Search

The widespread use of nanomaterials in daily life has led to increased concern about their potential neurotoxicity. Therefore, it is particularly important to establish a simple and reproducible assessment system. Representative nanomaterials, including cobalt nanoparticles (CoNPs), titanium dioxide nanoparticles (TiO2-NPs), and multiwall carbon nanotubes (MWCNTs), were compared in terms of their neurotoxicity and underlying mechanisms. In 0, 25, 50, and 75 μg/ml of these nanomaterials, the survival, locomotion behaviors, acetylcholinesterase (AchE) activity, reactive oxygen species production, and glutathione-S transferase 4 (Gst-4) activation in wildtype and transgenic Caenorhabditis elegans (C. elegans) were evaluated. All nanomaterials induced an imbalance in oxidative stress, decreased the ratio of survival, impaired locomotion behaviors, as well as reduced the activity of AchE in C. elegans. Interestingly, CoNPs and MWCNTs activated Gst-4 , but not TiO2-NPs. The reactive oxygen species scavenger, N-acetyl- l -cysteine, alleviated oxidative stress and Gst-4 upregulation upon exposure to CoNPs and MWCNTs, and rescued the locomotion behaviors. MWCNTs caused the most severe damage, followed by CoNPs and TiO2-NPs. Furthermore, oxidative stress and subsequent activation of Gst-4 were involved in nanomaterials-induced neurotoxicity. Our study provides a comprehensive comparison of the neurotoxicity and mechanisms of typical nanomaterials, which could serve as a model for hazard assessment of environmental pollutants using C. elegans as an experimental model system. [ABSTRACT FROM AUTHOR]

Premature infants with germinal matrix haemorrhage–intraventricular haemorrhage (GMH-IVH) suffer from neurobehavioural deficits as they enter childhood and adolescence. Yet the underlying mechanisms remain unclear. Impaired development and function of interneurons contribute to neuropsychiatric disorders. Therefore, we hypothesized that the occurrence of IVH would reduce interneuron neurogenesis in the medial ganglionic eminence and diminish the population of parvalbumin+ and somatostatin+ cortical interneurons. Because Sonic Hedgehog promotes the production of cortical interneurons, we also postulated that the activation of Sonic Hedgehog signalling might restore neurogenesis, cortical interneuron population, and neurobehavioural function in premature newborns with IVH. These hypotheses were tested in a preterm rabbit model of IVH and autopsy samples from human preterm infants. We compared premature newborns with and without IVH for intraneuronal progenitors, cortical interneurons, transcription factors regulating neurogenesis, single-cell transcriptome of medial ganglionic eminence and neurobehavioural functions. We treated premature rabbit kits with adenovirus expressing Sonic Hedgehog (Ad-Shh) or green fluorescence protein gene to determine the effect of Sonic Hedgehog activation on the interneuron production, cortical interneuron population and neurobehaviour. We discovered that IVH reduced the number of Nkx2.1+ and Dlx2+ progenitors in the medial ganglionic eminence of both humans and rabbits by attenuating their proliferation and inducing apoptosis. Moreover, IVH decreased the population of parvalbumin+ and somatostatin+ neurons in the frontal cortex of both preterm infants and kits relative to controls. Sonic Hedgehog expression and the downstream transcription factors, including Nkx2.1, Mash1, Lhx6 and Sox6, were also reduced in kits with IVH. Consistent with these findings, single-cell transcriptomic analyses of medial ganglionic eminence identified a distinct subpopulation of cells exhibiting perturbation in genes regulating neurogenesis, ciliogenesis, mitochondrial function and MAPK signalling in rabbits with IVH. More importantly, restoration of Sonic Hedgehog level by Ad-Shh treatment ameliorated neurogenesis, cortical interneuron population and neurobehavioural function in kits with IVH. Additionally, Sonic Hedgehog activation alleviated IVH-induced inflammation and several transcriptomic changes in the medial ganglionic eminence. Taken together, IVH reduced intraneuronal production and cortical interneuron population by downregulating Sonic Hedgehog signalling in both preterm rabbits and humans. Notably, activation of Sonic Hedgehog signalling restored interneuron neurogenesis, cortical interneurons and cognitive function in rabbit kits with IVH. These findings highlight disruption in cortical interneurons in IVH and identify a novel therapeutic strategy to restore cortical interneurons and cognitive function in infants with IVH. These studies can accelerate the development of new therapies to enhance the neurodevelopmental outcome of survivors with IVH. [ABSTRACT FROM AUTHOR]

Background Hydrogen sulfide (H2S), as the third gasotransmitter participates in both cellular physiological and pathological processes, including chemical-induced injuries. We recently reported acute acrylonitrile (AN) treatment inhibited endogenous H2S biosynthesis pathway in rat and astrocyte models. However, there is still no evidence to address the correlation between endogenous H2S and sub-chronic AN exposure. Objectives This study aims to explore the modulatory effects of prolonged AN exposure on endogenous H2S levels and its biosynthetic enzymes in rat blood, brain and liver. Methods A total of 50 male Sprague-Dawley rats were randomly divided into 5 groups, including the control group and AN-treated groups at dosages of 6.25, 12.5, 25 or 50 mg/kg. Rats received one exposure/day, 5 days/week, for 4 consecutive weeks. The rat bodyweight and brain/liver organ coefficient were detected, along with liver cytochrome P450 2E1(CYP2E1) expression. In addition, the H2S contents in rat serum and plasma, and in cerebral cortex and liver tissues were measured by methylene blue method. The expression of H2S-generating enzymes, including cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MPST) was also measured with Western blot both in rat cerebral cortex and liver. Results Subchronic exposure to AN significantly inhibited bodyweight-gain and increased the liver CYP2E1 expression compared with the control. In addition, AN significantly increased H2S levels in rat plasma and serum, but not in liver. The endogenous H2S level in rat cerebral cortex was also significantly increased upon AN treatment, when expression of the major H2S-generating enzymes, CBS and 3-MPST were significantly enhanced. However, hepatic protein levels of CBS and CSE were significantly increased, whereas hepatic levels of 3-MPST were significantly decreased. Conclusion This study showed that sub-chronic AN exposure increased endogenous H2S contents in rat blood and brain tissues, but not liver, which may be resulted from the distinct expression profile of H2S-producing enzymes in response to AN. The blood H2S contents may be applied as a potential novel biomarker for surveillance of chronically AN-exposed populations. Highlights Subchronic intraperitoneal exposure to acrylonitrile increased H2S content in rat blood and cerebral cortex, but not in liver. Distinct tissue expression profiles of H2S-producing enzymes contribute to the acrylonitrile-induced differential effects on the H2S level. Blood H2S level may be a biomarker for subchronic exposure to acrylonitrile. [ABSTRACT FROM AUTHOR]

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder that affects the competence of academic performance and social wellness in children and adults. The causes of ADHD are unclear. Both genetic and environmental factors contribute to the development of ADHD. The behavioral impairments in ADHD are associated with epigenetic changes in genes that are important for neurodevelopment. Among environmental causes of ADHD, the neurotoxin methylmercury (MeHg) is associated with an increased risk for ADHD. Developing children are susceptible to neurotoxic effects of prenatal MeHg exposure. Human epidemiology studies have shown that prenatal MeHg exposure could invoke epigenetic changes in genes that are involved in ADHD. In addition, the pathogenesis of ADHD involves dopaminergic system, which is a target of developmental MeHg exposure. MeHg-induced alterations in the dopaminergic system have a profound impact on behavioral functions in adults. As a trace level of MeHg (around nM) can induce long-lasting behavioral alterations, potential mechanisms of MeHg-induced functional changes in the dopaminergic system may involve epigenetic mechanisms. Here, we review the relevant evidence on developmental MeHg exposures and the risk for ADHD. We also point out research gaps in understanding environmental causes of ADHD. [ABSTRACT FROM AUTHOR]

Excess cobalt may lead to metallosis, characterized by sensorineural hearing loss, visual, and cognitive impairment, and peripheral neuropathy. In the present study, we sought to address the molecular mechanisms of cobalt-induced neurotoxicity, using Caenorhabditis elegans as an experimental model. Exposure to cobalt chloride for 2 h significantly decreased the survival rate and lifespan in nematodes. Cobalt chloride exposure led to increased oxidative stress and upregulation of glutathione S-transferase 4. Consistently, its upstream regulator skn-1 , a mammalian homolog of the nuclear factor erythroid 2-related factor 2, was activated. Among the mRNAs examined by quantitative real-time polymerase chain reactions, apoptotic activator egl-1 , proapoptotic gene ced-9 , autophagic (bec-1 and lgg-1), and mitochondrial fission regulator drp-1 were significantly upregulated upon cobalt exposure, concomitant with mitochondrial fragmentation, as determined by confocal microscopy. Moreover, drp-1 inhibition suppressed the cobalt chloride-induced reactive oxygen species generation, growth defects, and reduced mitochondrial fragmentation. Our novel findings suggest that the acute toxicity of cobalt is mediated by mitochondrial fragmentation and drp-1 upregulation. [ABSTRACT FROM AUTHOR]

Manganese (Mn) is an essential metal, but excessive exposures have been well-documented to culminate in neurotoxicity. Curiously, the precise mechanisms of Mn neurotoxicity are still unknown. One hypothesis suggests that Mn exerts its toxicity by inhibiting mitochondrial function, which then (if exposure levels are high and long enough) leads to cell death. Here, we used a Huntington's disease cell model with known differential sensitivities to manganese—ST Hdh Q7/Q7 and ST Hdh Q111/Q111 cells—to examine the effects of acute Mn exposure on mitochondrial function. We determined toxicity thresholds for each cell line using both changes in cell number and caspase-3/7 activation. We used a range of acute Mn exposures (0–300 µM), both above and below the cytotoxic threshold, to evaluate mitochondria-associated metabolic balance, mitochondrial respiration, and substrate dependence. In both cell lines, we observed no effect on markers of mitochondrial function at subtoxic Mn exposures (below detectable levels of cell death), yet at supratoxic exposures (above detectable levels of cell death) mitochondrial function significantly declined. We validated these findings in primary striatal neurons. In cell lines, we further observed that subtoxic Mn concentrations do not affect glycolytic function or major intracellular metabolite quantities. These data suggest that in this system, Mn exposure impairs mitochondrial function only at concentrations coincident with or above the initiation of cell death and is not consistent with the hypothesis that mitochondrial dysfunction precedes or induces Mn cytotoxicity. [ABSTRACT FROM AUTHOR]

Methylmercury (MeHg) is a well-known neurotoxicant; however, its role in metabolic diseases has been gaining wider attention. We have previously shown that MeHg causes metabolic alterations in Caenorhabditis elegans , leading to decreased nicotinamide adenine dinucleotide cofactor, mitochondrial dysfunction, and oxidative stress. We were, therefore, interested in whether MeHg also affects nutrient metabolism, particularly lipid homeostasis, which may contribute to the development of metabolic conditions such as obesity or metabolic syndrome (MS). RNA from wild-type worms exposed to MeHg was collected immediately after treatment and used for gene expression analysis by DNA microarray. MeHg differentially regulated 215 genes, 17 genes involved in lipid homeostasis, and 12 genes involved in carbohydrate homeostasis. Of particular interest was cebp-1 , the worm ortholog to human C/EBP, a pro-adipogenic transcription factor implicated in MS. MeHg increased the expression of cebp-1 as well as pro-adipogenic transcription factors sbp-1 and nhr-49 , triglyceride synthesis enzyme acl-6 , and lipid transport proteins vit-2 and vit-6. Concurrent with the altered gene expression, MeHg increased triglyceride levels, lipid storage, and feeding behaviors. Worms expressing mutant cebp-1 were protected from MeHg-induced alterations in lipid content, feeding behaviors, and gene expression, highlighting the importance of this transcription factor in the worm's response to MeHg. Taken together, our data demonstrate that MeHg induces biochemical, metabolic, and behavioral changes in C. elegans that can lead to metabolic dysfunction. [ABSTRACT FROM AUTHOR]

Laboratorial and epidemiological research has established a relationship between paraquat (PQ) exposure and a risk for Parkinson's disease. Previously, we have investigated the effects of nuclear factor erythroid 2 related factor 2 (Nrf2) and microRNAs in PQ-induced neurotoxicity, addressing the function of miR-380-3p, a microRNA dysregulated by PQ, as well as Nrf2 deficiency. Nrf2 is known to mediate the expression of a variety of genes, including noncoding genes. By chromatin immunoprecipitation, we identified the relationship between Nrf2 and miR-380-3p in transcriptional regulation. qRT-PCR, Western blots, and dual-luciferase reporter gene assay showed that miR-380-3p blocked the translation of the transcription factor specificity protein-3 (Sp3) in the absence of degradation of Sp3 mRNA. Results based on cell counting analysis, annexin v-fluorescein isothiocyanate/propidium iodide double-staining assay, and propidium iodide staining showed that overexpression of miR-380-3p inhibited cell proliferation, increased the apoptotic rate, induced cell cycle arrest, and intensified the toxicity of PQ in mouse neuroblastoma (N2a [Neuro2a]) cells. Knockdown of Sp3 inhibited cell proliferation and eclipsed the alterations induced by miR-380-3p in cell proliferation. Two mediators of apoptosis and cell cycle identified in previous studies as Sp3-regulated, namely cyclin-dependent kinase inhibitor 1 (p21) and calmodulin (CaM), were dysregulated by PQ, but not Sp3 deficiency. In conclusion, Nrf2-regulated miR-380-3p inhibited cell proliferation and enhanced the PQ-induced toxicity in N2a cells potentially by blocking the translation Sp3 mRNA. We conclude that CaM and p21 were involved in PQ-induced toxicity. [ABSTRACT FROM AUTHOR]

Methylmercury (MeHg) is an environmental pollutant that affects primarily the central nervous system (CNS), causing neurological alterations. An early symptom of MeHg poisoning is the loss of body weight and appetite. Moreover, the CNS has an important role in controlling energy homeostasis. It is known that in the hypothalamus nutrient and hormonal signals converge to orchestrate control of body weight and food intake. In this study, we investigated if MeHg is able to induce changes in the expression of key hypothalamic neuropeptides that regulate energy homeostasis. Thus, hypothalamic neuronal mouse cell line GT 1-7 was treated with MeHg at different concentrations (0, 0.5, 1, and 5 µM). MeHg induced the expression of the anorexigenic neuropeptide pro-omiomelanocortin (Pomc) and the orexigenic peptide Agouti-related peptide (Agrp) in a concentration-dependent manner, suggesting deregulation of mechanisms that control body weight. To confirm these in vitro observations, 8-week-old C57BL/6J mice (males and females) were exposed to MeHg in drinking water, modeling the most prevalent exposure route to this metal. After 30-day exposure, no changes in body weight were detected. However, MeHg treated males showed a significant decrease in fat depots. Moreover, MeHg affected the expression of hypothalamic neuropeptides that control food intake and body weight in a gender- and dose-dependent manner. Thus, MeHg increases Pomc mRNA only in males in a dose-dependent way, and it does not have effects on the expression of Agrp mRNA. The present study shows, for first time, that MeHg is able to induce changes in hypothalamic neuropeptides that regulate energy homeostasis, favoring an anorexigenic/catabolic profile. [ABSTRACT FROM AUTHOR]

Recent epidemiological data indicate that the popularity of electronic cigarettes (e-cigarettes), and consequently nicotine use, is rising in both adolescent and adult populations. As nicotine is a known developmental neurotoxin, these products present a potential threat for those exposed during early life stages. Despite this, few studies have evaluated the toxicity of e-cigarettes on the developing central nervous system. The goal of this study was to assess neurotoxicity resulting from early-life exposure to electronic cigarette aerosols in an in vivo model. Specifically, studies here focused on neuroparameters related to neuroinflammation and neurotrophins. To accomplish this, pregnant and neonatal C57BL/6 mice were exposed to aerosols produced from classic tobacco flavor e-cigarette cartridges (with [13 mg/ml] and without nicotine) during gestation (~3 weeks) and lactation (~3 weeks) via whole-body inhalation. Exposure to e-cigarette aerosols with and without nicotine caused significant reductions in hippocampal gene expression of Ngfr and Bdnf, as well as in serum levels of cytokines IL-1β, IL-2, and IL-6. Exposure to e-cigarette aerosols without nicotine enhanced expression of Iba-1, a specific marker of microglia, in the cornus ammonis 1 region of the hippocampus. Overall, our novel results indicate that exposure to e-cigarette aerosols, with and without nicotine, poses a considerable risk to the developing central nervous system. Consequently, e-cigarettes should be considered a potential public health threat, especially early in life, requiring further research and policy considerations. [ABSTRACT FROM AUTHOR]

Objectives: Exposure to manganese (Mn) may cause movement disorders, but less is known whether the effects persist after the termination of exposure. This study investigated the association between former exposure to Mn and fine motor deficits in elderly men from an industrial area with steel production. Methods: Data on the occupational history and fine motor tests were obtained from the second follow-up of the prospective Heinz Nixdorf Recall Study (2011-2014). The study population included 1232 men (median age 68 years). Mn in blood (MnB) was determined in archived samples (2000-2003). The association between Mn exposure (working as welder or in other at-risk occupations, cumulative exposure to inhalable Mn, MnB) with various motor functions (errors in line tracing, steadiness, or aiming and tapping hits) was investigated with Poisson and logistic regression, adjusted for iron status and other covariates. Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated for substantially impaired dexterity (errors >90th percentile, tapping hits <10th percentile). Results: The median of cumulative exposure to inhalable Mn was 58 µg m-3 years in 322 men who ever worked in at-risk occupations. Although we observed a partly better motor performance of exposed workers at group level, we found fewer tapping hits in men with cumulative Mn exposure >184.8 µg m-3 years (OR 2.15, 95% CI 1.17--3.94). MnB ≥ 15 µg l-1, serum ferritin ≥ 400 µg l-1, and gamma-glutamyl transferase ≥74 U l-1 were associated with a greater number of errors in line tracing. Conclusions: We found evidence that exposure to inhalable Mn may carry a risk for dexterity deficits. Whether these deficits can be exclusively attributed to Mn remains to be elucidated, as airborne Mn is strongly correlated with iron in metal fumes, and high ferritin was also associated with errors in line tracing. Furthermore, hand training effects must be taken into account when testing for fine motor skills. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is the result of complex interactions between genetic and environmental factors. Two chemically distinct environmental stressors relevant to PD are the metal manganese and the pesticide rotenone. Both are thought to exert neurotoxicity at least in part via oxidative stress resulting from impaired mitochondrial activity. Identifying shared mechanism of action may reveal clues towards an understanding of the mechanisms underlying PD pathogenesis. Here we compare the effects of manganese and rotenone in human-induced pluripotent stem cells-derived postmitotic mesencephalic dopamine neurons by assessing several different oxidative stress endpoints. Manganese, but not rotenone caused a concentration and time-dependent increase in intracellular reactive oxygen/nitrogen species measured by quantifying the fluorescence of oxidized chloromethyl 20,70-dichlorodihydrofluorescein diacetate (DCF) assay. In contrast, rotenone but not manganese caused an increase in cellular isoprostane levels, an indicator of lipid peroxidation. Manganese and rotenone both caused an initial decrease in cellular reduced glutathione; however, glutathione levels remained low in neurons treated with rotenone for 24h but recovered in manganese-exposed cells. Neurite length, a sensitive indicator of overall neuronal health was adversely affected by rotenone, but not manganese. Thus, our observations suggest that the cellular oxidative stress evoked by these 2 agents is distinct yielding unique oxidative stress signatures across outcome measures. The protective effect of rasagiline, a compound used in the clinic for PD, had negligible impact on any of oxidative stress outcome measures except a subtle significant decrease in manganese-dependent production of reactive oxygen/nitrogen species detected by the DCF assay. [ABSTRACT FROM AUTHOR]

The influence of routine guarana (Paullinia cupana) consumption on apparent tolerance to mercury intoxication has been proposed. The present study investigated this hypothesis in Caenorhabditis elegans, a suitable experimental model for studies in toxicology. Wild type (WT) and skn-1 (ok2315) worm strains were pretreated with guarana ethanolic extract (GEE) from larvae 1 (L1) to L4 stage and then exposed for 6 hours to methylmercury (MeHg). The analyses included evaluation of GEE's effects on lethality, developmental delay, feeding, locomotion, gene expression (sod-3, gst-4, sir-2.1, hsf-1, snn-1, mtl-1, mtl-2, aat-1, aat-2 and aat-3) and antioxidant activity. GEE pre-treatment had no aberrant effects on WT worms exposed to MeHg, and protected skn-1 (ok2315) worms, which are more susceptible to environmental stresses. The protective effects of GEE might be dependent on modulation of genes other than those directly involved in antioxidant activity. GEE increased the expression of genes involved in metal transport (aat-2), metal detoxification (mtl-1 and mtl-2) and antioxidant responses (sir-2.1 and sod-3). Thus, routine consumption of guarana might be beneficial in protecting against MeHg-induced toxicity. [ABSTRACT FROM AUTHOR]

Methylmercury (MeHg) is a neurotoxic contaminant of our fish supply that has been linked to dopaminergic (DAergic) dysfunction that characterizes Parkinson's disease. We have previously shown that MeHg causes both morphological and behavioral changes in the Caenorhabditis elegans DAergic neurons that are associated with oxidative stress. We were therefore interested in whether the redox sensitive cofactor nicotinamide adenine dinucleotide (NAD+) may be affected by MeHg and whether supplementation of NAD+may prevent MeHg-induced toxicities. Worms treated with MeHg showed depletion in cellular NAD+levels, which was prevented by NAD+supplementation prior to MeHg treatment. NAD+supplementation also prevented DAergic neurodegeneration and deficits in DAergic-dependent behavior upon MeHg exposure. In a mutant worm line that cannot synthesize NAD+from nicotinamide, MeHg lethality and DAergic behavioral deficits were more sensitive to MeHg than wildtype worms, demonstrating the importance of NAD+in MeHg toxicity. In wildtype worms, NAD+supplementation provided protection from MeHg-induced oxidative stress and mitochondrial dysfunction. These data show the importance of NAD+levels in the response to MeHg exposure. NAD+supplementation may be beneficial for MeHg-induced toxicities and preventing cellular damage involved in Parkinson's disease. [ABSTRACT FROM AUTHOR]

Neurotoxicity has been linked to a number of common drugs and chemicals, yet efficient and accurate methods to detect it are lacking. There is a need for more sensitive and specific biomarkers of neurotoxicity that can help diagnose and predict neurotoxicity that are relevant across animal models and translational from nonclinical to clinical data. Fluid-based biomarkers such as those found in serum, plasma, urine, and cerebrospinal fluid (CSF) have great potential due to the relative ease of sampling compared with tissues. Increasing evidence supports the potential utility of fluid-based biomarkers of neurotoxicity such as microRNAs, F2-isoprostanes, translocator protein, glial fibrillary acidic protein, ubiquitin C-terminal hydrolase L1, myelin basic protein, microtubule-associated protein-2, and total tau. However, some of these biomarkers such as those in CSF require invasive sampling or are specific to one disease such as Alzheimer's, while others require further validation. Additionally, neuroimaging methodologies, including magnetic resonance imaging, magnetic resonance spectroscopy, and positron emission tomography, may also serve as potential biomarkers and have several advantages including being minimally invasive. The development of biomarkers of neurotoxicity is a goal shared by scientists across academia, government, and industry and is an ideal topic to be addressed via the Health and Environmental Sciences Institute (HESI) framework which provides a forum to collaborate on key challenging scientific topics. Here we utilize the HESI framework to propose a consensus on the relative potential of currently described biomarkers of neurotoxicity to assess utility of the selected biomarkers using a nonclinical model. [ABSTRACT FROM AUTHOR]

Exposure to organophosphates (OPs) can lead to cognitive deficits and oxidative damage. Little is known about the relationship between behavioral deficits and oxidative stress within the context of such exposures. Accordingly, the first experiment was carried out to address this issue. Male Wistar rats were administered 250mg/kg of chlorpyrifos (CPF), 1.5mg/kg of diisopropylphosphorofluoridate (DFP), or 15mg/kg of parathion (PTN). Spatial learning in the water maze task was evaluated, and F2-isoprostanes (F2-IsoPs) and prostaglandin (PGE2) were analyzed in the hippocampus. A second experiment was designed to determine the degree of inhibition of brain acetylcholinesterase (AChE) activity, both the soluble and particulate forms of the enzyme, and to assess changes in AChE gene expression given evidence on alternative splicing of the gene in response to OP exposures. In addition, brain acylpeptide hydrolase (APH) activity was evaluated as a second target for OP-mediated effects. In both experiments, rats were sacrificed at various points to determine the time course of OPs toxicity in relation to their mechanism of action. Results from the first experiment suggest cognitive and emotional deficits after OPs exposure, which could be due to, at least in part, increased F2-IsoPs levels. Results from the second experiment revealed inhibition of brain AChE and APH activity at various time points post OP exposure. In addition, we observed increased brain read-through splice variant AChE (AChE-R) mRNA levels after 48h PTN exposure. In conclusion, this study provides novel data on the relationship between cognitive alterations and oxidative stress, and the diverse mechanisms of action along a temporal axis in response to OP exposures in the rat. [ABSTRACT FROM PUBLISHER]

Methylmercury (MeHg) is an environmental pollutant that biomagnifies throughout the aquatic food chain, thus representing a toxicological concern for humans subsiding on fish for their dietary intake. Although the developing brain is considered the critical target organ of MeHg toxicity, recent evidence indicates that the cardiovascular system may be the most sensitive in adults. However, data on the mechanisms mediating MeHg-induced cardiovascular toxicity are scarce. Based on the close relationship between cardiovascular disease and dyslipidemia, this study was designed to investigate the effects of long-term MeHg exposure on plasma lipid levels in mice, as well as their underlying mechanisms and potential relationships to MeHg-induced neurotoxicity. Our major finding was that long-term MeHg exposure induced dyslipidemia in rodents. Specifically, Swiss and C57BL/6 mice treated for 21 days with a drinking solution of MeHg (40mg/l, ad libitum) diluted in tap water showed increased total and non-HDL plasma cholesterol levels. MeHg-induced hypercholesterolemia was also observed in low-density lipoprotein receptor knockout (LDLr–/–) mice, indicating that this effect was not related to decreased LDLr-mediated cholesterol transport from blood to other tissues. Although the hepatic synthesis of cholesterol was unchanged, significant signs of nephrotoxicity (glomerular shrinkage, tubular vacuolization, and changed urea levels) were observed in MeHg-exposed mice, indicating that the involvement of nephropathy in MeHg-induced lipid dyshomeostasis may not be ruled out. Notably, Probucol (a lipid-lowering drug) prevented the development of hypercholesterolemia when coadministered with MeHg. Finally, hypercholesterolemic LDLr–/– mice were more susceptible to MeHg-induced cerebellar glial activation, suggesting that hypercholesterolemia in itself may pose a risk factor in MeHg-induced neurotoxicity. Overall, based on the strong and graded positive association between total as well as LDL cholesterol and risk of cardiovascular diseases, our data support the concept of MeHg-induced cardiovascular toxicity. [ABSTRACT FROM PUBLISHER]

Aims Pulmonary arterial endothelial cells (PAECs) express the enzymes needed for generation of l-arginine from intracellular l-citrulline but do not express the enzymes needed for de novo l-citrulline synthesis. Hence, l-citrulline levels in PAECs are dependent on l-citrulline transport. Once generated, l-arginine can be converted to l-citrulline and nitric oxide (NO) by the enzyme NO synthase. We sought to determine whether hypoxia, a condition aetiologically linked to pulmonary hypertension, alters the transport of l-citrulline and the expression of the sodium-coupled neutral amino acid transporters (SNATs) in PAECs from newborn piglets. Methods and results PAECs isolated from newborn piglets were cultured under normoxic and hypoxic conditions and used to measure SNAT1, 2, 3, and 5 protein expression and 14C-l-citrulline uptake. SNAT1 protein expression was increased, while SNAT2, SNAT3, and SNAT5 expression was unaltered in hypoxic PAECs. 14C-l-citrulline uptake was increased in hypoxic PAECs. Studies with inhibitors of System A (SNAT1/2) and System N (SNAT3/5) revealed that the increased 14C-l-citrulline uptake was largely due to System A-mediated transport. Additional studies were performed to evaluate SNAT protein expression and l-citrulline levels in lungs of piglets with chronic hypoxia-induced pulmonary hypertension and comparable age controls. Lungs from piglets raised in chronic hypoxia exhibited greater SNAT1 expression and higher l-citrulline levels than lungs from controls. Conclusion Increased SNAT1 expression and the concomitant enhanced ability to transport l-citrulline in PAECs could represent an important regulatory mechanism to counteract NO signalling impairments known to occur during the development of chronic hypoxia-induced pulmonary hypertension in newborns. [ABSTRACT FROM AUTHOR]

The wild-type (WT) Cprlox/lox (cytochrome P450 oxidoreductase, Cpr) mouse is an ideal model to assess the contribution of P450 enzymes to the metabolic activation and disposition of environmental xenobiotics. In the present study, we examined the effect of in utero exposure to benzo(a)pyrene [B(a)P] aerosol on Sp4 and N-methyl-D-aspartate (NMDA)–dependent systems as well as a resulting behavioral phenotype (object discrimination) in Cpr offspring. Results from in utero exposure of WT Cprlox/lox mice were compared with in utero exposed brain-Cpr-null offspring mice. Null mice were used as they do not express brain cytochrome P4501B1–associated NADPH oxidoreductase (CYP1B1-associated NADPH oxidoreductase), thus reducing their capacity to produce neural B(a)P metabolites. Subsequent to in utero (E14–E17) exposure to B(a)P (100 μg/m3), Cprlox/lox offspring exhibited: (1) elevated B(a)P metabolite and F2-isoprostane neocortical tissue burdens, (2) elevated concentrations of cortical glutamate, (3) premature developmental expression of Sp4, (4) decreased subunit ratios of NR2B:NR2A, and (5) deficits in a novelty discrimination phenotype monitored to in utero exposed brain-Cpr-null offspring. Collectively, these findings suggest that in situ generation of metabolites by CYP1B1-associated NADPH oxidoreductase promotes negative effects on NMDA-mediated signaling processes during the period when synapses are first forming as well as effects on a subsequent behavioral phenotype. [ABSTRACT FROM PUBLISHER]

Manganese (Mn) is an essential metal required for normal homeostasis. Humans chronically exposed to high Mn levels, however, may exhibit psychomotor signs secondary to increased brain Mn. As Mn and iron (Fe) share several cellular membrane transporters, decreased Fe levels resulting from Fe deficiency or anemia lead to increased brain Mn deposition. Conversely, decreased Mn levels are associated with abnormal brain Fe accumulation. To reduce potential Mn toxicity resulting from brain Mn accumulation, we proposed that increased dietary Fe would attenuate brain Mn deposition. To test this hypothesis, three groups of Sprague-Dawley rats were injected weekly (14 weeks) with Mn (3 mg/kg) and fed normal Fe (TX), Fe-supplemented (FeS), or Fe-deficient (FeD) chow. Control (CN) rats received normal dietary Fe and saline injections. Using magnetic resonance imaging, rats were imaged biweekly for 14 weeks to qualitatively monitor brain Mn and Fe accumulation. Both FeS and FeD had greater brain Mn deposition than TX rats. By week 3, R1 values, which correlate with Mn deposition, were statistically significantly increased (p < 0.05) in brain stem, cerebellum, cortex, midbrain, and striatum compared with CN or TX animals. By week 14, R1 values for all brain regions in FeS and FeD animals were statistically significantly increased (p < 0.05). By the end of the study, similar results were obtained for R2 values, a marker of Fe accumulation. These data suggest that Fe supplementation does not effectively protect and may even exacerbate brain Mn accumulation in mammals subchronically exposed to Mn. [ABSTRACT FROM AUTHOR]

Gene by environment interactions (G × E) are thought to underlie neurodevelopmental disorder, etiology, neurodegenerative disorders, including the multiple forms of autism spectrum disorder. However, there is limited biological information, indicating an interaction between specific genes and environmental components. The present study focuses on a major component of airborne pollutants, polycyclic aromatic hydrocarbons (PAHs), such as benzo(a)pyrene [B(a)P], which negatively impacts cognitive development in children who have been exposed in utero. In our study, prenatal exposure of Cprlox/lox timed-pregnant dams to B(a)P (0, 150, 300, and 600 μg/kg body weight via oral gavage) on embryonic day (E14–E17) consistent with our susceptibility-exposure paradigm was combined with the analysis of a replicated autism risk gene, the receptor tyrosine kinase, Met. The results demonstrate a dose-dependent increase in B(a)P metabolite generation in B(a)P-exposed Cprlox/lox offspring. Additionally, a sustained persistence of hydroxy metabolites during the onset of synapse formation was noted, corresponding to the peak of Met expression. Prenatal B(a)P exposure also downregulated Met RNA and protein levels and dysregulated normal temporal patterns of expression during synaptogenesis. Consistent with these data, transcriptional cell–based assays demonstrated that B(a)P exposure directly reduces human MET promoter activity. Furthermore, a functional readout of in utero B(a)P exposure showed a robust reduction in novel object discrimination in B(a)P-exposed Cprlox/lox offspring. These results confirm the notion that common pollutants, such as the PAH B(a)P, can have a direct negative impact on the regulated developmental expression of an autism risk gene with associated negative behavioral learning and memory outcomes. [ABSTRACT FROM AUTHOR]

Expansion of a polyglutamine tract in Huntingtin (Htt) leads to the degeneration of medium spiny neurons in Huntington's disease (HD). Furthermore, the HTT gene has been functionally linked to iron (Fe) metabolism, and HD patients show alterations in brain and peripheral Fe homeostasis. Recently, we discovered that expression of mutant HTT is associated with impaired manganese (Mn) uptake following overexposure in a striatal neuronal cell line and mouse model of HD. Here we test the hypothesis that the transferrin receptor (TfR)-mediated Fe uptake pathway is responsible for the HD-associated defects in Mn uptake. Western blot analysis showed that TfR levels are reduced in the mutant STHdhQ111/Q111 striatal cell line, whereas levels of the Fe and Mn transporter, divalent metal transporter 1 (DMT1), are unchanged. To stress the Fe transport system, we exposed mutant and wild-type cells to elevated Fe(III), which revealed a subtle impairment in net Fe uptake only at the highest Fe exposures. In contrast, the HD mutant line exhibited substantial deficits in net Mn uptake, even under basal conditions. Finally, to functionally evaluate a role for Fe transporters in the Mn uptake deficit, we examined Mn toxicity in the presence of saturating Fe(III) levels. Although Fe(III) exposure decreased Mn neurotoxicity, it did so equally for wild-type and mutant cells. Therefore, although Fe transporters contribute to Mn uptake and toxicity in the striatal cell lines, functional alterations in this pathway are insufficient to explain the strong Mn resistance phenotype of this HD cell model. [ABSTRACT FROM AUTHOR]

Ebselen (Ebs) and diphenyl diselenide [(PhSe)2] readily oxidize thiol groups. Here we studied mitochondrial swelling changes in mitochondrial potential (Δψm), NAD(P)H oxidation, reactive oxygen species production, protein aggregate formation, and oxygen consumption as ending points of their in vitro toxicity. Specifically, we tested the hypothesis that organochalchogens toxicity could be associated with mitochondrial dysfunction via oxidation of vicinal thiol groups that are known to be involved in the regulation of mitochondrial permeability (Petronilli et al. J. Biol. Chem., 269; 16638; 1994). Furthermore, we investigated the possible mechanism(s) by which these organochalchogens could disrupt liver mitochondrial function. Ebs and (PhSe)2 caused mitochondrial depolarization and swelling in a concentrationdependent manner. Furthermore, both organochalchogens caused rapid oxidation of the mitochondrial pyridine nucleotides (NAD(P)H) pool, likely reflecting the consequence and not the cause of increased mitochondrial permeability (Costantini, P., Chernyak, B. V., Petronilli, V., and Bernardi, P. (1996). Modulation of the mitochondrial permeability transition pore (PTP) by pyridine nucleotides and dithiol oxidation at two separate sites. J. Biol. Chem. 271, 6746-6751). The organochalchogens-induced mitochondrial dysfunction was prevented by the reducing agent dithiothreitol (DTT). Ebs- and (PhSe)2-induced mitochondrial depolarization and swelling were unchanged by ruthenium red (4μM), butylated hydroxytoluene (2.5μM), or cyclosporine A (1μM). N-ethylmaleimide enhanced the organochalchogensinduced mitochondrial depolarization, without affecting the magnitude of the swelling response. In contrast, iodoacetic acid did not modify the effects of Ebs or (PhSe)2 on the mitochondria. Additionally, Ebs and (PhSe)2 decreased the basal 2' 7' dichlorofluorescin diacetate (H2-DCFDA) oxidation and oxygen consumption rate in state 3 and increased it during the state 4 of oxidative phosphorylation and induced the formation of protein aggregates, which were prevented by DTT. However, DTT failed to reverse the formation of protein aggregates, when it was added after a preincubation of liver mitochondria with Ebs or (PhSe)2. Similarly, DTT did not reverse the Ebs- or (PhSe)2-induced Δψm collapse or swelling, when it was added after a preincubation period of mitochondria with chalcogenides. These results show that Ebs and (PhSe)2 can effectively induce mitochondrial dysfunction and suggest that effects of these compounds are associated with mitochondrial thiol groups oxidation. The inability of cyclosporine A to reverse the Ebs- and (PhSe)2-induced mitochondrial effects suggests that the redox-regulated mitochondrial permeability transition (MPT) pore was mechanistically regulated in a manner that is distinct from the classical MPT pore. [ABSTRACT FROM AUTHOR]

The neurotoxicity of methylmercury (MeHg) is well documented in both humans and animals. MeHg causes acute and chronic damage to multiple organs, most profoundly the central nervous system (CNS). Microglial cells are derived from macrophage cell lineage, making up ∼12% of cells in the CNS, yet their role in MeHg-induced neurotoxicity is not well defined. The purpose of the present study was to characterize microglial vulnerability to MeHg and their potential adaptive response to acute MeHg exposure. We examined the effects of MeHg on microglial viability, reactive oxygen species (ROS) generation, glutathione (GSH) level, redox homeostasis, and Nrf2 protein expression. Our data showed that MeHg (1–5μM) treatment caused a rapid (within 1 min) concentration- and time-dependent increase in ROS generation, accompanied by a statistically significant decrease in the ratio of GSH and its oxidized form glutathione disulfide (GSSG) (GSH:GSSG ratio). MeHg increased the cytosolic Nrf2 protein level within 1 min of exposure, followed by its nuclear translocation after 10 min of treatment. Consistent with the nuclear translocation of Nrf2, quantitative real-time PCR revealed a concentration-dependent increase in the messenger RNA level of Ho-1, Nqo1, and xCT 30 min post MeHg exposure, whereas Nrf2 knockdown greatly reduced the upregulation of these genes. Furthermore, we observed increased microglial death upon Nrf2 knockdown by the small hairpin RNA approach. Taken together, our study has demonstrated that microglial cells are exquisitely sensitive to MeHg and respond rapidly to MeHg by upregulating the Nrf2-mediated antioxidant response. [ABSTRACT FROM PUBLISHER]

Manganese (Mn) is a metal required by biological systems. However, environmental or occupational exposure to high levels of Mn can produce a neurological disorder called manganism, which has similarities to Parkinson's disease. Diethyl-2-phenyl-2-tellurophenyl vinylphosphonate (DPTVP) is an organotellurium compound with a high antioxidant activity, especially in the brain. The present study was designed to investigate the effects of long-term low-dose exposure to Mn in drinking water on behavioral and biochemical parameters in rats and to determine the effectiveness of vinylic telluride in attenuating the effects of Mn. After 4 months of treatment with MnCl2 (13.7 mg/kg), rats exhibited clear signs of neurobehavioral toxicity, including a decrease in the number of rearings in the open field and altered motor performance in rotarod. The administration of DPTVP (0.150 μmol/kg, ip, 2 weeks) improved the motor performance of Mn-treated rats, indicating that the compound could be reverting Mn neurotoxicity. Ex vivo, we observed that Mn concentrations in the Mn-treated group were highest in the striatum, consistent with a statistically significant decrease in mitochondrial viability and [3H]glutamate uptake, and increased lipid peroxidation. Mn levels in the hippocampus and cortex were indistinguishable from controls, and no significant differences were noted in the ex vivo assays in these areas. Treatment with DPTVP fully reversed the biochemical parameters altered by Mn. Furthermore, DPTVP treatment was also associated with a reduction in striatal Mn levels. Our results demonstrate that DPTVP has neuroprotective activity against Mn-induced neurotoxicity, which may be attributed to its antioxidant activity and/or its effect on striatal Mn transport. [ABSTRACT FROM PUBLISHER]

The parkinsonian symptoms and increased Mn accumulation in dopaminergic (DAergic) neurons of the basal ganglia implicate impaired dopamine signaling in the neurotoxic effects of chronic manganese overexposure. Using blood oxygenation level-dependent (BOLD) pharmacological magnetic resonance imaging (phMRI), we mapped brain responses to acute amphetamine (AMPH; 3 mg/kg, ip), which stimulates midbrain DAergic systems, in male Sprague- Dawley rats following 6 weeks of chronic MnCl2 (5 mg Mn/kg, one per week, iv) or saline treatment. Plasma Mn content, measured immediately following phMRI, was elevated twofold in Mntreated animals (p < 0.05), but the twofold increase in mean striatal Mn content did not reach significance. In saline-treated animals, AMPH stimulated robust positive BOLD responses throughout the basal ganglia and their reciprocally innervated connections. In contrast, acute AMPH stimulated a negative BOLD response in many of these structures in the Mn-treated group, resulting in significant differences between saline- and Mntreated AMPH-evoked BOLD responses within caudate putamen, globus pallidus, substantia nigra, mediodorsal thalamic nucleus, and somatosensory cortex. These results demonstrate the utility of AMPH-evoked phMRI as readout of the DAergic signaling in vivo and confirm the vulnerability of DAergic systems to Mn. [ABSTRACT FROM AUTHOR]

Depleted uranium (DU) is a dense and heavy metal used in armor, ammunition, radiation shielding, and counterbalances. The military usage has led to growing public concern regarding the health effects of DU. In this study, we used the nematode, Caenorhabditis elegans, to evaluate the toxicity of DU and its effects in knockout strains of metallothioneins (MTs), which are small thiol-rich proteins that have numerous functions, such as metal sequestration, transport, and detoxification. We examined nematode viability, the accumulation of uranium, changes in MT gene expression by quantitative reverse transcription-PCR, and the induction of green fluorescent protein under the control of the MT promoters, following exposure to DU. Our results indicate that (1) DU causes toxicity in a dose-dependent manner; (2) MTs are protective against DU exposure; and (3) nematode death by DU is not solely a reflection of intracellular uranium concentration. (4) Furthermore, only one of the isoforms of MTs, metallothionein-1 (mtl-1), appears to be important for uranium accumulation in C. elegans. These findings suggest that these highly homologous proteins may have subtle functional differences and indicate that MTs mediate the response to DU. [ABSTRACT FROM PUBLISHER]

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 10μM 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 (CMH2DCFDA)—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 14C-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. [ABSTRACT FROM PUBLISHER]

Depleted uranium (DU) is an extremely dense metal that is used in radiation shielding, counterbalances, armor, and ammunition. In light of the public concerns about exposure to DU and its potential role in Gulf War Syndrome (GWS), this study evaluated the neurotoxic potential of DU using focused studies on primary rat cortical neurons and the nematode Caenorhabditis elegans. We examined cell viability, cellular energy metabolism, thiol metabolite oxidation, and lipid peroxidation following exposure of cultured neurons to DU, in the form of uranyl acetate. We concurrently evaluated the neurotoxicity of uranyl acetate in C. elegans using various neuronal–green fluourescent protein reporter strains to visualize neurodegeneration. Our studies indicate that uranyl acetate has low cytotoxic potential, and uranium exposure does not result in significant changes in cellular energy metabolism, thiol metabolite oxidation, or lipid peroxidation. Furthermore, our C. elegans studies do not show any significant neurodegeneration following uranyl acetate exposure. Together, these studies suggest that DU, in the form of uranyl acetate, has low neurotoxic potential. These findings should alleviate the some of public concerns regarding DU as an etiologic agent of neurodegenerative conditions associated with GWS. [ABSTRACT FROM PUBLISHER]

We report on the uptake of MeHg in astrocytes and neurons, as well as specific indicators of neurotoxicity. Cerebellar granule neurons and astrocytes separately and in co-culture were cultured in the presence of MeHg and changes in 3-[4, 5-dimethylthiazol-2-yl]-2, 5 diphenyltetrazolium bromide (MTT)-reduction, lactate dehydrogenase (LDH) leakage, and cellular content of glutathione and amino acids were used as indicators of MeHg toxicity. Mitochondria in cortical astrocytes were slightly more sensitive than those in cerebellar astrocytes to the toxic effects of MeHg; furthermore, cellular integrity was better preserved in cerebellar astrocytes. When neurons and astrocytes from cerebellum were incubated in separable co-cultures using inserts, the astrocytes showed cellular damage at lower exposure to MeHg while neurons showed less changes compared to respective cell types in mono-cultures. Mercury uptake studies at 25 μM MeHg (10% serum present) showed that for neurons in co-culture the uptake was 1/3 compared to mono-cultures. In contrast, for astrocytes in co-culture, uptake was increased by 75%. A MeHg concentration-dependent increase of glutamate content in mono-cultures was noted. When MeHg concentration was increased to 10, 25, or 50 μM, neurons in co-cultures decreased their glutamate content, whereas astrocytes showed an increase. Other amino acids, such as glutamine, serine, valine, isoleucine, taurine, and phenylalanine were unaffected by MeHg. Glutathione content showed MeHg concentration-dependent changes in astrocytes and was increased in neurons in co-culture incubated with 5 μM MeHg. In conclusion, astrocytes appear to increase neuronal resistance, indicating a possible protective role for astrocytes in MeHg neurotoxicity. [ABSTRACT FROM AUTHOR]