Differential gene expression in rainbow trout (Oncorhynchus mykiss) liver and ovary after exposure to zearalenone

High-Resolution Magic Angle Spinning (HRMAS) NMR Identifies Oxidative Stress and Impairment of Energy Metabolism by Zearalenone in Embryonic Stages of Zebrafish (Danio rerio), Olive Flounder (Paralichthys olivaceus) and Yellowtail Snapper (Ocyurus chrysurus)

Zearalenone (ZEA) is a mycotoxin, commonly found in agricultural products, linked to adverse health impacts in humans and livestock. However, less is known regarding effects on fish as both ecological receptors and economically relevant "receptors" through contamination of aquaculture feeds. In the present study, a metabolomics approach utilizing high-resolution magic angle spinning nuclear magnetic resonance (HRMAS NMR) was applied to intact embryos of zebrafish (Danio rerio), and two marine fish species, olive flounder (Paralichthys olivaceus) and yellowtail snapper (Ocyurus chrysurus), to investigate the biochemical pathways altered by ZEA exposure. Following the assessment of embryotoxicity, metabolic profiling of embryos exposed to sub-lethal concentrations showed significant overlap between the three species and, specifically, identified metabolites linked to hepatocytes, oxidative stress, membrane disruption, mitochondrial dysfunction, and impaired energy metabolism. These findings were further supported by analyses of tissue-specific production of reactive oxygen species (ROS) and lipidomics profiling and enabled an integrated model of ZEA toxicity in the early life stages of marine and freshwater fish species. The metabolic pathways and targets identified may, furthermore, serve as potential biomarkers for monitoring ZEA exposure and effects in fish in relation to ecotoxicology and aquaculture.

Co-Occurrence and Levels of Mycotoxins in Fish Feeds in Kenya

This study determined the presence, levels and co-occurrence of mycotoxins in fish feeds in Kenya. Seventy-eight fish feeds and ingredients were sampled from fish farms and fish feed manufacturing plants and analysed for 40 mycotoxins using high-performance liquid chromatography-high resolution mass spectrometry. Twenty-nine (73%) mycotoxins were identified with 76 (97%) samples testing positive for mycotoxins presence. Mycotoxins with the highest prevalences were enniatin B (91%), deoxynivalenol (76%) and fumonisin B1 (54%) while those with the highest maximum levels were sterigmatocystin (<30.5-3517.1 µg/kg); moniliformin (<218.9-2583.4 µg/kg) and ergotamine (<29.3-1895.6 µg/kg). Mycotoxin co-occurrence was observed in 68 (87%) samples. Correlations were observed between the fumonisins; enniatins B and zearalenone and its metabolites. Fish dietary exposure estimates ranged between <0.16 and 43.38 µg/kg body weight per day. This study shows evidence of mycotoxin presence and co-occurrence in fish feeds and feed ingredients in Kenya. Fish exposure to these levels of mycotoxins over a long period of time may lead to adverse health effects due to their possible additive, synergistic or antagonist toxic effects. Measures to reduce fish feed mycotoxin contamination should be taken to avoid mycotoxicosis in fish and subsequently in humans and animals through residues.

Toxicity of mycotoxins in vivo on vertebrate organisms: A review

Mycotoxins are considered to be a major risk factor affecting human and animal health as they are one of the most dangerous contaminants of food and feed. This review aims to compile the research developed up to date on the toxicological effects that mycotoxins can induce on human health, through the examination of a selected number of studies in vivo. AFB1 shows to be currently the most studied mycotoxin in vivo, followed by DON, ZEA and OTA. Scarce data was found for FBs, PAT, CIT, AOH and Fusarium emerging mycotoxins. The majority of them concerned the investigation of immunotoxicity, whereas the rest consisted in the study of genotoxicity, oxidative stress, hepatotoxicity, cytotoxicity, teratogenicity and neurotoxicity. In order to assess the risk, a wide range of different techniques have been employed across the reviewed studies: qPCR, ELISA, IHC, WB, LC-MS/MS, microscopy, enzymatic assays, microarray and RNA-Seq. In the last decade, the attention has been drawn to immunologic and transcriptomic aspects of mycotoxins' action, confirming their toxicity at molecular level. Even though, more in vivo studies are needed to further investigate their mechanism of action on human health.

Fish as a model to assess chemical toxicity in bone

Environmental toxicology has been expanding as growing concerns on the impact of produced and released chemical compounds over the environment and human health are being demonstrated. Among the toxic effects observed in organisms exposed to pollutants, those affecting skeletal tissues (osteotoxicity) have been somehow overlooked in comparison to hepato-, immune-, neuro- and/or reproductive toxicities. Nevertheless, sub-lethal effects of toxicants on skeletal development and/or bone maintenance may result in impaired growth, reduced survival rate, increased disease susceptibility and diminished welfare. Osteotoxicity may occur by acute or chronic exposure to different environmental insults. Because of biologically and technically advantagous features - easy to breed and inexpensive to maintain, external and rapid rate of development, translucent larvae and the availability of molecular and genetic tools - the zebrafish (Danio rerio) has emerged in the last decade as a vertebrate model system of choice to evaluate osteotoxicity. Different experimental approaches in fish species and analytical tools have been applied, from in vitro to in vivo systems, from specific to high throughput methodologies. Current knowledge on osteotoxicity and underlying mechanisms gained using fish, with a special emphasis on zebrafish systems, is reviewed here. Osteotoxicants have been classified into four categories according to the pathway involved in the transduction of the osteotoxic effects: activation/inhibition of membrane and/or nuclear receptors, alteration of redox condition, mimicking of bone constituents and unknown pathways. Knowledge on these pathways is also reported here as it may provide critical insights into the development, production and release of future chemical compounds with none or low osteotoxicity, thus promoting the green/environmental friendly chemistry.

Gene Expression Profiling in Fish Toxicology: A Review

In this review, we present an overview of transcriptomic responses to chemical exposures in a variety of fish species. We have discussed the use of several molecular approaches such as northern blotting, differential display reverse transcription-polymerase chain reaction (DDRT-PCR), suppression subtractive hybridization (SSH), real time quantitative PCR (RT-qPCR), microarrays, and next-generation sequencing (NGS) for measuring gene expression. These techniques have been mainly used to measure the toxic effects of single compounds or simple mixtures in laboratory conditions. In addition, only few studies have been conducted to examine the biological significance of differentially expressed gene sets following chemical exposure. Therefore, future studies should focus more under field conditions using a multidisciplinary approach (genomics, proteomics and metabolomics) to understand the synergetic effects of multiple environmental stressors and to determine the functional significance of differentially expressed genes. Nevertheless, recent developments in NGS technologies and decreasing costs of sequencing holds the promise to uncover the complexity of anthropogenic impacts and biological effects in wild fish populations.

Proteomic analysis of anatoxin-a acute toxicity in zebrafish reveals gender specific responses and additional mechanisms of cell stress

Anatoxin-a is a potent neurotoxin produced by several genera of cyanobacteria. Deaths of wild and domestic animals due to anatoxin-a exposure have been reported following a toxic response that is driven by the inhibition of the acetylcholine receptors at neuromuscular junctions. The consequent neuron depolarization results in an overstimulation of the muscle cells. In order to unravel further molecular events implicated in the toxicity of anatoxin-a, a proteomic investigation was conducted. Applying two-dimensional gel electrophoresis (2DE) and MALDI-TOF mass spectrometry, we report early proteome changes in brain and muscle of zebrafish (Danio rerio) caused by acute exposure to anatoxin-a. In this regard, the test group of male and female zebrafish received an intraperitoneal (i.p.) injection of an anatoxin-a dose of 0.8µgg(-1) of fish body weight (bw) in phosphate buffered saline solution (PBS), while the control received an i.p. injection of PBS only. Five minutes after i.p. injection, brain and muscle tissues were collected, processed and analyzed with 2DE. Qualitative and quantitative analyzes of protein abundance allowed the detection of differences in the proteome of control and exposed fish groups, and between male and female fish (gender specific responses). The altered proteins play functions in carbohydrate metabolism and energy production, ATP synthesis, cell structure maintenance, cellular transport, protein folding, stress response, detoxification and protease inhibition. These changes provide additional insights relative to the toxicity of anatoxin-a in fish. Taking into account the short time of response considered (5min of response to the toxin), the changes in the proteome observed in this work are more likely to derive from fast occurring reactions in the cells. These could occur by protein activity regulation through degradation (proteolysis) and/or post-translational modifications, than from a differential regulation of gene expression, which may require more time for proteins to be synthesized and to produce changes at the proteomic level.

Joint MiRNA/mRNA expression profiling reveals changes consistent with development of dysfunctional corpus luteum after weight gain

Obese women exhibit decreased fertility, high miscarriage rates and dysfunctional corpus luteum (CL), but molecular mechanisms are poorly defined. We hypothesized that weight gain induces alterations in CL gene expression. RNA sequencing was used to identify changes in the CL transcriptome in the vervet monkey (Chlorocebus aethiops) during weight gain. 10 months of high-fat, high-fructose diet (HFHF) resulted in a 20% weight gain for HFHF animals vs. 2% for controls (p = 0.03) and a 66% increase in percent fat mass for HFHF group. Ovulation was confirmed at baseline and after intervention in all animals. CL were collected on luteal day 7-9 based on follicular phase estradiol peak. 432 mRNAs and 9 miRNAs were differentially expressed in response to HFHF diet. Specifically, miR-28, miR-26, and let-7b previously shown to inhibit sex steroid production in human granulosa cells, were up-regulated. Using integrated miRNA and gene expression analysis, we demonstrated changes in 52 coordinately regulated mRNA targets corresponding to opposite changes in miRNA. Specifically, 2 targets of miR-28 and 10 targets of miR-26 were down-regulated, including genes linked to follicular development, steroidogenesis, granulosa cell proliferation and survival. To the best of our knowledge, this is the first report of dietary-induced responses of the ovulating ovary to developing adiposity. The observed HFHF diet-induced changes were consistent with development of a dysfunctional CL and provide new mechanistic insights for decreased sex steroid production characteristic of obese women. MiRNAs may represent novel biomarkers of obesity-related subfertility and potential new avenues for therapeutic intervention.

Hypoxia and the pharmaceutical diclofenac influence the circadian responses of three-spined stickleback

Pollution with low concentrations of pharmaceuticals, especially when combined with low-oxygen conditions (hypoxia), is a threat to aquatic ecosystems worldwide. The non-steroidal anti-inflammatory drug diclofenac is commonly detected in wastewater effluents, and has potential to accumulate in the bile of fish. Diclofenac has been shown to activate aryl hydrocarbon receptor (AHR), which induces transcription in the metabolic enzyme cytochrome P450 1a (cyp1a). Previously, crosstalk has been shown to occur between AHR and hypoxia inducible factor 1 (HIF-1). In addition, both of these transcription factors interact with the proteins regulating circadian (24-h) rhythms in vertebrates. Yet little is known about the significance of these interactions during simultaneous exposure to chemicals and hypoxia in fish in vivo. We exposed wild-caught three-spined sticklebacks (Gasterosteus aculeatus) to diclofenac (1 μg/L, 14 days), hypoxia (2.0 mg/L, up to 24h) and the combination of both. We then analyzed markers of chemical biotransformation (EROD activity, cyp1a and ahr mRNA levels), glycolysis (lactate dehydrogenase (LDH) enzyme activity, ldh and enolase 1a mRNA levels), and the transcription of core circadian clock genes clock and period 1 in liver tissue. Samples were taken at three time points during the light period in order to address disturbances in the circadian variation of metabolic processes. The results show that mRNA levels and LDH activity tended to be lowest before the dark period, but this pattern was disturbed by hypoxia and diclofenac. Diclofenac and hypoxia co-exposure induced EROD activity more strongly than diclofenac exposure alone, while cyp1a mRNA level was increased also by hypoxia and diclofenac alone. LDH activity and mRNA expression showed a clear time-dependent response during hypoxia, which is consistent with the previously suggested decreased accumulation of HIF-1 during the dark period. Furthermore, LDH activity and transcription was disturbed by diclofenac, indicating important effects of environmental pollutants in disturbing natural acclimation. This study demonstrates the need for more studies to understand the potential disturbances in endogenous rhythms caused by environmental pollution in natural populations.

Developmental toxicity and estrogenic potency of zearalenone in zebrafish (Danio rerio)

Zearalenone (ZEA, F2) is one of the most common mycotoxins and the only known mycoestrogen. It enters the food and feed chain from contaminated cereals and infiltrates into sewage or natural waters posing potential threat to exposed livestock, wildlife and humans. Therefore evaluation of its biological effects is of international importance. We performed toxicological tests on zebrafish (Danio rerio) larvae and adults. Developmental toxicity was assessed by an extended (5 days) fish embryo toxicity test (FET). Effects of early ZEA exposure were concentration-dependent with LC50 and LC10 values of 893 and 335 μg/L. In larvae exposed to 500 μg/L and above, ZEA induced similar phenotype to has (heart-and soul) showing defects in heart and eye development and upward curvature of the body axis. From 250 μg/L at 72 hpf the gap in the melanophore streak at the base of the tail fin was missing and the fin fold was abnormal, suggesting disturbance in the development of the adult tail fin primordium. Estrogenic potency was measured on the basis of Vitellogenin (Vtg) protein (adults) levels and relative abundance of vitellogenin-1 mRNA (vtg-1) (larvae and adults). qRT-PCR in larvae proved to be sufficient substitute to adult tests and sensitive enough to detect ZEA in 0.1 μg/L concentrations, that is close to levels observed in wastewaters. Developmental defects reveal that besides direct estrogenic effects, zearalenone might interact with other ontogenic pathways.

Expression profiling in vivo demonstrates rapid changes in liver microRNA levels of whitefish (Coregonus lavaretus) following microcystin-LR exposure

At present, little is known about the role of miRNAs in liver response of fish to the cyanobacterial hepatotoxin microcystin-LR (MC-LR) treatment, despite the fact that the exposure is thought to underlie multiple acute and chronic effects. To address this question, we used the Real-Time PCR method to examine the differential expression of 6 miRNAs putatively playing roles in signal transduction (let-7c, miR-9b), apoptosis and cell cycle (miR-16a, miR-21a, miR-34a) and fatty acid metabolism (miR-122) in whitefish (Coregonus lavaretus) liver, during the first 48h after intraperitoneal injection of MC-LR (100 μg/kg body weight). In addition, we analyzed expression levels of 8 mRNAs and p53 protein, known to be involved in the cell response on the exposure to environmental stressors. Following the challenge we observed a rapid and transient increase in the mean (n=5) levels of individual miRNA expression (from 2.7-fold for miR-122 to 6.8-fold for let-7c), compared to the respective levels in control fish, which mostly peaked at 24h of the experiment. This increase was correlated with a reduction in the expression of mRNAs of genes coding for ferritin H (frih) and HNK Ras -like protein (p-ras) and an overexpression of mRNAs of genes coding for bcl2-associated X protein (bax), cyclin dependent kinase inhibitor 1a (cdkn1a), dicer (dcr), histone 2A (h2a) and p53. Expression of the remaining caspase 6 (cas6) mRNA did not change over 48 h of the treatment. Moreover, exposure to MC-LR did not alter whitefish p53 protein levels. Bearing in mind a variety of likely silencing targets for, and the onset of, the aberrant miRNA expression it may be concluded that they are involved in molecular pathways, such as liver cell metabolism, cell cycle regulation and apoptosis, and may contribute to the early phase of MC-LR induced hepatotoxicity.