The pathology of methylmercury poisoning (Minamata disease): The 50th Anniversary of Japanese Society of Neuropathology

Oleanolic acid-3-glucoside, a synthetic oleanane-type saponin, ameliorates methylmercury-induced dysfunction of synaptic transmission in mice

Methylmercury (MeHg) is widely distributed in nature and is known to cause neurotoxic effects. This study aimed to examine the anti-MeHg activity of oleanolic acid-3-glucoside (OA3Glu), a synthetic oleanane-type saponin derivative, by evaluating its effects on motor function, pathology, and electrophysiological properties in a mouse model of MeHg poisoning. Mice were orally administered 2 or 4 mg·kg-1·d-1 MeHg with or without 100 µg·kg-1·d-1 OA3Glu 5x/week for four weeks. Motor function was evaluated using beam-walking and dynamic weight-bearing (DWB) tests. High-dose MeHg exposure significantly increased the frequency of stepping off the hind leg while crossing the beam in the beam-walking test, and increased weight on forelegs when moving freely in the DWB test. OA3Glu treatment alleviated motor abnormality caused by high-dose MeHg exposure in both motor function tests. Additionally, OA3Glu treatment reduced the number of contracted Purkinje cells frequently observed in the cerebellum of MeHg-treated groups, although cerebrum histology was similar in all experimental groups. The synaptic potential amplitude in the cerebellum decreased as MeHg exposure increased, which was restored by OA3Glu treatment. Even in the cerebrum, where the effects of MeHg were not observed, the amplitude of the field potential was suppressed with increasing MeHg exposure but was restored with OA3Glu treatment. Taken together, the study findings suggest that OA3Glu improves neurotransmission and movement disorders associated with MeHg exposure via protection of Purkinje cells in the cerebellum while ameliorating pre/post-synaptic deficits in the cerebral cortex in which no changes were observed at the tissue level, potentially providing a treatment to mitigate MeHg toxicity.

JAK2/STAT3 signaling pathway mediates methylmercury toxicity in mouse astrocyte neuronal C8-D1A cell line

Methylmercury (MeHg) is an environmental pollutant. Consumption of contaminated fish is the main exposure route in humans, leading to severe neurological disorders. Upon ingestion MeHg reaches the brain and selectively accumulates in astrocytes disrupting glutamate and calcium homeostasis and increasing oxidative stress. Despite extensive research, the molecular mechanisms underlying MeHg neurotoxicity remain incompletely understood. The induction of nuclear factor erythroid 2-related factor 2 (Nrf2) and its role activating antioxidant responses during MeHg-induced oxidative injury have garnered significant attention as a potential therapeutic target against MeHg toxicity. However, recent studies indicate that the Nrf2 signaling pathway alone may not be sufficient to mitigate MeHg-induced damage, suggesting the existence of other protective mechanisms. The signal transducer and activator of transcription 3 (STAT3) plays a crucial role in cell growth and survival. Several studies have also highlighted its involvement in regulating redox homeostasis, thereby preventing oxidative stress through mechanisms that involve modulation of nuclear genes that encode electron transport complexes (ETC) and antioxidant enzymes. These characteristics suggest that STAT3 could serve as a viable mechanism to mitigate MeHg toxicity, either in conjunction with or as an alternative to Nrf2 signaling. Our previous findings demonstrated that MeHg activates the STAT3 signaling pathway in the GT1-7 hypothalamic neuronal cell line, suggesting its potential role in promoting neuroprotection. Here, to elucidate the role of the STAT3 signaling pathway in MeHg neurotoxicity, we pharmacologically inhibited STAT3 using AG490 in the C8D1A astrocytic cell line exposed to 10 µM MeHg. Our data demonstrated that pharmacological inhibition of STAT3 phosphorylation exacerbates MeHg-induced mortality, antioxidant responses, and ROS production, suggesting that STAT3 may contribute to neuroprotection against MeHg exposure in astrocytes.

Excellent Mercury Removal in High Sulfur Atmosphere Using a Novel CuS-BDC-2D Derived by Metal-Organic Frame

To effectively remove high concentrations of mercury in a high sulfur atmosphere of nonferrous smelting flue gas, a novel two-dimensional CuS-MOF (CuS-BDC-2D) material is synthesized by anchoring S to Cu sites in the Cu-BDC MOF. The highly dispersed CuS active sites and MOF framework structural properties in CuS-BDC-2D enable efficiently collaborate in capturing mercury. CuS-BDC-2D exhibits a layered floral structure with high specific surface area and thermal stability, with poor crystallinity. Compared to CuS and the three-dimensional CuS-MOF (CuS-BDC-3D) structure, CuS-BDC-2D demonstrates significantly higher mercury capture capacity due to the high exposure of active sites and defects sites in the two-dimensional material. Moreover, CuS-BDC-2D exhibits excellent resistance to sulfur, maintaining its high efficiency in removing Hg0 even at high levels of sulfur dioxide (SO2), such as 5000-20,000 ppm. The superior performance of CuS-BDC-2D makes it suitable for controlling mercury emissions in actual nonferrous smelting flue gas. This discovery also paves the way for the development of new mercury adsorbents, which can guide future advancements in this field.

Synchrotron speciation of umbilical cord mercury and selenium after environmental exposure in Niigata

The insidious and deadly nature of mercury's organometallic compounds is informed by two large scale poisonings due to industrial mercury pollution that occurred decades ago in Minamata and Niigata, Japan. The present study examined chemical speciation for both mercury and selenium in a historic umbilical cord sample from a child born to a mother who lived near the Agano River in Niigata. The mother had experienced mercury exposure leading to more than 50 ppm mercury measured in her hair and was symptomatic 9 years prior to the birth. We sought to determine the mercury and selenium speciation in the child's cord using Hg Lα1 and Se Kα1 high-energy resolution fluorescence detected X-ray absorption spectroscopy, the chemical speciation of mercury was found to be predominantly organometallic and coordinated to a thiolate. The selenium was found to be primarily in an organic form and at levels higher than those of mercury, with no evidence of mercury-selenium chemical species. Our results are consistent with mercury exposure at Niigata being due to exposure to organometallic mercury species.

The Human LRRK2 Modulates the Age-Dependent Effects of Developmental Methylmercury Exposure in Caenorhabditis elegans

Methylmercury (MeHg) neurotoxicity exhibits age-dependent effects with a latent and/or persistent neurotoxic effect on aged animals. Individual susceptibility to MeHg neurotoxicity is governed by both exposure duration and genetic factors that can magnify or mitigate the pathologic processes associated with this exposure. We previously showed the G2019S mutation of leucine-rich repeat kinase 2 (LRRK2) modulates the response of worms to high levels of MeHg, mitigating its effect on neuronal morphology in pre-vesicles in cephalic (CEP) dopaminergic neurons. Here we sought to better understand the long-term effects of MeHg exposure at low levels (100-fold lower than that in our previous report) and the modulatory role of the LRRK2 mutation. Worms exposed to MeHg (10 or 50 nM) at the larval stage (L1 stage) were compared at adult stages (young age: day 1 adult; middle age: day 5 adult; old age: day 10 adult) for the swimming speeds in M9 buffer, moving speeds during locomotion on an OP50-seeded plate, and the numbers of CEP dopaminergic pre-vesicles, vesicular structures originating from the dendrites of CEP for exportation of cellular content. In addition, the expression levels of Caenorhabditis elegans homologs of dopamine transporter (dat-1) and tyrosine hydroxylase (cat-2) were also analyzed at these adult stages. Our data showed that swimming speeds were reduced in wild-type worms at the day 10 adult stage at 50 nM MeHg level; yet, reduced swimming speeds were noted in the G2019S LRRK2 transgenic line upon MeHg exposures as low as 10 nM. Compared to locomotor speeds, swimming speeds appear to be more sensitive to the behavioral effects of developmental MeHg exposures, as the locomotor speeds were largely intact and indistinguishable from controls following MeHg exposures. Furthermore, we showed an age-dependent modulation of dat-1 and cat-2 expressions, which could also be modified by the LRRK2 mutation. Although MeHg exposures did not change the number of pre-vesicles, the LRRK2 mutation was associated with increased numbers of pre-vesicles in aged worms. Our data suggest that the latent behavioral effects of MeHg are sensitized by the G2019S LRRK2 mutation, and the underlying mechanism likely involves age-dependent changes in dopaminergic signaling.

Past mercury exposure and current symptoms of nervous system dysfunction in adults of a First Nation community (Canada)

BACKGROUND

The watershed in Asubpeeschoseewagong Netum Anishinabek (Grassy Narrows First Nation) territory has been contaminated by mercury (Hg) since 1962, resulting in very high Hg concentrations in fish, central to the community's culture, traditions, economy and diet. Biomarkers of Hg exposure (umbilical cord blood and hair/blood samples), monitored between 1970 and 1997, decreased over time. A recent Grassy Narrows Community Health Assessment (GN-CHA) survey included current symptoms of nervous system dysfunction. The present study aimed to cluster self-reported symptoms and examine their associations with past Hg exposure.

METHODS

The GN-CHA included 391 adults. Symptom clustering used a two-step segmentation approach. Umbilical cord Hg and/or yearly measurements of equivalent hair Hg were available for 242 participants. Structural Equation Models (SEM) displayed the associations between Hg exposure and clusters, with Hg exposure modelled as a latent variable or in separate variables (prenatal, childhood and having had hair Hg ≥ 5 μg/g at least once over the sampling period). Longitudinal Mixed Effects Models (LMEM) served to examine past hair Hg with respect to clusters.

RESULTS

A total of 37 symptoms bonded into 6 clusters, representing Extrapyramidal impairment, Sensory impairment, Cranial nerve disturbances, Gross motor impairment, Neuro-cognitive deficits and Affect/Mood disorders. Median Hg concentrations were 5 μg/L (1-78.5) and 1.1 μg/g (0.2-16) for umbilical cord and childhood hair, respectively. More than one-third (36.6%) had hair Hg ≥ 5 μg/g at least once. In SEM, latent Hg was directly associated with Extrapyramidal and Sensory impairment, Cranial nerve disturbances and Affect/Mood disorders. Direct associations were observed for prenatal exposure with Affect/Mood disorders, for childhood exposure with Extrapyramidal impairment and Cranial nerve disturbances, and for hair Hg ≥ 5 μg/g with Extrapyramidal and Sensory impairment. For all clusters, a further association between past Hg exposure and symptom clusters was mediated by diagnosed nervous system disorders. LMEM showed higher past hair Hg among those with higher scores for all clusters, except Affect/Mood disorders.

CONCLUSION

Our findings provide evidence that in this First Nation community, past Hg exposure from fish consumption was associated with later-life clusters of coexisting symptoms of nervous system dysfunction.

BMAA, Methylmercury, and Mechanisms of Neurodegeneration in Dolphins: A Natural Model of Toxin Exposure

Dolphins are well-regarded sentinels for toxin exposure and can bioaccumulate a cyanotoxin called β-N-methylamino-l-alanine (BMAA) that has been linked to human neurodegenerative disease. The same dolphins also possessed hallmarks of Alzheimer’s disease (AD), suggesting a possible association between toxin exposure and neuropathology. However, the mechanisms of neurodegeneration in dolphins and the impact cyanotoxins have on these processes are unknown. Here, we evaluate BMAA exposure by investigating transcription signatures using PCR for dolphin genes homologous to those implicated in AD and related dementias: APP, PSEN1, PSEN2, MAPT, GRN, TARDBP, and C9orf72. Immunohistochemistry and Sevier Münger silver staining were used to validate neuropathology. Methylmercury (MeHg), a synergistic neurotoxicant with BMAA, was also measured using PT-GC-AFS. We report that dolphins have up to a three-fold increase in gene transcription related to Aβ⁺ plaques, neurofibrillary tangles, neuritic plaques, and TDP-43⁺ intracytoplasmic inclusions. The upregulation of gene transcription in our dolphin cohort paralleled increasing BMAA concentration. In addition, dolphins with BMAA exposures equivalent to those reported in AD patients displayed up to a 14-fold increase in AD-type neuropathology. MeHg was detected (0.16–0.41 μg/g) and toxicity associated with exposure was also observed in the brain. These results demonstrate that dolphins develop neuropathology associated with AD and exposure to BMAA and MeHg may augment these processes.

Methylmercury myotoxicity targets formation of the myotendinous junction

Methylmercury (MeHg) is a ubiquitous environmental contaminant and developmental toxicant known to cause a variety of persistent motor and cognitive deficits. While previous research has focused predominantly on neurotoxic MeHg effects, emerging evidence points to a myotoxic role whereby MeHg induces defects in muscle development and maintenance. A genome wide association study for developmental sensitivity to MeHg in Drosophila has revealed several conserved muscle morphogenesis candidate genes that function in an array of processes from myoblast migration and fusion to myotendinous junction (MTJ) formation and myofibrillogenesis. Here, we investigated candidates for a role in mediating MeHg disruption of muscle development by evaluating morphological and functional phenotypes of the indirect flight muscles (IFMs) in pupal and adult flies following 0, 5, 10, and 15 μM MeHg exposure via feeding at the larval stage. Developmental MeHg exposure induced a dose-dependent increase in muscle detachments (myospheres) within dorsal bundles of the IFMs, which paralleled reductions eclosion and adult flight behaviors. These effects were selectively phenocopied by altered expression of kon-tiki (kon), a chondroitin sulfate proteoglycan 4/NG2 homologue and a central component of MTJ formation. MeHg elevated kon transcript expression at a crucial window of IFM development and transgene overexpression of kon could also phenocopy myosphere phenotypes and eclosion and flight deficits. Finally, the myosphere phenotype resulting from 10 μM MeHg was partially rescued in a background of reduced kon expression using a targeted RNAi approach. Our findings implicate a component of the MTJ as a MeHg toxicity target which broaden the understanding of how motor deficits can emerge from early life MeHg exposure.

Rethinking the Minamata Tragedy: What Mercury Species Was Really Responsible?

Industrial release of mercury into the local Minamata environment with consequent poisoning of local communities through contaminated fish and shellfish consumption is considered the classic case of environmental mercury poisoning. However, the mercury species in the factory effluent has proved controversial, originally suggested as inorganic, and more recently as methylmercury species. We used newly available methods to re-examine the cerebellum of historic Cat 717, which was fed factory effluent mixed with food to confirm the source. Synchrotron high-energy-resolution fluorescence detection-X-ray absorption spectroscopy revealed sulfur-bound organometallic mercury with a minor β-HgS phase. Density functional theory indicated energetic preference for α-mercuri-acetaldehyde as a waste product of aldehyde production. The consequences of this alternative species in the "classic" mercury poisoning should be re-evaluated.

Assessment of residents' total environmental exposure to heavy metals in China

Heavy metal pollution in the air, water, and soil has attracted substantial interest recently; however, assessment of the total human environmental exposure remains limited. Therefore, determining the total human environmental exposure is imperative for the management and control of heavy metal pollution. This study assessed the total environmental exposure levels of heavy metals as well as the exposure contributions of air, water, and soil, focusing on Hg, Cd, As, Pb, and Cr. Data from 3,855 volunteers from the cities of Taiyuan, Dalian, Shanghai, Wuhan, Chengdu, and Lanzhou allowed for comparison of the exposures in urban and rural areas. The levels of total human environmental exposure of Hg, Cd, As, Pb, and Cr were 1.82 × 10⁻⁶ mg/(kg·d), 1.58 × 10⁻⁶ mg/(kg·d), 3.87 × 10⁻⁵ mg/(kg·d), 1.79 × 10⁻⁵ and 7.47 × 10⁻⁵ mg/(kg·d), respectively. There were regional, urban-rural, sex, and age differences in the levels of heavy metal exposure. Water pollution was determined to be the largest contributor to heavy metal exposure, accounting for 97.87%, 92.50%, 80.51%, 76.16% and 79.46% of the Hg, Cd, As, Pb, and Cr, followed by air and soil pollution. These results can provide data to inform environmental protection policies and identify the priority pollutants that can help identify and prevent health risks due to overexposure to these heavy metal pollutants.

Human-induced pluripotent stems cells as a model to dissect the selective neurotoxicity of methylmercury

Methylmercury (MeHg) is a potent neurotoxicant affecting both the developing and mature central nervous system (CNS) with apparent indiscriminate disruption of multiple homeostatic pathways. However, genetic and environmental modifiers contribute significant variability to neurotoxicity associated with human exposures. MeHg displays developmental stage and neural lineage selective neurotoxicity. To identify mechanistic-based neuroprotective strategies to mitigate human MeHg exposure risk, it will be critical to improve our understanding of the basis of MeHg neurotoxicity and of this selective neurotoxicity. Here, we propose that human-based pluripotent stem cell cellular approaches may enable mechanistic insight into genetic pathways that modify sensitivity of specific neural lineages to MeHg-induced neurotoxicity. Such studies are crucial for the development of novel disease modifying strategies impinging on MeHg exposure vulnerability.

Notch Target Gene E(spl)mδ Is a Mediator of Methylmercury-Induced Myotoxicity in Drosophila

Methylmercury (MeHg) is a ubiquitous environmental contaminant and neurotoxicant that has long been known to cause a variety of motor deficits. These motor deficits have primarily been attributed to MeHg targeting of developing neurons and induction of oxidative stress and calcium dysregulation. Few studies have looked at how MeHg may be affecting fundamental signaling mechanisms in development, particularly in developing muscle. Studies in Drosophila recently revealed that MeHg perturbs embryonic muscle formation and upregulates Notch target genes, reflected predominantly by expression of the downstream transcriptional repressor Enhancer of Split mdelta [E(spl)mδ]. An E(spl)mδ reporter gene shows expression primarily in the myogenic domain, and both MeHg exposure and genetic upregulation of E(spl)mδ can disrupt embryonic muscle development. Here, we tested the hypothesis that developing muscle is targeted by MeHg via upregulation of E(spl)mδ using genetic modulation of E(spl)mδ expression in combination with MeHg exposure in developing flies. Developmental MeHg exposure causes a decreased rate of eclosion that parallels gross disruption of indirect flight muscle (IFM) development. An increase in E(spl) expression across the pupal stages, with preferential E(spl)mδ upregulation occurring at early (p5) stages, is also observed. E(spl)mδ overexpression in myogenic lineages under the Mef2 promoter was seen to phenocopy eclosion and IFM effects of developmental MeHg exposure; whereas reduced expression of E(spl)mδ shows rescue of eclosion and IFM morphology effects of MeHg exposure. No effects were seen on eclosion with E(spl)mδ overexpression in neural and gut tissues. Our data indicate that muscle development is a target for MeHg and that E(spl)mδ is a muscle-specific mediator of this myotoxicity. This research advances our knowledge of the target pathways that mediate susceptibility to MeHg toxicity, as well as a potential muscle development-specific role for E(spl)mδ.

Neurodegeneration Induced by Metals in Caenorhabditis elegans

Metals are a component of a variety of ecosystems and organisms. They can generally be divided into essential and nonessential metals. The essential metals are involved in physiological processes once the deficiency of these metals has been associated with diseases. Although iron, manganese, copper, and zinc are important for life, it has been evidenced that they are also involved in neuronal damage in many neurodegenerative disorders. Nonessential metals, which are metals without physiological functions, are present in trace or higher levels in living organisms. Occupational, environmental, or deliberate exposures to lead, mercury, aluminum, and cadmium are clearly correlated with the increase of toxicity and varied kinds of pathological situations. Actually, the field of neurotoxicology needs to satisfy two opposing demands: the testing of a growing list of chemicals and resource limitations and ethical concerns associated with testing using traditional mammalian species. Toxicological assays using alternative animal models may relieve some of this pressure by allowing testing of more compounds while reducing expenses and using fewer mammals. The nervous system is by far the more complex system in C. elegans. Almost a third of their cells are neurons (302 neurons versus 959 cells in adult hermaphrodite). It initially underwent extensive development as a model organism in order to study the nervous system, and its neuronal lineage and the complete wiring diagram of its nervous system are stereotyped and fully described. The neurotransmission systems are phylogenetically conserved from nematodes to vertebrates, which allows for findings from C. elegans to be extrapolated and further confirmed in vertebrate systems. Different strains of C. elegans offer a new perspective on neurodegenerative processes. Some genes have been found to be related to neurodegeneration induced by metals. Studying these interactions may be an effective tool to slow neuronal loss and deterioration.

Permeation thresholds for hydrophilic small biomolecules across microvascular and epithelial barriers are predictable on basis of conserved biophysical properties

Purpose

Neutral small hydrophiles are permeable to varying degrees, across the aqueous pores of phospholipid bilayer protein channels, with their potential for permeation into cells being predictable, on the basis of hydrophilicity and size. Here, it is hypothesized that permeation thresholds for small hydrophiles, across capillary zona occludens tight junction and inter-epithelial junction pore complexes are predictable, on the basis of predicted hydrophilicity in context of predicted molecular size and charge distribution, as are those of cations and anions, on the basis of predicted ionization in context of predicted atomic size.

Methods

Small hydrophiles are categorized by charge distribution. 2-dimensional plots of predicted hydrophilic octanol-to-water partition coefficient (HOWPC; unitless) and predicted van der Waals diameter (vdWD; nm) are generated for each category. The predicted HOWPC-to-vdWD ratio (nm^-1), and vdWDs for permeable hydrophile at the maximum and minimum HOWPC-to-vdWD, vdWD @ MAXimum HOWPC-to-vdWD and vdWD @ MINimum HOWPC-to-vdWD are determined. For cations and anions, the ionization-to-atomic diameter ratios (CI or AI-to-AD ratios; nm^-1) are determined.

Results

Per sizes of mixed and pure polyneutral hydrophiles, the permeation size maximum for hydrophiles across tight junction pore complexes is >0.69 ≤ 0.73 nanometers and across inter-epithelial junction pore complexes is ≥ 0.81 nanometers. For hydrophiles with anionicity or cationicity, the vdWDs @ MAXimum HOWPC-to-vdWD are less than those of mixed and polyneutral hydrophiles across both tight and inter-epithelial junctions, ranges specific to category and junction type. For cations, the permeation threshold across tight junctions is between the CI-to-AD ratio of Na+ (+2.69 nm^-1) and CH3-Hg+ (+2.36 nm^-1), with CH3-Hg+ and K+ (+2.20 nm^-1) being permeable; and for divalent cations, the threshold across inter-epithelial junctions is between the CI-to-AD ratio of Mg2+ (+6.25 nm^-1) and Ca2+ (+5.08 nm^-1) , Ca2+ being semi-permeable. For anions, the permeation threshold across tight junctions is between the AI-to-AD ratio of Cl- (-4.91 nm^-1) and Br- (-4.17 nm^-1), and the threshold across inter-epithelial junctions is between the AI-to-AD ratio of F- (-7.81 nm^-1) and Cl- (-4.91 nm^-1).

Conclusions

In silico modeling reveals that permeation thresholds, of small molecule hydrophiles, cations and anions across junctional pore complexes, are conserved in the physiologic state.

Electronic supplementary material

The online version of this article (doi:10.1186/s40203-015-0009-y) contains supplementary material, which is available to authorized users.

Mechanistic pathways of mercury removal from the organomercurial lyase active site

Bacterial populations present in Hg-rich environments have evolved biological mechanisms to detoxify methylmercury and other organometallic mercury compounds. The most common resistance mechanism relies on the H⁺-assisted cleavage of the Hg–C bond of methylmercury by the organomercurial lyase MerB. Although the initial reaction steps which lead to the loss of methane from methylmercury have already been studied experimentally and computationally, the reaction steps leading to the removal of Hg²⁺ from MerB and regeneration of the active site for a new round of catalysis have not yet been elucidated. In this paper, we have studied the final steps of the reaction catalyzed by MerB through quantum chemical computations at the combined MP2/CBS//B3PW91/6-31G(d) level of theory. While conceptually simple, these reaction steps occur in a complex potential energy surface where several distinct pathways are accessible and may operate concurrently. The only pathway which clearly emerges as forbidden in our analysis is the one arising from the sequential addition of two thiolates to the metal atom, due to the accumulation of negative charges in the active site. The addition of two thiols, in contrast, leads to two feasible mechanistic possibilities. The most straightforward pathway proceeds through proton transfer from the attacking thiol to Cys159 , leading to its removal from the mercury coordination sphere, followed by a slower attack of a second thiol, which removes Cys96. The other pathway involves Asp99 in an accessory role similar to the one observed earlier for the initial stages of the reaction and affords a lower activation enthalpy, around 14 kcal mol⁻¹, determined solely by the cysteine removal step rather than by the thiol ligation step. Addition of one thiolate to the intermediates arising from either thiol attack occurs without a barrier and produces an intermediate bound to one active site cysteine and from which Hg(SCH₃)₂ may be removed only after protonation by solvent-provided H₃O⁺. Thiolate addition to the active site (prior to any attack by thiols) leads to pathways where the removal of the first cysteine becomes the rate-determining step, irrespective of whether Cys159 or Cys96 leaves first. Comparisons with the recently computed mechanism of the related enzyme MerA further underline the important role of Asp99 in the energetics of the MerB reaction. Kinetic simulation of the mechanism derived from our computations strongly suggests that in vivo the thiolate-only pathway is operative, and the Asp-assisted pathway (as well as the conversion of intermediates of the thiolate pathway into intermediates of the Cys-assisted pathway) is prevented by steric factors absent from our model and related to the precise geometry of the organomercurial binding-pocket.

Accumulation of mercury in rice grain and cabbage grown on representative Chinese soils

A pot culture experiment was carried out to investigate the accumulation properties of mercury (Hg) in rice grain and cabbage grown in seven soil types (Udic Ferrisols, Mollisol, Periudic Argosols, Latosol, Ustic Cambosols, Calcaric Regosols, and Stagnic Anthrosols) spiked with different concentrations of Hg (CK, 0.25, 0.50, 1.00, 2.00, and 4.00 mg/kg). The results of this study showed that Hg accumulation of plants was significantly affected by soil types. Hg concentration in both rice grain and cabbage increased with soil Hg concentrations, but this increase differed among the seven soils. The stepwise multiple regression analysis showed that pH, Mn(II), particle size distribution, and cation exchange capacity have a close relationship with Hg accumulation in plants, which suggested that physicochemical characteristics of soils can affect the Hg accumulation in rice grain and cabbage. Critical Hg concentrations in seven soils were identified for rice grain and cabbage based on the maximum safe level for daily intake of Hg, dietary habits of the population, and Hg accumulation in plants grown in different soil types. Soil Hg limits for rice grain in Udic Ferrisols, Mollisol, Periudic Argosols, Latosol, Ustic Cambosols, Calcaric Regosols, and Stagnic Anthrosols were 1.10, 2.00, 2.60, 2.78, 1.53, 0.63, and 2.17 mg/kg, respectively, and critical soil Hg levels for cabbage are 0.27, 1.35, 1.80, 1.70, 0.69, 1.68, and 2.60 mg/kg, respectively.

Gene responses in the central nervous system of zebrafish embryos exposed to the neurotoxicant methyl mercury

Methyl mercury (MeHg) is a neurotoxicant with adverse effects on the development of the nervous system from fish to man. Despite a detailed understanding of the molecular mechanisms by which MeHg affects cellular homeostasis, it is still not clear how MeHg causes developmental neurotoxicity. We performed here a genome-wide transcriptional analysis of MeHg-exposed zebrafish embryos and combined this with a whole-mount in situ expression analysis of 88 MeHg-affected genes. The majority of the analyzed genes showed tissue- and region-restricted responses in various organs and tissues. The genes were linked to gene ontology terms like oxidative stress, transport and cell protection. Areas even within the central nervous system (CNS) are affected differently resulting in distinct cellular stress responses. Our study revealed an unexpected heterogeneity in gene responses to MeHg exposure in different tissues and neuronal subregions, even though the known molecular action of MeHg would predict a similar burden of exposed cells. The overall structure of the developing brain of MeHg-exposed embryos appeared normal, suggesting that the mechanism leading to differentiation of the CNS is not overtly affected by exposure to MeHg. We propose that MeHg disturbs the function of the CNS by disturbing the cellular homeostasis. As these cellular stress responses comprise genes that are also involved in normal neuronal activity and learning, MeHg may affect the developing CNS in a subtle manner that manifests itself in behavioral deficits.

Metals, oxidative stress and neurodegeneration: a focus on iron, manganese and mercury

Essential metals are crucial for the maintenance of cell homeostasis. Among the 23 elements that have known physiological functions in humans, 12 are metals, including iron (Fe) and manganese (Mn). Nevertheless, excessive exposure to these metals may lead to pathological conditions, including neurodegeneration. Similarly, exposure to metals that do not have known biological functions, such as mercury (Hg), also present great health concerns. This review focuses on the neurodegenerative mechanisms and effects of Fe, Mn and Hg. Oxidative stress (OS), particularly in mitochondria, is a common feature of Fe, Mn and Hg toxicity. However, the primary molecular targets triggering OS are distinct. Free cationic iron is a potent pro-oxidant and can initiate a set of reactions that form extremely reactive products, such as OH. Mn can oxidize dopamine (DA), generating reactive species and also affect mitochondrial function, leading to accumulation of metabolites and culminating with OS. Cationic Hg forms have strong affinity for nucleophiles, such as -SH and -SeH. Therefore, they target critical thiol- and selenol-molecules with antioxidant properties. Finally, we address the main sources of exposure to these metals, their transport mechanisms into the brain, and therapeutic modalities to mitigate their neurotoxic effects.

The Northern Norway mother-and-child contaminant cohort study: implementation, population characteristics and summary of dietary findings

OBJECTIVES

To describe the essential features of a new Northern Norway mother-and-child contaminant cohort study called MISA, including its rationale, content, implementation and selected findings (mostly dietary).

STUDY DESIGN

Cross-sectional with longitudinal aspects.

METHODS

Five hundred and fifteen eligible women were enrolled in early pregnancy, with 391 completing the study protocol that included a self-administrated food frequency questionnaire (FFQ) and donation of biological samples for contaminant analysis in the 2nd trimester, just after delivery, and 6 weeks postpartum. Macronutrient consumption was converted to energy intake, and the amounts of both macro- and micronutrients ingested were estimated. Some of the MISA findings were compared to data available in the Medical Birth Registry of Norway (MBRN).

RESULTS

Compared to all 2004-2006 mothers in Northern Norway, the study cohort women were about 2 years older and smoked less; on average, they had close to 16 years of education. Parity, gestational age and birth weight of the newborn were comparable as well. The estimated average dietary intake of 8.1 MJ per day was less than that recommended by the Nordic Nutritional Recommendations (NNR), but the intake of micronutrients per MJ complied.

CONCLUSIONS

Although the final cohort sample size was less than targeted, the generally good comparisons observed between MBRN-registered information for the study cohort and dropouts suggest that this occurrence introduced minimal bias. The agreement of the observed demographic and clinical characteristics of the cohort women and newborns with all births in Northern Norway implied acceptable external validity. Also, the dietary findings aligned well with Norwegian national data and guidelines and other studies, as did the high prevalence of breastfeeding. The MISA database is considered suitable for exploring associations between contaminant exposure and diet, enhancing our knowledge of the interplay of the physiological changes that occur in mothers with contaminant pharmacokinetics (including transfer to the infant before and after birth), and conducting prospective health studies of the children.

Indications of decreasing human PTS concentrations in North West Russia

BACKGROUND

The Russian Arctic covers an enormous landmass with diverse environments. It inhabits more than 20 different ethnic groups, all of them with various living conditions and food traditions. Indigenous populations with a traditional way of living are exposed to a large number of anthropogenic pollutants, such as persistent organic pollutants (POPs) and toxic metals, mainly through the diet. Human monitoring of persistent organic pollutants (POPs) and heavy metals in the Russian Arctic has only been performed on irregular intervals over the past 15 years, thus, there is still a lack of baseline data from many ethnic groups and geographical regions. The aim of the current study was to investigate concentrations of POPs and toxic metals in three groups of indigenous people from the Russian Arctic. Plasma concentrations of POPs were measured in one of the locations (Nelmin-Nos) in 2001-2003 which gave the unique opportunity to compare concentrations over time in a small Russian arctic community.

METHODS

During 2009 and early 2010, 209 blood samples were collected from three different study sites in North West Russia; Nelmin-Nos, Izhma and Usinsk. The three study sites are geographically separated and the inhabitants are expected to have different dietary habits and living conditions. All blood samples were analyzed for POPs and toxic metals.

RESULTS

PCB 153 was present in highest concentrations of the 18 PCBs analyzed. p,p'-DDE and HCB were the two most dominating OC pesticides. Males had higher concentrations of PCB 138, 153 and 180 than women and age was a significant predictor of PCB 153, 180, HCB and p,p'-DDD. Males from Izhma had significantly higher concentrations of HCB than males from the other study sites and women from Usinsk had higher concentrations of p,p'-DDE. Parity was a significant predictor of p,p'-DDE. Hg and Pb concentrations increased with increasing age and males had significantly higher concentrations of Pb than women. The study group from Izhma had significantly higher concentrations of Cd when controlling for age and gender and the study group from Usinsk had higher concentrations of Se than the others. Compared to the results from Nelmin-Nos in 2001-2003, a clear decrease in p,p'-DDE concentrations for both women and men was observed.

CONCLUSIONS

The current study indicates a significant reduction of several PTSs in human blood samples from North West Russia over the past 10 years.