Responses of the Proteome and Metabolome in Livers of Zebrafish Exposed Chronically to Environmentally Relevant Concentrations of Microcystin-LR

Microcystin-LR induces ferroptosis in intestine of common carp (Cyprinus carpio)

Previous studies provide comprehensive evidence of the environmental hazards and intestinal toxicity of microcystin-LR (MC-LR) exposure. However, little is known about the mechanisms underlying the injury of intestine exposed to MC-LR. Juvenile common carp (Cyprinus carpio) were exposed to MC-LR (0 and 10 μg/L) for 15 days. The results suggest that organic anion-transporting polypeptides 3a1, 4a1, 2b1, and 1d1 mediate MC-LR entry into intestinal tissues. Lesion morphological features (vacuolization, deformation and dilation of the endoplasmic reticulum [ER], absence of mitochondrial cristae in mid-intestine), up-regulated mRNA expressions of ER stress (eukaryotic translation initiation factor 2-alpha kinase 3, endoplasmic reticulum to nucleus signaling 1, activating transcription factor [ATF] 6, ATF4, DNA damage-inducible transcript 3), iron accumulation, and down-regulated activity of glutathione peroxidase (GPx) and glutathione (GSH) content were all typical characteristics of ferroptosis in intestinal tissue following MC-LR exposure. GSH levels in intestinal tissue corroborated as the most influential GSH/GPx 4- related metabolic pathway in response to MC-LR exposure. Verrucomicrobiota, Planctomycetes, Bdellovibrionota, Firmicutes and Cyanobacteria were correlated with the ferroptosis-related GSH following MC-LR exposure. These findings provide new perspectives of the ferroptosis mechanism of MC-LR-induced intestinal injury in the common carp.

Mass Spectrometry-Based Zebrafish Toxicometabolomics: A Review of Analytical and Data Quality Challenges

Metabolomics has achieved great progress over the last 20 years, and it is currently considered a mature research field. As a result, the number of applications in toxicology, biomarker, and drug discovery has also increased. Toxicometabolomics has emerged as a powerful strategy to provide complementary information to study molecular-level toxic effects, which can be combined with a wide range of toxicological assessments and models. The zebrafish model has gained importance in recent decades as a bridging tool between in vitro assays and mammalian in vivo studies in the field of toxicology. Furthermore, as this vertebrate model is a low-cost system and features highly conserved metabolic pathways found in humans and mammalian models, it is a promising tool for toxicometabolomics. This short review aims to introduce zebrafish researchers interested in understanding the effects of chemical exposure using metabolomics to the challenges and possibilities of the field, with a special focus on toxicometabolomics-based mass spectrometry. The overall goal is to provide insights into analytical strategies to generate and identify high-quality metabolomic experiments focusing on quality management systems (QMS) and the importance of data reporting and sharing.

Cell density-dependent regulation of microcystin synthetase genes (mcy) expression and microcystin-LR production in Microcystis aeruginosa that mimics quorum sensing

As the secondary metabolites of cyanobacterial harmful algal blooms (Cyano-HABs), microcystins (MCs) were generated under various environmental and cellular conditions. The understanding of the causes of MCs generation is of great interest in the field of water treatment and environmental science. In this work, we studied how Microcystis aeruginosa (FACHB-905) cell densities affect the MCs synthetase genes (mcy) expression, microcystin-LR (MC-LR) and quorum sensing molecules (Acyl-homoserine lactones (AHLs)) production. An electrochemical sensor was developed here for sensitive and quantitative detection of MC-LR that cultured at different cell densities. The results showed that mcy expression and MC-LR concentration started to increase when the cell density reached ca. 22 × 10⁶ cells/mL, and was significantly increased with increasing cell densities. Moreover, the up-regulation of AHLs with increasing cell densities revealed that MC-LR is quorum sensing-mediated. Our results undoubtedly confirmed that MC-LR was produced in a cell density-dependent way that mimics quorum sensing, and the minimum cell density (ca. 22 × 10⁶ cells/mL) that was required to produce MC-LR was provided and offered a reference standard for the prevention and control of MCs pollution in the actual water environment.

Effects of environmental contaminants in water resources on nonalcoholic fatty liver disease

The global prevalence of nonalcoholic fatty liver disease (NAFLD) has been increasing rapidly in recent years, which is now estimated to be over 25%. NAFLD is one of the most common chronic liver diseases in the world. At present, with the rapid development of economy and industrialization, many chemicals are released into the environment. These chemical contaminants in the environment might cause harm to human health and result in lipid metabolism disorder during long-term exposure. Moreover, the incentive of many NAFLD cases is unknown, and the environmental risk factors of NAFLD need to be urgently identified. Hence, we focus on the impacts of several popular environmental contaminants in water environment on the development and progression of NAFLD. These contaminants mainly include microcystins (MCs), disinfection by-products (DBPs), heavy metals (HMs), dioxins and polychlorinated biphenyls (PCBs). Through analyzing a great many epidemiological and toxicological studies, we have found positive associations between NAFLD and chronic exposure to these contaminants at the environmental levels. This review may enhance the understanding of liver damage caused by environmental pollutants, which are considered as tangible environmental risk factors for NAFLD.

Advances in the toxicology research of microcystins based on Omics approaches

Microcystins (MCs) are the most widely distributed cyanotoxins, which can be ingested by animals and human body in multiple ways, resulting in a threat to human health and the biodiversity of wildlife. Therefore, the study on toxic effects and mechanisms of MCs is one of the focuses of attention. Recently, the Omics techniques, i.e. genomics, transcriptomics, proteomics and metabolomics, have significantly contributed to the comprehensive understanding and revealing of the molecular mechanisms about the toxicity of MCs. This paper mainly reviews current literature using the Omics approaches to explore the toxicity mechanism of MCs in liver, gonad, spleen, brain, intestine and lung of multiple species. It was found that MCs can exert strong toxic effects on various metabolic activities and cell signal transduction in cell cycle, apoptosis, destruction of cell cytoskeleton and redox disorder, at protein, transcription and metabolism level. Meanwhile, it was also revealed that the alteration of non-coding RNAs (miRNA, circRNA and lncRNA, etc.) and gut microbiota plays an essential regulatory role in the toxic effects of MCs, especially in hepatotoxicity and reproductive toxicity. In addition, we summarized current research gaps and pointed out the future directions for research. The detailed information in this paper shows that the application and development of Omics techniques have significantly promoted the research on MCs toxicity, and it is also a valuable resource for exploring the toxic mechanism of MCs.

Promotion effect of microcystin-LR on liver tumor progression in krasV12 transgenic zebrafish following acute or subacute exposure

Microcystin-LR (MC-LR) is widely distributed in the natural environment and causes hepatotoxicity. However, whether MC-LR promotes liver tumor progression remains controversial. krasV12 transgenic zebrafish were used as an inducible liver tumor model to evaluate the potential tumor-promoting effect of MC-LR. First, krasV12 transgenic larvae were exposed to 0, 0.1 and 1 mg/L MC-LR with 20 mg/L doxycycline (Dox) for 4 d. The gray values and histopathological examinations of the liver demonstrated that MC-LR aggravated liver tumor progression, which could be inhibited by the Protein arginine methyltransferase 5 (Prmt5) inhibitor compound 5 (CMP5). Second, 1-month-old juvenile transgenic zebrafish were exposed to 0, 20 mg/L Dox, 1 μg/L MC-LR, and 20 mg/L Dox with 0.1 or 1 μg/L MC-LR for 15 d to determine whether the exposure to environmental concentrations of MC-LR promoted hepatocellular carcinoma (HCC) progression. We found that environmental concentrations of MC-LR increased the hepatosomatic index (HSI) and gray value (intensity/area) and promoted HCC progression. The results indicate that environmental concentrations of MC-LR have the potential to promote liver tumor progression. Taken together, the present study demonstrates that MC-LR can promote tumor in krasV12 transgenic zebrafish and that the upregulation of prmt5 expression might contribute to MC-LR-mediated promotion of liver tumorigenesis.

Effects of acute exposure to microcystins on hypothalamic-pituitary-adrenal (HPA), -gonad (HPG) and -thyroid (HPT) axes of female rats

Microcystins (MCs) are common, well-known cyanobacterial toxins that can affect health of humans. Recently, it has been reported that MCs affect endocrine functions. In the present study, for the first time, histopathology, concentrations of hormones and transcription of genes along the hypothalamic-pituitary-adrenal (HPA), hypothalamic-pituitary-gonad (HPG) and hypothalamic-pituitary-thyroid (HPT) axes were examined in rats exposed to microcystin-LR (MC-LR). Female, Sprague-Dawley (SD) rats were exposed acutely to MC-LR by a single intraperitoneal (i.p.) injection at doses of 0.5, 0.75, or 1 median lethal dose (LD₅₀), i.e. 36.5, 54.75, or 73 μg MC-LR/kg body mass (bm) then euthanized 24 hours after exposure. Acute exposure to MC-LR significantly increased relative mass of adrenal in a dose-dependent manner, but relative mass of hypothalamus, pituitary, ovary and thyroid were not significantly different from respective mass in controls. However, damage to all these tissues was observed by histology. Along the HPA axis, lesser concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were observed in blood serum of exposed individuals, relative to controls. For the HPG axis, concentrations of gonadotropin-releasing hormone (GnRH) and estradiol (E2) were significantly less in rats treated with MC-LR, but greater concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone (T) were observed. Along the HPT axis, MC-LR caused greater concentrations of thyroid-stimulating hormone (TSH), but lesser concentrations of thyrotropin-releasing hormone (TRH), free tetra-iodothyronine (fT4) and tri-iodothyronine (fT3). Significant positive/negative correlations of concentrations of hormones were observed among the HPA, HPG and HPT axes. In addition, profiles of transcription of genes for synthesis of hormones along the endocrine axes and nuclear hormone receptors in adrenal, ovary and thyroid were significantly altered. Therefore, these results suggested that MC-LR affected HPA, HPG and HPT axes and exerted endocrine-disrupting effects. Effects of MC-LR on crosstalk among these three axes need further studies.

The dynamics and release characteristics of microcystins in the plateau Lake Erhai, Southwest China

Microcystins (MCs) have seriously polluted drinking water supplies and have caused great harm to aquatic organisms and humans. Understanding the dynamics of MC concentrations and its influencing factors is necessary for drinking water safety. Many previous studies on MC pollution focused on intracellular MCs rather than on extracellular MCs, which are more difficult to remove by water treatment. So far, the release characteristics of MCs and the relationships between intracellular and extracellular MCs are still unclear. To explore these questions, a survey was conducted at 18 sites across Lake Erhai from May 2014 to April 2015 as in Lake Erhai the frequency and coverage area of cyanobacterial blooms have been increasing. Variation of extracellular MCs lagged behind that of intracellular MCs. The highest value of intracellular MCs was 1.07 μg L-1 in October 2014 and the highest extracellular MC concentration was 0.035 μg L-1 in November 2014. Intracellular MCs were positively influenced by MC-producing cyanobacterial biomass, water temperature (WT), pH, and conductivity (Cond). The extracellular MCs showed little correlation with cyanobacterial abundances and intracellular MC concentrations, but showed significant negative correlations with WT, pH, and Cond. These results indicated that high biomass and high intracellular MC concentrations did not quickly lead to large releases of MCs, and that when cyanobacterial cells died and blooms disappeared, MCs were intensively released into the water, posing the greatest threat to drinking water supply.

Challenges of using blooms of Microcystis spp. in animal feeds: A comprehensive review of nutritional, toxicological and microbial health evaluation

Microcystis spp., are Gram-negative, oxygenic, photosynthetic prokaryotes which use solar energy to convert carbon dioxide (CO₂) and minerals into organic compounds and biomass. Eutrophication, rising CO₂ concentrations and global warming are increasing Microcystis blooms globally. Due to its high availability and protein content, Microcystis biomass has been suggested as a protein source for animal feeds. This would reduce dependency on soybean and other agricultural crops and could make use of "waste" biomass when Microcystis scums and blooms are harvested. Besides proteins, Microcystis contain further nutrients including lipids, carbohydrates, vitamins and minerals. However, Microcystis produce cyanobacterial toxins, including microcystins (MCs) and other bioactive metabolites, which present health hazards. In this review, challenges of using Microcystis blooms in feeds are identified. First, nutritional and toxicological (nutri-toxicogical) data, including toxicity of Microcystis to mollusks, crustaceans, fish, amphibians, mammals and birds, is reviewed. Inclusion of Microcystis in diets caused greater mortality, lesser growth, cachexia, histopathological changes and oxidative stress in liver, kidney, gill, intestine and spleen of several fish species. Estimated daily intake (EDI) of MCs in muscle of fish fed Microcystis might exceed the provisional tolerable daily intake (TDI) for humans, 0.04 μg/kg body mass (bm)/day, as established by the World Health Organization (WHO), and is thus not safe. Muscle of fish fed M. aeruginosa is of low nutritional value and exhibits poor palatability/taste. Microcystis also causes hepatotoxicity, reproductive toxicity, cardiotoxicity, neurotoxicity and immunotoxicity to mollusks, crustaceans, amphibians, mammals and birds. Microbial pathogens can also occur in blooms of Microcystis. Thus, cyanotoxins/xenobiotics/pathogens in Microcystis biomass should be removed/degraded/inactivated sufficiently to assure safety for use of the biomass as a primary/main/supplemental ingredient in animal feed. As an ameliorative measure, antidotes/detoxicants can be used to avoid/reduce the toxic effects. Before using Microcystis in feed ingredients/supplements, further screening for health protection and cost control is required.

Update on the adverse effects of microcystins on the liver

Microcystins (MCs) are the most common cyanobacteria toxins in eutrophic water, which have strong hepatotoxicity. In the past decade, epidemiological and toxicological studies on liver damage caused by MCs have proliferated, and new mechanisms of hepatotoxicity induced by MCs have also been discovered and confirmed. However, there has not been a comprehensive and systematic review of these new findings. Therefore, this paper summarizes the latest advances in studies on the hepatotoxicity of MCs to reveal the effects and mechanisms of hepatotoxicity induced by MCs. Current epidemiological studies have confirmed that symptoms or signs of liver damage appear after human exposure to MCs, and a long time of exposure can even lead to liver cancer. Toxicological studies have shown that MCs can affect the expression of oncogenes by activating cell proliferation pathways such as MAPK and Akt, thereby promoting the occurrence and development of cancer. The latest evidence shows that epigenetic modifications may play an important role in MCs-induced liver cancer. MCs can cause damage to the liver by inducing hepatocyte death, mainly manifested as apoptosis and necrosis. The imbalance of liver metabolic homeostasis may be involved in hepatotoxicity induced by MCs. In addition, the combined toxicity of MCs and other toxins are also discussed in this article. This detailed information will be a valuable reference for further exploring of MCs-induced hepatotoxicity.

Short- and medium-term exposures of diazepam induce metabolomic alterations associated with the serotonergic, dopaminergic, adrenergic and aspartic acid neurotransmitter systems in zebrafish (Danio rerio) embryos/larvae

INTRODUCTION

Diazepam is a well-known psychoactive drug widely used worldwide for the treatment of anxiety, seizures, alcohol withdrawal syndrome, muscle spasms, sleeplessness, agitation, and pre/post-operative sedation. It is part of the benzodiazepine family, substances known to primarily act by binding and enhancing gamma-aminobutyric acid (GABA_A) receptors. The objective of the present work was to investigate the influence of short and medium-term diazepam exposures on neurotransmitters measured through targeted metabolomics using a zebrafish embryo model.

METHODS

Short-term (2.5 h) and medium-term (96 h) exposures to diazepam were performed at drug concentrations of 0.8, 1.6, 16, and 160 μg/L. Intervention groups were compared with a vehicle control group. Each group consisted of 20 zebrafish eggs/larvae. Metabolites related with neurotransmission were determined by ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS).

RESULTS

Thirty-six compounds were quantified. Significantly increased tryptophan and serotonin concentrations were found in the intervention groups receiving higher doses of diazepam in 2.5 h exposure (p < 0.05 control versus intervention groups). Tyrosine concentrations were higher (p < 0.05) at higher concentrations in 2.5 h exposure, but lower (p < 0.05) at higher concentrations in 96 h exposure. Both phenylalanine and aspartic acid concentrations were higher (p < 0.05) at higher doses in 2.5 h and 96 h exposure.

CONCLUSIONS

Short- and medium-term exposures to diazepam induce dose- and time-dependent metabolomic alterations associated with the serotonergic, dopaminergic/adrenergic, and aspartic acid neurotransmitter systems in zebrafish.

Ecological and toxicological assessments of anthropogenic contaminants based on environmental metabolomics

There has long been a great concern with growing anthropogenic contaminants and their ecological and toxicological effects on living organisms and the surrounding environment for decades. Metabolomics, a functional readout of cellular activity, can capture organismal responses to various contaminant-related stressors, acquiring direct signatures to illustrate the environmental behaviours of anthropogenic contaminants better. This review entails the application of metabolomics to profile metabolic responses of environmental organisms, e.g. animals (rodents, fish, crustacean and earthworms) and microorganisms (bacteria, yeast and microalgae) to different anthropogenic contaminants, including heavy metals, nanomaterials, pesticides, pharmaceutical and personal products, persistent organic pollutants, and assesses their ecotoxicological impacts with regard to literature published in the recent five years. Contaminant-induced metabolism alteration and up/down-regulation of metabolic pathways are revealed in typical organisms. The obtained insights of variations in global metabolism provide a distinct understanding of how anthropogenic contaminants exert influences on specific metabolic pathways on living organisms. Thus with a novel ecotechnique of environmental metabolomics, risk assessments of anthropogenic contaminants are profoundly demonstrated.

Hepatic oxidative stress and neurotoxicity in Pelophylax kl. esculentus frogs: Influence of long-term exposure to a cyanobacterial bloom

Although the long-term exposure of aquatic organisms to cyanobacterial blooms is a regular occurrence in the environment, the prooxidant and neurotoxic effects of such conditions are still insufficiently investigated in situ. We examined the temporal dynamics of the biochemical parameters in the liver of Pelophylax kl. esculentus frogs that inhabit the northern (N) side of Lake Ludaš (Serbia) with microcystins (MCs) produced in a cyanobacterial bloom over three summer months. The obtained data were compared with data on frogs that live on the southern (S), MC-free side of the same lake. Our results showed that the MC-producing bloom induced oxidative damage to proteins and lipids, observed as a decrease in the concentration of protein -SH groups and increased lipid peroxidation (LPO) in the liver of N frogs in comparison to S frogs. Glutathione (GSH) played a key role in the transient defense against the MC-induced development of LPO. The low glutathione peroxidase (GPx) activity detected in all groups of frogs from the N site was crucial for the observed prooxidant consequences. The bloom impaired cholinergic homeostasis as a result of a decrease in ChE activity. A delayed neurotoxic effect in relation to the prooxidant outcomes was observed. Our results also showed that even though the integrated biomarker response (IBR) of the antioxidant biomarkers increased during exposure, the individual biochemical parameters did not exhibit a well-defined time-dependent pattern because of specific adaptation dynamics and/or additional effects of the physicochemical parameters of the water. This comprehensive environmental ecotoxicological evaluation of the cyanobacterial bloom-induced biochemical alterations in the liver of frogs provides a new basis for further investigations of the prolonged, real-life ecotoxicity of the blooms.

Systematical exploration of the common solvent toxicity at whole organism level by behavioral phenomics in adult zebrafish

Common solvents are frequently used as carriers to dissolve chemicals with a hydrophobic property that is extensively applied in the industrial and biomedical fields. In this study, we aimed to systematically study the sub-chronic effect of ten common solvents at low concentration exposure in adult zebrafish and perform neurobehavioral assessments for mechanistic exploration. After exposed to ten common solvents, including methanol, ethanol (EtOH), dimethyl sulfoxide (DMSO), isopropanol, acetone, polyethylene glycol-400 (PEG-400), glycerol, butanol, pentane, and tetrahydrofuran for continuous 10 day at 0.1% concentration level, adult zebrafish were subjected to perform a serial of behavioral tests, such as novel tank, mirror biting, predator avoidance, social interaction and shoaling. Later, 20 behavioral endpoints obtained from these five tests were transformed into a scoring matrix. Principal component analysis (PCA) and hierarchy clustering were performed to evaluate and compare the zebrafish behavior profiling. By using this phenomic approach, we were able to systematically evaluate the toxicity of the common solvents in zebrafish at a neurobehavioral level for the first time and found each common solvent-induced unique behavioral alteration to produce fingerprint-like patterns in hierarchy clustering and heatmap analysis. Among all tested common solvents, acetone and PEG-400 displayed better biocompatibility and less toxicity since they triggered less behavioral and biochemical alterations while methanol and DMSO caused severe behavior alterations in zebrafish after chronic exposure of these solvents. We conclude the behavioral phenomic approach conducted in this study providing a powerful tool to a systematical exploration of the common solvent toxicity at the whole organism level.

Disentangling of the ecotoxicological signal using "omics" analyses, a lesson from the survey of the impact of cyanobacterial proliferations on fishes

Omics technologies offer unprecedented perspectives for the rational investigation of complex biological systems. Indeed, omics present the ability of offering an extensive perception of the biochemistry and physiology of the cell and of any perturbing consequences of contaminants through the joint investigation of thousands of molecular responses simultaneously; then it has recently conducted to a fervent attention by research ecotoxicologists. Beyond the presentation of latest advances, exemplified here by omics investigation of cyanobacterial deleterious effects on various fishes (at various experimental and biological scales and with various analytical tools and pipeline), the present review paper re-explores the promising perspectives and also the pitfalls of such holistic investigations of the ecotoxicological response of organisms for environmental assessment.

Application of transcriptomic and microRNA profiling in the evaluation of potential liver carcinogens

Hepatocarcinogens are agents that increase the incidence of liver cancer in exposed animals or humans. It is now established that carcinogenic exposures have a widespread impact on the transcriptome, inducing both adaptive and adverse changes in the activities of genes and pathways. Chemical hepatocarcinogens have also been shown to affect expression of microRNA (miRNA), the evolutionarily conserved noncoding RNA that regulates gene expression posttranscriptionally. Considerable effort has been invested into examining the involvement of mRNA in chemical hepatocarcinogenesis and their potential usage for the classification and prediction of new chemical entities. For miRNA, there has been an increasing number of studies reported over the past decade, although not to the same degree as for transcriptomic studies. Current data suggest that it is unlikely that any gene or miRNA signature associated with short-term carcinogen exposure can replace the rodent bioassay. In this review, we discuss the application of transcriptomic and miRNA profiles to increase mechanistic understanding of chemical carcinogens and to aid in their classification.

Long-term environmental exposure to microcystins increases the risk of nonalcoholic fatty liver disease in humans: A combined fisher-based investigation and murine model study

Microcystins (MCs) produced by cyanobacteria pose serious threats to human health. However, the contribution of long-term exposure to MCs to the development of nonalcoholic fatty liver disease (NAFLD) remains poorly documented. In this study, we estimated the environmental uptake of MCs by a small population of fishers who have lived for many years on Meiliang Bay of Lake Taihu, where cyanobacterial blooms occur frequently. Serum biochemical indices of liver function and their relationships with MC contamination in these people were also investigated. Moreover, to mimic the long-term effects of MC on the livers of fishers, an animal model was established in which mice were exposed to MC-LR at an environmentally relevant level, a reference level (the no-observed adverse effect level, NOAEL), and three times the NOAEL through drinking water for 12 months. We estimated the total daily intake of MCs by fishers through contaminated lake water and food to be 5.95 μg MC-LReq, far exceeding the tolerable daily intake (2.40 μg MC-LReq) proposed by the World Health Organization (WHO). More than 80% of participants had at least one abnormal serum marker. The indices of aspartate aminotransferase (AST)/alanine aminotransferase (ALT), triglyceride (TG), globulin (GLB), and lactate dehydrogenase (LDH) had close positive associations with MC contamination, indicating that both liver damage and lipid metabolism dysfunction were induced by chronic MC exposure. Furthermore, the animal experimental results showed that long-term exposure to MC-LR at the environmentally relevant level led to hepatic steatosis with molecular alterations in circadian rhythm regulation, lipid metabolic processes, and the cell cycle pathway. Exposure to MC-LR at or above the NOAEL worsened the pathological phenotype towards nonalcoholic steatohepatitis disease (NASH) or fibrosis. These results suggest that prolonged exposure to the reference level (NOAEL) of MC-LR could cause severe liver injury to mammals. People with long-term environmental exposure to MCs might be at high risk for developing NAFLD.

Persistent Exposure to Environmental Levels of Microcystin-LR Disturbs Cortisol Production via Hypothalamic-Pituitary-Interrenal (HPI) Axis and Subsequently Liver Glucose Metabolism in Adult Male Zebrafish (Danio rerio)

There is growing evidence that microcystin-LR (MC-LR) is a new endocrine disruptor, whereas the impacts of persistent exposure to MC-LR on the hypothalamic-pituitary-interrenal (HPI) axis and health hazards thereafter have not been investigated. In this work, adult male zebrafish (Danio rerio) were immersed into MC-LR solutions at concentrations of 0, 1, 5 and 25 μg/L for 30 d, respectively. The results showed that persistent MC-LR exposure caused an extensive upregulation of HPI-axis genes but an inhibition of brain nuclear receptors (gr and mr), which finally increased serum cortisol levels. Furthermore, the decreased expression of hepatic gr might partly be responsible for the strong inhibition on the expression of downstream genes involved in glucose metabolic enzymes, including gluconeogenesis-related genes (pepck, fbp1a, g6pca), glycogenolysis-related gene (pyg), glycolysis-related genes (gk, pfk1b, pk) and glycogenesis-related gene (gys2). These findings are in accordance with the decline in serum glucose, indicating that long-term MC-LR exposure caused a lower production of glucose relative to glucose lysis. Our above results firstly establish the link between persistent MC-LR exposure and impaired glucose metabolism, suggesting that long-term MC-LR-mediated stress might threaten fish’s health.

Integrative analysis of proteomic and metabonomics data for identification of pathways related to Rhizoma Paridis-induced hepatotoxicity

Clinical reports on hepatotoxicity that arise from Rhizoma Paridis have recently received widespread attention. Because the hepatotoxicity mechanism is little understood, this research strived to investigate the hepatotoxicity mechanism of Rhizoma Paridis extracts based on iTRAQ quantitative proteomics and metabonomics. The extraction solutions were administrated to rats for 7 days by gavage, and the hepatotoxicity was assessed through quantification of biochemical indexes and Oil red O staining. Additionally, the mechanism of hepatotoxicity was investigated by metabonomics based upon GC-MS and iTRAQ quantitative proteomics. The biochemical and histopathological analysis stood out that Rhizoma Paridis extract could induce liver injury, which was proved by the formation of fat droplets, the changes of mitochondrial structure, and biochemical parameters. The iTRAQ proteomics and metabonomics revealed that Rhizoma Paridis-induced hepatotoxicity was chiefly connected with the abnormal activity of mitochondrion function, which brought about oxidative stress injuries and inflammation, finally causing cell apoptosis. Collectively, we have provided previously uncharacterized hepatotoxic mechanism induced by Rhizoma Paridis and a reference to ensure its safe use in the future.

Similar hepatotoxicity response induced by Rhizoma Paridis in zebrafish larvae, cell and rat

Rhizoma Paridis, as a Traditional Chinese Medicine (TCM), has been used in clinic for thousands of years. Recently, the hepatic toxicity was reported in some published articles while its hepatotoxicity mechanisms have not been well established. Therefore, the present study was performed to determine the effect of Rhizoma Paridis treatment on the lipid deposition and metabolism, oxidative stress and mitochondrial dysfunction, and explore the underlying molecular mechanism through L02 cell, rat and zebrafish larvae. Rhizoma Paridis could diminish cell activity and cell proliferation, brought on cell apoptosis and elevated the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) compared with the control group, as evaluated in cell cultures. Rhizoma Paridis could result in the change of the liver structure and the liver function in the rat model and zebrafish larvae. Our results showed that Rhizoma Paridis could increase hepatic lipid accumulation, which was similar to the previous study and probably exerted toxic effect through intensive fatty acid lipogenesis, inhibition of fat degradation. Meanwhile, this experiment highlighted the importance of the oxidative stress, mitochondrial dysfunction, ER function, and the inflammation response in Rhizoma Paridis-induced disorder of hepatic lipid metabolism, which proposed a novel mechanism for interpretation of Rhizoma Paridis exposure inducing the disorder of lipid metabolism in vertebrates. Furthermore, the result of this experiment suggested that the toxicity response of zebrafish larvae was similar to the conventional model with a significant advantage.

Chronic Microcystin-LR Exposure Induces Abnormal Lipid Metabolism via Endoplasmic Reticulum Stress in Male Zebrafish

In order to explore effects of low levels of continuous microcystin-LR (MC-LR) (a cyanotoxin) exposure on hepatic lipid metabolism on the basis of the endoplasmic reticulum stress (ERS) pathway, we exposed adult male zebrafish to MC-LR (0, 1, 5, and 25 μg/L) for 60 days, and hepatic histopathology as well as lipid metabolic parameters were determined with mRNA levels of ERS signal molecules and downstream factors, along with genes associated with lipid metabolism in zebrafish liver. The results revealed that prolonged exposure to MC-LR remarkably altered the levels of hepatic total cholesterol and triglyceride and led to hepatic steatosis, which was also confirmed by hepatic cytoplasmic vacuolization in Hematoxylin/eosin (H&E) stain and lipid droplet accumulation in Oil Red O stain. The severity of hepatic damage and lipidation was increased in a dose-related manner. MC-LR exposure significantly upregulated transcriptional levels of ERS markers including hspa5, mapk8, and chop, indicating the occurrence of ERS in the liver of zebrafish. Concurrently, MC-LR significantly improved mRNA expression of unfolded protein response (UPR) pathway-related genes including atf6, eif2ak3, ern1, and xbp1s, suggesting that all of the three UPR branches were activated by MC-LR. MC-LR also induced significant upregulation of downstream lipid metabolism-related factors and genes including srebf1, srebf2, fatty acid synthase (fasn), acetyl-CoA carboxylase (acaca), stearoyl-CoA desaturase (scd), HMG CoA reductase (hmgcra), and HMG CoA synthase (hmgcs1), and downregulation of genes associated with lipolysis such as triglyceride hydrolase gene (atgl), hormone-sensitive enzyme gene (hsla), and carnitine palmitoyltransferase gene (cpt1aa). Our present results indicated that the cause of hepatic lipid accumulation by MC-LR was mainly by upregulating lipogenic and cholesterol genes but downregulating the expression of lipolytic genes through the induction of srebf1 and srebf2, which were involved in the activation of ERS signal pathways.

Waterborne microcystin-LR exposure induced chronic inflammatory response via MyD88-dependent toll-like receptor signaling pathway in male zebrafish

Waterborne microcystin-LR (MC-LR) released by cyanobacterial blooms in eutrophic water bodies have caused serious risk to aquatic animal and human health. In the present study, we for the first time conducted a comprehensive in vivo investigation on chronic inflammatory responses and its molecular pathways of different environmental relevant levels of MC-LR (0, 0.4, 2 and 10 μg/L) in male zebrafish (Danio rerio). The results showed that chronic MC-LR exposure caused splenic inflammatory changes including the formation of melano-macrophage centers, remarkable elevation of serum tumor necrosis factor alpha (TNFα) and interleukin 1 beta (IL1β) levels as well as significant upregulated expression of MyD88-dependent toll-like receptor (TLR/MyD88) signaling pathway genes (tlr4a, myd88, erk2, p38a, il1β and tnfα). The immunohistochemical and western blot results further validated that higher MC-LR concentrations tended to enhance the MyD88 signal. Moreover, significant decreases of serum C3 levels along with splenic c3b expression in the 10 μg/L exposure group proved that chronic MC-LR exposure could ultimately decrease the innate immunity of fish. Our findings revealed that chronic exposure of MC-LR could cause chronic inflammation through TLR/MyD88 signaling pathway and subsequently induce immune disorders in male zebrafish, which also urge us to pay more attention on the potential immunotoxicity of long-term exposure to low concentration of MC-LR.

Parental Transfer of Microcystin-LR-Induced Innate Immune Dysfunction of Zebrafish: A Cross-Generational Study

Transgenerational effects of microcystin-LR (MC-LR) released by cyanobacterial blooms have become a hot topic. In the present study, adult zebrafish pairs were exposed to 0, 0.4, 2, and 10 μg/L MC-LR for 60 days and the embryos (F1 generation) were hatched without or with continued MC-LR exposures at the same concentrations until 5 days postfertilization (dpf). The results showed the existence of MC-LR both in F0 gonads and in F1 embryos and indicated that MC-LR could be transferred directly from the F0 adult fish to F1 offspring. The adverse effects on sex hormone levels, sexual development, and fecundity in F0 generation along with abnormal development in F1 offspring were observed. Furthermore, downregulation of antioxidant genes (cat, mn-sod, gpx1a) and upregulation of innate immune-related genes (tlr4a, myd88, tnfα, il1β) as well as increased proinflammation cytokine contents (TNF-α, IL-1β, IL-6) were noticed in F1 offspring without/with continued MC-LR exposures. In addition, significant differences between the two F1 embryo treatments demonstrated that continuous MC-LR exposure could result in a higher degree of inflammatory response compared to those without MC-LR exposure. Our findings revealed that MC-LR could exert cross-generational effects of immunotoxicity by inhibiting the antioxidant system and activating an inflammatory response.

Responses of the proteome in testis of mice exposed chronically to environmentally relevant concentrations of Microcystin-LR

Microcystin-LR (MC-LR), a widespread environmental contaminant, has been shown to have potent acute testicular toxicity. However, magnitudes of toxic effects, induced by MCs, depend on route and magnitude of exposure to the toxin. In the present study, male mice were orally exposed 1, 10 or 100 μg/L MC-LR for 90 or 180 days, and pathological approach and the isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics were employed with testes. Proteomics revealed that a number of differentially altered proteins may be involved in MC-LR-induced chronic testicular toxicity. The biological process analysis indicated the altered proteins played an important role in biological adhesion, cellular process, response to stimulus or rhythmic process. The cellular component analysis revealed that most of the proteins with altered expression associated with cell part, extracellular region, extracellular region part, membrane, membrane part, organelle or organelle part. The molecular function showed that these proteins were critical in molecular transducer activity. Integrity analyses provide first compelling evidence that MC-LR significantly cause dysfunction of blood-testis barrier (BTB) through affecting tight junctions and gap junctions. Moreover, phosphatidylinositol 3-kinase (PI3K)/AKT eventually contributed to injury result from chronic low-level MC-LR treatment. Identification of proteins in testis responsive to MC-LR provides insights into molecular mechanisms of chronic toxicity of MCs.

Toxicological effects of As (V) in juvenile rockfish Sebastes schlegelii by a combined metabolomic and proteomic approach

Arsenic (As) is a metalloid element that is ubiquitous in the marine environment and its contamination has received worldwide attention due to its potential toxicity. Arsenic can induce multiple adverse effects, such as lipid metabolism disorder, immune system dysfunction, oxidative stress and carcinogenesis, in animals. Inorganic arsenic includes two chemical forms, arsenite (As (III)) and arsenate (As (V)), in natural environment. As (V) is the dominant form in natural waters. In the present study, metabolomic and proteomic alterations were investigated in juvenile rockfish Sebastes schlegelii exposed to environmentally relevant concentrations of As (V) for 14 d. The analysis of iTRAQ-based proteomics combined with untargeted NMR-based metabolomics indicated apparent toxicological effects induced by As (V) in juvenile rockfish. In details, the metabolites, including lactate, alanine, ATP, inosine and phosphocholine were significantly altered in As-treated groups. Proteomic responses suggested that As (V) could not only affected energy and primary metabolisms and signal transduction, but also influenced cytoskeleton structure in juvenile rockfish. This work suggested that the combined proteomic and metabolomic approach could shed light on the toxicological effects of pollutants in rockfish S. schlegelii.

Responses in the crucian carp (Carassius auratus) exposed to environmentally relevant concentration of 17α-Ethinylestradiol based on metabolomics

17α-ethynylestradiol (EE2), a ubiquitous synthetic endocrine disrupting chemical, was the principal component of contraceptive drugs and one of common hormone medications. The detrimental impact of EE2 on the reproduction of organisms was widely recognized. However, the underlying mechanisms of physiological and metabolome effects of EE2 on freshwater fish are still unclear. This study investigated the toxic effects and related mechanisms of EE2 on freshwater fish crucian carp (Carassius auratus) based on metabolomics. Crucian carp were exposed to EE2 at environmentally relevant concentration for 9 days, 18 days, and 27 days, and the biological responses were explored through analysis of the physiological endpoints, steroid hormones, and metabolome. The physiological endpoints of crucian carp had no distinct change after EE2 exposure. However, metabolomics analysis probed significant deviation based on chemometrics, indicating that the metabolomics approach was more sensitive to the effects of EE2 at environmentally relevant concentration to freshwater fish than the traditional endpoints. The alterations of 24 metabolites in gonad and 16 metabolites in kidney were induced by treatment with EE2, respectively, which suggesting the perturbations in amino acid metabolism, lipid metabolism, energy metabolism, and oxidative stress. Moreover, EE2 exposure could induce the disruption of lipid metabolism and then broke the homeostasis of endogenous steroid hormones. Metabolomics provided a new strategy for the studies on contaminant exposure at a low dose in the short term and gave important information for the toxicology and mechanism of EE2.

Proteomic analysis of the hepatotoxicity of Microcystis aeruginosa in adult zebrafish (Danio rerio) and its potential mechanisms

Microcystis aeruginosa is one of the main species of cyanobacteria that causes water blooms. M. aeruginosa can release into the water several types of microcystins (MCs), which are harmful to aquatic organisms and even humans. However, few studies have investigated the hepatotoxicity of M. aeruginosa itself in zebrafish in environments that simulate natural aquatic systems. The objective of this study was to evaluate the hepatotoxicity of M. aeruginosa in adult zebrafish (Danio rerio) after short-term (96 h) exposure and to elucidate the potential underlying mechanisms. Distinct histological changes in the liver, such as enlargement of the peripheral nuclei and sinusoids and the appearance of fibroblasts, were observed in zebrafish grown in M. aeruginosa culture. In addition, antioxidant enzyme activity was activated and protein phosphatase (PP) activity was significantly decreased with increasing microalgal density. A proteomic analysis revealed alterations in a number of protein pathways, including ribosome translation, immune response, energy metabolism and oxidative phosphorylation pathways. Western blot and real-time PCR analyses confirmed the results of the proteomic analysis. All results indicated that M. aeruginosa could disrupt hepatic functions in adult zebrafish, thus highlighting the necessity of ecotoxicity assessments for M. aeruginosa at environmentally relevant densities.

Study of BDE-47 induced Parkinson's disease-like metabolic changes in C57BL/6 mice by integrated metabolomic, lipidomic and proteomic analysis

As the predominant congener of polybrominated diphenyl ethers (PBDEs) detected in human serum, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) has been reported to induce neurotoxicity. However, the possible linkage between BDE-47 and typical neurodegenerative diseases such as Parkinson's disease (PD) is still unclear. Here we carried out omics studies using liquid chromatography-orbitrap mass spectrometry (LC-orbitrap MS) to depict the BDE-47 induced metabolic changes in C57BJ/L mice to explore the possible contribution of BDE-47 exposure to PD pathology. BDE-47 dissolved in corn oil was orally administered to mice for 30 consecutive days. Results of metabolomics and lipidomics studies of PD-related brain regions revealed significant metabolite changes in pathways involved in oxidative stress and neurotransmitter production. Moreover, isobaric tags for relative and absolute quantitation (iTRAQ) proteomics study of the striatum, which is the part of brain that is most intensively studied in PD pathogenesis, revealed that BDE-47 could induce neurotransmitter system disturbance, abnormal phosphorylation, mitochondrial dysfunction and oxidative stress. Overall, this study depicts the possible contribution of BDE-47 exposure to PD pathology and highlights the powerfulness of omics platforms to deepen the mechanistic understanding of environmental pollutant-caused toxicity.

Integrating multi-omics and regular analyses identifies the molecular responses of zebrafish brains to graphene oxide: Perspectives in environmental criteria

With the broad application of nanoparticles, nanotoxicology has attracted substantial attention in environmental science. However, the methods for detecting few and targeted genes or proteins, even single omics approaches, may miss other responses, including the major responses induced by nanoparticles. To determine the actual toxicological mechanisms of zebrafish brains induced by graphene oxide (GO, a popular carbon-based nanomaterial applied in various fields) at nonlethal concentrations, multi-omics and regular analyses were combined. The biomolecule responses were remarkable, although GO was not obviously observed in brain tissues. The trends for gene and protein changes were the same and accounted for 3.53% and 5.36% of all changes in the genome and proteome, respectively, suggesting a limitation of single omics analysis. Transcriptomics and proteomics analyses indicated that GO affected the functions or pathways of the troponin complex, actin cytoskeleton, monosaccharide transmembrane transporter activity, oxidoreductase activity and focal adhesion. Both metabolomics and proteomics revealed mitochondrial dysfunction and disruption of the citric acid cycle. The integrated analysis of omics, transmission electron microscopy and immunostaining confirmed that GO induced energy disruptions and mitochondrial damage by downregulating tubulin. The combination of multi-omics and regular analyses provides insights into the actual and highly influential mechanisms underlying nanotoxicity.

A Review of Cardiovascular Toxicity of Microcystins

The mortality rate of cardiovascular diseases (CVD) in China is on the rise. The increasing burden of CVD in China has become a major public health problem. Cyanobacterial blooms have been recently considered a global environmental concern. Microcystins (MCs) are the secondary products of cyanobacteria metabolism and the most harmful cyanotoxin found in water bodies. Recent studies provide strong evidence of positive associations between MC exposure and cardiotoxicity, representing a threat to human cardiovascular health. This review focuses on the effects of MCs on the cardiovascular system and provides some evidence that CVD could be induced by MCs. We summarized the current knowledge of the cardiovascular toxicity of MCs, with regard to direct cardiovascular toxicity and indirect cardiovascular toxicity. Toxicity of MCs is mainly governed by the increasing level of reactive oxygen species (ROS), oxidative stress in mitochondria and endoplasmic reticulum, the inhibition activities of serine/threonine protein phosphatase 1 (PP1) and 2A (PP2A) and the destruction of cytoskeletons, which finally induce the occurrence of CVD. To protect human health from the threat of MCs, this paper also puts forward some directions for further research.

Integrated analysis of proteomics and metabolomics reveals the potential sex determination mechanism in Odontobutis potamophila

Odontobutis potamophila is a valuable species for aquaculture in China, which shows asexually dimorphic growth pattern. In this study, the integrated proteomics and metabolomics were used to analyze the sex determination mechanism. A total of 2781 significantly different regulated proteins were identified by proteomics and 2693 significantly different expressed metabolites were identified by metabolomics. Among them, 2560 proteins and 1701 metabolites were significantly up-regulated in testes, whereas 221 proteins and 992 metabolites were significantly up-regulated in ovaries. Venn diagram analysis showed 513 proteins were differentially regulated at both protein and metabolite levels. Correlation analysis of differentially-regulated proteins and metabolites were identified by Gene Ontology annotation and Kyoto Encyclopedia of Genes and Genomes pathway analysis. The results showed lipid metabolism plays an important role in sex determination. The metabolites decanoyl-CoA, leukotriene, 3-dehydrosphinganine, and arachidonate were the biomarkers in testes, whereas estrone and taurocholate were the biomarkers in ovaries. Interaction networks of the significant differentially co-regulated proteins and metabolites in the process of lipid metabolism showed arachidonic acid metabolism and steroid hormone biosynthesis were the most important pathways in sex determination. The findings of this study provide valuable information for selective breeding of O. potamophila. SIGNIFICANCE OF THE STUDY: The male O. potamophila grows substantially larger and at a quicker rate than the female. Thus, males have greater economic value than females. However, limited research was done to analyze the sex determination mechanism of O. potamophila, which seriously hindered the development of whole-male O. potamophila breeding. In this study, four key proteins (Ctnnb1, Piwil1, Hsd17b1, and Dnali1), six most important biomarkers (decanoyl-CoA, leukotriene, 3-dehydrosphinganine, arachidonate, estrone, and taurocholate) and two key pathways (arachidonic acid metabolism and steroid hormone biosynthesis) in sex determination of O. potamophila were found by integrated application of iTRAQ and LC-MS techniques. The results give valuable information for molecular breeding of O. potamophila in aquaculture.

Learning and memory deficits and alzheimer's disease-like changes in mice after chronic exposure to microcystin-LR

Previous studies have demonstrated that toxins produced by toxic cyanobacterial blooms are hazardous materials. Although microcystin-LR (MC-LR) has been revealed to inflict damage to the brain, the mechanisms underlying its neurotoxicity as a result of chronic exposure to MC-LR are not fully described. In this study, the mice were exposed to MC-LR dissolved in drinking water at doses of 1, 7.5, 15, or 30 μg/L for 180 days. MC-LR accumulated mostly in the mouse hippocampus (55 ng/g dry weight) followed by cortex (28 ng/g dry weight) after exposure to MC-LR at 30 μg/L. MC-LR exposure at this concentration induced dysfunction of learning and memory, accompanied with apoptosis of neuronal cells (with 10% reduction of the neurons in the CA1 region and 15% in the CA2 region), reduction of spine density, accumulation of β-amyloid plaques 1-42 (Aβ1-42), and enhanced phosphorylation of tau (p-tau) in the brain, which is characteristic of Alzheimer's disease (AD). These data indicate that MC-LR may induce AD-like pathology. Following prolonged exposure, MC-LR significantly upregulated the ratio of proBDNF to BDNF by downregulating the tPA levels, thereby activating downstream signaling pathways to improve the expression of p-JNK, and c-Jun while to inhibit the expression of p-Creb and p-PKC. This study uncovered new molecular mechanisms that account for neurotoxicity after chronic exposure to MC-LR, which has wide-ranging implications for public health.

Microcystin-LR-regulated transcriptome dynamics in ZFL cells

Microcystin-LR (MC-LR) is a highly toxic hepatotoxin that poses great hazards to aquatic organisms and even human health. The zebrafish liver cell line (ZFL) is a valuable model for investigating toxicity and metabolism of toxicants. However, the toxicity of MC-LR and its effects on gene transcription of ZFL cells remains to be characterized. In this study, we determined the toxicity of MC-LR for ZFL cells and investigated the effects of MC-LR on cellular transcriptome dynamics. The EC₅₀ of MC-LR for ZFL cells was 80.123 μg/mL. The ZFL cells were exposed to 10 μg/mL MC-LR for 0, 1, 3, 6, 12 or 24 h, and RNA-sequencing was performed to analyze gene transcription. A total of 10,209 genes were found to be regulated by MC-LR. The numbers of up- and down-regulated genes at different time points ranged from 2179 to 3202 and from 1501 to 2597, respectively. Furthermore, 1543 genes underwent differential splicing (AS) upon MC-LR exposure, of which 620 were not identified as differentially expressed gene (DEG). The effects of MC-LR on cellular functions were highly time-dependent. MAPK (mitogen-activated protein kinase) and FoxO (forkhead box O) signaling pathways were the most prominent pathways activated by MC-LR. Steroid biosynthesis and terpenoid backbone biosynthesis were the most enriched for the down-regulated genes. A gene regulatory network was constructed from the expression profile datasets and the candidate master transcription factors were identified. Our results shed light on the molecular mechanisms of MC-LR cellular toxicity and the transcriptome landscapes of ZFL cells upon MC-LR toxicity.

Di-(2-ethylhexyl)-phthalate induces apoptosis via the PPARγ/PTEN/AKT pathway in differentiated human embryonic stem cells

[OBJECTIVE]: Di(2-ethylhexyl) phthalate (DEHP), a widely used plasticizer, may act as an endocrine disruptor and cause developmental toxicity. Differentiated human embryonic stem cells (hESCs) were used to investigate the underlying mechanism of the embryotoxicity induced by DEHP. [Materials and Methods] H9-hESCs were treated with DEHP at different concentrations for 10 days, and the cytotoxicity of DEHP on cell proliferation was determined using a cell-microelectronic sensing technique (Real-Time Cellular Analysis: RTCA). Based on the 50% inhibitory proliferation concentration (IC₅₀), differentiated H9-hESCs were treated with DEHP at 0, 50, 100, and 200 μg/ml for 120 h, followed by measurement of its toxic effects on the transcriptome by mRNA microarray and QuantiGene Plex (QGP). Proteins were detected by the iTRAQ-based proteomics method and the proteins related to the PPARγ/PTEN/Akt pathways were measured by western blotting. The progression of the cell cycle and apoptosis were characterized using flow cytometry (FCM). In other experiments, hESCs were pre-treated with GW9662 (20 μM), a specific PPARγ inhibitor, for 30 min, followed by exposure to GW9662 (20 μM) and DEHP (200 μg/ml) for 120 h to observe the underlying mechanism of DEHP's embryotoxicity. [RESULTS]: DEHP inhibited H9-hESC cell proliferation in a dose-dependent manner, with an IC₅₀ of 165.78 μg/ml. FCM results showed that DEHP could markedly induce cell cycle arrest and increase apoptosis. Gene microarray and QPG array analyses indicated that the peroxisome proliferator-activated receptor γ (PPARγ) was an apparent target for DEHP. We further demonstrated that DEHP could activate the PPARγ and upregulate the expression of PTEN downstream genes, and then play a negative role in the AKT signaling pathway. Cells pretreated with PPARγ inhibitor, GW9662, were shown to restore the effect of DEHP on the PPARγ/PTEN/AKT signaling pathway, and induce the recovery of cell cycle arrest and apoptosis. [CONCLUSION]: DEHP inhibited cell proliferation, promoted cell cycle arrest, and induced apoptosis through the PPARγ/PTEN/AKT signaling pathway in differentiated human embryonic stem cells. It suggested that DEHP exposure possibly cause reproductive or developmental toxicity in humans through the PPARγ signaling pathway.

Molecular effects of Microcystin-LA in tilapia (Oreochromis niloticus)

Nile tilapia (Oreochromis niloticus) is a freshwater phytoplanktivorous fish species reported to accumulate and tolerate large amounts of cyanotoxins such as microcystins (MCs). The present study aimed to investigate molecular responses to the acute exposure of Nile tilapia to the Microcystin-LA analogue (MC-LA). Thus, the specimens were sublethally exposed to 1000 μg kg^-1 of MC-LA for 12, 24, 48, and 96 h. Gene expression of PP1, PP2A, GST, GPX and actin was analyzed by quantitative PCR. The protein abundance profile of PP2A was determined by immunoblotting, while the integrity of its biological function was assessed by a phosphatase enzymatic assay. PP2A activity was significantly and strongly reduced by MC-LA. A resulting feedback mechanism significantly increased PP2A gene expression and protein abundance in all assessed times. However, a recovery of that phosphatase activity was not observed. In this study, the observed increase in GPX gene expression was the only response that could be directly related to the unknown factors associated to the fish survival to such high dose exposure.

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.

Linking Exoproteome Function and Structure to Anammox Biofilm Development

Extracellular proteins are of paramount importance in the cell-cell interactions of anammox biofilms. However, the inherent aggregation mechanisms of anammox have largely remained elusive. Herein, using a quartz sand extraction protocol and follow-up iTRAQ-based quantitative proteomics, we identified 367 extracellular proteins from initial colonizers, mature biofilm, and detached biofilm. The extracellular proteins were mainly membrane-associated. Most of the recovered proteins (226, 72.5%) originated from the phylum Planctomycetes. In summary, 215 and 190 of the 367 proteins recovered were up- and/or downregulated at least 1.2-fold during the biofilm formation and detachment periods, respectively. These differentially expressed proteins were dominantly involved in metal ion binding, which was regarded as strong evidence for their abilities to enhance ionic bridges in extracellular polymeric substances (EPS). Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) analysis of the biofilms further showed substantial levels of calcium and iron minerals. Critically, representative Sec-dependent secretory proteins affiliated with coccoid Planctomycetes, rod-shaped Proteobacteria, and filamentous Chloroflexi (11, 4, and 2 with differential expression, respectively) were found to have typical and abundant inner β-sheet structures, wherein hydrophobic moieties can promote anammox aggregation. Overall, these findings highlight links between differentially expressed protein functions and morphologic traits of anammox consortia during biofilm development.

Effects of different concentrations of Microcystis aeruginosa on the intestinal microbiota and immunity of zebrafish (Danio rerio)

Microcystis aeruginosa is a primary species of toxin-producing cyanobacteria. This study explored the effects of short-term exposure (96 h) to M. aeruginosa on the intestinal microflora variation and immune function of zebrafish. After exposure to different cell concentrations of M. aeruginosa, marked histological variation was observed in the intestine, such as goblet cells proliferation and intestinal desquamation. In addition high-concentration M. aeruginosa treatment (initial concentration: 1.59 × 10⁵ cells mL^-1) induced a significant increase in cytokine levels compared with other groups. Low-concentration M. aeruginosa treatment (initial concentration: 0.88 × 10⁵ cells mL^-1) promoted the transcription of inflammatory genes, while high-concentration treatment restrained the transcription of these genes. Moreover, M. aeruginosa exposure also changed the intestinal microbial diversity. At the phylum level, bacteria belonging to Proteobacteria were the most abundant in all groups, and Gammaproteobacteria were the dominant bacteria with major changes. Pathogenic microorganisms such as Shewanella, Plesiomonas, Halomonas, Pseudomonas, and Lactobacillus increased greatly after treatment with different cell concentrations of M. aeruginosa. This study indicates that M. aeruginosa induces an increase in zebrafish goblet cells and enhances the inflammatory response, which may produce detrimental effects in zebrafish, resulting in a greater proportion of pathogenic bacteria and intestinal injury. The results of this study will help improve the understanding of the effects of M. aeruginosa on the intestines of aquatic organisms.

Microcystin-leucine arginine inhibits gonadotropin-releasing hormone synthesis in mice hypothalamus

Microcystin-leucine arginine (MC-LR) causes serum testosterone declines and male reproductive disorders. However, the molecular mechanisms underlying the pathological changes are still unclear. In the present study, we aimed to investigate the toxic effects of MC-LR on gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus. Our results demonstrated that MC-LR could enter GnRH neurons and inhibit GnRH synthesis, resulting in the decrease of serum GnRH and testosterone levels. The inhibitory effects of MC-LR on GnRH synthesis were identified to be associated with activation of the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP response element-binding protein (CREB)/c-Fos signaling pathway. With miRNA microarray analyses, we found that miR-329-3p was down-regulated most dramatically in MC-LR-treated GT1-7 cells. We then further identified that miR-329-3p regulated PRKAR1A and PRKACB expression and thus influenced GnRH synthesis. This is the first study to explore the molecular mechanism underlying the inhibitory effects of MC-LR on GnRH synthesis in the hypothalamus. Our data have provided a new perspective in the development of diagnosis and treatment strategies for male infertility as a result of dysfunction of the hypothalamic-pituitary-gonadal axis.

Chronic exposure to microcystin-leucine-arginine promoted proliferation of prostate epithelial cells resulting in benign prostatic hyperplasia

Microcystin-leucine-arginine (MC-LR), as a most common and deleterious variant among all structural analogues of Microcystins (MCs), can cause male reproductive dysfunction. However, its toxic effects on prostate in adult mice have not been invested in detail. In this study, we observed that MC-LR could enter prostate tissues and induce focal hyperplasia and prostate inflammation. Moreover, increased levels of prostate specific antigen (PSA) and prostate acid phosphatase (PAP) in serum of mice following chronic exposure to MC-LR were detected. We also examined increased expression of forkhead box protein M1 (FOXM1) and PSA in human prostate epithelial cells (RWPE-1) treated with MC-LR at low levels, and FOXM1 could regulate PSA expression. Furthermore, MC-LR also induced expression of CyclinD1 via FOXM1/Wnt/β-catenin signaling pathways in RWPE-1 cells, promoting proliferation of prostate epithelial cells, resulting in prostatic hyperplasia in vivo. As a foreign substance, MC-LR also induced immune reaction in RWPE-1 cells mediated by NF-κB pathway, promoting production of pro-inflammatory cytokines and chemokines. Collectively, these findings demonstrated that MC-LR may induce prostatic hyperplasia and prostatitis in mice following chronic low-dose exposure to MC-LR. This work may provide new perspectives in developing new diagnosis and treatment strategies for MC-LR-induced prostatic toxicity.

Microcystin-LR affects the hypothalamic-pituitary-inter-renal (HPI) axis in early life stages (embryos and larvae) of zebrafish

Frequencies and durations of blooms of cyanobacteria are increasing. Some cyanobacteria can produce cyanotoxins including microcystins (MCs). MCs are the most common toxic products of hazardous algal blooms (HABs), with the greatest potential for exposure and to cause toxicity. Recently, MCs have been shown to disrupt endocrine functions. In this study, for the first time, effects of MC-LR on the hypothalamic-pituitary-inter-renal (HPI) axis during early embryonic development (embryos/larvae) of zebrafish (Danio rerio), were investigated. Embryos/larvae of zebrafish were exposed to 1, 10, 100, or 300 μg MC-LR/L during the period of 4-168 h post-fertilization (hpf). Exposure to 300 μg MC-LR/L resulted in significantly greater concentrations of whole-body cortisol than those in controls. Expressions of genes along the HPI axis and mineralocorticoid receptor (MR-) and glucocorticoid receptor (GR-) centered gene networks were evaluated by use of quantitative real-time PCR. Expression of mRNA for crh was significantly down-regulated by exposure to 300 μg MC-LR/L, while expressions of crhbp, crhr1, and crhr2 were significantly up-regulated, relative to controls. MC-LR caused significantly lesser levels of mRNA for steroidogenic genes including hmgra, star, and cyp17, but expression of mRNA for hsd20b was significantly greater than that of controls. Treatment with MC-LR also altered profiles of transcription of MR- and GR-centered gene networks, which might result in multiple responses. Taken together, these results demonstrated that MC-LR affected the corticosteroid-endocrine system of larvae of zebrafish. This study provided valuable insights into molecular mechanisms behind potential toxicity and endocrine disruption of MCs.

Microcystin-leucine arginine mediates apoptosis and engulfment of Leydig cell by testicular macrophages resulting in reduced serum testosterone levels

Microcystin-leucine arginine (MC-LR) causes decline of serum testosterone levels resulting in impaired spermatogenesis; however, the underlying molecular mechanisms are not fully understood. In this study, we aimed to investigate the effects of MC-LR exposure on the number of Leydig cells (LCs) in testis. Following chronic low dose exposure to MC-LR, the number of LCs was markedly decreased while macrophages were significantly increased. Then, we established a co-culture system to study the interaction between macrophages and LCs in the presence of MC-LR. No significant apoptosis of LCs cultured alone was observed after MC-LR (< 5 000 nM) treatment; however, apoptosis was robustly increased when LCs were co-cultured with macrophages in the presence of MC-LR. Further studies identified that MC-LR could stimulate macrophage to produce TNF-α, and secreted TNF-α induced LC apoptosis by binding to the tumor necrosis factor receptor 1 (TNFR1) on the LCs and thus activating reactive oxygen species (ROS)-p38MAPK signaling pathway. Furthermore, we also examined increased expression of Axl receptor and growth arrest-specific 6 (Gas6) in macrophages after MC-LR treatment. GAS6 mediates phagocytosis of apoptotic LCs by binding to the Axl receptor on macrophages and phosphatidylserine (PtdSer) on apoptotic LCs. Together, these results suggested that reduced serum testosterone levels may be associated with decrease of LCs as a result of LC apoptosis and phagocytosis by immune cells in MC-LR-treated mice.

The dose makes the poison

Some microcystins (MCs) might cause hepatotoxicity in animals and humans. MC-LR is also a tumor promoter and a suspect carcinogen. In 2010, the International Agency for Research on Cancer (IARC) classified MC-LR as a possible human carcinogen (Group 2B). Recently, an article entitled "Long-term, low-dose exposure to microcystin toxin does not increase the risk of liver tumor development or growth in mice" was published in Hepatology Research by Meaghan Labine and Gerald Y. Minuk. However, the experimental design was flawed and the conclusion is misleading. 1μg/L MC-LR in drinking water is the provisional guideline value established by the World Health Organization (WHO) for humans in 1998, based on a tolerable daily intake (TDI) of 0.04μg/kg body mass (BM). Assuming the mice drink 1.5mL/10g BM of water per day, the exposure dose would be 0.15μg/kg/d BM, about 270-fold less than 40μg/kg/d, the no-observed-adverse-effect level (NOAEL). Thus, the dose of MC-LR was too small and "unlikely to result in liver tumor development or enhance existing tumor growth", even with a long-term (28weeks) exposure. Presumably, they didn't consider inter-species variations between mice and humans, including toxicokinetics and toxicodynamics. Ranges of "low-dose" MCs for animals and humans should be defined. Also, the authors misunderstood or misrepresented several previous studies. Before drawing final conclusions on the carcinogenicity of MCs, further well-designed experiments are warranted.

The synergistic effects of waterborne microcystin-LR and nitrite on hepatic pathological damage, lipid peroxidation and antioxidant responses of male zebrafish

Hazardous materials from decaying cyanobacterial blooms, such as microcystin-LR (MC-LR) and nitrite pose serious challenges to aquatic organisms. To assess combined toxic effects of MC-LR and nitrite on hepatic pathology, lipid peroxidation and antioxidant responses of fish, adult male zebrafish (Danio rerio) were exposed to solutions with different combined concentrations of MC-LR (0, 3, 30 μg/L) and nitrite (0, 2, 20 mg/L) for 30 d. The results showed that hepatic pathological lesions progressed in severity and extent with increasing concentration of single factor MC-LR or nitrite and became more severe in co-exposure groups. Concurrently, significant increases in malondialdehyde (MDA) revealed the occurrence of oxidative stress caused by MC-LR, nitrite and both of them, which was indirectly verified by remarkable decreases in the total antioxidant capacity (T-AOC) as well as the transcription and activity of antioxidant enzymes (CAT and GPx). Hepatic mitochondria were damaged as the common action site of MC-LR and nitrite, suggesting that oxidative stress played a significant role in the mechanisms of the hepatotoxicity of MC-LR and nitrite. The depletion of hepatic glutathione (GSH) indicated the importance of GSH/glutathione-S-transferases (GST) system in these two chemicals detoxification. These results clearly illustrated that MC-LR and nitrite have synergistic effects on the histostructure, antioxidant capacity and detoxification capability in the liver of zebrafish. Therefore, the combined pollution of MC-LR and nitrite in eutrophic lakes can reduce the defense mechanism of the fish and accelerate the consumption of GSH, which compromise the survival of the fish during prolonged cyanobacterial blooms episodes.

Baseline levels of metabolites in different tissues of mussel Mytilus galloprovincialis (Bivalvia: Mytilidae)

The Mediterranean mussel Mytilus galloprovincialis (Lamarck 1819) is a popular shellfish commonly included in human diet and is routinely used as bioindicator in environmental monitoring programmes worldwide. Recently, metabolomics has emerged as a powerful tool both in food research and ecotoxicology for monitoring mussels' freshness and assessing the effects of environmental changes. However, there is still a paucity of data on complete metabolic baseline of mussel tissues. To mitigate this knowledge gap, similarities and differences in metabolite profile of digestive gland (DG), gills (G), and posterior adductor muscle (PAM) of aquaculture-farmed M. galloprovincialis were herein investigated by a proton nuclear magnetic resonance (¹H NMR)-based metabolomic approach and discussed considering their physiological role. A total of 44 metabolites were identified in mussel tissues and grouped in amino acids, energy metabolites, osmolytes, neurotransmitters, nucleotides, alkaloids, and miscellaneous metabolites. A PCA showed that mussel tissues clustered separately from each other, suggesting a clear differentiation in their metabolic profiles. A Venn diagram revealed that mussel DG, G and PAM shared 27 (61.36%) common metabolites, though with different concentrations. Osmolytes were found to dominate the metabolome of all tissues. The DG exhibited higher level of glutathione and carbohydrates. The G showed greater level of osmolytes and the exclusive presence of neurotransmitters, namely acetylcholine and serotonin. In PAM higher levels of energetics-related metabolites were found. Overall, findings from this study are helpful for a better understanding of mussel tissue-specific physiological functions as well as for future NMR-based metabolomic investigations of marine mussel health and safety.

Physiological effects caused by microcystin-producing and non-microcystin producing Microcystis aeruginosa on medaka fish: A proteomic and metabolomic study on liver

Cyanobacterial blooms have become a common phenomenon in eutrophic freshwater ecosystems worldwide. Microcystis is an important bloom-forming and toxin-producing genus in continental aquatic ecosystems, which poses a potential risk to Human populations as well as on aquatic organisms. Microcystis is known to produce along with various bioactive peptides, the microcystins (MCs) that have attracted more attention notably due to their high hepatotoxicity. To better understand the effects of cyanobacterial blooms on fish, medaka fish (Oryzias latipes) were sub-chronically exposed to either non-MC-producing or MC-producing living strains and, for this latter, to its subsequent MC-extract of Microcystis aeruginosa. Toxicological effects on liver have been evaluated through the combined approach of histopathology and 'omics' (i.e. proteomics and metabolomics). All treatments induce sex-dependent effects at both cellular and molecular levels. Moreover, the modalities of exposure appear to induce differential responses as the direct exposure to the cyanobacterial strains induce more acute effects than the MC-extract treatment. Our histopathological observations indicate that both non-MC-producing and MC-producing strains induce cellular impairments. Both proteomic and metabolomic analyses exhibit various biological disruptions in the liver of females and males exposed to strain and extract treatments. These results support the hypothesis that M. aeruginosa is able to produce bioactive peptides, other than MCs, which can induce toxicological effects in fish liver. Moreover, they highlight the importance of considering cyanobacterial cells as a whole to assess the realistic environmental risk of cyanobacteria on fish.

Microcystin-leucine-arginine causes blood-testis barrier disruption and degradation of occludin mediated by matrix metalloproteinase-8

Microcystin-leucine-arginine (MC-LR) can cause male reproductive disorders. However, the underlying mechanisms are not yet fully understood. In this study, we aimed to investigate the effects of MC-LR on the integrity of blood-testis barrier (BTB) and the related molecular mechanisms. Both transepithelial electrical resistance measurement in vitro and electron microscope observation ex vivo revealed that MC-LR caused disruption of the tight junction between Sertoli cells, which was paralleled by the degradation of occludin. We observed increased expression of matrix metalloproteinase-8 (MMP-8) upon exposure to MC-LR, and confirmed that abrogation of MMP-8 activity by specific inhibitors as well as transfection with MMP-8 shRNA could abolish the degradation of occludin. Our data demonstrated that MC-LR up-regulated nuclear levels of c-Fos and c-Jun through activating ERK and JNK, and increased NF-κB levels by activating the phosphatidylinositol 3-kinase (PI3K)/AKT cascades. Enhanced binding of c-Fos and NF-κB to the promoter of MMP-8 promoted the transcription of MMP-8 gene. Furthermore, miR-184-3p was significantly downregulated in SC following exposure to MC-LR through targeting MMP-8 expression. Together, these results confirmed that MC-LR-induced MMP-8 expression was regulated at both transcriptional and post-transcriptional levels, which was involved in MC-LR-induced degradation of occludin and BTB destruction. This work may provide new perspectives in developing new diagnosis and treatment strategies for MC-induced male infertility.

Reproductive and endocrine-disrupting toxicity of Microcystis aeruginosa in female zebrafish

Microcystis aeruginosa, a primary species in cyanobacterial blooms, is ubiquitously distributed in water. Microcystins (MCs) purified from M. aeruginosa can exert reproductive toxicity in fish. However, the effects of M. aeruginosa at environmentally relevant levels on the reproductive and endocrine systems of zebrafish are still unknown. The present study investigated the reproductive and endocrine-disrupting toxicity of M. aeruginosa on female zebrafish (Danio rerio) by short-term exposure (96 h). After exposure, marked histological lesions in the liver or gonads, such as nuclear pyknosis and deformation, were observed, and the fertilization rate and hatchability of eggs spawned from treated females were both significantly lower than they were in females in the control group, suggesting the possibility of transgenerational effects of M. aeruginosa exposure. Moreover, M. aeruginosa exposure decreased the concentration of 17β-estradiol (E2) and testosterone (T) in female zebrafish. Interestingly, the vtg1 transcriptional level significantly decreased in the liver, whereas plasma vitellogenin (VTG) protein levels increased. The present findings indicate that M. aeruginosa could modulate endocrine function by disrupting transcription of hypothalamic-pituitary-gonadal-liver (HPGL) axis-related genes, and impair the reproductive capacity of female zebrafish, suggesting that M. aeruginosa causes potential adverse effects on fish reproduction in Microcystis bloom-contaminated aquatic environments.

Excretion pattern and dynamics of glutathione detoxification of microcystins in Sprague Dawley rat

The excretion route and dynamics of the glutathione (GSH) conjugate of microcystin-RR (MCRR), MCRR-GSH, were quantitatively studied in Sprague Dawley rat exposed with MCRR-GSH via liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS). In the MCRR-GSH-treated rat, the average MCRR-Cysteine (MCRR-Cys)/MCRR-GSH ratio reached as high as 105.3, which indicated that the intermediate conjugate MCRR-GSH was rapidly converted to the product compound MCRR-Cys. Besides, MCRR was consistently detected in MCRR-GSH-treated rat, which suggested that MCRR can be dissociated from the MCRR-GSH conjugate and the reversibility of the MC-GSH conjugate. Results of total MC contents analysis in excrement showed that the total MC contents in urine were significantly higher than those in feces. The ratio of the total MC content in urine to feces was as high as 129.3, which demonstrates that the urine is the main route of excretion after MCRR-GSH-treatment. In urine, the MCRR-Cys concentration was 27.8-fold, 19.4-fold higher than MCRR-GSH and MCRR, respectively. Our results, for the first time, quantitatively found that MCRR-GSH was rapidly converted to MCRR-Cys after exposed to rat, and was excreted mainly through urine in the form of the MCRR-Cys conjugate. This study suggests that the GSH detoxification pathway of MCs could help to explain the greater sensitivity of mammals to MCs.