Mechanism of cytotoxicity of methylmercury. With special reference to microtubule disruption

Neurological risks arising from the bioaccumulation of heavy metal contaminants: A focus on mercury

This study investigated the concentrations of heavy metals in the water sources of the upstream region of the Huangpu River, the Yangtze River Estuary, and various areas in Shanghai, as well as the heavy metal concentrations in the blood of Shanghai residents. It aimed to analyze the heavy metal elements absorbed by the human body and the resulting pathological effects. The results revealed that surface water primarily contains five heavy metals: copper (Cu), lead (Pb), zinc (Zn), arsenic (As), and mercury (Hg), while water sediments primarily contain seven heavy metals: Cu, cadmium (Cd), Pb, chromium (Cr), Zn, As, and Hg. The main heavy metals present in the human body are Pb, Hg, As, and Cd. By reviewing previous articles, it was found that heavy metal concentrations in human blood are higher than those in surface water, suggesting uncertainties in the heavy metal content of surface water and its tendency to settle at the bottom. Furthermore, a comparison of heavy metal content in sediments revealed that Hg is the most readily absorbed heavy metal by the human body and is also a toxic environmental pollutant. Within the cell, Hg is highly toxic to mitochondria and may cause oxidative stress and neurodegenerative disease. This study concludes that water sediments serve as the major source of pollution in the human body and pose significant health risks, thereby necessitating the implementation of effective preventive measures.

Dietary Selenomethionine Reduce Mercury Tissue Levels and Modulate Methylmercury Induced Proteomic and Transcriptomic Alterations in Hippocampi of Adolescent BALB/c Mice

Methylmercury (MeHg) is a well-known environmental contaminant, particularly harmful to the developing brain. The main human dietary exposure to MeHg occurs through seafood consumption. However, seafood also contains several nutrients, including selenium, which has been shown to interact with MeHg and potentially ameliorate its toxicity. The aim of this study was to investigate the combined effects of selenium (as selenomethionine; SeMet) and MeHg on mercury accumulation in tissues and the effects concomitant dietary exposure of these compounds exert on the hippocampal proteome and transcriptome in mice. Adolescent male BALB/c mice were exposed to SeMet and two different doses of MeHg through their diet for 11 weeks. Organs, including the brain, were sampled for mercury analyses. Hippocampi were collected and analyzed using proteomics and transcriptomics followed by multi-omics bioinformatics data analysis. The dietary presence of SeMet reduced the amount of mercury in several organs, including the brain. Proteomic and RNA-seq analyses showed that both protein and RNA expression patterns were inversely regulated in mice receiving SeMet together with MeHg compared to MeHg alone. Several pathways, proteins and RNA transcripts involved in conditions such as immune responses and inflammation, oxidative stress, cell plasticity and Alzheimer’s disease were affected inversely by SeMet and MeHg, indicating that SeMet can ameliorate several toxic effects of MeHg in mice.

Alterations in the Atlantic cod (Gadus morhua) hepatic thiol-proteome after methylmercury exposure

Proteomic studies in general have demonstrated that the most effective and thorough analysis of biological samples requires subfractionation and/or enrichment prior to downstream processing. In the present study, Atlantic cod (Gadus morhua) liver samples were fractionated using activated thiol sepharose to isolate hepatic proteins containing free/reactive cysteines. This subset of proteins is of special interest when studying the physiological effects attributed to methylmercury (MeHg) exposure. Methylmercury is a persistent environmental contaminant that has a potent affinity toward thiol groups, and can directly bind proteins via available cysteine residues. Further, alterations in the cod thiol-proteome following MeHg exposure (2 mg/kg body weight) were explored with two-dimensional gel electrophoresis combined with downstream mass spectrometry analyses for protein identifications. Thirty-five protein spots were found to respond to MeHg exposure, and 13 of these were identified when searching cod-specific databases with acquired mass spectrometry data. Among the identified thiol-containing proteins, some are known to respond to MeHg treatment, including constituents of the cytoskeleton, and proteins involved in oxidative stress responses, protein synthesis, protein folding, and energy metabolism. Methylmercury also appeared to affect cod heme metabolism/turnover, producing significantly altered levels of hemoglobin and hemopexin in liver following metal exposure. The latter finding suggests that MeHg may also affect the hematological system in Atlantic cod.

Effect of methyl mercury induced free radical stress on nucleic acids and protein: Implications on cognitive and motor functions

Mercury pollution and acute neurotoxicity of mercury is well known. The recent reports suggest the adverse effect of low dose mercury, though the available literature is still silent on its mechanism. This study was therefore undertaken to probe the effect of low dose methyl mercury induced heavy metal toxicity on free radical stress and its impact on behaviour of male albino rats. Male albino rats were exposed to 1 mg/kg body wt of methylmercury chloride for seven days, on day 8 they were tested for motor and memory functions. They were sacrificed later for biochemical estimations for rate of lipid peroxidation, nucleic acids, proteins in cerebrum, cerebellum and brain stem. There was an increase in the rate of lipid peroxidation showing methyl mercury induced free radical stress. The motor and memory functions demonstrated a clear decline, besides there was a lowering in the levels of nucleic acids and proteins as compared to controls. The results are important in view of recent reports that methyl mercury induced free radical stress results in early ageing and may serve as an initiating factor more specifically for neurodegenerative disorders like Alzeihemer's disease and dementias. The current findings support the notion that incorporating dietary antioxidants like curcumin, ascorbic acid and α-tocopherol in routine diet from early age may help combat the risk of developing such disorders in ensuing years.

Methylmercury-induced neurotoxicity and apoptosis

Methylmercury is a widely distributed environmental toxicant with detrimental effects on the developing and adult nervous system. Due to its accumulation in the food chain, chronic exposure to methylmercury via consumption of fish and sea mammals is still a major concern for human health, especially developmental exposure that may lead to neurological alterations, including cognitive and motor dysfunctions. Mercury-induced neurotoxicity and the identification of the underlying mechanisms has been a main focus of research in the neurotoxicology field. Three major mechanisms have been identified as critical in methylmercury-induced cell damage including (i) disruption of calcium homeostasis, (ii) induction of oxidative stress via overproduction of reactive oxygen species or reduction of antioxidative defenses and (iii) interactions with sulfhydryl groups. In vivo and in vitro studies have provided solid evidence for the occurrence of neural cell death, as well as cytoarchitectural alterations in the nervous system after exposure to methylmercury. Signaling cascades leading to cell death induced by methylmercury involve the release of mitochondrial factors, such as cytochrome c and AIF with subsequent caspase-dependent or -independent apoptosis, respectively; induction of calcium-dependent proteases calpains; interaction with lysosomes leading to release of cathepsins. Interestingly, several pathways can be activated in parallel, depending on the cell type. In this paper, we provide an overview of recent findings on methylmercury-induced neurotoxicity and cell death pathways that have been described in neural and endocrine cell systems.

Antioxidants J811 and 17beta-estradiol protect cerebellar granule cells from methylmercury-induced apoptotic cell death

Cerebellar granule cells (CGC) have provided a reliable model for studying the toxicity of methylmercury (MeHg), a well-known neurotoxicant contaminating the environment. In the present study we report that doses of MeHg ranging from 0.1 microM to 1.5 microM activated apoptosis, as shown by cell shrinkage, nuclear condensation, and formation of high-molecular-weight DNA fragments. Nevertheless, caspase-3-like activity was not significantly induced, and the broad caspase inhibitor Z-VAD-FMK was not capable of protecting the cells. This argues for a minor role of caspases in the intracellular pathways leading to MeHg-induced cell death in CGC. Instead, proteolytic fragments obtained by specific calpain cleavage of procaspase-3 and alpha-fodrin were increased consistently in samples exposed to MeHg, pointing to a substantial activation of calpain. Notably, two antioxidants, 17beta-estradiol (10 microM) and the Delta(8,9)-dehydro derivative of 17alpha-estradiol J811 (10 microM), protected from MeHg damage, preventing morphological alterations, chromatin fragmentation, and activation of calpain. These findings underscore the key role of oxidative stress in MeHg toxicity, placing it upstream of calpain activation. The shielding effect of the 17beta-estradiol and the radical scavenger J811 is potentially relevant for the development of therapeutic strategies for MeHg intoxication.