Inhibition of human DNA ligase I activity by zinc and cadmium and the fidelity of ligation

Multiple generation exposure to ZnO nanoparticles induces loss of genomic integrity in Caenorhabditis elegans

Zinc oxide nanoparticles (ZnO NPs) are commonly used in industrial and household applications, prompting the assessment of their associated health risks. Previous studies indicated that ZnO NPs can induce somatic cell mutations, while the aging process appears to increase the mutagenicity of ZnO NPs. However, little is known about the influence of ZnO NPs on genome stability of germ cells, and non-exposed progeny. Here we show that 20 nm ZnO NPs exposure disrupts germ cell development, and elevates the overall mutation frequency of germ cells in Caenorhabditis elegans (C. elegans). We observed that pristine ZnO NPs elicit germ cell apoptosis to a greater extent than the 60-day aged ZnO NPs. By treating parental worms with ZnO NPs for seven successive generations, whole-genome sequencing data revealed that, although the frequency of point mutations is kept unchanged, large deletions are significantly increased in F8 worms. Furthermore, we found that the mutagenicity of ZnO NPs might be partially attributed to the release of Zn²⁺ ions. Together, our results demonstrate the genotoxic effects of ZnO NPs on germ cells, and the possible underlying mechanism. These findings suggest that germ cell mutagenicity is worthy of consideration for the health risk assessment of engineered NPs.

Effects of cadmium toxicity on diploid wheat (Triticum urartu) and the molecular mechanism of the cadmium response

Cadmium (Cd) is a widespread soil contaminant that readily accumulates in wheat, and posing a potential threat to human health. Our aim is to investigate Cd toxicity effect and molecular mechanisms for wheat. In this study, the physiological indexes, morphology, and gene expression patterns of diploid wheat (Triticum urartu) seedlings were evaluated after 2 and 5 d of a Cd treatment (10 μM CdSO₄). The Cd treatment resulted in increased proline and glutathione contents in shoots and roots, slight damage to leaf tips, severe damage to root tips, and increased root secretions. Transcriptome analysis showed that there were significantly more differentially expressed genes (DEGs) in shoots and roots after 5 d of Cd stress than after 2 d of Cd stress, and the DEGs of the shoots were more different than the roots. A Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that the pathways enriched under Cd treatment were "DNA replication" and "phenylpropanoid biosynthesis". These findings provide information about the responses to Cd stress in wheat, and provide a theoretical basis for reducing Cd toxicity and protecting food safety.

Interplay between DNA Polymerases and DNA Ligases: Influence on Substrate Channeling and the Fidelity of DNA Ligation

DNA ligases are a highly conserved group of nucleic acid enzymes that play an essential role in DNA repair, replication, and recombination. This review focuses on functional interaction between DNA polymerases and DNA ligases in the repair of single- and double-strand DNA breaks, and discusses the notion that the substrate channeling during DNA polymerase-mediated nucleotide insertion coupled to DNA ligation could be a mechanism to minimize the release of potentially mutagenic repair intermediates. Evidence suggesting that DNA ligases are essential for cell viability includes the fact that defects or insufficiency in DNA ligase are casually linked to genome instability. In the future, it may be possible to develop small molecule inhibitors of mammalian DNA ligases and/or their functional protein partners that potentiate the effects of chemotherapeutic compounds and improve cancer treatment outcomes.

6-Methoxyquinoline complexes as lung carcinoma agents: induction of oxidative damage on A549 monolayer and multicellular spheroid model

The aim of this work was to study the antitumor effects and the mechanisms of toxic action of a series of 6-methoxyquinoline (6MQ) complexes in vitro. The Cu(II) and Zn(II) complexes (Cu6MQ and Zn6MQ) are formulated as M(6MQ)₂Cl₂; the Co(II) and Ag(I) compounds (Co6MQ and Ag6MQ) are ionic with formulae [Ag(6MQ)₂]⁺NO₃^- and H(6MQ)⁺[Co(6MQ)Cl₃]^- (where H(6MQ)⁺ is the protonated ligand). We found that the copper complex, outperformed the Co(II), Zn(II) and Ag(I) complexes with a lower IC₅₀ (57.9 µM) in A549 cells exposed for 24 h. Cu6MQ decreased cell proliferation and induced oxidative stress detected with H₂DCFDA at 40 µM, which reduces GSH/GSSG ratio. This redox imbalance induced oxidative DNA damage revealed by the Micronucleus test and the Comet assay, which turned into a cell cycle arrest at G2/M phase and induced apoptosis. In multicellular spheroids, the IC₅₀ values tripled the monolayer model (187.3 µM for 24 h). At this concentration, the proportion of live/dead cells diminished, and the spheroids could not proliferate or invade. Although Zn6MQ also decreased GSH/GSSG ratio from 200 µM and the cytotoxicity is related to oxidative stress, the induction of the hydrogen peroxide levels only doubled the control value. Zn6MQ induced S phase arrest, which relates with the increased micronucleus frequency and with the induction of necrosis. Finally, our results reveal a synergistic activity with a 1:1 ratio of both complexes in the monolayer and multicellular spheroids.

Assessment of the individual and mixture toxicity of cadmium, copper and oxytetracycline, on the embryo-larval development of the sea urchin Paracentrotus lividus

Multiple pollutions by trace metals and pharmaceuticals have become one of the most important problems in marine coastal areas because of its excessive toxicity on organisms living in this area. This study aimed to assess the individual and mixture toxicity of Cu, Cd, and oxytetracycline frequently existing in the contaminated marine areas and the embryo-larval development of the sea urchin Paracentrotus lividus. The individual contamination of the spermatozoid for 1 h with the increasing concentrations of Cd, Cu, and OTC decreases the fertility rate and increases larvae anomalies in the order Cu > Cd > OTC. Moreover, the normal larva frequency and the length of spicules were more sensitive than the fertilization rate and normal gastrula frequency endpoints. The mixture toxicity assessed by multiple experimental designs showed clearly that concentrations of Cd, Cu, and OTC superior to 338 μg/L, 0.56 μg/L, and 0.83 mg/L, respectively, cause significant larva malformations.

Cadmium treatment suppresses DNA polymerase δ catalytic subunit gene expression by acting on the p53 and Sp1 regulatory axis

Cadmium (Cd) is a carcinogenic and neurotoxic environmental pollutant. Among the proposed mechanisms for Cd toxic effects, its ability to promote oxidative stress and to inhibit, in vitro, the activities of some Base Excision DNA Repair (BER) enzymes, such as hOGG1, XRCC1 and APE1, have been already established. However, the molecular mechanisms at the basis of these processes are largely unknown especially at sub-lethal doses of Cd and no information is available on the effect of Cd on the expression levels of BER enzymes. Here, we show that non-toxic treatment of neuronal cell lines, with pro-mitogenic doses of Cd, promotes a significant time- and dose-dependent down-regulation of DNA polymerase δ (POLD1) expression through a transcriptional mechanism with a modest effect on Polβ, XRCC1 and APE1. We further elucidated that the observed transcriptional repression on Polδ is acted by through competition by activated p53 on Sp1 at POLD1 promoter and by a squelching effect. We further proved the positive effect of Sp1 not only on POLD1 expression but also on Polβ, XRCC1 and APE1 expression, suggesting that Sp1 has pleiotropic effects on the whole BER pathway. Our results indicated that Cd-mediated impairment of BER pathway, besides acting on the enzymatic functions of some key proteins, is also exerted at the gene expression level of Polδ by acting on the p53-Sp1 regulatory axis. These data may explain not only the Cd-induced neurotoxic effects but also the potential carcinogenicity of this heavy metal.

Micronutrient-gene interactions related to inflammatory/immune response and antioxidant activity in ageing and inflammation. A systematic review

Recent longitudinal studies in dietary daily intake in human centenarians have shown that a satisfactory content of some micronutrients within the cells maintain several immune functions, a low grade of inflammation and preserve antioxidant activity. Micronutrients (zinc, copper, selenium) play a pivotal role in maintaining and reinforcing the performances of the immune and antioxidant systems as well as in affecting the complex network of the genes (nutrigenomic) with anti- and pro-inflammatory tasks. Genes of pro- and anti-inflammatory cytokines and some key regulators of trace elements homeostasis, such as Metallothioneins (MT), are involved in the susceptibility to major geriatric disease/disorders. Moreover, the genetic inter-individual variability may affect the nutrients' absorption (nutrigenetic) with altered effects on inflammatory/immune response and antioxidant activity. The interaction between genetic factors and micronutrients (nutrigenomic and nutrigenetic approaches) may influence ageing and longevity because the micronutrients may become also toxic. This review reports the micronutrient-gene interactions in ageing and their impact on the healthy state with a focus on the method of protein-metal speciation analysis. The association between micronutrient-gene interactions and the protein-metal speciation analysis can give a complete picture for a personalized nutrient supplementation or chelation in order to reach healthy ageing and longevity.

Micronutrient (Zn, Cu, Fe)-gene interactions in ageing and inflammatory age-related diseases: implications for treatments

In ageing, alterations in inflammatory/immune response and antioxidant capacity lead to increased susceptibility to diseases and loss of mobility and agility. Various essential micronutrients in the diet are involved in age-altered biological functions. Micronutrients (zinc, copper, iron) play a pivotal role either in maintaining and reinforcing the immune and antioxidant performances or in affecting the complex network of genes (nutrigenomic approach) involved in encoding proteins for a correct inflammatory/immune response. By the other side, the genetic inter-individual variability may affect the absorption and uptake of the micronutrients (nutrigenetic approach) with subsequent altered effects on inflammatory/immune response and antioxidant activity. Therefore, the individual micronutrient-gene interactions are fundamental to achieve healthy ageing. In this review, we report and discuss the role of micronutrients (Zn, Cu, Fe)-gene interactions in relation to the inflammatory status and the possibility of a supplement in the event of a micronutrient deficiency or chelation in presence of micronutrient overload in relation to specific polymorphisms of inflammatory proteins or proteins related of the delivery of the micronutriemts to various organs and tissues. In this last context, we report the protein-metal speciation analysis in order to have, coupled with micronutrient-gene interactions, a more complete picture of the individual need in micronutrient supplementation or chelation to achieve healthy ageing and longevity.

Investigation of ZnO nanoparticles' ecotoxicological effects towards different soil organisms

INTRODUCTION

Nanomaterials have widespread applications in several industrial sectors. ZnO nanoparticles (NPs) are among the most commonly used metal oxide NPs in personal care products, coating and paints. However, their potential toxicological impact on the environment is largely unexplored.

MATERIALS AND METHODS

The aim of this work was to evaluate whether ZnO nanoparticles exert toxic and genotoxic effects upon terrestrial organisms: plants (Lepidium sativum, Vicia faba), crustaceans (Heterocyipris incongruens), insects (Folsomia candida). To achieve this purpose, organisms pertaining to different trophic levels of the soil ecosystem have been exposed to ZnO NPs. In parallel, the selected soil organisms have been exposed to the same amount of Zn in its ionic form (Zn(2+)) and the effects have been compared.

RESULTS

The most conspicuous effect, among the test battery organisms, was obtained with the ostracod H. incongruens, which was observed to be the most sensitive organism to ZnO NPs. The root elongation of L. sativum was also mainly affected by exposure to ZnO NPs with respect to ZnCl(2), while collembolan reproduction test produced similar results for both Zn compounds. Slight genotoxic effects with V. faba micronucleus test were observed with both soils.

CONCLUSION

Nanostructured ZnO seems to exert a higher toxic effect in insoluble form towards different terrestrial organisms with respect to similar amounts of zinc in ionic form.

Genotoxicity of soluble and particulate cadmium compounds: impact on oxidative DNA damage and nucleotide excision repair

Water-soluble and particulate cadmium compounds are carcinogenic to humans. While direct interactions with DNA are unlikely to account for carcinogenicity, induction of oxidative DNA damage and interference with DNA repair processes might be more relevant underlying modes of action (recently summarized, for example, in Joseph , P. (2009) Tox. Appl. Pharmacol. 238 , 271 - 279). The present study aimed to compare genotoxic effects of particulate CdO and soluble CdCl(2) in cultured human cells (A549, VH10hTert). Both cadmium compounds increased the baseline level of oxidative DNA damage. Even more pronounced, both cadmium compounds inhibited the nucleotide excision repair (NER) of BPDE-induced bulky DNA adducts and UVC-induced photolesions in a dose-dependent manner at noncytotoxic concentrations. Thereby, the uptake of cadmium in the nuclei strongly correlated with the repair inhibition of bulky DNA adducts, indicating that independent of the cadmium compound applied Cd(2+) is the common species responsible for the observed repair inhibition. Regarding the underlying molecular mechanisms in human cells, CdCl(2) (as shown before by Meplan, C., Mann, K. and Hainaut, P. (1999) J. Biol. Chem. 274 , 31663 - 31670 ) and CdO altered the conformation of the zinc binding domain of the tumor suppressor protein p53. In further studies applying only CdCl(2), cadmium decreased the total nuclear protein level of XPC, which is believed to be the principle initiator of global genome NER. This led to diminished association of XPC to sites of local UVC damage, resulting in decreased recruitment of further NER proteins. Additionally, CdCl(2) strongly disturbed the disassembly of XPC and XPA. In summary, our data indicate a general nucleotide excision repair inhibition by cadmium compounds, which is most likely caused by a diminished assembly and disassembly of the NER machinery. These data reveal new insights into the mechanisms involved in cadmium carcinogenesis and provide further evidence that DNA repair inhibition may be one predominant mechanism in cadmium induced carcinogenicity.

Mechanism of cadmium-mediated inhibition of Msh2-Msh6 function in DNA mismatch repair

The observation that Cadmium (Cd(2+)) inhibits Msh2-Msh6, which is responsible for identifying base pair mismatches and other discrepancies in DNA, has led to the proposal that selective targeting of this protein and consequent suppression of DNA repair or apoptosis promote the carcinogenic effects of the heavy metal toxin. It has been suggested that Cd(2+) binding to specific sites on Msh2-Msh6 blocks its DNA binding and ATPase activities. To investigate the mechanism of inhibition, we measured Cd(2+) binding to Msh2-Msh6, directly and by monitoring changes in protein structure and enzymatic activity. Global fitting of the data to a multiligand binding model revealed that binding of about 100 Cd(2+) ions per Msh2-Msh6 results in its inactivation. This finding indicates that the inhibitory effect of Cd(2+) occurs via a nonspecific mechanism. Cd(2+) and Msh2-Msh6 interactions involve cysteine sulfhydryl groups, and the high Cd(2+):Msh2-Msh6 ratio implicates other ligands such as histidine, aspartate, glutamate, and the peptide backbone as well. Our study also shows that cadmium inactivates several unrelated enzymes similarly, consistent with a nonspecific mechanism of inhibition. Targeting of a variety of proteins, including Msh2-Msh6, in this generic manner would explain the marked broad-spectrum impact of Cd(2+) on biological processes. We propose that the presence of multiple nonspecific Cd(2+) binding sites on proteins and their propensity to change conformation on interaction with Cd(2+) are critical determinants of the susceptibility of corresponding biological systems to cadmium toxicity.

Impact of inorganic nutrients on maintenance of genomic stability

Maintenance of genome stability is of fundamental importance for counteracting carcinogenesis. Many human genome instability syndromes exhibit a predisposition to cancer. An increasing body of epidemiological evidence has suggested a link between nutrient status and risk of cancer. Like other chemicals, nutrients can be toxic when consumed in excess. It has become clear that both nutritional deficiency and toxicity can compromise the integrity of the genome. This article focuses on roles of inorganic trace nutrients, including selenium, copper, zinc, and iron, in the redox regulation of genome stability and how they relate to the pathologies of genomic instability syndromes and cancer.

Non-linear effects in the formation of DNA damage in medaka fish fibroblast cells caused by combined action of cadmium and ionizing radiation

Ionizing radiation-induced formation of genomic DNA damage can be modulated by nearby chemical species such as heavy metal ions, which can lead to non-linear dose response. To investigate this phenomenon, we studied cell survival and formation of 8-hydroxyguanine (8-OHG) base modifications and double strand breaks (DSB) caused by combined action of cadmium (Cd) and gamma radiation in cultured medaka fish (Oryzias latipes) fibroblast cells. Our data show that the introduction of Cd leads to a significant decrease in the fraction of surviving cells and to increased sensitivity of cells to ionizing radiation (IR). Cd also appears to cause non-linear increases in radiation-induced yields of 8-OHG and DSB as dose-yield plots of these lesions exhibit non-linear S-shaped curves with a sharp increase in the yields of lesions in the 10-20 microM range of Cd concentrations. The combined action of ionizing radiation and Cd leads to increased DNA damage formation compared to the effects of the individual stressors. These results are consistent with a hypothesis that the presence of Cd modulates the efficiency of DNA repair systems thus causing increases in radiation-induced DNA damage formation and decreases in cell survival.

Localization of metallothionein, heat shock protein (Hsp70), and superoxide dismutase expression in Hemidiaptomus roubaui (Copepoda, Crustacea) exposed to cadmium and heat stress

Immunohistochemical methods were applied in the present study to investigate the expression of stress proteins such as metallothioneins (MT), which are metal-binding proteins, and heat shock proteins (Hsp70), as well as an antioxidant enzyme (superoxide dismutase, SOD), in the freshwater crustacean copepod Hemidiaptomus roubaui (Richard, 1888) exposed to cadmium or heat stress. The results show a tissue-specific distribution of MT-like protein after cadmium exposure in the brain and in the nerve cord. Cadmium stress did not provoke inducible Hsp70 or SOD expression. Unlike cadmium, heat stress induced the expression of Hsp70 and SOD in the shell glands, a structure involved in the reproductive function, and more particularly in the formation of the diapause egg envelope. MT expression is not induced in animals exposed to heat stress.

DNA repair systems as targets of cadmium toxicity

Cadmium (Cd) is a heavy metal and a potent carcinogen implicated in tumor development through occupational and environmental exposure. Recent evidence suggests that proteins participating in the DNA repair systems, especially in excision and mismatch repair, are sensitive targets of Cd toxicity. Cd by interfering and inhibiting these DNA repair processes might contribute to increased risk for tumor formation in humans. In the present review, the information available on the interference of Cd with DNA repair systems and their inhibition is summarized. These actions could possibly explain the indirect contribution of Cd to mutagenic effects and/or carcinogenicity.

Cadmium induces the expression of specific stress proteins in sea urchin embryos

Marine organisms are highly sensitive to many environmental stresses, and consequently, the analysis of their bio-molecular responses to different stress agents is very important for the understanding of putative repair mechanisms. Sea urchin embryos represent a simple though significant model system to test how specific stress can simultaneously affect development and protein expression. Here, we used Paracentrotus lividus sea urchin embryos to study the effects of time-dependent continuous exposure to subacute/sublethal cadmium concentrations. We found that, between 15 and 24 h of exposure, the synthesis of a specific set of stress proteins (90, 72-70, 56, 28, and 25 kDa) was induced, with an increase in the rate of synthesis of 72-70 kDa (hsps), 56 kDa (hsp), and 25 kDa, which was dependent on the lengths of treatment. Recovery experiments in which cadmium was removed showed that while stress proteins continued to be synthesized, embryo development was resumed only after short lengths of exposure.

In vivo genotoxic effect of zinc sulfate in mouse peripheral blood leukocytes using Comet assay

Single stranded DNA breaks induced by Zinc sulfate in mice has been studied in vivo using Alkaline Single Cell Gel Electrophoresis (Comet assay). Mice were administered orally with doses of 5.70, 8.55, 11.40, 14.25, 17.10 and 19.95 mg/kg body weight of zinc sulfate respectively. The samples of whole blood were collected at 24, 48, 72, 96 hr and first week post-treatment and the assay was carried out to determine single strand DNA breaks as represented by comet tail-lengths. Results indicated a significant DNA damage at all the doses after treatment with zinc sulfate when compared to controls showing a clear dose-dependent response (p < 0.05). A gradual decrease in the tail-lengths from 48 hr post-treatment onwards was observed indicating a time dependent decrease in the DNA damage. The study confirms that zinc sulfate causes significant DNA damage at the doses used as revealed by comet assay.

Protective effect of zinc on cadmium-induced micronuclei in V79 cells

The induction of micronuclei (MN) in mitotically active cells has been widely used and promoted as a biological marker of exposure to environmental toxins. In our study the effect of zinc on cadmium genotoxicity was investigated in V 79 cells. The results indicate that cadmium chloride exposure for 24 h increased micronucleus frequency and the percentage of binucleated cells in dose-dependent manner. At the highest concentration of cadmium (50 microM Cd) 23 MN were found in 1000 cells. The protective effect of zinc on cadmium genotoxicity was investigated at lower concentrations (5-25 microM CdCl2). At 50 microM Cd, the number of MN increased significantly (16 MN).

Genotoxic effects of heavy metals: comparative investigation with plant bioassays

The potential use of micronucleus assays in plants for the detection of genotoxic effects of heavy-metal ions was investigated. Three different plant systems were comparatively investigated in micronucleus tests with Tradescantia pollen mother cells (Trad MCN) and micronucleus tests with meristematic root tip cells of Allium cepa and Vicia faba (Allium/ Vicia MCN). As3+, Pb2+, Cd2+, Zn2+ caused a dose-dependent increase of MCN frequencies in all three test systems. Cu2+ gave consistently negative responses in all three tests; Zn2+ caused only a moderate, statistically not significant increase of MCN frequencies in Vicia. The ranking of genotoxic potencies in all three tests was in the descending order: As3+ > Pb2+ > Cd2+ > Zn2+ Cu2+. In experiments with Tradescantia, induction of MCN was observed in a concentration range between 1 and 10 mM, whereas in tests with root tip cells, higher concentrations (10-1,000 mM) were required to show significant effects. Further increase of the exposure levels caused toxic effects (reduction of root growth), cell division delays, and a decrease of MCN frequencies. Comparisons by linear regression analyses indicated that the sensitivity of the three bioassays for heavy metals decreases in the order: Trad MCN > Vicia root MCN > Allium root MCN. In further experimental series, a soil sample which contained high concentrations of the five metals and a control soil were investigated. Aqueous soil extracts induced only weak effects in Trad MCN tests and no effects in the root tip assays, whereas cultivation of the plants in the soils resulted in a pronounced induction of MCN in the Tradescantia system and moderate effects in Vicia and Allium. In conclusion, the results of the study indicate that the Trad MCN assay detects the genotoxic effects of heavy metals and can be used for biomonitoring metal-contaminated soils.