Identification of Methylated Dithioarsenicals in the Urine of Rats Fed with Sodium Arsenite

The relevance of arsenic speciation analysis in health & medicine

Long term exposure to arsenic through consumption of contaminated groundwater has been a global issue since the last five decades; while from an alternate standpoint, arsenic compounds have emerged as unparallel chemotherapeutic drugs. This review highlights the contribution from arsenic speciation studies that have played a pivotal role in the progression of our understanding of the biological behaviour of arsenic in humans. We also discuss the limitations of the speciation studies and their association with the interpretation of arsenic metabolism. Chromatographic separation followed by spectroscopic detection as well as the utilization of biotinylated pull-down assays, protein microarray and radiolabelled arsenic have been instrumental in identifying hundreds of metabolic arsenic conjugates, while, computational modelling has predicted thousands of them. However, these species exhibit a variegated pattern, which supports more than one hypothesis for the metabolic pathway of arsenic. Thus, the arsenic species are yet to be integrated into a coherent mechanistic pathway depicting its chemicobiological fate. Novel biorelevant arsenic species have been identified due to significant evolution in experimental methodologies. However, these methods are specific for the identification of only a group of arsenicals sharing similar physiochemical properties; and may not be applicable to other constituents of the vast spectrum of arsenic species. Consequently, the identity of arsenic binding partners in vivo and the sequence of events in arsenic metabolism are still elusive. This resonates the need for additional focus on the extraction and characterization of both low and high molecular weight arsenicals in a combinative manner.

Increasing temperature and flooding enhance arsenic release and biotransformations in Swiss soils

Reductive dissolution is one of the main causes for arsenic (As) mobilisation in flooded soils while biomethylation and biovolatilisation are two microbial mechanisms that greatly influence the mobility and toxicity of As. Climate change results in more extreme weather events such as flooding and higher temperatures, potentially leading to an increase in As release and biotransformations. Here, we investigated the effects of flooding and temperature on As release, biomethylation and biovolatilisation from As-rich soils with different pH and source of As (one acidic and anthropogenic (Salanfe) and one neutral and geogenic (Liesberg)). Flooded soils incubated at 23 °C for two weeks showed a ~ 3-fold (Liesberg site) and ~ 7-fold (Salanfe site) increase in the total As concentration of soil solution compared to those incubated at 18 °C. Methyl- and thio-As species were found in the acidic soil and soil solution. High temperatures enhanced thiolation and methylation although inorganic As was predominant. We also show that volatile As fluxes increased more than 4-fold between treatments, from 18 ± 5 ng/kg/d at 18 °C to 75 ± 6 ng/kg/d at 23 °C from Salanfe soil. Our results suggest that high As soils with acidic pH can become an important source of As to the surrounding environment according to realistic climatic scenarios, and that biovolatilisation is very sensitive to increases in temperature. This study provides new data and further justifies further investigations into climate-induced changes on As release and speciation and its links to important factors such as microbial ecology and sulfate or iron biogeochemistry. SYNOPSIS: In the studied Swiss soils, elevated temperature increases arsenic mobility through volatilisation and methylation.

Changes in metabolomics and lipidomics in brain tissue and their correlations with the gut microbiome after chronic food-derived arsenic exposure in mice

Arsenic can cause neurodegenerative diseases of the brain, but the definite mechanism is still unknown. In this study, to discuss the disturbances on brain metabolome and lipidome under subchronic arsenic exposure, we treated mice with the arsenic-containing feed (concentration of total arsenic = 30 mg/kg) prepared in accordance with the proportion of rice arsenicals for 16 weeks and performed metabolomics and lipidomics studies respectively using UHPLC-Triple-TOF-MS/MS and UHPLC-Q Exactive Focus MS/MS on mice brain. In addition, the distributions of arsenical metabolites along the feed-gut-blood-brain chain were analyzed by ICP-MS and HPLC-ICP-MS, and fecal microbial variations were investigated by 16 s sequencing. The data showed that although only a tiny amount of arsenic (DMA=0.101 mg/kg, uAs=0.071 mg/kg) enters the brain through the blood-brain barrier, there were significant changes in brain metabolism, including 118 metabolites and 17 lipids. These different metabolites were involved in 30 distinct pathways, including glycometabolism, and metabolisms of lipid, nucleic acid, and amino acid were previously reported to be correlated with neurodegenerative diseases. Additionally, these different metabolites were significantly correlated with 12 gut bacterial OTUs, among which Lachnospiraceae, Muribaculaceae, Ruminococcaceae, and Erysipelotrichaceae were also previously reported to be related to the distortion of metabolism, indicating that the disturbance of metabolism in the brain may be associated with the disturbance of gut microbes induced by arsenic. Thus, the current study demonstrated that the brain metabolome and lipidome were significantly disturbed under subchronic arsenic exposure, and the disturbances also significantly correlated with some gut microbiome and may be associated with neurodegenerative diseases. Although preliminary, the results shed some light on the pathophysiology of arsenic-caused neurodegenerative diseases.

Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry for the Analysis of Complex Compounds in Serum and Its Application in Accurate Detection of Early Arsenic Exposure

With the acceleration of industrialization, environmental arsenic pollution is threatening human health. However, by the time clinical symptoms appear, arsenic toxicity has usually caused irreversible damage to the body, so it is important to establish a rapid and accurate screening method for early arsenic exposure. In this work, 32 female C57BL/6 mice were exposed to different concentrations of inorganic arsenic in drinking water for a week. By analyzing the changes in serum, more than 20 compounds were detected to increase or decrease with the increase of arsenic intake. The abnormal increase in inosine, xanthine, xanthosine, and hypoxanthine and the abnormal purine pathway were found at the same time. Dimethylarsenic acid, an important inorganic arsenic metabolite in the body, was also found in serum. Combined with statistical analysis, early arsenic exposure can be easily and quickly detected, and the potential health risks of short-term exposure can be revealed simultaneously.

A two-step approach for arsenic removal by exploiting an autochthonous Delftia sp. BAs29 and neutralized red mud

Groundwater arsenic contamination represents a global threat to human health. Among the proposed bioremediation applications, microbial transformation of arsenite (As (III)) seems to be the most favorable approach as it can be easily coupled with several adsorption techniques, without producing lethal by-products or demanding chemical addition. This study highlights the potential contribution of a highly efficient As (III) transforming bacteria Delftia sp. BAs29 followed by the adsorption of transformed arsenate (As (V)) using neutralized red mud under suitable treatment conditions. Diverse experimental conditions elucidated (inflow As (III) concentrations, flow rate) the rate and oxidation efficiency to mediate the process. Red mud is a waste by-product from the Bayer's process of the alumina industry, which when neutralized aids the removal of As (V). The neutralized red mud was characterized using X-ray diffraction (XRD) microanalysis, Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) and Fourier-transform infrared spectroscopy (FTIR). Arsenate adsorption using neutralized red mud was also studied as a function of pH and time, adsorbent dosage, and initial As (V) concentration. The adsorption process was significantly affected by the solution pH, which on decreasing gradually increased the adsorption efficiency. The maximum monolayer capacity for adsorption of 274.1 mg/g As (V) was found at optimum conditions of pH 4.0 and a contact time of 30 min at a temperature of 30 °C, respectively. Furthermore, this process significantly contributed in fabricating a two-step bio-filter column for the removal of total arsenic from groundwater. Graphical abstract.

Determination of arsenicals in mouse tissues after simulated exposure to arsenic from rice for sixteen weeks and the effects on histopathological features

The accumulation of arsenic in rice has become a worldwide concern. In this study, dose-dependency in tissues (intestine, liver and kidney) and blood distribution of inorganic arsenicals and their methylated metabolites were investigated in male C57BL/6 mice exposed to four arsenic species (arsenite [iAs]^III, arsenate [iAs]^V, monomethylarsonate [MMA]^V, and dimethylarsinate [DMA]^V) at four doses (control [C]: 0 μg/g, simulation [S]: 0.91 μg/g, medium [M]: 9.1 μg/g and high [H]: 30 μg/g) according to the arsenical composition in rice for 8 and 16 weeks. No adverse effects were observed, while body weight gain decreased in group H. Increases in total arsenic concentrations (C_tAs) and histopathological changes in the tissues occurred in all of the test groups. C_tAs presented a tendency of kidney > intestine > liver > blood and were time-/dose-dependent in the liver and kidney in groups M and H. In the intestine and blood, abundant iAs (23%-28% in blood and 36%-49% in intestine) was detected in groups M and H, and C_tAs decreased in group H from the 8th week to the 16th week. PMI decreased in the liver and SMI decreased in the kidney. These results indicate that the three tissues are injured through food arsenic. The intestine can also accumulate food arsenic, and the high arsenic dose will cause a deficiency in the absorbing function of the intestine. Thus, long-term exposure to arsenic-contaminated rice should be taken seriously attention.

Thiolation in arsenic metabolism: a chemical perspective

In recent years, methylated thioarsenicals have been widely detected in various biological and environmental matrices, suggesting their broad involvement and biological importance in arsenic metabolism. However, very little is known about the formation mechanism of methylated thioarsenicals and the relation between arsenic methylation and thiolation processes. It is timely and necessary to summarize and synthesize the reported information on thiolated arsenicals for an improved understanding of arsenic thiolation. To this end, we examined the proposed formation pathways of methylated oxoarsenicals and thioarsenicals from a chemical perspective and proposed a novel arsenic metabolic scheme, in which arsenic thiolation is integrated with methylation (instead of being separated from methylation as currently reported). We suggest in the new scheme that protein-bound pentavalent arsenicals are critical intermediates that connect methylation and thiolation, with protein binding of pentavalent methylated thioarsenical being a key step for arsenic thiolation. This informative review on arsenic thiolation from the chemical perspective will be helpful to better understand the arsenic metabolism at the molecular level and the toxicological effects of arsenic species.

Comparative cytotoxicity of fourteen trivalent and pentavalent arsenic species determined using real-time cell sensing

The occurrence of a large number of diverse arsenic species in the environment and in biological systems makes it important to compare their relative toxicity. The toxicity of arsenic species has been examined in various cell lines using different assays, making comparison difficult. We report real-time cell sensing of two human cell lines to examine the cytotoxicity of fourteen arsenic species: arsenite (As^III), monomethylarsonous acid (MMA^III) originating from the oxide and iodide forms, dimethylarsinous acid (DMA^III), dimethylarsinic glutathione (DMAG^III), phenylarsine oxide (PAO^III), arsenate (As^V), monomethylarsonic acid (MMA^V), dimethylarsinic acid (DMA^V), monomethyltrithioarsonate (MMTTA^V), dimethylmonothioarsinate (DMMTA^V), dimethyldithioarsinate (DMDTA^V), 3-nitro-4-hydroxyphenylarsonic acid (Roxarsone, Rox), and 4-aminobenzenearsenic acid (p-arsanilic acid, p-ASA). Cellular responses were measured in real time for 72hr in human lung (A549) and bladder (T24) cells. IC₅₀ values for the arsenicals were determined continuously over the exposure time, giving rise to IC₅₀ histograms and unique cell response profiles. Arsenic accumulation and speciation were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS). On the basis of the 24-hr IC₅₀ values, the relative cytotoxicity of the tested arsenicals was in the following decreasing order: PAO^III≫MMA^III≥DMA^III≥DMAG^III≈DMMTA^V≥As^III≫MMTTA^V>As^V>DMDTA^V>DMA^V>MMA^V≥Rox≥p-ASA. Stepwise shapes of cell response profiles for DMA^III, DMAG^III, and DMMTA^V coincided with the conversion of these arsenicals to the less toxic pentavalent DMA^V. Dynamic monitoring of real-time cellular responses to fourteen arsenicals provided useful information for comparison of their relative cytotoxicity.

Methylated and thiolated arsenic species for environmental and health research - A review on synthesis and characterization

Hundreds of millions of people around the world are exposed to elevated concentrations of inorganic and organic arsenic compounds, increasing the risk of a wide range of health effects. Studies of the environmental fate and human health effects of arsenic require authentic arsenic compounds. We summarize here the synthesis and characterization of more than a dozen methylated and thiolated arsenic compounds that are not commercially available. We discuss the methods of synthesis for the following 14 trivalent (III) and pentavalent (V) arsenic compounds: monomethylarsonous acid (MMA^III), dicysteinylmethyldithioarsenite (MMA^III(Cys)₂), monomethylarsonic acid (MMA^V), monomethylmonothioarsonic acid (MMMTA^V) or monothio-MMA^V, monomethyldithioarsonic acid (MMDTA^V) or dithio-MMA^V, monomethyltrithioarsonate (MMTTA^V) or trithio-MMA^V, dimethylarsinous acid (DMA^III), dimethylarsino-glutathione (DMA^III(SG)), dimethylarsinic acid (DMA^V), dimethylmonothioarsinic acid (DMMTA^V) or monothio-DMA^V, dimethyldithioarsinic acid (DMDTA^V) or dithio-DMA^V, trimethylarsine oxide (TMAO^V), arsenobetaine (AsB), and an arsenicin-A model compound. We have reviewed and compared the available methods, synthesized the arsenic compounds in our laboratories, and provided characterization information. On the basis of reaction yield, ease of synthesis and purification of product, safety considerations, and our experience, we recommend a method for the synthesis of each of these arsenic compounds.

Cellular arsenic transport pathways in mammals

Natural contamination of drinking water with arsenic results in the exposure of millions of people world-wide to unacceptable levels of this metalloid. This is a serious global health problem because arsenic is a Group 1 (proven) human carcinogen and chronic exposure is known to cause skin, lung, and bladder tumors. Furthermore, arsenic exposure can result in a myriad of other adverse health effects including diseases of the cardiovascular, respiratory, neurological, reproductive, and endocrine systems. In addition to chronic environmental exposure to arsenic, arsenic trioxide is approved for the clinical treatment of acute promyelocytic leukemia, and is in clinical trials for other hematological malignancies as well as solid tumors. Considerable inter-individual variability in susceptibility to arsenic-induced disease and toxicity exists, and the reasons for such differences are incompletely understood. Transport pathways that influence the cellular uptake and export of arsenic contribute to regulating its cellular, tissue, and ultimately body levels. In the current review, membrane proteins (including phosphate transporters, aquaglyceroporin channels, solute carrier proteins, and ATP-binding cassette transporters) shown experimentally to contribute to the passage of inorganic, methylated, and/or glutathionylated arsenic species across cellular membranes are discussed. Furthermore, what is known about arsenic transporters in organs involved in absorption, distribution, and metabolism and how transport pathways contribute to arsenic elimination are described.