A long-term observation of the environmental conditions of a factory manufacturing lead arsenate as an insecticide (studies on lead arsenate poisoning, Part 1).
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Air Pollutants↗
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A long-term health examination upon lead arsenate workers in an insecticides factory. (Studies on lead arsenate poisoning, Part 2).
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Arsenic↗
Arsenate substitutes for phosphate in the human red cell sodium pump and anion exchanger.
The sodium pump of human red blood cells mediates a Rb:Rb exchange that is dependent for maximal rates upon the simultaneous presence of intracellular ATP (or ADP) and phosphate. We have measured ouabain-sensitive 86Rb uptake into resealed ghosts of human red cells containing ADP and show that arsenate will substitute for phosphate in supporting the Rb:Rb exchange transport mode. The concentration dependence of arsenate-supported Rb:Rb exchange in ghosts containing 2 mM ADP shows both activating and inhibiting phases; the dependence upon phosphate shows similar characteristics. Elevation of the external [Rb] lowers the apparent affinity for arsenate since there is a shift to higher concentrations of arsenate in the activating and inhibiting phases of the arsenate concentration dependence curve. Similarly, elevation of [ADP] substantially reduces the inhibition of Rb:Rb exchange observed at higher [arsenate]. These effects are also observed in phosphate-supported Rb:Rb exchange. The phosphate requirement for Rb:Rb exchange involves phosphorylation of the sodium pump protein; the close agreement between the effects of arsenate and phosphate in supporting Rb:Rb exchange makes it likely that arsenylation of the sodium pump occurs during Rb:Rb exchange. Arsenate efflux from red blood cell ghosts into arsenate-free chloride medium is partially inhibited (77-80%) by DNDS (4,4'-dinitro-2,2'-stilbenedisulfonic acid), this compares with 82-87% inhibition by DNDS of phosphate efflux under the same conditions. It appears that Band III, the red cell anion transport system, accepts arsenate in a similar fashion to phosphate and that a fraction of the flux of both anions may occur through pathways other than Band III. Thus, in human red blood cells, both the sodium pump and the anion exchange transport system will accept arsenate as a phosphate congener and the protein-arsenate interactions are very similar to those with phosphate.
Arsenates↗
The impact of temperature on the acute toxicity of arsenate and arsenite to rainbow trout (Salmo gairdneri).
This research investigated the influence of temperature (5 or 15 degrees C) on the acute toxicity of waterborne arsenite and arsenate to rainbow trout. Trout exposed to arsenate at 5 degrees C had a 144-hr LC50 (95% fiducial limits) of 114.1 (106.7 to 121.9) mg liter-1, twice the value of 58 (50.6 to 66.4) mg liter-1 evident in fish exposed at 15 degrees C. Temperature had no effect on the toxicity of arsenite; 144-hr LC50's at 5 and 15 degrees C were 17.7 (16.5 to 18.9) and 20.7 (19.9 to 21.5) mg liter-1, respectively. When fish were exposed to 70 mg liter-1 arsenate for 72 hr, those held at 15 degrees C had mean whole-body arsenic levels that were five times higher than the levels in fish held at 5 degrees C. There were, however, essentially no differences in the patterns of arsenic uptake between 5 and 15 degrees C when the fish were exposed to arsenate at 0.7 or 1.2 of the 144-hr LC50 at each temperature, a strategy which compensates for (eliminates) temperature as a modifier of toxicity. Fish which were held in arsenate-free water after the 72-hr arsenate exposure depurated significantly more arsenic at 15 degrees C than at 5 degrees C. Despite this, it is apparent that enhanced uptake at 15 degrees C was the overriding factor controlling the differences in the expression of arsenate toxicity at the two temperatures.
Animals↗
Arsenic-75 nuclear magnetic resonance: study of the interaction of arsenate with various molecules of biological interest.
75As NMR (Nuclear Magnetic Resonance) was used as a probe of arsenate interactions in solution. The linewidth at half-height of the 75As NMR signal of arsenate was studied as a function of solution pH and temperature. Below pH 11.5, the 75As signal was too broad to be detected, but at higher pH, up to pH = 13.5, the signal became much narrower. This indicates that the arsenate species AsO4(3-) is quite symmetric, but the asymmetry of HAsO4(2-) is sufficient to cause extensive quadrupolar relaxation of the 75As nucleus. A full pH range 75As and proton NMR study of the interaction of arsenate with ethanol, ethylene glycol, glycerol, ribose, mannose, glucose, gluconic acid and acetate was undertaken in order to follow arsenate ester formation. The 75As line broadening effects and the proton ligand shifts observed indicate that complexation of arsenate by ribose, mannose, glucose, ethanol, ethylene glycol, and glycerol occurs at pH 12.7. However, no significant interaction is detected by NMR with gluconic acid or acetate. The effect of the nucleoside adenosine is quite small and those of phosphate and of the nucleotides AMP and ADP are negligible. The interaction of arsenate with potential cationic centers, such as the basic amino acids lysine and arginine and some macrocyclic triamines, was also studied. Such interaction depends on the pKa for protonation of the amine groups.
Acetates↗
Phosphate transport in arsenate-resistant mutants of Micrococcus lysodeikticus.
Two types of arsenate-resistant mutants of Micrococcus lysodeikticus were found: (i) mutants that grow in the presence of 10 mM but not 1 mM phosphate (Pi) with low uptake rate for Pi and arsenate, and (ii) mutants able to grow in the presence of 10 mM and 1 mM Pi, with a near-normal uptake rate for Pi but a low one for arsenate. The Km values for Pi transport and the Ki values for its competitive inhibition by arsenate were similar for the mutants and the wild type. Similar to the wild type, the mutants also accumulated Pi to high concentrations. In all strains, the transport of Pi was subject to repression by Pi. Mutant types showed lower Vmax but unaltered Km values for arsenate as compared to the wild type, and they accumulated arsenate to markedly lower levels. The results suggest a two-component transport system common to Pi and arsenate.
Arsenates↗
Effects of arsenate on the Ca2+ ATPase of sarcoplasmic reticulum.
The effect of arsenate on the partial reactions of the catalytic cycle of the Ca2+ ATPase of skeletal muscle of sarcoplasmic reticulum was studied. With the use of native vesicles it was found that arsenate accelerates the rate of ITP hydrolysis and inhibits both Ca2+ or Sr2+ uptake. These effects were not observed when ATP was used as substrate or, with the use of ITP, when leaky vesicles were assayed. Activation of ITP hydrolysis is related to an increase of the enzyme's apparent affinity for ITP. Arsenate increases the steady-state level of the phosphoenzyme formed from ITP. This depends on the concentration of both Pi and Ca2+, in the medium. Ca2+ and Sr2+ efflux were accelerated by arsenate. The fast Ca2+ efflux promoted by arsenate is impaired by external Ca2+. Arsenate competes with Pi for the phosphorylating site of the enzyme.
Adenosine Triphosphate↗
Constant rate exposure of pregnant hamsters to arsenate during early gestation.
We have examined the teratogenic and embryotoxic effects of constant-rate exposure of pregnant hamsters to arsenate by means of subcutaneous implants of osmotic minipumps. Different total exposure regimens were established by varying the duration of minipump implants and by varying the concentration of arsenate in the minipumps. Dams were killed on Day 13 of pregnancy, 5 days after the critical stage of organogenesis. Numbers of resorptions, dead fetuses, and living fetuses were obtained. Fetal weights, crown-rump lengths, and the incidence of malformations were recorded. Control animals were treated identically with minipumps containing demineralized water. The percentage of malformations per litter, a direct measure of teratogenesis, was dependent only upon the concentration of arsenate in the minipumps. The minimum teratogenic response was achieved with a dose of 70 mumol/kg dam/24 hr during the critical stages of organogenesis. The embryotoxic (fetotoxic) indicators, fetal weight and crown-rump length, decreased with increases in exposure time and with increased concentrations of arsenate. The resorption rate also depended directly upon duration of exposure and concentration of arsenate in the minipump.
Abnormalities, Drug-Induced↗
Reduction of arsenate to arsenite by the ArsC protein of the arsenic resistance operon of Staphylococcus aureus plasmid pI258.
The arsenic resistance operon of Staphylococcus aureus plasmid pI258 consists of three genes, arsR (encoding the repressor regulatory protein), arsB (the determinant of the membrane efflux protein that confers resistance by pumping arsenic from the cells), and arsC (the small gene whose protein product is required for arsenate resistance only, not for arsenite resistance). ArsC has now been shown to be an arsenate reductase, converting intracellular arsenate [As(V)] to arsenite [As(III)], which is then exported from the cells by an energy-dependent efflux process. The arsenate reductase activity was found in the soluble cytoplasmic fraction in Escherichia coli (and not associated with the periplasmic fraction or the sedimentable cell envelope). Purified ArsC protein coupled in vitro with thioredoxin plus dithiothreitol (but not 2-mercaptoethanol or reduced glutathione) to reduce arsenate to arsenite.
Adenosine Triphosphatases↗
Accumulation of arsenate, phosphate, and aspartate by Sreptococcus faecalis.
Uptake of arsenate and phosphate by Streptococcus faecalis 9790 is strictly dependent on concurrent energy metabolism and essentially unidirectional. targinine supports uptake only in presence of glycerol or related substances; glycerol is not directly involved in transport but depletes the cellular orthophosphate pool and thus relieves feedback inhibition of transport. Uptake of phosphate and arsenate is stimulated by K+ and by other permeant cations. The results suggest that electroneutrality is preserved by compensatory movement of either H+ or OH minus. Ionophores and N,N'-dicyclohexylcarbodiimide, which prevent establishment of a proton motive force, block the accumulation of thiomethylgalactoside and of threonine but not that of arsenate or phosphate. We conclude that arsenate accumulation requires adenosine 5'-triphosphate but is not driven by the proton-motive force. However, conditions and reagents that lower the cytoplasmic pH do inhibit accumulation of arsenate and phosphate, suggesting that uptake depends on the capacity of the cells to maintain a neutral or alkaline cytoplasm. We therefore propose that phosphate accumulation is an electroneutral exchange for OH driven by adenosine 5'-triphosphate or by a metabolite thereof. Accumulation of aspartate and glutamate also requires adenosine 5'-triphosphate but not the proton-motive force and may involve a similar mechanism.
Adenosine Triphosphate↗
The effects of urethane, sodium monohydrogen arsenate and selenocystine on crossing-over in Drosophila melanogaster.
The effects of 0 - 25 mM urethane, 0 - 50 muM selenocystine and 0 - 100 muM sodium monohydrogen arsenate on marker-exchange frequencies have been studied along a region of the X chromosome of Drosophila melanogaster marked by y, cv, v and f. Clear and consistent effects seen in concentration curves were usually but not always found significant in analyses of variance. Urethane concentration curves rose to a higher level at 0.5 to 3 mM and dropped to control levels between 10 and 25 mM. It is proposed that this reversibility was due to a competition between two categories of lesions mimicking natural recombination sites, those on unpaired regions of the chromosome competing with those on already paired regions for recombination-repair enzymes. Selenocystine affected exchange frequencies mainly toward the ends of the unmarked region, especially y - cv, negatively from 2 to 10 muM and positively above 10 muM. These effects are interpreted as being mediated by selenocystine control over restriction of synaptic pairing to terminal regions, especially y - cv. Interaction between urethane and selenocystine in two-chemical treatments satisfactorily support the above explantations for both the urethane and selenocystine effects. Sodium monohydrogen arsenate effects, tentatively attributed to the arsenate ion, differed markedly from those of the other chemicals: "arsenate" concentration curves for single-exchange classes tended to be broadly convex and those for double-exchange classes concave, while interactions with urethane tended to be synergistic or neutral except in one exchange class (that for single exchange in y - cv). No satisfactory explanation of the arsenate effects has yet been found. At 25 mM only, urethane caused male-specific, 95% pupal mortality.
Animals↗
The mitochondrial activation of sulfate and arsenate and their role in carcinogenesis.
Sulfate substitutes for phosphate in the transitory uncoupling of rat liver mitochondria induced by hydrazine when beta-hydroxybutyrate is the substrate. A high level of sulfate in the absence of added phosphate induces a pseudo state three of the mitochondria. Uncoupling is inhibited by rutamycin. Thus sulfate is activated by the mechanism usually utilized by phosphate, and the target for hydrazine is the bond holding electrophilic sulfate. ATP, ADP, PPi, and Mg++ protect against hydrazine, presumably by causing a conformational change of the phosphorylating enzymes which participate in oxidative phosphorylation. Arsenate also could substitute for phosphate in the transitory uncoupling induced by hydrazine. Uncoupling is again inhibited by rutamycin; thus arsenate is also activated by the enzymic mechanism usually utilized by phosphate. Since sulfate is known to enhance the carcinogenicity of certain carcinogens, these results expand the experimental confluence between oxidative phosphorylation and chemical carcinogenesis and also serve to explain at least in part the "toxic" effects of sulfate. Because of the analogous results with arsenate and sulfate, it is suggested that arsenate, like sulfate, may enhance the carcinogenicity of other carcinogens. The data are compatible with epidemiological studies which implicate some role in carcinogenesis for sulfate (often measured as a sulfur dioxide equivalent) and arsenate.
Animals↗
Teratogen concentration changes as the basis of the heat stress enhancement of arsenate teratogenesis in hamsters.
Hamster dams dosed continuously with arsenate and exposed to short-term hyperthermia produced a greater percentage of malformed offspring than did hamster dams dosed with arsenate alone. Hamsters receiving both treatments possessed elevated arsenic concentrations in the maternal blood and placentas immediately after cessation of the hyperthermic insult. Blood levels of arsenic were the same as those of animals not receiving the heat treatment within several hours post-hyperthermia; however, arsenic concentrations remained elevated in placentas, the duration being dependent on the dose of arsenate. We suggest that the rise in placental arsenic concentrations is the basis of the increase in the production of fetal malformations for hamsters treated continuously with arsenate and heat stressed during critical organogenesis.
Animals↗
The role of the methylation in the detoxication of arsenate in the rabbit.
The biotransformation, tissue retention, intracellular binding and biokinetics of arsenic were studied in rabbits exposed to [74As]arsenate (0.4 mg As/kg body wt., i.v.). Inhibition of the methyltransferase activity by injection of periodate-oxidized adenosine (PAD) caused a marked decrease of the formation of [74As]dimethylarsinic acid (DMA), which gave rise to 1.5-4 times increased tissue levels of 74As. This is almost the same as reported for rabbits given arsenite in combination with PAD and was due to a rapid reduction of the arsenate to arsenite which bound to the tissues. Only about 30% of the arsenate given was excreted unchanged in the urine, indicating that a large part was reduced to AsIII. Thus the methylation to DMA seems to be almost as important for the detoxication following exposure to arsenate as that following exposure to arsenite. In the rabbits with normal methylating capacity 50-70% of the produced AsIII was methylated to DMA. The liver was the only organ in which DMA was present 1 h after the administration, indicating that this is the main site of the methylation. The DMA was rapidly cleared from all tissues except the thyroid.
Animals↗
Intestinal absorption of arsenate in the chick.
The intestinal absorption of arsenate(As(V)) has been investigated in the chick by means of the in situ ligated duodenal loop technique. By this procedure, it was observed that arsenate is rapidly and essentially completely absorbed (80-95%) from the lumen at As(V) concentrations up to 5 mM, declining to about 50% absorption at 50 mM. Transfer from the intestinal lumen to the mucosal cells at low As(V) concentration (0.1 mM) is rapid, while transfer from the mucosal cells to the body occurs more slowly. At stable As(V) concentrations greater than 1 mM, fractional mucosal cell accumulation of As(V) remains constant, while fractional transfer to the body declines. However, total mucosal accumulation of As(V) and that transferred to the body increase in a linear logarithmic fashion from 0.05 to 5 mm As(V). The results indicate that As(V) readily penetrates both the mucosal and serosal surfaces of the epithelial membrane. Furthermore, arsenate and phosphate do not appear to share a common transport pathway in the duodenum and no evidence was obtained for any interaction between the two at this level. Vitamin D3 administration to rachitic chicks was effective in significantly elevating duodenal arsenate absorption, acting primarily to enhance serosal transport.
Administration, Oral↗
Whole-body arsenic concentrations in rainbow trout during acute exposure to arsenate.
This research explored the influence of temperature and waterborne arsenate exposure level on the whole-body arsenic (As) concentration in rainbow trout (Oncorhynchus mykiss) at loss of equilibrium (LOE), an acute toxicity endpoint. The mean median times (ET50s) to LOE for fish exposed to 120 mg arsenate liter-1 at 5 degrees C, as well as 60 and 120 mg liter-1 at 15 degrees C were 56.8, 210, and 34.8 hr, respectively. Despite the differences in ET50, the fish showed respective mean (SE) whole-body As concentrations of 8.6 (0.3), 8.1 (0.6), and 8.6 (0.4) micrograms As g-1, values which were not significantly different. Fish exposed to 240 mg arsenate liter-1 at 5 degrees C, which had a LOE ET50 of 32.2 hr, were observed to have a mean (SE) whole-body arsenic concentration of 13.5 micrograms g-1, significantly higher than the levels in fish from all other treatments. A 3-hr delay between LOE and sampling did not significantly alter whole-body As concentration. The results are discussed in terms of the utility of using whole-body As concentrations to interpret the impacts of arsenate on fish populations in the field.
Animals↗
Phosphate transport and arsenate resistance in the cyanobacterium Anabaena variabilis.
Cells of the cyanobacterium Anabaena variabilis starved for phosphate for 3 days took up phosphate at about 100 times the rate of unstarved cells. Kinetic data suggested that a new transport system had been induced by starvation for phosphate. The inducible phosphate transport system was quickly repressed by addition of Pi. Phosphate-starved cells were more sensitive to the toxic effects of arsenate than were unstarved cells, but phosphate could alleviate some of the toxicity. Arsenate was a noncompetitive inhibitor of phosphate transport; however, the apparent Ki values were high, particularly for phosphate-replete cells. Preincubation of phosphate-starved cells with arsenate caused subsequent inhibition of phosphate transport, suggesting that intracellular arsenate inhibited phosphate transport. This effect was not seen in phosphate-replete cells.
Arsenates↗
Expression and regulation of the antimonite, arsenite, and arsenate resistance operon of Staphylococcus xylosus plasmid pSX267.
The arsenate, arsenite, and antimonite resistance region of the Staphylococcus xylosus plasmid pSX267 was subcloned in Staphylococcus carnosus. The sequenced DNA region revealed three consecutive open reading frames, named arsR, arsB, and arsC. Expression studies in Escherichia coli with the bacteriophage T7 RNA polymerase-promoter system yielded three polypeptides with apparent molecular weights of 8,000, 35,000, and 15,000, which very likely correspond to ArsR, ArsB, and ArsC, respectively. ArsB was distinguished by its overall hydrophobic character, suggesting a membrane association. The arsenate, arsenite, and antimonite resistance was shown to be inducible by all three heavy metal ions. Inactivation of the first gene, arsR, resulted in constitutive expression of resistance. Similar results were obtained with transcriptional fusions of various portions of the ars genes with a lipase reporter gene, indicating a function of ArsR as a negative regulator of a putative promoter in front of arsR. The inactivation of arsR also resulted in reduction of resistance to arsenite and antimonite, while arsenate resistance was unaffected. The three ars genes conferred arsenite resistance in E. coli and arsenite as well as arsenate resistance in Bacillus subtilis.
Adenosine Triphosphatases↗