Specific interactions of mercury chloride with membranes and other ligands as revealed by mercury-NMR

Identification of medium- and mechanism-related pitfalls towards improved performance and applicability of electrochemical mercury(II) aptasensors

The importance of understanding the mercury (II) ion interactions with thymine-rich DNA sequences is the reason for multiple comparative investigations carried out with the use of optical detection techniques directly in the depth of solution. However, the results of such investigations have limited applicability in the interpretation of the Hg2+ binding phenomenon by DNA sequences in thin, interfacial (electrode/solution), self-organized monolayers immobilized on polarizable surfaces, often used for sensing purposes in electrochemical biosensors. Overlooking the careful optimization of the measurement conditions is the source of discrepancies in the interpretation of the registered electrochemical signal. In this study, the chosen effects accompanying the efficiency of surface related recognition of Hg2+ by polyThymine DNA sequences labelled with methylene blue were investigated by voltammetry, QCM and spectro-electrochemical techniques. As was shown, the composition of the biosensing layer and buffers or the analytical procedures have a significant impact on the registered electrochemical readout which translates into signal stability, the biosensor's working parameters or even the mechanism of detection. After elucidation of the above factors, the complete and ready-to-use biosensor-based analytical solution was proposed offering subpicomolar mercury ion determination with high selectivity (also in aqueous real samples), reusability, and high signal stability even after long-term storage. The developed procedures were successfully used during the miniaturization process with self-prepared (PVD) elastic transducers. The obtained sensor, together with the simplicity of its use, low manufacturing cost, and attractive analytical parameters (i.e., LOD < < Hg2+ WHO limit) can present an interesting alternative for on-site mercury ion detection in environmental samples.

Interaction of mercury species with proteins: towards possible mechanism of mercurial toxicology

The nature of the binding of mercurials (organic and inorganic) and their subsequent transformations in biological systems is a matter of great debate as several different hypotheses have been proposed and none of them has been conclusively proven to explain the characteristics of Hg binding with the proteins. Thus, the chemical nature of Hg-protein binding through the possible transportation mechanism in living tissues is critically reviewed herein. Emphasis is given to the process of transportation, and binding of Hg species with selenol-containing biomolecules that are appealing for toxicological studies as well as the advancement of environmental and biological research.

Demystifying mercury geochemistry in contaminated soil-groundwater systems with complementary mercury stable isotope, concentration, and speciation analyses

Interpretation of mercury (Hg) geochemistry in environmental systems remains a challenge. This is largely associated with the inability to identify specific Hg transformation processes and species using established analytical methods in Hg geochemistry (total Hg and Hg speciation). In this study, we demonstrate the improved Hg geochemical interpretation, particularly related to process tracing, that can be achieved when Hg stable isotope analyses are complemented by a suite of more established methods and applied to both solid- (soil) and liquid-phases (groundwater) across two Hg²⁺-chloride (HgCl₂) contaminated sites with distinct geological and physicochemical properties. This novel approach allowed us to identify processes such as Hg²⁺ (i.e., HgCl₂) sorption to the solid-phase, Hg²⁺ speciation changes associated with changes in groundwater level and redox conditions (particularly in the upper aquifer and capillary fringe), Hg²⁺ reduction to Hg⁰, and dark abiotic redox equilibration between Hg⁰ and Hg(II). Hg stable isotope analyses play a critical role in our ability to distinguish, or trace, these in situ processes. While we caution against the non-critical use of Hg isotope data for source tracing in environmental systems, due to potentially variable source signatures and overprinting by transformation processes, our study demonstrates the benefits of combining multiple analytical approaches, including Hg isotope ratios as a process tracer, to obtain an improved picture of the enigmatic geochemical behavior and fate of Hg at contaminated legacy sites.

Ni(II), Hg(II), and Pb(II) Coordination in the Prokaryotic Zinc-Finger Ros87

Zinc ion binding is a principal event in the achievement of the correct fold in classical zinc finger domains since the motif is largely unfolded in the absence of metal. In the case of a prokaryotic zinc finger, the larger βββαα domain contributes to the folding mechanism with a larger hydrophobic core. For these reasons, following the great amount of attention devoted to unveiling the effect of xenobiotic metal ion replacement in zinc fingers and in zinc-containing proteins in general, the prokaryotic zinc finger domain appears to be an interesting model for studying metal ion interaction with metalloproteins. Here, we explore the binding of Ni(II), Hg(II), and Pb(II) to Ros87, the DNA binding domain of the prokaryotic zinc finger protein Ros. We measured Ros87-metal ion dissociation constants and monitored the effects on the structure and function of the domain. Interestingly, we found that the protein folds in the presence of Ni(II) with important structural perturbations, while in the presence of Pb(II) and Hg(II) it does not appear to be significantly folded. Accordingly, an overall strong reduction in the DNA binding capability is observed for all of the examined proteins. Our data integrate and complement the information collected in the past few years concerning the functional and structural effects of metal ion substitution in classical zinc fingers in order to contribute to a better comprehension of the toxicity of these metals in biological systems.

Ionic Strength Differentially Affects the Bioavailability of Neutral and Negatively Charged Inorganic Hg Complexes

Mercury (Hg) bioavailability to bacteria in marine systems is the first step toward its bioamplification in food webs. These systems exhibit high salinity and ionic strength that will both alter Hg speciation and properties of the bacteria cell walls. The role of Hg speciation on Hg bioavailability in marine systems has not been teased apart from that of ionic strength on cell wall properties, however. We developed and optimized a whole-cell Hg bioreporter capable of functioning under aerobic and anaerobic conditions and exhibiting no physiological limitations of signal production to changes in ionic strength. We show that ionic strength controls the bioavailability of Hg species, regardless of their charge, possibly by altering properties of the bacterial cell wall. The unexpected anaerobic bioavailability of negatively charged halocomplexes may help explain Hg methylation in marine systems such as the oxygen-deficient zone in the oceanic water column, sea ice or polar snow.

Mercury-Pollution Induction of Intracellular Lipid Accumulation and Lysosomal Compartment Amplification in the Benthic Foraminifer Ammonia parkinsoniana

Heavy metals such as mercury (Hg) pose a significant health hazard through bioaccumulation and biomagnification. By penetrating cell membranes, heavy metal ions may lead to pathological conditions. Here we examined the responses of Ammonia parkinsoniana, a benthic foraminiferan, to different concentrations of Hg in the artificial sea water. Confocal images of untreated and treated specimens using fluorescent probes (Nile Red and Acridine Orange) provided an opportunity for visualizing the intracellular lipid accumulation and acidic compartment regulation. With increased Hg over time, we observed an increased number of lipid droplets, which may have acted as a detoxifying organelle where Hg is sequestered and biologically inactivated. Further, Hg seems to promote the proliferation of lysosomes both in terms of number and dimension that, at the highest level of Hg, resulted in cell death. We report, for the first time, the presence of Hg within the foraminiferal cell: at the basal part of pores, in the organic linings of the foramen/septa, and as cytoplasmic accumulations.

Influence of global change-related impacts on the mercury toxicity of freshwater algal communities

The climatic-change related increase of temperatures, are expected to alter the distribution and survival of freshwater species, ecosystem functions, and also the effects of toxicants to aquatic biota. This study has thus assessed, as a first time, the modulating effect of climate-change drivers on the mercury (Hg) toxicity of freshwater algal photosynthesis. Natural benthic algal communities (periphyton) have been exposed to Hg under present and future temperature scenarios (rise of 5 °C). The modulating effect of other factors (also altered by global change), as the quality and amount of suspended and dissolved materials in the rivers, has been also assessed, exposing algae to Hg in natural river water or a synthetic medium. The EC50 values ranged from the 0.15-0.74 ppm for the most sensitive communities, to the 24-40 ppm for the most tolerant. The higher tolerance shown by communities exposed to higher Hg concentrations, as Jabarrella was in agreement with the Pollution Induced Community Tolerance concept. In other cases, the dominance of the invasive diatom Didymosphenia geminata explained the tolerance or sensitivity of the community to the Hg toxicity. Results shown that while increases in the suspended solids reduced Hg bioavailability, changes in the dissolved materials - such as organic carbon - may increase it and thus its toxic effects on biota. The impacts of the increase of temperatures on the toxicological behaviour of periphyton (combining both changes at species composition and physiological acclimation) would be certainly modulated by other effects at the land level (i.e., alterations in the amount and quality of dissolved and particulate substances arriving to the rivers).

The structural and functional effects of Hg(II) and Cd(II) on lipid model systems and human erythrocytes: A review

The anthropogenic mobilization of mercury and cadmium into the biosphere has led to an increased and ineludible entry of these metals into biological systems. Here we discuss the impact of Hg(II) and Cd(II) on lipid model systems and human erythrocytes from a biophysical perspective. After a brief introduction to their implications on human health, studies that have investigated the effects of Hg(II) and Cd(II) on lipid model systems and human erythrocytes are discussed. In terms of lipids as toxicological target sites, predominantly variations in lipid head groups have been the source of investigation. However, as research in this field progresses, the effects of Hg(II) and Cd(II) on other structural features, such as acyl chain length and unsaturation, and other important lipid components and complex biomimetic lipid mixtures, will require further examinations. This review provides an analysis of what has been learned collectively from the diverse methodologies and experimental conditions used thus far. Consequently, there is a need for more comprehensive and thorough investigations into the effects of Hg(II) and Cd(II) on lipid membranes under consistent experimental conditions such as pH, ionic strength, temperature, and choice of lipid model system.

Binding of a ruthenium complex to a thioether ligand embedded in a negatively charged lipid bilayer: a two-step mechanism

The interaction between the ruthenium polypyridyl complex [Ru(terpy)(dcbpy)(H2O)](2+) (terpy = 2,2';6',2"-terpyridine, dcbpy = 6,6'-dichloro-2,2'-bipyridine) and phospholipid membranes containing either thioether ligands or cholesterol were investigated using UV-visible spectroscopy, Langmuir-Blodgett monolayer surface pressure measurements, and isothermal titration calorimety (ITC). When embedded in a membrane, the thioether ligand coordinated to the dicationic metal complex only when the phospholipids of the membrane were negatively charged, that is, in the presence of attractive electrostatic interaction. In such a case coordination is much faster than in homogeneous conditions. A two-step model for the coordination of the metal complex to the membrane-embedded sulfur ligand is proposed, in which adsorption of the complex to the negative surface of the monolayers or bilayers occurs within minutes, whereas formation of the coordination bond between the surface-bound metal complex and ligand takes hours. Finally, adsorption of the aqua complex to the membrane is driven by entropy. It does not involve insertion of the metal complex into the hydrophobic lipid layer, but rather simple electrostatic adsorption at the water-bilayer interface.

Hg- and Cd-induced modulation of lipid packing and monolayer fluidity in biomimetic erythrocyte model systems

The public health consequences that are associated with the low level exposure of various human populations to Cd(2+) and Hg(2+) are incompletely understood. In order to assess if interactions between these inorganic pollutants and erythrocyte biomembranes may contribute to their chronic toxicity, we have used a Langmuir trough to probe the effect of HgCl2 and CdCl2 on the packing and elasticity properties of biomimetic lipid monolayers using different lipid mixtures. These lipid films were deposited at room temperature on a biologically relevant subphase (1mM phosphate, 100mM NaCl at pH 7.4) in the absence and presence of 100μM HgCl2, CdCl2 and 1:1 mixtures thereof. The interactions of heavy metals with the lipids were monitored as changes in the surface pressure (π)-area (A) isotherms. In addition, metal induced changes to the elastic properties of the model systems were analyzed by area and compressibility data of phosphatidylcholine (PC) systems containing 0, 15, 30, 45 and 100% phosphatidylethanolamine (PE) and phosphatidylserine (PS). These mixtures revealed changes in lateral lipid packing as indicated by area expansion as well as enhanced film rigidity. The results demonstrate that both heavy metals affected the various lipid matrices, but metal mixtures showed the strongest impact. Based on these data, the adverse interaction of Hg(2+) and Cd(2+) with lipid bilayer membranes is identified as a feasible mechanism by which these toxic metals exert toxicity in mammalian cells. Interestingly, these metal interactions were found to depend on the lipid composition.

Remediation of mercury contaminated sites - A review

Environmental contamination caused by mercury is a serious problem worldwide. Coal combustion, mercury and gold mining activities and industrial activities have led to an increase in the mercury concentration in soil. The objective of this paper is to present an up-to-date understanding of the available techniques for the remediation of soil contaminated with mercury through considering: mercury contamination in soil, mercury speciation in soil; mercury toxicity to humans, plants and microorganisms, and remediation options. This paper describes the commonly employed and emerging techniques for mercury remediation, namely: stabilization/solidification (S/S), immobilization, vitrification, thermal desorption, nanotechnology, soil washing, electro-remediation, phytostabilization, phytoextraction and phytovolatilization.

Chemical form matters: differential accumulation of mercury following inorganic and organic mercury exposures in zebrafish larvae

Mercury, one of the most toxic elements, exists in various chemical forms each with different toxicities and health implications. Some methylated mercury forms, one of which exists in fish and other seafood products, pose a potential threat, especially during embryonic and early postnatal development. Despite global concerns, little is known about the mechanisms underlying transport and toxicity of different mercury species. To investigate the impact of different mercury chemical forms on vertebrate development, we have successfully combined the zebrafish, a well-established developmental biology model system, with synchrotron-based X-ray fluorescence imaging. Our work revealed substantial differences in tissue-specific accumulation patterns of mercury in zebrafish larvae exposed to four different mercury formulations in water. Methylmercury species not only resulted in overall higher mercury burdens but also targeted different cells and tissues than their inorganic counterparts, thus revealing a significant role of speciation in cellular and molecular targeting and mercury sequestration. For methylmercury species, the highest mercury concentrations were in the eye lens epithelial cells, independent of the formulation ligand (chloride versusl-cysteine). For inorganic mercury species, in absence of l-cysteine, the olfactory epithelium and kidney accumulated the greatest amounts of mercury. However, with l-cysteine present in the treatment solution, mercuric bis-l-cysteineate species dominated the treatment, significantly decreasing uptake. Our results clearly demonstrate that the common differentiation between organic and inorganic mercury is not sufficient to determine the toxicity of various mercury species.

IGF and GH mRNA levels are suppressed upon exposure to micromolar concentrations of cobalt and zinc in rainbow trout white muscle

The objective of this study was to assess the effects of cobalt and zinc exposure of rainbow trout (Oncorhynchus mykiss) on insulin like growth factors (IGF) and growth hormone (GH). Mature rainbow trouts were exposed to 0.42, 2.1, 4.2, 21 and 42μmol/L Co(2+) (added as CoCl(2)·6H(2)O) and 0.34, 1.7, 3.4, 17 and 34μmol/L Zn(2+) (added as ZnSO(4)i·7H(2)O). After 6, 12, 24 and 48h of treatment, expressions of white muscle IGF-I, IGF-II and GH mRNAs were measured by means of quantitative Real Time PCR. During the exposure experiments, no mortalities occurred. The most effective metal concentrations, which caused significant alterations, were determined to be 42μmol/L Co(2+) (10mg CoCl(2)·6H(2)O/L) and 3.4μmol/L Zn(+2) (1mg ZnSO(4)·7H(2)O/L). The following results were obtained for these concentrations. Expression of IGF-I did not change at 6h in zinc treatment while the decrease (p<0.05) was observed at 12h and 24h, and this decrease became stronger at 48h. Cobalt exposure caused a decrease in IGF-I mRNA level at 6h, 12h, 24h and 48h (p<0.05). Both zinc and cobalt exposure resulted in significant decreases in GH expression at 6h. Exposure of trout to Zn resulted in a decrease in expression of IGF-II starting from 6h whereas the significant decrease started at 6h in cobalt exposure and this decrease elevated at 24h. The results indicate that micromolar cobalt and zinc exposure causes significant attenuation in the expressions of these three genes' time dependently. Our findings show that IGF-I is the most resistant and GH is the most sensitive component against cobalt and zinc exposure. We conclude that IGF/GH axis might be strongly affected by the short term exposure to low micromolar concentrations of zinc and cobalt due to alterations of these genes.

Ammonium thiosulphate enhanced phytoextraction from mercury contaminated soil--results from a greenhouse study

According to the 'hard and soft' acid-base principle, mercury is a 'soft metal' and will preferentially form soluble chemical complexes with sulphur-containing ligands. In this work mercury uptake by Chenopodium glaucum L. growing on mercury-contaminated soil was promoted using ammonium thiosulphate. The relative geochemical fractionation of mercury in the soil was subsequently investigated as a function of plant growth with and without thiosulphate amendment. The results indicate that the solubility of mercury is significantly increased through the application of thiosulphate to the soil. Substantially higher mercury levels were found in C. glaucum L. treated with 2 g kg(-1) thiosulphate of soil when compared to the non-treated plants. Compared with initial soil, soluble and exchangeable fractions were increased both in planted and planted treated plants. However, no significant difference was observed between the soils of the planted and planted treated plants. The oxide-bound mercury concentration was significantly decreased for the planted soil (treated and non-treated) at the end of the experiment. Moreover, this fraction was highly correlated with the plant tissue mercury concentration. Taken together, thiosulphate assisted phytoextraction could be used to reduce environmental risk apparent for mercury-contaminated soil through reducing the oxide bound fractions, while managing the bioavailable fractions (compared with no treated plant).

In vivo formation and binding of SeHg complexes to the erythrocyte surface

The in vivo dynamics of selenium (Se) and mercury (Hg) interaction was studied in mouse tissues using direct visualization of individual Se, Hg, and SeHg particles on the surface of circulating erythrocytes. This high-resolution detection of Se and Hg was obtained by scanning electron microscopy coupled to X-ray microanalysis. BALB/c mice were injected in the peritoneal cavity with Se and Hg salts, and the animals were sacrificed 3 min after the Hg injection. Only a minority (9%) of the metal dots seen on mouse liver erythrocytes were SeHg complexes when Se and Hg salts were mixed together before injection. In contrast, the majority (73%) of metal dots on liver erythrocytes were SeHg complexes if Se was injected at least 5 min before Hg injection. All metal dots on liver erythrocytes were of SeHg complexes if Se was injected 9 or 12 min before the Hg injection. We conclude that the formation of stable in vivo SeHg complexes requires preliminary interaction of Se with a putative serum factor before complexes between Se and Hg are formed and are bound to the erythrocyte cell surface.

Adverse effects of cadmium on bull spermatozoa

Cadmium (Cd) is a widespread environmental pollutant. Because of its long biological half-life (10-30 years in humans), Cd accumulates in the biological systems such as gonads. The present study was designed to evaluate the effect of Cd in the concentration range 50-750 micromol/L, in vitro, on the membrane integrity, motility and acrosomal status of bull spermatozoa. The samples were processed for sperm analyses using semen-diluting fluid (phosphate-buffered saline, pH 7.2). A significant elevation in the malondialdehyde level/lipid peroxidation (LPO) rate and a decrease in the spermatocrit values, particularly at a concentration of 750 micromol/L Cd, indicated the deleterious effect of Cd on sperm membrane integrity. There was also a negative correlation between LPO rate and percentage of motile spermatozoa (r = 0.992). The gelatin test indicates that Cd may alter the integrity of acrosomal membranes and shows an abnormal acrosome reaction. In this regard, a strong negative correlation was found between LPO rate and % halos (bright clear zone around sperm heads after gelatin digestion) (r = 0.990). Taking the results together, Cd proved to be a potential toxicant in the category of environmental factors that induce membrane impairment, lower motility, and decrease the rate of acrosome reactions, leading to male infertility. Apparently, the presence of Cd in the environment and seminal plasma exerts a toxic effect on sperm cells.

In vitro mercury exposure on spermatozoa from normospermic individuals

Epidemiological evidence suggests that exposure to industrial metal aerosols is detrimental to the male reproductive system. Oxidative stress has been identified as a crucial factor leading to male factor infertility largely due to peroxidative damage to the sperm cell membrane. The objectives of the present study were to test the effect of mercury in the concentration range from 50 to 800 micromol(-1), in vitro, on the sperm membrane and DNA integrity, motility and acrosomal status of human spermatozoa. We found a significant increase in the Lipo Per Oxidation (LPO) indicating the deleterious effect of mercury on the sperm membrane integrity. This effect was prominent at the concentration of 800 microM mercury. There was also a strong negative correlation between LPO rate and percentage of viable spermatozoa (r = -0.941, p<0.001). Data obtained from SCGE assay technique revealed that mercury is capable of inducing DNA breaks in the sperm nuclei. Almost, 88% of DNA breaks were of double-stranded. The correlation between LPO rate and percentage of DNA breaks was found to be 0.918 (p<0.001). Performing the gelatin digestion test indicates that mercury was able to alter the integrity of acrosomal membranes showing an abnormal acrosome reaction. In this regard, a strong correlation was found between LPO rate and percentage of halos (r = -0.893, p<0.001). Taken together, mercury induced membrane impairments, lowered sperm viability, DNA breaks and a decreased rate in the acrosome reaction of human spermatozoa leading to sperm dysfunction. Entering mercury in the male gonads and seminal plasma may exert deleterious effects on the human spermatozoa. Hence, considering the wide spread use of mercury and its compounds, these metals should regarded with more concern.

The biotransformation of mercury in pH-stat cultures of microfungi

The biotransformation of mercury was monitored in Hymenoscyphus ericae (Read) Korf & Kernan, Neocosmospora vasinfecta E. F. Sm., and Verticillium terrestre (Link) Lindau following the exposure of these fungi to environmentally relevant doses of HgII(HgCl2) in aerated pH-controlled cultures. Mercury applied at 120 and 300 μg·L–1quickly associated with cells of N. vasinfecta. Within 3 h, approximately 80% of the remaining Hg in both treatments had been converted to β-HgS, and at 8 h, 15% and 53% of the original doses had been converted into volatile Hg0. Hymenoscyphus ericae was less efficient at converting HgIIto β-HgS, but it volatilized larger amounts of Hg0. A mercury-tolerant isolate of V. terrestre withstood levels of Hg in the parts per million. When exposed to 270, 1000, or 2000 μg·L–1HgCl2, 93% ± 3% of the amounts remaining in cultures of V. terrestre after 2 h was β-HgS. At 2 mg·L–1, 72% of the Hg was reduced to Hg0in 2 h. Volatilization accounts for the tolerance of V. terrestre to high doses of Hg, whereas the conversion of Hg to β-HgS was the major detoxifying mechanism at lower doses. The formation of β-HgS occurs preferentially with volatilization operating as the default pathway, when the former biotransformation mechanism is saturated.

Bull Spermatozoa under Mercury Stress

Defective sperm function is the most prevalent cause of male infertility and is difficult to treat. This study was designed to evaluate the effect of mercuric chloride (HgCl2) at 50-300 micromol/l concentration range, in vitro, on the sperm membrane and DNA integrity, viability, reduced glutathione (GSH) content and acrosomal status of the bull spermatozoa. The samples were processed for sperm analyses using semen-diluting fluid [phosphate-buffered saline (PBS), pH 7.2]. I recorded a meaningful increase in the lipid peroxidation (LPO) rate and a drastic fall in the spermatocrit values under mercury additions, dominantly at 300 microM mercury concentration, indicating a deleterious effect of mercury on the sperm membrane intactness. There was also a strong negative correlation between LPO rate and percentage of viable spermatozoa (r = -0.9, p < 0.001). GSH content was significantly impaired. Data obtained from Comet assay [single-cell gel electrophoresis (SCGE)] technique revealed that mercury is capable of inducing DNA breaks in the sperm nuclei. Interestingly, 90% of DNA breaks were double-stranded. The correlation between LPO rate and percentage of DNA breaks was found to be 0.9 (p < 0.001). Results of the gelatin test indicate that mercury is capable of altering the integrity of acrosomal membranes, showing an abnormal acrosome reaction. In this regard, a strong correlation was found between LPO rate and percentage of halos (r = -0.9, p < 0.001). In conclusion, mercury proved to be a potential oxidant in the category of 'environmental factors' to bull spermatozoa. Hence, considering the widespread use of mercury and its compounds, these metals should be regarded with more concern.

Comparative effects of dietary methylmercury on gene expression in liver, skeletal muscle, and brain of the zebrafish (Danio rerio)

Effects of dietary methylmercury (MeHg) on gene expression were examined in three organs (liver, skeletal muscle, and brain) of the zebrafish (Danio rerio). Adult male fish were fed over 7, 21, and 63 days on three different diets: one control diet (C0: 0.08 microg of Hg g(-1), dry wt) and two diets (C1 and C2) contaminated by MeHg at 5 and 13.5 microg of Hg g(-1), dry wt. Total Hg and MeHg concentrations were determined in the three organs after each exposure duration, and a demethylation process was evidenced only in the liver. Thirteen genes known to be involved in antioxidant defenses, metal chelation, active efflux of organic compounds, mitochondrial metabolism, DNA repair, and apoptosis were investigated by quantitative real-time RT-PCR and normalized according to actin gene expression. Surprisingly, no change in the expression levels of these genes was observed in contaminated brain samples, although this organ accumulated the highest mercury concentration (63.5 +/- 4.4 microg g(-1), dry wt after 63 days). This lack of genetic response could explain the high neurotoxicity of MeHg. coxI and cytoplasmic and mitochondrial sod gene expressions were induced early in skeletal muscle and later in liver, indicating an impact on the mitochondrial metabolism and production of reactive oxygen species. Results demonstrated that skeletal muscle was not only an important storage reservoir but was also affected by MeHg contamination. The expression of the metallothionein mt2 and the DNA repair rad51 genes was up-regulated in liver between 21 and 63 days, whereas in skeletal muscle, mt2 remained uninduced, and gadd and rad51 were found to be repressed.

A combinatorial approach to discover new chelators for optical metal ion sensing

This paper reports the synthesis and characterization of metal-binding indicators with diverse optical responses on exposure to various heavy metal ions. A combinatorial approach, based on azo coupling of diazonium salts with either phenolic compounds or aromatic amines, generated a library of azo dyes. Each reaction mixture, containing the product(s) of azo coupling, was incubated with a series of solutions, each containing a different heavy metal ion. The absorbance and, in some cases, fluorescence spectra of the resulting complexes were recorded. The metal chelates showed extensive diversity in their UV-visible absorbance spectra upon binding to selected metal ions. Of the azo dyes prepared, the terdentate dyes were particularly useful, providing distinct spectral responses to three or more metal ions in a panel of seven.

HgCl2 disrupts the structure of the human erythrocyte membrane and model phospholipid bilayers

The structural effects of Hg(II) ions on the erythrocyte membrane were studied through the interactions of HgCl2 with human erythrocytes and their isolated resealed membranes. Studies were carried out by scanning electron microscopy and fluorescence spectroscopy, respectively. Hg(II) induced shape changes in erythrocytes, which took the form of echinocytes and stomatocytes. This finding means that Hg(II) locates in both the outer and inner monolayers of the erythrocyte membrane. Fluorescence spectroscopy results indicate strong interactions of Hg(II) ions with phospholipid amino groups, which also affected the packing of the lipid acyl chains at the deep hydrophobic core of the membrane. HgCl2 also interacted with bilayers of dimyristoylphosphatidylcholine and dimyristoylphosphatidylethanolamine, representative of phospholipid classes located in the outer and inner monolayers of the erythrocyte membrane, respectively. X-ray diffraction indicated that Hg(II) ions induced molecular disorder to both phospholipid bilayers, while fluorescence spectroscopy of dimyristoylphosphatidylcholine large unilamellar vesicles confirmed the interaction of Hg(II) ions with the lipid polar head groups. All these findings point to the important role of the phospholipid bilayers in the interaction of Hg(II) on cell membranes.

Phytosorbent prepared from sunflower seed husks prevents mercuric chloride accumulation in kidney and muscle of adult rabbits

In the present study, the effect of a melanin-containing phytosorbent, "Victoria," on mercury accumulation in rabbits' tissues was studied. This phytosorbent is derived from black sunflower seed husks. Domestic rabbits were administered either one single nontoxic low-level dose of mercuric chloride (i.e., 50 microg/1 kg body weight [control group]) or combinations of mercury and the phytosorbent "Victoria" (i.e., experimental group). Mercury and phytosorbent were administered per os daily for 12 d. Mercury in tissues was determined by cold-vapor atomic absorption spectroscopy. Mercury in kidney and muscle of the experiment group was, on average, 25.8 and 4.7 times less, respectively, than in the control group. The authors concluded that the phytosorbent prevented accumulation of mercury in the kidney and muscle tissues and exerted a protective effect against mercury toxicity.

Methyl mercury interactions with phospholipid membranes as reported by fluorescence, 31P and 199Hg NMR

Methylmercury (CH3Hg(II)) interactions with multilamellar vesicles of dimyristoyl(DM)- and dipalmitoyl(DP)-phosphatidylcholine (PC), -phosphatidic acid (PA), -phosphatidylglycerol (PG), -phosphatidylserine (PS) and -phosphatidylethanolamine (PE) have been investigated from the metal viewpoint by solution 199Hg-NMR and from the membrane side by diphenylhexatriene fluorescence polarization and solid state 31P-NMR. Results can be summarized as follows: (1) CH3Hg(II) strong binding to membranes results in a progressive decrease of the free CH3HgOH 199Hg-NMR isotropic signal and because of a slow exchange, in the NMR time scale, between free and bound methylmercury pools the lipid/water partition coefficients, K(lw), of the CH3HgOH species can be determined in the lamellar gel (fluid) phase. It is found: K(lw)(DMPC) approximately 2 +/- 2 (2 +/- 2); K(lw)(DMPE) approximately 7 +/- 3 (16 +/- 3); K(lw)(DMPG) = 170 +/- 10 (110 +/- 10); K(lw)(DMPS) = 930 +/- 50 (1250 +/- 60); K(lw)(DMPA) = 1250 +/- 60 (300 +/- 20). CH3Hg(II) interactions with membrane phospholipids are therefore electrostatic in nature and the phosphate moiety is proposed as a potential binding site. (2) The presence of CH3HgOH stabilizes the PG gel phase and destabilizes that of PS. No effect is observed on PC, PA and PE thermotropism. (3) methylmercury promotes the formation of isotropic 31P-NMR lines with PG, PA and PE systems suggesting the presence of non-bilayer phases and hence membrane reorganization. The above effects are compared to those of inorganic mercury Hg(II) and discussed in the context of cell toxicity.

Interactions of inorganic mercury with phospholipid micelles and model membranes. A 31P-NMR study

The binding of inorganic mercury Hg(II) to phospholipid headgroups has been investigated by phosphorus-31 nuclear magnetic resonance of phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylcholine (PC) in water micellar and multilamellar phases. HgCl2 triggers the aggregation of phospholipid micelles, leading to a lipid-mercury precipitate that is no longer detectable by high-resolution 31P-NMR. The remaining signal area corresponds to micelles in the soluble fraction and is a non-linear function of the initial mercury-to-lipid molar ratio. Kinetics of micelle aggregation are exponential for the first 15 min and show a plateau tendency after 120 min. Apparent Hg(II) affinities for phospholipid headgroups are in the order: PE > PS > PC. The same binding specificity is observed when HgCl2 is added to (1:1) mixtures of different micelles (PE + PC; PS + PC). However, mercury binding to mixed micelles prepared with two lipids (PE/PC or PS/PC) induces the aggregation of both lipids. Hg(II) also leads to a 31P-NMR chemical shift anisotropy decrease of PC, PS and mixed (1:1) PE/PC multilamellar vesicles and markedly broadens PS spectra. This indicates that HgCl2 binding forces phospholipid headgroups to reorient and that the concomitant network formation leads to a slowing down of PS membrane collective motions. Formation of a gel-like lamellar phase characterized by a broad NMR linewidth is also observed upon HgCl2 binding to PE samples both in fluid (L alpha) or hexagonal (H(II)) phases. The PE hexagonal phase is no longer detected in the presence of HgCl2. Mixed PE/PC dispersions remain in the fluid phase upon mercury addition, indicating that no phase separation occurs. Addition of excess NaCl leads to the appearance of the non-reactive species HgCl4(2-) and induces the reversal of all the above effects.

Cadmium and methylmercury bioaccumulation by nymphs of the burrowing mayflyHexagenia rigida from the water column and sediment

Based on a three compartment microcosm-water column, natural sediment,Hexagenia rigida nymphs-an experimental study was set up to compare cadmium (Cd) and methylmercury (MeHg) bioaccumulation by a burrowing mayfly species, after exposure via the water column or the sediment as initial contamination sources. Results from a wide concentration range for each exposure condition revealed very marked differences between the two metals: MeHg was readily accumulated from the two contamination sources, leading to important metal concentrations in the nymphs after the 2 weeks' exposure; Cd bioaccumulation, on the other hand, was negligible when the metal was added to the water compartment, even though significant transfers were observed from the sediment source. The average Cd concentrations in the nymphs were proportional to the sediment contamination levels. Turbidity measurements in the water column, reflecting the bioturbation activity of the nymphs, revealed that the effect of Cd was significant, but only when the metal was initially added to the sediment. The results are discussed according to the uptake routes and the structural and functional properties of the biological barriers involved (gills and gut).

Interaction of inorganic mercury salts with model and red cell membranes: importance of lipid binding sites

The effect of two mercury salts, HgCl2 and Hg(NO3)2, on the thermotropic properties of phosphatidylserine (PS) model membranes and sonicated rat red cell membranes was investigated by fluorescence polarization. Both Hg(II) salts abolished the phase transition and decreased the membrane fluidity by interacting with PS. Maximal effect was observed at a Hg/PS ratio of 2.5-5 for mercuric chloride and at 1.5 for the nitrate salt. For both mercury compounds, 10 mM NaCl protected model membranes from the effects of Hg(II). HgCl2 and Hg(NO3)2 also decreased the fluidity of rat red cell membranes. Maximal effect was observed for 0.4 mM HgCl2 and 0.6 mM Hg(NO3)2, with 0.0125 mg protein/ml. Addition of NaCl to the Hg(II)-red cell system decreased the Hg(II)-induced perturbation of the thermotropic properties. For both membrane systems, the effects observed with Hg(NO3)2 were greater than those with HgCl2, which can be accounted for by the absence of competition with chloride ions in samples containing Hg(NO3)2.[Cl-] governs the availability of Hg(II) by determining its chemical speciation: increasing [Cl-] generates HgCl3- and HgCl4(2-), which do not interact with lipid binding sites. These results indicate that besides protein thiol groups, Hg(II)-lipid binding sites play an important role in the interaction of Hg(II) with red cell membranes that is qualitatively different from Hg(II) binding to protein thiol groups.

Effects of mesoionic xanthine analogs on Trypanosoma musculi development in mice

Two derivatives of the mesoionic thiazolo[3,2-a]pyrimidine-5,7-diones 1 were prepared and examined for in vivo antiprotozoan activity to study structure-activity relationships that might lead us to more active derivatives. Mesoionic compounds 1A and 1B were inoculated into Swiss Webster male mice with Trypanosoma musculi infection. The effects were measured by studying parasite populations during the course of patent period (days 9 through 15 post-infection). The injection of 200 micrograms of compound 1A along with 5 x 10(4) trypanosomes affected the level of parasitemia at both the peak and during days 9 to 13 post infection. Experimental animals that received drug 1A prior to and after infection with T. musculi developed significantly lower parasitemia as compared to the control animals at the height of parasite populations (day 11 of observation). The group that received the drug simultaneously with trypanosome infection had significantly lower parasitemias on day 11 and 13 of infection compared to the controls. The injection of 200 micrograms of mesoionic compound 1B along with 5 x 10(4) trypanosomes resulted in lower parasitemic levels in the prior treated and post inoculated groups on days 9 and 13 post-infection. Swiss Webster male mice treated with the test drug, compound 1B, simultaneously with an inoculation of parasites developed significant resistance against infection on days 9 and 11 post-infection. This trend was reversed for the rest of the observation period.