type and Nrf2^−/− mice. Female C57BL/6 mice with Wild-type and Nrf2^−/− were divided into five groups separately and the premature ovarian failure model were established by D-galactose and then Daphnetin and VE were given for treatment. After 42 days, ovaries tissue and serum were collected for biochemical determination, H&E staining, Immunohistochemical staining and western blot analysis. In the WT-POF group, ovarian function was broke, and the expression of the ovarian senescence-associated protein P16 and the level of oxidative stress were significantly increased, while the expression of the anti-senescence protein klotho was significantly decreased. In addition, the expression of Nrf2 and the antioxidases GCLC, HO-1 and NQO1 were decreased, but TXNIP and NLRP3 were significantly increased. Furthermore, the characteristics of premature ovarian failure were more significant in Nrf2 knockout mice than in wild-type mice, especially the expression of NLRP3 and TXNIP. Moreover, daphnetin, an Nrf2 activator, rescued d-gal-induced POF in a dose-dependent manner, while the protective effect was weakened or even lost in Nrf2 knockout mice. Our results suggested that daphnetin is likely to be a candidate drug for premature ovarian failure treatment and it is mostly possible referred to the molecular mechanism of increasing Nrf2 expression and inhibiting NLRP3 activation in the ovarian aging process.

Liver Sinusoidal Endothelial Cells at the Crossroad of Iron Overload and Liver Fibrosis

Significance: Liver fibrosis results from different etiologies and represents one of the most serious health issues worldwide. Fibrosis is the outcome of chronic insults on the liver and is associated with several factors, including abnormal iron metabolism. Recent Advances: Multiple mechanisms underlying the profibrogenic role of iron have been proposed. The pivotal role of liver sinusoidal endothelial cells (LSECs) in iron-level regulation, as well as their morphological and molecular dedifferentiation occurring in liver fibrosis, has encouraged research on LSECs as prime regulators of very early fibrotic events. Importantly, normal differentiated LSECs may act as gatekeepers of fibrogenesis by maintaining the quiescence of hepatic stellate cells, while LSECs capillarization precedes the onset of liver fibrosis. Critical Issues: In the present review, the morphological and molecular alterations occurring in LSECs after liver injury are addressed in an attempt to highlight how vascular dysfunction promotes fibrogenesis. In particular, we discuss in depth how a vicious loop can be established in which iron dysregulation and LSEC dedifferentiation synergize to exacerbate and promote the progression of liver fibrosis. Future Directions: LSECs, due to their pivotal role in early liver fibrosis and iron homeostasis, show great promises as a therapeutic target. In particular, new strategies can be devised for restoring LSECs differentiation and thus their role as regulators of iron homeostasis, hence preventing the progression of liver fibrosis or, even better, promoting its regression. Antioxid. Redox Signal. 35, 474-486.

NRF2 and Hypoxia-Inducible Factors: Key Players in the Redox Control of Systemic Iron Homeostasis

Significance: Oxygen metabolism and iron homeostasis are closely linked. Iron facilitates the oxygen-carrying capacity of blood, and its deficiency causes anemia. Conversely, excess free iron is detrimental for stimulating the formation of reactive oxygen species, causing tissue damage. The amount and distribution of iron thus need to be tightly regulated by the liver-expressed hormone hepcidin. This review analyzes the roles of key oxygen-sensing pathways in cellular and systemic regulation of iron homeostasis; specifically, the prolyl hydroxylase domain (PHD)/hypoxia-inducible factor (HIF) and the Kelch-like ECH-associated protein 1/NF-E2 p45-related factor 2 (KEAP1/NRF2) pathways, which mediate tissue adaptation to low and high oxygen, respectively. Recent Advances: In macrophages, NRF2 regulates genes involved in hemoglobin catabolism, iron storage, and iron export. NRF2 was recently identified as the molecular sensor of iron-induced oxidative stress and is responsible for BMP6 expression by liver sinusoidal endothelial cells, which in turn activates hepcidin synthesis by hepatocytes to restore systemic iron levels. Moreover, NRF2 orchestrates the activation of antioxidant defenses that are crucial to protect against iron toxicity. On the contrary, low iron/hypoxia stabilizes renal HIF2a via inactivation of iron-dependent PHD dioxygenases, causing an erythropoietic stimulus that represses hepcidin via an inhibitory effect of erythroferrone on bone morphogenetic proteins. Intestinal HIF2a is also stabilized, increasing the expression of genes involved in dietary iron absorption. Critical Issues: An intimate crosstalk between oxygen-sensing pathways and iron regulatory mechanisms ensures that fluctuations in systemic iron levels are promptly detected and restored. Future Directions: The realization that redox-sensitive transcription factors regulate systemic iron levels suggests novel therapeutic approaches. Antioxid. Redox Signal. 35, 433-452.

The Role of Iron in Benign and Malignant Hematopoiesis

Significance: Iron is an essential element required for sustaining a normal healthy life. However, an excess amount of iron in the bloodstream and tissue generates toxic hydroxyl radicals through Fenton reactions. Henceforth, a balance in iron concentration is extremely important to maintain cellular homeostasis in both normal hematopoiesis and erythropoiesis. Iron deficiency or iron overload can impact hematopoiesis and is associated with many hematological diseases. Recent Advances: The mechanisms of action of key iron regulators such as erythroferrone and the discovery of new drugs, such as ACE-536/luspatercept, are of potential interest to treat hematological disorders, such as β-thalassemia. New therapies targeting inflammation-induced ineffective erythropoiesis are also in progress. Furthermore, emerging evidences support differential interactions between iron and its cellular antioxidant responses of hematopoietic and neighboring stromal cells. Both iron and its systemic regulator, such as hepcidin, play a significant role in regulating erythropoiesis. Critical Issues: Significant pre-clinical studies are on the way and new drugs targeting iron metabolism have been recently approved or are undergoing clinical trials to treat pathological conditions with impaired erythropoiesis such as myelodysplastic syndromes or β-thalassemia. Future Directions: Future studies should explore how iron regulates hematopoiesis in both benign and malignant conditions. Antioxid. Redox Signal. 35, 415-432.

Interplay between nuclear factor erythroid 2-related factor 2 and inflammatory mediators in COVID-19-related liver injury

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 is a global pandemic and poses a major threat to human health worldwide. In addition to respiratory symptoms, COVID-19 is usually accompanied by systemic inflammation and liver damage in moderate and severe cases. Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that regulates the expression of antioxidant proteins, participating in COVID-19-mediated inflammation and liver injury. Here, we show the novel reciprocal regulation between NRF2 and inflammatory mediators associated with COVID-19-related liver injury. Additionally, we describe some mechanisms and treatment strategies.

The Association of a Single-Nucleotide Polymorphism in the Nuclear Factor (Erythroid-Derived 2)-Like 2 Gene With Adverse Drug Reactions, Multimorbidity, and Frailty in Older People

Susceptibility to adverse drug reactions (ADRs), multimorbidity, and frailty are associated with human aging, yet there is wide variation in the severity and age at which individuals are afflicted. Identifying genetic markers of increased risk of this phenotype would help stratify individuals to specialist interventions. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) regulates a cell's response to stressors, including the expression of enzymes involved in drug metabolism. Its expression has been shown to decline in animal aging models. In this study, we tested the hypothesis that Nrf2 gene (NFE2L2) transcription/translation decline in human aging and that single-nucleotide polymorphisms (SNPs) in the NFE2L2 gene are associated with increased ADR risk, multimorbidity, and frailty in older people. Gene expression and protein levels were measured in peripheral blood mononuclear cells donated from healthy patients aged 18-80 years old. NFE2L2 genotypes were determined at three loci in a subpopulation of patients recruited to the PRIME study (a multicenter prospective cohort study that followed older adults for 8 weeks post-discharge to determine ADR). Both NFE2L2 gene and Nrf2 protein expression declined significantly with age in human peripheral blood mononuclear cells. In the PRIME substudy population, the rs35652124 NFE2L2 SNP was associated with increased ADR risk and decreased frailty and multimorbidity scores.

Long-Term Aspartame Administration Leads to Fibrosis, Inflammasome Activation, and Gluconeogenesis Impairment in the Liver of Mice

BACKGROUND

Aspartame is an artificial sweetener used in foods and beverages worldwide. However, it is linked to oxidative stress, inflammation, and liver damage through mechanisms that are not fully elucidated yet. This work aimed to investigate the effects of long-term administration of aspartame on the oxidative and inflammatory mechanisms associated with liver fibrosis progression in mice.

METHODS

Mice were divided into two groups with six animals each: control and aspartame. Aspartame (80 mg/kg, via oral) or vehicle was administrated for 12 weeks.

RESULTS

Aspartame caused liver damage and elevated serum transaminase levels. Aspartame also generated liver fibrosis, as evidenced by histology analysis, and pro-fibrotic markers' upregulation, including transforming growth factor β 1, collagen type I alpha 1, and alpha-smooth muscle actin. Furthermore, aspartame reduced nuclear factor erythroid 2-related factor 2 (Nrf2) activation and enzymatic antioxidant activity and increased lipid peroxidation, which triggered NOD-like receptor containing protein 3 (NLRP3) inflammasome activation and p53 induction. Furthermore, aspartame reduced peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) levels, possibly through p53 activation. This PGC-1α deficiency could be responsible for the changes in lipid profile in serum, total lipid accumulation, and gluconeogenesis impairment in liver, evidenced by the gluconeogenic enzymes' downregulation, thus causing hypoglycemia.

CONCLUSIONS

This work provides new insights to understand the mechanisms related to the adverse effects of aspartame on liver tissue.

Age-related alteration in HNE elimination enzymes

4-hydroxynonenal (HNE, 4-hydroxy-2-nonenal) is a primary α,β-unsaturated aldehyde product of lipid peroxidation. The accumulation of HNE increases with aging and the mechanisms are mainly attributable to increased oxidative stress and decreased capacity of HNE elimination. In this review article, we summarize the studies on age-related change of HNE concentration and alteration of HNE metabolizing enzymes (GCL, GST, ALDHs, aldose reductase, and 20S-proteasome), and discuss potential mechanism of age-related decrease in HNE-elimination capacity by focusing on Nrf2 redox signaling.

Dietary Iron Overload Differentially Modulates Chemically-Induced Liver Injury in Rats

Hepatic iron overload is well known as an important risk factor for progression of liver diseases; however, it is unknown whether it can alter the susceptibility to drug-induced hepatotoxicity. Here we investigate the pathological roles of iron overload in two single-dose models of chemically-induced liver injury. Rats were fed a high-iron (Fe) or standard diet (Cont) for four weeks and were then administered with allyl alcohol (AA) or carbon tetrachloride (CCl₄). Twenty-four hours after administration mild mononuclear cell infiltration was seen in the periportal/portal area (Zone 1) in Cont-AA group, whereas extensive hepatocellular necrosis was seen in Fe-AA group. Centrilobular (Zone 3) hepatocellular necrosis was prominent in Cont-CCl₄ group, which was attenuated in Fe-CCl₄ group. Hepatic lipid peroxidation and hepatocellular DNA damage increased in Fe-AA group compared with Cont-AA group. Hepatic caspase-3 cleavage increased in Cont-CCl₄ group, which was suppressed in Fe-CCl₄ group. Our results showed that dietary iron overload exacerbates AA-induced Zone-1 liver injury via enhanced oxidative stress while it attenuates CCl₄-induced Zone-3 liver injury, partly via the suppression of apoptosis pathway. This study suggested that susceptibility to drugs or chemical compounds can be differentially altered in iron-overloaded livers.

Ferroptosis in Liver Diseases: An Overview

Ferroptosis is an iron-dependent form of cell death characterized by intracellular lipid peroxide accumulation and redox imbalance. Ferroptosis shows specific biological and morphological features when compared to the other cell death patterns. The loss of lipid peroxide repair activity by glutathione peroxidase 4 (GPX4), the presence of redox-active iron and the oxidation of polyunsaturated fatty acid (PUFA)-containing phospholipids are considered as distinct fingerprints of ferroptosis. Several pathways, including amino acid and iron metabolism, ferritinophagy, cell adhesion, p53, Keap1/Nrf2 and phospholipid biosynthesis, can modify susceptibility to ferroptosis. Through the decades, various diseases, including acute kidney injury; cancer; ischemia–reperfusion injury; and cardiovascular, neurodegenerative and hepatic disorders, have been associated with ferroptosis. In this review, we provide a comprehensive analysis of the main biological and biochemical mechanisms of ferroptosis and an overview of chemicals used as inducers and inhibitors. Then, we report the contribution of ferroptosis to the spectrum of liver diseases, acute or chronic. Finally, we discuss the use of ferroptosis as a therapeutic approach against hepatocellular carcinoma, the most common form of primary liver cancer.

Hepatocyte-specific deficiency of Nrf2 exacerbates carbon tetrachloride-induced liver fibrosis via aggravated hepatocyte injury and subsequent inflammatory and fibrogenic responses

BACKGROUND

Liver fibrosis, in which hepatocyte damage and inflammatory response play critical roles, is a physiological response to chronic or iterative liver injury and can progress to cirrhosis over time. Nuclear factor E2-related factor 2 (Nrf2) is a master transcription factor that regulates oxidative and xenobiotic stress responses as well as inflammation.

METHOD

To ascertain the cell-specific roles of Nrf2 in hepatocytes and myeloid lineage cells in the progression of liver fibrosis, mice lacking Nrf2 specifically in hepatocytes [Nrf2(L)-KO] and myeloid lineage cells [Nrf2(M)-KO] were generated to evaluate carbon tetrachloride (CCl₄)-induced liver injury, subsequent inflammation and fibrosis. In addition, mouse primary hepatocytes were used to investigate the underlying mechanisms.

RESULTS

Nrf2-mediated antioxidant response in the liver is responsive to acute CCl₄ exposure in mice. With repeated CCl₄ administration, Nrf2(L)-KO, but not Nrf2(M)-KO, mice showed more severe liver fibrosis than Nrf2-LoxP control mice. In addition, in response to acute CCl₄ exposure, Nrf2(L)-KO mice displayed aggravated liver injury, elevated lipid peroxidation and inflammatory response compared to control mice. In mouse primary hepatocytes, deficiency of Nrf2 resulted in more severe CCl₄-induced lipid oxidation and inflammatory response.

CONCLUSION

Deficiency of Nrf2 in hepatocytes sensitizes the cells to CCl₄-induced oxidative damage and inflammatory response, which are initiator and enhancer of subsequent hepatic inflammation and fibrosis. Thus, Nrf2 is a critical determinant of liver injury and fibrosis in response to CCl₄, suggesting that Nrf2 might be a valuable target for the intervention.

Activation of pCREB/Nrf-2 signaling mediates re-positioning of liraglutide as hepato-protective for methotrexate -induced liver injury (MILI)

Methotrexate (MTX) is commonly used to treat several types of cancer and autoimmune diseases. However, there is increasing concern over its organs toxicities particularly liver toxicity. Liraglutide, a glucagon like peptide-1 agonist, possesses antioxidant and anti-inflammatory features. This study aimed to explore the potential protective effect of liraglutide pre-treatment in ameliorating MTX-induced hepatotoxicity and to further investigate the underlying mechanisms. Rats received 1.2 mg/kg liraglutide intraperitoneal twice daily for 7 days before MTX. Results revealed that liraglutide significantly decreased activities of liver enzymes and oxidative stress in hepatocytes. Furthermore, NF-kB expression and related inflammatory markers (TNF-α, COX-2 and IL-6) were reduced in the pre-treatment group of liraglutide. These data validate the advantageous effects of liraglutide in MTX hepatotoxic animals. In addition, liraglutide increased the expression of the antioxidant transcription factor nuclear factor-erythroid 2-related factor 2 (Nrf-2), along with the transcription of downstream phosphorylated cAMP response element-binding protein (pCREB) which increases the activity of Nrf-2. Additionally, caspase-3 expression/activity and BAX/Bcl-2 ratio were decreased following liraglutide pre-treatment. In conclusion, it was confirmed that liraglutide enhanced the antioxidant activity of liver cells by activating the Nrf-2 and pCREB signaling, thereby, reducing liver cell inflammation and apoptosis induced by MTX.

Crosstalk of Nrf2 with the Trace Elements Selenium, Iron, Zinc, and Copper

Trace elements, like Cu, Zn, Fe, or Se, are important for the proper functioning of antioxidant enzymes. However, in excessive amounts, they can also act as pro-oxidants. Accordingly, trace elements influence redox-modulated signaling pathways, such as the Nrf2 pathway. Vice versa, Nrf2 target genes belong to the group of transport and metal binding proteins. In order to investigate whether Nrf2 directly regulates the systemic trace element status, we used mice to study the effect of a constitutive, whole-body Nrf2 knockout on the systemic status of Cu, Zn, Fe, and Se. As the loss of selenoproteins under Se-deprived conditions has been described to further enhance Nrf2 activity, we additionally analyzed the combination of Nrf2 knockout with feeding diets that provide either suboptimal, adequate, or supplemented amounts of Se. Experiments revealed that the Nrf2 knockout partially affected the trace element concentrations of Cu, Zn, Fe, or Se in the intestine, liver, and/or plasma. However, aside from Fe, the other three trace elements were only marginally modulated in an Nrf2-dependent manner. Selenium deficiency mainly resulted in increased plasma Zn levels. One putative mediator could be the metal regulatory transcription factor 1, which was up-regulated with an increasing Se supply and downregulated in Se-supplemented Nrf2 knockout mice.

Nrf2 controls iron homeostasis in haemochromatosis and thalassaemia via Bmp6 and hepcidin

Iron is critical for life but toxic in excess because of iron-catalysed formation of pro-oxidants that cause tissue damage in a range of disorders. The Nrf2 transcription factor orchestrates cell-intrinsic protective antioxidant responses, and the peptide hormone hepcidin maintains systemic iron homeostasis, but is pathophysiologically decreased in haemochromatosis and beta-thalassaemia. Here, we show that Nrf2 is activated by iron-induced, mitochondria-derived pro-oxidants and drives Bmp6 expression in liver sinusoid endothelial cells, which in turn increases hepcidin synthesis by neighbouring hepatocytes. In Nrf2 knockout mice, the Bmp6-hepcidin response to oral and parenteral iron is impaired and iron accumulation and hepatic damage are increased. Pharmacological activation of Nrf2 stimulates the Bmp6-hepcidin axis, improving iron homeostasis in haemochromatosis and counteracting the inhibition of Bmp6 by erythroferrone in beta-thalassaemia. We propose that Nrf2 links cellular sensing of excess toxic iron to control of systemic iron homeostasis and antioxidant responses, and may be a therapeutic target for iron-associated disorders.

Iron-Induced Liver Injury: A Critical Reappraisal

Iron is implicated in the pathogenesis of a number of human liver diseases. Hereditary hemochromatosis is the classical example of a liver disease caused by iron, but iron is commonly believed to contribute to the progression of other forms of chronic liver disease such as hepatitis C infection and nonalcoholic fatty liver disease. In this review, we present data from cell culture experiments, animal models, and clinical studies that address the hepatotoxicity of iron. These data demonstrate that iron overload is only weakly fibrogenic in animal models and rarely causes serious liver damage in humans, calling into question the concept that iron overload is an important cause of hepatotoxicity. In situations where iron is pathogenic, iron-induced liver damage may be potentiated by coexisting inflammation, with the resulting hepatocyte necrosis an important factor driving the fibrogenic response. Based on the foregoing evidence that iron is less hepatotoxic than is generally assumed, claims that assign a causal role to iron in liver injury in either animal models or human liver disease should be carefully evaluated.

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.

Rapamycin Induced Autophagy Inhibits Inflammation-Mediated Endplate Degeneration by Enhancing Nrf2/Keap1 Signaling of Cartilage Endplate Stem Cells

Cartilage endplate (CEP) calcification inhibits the transport of metabolites and nutrients in the intervertebral disk and is an important initiating factor of intervertebral disk degeneration. However, the mechanisms governing CEP degeneration have not been thoroughly elucidated. In this study, we established a mouse CEP degeneration model and showed that autophagy insufficiency caused the degeneration of CEP. We found that the inflammatory cytokine tumor necrosis factor-α (TNF-α) increased the level of intracellular reactive oxygen species (ROS) and caused cell senescence and osteogenic differentiation of cartilage endplate stem cells (CESCs), whereas rapamycin-induced autophagy protected CESCs from TNF-α-induced oxidative stress and cell senescence. Furthermore, rapamycin-induced autophagy helped CESCs maintain the chondrogenic properties and inhibited extracellular matrix protease expression and osteogenic differentiation. Further study revealed that autophagy activated by rapamycin or inhibited by chloroquine influenced the expression and nuclear translocation of Nrf2, thereby controlling the expression of antioxidant proteins and the scavenging of ROS. Taken together, the results indicate that rapamycin-induced autophagy enhances Nrf2/Keap1 signaling and promotes the expression of antioxidant proteins, thereby eliminating ROS, alleviating cell senescence, reducing the osteogenic differentiation of CESCs, and ultimately protecting CEPs from chronic inflammation-induced degeneration. Stem Cells 2019;37:828-840.

Nrf2: Molecular and epigenetic regulation during aging

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

Anti‑apoptotic effects of human placental hydrolysate against hepatocyte toxicity in vivo and in vitro

Apoptosis and oxidative stress are essential for the pathogenesis of acute liver failure and fulminant hepatic failure. Human placental hydrolysate (hPH) has been reported to possess antioxidant and anti-inflammatory properties. In the present study, the protective effects of hPH against D-galactosamine (D-GalN)- and lipopolysaccharide (LPS)-induced hepatocyte apoptosis were investigated in vivo. In addition, the molecular mechanisms underlying the anti-apoptotic activities of hPH against D-GalN-induced cell death in vitro were examined. Male Sprague-Dawley rats were injected with D-GaIN/LPS with or without the administration of hPH. Rats were sacrificed 24 h after D-GaIN/LPS intraperitoneal injection, and the blood and liver samples were collected for future inflammation and hepatotoxicity analyses. Changes in cell viability, apoptosis protein expression, mitochondrial mass, mitochondrial membrane potential, reactive oxygen species generation, and the levels of proteins and mRNA associated with a protective mechanism were determined in HepG2 cells pretreated with hPH for 2 h prior to D-GalN exposure. The findings suggested that hPH treatment effectively protected against D-GalN/LPS-induced hepatocyte apoptosis by reducing the levels of alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, interleukin-6, and tumor necrosis factor-α, and increasing the level of proliferating cell nuclear antigen. It was also found that hPH inhibited the apoptotic cell death induced by D-GalN. hPH activated the expression of antioxidant enzymes, including superoxide dismutase, glutathione peroxidase, and catalase, which were further upregulated by the Kelch-like ECH2-associated protein 1-p62-nuclear factor-erythroid 2-related factor 2 pathway, a component of oxidative stress defense mechanisms. Furthermore, hPH markedly reduced cytosolic and mitochondrial reactive oxygen species and rescued mitochondrial loss and dysfunction through the reduction of damage-regulated autophagy modulator, p53, and C/EBP homologous protein. Collectively, hPH exhibited a protective role in hepatocyte apoptosis by inhibiting oxidative stress and maintaining cell homeostasis. The underlying mechanisms may be associated with the inhibition of endoplasmic reticulum stress and minimization of the autophagy progress.

Nrf2 protects against oxidative stress induced by SiO2 nanoparticles

Aim: The aim of our study was to explore the role of nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) on the exposure of SiO2 nanoparticles (NPs) and its influence. Materials & methods: To understand the mechanism of NP-induced oxidative stress, the involvement of oxidative-stress-responding transcription factors and the Nrf2/antioxidant reactive element (ARE) signaling pathway in the toxicity of SiO2 NPs’ exposure was investigated via in vivo and in vitro models. Results: A549 cells showed a significant cytotoxic effect while A549-shNrf2 cells showed decreased cell viability after nm-SiO2 exposure. SiO2 NPs’ exposure activated the Nrf2/ARE signaling pathway. Nrf2−/− exposed mice showed increased reactive oxygen species, 8-hydroxyl deoxyguanosine level and decreased total antioxidant capacity. Nrf2/ARE signaling pathway activation disrupted, leading inhibition of heme oxygenase-1 and upregulation of PKR-like endoplasmic-reticulum-regulated kinase. Conclusion: Our findings suggested that Nrf2 could protect against oxidative stress induced by SiO2 NPs, and the Nrf2/ARE pathway might be involved in mild-to-moderate SiO2 NP-induced oxidative stress that was evident from dampened activity of Nrf2.