Sustained effects of developmental exposure to inorganic arsenic on hepatic gsto2 expression and mating success in zebrafish

The impacts of exposure to the pervasive environmental toxicant, inorganic arsenic (iAs), on human and fish health are well characterized and several lines of evidence suggest that some impacts can manifest years after exposure cessation. Using a developmental exposure protocol whereby zebrafish embryos were exposed to 0.5 and 1.5 mM iAs from 4-120 hours post fertilization (hpf) and then removed, we investigated the sustained effects of iAs on gene expression in the liver, survival, reproductive success, and susceptibility to iAs toxicity in the subsequent generation. Persistent exposure to iAs during development had substantial effects on the hepatic transcriptome, with 23% of all expressed genes significantly changed following developmental exposure. The gsto2 gene is involved in iAs metabolism and this gene was significantly downregulated in female livers 9 months after iAs was removed. Developmental exposure to 1.5 mM iAs, but not 0.5 mM, decreased survival by over 50% at 3 months of age. Adults that were developmentally exposed to 0.5 mM iAs had reduced mating success, but their offspring had no differences in observable aspects of development or their susceptibility to iAs toxicity. This demonstrates that developmental exposure of zebrafish to iAs reduces long-term survival, reproductive success and causes sustained changes to gsto2 expression in the liver.

Poison in the water: Arsenic's silent assault on fish health

Arsenic occurs across the world in freshwater and marine environments, menacing the survival of aquatic organisms. Organic and inorganic forms of this substance can be found, in which the inorganic form is more hazardous than the organic form. Most aquatic bodies contain inorganic arsenic species, but organic species are believed to be the dominant form of arsenic in the majority of fish. Natural and anthropogenic both are the sources of water contamination with arsenic. Its bioaccumulation and transfer from one trophic level to another in the aquatic food chain make arsenic a vital environmental issue. Continuous exposure to low concentrations of arsenic in aquatic organisms including fish leads to its bioaccumulation, which may affect organisms of higher trophic levels including large fishes or humans. Humans can be exposed to arsenic through the consumption of fish contaminated with arsenic. Hence, the present review facilitates our understanding about sources of arsenic, its bioaccumulation, food chain transfer, and its effect on the fish health. Also, "Poison in the Water: Arsenic's Silent Assault on Fish Health" serves as a wake-up call to recognize the pressing need to address arsenic contamination in water bodies. By understanding its devastating impact on fish health, we can strive to implement sustainable practices and policies that safeguard our precious aquatic environments and ensure the well-being of both wildlife and human communities that depend on them.

Joint Action Toxicity of Arsenic (As) and Lead (Pb) Mixtures in Developing Zebrafish

Arsenic (As) and lead (Pb) are environmental pollutants found in common sites and linked to similar adverse health effects. Multiple studies have investigated the toxicity of each metal individually or in complex mixtures. Studies defining the joint interaction of a binary exposure to As and Pb, especially during the earliest stages of development, are limited and lack confirmation of the predicted mixture interaction. We hypothesized that a mixture of As (iAsIII) and Pb will have a concentration addition (CA) interaction informed by common pathways of toxicity of the two metals. To test this hypothesis, developing zebrafish (1-120 h post fertilization; hpf) were first exposed to a wide range of concentrations of As or Pb separately to determine 120 hpf lethal concentrations. These data were then used in the CA and independent action (IA) models to predict the type of mixture interaction from a co-exposure to As and Pb. Three titration mixture experiments were completed to test prediction of observed As and Pb mixture interaction by keeping the Pb concentration constant and varying As concentrations in each experiment. The prediction accuracy of the two models was then calculated using the prediction deviation ratio (PDR) and Chi-square test and regression modeling applied to determine type of interaction. Individual metal exposures determined As and Pb concentrations at which 25% (39.0 ppm Pb, 40.2 ppm As), 50% (73.8 ppm Pb, 55.4 ppm As), 75% (99.9 ppm Pb, 66.6 ppm As), and 100% (121.7 ppm Pb, 77.3 ppm As) lethality was observed at 120 hpf. These data were used to graph the predicted mixture interaction using the CA and IA models. The titration experiments provided experimental observational data to assess the prediction. PDR values showed the CA model approached 1, whereas all PDR values for the IA model had large deviations from predicted data. In addition, the Chi-square test showed most observed results were significantly different from the predictions, except in the first experiment (Pb LC₂₅ held constant) with the CA model. Regression modeling for the IA model showed primarily a synergistic response among all exposure scenarios, whereas the CA model indicated additive response at lower exposure concentrations and synergism at higher exposure concentrations. The CA model was a better predictor of the Pb and As binary mixture interaction compared to the IA model and was able to delineate types of mixture interactions among different binary exposure scenarios.

Identification of collagen 1α3 in teleost fish species and typical collision induced internal fragmentations

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Identification of collagen 1α3 in several fish species using LC-MS.

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Visualization of collagen (type) similarity on the nucleotide and amino acid level.

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Assessment of database collagen annotations.

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Further investigation of the formation of pG⁺ fragment ions.

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Detailed description of collagen-specific collision induced internal fragment ion series.

In contrast to collagens 1α1 and 1α2, the more obscure collagen 1α3 is sparsely mentioned in literature. In skin collagen type 1 of teleosts (bony fish), however, the chain occurs in a heterotrimer together with collagens 1α1 and 1α2, which makes it one of the most abundant proteins in teleosts. As teleost fish species and gelatin (hydrolysate) prepared from their skin are a major source for food products and nutraceuticals, the goal of the study was to selectively identify collagen 1α3 in several fish species. Fish skin extracts and fish skin gelatins were analyzed using LC-MS. Depending on the amount of available genetic information different approaches were used to identify collagen 1α3. Additionally, collagen-specific collision induced internal fragmentations are discussed, which are important to consider during data analysis. Ultimately the presence of collagen 1α3 could be confirmed using LC-MS in multiple fish species.

Lipid Metabolism Alterations in a Rat Model of Chronic and Intergenerational Exposure to Arsenic

Chronic exposure to arsenic (As), whether directly through the consumption of contaminated drinking water or indirectly through the daily intake of As-contaminated food, is a health threat for more than 150 million people worldwide. Epidemiological studies found an association between chronic consumption of As and several pathologies, the most common being cancer-related disorders. However, As consumption has also been associated with metabolic disorders that could lead to diverse pathologies, such as type 2 diabetes mellitus, nonalcoholic fatty liver disease, and obesity. Here, we used ultra-performance liquid chromatography (UPLC) coupled to electrospray ionization/quadrupole time-of-flight mass spectrometry (ESI-QToF) to assess the effect of chronic intergenerational As exposure on the lipid metabolism profiles of serum from 4-month-old Wistar rats exposed to As prenatally and also during early life in drinking water (3 ppm). Significant differences in the levels of certain identified lysophospholipids, phosphatidylcholines, and triglycerides were found between the exposed rats and the control groups, as well as between the sexes. Significantly increased lipid oxidation determined by the malondialdehyde (MDA) method was found in exposed rats compared with controls. Chronic intergenerational As exposure alters the rat lipidome, increases lipid oxidation, and dysregulates metabolic pathways, the factors associated with the chronic inflammation present in different diseases associated with chronic exposure to As (i.e., keratosis, Bowen's disease, and kidney, liver, bladder, and lung cancer).

Use of proteomics to detect sex-related differences in effects of toxicants: implications for using proteomics in toxicology

This review provides an overview of results obtained when using proteome analysis for detecting sex-based differences in response to toxicants. It reveals implications to be taken into account when considering the use of proteomics in toxicological studies. It appears that results may differ when studying the same chemical in the same species in different target tissues. Another result of interest is the limited dose-response behavior of differential abundance patterns observed in studies where more than one dose level is tested. It is concluded that use of proteomics to study differences in modes of action of toxic compounds is an active area of research. The examples from use of proteomics to study sex-dependent differences also reveal that further studies are needed to provide reliable insight in modes of action, novel biomarkers or even novel therapies. To eventually reach this aim for this and other toxicological endpoints, it is essential to consider background variability, consequences of timing of toxicant administration, dose-response behavior, relevant species and target organ, species and organ variability and the presence of proteoforms.

Molecular cloning and tissue distribution of fatty acid binding protein-3 in goldfish (Carassius auratus) and its mRNA expression in response to cadmium and PAMPs

Fatty acid binding proteins (FABPs) are members of the conserved, multigene family of intracellular lipid binding proteins. In this study, the full-length cDNA of goldfish (Carassius auratus) FABP-3 (gfFABP-3) was successfully cloned. gfFABP-3 had an open reading frame of 402 bp and encoded a 133 amino acid polypeptide. The predicted gfFABP-3 protein included a lipocalin domain and displayed typical conserved FABP tertiary structures. Reverse transcription-PCR (RT-PCR) revealed that the gfFABP-3 gene was expressed in all tested tissues, with higher levels of expression in the testis, liver, heart, fat and kidney. After 24 h of cadmium exposure, gfFABP-3 was significantly upregulated in the gill, liver and spleen, but downregulated in the intestine, as compared to unexposed controls. gfFABP-3 expression was significantly downregulated in the spleen in goldfish challenged with LPS and Poly I:C. Our study provides a molecular characterization of goldfish FABP-3 and indicated that gfFABP-3 was potentially associated with the toxic effects of cadmium on lipid metabolism, and with the immune response to pathogenic infection.

Identification of potential biomarkers of hepatotoxicity by plasma proteome analysis of arsenic-exposed carp Labeo rohita

Arsenic (As) is a toxic environmental contaminant and potential human carcinogen. Chronic intake of arsenic-contaminated water and food leads to arsenicosis, a major public health problem in many parts of the world. Early detection of arsenic toxicity would greatly benefit patients; however, the detection of arsenicosis needs to be done early before onset of severe symptoms in which case the tools used for detection have to be both sensitive and reliable. In this context, the present study investigated plasma proteome changes in arsenic-exposed Labeo rohita, with the aim of identifying biomarkers for arsenicosis. Changes in the plasma proteome were investigated using gel-based proteomics technology. Using quantitative image analysis of the 2D proteome profiles, 14 unique spots were identified by MALDI-TOF/TOF MS and/or LC-MS/MS which included Apolipoprotein-A1 (Apo-A1) (6 spots), α-2 macroglobulin-like protein (A2ML) (2 spots), transferrin (TF) (3 spots) and warm-temperature acclimation related 65kDa protein (Wap65). The proteome data are available via ProteomeXchange with identifier PXD003404. Highly abundant protein spots identified in plasma from arsenic-exposed fish i.e. Apo-A1 (>10-fold), A2ML (7-fold) and Wap65 (>2-fold) indicate liver damage. It is proposed that a combination of these proteins could serve as useful biomarkers of hepatotoxicity and chronic liver disease due to arsenic exposure.

Gender-Specific Toxicological Effects of Chronic Exposure to Pure Microcystin-LR or Complex Microcystis aeruginosa Extracts on Adult Medaka Fish

Cyanobacterial blooms often occur in freshwater lakes and constitute a potential health risk to human populations, as well as to other organisms. However, their overall and specific implications for the health of aquatic organisms that are chronically and environmentally exposed to cyanobacteria producing hepatotoxins, such as microcystins (MCs), together with other bioactive compounds have still not been clearly established and remain difficult to assess. The medaka fish was chosen as the experimental aquatic model for studying the cellular and molecular toxicological effects on the liver after chronic exposures (28 days) to environmentally relevant concentrations of pure MC-LR, complex extracts of MC producing or nonproducing cyanobacterial biomasses, and of a Microcystis aeruginosa natural bloom. Our results showed a higher susceptibility of females to the different treatments compared to males at both the cellular and the molecular levels. Although hepatocyte lysis increased with MC-containing treatments, lysis always appeared more severe in the liver of females compare to males, and the glycogen cellular reserves also appeared to decrease more in the liver of females compared to those in the males. Proteomic investigations reveal divergent responses between males and females exposed to all treatments, especially for proteins involved in metabolic and homeostasis processes. Our observations also highlighted the dysregulation of proteins involved in oogenesis in female livers. These results suggest that fish populations exposed to cyanobacteria blooms may potentially face several ecotoxicological issues.

Zebrafish: an important tool for liver disease research

As the incidence of hepatobiliary diseases increases, we must improve our understanding of the molecular, cellular, and physiological factors that contribute to the pathogenesis of liver disease. Animal models help us identify disease mechanisms that might be targeted therapeutically. Zebrafish (Danio rerio) have traditionally been used to study embryonic development but are also important to the study of liver disease. Zebrafish embryos develop rapidly; all of their digestive organs are mature in larvae by 5 days of age. At this stage, they can develop hepatobiliary diseases caused by developmental defects or toxin- or ethanol-induced injury and manifest premalignant changes within weeks. Zebrafish are similar to humans in hepatic cellular composition, function, signaling, and response to injury as well as the cellular processes that mediate liver diseases. Genes are highly conserved between humans and zebrafish, making them a useful system to study the basic mechanisms of liver disease. We can perform genetic screens to identify novel genes involved in specific disease processes and chemical screens to identify pathways and compounds that act on specific processes. We review how studies of zebrafish have advanced our understanding of inherited and acquired liver diseases as well as liver cancer and regeneration.

Nmdmc overexpression extends Drosophila lifespan and reduces levels of mitochondrial reactive oxygen species

NAD-dependent methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase (NMDMC) is a bifunctional enzyme involved in folate-dependent metabolism and highly expressed in rapidly proliferating cells. However, Nmdmc physiological roles remain unveiled. We found that ubiquitous Nmdmc overexpression enhanced Drosophila lifespan and stress resistance. Interestingly, Nmdmc overexpression in the fat body was sufficient to increase lifespan and tolerance against oxidative stress. In addition, these conditions coincided with significant decreases in the levels of mitochondrial ROS and Hsp22 as well as with a significant increase in the copy number of mitochondrial DNA. These results suggest that Nmdmc overexpression should be beneficial for mitochondrial homeostasis and increasing lifespan.

Dramatic improvement of proteomic analysis of zebrafish liver tumor by effective protein extraction with sodium deoxycholate and heat denaturation

Majority of the proteomic studies on tissue samples involve the use of gel-based approach for profiling and digestion. The laborious gel-based approach is slowly being replaced by the advancing in-solution digestion approach. However, there are still several difficulties such as difficult-to-solubilize proteins, poor proteomic analysis in complex tissue samples, and the presence of sample impurities. Henceforth, there is a great demand to formulate a highly efficient protein extraction buffer with high protein extraction efficiency from tissue samples, high compatibility with in-solution digestion, reduced number of sample handling steps to reduce sample loss, low time consumption, low cost, and ease of usage. Here, we evaluated various existing protein extraction buffers with zebrafish liver tumor samples and found that sodium deoxycholate- (DOC-) based extraction buffer with heat denaturation was the most effective approach for highly efficient extraction of proteins from complex tissues such as the zebrafish liver tumor. A total of 4,790 proteins have been identified using shotgun proteomics approach with 2D LC, which to our knowledge is the most comprehensive study for zebrafish liver tumor proteome.

Stressor-induced proteome alterations in zebrafish: a meta-analysis of response patterns

Proteomics approaches are being increasingly applied in ecotoxicology on the premise that the identification of specific protein expression changes in response to a particular chemical would allow elucidation of the underlying molecular pathways leading to an adverse effect. This in turn is expected to promote the development of focused testing strategies for specific groups of toxicants. Although both gel-based and gel-free global characterization techniques provide limited proteome coverage, the conclusions regarding the cellular processes affected are still being drawn based on the few changes detected. To investigate how specific the detected responses are, we analyzed a set of studies that characterized proteome alterations induced by various physiological, chemical and biological stressors in zebrafish, a popular model organism. Our analysis highlights several proteins and protein groups, including heat shock and oxidative stress defense proteins, energy metabolism enzymes and cytoskeletal proteins, to be most frequently identified as responding to diverse stressors. In contrast, other potentially more specifically responding protein groups are detected much less frequently. Thus, zebrafish proteome responses to stress reported by different studies appear to depend mostly on the level of stress rather than on the specific stressor itself. This suggests that the most broadly used current proteomics technologies do not provide sufficient proteome coverage to allow in-depth investigation of specific mechanisms of toxicant action. We suggest that the results of any differential proteomics experiment performed with zebrafish should be interpreted keeping in mind the list of the most frequent responders that we have identified. Similar reservations should apply to any other species where proteome responses are analyzed by global proteomics methods. Careful consideration of the reliability and significance of observed changes is necessary in order not to over-interpret the experimental results and to prevent the proliferation of false positive linkages between the chemical and the cellular functions it perturbs. We further discuss the implications of the identified "top lists" of frequently responding proteins and protein families, and suggest further directions for proteomics research in ecotoxicology. Apart from improving the proteome coverage, further research should focus on defining the significance of the observed stress response patterns for organism phenotypes and on searching for common upstream regulators that can be targeted by specific assays.

Arsenic exposure alters expression of cell cycle and lipid metabolism genes in the liver of adult zebrafish (Danio rerio)

Adult zebrafish (Danio rerio) were used to investigate mRNA expression in the liver following 7-day and 21-day exposures to 0, 10, 50, or 500 ppb sodium arsenite. Arsenic exposure has been linked to several human disorders including cancers and cardiovascular and metabolic diseases. Quantitative PCR was employed to determine the mRNA expression of genes involved in cell cycle regulation [cyclin E1 (ccne1), WEE1 A kinase (wee1)], DNA damage repair [breast cancer 2 (brca2)] and lipid transport and metabolism [carnitine O-octanoyltransferase (crot), fatty acid binding protein-3 (fabp3) and 3-hydroxy-3-methylglutaryl-CoA synthase 1 (hmgcs1)]. Results from the 7-day exposure showed sex- and dose-specific changes in expression of wee1, brca2, crot and hmgcs1. No significant differences from controls were observed in fish exposed for 21 days. Expression of all genes, except ccne1, was significantly different between the 7- and 21-day exposures. The results presented here correlate with prior findings from our lab and others, and offer further insight into potential mechanisms of low-dose arsenic exposure.

Embryonic exposure to sodium arsenite perturbs vascular development in zebrafish

Exposure to arsenic in its inorganic form, arsenite, causes adverse effects to many different organs and tissues. Here, we have investigated arsenite-induced adverse effects on vascular tissues in the model organism zebrafish, Danio rerio. Zebrafish embryos were exposed to arsenite at different exposure windows and the susceptibility to vascular tissue damage was recorded at 72hours post fertilization (hpf). Intersegmental vessel sprouting and growth was most perturbed by exposure to arsenite during the 24-48hpf window, while disruption in the condensation of the caudal vein plexus was more often observed at the 48-72hpf exposure window, reflecting when these structures develop during normal embryogenesis. The vascular growth rate was decreased by arsenite exposure, and deviated from that of control embryos at around 24-26.5hpf. We further mapped changes in expression of key regulators of angiogenesis and vasculogenesis. Downregulation of vascular endothelial growth factor receptor 1/fms-related tyrosine kinase 1 (vegfr1/flt1) expression was evident already at 24hpf, coinciding with the decreased vascular growth rate. At later time points, matrix metalloproteinase 9 (mmp9) expression was upregulated, suggesting that arsenite affects the composition of the extracellular matrix. In total, the expression of eight key factors involved in different aspects of vascularization was significantly altered by arsenic exposure. In conclusion, our results show that arsenite is a potent vascular disruptor in the developing zebrafish embryo, a finding that calls for an evaluation of arsenite as a developmental vascular toxicant in mammalian model systems.

Development of a convenient in vivo hepatotoxin assay using a transgenic zebrafish line with liver-specific DsRed expression

Previously we have developed a transgenic zebrafish line (LiPan) with liver-specific red fluorescent protein (DsRed) expression under the fabp10a promoter. Since red fluorescence in the liver greatly facilitates the observation of liver in live LiPan fry, we envision that the LiPan zebrafish may provide a useful tool in analyses of hepatotoxicity based on changes of liver red fluorescence intensity and size. In this study, we first tested four well-established hepatotoxins (acetaminophen, aspirin, isoniazid and phenylbutazone) in LiPan fry and demonstrated that these hepatotoxins could significantly reduce both liver red fluorescence and liver size in a dosage-dependent manner, thus the two measurable parameters could be used as indicators of hepatotoxicity. We then tested the LiPan fry with nine other chemicals including environmental toxicants and human drugs. Three (mefenamic acid, lindane, and arsenate) behave like hepatotoxins in reduction of liver red fluorescence, while three others (17β-estradiol, TCDD [2,3,7,8-tetrachlorodibenzo-p-dioxin] and NDMA [N-nitrosodimethylamine]) caused increase of liver red fluorescence and the liver size. Ethanol and two other chemicals, amoxicillin (antibiotics) and chlorphenamine (pain killer) did not resulted in significant changes of liver red fluorescence and liver size. By quantitative RT-PCR analysis, we found that the changes of red fluorescence intensity caused by different chemicals correlated to the changes of endogenous fabp10a RNA expression, indicating that the measured hepatotoxicity was related to fatty acid transportation and metabolism. Finally we tested a mixture of four hepatotoxins and observed a significant reduction of red fluorescence in the liver at concentrations below the lowest effective concentrations of individual hepatotoxins, suggesting that the transgenic zebrafish assay is capable of reporting compound hepatotoxicity effect from chemical mixtures. Thus, the LiPan transgenic fry provide a rapid and convenient in vivo hepatotoxicity assay that should be applicable to high-throughput hepatotoxicity test in drug screening as well as in biomonitoring environmental toxicants.