Trivalent Inorganic Arsenic Research Articles

Chronic arsenic exposure suppresses proteasomal and autophagic protein degradation

Ubiquitin Proteasomal System (UPS) and autophagy dysregulation initiate cancer. These pathways are regulated by zinc finger proteins. Trivalent inorganic arsenic (iAs) displaces zinc from zinc finger proteins disrupting functions of important cellular proteins. The effect of chronic environmental iAs exposure (100 nM) on UPS has not been studied. We tested the hypothesis that environmental iAs exposure suppresses UPS, activating autophagy as a compensatory mechanism. We exposed skin (HaCaT and Ker-CT; independent quadruplicates) and lung (BEAS-2B; independent triplicates) cell cultures to 0 or 100 nM iAs for 7 or 8 weeks. We quantified ER stress (XBP1 splicing employing Reverse Transcriptase -Polymerase Chain Reaction), proteasomal degradation (immunoblots), and initiation and completion of autophagy (immunoblots). We demonstrate that chronic iAs exposure suppresses UPS, initiates autophagy, but suppresses autophagic protein degradation in skin and lung cell lines. Our data suggest that chronic iAs exposure inhibits autophagy which subsequently suppresses UPS.

The study on biological exposure index of occupational exposure to arsenic and its inorganic compounds

Objective: To establish biological exposure index (BEI) of occupational exposure to arsenic and its inorganic compounds through occupational epidemiology and the regression analysis of internal and external exposure of workers. Methods: In November 2021, 125 workers with occupational exposure to arsenic and its inorganic compounds and 49 office administrators in a non-ferrous metal smelter in Yunnan Province were selected as the exposure group and control group, respectively. Air samples from the workplace of the study subjects on weekdays were collected and arsenic concentrations were determined. Urine samples were collected in end-of-work weekend and high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) was used to detect the levels of trivalent inorganic arsenic (iAs(3+)) , pentavalent inorganic arsenic (iAs(5+)) , monomethyl arsenic (MMA) and dimethyl arsenic (DMA) in urine. The correlations between arsenic concentration in the workplace air and arsenic species in urine of workers were analyzed. Arsenic exposure concentration and the level of urinary arsenic (ΣiAs+MMA+DMA) of workers was analyzed by linear regression and the BEI of arsenic and its inorganic compounds in the workplace was proposed based on the results of micronucleus test. Results: The median of time-weighted average concentration (C(TWA)) of arsenic in the workplace air of the exposure group was 0.0116 mg/m(3), and the over-standard rate was 71.2% (89/125) . The concentrations of iAs(3+), iAs(5+), inorganic arsenic (iAs=ΣiAs(3+)+iAs(5+)) 、MMA、DMA and urinary arsenic in the exposure group were higher than those in the control group at the end of shift, and the differences were statistically significant (P<0.05) . The concentration of arsenic in the workplace air had the strongest correlation with the concentration of urinary arsenic at the end of the shift (r(s)=0.909, P<0.001) . The regression equation was lg (y) =7.662+2.968lg (x) (r=0.821, P<0.05) . According to the occupational exposure limit (OEL) of arsenic in China, the concentration of urinary arsenic in the end-of-work weekend was calculated to be 53.2 μg/L. Combined with the results of micronucleus test, the BEI of occupational exposure to arsenic and its inorganic compounds in the workplace was proposed to be 50 μg/L. Conclusion: The urinary arsenic in the end-of-work weekend can be used as a biomarker of occupational exposure to arsenic, and its BEI is recommended to be 50 μg/L.

Correlation analysis of urinary arsenic species and health effect indicators of occupational arsenic exposure workers

Objective: To explore the correlation between urinary arsenic and health effects through the determination and analysis of urinary arsenic levels in occupational arsenic exposed workers. Methods: In November 2021, 95 workers exposed to arsenic and its inorganic compounds and 31 administrative personnel from a non-ferrous metal smelter in Yunnan Province were selected as the contact group and control group, respectively. Urine forms of arsenic, blood tumor markers, liver function were detected, and micronucleus test was used to analyze the chromosome damage. The correlation between urine forms of arsenic and health effects were analyzed. Results: Compared with the control group, the concentrations of urinary trivalent inorganic arsenic (iAs(3+)) , pentavalent inorganic arsenic (iAs(5+)) , inorganic arsenic (iAs=ΣiAs(3+)+iAs(5+)) , monomethyl arsenic (MMA) , dimethyl arsenic (DMA) and urinary arsenic (ΣiAs+MMA+DMA) at the end of class in contact group were higher (P<0.05) . There was no statistically significant difference in blood tumor markers and liver function indicators between the two groups (P>0.05) . Compared with the control group, the peripheral blood micronucleus rate and cell micronucleus rate in the contact group were significantly increased (P<0.05) . The urinary arsenic, iAs(5+), inorganic arsenic and DMA were positively correlated with peripheral blood micronucleus rate in contact group (r(s)=0.48, 0.34, 0.37, 0.23, P<0.05) , and the urinary arsenic, iAs(5+), DMA were positively correlated with peripheral blood micronucleus rate (r(s)=0.48, 0.34, 0.26, P<0.05) . Conclusion: There is a significant correlation between different valence states of arsenic in the urine and abnormal health effects of occupational arsenic exposed workers. It is necessary to strengthen the detection of arsenic species in the urine of occupational arsenic exposed workers to better protect their health.

Arsenite Impairs BRCA1-Dependent DNA Double-Strand Break Repair, a Mechanism Potentially Contributing to Genomic Instability.

BRCA1 is a key player in maintaining genomic integrity with multiple functions in DNA damage response (DDR) mechanisms. Due to its thiol-rich zinc-complexing domain, the protein may also be a potential target for redox-active and/or thiol-reactive (semi)metal compounds. The latter includes trivalent inorganic arsenic, which is indirectly genotoxic via induction of oxidative stress and inhibition of DNA repair pathways. In the present study, we investigated the effect of NaAsO2 on the transcriptional and functional DDR. Particular attention was paid to the potential impairment of BRCA1-mediated DDR mechanisms by arsenite by comparing BRCA1-deficient and -proficient cells. At the transcriptional level, arsenite itself activated several DDR mechanisms, including a pronounced oxidative stress and DNA damage response, mostly independent of BRCA1 status. However, at the functional level, a clear BRCA1 dependency was observed in both cell cycle regulation and cell death mechanisms after arsenite exposure. Furthermore, in the absence of arsenite, the lack of functional BRCA1 impaired the largely error-free homologous recombination (HR), leading to a shift towards the error-prone non-homologous end-joining (NHEJ). Arsenic treatment also induced this shift in BRCA1-proficient cells, indicating BRCA1 inactivation. Although BRCA1 bound to DNA DSBs induced via ionizing radiation, its dissociation was impaired, similarly to the downstream proteins RAD51 and RAD54. A shift from HR to NHEJ by arsenite was further supported by corresponding reporter gene assays. Taken together, arsenite appears to negatively affect HR via functional inactivation of BRCA1, possibly by interacting with its RING finger structure, which may compromise genomic stability.

Effects of Varied Forms of Arsenic Stress on Seedling Growth and Arsenic Distribution in Honeysuckle Plants

At present, soil arsenic contamination is one of the prominent environmental problems. The arsenic concentration in honeysuckle exceeds the standard levels, thus affecting the quality of traditional Chinese medicine. In this study, the hydroponic method was employed to explore the effect of organic arsenic (dimethyl arsenic) and trivalent inorganic arsenic (NaAsO2) on the growth of honeysuckle plants. The study demonstrated that low concentrations of inorganic arsenic (10–20 mg/L) and 10–50 mg/L organic arsenic had a stimulating effect on the growth of honeysuckle plants. The activities of antioxidant enzymes (peroxidase and catalase) increased correspondingly. However, the antioxidant system in honeysuckle plants was damaged under high concentrations of inorganic arsenic (20–40 mg/L) and 50–70 mg/L organic arsenic. On exposure to 30 mg/L NaAsO2 or 50 mg/L dimethyl arsenic acid for 10 days, the activities of peroxidase and catalase, as well as the malondialdehyde content, increased with prolonged exposure. The micro X-ray fluorescence analysis revealed that the accumulated arsenic in the roots was transported from the central vascular cylinders to the outer part of the root with the increase in concentration and exposure duration of inorganic arsenic. However, organic arsenic stress did not result in significant variations in the distribution of arsenic with increasing concentrations of arsenic. The arsenic element was predominantly located in the middle woody part of the root. The distributions of arsenic in the stems and leaves, in terms of organic and inorganic arsenic stresses, were similar, with accumulation primarily in the cortex of the stem and veins of the leaves. As a commonly used bulk traditional Chinese medicine, honeysuckle has a wide range of product quality issues. Hence, exploring the absorption, distribution, and transport trends of heavy metals such as arsenic in the plant body is of great significance for scientifically evaluating the impact of heavy metal pollution on the quality of medicinal materials and exploring ways to reduce the accumulation of heavy metals in the medicinal parts of plants.

Morphological alterations in C57BL/6 mouse intestinal organoids as a tool for predicting chemical-induced toxicity.

Intestinal organoid may serve as an alternative model for toxicity testing. However, the linkage between specific morphological alterations in organoids and chemical-induced toxicity has yet to be defined. Here, we generated C57BL/6 mouse intestinal organoids and conducted a morphology-based analysis on chemical-induced toxicity. Alterations in morphology were characterized by large spheroids, hyperplastic organoids, small spheroids, and protrusion-loss organoids, which responded in a concentration-dependent manner to the treatment of four metal(loid)s including cadmium (Cd), lead (Pb), hexavalent chromium (Cr-VI), and inorganic trivalent arsenic (iAs-III). Notably, alterations in organoid morphology characterized by abnormal morphology rate were correlated with specific intestinal toxic effects, including reduction in cell viability and differentiation, induction of apoptosis, dysfunction of mucus production, and damage to epithelial barrier upon repeated administration. The benchmark dose (BMDL10) values of morphological alterations (0.007-0.195μM) were lower than those of conventional bioassays (0.010-0.907μM). We also established that the morphologic features of organoids upon Cd, Pb, Cr-VI, or iAs-III treatment were metal specific, and mediated by Wnt, bone morphogenetic protein, apoptosis induction, and Notch signaling pathways, respectively. Collectively, these findings provide novel insights into the relevance of morphological alterations in organoids to specific toxic endpoints and identify specific morphological alterations as potential indicators of enterotoxicity.

Arsenite Methyltransferase Is an Important Mediator of Hematotoxicity Induced by Arsenic in Drinking Water.

Chronic arsenic exposures via the consumption of contaminated drinking water are clearly associated with many deleterious health outcomes, including anemia. Following exposure, trivalent inorganic arsenic (AsIII) is methylated through a series of arsenic (+III oxidation state) methyltransferase (As3MT)-dependent reactions, resulting in the production of several intermediates with greater toxicity than the parent inorganic arsenicals. The extent to which inorganic vs. methylated arsenicals contribute to AsIII-induced hematotoxicity remains unknown. In this study, the contribution of As3MT-dependent biotransformation to the development of anemia was evaluated in male As3mt-knockout (KO) and wild-type, C57BL/6J, mice following 60-day drinking water exposures to 1 mg/L (ppm) AsIII. The evaluation of hematological indicators of anemia revealed significant reductions in red blood cell counts, hemoglobin levels, and hematocrit in AsIII-exposed wild-type mice as compared to unexposed controls. No such changes in the blood of As3mt-KO mice were detected. Compared with unexposed controls, the percentages of mature RBCs in the bone marrow and spleen (measured by flow cytometry) were significantly reduced in the bone marrow of AsIII-exposed wild-type, but not As3mt-KO mice. This was accompanied by increased levels of mature RBCS in the spleen and elevated levels of circulating erythropoietin in the serum of AsIII-exposed wild-type, but not As3mt-KO mice. Taken together, the findings from the present study suggest that As3MT-dependent biotransformation has an essential role in mediating the hematotoxicity of AsIII following drinking water exposures.

A sensitive conductivity sensor for arsenic detection in environmental samples

Arsenic is a poisonous contaminant affecting the environment as well as living beings, thus its determination is critical. The study describes the designing and fabrication of a conductometric biosystem for the indirect identification of arsenic in aqueous samples. The principle of detection is based on the measurement of the inhibition of immobilized papain catalytic efficiency in the presence of arsenic. A linear response against arsenic trioxide (as trivalent inorganic arsenic is toxic) by the developed biosystem was found in the range of 0.1–20 ppm (correlation coefficient = 0.96) with the lower limit of detection of 5 ppb. For optimum working conditions and the response of the designed biosystem, different parameters were optimized such as substrate concentration (14 mM), pH (7), and temperature around (35 °C ± 5 °C). The resultant data were statistically evaluated by analysis of variance and were found to be significant at α = 0.05 with a recovery rate of 101.6%. The biosystem displayed a high recovery with a lower detection limit, thus it can be utilized for environmental arsenic trioxide estimation.

Profiling of histone H3 trimethylation and distinct epigenetic pattern of chromosome Y in the transformed bronchial epithelial cells induced by consecutive arsenic treatment

Abstract Environmental arsenic is a known human carcinogen that is associated with cancers in lung, liver, skin, breast, bladder, kidney, prostate, etc. However, the underpinnings of malignant transformation of the normal cells in response to environmental arsenic exposure remain poorly understood, in part due to mixed signaling pathways elicited by arsenic, especially the inorganic trivalent arsenic (As 3+). In the present report we profiled the trimethylation status of histone H3 through global chromatin immunoprecipitation followed by sequencing (ChIP-seq) in the As 3+ -induced transformed cells and found an overall gain of active methylation of histone H3, the trimethylation of lysine 4 of histone H3 (H3K4me3), along with a diminished enrichment of the repressive marker H3K27me3 in the genome in the transformed cells relative to the control cells. Many oncogenic genes responsible for cell proliferation and selfrenewal of the cancer stem-like cells are enriched with H3K4me3 along with a reduced level of H3K27me3 and/or H3K9me3. In contrast, some genes encoding proteins with tumor suppressor-like activity showed reduced enrichment of the active marker, H3K4me3, but elevated levels of the repressive markers, H3K27me3 and H3K9me3. These data, thus, suggest that the carcinogenicity of As 3+ is achieved through regulating histone methylations that define the chromatin configuration and gene expression dynamics of the genome and the cell fate decision.

Deducing signaling pathways from parallel actions of arsenite and antimonite in human epidermal keratinocytes

Inorganic arsenic oxides have been identified as carcinogens in several human tissues, including epidermis. Due to the chemical similarity between trivalent inorganic arsenic (arsenite) and antimony (antimonite), we hypothesized that common intracellular targets lead to similarities in cellular responses. Indeed, transcriptional and proteomic profiling revealed remarkable similarities in differentially expressed genes and proteins resulting from exposure of cultured human epidermal keratinocytes to arsenite and antimonite in contrast to comparisons of arsenite with other metal compounds. These data were analyzed to predict upstream regulators and affected signaling pathways following arsenite and antimonite treatments. A majority of the top findings in each category were identical after treatment with either compound. Inspection of the predicted upstream regulators led to previously unsuspected roles for oncostatin M, corticosteroids and ephrins in mediating cellular response. The influence of these predicted mediators was then experimentally verified. Together with predictions of transcription factor effects more generally, the analysis has led to model signaling networks largely accounting for arsenite and antimonite action. The striking parallels between responses to arsenite and antimonite indicate the skin carcinogenic risk of exposure to antimonite merits close scrutiny.

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

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

Molecular mechanism of the increased tissue uptake of trivalent inorganic arsenic in mice with type 1 diabetes mellitus

Arsenic is associated with several adverse health outcomes, and people with diabetes may be more susceptible to arsenic. In this study, we found that arsenic levels in some tissues such as liver, kidney, and heart but not lung of type 1 diabetes mellitus (T1DM) mice were higher than in those of normal mice after a single oral dose of arsenic trioxide for 2 h. However, little is known about the molecular mechanism of the increased tissue uptake of trivalent inorganic arsenic in mice with T1DM. This study aimed to investigate the expression of the mammalian arsenic transporters aquaglyceroporins (AQPs) and glucose transporter 1 (GLUT1) in T1DM mice and compare them with those in normal mice. Results showed that the levels of AQP9 and GLUT1 mRNA and protein were higher in T1DM mouse liver than in the normal one. The levels of AQP7 mRNA and protein were higher in T1DM mouse kidney. In the heart, we observed that the levels of AQP7 and GLUT1 mRNA and protein were higher in T1DM mice, but the levels of AQP9 mRNA and protein in the lung had no significant difference between both mice. These results suggested that T1DM may increase the expression of transporters of trivalent inorganic arsenic and thus increase the arsenic uptake in specific tissues.

Assessing the Effects of Inorganic Arsenic on IL-1β and TNFɑ Secretion, Gene Expression, and DNA Methylation in Murine Macrophages to Gauge Immunotoxic Effects of Heavy Metals

Trivalent inorganic arsenic, arsenite, is a natural component of the earth and is often found in drinking water in areas where the composition is high. Some studies have suggested that, especially at moderate to high exposure levels, arsenite is toxic to individuals who are chronically exposed through drinking water, characterized by an increase in inflammatory cytokine release, specifically interleukin-1β (IL-1β) and tumor necrosis factor-ɑ (TNFɑ). Other epidemiological studies at low to moderate exposures did not find the same correlation with inflammation. We aim to characterize and quantify the effects of arsenite exposure to macrophages to gauge any potential inflammatory response. M1 macrophages are key players in inflammatory response and secrete IL-1β and TNFɑ in response to Danger Associated Molecular Patterns (DAMPs) released by neighboring cells undergoing necrosis, in coordination with Pathogen Associated Molecular Patterns (PAMPs), molecules associated with pathogens, such as lipopolysacchari...

Assessing the Effects of Inorganic Arsenic on IL‐1β and TNFɑ Secretion, Gene Expression, and DNA Methylation in Murine Macrophages to Gauge Immunotoxic Effects of Heavy Metals

Trivalent inorganic arsenic, arsenite, is a natural component of the earth and is often found in drinking water in areas where the composition is high. Some studies have suggested that, especially at moderate to high exposure levels, arsenite is toxic to individuals who are chronically exposed through drinking water, characterized by an increase in inflammatory cytokine release, specifically interleukin‐1β (IL‐1β) and tumor necrosis factor‐ɑ (TNFɑ). Other epidemiological studies at low to moderate exposures did not find the same correlation with inflammation. We aim to characterize and quantify the effects of arsenite exposure to macrophages to gauge any potential inflammatory response.M1 macrophages are key players in inflammatory response and secrete IL‐1β and TNFɑ in response to Danger Associated Molecular Patterns (DAMPs) released by neighboring cells undergoing necrosis, in coordination with Pathogen Associated Molecular Patterns (PAMPs), molecules associated with pathogens, such as lipopolysaccharide, or LPS. We obtained a murine macrophage cell line to study the effects of arsenic on inflammatory cytokine secretion in vitro. A dose response curve was developed including varying concentrations of arsenite with and without 50 ng/mL LPS, using the same treatments without arsenite as controls. Cytolethality was determined by differential staining and counting. Secretion of cytokines after 24 hours of exposure was quantified using ELISA. Results were statistically analyzed using Student's t‐test and One‐Way ANOVA. IL‐1β was not differentially secreted for any concentration of arsenite, but cytolethality and TNFɑ secretion were significantly increased for 200 nM arsenite with LPS as opposed to 200 nM arsenite without LPS, possibly indicating that some inflammatory augmentation occurs in the presence of both arsenite exposure and a PAMP.Future steps include analyzing alterations in expression of genes responsible for proteins involved in the secretory pathways of these cytokines. For example, the genes involved in manufacturing the pieces of the NLRP3 inflammasome, key in production of IL‐1β, or TNFɑ Converting Enzyme, involved in cleavage of the TNFɑ precursor, may be potential targets. Additionally, we will explore differential DNA methylation using methylation sensitive and insensitive restriction enzyme digestion to examine epigenetic control of cytokine secretion in response to arsenite. These results will be reported to appraise the immunotoxic effects of arsenic exposure.Support or Funding InformationThis research is supported by the Salisbury University Department of Biological Sciences and the Salisbury University Honors College.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Reorientation of the Methyl Group in MAs(III) is the Rate-Limiting Step in the ArsM As(III) S-Adenosylmethionine Methyltransferase Reaction.

The most common biotransformation of trivalent inorganic arsenic (As(III)) is methylation to mono-, di-, and trimethylated species. Methylation is catalyzed by As(III) S-adenosylmethionine (SAM) methyltransferase (termed ArsM in microbes and AS3MT in animals). Methylarsenite (MAs(III)) is both the product of the first methylation step and the substrate of the second methylation step. When the rate of the overall methylation reaction was determined with As(III) as the substrate, the first methylation step was rapid, whereas the second methylation step was slow. In contrast, when MAs(III) was used as the substrate, the rate of methylation was as fast as the first methylation step when As(III) was used as the substrate. These results indicate that there is a slow conformational change between the first and second methylation steps. The structure of CmArsM from the thermophilic alga Cyanidioschyzon merolae sp. 5508 was determined with bound MAs(III) at 2.27 Å resolution. The methyl group is facing the solvent, as would be expected when MAs(III) is bound as the substrate rather than facing the SAM-binding site, as would be expected for MAs(III) as a product. We propose that the rate-limiting step in arsenic methylation is slow reorientation of the methyl group from the SAM-binding site to the solvent, which is linked to the conformation of the side chain of a conserved residue Tyr70.

Alternative use of Bacillus subtilis spores: protection against environmental oxidative stress in human normal keratinocytes

Inorganic trivalent arsenic is a major environmental pollutant and exposure to human results in many pathologies, including keratosis and carcinoma. Here, we analyzed the effects of B. subtilis spores on human normal keratinocytes in the presence of sodium arsenite oxidative stress. Pre-treatment of cells with spores before inducing oxidative stress was able to keep normal levels of intracellular ROS, GSH and lipid peroxidation, as well as to inhibit the activation of the MAPK cascade. Moreover, spores showed a positive effect on cell proliferation, probably due to their binding on the cell surface and the activation of intracellular catalases. We found that spores exert their protective effect by the nuclear translocation of Nrf-2, involved in the activation of stress response genes. This, in turn, resulted in a protective effect against sodium arsenite stress injury, as oxidative stress markers were reported to physiological levels when cells were stressed before incubating them with spores. Therefore, B. subtilis spores can be considered as a new agent to counteract oxidative stress on normal human keratinocytes.

Effect of trivalent arsenicals on cell proliferation in mouse and human microvascular endothelial cells

Chronic exposure to high levels of inorganic arsenic (iAs) has been associated with cancerous and non-cancerous health effects, including cardiovascular effects. However, the mechanism for a presumed toxic effect of arsenic on vascular tissue is not clear. Our working hypothesis is that inorganic trivalent arsenic and its methylated metabolites react with cysteine-containing cellular proteins and alter their function leading to adverse events such as cytotoxicity or proliferation. In this study, human microvascular endothelial cells (HMEC1) and mouse microvascular endothelial cells (MFP-MVEC) were exposed to arsenite (iAsIII), monomethylarsonous acid (MMAIII), or dimethylarsinous acid (DMAIII) for 72h to evaluate cytotoxicity, and for 24, 48 or 72h to evaluate cell proliferation. Both cell lines showed similar LC50 values, from 0.1 to 2.4μM, for all three trivalent arsenicals. The endothelial cells treated with1nM to 1μM concentrations of the three trivalent arsenicals did not show increased cell proliferation at 24, 48 or 72h or increased rate of proliferation at 72h of exposure. Overall, cytotoxicity of trivalent arsenicals to microvascular endothelial cells is similar to their cytotoxicity to epithelial cells, and that these compounds are not mitogenic.

The Relationship between Liver Dysfunction and Arsenic Methylation in Mice

The different methyl metabolic products of inorganic arsenic lead to various toxicities. Arsenic has been demonstrated to induce hepatotoxicity by oxidative stress. The relationship between hepatic injury and inorganic methylation is not yet known. This study was designed to explore the relationship between arsenic methylation and liver oxidative stress induced by arsenic trioxide (ATO). Forty healthy KM mice were randomly divided into control group (0.9% saline) and As2O3 (1.0 mg/Kg/day, 2.0 mg/Kg/day, 4.0 mg/Kg/day) groups with gastric perfusion for five weeks using high-efficiency liquid chromatography and hydride genesis atomic fluorescence spectroscopy (HPLC-HGAFS). The products of arsenic trioxiode methylating, including trivalent inorganic arsenic (iAs 3+ ), pentavalent inorganic arsenic (iAs 5+ ), mono methyl arsenic (MMA), and dimethyl arsenic (DMA) in the liver were determined. The indexes of arsenic methylation, including primary methyl index (PMI) and second methyl index (SMI) were calculated. The level of hepatic function and activity of MDA, GSH, SOD, and TAOC were detected with kits. We found that the remaining arsenic metabolic products in liver significantly increased with the increasing doses of arsenic trioxide and the liver function and oxidative stress deteriorated. Negative correlations were found between MMA%, PMI and GSH, SOD, and TAOC, while DMA% and SMI positively correlated with the levels of ALT and AST. PMI and SMI negatively correlated with TAOC, GSH, SOD, ALT, and AST, positively linked with the level of MDA. The present study demonstrates that the hepatotoxicity induced by the arsenic accounts for deteriorating oxidative injury activized by arsenic methylation metabolism, providing additional evidence to suggest a mechanism of arsenic poisoning. Therefore, reducing the process of arsenic methylation may be potentially benefical in treating and – more importantly – preventing arseniasis.

Green tea and vitamin C ameliorate some neuro-functional and biochemical signs of arsenic toxicity in rats

Background/objectives: Nervous system damage is one of the consequences of oral exposure to waterborne inorganic arsenic. In this work, the role of oxidative status in the neurotoxicity of arsenic and the possible role of two foodborne antioxidants in ameliorating arsenic-related oxidative stress were investigated.Methods: Male Wistar rats were given 10 mg/kg b.w. of trivalent inorganic arsenic (in the form of NaAsO2), 5 day/week for 6 weeks by gavage, combined with vitamin C solution (1 g/l) or green tea infusion (2.5 g in 500 ml boiled water) as antioxidants given in the drinking fluid.Results: Body weight gain was reduced by arsenic from the second week and the antioxidants had no effect on that. Cortical evoked potentials had increased latency, tail nerve conduction velocity was reduced, and this latter effect was counteracted by the antioxidants. The effect of green tea was stronger than that of vitamin C, and green tea also diminished lipid peroxidation induced by As. There was fair correlation between brain As levels, electrophysiological changes, and lipid peroxidation, suggesting a causal relationship.Discussion: Natural antioxidants might be useful in the protection of the central nervous system against the toxicity of oral As.

Critical role of cellular glutathione homeostasis for trivalent inorganic arsenite-induced oxidative damage in human bronchial epithelial cells

Trivalent inorganic arsenic (iAs3+) is a powerful carcinogen that enhances the risk of lung cancer. Paradoxically, iAs3+ also shows substantial efficacy in the treatment of lung tumors. However, the exact molecular mechanisms underlying iAs3+-induced toxicity and therapeutic effect in lung remain unclear. In this study, the effects of iAs3+, sodium arsenite (NaAsO2) and arsenic trioxide (As2O3), on cell viability, apoptosis, genotoxicity and oxidative stress in cultured human bronchial epithelial cells were observed. Our results showed that NaAsO2 and As2O3 exposure could result in defects in cell proliferation and greatly enhance the level of oxidative damage. To clarify the critical role of glutathione (GSH) homeostasis in oxidative damage induced by iAs3+, we further measured the content of GSH, ratio of GSH to GSSG, and the activities of GSH-related enzymes involved in the process of GSH synthesis, recycling and utilization. Our data demonstrated that NaAsO2 and As2O3 disrupted the balance of GSH homeostasis, and NaAsO2- and As2O3-induced oxidative damage was closely associated with the imbalance in GSH synthesis, recycling and utilization. To better understand the physiologic significance of Nrf2 in maintaining GSH-homeostasis, the expression level of Nrf2 was measured after iAs3+ exposure. We found that the protein expression levels of Nrf2 were increased in both NaAsO2- and As2O3-treated cells. Collectively, our findings suggest that disturbed Nrf2-regulated GSH-homeostasis is associated with the oxidative damage triggered by iAs3+, and loss of GSH homeostasis might implicate in both the pathogenesis of iAs3+-induced lung diseases and anticancer activity of iAs3+.