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enic, a carcinogen, is assumed to induce global DNA hypomethylation by consuming the universal methyl donor S-adenosylmethionine (SAM) in the body. A previous study reported that a methyl-deficient diet (MDD) with arsenic intake greatly reduced global DNA methylation (the content of 5-methylcytosine) in the liver of male C57BL/6 mice. In the present study, we investigated the DNA methylation level, SAM content, and expression of DNA methyltransferases (DNMTs) in the liver of male and female C57BL/6 mice fed a methyl-sufficient diet (MSD), an MDD, or an MDD + arsenic. The DNA methylation level was accurately determined by measuring the content of genomic 5-methyldeoxycytidine (5medC) by high-performance liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) using stable-isotope-labeled 5medC and deoxycytidine (dC) as internal standards. The results of this study revealed that while the MDD and arsenic tended to reduce the genomic 5meC content in the male mice livers, the MDD + arsenic significantly increased the 5meC content in the female mice livers. Another unexpected finding was the small differences in 5meC content among the groups. The MDD and MDD + arsenic suppressed DNMT1 expression only in the male mice livers. In contrast, SAM content was reduced by the MDD and MDD + arsenic only in the livers of female mice, showing that the changes in 5meC content were not attributable to SAM content. The sex-dependent changes in 5meC content induced by methyl deficiency and arsenic may be involved in differences in male and female susceptibility to diseases via epigenetic modification of physiological functions. [ABSTRACT FROM AUTHOR]

It has been suggested that arsenic (+3 oxidation state) methyltransferase (AS3MT) plays a critical role in methylation of arsenic, and that arsenic-glutathione conjugate is a substrate for AS3MT-catalyzed methylation of arsenic. However, the mechanism of arsenic methylation in cells is not fully understood. Here, we have constructed T-REx-CHO-hAS3MTtr cells that transiently overexpress human AS3MT in response to tetracycline. The decreases in cell viability after exposure to sodium arsenite were greater in tetracycline-treated cells (tet(+) cells) than in untreated cells (tet(−) cells). Concentration of total cellular arsenic was significantly higher in tet(+) cells than in tet(−) cells. Speciation analyses of arsenic metabolites in whole cell lysates and cell culture medium were performed using both HepG2 cells and T-REx-CHO-hAS3MTtr cells. Speciation analyses of arsenic metabolites in lysates of T-REx-CHO-hAS3MTtr cells revealed that dimethylated arsenicals were the predominant arsenic metabolites in tet(+) cells, while methylated metabolites were not found in tet(−) cells. In contrast, less amount of methylated arsenic metabolites were found in the HepG2 cell lysates, and monomethylated trivalent arsenicals were the predominant methylated arsenic metabolites. Arsenate was found in the culture medium after 24 h culture with arsenite. A larger amount of arsenate was found in the culture medium of tet(+) or tet(−) cells compared to HepG2 cells. These findings indicated that AS3MT expression enhanced the cytotoxic effect of arsenite in tet(+) cells because these cells accumulated more arsenic metabolites than did the tet(−) cells, and accordingly, the tet(+) cells were more susceptible to arsenic than were the tet(−) cells. Oxidation-reduction of arsenic may be implicated in the toxic effects of arsenite. [ABSTRACT FROM AUTHOR]

Diphenylarsinic acid (DPAA), a possible product of degradation of arsenic-containing chemical weapons, was detected in well water in Kamisu City, Ibaraki Prefecture, Japan, in 2003. Although some individuals in this area have been affected by drinking DPAA-containing water, toxicological findings on DPAA are limited. To elucidate the mechanism of its toxicity, it is necessary to determine the metabolic behavior of DPAA in the body. In this study, pregnant cynomolgus monkeys at the 50th day of pregnancy were used. The monkeys were treated daily with 1.0 mg DPAA/kg body weight using a nasogastric tube, and the distribution and excretion of arsenic were examined after the repeated administration and 198–237 days after the last administration of DPAA. Fecal excretion was higher than urinary excretion (ca. 3:2 ratio), and arsenic accumulated in the hair and erythrocytes. Distribution of DAPP to plasma and hemolyzed erythrocytes was also examined by high-performance liquid chromatography–inductively coupled argon plasma mass spectrometry (HPLC–ICP MS). Two peaks were found in the elution profile of arsenic, due to free and probably protein-bound DPAA. The protein-bound arsenic compounds were presumably trivalent diphenylarsenic compounds, since free DPAA was recovered after treatment of heat-denatured samples with hydrogen peroxide. [ABSTRACT FROM AUTHOR]

The metabolism of arsenic is generally accepted to proceed by repetitive reduction and oxidative methylation; the latter is mediated by arsenic methyltransferase (Cyt19). In human urine, the major metabolites of inorganic arsenicals such as arsenite (iAsIII) and arsenate (iAsV) are monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV). On the other hand, in rat bile, the major metabolites of iAsIII have been reported to be arsenic-glutathione (As-GSH) complexes. In the present study we investigate whether these As-GSH complexes are substrates for arsenic methyltransferase by using human recombinant Cyt19. Analyses by high-performance liquid chromatography-inductively coupled plasma mass spectrometry suggested that arsenic triglutathione (ATG) was generated nonenzymatically from iAsIII when GSH was present at concentrations 2 mM or higher. Human recombinant Cyt19 catalyzed transfer of a methyl group fromS-adenosyl-l-methionine to arsenic and produced monomethyl and dimethyl arsenicals. The methylation of arsenic was catalyzed by Cyt19 only when ATG was present in the reaction mixture. Moreover, monomethylarsonic diglutathione (MADG) was a substrate of Cyt19 for further methylation to dimethylarsinic glutathione (DMAG). On the other hand, monomethylarsonous acid (MMAIII), a hydrolysis product of MADG, was not methylated to dimethyl arsenical by Cyt19. These results suggest that As-GSH complexes such as ATG and MADG were converted by Cyt19 to MADG and DMAG, respectively. Both MADG and DMAG were unstable in solution when the GSH concentration was lower than 1 mM, and were hydrolyzed and oxidized to MMAV and DMAV, respectively. Metabolism of iAsIII to methylated arsenicals by Cyt19 was via ATG and MADG rather than by oxidative methylation of iAsIII and MMAIII. [ABSTRACT FROM AUTHOR]

Clark 1 (diphenylarsine chloride) and Clark 2 (diphenylarsine cyanide) were used as chemical weapon agents (CWA), and the soil contamination by these CWA and their degraded products, diphenyl and phenyl arsenicals, has been one of the most serious environmental issues. In a series of comparisons in toxicity between trivalent and pentavalent arsenicals we investigated differences in the accumulation and toxicity of phenylarsine oxide (PAO3+) and phenylarsonic acid (PAA5+) in rat heart microvascular endothelial cells. Both the cellular association and toxicity of PAO3+ were much higher than those of PAA5+, and LC50 values of PAO3+ and PAA5+ were calculated to be 0.295 µM and 1.93 mM, respectively. Buthionine sulfoximine, a glutathione depleter, enhanced the cytotoxicity of both PAO3+ and PAA5+.N-Acetyl-l-cysteine (NAC) reduced the cytotoxicity and induction of heme oxygenase-1 (HO-1) mRNA in PAO3+-exposed cells, while NAC affected neither the cytotoxicity nor the HO-1 mRNA level in PAA5+-exposed cells. The effect of NAC may be due to a strong affinity of PAO3+ to thiol groups because both NAC and GSH inhibited the cellular accumulation of PAO3+, but PAA3+ increased tyrosine phosphorylation levels of cellular proteins. These results indicate that the inhibition of protein phosphatases as well as the high affinity to cellular components may confer PAO3+ the high toxicity. [ABSTRACT FROM AUTHOR]

Intake of inorganic arsenic is known to cause vascular diseases as well as skin lesions and cancer in humans. We investigated the differences in cytotoxicity, uptake rate of arsenic, and gene expression of antioxidative enzymes between arsenite (As3+)- and arsenate (As5+)-exposed rat heart microvessel endothelial cells. As3+ was more cytotoxic than As5+, and LC50 values were calculated to be 36 and 220 µM, respectively. As3+ (1–25 µM) increased mRNA levels of antioxidant enzymes such as heme oxygenase-1 (HO-1), thioredoxin peroxidase 2, NADPH dehydrogenase, and glutathione S-transferase P subunit. HO-1 mRNA levels showed the most remarkable increase in response to As3+. cDNA microarray analysis indicated that there was no prominent difference in arsenic-induced transcriptional changes between As3+- and As5+-exposed cells, when the cells were exposed to one-fourth the LC50 concentration of arsenic (9 and 55 µM for As3+ and As5+, respectively). N-acetyl-l-cysteine (NAC) reduced both the cytotoxicity of inorganic arsenic and the HO-1 mRNA level, and buthionine sulfoximine enhanced cytotoxicity of inorganic arsenic. As3+ was taken up by the endothelial cells 6–7 times faster than As5+, and the presence of NAC in the culture medium did not change the uptake rate of As3+.These results suggest that the effects of NAC on arsenic-induced cytotoxicity and oxidative stress were due to the antioxidative role of non-protein thiols and not to chelation of arsenic in the culture medium. The difference in cellular uptake of arsenic between As3+ and As5+ appeared not to be due to the ionic charge on arsenic (at physiological pH, trivalent arsenic is neutral whereas pentavalent arsenic is negatively charged). These results suggest that the higher toxicity of As3+ compared with that of As5+ is probably due to the faster uptake of As3+ by endothelial cells, and inorganic arsenic exerts its toxicity at least in part via intracellular oxidative stress. [ABSTRACT FROM AUTHOR]

Background: Lead is a toxic metal abundant in the environment. Consumption of food contaminated at low levels of lead, especially by small children and pregnant women, raises a health concern. Methods: Duplicated food portions and drinking water were collected over 3 days from 88 children and 87 pregnant women in Shimotsuke, Tochigi, Japan. Participants were recruited in this study between January 2014 and October 2015. Dust was also collected from their homes. Lead concentrations were measured and consequent oral lead exposure levels were estimated for this population at high risk to environmental toxicants. Lead concentrations of peripheral and cord blood, taken from children and pregnant women, and were also analyzed. Results: Lead concentrations in food, drinking water, and house dust were low in general. Oral lead exposure to lead was higher for children (Mean ± SEM; 5.21 ± 0.30 μg/kg BW/week) than in pregnant women (1.47 ± 0.13 μg/kg BW/week). Food and house dust were main sources of lead contamination, but the contribution of house dust widely varied. Means ± SEM of peripheral and cord blood lead concentrations were 0.69 ± 0.04 μg/dL and 0.54 ± 0.05 μg/dL, respectively for pregnant women and 1.30 ± 0.07 μg/dL (peripheral only) in children. We detect no correlation between smoking situations and blood lead concentration in pregnant women. Conclusion: We conclude that oral lead exposure levels for Japanese children and pregnant women were generally low, with higher concentrations and exposure for children than for pregnant women. More efforts are necessary to clarify the sources of lead contamination and reduce lead exposure of the population at high risk even in Japan. [ABSTRACT FROM AUTHOR]

Background: The Japan Environment and Children’s Study (JECS) is a nation-wide birth cohort study investigating environmental effects on children’s health and development. In this study, the exposure characteristics of the JECS participating mothers were summarized using two questionnaires administered during pregnancy. Methods: Women were recruited during the early period of their pregnancy. We intended to administer the questionnaire during the first trimester (MT1) and the second/third trimester (MT2). The total number of registered pregnancies was 103,099. Results: The response rates of the MT1 and MT2 questionnaires were 96.8% and 95.1%, respectively. The mean gestational ages (SDs) at the time of the MT1 and MT2 questionnaire responses were 16.4 (8.0) and 27.9 (6.5) weeks, respectively. The frequency of participants who reported “lifting something weighing more than 20 kg” during pregnancy was 5.3% for MT1 and 3.9% for MT2. The Cohen kappa scores ranged from 0.07 to 0.54 (median 0.31) about the occupational chemical use between MT1 and MT2 questionnaires. Most of the participants (80%) lived in either wooden detached houses or steel-frame collective housing. More than half of the questionnaire respondents answered that they had “mold growing somewhere in the house”. Insect repellents and insecticides were used widely in households: about 60% used “moth repellent for clothes in the closet,” whereas 32% applied “spray insecticide indoors” or “mosquito coil or an electric mosquito repellent mat.” Conclusions: We summarized the exposure characteristics of the JECS participants using two maternal questionnaires during pregnancy. [ABSTRACT FROM AUTHOR]