ifferential Gene Expression in Zebrafish (Danio rerio) Following Exposure to Gaseous Diffusion Plant Effluent and Effluent Receiving Stream Water

Fulvic acid accelerates hatching and stimulates antioxidative protection and the innate immune response in zebrafish larvae

Aquaculture plays a pivotal role in covering dietary animal protein demands and restocking endangered fish populations. However, high mortality takes place at the earliest life stages: prior and immediately after hatching. Improving growth and health parameters by immunostimulants is widely used in older fish, but rarely studied in larvae. Fulvic acids (FAs) are natural substances found in soil and water. Using zebrafish as a model organism, we evaluated the effects of exposure to a FA at concentrations ranging from 1 to 500 mg C/L (mg dissolved organic carbon per liter) on embryonic development. Furthermore, the concentration of reactive oxygen species (ROS) inside the larvae as well as the molecular mechanisms involved in growth, immune response, and antioxidative protection were determined at 5, 50, and 500 mg C/L. 20 to 200 mg C/L accelerated the hatching, which was mediated by increased expression of ifg-1, gh, and he1-α. Furthermore, lyz and mpx were significantly increased at 5 and 50 mg C/L. A concentration of 500 mg C/L induced genes involved in the protection against ROS (nrf-2, keap-1, cat, sod-1), increased the concentration of ROS inside the larvae and caused tissue damage and mortality. Interestingly, 50 mg C/L activated ROS protection as well (nrf-2, sod-2), while no increase of ROS was found in the larvae. Our results show, that FA at low to medium concentrations can increase the health of larvae, but becomes detrimental at higher concentrations.

Hepatoprotective effects of zinc (II) via cytochrome P-450/reactive oxygen species and canonical apoptosis pathways after arsenite waterborne exposure in common carp

Chronic arsenicosis has threatened the survival of aquatic animals with molecular mechanisms yet clear. In the present study, liver damage was evident by fluctuated activities of transaminases and declined ATPases in common carp under arsenic (As) exposure for 30 days. Mechanically, As significantly decreased cytochrome P-1A (CYP1A) activity and increased reactive oxygen species (ROS) content, which corroborated mitochondrial dysfunction in the hepatocytes. This hypothesis was further suggested by Caspase-3-executed apoptosis by death receptor pathway (Fas, TNF-α and Caspase-8) and mitochondrial pathway (Bax, Bcl-2 and Caspase-9). The above results indicated that As-elicited oxidative damage lead to apoptotic hepatic injury in carp. On the contrary, zinc (Zn) exerted an ROS scavenger and an antidote to As in the present model evidenced by alleviated liver injury and restored liver function index. Moreover, Zn and As co-administration displayed partially recovered CYPs enzyme system and quenched apoptotic positive cells compared As treated alone. These outcomes could be applied to develop counter practices based on Zn preparations to decrease the biotoxicity of As.

Gene expression patterns and related enzymatic activities of detoxification and oxidative stress systems in zebrafish larvae exposed to the 2,4-dichlorophenoxyacetic acid herbicide

The present study aims to assess the effects of 2,4-D herbicide on biotransformation and oxidative stress status of zebrafish larvae. Animals were exposed to a range of sublethal concentrations (0.02-0.8 mg/L) and biomarkers at transcriptomic level and biochemical level were assessed. Chemical analysis with showed that the bioaccumulation of 2,4-D in 96 hpf zebrafish larvae were increased in a concentration-dependent manner. This herbicide induced significant effects at both gene expression and enzymatic activities levels after at 96 hpf. Results of mRNA expression showed a differential transcription regulation with all target genes depending on the tested concentrations. The mRNA level of gsr and cyp1a were up regulated at the highest dose of herbicide (0.8 mg/L). The gene expression of gstp1 showed an up regulation at lower dose (0.02 mg/L) and a down regulation at the highest dose (0.8 mg/L) of 2,4-D. A significant induction of EROD activity and inhibition of GST activity were noted in groups exposed to 0.8 mg/L of 2,4-D. Considering the antioxidant defenses, the activity of CAT was increased in larvae exposed to 0.8 mg/L of herbicide and GPx activity was induced at lower doses of 2,4-D (0.02 and 0.051 mg/L). Moreover, peroxidative damage, assessed as MDA content, was markedly increased in larvae exposed to high 2,4-D concentration. Overall, the present study data indicate that bioaccumulation of 2,4-D in 96 hpf zebrafish larvae and alterations in detoxification and oxidative stress related parameters, likely associated with ROS production, which may endanger the embryo-larval stages development of fish.

Oxidative stress induced by fluoroquinolone enrofloxacin in zebrafish (Danio rerio) can be ameliorated after a prolonged exposure

The purpose of our experiment was to evaluate the effect of enrofloxacin on biotransformation, oxidative stress and mRNA expression of related genes in fish as a non-target organisms. Zebrafish (Danio rerio) juveniles were treated with enrofloxacin at concentrations of 5, 10 and 500 μg/L for 14 days. A three-day-long test caused changes of catalytic activity of glutathione peroxidase and glutathione-S-transferase. Moreover, lipid peroxidation was observed at the highest concentration. No significant changes either in catalytic activity of antioxidant enzymes or elevated lipid peroxidation were observed from sampling day 7 on. mRNA expression of genes encoding antioxidant enzymes was also not affected by enrofloxacin after a 14-day exposure. This suggests the ability of D. rerio juveniles to adapt to enrofloxacin in a short time period. Moreover, enrofloxacin was not shown to affect collagen, cathepsin K, optic atrophy 1 and pyruvate kinase L/R mRNA expression in this study.

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.

Transcriptional profiles of glutathione-S-Transferase isoforms, Cyp, and AOE genes in atrazine-exposed zebrafish embryos

Glutathione-S-transferase (GST) superfamily consists of multiple members involved in xenobiotic metabolism. Expressional pattern of the GST isoforms in adult fish has been used as a biomarker of exposure to environmental chemicals. However, GST transcriptional responses vary across organs, thus requiring a cross-tissue examination of multiple mRNAs for GST profiling in an animal after chemical exposure. Zebrafish embryos express all GST isoforms as adult fish and could therefore represent an alternative model for identification of biomarkers of exposure. To evaluate such a possibility, we studied a set of cytosolic and microsomal GST isoform-specific expression profiles in the zebrafish embryos after exposure to atrazine, a widely used herbicide. Expression of the GST isoforms was compared with that of CYP genes involved in the phase I of xenobiotic metabolism and antioxidant enzyme (AOE) genes. Using quantitative real-time PCR, we showed dynamic changes in the expressional pattern of twenty GST isoforms, cyp1a, cyp3a65, ahr2, and four AOEs in early development of zebrafish. Acute (48 and 72 h) exposure of 24 h-old embryos to atrazine, from environmentally relevant (0.005 mg/L) to high (40 mg/L) concentrations, caused a variety of transient, albeit minor changes (<2.5-fold) in the GST isoforms, ahr2 and AOE genes response. However, expression of cyp1a and cyp3a65 mRNA was markedly and consistently induced by high doses of atrazine (5 and 40 mg/L). In summary, an analysis of the response of multiple systems in the zebrafish embryos provided a comprehensive understanding of atrazine toxicity and its potential impact on biological processes.

Effects of the non-steroidal anti-inflammatory drug(NSAID) naproxen on gene expression of antioxidant enzymes in zebrafish (Danio rerio)

The aim of this study was to investigate the effects of naproxen on the gene expression of antioxidant enzymes in adult zebrafish. Surprisingly, after 2 weeks exposure no significant effect on the mRNA expression of the target genes was found in the liver. However, mRNA levels of three genes were altered significantly in the intestine. The expression of Ucp-2 decreased at the environmental concentration of 1μg/L while mRNA expression of GST p2 increased at the concentration of 100μg/L. The mRNA level for the antioxidant enzyme CAT was up-regulated significantly at both the concentrations used. Exposure to naproxen caused only moderate effects on the expression of antioxidant genes in the intestine rather than in the liver, which demonstrates that the intestine is more sensitive to waterborne naproxen exposure than the liver. Interestingly, the adverse side effects of NSAIDs occur in the gastrointestinal tract of humans. To our knowledge, this is the first study that has focused on transcriptional effects of naproxen on zebrafish.

Gene transcription reflects poor health status of resident European eel chronically exposed to environmental pollutants

Understanding the effects of chronic exposure to pollutants on the genome and transcriptome of diadromous fish populations is crucial for their resilience under combined anthropogenic and environmental selective pressures. The catadromous European eel (Anguilla anguilla L.) has suffered a dramatic decline in recruitment for three decades, necessitating a thorough assessment of the transcriptional effects of environmental pollutants on resident and migrating eels in natural systems. We investigated the relationship between muscular bioaccumulation levels of metals (Hg, Cd, Pb, Cu, Zn, Ni, Cr, As and Se), PCBs and organochlorine pesticides (DDTs), the health status (condition factor and lipid reserves) and the associated transcriptional response in liver and gill tissues for genes involved in metal detoxification (metallothionein, MT) and oxidative metabolism (cytochrome P4501A, CYP1A) of xenobiotic compounds. In total 84 resident eels originating from three Belgian river basins (Scheldt, Meuse and Yzer) were analyzed along with five unpolluted aquaculture samples as control group. There was a large spatial variation in individual contaminant intensity and profile, while tissue pollution levels were strongly and negatively associated with condition indices, suggesting an important impact of pollution on the health of sub-adult resident eels. Gene transcription patterns revealed a complex response mechanism to a cocktail of pollutants, with a high variation at low pollution levels, but strongly down-regulated hepatic and gill gene transcription in highly polluted eels. Resident eels clearly experience a high pollution burden and seem to show a dysfunctional gene transcription regulation of detoxification genes at higher pollutant levels, correlated with low energy reserves and condition. To fully understand the evolutionary implications of pollutants on eel reproductive fitness, analyses of mature migrating eels and the characterization of their transcriptome-wide gene transcription response would be appropriate to unveil the complex responses associated with multiple interacting stressors and the long-term consequences at the entire species level. In the meanwhile, jointly monitoring environmental and tissue pollution levels at a European scale should be initiated, while preserving high quality habitats to increase the recovery chance of European eel in the future.

Temperature dependence of long-term cadmium toxicity in the zebrafish is not explained by liver oxidative stress: evidence from transcript expression to physiology

Standard ecotoxicity tests are performed at species' specific standard temperatures, but temperature is known to affect chemical toxicity. A temperature increase has been shown to increase cadmium toxicity in several aquatic species but information in fish is scarce. Based on literature we hypothesize that with increasing temperature, cadmium accumulation and oxidative stress increase, resulting in increased toxicity. In this study zebrafish acclimated to 12, 18, 26 (standard temperature) or 34°C for one month, were exposed to 5 μM cadmium for 4 or 28 days at the respective acclimation temperature. Cadmium toxicity (mortality) increased with increasing temperature. PCA showed that the high mortality at 34°C was closely correlated to an increasing tissue cadmium accumulation with increasing temperature, but not to liver oxidative damage under the form of protein carbonyl content or lipid peroxidation (measured as malondialdehyde levels) or liver antioxidative potential. Instead, acclimation to 12°C induced the highest oxidative damage to liver proteins and lipids, and transcript levels of glucose-6P-dehydrogenase, 6P-gluconate-dehydrogenase and glutathione peroxidase were particularly good markers of cold-induced oxidative stress. At this low temperature there was no interaction with cadmium exposure and there was no sign of cadmium sensitivity. Contrastingly, the combined effect of high temperature and cadmium exposure on mortality proved synergistic. Therefore we conclude that interactions between temperature and cadmium toxicity increased with increasing temperature and that this probably played part in increasing cadmium sensitivity. Increased cadmium compartmentalization and protein carbonyl content in liver of zebrafish acclimated to the standard temperature of 26°C probably played part in increased sensitivity towards the same cadmium body burden compared to lower temperatures. On the one hand we recognize and this study even confirms the importance of applying standard temperatures in standard ecotoxicity tests to ensure inter-study comparability. On the other hand temperatures in the field may deviate from standard temperatures and accounting for deviating temperatures, which can alter chemical sensitivity, in regulation can improve environmental protection.

Transcriptomic analyses in a benthic fish exposed to contaminated estuarine sediments through laboratory and in situ bioassays

The transcription of contaminant response-related genes was investigated in juvenile Senegalese soles exposed to sediments from three distinct sites (a reference plus two contaminated) of a Portuguese estuary (the Sado, W Portugal) through simultaneous 28-day laboratory and in situ bioassays. Transcription of cytochrome P450 1A (CYP1A), metallothionein 1 (MT1), glutathione peroxidase (GPx), catalase (CAT), caspase 3 (CASP3) and 90 kDa heat-shock protein alpha (HSP90AA) was surveyed in the liver by real-time PCR. CASP3 transcription analysis was complemented by surveying apoptosis through the TUNEL reaction. After 14 days of exposure, relative transcription was either reduced or decreased in fish exposed to the contaminated sediments, revealing a disturbance stress phase during which animals failed to respond to insult. After 28 days of exposure all genes' transcription responded to contamination but laboratory and in situ assays depicted distinct patterns of regulation. Although sediments revealed a combination of organic and inorganic toxicants, transcription of the CYP1A gene was consistently correlated to organic contaminants. Metallothionein regulation was found correlated to metallic and organic xenobiotic contamination in the laboratory and in situ, respectively. The transcription of oxidative stress-related genes can be a good indicator of general stress but caution is mandatory when interpreting the results since regulation may be influenced by multiple factors. As for MT1, HSP90 up-regulation has potential to be a good indicator for total contamination, as well as the CASP3 gene, even though hepatocyte apoptosis depicted values inconsistent with sediment contamination, showing that programmed cell death did not directly depend on caspase transcription alone.