Methylmercury chronic exposure affects the expression of DNA single-strand break repair genes, induces oxidative stress, and chromosomal abnormalities in young dyslipidemic APOE knockout mice

Quantification of heavy metal exposure in a British population cohort links total mercury levels in plasma with skin tissue-specific changes in mitochondrial-related gene expression

Heavy metals in our direct environment have profound effects on human health and while some are essential for life, others can be toxic. In vivo studies often focus on clinical features caused by overexposure to, or by deprivation of a heavy metal. However, to understand the cellular impact of heavy metals on health, studies in healthy volunteers before symptom onset are needed. Here, we explored the impact of mercury, lead and selenium in over 800 British female twins on multi-tissue gene expression levels as an intermediate phenotype. Total mercury, lead and selenium concentrations were determined in plasma as a proxy for heavy metal exposure. We identified significant associations between total mercury levels measured in plasma, that fall within normal ranges, and expression of 873 genes within skin tissue, including PUSL1, SAMD10, ERCC1, MRPL17, NDUFB8, SELENOH, SEC31A, and KAT7P1. Functional analysis of genes associated with total mercury levels in plasma show a strong link to the mitochondrial oxidative phosphorylation pathway (p-value = 3.02 × 10-10). Analysis of mitochondrial-specific gene expression supported involvement of genes of oxidative phosphorylation complexes (MT-ND4L, and MT-ND5), which are encoded in mitochondrial DNA. These results suggest that mercury is likely detrimental to the energy metabolism of mitochondria. We also tested for associations between total mercury levels in plasma and gene expression in adipose and whole blood samples, but did not identify significant associations in these tissues, nor with lead or selenium in any tissue. Our results demonstrate that subtoxic mercury exposure leaves a clear molecular signature. It also underscores the necessity of conducting tissue-specific association studies to accurately capture the molecular impact of environmental exposures, as only relevant tissues will manifest a response to environmental exposures.

The impact of mercury exposure on male reproduction: Mechanistic insights

Mercury is a pervasive environmental toxin with significant negative effects on human health. In occupational settings, incidents such as the Minamata and Niigata disease in Japan and the large-scale methylmercury poisoning in Iraq have highlighted the severe health impacts of mercury exposure. It is widely accepted that all forms of mercury including methylmercury and mercuric chloride have the potential to induce toxic effects in mammals, and there is increasing concern about the impact of environmentally relevant levels of mercury on reproductive functions. This review summarizes current knowledge on the mechanisms of mercury toxicity, focusing specifically on its impact on male reproductive health across species. We searched the literature and found that mercury exposure is associated with testicular degeneration, altered spermatogenesis, and Leydig cell deformation. In addition, mercury can disrupt sperm motility, steroidogenesis and interfere with the hypothalamic-pituitary-gonadal axis by generation of reactive oxygen species, inducing mitochondrial dysfunction, epigenetic changes, and DNA damage. At the molecular level, mercury has been found to dysregulate the expression of key steroidogenic and spermatogenic genes, significantly reducing overall fertility potential. However, specific mechanisms of action remain to be fully elucidated. Similarly, comprehensive data on the potential transgenerational effects of paternal mercury exposure are lacking. In this review, we discuss both animal and human studies, and highlight the need for further research due to lack of standardization and control for variables such as lifestyle, immune system function, and exposure concentrations.

Re-thinking the link between exposure to mercury and blood pressure

Hypertension or high blood pressure (BP) is a prevalent and manageable chronic condition which is a significant contributor to the total global disease burden. Environmental chemicals, including mercury (Hg), may contribute to hypertension onset and development. Hg is a global health concern, listed by the World Health Organization (WHO) as a top ten chemical of public health concern. Most people are exposed to some level of Hg, with vulnerable groups, including Indigenous peoples and small-scale gold miners, at a higher risk for exposure. We published a systematic review and meta-analysis in 2018 showing a dose-response relationship between Hg exposure and hypertension. This critical review summarizes the biological effects of Hg (both organic and inorganic form) on the underlying mechanisms that may facilitate the onset and development of hypertension and related health outcomes and updates the association between Hg exposure (total Hg concentrations in hair) and BP outcomes. We also evaluated the weight of evidence using the Bradford Hill criteria. There is a strong dose-response relationship between Hg (both organic and inorganic) exposure and BP in animal studies and convincing evidence that Hg contributes to hypertension by causing structural and functional changes, vascular reactivity, vasoconstriction, atherosclerosis, dyslipidemia, and thrombosis. The underlying mechanisms are vast and include impairments in antioxidant defense mechanisms, increased ROS production, endothelial dysfunction, and alteration of the renin-angiotensin system. We found additional 16 recent epidemiological studies that have reported the relationship between Hg exposure and hypertension in the last 5 years. Strong evidence from epidemiological studies shows a positive association between Hg exposure and the risk of hypertension and elevated BP. The association is mixed at lower exposure levels but suggests that Hg can affect BP even at low doses when co-exposed with other metals. Further research is needed to develop robust conversion factors among different biomarkers and standardized measures of Hg exposure. Regulatory agencies should consider adopting a 2 µg/g hair Hg level as a cut-off for public health regulation, especially for adults older than child-bearing age.

Associations of Prenatal Mercury Exposure and PUFA with Telomere Length and mtDNA Copy Number in 7-Year-Old Children in the Seychelles Child Development Nutrition Cohort 2

BACKGROUND

Telomere length (TL) and mitochondrial DNA copy number (mtDNAcn) variations are linked to age-related diseases and are associated with environmental exposure and nutritional status. Limited data, however, exist on the associations with mercury exposure, particularly early in life.

OBJECTIVE

We examined the association between prenatal mercury (Hg) exposure and TL and mtDNAcn in 1,145 Seychelles children, characterized by a fish-rich diet.

METHODS

Total mercury (THg) was determined in maternal hair at delivery and cord blood. TL and mtDNAcn were determined relative to a single-copy hemoglobin beta gene in the saliva of 7-y-old children. Linear regression models assessed associations between THg and relative TL (rTL) and relative mtDNAcn (rmtDNAcn) while controlling for maternal and cord serum polyunsaturated fatty acid (PUFA) status and sociodemographic factors. Interactions between THg and child sex, PUFA, and telomerase genotypes were evaluated for rTL and rmtDNAcn.

RESULTS

Higher THg concentrations in maternal hair and cord blood were associated with longer rTL [β = 0.009 ; 95% confidence interval (CI): 0.002, 0.016 and β = 0.002 ; 95% CI: 0.001, 0.003, respectively], irrespective of sex, PUFA, or telomerase genotypes. Maternal serum n-6 PUFA and n-6/n-3 ratio were associated with shorter [β = - 0.24 ; 95% CI: - 0.33 , - 0.15 and β = - 0.032 ; 95% CI: - 0.048 , - 0.016 , respectively] and n - 3 PUFA with longer (β = 0.34 ; 95% CI: 0.032, 0.65) rTL. Cord blood n-6 PUFA was associated with longer (β = 0.15 ; 95% CI: 0.050, 0.26) rTL. Further analyses revealed linoleic acid in maternal blood and arachidonic acid in cord blood as the main drivers of the n-6 PUFA associations. No associations were observed for THg and PUFA with rmtDNAcn.

DISCUSSION

Our results indicate that prenatal THg exposure and PUFA status are associated with rTL later in childhood, although not consistently aligned with our initial hypothesis. Subsequent research is needed to confirm this finding, further evaluate the potential confounding of fish intake, and investigate the underlying molecular mechanisms to verify the use of rTL as a true biomarker of THg exposure. https://doi.org/10.1289/EHP14776.

Co-exposure to multiple heavy metals and metalloid induces dose dependent modulation in antioxidative, inflammatory, DNA damage and apoptic pathways progressing to renal dysfunction in mice

Humans are exposed to a cocktail of heavy metal toxicants at the same time in the environment rather than single metal. The kidney is often a site of early damage due to high renal contact to these pollutants. This study was done to examine the cumulative toxic effect of multiple elements prevalent in the environment. To explore the effect of subchronic exposure to heavy metal mixture male and female Swiss albino mice were randomly divided into 14 groups and given varying doses [MPL (maximum permissible limit), 1X, 5X, 10X, 50X, or 100X] of the multiple metals and metalloid mixtures via drinking water for 8 weeks. It was determined that metal treatment caused increased metal load in renal tissue. The kidney function deteriorated in response to 10X, 50X, 100X concentration of the dosing mixture was found associated to oxidative stress, glomerular damage, necrosis, cell death and further exacerbation of the inflammation.

Impact of the environmental pollution on cardiovascular diseases: From epidemiological to molecular evidence

Environmental pollution poses a significant threat to human health, particularly concerning its impact on cardiovascular diseases (CVDs). This review synthesizes epidemiological and molecular evidence to elucidate the intricate relationship between environmental pollutants and CVDs. Epidemiological studies highlight the association between exposure to air, water, and soil pollutants and increased CVD risk, including hypertension, coronary artery disease, and stroke. Furthermore, molecular investigations unravel the underlying mechanisms linking pollutant exposure to CVD pathogenesis, such as oxidative stress, inflammation, endothelial dysfunction, and autonomic imbalance. Understanding these molecular pathways is crucial for developing targeted interventions and policy strategies to mitigate the adverse effects of environmental pollution on cardiovascular health. By integrating epidemiological and molecular evidence, this review provides insights into the complex interplay between environmental factors and CVDs, emphasizing the urgent need for comprehensive preventive measures and environmental policies to safeguard public health.

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.

Deciphering the Global Proteomic Profile Involved in Methylmercury-Induced Cerebellar Neurodegeneration and Motor Dysfunction in Adult Rats

Mercury is a ubiquitous pollutant in the environment with potential neurotoxic effects. Several populations are susceptible to mercurial exposure, especially methylmercury (MeHg) at low doses for long periods through food consumption. Given this, the present work aimed to assess the effects of long-term MeHg exposure on the cerebellum of rats from a translational perspective using a representative dose, assessing molecular, biochemical, morphological, and behavioral parameters. The model was produced by administering 40 µg/kg of MeHg for 60 days to adult male Wistar rats by oral gavage. As a result of this exposure, the animals presented motor deficits in open field and rotarod tests which were associated with an increase in total mercury content in cerebellar parenchyma, a reduction in antioxidant competence against peroxyl radicals, and increased nitrite and lipid peroxidation levels. The proteomic approach showed 317 modulated proteins. Such findings were associated with reductions in mature neuron and Purkinje cell densities and glial fibrillary acidic protein immunostained areas and increased microglial density. In addition, decreases in myelin basic protein and synaptophysin immunostaining were also observed. The results thus provided new evidence of the mechanisms underlying complex MeHg-induced neurodegeneration, especially the proteins underlying the biochemical and morphological features associated with motor dysfunction.