Thiolated arsenicals in arsenic metabolism: Occurrence, formation, and biological implications

Meta-omics analysis reveals the marine arsenic cycle driven by bacteria

Arsenic is a toxic element widely distributed in the Earth's crust and ranked as a class I human carcinogen. Microbial metabolism makes significant contributions to arsenic detoxification, migration and transformation. Nowadays, research on arsenic is primarily in areas affected by arsenic pollution associated with human health activities. However, the biogeochemical traits of arsenic in the global marine ecosystem remain to be explicated. In this study, we revealed that seawater environments were primarily governed by the process of arsenate reduction to arsenite, while arsenite methylation was predominant in marine sediments which may serve as significant sources of arsenic emission into the atmosphere. Significant disparities existed in the distribution patterns of the arsenic cycle between surface and deep seawaters at middle and low latitudes, whereas these situations tend to be similar in the Arctic and Antarctic oceans. Significant variations were also observed in the taxonomic diversity and core microbial community of arsenic cycling across different marine environments. Specifically, γ-proteobacteria played a pivotal role in the arsenic cycle in the whole marine environment. Temperature, dissolved oxygen and phosphate were the crucial factors that related to these differentiations in seawater environments. Overall, our study contributes to a deeper understanding of the marine arsenic cycle.

Recent developments in speciation and determination of arsenic in marine organisms using different analytical techniques. A review

Marine organisms play a vital role as the main providers of essential and functional food. Yet they also constitute the primary pathway through which humans are exposed to total arsenic (As) in their diets. Since it is well known that the toxicity of this metalloid ultimately depends on its chemical forms, speciation in As is an important issue. Most relevant articles about arsenic speciation have been investigated. This extended not only from general knowledge about As but also the toxicity and health related issues resulting from exposure to these As species from the food ecosystem. There can be enormous side effects originating from exposure to As species that must be measured quantitatively. Therefore, various convenient approaches have been developed to identify different species of As in marine samples. Different extraction strategies have been utilized based on the As species of interest including water, methanol and mixtures of both, and many other extraction agents have been explained in this article. Furthermore, details of hyphenated techniques which are available for detecting these As species have been documented, especially the most versatile and applied technique including inductively coupled plasma mass spectrometry.

Dimethylmonothioarsinic acid (DMMTAV) differentially modulates the expression of AHR-regulated cytochrome P450 1A enzymes in vivo and in vitro

Dimethylmonothioarsinic acid (DMMTAV), a pentavalent thio-arsenic derivative, has been found in bodily fluids and tissues including urine, liver, kidney homogenates, plasma, and red blood cells. Although DMMTAV is a minor metabolite in humans and animals, its substantial toxicity raises concerns about potential carcinogenic effects. This toxicity could be attributed to arsenicals' ability to regulate cytochrome P450 1 A (CYP1A) enzymes, pivotal in procarcinogen activation or detoxification. The current study investigates DMMTAV's impact on CYP1A1/2 expression, individually and in conjunction with its inducer, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). C57BL/6 mice were intraperitoneally injected with 6 mg/kg DMMTAV, alone or with 15 μg/kg TCDD, for 6 and 24 h. Similarly, Hepa-1c1c7 cells were exposed to DMMTAV (0.5, 1, and 2 μM) with or without 1 nM TCDD for 6 and 24 h. DMMTAV hindered TCDD-induced elevation of Cyp1a1 mRNA, both in vivo (at 6 h) and in vitro, associated with reduced CYP1A regulatory element activation. Interestingly, in C57BL/6 mice, DMMTAV boosted TCDD-induced CYP1A1/2 protein and activity, unlike Hepa-1c1c7 cells where it suppressed both. DMMTAV co-exposure increased TCDD-induced Cyp1a2 mRNA. While Cyp1a1 mRNA stability remained unchanged, DMMTAV negatively affected protein stability, indicated by shortened half-life. Baseline levels of CYP1A1/2 mRNA, protein, and catalytic activities showed no significant alterations in DMMTAV-treated C57BL/6 mice and Hepa-1c1c7 cells. Taken together, these findings indicate, for the first time, that DMMTAV differentially modulates the TCDD-mediated induction of AHR-regulated enzymes in both liver of C57BL/6 mice and murine Hepa-1c1c7 cells suggesting that thio-arsenic pentavalent metabolites are extremely reactive and could play a role in the toxicity of arsenic.

Differential modulation of cytochrome P450 enzymes by arsenicals in non-human experimental models

Arsenic is a hazardous heavy metalloid that imposes threats to human health globally. It is widely spread throughout the environment in various forms. Arsenic-based compounds are either inorganic compounds (iAs) or organoarsenicals (oAs), where the latter are biotically generated from the former. Exposure to arsenic-based compounds results in varying biochemical derangements in living systems, leading eventually to toxic consequences. One important target for arsenic in biosystems is the network of metabolic enzymes, especially the superfamily of cytochrome P450 enzymes (CYPs) because of their prominent role in both endobiotic and xenobiotic metabolism. Therefore, the alteration of the CYPs by different arsenicals has been actively studied in the last few decades. We have previously summarized the findings of former studies investigating arsenic associated modulation of different CYPs in human experimental models. In this review, we focus on non-human models to get a complete picture about possible CYPs alterations in response to arsenic exposure.

Effects of Dietary Intake of Arsenosugars and Other Organic Arsenic Species on Studies of Arsenic Methylation Efficiency in Humans

Extensive research has used dimethylarsinic acid (DMA) in urine as a marker of arsenic methylation. The premise is that humans methylate inorganic arsenicals to monomethylarsonic acid (MMA) and DMA and excrete these arsenic species into the urine. However, DMA in urine not only comes from the methylation of inorganic arsenic but also could be a result of metabolism of other arsenic species, such as arsenosugars and arsenolipids. Most environmental health and epidemiological studies of arsenic methylation might have overlooked confounding factors that contribute to DMA in urine. Here we critically evaluate reported studies that used methylation indexes, concentration ratios of methylated arsenicals, or the percentage of DMA in urine as markers of arsenic methylation efficiency. Dietary intake of arsenosugars potentially confounds the calculation and interpretation of the arsenic methylation efficiencies. Many studies have not considered incidental dietary intake of arsenosugars, arsenolipids, and other organic arsenic species. Future studies should consider the dietary intake of diverse arsenic species and their potential effect on the urinary concentrations of DMA.

Determining the trophic transfer of metal(loid)s and arsenic speciation in freshwater aquatic organisms by quantifying diet compositions

Bioaccumulation through diet is the predominant source of metal(loid)s in fishes; however, the trophic transfer of metal(loid)s from the diet to aquatic organisms remains largely unclear. In this study, aquatic organisms and five potential food sources (leaf litter, coarse and fine particulate organic matter (CPOM and FPOM, respectively), epilithon and fish) were collected around the Shimen Realgar Mine of China. Stomach content analysis and stable nitrogen and carbon isotope analysis, combined with a new Bayesian mixing model (MixSIAR), were used to quantify diet compositions of aquatic organisms. The δ¹³C and δ¹⁵N values varied among fish sizes and sampling sites and were probably related to the diet shift of aquatic organisms. The MixSIAR modelling results showed that the aquatic organisms' food sources were mainly composed of FPOM (9%-68%) and epilithon (15%-65%), with leaf litter, CPOM and fish accounting for smaller proportions (2%-30%). Concentrations ranged from 0.91 to 1298 mg/kg for As, 0.01-1.30 mg/kg for Cd, 0.12-37.79 mg/kg for Pb, 0.63-1158 mg/kg for Cr, 1.22-411 mg/kg for Cu, 0.82-1772 mg/kg for Mn, 0.31-542 mg/kg for Ni and 21.84-1414 mg/kg for Zn in all the collected samples, including the aquatic organisms and the relevant food sources. The metal(loid) concentrations in the CPOM, FPOM and epilithon were significantly higher than those in aquatic organisms and leaf litter. In addition, the biomagnification factors were all less than 1, indicating a biodilution from diet to freshwater organisms. The predominant As species were organic As in aquatic organisms, while inorganic As was common in their food sources, indicating that As biotransformation occurred within the freshwater food chain.

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.

Nanocarrier-based delivery of arsenic trioxide for hepatocellular carcinoma therapy

Hepatocellular carcinoma (HCC) poses a severe threat to human health and economic development. Despite many attempts at HCC treatment, most are inevitably affected by the genetic instability and variability of tumor cells. Arsenic trioxide (ATO) has shown to be effective in HCC. However, time-consuming challenges, especially the optimal concentration in tumor tissue and bioavailability of ATO, remain to be overcome for its transition from the bench to the bedside. To bypass these issues, nanotechnology-based delivery systems have been developed for prevention, diagnosis, monitoring and treatment in recent years. This article is a systematic overview of the latest contributions and detailed insights into ATO-loaded nanocarriers, with particular attention paid to strategies for improving the efficacy of nanocarriers of ATO.

Arsenolipids in raw and cooked seafood products in southwest China: A non-targeted analysis

Arsenolipids are the primary form of arsenic in the fat of marine organisms. Because seafood is a common source of arsenic exposure and some arsenolipids are toxic, studying the abundance and species of arsenolipids in seafood is crucial for health risk assessment. Current arsenolipid research is confined by analytical techniques and limited to raw seafood analysis, despite the fact that most seafood is ingested cooked. Therefore, the aim of this study is to evaluate which seafood contributes to arsenolipid dietary intake and investigate the changes in arsenolipids before and after cooking. In Chongqing, China, popular seafood such as clam, shrimp, oyster, abalone, hairtail, and yellow croaker were collected. The raw and cooked samples prepared from these seafood products were examined using a non-targeted screening approach established for arsenolipids, which coupled high-performance liquid chromatography with data-independent high-resolution quadrupole-time-of-flight electrospray ionization tandem mass spectrometry. Arsenic-containing hydrocarbons (AsHC330, AsHC332, and AsHC360), arsenic-containing fatty acids (AsFA362, AsFA390, AsFA404, AsFA418, and AsFA422), trimethylarsine oxide, and thiolated trimethylarsinic acid were detected. The species of arsenolipids in each type of seafood remained intact after heating in the microwave oven. In cooked samples, the concentrations of AsFA362 and AsFA390 were significantly lower than in raw samples, whereas the concentrations of other arsenolipids were unchanged. Microwave cooking did not result in the thiolation of the detected arsenolipids. The most detected species in raw and cooked samples were AsFA362, AsFA390, and AsFA418. Most arsenolipid species were found in the highest levels in hairtails and yellow croakers. It is the first time that arsenolipids have been found in the oyster, abalone, abalone liver, and yellow croaker. The present study contributes to a better understanding of arsenolipids exposure from seafood, which is useful for assessing the health risks of arsenic.

Dimethylmonothioarsenate Is Highly Toxic for Plants and Readily Translocated to Shoots

Arsenic is one of the most relevant environmental pollutants and human health threats. Several arsenic species occur in soil pore waters. Recently, it was discovered that these include inorganic and organic thioarsenates. Among the latter, dimethylmonothioarsenate (DMMTA) is of particular concern because in mammalian cells, its toxicity was found to exceed even that of arsenite. We investigated DMMTA toxicity for plants in experiments with Arabidopsis thaliana and indeed observed stronger growth inhibition than with arsenite. DMMTA caused a specific, localized deformation of root epidermal cells. Toxicity mechanisms apparently differ from those of arsenite since no accumulation of reactive oxygen species was observed in DMMTA-exposed root tips. Also, there was no contribution of the phytochelatin pathway to the DMMTA detoxification as indicated by exposure experiments with respective mutants and thiol profiling. RNA-seq analysis found strong transcriptome changes dominated by stress-responsive genes. DMMTA was taken up more efficiently than the methylated oxyarsenate dimethylarsenate and highly mobile within plants as revealed by speciation analysis. Shoots showed clear indications of DMMTA toxicity such as anthocyanin accumulation and a decrease in chlorophyll and carotenoid levels. The toxicity and efficient translocation of DMMTA within plants raise important food safety issues.

Arsenic bioaccumulation and biotransformation in aquatic organisms

Arsenic exists universally in freshwater and marine environments, threatening the survival of aquatic organisms and human health. To elucidate arsenic bioaccumulation and biotransformation processes in aquatic organisms, this review evaluates the dissolved uptake, dietary assimilation, biotransformation, and elimination of arsenic in aquatic organisms and discusses the major factors influencing these processes. Environmental factors such as phosphorus concentration, pH, salinity, and dissolved organic matter influence arsenic absorption from aquatic systems, whereas ingestion rate, gut passage time, and gut environment affect the assimilation of arsenic from foodstuffs. Arsenic bioaccumulation and biotransformation mechanisms differ depending on specific arsenic species and the involved aquatic organism. Although some enzymes engaged in arsenic biotransformation are known, deciphering the complicated synthesis and degradation pathway of arsenobetaine remains a challenge. The elimination of arsenic involves many processes, such as fecal excretion, renal elimination, molting, and reproductive processes. This review facilitates our understanding of the environmental behavior and biological fate of arsenic and contributes to regulation of the environmental risk posed by arsenic pollution.

Arsenic Toxicity on Metabolism and Autophagy in Adipose and Muscle Tissues

Arsenic, a naturally occurring metalloid derived from the environment, has been studied worldwide for its causative effects in various cancers. However, the effects of arsenic toxicity on the development and progression of metabolic syndrome, including obesity and diabetes, has received less attention. Many studies suggest that metabolic dysfunction and autophagy dysregulation of adipose and muscle tissues are closely related to the development of metabolic disease. In the USA, arsenic contamination has been reported in some ground water, soil and grain samples in major agricultural regions, but the effects on adipose and muscle tissue metabolism and autophagy have not been investigated much. Here, we highlight arsenic toxicity according to the species, dose and exposure time and the effects on adipose and muscle tissue metabolism and autophagy. Historically, arsenic was used as both a poison and medicine, depending on the dose and treatment time. In the modern era, arsenic intoxication has significantly increased due to exposure from water, soil and food, which could be a contributing factor in the development and progression of metabolic disease. From this review, a better understanding of the pathogenic mechanisms by which arsenic alters metabolism and autophagy regulation could become a cornerstone leading to the development of therapeutic strategies against arsenic-induced toxicity and metabolic disease.

Dimethylmonothioarsinic acid and dimethyldithioarsinic acid in the environment: Sorption characteristics on 2-line ferrihydrite and acute toxicity to Daphnia magna

Dimethylmonothioarsinic acid (DMMTA(V)) and dimethyldithioarsinic acid (DMDTA(V)), which are commonly found in landfill leachate and pore water of rice paddy soil, have attracted considerable attention for their high toxicity. This study aims to evaluate the behavior and potential risks of DMMTA(V) and DMDTA(V) in the environment by conducting an equilibrium sorption test using 2-line ferrihydrite and acute toxicity (immobilization) test using Daphnia magna. The overall maximum sorption capacity (q_m) derived by the Langmuir isotherm model showed an increase in the order of inorganic arsenate (As(V)) > dimethylarsinic acid (DMA(V)) > DMMTA(V) > DMDTA(V), which was likely due to steric hindrance due to the presence of methyl and thiol groups. Moreover, DMMTA(V) and DMDTA(V) showed no or negligible change in q_m with pH change, while q_m decreased rapidly with increasing pH in As(V) and DMA(V). The 50% inhibition concentrations (IC50) for As(V), DMA(V), DMMTA(V), and DMDTA(V), which were measured after 48 h exposure to D. magna, were 9.5, > 30, 1.7, and 6.5 mg/L, respectively. Overall, the results demonstrated that DMMTA(V) and DMDTA(V) have high mobility and eco-toxicity in the environment and that methylated thioarsenicals should be accurately monitored and controlled.

Arsenic and Human Health: Genotoxicity, Epigenomic Effects, and Cancer Signaling

Arsenic is a well-known element because of its toxicity. Humans as well as plants and animals are negatively affected by its exposure. Some countries suffer from high levels of arsenic in their tap water and soils, which is considered a primary arsenic-linked risk factor for living beings. Humans generally get exposed to arsenic by contaminated drinking waters, resulting in many health problems, ranging from cancer to skin diseases. On the other hand, the FDA-certified drug arsenic trioxide provides solutions for various diseases, including several types of cancers. This issue emphasizes the importance of speciation of the metalloid elements in terms of impacts on health. When species get exposed to arsenic, it affects the cells altering their involvement. It can lead to abnormalities in inflammatory mechanisms and the immune system which contribute to the negative impacts generated on the body. The poisoning originating from arsenic gives rise to various biological signs on the body which can be useful for the diagnosis. It is important to find true biomarkers for the detection of arsenic poisoning. In view of its application in medicine and biology, studies on understanding the biological activity of arsenic have increased. In this review, we aim at summarizing the current state of knowledge of arsenic and the mechanism behind its toxicity including genotoxicity, oxidative insults, epigenomic changes, and alterations in cellular signaling.

Arsenic: Various species with different effects on cytochrome P450 regulation in humans

Arsenic is well-recognized as one of the most hazardous elements which is characterized by its omnipresence throughout the environment in various chemical forms. From the simple inorganic arsenite (iAsIII) and arsenate (iAsV) molecules, a multitude of more complex organic species are biologically produced through a process of metabolic transformation with biomethylation being the core of this process. Because of their differential toxicity, speciation of arsenic-based compounds is necessary for assessing health risks posed by exposure to individual species or co-exposure to several species. In this regard, exposure assessment is another pivotal factor that includes identification of the potential sources as well as routes of exposure. Identification of arsenic impact on different physiological organ systems, through understanding its behavior in the human body that leads to homeostatic derangements, is the key for developing strategies to mitigate its toxicity. Metabolic machinery is one of the sophisticated body systems targeted by arsenic. The prominent role of cytochrome P450 enzymes (CYPs) in the metabolism of both endobiotics and xenobiotics necessitates paying a great deal of attention to the possible effects of arsenic compounds on this superfamily of enzymes. Here we highlight the toxicologically relevant arsenic species with a detailed description of the different environmental sources as well as the possible routes of human exposure to these species. We also summarize the reported findings of experimental investigations evaluating the influence of various arsenicals on different members of CYP superfamily using human-based models.

The dynamic changes of arsenic biotransformation and bioaccumulation in muscle of freshwater food fish crucian carp during chronic dietborne exposure

Dietary uptake is the major way that inorganic arsenic (iAs) enters into benthic fish; however, the metabolic process of dietborne iAs in fish muscle following chronic exposure remains unclear. This was a 40-day study on chronic dietborne iAs [arsenite (AsIII) and arsenate (AsV)] exposure in the benthic freshwater food fish, the crucian carp (Carassius auratus), which determined the temporal profiles of iAs metabolism and toxicokinetics during exposure. We found that an adaptive response occurred in the fish body after iAs dietary exposure, which was associated with decreased As accumulation and increased As transformation into a non-toxic As form (arsenobetaine). The bioavailability of dietary AsIII was lower than that of AsV, probably because AsIII has a lower ability to pass through fish tissues. Dietary AsV exhibited a high potential for transformation into AsIII species, which then accumulated in fish muscle. The largely produced AsIII considered more toxic at the earlier stage of AsV exposure should attract sufficient attention to human exposure assessment. Therefore, the pristine As species and exposure duration had significant effects on As bioaccumulation and biotransformation in fish. The behavior determined for dietborne arsenic in food fish is crucial for not only arsenic ecotoxicology but also food safety.

In Vitro Mitigation of Arsenic-Induced Toxicity by Reduced Glutathione in Rat Pulp Cells

Objective:

Despite the controversial results regarding the amount of arsenic (As) in mineral trioxide aggregate (MTA) and MTA-like cements, it is prudent to assess the effect of this heavy metal on pulpal cells and search for methods to attenuate its toxicity. This study investigated the toxic effect of As on pulpal-like cells and evaluated the influence of reduced glutathione (GSH) on As-induced toxicity.

Methods:

The cytotoxicity of 50 µm As, 50 µm As+50 µM GSH, 50µm As+500 µM GSH or 50 µm As+5000 µM GSH on rat pulpal cells (RPC-C2A) was evaluated at 24 hours and 72 hours. Cell culture in fresh medium without experimental solution served as the control. Cell viability was measured by means of 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide (MTT) assay and the optical density was measured with microplate reader. The morphology of the cultured cells was observed under phase contrast microscope. Cytotoxicity data were analyzed by two-way ANOVA and Tukey post hoc tests (P<0.05).

Results:

There were statistically significant differences in cell viability amongst the tested groups (P<0.05). As elicited remarkable toxic effect on pulpal cells, while 5000 µM GSH protected the cells from As-induced damage at 24-hour exposure time. The cultured control cells were polygonal-shaped; however, As-treated cells exhibited contracted and spherical morphology with increased intercellular spaces indicative of cellular death and decreased proliferation.

Conclusion:

As negatively affected the viability of pulpal cells; however, controlled concentration of GSH had a short-term protective effect against As-induced toxicity. Future research is warranted on the clinical use of GSH with MTA and MTA-like cements to minimize initial inflammation resulting from As release during the setting of the aforementioned cements thus enhancing the success of procedures where these cements are placed in direct contact with vital pulp tissues.

Feeding Arsenic-Containing Rice Bran to Growing Pigs: Growth Performance, Arsenic Tissue Distribution, and Arsenic Excretion

This research was conducted to study the growth performance, arsenic (As) tissue distribution, and As excretion of pigs fed As-containing rice bran. Twenty gilts (26.3 kg) were randomly assigned to 3 dietary treatments (n = 6 or 7) with Diets I, II, and III containing 0, 36.7, and 73.5% rice bran and 0, 306, and 612 ppb As, respectively. Pigs were fed for 6 weeks, and their growth performance and daily activities were examined. Fecal, blood, and hair samples were collected immediately before and after the 6-weeks. At the end of the 6-weeks, pigs were slaughtered; the liver, kidney, muscle, and urine samples were collected. No pig showed any unhealthy signs throughout the trial. The average daily feed intake, average daily gain, and final body weight of Diet III pigs were lower (p ≤ 0.001) than Diet I pigs. The gain to feed ratios were not different among the treatments. The fecal, hair, kidney, and urinary As concentrations of both Diets II and III pigs were higher than Diet I pigs. The hair As concentration of Diet III pigs was higher than Diet II pigs, but no difference was found in the fecal, urinary, kidney, or muscle As concentrations between Diets II and III pigs. The blood and muscle As concentrations were below 10 ppb. These results suggest that 73.5% dietary rice bran inclusion compromised growth performance, whereas the 36.7% inclusion did not. The fecal As data imply that dietary As was poorly absorbed by the gastrointestinal tract. The tissue As data indicate that the absorbed As was rapidly cleared from the blood with some retained in various organs and others eliminated via urine. The hair As concentration was much higher than that of liver and kidney. The muscle As data suggest that the pork produced from the pigs fed a typical As-containing rice bran as used in this study is safe for human consumption.

Removal of As(III) from Water Using the Adsorptive and Photocatalytic Properties of Humic Acid-Coated Magnetite Nanoparticles

The oxidation of highly toxic arsenite (As(III)) was studied using humic acid-coated magnetite nanoparticles (HA-MNP) as a photosensitizer. Detailed characterization of the HA-MNP was carried out before and after the photoinduced treatment of As(III) species. Upon irradiation of HA-MNP with 350 nm light, a portion of the As(III) species was oxidized to arsenate (As(V)) and was nearly quantitatively removed from the aqueous solution. The separation of As(III) from the aqueous solution is primarily driven by the strong adsorption of As(III) onto the HA-MNP. As(III) removals of 40–90% were achieved within 60 min depending on the amount of HA-MNP. The generation of reactive oxygen species (•OH and ¹O₂) and the triplet excited state of HA-MNP (³HA-MNP*) was monitored and quantified during HA-MNP photolysis. The results indicate ³HA-MNP* and/or singlet oxygen (¹O₂) depending on the reaction conditions are responsible for converting As(III) to less toxic As(V). The formation of ³HA-MNP* was quantified using the electron transfer probe 2,4,6-trimethylphenol (TMP). The formation rate of ³HA-MNP* was 8.0 ± 0.6 × 10⁻⁹ M s⁻¹ at the TMP concentration of 50 µM and HA-MNP concentration of 1.0 g L⁻¹. The easy preparation, capacity for triplet excited state and singlet oxygen production, and magnetic separation suggest HA-MNP has potential to be a photosensitizer for the remediation of arsenic (As) and other pollutants susceptible to advanced oxidation.

Antimony and its compounds: Health impacts related to pulmonary toxicity, cancer, and genotoxicity

Although occupational exposure to antimony and its compounds can produce pulmonary toxicity, human carcinogenic impacts have not been observed. Inhalation studies with respirable antimony trioxide particles administered to rats and mice have, however, induced carcinogenic responses in the lungs and related tissue sites. Genotoxicity studies conducted to elucidate mechanism(s) for tumor induction have produced mixed results. Antimony compounds do not induce gene mutations in bacteria or cultured mammalian cells, but chromosome aberrations and micronuclei have been observed, usually at highly cytotoxic concentrations. Indirect mechanisms of genotoxicity have been proposed to mediate these responses. In vivo genotoxicity tests have generally yielded negative results although several positive studies of marginal quality have been reported. Genotoxic effects may be related to indirect modes of action such as the generation of excessive reactive oxygen species (ROS), altered gene expression or interference with DNA repair processes. Such indirect mechanisms may exhibit dose-response thresholds. For example, interaction of ROS with in vivo antioxidant systems could yield a threshold for genotoxicity (and cancer) only at concentrations above the capacity of antioxidant defense mechanisms to control and/or eliminate damage from ROS.

Arsenic species in electronic cigarettes: Determination and potential health risk

Human exposure to contaminants from electronic cigarettes (e-cigarettes) and the associated health effects are poorly understood. There has been no report on the speciation of arsenic in e-liquid (solution used for e-cigarettes) and aerosols. We report here determination of arsenic species in e-liquids and aerosols generated from vaping the e-liquid. Seventeen e-liquid samples of major brands, purchased from local and online stores in Canada and China, were analyzed for arsenic species using high-performance liquid chromatography and inductively coupled plasma mass spectrometry. Aerosols condensed from vaping the e-liquids were also analyzed and compared for arsenic species. Six arsenic species were detected, including inorganic arsenate (iAs^V), arsenite (iAs^III), monomethylarsonic acid (MMA), and three new arsenic species not reported previously. In e-liquids, iAs^III was detected in 59%, iAs^V in 94%, and MMA in 47% of the samples. In the condensate of aerosols from vaping the e-liquids, iAs^III was detected in 100%, iAs^V in 88%, and MMA in 13% of the samples. Inorganic arsenic species were predominant in e-liquids and aerosols of e-cigarettes. The concentration of iAs^III in the condensate of aerosols (median 3.27 μg/kg) was significantly higher than that in the e-liquid (median 1.08 μg/kg) samples. The concentration of inorganic arsenic in the vaping air was approximately 3.4 μg/m³, which approaches to the permissible exposure limit (10 μg/m³) set by the United States Occupational Safety and Health Administration (OSHA). According to the Environmental Protection Agency's unit risk factor (4.3 × 10^-3 per μg/m³) for inhalation exposure to inorganic arsenic in the air, the estimated excess lung cancer risk from lifetime exposure to inorganic arsenic in the e-cigarette vaping air (3.4 μg/m³), assuming e-cigarette vaping at 1% of the time, is as high as 1.5 × 10^-4. These results raise health concerns over the exposure to arsenic from electronic cigarettes.

Arsenic and the gastrointestinal tract microbiome

Arsenic is a toxin, ranking first on the Agency for Toxic Substances and Disease Registry and the Environmental Protection Agency Priority List of Hazardous Substances. Chronic exposure increases the risk of a broad range of human illnesses, most notably cancer; however, there is significant variability in arsenic-induced disease among exposed individuals. Human genetics is a known component, but it alone cannot account for the large inter-individual variability in the presentation of arsenicosis symptoms. Each part of the gastrointestinal tract (GIT) may be considered as a unique environment with characteristic pH, oxygen concentration, and microbiome. Given the well-established arsenic redox transformation activities of microorganisms, it is reasonable to imagine how the GIT microbiome composition variability among individuals could play a significant role in determining the fate, mobility and toxicity of arsenic, whether inhaled or ingested. This is a relatively new field of research that would benefit from early dialogue aimed at summarizing what is known and identifying reasonable research targets and concepts. Herein, we strive to initiate this dialogue by reviewing known aspects of microbe-arsenic interactions and placing it in the context of potential for influencing host exposure and health risks. We finish by considering future experimental approaches that might be of value.

Analytical Methodologies for the Determination of Organoarsenicals in Edible Marine Species: A Review

Setting regulatory limits for arsenic in food is complicated, owing to the enormous diversity of arsenic metabolism in humans, lack of knowledge about the toxicity of these chemicals, and lack of accurate arsenic speciation data on foodstuffs. Identification and quantification of the toxic arsenic compounds are imperative to understanding the risk associated with exposure to arsenic from dietary intake, which, in turn, underscores the need for speciation analysis of the food. Arsenic speciation in seafood is challenging, owing to its existence in myriads of chemical forms and oxidation states. Interconversions occurring between chemical forms, matrix complexity, lack of standards and certified reference materials, and lack of widely accepted measurement protocols present additional challenges. This review covers the current analytical techniques for diverse arsenic species. The requirement for high-quality arsenic speciation data that is essential for establishing legislation and setting regulatory limits for arsenic in food is explored.

Organoarsenicals in Seafood: Occurrence, Dietary Exposure, Toxicity, and Risk Assessment Considerations - A Review

Diet, especially seafood, is the main source of arsenic exposure for humans. The total arsenic content of a diet offers inadequate information for assessment of the toxicological consequences of arsenic intake, which has impeded progress in the establishment of regulatory limits for arsenic in food. Toxicity assessments are mainly based on inorganic arsenic, a well-characterized carcinogen, and arsenobetaine, the main organoarsenical in seafood. Scarcity of toxicity data for organoarsenicals, and the predominance of arsenobetaine as an organic arsenic species in seafood, has led to the assumption of their nontoxicity. Recent toxicokinetic studies show that some organoarsenicals are bioaccessible and cytotoxic with demonstrated toxicities like that of pernicious trivalent inorganic arsenic, underpinning the need for speciation analysis. The need to investigate and compare the bioavailability, metabolic transformation, and elimination from the body of organoarsenicals to the well-established physiological consequences of inorganic arsenic and arsenobetaine exposure is apparent. This review provides an overview of the occurrence and assessment of human exposure to arsenic toxicity associated with the consumption of seafood.

The Human Gut Microbiome's Influence on Arsenic Toxicity

PURPOSE OF REVIEW

Arsenic exposure is a public health concern of global proportions with a high degree of interindividual variability in pathologic outcomes. Arsenic metabolism is a key factor underlying toxicity, and the primary purpose of this review is to summarize recent discoveries concerning the influence of the human gut microbiome on the metabolism, bioavailability, and toxicity of ingested arsenic. We review and discuss the current state of knowledge along with relevant methodologies for studying these phenomena.

RECENT FINDINGS

Bacteria in the human gut can biochemically transform arsenic-containing compounds (arsenicals). Recent publications utilizing culture-based approaches combined with analytical biochemistry and molecular genetics have helped identify several arsenical transformations by bacteria that are at least possible in the human gut and are likely to mediate arsenic toxicity to the host. Other studies that directly incubate stool samples in vitro also demonstrate the gut microbiome's potential to alter arsenic speciation and bioavailability. In vivo disruption or elimination of the microbiome has been shown to influence toxicity and body burden of arsenic through altered excretion and biotransformation of arsenicals. Currently, few clinical or epidemiological studies have investigated relationships between the gut microbiome and arsenic-related health outcomes in humans, although current evidence provides strong rationale for this research in the future.

SUMMARY

The human gut microbiome can metabolize arsenic and influence arsenical oxidation state, methylation status, thiolation status, bioavailability, and excretion. We discuss the strength of current evidence and propose that the microbiome be considered in future epidemiologic and toxicologic studies of human arsenic exposure.

Arsenic exposure: A public health problem leading to several cancers

Arsenic, a metalloid and naturally occurring element, is one of the most abundant elements in the earth's crust. Water is contaminated by arsenic through natural sources (underground water, minerals and geothermal processes) and anthropogenic sources such as mining, industrial processes, and the production and use of pesticides. Humans are exposed to arsenic mainly by drinking contaminated water, and secondarily through inhalation and skin contact. Arsenic exposure is associated with the development of vascular disease, including stroke, ischemic heart disease and peripheral vascular disease. Also, arsenic increases the risk of tumors of bladder, lungs, kidneys and liver, according to the International Agency for Research on Cancer and the Food and Drug Administration. Once ingested, an estimated 70-90% of inorganic arsenic is absorbed by the gastrointestinal tract and widely distributed through the blood to different organs, primarily to the liver, kidneys, lungs and bladder and secondarily to muscle and nerve tissue. Arsenic accumulates in the organs, especially in the liver. Its excretion mostly takes place through urination. The toxicokinetics of arsenic depends on the duration of exposure, pathway of ingestion, physicochemical characteristics of the compound, and affected biological species. The present review outlines of arsenic toxic effects focusing on different cancer types whit highest prevalence's by exposure to this metalloid and signaling pathways of carcinogenesis.

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.

State of the science review of the health effects of inorganic arsenic: Perspectives for future research

Human exposure to inorganic arsenic (iAs) is a global health issue. Although there is strong evidence for iAs-induced toxicity at higher levels of exposure, many epidemiological studies evaluating its effects at low exposure levels have reported mixed results. We comprehensively reviewed the literature and evaluated the scientific knowledge on human exposure to arsenic, mechanisms of action, systemic and carcinogenic effects, risk characterization, and regulatory guidelines. We identified areas where additional research is needed. These priority areas include: (1) further development of animal models of iAs carcinogenicity to identify molecular events involved in iAs carcinogenicity; (2) characterization of underlying mechanisms of iAs toxicity; (3) assessment of gender-specific susceptibilities and other factors that modulate arsenic metabolism; (4) sufficiently powered epidemiological studies to ascertain relationship between iAs exposure and reproductive/developmental effects; (5) evaluation of genetic/epigenetic determinants of iAs effects in children; and (6) epidemiological studies of people chronically exposed to low iAs concentrations.

Antimony speciation in the environment: Recent advances in understanding the biogeochemical processes and ecological effects

Antimony (Sb) is a toxic metalloid, and its pollution has become a global environmental problem as a result of its extensive use and corresponding Sb-mining activities. The toxicity and mobility of Sb strongly depend on its chemical speciation. In this review, we summarize the current knowledge on the biogeochemical processes (including emission, distribution, speciation, redox, metabolism and toxicity) that trigger the mobilization and transformation of Sb from pollution sources to the surrounding environment. Natural phenomena such as weathering, biological activity and volcanic activity, together with anthropogenic inputs, are responsible for the emission of Sb into the environment. Sb emitted in the environment can adsorb and undergo redox reactions on organic or inorganic environmental media, thus changing its existing form and exerting toxic effects on the ecosystem. This review is based on a careful and systematic collection of the latest papers during 2010-2017 and our research results, and it illustrates the fate and ecological effects of Sb in the environment.

Thiolated arsenic in natural systems: What is current, what is new and what needs to be known

Thiolated arsenic compounds are the sulfur analogous substructures of oxo-arsenicals as the arsinoyl (As = O) is substituted by an arsinothioyl (As = S) group. Relatively brief history of thioarsenic research, mostly in the current decade has endeavored to understand their consequences in the natural environment. However, thioarsenic related aspects have by far not attached much research concern on global scale compared to other arsenic species. This review attempts to provide a critical overview for the first time on formation mechanisms of thioarsenicals, their chemistry, speciation and analytical methodologies in order to provide a rational assessment of what is new, what is current, what needs to be known or what should be done in future research. Thioarsenic compounds play a vital role in determining the biogeochemistry of arsenic in sulfidic environments under reducing conditions. Thioarsenic species are widely immobilized by naturally occurring processes such as the adsorption on iron (oxyhydr)oxides and precipitation on iron sulfide minerals. Accurate measurement of thioarsenic species is a challenging task due to their instability upon pH, temperature, redox potential, and concentrations of oxygen, sulfur and iron. Assessment of direct and indirect effects of toxic thioarsenic species on global population those who frequently get exposed to high levels of arsenic is an urgent necessity. Dimethylmonothioarsinic acid (DMMTA^V) is the most cytotoxic arsenic metabolite having similar toxicological effects as dimethylarsinous acid (DMA^III) in human and animal tissues. The formation and chemical analysis of thioarsenicals in soil and sediments are highly unknown. Therefore, future research needs to be more inclined towards in determining the molecular structure of unknown thioarsenic complexes in various environmental suites. Contemporary approaches hyphenated to existing technologies would pave the way to overcome critical challenges of thioarsenic speciation such as standards synthesis, structural determination, quantification and sample preservation in future research.

Prenatal co-exposure to neurotoxic metals and neurodevelopment in preschool children: The Environment and Childhood (INMA) Project

We sought to determine whether prenatal co-exposure to As, Cd, Hg, Mn, and Pb was associated with impaired neurodevelopment in preschool children from the Spanish Environment and Childhood (INMA) Project, using the placenta as exposure matrix. We measured metal levels in placenta tissue samples randomly selected from five of the seven population-based birth cohorts participating in the INMA Project, collected between 2000 and 2008. Neuropsychological assessment of cognitive and motor function was carried through the use of the McCarthy Scales of Children's Abilities (MSCA) at the age of 4-5years. Data on placental metal levels, MSCA scores, and relevant covariates was available for 302 children. Mn was detected in all placental samples, Cd in nearly all placentas (99%) and As, Hg, and Pb in 22%, 58%, and 17% of the placentas, respectively. After adjusting for potential confounders, detectable As levels were associated with decrements in global and verbal executive functions and quantitative abilities; detectable Hg was associated with lower scores on the verbal function of posterior cortex in a dose-response manner, and non-linearly related to poorer motor function and gross motor skills; and Mn levels were associated with decrement in perceptual-performance skills in a dose-response manner but with better memory span and quantitative skills. A synergistic interactive effect was found between As and Pb with respect to the general cognitive score, whereas an antagonistic interaction was found between Mn and Hg. Prenatal exposure to As and Hg may be a risk factor for cognitive and motor impairment in children, while the effects of Cd and Mn on neurodevelopment are less clear. Future studies should examine combined and interactive effects of exposure to multiple metals during vulnerable periods of brain development prospectively.

Metabolism of a Phenylarsenical in Human Hepatic Cells and Identification of a New Arsenic Metabolite

Environmental contamination and human consumption of chickens could result in potential exposure to Roxarsone (3-nitro-4-hydroxyphenylarsonic acid), an organic arsenical that has been used as a chicken feed additive in many countries. However, little is known about the metabolism of Roxarsone in humans. The objective of this research was to investigate the metabolism of Roxarsone in human liver cells and to identify new arsenic metabolites of toxicological significance. Human primary hepatocytes and hepatocellular carcinoma HepG2 cells were treated with 20 or 100 μM Roxarsone. Arsenic species were characterized using a strategy of complementary chromatography and mass spectrometry. The results showed that Roxarsone was metabolized to more than 10 arsenic species in human hepatic cells. A new metabolite was identified as a thiolated Roxarsone. The 24 h IC₅₀ values of thiolated Roxarsone for A549 lung cancer cells and T24 bladder cancer cells were 380 ± 80 and 42 ± 10 μM, respectively, more toxic than Roxarsone, whose 24 h IC₅₀ values for A549 and T24 were 9300 ± 1600 and 6800 ± 740 μM, respectively. The identification and toxicological studies of the new arsenic metabolite are useful for understanding the fate of arsenic species and assessing the potential impact of human exposure to Roxarsone.

Rapid evaluation of arsenic contamination in paddy soils using field portable X-ray fluorescence spectrometry

Arsenic (As) in paddy fields is deteriorating food security and human health through rice ingestion. Rice is the dominant food source of arsenic exposure to half of the world's population. Therefore, an in situ effective method for As risk evaluation in paddy soil is strongly needed to avoid As exposure through rice ingestion. Herein, we developed a rapid analytical methodology for determination of As in plant tissues using field portable X-ray fluorescence spectrometry (FP-XRF). This method was applied to rice roots in order to evaluate the As contamination in paddy soils. The results showed that rice roots with iron plaques were superior to rhizosphere soils for generating FP-XRF signals, especially for field sites with As concentrations lower than the soil detection limit of FP-XRF (30.0mg/kg). Moreover, the strong linear relationships of As concentrations between the rice roots and corresponding leaves and grains proved that the rice root, rather than the soil, is a better predictor of As concentrations in rice grains. The research provides an efficient As monitoring method for As contaminated paddy fields by using wetland plant roots with iron plaques and XRF-based analytical techniques.

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.