Dimethylarsinate Research Articles

The effect of arsenicals on alkaloid production by cell suspension cultures of Catharanthus roseus

AbstractThe effect of arsenic compounds on indole alkaloid production by cell suspension cultures of Catharanthus roseus was investigated. The analysis of indole alkaloids was achieved by using thermospray liquid chromatography‐mass spectrometry (LC MS) which facilitated the rapid screening of alkaloid composition in cultures treated with different arsenicals at different times in their growth cycle.Treatment with dimethylarsinate (DMA), a non‐selective herbicide, has a drastic inhibitory effect on alkaloid production although it is the least toxic arsenical to growth. Tryptamine, an early precursor in the biosynthesis of indole alkaloids, accumulates in cells treated with DMA, indicating that the initial step of condensation of tryptamine with secologanin is inhibited. Treatment with DMA during the early stationary phase of culture growth enhances the accumulation of some alkaloids, although some, such as catharanthine, are suppressed.The arsenicals arsenate and methylarsonate (MMA) have an inhibitory effect on alkaloid production when applied during the early growth stages. In contrast to MMA and DMA, arsenate has a stimulatory effect on catharanthine production when introduced to the culture during its early stationary phase.Thus the changes in the pattern of alkaloid accumulation on addition of arsenicals are dependent on the arsenic species and its concentration, as well as the time of application. This variable response indicates that each arsenical has a distinct mode of action on the secondary metabolic pathways of C. roseus.

Determination of arsenic speciation by liquid chromatography—hydride generation inductively coupled plasma atomic emission spectrometry with on-line UV photooxidation

The determination is described of the six arsenic species arsenite, arsenate, monomethylarsonate (MMA), dimethylarsinate (DMA), arsenobetaine and arsenocholine by hydride generation inductively coupled plasma atomic emission spectrometry after liquid chromatographic separation and on-line photooxidation. An anion-exchange polymer-based column is used for separation. The details of the photoreactor designed to transform arsenobetaine and arsenocholine into simpler species that can be reduced are presented. The reducing conditions to obtain the arsine from arsenate (as the final product of the photooxidation process) are optimized. The overall assembly is presented and using the optimized operating condition the quality parameters (detection limits, precision and accuracy) for all the arsenic species are reported. These parameters for arsenic, arsenate, MMA and DMA are compared with those obtained without photooxidation. The introduction of a new step on-line in the coupling does not produce any loss of quality of information or a significant increase in analysis time.

Accumulation and toxic effect of organometallic compounds on algae

AbstractThis paper reports toxic effects and bioaccumulation factors of organometallic compounds, mainly organotin species, on algae. We selected two species of microalgae as test algae: one was Scenedesmus obliquus as a representative of fresh‐water algae, the other Dunaliella salina and Dunaliella viridis, to represent commonly mixed algae which exist abundantly in Tianjin Harbor, People's Republic of China. For comparison, Chlorella vulgaris was also used in this study. The toxic effect of ten organometallic compounds on the freshwater alga, S. obliquus, was investigated. The ten compounds were (as chlorides) tributyltin (TBT); triphenyltin (TPT); trimethyltin (TMT); dibutyltin (DBT); diphenyltin (DPT); dimethyltin (DMT); trimethyl‐lead acetate (TML); dimethyl‐arsine (DMA) and two new mixed‐alkyltin pesticides, dicyclohexylmethylitin acetate (Cy2MTA) and dicyclohexylmethyltin isobutyrate (Cy2MTB). The order of toxicity of these compounds in fresh‐water algae, S. obliquus, was TBT>TPT>DBT> Cy2MTA=TML> Cy2MTB>DPT>TMT>DMA>DMT, according to 96 h EC50 values attained. The ten toxicants were divided into three groups according to the sequence of their toxicities; (a) TBT, TPT; (b) DBT, Cy2MTA, TML, Cy2MTB; (c) DPT, TMT, DMA, DMT. In each group the EC50 values of each compound were quite similar. The difference of EC50 values between two vicinal groups was approximately one order of magnitude. The bioconcentration factor (BCF) of TBT and TPT compared with water in the freshwater alga S. obliquus was >3.32 × 105 and 1.14 × 105, respectively. The BCF of the marine mixed algae was >3.48 × 105. The marine microalga, Chlorella vulgaris, was adaptable to TBT at lower concentration. TBT at high concentration only inhibited the growth of S. obliquus, but it could cause chlorosis anddisintegration of D. salina and D. viridis. Resistance to toxicity of algae against TBT appears in order as follows: C. vulgaris>S. obliquus>D. salina and D. viridis. TBT was metabolized by algae to a less toxic product, DBT. The existence of algal cells accelerated the concentration reduction of TBT. The toxic mechanism of TBT was also studied.

Arsenic Species Separation by IELC-ICP/OES: Arsenochoune Behavior

Abstract The separation conditions and quantification of As(III), As(V), monomethylarsenate (MMA), dimethylarsinate (DMA), arsenobetaine (AsBet) and arsenocholine (AsChol) are studied by Liquid Chromatography (LC) coupled directlv to an Inductively Coupled Plasma Optical Emission Spectroscopy (ICP/OES) system. The separation conditions are optimized to improve the resolution of the six arsenic species. Arsenocholine shows a particular pattern of behaviour when phosphate is used as eluent: two peaks are observed in the chromatogram, thus a svstematic study assaving different pH and concentration of phosphate is carried out to improve resolution and analvsis time when the six arsenic compounds are analyzed in a mixture. Boric acid as mobile phase avoids the splitting of the arsenocholine peak and leads to a good separation of the six arsenic compounds. Detection limits are stablished for the six arsenic species.

The biotransformation of monomethylarsonate and dimethylarsinate into arsenobetaine in seawater and mussels

AbstractWater‐soluble 3H‐labeled arsenic compounds were phenol‐extracted from mussels (Mytilus edulis) and seawater after exposure to [3H]monomethylarsonate (MMAA) and [3H]dimethylarsinate (DMAA). Varying amounts of [3H] arsenobetaine were found in mussels and seawater, depending upon the experimental conditions. The results indicate that arsenobetaine is principally biosynthesized by microscopic organisms in the seawater and that it is bioaccumulated by mussels. Total arsenic concentrations in mussel flesh, byssal threads and shells were also determined, showing concentration increases in all three compartments.

Human Studies Do Not Support the Methylation Threshold Hypothesis for the Toxicity of Inorganic Arsenic

Inorganic arsenic (In-As) is an established human carcinogen. Methylation to monomethylarsonate (MMA) and dimethylarsinate (DMA) is believed to be the detoxification mechanism for In-As. Urinary measurement of In-As, MMA, and DMA is considered a good biological marker of internal dose to In-As, since it excludes other ingested forms of arsenic which are much less toxic, and because urinary excretion is the main form of elimination of In-As. A methylation threshold hypothesis for In-As has been proposed, stating that after exposure to In-As reaches a certain level or threshold, methylation capacity begins to decline, thus increasing the toxic effects of In-As. We investigated the validity of this hypothesis by analyzing the data from studies which measured urinary In-As, MMA, and DMA in different populations, ranging from background to high occupational and environmental exposure groups. We also present data from our study of a highly exposed population in California. Our analysis focused on the proportion of urinary In-As remaining in the unmethylated form [In-As/(In-As + MMA + DMA)]. The results indicate that epidemiological and experimental human data do not support the methylation threshold hypothesis. On average, 20-25% In-As remains unmethylated regardless of the exposure level. The wide range of interindividual variability in methylation capacity found in some studies warrants further investigation.

Separation of seven arsenic compounds by high-performance liquid chromatography with on-line detection by hydrogen–argon flame atomic absorption spectrometry and inductively coupled plasma mass spectrometry

Seven molecular forms of arsenic were separated by anion- and cation-exchange high-performance liquid chromatography (HPLC) with on-line detection by flame atomic absorption spectrometry (FAAS). The interfacing was established by a vented poly(tetrafluoroethylene) capillary tubing connecting the HPLC column to the nebulizer of the atomic absorption spectrometer. Arsenite, arsenate, monomethylarsonate (MMA) and dimethylarsinate (DMA) were separated from each other and from the co-injected cationic arsenic compounds, arsenobetaine (AsB), arsenocholine (AsC) and the tetramethylarsonium ion (TMAs) on an organic polymeric anion-exchange column with 0.1 mol dm–3 carbonate at pH 10.3 as the mobile phase. The three cationic species were separated from each other and from the co-injected anionic species on a silica based cation-exchange column with pyridine at a pH of 2.65 as the mobile phase. The signal-to-noise ratio of the on-line AAS detector was optimized. This involved the use of the hydrogen–argon–entrained air flame, a slotted tube atom trap in the flame for signal enhancement, electronic noise damping and a high-intensity light source. The detection limits in µg cm–3, using 100 mm3 injections of mixtures of arsenic standards into the HPLC system were: arsenite, AsIII 1.1; arsenate, Asv 1.4; MMA 1.4; DMA 0.7; AsB 0.3; AsC 0.5; and the TMAs 0.4. The HPLC–AAS system was used for the analysis of arsenic species in aqueous extracts of soil samples from a polluted land site. Only arsenate was found in the soil extracts. For comparison, inductively coupled plasma mass spectrometry was also used as an on-line detection technique with the same HPLC systems.

Plasma-assisted decomposition of trimethylarsine

The downstream near afterglow region of a hydrogen plasma is used to decompose and convert trimethylarsine (TMAs) into methylarsine homologs [(CH3)3−xAsHx, where x=1,2,3] including that of arsine (x=3). Approximately 30%, 17%, and 10% of the TMAs is converted into dimethylarsine (DMAs), monomethylarsine (MMAs), and arsine, respectively, while 28% remains undecomposed. Hydrogen is replaced by deuterium to isotopically verify that the origin of the arsenic hydrogenation occurring during gas conversion arises from both the plasma gas and fragmented hydrogen from the TMAs. Deuterium tagging of the MMAs, DMAs, and hydrocarbon byproducts is consistent with TMAs decomposition via plasma initiated CH3 radical removal and explains why the predominant light stable hydrocarbon produced is methane while ethane and acetylene account for the main higher hydrocarbons.

Cellular metabolism of arsenic studied in mammalian cellsin vitro

The cytotoxicity of trivalent and pentavalent inorganic arsenic was studied in cultured mouse fibroblasts. Concentrations of As(III) in the μM range and approximately 10-fold higher concentrations of As(V) led to a reduction of cellular proliferation and viability with a concomitant increase of LDH release and stimulation of lactate production. Cells pretreated with a low As(III) concentration were less sensitive to toxic doses of As(III) or As(V).Uptake of As(III) by the cells was greater than that of As(V). Both forms of inorganic arsenic were converted intracellularly to monomethylarsonic (MMA) and dimethylarsinic (DMA) acids, which were subsequently released into the culture medium. In As-pretreated cells, which proved more resistant to As toxicity, biotransformation of inorganic to MMA and DMA was increased.

OMVPE growth of GaAs using dimethylarsine

The use of AsH 3 and PH 3 sources in organometallic vapor phase epitaxy (OMVPE) has been a constant concern due to their extreme toxicity. Great effort has been made in recent years to replace these sources with either elemental or organometallic compound sources. This paper describes growth of GaAs using dimethylarsine (DMAs) and trimethylgallium (TMGa) in an atmospheric pressure OMVPE reactor. Three principal parameters, the growth temperature, V/III ratio, and growth rate, have been varied to investigate the resultant changes in the properties of the epitaxial layers. The as-grown GaAs epilayers are p-type with carrier concentrations dependent upon the growth rate. For a TMGa partial pressure of 2.3 × 10 −4 atm, a hole concentration as high as 10 17 cm −3 is obtained. As the TMGa partial pressure is decreased to 2.3 × 10 −5 atm, the hole concentration decreases correspondingly to 10 16 cm −3. It can be further reduced to the low 10 15 cm −3 range at a TMGa partial pressure of 1.2 × 10 −5 atm. Low temperature photoluminescence measurements and the temperature dependence of the hole concentration indicate that he acceptor impurity is carbon residing on the As sublattice. Intentional Te doping to produce n-type epilayers results in electron mobilities as high as 5000 cm 2/V · s at room temperature. These results suggest that the single H in DMAs contributes too little to the recombination of CH 3 radicals from both the TMGa and DMAs decomposition to avoid carbon contamination.

Speciation of arsenic in urine using high-performance liquid chromatography with inductively coupled plasma mass spectrometric detection

High-performance liquid chromatography (HPLC) has been coupled with inductively coupled plasma mass spectrometry (ICP-MS) for the speciation of four arsenic compounds commonly found in urine. Arsenite (As3+), arsenate (As5+), dimethylarsinate (DMA) and monomethylarsonate (MMA) were separated via anion-exchange HPLC and detected on-line using ICP-MS. The absolute detection limits ranged from 20 to 91 pg of arsenic in aqueous media and 36–96 pg in urine. The four species were determined in two freeze-dried urine standards using the method of standard additions. The total of the four species was found to be within 13% of the average reported total arsenic concentration for both freeze-dried urine standards containing elevated levels of As5+. The relative standard deviation of peak-height measurements was less than 10% for each of the four species in urine. The determination of As3+ is complicated by the presence of an interfering peak, which is believed to arise from the co-elution of chlorine-containing species and subsequent formation of 40Ar35CI+ ions (m/z= 75).

The origin of arsenobetaine in marine animals

AbstractTrimethyl(carboxymethyl)arsonium zwitterion (arsenobetaine) is virtually ubiquitous in marine animals consumed by man. Experimental work on the transformation of arsenate to arsenobetaine in the marine environment is reviewed. Current evidence favors the conversion of arsenate to dimethyl(ribosyl)arsine oxides by algae, and the microbially mediated transformation of dimethyl(ribosyl)arsine oxides to arsenobetaine or to its immediate precursors in the sediments. Information about the transfer of arsenobetaine from the sediments to marine animals is lacking.

Determination of inorganic arsenic and organic arsenic compounds in marine organisms by hydride generation/cold trap/gas chromatography— mass spectrometry

AbstractThe behavior of arsenite, methylarsonic acid, dimethylarsinic acid, trimethylarsine oxide, dimethyl‐R‐arsine oxides, and trimethyl‐R‐arsonium compounds (R = carboxymethyl, 2‐carboxyethyl, 2‐hydroxyethyl) toward sodium borohydride and hot aqueous sodium hydroxide was investigated. The arsines obtained by sodium borohydride reduction of the undigested and digested solutions were collected in a liquid‐nitrogen cooled trap, separated with a gas chromatograph, and detected with a mass spectrometer in the selected‐ion‐monitoring mode. The investigated arsenic compounds were stable in hot 2 mol dm−3 sodium hydroxide except arsenobetaine [trimethyl(carboxymethyl)arsonium zwitterion] that was converted to trimethylarsine oxide, and dimethyl(ribosyl)arsine oxides that were decomposed to dimethylarsinic acid. Hydride generation before and after digestion of extracts from marine organisms allowed inorganic arsenic, methylated arsenic, arsenobetaine, and ribosyl arsenic compounds to be identified and quantified. This method was applied to extracts from shellfish, fish, crustaceans, and seaweeds.

Chemical form-dependent induction of hepatic zincthionein by arsenic administration and effect of co-administered selenium in mice

Four arsenic compounds ( m-arsenite, arsenate, methylarsonate (MMA), and dimethylarsinate (DMA) were administered to mice, either orally or by intraperitoneal injection, and the amounts of induced hepatic zinc-thionein (Zn-Th) were determined to investigate the chemical form dependency in metallothionein induction by arsenic. Several mice died within 24 h following intraperitoneal injection. The toxicity estimated from the lethality was in the order of m-arsenite >arsenate ⪢ DMA ≈ MMA. Although all 4 arsenic compounds more or less induced Zn-Th following intraperitoneal injection, the dose of inorganic arsenic compounds observed to cause induction was one order lower than that of organic arsenic compounds. The induction of hepatic Zn-Th was also observed following oral administration, and inorganic arsenic compounds were again found to be more effective inducers via this route. To study the interactions of m-arsenite and selenite with regard to the amounts of Zn-Th induced, the two compounds were co-administered intraperitoneally. The amount of hepatic Zn-Th induced by the co-administration was one-fifth of that observed after selenite administration, and was almost the same as that after m-arsenite injection. Namely, when co-administered m-arsenite had the effect of lowering the level of Zn-Th induced following selenite administration, but the converse phenomenon was not observed.

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

Previous studies have shown that several factors may influence the methylation of inorganic arsenic by rat liver in vitro (Buchet and Lauwerys, 1985). The present study attempts to assess the relevance of these observations in vivo. Like man, rat inactivates inorganic arsenic by methylation to monomethylarsoni (MMA) and dimethylarsinic (DMA) acids which are excreted in urine along with unchanged inorganic arsenic (Asi). The administration of S-adenosylmethionine alone or in association with reduced (GSH) or oxidized glutathione or acetylcysteine and the increase of hepatic GSH level by butylated hydroxytoluene pretreatment do not stimulate the urinary excretion of the methylated arsenic metabolites following a challenge dose of inorganic arsenic. Conversely a reduction of the hepatic GSH level by phorone pretreatment greatly modifies the metabolism of inorganic arsenic in vivo. A reduction exceeding 90% of the control value leads to a decreased urinary excretion of MMA and DMA and an increased urinary excretion of inorganic arsenic. This is also associated with an increased accumulation of inorganic arsenic in the liver. This suggests that a drastic reduction of GSH level in liver not only impairs the methylation of inorganic arsenic but also impairs its biliary excretion. When GSH depletion is less severe, the total amount of arsenic excreted in urine after a challenge dose of NaAsO 2 is not significantly different from that found in unpretreated animals but the proportion of the three metabolic forms is different: MMA is reduced whereas Asi and DMA tend to increase. These changes resemble those found in patients with liver insufficiency ( J. P. Buchet, A. Geubel, S. Pauwels, P. Mahieu, and R. Lauwerys (1984). The influence of liver disease on the methylation of arsenite in humans. Arch. Toxicol. 55, 151–154). Long-term pretreatment of rats with CCl 4 slightly reduces the amount of MMA and DMA excreted in urine following a challenge dose of inorganic arsenic. This effect may result from a reduction of GSH transferase activity by CCl 4. This study demonstrates the important role of liver GSH in the metabolism of inorganic arsenic in vivo

The determination method of arsenic compounds by high performance liquid chromatography with inductively coupled argon plasma emission spectrometry and its application to shellfishes.

In Dowex 50 column chromatography, arsenate, arsenite and methylarsonate (MAA) were quantitatively recovered in the unadsorbed fraction, dimethylarsinate (DMA) and arsenobetaine (AB) in the NH4OH fraction and arsenocholine (AC) in the HCI fraction. These arsenic compounds were subjected to HPLC using ion-exchangers and specifically monitored with an inductively coupled argon plasma emission spectrometer (ICP). Mutual separation of arsenate, arsenite, MAA and DMA was achieved on Nucleosil 10SB (anion exchanger) with 0.02M phosphate buffer (pH 7.0) and that of DMA, AB and AC on Nucleosil 10SA (cation exchanger) with 0.1M pyridineformate buffer (pH 3.1). A linear relationship between the peak height and the arsenic amount was obtained for each arsenic compound. Based on these results, a HPLC-ICP method combiped with the pre-treatment on Dowex 50 was postulated for the determination of the six arsenic compounds. By this HPLC-ICP method, it was found that the major arsenic compound in the shellfishes analyzed was AB regardless of their feeding habits. In the mid-gut gland of the carnivorous gastropod C. sauliae, AC was also detected as a minor component.

Sulphur-arsenic ligands: synthesis and characterization of some rhenium(I), ruthenium(II), rhodium(III) and gold(I) complexes of bis(dimethylarsino)sulphide(Me 2AsSAsMe 2) and dimethyl(methylthio)arsine(Me 2AsSMe)

The complexes [{RuCl 2(CO) 3} 2(Me 2AsSAsMe 2)], [RuCl 2(CO) 2(Me 2AsSAsMe 2) 2], [RuCl 2(CO) 2(Me 2AsSMe) 2], [ReX(CO) 3(Me 2AsSAsMe 2)] (X = Cl, Br or I), [RhCl 2(C 5Me 5)(Me 2AsSMe)], [AuCl(Me 2AsSMe)] and [(AuCl) 2(Me 2AsSAsMe 2)] have been synthesized from the electron-rich ligands Me 2AsSAsMe 2 and Me 2AsSMe. IR and NMR spectrometry along with mass spectra have given sufficient data to indicate structures for all of these products. In all complexes of both ligands, binding to metal is invariably via arsenic and not sulphur. Me 2AsSAsMe 2 has now been shown to be capable of monodentate, bridging and chelating modes of complexation.

Sulphur–arsenic ligands. Dimethyl(methylthio)arsine complexes of halogenotrimethylplatinum(IV) and tricarbonylhalogenorhenium(I)

Dimethyl(methylthio)arsine, AsMe2(SMe)(L), is a potentially ambidentate ligand with the possibility of arsine and/or sulphur co-ordination to a transition metal. We have investigated the reaction of the ligand for the scission of the tetrameric trimethylplatinum halides, and that for carbon monoxide displacement from the rhenium pentacarbonyl halides. In both of these reactions organic arsines and sulphides individually are known to be effective, producing well characterised stable products. Ligand L reacts with [(PtXMe3)4](X = Cl, Br, or I) and with [ReX(CO)5](X = Cl, Br, or I) to yield respectively fac-[PtXMe3L2] and fac-[ReX(CO)3L2] in good yield. Hydrogen-1 and 13C n.m.r. studies demonstrate that in all complexes the ligand behaves in a monodentate manner with exclusively arsenic–metal bonds. In solution the compounds give no indications of any fluxional behaviour in the temperature range –80 to +80°C. The fac structure of all of these complexes gives rise to the interesting observation that all three methyl groups in the co-ordinated ligand AsMe2(SMe) are non-equivalent.

Concentration and chemical status of arsenic in the blood of pregnant hamsters during critical embryogenesis: 2. Acute exposure

We have determined the concentration and chemical composition of arsenic in the blood of pregnant hamsters between 0.2 and 6 hr after an intraperitoneal injection of a teratogenic dose of radiolabeled sodium arsenate on the morning of the eighth day of gestation. Arsenic was present in plasma and red cells 0.20 hr postinjection. The plasma arsenic concentration reached a maximum of 220 mumole/kg blood near 0.5 hr postinjection. Plasma arsenic existed entirely as low-molecular-weight species. Both arsenite and dimethylarsinate (DMA) were present in plasma 0.20 hr postinjection, indicating that arsenate reduction and methylation of arsenic are rapidly initiated. However, the arsenite contribution remained small while the DMA contribution increased with time. Red cell arsenic included macromolecular arsenic (AsP) as well as three low-molecular-weight forms. The contribution of DMA remained small, but arsenite and AsP contributions increased with time. These findings identify the maternal blood concentration and chemical status of arsenic following the administration of a teratogenic dose of arsenate during the period of organogenesis. They could prove useful for predicting the likelihood of a teratogenic outcome in other mammalian species.

Arsenic uptake, cytotoxicity and detoxification studied in mammalian cells in culture.

The cytotoxicity of trivalent and pentavalent inorganic arsenic salts was determined in mouse fibroblasts in vitro. Concentrations of As (III) in the microM range led to a reduction of proliferation and viability with a concomitant increase in LDH release and stimulation of lactic acid production. Similar effects were noted with approximately 10-fold greater molar concentrations of As(V). Cells pretreated with a low As(III) concentration are less sensitive to toxic doses of As(III) or As(V). Uptake of As(III) by the fibroblasts is greater than that of As(V). Both forms of inorganic arsenic are converted intracellularly to monomethylarsonic (MMA) and dimethylarsinic (DMA) acids, which are then released into the culture medium. In As-pretreated cells, which are more resistant to As toxicity, biotransformation of inorganic arsenic to MMA and DMA is increased.