Biological and behavioral factors modify urinary arsenic metabolic profiles in a U.S. population

BACKGROUND

Because some adverse health effects associated with chronic arsenic exposure may be mediated by methylated arsenicals, interindividual variation in capacity to convert inorganic arsenic into mono- and di-methylated metabolites may be an important determinant of risk associated with exposure to this metalloid. Hence, identifying biological and behavioral factors that modify an individual's capacity to methylate inorganic arsenic could provide insights into critical dose-response relations underlying adverse health effects.

METHODS

A total of 904 older adults (≥45 years old) in Churchill County, Nevada, who chronically used home tap water supplies containing up to 1850 μg of arsenic per liter provided urine and toenail samples for determination of total and speciated arsenic levels. Effects of biological factors (gender, age, body mass index) and behavioral factors (smoking, recent fish or shellfish consumption) on patterns of arsenicals in urine were evaluated with bivariate analyses and multivariate regression models.

RESULTS

Relative contributions of inorganic, mono-, and di-methylated arsenic to total speciated arsenic in urine were unchanged over the range of concentrations of arsenic in home tap water supplies used by study participants. Gender predicted both absolute and relative amounts of arsenicals in urine. Age predicted levels of inorganic arsenic in urine and body mass index predicted relative levels of mono- and di-methylated arsenic in urine. Smoking predicted both absolute and relative levels of arsenicals in urine. Multivariate regression models were developed for both absolute and relative levels of arsenicals in urine. Concentration of arsenic in home tap water and estimated water consumption were strongly predictive of levels of arsenicals in urine as were smoking, body mass index, and gender. Relative contributions of arsenicals to urinary arsenic were not consistently predicted by concentrations of arsenic in drinking water supplies but were more consistently predicted by gender, body mass index, age, and smoking.

CONCLUSIONS

These findings suggest that analyses of dose-response relations in arsenic-exposed populations should account for biological and behavioral factors that modify levels of inorganic and methylated arsenicals in urine. Evidence of significant effects of these factors on arsenic metabolism may also support mode of action studies in appropriate experimental models.

Cytotoxicity, apoptosis and DNA damage induced by Alpinia galanga rhizome extract

Alpinia galanga, or galangal, has been a popular condiment used in Thai and Asian cuisine for many years. However, relatively little is known of the potential beneficial or adverse health effects of this spice. This study was conducted to analyze the capacity of galangal extract to induce cytotoxicity and DNA damage in six different human cell lines including normal and p53-inactive fibroblasts, normal epithelial and tumour mammary cells and a lung adenocarcinoma cell line. We deliberately focused on treatment with the crude aqueous extract of galangal rhizomes, rather than compounds extracted into an organic solvent, to more closely reflect the mode of dietary consumption of galangal. The cell lines displayed a broad range of cytotoxicity. There was no evidence for preferential cytotoxicity of tumour cells, but there was an indication that p53-active cell lines may be more sensitive than their p53-inactive counterparts. The contribution of apoptosis to total cell killing was only appreciable after exposure to 300 microg/mL of extract. Apoptosis appeared to be independent of p53 expression. Exposure to as little as 100 microg/mL galangal extract generated a significant level of DNA single-strand breaks as judged by the single-cell gel electrophoresis technique (comet assay). The three major UV-absorbing compounds in the aqueous extract were identified by mass spectrometry as 1'-acetoxychavicol acetate and its deacetylated derivatives. However, when tested in A549 human lung adenocarcinoma cells, these compounds were not responsible for the cytotoxicity induced by the complete aqueous extract.

Human nails as a biomarker of arsenic exposure from well water in Inner Mongolia: comparing atomic fluorescence spectrometry and neutron activation analysis

Arsenic (As) is found naturally in the geological strata within the Ba Men Region of Inner Mongolia, China. A study was conducted to compare the total As measurements from two analytical techniques: instrumental neutron activation analysis (INAA) and atomic fluorescence spectrometry (AFS), and to verify nails as an exposure biomarker in this population. In 1999, nail and water samples were collected in a pilot study. Fingernails and toenails were pooled from 32 participants and analysed for total As by both INAA and AFS. Mean nail As values were 14.8+/-2.4 and 19.4+/-2.8 microg g-1 (+/-SEM) for INAA and AFS, respectively. Results from these two methods were significantly correlated (r=0.93, p<0.0001). In 2000, a second study was conducted and INAA was used to measure total As in toenails from 314 Ba Men residents. Well water samples were collected from 121 households and analysed by AFS. A significant correlation was observed between toenail and well water As (r=0.84, p<0.0001). Based on the results, INAA was significantly correlated with AFS and proved to be a reliable measure of nail As levels. In this population, toenail samples are a useful internal As exposure biomarker from drinking water sources.

Factors influencing the removal of thymine glycol from DNA in gamma-irradiated human cells

The toxic and mutagenic effects of ionizing radiation are believed to be caused by damage to cellular DNA. We have made use of a novel immunoassay for thymine glycol to examine the removal of this lesion from the DNA of irradiated human cells. Because of the sensitivity of the assay, we have been able to keep the radiation doses at or below the standard clinical dose of 2 Gy. Our initial observations indicated that although removal of thymine glycol is > 80% complete by 4 h post-irradiation with 2 Gy, there is a lag of 30-60 min before repair commences. However, if cells are irradiated with 0.25 Gy 4 h prior to the 2-Gy dose, removal of the thymine glycols commences immediately after the second irradiation, suggesting that repair of thymine glycol is inducible. Our current studies are directed at two aspects of the repair process, (1) factors involved in the repair process leading up to and including glycosylase-mediated removal of thymine glycol and (2) the control of the inducible response. We have observed that mutation of the XPG gene drastically reduced the level and rate of global removal of thymine glycol (induced by 2-Gy irradiation), and there was no evidence for an inducible response. Similar results were seen with a Cockayne syndrome B (CSB) cell line. We have also examined repair in quiescent and phytohemagglutinin-stimulated human lymphocytes. Both show similar kinetics for the rate of removal of thymine glycol under induced and noninduced conditions.

Detection of human immunodeficiency virus type 1 reverse transcriptase using aptamers as probes in affinity capillary electrophoresis

An affinity capillary electrophoresis/laser-induced fluorescence (CE/LIF) assay was developed for direct and specific detection of reverse transcriptase (RI) of the type 1 human immunodeficiency virus (HIV-1) using fluorescently labeled single-stranded DNA aptamers as probes. The aptamer used (RT 26) is specific for HIV-1 RT, and it exhibited no cross-reactivity with RTs of the enhanced avian myeloblastosis virus (AMV), the Moloney murine leukemia virus (MMLV), or denatured HIV-1 RT. An affinity complex of RT 26-HIV-1 RT was readily formed, and calibration curves were linear up to 50 nM (6 microg/mL) HIV-1 RT concentration, with both the free probe and complex peak usable for analytical quantitation. Cell culture media (RPMI with 10% fetal bovine serum) interfered with the assay and aptamer-HIV-1 RT binding. Nonspecific binding was observed in low or undiluted culture, necessitating at least 100-fold dilution for analysis of raw culture samples.

Analyses of micronuclei in exfoliated epithelial cells from individuals chronically exposed to arsenic via drinking water in inner Mongolia, China

The groundwater in Bayingnormen (Ba Men), located in Central West Inner Mongolia, China, is naturally contaminated with arsenic at concentrations ranging from 50 microg/L to 1.8 mg/L. Various adverse health effects in this region, including cancer, have been linked to arsenic exposure via drinking water. A pilot study was undertaken to evaluate frequencies of micronuclei (MN), as measures of chromosomal alterations, in multiple exfoliated epithelial cell types from residents of Ba Men chronically exposed to arsenic via drinking water. Buccal mucosal cells, airway epithelial cells in sputum, and bladder urothelial cells were collected from 19 residents exposed to high levels of arsenic in drinking water (527.5 +/- 24 microg/l), and from 13 control residents exposed to relatively low levels of arsenic in drinking water (4.4 +/- microg/L). Analytical results from these individuals revealed that MN frequencies in the high-exposure group were significantly elevated to 3.4-fold over control levels for buccal and sputum cells, and to 2.7-fold over control for bladder cells (increases in MN frequency significant at p < .001 for buccal cells; p < .01 for sputum cells; p < .05 for bladder cells). When smokers were excluded from high-exposure and control groups the effects of arsenic were observed to be greater, although only in buccal and sputum cells; approximately 6-fold increases in MN frequency occurred in these tissues. The results indicate that residents of Ba Men chronically exposed to high levels of arsenic in drinking water reveal evidence of genotoxicity in multiple epithelial cell types; higher levels of induced MN were observed in buccal and sputum cells than in bladder cells.

Synthesis, characterization, and applications of a fluorescent probe of DNA damage

We have designed and generated a 90-mer oligonucleotide that contains a single adduct of benzo[a]pyrene diol epoxide (BPDE) and that is fluorescently labeled. The known amount of BPDE adduct in a given length of DNA makes this probe a useful standard for DNA damage assay. The BPDE-90-mer was fluorescently labeled with tetramethylrhodamine to allow for high sensitivity detection with laser-induced fluorescence (LIF). The binding of both double-stranded and single-stranded BPDE-90-mer with three anti-BPDE antibodies was studied using affinity capillary electrophoresis (CE). Formation of antibody complex with BPDE-90-mer results in a shift in migration time from that of the unbound BPDE-90-mer. Affinity CE/LIF studies suggest that antibody 8E11 has high-affinity suitable for immunoassay of BPDE-DNA adducts. A competitive immunoassay using the fluorescent probe and CE/LIF is demonstrated for the analysis of BPDE-DNA adducts in A549 human lung carcinoma cells incubated with 2.5, 5, and 10 microM BPDE for 2 h. The design of the 90-mer probe is flexible to substitute different DNA damage types with relative ease. The fluorescent 90-mer is composed of six shorter oligonucleotides. The sequence of the two center oligonucleotides may be changed depending on the desired DNA lesion measurement. By inserting different damaged oligonucleotides, a variety of DNA damage systems can be investigated using the same CE/LIF approach.

Detection of DNA adducts of benzo[a]pyrene using immunoelectrophoresis with laser-induced fluorescence. Analysis of A549 cells

Detection of benzo[a]pyrene diol epoxide (BPDE)-damaged DNA in a human lung carcinoma cell line (A549) has been performed using free zone affinity capillary electrophoresis with laser-induced fluorescence (LIF). Using BPDE as a model carcinogenic compound, the speed, sensitivity and specificity of this technique was demonstrated. Under free zone conditions, an antibody bound adduct was baseline-resolved from an unbound adduct in less than 2 min. The efficiencies of separation were in excess of 6 x 10(5) and 1 x 10(6) plates per meter for the antibody-bound and unbound adducts, respectively. Separation using a low ionic strength buffer permitted the use of a high electric field (830 V/cm) without the loss of resolving power. Using LIF detection, a concentration detection limit of roughly 3 x 10(-10) M was achieved for a 90-mer oligonuleotide containing a single BDPE. The use of formamide in the incubation buffer to enhance denaturing of DNA did not affect the stability of the complex between the antibody and the adducts. Using a fluorescently labeled BPDE-modified DNA adduct probe, a competitive assay was established to determine the levels of BPDE-DNA adducts in A549 cells.

Speciation of arsenic using solid phase extraction cartridges

Various solid phase extraction (SPE) cartridges were investigated for speciation of arsenite [As(III)], arsenate [As(v)], monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). Cartridges containing different types of sorbent materials were tested for arsenic retention and elution characteristics. Alumina cartridges were found to completely retain all the four target arsenic species, and are suitable for removal and preconcentration purposes. For speciation analysis, different arsenic species were separated on the basis of their selective retention on and elution from specific cartridges. DMA was retained on a resin-based strong cation exchange cartridge and eluted with 1.0 M HCl. MMA and As(v) were both retained on a silica-based strong anion exchange cartridge and sequentially eluted with 60 mM acetic acid (for MMA) and 1.0 M HCl [for As(v)]. As(III) was not retained on either cartridge and remained in solution. Arsenic species in solution and those eluted from the cartridges were subsequently quantified by using flow injection with hydride generation atomic fluorescence spectrometry (FI-HGAFS) and hydride generation atomic absorption spectrometry (FI-HGAAS). A detection limit of 0.05 microg L(-1) arsenic in water sample was achieved using HGAFS. An application of the method was demonstrated at a drinking water treatment facility. As(III) and As(v) species were determined in water at various stages of treatment. The method is suitable for routine determination of trace levels of arsenic in drinking water to comply with more stringent environmental regulations.

Studies of protein--DNA interactions by capillary electrophoresis/laser-induced fluorescence polarization

Protein-DNA interactions were studied on the basis of capillary electrophoretic separation of bound from free fluorescent probe followed by on-line detection with laser-induced fluorescence polarization. Changes in electrophoretic mobility and fluorescence anisotropy upon complex formation were monitored for the determination of binding affinity and stoichiometry. The method was applied to study the interactions of single-stranded DNA binding protein (SSB) with synthetic oligonucleotides and single-stranded DNA. Increases in fluorescence anisotropy and decreases in electrophoretic mobility upon their binding to SSB were observed for the fluorescently labeled 11-mer and 37-mer oligonucleotide probes. Fluorescence anisotropy and electrophoretic mobility were used to determine the binding constants of the SSB with the 11-mer (5 x 10(6) M(-1)) and the 37-mer (23 x 10(6) M(-1)). Alternatively, a fluorescently labeled SSB was used as a probe, and the formation of multiple protein-DNA complexes that differ in stoichiometry was observed. The results demonstrate the applicability of the method to study complex interactions between protein and DNA.

Speciation of key arsenic metabolic intermediates in human urine

Biomethylation is the major human metabolic pathway for inorganic arsenic, and the speciation of arsenic metabolites is essential to a better understanding of arsenic metabolism and health effects. Here we describe a technique for the speciation of arsenic in human urine and demonstrate its application to the discovery of key arsenic metabolic intermediates, monomethylarsonous acid (MMAIII) and dimethylarsinous acid (DMAIII), in human urine. The study provides a direct evidence in support of the proposed arsenic methylation pathway in the human. The finding of MMAIII and DMAIII in human urine, along with recent studies showing the high toxicity of these arsenicals, suggests that the usual belief of arsenic detoxification by methylation needs to be reconsidered. The arsenic speciation technique is based on ion pair chromatographic separation of arsenic species on a 3-micron particle size column at 50 degrees C followed by hydride generation atomic fluorescence detection. Speciation of MMAIII, DMAIII, arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV) in urine samples is complete in 6 min with detection limits of 0.5-2 micrograms/L. There is no need for any sample pretreatment. The capability of rapid analysis of trace levels of arsenic species, which resulted in the findings of the key metabolic intermediates, makes the technique useful for routine arsenic speciation analysis required for toxicological and epidemiological studies.

Determination of monomethylarsonous acid, a key arsenic methylation intermediate, in human urine

In this study we report on the finding of monomethylarsonous acid [MMA(III)] in human urine. This newly identified arsenic species is a key intermediate in the metabolic pathway of arsenic biomethylation, which involves stepwise reduction of pentavalent to trivalent arsenic species followed by oxidative addition of a methyl group. Arsenic speciation was carried out using ion-pair chromatographic separation of arsenic compounds with hydride generation atomic fluorescence spectrometry detection. Speciation of the inorganic arsenite [As(III)], inorganic arsenate [As(V)], monomethylarsonic acid [MMA(V)], dimethylarsinic acid [DMA(V)], and MMA(III) in a urine sample was complete in 5 min. Urine samples collected from humans before and after a single oral administration of 300 mg sodium 2,3-dimercapto-1-propane sulfonate (DMPS) were analyzed for arsenic species. MMA(III) was found in 51 out of 123 urine samples collected from 41 people in inner Mongolia 0-6 hr after the administration of DMPS. MMA(III )in urine samples did not arise from the reduction of MMA(V) by DMPS. DMPS probably assisted the release of MMA(III) that was formed in the body. Along with the presence of MMA(III), there was an increase in the relative concentration of MMA(V) and a decrease in DMA(V) in the urine samples collected after the DMPS ingestion.

Measuring DNA damage using capillary electrophoresis with laser-induced fluorescence detection

Damage to cellular DNA is implicated in the early stages of carcinogenesis and in the cytotoxicity of many anticancer agents, including ionizing radiation. Sensitive techniques are required for measuring cellular levels of DNA damage. We describe in detail a novel immunoassay that makes use of the resolving power of capillary electrophoresis and the sensitivity of laser-induced fluorescence detection. An example is given of the detection of thymine glycol in DNA produced by irradiation of human cells with a clinical dose of 2 Gy. A detection limit of approximately 10(-21) mol allowed us to monitor the repair of the lesion and to suggest that the cellular repair response may be inducible.

Occurrence of monomethylarsonous acid in urine of humans exposed to inorganic arsenic

Monomethylarsonous acid (MMA(III)) has been detected for the first time in the urine of some humans exposed to inorganic arsenic in their drinking water. Our experiments have dealt with subjects in Romania who have been exposed to 2.8, 29, 84, or 161 microg of As/L in their drinking water. In the latter two groups, MMA(III) was 11 and 7% of the urinary arsenic while the monomethylarsonic acid (MMA(V)) was 14 and 13%, respectively. Of our 58 subjects, 17% had MMA(III) in their urine. MMA(III) was not found in urine of any members of the group with the lowest level of As exposure. If the lowest-level As exposure group is excluded, 23% of our subjects had MMA(III) in their urine. Our results indicate that (a) future studies concerning urinary arsenic profiles of arsenic-exposed humans must determine MMA(III) concentrations, (b) previous studies of urinary profiles dealing with humans exposed to arsenic need to be re-examined and re-evaluated, and (c) since MMA(III) is more toxic than inorganic arsenite, a re-examination is needed of the two hypotheses which hold that methylation is a detoxication process for inorganic arsenite and that inorganic arsenite is the major cause of the toxicity and carcinogenicity of inorganic arsenic.

DMPS-arsenic challenge test. II. Modulation of arsenic species, including monomethylarsonous acid (MMA(III)), excreted in human urine

The administration of sodium 2,3-dimercapto-1-propane sulfonate (DMPS) to humans chronically exposed to inorganic arsenic in their drinking water resulted in the increased urinary excretion of arsenic, the appearance and identification of monomethylarsonous acid (MMA(III)) in their urine, and a large decrease in the concentration and percentage of urinary dimethylarsinic acid (DMA). This is the first time that MMA(III) has been detected in the urine. In vitro biochemical experiments were then designed and performed to understand the urinary appearance of MMA(III) and decrease of DMA. The DMPS-MMA(III) complex was not active as a substrate for the MMA(III) methyltransferase. The experimental results support the hypothesis that DMPS competes with endogenous ligands for MMA(III), forming a DMPS-MMA complex that is readily excreted in the urine and points out the need for studying the biochemical toxicology of MMA(III). It should be emphasized that MMA(III) was excreted in the urine only after DMPS administration. The results of these studies raise many questions about the potential central role of MMA(III) in the toxicity of inorganic arsenic and to the potential involvement of MMA(III) in the little-understood etiology of hyperkeratosis, hyperpigmentation, and cancer that can result from chronic inorganic arsenic exposure.

Sample preparation and storage can change arsenic speciation in human urine

BACKGROUND

Stability of chemical speciation during sample handling and storage is a prerequisite to obtaining reliable results of trace element speciation analysis. There is no comprehensive information on the stability of common arsenic species, such as inorganic arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid, dimethylarsinic acid, and arsenobetaine, in human urine.

METHODS

We compared the effects of the following storage conditions on the stability of these arsenic species: temperature (25, 4, and -20 degrees C), storage time (1, 2, 4, and 8 months), and the use of additives (HCl, sodium azide, benzoic acid, benzyltrimethylammonium chloride, and cetylpyridinium chloride). HPLC with both inductively coupled plasma mass spectrometry and hydride generation atomic fluorescence detection techniques were used for the speciation of arsenic.

RESULTS

We found that all five of the arsenic species were stable for up to 2 months when urine samples were stored at 4 and -20 degrees C without any additives. For longer period of storage (4 and 8 months), the stability of arsenic species was dependent on urine matrices. Whereas the arsenic speciation in some urine samples was stable for the entire 8 months at both 4 and -20 degrees C, other urine samples stored under identical conditions showed substantial changes in the concentration of As(III), As(V), monomethylarsonic acid, and dimethylarsinic acid. The use of additives did not improve the stability of arsenic speciation in urine. The addition of 0.1 mol/L HCl (final concentration) to urine samples produced relative changes in inorganic As(III) and As(V) concentrations.

CONCLUSIONS

Low temperature (4 and -20 degrees C) conditions are suitable for the storage of urine samples for up to 2 months. Untreated samples maintain their concentration of arsenic species, and additives have no particular benefit. Strong acidification is not appropriate for speciation analysis.

Capillary electrophoretic immunoassays for digoxin and gentamicin with laser-induced fluorescence polarization detection

New immunoassays for therapeutic drugs digoxin and gentamicin have been described, which involved the separation of free and antibody-bound drug by capillary electrophoresis (CE) and the detection by laser-induced fluorescence polarization (LIFP). While the fluorescein-labeled digoxin and gentamicin (tracers) displayed negligible fluorescence polarization in solution, the complex formation between these small molecules and their antibodies resulted in substantial increases in fluorescence polarization due to the increase in molecular size. The LIFP detection, capable of measuring vertically and horizontally polarized fluorescence components simultaneously, provides enhanced capability for the identification of complex in capillary electrophoretic immunoassays. Proper adjustments of the running buffer pH and the ratio of antibody to tracer are essential for optimization of the performance of these assays. The digoxin-antibody complex remained stable during CE separation with running buffer pH ranging from 9.3 to 12. Calibration curves covering a concentration range of 0.05 to 0.5 ng/ml were obtained with a running buffer of pH 12. The concentration and mass detection limits were 0.02 ng/ml and 26 zmol, respectively. For gentamicin assay, the running buffer pH 10 was used to reduce the adsorption of the tracer while minimizing the dissociation of the antibody-tracer complex during the separation. The calibration curves covered a concentration range 0.05-1.0 microg/ml, with a concentration detection limit of 25 ng/ml and a mass detection limit of 52 amol of gentamicin.

Fluorescence polarization studies of affinity interactions in capillary electrophoresis

Capillary electrophoresis (CE) combined with molecular recognition for ultrasensitive bioanalytical applications often requires the formation of stable complexes between an analyte and its binding partner. Previous studies of binding interactions using CE involve multiple-step titration experiments and are time-consuming. We describe a simple method based on laser-induced fluorescence polarization (LIFP) detection for CE separation, which allows for on-line monitoring of affinity complex formation. Because fluorescence polarization is sensitive to changes in the rotational diffusion arising from molecular association or dissociation, it is capable of providing information on the formation of affinity complexes prior to or during CE separation. Applications of the CE/LIFP method to three binding systems including vancomycin and its antibody, staphylococcal enterotoxin A and its antibody, and trp operator and trp repressor were demonstrated, representing peptide-protein, protein-protein, and DNA-protein interactions. The affinity complexes were readily distinguished from the unbound molecules on the basis of their fluorescence polarization. The relative increase in fluorescence polarization upon complex formation varied with the molecular size of the binding pairs.

Capillary electrophoresis coupled with laser-induced fluorescence polarization as a hybrid approach to ultrasensitive immunoassays

Immunoassays using capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) is a powerful approach to the determination of trace amounts of analytes in a complex biological matrix. However, its applicability is limited by the requirement that the free and bound tracer (fluorescently labeled compound) be resolved for their identification and quantitation. Here we show that replacing LIF with laser-induced fluorescence polarization (LIFP) permits ultrasensitive immunoassays to be performed with or without the separation of the free and bound tracer. A binding system involving cyclosporin A (CyA) and monoclonal antibody to CyA was chosen to demonstrate both homogeneous and heterogeneous immunoassay approaches. In the homogeneous scheme where the free and bound tracer were not separated, the fluorescence polarization of the mixture was a quantitative measure of the antibody-bound tracer. The concentration and mass detection limits for CyA using the homogeneous competitive assay were found to be 1 nM and 1 amol (10(-18) mol), respectively. The heterogeneous assay involved a nearly baseline separation of the free and bound tracer using CE with a phosphate running buffer of pH 7.0. The complex of the tracer with the antibody had a fluorescence polarization of approximately 0.24 whereas the free tracer had negligible polarization. The fluorescence polarization was independent of analyte concentration, and the fluorescence intensity of either the free or bound tracer was used for quantitation. Results from both assays suggest that the CE-LIFP approaches may have a wider application than the immunoassays based on either CE-LIF or fluorescence polarization alone.

Competitive immunoassay for staphylococcal enterotoxin A using capillary electrophoresis with laser-induced fluorescence detection

Staphylococcal enterotoxins are a family of toxic proteins secreted by S. aureus. Using capillary electrophoresis (CE) linked with laser-induced fluorescence, a highly sensitive and selective assay using antibody-antigen recognition was developed for the determination of Staphylococcal enterotoxin A. Staphylococcal enterotoxin A (SEA) was chemically labeled with fluorescein and the product was used as a fluorescent tracer. A competitive assay was developed to detect SEA at concentrations between 0.3 nM and 6.5 nM with standard deviations of less than 5%. The detection limit was found to be 3 amol with the potential improvement by further optimization of the assay. No cross-reactivity between staphylococcal enterotoxin B and the SEA antibody was found at the concentrations used for the CE immunoassay.

Excretion of arsenic in urine as a function of exposure to arsenic in drinking water

Urinary arsenic (As) concentrations were evaluated as a biomarker of exposure in a U.S. population chronically exposed to inorganic As (InAs) in their drinking water. Ninety-six individuals who consumed drinking water with As concentrations of 8-620 microg/L provided first morning urine voids for up to 5 consecutive days. The study population was 56% male, and 44% was younger than 18 years of age. On one day of the study period, all voided urines were collected over a 24-hr period. Arsenic intake from drinking water was estimated from daily food diaries. Comparison between the concentration of As in individual urine voids with that in the 24-hr urine collection indicated that the concentration of As in urine was stable throughout the day. Comparison of the concentration of As in each first morning urine void over the 5-day study period indicated that there was little day-to-day variation in the concentration of As in urine. The concentration of As in drinking water was a better predictor of the concentration of As in urine than was the estimated intake of As from drinking water. The concentration of As in urine did not vary by gender. An age-dependent difference in the concentration of As in urine may be attributed to the higher As dosage rate per unit body weight in children than in adults. These findings suggest that the analysis of a small number of urine samples may be adequate to estimate an individual's exposure to InAs from drinking water and that the determination of the concentration of InAs in a drinking water supply may be a useful surrogate for estimating exposure to this metalloid.

Zinc exposure in Chinese foundry workers

BACKGROUND

Inhalational exposure to zinc oxide fumes is associated with metal fume fever, a self-limited but very uncomfortable condition closely resembling influenza. Very little is known regarding the toxicokinetics of inhaled zinc, making the interpretation of zinc measurements in serum and urine problematic.

METHODS

Twenty workers in a zinc foundry in Baiyin, Peoples' Republic of China, were investigated with serial examinations by a physician, chest radiographs, and spirometry. Exposure assessment consisted of the measurement of zinc in serum, urine, and personal air samples.

RESULTS

No cases of metal fume fever were observed during the study period despite exposures to as high as 36.3 mg/m3 over less than 4 hr. In addition, no radiographic or functional changes were noted. Serum zinc levels of all workers were within the reference range and did not correlate with external exposure measurements. However, elevations were noted in urinary zinc levels, which showed a significant association (Spearman's correlation coefficient = 0.47, P = 0.04) between exposure to zinc and urine zinc.

CONCLUSIONS

These results provide exposure measurements for zinc at which workers demonstrate tolerance to the development of metal fume fever. Furthermore, they suggest that urine may be the preferred biological medium for the assessment of zinc exposure.

Single cell studies of enzymatic hydrolysis of a tetramethylrhodamine labeled triglucoside in yeast

Several hundred molecules of enzyme reaction products were detected in a single spheroplast from yeast cells incubated with a tetramethylrhodamine (TMR) labeled triglucoside, alpha-d-Glc(1-->2)alpha-d-Glc(1-->3)alpha-d-Glc-O(CH2)8CONHCH2- CH2NH- COTMR. Product detection was accomplished using capillary electrophoresis and laser induced fluorescence following the introduction of a single spheroplast into the separation capillary. The in vivo enzymatic hydrolysis of the TMR-trisaccharide involves at least two enzymes, limited by processing alpha-glucosidase I, producing TMR-disaccharide, TMR-monosaccharide, and the free TMR-linking arm. Hydrolysis was reduced by preincubation of the cells with the processing enzyme inhibitor castanospermine. Confocal laser scanning microscopy studies confirmed the uptake and internalization of fluorescent substrate. This single cell analysis methodology can be applied for the in vivo assay of any enzyme with a fluorescent substrate.

Competitive immunoassay for cyclosporine using capillary electrophoresis with laser induced fluorescence polarization detection

Frequent monitoring of immunosuppressive drug cyclosporine A (CsA) in blood samples of tissue transplant patients is required in clinical practice because of the narrow therapeutic range between the immunosuppressive effect and the toxic effect of this drug. We describe a competitive immunoassay capillary electrophoresis (CE) with laser induced fluorescence polarization detection method, which is rapid and sensitive for the determination of CsA. The method is based on the competitive immunochemical reaction between the analyte and fluorescent hapten (CsA*) with the antibody, CE separation of the antibody bound and free fluorescent CsA*, followed by the laser induced fluorescence polarization detection (LIFP) of the fluorescent species. The method detection limit is governed by the stability of the antibody-CsA* complex rather than by the detector noise. The use of post-column sheath flow cuvette LIFP detection resulted in excellent detection limit, typically 0.9 nM (or 9.10(-19) mol for 1 nl injection) of CsA. CsA in whole blood samples from organ transplant patients were measured and results agreed well with those obtained by using a standard fluorescence polarization immunoassay. Each determination took less than 3 min. The CsA metabolites AM9 and AM19 were also determined by using this technique, and their cross-reactivities with the antibody were 13% and 2%, respectively.

Inducible repair of thymine glycol detected by an ultrasensitive assay for DNA damage

An ultrasensitive assay for measuring DNA base damage is described that couples immunochemical recognition with capillary electrophoresis and laser-induced fluorescence detection. The method provides a detection limit of 3 x 10(-21) moles, an improvement of four to five orders of magnitude over current methods. Induction and repair of thymine glycols were studied in irradiated A549 cells (a human lung carcinoma cell line). Exposure of these cells to a low dose of radiation (0.25 Gray) 4 hours before a clinically relevant dose (2 Gray) enhanced removal of thymine glycols after the higher dose. These data provide evidence for an inducible repair response for radiation-induced damage to DNA bases.

Short-column liquid chromatography with hydride generation atomic fluorescence detection for the speciation of arsenic

Increasing concerns over human exposure to arsenic and more stringent environmental regulations require rapid determination of trace levels of individual arsenic species, which presents an analytical challenge. We describe a method that is capable of speciating nanogram-per-milliliter levels of arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMAA), and dimethylarsinic acid (DMAA) within 3 min. Speciation of two common inorganic species in drinking water, As(III) and As(V), is complete in 1.5 min. The method is based on a combination of fast high-performance liquid chromatography (HPLC) separation of arsenic species on 3-cm HPLC guard columns and the sensitive detection of arsenic hydride by atomic fluorescence spectrometry. Detection limits for the four arsenic species in urine samples are 0.4-0.8 ng/mL. This simple method allows for the direct speciation of arsenic present in natural water samples and in human urine samples from the general population, with no need of any sample pretreatment. Our results from the determination of arsenic species in urine and water standard reference materials are in good agreement with the certified values of total arsenic concentration. The method has been successfully applied to speciation studies of metabolism of arsenosugars following the consumption of arsenosugar-containing mussels by human volunteers. Speciation of arsenic in urine samples collected from four volunteers after the ingestion of musseles reveals significant increases of DMAA concentration, resulting from the metabolism of arsenosugars. These results suggest that the commonly used biomarkers for assessing human exposure to inorganic arsenic, which are based on the determination of urinary arsenite, arsenate, MMAA, and DMAA, are not reliable when arsenosugar-containing seafood is ingested.

Effect of arsenosugar ingestion on urinary arsenic speciation

We developed and evaluated a method for the determination of microgram/L concentrations of individual arsenic species in urine samples. We have mainly studied arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMAA), and dimethylarsinic acid (DMAA) because these are the most commonly used biomarkers of exposure by the general population to inorganic arsenic and because of concerns over these arsenic species on their toxicity and carcinogenicity. We have also detected five unidentified urinary arsenic species resulting from the metabolism of arsenosugars. We combined ion pair liquid chromatography with on-line hydride generation and subsequent atomic fluorescence detection (HPLC/HGAFS). Detection limits, determined as three times the standard deviation of the baseline noise, are 0.8, 1.2, 0.7, and 1.0 mu/L arsenic for arsenite, arsenate, MMAA, and DMAA, respectively. These correspond to 16, 24, 14, and 20 pg of arsenic, respectively, for a 20-muL sample injected for analysis. The excellent detection limit enabled us to determine trace concentrations of arsenic species in urine samples from healthy subjects who did not have excess exposure to arsenic. There was no need for any sample pretreatment step. We used Standard Reference Materials, containing both normal and increased concentrations of arsenic, to validate the method. Interlaboratory studies with independent techniques also confirmed the results obtained with the HPLC/HGAFS method. We demonstrated an application of the method to the determination of arsenic species in urine samples after the ingestion of seaweed by four volunteers. We observed substantial increases of DMAA concentrations in the samples collected from the volunteers after the consumption of seaweed. The increase of urinary DMAA concentration is due to the metabolism of arsenosugars that are present in the seaweed. Our results suggest that the commonly used biomarkers of exposure to inorganic arsenic, based on the measurement of arsenite, arsenate, MMAA, and DMAA, are not reliable when arsenosugars are ingested from the diet.

Study of the enzymatic transformation of fluorescently labeled oligosaccharides in human epidermoid cells using capillary electrophoresis with laser-induced fluorescence detection

Isomeric oligosaccharides of both beta Gal(1-->3)beta GlcNAc (type I) series and beta Gal(1-->4)beta GlcNAc (type II) series were studied by using capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. A mixture of phenylboronic acid and sodium tetraborate was used in the CE running buffers to improve the electrophoretic separation of the oligosaccharides. Both series of the tetramethylrhodamine (TMR)-labeled substrates [beta Gal(1-->3)beta GlcNAc-O-TMR and beta Gal(1-->4)beta GlcNAc-O-TMR) and their potential enzymatic products were baseline resolved using CE. The high resolution provided by CE and the excellent detection limit (8.10(-23) mol, or 50 molecules) by LIF allowed for the determination of minor enzyme products in the presence of excess unreacted substrate. The action of competing enzymes acting on the common type I sequence was monitored after the incubation of human epidermoid carcinoma cells (A431) with a fluorescent substrate (beta Gal(1-->3)beta GlcNAc-O-TMR). The CE-LIF analyses showed the formation of both synthetic and hydrolytic products, suggesting the actions of glycosyltransferases and glycosidases in the cells.

Human urinary arsenic excretion after one-time ingestion of seaweed, crab, and shrimp

We studied chemical speciation of arsenic compounds in urine samples by using HPLC with inductively coupled plasma mass spectrometry detection. We examined urinary arsenic excretion patterns and the arsenic species excreted from nine human subjects who ingested seaweed products and crab (or shrimp). Fast urinary excretion of unchanged arsenobetaine was seen after ingestion of crab and shrimp, which contain arsenobetaine as the major arsenic species. In contrast, the arsenosugars, which comprise the major arsenic species in seaweed, are metabolized and have a longer retention time in the human body. When nine volunteers ingested the commercial seaweed product nori, both the urinary arsenic excretion pattern and the excreted arsenic species varied from individual to individual, and as many as six metabolites could be detected. It seems that arsenosugars are not decomposed by stomach acid and that reactions involving enzymatic and (or) microbial activity in the human body may be responsible for the metabolism of arsenosugars.

Human urinary arsenic excretion after one-time ingestion of seaweed, crab, and shrimp

We studied chemical speciation of arsenic compounds in urine samples by using HPLC with inductively coupled plasma mass spectrometry detection. We examined urinary arsenic excretion patterns and the arsenic species excreted from nine human subjects who ingested seaweed products and crab (or shrimp). Fast urinary excretion of unchanged arsenobetaine was seen after ingestion of crab and shrimp, which contain arsenobetaine as the major arsenic species. In contrast, the arsenosugars, which comprise the major arsenic species in seaweed, are metabolized and have a longer retention time in the human body. When nine volunteers ingested the commercial seaweed product nori, both the urinary arsenic excretion pattern and the excreted arsenic species varied from individual to individual, and as many as six metabolites could be detected. It seems that arsenosugars are not decomposed by stomach acid and that reactions involving enzymatic and (or) microbial activity in the human body may be responsible for the metabolism of arsenosugars.