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At least 19 recordsLinked to original sources
PubMed1995

Sensitization to x-rays by sodium arsenite or heat in normal cells and in cells with an induced tolerance for heat and arsenite.

In this study we compared sensitization to x-rays by heat or sodium arsenite and the effect of an induced heat or arsenite resistance on radiosensitization. Treatment of Reuber H35 hepatoma cells with either heat or arsenite causes a dose-dependent radiosensitization. Based on a comparison of isosurvival doses for arsenite and heat, arsenite causes a stronger enhancement of the radiosensitivity. Radiosensitization increases exponentially with increasing sensitizer dose. It is gradually lost when the time interval between irradiation and treatment with heat or arsenite increases, depending on the treatment sequence. For x-rays prior to heat, radiosensitization disappears approximately twice as fast as in the reverse case. Arsenite radiosensitization shows approximately the same kinetics for an isoeffective combination, but slightly longer times are needed for the complete clearance of the interaction. As with heat, an exposure to arsenite induces a stress response in cultured cells which results in the development of an increased tolerance towards a second exposure. Heat and arsenite induce self- as well as cross-tolerance. The reduction in arsenite or heat toxicity in tolerant cells is correlated with a reduction in radiosensitization. The mechanisms for heat and arsenite cytotoxicity appear to be different. A combination of non-toxic doses of heat and arsenite has a synergistic effect on the cytotoxicity. One hour incubation with 0.02 mM arsenite at 41 degrees C has the same cytotoxicity as 0.2 mM after 3 h incubation at 37 degrees C, and the amount of radiosensitization induced by these treatments is approximately the same.

Animals↗
PubMed2001

Effects of arsenite on p53, p21 and cyclin D expression in normal human fibroblasts -- a possible mechanism for arsenite's comutagenicity.

Arsenite, the most likely environmental carcinogenic form of arsenic, is not significantly mutagenic at non-toxic concentrations, but is able to enhance the mutagenicity of other agents. Evidence suggests that this comutagenic effect of arsenite is due to inhibition of DNA repair, but no specific repair enzyme has been found to be sensitive to low (<1 microM) concentrations of arsenite. To determine whether arsenite affects signaling which might alter DNA repair, this study assesses the effect of arsenite on p53-related signal transduction pathways after ionizing radiation. Long-term (14 day) low dose (0.1 microM) arsenite caused a modest increase in p53 expression in WI38 normal human fibroblasts, while only toxic (50 microM) concentrations increased p53 levels after short-term (18 h) exposure. When cells were irradiated (6 Gy), p53 and p21 protein concentrations were increased after 4h, as expected. Both long-term, low dose and short-term, high dose exposure to arsenite greatly suppressed the radiation-induced increase in p21 abundance. In addition, long-term, low dose (but not short-term, high dose) exposure to arsenite resulted in increased expression of cyclin D1. These results show that in cells treated with arsenite, p53-dependent increase in p21 expression, normally a block to cell cycle progression after DNA damage, is deficient. At the same time, low (non-toxic) exposure to arsenite enhances positive growth signaling. We suggest that the absence of normal p53 functioning, along with increased positive growth signaling in the presence of DNA damage may result in defective DNA repair and account for the comutagenic effects of arsenite.

Arsenites↗
PubMed1995

Enhancement of the stress response by low concentrations of arsenite in arsenite-pretreated Reuber H35 hepatoma cells.

The present study is aimed at determining whether the induction of heat-shock protein (hsp) synthesis, heat-shock mRNAs, and tolerance development after arsenite application has been sensitized to low concentrations of arsenite in Reuber H35 rat hepatoma cells. Using a step-down arsenite treatment, consisting of a 1-hr pretreatment with 100 or 300 microM followed by an incubation with a lower concentration (1-10 microM), H35 cells were shown to exhibit increased sensitivity to low concentrations of sodium arsenite shortly after exposure to the high arsenite concentration, but not any longer when the low concentration was applied 4 hr after pretreatment. In this paper it is shown that exposure of H35 cells to sodium arsenite concentrations of 100 or 300 microM for 1 hr rapidly changes the sensitivity toward a second arsenite treatment with respect to the induction of the heat-shock response. It was observed that under conditions of enhanced sensitivity, an additional increase occurred in hsp synthesis as well as in hsp mRNA (as exemplified by hsp68 mRNA behavior) when low concentrations of arsenite were applied to arsenite pretreated cells. Since no effect of these low concentrations was observed in nonpretreated cells, the effect of step-down treatment results in a higher effect than could be expected based on summation. Furthermore, in sensitized cultures, cells are able to develop a higher level of tolerance in the presence of low concentrations of arsenite. It can be concluded that during a transient period of enhanced sensitivity, low concentrations of the original stressor are able to enhance hsp synthesis and to induce a higher level of tolerance in comparison with control cultures that are sensitized but not incubated in the presence of low concentrations of the original stressor.

Animals↗
PubMed2004

Molybdenum-containing arsenite oxidase of the chemolithoautotrophic arsenite oxidizer NT-26.

The chemolithoautotroph NT-26 oxidizes arsenite to arsenate by using a periplasmic arsenite oxidase. Purification and preliminary characterization of the enzyme revealed that it (i) contains two heterologous subunits, AroA (98 kDa) and AroB (14 kDa); (ii) has a native molecular mass of 219 kDa, suggesting an alpha2beta2 configuration; and (iii) contains two molybdenum and 9 or 10 iron atoms per alpha2beta2 unit. The genes that encode the enzyme have been cloned and sequenced. Sequence analyses revealed similarities to the arsenite oxidase of Alcaligenes faecalis, the putative arsenite oxidase of the beta-proteobacterium ULPAs1, and putative proteins of Aeropyrum pernix, Sulfolobus tokodaii, and Chloroflexus aurantiacus. Interestingly, the AroA subunit was found to be similar to the molybdenum-containing subunits of enzymes in the dimethyl sulfoxide reductase family, whereas the AroB subunit was found to be similar to the Rieske iron-sulfur proteins of cytochrome bc1 and b6f complexes. The NT-26 arsenite oxidase is probably exported to the periplasm via the Tat secretory pathway, with the AroB leader sequence used for export. Confirmation that NT-26 obtains energy from the oxidation of arsenite was obtained, as an aroA mutant was unable to grow chemolithoautotrophically with arsenite. This mutant could grow heterotrophically in the presence of arsenite; however, the arsenite was not oxidized to arsenate.

Alphaproteobacteria↗
PubMed1984

Characterization of arsenite-complexed xanthine oxidase at room temperature. Spectral properties and pH-dependent redox behavior of the molybdenum-arsenite center.

Several aspects of the interaction of xanthine oxidase with arsenite are investigated. Room temperature potentiometric titrations using EPR to monitor Molybdenum reduction reveal midpoint potentials of -225 mV for the Mo(VI)-arsenite/Mo(V)-arsenite couple and -440 mV for the Mo(V)-arsenite/Mo(IV)-arsenite couple at pH 8.3. Under the same conditions, the values for native enzyme are -395 mV and -420 mV, respectively. The predicted effects of the altered Mo(VI)/Mo(V) potential on the distributions of reducing equivalents in partially reduced enzyme are compared with the experimentally observed effects in optical experiments. The bleaching that occurs on reduction of the chromophore that is generated when arsenite binds to oxidized enzyme is characterized and found to be associated with reduction of Mo(V)-arsenite to Mo(V)-arsenite. This probe enables determination of the midpoint potential for this conversion using optical data. From such data at a series of pH values ranging from 6.15 to 9.9, a pH dependence of -60 mV/pH unit increase is determined for this couple above pH 7. The ability of arsenite to bind to reduced xanthine oxidase and to desulfo enzyme are also investigated. Reduced active enzyme binds arsenite much more tightly (Kd less than 0.1 microM) and more rapidly than does oxidized active enzyme (Kd = 8 microM); oxidized desulfo enzyme binds arsenite almost as tightly (Kd = 20 microM) as does the oxidized active enzyme.

Animals↗
PubMed1994

A proteolytic activity enhanced by arsenite in Chinese hamster ovary cells: possible involvement in arsenite-induced cell killing.

Treatment of Chinese hamster ovary (CHO-K1) cells with 10 microM sodium arsenite for 24 h resulted in enhancement of a proteolytic activity toward the chromogenic substrate CBZ-Phe-Arg-AMC. Presence of dithiothreitol and a pH between 4 and 6 were required for displaying its full hydrolytic activity. According to its substrate- and inhibitor-specificity, this arsenite-induced proteolytic activity was very similar to lysosomal cathepsin B. Arsenite cytotoxicity was further shown to be partially prevented by inhibitors that inhibited the arsenite-induced protease, such as antipain and chymostatin, but not by protease inhibitors without inhibitory effects on the arsenite-induced protease. Our present results suggest that the arsenite-induced protease activity may be involved in arsenite's killing effects.

Animals↗
PubMed1984

A plasmid-encoded arsenite pump produces arsenite resistance in Escherichia coli.

The arsenate resistance operon of R-factor R773, a conjugative resistance plasmid, has two functional regions, a promoter-proximal region encoding resistance to arsenite and antimonate, and a promoter-distal one encoding arsenate resistance. Cells bearing arsenite resistance plasmids exhibited reduced accumulation of 74AsO2-. When resistant cells were depleted of endogenous energy reserves and then loaded with 74AsO2-, active extrusion of the ion was observed when an energy source was supplied. Intracellular ATP was required for extrusion, but a proton motive force was neither necessary nor sufficient. An arsenite-sensitive mutant was unable to extrude arsenite, while an arsenate-sensitive mutant had normal arsenite transport. These results suggest that the action of a plasmid-encoded primary arsenite efflux pump is the mechanism of arsenite resistance.

Adenosine Triphosphate↗
PubMed1994

Induction of arsenite tolerance and thermotolerance by arsenite occur by different mechanisms.

Both V79 and As/R28A cells (an arsenite-resistant Chinese hamster V79 cell variant) show increased resistance to toxic concentrations of arsenite after pretreatment with a nontoxic concentration. The induced tolerance can be completely inhibited by actinomycin D or cycloheximide. Pretreatment with a nontoxic heat shock (45 degrees C, 10 min) resulted in a clear increased thermotolerance in both cell lines but failed to induce arsenite tolerance in either cell line. Pretreatment with arsenite induced a thermotolerance in V79 cells but not in As/R28A cells. These results are consistent with a model whereby the signal for induction of arsenite tolerance involves binding of arsenite to a protein effector which is amplified in the As/R28A line, thereby preventing action of arsenite in the regulation of heat shock factor which induces the heat shock response.

Animals↗
PubMed2004

Arsenite oxidation by the heterotroph Hydrogenophaga sp. str. NT-14: the arsenite oxidase and its physiological electron acceptor.

Heterotrophic arsenite oxidation by Hydrogenophaga sp. str. NT-14 is coupled to the reduction of oxygen and appears to yield energy for growth. Purification and partial characterization of the arsenite oxidase revealed that it (1). contains two heterologous subunits, AroA (86 kDa) and AroB (16 kDa), (2). has a native molecular mass of 306 kDa suggesting an alpha(3)beta(3) configuration, and (3). contains molybdenum and iron as cofactors. Although the Hydrogenophaga sp. str. NT-14 arsenite oxidase shares similarities to the arsenite oxidases purified from NT-26 and Alcaligenes faecalis, it differs with respect to activity and overall conformation. A c-551-type cytochrome was purified from Hydrogenophaga sp. str. NT-14 and appears to be the physiological electron acceptor for the arsenite oxidase. The cytochrome can also accept electrons from the purified NT-26 arsenite oxidase. A hypothetical electron transport chain for heterotrophic arsenite oxidation is proposed.

Amino Acid Sequence↗
PubMed1996

Arsenite efflux is inhibited by verapamil, cyclosporin A, and GSH-depleting agents in arsenite-resistant Chinese hamster ovary cells.

We have previously demonstrated that arsenite-resistant SA7 cells can extrude arsenite more effectively and completely than their parental Chinese hamster ovary cells. Our present results show that arsenite efflux from SA7 cells is inhibited by chemosensitizing agents to multidrug resistant-associated protein: verapamil and cyclosporin A and by glutathione-depleting agents: dinitrofluorobenzene and diethyl maleate. These results suggest that arsenite extrusion in SA7 cells may be mediated by a GSH-dependent and verapamil- and cyclosporin A-sensitive membrane transport system. Since arsenite extrusion was found dose-dependently inhibited by energy poison [potassium cyanide (KCN)] and an ATPase inhibitor (sodium vanadate), ATP is apparently required for arsenite extrusion in SA7 cells.

Animals↗
PubMed2006

Protein film voltammetry of arsenite oxidase from the chemolithoautotrophic arsenite-oxidizing bacterium NT-26.

The chemolithoautotrophic bacterium NT-26 (isolated from a gold mine in the Northern Territory of Australia) is unusual in that it acquires energy by oxidizing arsenite to arsenate while most other arsenic-oxidizing organisms perform this reaction as part of a detoxification mechanism against the potentially harmful arsenite [present as As(OH)(3) at neutral pH]. The enzyme that performs this reaction in NT-26 is the molybdoenzyme arsenite oxidase, and it has been previously isolated and characterized. Here we report the direct (unmediated) electrochemistry of NT-26 arsenite oxidase confined to the surface of a pyrolytic graphite working electrode. We have been able to demonstrate that the enzyme functions natively while adsorbed on the electrode where it displays stable and reproducible catalytic electrochemistry in the presence of arsenite. We report a pH dependence of the catalytic electrochemical potential of -33 mV/pH unit that is indicative of proton-coupled electron transfer. We also have performed catalytic voltammetry at a number of temperatures between 5 and 25 degrees C, and the catalytic current (proportional to the turnover number) follows simple Arrhenius behavior.

Alcaligenes faecalis↗
PubMed2006

Whole-cell arsenite biosensor using photosynthetic bacterium Rhodovulum sulfidophilum. Rhodovulum sulfidophilum as an arsenite biosensor.

An arsenite biosensor plasmid was constructed in Escherichia coli by inserting the operator/promoter region of the ars operon and the arsR gene from E. coli and the crtA gene, which is responsible for carotenoid synthesis in the photosynthetic bacterium, Rhodovulum sulfidophilum, into the broad-host-range plasmid vector, pRK415. The biosensor plasmid, pSENSE-As, was introduced into a crtA-deleted mutant strain of R. sulfidophilum (CDM2), which is yellow in culture due to its content of spheroiden (SE) and demethylspheroidene (DMSE). CDM2 containing pSENSE-As changed from yellow to red by the addition of arsenite, which caused enzymatic transformation of SE and DMSE to spheroidenone (SO) and demethylspheroidenone (DMSO). Reverse transcriptase PCR analysis showed that the color change depended on transcription of the crtA gene in pSENSE-As. The color change could be clearly recognized with the naked eye at 5 microg/l arsenite. The biosensor strain did not respond to other metals except for bismuth and antimony, which caused significant accumulation of SO and DMSO in the cells at 60 and 600 microg/l, respectively. This biosensor indicates the presence of arsenite with a bacterial color change without the need to add a special reagent or substrate for color development, enabling this pollutant to be monitored in samples by the naked eye in sunlight, even where electricity is not available.

Antimony↗
PubMed1991

Arsenite as the probable active species in the human carcinogenicity of arsenic: mouse micronucleus assays on Na and K arsenite, orpiment, and Fowler's solution.

Sodium arsenite, potassium arsenite, and Fowler's solution (arsenic trioxide dissolved in potassium bicarbonate) are equally active in the mouse bone marrow micronucleus assay (approximately 10 mg/kg by IP injection). The natural ore orpiment (principally As2S3) was inactive despite blood levels of arsenic of 300 to 900 ng/mL in treated mice at 24 hr. Sodium arsenite was active in three strains of mice. It is suggested that the human lung cancer observed among arsenic ore smelters and the skin cancer among people exposed therapeutically to Fowler's solution, have, as their common origin, the genotoxic arsenite ion AsO2-. The difficulty experienced when attempting to demonstrate rodent carcinogenicity for derivatives of arsenic suggests that the bone marrow micronucleus assay may act as a useful assay for potentially carcinogenic arsenic derivatives.

Animals↗
PubMed2001

Arsenite-inducible RNA-associated protein (AIRAP) protects cells from arsenite toxicity.

Exposure of cells to arsenicals activates multiple stress pathways resulting in the induction of specific genes whose identity and role in the adaptation to arsenical-induced cellular stress are poorly understood. We report here the identification of a novel gene encoding an arsenite-inducible, cysteine- and histidine-rich RNA-associated protein, AIRAP, that is conserved among mammals, Drosophila and C elegans. Immunochemistry and cell fractionation experiments indicate that, when induced, AIRAP is present in both the nucleus and the cytoplasm, and cross-linking experiments indicate that it associates with RNA in vivo. The expression of a C elegans homologue of AIRAP, aip-1, is also induced by exposure to arsenite, and expression of an aip-1::gfp transgene is most pronounced in hypodermal cells. RNA-mediated interference (RNAi) of aip-1 lowers the resistance of nematodes to arsenite yet does not appear to affect viability under standard growth conditions. These experiments suggest a role for AIRAP/AIP-1 in protecting cells from the toxic effects of arsenite.

Animals↗
PubMed2002

Anaerobic oxidation of arsenite in Mono Lake water and by a facultative, arsenite-oxidizing chemoautotroph, strain MLHE-1.

Arsenite [As(III)]-enriched anoxic bottom water from Mono Lake, California, produced arsenate [As(V)] during incubation with either nitrate or nitrite. No such oxidation occurred in killed controls or in live samples incubated without added nitrate or nitrite. A small amount of biological As(III) oxidation was observed in samples amended with Fe(III) chelated with nitrolotriacetic acid, although some chemical oxidation was also evident in killed controls. A pure culture, strain MLHE-1, that was capable of growth with As(III) as its electron donor and nitrate as its electron acceptor was isolated in a defined mineral salts medium. Cells were also able to grow in nitrate-mineral salts medium by using H(2) or sulfide as their electron donor in lieu of As(III). Arsenite-grown cells demonstrated dark (14)CO(2) fixation, and PCR was used to indicate the presence of a gene encoding ribulose-1,5-biphosphate carboxylase/oxygenase. Strain MLHE-1 is a facultative chemoautotroph, able to grow with these inorganic electron donors and nitrate as its electron acceptor, but heterotrophic growth on acetate was also observed under both aerobic and anaerobic (nitrate) conditions. Phylogenetic analysis of its 16S ribosomal DNA sequence placed strain MLHE-1 within the haloalkaliphilic Ectothiorhodospira of the gamma-PROTEOBACTERIA: Arsenite oxidation has never been reported for any members of this subgroup of the PROTEOBACTERIA:

Anaerobiosis↗
PubMed1985

Acetylcholinesterase: inhibition by tetranitromethane and arsenite. Binding of arsenite by tyrosine residues.

Tetranitromethane inhibits acetylcholinesterase with respect to the hydrolysis of both acetylthiocholine and indophenyl acetate. The loss of activity with indophenyl acetate, a poor substrate, is preceded by an increase in enzyme activity. Only 12 of the 21 tyrosine residues/monomer of enzyme are susceptible to nitration. Loss of activity with respect to indophenyl acetate occurs well after no further nitration of tyrosines occurs and must be due to the modification of other residues. Incubation of the enzyme with arsenite before nitration results in the nitration of only 10 tyrosines. This experiment reveals that the structural basis for the binding of arsenite is the formation of a diester with two tyrosine residues.

Acetylcholinesterase↗
PubMed2004

Effects of arsenite on UROtsa cells: low-level arsenite causes accumulation of ubiquitinated proteins that is enhanced by reduction in cellular glutathione levels.

Chronic arsenic exposure increases risk for the development of diabetes, vascular disease, and cancers of the skin, lung, kidney, and bladder. This study investigates the effects of arsenite [As(III)] on human urothelial cells (UROtsa). As(III) toxicity was determined by exposing confluent UROtsa cells to As(III) (0.5-200 microM). Depleting cellular glutathione levels with buthionine sulfoximine (BSO) potentiated the toxicity of As(III). Cell viability was assessed with the (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. UROtsa cell ability to biotransform As(III) was determined by dosing cells with environmentally relevant concentrations of As(III) followed by HPLC/ICP-MS analysis of cell media and lysate. Both pentavalent and trivalent monomethylated products were detected. Although cytotoxicity was observed at high doses of As(III) (approximately 100 microM) in UROtsa cells, perturbations of a variety of molecular processes occurred at much lower doses. Exposure to low-level As(III) (0.5-25 microM) causes an accumulation of ubiquitin (Ub)-conjugated proteins. This effect is enhanced when cellular glutathione levels have been reduced with BSO treatment. Because As(III) has many effects on UROtsa cells, a greater understanding of how As(III) is affecting cellular proteins in a target tissue will lead to a better understanding of the mechanism of toxicity and pathogenesis for low-level As(III).

Arsenic↗