Evaluation of neurobehavioral impairment in methylmercury-treated KK-Ay mice by dynamic weight-bearing test

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

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

Association between Heavy Metals, Metalloids and Metabolic Syndrome: New Insights and Approaches

Metabolic syndrome (MetS) is an important public health issue that affects millions of people around the world and is growing to pandemic-like proportions. This syndrome is defined by the World Health Organization (WHO) as a pathologic condition characterized by abdominal obesity, insulin resistance, hypertension, and hyperlipidemia. Moreover, the etiology of MetS is multifactorial, involving many environmental factors, including toxicant exposures. Several studies have associated MetS with heavy metals exposure, which is the focus of this review. Environmental and/or occupational exposure to heavy metals are a major risk, contributing to the development of chronic diseases. Of particular note, toxic metals such as mercury, lead, and cadmium may contribute to the development of MetS by altering oxidative stress, IL-6 signaling, apoptosis, altered lipoprotein metabolism, fluid shear stress and atherosclerosis, and other mechanisms. In this review, we discuss the known and potential roles of heavy metals in MetS etiology as well as potential targeted pathways that are associated with MetS. Furthermore, we describe how new approaches involving proteomic and transcriptome analysis, as well as bioinformatic tools, may help bring about an understanding of the involvement of heavy metals and metalloids in MetS.

Weight bearing as a measure of disease progression in experimental autoimmune encephalomyelitis

Motor disability in multiple sclerosis is often modeled using experimental autoimmune encephalomyelitis (EAE) and assessed using the clinical score (CS), an observer-dependent tool that can lead to potential bias. The Advanced Dynamic Weight Bearing (ADWB) system was evaluated as an observer-independent measurement of EAE symptoms. ADWB detected weight shifts onto the front paws as mice develop hindlimb motor disability. CS and ADWB were strongly correlated, indicated that these measures are comparable and suggesting that ADWB may be an appropriate observer-independent tool for the assessment of EAE progression.

Methylmercury-Induced Metabolic Alterations in Caenorhabditis elegans Are Diet-Dependent

Methylmercury (MeHg) is a well-known neurotoxicant; however, its role in metabolic diseases has been gaining wider attention. Chronic exposure to MeHg in human populations shows an association with diabetes mellitus and metabolic syndrome (MS). As the incidences of both obesity and MS are on the rise globally, it is important to understand the potential role of MeHg in the development of the disease. There is a dearth of information on dietary interactions between MeHg and lipids, which play an important role in developing MS. We have previously shown that MeHg increases food seeking behaviors, lipid levels, fat storage, and pro-adipogenic gene expression in C. elegans fed the standard OP50 Escherichia coli diet. However, we hypothesized that these metabolic changes could be prevented if the worms were fed a bacterial diet lower in lipid content. We tested whether C. elegans developed metabolic alterations in response to MeHg if they were fed two alternative E. coli strains (HT115 and HB101) that are known absorb significantly less lipids from their media. Additionally, to explore the effect of a high-lipid and high-cholesterol diet on MeHg-induced metabolic dysfunction, we supplemented the OP50 strain with twice the standard concentration of cholesterol in the nematode growth media. Wild-type worms fed either the HB101 or HT115 diet were more resistant to MeHg than the worms fed the OP50 diet, showing a significant right-hand shift in the dose–response survival curve. Worms fed the OP50 diet supplemented with cholesterol were more sensitive to MeHg, showing a significant left-hand shift in the dose–response survival curve. Changes in sensitivity to MeHg by differential diet were not due to altered MeHg intake in the worms as measured by inductively coupled mass spectrometry. Worms fed the low-fat diets showed protection from MeHg-induced metabolic changes, including decreased food consumption, lower triglyceride content, and lower fat storage than the worms fed either of the higher-fat diets. Oxidative stress is a common characteristic of both MeHg exposure and high-fat diets. Worms fed either OP50 or OP50 supplemented with cholesterol and treated with MeHg had significantly higher levels of reactive oxygen species, carbonylated proteins, and loss of glutathione than the worms fed the HT115 or HB101 low-lipid diets. Taken together, our data suggest a synergistic effect of MeHg and dietary lipid levels on MeHg toxicity and fat metabolism in C. elegans, which may affect the ability of MeHg to cause metabolic dysfunction.

Toxicokinetics of methylmercury in diabetic KK-Ay mice and C57BL/6 mice

We compared the toxicokinetics of methylmercury (MeHg) in KK-Ay type 2 diabetic mice and C57BL/6J mice to evaluate how metabolic changes associated with diabetes affect MeHg toxicokinetics. A single dose of MeHg (0.2, 1, or 5 mg mercury/kg) was administered orally to 12-week-old KK-Ay and C57BL/6J male mice. Total mercury concentrations in plasma, blood cells, whole blood, and tissues (brain, kidneys, liver, and pancreas) were measured after 4, 7, 11, and 14 days. The volume of distribution/bioavailability and the elimination rate constant per day were higher in KK-Ay mice, while the terminal elimination half-life was lower in almost all samples of KK-Ay mice. The area under the curve was lower in all blood and almost all tissue samples from KK-Ay mice. Total clearance/bioavailability was lower in all blood and tissue samples of KK-Ay mice at all MeHg doses. These results indicate that MeHg is more rapidly absorbed by, and eliminated from, the blood cells, brain, liver, kidney, and pancreas of KK-Ay mice under the experimental conditions. Different patterns of tissue-to-plasma and tissue-to-whole blood partition coefficients suggest that notable differences in MeHg transfer between plasma and blood cells affect its distribution in tissues of the two mouse strains. These findings are useful to understand the selective distribution of MeHg to target organs and the sensitivity to MeHg in pathological states.

Activation of MIP-2 and MCP-5 Expression in Methylmercury-Exposed Mice and Their Suppression by N-Acetyl-L-Cysteine

Methylmercury (MeHg) is a well-known neurotoxin of the central nervous system (CNS). Neuroinflammation is one of the main pathways of MeHg-induced CNS impairment. This study aims to investigate the expressions of IL-6, MIP-2, and MCP-5, as biomarkers in relation with MeHg-induced CNS impairment and N-acetyl-L-cysteine (NAC) treatment in mice, as well as histopathological changes of brain tissue and clinical symptom such as ataxia. Twenty male Balb/c mice, aged 8-9 weeks, were divided into 4 groups and treated with saline (control), NAC [150 mg/kg body weight (BW) day], MeHg (4 mg Hg/kg BW), or a combination of MeHg and NAC for 17 days. MeHg induced the expression of IL-6, MIP-2, and MCP-5 in the serum, with median values (those in controls) of 55.06 (9.44), 15.94 (9.30), and 458.91 (239.91) mg/dl, respectively, and a statistical significance was observed only in IL-6 expression (p < 0.05). MIP-2 and MCP-5 expressions tended to increase in the cerebrum of MeHg-treated group compared with controls; however, the difference was not statistically significant. MeHg treatment also increased IL-6 expression in the cerebellum (7.73 and 4.81 mg/dl in MeHg-treated group and controls, respectively), with a marginal significance. NAC significantly suppressed MeHg-induced IL-6 and MIP-2 expressions in the serum (p < 0.05 for both), and slightly reduced MCP-5 expression in the cerebrum. Ataxia was observed in all MeHg-treated mice after 9-day exposure as well as the decrease of intact Purkinje cells in brain tissue (p < 0.05). These findings suggest that MeHg induced neurotoxicity by elevating the expression of IL-6, MIP-2, and MCP-5 and causing ataxia symptoms, and NAC reduced MeHg-mediated effects on the CNS.

Inorganic mercury-induced MIP-2 expression is suppressed by N-acetyl-L-cysteine in RAW264.7 macrophages

Macrophages play an important role in neurotoxicity caused by methylmercury exposure through inflammatory responses. Methylmercury is known to demethylate to inorganic mercury in the brain, and macrophages are likely to be involved in this process. However, the inflammatory responses of macrophages against exposure to inorganic mercury are unclear. In the present study, inflammatory cytokine expression profiles were examined in the presence of non-toxic doses of inorganic mercury (Hg²⁺) using RAW264.7 macrophages, focusing on the expression of C-X-C motif chemokine 2 (MIP-2)/platelet-derived growth factor-inducible protein KC (KC) and C-C motif chemokine 12 (MCP-5). Furthermore, the suppressive effect of N-acetyl-L-cysteine (NAC) on inorganic mercury-induced MIP-2 expression was also examined. Inorganic mercury-induced mRNA expression was measured using reverse transcription-quantitative PCR. The mRNA expression of MIP-2 and MCP-5 was significantly upregulated by exposure to 20 µM Hg²⁺ (non-toxic levels), but not that of KC. The suppressive effect of NAC on these cytokine expression levels was examined by its addition to the culture medium together with Hg²⁺ (co-treatment), and pre- and post-treatments in which the cells were treated with NAC before and after Hg²⁺ exposure, respectively. Hg²⁺-upregulated MIP-2 expression was suppressed by NAC regardless of the time sequence of the treatment, suggesting that the suppressive role of NAC in Hg²⁺-induced inflammation manifests as a possible chelator and antioxidant/reactive oxygen species scavenger.

Aqueous Coriandrum sativum L. extract promotes neuroprotection against motor changes and oxidative damage in rat progeny after maternal exposure to methylmercury

This study aimed to investigate the effects of Coriandrum sativum aqueous extract (CSAE) on the rat progeny of mothers exposed to methylmercury (MeHg). The presence of bioactive compounds and CSAE's antioxidant capacity been evaluated, and the offspring were assessed for their total mercury levels, motor behavioral parameters and oxidative stress in the cerebellum. The analysis of the bioactive compounds revealed significant amounts of polyphenols, flavonoids, and anthocyanins, as well as a variety of minerals. A DPPH test showed the CSAE had important antioxidant activity. The MeHg + CSAE group performed significantly better spontaneous locomotor activity, palmar grip strength, balance, and motor coordination in behavioral tests compared the MeHg group, as well as in the parameters of oxidative stress, with similar results to those of the control group. The MeHg + CSAE group also had significantly reduced mercury levels in comparison to the MeHg group. Based on the behavioral tests, which detected large locomotor, balance, and coordination improvements, as well as a reduction in oxidative stress, we conclude that CSAE had positive functional results in the offspring of rats exposed to MeHg.