Role of Nrf2 antioxidant defense in mitigating cadmium-induced oxidative stress in the olfactory system of zebrafish

Protective effects of sulforaphane against toxic substances and contaminants: A systematic review

BACKGROUND

Sulforaphane (SFN) is a dietary isothiocyanate, derived from glucoraphanin, present in cruciferous vegetables belonging to the Brassica genus. It is a biologically active phytochemical that acts as a nuclear factor erythroid 2-related factor 2 (Nrf2) inducer. Thus, it has been reported to have multiple protective functions including anticancer responses and protection against a toxic agent's action.

PURPOSE

The present work systematically reviewed and synthesised the protective properties of sulforaphane against a toxic agent. This review reveals the mechanism of the action of SFN in each organ or system.

METHODS

The PRISMA guideline was followed in this sequence: researched literature, organised retrieved documents, abstracted relevant information, assessed study quality and bias, synthesised data, and prepared a comprehensive report. Searches were conducted on Science Direct and PubMed using the keywords "Sulforaphane" AND ("protective effects" OR "protection against").

RESULTS

Reports showed that liver and the nervous system are the target organs on which attention was focused, and this might be due to the key role of oxidative stress in liver and neurodegenerative diseases. However, protective activities have also been demonstrated in the lungs, heart, immune system, kidneys, and endocrine system. SFN exerts its protective effects by activating the Nrf2 pathway, which enhances antioxidant defenses and reduces oxidative stress. It also suppresses inflammation by decreasing interleukin production. Moreover, SFN inhibits apoptosis by preventing caspase 3 cleavage and increasing Bcl2 levels. Overall, SFN demonstrates multifaceted mechanisms to counteract the adverse effects of toxic agents.

CONCLUSION

SFN has potential clinical applications as a chemoprotective agent. Nevertheless, more studies are necessary to set the safe doses of SFN in humans.

Tetramethylpyrazine Antagonizes the Subchronic Cadmium Exposure-Induced Oxidative Damage in Mouse Livers via the Nrf2/HO-1 Pathway

Hepatic oxidative stress is an important mechanism of Cd-induced hepatotoxicity, and it is ameliorated by TMP. However, this underlying mechanism remains to be elucidated. To investigate the mechanism of the protective effect of TMP on liver injuries in mice induced by subchronic cadmium exposure, 60 healthy male ICR mice were randomly divided into five groups of 12 mice each, namely, control (CON), Cd (2 mg/kg of CdCl2), Cd + 100 mg/kg of TMP, Cd + 150 mg/kg of TMP, and Cd + 200 mg/kg of TMP, and were acclimatized and fed for 7 d. The five groups of mice were gavaged for 28 consecutive days with a maximum dose of 0.2 mL/10 g/day. Except for the control group, all groups were given fluoride (35 mg/kg) by an intraperitoneal injection on the last day of the experiment. The results of this study show that compared with the Cd group, TMP attenuated CdCl2-induced pathological changes in the liver and improved the ultrastructure of liver cells, and TMP significantly decreased the MDA level (p < 0.05) and increased the levels of T-AOC, T-SOD, and GSH (p < 0.05). The results of mRNA detection show that TMP significantly increased the levels of Nrf2 in the liver compared with the Cd group as well as the HO-1 and mRNA expression levels in the liver (p < 0.05). In conclusion, TMP could inhibit oxidative stress and attenuate Cd group-induced liver injuries by activating the Nrf2 pathway.

Melatonin as an Ameliorative Agent Against Cadmium- and Lead-Induced Toxicity in Fish: an Overview

Diverse anthropogenic activities and lack of knowledge on its consequences have promoted serious heavy metal contaminations in different aquatic systems throughout the globe. The non-biodegradable nature of most of these toxic heavy metals has increased the concern on their possible bioaccumulation in aquatic organisms as well as in other vertebrates. Among these aquatic species, fish are most sensitive to such contaminated water that not only decreases their chance of survivability in the nature but also increases the probability of biomagnifications of these heavy metals in higher order food chain. After entering the fish body, heavy metals induce detrimental changes in different vital organs by impairing multiple physiological and biochemical pathways that are essential for the species. Such alterations may include tissue damage, induction of oxidative stress, immune-suppression, endocrine disorders, uncontrolled cell proliferation, DNA damage, and even apoptosis. Although uncountable reports have explored the toxic effects of different heavy metals in diverse fish species, but surprisingly, only a few attempts have been made to ameliorate such toxic effects. Since, oxidative stress seems to be the underlying common factor in such heavy metal-induced toxicity, therefore, a potent and endogenous antioxidant with no side effect may be an appropriate therapeutic solution. Apart from summarizing the toxic effects of two important toxicants, i.e., cadmium and lead in fish, the novelty of the present treatise lies in its arguments in favor of using melatonin, an endogenous free radical scavenger and indirect antioxidant, in ameliorating the toxic effects of heavy metals in any fish species.

Effects of α-Lipoic Acid Supplementation on Growth Performance, Liver Histology, Antioxidant and Related Genes Expression of Hybrid Grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂)

This study aimed to assess the impact of α-lipoic acid on the growth performance, antioxidant capacity and immunity in hybrid groupers (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatus) fed with a high-lipid diet. Groupers (8.97 ± 0.01 g) were fed six different diets, with α-lipoic acid content in diets being 0, 400, 800, 1200, 1600, and 2000 mg/kg, named S1, S2, S3, S4, S5, and S6, respectively. The results show that the addition of 2000 mg/kg α-lipoic acid in the diet inhibited the growth, weight gain rate (WGR), and specific growth rate (SGR), which were significantly lower than other groups. In serum, catalase (CAT) and superoxide dismutase (SOD) were significantly higher in the S5 group than in the S1 group. In the liver, CAT, SOD and total antioxidative capacity (T-AOC) levels were significantly increased in α-lipoic acid supplemented groups. α-lipoic acid significantly upregulated liver antioxidant genes sod and cat, anti-inflammatory factor interleukin 10 (il10) and transforming growth factor β (tgfβ) mRNA levels. Conclusion: the addition of 2000 mg/kg of α-lipoic acid inhibits the growth of hybrid groupers. In addition, 400-800 mg/kg α-lipoic acid contents improve the antioxidant capacity of groupers and have a protective effect against high-lipid-diet-induced liver oxidative damage.

Arrestin domain-containing protein 1-mediated microvesicles (ARMMs) protect against cadmium-induced neurotoxicity

Exposure to environmental heavy metals such as cadmium (Cd) is often linked to neurotoxicity but the underlying mechanisms remain poorly understood. Here we show that Arrestin domain-containing protein 1 (ARRDC1)-mediated microvesicles (ARMMs)--an important class of extracellular vesicles (EVs) whose biogenesis occurs at the plasma membrane--protect against Cd-induced neurotoxicity. Cd increased the production of EVs, including ARMMs, in a human neural progenitor cell line, ReNcell CX (ReN) cells. ReN cells that lack ARMMs production as a result of CRISPR-mediated ARRDC1 knockout were more susceptible to Cd toxicity as evidenced by increased LDH production as well as elevated level of oxidative stress markers. Importantly, adding ARMMs back to the ARRDC1-knockout ReN cells significantly reduced Cd-induced toxicity. Consistent with this finding, proteomics data showed that anti-oxidative stress proteins are enriched in ARMMs secreted from ReN cells. Together our study reveals a novel protective role of ARMMs in Cd neurotoxicity and suggests that ARMMs may be used therapeutically to reduce neurotoxicity caused by exposure to Cd and potentially other metal toxicants.

New perspective on mechanism in muscle toxicity of ochratoxin A: Model of juvenile grass carp (Ctenopharyngodon idella)

Ochratoxin A (OTA) is a common fungal toxin that pollutes raw materials of aquatic feeds (such as corn, soybean meal, and wheat). This study explored the effects of OTA through diet on muscle toxicity in juvenile grass carp (Ctenopharyngodon idella). The following results were obtained for the muscle. (1) With an increase in dietary OTA, the residue of OTA in muscle increased, muscle fiber diameter and density decreased, and even muscle fiber breakage. (2) OTA caused oxidative stress by downregulating GPx1 (a, b) and Trx via inhibited the PGC1-α/Nrf2 signaling pathway. (3) OTA exacerbated endoplasmic reticulum stress in the muscle by causing endoplasmic reticulum expansion (results of transmission electron microscopy) and upregulating the expression of GRP78, eIF2α, ATF6, PERK, and CHOP. (4) OTA reduced muscle fiber diameter by inhibiting protein synthesis (AKT, TOR, and S6K1) and promoting the mRNA expression of protein degradation-related genes (MURF1, MAFBX, and FoxO3a), as well as by reducing AKT and promoting the immunofluorescence expression of FoxO3. (5) OTA inhibits collagen deposition by downregulating TGF-β1, TGF-βR1, Smad2, Smad3, Smad4, CTGF, TIMP, PHD, and LOX mRNA expressions as well as the CTGF immunofluorescence expression. Moreover, based on the GSH and collagen content contents, the upper safe dose for OTA-induced toxicity was 963.6 and 1129.6 μg/kg diet, respectively. Using the example of OTA, our research has provided new insights that raise concerns about the quality of aquatic products by exploring muscle toxicity caused by mycotoxins.

The role of Nrf2 signaling pathway in the mud crab (Scylla paramamosain) in response to Vibrio parahaemolyticus infection

The transcription factor Nrf2 plays vital roles in detoxification and antioxidant enzymes against oxidative stress. However, the function of Nrf2 in crustaceans is not well studied. In this study, a novel Nrf2 gene from the mud crab (Sp-Nrf2) was identified. It was encoded 245 amino acids. Sp-Nrf2 expression was ubiquitously expressed in all tested tissues, with the highest expression level in the gill. Sp-Nrf2 protein was mainly located in the nucleus. The expression levels of Sp-Nrf2, and antioxidant-related genes (HO-1 and NQO-1) were induced after Vibrio parahaemolyticus infection, indicating that Nrf2 signaling pathway was involved in the responses to bacterial infection. Over-expression of Sp-Nrf2 could improve cell viability after H₂O₂ exposure, indicating that Sp-Nrf2 might relieve oxidative stress. Silencing of Sp-Nrf2 in vivo decreased HO-1 and NQO-1 expression. Moreover, knocking down Sp-Nrf2 in vivo can increase malondialdehyde content and the mortality of mud crabs after V. parahaemolyticus infection. Our results indicated that Nrf2 signaling pathway played a significant role in immune response against bacterial infection.

Evaluation of the oxidative toxicity induced by lead, manganese, and cadmium using genetically modified nrf2a-mutant zebrafish

Heavy metal pollution has become a serious environmental concern and a threat to public health. Three of the most common heavy metals are cadmium (Cd), lead (Pb), and manganese (Mn). Nuclear factor erythroid 2-related factor 2 (Nrf2) is an important transcription factor activated in the response to oxidative stress. In this study, mutant zebrafish with an nrf2a deletion of 7 bp were constructed by the CRISPR/Cas9 system to investigate the oxidative toxicity of these three heavy metals. The results of general toxicity tests showed that Pb exposure did not cause significant damage to mutant zebrafish compared with wild-type (WT) zebrafish. However, high Mn exposure increased mortality and malformation rates in mutant zebrafish. Of concern, Cd exposure caused significant toxic damage, including increased mortality and malformation rates, apoptosis of brain neurons, and severe locomotor behavior aberration in mutant zebrafish. The results of qRT-PCR indicated that Cd exposure could induce the activation of genes related to oxidative stress resistance in WT zebrafish, while the expression of these genes was inhibited in mutant zebrafish. This study showed that of the three heavy metals, Cd had the strongest oxidative toxicity, Mn had medium toxicity, and Pb had the weakest toxicity.

Chronic hypoxia and Cu2+ exposure induce gill remodeling of largemouth bass through endoplasmic reticulum stress, mitochondrial damage and apoptosis

Hypoxia and Cu²⁺ pollution often occur simultaneously in aquatic ecosystems and jointly affect physiology of fish. As the respiratory and ion exchange tissue of fish, how gill responds to the stress induced by these two abiotic environmental factors is still unclear. We have conducted a study by exposing largemouth bass (Micropterus salmoides) to hypoxia (2.0 mg·L^-1) and/or Cu²⁺ (0.5 mg·L^-1) for 28 days to answer this question. We subsequently studied respiratory rate, Cu²⁺ transport, endoplasmic reticulum (ER) stress, mitochondrial damage, and morphology in gill tissue on day 7, 14, 21 and 28. We found that hypoxia exposure increased the respiratory rate of largemouth bass, reflecting the response of largemouth bass to cope with hypoxia. Of note, Cu²⁺ entered gill by specifically binding to CTR1 and its accumulation dramatically in gill disrupted the response of largemouth bass to hypoxia. Hypoxia and/or Cu²⁺ exposure led to ER stress and mitochondrial damage in gills of largemouth bass. ER stress and mitochondrial damage induced apoptosis by activating caspase-8 and caspase-9 signaling pathways, respectively. Apoptosis induced by hypoxia and Cu²⁺ exposure had a positive and synergistic effect on gill remodeling by reducing interlamellar cell masses. In addition, Cu²⁺ exposure induced hypoxia-like remodeling to gill morphology through mechanisms similar to hypoxia exposure. Most of gene expression changed mainly within 21 days and recovered to the control level on day 28, reflecting the acclimation of largemouth bass to hypoxia and/or Cu²⁺ exposure at gene expression level. Overall, our research suggests that chronic hypoxia and Cu²⁺ exposure could induce gill remodeling of largemouth bass through ER stress, mitochondrial damage and apoptosis. The outcomes could provide an insight for fish environmental adaptation and environmental toxicology.

The multiple biotoxicity integrated study in grass carp (Ctenopharyngodon idella) caused by Ochratoxin A: Oxidative damage, apoptosis and immunosuppression

Ochratoxin A (OTA) is a common hazardous food contaminant that seriously endangers human and animal health. However, limited study is focused on aquatic animal. This research investigated the multiple biotoxicity of OTA on spleen (SP) and head kidney (HK) in grass carp and its related mechanism. Our data showed that, dietary supplemented with OTA above 1209 μg/kg caused histopathological damages by decreasing the number of lymphocytes and necrotizing renal parenchymal cells. Meanwhile, OTA caused oxidative damage and reduced the isoforms mRNAs transcripts of antioxidant enzymes (e.g., GPX1, GPX4, GSTO) partly due to suppressing NF-E2-related factor 2 (Nrf2). OTA triggered apoptosis through mitochondria and death receptor pathway potentially by p38 mitogen-activated protein kinase (p38MAPK) activation. Besides, OTA exacerbated inflammation by down-regulation of anti-inflammatory factor (e.g., IL-10, IL-4) and up-regulations of pro-inflammatory factors (e.g., TNF-α, IL-6), which could be ascribed to signaling meditation of Janus kinase / signal transducer and activator of transcription (JAK/STAT). Additionally, the safe upper limits of OTA were estimated to be 677.6 and 695.08 μg/kg based on the immune-related indexes (C3 contents in the SP and LZ activities in the HK, respectively). Our study has provided a wide insight for toxicological assessment of feed pollutant in aquatic animals.

Taurine Alleviates Cadmium-Induced Toxicity via Genetically Specific Strategies in Two Strains of Gibel Carp (Carassius gibelio)

Our previous studies in gibel carp (Carassius gibelio) have shown that cadmium (Cd) exposure elicits deleterious effects depending on the genetic background, and thus we hypothesized that mitigation via nutritional intervention may vary between strains. Therefore, two gibel carp strains (the A and F strains) were fed diets supplemented with 0% or 1% taurine for 8 weeks prior to 96 h Cd exposure, and the responses of antioxidant pathways, endoplasmic reticulum (ER) stress, autophagy, and apoptosis were investigated. The results showed that taurine supplementation had no effect on the growth performance of gibel carp. After Cd exposure, histological damage to mitochondria and ER, induction of oxidative stress and antioxidant responses, occurrence of ER stress, and apoptotic signals were observed in the livers. Upon the diet effects, taurine supplementation alleviated the ER-stress-induced autophagy and apoptosis after Cd exposure and stimulated antioxidant pathways. Regarding the difference between strains, taurine played a protective role in alleviating Cd toxicity through the antioxidant response, ER stress, and autophagy in the F strain, whereas such effects were achieved by the attenuation of apoptosis in the A strain. Taken together, our results demonstrate the potential use of taurine in the mitigation of heavy metal toxicity in aquatic organisms.

Interference with zinc homeostasis and oxidative stress induction as probable mechanisms for cadmium-induced embryo-toxicity in zebrafish

The present study was conducted to provide new insights into the mechanisms that may be responsible for cadmium (Cd)-induced toxicity in zebrafish larvae as well as the role of the trace element zinc (Zn) in reversing Cd harmful effects. For this purpose, zebrafish eggs were exposed to Cd or/and Zn for 96 h. The effects on morphological aspect; mortality rate; Cd, Zn, and metallothionein (MT) levels; oxidative stress biomarkers; as well as molecular expression of some genes involved in Zn metabolism (Zn-MT, ZIP10, and ZnT1) and in antioxidant defense system (Cu/Zn-SOD, CAT and GPx) were examined. Our results showed that Cd toxicity was exerted, initially, by an interference with Zn metabolism. Thus, Cd was able to modify the expression of the corresponding genes so as to ensure its intracellular accumulation at the expense of Zn, causing its depletion. An oxidative stress was then generated, representing the second mode of Cd action which resulted in developmental anomalies and subsequently mortality. Interestingly, significant corrections have been noted following Zn supplementation based, essentially, on its ability to interact with the toxic metal. The increases of Zn bioavailability, the improvement of the oxidative status, as well as changes in Zn transporter expression profile are part of the protection mechanisms. The decrease of Cd-induced MTs after Zn supplement, both at the protein and the mRNA level, suggests that the protection provided by Zn is ensured through mechanisms not involving MT expression but which rather depend on the oxidative status.

Mechanism of Cadmium Exposure Induced Hepatotoxicity in the Mud Crab (Scylla paramamosain): Activation of Oxidative Stress and Nrf2 Signaling Pathway

Cadmium, one of the most toxic heavy metals, can cause severe oxidative damage to aquatic animals. However, the mechanism whereby the mud crabs respond to cadmium exposure remains unclear. This study investigated the effects of cadmium exposure on oxidative stress and histopathology changes and evaluated the role of the Nrf2 signaling pathway in regulating responses to cadmium-induced hepatotoxicity were investigated in mud crabs. Mud crabs were exposed to 0, 0.01, 0.05, and 0.125 mg/L cadmium for 21 d. The present results indicated that cadmium exposure increased hydrogen peroxide (H₂O₂) production, lipid peroxidation and tissue damage, but decreased the activity of superoxide dismutase (SOD) and catalase (CAT), and caused lipid peroxidation and tissue damage. The results of an integrated biomarker index analysis suggested that the toxicity of cadmium was positively related to cadmium concentration. The expression levels of the Nrf2 signaling pathway (Nrf2, metallothionein, and cytochrome P450 enzymes) were up-regulated after cadmium exposure. Silencing of Nrf2 in vivo decreased antioxidant gene (SOD, CAT, and glutathione S-transferase) expression, suggesting that Nrf2 can regulate antioxidant genes. Knocking down Nrf2 in vivo also significantly decreased the activity of SOD and CAT after cadmium exposure. Moreover, silencing of Nrf2 in vivo enhanced H₂O₂ production and the mortality rates of mud crabs after cadmium exposure. The present study indicated that cadmium exposure induced hepatotoxicity in the mud crab by increasing H₂O₂ content, which decreased the antioxidant capacity, leading to cell injury. In addition, the Nrf2 is activated to bound with antioxidant response element, initiating the expression of antioxidant enzyme genes during cadmium induced hepatotoxicity in the mud crabs.

New Insight on the Immune Modulation and Physical Barrier Protection Caused by Vitamin A in Fish Gills Infected With Flavobacterium columnare

In this study, we have investigated the influence of vitamin A on gill barrier function of grass carp (Ctenopharyngodon idella) infected with Flavobacterium columnare. The fish were fed different concentrations of vitamin A diets for 10 weeks and then infected with F. columnare by immersion. We observed that optimal vitamin A significantly prevented gill rot morbidity in fish infected with F. columnare. Further investigations revealed that vitamin A boosted the gill immunity by increasing the contents of complements (C3 and C4), activities of acid phosphatase (ACP) and lysozyme, mRNAs of β-defensin-1, liver-expressed antimicrobial peptide 2A and 2B (LEAP-2A and LEAP-2B), hepcidin, and anti-inflammatory cytokines like transforming growth factor β1 (TGF-β1), TGF-β2, interleukin-10 (IL-10), and IL-11. It also enhanced the levels of various related signaling molecules including inhibitor protein κBα (IκBα), target of rapamycin (TOR), and ribosome protein S6 kinase 1 (S6K1) but downregulated the expression of pro-inflammatory cytokines including IL-1β, IL-8, tumor necrosis factor α (TNF-α), and interferon γ2 (IFN-γ2) and related signaling molecules including nuclear factor κB p65 (NF-κB p65) (rather than NF-κB p52), IκB kinase β (IKKβ), IKKγ (rather than IKKα), eIF4E-binding protein 1 (4E-BP1), and 4E-BP2 mRNA levels in fish gills. In addition, dietary vitamin A markedly lowered the concentrations of reactive oxygen species (ROS), malondialdehyde (MDA), and protein carbonyl (PC), increased both the activities and mRNAs of copper/zinc superoxide dismutase (Cu/ZnSOD), MnSOD, glutathione transferases (GSTs), glutathione peroxidase (GPx), and glutathione reductase (GR) associated with upregulation of NF-E2-related factor 2 (Nrf2) mRNAs and downregulation of Kelch-like-ECH-associated protein (Keap1a) and Keap1b mRNAs. Moreover, vitamin A decreased the mRNAs of different apoptotic mediators [caspases 8, 9, 3 (rather than 7)] associated with downregulation of signaling molecule p38 mitogen-activated protein kinase (p38MAPK) mRNAs in fish gills. Besides, vitamin A promoted tight junction (TJ) complex mRNAs [including claudin-b, -c, -3, -7, -12, occludin, and zonula occludens-1 (ZO-1)] that have been linked to the downregulation of myosin light chain kinase (MLCK) signaling. Taken together, the current study demonstrated for the first time that vitamin A markedly enhanced gill health associated with immune modulation and physical barrier protection. Based on protecting fish against gill rot morbidity, ACP activity, and against lipid peroxidation, optimum vitamin A concentrations in on-growing grass carp (262-997 g) were found to be 1,991, 2,188, and 2,934 IU/kg diet, respectively.

Photo-enhanced toxicity of crude oil on early developmental stages of Atlantic cod (Gadus morhua)

Photo-enhanced toxicity of crude oil is produced by exposure to ultraviolet (UV) radiation. Atlantic cod (Gadus morhua) embryos were exposed to crude oil with and without UV radiation (290-400 nm) from 3 days post fertilization (dpf) until 6 dpf. Embryos from the co-exposure experiment were continually exposed to UV radiation until hatching at 11 dpf. Differences in body burden levels and cyp1a expression in cod embryos were observed between the exposure regimes. High doses of crude oil produced increased mortality in cod co-exposed embryos, as well as craniofacial malformations and heart deformities in larvae from both experiments. A higher number of differentially expressed genes (DEGs) and pathways were revealed in the co-exposure experiment, indicating a photo-enhanced effect of crude oil toxicity. Our results provide mechanistic insights into crude oil and photo-enhanced crude oil toxicity, suggesting that UV radiation increases the toxicity of crude oil in early life stages of Atlantic cod.

Role of nuclear pregnane X receptor in Cu-induced lipid metabolism and xenobiotic responses in largemouth bass (Micropterus salmoides)

The pregnane X receptor (PXR) is a master xenobiotic-sensing receptor in response to toxic byproducts, as well as a key regulator in intermediary lipid metabolism. Therefore, the present study was conducted to investigate the potential role of PXR in mediating the lipid dysregulation and xenobiotic responses under Cu-induced stress in largemouth bass (Micropterus salmoides). Four groups of largemouth bass (52.66 ± 0.03 g) were treated with control, Cu waterborne (9.44 μmol/L), Cu+RIF (Rifampicin, 100 mg/kg, PXR activator), and Cu+KET (Ketoconazole, 20 mg/kg, PXR inhibitor) for 48 h. Results showed that Cu exposure significantly elevated the plasma stress indicators and triggered antioxidant systems to counteract Cu-induced oxidative stress. Acute Cu exposure caused liver steatosis, as indicated by the significantly higher levels of plasma triglycerides (TG), lipid droplets, and mRNA levels of lipogenesis genes in the liver. Liver injuries were detected, as shown by hepatocyte vacuolization and severe apoptotic signals after Cu exposure. Importantly, Cu exposure significantly stimulated mRNA levels of PXR, suggesting the response of this regulator in the xenobiotic response. The pharmacological intervention of PXR by the agonist and antagonist significantly altered hepatic mRNA levels of PXR, implying that RIF and KET were effective agents of PXR in largemouth bass. Administration of RIF significantly exacerbated liver steatosis, and such alterations were dependent on the regulations on pparγ and cd36 rather than srebp1 signaling, which suggested that PXR-PPARγ might be another pathway for Cu-induced lipid deposition in fish. Whereas, KET administration showed reverse effects on lipid metabolism as indicated by the lower hepatic TG levels, suppressed mRNA levels of pparγ and cd36. Activation of PXR stimulated autophagy and inhibited apoptosis, leading to lower hepatic vacuolization; while inhibition of PXR showed higher apoptotic signals, inhibition of autophagic genes and stimulation of apoptotic genes. Taken together, PXR played a cytoprotective role in Cu-induced hepatotoxicity through regulations on autophagy and apoptosis. Overall, our data has demonstrated for the first time on the dual roles of PXR as a co-regulator in mediating xenobiotic responses and lipid metabolism in fish, which implying the potential of PXR as a therapy target for xenobiotics-induced lipid dysregulation and hepatotoxicity.

Persistent activation of Nrf2 promotes a vicious cycle of oxidative stress and autophagy inhibition in cadmium-induced kidney injury

Nuclear factor erythroid 2-related factor 2 (Nrf2) serves as the master regulator of antioxidant signaling and inhibition or hyperactivation of Nrf2 pathway will result in the redox imbalance to induce tissue injury. Herein, we established cadmium (Cd)-exposed rat kidney injury model by intraperitoneal injection with CdCl₂ (1.5 mg/kg body weight) and cytotoxicity model of NRK-52E cells by CdCl₂ (5 μM) exposure to reveal the role of Nrf2 hyperactivation in Cd-induced nephrotoxicity. Data from the in vitro and in vivo study showed that Cd caused Nrf2 nuclear retention due to nuclear-cytoplasmic depletion of Kelch-like ECH-associated protein 1 (Keap1) and Sequestosome-1(SQSTM1/p62) accumulation, leading to the persistent activation of Nrf2. Moreover, we established inhibited models of Cd-induced prolonged Nrf2 activation using siRNA-mediated gene silencing in vitro and pharmacological inhibition in vivo for subsequent assays. First, Cd-induced cytotoxicity, renal injury and concomitant oxidative stress were markedly alleviated by Nrf2 inhibition. Second, Cd-induced autophagy inhibition was notably alleviated by Nrf2 inhibition. Further, we revealed underlying molecular mechanisms of the crosstalk between persistent activation of Nrf2 and autophagy inhibition in Cd-induced nephrotoxicity. Data showed that Cd-induced lysosomal dysfunction evidenced by impaired lysosomal biogenesis and degradation capacity was markedly recovered by Nrf2 inhibition. Meanwhile, Cd-impaired autophagosome-lysosome fusion was obviously restored by Nrf2 inhibition. In conclusion, our findings revealed that persistent activation of Nrf2 promoted a vicious cycle of oxidative stress and autophagy inhibition in Cd-induced nephrotoxicity.

Metabolic changes and stress damage induced by ammonia exposure in juvenile Eriocheir sinensis

The application of nitrogen fertilizers in the rice-crab co-culture system may expose juvenile Eriocheir sinensis to high ammonia concentrations within a short period of time, potentially causing death. Currently, the molecular mechanism underlying ammonia toxicity in juvenile Eriocheir sinensis remains poorly understood. This study compared the effects of 24 h exposure to different total ammonia-N concentrations (0, 10.47, and 41.87 mg/L) on antioxidant enzyme activities and tandem mass tag (TMT)-based proteomics in the hepatopancreas of juvenile Eriocheir sinensis. During the experiment, water temperature and pH were maintained at 20.4 ± 1.4 °C and 7.69 ± 0.46, respectively. Proteomic data demonstrated that Eriocheir sinensis used different metabolic regulatory mechanisms to adapt to varying ammonia conditions. The tricarboxylic acid (TCA) cycle, glycogen degradation, and oxidative phosphorylation showed marginally upregulated trends under low ammonia exposure. High ammonia stress caused downregulation of the TCA cycle and provided energy by enhancing oxidative phosphorylation, fatty acid beta oxidation, gluconeogenesis, and glycogen degradation. The detoxification of ammonia into urea and glutamine was suppressed under high ammonia stress. Finally, ammonia exposure induced oxidative stress and caused protein damage. Antioxidant enzyme activity analysis further revealed that exposure to high concentrations of ammonia may induce more severe oxidative stress. This study provides a global perspective on the mechanisms underlying ammonia exposure-induced metabolic changes and stress damage in juvenile Eriocheir sinensis.

Evaluation of the hair cell regeneration and claudin b and phoenix gene expression during exposure to low concentrations of cadmium and zinc in early developing zebrafish larvae

Zebrafish possess hair cells on the body surface similar to that of mammals inner hear, in particular in the neuromasts, and due to its ability in regenerating damaged hair cells, is regularly used as a powerful animal model to study in vivo cytotoxicity. Among the factors leading to hair cell disruption, metal ions are of particular concern since they are important environmental pollutants. To date, several studies on zebrafish hair cell regeneration after metal exposure exist, while no data on regeneration during continuous metal exposure are available. In the present study, neuromast hair cell disruption and regeneration were assessed in zebrafish larvae for the first time during zinc (Zn) and cadmium (Cd) continuous exposure and a visual and molecular approach was adopted. Fluorescent vital dye DASPEI was used to assess hair cell regeneration and the gene expression of claudin b (cldnb) and phoenix (pho), was analyzed. Metallotionein-2 (mt2) gene expression was used as standard molecular marker of metal toxicity and confirmed the higher toxicity of Cd compared to Zn. In addition, Cd caused a delay in hair cell regeneration compared to Zn. Molecular analysis showed cldnb gene expression increased in relation to the metal concentrations used, confirming the involvement of this gene in hair cell regeneration. On the contrary, a dramatic decrease of pho gene expression was observed in Cd exposed groups, suggesting a negative impact of Cd on pho expression, thus negatively interfering with hair cell regeneration in zebrafish larvae exposed to this metal.

Copper: benefits and risks for poultry, livestock, and fish production

Protein production from animal origin should increase to meet the needs of a growing global population. This article presents an overview on copper (Cu) forms and their importance for animals' physiological functions. Moreover, it will focus on the current and promising nano-Cu applications in poultry, livestock, and fish production systems. Use of Cu as a feed additive directly or indirectly impacts the human food chain and may affect the safety and/or quality of food. Finally, the expected risks and hazards related to the use of nano-Cu that can affect animals, humans, and the environment are described. It is concluded that nano-Cu applications have the potential to provide an efficient solution for reducing the Cu amount in the poultry, livestock, and fish diets, which can help in reducing costs and environmental contamination and increasing animals' productivity. However, concerns over the safety of nano-Cu applications hamper their immediate implementation. Thus, rigorous risk assessments should be conducted to ensure the safety of animal-origin products in the case of supplementation animal diets with nano-copper.

Sub-Lethal Peak Exposure to Insecticides Triggers Olfaction-Mediated Avoidance in Zebrafish Larvae

In agricultural areas, insecticides inevitably reach water bodies via leaching or run-off. While designed to be neurotoxic to insects, insecticides have adverse effects on a multitude of organisms due to the high conservation of the nervous system among phyla. To estimate the ecological effects of insecticides, it is important to investigate their impact on non-target organisms such as fish. Using zebrafish as the model, we investigated how different classes of insecticides influence fish behavior and uncovered neuronal underpinnings of the associated behavioral changes, providing an unprecedented insight into the perception of these chemicals by fish. We observed that zebrafish larvae avoid diazinon and imidacloprid while showing no response to other insecticides with the same mode of action. Moreover, ablation of olfaction abolished the aversive responses, indicating that fish smelled the insecticides. Assessment of neuronal activity in 289 brain regions showed that hypothalamic areas involved in stress response were among the regions with the largest changes, indicating that the observed behavioral response resembles reactions to stimuli that threaten homeostasis, such as changes in water chemistry. Our results contribute to the understanding of the environmental impact of insecticide exposure and can help refine acute toxicity assessment.

The Role of Toxic Metals and Metalloids in Nrf2 Signaling

Nuclear factor erythroid 2-related factor 2 (Nrf2), an emerging regulator of cellular resistance to oxidants, serves as one of the key defensive factors against a range of pathological processes such as oxidative damage, carcinogenesis, as well as various harmful chemicals, including metals. An increase in human exposure to toxic metals via air, food, and water has been recently observed, which is mainly due to anthropogenic activities. The relationship between environmental exposure to heavy metals, particularly cadmium (Cd), lead (Pb), mercury (Hg), and nickel (Ni), as well as metaloid arsenic (As), and transition metal chromium (Cr), and the development of various human diseases has been extensively investigated. Their ability to induce reactive oxygen species (ROS) production through direct and indirect actions and cause oxidative stress has been documented in various organs. Taking into account that Nrf2 signaling represents an important pathway in maintaining antioxidant balance, recent research indicates that it can play a dual role depending on the specific biological context. On one side, Nrf2 represents a potential crucial protective mechanism in metal-induced toxicity, but on the other hand, it can also be a trigger of metal-induced carcinogenesis under conditions of prolonged exposure and continuous activation. Thus, this review aims to summarize the state-of-the-art knowledge regarding the functional interrelation between the toxic metals and Nrf2 signaling.

Differential regulation of endoplasmic reticulum stress-induced autophagy and apoptosis in two strains of gibel carp (Carassius gibelio) exposed to acute waterborne cadmium

Previous studies illustrated that gibel carp F strain displays better lipid mobilization and antioxidant ability and compared to the A strain. We therefore hypothesized that the F strain would exhibit superior defense to cadmium exposure. Comparative studies were conducted between A and F strains using plasma stress biomarkers, histological observations, and analysis of hepatic molecular events to examine exposure to waterborne Cd (11.9 mg L^-1) for 48 h and 96 h. Waterborne Cd exposure stimulated stress response and hepatic metallothionein mRNA induction in both gibel carp strains confirming exposure. Antioxidant responses were stimulated to counteract Cd toxicity, suggested by the upregulation of mRNA levels of genes associated with nuclear factor erythroid 2-related factor 2 (nrf2) signaling. Cd exposure induced endoplasmic reticulum (ER) stress, meanwhile, branches of genes in unfolded protein response (UPR) were activated. Slight time-dependent effects were implied by greater ER stress, UPR, and apoptosis signals with the duration of Cd exposure. Genotype-specific effects were identified, revealing that the F strain showed greater stress at 96 h exposure and higher antioxidant response compared to the A strain, as indicated by the mRNA levels of genes in nrf2 signaling. ER stress and UPR were also stronger in the F strain after Cd exposure. In contrast, the A strain showed higher autophagy and apoptosis response compared to the F strain. Collectively, combined autophagy and apoptosis were triggered under ER stress, which might serve as defense strategies in both gibel carp strains. The F strain showed greater antioxidant detoxification response and UPR to mitigate Cd toxicity, whereas excessive ER stress contributed to higher autophagy and apoptosis in the A strain. The present study uncovered the differential regulation and defense strategies in fish strains exposed to metal exposure.

Flow cytometry in the analysis of hematological parameters of tilapias: applications in environmental aquatic toxicology

Blood tissue has been used to assess animal health and the environment in which they live. This tissue is easily acquired and has the ability to respond to various adverse conditions. Several techniques have been employed in the detection of xenobiotic-induced cell damage in blood cells. In general, traditionally used technologies, such as cellular analysis in blood smears, are time-consuming and require great analytical capacity. The present study proposes flow cytometry as a method to detect changes in blood cell populations. Tilapia (Oreochromis niloticus) was selected as a model for plotting the profile of fish blood cell populations after exposure to xenobiotics without euthanizing animals or using cell markers. Populations of erythrocytes and lymphocytes were detected only by combining the techniques of FACSAria cell sorting and light microscopy. Systemic deleterious effects were found through blood analysis, such as an increased lymphocyte-rich population at 48 h of exposure followed by a subsequent decrease. Moreover, the time-dependent expression of Nrf2 suggests its participation in increased membrane disruption, indicating it has a central role in erythrocyte lifespan. The present results shed light on the viability of using flow cytometry for blood analysis of living fish.

Cadmium induced oxystress alters Nrf2-Keap1 signaling and triggers apoptosis in piscine head kidney macrophages

Cadmium (Cd) with no known functional role in any life-form has myriad of harmful effects. The present study was designed to elucidate the mechanism of Cd-induced oxystress generation and its impact on antioxidant and apoptosis signaling pathways in head kidney macrophage (HKM) of Channa punctatus Bloch. Fish were sampled and acclimatized with one group treated with cadmium chloride (CdCl₂) (1.96 mg/L) and another as untreated control group, both kept under observation for 7 days. Exposure to Cd caused ultrastructural changes along with reduced head kidney somatic index (HKSI). Significantly increased levels of reactive oxygen species (ROS), respiratory burst activity, lipid peroxidation, DNA fragmentation and superoxide dismutase were found in the HKM from the treated group as compared to control. In contrast, antioxidant enzymes like catalase and reduced glutathione activity decreased in the Cd exposed group. The suppressed antioxidant activity was further confirmed and corroborated from the altered expression of Kelch-like ECH-associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor 2 (Nrf2) genes, the major player of antioxidant pathway. Cd induced alteration in Nrf2-Keap1 signaling pathway was also validated by the diminished levels of Nrf2 dependent expression of protein like heme oxygenase-1 (HO-1). The flow cytometry analysis supported the event of apoptosis in Cd exposed group as compared to control, which was further confirmed by the upregulated expression of caspase-3, caspase-8, caspase-9, TNF-α and p53 genes from the real-time gene expression study. In addition, altered protein level of cytochrome C validates the incidence of apoptosis. Altogether, our results demonstrate that exposure to Cd caused oxidative stress in HKM of Channa punctatus Bloch. by compromising the antioxidant enzyme activities via the down regulation of expression of genes related to antioxidant signaling pathway besides encouraging apoptosis via both mitochondrial and death receptor pathway.

The role of Nrf2 in mitigating cadmium-induced oxidative stress of Marsupenaeus japonicus

Nuclear factor-erythroid 2-related factor-2 (Nrf2) is an important modulator of cellular responses against Cd in mammalian cells. However, whether such modulation is conserved in Marsupenaeus japonicas remains unknown.In our study, the shrimps were injected with dsRNA targeting Nrf2 at 4 μg g^-1 body weight (b.w.) or sulforaphane (SFN) at 5 μg g^-1 b.w., and then were exposed to 40 mg L^-1 CdCl₂ for 48 h. After Nrf2 knockdown, the Cd content increased, but decreased in the SFN group. This suggested that Nrf2 could promote Cd excretion. A terminal deoxynulceotidyl transferase nick-end-labeling (TUNEL) assay revealed that the Nrf2 knockdown increased the number of apoptotic cells in M. japonicas, while SFN decreased the number of apoptotic cells. After Nrf2 knockdown, the total antioxidant capacity (T-AOC), superoxide dismutase (Sod) activity, and related gene expression decreased significantly, while the malondialdehyde (MDA) content increased remarkably. By contrast, SFN injection alleviated the oxidative stress, as evidenced by increased T-AOC, Sod activity, sod mRNA expression and a reduced MDA content. Similarly, detoxification related enzyme activities (ethoxyresorufin O-deethylase and glutathione-S-transferase (GST)) and their corresponding gene expressions (cyp3a (cytochrome P450 family 3 subfamily A) and gst) were suppressed in the ds-Nrf2 injection group, while they were elevated in the SFN group. In addition, ds-Nrf2 activated mitochondrial apoptotic pathway, as evidenced the mRNA and protein levels of caspase-3, Bcl2 associated X protein (Bax), and p53, while SFN treatment suppressed them. These results displayed that in M. japonicus Cd-induced cellular oxidative damage probably acts via the Nrf2 pathway.

Identification of the Nrf2 in the fathead minnow muscle cell line: role for a regulation in response to H2O2 induced the oxidative stress in fish cell

The Nrf2 (nuclear factor erythroid 2-related factor 2) plays a central role in cell protection against a wide variety of environmental stressors through the Nrf2-Keap1 (Kelch-like ECH-associated protein 1) pathway, but its involvement in modulation of antioxidant system of fish cell is still largely unexplored. The present study focused on the molecular cloning and silencing of the Nrf2 in the fathead minnow muscle cell line (FHM) in response to the oxidative stress induced by H₂O₂. A full-length cDNA of coding Nrf2 was cloned from FHM cells by RT-PCR and RACE approaches. The obtained cDNA covered 2578 bp with an open reading frame (1770 bp) of encoding 589 amino acids. Sequence alignment and phylogenetic analysis revealed a high degree of conservation (51-86%) among 16 fishes. Based on the cloned Nrf2 sequence, the siRNA-242 of targeting Nrf2 with the best knocking down efficiency was designed and detected. Then, the mRNA levels of Keap1, Nrf2, Maf (musculoaponeurotic fibrosarcoma oncogene), and HO-1 (haemoxygenase-1); the activities of T-SOD (total superoxide dismutase), CAT (catalase), and GSH-PX (glutathione peroxidase); the levels of GSH (glutathione) and MDA (malonaldehyde); and the cell cycle and apoptosis were analyzed to investigate the molecular responses after H₂O₂ exposure. These results showed a coordinated transcriptional regulation of Keap1, Maf, and HO-1 and antioxidants (T-SOD, GSH, CAT, and GSH-PX) and MDA levels after H₂O₂ exposure, leading to oxidative damage and apoptosis. These findings provided an insight to understand the mechanisms of Nrf2 against oxidative stress in fish.

MiRNAs-Modulation of Nrf2 Signaling Networks in Regulation Oxidative Stress of Chinese Perch Skeletal Muscle After Fasting Treatment

Nrf2 is an important transcription factor involved in the antioxidant response and is widely expressed in animal tissues. The function of Nrf2 is regulated by its negative regulator Keap1 by inducing its cytoplasmic degradation. Recent studies have suggested that Nrf2 is also regulated post-transcriptionally via miRNAs. However, to date, how miRNAs regulate Nrf2 in fish skeletal muscles is unknown. In this study, the full-length cDNAs with 2398 bp of the Nrf2 was firstly cloned by SMART RACE amplification tools from Chinese perch. The Nrf2 gene structure and its 3'-UTR region for possible miRNA binding sites, as well as its spatial expression profile were assayed. Then, we employed TargetScan Fish tool MiRNAnome to predict putative sites for five miRNAs including miR-181a-5p, MiR-194a, MiR-216a, miR-459-5p, and miR-724. Using qRT-PCR assay, we found that Nrf2 mRNA levels have negative correlation with all five miRNAs expression in muscle of nutritionally deprived fish, and that ectopic expression of miR-181a-5p alone reduces Nrf2 mRNA levels. Luciferase reporter assay in a heterologous cell system revealed that each of the five miRNAs reduced Nrf2 expression, suggesting a direct regulatory mechanism. Moreover, the miR-181a-5p suppression using specific antagomir led to a significant increase in Nrf2 expression in vivo. At the same time, the expression levels of the antioxidant enzymes CAT, ZnSOD, GPx, GSTA, and GSTA genes increased significantly after injecting miR-181a-5p antagomir. Taken together, these findings provide evidence that miRNAs are involved in the Nrf2 signaling networks in regulation of oxidative stress in fish, at least in Chinese perch muscle.

Short exposure to cadmium disrupts the olfactory system of zebrafish (Danio rerio) - Relating altered gene expression in the olfactory organ to behavioral deficits

Fish strongly rely on olfaction as a variety of essential behaviors such as foraging and predator avoidance are mediated by the olfactory system. Cadmium (Cd) is known to impair olfaction and accumulate in the olfactory epithelium (OE) and bulb (OB) of fishes. In the present study, the acute toxicity of Cd on olfaction in zebrafish (Danio rerio) was characterized on the molecular and behavioral level. To this end, quantitative real-time PCR was performed in order to analyze the expression of selected genes in both the OE and OB. Moreover, the response of zebrafish to an alarm cue was investigated. Following 24 h of exposure to Cd, the expression of genes associated with olfactory sensory neurons was reduced in the OE. Furthermore, the antioxidant genes peroxiredoxin 1 (prdx1) and heme oxygenase 1 (hmox1), as well as the metallothionein 2 gene (mt2) were upregulated in the OE, whereas hmox1 and the stress-inducible heat shock protein 70 gene (hsp70) were upregulated in the OB upon exposure to Cd. Following stimulation with a conspecific skin extract, zebrafish displayed a considerable disruption of the antipredator behavior with increasing Cd concentration. Taken together, Cd impaired olfaction in zebrafish, thereby disrupting the antipredator response, which is crucial for the survival of individuals. Cellular stress followed by disruption of olfactory sensory neurons may have contributed to the observed behavioral deficits.

Dietary nanoencapsulated quercetin homeostated transcription of redox-status orchestrating genes in zebrafish (Danio rerio) exposed to silver nanoparticles

The present study assessed the protective effect of chitosan-nanoencapsulated quercetin (Qu-ChiNPs) against oxidative stress caused by silver nanoparticles (AgNPs). To this end, the transcription of prime genes regulating hepatic Keap1-Nrf2 pathway as well as downstream antioxidant enzymes were monitored prior to and after oxidative stress by AgNPs. Zebrafish (Danio rerio; n = 225) was assigned into five experimental groups based on feeding with diets supplemented with different additives as follows: negative and positive control groups, without additive; ChiNPs, 400 mg nanochitosan per kg diet; Quercetin, 400 mg free quercetin per kg diet; and Qu-ChiNPs, 400 mg Qu-ChiNPs per kg diet. At the end of the feeding trial (40 days), the experimental groups, except the negative control, were exposed to sublethal concentration of AgNPs (0.15 mg L^-1) for 96h. Before exposure to AgNPs, free quercetin-treated diet significantly upregulated Keap1, Nrf2, Cat, SOD, GPx, and GST genes in the liver tissue when compared with the control diet, whereas Qu-Chi.NPs downregulated their transcription to the lowest levels. After exposure to AgNPs, all genes exhibited different responses in the AgNPs-exposed groups. The highest transcription of Nrf2, Cat, SOD, GPx, and GST was observed in the positive group, with being upregulated about 8, 10, 8, 8, and 7 times, respectively, when compared to the respective ones in the negative control. However, Keap1 showed a reverse response with being transcripted 12 times lower. The quercetin treatments, especially Qu-Chi.NPs, significantly reduced the transcription of Nrf2, Cat, SOD, GPx, and GST genes, yet enhanced Keap1 expression. Qu-Chi.NPs reduced the expression of Nrf2, SOD, Cat, GPx, and GST about 11, 10, 15, 10, and 10 times, respectively, yet increased that of Keap1 about 12 times. Taken together, nanoencapsulation can improve the antioxidant efficacy of quercetin against AgNPs toxicity and might reduce involvement of the cellular antioxidant system through tuning redox status. More broadly, it would be interesting to assess the effects of Qu-Chi.NPs against other metallic and organic oxidative stressors or pollutants.

Effects of dietary Cu and Zn on the accumulation, oxidative stress and the expressions of immune-related genes in the livers of Nile tilapia (Oreochromis niloticus)

Excess Cu and Zn can cause many adverse effects in fish. However, few studies have addressed the effects of dietary Cu and Zn on antioxidant physiology and immunity and the underlying mechanisms in fishes. In this study, accumulation of Cu and Zn, effects on the antioxidant enzymes and the transcriptional expressions of immune-related genes were examined in the Oreochromis niloticus fed the Cu and/or Zn enriched duckweed. The results showed that the liver and intestine had the highest accumulation of Cu²⁺ and Zn²⁺ while the muscle had the lowest accumulation of these two metals. The activities of SOD, CAT, GPx and the contents of GSH, GSSG in the liver of all treatment groups were significantly decreased compared to the control group. MDA content was significantly elevated in all treatment groups after feeding for 21 days, implying lipid peroxidation in the liver. In the Cu + Zn group, the activities of SOD, GPx and the GSSG content in the liver were significantly decreased. Compared with the Zn group, the LZM activity in the Cu + Zn group was reversed after feeding for 42 days (P < 0.05). The transcriptional expressions of immune-related genes (TNF-α, INF-γ and IL-1β) in Cu, Zn, Cu + Zn groups were significantly inhibited compared with the control group after treatment for 21 days. Compared with the Cu + Zn group, the level of INF-γ transcripts was significantly reduced in the Cu and Zn group, while the TNF-α expression was elevated after treatment for 42 days. Cu and Zn had synergistic effects on the antioxidant system. Cu has greater effects than Zn on the immunity of O. niloticus. This study demonstrates that dietary Cu and Zn may pose a potential threat to the tilapia populations.

Inconsistently impairment of immune function and structural integrity of head kidney and spleen by vitamin A deficiency in grass carp (Ctenopharyngodon idella)

To investigate effects of vitamin A (VA) on fish immune function and structural integrity in the head kidney and spleen of fish, total of 540 on-growing grass carp (Ctenopharyngodon idella) were divided into six groups, feeding graded levels of VA (0, 600, 1200, 1800, 2800 and 3800 IU/kg diet) for 70 days. Results showed that dietary VA deficiency depressed antibacterial ability and aggravated inflammatory response partially linked to nuclear factor κB p65 (NF-κB p65) and target of rapamycin (TOR) signaling pathways in the head kidney and spleen of fish. Meanwhile, VA deficiency caused oxidative damage, apoptosis and disruption of tight junctions (TJs), which were partially attributed to the down-regulation of NF-E2-related factor 2 (Nrf2) signaling mediated antioxidant ability, the up-regulation of p38 mitogen-activated protein kinase (p38MAPK) signaling mediated apoptosis and myosin light chain kinase (MLCK) signaling mediated disruption of tight junctions (TJs). Taken together, current study firstly demonstrated that VA deficiency decreased the immune function and damaged the structural integrity of the head kidney and spleen in fish.

Mechanotransduction Activity Facilitates Hair Cell Toxicity Caused by the Heavy Metal Cadmium

Hair cells are sensitive to many insults including environmental toxins such as heavy metals. We show here that cadmium can consistently kill hair cells of the zebrafish lateral line. Disrupting hair cell mechanotransduction genetically or pharmacologically significantly reduces the amount of hair cell death seen in response to cadmium, suggesting a role for mechanotransduction in this cell death process, possibly as a means for cadmium uptake into the cells. Likewise, when looking at multiple cilia-associated gene mutants that have previously been shown to be resistant to aminoglycoside-induced hair cell death, resistance to cadmium-induced hair cell death is only seen in those with mechanotransduction defects. In contrast to what was seen with mechanotransduction, significant protection was not consistently seen from other ions previously shown to compete for cadmium uptake into cells or tissue including zinc and copper. These results show that functional mechanotransduction activity is playing a significant role in cadmium-induced hair cell death.

CRISPR-Generated Nrf2a Loss- and Gain-of-Function Mutants Facilitate Mechanistic Analysis of Chemical Oxidative Stress-Mediated Toxicity in Zebrafish

The transcription factor Nrf2a induces a cellular antioxidant response and provides protection against chemical-induced oxidative stress, as well as playing a critical role in development and disease. Zebrafish are a powerful model to study the role of Nrf2a in these processes but have been limited by reliance on transient gene knockdown techniques or mutants with only partial functional alteration. We developed several lines of zebrafish carrying different null (loss of function, LOF) or hyperactive (gain of function, GOF) mutations to facilitate our understanding of the Nrf2a pathway in protecting against oxidative stress. The mutants confirmed Nrf2a dependence for induction of the antioxidant genes gclc, gstp, prdx1, and gpx1a and identified a role for Nrf2a in the baseline expression of these genes, as well as for sod1. Specifically, the 4-fold induction of gstp by tert-butyl hydroperoxide (tBHP) in wild type fish was abolished in LOF mutants. In addition, baseline gstp expression in GOF mutants increased by 12.6-fold and in LOF mutants was 0.8-fold relative to wild type. Nrf2a LOF mutants showed increased sensitivity to the acute toxicity of cumene hydroperoxide (CHP) and tBHP throughout the first 4 days of development. Conversely, GOF mutants were less sensitive to CHP toxicity during the first 4 days of development and were protected against the toxicity of both hydroperoxides after 4 dpf. Neither gain nor loss of Nrf2a modulated the toxicity of R-(-)-carvone (CAR), despite the ability of this compound to potently induce Nrf2a-dependent antioxidant genes. Similar to other species, GOF zebrafish mutants exhibited significant growth and survival defects. In summary, these new genetic tools can be used to facilitate the identification of downstream gene targets of Nrf2a, better define the role of Nrf2a in the toxicity of environmental chemicals, and further the study of diseases involving altered Nrf2a function.

Toxic effects of waterborne nitrite exposure on antioxidant responses, acetylcholinesterase inhibition, and immune responses in olive flounders, Paralichthys olivaceus, reared in bio-floc and seawater

Paralichthys olivaceus (mean weight, 280.1 ± 10.5 g; mean length, 28.37 ± 2.3 cm) was reared in bio-floc and seawater for 6 months to determine the toxic effects of waterborne nitrite exposure (0, 25, 50, 100, and 200 mg/L) for 1 week, compared to those observed with bio-floc and seawater only. The effects on antioxidant activity, immune responses, and acetylcholinesterase activity were measured. Following nitrite exposure, superoxide dismutase activity in the liver and gills was significantly elevated and catalase activity was significantly increased, except for in the gills of P. olivaceus reared in bio-floc. Further, glutathione S-transferase activity was significantly elevated in the liver and gills, and glutathione was significantly lower. Meanwhile, acetylcholinesterase activity in the liver and gills was significantly inhibited and plasma lysozyme activity and immunoglobulin M were considerably elevated.

Trehalose suppresses cadmium-activated Nrf2 signaling pathway to protect against spleen injury

Cadmium (Cd), as a kind of ubiquitous and highly toxic heavy metal pollutants, has been known to result in immunotoxicity in animals. As a multifunctional bioactivity disaccharide, trehalose (Tre) is characterized by antioxidative, antiapoptotic, and accelerating autophagy. In this study, Sprague-Dawley (SD) rats were fed with cadmium chloride (CdCl₂) and/or Tre to explore the molecular mechanisms of Tre-protected against spleen injury caused by Cd exposure. Firstly, the results showed that Tre partially recovered splenic pathological changes induced by Cd exposure. Secondly, Tre dramatically declined the level of methane dicarboxylic aldehyde (MDA) and elevated the level of total antioxidant capacity (T-AOC) to weaken oxidative stress caused by Cd exposure in spleen tissue. Moreover, the results showed that Tre significantly suppressed Cd-induced the nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) and up-regulated the protein expression of nuclear Nrf2. Thirdly, Tre remarkably reduced the protein expression of sequestosome 1 (p62/SQSTM1) and microtubule-associated protein light chain 3II (LC-3II) to restore autophagy inhibition induced by Cd exposure. Finally, the results of TUNEL and the expression of apoptosis marker proteins showed that Tre significantly inhibited Cd-induced apoptosis in spleen tissue to exert its protective effects. In summary, the results indicated that Tre modulated Nrf2 signaling pathway, which interacted with apoptosis and autophagy to against Cd-induced spleen injury, providing potential therapeutic strategies for the prevention and treatment of Cd-related immune system diseases.

The molecular mechanism of Nrf2-Keap1 signaling pathway in the antioxidant defense response induced by BaP in the scallop Chlamys farreri

In this study, we cloned the full-length cDNA of the Kelch-like ECH-associated protein 1 (Keap1) from the scallops Chlamys farreri (C. farreri). Sequences alignment and phylogenetic analysis showed that CfKeap1 was highly specific in the scallops, and the amino acid sequence identity value is closer to that in zebrafish Keap1b and Nothobranchius furzeri Keap1b than Keap1a. The highest transcription level of CfKeap1 expression was detected in the digestive glands. The gene expressions of CfKeap1, NF-E2-related nuclear factor 2 (Nrf2), Superoxide Dismutase (SOD), Catalase (CAT) and Glutathione Peroxidase (GPx) in digestive glands were evaluated by quantitative real-time PCR (qRT-PCR) after being exposed to benzo(a)pyrene (BaP) (0.25, 1and 4 μg/L) for 15 days, which indicated that the activation of Nrf2 and Keap1 expression can be significantly induced under BaP exposure. RNA interference (RNAi) experiments were conducted to examine the expression profiles of CfKeap1, Nrf2, antioxidant genes (Cu/Zn-SOD, CAT and GPx), mitogen-activated protein kinase (MAPKs) and protein kinase C (PKC) signaling pathways key genes in digestive glands and gills when exposed to BaP. Results showed that the mRNA level of CfKeap1 was significantly decreased by 60.69% and59.485%. The changes of CfKeap1 and Nrf2 suggested that the enhancement of Keap1 expression stimulating Nrf2 degradation. Furthermore, the expression of antioxidant genes were consistent with the Nrf2 gene, which suggesting that Nrf2-Keap1 signaling pathway is required for the induction of antioxidant genes. Besides, the changes of PKC, c-Jun N-terminal kinase (JNK) and p38 genes expression suggested that PKC and MAPKs signaling pathways played a synergistic role with Nrf2-Keap1 signaling pathway in the anti-oxidative defense system of bivalve molluscs. In conclusion, these data demonstrated that Keap1 can sense nucleophilic or oxidative stress factors to regulate the Nrf2 signaling pathway together with Cul3-based E3 Ubiquitin Ligase (E3), and the Nrf2-Keap1 signaling pathway played an important role in modulating gene expression of antioxidant enzymes in bivalve mollusks.

Single and combined exposures of waterborne Cu and Cd induced oxidative stress responses and tissue injury in female rare minnow (Gobiocypris rarus)

Copper (Cu) and cadmium (Cd) are two kinds of abundant toxic metals in aquatic ecosystem. The present study evaluated the effects of waterborne Cu and Cd on oxidative stress responses and histological alterations in female rare minnow (Gobiocypris rarus). Fish were exposed for 7 days to: (i) control (no added Cu or Cd), (ii) waterborne Cu (39.2 μg L^-1), (iii) waterborne Cd (299.6 μg L^-1), and (iv) Cu and Cd in mixture (19.6 and 149.8 μg L^-1, respectively). Antioxidant enzyme activities and gene mRNA abundance in fish tissues (gills, liver, and ovaries) were induced by Cu and Cd exposures, both individually and in mixture, at day 1, but an asynchronous response was observed between most enzyme activities and gene mRNA abundance following 7 days exposure. Biochemical analysis and histological observation indicated that exposure to Cu and Cd, alone and in combination, caused evident damage to lipids and tissue structure in gills, liver and ovaries. Comparing with single Cu or Cd exposure, Cu and Cd co-exposure induced greater increase in the mRNA expression of most antioxidant genes and caused more severe lesions in fish tissues, which suggested that exposure to waterborne Cu and Cd in mixture might increase their individual toxicity. Furthermore, positive relationships between nuclear factor erythroid 2-related factor (Nrf2) expression and expression of manganese superoxide dismutase (Mn-SOD) and catalase (CAT) were also observed in the present study, which suggested that Cu or/and Cd induced expression of these antioxidant genes were might through activation of Nrf2.

The neuroprotective mechanisms and effects of sulforaphane

Sulforaphane (SFN) is a phytochemical found in cruciferous vegetables. It has been shown to have many protective effects against many diseases, including multiple types of cancer. SFN is a potent activator of the nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant response element (ARE) genetic pathway. Upregulation of Nrf2-ARE increases the availability of multiple antioxidants. A substantial amount of preclinical research regarding the ability of SFN to protect the nervous system from many diseases and toxins has been done, but only a few small human trials have been completed. Preclinical data suggest that SFN protects the nervous system through multiple mechanisms and may help reduce the risk of many diseases and reduce the burden of symptoms in existing conditions. This review focuses on the literature regarding the protective effects of SFN on the nervous system. A discussion of neuroprotective mechanisms is followed by a discussion of the protective effects elicited by SFN administration in a multitude of neurological diseases and toxin exposures. SFN is a promising neuroprotective phytochemical which needs further human trials to evaluate its efficacy in preventing and decreasing the burden of many neurological diseases.

The Olfactory System of Zebrafish as a Model for the Study of Neurotoxicity and Injury: Implications for Neuroplasticity and Disease

The olfactory system, composed of the olfactory organs and the olfactory bulb, allows organisms to interact with their environment and through the detection of odor signals. Olfaction mediates behaviors pivotal for survival, such as feeding, mating, social behavior, and danger assessment. The olfactory organs are directly exposed to the milieu, and thus are particularly vulnerable to damage by environmental pollutants and toxicants, such as heavy metals, pesticides, and surfactants, among others. Given the widespread occurrence of olfactory toxicants, there is a pressing need to understand the effects of these harmful compounds on olfactory function. Zebrafish (Danio rerio) is a valuable model for studying human physiology, disease, and toxicity. Additionally, the anatomical components of the zebrafish olfactory system are similar to those of other vertebrates, and they present a remarkable degree of regeneration and neuroplasticity, making it an ideal model for the study of regeneration, reorganization and repair mechanisms following olfactory toxicant exposure. In this review, we focus on (1) the anatomical, morphological, and functional organization of the olfactory system of zebrafish; (2) the adverse effects of olfactory toxicants and injury to the olfactory organ; and (3) remodeling and repair neuroplasticity mechanisms following injury and degeneration by olfactory toxicant exposure.

Vitamin A deficiency impairs intestinal physical barrier function of fish

The present study was the first to investigate the effects of dietary vitamin A (VA) on the intestinal physical barrier function associated with oxidation, antioxidant system, apoptosis and cell-cellular tight junction (TJ) in the proximal (PI), mid (MI) and distal (DI) intestines of young grass carp (Ctenopharyngodon idella). Fish were fed graded levels of dietary VA for 10 weeks, and then a challenge test using an injection of Aeromonas hydrophila was conducted for 14 days. Results indicated that dietary VA deficiency caused oxidative damage to fish intestine partly by the reduced non-enzymatic antioxidant components glutathione (GSH) and VA contents as well as reduced antioxidant enzyme activities [not including manganese superoxide dismutase (MnSOD)]. Further results observed that the decreased antioxidant enzyme activities by VA deficiency were partly related to the down-regulation of their corresponding mRNA levels which were regulated by the down-regulation of NF-E2-related factor 2 (Nrf2) mRNA levels and up-regulation of kelch-like-ECH-associated protein (Keap1a) (rather than Keap1b) mRNA levels in three intestinal segments of fish. Meanwhile, VA deficiency up-regulated the mRNA levels of the apoptosis signalling [caspase-3, caspase-8, caspase-9 (rather than caspase-7)] associated with the inhibition of the target of rapamycin (TOR) signalling pathway in three intestinal segments of fish. Additionally, VA deficiency decreased the mRNA levels of TJ complexes [claudin-b, claudin-c, claudin-3, claudin-12, claudin-15a, occludin and zonula occludens-1 (ZO-1) in the PI, MI and DI, as well as claudin-7 and claudin-11a in the MI and DI] linked to the up-regulation of myosin light chain kinase (MLCK) signalling. These results suggested that VA deficiency impaired structural integrity in three intestinal segments of fish. Meanwhile, excessive VA also showed similar negative effects on these indexes. Taken together, the current study firstly demonstrated that VA deficiency impaired physical barrier functions associated with impaired antioxidant capacity, aggravated cell apoptosis and disrupted TJ complexes in the PI, MI and DI, but different segments performed different actions in fish. Based on protecting fish against protein oxidation, the optimal VA levels for grass carp were estimated to be 2622 IU/kg diet.

Sulforaphane Protect Against Cadmium-Induced Oxidative Damage in mouse Leydigs Cells by Activating Nrf2/ARE Signaling Pathway

Cadmium (Cd) is harmful for humans and animals, especially for the reproductive system. However, the mechanism of its toxicity has not been elucidated, and how to alleviate its toxicity is very important. This study aimed to explore the role and mechanism of action of sulforaphane (SFN) in protecting mouse Leydigs (TM3) cells from cadmium (Cd)-induced damage. The half-maximal inhibitory concentration (IC₅₀) of Cd and the safe doses of SFN were determined using a methyl thiazolyl tetrazolium (MTT) assay. The testosterone secretion from TM3 cells was measured using the enzyme-linked immunosorbent assay. The intracellular oxidative stress was evaluated using corresponding kits. The cell apoptosis was detected using flow cytometry. The mRNA expression of genes associated with NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE) signaling was detected using reverse transcription–polymerase chain reaction, including Nrf2, heme oxygenase I (HO-1), glutathione peroxidase (GSH-Px), NAD(P)H:quinone acceptor oxidoreductase 1 (NQO1), and γ-glutamylcysteine synthetase (γ-GCS). The protein expression of Nrf2, GSH-Px, HO-1, γ-GCS, and NQO1 was detected using Western blot analysis. The results showed that the IC₅₀ of Cd to TM3 cells was 51.4 µmol/L. SFN reduced the release of lactate dehydrogenase from Cd-exposed cells. Cd + SFN 2.5 treatment significantly elevated testosterone concentration compared with the Cd group (p < 0.05). SFN significantly increased total superoxide dismutase (T-SOD) and GSH-Px activity and GSH content in Cd-treated cells (p < 0.05; p < 0.01), inhibited the production of malondialdehyde or reactive oxygen species caused by Cd (p < 0.05; p < 0.01), and reduced the apoptotic rate of Cd-induced TM3 cells (p < 0.01). SFN upregulated the mRNA expression of Nrf2, GSH-Px, HO-1, NQO1, and γ-GCS in Cd-treated cells, indicating the protective effect of SFN against Cd-induced oxidative stress or cell apoptosis by activating the Nrf2/ARE signaling pathway.

Kinetics of Glutathione Depletion and Antioxidant Gene Expression as Indicators of Chemical Modes of Action Assessed in Vitro in Mouse Hepatocytes with Enhanced Glutathione Synthesis

Here we report a vertically integrated in vitro - in silico study that aims to elucidate the molecular initiating events involved in the induction of oxidative stress (OS) by seven diverse chemicals (cumene hydroperoxide, t-butyl hydroperoxide, hydroquinone, t-butyl hydroquinone, bisphenol A, Dinoseb, and perfluorooctanoic acid). To that end, we probe the relationship between chemical properties, cell viability, glutathione (GSH) depletion, and antioxidant gene expression. Concentration-dependent effects on cell viability were assessed by MTT assay in two Hepa-1 derived mouse liver cell lines: a control plasmid vector transfected cell line (Hepa-V), and a cell line with increased glutamate-cysteine ligase (GCL) activity and GSH content (CR17). Changes to intracellular GSH content and mRNA expression levels for the Nrf2-driven antioxidant genes Gclc, Gclm, heme oxygenase-1 ( Hmox1), and NADPH quinone oxidoreductase-1 ( Nqo1) were monitored after sublethal exposure to the chemicals. In silico models of covalent and redox reactivity were used to rationalize differences in activity of quinones and peroxides. Our findings show CR17 cells were generally more resistant to chemical toxicity and showed markedly attenuated induction of OS biomarkers; however, differences in viability effects between the two cell lines were not the same for all chemicals. The results highlight the vital role of GSH in protecting against oxidative stress-inducing chemicals as well as the importance of probing molecular initiating events in order to identify chemicals with lower potential to cause oxidative stress.

The role of Nrf2-Keap1 signaling pathway in the antioxidant defense response induced by PAHs in the calm Ruditapes philippinarum

The NF-E2-related factor 2 (Nrf2) is a master regulator of cellular responses against environmental stresses. In this study we cloned the full-length cDNAs of the RpNrf2 encompassed 2823 bp from the clam Ruditapes philippinarum (R. philippinarum). Sequences alignment and phylogenetic analysis showed that Nrf2 was highly specific in the clams. RpNrf2 expression was detected in gill, digestive gland, mantle and adductor, which the highest transcription level was observed in gill and digestive gland. The gene expressions of RpNrf2, Kelch-like-ECH-associated Protein 1 (Keap1), Cul3-based E3 Ubiquitin Ligase (E3), Glutathione S-transferase (GST-pi), Superoxide Dismutase (SOD), Catalase (CAT) and Glutathione Peroxidase (GPx) in digestive gland was evaluated by real-time PCR after being exposed to benzo(a)pyrene (BaP) (0.25, 1and 4 μg/L) for 15 days, which showed that the expression of Nrf2 significantly increased at day 1 and day 6 after exposure (p < 0.05), and there was a negative relationship between the mRNA levels of Nrf2 and Keap1 that indicates the enhancement of Keap1 expression stimulating Nrf2 degradation. RNA interference experiments were conducted to examine the expression profiles of RpNrf2, antioxidant and detoxification genes (GST-pi, Cu/Zn-SOD, CAT and GPx) and Lipid Peroxidase (LPO) level in digestive gland exposed to BaP. The results showed that the mRNA level of Nrf2 was significantly decreased by 63.2%, and the changes of antioxidant and detoxification genes expression were consistent with the Nrf2 gene suggesting that Nrf2 is required for the induction of antioxidant and detoxification genes. Besides, the LPO levels expressed by malondialdehyde (MDA) contents were significant higher compared with the control group at 72 h post dsRNA-Nrf2 injection. In conclusion, our data demonstrated that Keap1 can sense nucleophilic or oxidative stress factors to regulate the Nrf2 signaling pathway together with E3 and Nrf2 signaling pathway plays an important role in modulating gene expression of antioxidant enzymes in bivalve mollusks.

Comparative effects of cadmium, zinc, arsenic and chromium on olfactory-mediated neurobehavior and gene expression in larval zebrafish (Danio rerio)

Studies have shown that olfactory-mediated behaviors that are critical to survival can be disrupted by exposure to certain metals. Polluted waterways often contain elevated levels of metals, yet only a subset have been characterized for their potential to cause olfactory toxicity. A larval zebrafish behavioral assay was developed to characterize concentration-response curves for zinc (Zn), hexavalent chromium (Cr), and arsenate (As) olfaction inhibition. Cadmium (Cd), an established olfactory toxicant, was used as a positive control. As expected, following a 24-hour exposure to Cd, we observed a reduced response to taurocholic acid (TCA), a substrate for ciliated olfactory sensory neurons (OSNs), thus validating the behavioral assay. Zn exposure similarly decreased the olfactory response toward TCA, (IC₅₀: 36 μg/L and 76 μg/L, for Cd and Zn, respectively). The response towards a secondary odorant L-cysteine (Cys), a substrate for ciliated and microvillous OSNs, was significantly altered by both Cd and Zn exposure, although the response to Cys was not completely removed in Zn treated larvae, suggesting preferential toxicity towards ciliated OSNs. No significant changes in olfactory responses were observed following Cr and As exposures. Exposures to binary mixtures of Cd and Zn indicated that Zn had a protective effect against Cd toxicity at low Zn concentrations. QuantiGene (QDP) RNA analysis revealed Cd to be a potent inducer of metallothionein 2 (mt2) mRNA in zebrafish larvae, and Zn to be a weak mt2 inducer, suggesting a protective role of mt2 in Cd and Zn olfactory injury. By contrast, QDP analysis of eight other genes important in mitigating the effects of oxidative stress suggested an antioxidant response to Cd, but not Zn, As, and Cr suggesting that oxidative stress was not a primary mechanism of Zn-induced olfactory dysfunction. In summary, our study indicates that Zn inhibits zebrafish olfaction at environmental concentrations and may potentially mitigate Cd induced olfactory dysfunction when present in mixtures. The zebrafish behavioral trough assay incorporating the odorants L-cysteine and TCA is an effective assay to assess the effects of metals on olfactory function.

Redox stress and signaling during vertebrate embryonic development: Regulation and responses

Vertebrate embryonic development requires specific signaling events that regulate cell proliferation and differentiation to occur at the correct place and the correct time in order to build a healthy embryo. Signaling pathways are sensitive to perturbations of the endogenous redox state, and are also susceptible to modulation by reactive species and antioxidant defenses, contributing to a spectrum of passive vs. active effects that can affect redox signaling and redox stress. Here we take a multi-level, integrative approach to discuss the importance of redox status for vertebrate developmental signaling pathways and cell fate decisions, with a focus on glutathione/glutathione disulfide, thioredoxin, and cysteine/cystine redox potentials and the implications for protein function in development. We present a tissue-specific example of the important role that reactive species play in pancreatic development and metabolic regulation. We discuss NFE2L2 (also known as NRF2) and related proteins, their roles in redox signaling, and their regulation of glutathione during development. Finally, we provide examples of xenobiotic compounds that disrupt redox signaling in the context of vertebrate embryonic development. Collectively, this review provides a systems-level perspective on the innate and inducible antioxidant defenses, as well as their roles in maintaining redox balance during chemical exposures that occur in critical windows of development.

Neurotoxicity Linked to Dysfunctional Metal Ion Homeostasis and Xenobiotic Metal Exposure: Redox Signaling and Oxidative Stress

SIGNIFICANCE

Essential metals such as copper, iron, manganese, and zinc play a role as cofactors in the activity of a wide range of processes involved in cellular homeostasis and survival, as well as during organ and tissue development. Throughout our life span, humans are also exposed to xenobiotic metals from natural and anthropogenic sources, including aluminum, arsenic, cadmium, lead, and mercury. It is well recognized that alterations in the homeostasis of essential metals and an increased environmental/occupational exposure to xenobiotic metals are linked to several neurological disorders, including neurodegeneration and neurodevelopmental alterations. Recent Advances: The redox activity of essential metals is key for neuronal homeostasis and brain function. Alterations in redox homeostasis and signaling are central to the pathological consequences of dysfunctional metal ion homeostasis and increased exposure to xenobiotic metals. Both redox-active and redox-inactive metals trigger oxidative stress and damage in the central nervous system, and the exact mechanisms involved are starting to become delineated.

CRITICAL ISSUES

In this review, we aim to appraise the role of essential metals in determining the redox balance in the brain and the mechanisms by which alterations in the homeostasis of essential metals and exposure to xenobiotic metals disturb the cellular redox balance and signaling. We focus on recent literature regarding their transport, metabolism, and mechanisms of toxicity in neural systems.

FUTURE DIRECTIONS

Delineating the specific mechanisms by which metals alter redox homeostasis is key to understand the pathological processes that convey chronic neuronal dysfunction in neurodegenerative and neurodevelopmental disorders. Antioxid. Redox Signal. 28, 1669-1703.