Low dose of arsenic trioxide triggers oxidative stress in zebrafish brain: expression of antioxidant genes

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.

Downregulation of B7-H4 in the MHCC97-H hepatocellular carcinoma cell line by arsenic trioxide

Arsenic trioxide (As2O3; ATO), a compound which is characterized by its ability to function as a potent anticancer agent, has been investigated in a variety of carcinomas. B7‑H4, a transmembrane protein, may inhibit the function of the T cell effector, and therefore, may be useful in investigating different types of tumor therapies. However, few studies have been published previously associated with the roles of ATO and B7‑H4 in human hepatocellular carcinoma (HCC). The aim of the present study was to investigate the anti‑invasive role of ATO in HCC, to determine the effect of ATO treatment on the expression of B7‑H4 and to further assess the possible underlying mechanisms. Following treatment of the cells with 2, 4 and 8 µM ATO for 48 h, cell counting kit‑8 (CCK‑8), Transwell and western blot assays were used to determine the extent of human MHCC97‑H HCC cell proliferation, apoptosis, invasion and B7‑H4 expression, respectively. The results revealed that 1 µM ATO markedly decreased cellular proliferation, and ATO administered at concentrations of 0.1, 0.2 and 0.5 µM markedly inhibited the migration and invasion of the human MHCC97‑H HCC cell line. The expression of B7‑H4 in the treatment groups was markedly reduced. Signal transduction mediated via the Janus kinase 2/signal transducers and activators of transcription 3 pathway was inhibited upon treatment with 0.1, 0.2 and 0.5 µM ATO. Additionally, the protein expression levels of matrix metalloproteinase 2 and vascular endothelial growth factor were markedly reduced in HCC cells upon treatment with ATO. In conclusion, ATO may reduce the protein expression levels of B7‑H4 in MHCC97‑H HCC cells, and further affected HCC tumorigenesis and progression. ATO may be a putative agent for the development of therapeutic strategies against human liver cancer.

Effects of intratracheally instilled laser printer-emitted engineered nanoparticles in a mouse model: A case study of toxicological implications from nanomaterials released during consumer use

Incorporation of engineered nanomaterials (ENMs) into toners used in laser printers has led to countless quality and performance improvements. However, the release of ENMs during printing (consumer use) has raised concerns about their potential adverse health effects. The aim of this study was to use "real world" printer-emitted particles (PEPs), rather than raw toner powder, and assess the pulmonary responses following exposure by intratracheal instillation. Nine-week old male Balb/c mice were exposed to various doses of PEPs (0.5, 2.5 and 5 mg/kg body weight) by intratracheal instillation. These exposure doses are comparable to real world human inhalation exposures ranging from 13.7 to 141.9 h of printing. Toxicological parameters reflecting distinct mechanisms of action were evaluated, including lung membrane integrity, inflammation and regulation of DNA methylation patterns. Results from this in vivo toxicological analysis showed that while intratracheal instillation of PEPs caused no changes in the lung membrane integrity, there was a pulmonary immune response, indicated by an elevation in neutrophil and macrophage percentage over the vehicle control and low dose PEPs groups. Additionally, exposure to PEPs upregulated expression of the Ccl5 (Rantes), Nos1 and Ucp2 genes in the murine lung tissue and modified components of the DNA methylation machinery (Dnmt3a) and expression of transposable element (TE) LINE-1 compared to the control group. These genes are involved in both the repair process from oxidative damage and the initiation of immune responses to foreign pathogens. The results are in agreement with findings from previous in vitro cellular studies and suggest that PEPs may cause immune responses in addition to modifications in gene expression in the murine lung at doses that can be comparable to real world exposure scenarios, thereby raising concerns of deleterious health effects.

Subacute effects of low dose lead nitrate and mercury chloride exposure on kidney of rats

Lead nitrate and mercury chloride are the most common heavy metal pollutants. In the present study, the effects of lead and mercury induced nephrotoxicity were studied in Wistar rats. Lead nitrate (LN, 45 mg/kg b.w/day) and mercury chloride (MC, 0.02 mg/kg b.w/day) and their combination were administered orally for 28 days. Four groups of rats were used in the study: control, LN, MC and LN plus MC groups. Serum biochemical parameters, lipid peroxidation, antioxidant enzymes and histopathological changes in kidney tissues were investigated in all treatment groups. LN and MC caused severe histopathological changes. It was shown that LN, MC and also co-treatment with LN and MC exposure induced significant increase in serum urea, uric acid and creatinine levels. There were also statistically significant changes in antioxidant enzyme activities (SOD, CAT, GPx and GST) and lipid peroxidation (MDA) in all groups except control group. In this study, we showed that MC caused more harmful effects than LN in rats.

Transcriptional changes in Atlantic salmon (Salmo salar) after embryonic exposure to road salt

Road salt is extensively used as a deicing chemical in road maintenance during winter and has in certain areas of the world led to density stratifications in lakes and ponds, and adversely impacted aquatic organisms in the recipients of the road run-off. Aquatic vertebrates such as fish have been particularly sensitive during fertilisation, as the fertilisation of eggs involves rapid uptake of the surrounding water, reduction in egg swelling and in ovo exposure to high road salt concentrations. The present study aimed to identify the persistent molecular changes occurring in Atlantic salmon (Salmo salar) eggs after 24h exposure to high concentrations (5000 mg/L) of road salt at fertilisation. The global transcriptional changes were monitored by a 60k salmonid microarray at the eyed egg stage (cleavage stage, 255 degree days after fertilisation) and identified a high number of transcripts being differentially regulated. Functional enrichment, pathway and gene-gene interaction analysis identified that the differentially expressed genes (DEGs) were mainly associated with toxiciologically relevant processes involved in osmoregulation, ionregulation, oxidative stress, metabolism (energy turnover), renal function and developmental in the embryos. Quantitative rtPCR analysis of selected biomarkers, identified by global transcriptomics, were monitored in the eggs for an extended range of road salt concentrations (0, 50, 100, 500 and 5000 mg/L) and revealed a positive concentration-dependent increase in cypa14, a gene involved in lipid turnover and renal function, and nav1, a gene involved in neuraxonal development. Biomarkers for osmoregulatory responses such as atp1a2, the gene encoding the main sodium/potassium ATP-fueled transporter for chloride ions, and txdc9, a gene involved in regulation of cell redox homeostasis (oxidative stress), displayed apparent concentration-dependency with exposure, although large variance in the control group precluded robust statistical discrimination between the groups. A No Transcriptional Effect Level (NOTEL) of 50mg/L road salt was found to be several orders of magnitude lower than the adverse effects documented in developing fish embryos elsewhere, albeit at concentrations realistic in lotic systems receiving run-off from road salt. It remains to be determined whether these transcriptional changes may cause adverse effects in fish at ecologically relevant exposure concentrations of road salt.

A multivariate assessment of innate immune-related gene expressions due to exposure to low concentration individual and mixtures of four kinds of heavy metals on zebrafish (Danio rerio) embryos

Concerns over the potential health effects of mixtures of low concentration heavy metals on living organisms keep growing by the day. However, the toxicity of low concentration metal mixtures on the immune system of fish species has rarely been investigated. In this study, the zebrafish model was employed to investigate the effect on innate immune and antioxidant-related gene expressions, on exposure to environmentally relevant concentrations of individual and mixtures of Pb (0.01 mg/L), Hg (0.001 mg/L), As (0.01 mg/L) and Cd (0.005 mg/L). Messenger-RNA (mRNA) levels of IL1β, TNF-α, IFNγ, Mx, Lyz, C3B and CXCL-Clc which are closely associated with the innate immune system were affected after exposing zebrafish embryos to metals for 120 h post fertilization (hpf). Individual and mixtures of metals exhibited different potentials to modulate innate-immune gene transcription. IL1β genes were significantly up regulated on exposure to Pb + As (2.01-fold) and inhibited on exposure to Pb + Hg + Cd (0.13-fold). TNF-α was significantly inhibited on exposure to As (0.40-fold) and Pb + As (0.32-fold) compared to control. Metal mixtures generally up regulated IFNγ compared to individual metals. Additionally, antioxidant genes were affected, as CAT and GPx gene expressions generally increased, whiles Mn-SOD and Zn/Cu-SOD reduced. Multivariate analysis showed that exposure to individual metals greatly influenced modulation of innate immune genes; whiles metal mixtures influenced antioxidant gene expressions. This suggests that beside oxidative stress, there may be other pathways influencing gene expressions of innate immune and antioxidant-related genes. Low concentration heavy metals also affect expression of development-related (wnt8a and vegf) genes. Altogether, the results of this study clearly demonstrate that low concentration individual and mixtures of metals in aquatic systems will greatly influence the immune system. It is indicative that mechanisms associated with toxicity of metal mixtures is complex, however, further studies to elucidate them are ongoing in our research laboratory.

Ectoine alleviates behavioural, physiological and biochemical changes in Daphnia magna subjected to formaldehyde

Ectoine (ECT) is produced by halophilic microorganisms in response to various stressful factors. Its protective properties in bacteria and some populations of isolated cells are known; however, no data are available on its protective influence on aquatic invertebrates subjected to a common pollutant, formaldehyde (FA). The purpose of this study was to determine the effects of FA alone (at 20 and 60 mg/L) and in the combination with various concentrations of ECT (5, 10 and 25 mg/L) at various times of exposure on behavioural, physiological and biochemical parameters of Daphnia magna. Specifically, mortality, heart rate, thoracic limb movement, reduced glutathione (GSH)/oxidised glutathione (GSSG) ratio, catalase (CAT) activity and nitric oxide (NOx) levels were determined. The results showed that both concentrations of FA when administered alone induced significant alterations of the determined parameters. On the other hand, animals treated with the combinations of FA + ECT showed decreased mortalities, attenuated inhibition of heart rates and thoracic limb activities, less decreased GSH/GSSG ratios, lower stimulation of CAT activities and NOx levels when compared to the crustaceans subjected to FA alone. The most distinct attenuation of toxic effects was observed in the combinations in which the highest concentrations of ECT were used. The results suggest that oxidative stress induced by FA in daphnids is likely to be alleviated by the antioxidative action of ECT.

Silver nanoparticles induce tight junction disruption and astrocyte neurotoxicity in a rat blood-brain barrier primary triple coculture model

BACKGROUND

Silver nanoparticles (Ag-NPs) can enter the brain and induce neurotoxicity. However, the toxicity of Ag-NPs on the blood-brain barrier (BBB) and the underlying mechanism(s) of action on the BBB and the brain are not well understood.

METHOD

To investigate Ag-NP suspension (Ag-NPS)-induced toxicity, a triple coculture BBB model of rat brain microvascular endothelial cells, pericytes, and astrocytes was established. The BBB permeability and tight junction protein expression in response to Ag-NPS, NP-released Ag ions, and polystyrene-NP exposure were investigated. Ultrastructural changes of the microvascular endothelial cells, pericytes, and astrocytes were observed using transmission electron microscopy (TEM). Global gene expression of astrocytes was measured using a DNA microarray.

RESULTS

A triple coculture BBB model of primary rat brain microvascular endothelial cells, pericytes, and astrocytes was established, with the transendothelial electrical resistance values >200 Ω·cm(2). After Ag-NPS exposure for 24 hours, the BBB permeability was significantly increased and expression of the tight junction (TJ) protein ZO-1 was decreased. Discontinuous TJs were also observed between microvascular endothelial cells. After Ag-NPS exposure, severe mitochondrial shrinkage, vacuolations, endoplasmic reticulum expansion, and Ag-NPs were observed in astrocytes by TEM. Global gene expression analysis showed that three genes were upregulated and 20 genes were downregulated in astrocytes treated with Ag-NPS. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the 23 genes were associated with metabolic processes, biosynthetic processes, response to stimuli, cell death, the MAPK pathway, and so on. No GO term and KEGG pathways were changed in the released-ion or polystyrene-NP groups. Ag-NPS inhibited the antioxidant defense of the astrocytes by increasing thioredoxin interacting protein, which inhibits the Trx system, and decreasing Nr4a1 and Dusp1. Meanwhile, Ag-NPS induced inflammation and apoptosis through modulation of the MAPK pathway or B-cell lymphoma-2 expression or mTOR activity in astrocytes.

CONCLUSION

These results draw our attention to the importance of Ag-NP-induced toxicity on the neurovascular unit and provide a better understanding of its toxicological mechanisms on astrocytes.

Activation of NRF2 pathway in spleen, thymus as well as peripheral blood mononuclear cells by acute arsenic exposure in mice

Arsenic has already been demonstrated to activate the nuclear factor erythroid 2-related factor 2 (NRF2) in many different organs and cell lines. The present study tried to explore the expression of NRF2 pathway by acute arsenic exposure in immune system in vivo. Our results showed that treatment with arsenic (sodium arsenite, 5, 10 and 20mg/kg, intra-gastrically) increased the expression of NRF2 and its downstream targets heme oxygenase-1 (HO-1), glutathione-S-transferase (GST), glutamate-cysteine ligase (GCL) and glutathione reductase (GR) consistently in spleen, thymus, as well as peripheral blood mononuclear cells (PBMCs), as early as treatment from 6h. Arsenic was also detected to up-regulate the mRNA levels of Hmox1, NAD(P)H: quinine oxidoreductase 1 (Nqo1), Gclc and Gclm in spleen and thymus. Besides, we detected the enhancement of Kelch-like ECH-associated protein (KEAP1) expression in these immune organs and immunocytes. What's more, our results also found the imbalanced oxidative redox status under the circumstances that arsenic activated NRF2 pathway, reflected by the generation of lipid peroxidation, as well as the reduction of antioxidative capacities in both spleen and thymus. Taken together, our results here strongly suggested the expression and activation of NRF2 pathway by acute arsenic exposure in immune system in vivo. Further studies are being investigated to explore the possible roles and functions of NRF2 pathway stimulation in the regulation of immune responses of this metalloid.

Sodium fluoride affects zebrafish behaviour and alters mRNA expressions of biomarker genes in the brain: Role of Nrf2/Keap1

Sodium fluoride (NaF), used as pesticides and for industrial purposes are deposited in the water bodies and therefore affects its biota. Zebrafish exposed to NaF in laboratory condition showed hyperactivity and frequent surfacing activity, somersaulting and vertical swimming pattern as compared to the control group. Reactive oxygen species level was elevated and glutathione level was depleted along with increased malondialdehyde content in the brain. Levels of glutathione-s-transferase (GST), catalase (CAT) and superoxide dismutase were also elevated in the treatment groups. Expression of mRNA of nuclear factor erythroid 2 related factor 2 (Nrf2) and its inhibitor Kelch-like ECH-associated protein 1 (Keap1) during stress condition were observed along with Gst, Cat, NADPH: quinone oxidoreductase 1(Nqo1) and p38. Except Keap1, all other genes exhibited elevated expression. Nrf2/Keap1 proteins had similar expression pattern as their corresponding mRNA. The findings in this study might help to understand the molecular mechanism of fluoride induced neurotoxicity in fish.

Arsenic-induced Histological Alterations in Various Organs of Mice

Deposition of arsenic in mice through groundwater is well documented but little is known about the histological changes of organs by the metalloid. Present study was designed to evaluate arsenic-induced histological alterations in kidney, liver, thoracic artery and brain of mice which are not well documented yet. Swiss albino male mice were divided into 2 groups and treated as follows: Group 1: control, 2: arsenic (sodium arsenite at 10 mg/kg b.w. orally for 8 wks). Group 2 showed marked degenerative changes in kidney, liver, thoracic artery, and brain whereas Group 1 did not reveal any abnormalities on histopathology. We therefore concluded that arsenic induces histological alterations in the tested organs.

Protective effects of ectoine on behavioral, physiological and biochemical parameters of Daphnia magna subjected to hydrogen peroxide

Ectoine (ECT) is an osmoprotectant produced by halophilic microorganisms inducing protective effects against various stressful factors. However, little is known about its influence on aquatic invertebrates subjected to hydrogen peroxide (H2O2)-a commonly used oxidative disinfectant. Therefore, the aim of our study was to determine the effects of H2O2 alone (at 5 and 10 mg/L) and in the combination with various concentrations of ECT (5, 10 and 25 mg/L) on behavioral, physiological and biochemical parameters of Daphnia magna. The following endpoints were determined: mortality, heart rate, thoracic limb movement, total glutathione (GSH)/oxidized glutathione (GSSG) ratio, catalase (CAT) activity and nitric oxide (NOx) level. The study showed that daphnids exposed to the combination of H2O2+ECT showed decreased mortality, attenuated inhibition of heart rate and thoracic limb activity, less decreased GSH/GSSG ratio, lower stimulation of CAT activity and NOx level when compared to the crustaceans exposed to H2O2 alone. The most pronounced alleviation of toxic effects was observed in the combination of 5 mg/L H2O2+25 mg/L ECT. The results suggest that protective effects of ECT in D. magna subjected to H2O2 may be related to antioxidative properties of the osmoprotectant.