Showing papers on "Zinc toxicity published in 2016"

Hydrogen sulfide alleviates zinc toxicity by reducing zinc uptake and regulating genes expression of antioxidative enzymes and metallothioneins in roots of the cadmium/zinc hyperaccumulator Solanum nigrum L.

Abstract: Zinc (Zn) is a toxic element for plant at high concentrations. As a biologically active gaseous molecule, hydrogen sulfide (H2S) regulates plant growth and development. The aim of this study is to reveal the ameliorative effects of H2S on the physiological and molecular responses of a hyperaccumulator to Zn toxicity. Growth analysis, biochemical and zymological methods, fluorescent microscopic imaging, western-blot and quantitative real-time PCR analysis were performed to investigate the roles of NaHS (a donor of H2S) on the cadmium (Cd)/Zn hyperaccumulator, Solanum nigrum L. H2S ameliorated excess Zn-induced growth inhibition, especially in roots. H2S decreased free cytosolic Zn2+ content in roots which was correlated well with the down-regulation of Zn uptake and homeostasis related genes expression. Besides, H2S further enhanced the expression of the metallothioneins (MTs). Moreover, Zn-induced oxidative stress was also alleviated by H2S. The alleviation of H2S on excess Zn toxicity in S. nigrum is presumably attributed to: (1) the decrease in Zn accumulation via down-regulation of Zn uptake and homeostasis related genes expression; (2) the enhancement in the expression of MTs which chelate excess Zn; (3) the change in the genes expression of antioxidative enzymes, leading to H2O2 reduction.

Sublethal Toxicity Endpoints of Heavy Metals to the Nematode Caenorhabditis elegans

Abstract: Caenorhabditis elegans, a free-living nematode, is commonly used as a model organism in ecotoxicological studies. The current literatures have provided useful insight into the relative sensitivity of several endpoints, but few direct comparisons of multiple endpoints under a common set of experimental conditions. The objective of this study was to determine appropriate sublethal endpoints to develop an ecotoxicity screening and monitoring system. C. elegans was applied to explore the sublethal toxicity of four heavy metals (copper, zinc, cadmium and chromium). Two physiological endpoints (growth and reproduction), three behavioral endpoints (head thrash frequency, body bend frequency and feeding) and two enzymatic endpoints (acetylcholine esterase [AChE] and superoxide dismutase [SOD]) were selected for the assessment of heavy metal toxicity. The squared correlation coefficients (R2) between the responses observed and fitted by Logit function were higher than 0.90 and the RMSE were lower than 0.10, indicating a good significance statistically. There was no significant difference among the half effect concentration (EC50) endpoints in physiological and behavioral effects of the four heavy metals, indicating similar sensitivity of physiological and behavioral effects. AChE enzyme was more sensitive to copper, zinc, and cadmium than to other physiological and behavioral effects, and SOD enzyme was most sensitive to chromium. The EC50 of copper, zinc, and cadmium, to the AChE enzyme in the nematodes were 0.68 mg/L, 2.76 mg/L, and 0.92 mg/L respectively and the EC50 of chromium to the SOD enzyme in the nematode was 1.58 mg/L. The results of this study showed that there was a good concentration-response relationship between all four heavy metals and the sublethal toxicity effects to C. elegans. Considering these sublethal endpoints in terms of simplicity, accuracy, repeatability and costs of the experiments, feeding is the relatively ideal sublethal toxicity endpoint of heavy metals to C. elegans.

Mechanisms of zinc toxicity in the galaxiid fish, Galaxias maculatus

Abstract: Zinc (Zn) is an essential metal, which is ubiquitous in aquatic environments occurring both naturally, and through anthropogenic inputs. This study investigated impacts of sub-lethal Zn exposure in the galaxiid fish Galaxias maculatus. Known as inanga, this amphidromous fish is widespread throughout the Southern hemisphere, but to date almost nothing is known regarding its sensitivity to elevated environmental metals. Fish were exposed to environmentally-relevant concentrations of Zn (control, 8, 270 and 1000μgL(-1)) over 96h. End-points measured included those relating to ionoregulatory disturbance (whole body calcium and sodium influx), oxygen consumption (respirometry), oxidative stress (catalase activity and lipid peroxidation) and whole body accumulation of Zn. Zn exposure caused increases in catalase activity and lipid peroxidation, but only at the highest exposure level tested. Zn also significantly inhibited calcium influx, but stimulated sodium influx, at 1000μgL(-1). The sub-lethal changes induced by Zn exposure in inanga appear to be conserved relative to other, better-studied species. These data are the first to explore the sensitivity of juvenile galaxiid fish to Zn, information that will be critical to ensuring adequate environmental protection of this important species.

Differential Targeting of SLC30A10/ZnT10 Heterodimers to Endolysosomal Compartments Modulates EGF-Induced MEK/ERK1/2 Activity.

Abstract: The solute carrier 30A (SLC30A) family of zinc exporters transports zinc into the lumen of intracellular organelles in order to prevent zinc toxicity. We reported that formation of tyrosine dimers is required for ZnT3 (zinc transporter 3) zinc transport activity and targeting to synaptic-like microvesicles (SLMVs) in PC12 cells and the formation of ZnT3/ZnT10 heterodimers. Here, we focused on ZnT10 to determine the role of heterodimerization in the sorting of ZnTs in the endolysosomal pathway. Using cell fractionation, immunoprecipitation and immunofluorescence approaches, we found that ZnT10 resides in transferrin receptor and Rab5-positive endosomes and forms covalent heterodimers and oligomers with ZnT2, ZnT3 and ZnT4. The interaction of ZnT10 with ZnT3, mediated by dityrosine bonds, was unable to target ZnT10 into SLMVs in vitro or into synaptic vesicles isolated from mouse brain in vivo. However, ZnT3/ZnT10 heterodimers regulate epidermal growth factor receptor (EGF-R) signaling by increasing the phosphorylation of mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinase (ERK1/2), but not EGF-R, C-Raf or Akt phosphorylation in response to EGF. Further, mutation of tyrosine 4 in ZnT10 reduced ZnT3/ZnT10 dityrosine-mediated heterodimerization and zinc transport, as well as MEK and ERK1/2 phosphorylation, which were also reduced by the zinc chelator TPEN. Phosphorylation of these kinases is likely to occur in the cytosol as no differences in phosphorylation were observed in membrane fractions of control and ZnT3/ZnT10-expressing cells. We propose that ZnT10 plays a role in signal transduction, which is mediated by homo and heterodimerization with other ZnTs.

Growth, biochemical variables, and zinc bioaccumulation in Nile tilapia, Oreochromis niloticus (L.) as affected by water-born zinc toxicity and exposure period

Abstract: The present study was carried out to investigate the effect of sublethal zinc (Zn) concentrations on growth performance, biochemical variables, and Zn residues in various organs of Nile tilapia, Oreochromis niloticus (L.). Fish (25 ± 0.5 g) were exposed to 0.0, 3.5, or 7.0 mg Zn L−1 for 1 or 6 weeks. Fish growth was significantly reduced with increasing Zn concentrations. However, fish exposed to 7.0 mg Zn L−1 grew less quickly than those of the control group. Likewise, best feed intake and feed conversion ratio were obtained at the control group. Furthermore, glucose, aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatinine, and cortisol increased significantly with increasing Zn concentrations and exposure time, with maximal values in the 7.0 mg Zn L−1 treatment after 6 weeks. Meanwhile, highest values of serum protein and lipids were obtained in the control fish reared for 6 week, whereas their lowest values were observed in fish exposed to 7.0 mg Zn L−1 for 1 week. There was no significant change in whole-body moisture content of fish due to Zn exposure, although crude protein and total lipid contents decreased significantly with increasing Zn concentrations. In addition, Zn exposure increased total ash contents and Zn residues in different investigated fish organs. The Zn concentrations in all fish organs were time-dependant and the Zn residues after 1 week were found to follow the order of gills > liver > kidney > muscle, meanwhile after 6 weeks it followed the order of liver > kidney > gill > muscle. The present findings revealed that liver and kidney tissues are the prime sites of Zn bioaccumulation, while Zn load in the muscle was for low as compared to other organs.

Single and Combined Exposure to Zinc- and Copper-Containing Welding Fumes Lead to Asymptomatic Systemic Inflammation.

Abstract: Objective Recently, it has been shown that exposure to welding fumes containing both zinc and copper leads to asymptomatic systemic inflammation in humans as shown by an increase of blood C-reactive protein. In the present study, it was investigated which metal is responsible for this effect. Methods Fifteen healthy male subjects were exposed under controlled conditions to welding fumes containing either zinc, or copper, or copper and zinc. Results For each exposure blood C-reactive protein increased. Conclusions Copper- and zinc-containing welding fumes are able to induce systemic inflammation.

Exogenous 24-epibrassinolide alleviates zinc-induced toxicity in eggplant (Solanum melongena L.) seedlings by regulating the glutathione-ascorbate-dependent detoxification pathway

Abstract: Excessive zinc (Zn) uptake is toxic to both plants and animals. 24-Epibrassinolide (EBL), a plant steroid hormone, plays a pivotal role in regulating plant resistance to various stresses. In this s...

Toxicity induced by a metal mixture (Cd, Pb and Zn) in the yeast Pichia kudriavzevii: The role of oxidative stress

Abstract: The present work aims to contribute for the elucidation of the role of oxidative stress in the toxicity associated with the exposure of Pichia kudriavzevii to multi-metals (Cd, Pb and Zn). Cells of the non-conventional yeast P. kudriavzevii exposed for 6 h to the action of multi-metals accumulated intracellular reactive oxygen species (ROS), evaluated through the oxidation of the probe 2',7'-dichlorodihydrofluorescein diacetate. A progressive loss of membrane integrity (monitored using propidium iodide) was observed in multi-metal-treated cells. The triggering of intracellular ROS accumulation preceded the loss of membrane integrity. These results suggest that the disruption of membrane integrity can be attributed to the oxidative stress. The exposure of yeast cells to single metal showed that, under the concentrations tested, Pb was the metal responsible for the induction of the oxidative stress. Yeast cells coexposed to an antioxidant (ascorbic acid) and multi-metals did not accumulate intracellular ROS, but loss proliferation capacity. Together, the data obtained indicated that intracellular ROS accumulation contributed to metal toxicity, namely for the disruption of membrane integrity of the yeast P. kudriavzevii. It was proposed that Pb toxicity (the metal responsible for the toxic symptoms under the conditions tested) result from the combination of an ionic mechanism and the intracellular ROS accumulation.

A novel mechanism for the pyruvate protection against zinc-induced cytotoxicity: mediation by the chelating effect of citrate and isocitrate.

Abstract: Intracellular accumulation of free zinc contributes to neuronal death in brain injuries such as ischemia and epilepsy. Pyruvate, a glucose metabolite, has been shown to block zinc neurotoxicity. However, it is largely unknown how pyruvate shows such a selective and remarkable protective effect. In this study, we sought to find a plausible mechanism of pyruvate protection against zinc toxicity. Pyruvate almost completely blocked cortical neuronal death induced by zinc, yet showed no protective effects against death induced by calcium (ionomycin, NMDA) or ferrous iron. Of the TCA cycle intermediates, citrate, isocitrate, and to a lesser extent oxaloacetate, protected against zinc toxicity. We then noted with LC–MS/MS assay that exposure to pyruvate, and to a lesser degree oxaloacetate, increased levels of citrate and isocitrate, which are known zinc chelators. While pyruvate added only during zinc exposure did not reduce zinc toxicity, citrate and isocitrate added only during zinc exposure, as did extracellular zinc chelator CaEDTA, completely blocked it. Furthermore, addition of pyruvate after zinc exposure substantially reduced intracellular zinc levels. Our results suggest that the remarkable protective effect of pyruvate against zinc cytotoxicity may be mediated indirectly by the accumulation of intracellular citrate and isocitrate, which act as intracellular zinc chelators.

QTL underlying iron and zinc toxicity tolerances at seedling stage revealed by two sets of reciprocal introgression populations of rice (Oryza sativa L.)

Abstract: Iron and zinc are two trace elements that are essential for rice. But they are toxic at higher concentrations, leading to severe rice yield losses especially in acid soils and inland valleys. In this study, two reciprocal introgression line (IL) populations sharing the same parents were used with high-density SNP bin markers to identify QTL tolerant to iron and zinc toxicities. The results indicated that the japonica variety 02,428 had stronger tolerance to iron and zinc toxicities than the indica variety Minghui 63. Nine and ten QTL contributing to iron and zinc toxicity tolerances, respectively, were identified in the two IL populations. The favorable alleles of most QTL came from 02,428. Among them, qFRRDW2, qZRRDW3, and qFRSDW11 appeared to be independent of genetic background. The region C11S49–C11S60 on chromosome 11 harbored QTL affecting multiple iron and zinc toxicity tolerance-related traits, indicating partial genetic overlap between the two toxicity tolerances. Our results provide essential information and materials for developing excellent rice cultivars with iron and/or zinc tolerance by marker-assisted selection (MAS).

Evaluation of Serum Zinc Levels in Hyperbilirubinemic Neonates Before and After Phototherapy.

Abstract: Background The existing therapeutic methods for neonatal jaundice are costly, time-consuming and potentially risky. Zinc salts can reduce phototherapy duration by precipitating unconjugated bilirubin in the intestine (bilirubin and zinc can form a complex in physiologic pH); however, zinc toxicity is an issue that must be considered since theoretically bilirubin reduction by phototherapy may increase serum zinc levels, making additional zinc supplementation the potential cause of zinc toxicity. Objectives So, our purpose was evaluating the serum zinc level alterations before and after phototherapy, in hyperbilirubinemic newborns. Materials and methods A prospective cohort study was performed at the children's medical center of Tehran University of Medical Sciences from 2012 to 2014. Healthy, full-term exclusively breast fed newborns with non-hemolytic jaundice were enrolled in the study. Participants were divided into two groups based on serum bilirubin levels (TSB Results Phototherapy was associated with a significant increase in the serum zinc level in neonates with severe hyperbilirubinemia (TSB ≥ 18 mg/dL) but not in those with mild-moderate hyperbilirubinemia (TSB 200) in only neonates with severe hyperbilirubinemia. Conclusions Phototherapy increases serum zinc level by reducing bilirubin level so that additional supplementation of this element can lead potentially to zinc toxicity.

Transgenic zebrafish biosensor for the detection of cadmium and zinc toxicity.

Abstract: A transgenic zebrafish ( Danio rerio ) biosensor for zinc and cadmium was developed. For this, zebrafish metallothionein promoter cloned upstream to the DsRed2 gene in Tol2 transposon vector was microinjected into one/two-celled zebrafish embryos. The F1 embryos (48 h post-fertilized) of confirmed transgenics were exposed to sub-lethal doses of Cd 2+ , Cu 2+ , Hg 2+ and Zn 2+ for 8 h. Reporter expression was visualized as fluorescence signal and quantified using realtime PCR system. The reporter expression increased with increasing metal ion concentration. Cadmium is the most potent inducer with 4.6-fold induction followed by zinc (2.3-fold). These zebrafish biosensors could be used as a preliminary testing tool to detect heavy metals in water bodies.

Zinc tolerance of freshwater diatoms isolated from sites with zinc pollution; and pH effect on zinc toxicity

Abstract: The aim with this study was to observe the zinc (Zn), tolerance for different strains isolated from sites with Zn pollution and to observe if lower pH decreases the Zn toxicity. Another aim was to see if malformations could be an indicator for Zn pollution. Zn is found naturally in the bedrock, sediment and waterbodies. Mining is one activity which had led to high values of Zn > 60 mg Zn l⁻¹ in some areas in Sweden. Today diatoms are used as indicators for organic pollution, the amount of nutrients and also for the pH condition. Due to problem with high values of metals, the diatom indicator has been developed further to also involve detection of metal pollution. Zn can affect diatoms growth rate, photosynthesis, cell division as well as their silica transport and thereby leading to malformed diatoms. In this study Zn toxicity was observed as decrease in number of cells, degree of malformations and as a decrease in the photosystem II efficiency. The hypotheses for the study are the following: the tested strains isolated from polluted sites would have higher tolerance to Zn than diatoms isolated from non- polluted sites, Zn would be less toxic in pH 5 compared to pH 7 and malformations could indicate Zn pollution. The observed results confirmed the hypothesis regarding the tested strains having higher tolerance towards Zn than diatoms from non- polluted sites, by the approximated EC ₅₀ values of 0,91; 1,35 and 2,27 mg Zn l⁻¹ respectively. However, the observed results for the hypothesis regarding the lower pH decreasing the Zn toxicity, were contradictory. The hypothesis was verified by higher EC ₅₀ values for the cell growth and fluorescence in pH 5 than in pH 7 for the short term experiments. Whereas the hypothesis was rejected by a higher degree of malformation in pH 5 than in pH 7 and by a higher cell growth in pH 7 than in pH 5 in the long term experiment. The different results regarding the pH effect on Zn toxicity might be explained by the different exposure times, probably the low pH is causing more stress to the cells pre-grown in pH 7 than it relieves the Zn toxicity. The long term experiment displayed significant more malformations in the higher Zn concentrations in comparison to the controls under both pH 5 and 7, and verified that malformations could detect high Zn concentrations and indicate Zn pollution.

Responsiveness of Total Plasma Protein After Administration of Some Toxic Heavy Metals in an Indian Teleost (Clarias batrachus L.)

Abstract: Heavy metals of acetate salts of lead, zinc, copper and mercury cause serious toxic effects on protein biosynthesis. These metal salts reduce the plasma protein content. A dose-response relationship is found to occur in this blood parameter in the experimental fish in comparison to the control group of fishes. Both groups are fed. Higher dose of those chemical agents are much responsive to cause harmful effects on fish plasma protein amount. All the heavy metals toxicity except zinc toxicity are shown to be continued (reduced) upto day 42 but the decrease in the said parameter is more marked with zinc salt on day 7 only. The present investigation is an attempt to evaluate the relationship of this haematological parameter with the physiological status among the heavy metal polluted fishes during chronic treatment.

Bioassay of the Ultrastructural characteristics in the kidney and liver of the African catfish, Clariasgariepinus juveniles exposed to graded concentration of zinc

Abstract: Bioassay in the structural deformation of the kidney and the liver of African catfish, Clariasgareipinus exposed to graded concentration of zinc was determine for a period of 96 hours. The stock solution was prepared with zinc and the fish juveniles were exposed to the following concentration in mg/L : 0.5, 0.75. 1.00, 1.25 and 1.50 with a control of 0.0mg/L where the zinc was not introduced. The kidney and the liver of the dead fish were dissected and subjected to histology test.The regression plot of the probit value transformed mortality against the concentration of zinc showed a strong relationship with the death of the fish exposed to the concentration of the metal with R2 value of 0.8725. Similarly the regression plot of the percentage mortality of the fish juveniles with zinc concentration indicate a very strong relationship with the toxicity of the metal that results to death of the fish at varied concentration with a R2 value of 0.99754. All the same probit transformed mortality and the log transformed concentration of zinc depict a very weak relationship between zinc toxicity and the lethality of the fish with a very low R2 value of 0.0873. All the same no death was observed in the control throughout the 96 hours period of the study while the lowest death of 15% was recorded in the 0.5mg/L and the highest of 60% in the 1.50mg/L concentration of zinc. The LC50 was determined to be 1.25mg/L during the study time. The result of the bioassay in the ultrastructural characteristics showed pathological lesion in the kidney and vacuolation of the hepatocytes of liver of the fish. The DO of the water was below the recommended level for the survival of the fish in the waters that the concentration of zinc was introduced and may cause distress to the fish. The fish showed erratic movement and distressful behavoiur where they were exposed to zinc and eventually the ones that could not tolerate the toxicity of the metal died. The study conclude that the fish should not be exposed to the elevated concentration of zinc as it is toxic and recommend that anthropogenic activities that release zinc into the environment should be controlled.

Zinc content in berries: The importance for human health

Abstract: Berries have become inevitable part of the diet of conscious men. Even though berries are not the richest source of zinc, there are agricultural practices that increase zinc content in surface soils. Being markedly involved in the human physiology and bio-chemistry, zinc is also a common component of plant metabolic pathways. A zinc defficiency occurs in plants mostly in calcareous and alkaline soils, affecting young leaves first. The toxicity and intolerence of zinc, which occur in the soils with prolonged use of fertilizers containing zinc among other elements, are greater problems than zinc deficiency. Zinc toxicity is often associated with the deficiency of magnesium, iron or manganese. In humans, zinc deficiency leads to acrodermatitis enteropathica, growth retardation, hypogonadism, depressed mental function, impaired cognitive functions and immune disorders, affecting males and females in the developing world. Serum zinc was correlated with the severity of depression and low serum zinc levels were found in depressed patients, suggesting that serum zinc could be the marker of depression. Diverse neurodegenerative processes, as Alzheimer's disease, may change the cellular zinc level, raising it to the level where zinc contributes to the progression of the disease. Zinc plays a pivotal role in few signal transduction and gene expression pathways, including that of cytokine genes. Zinc also holds a key position for multiple functions of cell metabolism, retinal development and specific retinal functions. Zinc in therapeutic dosages was effective in decreasing the incidence of infections. Zinc lozenges reduced the duration and severity of the common cold.