Determination of arsenic speciation and the possible source of methylated arsenic in Panax Notoginseng.

Arsenic species and a possible source of methylated arsenic in a Panax Notoginseng (PN) medicinal plant were explored to further understand the change of inorganic arsenic to the less toxic methylated form to minimize the health risks associated with its medicinal use. Arsenic speciation in PN from major planting areas was determined using high-performance liquid chromatography coupled with hydride generator-atomic fluorescence (HPLC-HG-AFS). Pot experiments were performed to explore the source of methylated arsenic in PN, and the arsenite methyltransferase (arsM) gene abundance was determined using quantitative reverse transcription PCR (q-RTPCR). Methylated arsenic (monomethylarsonic acid (MMA) + dimethylarsinic acid (DMA)) accounted for 43% ± 30% of the total arsenic in PN from planting areas, while the primary species in soil was As(V) (94% ± 0.12%). In the pot experiments, methylated arsenic accounted for 37%-49% of the total arsenic in PN, and As (V) was the primary species in soil (>98%). The four detected arsenic species in PN increased as the amount of As added to soil increased. The methylated arsenic contents in the PN root were significantly positively correlated with the ArsM gene abundance in soil, suggesting that methylated arsenic in PN is likely from the planting soil.

[Distribution of arsenic species and its DNA damage in subchronic arsenite-exposed mice].

OBJECTIVE: To study the arsenic distribution, speciation, its effects on the balance of other elements and the DNA damage by subchronic arsenite exposure in mice. METHODS: The 8-week-old C57BL/6N mice were matched by weight and divided into control group and supplementation group, which were given 0 or 10 microg/ml of sodium arsenite in the drinking water, and continuous exposed for 6 months. RESULTS: Arsenic was found in various tissues and organs. The highest ones were in the kidney, lung and liver, reached (563.9 +/- 222.5), (458.6 +/- 191.0) and (279.8 +/- 81.2) ng/g, respectively while the lowest in the blood and brain, reached (82.2 +/- 26.7) ng/ml and (101.8 +/- 30.1) ng/g, respectively. Arsenic exists mainly in the form of dimethylarsinous acid (DMA). Compared to the control group, there was a significant difference (P < 0.05) between arsenic and chromium, copper, zinc, selenium, lead in some organs of arsenic exposed group, but not cadmium. Furthermore, the 8-hydroxydeoxyguanosine (8-OHdG) level of the exposed group was (149.1 +/- 1.0) ng/ml, which was significantly higher than the control group of (76.4 +/- 27.9) ng/ml. CONCLUSION: Arsenic accumulated in various tissues and organs mainly in the form of DMA, which affected the balance of chromium, copper, zinc, selenium and lead in the body, and led to DNA damage after subchronic exposure.

In vitro study of intestinal transport of inorganic and methylated arsenic species by Caco-2/HT29-MTX cocultures.

This study characterizes intestinal absorption of arsenic species using in vitro system Caco-2/HT29-MTX cocultures in various proportions (100/0 to 30/70). The species assayed were As(V), As(III), monomethylarsonic acid [MMA(V)], monomethylarsonous acid [MMA(III)], dimethylarsinic acid [DMA(V)], and dimethylarsinous acid [DMA(III)]. The results show that the apparent permeability (P(app)) values of pentavalent species increase significantly in the Caco-2/HT29-MTX cocultures in comparison with the Caco-2 monoculture, probably because of enhancement of paracellular transport. For MMA(III) and DMA(III), P(app) decreases in the Caco-2/HT29-MTX cell model, and for As(III), there is no change in P(app) between the two culture models. Transport studies of arsenic solubilized from cooked foods (rice, garlic, and seaweed) after applying an in vitro gastrointestinal digestion showed that arsenic absorption also varies with the model used, increasing with the incorporation of HT29-MTX in the culture. These results show the importance of choosing a suitable in vitro model when evaluating intestinal arsenic absorption processes.

[Effect of subchronic realgar exposure on Glu and Gln in infant rat brain].

OBJECTIVE: To study the effect of realgar on Glu and Gln on rat brain tissues. METHODS: Forty-eight Wistar rats were divided into 4 groups randomly:control group,low dosage group, moderate dosage group and high dosage group. The treatment groups were treated with realgar by gastric perfusion at a dosage of 0.3 g/kg, 0.9 g/kg, 2.7 g/kg and the control group ones were orally given the same volume of 0.5% sodium carboxymethylcellulose (CMC-Na) for 6 weeks. The contents of inorganic arsenic, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in brain tissues were measured by hydride generation-atomic absorption (HG-AAS) method. The contents of amino acid neurotransmitters in brain tissues of rats were determined by means of high performance liquid chromatography with precolumn derivatization. RESULTS: The levels of MMA and DMA in brain increased as the dosage of realgar increased, while the second methylation index declined. Compared with control group,the levels of Glu was significantly decreased in realgar treated group (P < 0.05); Gln also tended to decrease and that of low dosage group was obviously decreased compared with controls. CONCLUSION: Realgar exposure can cause accumulation of MMA and DMA,declination of second methylation index and the reduction of Glu and Gln in brain tissue.

Influence of aggregated particles on biodegradation activities for dimethylarsinic acid (DMA) in Lake Kahokugata.

Aquatic arsenic cycles mainly depend on microbial activities that change the arsenic chemical forms and influence human health and organism activities. The microbial aggregates degrading organic matter are significantly related to the turnover between inorganic arsenic and organoarsenic compounds. We investigated the effects of microbial aggregates on organoarsenic mineralization in Lake Kahokugata using lake water samples spiked with dimethylarsinic acid (DMA). The lake water samples converted 1 µmol L(-1) of DMA to inorganic arsenic for 28d only under anaerobic and dark conditions in the presence of microbial activities. During the DMA mineralization process, organic aggregates >5.0 µm with bacterial colonization increased the densities. When the organic aggregates >5.0 µm were eliminated from the lake water samples using filters, the degradation activities were reduced. DMA in the lake water would be mineralized by the microbial aggregates under anaerobic and dark conditions. Moreover, DMA amendment enhanced the degradation activities in the lake water samples, which mineralized 50 µmol L(-1) of DMA. The DMA-amended aggregates >5.0 µm completely degraded 1 µmol L(-1) of DMA with a shorter incubation time of 7d. The supplement of KNO(3) and NaHCO(3) to lake water samples also shortened the DMA-degradation period. Presumably, the bacterial aggregates involved in the chemical heterotrophic process would contribute to the DMA-biodegradation process in Lake Kahokugata, which is induced by the DMA amendment.

Fate and bioavailability of arsenic in organo-arsenical pesticide-applied soils. Part-I: incubation study.

A laboratory incubation study was conducted to estimate geochemical speciation and in vitro bioavailability of arsenic as a function of soil properties. Two chemically-variant soil types were chosen, based on their potential differences with respect to arsenic reactivity: an acid sand with minimal arsenic retention capacity and a sandy loam with relatively high concentration of amorphous Fe/Al-oxides, considered a sink for arsenic. The soils were amended with dimethylarsenic acid (DMA) at three rates: 45, 225, and 450 mg/kg. A sequential extraction scheme was employed to identify the geochemical forms of arsenic in soils, which were correlated with the "in vitro" bioavailable fractions of arsenic to identify the most bioavailable species. Arsenic bioavailability and speciation studies were done at 0 time (immediately after spiking the soils with pesticide) and after four-months incubation. Results show that soil properties greatly impact geochemical speciation and bioavailability of DMA; soils with high concentrations of amorphous Fe/Al oxides retain more arsenic, thereby rendering them less bioavailable. Results also indicate that the use of organic arsenicals as pesticides in mineral soils may not be a safe practice from the viewpoint of human health risk.

Anaerobic microbial mobilization and biotransformation of arsenate adsorbed onto activated alumina.

Due to the enactment of a stricter drinking water standard for arsenic in the United States, larger quantities of arsenic will be treated resulting in larger volumes of treatment residuals. The current United States Environmental Protection Agency recommendation is to dispose spent adsorbent residuals from arsenic treatment into non-hazardous municipal solid waste (MSW) landfills. The potential of microorganisms to alter the speciation affecting the mobility of arsenic in the disposal environment is therefore a concern. The purpose of this paper was to evaluate the potential of an anaerobic microbial consortium to biologically mobilize arsenate (As(V)) adsorbed onto activated alumina (AA), a common adsorbent used for treating arsenic in drinking water. Three anaerobic columns (0.27 l) packed with 100 g dry weight of AA containing 0.657 mg adsorbed As(V) (expressed as arsenic) per gram dry weight were continuously flushed with synthetic landfill leachate for 257 days. The fully biologically active column was inoculated with methanogenic anaerobic sludge (10 g volatile suspended solids l(-1) column) and was operated with a mixture of volatile fatty acids (VFA) in the feed (2.5 g chemical oxygen demand l(-1) feed). At the end of the experiment, 37% of the arsenic was removed from the column, of which 48% was accounted for by arsenical species identified in the column effluent. The most important form of arsenic eluted was arsenite (As(III)), accounting for nearly all of the identified arsenic in periods of high mobilization. Additionally, two methylated metabolites, methylarsonic acid and dimethylarsinic acid were observed. Mobilization of arsenic is attributed to the biological reduction of As(V) to As(III) since literature data indicates that As(III) is more weakly adsorbed to AA compared to As(V). Batch and continuous assays confirmed that VFA, present in landfill leachates, served as an electron donating substrate supporting enhanced rates of As(V) reduction to As(III). Two control columns, lacking inoculum and/or VFA in the feed displayed low mobilization of arsenic compared to the fully biologically active column. Therefore, leachates generated in MSW landfills could potentially result in the biologically catalyzed mobilization of arsenic from As(V)-laden drinking water residuals.

Dose-dependent biotransformation of arsenite in rats--not S-adenosylmethionine depletion impairs arsenic methylation at high dose.

Arsenite (AsIII) is eliminated via excretion and methylation. Monomethylarsonous acid (MMAsIII) is a super toxic metabolite of AsIII, while dimethylarsinic acid produced in the next metabolic step is relatively atoxic. Since the role of methylation in the acute toxicity and elimination of AsIII in vivo is unclear, we have examined the excretion and tissue retention of AsIII and its metabolites in rats exposed to increasing AsIII doses. Rats were injected i.v. with 20, 50 and 125 micromol/kg AsIII and arsenic metabolites in bile, urine and tissues were analysed. The excretion of AsIII increased almost proportionately to the dose, while its concentration in tissues rose more than proportionately. In contrast, the excretion and tissue concentrations of methylated metabolites increased less than the dosage, or they even decreased after injection of the largest dose of AsIII. To elucidate the mechanism of the dose-dependent decrease of methylation, we quantified S-adenosylmethionine (SAME), glutathione (GSH), and adenine nucleotides in the liver of AsIII-injected rats. AsIII decreased the hepatic concentrations of GSH and adenosine 5'-triphosphate (ATP) and the energy charge in a dose-dependent manner, but increased the level of SAME. Thus, impaired methylation after AsIII overdose is not due to SAME shortage, but probably to methyltransferase inhibition. It appears that exhausted elimination capacity of AsIII, rather than MMAsIII produced from AsIII, contributes significantly to the acute toxicity of AsIII. After GSH depletion the retained AsIII can increasingly inhibit SH-enzymes, thus causing ATP depletion and energetic disorder.

Influence of dietary selenium on the disposition of arsenate in the female B6C3F1 mouse.

Interactions between arsenic (As) and selenium (Se) at the metabolic level are multifaceted and complex. These interactions are of practical significance because populations in various parts of the world are simultaneously exposed to inorganic As in drinking water and Se mainly in the diet at varying levels. The primary goal of this study was to investigate whether differing dietary Se status would alter the profile of urinary metabolites or their time course for elimination after exposure to arsenate [As(V)]. Weanling female B6C3F1 mice were maintained for 28 d on either a control diet of powdered rodent meal sufficient in Se (A, 0.2 ppm) or Torula yeast-based (TYB) diets deficient (B, 0.02 ppm Se), sufficient (C, 0.2 ppm Se), or excessive (D, 2.0 ppm Se) in Se; mice then received by oral gavage 5 mg (As)/kg as sodium [73As] arsenate. The time course for elimination of total arsenic and metabolites in urine was measured over a 48-h period, and total arsenic was determined in feces and tissues at 48 h. Mice on the Se excess diet excreted a significantly higher percentage of urinary As as inorganic As, with a significantly decreased ratio of organic to inorganic As compared to Se-sufficient mice, suggesting that As methylation was decreased. Mice on the Se-deficient diet appeared to eliminate As(V), arsenite, and dimethylarsinic acid (DMA) in urine more slowly than Se-sufficient mice; however, further studies are required to confirm this finding. Mice on the Se-sufficient meal diet (A) excreted significantly less (by percent) arsenate-derived radioactivity in urine and more in feces compared to mice on the Se-sufficient TYB diet (C), with total elimination being similar for both groups. This indicates that mice on the meal diet absorbed significantly less As(V) than mice on the TYB diet, and this may be due to more fiber or "bulk" in the meal diet. This finding emphasizes the importance of considering dietary composition when interpreting and comparing As disposition studies. Overall this study provides suggestive evidence that dietary Se status alters As metabolism and disposition. This indicates that dietary Se status may be an issue that should be considered in the design and interpretation of epidemiologic studies.

Study of factors influencing the in vivo methylation of inorganic arsenic in rats.

Previous studies have shown that several factors may influence the methylation of inorganic arsenic by rat liver in vitro (Buchet and Lauwerys, 1985). The present study attempts to assess the relevance of these observations in vivo. Like man, rat inactivates inorganic arsenic by methylation to monomethylarsonic (MMA) and dimethylarsinic (DMA) acids which are excreted in urine along with unchanged inorganic arsenic (Asi). The administration of S-adenosylmethionine alone or in association with reduced (GSH) or oxidized glutathione or acetylcysteine and the increase of hepatic GSH level by butylated hydroxytoluene pretreatment do not stimulate the urinary excretion of the methylated arsenic metabolites following a challenge dose of inorganic arsenic. Conversely a reduction of the hepatic GSH level by phorone pretreatment greatly modifies the metabolism of inorganic arsenic in vivo. A reduction exceeding 90% of the control value leads to a decreased urinary excretion of MMA and DMA and an increased urinary excretion of inorganic arsenic. This is also associated with an increased accumulation of inorganic arsenic in the liver. This suggests that a drastic reduction of GSH level in liver not only impairs the methylation of inorganic arsenic but also impairs its biliary excretion. When GSH depletion is less severe, the total amount of arsenic excreted in urine after a challenge dose of NaAsO2 is not significantly different from that found in unpretreated animals but the proportion of the three metabolic forms is different: MMA is reduced whereas Asi and DMA tend to increase. These changes resemble those found in patients with liver insufficiency (J.P. Buchet, A. Geubel, S. Pauwels, P. Mahieu, and R. Lauwerys (1984). The influence of liver disease on the methylation of arsenite in humans. Arch. Toxicol. 55, 151-154). Long-term pretreatment of rats with CCl4 slightly reduces the amount of MMA and DMA excreted in urine following a challenge dose of inorganic arsenic. This effect may result from a reduction of GSH transferase activity by CCl4. This study demonstrates the important role of liver GSH in the metabolism of inorganic arsenic in vivo.