Inorganic Arsenic Metabolites Research Articles

Associations of gestational and early-life exposure to toxic metals and fluoride with a diagnosis of food allergy or atopic eczema at 1 year of age

Studies have indicated that early-life exposure to toxic metals and fluoride affects the immune system, but evidence regarding their role in allergic disease development is scarce. We aimed to evaluate the relations of exposure to such compounds in 482 pregnant women and their infants (4 months of age) with food allergy and atopic eczema diagnosed by a paediatric allergologist at 1 year of age within the Swedish birth-cohort NICE (Nutritional impact on Immunological maturation during Childhood in relation to the Environment). Urinary cadmium and erythrocyte cadmium, lead, and mercury concentrations were measured by inductively coupled plasma mass spectrometry (ICP-MS), urinary inorganic arsenic metabolites by ICP-MS after separation by ion exchange chromatography, and urinary fluoride by an ion-selective electrode. The prevalence of food allergy and atopic eczema was 8 and 7%, respectively. Gestational urinary cadmium, reflecting chronic exposure, was associated with increased odds of infant food allergy (OR [95% CI]: 1.34 [1.09, 1.66] per IQR [0.08 μg/L]). Both gestational and infant urinary fluoride were associated, albeit at a statistically non-significant level, with increased atopic eczema odds (1.48 [0.98, 2.25], 1.36 [0.95, 1.95], per doubling, respectively). By contrast, gestational and infant erythrocyte lead was associated with decreased odds of atopic eczema (0.48 [0.26, 0.87] per IQR [6.6 μg/kg] and 0.38 [0.16, 0.91] per IQR [5.94 μg/kg], respectively), and infant lead with decreased odds of food allergy (0.39 [0.16, 0.93] per IQR [5.94 μg/kg]). Multivariable adjustment had marginal impact on the estimates above. After additional adjustment for fish intake biomarkers, the methylmercury associated atopic-eczema odds were considerably increased (1.29 [0.80, 2.06] per IQR [1.36 μg/kg]). In conclusion, our results indicate that gestational cadmium exposure might be associated with food allergy at 1 year of age and, possibly, early-life exposure to fluoride with atopic eczema. Further prospective and mechanistic studies are needed to establish causality.

Metabolomics Analysis of Chronic Exposure to Dimethylarsenic Acid in Mice and Toxicity Assessment of Organic Arsenic in Food.

Dimethylarsenic acid is a natural organic arsenic in seafood and one of the important metabolites of inorganic arsenic, which is generally considered to have low or no toxicity. However, due to the controversy of the toxicity of organic arsenic, the food safety standard of organic arsenic has not been established until now, and the effects of organic arsenic on chronic toxicity and the overall metabolic level of animals are rarely reported. In our study, 64 female C57BL/6 mice were exposed to different concentrations of dimethylarsenic acid with water intake. Fifteen metabolites in serum were detected to be altered with the increase of arsenic concentration and exposure time. Dimethylarsenic acid exposure significantly affected the overall metabolic level of mice, and the related effects were not recovered shortly after the suspension of arsenic intake. Although arsenic was excreted largely in urine and feces, continued dimethylarsenic acid exposure could still lead to arsenic accumulation in the liver and kidneys and cause mild nephritis in mice.

Arsenic exposure and biomarkers for oxidative stress and telomere length in indigenous populations in Bolivia

BackgroundWomen living in the Bolivian Andes are environmentally exposed to arsenic, yet there is scarce information about arsenic-related effects in this region. Several biomarkers for telomere length and oxidative stress (mitochondrial DNA copy number, mtDNAcn; 8-Oxo-2′-deoxyguanosine, 8-oxo-dG; and 4-hydroxy nonenal mercapturic acid, 4-HNE-MA) have been previously linked to arsenic, and some of which are prospective biomarkers for cancer risk. Objective and hypothesisTo evaluate associations between arsenic exposure and telomere length, mtDNAcn, 8-oxo-dG, and 4-HNE-MA in Bolivians. Arsenic exposure was hypothesized to be positively associated with all four toxicity biomarkers, particularly in individuals with a less efficient arsenic metabolism. MethodsThe study encompassed 193 indigenous women. Arsenic exposure was assessed in urine as the sum of inorganic arsenic metabolite concentrations (U-As) measured by HPLC-HG-ICP-MS, and in whole blood as total arsenic (B-As) measured by ICP-MS. Efficiency of arsenic metabolism was evaluated by a polymorphism (rs3740393) in the main arsenic methylating gene AS3MT measured by TaqMan allelic discrimination, and by the relative fractions of urinary inorganic arsenic metabolites. Telomere length and mtDNAcn were determined in peripheral blood leukocytes by quantitative PCR, and urinary 8-oxo-dG and 4-HNE-MA by LC-MS/MS. ResultsU-As and B-As were associated with longer telomeres and higher mtDNAcn, particularly in women with a less efficient arsenic metabolism. Urinary 8-oxo-dG and 4-HNE-MA were positively associated with U-As, but only 4-HNE-MA was associated with B-As. Arsenic metabolism efficiency did not have a clear effect on the concentrations of either of these biomarkers. ConclusionBolivian women showed indications of arsenic toxicity, measured by four different biomarkers. Telomere length, mtDNAcn, and 4-HNE-MA were positively associated with both U-As and B-As. The association of arsenic exposure with telomere length and mtDNAcn was only present in Bolivian women with a less efficient metabolism. These findings call for additional efforts to evaluate and reduce arsenic exposure in Bolivia.

Arsenic and Protein Expression: It might help to know the mechanism of As toxicity

Arsenic and Protein Expression: It might help to know the mechanism of As toxicity

Does and duration of exposure time dependent regulation of proteins in the urinary bladder of hamsters exposed to sodium arsenite

Does and duration of exposure time dependent regulation of proteins in the urinary bladder of hamsters exposed to sodium arsenite

Regulation of transgelin and GST-pi proteins in the tissues of hamsters exposed to sodium arsenite

Regulation of transgelin and GST-pi proteins in the tissues of hamsters exposed to sodium arsenite

Origins, fate, and actions of methylated trivalent metabolites of inorganic arsenic: progress and prospects.

The toxic metalloid inorganic arsenic (iAs) is widely distributed in the environment. Chronic exposure to iAs from environmental sources has been linked to a variety of human diseases. Methylation of iAs is the primary pathway for metabolism of iAs. In humans, methylation of iAs is catalyzed by arsenic (+ 3 oxidation state) methyltransferase (AS3MT). Conversion of iAs to mono- and di-methylated species (MAs and DMAs) detoxifies iAs by increasing the rate of whole body clearance of arsenic. Interindividual differences in iAs metabolism play key roles in pathogenesis of and susceptibility to a range of disease outcomes associated with iAs exposure. These adverse health effects are in part associated with the production of methylated trivalent arsenic species, methylarsonous acid (MAsIII) and dimethylarsinous acid (DMAsIII), during AS3MT-catalyzed methylation of iAs. The formation of these metabolites activates iAs to unique forms that cause disease initiation and progression. Taken together, the current evidence suggests that methylation of iAs is a pathway for detoxification and for activation of the metalloid. Beyond this general understanding of the consequences of iAs methylation, many questions remain unanswered. Our knowledge of metabolic targets for MAsIII and DMAsIII in human cells and mechanisms for interactions between these arsenicals and targets is incomplete. Development of novel analytical methods for quantitation of MAsIII and DMAsIII in biological samples promises to address some of these gaps. Here, we summarize current knowledge of the enzymatic basis of MAsIII and DMAsIII formation, the toxic actions of these metabolites, and methods available for their detection and quantification in biomatrices. Major knowledge gaps and future research directions are also discussed.

Lead exposure and indices of height and weight in Uruguayan urban school children, considering co-exposure to cadmium and arsenic, sex, iron status and dairy intake

Child growth depends on complex factors including diet, nutritional status, socioeconomic, and sanitary conditions, and exposure to environmental chemicals. Lead exposure is known to impair growth in young children but effects in school-age children are less clear. The effects of co-exposure to low-level lead and other toxic metals on child growth are not well understood. We examined cross-sectional associations of blood lead (BLL) with growth indices (Z scores of body mass index for age, BAZ, and height for age, HAZ) in Uruguayan urban school children (n = 259; ~7 y). Potential differences in these associations in children with lower vs. higher urinary inorganic arsenic metabolites (U–As), urinary cadmium (U–Cd), sex (42% girls), iron deficiency (ID, 39% children), or intake of dairy foods below recommended levels were examined. BLL was measured using AAS, U–As using HPLC-HGICP-MS, and U–Cd using ICP-MS. Dietary information was obtained by two 24-h recalls completed by caregivers. Children's linear growth was within age and sex-appropriate reference values. Overweight (BAZ > 1 2 SD) was found in 20.1%, and obesity (BAZ > 2 SD) in 18.5%, of children. Ranges (5th, 95th percentile) of biomarker concentrations were: BLL, 0.8–7.8 μg/dL; U–Cd, 0.01–0.2 μg/L, and U–As, 4.0–27.3 μg/L. BLL was inversely associated with HAZ ([95% CI]: 0.10 [-0.17, −0.03]) in covariate-adjusted models. Although this association was slightly more pronounced in girls, children without ID, and children with lower U–As, there was little evidence of effect modification due to overlapping CIs in stratified models. BLLs were not associated with BAZ, except for a suggestion of a negative relationship in girls (−0.10 [-0.23, 0.02]) but not boys [0.001 [-0.11, 0.12]). Our findings indicate that exposure to low levels of lead was associated with lower HAZ in apparently normally growing urban school children. Larger future studies should help elucidate if these associations persist over time and across populations.

Joint effects of genomic markers and urinary methylation capacity associated with inorganic arsenic metabolism on the occurrence of cancers among residents in arseniasis-endemic areas: A cohort subset with average fifteen-year follow-up

BackgroundChronic exposure to inorganic arsenic results in many cancers in susceptible persons. The metabolism of inorganic arsenic and genomic susceptibility are thought to be associated with cancer occurrence. MethodsThis study aims to examine the interaction of genomic susceptibility markers and urinary methylation capacity indicators involved in inorganic arsenic metabolism with all-cancer occurrence. This study conducted a follow-up on 96 residents to determine their urinary inorganic arsenic metabolites and genomic assay from an arseniasis area. Among them, 24 cancer developed. Multivariable Cox proportional hazards model was used to determine and estimate the candidate independent variables for cancer development. ResultsThe residents with high inorganic arsenic exposure, high primary methylation index (PMI; MMA/InAs) (but lower secondary methylation index (SMI)), and non-heterogeneity type of genomic markers, including GSTO1, AS3MT, and MPO, tend to develop cancers. Subjects with higher PMI are at higher risk of developing cancers (HR = 1.66; 95% CI = 1.30–2.12). Cancer occurrence was greater among the CC type of GSTO1 (HR = 3.33; 95% CI = 1.11–10.00), CC type of AS3MT (HR = 19.21; 95% CI = 1.16–318.80), and AA type of MPO (HR = 13.40; 95% CI = 1.26–142.40). After adjusting confounders, a mutually moderating effect was revealed between genomic markers and methylation capacity on cancer occurrence. ConclusionsThis study found the hypermethylation responses to inorganic arsenic exposure and an array of genomic markers may increase the susceptibility of a wide range of organ cancers. The findings indicated a high-risk arsenic-exposed population to develop cancers. The phenotype of arsenic metabolism and genomic polymorphism suggested a potential preventive strategy for arsenic carcinogenesis.

Children exposure to inorganic and organic arsenic metabolites: A cohort study in Northeast Italy

The aim of this study was to provide urinary levels of total arsenic (TAs) and As species as arsenobetaine (AsB), arsenocholine (AsC), inorganic As (i.e., [As(III)+As(V)]), methylarsonic acid (MMA) and dimethylarsinic acid (DMA) in 7 year-old-children (n = 200) enrolled in the Northern Adriatic Cohort II (NACII), a prospective cohort in a coastal area of Northeast Italy. TAs was determined by sector field-inductively coupled plasma mass spectrometry (SF-ICP-MS) and AsB, AsC, As(III), As(V), MMA and DMA by ion chromatography coupled to ICP-MS (IC-ICP-MS). The geometric mean (GM) for TAs was 12.9 μg/L and for [iAs + MMA + DMA] was 4.26 μg/L. The species AsB (GM of 5.09 μg/L) and DMA (GM of 3.20 μg/L) had the greatest percentage contribution to TAs levels; a greater percentage contribution from AsB is seen at TAs >10 μg/L and from DMA at TAs <10 μg/L. Urinary [iAs + MMA] levels were positively associated with [iAs + MMA + DMA] and DMA with AsB levels. Fish, shellfish and crustaceans consumption increased the AsB and TAs levels, while rice intake, mothers’ education level and selenium (Se) concentration influenced the DMA concentration. Children have a high capacity to metabolize and detoxify the iAs because of the higher secondary methylation index (ratio DMA/MMA) with respect to primary methylation index (ratio MMA/iAs). In addition, the median level of [iAs + MMA + DMA] in the whole population of children was lower than the Biomonitoring Equivalent (BE) value for non-cancer endpoints. Also the Margin of Safety (MOS) value based on the population median was greater than 1, thus the exposure to the toxicologically relevant As species was not likely to be of concern.

Mechanistic insights into the enhanced removal of roxsarsone and its metabolites by a sludge-based, biochar supported zerovalent iron nanocomposite: Adsorption and redox transformation

Roxarsone is a phenyl-substituted arsonic acid comprising both arsenate and benzene rings. Few adsorbents are designed for the effective capture of both the organic and inorganic moieties of ROX molecules. Herein, nano zerovalent iron (nZVI) particles were incorporated on the surface of sludge-based biochar (SBC) to fabricate a dual-affinity sorbent that attracts both the arsenate and benzene rings of ROX. The incorporation of nZVI particles significantly increased the binding affinity and sorption capacity for ROX molecules compared to pristine SBC and pure nZVI. The enhanced elimination of ROX molecules was ascribed to synergetic adsorption and degradation reactions, through π-π* electron donor/acceptor interactions, H-bonding, and As-O-Fe coordination. Among these, the predominate adsorption force was As-O-Fe coordination. During the sorption process, some ROX molecules were decomposed into inorganic arsenic and organic metabolites by the reactive oxygen species (ROS) generated during the early stages of the reaction. The degradation pathways of ROX were proposed according to the oxidation intermediates. This work provides a theoretical and experimental basis for the design of adsorbents according to the structure of the target pollutant.

PO-081 Hypermethylation responses to inorganic arsenic exposure may increase the risk of liver cancer occurrence

Introduction Exposure to inorganic arsenic (InAs) has been known as a risk factor for liver cancer. However, documents have indicated that specific forms of arsenic may inhibit the activity of hepatitis viruses. This study investigated the association between InAs exposure and liver cancer occurrence while examining the effects of arsenic methylation capacity in an exposed cohort. Material and methods This study followed 4056 residents, an average of 19.2 years of follow-up, from an arseniasis area in Taiwan, and identified 90 liver cancer cases. The inorganic arsenic metabolites were determined by ICP-MS and methylation capacity was calculated from the combination of InAs, monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). The primary methylation index (MMA/InAs) and the secondary methylation index (DMA/MMA) and their median high/low combinations were used. Cox proportional hazards model was performed to calculate the hazard ratio (HR) of liver cancer occurrence. Results and discussions The analyses revealed a significant association between liver cancer occurrence and arsenic methylation capacity, which demonstrated a lower risk of the participants with low secondary methylation index. The results showed that participants with lower primary and lower secondary methylation index than their respective median values were at a lower risk of liver cancer (HRs from 0.230 to 0.231) than those with high methylation capacity. The incidence density of liver cancer ranging from 48.2/100,000 (year-1) to 100.4/100,000 (year-1) for residents with low secondary methylation index and from 99.1/100,000 (year-1) to 186.8/100,000 (year-1) for residents with high secondary methylation index when the arsenic exposure dose was classified into quartiles. Conclusion Hypomethylation responses to InAs exposure may associate with lower liver cancer occurrence. Two mechanisms were conjectured. First, a specific forms of arsenic may inhibit the hepatitis viral activity. Second, hypermethylation activities among residents chronically exposed to inorganic arsenic may induce arsenic carcinogenesis, which warrants for further investigations.

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.

Environmental exposure to arsenic and chromium in an industrial area

Arsenic and chromium are widespread environmental contaminants that affect global health due to their toxicity and carcinogenicity. To date, few studies have investigated exposure to arsenic and chromium in a population residing in a high-risk environmental area. The aim of this study is to evaluate the exposure to arsenic and chromium in the general population with no occupational exposure to these metals, resident in the industrial area of Taranto, Southern Italy, through biological monitoring techniques. We measured the levels of chromium, inorganic arsenic, and methylated metabolites, in the urine samples of 279 subjects residing in Taranto and neighboring areas. Qualified health staff administered a standardized structured questionnaire investigating lifestyle habits and controlling for confounding factors. The biological monitoring data showed high urinary concentrations of both the heavy metals investigated, particularly Cr. On this basis, it will be necessary to carry out an organized environmental monitoring program, taking into consideration all exposure routes so as to correlate the environmental concentrations of these metals with the biomonitoring results.

Relation of dietary inorganic arsenic exposure and urinary inorganic arsenic metabolites excretion in Japanese subjects

ABSTRACTInorganic arsenic (InAs) is a ubiquitous metalloid that has been shown to exert multiple adverse health outcomes. Urinary InAs and its metabolite concentration has been used as a biomarker of arsenic (As) exposure in some epidemiological studies, however, quantitative relationship between daily InAs exposure and urinary InAs metabolites concentration has not been well characterized. We collected a set of 24-h duplicated diet and spot urine sample of the next morning of diet sampling from 20 male and 19 female subjects in Japan from August 2011 to October 2012. Concentrations of As species in duplicated diet and urine samples were determined by using liquid chromatography-ICP mass spectrometry with a hydride generation system. Sum of the concentrations of urinary InAs and methylarsonic acid (MMA) was used as a measure of InAs exposure. Daily dietary InAs exposure was estimated to be 0.087 µg kg−1 day−1 (Geometric mean, GM), and GM of urinary InAs+MMA concentrations was 3.5 ng mL−1. Analysis of covariance did not find gender-difference in regression coefficients as significant (P > 0.05). Regression equation Log 10 [urinary InAs+MMA concentration] = 0.570× Log 10 [dietary InAs exposure level per body weight] + 1.15 was obtained for whole data set. This equation would be valuable in converting urinary InAs concentration to daily InAs exposure, which will be important information in risk assessment.

Dimethylarsinic acid modulates the aryl hydrocarbon receptor-regulated genes in C57BL/6 mice: in vivo study

1. Dimethylarsinic acid (DMA(V)) is the major metabolite of inorganic arsenic in human body. Thus we investigated the effect of DMA(V) on the alteration of phase I (typified by Cyp1a) and phase II (typified by Nqo1) AhR-regulated genes in vivo. C57BL/6 mice received DMA(V) (13.3 mg/kg, i.p.) with or without TCDD (15 μg/kg, i.p.), thereafter the liver, lung, and kidney were harvested at 6 and 24 h post-treatment.2. Results demonstrated that DMA(V) has no significant effect on Cyp1a mRNA and protein expression or catalytic activity in the liver. On the other hand, DMA(V) significantly potentiated the TCDD-mediated induction of Cyp1a mRNA and protein expression, with a subsequent potentiation of catalytic activity in the lung. Moreover, DMA(V) significantly inhibited the TCDD-mediated induction of Cyp1a mRNA and protein expression with subsequent inhibition of catalytic activity in the kidney.3. Regarding to phase II AhR-regulated genes, DMA(V) has no significant effect on Nqo1 mRNA and protein expression, or activity neither in the liver, lung, or kidney.4. In conclusion, the present work demonstrates for the first time that DMA(V) modulates AhR-regulated genes in a tissue- and enzyme-specific manner. This modulation may play a crucial role in arsenic-induced toxicity and carcinogenicity.

Non-occupational exposure to heavy metals of the residents of an industrial area and biomonitoring.

In areas at high environmental risk, a major issue is the assessment of the exposure of the general population to industrial pollutants. To date, few studies have investigated exposure to heavy metals in a population residing in a high risk environmental area. The aim of this study is to evaluate the exposure to heavy metals in the industrial area of Taranto, Southern Italy, through biological monitoring techniques. We measured the levels of inorganic arsenic and methylated metabolites, lead, cadmium, chromium, and manganese in the urine samples of 279 subjects residing in Taranto and neighboring areas. After obtaining informed consent from each participant, qualified health staff administered a standardized structured questionnaire investigating lifestyle habits and assessing any confounding factors. The biological monitoring data showed high urinary concentrations of nearly all of the heavy metals investigated. These findings could be related to the presence of industrial plants and is sufficient to warrant the expectation that local and national institutions should be required to adopt preventive measures to reduce the environmental exposure of the general population to heavy metals.

Dietary micronutrient intake and its relationship with arsenic metabolism in Mexican women

IntroductionConcentrations of inorganic arsenic (iAs) metabolites in urine present intra- and interindividual variations, which are determined not only by the magnitude of exposure to iAs, but also by differences in genetic, environmental and dietary factors. ObjectiveTo evaluate whether differences in dietary intake of selected micronutrients are associated with the metabolism of iAs. MethodsThe intake of 21 micronutrients was estimated for 1027 women living in northern Mexico using a food frequency questionnaire. Concentration of urinary metabolites of iAs was determined by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) and the proportion of iAs metabolites was calculated (%iAs, monomethylarsonic acid [%MMA] and dimethylarsinic acid [%DMA]), as well as ratios corresponding to the first (MMA/iAs), second (DMA/MMA) and total methylation (DMA/iAs). ResultsAfter adjustment for covariates, it was found that methionine, choline, folate, vitamin B12, Zn, Se and vitamin C favor elimination of iAs mainly by decreasing the %MMA and/or increasing %DMA in urine. ConclusionsOur results confirm that diet contributes to the efficiency of iAs elimination. Further studies are needed to assess the feasibility of dietary interventions that modulate the metabolism of iAs and the consequent risk of diseases related to its exposure.

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

Biotransformation of inorganic arsenic results in the formation of methylarsenicals of both oxygen and sulfur analogues. Aiming to improve our understanding of metabolism of inorganic arsenic in animals, we conducted an animal feeding study with an emphasis on identifying new arsenic metabolites. Female F344 rats were given 0, 1, 10, 25, 50, and 100 μg/g of arsenite (iAs(III)) in the diet. Arsenic species in rat urine were determined using high performance liquid chromatography (HPLC) separation and inductive coupled plasma mass spectrometry (ICPMS) and electrospray ionization tandem mass spectrometry (ESI MS/MS) detection. Nine arsenic species were detected in the urine of the iAs(III)-dosed rats. Seven of these arsenic species were consistent with previous reports, including iAs(III), arsenate, monomethyarsonic acid, dimethylarsinic acid, trimethylarsine oxide, monomethylmonothioarsonic acid, and dimethylmonothioarsinic acid. Two new methyldithioarsencals, monomethyldithioarsonic acid (MMDTA(V)) and dimethyldithioarsinic acid (DMDTA(V)), were identified for the first time in the urine of rats treated with iAs(III). The concentrations of both MMDTA(V) and DMDTA(V) in rat urine were dependent on the dosage of iAs(III) in diet. The concentration of DMDTA(V) was approximately 5 times higher than that of MMDTA(V). MMDTA(V) has not been identified in any biological samples of animals, and DMDTA(V) has not been reported as a metabolite of inorganic arsenic in the rats. The identification of novel methylated dithioarsenicals as metabolites of inorganic arsenic in the rat urine provided further insights into the understanding of the metabolism of arsenic.

Reduction of the Pentavalent Arsenical Dimethylarsinic Acid and the GSTO1 Substrate S-(4-Nitrophenacyl)glutathione by Rat Liver Cytosol: Analyzing the Role of GSTO1 in Arsenic Reduction.

Dimethylarsinic acid (DMAs(V)) is the major urinary metabolite of inorganic arsenic. The relatively atoxic DMAs(V) is reduced in the body to the much more toxic and thiol-reactive dimethylarsinous acid (DMAs(III)). Glutathione S-transferase omega 1 (GSTO1) can catalyze this toxification step; however, its role in the reduction of DMAs(V) in vivo or by tissue extracts is unclear. Therefore, we assessed the role of GSTO1 in the reduction of DMAs(V) to DMAs(III) by rat liver cytosol. The experiments revealed that glutathione (GSH) supported the cytosolic DMAs(V) reduction specifically and that GSH analogues and GSH conjugates, such as S-alkylglutathiones and S-(4-nitrophenacyl)glutathione (4-NPG; a GSTO1 specific substrate), inhibited the formation of DMAs(III). Observations in line with the view that GSTO1 catalyzes the cytosolic reduction of DMAs(V) include (i) findings pointing to the presence of a GSH-binding site on the DMAs(V)-reducing cytosolic enzyme, (ii) identical responsiveness of the DMAs(V)- and 4-NPG-reducing activities in rat liver cytosol to the GSTO1 specific inhibitors KT53 and chloromethylfluorescein diacetate, and (iii) perfect coelution of the two activities during affinity and anion exchange chromatography of cytosolic proteins. Other observations appear ambiguous as to the role of GSTO1 in the cytosolic reduction of DMAs(V). These include the different sensitivities of the DMAs(V)-reducing and GSTO1 activities to aurothioglucose, trivalent antimony, and zinc ions, as well as the preserved GSTO1 activity in cytosols whose DMAs(V)-reducing activity was lost due to spontaneous thiol oxidation. These disparate findings may be reconciled by assuming that GSTO1 catalyzes the reduction of both DMAs(V) and 4-NPG in rat liver cytosol; however, the enzyme employs different sites and/or mechanisms when reducing these substrates.