Antioxidant responses and NRF2 in synergistic developmental toxicity of PAHs in zebrafish

Environmentally Relevant Concentrations of Triphenyl Phosphate (TPhP) Impact Development in Zebrafish

A common flame-retardant and plasticizer, triphenyl phosphate (TPhP) is an aryl phosphate ester found in many aquatic environments at nM concentrations. Yet, most studies interrogating its toxicity have used µM concentrations. In this study, we used the model organism zebrafish (Danio rerio) to uncover the developmental impact of nM exposures to TPhP at the phenotypic and molecular levels. At concentrations of 1.5-15 nM (0.5 µg/L-5 µg/L), chronically dosed 5dpf larvae were shorter in length and had pericardial edema phenotypes that had been previously reported for exposures in the µM range. Cardiotoxicity was observed but did not present as cardiac looping defects as previously reported for µM concentrations. The RXR pathway does not seem to be involved at nM concentrations, but the tbx5a transcription factor cascade including natriuretic peptides (nppa and nppb) and bone morphogenetic protein 4 (bmp4) were dysregulated and could be contributing to the cardiac phenotypes. We also demonstrate that TPhP is a weak pro-oxidant, as it increases the oxidative stress response within hours of exposure. Overall, our data indicate that TPhP can affect animal development at environmentally relevant concentrations and its mode of action involves multiple pathways.

Dietary inclusion of Clostridium butyricum cultures alleviated impacts of high-carbohydrate diets in largemouth bass (Micropterus salmoides)

A 60-d feeding trial was conducted to explore the potential regulatory effects of dietary Clostridium butyricum cultures (CBC) supplementation in high-carbohydrate diet (HCD) on carbohydrate utilisation, antioxidant capacity and intestinal microbiota of largemouth bass. Triplicate groups of largemouth bass (average weight 35·03 ± 0·04 g), with a destiny of twenty-eight individuals per tank, were fed low-carbohydrate diet and HCD supplemented with different concentration of CBC (0 %, 0·25 %, 0·50 % and 1·00 %). The results showed that dietary CBC inclusion alleviated the hepatic glycogen accumulation induced by HCD intake. Additionally, the expression of hepatic ampkα1 and insulin signaling pathway-related genes (ira, irb, irs, p13kr1 and akt1) increased linearly with dietary CBC inclusion, which might be associated with the activation of glycolysis-related genes (gk, pfkl and pk). Meanwhile, the expression of intestinal SCFA transport-related genes (ffar3 and mct1) was significantly increased with dietary CBC inclusion. In addition, the hepatic antioxidant capacity was improved with dietary CBC supplementation, as evidenced by linear decrease in malondialdehyde concentration and expression of keap1, and linear increase in antioxidant enzyme activities (total antioxidative capacity, total superoxide dismutase and catalase) and expression of antioxidant enzyme-related genes (nrf2, sod1, sod2 and cat). The analysis of bacterial 16S rRNA V3-4 region indicated that dietary CBC inclusion significantly reduced the enrichment of Firmicutes and potential pathogenic bacteria genus Mycoplasma but significantly elevated the relative abundance of Fusobacteria and Cetobacterium. In summary, dietary CBC inclusion improved carbohydrate utilization, antioxidant capacity and intestinal microbiota of largemouth bass fed HCD.

A complex mixture of polycyclic aromatic compounds causes embryotoxic, behavioral, and molecular effects in zebrafish larvae (Danio rerio), and in vitro bioassays

Polycyclic aromatic compounds (PACs) are prevalent in the environment, typically found in complex mixtures and high concentrations. Our understanding of the effects of PACs, excluding the 16 priority polycyclic aromatic hydrocarbons (16 PAHs), remains limited. Zebrafish embryos and in vitro bioassays were utilized to investigate the embryotoxic, behavioral, and molecular effects of a soil sample from a former gasworks site in Sweden. Additionally, targeted chemical analysis was conducted to analyze 87 PACs in the soil, fish, water, and plate material. CALUX® assays were used to assess the activation of aryl hydrocarbon and estrogen receptors, as well as the inhibition of the androgen receptor. Larval behavior was measured by analyzing activity during light and darkness and in response to mechanical stimulation. Furthermore, qPCR analyses were performed on a subset of 36 genes associated with specific adverse outcomes, and the total lipid content in the larvae was measured. Exposure to the sample resulted in embryotoxic effects (LC50 = 0.480 mg dry matter soil/mL water). The mixture also induced hyperactivity in darkness and hypoactivity in light and in response to the mechanical stimulus. qPCR analysis revealed differential regulation of 15 genes, including downregulation of opn1sw1 (eye pigmentation) and upregulation of fpgs (heart failure). The sample caused significant responses in three bioassays (ERα-, DR-, and PAH-CALUX), and the exposed larvae exhibited elevated lipid levels. Chemical analysis identified benzo[a]pyrene as the predominant compound in the soil and approximately half of the total PAC concentration was attributed to the 16 PAHs. This study highlights the value of combining in vitro and in vivo methods with chemical analysis to assess toxic mechanisms at specific targets and to elucidate the possible interactions between various pathways in an organism. It also enhances our understanding of the risks associated with environmental mixtures of PACs and their distribution during toxicity testing.

6-Gingerdione Reduces Apoptotic Conditions in HepG2 Cells and Inhibits Inflammatory Cytokine Gene Expression in Alcoholic Liver Injured Zebrafish Larvae

Antioxidant natural products and their analogs especially phenolic compounds, exhibit diverse biological properties, including anti-inflammatory, antioxidant, and anticancer activities. Ginger which is widely used worldwide for various beneficial effects also contains several phenolic antioxidants, and 6-gingerol is one of the natural products studied extensively. However, the molecular mechanism of synthetically synthesized 6-gingerdione (compound 1) from 6-gingerol was not known. In this study, compound 1 and methylated 6-gingerdione (compound 2) were obtained semi synthetically from 6-gingerol. Compound 1 and 2 are subjected to SwissADME prediction. Then the protective effect of compound 1 was analyzed in 2 % EtOH induced HepG2 cells and zebrafish larvae. Hydroxyl and nitric oxide scavenging assays reveal that compound 1 showed more antioxidant activity than compound 2 at 50 μM. Moreover, compound 1 exhibited good anti-inflammatory activity via lipoxygenase inhibition and proteinase inhibition. Apoptosis and oxidative stress in HepG2 cells were induced by 2 % EtOH and treated with compound 1. Compound 1 significantly inhibited the EtOH induced nitric oxide production, apoptosis, and ROS generation in HepG2 cells. Encouraged by the in-vitro antioxidant and anti-inflammatory activities, compound 1 was then investigated for its protective effect in 2 % EtOH induced ALD zebrafish larva. Compound 1 protected the zebrafish larvae from liver injury by suppressing inflammatory (COX-2, TNF-α, and IL-1β) and lipogenic genes (C/EBP-α, SREBP1, and IL-1β) while upregulating the antioxidant gene. Our findings indicate that compound 1 synthesized from 6-gingerol ameliorated liver injury that likely, contributes to its potential antioxidant and anti-inflammatory properties.

Deacetyl epoxyazadiradione protects aminoglycoside antibiotic-induced renal cell apoptosis, in vitro

Aminoglycoside antibiotics such as gentamicin are used frequently to treat bacterial infections in humans. Excessive consumption of these antibiotics lead to renal dysfunction. One of the factors contributing to renal dysfunction is oxidative damage, which causes apoptosis. Hence, this study investigates the effect of the antioxidant compound deacetyl epoxyazadiradione (DEA) in reducing cell death induced by gentamicin treatment in kidney cells (Madin-Darby canine kidney cells). The antioxidant experiments showed that reactive oxygen species level is decreased up to 27.06 ± 0.18% in 150 µM of DEA treatment. At this concentration, the activity of antioxidant enzymes such as superoxide dismutase increased from 0.4 ± 0.04 to 1.46 ± 0.05 µmol/min/L and catalase increased from 7.48 ± 0.39 to 17.6 ± 0.74 U/mg. The relative folds of gene expression of mitochondrial enzymes such as GST, GPx and GR restored from 0.596 ± 0.019, 0.521 ± 0.013 and 0.775 ± 0.014 to 0.866 ± 0.013, 0.669 ± 0.015 and 0.8615 ± 0.028, respectively. Consequently, the percentage of cell viability increases upto 91.8 ± 2.01 from 61.93 ± 1.63 with much less fragmentation in genomic DNA. Additionally, molecular docking results showed that DEA could bind to Bax, Bcl- 2, Caspase- 3 and Caspase- 9 proteins. These results indicate that DEA could reduce cell apoptosis by reducing oxidative stress due to antibiotics and interrupting the apoptotic signal pathway in kidney cells.

Neuroprotective effect of Biochanin a against Bisphenol A-induced prenatal neurotoxicity in zebrafish by modulating oxidative stress and locomotory defects

Exogenous toxicants cause oxidative stress and damage to brain cells, resulting in inflammation. Neuroinflammation is important in the pathobiology of various neurological illnesses, including Alzheimer's disease (AD). In this context, Bisphenol A (BPA), a common toxin, causes oxidative damage and has been linked to neurological problems. An O-methylated isoflavone known as Biochanin A (5,7-dihydroxy-4'-methoxy-isoflavone, BCA) is considered to be a phytoestrogen, which is abundant in some legume plants and soy which have preventive effects against cancer, osteoporosis, menopausal symptoms and oxidative stress. However, the mechanism by which BCA protected the prenatal neurological stress are not known. So that, in this study we investigated the BCA neuroprotective effect against BPA-induced neuroinflammation in zebrafish embryo models. For this study, fertilized zebrafish embryos are exposed to BPA (1 µM) with or without BCA. Our finding suggested that BCA co-exposure prevented the depletion of antioxidant defense enzymes by BPA and reduced the production of intracellular ROS production, superoxide anion (O₂^-), lipid peroxidation (LPO), lactate dehydrogenase (LDH) and nitric oxide (NO) levels in the head that aided in safeguarding neuronal development. Baseline locomotion was rendered and a total distance was calculated to assess the motor function. Exposure to BCA increased acetylcholinestrase (AChE) and improved motor neuron functions. It also reduced the pro-inflammatory response expression and prevented neuroinflammation. Our study suggests that BCA has a positive role in the attenuation or amelioration of neuronal oxidative damage and locomotory behaviour induced by BPA.

Deacetylepoxyazadiradione Derived from Epoxyazadiradione of Neem (Azadirachta indica A. Juss) Fruits Mitigates LPS-Induced Oxidative Stress and Inflammation in Zebrafish Larvae

Reactive oxygen species (ROS) produced by cell metabolism have a duplex role in oxidation and inflammation reactions which involve cell damage or repair responses. Excess ROS production has detrimental effects on the survival of cells. We examined the protective effect of a semi-natural compound NF2 (deacetylepoxyazadiradione), for its protective activity against free radical-mediated stress and inflammatory response to lipopolysaccharide (LPS) using zebrafish larvae. Preliminary antioxidant assays indicated an increase in scavenging of free radicals from NF2 than NF1 (Epoxyazadiradione) in a concentration-dependent manner. Cell cytotoxicity was determined using rat myoblast cell lines (L6), and more than 95 % of cell viability was obtained. Zebrafish developmental toxicity test indicated that NF2 is not toxic even at 150 μM. The percentage of ROS, lipid peroxidation, nitric oxide and apoptosis were reduced significantly in NF2 treated LPS-stressed zebrafish larvae. The reduced number of employed macrophages on NF2 treatment was observed in neutral red dye-marked macrophage localization images. Relative expression of antioxidant genes in zebrafish larvae after treatment with NF2 is significantly increased. The RT-PCR quantification of antioxidant and anti-inflammatory gene expression indicated decreased relative folds of pro-inflammatory cytokines, iNOS and increased relative folds of mitochondrial antioxidant genes (GR, GST and GPx) in LPS stressed zebrafish larvae after treatment with NF2. From the overall obtained results, it can be concluded that NF2 reduced the oxidative stress and inflammatory response by scavenging free radicals caused by LPS.

Chemical Contamination in Bread from Food Processing and Its Environmental Origin

Acrylamide (AA), furan and furan derivatives, polycyclic aromatic amines (PAHs), monochloropropanediols (MCPDs), glycidol, and their esters are carcinogens that are being formed in starchy and high-protein foodstuffs, including bread, through baking, roasting, steaming, and frying due to the Maillard reaction. The Maillard reaction mechanism has also been described as the source of food processing contaminants. The above-mentioned carcinogens, especially AA and furan compounds, are crucial substances responsible for the aroma of bread. The other groups of bread contaminants are mycotoxins (MTs), toxic metals (TMs), and pesticides. All these contaminants can be differentiated depending on many factors such as source, the concentration of toxicant in the different wheat types, formation mechanism, metabolism in the human body, and hazardous exposure effects to humans. The following paper characterizes the most often occurring contaminants in the bread from each group. The human exposure to bread contaminants and their safe ranges, along with the International Agency for Research on Cancer (IARC) classification (if available), also have been analyzed.

Effect of starvation and refeeding on reactive oxygen species, autophagy and oxidative stress in Chinese perch (Siniperca chuatsi) muscle growth

In skeletal muscle, autophagy regulates the development and growth of muscle fibres and maintains the normal muscle metabolism. Under starvation and refeeding conditions, the effect of reactive oxygen species (ROS) levels on skeletal muscle autophagy is still unclear, although the excessive accumulation of ROS has been shown to increase autophagy in cells. The purpose of this study was to explore the effects of starvation and diet after starvation on the autophagy of adult Chinese perch muscle, and to determine the level of ROS in the muscle. We performed zero (Normal control), three and seven starvation treatments on adult Chinese perch, and returned to normal feeding for 3 days after starvation for 7 days. In the muscles of the adult Chinese perch muscle after 3 days of starvation, the autophagy marker protein LC3 and the number of autophagosomes remained basically the same as in the normal feeding situation. However, on starvation for 7 days, the mitochondrial autophagy was sensitive and the number of autophagosomes increased, but the antioxidant-related molecules (malondialdehyde, catalase, glutathione S-transferase, glutathione and anti-superoxide anion) decreased and the accumulation of ROS was obvious. In addition, the extended starvation time also increased the level of LC3 protein. However, by refeeding after starvation this nutritional stress resulted in a decrease in ROS levels and a partial restoration of antioxidant enzyme activity. Our data show that in the adult Chinese perch muscle, starvation could reduce the antioxidant activity through the accumulation of ROS, and that the number of autophagosomes continues to increase. Refeeding after starvation could effectively compensate for the level of ROS, and restore the mRNA abundance of antioxidant genes and the activity of antioxidant enzymes to reduce autophagy and improve feed efficiency. Further research should optimize starvation conditions to reduce autophagy in muscles and maintain normal muscle metabolism.

Amelioration of acrylamide induced neurotoxicity by benzo[b]thiophene analogs via glutathione redox dynamics in zebrafish larvae

Acrylamide is a thermal process contaminant, which gets global attention due to its neurotoxic nature and its omnipresence in carbohydrate-rich foods. Chronic exposure to acrylamide leads to neuronal deterioration and motor dysfunction. Acrylamide could severely affect the antioxidant defense system, especially in the developing brain leading to premature neurological disorders. Acrylamide forms adduct in presynaptic neurons leading to neuroinflammation which is also a factor to consider. In this present study, we have explored whether our benzo[b]thiophene analogs, 1-(3-hydroxybenzo[b]thiophen-2-yl) ethanone (BP) and 1-(3-hydroxybenzo[b]thiophen-2-yl) propan-1-one hydrate (EP) with antioxidant activity, could inhibit the acrylamide-induced neurotoxicity-like behavior in zebrafish larvae. The experiment was set up to expose 3 days post fertilized (dpf) larvae to acrylamide (0.75 mM) for 3 days with or without compounds (80 µM). Locomotion behavioral analysis, antioxidants, glutathione, and acetylcholineesterase activity in the head region were analyzed after one day of the experimental procedure. We witnessed a restoration effect on glutathione redox dynamics. Since glutathione plays a crucial role in the detoxification of acrylamide, it is necessary to maintain the glutathione redox cycle to eliminate acrylamide from the body. BP and EP reduced the pro-inflammatory transcript in the head, which correlates with the reduction in oxidative stress. Finally, BP and EP showed a positive effect on synaptic vesicle cycling transcript and partially restores the motor neuron response to stimuli. Findings in this study showed the ability of compound BP and EP possess therapeutic value in oxidative stress-associated neurological disorders.

Silencing of Nrf2 in Litopenaeus vannamei, decreased the antioxidant capacity, and increased apoptosis and autophagy

Nuclear factor E2-related factor 2 (Nrf2) is a multifunctional transcription factor that plays an important role in antioxidant activities. However, its effect on antioxidant capacity in Litopenaeus vannamei, an economically important crustacean, remains unclear. In this study, the role of Nrf2 in response to oxidative stress in L. vannamei was determined by its effect on relevant gene expression and enzymatic activity. Nrf2 was cloned and analyzed. Results revealed that Nrf2 contains a 1575 bp open reading frame encoding 524 amino acids and a conserved bZIP Maf domain. The sequence similarity of Nrf2 between L. vannamei and Homarus americanus is 81%. Although the Nrf2 expression was detected in all tissues, the Nrf2 expression levels were the highest in the hepatopancreas, followed by the eyestalk and muscle. RNA interference significantly decreased the expression of antioxidant-related genes (SOD, GPX, CAT, Trx, and HO-1; p < 0.05), significantly upregulated the expression of autophagy genes (Atg3, Atg4, Atg5, Atg10, and Atg12; p < 0.05) and apoptosis genes (Caspase-3 and P53; p < 0.05). Moreover, SOD, CAT, and GPX enzyme activities decreased whereas the MDA activity increased. The histological results of the shrimp injected with dsRNA-Nrf2 showed that the hepatic tubules were irregularly arranged, the lumen was abnormal, and a few hepatic tubules were significantly enlarged compared with those of the dsRNA-EGFP group. The hepatocytes were also vacuolated. In conclusion, this study provided evidence that Nrf2 is involved in the regulation of antioxidant capacity, oxidative stress, apoptosis, and autophagy in shrimp.

GR15 peptide of S-adenosylmethionine synthase (SAMe) from Arthrospira platensis demonstrated antioxidant mechanism against H2O2 induced oxidative stress in in-vitro MDCK cells and in-vivo zebrafish larvae model

GR15 is a short molecule or peptide composed of aliphatic amino acids and possesses to have antioxidant properties. The GR15, ¹GGGAFSGKDPTKVDR¹⁵ was identified from the protein S-adenosylmethionine synthase (SAMe) expressed during the sulfur departed state of Arthrospira platensis (spirulina or cyanobacteria). The in-silico assessment and the structural features of GR15 showed its antioxidant potency. Real-time PCR analysis found the up-regulation of ApSAMe expression on day 15 against oxidative stress due to 10 mM H₂O₂ treatment in A. platensis (Ap). The antioxidant activity of GR15 was accessed by the cell-free antioxidant assays such as ABTS, SARS, HRAS and NO; the results showed dose-dependent antioxidant activity. The toxicity assay was performed in both in vitro and in vivo models, in which peptide does not exhibit any toxicity in MDCK cell and zebrafish embryos. The intercellular ROS reduction potential of GR15 peptide was also investigated in both in vitro and in vivo models including LDH assay, antioxidant enzymes (SOD and CAT), and fluorescent staining assay (DCFDA, Hochest and Acridine orange sting) was performed; the results showed that the GR15 peptide was effectively reduced the ROS level. Further, RT-PCR demonstrated that GR15 enhanced the antioxidant property and also up-regulated the antioxidant gene, thus reduced the ROS level in both in vitro and in vivo models. Based on the results obtained from this study, we propose that GR15 has the potential antioxidant ability; hence further research can be directed towards the therapeutic product or drug development against disease caused by oxidative stress.

Riboceine Rescues Auranofin-Induced Craniofacial Defects in Zebrafish

Craniofacial abnormalities are a common group of congenital developmental disorders that can require intensive oral surgery as part of their treatment. Neural crest cells (NCCs) contribute to the facial structures; however, they are extremely sensitive to high levels of oxidative stress, which result in craniofacial abnormalities under perturbed developmental environments. The oxidative stress-inducing compound auranofin (AFN) disrupts craniofacial development in wildtype zebrafish embryos. Here, we tested whether the antioxidant Riboceine (RBC) rescues craniofacial defects arising from exposure to AFN. RBC rescued AFN-induced cellular apoptosis and distinct defects of the cranial cartilage in zebrafish larvae. Zebrafish embryos exposed to AFN have higher expression of antioxidant genes gstp1 and prxd1, with RBC treatment partially rescuing these gene expression profiles. Our data suggest that antioxidants may have utility in preventing defects in the craniofacial cartilage owing to environmental or genetic risk, perhaps by enhancing cell survival.

Non-Clinical Investigation of Tuberculosis Drugs: Conjugated Norbornene- Based Nanocarriers Toxic Impacts on Zebrafish

INTRODUCTION:

Rifampicin conjugated (R-CP), and rifampicin -isoniazid dual conjugated (RI-CP) norbornene-derived nanocarriers are newly designed for pH stimuli-responsive delivery of tuberculosis (TB) drugs. Its biosafety level is yet to be well established.

OBJECTIVES:

To assess the impacts of the nanocarriers on liver cells using zebrafish animal model and human liver cell line model (HepG2).

METHODS:

Initially, lethal dose concentration for the norbornene-derived nanocarrier systems in zebrafish was determined. The toxic effects were analysed at the sub-lethal drug concentration by histopathological study, total GSH level, gene expression and DNA damage in zebrafish liver cells. Fish erythrocyte nuclear abnormalities were also evaluated. Cell viability and oxidative stress level (ROS generation) after exposure to the nanoconjugates was determined using HepG2 cell in the in vitro study.

RESULTS:

In vivo studies of both R-CP and RI-CP showed 100% mortality at 96 hours for exposure concentration >100mg/l and showed toxic changes in zebrafish liver histology, GSH, and DNA damage levels. A noticeable upregulated PXR, CYP3A and cyp2p6 genes was observed in RI-CP exposure than in RIF or R-CP molecules. The in vitro study revealed a dose-dependent effect on cell viability and ROS generation for RIF, R-CP and RI-CP exposures in HepG2 cells.

CONCLUSION:

The current study reports that the rifampicin conjugated (R-CP) and rifampicin-isoniazid conjugated (RI-CP) norbornene derived nanocarriers exhibit enhanced toxic responses in both adult zebrafish and HepG2 cells. The pH-sensitive norbornene derived nanocarriers on conjugation with different drugs exhibited varied impacts on hepatic cells. Hence the present investigation recommends a complete metabolomics analysis and norbornene carrier-drug interaction study to be performed for each drug conjugated norbornene nanocarrier to ensure its biosafety.

Climate change affects the parasitism rate and impairs the regulation of genes related to oxidative stress and ionoregulation of Colossoma macropomum

Global climate change represents a critical threat to the environment since it influences organismic interactions, such as the host-parasite systems, mainly in ectotherms including fishes. Rising temperature and CO₂ are predicted to affect this interaction other and critical physiological processes in fish. Herein, we investigated the effects of different periods of exposure to climate change scenarios and to two degrees of parasitism by monogeneans in the host-parasite interaction, as well as the antioxidant and ionoregulatory responses of tambaqui (Colossoma macropomum), an important species in South American fishing and aquaculture. We hypothesized that temperature and CO₂ changes in combination with parasite infection would interfere with the host's physiological processes that are related to oxidative stress and ionoregulation. We experimentally exposed C. macropomum to low and high levels of parasitism in the current and extreme climate scenarios (4.5 °C and 900 ppm CO₂ above current levels) for periods of seven and thirty days and we use as analyzed factors; the exposure time, the climate scenario and parasitism level in a 2 × 2 × 2 factorial through a three-way ANOVA as being fish the experimental unit (n = 8). An analysis of gill enzymatic and gene expression profile was performed to assess physiological (SOD, GPx and Na⁺/K⁺-ATPase enzymes) and molecular (Nrf2, SOD1, HIF-1α and NKA α1a genes) responses. A clear difference in the parasitism levels of individuals exposed to the extreme climate scenario was observed with a rapid and aggressive increase that was higher after 7 days of exposure though showed a decrease after 30 days. The combination of exposure to the extreme climate change scenario and parasitism caused oxidative stress and osmoregulatory disturbance, which was observed through the analysis of gene expression (Nrf2, SOD1, HIF-1α and NKA α1a) and antioxidant and ionoregulatory enzymes (SOD, GPx and Na⁺/K⁺-ATPase) on the host, possibly linked to inflammatory processes caused by the high degree of parasitism. In the coming years, these conditions may result in losses of performance for this species, and as such will represent ecological damage and economical losses, and result in a possible vulnerability in relation to food security.

Molecular Cloning and Characterization of Sirtuin 1 and Its Potential Regulation of Lipid Metabolism and Antioxidant Response in Largemouth Bass (Micropterus salmoides)

Sirtuin 1 (SIRT1) of largemouth bass (Micropterus salmoides) was cloned and characterized in the present study and the influence of SIRT1 activation induced by resveratrol inclusion on the expression of genes related to lipid metabolism and antioxidation was also investigated. The SIRT1 of largemouth bass, with full-length cDNA sequence of 3395bp encoding 695 amino acids, was mainly expressed in gonad, heart and liver. The analysis of multiple sequence alignment revealed that, in accordance with other species, SIRT1 of largemouth bass contained highly conserved substrate-binding site and NAD⁺ binding site. The result of subcellular localization displayed that SIRT1 of largemouth bass was mainly localized in the nucleus. The inclusion of 1.0 and 2.5‰ dietary RSV, a natural SIRT1 activator, significantly elevated the SIRT1 protein expression. Meanwhile, the phosphorylation of AKT1 and FoxO1 followed similar pattern with that of SIRT1, indicating the activation of insulin pathway, which may result in the inhibition of lipogenesis and activation of lipolysis, and reduced hepatic triglycerides content. Additionally, the activation of SIRT1 induced by dietary RSV elevated the antioxidant capacity at both transcriptional level and enzymatic level, which was probably mediated by the transcription factor Nrf2. In above, SIRT1 was suggested to be involved in improving antioxidant capacity and alleviating hepatic lipid deposition in largemouth bass.

Kirenol Inhibits B[a]P-Induced Oxidative Stress and Apoptosis in Endothelial Cells via Modulation of the Nrf2 Signaling Pathway

Atherosclerosis is a persistent inflammatory disorder specified by the dysfunction of the arteries, the world's leading cause of cardiovascular diseases. We sought to determine the effectiveness of KRL in B[a]P-induced oxidative stress and programmed cell death in endothelial cells. Western blotting, real-time PCR, DCFH2-DA, and TUNEL staining were performed to detect pPI3K, pAKT, Nrf2, HO-1, NQO-1, Bcl2, Bax, and caspase-3 on the HUVECs. Through the pretreatment of KRL, a drastic enhancement was observed in the cell viability of HUVECs, whereas DNA damage and generation of reactive oxygen species induced by B[a]P was suppressed. KRL's potential use as an antioxidant was observed to have a direct correlation with an antioxidant gene's augmented expression and the nuclear translocation activation of Nrf2, even during the event when B[a]P was found to be absent. In addition, this study proved that the signaling cascades of PI3K/AKT mediated Nrf2 translocation. Activation of suppressed nuclear Nrf2 and reduced antioxidant genes across cells interacting with an LY294002 confirmed this phenomenon. In addition, knockdown of Nrf2 by Nrf2-siRNA transfection abolished the protective effects of KRL on HUVECs cells against oxidative damage. Finally, the expression of apoptotic proteins also supported the hypothesis that KRL may inhibit endothelial dysfunction. This study showed that KRL potentially prevents B[a]P-induced redox imbalance in the vascular endothelium by inducing the Nrf2 signaling via the PI3K/AKT pathway.

Effects of the brominated flame retardant, TBCO, on development of zebrafish (Danio rerio) embryos

Brominated flame retardants (BFRs) can enter aquatic environments where they can have adverse effects on organisms. The BFR, 1,2,5,6-Tetrabromocyclooctane (TBCO), has been introduced as a potential replacement for the major use BRF, Hexabromocyclododecane (HBCD). However, little is known about effects of TBCO on aquatic organisms. Using zebrafish (Danio rerio) as a model species, objectives of this study were to determine whether TBCO has adverse effects on early life-stages and to investigate the molecular and biochemical mechanisms of any effects on development. Exposure to TBCO caused a concentration dependant increase in mortality, decrease in heart rate, and increase in incidences of spinal curvature and uninflated swim bladders. Neither peroxidation of lipids or mRNA abundances of genes important for the response to oxidative stress were greater in embryos exposed to TBCO suggesting effects were not caused by oxidative stress. The mRNA abundance of cytochrome p4501a was not greater in embryos exposed to TBCO suggesting that effects were not caused by activation of the aryl hydrocarbon receptor. Finally, mRNA abundances of genes important for development and inflation of the swim bladder were not affected by TBCO. Overall, TBCO causes adverse effects on early life-stages of zebrafish, but mechanisms of effects require further investigation.

Benzo[a]pyrene exposure and overcrowding stress impacts anxiety-like behavior and impairs learning and memory in adult zebrafish, Danio rerio

Benzo[a]pyrene (B[a]P), a prototype of polycyclic aromatic hydrocarbons and ubiquitous environmental pollutant, alters neurobehavioral responses in aquatic organisms like zebrafish. Increasing organic load on water bodies causes population explosion leading to overcrowding (OC) stress. The effect of OC stress on neurobehavioral alterations remains unclear. The objective of our study is to elucidate the impact of OC stress on behavioral alterations and neurodegenerative phenotypes on exposure to B[a]P in zebrafish. We demonstrate the effects of OC stress (12 fish/L) on acute waterborne exposure to B[a]P (0.2 mg L^-1 ) in adult wild zebrafish. Anxiety-like behavior, learning, and memory impairment were assayed by novel tank diving test, light/dark preference test, and T-maze test. Oxidative stress bio-markers were assayed along with histopathological changes in zebrafish brain. OC stress significantly impaired the learning ability and mood behavior by increasing the number of transition and time spent in the alter zones. Increased lipid peroxidation and protein carbonyl formation with significant decreased catalase activity and reduced glutathione level showed oxidative stress on exposure to OC stress and B[a]P. Pyknotic neuronal counts dramatically increased in periventricular grey zone of optic tectum brain region of zebrafish. Our findings showed that OC stress modulates the B[a]P-induced behavioral alterations causing learning and memory deficiency with histopathological changes in adult zebrafish brain. OC stress may act as an early risk factor for the eventual development of cognitive impairments and B[a]P exposure plays a key role in mediating both the facilitating and impairing actions of OC stress in memory processes.

Exposure to hydrocarbons and chlorpyrifos alters the expression of nuclear receptors and antioxidant, detoxifying, and immune response proteins in the liver of the rainbow trout, Oncorhynchus mykiss

The development of oil and gas production together with the fruit production in nearby areas of North Patagonia, Argentina, suggests aquatic pollution scenarios which include permanent oil pollution combined with short events of pesticides application. It has been reported that oil hydrocarbons activate the aryl hydrocarbon receptor (AhR) pathway in the rainbow trout, Oncorhynchus mykiss, and that the insecticide Chlorpyrifos (CPF) interacts with these effects. Thus, it is interesting to investigate whether hydrocarbons and insecticides, applied by separate or combined, can affect fish health and reproductive signaling by acting on different nuclear receptors' regulatory pathways. To study this kind of interactions, we exposed juvenile rainbow trout to water accommodated fraction (WAF) of crude oil (62 μg L^-1 TPH) for 48 h and subsequently exposed the livers ex vivo to the insecticide Chlorpyrifos (CPF) (20 µg L^-1) for 1 h. We analyzed the mRNA expression of nuclear receptors and proteins involved in detoxifying, antioxidant, immune and apoptosis responses by qRT-PCR. We also performed histopathological analysis. WAF induced the expression of the androgen (AR) and the Liver X receptor (LXR) by 8- and 3-fold, respectively. AR induction was reversed by subsequent exposure to CPF. The progesterone receptor (PR) and glucocorticoid receptor (GR) were increased 2-fold and 3-fold by WAF respectively, while estrogen and mineralocorticoid receptors were not affected. GR was also induced by CPF with an additive effect in the WAF-CPF treatment. The antioxidant genes, gamma glutamyl transferase (GGT), superoxide dismutase (SOD1) were induced by WAF (2-3-fold). WAF upregulated the ATP Binding Cassette Subfamily C Member 2 (ABCC2, MRP2) (4-fold) and downregulated alkaline phosphatase. WAF also induced the inflammatory interleukins (IL) IL-8, and IL-6 and the anti-inflammatory IL-10, while CPF induced the inflammatory tumor necrosis factor (-α) and IL-6, and activated the intrinsic apoptotic pathway through the induction of caspases 3 and 9. Both, WAF and CPF downregulated the expression of the extrinsic apoptosis initiator caspase 8 and the inflammatory caspase 1. In conclusion, WAF hydrocarbons alter O. mykiss endocrine regulation by inducing AR, PR and GR. The subsequent exposure to CPF reverses AR, suggesting a complex interaction of different pollutants in contaminated environments, WAF hydrocarbons alter liver metabolism by inducing the expression of LXR, GR, antioxidant and detoxifying enzymes, and both inflammatory and anti-inflammatory cytokines, and causing mild hepatic steatosis. CPF activates inflammatory and stress responses associated with the induction of inflammatory cytokines together with apoptosis initiator and executioner caspases.

MS-222 induces biochemical and transcriptional changes related to oxidative stress, cell proliferation and apoptosis in zebrafish embryos

MS-222, the most widely used anaesthetic in fish, has been shown to induce embryotoxic effects in zebrafish. However, the underlying molecular effects are still elusive. This study aimed to investigate the effects of MS-222 exposure during early developmental stages by evaluating biochemical and molecular changes. Embryos were exposed to 50, 100 or 150 mg L^-1 MS-222 for 20 min at one of three developmental stages (256-cell, 50% epiboly, or 1-4 somite stage) and oxidative-stress, cell proliferation and apoptosis-related parameters were determined at two time-points (8 and 26 hpf). Following exposure during the 256-cell stage, the biochemical redox balance was not affected. The genes associated with glutathione homeostasis (gstpi and gclc) were affected at 8 hpf, while genes associated with apoptosis (casp3a and casp6) and cellular proliferation (pcna) were found affected at 26 hpf. An inverted U-shaped response was observed at 8 hpf for catalase activity. After exposure at the 50% epiboly stage, the gclc gene associated with oxidative stress was found upregulated at 8 hpf, while gstpi was downregulated and casp6 was upregulated later on, coinciding with a decrease in glutathione peroxidase (GPx) activity and a non-monotonic elevation of protein carbonyls and casp3a. Additionally, MS-222 treated embryos showed a decrease in DCF-staining at 26 hpf. When exposure was performed at the 1-4 somite stage, a similar DCF-staining pattern was observed. The activity of GPx was also affected whereas RT-qPCR showed that caspase transcripts were dose-dependently increased (casp3a, casp6 and casp9). The pcna mRNA levels were also found to be upregulated while gclc was changed by MS-222. These results highlight the impact of MS-222 on zebrafish embryo development and its interference with the antioxidant, cell proliferation and cellular death systems by mechanisms still to be explained; however, the outcomes point to the Erk/Nrf2 signalling pathway as a target candidate.

Modulation and Protection Effects of Antioxidant Compounds against Oxidant Induced Developmental Toxicity in Zebrafish

The antioxidant effect of compounds is regularly evaluated by in vitro assays that do not have the capability to predict in vivo protective activity or to determine their underlying mechanisms of action. The aim of this study was to develop an experimental system to evaluate the in vivo protective effects of different antioxidant compounds, based on the zebrafish embryo test. Zebrafish embryos were exposed to tert-butyl hydroperoxide (tBOOH), tetrachlorohydroquinone (TCHQ) and lipopolysaccharides from Escherichia coli (LPS), chemicals that are known inducers of oxidative stress in zebrafish. The developmental toxic effects (lethality or dysmorphogenesis) induced by these chemicals were modulated with n-acetyl l-cysteine and Nω-nitro l-arginine methyl ester hydrochloride, dimethyl maleate and dl-buthionine sulfoximine in order to validate the oxidant mechanism of oxidative stress inducers. The oxidant effects of tBOOH, TCHQ, and LPS were confirmed by the determination of significant differences in the comparison between the concentration–response curves of the oxidative stress inducers and of the modulators of antioxidant status. This concept was also applied to the study of the effects of well-known antioxidants, such as vitamin E, quercetin, and lipoic acid. Our results confirm the zebrafish model as an in vivo useful tool to test the protective effects of antioxidant compounds.

Antioxidant defenses and non-specific immunity at enzymatic and transcriptional levels in response to dietary carbohydrate in a typical carnivorous fish, hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂)

The present study was conducted to explore the influence of dietary carbohydrate on antioxidant capacity and non-specific immunity of hybrid grouper, which would contribute to determine the tolerable dietary carbohydrate content. Seven diets with grade levels of carbohydrate (5.27, 8.95, 11.49, 14.37, 17.78, 20.82 and 23.65%) were fed to triplicate groups of fish for 10 weeks. Results showed that the inclusion of carbohydrate above 11.49% produced significant increased content of hydrogen peroxide (H₂O₂) in liver and malondialdehyde (MDA) in both serum and liver. The specific activity of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (Gpx) and total antioxidative capacity (T-AOC) were significantly elevated with the increase of dietary carbohydrate from 8.95 to 23.65%, which may be associated with the reduced hepatic soluble protein content. However, opposite variation was observed in the expression of antioxidant related genes (SOD1 and Gpx), which was partly caused by the activation of NF-E2-related factor 2 (Nrf2) and inhibition of Kelch-like-ECH-associated protein 1 (Keap1) at the transcriptional level. The immunoglobulin M (lgM) content and activity of lysozyme and CCP in serum significantly depressed when dietary carbohydrate was above 11.49%. The expression of pro-inflammatory cytokines (TNF-α, IL-1β and IL-8) was significantly increased with the increase of dietary carbohydrate from 5.27 to 8.95% and thereafter significantly reduced, which was consistent with the changed expression of toll-like receptor 2 (TLR2) and nuclear factor κΒ (NF-κΒ). In above, high dietary carbohydrate significantly impaired the antioxidant capacity and reduced the non-specific immunity of hybrid grouper, and the tolerable dietary carbohydrate content should not exceed 11.49%.

Embryo/larval toxicity and transcriptional effects in zebrafish (Danio rerio) exposed to endocrine active riverbed sediments

Sediment toxicity plays a fundamental role in the health of inland fish communities; however, the assessment of the hazard potential of contaminated sediments is not a common objective in environmental diagnostics or remediation. This study examined the potential of transcriptional endpoints investigated in zebrafish (Danio rerio) exposed to riverbed sediments in ecotoxicity testing. Embryo-larval 10-day tests were conducted on sediment samples collected from five sites (one upstream and four downstream of the city of Milan) along a polluted tributary of the Po River, the Lambro River. Sediment chemistry showed a progressive downstream deterioration in river quality, so that the final sampling site showed up to eight times higher concentrations of, for example, triclosan, galaxolide, PAH, PCB, BPA, Ni, and Pb, compared with the uppermost site. The embryo/larval tests showed widespread toxicity although the middle river sections evidenced worse effects, as evidenced by delayed embryo development, hatching rate, larval survival, and growth. At the mRNA transcript level, the genes encoding biotransformation enzymes (cyp1a, gst, ugt) showed increasing upregulations after exposure to sediment from further downstream sites. The genes involved in antioxidant responses (sod, gpx) suggested that more critical conditions may be present at downstream sites, but even upstream of Milan there seemed to be some level of oxidative stress. Indirect evidences of potential apoptotic activity (bcl2/bax < 1) in turn suggested the possibility of genotoxic effects. The genes encoding for estrogen receptors (erα, erβ1, erβ2) showed exposure to (xeno)estrogens with a progressive increase after exposure to sediments from downstream sites, paralleled by a corresponding downregulation of the ar gene, likely related to antiandrogenic compounds. Multiple levels of thyroid disruption were also evident particularly in downstream zebrafish, as for thyroid growth (nkx2.1), hormone synthesis and transport (tg, ttr, d2), and signal transduction (trα, trβ). The inhibition of the igf2 gene reasonably reflected larval growth inhibitions. Although none of the sediment chemicals could singly explain fish responses, principal component analysis suggested a good correlation between gene transcripts and the overall trend of contamination. Thus, the combined impacts from known and unknown covarying chemicals were proposed as the most probable explanation of fish responses. In summary, transcriptional endpoints applied to zebrafish embryo/larval test can provide sensitive, comprehensive, and timeliness information which may greatly enable the assessment of the hazard potential of sediments to fish, complementing morphological endpoints and being potentially predictive of longer studies.

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.

Mapping glutathione utilization in the developing zebrafish (Danio rerio) embryo

Glutathione (GSH), the most abundant vertebrate endogenous redox buffer, plays key roles in organogenesis and embryonic development, however, organ-specific GSH utilization during development remains understudied. Monochlorobimane (MCB), a dye conjugated with GSH by glutathione-s-transferase (GST) to form a fluorescent adduct, was used to visualize organ-specific GSH utilization in live developing zebrafish (Danio rerio) embryos. Embryos were incubated in 20 μM MCB for 1 h and imaged on an epifluorescence microscope. GSH conjugation with MCB was high during early organogenesis, decreasing as embryos aged. The heart had fluorescence 21-fold above autofluorescence at 24 hpf, dropping to 8.5-fold by 48 hpf; this increased again by 72 hpf to 23.5-fold, and stayed high till 96 hpf (18-fold). The brain had lower fluorescence (10-fold) at 24 and 48 hpf, steadily increasing to 30-fold by 96 hpf. The sensitivity and specificity of MCB staining was then tested with known GSH modulators. A 10-min treatment at 48 hpf with 750 μM tert-butylhydroperoxide, caused organ-specific reductions in staining, with the heart losing 30% fluorescence, and, the brain ventricle losing 47% fluorescence. A 24 h treatment from 24-48 hpf with 100 μM of N-Acetylcysteine (NAC) resulted in significantly increased fluorescence, with the brain ventricle and heart showing 312% and 240% increases respectively, these were abolished upon co-treatment with 5 μM BSO, an inhibitor of the enzyme that utilizes NAC to synthesize GSH. A 60 min 100 μM treatment with ethacrynic acid, a specific GST inhibitor, caused 30% reduction in fluorescence across all measured structures. MCB staining was then applied to test for GSH disruptions caused by the toxicants perfluorooctanesulfonic acid and mono-(2-ethyl-hexyl)phthalate; MCB fluorescence responded in a dose, structure and age-dependent manner. MCB staining is a robust, sensitive method to detect spatiotemporal changes in GSH utilization, and, can be applied to identify sensitive target tissues of toxicants.

A Novel Zebrafish Model for Assessing In Vivo Delivery of Morpholino Oligomers

Morpholino oligomers have great therapeutic potential for treatment of a broad range of human diseases, including viral, bacterial, age-related, and genetic diseases, but they suffer from poor systemic delivery into cells. Although various approaches have been undertaken to address the delivery problem, it remains as the major barrier of morpholinos to be used as effective therapeutics. This slow development is in part due to the cost of materials and the animal models used for screening the efficacy and safety of those delivery approaches. The need to have an inexpensive vertebrate model for assessing in vivo delivery of morpholinos is evident. Therefore, we have produced a novel transgenic zebrafish model containing a dual reporter cassette for determination of in vivo delivery, bio-distribution, and safety of a morpholino. The levels of morpholino delivered to the cells in various tissues can be determined by changes in reporter gene expressions caused by morpholino-induced exon skipping. This chapter provides a description of the reagents, equipment, and procedure for successful retro-orbital injection of a peptide-conjugated morpholino into the blood stream of the adult zebrafish to cause targeted exon skipping in the heart of the zebrafish.

Cardiovascular Effects of PCB 126 (3,3',4,4',5-Pentachlorobiphenyl) in Zebrafish Embryos and Impact of Co-Exposure to Redox Modulating Chemicals

The developing cardiovascular system of zebrafish is a sensitive target for many environmental pollutants, including dioxin-like compounds and pesticides. Some polychlorinated biphenyls (PCBs) can compromise the cardiovascular endothelial function by activating oxidative stress-sensitive signaling pathways. Therefore, we exposed zebrafish embryos to PCB126 or to several redox-modulating chemicals to study their ability to modulate the dysmorphogenesis produced by PCB126. PCB126 produced a concentration-dependent induction of pericardial edema and circulatory failure, and a concentration-dependent reduction of cardiac output and body length at 80 hours post fertilization (hpf). Among several modulators tested, the effects of PCB126 could be both positively and negatively modulated by different compounds; co-treatment with α-tocopherol (vitamin E liposoluble) prevented the adverse effects of PCB126 in pericardial edema, whereas co-treatment with sodium nitroprusside (a vasodilator compound) significantly worsened PCB126 effects. Gene expression analysis showed an up-regulation of cyp1a, hsp70, and gstp1, indicative of PCB126 interaction with the aryl hydrocarbon receptor (AhR), while the transcription of antioxidant genes (sod1, sod2; cat and gpx1a) was not affected. Further studies are necessary to understand the role of oxidative stress in the developmental toxicity of low concentrations of PCB126 (25 nM). Our results give insights into the use of zebrafish embryos for exploring mechanisms underlying the oxidative potential of environmental pollutants.

Beyond the obvious: Environmental health implications of polar polycyclic aromatic hydrocarbons

The genotoxic, mutagenic and carcinogenic effects of polar polycyclic aromatic hydrocarbons (polar PAHs) are believed to surpass those of their parent PAHs; however, their environmental and human health implications have been largely unexplored. Oxygenated PAHs (oxy-PAHs) is a critical class of polar PAHs associated with carcinogenic effects without enzymatic activation. They also cause an upsurge in reactive oxygen species (ROS) in living cells. This results in oxidative stress and other consequences, such as abnormal gene expressions, altered protein activities, mutagenesis, and carcinogenesis. Similarly, some nitrated PAHs (N-PAHs) are probable human carcinogens as classified by the International Agency for Research on Cancer (IARC). Heterocyclic PAHs (polar PAHs containing nitrogen, sulphur and oxygen atoms within the aromatic rings) have been shown to be potent endocrine disruptors, primarily through their estrogenic activities. Despite the high toxicity and enhanced environmental mobility of many polar PAHs, they have attracted only a little attention in risk assessment of contaminated sites. This may lead to underestimation of potential risks, and remediation end points. In this review, the toxicity of polar PAHs and their associated mechanisms of action, including their role in mutagenic, carcinogenic, developmental and teratogenic effects are critically discussed. This review suggests that polar PAHs could have serious toxicological effects on human health and should be considered during risk assessment of PAH-contaminated sites. The implications of not doing so were argued and critical knowledge gaps and future research requirements discussed.

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.

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.

Nrf2a modulates the embryonic antioxidant response to perfluorooctanesulfonic acid (PFOS) in the zebrafish, Danio rerio

The glutathione redox system undergoes precise and dynamic changes during embryonic development, protecting against and mitigating oxidative insults. The antioxidant response is coordinately largely by the transcription factor Nuclear factor erythroid-2 (Nrf2), an endogenous sensor for cellular oxidative stress. We have previously demonstrated that impaired Nrf family signaling disrupts the glutathione redox system in the zebrafish embryo, and that impaired Nrf2 function increases embryonic sensitivity to environmental toxicants. Here, we investigated the persistent environmental toxicant and reported pro-oxidant perfluorooctanesulfonic acid (PFOS), and its impact on the embryonic glutathione-mediated redox environment. We further examined whether impaired Nrf2a function exacerbates PFOS-induced oxidative stress and embryotoxicity in the zebrafish, and the potential for Nrf2-PPAR crosstalk in the embryonic adaptive response. Wild-type and nrf2afh318-/- mutant embryos were exposed daily to 0 (0.01% v/v DMSO), 16, 32, or 64 μM PFOS beginning at 3 h post fertilization (hpf). Embryonic glutathione and cysteine redox environments were examined at 72 hpf. Gross embryonic toxicity, antioxidant gene expression, and apoptosis were examined at 96 hpf. Mortality, pericardial edema, and yolk sac utilization were increased in wild-type embryos exposed to PFOS. Embryonic glutathione and cysteine redox couples and gene expression of Nrf2 pathway targets were modulated by both exposure and genotype. Apoptosis was increased in PFOS-exposed wild-type embryos, though not in nrf2a mutants. In silico examination of putative transcription factor binding site suggested potential crosstalk between Nrf2 and PPAR signaling, since expression of PPARs and gene targets was modulated by both PFOS exposure and Nrf2a genotype. Overall, this work demonstrates that nrf2a modulates the embryonic response to PFOS, and that PPAR signaling may play a role in the embryonic adaptive response to PFOS.

The impaired immune function and structural integrity by dietary iron deficiency or excess in gill of fish after infection with Flavobacterium columnare: Regulation of NF-κB, TOR, JNK, p38MAPK, Nrf2 and MLCK signalling

The aim of this study was to investigate the effects and potential mechanisms of dietary iron on immune function and structural integrity in gill of young grass carp (Ctenopharyngodon idella). A total of 630 grass carp (242.32 ± 0.58 g) were fed diets containing graded levels of iron at 12.15 (basal diet), 35.38, 63.47, 86.43, 111.09, 136.37 and 73.50 mg/kg for 60 days. Subsequently, a challenge test was conducted by infection with Flavobacterium columnare to investigate the effects of dietary iron on gill immune function and structural integrity in young grass carp. First, the results indicated that compared with the optimal iron level, iron deficiency decreased lysozyme (LZ) and acid phosphatase (ACP) activities, complement 3 (C3), C4 and immunoglobulin M (IgM) contents, and down-regulated the mRNA levels of antibacterial peptides, anti-inflammatory cytokines (except IL-4/13B), inhibitor of κBα (IκBα), target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6K1). In contrast, iron deficiency up-regulated the mRNA levels of pro-inflammatory cytokines (except IL-6 and IFN-γ2), nuclear factor κB p65 (NF-κBp65), IκB kinases α (IKK), IKKβ, IKKγ, eIF4E-binding protein 1 (4E-BP1) and 4E-BP2 in gill of young grass carp, indicating that iron deficiency could impair immune function in fish gill. Second, iron deficiency down-regulated the mRNA levels of inhibitor of apoptosis protein (IAP) and myeloid cell leukemia 1 (Mcl-1), decreased activities and mRNA levels of antioxidant enzymes, down-regulated the mRNA levels of NF-E2-related factor 2 (Nrf2) and tight junction proteins (except claudin-12 and -15), and simultaneously increased malondialdehyde (MDA), protein carbonyl (PC) and reactive oxygen species (ROS) contents. Iron deficiency also up-regulated mRNA levels of cysteinyl aspartic acid-protease (caspase) -2, -7, -8, -9, Fas ligand (FasL), apoptotic protease activating factor-1 (Apaf-1), B-cell-lymphoma-2 associated X protein (Bax), p38 mitogen-activated protein kinase (p38MAPK), Kelch-like ECH-associating protein (Keap) 1a, Keap1b, claudin-12, -15 and MLCK, indicating that iron deficiency could disturb the structural integrity of gill in fish. Third, iron excess impaired immune function and structural integrity in gill of young grass carp. Forth, there was a better effect of ferrous fumarate than ferrous sulfate in young grass carp. Finally, the iron requirements based on ability against gill rot, ACP activity and MDA content in gill of young grass carp were estimated to be 76.52, 80.43 and 83.17 mg/kg, respectively.

Effects of various feeding patterns of Bacillus coagulans on growth performance, antioxidant response and Nrf2-Keap1 signaling pathway in juvenile gibel carp (Carassius auratus gibelio)

The present study was conducted to evaluate the effects of various Bacillus coagulans feeding patterns on growth, antioxidant parameter and Nrf2 pathway in juvenile gibel carp. The similar size of gibel carp (initial weight: 14.33 ± 0.15 g) were subjected to three levels of B. coagulans supplementation (0, 500, and 1000 mg/kg) and two feeding modes (supplementing B. coagulans continuously or for two days of B. coagulans after 5 days of a basal diet) according to a 3 × 2 factorial design. The fish that were continuously fed 500 mg/kg B. coagulans (P2) and those fed the first basal diet for 5 days followed by 500 mg/kg or 1000 mg/kg B.coagulans for 2 days (P4 or P5) showed higher weight gain rate and specific growth rate than the other groups. Blood respiratory burst (RB), myeloperoxidase (MPO), and anti-superoxide anion free radical (AFASER) activities in the P4 group were higher than those of the control. White blood cell count (WBC), RB activity, MPO activity, and glutathione (GSH) content in the P5 group were also higher than those of the control. A similar higher trend was observed in the gene expressions of NADPH oxidase 2 (NOX2), NFE2-related factor (Nrf2), Kelch-like-ECH-associated protein(Keap1) in the P4 and NOX2, NRF2, CNC homolog 1 (Bach1), peroxiredoxin 2 (Prx2) in the P5 group compared with the control. Additionally, we observed a significantly lower level of plasma aspartate aminotransferase (AST), lower activity of alanine aminotransferase (ALT), a higher level of MPO, higher GPX activity, and increased NRF2 and Prx2 expression were all observed in the P2 treatment group compared with the control. Furthermore, the malondialdehyde (MDA) content in the P2, P3, and P4 groups was lower than that of the control. These results indicate that a diet supplemented with appropriate levels of B.coagulans could improve the growth, immune response, and antioxidant capability of gibel carp. We concluded that the pattern of two days of 500 or 1000 mg/kg B. coagulans after 5 days of a basal diet was recommended for gibel carp.

Alteration in DNA structure, molecular responses and Na+ -K+ -ATPase activities in the gill of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) in response to sub-lethal verapamil

The ecotoxicological consequences of residues from pharmaceutical drugs on aquatic biota have necessitated the development of sensitive and reliable techniques to assess the impact of these xenobiotics on aquatic organisms. This study investigated the alteration in DNA structure, molecular responses and the activities of Na⁺ -K⁺ -ATPase and antioxidant enzymes in the gill of Nile tilapia, Oreochromis niloticus, exposed to long-term effects at the concentrations (0.14, 0.28 and 0.57mgL^-1) of verapamil in static renewal system for 15, 30, 45 and 60 days. Evaluation of DNA structure, using single cell gel electrophoresis, revealed certain degree of DNA damages in the gill in a time and concentration-dependent relationship. Transcription of mRNA of superoxide dismutase (sod), catalase (cat) and heat shock protein (hsp70) genes in the gill of the fish showed the genes were up-regulated. Na⁺-K⁺-ATPase activity was inhibited in a concentration and time dependent manner. The indices of oxidative stress biomarkers (lipid peroxidation and carbonyl protein) as well as superoxide dismutase, glutathione peroxidase, glutathione-S-transferase were elevated in the treated fish in comparison to the control. Further, the level of reduced glutathione and catalase activity were inhibited at 0.28mgL^-1 after day 30. Long-term exposure to sub-lethal concentration of verapamil can cause DNA damages, molecular effects and oxidative stress in O. niloticus. The biomarkers analysed can be used as early warning signals in environmental biomonitoring and assessment of drug contamination in aquatic ecosystem.

The role of Nrf1 and Nrf2 in the regulation of glutathione and redox dynamics in the developing zebrafish embryo

Redox signaling is important for embryogenesis, guiding pathways that govern processes crucial for embryo patterning, including cell polarization, proliferation, and apoptosis. Exposure to pro-oxidants during this period can be deleterious, resulting in altered physiology, teratogenesis, later-life diseases, or lethality. We previously reported that the glutathione antioxidant defense system becomes increasingly robust, including a doubling of total glutathione and dynamic shifts in the glutathione redox potential at specific stages during embryonic development in the zebrafish, Danio rerio. However, the mechanisms underlying these changes are unclear, as is the effectiveness of the glutathione system in ameliorating oxidative insults to the embryo at different stages. Here, we examine how the glutathione system responds to the model pro-oxidants tert-butylhydroperoxide and tert-butylhydroquinone at different developmental stages, and the role of Nuclear factor erythroid 2-related factor (Nrf) proteins in regulating developmental glutathione redox status. Embryos became increasingly sensitive to pro-oxidants after 72h post-fertilization (hpf), after which the duration of the recovery period for the glutathione redox potential was increased. To determine whether the doubling of glutathione or the dynamic changes in glutathione redox potential are mediated by zebrafish paralogs of Nrf transcription factors, morpholino oligonucleotides were used to knock down translation of Nrf1 and Nrf2 (nrf1a, nrf1b, nrf2a, nrf2b). Knockdown of Nrf1a or Nrf1b perturbed glutathione redox state until 72 hpf. Knockdown of Nrf2 paralogs also perturbed glutathione redox state but did not significantly affect the response of glutathione to pro-oxidants. Nrf1b morphants had decreased gene expression of glutathione synthesis enzymes, while hsp70 increased in Nrf2b morphants. This work demonstrates that despite having a more robust glutathione system, embryos become more sensitive to oxidative stress later in development, and that neither Nrf1 nor Nrf2 alone appear to be essential for the response and recovery of glutathione to oxidative insults.

Dietary protein levels regulated antibacterial activity, inflammatory response and structural integrity in the head kidney, spleen and skin of grass carp (Ctenopharyngodon idella) after challenged with Aeromonas hydrophila

This study investigated the effects of dietary protein levels on disease resistance, immune function and structural integrity in the head kidney, spleen and skin of grass carp (Ctenopharyngodon idella). A total of 540 grass carp (264.11 ± 0.76 g) were fed six diets containing graded levels of protein (143.1, 176.7, 217.2, 257.5, 292.2 and 322.8 g digestible protein kg^-1 diet) for 8 weeks. After the growth trial, fish were challenged with Aeromonas hydrophila for 14 days. The results indicated that optimal levels of dietary protein: (1) (1) increased the lysozyme (LA) and acid phosphatase (ACP) activities and the complement 3 (C3) and C4 contents, up-regulated antimicrobial peptides, anti-inflammatory cytokines, inhibitor of κBα, target of rapamycin and ribosomal protein S6 kinases 1 mRNA levels, whereas down-regulated pro-inflammatory cytokines, nuclear factor kappa B (NF-κB) P65, IKKβ, IKKγ, eIF4E-binding proteins (4E-BP) 1 and 4E-BP2 mRNA levels in the head kidney, spleen and skin of grass carp (P < 0.05), suggesting that optimal level of dietary protein could enhance immune function in the head kidney, spleen and skin of fish; (2) increased the activities and mRNA levels of antioxidant enzymes, enhanced the glutathione content, decreased reactive oxygen species, malondialdehyde (MDA) and protein carbonyl contents, and up-regulated the mRNA levels of NF-E2-related factor 2, B-cell lymphoma protein-2, inhibitor of apoptosis proteins, myeloid cell leukemia-1 and tight junction complexes, whereas down-regulated Kelch-like-ECH-associated protein (Keap) 1b, cysteinyl aspartic acid-protease 3, 8, 9, Fas ligand, apoptotic protease activating factor-1, Bcl-2 associated X protein and myosin light chain kinase mRNA levels in the head kidney, spleen and skin of grass carp (P < 0.05), indicating that optimal level of dietary protein could improve structural integrity in the head kidney, spleen and skin of fish. Finally, based on the skin hemorrhage and lesion morbidity, LA activity and MDA content, the optimal levels of dietary protein for grass carp (264 g-787 g) were estimated to be 241.45 g kg^-1 diet (217.68 g digestible protein kg^-1 diet), 301.68 g kg^-1 diet (265.48 g digestible protein kg^-1 diet) and 307.84 g kg^-1 diet (272.71 g digestible protein kg^-1 diet), respectively.

Real-time quantification of subcellular H2O2 and glutathione redox potential in living cardiovascular tissues

Detecting and measuring the dynamic redox events that occur in vivo is a prerequisite for understanding the impact of oxidants and redox events in normal and pathological conditions. These aspects are particularly relevant in cardiovascular tissues wherein alterations of the redox balance are associated with stroke, aging, and pharmacological intervention. An ambiguous aspect of redox biology is how redox events occur in subcellular organelles including mitochondria, and nuclei. Genetically-encoded Rogfp2 fluorescent probes have become powerful tools for real-time detection of redox events. These probes detect hydrogen peroxide (H₂O₂) levels and glutathione redox potential (E_GSH), both with high spatiotemporal resolution. By generating novel transgenic (Tg) zebrafish lines that express compartment-specific Rogfp2-Orp1 and Grx1-Rogfp2 sensors we analyzed cytosolic, mitochondrial, and the nuclear redox state of endothelial cells and cardiomyocytes of living zebrafish embryos. We provide evidence for the usefulness of these Tg lines for pharmacological compounds screening by addressing the blocking of pentose phosphate pathways (PPP) and glutathione synthesis, thus altering subcellular redox state in vivo. Rogfp2-based transgenic zebrafish lines represent valuable tools to characterize the impact of redox changes in living tissues and offer new opportunities for studying metabolic driven antioxidant response in biomedical research.

The decreased growth performance and impaired immune function and structural integrity by dietary iron deficiency or excess are associated with TOR, NF-κB, p38MAPK, Nrf2 and MLCK signaling in head kidney, spleen and skin of grass carp (Ctenopharyngodon idella)

This study was conducted to investigate the effects of dietary iron on the growth, and immune function and structural integrity in head kidney, spleen and skin as well as the underlying signaling of young grass carp (Ctenopharyngodon idella). Total 630 grass carp (242.32 ± 0.58 g) were fed diets containing graded levels of iron at 12.15 (basal diet), 35.38, 63.47, 86.43, 111.09, 136.37 mg/kg (diets 2-6 were added with ferrous fumarate) and 73.50 mg/kg (diet 7 was added with ferrous sulfate) diet for 60 days. Then, a challenge test was conducted by infection of Aeromonas hydrophila for 14 days. The results firstly showed that compared with optimal iron level, iron deficiency decreased lysozyme (LZ) and acid phosphatase (ACP) activities, complement 3 (C3), C4 and immunoglobulin M (IgM) contents and down-regulated the mRNA levels of antibacterial peptides, anti-inflammatory cytokines, inhibitor of κBα (IκBα), target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6K1), whereas up-regulated the mRNA levels of pro-inflammatory cytokines, nuclear factor kappa B (NF-κB) p65, IκB kinases β (IKKβ) and eIF4E-binding protein (4E-BP) in head kidney and spleen of young grass carp (P < 0.05), indicating that iron deficiency impaired immune function in head kidney and spleen of fish. Secondly, iron deficiency down-regulated the mRNA levels of B-cell lymphoma-2 (Bcl-2), myeloid cell leukemia 1 (Mcl-1), and inhibitor of apoptosis protein (IAP), and decreased activities and mRNA levels of antioxidant enzymes, down-regulated the mRNA levels of NF-E2-related factor 2 (Nrf2) and tight junction complexes, and up-regulated mRNA levels of cysteinyl aspartic acid-protease (caspase) -2, -3, -7, -8, -9, apoptotic protease activating factor-1 (Apaf-1), Bcl-2 associated X protein (Bax), Fas ligand (FasL), p38 mitogen-activated protein kinase (p38MAPK), Kelch-like ECH-associating protein (Keap) 1a, Keap1b, claudin-12 and myosin light chain kinase (MLCK), and increased malondialdehyde (MDA), protein carbonyl (PC) and reactive oxygen species (ROS) contents in head kidney and spleen of young grass carp (P < 0.05), indicating that iron deficiency impaired structural integrity in head kidney and spleen of fish. Thirdly, iron deficiency increased skin hemorrhage and lesion morbidity, and impaired immune function and structural integrity in skin of fish. Fourthly, iron excess decreased growth and impaired the immune function and structural integrity in head kidney, spleen and skin of fish. Besides, in young grass carp, based on PWG and ability against skin hemorrhage and lesion, the efficacy of ferrous fumarate relative to ferrous sulfate was 140.32% and 126.48%, respectively, and the iron requirements based on PWG, ability against skin hemorrhage and lesion, ACP activities and MDA contents in head kidney and spleen were estimated to be 75.65, 87.03, 79.74, 78.93, 83.17 and 82.14 mg/kg diet (based on ferrous fumarate), respectively.

A targeted gene expression platform allows for rapid analysis of chemical-induced antioxidant mRNA expression in zebrafish larvae

Chemical-induced oxidative stress and the biochemical pathways that protect against oxidative damage are of particular interest in the field of toxicology. To rapidly identify oxidative stress-responsive gene expression changes in zebrafish, we developed a targeted panel of antioxidant genes using the Affymetrix QuantiGene Plex (QGP) platform. The genes contained in our panel include eight putative Nrf2 (Nfe2l2a)-dependent antioxidant genes (hmox1a, gstp1, gclc, nqo1, prdx1, gpx1a, sod1, sod2), a stress response gene (hsp70), an inducible DNA damage repair gene (gadd45bb), and three reference genes (actb1, gapdh, hprt1). We tested this platform on larval zebrafish exposed to tert-butyl hydroperoxide (tBHP) and cadmium (Cd), two model oxidative stressors with different modes of action, and compared our results with those obtained using the more common quantitative PCR (qPCR) method. Both methods showed that exposure to tBHP and Cd induced expression of prdx1, gstp1, and hmox1a (2- to 12-fold increase via QGP), indicative of an activated Nrf2 response in larval zebrafish. Both compounds also elicited a general stress response as reflected by elevation of hsp70 and gadd45bb, with Cd being the more potent inducer. Transient changes were observed in sod2 and gpx1a expression, whereas nqo1, an Nrf2-responsive gene in mammalian cells, was minimally affected by either tBHP or Cd chemical exposures. Developmental expression analysis of the target genes by QGP revealed marked upregulation of sod2 between 0-96hpf, and to a lesser extent, of sod1 and gstp1. Once optimized, QGP analysis of these experiments was accomplished more rapidly, using far less tissue, and at lower total costs than qPCR analysis. In summary, the QGP platform as applied to higher-throughput zebrafish studies provides a reasonable cost-effective alternative to qPCR or more comprehensive transcriptomics approaches to rapidly assess the potential for chemicals to elicit oxidative stress as a mechanism of chemical toxicity.

A bioenergetics assay for studying the effects of environmental stressors on mitochondrial function in vivo in zebrafish larvae

Mitochondria, an integral component of cellular energy metabolism and other key functions, are extremely vulnerable to damage by environmental stressors. Although methods to measure mitochondrial function in vitro exist, sensitive, medium- to high-throughput assays that assess respiration within physiologically-relevant whole organisms are needed to identify drugs and/or chemicals that disrupt mitochondrial function, particularly at sensitive early developmental stages. Consequently, we have developed and optimized an assay to measure mitochondrial bioenergetics in zebrafish larvae using the XF^e24 Extracellular Flux Analyzer. To prevent larval movement from confounding oxygen consumption measurements, we relied on MS-222-based anesthetization. We obtained stable measurement values in the absence of effects on average oxygen consumption rate and subsequently optimized the use of pharmacological agents for metabolic partitioning. To confirm assay reproducibility we demonstrated that triclosan, a positive control, significantly decreased spare respiratory capacity. We then exposed zebrafish from 5 hours post-fertilization (hpf) to 6days post-fertilization (dpf) to three polycyclic aromatic hydrocarbons (PAHs) - benzo(a)pyrene (BaP), phenanthrene (Phe), and fluoranthene (FL) - and measured various fundamental parameters of mitochondrial respiratory chain function, including maximal respiration, spare respiratory capacity, mitochondrial and non-mitochondrial respiration. Exposure to all three PAHs decreased spare respiratory capacity and maximal respiration. Additionally, Phe exposure increased non-mitochondrial respiration and FL exposure decreased mitochondrial respiration and increased non-mitochondrial respiration. Overall, this whole organism-based assay provides a platform for examining mitochondrial dysfunction in vivo at critical developmental stages. It has important implications in biomedical sciences, toxicology and ecophysiology, particularly to examine the effects of environmental chemicals and/or drugs on mitochondrial bioenergetics.

Glutathione and zebrafish: Old assays to address a current issue

Several xenobiotic agents (e.g. metals, polycyclic aromatic hydrocarbons, nanoparticles, etc.) commonly involve the generation of reactive oxygen species (ROS) and oxidative stress as part of their toxic mode of action. Among piscine models, the zebrafish is a popular vertebrate model to study toxicity of various xenobiotic agents. Similarly to other vertebrates, zebrafish possess an extensive antioxidant system, including the reduced form of glutathione (GSH), which is an important antioxidant that acts alone or in conjunction with enzymes, such as glutathione peroxidase (GPx). Upon interaction with ROS, GSH is oxidized, resulting in the formation of glutathione disulfide (GSSG). GSSG is recycled by an auxiliary antioxidant enzyme glutathione reductase (GR). This article outlines detailed methods to measure the concentrations of GSH and GSSG, as well as the activities of GPx and GR in zebrafish larvae as robust and economical means to assess oxidative stress. The studies that have assessed these endpoints in zebrafish and alternative methods are also discussed. We conclude that the availability of these robust and economical methods support the use of zebrafish as a model organism in studies evaluating redox biology, as well as the induction of oxidative stress following exposure to toxic agents.

Effect of PMA-induced protein kinase C activation on development and apoptosis in early zebrafish embryos

Protein kinase C (PKC) isoforms have been implicated in several key steps during early development, but the consequences of xenobiotic-induced PKC activation during early embryogenesis are still unknown. In this study, zebrafish embryos were exposed to a range of phorbol 12-myristate 13-acetate (PMA) concentrations (0-200μg/L) at different time points after fertilization. Results showed that 200μgPMA/L caused development of yolk bags, cardiac edema, slow blood flow, pulsating blood flow, slow pulse, elongated heart, lack of tail fins, curved tail, and coagulation. PMA exposure decreased survival rate of the embryos starting within the first 24h and becoming more pronounced after prolonged exposure (96h). PMA increased the number of apoptotic cells in the brain region as demonstrated by acridine orange staining and caused up-regulation of caspase 9 (casp9) and p53 up-regulated modulator of apoptosis (puma) mRNA in whole embryos. PMA caused oxidative stress in the embryos as demonstrated by decreased mRNA expression of catalase and superoxide dismutase 2. Inhibition of Pkc with GF109203X improved overall survival rate, reduced apoptosis in the brain and decreased expression of casp9 and puma in the PMA-exposed embryos. However, Pkc inhibition neither prevented development of deformities nor reversed oxidative stress in the PMA-exposed embryos. These data suggest that direct over-activation of Pkc during early embryogenesis of zebrafish is associated with apoptosis and decreased survival rate of the embryos.

Toward the Design of Less Hazardous Chemicals: Exploring Comparative Oxidative Stress in Two Common Animal Models

Sustainable molecular design of less hazardous chemicals presents a potentially transformative approach to protect public health and the environment. Relationships between molecular descriptors and toxicity thresholds previously identified the octanol-water distribution coefficient, log D, and the HOMO-LUMO energy gap, ΔE, as two useful properties in the identification of reduced aquatic toxicity. To determine whether these two property-based guidelines are applicable to sublethal oxidative stress (OS) responses, two common aquatic in vivo models, the fathead minnow (Pimephales promelas) and zebrafish (Danio rerio), were employed to examine traditional biochemical biomarkers (lipid peroxidation, DNA damage, and total glutathione) and antioxidant gene activation following exposure to eight structurally diverse industrial chemicals (bisphenol A, cumene hydroperoxide, dinoseb, hydroquinone, indene, perfluorooctanoic acid, R-(-)-carvone, and tert-butyl hydroperoxide). Bisphenol A, cumene hydroperoxide, dinoseb, and hydroquinone were consistent inducers of OS. Glutathione was the most consistently affected biomarker, suggesting its utility as a sensitivity response to support the design of less hazardous chemicals. Antioxidant gene expression (changes in nrf2, gclc, gst, and sod) was most significantly (p < 0.05) altered by R-(-)-carvone, cumene hydroperoxide, and bisphenol A. Results from the present study indicate that metabolism of parent chemicals and the role of their metabolites in molecular initiating events should be considered during the design of less hazardous chemicals. Current empirical and computational findings identify the need for future derivation of sustainable molecular design guidelines for electrophilic reactive chemicals (e.g., SN2 nucleophilic substitution and Michael addition reactivity) to reduce OS related adverse outcomes in vivo.

The transcription factor, Nuclear factor, erythroid 2 (Nfe2), is a regulator of the oxidative stress response during Danio rerio development

Development is a complex and well-defined process characterized by rapid cell proliferation and apoptosis. At this stage in life, a developmentally young organism is more sensitive to toxicants as compared to an adult. In response to pro-oxidant exposure, members of the Cap'n'Collar (CNC) basic leucine zipper (b-ZIP) transcription factor family (including Nfe2 and Nfe2-related factors, Nrfs) activate the expression of genes whose protein products contribute to reduced toxicity. Here, we studied the role of the CNC protein, Nfe2, in the developmental response to pro-oxidant exposure in the zebrafish (Danio rerio). Following acute waterborne exposures to diquat or tert-buytlhydroperoxide (tBOOH) at one of three developmental stages, wildtype (WT) and nfe2 knockout (KO) embryos and larvae were morphologically scored and their transcriptomes sequenced. Early in development, KO animals suffered from hypochromia that was made more severe through exposure to pro-oxidants; this phenotype in the KO may be linked to decreased expression of alas2, a gene involved in heme synthesis. WT and KO eleutheroembryos and larvae were phenotypically equally affected by exposure to pro-oxidants, where tBOOH caused more pronounced phenotypes as compared to diquat. Comparing diquat and tBOOH exposed embryos relative to the WT untreated control, a greater number of genes were up-regulated in the tBOOH condition as compared to diquat (tBOOH: 304 vs diquat: 148), including those commonly found to be differentially regulated in the vertebrate oxidative stress response (OSR) (e.g. hsp70.2, txn1, and gsr). When comparing WT and KO across all treatments and times, there were 1170 genes that were differentially expressed, of which 33 are known targets of the Nrf proteins Nrf1 and Nrf2. More specifically, in animals exposed to pro-oxidants a total of 968 genes were differentially expressed between WT and KO across developmental time, representing pathways involved in coagulation, embryonic organ development, body fluid level regulation, erythrocyte differentiation, and oxidation-reduction, amongst others. The greatest number of genes that changed in expression between WT and KO occurred in animals exposed to diquat at 2h post fertilization (hpf). Across time and treatment, there were six genes (dhx40, cfap70, dnajb9b, slc35f4, spi-c, and gpr19) that were significantly up-regulated in KO compared to WT and four genes (fhad1, cyp4v7, nlrp12, and slc16a6a) that were significantly down-regulated. None of these genes have been previously identified as targets of Nfe2 or the Nrf family. These results demonstrate that the zebrafish Nfe2 may be a regulator of both primitive erythropoiesis and the OSR during development.

Effects of dietary protein levels on the disease resistance, immune function and physical barrier function in the gill of grass carp (Ctenopharyngodon idella) after challenged with Flavobacterium columnare

The effects of dietary protein levels on the disease resistance, gill immune function and physical barrier function of grass carp (Ctenopharyngodon idella) were investigated in this study. A total of 540 grass carp (264.11 ± 0.76 g) were fed six diets containing graded levels of protein (143.1, 176.7, 217.2, 257.5, 292.2 and 322.8 g digestible protein kg(-1) diet) for 8 weeks. After the growth trial, fish were challenged with Flavobacterium columnare for 3 days. The results indicated that optimal levels of dietary protein had the following effects: (1) the production of antibacterial components increased, and anti-inflammatory cytokines, inhibitor of κBα, target of rapamycin and ribosomal protein S6 kinases 1 mRNA levels were up-regulated, whereas mRNA levels of pro-inflammatory cytokines, nuclear factor kappa B (NF-κB) P65, NF-κB P52, IκB kinase (IKK) α, IKKβ, IKKγ, eIF4E-binding proteins (4E-BP) 1 and 4E-BP2 were down-regulated in the gills of grass carp (P < 0.05), indicating that fish gill immune function was enhanced at an optimal level of dietary protein; (2) the activities and mRNA levels of antioxidant enzymes and glutathione content increased, the contents of reactive oxygen species, malondialdehyde and protein carbonyl (PC) decreased, and NF-E2-related factor 2, B-cell lymphoma protein-2, inhibitor of apoptosis proteins, myeloid cell leukemia-1 and tight junction complexes mRNA levels were up-regulated, whereas Kelch-like-ECH-associated protein (Keap) 1a, Keap1b, cysteinyl aspartic acid-protease 3, 8, 9, fatty acid synthetase ligand, apoptotic protease activating factor-1, Bcl-2 associated X protein, c-Jun N-terminal protein kinase, myosin light chain kinase and p38 mitogen-activated protein kinase mRNA levels were down-regulated in the gills of grass carp (P < 0.05), indicating that the fish gill physical barrier function improved at an optimal level of dietary protein. Finally, based on the gill rot morbidity, ACP activity and PC content, the optimal levels of dietary protein for grass carp were estimated to be 286.65 g kg(-1) diet (253.73 g digestible protein kg(-1) diet), 290.46 g kg(-1) diet (257.76 g digestible protein kg(-1) diet) and 296.25 g kg(-1) diet (260.69 g digestible protein kg(-1) diet), respectively.