Accumulation of mercury, selenium and their binding proteins in porcine kidney and liver from mercury-exposed areas with the investigation of their redox responses

MALDI-TOF-MS and XAS analysis of complexes formed by metallothionein with mercury and/or selenium

Mercury (Hg) is highly toxic while selenium (Se) has been found to antagonize Hg. Both Hg and Se have been found to induce metallothioneins (MTs). In this study, the complexes formed by metallothionein-1 (MT-1) with HgCl₂ and/or Na₂SeO₃ was studied using matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and X-ray absorption spectrometry (XAS). MALDI-TOF-MS and XAS indicated the formation of Hg-S bond or Se-S bond when MT-1 reacted with HgCl₂ or Na₂SeO₃, respectively. The bond lengths of Hg-S and coordination number in MT-Hg are 2.41 ± 0.02 Å and 3.10 and in MT-Se are 2.50 ± 0.03 Å and 2.69. A MT-Se-Hg complex was formed when MT-1 reacted with both HgCl₂ and Na₂SeO₃, in which the neighboring atom of Hg is Se, while the neighboring atoms of Se are S and Hg. Our study is an important step towards a better understanding of the interaction of HgCl₂ and/or Na₂SeO₃ with proteins like MT-1.

Evaluating the concentrations of total mercury, methylmercury, selenium, and selenium:mercury molar ratios in traditional foods of the Bigstone Cree in Alberta, Canada

Traditional foods provide nutritional, social, and economic benefits for Indigenous communities; however, anthropogenic activities have raised concerns about mercury (Hg), especially methylmercury (MeHg), in these foods. This issue may be of particular concern for communities near large industrial activities, including the Bigstone Cree Nation adjacent to the Athabasca oil sands region, Canada. This community-led study sought to assess variation in THg and MeHg concentrations among traditional food types (plants or animals), species, and tissues (muscles, organs), and variation in concentrations of the micronutrient selenium (Se)- thought to protect against Hg toxicity-and Se:THg ratios. Thirteen plant and animal species were collected in 2015 by Bigstone Cree community members. We quantified THg, Se, and Se:THg ratios in 65 plant and 111 animal samples and MeHg in 106 animal samples. For plants, the lichen, old man's beard (Usnea spp.), showed the highest concentrations of THg and Se (0.11 ± 0.02 and 0.08 ± 0.01 μg g^-1 w. w., respectively) and also had a low Se:THg molar ratio. Concentrations of THg, MeHg, and Se differed among animal samples (P < 0.010), showing variation among species and among tissues/organs. Generally, concentrations of THg and MeHg were highest in aquatic animals, which also had relatively low Se:THg molar ratios. Overall results revealed substantial variation in the patterns of THg, MeHg, Se and Se:THg ratios across this comprehensive basket of traditional foods. Thus, measuring concentrations of THg alone, without considering MeHg and potential associations with Se, may not adequately convey the exposure to Hg in traditional foods.

Nanoelemental selenium alleviated the mercury load and promoted the formation of high-molecular-weight mercury- and selenium-containing proteins in serum samples from methylmercury-poisoned rats

Selenite (Se⁴⁺) has been found to counteract the neurotoxicity of methylmercury (MeHg) in MeHg-poisoned rats. However, Se⁴⁺ has narrow range between its toxic and beneficial effects. Nanoelemental selenium (SeNPs) was found to be less toxic than other forms of Se such as Se⁴⁺. In this study, the effects of SeNPs on the load of mercury (Hg) in rats were investigated. Hyphenated technique based on size-exclusion chromatography coupled with UV and inductively coupled plasma mass spectrometry (SEC-ICP-MS) detection and synchrotron radiation X-ray fluorescence spectroscopy (SR-XRF) were used to analyze the Hg-Se-containing proteins in the serum from MeHg-poisoned rats. The Hg-Se-containing fractions monitored by UV and ICP-MS were further characterized by MALDI-TOF-MS. Elevated serum Hg and Se levels were found in MeHg-poisoned rats after SeNPs treatment. Three main Hg-containing bands with molecular weights (MWs) of 25, 62 and 140 kDa were detected in the control samples. Treatment with SeNPs increased the Hg content in proteins at 62 and 170 kDa and decreased the Hg content at 25 kDa. The fraction with 25 kDa was assigned to metallothioneins (MTs), and fractions with 40 and 75 kDa were assigned to albumin. This study showed that the low-toxicity SeNPs could reduce the Hg load in the tissues and promote the formation of high molecular weight Hg- and Se-containing proteins in MeHg-poisoned rats.

Niacin prevents mitochondrial oxidative stress caused by sub-chronic exposure to methylmercury

Humans and animals can be exposed to different chemical forms of mercury (Hg) in the environment. For example, methylmercury (MeHg)-contaminated fish is part of the basic diet of the riparian population in the Brazilian Amazon Basin, which leads to high total blood and plasma Hg levels in people living therein. Hg induces toxic effects mainly through oxidative stress. Different compounds have been used to prevent the damage caused by MeHg-induced reactive oxygen species (ROS). This study aims to investigate the in vivo effects of sub-chronic exposure to low MeHg levels on the mitochondrial oxidative status and to evaluate the niacin protective effect against MeHg-induced oxidative stress. For this purpose, Male Wistar rats were divided into four groups: control group, treated with drinking water on a daily basis; group exposed to MeHg at a dose of 100 µg/kg/day; group that received niacin at a dose of 50 mg/kg/day in drinking water, with drinking water being administered by gavage; group that received niacin at a dose of 50 mg/kg/day in drinking water as well as MeHg at a dose of 100 µg/kg/day. After 12 weeks, the rats, which weighed 500-550 g, were sacrificed, and their liver mitochondria were isolated by standard differential centrifugation. Sub-chronic exposure to MeHg (100 µg/kg/day for 12 weeks) led to mitochondrial swelling (p < 0.05) and induced ROS overproduction as determined by increased DFCH oxidation (p < 0.05), increased gluthatione oxidation (p < 0.05), and reduced protein thiol content (p < 0.05). In contrast, niacin supplementation inhibited oxidative stress, which counteracted and minimized the toxic MeHg effects on mitochondria.

Effects of methyl mercury exposure on pancreatic beta cell development and function

Methyl mercury is an environmental contaminant of worldwide concern. Since the discovery of methyl mercury exposure due to eating contaminated fish as the underlying cause of the Minamata disaster, the scientific community has known about the sensitivity of the developing central nervous system to mercury toxicity. Warnings are given to pregnant women and young children to limit consumption of foods containing methyl mercury to protect the embryonic, fetal and postnatally developing central nervous system. However, evidence also suggests that exposure to methyl mercury or various forms of inorganic mercury may also affect development and function of other organs. Numerous reports indicate a worldwide increase in diabetes, particularly type 2 diabetes. Quite recently, methyl mercury has been shown to have adverse effects on pancreatic beta (β) cell development and function, resulting in insulin resistance and hyperglycemia and may even lead to the development of diabetes. This review discusses possible mechanisms by which methyl mercury exposure may adversely affect pancreatic β cell development and function, and the role that methyl mercury exposure may have in the reported worldwide increase in diabetes, particularly type 2 diabetes. While additional information is needed regarding associations between mercury exposure and specific mechanisms of the pathogenesis of diabetes in the human population, methyl mercury's adverse effects on the body's natural sources of antioxidants suggest that one possible therapeutic strategy could involve supplementation with antioxidants. Thus, it is important that additional investigation be undertaken into the role of methyl mercury exposure and reduced pancreatic β cell function. Copyright © 2016 John Wiley & Sons, Ltd.

Sources of Mercury Exposure to Children in Low- and Middle-Income Countries

BACKGROUND

Many children in low- and middle-income countries face enhanced risks of exposure to contaminants via the environment, parental occupation, and other routes. While mercury (Hg) is a global pollutant whose transport properties allow it to have an impact even in pristine areas, the presence of significant Hg sources in the developing world can cause localized effects that are more severe than those observed in other areas.

OBJECTIVES

This paper provides a narrative review of sources of Hg exposure to people in the developing world with a particular focus on children, and presents an overview of key aspects to this important issue.

METHODS

We searched Web of Knowledge and Google Scholar using keywords including combinations of "mercury" and one or more of the following: "children," "exposure," "breast milk," "artisanal mining," "prenatal," "religion," "medicine," "dental amalgam," "chlor-alkali," "VCM," "vaccine," "e-waste," "industry," "beauty," "cosmetics," "strategies," "child labor," "costs," and "developing countries" to find peer-reviewed articles pertaining to Hg exposure in the developing world.

RESULTS

Sources of Hg exposure include mining, consumption, industrial operations, religious practices, traditional medicines, beauty products, vaccines, dental amalgams, and waste scavenging and recycling.

CONCLUSION

Children in the developing world are often subject to higher levels of Hg exposure than those living in developed countries due to the higher prevalence of Hg-intensive industrial processes and consumer products, lack of environmental regulation, and limits in mobility and food choices, among other factors. This issue can be addressed through additional research to fill in data gaps on exposure sources, establish sound and enforceable policies, and increase education and participation in affected communities. Challenges to addressing this problem include limited resources for needed equipment, training, and manpower to implement solutions.

Toxic and essential elements changed in black-legged kittiwakes (Rissa tridactyla) during their stay in an Arctic breeding area

Seasonal fluctuations in mercury (Hg), cadmium (Cd), zinc (Zn), copper (Cu) and selenium (Se) concentrations were studied in black-legged kittiwakes (Rissa tridactyla) from Kongsfjorden, Svalbard (79°57'N, 12°12'E). Element concentrations were determined in muscle and liver tissue in kittiwakes collected in May, July and October 2007. Stable isotopes of carbon (δ(13)C) and nitrogen (δ(15)N) were analysed in muscle tissue to calculate trophic position (TP) and examine the possible influence of carbon source on element accumulation. Metallothionein (MT) concentrations in liver, as well as Hg and Cd concentration in size-fractionated liver supernatant were determined to evaluate the association between elements and MT. Mercury concentrations declined from May through July to October in both tissues, while concentrations of Cd were similar in May and July and lower in October. A decline in TP between May and July, indicating a shift from fish-based diet towards an invertebrate-based diet explains the declining Hg concentration. The low Hg and Cd concentrations in October may be a result of an increased elimination, probably related to moulting. Selenium decreased in the same manner as Hg in liver and muscle, possibly related to the formation of Se-Hg complexes. Zinc and Cu did not fluctuate in muscle tissue, whereas hepatic Zn concentrations where highest in May. Hepatic Zn concentrations were higher in females compared to males in May, possibly related to egg production. Hepatic MT concentrations were lower in October compared to July, following the same trend as Hg and Cd. Cadmium was predominantly bound to the MT fraction of proteins in liver tissue, whereas Hg was associated with the larger proteins, indicating that MT was not sequestering Hg in the kittiwakes.

Study of selenium intake and disposition in various matrices based on mathematical algorithms derived from pooled biomonitoring data

Biomonitoring is increasingly used to assess exposure to selenium (Se) in the population. However, there is little harmonization among protocols used in the different studies (varying biological matrices, differences in expression of results (concentrations versus amounts, units)). This makes inter-comparison of biomonitoring results across studies difficult. From a public health risk perspective, it also becomes challenging to estimate baseline levels in biological matrices for populations exposed by various sources. The aim of this study was thus to perform a systematic analysis of the relationship between Se intakes and biological concentrations based on published data. Inclusion and exclusion criteria were used and led to select 75 published biomonitoring data in humans from an extended review of Se biomonitoring studies. This represents 8 628 individuals who provided biological samples aiming at documenting Se exposure and/or Se concentrations in two or more biological matrices. Mathematical algorithms that relate Se intakes to biological concentrations and establish matrix-to-matrix associations were derived from these pooled biomonitoring data. Logarithmic regressions showed good correlations between Se intakes and whole blood concentrations (R(2)=0.884), plasma concentrations (R(2)=0.863) and urinary excretion rates (R(2)=0.958). Blood and plasma concentrations were also strongly related (R(2)=0.874), as were whole blood concentrations and urinary excretion rates (R(2)=0.953). The interpretation of the log-regression coefficients allowed illustrating Se physiology. Se concentrations in plasma tend to plateau when daily intake exceed 150 μg/d, whereas Se in urine increases rapidly above this threshold. The application of the algorithms to other independent data sets in order to reconstruct past Se intakes confirmed that interpretation of results on the basis of Se in integuments may be misleading if external contamination is not avoided. This approach based on pooled data covered a wide range of exposure and the large number of data integrated increased the level of confidence of results.

Proteomic analysis of kidneys from selenoprotein M transgenic rats in response to increased bioability of selenium

BACKGROUND

To characterize changes in global protein expression in kidneys of transgenic rats overexpressing human selenoprotein M (SelM) in response to increased bioabivility of selenium (Sel), total proteins extracted from kidneys of 10-week-old CMV/hSelM Tg and wild-type rats were separated by 2-dimensional gel electrophoresis and measured for changes in expression.

RESULTS

Ten and three proteins showing high antioxidant enzymatic activity were up- and down-regulated, respectively, in SelM-overexpressing CMV/hSelM Tg rats compared to controls based on an arbitrary 2-fold difference. Up-regulated proteins included LAP3, BAIAP2L1, CRP2, CD73 antigen, PDGF D, KIAA143 homolog, PRPPS-AP2, ZFP313, HSP-60, and N-WASP, whereas down-regulated proteins included ALKDH3, rMCP-3, and STC-1. After Sel treatment, five of the up-regulated proteins were significantly increased in expression in wild-type rats, whereas there were no changes in CMV/hSelM Tg rats. Only two of the down-regulated proteins showed reduced expression in wild-type and Tg rats after Sel treatment.

CONCLUSIONS

These results show the primary novel biological evidences that new functional protein groups and individual proteins in kidneys of Tg rats relate to Sel biology including the response to Sel treatment and SelM expression.

Organic selenium supplementation increases mercury excretion and decreases oxidative damage in long-term mercury-exposed residents from Wanshan, China

Due to a long history of extensive mercury mining and smelting activities, local residents in Wanshan, China, are suffering from elevated mercury exposure. The objective of the present study was to study the effects of oral supplementation with selenium-enriched yeast in these long-term mercury-exposed populations. One hundred and three volunteers from Wanshan area were recruited and 53 of them were supplemented with 100 μg of organic selenium daily as selenium-enriched yeast while 50 of them were supplemented with the nonselenium-enriched yeast for 3 months. The effects of selenium supplementation on urinary mercury, selenium, and oxidative stress-related biomarkers including malondialdehyde and 8-hydroxy-2-deoxyguanosine were assessed. This 3-month selenium supplementation trial indicated that organic selenium supplementation could increase mercury excretion and decrease urinary malondialdehyde and 8-hydroxy-2-deoxyguanosine levels in local residents.

Linking protein oxidation to environmental pollutants: redox proteomic approaches

Environmental pollutants, such as compounds used in agriculture or deriving from vehicles, industries and human activities, can represent major concern for human health since they are considered to contribute significantly to many diseased states with major public health significance. Besides considerable epidemiological evidence linking environmental pollutants with adverse health effects, little information is provided on the effects of these compounds at the cellular and molecular level. Though oxidative stress is generally acknowledged as one of the most important mechanisms of action for pollutant-induced toxicity, redox proteomics, the elective tool to identify post-translationally oxidized proteins, is still in its very infancy in this field of investigation. This review will provide the readers with an outline of the use of redox proteomics in evaluating pollutant-induced oxidative damage to proteins in various biological systems. Future potential applications of redox proteomic approaches from an environmental point of view will be discussed as well.

Evidences of non-reactive mercury-selenium compounds generated from cultures of Pseudomonas fluorescens

This work was designed to determine chemically inert mercury-selenium (Hg-Se) compounds formed in a culture of Pseudomonas fluorescens exposed to Hg(2+) and Se(IV) (selenite). To isolate these compounds, different digestion methods were studied and sodium dodecyl sulfate (SDS) lysis was selected. The Hg(0) and non-reactive Hg were determined in two series of cultures containing 0.0-6.00 μg L(-1) Se(IV) (0.0-76.0 μmol L(-1)) in combination with low 5.00 μg L(-1) (0.025 μmol L(-1)) or high 100 μg L(-1) (0.500 μmol L(-1)) Hg(2+). It was found that Hg(0) formed in the culture decreased with the increase of initial Se(IV), while the non-reactive Hg increased with the Se(IV). In cultures with low initial [Hg(2+)], a median Se(IV) (2.0 μg L(-1) or 25.3 μmol L(-1)) resulted in about 70% of the added Hg(2+) sequestered as non-reactive Hg, and in culture with high initial Hg(2+), about 40% was sequestered. P. fluorescens was proved to be indispensible for the formation of the non-reactive Hg-Se compounds. The Hg:Se molar ratio in the non-reactive Hg-Se compounds was close to 1, suggesting the existence of mercuric selenide in cells. Mechanisms for the formation of the non-reactive Hg-Se compounds are proposed.

Octylguanidine ameliorates the damaging effect of mercury on renal functions

Mercurials are known to induce morphological and functional modifications in kidney. The protective effect of octylguanidine on the injury induced by Hg(2+) on renal functions was studied. Octylguanidine administered at a dose of 10 mg/kg body weight prevented the damage induced by Hg(2+) administration at a dose of 3 mg/kg body weight. The findings indicate that octylguanidine spared mitochondria from Hg(2+)-poisoning by preserving their ability to retain matrix content, such as accumulated Ca(2+) and pyridine nucleotides. The hydrophobic amine also protected mitochondria from the Hg(2+)-induced loss of the transmembrane potential, and from the oxidative injury of mitochondrial DNA. In addition, octylguanidine maintained renal functions, such as normal values of creatinine clearance and blood urea nitrogen (BUN), and serum creatinine after Hg(2+) administration. It is proposed that octylguanidine protects kidney by inhibiting Hg(2+) uptake to kidney tissue, and in consequence its binding to mitochondrial membrane through a screening phenomenon, in addition to its known action as inhibitor of permeability transition.

Selenite and selenate effects on mercury (Hg(2+)) uptake and distribution in tilapia, Oreochromis niloticus L., assessed by chronic bioassay

Aquatic organisms are considered excellent biomarkers of mercury (Hg) occurrence in the environment. Selenium (Se) acts in antagonism to this metal, stimulating its elimination, and reducing its toxicity. In this paper, tilapia (Oreochromis niloticus) were chronically acclimated in sub-lethal Hg(2+), Hg(2+) + Se(4+) and Hg(2+) + Se(6+) concentrations. Distribution and bioaccumulation of both elements were evaluated in fish tissues. The kidney was the main target of the Hg and Se uptake, and the presence of Hg induced the Se hepatic elimination. The Hg bioaccumulation in the gill, spleen and heart were higher in the presence of Se(6+) than in the presence of Se(4+).

The interaction of selenium and mercury in the accumulations and oxidative stress of rat tissues

This study evaluates the interaction of selenium (Se) and mercury (Hg) in the accumulations and oxidative stress of rat tissues. Rats were divided into five groups including one control (n=9) and four treated groups including M-Hg (n=9), L-Hg+Se (n=11), M-Hg+Se (n=10), and H-Hg+Se (n=10) group. Treated groups of rats were instilled with different amounts of mercuric chloride (HgCl(2)) and dl-selenomethionine (SeMet) by gavage since pregnancy of their mothers. Atomic fluorescence spectroscopy (AFS) was applied for mercury and selenium quantification. Glutathione (GSH), malondialdehyde (MDA), and total superoxide dismutase (SOD) activity of tissues were detected using biochemical methods. Results showed that Hg was deposited mainly in kidney. Se could decrease Hg content in kidney but increase it in blood and liver. Hg decreased GSH and SOD and increased MDA levels in most detected tissues, while Se took on a counteraction effect in same tissues. This study suggests that interactions of Se and Hg affect their accumulation and Se may antagonize Hg-induced inhibition on organic activities.

Low nanomolar concentration of mercury chloride increases vascular reactivity to phenylephrine and local angiotensin production in rats

Exposure to mercury at nanomolar level affects cardiac function but its effects on vascular reactivity have yet to be investigated. Pressor responses to phenylephrine (PHE) were investigated in perfused rat tail arteries before and after treatment with 6 nM HgCl2 during 1 h, in the presence (E+) and absence (E-) of endothelium, after L-NAME (10(-4) M), indomethacin (10(-5 )M), enalaprilate (1 microM), tempol (1 microM) and deferoxamine (300 microM) treatments. HgCl2 increased sensitivity (pD2) without modifying the maximum response (Emax) to PHE, but the pD2 increase was abolished after endothelial damage. L-NAME treatment increased pD2 and Emax. However, in the presence of HgCl2, this increase was smaller, and it did not modify Emax. After indomethacin treatment, the increase of pD2 induced by HgCl2 was maintained. Enalaprilate, tempol and deferoxamine reversed the increase of pD2 evoked by HgCl2. HgCl2 increased the angiotensin converting enzyme (ACE) activity explaining the result obtained with enalaprilate. Results suggest that at nanomolar concentrations HgCl2 increase the vascular reactivity to PHE. This response is endothelium mediated and involves the reduction of NO bioavailability and the action of reactive oxygen species. The local ACE participates in mercury actions and depends on the angiotensin II generation.

Role of Docosahexaenoic Acid in Modulating Methylmercury-Induced Neurotoxicity

The effect of docosahexaenoic acid (DHA) in modulating methylmercury (MeHg)-induced neurotoxicity was investigated in C6-glial and B35-neuronal cell lines. Gas chromatography measurements indicated increased DHA content in both the cell lines after 24 h supplementation. Mitochondrial activity evaluated by 3-(4, 5-dimethylthiazol-2-yl)-2, 5 diphenyltetrazolium bromide (MTT) reduction indicated that 10 microM MeHg treatment for 50 min led to a significant (p < 0.001) and similar decrease in MTT activity in both the cell lines. However, DHA pretreatment led to more pronounced depletion (p < 0.05) in the MTT activity in C6 cells as compared to B35 cells. The depletion of glutathione (GSH) content measured with the fluorescent indicator monochlorobimane was more apparent (p < 0.001) in C6 cells treated with DHA and MeHg. The amount of reactive oxygen species (ROS) detected with the fluorescent indicator -- chloromethyl derivative of dichloro dihydro fluorescein diacetate (CMH(2)DCFDA) -- indicated a fourfold increase in C6 cells (p < 0.001) as compared to twofold increase in B35 cells (p < 0.001) upon DHA and MeHg exposure. However, the cell-associated MeHg measurement using (14)C-labeled MeHg indicated a decrease (p < 0.05) in MeHg accumulation upon DHA exposure in both the cell lines. These findings provide experimental evidence that although pretreatment with DHA reduces cell-associated MeHg, it causes an increased ROS (p < 0.001) and GSH depletion (p < 0.05) in C6 cells.

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.

Methylmercury induces oxidative injury, alterations in permeability and glutamine transport in cultured astrocytes

The neurotoxicity of high levels of methylmercury (MeHg) is well established both in humans and experimental animals. Astrocytes accumulate MeHg and play a prominent role in mediating MeHg toxicity in the central nervous system (CNS). Although the precise mechanisms of MeHg neurotoxicity are ill-defined, oxidative stress and altered mitochondrial and cell membrane permeability appear to be critical factors in its pathogenesis. The present study examined the effects of MeHg treatment on oxidative injury, mitochondrial inner membrane potential, glutamine uptake and expression of glutamine transporters in primary astrocyte cultures. MeHg caused a significant increase in F(2)-isoprostanes (F(2)-IsoPs), lipid peroxidation biomarkers of oxidative damage, in astrocyte cultures treated with 5 or 10 microM MeHg for 1 or 6 h. Consistent with this observation, MeHg induced a concentration-dependant reduction in the inner mitochondrial membrane potential (DeltaPsi(m)), as assessed by the potentiometric dye, tetramethylrhodamine ethyl ester (TMRE). Our results demonstrate that DeltaPsi(m) is a very sensitive endpoint for MeHg toxicity, since significant reductions were observed after only 1 h exposure to concentrations of MeHg as low as 1 microM. MeHg pretreatment (1, 5 and 10 microM) for 30 min also inhibited the net uptake of glutamine ((3)H-glutamine) measured at 1 min and 5 min. Expression of the mRNA coding the glutamine transporters, SNAT3/SN1 and ASCT2, was inhibited only at the highest (10 microM) MeHg concentration, suggesting that the reduction in glutamine uptake observed after 30 min treatment with lower concentrations of MeHg (1 and 5 microM) was not due to inhibition of transcription. Taken together, these studies demonstrate that MeHg exposure is associated with increased mitochondrial membrane permeability, alterations in glutamine/glutamate cycling, increased ROS formation and consequent oxidative injury. Ultimately, MeHg initiates multiple additive or synergistic disruptive mechanisms that lead to cellular dysfunction and cell death.