Physiological changes and differential gene expression in mummichogs (Fundulus heteroclitus) exposed to arsenic

Molecular docking prediction and hepatoprotective potential of genistein-enriched diet against arsenic toxicity in juvenile nile tilapia: implications for ER stress and oxidative damage

The current study evaluated the effects of genistein (GEN) supplementation to alleviate the arsenic (As)-induced hepatotoxicity in Oreochromis niloticus. This was conducted in two steps: a computational prediction study (in silico) and an experimental investigation (in vivo). The prediction step involved molecular docking analysis to assess the interactions between GEN and key stress-related mRNAs in Nile tilapia. In the experimental phase, 160 Nile tilapia fingerlings were randomly assigned to four treatment groups (in four replicates/group) for 60 days: (1) a control group fed a basal diet, (2) a GEN group receiving a GEN-supplemented diet (500 mg/kg), (3) an As group exposed to 10 µg/L As, and (4) an As + GEN group, in which fish was exposed to As and fed the GEN-supplemented diet. The computational assessment of GEN's binding ability revealed strong interactions with key mRNAs associated with inflammation and misfolded protein responses. The in vivo results revealed that GEN significantly alleviated As-induced hepatic oxidative stress and hepatocellular damage by restoring liver enzyme levels, lipid profiles, and bilirubin content and restoring the serum proteins to near-normal values. Additionally, GEN downregulated the expression of endoplasmic reticulum (ER) stress- and inflammation-related genes in the liver tissue of the As + GEN group, compared to the As-exposed fish fed on a basal diet. Additionally, the histopathological analysis further confirmed that GEN supplementation mitigated hepatic tissue damage, reducing necrosis, congestion, and inflammatory cell infiltration. In conclusion, GEN supplementation effectively counteracted As-induced hepatotoxicity in Nile tilapia by modulating oxidative stress, ER stress, and inflammation while preserving liver structure and function. Also, the molecular docking results suggest that GEN interacts with the mRNAs of inflammatory and misfolded protein targets, which are increased due to exposure to As-contaminated water. All our findings highlight GEN as a promising natural dietary additive for improving hepatic health in fish inhabiting As-contaminated environments.

Effects of Co-Exposure of Nanoparticles and Metals on Different Organisms: A Review

Wide nanotechnology applications and the commercialization of consumer products containing engineered nanomaterials (ENMs) have increased the release of nanoparticles (NPs) to the environment. Titanium dioxide, aluminum oxide, zinc oxide, and silica NPs are widely implicated NPs in industrial, medicinal, and food products. Different types of pollutants usually co-exist in the environment. Heavy metals (HMs) are widely distributed pollutants that could potentially co-occur with NPs in the environment. Similar to what occurs with NPs, HMs accumulation in the environment results from anthropogenic activities, in addition to some natural sources. These pollutants remain in the environment for long periods and have an impact on several organisms through different routes of exposure in soil, water, and air. The impact on complex systems results from the interactions between NPs and HMs and the organisms. This review describes the outcomes of simultaneous exposure to the most commonly found ENMs and HMs, particularly on soil and aquatic organisms.

Barbosa-Filho, Lucia Helena S. de S. Pereira, Catarina A. Lopes, Sérgio C. Moreira, Rafael C.C. Rocha, Tatiana D. Saint’Pierre, Paula Baldassin, Salvatore Siciliano. First record of a morphologically abnormal and highly metal-contaminated Spotback Skate Atlantoraja castelnaui (Rajiformes: Arhynchobatidae) from southeastern Rio de Janeiro, Brazil

This paper reports the first record of a morphologically abnormal and highly metal-contaminated Spotback Skate Atlantoraja castelnaui (Ribeiro, 1907) (Elasmobranchii, Rajidae) in Rio de Janeiro, Brazil. Incomplete fusion of the right pectoral fin with the head was observed, while a radiography indicated muscle sheaf discontinuity near the rostrum.  Extremely high contamination by several elements, including teratogenic As, Hg and Cd in the individual was detected.  The observed morphological deformity may be due to high concentrations of teratogenic elements in the environment, possibly playing a role in abnormal embryonic development in egg cases exposed to high environmental concentrations of these contaminants.  Atlantoraja castelnaui is the least biologically understood member of the genus Atlantoraja, and this paper furthers both morphological observations and ecotoxicological assessments on this species. 

Cytotoxic and genotoxic effects of arsenic on erythrocytes of Oryzias latipes: Bioremediation using Spirulina platensis

BACKGROUND

Exposure to the environmental pollutants poses a serious threat to aquatic organism. The arsenic exposure in fish increases the risk of developing serious alterations from embryo to adult.

OBJECTIVES

The present investigation was done to study the toxic effects of heavy metal arsenic [As(III)] on medaka (Oryzias latipes). Morphological alterations, apoptosis, nuclear abnormalities, and genotoxic biomarkers in erythrocytes were used to determine the stress caused by arsenic (As) exposure.

METHODS

Medaka was exposed to As for 15 days at two toxic sublethal concentrations (7 ppm and 10 ppm) in combination with Spirulina platensis (SP) treatment as antioxidant algae at 200 mg/L.

RESULTS

Results were consistent with a previous study results on tilapia. Exposure of medaka to As resulted in a dose-dependent increase in most the biomarkers used in the current study. Fish exposed to10 ppm As showed highest level of DNA damage. For the first time to our knowledge, using SP to counter the As toxicity in medaka, DNA damage restored to control levels.

CONCLUSION

Accordingly, those results suggests that SP can protect medaka in aquaculture against As-induced damage by its ability as reactive oxygen species (ROS) reducer, antioxidant role, and DNA damage scavenger.

Assessment of arsenic trioxide toxicity on cock muscular tissue: alterations of oxidative damage parameters, inflammatory cytokines and heat shock proteins

To evaluate the toxicity of arsenic trioxide (As₂O₃) in the muscular tissues (wing, thigh and pectoral) of birds, 72 one-day-old Hy-line cocks were selected and randomly divided into four groups. They were fed either a commercial diet or an arsenic-supplemented diet containing 7.5, 15 or 30 mg/kg As₂O₃. The experiment lasted for 90 days and the samples of muscular tissues were collected at 30, 60 and 90 days. The results showed that As₂O₃ exposure significantly lowered the activities of antioxidant enzymes (catalase (CAT), glutathione peroxidase (GSH-Px)) and inhibition ability of hydroxyl radicals (OH) and increased the malondialdehyde (MDA) contents. Furthermore, the mRNA levels of inflammatory cytokines (tumor necrosis factor-α (TNF-α), nuclear factor-kappa B (NF-κB), cyclooxygenase-2 (COX-2), inducible NO synthase (iNOS), prostaglandin E synthase (PTGEs)) and heat shock proteins (HSPs) in muscular tissue were significantly upregulated in the As₂O₃ exposure groups. The results indicated that As₂O₃ exposure resulted in oxidative damage, induced the inflammatory response, and influenced the mRNA levels of HSPs in muscular tissue of cocks. Additionally, the results suggested that HSPs possibly resisted due to the As₂O₃ exposure-induced oxidative stress and inflammatory response, which provided a favorable environment and played protective roles in the muscular tissues of cocks. The information presented in this study is helpful to understand the mechanism of As₂O₃ toxicity in bird muscular tissues.

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.

Effects of low arsenic concentration exposure on freshwater fish in the presence of fluvial biofilms

Arsenic (As) is a highly toxic element and its carcinogenic effect on living organisms is well known. However, predicting real effects in the environment requires an ecological approach since toxicity is influenced by many environmental and biological factors. The purpose of this paper was to evaluate if environmentally-realistic arsenic exposure causes toxicity to fish. An experiment with four different treatments (control (C), biofilm (B), arsenic (+As) and biofilm with arsenic (B+As)) was conducted and each one included sediment to enhance environmental realism, allowing the testing of the interactive effects of biofilm and arsenic on the toxicity to fish. Average arsenic exposure to Eastern mosquitofish (Gambusia holbrooki) was 40.5 ± 7.5 μg/L for +As treatment and 34.4 ± 1.4 μg/L for B+As treatment for 56 days. Fish were affected directly and indirectly by this low arsenic concentration since exposure did not only affect fish but also the function of periphytic biofilms. Arsenic effects on the superoxide dismutase (SOD) and glutathione reductase (GR) activities in the liver of mosquitofish were ameliorated in the presence of biofilms at the beginning of exposure (day 9). Moreover, fish weight gaining was only affected in the treatment without biofilm. After longer exposure (56 days), effects of exposure were clearly seen. Fish showed a marked increase in the catalase (CAT) activity in the liver but the interactive influence of biofilms was not further observed since the arsenic-affected biofilm had lost its role in water purification. Our results highlight the interest and application of incorporating some of the complexity of natural systems in ecotoxicology and support the use of criterion continuous concentration (CCC) for arsenic lower than 150 μg/L and closer to the water quality criteria to protect aquatic life recommended by the Canadian government which is 5 μg As/L.

Arsenic induced hematological and biochemical responses in nutritionally important catfish Clarias batrachus (L.)

The impact of sublethal toxicity of sodium arsenite on hematological and certain biochemical parameters of the fresh water catfish Clarias batrachus has been analyzed following exposure of sublethal concentration (1 mg/L; 5% of LC₅₀ value) of sodium arsenite for 10, 30, 45, and 60 days. Arsenic bioaccumulation in the blood tissue of the fish increased progressively with increased period of exposure. The values of total erythrocyte count (TECs), total leucocytes count (TLCs), hemoglobin concentration, and packed cell volume (PCV) 1.40 ± 0.03 × 10⁶/mm³, 174.83 ± 2.74 × 10³/mm³, 5.01 ± 0.26 g/100 ml, 25.00 ± 1.06 were observed respectively at the end of 60 days of exposure. The results of hematological indices were found to be 179.23 ± 8.81fl/cell for mean corpuscular volume (MCV), 35.92 ± 1.89 pg/cell for mean corpuscular hemoglobin (MCH) and 20.17 ± 1.12 g/dl for mean corpuscular hemoglobin concentration (MCHC). The present findings are clearly indicating severe fish anemia due to the arsenic salt exposure. The continued arsenic toxicity results in decreased serum protein concentration that might be a cause for the loss of weight as well as weakness in the fish.

Effects of titanium dioxide nanoparticles on lead bioconcentration and toxicity on thyroid endocrine system and neuronal development in zebrafish larvae

Nanoparticles (NPs) have attracted considerable attention because of their wide range of applications. Interactions between heavy metals (e.g., Pb) and NPs in aquatic environments may modify the bioavailability and toxicity of heavy metals. Therefore, this study investigated the influence of NPs (e.g., nano-TiO2) on the bioavailability and toxicity of Pb and its effects in the thyroid endocrine and nervous systems of zebrafish (Danio rerio) larvae. Zebrafish embryos (2-h post-fertilization) were exposed to five concentrations of Pb alone (0, 5, 10, 20, and 30μg/L) or in combination with nano-TiO2 (0.1mg/L) until 6 days post-fertilization. Results showed that the bioconcentration of Pb was significantly enhanced when combined with nano-TiO2 than when used alone. Zebrafish exposure to Pb alone at 30μg/L significantly decreased the thyroid hormone levels (T4 and T3), whereas nano-TiO2 treatment alone did not produce detectable changes. The levels of T4 and T3 were further decreased when Pb was combined with nano-TiO2 than when used alone. The transcription of the thyroid hormone-related factor tg gene was remarkably down-regulated by Pb treatment alone but up-regulated when Pb was combined with nano-TiO2. The significant up-regulation of tshβ gene and the down-regulation of TTR gene expression in the hypothalamic-pituitary-thyroid were observed in Pb with or without nano-TiO2 treatment groups. In addition, the transcription of genes involved in central nervous system (CNS) development (α-tubulin, mbp, gfap and shha) were significantly down-regulated by Pb and nano-TiO2 co-exposure as compared with Pb exposure alone. The locomotion activity analyzes confirmed that nano-TiO2 might enhance the toxicity of Pb to CNS development. These results suggest that nano-TiO2 increase bioconcentration of lead, which lead to the disruption of thyroid endocrine and neuronal system in zebrafish larvae.

The Elizabeth River Story: A Case Study in Evolutionary Toxicology

The Elizabeth River system is an estuary in southeastern Virginia, surrounded by the towns of Chesapeake, Norfolk, Portsmouth, and Virginia Beach. The river has played important roles in U.S. history and has been the location of various military and industrial activities. These activities have been the source of chemical contamination in this aquatic system. Important industries, until the 1990s, included wood treatment plants that used creosote, an oil-derived product that is rich in polycyclic aromatic hydrocarbons (PAH). These plants left a legacy of PAH pollution in the river, and in particular Atlantic Wood Industries is a designated Superfund site now undergoing remediation. Numerous studies examined the distribution of PAH in the river and impacts on resident fauna. This review focuses on how a small estuarine fish with a limited home range, Fundulus heteroclitus (Atlantic killifish or mummichog), has responded to this pollution. While in certain areas of the river this species has clearly been impacted, as evidenced by elevated rates of liver cancer, some subpopulations, notably the one associated with the Atlantic Wood Industries site, displayed a remarkable ability to resist the marked effects PAH have on the embryonic development of fish. This review provides evidence of how pollutants have acted as evolutionary agents, causing changes in ecosystems potentially lasting longer than the pollutants themselves. Mechanisms underlying this evolved resistance, as well as mechanisms underlying the effects of PAH on embryonic development, are also described. The review concludes with a description of ongoing and promising efforts to restore this historic American river.

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 arsenic exposure reduces the number of muscle fibers in killifish (Fundulus heteroclitus)

Arsenic is a contaminant of drinking water and has been correlated with adverse developmental outcomes such as low birth weight, reduced weight gain, and altered locomotor activity. Previous research has shown that killifish (Fundulus heteroclitus) exposed to high arsenic levels during embryogenesis had smaller muscle fiber diameters. The current study was designed to determine whether changes in muscle fibers persisted, were exacerbated, or resolved over time. Killifish embryos were exposed to 0-5 ppm arsenite and, upon hatching, were transferred into either clean water or continued receiving the same exposure to arsenic for up to 16 weeks. Arsenic significantly decreased the weight of both embryonic-only exposed juveniles and continuously exposed juveniles between 4 and 16 weeks of development at concentrations as low as 0.8 ppm. Although arsenite exposure increased the percentage of small diameter fibers during the early weeks, fiber diameters returned to control levels in the embryonic-only exposed fish. However, muscle fiber density was still reduced to 85.7%, 80.3%, and 73.8% of control for the 0.8, 2, and 5 ppm embryonic-only exposure groups, respectively, even after 16 weeks of development. These results indicate that while continuous exposure to arsenic may alter the size of muscle fibers, embryonic-only exposure to arsenic has lasting effects on the number of muscle fibers formed.

Arsenic induced toxicity and histopathological changes in gill and liver tissue of freshwater fish, tilapia (Oreochromis mossambicus)

Acute toxicity of arsenic to tilapia (Oreochromis mossambicus) and its histopathological impacts on gill and liver tissue were evaluated. The median lethal concentration (96 h; LC50) of arsenic (NaAsO₂) was calculated as 28.22 ppm in repeated semi static test method. Fish were exposed to 3 ppm, 28 ppm and 56 ppm concentrations of NaAsO₂ and gill and liver samples were collected after 48 h, 96 h and 192 h of exposure. The changes in gill were characterized by epithelial hyperplasia, epithelial lifting and oedema, lamellar fusion, aneurism, desquamation and necrosis, whereas, the liver tissue showed focal lymphocytic and macrophage infiltration, congestion, vacuolization and shrinkage of hepatocytes, dilation of sinusoids, cloudy swelling, vacuolar degeneration, focal necrosis and nuclear hypertrophy. The result showed that acute arsenic toxicity severely affects the normal behavior and vital organs which is deleterious for the exposed fish.

Trophic status and metal bioaccumulation differences in multiple fish species exposed to coal ash-associated metals

On December 22, 2008 a dike containing coal fly ash from the Tennessee Valley Authority Kingston Fossil Plant near Kingston Tennessee USA failed and resulted in the largest coal ash spill in U.S. history. Coal ash, a by-product of coal combustion, is known to contain multiple contaminants of concern, including arsenic and selenium. The purpose of this study was to investigate species differences in the bioaccumulation of arsenic and selenium and potential factors contributing to these differences (i.e., trophic dynamics and gut pH) in the vicinity of the Kingston coal ash spill. Elevated levels of arsenic and selenium were observed in various tissues of largemouth bass, white crappie, bluegill and redear sunfish from sites associated with the Kingston coal ash spill. Highest concentrations of selenium were found in redear sunfish with liver concentrations as high as 24.83mg/kg dry weight and ovary concentrations up to 10.40mg/kg dry weight at coal ash-associated sites. Investigations into the gut pH and trophic dynamics of redear sunfish and bluegill demonstrated a large difference in the gut physiology between these two species. Redear sunfish stomach and intestinal pH was found to be 1.1 and 0.16 pH units higher than in bluegill, respectively. In addition, fish from coal ash-associated sites showed enrichment differences ((15)N and (13)C) compared to no ash sites, indicating differences in food web dynamics between sites. These results imply the incorporation of coal ash-associated compounds into local food webs and/or a shift in diet at ash sites compared to the no ash reference sites. Based on these results, further investigation into a broader food web at ash-associated sites is warranted.

A novel aquaporin 3 in killifish (Fundulus heteroclitus) is not an arsenic channel

The Atlantic killifish (Fundulus heteroclitus) is a model environmental organism that has an extremely low assimilation rate of environmental arsenic. As a first step in elucidating the mechanism behind this phenomenon, we used quantitative real-time PCR to identify aquaglyceroporins (AQPs), which are arsenite transporters, in the killifish gill. A novel homolog killifish AQP3 (kfAQP3a) was cloned from the killifish gill, and a second homolog was identified as the consensus from a transcriptome database (kfAQP3b). The two were 99% homologous to each other, 98% homologous to a previously identified killifish AQP3 from embryos (kfAQP3ts), and 78% homologous to hAQP3. Expression of kfAQP3a in Xenopus oocytes significantly enhanced water, glycerol, and urea transport. However, kfAQP3a expressed in HEK293T cells did not transport significant amounts of arsenic. All sequence motifs thought to confer the ability of AQP3 to transport solutes were conserved in kfAQP3a, kfAQP3b, and kfAQP3ts; however, the C-terminal amino acids were different in kfAQP3a versus the other two homologs. Replacement of the three C-terminal amino acids of kfAQP3 (GKS) with the three C-terminal amino acids of kfAQP3b and kfAQP3ts (ANC) was sufficient to enable kfAQP3a to robustly transport arsenic. Thus, the C-terminus of kfAQP3b and kfAQP3ts confers arsenic selectivity in kfAQP3. Moreover, kfAQP3a, the only AQP expressed in killifish gill, is the first aquaglyceroporin identified that does not transport arsenic, which may explain, in part, why killifish poorly assimilate arsenic and are highly tolerant to environmental arsenic.

Sodium arsenite represses the expression of myogenin in C2C12 mouse myoblast cells through histone modifications and altered expression of Ezh2, Glp, and Igf-1

Arsenic is a toxicant commonly found in water systems and chronic exposure can result in adverse developmental effects including increased neonatal death, stillbirths, and miscarriages, low birth weight, and altered locomotor activity. Previous studies indicate that 20 nM sodium arsenite exposure to C2C12 mouse myocyte cells delayed myoblast differentiation due to reduced myogenin expression, the transcription factor that differentiates myoblasts into myotubes. In this study, several mechanisms by which arsenic could alter myogenin expression were examined. Exposing differentiating C2C12 cells to 20 nM arsenic increased H3K9 dimethylation (H3K9me2) and H3K9 trimethylation (H3K9me3) by 3-fold near the transcription start site of myogenin, which is indicative of increased repressive marks, and reduced H3K9 acetylation (H3K9Ac) by 0.5-fold, indicative of reduced permissive marks. Protein expression of Glp or Ehmt1, a H3-K9 methyltransferase, was also increased by 1.6-fold in arsenic-exposed cells. In addition to the altered histone remodeling status on the myogenin promoter, protein and mRNA levels of Igf-1, a myogenic growth factor, were significantly repressed by arsenic exposure. Moreover, a 2-fold induction of Ezh2 expression, and an increased recruitment of Ezh2 (3.3-fold) and Dnmt3a (~2-fold) to the myogenin promoter at the transcription start site (-40 to +42), were detected in the arsenic-treated cells. Together, we conclude that the repressed myogenin expression in arsenic-exposed C2C12 cells was likely due to a combination of reduced expression of Igf-1, enhanced nuclear expression and promoter recruitment of Ezh2, and altered histone remodeling status on myogenin promoter (-40 to +42).

Arsenic exposure to killifish during embryogenesis alters muscle development

Epidemiological studies have correlated arsenic exposure in drinking water with adverse developmental outcomes such as stillbirths, spontaneous abortions, neonatal mortality, low birth weight, delays in the use of musculature, and altered locomotor activity. Killifish (Fundulus heteroclitus) were used as a model to help to determine the mechanisms by which arsenic could impact development. Killifish embryos were exposed to three different sodium arsenite concentrations and were collected at 32 h post-fertilization (hpf), 42 hpf, 168 hpf, or < 24 h post-hatch. A killifish oligo microarray was developed and used to examine gene expression changes between control and 25-ppm arsenic-exposed hatchlings. With artificial neural network analysis of the transcriptomic data, accurate prediction of each group (control vs. arsenic-exposed embryos) was obtained using a small subset of only 332 genes. The genes differentially expressed include those involved in cell cycle, development, ubiquitination, and the musculature. Several of the genes involved in cell cycle regulation and muscle formation, such as fetuin B, cyclin D-binding protein 1, and CapZ, were differentially expressed in the embryos in a time- and dose-dependent manner. Examining muscle structure in the hatchlings showed that arsenic exposure during embryogenesis significantly reduces the average muscle fiber size, which is coupled with a significant 2.1- and 1.6-fold upregulation of skeletal myosin light and heavy chains, respectively. These findings collectively indicate that arsenic exposure during embryogenesis can initiate molecular changes that appear to lead to aberrant muscle formation.

Genetic damage induced by lead chloride in different tissues of fresh water climbing perch Anabas testudineus (Bloch)

The present investigation was undertaken to study the induction of DNA damage by lead chloride (PbCl(2)) in freshwater climbing perch Anabas testudineus using alkaline single cell gel electrophoresis (comet assay). Based on the LC(50) values of lead chloride of A. testudineus three different concentrations viz., 0.1, 1.0 and 2.0 mg/L were selected to expose fish. The DNA damage was observed in the gill, kidney and liver tissue as the percentage of DNA in comet tails and comet heads in the tissue of the exposed fish. DNA damage at different concentrations showed sensitivity to particular tissue. The liver tissue exhibited significantly (p < 0.01) higher DNA damage, followed by kidney and gill. However, the DNA damage was found to be dose dependent; at 2 mg/L of PbCl(2) the tail and head DNA of liver tissue were 57.84% and 39.49%, in kidney tissue the values were 52.36% and 44.97% whereas in gill tissue the values were 48.86% and 48.96% respectively. The current study explored the utility of the comet assay for in vivo laboratory studies using A. testudineus species for screening the genotoxic potential of lead chloride.

Acute exposure of arsenic tri-oxide produces hyperglycemia in both sexes of an Indian teleost, Clarias batrachus (Linn.)

The present investigation has been conducted to study of the effect of acute exposure of sublethal doses of arsenic tri-oxide (As(2)O(3)) on blood glucose level in an Indian teleost, Clarias batrachus, during their post-breeding season (October to January). The effect was correlated with the sex and doses used with time. Acute exposure of As(2)O(3) of 5, 10 and 15 mg/l for six consecutive days (i.e., 144 h) has been conducted on both sexes of C. batrachus. During the present investigation, it was noticed that the females were more reactive to arsenic in producing hyperglycemia compared to their male counterparts. The difference between males and females to produce hyperglycemia on exposure to arsenic appears to be dose dependent, as lower doses of 5 and 10 mg/l exhibit less difference between the two sexes compared to the highest dose order of 15 mg/l. After 96 h of treatment, a normoglycemic condition was observed in both sexes. However, no significant differences in average normal blood glucose levels were noticed in male and female C. batrachus during the post-breeding season.

Assessing the genotoxic potentials of arsenic in tilapia (Oreochromis mossambicus) using alkaline comet assay and micronucleus test

This experiment was conducted to study the genotoxic potentials of sodium arsenite (NaAsO(2)) in freshwater fish Oreochromis mossambicus by using alkaline comet assay and micronucleus (MN) test. Fish were exposed to three different concentrations (3 ppm, 28 ppm and 56 ppm) of arsenic and gill, liver and blood tissue samples were collected after 48 h, 96 h and 192 h of exposure. Arsenic exposure induced DNA damage in all tissues examined in a concentration dependent manner. A significant (p<0.05) increase in the comet tail DNA (%) of the exposed fish liver, gill, and blood was observed after 48 h and 96 h of exposure, but a decline in DNA damage was recorded in all the tissues at all the three concentrations studied after 192 h of exposure. Liver tissue exhibited significantly (p<0.05) higher DNA damage at all the concentrations examined, followed by gill and blood. Higher liver tail DNA (51.38 ± 0.21%) refers that it is more prone to injury to arsenic toxicity than the gill and blood. In blood samples arsenic induced micronucleus formation in a concentration dependent manner and highest (5.8 ± 0.46%) value was recorded in 56 ppm after 96 h of exposure, whereas, it was decreased after 192 h of exposure at all the three concentrations of NaAsO(2) examined which refers to the DNA repairing ability of fish to arsenic toxicity. The results of this study depict the genotoxic potentials of arsenic to fish which in turns provide insight on advanced study in aquatic toxicology.

Hematological, biochemical and ionoregulatory responses of Indian major carp Catla catla during chronic sublethal exposure to inorganic arsenic

In the present study the acute toxicity of arsenic trioxide in fingerlings of Catla catla an Indian major carp was evaluated with renewal bioassay method. The median lethal concentration of arsenic trioxide to the fish C. catla for 96 h was found to be 20.41 ppm (with 95% confidence limits). From this a non-lethal dose of (2.041 ppm; 1/10th of LC 50 96 value) was selected and fingerlings were exposed to 35 d and hematological, biochemical and ionoregulatory responses were studied at days 7, 14, 21, 28 and 35. Arsenic trioxide produced a significant increase in hemoglobin, hematocrit, WBC count, plasma GPT levels and reduction in RBC count, plasma sodium, chloride, potassium, glucose, protein, GOT, LDH levels as compared to the control group. Gill Na(+)/K(+)-ATPase activity was influenced by arsenic trioxide exposure. A biphasic response was noted in the value of MCH and MCV. However the MCHC level was not altered in arsenic trioxide treated fish throughout the study period. Results of the present investigation suggest that arsenic trioxide affects the hematological, biochemical and ionoregulatory parameters of fish and alterations of these parameters can be useful in environmental biomonitoring of arsenic contamination.

Sodium arsenite delays the differentiation of C2C12 mouse myoblast cells and alters methylation patterns on the transcription factor myogenin

Epidemiological studies have correlated arsenic exposure with cancer, skin diseases, and adverse developmental outcomes such as spontaneous abortions, neonatal mortality, low birth weight, and delays in the use of musculature. The current study used C2C12 mouse myoblast cells to examine whether low concentrations of arsenic could alter their differentiation into myotubes, indicating that arsenic can act as a developmental toxicant. Myoblast cells were exposed to 20 nM sodium arsenite, allowed to differentiate into myotubes, and expression of the muscle-specific transcription factor myogenin, along with the expression of tropomyosin, suppressor of cytokine signaling 3 (Socs3), prostaglandin I2 synthesis (Ptgis), and myocyte enhancer 2 (Mef2), was investigated using QPCR and immunofluorescence. Exposing C2C12 cells to 20 nM sodium arsenite delayed the differentiation process, as evidenced by a significant reduction in the number of multinucleated myotubes, a decrease in myogenin mRNA expression, and a decrease in the total number of nuclei expressing myogenin protein. The expression of mRNA involved in myotube formation, such as Ptgis and Mef2 mRNA, was also significantly reduced by 1.6-fold and 4-fold during differentiation. This was confirmed by immunofluorescence for Mef2, which showed a 2.6-fold reduction in nuclear translocation. Changes in methylation patterns in the promoter region of myogenin (-473 to +90) were examined by methylation-specific PCR and bisulfite genomic sequencing. Hypermethylated CpGs were found at -236 and -126 bp, whereas hypomethylated CpGs were found at -207 bp in arsenic-exposed cells. This study indicates that 20 nM sodium arsenite can alter myoblast differentiation by reducing the expression of the transcription factors myogenin and Mef2c, which is likely due to changes in promoter methylation patterns. The delay in muscle differentiation may lead to developmental abnormalities.

Dose-responsive gene expression changes in juvenile and adult mummichogs (Fundulus heteroclitus) after arsenic exposure

The present study investigated arsenic's effects on mummichogs (Fundulus heteroclitus), while also examining what role that gender or exposure age might play. Adult male and female mummichogs were exposed to 172 ppb, 575 ppb, or 1720 ppb arsenic as sodium arsenite for 10 days immediately prior to spawning. No differences were noted in the number or viability of eggs between the groups, but there was a significant increase in deformities in 1720 ppb arsenic exposure group. Total RNA from adult livers or 6-week old juveniles was used to probe custom macroarrays for changes in gene expression. In females, 3% of the genes were commonly differentially expressed in the 172 and 575 ppb exposure groups compared to controls. In the males, between 1.1 and 3% of the differentially expressed genes were in common between the exposure groups. Several genes, including apolipoprotein and serum amyloid precursor were commonly expressed in either a dose-responsive manner or were dose-specific, but consistent across genders. These patterns of regulation were confirmed by QPCR. These findings will provide us with a better understanding of the effects of dose, gender, and exposure age on the response to arsenic.

SNP identification, verification, and utility for population genetics in a non-model genus

Background

By targeting SNPs contained in both coding and non-coding areas of the genome, we are able to identify genetic differences and characterize genome-wide patterns of variation among individuals, populations and species. We investigated the utility of 454 sequencing and MassARRAY genotyping for population genetics in natural populations of the teleost, Fundulus heteroclitus as well as closely related Fundulus species (F. grandis, F. majalis and F. similis).

Results

We used 454 pyrosequencing and MassARRAY genotyping technology to identify and type 458 genome-wide SNPs and determine genetic differentiation within and between populations and species of Fundulus. Specifically, pyrosequencing identified 96 putative SNPs across coding and non-coding regions of the F. heteroclitus genome: 88.8% were verified as true SNPs with MassARRAY. Additionally, putative SNPs identified in F. heteroclitus EST sequences were verified in most (86.5%) F. heteroclitus individuals; fewer were genotyped in F. grandis (74.4%), F. majalis (72.9%), and F. similis (60.7%) individuals. SNPs were polymorphic and showed latitudinal clinal variation separating northern and southern populations and established isolation by distance in F. heteroclitus populations. In F. grandis, SNPs were less polymorphic but still established isolation by distance. Markers differentiated species and populations.

Conclusions

In total, these approaches were used to quickly determine differences within the Fundulus genome and provide markers for population genetic studies.

Fundulus as the premier teleost model in environmental biology: opportunities for new insights using genomics

A strong foundation of basic and applied research documents that the estuarine fish Fundulus heteroclitus and related species are unique laboratory and field models for understanding how individuals and populations interact with their environment. In this paper we summarize an extensive body of work examining the adaptive responses of Fundulus species to environmental conditions, and describe how this research has contributed importantly to our understanding of physiology, gene regulation, toxicology, and ecological and evolutionary genetics of teleosts and other vertebrates. These explorations have reached a critical juncture at which advancement is hindered by the lack of genomic resources for these species. We suggest that a more complete genomics toolbox for F. heteroclitus and related species will permit researchers to exploit the power of this model organism to rapidly advance our understanding of fundamental biological and pathological mechanisms among vertebrates, as well as ecological strategies and evolutionary processes common to all living organisms.