Showing papers on "Zinc toxicity published in 2004"

Assessment of the risk of deficiency in populations and options for its control

Abstract: Chapter 1: Overview of Zinc Nutrition S99 1.1 Biological functions of zinc S99 1.2 Tissue zinc distribution and reserves S99 1.3 Zinc metabolism S100 1.4 Importance of zinc for human health S101 1.5 Human zinc requirements S105 1.5.1 Adult men S106 1.5.2 Adult women S109 1.5.3 Children S110 1.5.4 Pregnancy S111 1.5.5 Lactation S112 1.6 Dietary sources of zinc and suggested revisions of Recommended Daily Intakes S112 1.6.1 Dietary sources of zinc and factors affecting the proportion of zinc available for absorption ........ S112 1.6.2 Revised estimates of dietary requirements and recommended intakes for zinc S114 1.7 Zinc toxicity S118 1.8 Causes of zinc deficiency and groups at high risk S121 1.9 Summary S123

Efflux and compartmentalization of zinc by members of the SLC30 family of solute carriers.

Abstract: All of the members of this family are thought to facilitate zinc efflux from the cytoplasm either into various intracellular compartments (endosomes, secretory granules, synaptic vesicles, Golgi apparatus, or trans-Golgi network) or across the plasma membrane. Thus, these transporters are thought to help maintain zinc homeostasis and facilitate transport of zinc into specialized intracellular compartments. Counterparts of the SLC30 family are found in all organisms. Most of the members of this class are predicted to have 6 transmembrane domains with both N- and C-termini on the cytoplasmic side of the membrane. Expression of rodent Znt1, Znt2 or Znt4 cDNAs in mammalian cells can confer resistance to zinc toxicity. Loss of function of the mouse Znt1 is embryonic lethal, loss of mouse Znt3 prevents accumulation of zinc in synaptic vesicles, nonfunctional mouse Znt4 (lethal milk) results in zinc-deficient milk, and Znt5-null mice display bone abnormalities and heart failure. No mutations in human counterparts of any of the members of the SLC30 family have been described.

Protection against zinc toxicity by metallothionein and zinc transporter 1

Abstract: Cells protect themselves from zinc toxicity by inducing proteins such as metallothionein (MT) that bind it tightly, by sequestering it in organelles, or by exporting it. In this study, the interplay between zinc binding by MT and its efflux by zinc transporter 1 (ZnT1) was examined genetically. Inactivation of the Znt1 gene in baby hamster kidney (BHK) cells that do not express their Mt genes results in a zinc-sensitive phenotype and a high level of “free” zinc. Restoration of Mt gene expression increases resistance to zinc toxicity ≈4-fold, but only slightly reduces free zinc levels. Expression of ZnT1 provides greater protection (≈7-fold) and lowers free zinc substantially. Selection for zinc resistance in BHK cells that cannot synthesize either MT or ZnT1 is ineffective. However, parental BHK cells that grow in high concentrations (>500 μM) of zinc can be selected; these cells have amplified their endogenous Znt1 genes. The Znt1 gene is also amplified in zinc-resistant mouse cells that cannot induce their Mt genes. However, if Mt genes can be expressed, then they are preferentially amplified. Thus, both ZnT1 and MT genes contribute to zinc resistance in BHK cells, whereas ZnT1 plays a larger role in regulating free zinc levels.

Effect of Zinc Salts on Respiratory Syncytial Virus Replication

Abstract: Zinc supplementation decreases the morbidity of lower respiratory tract infection in pediatric patients in the developing world We sought to determine if zinc mediates a specific inhibitory effect against the major cause of pediatric lower respiratory tract disease, respiratory syncytial virus (RSV) We determined the in vitro inhibitory effect of three zinc salts (zinc acetate, lactate, and sulfate) on the replication of RSV at various concentrations of 10 and 1 mM and 100 and 10 μM The degree of inhibition of RSV replication was examined in the presence of zinc during preincubation, adsorption, or penetration and was compared with that caused by salts of other divalent cations Complete inhibition of RSV plaque formation was observed at 1 and 10 mM, representing reductions that were ≥10 6 -fold At the lowest concentration tested, 10 μM, we observed ≥1,000-fold reductions in RSV yield when zinc was present during preincubation, adsorption, penetration, or egress of virus The therapeutic indices, determined as ratios of 50% toxicity concentration to 50% inhibitory concentration, were 100, 150, and 120 for zinc acetate, zinc lactate, and zinc sulfate, respectively The inhibitory effect of zinc salts on RSV was concentration dependent and was not observed with other salts containing divalent cations such as calcium, magnesium, and manganese RSV plaque formation was prevented by pretreatment of HEp-2 cell monolayer cultures with zinc or by addition of zinc to methylcellulose overlay media after infection The results of this study suggest that zinc mediates antiviral activity on RSV by altering the ability of the cell to support RSV replication

Mouse zinc transporter 1 gene provides an essential function during early embryonic development.

Abstract: The SLC30 family of cation diffusion transporters includes at least nine members in mammals, most of which have been documented to play a role in zinc transport. The founding member of this family, Znt1, was discovered by virtue of its ability to efflux zinc from cells and to protect them from zinc toxicity. However, its physiological functions remain unknown. To address this issue, mice with targeted knockout of the Znt1 gene were generated by homologous recombination in embryonic stem cells. Heterozygous Znt1 mice were viable. In contrast, homozygous Znt1 mice died in utero soon after implantation due to a catastrophic failure of embryonic development. Although extraembryonic membranes formed around these embryos, the embryo proper failed to undergo morphogenesis past the egg cylinder stage and was amorphous by d9 of pregnancy. Expression of the Znt1 gene was detected predominantly in trophoblasts and in the maternal deciduum during the postimplantation period (d5 to d8). The failure of homozygous Znt1 embryos to develop could not be rescued by manipulating maternal dietary zinc (either excess or deficiency) during pregnancy. However, embryos in Znt1 heterozygous females were ∼3 times more likely to develop abnormally when exposed to maternal dietary zinc deficiency during later pregnancy than were those in wildtype females. These studies suggest that Znt1 serves an essential function of transporting maternal zinc into the embryonic environment during the egg cylinder stage of development, and further suggest that Znt1 plays a role in zinc homeostasis in adult mice. genesis 40:74–81, 2004. © 2004 Wiley-Liss, Inc.

Zinc and Excitotoxic Brain Injury: A New Model:

Abstract: It has been nearly 15 years since the suggestion that synaptically released Zn2+ might contribute to excitotoxic brain injury after seizures, stroke, and brain trauma. In the original "zinc-translocation" model, it was proposed that synaptically released Zn2+ ions penetrated postsynaptic neurons, causing injury. According to the model, chelating zinc in the cleft was predicted to be neuroprotective. This proved to be true: zinc chelators have proved to be remarkably potent at reducing excitotoxic neuronal injury in many paradigms. Promising new zinc-based therapies for stroke, head trauma, and epileptic brain injury are under development. However, new evidence suggests that the original translocation model was incomplete. As many as three sources of toxic zinc ions may contribute to excitotoxicity: presynaptic vesicles, postsynaptic zinc-sequestering proteins, and (more speculatively) mitochondrial pools. The authors present a new model of zinc currents and zinc toxicity that offers expanded opportunities for zinc-selective therapeutic chelation interventions.

Bioavailability and chronic toxicity of zinc to juvenile rainbow trout (Oncorhynchus mykiss): comparison with other fish species and development of a biotic ligand model.

Abstract: In this study, the effects of modifying Ca (0.2-4 mM), Mg (0.05-3 mM), Na (0.75-5 mM), and pH (5.5-7.5) on the chronic toxicity of zinc to juvenile rainbow trout (Oncorhynchus mykiss) were investigated using standard 30-d assays in which survival and growth were monitored. Survival was observed to be a more sensitive end point than growth, and mortality mainly occurred during the initial stages of the exposure. This suggested that the mode of action of zinc toxicity was mainly of an acute nature. A review and analysis of existing literature demonstrated similar results for most other fish species investigated. Overall, up to a 30-fold variation of zinc toxicity was observed, as indicated by no observed effect concentrations varying between 32.7 and 974 microg of Zn L(-1). Increased concentrations of Ca2+, Mg2+, Na+, and H+ (within the tested ranges) resulted in a reduction of chronic zinc toxicity by a factor of 12, 3, >2, and 2, respectively. This suggests the major importance of Ca competing with zinc and protecting against zinc toxicity, which seems to be a ubiquitous concept in fish species (and probably also invertebrate). On the basis of the toxicity data obtained, a chronic biotic ligand model (BLM) was developed that takes into account both chemical speciation of zinc and competition between zinc and the above-mentioned cations. The developed model was able to predict chronic effect concentrations with an error of less than a factor of 2 in most cases. Hence, it was concluded that the chronic Zn BLM can reduce toxicity variability due to bioavailability to a considerable extent and that the BLM can become an important tool in criteria setting and risk assessment practice of zinc and zinc substances.

ZnT-1 expression in astroglial cells protects against zinc toxicity and slows the accumulation of intracellular zinc

Abstract: Zinc ions are emerging as an important factor in the etiology of neurodegenerative disorders and in brain damage resulting from ischemia or seizure activity. High intracellular levels of zinc are toxic not only to neurons but also to astrocytes, the major population of glial cells in the brain. In the present study, the role of ZnT-1 in reducing zinc-dependent cell damage in astrocytes was assessed. Zinc-dependent cell damage was apparent within 2 h of exposure to zinc, and occurred within a narrow range of approximately 200 microM. Pretreatment with sublethal concentrations of zinc rendered astrocytes less sensitive to toxic zinc levels, indicating that preconditioning protects astrocytes from zinc toxicity. Fluorescence cell imaging revealed a steep reduction in intracellular zinc accumulation for the zinc-pretreated cells mediated by L-type calcium channels. Heterologous expression of ZnT-1 had similar effects; intracellular zinc accumulation was slowed down and the sensitivity of astrocytes to toxic zinc levels was reduced, indicating that this is specifically mediated by ZnT-1 expression. Immunohistochemical analysis demonstrated endogenous ZnT-1 expression in cultured astroglia, microglia, and oligodendrocytes. Pretreatment with zinc induced a 4-fold increase in the expression of the putative zinc transporter ZnT-1 in astroglia as shown by immunoblot analysis. The elevated ZnT-1 expression following zinc priming or after heterologous expression of ZnT-1 may explain the reduced zinc accumulation and the subsequent reduction in sensitivity toward toxic zinc levels. Induction of ZnT-1 may play a protective role when mild episodes of stroke or seizures are followed by a massive brain insult.

ZnT-1 expression in astroglial cells protects against zinc toxicity and slows the accumulation of intracellular zinc [Erratum in: Glia. vol 48, pg 346, 2004]

Abstract: Zinc ions are emerging as an important factor in the etiology of neurodegenerative disorders and in brain damage resulting from ischemia or seizure activity High intracellular levels of zinc are toxic not only to neurons but also to astrocytes, the major population of glial cells in the brain In the present study, the role of ZnT-1 in reducing zinc-dependent cell damage in astrocytes was assessed Zinc-dependent cell damage was apparent within 2 h of exposure to zinc, and occurred within a narrow range of ∼200 μM Pretreatment with sublethal concentrations of zinc rendered astrocytes less sensitive to toxic zinc levels, indicating that preconditioning protects astrocytes from zinc toxicity Fluorescence cell imaging revealed a steep reduction in intracellular zinc accumulation for the zinc-pretreated cells mediated by L-type calcium channels Heterologous expression of ZnT-1 had similar effects; intracellular zinc accumulation was slowed down and the sensitivity of astrocytes to toxic zinc levels was reduced, indicating that this is specifically mediated by ZnT-1 expression Immunohistochemical analysis demonstrated endogenous ZnT-1 expression in cultured astroglia, microglia, and oligodendrocytes Pretreatment with zinc induced a 4-fold increase in the expression of the putative zinc transporter ZnT-1 in astroglia as shown by immunoblot analysis The elevated ZnT-1 expression following zinc priming or after heterologous expression of ZnT-1 may explain the reduced zinc accumulation and the subsequent reduction in sensitivity toward toxic zinc levels Induction of ZnT-1 may play a protective role when mild episodes of stroke or seizures are followed by a massive brain insult

Comparison of the effect of different pH buffering techniques on the toxicity of copper and zinc to Daphnia magna and Pseudokirchneriella subcapitata.

Abstract: During the time-course of ecotoxicity tests with algae and chronic (reproductive) toxicity tests with daphnids, in which algae are present as a food source, pH can dramatically increase due to photosynthetic activity. As pH changes can significantly affect metal speciation and thus its bioavailability, it may be necessary to buffer the pH of the exposure medium. One class of buffers (Good’s N-subtituted aminosulfonic acids) are increasingly being used in biological and chemical applications, including ecotoxicity testing. However, the potential effect of these buffers on metal toxicity has, so far, scarcely been examined. In this study we investigated if MOPS (3-N morpholino propane sulfonic acid) affected the toxicity of copper and zinc to two standard test organisms: the cladoceran Daphnia magna and the green alga Pseudokirchneriella subcapitata. First, we demonstrate that up to a concentration of 750 mg l−1 (which proved to be sufficient for pH buffering) MOPS did not affect 21-day net reproduction of D. magna or the 72-h population growth of P. subcapitata. Second, we conducted bioassays in copper and zinc spiked standard media for the pH range 6 – 8. For D. magna the possible effect of 750 mg l−1 MOPS on acute copper and zinc toxicity was investigated by performing parallel 48-h toxicity tests in NaHCO3 and MOPS buffered test media. Seventy-two hour growth inhibition assays with P. subcapitata were performed in parallel in MOPS and NaHCO3 buffered test media and in test media with daily manual pH adjustment with HCl. For daphnids no significant differences in copper and zinc toxicity were observed between MOPS or NaHCO3 buffered test media. For algae no significant differences in metal toxicity were observed between MOPS and HCl buffered media, but in test media buffered with NaHCO3 an increased copper and zinc toxicity was observed as a consequence of pH increases during the test. Clearly, the results of this study demonstrate the importance of pH buffering in metal toxicity testing and the suitability of the MOPS buffer for that purpose.

Effects of chronic dietary copper exposure on growth and reproduction of Daphnia magna

Abstract: A matter of current, intense debate with regard to the effects of metals on biological systems is the potential toxicity of metals associated with food particles. Recently developed biotic ligand models (BLM), which predict the toxicity of waterborne metals, may not be valid if the dietary exposure route contributes to metal toxicity. The present study is, to our knowledge, the first that investigates the potential toxicity of dietary copper to a freshwater invertebrate (i.e., Daphnia magna) feeding on a live diet (i.e., the green alga Pseudokircheneriella subcapitata). Algae were exposed for 3 d to different copper concentrations, resulting in algal copper burdens between approximately 6.2 X 10(-16) and 250 x 10(-16) g cell(-1). These algae were then used as food in chronic, 21-d D. magna toxicity tests in which growth, reproduction, and copper accumulation were assessed. Three exposure scenarios were tested: A waterborne exposure, a dietary exposure, and a combined waterborne and dietary exposure. Although exposure to dietary copper resulted in an increased copper body burden of the adult daphnids, it did not contribute to toxicity and did not affect the 21-d effect concentrations expressed as waterborne copper, indicating that the previously established good predictive capacity of the chronic D. magna BLM is not affected. On the contrary, exposure to the highest dietary copper levels resulted in an increase of as much as 75% in growth and reproduction. To our knowledge, this is the first evidence that dietary copper exposure of a freshwater invertebrate feeding on a live diet resulted in a beneficial effect.

Protection by pyruvate of rat retinal cells against zinc toxicity in vitro, and pressure-induced ischemia in vivo.

Abstract: Purpose To examine whether zinc accumulation occurs during retinal neuronal death after pressure-induced ischemia in rats and whether pyruvate protects against such death. Methods To induce transient retinal ischemia, intraocular pressure was increased above systolic pressure for 65 minutes. Pyruvate was administered through the tail vein for 12 hours after ischemia to determine its effect on degeneration of retinal neurons. Retinas were removed and sectioned, and zinc accumulation was visualized with N-(6-methoxy-8-quinolyul)-p-carboxybenzoyl-sylphonamide (TFL-Zn) fluorescence microscopy, and neuronal death was determined with acid fuchsin staining. For in vitro studies, retinal cell cultures were prepared from newborn rat pups and used for experiments at days in vitro (DIV) 7 to 10. Results After retinal ischemia, staining revealed that most zinc-accumulating neurons were injured neurons, suggesting that endogenous zinc may contribute to ischemic neuronal death in the retina. In vitro studies showed that 15 minutes of exposure to 300 to 500 microM zinc resulted in the death of a substantial number of retinal cells in culture, and that this death was preceded by poly(ADP-ribose) polymerase (PARP)-mediated depletion of nicotinamide-adenine dinucleotide (NAD+) and adenosine triphosphate (ATP). Pyruvate, but not lactate, protected against this zinc-induced cell death in vitro. Consistent with this finding, in vivo studies showed that compared with control rats, pyruvate-treated rats had a substantial reduction in the number of cells showing signs of cell death. Conclusions The present results suggest endogenous zinc contributes to retinal cell death after ischemia. Pyruvate potently protected against zinc toxicity in cultured rat retinal cells and reduced ischemia-induced cell death in rat retinas.

Zinc rhizotoxicity in wheat and radish is alleviated by micromolar levels of magnesium and potassium in solution culture

Abstract: The effects of excess zinc (Zn) on solution-cultured wheat (Triticum aestivum L., cv. Yecora Rojo) and radish (Raphanus sativus L., cv. Cherry Belle) were studied, using both short-term root elongation studies and longer term split-root experiments. Alleviation of Zn rhizotoxicity by Mg and K was observed, with especially dramatic alleviation of root stunting by Mg. In the short-term studies using a simple medium (2 mM CaCl2 ,p H 6.0), Mg concentrations of 1–5 µM were able to significantly alleviate rhizotoxicity caused by Zn concentrations as high as 60 µM. In the split-root studies, 100 µM Mg was sufficient to abolish Zn toxicity in both wheat and radish. Paradoxically, Mg enhanced uptake and translocation of Zn while simultaneously alleviating toxicity in these longer-term experiments. In short-term experiments, additions of K (0 to 200 µM) to the basal medium alleviated Zn rhizotoxicity to a more limited extent. In split-root experiments, however, the absence or presence of K in test solutions did not affect plant growth or Zn uptake. When increased from a physiological minimum (e.g., 200 µM), Ca also alleviates Zn toxicity, but the effect is very modest in comparison to that of Mg. The results are discussed in relation to the use of short-term assays of metal tolerance in simple salt solutions, and in relation to possible roles of Mg in the physiology of Zn toxicity.

Zinc toxicosis in a free-flying trumpeter swan (Cygnus buccinator).

Abstract: A trumpeter swan (Cygnus buccinator) was observed near a mill pond in Picher, Oklahoma, USA. It became weakened and emaciated after about 1 mo, was captured with little resistance, and taken into captivity for medical care. Serum chemistry results were consistent with hepatic, renal, and muscular damage. Serum zinc concentration was elevated at 11.2 parts per million (ppm). The swan was treated for suspected heavy-metal poisoning, but died overnight. Gross postmortem findings were emaciation and pectoral muscle atrophy. Histopathologic lesions in the pancreas included mild diffuse disruption of acinar architecture, severe diffuse depletion or absence of zymogen granules, occasional apoptotic bodies in acinar epithelial cells, and mild interstitial and capsular fibrosis. Zinc concentration in pancreas was 3,200 ppm wet weight, and was similar to that reported in the pancreases of waterfowl known to be killed by zinc toxicity. Zinc concentrations in liver (154 ppm) and kidneys (145 ppm) also were elevated. Acute tubular necrosis of the collecting tubules of the kidneys was also possibly due to zinc toxicity. To the authors' knowledge, this is the first confirmed case of zinc poisoning in a trumpeter swan associated with mining wastes.

A Mechanism for Zinc Toxicity in Neuroblastoma Cells.

Abstract: Zinc is an important component of proteins essential for normal functioning of the brain. However, it has been shown in vitro that this metal, at elevated levels, can be toxic to cells leading to their death. We investigated possible mechanisms of cell death caused by zinc: firstly, generation of reactive oxygen species, and secondly, the activation of the MAP-kinase pathway. Cell viability was assessed by means of the methyl-thiazolyl tetrazolium salt (MTT) assay and confirmed by tetramethylrhodamine methyl ester (TMRM) staining. We measured the phosphorylation status of Erk and p38 as indicators of MAP-kinase activity, using Western Blot techniques. A time curve was established when neuroblastoma (N2α) cells were exposed to 100 μM of zinc for 4, 12, and 24 h. Zinc caused a significant reduction in cell viability as early as 4 h, and indirectly stimulated the accumulation of reactive oxygen species as determined by 2.7 dichlorodihydrofluorescein diacetate (DCDHF) staining and confocal microscopy. Investigation of the MAP-kinase pathway indicated that Erk was downregulated, while p38 was stimulated. Our results therefore led us to conclude that in vitro, zinc toxicity involved the generation of reactive oxygen species and the activation of the MAP-kinase pathway.

Effect of metal mixtures (Cd and Zn) on body weight in terrestrial isopods.

Abstract: The aim of this study was to determine the effect of exposure to cadmium and zinc mixtures on the weight of terrestrial isopods Experiments were conducted using uncontaminated specimens of P laevis The isopods were exposed to various concentrations of cadmium and zinc sulfate in single- and mixed-metal experiments The mean weight of the unexposed isopods in the control group increased over the 6 weeks of observation It was concluded that cadmium and zinc, administered separately, had a negative effect on the weight of P laevis The weight change (gain or loss) of P laevis in the exposures to mixtures of cadmium and zinc sulfate were different from those of woodlice where Cd and Zn were administered separately Combination of the lowest concentrations of Cd and Zn (20 and 1000 mg x kg(-1)) produced a stimulating effect compared to the control Weight changes of the other two combinations of Cd and Zn (80/4000 and 160/8000 mg x kg(-1)) showed no differences from those of the control, and weight changes of woodlice exposed to Cd and Zn mixtures were mostly the same as those of the control over the 6-week exposure period It can thus be concluded that mixtures of Cd and Zn have an antagonistic effect on each other in terms of weight of P laevis

Potassium attenuates zinc-induced death of cultured cortical astrocytes.

Abstract: Transient global ischemia induces CA1 hippocampal neuronal death without astrocyte death, perhaps mediated in part by the toxic translocation of zinc from presynaptic terminals to postsynaptic neurons. We tested the hypothesis that cellular depolarization, which occurs in the ischemic brain due to increased extracellular potas- sium and energy failure, might contribute to astrocyte resistance to zinc-induced death. We previously reported that neurons in mixed cortical neuronal-astrocyte cultures were more vulnerable to a 5-15-min exposure to Zn 2 than astrocytes in the same cultures. In the present report, we show that (1) neurons in isolation or in conjunction with astro- cytes were 2-3-fold more sensitive to a 15-min nondepolarizing Zn 2 exposure than are glia; (2) KCl-induced depolarization attenuated glial vulnerability to zinc toxicity but potentiated neuronal vulnerability to zinc toxicity; (3) Zn 2 -induced glial death was attenuated by T-type Ca 2 channel blockade, as well as compounds that increase NAD levels; and (4) both astrocytic 65 Zn 2 accumulation and the increase in astrocytic (Zn 2 )i induced by Zn 2 exposure were also attenuated by depolarization or T-type Ca 2 chan- nel blockers. Zn 2 -induced cell death in astrocytes was at least in part apoptotic, as caspase-3 was activated, and the caspase inhibitor Z-Val-Ala-Asp-fluoromethylketone partially attenuated Zn 2 -induced death. The levels of peak (Zn 2 )i achieved in astro- cytes during this toxic nondepolarizing Zn 2 exposure (250 nM) were substantially greater than those achieved in neurons (40 nM). In glia, exposure to 400 MZ n 2 induced a 13-mV depolarization, which can activate T-type Ca 2 channels. This Zn 2 - induced astrocyte death, like neuronal death, was attenuated by the addition of pyru- vate or niacinamide to the exposure medium. © 2004 Wiley-Liss, Inc.

Toxicological characterization of the new water cleaning product and its waste by-product.

Abstract: Water extracts genotoxicity of the coagulant produced from industrial waste (red mud and waste base) and its waste mud remained after waste water treatment by the coagulation/flocculation process were studied. Tests were conducted in order to confirm nontoxicity of this new product prior to commercial production and usage and also to recommend a safe way for a handling and disposal of the remaining waste material. The toxicity investigation included (i) determining frequency of the cell survival, (ii) the Ames assays, (iii) micronucleus assay, and (iv) cell proliferation kinetics (expressed as mitotic index). These techniques were also employed in toxicity testing of the different concentrations of metal salts, zinc chloride, and lead nitrate in this case since these two elements were present in high concentrations in the waste water intended for the purification with the new coagulant. Mixture of metal salts in the concentrations that represent maximum allowed values for water extracts of technological waste was also tested. Two strains of Salmonella typhimurium, TA98, and TA100 were used for determining cytotoxicity and for the Ames test, while the cytogenetic investigations were performed on human peripheral blood lymphocytes. Water extracts of the coagulant and its waste mud did not induce a significant increase of the micronuclei in human peripheral blood lymphocytes. They also did not disturb lymphocyte proliferation kinetics in vitro. As regards lead nitrate it proved not to be cytotoxic on bacterial strains in the tested concentration range (1-100 mg/L), whereas zinc chloride showed cytotoxic effect for the concentrations above 25 mg/L. The Ames test results for the noncytotoxic concentrations of these metals were negative. Comparing to the negative control a significantly higher number of the micronuclei was determined after the treatment of the whole blood with 100 mg/L of zinc chloride, as well as with 10 and 100 mg/L of lead nitrate. A linear, dose dependent increase was obtained for both salts. Similar results were obtained on the basis of the mitotic index.

Decreased zinc toxicity resulting from doxorubicin without increased GSSG export in three human lung cell lines.

Abstract: Zinc-mediated cytotoxicity is recognized, at least in part, by a decrease of reduced glutathione (GSH) and an increase in the oxidized form of glutathione (GSSG). Doxorubicin is a common inducer of multidrug-resistance-associated proteins and such proteins might, furthermore, be associated by an increased GSSG export rate. Therefore, zinc-mediated toxicity should be abolished after doxorubicin pretreatment. In the present study, zinc toxicity was characterized by methionine incorporation, glutathione content, and the GSSG/GSH ratio. Experiments were performed in three established lung cell lines comparing doxorubicin-pretreated cells with controls. Zinc-mediated toxicity was significantly decreased after pretreatment with doxorubicin as assessed by methionine-incorporation inhibition, GSH depletion, and/or GSSG increase in the two nonmalignant cell lines. Unexpectedly, zinc-associated GSSG export was not increased after doxorubicin pretreatment. This inconsistency might be explained as a result of a decreased zinc content in these cells, probably because of an increased export rate of zinc. The findings are in contradiction to the opinion of metal excretion by multidrug-resistance-associated proteins, matched to GSH conjugate excretion, as it is discussed for cadmium, for example.

PROTECTIVE EFFECT OF Se AGAINST Zn TOXICITY ON ULTRASTRUTURE OF PAVLOVA VIRIDIS TSENG (HAPTOPHYCEAE)

Abstract: The protective effects of selenium against zinc toxicity in the flagellate alga Pavlova viridis were investigated using transmission electron microscopy. Cells from a control and two experimental groups were compared for their ultrastructural characteristics. In experimental group one, the culture medium was treated with 15 mg L -1 Zn (ZnSO 4·7H 2O), while in group two, it with both 15 mg L -1 Se (Na 2SeO 3·5H 2O) and 15 mg L -1Zn. The results showed that the independent use of Zn at a concentration of 15 mg L -1 caused serious damage to the chloroplast tetrolobes in the algae, yet this effect was prevented in the presence of Se. The algal cells affected by Zn had variously-sized, electron-dense bodies in cytoplasm and chloroplast matrix. In contrast, the cells treated with both Zn and Se were characterized by the occurrence of electron-dense particles in vacuole inclusion body. Accordingly, the following hypothesis was made: when acting alone, the extra Zn in P. viridis cells was compartmented in particular molecules, identified as electron-dense bodies, whereas this process was inhibited by the formation of Zn selenides, in which the Zn was inactivated, thereby protecting the cells against Zn toxicity. Fig 3, Tab 1, Ref 28