Showing papers on "Sodium arsenite published in 1993"

Reactions of arsenic(III) and arsenic(V) species with glutathione

Abstract: Arsenic is metabolized by living systems using oxidation-reduction and methylation reactions, and reduced glutathione (GSH) has been shown to be important in that metabolism. In this study, the solution reactions between GSH and arsenate, arsenite, and their methylated metabolites, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), were characterized using 1H and 13C NMR under a nitrogen atmosphere. Binding to GSH through the thiol group was primarily followed by shifts in the carbon atom bonded to the sulfhydryl group of the cysteinyl residue, i.e., the CH2 carbon atom and the protons bonded to it. The methylated metabolites also showed shifts in the methyl groups attached to the arsenic atom after reaction with GSH. Sodium arsenite, As(III), bound to GSH to form an As(SG)3 complex in solution as indicated by NMR spectra. The identity of the complex was confirmed by FAB-MS after isolation of the compound. Mixtures of sodium arsenate, As(V), and GSH showed that arsenate oxidized GSH in D2O solutions at pH 7 to form oxidized glutathione (GSSG). When the molar ratio of As:GSH exceeded 1:2, evidence for the formation of As(SG)3 was observed. MMA and DMA are both As(V) species, and mixtures with GSH showed oxidation to GSSG initially followed by formation of CH3.As(SG)2 and (CH3)2.As.SG, respectively. The effects of GSH on arsenic metabolism may result from direct reactions between the two compounds.

Arsenite enhances DNA double-strand breaks and cell killing of methyl methanesulfonate-treated cells by inhibiting the excision of alkali-labile sites.

Abstract: Analysis of DNA strand breaks by alkaline elution indicates that DNA repair of Chinese hamster ovary cells treated with methyl methanesulfonate (MMS) was inhibited by sodium arsenite. Comparing the profiles of a 36-min elution with buffer pH 12.1 and a 12-h elution with buffer pH 12.4 revealed that alkali-labile sites were increased more than frank breaks in the combined treatment with MMS plus arsenite. Enhancement of alkali-labile sites was detected with low doses of MMS and arsenite, whereas enhancement of frank breaks required higher doses of MMS and arsenite. Double-strand breaks were detected after incubating the MMS-treated cells in an arsenite-containing medium for 18 or 12 h but not less than 6 h. No double-strand breaks were detected when MMS-damaged cells were posttreated with arsenite for 3 h; however, double-strand breaks were detected after further incubating these cells in arsenite-free medium for 18 h. Thus, inhibition of arsenite on the excision of methylated bases may have accumulated a large number of alkali-labile sites in the parental strands, and DNA replication may then generate breaks in the non-methylated daughter strands. Double-strand breaks may result from overlapping gaps between the parental and daughter strands and/or postreplication repair. These double-strand breaks may then result in the synergistic cell death as observed with posttreatment of MMS-damaged cells with arsenite for 1 or 3 h.

Synthesis and accumulation of stress proteins in tissues of arsenite-exposed fathead minnows (Pimephales promelas)

Abstract: The stress protein response (SPR) is a ubiquitous, protective, and defensive mechanism that enables cells to tolerate environmental perturbations. Induction of the SPR involves the increased transcription of stress protein genes, the products of which function in protein folding, multimeric protein assembly, receptor interactions, and heme catabolism, and so forth. The potential of this response as an indicator of water quality was evaluated in gill and striated muscle tissues of fathead minnows (Pimephales promelas) exposed to a wide range of concentrations of sodium arsenite for various lengths of time. The SPR in gill was elicited rapidly, occurring by 2 h exposure at 25 mg/L. The response was tissue specific. In gill, synthesis and accumulation rates of 20-, 40-, 70-, 72-, and 74-kD proteins were significantly increased, compared to controls. In muscle, 20-, 30-, 68-, 70-, and 90-kD proteins also showed significantly increased syntheses and accumulations. Synthesis and accumulation rates of arsenite-induced proteins 20-, 70-, 72-, and 74-kD in gill were significantly correlated with mortality. However, in striated muscle, only the 70-kD was significantly correlated with mortality.

Induction of chromatid breaks and tetraploidy in Chinese hamster ovary cells by treatment with sodium arsenite during the G2 phase.

Abstract: Treatment of Chinese hamster ovary (CHO) cells with sodium arsenite during the G2 phase induced poorly condensed chromosomes and chromatid breaks. The induction of chromatid breaks was confirmed by the appearance of micronucleated cells after arsenite-treated G2 cells were allowed to re-enter interphase. When the duration of the G2 phase was artificially divided into 4 periods, more chromatid breaks were induced by treatment with arsenite during the very early G2 phase (or G2/S boundary). In addition to the induction of chromatid breaks, arsenite treatment also remarkably retarded the re-entry of mitotic cells into interphase. By replating and incubating arsenite-treated G2 cells in drug-free medium, we subsequently observed the appearance of a population of cells whose DNA content was between 4C and 8C, and metaphase cells with near-tetraploid chromosome numbers in the next mitotic division.

Serum-stimulated cell cycle progression and stress protein synthesis in C3H10T1/2 fibroblasts treated with sodium arsenite.

Abstract: In this work, we demonstrated that a nonlethal dose of arsenite administered to quiescent C3H10T1/2 fibroblasts can enhance the mitogenic effect of suboptimal concentrations of serum. The mitogenic effect was dependent on the serum concentration and on the time interval between the administration of arsenite and that of serum. This suggests that mitogen sensitivity changes in time after arsenite treatment. It is shown that the concentrations of arsenite that enhance the mitogenic effect of serum also increase the mRNA levels of c-fos, HSP68, and HSP84 and induce the specific synthesis of Heat Shock Proteins (HSPs). The physiological significance of this phenomenon is most likely to counteract the long-term toxic effect of arsenite by early induction of compensation for cell loss.

Enhanced phosphorylation of a 65 kDa protein is associated with rapid induction of stress proteins in 9L rat brain tumor cells.

Abstract: Induction of heat-shock proteins and glucose-regulated proteins in 9L rat brain tumor cells can be differentially elicited by sodium arsenite, cadmium chloride, zinc chloride, copper sulfate, sodium fluoride, and L-azetidine-2-carboxylic acid. The kinds of stress protein induced by the above chemicals varied considerably, mainly determined by the nature and the concentration of the chemicals, as well as the treatment protocols. In addition, at the concentrations where stress proteins can be induced, the above chemicals were able to suppress general protein synthesis and were cytotoxic. Enhanced phosphorylation of a protein with an apparent molecular weight of 65 kDa was detected during the induction of stress proteins except in azetidine treatments during which uptake of phosphate by the cells was impaired after prolonged incubation. The phosphate moiety on the 65 kDa phosphoprotein appeared to be alkaline-stable and two-dimensional gel electrophoresis revealed that the phosphoprotein resolved into four isoforms with isoelectric points ranging from 5.1 to 5.6. Enhanced phosphorylation of the same protein was also detected in heat-shocked and withangulatin A-treated 9L cells in which stress proteins were induced. It is suggested that this phosphoprotein may be a common target for heat stress response-stimulated phosphorylation and important in the further metabolic responses of the cell to stress. © 1993 Wiley-Liss, Inc.

Effects of arsenic on DNA synthesis in human lymphocytes.

Abstract: Effects of arsenic on DNA synthesis in human lymphocytes were biphasic: Either trivalent (arsenic trioxide and sodium arsenite) or pentavalent (sodium arsenate) arsenic compounds at very low concentrations enhanced DNA synthesis in human lymphocytes stimulated by phytohemagglutinin (PHA), whereas higher concentrations inhibited DNA synthesis. There were differences among individual susceptibilities to arsenic-induced DNA synthesis. Either stimulating or inhibiting effects of trivalent arsenic on DNA synthesis in PHA-stimulated lymphocytes were always stronger than those of pentavalent arsenic. Both trivalent and pentavalent arsenic could be rapidly taken up into the human lymphocytes and immediately stimulate or inhibit DNA synthesis. A possible dual effect of arsenic at very low concentrations as both comutagen and inhibitor of mutagenesis is discussed.

Effect of amino acid analogs on the development of thermotolerance and on thermotolerant cells

Abstract: Exposure of HA-1 Chinese hamster fibroblasts to amino acid analogs has been shown to have a heat-sensitizing effect as well as inducing the heat shock response (Li and Laszlo, 1985a). In this study, we have examined the effect of amino acid analogs on the development of thermotolerance after a brief heat shock or exposure to sodium arsenite and the effect of amino acid analogs on cells that are already thermotolerant. Exposure of HA-1 cells to amino acid analogs inhibited the development of thermotolerance following a mild heat shock or treatment with sodium arsenite. However, cells that were already thermotolerant were resistant to the sensitizing action of amino acid analogs. The refractoriness of thermotolerant cells to amino acid analog treatment developed in parallel with thermotolerance. The uptake of the arginine analog, canavanine, and its incorporation into proteins was not altered in the thermotolerant cells. Furthermore, another biological consequence of exposure to amino acid analogs, sensitization to ionizing radiation, also was not altered in the thermotolerant cells. The inhibition of the development of thermotolerance by amino acid analogs and the refractoriness of thermotolerant cells to the heat-sensitizing action of amino acid analogs lend further support the role of heat-shock proteins in the phenomenon of thermotolerance. © 1993 Wiley-Liss, Inc.

Arsenite induced sensitization and self-tolerance of Reuber H35 hepatoma cells.

Abstract: Our data show that a short incubation with arsenite (30-300 microM) induces a biphasic change in cellular sensitivity towards a second exposure to arsenite. A transient sensitization was followed by the development of self-tolerance. Sensitization was measured using the step-down protocol; i.e., application of a high dose of arsenite pretreatment (100 or 300 microM) followed immediately by incubation in a low dose of arsenite (1-30 microM), with extensive rinsing in between. Whereas no effect of 1 and 3 microM on cellular survival is observed without pretreatment, a large decrease in cell survival can be established when these low doses of arsenite are applied immediately after a 1 hr pretreatment with 100 or 300 microM arsenite. According to the step-down protocol, a high dose of toxic compounds is applied and is followed by prolonged incubation in a lower concentration of the initial toxic compound. This might be a more accurate model for studying the effects of toxic insults on cells and organisms in the manner in which they occur in their natural environment. The level of tolerance was determined by a 1 hr test treatment with 300 microM arsenite applied at different times after pretreatment. Using this fractionated treatment protocol, it was established that tolerance increases with the increasing time intervals between the sodium arsenite treatments, during the 6 hr studied. These observations suggest that sensitization gradually decreases, whereas tolerance develops. Furthermore, our data indicate that the condition of pretreatment determines the extent to which the early sensitivity increases, as well as the development of tolerance later on. A relatively high arsenite concentration leads to more sensitized cells, which are transformed into more tolerant cells in comparison with the effect of a lower arsenite concentration.

Use of crude extract of garlic (Allium sativum L.) in reducing cytotoxic effects of arsenic in mouse bone marrow

Abstract: A relatively high concentration of crude extract of garlic, (Allium sativum L.)--single clove variety, was found to reduce the cytotoxic effects of three doses of sodium arsenite, corresponding to 1/10, 1/30 and 1/50 of the LD50 in laboratory bred male Swiss albino mice. The animals were given a single oral dose of the chemical, together with the extract, and effects were observed after 24 h in bone marrow cells following the colchicine–fixation–airdry–Giemsa schedule. The endpoints scored were chromosomal aberrations and damaged cells.

Modification of Cytotoxic Effects of Inorganic Arsenic by a Crude Extract of Allium sativum L. in Mice

Abstract: A crude extract of Allium sativum (100 mg/kg b.w./day) was administered orally to Swiss albino mice with a normal diet for 30 days. Sodium arsenite, a known cytotoxic agent, was given subcutaneously in normal saline to mice (0.1 mg/kg b.w. = 1/50 of LD50) on days 7,14,21 AND 30 of experiments. Chromosomal studies were conducted on bone marrow preparations following the colchicine-air-drying Giemsa schedule. The frequency of chromosomal aberrations was significantly lower in animals maintained on crude plant extract as a dietary supplement during exposure to sodium arsenite as compared to those treated with arsenite alone. A crude extract of Allium sativum thus protects against the clastogenicity of sodium arsenite.

Effects of arsenic on DNA synthesis in human lymphocytes stimulated by phytohemagglutinin.

Abstract: Effects of arsenic on DNA synthesis in human lymphocytes were biphasic: either trivalent (arsenic trioxide and sodium arsenite) or pentavalent (sodium arsenate) arsenic compounds at very low concentrations enhanced DNA synthesis in human lymphocytes stimulated by phytohemagglutinin (PHA), whereas higher concentrations inhibited DNA synthesis. There were differences among individual susceptibities to arsenic-induced DNA synthesis. Either stimulating or inhibiting effects of trivalent arsenic on DNA synthesis in PHA-stimulated lymphocytes were always stronger than those of pentavalent arsenic. It was also shown that both trivalent and pentavalent arsenic could be rapidly taken up into the human lymphocytes, and immediately stimulated or inhibited DNA synthesis. A possible dual effect of arsenic at very low concentrations as both comutagen and inhibitor of mutagenesis is discussed.

Effects of arsenite treatment on NAD(P)H:quinone acceptor oxidoreductase activity in liver, lung, kidney, and heart of the rat. Comparison to induction by the polyaromatic hydrocarbon, beta-naphthoflavone.

Abstract: Arsenite is a potent toxin, a carcinogen, and an inducer of heat shock proteins. In this study we found that arsenite is also a novel inducer of NAD(P)H:quinone acceptor oxidoreductase (QOR) [EC 1.6.99.2] in both liver and kidney. The increases in activity were unlinked to those caused by prior treatment with the polyaromatic hydrocarbon inducer, beta-naphthoflavone suggesting different mechanisms of induction. A single dose of sodium arsenite (75 mumol/kg sc) caused a 4-fold and 2-fold increase in activity in kidney and liver, respectively, whereas beta-naphthoflavone (60 mg/kg ip once daily for 4 days) caused a 10-fold and 4.7-fold increase in kidney and liver, respectively. This is the first study of a metalloid inducing QOR activity. Arsenite is chemically unlike any other inducer described for QOR, which include phenolic antioxidants and Michael acceptors, polyaromatic hydrocarbons, and hydrogen peroxide. Arsenite also increased glutathione S-transferase [EC 2.5.1.18] activity in rat kidney. Arsenite could be inducing QOR in liver and kidney and the glutathione S-transferase activity in kidney by an oxidant stress mechanism.