Distribution and speciation of arsenic after intravenous administration of monomethylmonothioarsonic acid in rats.

Quite a few new thioarsenicals have recently been found in urine of arsenic-exposed humans and animals, and some of them have been shown to be highly toxic to cells. However, little is known about their toxic effects and metabolism in the body. In order to elucidate the toxic mechanism of thioarsenicals, we further focused on the distribution and metabolism of monomethylmonothioarsonic acid (MMMTA(V)) in rats. MMMTA(V) was synthesized chemically and injected intravenously into rats at the dose of 0.5mg As/kg, followed by speciation analysis of selected organs and body fluids at 10 min and 12h after the injection. MMMTA(V) was excreted into urine in its intact form, and approximately 35% of the dose was recovered in urine at 12h after the injection, suggesting that MMMTA(V) was taken up more effectively by organs/tissues than non-thiolated, monomethylarsonous acid (MMA(V)) previously studied. On the other hand, the liver and kidneys contained arsenic that was in a protein-binding form with free forms of DMA(V) or DMDTA(V) at 10 min, and disappeared at 12h after the injection. Moreover, these bound arsenic species in kidneys were converted back to MMA(V) after oxidation with H(2)O(2), suggesting that the arsenic bound to proteins had been reduced within the body and was in a trivalent oxidation state. In red blood cells (RBCs), most of the arsenic was in the form of DMA(III) bound to hemoglobin (Hb), and approximately 40% of the dose was recovered in RBCs at 12h after injection. These results indicate that arsenic accumulated preferentially in RBCs after being transformed to DMA(III). In addition, we have also discussed the effect of MMMTA(V) on viability of human bladder cancer T24 cells in comparison with MMA(V). Consequently, MMMTA(V) was assumed to be a more toxic arsenic metabolite than non-thiolated MMA(V).

Distribution and metabolism of four different dimethylated arsenicals in hamsters.

Arsenic toxicity and distribution are highly dependent on animal species and its chemical species. Recently, thioarsenical has been recognized in highly toxic arsenic metabolites, which was commonly found in human and animal urine. In the present study, we revealed the mechanism underlying the distribution and metabolism of non-thiolated and thiolated dimethylarsenic compounds such as dimethylarsinic acid (DMA(V)), dimethylarsinous acid (DMA(III)), dimethylmonothioarsinic acid (DMMTA(V)), and dimethyldithioarsinic acid (DMDTA(V)) after the administration of them into femoral vein of hamsters. DMA(V) and DMDTA(V) distributed in organs and body fluids were in their unmodified form, while DMA(III) and DMMTA(V) were bound to proteins and transformed to DMA(V) in organs. On the other hand, DMA(V) and DMDTA(V) were mostly excreted into urine as their intact form 1 h after post-injection, and more than 70% of the doses were recovered in urine as their intact form. By contrast, less than 8-14% of doses were recovered in urine as DMA(V), while more than 60% of doses were distributed in muscles and target organs (liver, kidney, and lung) of hamsters after the injection of DMMTA(V) and DMA(III). However, in red blood cells (RBCs), only a small amount of the arsenicals was distributed (less than 4% of the doses) after the injection of DMA(III) and DMMTA(V), suggesting that the DMA(III) and DMMTA(V) were hardly accumulated in hamster RBCs. Based on these observations, we suggest that although DMMTA(V) and DMDTA(V) are thioarsenicals, DMMTA(V) is taken up efficiently by organs, in a manner different from that of DMDTA(V). In addition, the distribution and metabolism of DMMTA(V) are like in manner similar to DMA(III) in hamsters, while DMDTA(V) is in a manner similar to DMA(V).

Complexability of o-bisguanidinobenzenes with arsenic and phosphoric acids in solution and solid states, and the potential use of their immobilized derivatives as solid base ligands for metal salts and arsenic acid.

The role of o-bisguanidinobenzenes (BGBs) as new Brønsted base ligands for arsenic and phosphoric acids was examined. In solution state, complexation was evaluated by Job's plot in (1)H NMR experiment, indicating a 1:1 complex formation, whereas in solid state crystalline structures of complexes obtained were addressed by X-ray crystallographic analysis and/or solid state (13)C NMR experiment, in which 1:2 complexes between the BGB and the acid components were normally formed. Based on these results, Merrifield and Hypogel resin-anchored BGBs were designed and prepared as the corresponding polymer-supported host ligands. Evaluation of their coordination ability with metal salts (ZnCl(2) and CoCl(2)) and arsenic acid in aqueous media by ICP-MS showed that the latter Hypogel resin-anchored BGBs acted as effective immobilized base ligands.

Evidence for toxicity differences between inorganic arsenite and thioarsenicals in human bladder cancer cells.

Arsenic toxicity is dependent on its chemical species. In humans, the bladder is one of the primary target organs for arsenic-induced carcinogenicity. However, little is known about the mechanisms underlying arsenic-induced carcinogenicity, and what arsenic species are responsible for this carcinogenicity. The present study aimed at comparing the toxic effect of DMMTA(V) with that of inorganic arsenite (iAs(III)) on cell viability, uptake efficiency and production of reactive oxygen species (ROS) toward human bladder cancer EJ-1 cells. The results were compared with those of a previous study using human epidermoid carcinoma A431 cells. Although iAs(III) was known to be toxic to most cells, here we show that iAs(III) (LC(50)=112 microM) was much less cytotoxic than DMMTA(V) (LC(50)=16.7 microM) in human bladder EJ-1 cells. Interestingly, pentavalent sulfur-containing DMMTA(V) generated a high level of intracellular ROS in EJ-1 cells. However, this was not observed in the cells exposed to trivalent inorganic iAs(III) at their respective LC(50) dose. Furthermore, the presence of N-acetyl-cysteine completely inhibited the cytotoxicity of DMMTA(V) but not iAs(III), suggesting that production of ROS was the main cause of cell death from exposure to DMMTA(V), but not iAs(III). Because the cellular uptake of iAs(III) is mediated by aquaporin proteins, and because the resistance of cells to arsenite can be influenced by lower arsenic uptake due to lower expression of aquaporin proteins (AQP 3, 7 and 9), the expression of several members of the aquaporin family was also examined. In human bladder EJ-1 cells, mRNA/proteins of AQP3, 7 and 9 were not detected by reverse transcription polymerase chain reaction (RT-PCR)/western blotting. In A431 cells, only mRNA and protein of AQP3 were detected. The large difference in toxicity between the two cell lines could be related to their differences in uptake of arsenic species.

Systemic distribution and speciation of diphenylarsinic acid fed to rats.

Diphenylarsinic acid (DPAA) is an environmental degradation product of diphenylarsine chloride or diphenylarsine cyanide, which were chemical warfare agents produced by Japan during the World War II. DPAA is now considered a dangerous environmental pollutant in Kamisu, Japan, where it is suspected of inducing health effects that include articulation disorders (cerebellar ataxia of the extremities and trunk), involuntary movements (myoclonus and tremor), and sleep disorders. In order to elucidate the toxic mechanism of DPAA, we focused on the distribution and metabolism of DPAA in rats. Systemic distribution of DPAA was determined by administering DPAA orally to rats at a single dose of 5.0 mg As/kg body weight, followed by speciation analysis of selected organs and body fluids. Most of the total arsenic burden was recovered in the urine (23% of the dose) and feces (27%), with the distribution in most other organs/tissues being less than 1%. However, compared with the typical distribution of inorganic dietary arsenic, DPAA administration resulted in elevated levels in the brain, testes and pancreas. In contrast to urine, in which DPAA was found mostly in its unmodified form, the tissues and organs contained arsenic that was mostly bound to non-soluble and soluble high molecular weight proteins. These bound arsenic species could be converted back to DPAA after oxidation with H(2)O(2), suggesting that the DPAA bound to proteins had been reduced within the body and was in a trivalent oxidation state. Furthermore, we also detected two unknown arsenic metabolites in rat urine, which were assumed to be hydroxylated arsenic metabolites.

Copper accumulation and compartmentalization in mouse fibroblast lacking metallothionein and copper chaperone, Atox1.

Copper (Cu) is the active center of some enzymes because of its redox-active property, although that property could have harmful effects. Because of this, cells have strict regulation/detoxification systems for this metal. In this study, multi-disciplinary approaches, such as speciation and elemental imaging of Cu, were applied to reveal the detoxification mechanisms for Cu in cells bearing a defect in Cu-regulating genes. Although Cu concentration in metallothionein (MT)-knockout cells was increased by the knockdown of the Cu chaperone, Atox1, the concentrations of the Cu influx pump, Ctr1, and another Cu chaperone, Ccs, were paradoxically increased; namely, the cells responded to the Cu deficiency despite the fact that cellular Cu concentration was actually increased. Cu imaging showed that the elevated Cu was compartmentalized in cytoplasmic vesicles. Together, the results point to the novel roles of MT and cytoplasmic vesicles in the detoxification of Cu in mammalian cells.

Effects of chemical species of selenium on maternal transfer during pregnancy and lactation.

AIMS: This study compares the transfer from mother to fetuses and pups of selenium (Se) in the form of selenite, selenate, and selenomethionine (SeMet) labeled with different homo-elemental isotopes. MAIN METHODS: To completely substitute endogenous Se with natural abundance with Se enriched with a single stable isotope (82Se), female Wistar rats delivered by mother fed 82Se-selenite were fed Se-deficient diet and drinking water containing 82Se-selenite immediately after weaning, and then mated with male Wistar rat at the age of 15-17 weeks. The pregnant rats were divided into two groups. One group was fed Se-deficient diet and drinking water containing 76Se-selenite, 78Se-selenate, and 77Se-SeMet from gestation days 11 to 20. The other group was fed the same diet and drinking water containing the three Se species after delivery for 10 days of lactation. Non-pregnant rats were also fed Se mixture and Se-deficient diet for 10 days. KEY FINDING: Tissue and plasma Se concentrations showed significant changes among non-pregnant, pregnant, and lactating rats. The peak corresponding to selenoprotein P (Sel P) in serum of pregnant rats was reduced. The concentration of 77Se originating from SeMet was higher than those of 76Se from selenite and 78Se from selenate in the stomach content of pups. SIGNIFICANCE: Inorganic Se species are more preferably transformed into Sel P than SeMet, and Sel P is effectively incorporated into placenta during pregnancy. On the other hand, SeMet is a more efficient Se source than inorganic Se species during lactation.

A SEC-HPLC-ICP MS hyphenated technique for identification of sulfur-containing arsenic metabolites in biological samples.

The present study describes the synthesis and characterization of thioarsenicals using electro-spray ionization-MS and time of flight-MS. Separation of thioarsenicals was found to be better by size-exclusion column compared to anion exchange column coupled with HPLC-inductively coupled argon plasma mass spectrometer (ICP MS). Although four thioarsenicals were confirmed as dimethylthioarsinous acid (m/z=138), methylmonothioarsonous acid (m/z=122), dimethyldithioarsinic acid (m/z=170) and methyltrithioarsonic acid (m/z=188), it is noted that HPLC-ICP MS alone were not sufficient for their identification. Also, none of them was stable with time. This is the first report detailing the synthesis and identification of methyltrithioarsonic acid. Both dimethyldithioarsinic acid and dimethylthioarsinous acid were detected in human nail samples while dimethyldithioarsinic acid was found in urine samples. So, the above technique could be applicable to the identification of sulfur-containing biomolecules in the biological samples.

Reaction mechanism underlying the in vitro transformation of thioarsenicals.

Thioarsenicals have been paid much attention due to the toxicity of arsenic, since some of them are highly toxic and commonly found in the urine of mammals. We previously reported that thioarsenicals might be produced in red blood cells (RBCs). Here, we further characterized the mechanism underlying the production and metabolism of thioarsenicals in RBCs using 34S-labeled dimethylmonothioarsinic acid (34S-DMMTA(V)) and purified rat hemoglobin (Hb) or a rat RBC lysate. 34S-DMMTA(V) did not bind to Hb on incubation with purified rat Hb, remaining in its original form. However, when 34S-DMMTA(V) was incubated with a rat RBC lysate, only arsenic, i.e., not sulfur (34S), was detected in a form bound to Hb (As-Hb). In addition, another arsenic product containing sulfur (34S) in the molar ratio of 34S/As=2 was detected, which was assigned as dimethyldithioarsinic acid (DMDTA(V)), suggesting that arsenic does not bind to Hb in the form of 34S-DMMTA(V) but does so in the form of dimethylarsinous acid (DMA(III)). Namely, DMMTA(V) appeared to be hydrolyzed into dimethylarsinic acid (DMA(V)) and H34S-, and the released H34S- reacted with DMMTA(V) to produce DMDTA(V). Thus, DMMTA(V) was transformed into DMDTA(V) and DMA(V) (2DMMTA(V) ->DMDTA(V)+DMA(V)), the latter product being reduced to DMA(III) in the presence of GSH and bound to Hb. In a separate experiment, (H34S-DMMTA(V) was incubated with sulfide (Na2S) and GSH. Although DMMTA(V) was not transformed into DMDTA(V) in the presence of only Na2S or GSH, it was transformed into DMDTA(V) in the presence of both Na2S and GSH. Our results suggest that DMMTA(V) is hydrolyzed enzymatically into DMA(V) and sulfide, the former being reduced to DMA(III) and bound to Hb, and the latter reacting with DMMTA(V) to yield DMDTA(V). Thus, DMMTA(V) is transformed into DMDTA(V) and DMA(V) through a hydrolytic reaction in a manner similar to a disproportionation reaction, DMA(V) being reduced and bound to Hb (As-Hb), and DMDTA(V) being produced more in the presence of sulfides in the medium.

Narrow-bore HPLC-ICP-MS for speciation of copper in mutant mouse neonates bearing a defect in Cu metabolism.

Minute amounts of tissue supernatants from mouse neonates bearing a mutation in the copper (Cu)-transporter gene, Atp7a, were injected into narrow-bore HPLC coupled with an inductively coupled plasma-mass spectrometer (ICP-MS) to examine Cu metabolism. In the 14-day-old mutant neonates, Cu accumulated in the intestine in the metallothionein (MT)-bound form, and mRNA expression of the two MT isoforms was increased. Meanwhile, Cu in the MT-bound form (Cu-MT) was depleted in the liver and mRNA expression decreased in comparison with wild-type mice. These results suggest that Cu is not secreted by intestinal microvillus cells into bloodstream due to the defect of Atp7a, and systemic depletion of Cu occurred. On the other hand, in the kidneys of mutant mice, Cu accumulated in the MT-bound form despite the fact that mRNA expression of the two MT isoforms was low. Part of Cu-MT in microvillus cells may be released into bloodstream at turnover and be preferably taken up by the kidneys. Consequently, the mRNA expression of MT isoforms was not always coincident with the amounts of MT proteins binding Cu, and narrow bore HPLC-ICP-MS used for MT protein determination is a complementary technique to real-time RT-PCR used for MT mRNA determination in Cu speciation.

Identification of the major arsenic-binding protein in rat plasma as the ternary dimethylarsinous-hemoglobin-haptoglobin complex.

Chronic exposure to arsenic causes a wide range of diseases such as hyperkeratosis, cardiovascular diseases, and skin, lung, and bladder cancers, and millions of people are chronically exposed to arsenic worldwide. However, little is known about the mechanisms underlying these toxic actions. The metabolism of arsenic is essential for understanding the toxic actions. Here, we identified the major arsenic-binding protein (As-BP) in the plasma of rats after oral administration of arsenite by the use of two different HPLC columns, gel filtration and anion exchange ones, coupled with an inductively coupled argon plasma mass spectrometer (ICP MS). The molecular mass of the As-BP was estimated to be 90 kDa based on results using the former column, and arsenic bound to this protein only in the form of dimethylarsinous acid (DMA (III)) in the plasma in vivo. In addition, the purified As-BP was shown to consist of two different proteins, haptoglobin (Hp) of 37 kDa (three bands) and the hemoglobin (Hb) alpha chain of 14 kDa (single band), using sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS), respectively, suggesting that the As-BP was the ternary DMA (III)-Hb-Hp complex. To confirm the present observations, an arsenic-binding assay was carried out in vitro . Although DMA (III) bound directly to fresh rat plasma proteins, they were different from that identified in vivo. However, when a DMA (III)-exposed rat RBC lysate (DMA (III) binds to Hb in rat RBCs) was added to control rat plasma, a new arsenic peak increased at the expense of the arsenic-Hb one. Furthermore, this new arsenic peak was consistent with the As-BP identified in the plasma in vivo, suggesting that arsenic bound to Hb further binds to haptoglobin (Hp), forming the ternary As-Hb-Hp complex.

Comparison of distribution and metabolism between tellurium and selenium in rats.

Tellurium (Te) has shown recent increase in use as a component of optical magnetic disks having phase-change property, such as digital versatile disk-random access memory (DVD-RAM) and DVD-rewritable (DVD-RW). However, the toxicity and metabolic pathway of Te remain unclear despite its being known as a non-essential and harmful metalloid. This study was performed to gain an insight into Te metabolism in the body. The mechanism for the distinction of Te from selenium (Se), an essential metalloid belonging to the same group as Te, was also clarified. Rats were given drinking water containing tellurite and (82)Se-labeled selenite at the same concentration, and the concentrations of these metalloids in organs, body fluid and excreta were determined 2 days later. The results demonstrate that urinary and fecal excretion of Te was, respectively, lower and higher than that of exogenous (labeled) Se, suggesting that Te was less absorbed than Se. The ingested Te was transformed, i.e., methylated in organs and effluxed into bloodstream, and the effluxed Te was highly accumulated in rat red blood cells (RBCs) in the form of dimethylated Te. In contrast, Se was not accumulated in RBCs. Finally, Te was excreted in urine as trimethyltelluronium and might be exhaled as dimethyltelluride. The results suggest that the metabolism of Te was distinct from that of Se in rats.

Theoretical calculations and reaction analysis on the interaction of pentavalent thioarsenicals with biorelevant thiol compounds.

To obtain a rational understanding of the extraordinary interaction of pentavalent thioarsenicals with biorelevant thiol compounds, we carried out ab initio calculations on related arsenic compounds and discussed the correlation between the distribution of observed arsenic species in actual reaction systems and the corresponding calculated reaction enthalpies. Previously, it was considered that pentavalent arsenicals do not form thiol conjugates. However, the dimethylmonothioarsinic acid-glutathione conjugate (DMMTAV-GSH) was recently reported as the first stable conjugate of a pentavalent arsenical with a thiol compound. We carried out detailed analysis of the DMMTAV-GSH formation reaction and demonstrated that this conjugate could be formed nonenzymatically under weakly acidic conditions. On the basis of the ab initio calculations, this conjugation was an exothermic reaction (delta H = -4.85 kcal/mol) and gave the minimum energy point during the reaction sequence of DMMTAV with a thiol compound. However, in the case of dimethylarsinic acid (DMAV), a corresponding oxo acid to DMMTAV, conjugation with a thiol compound is an endothermic reaction (delta H = +0.06 kcal/mol). The minimum energy point of the reaction sequence of DMAV with a thiol compound was the formation of a trivalent dimethylarsinous acid (DMAIII)-GSH conjugate. Because the formation of arsenic-sulfur bonds is one of the major mechanisms for arsenic toxicity, these energetic results could account for the extraordinary behaviors and toxicities of thioarsenicals in vivo and in vitro in comparison with those of the corresponding oxo acids.

Formation of dimethylthioarsenicals in red blood cells.

The bladder and skin are the primary targets for arsenic-induced carcinogenicity in mammals. Thioarsenicals dimethylmonothioarsinic (DMMTA(V)) and dimethyldithioarsinic (DMDTA(V)) acids are common urinary metabolites, the former being much more toxic than non-thiolated dimethylarsinic acid (DMA(V)) and comparable to dimethylarsinous acid (DMAIII) in epidermoid cells, suggesting that the metabolic production of thioarsenicals may be a risk factor for the development of cancer in these organs. To reveal their production sites (tissues/body fluids), we examined the uptake and transformation of the four dimethylated arsenicals by incubation with rat and human red blood cells (RBCs). Although DMA(V) and DMDTA(V) were not taken up by either type of RBCs, DMAIII and DMMTA(V) were taken up by both (more efficiently by rat ones), though DMMTA(V) was taken up slowly, and then the arsenic transformed into DMDTA(V) was excreted from both types of animal RBCs. On the other hand, although DMA(III) taken up rapidly by rat RBCs was retained in the RBCs, that taken up by human RBCs was immediately transformed into DMMTA(V) and then excreted into the incubation medium without being retained in the RBCs. In a separate experiment, arsenic remaining in primary rat hepatocytes after incubation with 1.5 microM DMAIII was recovered from the incubation medium in the forms of DMA(V) and DMMTA(V) in the presence of human RBCs, but not in the presence of rat RBCs (in which the arsenic was bound to hemoglobin). Thus, DMMTA(V) was detected in the medium only in the presence of human RBCs and increased with incubation time. It was proposed that arsenic is excreted from hepatocytes into the bloodstream in the form of DMAIII and then taken up by RBCs in humans, where it is transformed into DMMTA(V) and then excreted again into the bloodstream.

Methylation and demethylation of intermediates selenide and methylselenol in the metabolism of selenium.

All nutritional selenium sources are transformed into the assumed common intermediate selenide for the syntheses of selenoproteins for utilization and/or of selenosugar for excretion. Methylselenol [monomethylselenide, MMSe] is the assumed intermediate leading to other methylated metabolites, dimethylselenide (DMSe) and trimethylselenonium (TMSe) for excretion, and also to the intermediate selenide from methylselenocysteine and methylseleninic acid (MSA). Here, related methylation and demethylation reactions were studied in vitro by providing chemically reactive starting substrates (76Se-selenide, 77Se-MMSe and 82Se-DMSe) which were prepared in situ by the reduction of the corresponding labeled proximate precursors (76Se-selenite, 77Se-MSA and 82Se-dimethylselenoxide (DMSeO), respectively) with glutathione, the three substrates being incubated simultaneously in rat organ supernatants and homogenates. The resulting chemically labile reaction products were detected simultaneously by speciation analysis with HPLC-ICP-MS after converting the products and un-reacted substrates to the corresponding oxidized derivatives (selenite, MSA and DMSeO). The time-related changes in selenium isotope profiles showed that demethylation of MMSe to selenide was efficient but that of DMSe to MMSe was negligible, whereas methylation of selenide to MMSe, and MMSe to DMSe were efficient, and that of DMSe to TMSe occurred less efficiently. The present methylation and demethylation reactions on equilibrium between selenide, MMSe and DMSe without producing selenosugar and selenoproteins indicated that DMSe rather than TMSe is produced as the end product, suggesting that DMSe is to be excreted more abundantly than TMSe. Organ-dependent differences in the methylation and demethylation reactions were characterized for the liver, kidney and lung.

Preferential organ distribution of methylselenol source Se-methylselenocysteine relative to methylseleninic acid.

It has been proposed that Se-methylselenocysteine (MeSeCys) and methylseleninic acid (MSA(IV)) are efficiently transformed through the beta-lyase and reduction reactions, respectively, into methylselenol, the assumed biologically active selenometabolite responsive for the anti-carcinogenicity and anti-oxidant actions of selenium. The bioavailability and distribution of the two selenium sources in major organs/tissues were compared under exactly identical conditions. Namely, labeled selenium sources (76)Se-MeSeCys and (77)Se-MSA(IV), at a single oral dose of 10 microg Se/kg body weight each, were administered simultaneously to rats that had been depleted of natural abundance selenium with a single isotope (78)Se. The same dose of (82)Se-selenite was also administered as a reference selenium source. The distributions of the three labeled selenium isotopes were determined 3 h after the administration in 13 organs/tissues/blood. MeSeCys was taken up more efficiently by most organs, especially the pancreas and duodenum, than MSA(IV) and selenite, the latter two sources being taken up similarly to each other except for in the kidney, liver, and spleen, where the three labeled isotopes were detected at comparable concentrations. The labeled selenium in the liver supernatant was speciated by HPLC inductively coupled argon plasma-mass spectrometry (ICP-MS), and it was suggested that MeSeCys was delivered in its intact form to organs, and then transformed into methylselenol. In addition to the known properties of that MeSeCys is chemically more stable than MSA(IV) and is a naturally occurring edible product, and that MeSeCys produces methylselenol much more efficiently than a homologous selenoamino acid selenomethionine, the present study revealed that MeSeCys is more efficiently distributed than MSA(IV) in its intact form, and then produces methylselenol, suggesting that MeSeCys is the best methylselenol source in most organs/tissues.

In vitro translation with [34S]-labeled methionine, selenomethionine, and telluromethionine.

Heteroisotope and heteroatom tagging with [(34)S]-enriched methionine (Met), selenomethionine (SeMet), and telluromethionine (TeMet) was applied to in vitro translation. Green fluorescent protein (GFP) and JNK stimulatory phosphatase-1 (JSP-1) genes were translated with wheat germ extract (WGE) in the presence of Met derivatives. GFPs containing Met derivatives were subjected to HPLC coupled with treble detection, i.e., a photodiode array detector, a fluorescence detector, and an inductively coupled plasma mass spectrometer (ICP-MS). The activities of JSP-1-containing Met derivatives were also measured. GFP and JSP-1 containing [(34)S]-Met and SeMet showed comparable fluorescence intensities and enzyme activities to those containing naturally occurring Met. TeMet was unstable and decomposed in WGE, whereas SeMet was stable throughout the experimental period. Thus, although Te was the most sensitive to ICP-MS detection among S, Se, and Te, TeMet was less incorporated into the proteins than Met and SeMet. Finally, the potential of heteroisotope and heteroatom tagging of desired proteins in in vitro translation followed by ICP-MS detection was discussed. [figure: see text] TeMet was less incorporated into GFP than Met and SeMet due to its instability in WGE.

Impact of arsenic in foodstuffs on the people living in the arsenic-affected areas of West Bengal, India.

Although the accumulation of arsenic (As) in human blood is linked with some diseases and with occupational exposure, there are few reports on speciation of As in blood. On the basis of our earlier article, elevated level of arsenicals in human urine and blood were found in the ex-exposed population via As-containing drinking water. The aim of the present study was to get an insight on impact of As in foodstuffs on the people living in the As-affected areas. Moreover, speciation of arsenicals in urine, and water-samples found in arsenobetaine (AsB). Since sampling population (n=25) was not taking any seafood, As in foodstuffs was thought to be the prime source for this discrepancy. So, speciation of methanol extract of freeze-dried red blood cells (RBCs) and foodstuffs, and trichloro acetic acid (TCA) treated plasma by high performance liquid chromatography-inductively coupled argon plasma mass spectrometer (HPLC-ICP MS) collected from the study population (n=33) was carried out to support our hypothesis. Results showed that urine contained AsB (1.7%), arsenite (iAs(III)) (14.3), arsenate (iAs(V)) (4.9), monomethylarsonous acid (MMA(III)) (0.64), monomethylarsonic acid (MMA(V)) (13.6), dimethylarsinous acid (DMA(III)) (7.7), and dimethylarsinic acid (DMA(V)) (65.4). Blood contained 21.3 microg L(- 1) (mean) As and of which 27.3% was in plasma and 72.7% in RBCs. RBCs contained AsB (21.6%) and DMA(V) (78.4) and blood plasma contained AsB (12.4%), iAs(III) (25.9), MMA(V) (30.3), and DMA(V) (31.4). Furthermore, speciation of As in foodstuffs showed that most of them contained AsB (3.54-25.81 microg kg(- 1)) (25.81-312.44 microg kg(- 1)) along with iAs(III) (9.62-194.93), iAs(V) (17.63-78.33), MMA(V) (9.47-73.22) and DMA(V) (13.43-101.15) that supported the presence of AsB and elevated As in urine and blood samples of the present study group. Inorganic As (iAs) predominates in rice (67.17-86.62%) and in spices (40-90.35%), respectively over organic As. So, As in the food chain is a real threat to human health.

Toxicity of dimethylmonothioarsinic acid toward human epidermoid carcinoma A431 cells.

Chronic ingestion of arsenic-contaminated drinking water induces skin lesions and urinary bladder cancer in humans. It is now recognized that thioarsenicals such as dimethylmonothioarsinic acid (DMMTA (V)) are commonly excreted in the urine of humans and animals and that the production of DMMTA (V) may be a risk factor for the development of the diseases caused by arsenic. The toxicity of DMMTA (V) was compared with that of related nonthiolated arsenicals with respect to cell viability, uptake ability, generation of reactive oxygen species (ROS), and cell cycle progression of human epidermoid carcinoma A431 cells, arsenate (iAs (V)), arsenite (iAs (III)), dimethylarsinic acid (DMA (V)), and dimethylarsinous acid (DMA (III)) being used as reference nonthiolated arsenicals. DMMTA (V) (LC 50 = 10.7 microM) was shown to be much more cytotoxic than iAs (V) (LC 50 = 571 microM) and DMA (V) (LC 50 = 843 microM), and its potency was shown to be close to that of trivalent arsenicals iAs (III) (LC 50 = 5.49 microM) and DMA (III) (LC 50 = 2.16 microM). The greater cytotoxicity of DMMTA (V) was associated with greater cellular uptake and distribution, and the level of intracellular ROS remarkably increased in A431 cells upon exposure to DMMTA (V) compared to that after exposure to other trivalent arsenicals at the respective LC 50. Exposure of DMMTA (V) to cells for 24 h induced cell cycle perturbation. Namely, the percentage of cells residing in S and G2/M phases increased from 10.2 and 15.6% to 46.5 and 20.8%, respectively. These results suggest that although DMMTA (V) is a pentavalent arsenical, it is taken up efficiently by cells and causes various levels of toxicity, in a manner different from that of nonthiolated pentavalent arsenicals, demonstrating that DMMTA (V) is one of the most toxic arsenic metabolites. The high cytotoxicity of DMMTA (V) was explained and/or proposed by (1) efficient uptake by cells followed by (2) its transformation to DMA (V), (3) producing ROS in the redox equilibrium between DMA (V) and DMA (III) in the presence of glutathione.

Selenocysteine beta-lyase and methylselenol demethylase in the metabolism of Se-methylated selenocompounds into selenide.

The lyase activity toward Se-methylated selenoamino acids and the demethylase activity toward methylselenol in the metabolism of selenium were characterized in vitro. The beta- and gamma-lyase activities toward selenomethionine (SeMet) and Se-methylselenocysteine (MeSeCys), respectively, were compared under exactly identical conditions by incubating 77Se-SeMet and 76Se-MeSeCys simultaneously in a liver supernatant, and then estimated by the decreases in the labeled starting selenoamino acids (MeSeCys and SeMet), and also by the increases in the labeled enzyme products (methylselenol and selenide) after oxidation to methylseleninic acid (MSA(IV)) and selenite, respectively, by HPLC-inductively coupled plasma-mass spectrometry (ICP-MS). Only 76Se-MeSeCys was decreased and only 76Se-selenite was produced, suggesting that conversion of MeSeCys to methylselenol by beta-lyase followed by that of methylselenol to selenide by demethylase actively occurred in the liver supernatant. The demethylase activity was characterized by incubating 77Se-methylselenol produced in situ from 77Se-MSA(IV) and glutathione in a partially purified enzyme preparation. It was found that demethylation takes place directly through an attack by a hydroxide anion on the methyl group of methylselenol producing selenide and methanol, selenide being detected on HPLC-ICP-MS after oxidation to selenite, and methanol on GC-MS. It was concluded that beta- but not gamma-lyase activity could be detected in a liver supernatant, and that the resulting methylselenol product is demethylated through hydrolysis, with methanol and selenide being produced (MeSeCys-->CH3SeH-->HSeH + CH3OH).