Showing papers in "Metallomics in 2013"

An overview of heavy metal challenge in plants: from roots to shoots

Abstract: Heavy metals are often present naturally in soils, but many human activities (e.g. mining, agriculture, sewage processing, the metal industry and automobiles) increase their prevalence in the environment resulting in concentrations that are toxic to animals and plants. Excess heavy metals affect plant physiology by inducing stress symptoms, but many plants have adapted to avoid the damaging effects of metal toxicity, using strategies such as metal chelation, transport and compartmentalization. Understanding the molecular basis of heavy metal tolerance in plants will facilitate the development of new strategies to create metal-tolerant crops, biofortified foods and plants suitable for the phytoremediation of contaminated sites.

Anti-proliferative and anti-tumor activity of silver(I) compounds

Abstract: Silver is proving to have a number of medicinal applications; as an antiseptic, an antibacterial, and an anti-inflammatory, while any biological role for it is currently unknown. Silver compounds and their therapeutic potentials are under consideration from many research groups, while a number of early reviews recording the advances of silver(I) chemistry are also available. However there is no recent report on the screening for the antitumor potential of silver(I) compounds. This review focuses upon results obtained on the anti-proliferative activity of silver compounds in the past years. This survey shows that silver(I) complexes containing various type of ligands such as carboxylic acids, amino acids, nitrogen, phosphorus or sulfur donor ligands, exhibit selectivity against a variety of cancer cells. The role of the coordination number, which is related to either the stability or hydrophilicity–lipophilicity of a complex, is not clearly elucidated within this review.

Transition metals in plant photosynthesis

Abstract: Transition metals are involved in essential biological processes in plants since they are cofactors of metalloproteins and also act as regulator elements. Particularly, plant chloroplasts are organelles with high transition metal ion demand because metalloproteins are involved in the photosynthetic electron transport chain. The transition metal requirement of photosynthetic organisms greatly exceeds that of non-photosynthetic organisms, and either metal deficiency or metal excess strongly impacts photosynthetic functions. In chloroplasts, the transition metal ion requirement needs a homeostasis network that strictly regulates metal uptake, chelation, trafficking and storage since under some conditions metals cause toxicity. This review gives an overview of the current understanding of main features concerning the role of copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) in plant photosynthesis as well as the mechanisms involved in their homeostasis within chloroplasts. The metalloproteins functioning in photosynthetic proteins of plants as well as those proteins participating in the metal transport and metal binding assembly are reviewed. Furthermore, the role of nickel (Ni) in artificial photosynthesis will be discussed.

Diversity and distribution of plant metallothioneins: a review of structure, properties and functions

Abstract: More than 30 years have passed since the discovery of the first plant metallothionein in wheat embryos, from which the emergence of a uniquely diverse metallothionein family with a fascinating array of structural nuances and molecular properties has been witnessed. Metallothioneins are not only constitutively expressed, but the production of different types of plant metallothionein is also stimulated by a myriad of endogenous and exogenous agents in both a temporally and spatially regulated manner. This ubiquitous, yet discrete expression of metallothioneins not only signifies their importance for plant survival and development, but also suggests a functional divergence for the individual plant metallothionein subfamilies. Understanding why one type of plant metallothionein has more advantageous structural and metal binding attributes over another for a given biological process is a crucial piece in the puzzle of assigning physiological functions to these proteins. In this review, we discuss how in vivo and in vitro studies have advanced our understanding of the structure–property–function relationship for the plant metallothionein family. In particular, we highlight the progress that has been made for the Type 4 plant metallothioneins.

The induction of mitochondria-mediated apoptosis in cancer cells by ruthenium(II) asymmetric complexes

Abstract: Four ruthenium(II) asymmetric complexes, [Ru(bpy)2(PAIDH)]2+ (bpy = 2,2′-bipyridine, PAIDH = 2-pyridyl-1H-anthra[1,2-d]imidazole-6,11-dione, 1), [Ru(phen)2(PAIDH)]2+ (phen = 1,10-phenanthroline, 2), [Ru(dmp)2(PAIDH)]2+ (dmp = 4,7-dimethyl-1,10-phenanthroline, 3) and [Ru(dip)2(PAIDH)]2+ (dip = 4,7-diphenyl-1,10-phenanthroline, 4), have been synthesized and characterized. These complexes displayed potent anti-proliferation activity against various cancer cell lines and had high selectivity between tumor cells and normal cells. HeLa cells exhibited the highest sensitivity to complex 4, accounting for the greatest cellular uptake. Complex 4 was shown to accumulate preferentially in the mitochondria of HeLa cells and induced apoptosis via the mitochondrial pathway, which involved ROS generation, mitochondrial membrane potential depolarisation, and Bcl-2 and caspase family members activation. These results demonstrated that complex 4 induced cancer cell apoptosis by acting on mitochondrial pathways.

An update on magnesium homeostasis mechanisms in plants

Abstract: Worldwide, nearly two-thirds of the population do not consume the recommended amount of magnesium (Mg) in their diet. Furthermore, low Mg status (hypomagnesaemia) is known to contribute to a number of human chronic disease conditions. Because the principal dietary Mg source is of plant origin, agronomic and genetic biofortification strategies are aimed at improving nutritional Mg content in food crops to overcome this mineral deficiency in humans. This update incorporates the contributions of annotated permeases involved in Mg uptake, storage and recycling with a schematic model of Mg movement at the organ and cellular levels in the model species Arabidopsis thaliana. Furthermore, approaches using mutagenesis or natural ionomic variation to identify loci involved in Mg homeostasis in roots, leaves and seeds will be summarised. A brief overview will be presented on how Arabidopsis research can help to develop strategies for biofortification of crops.

Trans-generational impact of cerium oxide nanoparticles on tomato plants

Abstract: Cerium oxide nanoparticles (CeO2-NPs) are increasingly used in polishing, engine enhancement agents and many other products. Even though the acute toxicity of CeO2-NPs to plants has been investigated, the long-term effects of CeO2-NPs in the environment are still unknown. The main objective of this study was to investigate whether the treatment of tomato plants with relatively low concentrations of CeO2-NPs (10 mg L(-1)) through their lifecycle would affect the seed quality and the development of second generation seedlings. The results indicated that second generation seedlings grown from seeds collected from treated parent plants with CeO2-NPs (treated second generation seedlings) were generally smaller and weaker, as indicated by their smaller biomass, lower water transpiration and slightly higher reactive oxygen species content. An interesting phenomenon noticed in the study was that the second generation seedlings grown from treated seeds developed extensive root hairs compared with the control second generation seedlings (seedlings grown from seeds collected from untreated parent plants) regardless of the treatment. Treated second generation seedlings also accumulate a higher amount of ceria than control second generation seedlings under the same treatment conditions even though such differences are not statistically significant.

Localization of copper and copper transporters in the human brain.

Abstract: Disturbances in brain copper result in rare and severe neurological disorders and may play a role in the pathogenesis and progression of multiple neurodegenerative diseases. Our current understanding of mammalian brain copper transport is based on model systems outside the central nervous system and no data are available regarding copper transport systems in the human brain. To address this deficit, we quantified regional copper concentrations and examined the distribution and cellular localization of the copper transport proteins Copper transporter 1, Atox1, ATP7A, and ATP7B in multiple regions of the human brain using inductively coupled plasma-mass spectrometry, Western blot and immunohistochemistry. We identified significant relationships between copper transporter levels and brain copper concentrations, supporting a role for these proteins in copper transport in the human brain. Interestingly, the substantia nigra contained twice as much copper than that in other brain regions, suggesting an important role for copper in this brain region. Furthermore, ATP7A levels were significantly greater in the cerebellum, compared with other brain regions, supporting an important role for ATP7A in cerebellar neuronal health. This study provides novel data regarding copper regulation in the human brain, critical to understand the mechanisms by which brain copper levels can be altered, leading to neurological disease.

Fluorescent silver(I) and gold(I)-N-heterocyclic carbene complexes with cytotoxic properties: mechanistic insights.

Abstract: Silver(I) and gold(I)–N-heterocyclic carbene (NHC) complexes bearing a fluorescent anthracenyl ligand were examined for cytotoxicity in normal and tumor cells. The silver(I) complex exhibits greater cytotoxicity in tumor cells compared with normal cells. Notably, in cell extracts, this complex determines a more pronounced inhibition of thioredoxin reductase (TrxR), but it is ineffective towards glutathione reductase (GR). Both gold and silver complexes lead to oxidation of the thioredoxin system, the silver(I) derivative being particularly effective. In addition, the dimerization of peroxiredoxin 3 (Prx3) was also observed, demonstrating the ability of these compounds to reach the mitochondrial target. The fluorescence microscopy visualization of the subcellular distribution of the complexes shows a larger diffusion of these molecules in tumor cells with respect to normal cells.

Molecular strategies of microbial iron assimilation: from high-affinity complexes to cofactor assembly systems

Abstract: Microorganisms have to cope with restricted iron bioavailability in most environmental habitats as well as during host colonization. The continuous struggle for iron has brought forth a plethora of acquisition and assimilation strategies that share several functional and mechanistic principles. One common theme is the utilization of high-affinity chelators for extracellular iron mobilization, generally known as siderophore-dependent iron acquisition. This basic strategy is related with another central aspect of microbial iron acquisition, which is the release of the mobilized iron from extracellular sources to allow its transfer and incorporation into metabolically active proteins. A variety of mechanisms which are often coupled with high-affinity uptake have evolved to facilitate the removal of iron from siderophore ligands; however, they differ in many key aspects including substrate specificities and release efficiencies. The most sophisticated iron release pathways comprise processes of specific hydrolysis and reduction of ferric siderophores, especially in the case of high-affinity iron complexes with greatly negative redox potentials that often represent crucial factors for virulence development in bacterial and fungal pathogens. During the following steps of iron utilization, the acquired metal is transferred through intracellular trafficking pathways which may include diverse storage compartments in order to be directed to cofactor assembly systems and to final protein targeting. Several of these iron channeling routes have been described recently and provide first insights into the later steps of iron assimilation that characterize an essential part of the cellular iron homeostasis network.

Toxicity of vanadium on isolated rat liver mitochondria: a new mechanistic approach

Abstract: Vanadium as a trace element is considered essential for animals; however it has not yet been recognized as a micronutrient for humans. Most of the information on the biological effects of vanadium was related to metal's insulin-like, anti-hyperlipidemic and anticancer properties in low concentrations. According to the previous literature, mitochondria were proposed as an important target for vanadium cytotoxicity. In this study, the mitochondrial toxicity mechanisms of sodium metavanadate (vanadium V or V5+) were investigated in the isolated mitochondria obtained from rat liver by differential centrifugation and mitochondrial toxicity endpoints as well as mitochondrial sources of ROS formation were determined in both in vivo and in vitro using specific substrates and inhibitors. Single injection of V5+ into Wistar rat (10, 20 and 40 mg kg−1, i.p.) caused a significant increase in serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Isolated mitochondria from the V5+-treated rat liver showed a marked elevation in oxidative stress parameters accompanied by mitochondrial membrane potential (MMP) collapse as compared to a control group. On the other hand, our in vitro results with isolated mitochondria showed that different concentrations of V5+ (25–200 μM) induced significant (P < 0.05) progress in mitochondrial ROS formation, ATP depletion, GSH oxidation, mitochondrial outer membrane rupture, mitochondrial swelling and cytochrome c release before the mitochondrial potential collapse ensued. We also showed that the V5+ interaction with respiratory complex III is the major source of V5+-induced ROS formation. In general, our in vivo and in vitro data strongly supported that the V5+-induced liver toxicity is a result of the metal disruptive effect on the mitochondrial respiratory complexes I, II and III which are the obvious causes of metal-induced ROS formation and ATP depletion in liver cells which leads to cell death signalling via MPT pore opening and cytochrome c release.

The effect of Cu2+ and Zn2+ on the Aβ42 peptide aggregation and cellular toxicity

Abstract: The coordination chemistry of Cu and Zn metal ions with the amyloid β (Aβ) peptides has attracted a lot of attention in recent years due to its implications in Alzheimer's disease. A number of reports indicate that Cu and Zn have profound effects on Aβ aggregation. However, the impact of these metal ions on Aβ oligomerization and fibrillization is still not well understood, especially for the more rapidly aggregating and more neurotoxic Aβ42 peptide. Here we report the effect of Cu2+ and Zn2+ on Aβ42 oligomerization and aggregation using a series of methods such as Thioflavin T (ThT) fluorescence, native gel and Western blotting, transmission electron microscopy (TEM), and cellular toxicity studies. Our studies suggest that both Cu2+ and Zn2+ ions inhibit Aβ42 fibrillization. While presence of Cu2+ stabilizes Aβ42 oligomers, Zn2+ leads to formation of amorphous, non-fibrillar aggregates. The effects of temperature, buffer, and metal ion concentration and stoichiometry were also studied. Interestingly, while Cu2+ increases the Aβ42-induced cell toxicity, Zn2+ causes a significant decrease in Aβ42 neurotoxicity. While previous reports have indicated that Cu2+ can disrupt β-sheets and lead to non-fibrillar Aβ aggregates, the neurotoxic consequences were not investigated in detail. The data presented herein including cellular toxicity studies strongly suggest that Cu2+ increases the neurotoxicity of Aβ42 due to stabilization of soluble Aβ42 oligomers.

Contrasting Cu, Fe, and Zn isotopic patterns in organs and body fluids of mice and sheep, with emphasis on cellular fractionation

Abstract: We report Cu, Fe, and Zn natural isotope compositions in organs, body fluids, diets and feces of mice and sheep. Large and systematic isotope variability is observed, notably in the δ66Zn in liver and δ65Cu in kidneys, but significant differences exist between mice, sheep and humans, especially in the δ66Zn value of blood. The results are interpreted with reference to current knowledge of metal trafficking and redox conditions in cells. In general, the light isotopes preferentially fractionate into ‘softer’ bonds involving sulfur such as cysteine and glutathione, whereas heavy isotopes fractionate into ‘harder’ bonds involving nitrogen (histidine) and even more oxygen, notably hydroxides, phosphates, and carbonates. Bonds involving the reduced forms Cu+ and Fe2+ are enriched in the light isotopes relative to bonds involving the oxidized Cu2+ and Fe3+ forms. Differences in blood Zn isotope abundances between mice, sheep and humans may reflect a different prevalence of Zn ZIP transporters. The isotopically heavy Cu in the kidneys may reflect isotope fractionation during redox processes and may be relevant to ascorbate degradation into oxalate.

Association of arsenic with nutrient elements in rice plants

Abstract: Rice is the main cereal crop that feeds half of the world's population, and two thirds of the Chinese population. Arsenic (As) contamination in paddy soil and irrigation water elevates As concentration in rice grains, thus rice consumption is an important As intake route for populations in south and south-east Asia, where rice is the staple food. In addition to direct toxicity of As to human, As may limit the accumulation of micro-nutrients in rice grains, such as selenium (Se) and zinc (Zn). These micro-nutrients are essential for humans, while mineral deficiencies, especially iron (Fe) and Zn, are prevalent in China. Therefore, it is important to understand the interactions between As and micro-nutrients in rice plants, which is the principal source of these nutrients for people on rice diets. In addition, during the processes of As uptake, translocation and transformation, the status of macro-nutrients (e.g. silicon (Si), phosphors (P), sulfur (S)) are important factors affecting As dynamics in soil–plant systems and As accumulation in rice grains. Recently, synchrotron-based spectroscopic techniques have been applied to map the distribution of As and nutrient elements in rice plants, which will aid to understand how As are accumulated, complexed and transported within plants. This paper reviews the interactions between As and macro-nutrients, as well as micro-nutrients in rice plants.

Iron-responsive bacterial small RNAs: variations on a theme

Abstract: For most living organisms, iron is both essential and potentially toxic, making the precise maintenance of iron homeostasis necessary for survival. To manage this paradox, bacteria regulate the acquisition, utilization, and storage of iron in response to its availability. The iron-dependent ferric uptake repressor (Fur) often mediates this iron-responsive regulation by both direct and indirect mechanisms. In 2002, Masse and Gottesman identified a novel target of Fur-mediated regulation in Escherichia coli: a gene encoding a small regulatory RNA (sRNA) termed RyhB. Under conditions of iron-limitation, RyhB is produced and functions to regulate the expression of several target genes encoding iron-utilizing enzymes, iron acquisition systems, and iron storage factors. This pivotal finding provided the missing link between environmental iron-limitation and previously observed decreases in certain iron-dependent metabolic pathways, a phenomenon now referred to as an “iron-sparing” response. The discovery of RyhB opened the door to the rapidly expanding field of bacterial iron-regulated sRNAs, which continue to be identified and described in numerous bacterial species. Most striking are findings that the impact of iron-responsive sRNA regulation often extends beyond iron homeostasis, particularly with regard to production of virulence-associated factors by pathogenic bacteria. This review discusses trends in the collective body of work on iron-regulated sRNAs, highlighting both the regulatory mechanisms they utilize to control target gene expression and the impact of this regulation on basic processes controlling bacterial physiology and virulence.

Molybdenum metabolism in plants

Abstract: The viability of plants relies on molybdenum, which after binding to the organic moiety of molybdopterin forms the molybdenum cofactor (Moco) and acquires remarkable redox properties. Moco is in the active site of critical molybdoenzymes, which use to work as small electron transport chains and participate in N and S metabolism, hormone biosynthesis, toxic compound transformations and other important processes not only in plants but also in all the other kingdoms of life. Molybdate metabolism in plants is reviewed here, with special attention to two main aspects, the different molybdate transporters that with a very high affinity participate in molybdenum acquisition and the recently discovered Moco enzyme amidoxime-reducing component. Their functionality is starting to be understood.

A platinum complex that binds non-covalently to DNA and induces cell death via a different mechanism than cisplatin

Abstract: Cisplatin and some of its derivatives have been shown to be very successful anticancer agents. Their main mode of action has been proposed to be via covalent binding to DNA. However, one of the limitations of these drugs is their poor activity against some tumours due to intrinsic or acquired resistance. Therefore, there is interest in developing complexes with different binding modes and mode of action. Herein we present a novel platinum(II)–terpyridine complex (1) which interacts non-covalently with DNA and induces cell death via a different mechanism than cisplatin. The interaction of this complex with DNA was studied by UV/Vis spectroscopic titrations, fluorescent indicator displacement (FID) assays and circular dichroism (CD) titrations. In addition, computational docking studies were carried out with the aim of establishing the complex's binding mode. These experimental and computational studies showed the complex to have an affinity constant for DNA of ∼104 M−1, a theoretical free energy of binding of −10.83 kcal mol−1 and selectivity for the minor groove of DNA. Long-term studies indicated that 1 did not covalently bind (or nick) DNA. The cancer cell antiproliferative properties of this platinum(II) complex were probed in vitro against human and murine cell lines. Encouragingly the platinum(II) complex displayed selective toxicity for the cancerous (U2OS and SH-SY5Y) and proliferating NIH 3T3 cell lines. Further cell based studies were carried out to establish the mode of action. Cellular uptake studies demonstrated that the complex is able to penetrate the cell membrane and localize to the nucleus, implying that genomic DNA could be a cellular target. Detailed immunoblotting studies in combination with DNA-flow cytometry showed that the platinum(II) complex induced cell death in a manner consistent with necrosis.

Calciomics: integrative studies of Ca2+-binding proteins and their interactomes in biological systems.

Abstract: Calcium ion (Ca2+), the fifth most common chemical element in the earth's crust, represents the most abundant mineral in the human body. By binding to a myriad of proteins distributed in different cellular organelles, Ca2+ impacts nearly every aspect of cellular life. In prokaryotes, Ca2+ plays an important role in bacterial movement, chemotaxis, survival reactions and sporulation. In eukaryotes, Ca2+ has been chosen through evolution to function as a universal and versatile intracellular signal. Viruses, as obligate intracellular parasites, also develop smart strategies to manipulate the host Ca2+ signaling machinery to benefit their own life cycles. This review focuses on recent advances in applying both bioinformatic and experimental approaches to predict and validate Ca2+-binding proteins and their interactomes in biological systems on a genome-wide scale (termed “calciomics”). Calmodulin is used as an example of Ca2+-binding protein (CaBP) to demonstrate the role of CaBPs on the regulation of biological functions. This review is anticipated to rekindle interest in investigating Ca2+-binding proteins and Ca2+-modulated functions at the systems level in the post-genomic era.

Synaptic Zn2+ homeostasis and its significance

Abstract: The decrease in serum zinc is linked to the hypothalamic–pituitary–adrenal (HPA) axis activation that increases the serum glucocorticoid level, indicating the importance of zinc homeostasis in physiological function. Zinc homeostasis in the brain is maintained through the blood–brain and blood–cerebrospinal fluid barriers. At young age, however, the increase in zinc concentration in the brain extracellular fluid along with brain development is suppressed under chronic zinc deficiency, followed by suppression of the increase in zinc in the synaptic vesicles that serves as the Zn2+ signal. Zn2+ is released from glutamatergic (zincergic) neuron terminals and serves as the Zn2+ signal in the intracellular (cytosol) compartment through calcium-permeable channels in addition to the extracellular compartment. Synaptic Zn2+ signals may participate in synaptic plasticity such as long-term potentiation (LTP) and cognitive function. Both the lack and excess of synaptic Zn2+ signals may affect them. Because there is limited evidence for the significance of Zn2+ signaling, the exact relationship between synaptic Zn2+ function and cognitive activity remains to be solved. Synaptic Zn2+ homeostasis seems to be controlled by the two major pools of Zn2+, i.e., the synaptic vesicle and the extracellular compartment, in the brain. Synaptic Zn2+ homeostasis is affected by the enhanced glutamatergic (zincergic) neuron activity. This paper summarizes the significance of synaptic Zn2+ homeostasis in zincergic neuron activity.

A potential role of microRNAs in plant response to metal toxicity

Abstract: MicroRNAs (miRNAs) regulate plant growth and development by silencing gene expression at post-transcriptional level. Recent studies have shown that miRNAs are the regulators of plant response to environmental stresses. Also, genome-wide profiling of small RNAs reveals that many miRNAs are in response to heavy metals. Identification of the targets of metal-regulated miRNAs demonstrated that most of the target genes are involved in diverse metabolic pathways including sulphate allocation and assimilation, phytohormone signalling, antioxidation, and miRNA biogenesis. Thus, the high-throughput sequencing of small RNAs provides a powerful tool for mining a number of known and unknown miRNAs in plants in response to metal stress. Here, we discuss recent studies focusing on the newly identified miRNAs and their potential targets in plants and propose a new scenario involving plant tolerance to metal toxicity as part of the dynamic network that defines the potential roles of miRNAs in plant adaptation to heavy metal stress.

The CTR/COPT-dependent copper uptake and SPL7-dependent copper deficiency responses are required for basal cadmium tolerance in A. thaliana

Abstract: Copper (Cu) homeostasis in plants is maintained by at least two mechanisms: (1) the miRNA-dependent reallocation of intracellular Cu among major Cu-enzymes and important energy-related functions; (2) the regulation of the expression of Cu transporters including members of the CTR/COPT family. These events are controlled by the transcription factor SPL7 in Arabidopsis thaliana. Cadmium (Cd), on the other hand, is a non-essential and a highly toxic metal that interferes with homeostasis of essential elements by competing for cellular binding sites. Whether Cd affects Cu homeostasis in plants is unknown. We found that Cd stimulates Cu accumulation in roots of A. thaliana and increases mRNA expression of three plasma membrane-localized Cu uptake transporters, COPT1, COPT2 and COPT6. Further analysis of Cd sensitivity of single and triple copt1copt2copt6 mutants, and transgenic plants ectopically expressing COPT6 suggested that Cu uptake is an essential component of Cd resistance in A. thaliana. Analysis of the contribution of the SPL7-dependent pathway to Cd-induced expression of COPT1, COPT2 and COPT6 showed that it occurs, in part, through mimicking the SPL7-dependent transcriptional Cu deficiency response. This response also involves components of the Cu reallocation system, miRNA398, FSD1, CSD1 and CSD2. Furthermore, seedlings of the spl7-1 mutant accumulate up to 2-fold less Cu in roots than the wild-type, are hypersensitive to Cd, and are more sensitive to Cd than the triple copt1copt2copt6 mutant. Together these data show that exposure to excess Cd triggers SPL7-dependent Cu deficiency responses that include Cu uptake and reallocation that are required for basal Cd tolerance in A. thaliana.

Is aging recorded in blood Cu and Zn isotope compositions

Abstract: Recent isotopic observations of animal samples indicate body accumulation of heavy zinc and light copper throughout life. This hypothesis has never been tested for humans, but the existence of a relationship between blood isotopic composition and age could be promising for age assessment methodologies. Dietary habits can also influence the blood zinc isotope composition, being an additional source of isotopic variation. In order to reduce this putative source of variation, we selected a population living in an isolated area (Sakha Republic, Russia) where diverse foods are of limited availability. We sampled blood from 8 male and 31 female Yakut volunteers between the ages of 18 and 74. Zinc, iron and copper were purified by liquid chromatography on ion exchange resin and their stable isotope ratios were measured using multiple-collector inductively coupled plasma mass spectrometry. According to observations of animal samples, the (66)Zn/(64)Zn ratio increases with age. We also observe that the (65)Cu/(63)Cu ratio decreases with age, whereas iron isotopic compositions are unrelated to age. The copper and zinc isotope compositions of the Yakut's blood are significantly lighter and heavier, respectively, than in samples of European and Japanese populations. The Yakut is a circumpolar population in which individuals have an elevated basal metabolic rate in response to cold stress. This elevated basal metabolic rate could enhance copper and zinc isotopic fractionation by accelerating the turnover of the copper and zinc stores.

Metallobiology of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity

Abstract: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a potent toxin used to selectively destroy dopaminergic neurons in the substantia nigra and induce parkinsonism. MPTP is metabolised to the 1-methyl-4-phenylpyridinium ion (MPP+) in glia, after which it enters the neuron via the dopamine transporter and results in elevated levels of oxidative stress. The mechanism through which MPP+ causes cell death is thought to involve redox-active metals, particularly iron (Fe). This review will examine how cellular metal metabolism is altered following MPTP insult, and how this relates to metal dyshomeostasis in idiopathic Parkinson's disease. This includes both cell damage arising from increased metal concentration, and how metal-binding proteins respond to MPTP-induced neurotoxicity. Implications for using MPTP as a model for human Parkinson's disease will be discussed in terms of cell metallobiology.

The use of X-ray absorption and synchrotron based micro-X-ray fluorescence spectroscopy to investigate anti-cancer metal compounds in vivo and in vitro.

Abstract: X-ray absorption spectroscopy (XAS) and micro-synchrotron based X-ray fluorescence (micro-SXRF) are element specific spectroscopic techniques and have been proven to be valuable tools for the investigation of changes in the chemical environment of metal centres. XAS allows the determination of the oxidation state, the coordination motif of the probed element, the identity and the number of adjacent atoms and the absorber–ligand distances. It is further applicable to nearly all types of samples independent of their actual physical state (solid, liquid, gaseous) down to μM concentrations. Micro-SXRF can provide information on the distribution and concentration of multiple elements within a sample simultaneously, allowing for the chemical state of several elements within subcellular compartments to be probed. Modern third generation synchrotrons offer the possibility to investigate the majority of the biologically relevant elements. The biological mode of action of metal-based compounds often involves interactions with target and/or transport molecules. The presence of reducing agents may also give rise to changes in the coordination sphere and/or the oxidation state. XAS and micro-SXRF are ideal techniques for investigating these issues. This tutorial review introduces the use of XAS and micro-SXRF techniques into the field of inorganic medicinal chemistry. The results obtained for platinum, ruthenium, gallium, gold and cobalt compounds within the last few years are presented.

The BaeSR regulon is involved in defense against zinc toxicity in E. coli.

Abstract: Intracellular zinc homeostasis is regulated by an extensive network of transporters, ligands and transcription factors. The zinc detoxification functions of three transporters and a periplasmic protein regulated by the BaeSR two-component system were explored in this work by evaluating the effect of single gene knockouts in the BaeSR regulon on the cell growth rate, free zinc, total zinc and total copper after zinc shock. Two exporters, MdtABC and MdtD, and the periplasmic protein, Spy, are involved in zinc detoxification based on the growth defects at high cell density and increases in free (>1000-fold) and total zinc/copper (>2-fold) that were observed in the single knockout strains upon exposure to zinc. These proteins complement the ATP-driven zinc export mediated by ZntA in E. coli to limit zinc toxicity. These results highlight the functions of the BaeSR regulon in metal homeostasis.

Quantitative bioimaging of platinum in polymer embedded mouse organs using laser ablation ICP-MS

Abstract: A novel quantification approach for tissue imaging using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) based on tissue embedding in cold-curing resins (Technovit 7100) is presented. With respect to massive side effects on cisplatin, the platinum distribution at different time intervals after cisplatin treatment of mice was determined quantitatively in different tissues including cochlea, testis and kidney. For this purpose, cold-curing resin blocks spiked with different amounts of platinum acetyl acetonate prior to curing were ablated after sectioning at 5 μm thickness and were analysed using ICP-MS after microwave digestion. High spatial resolution and limits of detection in the low ppb range (8 μg kg(-1)) were achieved using a simple and efficient sample preparation. External calibration using the Technovit 7100 standards proved to yield precise and reproducible quantification results. The distribution and retention behaviour of cisplatin in the organs was investigated using the new calibration method.

Comparison of cytotoxicity and expression of metal regulatory genes in zebrafish (Danio rerio) liver cells exposed to cadmium sulfate, zinc sulfate and quantum dots

Abstract: Recent advances in the ability to manufacture and manipulate materials at the nanometer scale have led to increased production and use of many types of nanoparticles. Quantum dots (QDs) are small, fluorescent nanoparticles composed of a core of semiconductor material (e.g. cadmium selenide, zinc sulfide) and shells or dopants of other elements. Particle core composition, size, shell, and surface chemistry have all been found to influence toxicity in cells. The aim of this study was to compare the toxicities of ionic cadmium (Cd) and zinc (Zn) and Cd- and Zn-containing QDs in zebrafish liver cells (ZFL). As expected, Cd2+ was more toxic than Zn2+, and the general trend of IC50-24 h values of QDs was determined to be CdTe < CdSe/ZnS or InP/ZnS, suggesting that ZnS-shelled CdSe/ZnS QDs were more cytocompatible than bare core CdTe crystals. Smaller QDs showed greater toxicity than larger QDs. Isolated mRNA from these exposures was used to measure the expression of metal response genes including metallothionein (MT), metal response element-binding transcription factor (MTF-1), divalent metal transporter (DMT-1), zrt and irt like protein (ZIP-1) and the zinc transporter, ZnT-1. CdTe exposure induced expression of these genes in a dose dependent manner similar to that of CdSO4 exposure. However, CdSe/ZnS and InP/ZnS altered gene expression of metal homeostasis genes in a manner different from that of the corresponding Cd or Zn salts. This implies that ZnS shells reduce QD toxicity attributed to the release of Cd2+, but do not eliminate toxic effects caused by the nanoparticles themselves.

Evaluation of quantitative probes for weaker Cu(I) binding sites completes a set of four capable of detecting Cu(I) affinities from nanomolar to attomolar

Abstract: Copper plays essential roles in biology, but abnormal interactions are damaging. Reliable quantification of copper–protein interactions will underpin the molecular understanding of copper nutrition and toxicity. We have previously established two high affinity probes, Bathocuproine disulfonate (Bcs) and Bicinchoninate (Bca) anions, that are capable of in vitro quantification of Cu(I) binding with affinities from pico- to atto-molar concentrations. Quantitative probes are required for Cu(I) binding of lower affinity for proteins and peptides typically associated with neurodegenerative diseases. The present work evaluates two classic Fe(II) ligands Ferene S (Fs) and Ferrozine (Fz) as quantitative probes for Cu(I). Both react with Cu(I) quantitatively to yield well-defined complex anions [CuI(Fs)2]3− (λmax = 484 nm, e = 6700 cm−1 M−1) and [CuI(Fz)2]3− (λmax = 470 nm, e = 4320 cm−1 M−1). These complexes are sensitive to aerial oxidation (E1/2 ∼ +0.36 V vs. SHE) and to substitution by other ligands (e.g., Cl−, MeCN). However, they can be protected effectively under anaerobic conditions by suitable reductants and an excess of the free probe ligands. Formation constants β2 were determined by two approaches: direct metal ion titration and ligand competition. They provided estimates which differed by ∼3 orders of magnitude. The sources of these differences were examined carefully to consolidate the affinities of the two probes to a unified standard (1015.1 M−2 for Fz and 1013.7 M−2 for Fs). It is apparent that application of direct metal ion titrations to quantification of Cu(I) binding affinities is problematical and should be avoided. The four ligands Bcs, Bca, Fz and Fs in combination form a set of versatile probes for ligand competition experiments and are capable of detecting and differentiating an extended spectrum of Cu(I) binding affinities from nano- to atto-molar concentrations. Selected examples of quantification of weaker Cu(I) binding in proteins and peptides are provided, including that of an amyloid-β peptide.

Analytical methods for copper, zinc and iron quantification in mammalian cells

Abstract: Highly complex analytical methods with different accuracies of measurement, reproducibilities and ease of analyses are currently being used to quantify metals in cellular media and tissue samples. In this review, the analytical methods commonly used for iron, copper and zinc quantification in mammalian cells are presented and discussed. Herein, we present a literature survey of the most commonly found concentrations of these metals in various mammalian cells in culture and tissues. The aim of this review is to help researchers in metallomic-related areas identify the method that best suits their needs for the accurate quantification of these metals in cells. This accuracy goes beyond simple knowledge of the limit of detection of each technique and needs to be evaluated through comparisons with similar previous studies.

Iron distribution through the developmental stages of Medicago truncatula nodules

Abstract: Paramount to symbiotic nitrogen fixation (SNF) is the synthesis of a number of metalloenzymes that use iron as a critical component of their catalytical core. Since this process is carried out by endosymbiotic rhizobia living in legume root nodules, the mechanisms involved in iron delivery to the rhizobia-containing cells are critical for SNF. In order to gain insight into iron transport to the nodule, we have used synchrotron-based X-ray fluorescence to determine the spatio-temporal distribution of this metal in nodules of the legume Medicago truncatula with hitherto unattained sensitivity and resolution. The data support a model in which iron is released from the vasculature into the apoplast of the infection/differentiation zone of the nodule (zone II). The infected cell subsequently takes up this apoplastic iron and delivers it to the symbiosome and the secretory system to synthesize ferroproteins. Upon senescence, iron is relocated to the vasculature to be reused by the shoot. These observations highlight the important role of yet to be discovered metal transporters in iron compartmentalization in the nodule and in the recovery of an essential and scarce nutrient for flowering and seed production.