The metabolism of inorganic arsenic oxides, gallium arsenide, and arsine: a toxicochemical review

Exposure to gallium arsenide nanoparticles in a research facility: a case study using molecular beam epitaxy

We evaluated GaAs nanoparticle-concentrations in the air and on skin and surfaces in a research facility that produces thin films, and to monitored As in the urine of exposed worker. The survey was over a working week using a multi-level approach. Airborne personal monitoring was implemented using a miniature diffusion size classifier (DiSCMini) and IOM sampler. Environmental monitoring was conducted using the SKC Sioutas Cascade Impactor to evaluate dimensions and nature of particles collected. Surfaces contamination were assessed analyzing As and Ga in ghost wipes. Skin contamination was monitored using tape strips. As and Ga were analyzed in urines collected every day at the beginning and end of the shift. The greatest airborne exposure occurred during the cutting operations of the GaAs Sample (88883 np/cm3). The highest levels of contamination were found inside the hood (As max = 1418 ng/cm2) and on the laboratory floor (As max = 251 ng/cm2). The average concentration on the worker's skin at the end of the work shift (3.36 ng/cm2) was more than 14 times higher than before the start of the shift. In weekly urinary biomonitoring an average As concentration of 19.5 µg/L, which was above the Società Italiana Valori di Riferimento (SIVR) reference limit for the non-occupational population (2.0 - 15 µg/L), but below the ACGIH limit (30 µg/L). Overall, airborne monitoring, surface sampling, skin sampling, and biomonitoring of worker confirmed the exposure to As of workers. Systematic cleaning operations, hood implementation and correct PPE management are needed to improve worker protection.

Biomonitoring of inorganic arsenic species in pregnancy

Exposure assessment of inorganic arsenic is challenging due to the existence of multiple species, complexity of arsenic metabolism, and variety of exposure sources. Exposure assessment of arsenic during pregnancy is further complicated by the physiological changes that occur to support fetal growth. Given the well-established toxicity of inorganic arsenic at high concentrations, continued research into the potential health effects of low-level exposure on maternal and fetal health is necessary. Our objectives were to review the value of and challenges inherent in measuring inorganic arsenic species in pregnancy and highlight related research priorities. We discussed how the physiological changes of pregnancy influence arsenic metabolism and necessitate the need for pregnancy-specific data. We reviewed the biomonitoring challenges according to common and novel biological matrices and discussed how each matrix differs according to half-life, bioavailability, availability of laboratory methods, and interpretation within pregnancy. Exposure assessment in both established and novel matrices that accounts for the physiological changes of pregnancy and complexity of speciation is a research priority. Standardization of laboratory method for novel matrices will help address these data gaps. Research is particularly lacking in contemporary populations of pregnant women without naturally elevated arsenic drinking water concentrations (i.e. <10 µg/l).

The interplay of arsenic, silymarin, and NF-ĸB pathway in male reproductive toxicity: A review

Arsenic toxicity is one of the most trending reasons for several malfunctions, particularly reproductive toxicity. The exact mechanism of arsenic poisoning is a big question mark. Exposure to arsenic reduces sperm count, impairs fertilization, and causes inflammation and genotoxicity through interfering with autophagy, epigenetics, ROS generation, downregulation of essential protein expression, metabolite changes, and hampering several signaling cascades, particularly by the alteration of NF-ĸB pathway. This work tries to give a clear idea about the different aspects of arsenic resulting in male reproductive complications, often leading to infertility. The first part of this article explains the implications of arsenic poisoning and the crosstalk of the NF-ĸB pathway in male reproductive toxicity. Silymarin is a bioactive compound that exerts anti-cancer and anti-inflammatory properties and has demonstrated hopeful outcomes in several cancers, including colon cancer, breast cancer, and skin cancer, by downregulating the hyperactive NF-ĸB pathway. The next half of this article thus sheds light on silymarin's therapeutic potential in inhibiting the NF-ĸB signaling cascade, thus offering protection against arsenic-induced male reproductive toxicity.

Targeting Cell Death Mechanism Specifically in Triple Negative Breast Cancer Cell Lines

Triple negative breast cancer (TNBC) is currently associated with a lack of treatment options. Arsenic derivatives have shown antitumoral activity both in vitro and in vivo; however, their mode of action is not completely understood. In this work we evaluate the response to arsenate of the double positive MCF-7 breast cancer cell line as well as of two different TNBC cell lines, Hs578T and MDA-MB-231. Multimodal experiments were conducted to this end, using functional assays and microarrays. Arsenate was found to induce cytoskeletal alteration, autophagy and apoptosis in TNBC cells, and moderate effects in MCF-7 cells. Gene expression analysis showed that the TNBC cell lines’ response to arsenate was more prominent in the G2M checkpoint, autophagy and apoptosis compared to the Human Mammary Epithelial Cells (HMEC) and MCF-7 cell lines. We confirmed the downregulation of anti-apoptotic genes (MCL1, BCL2, TGFβ1 and CCND1) by qRT-PCR, and on the protein level, for TGFβ2, by ELISA. Insight into the mode of action of arsenate in TNBC cell lines it is provided, and we concluded that TNBC and non-TNBC cell lines reacted differently to arsenate treatment in this particular experimental setup. We suggest the future research of arsenate as a treatment strategy against TNBC.

Improved Micro-X-ray Fluorescence Confocal Imaging of Two-Dimensional Distribution of Arsenic Concentration in Cucumber Hypocotyls Using Synchrotron Radiation

An optimized micro-X-ray fluorescence confocal imaging (μXRF-CI) analytical method has been developed to determine the 2D distribution of elemental composition in small (1–3 mm) biological objects at a 10–20 μm spatial resolution. Plants take up chemical elements from soil, and the vascular system transports them toward shoots. In order to obtain biochemical information related to this biological process, 2D distributions of chemical elements in roots and in hypocotyls of cucumber plants were analyzed by synchrotron radiation based on micro-X-ray fluorescence computer tomography and μXRF-CI techniques. The experiments were carried out at HASYLAB Beamline L of the DORIS-III storage ring in Hamburg, a facility that provided optimal physical conditions for developing and performing these unique analyses: high flux monochromatic synchrotron beam, X-ray optical elements, precision moving stages, and silicon drift detectors. New methodological improvements and experimental studies were carried out for applicability of lyophilized samples and cryo-cooling. Experimental parameters were optimized to maximize the excitation yield of arsenic Kα radiation and improvement of the spatial resolution of the μXRF-CI analytical method.

Recycling Ag, As, Ga of waste light-emitting diodes via subcritical water treatment

From environmental security and resource recovery viewpoint, hydrothermal technology was adopted to recycle Ag, As, and Ga from waste LEDs in present study. Waste LEDs packaging materials (Polyphthalamide (PPA), epoxy resin, and brominated flame retardant (BFR)), which are difficult to degrade under normal conditions, can be effectively decomposed through two steps of hydrothermal treatment. As and Ga were leached and silver was successfully recovered. Under the optimal process parameters (300 ℃, 300r/min, 3% volume ratio of H₂O₂,400 min), the leaching rates of As and Ga are 98.4% and 80.5%, respectively. Ag and sapphire substrate were left and obtained together. Ag remains in the form of original metal, and almost no Ag ion was detected in the hydrothermal solution. In addition, As species in aqueous systems were simulated and inferred. The simulation results showed that As compounds that exist in the leaching solution is in liquid form and mainly exist as H₂AsO₄^-. Under optimum processing conditions, almost 100% epoxy resin was decomposed. The degradation mechanism may be illuminated through the free radical reaction, and the possible decomposition pathways were speculated. The study proposed a process to recycle Ag, As, and Ga from scrapped LEDs and information could be useful for recycling other e-wastes.

Arsenic metabolism differs between child and adult patients during acute arsenic poisoning

Epidemiological studies on chronic arsenic poisoning have clarified the relationship between various adverse effects and methylation efficiency or methylation capacity. However, no study has similarly investigated such effects on patients with acute arsenic poisoning. In the present work, we studied 61 patients with acute oral arsenic poisoning occurring after consumption of an arsenic trioxide-laced meal (curry soup). The cohort included children (defined as under 15 year old [y/o], n = 22) and adults (over 16 y/o, n = 39) whose urinary arsenic profiles were analyzed. None of these patients had received treatment with chelating agents. The estimated median (IQR) arsenic intake was 64.5 mg (48.3-80.5 mg) in children and 76.0 mg (56.0-91.0 mg) in adults, and these values were not significantly different. Symptoms of poisoning in children improved approximately 1 week after hospitalization. However, the symptoms in most adults deteriorated with severe signs of arsenic poisoning. Urinary arsenic profiles of all the patients were analyzed to obtain the following information: % monomethylarsonic acid (MMA), % dimethylarsinic acid (DMA), second methylation ratio (DMA/MMA), and secondary methylation index (SMI, DMA/MMA + DMA). The levels of these parameters may help identify patients at risk for worsening symptoms. %MMA, an indicator of incomplete methylation, increased more in adults, who experienced more severe symptom progression, compared with children. In contrast, %DMA, which indicates more complete and efficient methylation, increased particularly in children with mild symptoms. Overall the present results indicate that children possess an excellent capacity for methylation (second methylation ratio) of arsenic to DMA and therefore, experience relatively less severe progression of symptomology during acute arsenic poisoning.

Adsorption of Arsenic Ions Transforms Surface Reactivity of Engineered Cerium Oxide Nanoparticles

Cerium oxide (CeO₂) nanoparticles (NPs) are massively used as abrasives in the chemical and mechanical polishing (CMP), an essential process to manufacture semiconductor wafers. The CMP process for arsenide-based semiconductor materials produces wastewater with co-occurring arsenic (As) ions and CeO₂ NPs. We found that CeO₂ NPs adsorbed both arsenite (As(III)) and arsenate (As(V)) ions and the adsorption isotherms suggested different adsorption energies and capacities of the two species. Applying the ferric reducing ability for nanoparticle assay, we revealed that the adsorbed As(III) and As(V) each reduced CeO₂ NP surface reactivity but followed different mechanisms. The adsorbed As(III) ions below a critical coverage (110 mmol/kg) increased occupation of Ce 4f orbitals and thus reduced electron mobility of the original CeO₂ NPs. The adsorbed As(V) ions withdrew electrons from Ce 4f orbitals and likely became oxidizing agents that greatly inhibited the original surface reducing ability. Electron paramagnetic resonance analysis further revealed that adsorbed As(III) and As(V) ions decreased the propensity of CeO₂ NPs to produce reactive oxygen species. This work highlights the importance of examining NPs in their post-use phases in which surface reactivity and hazard potential can be greatly altered by chemical exposure history and NP surface transformations.

The relationship between PNP, GSTO-1, AS3MT and ADRB3 gene polymorphisms and urinary arsenic concentration among copper smelter and refinery employers

INTRODUCTION

The aim of this study was to assess the relationship between polymorphisms of genes encoding enzymes involved in arsenic metabolism and urinary arsenic concentration in people occupationally exposed to arsenic.

MATERIALS AND METHODS

The data from 113 employers directly exposed to lead, cadmium, and arsenic in copper smelter in Legnica and Glogow were collected. Urinary arsenic concentration was measured. In addition, blood level of cadmium, lead, and zinc protoporphyrins was assayed. Genetic analyses included polymorphism of PNP (rs 1130650), GSTO-1 (rs 4925), AS3MT (rs 11191439), and ADRB3 (rs4994) genes.

RESULTS

Individuals occupationally exposed to arsenic compounds, who have allele T in homozygous constellation in locus rs 1130650 of PNP gene, are predisposed to lower urinary arsenic concentration, while AA homozygosity in locus rs 4925 of GSTO-1 gene may result in statistically significant higher urinary arsenic concentration. Polymorphisms of AS3MT and ADRB3 genes showed no statistically significant correlation with urinary arsenic, however, there was a tendency to higher arsenic concentration in allele A carriers in locus rs4994 of ADRB3 gene and in allele T carriers in rs 11191439 of AS3MT gene.

CONCLUSION

This study indicates that arsenic absorption and metabolism depend on polymorphisms of genes encoding PNP and GSTO-1. Individuals with disadvantageous constellation of polymorphisms are more susceptible to harmful effects of arsenic exposure.

RNA Sequencing Analyses Reveal the Potential Mechanism of Pulmonary Injury Induced by Gallium Arsenide Particles in Human Bronchial Epithelioid Cells

Extensive use of gallium arsenide (GaAs) has led to increased exposure to humans working in the semiconductor industry. This study employed physicochemical characterization of GaAs obtained from a workplace, cytotoxicity analysis of damage induced by GaAs in 16HBE cells, RNA-seq and related bioinformatic analysis, qRT-PCR verification and survival analysis to comprehensively understand the potential mechanism leading to lung toxicity induced by GaAs. We found that GaAs-induced abnormal gene expression was mainly related to the cellular response to chemical stimuli, the regulation of signalling, cell differentiation and the cell cycle, which are involved in transcriptional misregulation in cancer, the MAPK signalling pathway, the TGF-β signalling pathway and pulmonary disease-related pathways. Ten upregulated genes (FOS, JUN, HSP90AA1, CDKN1A, ESR1, MYC, RAC1, CTNNB1, MAPK8 and FOXO1) and 7 downregulated genes (TP53, AKT1, NFKB1, SMAD3, CDK1, E2F1 and PLK1) related to GaAs-induced pulmonary toxicity were identified. High expression of HSP90AA1, RAC1 and CDKN1A was significantly associated with a lower rate of overall survival in lung cancers. The results of this study indicate that GaAs-associated toxicities affected the misregulation of oncogenes and tumour suppressing genes, activation of the TGF-β/MAPK pathway, and regulation of cell differentiation and the cell cycle. These results help to elucidate the molecular mechanism underlying GaAs-induced pulmonary injury.

Physiological status and functional anatomy of zebra fish (Danio rerio) exposed to various levels of Ga3

Gallium (Ga) is one of the intermetallic elements that has been used in cancer treatment for a long time. However, Ga compounds are increasingly being used to make high-speed semiconductors and photoelectric devices. The current work investigated physiological and pathological changes in zebra fish (Danio rerio) exposed to various Ga³⁺ levels (0.55, 1.5, and 3.85 mg/L) over a 14-day test period. Decreases in oxygen consumption were significant (p < 0.05) for groups exposed to 3.85 Ga³⁺ mg/L; this was associated with the fusion of zebra fish gills lamellae. Serum biochemical changes (including aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase) were consistent with observations of damage to organelles within the hepatocytes at higher Ga³⁺ exposure levels (1.5 and 3.85 mg/L) in zebra fish. We propose <0.55 Ga³⁺ mg/L as a biologically safe concentration that can be used to establish water quality criteria for this teleost model.

Cytotoxicity Assessment of Gallium- and Indium-Based Nanoparticles Toward Human Bronchial Epithelial Cells Using an Impedance-Based Real-Time Cell Analyzer

The semiconductor manufacturing sector plans to introduce III/V film structures (eg, gallium arsenide (GaAs), indium arsenide (InAs) onto silicon wafers due to their high electron mobility and low power consumption. Aqueous solutions generated during chemical and mechanical planarization of silicon wafers can contain a mixture of metal oxide nanoparticles (NPs) and soluble indium, gallium, and arsenic. In this work, the cytotoxicity induced by Ga- and In-based NPs (GaAs, InAs, Ga₂O₃, In₂O₃) and soluble III-V salts on human bronchial epithelial cells (16HBE14o-) was evaluated using a cell impedance real-time cell analysis (RTCA) system. The RTCA system provided inhibition data at different concentrations for multiple time points, for example, GaAs (25 mg/L) caused 60% inhibition after 8 hours of exposure and 100% growth inhibition after 24 hours. Direct testing of As(III) and As(V) demonstrated significant cytotoxicity with 50% growth inhibition concentrations after 16-hour exposure (IC₅₀) of 2.4 and 4.5 mg/L, respectively. Cell signaling with rapid rise and decrease in signal was unique to arsenic cytotoxicity, a precursor of strong cytotoxicity over the longer term. In contrast with arsenic, soluble gallium(III) and indium(III) were less toxic. Whereas the oxide NPs caused low cytotoxicity, the arsenide compounds were highly inhibitory (IC₅₀ of GaAs and InAs = 6.2 and 68 mg/L, respectively). Dissolution experiments over 7 days revealed that arsenic was fully leached from GaAs NPs, whereas only 10% of the arsenic was leached out of InAs NPs. These results indicate that the cytotoxicity of GaAs and InAs NPs is largely due to the dissolution of toxic arsenic species.

Microbial toxicity of gallium- and indium-based oxide and arsenide nanoparticles

III-V semiconductor materials such as gallium arsenide (GaAs) and indium arsenide (InAs) are increasingly used in the fabrication of electronic devices. There is a growing concern about the potential release of these materials into the environment leading to effects on public and environmental health. The waste effluents from the chemical mechanical planarization process could impact microorganisms in biological wastewater treatment systems. Currently, there is only limited information about the inhibition of gallium- and indium-based nanoparticles (NPs) on microorganisms. This study evaluated the acute toxicity of GaAs, InAs, gallium oxide (Ga₂O₃), and indium oxide (In₂O₃) particulates using two microbial inhibition assays targeting methanogenic archaea and the marine bacterium, Aliivibrio fischeri. GaAs and InAs NPs were acutely toxic towards these microorganisms; Ga₂O₃ and In₂O₃ NPs were not. The toxic effect was mainly due to the release of soluble arsenic species and it increased with decreasing particle size and with increasing time due to the progressive corrosion of the NPs in the aqueous bioassay medium. Collectively, the results indicate that the toxicity exerted by the arsenide NPs under environmental conditions will vary depending on intrinsic properties of the material such as particle size as well as on the dissolution time and aqueous chemistry.

Polyamine-stimulation of arsenic-transformed keratinocytes

Tumor promotion is strongly associated with inflammation and increased polyamine levels. Our understanding of relevant mechanisms responsible for arsenic-induced cancer remains limited. Previous studies suggest that arsenic targets and dysregulates stem cell populations that remain dormant in the skin until promoted to be recruited out of the bulge stem cell region, thus giving rise to skin tumors. In this study, we explored a possible mechanism by which increased keratinocyte polyamine biosynthesis promotes tumorsphere formation and invasiveness of arsenic-transformed HaCaT keratinocytes (As-HaCaT). Unlike parental HaCaT cells, As-HaCaT cells were tumorigenic in athymic nude mice, and the CD45negative epithelial tumor cells had enriched expression of Toll-Like Receptor 4 (TLR4), CD34 and CXCR4 as did As-HaCaT tumorsphere cultures compared to As-HaCaT monolayer cultures. Ornithine decarboxylase (ODC) overexpressing keratinocytes (Ker/ODC) release increased levels of the alarmin high mobility group box 1 (HMGB1). Ker/ODC conditioned medium (CM) stimulated As-HaCaT but not parental HaCaT tumorsphere formation, and this was inhibited by glycyrrhizin, an inhibitor of HMGB1, and by TAK242, an inhibitor of the HMGB1 receptor TLR4. Compared to parental HaCaT cells, As-HaCaT cells demonstrated greater invasiveness across a Matrigel-coated filter using either fibroblast CM or SDF-1α as chemoattractants. Addition of Ker/ODC CM or HMGB1 dramatically increased As-HaCaT invasiveness. Glycyrrhizin and TAK242 inhibited this Ker/ODC CM-stimulated invasion of As-HaCaT cells but not HaCaT cells. These results show that polyamine-dependent release of HMGB1 promotes the expansion of stem cell-like subpopulations in arsenic-transformed keratinocytes while also increasing their invasiveness, suggesting that polyamines may be a potential therapeutic target for the prevention and treatment of arsenic-initiated skin cancers.

A case-control analysis of maternal diet and risk of neural tube defects in Bangladesh

OBJECTIVES

Mothers need a nutrient-rich diet for healthy neural tube development. Neural tube defect risk can be reduced through fortifying grain products with folic acid and taking folic acid supplements. Fortification is not required in Bangladesh. Maternal supplement use rates are low, similar to other countries. This study evaluates maternal dietary intake during pregnancy to identify possible interventions.

METHODS

A food frequency questionnaire (FFQ) assessed maternal diet. The primary aim compared dietary intake (calories, fat, carbohydrate, protein, fiber, vitamins, and minerals) between mothers of infants with myelomeningocele (cases) and mothers of controls. Secondary aims included (i) comparing foods consumed and (ii) evaluating if rice intake correlated with arsenic exposure. Paired t-tests, Wilcoxon signed rank tests, McNemar's chi-squared test, and linear regression were used.

RESULTS

This study included 110 matched mother-infant pairs (55 cases/55 controls). Mothers of cases and mothers of controls had similar caloric intake [median 2406 kcal/day vs. 2196 kcal/day (p = 0.071)]. Mothers in both groups consumed less than half the daily recommended 600 μg of folate. Diets were potentially deficient in vitamins A, D, E, potassium, sodium, and iron. Steamed rice was the primary food consumed for both groups, and this rice intake was not associated with toenail arsenic.

CONCLUSIONS

Dietary interventions should increase folate, vitamins A, D, E, potassium, sodium, and iron intake in Bangladeshi mothers. Folic acid fortification of grain products maybe the only viable strategy to achieve adequate folate intake for mothers. Given the central role of rice to the Bangladeshi diet, fortifying rice may be a viable option.

Fate and migration of arsenic in large-scale anaerobic landfill

The fate and migration of arsenic in a large-scale anaerobic landfill site was investigated by characterization of the total As content and its speciation using a sequential extraction procedure. The total As content in the anaerobic landfill varied greatly with age of the deposited refuse, ranging from 15.26 ± 4.18 mg kg^-1 to 38.41 ± 10.41 mg kg^-1. There was an increasing trend from the upper layer to a depth of 18-19 m, followed by a decrease in the lower layer. Sequential extraction results showed that As present in exchangeable and weak-acid soluble forms (F1) varied from 0.08 ± 0.01 mg kg^-1 to 12.61 ± 0.92 mg kg^-1, but from 1.28 ± 0.11 mg kg^-1 to 8.40 ± 0.23 mg kg^-1 in reducible forms (F2). Oxidizable (F3) and residual (F4) forms of As, which were much more stable and for which the environmental risk correspondingly decreased, accounted for 24.21%-58.70% and 10.11%-30.90% of the total As content, respectively. Nitrate and carbonate had a strong influence on the distribution of As in F1 species; ferric ion affected As distribution in F2; both ferrous ion and dissolved oxygen content contributed to F3 distribution; As in F4 was associated with crystalline minerals structures and was only weakly affected by environmental factors. The deposition process could be divided into six phases to interpret As migration and distribution within the anaerobic landfill after closure.

Gallium arsenide (GaAs) leaching behavior and surface chemistry changes in response to pH and O2

Gallium arsenide (GaAs) is a material widely used in electronic devices. Disposal of electronic waste containing GaAs in municipal solid waste landfills raises concerns about the public health and ecological risks associated with the potential release of toxic arsenic (As) species. In this study, different tests were performed to investigate the leaching behavior of particulate GaAs in aqueous solutions. In the U.S. Toxicity Characteristic Leaching Procedure (TCLP) and California Waste Extraction Test (WET), the concentrations of As released from the GaAs particles were about 2.6-2.8-fold higher than the regulatory limit (5 mg/L). A much higher As concentration (72 mg/L), accounting for as much as 15.4% of the initial As in GaAs, was solubilized in a pH-7.6 synthetic landfill leachate under ambient atmosphere after 120 days. Additional tests performed to evaluate the dissolution of GaAs under a range of redox conditions, pH levels, ionic strength, and presence of organic constituents commonly found in landfills revealed that oxic environments and mildly alkaline conditions (pH 8.1-8.5) promote release of As (chiefly arsenite) and gallium species to the surrounding aqueous environment. The rate of As release in long-term exposure experiments was initially constant but later progressively diminished, likely due to the formation of a passivating layer on the surface of GaAs consisting of corrosion products rich in poorly soluble gallium oxides (Ga₂O₃ and Ga(OH)₃). This hypothesis was confirmed by surface analysis of GaAs particles subjected to leaching using X-ray photoelectron spectroscopy (XPS). These findings suggest that further research is needed to assess the potential release of toxic As from electronic waste in municipal landfills.

Assessment of museum staff exposure to arsenic while handling contaminated exhibits by urinalysis of arsenic species

Preservation of museum objects with inorganic arsenic compounds and contamination of the surroundings has previously been documented. The present study addresses the exposure of museum staff by measuring arsenicals in urine.

After 1 week without exposure, urinary samples were taken before and after handling of preserved skins and analysed by HPLC-ICP-MS for inorganic arsenic, arsenic metabolites and arsenobetaine. The sum of inorganic arsenic and metabolites was an index of exposure. Information about work and seafood intake was obtained by questionnaire.

One out of five subjects had a work-related rise in the exposure index of 18.1 μg As/L to a post-exposure level of 37.1 μg As/L. Four subjects had no certain exposure-related increase in the index.

The study indicates that museum staff may be exposed to arsenic from handling arsenic-preserved objects and supports the use of specified arsenic analysis to avoid interference from organic arsenic.

Metabolism, toxicity and anticancer activities of arsenic compounds

A variety of studies indicated that inorganic arsenic and its methylated metabolites have paradoxical effects, namely, carcinogenic and anticancer effects. Epidemiological studies have shown that long term exposure to arsenic can increase the risk of cancers of lung, skin or bladder in man, which is probably associated with the arsenic metabolism. In fact, the enzymatic conversion of inorganic arsenic by Arsenic (+3 oxidation state) methyltransferase (AS3MT) to mono- and dimethylated arsenic species has long been considered as a major route for detoxification. However, several studies have also indicated that biomethylation of inorganic arsenic, particularly the production of trivalent methylated metabolites, is a process that activates arsenic as a toxin and a carcinogen. On the other hand, arsenic trioxide (As2O3) has recently been recognized as one of the most effective drugs for the treatment of APL. However, elaboration of the cytotoxic mechanisms of arsenic and its methylated metabolites in eradicating cancer is sorely lacking. To provide a deeper understanding of the toxicity and carcinogenicity along with them use of arsenic in chemotherapy, caution is required considering the poor understanding of its various mechanisms of exerting toxicity. Thereby, in this review, we have focused on arsenic metabolic pathway, the roles of the methylated arsenic metabolites in toxicity and in the therapeutic efficacy for the treatments of solid tumors, APL and/or non-APL malignancies.

The Pyruvate and α-Ketoglutarate Dehydrogenase Complexes of Pseudomonas aeruginosa Catalyze Pyocyanin and Phenazine-1-carboxylic Acid Reduction via the Subunit Dihydrolipoamide Dehydrogenase

Phenazines are a class of redox-active molecules produced by diverse bacteria and archaea. Many of the biological functions of phenazines, such as mediating signaling, iron acquisition, and redox homeostasis, derive from their redox activity. Although prior studies have focused on extracellular phenazine oxidation by oxygen and iron, here we report a search for reductants and catalysts of intracellular phenazine reduction in Pseudomonas aeruginosa Enzymatic assays in cell-free lysate, together with crude fractionation and chemical inhibition, indicate that P. aeruginosa contains multiple enzymes that catalyze the reduction of the endogenous phenazines pyocyanin and phenazine-1-carboxylic acid in both cytosolic and membrane fractions. We used chemical inhibitors to target general enzyme classes and found that an inhibitor of flavoproteins and heme-containing proteins, diphenyleneiodonium, effectively inhibited phenazine reduction in vitro, suggesting that most phenazine reduction derives from these enzymes. Using natively purified proteins, we demonstrate that the pyruvate and α-ketoglutarate dehydrogenase complexes directly catalyze phenazine reduction with pyruvate or α-ketoglutarate as electron donors. Both complexes transfer electrons to phenazines through the common subunit dihydrolipoamide dehydrogenase, a flavoprotein encoded by the gene lpdG Although we were unable to co-crystallize LpdG with an endogenous phenazine, we report its X-ray crystal structure in the apo-form (refined to 1.35 Å), bound to NAD⁺ (1.45 Å), and bound to NADH (1.79 Å). In contrast to the notion that phenazines support intracellular redox homeostasis by oxidizing NADH, our work suggests that phenazines may substitute for NAD⁺ in LpdG and other enzymes, achieving the same end by a different mechanism.

Reproductive and Developmental Toxicity of Arsenic in Rodents: A Review

Arsenic is a recognized reproductive toxicant in humans and induces malformations, especially neural tube defects, in laboratory animals. Early studies showed that murine malformations occurred only when a high dose of inorganic arsenic was given by intravenous or intraperitoneal injection in early gestation. Oral gavage of inorganic arsenic at maternally toxic doses caused reduced fetal body weight and increased resorptions. Recently, arsenic reproductive and developmental toxicity has been studied in situations more similar to human exposures and using broader endpoints, such as behavioral changes and gene expression. For the general population, exposure to arsenic is mostly oral, particularly via drinking water, repeated and prolonged over time. In mice and rats, methylated or inorganic arsenic via drinking water or by repeated oral gavage induced male and female reproductive and developmental toxicities. Furthermore, at nonmaternally toxic levels, inorganic arsenic given to pregnant dams via drinking water affected fetal brain development and postnatal behaviors. However, arsenic given by repeated oral gavage to pregnant mice and rats was not morphologically teratogenic. In this review of arsenic reproductive and developmental toxicity in rats and mice, the authors summarize recent in vivo studies and discuss possible underlying mechanisms. The influences of folate, selenium, zinc, and arsenic methylation on arsenic reproductive and developmental toxicity are also discussed.

1HNMR-based metabonomic study of sub-chronic hepatotoxicity induced by realgar

ETHNOPHARMACOLOGICAL RELEVANCE

Realgar has been used as a traditional Chinese medicine (TCM) for thousands of years. Recently, a number of realgar or realgar-containing medicines poisoning cases have been reported. However, the toxicological mechanism of realgar has not been clearly clarified. In present study, the subchronic hepatotoxicity of realgar on mice was investigated using ¹HNMR-based metabonomic approaches.

MATERIALS AND METHODS

Twenty-eight male mice were divided into control group and low (0.15g/kg), middle (0.45g/kg), high (1.35g/kg) dosage realgar exposed groups. Their plasma and urine samples were used for NMR spectroscopic metabolic profiling. Principal component analysis (PCA) and pathway analysis were used to detect the hepatotoxic effects of realgar. Liver histopathological examination and plasma clinical chemistry analyses were also performed.

RESULTS

Plasma clinical chemistry analyses showed increased levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), total protein (TP), total cholesterol (TC) and choline esterase (CHE) in realgar-exposed mice indicating liver injury. The PCA score plots showed the metabolic profiles of realgar-exposed mice apparently separated from the controls. Obvious dose-dependent changes of metabolites in urine and plasma of realgar-exposed mice were observed. From the loading plots and boxplots results, the concentrations of VLDL/LDL, 3-HB, lactate, acetate, acetoacetate, creatine, glutamate, methionine, NAc, TMAO, alanine in plasma and pyruvate, succinate, 2-oxoglutarate, DMA, citrate, hippurate, glycine, taurine, phenylalanine, lactate in urine were significantly changed in realgar-exposed mice. The change trends of metabolites in urine and plasma from mice sub-chronic exposed to realgar are similar to those reported in rats acute exposed to realgar, which indicate the acute and sub-chronic toxic mechanism of realgar are same. The disturbed metabolic pathway include energy metabolism, amino acids metabolism and gut bacteria metabolism.

CONCLUSIONS

The present work illustrated the NMR-based metabonomic approach can capture and probe the metabolic alterations induced by traditional Chinese medicine in the toxicological effects.

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

Arsenic (As) is a notoriously toxic pollutant of health concern worldwide with potential risk of cancer induction, but meanwhile it is used as medicines for the treatment of different conditions including hematological cancers. Arsenic can undergo extensive metabolism in biological systems, and both toxicological and therapeutic effects of arsenic compounds are closely related to their metabolism. Recent studies have identified methylated thioarsenicals as a new class of arsenic metabolites in biological systems after exposure of inorganic and organic arsenicals, including arsenite, dimethylarsinic acid (DMA^V), dimethylarsinous glutathione (DMA^IIIGS), and arsenosugars. The increasing detection of thiolated arsenicals, including monomethylmonothioarsonic acid (MMMTA^V), dimethylmonothioarsinic acid (DMMTA^V) and its glutathione conjugate (DMMTA^VGS), and dimethyldithioarsinic acid (DMDTA^V) suggests that thioarsenicals may be important metabolites and play important roles in arsenic toxicity and therapeutic effects. Here we summarized the reported occurrence of thioarsenicals in biological systems, the possible formation pathways of thioarsenicals, and their toxicity, and discussed the biological implications of thioarsenicals on arsenic metabolism, toxicity, and therapeutic effects.

Biological and environmental hazards associated with exposure to chemical warfare agents: arsenicals

Arsenicals are highly reactive inorganic and organic derivatives of arsenic. These chemicals are very toxic and produce both acute and chronic tissue damage. On the basis of these observations, and considering the low cost and simple methods of their bulk syntheses, these agents were thought to be appropriate for chemical warfare. Among these, the best-known agent that was synthesized and weaponized during World War I (WWI) is Lewisite. Exposure to Lewisite causes painful inflammatory and blistering responses in the skin, lung, and eye. These chemicals also manifest systemic tissue injury following their cutaneous exposure. Although largely discontinued after WWI, stockpiles are still known to exist in the former Soviet Union, Germany, Italy, the United States, and Asia. Thus, access by terrorists or accidental exposure could be highly dangerous for humans and the environment. This review summarizes studies that describe the biological, pathophysiological, toxicological, and environmental effects of exposure to arsenicals, with a major focus on cutaneous injury. Studies related to the development of novel molecular pathobiology-based antidotes against these agents are also described.

Attenuative role of mangiferin in oxidative stress-mediated liver dysfunction in arsenic-intoxicated murines

Mangiferin (MAG), a natural xanthone mainly derived from mangoes, possesses great antioxidative potentials. The present study has been carried out to investigate the hepato-protective role of MAG, against arsenic (As)-induced oxidative damages in the murine liver. As, a well-known toxic metalloid, is ubiquitously found in nature and has been reported to affect nearly all the organs of the human body via oxidative impairment. Administration of As in the form of sodium arsenite (NaAsO2 ) at a dose of 10 mg/kg body weight for 3 months abruptly increased reactive oxygen species (ROS) level, led to oxidative stress and significantly depleted the first line of antioxidant defense system in the body. Moreover, As caused apoptosis in hepatocytes. Treatment with MAG at a dose of 40 mg/kg for body weight for 30 days simultaneously and separately after NaAsO2 administration decreased the ROS production and attenuated the alterations in the activities of all antioxidant indices. MAG also protected liver against the NaAsO2 -induced apoptosis and disintegrated hepatocytes, thus counteracting with As-induced toxicity. It could significantly inhibit the expression of different proapoptotic caspases and upregulate the expression of survival molecules such as Akt and Nrf2. On inhibiting Akt (by PI3K inhibitor, LY294002) and ERK1/2 (by ERK1/2 inhibitor, PD98059) specifically, caspase 3 got activated abolishing mangiferin's protective role on As-induced hepatotoxicity. So here, we have briefly elucidated the signaling cascades involved in As-induced apoptotic cell death in the liver and also the detailed cellular mechanism by which MAG provides protection to this organ. © 2016 BioFactors, 42(5):515-532, 2016.

Arsenic impacted the development, thyroid hormone and gene transcription of thyroid hormone receptors in bighead carp larvae (Hypophthalmichthys nobilis)

Arsenic (As) contamination in aquatic environment adversely impacts aquatic organisms. The present study assessed the toxicity of different As species and concentrations on bighead carp (Hypophthalmichthys nobilis) at early life stage, a major fish in Yangtze River, China. We measured the changes in embryo and larvae survival rate, larvae aberration, concentrations of thyroid hormone thyroxine, and transcription levels of thyroid hormone receptors (TRs) in fish larvae after exposing to arsenite (AsIII) or arsenate (AsV) at 0, 10, 30, 50, 100, or 150 μg L(-1) for 78 h. As concentrations ≤ 150 μg L(-1) had limited effect on embryo survival rate (6-8% inhibition), but larvae survival rate decreased to 53-57% and larvae aberration rate increased to 20-24% after As exposure. Moreover, thyroxine levels elevated by 23% and 50% at 100 μg L(-1) AsIII and 150 μg L(-1) AsV. Besides, AsIII and AsV decreased the transcriptional levels of TRα by 72 and 53%, and TRβ by 91 and 81% at 150 μg L(-1) As. Our data showed that AsIII and AsV had limited effect on carp embryo survival, but they were both toxic to carp larvae, with AsIII showing more effect than AsV. As concentrations <150μg L(-1) adversely influenced the development of bighead carp larvae and disturbed their thyroid hormone homeostasis.

Renal function is associated with indicators of arsenic methylation capacity in Bangladeshi adults

BACKGROUND

Arsenic (As) methylation capacity in epidemiologic studies is typically indicated by the proportions of inorganic As (%InAs), monomethylarsonic acid (%MMA), and dimethylarsinic acid (%DMA) in urine as a fraction of total urinary As. The relationship between renal function and indicators of As methylation capacity has not been thoroughly investigated.

OBJECTIVES

Our two aims were to examine (1) associations between estimated glomerular filtration rate (eGFR) and %As metabolites in blood and urine, and (2) whether renal function modifies the relationship of blood %As metabolites with respective urinary %As metabolites.

METHODS

In a cross-sectional study of 375 As-exposed Bangladeshi adults, we measured blood and urinary As metabolites, and calculated eGFR from plasma cystatin C.

RESULTS

In covariate-adjusted linear models, a 1 ml/min/1.73 m(2) increase in eGFR was associated with a 0.39% increase in urinary %InAs (p<0.0001) and a mean decrease in urinary %DMA of 0.07 (p=0.0005). In the 292 participants with measurable blood As metabolites, the associations of eGFR with increased blood %InAs and decreased blood %DMA did not reach statistical significance. eGFR was not associated with urinary or blood %MMA in covariate-adjusted models. For a given increase in blood %InAs, the increase in urinary %InAs was smaller in those with reduced eGFR, compared to those with normal eGFR (p=0.06); this effect modification was not observed for %MMA or %DMA.

CONCLUSIONS

Urinary excretion of InAs may be impaired in individuals with reduced renal function. Alternatively, increased As methylation capacity (as indicated by decreased urinary %InAs) may be detrimental to renal function.

Mechanisms of action for arsenic in cardiovascular toxicity and implications for risk assessment

The possibility of an association between inorganic arsenic (iAs) exposure and cardiovascular outcomes has received increasing attention in the literature over the past decade. The United States Environmental Protection Agency (US EPA) is currently revising its Integrated Risk Assessment System (IRIS) review of iAs, and one of the non-cancer endpoints of interest is cardiovascular disease (CVD). Despite the increased interest in this area, substantial gaps remain in the available information, particularly regarding the mechanism of action (MOA) by which iAs could cause or exacerbate CVD. Few studies specifically address the plausibility of an association between iAs and CVD at the low exposure levels which are typical in the United States (i.e., below 100 μg As/L in drinking water). We have conducted a review and evaluation of the animal, mechanistic, and human data relevant to the potential MOAs of iAs and CVD. Specifically, we evaluated the most common proposed MOAs, which include disturbance of endothelial function and hepatic dysfunction. Our analysis of the available evidence indicates that there is not a well-established MOA for iAs in the development or progression of CVD. Few human studies of the potential MOAs have addressed plausibility at low doses and the applicability of extrapolation from animal studies to humans is questionable. However, the available evidence indicates that regardless of the specific MOA, the effects of iAs on physiological processes at the cellular level appear to operate via a threshold mechanism. This finding is consistent with the lack of association of CVD with iAs exposure in humans at levels below 100 μg/L, particularly when considering important exposure and risk modifiers such as nutrition and genetics. Based on this analysis, we conclude that there are no data supporting a linear dose-response relationship between iAs and CVD, indicating this relationship has a threshold.

Arsenate stimulates glutathione export from viable cultured rat cerebellar granule neurons

Arsenate is an environmental pollutant which contaminates the drinking water of millions of people worldwide. Numerous in vitro studies have investigated the toxicity of arsenate for a large number of different cell types. However, despite the known neurotoxic potential of arsenicals, little is known so far about the consequences of an exposure of neurons to arsenate. To investigate acute effects of arsenate on the viability and the glutathione (GSH) metabolism of neurons, we have exposed primary rat cerebellar granule neuron cultures to arsenate. Incubation of neurons for up to 6 h with arsenate in concentrations of up to 10 mM did not acutely compromise the cell viability, although the cells accumulated substantial amounts of arsenate. However, exposure to arsenate caused a time- and concentration-dependent increase in the export of GSH from viable neurons with significant effects observed for arsenate in concentrations above 0.3 mM. The arsenate-induced stimulation of GSH export was abolished upon removal of arsenate and completely prevented by MK571, an inhibitor of the multidrug resistance protein 1. These results demonstrate that arsenate is not acutely toxic to neurons but can affect the neuronal GSH metabolism by stimulating GSH export.

Kinetics and activation parameters of the reaction of organoarsenic(V) compounds with glutathione

In this work the kinetics of the reaction of glutathione (GSH) with the organoarsenic(V) compounds phenylarsonic acid (PAA), 4-hydroxy-3-nitrophenylarsonic acid (HNPAA), p-aminophenylarsonic acid (p-APAA) and o-aminophenylarsonic acid (o-APAA) as well as monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) is investigated. The reaction progress is monitored in real time by (1)H NMR, allowing the determination of rate coefficients and half-lives as well as activation parameters. The reaction consists of two steps: redox reaction and conjugation. In all investigated systems the conjugation is fast compared to the redox reaction and, therefore, rate determining. All investigated phenylarsonic acids follow the same rate law, showing overall reaction orders of 3 and half-lives between 47.7 ± 0.2 and 71.0 ± 3.6 min. The methylated compounds react slower, showing half-lives of 76.6 ± 0.4 and 444 ± 10 min for DMAA and MMAA, respectively. Enthalpies of activation range from 20 to 36 (± 2) kJ mol(-1) and the entropies of activation are within -154 and -97(± 7)J mol(-1)K(-1). The results reveal a correlation of the toxicity of the arsenic compound and the reaction rate with GSH. This may pave the way for the estimation of the toxicity of such compounds by simple kinetic studies.

Higher urinary heavy metal, phthalate and arsenic concentrations accounted for 3-19% of the population attributable risk for high blood pressure: US NHANES, 2009-2012

The link between environmental chemicals and human health has emerged, but has not been completely examined in terms of its risk factors. Therefore, we aimed to study the relationships of different sets of urinary environmental chemical concentrations and high blood pressure (BP) in a national, population-based study. Data were retrieved from the United States National Health and Nutrition Examination Surveys, 2009-2012, including demographics, BP readings and urinary environmental chemical concentrations. Analyses included χ(2)-test, t-test, survey-weighted logistic regression models and population attributable risk estimation. Urinary cesium (odds ratio (OR) 1.52, 95% confidence interval (CI) 1.06-2.18, P=0.026), molybdenum (OR 1.45, 95% CI 1.04-2.02, P=0.029), lead (OR 1.49, 95% CI 1.12-1.98, P=0.009), platinum (OR 1.66, 95% CI 1.14-2.21, P=0.002), antimony (OR 1.44, 95% CI 1.12-1.86, P=0.008) and tungsten (OR 1.48, 95% CI 1.22-1.79, P<0.001) concentrations were observed to be associated with high BP. Similar results were observed for mono-2-ethyl-5-carboxypentyl (OR 1.29, 95% CI 1.04-1.59, P=0.024), mono-n-butyl (OR 1.36, 95% CI 1.11-1.67, P=0.005), mono-2-ethyl-5-hydroxyhexyl (OR 1.21, 95% CI 1.01-1.46, P=0.041), mono-n-methyl (OR 1.24, 95% CI 1.01-1.46, P=0.014), mono-2-ethyl-5-oxohexyl (OR 1.21, 95% CI 1.01-1.45, P=0.036), mono-benzyl (OR 1.41, 95% CI 1.15-1.74, P=0.002), dimethylarsonic acid (OR 1.38, 95% CI 1.08-1.76, P=0.012) and trimethylarsine oxide (OR 2.56, 95% CI 1.29-5.07, P=0.010) concentrations. Each chemical could account for 3-19% of the population attributable risk for high BP. A small sex difference was found. However, there are no associations between environmental parabens and pesticides and high BP. Urinary heavy metal, phthalate and arsenic concentrations were associated with high BP, although a causal effect cannot be established. Elimination of environmental chemical exposure in humans still needs to be pursued.

Higher urinary heavy metal, arsenic, and phthalate concentrations in people with high blood pressure: US NHANES, 2009-2010

BACKGROUND

A link between environmental chemicals and human health has emerged but not complete in risk factors. This work aimed to study the relationships of different sets of urinary environmental chemical concentrations and risk of high blood pressure (BP) in a national, population-based study.

METHODS

Data was retrieved from United States National Health and Nutrition Examination Surveys, 2009-2010, including demographics, BP readings and urinary environmental chemical concentrations. Analyses included t-test and survey-weighted logistic regression models.

RESULTS

Urinary mercury concentrations were not associated with high BP (OR = 1.19, 95% CI 0.97-1.48, p = 0.095). Urinary cobalt (OR = 1.35, 95% CI 1.01-1.81, p = 0.044), lead (OR = 1.77, 95% CI 1.31-2.38, p = 0.001), antimony (OR = 1.37, 95% CI 1.09-1.72, p = 0.010) and tungsten (OR = 1.52, 95% CI 1.27-1.81, p < 0.001) concentrations were observed to increase the risk of high BP. There are no clear associations between environmental parabens and high BP. The effect of environmental bisphenol A (OR = 1.14, 95% CI 1.00-1.30, p = 0.051) disappeared after additionally adjusting for subsample weighting (OR = 1.12, 95% CI 0.93-1.35, p = 0.225). People with higher urinary mono-2-ethyl-5-carboxypentyl phthalate (OR = 1.26, 95% CI 1.00-1.58, p = 0.051), mono-n-butyl phthalate (OR = 1.19, 95% CI 1.01-1.41, p = 0.042) and mono-n-methyl phthalate metabolites (OR = 1.16, 95% CI 1.03-1.32, p = 0.021) tended to have high BP. Moreover, urinary o-phenyl phenol concentrations (OR = 1.49, 95% CI 1.25-1.77, p < 0.001) and dimethylarsonic acid concentrations (OR = 1.35, 95% CI 1.06-1.73, p = 0.019) were also seen to be associated with high BP.

CONCLUSIONS

Urinary environmental chemical concentrations were associated with risk of high BP, although the causal effect cannot be established. Elimination of environmental chemicals in humans would need to be continued.

Higher urinary heavy metal, phthalate, and arsenic but not parabens concentrations in people with high blood pressure, U.S. NHANES, 2011-2012

Link between environmental chemicals and human health has emerged but not been completely examined in risk factors. Therefore, it was aimed to study the relationships of different sets of urinary environmental chemical concentrations and risk of high blood pressure (BP) in a national, population-based study. Data were retrieved from United States National Health and Nutrition Examination Surveys, 2011–2012 including demographics, BP readings, and urinary environmental chemical concentrations. Analyses included chi-square test, t-test and survey-weighted logistic regression modeling. After full adjustment (adjusting for urinary creatinine, age, sex, ethnicity, and body mass index), urinary cesium (OR 1.56, 95%CI 1.11–2.20, P = 0.014), molybden (OR 1.46, 95%CI 1.06–2.01, P = 0.023), manganese (OR 1.42, 95%CI 1.09–1.86, P = 0.012), lead (OR 1.58, 95%CI 1.28–1.96, P < 0.001), tin (OR 1.44, 95%CI 1.25–1.66, P < 0.001), antimony (OR 1.39, 95%CI 1.10–1.77, P = 0.010), and tungsten (OR 1.49, 95%CI 1.25–1.77, P < 0.001) concentrations were observed to be associated with high BP. People with higher urinary mono-2-ethyl-5-carboxypentyl phthalate (OR 1.33, 95%CI 1.00–1.62, P = 0.006), mono-n-butyl phthalate (OR 1.35, 95%CI 1.13–1.62, P = 0.002), mono-2-ethyl-5-hydroxyhexyl (OR 1.25, 95%CI 1.05–1.49, P = 0.014), mono-n-methyl phthalate (OR 1.26, 95%CI 1.07–1.48, P = 0.007), mono-2-ethyl-5-oxohexyl (OR 1.25, 95%CI 1.07–1.48, P = 0.009), and monobenzyl phthalate (OR 1.40, 95%CI 1.15–1.69, P = 0.002) tended to have high BP as well. However, there are no clear associations between environmental parabens and high BP, nor between pesticides and high BP. In addition, trimethylarsine oxide (OR 2.47, 95%CI 1.27–4.81, P = 0.011) and dimethylarsonic acid concentrations (OR 1.42, 95%CI 1.12–1.79, P = 0.006) were seen to be associated with high BP. In sum, urinary heavy metal, phthalate, and arsenic concentrations were associated with high BP, although the causal effect cannot be established from the current study design. Elimination of environmental chemicals in humans would still need to be continued.

Mthfr gene ablation enhances susceptibility to arsenic prenatal toxicity

BACKGROUND

In utero exposure to arsenic is known to adversely affect reproductive outcomes. Evidence of arsenic teratogenicity varies widely and depends on individual genotypic differences in sensitivity to As. In this study, we investigated the potential interaction between 5,10-methylenetetrahydrofolate reductase (Mthfr) genotype and arsenic embryotoxicity using the Mthfr knockout mouse model.

METHODS

Pregnant dams were treated with sodium arsenate, and reproductive outcomes including: implantation, resorption, congenital malformation and fetal birth weight were recorded at E18.5.

RESULTS

When the dams in Mthfr(+/-)×Mthfr(+/-) matings were treated with 7.2 mg/kg As, the resorption rate increased to 43.4%, from a background frequency of 7.2%. The As treatment also induced external malformations (40.9%) and significantly lowered the average fetal birth weight among fetuses, without any obvious toxic effect on the dam. When comparing the pregnancy outcomes resulting from different mating scenarios (Mthfr(+/+)×Mthfr(+/-), Mthfr(+/-)×Mthfr(+/-) and Mthfr(-/-)×(Mthfr+/-)) and arsenic exposure; the resorption rate showed a linear relationship with the number of null alleles (0, 1 or 2) in the Mthfr dams. Fetuses from nullizygous dams had the highest rate of external malformations (43%) and lowest average birth weight. When comparing the outcomes of reciprocal matings (nullizygote×wild-type versus wild-type×nullizygote) after As treatment, the null dams showed significantly higher rates of resorptions and malformations, along with lower fetal birth weights.

CONCLUSIONS

Maternal genotype contributes to the sensitivity of As embryotoxicity in the Mthfr mouse model. The fetal genotype, however, does not appear to affect the reproductive outcome after in utero As exposure.

Arsenic-Induced Hepatic Toxicity and Its Attenuation by Fruit Extract of Emblica officinalis (Amla) in Mice

Arsenic a metalloid and environmental contaminated has been found to be associated with public health problems in the affected areas. It is naturally occurred in groundwater and its accumulation in plant and animals leads to toxicity in several tissues most notably hepatic organ. Arsenic exposures (3 mg/kg body weight/day for 30 days) in mice exhibited increased arsenic and Zn levels in hepatocytes associated with enhanced oxidative stress in hepatocytes while there were no significantly changes were observed in Cu level. An increase in the lipid peroxidation and decrease in the levels of reduced glutathione and activity of superoxide dismutase, catalase, and glutathione peroxidase were observed in arsenic treated mice as compared to controls. Arsenic exposure in mice also caused a significant change in serum biomarkers in the SGOT, SGPT and creatinine as compared to the controls. There were no significant changes in the serum levels of total protein in these mice. Co-administration of arsenic and fruit extract of amla (500 mg/kg body weight/day for 30 days) caused a significant reduction of arsenic transference associated with significantly decreases hepatic arsenic levels and balanced the antioxidant enzyme and levels of serum hepatic enzymes like SGOT and SGPT. The results of the present study clearly demonstrate the antioxidant property of amla that could be responsible for its protective efficacy in arsenic induced hepatic toxicity.

Arsenic metabolism and thioarsenicals

Arsenic has received considerable attention in the world, since it can lead to a multitude of toxic effects and has been recognized as a human carcinogen causing cancers. Here, we focus on the current state of knowledge regarding the proposed mechanisms of arsenic biotransformation, with a little about cellular uptake, toxicity and clinical utilization of arsenicals. Since pentavalent methylated metabolites were found in animal urine after exposure to iAs(III), methylation was considered to be a detoxification process, but the discovery of methylated trivalent intermediates and thioarsenicals in urine has diverted the view and gained much interest regarding arsenic biotransformation. To further investigate the partially understood phenomena relating to arsenic toxicity and the uses of arsenic as a drug, it is important to elucidate the exact pathways involved in metabolism of this metalloid, as the toxicity and the clinical uses of arsenic can be best recognized in context of its biotransformation. Thereby, in this perspective, we have focused on arsenic metabolic pathways including three proposed mechanisms: a classic pathway by Challenger in 1945, followed by a new metabolic pathway proposed by Hayakawa in 2005 involving arsenic-glutathione complexes, while the third is a new reductive methylation pathway that is proposed by our group involving As-protein complexes. According to previous and present in vivo and in vitro experiments, we conclude that the methylation reaction takes place with simultaneous reductive rather than stepwise oxidative methylation. In addition, production of pentavalent methylated arsenic metabolites are suggested to be as the end product of metabolism, rather than intermediates.

Mitigation of hepatotoxic effects of arsenic trioxide through omega-3 fatty acid in rats

Arsenic trioxide (As2O3) is an effective drug in the treatment of leukaemia and many solid tumours. In clinical trials, arsenic therapy is closely associated with hepatic toxicity. The present study was designed to investigate the efficacy of omega-3 fatty acid against As2O3-induced hepatotoxicity. A 4 mg/kg body weight (bw) of As2O3 was orally administered to Wistar male rats for 45 days. Hepatotoxicity was evaluated by biochemical tests, antioxidant assays and histopathological examinations. Arsenic accumulation was found in the liver tissue of rats treated with As2O3. Hepatoprotective efficacy of omega-3 fatty acid was analysed by the combination therapy with As2O3. In vivo studies revealed a significant rise in lipid peroxidation with concomitant decline in reduced glutathione, glutathione-dependant antioxidant enzymes and antiperoxidative enzymes in the liver tissue of rats treated with arsenic. The supplementation of omega-3 fatty acid at a dose of 50 mg/kg bw with As2O3 offers ameliorative effect against hepatocellular toxicity. Omega-3 fatty acid maintained hepatic marker enzymes, antioxidant enzymes and decreased lipid peroxidation. The combination treatment clearly reduced the hepatic structural abnormalities such as haemorrhage, necrosis and cholangiofibrosis in the rats treated with arsenic. This study concludes that the omega-3 fatty acid might be useful for the protection against As2O3-induced hepatotoxicity.

Predicting later-life outcomes of early-life exposures

BACKGROUND

In utero exposure of the fetus to a stressor can lead to disease in later life. Epigenetic mechanisms are likely mediators of later-life expression of early-life events.

OBJECTIVES

We examined the current state of understanding of later-life diseases resulting from early-life exposures in order to identify in utero and postnatal indicators of later-life diseases, develop an agenda for future research, and consider the risk assessment implications of this emerging knowledge.

METHODS

This review was developed based on our participation in a National Research Council workshop titled "Use of in Utero and Postnatal Indicators to Predict Health Outcomes Later in Life: State of the Science and Research Recommendations." We used a case study approach to highlight the later-life consequences of early-life malnutrition and arsenic exposure.

DISCUSSION

The environmental sensitivity of the epigenome is viewed as an adaptive mechanism by which the developing organism adjusts its metabolic and homeostatic systems to suit the anticipated extrauterine environment. Inappropriate adaptation may produce a mismatch resulting in subsequent increased susceptibility to disease. A nutritional mismatch between the prenatal and postnatal environments, or early-life obesogen exposure, may explain at least some of the recent rapid increases in the rates of obesity, type 2 diabetes, and cardiovascular diseases. Early-life arsenic exposure is also associated with later-life diseases, including cardiovascular disease and cancer.

CONCLUSIONS

With mounting evidence connecting early-life exposures and later-life disease, new strategies are needed to incorporate this emerging knowledge into health protective practices.

Qualitative and quantitative characterization of the arsenic-binding behaviour of sulfur-containing peptides and proteins by the coupling of reversed phase liquid chromatography to electrospray ionization mass spectrometry

Phenylarsenic-substituted cysteine-containing peptides and proteins were completely differentiated from their unbound original forms by the coupling of reversed phase liquid chromatography with electrospray ionization mass spectrometry. The analysis of biomolecules possessing structure-stabilizing disulfide bridges after reduction provides new insights into requirements concerning the accessibility of cysteine residues for reducing agents as well as for arsenic compounds in a spatial protein structure. Complementary binding studies performed using direct ESI-MS without chromatographic coupling in different solvent systems demonstrated that more than one binding site were activated for aprotinin and lysozyme in denaturing solvents because of a stronger defolding. From the intensities of the different charge states occurring in the mass spectra as well as from the LC elution behaviour, it can be deduced that the folding state of the arsenic-bound protein species resembles the native, oxidized conformation. In contrast, although the milk protein α-lactalbumin has several disulfide bridges, only one phenylarsenic moiety was bound under strongly denaturing conditions. Because of the charge state distribution in the ESI mass spectra, a conformational change to a molten globule structure is assumed. For the second considered milk protein ß-lactoglobulin, a noncovalent interaction with phenylarsine oxide was detected. In general, smaller apparent binding constants for the condensation reactions of the biomolecules with phenylarsine oxide leading to covalent arsenic-sulfur bindings were determined from direct injection ESI-MS measurements than from LC-ESI-MS coupling. The following order of binding affinities for one phenylarsenic group can be assumed from both ESI-MS and LC-ESI-MS: nonapeptide vasopressin > nonapeptide vasotocin > lysozyme > aprotinin > α-lactalbumin > thioredoxin. Kinetic investigations by LC-ESI-MS yielded a partial reaction order of 2 for vasopressin, Lys and α-lactalbumin and corresponding half-lives of 0.93, 2.56 and 123.5 min, respectively.

ZIP8 expression in human proximal tubule cells, human urothelial cells transformed by Cd+2 and As+3 and in specimens of normal human urothelium and urothelial cancer

Background

ZIP8 functions endogenously as a Zn⁺²/HCO₃^- symporter that can also bring cadmium (Cd⁺²) into the cell. It has also been proposed that ZIP8 participates in Cd-induced testicular necrosis and renal disease. In this study real-time PCR, western analysis, immunostaining and fluorescent localization were used to define the expression of ZIP8 in human kidney, cultured human proximal tubule (HPT) cells, normal and malignant human urothelium and Cd⁺² and arsenite (As⁺³) transformed urothelial cells.

Results

It was shown that in the renal system both the non-glycosylated and glycosylated form of ZIP8 was expressed in the proximal tubule cells with localization of ZIP8 to the cytoplasm and cell membrane; findings in line with previous studies on ZIP8. The studies in the bladder were the first to show that ZIP8 was expressed in normal urothelium and that ZIP8 could be localized to the paranuclear region. Studies in the UROtsa cell line confirmed a paranuclear localization of ZIP8, however addition of growth medium to the cells increased the expression of the protein in the UROtsa cells. In archival human samples of the normal urothelium, the expression of ZIP8 was variable in intensity whereas in urothelial cancers ZIP8 was expressed in 13 of 14 samples, with one high grade invasive urothelial cancer showing no expression. The expression of ZIP8 was similar in the Cd⁺² and As⁺³ transformed UROtsa cell lines and their tumor transplants.

Conclusion

This is the first study which shows that ZIP8 is expressed in the normal urothelium and in bladder cancer. In addition the normal UROtsa cell line and its transformed counterparts show similar expression of ZIP8 compared to the normal urothelium and the urothelial cancers suggesting that the UROtsa cell line could serve as a model system to study the expression of ZIP8 in bladder disease.

Chronic occupational exposure to arsenic induces carcinogenic gene signaling networks and neoplastic transformation in human lung epithelial cells

Chronic arsenic exposure remains a human health risk; however a clear mode of action to understand gene signaling-driven arsenic carcinogenesis is currently lacking. This study chronically exposed human lung epithelial BEAS-2B cells to low-dose arsenic trioxide to elucidate cancer promoting gene signaling networks associated with arsenic-transformed (B-As) cells. Following a 6month exposure, exposed cells were assessed for enhanced cell proliferation, colony formation, invasion ability and in vivo tumor formation compared to control cell lines. Collected mRNA was subjected to whole genome expression microarray profiling followed by in silico Ingenuity Pathway Analysis (IPA) to identify lung carcinogenesis modes of action. B-As cells displayed significant increases in proliferation, colony formation and invasion ability compared to BEAS-2B cells. B-As injections into nude mice resulted in development of primary and secondary metastatic tumors. Arsenic exposure resulted in widespread up-regulation of genes associated with mitochondrial metabolism and increased reactive oxygen species protection suggesting mitochondrial dysfunction. Carcinogenic initiation via reactive oxygen species and epigenetic mechanisms was further supported by altered DNA repair, histone, and ROS-sensitive signaling. NF-κB, MAPK and NCOR1 signaling disrupted PPARα/δ-mediated lipid homeostasis. A 'pro-cancer' gene signaling network identified increased survival, proliferation, inflammation, metabolism, anti-apoptosis and mobility signaling. IPA-ranked signaling networks identified altered p21, EF1α, Akt, MAPK, and NF-κB signaling networks promoting genetic disorder, altered cell cycle, cancer and changes in nucleic acid and energy metabolism. In conclusion, transformed B-As cells with their whole genome expression profile provide an in vitro arsenic model for future lung cancer signaling research and data for chronic arsenic exposure risk assessment.

Mitochondrial myopathy caused by arsenic trioxide therapy

Arsenic trioxide (ATO) has been successfully used as a treatment for acute promyelocytic leukemia (APL) for more than a decade. Here we report a patient with APL who developed a mitochondrial myopathy after treatment with ATO. Three months after ATO therapy withdrawal, the patient was unable to walk without assistance and skeletal muscle studies showed a myopathy with abundant cytoplasmic lipid droplets, decreased activities of the mitochondrial respiratory chain complexes, multiple mitochondrial DNA (mtDNA) deletions, and increased muscle arsenic content. Six months after ATO treatment was interrupted, the patient recovered normal strength, lipid droplets had decreased in size and number, respiratory chain complex activities were partially restored, but multiple mtDNA deletions and increased muscle arsenic content persisted. ATO therapy may provoke a delayed, severe, and partially reversible mitochondrial myopathy, and a long-term careful surveillance for muscle disease should be instituted when ATO is used in patients with APL.

Characterization of the role of protein-cysteine residues in the binding with sodium arsenite

To better characterize the interaction of protein-cysteines with sodium arsenite, arsenic-binding proteins were identified from the arsenic-resistant Chinese hamster ovary cell line SA7 using a p-aminophenylarsine oxide (PAO)-agarose matrix in combination with proteomic techniques. Twenty of the isolated arsenic-binding proteins were further peptide-mapped by MALDI-Q-TOF-MS. The binding capacity of PAO-agarose-retained proteins was then verified by re-applying Escherichia coli overexpressed recombinant proteins with various numbers of cysteine residues onto the PAO-agarose matrix. The results showed that recombinant heat shock protein 27 (HSP27, with one cysteine residue), reticulocalbin-3 (RCN3, with no cysteine residue), galectin-1 (GAL1, with six cysteine residues), but not peroxiredoxin 6 (Prdx6, with one cysteine residue but not retained by the PAO-agarose matrix), were bound to the PAO-agarose matrix. The six free cysteine residues in GAL1 were individually or double-mutated to alanine by means of site-directed mutagenesis and subjected to CD and ICP-MS analysis. The binding capacity of GAL1 for sodium arsenite was significantly attenuated in C16A, C88A and all double mutant clones. Taken together, our current data suggest that the cysteine residues in GAL1 may play a critical role in the binding of arsenic, but that in the case of RCN3 and Prdx6, this interaction may be mediated by other factors.

Nutritional manipulation of one-carbon metabolism: effects on arsenic methylation and toxicity

Exposure to arsenic (As) through drinking water is a substantial problem worldwide. The methylation of As, a reactive metalloid, generates monomethyl- (MMA) and dimethyl-arsenical (DMA) species. The biochemical pathway that catalyzes these reactions, one-carbon metabolism, is regulated by folate and other micronutrients. Arsenic methylation exerts a critical influence on both its urinary elimination and chemical reactivity. Mice having the As methyltransferase null genotype show reduced urinary As excretion, increased As retention, and severe systemic toxicity. The most toxic As metabolite in vitro is MMA^III, an intermediate in the generation of DMA^V, a much less toxic metabolite. These findings have raised the question of whether As methylation is a detoxification or bioactivation pathway. Results of population-based studies suggest that complete methylation of inorganic As to DMA is associated with reduced risk for As-induced health outcomes, and that nutrients involved in one-carbon metabolism, such as folate, can facilitate As methylation and elimination.

Renal, hepatic, pulmonary and adrenal tumors induced by prenatal inorganic arsenic followed by dimethylarsinic acid in adulthood in CD1 mice

Inorganic arsenic, an early life carcinogen in humans and mice, can initiate lesions promotable by other agents in later life. The biomethylation product of arsenic, dimethylarsinic acid (DMA), is a multi-site tumor promoter. Thus, pregnant CD1 mice were given drinking water (0 ppm or 85 ppm arsenic) from gestation day 8 to 18 and after weaning male offspring received DMA (0 ppm or 200 ppm; drinking water) for up to 2 years. No renal tumors occurred in controls or DMA alone treated mice while gestational arsenic exposure plus later DMA induced a significant renal tumor incidence of 17% (primarily renal cell carcinoma). Arsenic plus DMA or arsenic alone also increased renal hyperplasia over control but DMA alone did not. Arsenic alone, DMA alone and arsenic plus DMA all induced urinary bladder hyperplasia (33-35%) versus control (2%). Compared to control (6%), arsenic alone tripled hepatocellular carcinoma (20%), and arsenic plus DMA doubled this rate again (43%), but DMA alone had no effect. DMA alone, arsenic alone, and arsenic plus DMA increased lung adenocarcinomas and adrenal adenomas versus control. Overall, DMA in adulthood promoted tumors/lesions initiated by prenatal arsenic in the kidney and liver, but acted independently in the urinary bladder, lung and adrenal.

Arsenic trioxide treatment decreases the oxygen consumption rate of tumor cells and radiosensitizes solid tumors

Arsenic trioxide (As(2)O(3)) is an effective therapeutic against acute promyelocytic leukemia and certain solid tumors. Because As(2)O(3) inhibits mitochondrial respiration in leukemia cells, we hypothesized that As(2)O(3) might enhance the radiosensitivity of solid tumors by increasing tumor oxygenation [partial pressure of oxygen (pO(2))] via a decrease in oxygen consumption. Two murine models of radioresistant hypoxic cancer were used to study the effects of As(2)O(3). We measured pO(2) and the oxygen consumption rate in vivo by electron paramagnetic resonance oximetry and (19)fluorine-MRI relaxometry. Tumor perfusion was assessed by Patent blue staining. In both models, As(2)O(3) inhibited mitochondrial respiration, leading to a rapid increase in pO(2). The decrease in oxygen consumption could be explained by an observed decrease in glutathione in As(2)O(3)-treated cells, as this could increase intracellular reactive oxygen species that can disrupt mitochondrial membrane potential. When tumors were irradiated during periods of As(2)O(3)-induced augmented oxygenation, radiosensitivity increased by 2.2-fold compared with control mice. Notably, this effect was abolished when temporarily clamped tumors were irradiated. Together, our findings show that As(2)O(3) acutely increases oxygen consumption and radiosensitizes tumors, providing a new rationale for clinical investigations of As(2)O(3) in irradiation protocols to treat solid tumors.