Arsenic toxicity in mammals and aquatic animals: a comparative biochemical approach

A metabolomic investigation on arsenic-induced toxicological effects in the clam Ruditapes philippinarum under different salinities

Arsenic is an important contaminant in the Bohai marine ecosystem due to the anthropogenic activities. In this work, we investigated the toxicological effects of arsenic in Ruditapes philippinarum under different seawater salinities using NMR-based metabolomics. Under normal salinity (31.1 ppt), arsenic decreased the levels of amino acids (glutamate, β-alanine, etc.), and increased the levels of betaine and fumarate. The metabolic biomarkers including decreased threonine, histidine, ATP and fumarate were found in the muscles of arsenic-treated clams under medium salinity (23.3 ppt). However, only elevated ATP and depleted succinate were detected in the arsenic-exposed clam samples under low salinity (15.6 ppt). These differential metabolic biomarkers indicated that arsenic could induce osmotic stress and disturbance in energy metabolism in clam under normal and medium salinities. However, arsenic caused only disturbance in energy metabolism in clam under low salinity. Overall, our results demonstrated that seawater salinity could influence the toxicological effects of arsenic.

Is there a Trojan-horse effect during magnetic nanoparticles and metalloid cocontamination of human dermal fibroblasts?

This study investigates the issue of nanoparticles/pollutants cocontamination. By combining viability assays, physicochemical and structural analysis (to probe the As speciation and valence), we assessed how γFe(2)O(3) nanoparticles can affect the cytotoxicity, the intra- and extracellular speciation of As(III). Human dermal fibroblasts were contaminated with γFe(2)O(3) nanoparticles and As(III) considering two scenarios: (i) a simultaneous coinjection of the nanoparticles and As, and (ii) an injection of the nanoparticles after 24 h of As adsorption in water. In both scenarios, we did not notice significant changes on the nanoparticles surface charge (zeta potential ∼ -10 mV) nor hydrodynamic diameters (∼950 nm) after 24 h. We demonstrated that the coinjection of γFe(2)O(3) nanoparticles and As in the cellular media strongly affects the complexation of the intracellular As with thiol groups. This significantly increases at low doses the cytotoxicity of the As nonadsorbed at the surface of the nanoparticles. However, once As is adsorbed at the surface the desorption is very weak in the culture medium. This fraction of As strongly adsorbed at the surface is significantly less cytotoxic than As itself. On the basis of our data and the thermodynamics, we demonstrated that any disturbance of the biotransformation mechanisms by the nanoparticles (i.e., surface complexation of thiol groups with the iron atoms) is likely to be responsible for the increase of the As adverse effects at low doses.

Urinary arsenic levels in the French adult population: the French National Nutrition and Health Study, 2006-2007

The French Nutrition and Health Survey (ENNS) was conducted to describe dietary intakes, nutritional status, physical activity, and levels of various biomarkers for environmental chemicals (heavy metals and pesticides) in the French population (adults aged 18-74 years and children aged 3-17 years living in continental France in 2006-2007). The aim of this paper was to describe the distributions of total arsenic and the sum of iAs+MMA+DMA in the general adult population, and to present their main risk factors. In the arsenic study, 1500 and 1515 adults (requested to avoid seafood intake in the previous 3 days preceding urine collection) were included respectively for the analysis of the sum of inorganic arsenic (iAs) and its two metabolites, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), and for the total arsenic. Results were presented as geometric means and selected percentiles of urinary arsenic concentrations (μg/L) and creatinine-adjusted urinary arsenic (μg/g of creatinine) for total arsenic, and the sum of inorganic arsenic and metabolites (iAs+MMA+DMA). The geometric mean concentration of the sum of iAs+MMA+DMA in the adult population living in France was 3.34 μg/g of creatinine [3.23-3.45] (3.75 μg/L [3.61-3.90]) with a 95th percentile of 8.9 μg/g of creatinine (10.68 μg/L). The geometric mean concentration of total arsenic was 11.96 μg/g of creatinine [11.41-12.53] (13.42 μg/L [12.77-14.09]) with a 95th percentile of 61.29 μg/g of creatinine (72.75 μg/L). Urinary concentrations of total arsenic and iAS+MMA+DMA were influenced by sociodemographic and economic factors, and by risk factors such as consumption of seafood products and of wine. In our study, covariate-adjusted geometric means demonstrated several slight differences, due to consumption of fish, shellfish/crustaceans or wine. This study provides the first reference value for arsenic in a representative sample of the French population not particularly exposed to high levels of arsenic (10 μg/g of creatinine). It shows that urinary arsenic concentrations in the French adult population (in particular concentrations of iAs+MMA+DMA) were relatively low compared with foreign data.

Arsenic triggers the nitric oxide (NO) and S-nitrosoglutathione (GSNO) metabolism in Arabidopsis

Environmental contamination by arsenic constitutes a problem in many countries, and its accumulation in food crops may pose health complications for humans. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are involved at various levels in the mechanism of responding to environmental stress in higher plants. Using Arabidopsis seedlings exposed to different arsenate concentrations, physiological and biochemical parameters were analyzed to determine the status of ROS and RNS metabolisms. Arsenate provoked a significant reduction in growth parameters and an increase in lipid oxidation. These changes were accompanied by an alteration in antioxidative enzymes and the nitric oxide (NO) metabolism, with a significant increase in NO content, S-nitrosoglutathione reductase (GSNOR) activity and protein tyrosine nitration as well as a concomitant reduction in glutathione and S-nitrosoglutathione (GSNO) content. Our results indicate that 500 μM arsenate (AsV) causes nitro-oxidative stress in Arabidopsis, being the glutathione reductase and the GSNOR activities clearly affected.

Genotoxic potential of arsenic at its reference dose

Arsenic, a highly hazardous contaminant in our drinking water, accounts for various toxic effects (including cancer) in human. However, intake of arsenic @0.3 μg kg(-1)day(-1) through drinking water, containing arsenic at its guideline value or maximum contaminant limit (10 μg L(-1)), has been estimated to pose very little or no measurable risk to cancer in humans. The value also appears to be equal to the human reference dose (or index dose) of arsenic based on human skin toxicity data. The present work was a quantitative assessment of the genotoxic potential of arsenic in mice at doses equivalent to its human reference dose as well as its multiples. Significant increases in the frequencies of chromosome abnormalities in the bone marrow cells were registered over the control level upon exposure to all the doses of arsenic including its reference dose (or index dose). The assessment of arsenic genotoxicity in humans at low doses will therefore be highly instrumental in establishing a permissible limit of arsenic in drinking water.

Interaction of ABC transport proteins with toxic metals at the level of gene and transport activity in the PLHC-1 fish cell line

The aim of this study was to investigate the interaction of four toxic metals with ABC transport proteins in piscine cell line PLHC-1. Cells were exposed for 24 h to 0.01-1 μM of CdCl(2), HgCl(2), As(2)O(3), or K(2)Cr(2)O(7) and the expression of a series of ABC genes (abcb1, abcc1-4) was determined using qRT-PCR. Using the fluorescent model substrates calcein-AM and monochlorbimane we measured interaction of metals with the transport activity of ABC transporters. P-glycoprotein (P-gp) activity was measured in PLHC-1/dox (P-gp overexpressing cells) while activity and interactions of metals with MRPs was measured in PLHC-1/wt cells. After 24 h exposure, abcc2-4 genes were dose-dependently up-regulated by all metals, while abcb1 and abcc1 were less affected. Up-regulation of abcc2 was more pronounced, with up to 8-fold increase in expression. Abcc3 and abcc4 were moderately inducible by HgCl(2) with 3.3-fold and 2.2-fold, respectively. All metals caused a significant inhibition of both P-gp (2.9- to 4-fold vs. controls) and MRP (1.3- to 1.8-fold) transport activities. Modulation of ABC genes and transport activities was further investigated in PLHC-1/wt cells exposed to 1 μM HgCl(2) for 72 h and in Hg resistant cells selected by long term cultivation of PLHC-1/wt cells in increasing concentrations of HgCl(2). Exposure to HgCl(2) for 72 h induced MRP genes expression and efflux activity. The long term cultivation of PLHC-1/wt cells in HgCl(2), did not cause prolonged up-regulation of the tested abc genes but resulted in higher MRP transport activities as determined by the increased sensitivity of these cells to MK571 (MRP specific inhibitor). Results of the present study indicated specific interaction of metals with selected ABC transport proteins. Modulation of ABC transporters takes place at both transcriptional and functional level. An active involvement of efflux pumps in Hg clearance in fish is suggested.

Chemical activation of a high-affinity glutamate transporter in human erythrocytes and its implications for malaria-parasite–induced glutamate uptake

Human erythrocytes have a low basal permeability to L-glutamate and are not known to have a functional glutamate transporter. Here, treatment of human erythrocytes with arsenite was shown to induce the uptake of L-glutamate and D-aspartate, but not that of D-glutamate or L-alanine. The majority of the arsenite-induced L-glutamate influx was via a high-affinity, Na+-dependent system showing characteristics of members of the “excitatory amino acid transporter” (EAAT) family. Western blots and immunofluorescence assays revealed the presence of a member of this family, EAAT3, on the erythrocyte membrane. Erythrocytes infected with the malaria parasite Plasmodium falciparum take up glutamate from the extracellular environment. Although the majority of uptake is via a low-affinity Na+-independent pathway there is, in addition, a high-affinity uptake component, raising the possibility that the parasite activates the host cell glutamate transporter.

In vitro evaluation of co-exposure of arsenium and an organic nanomaterial (fullerene, C₆₀) in zebrafish hepatocytes

Taking into account the concept of the "Trojan Horse", where contaminants may have its entry into specific organs potentiated by its association with nanomaterials, the aim of this study was to analyze the joint toxic effects induced by an organic nanomaterial, fullerene (C(60)) with the metalloid arsenic (As(III)). Hepatocytes of zebrafish Danio rerio were exposed to As(III) (2.5 or 100 μM), C(60) or As+C(60) for 4h, not altering cells viability. Intracellular reactive oxygen species concentration was reduced in cells exposed only to the C(60) (1mg/L) and in the treatment of 100 μM As(III)+C(60). Co-exposure with C(60) abolished the peak of the antioxidant glutathione (GSH) registered in cells exposed to the lowest As(III) concentration (2.5 μM). A similar result was observed in terms of lipid damage (TBARS). Total antioxidant capacity was significantly higher at both As(III) concentrations co-exposed to C(60) when compared with the control group. Activity of glutathione-S-transferase omega, a limiting enzyme in the methylation pathway of As(III), was reduced in the 100 μM As(III)+C(60) treatment. Cells co-exposed to C(60) had a significantly higher accumulation of As(III), showing a "Trojan Horse" effect which did not result in higher cell toxicity. Instead, co-exposure of As(III) with C(60) showed to reduce cellular injury.

Comparison of arsenate and cadmium toxicity in a freshwater amphipod (Gammarus pulex)

Cadmium is largely documented on freshwater organisms while arsenic, especially arsenate, is rarely studied. The kinetic of the LC50s values for both metals was realized on Gammarus pulex. Physiological [i.e. metal concentration in body tissues, bioconcentration factor (BCF)] effects and behavioural responses (via pleopods beats) were investigated after 240-h exposure. Arsenate LC50 value was 100 fold higher than Cd-LC50 value after 240-h exposure, while concentrations in gammarids were similar for both metals at their respective LC50s. BCF decreased with increasing cadmium concentration while BCF remained stable with increasing arsenate concentration. Moreover, BCF was between 148 and 344 times lower for arsenate than cadmium. A significant hypoventilation was observed for cadmium concentrations exceeding or close to the 240h-LC50(Cd), while gammarids hyperventilated for the lowest arsenate concentrations and hypoventilated for the highest arsenate concentrations. We discussed the relationships between potential action mechanisms of these two metals and observed results.

Arsenate replacing phosphate: alternative life chemistries and ion promiscuity

A newly identified bacterial strain that can grow in the presence of arsenate and possibly in the absence of phosphate, has raised much interest, but also fueled an active debate. Can arsenate substitute for phosphate in some or possibly in most of the absolutely essential phosphate-based biomolecules, including DNA? If so, then the possibility of alternative, arsenic-based life forms must be considered. The physicochemical similarity of these two oxyanions speaks in favor of this idea. However, arsenate-esters and arsenate-diesters in particular are extremely unstable in aqueous media. Here, we explore the potential of arsenate to be used as substrate by phosphate-utilizing enzymes. We review the existing literature on arsenate enzymology, that intriguingly, dates back to the 1930s. We address the issue of how and to what degree proteins can distinguish between arsenate and phosphate and what is known in general about oxyanion specificity. We also discuss how phosphate-arsenate promiscuity may affect evolutionary transitions between phosphate- and arsenate-based biochemistry. Finally, we highlight potential applications of arsenate as a structural and mechanistic probe of enzymes whose catalyzed reactions involve the making or breaking of phosphoester bonds.