Activation of interleukin-6 and -8 expressions by methylmercury in human U937 macrophages involves RelA and p50.

The accumulation of macrophages has been observed around lesions of the brain in patients with Minamata disease. In this condition, mercury has been detected histochemically in macrophages throughout the brain. However, the role of macrophages in the neurotoxicity of methylmercury (MeHg) and the molecular mechanisms of their response to MeHg exposure remain to be elucidated. Here, we investigated how MeHg affects the expression of proinflammatory cytokines such as interleukin (IL)-6 and IL-8 in cultured human U937 macrophages. Compared with controls, IL-6 and IL-8 mRNA expression was maximally induced in U937 macrophages after treatment with 10 µM MeHg for 6 h. The protein secretion of IL-6 and IL-8 was significantly stimulated by MeHg in U937 macrophages. Results from luciferase reporter assay indicated functional activation of nuclear factor kappa B and the involvement of subunit RelA and p50 in MeHg-induced IL-6 and IL-8 activation, which was confirmed by siRNA knockdown experiments. MeHg exposure at 4 µM also significantly induced IL-8 expression in U-87 MG cells at mRNA and protein level, indicating that IL-8 induction might be a general mode of action of MeHg treatment among different cell types. These results indicate a possible involvement of an early inflammatory response, including IL-6 and IL-8 expression in the pathogenesis of MeHg. N-acetyl-l-cysteine suppressed MeHg-induced activation of IL-6 and IL-8 mRNA expression in U937 macrophages, indicating the effectiveness of N-acetyl-l-cysteine as a therapeutic drug in MeHg-induced inflammation. Copyright © 2016 John Wiley & Sons, Ltd.

Design of novel rho kinase inhibitors using energy based pharmacophore modeling, shape-based screening, in silico virtual screening, and biological evaluation.

Rho-associated protein kinase (ROCK) plays a key role in regulating a variety of cellular processes, and dysregulation of ROCK signaling or expression is implicated in numerous diseases and infections. ROCK proteins have therefore emerged as validated targets for therapeutic intervention in various pathophysiological conditions such as diabetes-related complications or hepatitis C-associated pathogenesis. In this study, we report on the design and identification of novel ROCK inhibitors utilizing energy based pharmacophores and shape-based approaches. The most potent compound 8 exhibited an IC50 value of 1.5 µM against ROCK kinase activity and inhibited methymercury-induced neurotoxicity of IMR-32 cells at GI50 value of 0.27 µM. Notably, differential scanning fluorometric analysis revealed that ROCK protein complexed with compound 8 with enhanced stability relative to Fasudil, a validated nanomolar range ROCK inhibitor. Furthermore, all compounds exhibited ≥96 µM CC50 (50% cytotoxicity) in Huh7 hepatoma cells, while 6 compounds displayed anti-HCV activity in HCV replicon cells. The identified lead thus constitutes a prototypical molecule for further optimization and development as anti-ROCK inhibitor.

Effects of selenite and chelating agents on mammalian thioredoxin reductase inhibited by mercury: implications for treatment of mercury poisoning.

Mercury toxicity is a highly interesting topic in biomedicine due to the severe endpoints and treatment limitations. Selenite serves as an antagonist of mercury toxicity, but the molecular mechanism of detoxification is not clear. Inhibition of the selenoenzyme thioredoxin reductase (TrxR) is a suggested mechanism of toxicity. Here, we demonstrated enhanced inhibition of activity by inorganic and organic mercury compounds in NADPH-reduced TrxR, consistent with binding of mercury also to the active site selenolthiol. On treatment with 5 µM selenite and NADPH, TrxR inactivated by HgCl(2) displayed almost full recovery of activity. Structural analysis indicated that mercury was complexed with TrxR, but enzyme-generated selenide removed mercury as mercury selenide, regenerating the active site selenocysteine and cysteine residues required for activity. The antagonistic effects on TrxR inhibition were extended to endogenous antioxidants, such as GSH, and clinically used exogenous chelating agents BAL, DMPS, DMSA, and α-lipoic acid. Consistent with the in vitro results, recovery of TrxR activity and cell viability by selenite was observed in HgCl(2)-treated HEK 293 cells. These results stress the role of TrxR as a target of mercurials and provide the mechanism of selenite as a detoxification agent for mercury poisoning.

Vitamin K has the potential to protect neurons from methylmercury-induced cell death in vitro.

Vitamin K (VK) has a protective effect on neural cells. Methylmercury is a neurotoxicant that directly induces neuronal death in vivo and in vitro. Therefore, in the present study, we hypothesized that VK inhibits the neurotoxicity of methylmercury. To prove our hypothesis in vitro, we investigated the protective effects of VKs (phylloquinone, vitamin K(1); menaquinone-4, vitamin K(2) ) on methylmercury-induced death in primary cultured neurons from the cerebella of rat pups. As expected, VKs inhibited the death of the primary cultured neurons. It has been reported that the mechanisms underlying methylmercury toxicity involve a decrement of intracellular glutathione (GSH). Actually, treatment with GSH and a GSH inducer, N-acetyl cysteine, inhibited methylmercury-induced neuronal death in the present study. Thus, we investigated whether VKs also have protective effects against GSH-depletion-induced cell death by employing two GSH reducers, L-buthionine sulfoximine (BSO) and diethyl maleate (DEM), in primary cultured neurons and human neuroblastoma IMR-32 cells. Treatment with VKs affected BSO- and DEM-induced cell death in both cultures. On the other hand, the intracellular GSH assay showed that VK(2), menaquinone-4, did not restore the reduced GSH amount induced by methylmercury or BSO treatments. These results indicate that VKs have the potential to protect neurons against the cytotoxicity of methylmercury and agents that deplete GSH, without increasing intracellular GSH levels. The protective effect of VKs may lead to the development of treatments for neural diseases involving GSH depletion.

Modulation of methylmercury uptake by methionine: prevention of mitochondrial dysfunction in rat liver slices by a mimicry mechanism.

Methylmercury (MeHg) is an ubiquitous environmental pollutant which is transported into the mammalian cells when present as the methylmercury-cysteine conjugate (MeHg-Cys). With special emphasis on hepatic cells, due to their particular propensity to accumulate an appreciable amount of Hg after exposure to MeHg, this study was performed to evaluate the effects of methionine (Met) on Hg uptake, reactive species (RS) formation, oxygen consumption and mitochondrial function/cellular viability in both liver slices and mitochondria isolated from these slices, after exposure to MeHg or the MeHg-Cys complex. The liver slices were pre-treated with Met (250 µM) 15 min before being exposed to MeHg (25 µM) or MeHg-Cys (25 µM each) for 30 min at 37 °C. The treatment with MeHg caused a significant increase in the Hg concentration in both liver slices and mitochondria isolated from liver slices. Moreover, the Hg uptake was higher in the group exposed to the MeHg-Cys complex. In the DCF (dichlorofluorescein) assay, the exposure to MeHg and MeHg-Cys produced a significant increase in DFC reactive species (DFC-RS) formation only in the mitochondria isolated from liver slices. As observed with Hg uptake, DFC-RS levels were significantly higher in the mitochondria treated with the MeHg-Cys complex compared to MeHg alone. MeHg exposure also caused a marked decrease in the oxygen consumption of liver slices when compared to the control group, and this effect was more pronounced in the liver slices treated with the MeHg-Cys complex. Similarly, the loss of mitochondrial activity/cell viability was greater in liver slices exposed to the MeHg-Cys complex when compared to slices treated only with MeHg. In all studied parameters, Met pre-treatment was effective in preventing the MeHg- and/or MeHg-Cys-induced toxicity in both liver slices and mitochondria. Part of the protection afforded by Met against MeHg may be related to a direct interaction with MeHg or to the competition of Met with the complex formed between MeHg and endogenous cysteine. In summary, our results show that Met pre-treatment produces pronounced protection against the toxic effects induced by MeHg and/or the MeHg-Cys complex on mitochondrial function and cell viability. Consequently, this amino acid offers considerable promise as a potential agent for treating acute MeHg exposure.

Antagonistic interaction of mercury and selenium in a marine fish is dependent on their chemical species.

It is well-known that selenium (Se) shows protective effects against mercury (Hg) bioaccumulation and toxicity, but the underlying effects of Se chemical species, concentration, and administration method are poorly known. In this study, we conducted laboratory studies on a marine fish Terapon jurbua to explain why Hg accumulation is reduced in the presence of Se observed in field studies. When Se and Hg were administrated concurrently in the fish diets, different Se species including selenite, selenate, seleno-dl-cystine (SeCys), and seleno-dl-methionine (SeMet) affected Hg bioaccumulation differently. At high concentration in fish diet (20 µg g(-1) normally), selenate and SeCys significantly reduced the dietary Hg(II) assimilation efficiency (AE) from 38% to 26%. After the fish were pre-exposed to dietary selenite or SeMet (7 µg g(-1) normally) for 22 days with significantly elevated Se body concentrations, the Hg(II) AEs were pronouncedly reduced (from 41% to 15-26%), whereas the dissolved uptake rate constant and elimination rate constant were less affected. In contrast to Hg(II), all the MeHg biokinetic parameters remained relatively constant whether Se was administrated simultaneously with the fish diet or when the fish were pre-exposed to Se with elevated body concentrations. Basic biokinetic measurements thus revealed that Se had direct interaction with Hg(II) during dietary assimilation rather than with MeHg and that different Se species had variable effects on Hg assimilation.

Carbon monoxide derived from heme oxygenase-2 mediates reduction of methylmercury toxicity in SH-SY5Y cells.

We examined the contribution of carbon monoxide (CO), an enzymatic product of heme oxygenase (HO), to methylmercury (MeHg) cytotoxicity in SH-SY5Y cells, because this gas molecule is reported to activate Nrf2, which plays a protective role against MeHg-mediated cell damage. Exposure of SH-SY5Y cells to CO gas resulted in protection against MeHg cytotoxicity, with activation of Nrf2. Interestingly, pretreatment with tin-protoporphyrin IX, a specific inhibitor of HO, caused a reduction in basal Nrf2 activity and thus enhanced sensitivity to MeHg. No induction of isoform 1 of HO (HO-1) was seen during MeHg exposure, but constitutive expression of isoform 2 (HO-2) occurred, suggesting that CO produced by HO-2 is the main participant in the protection against MeHg toxicity. Studies of small interfering RNA-mediated knockdown of HO-2 in the cells supported this possibility. Our results suggest that CO gas and its producing enzyme HO-2 are key molecules in cellular protection against MeHg, presumably through basal activation of Nrf2.

Evaluation of cytoprotective effects of compounds isolated from Copaifera langsdorffii Desf. against induced cytotoxicity by exposure to methylmercury and lead.

Copaifera langsdorffii L. is one of the most known medicinal species in Brazil. Its leaves are rich in phenolic compounds with potential biological activities as an antioxidant and chelating agent. This paper reports the isolation of four compounds from the hydroalcoholic extract of the leaves of C. langsdorffii and the investigation of their possible cytoprotective effects against heavy metal poisoning. Quercitrin (1), afzelin (2), 3,5-di-O-(3-O-methyl galloyl) quinic acid (3) and 4,5-di-O-(3-O-methyl galloyl) quinic acid (4), were associated with toxic doses of methylmercury and lead and evaluated by Alamar blue cell viability assays in HepG2 and PC12. The compounds displayed significant cytoprotective effect for the HepG2 cell line against both metals. Compounds 1-4 did not protect PC12 cells against methylmercury induced-cytotoxicity, but at lower concentrations, they protected against lead induced-cytotoxicity. The evaluated compounds showed a promising cytoprotection effect against exposure to heavy metals and should be further investigated as protective agents.

Effects of chelators on mercury, iron, and lead neurotoxicity in cortical culture.

Chelation therapy for the treatment of acute, high dose exposure to heavy metals is accepted medical practice. However, a much wider use of metal chelators is by alternative health practitioners for so called "chelation therapy". Given this widespread and largely unregulated use of metal chelators it is important to understand the actions of these compounds. We tested the effects of four commonly used metal chelators, calcium disodium ethylenediaminetetraacetate (CaNa2EDTA), D-penicillamine (DPA), 2,3 dimercaptopropane-1-sulfonate (DMPS), and dimercaptosuccinic acid (DMSA) for their effects on heavy metal neurotoxicity in primary cortical cultures. We studied the toxicity of three forms of mercury, inorganic mercury (HgCl2), methyl mercury (MeHg), and ethyl mercury (thimerosal), as well as lead (PbCl2) and iron (Fe-citrate). DPA had the worst profile of effects, providing no protection while potentiating HgCl2, thimerosal, and Fe-citrate toxicity. DMPS and DMSA both attenuated HgCl2 toxicity and potentiated thimerosal and Fe toxicity, while DMPS also potentiated PbCl2 toxicity. CaNa2EDTA attenuated HgCl2 toxicity, but caused a severe potentiation of Fe-citrate toxicity. The ability of these chelators to attenuate the toxicity of various metals is quite restricted, and potentiation of toxicity is a serious concern. Specifically, protection is provided only against inorganic mercury, while it is lacking against the common form of mercury found in food, MeHg, and the form found in vaccines, thimerosal. The potentiation of Fe-citrate toxicity is of concern because of iron's role in oxidative stress in the body. Potentiation of iron toxicity could have serious health consequences when using chelation therapy.

Curcumin protects against methylmercury-induced cytotoxicity in primary rat astrocytes by activating the Nrf2/ARE pathway independently of PKCδ.

Methylmercury (MeHg) is a ubiquitous environmental toxicant that leads to long-lasting neurological deficits in animals and humans. Curcumin, a polyphenol obtained from the rhizome of turmeric, has well-known antioxidant functions. Here, we evaluated curcumin's efficacy in mitigating MeHg-induced cytotoxicity and further investigated the underlying mechanism of this neuroprotection in primary rat astrocytes. Pretreatment with curcumin (2, 5, 10 and 20 µM for 3, 6, 12 or 24 h) protected against MeHg-induced (5 µM for 6 h) cell death in a time and dose-dependent manner. Curcumin (2, 5, 10 or 20 µM) pretreatment for 12 h significantly ameliorated the MeHg-induced astrocyte injury and oxidative stress, as evidenced by morphological alterations, lactate dehydrogenase (LDH) release, reactive oxygen species (ROS) generation, and glutathione (GSH) and catalase (CAT) levels. Moreover, curcumin pretreatment increased Nrf2 nuclear translocation and downstream enzyme expression, heme oxygenase-1 (HO-1) and NADPH quinone reductase-1 (NQO1). Knockdown of Nrf2 with siRNA attenuated the protective effect of curcumin against MeHg-induced cell death. However, both the pan-protein kinase C (PKC) inhibitor, Ro 31-8220, and the selective PKCδ inhibitor, rottlerin, failed to suppress the curcumin-activated Nrf2/Antioxidant Response Element(ARE) pathway and attenuate the protection exerted by curcumin. Taken together, these findings confirm that curcumin protects against MeHg-induced neurotoxicity by activating the Nrf2/ARE pathway and this protection is independent of PKCδ activation. More studies are needed to understand the mechanisms of curcumin cytoprotection.

Docosahexaenoic acid enhances methylmercury-induced endoplasmic reticulum stress and cell death and eicosapentaenoic acid potentially attenuates these effects in mouse embryonic fibroblasts.

Fish consumption has both the risk of methylmercury (MeHg) poisoning and the benefit of obtaining n-3 polyunsaturated fatty acids (n-3 PUFAs), particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). However, the cellular interaction between MeHg and PUFAs remains unknown. Therefore, the aim of this study was to investigate the effects of MeHg and n-3 PUFA exposure on mouse embryonic fibroblasts (MEFs). The results showed that EPA had a negligible effect on MeHg-induced cell death, whereas DHA promoted it. Thiobarbituric acid reactive substance (TBARS) concentrations in cells exposed to DHA and MeHg were higher than in those exposed to EPA and MeHg. Treatment with DHA and MeHg markedly induced the expression of endoplasmic reticulum (ER) stress (CHOP and DNAJB9) and Nrf2 target gene (p62 and HMOX-1) mRNA levels. Unexpectedly, EPA supplementation in addition to DHA and MeHg attenuated DHA- and MeHg-induced cell death and suppressed ER stress and expression of Nrf2 target genes. Our results revealed a differential impact of DHA and EPA on MeHg-induced cell death, and combined treatment with DHA and EPA along with MeHg attenuated MeHg-induced toxicity.

Methylmercury increases N-methyl-D-aspartate receptors on human SH-SY 5Y neuroblastoma cells leading to neurotoxicity.

Methylmercury (MeHg) is a known neurotoxin, yet the mechanism for low dose chronic toxicity is still not clear. While N-methyl-D-aspartate receptors (NMDARs) were found to be induced after exposure to MeHg in a mink model, its role on neurotoxicity is not known. The aims of this study were to investigate the expression and the functional roles of NMDARs on the induction of cell death in the human SH-SY 5Y neuroblastoma cell line after exposure to MeHg. NMDARs were measured using a radiolabeled phencyclidine receptor ligand [(3)H] (MK801) and cell death was quantified using fluorogenic substrates specific for caspase-3 (DEVD-AFC) and lactate dehydrogenase (LDH) release. We found a significant increase in NMDARs followed by increased caspase-3 activity after 4 h of exposure to MeHg (0.25-1 microM). Necrotic cell death was found after 4 and 24 h of exposure to MeHg (0.25-5 microM). The NMDAR antagonists dizocilpine ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-iminemaleate [(+)-MK801]) and Memantine (1-amino-3,5-dimethyl-adamantane) (10 microM) completely attenuated MeHg-mediated cell death by blocking NMDARs, thus demonstrating the importance of NMDARs in mercury neurotoxicity. Intracellular calcium chelator BAPTA-AM (1 microM) partially attenuated the neurotoxicity effect of 1 microM MeHg. These results suggest that MeHg toxicity can be mediated through the binding and increase of NMDARs.

Identification of a methioninase inhibitor, myrsinoic acid B, from Myrsine seguinii Lév., and its inhibitory activities.

A methioninase inhibitor from Myrsine seguinii was purified and identified as myrsinoic acid B. Its inhibitory activities as to crude methioninase from periodontal bacteria such as Fusobacterium nucleatum, Porphyromonas gingivalis, and Treponema denticola were determined. The IC50 values were 10.5, 82.4, and 30.3 microM respectively.

Dietary fats modulate methylmercury-mediated systemic oxidative stress and oxidative DNA damage in rats.

We examined the effects of dietary fats on methylmercury (MeHg)-induced systemic oxidative stress and oxidative DNA damage in liver and kidney of male Sprague-Dawley rats. Rats were treated with a casein-based purified isocaloric diet containing 15% by weight soy oil, docosahexaenoic acid (DHA), seal oil, fish oil, or lard for 28 days, and then gavaged with 0, 1, or 3 mg MeHg/kg BW/day for 14 days. Urine was analyzed for 8-hydroxydeoxyguanosine (8-OHdG) and isoprostane, and serum for total antioxidant capacity (TAC). Liver and kidney were analyzed immunohistochemically for 8-OHdG. Both diet and MeHg showed significant main effects on some of these markers. As compared with the vehicle control, 3 mg MeHg/kg BW significantly increased urinary 8-OHdG in the lard group, urinary isoprostane in the DHA, seal oil, and fish oil groups, while significantly decreasing serum TAC in the lard and fish oil groups. In all dietary groups, 8-OHdG positive staining was located mainly in the nuclei of various cell types in liver and kidney. MeHg expressed a significant main increasing effect on 8-OHdG-positive cells in kidney. These results suggest that both dietary fats and MeHg are important mediators of systemic oxidative stress and oxidative DNA damage.

Biomarkers of exposure and effect as indicators of the interference of selenomethionine on methylmercury toxicity.

The present study was conducted to clarify the interference of selenomethionine (SeMet) on methylmercury (MeHg) toxicity through the evaluation of changes in biomarkers of exposure and effect in rats exposed to MeHg and co-exposed to MeHg and SeMet. Male Wistar rats received two intraperitoneally (i.p.) administrations, either MeHg (1.5mg/kg body weight), SeMet alone (1mg/kg body weight) or combined MeHg and SeMet, followed by 3 weeks of rat urine collection and neurobehavioural assays. The effects of different administrations were investigated by the quantification of total mercury in kidney and brain, analysis of urinary porphyrins, determination of hepatic GSH and evaluation of motor activity functions (rearing and ambulation). MeHg exposure resulted in a significant increase of urinary porphyrins during the 3 weeks of rat urine collection, where as it caused a significant decrease in motor activity only at the first day after cessation of rat exposure. Additionally, SeMet co-exposure was able to normalize the porphyrins excretion, and a tendency to restore rat motor activity was observed, on the first day after cessation of exposure. Brain and kidney mercury levels increased significantly in rats exposed to MeHg; however, in co-exposed rats to SeMet no significant changes in Hg levels were found as compared to rats exposed to MeHg alone. Hence, the present study shows that urinary porphyrins are sensitive and persistent indicators of MeHg toxicity and demonstrates for the first time that SeMet reduces its formation. Finally, these results confirm that the mechanism of interaction between SeMet and MeHg cannot be explained by the reduction of Hg levels in target organs and suggestions are made to clarify the interference of SeMet on MeHg toxicity.

Cipura paludosa extract prevents methyl mercury-induced neurotoxicity in mice.

Cipura paludosa (Iridaceae), a native plant widely distributed in the north of Brazil, is used in traditional medicine as an anti-inflammatory and analgesic agent, against tuberculosis and gonorrhoea and for regulation of menstrual flow. However, scientific studies on the pharmacological properties of C. paludosa are scarce. We have examined the potential protective effects of the ethanolic extract of C. paludosa against methyl mercury (MeHg)-induced neurotoxicity in adult mice. MeHg was diluted in drinking water (40 mg/l, freely available) and the ethanolic C. paludosa extract (CE) was diluted in a 150 mM NaCl solution and administered by gavage (10 and 100 mg/kg body weight, respectively, twice a day). Because treatment lasted for 14 days and each animal weighed around 40 g, the total dosage of plant extract given to each mouse was 5.6 and 56 g, respectively. After the treatment period, MeHg exposure induced a significant deficit in the motor coordination, which was evident by a reduction (90%) in the falling latency in the rotarod apparatus. Interestingly, this phenomenon was completely recovered to control levels by CE co-administration, independent of dosages. MeHg exposure inhibited cerebellar glutathione peroxidase (mean percentage inhibition of 42%) - an important enzyme involved in the detoxification of endogenous peroxides - and this effect was prevented by co-administration of CE. Conversely, MeHg exposure increased cerebellar glutathione reductase activity (mean percentage inhibition of 70%), and this phenomenon was not affected by C. paludosa co-administration. Neither MeHg nor CE changed the cerebellar glutathione levels. This study has shown for the first time, the in vivo protective effects of CE against MeHg-induced neurotoxicity. In addition, our findings encourage studies concerning the beneficial effects of C. paludosa on neurological conditions related to excitotoxicity and oxidative stress.

Sulforaphane Prevents Methylmercury-Induced Oxidative Damage and Excitotoxicity Through Activation of the Nrf2-ARE Pathway.

Methylmercury (MeHg) is a prominent environmental neurotoxicant, which induces oxidative damage and an indirect excitotoxicity caused by altered glutamate (Glu) metabolism. However, the interaction between oxidative damage and excitotoxicity in MeHg-exposed rats has not been fully recognized. Here, we explored the interaction between oxidative damage and excitotoxicity and evaluated the preventive effects of sulforaphane (SFN) on MeHg-induced neurotoxicity in rat cerebral cortex. Seventy-two rats were randomly assigned to four groups: control group, MeHg-treated groups (4 and 12 µmol/kg), and SFN pretreatment group. After treatment (28 days), the rats were killed and the cerebral cortex was analyzed. Then, Hg, glutathione (GSH), malondialdehyde (MDA), protein sulfhydryl, protein carbonyl, 8-hydroxy-2-deoxyguanosine (8-OHdG), and the levels of reactive oxygen species (ROS) and apoptosis were examined. Glu and glutamine (Gln) levels, glutamine synthetase (GS), phosphate-activated glutaminase (PAG), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), Na+-K+-ATPase and Ca2+-ATPase activities, intracellular Ca2+ levels, and the mRNA and protein expressions of Nrf2, Nrf2-regulated gene products, and N-methyl-D-aspartate receptors (NMDARs) were investigated in rat cerebral cortex. In our study, MeHg exposure not only induced Hg accumulation, apoptosis, ROS formation, GSH depletion, inhibition of antioxidant enzyme activities, and activation of Nrf2-ARE pathway signaling but also caused lipid, protein, and DNA peroxidative damage in a dose-dependent manner in rat cerebral cortex. Moreover, MeHg treatment significantly altered Gln/Glu cycling and NMDAR expression and resulted in calcium overloading. Furthermore, the present study also indicated that SFN pretreatment significantly reinforced the activation of the Nrf2-ARE pathway, which could prevent the toxic effects of MeHg exposure. Collectively, MeHg initiates multiple additive or synergistic disruptive mechanisms that lead to oxidative damage and excitotoxicity in rat cerebral cortex; pretreatment with SFN might prevent the MeHg-induced neurotoxicity by reinforcing the activation of the Nrf2-ARE pathway and then downregulating the interaction between oxidative damage and excitotoxicity pathways.

Co-consumption of selenium and vitamin E altered the reproductive and developmental toxicity of methylmercury in rats.

Methylmercury (MeHg), an environmental contaminant primarily found in fish and seafood, may pose long-term health risks to pregnant women and their developing children. The objective of this study was to determine whether co-consumption of nutritional supplements would alter the effects of MeHg on reproductive and developmental toxicity using a rodent model. Adult female rats were fed a diet containing additional selenium (1 ppm), additional vitamin E (225 IU/kg) or a combination of the two for 4 weeks before oral dosing of MeHg (1.25 mg/kg/day). Treatment with MeHg and dietary supplementation continued throughout pregnancy after which the dams were allowed to deliver their offspring. In addition to routine evaluations including periodic body weight measurements and daily clinical signs observations, dams and pups were evaluated for auditory startle habituation and pups were evaluated for developmental landmarks and reflexology. The dams and offspring were euthanized approximately 4 weeks after birth of the offspring. Results indicated that treatment with MeHg caused adverse effects on both reproduction of the dams and decreased progeny survival. However, the dams showed significant improvement in body weight gain during lactation and average auditory startle response time when the diet was enriched with both selenium and vitamin E. The combination of both vitamin E and Se also resulted in a significant increase in post-natal survival when compared to MeHg-treated group. There was no nutrient effect on the MeHg toxicity shown in offspring physical landmarks, performance in reflex tests and assessment of simple auricular startle response. Also, accelerated development as indicated by earlier opening in the pups of the supplemental diet groups was observed. These results suggest that antioxidant nutrients in the diet may alter MeHg reproductive and developmental toxicity. The underlying and human health implications warrant further investigations.

Methylmercury upregulates RE-1 silencing transcription factor (REST) in SH-SY5Y cells and mouse cerebellum.

Methylmercury (MeHg) is a highly neurotoxic compound that, in adequate doses, can cause damage to the brain, including developmental defects and in severe cases cell death. The RE-1-silencing transcription factor (REST) has been found to be involved in the neurotoxic effects of environmental pollutants such as polychlorinated biphenyls (PCBs). In this study, we investigated the effects of MeHg treatment on REST expression and its role in MeHg-induced neurotoxicity in neuroblastoma SH-SY5Y cells. We found that MeHg exposure caused a dose- and time- dependent apoptotic cell death, as evidenced by the appearance of apoptotic hallmarks including caspase-3 processing and annexin V uptake. Moreover, MeHg increased REST gene and gene product expression. MeHg-induced apoptotic cell death was completely abolished by REST knockdown. Interestingly, MeHg (1µM/24h) increased the expression of REST Corepressor (Co-REST) and its binding with REST whereas the other REST cofactor mammalian SIN3 homolog A transcription regulator (mSin3A) was not modified. In addition, we demonstrated that the acetylation of histone protein H4 was reduced after MeHg treatment and was critical for MeHg-induced apoptosis. Accordingly, the pan-histone deacetylase inhibitor trichostatin-A (TSA) prevented MeHg-induced histone protein H4 deacetylation, thereby reverting MeHg-induced neurotoxic effect. Male mice subcutaneously injected with 10mg/kg of MeHg for 10 days showed an increase in REST expression in the granule cell layer of the cerebellum together with a decrease in histone H4 acetylation. Collectively, we demonstrated that methylmercury exposure can cause neurotoxicity by activating REST gene expression and H4 deacetylation.

Neuroprotective Effect of Portulaca oleraceae Ethanolic Extract Ameliorates Methylmercury Induced Cognitive Dysfunction and Oxidative Stress in Cerebellum and Cortex of Rat Brain.

Methylmercury (MeHg) is highly toxic, and its principal target tissue in human is the nervous system, which has made MeHg intoxication a public health concern for many decades. Portulaca oleraceae (purslane), a member of the Portulacaceae family, is widespread as a weed and has been ranked the eighth most common plant in the world. In this study, we sought for potential beneficial effects of Portulaca oleracea ethanolic extract (POEE) against the neurotoxicity induced by MeHg in cerebellum and cortex of rats. Male Wistar rats were administered with MeHg orally at a dose of 5 mg/kg b.w. for 21 days. Experimental rats were given MeHg and also administered with POEE (4 mg/kg, orally) 1 h prior to the administration of MeHg for 21 days. After MeHg exposure, we determine the mercury concentration by atomic absorption spectroscopy (AAS); mercury content was observed high in MeHg-induced group. POEE reduced the mercury content. We also observed that the activities of catalase, superoxide dismutase, glutathione peroxidase, and the level of glutathione were reduced. The levels of glutathione reductase and thiobarbituric acid reactive substance were found to be increased. The above biochemical changes were found to be reversed with POEE. Behavioral changes like decrease tail flick response, longer immobility time, and decreased motor activity were noted down during MeHg exposure. POEE pretreatment offered protection from these behavioral changes. MeHg intoxication also caused histopathological changes in cerebellum and cortex, which was found to be normalized by treatment with POEE. The present results indicate that POEE has protective effect against MeHg-induced neurotoxicity.