The role of thiols, dithiols, nutritional factors and interacting ligands in the toxicology of mercury

Mercury and Chlorinated Pesticides on the Highest Level of the Food Web as Exemplified by Herring from the Southern Baltic and African Penguins from the Zoo

Aquatic birds are often used as a health indicator of the marine ecosystem. African penguins living in the zoo make good research material as they form a link between the marine and the terrestrial ecosystem in terms of xenobiotic circulation. Tests were performed on whole herring-the food of the penguins-as well as on bird muscle, liver, brain, eggs, feathers and guano in order to determine total mercury, aldrin, dieldrin, endrin, isodrin, endosulfan isomers, endosulfan sulfate, methoxychlor, dichlorodiphenyltrichloroethane (DDT) and its metabolites. In herring and penguin, the tests did not show the presence of β-endosulfan, endosulfan sulfate, aldrin and isodrin. It was shown that penguins absorb about 36.8 μg of organochlorine pesticides and 4.6 μg of mercury with their food on a daily basis. Xenobiotics accumulate mostly in the liver, from where they are transported to the muscles and the brain, where the highest bioaccumulation factor is reached by endrin and pp'-DDT. Conceivably, the older the penguin, the higher is the concentration level of pesticides in its liver and brain. Molting was found to be the most effective way of eliminating mercury, dieldrin and methoxychlor from the system. Insecticides, such as DDT and its metabolites, were removed most effectively by females through laying of eggs. The standard four eggs laid within a year may have contained up to 20 % of the total amount of pesticides which had been absorbed with food, but no more than 5 % of mercury.

Chelation: harnessing and enhancing heavy metal detoxification--a review

Toxic metals such as arsenic, cadmium, lead, and mercury are ubiquitous, have no beneficial role in human homeostasis, and contribute to noncommunicable chronic diseases. While novel drug targets for chronic disease are eagerly sought, potentially helpful agents that aid in detoxification of toxic elements, chelators, have largely been restricted to overt acute poisoning. Chelation, that is multiple coordination bonds between organic molecules and metals, is very common in the body and at the heart of enzymes with a metal cofactor such as copper or zinc. Peptides glutathione and metallothionein chelate both essential and toxic elements as they are sequestered, transported, and excreted. Enhancing natural chelation detoxification pathways, as well as use of pharmaceutical chelators against heavy metals are reviewed. Historical adverse outcomes with chelators, lessons learned in the art of using them, and successes using chelation to ameliorate renal, cardiovascular, and neurological conditions highlight the need for renewed attention to simple, safe, inexpensive interventions that offer potential to stem the tide of debilitating, expensive chronic disease.

2-Seleno-1-alkylbenzimidazoles and their Diselenides: Synthesis and Structural Characterization of a 2-Seleno-1-methylbenzimidazole Complex of Mercury

2-Seleno-1-methylbenzimidazole, H(sebenzimMe), can be synthesized from 1-methylbenzimidazole by sequential treatment with (i) BunLi, (ii) elemental selenium and (iii) HCl(aq). This method is also applicable to the synthesis of 2-seleno-1-t-butylbenzimidazole, H(sebenzimBut ). Single crystal X-ray diffraction and NMR spectroscopic data demonstrate that H(sebenzimMe) and H(sebenzimBut ) exist as the selone rather than the selenol tautomers, which is in accord with the results of density functional theory (B3LYP) calculations. The data also indicate that the selone is best represented as a C+-Se- zwitterion rather than as a C=Se doubly bonded species. Aerobic oxidation of H(sebenzimMe) and H(sebenzimBut ) in the presence of Et3N yields the diselenides, (sebenzimMe)2 and (sebenzimBut )2. In addition, H(sebenzimMe) reacts with HgCl2 to give [H(sebenzimMe)]2HgCl2, the first structurally characterized example of a 2-seleno-1-alkylimidazole mercury complex.

Exposure to lead in water and cysteine non-oxidative metabolism in Pelophylax ridibundus tissues

Chronic, low-level exposure to metals is an increasing global problem. Lead is an environmentally persistent toxin that causes many lead-related pathologies, directly affects tissues and cellular components or exerts an effect of the generation of reactive oxygen species causing a diminished level of available sulfhydryl antioxidant reserves. Cysteine is one of substrates in the synthesis of glutathione - the most important cellular antioxidant, and it may also undergo non-oxidative desulfuration that produces compounds containing sulfane sulfur atoms. The aim of the experiment was to examine changes of the non-oxidative metabolism of cysteine and the levels of cysteine and glutathione in the kidneys, heart, brain, liver and muscle of Marsh frogs (Pelophylax ridibundus) exposed to 28mg/L Pb(NO(3))(2) for 10 days. The activities of sulfurtransferases, enzymes related to the sulfane sulfur metabolism - 3-mercaptopyruvate sulfurtransfearse, γ-cystathionase and rhodanese - were detected in tissue homogenates. The activity of sulfurtransferases was much higher in the kidneys of frogs exposed to lead in comparison to control frogs, not exposed to lead. The level of sulfane sulfur remained unchanged. Similarly, the total level of cysteine did not change significantly. The total levels of glutathione and the cysteine/cystine and GSH/GSSG ratios were elevated. Thus, it seems that the exposure to lead intensified the metabolism of sulfane sulfur and glutathione synthesis in the kidneys. The results presented in this work not only confirm the participation of GSH in the detoxification of lead ions and/or products appearing in response to their presence, such as reactive oxygen species, but also indicate the involvement of sulfane sulfur and rhodanese in this process (e.g. brain). As long as the expression of enzymatic proteins (rhodanese, MPST and CST) is not examined, no answer will be provided to the question whether changes in their activity are due to differences in the concentrations of substrates and/or compounds affecting their activity or to changes in their level in response to some parameters, e.g. associated with oxidative stress.

Cadmium(Cd)-induced oxidative stress down-regulates the gene expression of DNA mismatch recognition proteins MutS homolog 2 (MSH2) and MSH6 in zebrafish (Danio rerio) embryos

DNA mismatch repair (MMR) of simple base mismatches and small insertion-deletion loops in eukaryotes is initiated by the binding of the MutS homolog 2 (MSH2)-MSH6 heterodimer to mismatched DNA. Cadmium (Cd) is a genotoxic heavy metal that has been recognized as a human carcinogen. Oxidant stress and inhibition of DNA repair have been proposed as major factors underlying Cd genotoxicity. Our previous studies indicated the ability of Cd to disturb the gene expression of MSH6 in zebrafish (Danio rerio) embryos. This study was undertaken to explore if Cd-induced oxidative stress down-regulated MSH gene activities. Following the exposure of zebrafish embryos at 1 h post fertilization (hpf) to sublethal concentrations of Cd at 3-5 μM for 4 or 9 h, a parallel down-regulation of MSH2, MSH6 and Cu/Zn superoxide dismutase (Cu/Zn-SOD) gene expression was detected by real-time RT-PCR and the expression levels were 40-50% of control after a 9-h exposure. Cd exposure also induced oxidative stress, yet no inhibition of catalase gene activity was observed. Whole mount in situ hybridization revealed a wide distribution of msh6 mRNA in the head regions of 10 hpf embryos and pretreatment of embryos with antioxidants butylhydroxytoluene (BHT), d-mannitol or N-acetylcysteine (NAC) at 1-10 μM restored Cd-suppressed msh6 expression. QPCR confirmed the protective effects of antioxidants on Cd-suppressed msh2/msh6 mRNA production. Down-regulated MSH gene activities reaching about 50% of control were also induced in embryos exposed to paraquat, a reactive oxygen species (ROS)-generating herbicide, or hydrogen peroxide at 200 μM. Hence, Cd at sublethal levels down-regulates msh2/msh6 expression primarily via ROS as signaling molecules. The transcriptional activation of human msh6 is known to be fully dependent on the specificity factor 1 (Sp1). Cd failed to inhibit the DNA binding activity of zebrafish Sp1 unless at lethal concentrations based on band shift assay, therefore excluding the involvement of Sp1 inactivation in Cd-induced MSH gene inhibition in zebrafish embryos.

Low mercury concentration produces vasoconstriction, decreases nitric oxide bioavailability and increases oxidative stress in rat conductance artery

Mercury is an environmental pollutant that reduces nitric oxide (NO) bioavailability and increases oxidative stress, having a close link with cardiovascular diseases, as carotid atherosclerosis, myocardial infarction, coronary heart disease and hypertension. One of the main sites affected by oxidative stress, which develops atherosclerosis, is the aorta. Under acute exposure to low mercury concentrations reactive oxygen species (ROS) production were only reported for resistance vessels but if low concentrations of mercury also affect conductance arteries it is still unclear. We investigated the acute effects of 6 nM HgCl(2) on endothelial function of aortic rings measuring the reactivity to phenylephrine in rings incubated, or not, with HgCl(2) for 45 min, the protein expression for cyclooxygenase 2 (COX-2) and the AT1 receptor. HgCl(2) increased Rmax and pD2 to phenylephrine without changing the vasorelaxation induced by acetylcholine and sodium nitroprusside. Endothelial damage abolished the increased reactivity to phenylephrine. The increase of Rmax and pD2 produced by L-NAME was smaller in the presence of HgCl(2). Enalapril, losartan, indomethacin, furegrelate, the selective COX-2 inhibitor NS 398, superoxide dismutase and the NADPH oxidase inhibitor apocynin reverted HgCl(2) effects on the reactivity to phenylephrine, COX-2 protein expression was increased, and AT1 expression reduced. At low concentration, below the reference values, HgCl(2) increased vasoconstrictor activity by reducing NO bioavailability due to increased ROS production by NADPH oxidase activity. Results suggest that this is due to local release of angiotensin II and prostanoid vasoconstrictors. Results also suggest that acute low concentration mercury exposure, occurring time to time could induce vascular injury due to endothelial oxidative stress and contributing to increase peripheral resistance, being a high risk factor for public health.

Consumption of tomato products is associated with lower blood mercury levels in Inuit preschool children

Some evidence suggests that various diet components and nutrients, including vegetables, fruit and food-derived antioxidants, could mitigate contaminant exposure and/or adverse health effects of contaminants. To examine the effect of the consumption of tomato products on blood mercury levels in Inuit preschool children, 155 Inuit children (25.0±9.1months) were recruited from 2006-2008 in Nunavik childcare centers (northern Québec, Canada). Food frequency questionnaires were completed at home and at the childcare center, and total blood mercury concentration was measured by inductively coupled plasma-mass spectrometry. Multivariate regression analysis was performed after multiple imputation. The median blood concentration of mercury was 9.5nmol/L. Age, duration of breastfeeding, annual consumption frequency of seal meat, and monthly consumption frequency of tomato products were significant predictors of blood mercury levels, whereas annual consumption frequencies of beluga muktuk, walrus, Arctic char, and caribou meat were not. Each time a participant consumed tomato products during the month before the interview was associated with a 4.6% lower blood mercury level (p=0.0005). All other significant predictors in the model were positively associated with blood mercury levels. Further studies should explore interactions between consumption of healthy store-bought foods available in Arctic regions and contaminant exposure.

Evaluation of the association of mercury(II) with some dicysteinyl tripeptides

The present study was undertaken to gain insight into the associations of mercury(II) with dicysteinyl tripeptides in buffered media at pH 7.4. We investigated the effects of increasing the distance between cysteinyl residues on mercury(II) associations and complex formations. The peptide-mercury(II) formation constants and their associated thermodynamic parameters in 3-(N-morpholino)propanesulfonic acid (MOPS) buffered solutions were evaluated by isothermal titration calorimetry. Complexes formed in different relative ratios of mercury(II) to cysteinyl peptides in ammonium formate buffered solutions were characterized by LTQ Orbitrap mass spectrometry. The results from these studies show that n-alkyl dicysteinyl peptides (CP 1-4), and an aryl dicysteinyl peptide (CP 5) can serve as effective "double anchors" to accommodate the coordination sites of mercury(II) to form predominantly one-to-one Hg(peptide) complexes. The aryl dicysteinyl peptide (CP 5) also forms the two-to-two Hg(2)(peptide)(2) complex. In the presence of excess peptide, Hg(peptide)(2) complexes are also detected. Notably, increasing the distance between the ligating groups or "anchor points" in CP 1-5 does not significantly affect their affinity for mercury(II). However, the enthalpy change (ΔH) values (ΔH(1) ~ -91 kJ mol(-1) and ΔH(2) ~ -66 kJ mol(-1)) for complex formation between CP 4 and 5 with mercury(II) are about one and a half times larger than the related values for CP 1, 2 and 3 (ΔH(1) ~ -66 kJ mol(-1) and ΔH(2) ~ 46 kJ mol(-1)). The corresponding entropy change (ΔS) values (ΔS(1) ~ -129 J K(-1) mol(-1) and ΔS(2) ~ -116 J K(-1) mol(-1)) of the structurally larger dicysteinyl peptides CP 4 and 5 are less entropically favorable than for CP 1, 2 and 3 (ΔS(1) ~ -48 J K(-1) mol(-1) and ΔS(2) ~ -44 J K(-1) mol(-1)). Generally, these associations result in a decrease in entropy, indicating that these peptide-mercury complexes potentially form highly ordered structures. The results from this study show that dicysteinyl tripeptides are effective in binding mercury(II) and they are promising motifs for the design of multi-cysteinyl peptides for binding more than one mercury(II) ion per peptide.

Heavy metal toxicity and the environment

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least five times greater than that of water. Their multiple industrial, domestic, agricultural, medical, and technological applications have led to their wide distribution in the environment, raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the US Environmental Protection Agency and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.

Electroanalytical and isothermal calorimetric study of As(III) complexation by the metal poisoning remediators, 2,3-dimercapto-1-propanesulfonate and meso-2,3-dimercaptosuccinic acid

A recently developed methodology, which combines voltammetry, ITC, ESI-MS and several chemometric tools, has been applied for the first time to the study of As(III) complexes. The ligands considered, DMSA and DMPS, are commonly used to treat heavy metal poisoning. The study yields a reliable and consistent picture of the binding of As(III) by the chelating therapy agents DMSA and DMPS providing an unambiguous description of the stoichiometries of the complexes (ML(2), with the occasional appearance of ML in the case of DMSA), both ligands have stability constants of the same order, with a logβ(2) of 9.2 and 9.8, respectively. These values confirm the potential efficiency of both ligands in the treatment of As(III) poisoning.

Toxic effects of mercury on the cardiovascular and central nervous systems

Environmental contamination has exposed humans to various metal agents, including mercury. This exposure is more common than expected, and the health consequences of such exposure remain unclear. For many years, mercury was used in a wide variety of human activities, and now, exposure to this metal from both natural and artificial sources is significantly increasing. Many studies show that high exposure to mercury induces changes in the central nervous system, potentially resulting in irritability, fatigue, behavioral changes, tremors, headaches, hearing and cognitive loss, dysarthria, incoordination, hallucinations, and death. In the cardiovascular system, mercury induces hypertension in humans and animals that has wide-ranging consequences, including alterations in endothelial function. The results described in this paper indicate that mercury exposure, even at low doses, affects endothelial and cardiovascular function. As a result, the reference values defining the limits for the absence of danger should be reduced.

N-acetyl cysteine treatment reduces mercury-induced neurotoxicity in the developing rat hippocampus

Mercury is an environmental toxicant that can disrupt brain development. However, although progress has been made in defining its neurotoxic effects, we know far less about available therapies that can effectively protect the brain in exposed individuals. We previously developed an animal model in which we defined the sequence of events underlying neurotoxicity: Methylmercury (MeHg) injection in postnatal rat acutely induced inhibition of mitosis and stimulated apoptosis in the hippocampus, which later resulted in intermediate-term deficits in structure size and cell number. N-acetyl cysteine (NAC) is the N-acetyl derivative of L-cysteine used clinically for treatment of drug intoxication. Here, based on its known efficacy in promoting MeHg urinary excretion, we evaluated NAC for protective effects in the developing brain. In immature neurons and precursors, MeHg (3 μM) induced a >50% decrease in DNA synthesis at 24 hr, an effect that was completely blocked by NAC coincubation. In vivo, injection of MeHg (5 μg/g bw) into 7-day-old rats induced a 22% decrease in DNA synthesis in whole hippocampus and a fourfold increase in activated caspase-3-immunoreactive cells at 24 hr and reduced total cell numbers by 13% at 3 weeks. Treatment of MeHg-exposed rats with repeated injections of NAC abolished MeHg toxicity. NAC prevented the reduction in DNA synthesis and the marked increase in caspase-3 immunoreactivity. Moreover, the intermediate-term decrease in hippocampal cell number provoked by MeHg was fully blocked by NAC. Altogether these results suggest that MeHg toxicity in the perinatal brain can be ameliorated by using NAC, opening potential avenues for therapeutic intervention.

Hepatoprotective effect of coenzyme Q10 in rats with acetaminophen toxicity

The potential protective effect of coenzyme Q10 against acute liver injury induced by a single dose of acetaminophen (700 mg/kg, p.o.) was investigated in rats. Coenzyme Q10 treatment was given as two i.p. injections, 10 mg/kg each, at 1 and 12 h following acetaminophen administration. Coenzyme Q10 significantly reduced the levels of serum aminotransferases, suppressed lipid peroxidation, prevented the decreases of reduced glutathione and catalase activity, decreased the elevations of tumor necrosis factor-α and nitric oxide as well as attenuating the reductions of selenium and zinc ions in liver tissue resulting from acetaminophen administration. Histopathological liver tissue damage mediated by acetaminophen was ameliorated by coenzyme Q10. Immunohistochemical analysis revealed that coenzyme Q10 significantly decreased the acetaminophen-induced overexpression of inducible nitric oxide synthase, nuclear factor-κB, caspase-3 and p53 in liver tissue. It was concluded that coenzyme Q10 protects rat liver against acute acetaminophen hepatotoxicity, most probably through its antioxidant, anti-inflammatory and antiapoptotic effects.

Marine n-3 fatty acids alter the proteomic response to methylmercury in Atlantic salmon kidney (ASK) cells

Fish based diets have been linked to the amelioration of methylmercury (MeHg) induced symptoms in several epidemiological studies, particularly due to their contents of marine n-3 fatty acids. It has been suggested that n-3 fatty acids may mask the detrimental effects of MeHg due to their beneficial effect on the same biological functions which are negatively affected by MeHg. However, in vitro studies have implied that there may be direct interactions between the marine n-3 FAs and MeHg, which ameliorates MeHg toxicity through interactions at a biological level. To understand how marine n-3 FAs and MeHg interact in fish as a biological system, we wanted to investigate molecular interaction in a fish cell system. Atlantic salmon kidney (ASK) cells were pre-incubated with the marine n-3 FAs docosahexaenoic acid (22:6n-3, DHA) and eicosapentaenoic acid (20:5n-3, EPA) before exposing them to MeHg. Modulating effects of the marine FAs on MeHg toxicity were subsequently assessed using the exploratory technique of proteomics, in a factorial design. Thirty-four differentially regulated proteins were identified. From these; twenty-seven were shown to be differentially regulated by MeHg, twelve were regulated by the fatty acids, and another eight showed interaction effects between MeHg and the FAs. Several of the proteins were concomitantly affected by MeHg- and FA-main effects, as well as interaction effects. Functional annotations and pathway analysis of the proteins revealed that marine n-3 FAs and MeHg concurrently affected the abundance of protein markers relating to such molecular mechanisms as: cell signaling, calcium homeostasis, structural integrity, apoptosis, and energy metabolism. In conclusion, both marine n-3 FAs and MeHg can differentially affect the abundances of the same proteins, indicating modulating effects of EPA and DHA on MeHg metabolism, and possibly on its toxicity.

Mercury exposure and mechanism of response in large game using the Almadén mercury mining area (Spain) as a case study

Mercury (Hg) accumulation, transfer, defense mechanism and adverse effects were studied in red deer (Cervus elaphus) and wild boar (Sus scrofa) from the Almadén mining district (Spain), the largest (285,000 t of Hg) and the oldest (more than 2000 years) Hg mine/refining operation site in the world. Red deer (n=168) and wild boar (n=58) liver, kidney, bones (metacarpus), testis and muscle were analyzed for total Hg and selenium (Se) within a range of distances to the Almadén mining district. The highest Hg concentrations were found in kidney (0.092 and 0.103 μg/g d.w. for red deer and wild boar, respectively) followed by the levels in liver (0.013 and 0.023 μg/g d.w. for red deer and wild boar, respectively). A significant correlation (r=-0.609, p=0.007) was found between Hg concentrations and distance to the Almadén Hg mining district. However, both red deer and wild boar closest to the mining area still showed mercury concentrations well below the concentration associated with clinical signs of Hg poisoning. Highest Se concentrations were found in kidney (2.60 and 6.08 μg/g in red deer and wild boar, respectively) and testis (2.20 μg/g in red deer). For selenium, differences between red deer and wild boar were statistically significant (p<0.05) in all tissues, concentrations being higher in wild boar than in red deer. In the diagnosis of Se deficiency, the vast majority of the examined red deer livers were deficient. A significant correlation was found between Hg and Se in kidney (r=0.386, p>0.001 for red deer and r=0.567, p=0.005 for wild boar). Liver GSSG concentrations were negatively correlated to total mercury and Hg:Se molar ratio in male deer, which could indicate a hormetic response to Hg exposure. Moreover, a positive association was found between the antioxidant element Se and antioxidant vitamins in red deer tissues.

Environmental conditions constrain the distribution and diversity of archaeal merA in Yellowstone National Park, Wyoming, U.S.A

The distribution and phylogeny of extant protein-encoding genes recovered from geochemically diverse environments can provide insight into the physical and chemical parameters that led to the origin and which constrained the evolution of a functional process. Mercuric reductase (MerA) plays an integral role in mercury (Hg) biogeochemistry by catalyzing the transformation of Hg(II) to Hg(0). Putative merA sequences were amplified from DNA extracts of microbial communities associated with mats and sulfur precipitates from physicochemically diverse Hg-containing springs in Yellowstone National Park, Wyoming, using four PCR primer sets that were designed to capture the known diversity of merA. The recovery of novel and deeply rooted MerA lineages from these habitats supports previous evidence that indicates merA originated in a thermophilic environment. Generalized linear models indicate that the distribution of putative archaeal merA lineages was constrained by a combination of pH, dissolved organic carbon, dissolved total mercury and sulfide. The models failed to identify statistically well supported trends for the distribution of putative bacterial merA lineages as a function of these or other measured environmental variables, suggesting that these lineages were either influenced by environmental parameters not considered in the present study, or the bacterial primer sets were designed to target too broad of a class of genes which may have responded differently to environmental stimuli. The widespread occurrence of merA in the geothermal environments implies a prominent role for Hg detoxification in these environments. Moreover, the differences in the distribution of the merA genes amplified with the four merA primer sets suggests that the organisms putatively engaged in this activity have evolved to occupy different ecological niches within the geothermal gradient.

Novel lipid-soluble thiol-redox antioxidant and heavy metal chelator, N,N'-bis(2-mercaptoethyl)isophthalamide (NBMI) and phospholipase D-specific inhibitor, 5-fluoro-2-indolyl des-chlorohalopemide (FIPI) attenuate mercury-induced lipid signaling leading to protection against cytotoxicity in aortic endothelial cells

Here, we investigated thiol-redox-mediated phospholipase D (PLD) signaling as a mechanism of mercury cytotoxicity in mouse aortic endothelial cell (MAEC) in vitro model utilizing the novel lipid-soluble thiol-redox antioxidant and heavy metal chelator, N,N'-bis(2-mercaptoethyl)isophthalamide (NBMI) and the novel PLD-specific inhibitor, 5-fluoro-2-indolyl des-chlorohalopemide (FIPI). Our results demonstrated (i) mercury in the form of mercury(II) chloride, methylmercury, and thimerosal induced PLD activation in a dose- and time-dependent manner; (ii) NBMI and FIPI completely attenuated mercury- and oxidant-induced PLD activation; (iii) mercury induced upstream phosphorylation of extracellular-regulated kinase 1/2 (ERK1/2) leading to downstream threonine phosphorylation of PLD(1) which was attenuated by NBMI; (iv) mercury caused loss of intracellular glutathione which was restored by NBMI; and (v) NBMI and FIPI attenuated mercury- and oxidant-induced cytotoxicity in MAECs. For the first time, this study demonstrated that redox-dependent and PLD-mediated bioactive lipid signaling was involved in mercury-induced vascular EC cytotoxicity which was protected by NBMI and FIPI.

Glutathione enzyme and selenoprotein polymorphisms associate with mercury biomarker levels in Michigan dental professionals

Mercury is a potent toxicant of concern to both the general public and occupationally exposed workers (e.g., dentists). Recent studies suggest that several genes mediating the toxicokinetics of mercury are polymorphic in humans and may influence inter-individual variability in mercury accumulation. This work hypothesizes that polymorphisms in key glutathione synthesizing enzyme, glutathione S-transferase, and selenoprotein genes underlie inter-individual differences in mercury body burden as assessed by analytical mercury measurement in urine and hair, biomarkers of elemental mercury and methylmercury, respectively. Urine and hair samples were collected from a population of dental professionals (n=515), and total mercury content was measured. Average urine (1.06±1.24 microg/L) and hair mercury levels (0.49±0.63 microg/g) were similar to national U.S. population averages. Taqman assays were used to genotype DNA from buccal swab samples at 15 polymorphic sites in genes implicated in mercury metabolism. Linear regression modeling assessed the ability of polymorphisms to modify the relationship between mercury biomarker levels and exposure sources (e.g., amalgams, fish consumption). Five polymorphisms were significantly associated with urine mercury levels (GSTT1 deletion), hair mercury levels (GSTP1-105, GSTP1-114, GSS 5'), or both (SEPP1 3'UTR). Overall, this study suggests that polymorphisms in selenoproteins and glutathione-related genes may influence elimination of mercury in the urine and hair or mercury retention following exposures to elemental mercury (via dental amalgams) and methylmercury (via fish consumption).

Mammalian metallothionein in toxicology, cancer, and cancer chemotherapy

The present paper centers on mammalian metallothionein 1 and 2 in relationship to cell and tissue injury beginning with its reaction with Cd²⁺ and then considering its role in the toxicology and chemotherapy of both metals and non-metal electrophiles and oxidants. Intertwined is a consideration of MTs role in tumor cell Zn²⁺ metabolism. The paper updates and expands on our recent review by Petering et al. (Met Ions Life Sci 5:353-398, 2009).

Effects of heavy metal cations on the mitochondrial ornithine/citrulline transporter reconstituted in liposomes

The effect of heavy metal cations on the mitochondrial ornithine/citrulline transporter was tested in proteoliposomes reconstituted with the protein purified from rat liver. The transport activity was measured as [(3)H]ornithine uptake in proteoliposomes containing internal ornithine (ornithine/ornithine antiport mode) or as [(3)H]ornithine efflux in the absence of external substrate (ornithine/H(+) transport mode). 0.1 mM Cu(2+), Pb(2+), Hg(2+), Cd(2+) and Zn(2+) strongly inhibited (more than 85%) the antiport; whereas Mn(2+), Co(2+) and Ni(2+) inhibited less efficiently (25, 47 and 69%, respectively). The IC(50) values of the transporter for the different metal ions ranged from 0.71 to 350 μM. Co(2+) and Ni(2+) also inhibited the [(3)H]ornithine efflux whereas Cu(2+), Pb(2+), Hg(2+), Cd(2+) and Zn(2+) stimulated the [(3)H]ornithine efflux. The stimulation of the [(3)H]ornithine efflux by Cu(2+) and Cd(2+) (as well as by Pb(2+), Hg(2+) and Zn(2+)) was not prevented by NEM and was reversed by DTE. These features indicated that the inhibition of the antiport was due to the interaction of the Cu(2+), Pb(2+), Hg(2+), Cd(2+) and Zn(2+) with a population of SH groups, of the transporter, responsible for the inhibition of the physiological function; whereas the stimulation of [(3)H]ornithine efflux was due to the induction of a pore-like function of the transporter caused by interaction of cations with a different population of SH groups. Differently, the inhibition of the ornithine transporter by Ni(2+), Co(2+) or Mn(2+) was caused by interaction with the substrate binding site, as indicated by the competitive or mixed inhibition.

The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances

Whilst facing a worldwide fast increase of food and environmental allergies, the medical community is also confronted with another inhomogeneous group of environment-associated disabling conditions, including multiple chemical sensitivity (MCS), fibromyalgia, chronic fatigue syndrome, electric hypersensitivity, amalgam disease and others. These share the features of poly-symptomatic multi-organ cutaneous and systemic manifestations, with postulated inherited/acquired impaired metabolism of chemical/physical/nutritional xenobiotics, triggering adverse reactions at exposure levels far below toxicologically-relevant values, often in the absence of clear-cut allergologic and/or immunologic involvement. Due to the lack of proven pathogenic mechanisms generating measurable disease biomarkers, these environmental hypersensitivities are generally ignored by sanitary and social systems, as psychogenic or "medically unexplained symptoms". The uncontrolled application of diagnostic and treatment protocols not corresponding to acceptable levels of validation, safety, and clinical efficacy, to a steadily increasing number of patients demanding assistance, occurs in many countries in the absence of evidence-based guidelines. Here we revise available information supporting the organic nature of these clinical conditions. Following intense research on gene polymorphisms of phase I/II detoxification enzyme genes, so far statistically inconclusive, epigenetic and metabolic factors are under investigation, in particular free radical/antioxidant homeostasis disturbances. The finding of relevant alterations of catalase, glutathione-transferase and peroxidase detoxifying activities significantly correlating with clinical manifestations of MCS, has recently registered some progress towards the identification of reliable biomarkers of disease onset, progression, and treatment outcomes.

Exposure to low mercury concentration in vivo impairs myocardial contractile function

Increased cardiovascular risk after mercury exposure has been described but cardiac effects resulting from controlled chronic treatment are not yet well explored. We analyzed the effects of chronic exposure to low mercury concentrations on hemodynamic and ventricular function of isolated hearts. Wistar rats were treated with HgCl₂ (1st dose 4.6 μg/kg, subsequent dose 0.07 μg/kg/day, im, 30 days) or vehicle. Mercury treatment did not affect blood pressure (BP) nor produced cardiac hypertrophy or changes of myocyte morphometry and collagen content. This treatment: 1) in vivo increased left ventricle end diastolic pressure (LVEDP) without changing left ventricular systolic pressure (LVSP) and heart rate; 2) in isolated hearts reduced LV isovolumic systolic pressure and time derivatives, and β-adrenergic response; 3) increased myosin ATPase activity; 4) reduced Na+-K+ ATPase (NKA) activity; 5) reduced protein expression of SERCA and phosphorylated phospholamban on serine 16 while phospholamban expression increased; as a consequence SERCA/phospholamban ratio reduced; 6) reduced sodium/calcium exchanger (NCX) protein expression and α-1 isoform of NKA, whereas α-2 isoform of NKA did not change. Chronic exposure for 30 days to low concentrations of mercury does not change BP, heart rate or LVSP but produces small but significant increase of LVEDP. However, in isolated hearts mercury treatment promoted contractility dysfunction as a result of the decreased NKA activity, reduction of NCX and SERCA and increased PLB protein expression. These findings offer further evidence that mercury chronic exposure, even at small concentrations, is an environmental risk factor affecting heart function.

Mangiferin attenuates methylmercury induced cytotoxicity against IMR-32, human neuroblastoma cells by the inhibition of oxidative stress and free radical scavenging potential

Mangiferin (MGN), a C-glucosylxanthone was investigated for its ability to protect against methylmercury (MeHg) induced neurotoxicity by employing IMR-32 (human neuroblastoma) cell line. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] and clonogenic cell survival assays confirmed the efficacy of MGN supplementation in attenuating MeHg-induced cytotoxicity. Pre-treatment with MGN significantly (p<0.01) inhibited MeHg-induced DNA damage (micronuclei, olive tail moment and % tail DNA) thereby demonstrating MGN's antigenotoxic potential. Also, pre-treatment with MGN significantly reduced MeHg-induced oxidative stress, intra-cellular Ca(2+) influx and inhibited depolarization of mitochondrial membrane. MGN pre-treated cells demonstrated a significant (p<0.05) increase in the GSH and GST levels followed by a significant (p<0.05) decrease in malondialdehyde (MDA) formation. In addition, inhibition of MeHg induced apoptotic cell death by MGN was demonstrated by microscopic, Annexin-V FITC and DNA fragmentation assays and further confirmed by western blot analysis. The present findings indicated the protective effect of MGN against MeHg induced toxicity, which may be attributed to its anti-genotoxic, anti-apoptotic and anti-lipid peroxidative potential plausibly because of its free radical scavenging ability, which reduced the oxidative stress and in turn facilitated the down-regulation of mitochondrial apoptotic signalling pathways.

New solid-phase-nanoscavenger for the analytical enrichment of mercury from water

A nanoscavenger of mercaptopropyl-modified silica microparticles has been developed for the determination of trace levels of mercury(II) in water. The synthesis of silica microparticles nanoscavengers is carried out by modification of pre-formed silica particles with mercaptopropyltrimethoxysilane or by incorporating the thiol modification agent during the growth of the silica particles. The silica nanoscavengers were characterized by SEM, TGA, particle analyzer, IR and the parameters influencing the extraction and recovery phases of the preconcentration process were performed by AAS. The results show that careful choice of particle size and surface characteristics produce a new mercapto-silica-nanoscavenger that disperses in water as a quasi-stable sol. This permits the facile recovery of the mercury-loaded nanoscavenger particles. No agitation is required during the mercury extraction as the dispersion is maintained by Brownian motion and slow gravitational sedimentation. The technique overcomes a number of problems, such as cross-contamination and decreases in mercury concentration during sample transportation to the laboratory. Recovery achieved reaches >97 ± 4% over a wide range of preconcentration factors. At a preconcentration factor of 50 the limit of detection (3σ) was 0.19 ng mL(-1). The method is environmentally friendly as only 300 mg of mercapto-nanoscavenger is used, no organic solvent is required for the extraction and the experiment is performed without the need for manual or mechanical agitation.

The B°AT1 amino acid transporter from rat kidney reconstituted in liposomes: kinetics and inactivation by methylmercury

The neutral amino acid transporter B°-like from rat kidney, previously reconstituted in liposomes, was identified as B°AT1 by a specific antibody. Collectrin was present in the brush-border extract but not in functionally active proteoliposomes, indicating that it was not required for the transport function. Neutral amino acids behaved as competitive inhibitors of the glutamine transport mediated by B°AT1 with half saturation constants ranging from 0.13 to 4.74mM. The intraliposomal half saturation constant for glutamine was 2.0mM. By a bisubstrate kinetic analysis of the glutamine-Na(+) cotransport, a random simultaneous mechanism was found. Methylmercury and HgCl(2) inhibited the transporter; the inhibition was reversed by dithioerythritol, Cys and, at a lower extent, N-acetylcysteine but not by S-carboxymethylcysteine. The IC(50) of the transporter for methylmercury and HgCl(2) was 1.88 and 1.75μM, respectively. The reagents behaved as non-competitive inhibitors toward both glutamine and Na(+) and no protection by glutamine or Na(+) was found for the two inhibitors.

A thermophilic bacterial origin and subsequent constraints by redox, light and salinity on the evolution of the microbial mercuric reductase

Mercuric reductase (MerA) is central to the mercury (Hg) resistance (mer) system, catalyzing the reduction of ionic Hg to volatile Hg(0). A total of 213 merA homologues were identified in sequence databases, the majority of which belonged to microbial lineages that occupy oxic environments. merA was absent among phototrophs and in lineages that inhabit anoxic environments. Phylogenetic reconstructions of MerA indicate that (i) merA originated in a thermophilic bacterium following the divergence of the Archaea and Bacteria with a subsequent acquisition in Archaea via horizontal gene transfer (HGT), (ii) HGT of merA was rare across phylum boundaries and (iii) MerA from marine bacteria formed distinct and strongly supported lineages. Collectively, these observations suggest that a combination of redox, light and salinity conditions constrain MerA to microbial lineages that occupy environments where the most oxidized and toxic form of Hg, Hg(II), predominates. Further, the taxon-specific distribution of MerA with and without a 70 amino acid N-terminal extension may reflect intracellular levels of thiols. In conclusion, MerA likely evolved following the widespread oxygenation of the biosphere in a thermal environment and its subsequent evolution has been modulated by the interactions of Hg with the intra- and extracellular environment of the organism.

Influence of mercury bioaccessibility on exposure assessment associated with consumption of cooked predatory fish in Spain

BACKGROUND

Predatory fish tend to accumulate high levels of mercury (Hg). Food safety assessment of these fish has been carried out on the raw product. However, the evaluation of the risk from Hg concentrations in raw fish might be modified if cooking and bioaccessibility (the contaminant fraction that solubilises from its matrix during gastrointestinal digestion and becomes available for intestinal absorption) were taken into account. Data on Hg bioaccessibility in raw predatory fish sold in Spain are scarce and no research on Hg bioaccessibility in cooked fish is available. The aim of the present study was to evaluate Hg bioaccessibility in various kinds of cooked predatory fish sold in Spain to estimate their health risk.

RESULTS

Both Hg and bioaccessible Hg concentrations were analysed in raw and cooked fish (swordfish, tope shark, bonito and tuna). There were no changes in Hg concentrations during cooking. However, Hg bioaccessibility decreased significantly after cooking (42 ± 26% in raw fish and 26 ± 16% in cooked fish), thus reducing in swordfish and tope shark the Hg concentration to which the human organism would be exposed.

CONCLUSION

In future, cooking and bioaccessibility should be considered in risk assessment of Hg concentrations in predatory fish.

The "magic numbers" of metallothionein

Metallothioneins (MT) are a family of small cysteine rich proteins, which since their discovery in 1957, have been implicated in a range of roles including toxic metal detoxification, protection against oxidative stress, and as a metallochaperone involved in the homeostasis of both zinc and copper. The most well studied member of the family is the mammalian metallothionein, which consists of two domains: a β-domain with 9 cysteine residues, which sequesters 3 Cd(2+) or Zn(2+) or 6 Cu(+) ions, and an α-domain with 11 cysteine residues and, which sequesters 4 Cd(2+) or Zn(2+) or 6 Cu(+) ions. Despite over half a century of research, the exact functions of MT are still unknown. Much of current research aims to elucidate the mechanism of metal binding, as well as to isolate intermediates in metal exchange reactions; reactions necessary to maintain homeostatic equilibrium. These studies further our understanding of the role(s) of this remarkable and ubiquitous protein. Recently, supermetallated forms of the protein, where supermetallation describes metallation in excess of traditional levels, have been reported. These species may potentially be the metal exchange intermediates necessary to maintain homeostatic equilibrium. This review focuses on recent advances in the understanding of the mechanistic properties of metal binding, the implications for the metal induced protein folding reactions proposed for metallothionein metallation, the value of "magic numbers", which we informally define as the commonly determined metal-to-protein stoichiometric ratios and the significance of the new supermetallated states of the protein and the possible interpretation of the structural properties of this new metallation status. Together we provide a commentary on current experimental and theoretical advances and frame our consideration in terms of the possible functions of MT.

Oxidative properties of iodine-adducts of propylthiouracil and methimazole: direct synthesis of mercury(II) complexes from the reaction with liquid mercury

The I(2)-adducts of drugs propylthiouracil (PTU) and methimazole (MeImSH) oxidize liquid mercury in dichloromethane to separate in good yield the neutral complexes [HgI(2)(PTU)(2)·MeOH] (1), [HgI(2)(PTU)(2)·HgI(2)] (2), and [Hg(2)I(4)(MeImSH)(2)] (3). The single crystal X-ray diffraction analysis of 1-2 shows that the Hg(II) center is coordinated by two sulfur atoms and by two iodine atoms in a tetrahedral geometry. In complex 2 almost linear molecules of HgI(2) result encapsulated in the crystal packing enfolded by the hydrophobic propyl appendages of coordinated units of PTU. X-ray analysis of complex 3 shows the presence of dimeric [Hg(2)I(4)(MeImSH)(2)] molecules to form Hg(2)S(2)I(4) cores. The intra- and intermolecular hydrogen bonds concerning PTU and MeImSH have been evaluated. The oxidation of Hg(0) to Hg(II) requires a two-electron transfer process accomplished by an oxidative addition from the "activated" iodine moiety. The oxidizing and complexing properties of PTU-I(2) and MeImSH-I(2) have been interpreted considering the S-donor to I(2) interaction that leads to a charge separation between the sulfur-bound iodine atom S-I and the terminal I atom. Compounds 1, 2, and 3 react with tetraethylammonium iodide to separate the compound (Et(4)N)(2)[HgI(4)] with the release of free PTU and MeImSH, respectively. The reported dissolution technique could be applied to the recovery of mercury from waste electrical and electronic equipment (WEEE) scrap, the nature of complexes 1-3 makes it possible the easy separation of the mercury as tetraiodomercurate anion and the recycling of the donors.

Complex methylmercury-cysteine alters mercury accumulation in different tissues of mice

Methylmercury (MeHg) can cause deleterious effects in vertebrate tissues, particularly in the central nervous system. MeHg interacts with sulfhydryl groups from low and high molecular weight thiols in the blood, which can facilitate MeHg uptake into different tissues. The purpose of this study was to examine the effect of MeHg-Cysteine (MeHg-Cys) complex administration on Hg-uptake in cerebral areas (cortex and cerebellum), liver and kidney of adult mice. Animals were divided into four groups: control (1 mL/kg distilled water), MeHg (2 mg/kg), Cys (2 mg/kg) and MeHg-Cys complex (0.8 molar ratio). Mice received one intraperitoneal injection per day for 60 consecutive days. Treatment with MeHg significantly increased mercury concentrations in all tissues analysed when compared with the control group. The accumulation of mercury in brain and in liver was further increased in animals that received MeHg-Cys complex when compared with the MeHg alone group. However, renal Hg decreased in MeHg-Cys treated mice, when compared with the group treated only with MeHg. In summary, the transport of MeHg-Cys complex was tissue-specific, and we observed an increase in its uptake by liver and brain as well as a decrease in kidney.

Coenzyme Q10 counteracts testicular injury induced by sodium arsenite in rats

The protective effect of coenzyme Q10 against testicular toxicity induced by sodium arsenite (10mg/kg/day, orally for two consecutive days) was investigated in rats. Coenzyme Q10 treatment (10mg/kg/day, i.p.) was applied for five consecutive days, starting three days before arsenite administration. Coenzyme Q10 significantly increased serum testosterone level which was reduced by sodium arsenite. Coenzyme Q10 significantly suppressed lipid peroxidation, restored the depleted antioxidant defenses, and attenuated the increases of tumor necrosis factor-α and nitric oxide resulted from arsenic administration. Also, the elevation of arsenic ion, and the reductions of selenium and zinc ions in testicular tissue were mitigated by coenzyme Q10. Histopathological examination showed that testicular injury mediated by arsenic was ameliorated by coenzyme Q10 treatment. Immunohistochemical analysis revealed that coenzyme Q10 significantly decreased the arsenic-induced expression of inducible nitric oxide synthase, nuclear factor-κB, Fas ligand and caspase-3 in testicular tissue. It was concluded that coenzyme Q10 represents a potential therapeutic option to protect the testicular tissue from the detrimental effects of arsenic intoxication.

Environmentally induced oxidative stress in aquatic animals

Reactive oxygen species (ROS) are an unenviable part of aerobic life. Their steady-state concentration is a balance between production and elimination providing certain steady-state ROS level. The dynamic equilibrium can be disturbed leading to enhanced ROS level and damage to cellular constituents which is called "oxidative stress". This review describes the general processes responsible for ROS generation in aquatic animals and critically analyses used markers for identification of oxidative stress. Changes in temperature, oxygen levels and salinity can cause the stress in natural and artificial conditions via induction of disbalance between ROS production and elimination. Human borne pollutants can also enhance ROS level in hydrobionts. The role of transition metal ions, such as copper, chromium, mercury and arsenic, and pesticides, namely insecticides, herbicides, and fungicides along with oil products in induction of oxidative stress is highlighted. Last years the research in biology of free radicals was refocused from only descriptive works to molecular mechanisms with particular interest to ones enhancing tolerance. The function of some transcription regulators (Keap1-Nrf2 and HIF-1α) in coordination of organisms' response to oxidative stress is discussed. The future directions in the field are related with more accurate description of oxidative stress, the identification of its general characteristics and mechanisms responsible for adaptation to the stress have been also discussed. The last part marks some perspectives in the study of oxidative stress in hydrobionts, which, in addition to classic use, became more and more popular to address general biological questions such as development, aging and pathologies.

Organochlorine and metal contaminants in traditional foods from St. Lawrence Island, Alaska

Marine mammals (bowhead whale, walrus, and various seals) constitute the major component of the diet of the Yupik people of St. Lawrence Island, Alaska. St. Lawrence Island residents have higher serum concentrations of polychlorinated biphenyls (PCB) than in the general U.S. population. In order to determine potential sources, traditional food samples were collected from 2004 to 2009 and analyzed for PCBs, three chlorinated pesticides, and seven heavy metals (mercury, copper, zinc, arsenic, selenium, cadmium, and lead). Concentrations of PCB in rendered oils (193-421 ppb) and blubber (73-317 ppb) from all marine mammal samples were at levels that trigger advisories for severely restricted consumption, using U.S. Environmental Protection Agency (EPA) fish consumption advisories. Concentrations of pesticides were lower, but were still elevated. The highest PCB concentrations were found in polar bear (445 ppb) and the lowest in reindeer adipose tissue (2 ppb). Marine mammal and polar bear meat in general have PCB concentrations that were 1-5% of those in rendered oils or adipose tissue. PCB concentrations in organs were higher than meat. Concentrations of metals in oils and meats from all species were relatively low, but increased levels of mercury, cadmium, copper, and zinc were present in some liver and kidney samples. Mercury and arsenic were found in lipid-rich samples, indicating organometals. These results show that the source of the elevated concentrations of these contaminants in the Yupik population is primarily from consumption of marine mammal blubber and rendered oils.