Effects on and transfer across the blood-brain barrier in vitro-Comparison of organic and inorganic mercury species

Genome-Scale Screening of Saccharomyces cerevisiae Deletion Mutants to Gain Molecular Insight into Tolerance to Mercury Ions

Mercury (Hg) is a global pollutant and a bioaccumulative toxin that seriously affects the environment. Though increasing information has been obtained on the mechanisms involved in mercury toxicity, there is still a knowledge gap between the adverse effects and action mechanisms, especially at the molecular level. In the current study, we screened a diploid library of Saccharomyces cerevisiae single-gene deletion mutants to identify the nonessential genes associated with increased sensitivity to mercury ions. By genome-scale screening, we identified 64 yeast single-gene deletion mutants. These genes are involved in metabolism, transcription, antioxidant activity, cellular transport, transport facilitation, transport routes, and the cell cycle, as well as in protein synthesis, folding, modification, and protein destination. The concentration of mercury ions was different in the cells of yeast deletion mutants. Moreover, the disruption of antioxidant systems may play a key role in the mercurial toxic effects. The related functions of sensitive genes and signal pathways were further analyzed using bioinformatics-related technologies. Among 64 sensitive genes, 37 genes have human homologous analogs. Our results may provide a meaningful reference for understanding the action mode, cellular detoxification, and molecular regulation mechanisms of mercury toxicity.

Online monitoring of epithelial barrier kinetics and cell detachment during cisplatin-induced toxicity of renal proximal tubule cells

Real-time and non-invasive assessment of tissue health is crucial for maximizing the potential of microphysiological systems (MPS) for drug-induced nephrotoxicity screening. Although impedance has been widely considered as a measure of the barrier function, it has not been incorporated to detect cell detachment in MPS with top and bottom microfluidic channels separated by a porous membrane. During cell delamination from the porous membrane, the resistance between both channels decreases, while capacitance increases, allowing the detection of such detachment. Previously reported concepts have solely attributed the decrease in the resistance to the distortion of the barrier function, ignoring the resistance and capacitance changes due to cell detachment. Here, we report a two-channel MPS with integrated indium tin oxide (ITO) electrodes capable of measuring impedance in real time. The trans-epithelial electrical resistance (TEER) and tissue reactance (capacitance) were extracted from the impedance profiles. We attributed the anomalous initial increase observed in TEER, upon cisplatin administration, to the distortion of tight junctions. Cell detachment was captured by sudden jumps in capacitance. TEER profiles illuminated the effects of cisplatin and cimetidine treatments in a dose-dependent and polarity-dependent manner. The correspondence between TEER and barrier function was validated for a continuous tissue using the capacitance profiles. These results demonstrate that capacitance can be used as a real-time and non-invasive indicator of confluence and will support the accuracy of the drug-induced cytotoxicity assessed by TEER profiles in the two-channel MPS for the barrier function of a cell monolayer.

Neurotoxic effects of metals on blood brain barrier impairment and possible therapeutic approaches

Exposure to neurotoxic and heavy metals (Pb2+, As3+, Mn2+, Cd2+, etc) has increased over time and has shown to negatively affect brain health. Heavy metals can cross the blood brain barrier (BBB) in various ways including receptor or carrier-mediated transport, passive diffusion, or transport via gaps in the endothelial cells of the brain. In high concentrations, these metals have been shown to cause structural and functional impairment to the BBB, by inducing oxidative stress, ion dyshomeostasis, tight junction (TJ) loss, astrocyte/pericyte damage and interference of gap junctions. The structural and functional impairment of the BBB results in increased BBB permeability, which ultimately leads to accumulation of these heavy metals in the brain and their subsequent toxicity. As a result of these effects, heavy metals are correlated with various neurological disorders. The pathological effects of these heavy metals can be effectively mitigated via chelation. In addition, it is possible to treat the associated disorders by counteracting the molecular mechanisms associated with the brain and BBB impairment.

Health risk assessment for human mercury exposure from Cinnabaris-containing Baizi Yangxin Pills in healthy volunteers Po administration

BACKGROUND

Cinnabaris (α-HgS), a mineral traditional Chinese material medica, has been used in combination with other herbs manifesting some definite therapeutic effects for thousands of years. But the currently reported mercury poisoning incidents raised the doubts about the safety of Cinnabaris-containing traditional Chinese medicines (TCMs). Baizi Yangxin Pills (BZYXP) is a Cinnabaris-containing TCM widely used in clinical practice. This study evaluated the health risk of mercury exposure from BZYXP in healthy volunteers based on the total mercury and mercury species analysis of blood and urine after single and multiple doses of BZYXP.

METHODS

Blood pharmacokinetics and urinary excretion studies of mercury were compared between single (9 g, once daily) and multiple doses (9 g, twice daily, continued for 7 days) of BZYXP. The whole blood and urine samples were collected at the specific points or periods after the administration of BZYXP. The total mercury and mercury species in blood and urine samples were determined by cold vapor-atomic fluorescence spectrometry (CV-AFS) and HPLC-CV-AFS, respectively.

RESULTS

The mercury was excreted slowly and accumulated obviously after continuous exposure of BZYXP. Moreover, the well-known neurotoxin methylmercury (MeHg) was detected in blood samples after 7 days' administration of BZYXP. In the urine samples, only Hg(II) was detected. Therefore, long-term use of BZYXP will cause mercury poisoning due to mercury's high accumulative properties and MeHg formation.

CONCLUSION

Cinnabaris-containing TCMs such as BZYXP should be restricted to cases in which alternatives are available, and the blood mercury species profile should be monitored during the long-term clinical medication.

Structural Impact of Steroidal Glycoalkaloids: Barrier Integrity, Permeability, Metabolism, and Uptake in Intestinal Cells

SCOPE

Potato tubers represent an essential food component all over the world and an important supplier of carbohydrates, fiber, and valuable proteins. However, besides their health promoting effects, potatoes contain α-solanine and α-chaconine, which are toxic steroidal glycoalkaloids (SGAs). Other solanaceous plants like eggplants and tomatoes produce SGAs as well, different in their chemical structure. This study aims to investigate toxic effects (cholinesterase inhibition, membrane, and barrier disruption), permeability, metabolism, and structure-activity relationships of SGAs.

METHODS AND RESULTS

α-solanine, α-chaconine, α-solasonine, α-solamargine, α-tomatine, and their respective aglycones solanidine, solasodine, and tomatidine are analyzed using Ellman assay, cellular impedance spectroscopy, cell extraction, and Caco-2 intestinal model. Additionally, metabolism is analyzed by HPLC-MS techniques. The study observes dependencies of barrier disrupting potential and cellular uptake on the carbohydrate moiety of SGAs, while permeability and acetylcholinesterase (AChE) inhibition are dominated by the steroid backbone. SGAs show low permeabilities across Caco-2 monolayers in subtoxic concentrations. In contrast, their respective aglycones reveal higher permeabilities, but are extensively metabolized.

CONCLUSION

Besides structure-activity relationships, this study provides new information on the overall effects of steroidal alkaloids on intestinal cells and closes a gap of knowledge for the metabolic pathway from oral uptake to final excretion.

Recapitulation of Structure-Function-Regulation of Blood-Brain Barrier under (Patho)Physiological Conditions

The blood-brain barrier (BBB) is a remarkable and intricate barrier that controls the exchange of molecules between the bloodstream and the brain. Its role in maintaining the stability of the central nervous system cannot be overstated. Over the years, advancements in neuroscience and technology have enabled us to delve into the cellular and molecular components of the BBB, as well as its regulation. Yet, there is a scarcity of comprehensive reviews that follow a logical framework of structure-function-regulation, particularly focusing on the nuances of BBB regulation under both normal and pathological conditions. This review sets out to address this gap by taking a historical perspective on the discovery of the BBB and highlighting the major observations that led to its recognition as a distinct brain barrier. It explores the intricate cellular elements contributing to the formation of the BBB, including endothelial cells, pericytes, astrocytes, and neurons, emphasizing their collective role in upholding the integrity and functionality of the BBB. Furthermore, the review delves into the dynamic regulation of the BBB in physiological states, encompassing neural, humoral, and auto-regulatory mechanisms. By shedding light on these regulatory processes, a deeper understanding of the BBB's response to various physiological cues emerges. This review also investigates the disruption of the BBB integrity under diverse pathological conditions, such as ischemia, infection, and toxin exposure. It elucidates the underlying mechanisms that contribute to BBB dysfunction and explores potential therapeutic strategies that aim to restore the BBB integrity and function. Overall, this recapitulation provides valuable insights into the structure, functions, and regulation of the BBB. By integrating historical perspectives, cellular elements, regulatory mechanisms, and pathological implications, this review contributes to a more comprehensive understanding of the BBB and paves the way for future research and therapeutic interventions.

Spodium Bonds Involving Methylmercury and Ethylmercury in Proteins: Insights from X-ray Analysis and Computations

In this study, the stability, directionality, and physical nature of Spodium bonds (SpBs, an attractive noncovalent force involving elements from group 12 and Lewis bases) between methylmercury (MeHg) and ethylmercury (EtHg) and amino acids (AAs) have been analyzed from both a structural (X-ray analysis) and theoretical (RI-MP2/def2-TZVP level of theory) point of view. More in detail, an inspection of the Protein Data Bank (PDB) reported evidence of noncovalent contacts between MeHg and EtHg molecules and electron-rich atoms (e.g., O atoms belonging to the protein backbone and S atoms from MET residues or the π-systems of aromatic AAs such as TYR or TRP). These results were rationalized through a computational study using MeHg coordinated to a thiolate group as a theoretical model and several neutral and charged electron-rich molecules (e.g., benzene, formamide, or chloride). The physical nature of the interaction was analyzed from electrostatics and orbital perspectives by performing molecular electrostatic potential (MEP) and natural bonding orbital (NBO) analyses. Lastly, the noncovalent interactions plot (NCIplot) technique was used to provide a qualitative view of the strength of the Hg SpBs and compare them to other ancillary interactions present in these systems as well as to shed light on the extension of the interaction in real space. We believe that the results derived from our study will be useful to those scientists devoted to protein engineering and bioinorganic chemistry as well as to expanding the current knowledge of SpBs among the chemical biology community.

Blood-cerebrospinal fluid barrier permeability of metals/metalloids and its determinants in pediatric patients

Concerns regarding adverse effects of metal/metalloids exposure on brain development and neurological disorders among children are increasing. However, the transport patterns of metals/metalloids across the blood-cerebrospinal fluid barrier (BCSFB) need to be clarified in children. A total of 99 Chinese pediatric patients were enrolled from February 2020 to August 2021, with a median age of 6.76 months. We detected 16 metal/metalloid levels in matched serum and cerebrospinal fluid (CSF) samples using inductively coupled plasma mass spectrometry. The BCSFB permeability of metals/metalloids were estimated and the potential effects of biomedical parameters were explored. Most metals/metalloids were detectable among > 80.0% of CSF samples. Significant correlations were observed between strontium (Sr, r = 0.46), molybdenum (Mo, r = 0.50), and cadmium (Cd, r = 0.24) concentrations in serum and CSF (P < 0.05). Ratios of metal/metalloid levels in CSF to serum (Rmetal) ranged from 0.02 to 0.74, and hazardous metals/metalloids including arsenic (As), Cd, lead (Pb), thallium (Tl), and manganese (Mn) showed high transfer efficiencies across the BCSFB (Rmetals > 0.5). With the adjustment of age and sex, albumin, β2-microglobulin, and total protein levels in CSF were positively associated with copper (Cu) permeability (FDR-adjusted P < 0.05), while glucose in CSF was negatively correlated with calcium (Ca), Cu, Sr, and Mo BCSFB permeability (FDR-adjusted P < 0.05). Q-Alb promoted Cu permeability across the BCSFB (FDR-adjusted P < 0.001), while C-reactive protein levels in serum were positively associated with selenium (Se) permeability (FDR-adjusted P = 0.046). For the first time, our findings provided data for the BCSFB permeability of 16 metals/metalloids in children, and indicated that some biomedical parameters could influence the transformation of metals/metalloids from serum to CSF. Metals/metalloids with strong BCSFB permeability warrant attention for their potential neurotoxicity.

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 comprehensive review on bio-stimulation and bio-enhancement towards remediation of heavy metals degeneration

Pollution of heavy metals is one of the risky contaminations that should be managed for all intents and purposes of general well-being concerns. The bioaccumulation of these heavy metals inside our bodies and pecking orders will influence our people in the future. Bioremediation is a bio-mechanism where residing organic entities use and reuse the squanders that are reused to one more form. This could be accomplished by taking advantage of the property of explicit biomolecules or biomass that is equipped for restricting by concentrating the necessary heavy metal particles. The microorganisms can't obliterate the metal yet can change it into a less harmful substance. In this unique circumstance, this review talks about the sources, poisonousness, impacts, and bioremediation strategies of five heavy metals: lead, mercury, arsenic, chromium, and manganese. The concentrations here are the ordinary strategies for bioremediation such as biosorption methods, the use of microbes, green growth, and organisms, etc. This review demonstrates the toxicity of heavy metal contamination degradation by biotransformation through bacterioremediation and biodegradation through mycoremediation.

Thioredoxin Reductase Inhibitors as Potential Antitumors: Mercury Compounds Efficacy in Glioma Cells

Glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, like many other tumors, expresses high levels of redox proteins, such as thioredoxin (Trx) and thioredoxin reductase (TrxR), allowing tumor cells to cope with high levels of reactive oxygen species (ROS) and resist chemotherapy and radiotherapy. Thus, tackling the activity of these enzymes is a strategy to reduce cell viability and proliferation and most importantly achieve tumor cell death. Mercury (Hg) compounds are among the most effective inhibitors of TrxR and Trx due to their high affinity for binding thiols and selenols. Moreover, organomercurials such as thimerosal, have a history of clinical use in humans. Thimerosal effectively crosses the blood–brain barrier (BBB), thus reaching effective concentrations for the treatment of GBM. Therefore, this study evaluated the effects of thimerosal (TmHg) and its metabolite ethylmercury (EtHg) over the mouse glioma cell line (GL261), namely, the inhibition of the thioredoxin system and the occurrence of oxidative cellular stress. The results showed that both TmHg and EtHg increased oxidative events and triggered cell death primarily by apoptosis, leading to a significant reduction in GL261 cell viability. Moreover, the cytotoxicity of TmHg and ETHg in GL261 was significantly higher when compared to temozolomide (TMZ). These results indicate that EtHg and TmHg have the potential to be used in GBM therapy since they strongly reduce the redox capability of tumor cells at exceedingly low exposure levels.

Comprehensive Review Regarding Mercury Poisoning and Its Complex Involvement in Alzheimer's Disease

Mercury (Hg) is considered one of the most widespread toxic environmental pollutants, which seems to have multiple effects on organisms even at low concentrations. It has a critical role in many health problems with harmful consequences, with Hg primarily targeting the brain and its components, such as the central nervous system (CNS). Hg exposure was associated with numerous CNS disorders that frequently trigger Alzheimer's disease (AD). Patients with AD have higher concentrations of Hg in blood and brain tissue. This paper aims to emphasize a correlation between Hg and AD based on the known literature in the occupational field. The outcome shows that all these concerning elements could get attributed to Hg. However, recent studies did not investigate the molecular level of Hg exposure in AD. The present review highlights the interactions between Hg and AD in neuronal degenerations, apoptosis, autophagy, oxidative stress (OS), mitochondrial malfunctions, gastrointestinal (GI) microflora, infertility and altering gene expression.

Bioremediation: An effective approach of mercury removal from the aqueous solutions

Mercury (Hg(II)) is the 16th rarest element present in the earth's crust. Due to rapid industrialization and urban expansions, the mercury concentration has been elevated in the environment. Hg(II) contamination in the aqueous environment has become a great challenge for human beings. The main source of Hg(II) in the aqueous phase is untreated effluent industries (such as the paper industry). Hg(II) is non-biodegradable in nature and even its trace amount in an aqueous environment can pose chronic threats among the humans (damage to the central nervous system, respiratory system, and cardiovascular system, mutation of DNA), animals, and aquatic creatures. Therefore, the removal of mercury from aqueous solutions is an urgent need of the modern era. The conventional techniques such as ion exchange, precipitation, membrane filtrations are costly and also generate byproducts in the environment. Bioremediation is a sustainable, environmentally sound, and cost-effective technique to remove Hg(II) from the aqueous solutions. In this process, naturally occurring microorganisms are utilized to remove the Hg(II) from the aqueous solutions. Lentinus edodes, U. lactuca, and Typha domingensis are found to have great potential to remove mercury from water ranged from ~100 mg g^-1 to 337 mg g^-1.

Mechanisms of oxidative stress in methylmercury-induced neurodevelopmental toxicity

Methylmercury (MeHg) is a long-lasting organic environmental pollutant that poses a great threat to human health. Ingestion of seafood containing MeHg is the most important way by which it comes into contact with human body, where the central nervous system (CNS) is the primary target of MeHg toxicity. During periods of pre-plus postnatal, in particular, the brain of offspring is vulnerable to specific developmental insults that result in abnormal neurobehavioral development, even without symptoms in mothers. While many studies on neurotoxic effects of MeHg on the developing brain have been conducted, the mechanisms of oxidative stress in MeHg-induced neurodevelopmental toxicity is less clear. Hitherto, no single process can explain the many effects observed in MeHg-induced neurodevelopmental toxicity. This review summarizes the possible mechanisms of oxidative stress in MeHg-induced neurodevelopmental toxicity, highlighting modulation of Nrf2/Keap1/Notch1, PI3K/AKT, and PKC/MAPK molecular pathways as well as some preventive drugs, and thus contributes to the discovery of endogenous and exogenous molecules that can counteract MeHg-induced neurodevelopmental toxicity.

Capabilities of selenoneine to cross the in vitro blood-brain barrier model

The naturally occurring selenoneine (SeN), the selenium analogue of the sulfur-containing antioxidant ergothioneine, can be found in high abundance in several marine fish species. However, data on biological properties of SeN and its relevance for human health are still scarce. This study aims to investigate the transfer and presystemic metabolism of SeN in a well-established in vitro model of the blood-brain barrier (BBB). Therefore, SeN and the reference Se species selenite and Se-methylselenocysteine (MeSeCys) were applied to primary porcine brain capillary endothelial cells (PBCECs). Se content of culture media and cell lysates was measured via ICP-MS/MS. Speciation analysis was conducted by HPLC-ICP-MS. Barrier integrity was shown to be unaffected during transfer experiments. SeN demonstrated the lowest transfer rates and permeability coefficient (6.7 × 10-7 cm s-1) in comparison to selenite and MeSeCys. No side-directed accumulation was observed after both-sided application of SeN. However, concentration-dependent transfer of SeN indicated possible presence of transporters on both sides of the barrier. Speciation analysis demonstrated no methylation of SeN by the PBCECs. Several derivatives of SeN detected in the media of the BBB model were also found in cell-free media containing SeN and hence not considered to be true metabolites of the PBCECs. In concluding, SeN is likely to have a slow transfer rate to the brain and not being metabolized by the brain endothelial cells. Since this study demonstrates that SeN may reach the brain tissue, further studies are needed to investigate possible health-promoting effects of SeN in humans.

Cell barrier characterization in transwell inserts by electrical impedance spectroscopy

We describe an impedance-based method for cell barrier integrity testing. A four-electrode electrical impedance spectroscopy (EIS) setup can be realized by simply connecting a commercial chopstick-like electrode (STX-1) to a potentiostat allowing monitoring cell barriers cultivated in transwell inserts. Subsequent electric circuit modeling of the electrical impedance results the capacitive properties of the barrier next to the well-known transepithelial electrical resistance (TEER). The versatility of the new method was analyzed by the EIS analysis of a Caco-2 monolayer in response to (a) different membrane coating materials, (b) two different permeability enhancers ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) and saponin, and (c) sonoporation. For the different membrane coating materials, the TEERs of the standard and new protocol coincide and increase during cultivation, while the capacitance shows a distinct maximum for three different surface materials (no coating, Matrigel®, and collagen I). The permeability enhancers cause a decline in the TEER value, but only saponin alters the capacitance of the cell layer by two orders of magnitude. Hence, cell layer capacitance and TEER represent two independent properties characterizing the monolayer. The use of commercial chopstick-like electrodes to access the impedance of a barrier cultivated in transwell inserts enables remarkable insight into the behavior of the cellular barrier with no extra work for the researcher. This simple method could evolve into a standard protocol used in cell barrier research.

Toxicity and risk assessment of mercury exposures from cinnabar and Baizi Yangxin Pills based on pharmacokinetic and tissue distribution studies

ETHNOPHARMACOLOGICAL RELEVANCE

Baizi Yangxin Pills (BZYXP), a popular cinnabar (α-HgS) contained Traditional Chinese Medicines (TCMs) is widely used in clinical trials. However, mercury is one of the most toxic elements. The adverse effects of cinnabar-containing TCMs have been occasionally reported in recent years, leading to the growing concerns about their toxicity and safety.

AIM OF THE STUDY

The health risks of BZYXP and cinnabar related to the mercury exposures were evaluated through blood pharmacokinetic and tissue distribution studies in rats.

MATERIALS AND METHODS

The distribution of absorbed mercury in rats' blood and tissues were measured by the developed cold-vapor atomic fluorescence spectrometric method. And the tissue damages were determined through the histopathological examinations. For single dose study, the low and high oral doses were equivalent to 1 and 10-fold therapeutic dose, respectively. The multiple doses study was conducted at low and high dose levels every 12 h for 30 consecutive days.

RESULTS

Significant differences of mercury blood pharmacokinetic and tissue distribution characteristics were observed between the corresponding BZYXP and cinnabar groups. The herbal ingredients in BZYXP promoted the absorption of bio-accessible mercury of cinnabar and prolonged the elimination process, posing potential health risks. Although mercury was found easily accumulated in kidney, liver and brain tissues, kidney and liver didn't show obvious damages even after 30 days consecutive administration of BZYXP or cinnabar at 10-fold clinically equivalent doses. But brain did show some histopathological changes, and autonomic activities of rats decreased, pointing the potential neurotoxicity.

CONCLUSIONS

Mercury tend to be accumulated especially when over-dose or prolonged medication with cinnabar-containing TCMs are given. The mercury exposures even at therapeutic doses of BZYXP or cinnabar do pose health risks from the neurotoxicity point of view.

Deleterious effects of chronic mercury exposure on in vitro LTP, memory process, and oxidative stress

Heavy metal contamination in aquatic environments plays an important role in the exposure of humans to these toxicants. Among these pollutants, mercury (Hg) is one main concern due to its high neurotoxicity and environmental persistence. Even in low concentrations, Hg bioaccumulation is a major threat to human health, with higher impact on populations whose diet has fish as chief consumption. Mercury compounds have high affinity for neuronal receptors and proteins, which gives Hg its cumulative feature and have the ability to cross cell membranes and blood-brain barrier to show their neurotoxicity. Intoxication with Hg increases levels of reactive oxygen species (ROS), thus depleting faster the resource of antioxidant proteins. To evaluate Hg-induced hippocampal ROS production, synaptic plasticity, anxiety, and memory, a total of 11 male Wistar rats were exposed to HgCl₂ (Hg₃₀ group) to produce a residual concentration of 8 ng/mL at the end of 30 days. Behavioral tests (plus-maze discriminative avoidance task), in vitro electrophysiology, and ROS assays were performed. Western blot assay showed decreased levels of antioxidant proteins GPx and SOD in Hg₃₀ group. Increased ROS production was observed in the CA1 and CA3 regions in the Hg-exposed group. Plus-maze task detected long-term memory impairment in Hg₃₀ group, linked to poorer in vitro long-term potentiation as compared to control group. Hg intoxication also promoted higher anxiety-like behavior in the exposed animals. In conclusion, our data suggests that low doses of HgCl₂ resulted in impaired long-term memory and unbalance between decreased antioxidant protein expression and increased ROS production in the hippocampus.

Examining the evidence that ethylmercury crosses the blood-brain barrier

Scientific research can provide us with factual, repeatable, measurable, and determinable results. As such, scientific research can provide information that can be used in the decision-making process in the care of patients and in public policy. Although it has been suggested that ethylmercury (C₂H₅Hg⁺)-containing compounds do not cross the blood-brain barrier (BBB), this review examines the literature that addresses the question as to whether ethylmercury-containing compounds cross the BBB. The review will begin with cellular studies that provide evidence for the passive and active transport of mercury species across the BBB. Then, animal and clinical studies will be presented that specifically examine whether mercury accumulates in the brain after exposure to ethylmercury-containing compounds or Thimerosal (an ethylmercury-containing compound used as a preservative in vaccines and other drugs that metabolizes or degrades to ethylmercury-containing compounds and thiosalicylate). The results indicate that ethylmercury-containing compounds are actively transported across membranes by the L (leucine-preferring)-amino acid transport (LAT) system, the same as methylmercury-containing compounds. Further, 22 studies from 1971 to 2019 show that exposure to ethylmercury-containing compounds (intravenously, intraperitoneally, topically, subcutaneously, intramuscularly, or intranasally administered) results in accumulation of mercury in the brain. In total, these studies indicate that ethylmercury-containing compounds and Thimerosal readily cross the BBB, convert, for the most part, to highly toxic inorganic mercury-containing compounds, which significantly and persistently bind to tissues in the brain, even in the absence of concurrent detectable blood mercury levels.

Mercury Accumulation and Effects in the Brain of the Atlantic Sharpnose Shark (Rhizoprionodon terraenovae)

Few published studies have examined whether the elevated concentrations of the nonessential toxic metal mercury (Hg) often observed in shark muscle also occur in the shark brain or whether Hg accumulation affects shark neurophysiology. Therefore, this study examined accumulation and distribution of Hg in the shark brain, as well as effects of Hg on oxidative stress in the shark central nervous system, with particular focus on the Atlantic sharpnose shark (Rhizoprionodon terraenovae). Sharks were collected along the southeastern U.S. coast throughout most of this species' U.S. geographical range. Total Hg (THg) concentrations were measured in and compared between shark muscle and brain, whereas known biomarkers of Hg-induced neurological effects, including glutathione depletion, lipid peroxidation, and concentrations of a protein marker of glial cell damage (S100b), were measured in shark cerebrospinal fluid. Brain THg concentrations were correlated with muscle THg levels but were significantly lower and did not exceed most published thresholds for neurological effects, suggesting limited potential for detrimental responses. Biomarker concentrations supported this premise, because these data were not correlated with brain THg levels. Hg speciation also was examined. Unlike muscle, methylmercury (MeHg) did not comprise a high percentage of THg in the brain, suggesting that differential uptake or loss of organic and inorganic Hg and/or demethylation of MeHg may occur in this organ. Although Hg accumulation in the shark brain generally fell below toxicity thresholds, higher THg levels were measured in the shark forebrain compared with the midbrain and hindbrain. Therefore, there is potential for selective effects on certain aspects of shark neurophysiology if brain Hg accumulation is increased.

Vascular Dysfunction Induced by Mercury Exposure

Methylmercury (MeHg) causes severe damage to the central nervous system, and there is increasing evidence of the association between MeHg exposure and vascular dysfunction, hemorrhage, and edema in the brain, but not in other organs of patients with acute MeHg intoxication. These observations suggest that MeHg possibly causes blood-brain barrier (BBB) damage. MeHg penetrates the BBB into the brain parenchyma via active transport systems, mainly the l-type amino acid transporter 1, on endothelial cell membranes. Recently, exposure to mercury has significantly increased. Numerous reports suggest that long-term low-level MeHg exposure can impair endothelial function and increase the risks of cardiovascular disease. The most widely reported mechanism of MeHg toxicity is oxidative stress and related pathways, such as neuroinflammation. BBB dysfunction has been suggested by both in vitro and in vivo models of MeHg intoxication. Therapy targeted at both maintaining the BBB and suppressing oxidative stress may represent a promising therapeutic strategy for MeHg intoxication. This paper reviews studies on the relationship between MeHg exposure and vascular dysfunction, with a special emphasis on the BBB.

Organ-specific differences in mercury speciation and accumulation across ringed seal (Phoca hispida) life stages

Methylmercury (MeHg) is a central nervous system toxicant and exposures can adversely affect the health of marine mammals. Mercuric selenide (HgSe) in marine mammal tissues is hypothesized to result from a protective detoxification mechanism, but toxicokinetic processes contributing to its formation are poorly understood. Here, new data is reported on speciated Hg concentrations in multiple organs of n = 56 ringed seals (Phoca hispida) from Labrador, Canada, and compare concentrations to previously published data from Greenland seals. A higher proportion of Hg is found to accumulate in the kidney of young-of-the-year (YOY) ringed seals compared to adults. A toxicokinetic model for Hg species is developed and evaluated to better understand factors affecting variability in Hg concentrations among organs and across life stages. Prior work postulated that HgSe formation only occurs in the liver of mature seals, but model results suggest HgSe formation occurs across all life stages. Higher proportions of HgSe in mature seal livers compared to YOY seals likely results from the slow accumulation and elimination of HgSe (total body half-life = 500 days) compared to other Hg species. HgSe formation in the liver reduces modeled blood concentrations of MeHg by only 6%. Thus, HgSe formation may not substantially reduce MeHg transport across the blood-brain barrier of ringed seals, leaving them susceptible to the neurotoxic effects of MeHg exposure.

Consolidating probiotic with dandelion, coriander and date palm seeds extracts against mercury neurotoxicity and for maintaining normal testosterone levels in male rats

Objective

Heavy metals are major elements polluting our universe. The inhalation, ingestion or even contacting human body with these elements results in huge health problems. The most common pollutant in our surrounding is mercury. Therefore, the present study aimed to elucidating the protective ability of hot water extracts of dandelion (DA), coriander (CO), date palm seeds (DS), probiotic supernatant (PS) and their combined mixture against mercury-induced neurotoxicity and altered testosterone levels in male rats.

Methods

Fifty six male rats were randomly allotted into seven groups (n = 8 rats/group). Group1 (negative control; NC) animals were fed on the basal diet only, group2 (positive controls; PC) animals were fed on the basal diet and given an aqueous solution of mercuric chloride (25 ppm mercuric) in drinking water. Animals of the antioxidant-treated groups (3–7) were fed on the basal diet and given an aqueous solution of mercuric chloride (25 ppm mercuric) in drinking water together with the herbal antioxidant extracts and probiotics (25 ml/rat/day) throughout the experimental period. Where, group3 (Hg/CO) given coriander extract, group4 (Hg/DA) given dandelion extract, group5 (Hg/DS) given date palm seeds extract, group6 (Hg/PS) given probiotic supernatant, and group7 (Hg/Mix) given mixture of equal quantities of probiotic supernatant together with the three herbal extracts. The treatment lasted for 6 weeks, animals were sacrificed and blood samples were collected. Blood testosterone, enzyme activity and histopathological sections were performed.

Results

The obtained data exhibited that mercury intoxication revealed increases of lactic dehydrogenase and decreases of glutathione-s-transferase and testosterone. Light microscopic investigations of the brain cortex and cerebellum were suggestive of multiple foci of inflammation, cellular infiltration, gliosis and degeneration. Moreover, decreased glial fibrillary acidic protein (GFAP)-immunoreactivity and potential astrocyte toxicity both reflected impaired neuro-protective function of astrocytes necessary for maintaining the brain structure and function.

Conclusion

Administration of the herbal extracts and their mixture with probiotics enhance the body defense and contain protective factor against mercury neurotoxicity and for maintaining normal testosterone levels in male rats. Also, treatment restored the normal control levels of biochemical attributes and histological architecture.

Impact of glutamine on the effect of neopterin in methyl mercury-exposed neurons

Exposure to methyl mercury (MeHg), induces blood-brain barrier damage leading to non-selective influx of cytotoxic agents, besides the entrance of inflammatory cells into the brain. However, there is no data available regarding the effects of co-treatment of neopterin and interferon-gamma (IFN-gamma) in MeHgexposed SH-SY5Y dopaminergic neurons. MeHg-exposed SH-SY5Y human neuroblastoma cells were treated with neopterin and IFN-gamma in the presence and absence of L-Glutamine. Cell viability was determined by MTT assay. Oxidative stress intensity coefficient was calculated by taking into consideration the amount of nitric oxide production per viable neuron. 5μM MeHg was found to be more toxic than 1μM or 2μM doses of MeHg for SH-SY5Y cells in glutamine-containing medium. Furthermore, 0.1μM neopterin supplementation significantly increased the neuronal cell viability while, oxidative stress significantly decreased. Glutamine supplementation in culture medium, not only enhanced the MeHg toxicity, but also supported the antioxidant effect of neopterin. These results indicate that neopterin has a protective effect on MeHg toxicity in SH-SY5Y neurons. Neopterin was more effective in improving the total mitochondrial metabolic activity of cells exposed to 5μM MeHg in comparison to IFN-gamma. Although IFN-gamma supplementation alone partially improved 5μM MeHg toxicity on neurons, it weakened the protective effect of neopterin.

Arsenic-containing hydrocarbons disrupt a model in vitro blood-cerebrospinal fluid barrier

Lipid-soluble arsenicals, so-called arsenolipids, have gained a lot of attention in the last few years because of their presence in many seafoods and reports showing substantial cytotoxicity emanating from arsenic-containing hydrocarbons (AsHCs), a prominent subgroup of the arsenolipids. More recent in vivo and in vitro studies indicate that some arsenolipids might have adverse effects on brain health. In the present study, we focused on the effects of selected arsenolipids and three representative metabolites on the blood-cerebrospinal fluid barrier (B-CSF-B), a brain-regulating interface. For this purpose, we incubated an in vitro model of the B-CSF-B composed of porcine choroid plexus epithelial cells (PCPECs) with three AsHCs, two arsenic-containing fatty acids (AsFAs) and three representative arsenolipid metabolites (dimethylarsinic acid, thio/oxo-dimethylpropanoic acid) to examine their cytotoxic potential and impact on barrier integrity. The toxic arsenic species arsenite was also tested in this way and served as a reference substance. While AsFAs and the metabolites showed no cytotoxic effects in the conducted assays, AsHCs showed a strong cytotoxicity, being up to 1.5-fold more cytotoxic than arsenite. Analysis of the in vitro B-CSF-B integrity showed a concentration-dependent disruption of the barrier within 72 h. The correlation with the decreased plasma membrane surface area (measured as capacitance) indicates cytotoxic effects. These findings suggest exposure to elevated levels of certain arsenolipids may have detrimental consequences for the central nervous system.

The Content of Mercury in Herbal Dietary Supplements

The dietary supplement market in Poland has been growing rapidly, and the number of registered products and their consumption increases steadily. Among the most popular and the easiest to get are herbal supplements, available in any supermarket. The aim of this paper was to investigate the mercury content in the herbal supplements. The dietary supplements that have been examined (24) are available on the Polish market and contain one or more herbal ingredients. Supplements were pulverized in porcelain mortar and identified by AMA 254 atomic absorption spectrometer. The range of variations for all tested supplements was within 0.02-4293.07 μg/kg. The arithmetic mean of the total result was 193.77 μg/kg. A higher mercury content then this mean was found in preparations-bamboo shoots and alga Chlorella pyrenoidosa. The studies have shown that mercury is present in every examined herbal supplement, and its content exceeds in two preparations (with bamboo and alga) the permissible limit of 0.10 mg/kg. There were statistically significant differences in the occurrence of mercury depending on the herbal ingredient in the supplement. The lowest content was found in the preparation with Tanacetum parthenium and the highest with bamboo shoots. The mercury content in the tested herbal supplements was statistically significant in the form of a supplement-a tablet and a capsule. Daily, weekly, monthly, and yearly consumption of mercury with examined supplements was calculated-the results did not exceed the PTWI-provisional tolerable weekly intake of mercury. To increase consumer safety, it is imperative to conduct further research on dietary supplements and implement a stricter quality control of the dietary supplements.

Comparative study on toxicity of methylmercury chloride and methylmercury hydroxide to the human neuroblastoma cell line SH-SY5Y

Toxicities of methylmercury chloride (CH₃HgCl) and methylmercury hydroxide (CH₃HgOH) to cultured neuroblastoma cell line SH-SY5Y in vitro are evaluated. This is the comparative study between two methylmercury compounds to find out the extent of toxicity of these compounds are toxic to SH-SY5Y cell line. Both cytotoxicity and genotoxicity experiments were carried out to find out the more toxic compound. For cytotoxicity study, four staining assay methods independently with trypan blue (TB), acridine orange/ethidium bromide (AO/EB), 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl tetrazolium bromide (MTT), and neutral red (NR) were used and the comet assay method was done for genotoxicity study. The obtained toxicity data were used for probit analysis. In cytotoxicity, CH₃HgCl had minimum inhibitory concentration (MIC) value in each assay method as 3 mg/L invariably; LC₂₅ values were in the range 7.41 to 10.23 mg/L, and LC₅₀ values were 14.79 to 15.48 mg/L; while LC₇₅ values were 20.89 to 26.91 mg/L. Moreover, LC₁₀₀ value was 30 mg/L, known from comet assay experiments for CH₃HgCl. Similarly for CH₃HgOH, the MIC value in each assay method was invariably 3 mg/L, the LC₂₅ values were in the range 12.58 to 16.59 mg/L, and LC₅₀ values were 19.49 to 23.44 mg/L; LC₇₅ values were 27.54 to 30.90 mg/L and LC₁₀₀ value was 42 mg/L in each assay done for cytotoxicity and genotoxicity studies. Computed DNA fragmentation indices in comet assays were 98.6 ± 0.57 30 mg/L with CH₃HgCl and 76 ± 5.29 30 mg/L with CH₃HgOH. This study clearly indicated that methylmercury chloride is more toxic than methylmercury hydroxide to SH-SY5Y cell line. Toxicity of Hg had been quantified with in vitro cultured human neuroblastoma cell line; since it has neurotoxic effects, its neural evaluation has implications in environmental health issues.

Bioaccessibility and health risk assessment of mercury in cinnabar containing Traditional Chinese Medicines

Cinnabar (α-HgS), has been formulated in Traditional Chinese Medicines (TCMs) for thousands of years. Since the total Hg content was accepted widely as the toxicity criteria, the safety alerts have been issued about the cinnabar containing TCMs for exceeding Hg limits. However, cinnabar is almost insoluble in water, the oral absorption is extremely low. Hence, it is not suitable to use the total Hg content alone to evaluate the toxicity of cinnabar containing TCMs. In instead, the bioaccessible Hg is a much reasonable safety indicator. In this study, bioaccessible Hg contents of 29 cinnabar containing TCMs were determined by cold vapor-atomic fluorescence spectrometry after in vitro extractions with the simulated gastrointestinal fluids, while the total Hg contents were determined after acid digestion. According to the daily dosages, the bioaccessible Hg exposures of these TCMs were evaluated, and most of them were within the permitted daily exposure set by the International Council for Harmonisation, demonstrating that these TCMs are safe when administrated following the instructions. However, the obtained results also suggested that the Hg exposure could also be influenced by the herbal ingredients in TCMs and the bioactivities in gastrointestinal tract, indicating the possible health risks after excessive or long-term medication of cinnabar containing TCMs. Considering the influencing factors of the Hg intakes after oral administration of cinnabar containing TCMs, the bioaccessible Hg exposure should be considered as a more rational criterion for evaluating the health risks than the total Hg content. Furthermore, precautions should also be taken to ensure safe usages of cinnabar containing TCMs from both the cinnabar contents and the processing procedures points of view, as well as the daily dosage regimen, for all of them are directly related with the bioaccessible Hg exposures.

The toxicology of mercury: Current research and emerging trends

Mercury (Hg) is a persistent bio-accumulative toxic metal with unique physicochemical properties of public health concern since their natural and anthropogenic diffusions still induce high risk to human and environmental health. The goal of this review was to analyze scientific literature evaluating the role of global concerns over Hg exposure due to human exposure to ingestion of contaminated seafood (methyl-Hg) as well as elemental Hg levels of dental amalgam fillings (metallic Hg), vaccines (ethyl-Hg) and contaminated water and air (Hg chloride). Mercury has been recognized as a neurotoxicant as well as immunotoxic and designated by the World Health Organization as one of the ten most dangerous chemicals to public health. It has been shown that the half-life of inorganic Hg in human brains is several years to several decades. Mercury occurs in the environment under different chemical forms as elemental Hg (metallic), inorganic and organic Hg. Despite the raising understanding of the Hg toxicokinetics, there is still fully justified to further explore the emerging theories about its bioavailability and adverse effects in humans. In this review, we describe current research and emerging trends in Hg toxicity with the purpose of providing up-to-date information for a better understanding of the kinetics of this metal, presenting comprehensive knowledge on published data analyzing its metabolism, interaction with other metals, distribution, internal doses and targets, and reservoir organs.

In vivo formation of natural HgSe nanoparticles in the liver and brain of pilot whales

To understand the biochemistry of methylmercury (MeHg) that leads to the formation of mercury-selenium (Hg-Se) clusters is a long outstanding challenge that promises to deepen our knowledge of MeHg detoxification and the role Se plays in this process. Here, we show that mercury selenide (HgSe) nanoparticles in the liver and brain of long-finned pilot whales are attached to Se-rich structures and possibly act as a nucleation point for the formation of large Se-Hg clusters, which can grow with age to over 5 μm in size. The detoxification mechanism is fully developed from the early age of the animals, with particulate Hg found already in juvenile tissues. As a consequence of MeHg detoxification, Se-methionine, the selenium pool in the system is depleted in the efforts to maintain essential levels of Se-cysteine. This study provides evidence of so far unreported depletion of the bioavailable Se pool, a plausible driving mechanism of demonstrated neurotoxic effects of MeHg in the organism affected by its high dietary intake.