Xiufen Lu

Arsenic speciation analysis

Nearly two dozen arsenic species are present in the environmental and biological systems. Differences in their toxicity, biochemical and environmental behaviors require the determination of these individual arsenic species. Considerable analytical progresses have been made toward arsenic speciation analysis over the last decade. Hyphenated techniques involving a highly efficient separation and a highly sensitive detection have become the techniques of choice. Methods based on high-performance liquid chromatography separation with inductively coupled plasma mass spectrometry, hydride generation atomic spectrometry, and electrospray mass spectrometry detection have been shown most useful for arsenic speciation in environmental and biological matrices. These hyphenated techniques have resulted in the determination of new arsenic species, contributing to a better understanding of arsenic metabolism and biogeochemical cycling. Methods for extracting arsenic species from solid samples and for stabilizing arsenic species in solutions are required for obtaining reliable arsenic speciation information.

Detection of Escherichia coli O157:H7 Using Gold Nanoparticle Labeling and Inductively Coupled Plasma Mass Spectrometry

O157:H7 is a serotype of enterohemorrhagic Escherichia coli (EHEC) and one of the major causes of food-borne illness. Protection of food safety against bacterial contamination and rapid diagnosis of infection require simple and fast assays for detection of bacterial pathogens, including E. coli O157:H7. We describe here a rapid and sensitive assay for the E. coli O157:H7 bacteria by using antibody affinity binding, gold nanoparticle (Au NP) labeling, and inductively coupled plasma mass spectrometry (ICPMS) detection. Taking advantage of the signal amplification property of Au NPs and the high sensitivity of ICPMS, the assay was able to detect as few as 500 E. coli O157:H7 cells in 1 mL of sample (500 CFU/mL). Tests with nonpathogenic E. coli (DH5alpha, AlphaTauCC35218, and ATCC25922) showed high specificity of the assay for E. coli O157:H7. Each assay was completed within 40 min. Demonstration of this assay for E. coli O157:H7 suggests its potential for detecting a variety of bacterial pathogens.

Aptamer-Linked Assay for Thrombin Using Gold Nanoparticle Amplification and Inductively Coupled Plasma−Mass Spectrometry Detection

We describe a sensitive and specific sandwich assay for human alpha-thrombin. The assay takes advantage of sandwich binding of two affinity aptamers for increased specificity, gold nanoparticles for signal amplification, magnetic beads for fast magnetic separation, and inductively coupled plasma mass spectrometry for ultrasensitive detection. Other proteins, such as immunoglobulin G, serum albumin, transferrin, fibrinogen, and lysozyme did not show interference with the assay for human alpha-thrombin. The detection limit of human alpha-thrombin was as low as 0.5 fmol, corresponding to 10 pM thrombin in 50 microL, and the dynamic range covered approximately 3 orders of magnitude.

Arsenic on the hands of children after playing in playgrounds.

Increasing concerns over the use of wood treated with chromated copper arsenate (CCA) in playground structures arise from potential exposure to arsenic of children playing in these playgrounds. Limited data from previous studies analyzing arsenic levels in sand samples collected from CCA playgrounds are inconsistent and cannot be directly translated to the amount of children’s exposure to arsenic. The objective of this study was to determine the quantitative amounts of arsenic on the hands of children in contact with CCA-treated wood structures or sand in playgrounds. We compared arsenic levels on the hands of 66 children playing in eight CCA playgrounds with levels of arsenic found on the hands of 64 children playing in another eight playgrounds not constructed with CCA-treated wood. The children’s age and duration of playtime were recorded at each playground. After play, children’s hands were washed in a bag containing 150 mL of deionized water. Arsenic levels in the hand-washing water were quantified by inductively coupled plasma mass spectrometry. Our results show that the ages of the children sampled and the duration of play in the playgrounds were similar between the groups of CCA and non-CCA playgrounds. The mean amount of water-soluble arsenic on children’s hands from CCA playgrounds was 0.50 μg (range, 0.0078–3.5 μg). This was significantly higher (p < 0.001) than the mean amount of water-soluble arsenic on children’s hands from non-CCA playgrounds, which was 0.095 μg (range, 0.011–0.41 μg). There was no significant difference in the amount of sand on the children’s hands and the concentration of arsenic in the sand between the CCA and non-CCA groups. The higher values of arsenic on the hands of children playing in the CCA playgrounds are probably due to direct contact with CCA-treated wood. Washing hands after play would reduce the levels of potential exposure because most of the arsenic on children’s hands was washed off with water. The maximum amount of arsenic on children’s hands from the entire group of study participants was < 4 μg, which is lower than the average daily intake of arsenic from water and food.

Effects of dietary folate intake and folate binding protein-1 (Folbp1) on urinary speciation of sodium arsenate in mice

In most mammalian species, arsenic biotransformation occurs primarily by biomethylation with dimethylarsinic acid being the predominant metabolite excreted in the urine. Folbp1 (folate binding protein-1) mediated intracellular folate uptake is one route by which cells harvest folate cofactors. In light of the likely relationship between folate biochemistry and arsenic biotransformation, our experiments were designed to test: (1) whether Folbp1 is an important determinant in arsenic biotransformation, by performing urinary arsenic speciation in Folbp1 nullizygous (Folbp1(-/-)) and wildtype control mice, and (2) whether dietary folate deficiency alters arsenic biotransformation in these mice. Compared to normal folate intake, folate deficiency caused lower amounts of arsenic to be excreted in the urine of both the wildtype controls and Folbp1(-/-) mice. Folbp1(-/-) mice excreted more dimethylarsinic acid than wildtype control mice during folate deficiency, but not during normal folate intake. The present data suggest that inadequate folate intake may result in decreased biotransformation and excretion of arsenic, which is likely to increase arsenic exposure and related toxicities.

Increased Mortality Associated with Well-Water Arsenic Exposure in Inner Mongolia, China

We conducted a retrospective mortality study in an Inner Mongolian village exposed to well water contaminated by arsenic since the 1980s. Deaths occurring between January 1, 1997 and December 1, 2004 were classified according to underlying cause and water samples from household wells were tested for total arsenic. Heart disease mortality was associated with arsenic exposure, and the association strengthened with time exposed to the water source. Cancer mortality and all-cause mortality were associated with well-water arsenic exposure among those exposed 10–20 years. This is the first study to document increased arsenic-associated mortality in the Bayingnormen region of Inner Mongolia.

Complementary chromatography separation combined with hydride generation―inductively coupled plasma mass spectrometry for arsenic speciation in human urine

This study aimed to establish complementary high performance liquid chromatography (HPLC) methods including three modes of separation: ion pairing, cation exchange, and anion exchange chromatography, with detection by inductively coupled plasma mass spectrometry (ICPMS). The ion pairing mode enabled the separation of inorganic arsenate (As(V)), monomethylarsonic acid (MMA(V)), and dimethylarsinic acid (DMA(V)). However, the ion pair mode was unable to differentiate inorganic arsenite (As(III)) from arsenobetaine (AsB); instead, cation exchange chromatography was used to isolate and quantify AsB. Anion exchange chromatography was able to speciate all of the aforementioned arsenic species. Potential inaccurate quantification problem with urine sample containing elevated concentration of AsB, which eluted immediately after As(III) in anion exchange or ion pairing mode, was overcame by introducing a post-column hydride generation (HG) derivatization step. Incorporating HG between HPLC and ICPMS improved sensitivity and specificity by differentiating AsB from hydride-forming arsenic species. This paper emphasizes the usefulness of complementary chromatographic separations in combination with HG-ICPMS to quantitatively determine concentrations of As(III), DMA(V), MMA(V), As(V), and AsB in the sub-microgram per liter range in human urine.

Comparative cytotoxicity of fourteen trivalent and pentavalent arsenic species determined using real-time cell sensing ☆

The occurrence of a large number of diverse arsenic species in the environment and in biological systems makes it important to compare their relative toxicity. The toxicity of arsenic species has been examined in various cell lines using different assays, making comparison difficult. We report real-time cell sensing of two human cell lines to examine the cytotoxicity of fourteen arsenic species: arsenite (AsIII), monomethylarsonous acid (MMAIII) originating from the oxide and iodide forms, dimethylarsinous acid (DMAIII), dimethylarsinic glutathione (DMAGIII), phenylarsine oxide (PAOIII), arsenate (AsV), monomethylarsonic acid (MMAV), dimethylarsinic acid (DMAV), monomethyltrithioarsonate (MMTTAV), dimethylmonothioarsinate (DMMTAV), dimethyldithioarsinate (DMDTAV), 3-nitro-4-hydroxyphenylarsonic acid (Roxarsone, Rox), and 4-aminobenzenearsenic acid (p-arsanilic acid, p-ASA). Cellular responses were measured in real time for 72hr in human lung (A549) and bladder (T24) cells. IC50 values for the arsenicals were determined continuously over the exposure time, giving rise to IC50 histograms and unique cell response profiles. Arsenic accumulation and speciation were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS). On the basis of the 24-hr IC50 values, the relative cytotoxicity of the tested arsenicals was in the following decreasing order: PAOIII≫MMAIII≥DMAIII≥DMAGIII≈DMMTAV≥AsIII≫MMTTAV>AsV>DMDTAV>DMAV>MMAV≥Rox≥p-ASA. Stepwise shapes of cell response profiles for DMAIII, DMAGIII, and DMMTAV coincided with the conversion of these arsenicals to the less toxic pentavalent DMAV. Dynamic monitoring of real-time cellular responses to fourteen arsenicals provided useful information for comparison of their relative cytotoxicity.

Arsenic speciation in the blood of arsenite-treated F344 rats.

Arsenic speciation in blood can improve understanding of the metabolism and toxicity of arsenic. In this study, arsenic species in the plasma and red blood cells (RBCs) of arsenite-treated female F344 rats were characterized using anion exchange and size exclusion chromatography separation with inductively coupled plasma mass spectrometry (ICPMS) and electrospray ionization tandem mass spectrometry (ESI MS/MS) detection. Arsenite (iAs(III)), arsenate (iAs(V)), monomethylarsonic acid (MMA(V)), dimethylarsinic acid (DMA(V)), trimethylarsine oxide (TMAO(V)), monomethylmonothioarsonic acid (MMMTA(V)), and dimethylmonothioarsinic acid (DMMTA(V)) were detected in the plasma, with DMA(V) being the predominant metabolite. Upon oxidative pretreatment with 5% hydrogen peroxide (H2O2), plasma proteins released bound arsenic in the form of DMA(V) as the major species and MMA(V) as the minor species. The ratio of protein-bound arsenic to total arsenic decreased with increasing dosage of iAs(III) administered to the rats, suggesting a possible saturation of the binding capacity of the plasma proteins. The proportion of the protein-bound arsenic in the plasma varied among rats. In the H2O2-treated lysates of red blood cells of rats, DMA(V) was consistently found as the predominant arsenic species, probably reflecting the preferential binding of dimethylarsinous acid (DMA(III)) to rat hemoglobin. iAs(V), MMA(V), and trimethylarsine oxide (TMAO(V)) were also detected in the hydrogen peroxide-treated lysates of red blood cells. Importantly, DMMTA(V) and MMMTA(V) have not been reported in rat blood, and the present finding of DMMTA(V) and MMMTA(V) in the rat plasma is toxicologically relevant because these pentavalent thioarsenicals are more toxic than their counterparts DMA(V) and MMA(V). Identifying novel thiolated arsenicals and determining protein-bound arsenicals in the blood provide useful insights into the metabolism and toxicity of arsenic in animals.

Inorganic Arsenic–Induced Intramitochondrial Granules in Mouse Urothelium

Based on epidemiological data, chronic exposure to high levels of inorganic arsenic in the drinking water is carcinogenic to the urinary bladder of humans. Recently, models have been developed involving transplacental administration of inorganic arsenic and subsequent administration of another substance that produces a low incidence of urogenital neoplasms. Administration of arsenite or arsenate in the diet or drinking water to five-to eight-week-old mice or rats rapidly induces urothelial cytotoxicity and regenerative hyperplasia. In mice administered arsenite, we observed eosinophilic intracytoplasmic granules present in the urothelial cells. These granules were not present in urothelial cells of untreated mice or in treated or untreated rats. By transmission electron microscopy, the granules were located within the mitochondrial matrix, that is, mitochondrial inclusions. Arsenic, primarily as arsenite, was present in partially purified mitochondria containing these granules. Cells containing the granules were not usually associated with degenerative changes. Lack of these granules in rats suggests that they are not necessary for inorganic arsenic–induced urothelial cytotoxicity or hyperplasia. These granules have also been observed with exposures to other metals in other tissues and other species, suggesting that they represent a protective mechanism against metal-induced toxicity.