Transport of inorganic mercury and methylmercury in target tissues and organs

Membrane transporters modulating the toxicity of arsenic, cadmium, and mercury in human cells

Non-essential metals are extremely toxic to living organisms, posing significant health risks, particularly in developing nations where they are a major contributor to illness and death. Although their toxicity is widely acknowledged, the mechanisms by which they are regulated within human cells remain incompletely understood. Specifically, the role of membrane transporters in mediating heavy metal toxicity is not well comprehended. Our study demonstrates how specific transporters can modulate the toxicity of cadmium, mercury, and the metalloid arsenic in human cells. Using CRISPR/Cas9 loss-of-function screens, we found that the multidrug resistance protein MRP1/ABCC1 provided protection against toxicity induced by arsenic and mercury. In addition, we found that SLC39A14 and SLC30A1 increased cellular sensitivity to cadmium. Using a reporter cell line to monitor cellular metal accumulation and performing a cDNA gain-of-function screen, we were able to clarify the function of SLC30A1 in controlling cadmium toxicity through the modulation of intracellular zinc levels. This transporter-wide approach provides new insights into the complex roles of membrane transporters in influencing the toxicity of arsenic, cadmium, and mercury in human cell lines.

Novel Insights into Hg0 Oxidation in Rice Leaf: Catalase Functions and Transcriptome Responses

Rice leaves can assimilate atmospheric mercury (Hg0), which is accumulated by grains and causes health risks to rice consumers. However, the molecular mechanisms underlying Hg0 assimilation in rice leaves remain poorly understood. Here, we investigated catalase's (CAT) function in Hg0 oxidation within rice leaves, as well as the Hg speciation and transcriptomic profiles of rice leaves exposed to Hg0. The inactivation of catalase reduced Hg0 oxidation by 91% in the leaf homogenate and the Hg0 oxidation rate increased along with CAT activity, showing the CAT's function in Hg0 oxidation. Hg0 was converted to Hg(cysteine)2 complexes in the leaf. Transcriptomic results revealed that the expression levels of both OsCATA and OsCATB (catalase-encoding genes) increased with Hg concentration, suggesting the involvement of catalase-related molecular network in Hg0 oxidation. Upstream transcription factors, including NAC (NAM-no apical meristem, ATAF-Arabidopsis transcription activation factor, and CUC-cup-shaped cotyledon), and ethylene-responsive transcription factor, are likely involved in catalase expression. Genes related to cysteine metabolism and amino acid transport appeared to regulate Hg accumulation. Our findings demonstrate the important function of catalase in Hg0 oxidation within rice and are fundamental for developing genetically modified rice cultivars to minimize human Hg exposure health risks.

Determination of Toxic Elements in Cannabinoid and Opioid Drugs and Their Impact on Addicts' Health: A Comparative Study

Drug addiction is associated with significant health risks, including cardiovascular complications, cancer, and mental disorders. Illicit drugs, such as cannabinoids and opioids, including prescription medications, are widely consumed and have profound health consequences. Understanding the health effects of the toxic elements in these substances is critical for overdose prevention and effective recovery strategies. This study aimed to determine toxic elements, including arsenic (As), cadmium (Cd), mercury (Hg), and nickel (Ni), in cannabinoid and opioid drugs and in biological samples (whole blood, scalp hair, and serum) from 311 male drug abuse patients aged 15-60 years with a history of drug abuse. The participants were categorized into three age groups. The comparative analysis involved 113 reference subjects of the same age groups. The sample preparation employed microwave-assisted acid digestion, and the toxic elements were quantified using atomic absorption spectrophotometry. Accuracy was ensured using certified reference materials for hair, whole blood, and serum samples. Drug-addicted subjects had significantly higher concentrations of toxic elements (arsenic, cadmium, mercury, and nickel) in biological samples than referent subjects (p > 0.001). Elevated levels of these toxic elements may increase susceptibility to infections, possibly due to malnutrition, drug-related effects, and additional contaminants. These findings necessitate further studies to explore the long-term health outcomes, potential treatment options, and broader socioeconomic impacts of substance abuse. This study serves as a baseline for future research in this critical public health field.

Dietary protein affects tissue accumulation of mercury and induces hepatic Phase I and Phase II enzyme expression after co-exposure with methylmercury in mice

Methylmercury (MeHg) is a ubiquitous environmental contaminant, well known for its neurotoxic effects. MeHg can interact with several nutrients in the diet and affect nutrient metabolism, however the interaction between MeHg and dietary proteins has not been thoroughly investigated. Male BALB/c mice were fed diets based on either casein, cod or chicken as protein sources, which were or were not spiked with MeHg (3.5 mg Hg kg-1). Following 13 weeks of dietary exposure to MeHg, the animals accumulated mercury in a varying degree depending on the diet, where the levels of mercury were highest in the mice fed casein and MeHg, lower in mice fed cod and MeHg, and lowest in mice fed chicken and MeHg in all tissues assessed. Assessment of gut microbiota revealed differences in microbiota composition based on the different protein sources. However, the introduction of MeHg eliminated this difference. Proteomic profiling of liver tissue uncovered the influence of the dietary protein sources on a range of enzymes related to Phase I and Phase II detoxification mechanisms, suggesting an impact of the diet on MeHg metabolism and excretion. Also, enzymes linked to pathways including methionine and glycine betaine cycling, which in turn impact the production of glutathione, an important MeHg conjugation molecule, were up-regulated in mice fed chicken as dietary protein. Our findings indicate that dietary proteins can affect expression of hepatic enzymes that potentially influence MeHg metabolism and excretion, highlighting the relevance of considering the dietary composition in risk assessment of MeHg through dietary exposure.

A highly sensitive and selective fluorescent "on-off-on" peptide-based probe for sequential detection of Hg2+ and S2- ions: Applications in living cells and zebrafish imaging

Mercury ions (Hg2+) and sulfur ions (S2-), have caused serious harm to the ecological environment and human health as two kinds of highly toxic pollutants widely used. Therefore, the visual quantitative determination of Hg2+ and S2- is of great significance in the field of environmental monitoring and medical therapy. In this study, a novel fluorescent "on-off-on" peptide-based probe DNC was designed and synthesized using dipeptide (Asn-Cys-NH2) as the raw material via solid phase peptide synthesis (SPPS) technology with Fmoc chemistry. DNC displayed high selectivity in the recognition of Hg2+, and formed non-fluorescence complex (DNC-Hg2+) through 2:1 binding mode. Notably, DNC-Hg2+ complex generated in situ was used as relay response probe for highly selective sequential detection of S2- through reversible formation-separation. DNC achieved highly sensitive detection of Hg2+ and S2- with the detection limits (LODs) of 8.4 nM and 5.5 nM, respectively. Meanwhile, DNC demonstrated feasibility for Hg2+ and S2- detections in two water samples, and the considerable recovery rate was obtained. More importantly, DNC showed excellent water solubility and low toxicity, and was successfully used for consecutive discerning Hg2+ and S2- in test strips, living cells and zebrafish larvae. As an effective visual analysis method in the field, smartphone RGB Color Picker APP realized semi-quantitative detections of Hg2+ and S2- without the need for complicated device.

Mercury exposure in ringed seals (Pusa hispida saimensis) in Lake Saimaa, Finland, and the placenta as a possible non-invasive biomonitoring tool

The Saimaa ringed seal (Pusa hispida saimensis) is a subspecies of ringed seal, landlocked in Lake Saimaa, Finland. The small population of less than 500 seals is facing many human-induced threats, including chemical contaminants. Mercury, in particular, has previously been suggested to be one of the chemicals affecting the viability of this endangered population. We analysed mercury concentrations from placentas and lanugo pup tissues (blubber, brain, kidney, liver, and muscle) to determine current prenatal exposure levels. These pups were found dead in or near birth lairs and were less than 3 months old. Additionally, we used threshold values available in the literature to estimate the potential mercury toxicity to the Saimaa ringed seal. We also determined selenium concentrations for its potential to alleviate the adverse effects of mercury. We further supplemented our study with brain samples collected from various seal age classes. These seals were found dead by either natural causes or by being caught in gillnets. The analysed chemicals were present in all tissues. For lanugo pups, mercury concentrations were the highest in the kidney and liver, whereas the highest selenium to mercury molar ratio was observed in placentas. The toxicity evaluation suggested that, in severe cases, mercury may cause adverse effects in lanugo and older pups. In these cases, the selenium concentrations were low and selenium to mercury ratio was below 1:1 threshold ratio and thus unlikely to provide adequate protection from the adverse effects of mercury. Furthermore, adverse effects are more likely to occur in adult seals, as mercury bioaccumulates, leading to higher concentrations in older individuals. Placental mercury concentrations correlated to those in the livers and muscle tissues of lanugo pups. This, together with the fact that placentas can be collected non-invasively and in good condition, provides a potential novel method for biomonitoring mercury exposure in Saimaa ringed seals.

Association of maternal blood mercury concentration during the first trimester of pregnancy with birth outcomes

Exposure to mercury has been associated with adverse effects on pregnancy outcomes. However, there is limited literature on mercury exposure and pregnancy outcomes in Chinese pregnant women. Our study was to investigate the possible association between maternal mercury exposure and spontaneous preterm birth and birth weight. This study was a nested case-control study. The association between blood mercury concentration and both spontaneous preterm birth and birth weight was analyzed using conditional logistic regression and linear regression adjusted for the potential confounding factors, respectively. The dose-response relationship between mercury concentration and birth outcomes was estimated using restricted cubic spline regression. The mean concentration of mercury was 2.8 ± 2.2 µg/L. A positive relationship was observed between maternal blood mercury concentration and SPB when analyzed as a continuous variable. However, it was not found to be statistically significant (adjusted OR = 1.10, 95% CI = 0.95-1.26, P = 0.202). Moderate mercury exposure was associated with a higher risk of SPB (Q3 vs. Q1: crude OR = 2.50, 95% CI = 1.16-5.41, P = 0.02; adjusted OR = 3.49, 95% CI = 1.33-9.11, P = 0.011). After considering the combined effects of chemicals other than mercury exposure (including lead, selenium, and cadmium), the results remained consistent. There was no statistically significant association between blood mercury levels and birth weight (adjusted coefficient = 18.64, P-value = 0.075). There were no statistically significant dose-response associations between mercury concentration and birth outcomes (SPB: P = 0.076; birth weight: P = 0.885). Public health policies should focus on reducing environmental releases of mercury, improving food safety standards, and providing education to pregnant women about the risks of mercury exposure and preventive measures.

A novel ratiometric peptide-based fluorescent probe for sequential detection of Hg2+ and S2- ions and its application in living cells and zebrafish imaging

A new ratiometric peptide-based fluorescent probe DWPH was designed and synthesized, comprising dansyl fluorophore as a fluorescent dye, and tripeptide backbone (Trp-Pro-His-NH2) as a recognition group. The addition of Hg2+ caused the maximum emission peak of DWPH to blue shift from 560 nm to 510 nm. DWPH exhibited large Stokes shift (230 nm), satisfactory water solubility (100 % aqueous medium), good selectivity (only Hg2+), high sensitivity (24.6 nM), rapid response (within 50 s) and strong anti-interference ability for Hg2+ detection over a wide pH range (7-11). Additionally, the complex DWPH-Hg2+ as a relay response probe could also be applied to S2- according to displacement approach. Notably, the detection limit for S2- was calculated as 23.3 nM, exhibiting that DWPH showed great potential for environmental monitoring and bioimaging. In addition, DWPH were successfully used to determine Hg2+ and S2- in living cells and zebrafish based on excellent permeability and low cytotoxicity. What's more, the gradient concentration color changes of Hg2+ and S2- were combined with the smartphone APP to obtain red-green-blue (RGB) values, thus enabling rapid semi-quantitative detection of Hg2+ and S2- without expensive instruments.

High resolution visualisation of tiemannite microparticles, essential in the detoxification process of mercury in marine mammals

The North Sea is an ecologically rich habitat for marine wildlife which has also been impacted by industrial developments and anthropogenic emissions of contaminants such as mercury. Marine mammals are particularly susceptible to mercury exposure, due to their trophic position, long lifespan, and dependence on (increasingly contaminated) aquatic prey species. To mitigate impact, marine mammals can detoxify methylmercury by binding it to selenium-containing biomolecules, creating insoluble mercury selenide granules. Here, liver, kidney, muscle, and brain samples from an adult male bottlenose dolphin (Tursiops truncatus) with known elevated mercury concentrations were analysed through scanning electron microscopy (SEM). Tiemannite (HgSe) deposits were identified in all organs, ranging from 400 nm to 5 μm in diameter, with particle size being organ-dependent. Although reported in other studies, this is the first time that the three-dimensional nature of tiemannite is captured in marine mammal tissue.

Mirabegron, dependent on β3-adrenergic receptor, alleviates mercuric chloride-induced kidney injury by reversing the impact on the inflammatory network, M1/M2 macrophages, and claudin-2

The β3-adrenergic receptor (β3-AR) agonism mirabegron is used to treat overactive urinary bladder syndrome; however, its role against acute kidney injury (AKI) is not unveiled, hence, we aim to repurpose mirabegron in the treatment of mercuric chloride (HgCl2)-induced AKI. Rats were allocated into normal, normal + mirabegron, HgCl2 untreated, HgCl2 + mirabegron, and HgCl2 + the β3-AR blocker SR59230A + mirabegron. The latter increased the mRNA of β3-AR and miR-127 besides downregulating NF-κB p65 protein expression and the contents of its downstream targets iNOS, IL-4, -13, and -17 but increased that of IL-10 to attest its anti-inflammatory capacity. Besides, mirabegron downregulated the protein expression of STAT-6, PI3K, and ERK1/2, the downstream targets of the above cytokines. Additionally, it enhanced the transcription factor PPAR-α but turned off the harmful hub HNF-4α/HNF-1α and the lipid peroxide marker MDA. Mirabegron also downregulated the CD-163 protein expression, which besides the inhibited correlated cytokines of M1 (NF-κB p65, iNOS, IL-17) and M2 (IL-4, IL-13, CD163, STAT6, ERK1/2), inactivated the macrophage phenotypes. The crosstalk between these parameters was echoed in the maintenance of claudin-2, kidney function-related early (cystatin-C, KIM-1, NGAL), and late (creatinine, BUN) injury markers, besides recovering the microscopic structures. Nonetheless, the pre-administration of SR59230A has nullified the beneficial effects of mirabegron on the aforementioned parameters. Here we verified that mirabegron can berepurposedto treat HgCl2-induced AKI by activating the β3-AR. Mirabegron signified its effect by inhibiting inflammation, oxidative stress, and the activated M1/M2 macrophages, events that preserved the proximal tubular tight junction claudin-2 via the intersection of several trajectories.

Mercury-induced excitotoxicity in presynaptic brain nerve terminals: modulatory effects of carbonaceous airborne particulate simulants

Multipollutant approach is a breakthrough in up-to-date environmental quality and health risk estimation. Both mercury and carbonaceous air particulate are hazardous neurotoxicants. Here, the ability of carbonaceous air particulate simulants, i.e. carbon dots obtained by heating of organics, and nanodiamonds, to influence Hg2+-induced neurotoxicity was monitored using biological system, i.e. presynaptic rat cortex nerve terminals. Using HgCl2 and classical reducing/chelating agents, an adequate synaptic parameter, i.e. the extracellular level of key excitatory neurotransmitter L-[14C]glutamate, was selected for further analysis. HgCl2 starting from 5 µM caused an acute and concentration-dependent increase in the extracellular L-[14C]glutamate level in nerve terminals. Combined application of Hg2+ and carbon dots from heating of citric acid/urea showed that this simulant was able to mitigate in an acute manner excitotoxic Hg2+-induced increase in the extracellular L-[14C]glutamate level in nerve terminals by 37%. These carbon dots and Hg2+ acted as a complex in nerve terminals that was confirmed with fluorimetric data on Hg2+-induced changes in their spectroscopic features. Nanodiamonds and carbon dots from β-alanine were not able to mitigate a Hg2+-induced increase in the extracellular L-[14C]glutamate level in nerve terminals. Developed approach can be applicable for monitoring capability of different particles/compounds to have Hg2+-chelating signs in the biological systems. Therefore, among testing simulants, the only carbon dots from citric acid/urea were able to mitigate acute Hg2+-induced neurotoxicity in nerve terminals, thereby showing a variety of effects of carbonaceous airborne particulate in situ and its potential to interfere and modulate Hg2+-associated health hazard.

Genome-Wide Association Study of Blood Mercury in European Pregnant Women and Children

Mercury has high industrial utility and is present in many products, and environmental contamination and occupational exposure are widespread. There are numerous biological systems involved in the absorption, metabolism, and excretion of Hg, and it is possible that some systems may be impacted by genetic variation. If so, genotype may affect tissue concentrations of Hg and subsequent toxic effects. Genome-wide association testing was performed on blood Hg samples from pregnant women of the Avon Longitudinal Study of Parents and Children (n = 2893) and children of the Human Early Life Exposome (n = 1042). Directly-genotyped single-nucleotide polymorphisms (SNPs) were imputed to the Haplotype Reference Consortium r1.1 panel of whole genotypes and modelled againstlog-transformed Hg. Heritability was estimated using linkage disequilibrium score regression. The heritability of Hg was estimated as 24.0% (95% CI: 16.9% to 46.4%) in pregnant women, but could not be determined in children. There were 16 SNPs associated with Hg in pregnant women above a suggestive p-value threshold (p < 1 × 10-5), and 21 for children. However, no SNP passed this threshold in both studies, and none were genome-wide significant (p < 5 × 10-8). SNP-Hg associations were highly discordant between women and children, and this may reflect differences in metabolism, a gene-age interaction, or dose-response effects. Several suggestive variants had plausible links to Hg metabolism, such as rs146099921 in metal transporter SLC39A14, and two variants (rs28618224, rs7154700) in potassium voltage-gated channel genes. The findings would benefit from external validation, as suggestive results may contain both true associations and false positives.

A mitochondrion-targeted fluorescent probe based on ESIPT phthalimide for the detection of Hg2+ with large Stokes shift

A novel mitochondrion-targeted Hg2+-specific fluorescent probe 1 based on ESIPT phthalimide was designed and synthesized for the first time. Owing to the blockage of the ESIPT process between the hydroxy group and the carbonyl oxygen of the imide by the diphenylphosphinothioate group, 1 was almost nonfluorescent. After reacting with Hg2+, 1 exhibited a dramatic fluorescence enhancement due to the recovery of the ESIPT process through Hg2+-induced desulfurization-hydrolysis of the diphenylphosphinothioate moiety and the cleavage of the P-O bond. 1 showed a large Stokes shift, rapid response and high sensitivity and selectivity for Hg2+ over other metal ions. Moreover, 1 was successfully employed to image Hg2+ in the mitochondria of living cells.

Pollutants in aquatic system: a frontier perspective of emerging threat and strategies to solve the crisis for safe drinking water

Water is an indispensable natural resource and is the most vital substance for the existence of life on earth. However, due to anthropogenic activities, it is being polluted at an alarming rate which has led to serious concern about water shortage across the world. Moreover, toxic contaminants released into water bodies from various industrial and domestic activities negatively affect aquatic and terrestrial organisms and cause serious diseases such as cancer, renal problems, gastroenteritis, diarrhea, and nausea in humans. Therefore, water treatments that can eliminate toxins are very crucial. Unfortunately, pollution treatment remains a difficulty when four broad considerations are taken into account: effectiveness, reusability, environmental friendliness, and affordability. In this situation, protecting water from contamination or creating affordable remedial techniques has become a serious issue. Although traditional wastewater treatment technologies have existed since antiquity, they are both expensive and inefficient. Nowadays, advanced sustainable technical approaches are being created to replace traditional wastewater treatment processes. The present study reviews the sources, toxicity, and possible remediation techniques of the water contaminants.

Coordination of Mercury(II) in Water Promoted over Hydrolysis in Solvated Clusters [Hg(H2O)1-6](aq)2+: Insights from Relativistic Effects and Free Energy Analysis

Understanding the nature of the interaction between mercury(II) ions, Hg2+, and water molecules is crucial to describe the stability and chemical behavior of structures formed during solvation, as well as the conditions that favor the Hg2+ coordination or inducing water hydrolysis. In our study, we explored exhaustively the potential energy surface of Hg2+ with up to six water molecules. We analyzed electronic and Gibbs free energies, binding, and nuclear magnetic resonance parameters. We used the zeroth-order regular approximation Hamiltonian, including scalar and spin-orbit relativistic corrections for free energy calculations and geometry optimizations to explore the interplay between electron correlation and relativistic effects. We analyzed intermolecular interactions with energy decomposition analysis, quantum theory of atoms in molecules, and natural bond orbital. Additionally, we used the four-component Dirac Hamiltonian to compute solvent effect on the magnetic shielding and J-coupling constants. Our results revealed that the water hydrolysis by Hg2+ requires a minimum of three water molecules. We found that the interaction between Hg2+ and water molecules is an orbital interaction due to relativistic effects and the most stable structures are opened-shape clusters, reducing the number of oxygen-mercury contacts and maximizing the formation of hydrogen bonds among water molecules. In these types of clusters, Hg2+ promotes the water hydrolysis over coordination with oxygen atoms. However, when we considered the change associated with the transfer of a cluster from the ideal gas to a solvated system, our solvation free energy analysis revealed that closed-shape clusters are more favorable, maximizing the number of oxygen-mercury contacts and reducing the formation of hydrogen bonds among water molecules. This finding suggests that, under room conditions, the coordination of Hg2+ is more favorable than hydrolysis. Our results have significant implications for understanding Hg2+ behavior in water, helping to develop targeted strategies for mercury remediation and management, and contributing to advancements in the broader field of environmental chemistry.

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.

A method for reliable quantification of mercury in occupational and environmental medical urine samples by inductively coupled plasma mass spectrometry

Over the last years, inductively coupled plasma mass spectrometry (ICP-MS) has been applied as a method for human-biomonitoring of metals in the concentration range of occupational and environmental medicine. In large scale routine monitoring, the determination of mercury (Hg) by ICP-MS remains challenging due to several reasons. Amongst others, stability of dissolved Hg and avoiding memory effects are the key facts for reliable quantification. To address these issues, we developed a robust approach for biomonitoring of mercury in human urine samples by ICP-MS. Using a solution containing HNO₃, HCl and thiourea, prepared samples and calibrators were stabilized for up to 72 h. A rinse time of only 30 seconds efficiently prevented contamination of consecutive samples with Hg concentrations up to 30 μg L^-1, hence significantly reducing acquisition times compared to published methods. Recovery experiments revealed iridium as an ideal internal standard to compensate matrix effects independently from creatinine concentration. Recoveries of 95.0-104.0% were obtained for Hg levels covering the range of biomonitoring guidance values established by the German Human-Biomonitoring Commission. Excellent intra-day precision and inter-day precision of ≤3.0% for two different Hg levels were achieved. The detection and quantification limit accounted for 21.7 ng L^-1 and 65.6 ng L^-1, respectively, enabling reliable quantification even in the range of environmental background exposures. Additionally, the method was externally validated by successful participation in the inter-laboratory comparison program G-EQUAS. With the developed method, we hence provide a sensitive and robust tool for mercury exposure assessments in future large scale human-biomonitoring studies.

Effects of Non-Essential "Toxic" Trace Elements on Pregnancy Outcomes: A Narrative Overview of Recent Literature Syntheses

Adverse pregnancy outcomes and their complications cause increased maternal and neonatal morbidity and mortality and contribute considerably to the global burden of disease. In the last two decades, numerous narrative and systematic reviews have emerged assessing non-essential, potentially harmful, trace element exposure as a potential risk factor. This narrative review summarizes the recent literature covering associations between exposure to cadmium, lead, arsenic, and mercury and pregnancy outcomes and highlights common limitations of existing evidence that may hinder decision-making within public health. Several initial scoping searches informed our review, and we searched PubMed (latest date July 2022) for the literature published within the last five years reporting on cadmium, lead, arsenic, or mercury and pre-eclampsia, preterm birth, or prenatal growth. Pre-eclampsia may be associated with cadmium and strongly associated with lead exposure, and exposure to these metals may increase risk of preterm birth. Many reviews have observed cadmium to be negatively associated with birth weight. Additionally, lead and arsenic exposure may be negatively associated with birth weight, with arsenic exposure also adversely affecting birth length and head circumference. These findings should be interpreted with caution due to the limitations of the reviews summarized in this paper, including high heterogeneity due to different exposure assessment methods, study designs, and timing of sampling. Other common limitations were the low quality of the included studies, differences in confounding variables, the low number of studies, and small sample sizes.

In Vivo Mercury (De)Methylation Metabolism in Cephalopods under Different pCO2 Scenarios

This work quantified the accumulation efficiencies of Hg in cuttlefish, depending on both organic (MeHg) and inorganic (Hg(II)) forms, under increased pCO₂ (1600 μatm). Cuttlefish were fed with live shrimps injected with two Hg stable isotopic tracers (Me²⁰²Hg and ¹⁹⁹Hg(II)), which allowed for the simultaneous quantification of internal Hg accumulation, Hg(II) methylation, and MeHg demethylation rates in different organs. Results showed that pCO₂ had no impact on Hg bioaccumulation and organotropism, and both Hg and pCO₂ did not influence the microbiota diversity of gut and digestive gland. However, the results also demonstrated that the digestive gland is a key organ for in vivo MeHg demethylation. Consequently, cuttlefish exposed to environmental levels of MeHg could exhibit in vivo MeHg demethylation. We hypothesize that in vivo MeHg demethylation could be due to biologically induced reactions or to abiotic reactions. This has important implications as to how some marine organisms may respond to future ocean change and global mercury contamination.

Sample Preparation and Analytical Techniques in the Determination of Trace Elements in Food: A Review

Every human being needs around 20 essential elements to maintain proper physiological processes. However, trace elements are classified as beneficial, essential, or toxic for living organisms. Some trace elements are considered essential elements for the human body in adequate quantities (dietary reference intakes, DRIs), while others have undetermined biological functions and are considered undesirable substances or contaminants. Pollution with trace elements is becoming a great concern since they can affect biological functions or accumulate in organs, causing adverse effects and illnesses such as cancer. These pollutants are being discarded in our soils, waters, and the food supply chain due to several anthropogenic factors. This review mainly aims to provide a clear overview of the commonly used methods and techniques in the trace element analysis of food from sample preparations, namely, ashing techniques, separation/extraction methods, and analytical techniques. Ashing is the first step in trace element analysis. Dry ashing or wet digestion using strong acids at high pressure in closed vessels are used to eliminate the organic matter. Separation and pre-concentration of elements is usually needed before proceeding with the analytical techniques to eliminate the interferences and ameliorate the detection limits.

A novel peptide-based relay fluorescent probe with a large Stokes shift for detection of Hg2+ and S2- in 100 % aqueous medium and living cells: Visual detection via test strips and smartphone

Herein, a novel relay peptide-based fluorescent probe DGRK was synthesized via solid phase peptide synthesis (SPPS) technology. DGRK exhibited excellent water-solubility, good stability, remarkably large Stokes shift (230 nm) and high selectivity response to Hg²⁺ with a non-fluorescence complex DGRK-Hg²⁺ formation via a 1:1 binding mode. Further studies indicated that the DGRK-Hg²⁺ complex could act as a secondary probe for rapidly and sequentially detecting S^2- based on fluorescent "off-on" response, and without interference from a range of anions. The limit of detection (LOD) for Hg²⁺ and S^2- were calculated to be 33.6 nM and 60.9 nM, respectively. In addition, The reversibility of interaction of confirmed that the continuous and reversible recognition behavior of Hg²⁺ and S^2- by the probe DGRK, and could be cycled more than 5 times. In addition, DGRK could be successfully applied to the fluorescence imaging of Hg²⁺ and S^2- in two living cells based on excellent cells permeability and low cytotoxicity. Meanwhile, DGRK was successfully used to create the low-cost and portable test strips for visual detection and rapid analysis under 365 nm UV lamp, and the test strips combined with a smartphone (RGB color) was successfully applied to the semi-quantitative analysis and monitoring of dynamic changes of Hg²⁺ levels.

Evidence on Neurotoxicity after Intrauterine and Childhood Exposure to Organomercurials

Although the molecular mechanisms underlying methylmercury toxicity are not entirely understood, the observed neurotoxicity in early-life is attributed to the covalent binding of methylmercury to sulfhydryl (thiol) groups of proteins and other molecules being able to affect protein post-translational modifications from numerous molecular pathways, such as glutamate signaling, heat-shock chaperones and the antioxidant glutaredoxin/glutathione system. However, for other organomercurials such as ethylmercury or thimerosal, there is not much information available. Therefore, this review critically discusses current knowledge about organomercurials neurotoxicity-both methylmercury and ethylmercury-following intrauterine and childhood exposure, as well as the prospects and future needs for research in this area. Contrasting with the amount of epidemiological evidence available for methylmercury, there are only a few in vivo studies reporting neurotoxic outcomes and mechanisms of toxicity for ethylmercury or thimerosal. There is also a lack of studies on mechanistic approaches to better investigate the pathways involved in the potential neurotoxicity caused by both organomercurials. More impactful follow-up studies, especially following intrauterine and childhood exposure to ethylmercury, are necessary. Childhood vaccination is critically important for controlling infectious diseases; however, the safety of mercury-containing thimerosal and, notably, its effectiveness as preservative in vaccines are still under debate regarding its potential dose-response effects to the central nervous system.

Concomitant selenoenzyme inhibitor exposures as etiologic contributors to disease: Implications for preventative medicine

The physiological activities of selenium (Se) occur through enzymes that incorporate selenocysteine (Sec), a rare but important amino acid. The human genome includes 25 genes coding for Sec that employ it to catalyze challenging reactions. Selenoenzymes control thyroid hormones, calcium activities, immune responses, and perform other vital roles, but most are devoted to preventing and reversing oxidative damage. As the most potent intracellular nucleophile (pKa 5.2), Sec is vulnerable to binding by metallic and organic soft electrophiles (E*). These electron poor reactants initially form covalent bonds with nucleophiles such as cysteine (Cys) whose thiol (pKa 8.3) forms adducts which function as suicide substrates for selenoenzymes. These adducts orient E* to interact with Sec and since Se has a higher affinity for E* than sulfur, the E* transfers to Sec and irreversibly inhibits the enzyme's activity. Organic electrophiles have lower Se-binding affinities than metallic E*, but exposure sources are more abundant. Individuals with poor Se status are more vulnerable to the toxic effects of high E* exposures. The relative E*:Se stoichiometries remain undefined, but the aggregate effects of multiple E* exposures are predicted to be additive and possibly synergistic under certain conditions. The potential for the combined Se-binding effects of common pharmaceutical, dietary, or environmental E* require study, but even temporary loss of selenoenzyme activities would accentuate oxidative damage to tissues. As various degenerative diseases are associated with accumulating DNA damage, defining the effects of complementary E* exposures on selenoenzyme activities may enhance the ability of preventative medicine to support healthy aging.

In utero and lactational exposure to methylmercury elicits physical-chemical and morphological damages in the alveolar bone of offspring rats: The first toxicological findings

Methylmercury (MeHg) is the most common organic form of mercury (Hg) that humans are exposed and is considered an environmental pollutant. Several populations that live in endemic regions of MeHg exposure are subject to the toxicant for long periods, including pregnant women and children, causing damage to several organs during early periods of development. Alveolar bone is an essential structure for the oral cavity, responsible for supporting teeth and masticatory forces. However, evidence on the effects of MeHg on alveolar bone and the intrauterine and lactation period is lacking. Thus, this study aimed to investigate the effects of MeHg exposure during gestation and lactation on the developing alveolar bone of offspring rats after maternal exposure. Dams were exposed during 41 days of pregnancy and lactation, and the mandibles of the offspring were collected. The alveolar bone was analyzed by Fourier Transform Infrared Spectroscopy to evaluate the physicochemical composition; by Scanning Electron Microscopy for ultrastructural evaluation; by histopathological, histochemical, and morphometric for tissue analyses. In addition, bone quality was assessed by X-ray microtomography. MeHg exposure altered the mineral composition and caused histological damage associated with a lower quantity and thickness of bone trabeculae, as well as reduced osteocyte density and collagen fiber content. A reduction in trabecular thickness and bone volume and an increase in trabecular spaces were observed and were associated with anatomical compromise of the vertical bone dimensions. Thus, the results suggest that the developing alveolar bone is susceptible to the toxic effects of MeHg when organisms are exposed during intrauterine and lactation periods. From a translational perspective, these changes in the alveolar bone can help us understand possible abnormalities induced by toxic metals and highlight the need for care for structures other than those already seen as targets for damage triggered by environmental MeHg exposure.

RETRACTED: Carveol ameliorates mercury-induced oxidative stress, neuroinflammation, and neurodegeneration in a mouse brain

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editors-in-Chief. Sections of panels from Figure 7B appear similar to each other. Also, inconsistencies have been noticed between the text of the subsection 2.5.4. ‘Morris Water Maze (MWM) test’ and Figure 6E. The journal records indicated that the names of the authors Sajid Rashid, Nadia Hussain, Mehreen Gul, Muhammad Ikram and Jingbo Li were added to the revised version of the article without exceptional approval by the handling Editor, which is contrary to the journal policy on changes to authorship.

Breast milk contribution to tissue mercury levels in rat pups examined by cross-fostering at birth

The developing perinatal brain is vulnerable to methylmercury (MeHg) exposure. The contribution of breast milk to tissue MeHg levels in offspring is a significant public health concern because breast milk contains a certain amount of MeHg. Here, the contribution of MeHg transferred via breast milk to the Hg levels in the tissues of pups (Wistar rats) was investigated. Mated maternal rats were fed a MeHg (2 ppm)-supplemented or a control diet during pregnancy. Following parturition, male neonates from each group were cross-fostered between exposed or control dams, and they were further raised by dams fed a MeHg-supplemented diet or a control diet during lactation. Consequently, we evaluated three pup groups, which were raised by dams exposed to MeHg during pregnancy (P pups), lactation (L pups), or pregnancy and lactation (PL pups). Total mercury (THg) concentrations in the tissues of the offspring were measured at birth (postnatal day 0 [PD0]), during lactation (PD6, PD12, and PD19), and after weaning (PD29 and PD36). Blood and brain THg levels in the P and PL pups declined dramatically during lactation, however, there were no considerable differences between the two groups at PD6 and PD12. In contrast, blood and brain THg levels in the L pups increased slightly during lactation. The increase in the THg levels in the blood and brain of L pups at PD12 were approximately 3.3% and 1.5%, respectively, compared to the corresponding THg levels in the neonates in the P and PL groups. Our results suggest that if the MeHg exposure level during pregnancy is not high enough to cause neuronal development defects in the fetus, the exposure via breast milk is not a significant concern.

Concentrations of nucleophilic sulfur species in small Indian mongoose (Herpestes auropunctatus) in Okinawa, Japan

Reactive sulfur species (RSS), such as hydrogen per (poly)sulfide, cysteine per (poly)sulfide, glutathione per (poly)sulfide, and protein-bound per (poly)sulfides, can easily react with environmental electrophiles such as methylmercury (MeHg), because of their high nucleophilicity. These RSS are produced by enzymes such as cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) and are found in mammalian organs. Organs of wildlife have not been analyzed for hydrogen sulfide, cysteine, glutathione, and RSS. In this study, low molecular weight nucleophilic sulfur substances, including RSS, were quantified by stable isotope dilution assay-based liquid chromatography-mass spectrometry using β-(4-hydroxyphenyl)ethyl iodoacetamide to capture the target chemicals in the small Indian mongoose which species possesses high mercury content as same as some marine mammals. Western blotting revealed that the mongoose organs (liver, kidney, cerebrum, and cerebellum) contained proteins that cross-reacted with anti-CBS and CSE antibodies. The expression patterns of these enzymes were similar to those in mice, indicating that mongoose organs contain CBS and CSE. Moreover, bis-methylmercury sulfide (MeHg)₂S, which is a low toxic compound in comparison to MeHg, was found in the liver of this species. These results suggest that the small Indian mongoose produces RSS and monothiols associated with detoxification of electrophilic organomercury. The animals which have high mercury content in their bodies may have function of mercury detoxification involved not only Se but also RSS interactions.

Environmentally Toxic Solid Nanoparticles in Noradrenergic and Dopaminergic Nuclei and Cerebellum of Metropolitan Mexico City Children and Young Adults with Neural Quadruple Misfolded Protein Pathologies and High Exposures to Nano Particulate Matter

Quadruple aberrant hyperphosphorylated tau, beta-amyloid, α-synuclein and TDP-43 neuropathology and metal solid nanoparticles (NPs) are documented in the brains of children and young adults exposed to Metropolitan Mexico City (MMC) pollution. We investigated environmental NPs reaching noradrenergic and dopaminergic nuclei and the cerebellum and their associated ultrastructural alterations. Here, we identify NPs in the locus coeruleus (LC), substantia nigrae (SN) and cerebellum by transmission electron microscopy (TEM) and energy-dispersive X-ray spectrometry (EDX) in 197 samples from 179 MMC residents, aged 25.9 ± 9.2 years and seven older adults aged 63 ± 14.5 years. Fe, Ti, Hg, W, Al and Zn spherical and acicular NPs were identified in the SN, LC and cerebellar neural and vascular mitochondria, endoplasmic reticulum, Golgi, neuromelanin, heterochromatin and nuclear pore complexes (NPCs) along with early and progressive neurovascular damage and cerebellar endothelial erythrophagocytosis. Strikingly, FeNPs 4 ± 1 nm and Hg NPs 8 ± 2 nm were seen predominantly in the LC and SN. Nanoparticles could serve as a common denominator for misfolded proteins and could play a role in altering and obstructing NPCs. The NPs/carbon monoxide correlation is potentially useful for evaluating early neurodegeneration risk in urbanites. Early life NP exposures pose high risk to brains for development of lethal neurologic outcomes. NP emissions sources ought to be clearly recognized, regulated, and monitored; future generations are at stake.

Effects of inorganic mercury exposure in the alveolar bone of rats: an approach of qualitative and morphological aspects

BACKGROUND

In comparison to organic mercury (MeHg), the environmental inorganic mercury (IHg) can be found in some skin-lightening cosmestics were considered "harmless" for a long time. However, recent studies have shown that long-term exposure to low doses of IHg may affect biological systems. Therefore, this study investigated the effects of IHg long-term exposure to the alveolar bone of adult rats.

METHODS

Adult Wistar rats were distributed in control and HgCl₂ exposed (0.375 mg/kg/day). After 45 days, the rats were euthanized and both blood and hemimandibles were collected. Total blood Hg levels were measured and both inorganic and organic components of the alveolar bone were determined through XRD and ATR-FTIR. The microstructure of the alveolar bone was assessed by using micro-CT and the morphometric analysis was performed by using stereomicroscopy.

RESULTS

Alterations in the physicochemical components of the alveolar bone of exposed animals were observed. The bone changes represented a tissue reaction at the microstructural level, such as bone volume increase. However, no significant dimensional changes (bone height) were observed.

CONCLUSION

Exposure to IHg at this dose can promote microstructural changes and alteration in the organic and inorganic components in the alveolar bone.

Toxic metals and metalloids: Uptake, transport, detoxification, phytoremediation, and crop improvement for safer food

Agricultural soils are under threat of toxic metal/metalloid contamination from anthropogenic activities, leading to excessive accumulation of arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg) in food crops that poses significant risks to human health. Understanding how these toxic metals and their methylated species are taken up, translocated, and detoxified is prerequisite to developing strategies to limit their accumulation for safer food. Toxic metals are taken up and transported across different cellular compartments and plant tissues via various transporters for essential or beneficial nutrients, e.g. As by phosphate and silicon transporters, and Cd by manganese (Mn), zinc (Zn), and iron (Fe) transporters. These transport processes are subjected to interactions with nutrients and the regulation at the transcriptional and post-translational levels. Complexation with thiol-rich compounds, such as phytochelatins, and sequestration in the vacuoles are the common mechanisms for detoxification and for limiting their translocation. A number of genes involved in toxic metal uptake, transport, and detoxification have been identified, offering targets for genetic manipulation via gene editing or transgenic technologies. Natural variations in toxic metal accumulation exist within crop germplasm, and some of the quantitative trait loci underlying these variations have been cloned, paving the way for marker-assisted breeding of low metal accumulation crops. Using plants to extract and remove toxic metals from soil is also possible, but this phytoremediation approach requires metal hyperaccumulation for efficiency. Knowledge gaps and future research needs are also discussed.

From Molecules to Behavior in Long-Term Inorganic Mercury Intoxication: Unraveling Proteomic Features in Cerebellar Neurodegeneration of Rats

Mercury is a severe environmental pollutant with neurotoxic effects, especially when exposed for long periods. Although there are several evidences regarding mercury toxicity, little is known about inorganic mercury (IHg) species and cerebellum, one of the main targets of mercury associated with the neurological symptomatology of mercurial poisoning. Besides that, the global proteomic profile assessment is a valuable tool to screen possible biomarkers and elucidate molecular targets of mercury neurotoxicity; however, the literature is still scarce. Thus, this study aimed to investigate the effects of long-term exposure to IHg in adult rats’ cerebellum and explore the modulation of the cerebellar proteome associated with biochemical and functional outcomes, providing evidence, in a translational perspective, of new mercury toxicity targets and possible biomarkers. Fifty-four adult rats were exposed to 0.375 mg/kg of HgCl₂ or distilled water for 45 days using intragastric gavage. Then, the motor functions were evaluated by rotarod and inclined plane. The cerebellum was collected to quantify mercury levels, to assess the antioxidant activity against peroxyl radicals (ACAPs), the lipid peroxidation (LPO), the proteomic profile, the cell death nature by cytotoxicity and apoptosis, and the Purkinje cells density. The IHg exposure increased mercury levels in the cerebellum, reducing ACAP and increasing LPO. The proteomic approach revealed a total 419 proteins with different statuses of regulation, associated with different biological processes, such as synaptic signaling, energy metabolism and nervous system development, e.g., all these molecular changes are associated with increased cytotoxicity and apoptosis, with a neurodegenerative pattern on Purkinje cells layer and poor motor coordination and balance. In conclusion, all these findings feature a neurodegenerative process triggered by IHg in the cerebellum that culminated into motor functions deficits, which are associated with several molecular features and may be related to the clinical outcomes of people exposed to the toxicant.

Formation Mechanism and Toxicological Significance of Biogenic Mercury Selenide Nanoparticles in Human Hepatoma HepG2 Cells

It is widely recognized that the toxicity of mercury (Hg) is attenuated by the simultaneous administration of selenium (Se) compounds in various organisms. In this study, we revealed the mechanisms underlying the antagonistic effect of sodium selenite (Na₂SeO₃) on inorganic Hg (Hg²⁺) toxicity in human hepatoma HepG2 cells. Observations by transmission electron microscopy indicated that HgSe (tiemannite) granules of up to 100 nm in diameter were accumulated in lysosomal-like structures in the cells. The HgSe granules were composed of a number of HgSe nanoparticles, each measuring less than 10 nm in diameter. No accumulation of HgSe nanoparticles in lysosomes was observed in the cells exposed to chemically synthesized HgSe nanoparticles. This suggests that intracellular HgSe nanoparticles were biologically generated from Na₂SeO₃ and Hg²⁺ ions transported into the cells and were not derived from HgSe nanoparticles formed in the extracellular fluid. Approximately 85% of biogenic HgSe remained in the cells at 72 h post culturing, indicating that biogenic HgSe was hardly excreted from the cells. Moreover, the cytotoxicity of Hg²⁺ was ameliorated by the simultaneous exposure to Na₂SeO₃ even before the formation of insoluble HgSe nanoparticles. Our data confirmed for the first time that HepG2 cells can circumvent the toxicity of Hg²⁺ through the direct interaction of Hg²⁺ with a reduced form of Se (selenide) to form HgSe nanoparticles via a Hg-Se soluble complex in the cells. Biogenic HgSe nanoparticles are considered the ultimate metabolite in the Hg detoxification process.

Sexual dimorphism in inorganic mercury toxicokinetics and the attendant lipotoxic and non-lipotoxic dyslipidemia in the rat

The influence of variability in the biology of living organisms is poorly appreciated in toxicology. However, multiple lines of evidence indicate that sex-differences modulate toxicokinetics and toxicodynamics from cellular/molecular to whole animal levels resulting in different toxic responses of living organisms to xenobiotics exposure. In order to investigate the influence of sex in inorganic mercury (Hg) exposure, male and female Wistar rats were exposed to 0.5, 1.0 and 1.5 mg Hg/kg body weight orally as HgCl₂ twice a week for 12 weeks. Higher Hg levels in the females (except heart) as compared to males were observed in the animals. At the highest dose of inorganic Hg, female renal Hg content was 3.3 times higher than that of the males. Mixed sexual dimorphism characterised circulating-lipid- and organ-lipid lipotoxic and non-lipotoxic dyslipidemia. The highest dose of inorganic Hg, induced hypercholesterolemia in the males as opposed to hypocholesterolemia in the female. Plasma and erythrocyte free fatty acids increased in both sexes, although the increase was more pronounced in the male. Reverse cholesterol transport was inhibited in the male at the highest dose of Hg, whereas female HDL became enriched with cholesterol. Female erythrocytes had all their lipids increased, whereas only male erythrocyte triglyceride increased. Brain cholesterol and phospholipids, and splenic phospholipids were depleted in both sexes. Our findings indicate that inorganic Hg exposure appears to affect Hg and lipid kinetics differently in both sexes, thus underscoring the need to develop sex-tailored approaches in the treatment of metal toxicosis and its metabolic outcomes.

•

The influence of sex in inorganic Hg exposure was investigated in the rat.

•

Higher Hg levels in females compared to males were observed.

•

Sexual dimorphism characterised inorganic Hg-induced dyslipidemia.

•

Inorganic Hg exposure affects Hg and lipid kinetics differently in both sexes.

Developmental Toxicology of Metal Mixtures in Drosophila: Unique Properties of Potency and Interactions of Mercury Isoforms

Mercury ranks third on the U.S. Agency of Toxic Substances and Disease Registry priority list of hazardous substances, behind only arsenic and lead. We have undertaken uncovering the mechanisms underlying the developmental toxicity of methylmercury (MeHg), inorganic mercury (HgCl2), lead acetate (Pb), and sodium arsenite (As). To probe these differences, we used the Drosophila model, taking advantage of three developmental transitions-pupariation, metamorphosis, and eclosion-to differentiate potentially unique windows of toxicity. We elaborated dose response profiles for each individual metal administered in food and accounted for internal body burden, also extending analyses to evaluate combinatorial metal mixture effects. We observed all four metals producing larval lethality and delayed pupariation, with MeHg being most potent. Compared to other metals, MeHg's potency is caused by a higher body burden with respect to dose. MeHg uniquely caused dose-dependent failure in eclosion that was unexpectedly rescued by titrating in HgCl2. Our results highlight a unique developmental window and toxicokinetic properties where MeHg acts with specificity relative to HgCl2, Pb, and As. These findings will serve to refine future studies aimed at revealing tissue morphogenesis events and cell signaling pathways, potentially conserved in higher organisms, that selectively mediate MeHg toxicity and its antagonism by HgCl2.

C-phycoerythrin from Phormidium persicinum Prevents Acute Kidney Injury by Attenuating Oxidative and Endoplasmic Reticulum Stress

C-phycoerythrin (C-PE) is a phycobiliprotein that prevents oxidative stress and cell damage. The aim of this study was to evaluate whether C-PE also counteracts endoplasmic reticulum (ER) stress as a mechanism contributing to its nephroprotective activity. After C-PE was purified from Phormidium persicinum by using size exclusion chromatography, it was characterized by spectrometry and fluorometry. A mouse model of HgCl₂-induced acute kidney injury (AKI) was used to assess the effect of C-PE treatment (at 25, 50, or 100 mg/kg of body weight) on oxidative stress, the redox environment, and renal damage. ER stress was examined with the same model and C-PE treatment at 100 mg/kg. C-PE diminished oxidative stress and cell damage in a dose-dependent manner by impeding the decrease in expression of nephrin and podocin normally caused by mercury intoxication. It reduced ER stress by preventing the activation of the inositol-requiring enzyme-1α (IRE1α) pathway and avoiding caspase-mediated cell death, while leaving the expression of protein kinase RNA-like ER kinase (PERK) and activating transcription factor 6α (ATF6α) pathways unmodified. Hence, C-PE exhibited a nephroprotective effect on HgCl₂-induced AKI by reducing oxidative stress and ER stress.

The Antioxidant Effect of Medicago sativa L. (Alfalfa) Ethanolic Extract against Mercury Chloride (HgCl2) Toxicity in Rat Liver and Kidney: An In Vitro and In Vivo Study

Heavy metals such as mercury are some of the environmental pollutants and can induce toxicity by bioaccumulation and oxidative damage. This study aimed to investigate the effect of ethanolic extract of Medicago sativa L. (Alfalfa) on mercury damage in the kidney and liver of rats. Thirty Wistar rats were randomly divided into five groups, the control group, S group (2 mg/kg mercury chloride), and T1, T2, and T3 groups that, in addition to mercury, received doses of 250, 500, and 750 mg/kg of the alfalfa extract. On the last day, blood samples were taken, and the serum was separated to measure biochemical and oxidative stress parameters in the kidney and liver. A part of the kidney and liver was also used for histopathological evaluation. Total phenols and flavonoids were 40.45 ± 2.12 and 14.36 ± 0.45 mg/g, respectively, whereas IC₅₀ was 245.18 ± 19.76 μg/ml. The body weight significantly decreased in the S group compared to other groups, while treatment with different doses of alfalfa extract increased the body weight. Mercury concentration in the kidney was higher than that in the liver. The serum levels of urea, creatinine, alanine aminotransferase (ALT), and alkaline phosphatase (ALP) significantly increased in the S group compared to the control group, while treatment with different doses of alfalfa extract increased their levels. Moreover, an increase in malondialdehyde (MDA) and a decrease in glutathione peroxidase (GPx), catalase (CAT), total antioxidant capacity (TAC), and superoxide dismutase (SOD) activity were observed in the S group. The level of these parameters significantly improved in the groups receiving the extract compared to the S group. Furthermore, the histopathological evaluation showed glomerular and tubular damage and hepatic necrosis in the S group and that these conditions improved in the T3 group. The findings of this study showed that the ethanolic extract of alfalfa in a dose-dependent manner has potentially unique protective effects against mercury poisoning in the kidney and liver.

Cinnabar protects serum-nutrient starvation induced apoptosis by improving intracellular oxidative stress and inhibiting the expression of CHOP and PERK

Cinnabar has been used for treatment of various disorders for thousands of years. The medical use of cinnabar, however, has been controversial because of its heavy metal mercury content. A large quantity of studies indicate that the toxicity of cinnabar is far below other inorganic or organic mercury-containing compounds. Yet, the underlying molecular basis has remained unresolved. Here, we investigated the beneficial effects of cinnabar on serum-nutrient starvation-elicited cell injury. Our findings showed that treatment of human renal proximal tubular cells (HK-2) with 4 nM cinnabar effectively inhibited nutrient deprivation induced apoptosis, reduced intracellular reactive oxygen species generation and increased GSH content, which was contrary to the exacerbated apoptotic cell death and oxidative stress in cells treated with HgCl₂ at equal mercury concentration. In addition, cinnabar exerted robust antioxidative and antiapoptotic effects in cells under dual challenges of nutrient deprivation and treatment of H₂O₂. The protein expression levels of both CHOP and PERK were remarkably down-regulated in the cells treated with cinnabar compared to the control cells or cells treated with HgCl₂. Overall, our data indicates that cinnabar at low concentration exerts anti-oxidative stress and anti-apoptosis effects by inhibiting the expression of the endoplasmic reticulum stress pathway proteins CHOP and PERK.

Current and historical nephric and hepatic mercury concentrations in terrestrial mammals in Poland and other European countries

The long-term anthropogenic release of mercury (Hg) into the environment has led to contamination of the biosphere, with all forms of Hg showing toxic effects and the ability to accumulate in organisms. Since the 1970s, efforts have been made in Western Europe to reduce Hg emissions and for the economic use of Hg, leading to a reduction in Hg exposure to humans and entire ecosystems. The purpose of this research was to present the total mercury (THg) burden in three mustelids (the piscivorous Eurasian otter and American mink, and the invertebrativorous European badger) inhabiting north-western Poland (mostly floodplains) and other European countries (literature data). Moreover, we wanted to investigate whether reductions in the environmental Hg burden in Europe have resulted in reductions in liver and kidney levels in wild terrestrial mammals (Eurasian otter, wild boar, red deer, roe deer, cervids, leporids, rodents, and ecotrophic groups: piscivorous mustelids, non-mustelids whose diets include aquatic prey, canids and other carnivores, omnivores, herbivores), between samples collected before and after 2000. We revealed significantly higher nephric THg levels in roadkilled than in trapped American minks. As roadkilled piscivorous mustelids from the same floodplain had similar hepatic and nephric THg concentrations, we suggest that the European research on Hg ecotoxicology should more often use alien American mink instead of the protected Eurasian otter. Badgers inhabiting Polish and other European floodplains bioaccumulated higher amounts of THg than those from other areas, and as such, may be recommended as bioindicator of mercury soil contamination. Our analysis of abundant data on mammalian hepatic and nephric THg concentrations (excluding non-piscivores mustelids) showed that in 12 of 21 cases, Hg concentrations had dropped significantly since 2000. This data signals a reduction in Hg contamination in terrestrial mammals, such as the Eurasian otter, and may be reason for cautious optimism.

Interaction of mercury ion (Hg2+) with blood and cytotoxicity attenuation by serum albumin binding

Blood mercury reflects the amount available from tissues, which is an indication of the exposure level. Here we confirm that Hg²⁺ caused hemolytic effects at high concentrations; while at light concentrations, most of the ions were bound to human serum albumin (HSA). The binding mechanism of Hg²⁺ to HSA has been investigated, which indicated that the presence of Hg²⁺ significantly perturbed the structure of HSA and quenched the fluorescence of protein in a hybrid dynamic and static mode. Hg²⁺ was preferably bound to cysteine and cystine, where the R‒S‒S‒R structure is responsible for maintaining the protein's structure by stabilizing the α-helical bundles. The metal-protein interaction mitigated the cellular toxicity as concealed by A498 cell lines. The fundamental and comprehensive data in this work is beneficial to elucidating and understanding the identification and binding mechanisms of heavy metals with proteins, as well as possible risks on human beings and the environment.

Associations between exposure to heavy metals and the risk of chronic kidney disease: a systematic review and meta-analysis

We performed a systematic review and meta-analysis to examine the relationship between heavy metals (HMs) exposure and the risk of chronic kidney disease (CKD). Databases of Web of Science, Embase, MEDLINE, and Scopus were searched through June 2020 to identify studies assessing the relationships between exposure to HMs (i.e. cadmium, lead, arsenic, mercury) and the risk of CKD, evaluated by decreased estimated glomerular filtration rate (eGFR) and/or increased proteinuria risks in adults (≥18 years). Data were pooled by random-effects models and expressed as weighted mean differences and 95% confidence intervals. The risk of bias was assessed by the Newcastle-Ottawa scale (NOS). Twenty-eight eligible articles (n = 107,539 participants) were included. Unlike eGFR risk (p = 0.10), Cadmium exposure was associated with an increased proteinuria risk (OR = 1.35; 95% CI: 1.13, 1.61; p < 0.001; I² = 79.7%). Lead exposure was associated with decreased eGFR (OR = 1.12; 95%CI: 1.03, 1.22; p = 0.008; I² = 87.8%) and increased proteinuria (OR = 1.25; 95% CI: 1.04, 1.49; p = 0.02; I² = 79.6) risks. Further, arsenic exposure was linked to a decreased eGFR risk (OR = 1.55; 95% CI: 1.05, 2.28; p = 0.03; I² = 89.1%) in contrast to mercury exposure (p = 0.89). Only two studies reported the link between arsenic exposure and proteinuria risk, while no study reported the link between mercury exposure and proteinuria risk. Exposure to cadmium, lead, and arsenic may increase CKD risk in adults, albeit studies were heterogeneous, warranting further investigations. Our observations support the consideration of these associations for preventative, diagnostic, monitoring, and management practices of CKD.

Seafood and health: What you need to know?

Seafood, including fish and shellfish, provides an ideal package of nutrients and is an important part of a healthy diet. Strong evidence has shown that eating fish and other seafoods improve brain, eye, and heart health. The new 2020-2025 Dietary Guidelines for Americans (DGA) recommend that Americans of all ages should eat more seafood-at least twice a week-particularly pregnant women and young children. However, less than one in five Americans heed that advice. About one-third of Americans eat seafood once a week, while nearly half eat fish only occasionally or not at all. This calls for a drastic shift in the American diet to vary protein sources and include more seafood products in order to receive the most health benefits. This chapter covers (1) seafood nutrition and health benefits, (2) seafood's protective effects against mercury toxicity, (3) selenium health benefit values (HBVs), and (4) challenges and opportunities for seafood production, demand and sustainability. This chapter aims to convey recent advances in science-based information to increase public awareness of seafood safety, nutrition and health benefits of seafood as part of a healthy diet, and to advocate healthy eating with smart food choices by promoting two servings of seafood per week. This will support the healthy eating patterns and promotes a minimum two to three servings of seafood recommended by the current DGA.

Mercury interactions with selenium and sulfur and the relevance of the Se:Hg molar ratio to fish consumption advice

Eating fish is often recommended as part of a healthful diet. However, fish, particularly large predatory fish, can contain significant levels of the highly toxic methylmercury (MeHg). Ocean fish in general also contain high levels of selenium (Se), which is reported to confer protection against toxicity of various metals including mercury (Hg). Se and Hg have a high mutual binding affinity, and each can reduce the toxicity of the other. This is an evolving area of extensive research and controversy with variable results in the animal and epidemiologic literature. MeHg is toxic to many organ systems through high affinity for -SH (thiol) ligands on enzymes and microtubules. Hg toxicity also causes oxidative damage particularly to neurons in the brain. Hg is a potent and apparently irreversible inhibitor of the selenoenzymes, glutathione peroxidases (GPX), and thioredoxin reductases (TXNRD) that are important antioxidants, each with a selenocysteine (SeCys) at the active site. Hg binding to the SeCys inhibits these enzymes, accounting in part for the oxidative damage that is an important manifestation of Hg toxicity, particularly if there is not a pool of excess Se to synthesize new enzymes. A molar excess of Se reflected in an Se:Hg molar ratio > 1 is often invoked as evidence that the Hg content can be discounted. Some recent papers now suggest that if the Se:Hg molar ratio exceeds 1:1, the fish is safe and the mercury concentration can be ignored. Such papers suggested that the molar ratio rather than the Hg concentration should be emphasized in fish advisories. This paper examines some of the limitations of current understanding of the Se:Hg molar ratio in guiding fish consumption advice; Se is certainly an important part of the Hg toxicity story, but it is not the whole story. We examine how Hg toxicity relates also to thiol binding. We suggest that a 1:1 molar ratio cannot be relied on because not all of the Se in fish or in the fish eater is available to interact with Hg. Moreover, in some fish, Se levels are sufficiently high to warrant concern about Se toxicity.

Changes in mercury distribution and its body burden in delphinids affected by a morbillivirus infection: Evidences of methylmercury intoxication in Guiana dolphin

An unusual mortality event (UME) attributed to morbillivirus infection was identified in two Guiana dolphin populations from the Southeastern Brazilian coast. The aim of this study was to characterize total mercury (THg), methylmercury (MeHg) and selenium (Se) bioaccumulation and body burden in Guiana dolphins from Sepetiba Bay (RJ) collected before (n = 61) and during the UME (n = 20). Significantly lower Se concentrations were found in the livers of individuals collected during the UME (Mann-Whitney test; p = 0.03), probably due to impairment of the detoxification process in the liver. There were differences in THg and Se concentrations in the organs and tissues of individuals (Kruskal-Wallis test, p < 0.05), but not MeHg (Kruskal-Wallis test, p = 0.07). For THg, the liver showed the higher concentrations and differed among organs and tissues analyzed such as blubber (Tukey's test for unequal N; p = 0.003). For Se concentrations, the skin and kidney presented the higher concentrations and varied among other tissues/organs, like muscle (Tukey's test for unequal N; p = 0.02). Differences in body burdens were observed among specimens collected previously and during the UME probably due to the remobilization and transport of the muscle-stored MeHg to other tissues/organs. This abrupt input of MeHg into the bloodstream may cause serious health damage. Indeed, evidences of methylmercury intoxication was observed in Guiana dolphins in Sepetiba Bay. In conclusion, bioaccumulation patterns, the detoxification process and body burden were affected by morbillivirus.

Mercury isotopes of key tissues document mercury metabolic processes in seabirds

Seabirds accumulate significant amounts of mercury (Hg) due to their long-life span together with their medium to high trophic position in marine food webs. Hg speciation and Hg isotopic analyses of total Hg in different tissues (pectoral muscles, liver, brain, kidneys, blood and feathers) were assessed to investigate their detoxification mechanisms. Three species with contrasted ecological characteristics were studied: the Antarctic prion (zooplankton feeder), the white-chinned petrel (pelagic generalist consumer) and the southern giant petrel (scavenger on seabirds and marine mammals). The difference of mass-dependent fractionation (MDF, δ²⁰²Hg) values between liver and muscles (up to 0.94 ‰) in all three seabirds strongly suggests hepatic demethylation of the isotopically lighter methylmercury (MeHg) and subsequent redistribution of the isotopically heavier fraction of MeHg towards the muscles. Similarly, higher δ²⁰²Hg values in feathers (up to 1.88 ‰) relative to muscles and higher proportion of MeHg in feathers (94-97%) than muscles (30-70%) likely indicate potential MeHg demethylation in muscle and preferential excretion of MeHg (isotopically heavier) in the growing feathers during moult. The extents of these key detoxification processes were strongly dependent on the species-specific detoxification strategies and levels of dietary MeHg exposure. We also found higher mass-independent fractionation (MIF, Δ¹⁹⁹Hg) values in feathers relative to internal tissues, possibly due to different integration times of Hg exposure between permanently active organs and inert tissues as feathers. Hg isotope variations reported in this study show evidence of detoxification processes in seabirds and propose a powerful approach for deep investigation of the Hg metabolic processes in seabirds.

Total mercury levels in the muscle and liver of livestock and game animals in Poland, 2009-2018

The bioaccumulation of mercury (Hg) in the food chain may pose a threat to human health. The risk of dietary Hg intake is mostly caused by the consumption of fish and seafood, therefore the knowledge on the exposure from land animal products is limited. In our article, we summarized the results of analyses of Hg in muscle tissue and liver of different livestock and game animals obtained during ten years of official monitoring that was carried out in Poland from 2009 to 2018. The majority of the results in muscle tissue were below the limits of quantification (LOQs). The mean Hg concentrations in muscle tissue ranged from 0.6 to 5.6 μg kg^-1 of wet weight and the mean liver Hg concentrations were within the range of 0.8-16.4 μg kg^-1 of wet weight, with lowest levels in chickens and highest in wild boars. The results revealed decreasing trends in liver Hg in cattle and cervids over the years, which was congruous with decreasing emission of Hg in Europe. Our results showed that the consumption of meat and liver of livestock and game animals in Poland may be considered to be safe for human health, which was confirmed by the low number of noncompliant samples relative to the applicable legal limits, as well as by estimated dietary exposure.

Differential susceptibility of PC12 and BRL cells and the regulatory role of HIF-1α signaling pathway in response to acute methylmercury exposure under normoxia

Hypoxia-inducible factor 1 (HIF-1) is a critical nuclear transcription factor for adaptation to hypoxia; its regulatable subunit, HIF-1α, is a cytoprotective regulatory factor. We examined the effects of methylmercury (MeHg) in rat adrenal pheochromocytoma (PC12) cells and the rat hepatocyte cell line BRL. MeHg treatment led to time- and concentration-dependent toxicity in both lines with statistically significant cytotoxic effects at 5 μM and 10 μM in PC12 and BRL, respectively, at 0.5 h. HIF-1α protein levels were significantly decreased at 2.5 (PC12) and 5 (BRL) μM MeHg. Furthermore, MeHg reduced the protein levels of HIF-1α and its target genes (glucose transporter-1, vascular endothelial growth factor-A and erythropoietin). Overexpression of HIF-1α significantly attenuated MeHg-induced toxicity in both cell types. Notably, cobalt chloride, a pharmacological inducer of HIF-1α, significantly attenuated MeHg-induced toxicity in BRL but not PC12. In both cell lines, an inhibitor of prolyl hydroxylase, 3, 4-dihydroxybenzoic acid, and the proteasome inhibitor carbobenzoxy-L-leucyl-L-leucyl-L-leucinal(MG132), antagonized MeHg toxicity, while 2-methoxyestradiol, a HIF-1α inhibitor, significantly increased it. These data establish that: (a) neuron-like PC12 cells are more sensitive to MeHg than non-neuronal BRL cells; (b) HIF-1α plays a similar role in MeHg-induced toxicity in both cell lines; and (c) upregulation of HIF-1α offers general cytoprotection against MeHg toxicity in PC12 and BRL cell lines.

Methylmercury exposure during the vulnerable window of the cerebrum in postnatal developing rats

The developing brain is known to be sensitive to the toxic effects of methylmercury (MeHg). The effects of toxic levels of MeHg exposure during the most seemingly vulnerable window of the cerebrum are not well studied. In this study, we aimed to examine the specific effects of toxic levels of MeHg on neurobehavior, neurodegeneration, and selenoenzyme activity in the cerebrum of infant rats. Male Wistar rats (n = 8/group) were orally treated with MeHg at an acute toxic dose (8 mg Hg/kg/day) for 10 consecutive days starting on postnatal day 14 (P14). The MeHg-exposed rats showed a significant reduction in body weight after day 8 and severe neurological symptoms similar to dystonia on day 12 (P25). Motor coordination deficits determined using the rotarod performance test and short-term memory impairment determined using the Y-maze task were observed in the MeHg-exposed rats on day 11 (P24). The MeHg-exposed rats sacrificed on day 12 showed severe cerebral neuronal degeneration, reactive astrocytosis, and TUNEL-positive apoptotic nuclei, with the cerebral Hg concentration of 15.0 ± 1.6 μg/g. Furthermore, the activities of glutathione peroxidase and thioredoxin reductase in the cerebrum in MeHg-exposed rats were lower than those in control. These results indicate that MeHg exposure to infant rats will be useful to predict the effects of MeHg at the cerebral growth spurt in humans.

Transcriptomic and Proteomic Tools in the Study of Hg Toxicity: What Is Missing?

Mercury is a hazardous substance that has unique neurodevelopmental toxic effects in humans. However, the precise sequence of molecular events that culminate in Hg-induced neuropathology is still unknown. Though the omics studies have been generating an enormous amount of new data about Hg toxicity, our ability to interpret such a large quantity of information is still limited. In this opinion article, we will reinforce the necessity of new high throughput and accurate analytical proteomic methodologies, especially, thiol and selenol-proteome. Overall, we posit that improvements in thiol- and selenol-proteomic analyses will be pivotal in identifying the primary cellular targets of Hg. However, a better understanding of the complex cascades and molecular pathways involved in its toxicity will require extensive complementary studies in more complex systems.